[dkubb]

Another nice side benefit is that you are able to use git bisect to find bugs more easily. If some of the commits fail the build then it becomes difficult to separate commits that actually introduce a bug from those that are just incomplete.

The team I work with has recently started making sure every commit passes the build and it's had some fantastic results in our productivity. We know every individual commit passes on it's own. If we cherry-pick something in that it's most likely going to pass; so if it fails then usually the problem is in that specific commit, not one made days or weeks ago.

[twic]

You don't have to rewrite history to do this. You just have to run your tests before committing. You know, like people used to in the old days.

Indeed, i think the widespread rewriting of history that goes on in the Git world makes it more likely that there will be failing commits, because every time you rewrite, you create a sheaf of commits which have never been tested.

Now, in your case, it sounds like you have set up processes to check these commits, and that's absolutely great. Everyone should do this! But why not combine this with a non-rewriting, test-before-commit process that produces fewer broken commits in the first place?

[nhaehnle]

Running test before committing locally adds a lot of friction. It often happens to me that I work on a feature in component A, and in doing so, realize that it would be great to have some additional feature in component B (or perhaps there's a bug that needs to be fixed).

As long as the components are logically separate, it's usually a good idea to make those changes in separate commits. While you can do that using selective git add, I personally often find it more convenient to just have a whole bunch of rather small "WIP" commits that you later group and squash together in a rebase.

Not least of the reason is that I like to make local commits often in general anyway, even when I know that the current state does not even compile. It's a form of backup. In that case, I really don't want to have to run tests before making commits.

And obviously, all of this only applies to my local work that will never be used by anybody else.

[twic]

When you come up with the idea for a feature in component B, or a bug to fix, rather than implementing it, make a note of it, and carry on with what you were doing. Once that's done and committed, you can go back to the other thing. That way, you end up with coherent separate commits, that you can test individually as you make them, without having to rewrite history. Not only that, but you can give each commit your full attention as you work on it, rather than spreading your attention over however many things.

Again, this is the traditional way of doing things (as an aside, in pair programming, one of the roles of the navigator is to maintain these notes of what to do next, so the pair can focus on one thing at a time). Seen from this perspective, history rewriting is again a way to cover up poor, undisciplined programming practice.

[nhaehnle]

It's possible that we just have different styles of working.

Still, to clarify: Not all, but some of the situations I have in mind are situation where the changes in component A cannot possibly work without the changes in component B.

So an alternative workflow could rather be: Stash all your changes made so far, then do the changes in component B, commit, and then reapply the stashed changes in component A. That's something I've tried in the past, and it can work. However, it has downsides as well. In particular, having the in-progress changes in component A around actually helps by providing the context to guide the changes in component B. So you avoid situations where, after you've continued working on component A, you realize that there's still something missing to component B after all (which may be something as silly as an incorrect const-qualifier).

It's also possible that our preferences depend on the kind of projects we're working on. What I've described is something that has turned out to work well for me on a large C++ code base, where being able to compile the work-in-progress state for both components simultaneously is very useful to catch the kind of problems like incorrect const-qualifiers I've mentioned before.

I could imagine that on a different type of project your way works just as well. For example, in a project where unit testing is applicable and development policy, so that you'd write separate tests for your changes to component B anyway, being able to co-test the work-in-progress state across components is not as important because you're already testing via unit tests.

[twic]

I agree that the situation where you need the changes in B to make the changes in A is both genuine and annoying!

I have often taken the stash A - change B - commit B - pop A - finish A route. If you know what changes to B you need, it's fine, but you're right, the changes to A can be useful context.

In that case, you can make the changes to B with the changes to A still around, then stash A, run the tests, commit, pop A, and continue. Then you can have the best of both worlds, and you still don't need to edit history.

If you just can't make the changes to B without the changes to A, then they probably belong in a single commit, and you've just identified a possible coupling that needs refactoring as a bonus.

[dkubb]

Yeah, obviously we do that (well maybe not so obvious to some, but I never push unless the tests pass). We sometimes perform lots of other things like static analysis that get in the way of a rapid feedback loop. We also run mutation testing, which can sometimes take several hours for the whole codebase -- although we don't have this run on every commit, just ones that we merge into a specific branch.

The problem I have with non-linear commit history is that I find it impossible to keep all the paths straight in my head when I am trying to understand a series of changes. Maybe you can do that, and I think that's awesome, but I like to see a master branch and then smaller feature branches that break off and then combine back with master.

[CrystalGamma]

A tool that does not naively sort the commits by date but groups linear parts of history together should allow for better overview.

[comex]

Maybe, but testing does not prevent all bugs and what happens once bisecting is needed still needs to be considered.