Re: In some rebases, `exec git -C ...` has wrong working directory

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

Hi William,

On Thu, 26 Apr 2018, William Chargin wrote:

> Here is a repro script:
> 
>     #!/bin/sh
>     set -eux
>     git --version
>     tmpdir="$(mktemp -d)"
>     cd "${tmpdir}"
>     mkdir target repo
>     cd repo
>     git init
>     touch file; git add file
>     git commit -m "Initial commit"
>     git rebase HEAD --exec "git -C ${tmpdir}/target init"

We do take pains to pass the GIT_DIR to the exec'ed command, and it is the
GIT_DIR of the worktree in which the rebase runs.

> The end of this script prints something like
> 
>     Executing: git -C /tmp/tmp.gd2q51jO93/target init
>     Reinitialized existing Git repository in /tmp/tmp.gd2q51jO93/repo/.git/
>     Successfully rebased and updated refs/heads/master.

So that is actually what I expected.

I might even have one or two scripts relying on that feature, where
something like

	exec git -C /somewhere/else show HEAD:some-file >some-other-file

is executed, and works.

> But this is wrong: the repository should be initialized in `target`, not
> reinitialized in `repo`.
> 
> Notes:
> 
>   - This propagates to subprocesses: if you run `exec make test` and
>     your test suite ends up calling `git -C`, then the same problem
>     occurs.
> 
>   - Substituting `rebase --root` for `rebase HEAD` causes the problem to
>     go away.
> 
>   - The `rebase HEAD` exec context adds the `GIT_DIR` environment
>     variable, and this is sufficient to reproduce the problem:
>     running `GIT_DIR="$PWD" git -C /tmp/target init` puts the repo in
>     the current working directory. The `rebase --root` context adds no
>     such environment variable. (You can use `--exec 'env >tempfile'` to
>     verify these.)
> 
> My `git --version` is 2.16.2.

Even `pu` has the same behavior.

I do not think that we can sensibly *remove* GIT_DIR from the environment
variables passed to the exec'ed command, as we have been doing that for
ages, and some scripts (as demonstrated above) started relying on that
behavior. So if we changed it, we would break backwards-compatibility,
which is something we try to avoid very much in Git.

Maybe you could a contribute a patch to the documentation? Something that
tells people who use the `--exec` option that they want to prefix their
command with `unset GIT_DIR; ` when their command wants to work with a
different Git repository than the current one?

Ciao,
Johannes