Re: git aliases and GIT_PREFIX

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Federico,

On Thu, 28 Oct 2021, Federico Kircheis wrote:

> today I reported what I believed to be a bug on
>
>  https://github.com/git-for-windows/git/issues/3496
>
> and learned about GIT_DIR when working with aliases and git worktree.
>
> It's annoying that GIT_DIR it is defined only if (as far as I've understood)
> working from a worktrees or submodule, as it does not seem to be related to
> those type of repositories.

To clarify: `GIT_DIR` is set when executing an alias in a worktree other
than the primary one (and probably also in submodules), but not when
executing in a primary worktree.

> This is also irritating because apparently working aliases breaks when being
> executed from those repositories.

To clarify: an alias that wants to switch to a different repository and
execute Git commands there works well in a primary worktree. But when you
switch to a different repository while executing an alias from a secondary
worktree, it will fail because of `GIT_DIR` having been set.

> I believe it would be better if GIT_DIR it's either always set or never
> (could someone enlighten me why the variable is needed in first place?).

The fact that `GIT_DIR` is not set when calling an alias in a primary
worktree suggests that the behavior in secondary worktrees is not by
design. We should therefore be able to stop setting it there.

The question is: what code is responsible for setting it only in some
circumstances but not others?

Federico, do you have any experience in debugging C code? If so, it would
be good if you could take a crack at investigating this.

Ciao,
Johannes