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Comment by gouggoug | Hacker News Reader

I will always fight tooth and nail against squash merge.

Squash merge has the major disadvantage of getting rid of valuable meaningful git history.

Squash merge is not the proper solution for keeping your git history clean, it is a hack using the side effect of squash.

Keeping your git history clean is a matter of policy, best-practices and education:

Developers should be required to submit _clean_ PRs, that is, PR's whose git history has been organized and refactored in such a way that it removed "clean up commits", "typo fix", etc.

When you squash merge a feature branch that has thousands of lines of code, and 6 months later you have a bug introduced by this feature branch, it becomes extremely hard to find which line introduced the bug.

On the other hand, if you kept the history, and if this history was clean from the get go, it becomes easy to read the commits one-by-one and understand the issue.

Don't use squash+merge.

edit: I see numerous comment saying, in essence, "squash+merge" is what gets rid of the dirty history. No, developers must learn the existence of `git rebase --interactive`, which is the command to use to clean your git history[0]. "squash" is one possible action, among others, that helps cleaning the history.

[0]: https://git-scm.com/book/en/v2/Git-Tools-Rewriting-History

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> Developers should be required to submit _clean_ PRs, that is, PR's whose git history has been organized and refactored in such a way that it removed "clean up commits", "typo fix", etc.

A complete and utter waste of time. You spend more time messing about with rebase than solving problems.

When you're digging through VCS history due to a bug you often ignore the commit message anyway - if the code did what it seemed to do you wouldn't be there.

Could not agree more...I wish I had more of substance to add, but an upvote didn't feel sufficient

Agreed but I also think this depends heavily on context. If the organization cares a lot of clean commit messages, have a nice git history, and want PRs to be submitted in a clean state, great!

This is not always the case. I've worked on codebases where we rarely scan the git history messages for anything useful, it's just as easy for us to dig into the code to figure out what's wrong.

It's a prime example of engineers mistaking aesthetics for utility.

> A complete and utter waste of time. You spend more time messing about with rebase than solving problems.

Eh. Not really. A clean history is a good resource for figuring out what was changed and why. Cleaning up history isn't even that much work anyway.

> When you're digging through VCS history due to a bug you often ignore the commit message anyway - if the code did what it seemed to do you wouldn't be there.

Only if the commit messages are shitty, which unfortunately they often are. I try to summarize what I'm changing and what I indent those changes to accomplish, because if there's one thing I hate doing, it's spending more time than necessary to puzzle out what I (or a coworker) was thinking at the time.

VCS history can be a pretty powerful tool, but a messy history discourages the use of it.

amen!

really, do people even use git bisect? If you do, you go through some rite of passage and I've seen people including myself make better (not perfect) commits. It remains a black art to gauge what the perfect amount of work in a commit should be.

Strongly disagree. Mainline branch commit history should be clean atomic commits that you can roll back. Otherwise you are just asking for trouble on any merge conflict or hotfix scenario.

> A complete and utter waste of time. You spend more time messing about with rebase than solving problems.

I'm also one of those "micro committers".

Because of this attitude, many hundreds pedantic commit rebases after, I'm now a better programmer (and I also spend next to no time with that type of rebases).

This is because I have now a much higher capacity (and speed) of breaking down problems into smaller, self-contained, steps.

There is a common understanding that VCs are just storages. VCs actually map the mental model of the developer. Having a precise, clear, granular VC history has a bidirectional relationship with being a precise, granular, clear developer.

> You spend more time messing about with rebase than solving problems

Rebase should be quick and straightforward. If it's not, you've got bigger problems.

By rebasing, you're taking responsibility for changing the codebase as it exists now, rather than how it used to be.

I think I'm missing something here. How valuable is to have 20 commits of "fix this error" , "fix the fix of the error", "revert all fixes", "real fix".... etc? I'd argue a PR with many commits such as these, conveys little no no useful information, when the actual change is 1-3 LOC.

what about cleaning and filtering out useless commits, by soft reseting the branch and commiting just the actual changes to merge. Sure, it can take a lot of time, but it's done once, by you, after all you're supplying the changes. And if it takes a really long time, you're doing it wrong in the first place by submitting PRs with many LOC.

Have you tried rebasing branches with dozens of short useless commits? That's a real waste of time, and everyone needs to do this if you want to update your main branch. So you've now multiplied the amount of wasted time for everyone.

> what about cleaning and filtering out useless commits, by soft reseting the branch and commiting just the actual changes to merge.

So... squashing?

Yes, but the author of the code, who would presumably know their intent, gets to choose how many commits to squash to instead of just one. This means that they can preserve the development process in a logical way.

What if the change really should be split into multiple commits. Having a mega commit affecting hundreds of lines across tens of files doesn't make reviewing the change easy, and reverting it will result in conflicts.

I would ask such changes to be split into multiple independent PRs

Then you essentially double the number of commits for a particular change, since it then becomes:

1. first related change

2. first merge commit

3. second related change

4. second merge commit

5. third related change

6. ...

Instead of just having all related changes in several commits with a merge commit at the end that groups those related changes.

The number of commits does not matter. What matters is the quality of it. My opinion is that each PR should be an independent and working unit.

If you have a too-huge PR that can be subdivided, it almost always means you have multiple units of work (feature/fixes) into one branch/PR.

The reason I agree with the article and use squash is that it allows us to have a different history between master and the local branches. Developers can freely subdivide each feature into how many commits are useful to their mindset and workflow, while the master branch will remain clean.

In my experience, the individual scope of each commit on the master branch is almost always correlated to the scope of one code review, and thus one PR.

Then there really is no need to even have merge commits. But, as far as I know, there no way to disable the creation of a merge commit when using the merge button on the github PR page.

The one thing you lose with just making one PR per commit is the relationship between a set of commits used to implement a feature. One commit involves some retractoring to make it easier to cleanly implement the feature. The other commit would be the feature and tests, and the last commit would be to add calls/references to that feature.

If these commits were kept in the same branch and merged in a single PR, then it would be easy to see the relation between them. If they were merged as 3 separate PRs, then it would be more difficult to see why the refactoring was done, especially if PRs for unrelated changes were merged in the interim.

It's not that those commits are in any way useful, it's that this "fix the error" commit might be 3 commits after the commit it belongs to. If there are no conflicts, `!fixup` will handle it for you; But since this is the real world, you're likely going to waste huge amounts of time solving conflicts that help no one.

My solution is:

- small-scoped PRs

- attempt to keep sub-commits readable, but don't waste time on them

Squashed commits also link to the PR where not only do you get the original commit list, but also get the whole discussion around the code.

> How valuable is to have 20 commits of "fix this error" , "fix the fix of the error", "revert all fixes", "real fix".... etc? I'd argue a PR with many commits such as these, conveys little no no useful information, when the actual change is 1-3 LOC.

I'm not saying that I wouldn't broadly discourage the worst of that but most people do not commit every changed line so it is rarely a problem in practice.

What does become a problem are people who insist on "clean history", "re-order these commits", etc etc at PR stage when you both agree the functional problem is done/fixed and now the negotiation has moved on to your git history. I do contract work (read: move around a lot) and this social anti-pattern comes up very often. Usually one guy who's into it throwing his weight around.

Would it surprise you to learn there is a large crossover because people who do this and people who go forensic on other cosmetic stuff: whitespace, syntax, etc?! :)

I've used these commits to identify the correct fix for bugs before. An early commit changed something to do X, but did it wrong. A "more fixes" commit tried to fix it but made it do Y.

It was obvious that the later commit was wrong and I could fix it to do X. If it were squashed I would have thought the original intent was to do Y and spent way more time trying to figure out how to fix it.

Obviously it's not guaranteed but throwing away that information is a bad idea if it's just for some arbitrary aesthetics. Same goes for rebasing to clean up the commit history, which would ostensibly do the same.

Do people here have examples of some bugs for which they had to resort to VCS history to find the cause? I'm struggling to picture a single bug in my whole career where this would have been quicker than just following the logic of the code. If there's information in commit messages that isn't evident in the code itself, that seems a terrible way to live.

As wrote in another comment, bisecting (which is for me a significant tool) relies on history (specifically, a granular one). However, it also must a disciplined history.

What's an example of a bug you've had to bisect for recently? Forgive me, it just seems like such a last resort thing.

I don't bisect regularly, but when I do, it's usually trying to figure out what the original reason for introducing the code that is problematic is. The entire point is on projects big enough, you may not be able to just "follow the logic" enough to know that your fix the to apparent bug isn't re-introducing some regression that was fixed previously.

So bisect to me, is a way to figure out where and why the code was changed the way that it was, so I have a better understanding of the changes I can make going forward.

That doesn't mean the change made in the past was correct and must be maintained (obviously something is broken), or that it might be that the obvious solution based on following the code logic is correct. But that doesn't mean I wasted time making sure I best understand the reasoning behind the changes made. But this is also why I don't resort to it very often, because it isn't necessary in all cases (I'd even say it isn't necessary in most cases).

Bisect also allows you to see other changes made in the commit in question, and around that commit, so you get a better overall picture of the logic.

If you've got a codebase where the intent of the code isn't clear, where you can't track bugs, and where you can't fix them without being confident you're not breaking other stuff, surely those are all fundamental problems worth addressing?

Yes, but those things take time to address and in the meantime the need to make changes that address more immediate needs doesn't go away. Bisect specifically helps if you've got an easily reproducible bug in a hairy part of the codebase and you know that bug could be arbitrarily old but is on a path that recently started getting exercised much more often. I use it maybe once a month but when I do it is very nice to have that context of how the bug happened and any other places that might need to be fixed.

Sure, but at that point there's a whole raft of practices that seem more important than 'having a nice commit history'.

Bisect doesn't require a nice commit history, just a granular one (well, it doesn't require a granular one either but it's a bit less helpful if it lets you identify the problem commit as the +18000/-7000 LOC "Overhaul payment system <7 paragraph description of new payment system>" than if it drops you on the +3/-3 LOC "fix encoding bug <no description of what the bug is or what the fix does>")

Edit: I should also add that if you use github, squash-merging pull requests is fine because you can pull down and check out the pull request branch and run bisect on that. Or more generally if you don't delete history and keep a record of what commits were squashed to make your giant commit, your friendly local maintenance programmer might grumble slightly but will still be able to work effectively. Just please avoid erasing history entirely.

I can give you an example though I have to be sort of vague for obvious reasons too. In fact, I have been bisecting to find the cause of a bug 3 times in the past 3 to 4 weeks.

Customer Service reported a problem with something that my team is responsible for. I knew almost for certain that we didn't break it. I had a vague idea that another team might have broken it by a recent-ish change to a different service that we both rely on but aren't the maintainers of (we have a monorepo). In fact they made multiple changes to it recently (they put me on the PR for awareness).

I don't know the code for that service but it was really easy to check for the occurrence of the bug (literally two clicks in the UI to reproduce or not reproduce). Instead of trying to understand a service that I don't own, which would require mental concentration, I randomly checked out a commit from 4 weeks ago, tested => bug not reproducible and started a bisect. I was actually gonna be stuck in some meetings for the next few hours but bisecting is mechanical, so I was able to just do it on the side (deploying is a little bit of waiting in between, you gotta refresh etc.) and a little later I was able to just paste a very neutral "XYZ is the first bad commit" into the ticket. Totally cuts down on the 'drama' too as you're not simply 'accusing' someone else of causing an issue in _your_ part of the application. It's just there, very neutral, there's the commit that caused it. Git told me!

But that just sounds like an _incredible_ amount of effort and even at the end you still don't actually know the cause of the bug. Surely you just raise it to someone who owns the code in question? It sounds like you know who they are already?

Until you have done it it may sound like an incredible amount of effort but in fact it isn't at all. Your reality might be different, but we also deal with different time zones. In this particular example the other team was in a different time zone and already gone for the day. The easiest and most efficient way was a 'dumb' bisect.

If you _only_ raise it to the team in question, you have nothing in hand but suspicions. Their natural reaction is most probably going to be "No can't be us, must be something/someone else" and you've wasted an entire day waiting for their response that was predictable anyway and you've also just increased both their and your own irritation level. Their's because they probably feel like you're trying to blame them for something they feel is not their fault. Your own because you've just wasted a day trying to solve this and meanwhile customer service thinks you caused a regression.

A bisect that literally took zero brain cycles and told me which commit caused it before I was even halfway done with my meetings allowed me to let them know exactly which commit caused it without a doubt (unless your company is so broken that they wouldn't even believe the bisect output :)). This also gives them very valuable information because instead of them now trying to have to figure out which of their changes maybe caused this thing I'm 'accusing' them of, they have a single commit, which is directly tied to a single ticket. In this particular case, the developer in question actually knew right away from seeing the commit message/ticket number what particular part of their change was the cause of the issue, without even having to dig through the code.

If an issue isn't urgent and you aren't going to fix it, why spend time on it? Why not send it to the team that you already know is responsible? Why do you have teams that refuse to investigate their own issues and instead have weird emotional reactions to bug reports? Why are they more likely to accept a git bisect that took zero brain cycles from you rather than do it themselves in zero brain cycles? This all just sounds completely dysfunctional. Flee!

Not the GP, but this kind of thing can happen all of the time.

The people experiencing the bug don't know who is responsible so they arbitrarily pick someone. The bug could get passed back and forth endlessly between teams until somebody isolates it a little better and bisecting is a good tool for doing that. Just doing the bisecting rather than arguing with the other team about who should do the bisecting is a way to get things done. If it does turn out to be the other team, it may be easier to convince the other team to take on similar requests in the future.

As my sibling already points out correctly, no need to flee, not completely dysfunctional at all and very very common in both functional, semi-functional and yes also dysfunctional companies.

At the point where I have _not_ done the bisect, I in fact do not actually _know_ who is responsible. I have a suspicion, a hunch, an assumption. Assumptions are bad and need to be validated. I can either let the other team that I suspect validate it. If it turns out that I was wrong, I have both wasted their and my own time and reduced my credibility. What then? I try to suspect another team and try the same thing again? That's what happens in a lot of large companies all the time. Nobody looks into anything and just tries to pawn it off to someone else. If someone tried this more than a couple of times with me, I definitely know what I would do the third time around.

They are more likely to accept a bisect from me, because it shows that I am not simply trying to pawn something off to them based on a mere assumption. It shows that I care and that I validate my assumptions and don't just try to pawn things off to other teams and play 'hot potato'. That would indeed be dysfunctional.

What's so incredible about spending a bit of time parallel to other things on identifying a bug?

To keep in mind that in cases where a bug can be programmatically reproducible (typically, existing or "upcoming" automated test coverage), bisect can be automated trivially.

For example when a bug has messed up data and you want to know when it was introduced. Then you know how far you have to go back to correct it.

Other times knowing how it was introduced can give you a sense of what the change the original author was trying to make.

As parent said, history is not just commit messages.

Trivial example from yesterday: "this worked last week... what did they even touch inbetween?", look at the most relevant commit diff, context makes it obvious someone just accidentally deleted a line too many while replacing a code block.

For more complex stuff, it's helpful for "what were they trying to do with this line", "what's the requirements document they worked off when they wrote this", "which other versions are likely to have this bug too", "Is this new and I can go ask whoever wrote this about it or is it years old", ...

What follows is a summary of a time bisect saved a team I was on from a lot of pain. It's been a long time so I may have some details wrong, but the point should be clear.

Years ago I worked at an e-commerce shop.

One fine day we discovered that the checkout process had been broken in a very particular corner case at some point in the past several months.

No one had any idea how it had happened.

Most of the team was trying to work out what could have possibly gone wrong by staring intently at code in their IDEs and debuggers while stepping through reproductions.

I thought, "everyone's already doing that - I'll try a bisect, since we have a reliable reproduction for this inscrutable weirdness."

It took maybe twenty minutes before I could point to a < twenty-line change.

The author of said change was flummoxed at the breakage, as it was nowhere near the actual checkout code, but a few minutes of the whole team staring at it revealed a classic piece of PHP spaghetti insanity that had managed to break the checkout process (I no longer recall the specific issue - might've been global variable name collision).

I think it would have taken hours before we got to an answer without bisect.

Granted, it only worked so well because of good commit hygiene (which I had trained everyone to use when I introduced git and code review to that team), but it showed quite clearly how useful good commit hygiene is when paired with bisect.

> Do people here have examples of some bugs for which they had to resort to VCS history to find the cause?

A more common scenario is to run git blame on the files you plan to modify to see what commits were responsible for them. If the message is detailed enough, you can avoid introducing a regression because you altered logic introduced by a commit to fix a bug.

> If there's information in commit messages that isn't evident in the code itself, that seems a terrible way to live.

Good commit messages include why a change was made, which usually isn't really reflected in the code itself. Comments may be outdated if the code is changed without updating the comments, but the git blame output for a line of code is timeless because the associated between that commit and line of code isn't lost until the line itself is updated.

* Commit that added line was fixing something unrelated; deduced line was duplicated in merge resolution. * Line was comparing two different enums for equality and failing; commit history showed one enum had been an int and the commit message that changed it explained why the author thought the comparison was safe anyway, so we could ask why that wasn't true

Plus even when the _cause_ is in the code, I constantly check "what's the history of this function?" while trying to figure out whether the code was always intended to do this crazy thing or whether it's been morphed by recent changes. I have "Show selection history" mapped to Ctrl+Shift+G+H in PyCharm.

I've used version control history to verify that a mysterious bug was not caused by any changes in the codebase. Instead, we were set up to automatically incorporate minor version changes in dependencies, one of which improperly had a breaking change.

This class of bug is impossible to find by following the logic of the code because it's not in the code.

"had to" is a stretch, but as the first example from GitHub: https://github.com/ankidroid/Anki-Android/issues/7781

There's a lot of value in bisecting to find the exact commit, moving from "this is probably the commit that broke it" to "this is exactly the commit which broke it"

Typical workflow:

* branch off master

* Write a test which passes at some point in the past, and fails on HEAD

* rebase the test into the branch at the point in the past, so bisect works

* git bisect to pinpoint the bug

With a non-squashed and a history where each commit builds, `git bisect` points to the exact failing commit and makes the investigation trivial

An additional advantage is that you're not wasting time investigating: the unit test can be used as a regression test

I agree with you in part, depending on the project, if that means just squashing it down first. This at least can keep the integration branch somewhat sane and without a bunch of intermediate commits that are junk and won't build.

For this reason I prefer people to rebase on the integration branch instead of merging it in to stay current; unless there is a reason not to. And a lot of open source projects require PRs that to be pre-squashed or be able to be squashed before merging!

However, there is a time and place still for deliberately crafting the PR commits. For instance if you are wanting the reviewer to be able to review chunks of the PR in isolation/stages, or if you want each of the commits to be buildable.. I suppose also for review/testing.

This all depends on the project and other factors like the wider org.

> A complete and utter waste of time. You spend more time messing about with rebase than solving problems.

Unless you're using a garbage client (eg, the git CLI) a rebase to get rid of the "typo" "oops" type commits (when you forgot something) takes I'd say 10-20 seconds.

Most commonly I do this when I have several changes on the go at once and forget to commit a fixed unit test, new import, or something like that. I usually realize it right away, so my commit will usually be "add test" or "amend 2 commits ago" or something to remind myself which one it goes to (and it sticks out, because my other commits are usually in the format "PROJ-1234: Add new --host command-line option").

> When you're digging through VCS history due to a bug you often ignore the commit message anyway - if the code did what it seemed to do you wouldn't be there.

I presume this is doing a bisect or something to narrow down where a bug was introduced?

My experience comes from the opposite side. Usually I identify the line of code causing a bug, it makes me go "wtf, what is this even supposed to be doing?" so I do a git blame. Hopefully the commit message is useful and ideally leads me back to the original bug/ticket, so I can figure out what the original intent/fix was, rather than inadvertently breaking something (or re-causing a different bug it fixed). I'll also note that in code that is well-commented and well-tested, this step is rarely necessary.

As an example, say I come across something like this:

    if (port > 443) ignoreErrors = true;

Clearly, this was added to solve some some problem, but even without any context it's pretty obviously a bad solution to whatever that problem is. Git blame lets me go back to see what the original reason/bug was, evaluate if it's still relevant and then either fix it properly or safely remove this line.

> My experience comes from the opposite side. Usually I identify the line of code causing a bug, it makes me go "wtf, what is this even supposed to be doing?" so I do a git blame.

If the commit message is something like: PROJECT-TICKETNUMBER Description, you can you know... see the ticket/issue along with full details and discussions?

> I'll also note that in code that is well-commented and well-tested, this step is rarely necessary.

This is the most important line from this comment.

If I'm using blame or bisect, it means I did something wrong.

I merge 10 times a day - and if it takes me a minute, because I'm slower than you - that means it's ten minutes a day. Add the cognitive load of the whole process and the added time of explaining it to other team members - 10 minutes is an underestimate.

I'm going to spend that time writing tests and comments, since even you note that they're the better option.

Squash is good enough. I spend my energy improving the right things.

git CLI isn't so bad for that, why? I do --fixup commits all the time, git commit -i gives me all the power to reorder, merge and even split commits.

Fixup with autosquash is so damn convinient. I wonder if the people complaining have ever used them.

While the typical basic rebase isn't so bad from the CLI, something like magit is faster, and much much faster for anything apart from the basic rebases.

Whoa whoa, hold your horses. I have used nothing _but_ the git CLI for all my commits, rebases and squashes for the better part of 10 years now.

I do agree with you though that rebasing and squashing are absolutely easy and awesome and whoever doesn't agree probably comes at it from a badly run repository with utterly bad practices and it would probably _benefit_ from a proper squashing and rebasing practice.

Have people not seen autosquash when rebasing? And the --fixup and --squash options to commit?

Check those out. It makes the rebase automated with correct commits getting fixed up or squashed as you desire.

> A complete and utter waste of time. You spend more time messing about with rebase than solving problems.

You won't think that when customers report a regression that was introduced some time in the last year.

You have apparently never had the benefit of a properly run git repository.

Our master has straight history. We always rebase to merge a PR and we have build scripts that check this as well. You will not be able to merge a PR that tries to get more than one commit onto master, if the commits touch more than one of the modules (we have a monorepo with lots of individual services). Until the PR has been approved we leave individual commits on the branch though as that can be helpful.

I have not had to "mess" with rebases ever. Most rebases apply cleanly and if they don't the conflict resolution is mostly very easy. The 'hardest' conflicts to solve were actually in the end the easiest to solve, because all you had to do was to `git rebase --skip` the appropriate commits. Of course some developers that didn't know better spent hours trying to do those conflict resolutions and complained loudly. Fortunately they were that loud, so we caught it and just did the skipping. Everything applied cleanly without any conflicts after that.

It's pretty awesome to have one commit per ticket on master and especially if something goes wrong. I can easily `git bisect` to find which ticket introduced a bug or a regression and I don't ever have to mess around. All commits have to have a ticket number in the commit message.

It also enables firefighters to almost mechanically solve production issues. Prod is broken after the last production deploy? There's very very likely only one new commit since the last deploy before that (or maybe a few). In any case, just revert to the commit of the previous deploy, lock down the deployments and now you have time to properly solve the issue without time pressure. If there was more than one commit and you can pinpoint which of them caused the issue it would even be very easy to just revert that one commit and let deployments continue. No dealing with 27 commits that make up one ticket.

Know thy tools!

> You will not be able to merge a PR that tries to get more than one commit onto master

What value does the merge commit in the PR provide if a PR only has a single commit? Couldn't you essentially halve the number of commits in the commit history by amending the single PR commit message to contain the text that the merge commit will contain anyway?

In case it wasn't clear from my post, I am very all over the place with the word 'merge'. I usually use it to describe the concept. We don't ever have actual merge commits. We merge by rebasing and that then makes the 'merge' just a fast forward.

When a bug is found in production, it should usually be fixed by:

1. Make a commit supplying the test coverage that was evidently lacking.

2. Make a commit supplying the fix.

Everything you say is valid. However, what I just described is the simplest and clearest example of valuable multi-commit-per-ticket git history.

I myself do and encourage my guys to do multiple commits to checkpoint their work. Also for bug fixes as you describe, first commit is the test proving its broken. This should turn the build red. Then another commit with the fix which makes the build green. All of this on the branch. PR it like that. It's valuable to see this history.

Once the PR is approved and before merging to master, rebase abd squash. The build failing intermediate commit is no longer valuable.

There's negative value in having a commit in the history which turns the build red; it should be removed, but the requirement that the branch is squashed onto master doesn't follow.

It'd be a perfectly valid alternative in some cases to clean the commit history and rebase a number of atomic commits onto master if it would make the history more readable.

Suppose

(a) You suddenly realize that the production code in the main (not deployed) branch is incorrect

(b) There is no test coverage for the bug

In this situation you think there is negative value in committing a failing test that will make the build go red? Perhaps you were forgetting that sometimes commits alter production code paths and sometimes they alter test code?

If you turn the main branch red, you affect the workflows of all developers who pull until you turn the build green again. It may also affect git bisect depending on the bisect workflow used.

The ideal would be to revert the change if known, or disable deployment on the branch until the issue is fixed with an ignored test*. I feel a workflow where you explicitly break the build [incl. tests] when a bug is discovered isn't ideal.

I agree. This is not how I meant it (OP here again).

Our master is alway kept green. If master is not green we are dead in the water. If something happens and master is not green we can not deploy any fixes.

As you say we either revert the breaking commit and push that out fast or we deploy the last known good commit. This may just be HEAD^ if there was only one new commit going out. It might also be several commits ago. Depends on what got merged recently and made it into that deploy.

On bisecting: we keep the actual images for some time. So if you don't need to bisect something rather old, then you don't need to build anything to bisect. Only deploy and check whether you had a good or bad commit. A deploy takes less than a minute usually vs a ~10 minute build.

> The build failing intermediate commit is no longer valuable.

At times what you say will be correct, but it's not at all obvious that what you say is always correct. Suppose that subsequently the authors of the fix in question have a horrible realization that there is something wrong with their fix, and furthermore they are panicking. Now, as a helpful colleague introducing some calm to the situation, wouldn't it be reasonable to recommend that they go back to the state of the codebase where (a) the original bug is present, and (b) it is demonstrated by a test?

But with your squash, no such state exists on main[0]. To my mind it feels a bit janky to have to check out some non-master commit from a feature branch to go to that codebase state.

[0] I am not an ideologue but I do kind of like main over master as it is shorter and clearer.

I usually go with what makes sense in most situations instead of complicating my life with stuff that may, perhaps, one day, if the moon is full and the stars are misaligned not work perfectly.

That said, I do not need to have an individual commit to do what you are saying. In fact our default is to remove all branches after the merge to master. But each fix is just one commit anyway. So the state you describe is actually just the commit on master that is before the fix. No need for finding old branches and finding the commit that has the test only.

The thing with the tests is also that this is an ideal scenario. Not everyone does this. I don't always do it either or can't do it. But I strive to. So relying on it would be bad. To do what you said regardless of whether there was a first commit with a test or not I simply need that one squashed commit, which is very likely very small and create a patch (simple diff of that commit and the previous commit meaning) and then remove all changes that aren't tests and apply this to the pre-fix commit. This is very likely very easy because tests are in separate folders and it's a small patch file. Probably takes less than a minute to do. Will not always work 100% but good enough in many cases and I can count on one hand how often this would have been needed in my entire career.

(in fact I did this for a similar thing recently. I needed to apply some of the code from a spike. I created the patch, deleted unwanted stuff from the patch file and then applied it. Easiest ticket I did in a while ;))

Basically: 'git diff <prevCommitHash> > abcd.patch' then 'git checkout <prevCommitHash>'. 'vi abcd. patch' aaand 'patch -p1 < abcd.patch'

Re: Master. That's the name of the branch as per git default. Not much I can do there ;)

> if the commits touch more than one of the modules (we have a monorepo with lots of individual services)

That seems wrong to me - a big advantage to having a monorepo is that when you need to make a change to how two services work together, you can do so with a single atomic commit.

I may not have been clear. You can merge a single commit to master (as a fast forward rebase) regardless of how many modules it touches. But you can't do it with more than one commit. It will refuse this because we don't want non squashed stuff on master and it was an easy enough hack to prevent that. Yes it's not fool proof but works well enough so far. It discourages feature branches too which we also want. All these scripts are part of the monorepo and if I need a feature branch for something I can easily exclude that branch in these checks. I've only done that once in the last few years.

This stuff is also very fluid and changed and improved as we go. If the easy solution turns out to not work well enough for enough common cases _then_ we spend more time making it better. Otherwise 'good enough' does the trick for us. YMMV depending on your company size and developer culture. E.g. you might have too many cowboys that just add exceptions all the time or remove the checks entirely. Nobody can help you there. Fire then or flee ;)

> A complete and utter waste of time. You spend more time messing about with rebase than solving problems.

That can be avoided by only staging and committing changes when the change is actually completely implemented. For example, I'll make a change and then I'll stage it as follows:

1. Stage and commit a new method and associated unit tests

2. Stage and commit calls to the new method

3. Stage and commit the version update

Having to go through extensive rebasing is really an issue with treating version control as a back up system rather than a way to record individual units of work with well crafted commit messages that describe what and why the change was made.

I do agree that PRs should have a clean history. However:

- Services like GitHub allow you to restore the original branch, so you never actually lose history. So I don't see any major drawbacks of squashing on merge.

- If your PRs are several thousand lines long, they probably should've been broken up into multiple PRs (your reviewer will appreciate it)

Spot-on for both counts. Preserving a PR's individual commits in the master branch is insane - many of those commits won't represent a fully working system anyway, so why keep them in master?

> many of those commits won't represent a fully working system anyway

This is entirely within the control of the developer(s) working on the project. Whether it's worth it is up to the people working on it. It's certainly not insane though - it's much easier to fix merge/rebase conflicts when each commit is small and easy to reason about.

> it's much easier to fix merge/rebase conflicts when each commit is small and easy to reason about.

I agree, but I'd say it in the context of PRs. It's much easier to fix issues (and avoid them) when _PRs_ are small & easy to reason about.

It's entirely not insane _on the premise that the history is clean_. That's the whole argument that is being made here.

If you think that "Preserving a PR's individual commits in the master branch is insane - many of those commits won't represent a fully working system anyway", your issue _is_ "that your commits don't represent a fully working system anyway", _that_ is what you need to fix.

You need to make sure your history _does_ represent multiple small digestible atomic chunk of codes, that are understandable individually.

By squashing, you're not fixing the root cause, you're treating the symptoms.

> - Services like GitHub allow you to restore the original branch, so you never actually lose history. So I don't see any major drawbacks of squashing on merge.

There's definitely a drawback, and it's bisecting, which is actually a big deal.

Bisecting allows in a semi-automated (depending on the issue) bisecting what otherwise can be a large diff.

But of course, it requires a disciplined history - otherwise, bisecting just won't work.

Can't you just bisect twice. Once to find the PR and a second time within the PR's branch?

AFAIK, if you squash merge, the SCM (intended as the repository, both local and remote) will keep only a single commit; the commits breakdown will be in GitHub's (intended as a service) history.

So, if your PR has a clean history in the first place (clean as in multiple small digestible, atomic commits, that are easy to review in isolation), why get rid of it with a squash?

Is there a fundamental drawback to keeping that clean history? _It's already here_

I would agree with your points if not for the fact that "clean up commits" or "typo fix" is a necessary result of PR's.

Your teammate will request changes in your code, and the only way to cleanly communicate "yes I made that change, and ONLY that change" is through these clean-up commits.

Otherwise, if you amend/force-push or open an entirely new PR, 99% of the diff are things that your team has already seen and reviewed.

Squash merges let you clearly communicate how you addressed PR comments, while also keeping the master history clean.

> Otherwise, if you amend/force-push or open an entirely new PR, 99% of the diff are things that your team has already seen and reviewed.

gerrit has solved this issue for years by showing the diffs between each successive revision of a patch.

e.g. look here the files at different origin patchsets : https://codereview.qt-project.org/c/qt/qtwayland/+/321246/3....

This was a feature of ReviewBoard as well. The history of code review changes was maintained by the tool separately from commit history.

It took me a while to get a workflow that actually works with Gerrit, and I occasionally think of trying to do some kind of autosquash so I can have successive commits locally. In practice I just use --amend all the time.

Careful use of setting upstream and of course pull=rebase makes keeping up with trunk manageable.

You can also use git-range-diff[1].

[1] http://git-scm.com/docs/git-range-diff

how does that work if the old version of the amended commit has been gc'd ?

And as it happens, Reviewable also deals with this perfectly fine. In fact, it appears that most any code review tool save GitHub is perfectly all right with amend/force-push...

Fixup commits are a good way to work around this. https://git-scm.com/docs/git-commit#Documentation/git-commit...

You still create your "clean up" commits, but it's done in a way where git can automatically squash everything back together in the end.

Huh, never knew about this. Seems quite useful. Thanks!

I don't mind this. I want my reviewers to look at the state of the new code - not the diff, and not the diff of the diff.

Address PR comments using the PR comments.

I am in agreement however I suspect many developers have never seen the usage of "git bisect" to track down a bug and fix it. Once you see the power of that, I think one can come to appreciate more the granular git history that is present when not using squash commits.

Of course, git bisect still works with squash commits it just makes your job as the bug fixer much harder because typically squashed commits are quite large so you have to figure out what in the N lines of code introduced the defect.

I would beg to differ. How large your commits are, depends on your tickets. As I've just explained in another reply, squash merging with rebases does not have any direct correlation with how large your commits are or whether you can use long lived feature branches.

We do sometimes use feature branches for example (very sparingly) but then that feature branch becomes a temporary 'master' that we squash merge to and the feature branch does _not_ get squashed but the individual commits suddenly all appear on master after rebasing, which results in a nice fast-forward 'merge'. Those feature branches are the result of multiple tickets which all have their own individual commits and which could all have made directly against master using the squash merge strategy, except there were 'reasons' not to (which I usually try to dispel and work with master directly but it's not always possible).

Hey, so this POV comes up a lot, and I have to say that I think it mistakes how git commits should work, but I’ll add that you can sort of have both.

First, in a production branch, git commits should be thought of as functions. Like “Apply commit X, get feature Y, unapply it and you get the reverse”. So the problem with preserving full git history in master is that it breaks that invariant. You have to sort of do like a range of commits, but then that doesn’t really always work because often times other commits can be interleaved into yours.

To understand how I mean, just look at Linux or open source software projects, where the technical experts are more or less gatekeepers and aren’t accountable to any other influence. You’ll find that commits work this way, and their history is squashed. (Maintainers will also force you to rebase before merging and basically put all the work on you to get the PR in ship shape, which is a lot different from a corporate environment)

Ok, but then to your point about preserving valuable, more granular commits, well, the solution is you just leave that remote branch up, either in your fork or elsewhere (but probably in your fork). These branches should have formal names identifying a ticket (at work) or an RFC or whatever, so it should be easy for people to discover what happened. They can see this remote issued a PR to this remote to implement RFC-123 or whatever, and they can go to that remote and see the granular commits if you preserved.

Sorry, this is like a never ending debate and there are very strong opinions, but I sincerely think that in this situation there is actually a right answer. People who already know how to do this or are super familiar with open source, maintainers or team leads or whatever, I think don’t see the point in fighting over it, since they can just enforce whatever they want in their gatekeeper role. However, the truth is that there’s sort of a fundamental misunderstanding that the majority of the population has around git and I think it’s better to engage and explain when you get the chance.

> First, in a production branch, git commits should be thought of as functions. Like “Apply commit X, get feature Y, unapply it and you get the reverse”. So the problem with preserving full git history in master is that it breaks that invariant. You have to sort of do like a range of commits, but then that doesn’t really always work because often times other commits can be interleaved into yours.

Merge commits allow you to do exactly that. If you have a branch with, say 15 commits, you can merge that branch _with a merge commit_, preserving all 15 commits, but if you need to revert, you revert the merge, which automatically reverts all 15 commits.

> Ok, but then to your point about preserving valuable, more granular commits, well, the solution is you just leave that remote branch up

So you went through all the trouble of making your git history something clean and valuable. And now, instead of merging it as-is with a merge commit into main, you squash the entire history (that you literally just spent time making useful) into main.

Now, because you think you might need this history (that you spent time making pretty and valuable), you come up with a whole process of creating a remote branch, giving it a name that follows specific conventions and whatnot, you also make the decision that you'll keep these branches forever, and, you need a way to link that remote branch to the squashed history.

What is the point of this whole process? When you could simply merge your feature branch (with its pretty and useful history you spent time working on) in main and be done with it?

I have a feeling this whole process you came up with stems from the fact that you don't seem to be aware that you can revert a merge commit.

No I understand, I’m just saying in the real world that’s not how projects are maintained.

> Squash merge has the major disadvantage of getting rid of valuable meaningful git history.

I think the main point of the article is that the Git history is often *not* valuable (because it's hard to enforce good commit messages). Your later points are very valid, however, and that's why I argue for smaller pull requests (and never merging a PR into main that leaves it in a broken state).

> Developers should be required to submit _clean_ PRs, that is, PR's whose git history has been organized and refactored in such a way that it removed "clean up commits", "typo fix", etc.

The only way I've ever seen this accomplished is through Github squash and merge.

> When you squash merge a feature branch that has thousands of lines of code, and 6 months later you have a bug introduced by this feature branch, it becomes extremely hard to find which line introduced the bug.

The article makes an argument that each commit should be "a single logical change." Squashing thousands of lines of code from a long-running feature branches into a single commit is obviously not what the author is suggesting.

maybe its not 100% one way or the other?

I love squash for somethings, but not others

today I brought in one big merge, 20+ commits , so don't squash it.

but I also have 20 "little fix" branches, with 1,2 commits each which I merge all together and squash in as one merge to main.

This is exactly how i run my project.

Amazing that folks get into these "two sides" debate. The reality is always a grey area. And you should be flexible enough to see the benefits of the different variations. With some guidelines on how to make a decision.

hah, a big merge. in the next month or so, i will need to merge a branch with nearly 500 commits that change more that 15k lines of code, under development for more than a year.

but yeah, like your "one big merge", i do not intend to squash it (though there are actually some arguments in favor that only kick on with a merge of this size).

I would argue that this feature branch of yours is way too long lived :) But I get it, sometimes you can't change some things in a corporate environment.

I would like to know though, if those 500 commits are all individual PRs/tickets that originally might have been 3798 commits but each PR that got merged into the feature branch was squashed? Or are these 500 individual commits that are potentially interleaved, meaning commit #246 is for ticket ABC, commit #247 to #251 is ticket XYZ, #252 to #255 is ticket ABC again etc.?

I'm basically re-commenting here but I think if the 500 commits are commits that if you didn't have to have a long-lived feature branch for some reason you would've made those exact 500 commit to master using squash-merge, then it's fine to rebase the feature branch on master and do a fast-forward 'merge' that makes all of those 500 commits suddenly appear on master (find except for the fact that you had _one year_ feature branch :))

I'm not in a corporate environment. ardour.org is it.

The 500 commits cover a development process that radically alters a fundamental data representation within the software. It was difficult to design, difficult to implement, difficult to test. The whole process has simply taken a long time, and we've had other orthogonal development taking place in master.

You are definitely in a different world. As a dev I really like SaaS as incremental changes are much easier to do. I bet you've weighed the pros and cons of making those changes incrementally vs. as a big bang change.

I try to avoid feature branches with "thousands of lines of code" on most of my teams, and have been pretty successful. Those types of feature branches create a lot of other problems. On the other hand, small, incremental pull requests that get merged back to master and have really short lifespans, along with things like feature flags to decouple delivering code from delivering functionality have worked really well.

In this world, squash merges are awesome, because any squash merge is basically a "commit" in the other world, and developers can feel free to commit however they want within the branch.

So, the only way that I can think that having the squash commit broken into individual commits would help to find the one broken line is because it would enable git bisect to find the failing commit.

However, that implies that each individual commit inside that feature branch worked on its own. If that is the case, a better suggestion would be to break up the giant feature branch into smaller sub features that can be merged as they are completed

Even though most work can be split into a sequence of valid commits (i.e. sub-features), it's often not obvious how to best break up the larger feature before working on it.

Sure, but I don’t see how that changes the situation. There are three possibilities; you make a series of commits that are each complete and can run on their own, you make a series of commits that can’t be run on their own, or you make one big commit at the end with the full feature.

If you are doing option 1, you could make one PR per commit, and each one could be squashed onto the main branch (although a single commit squash doesn’t do much). You can then use git bisect at a later time to find out which of those commits broke something.

If you make a series of smaller, but non-functional commits, you won’t be able to use git bisect no matter if you squash them or not. If you squash them, git bisect will only tell you that the whole series of commits introduced a bug or not. If you don’t squash, git bisect won’t work because the build and/or tests will fail on the non-functional commits. You don’t gain better discoverability by not-squashing.

The third option of one big commit makes squashing a moot point. Either way you only get one commit.

My point is that you don’t get better discovery power by not squashing.

> you could make one PR per commit, and each one could be squashed onto the main branch (although a single commit squash doesn’t do much). You can then use git bisect at a later time to find out which of those commits broke something.

You can, and I've tried doing this (both writing code and as a reviewer), but I've found it to mostly have disadvantages compared to a single merge request with all the commits:

* The reviewer gets less context for the earlier commits. Usually, a sequence of commits like this starts out by doing refactoring/redesigning of existing code, with the later commits adding new functionality. If the earlier commits add a new abstraction, it's much easier to evaluate if it's a good design or not if you get to see the actual use of the new abstraction (in the later commits).

* It takes more time, both for the reviewer and the submitter. For the reviewer, each "iteration" of the review might be shorter, but there will be more iterations in total, since they're only looking at a subset of the changes at once. If the reviewer only looks at merge requests a few times per day (to strike a balance between being responsive and avoiding interruptions), this translates to longer total time.

Sometimes it does make more sense to do. If the total set of changes is very large, it's probably a good idea to split it up (though not necessarily to single commits). Likewise, if your early commits make fundamental changes to the design of the code and might need a complete do-over after review, it might make more sense to present that part separately (though see the first item above). But in my experience, it usually just leads to more work and more context switching for everyone involved.

> If you make a series of smaller, but non-functional commits, you won’t be able to use git bisect no matter if you squash them or not.

I agree that this is the worst of all options.

I see your points, but I disagree. FWIW, I also adopted the squash-merge only strategy with no regrets.

> Squash merge has the major disadvantage of getting rid of valuable meaningful git history.

It's not lost, at all -- it's in the branch it was squash-merged from. The point is that the topic/fix/experimental branch will likely have lots of history, including discarded ideas and other 'meanderings'. Every commit in that branch is meaningful in that it was a discrete step in that path. But, eventually what is _finally_ in that branch is what is relevant when merging to master. All that extra history in master would create confusion (and has for many in projects I've worked on).

If the discipline is that every commit must be a meaningful, viable point _in master_, then a merge of the history would make sense -- but I've never seen that possible (or even desired) in practice.

Mandatory squash merge would be very bad, right. But it sounds like success of this policy is highly dependent on the code size of average PR. I really liked to work at place where commits were usually squash-rebased, which got rid of most "typo"s, but long lived huge feature branches lived mostly usual life. And if possible, some logically atomic and finished groundwork parts of feature branches were extracted and squash-rebased into master ahead of time, slimming feature branch, sometimes to the point that feature branch could be squash-rebased too. Git blame was VERY pleasant to work with, and git-bisect would actually work if need would arise.

Using squash-merge doesn't mean that you can't use long-lived feature branches if that's something that you need for whatever reason.

It just means that you basically have a multi-stage squash merge strategy. We do this from time to time. We only allow rebased squash-merge to master. When we do have a long-lived feature branch for something then this feature branch basically becomes the master for the individual ticket branches and at the end, the feature branch is rebased onto master and merged as a fast forward. It can result in 50 commits appearing on master all at once but each of those commits is an individual small commit just as if they had been done directly with master and the squash-merge strategy. We rebase this feature branch on master very regularly too (once per sprint actually) to keep up to date with master. We also try not to do any long lived feature branches in the first place.

Disagree, having a bunch of commits made up of undo, redo , dunno what I'm doing , oh no now I know, commits is pretty annoying. Squash solves that (for me, when dealing with other peoples merges). Obviously just my opinion etc

The problem is real and the parent commenter addresses it: learn interactive rebasing to craft a beautiful commit history.

I think you are using got commit log as a form of documentation.

I half-agree. I don't agree devs should spend (much) time cleaning up their logs as opposed to actually writing docs (inline) that help the next person

I do agree that there is rarely a good (even half good) history of decisions. This is never the Jira / tickets kept outside of the system.

But it is also no good abusing the commit log as a form of ... journal. (I know that sounds silly but )

I think an actual journal / blog kept by the dev lead will be much more useful

There's definitely value in putting documentation where it will be seen. For developers, writing in a code comment or commit message is a good bet. If there's an issue, they'll be in the code, and they'll be in the commit log, and they'll see what you've written.

At times I've been asked to document things in a company wiki. Typically nobody reads it and it never gets updated when others make changes to the code.

> Squash merge has the major disadvantage of getting rid of valuable meaningful git history.

There are reasons against it but the real world is messy. Developers tend to commit things, recommit, undo, redo, move things around. Is this valuable history? It can be but I would say 99% of the time it's more valuable to have a good commit message about what was intended rather than what actually happened.

The idea of squash merge is to make the history clean from the get-go as you said.

> Developers tend to commit things, recommit, undo, redo, move things around.

I see 2-3 distinct final commits in that list there, ones that should be separate and not squashed into one:

* commit, recommit, undo (squash these ones, and depending on how much "undo" does could eliminate this entirely)

* redo (what exactly is in this one depends on how much "undo" did in the prior, and how the "redo" was done)

* move things around (feature is seemingly already working and this is a distinct separate "improve the code" step)

> Is this valuable history?

Keeping that last one separate is absurdly valuable when trying to figure out why the code acts the way it does, when a bug is reported later. A lot of bugs I encounter were in those steps when someone makes a simple typo moving the code around, and having it in the history makes it obvious it wasn't an intended change.

If only there was a way to have our cake and eat it too.

I'm assuming there is because I'm assuming those squashed commits are floating somewhere in the reflog and somehow connected to the squashed commits in a way that should still let you bisect if only we had a tool to make it not suck.

Alas, maybe someone with greater git-fu can inform us.

There are, as I answered separately:

`git log -p --first-parent`

In the article he says he keeps the original branch with all of the history around after they squash them with a reference to the original PR in the squashed merge commit message. So you can always just checkout the original branch and go digging in the full history.

Unwieldy to keep branches around even on moderate sized teams/projects. You don't need them to have a `squashed` view of history when needed. I am surprised that developers still cling to this outdated squashing regimen when pull request tools found on github, gitlab, bitbucket etc. already provide synthetic squash views derived from atomic commits by default.

How is it unwieldy? They don't even show up locally when you `git branch` unless you've checked them out. Otherwise they just sit there doing nothing, there is literally no maintenance required on them once they've been squashed into mainline. Most central repositories end up having hundreds (or even thousands) of "finished" branches that nobody ever looks at anyway.

Depends on configuration if you wind up having that many. I use `git branch -v` often to figure out what branch a colleague is working on. I guess I could apply my same logic and use filtering tools here as well. But I don't see the benefit of squashing the merge commits when git CLI, github etc. can give you the same view without the gratuitous data loss.

They show Github in their screenshots, and on Github you can delete a branch and the original commit history in the UI is still kept and available. So you don't have the branches locally, but Github still has them around.

OpenOffice did what looks a bit like a "squash merge" way back in the day. It's a nightmare to work out where things got changed. I don't recommend it.

I quite agree. Fix your commit history via an interactive rebase before you push. Learn to love fixup.

> On the other hand, if you kept the history, and if this history was clean from the get go, it becomes easy to read the commits one-by-one and understand the issue.

Or git-bisect.

Yes, git bisect.

But what does git bisect require to be useful?

A set of small atomic commits that make it easy to identify which line of code might be the origin of a very subtle bug you're looking for. Squash+merge will not provide you with such history, and make bisecting much less useful.

As long as CI is run on all commits, I’ll agree.

If you don’t run CI on every commit, then you have to balance nicer commits a higher likelihood of bisecting not working as easily.

Squash merge is for people who are so wedded to the idea that you should guess why the code is the way that it is instead of looking it up, that they want to make sure nobody else can do it either.

You know, assholes.

It’s fine if you don’t want to use something, or use it, as long as it doesn’t drag your whole team into your decision. Which squash merge does.

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