Git Bisect: Only the Current Branch
Las cadenas se cortan por el eslabón mas débil / Chains break by the weakest link by hernanpba is licensed under CC BY-SA
Git Bisect’s Usefulness
Imagine that at some point you’ve discovered that a bug/failure is present and you aren’t exactly sure when it was introduced. This is when git bisect comes into the picture. With a little bit of setup, it helps binary search through changes to uncover the commit that introduced the issue.
There are a bunch of tips/tricks and usages of git bisect, but I’ll leave that to the official documentation and possibly future posts (it is a very useful tool to be familiar with).
Working on a Feature Branch
I almost always make changes using feature branches (i.e., branching off of main and eventually merging the branch back into main). In projects that have large test suites (where you wouldn’t want to run the whole thing frequently), I only run the tests of files I’m working in. There is a small chance that I might break something in a part of the codebase that I wasn’t running the tests for, but it can happen. I tend to commit often while working, so to figure out what broke, I have to find which commit is responsible for the issue.
Manual Way
The following is how I would approach this using git bisect. The general idea is to only bisect the commits that exist on the feature branch.
# While on the feature branch that I've been working on
# Start bisect
git bisect start
# Find SHA of where the branch diverged from main
# Mark that commit as 'good', as everything prior would have been okay
git bisect good <branching-sha>
# Mark the current branch's SHA as 'bad' since something is broken now
git bisect bad HEAD
# Run the script/test command to bisect and find the error commit
git bisect run <script/test-command>
When I’m done inspecting the identified commit, then I can git bisect reset.
Automated Way
I’ve made a script that ends up automating the commands and the finding of the SHA. This makes it so I can use a single command and achieve the same results as the manual way:
# While on the feature branch that I've been working on
# Use bisect-branch passing the target branch I diverged from and the
# script/test command to bisect and find the error commit
git bisect-branch -b main <script/test-command>
When I’m done inspecting the identified commit, then I can git bisect reset.
The git-bisect-branch Script
This GitHub Gist will be the canonical reference of the git-branch-bisect script (and will see updates as needed).
#!/usr/bin/env bash
while getopts 'b:dh' OPTION; do
case "$OPTION" in
b)
divergent_branch=$OPTARG
;;
d)
debug=true
;;
h)
echo "This is a script that performs a git-bisect over all commits from the current branch's HEAD to where the branch diverged from the supplied branch."
echo ""
echo "script usage: git-bisect-branch [-b branch] [-d] [-h] run_command" >&2
echo ""
echo "example: git-bisect-branch -d -b main ruby test.rb"
echo ""
echo "Arguments:"
echo " - Use '-b' to specify the branch from which your current branch has diverged, this should typically be 'main'/'master'."
echo " - Use '-d' to debug internal variables and see the verbose output of git commands."
echo " - Use '-h' to see this message."
echo " - The remainder of the command is interpreted as the run_command, that will be running at each bisect step."
echo ""
echo "If this script is on your PATH, you will be able to use it like 'git bisect-branch'."
echo ""
exit 1
;;
esac
done
shift "$(($OPTIND -1))"
run_command=$*
current_branch=$(git branch --show-current)
current_branch_sha=$(git rev-parse HEAD)
if [ -z "$divergent_branch" ]
then
echo "No branch argument supplied. Should be the 'main/master' branch name"
exit
fi
if [ -z "$run_command" ]
then
echo "No run_command argument supplied. Should be the command you will use to run tests for each bisect step"
exit
fi
branching_sha=$(git merge-base $divergent_branch $current_branch)
echo "Starting bisect of commits on '$current_branch' branch ($current_branch_sha) since branching from '$divergent_branch' branch ($branching_sha)"
print_hline () {
printf '%.s─' $(seq 1 $(tput cols))
}
if [ -n "$debug" ]
then
print_hline
echo "run_command: $run_command"
echo "current_branch: $current_branch"
echo "current_branch_sha: $current_branch_sha"
echo "divergent_branch: $divergent_branch"
echo "branching_sha: $branching_sha"
print_hline
git bisect start
git bisect good $branching_sha
git bisect bad $current_branch_sha
git bisect run $run_command
echo ""
print_hline
else
git bisect start > /dev/null
git bisect good $branching_sha > /dev/null
git bisect bad $current_branch_sha > /dev/null
git bisect run $run_command > /dev/null
fi
echo "Don't forget to 'git bisect reset'"