exclude Jest snapshots from git whitespace check

Question

I am trimming whitespace from git commits using git diff-index --check --cached HEAD --. I want to add Jest tests using snapshots, but the snapshot files include whitespace and my tests will always fail if I remove it. So I want to exclude the *.js.snap files from the whitespace check. How do I tell git to exclude *.js.snap (or, alternatively, **/__snapshots/*) files from git diff-index? I'm using bash on OSX.

In the meantime, I'm working around the problem by changing my commit hook to be interactive:

# If there are whitespace errors, print the offending file names and fail.
git diff-index --check --cached HEAD --
if [ $? -ne 0 ]; then
    # Allows us to read user input below, assigns stdin to keyboard
    exec < /dev/tty

    while true; do
        echo "Your commit introduces trailing whitespace.  Are you sure you want to commit? y/n"
        read yn
        case $yn in
            y ) exit 0;;
            n ) exit 1;;
        esac
    done
fi

Answer 1

Git does have a way of specifying paths to exclude, though it's poorly documented and apparently not very well known. It's known as pathspec, and in this case can be used as follows:

git diff-index --check --cached HEAD -- ':!*.js.snap' .

where : is the special character that specifies that the pathspec is not just a regular path, and '!' specifies that files matching the rest of the path should be excluded from the list of matches.

Not as straightforward as Mercurial's -X or --exclude, but it's there.

Answer 2

As mentioned here, the path argument of git diff-index is of glob-style pattern, interpreted by the shell.

So this is more a shell issue than a git command problem.

See for instance "How can I use inverse or negative wildcards when pattern matching in a unix/linux shell?"

You can either try and activate shopt extglob, or (simpler), do a post-step to your script, looking (with git status) for any modified files with **/__snapshots/* in their full pathname, and cancelling their modification (git checkout).