How to get list of all changed files or current working directory in hook or run hook in current working directory

[jremus]

I am working on custom Git prepare-commit-msg and commit-msg hook scripts that both need to process the complete list of changed files. This must work for commit, amend, and reword and for both prepare-commit-msg and commit-msg hooks.

I am facing the following issues:

• git diff --staged --name-only returns the list of changed files only for "normal" commits. For amend it returns only the additional changed files. For reword it returns nothing.
• git diff-tree --no-commit-id --name-only -r $SHA1 returns only the list of changed files of an existing commit. This would allow to collect existing changes during amend in a prepare-commit-msg hook. But due to the lack of a SHA1 it does not work in a commit-msg hook.

Therefore I have resorted to parsing the comments about changed files generated by Git into the commit message. This works well when invoking Git from the toplevel directory of the working tree. When invoking Git from a subdirectory the paths of the changed files in the comments are relative to the current working directory.

In theory it would be easy to convert those paths relative to the current working directory back to paths relative to the toplevel directory of the working tree:

GIT_TOPLEVEL="$(git rev-parse --show-toplevel 2>/dev/null)"
...
file="$(realpath --relative-to="$GIT_TOPLEVEL" "$file")"

But Lefthook apparently invokes Git hook scripts from the toplevel directory of the working tree. Therefore I don't have access to the current working directory the user invoked Git in from within my hook script.

I tried to get Lefthook to execute my hook from the current working directory without success:

prepare-commit-msg:
  commands:
    myhook:
      #root: "$."
      #root: "$(pwd)"
      #root: "$(realpath --relative-to=$(git rev-parse --show-toplevel) $(pwd))"
      run: .lefthook/prepare-commit-msg/myhook.sh {0}
  scripts:
    "myhook.sh":
      runner: bash
      skip: true

To resolve my issue I either need a mean to:

• get the complete list of changes files using some Git command,
• get the current working directory the user invoked Git from within my hook script, or
• have Lefthook invoke my hook script from the current working directory instead of the toplevel directory of the working tree.

Thanks in advance!

[mrexox]

Hey! That's a good question. Lefthook always sets the git root as a root for all subcommands. This is crucial because it souldn't matter what folder you are running git commit from – the commands should behave the same way. I'm afraid that the only way to change this behavior would be providing the ENV variable with explicit folder location.

Why is it important to run git from within different folders? Are you trying to partially commit each folder? I'm just curious. I'd be glad to know more about your use case.

[jremus]

My usecase is to generate (in prepare-commit-msg) template and later validate (in commit-msg) fortunately slowly becoming extinct GNU Changelog entries for every changed file into the Git commit message.

As a developer I would like to be able to run Git commands from any subfolder of my Git working tree. For the time being I can certainly work around the issue by forcing myself to run them from the toplevel directory.

Note that the Git hook manager overcommit has implemented logic to determine the full list of changed files for pre-commit hooks (see sds/overcommit#146 for details and motivation). So there may be a use case for pre-commit hooks too, possibly also extending Lefthook likewise. Not sure about the later though, as I think their logic to detect amend is rather fragile.

It is sad that Git apparently does not provide a programatic mean to obtain the full list of changed files (as produced by Git in the commit message comments) from within any hook where that could matter.

May I suggest to use "PREFIX" in the name, if you considder to implement an ENV variable,? That would use Git terminology (see man git rev-parse | less -p --prefix). Another option would be to make it configurable from the Lefthook configuration per command/script, whether it should be run from the toplevel (default) or current working directory (e.g. run_in_toplevel: false).