Resolve worktree .git files to repository .git directory

[jkylling]

Context

Fix #639
I have not tested this change end to end.

Contributor Checklist

• Added relevant integration or unit tests to verify the changes
• Update the Readme or any other documentation (including relevant Javadoc)
• Ensured that tests pass locally: mvn clean package
• Ensured that the code meets the current checkstyle coding style definition: mvn clean verify -Pcheckstyle -Dmaven.test.skip=true -B

[xkrogen]

Thanks for the investigation @jkylling ! Not the most elegant fix, but practical and does seem to solve the issue

[TheSnoozer]

Do you have better suggestions @xkrogen?

[xkrogen]

I took a quick read through the Details section for git-worktree and the worktree-related stuff in gitrepository-layout. It seems like this should work if we assume the GIT_DIR and GIT_COMMON_DIR environment variables aren't set. Not sure if we should consider them here?

There is also the potential situation where .git is a text file containing a gitpath spec, instead of a directory. Also not sure if git-commit-id handles this situation generally; if so, should we also handle that here?

[jkylling]

@TheSnoozer I've gone through the contributor checklist and fixed the check style violations. Do you think we should merge this?

[TheSnoozer]

Thanks again for your contribution! Merged now.

[xkrogen]

Hey @TheSnoozer just curious when you expect this to go into a release? I'm not familiar with the release lifecycle of this project, just wondering when I'll be able to adopt it downstream.

Big thanks to both of you btw :)

[TheSnoozer]

The release cycle is to wait until someone mentions they want a release ;-)

Will do that as soon as I have time (sorry this project is still only my free time) :-)

[TheSnoozer]

Released now as 7.0.0 via #623.

[xkrogen]

Heh awesome ... Thanks so much @TheSnoozer !