52 lines
2.3 KiB
Markdown
52 lines
2.3 KiB
Markdown
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---
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layout: post
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title: "Using Git bisect to find the first good commit"
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date: 2015-02-26 10:42:56+00:00
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tags: [git]
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permalink: /blog/2015/2/26/using-git-bisect-to-find-the-first-good-commit
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published: true
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author:
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name: Gergely Polonkai
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email: gergely@polonkai.eu
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---
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Few months ago we “implemented” a bug in our software, which was released
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to the customers. We continued development for two weeks when the first
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customer ticket arrived about the bug. We successfully reproduced it with
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the customer’s version, but not with the development sources; it turned out
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that one of the developers unconsciously fixed the bug. The devs spent some
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hours finding where the fix lied before coming to me like “There is
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`git-bisect` which we can use to find the commit where we messed up things.
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Is there a way to find where we fixed it?”
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For those who don’t know this feature, you have to mark a known “good” and
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“bad” commit, then git-bisect will go through the commits between this two,
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present you the corresponding snapshots, and you have to mark each of them
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as “good” or “bad”. At the end, you will get a commit hash where the bug
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first occured.
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As it turned out, our developers’ problem rooted in the naming convention
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of git-bisect: they assumed that the “good” commit must be a working one,
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while a “bad” one must be the buggy. In this case, we did the following:
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The commit with the customer’s release tag was marked as good (even though
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this had the bug), and the latest commit on our development branch was
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marked as “bad” (even though the bug was fixed by then). Now with every
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snapshot presented by git-bisect we had to do the opposite what you usually
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do: mark commits still having the bug as “good”, and commits that don’t as
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“bad”. At the end, we had the hash of the commit that fixed the bug (among
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some other things; luckily, the developer who pushed that commit had a
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workflow that introduced a lot of cherry-picking and squashing before the
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push, so he could easily find the bit that actually fixed the problem in
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his local repository with the same technique).
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[This StackOverflow answer](http://stackoverflow.com/a/17153598/1305139)
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suggests the very same, but with some aliases:
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{% highlight ini %}
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[alias]
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bisect-fixed = bisect bad
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bisect-unfixed = bisect good
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{% endhighlight %}
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