Isn't this solved if you squash the commits when merging the PR? I personally don't care that much about the commits inside a PR, the are just temporary because when a PR is merged they are squashed and you only get one commit for the whole feature on the main branches
It only worked that well because the team had all internalized my advice to write small, coherent commits, so the bisect landed on a ten-line change.
I strongly dislike the recent trend towards squashing every branch into a single monster commit.
I am convinced that very few know about git bisect, much less use it regularly.
Yes, unfortunately not all companies have a high hiring bar. Some
This could probably be helpful https://mtlynch.io/code-review-love/
7. Break up large changelists
Instead of changing everything at once, can you change the dependencies first and add the new feature in a subsequent changelist? Can you keep the codebase in a sane state if you add half of the feature now and the other half in the next changelist?
And I say that if you can’t review a PR as a single patch, there’s bigger problem. As a reviewer, the only thing that matters is the change and its purpose, not a particular workflow/ritual.
Certainly a way to do things. Not the most useful or productive… but it's a way for sure.
`git bisect --first-parent` lets you start with your integration points (your PR merge commits), and because presumably you have Continuous Integration and make sure integrations points build and test successfully that should be a rather quick discovery run, and then when you discover the PR that introduced the issue, you have an opportunity to drill down into the even smaller specific change inside that PR that introduced the issue.
Merge commits are a navigation tool and an integration log. It seems useful to me to prefer them over rebases and squashes.
But what would be the point?
Let’s say you found an issue in the first commit of the PR (assuming it’s curated and every commit can compile). But the PR is atomic, and later commits rely on the assumption made in the first one. You would need to replay the later changes as well to figure out the impact.
Squashing PR means you consider changes at an holistic level regardless of the workflow that created them. If a PR fails with a regression test, the whole thing is suspect, and I don’t really care when in the workflow it was introduced.
If I have a PR titled “Add support for flac files” that introduced a regression, I don’t really want to know if the bug is on the commit “extract sampling information” or the commit “support flac tags”, because what got released was the PR, not individual commits. Just like no one care if a typo was introduced in draft 5 or draft 8. The only things that matters is when it got published.
For me PR are releasable patches. Individual commits in them are the engineer’s workbench. Whether you want to curate the latter is up to you, as long as the PR is atomic.
The ability to drill down with a second `git bisect` run (now with a known base and end commit, and even the ability to again use `--first-parent` to ignore merges inside the PR commit range) into the original contents of the PR is the ability to automate finding your needle in a 10-line change with its own git commit message and its context in the original conversation flow in the original PR.
That's a powerful ability.
Sure, you can probably comb the complete 100 or 1000 or 10,000 line PR to find the exact lines that caused that regression, you've narrowed down already to one useful haystack, but it's nice to have an optional second layer to break your haystacks down further sometimes.
(Especially if it turns out to be a regression from a merge commit inside that PR. Accidental bad merges happen all the time. Spotting them is hard sometimes. Spotting them after a rebase/squash happened is sometimes impossible because there's no unique record of the conflict resolutions unlike with a merge commit.)
But the PR is one single atomic changes. even if it 100 or 1000 lines. This very measure makes it easy to review because there’s only one assumption change PR A (the good one) and PR B (the bad one and and also the current one).
Don’t forget that the codebase will also have several modules. With just one single patch, I can see which modules are affected and then reason where the bug may be. Using merge may not have helped as the 10 line changes in an individual commit may have been because that’s where I integrated stuff that was unused in the previous commits before the merge. That’s why an holistic view matters.
> Spotting them after a rebase/squash happened is sometimes impossible because there's no unique record of the conflict resolutions unlike with a merge commit
That’s something I never needed because the only thing that matters is codebase at state A, and codebase at state B, and the diff between those two states. Ideally, a single reason for the transition between the two.
There are so many such scenarios where more information is better. If you've got a good PR tool it might save caches of those branches pre-squash some amount of time and you can do some of that sort of archeology in your PR tool, but even GitHub will sometimes garbage collect PR commits from deleted branches eventually.
The git DAG being a two-dimensional data structure is a useful tool. I find that I want to preserve as much information as possible, including using `git merge --no-ff` in additional scenarios that many use `git rebase` for because I don't know when I will need that (integration or testing or process change) information, but if I find that I need that information it is good to have it.
It's related to the same reason we don't throw out commit messages on ancient commits. In my experience, no matter how outdated that information gets, you are going to find surprising reasons to need it. Source control isn't just about recent history, even if that is most of your day-to-day needs. Sometimes you do need to revisit the past and you don't always know exactly what you will need from that past until you do need that information search.
That mostly a staple of the merge workflows where people are crisscrossing merges all over the place. At the end you have those horrendous diffs.
A rebase (and squash) only considers the tip of the main branch (which is a working state) and add changes that bring it to the next working state. You’re always aware of the latest working model of the code because that’s the starting point of your work (not something from $days ago). There’s no bad merges in the history of the PR branch.
Any time you integrate two branches, no matter how long running or short running, you have possible merge conflicts. Like I said, I prefer keeping that integration log as a tangible source control artifact. I understand how many people don't care for it. But don't mistake it for solely an aesthetic choice. Merge conflicts are a necessary part of source control and sweeping them under the rug is one way with dealing with them, but in my opinion not exactly the healthiest way.
[0] ETA: Merge conflicts are not just a technical issue, but a communications and coordination issue. Software development is a social activity and as long as it is a social activity it creates merge conflicts.
> Merge conflicts are a necessary part of source control and sweeping them under the rug is one way with dealing with them, but in my opinion not exactly the healthiest way.
I don’t agree that retaining them is necessary. Merge workflows encourage long running branches. Sometimes divergence in understanding does not create conflicts and that’s how regression happens.
With most rebase workflow, the commit list is often kept short (which is why squashing them is often correct). Most of mine have been below five. Such patch is easy to review and reason according to the latest knowledge of the code. Also easier to cherrypick and apply to an old version of the code.
"Merge early and often" is just as useful of a concept as "rebase often". The workflow is often exactly the same. The only real difference is extra commits to mark the merge points, and the extra commits are mostly just a UI issue when code reviewing.
A good PR UI (and GitHub isn't always, but it tries) doesn't show commits brought in from the base branch. (I think GitHub would have a simpler thing if it defaulted to a simpler `--first-parent` approach (rather than trying to math from the base branch) with an option to drill down, but I'm not a a GitHub UX designer.
Don't confuse the workflow with the DAG shape, that is more aesthetic than not.
In theory, yes. Squashing is an extreme approach to merging fixup commits.
It also throws the baby out with the bathwater by removing individual commits that explain and clarify how and why some changes were introduced as part or a PR.
If your PRs are tiny and don't introduce major changes then squashing is ok. Instead, you should do the right thing and curate the set of commits featuring in your PR.
It's ironically easier to create a messy agent work branch then have the agent cherry pick independent PRs from it into atomic commits post-work.
You seem confused. In the age of AI your ai code assistants already do task-specific commits. In fact, you can easily create a skill to have ai do that for you. It can even use git history split.
You see where this is going?
Our right thing sounds different to your right thing. Our right thing is PRs less than 500~ lines, and a single logical change only if the overall goal is complex.
For example, in your "right thing" it sounds like you'll have a refactor commit somewhere in the chain of commits in your PR, that might introduce 2000 lines of change, and other logically coupled changes in the same PR, all resulting in a large PR.
We prefer smaller, complete, mergable PRs. And therefore we normally only ever start with a single commit in the PR because the dev squashes everything before raising.
I don't know which way is better, but I do know that when I come across large PRs, I zone out and review quality drops. In fact, I just don't approve them.
You tidy up and rebase before making a PR. Anything else is really disrespectful of your reviewer's time. That is also how all the larger open source projects operate.
> you only get one commit for the whole feature
If you are doing one logical commit per PR, you are doing way too many PRs.
Alternatively you don't have a working review process.
Presenting a series of patches is good in an email format because when I’m adding them, I can evaluate each and decide whether I want it or not. But GitHub (and forges that copies it) is lacking in that regards without me taking over the branch.
So the word is to make the PR the unit of changes, and only review the whole diff, not the individual commit.
Other use cases exist where each individual commit adds value / changes something important / is atomic. Which one is best depends on the use case.
What should definitely be avoided (or, what should not end up in main) is "work log" commits. Many people use git commit like a save / checkpoint operation, that's the kind of thing nobody needs to read. That's the "fix" commits.
Succinct guideline:
Good commits: "When applied, this commit will <commit message>"
Bad commits: "I did <commit message>"
Then whether it's one commit or the result of a squash merge it doesn't really matter much anymore.