Re: [PATCH] githooks: discuss Git operations in foreign repositories

>
> From: Eric Sunshine <sunshine@sunshineco.com>
>
> Hook authors are periodically caught off-guard by difficult-to-diagnose
> errors when their hook invokes Git commands in a repository other than
> the local one. In particular, Git environment variables, such as GIT_DIR
> and GIT_WORK_TREE, which reference the local repository cause the Git
> commands to operate on the local repository rather than on the
> repository which the author intended. This is true whether the
> environment variables have been set manually by the user or
> automatically by Git itself. The same problem crops up when a hook
> invokes Git commands in a different worktree of the same repository, as
> well.
>
> Recommended best-practice[1,2,3,4,5,6] for avoiding this problem is for
> the hook to ensure that Git variables are unset before invoking Git
> commands in foreign repositories or other worktrees:
>
>     unset $(git rev-parse --local-env-vars)
>
> However, this advice is not documented anywhere. Rectify this
> shortcoming by mentioning it in githooks.txt documentation.
>
> [1]: https://lore.kernel.org/git/YFuHd1MMlJAvtdzb@coredump.intra.peff.net/
> [2]: https://lore.kernel.org/git/20200228190218.GC1408759@coredump.intra.peff.net/
> [3]: https://lore.kernel.org/git/20190516221702.GA11784@sigill.intra.peff.net/
> [4]: https://lore.kernel.org/git/20190422162127.GC9680@sigill.intra.peff.net/
> [5]: https://lore.kernel.org/git/20180716183942.GB22298@sigill.intra.peff.net/
> [6]: https://lore.kernel.org/git/20150203163235.GA9325@peff.net/
>
> Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
> ---
>     githooks: discuss Git operations in foreign repositories
>
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1457%2Fsunshineco%2Fhookenv-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1457/sunshineco/hookenv-v1
> Pull-Request: https://github.com/gitgitgadget/git/pull/1457
>
>  Documentation/githooks.txt | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt
> index a16e62bc8c8..6e9a5420b7c 100644
> --- a/Documentation/githooks.txt
> +++ b/Documentation/githooks.txt
> @@ -31,6 +31,17 @@ Hooks can get their arguments via the environment, command-line
>  arguments, and stdin. See the documentation for each hook below for
>  details.
>
> +If your hook needs to invoke Git commands in a foreign repository or in a
> +different working tree of the same repository, then it should clear local Git
> +environment variables, such as `GIT_DIR`, `GIT_WORK_TREE`, etc., which could
> +interfere with Git operations in the foreign repository since those variables
> +will be referencing the local repository and working tree. For example:
> +
> +------------
> +local_desc=$(git describe)
> +foreign_desc=$(unset $(git rev-parse --local-env-vars); git -C ../foreign-repo describe)
> +------------
> +
>  `git init` may copy hooks to the new repository, depending on its
>  configuration. See the "TEMPLATE DIRECTORY" section in
>  linkgit:git-init[1] for details. When the rest of this document refers
>
> base-commit: a38d39a4c50d1275833aba54c4dbdfce9e2e9ca1
> --
> gitgitgadget