Crafting a PR as an easily-consumed, logical sequence of commits is particularly useful in open source.
1. It makes review much easier, which is both important because core maintainer effort is the most precious resource in open source, and because it increases the likelihood that your PR will be accepted.
2. It makes it easier for people to use the history for analysis, which is especially important when you may not be able to speak directly to the original author.
These reasons also apply in commercial environments of course, but to a lesser extent.
For me, organizing my PRs this way is second nature and only nominal effort, because I'm extremely comfortable with Git, including the following idiom which serves as a more powerful form of `git commit --amend`:
git add -p
git commit --fixup COMMIT_ID
git stash
git rebase -i --autosquash COMMIT_ID~
An additional benefit is that this methodology doesn't work well for huge changesets, so it discourages the anti-pattern of long-lived topic branches. :)
> For that matter, why merge? Rebase it on top.
Yes, that works for me although it might not work for people who aren't going to the same lengths to craft a logical history. I have no interest in preserving my original WIP commits — my goal is to create something that is easy to review.
BUT... the PR should ultimately be merged with a merge commit. Then when you have a bug you can run `git bisect` on merges only, which is good enough.
> 2. It makes it easier for people to use the history for analysis, which is especially important when you may not be able to speak directly to the original author.
I've been on a maintenance team for ~5 years and this has saved me so many times in svn, where you can't squash, for weird edge cases caused by a change a decade or more ago. It's the reason I'm against blind squashes in git.
My favorite was, around 2022, discovering something that everyone believed was released in 2015, but was temporarily reverted in 2016 while dealing with another bug, that the original team forgot to re-release. If the 2016 reversion had been squashed along with the other bug, I might never have learned it was intended to be temporary.
I'm fine with manually squashing "typo" commits, but these individual ones are the kind where you can't know ahead of time if they'll be useful. It's better to keep them, and use "git log --first-parent" if you only want the overview of merges.
Someone did this to code meant to cut our web crawler bandwidth and someone didn’t notice it for like two years after it got toggled back off. So stupid. We were able to shrink the cluster after enabling it again.
I have an exactly opposite preference. Give me a big change to review. Going commit by commit or any imposed steps is not how I write code or how I understand code.
If you did not approach it through literate programming, I just prefer all of the thousands of lines at once.
Reviewing individual changes that may not even build properly is a waste of time; reviewing thousands lines of lines at once is also a bad idea.
Each unit of code (PR, commit, CL, whatever you want to call it) you send for review should be able to stand on its own, or at the very least least not break anything because it's not hooked into anything important yet.
You're in luck! For you, there is `git diff`.
(And for me as well — both the individual commits and the PR-level summary are useful.)
So, those of us who prefer commit-sized chunking don't have to do anything special to accommodate your preference.
It doesn't go the other way, of course, if you present one big commit to me. But so long as your code is well-commented (heh) and the PR isn't too huge (heh heh) and you don't intersperse file renamings (heh heh heh) or code formatting changes (heh heh heh heh) which make it extremely difficult to see what you changed... no problem!
> or code formatting changes (heh heh heh heh) which make it extremely difficult to see what you changed...
One of the "individual commits saved me" cases was when one of these introduced a bug. They tried to cut the number of lines in half by moving conditions around, not intending to make any functional changes, but didn't account for a rare edge case. It was in a company-shared library and we didn't find it until upgrading it on one of our products a year or two after the change.
One of the reasons I don't like a policy of "every commit must pass CI" is that I prefer to perform verbatim file moves in a dedicated commit (which inevitably breaks CI) with no logical changes at all, then modify code as necessary to accommodate the move in a separate commit. It makes review and debugging much easier.
This is my main use for branches or pull requests. For most of my work, I prefer to merge a single well-crafted commit, and make multiple pull requests if I can break it up. However, every merge request to the trunk has to pass CI, so I'll do things like group a "red/green/refactor" triplet into a single PR.
The first one definitely won't pass CI, the second one might pass CI depending on the changes and whether the repository is configured to consider certain code quality issues CI failures (e.g., in my "green" commits, I have a bias for duplicating code instead of making a new abstraction if I need to do the same thing in a subtly different way), and then the third one definitely passes because it addresses both the test cases in the red commit and any code quality issues in the green commit (such as combining the duplicated code together into a new abstraction that suits both use cases).
You are model citizen with those file moves. Totally agree with how that can be very disruptive for legibility and comprehension of changes.
Also for a year from now when I’m wondering wtf I was thinking when I put that bug into the code. Was a thinking of a different corner case? Or not at all?
> Can someone explain why anyone would want non-squashed PRs?
>
> For the 5% of engineers that diligently split each PR into nice semantic changes, I suppose that's nice. But the vast majority of engineers don't do this.
I think cause and effect are the other way around here. You write and keep work-in-progress commits without caring about changes because the history will be discarded and the team will only look at pull requests as a single unit, and write tidy distinct commits because the history will be kept and individual commits will be reviewed.
I've done both, and getting everyone to do commits properly is much nicer, though GitHub and similar tools don't really support or encourage it. If you work with repository history a lot (for example, you have important repositories that aren't frequently committed to, or maintain many different versions of the project) it's invaluable. Most projects don't really care about the history—only the latest changes—and work with pull-requests, which is why they tend to use the squashed pull request approach.
It’s mostly because pull requests are what is being tested in CI, not individual commits. Might as well squash as nobody wants to deal with untested in-between crap.
If you mean stacked PRs, yeah GitHub absolutely sucks. Gerrit a decade ago was a better experience.
That's a problem with your CI. You can configure it to test all commits which make up the PR.
My CI takes 20+ mins and costs meaningful $ per run. Not happening.
> That's a problem with your CI.
Yes, but not in the way you think.
> For the 5% of engineers that diligently split each PR into nice semantic changes, I suppose that's nice. But the vast majority of engineers don't do this.
Here's a simple reason: at my company, if you don't do this, you get fired.
This is basic engineering hygiene.
Yep.
Those 5% shouldn't be approving PRs without it.
Those 95% shouldn't be code owners.
Nice things can be had, you just have to work for them.
> If you truly care about making more semantic history, split the work into multiple PRs.
This exactly - if your commit history for a PR is interesting enough to split apart, then the original PR was too large and should have been split up to begin with.
This is also a team culture thing - people won't make "clean" commits into a PR if they know people aren't going to be bisecting into them and trying to build. OTOH, having people spend time prepping good commits is potentially time wasted if nobody ever looks at the PR commit history aside from the PR reviewers.
If I have a feature branch, and as part of that feature change, I did a simple refactor of something, I definitely want that committed as two separate commits in the PR, because you can look at the changes in isolation and it makes them a LOT easier to follow. And if you prefer, you can look at the diff of the entire PR in one single view. I don’t see the downside.
And please do not come back with “you shouldn’t do a refactor as part of a feature change.” We don’t need to add bureaucracy to avoid a problem caused by failure to understand the power of good version control.
This bureaucracy has very low overhead. Squash-merge the feature and then the refactor, or the refactor then the feature. Also makes reviewing each quicker.
the feature isn't ready for merge when the refactor happens ....
> For that matter, why merge? Rebase it on top. It's so much cleaner. It's atomic and hermetic.
With an explicit merge, you keep two histories, yet mostly care about the "main" one. With rebase, you're effectively forgetting there ever was a separate history, and chose to rewrite the history when "effectively merging" (rebasing).
There's value in both, mostly seems to come down to human preference. As long as the people that will be working with it agrees, I personally don't care either way which one, granted it's consistently applied.
Rebasing is slower in practice to trunk based development and CI, while merging and squashing are moving farther away.
Squashed PR allow you to see a single commit, while rebased PRs show up as multiple. The squash has the defect that you can’t rebase PRs that were on top.
But a MERGE… is a single commit on Master, while keeping the detailed history!
- We just don’t use the merge because they are ugly,
- And they’re only ugly because the visualizers make them ugly.
It’s a tooling problem. The merge is the correct implementation. (and yet I use the rebase-fast-forward).
You can squash after rebasing or merge a PR without squashing.
> Each PR being squashed to 1 commit is nice and easy to reason about. If you truly care about making more semantic history, split the work into multiple PRs.
I don't argue with your point (even if I am obsessive about commits separation), but one needs to keep in mind that the reverse also applies, that is, on other end of the spectrum, there are devs who create kitchen-sink PRs which include, for example, refactorings, which make squashed PRs harder to reasons about.
> Can someone explain why anyone would want non-squashed PRs?
So you can differentiate the plumbing from the porcelain.
If all the helpers, function expansions, typo corrections, and general renamings are isolated, what remains is the pure additional functional changes on its own. It makes reviewing changes much easier.
Making human-readable commit history is not that hard with a little practice. It's one of the big benefits of tools like magit or jj. My team started doing it a few weeks ago, and it's made reviewing PRs substantially easier.
+1: EdaMagit has been a game changer for me wrt reordering commits, fusing them together, and writing at least 1-2 sentences of proper commit messages after the fact.
I would definitely neither accept a pull request where the individual commits were testing and iteration, nor a pull request with hundreds of lines of changes are in a single commit. (New code, maybe.) It's not about ceremony; it's about knowing what changed and why.
If you ever worked with stacked PRs, and the top one gets squashed and merged it often becomes a nightmare to rebase the rest of the PRs to bring them up to date.
I wish this was easier. I have a workflow that I use to create stacked PRs which involves changing the target branch of the next PR to `main` after merging its predecessor, but it is too fragile to institute as a policy.
However, this is also just a more specific version of the general problem that long-lived, elaborate topic branches are difficult to work with.
jj makes this mostly trivial - well worth checking out if you’d like to work this way, but GitHub gets in the way.
git merge --no-ff
git log --first-parent
git bisect --first-parent
The above gives you clean PR history in the main branch while retaining detailed work history in (merged) feature branches.
I really don't understand why would I squash having git merge --no-ff at my disposal...
Hoo boy is it fun to figure out where things went wrong when the real commit history was thrown away to make it look prettier. Especially a mistake from a merge conflict.
I had to stop two devs from fisticuffs. One of them used merge and manufactured a bug in the other’s code and was making a stink about it in the middle of the cubicles.
Merges lie I worse ways than rebase does. Hands down. With rebase I break my own shit. With merge I can break yours. Since your code is already merges into trunk, it has fewer eyes on it now and it’s on me to make sure my code works with yours and not vice versa.
I don't follow. In either case two branches are combined into one:
With a merge commit anyone can see each original path, and the merge result (with its author), and even try the three-way merge again. With a rebase, the original context is lost (the original commits were replaced by the rebased versions).
A rebase is a lossy projection of the same operation. A rebase lies about its history, a merge does not.
I'd take fully squashed PRs over endless "fix thing" and "updated wip"... but if you work in a way that leaves a couple meaningful commits, that's even better. Sometimes I end up in this state naturally by having a feature branch, which I work on in sub branches, each being squashed into a single final commit. Or when the bulk of the logic is on one commit, but then a test case or two are added later, or a configuration needs changing.
I like merge commits because they preserve the process of the review.
What you have there is people hiding their neuroses and lack of commit hygiene and that’s avoiding the problem not fixing it.
> I like merge commits because they preserve the process of the review.
I appreciate that, but I still can't square it with my world view.
GitHub or whatever tool you use preserves all the comments and feedback and change history if you ever need to go back and reference it. Such instances are limited, and in my experience it's mainly politics and not technical when this happens. The team's PR discussion itself isn't captured in git, so it's lossy to expect this type of artifact to live in git anyway. It's also much less searchable and less first class than just going back to GitHub to access this.
Ultimately, these software development artifacts aren't relevant to the production state of the software you're deploying. It feels muddled to put an incomplete version of it into your tree when the better source of truth lives outside.
Usually the merge commit is what has the link to the PR/MR. So it's the best way to actually find it.
> Ultimately, these software development artifacts aren't relevant to the production state of the software you're deploying. It feels muddled to put an incomplete version of it into your tree when the better source of truth lives outside.
You could make the same claim about the entire history. Git is a development tool, production just needs a working cut of the source.
I have always been very careful with git histories and often rewrite/squash them before final review/merge. Often my rewritten histories have nothing to do with the original history and commits are logically/intuitively separated and individually testable.
That said, very few people seem to be like me. Most people have no concept of what a clear commit history is. I think it's kind of similar to how most people are terrible written communicators. Few people have any clue how to express themselves clearly. The easiest way to deal with people like this is to just have them squash their PRs. This way you can at least enforce some sanity at review and then the final commit should enforce some standards.
I agree on rebasing instead of straight merging, but even that's too complicated for most people.
You can just inspect merge commits, you can also just bisect over merge commits.
Splitting work into multiple PRs is unnecessary ritual.
I have never reasoned about git history or paid attention to most commit messages or found any of it useful compared to the contents of the change.
When I used git bisect with success it was on unknown projects. Known projects are easy to debug.
Because github doesn't support stacked diffs, basically.
T_T
I manage a team of developers, and I don't think any of us squash commits, and I really don't care. It's been working fine for 8 years at this job.
We keep our git use extremely simple, we don't spend much time even thinking about git. The most we do with git is commit, push, and merge (and stash is useful too). Never need to rebase or get any deeper into git. Doing anything complicated with git is wasting development time. Squashing commits isn't useful to us at all. We have too much forward velocity to worry that some commit isn't squashed. If a bug does come up, we move forward and fix it, the git history doesn't really figure into our process much, if at all.
Squash is just something you do at the point of merging. It's a single option during the merge and doesn't have you doing any more work than a merge that you don't squash. I don't know about github, but I know in gitlab it's a simple checkbox in the merge request (and it can be set to be checked by default by the admin if they want).
That's great for you, but squashing commits doesn't do anything for our team. It hides somewhat useful information, which never seemed like a good thing to me.
Other teams at my company are obsessive about squashing, and I am glad I don't work on those teams. They are frustrating to work with, they are notoriously slow to ship anything, and their product still breaks even with all their processes and hurdles to getting anything shipped. Teams that demand squashing simply don't impress me at all.
There is no free lunch, the same people that can't be bothered to make atomic semantic commits are the same people that will ruin your bisect with a commit that doesn't build or has some other unrelated run failure. People that don't care can't be fixed by tools.
The advice around PRs rings hollow, after all they were invented by the very people that don't care - which is why they show all changes by default and hide the commits away, commit messages buried after 5 clicks. And because this profession is now filled with people that don't care, add the whole JIRA ticket and fix version rigmarole on top - all kinds of things that show up in some PMs report but not in my console fixing an issue that requires history.