A git pre-commit hook for automatically formatting Go code
One of the (many) wonderful things about the Go programming language is the gofmt
tool, which formats your source in a canonical way. I thought it would be nice to integrate this in my git
workflow by adding it in a pre-commit hook to automatically format my source code when I committed it.
The Go distribution contains a git pre-commit hook that checks whether the source code is formatted, and aborts the commit if it isn’t. I don’t remember if I was aware of this at the time (or if it even existed at the time, or if it is new), but I wanted it to go ahead and format the code for me.
I found a few solutions online, but they were all missing something—support for partial commits. I frequently use git add -p
/git gui
to commit a subset of the changes I’ve made to a file, the existing solutions would end up adding the entire set of changes to my commit.
I ended up writing a solution that only formats the version of the that is staged for commit; here’s my .git/hooks/pre-commit
:
#!/bin/bash
# This would only loop over files that are already staged for commit.
# git diff --cached --numstat |
# while read add del file; do
# …
# done
shopt -s globstar
for file in **/*.go; do
tmp="$(mktemp "$file.bak.XXXXXXXXXX")"
mv "$file" "$tmp"
git checkout "$file"
gofmt -w "$file"
git add "$file"
mv "$tmp" "$file"
done
It’s still not perfect. It will try to operate on every *.go
file—which might do weird things if you have a file that hasn’t been checked in at all. This also has the effect of formatting files that were checked in without being formatted, but weren’t modified in this commit.
I don’t remember why I did that—as you can see from the comment, I knew how to only select files that were staged for commit. I haven’t worked on any projects in Go in a while—if I return to one of them, and remember why I did that, I will update this page.