Spurious GIT_DIR set when in a worktree [was Re: Nested submodule status bug]

[Damien Robert <damien.olivier.robert@gmail.com>]

> Ok, so using GIT_TRACE and GIT_TRACE_STATUS and doing some debugging I
> understand the cause of the bug. When using the alias,
> the GIT_DIR environment is set to the bar module:
>     GIT_DIR=/tmp/test/foo/.git/modules/bar
> and is exported.
> 
> That's explain why in `baz` the status report the status of the `bar`
> directory.

And looking at setup.c:760 it appears that `set_git_dir` (which set up among
other things the GIT_DIR env) is called because we are in a worktree.

More precisely: we have discovered a git dir (a git file), so we call
setup_discovered_git_dir, which itself calls setup_explicit_git_dir because
we are in a work tree environment. And set_up_explicit_git_dir calls
set_git_dir.


So I don't know what's the proper way to fix this. Keep track when we add
ourselves the GIT_DIR rather than when it is already provided and remove it
before executing a shell alias? Don't run the full configuration setup when
we are executing a shell alias anyway?

I am adding Nguyễn Thái Ngọc Duy to the discussion (I hope this is the
proper etiquette).

Best regards,
Damien