$1 necessity in commit-msg hook

[privatenumber]

In the docs, using $1 is recommended for the commit-msg hook. I'm curious if passing in $1 is actually necessary here:

npx --no-install commitlint --edit $1

Upon testing, $1 always seems to evaluate to .git/COMMIT_EDITMSG (which is also the default value for commitlint -e). Although I have read sources that say $1 evaluates to the commit message itself (rather than a file path containing it), I have not found that to be the case, which I confirmed with the Git hooks docs:

It takes a single parameter, the name of the file that holds the proposed commit log message.

Is there an edge case where $1 evaluates to a different path that this is trying to handle? Or can it be safely omitted?

[privatenumber]

@typicode

Pinging you in case you missed this.

[typicode]

Hi @privatenumber,

Sorry I don't know. Maybe if you're using Git submodule, path may be different.

In any case, I think I'd stay safe and follow Git hooks docs to avoid any edge case.

[privatenumber]

I investigated in the git source code and it seems like $1 always ends with /COMMIT_EDITMSG.

The .git directory can be configured so the directory path may be different. I haven't worked with submodules enough but perhaps this is can be different for submodules too, as you speculate.

Anyway, it should be safe to assume .git/COMMIT_EDITMSG as long as you're not changing the .git directory.

Investigation

1. The commit-msg commit hook is called here with argument git_path_commit_editmsg():
   https://github.com/git/git/blob/715d08a9e51251ad8290b181b6ac3b9e1f9719d7/builtin/commit.c#L1088

2. git_path_commit_editmsg is defined using GIT_PATH_FUNC here:
   https://github.com/git/git/blob/715d08a9e51251ad8290b181b6ac3b9e1f9719d7/sequencer.c#L44

3. GIT_PATH_FUNC is defined here:
   https://github.com/git/git/blob/715d08a9e51251ad8290b181b6ac3b9e1f9719d7/path.h#L155-L162

4. Since COMMIT_EDITMSG is hard-coded to git_path_commit_editmsg(), it seems $1 will always be $GIT_DIR/COMMIT_EDITMSG where $GIT_DIR can be configured.

[typicode]

Thanks for the very detailed research 👍