"not a git repository" when running pre-commit hook on older git client

[rogalski]

This bug is based on my experiments with darker on closed-source repo.
I am not at liberty to disclose any code. We'll have to work on recreating failure criteria on our own.

Steps to reproduce:

1. Use darker as pre-commit hook with older Git (e.g. Git 2.7.x on Ubuntu 16.04 LTS)
2. Modify python file stored in subdirectory of repository, e.g. /repository/subdir/file.py
3. Run darker in pre-commit hook, e.g. using pre-commit.

What happens:

1. Common root is resolved to /repository/subdir, not /repository
2. Unfortunately, older Git client runs hook with GIT_DIR=.git environment variable
3. This environment variable disables traversal in search for actual .git directory
4. Git expects (due to cwd and env vars) that repo is in /repository/subdirectory/.git, not /repository/.git
5. Darker crashes with not a repository error.

Possible fixes:

1. Leave as it is (treat old Git client as unsupported)
2. Drop GIT_DIR from our git subprocess invocations
3. Run traversal manually to always use repository top-level dir as cwd

[akaihola]

Thanks @rogalski, that's very informative! This may be a duplicate of issue #112.

Could you try upgrading darker to master in your .pre-commit.yaml

- repo: https://github.com/akaihola/darker
  rev: master

to see whether #185 fixed this (included in the soon-to-be-released 1.3.1 version) as an unintended side effect?

(The original intention of #185 was to just add a fixed locale to Git invocations, but it turned out all other environment variables were removed, too.)

[akaihola]

Ping @rogalski, could you try if #203 is solved already in master?

[akaihola]

@rogalski, does version 1.3.2 solve this problem?

[akaihola]

I tried to reproduce the original /repository/subdir/file.py example in an Ubuntu 16.04 Docker image by installing Python 3.6 from the deadsnakes repository and then pip installing pre-commit.

Unfortunately I couldn't get the not a repository error with any version of Darker.

I'm closing this issue – @rogalski please submit it again with step-by-step instructions for reproducing the problem if the latest Darker version still vails.