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
#!/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.