自动化寻找问题commit的利器: git bisect run

October 01, 2019

tags:

线性的代码提交历史，能给自动化定位问题带来很大帮助，使得我们可以从当前有问题的提交回溯，找到历史上第一个有问题的提交。更棒的是，我们还可以使用折半查找的办法，用O(LogN)的时间找到那个有问题的提交。

比如，在一个代码仓中，有C101 ~C200 的线性提交历史。我们知道一个测试在C101处通过测试，但是在C200处失败。我们可以依次checkout C101、C102，直到C200，每次checkout之后运行测试，从而能找到第一个让测试失败的提交。

另外，git 提供了一个工具，git bisect，帮助我们使用折半查找。如果我们有自动化的测试脚本，还可以使用git bisect run来进一步自动化。我创建了一个用来演示的repo。下面是一个运行的输出：

> git bisect start
> git bisect bad HEAD

# find the commit id for C101
> git log --grep='C101' --oneline | cat
37f5823 C101 - change another number
> git bisect good 37f5823
Bisecting: 49 revisions left to test after this (roughly 6 steps)
[086697d6e7359d9e8d5478a760e07cd295ffc30b] C150 - some change

> git bisect run bash test.sh
running bash test.sh
Test Passed
Bisecting: 24 revisions left to test after this (roughly 5 steps)
[35d8ef662b82d3d9ece4d78cb07e996182671417] C175 - some change
running bash test.sh
Test Passed
Bisecting: 12 revisions left to test after this (roughly 4 steps)
[69bd28f607c733f0da71a8d30e99ff1be9f6baca] C187 - some change
running bash test.sh
Test Failed
Bisecting: 5 revisions left to test after this (roughly 3 steps)
[94a263f8e014c54fa4715be10fb09864fb15923e] C181 - some change
running bash test.sh
Test Failed
Bisecting: 2 revisions left to test after this (roughly 2 steps)
[fe6062f2e90be523a920796aa0cb08ea8e2a8f8e] C178 - some change
running bash test.sh
Test Passed
Bisecting: 0 revisions left to test after this (roughly 1 step)
[20d83815050683e8d04eba6dbab60ce0b3b57b59] C180 - some change
running bash test.sh
Test Passed
94a263f8e014c54fa4715be10fb09864fb15923e is the first bad commit   # <-- result found
commit 94a263f8e014c54fa4715be10fb09864fb15923e
Author: Jason Ge <gejun_1978@yahoo.comgc
Date:   Tue Oct 1 16:50:32 2019 +0800

    C181 - some change

    Summary: add one line

    Test: none

:100644 100644 a413ec3d7ad61d11032ea57df7859028c8504c65 0240cded988f3be236923bf104fced2f1143b53b M	inventory.csv
bisect run success

> git bisect reset
Previous HEAD position was 20d8381 C180 - some change
Switched to branch 'master'
Your branch is ahead of 'origin/master' by 104 commits.
  (use "git push" to publish your local commits)

可以看到，git bisect run自动查找到C181是第一个问题提交：

94a263f8e014c54fa4715be10fb09864fb15923e is the first bad commit   # <-- result found
commit 94a263f8e014c54fa4715be10fb09864fb15923e
Author: Jason Ge <gejun_1978@yahoo.comgc
Date:   Tue Oct 1 16:50:32 2019 +0800

    C181 - some change

    Summary: add one line

    Test: none

:100644 100644 a413ec3d7ad61d11032ea57df7859028c8504c65 0240cded988f3be236923bf104fced2f1143b53b M	inventory.csv
bisect run success

Jason Ge 葛俊

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