As someone who used phabricator and mercurial, using GitHub and git again feels like going back to the stone ages. Hopefully this and jujutsu can recreate stacked-diff flow of phabricator.
It’s not just nice for monorepos. It makes both reviewing and working on long-running feature projects so much nicer. It encourages smaller PRs or diffs so that reviews are quick and easy to do in between builds (whereas long pull requests take a big chunk of time).
I'm so glad git won the dvcs war. There was a solid decade where mercurial kept promoting itself as "faster than git*†‡" and every time I tried it wound up being dog slow (always) or broken (some of the time). Git is fugly but it's fast, reliable, and fugly, and I can work with that.
> I'm so glad git won the dvcs war. There was a solid decade where mercurial kept promoting itself as "faster than git".
It wasn't the Mercurial team saying it was faster than Git; that was Facebook after contributing a bunch of patches after testing Mercurial on their very large mono-repo in 2014 [1]:
For our repository, enabling Watchman integration has made Mercurial’s status command more than 5x faster than Git’s status command. Other commands that look for changed files–like diff, update, and commit—also became faster.
In fact they liked Mercurial so much they essentially cloned it to create their own dvcs, Sapling [2]. (An aside: Facebook did all of this because it was taking too long getting new engineers up to speed with Git. Shocker.)
Today, most of the core of Mercurial has been rewritten in Rust; when Facebook did their testing, Mercurial was nearly 100% Python. That's where the "Mercurial is slow" thing came from; launching a large Python 2.x app took a while back in the day.
I was messing with an old Mercurial repo recently… it was like a breath of fresh air. If I can push to GitHub using Mercurial… sign me up.
You can push to GitHub using Sapling. I wish Sapling open source was given more love, as the experience for non-Facebookers is subpar. No bash completion outside the box, no distro packages, no good help pages, random issues interacting with a Git repo...
Sounds like what my teachers used to say: “a personal problem”. Literally nobody outside FB knows what they’re missing and until they fix that, literally nobody cares.
No, the "hg is fast" marketing claim that retreated to "hg is Big-O fast and you are dumb for caring about constant terms and factors even if they clearly dominate your use case" predates 2014 and the Facebook patches. These talking points were old in 2010. Mercurial was always dog slow and always gaslighting about it.
I'm glad BigCo made tools to serve their needs, but their needs aren't my needs or most peoples' needs.
> Mercurial has been rewritten in Rust
I'm glad they saw the light eventually! Ditto for the rest of the Rust Tooling Renaissance.
What is kind of funny here is that you're right locally. At the same time, the larger tech companies (Meta and Google, specifically) ended up building off of hg and not git because (at the time, especially) git cannot scale up to their use cases. So while the git CLI was super fast, and the hg CLI was slow, "performance" means more than just CLI speed.
I was never a fan of hg either, but now I can use jj, and get some of those benefits without actually using it directly.
>At the same time, the larger tech companies (Meta and Google, specifically) ended up building off of hg and not git because (at the time, especially) git cannot scale up to their use cases.
Fun story: I don't really know what Microsoft's server-side infra looked like when they migrated the OS repo to git (which, contrary to the name, contains more than just stuff related to the Windows OS), but after a few years they started to hit some object scaling limitations where the easiest solution was to just freeze the "os" repo and roll everyone over to "os2".
They wrote something that allowed them to virtualize Git -- can't remember the name of that. But it basically hydrated files on-demand when accessed in the filesystem.
The problem was I think something to do with like the number of git objects that it was scaling to causing crazy server load or something. I don't remember the technical details, but definitely something involving the scale of git objects.
Probably a lot of Googlers don't know. It's ancient history, was called google3 even in 2006 when I first joined.
google1 = code written by Larry, Sergey and employee number 1 (Craig). A hacky pile of Python scripts, dumped fairly quickly.
google2 = the first properly engineered C++ codebase. Protobufs etc were in google2. But the build system was some jungle of custom Makefiles, or something like that. I never saw it directly.
google3 = the same code as google2 but with a new custom build system that used Python scripts to generate Makefiles. I suppose it required a new repository so they could port everything over in parallel with code being worked on in google2. P4 was apparently not that great at branches and google3 didn't use them. Later the same syntax for the build files was kept but turned into a new languages called Starlark and the Makefile generator went away in favor of Blaze, which directly interpreted them.
Yes, the server is based on Perforce, called Piper, but the CLI is based on mercurial. So locally you're doing hg and then when you create a CL, it translates it into what p4 needs.
Right, and I'm glad there are projects serving The Cathedral, but I live in The Bazaar so I'm glad The Bazaar won.
The efforts to sell priest robes to fruit vendors were a little silly, but I'm glad they didn't catch on because if they had caught on they no longer would have been silly.
I might be the outlier, but am I the only one who doesn't care much about the speed of git?
I've been using git since 2011 as my main vcs for personal and professional work as a freelancer contractor. Whenever I "wait" for git, it is either limited by the bandwidth (git clone) or by the amount of commit hooks that I implemented for linting, verification etc. The percentage of time actually spent in git internal execution must be a tiny fraction of my day to day usage. What IS affecting me (and my the teams I work in) is usability and UX experience. I.e. if people would screw up stuff (no matter if in git or mercurial) we spent far more time fixing this - I don't think the impmentation speed would matter here.
The only case I can imagine is when doing a full checkout of a big repo, but even there, there is --depth which is quite practical.
Isn't it kind of like how you don't care much about the oxygen content of the air around you, but you'd miss it if it was gone? I've done development with Mercurial, simple processes were irritatingly slow, particularly if you stray from the better-supported opinionated path.
I spent a long time educating teams of developers about git's usability quirks. I don't do that as much anymore - partly because the quirks have been worked out, partly because the developers have better guardrails and resources to learn from.
This whole time (the past 15 years) git has been getting faster without most of us noticing, because big companies have been investing in speeding it up. The reason you don't notice or care is that they work on a very different scale. Thousands of users, thousands of PRs per day, millions of CI/CD jobs all hitting the repo.
Now the cycle is repeating again because these numbers are shooting through the roof because of agentic coding.
Mercurial's model is different from Git that these things you list does not make sense there.
Rebase does not make sense in Mercurial because it has the concept of fixed branches. A commit is permanently linked to the branch on which it was made. So you are supposed to use merges.
I know. It's an opinion about how to develop that a lot of people hold - a declining proportion, mind you, like Mecurial's declining market share - and it's one that they're able to represent in Git's model, with Git's features. They're even able to do it without exposing me to it. But the same isn't true in reverse. Strictly superior?
Believe me, I tried to have an open mind about it. Then one day I was getting ready to go on a work trip with a half-finished feature on my work laptop, and realised there was simply no in-model way for backing that wip up to the repo. If I lost my laptop, I lost the progress. mercurial-scm fails at SCM.
>in-model way for backing that wip up to the repo.
That is because you have this notion of a "clean history", (which IIUC prevented you from making this permanent wip commit) which in reality does not have a lot of use. For most project, "useful history" or "real history" is better than a "clean" history.
It doesn't seem to support Mercurial though (not to imply that you were implying that it did). All I can find in this proxy/mirror thing to integrate it by presenting the Mercurial repo as a Git server:
https://peterlavalle.github.io/post/forgejo-actions/
Whatever your opinion on one tool or another might be - it does seem weird that the "market" has been captured by what you are saying is a lesser product.
So far you've only gotten responses to "how can a worse product win?", and they are valid, but honestly the problem here is that Mercurial is not a better product in at least one very important way: branches.
You can visit any resource about git and branches will have a prominent role. Git is very good at branches. Mercurial fans will counter by explaining one of the several different branching options it has available and how it is better than the one git has. They may very well be right. It also doesn't matter, because the fact that there's a discussion about what branching method to use really just means Mercurial doesn't solve branches. For close to 20 years the Mercurial website contained a guide that explained only how to have "branches" by having multiple copies of the repository on your system. It looks like the website has now been updated: it doesn't have any explanation about branches at all that I can find. Instead it links to several different external resources that don't focus on branches either. One of them mentions "topic", introduced in 2015. Maybe that's the answer to Git's branching model. I don't care enough to look into it. By 2015 Git had long since won.
Mercurial is a cool toolbox of stuff. Some of them are almost certainly better than git. It's not a better product.
To me mercurials branching is closer to the development process and preserves more information, because it records the original branch a commit was made.
Git does not have such concept. That is a trade off and that trade off works great for projects managed like Linux kernel. But for smaller projects where there is a limited number of people working, the information preserved by mercurial could be very valuable.
It also had some really interesting ideas like change set evolution, which enabled history re-writing after a branch has been published. Don't know its current status and how well it turned out to be..
It's interesting that branches, which is a marquee feature of git, became less important at the same time as git ate all the other vcs. Outside of OS projects, almost all development is trunk based with continuous releases.
Maybe branching was an important reason to adopt git but now we'd probably be ok with a vcs that doesn't even support them.
Not sure if it's true. I mean, I do agree with the core of it, but how do you even do PRs and resolve conflicts, if there are no branches and a developer cannot efficiently update his code against the last (remote) version of master branch?
This is so strange, because, at a low level, a branch isn't even a "thing" in git. There is no branch object type in git, it's literally just a pointer to a commit, functionally no different from a tag except for the commands that interact with it.
Meanwhile mercurial has bookmarks. TBF I'm not sure when it got those but they've been around forever at this point. The purpose is served.
I think there are (or perhaps were) some product issues regarding the specifics of various workflows. But at least some of that is simply the inertia of entrenched workflows and where there are actual downsides the (IMO substantial) advantages need to be properly weighed against them.
Personally I think it just comes down to the status quo. Git is popular because it's popular, not because it's noticably superior.
Worse products win all the time. Inertia is almost impossible to overcome. VHS vs Betamax is a classic. iPod wasn’t the best mp3 player but being a better mp3 player wasn’t enough to claw market share.
Google and Meta don’t use Git and GitHub. Sapling and Phabricator much much better (when supported by a massive internal team)
I mean, in the fickle world that is TECH, I am struggling to believe that that's what's happened.
I personally went from .latest.latest.latest.use.this (naming versions as latest) to tortoise SVN (which I struggled with) to Git (which I also was one of those "walk around with a few memorised commands" people that don't actually know how to use it) to reading the fine manual (well 2.5 chapters of it) to being an evangalist.
I've tried Mercurial, and, frankly, it was just as black magic as Git was to me.
That's network effects.
But my counter is - I've not found Mercurial to be any better, not at all.
I have made multiple attempts to use it, but it's just not doing what I want.
And that's why I'm asking, is it any better, or not.
Networking effects are significantly strengthened by necessary user buy in. VC is hard, and every tool demands its users to spend a non-significant amount of time learning it. I would guess the time to move from black magic to understanding most of git is ~100h for most people.
The thing is, to understand which one is actually better, you would have to give the same amount of investment in the second tool, which is not something most people are willing to do if the first tool is "good enough". That's how Python became the default programming language; people don't miss features they do not understand.
A little over a decade ago, with only svn experience, I tried both mercurial and git. There was something about how mercurial handled branches that I found extremely confusing (don't remember what), while git clicked immediately - even without reading the manual.
Mercurial has a more consistent CLI, a really good default GUI (TortoiseHg), and the ability to remember what branch a commit was made on. It's a much easier tool to teach to new developers.
Hmm, that feels a bit subjective - I'm not going to say X is easier than Y when I've just finished saying that I found both tools to have a lot of black magic happening.
But what I will point out, for better or worse, people are now looking at LLMs as Git masters, which is effectively making the LLM the UI which is going to have the effect of removing any assumed advantage of whichever is the "superior" UX
I do wish to make absolutely clear that I personally am not yet ready to completely delegate VCS work to LLMs - as I have pointed out I have what I like to think of as an advanced understanding of the tools, which affords me the luxury of not having an LLM shoot me in the foot, that is soley reserved as my own doing :)
"better" in that sentence is very specific. Worse is also worse, and if you're one of the people for whom the "better" side of a solution doesn't apply, you're left with a mess that people celebrate.
Not always, but in this case the superior product (i.e. VHS) won. At initial release, Beta could only record an hour of content, while VHS could record 2 hours. Huge difference in functionality. The quality difference was there, but pretty modest.
I suppose one lesson could be that there are different dimensions of superiority, different products may be superior in different ways.
Of course, products also can win market dominance for reasons external to the product's quality itself (marketing, monopoly lock-in, other network effects, consumer preferences on something other than product quality itself, etc).
> The issue is solely that OG Mercurial was written in Python.
Are we back to "programming language X is slow" assertions? I thought those had died long ago.
Better algorithms win over 'better' programming languages every single time. Git is really simple and efficient. You could reimplement it in Python and I doubt it would see any significant slowness. Heck, git was originally implemented as a handful of low level binaries stitched together with shell scripts.
Every time I've rewritten something from Python into Java, Scala, or Rust it has gotten around ~30x faster. Plus, now I can multithread too for even more speedups.
Python is absurdly slow - every method call is a string dict lookup (slots are way underused), everything is all dicts all the time, the bytecode doesn't specialize at all to observed types, it is a uniquely horrible slow language.
I love it, but python is almost uniquely a slow language.
Algorithms matter, but if you have good algorithms, or you're already linear time and just have a ton of data, rewriting something from a single-threaded Python program to a multithreaded rust program I've seen 500x speedups, where the algorithms were not improved at all.
It's the difference between a program running overnight vs. in 30 seconds. And if there are problems, the iteration speed from that is huge.
To be fair, Python as implement today is horribly slow. You could leave the language the same but apply all the tricks and heroic efforts they used to make JavaScript fast. The language would be the same, but the implementations would be faster.
Of course, in practice the available implementations are very much part of the language and its ecosystems; especially for a language like Python which is so defined by its dominant implementation of CPython.
Fair! I guess I didn't mean language as such, but as used.
But a lot of the monkey-patching kind of things and dynamism of python also means a lot of those sorts of things have to be re-checked often for correctness, so it does take a ton of optimizations off the table. (Of course, those are rare corner cases, so compilers like pypy have been able to optimize for the "happy case" and have a slow fall-back path - but pypy had a ton of incompatibility issues and now seems to be dying).
Python has a JIT compiling version in GraalPy. If you have pure Python it works well. The problem is, a lot of Python code is just callouts to C++ ML libs these days and the Python/C interop boundary just assumes you're using CPython and requires other runtimes to emulate it.
You don't even need to go all V8, you could just build something like LuaJIT and get most of the way there. LuaJIT is like 10k LOCs and V8 is 3M LOC.
The real reason is that it is a deliberate choice by the CPython project to prefer extensibility and maintainability to performance. The result is that python is a much more hackable language, with much better C interop than V8 or JVM.
I've rewritten a python tool in go, 1:1. And that turned something that was so slow that it was basically a toy, into something so fast that it became not just usable, but an essential asset.
Later on I also changed some of the algorithms to faster ones, but their impact was much lower than the language change.
I don’t know if people think this way anymore, but Python gained traction to some degree as a prototyping language. Verify the logic and structures, then implement the costly bits or performance sensitive bits in a more expense-to-produce more performant language.
Which is only to say: that rewrite away from python story can also work to show python doing its job. Risk reduction, scaffolding, MVP validation.
> git was originally implemented as a handful of low level binaries stitched together with shell scripts.
A bunch of low level binaries stitched together with shell scripts is a lot faster than python, so not really sure what the point of this comparison is.
Python is an extremely versatile language, but if what you're doing is computing hashes and diffs, and generally doing entirely CPU-bound work, then it's objectively the wrong tool, unless you can delegate that to a fast, native kernel, in which case you're not actually using Python anymore.
Well, you can and people do use Python to stitch together low level C code. In that sense, you could go the early git approach, but use Python instead of shell as the glue.
Their point was that by offloading the bottlenecks to C, you've essentially conceded that Python isn't fast enough for them, which was the original point made above
> Are we back to "programming language X is slow" assertions? thought those had died long ago.
Yes we are? The slow paths of mercurial have been rewritten in C (and more recently in Rust) and improved the perf story substantially, without taking away from the wild modularity and extensibility hg always had.
> You could reimplement it in Python and I doubt it would see any significant slowness
I doubt it wouldn't be significantly slower. I can't disprove it's possible to do this but it's totally possible for you to prove your claim, so I'd argue that the ball is in your court.
Python is by far the slowest programming language, an order of magnitude slower than other languages
One of the reason mercurial lost the dvcs battle is because of its performance - even the mercurial folks admitted that was at least in part because of python
You must belong to the club of folks who use hashmaps to store 100 objects. It's amazing how much we've brainwashed folks to focus on algorithms and lose sight of how to actually properly optimize code. Being aware of how your code interacts with cache is incredibly important. There are many cases of using slower algorithms to do work faster purely because it's more hardware friendly.
The reason that some more modern tools, like jj, really blow git out of the water in terms of performance is because they make good choices, such as doing a lot of transformations entirely in memory rather than via the filesystem. It's also because it's written in a language that can execute efficiently. Luckily, it's clear that modern tools like jj are heavily inspired by mercurial so we're not doomed to the ux and performance git binds us with.
> You must belong to the club of folks who use hashmaps to store 100 objects.
Apparently I belong to the same club -- when I'm writing AWK scripts. (Arrays are hashmaps in a trenchcoat there.) Using hashmaps is not necessarily an indictment you apparently think it is, if the access pattern fits the problem and other constraints are not in play.
> It's amazing how much we've brainwashed folks to focus on algorithms and lose sight of how to actually properly optimize code. Being aware of how your code interacts with cache is incredibly important.
By the time you start worrying about cache locality you have left general algorithmic concerns far behind. Yes, it's important to recognize the problem, but for most programs, most of the time, that kind of problem simply doesn't appear.
It also doesn't pay to be dogmatic about rules, which is probably the core of your complaint, although unstated. You need to know them, and then you need to know when to break them.
You barely have to try to have Python be noticeably slow. It's the only language I have ever used where I was even aware that a programming language could be slow.
They died because everyone knows that Python is infact very very slow. And that’s just totally fine for a vast number of glue operations.
It’s amusing you call Git fast. It’s notoriously problematic for large repos such that virtually every BigTech company has made a custom rewrite at some point or another!
Now that is interesting too, because git is very fast for all I have ever done. It may not scale to Google monorepo size, it would ve the wrong tool for that. But if you are talking Linux kernel source scale, it asolutely, is fast enough even for that.
For everything I've ever done, git was practically instant (except network IO of course). It's one of the fastest and most reliable tools I know. If it isn't fast for you, chances are you are on a slow Windows filesysrem additionally impeded by a Virus scanner.
The fact that Git has an extremely strong preference for storing full and complete history on every machine is a major annoyance! “Except for network IO” is not a valid excuse imho. Cloning the Linux kernel should take only a few seconds. It does not. This is slow and bad.
The mere fact that Git is unable to handle large binary files makes it an unusable tool for literally every project I have ever worked on in my entire career.
Takes 21 seconds on my work laptop, indeed a corporate Windows laptop with antivirus installed. Majority of that time is simply network I/O. The cloned repository is 276 MB large.
Actually checking the kernel out takes 90 seconds. This amounts to creating 99195 individual files, totaling 2 GB of data. Expect this to be ~10 times faster on a Linux file system.
Git LFS is a gross hack that results in pain and suffering. Effectively all games use Perforce because Git and GitLFS suck too much. It’s a necessary evil.
Define "large"; I've never ran into serious performance issues during the ~15 years I've used Git, which either means the projects I've worked in aren't actually large large, or Git is fast enough for most use cases.
I continue to use gerrit explicitly because I cannot stand github reviews. Yes, in theory, make changes small. But if I'm doing larger work (like updating a vendored dep, that I still review), reviewing files is... not great... in github.
Can these tools e.g. do per-commit review? I mean, it's not the UI what's the problem (though it's not ideal), it's the whole idea of commenting the entire PR at once, partly ignoring the fact that the code in it changes with more commits pushed.
Phabricator and even Gerrit are significantly nicer.
Unless you have a “every commit must build” rule, why would you review commits independently? The entire PR is the change set - what’s problematic about reviewing it as such?
There's a certain set of changes which are just easier to review as stacked independent commits.
Like, you can do a change that introduced a new API and one that updates all usages.
It's just easier to review those independently.
Or, you may have workflows where you have different versions of schemas and you always keep the old ones. Then you can do two commits (copy X to X+1; update X+1) where the change is obvious, rather than seeing a single diff which is just a huge new file.
I'm sure there's more cases. It's not super common but it is convenient.
> Unless you have a “every commit must build” rule, why would you review commits independently?
Security. Imagine commit #1 introduces a security vulnerability (backdoor) and the features. Then #2 introduces a non-obvious, harmless bug and closes the vulnerability introduced in #1 [0]. At some point, the bug will surface and rolling back commit #2 will be an easy fix, re-introducing your bug.
Alternatively, one of the earlier commits might, for example, contain credential dumping code. Once that commit is mainlined, CI might either automatically run on it or will be able to be run on it since it's no longer marked as unsafe PR.
[0] Think something like #1 introduces array access and #2 adds a bounds-check in a function a layer above - a reviewer with the whole context will see the bounds check and (possibly) consider it fine, but to someone rolling back a commit the necessity will not be obvious.
Squash merge is an artifact of PRs encouraging you to add commits instead of amending them, due to GitHub not being able to show you proper interdiffs, and making comments disappear when you change a diff at that line. In that context, when you add fixup commits, sure, squashing makes sense, but the stacked diffs approach encourages you to create commits that look like you want them to look like directly, instead of requiring you to roll them up at the end.
Boy do I hate Github/Lab/Bucket style code reviews with a burning passion. Who the hell loses code review history? A record of the very thing that made my code better? The "why" of it all, that I am guaranteed to forget tomorrow morning.
Nobody would be using `--force` or `--force-with-lease` as a normal part of development workflow, of their own volition, if they had read that part of the git-push manpage and been horrified (as one should be).
The magit key sequence for this abominable operation is `P "f-u"`. And every single time I am forced to do it, I read "f-u" as it ought to be read.
Rebase-push is the way to do it (patch sets in Gerrit).
Rebase-force-push is absolutely not.
You see, any development workflow inevitably has to integrate changes from at least one other branch (typically latest develop or master), without destroying change history, nor review history. Gerrit makes this trivial.
It's a bit difficult to convey exactly why I'm so rah-rah Gerrit, because it is a matter of day-to-day experience of
- Well, a single commit of a few lines to maybe a hundred lines *is* the correct unit of code review, rebase, revert etc. Manually "Sizing PRs" to that review context size is utter BS. I have better things to do in life than to book-keep PR sizes. Make a single well-contained, revertible commit. Then keep making those. And now you have a commit history that is clean, that you can merge, bisect, and bulk-revert at will. Octopus merges are a good thing. `git-log` is *designed* to let us view changes in any sequence we wish, *including* the so-called "linear" history. `git log --online`.
- Trivial for committer to send up reviews-preserving rebase-push responses to commit reviews (NO force-push, ever --- that's an "admin" action to *evict* / permanently wipe out disaster scenarios such as when someone accidentally commits and pushes out a plaintext secret or a giant blob of the executable of the source code etc.).
- Fast-for-the-reviewer, per-commit, diff-based, inline-commenting code reviews.
- The years-apart experience of being able to dig into any part of one's (immutable) software change history to offer a teaching moment to someone new to the team.
Same here. Don't understand why Github hasn't supported this until now. I'm tired of reviewing PRs with thousands of lines of changes, which are getting worse nowadays with vibe coding.
What does Facebook use internally these days. I'm amazed that the state of review tools is still at or behind what we had a decade ago for the most part.
tangled.org supports native stacking with jujutsu, unlike github's implementation, you don't need to create a new branch per change: https://blog.tangled.org/stacking/
My understanding was that that was more a function of how arc submitted stuff to Phabricator, rather than solely Phabricator itself. arc at submission time submitted a bunch of different commits as a single Phabricator DREV or whatever the terminology is/was (basically a DREV is the {domain}/D123 webpage you'd do a review on). But other tools that submitted commits to Phabricator instances (and maybe even arc itself with the right flag?) submitted each commit as its own separate DREV, so each commit got its own separate /D{N} page and its own review, but all linked together in a stack. And then still landed as separate commits in the actual repo. This is how code submission works with Mozilla's use of Phabricator.
You can get what you want from `git log --first-parent` without having to toss out information.
See how the Linux kernel handles git history to see a good example of non-linear history and where it helps. They use merge commits, ie commits with more than one ancestor, all the time.
I might be missing something, but what I need is not "stacked PR" but a proper UI and interface to manage single commit:
- merge some commits independently when partial work is ready.
- mark some commit as reviewed.
- UI to do interactive rebase and and squash and edit individual commits. (I can do that well from the command line, but not when using the GitHub interface, and somehow not everyone from my team is familiar with that)
- ability to attach a comment to a specific commit, or to the commit message.
- better way to visualize what change over time in each forced push/revision (diff of diff)
Git itself already has the concept of commit. Why put this "stacked PR" abstraction on top of it?
It's basically trying to bring the stacked diff workflow pioneered by Phabricator to GitHub.
The idea is that it allows you to better handle working on top of stuff that's not merged yet, and makes it easier for reviewers to review pieces of a larger stack of work independently.
It's really useful in larger corporate environments.
I've used stacked PRs when doing things like upgrading react-native in a monorepo. It required a massive amount of changes, and would be really hard to review as a single pull request. It has to be landed all at once, it's all or nothing. But being able to review it as smaller independent PRs is helpful.
Stacking PRs is also useful even when you don't need to merge the entire stack at once.
To my knowledge, stacked diffs were first done in the Linux kernel as stacks of patches sent over email. From there they spread to Google and Facebook. (Source: I worked on Facebook's source control team from 2012-2018 and did a lot of work to enable stacked diffs there.)
Right, I was thinking from a web-based UI. The "pull request" term is from git (AFAIK), but git itself was built to accommodate the earlier concept of mailing patches around. (Source: I've been using version control since RCS/SCCS days and contributed here and there to git in its infancy. Also an early user/contributor to Gerrit.)
Possibly from github. It got popularized there at least, encouraging forking code, and is why so many people say "pull request" when they mean "merge request".
GitHub took the "pull request" terminology from Git. A kernel developer (say) would have a bunch of changes ready in their local Git server and would request a pull from Linus, hence a pull request. There's literally a command for it:
At some point, a derivative idea becomes so different from the original one that it’s a novel idea in essence. Just like SMS is ultimately a derivative of cuneiform tablets, and yet it isn’t in any meaningful sense.
I don't think mailing stacks of patches is that different? As someone who built this stuff it was pretty obvious to me that web-based patch stack management was a relatively small evolution over mailing lists. Tools like patchwork bridged the gap initially, and we were quite familiar with them.
I'm not in a large corporate environment, but that also means we're not always a well oiled machine, and sometimes i am writing faster than the reviewer can review for a period of time -- and i really need the stacking then too.
You head to the farthest branch in the chain, fetch the latest main, and run `git rebase --update-refs main` (I prefer interactive mode myself) and then force push all of the branches from start to the end.
Before this feature when you were doing it manually, it was a huge problem. One of the points of this feature, is it automates rebasing the whole stack.
I don't use Github but I do work at one of the companies that popularized this workflows and it is extremely not a big deal. Pull, rebase, resolve conflicts if necessary, resubmit.
Constantly rewriting git history with squashes, rebases, manual changes, and force pushes has always seemed like leaving a loaded gun pointed at your foot to me.
Especially since you get all of the same advantages with plain old stream on consciousness commits and merges using:
I find rebases are only a footgun because the standard git cli is so bad at representing them - things like --force being easier to write than --force-with-lease, there being no way to easily absorb quick fixes into existing commits, interdiffs not really being possible without guesswork, rebases halting the entire workflow if they don't succeed, etc.
I've switched over pretty much entirely to Jujutsu (or JJ), which is an alternative VCS that can use Git as its backend so it's still compatible with Github and other git repos. My colleagues can all use git, and I can use JJ without them noticing or needing to care. JJ has merges, and I still use them when I merge a set of changes into the main branch once I've finished working on it, but it also makes rebases really simple and eliminates most of the footguns. So while I'm working on my branch, I can iteratively make a change, and then squash it into the commit I'm working on. If I refactor something, I can split the refactor out so it's in a separate commit and therefore easiest to review and test. When I get review feedback, I can squash it directly into the relevant commit rather than create a new commit for it, which means git blame tends to be much more accurate and helpful - the commit I see in the git blame readout is always the commit that did the change I'm interested in, rather than maybe the commit that was fixing some minor review details, or the commit that had some typo in it that was fixed in a later commit after review but that relationship isn't clear any more.
And while I'm working on a branch, I still have access to the full history of each commit and how it's changed over time, so I can easily make a change and then undo it, or see how a particular commit has evolved and maybe restore a previous state. It's just that the end result that gets merged doesn't contain all those details once they're no longer relevant.
+1 on this, I also switched to jj when working with any git repo.
What's funny is how much better I understand git now, and despite using jj full time, I have been explaining concepts like rebasing, squashing, and stacked PRs to colleagues who exclusively use git tooling
The magic of the git cli is that it gives you control. Meaning whatever you want to do can be done. But it only gives you the raw tools. You'll need to craft your own workflow on top of that. Everyone's workflow is different.
> So while I'm working on my branch, I can iteratively make a[...]which means git blame tends to be much more accurate and helpful
Everything here I can do easily with Magit with a few keystroke. And magit sits directly on top of git, just with interactivity. Which means if I wanted to I could write a few scripts with fzf (to helps with selection) and they would be quite short.
> And while I'm working on a branch, I still have access to the full history of each commit...
Not sure why I would want the history for a specific commit. But there's the reflog in git which is the ultimate undo tool. My transient workspace is only a few branches (a single one in most cases). And that's the few commits I worry about. Rebase and Revert has always been all I needed to alter them.
> But there's the reflog in git which is the ultimate undo tool.
That one sentence outs you as someone who isn't familiar with JJ.
Here is something to ponder. Despite claims to the contrary, there are many git commands that can destroy work, like `git reset --hard`. The reflog won't save you. However there is literally no JJ command that can't be undone. So no JJ command will destroy your work irretrievably.
I’ve just tested that exact command and the reflog is storing the changes. It’s different from the log command which displays the commit tree for the specified branch. The reflog stores information about operations that updates branches and other references (rebase, reset, amend, commit,…). So I can revert the reset, or a pull.
the best implementation i've worked with was SuperSmartLog (SSL) at Meta, which was open-sourced at interactive smartlog (https://sapling-scm.com/docs/addons/isl/). There are also extension for it in VSCode, etc.
Surprisingly it never gained the adoption it deserved.
It is a table stakes missing feature.. for a long time. Clown seems appropriate, every project I've worked on in github we end up copying a github yml action to allow us to do this with one comment '/fast-forward', just is silly at this point that github doesn't natively support it.
Does it fix the current UX issue with Squash & Merge?
Right now I manually do "stacked PRs" like this:
main <- PR A <- PR B (PR B's merge target branch is PR A) <- PR C, etc.
If PR B merges first, PR A can merge to main no problems. If PR A merges to main first, fixing PR B is a nightmare. The GitHub UI automatically changes the "target" branch of the PR to main, but instantly conflicts spawn from nowhere. Try to rebase it and you're going to be manually looking at every non-conflicting change that ever happened on that branch, for no apparent reason (yes, the reason is that PR A merging to main created a new merge commit at the head of main, and git just can't handle that or whatever).
So I don't really need a new UI for this, I need the tool to Just Work in a way that makes sense to anyone who wasn't Linus in 1998 when the gospel of rebase was delivered from On High to us unwashed Gentry through his fingertips..
Yes, we handle this both in the CLI and server using git rebase --onto
git rebase --onto <new_commit_sha_generated_by_squash> <original_commit_sha_from_tip_of_merged_branch> <branch_name>
So for ex in this scenario:
PR1: main <- A, B (branch1)
PR2: main <- A, B, C, D (branch2)
PR3: main <- A, B, C, D, E, F (branch3)
When PR 1 and 2 are squash merged, main now looks like:
S1 (squash of A+B), S2 (squash of C+D)
Then we run the following:
git rebase --onto S2 D branch3
Which rewrites branch3 to:
S1, S2, E, F
This operation moves the unique commits from the unmerged branch and replays them on top of the newly squashed commits on the base branch, avoiding any merge conflicts.
Conflicts spawn most likely because PR A was squashed, and once you squash Git doesn't know that PR B's ancestors commits are the same thing as the squashed commit on main.
No idea if this feature fixes this.
Edit: Hopefully `gh stack sync` does the rebasing correctly (rebase --onto with the PR A's last commit as base)
> Conflicts spawn most likely because PR A was squashed, and once you squash Git doesn't know that PR B's ancestors commits are the same thing as the squashed commit on main.
Yeah, and I kind of see how git gets confused because the squashed commits essentially disappear. But I don't know why the rebase can't be smart when it sees that file content between the eventual destination commit (the squash) is the same as the tip of the branch (instead of rebasing one commit at a time).
The tip of B is the list of changes of both A and B, while the tip of main is now the squashed version of the changes of A. Unless a branch tracks the end of A in the PR B, It looks like more you want to apply A and B on top of A again.
A quick analogy to math
main is X
A is 3
B is 5
Before you have X + 3 + 5 which was equivalent to X + 8, but then when you squash A on on X, it looks like (X + 3) + (3 + 5) from `main`'s point of view, while from B, it should be X + (3 + 5). So you need to rebase B to remove its 3 so that it can be (X + 3) + 5.
Branches only store the commits at the top. The rest is found using the parent metadata in each commits (a linked list. Squashing A does not remove its commits. It creates a new one, and the tip of `main` as its parent and set the new commit as the tip of `main`. But the list of commits in B still refer to the old tip of `main` as their ancestor and still includes the old commits of A. Which is why you can't merge the PR because it would have applies the commits of A twice.
It does some merge magic so that PR B shows the correct diff; and does so without needing to force push, so on your side you can just "git pull" and continue working.
Of course I expect this repo to become obsolete when GitHub makes their native stacking public.
I agree that this is annoying and unintuitive. But I don’t see the simplest solution here, so:
All you need to do is pull main, then do an interactive rebase with the next branch in your stack with ‘git rebase -i main’, then drop all the commits that are from the branch you just merged.
This is what i often do, but i have never been able to get many coworkers onboard. In my experience I’d say less than 5% of all software folk i’ve worked with are willing to do an interactive rebase; everyone else finds it too scary
I'm not sure I follow your workflow exactly. If PR B is merged, then I'd expect PR A to already be merged (I'd normally branch off of A to make B.)
That said, after the squash merge of A and git fetch origin, you want something like git rebase --update-refs --onto origin/main A C (or whatever the tip of the chain of branches is)
The --update-refs will make sure pr B is in the right spot. Of course, you need to (force) push the updated branches. AFAICT the gh command line tool makes this a bit smoother.
If I'm following correctly, the conflicts arise from other commits made to main already - you've implicitly caught branch A up to main, and now you need catch branch B up to main, for a clean merge.
I don't see how there is any other way to achieve this cleanly, it's not a git thing, it's a logic thing right?
I've no issue with the logic of needing to update feature branches before merging, that's pretty bread and butter. The specific issue with this workflow is that the "update branch" button for PR B is grayed out because there are these hallucinated conflicts due to the new squash commit.
The update branch button works normally when I don't stack the PRs, so I don't know. It just feels like a half baked feature that GitHub automatically changes the PR target branch in this scenario but doesn't automatically do whatever it takes for a 'git merge origin/main' to work.
> the "update branch" button for PR B is grayed out because there are these hallucinated conflicts due to the new squash commit
Those are not hallucinated. PR B still contains all the old commits of A which means merging would apply them twice. The changes in PR B are computed according to the oldest commits belonging to PR B and main which is the parent of squashed A. That would essentially means applying A twice which is not good.
As for updating PR B, PR B doesn't know where PR A (that are also in PR B) ends because PR A is not in main. Squashed A is a new commit and its diff corresponds to the diff of a range of commits in PR B (the old commits of PR A), not the whole B. There's a lot of metadata you'd need to store to be able to update PR B.
I guess to me, I'm looking at it from the perspective of diffing the repo between the squashed commit on main and the tip of the incoming PR. If there are merge conflicts during the rebase in files that don't appear in that diff, I consider that a hallucination, because those changes must already in the target branch and no matter what happened to those files along the way to get there, it will always be a waste of my time to see them during an interactive rebase.
I don't think we need to store any additional metadata to make the rebase just slightly more smarter and able to skip over the "obvious" commits in this way, but I'm also just a code monkey, so I'm sure there are Reasons.
You’re looking at it from the perspective of a human reasoning. But a computer is a simple machine (what it can do, not how it does it). What seems obvious to you could be a complicated algorithm.
Git store all its information as a directed acyclic graph (a tree) of commits. The leaves of that tree have names, and are what we called branches. Each commit points to a tree (also a tree data structure) where the nodes are blobs (files) and sub trees. But that tree only stores the files that has been changed since the last commit. Git does not store diffs. Diffs are computed as needed.
This why the common ancestor commit is important. From there, a version of the working directory is computed for each branch (main-with-squashed-A and PR B). Files that have not been changed since PR A are ok, but everything else will be different, especially if you’ve modified the same lines.
Squashed A is a brand new commit with a new tree that PR B does not know about. You need to recompute PR B on top of Squashed A, (which will create new commits for PR B).
No, it's a Git thing arising from squash commits. There are workflows to make it work (I've linked the cleanest one I know that works without force pushing), but ultimately they're basically all hacks. https://www.patrickstevens.co.uk/posts/2023-10-18-squash-sta...
Yep that's how I do it if I have to deal with stacked PRs. I also just never use rebase once anything has happened in a PR review that incurs historical state, like reviews or other people checking out the branch (that I know of, anyways). I'll rebase while it's local to keep my branch histories tidy, but I'll merge from upstream once shared things are happening. There are a bunch of tools out there for merging/rebasing entire branch stacks, I use https://github.com/dashed/git-chain.
You "just" need to know the original merge-base of PR B to fix this. github support is not really required for that. To me that's the least valuable part of support for stacked PRs since that is already doable yourself.
The github UI may change the target to main but your local working branch doesn't, and that's where you `rebase --onto` to fix it, before push to origin.
It's appropriate for github to automatically change the target branch, because you want the diff in the ui to be representative. IIRC gitlab does a much better job of this but this is already achievable.
What is actually useful with natively supported stacks is if you can land the entire stack together and only do 1 CI/actions run. I didn't read the announcement to see if it does that. You typically can't do that even if you merge PR B,C,D first because each merge would normally trigger CI.
EDIT: i see from another comment (apparently from a github person) that the feature does in fact let you land the entire stack and only needs 1 CI run. wunderbar!
Oh that's annoying, seems to me there wouldn't have been an issue if you just merged B into A after merging A into main, or the other way around but that already works fine as you pointed out.
I mean if you've got a feature set to merge into dev, and it suddenly merges into main after someone merged dev into main then that's very annoying.
I never understood the PR=branch model GitHub defaulted to. Stacked commits (ala Phabricator/Gerrit) always jived more with how my brain reasons about changes.
Glad to see this option. I guess I'll have to install their CLI thing now.
I must have missed that. Amazing! From a reviewer's POV, this will be so nice to at the very least remove diff noise for PRs built on top of another PR. I usually refrain from reviewing child PRs until the parent is merged and the child can be rebased, for the sole reason that the diffs are hard to review i.r.t. what came from where.
Stacked PRs can be created via the UI, API, or CLI.
You can also run a combination of these. For ex, use another tool like jj to develop locally, push up the branches, and use the gh CLI to batch create a stack of n PRs, without touching local state.
CLI is great because now I can tell my AI agent to do it. “Fix all dependabot security issues (copy logs) and run tests to validate functionality. Create each dependency as its own stack (or commit) so that contributors may review each library update easily.”
Everyone will have their own way of structuring stacks, but I've found it great for the agent to plan a stack structure that mirrors the work to be done.
My point is that Git is just a component of the GitHub tool, and the GitHub CLI is quite good and helps automate many things in GitHub. For example, even just using `gh browse` and `gh pr create --web` and `gh pr view --web` are fantastic tools.
Huh interesting, my mental model is unable to see any difference between them.
I mean a branch is just jamming a flag into a commit with a polite note to move the flag along if you're working on it. You make a long trail, leave several flags and merge the whole thing back.
Of course leaving multiple waypoints only makes sense if merging the earlier parts makes any sense, and if the way you continue actually depends on the previous work.
If you can split it into several small changes made to a central branch it's a lot easier to merge things. Otherwise you risk making a new feature codependent on another even if there was no need to.
As a solo dev I rarely need stacked PRs, but the underlying problem, keeping PRs small and reviewable, is real even when you're your own reviewer. I've found that forcing myself to break work into small branches before I start (rather than retroactively splitting a giant branch) is the actual discipline. The tooling just makes it less painful when you don't.
Curious whether this changes anything for the AI-assisted workflow. Right now I let Claude Code work on a feature branch and it naturally produces one big diff. Stacked PRs could be interesting if agents learned to split their own work into logical chunks.
It's easier to pile on a lot of changes with AI assisted workflows. And reviewing all that is definitely a challenge just because of the volume of changes. I've actually stopped pretending I can review everything in detail because it makes me a bottleneck in the process. Anything that makes reviewing easier is welcome.
To me, stacked PRs seems overly complicated. It seems to boil down to propagating git rebases through stacks of interdependent branches.
I'm fine with that as long as I don't have to deal with people force pushing changes and routinely rewriting upstream history. It's something you probably should do in your own private fork of a repository that you aren't sharing with anyone. Or if you are, you need to communicate clearly. But if the goal is to produce a stack of PRs that in the end merge cleanly, stacked PRs might be a good thing.
As soon as you have multiple collaborators working on a feature branch force pushing can become a problem and you need to impose some rules. Because otherwise you might end up breaking people's local branches and create work for them. The core issue here is that in many teams, people don't actually fork the main repository and have push access to the main repository. Which emulates the central repository model that people were used to twenty years ago. Having push access is not normal in most OSS projects. I've actually gotten the request from some rookie developers that apparently don't get forking to "please give me access to your repository" on some of my OSS projects.
A proper pull request (whether stacked or not) to an OSS project needs to be clean. If you want to work on some feature for weeks you of course need mechanisms to stay on top of up stream changes. OSS maintainers will probably reject anything that looks overly messy to merge. That's their job.
I spend more time in planning and steering the AI implementation than I do on reviewing it's outputs.
I do the obvious checks like tests and spin up a dev instance to make sure the feature works like I want it too, but very rarely am I reviewing every line of code these days.
I have had a lot of success with Claude and jj, telling it to take the stack of work it's done and build me a new stack on top of trunk that's centered around ease of reviewing.
It sometimes will hallucinate older CLI options, because jj has changed at various times, but it's pretty decent with it at this point. The harder part is that a lot of plugins hardcode git into them.
The tooling for that already exists, since a PR can consist of multiple Git commits and you can look at them separately in the UI. I don't know whether agents are any good at navigating that, but if not, they won't do any better with stacked PRs. Stacked PRs do create some new affordances for the review process, but that seems different from what you're looking for.
Looking at multiple commits is not a good workflow:
* It amounts to doing N code reviews at once rather than a few small reviews which can be done individually
* Github doesn't have any good UI to move between commits or to look at multiple at once. I have to find them, open them in separate tabs, etc.
* Github's overall UX for reviewing changes, quickly seeing a list of all comments, etc. is just awful. Gerrit is miles ahead. Microsoft's internal tooling was better 16 years ago.
* The more commits you have to read through at once the harder it is to keep track of the state of things.
>It amounts to doing N code reviews at once rather than a few small reviews which can be done individually
I truly do not comprehend this view. How is reviewing N commits different from/having to do less reviews reviewing N separate pull requests? It's the same constant.
Small reviews allow moving faster for both the author and reviewer.
A chain of commits:
* Does not go out for review until the author has written all of them
* Cannot be submitted even in partial form until the reviewer has read all of them
Reviewing a chain of commits, as the reviewer I have to review them all. For 10 commits, this means setting aside an hour or whatever - something I will put off until there's a gap in my schedule.
For stacked commits, they can go out for review when each commit is ready. I can review a small CL very quick and will generally do so almost as soon as I get the notification. The author is immediately unblocked. Any feedback I have can be addressed immediately before the author keeps building on top of it.
Let's compare 2 approaches to delivering commits A, B, C.
Single PR with commits A, B, C: You must merge all commits or no commits. If you don't approve of all the commits, then none of the commits are approved.
3 stacked PRs: I approve PR A and B, and request changes on PR C. The developer of this stack is on vacation. We can incrementally deliver value by merging PRs A and B since those particular changes are blocking some other engineer's work, and we can wait until dev is back to fix PR C.
This seems to be the root of the problem. Nothing stops a reviewer merging some commits of a PR, except a desire to avoid the git CLI tooling (or your IDE's support, or....). The central model used in a lot of companies requires the reviewee to do the final merge, but this has never been how git was meant to be used and it doesn't have to be used that way. The reviewer can also do merges. Merge (of whichever commits) = approval, in that model.
Yes, the root of the problem is the workflow of the company being centered around GitHub instead of Git itself.
This feature helps improve GitHub so it's useful for companies that do this this way.
At our company, only admin users can actually directly git push to main/master. Everything else HAS to be merged via github and pass through the merge queue.
So this stacked PRs feature will be very helpful for us.
Maybe there’s a git trick I don’t know, but I’ve found making small branches off each other painful. I run into trouble when I update an earlier branch and all the dependent branches get out of sync with it. When those earlier branches get rebased into master it becomes a pain to update my in-progress branches as well
If I understood you correctly, you want to propagate changes in a branch to other branches that depend on it? Then --update-refs is for you[1]. That way, you only need to update the "latest" branch.
Stacking branches for any extended period of time is definitely a poor mixing of the concepts of branches and commits. If you have a set of changes you need to keep in order, but you also need to maintain multiple silos where you can cleanly allow the code to diverge, that divergence constitutes the failure of your efforts to keep the changes in order.
Until you can make it effortless, maintaining a substantial commit structure and constantly rebasing to add changes to the proper commit quickly turns into more effort than just waiting to the end and manually editing a monster diff into multiple sensible commits. But we take the challenge and tell ourselves we can do better if we're proactive.
I take from GP that they try to make their branches small, and keep the cycle of development->review->merging small, so that the problem stacked PRs seeks to solve doesn't materialize in the first place.
Stacked PRs in my experience has primarily been a request to merge in a particular order. If you're the only merger, as in GP's case, there's no need to request this of yourself.
Whenever I send a big diff. I spend some time annotating with comment first to helps the reviewer. A good summary of the changes in the description, the I annotate the diff of the PR, explaining approaches, the design of a specific changes, tricky part of the code, boilerplate,... Trying to guess the context is where the review bottleneck is, so I present it alongside the code.
Very cool that GitHub actually put stacks in the UI vs. GitLab's `glab stack`[0] (which looks just like the `gh stack` part of GitHub's thing).
One part that seems like it's going to feel a little weird is how merging is set up[1].
That is, if I merge the bottom of the stack, it'll rebase the others in the stack, which will probably trigger a CI test run. So, if I have three patches in the stack, and I want to merge the bottom two, I'd merge one, wait for tests to run on the other, merge the second vs. merge just those two in one step (though, without having used it, can't be sure about how this'd work in practice—maybe there's some way to work around this with restacking?)
> So, if I have three patches in the stack, and I want to merge the bottom two, I'd merge one, wait for tests to run on the other, merge the second vs. merge just those two in one step
As we have it designed currently, you would have to wait for CI to pass on the bottom two and then you can merge the bottom two in one step. The top of the stack would then get rebased, which will likely trigger another CI run.
Thanks for the callout - we'll update those docs to make it clear multiple PRs can be merged at once.
Just using git, you'd send a set of patches, which can be reviewed, tested and applied individually.
The PR workflow makes a patch series an undivisible set of changes, which must be reviewed, tested and applied in unison.
And stacked PRs tries to work around this issue, but the issue is how PRs are implemented in the first place.
What you really want is the ability to review individual commits/patches again, rather than work on entire bundles at once. Stacked PRs seems like a second layer of abstraction to work around issues with the first layer of abstractions.
The teams that I have worked with still apply the philosophy you’re describing, but they consider PRs to be the “commit”, i.e. the smallest thing that is sane to apoly individually.
Then the commits in the PR are not held to the standard of being acceptable to apply, and they are squashed together when the PR is merged.
This allows for a work flow in which up until the PR is merged the “history of developing the PR” is preserved but once it is merged, the entire PR is applied as one change to the main branch.
This workflow combined with stacked PRs allows developers to think in terms of the “smallest reviewable and applicable change” without needing to ensure that during development their intermediate states are safe to apply to main.
Doesn’t this mean that a first review might request that a specific change be reverted, and then a later reviewer reviews that reversion? That’s essentially reviewing a noop, but understanding the it’s a noop requires carefully checking all previous now-invalidated changes.
Squashing is fine if you’re just making a mess of temporary commits as you work and you don’t want to keep any of those changes separate in master, but that’s not a useful review workflow. A lot of times I’ve built a feature in a way that decomposed naturally into e.g. two commits: one to do a preparatory refactor (which might have a lot of noisy and repetitive changes, like changing a function signature) and another to actually change the behavior. You want those changes to be separate because it makes the changes easier to review; the reviewer quickly skims the first commit, observes that it’s a mechanical refactor, and the change in behavior has its own, smaller commit without all the noise.
“What if there’s feedback and you need to make changes after the code review?” Then I do the same thing I did before I posted the code review: make separate “fixup” commits and do an interactive rebase to squash them into my commits. (And yes, I do validate that the intermediate commits build cleanly.)
There’s nothing you get from stacked PR’s that you don’t also get from saying “please review my feature branch commit by commit”.
Yes what you’re describing is literally the thing GitHub has built but instead of having to make a bunch of compromises, there is dedicated UI and product metaphor for it.
Some examples of compromises:
You can’t merge partially merge a large “review commit by commit” PR so you are forced to wait until it is all ready to merge.
Exactly! A stack of PRs is really the same beast as a branch of commits.
The traditional tools (mailing-lists, git branches, Phabricator) represented each change as a difference between an old version of the code and the proposed new version. I believe Phabricator literally stored the diff. They were called “diffs” and you could make a new one by copying and pasting into a <textarea> before pressing save*.
The new fangled stuff (GitHub and its clones) recorded your change as being between branches A and B, showed you the difference on the fly, and let you modify branch B. After fifteen years of this we are now seeing the option for branch A to be something other than main, or at least for this to be a well supported workflow.
In traditional git land, having your change as a first class object — an email or printout or ph/D1234 with the patch included — was the default workflow!
Still not sure this is the right solution. My problem is if one of your first stages gets rejected in review or requires significant changes, it invalidates so much work that comes after it. I've always when possible preferred to get small stuff merged in to production as it happens rather than build an entire feature and put it up for review.
> it invalidates so much work that comes after it.
No, not necessarily.
I work on a large repo and new features often involve changes to 3 different services: 2 from the backend, and the frontend UI. Sending a single PR with changes to all 3 services is really not ideal: the total diff size in a feature I added recently was maybe 600+ lines, and the reviewers for frontend and backend changes are different people. The changes in the 2 backend services can be thought of as business logic on one side and interactions with external platforms on the other. The business logic can't work without integrating calls to external APIs, and the UI can't work without the business logic.
These days I open 3 separate PRs and the software only works once all 3 are merged and built. It would be great to have all of them as a single package that's still testable and reviewable as 3 distinct parts. The UI reviewer can check out the whole stacked PR and see it running locally with a functional backend, something that's not possible without a lot of manual work when we have 3 PRs.
The LLVM community used this model for years with Phabricator before it was EOL'd and moving to GH and PRs was forced. It's a proven model and works very well in complex code bases, multiple components and dependencies that can have very different reviewer groups. E.g:
1) A foundational change to the IR is the baseline commit
2) Then some tweaks on top to lay the groundwork for uses of that change
3) Some implementation of a new feature that uses the new IR change
4) A final change that flips the feature flag on to enable by default.
Each of these changes are dependent on the last. Without stacked PRs you have o only one PR and reviewing this is huge. Maybe thousands of lines of complex code. Worse, some reviewers only need to see some parts of it and not the rest.
Stacked diffs were a godsend and the LLVM community's number one complaint about moving to GitHub was losing this feature.
this works much better in Phabricator because commits to diffs are a 1:1 relationship, diffs are updated by amending the commit, etc., the Github implementation does seem a bit like gluing on an additional feature.
Right, a PR is "just" a set of commits (all must be in the same branch) that are intended to land atomically.
Stacked PRs are not breaking up a set of commits into divisible units. Like you said, you can already do that yourself. They let you continue to work off of a PR as your new base. This lets you continue to iterate asynchronously to a review of the earlier PRs, and build on top of them.
You often, very often, need to stage your work into reviewer-consumable units. Those units are the stack.
I've been using `git town`[1] for years to managed stacked PR's alone with Github PR's[2] and juniors I have introduced it to have really found it a helpful mental model when developing features.
I hope the Gitub CLI will include syncing[3] 'stacks' locally with upstream in a similar way.
There’s a startup callled Graphite dedicated to stacked PRs. I have been using them for a while now I always wonder why github doesn’t implement something similar to this. I probaly will try and switch to GitHub to see if it works flawlessly
IME the github workflow promotes bad commit hygiene by making squashing or rebasing as-is an either-or choice in the web GUI.
This will help some since you can more easily split PRs into units that make sense to squash at the end, but it still seems like not doing this on a per-commit basis is a disadvantage compared to Gerrit. With Gerrit I can use all the built-in Git rebase/squash/fixup tools to manage the commit stack and push everything in one go. I don't think there's a nearly as convenient a way to work with stacked branches in Git.
I've been doing stacked PRs for ~2 years now. Thus, I don't quite see the need for this CLI. Git has had some additions in the last few years that make this work natively – specifically the --update-refs flag[1] or the rebase.updateRefs config. Combined with `git commit --fixup`, rebase.autoStash, and rebase.autoSquash rebasing stacks becomes a breeze (as long as you work off from the tip of your stack). Add in git-absorb[2] and the heavy-lifting is taken care of.
My biggest gripe with GitHub when working with stacks – and something that's not clarified in these docs – is whether fast-forward merges are possible. Its "Merge with rebase" button always rewrites the commit. They do mention that the stack needs to be rebased in order to merge it. My workaround has been `git merge --ff-only top-branch-of-stack` to merge the entire stack locally into main (or anything in between actually) and then push. GitHub neatly recognizes that each PR in the stack is now in main and marks them all as merged. If there are subsequent PRs that weren't merged it updates the base branch.
Having said that, it's great to see GitHub getting a proper UI for this. It's also great that it understands the intent that branch B that goes on top of branch A is a stack and thus CI runs against. I just hope that it's not mandatory to use their CLI in order to create stacks. They do cover this briefly in the FAQ[3], but it might be necessary to use `gh stack init --adopt branch-a branch-b branch-c`. On the other hand, if that removes the need to manually create the N PRs for my stack, that's nice.
> Git has had some additions in the last few years that make this work natively – specifically the --update-refs flag[1] or the rebase.updateRefs config. Combined with `git commit --fixup`, rebase.autoStash, and rebase.autoSquash rebasing stacks becomes a breeze (as long as you work off from the tip of your stack). Add in git-absorb[2] and the heavy-lifting is taken care of.
...or you don't bother with all that and simply do:
Not at all. One of the tricks of using AI is context management and managing the Git history yourself can be a big part of that. If the AI has a stupid idea and implements it, even when you tell it, “that was a stupid idea, don’t do that, change it back”, the history could persist and the stupid idea will poison the context window every time an agent reads the commit history. It’s even worse if you had the stupid idea!
Also, my current workflow actually has hooks to block agents from creating or changing commits. I know at some point this will be a limit to scaling, but I think that will result in me spending more rather than less time in git.
Maybe this is just a skill issue, but even with several attempts I just can't figure out why I would use stacked diffs/PRs. Though maybe that's because of the way I work?
I notice a lot of examples just vaguely mention "oh, you can have others review your previous changes while you continue working", but this one doesnt make sense to me. Often times, the first set of commits doesn't even make it to the end result. I'm working on a feature using lexical, and at this point I had to rewrite the damn thing 3 times. The time of other devs is quite valuable and I can't imagine wasting it by having them review something that doesn't even make it in.
Now, I have been in situations where I have some ready changes and I need to build something on top. But it's not something just making another branch on top + rebase once the original is merged wouldn't solve.
Imagine you have some task you are working on, and you wish to share your progress with people in bite sized chunks that they can review one at a time, but you also don’t want to wait for their reviews before you continue working on your task.
Using a stacked set of PRs you can continue producing new work, which depends on the work you’ve already completed, without waiting for the work you’ve already completed to be merged, and without putting all your work into one large PR.
Yeah that is a “stacked” pr. The tooling is nice especially when have a larger stack and make changes to the first branch. Update refs + push all branches, same with merging and rebasing onto main.
in Phabricator you either abandon the original diffs entirely, or you amend them. you don't just stack more commits with meaningless messages like "WIP", "lint fix", etc. on top.
> The time of other devs is quite valuable and I can't imagine wasting it by having them review something that doesn't even make it in.
this is now what stacked diffs are for. stacked diffs doesn't mean putting up code that isn't ready. for example you are updating some library that needs an API migration, or compiler version that adds additional stricter errors. you need to touch hundreds of files around the repository to do this. rather than putting up one big diff (or PR) you stack up hundreds of them that are trivial to review on their own, they land immediately (mitigating the risk of merge conflicts as you keep going) then one final one that completes the migration.
I also branch out, and rebase. Also, keep updating and rebasing until merged. It’s tedious when PR take ages for approval, as I keep creating new branches on top of each other.
So, when I saw this announcement seemed interesting but don’t see the point of it yet.
I thrive on stacked PRs but this sure seems like a weird way to implement support for it. Just have each branch point to their parent in the chain, the end. Just native Git. I've been longing for better GitHub support for this but the CLI is not where I need that support: just the UI.
Rebasing after merging a base branch becomes a pain though, when you do this. IMO the CLI will be nice to automate the process of rebasing each branch on its parent.
The CLI is completely optional, you can create stacked PRs purely via the UI.
Also the rationale for having a chain of branches pointing to each other was so the diff in a PR shows just the relevant changes from the specific branch, not the entire set of changes going back to the parent/trunk.
How does GitHub determine if a PR is part of a stack? Is it automatically detected so that I don't need to adjust my tooling that already creates chained PRs?
+1 this isn’t something new, it’s been possible all along in native git if you’re willing to do branch management and rebasing yourself. Just without the fancy UI / stack map.
Does this work from a fork? That is, can I file a stacked PR to a project not owned by me, by creating branches in my forked project? Previously I asked AI about how to contribute stacked PR, it told me that I can only do it when I have push privileges to the repo, not from a fork, and the doc here is ambiguous.
----
OK, I found this from official docs, so this feature is now quite useless to me:
> Can stacks be created across forks?
> No, Stacked PRs currently require all branches to be in the same repository. Cross-fork stacks are not supported.
I have never got a good answer to "can't you just make smaller PRs". This is convoluted tooling (needs its own CLI) for something you could achieve with just learning how git works.
IMO this tool is basically allowing you to do that, it just takes care of the bookkeeping to associate the series of smaller PRs with eachother which is possible today but requires a lot of clicking.
If there is a stack of size n and you make a modification at the first change, closest to the trunk, is there a single git command you can run to rebase the other n-1 branches and ensure they remote branches are updated?
Assuming you're currently on the most recent branch (furthest from the trunk), `git rebase -i --update-refs trunk` will rebase all the intermediate branches. If you need to make a change to the first branch nearest the trunk, either use `edit` in the interactive rebase, or make a fixup commit and enable autosquash for the rebase. The `--update-refs` flag makes sure that all the intermediate branches get updated during the rebase.
Then, to push them all, something like `git push origin 'refs/heads/yourname/*'` will push all branches prefixed with `yourname/`. It's a bit stupid that one can't just do `git push 'yourname/*'` though.
I agree that a `gh stack` command is not needed, but this feels to me like just a better UI feature for a good git workflow. It literally is about making multiple smaller PRs that build on top of each other.
The question is, why are you not just merging them into main as you go? It's a bit of a smell when you "need" to merge branches into branches. It shows a lack of safety and ease in deployments, which is the real problem to solve IMO.
Right, so 'just work the way the tool requires instead of making the tool work the way you want'. I would prefer the tool worked the way I want and the way I think of the changes instead.
Super excited to give this a whirl - i've been messing with graphite's `gt` command for stacking and it's been relatively decent but I didn't love needing to bring in another tool/service/account when I only care about the stacking behaviour. Was a fun experiment but nice I can simplify back onto `gh` and `git`
I hope that GitHub continues copying Graphite's homework in terms of functionality, because from what I can see they don't have equivalents to `gt split`, absorb, and so on. Those can be very useful in the right contexts.
This is awesome honestly, Stacked PRs are one of those features that feels obvious in hindsight. Breaking a n-line PR into 3 focused layers where each one is independently reviewable is a huge win for both the author and reviewer. The native GitHub UI with the stack navigator is the right call too, and there's no reason this should require a third-party tool.
One thing I keep thinking about in this same direction: even within a single layer of a stack, line-level diffs are still noisy. You rename a function and update x call sites, the diff shows y changed lines. A reviewer has to mentally reconstruct "oh this is just a rename" from raw red/green text.
Semantic diffing (showing which functions, classes, methods were added/modified/deleted/moved) would pair really well with stacks. Each layer of the stack becomes even easier to review when the diff tells you "modified function X, added function Y" instead of just showing changed lines.
I've been researching something in this direction, https://ataraxy-labs.github.io/sem/. It does entity-level diffs, blame, and impact analysis. Would love to see forges like GitHub move in this direction natively. Stacked PRs solve the too much at once problem. Semantic diffs solve the "what actually changed" problem. Together they'd make code review dramatically better.
I already do this using git branched. Whenever I have features that depends on one another I create a feature branch and then stack branches on top of each other for individual feature so it's easy for the reviewer to go through the code and and also keep the PR size quite small. Also this gives me freedom to push more than one commit for each branch to fix things.
The only annoying part is that I have to keep on merging the base branch to the feature branch constantly to keep it up-to date. If Github can provide a feature to do that automatically, then that would be perfect. Other than that, I don't see any advantage on this stacked PR approach they are proposing.
I think the only thing I miss from GitLab was being able to make merge requests depend on other merge requests, even across repositories. So I could make a backend repository MR depend on a library repository MR, and even enable auto-merge that’d fire when the backend MR was reviewed and the dependency was also merged.
GitLab's UI around MRs (PRs) is IMO miles better than what GH's been offering. Try creating a PR from branch A to main, and then rebasing A. GitLab handles this fine and can show you changes between the two revisions; GitHub is completely lost.
That's not "how it works", that's "how you['re supposed to] use it"… for "how it works" I would've expected something like "the git branches are named foo1 foo2 and foo3 and we recognize that lorem ipsum dolor sit amet…"
…which, if you click the overview link, it says "The CLI is not required to use Stacked PRs — the underlying git operations are standard. But it makes the workflow simpler, and you can create Stacked PRs from the CLI instead of the UI." … erm … how about actually explaining what the git ops are? A link, maybe? Is it just the PRs having common history?
…ffs…
(In case it's not obvious: I couldn't care less for using a GH specific CLI tool.)
> Large pull requests are hard to review, slow to merge, and prone to conflicts. Reviewers lose context, feedback quality drops, and the whole team slows down.
OK, yeah, I’m with you.
> Stacked PRs solve this by breaking big changes into a chain of small, focused pull requests that build on each other — each one independently reviewable.
I don’t get this part. It seems like you are just wasting your own time building on top of unreviewed code in branches that have not been integrated in trunk. If your reviews are slow, fix that instead of running ahead faster than your team can actually work.
I think it is conceptually the same but multiple PRs gives you the tools to manage the commits properly which GitHub is missing. You can't do the equivalent of `git rebase -i` in the GitHub UI to squash a fixup into a previous commit. Having each change in it's own PR enables that workflow using the existing GitHub UI.
Stacked PRs track changes through updates and can be integrated progressively as they get validated.
They also allow reviewing commits individually, which is very frustrating to do without dedicated support (unless you devolve back to mailing list patch stacks).
I don't think this is it. The main driver is that several operations in GH are scoped around a PR, not a commit. So the reason you need stacked PRs is that the layer of tooling above `git` is designed to work on logical groups of commits called a PR.
Right, the argument against: "how is this any different than splitting into single commits?" is simply: In general you want just one level above a commit which is the PR
Commits are immutable and you never know which feedback goes stale when you add another commit.
I'm not a huge fan, since stacked PRs mean the underlying issues don't get addressed (reviews clearly taking too long, too much content in there), but it seems they want something that works for their customers, right now, as they work in real life.
When you edit a commit, it creates a new commit. They are immutable. You can still find the old commit via the reflog, until it gets eventually gc'd.
If I had to guess a reason they were downvoted (and I didn't downvote, to be clear), it's probably because people see stacked diffs as specifically solving "reviews clearly taking too long, too much content in there", and so it feels contradictory. Then again, as I said, I didn't downvote!
It would be the same if commits were meaningful things. But typically they're not. The PR is the meaningful thing. A commit is something like "fix the lint error".
CI runs on each PR, you get a whole PR message and discussion/review interface for each PR. Each PR can itself consist of multiple commits. You can have stacked PRs from different authors (though from another comment it sounds like they may not have implemented that).
It's a big improvement (assuming they've done it right).
'Large pull requests are hard to review' is a good reason to keep PRs small, but small PRs also encourage continuous integration/delivery/deployment. Stacked PRs sound like they encourage long-lived feature branches instead.
Looks interesting, but it seems you need to know the final shape of the stack before you start creating Pull Requests. So it's useful if you create Pull Request A, then immediately start working on something that builds on top of A, create a Pull Request for that (while A is still a PR), then you can do A->B->C
Here's something that would be useful: To break down an already big PR into multiples that make up a stack. So people can create a stack and add layers, but somehow re-order them (including adding something new at the first position).
It appears the CLI is only half-baked so far. Given how many things they've borrowed from Graphite (a tool which adds this type of workflow), it should only be a matter of time until they add a `split` command. Graphite lets you split a large set of changes by commit or by hunk which is very handy.
It looks like in the UI if you base a PR on another branch you can just check a box to make it a stack. So I don't think you have to know the full shape of the stack in advance unless you're using the cli.
I use jj to stack branches so i'll just be using the UI to do github pr stacks.
This just reeks to me of bad practice. Why use this as opposed to breaking your change into smaller PRs and merging them individually behind a feature flag or similar? With this, you have a marginally better UX for reviewing through the Github website, but the underlying issues are the same. The change being introduced is not sufficiently testable by itself, or it's (somehow) too tightly coupled to other parts of the UI/codebase that it can't be split. You still need to test for integration issues at every point of the stack, and some architecture issues or points of code reuse can't be seen from stacked changes like this.
Not for me, but I'm glad it fits other people's workflows. I just hope it doesn't encourage people to try make poorly reasoned changes!
When I've reached for stacked PRs (in the past, not using this feature) it's precisely because I've split my change into smaller PRs being merged individually.
I've just written those smaller PRs at once, or in quick enough succession that the previous PRs weren't merged before the later ones were ready. And the later ones relied on the previous ones because that's how working on a feature works.
The earlier PRs are absolutely reviewable and testable without relying on the later ones. The later ones are just treating the earlier ones as part of the codebase. I.e. everything here looks like two different PRs except the timing.
An obvious example would be "implement API for a feature" and then "implement UI that uses that API". Two different PRs. The second fundamentally relies on the first.
This is a perfect example that I've often seen in practice. There's nothing blocking in this workflow at all, and no reason these changes cannot be made in independent changes. e.g.
1) API implementation - Including tests and docs this should be perfectly acceptable to merge and review independently
2) UX implementation - Feature flagged, dummy API responses, easy to merge + review
3) One quick "glue" PR where the feature can be integration tested etc
This prevents awful merge conflicts, multiple rounds of increasingly complex stacked reviews, and a host of other annoyances.
Is there any reason that the stacked PR workflow is better that I'm ignoring or overlooking?
You're creating more work for no reason. There is absolutely no reason to make dummy API responses, a feature flag (well unless you want to delay public release of the features - domain dependent here), or a glue PR.
Moreover you haven't even eliminated the dependency. The UI PR requires knowing that the dummy API responses you've created fit the right format - i.e. approval of the API PR up to small nits.
Just test against the actual implementation from the start. Even without stacked PRs just leave the second as a draft with both sets of commits until the first is merged then rebase and make it.
Stacked PRs are superior here because they eliminate that extra work of the draft PR and parallelize the review process slightly better.
I do this as well, but there is a workflow problem to solve and that is: getting PRs merged when they need to be to continue working.
It's not a simple problem to solve, we can't all just jump because someone finished some work after all. But if the PRs are OK to rubber stamp, and merge, and they're safely behind a feature flag, then it could just be as simple as letting the submitter merge without the need for an extra review. That can of course be contentious, but then we can ask "why not?" and figure out what non-human gateways need to be added to help make it possible etc.
I'm finding myself increasingly interested in understanding what friction can be removed from the software review, merge and release process, without sacrificing safe, well tested, understandable code that follows good standards.
Let's say I have the canonical example of a stack from main via a backend-pr and a frontend-pr. When my stack is done I send it for review to one frontend reviewer and one backend reviewer.
Usually when you develop a "full stack" thing you continuously massage the backend into place while developing frontend stuff. If you have 10 commits for frontend and 10 for backend, they might start with 5 for backend, then 5 commits to each branch to iron out the interface and communication, and finally 5 commits on the frontend. Let's call these commits B1 through B10 and F1 through F10. Initially I have a backend branch based on main wuth commits B1 through B5.
Then I have a frontend branch based on B5 with commits F1 through F5. But now I need to adjust the backend again and I make change B6. Now I need to rebase my frontend branch to sit on B6? And then I make F6 there (And so on)?
And wouldn't this separation normally be obvious e.g. by paths? If I have a regular non-stack PR with 20 commits and 50 changed files, then 25 files will be in /backend and 25 in /frontend.
Sure, the reviewers who only review /frontend/* might now see half the commits being empty of relevant changes. But is that so bad?
> If you have 10 commits for frontend and 10 for backend
In this model, you tend to want to amend, rather than add more commits. And so:
> they might start with 5 for backend, then 5 commits to each branch to iron out the interface and communication,
You don't add more commits here, you modify the commits in your stack instead.
> Now I need to rebase my frontend branch to sit on B6?
Yes, when you change something lower in the stack, the things on top need to be rebased. Because your forge understands that they're stacked, it can do this for you. And if there's conflicts, let you know that you need to resolve them, of course.
But in general, because you are amending the commits in the stack rather than adding to it, you don't need to move anything around.
> And wouldn't this separation normally be obvious e.g. by paths?
In the simplest case, sure. But for more complex work, that might not be the case. Furthermore, you said you have five commits for each; within those sets of five, this separation won't exist.
What a time to be alive. Stacked PRs are now a native feature of Github, even with first-class support for your ai agents. Vibeslop your whole Jira Backlog. Don't fear the merge anymore. Just make any feature branch a long-lived branch by stacking one upon another like bricks.
I'm old enough to have worked with SVN and young enough to have taught engineers to avoid stacking PR in Git. All wisdom has been lost and will probably be rediscovered in another time by another generation.
Yeah, not sure what this solves that doing multiple PRs from one feature branch into another doesn't solve. But building behavior that into AI agents wouldn't be cool enough, I guess.
I think the core conceptual difference between a stacked diff and PRs as we use them in open source is the following:
A PR is basically a cyberspatial concept saying "I, as a dog on the internet, am asking you to accept my patches" like a mailing list - this encourages trying to see the truth in the whole. A complete feature. More code in one go because you haven't pre-agreed the work.
Stacks are for the opposite social model. You have already agreed what you'll all be working on but you want to add a reviewer in a harmonious way. This gives you the option to make many small changes, and merge from the bottom
> a chain of small, focused pull requests that build on each other — each one independently reviewable.
I have never understood what this even means.
Either changes are orthogonal (and can be merged independently), or they’re not. If they are, they can each be their own PR. If they’re not, why do you want to review them independently?
If you reject change A and approve change B, nothing can merge, because B needs A to proceed. If you approve change A and reject change B, then the feature is only half done.
Is it just about people wanting to separate logical chunks of a change so they can avoid get distracted by other changes? Because that seems like something you can already do by just breaking a PR into commits and letting people look at one of those at a time.
I’ve tried my best to give stacked-diff proponents the benefit of the doubt but none of it actually makes sense to me.
The canonical example here is a feature for a website that requires both backend and frontend work. The frontend depends on the backend, but the backend does not depend on the frontend. This means that the first commit is "independent" in the sense that it can land without the second, but the second is not, hence, a stack. The root of the stack can always be landed independently of what is on top of it, while the rest of the stack is dependent.
> If they’re not, why do you want to review them independently?
For this example, you may want review from both a backend engineer and a frontend engineer. That said, see this too though:
> that seems like something you can already do by just breaking a PR into commits and letting people look at one of those at a time.
If you do this in a PR, both get assigned to review the whole thing. Each person sees the code that they don't care about, because they're grouped together. Notifications go to all parties instead of the parties who care about each section. Both reviews can proceed independently in a stack, whereas they happen concurrently in a PR.
> If you approve change A and reject change B, then the feature is only half done.
It depends on what you mean by "the feature." Seen as one huge feature, then yes, it's true that it's not finished until both land. But seen as two separate but related features, it's fine to land the independent change before the dependent one: one feature is finished, but the other is not.
If the layers of a stack have a disjoint set of reviewers things are viewed in separation which might lead to issues if there is no one reviewing the full picture.
That is why your forge will show that these two things are related to each other, and you may have the same person assigned to review both. It can show you this particular change in the context of the rest of them. But not every reviewer will always want to see all of the full context at all times.
> If you do this in a PR, both get assigned to review the whole thing. Each person sees the code that they don't care about, because they're grouped together.
There are two separate issues you’re bringing up:
- Both groups being “assigned” the PR: fixable with code owners files. It’s more elegant than assigning diffs to people: groups of people have ownership over segments of the codebase and are responsible for approving changes to it. Solves the problem way better IMO.
- Both groups “seeing” all the changes: I already said GitHub lets you view single commits during PR review. That is already a solved problem.
And I didn’t even bring up the fact that you can just open a second PR for the frontend change that has the backend commit as the parent. Yes, the second PR is a superset of the first, but we’ve already established that (1) the second change isn’t orthogonal to the first one and can’t be merged independently anyway, and (2) reviewers can select only the commits that are in the frontend range. Generally you just mark the second PR as draft until the first one merges (or do what Gitlab does and mark it as “depends on” the first, which prevents it from merging until the first one is done.) The first PR being merged will instantly make the second PR’s diff collapse to just the unique changes once you rebase/merge in the latest main, too.
All of this is to explain how we can already do pretty much all of this. But in reality, it’s silly to have people review change B if change A hasn’t landed yet. A reviewer from A may completely throw the whole thing out and tell you to start over, or everything could otherwise go back to the drawing board. Making reviewers look at change B before this is done, is a potential for a huge waste of time. But then you may think reviewers from change B may opt to make the whole plan go back to the drawing board too, so what makes A so special? And the answer is it’s both a bad approach: just make the whole thing in one PR, and discuss it holistically. Code owners files are for assigning ownership, and breaking things into separate commits is to help people look at a subset of the changes. (Or just, like, have them click on the folder in the source tree they care about. This is not a problem that needs a whole new code review paradigm.)
Code owners automatically assigns reviewers. You still end up in the state where many groups are assigned to the same PR, rather than having independent reviews.
> I already said GitHub lets you view single commits during PR review.
Yes, you can look at them, but your review is still in the context of the full PR.
> And I didn’t even bring up the fact that you can just open a second PR for the frontend change that has the backend commit as the parent.
The feature being discussed here is making this a first-class feature of the platform, much nicer to use. The second PR is "stacked" on top of the first.
> You still end up in the state where many groups are assigned to the same PR
> Yes, you can look at them, but your review is still in the context of the full PR.
Why is this a bad thing? I don’t get it. This has literally never been a problem once in my career. Is the issue that people can’t possibly scroll past another discussion? Or… I seriously am racking my brain trying to imagine why it’s a bad thing to have more than one stakeholder in a discussion.
I can think of a lot of reasons why doing the opposite, and siloing off discussions, leads to disaster. That is something I’ve encountered constantly in my career. We start out running an idea past group A, they iterate, then once we reach a consensus we bring the conclusion to group B and they have concerns. But oh, group A already agreed to this so you need to get on board. So group B feels railroaded. Then more meetings are called and we finally bring all the stakeholders together to discuss, and suddenly hey, group A and B both only had a partial view of the big picture, and why didn’t we all discuss this together in the first place? That’s happened more times in my career than I can count. The number of times group B is mad that they have to move their finger to scroll past what group A is talking about? Exactly zero.
It's totally possible that you aren't the target audience for this sort of feature. It tends to be more useful in very large team and/or monorepo contexts.
This isn't about siloing discussions: it's about focus. You can always see the full stack if you want to go look at the other parts, the key is that you don't have to.
The goal is to get thoroughly reviewed changes. It's much easier to review five 100 line changes than one 500 line one, and it's easier to review five 500 line changes than it is a 2500 line one. Keeping commits small and tightly reviewed leads to better outcomes in the end. Massive PRs lead to rubber stamps of +1.
I agree that that scenario sounds like a nightmare. But I don't think that a PR is the right place to solve that problem: it sounds like something that should have been sorted before any of the code was written in the first place.
> It's much easier to review five 100 line changes than one 500 line one, and it's easier to review five 500 line changes than it is a 2500 line one.
This is true if the changes are orthogonal and are truly independent. One should always favor small independent changes if one can.
But when changes are all actually part of the same unit, and aren’t separable (apart from maybe the first of N of them which may be mergeable independently), proponents always seem to advocate that stacked diffs can somehow change this fact. “Oh if only we had stacked diffs we could break this into smaller changes”, ignoring the fact that no, they’d still be ordered and dependent on one another.
Stacked diffs seem like a UI convenience for reviewers… that’s fine I guess. GitHub is basically what you get when you ask the question “how can we make code review as tedious and unhelpful as possible”, and literally anything would be better than what we have (seriously I could fill a book with how bad GitHub is. I don’t think I could design a worse experience if I tried.) So, maybe I should just be happy they’re trying anything.
In stacked diffs systems, the idea is that the base of the stack (once reviewed) can always be merged independently, so you're totally right that like, if you just purely think you can split things up when they shouldn't be split up, that would be bad.
This is the model that the kernel uses, as well as tons of other projects (any Gerrit user, for example), and so it has gotten real-world use and at scale. That said, everyone is also entitled to their preferences :)
The kernel uses a mailing list, and a “review” means a mailing list thread. With some nice CLI tools to integrate with git when you want to actually apply the patch (or start a review thread.)
In that world, “[PATCH 2/5]” (or whatever) in the subject title, and a different CC list for each patch, is a nice way to be able to ensure different subsets of the patch series have different discussions. That’s great.
But if you’re going to compare this to a GitHub UI, you have to choose the basis for comparison, because the two are so utterly different. Choosing one aspect (can we make sure discussions are kept separate), and saying “therefore the kernel uses stacked diffs” is a huge misrepresentation of how different GitHub’s approach is.
Because the kernel approach is the platonic ideal of a code review: it’s a simple threaded discussion between stakeholders, centered around a topic (the patch, which is inlined right in the email.) I would wager close zero kernel maintainer actually look at the diffs exclusively via their email client. They probably just check out the changes locally and look at them, and the purpose of the mailing list is to facilitate focused discussion on parts of the change (which is all we really want, in the end.)
GitHub has so thoroughly shit the bed on actually developing a good model of “threaded discussion about a change”, that you have to change the way you think about git’s model to fix how awful GitHub is at allowing review discussion to stay focused. You shouldn’t need to think about stacked diffs and multiple PR’s. You should use git branches as intended, multiple commits representing changes, and a merge meaning “this branch makes it or not.” That GitHub’s UI for discussing subsets of a change is so abysmal, does not mean the model is wrong. It means their discussion system is so abysmal that a mailing list TUI can run circles around it. Fixing this is GitHub’s problem, and doesn’t require any changes to how PR’s should be split up.
If you have a 2500-line PR with 5 500-line commits, GitHub should not require you to split things up further in any way, just to unfuck their discussion system.
Random idea I spent 10 seconds thinking about: let me start a “here’s a thread discussing the UI changes” and add folks to it, and “here’s a thread discussing the backend changes”, and add folks to that. I can then say “let’s not merge this until both threads are green”. You still see the whole change in the UI. (You can click directories to drill into the changes, that solves the “but the diff is too big” issue.) Discussion on a chunk of the diff is scoped to a discussion thread, which you select when sending the message. Thus, all discussion on any part of the diff is still scoped to a “discussion thread” of arbitrary subsets of stakeholders.
None of this needs me to change how I split up my git branches, an entire logical change is still either “merged” or “not-merged” (seriously who cares about the Pyrrhic victory of merging only change 1/N), and if we want to limit scopes of discussion to subsets of a change, we can just… do that.
Sorry, I am talking about stacked diffs in general, not this specific implementation on GitHub. That "Patch 2/5" is five stacked diffs, on top of each other. Forges that are stacked-diff native do that same kernel flow, just on the web instead of over email. You can also see this corroborated over here: https://news.ycombinator.com/item?id=47758251
All of the advantages, like "it’s a simple threaded discussion between stakeholders, centered around a topic", is exactly why people like stacked diffs over PRs.
GitHub is doing "stacked PRs", which is like stacked diffs but more like PRs in the sense that they're stacked branches rather than stacked diffs. I agree that this seems less ideal, but they also are putting it into an existing project, rather than rebuilding everything around it. There's pros and cons to both approaches, but I agree that I'd prefer a native system built for this, personally. I'm still glad they're going to be popularizing the general concept.
> Sorry, I am talking about stacked diffs in general, not this specific implementation on GitHub
My point is that the LKML and what GitHub do is so different that the definition of “stacked diffs in general” can only describe a tiny aspect of each, if you want to call both of their approaches by the same name. From where I sit, the only common element between them is “they offer a way to keep discussion separated.”
If that’s all people are actually complaining about, there are a thousand better ways to “keep discussion separated” that don’t require me to pretend that it’s ok that only a subset of my branch is ok to merge.
In git, a branch is the thing you either merge or don’t. You merge multiple commits at once, or you don’t. It’s a great model. Breaking up the branch into smaller pieces, and giving people the impression it’s ok to merge the first commit but not the rest, just to unfuck the discussion UX, is putting the cart before the horse. I make a branch strictly because I want it to either all merge or none of it merge. It’s the only sensible approach in my book. If a discussion system is so bad that this is unworkable, it means the discussion system is bad, it doesn’t mean the conceptual model of a merge is bad.
> My point is that the LKML and what GitHub do is so different that the definition of “stacked diffs in general” can only describe a tiny aspect of each
That's fine, what I mean is, when we started this convo, I thought you were asking about the general concept of stacked diffs, not the specifics of what GitHub is releasing here. That's my mistake for misunderstanding, sorry about that.
This is also (assumedly, anyway) why they're calling this "stacked PRs" and not "stacked diffs," because what they're doing is slightly different than Gerrit, Phabricator, Critique, etc.
Thanks for indulging me so far, by the way, I really appreciate this discussion, it's very stimulating.
After thinking about the whole thing I think I can summarize my opinion a lot better now:
Stacked diffs are a category error. Units of discussion, and units of integration, should not be conflated.
A branch is my unit of intended integration: merge all of it or none of it. The fact that reviewers need smaller slices to discuss does not imply those slices should become independently landable history objects. That’s a UX concern for the review tool, not something I should have to encode into Git history.
The ideal system would let me seed discussion however I want (by commit, by path, by subsystem, by semantic region of the diff, etc) without forcing me to pretend those are separate merge units.
Github nails the "merge unit" (CI runs against the whole branch, the branch either merges or doesn't, etc), but absolutely fumbles in the discussion part. I hate that I'd have to change the merge unit just to fix their discussion UX.
- the first PR in the stack creates a search index.
- the second one adds a search API handler.
- the last few do the UI.
these are all related. you are right that you can do this by breaking a change into commits, and effectively that is what i do with jujutsu. when i submit my commits to the UI, they form a PR stack. the commits are individually reviewable and updatable in this stacking model.
gh's model is inherently different in that they want you to create a new branch for every new change, which can be quite a nuisance.
> - the first PR in the stack creates a search index.
> - the second one adds a search API handler.
> - the last few do the UI.
So you're saying you're going to merge (and continuously integrate, perhaps to production) a dangling, unused search index, consuming resources with no code using it, just to make your review process easier?
It's very depressing that review UX is so abysmal that you have to merge features before they're done just to un-fuck it.
Why can't the change still be a big branch that is either all merged or not... and people can review it in chunks? Why do we require that the unit of integration equals the unit of review?
The perverse logic always goes something like this:
"This PR is too big, break it up into several"
Why?
"It's easier to review small, focused changes"
Why can't we do that in one PR?
"Because... well, you see GitHub's UI makes it really hard to ..."
And that ends up being the root-cause answer. I should be able to make a 10,000 line change in a single commit if I want, and reviewers should be able to view subsets of it however they want: A thread of discussion for the diffs within the `backend` folder. A thread of discussion for the diffs within the `frontend` folder, etc etc. Or at the very least I should be able to make a single branch with multiple commits based on topic (and under no obligation for any of them to even compile, let alone be merge-able) and it should feel natural to review each commit independently. None of this should require me to contort the change into allowing integration partially-completed work, just to allow the review UX to be manageable.
This is not just about the UI, it's about the mental model and management of the changes.
Just covering the review process:
Yes, you can structure your PR into 3 commits to be reviewed separately. I occasionally structure my PRs like this - it does help in some cases. But if those separate parts are large, you really want more structure around it than just a commit.
For example, let's say you have parts A, B and C, with B depending on A, and C depending on B.
1. I may want to open a PR for A while still working on B. Someone may review A soon, in which case I can merge immediately. Or perhaps it will only be reviewed after I finished C, in which case I'll use a stacked PR.
2. The PR(s) may need follow up changes after initial review. By using stacked PRs instead of just separate commits, I can add more commits to the individual PRs. That makes it clear what parts those commits are relevant to, and makes it easy to re-review the individual parts with updated changes. Separate commits don't give you that.
Stacked PRs is not a workflow I'd use often, but there are cases where it's a valuable tool.
Then apart from the review process, there are lots of advantages to keeping changes small. Typically, the larger a change, the longer it lives in a separate branch. That gives more time for merge conflicts to build up. That gives more time for underlying assumptions to change. That makes it more difficult to keep a mental map of all the changes that will be merged.
There are also advantages to deploying small changes at a time, that I won't go into here. But the parent's process of potentially merging and deploying the search index first makes a lot of sense. The extra overhead of managing the index while it's "unused" for a couple of days is not going to hurt you. It allows early testing of the index maintenance in production, seeing the performance overhead and other effects. If there's an issue, it's easy to revert without affecting users.
The overall point is that as features become large, the entire lifecycle becomes easier to manage if you can split it into smaller parts. Sometimes the smaller parts may be user-visible, sometimes not. For features developed in a day or two, there's no need to split it further. But if it will span multiple weeks, in a project with many other developers working on, then splitting into smaller changes helps a lot.
Stacked PRs is not some magical solution here, but it is one tool that helps manage this.
> But if those separate parts are large, you really want more structure around it than just a commit.
Why? I reject the notion that large commits should be intrinsically hard to review.
GitHub already has the concept of "code owners", which are people who have ownership/review responsibility over slices of the codebase, based on globs/pattern matching. But they don't implement the other half of that, which is that a reviewer should be able to see a projection of a given PR, which matches the part of the repo they're the owner of.
There. That solves the entire problem of "this is too big, I can't look at all of it" (because your code ownership says this is the chunk of codebase you say you care about), and if that still isn't sufficient, there's a zillion UI features GitHub could add that they simply don't. Why can't I "focus" on a subset of the changes during review, in a way that helps me ignore unrelated discussions/changes? That is, even if I'm not code owner of the `frontend/` folder, why isn't there a UI affordance that says "let me focus on changes inside `frontend/` and ignore discussions/etc for the rest"?
> By using stacked PRs instead of just separate commits, I can add more commits to the individual PRs
Or you could just add commits to the PR, and if GitHub got the damned UI right, it would be natural to see the "slice" you care about, for all the new commits. Having to rearrange commits into separate PR's and slice-and-dice followup changes to file them into the right PR unit, is (to me) a workaround for how shitty GitHub's review UX is. It really shouldn't be this way.
> Then apart from the review process, there are lots of advantages to keeping changes small [...]
I agree with you on most of these points, but the decision to land smaller changes earlier should be made based on things like "let's get early feedback behind a feature flag" or "let's see how this chunk behaves in production so we can validate assumptions", or "let's merge what we have now so to cut back on conflicts", etc. That's all fine. But I'm vehemently opposed to being required to slice up my changes this way, just to work around a terrible review UI.
Personally, I review code in my development environment GitHub's UI is nonsensically terrible to read code. I could go on for hours about this[0], but when looking in my IDE I can drill into a subfolder and look at the diffs there. I can click and follow symbols. I can look at the individual diff history for any wildcarded subset of the repo, and see how the change was broken into commits. If I'm typing up some feedback to say "try doing it this way instead", I can actually try it myself first to make sure I'm not suggesting that someone do something that doesn't even compile.
And GH's discussion UX is by far the worst part of all of it. If you have a thread of discussions around a line of code, then wake up the next morning and want to see what new comments have been added? Good luck. Your best bet is to check your email inbox, because the comments are actually shown to you there. Using GitHub's "inbox" feature? All that is is a link to PR's you have to look at, with no hints at "why" (it could be a CI run finished for all you know.) Good luck figuring out "why" a PR is on your list. Did someone @-mention you? Who knows. So, find the blue dot next to the PR, click it, and then figure out for yourself what changed since the last time you looked. No, you can't just scroll and find it because GitHub hides half the discussions by default. So you have to go and expand all the collapsed sections to hopefully find that conversation you were having yesterday. But oh, you can only find it in the diff tab. So you click that, but the relevant file is collapsed by default ("Large diffs are not rendered blah blah"), so then click that. Then you may find that discussion.
Contrast this to a mailing list. The discussions are... discussion threads. You pick up where you left off. People's comments are right there in your inbox, newest one on top (or whatever your preference is.) You get notified when there's a new message, and when you tap the notification, it's the actual message, not some link to the PR that makes you click 6 more things to maybe find the message that just happened.
[0] like how the first thing you have to do when opening up the changes tab is ctrl+f search for "Large diffs are not rendered by default" to find the actually-important diffs that are not shown to you because GitHub's backend can't scale to rendering large diffs without friction. Countless times I've been burned by approving a PR because I don't see it making a change to some functionality, only to find out it actually did make said change, but GitHub just decided not to show me it. Seriously, the "large diffs" are the most important ones, and those are the ones you don't see without extra clicks. The mind boggles.)
nevermind, I see what's happening in the UI. Each `jj` change is preserved in the UI and we can see multiple versions of the same change. The stack then is not really a stack of PRs but a stack of changes (where each change has its own history, i.e., the interdiff view). Did I get it mostly right?
yes, thats right! when you submit a branch, you can choose to "stack" it, so the individual commits in the branch turn into separate PRs. these PRs evolve individually, can be merged individually, and be reviewed individually. you can also set different reviewers/labels for different PRs in the stack.
you're upgrading the repository from language version 1 to 2, version 2 adds new compiler errors that rejects some old code, or the library has removed some old deprecated API the repository was still using in some places—the key here being that it can't be something that needs to be completely atomic.
you have hundreds or thousands of files to fix. that is unreviewable as a single commit, but as a per-file, per-library, per-oncall, etc. commit it is not that bad.
> you have hundreds or thousands of files to fix. that is unreviewable as a single commit, but as a per-file, per-library, per-oncall, etc. commit it is not that bad
Why is it intrinsically unreviewable as a single commit? Why can't the discussion/review system allow scoping discussions to a single folder of the change, or a single library, or a particular code-owner's "slice" of the repo, etc? The answer to this question is always unsatisfactory to me. It always ends up being "because GitHub's UI makes it hard to <foo>" and it's just taken as an immutable law of the universe that we're stuck with that UI's limitations.
If a change is huge, find some basis by which to discuss it in smaller chunks. That basis doesn't have to be the PR itself (such that you have to make smaller PR's to make discussion manageable.) It can be a subdirectory of the diff. A wildcard-match over the source files. Whatever the case needs to be, the idea is still that the discussion UX shouldn't make reviewing large changes painful.
Why do we tolerate the fact that GitHub doesn't let you say "approved for changes in `frontend/*`" or "approved for the changes I'm a code-owner of", and have the PR check system mark the PR as approved once all slices have been approved? Why do we tolerate that a thousand-file change is "unreviewable"? Instead we have to change our unit of integration, allowing partially-complete work to be merged, just because the review UX sucks.
Why would you waste time faffing about building B on top of a fantasy version of A? Your time is probably better spent reviewing your colleague’s feature X so they can look at your A.
Couldn’t they do that in one PR? Seriously, couldn’t you just say “hey Alice, could you review the A parts of this PR” and “hey Bob, could you review the B parts”, then only merge once both of them approve? Even GitHub, for all its faults, supports code owners files, such that this can even be policy.
Technically yes, but the work for A and B may not be done at the same time so you may want to get a head start on getting A reviewed while B is still being worked on.
As a counter example. Why use multiple PRs when you can always just merge them into a single one. It's possible to make huge PRs with a bunch of different changes all included, but then the GitHub tools with managing stuff don't really work that well and you have to just do everything as comments instead of being about to actually accept a single accepted change for example.
It was announced in like November of last year, so it's certainly taken some time. The announcement was by some senior management at GitHub, so it has some degree of buy-in.
Interesting to see how their CLI compares with GitLab's CLI interface for stacked diffs (the only support they offer at the moment): https://docs.gitlab.com/user/project/merge_requests/stacked_.... Most things are the same (up/down/top/bottom vs. next/prev/first/last, init vs. create), but both feel quite limiting. I've heard of other systems such as Gerrit that offer better native support, but have not tried out any for myself.
People have been building stacked PR workflows on top of GitHub for a while now. It's great to see that the message seems to have finally landed at GitHub, but what is actually new here in GitHub itself (i.e., not counting the gh CLI tool)?
There seems to be a native stack navigation widget on the PR page, which is certainly a welcome addition.
The most important question though is whether they finally fixed or are going to fix the issues that prevent submitting stacked PRs from forks. I don't see any indication about that on the linked page.
They haven't fixed the fork issue, the FAQ clarifies this. I suspect the target audience is squash merging corpos. Everyone else can just do normal PRs with atomic commits reviewed individually...
Is this going to be a part of triage task? If so, it makes sense. Whether a human developer or an AI made a big PR, AI goes review it and if necessary makes stacked PRs. I don’t see any human contributors using this feature to be honest because it’s an extra work and they should have found a better way to suggest a large PR.
My main question about this is does it keep review history properly after a rebase to restack PRs? Eg if I have reviewed PR for branch A and now its been rebased onto B by this tool and then more changes are made to A, does "review changes since" work in A's PR? This has been the main thing stopping me from wanting to use rebase to stack PRs and if they've fixed this somehow then I'm interested.
Wow i really need this, we had a refactor our monorepo (dotnet 8 -> 10 and angular 19 -> 21) which resulted in many small changes (like refactoring to signals, moving components to standalone) and we try to group changes into commits by what was fixed, but this had the downside of some commits beeing huge while others small, this would have helped us alot grouping commits together and having cleaner commit messages.
Phabricator is open source and has been for years. It has had a bumpy ride over the last few years though. Although I guess having written that I assume the internal meta one is much better
Huh, that's news to me. I had to do some googling and the only one I could find was by Phalicity which seems to be from a Meta employee who left and made it into a company (a la Statsig, or to some extent Graphite)
Seems that company shutdown though a while ago and it got forked into Phorge, but either way I assume there's some divergence from what's internal at this point.
Still I'll look into it, it does look neat and might suit my preferences still. Thanks for the headsup :)
Curious how / how well it deals with conflicts in the different branches that are part of the stack. Is there some support for managing that, or what happens when two of the branches don't rebase / merge cleanly?
> If a rebase conflict occurs, the operation pauses and prints the conflicted files with line numbers. Resolve the conflicts, stage with git add, and continue with --continue. To undo the entire rebase, use --abort to restore all branches to their pre-rebase state.
So it tries to replay commits in the stack and will stop halfway through that individual stack (layer?) to let you fix it if there's a conflict.
One mistake I see across many organizations is that sometimes they overthink how much order should matter.
Sure, your application has a dependency on that database, but it doesn't necessarily mean you can't deploy the application before having a database. If possible, make it acceptable for your application to stay in a crashloop until your database is online.
I agree with you and further will add that modularity+atomicity are the ideal state for the vast majority of software applications… but in reality, most organizations can not afford to rewrite their software to the extent required to achieve this, if it wasn’t planned from the start.
The `gh stack` CLI sounds essential for people using git, but I hope it doesn't become required, as people using things like jj/sl should be able to work with stacks. `gs submit`/`gs push` being the interface is fine, but `gs init` and `gs add` should be optional.
They confirmed below that you should be able to use this with jj just fine, just like you can already use gh to create a PR that you've authored with jj: https://news.ycombinator.com/item?id=47759426
Very curious about this as especially with more use of AI in the development process I have seen PR size has increased. So looking forward to general availability.
Even though moments where I would reach for it are rare, this is a very welcome feature. In times when I could have used it, it was not difficult to emulate via more branches, consistent naming, referencing the PRs, etc. Not difficult, but definitely tedious, and always left me feeling less organized than I like to feel.
This is probably driven to be more usable with AI agents, but smaller prs can create more code as they need to enforce more backwards compability, this can also lead to more code or more maintenance work.
Honestly I don’t see the benefit of smaller prs, except driving vanity scores?
Very much looking forward to getting this on Renovate - we require squash-merge via Merge Queue (with no per-PR override available in GitHub, despite asking) and so when I've got multiple changes, it's a lot of wrangling and rebasing
If this works as smoothly as it sounds, that'll significantly reduce the overhead!
Pretty cool to see stacks being given due attention. Also check out git-spice, which works with Gitlab (possibly others). Personally I use git-spice in place of all the conventional git commands.
Just when I’ve gotten used to having 3 or more PRs in parallel with a local octopus working tree with jj. Maybe my colleagues will see the light at least.
It's awesome that they're adding a UI for stacked branches¹! The UX of the CLI tool seems weird, though. Why do I need to explicitly create and add branches to the stack if all I really want is to open PRs from my commits? Here's the workflow that I built for myself instead:
∙ `git checkout -b feature-branch-xyz`
∙ make a few commits, perhaps some fixups, rebase, whatever
∙ start tig, look at the history, decide at which points I want to break the branch into stacked PRs, and mark those points using shift-s (which calls my own `git gh-stack branch create $commit` and creates a specially named branch there)
∙ `git gh-stack sync` — collects all the specially named branches, builds a graph of how they're stacked on one another, pushes them, opens stacked PRs
GitHub has had some "support" for stacked PRs for a while, so merging the first one to main will automatically change the target branch of the second to main.
If I need to change anything, I can just `git rebase --interactive --update-refs`, amend commits, split commits, rearrange commits, and then running `git gh-stack sync` will update the PRs for me. If I split a commit in the middle and shift-s to mark it, it will open an extra PR and restack everything to update the order.
Furthermore, the "PR stack" doesn't actually need to be a stack (linear chain), it can be a tree. If I know that some commits are independent of the rest, I don't need to create a separate stack, I just create another local branch, mark PR-ready commits with shift-s, and `git gh-stack sync` will do the right thing. If I need to rebase the whole tree on top of current main, then `git rebase -i --rebase-merges --update-refs` does the job.
I guess what I'm saying is that as someone who's been using git since its inception, it feels much more natural to just do everything in git, and then have a single command that pushes my work to GitHub. And I think this might work even better with jujutsu — just point `git gh-stack sync` at the branches jj makes and it'll make a stack/tree of PRs out of them. :-)
¹) I mean, I'd much rather they added a UI for reviewing PRs commit-by-commit, with the option to approve/request-changes on each, and the possibility to merge the first few approved ones while continuing work on the rest… But in a world of almost every $dayjob insisting on squash-merging, a UI for stacked PRs is a total game changer, positively.
great, I'll directly compare it to graphite.com - the main point really is the user interface in my opinion. Still a bit sceptical whether github can out-deliver here, but happy to be proven wrong!
Has anyone already tried that was a graphite user before?
Yes, except with a proper UI. Also while you could do this on GitHub before in the same way that that Gitlab feature works, it didn't work cross-repo so in practice it wasn't an option for most open source code.
I can't remember if Gitlab has the same limitations but I do remember trying to use Gitlab's stacked diffs and finding them to not work very well. Can't remember why tbh.
For sure. If you are in a monorepo this solution works but if you have distinct microservice repositories it would help to coordinate pr #827 on repo-A and pr #1092 on repo-B are related and need to ship in a certain order.
How would that work? Commits in different repos aren't ordered relative to one another. I suppose you could have a "don't let me merge this PR until after this other PR is merged" feature, but you could do that with a GitHub Action; it doesn't really need dedicated backend or UI support.
In practical terms: I manually write a list of PRs, and maintain that list in the description of each of the PRs. Massive duplication. But it clearly shows the merge train.
At first I thought this was a user submitted project due to the subdomain of github.com but then realize the subdomain is also github. Is this an official channel for this sort of thing? Surprised this isn't on the official blog.
There’s a special case where certain official orgs can continue to use github.com instead of github.io for their Pages domain, and that’s how you end up with:
microsoft broke nearly all classic web support (noscript/basic (x)html).
Since I can still login, is there a web API (using CURL and some identifying session token I could retrieve from my login) I could use to actually do "something". For instance, be involved in the issues of some project?
(for me, that would be mostly valve stuff on linux based OSes)
“You cannot merge a PR in the middle of the stack before the PRs below it are merged.”
Huh? Some stacks need to land all at once and need to be reviewed (and merged) from the top down. It’s not uncommon, in my org at least, to review an entire stack and merge 3 into 2 and then 2 into 1 and then 1 into main. If 2 merges before 3, you just rebase 3 onto 1.
If only there were some way to logically break up large pull requests into smaller pieces... Some way of creating a checkpoint with a diff including your changes, and some kind of message explaining the context behind the change... some way to "commit" a change to the record of the repository...
Part of the idea behind stacked PRs is to keep your commits focused and with isolated changes that are meaningful.
A stacked PR allows you to construct a sequence of PRs in a way that allows you to iterate on and merge the isolated commits, but blocks merging items higher in the stack until the foundational changes are merged.
Stacked PRs tend to encourage a series of well-organized commits, because you review each commit separately, rather than together.
What they do that the single branch cannot is things like "have a disjoint set of reviewers where some people only review some commits", and that property is exactly why it encourages more well-organized commits, because you are reviewing them individually, rather than as a massive whole.
They also encourage amending existing commits rather than throwing fixup commits onto the end of a branch, which makes the original commit better rather than splitting it into multiple that aren't semantically useful on their own.
I think the point the GP was trying to make is that the GitHub UI ought to be able to allow you to submit a branch with multiple well-organized commits and review each commit separately with its own PR. The curation of the commits that you'd do for stacked PRs could just as easily be done with commits on a single branch; some of us don't just toss random WIP and fixup commits on a branch and leave it to GitHub to squash at the end. I.e., it's the GitHub UI rather than Git that has been lacking.
(FWIW, I'm dealing with this sort of thing at work right now - working on a complex branch, rewriting history to keep it as a sequence of clean testable and reviewable commits, with a plan to split them out to individual PRs when I finish.)
> I think the point the GP was trying to make is that the GitHub UI ought to be able to allow you to submit a branch with multiple well-organized commits and review each commit separately with its own PR
So the point he's trying to make is that Gituhub UI should support Stacked PRs but call them something else because he doesn't like the name?
> I think the point the GP was trying to make is that the GitHub UI ought to be able to allow you to submit a branch with multiple well-organized commits and review each commit separately with its own PR.
That's what this feature is, conceptually. In practice, it does seem slightly more cumbersome due to the fact that they're building it on top of the existing, branch-based PR system, but if you want to keep it to one commit, you can (and that's how I've been working with PRs for a while now regardless, honestly).
They confirmed in other comments here that you don't have to use the CLI, just like you don't have to use gh in general to make pull requests, it's just that they think the experience is nicer with it. This is largely a forge-side UI change.
I've done this manually by building a big feature branch and asking an LLM to extract out functionality for a portion of it.
For the former, it would seem to split based on frontend/backend, etc. rather than what semantically makes the most sense and for the latter it would include changes I don't want and forget some I do want. But I haven't tried this a lot.
Not really. Without seeing the entire changeset for a PR, you'd have to mentally keep track of what the current state of everything is unless you're a commit minimalist and presquash.
If we're speaking strictly code review, because you can actually make sense of the changeset for the child PR by not including its unmerged parent's changeset.
I'm surprised no-one has commented on the "sign up for the waitlist" button being a Microsoft Office form that wants your email address and GitHub handle. This feels like an elaborate phishing attack more than a serious feature announcement.
> This is a docs site that was made to share the spec and CLI for private preview customers that ended up getting picked up. This will move to GitHub docs once it’s in public preview.
The biggest challenge for us are PRs that need to be coordinated across multiple repos. API + client for example. It doesn't sound like stacked PRs solve that problem, right? Description specifically states single repo.
github.github.com? Not the first time github does something highly weird with their domains (like publishing docs from a subdomain of their public github pages service)
I think they have a culture of circumventing 'official' channels and whoever is in charge of a thing is whoever publishes the thing.
I think it's a great way to train users to get phished by github impostors, if tomorrow we see an official download from official.github.com or even official-downloads.github.io, sure it's phishy, but it's also something that github does.
It's also 100% the kind of issues that, if it happens, the user will be blamed.
I would recommend github to stop doing this stuff and have a centralized domain to publish official communications and downloads from. Github.github.com? Come on, get serious.
TL;DR: DO NOT DOWNLOAD ANYTHING from this site, (especially not npm/npx/pnpm/bun/npjndsa) stuff. It's a Github Pages site, just on a subdomain that looks official, theoretically it might be no different from an attacker to obtain access to dksabdkshab.github.com than github.github.com. Even if it is official, would you trust the intern or whoever managed to get a subdomain to not get supply chained? github.github.com just think about it.
in github's defense. This is a bit more nuanced, less objectively wrong domain posture issue. It will only matter if one security mechanism (subdomain control) fails.
The quoted microsoft examples are way worse. I see this with outbound email systems a lot, which is especially dangerous because email is a major surface of attack.
I feel like we already have enough abstractions in this space. Having any constraints at all in your tools is actually a good thing. PRs on top of ordinary git was a good step. This seems like one too many.
I honestly don't even get the PR addiction. Github has shaped devs workflows way too much. My best experience with git was when I realized that I can just have an blatantly simple workflow and explain it even to the junior-est dev in a few minutes. The reliance on github is somehow telling me that people stopped thinking about things they can actually control.
As someone who used phabricator and mercurial, using GitHub and git again feels like going back to the stone ages. Hopefully this and jujutsu can recreate stacked-diff flow of phabricator.
It’s not just nice for monorepos. It makes both reviewing and working on long-running feature projects so much nicer. It encourages smaller PRs or diffs so that reviews are quick and easy to do in between builds (whereas long pull requests take a big chunk of time).
I'm so glad git won the dvcs war. There was a solid decade where mercurial kept promoting itself as "faster than git*†‡" and every time I tried it wound up being dog slow (always) or broken (some of the time). Git is fugly but it's fast, reliable, and fugly, and I can work with that.
> I'm so glad git won the dvcs war. There was a solid decade where mercurial kept promoting itself as "faster than git".
It wasn't the Mercurial team saying it was faster than Git; that was Facebook after contributing a bunch of patches after testing Mercurial on their very large mono-repo in 2014 [1]:
For our repository, enabling Watchman integration has made Mercurial’s status command more than 5x faster than Git’s status command. Other commands that look for changed files–like diff, update, and commit—also became faster.
In fact they liked Mercurial so much they essentially cloned it to create their own dvcs, Sapling [2]. (An aside: Facebook did all of this because it was taking too long getting new engineers up to speed with Git. Shocker.)
Today, most of the core of Mercurial has been rewritten in Rust; when Facebook did their testing, Mercurial was nearly 100% Python. That's where the "Mercurial is slow" thing came from; launching a large Python 2.x app took a while back in the day.
I was messing with an old Mercurial repo recently… it was like a breath of fresh air. If I can push to GitHub using Mercurial… sign me up.
[1]: https://engineering.fb.com/2014/01/07/core-infra/scaling-mer...
[2]: https://sapling-scm.com/
You can push to GitHub using Sapling. I wish Sapling open source was given more love, as the experience for non-Facebookers is subpar. No bash completion outside the box, no distro packages, no good help pages, random issues interacting with a Git repo...
Sapling and JJ can sort it out, the outside world will only care for one of them.
> Sapling and JJ can sort it out, the outside world will only care for one of them.
I was immediately intrigued when I learned that JJ has revsets [1], just like Mercurial.
[1]: https://docs.jj-vcs.dev/latest/revsets/
Sounds like what my teachers used to say: “a personal problem”. Literally nobody outside FB knows what they’re missing and until they fix that, literally nobody cares.
> Sounds like what my teachers used to say: “a personal problem”.
They don’t sound like a very good teacher.
Judging by the amount of adults wandering around thinking their personal problems are everyone else’s problem… they were pretty good teachers.
No, the "hg is fast" marketing claim that retreated to "hg is Big-O fast and you are dumb for caring about constant terms and factors even if they clearly dominate your use case" predates 2014 and the Facebook patches. These talking points were old in 2010. Mercurial was always dog slow and always gaslighting about it.
I'm glad BigCo made tools to serve their needs, but their needs aren't my needs or most peoples' needs.
> Mercurial has been rewritten in Rust
I'm glad they saw the light eventually! Ditto for the rest of the Rust Tooling Renaissance.
What is kind of funny here is that you're right locally. At the same time, the larger tech companies (Meta and Google, specifically) ended up building off of hg and not git because (at the time, especially) git cannot scale up to their use cases. So while the git CLI was super fast, and the hg CLI was slow, "performance" means more than just CLI speed.
I was never a fan of hg either, but now I can use jj, and get some of those benefits without actually using it directly.
>At the same time, the larger tech companies (Meta and Google, specifically) ended up building off of hg and not git because (at the time, especially) git cannot scale up to their use cases.
Fun story: I don't really know what Microsoft's server-side infra looked like when they migrated the OS repo to git (which, contrary to the name, contains more than just stuff related to the Windows OS), but after a few years they started to hit some object scaling limitations where the easiest solution was to just freeze the "os" repo and roll everyone over to "os2".
“roll everyone over to os2”
The IBM crowd may feel vindicated at last.
So 30 odd years later, MS went from working on OS/2 to working on OS2?
I guess what's old is new again.
didn't msft write an ~entire new file system specifically to scale git to the windows code base?
I have fuzzy memories on reading about it.
They wrote something that allowed them to virtualize Git -- can't remember the name of that. But it basically hydrated files on-demand when accessed in the filesystem.
The problem was I think something to do with like the number of git objects that it was scaling to causing crazy server load or something. I don't remember the technical details, but definitely something involving the scale of git objects.
I thought Microsoft made a number of improvements to git to allow it work with all of their internal repos.
I have heard that the Google monorepo is called google3 but I don't know why. Maybe those things are common...
Probably a lot of Googlers don't know. It's ancient history, was called google3 even in 2006 when I first joined.
google1 = code written by Larry, Sergey and employee number 1 (Craig). A hacky pile of Python scripts, dumped fairly quickly.
google2 = the first properly engineered C++ codebase. Protobufs etc were in google2. But the build system was some jungle of custom Makefiles, or something like that. I never saw it directly.
google3 = the same code as google2 but with a new custom build system that used Python scripts to generate Makefiles. I suppose it required a new repository so they could port everything over in parallel with code being worked on in google2. P4 was apparently not that great at branches and google3 didn't use them. Later the same syntax for the build files was kept but turned into a new languages called Starlark and the Makefile generator went away in favor of Blaze, which directly interpreted them.
At least, that's the story I vaguely recall.
It's the third attempt of building the mono repo.
But not the 3rd mono repo on the same technology to avoid some scaling limit.
It's not that.
Thanks for explaining!
Small nit: Googles monorepo is based on Perforce.
I think what happened is Google bought a license for source code and customised it.
Yes, the server is based on Perforce, called Piper, but the CLI is based on mercurial. So locally you're doing hg and then when you create a CL, it translates it into what p4 needs.
Depends on what frontend tool you use. You can use either. These days you can also use jj. I'm not sure the backend resembles peforce any longer.
> Google bought a license for source code and customised it.
That makes sense because vanilla Perforce is unbearably slow and impossible to scale.
Last I checked, it was bought by Private Equity firms and actual product development had more or less stopped.
Right, and I'm glad there are projects serving The Cathedral, but I live in The Bazaar so I'm glad The Bazaar won.
The efforts to sell priest robes to fruit vendors were a little silly, but I'm glad they didn't catch on because if they had caught on they no longer would have been silly.
GNU Bazaar thoroughly lost, last release was 2016, Canonical retired it last year: https://en.wikipedia.org/wiki/GNU_Bazaar
GP is taking about this[0] but it's quite hilarious that a VCS exists with that name.
0: https://en.wikipedia.org/wiki/The_Cathedral_and_the_Bazaar
It's not a coincidence, it was called like that as a reference to facilitating distributed development.
I might be the outlier, but am I the only one who doesn't care much about the speed of git? I've been using git since 2011 as my main vcs for personal and professional work as a freelancer contractor. Whenever I "wait" for git, it is either limited by the bandwidth (git clone) or by the amount of commit hooks that I implemented for linting, verification etc. The percentage of time actually spent in git internal execution must be a tiny fraction of my day to day usage. What IS affecting me (and my the teams I work in) is usability and UX experience. I.e. if people would screw up stuff (no matter if in git or mercurial) we spent far more time fixing this - I don't think the impmentation speed would matter here.
The only case I can imagine is when doing a full checkout of a big repo, but even there, there is --depth which is quite practical.
Isn't it kind of like how you don't care much about the oxygen content of the air around you, but you'd miss it if it was gone? I've done development with Mercurial, simple processes were irritatingly slow, particularly if you stray from the better-supported opinionated path.
I spent a long time educating teams of developers about git's usability quirks. I don't do that as much anymore - partly because the quirks have been worked out, partly because the developers have better guardrails and resources to learn from.
This whole time (the past 15 years) git has been getting faster without most of us noticing, because big companies have been investing in speeding it up. The reason you don't notice or care is that they work on a very different scale. Thousands of users, thousands of PRs per day, millions of CI/CD jobs all hitting the repo.
Now the cycle is repeating again because these numbers are shooting through the roof because of agentic coding.
I remember using darcs, but the repos I was using it with were so small as to performance really not mattering…
I remember darcs fondly but even with tiny repos (maybe 5-6 people working on it) we hit the "exponential merge" issues.
It worked just fine 99% of the time and then 1% it became completely unusable.
I definitely miss Darcs. I still use it very occasionally, but only with very small repos.
This matches my experience 100%. I was about to write a similar comment before I see yours.
I just used it because I preferred the UX.
Mercurial has a strictly superior API. The issue is solely that OG Mercurial was written in Python.
Git is super mid. It’s a shame that Git and GitHub are so dominant that VCS tooling has stagnated. It could be so so so much better!
Mercurial can't rebase without an extension, or force push. Are you using a definition of strictly superior that means it has fewer features?
Mercurial's model is different from Git that these things you list does not make sense there.
Rebase does not make sense in Mercurial because it has the concept of fixed branches. A commit is permanently linked to the branch on which it was made. So you are supposed to use merges.
Same with force-pushing.
I know. It's an opinion about how to develop that a lot of people hold - a declining proportion, mind you, like Mecurial's declining market share - and it's one that they're able to represent in Git's model, with Git's features. They're even able to do it without exposing me to it. But the same isn't true in reverse. Strictly superior?
Believe me, I tried to have an open mind about it. Then one day I was getting ready to go on a work trip with a half-finished feature on my work laptop, and realised there was simply no in-model way for backing that wip up to the repo. If I lost my laptop, I lost the progress. mercurial-scm fails at SCM.
>in-model way for backing that wip up to the repo.
That is because you have this notion of a "clean history", (which IIUC prevented you from making this permanent wip commit) which in reality does not have a lot of use. For most project, "useful history" or "real history" is better than a "clean" history.
That is what mercurial caters to.
When I ask for this people like to explain that these are bad features nobody should want.
And they would be right, https://news.ycombinator.com/item?id=47766632
Maybe forgejo has a shot?
It doesn't seem to support Mercurial though (not to imply that you were implying that it did). All I can find in this proxy/mirror thing to integrate it by presenting the Mercurial repo as a Git server: https://peterlavalle.github.io/post/forgejo-actions/
Unfortunatly out-of-the-box llm agents only focus on github support, creating friction.
So pi.dev + forgejo?
Whatever your opinion on one tool or another might be - it does seem weird that the "market" has been captured by what you are saying is a lesser product.
IOW, what do you know that nobody else does?
So far you've only gotten responses to "how can a worse product win?", and they are valid, but honestly the problem here is that Mercurial is not a better product in at least one very important way: branches.
You can visit any resource about git and branches will have a prominent role. Git is very good at branches. Mercurial fans will counter by explaining one of the several different branching options it has available and how it is better than the one git has. They may very well be right. It also doesn't matter, because the fact that there's a discussion about what branching method to use really just means Mercurial doesn't solve branches. For close to 20 years the Mercurial website contained a guide that explained only how to have "branches" by having multiple copies of the repository on your system. It looks like the website has now been updated: it doesn't have any explanation about branches at all that I can find. Instead it links to several different external resources that don't focus on branches either. One of them mentions "topic", introduced in 2015. Maybe that's the answer to Git's branching model. I don't care enough to look into it. By 2015 Git had long since won.
Mercurial is a cool toolbox of stuff. Some of them are almost certainly better than git. It's not a better product.
To me mercurials branching is closer to the development process and preserves more information, because it records the original branch a commit was made.
Git does not have such concept. That is a trade off and that trade off works great for projects managed like Linux kernel. But for smaller projects where there is a limited number of people working, the information preserved by mercurial could be very valuable.
It also had some really interesting ideas like change set evolution, which enabled history re-writing after a branch has been published. Don't know its current status and how well it turned out to be..
It's interesting that branches, which is a marquee feature of git, became less important at the same time as git ate all the other vcs. Outside of OS projects, almost all development is trunk based with continuous releases.
Maybe branching was an important reason to adopt git but now we'd probably be ok with a vcs that doesn't even support them.
Not sure if it's true. I mean, I do agree with the core of it, but how do you even do PRs and resolve conflicts, if there are no branches and a developer cannot efficiently update his code against the last (remote) version of master branch?
This is so strange, because, at a low level, a branch isn't even a "thing" in git. There is no branch object type in git, it's literally just a pointer to a commit, functionally no different from a tag except for the commands that interact with it.
Meanwhile mercurial has bookmarks. TBF I'm not sure when it got those but they've been around forever at this point. The purpose is served.
I think there are (or perhaps were) some product issues regarding the specifics of various workflows. But at least some of that is simply the inertia of entrenched workflows and where there are actual downsides the (IMO substantial) advantages need to be properly weighed against them.
Personally I think it just comes down to the status quo. Git is popular because it's popular, not because it's noticably superior.
That's the definition of a tree though. Everything has a parent, no cycles allowed.
GitHub had a business model where public repos were free. BitBucket didn’t.
That’s it. That’s why git won, you could put up open source libs with one for free and not the other.
Which is extra funny as the centralized service was the most important part of decentralized version control.
>the centralized service was the most important part of decentralized version control.
I've often thought this about github
JWZ is still blocking traffic from HN so you can't click to read this but you can copy/paste it into a new tab or open it in a incognito window:
https://www.jwz.org/doc/worse-is-better.html
Worse products win all the time. Inertia is almost impossible to overcome. VHS vs Betamax is a classic. iPod wasn’t the best mp3 player but being a better mp3 player wasn’t enough to claw market share.
Google and Meta don’t use Git and GitHub. Sapling and Phabricator much much better (when supported by a massive internal team)
What was the better mp3 player than the iPod?
unironically Zune is goated in its own way
anything from Cowon. Always has been
Anything from iriver.
sansa clip+
Network effects and marketing can easily prevent better tools from winning.
I mean, in the fickle world that is TECH, I am struggling to believe that that's what's happened.
I personally went from .latest.latest.latest.use.this (naming versions as latest) to tortoise SVN (which I struggled with) to Git (which I also was one of those "walk around with a few memorised commands" people that don't actually know how to use it) to reading the fine manual (well 2.5 chapters of it) to being an evangalist.
I've tried Mercurial, and, frankly, it was just as black magic as Git was to me.
That's network effects.
But my counter is - I've not found Mercurial to be any better, not at all.
I have made multiple attempts to use it, but it's just not doing what I want.
And that's why I'm asking, is it any better, or not.
Networking effects are significantly strengthened by necessary user buy in. VC is hard, and every tool demands its users to spend a non-significant amount of time learning it. I would guess the time to move from black magic to understanding most of git is ~100h for most people.
The thing is, to understand which one is actually better, you would have to give the same amount of investment in the second tool, which is not something most people are willing to do if the first tool is "good enough". That's how Python became the default programming language; people don't miss features they do not understand.
A little over a decade ago, with only svn experience, I tried both mercurial and git. There was something about how mercurial handled branches that I found extremely confusing (don't remember what), while git clicked immediately - even without reading the manual.
So at least for me, git was clearly better.
Mercurial later added bookmarks which work like Git branches. These make more sense to me as well.
Did bookmarks moved as you made commits, like a branch pointer in git does?
Yup: https://mercurial-scm.org/help/commands/bookmarks
Mercurial has a more consistent CLI, a really good default GUI (TortoiseHg), and the ability to remember what branch a commit was made on. It's a much easier tool to teach to new developers.
Hmm, that feels a bit subjective - I'm not going to say X is easier than Y when I've just finished saying that I found both tools to have a lot of black magic happening.
But what I will point out, for better or worse, people are now looking at LLMs as Git masters, which is effectively making the LLM the UI which is going to have the effect of removing any assumed advantage of whichever is the "superior" UX
I do wish to make absolutely clear that I personally am not yet ready to completely delegate VCS work to LLMs - as I have pointed out I have what I like to think of as an advanced understanding of the tools, which affords me the luxury of not having an LLM shoot me in the foot, that is soley reserved as my own doing :)
That worse is better, and some people don't know better or care.
"better" in that sentence is very specific. Worse is also worse, and if you're one of the people for whom the "better" side of a solution doesn't apply, you're left with a mess that people celebrate.
Welcome to VHS and Betamax. the superior product does not always win the market.
Not always, but in this case the superior product (i.e. VHS) won. At initial release, Beta could only record an hour of content, while VHS could record 2 hours. Huge difference in functionality. The quality difference was there, but pretty modest.
I suppose one lesson could be that there are different dimensions of superiority, different products may be superior in different ways.
Of course, products also can win market dominance for reasons external to the product's quality itself (marketing, monopoly lock-in, other network effects, consumer preferences on something other than product quality itself, etc).
> The issue is solely that OG Mercurial was written in Python.
Are we back to "programming language X is slow" assertions? I thought those had died long ago.
Better algorithms win over 'better' programming languages every single time. Git is really simple and efficient. You could reimplement it in Python and I doubt it would see any significant slowness. Heck, git was originally implemented as a handful of low level binaries stitched together with shell scripts.
Every time I've rewritten something from Python into Java, Scala, or Rust it has gotten around ~30x faster. Plus, now I can multithread too for even more speedups.
Python is absurdly slow - every method call is a string dict lookup (slots are way underused), everything is all dicts all the time, the bytecode doesn't specialize at all to observed types, it is a uniquely horrible slow language.
I love it, but python is almost uniquely a slow language.
Algorithms matter, but if you have good algorithms, or you're already linear time and just have a ton of data, rewriting something from a single-threaded Python program to a multithreaded rust program I've seen 500x speedups, where the algorithms were not improved at all.
It's the difference between a program running overnight vs. in 30 seconds. And if there are problems, the iteration speed from that is huge.
> [...], it is a uniquely horrible slow language.
To be fair, Python as implement today is horribly slow. You could leave the language the same but apply all the tricks and heroic efforts they used to make JavaScript fast. The language would be the same, but the implementations would be faster.
Of course, in practice the available implementations are very much part of the language and its ecosystems; especially for a language like Python which is so defined by its dominant implementation of CPython.
Fair! I guess I didn't mean language as such, but as used.
But a lot of the monkey-patching kind of things and dynamism of python also means a lot of those sorts of things have to be re-checked often for correctness, so it does take a ton of optimizations off the table. (Of course, those are rare corner cases, so compilers like pypy have been able to optimize for the "happy case" and have a slow fall-back path - but pypy had a ton of incompatibility issues and now seems to be dying).
Javascript has a lot of the same theoretical dynamism, yet V8 and WebkitCore were able to make it fast
Yes, with heroic effort. It's really a triumph of compiler / vm engineers over language designers.
Python has a JIT compiling version in GraalPy. If you have pure Python it works well. The problem is, a lot of Python code is just callouts to C++ ML libs these days and the Python/C interop boundary just assumes you're using CPython and requires other runtimes to emulate it.
You don't even need to go all V8, you could just build something like LuaJIT and get most of the way there. LuaJIT is like 10k LOCs and V8 is 3M LOC.
The real reason is that it is a deliberate choice by the CPython project to prefer extensibility and maintainability to performance. The result is that python is a much more hackable language, with much better C interop than V8 or JVM.
> every method call is a string dict lookup
Doesn't the Python VM have inline caches? [0]
https://en.wikipedia.org/wiki/Inline_caching
I think that's a new thing from like python 3.12+ or something after I stopped using Python as much.
It didn't used to.
EDIT: python 3.11+: https://peps.python.org/pep-0659/
I've rewritten a python tool in go, 1:1. And that turned something that was so slow that it was basically a toy, into something so fast that it became not just usable, but an essential asset.
Later on I also changed some of the algorithms to faster ones, but their impact was much lower than the language change.
I don’t know if people think this way anymore, but Python gained traction to some degree as a prototyping language. Verify the logic and structures, then implement the costly bits or performance sensitive bits in a more expense-to-produce more performant language.
Which is only to say: that rewrite away from python story can also work to show python doing its job. Risk reduction, scaffolding, MVP validation.
> git was originally implemented as a handful of low level binaries stitched together with shell scripts.
A bunch of low level binaries stitched together with shell scripts is a lot faster than python, so not really sure what the point of this comparison is.
Python is an extremely versatile language, but if what you're doing is computing hashes and diffs, and generally doing entirely CPU-bound work, then it's objectively the wrong tool, unless you can delegate that to a fast, native kernel, in which case you're not actually using Python anymore.
Well, you can and people do use Python to stitch together low level C code. In that sense, you could go the early git approach, but use Python instead of shell as the glue.
Their point was that by offloading the bottlenecks to C, you've essentially conceded that Python isn't fast enough for them, which was the original point made above
Fair point!
> Are we back to "programming language X is slow" assertions? thought those had died long ago.
Yes we are? The slow paths of mercurial have been rewritten in C (and more recently in Rust) and improved the perf story substantially, without taking away from the wild modularity and extensibility hg always had.
> Better algorithms win over 'better' programming languages every single time.
That's often true, but not "every single time".
> You could reimplement it in Python and I doubt it would see any significant slowness
I doubt it wouldn't be significantly slower. I can't disprove it's possible to do this but it's totally possible for you to prove your claim, so I'd argue that the ball is in your court.
Python is by far the slowest programming language, an order of magnitude slower than other languages
One of the reason mercurial lost the dvcs battle is because of its performance - even the mercurial folks admitted that was at least in part because of python
You must belong to the club of folks who use hashmaps to store 100 objects. It's amazing how much we've brainwashed folks to focus on algorithms and lose sight of how to actually properly optimize code. Being aware of how your code interacts with cache is incredibly important. There are many cases of using slower algorithms to do work faster purely because it's more hardware friendly.
The reason that some more modern tools, like jj, really blow git out of the water in terms of performance is because they make good choices, such as doing a lot of transformations entirely in memory rather than via the filesystem. It's also because it's written in a language that can execute efficiently. Luckily, it's clear that modern tools like jj are heavily inspired by mercurial so we're not doomed to the ux and performance git binds us with.
> You must belong to the club of folks who use hashmaps to store 100 objects.
Apparently I belong to the same club -- when I'm writing AWK scripts. (Arrays are hashmaps in a trenchcoat there.) Using hashmaps is not necessarily an indictment you apparently think it is, if the access pattern fits the problem and other constraints are not in play.
> It's amazing how much we've brainwashed folks to focus on algorithms and lose sight of how to actually properly optimize code. Being aware of how your code interacts with cache is incredibly important.
By the time you start worrying about cache locality you have left general algorithmic concerns far behind. Yes, it's important to recognize the problem, but for most programs, most of the time, that kind of problem simply doesn't appear.
It also doesn't pay to be dogmatic about rules, which is probably the core of your complaint, although unstated. You need to know them, and then you need to know when to break them.
> I thought those had died long ago.
No, it's always been true. It's just that at some point people got bored and tired of pointing it out.
You barely have to try to have Python be noticeably slow. It's the only language I have ever used where I was even aware that a programming language could be slow.
They died because everyone knows that Python is infact very very slow. And that’s just totally fine for a vast number of glue operations.
It’s amusing you call Git fast. It’s notoriously problematic for large repos such that virtually every BigTech company has made a custom rewrite at some point or another!
Now that is interesting too, because git is very fast for all I have ever done. It may not scale to Google monorepo size, it would ve the wrong tool for that. But if you are talking Linux kernel source scale, it asolutely, is fast enough even for that.
For everything I've ever done, git was practically instant (except network IO of course). It's one of the fastest and most reliable tools I know. If it isn't fast for you, chances are you are on a slow Windows filesysrem additionally impeded by a Virus scanner.
The fact that Git has an extremely strong preference for storing full and complete history on every machine is a major annoyance! “Except for network IO” is not a valid excuse imho. Cloning the Linux kernel should take only a few seconds. It does not. This is slow and bad.
The mere fact that Git is unable to handle large binary files makes it an unusable tool for literally every project I have ever worked on in my entire career.
git clone --bare --depth=1 https://github.com/torvalds/linux
Takes 21 seconds on my work laptop, indeed a corporate Windows laptop with antivirus installed. Majority of that time is simply network I/O. The cloned repository is 276 MB large.
Actually checking the kernel out takes 90 seconds. This amounts to creating 99195 individual files, totaling 2 GB of data. Expect this to be ~10 times faster on a Linux file system.
So what's your problem?
Git-lfs exists for a while now. Does that fix your issue? Or do you mean that it doesn’t support binary diffs?
Git LFS is a gross hack that results in pain and suffering. Effectively all games use Perforce because Git and GitLFS suck too much. It’s a necessary evil.
Git handles large text files and large directories fairly poorly too.
Git is not remotely fast for large projects.
Define "large"; I've never ran into serious performance issues during the ~15 years I've used Git, which either means the projects I've worked in aren't actually large large, or Git is fast enough for most use cases.
I continue to use gerrit explicitly because I cannot stand github reviews. Yes, in theory, make changes small. But if I'm doing larger work (like updating a vendored dep, that I still review), reviewing files is... not great... in github.
Most editors have some kind of way to review github PRs in your editor. VSCode has a great one. I use octo.nvim since I use neovim.
Can these tools e.g. do per-commit review? I mean, it's not the UI what's the problem (though it's not ideal), it's the whole idea of commenting the entire PR at once, partly ignoring the fact that the code in it changes with more commits pushed.
Phabricator and even Gerrit are significantly nicer.
Unless you have a “every commit must build” rule, why would you review commits independently? The entire PR is the change set - what’s problematic about reviewing it as such?
There's a certain set of changes which are just easier to review as stacked independent commits.
Like, you can do a change that introduced a new API and one that updates all usages.
It's just easier to review those independently.
Or, you may have workflows where you have different versions of schemas and you always keep the old ones. Then you can do two commits (copy X to X+1; update X+1) where the change is obvious, rather than seeing a single diff which is just a huge new file.
I'm sure there's more cases. It's not super common but it is convenient.
> Unless you have a “every commit must build” rule, why would you review commits independently?
Security. Imagine commit #1 introduces a security vulnerability (backdoor) and the features. Then #2 introduces a non-obvious, harmless bug and closes the vulnerability introduced in #1 [0]. At some point, the bug will surface and rolling back commit #2 will be an easy fix, re-introducing your bug.
Alternatively, one of the earlier commits might, for example, contain credential dumping code. Once that commit is mainlined, CI might either automatically run on it or will be able to be run on it since it's no longer marked as unsafe PR.
[0] Think something like #1 introduces array access and #2 adds a bounds-check in a function a layer above - a reviewer with the whole context will see the bounds check and (possibly) consider it fine, but to someone rolling back a commit the necessity will not be obvious.
In stacked diffs system, each commit is expected to land cleanly, yes.
But isn't that why you would squash before merging your PR? If you define a rule that PRs must be squashed you would still have the per commit build.
Squash merge is an artifact of PRs encouraging you to add commits instead of amending them, due to GitHub not being able to show you proper interdiffs, and making comments disappear when you change a diff at that line. In that context, when you add fixup commits, sure, squashing makes sense, but the stacked diffs approach encourages you to create commits that look like you want them to look like directly, instead of requiring you to roll them up at the end.
Same team, and a rare hill I'm willing to die on.
Rant incoming...
Boy do I hate Github/Lab/Bucket style code reviews with a burning passion. Who the hell loses code review history? A record of the very thing that made my code better? The "why" of it all, that I am guaranteed to forget tomorrow morning.
Nobody would be using `--force` or `--force-with-lease` as a normal part of development workflow, of their own volition, if they had read that part of the git-push manpage and been horrified (as one should be).
The magit key sequence for this abominable operation is `P "f-u"`. And every single time I am forced to do it, I read "f-u" as it ought to be read.
Rebase-push is the way to do it (patch sets in Gerrit).
Rebase-force-push is absolutely not.
You see, any development workflow inevitably has to integrate changes from at least one other branch (typically latest develop or master), without destroying change history, nor review history. Gerrit makes this trivial.
It's a bit difficult to convey exactly why I'm so rah-rah Gerrit, because it is a matter of day-to-day experience of
... to name a few key ones.(edit: add point about review size)
Slapping this "stacked diff" business on top of something so broken as Github/lab/bucket is a concrete example of... https://en.wikipedia.org/wiki/Lipstick_on_a_pig
I miss the Phabricator review UI so much.
Same here. Don't understand why Github hasn't supported this until now. I'm tired of reviewing PRs with thousands of lines of changes, which are getting worse nowadays with vibe coding.
Why not use gerrit? It's pretty similar.
is it? it's insanely ugly and interactions seem bizarre
What does Facebook use internally these days. I'm amazed that the state of review tools is still at or behind what we had a decade ago for the most part.
It’s still phabricator
Any idea if their internal version has improved dramatically since they stopped maintaining the public version?
I don't think they ever maintained the public project. Priestly spun off a company to do that.
It has improved massively by 2023 when I left.
Me too. And I'm speaking from using it at Rdio 15 years ago.
Nothing since (Gerrit, Reviewboard, Github, Critique) has measured up...
Thanks for your work on Rdio. I miss it. Were you around when that guy managed to spam plays to get fake albums to the top of the charts?
tangled.org supports native stacking with jujutsu, unlike github's implementation, you don't need to create a new branch per change: https://blog.tangled.org/stacking/
Oh, phabricator. I hated that tool with a passion. It always destroyed my carefully curated PR branch history.
See https://stackoverflow.com/questions/20756320/how-to-prevent-...
My understanding was that that was more a function of how arc submitted stuff to Phabricator, rather than solely Phabricator itself. arc at submission time submitted a bunch of different commits as a single Phabricator DREV or whatever the terminology is/was (basically a DREV is the {domain}/D123 webpage you'd do a review on). But other tools that submitted commits to Phabricator instances (and maybe even arc itself with the right flag?) submitted each commit as its own separate DREV, so each commit got its own separate /D{N} page and its own review, but all linked together in a stack. And then still landed as separate commits in the actual repo. This is how code submission works with Mozilla's use of Phabricator.
Well, I didn't care whether it was phabricator or whatever it was using. It was bad.
Good. That's the point.
The point of what?
I hope they fixed phabricator in the meantime.
The point is the main branch reflects the "units" of change, not the individual commits to get there.
One merged pr is a unit of change, at the end of the day the steps you took to produce it aren't relevant to others.
My opinion of course, I'm open to understanding why preserving individual commits is beneficial
You can get what you want from `git log --first-parent` without having to toss out information.
See how the Linux kernel handles git history to see a good example of non-linear history and where it helps. They use merge commits, ie commits with more than one ancestor, all the time.
A unit of change is a commit. I have no idea why you'd think a PR is a unit of change.
Does your org approve specific commits or PRs overall?
PRs. This is largely why we don't do stacked PRs: they can just be a chain of commits in one PR
I might be missing something, but what I need is not "stacked PR" but a proper UI and interface to manage single commit:
- merge some commits independently when partial work is ready.
- mark some commit as reviewed.
- UI to do interactive rebase and and squash and edit individual commits. (I can do that well from the command line, but not when using the GitHub interface, and somehow not everyone from my team is familiar with that)
- ability to attach a comment to a specific commit, or to the commit message.
- better way to visualize what change over time in each forced push/revision (diff of diff)
Git itself already has the concept of commit. Why put this "stacked PR" abstraction on top of it?
Or is there a difference I don't see?
It's basically trying to bring the stacked diff workflow pioneered by Phabricator to GitHub.
The idea is that it allows you to better handle working on top of stuff that's not merged yet, and makes it easier for reviewers to review pieces of a larger stack of work independently.
It's really useful in larger corporate environments.
I've used stacked PRs when doing things like upgrading react-native in a monorepo. It required a massive amount of changes, and would be really hard to review as a single pull request. It has to be landed all at once, it's all or nothing. But being able to review it as smaller independent PRs is helpful.
Stacking PRs is also useful even when you don't need to merge the entire stack at once.
> stacked diff workflow pioneered by Phabricator
Ahem, pioneered by gerrit. But actually, I'm almost certain even that wasn't original art. I think gerrit just brought it to git.
https://www.gerritcodereview.com/about.html
To my knowledge, stacked diffs were first done in the Linux kernel as stacks of patches sent over email. From there they spread to Google and Facebook. (Source: I worked on Facebook's source control team from 2012-2018 and did a lot of work to enable stacked diffs there.)
Right, I was thinking from a web-based UI. The "pull request" term is from git (AFAIK), but git itself was built to accommodate the earlier concept of mailing patches around. (Source: I've been using version control since RCS/SCCS days and contributed here and there to git in its infancy. Also an early user/contributor to Gerrit.)
> The "pull request" term is from git (AFAIK)
Possibly from github. It got popularized there at least, encouraging forking code, and is why so many people say "pull request" when they mean "merge request".
GitHub took the "pull request" terminology from Git. A kernel developer (say) would have a bunch of changes ready in their local Git server and would request a pull from Linus, hence a pull request. There's literally a command for it:
https://git-scm.com/docs/git-request-pull
The command is so old it's still written in shell:
https://github.com/git/git/blob/master/git-request-pull.sh
It was first added July 27, 2005:
https://github.com/git/git/commit/ab421d2c7886341c246544bc8d...
https://lore.kernel.org/git/20050726073036.GJ6098@mythryan2....
But even then, it simply codified existing terminology.
Ah, someone else did the research, so minimally BitKeeper had the "pull" command first and the term "pull request" falls naturally from that:
https://rdnlsmith.com/posts/2023/004/pull-request-origins/
Congrats and thank you. You helped build one of the best devex experiences I've ever had the pleasure of working with :)
At some point, a derivative idea becomes so different from the original one that it’s a novel idea in essence. Just like SMS is ultimately a derivative of cuneiform tablets, and yet it isn’t in any meaningful sense.
I don't think mailing stacks of patches is that different? As someone who built this stuff it was pretty obvious to me that web-based patch stack management was a relatively small evolution over mailing lists. Tools like patchwork bridged the gap initially, and we were quite familiar with them.
Imagine gettting a cuneiform tablet by courier telling you that you have unpaid parking tickets in a state you've never driven in
Gerrit was forked from Rietveld. Not sure if Rietveld or Gerrit are better though.
https://github.com/rietveld-codereview/rietveld https://en.wikipedia.org/wiki/Rietveld_(software) https://codereview.appspot.com/
I'm not in a large corporate environment, but that also means we're not always a well oiled machine, and sometimes i am writing faster than the reviewer can review for a period of time -- and i really need the stacking then too.
Even with one developer on a repo this sounds like useful
What if main/master moves in between reviews?
You head to the farthest branch in the chain, fetch the latest main, and run `git rebase --update-refs main` (I prefer interactive mode myself) and then force push all of the branches from start to the end.
1: https://git-scm.com/docs/git-rebase#Documentation/git-rebase...
Before this feature when you were doing it manually, it was a huge problem. One of the points of this feature, is it automates rebasing the whole stack.
Rebase the stack onto main.
you just rebase it? what's the big deal?
I don't use Github but I do work at one of the companies that popularized this workflows and it is extremely not a big deal. Pull, rebase, resolve conflicts if necessary, resubmit.
Constantly rewriting git history with squashes, rebases, manual changes, and force pushes has always seemed like leaving a loaded gun pointed at your foot to me.
Especially since you get all of the same advantages with plain old stream on consciousness commits and merges using:
git merge --no-ff
git log --first-parent
git bisect --first-parent
I find rebases are only a footgun because the standard git cli is so bad at representing them - things like --force being easier to write than --force-with-lease, there being no way to easily absorb quick fixes into existing commits, interdiffs not really being possible without guesswork, rebases halting the entire workflow if they don't succeed, etc.
I've switched over pretty much entirely to Jujutsu (or JJ), which is an alternative VCS that can use Git as its backend so it's still compatible with Github and other git repos. My colleagues can all use git, and I can use JJ without them noticing or needing to care. JJ has merges, and I still use them when I merge a set of changes into the main branch once I've finished working on it, but it also makes rebases really simple and eliminates most of the footguns. So while I'm working on my branch, I can iteratively make a change, and then squash it into the commit I'm working on. If I refactor something, I can split the refactor out so it's in a separate commit and therefore easiest to review and test. When I get review feedback, I can squash it directly into the relevant commit rather than create a new commit for it, which means git blame tends to be much more accurate and helpful - the commit I see in the git blame readout is always the commit that did the change I'm interested in, rather than maybe the commit that was fixing some minor review details, or the commit that had some typo in it that was fixed in a later commit after review but that relationship isn't clear any more.
And while I'm working on a branch, I still have access to the full history of each commit and how it's changed over time, so I can easily make a change and then undo it, or see how a particular commit has evolved and maybe restore a previous state. It's just that the end result that gets merged doesn't contain all those details once they're no longer relevant.
+1 on this, I also switched to jj when working with any git repo.
What's funny is how much better I understand git now, and despite using jj full time, I have been explaining concepts like rebasing, squashing, and stacked PRs to colleagues who exclusively use git tooling
--force-with-lease is useless if you ever use tools that refresh git status.
The magic of the git cli is that it gives you control. Meaning whatever you want to do can be done. But it only gives you the raw tools. You'll need to craft your own workflow on top of that. Everyone's workflow is different.
> So while I'm working on my branch, I can iteratively make a[...]which means git blame tends to be much more accurate and helpful
Everything here I can do easily with Magit with a few keystroke. And magit sits directly on top of git, just with interactivity. Which means if I wanted to I could write a few scripts with fzf (to helps with selection) and they would be quite short.
> And while I'm working on a branch, I still have access to the full history of each commit...
Not sure why I would want the history for a specific commit. But there's the reflog in git which is the ultimate undo tool. My transient workspace is only a few branches (a single one in most cases). And that's the few commits I worry about. Rebase and Revert has always been all I needed to alter them.
> But there's the reflog in git which is the ultimate undo tool.
That one sentence outs you as someone who isn't familiar with JJ.
Here is something to ponder. Despite claims to the contrary, there are many git commands that can destroy work, like `git reset --hard`. The reflog won't save you. However there is literally no JJ command that can't be undone. So no JJ command will destroy your work irretrievably.
I’ve just tested that exact command and the reflog is storing the changes. It’s different from the log command which displays the commit tree for the specified branch. The reflog stores information about operations that updates branches and other references (rebase, reset, amend, commit,…). So I can revert the reset, or a pull.
Until someone merges master into their feature branch rather than rebasing it. (And then that branch later gets merged.)
This shouldn't be a problem if you stick to commits and merges. --first-parent will skip past commits, including merge commits, in merged branches.
Fair – but not if it's not their feature branch but their local master; they pull & merge the remote changes and then push the result.
I agree. PR merges for me are bisect points. That's when changes are introduced. Individual commits don't even always build.
And I don't rebase or squash because I need provenance in my job.
You are describing gerrit.
https://www.gerritcodereview.com/
Workflows can vary, but what I like:
PR/MR is an "atomic" change (ideally the smallest change that can be landed separately - smallest makes it easier to review, bisect and revert)
Individual commits (or what "versions" are in Phabricator) are used for the evolution of the PR/MR to achieve that change.
But really I have 2 use cases for the commits:
1. the PR/MR is still too big, so I split it into individual commits (I know they will land together)
2. I keep the history of the evolution of the PR/MR in the commits ("changed foo to bar cause its a better approach")
the best implementation i've worked with was SuperSmartLog (SSL) at Meta, which was open-sourced at interactive smartlog (https://sapling-scm.com/docs/addons/isl/). There are also extension for it in VSCode, etc.
Surprisingly it never gained the adoption it deserved.
We’ve got this over on Tangled. :) https://tangled.org
yeah interdiffing and being able to cherrypick in a review just there and getting it done is nice.
Perhaps a future iteration of this feature will at least allow us to do something like merge just steps of it if they can be reordered.
You want something like Gerrit.
Meanwhile, you still can't do fast-forward merges in GitHub :clown: https://github.com/orgs/community/discussions/4618
And it doesn't even rebase and merge correctly with fast-forward if there it's a clean set of commits! https://github.com/orgs/community/discussions/5524
> :clown:
We're neither on reddit nor on twitter, avoid that please.
It is a table stakes missing feature.. for a long time. Clown seems appropriate, every project I've worked on in github we end up copying a github yml action to allow us to do this with one comment '/fast-forward', just is silly at this point that github doesn't natively support it.
Right. Just use directly.
Does it fix the current UX issue with Squash & Merge?
Right now I manually do "stacked PRs" like this:
main <- PR A <- PR B (PR B's merge target branch is PR A) <- PR C, etc.
If PR B merges first, PR A can merge to main no problems. If PR A merges to main first, fixing PR B is a nightmare. The GitHub UI automatically changes the "target" branch of the PR to main, but instantly conflicts spawn from nowhere. Try to rebase it and you're going to be manually looking at every non-conflicting change that ever happened on that branch, for no apparent reason (yes, the reason is that PR A merging to main created a new merge commit at the head of main, and git just can't handle that or whatever).
So I don't really need a new UI for this, I need the tool to Just Work in a way that makes sense to anyone who wasn't Linus in 1998 when the gospel of rebase was delivered from On High to us unwashed Gentry through his fingertips..
Yes, we handle this both in the CLI and server using git rebase --onto
So for ex in this scenario: When PR 1 and 2 are squash merged, main now looks like: Then we run the following: Which rewrites branch3 to: This operation moves the unique commits from the unmerged branch and replays them on top of the newly squashed commits on the base branch, avoiding any merge conflicts.We dealt with this headache for 7+ years at my former employer. Thanks so much for this.
That’s how I’ve been working for years now. Does anyone know how this gh stacks work internally? Does it do the same thing under the hood?
I’m conflicted about it, seems like a good convenience, but I wouldn’t want my team to get dependent on an exclusive feature of a single provider
(You're replying to someone from product at GitHub, they're explaining that's how it works there)
Conflicts spawn most likely because PR A was squashed, and once you squash Git doesn't know that PR B's ancestors commits are the same thing as the squashed commit on main.
No idea if this feature fixes this.
Edit: Hopefully `gh stack sync` does the rebasing correctly (rebase --onto with the PR A's last commit as base)
> Conflicts spawn most likely because PR A was squashed, and once you squash Git doesn't know that PR B's ancestors commits are the same thing as the squashed commit on main.
Yeah, and I kind of see how git gets confused because the squashed commits essentially disappear. But I don't know why the rebase can't be smart when it sees that file content between the eventual destination commit (the squash) is the same as the tip of the branch (instead of rebasing one commit at a time).
Because at first your have this
Then you'll have The tip of B is the list of changes of both A and B, while the tip of main is now the squashed version of the changes of A. Unless a branch tracks the end of A in the PR B, It looks like more you want to apply A and B on top of A again.A quick analogy to math
Before you have X + 3 + 5 which was equivalent to X + 8, but then when you squash A on on X, it looks like (X + 3) + (3 + 5) from `main`'s point of view, while from B, it should be X + (3 + 5). So you need to rebase B to remove its 3 so that it can be (X + 3) + 5.Branches only store the commits at the top. The rest is found using the parent metadata in each commits (a linked list. Squashing A does not remove its commits. It creates a new one, and the tip of `main` as its parent and set the new commit as the tip of `main`. But the list of commits in B still refer to the old tip of `main` as their ancestor and still includes the old commits of A. Which is why you can't merge the PR because it would have applies the commits of A twice.
I made a tool that adresses this precise problem: https://github.com/scortexio/autorestack-action/
It does some merge magic so that PR B shows the correct diff; and does so without needing to force push, so on your side you can just "git pull" and continue working.
Of course I expect this repo to become obsolete when GitHub makes their native stacking public.
I agree that this is annoying and unintuitive. But I don’t see the simplest solution here, so:
All you need to do is pull main, then do an interactive rebase with the next branch in your stack with ‘git rebase -i main’, then drop all the commits that are from the branch you just merged.
This is what i often do, but i have never been able to get many coworkers onboard. In my experience I’d say less than 5% of all software folk i’ve worked with are willing to do an interactive rebase; everyone else finds it too scary
I typically prefix my commit messages with the ticket number to make it easier to spot the commits to drop.
I'm not sure I follow your workflow exactly. If PR B is merged, then I'd expect PR A to already be merged (I'd normally branch off of A to make B.)
That said, after the squash merge of A and git fetch origin, you want something like git rebase --update-refs --onto origin/main A C (or whatever the tip of the chain of branches is)
The --update-refs will make sure pr B is in the right spot. Of course, you need to (force) push the updated branches. AFAICT the gh command line tool makes this a bit smoother.
If I'm following correctly, the conflicts arise from other commits made to main already - you've implicitly caught branch A up to main, and now you need catch branch B up to main, for a clean merge.
I don't see how there is any other way to achieve this cleanly, it's not a git thing, it's a logic thing right?
I've no issue with the logic of needing to update feature branches before merging, that's pretty bread and butter. The specific issue with this workflow is that the "update branch" button for PR B is grayed out because there are these hallucinated conflicts due to the new squash commit.
The update branch button works normally when I don't stack the PRs, so I don't know. It just feels like a half baked feature that GitHub automatically changes the PR target branch in this scenario but doesn't automatically do whatever it takes for a 'git merge origin/main' to work.
> the "update branch" button for PR B is grayed out because there are these hallucinated conflicts due to the new squash commit
Those are not hallucinated. PR B still contains all the old commits of A which means merging would apply them twice. The changes in PR B are computed according to the oldest commits belonging to PR B and main which is the parent of squashed A. That would essentially means applying A twice which is not good.
As for updating PR B, PR B doesn't know where PR A (that are also in PR B) ends because PR A is not in main. Squashed A is a new commit and its diff corresponds to the diff of a range of commits in PR B (the old commits of PR A), not the whole B. There's a lot of metadata you'd need to store to be able to update PR B.
I guess to me, I'm looking at it from the perspective of diffing the repo between the squashed commit on main and the tip of the incoming PR. If there are merge conflicts during the rebase in files that don't appear in that diff, I consider that a hallucination, because those changes must already in the target branch and no matter what happened to those files along the way to get there, it will always be a waste of my time to see them during an interactive rebase.
I don't think we need to store any additional metadata to make the rebase just slightly more smarter and able to skip over the "obvious" commits in this way, but I'm also just a code monkey, so I'm sure there are Reasons.
You’re looking at it from the perspective of a human reasoning. But a computer is a simple machine (what it can do, not how it does it). What seems obvious to you could be a complicated algorithm.
Git store all its information as a directed acyclic graph (a tree) of commits. The leaves of that tree have names, and are what we called branches. Each commit points to a tree (also a tree data structure) where the nodes are blobs (files) and sub trees. But that tree only stores the files that has been changed since the last commit. Git does not store diffs. Diffs are computed as needed.
This why the common ancestor commit is important. From there, a version of the working directory is computed for each branch (main-with-squashed-A and PR B). Files that have not been changed since PR A are ok, but everything else will be different, especially if you’ve modified the same lines.
Squashed A is a brand new commit with a new tree that PR B does not know about. You need to recompute PR B on top of Squashed A, (which will create new commits for PR B).
No, it's a Git thing arising from squash commits. There are workflows to make it work (I've linked the cleanest one I know that works without force pushing), but ultimately they're basically all hacks. https://www.patrickstevens.co.uk/posts/2023-10-18-squash-sta...
This is actually a reasonable workflow. Although requires some preparation. I’ll try it out!
Yep that's how I do it if I have to deal with stacked PRs. I also just never use rebase once anything has happened in a PR review that incurs historical state, like reviews or other people checking out the branch (that I know of, anyways). I'll rebase while it's local to keep my branch histories tidy, but I'll merge from upstream once shared things are happening. There are a bunch of tools out there for merging/rebasing entire branch stacks, I use https://github.com/dashed/git-chain.
You "just" need to know the original merge-base of PR B to fix this. github support is not really required for that. To me that's the least valuable part of support for stacked PRs since that is already doable yourself.
The github UI may change the target to main but your local working branch doesn't, and that's where you `rebase --onto` to fix it, before push to origin.
It's appropriate for github to automatically change the target branch, because you want the diff in the ui to be representative. IIRC gitlab does a much better job of this but this is already achievable.
What is actually useful with natively supported stacks is if you can land the entire stack together and only do 1 CI/actions run. I didn't read the announcement to see if it does that. You typically can't do that even if you merge PR B,C,D first because each merge would normally trigger CI.
EDIT: i see from another comment (apparently from a github person) that the feature does in fact let you land the entire stack and only needs 1 CI run. wunderbar!
Oh that's annoying, seems to me there wouldn't have been an issue if you just merged B into A after merging A into main, or the other way around but that already works fine as you pointed out.
I mean if you've got a feature set to merge into dev, and it suddenly merges into main after someone merged dev into main then that's very annoying.
Finally!
I never understood the PR=branch model GitHub defaulted to. Stacked commits (ala Phabricator/Gerrit) always jived more with how my brain reasons about changes.
Glad to see this option. I guess I'll have to install their CLI thing now.
My only complaint off the bat is the reliance on the GH CLI, which I don't use either. But maybe by the time it's GA they'll have added UI support.
You can in fact do this from the web UI: https://github.github.com/gh-stack/guides/ui/#creating-a-sta...
I must have missed that. Amazing! From a reviewer's POV, this will be so nice to at the very least remove diff noise for PRs built on top of another PR. I usually refrain from reviewing child PRs until the parent is merged and the child can be rebased, for the sole reason that the diffs are hard to review i.r.t. what came from where.
damn, I missed it as well
presenting only cli commands in announcement wasn't a good choice
Stacked PRs can be created via the UI, API, or CLI.
You can also run a combination of these. For ex, use another tool like jj to develop locally, push up the branches, and use the gh CLI to batch create a stack of n PRs, without touching local state.
Amazing. Though this wasn't super obvious from the landing page or docs I read.
It seems partially exposed in the UI with that dropdown. There's an 'add' and 'unstack' button.
Probably relies on some internal metadata.
CLI is great because now I can tell my AI agent to do it. “Fix all dependabot security issues (copy logs) and run tests to validate functionality. Create each dependency as its own stack (or commit) so that contributors may review each library update easily.”
Wait 10 minutes and you’re done.
We're shipping a skill file with the CLI: https://skills.sh/github/gh-stack/gh-stack
Everyone will have their own way of structuring stacks, but I've found it great for the agent to plan a stack structure that mirrors the work to be done.
Why don't you use the CLI?
Because git is all I need.
Then why are you using GitHub? :)
My point is that Git is just a component of the GitHub tool, and the GitHub CLI is quite good and helps automate many things in GitHub. For example, even just using `gh browse` and `gh pr create --web` and `gh pr view --web` are fantastic tools.
Huh interesting, my mental model is unable to see any difference between them.
I mean a branch is just jamming a flag into a commit with a polite note to move the flag along if you're working on it. You make a long trail, leave several flags and merge the whole thing back.
Of course leaving multiple waypoints only makes sense if merging the earlier parts makes any sense, and if the way you continue actually depends on the previous work.
If you can split it into several small changes made to a central branch it's a lot easier to merge things. Otherwise you risk making a new feature codependent on another even if there was no need to.
As a solo dev I rarely need stacked PRs, but the underlying problem, keeping PRs small and reviewable, is real even when you're your own reviewer. I've found that forcing myself to break work into small branches before I start (rather than retroactively splitting a giant branch) is the actual discipline. The tooling just makes it less painful when you don't.
Curious whether this changes anything for the AI-assisted workflow. Right now I let Claude Code work on a feature branch and it naturally produces one big diff. Stacked PRs could be interesting if agents learned to split their own work into logical chunks.
It's easier to pile on a lot of changes with AI assisted workflows. And reviewing all that is definitely a challenge just because of the volume of changes. I've actually stopped pretending I can review everything in detail because it makes me a bottleneck in the process. Anything that makes reviewing easier is welcome.
To me, stacked PRs seems overly complicated. It seems to boil down to propagating git rebases through stacks of interdependent branches.
I'm fine with that as long as I don't have to deal with people force pushing changes and routinely rewriting upstream history. It's something you probably should do in your own private fork of a repository that you aren't sharing with anyone. Or if you are, you need to communicate clearly. But if the goal is to produce a stack of PRs that in the end merge cleanly, stacked PRs might be a good thing.
As soon as you have multiple collaborators working on a feature branch force pushing can become a problem and you need to impose some rules. Because otherwise you might end up breaking people's local branches and create work for them. The core issue here is that in many teams, people don't actually fork the main repository and have push access to the main repository. Which emulates the central repository model that people were used to twenty years ago. Having push access is not normal in most OSS projects. I've actually gotten the request from some rookie developers that apparently don't get forking to "please give me access to your repository" on some of my OSS projects.
A proper pull request (whether stacked or not) to an OSS project needs to be clean. If you want to work on some feature for weeks you of course need mechanisms to stay on top of up stream changes. OSS maintainers will probably reject anything that looks overly messy to merge. That's their job.
I spend more time in planning and steering the AI implementation than I do on reviewing it's outputs.
I do the obvious checks like tests and spin up a dev instance to make sure the feature works like I want it too, but very rarely am I reviewing every line of code these days.
I have had a lot of success with Claude and jj, telling it to take the stack of work it's done and build me a new stack on top of trunk that's centered around ease of reviewing.
I once threatened Claude have to learn JJ after doing some crazy git rebase gymnastics. The problem is clearly that I don't know jj
It sometimes will hallucinate older CLI options, because jj has changed at various times, but it's pretty decent with it at this point. The harder part is that a lot of plugins hardcode git into them.
The tooling for that already exists, since a PR can consist of multiple Git commits and you can look at them separately in the UI. I don't know whether agents are any good at navigating that, but if not, they won't do any better with stacked PRs. Stacked PRs do create some new affordances for the review process, but that seems different from what you're looking for.
Looking at multiple commits is not a good workflow:
* It amounts to doing N code reviews at once rather than a few small reviews which can be done individually
* Github doesn't have any good UI to move between commits or to look at multiple at once. I have to find them, open them in separate tabs, etc.
* Github's overall UX for reviewing changes, quickly seeing a list of all comments, etc. is just awful. Gerrit is miles ahead. Microsoft's internal tooling was better 16 years ago.
* The more commits you have to read through at once the harder it is to keep track of the state of things.
>It amounts to doing N code reviews at once rather than a few small reviews which can be done individually
I truly do not comprehend this view. How is reviewing N commits different from/having to do less reviews reviewing N separate pull requests? It's the same constant.
Small reviews allow moving faster for both the author and reviewer.
A chain of commits:
* Does not go out for review until the author has written all of them
* Cannot be submitted even in partial form until the reviewer has read all of them
Reviewing a chain of commits, as the reviewer I have to review them all. For 10 commits, this means setting aside an hour or whatever - something I will put off until there's a gap in my schedule.
For stacked commits, they can go out for review when each commit is ready. I can review a small CL very quick and will generally do so almost as soon as I get the notification. The author is immediately unblocked. Any feedback I have can be addressed immediately before the author keeps building on top of it.
Let's compare 2 approaches to delivering commits A, B, C.
Single PR with commits A, B, C: You must merge all commits or no commits. If you don't approve of all the commits, then none of the commits are approved.
3 stacked PRs: I approve PR A and B, and request changes on PR C. The developer of this stack is on vacation. We can incrementally deliver value by merging PRs A and B since those particular changes are blocking some other engineer's work, and we can wait until dev is back to fix PR C.
> You must merge all commits or no commits
This seems to be the root of the problem. Nothing stops a reviewer merging some commits of a PR, except a desire to avoid the git CLI tooling (or your IDE's support, or....). The central model used in a lot of companies requires the reviewee to do the final merge, but this has never been how git was meant to be used and it doesn't have to be used that way. The reviewer can also do merges. Merge (of whichever commits) = approval, in that model.
Yes, the root of the problem is the workflow of the company being centered around GitHub instead of Git itself.
This feature helps improve GitHub so it's useful for companies that do this this way.
At our company, only admin users can actually directly git push to main/master. Everything else HAS to be merged via github and pass through the merge queue.
So this stacked PRs feature will be very helpful for us.
It's crazy that you're getting downvoted for this take.
This isn't reddit people. You're not supposed to downvote just because you disagree. Downvotes are for people who are being assholes, spamming, etc...
If you disagree with a take, reply with a rebuttal. Don't just click downvote.
Historically, hn etiquette is that it's fine to downvote for disagreement. This came from pg himself.
That said, while he hasn't posted here for a long time, this is still in the guidelines:
> Please don't post comments saying that HN is turning into Reddit. It's a semi-noob illusion, as old as the hills.
https://news.ycombinator.com/newsguidelines.html
Well, I stand corrected.
Maybe there’s a git trick I don’t know, but I’ve found making small branches off each other painful. I run into trouble when I update an earlier branch and all the dependent branches get out of sync with it. When those earlier branches get rebased into master it becomes a pain to update my in-progress branches as well
If I understood you correctly, you want to propagate changes in a branch to other branches that depend on it? Then --update-refs is for you[1]. That way, you only need to update the "latest" branch.
[1] https://andrewlock.net/working-with-stacked-branches-in-git-...
Stacking branches for any extended period of time is definitely a poor mixing of the concepts of branches and commits. If you have a set of changes you need to keep in order, but you also need to maintain multiple silos where you can cleanly allow the code to diverge, that divergence constitutes the failure of your efforts to keep the changes in order.
Until you can make it effortless, maintaining a substantial commit structure and constantly rebasing to add changes to the proper commit quickly turns into more effort than just waiting to the end and manually editing a monster diff into multiple sensible commits. But we take the challenge and tell ourselves we can do better if we're proactive.
This is what I understood as well, but it sounded like GP had success doing it; so I was curious if there was a trick I didn’t know about
I take from GP that they try to make their branches small, and keep the cycle of development->review->merging small, so that the problem stacked PRs seeks to solve doesn't materialize in the first place.
Stacked PRs in my experience has primarily been a request to merge in a particular order. If you're the only merger, as in GP's case, there's no need to request this of yourself.
Whenever I send a big diff. I spend some time annotating with comment first to helps the reviewer. A good summary of the changes in the description, the I annotate the diff of the PR, explaining approaches, the design of a specific changes, tricky part of the code, boilerplate,... Trying to guess the context is where the review bottleneck is, so I present it alongside the code.
I understand that's what the feature is trying to solve.
If you visit the webpage it gives you integration instructions for agents
Very cool that GitHub actually put stacks in the UI vs. GitLab's `glab stack`[0] (which looks just like the `gh stack` part of GitHub's thing).
One part that seems like it's going to feel a little weird is how merging is set up[1].
That is, if I merge the bottom of the stack, it'll rebase the others in the stack, which will probably trigger a CI test run. So, if I have three patches in the stack, and I want to merge the bottom two, I'd merge one, wait for tests to run on the other, merge the second vs. merge just those two in one step (though, without having used it, can't be sure about how this'd work in practice—maybe there's some way to work around this with restacking?)
[0]: <https://docs.gitlab.com/cli/stack/>
[1]: <https://github.github.com/gh-stack/guides/stacked-prs/#mergi...>
> So, if I have three patches in the stack, and I want to merge the bottom two, I'd merge one, wait for tests to run on the other, merge the second vs. merge just those two in one step
As we have it designed currently, you would have to wait for CI to pass on the bottom two and then you can merge the bottom two in one step. The top of the stack would then get rebased, which will likely trigger another CI run.
Thanks for the callout - we'll update those docs to make it clear multiple PRs can be merged at once.
I really don't get the point of stacked PRs.
Just using git, you'd send a set of patches, which can be reviewed, tested and applied individually.
The PR workflow makes a patch series an undivisible set of changes, which must be reviewed, tested and applied in unison.
And stacked PRs tries to work around this issue, but the issue is how PRs are implemented in the first place.
What you really want is the ability to review individual commits/patches again, rather than work on entire bundles at once. Stacked PRs seems like a second layer of abstraction to work around issues with the first layer of abstractions.
The teams that I have worked with still apply the philosophy you’re describing, but they consider PRs to be the “commit”, i.e. the smallest thing that is sane to apoly individually.
Then the commits in the PR are not held to the standard of being acceptable to apply, and they are squashed together when the PR is merged.
This allows for a work flow in which up until the PR is merged the “history of developing the PR” is preserved but once it is merged, the entire PR is applied as one change to the main branch.
This workflow combined with stacked PRs allows developers to think in terms of the “smallest reviewable and applicable change” without needing to ensure that during development their intermediate states are safe to apply to main.
Doesn’t this mean that a first review might request that a specific change be reverted, and then a later reviewer reviews that reversion? That’s essentially reviewing a noop, but understanding the it’s a noop requires carefully checking all previous now-invalidated changes.
No, each PR is based on the previous one, so the reviewer only needs to consider the ideas that are new in each PR one at a time.
Squashing is fine if you’re just making a mess of temporary commits as you work and you don’t want to keep any of those changes separate in master, but that’s not a useful review workflow. A lot of times I’ve built a feature in a way that decomposed naturally into e.g. two commits: one to do a preparatory refactor (which might have a lot of noisy and repetitive changes, like changing a function signature) and another to actually change the behavior. You want those changes to be separate because it makes the changes easier to review; the reviewer quickly skims the first commit, observes that it’s a mechanical refactor, and the change in behavior has its own, smaller commit without all the noise.
“What if there’s feedback and you need to make changes after the code review?” Then I do the same thing I did before I posted the code review: make separate “fixup” commits and do an interactive rebase to squash them into my commits. (And yes, I do validate that the intermediate commits build cleanly.)
There’s nothing you get from stacked PR’s that you don’t also get from saying “please review my feature branch commit by commit”.
Yes what you’re describing is literally the thing GitHub has built but instead of having to make a bunch of compromises, there is dedicated UI and product metaphor for it.
Some examples of compromises:
You can’t merge partially merge a large “review commit by commit” PR so you are forced to wait until it is all ready to merge.
Exactly! A stack of PRs is really the same beast as a branch of commits.
The traditional tools (mailing-lists, git branches, Phabricator) represented each change as a difference between an old version of the code and the proposed new version. I believe Phabricator literally stored the diff. They were called “diffs” and you could make a new one by copying and pasting into a <textarea> before pressing save*.
The new fangled stuff (GitHub and its clones) recorded your change as being between branches A and B, showed you the difference on the fly, and let you modify branch B. After fifteen years of this we are now seeing the option for branch A to be something other than main, or at least for this to be a well supported workflow.
In traditional git land, having your change as a first class object — an email or printout or ph/D1234 with the patch included — was the default workflow!
*Or some other verb meaning save.
It’s useful for large PRs in large repos with many contributors. It reduces the burden for reviewers.
Still not sure this is the right solution. My problem is if one of your first stages gets rejected in review or requires significant changes, it invalidates so much work that comes after it. I've always when possible preferred to get small stuff merged in to production as it happens rather than build an entire feature and put it up for review.
> it invalidates so much work that comes after it.
No, not necessarily.
I work on a large repo and new features often involve changes to 3 different services: 2 from the backend, and the frontend UI. Sending a single PR with changes to all 3 services is really not ideal: the total diff size in a feature I added recently was maybe 600+ lines, and the reviewers for frontend and backend changes are different people. The changes in the 2 backend services can be thought of as business logic on one side and interactions with external platforms on the other. The business logic can't work without integrating calls to external APIs, and the UI can't work without the business logic.
These days I open 3 separate PRs and the software only works once all 3 are merged and built. It would be great to have all of them as a single package that's still testable and reviewable as 3 distinct parts. The UI reviewer can check out the whole stacked PR and see it running locally with a functional backend, something that's not possible without a lot of manual work when we have 3 PRs.
The LLVM community used this model for years with Phabricator before it was EOL'd and moving to GH and PRs was forced. It's a proven model and works very well in complex code bases, multiple components and dependencies that can have very different reviewer groups. E.g: 1) A foundational change to the IR is the baseline commit 2) Then some tweaks on top to lay the groundwork for uses of that change 3) Some implementation of a new feature that uses the new IR change 4) A final change that flips the feature flag on to enable by default.
Each of these changes are dependent on the last. Without stacked PRs you have o only one PR and reviewing this is huge. Maybe thousands of lines of complex code. Worse, some reviewers only need to see some parts of it and not the rest.
Stacked diffs were a godsend and the LLVM community's number one complaint about moving to GitHub was losing this feature.
this works much better in Phabricator because commits to diffs are a 1:1 relationship, diffs are updated by amending the commit, etc., the Github implementation does seem a bit like gluing on an additional feature.
Right, a PR is "just" a set of commits (all must be in the same branch) that are intended to land atomically.
Stacked PRs are not breaking up a set of commits into divisible units. Like you said, you can already do that yourself. They let you continue to work off of a PR as your new base. This lets you continue to iterate asynchronously to a review of the earlier PRs, and build on top of them.
You often, very often, need to stage your work into reviewer-consumable units. Those units are the stack.
I've been using `git town`[1] for years to managed stacked PR's alone with Github PR's[2] and juniors I have introduced it to have really found it a helpful mental model when developing features.
I hope the Gitub CLI will include syncing[3] 'stacks' locally with upstream in a similar way.
[1]: https://www.git-town.com/stacked-changes.html
[2]: https://github.com/marketplace/actions/git-town-github-actio...
[3]: https://www.git-town.com/commands/sync.html
There’s a startup callled Graphite dedicated to stacked PRs. I have been using them for a while now I always wonder why github doesn’t implement something similar to this. I probaly will try and switch to GitHub to see if it works flawlessly
They recently got bought by Cursor.
Yep, very happy with graphite at work.
Same, our team has been on it for a year and it's very good.
IME the github workflow promotes bad commit hygiene by making squashing or rebasing as-is an either-or choice in the web GUI.
This will help some since you can more easily split PRs into units that make sense to squash at the end, but it still seems like not doing this on a per-commit basis is a disadvantage compared to Gerrit. With Gerrit I can use all the built-in Git rebase/squash/fixup tools to manage the commit stack and push everything in one go. I don't think there's a nearly as convenient a way to work with stacked branches in Git.
I've been doing stacked PRs for ~2 years now. Thus, I don't quite see the need for this CLI. Git has had some additions in the last few years that make this work natively – specifically the --update-refs flag[1] or the rebase.updateRefs config. Combined with `git commit --fixup`, rebase.autoStash, and rebase.autoSquash rebasing stacks becomes a breeze (as long as you work off from the tip of your stack). Add in git-absorb[2] and the heavy-lifting is taken care of.
My biggest gripe with GitHub when working with stacks – and something that's not clarified in these docs – is whether fast-forward merges are possible. Its "Merge with rebase" button always rewrites the commit. They do mention that the stack needs to be rebased in order to merge it. My workaround has been `git merge --ff-only top-branch-of-stack` to merge the entire stack locally into main (or anything in between actually) and then push. GitHub neatly recognizes that each PR in the stack is now in main and marks them all as merged. If there are subsequent PRs that weren't merged it updates the base branch.
Having said that, it's great to see GitHub getting a proper UI for this. It's also great that it understands the intent that branch B that goes on top of branch A is a stack and thus CI runs against. I just hope that it's not mandatory to use their CLI in order to create stacks. They do cover this briefly in the FAQ[3], but it might be necessary to use `gh stack init --adopt branch-a branch-b branch-c`. On the other hand, if that removes the need to manually create the N PRs for my stack, that's nice.
[1]: https://git-scm.com/docs/git-rebase#Documentation/git-rebase...
[2]: https://github.com/tummychow/git-absorb
[3]: https://github.github.com/gh-stack/faq/#will-this-work-with-...
I think the CLI is useful for pushing. What do you use to push all the rebased child branches?
My git config for pushing is set to push.default=current. For rebased stacks I have an alias that does this:
In other words, I force push all branches that have a matching upstream by changing my config on the fly.> Git has had some additions in the last few years that make this work natively – specifically the --update-refs flag[1] or the rebase.updateRefs config. Combined with `git commit --fixup`, rebase.autoStash, and rebase.autoSquash rebasing stacks becomes a breeze (as long as you work off from the tip of your stack). Add in git-absorb[2] and the heavy-lifting is taken care of.
...or you don't bother with all that and simply do:
- gh stack init
- gh stack push
- gh stack submit
Sure, that's possible. I can also use the GitHub app and use a Git abstraction where I don't have to understand Git at all.
The point is that I want to use Git, a tool and skill that is portable to other platforms.
That's like, most AI obsoleteable skill you could pick.
Not at all. One of the tricks of using AI is context management and managing the Git history yourself can be a big part of that. If the AI has a stupid idea and implements it, even when you tell it, “that was a stupid idea, don’t do that, change it back”, the history could persist and the stupid idea will poison the context window every time an agent reads the commit history. It’s even worse if you had the stupid idea!
Also, my current workflow actually has hooks to block agents from creating or changing commits. I know at some point this will be a limit to scaling, but I think that will result in me spending more rather than less time in git.
> The point is that I want to use Git, a tool and skill that is portable to other platforms.
You want to use git.
Most people around you want to get things done.
Maybe this is just a skill issue, but even with several attempts I just can't figure out why I would use stacked diffs/PRs. Though maybe that's because of the way I work?
I notice a lot of examples just vaguely mention "oh, you can have others review your previous changes while you continue working", but this one doesnt make sense to me. Often times, the first set of commits doesn't even make it to the end result. I'm working on a feature using lexical, and at this point I had to rewrite the damn thing 3 times. The time of other devs is quite valuable and I can't imagine wasting it by having them review something that doesn't even make it in.
Now, I have been in situations where I have some ready changes and I need to build something on top. But it's not something just making another branch on top + rebase once the original is merged wouldn't solve.
Is this really worth so much hype?
We use this feature extensively at $dayjob.
Imagine you have some task you are working on, and you wish to share your progress with people in bite sized chunks that they can review one at a time, but you also don’t want to wait for their reviews before you continue working on your task.
Using a stacked set of PRs you can continue producing new work, which depends on the work you’ve already completed, without waiting for the work you’ve already completed to be merged, and without putting all your work into one large PR.
I've always done this by just creating new PRs that are based on the branch of the old one. Maybe this is a UI improvement?
Yes, you can do that, but there's lots of things about it that are awkward. This makes it a more first-class feature.
Yeah that is a “stacked” pr. The tooling is nice especially when have a larger stack and make changes to the first branch. Update refs + push all branches, same with merging and rebasing onto main.
You can review PR’s commit by commit, and you can ask people to review PR’s commit by commit. Not a big deal.
Then you lose the ability to merge the portion of work which has been agreed to, until the whole change overall has been agreed to.
in Phabricator you either abandon the original diffs entirely, or you amend them. you don't just stack more commits with meaningless messages like "WIP", "lint fix", etc. on top.
> The time of other devs is quite valuable and I can't imagine wasting it by having them review something that doesn't even make it in.
this is now what stacked diffs are for. stacked diffs doesn't mean putting up code that isn't ready. for example you are updating some library that needs an API migration, or compiler version that adds additional stricter errors. you need to touch hundreds of files around the repository to do this. rather than putting up one big diff (or PR) you stack up hundreds of them that are trivial to review on their own, they land immediately (mitigating the risk of merge conflicts as you keep going) then one final one that completes the migration.
I also branch out, and rebase. Also, keep updating and rebasing until merged. It’s tedious when PR take ages for approval, as I keep creating new branches on top of each other.
So, when I saw this announcement seemed interesting but don’t see the point of it yet.
I thrive on stacked PRs but this sure seems like a weird way to implement support for it. Just have each branch point to their parent in the chain, the end. Just native Git. I've been longing for better GitHub support for this but the CLI is not where I need that support: just the UI.
Rebasing after merging a base branch becomes a pain though, when you do this. IMO the CLI will be nice to automate the process of rebasing each branch on its parent.
Agreed. I do have tooling for a rebase + push flow, but it simply calls native git commands.
The CLI is completely optional, you can create stacked PRs purely via the UI.
Also the rationale for having a chain of branches pointing to each other was so the diff in a PR shows just the relevant changes from the specific branch, not the entire set of changes going back to the parent/trunk.
Curious how you're thinking about it?
> so the diff in a PR shows just the relevant changes from the specific branch
That's exactly right.
> you can create stacked PRs purely via the UI
How?
I see from the docs https://github.github.com/gh-stack/introduction/overview:
> When a pull request is part of a stack
How does GitHub determine if a PR is part of a stack? Is it automatically detected so that I don't need to adjust my tooling that already creates chained PRs?
+1 this isn’t something new, it’s been possible all along in native git if you’re willing to do branch management and rebasing yourself. Just without the fancy UI / stack map.
Yes! Maybe that feature will come next.
Does this work from a fork? That is, can I file a stacked PR to a project not owned by me, by creating branches in my forked project? Previously I asked AI about how to contribute stacked PR, it told me that I can only do it when I have push privileges to the repo, not from a fork, and the doc here is ambiguous.
----
OK, I found this from official docs, so this feature is now quite useless to me:
> Can stacks be created across forks?
> No, Stacked PRs currently require all branches to be in the same repository. Cross-fork stacks are not supported.
I have never got a good answer to "can't you just make smaller PRs". This is convoluted tooling (needs its own CLI) for something you could achieve with just learning how git works.
IMO this tool is basically allowing you to do that, it just takes care of the bookkeeping to associate the series of smaller PRs with eachother which is possible today but requires a lot of clicking.
If there is a stack of size n and you make a modification at the first change, closest to the trunk, is there a single git command you can run to rebase the other n-1 branches and ensure they remote branches are updated?
Not a single one, but it can be done with 2.
Assuming you're currently on the most recent branch (furthest from the trunk), `git rebase -i --update-refs trunk` will rebase all the intermediate branches. If you need to make a change to the first branch nearest the trunk, either use `edit` in the interactive rebase, or make a fixup commit and enable autosquash for the rebase. The `--update-refs` flag makes sure that all the intermediate branches get updated during the rebase.
Then, to push them all, something like `git push origin 'refs/heads/yourname/*'` will push all branches prefixed with `yourname/`. It's a bit stupid that one can't just do `git push 'yourname/*'` though.
I agree that a `gh stack` command is not needed, but this feels to me like just a better UI feature for a good git workflow. It literally is about making multiple smaller PRs that build on top of each other.
The question is, why are you not just merging them into main as you go? It's a bit of a smell when you "need" to merge branches into branches. It shows a lack of safety and ease in deployments, which is the real problem to solve IMO.
Because sometimes there are changes that need to land as all or nothing.
Right, so 'just work the way the tool requires instead of making the tool work the way you want'. I would prefer the tool worked the way I want and the way I think of the changes instead.
I find this puzzling. It does not seem to allow to stack PRs on top of other people's PRs?
There is already an option to enable review comments on individual commits (see the API endpoint here: https://docs.github.com/en/rest/guides/working-with-comments...). Self-stacking PRs seem redundant.
Still feels like an alpha version right now. I'm sure they will add it later.
Graphite (which they seem to be inspired by) has frozen branches exactly for that use case:
https://graphite.com/blog/introducing-frozen-branches
This API leaves a comment, on the commit; not quite the same thing since in GH, several operations are tied to PRs and not to commits.
Super excited to give this a whirl - i've been messing with graphite's `gt` command for stacking and it's been relatively decent but I didn't love needing to bring in another tool/service/account when I only care about the stacking behaviour. Was a fun experiment but nice I can simplify back onto `gh` and `git`
I hope that GitHub continues copying Graphite's homework in terms of functionality, because from what I can see they don't have equivalents to `gt split`, absorb, and so on. Those can be very useful in the right contexts.
This is awesome honestly, Stacked PRs are one of those features that feels obvious in hindsight. Breaking a n-line PR into 3 focused layers where each one is independently reviewable is a huge win for both the author and reviewer. The native GitHub UI with the stack navigator is the right call too, and there's no reason this should require a third-party tool.
One thing I keep thinking about in this same direction: even within a single layer of a stack, line-level diffs are still noisy. You rename a function and update x call sites, the diff shows y changed lines. A reviewer has to mentally reconstruct "oh this is just a rename" from raw red/green text.
Semantic diffing (showing which functions, classes, methods were added/modified/deleted/moved) would pair really well with stacks. Each layer of the stack becomes even easier to review when the diff tells you "modified function X, added function Y" instead of just showing changed lines.
I've been researching something in this direction, https://ataraxy-labs.github.io/sem/. It does entity-level diffs, blame, and impact analysis. Would love to see forges like GitHub move in this direction natively. Stacked PRs solve the too much at once problem. Semantic diffs solve the "what actually changed" problem. Together they'd make code review dramatically better.
I already do this using git branched. Whenever I have features that depends on one another I create a feature branch and then stack branches on top of each other for individual feature so it's easy for the reviewer to go through the code and and also keep the PR size quite small. Also this gives me freedom to push more than one commit for each branch to fix things.
The only annoying part is that I have to keep on merging the base branch to the feature branch constantly to keep it up-to date. If Github can provide a feature to do that automatically, then that would be perfect. Other than that, I don't see any advantage on this stacked PR approach they are proposing.
Seems to mainly be useful for monorepos as currently designed. Or, to replace a long-lived feature/refactor branch.
Whatbmakes you say that? Devs use stacked PRs in small and large repos today.
Their examples show combined backend and frontend changes on the same monorepo in different PRs.
As far as splitting work into different PRs that need coordinated merging, I've only ever encountered that when it's a long lived refactor / feature.
I think the only thing I miss from GitLab was being able to make merge requests depend on other merge requests, even across repositories. So I could make a backend repository MR depend on a library repository MR, and even enable auto-merge that’d fire when the backend MR was reviewed and the dependency was also merged.
GitLab's UI around MRs (PRs) is IMO miles better than what GH's been offering. Try creating a PR from branch A to main, and then rebasing A. GitLab handles this fine and can show you changes between the two revisions; GitHub is completely lost.
> How It Works
> The gh stack CLI handles the local workflow […]
That's not "how it works", that's "how you['re supposed to] use it"… for "how it works" I would've expected something like "the git branches are named foo1 foo2 and foo3 and we recognize that lorem ipsum dolor sit amet…"
…which, if you click the overview link, it says "The CLI is not required to use Stacked PRs — the underlying git operations are standard. But it makes the workflow simpler, and you can create Stacked PRs from the CLI instead of the UI." … erm … how about actually explaining what the git ops are? A link, maybe? Is it just the PRs having common history?
…ffs…
(In case it's not obvious: I couldn't care less for using a GH specific CLI tool.)
> Large pull requests are hard to review, slow to merge, and prone to conflicts. Reviewers lose context, feedback quality drops, and the whole team slows down.
OK, yeah, I’m with you.
> Stacked PRs solve this by breaking big changes into a chain of small, focused pull requests that build on each other — each one independently reviewable.
I don’t get this part. It seems like you are just wasting your own time building on top of unreviewed code in branches that have not been integrated in trunk. If your reviews are slow, fix that instead of running ahead faster than your team can actually work.
This _is_ a solution to slow reviews. Smaller reviews are faster to get in. And many small reviews take less time to review than one large review.
Plus there's no review that's instant. Being able to continue working is always better.
I am not arguing against small PRs.
Stacking PRs are not a way to make changes smaller and therefore not making reviews easier.
how is this different than viewing a PR one commit at a time?
I think it is conceptually the same but multiple PRs gives you the tools to manage the commits properly which GitHub is missing. You can't do the equivalent of `git rebase -i` in the GitHub UI to squash a fixup into a previous commit. Having each change in it's own PR enables that workflow using the existing GitHub UI.
Split into individual PRs, which works better for how a lot of companies do code review.
Stacked PRs track changes through updates and can be integrated progressively as they get validated.
They also allow reviewing commits individually, which is very frustrating to do without dedicated support (unless you devolve back to mailing list patch stacks).
Each commit can be merged independently as they're reviewed.
I don't think this is it. The main driver is that several operations in GH are scoped around a PR, not a commit. So the reason you need stacked PRs is that the layer of tooling above `git` is designed to work on logical groups of commits called a PR.
Right, the argument against: "how is this any different than splitting into single commits?" is simply: In general you want just one level above a commit which is the PR
One of the advertised features of this is being able to merge all the PRs at once. Which would also be the case for multiple commits in a single PR.
That's possible but not mandatory. In the current UX you can only approve/submit all or none.
Commits are immutable and you never know which feedback goes stale when you add another commit.
I'm not a huge fan, since stacked PRs mean the underlying issues don't get addressed (reviews clearly taking too long, too much content in there), but it seems they want something that works for their customers, right now, as they work in real life.
> Commits are immutable
I guess this is why you're getting downvoted. Commits can be edited.
When you edit a commit, it creates a new commit. They are immutable. You can still find the old commit via the reflog, until it gets eventually gc'd.
If I had to guess a reason they were downvoted (and I didn't downvote, to be clear), it's probably because people see stacked diffs as specifically solving "reviews clearly taking too long, too much content in there", and so it feels contradictory. Then again, as I said, I didn't downvote!
It would be the same if commits were meaningful things. But typically they're not. The PR is the meaningful thing. A commit is something like "fix the lint error".
CI runs on each PR, you get a whole PR message and discussion/review interface for each PR. Each PR can itself consist of multiple commits. You can have stacked PRs from different authors (though from another comment it sounds like they may not have implemented that).
It's a big improvement (assuming they've done it right).
'Large pull requests are hard to review' is a good reason to keep PRs small, but small PRs also encourage continuous integration/delivery/deployment. Stacked PRs sound like they encourage long-lived feature branches instead.
Depends on what you consider long-lived.
I typically generate stacks of 3-5 PRs in 1-2 days now (in a gen-AI world).
Looks interesting, but it seems you need to know the final shape of the stack before you start creating Pull Requests. So it's useful if you create Pull Request A, then immediately start working on something that builds on top of A, create a Pull Request for that (while A is still a PR), then you can do A->B->C
Here's something that would be useful: To break down an already big PR into multiples that make up a stack. So people can create a stack and add layers, but somehow re-order them (including adding something new at the first position).
It appears the CLI is only half-baked so far. Given how many things they've borrowed from Graphite (a tool which adds this type of workflow), it should only be a matter of time until they add a `split` command. Graphite lets you split a large set of changes by commit or by hunk which is very handy.
It looks like in the UI if you base a PR on another branch you can just check a box to make it a stack. So I don't think you have to know the full shape of the stack in advance unless you're using the cli.
I use jj to stack branches so i'll just be using the UI to do github pr stacks.
Well, I have been waiting for this for YEARS.
Every time I try to do it manually, I wind up screwing everthing up.
Very interested ot check it out.
This just reeks to me of bad practice. Why use this as opposed to breaking your change into smaller PRs and merging them individually behind a feature flag or similar? With this, you have a marginally better UX for reviewing through the Github website, but the underlying issues are the same. The change being introduced is not sufficiently testable by itself, or it's (somehow) too tightly coupled to other parts of the UI/codebase that it can't be split. You still need to test for integration issues at every point of the stack, and some architecture issues or points of code reuse can't be seen from stacked changes like this.
Not for me, but I'm glad it fits other people's workflows. I just hope it doesn't encourage people to try make poorly reasoned changes!
When I've reached for stacked PRs (in the past, not using this feature) it's precisely because I've split my change into smaller PRs being merged individually.
I've just written those smaller PRs at once, or in quick enough succession that the previous PRs weren't merged before the later ones were ready. And the later ones relied on the previous ones because that's how working on a feature works.
The earlier PRs are absolutely reviewable and testable without relying on the later ones. The later ones are just treating the earlier ones as part of the codebase. I.e. everything here looks like two different PRs except the timing.
An obvious example would be "implement API for a feature" and then "implement UI that uses that API". Two different PRs. The second fundamentally relies on the first.
This is a perfect example that I've often seen in practice. There's nothing blocking in this workflow at all, and no reason these changes cannot be made in independent changes. e.g.
1) API implementation - Including tests and docs this should be perfectly acceptable to merge and review independently 2) UX implementation - Feature flagged, dummy API responses, easy to merge + review 3) One quick "glue" PR where the feature can be integration tested etc
This prevents awful merge conflicts, multiple rounds of increasingly complex stacked reviews, and a host of other annoyances.
Is there any reason that the stacked PR workflow is better that I'm ignoring or overlooking?
You're creating more work for no reason. There is absolutely no reason to make dummy API responses, a feature flag (well unless you want to delay public release of the features - domain dependent here), or a glue PR.
Moreover you haven't even eliminated the dependency. The UI PR requires knowing that the dummy API responses you've created fit the right format - i.e. approval of the API PR up to small nits.
Just test against the actual implementation from the start. Even without stacked PRs just leave the second as a draft with both sets of commits until the first is merged then rebase and make it.
Stacked PRs are superior here because they eliminate that extra work of the draft PR and parallelize the review process slightly better.
I do this as well, but there is a workflow problem to solve and that is: getting PRs merged when they need to be to continue working.
It's not a simple problem to solve, we can't all just jump because someone finished some work after all. But if the PRs are OK to rubber stamp, and merge, and they're safely behind a feature flag, then it could just be as simple as letting the submitter merge without the need for an extra review. That can of course be contentious, but then we can ask "why not?" and figure out what non-human gateways need to be added to help make it possible etc.
I'm finding myself increasingly interested in understanding what friction can be removed from the software review, merge and release process, without sacrificing safe, well tested, understandable code that follows good standards.
Let's say I have the canonical example of a stack from main via a backend-pr and a frontend-pr. When my stack is done I send it for review to one frontend reviewer and one backend reviewer.
Usually when you develop a "full stack" thing you continuously massage the backend into place while developing frontend stuff. If you have 10 commits for frontend and 10 for backend, they might start with 5 for backend, then 5 commits to each branch to iron out the interface and communication, and finally 5 commits on the frontend. Let's call these commits B1 through B10 and F1 through F10. Initially I have a backend branch based on main wuth commits B1 through B5.
Then I have a frontend branch based on B5 with commits F1 through F5. But now I need to adjust the backend again and I make change B6. Now I need to rebase my frontend branch to sit on B6? And then I make F6 there (And so on)?
And wouldn't this separation normally be obvious e.g. by paths? If I have a regular non-stack PR with 20 commits and 50 changed files, then 25 files will be in /backend and 25 in /frontend.
Sure, the reviewers who only review /frontend/* might now see half the commits being empty of relevant changes. But is that so bad?
> If you have 10 commits for frontend and 10 for backend
In this model, you tend to want to amend, rather than add more commits. And so:
> they might start with 5 for backend, then 5 commits to each branch to iron out the interface and communication,
You don't add more commits here, you modify the commits in your stack instead.
> Now I need to rebase my frontend branch to sit on B6?
Yes, when you change something lower in the stack, the things on top need to be rebased. Because your forge understands that they're stacked, it can do this for you. And if there's conflicts, let you know that you need to resolve them, of course.
But in general, because you are amending the commits in the stack rather than adding to it, you don't need to move anything around.
> And wouldn't this separation normally be obvious e.g. by paths?
In the simplest case, sure. But for more complex work, that might not be the case. Furthermore, you said you have five commits for each; within those sets of five, this separation won't exist.
What a time to be alive. Stacked PRs are now a native feature of Github, even with first-class support for your ai agents. Vibeslop your whole Jira Backlog. Don't fear the merge anymore. Just make any feature branch a long-lived branch by stacking one upon another like bricks.
I'm old enough to have worked with SVN and young enough to have taught engineers to avoid stacking PR in Git. All wisdom has been lost and will probably be rediscovered in another time by another generation.
Yeah, not sure what this solves that doing multiple PRs from one feature branch into another doesn't solve. But building behavior that into AI agents wouldn't be cool enough, I guess.
I think the core conceptual difference between a stacked diff and PRs as we use them in open source is the following:
A PR is basically a cyberspatial concept saying "I, as a dog on the internet, am asking you to accept my patches" like a mailing list - this encourages trying to see the truth in the whole. A complete feature. More code in one go because you haven't pre-agreed the work.
Stacks are for the opposite social model. You have already agreed what you'll all be working on but you want to add a reviewer in a harmonious way. This gives you the option to make many small changes, and merge from the bottom
> a chain of small, focused pull requests that build on each other — each one independently reviewable.
I have never understood what this even means.
Either changes are orthogonal (and can be merged independently), or they’re not. If they are, they can each be their own PR. If they’re not, why do you want to review them independently?
If you reject change A and approve change B, nothing can merge, because B needs A to proceed. If you approve change A and reject change B, then the feature is only half done.
Is it just about people wanting to separate logical chunks of a change so they can avoid get distracted by other changes? Because that seems like something you can already do by just breaking a PR into commits and letting people look at one of those at a time.
I’ve tried my best to give stacked-diff proponents the benefit of the doubt but none of it actually makes sense to me.
The canonical example here is a feature for a website that requires both backend and frontend work. The frontend depends on the backend, but the backend does not depend on the frontend. This means that the first commit is "independent" in the sense that it can land without the second, but the second is not, hence, a stack. The root of the stack can always be landed independently of what is on top of it, while the rest of the stack is dependent.
> If they’re not, why do you want to review them independently?
For this example, you may want review from both a backend engineer and a frontend engineer. That said, see this too though:
> that seems like something you can already do by just breaking a PR into commits and letting people look at one of those at a time.
If you do this in a PR, both get assigned to review the whole thing. Each person sees the code that they don't care about, because they're grouped together. Notifications go to all parties instead of the parties who care about each section. Both reviews can proceed independently in a stack, whereas they happen concurrently in a PR.
> If you approve change A and reject change B, then the feature is only half done.
It depends on what you mean by "the feature." Seen as one huge feature, then yes, it's true that it's not finished until both land. But seen as two separate but related features, it's fine to land the independent change before the dependent one: one feature is finished, but the other is not.
If the layers of a stack have a disjoint set of reviewers things are viewed in separation which might lead to issues if there is no one reviewing the full picture.
That is why your forge will show that these two things are related to each other, and you may have the same person assigned to review both. It can show you this particular change in the context of the rest of them. But not every reviewer will always want to see all of the full context at all times.
> If you do this in a PR, both get assigned to review the whole thing. Each person sees the code that they don't care about, because they're grouped together.
There are two separate issues you’re bringing up:
- Both groups being “assigned” the PR: fixable with code owners files. It’s more elegant than assigning diffs to people: groups of people have ownership over segments of the codebase and are responsible for approving changes to it. Solves the problem way better IMO.
- Both groups “seeing” all the changes: I already said GitHub lets you view single commits during PR review. That is already a solved problem.
And I didn’t even bring up the fact that you can just open a second PR for the frontend change that has the backend commit as the parent. Yes, the second PR is a superset of the first, but we’ve already established that (1) the second change isn’t orthogonal to the first one and can’t be merged independently anyway, and (2) reviewers can select only the commits that are in the frontend range. Generally you just mark the second PR as draft until the first one merges (or do what Gitlab does and mark it as “depends on” the first, which prevents it from merging until the first one is done.) The first PR being merged will instantly make the second PR’s diff collapse to just the unique changes once you rebase/merge in the latest main, too.
All of this is to explain how we can already do pretty much all of this. But in reality, it’s silly to have people review change B if change A hasn’t landed yet. A reviewer from A may completely throw the whole thing out and tell you to start over, or everything could otherwise go back to the drawing board. Making reviewers look at change B before this is done, is a potential for a huge waste of time. But then you may think reviewers from change B may opt to make the whole plan go back to the drawing board too, so what makes A so special? And the answer is it’s both a bad approach: just make the whole thing in one PR, and discuss it holistically. Code owners files are for assigning ownership, and breaking things into separate commits is to help people look at a subset of the changes. (Or just, like, have them click on the folder in the source tree they care about. This is not a problem that needs a whole new code review paradigm.)
> fixable with code owners files.
Code owners automatically assigns reviewers. You still end up in the state where many groups are assigned to the same PR, rather than having independent reviews.
> I already said GitHub lets you view single commits during PR review.
Yes, you can look at them, but your review is still in the context of the full PR.
> And I didn’t even bring up the fact that you can just open a second PR for the frontend change that has the backend commit as the parent.
The feature being discussed here is making this a first-class feature of the platform, much nicer to use. The second PR is "stacked" on top of the first.
> You still end up in the state where many groups are assigned to the same PR
> Yes, you can look at them, but your review is still in the context of the full PR.
Why is this a bad thing? I don’t get it. This has literally never been a problem once in my career. Is the issue that people can’t possibly scroll past another discussion? Or… I seriously am racking my brain trying to imagine why it’s a bad thing to have more than one stakeholder in a discussion.
I can think of a lot of reasons why doing the opposite, and siloing off discussions, leads to disaster. That is something I’ve encountered constantly in my career. We start out running an idea past group A, they iterate, then once we reach a consensus we bring the conclusion to group B and they have concerns. But oh, group A already agreed to this so you need to get on board. So group B feels railroaded. Then more meetings are called and we finally bring all the stakeholders together to discuss, and suddenly hey, group A and B both only had a partial view of the big picture, and why didn’t we all discuss this together in the first place? That’s happened more times in my career than I can count. The number of times group B is mad that they have to move their finger to scroll past what group A is talking about? Exactly zero.
It's totally possible that you aren't the target audience for this sort of feature. It tends to be more useful in very large team and/or monorepo contexts.
This isn't about siloing discussions: it's about focus. You can always see the full stack if you want to go look at the other parts, the key is that you don't have to.
The goal is to get thoroughly reviewed changes. It's much easier to review five 100 line changes than one 500 line one, and it's easier to review five 500 line changes than it is a 2500 line one. Keeping commits small and tightly reviewed leads to better outcomes in the end. Massive PRs lead to rubber stamps of +1.
I agree that that scenario sounds like a nightmare. But I don't think that a PR is the right place to solve that problem: it sounds like something that should have been sorted before any of the code was written in the first place.
> It's much easier to review five 100 line changes than one 500 line one, and it's easier to review five 500 line changes than it is a 2500 line one.
This is true if the changes are orthogonal and are truly independent. One should always favor small independent changes if one can.
But when changes are all actually part of the same unit, and aren’t separable (apart from maybe the first of N of them which may be mergeable independently), proponents always seem to advocate that stacked diffs can somehow change this fact. “Oh if only we had stacked diffs we could break this into smaller changes”, ignoring the fact that no, they’d still be ordered and dependent on one another.
Stacked diffs seem like a UI convenience for reviewers… that’s fine I guess. GitHub is basically what you get when you ask the question “how can we make code review as tedious and unhelpful as possible”, and literally anything would be better than what we have (seriously I could fill a book with how bad GitHub is. I don’t think I could design a worse experience if I tried.) So, maybe I should just be happy they’re trying anything.
In stacked diffs systems, the idea is that the base of the stack (once reviewed) can always be merged independently, so you're totally right that like, if you just purely think you can split things up when they shouldn't be split up, that would be bad.
This is the model that the kernel uses, as well as tons of other projects (any Gerrit user, for example), and so it has gotten real-world use and at scale. That said, everyone is also entitled to their preferences :)
> This is the model that the kernel uses
Nah.
The kernel uses a mailing list, and a “review” means a mailing list thread. With some nice CLI tools to integrate with git when you want to actually apply the patch (or start a review thread.)
In that world, “[PATCH 2/5]” (or whatever) in the subject title, and a different CC list for each patch, is a nice way to be able to ensure different subsets of the patch series have different discussions. That’s great.
But if you’re going to compare this to a GitHub UI, you have to choose the basis for comparison, because the two are so utterly different. Choosing one aspect (can we make sure discussions are kept separate), and saying “therefore the kernel uses stacked diffs” is a huge misrepresentation of how different GitHub’s approach is.
Because the kernel approach is the platonic ideal of a code review: it’s a simple threaded discussion between stakeholders, centered around a topic (the patch, which is inlined right in the email.) I would wager close zero kernel maintainer actually look at the diffs exclusively via their email client. They probably just check out the changes locally and look at them, and the purpose of the mailing list is to facilitate focused discussion on parts of the change (which is all we really want, in the end.)
GitHub has so thoroughly shit the bed on actually developing a good model of “threaded discussion about a change”, that you have to change the way you think about git’s model to fix how awful GitHub is at allowing review discussion to stay focused. You shouldn’t need to think about stacked diffs and multiple PR’s. You should use git branches as intended, multiple commits representing changes, and a merge meaning “this branch makes it or not.” That GitHub’s UI for discussing subsets of a change is so abysmal, does not mean the model is wrong. It means their discussion system is so abysmal that a mailing list TUI can run circles around it. Fixing this is GitHub’s problem, and doesn’t require any changes to how PR’s should be split up.
If you have a 2500-line PR with 5 500-line commits, GitHub should not require you to split things up further in any way, just to unfuck their discussion system.
Random idea I spent 10 seconds thinking about: let me start a “here’s a thread discussing the UI changes” and add folks to it, and “here’s a thread discussing the backend changes”, and add folks to that. I can then say “let’s not merge this until both threads are green”. You still see the whole change in the UI. (You can click directories to drill into the changes, that solves the “but the diff is too big” issue.) Discussion on a chunk of the diff is scoped to a discussion thread, which you select when sending the message. Thus, all discussion on any part of the diff is still scoped to a “discussion thread” of arbitrary subsets of stakeholders.
None of this needs me to change how I split up my git branches, an entire logical change is still either “merged” or “not-merged” (seriously who cares about the Pyrrhic victory of merging only change 1/N), and if we want to limit scopes of discussion to subsets of a change, we can just… do that.
Sorry, I am talking about stacked diffs in general, not this specific implementation on GitHub. That "Patch 2/5" is five stacked diffs, on top of each other. Forges that are stacked-diff native do that same kernel flow, just on the web instead of over email. You can also see this corroborated over here: https://news.ycombinator.com/item?id=47758251
All of the advantages, like "it’s a simple threaded discussion between stakeholders, centered around a topic", is exactly why people like stacked diffs over PRs.
GitHub is doing "stacked PRs", which is like stacked diffs but more like PRs in the sense that they're stacked branches rather than stacked diffs. I agree that this seems less ideal, but they also are putting it into an existing project, rather than rebuilding everything around it. There's pros and cons to both approaches, but I agree that I'd prefer a native system built for this, personally. I'm still glad they're going to be popularizing the general concept.
> Sorry, I am talking about stacked diffs in general, not this specific implementation on GitHub
My point is that the LKML and what GitHub do is so different that the definition of “stacked diffs in general” can only describe a tiny aspect of each, if you want to call both of their approaches by the same name. From where I sit, the only common element between them is “they offer a way to keep discussion separated.”
If that’s all people are actually complaining about, there are a thousand better ways to “keep discussion separated” that don’t require me to pretend that it’s ok that only a subset of my branch is ok to merge.
In git, a branch is the thing you either merge or don’t. You merge multiple commits at once, or you don’t. It’s a great model. Breaking up the branch into smaller pieces, and giving people the impression it’s ok to merge the first commit but not the rest, just to unfuck the discussion UX, is putting the cart before the horse. I make a branch strictly because I want it to either all merge or none of it merge. It’s the only sensible approach in my book. If a discussion system is so bad that this is unworkable, it means the discussion system is bad, it doesn’t mean the conceptual model of a merge is bad.
> My point is that the LKML and what GitHub do is so different that the definition of “stacked diffs in general” can only describe a tiny aspect of each
That's fine, what I mean is, when we started this convo, I thought you were asking about the general concept of stacked diffs, not the specifics of what GitHub is releasing here. That's my mistake for misunderstanding, sorry about that.
This is also (assumedly, anyway) why they're calling this "stacked PRs" and not "stacked diffs," because what they're doing is slightly different than Gerrit, Phabricator, Critique, etc.
Thanks for indulging me so far, by the way, I really appreciate this discussion, it's very stimulating.
After thinking about the whole thing I think I can summarize my opinion a lot better now:
Stacked diffs are a category error. Units of discussion, and units of integration, should not be conflated.
A branch is my unit of intended integration: merge all of it or none of it. The fact that reviewers need smaller slices to discuss does not imply those slices should become independently landable history objects. That’s a UX concern for the review tool, not something I should have to encode into Git history.
The ideal system would let me seed discussion however I want (by commit, by path, by subsystem, by semantic region of the diff, etc) without forcing me to pretend those are separate merge units.
Github nails the "merge unit" (CI runs against the whole branch, the branch either merges or doesn't, etc), but absolutely fumbles in the discussion part. I hate that I'd have to change the merge unit just to fix their discussion UX.
we have been stacking on tangled.org for a while now, you can see a few examples of stacks we have made here: https://tangled.org/tangled.org/core/pulls?state=merged&q=st...
for example, this stack adds a search bar: https://tangled.org/tangled.org/core/pulls/1287
- the first PR in the stack creates a search index.
- the second one adds a search API handler.
- the last few do the UI.
these are all related. you are right that you can do this by breaking a change into commits, and effectively that is what i do with jujutsu. when i submit my commits to the UI, they form a PR stack. the commits are individually reviewable and updatable in this stacking model.
gh's model is inherently different in that they want you to create a new branch for every new change, which can be quite a nuisance.
have written more about the model here: https://blog.tangled.org/stacking/
> - the first PR in the stack creates a search index.
> - the second one adds a search API handler.
> - the last few do the UI.
So you're saying you're going to merge (and continuously integrate, perhaps to production) a dangling, unused search index, consuming resources with no code using it, just to make your review process easier?
It's very depressing that review UX is so abysmal that you have to merge features before they're done just to un-fuck it.
Why can't the change still be a big branch that is either all merged or not... and people can review it in chunks? Why do we require that the unit of integration equals the unit of review?
The perverse logic always goes something like this:
"This PR is too big, break it up into several"
Why?
"It's easier to review small, focused changes"
Why can't we do that in one PR?
"Because... well, you see GitHub's UI makes it really hard to ..."
And that ends up being the root-cause answer. I should be able to make a 10,000 line change in a single commit if I want, and reviewers should be able to view subsets of it however they want: A thread of discussion for the diffs within the `backend` folder. A thread of discussion for the diffs within the `frontend` folder, etc etc. Or at the very least I should be able to make a single branch with multiple commits based on topic (and under no obligation for any of them to even compile, let alone be merge-able) and it should feel natural to review each commit independently. None of this should require me to contort the change into allowing integration partially-completed work, just to allow the review UX to be manageable.
This is not just about the UI, it's about the mental model and management of the changes.
Just covering the review process:
Yes, you can structure your PR into 3 commits to be reviewed separately. I occasionally structure my PRs like this - it does help in some cases. But if those separate parts are large, you really want more structure around it than just a commit.
For example, let's say you have parts A, B and C, with B depending on A, and C depending on B.
1. I may want to open a PR for A while still working on B. Someone may review A soon, in which case I can merge immediately. Or perhaps it will only be reviewed after I finished C, in which case I'll use a stacked PR. 2. The PR(s) may need follow up changes after initial review. By using stacked PRs instead of just separate commits, I can add more commits to the individual PRs. That makes it clear what parts those commits are relevant to, and makes it easy to re-review the individual parts with updated changes. Separate commits don't give you that.
Stacked PRs is not a workflow I'd use often, but there are cases where it's a valuable tool.
Then apart from the review process, there are lots of advantages to keeping changes small. Typically, the larger a change, the longer it lives in a separate branch. That gives more time for merge conflicts to build up. That gives more time for underlying assumptions to change. That makes it more difficult to keep a mental map of all the changes that will be merged.
There are also advantages to deploying small changes at a time, that I won't go into here. But the parent's process of potentially merging and deploying the search index first makes a lot of sense. The extra overhead of managing the index while it's "unused" for a couple of days is not going to hurt you. It allows early testing of the index maintenance in production, seeing the performance overhead and other effects. If there's an issue, it's easy to revert without affecting users.
The overall point is that as features become large, the entire lifecycle becomes easier to manage if you can split it into smaller parts. Sometimes the smaller parts may be user-visible, sometimes not. For features developed in a day or two, there's no need to split it further. But if it will span multiple weeks, in a project with many other developers working on, then splitting into smaller changes helps a lot.
Stacked PRs is not some magical solution here, but it is one tool that helps manage this.
> But if those separate parts are large, you really want more structure around it than just a commit.
Why? I reject the notion that large commits should be intrinsically hard to review.
GitHub already has the concept of "code owners", which are people who have ownership/review responsibility over slices of the codebase, based on globs/pattern matching. But they don't implement the other half of that, which is that a reviewer should be able to see a projection of a given PR, which matches the part of the repo they're the owner of.
There. That solves the entire problem of "this is too big, I can't look at all of it" (because your code ownership says this is the chunk of codebase you say you care about), and if that still isn't sufficient, there's a zillion UI features GitHub could add that they simply don't. Why can't I "focus" on a subset of the changes during review, in a way that helps me ignore unrelated discussions/changes? That is, even if I'm not code owner of the `frontend/` folder, why isn't there a UI affordance that says "let me focus on changes inside `frontend/` and ignore discussions/etc for the rest"?
> By using stacked PRs instead of just separate commits, I can add more commits to the individual PRs
Or you could just add commits to the PR, and if GitHub got the damned UI right, it would be natural to see the "slice" you care about, for all the new commits. Having to rearrange commits into separate PR's and slice-and-dice followup changes to file them into the right PR unit, is (to me) a workaround for how shitty GitHub's review UX is. It really shouldn't be this way.
> Then apart from the review process, there are lots of advantages to keeping changes small [...]
I agree with you on most of these points, but the decision to land smaller changes earlier should be made based on things like "let's get early feedback behind a feature flag" or "let's see how this chunk behaves in production so we can validate assumptions", or "let's merge what we have now so to cut back on conflicts", etc. That's all fine. But I'm vehemently opposed to being required to slice up my changes this way, just to work around a terrible review UI.
Personally, I review code in my development environment GitHub's UI is nonsensically terrible to read code. I could go on for hours about this[0], but when looking in my IDE I can drill into a subfolder and look at the diffs there. I can click and follow symbols. I can look at the individual diff history for any wildcarded subset of the repo, and see how the change was broken into commits. If I'm typing up some feedback to say "try doing it this way instead", I can actually try it myself first to make sure I'm not suggesting that someone do something that doesn't even compile.
And GH's discussion UX is by far the worst part of all of it. If you have a thread of discussions around a line of code, then wake up the next morning and want to see what new comments have been added? Good luck. Your best bet is to check your email inbox, because the comments are actually shown to you there. Using GitHub's "inbox" feature? All that is is a link to PR's you have to look at, with no hints at "why" (it could be a CI run finished for all you know.) Good luck figuring out "why" a PR is on your list. Did someone @-mention you? Who knows. So, find the blue dot next to the PR, click it, and then figure out for yourself what changed since the last time you looked. No, you can't just scroll and find it because GitHub hides half the discussions by default. So you have to go and expand all the collapsed sections to hopefully find that conversation you were having yesterday. But oh, you can only find it in the diff tab. So you click that, but the relevant file is collapsed by default ("Large diffs are not rendered blah blah"), so then click that. Then you may find that discussion.
Contrast this to a mailing list. The discussions are... discussion threads. You pick up where you left off. People's comments are right there in your inbox, newest one on top (or whatever your preference is.) You get notified when there's a new message, and when you tap the notification, it's the actual message, not some link to the PR that makes you click 6 more things to maybe find the message that just happened.
[0] like how the first thing you have to do when opening up the changes tab is ctrl+f search for "Large diffs are not rendered by default" to find the actually-important diffs that are not shown to you because GitHub's backend can't scale to rendering large diffs without friction. Countless times I've been burned by approving a PR because I don't see it making a change to some functionality, only to find out it actually did make said change, but GitHub just decided not to show me it. Seriously, the "large diffs" are the most important ones, and those are the ones you don't see without extra clicks. The mind boggles.)
Each of your stacked PRs only has one commit. Do you have any examples with multiple commits per PR in a stack?
PS: I love the concept of tangled. I currently use `sourcehut` but may soon move to tangled.
nevermind, I see what's happening in the UI. Each `jj` change is preserved in the UI and we can see multiple versions of the same change. The stack then is not really a stack of PRs but a stack of changes (where each change has its own history, i.e., the interdiff view). Did I get it mostly right?
yes, thats right! when you submit a branch, you can choose to "stack" it, so the individual commits in the branch turn into separate PRs. these PRs evolve individually, can be merged individually, and be reviewed individually. you can also set different reviewers/labels for different PRs in the stack.
you're upgrading the repository from language version 1 to 2, version 2 adds new compiler errors that rejects some old code, or the library has removed some old deprecated API the repository was still using in some places—the key here being that it can't be something that needs to be completely atomic.
you have hundreds or thousands of files to fix. that is unreviewable as a single commit, but as a per-file, per-library, per-oncall, etc. commit it is not that bad.
> you have hundreds or thousands of files to fix. that is unreviewable as a single commit, but as a per-file, per-library, per-oncall, etc. commit it is not that bad
Why is it intrinsically unreviewable as a single commit? Why can't the discussion/review system allow scoping discussions to a single folder of the change, or a single library, or a particular code-owner's "slice" of the repo, etc? The answer to this question is always unsatisfactory to me. It always ends up being "because GitHub's UI makes it hard to <foo>" and it's just taken as an immutable law of the universe that we're stuck with that UI's limitations.
If a change is huge, find some basis by which to discuss it in smaller chunks. That basis doesn't have to be the PR itself (such that you have to make smaller PR's to make discussion manageable.) It can be a subdirectory of the diff. A wildcard-match over the source files. Whatever the case needs to be, the idea is still that the discussion UX shouldn't make reviewing large changes painful.
Why do we tolerate the fact that GitHub doesn't let you say "approved for changes in `frontend/*`" or "approved for the changes I'm a code-owner of", and have the PR check system mark the PR as approved once all slices have been approved? Why do we tolerate that a thousand-file change is "unreviewable"? Instead we have to change our unit of integration, allowing partially-complete work to be merged, just because the review UX sucks.
Why do you insist on a different but functionally equivalent solution to the problem?
It's weird.
> Why do we tolerate the fact that GitHub doesn't let you say "approved for changes in `frontend/*`
That's literally what stacked PRs are adding.
Feature B depends on feature A, but you don't need B to understand A. Why wouldn't you create separate PRs?? It is faster to review and deploy.
Of course you would create separate PRs.
Why would you waste time faffing about building B on top of a fantasy version of A? Your time is probably better spent reviewing your colleague’s feature X so they can look at your A.
>If you reject change A and approve change B, nothing can merge
The feature is also half done in this case. The author can fix up the concerns the reviewer had in A and then both can be merged at the same time.
Couldn’t they do that in one PR? Seriously, couldn’t you just say “hey Alice, could you review the A parts of this PR” and “hey Bob, could you review the B parts”, then only merge once both of them approve? Even GitHub, for all its faults, supports code owners files, such that this can even be policy.
Technically yes, but the work for A and B may not be done at the same time so you may want to get a head start on getting A reviewed while B is still being worked on.
As a counter example. Why use multiple PRs when you can always just merge them into a single one. It's possible to make huge PRs with a bunch of different changes all included, but then the GitHub tools with managing stuff don't really work that well and you have to just do everything as comments instead of being about to actually accept a single accepted change for example.
The vibecoded frontend makes the product look like a side project.
Is it?
It was announced in like November of last year, so it's certainly taken some time. The announcement was by some senior management at GitHub, so it has some degree of buy-in.
Thank goodness. It was a pain to do this manually
Interesting to see how their CLI compares with GitLab's CLI interface for stacked diffs (the only support they offer at the moment): https://docs.gitlab.com/user/project/merge_requests/stacked_.... Most things are the same (up/down/top/bottom vs. next/prev/first/last, init vs. create), but both feel quite limiting. I've heard of other systems such as Gerrit that offer better native support, but have not tried out any for myself.
People have been building stacked PR workflows on top of GitHub for a while now. It's great to see that the message seems to have finally landed at GitHub, but what is actually new here in GitHub itself (i.e., not counting the gh CLI tool)?
There seems to be a native stack navigation widget on the PR page, which is certainly a welcome addition.
The most important question though is whether they finally fixed or are going to fix the issues that prevent submitting stacked PRs from forks. I don't see any indication about that on the linked page.
They haven't fixed the fork issue, the FAQ clarifies this. I suspect the target audience is squash merging corpos. Everyone else can just do normal PRs with atomic commits reviewed individually...
Is this going to be a part of triage task? If so, it makes sense. Whether a human developer or an AI made a big PR, AI goes review it and if necessary makes stacked PRs. I don’t see any human contributors using this feature to be honest because it’s an extra work and they should have found a better way to suggest a large PR.
That page looks vaguely AI generated
My main question about this is does it keep review history properly after a rebase to restack PRs? Eg if I have reviewed PR for branch A and now its been rebased onto B by this tool and then more changes are made to A, does "review changes since" work in A's PR? This has been the main thing stopping me from wanting to use rebase to stack PRs and if they've fixed this somehow then I'm interested.
Wow i really need this, we had a refactor our monorepo (dotnet 8 -> 10 and angular 19 -> 21) which resulted in many small changes (like refactoring to signals, moving components to standalone) and we try to group changes into commits by what was fixed, but this had the downside of some commits beeing huge while others small, this would have helped us alot grouping commits together and having cleaner commit messages.
I loved using sapling / mercurial so much at work that I ended up using the sapling SCM vsc extension at home all the time for personal work.
Only downside is that Phabricator is not open source so viewing it in most things sucks. Hoping now I can get a much better experience
Phabricator is open source and has been for years. It has had a bumpy ride over the last few years though. Although I guess having written that I assume the internal meta one is much better
Huh, that's news to me. I had to do some googling and the only one I could find was by Phalicity which seems to be from a Meta employee who left and made it into a company (a la Statsig, or to some extent Graphite)
Seems that company shutdown though a while ago and it got forked into Phorge, but either way I assume there's some divergence from what's internal at this point.
Still I'll look into it, it does look neat and might suit my preferences still. Thanks for the headsup :)
Curious how / how well it deals with conflicts in the different branches that are part of the stack. Is there some support for managing that, or what happens when two of the branches don't rebase / merge cleanly?
> If a rebase conflict occurs, the operation pauses and prints the conflicted files with line numbers. Resolve the conflicts, stage with git add, and continue with --continue. To undo the entire rebase, use --abort to restore all branches to their pre-rebase state.
So it tries to replay commits in the stack and will stop halfway through that individual stack (layer?) to let you fix it if there's a conflict.
One mistake I see across many organizations is that sometimes they overthink how much order should matter.
Sure, your application has a dependency on that database, but it doesn't necessarily mean you can't deploy the application before having a database. If possible, make it acceptable for your application to stay in a crashloop until your database is online.
I agree with you and further will add that modularity+atomicity are the ideal state for the vast majority of software applications… but in reality, most organizations can not afford to rewrite their software to the extent required to achieve this, if it wasn’t planned from the start.
The `gh stack` CLI sounds essential for people using git, but I hope it doesn't become required, as people using things like jj/sl should be able to work with stacks. `gs submit`/`gs push` being the interface is fine, but `gs init` and `gs add` should be optional.
They confirmed below that you should be able to use this with jj just fine, just like you can already use gh to create a PR that you've authored with jj: https://news.ycombinator.com/item?id=47759426
Very curious about this as especially with more use of AI in the development process I have seen PR size has increased. So looking forward to general availability.
Even though moments where I would reach for it are rare, this is a very welcome feature. In times when I could have used it, it was not difficult to emulate via more branches, consistent naming, referencing the PRs, etc. Not difficult, but definitely tedious, and always left me feeling less organized than I like to feel.
This is probably driven to be more usable with AI agents, but smaller prs can create more code as they need to enforce more backwards compability, this can also lead to more code or more maintenance work.
Honestly I don’t see the benefit of smaller prs, except driving vanity scores?
Like I’m not saying you should
Very much looking forward to getting this on Renovate - we require squash-merge via Merge Queue (with no per-PR override available in GitHub, despite asking) and so when I've got multiple changes, it's a lot of wrangling and rebasing
If this works as smoothly as it sounds, that'll significantly reduce the overhead!
1. Finally. Pull requests are consanguine and bizarre.
2. I'm not a huge fan of having to use a secondary tool that isn't formally a layer around git / like jj as opposed to github
Pretty cool to see stacks being given due attention. Also check out git-spice, which works with Gitlab (possibly others). Personally I use git-spice in place of all the conventional git commands.
Sounds like a merge-conflict nightmare
Freaking finally.
I’ve been trying to convince my boss to buy Graphite for this, seems like Github is getting their a* in gear after Cursor bought them.
If Jetbrains ever implements support for them in IntelliJ I will be in Heaven.
Meta has something similar to this using mercurial. It was awesome.
This is useful. Managing dependencies across PRs has always been tricky — nice to see better workflows evolving.
Just when I’ve gotten used to having 3 or more PRs in parallel with a local octopus working tree with jj. Maybe my colleagues will see the light at least.
Hah, first time seeing github.github.com
First thing that came to mind was git butler.
Interesting to see how this integrates with any release flows that use a lot of tags or feature flagging.
It's awesome that they're adding a UI for stacked branches¹! The UX of the CLI tool seems weird, though. Why do I need to explicitly create and add branches to the stack if all I really want is to open PRs from my commits? Here's the workflow that I built for myself instead:
∙ `git checkout -b feature-branch-xyz`
∙ make a few commits, perhaps some fixups, rebase, whatever
∙ start tig, look at the history, decide at which points I want to break the branch into stacked PRs, and mark those points using shift-s (which calls my own `git gh-stack branch create $commit` and creates a specially named branch there)
∙ `git gh-stack sync` — collects all the specially named branches, builds a graph of how they're stacked on one another, pushes them, opens stacked PRs
GitHub has had some "support" for stacked PRs for a while, so merging the first one to main will automatically change the target branch of the second to main.
If I need to change anything, I can just `git rebase --interactive --update-refs`, amend commits, split commits, rearrange commits, and then running `git gh-stack sync` will update the PRs for me. If I split a commit in the middle and shift-s to mark it, it will open an extra PR and restack everything to update the order.
Furthermore, the "PR stack" doesn't actually need to be a stack (linear chain), it can be a tree. If I know that some commits are independent of the rest, I don't need to create a separate stack, I just create another local branch, mark PR-ready commits with shift-s, and `git gh-stack sync` will do the right thing. If I need to rebase the whole tree on top of current main, then `git rebase -i --rebase-merges --update-refs` does the job.
I guess what I'm saying is that as someone who's been using git since its inception, it feels much more natural to just do everything in git, and then have a single command that pushes my work to GitHub. And I think this might work even better with jujutsu — just point `git gh-stack sync` at the branches jj makes and it'll make a stack/tree of PRs out of them. :-)
https://github.com/liskin/dotfiles/blob/home/bin/git-gh-stac... if anyone's curious. It's just a few hundred lines of code. Building the graph is done by `git log --simplify-by-decoration`. Opening PRs is shelled out to `gh pr create`.
¹) I mean, I'd much rather they added a UI for reviewing PRs commit-by-commit, with the option to approve/request-changes on each, and the possibility to merge the first few approved ones while continuing work on the rest… But in a world of almost every $dayjob insisting on squash-merging, a UI for stacked PRs is a total game changer, positively.
great, I'll directly compare it to graphite.com - the main point really is the user interface in my opinion. Still a bit sceptical whether github can out-deliver here, but happy to be proven wrong!
Has anyone already tried that was a graphite user before?
This needs to be supported on `git` level first imho, not by a forge vendor.
What would this being supported by git mean to you?
Reminder that if your agent can create PRs then it can merge them too: https://github.com/orgs/community/discussions/182732
What's difference between stacked PRs and merge trains in gitlab?
Merge trains are an integration method. In GitHub that’s called merge queues.
Stacked PRs are a development method, for managing changes which are separate but dependent on one another (stacked).
The two are orthogonal they can be used together or independently (or not at all).
Ahh so stacked diffs? https://docs.gitlab.com/user/project/merge_requests/stacked_...
Yes, except with a proper UI. Also while you could do this on GitHub before in the same way that that Gitlab feature works, it didn't work cross-repo so in practice it wasn't an option for most open source code.
I can't remember if Gitlab has the same limitations but I do remember trying to use Gitlab's stacked diffs and finding them to not work very well. Can't remember why tbh.
This feature is 10 years late
Cool. Now let me do it across multiple repos. I often end up with 10 or 20 PRs across a half dozen repos that need to be merged in specific order.
For sure. If you are in a monorepo this solution works but if you have distinct microservice repositories it would help to coordinate pr #827 on repo-A and pr #1092 on repo-B are related and need to ship in a certain order.
Exact problem we've run into at work. We've ended up having to write external merge coordination in order to not break our dev deployments.
Who hurt you?
Their manager who suggested that everything be a microservice, but everything depends on each other.
Microservices, by the sound of the original comment
Microservices without a monorepo is hell
They've opted for critical damage.
How would that work? Commits in different repos aren't ordered relative to one another. I suppose you could have a "don't let me merge this PR until after this other PR is merged" feature, but you could do that with a GitHub Action; it doesn't really need dedicated backend or UI support.
> How would that work?
In practical terms: I manually write a list of PRs, and maintain that list in the description of each of the PRs. Massive duplication. But it clearly shows the merge train.
Oh cool, soon people will stop being incapable of working with me.
Interesting direction. Curious how this compares with traditional transformer-based approaches in real use cases.
man, why is this waitlisted. this should have been a feature 10 years ago
cherry picking is so fragile, this is at least a step in the right direction
Wondering how all of those startups that implement this for GitHub feel right now.
sherlocked
this was released about 7 years ago, no?
At first I thought this was a user submitted project due to the subdomain of github.com but then realize the subdomain is also github. Is this an official channel for this sort of thing? Surprised this isn't on the official blog.
It's in private preview. Probably they'll put it in the main docs and such once it's open to everyone.
it's a GitHub Pages site in the @GitHub org from a repo called gh-stack (i.e. the repo is at https://github.com/github/gh-stack/).
There’s a special case where certain official orgs can continue to use github.com instead of github.io for their Pages domain, and that’s how you end up with:
https://github.github.com/gh-stack/
from the code:
Should Pages owned by this user be regarded as “Official GitHub properties”?
def github_owned_pages? GitHub.github_owned_pages.include?(login) end
# Orgs/users that are owned by GitHub and should be allowed to use # `github.com` URLs. # # Returns an Array of String User/Organization logins. ...
It's their 'GitHub' org GitHub Pages domain - it's just .com instead of .io (not to be confused with their gh.io link shortener)
microsoft broke nearly all classic web support (noscript/basic (x)html).
Since I can still login, is there a web API (using CURL and some identifying session token I could retrieve from my login) I could use to actually do "something". For instance, be involved in the issues of some project?
(for me, that would be mostly valve stuff on linux based OSes)
Any pointers?
the Website for the release statement look soooooo bad
“You cannot merge a PR in the middle of the stack before the PRs below it are merged.”
Huh? Some stacks need to land all at once and need to be reviewed (and merged) from the top down. It’s not uncommon, in my org at least, to review an entire stack and merge 3 into 2 and then 2 into 1 and then 1 into main. If 2 merges before 3, you just rebase 3 onto 1.
If only there were some way to logically break up large pull requests into smaller pieces... Some way of creating a checkpoint with a diff including your changes, and some kind of message explaining the context behind the change... some way to "commit" a change to the record of the repository...
Part of the idea behind stacked PRs is to keep your commits focused and with isolated changes that are meaningful.
A stacked PR allows you to construct a sequence of PRs in a way that allows you to iterate on and merge the isolated commits, but blocks merging items higher in the stack until the foundational changes are merged.
What can stacked PRs do that a series of well-organized commits in a single branch can't?
Stacked PRs tend to encourage a series of well-organized commits, because you review each commit separately, rather than together.
What they do that the single branch cannot is things like "have a disjoint set of reviewers where some people only review some commits", and that property is exactly why it encourages more well-organized commits, because you are reviewing them individually, rather than as a massive whole.
They also encourage amending existing commits rather than throwing fixup commits onto the end of a branch, which makes the original commit better rather than splitting it into multiple that aren't semantically useful on their own.
I think the point the GP was trying to make is that the GitHub UI ought to be able to allow you to submit a branch with multiple well-organized commits and review each commit separately with its own PR. The curation of the commits that you'd do for stacked PRs could just as easily be done with commits on a single branch; some of us don't just toss random WIP and fixup commits on a branch and leave it to GitHub to squash at the end. I.e., it's the GitHub UI rather than Git that has been lacking.
(FWIW, I'm dealing with this sort of thing at work right now - working on a complex branch, rewriting history to keep it as a sequence of clean testable and reviewable commits, with a plan to split them out to individual PRs when I finish.)
> I think the point the GP was trying to make is that the GitHub UI ought to be able to allow you to submit a branch with multiple well-organized commits and review each commit separately with its own PR
So the point he's trying to make is that Gituhub UI should support Stacked PRs but call them something else because he doesn't like the name?
> I think the point the GP was trying to make is that the GitHub UI ought to be able to allow you to submit a branch with multiple well-organized commits and review each commit separately with its own PR.
That's what this feature is, conceptually. In practice, it does seem slightly more cumbersome due to the fact that they're building it on top of the existing, branch-based PR system, but if you want to keep it to one commit, you can (and that's how I've been working with PRs for a while now regardless, honestly).
They confirmed in other comments here that you don't have to use the CLI, just like you don't have to use gh in general to make pull requests, it's just that they think the experience is nicer with it. This is largely a forge-side UI change.
There are tools that use LLMs to do this.
I've done this manually by building a big feature branch and asking an LLM to extract out functionality for a portion of it.
For the former, it would seem to split based on frontend/backend, etc. rather than what semantically makes the most sense and for the latter it would include changes I don't want and forget some I do want. But I haven't tried this a lot.
So much effort has been spent beating git until it's just CVS with bells on.
The stacked diffs flow is much closer to the kernel flow for git than the traditional GitHub PR flow is.
Yeah, I feel like just being able to review a PR commit-by-commit with a nice interface would just suffice.
Not really. Without seeing the entire changeset for a PR, you'd have to mentally keep track of what the current state of everything is unless you're a commit minimalist and presquash.
How does that differ from this where you need to keep track of state and the whole change in the stack?
If we're speaking strictly code review, because you can actually make sense of the changeset for the child PR by not including its unmerged parent's changeset.
For me that would mean avoiding tiny commits, and I wouldn't want to do that
What might that be?
I'm surprised no-one has commented on the "sign up for the waitlist" button being a Microsoft Office form that wants your email address and GitHub handle. This feels like an elaborate phishing attack more than a serious feature announcement.
This feels like a workaround for git's contradictory ergonomics.
Aside:
> This is a docs site that was made to share the spec and CLI for private preview customers that ended up getting picked up. This will move to GitHub docs once it’s in public preview.
(https://x.com/matthewisabel)
what happened to the old gerrit reviews, I loved its handling on incremental patchsets. github is primitive by comparison.
The biggest challenge for us are PRs that need to be coordinated across multiple repos. API + client for example. It doesn't sound like stacked PRs solve that problem, right? Description specifically states single repo.
They do not no. Afaik GitHub has little to nothing that is cross repository.
Can we merge from GitHub UI without rewriting the commit already?
github.github.com? Not the first time github does something highly weird with their domains (like publishing docs from a subdomain of their public github pages service)
I think they have a culture of circumventing 'official' channels and whoever is in charge of a thing is whoever publishes the thing.
I think it's a great way to train users to get phished by github impostors, if tomorrow we see an official download from official.github.com or even official-downloads.github.io, sure it's phishy, but it's also something that github does.
It's also 100% the kind of issues that, if it happens, the user will be blamed.
I would recommend github to stop doing this stuff and have a centralized domain to publish official communications and downloads from. Github.github.com? Come on, get serious.
TL;DR: DO NOT DOWNLOAD ANYTHING from this site, (especially not npm/npx/pnpm/bun/npjndsa) stuff. It's a Github Pages site, just on a subdomain that looks official, theoretically it might be no different from an attacker to obtain access to dksabdkshab.github.com than github.github.com. Even if it is official, would you trust the intern or whoever managed to get a subdomain to not get supply chained? github.github.com just think about it.
https://news.ycombinator.com/item?id=47614038
in github's defense. This is a bit more nuanced, less objectively wrong domain posture issue. It will only matter if one security mechanism (subdomain control) fails.
The quoted microsoft examples are way worse. I see this with outbound email systems a lot, which is especially dangerous because email is a major surface of attack.
I feel like we already have enough abstractions in this space. Having any constraints at all in your tools is actually a good thing. PRs on top of ordinary git was a good step. This seems like one too many.
I honestly don't even get the PR addiction. Github has shaped devs workflows way too much. My best experience with git was when I realized that I can just have an blatantly simple workflow and explain it even to the junior-est dev in a few minutes. The reliance on github is somehow telling me that people stopped thinking about things they can actually control.