Programming @kbin.social danrot @kbin.social 9mo ago

git bisect and the importance of a clean history

danielrotter.at git bisect and the importance of a clean history

The value of a clean git history is often underestimated. I will explain one of the advantages based on the git bisect command.

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All of this can only work with a clean git history containing only working commits.

This isn't really true.

You can use git bisect skip to skip commits that can't be evaluated. So if you are tracking down the failure of test foo and this commit fails to build, you can skip it.

If all merged commits are green then you can use --first-parent to avoid testing inside a development branch. This way you can identify which merge caused the issue, even if other merges had broken commits.

So it is easier in general if you have all working commits, but it isn't necessary. Really as long as you have green history on your main branch you will be able to get good results without much effort. I would highly suggest using some sort of merge-queue based workflow to ensure that the master branch is always green.

I would generally prefer using --first-parent rather than forcing squashing. As smaller commits can be much easier to understand and the fact that commit IDs don't change when being merged can make it much easier to manage stacked PRs and hotfix backporting.
- I agree that some stuff is easier when not squashing commits, but for the teams I've been working with I've felt that the pros of squashing outweigh the cons, but of course YMMV.
  
  But I didn't know about git bisect skip, thanks for the tip! But sincere question: What happens if there are e.g. three adjacent broken commits? If I have skip all three of those and the error was introduced in one of them, then git cannot tell me which commit introduced the error, right?