Re: Git clone fails during pre-commit hook due to GIT_WORK_TREE=. (regression 2.5 -> 2.6)

[Stefan Beller <sbeller@google.com>]

+to Nguyễn Thái Ngọc Duy <pclouds@gmail.com>

On Mon, Nov 23, 2015 at 6:22 PM, Anthony Sottile <asottile@umich.edu> wrote:
> * Short description of the problem *
>
> It seems GIT_WORK_DIR is now exported invariantly when calling git
> hooks such as pre-commit.  If these hooks involve cloning repositories
> they will not fail due to this exported environment variable.  This
> was not the case in prior versions (such as v2.5.0).
>
> * Simple reproduction *
>
> ```
> $ cat test.sh
> #!/usr/bin/env bash
> set -ex
>
> rm -rf test
>
> # Exit non {0, 1} to abort git bisect
> make -j 8 > /dev/null || exit 2
>
> # Put our new git on the path
> PATH="$(pwd):$PATH"
>
> git init test
>
> pushd test
> mkdir -p .git/hooks
> echo 'git clone git://github.com/asottile/css-explore css-explore' >
> .git/hooks/pre-commit
> chmod 755 .git/hooks/pre-commit
>
> git commit -m foo --allow-empty || exit 1
> ```
>
> * Under 2.6.3 *
>
> ```
> $ ./test.sh
>
> ...
>
> + git init test
> warning: templates not found /home/anthony/share/git-core/templates
> Initialized empty Git repository in /home/anthony/workspace/git/test/.git/
> + pushd test
> ~/workspace/git/test ~/workspace/git
> + mkdir -p .git/hooks
> + echo 'git clone git://github.com/asottile/css-explore css-explore'
> + chmod 755 .git/hooks/pre-commit
> + git commit -m foo --allow-empty
> fatal: working tree '.' already exists.
> + exit 1
> ```
>
> * Under 2.5 *
>
> ```
> $ ./test.sh
>
> ...
>
> + git init test
> warning: templates not found /home/anthony/share/git-core/templates
> Initialized empty Git repository in /home/anthony/workspace/git/test/.git/
> + pushd test
> ~/workspace/git/test ~/workspace/git
> + mkdir -p .git/hooks
> + echo 'git clone git://github.com/asottile/css-explore css-explore'
> + chmod 755 .git/hooks/pre-commit
> + git commit -m foo --allow-empty
> Cloning into 'css-explore'...
> warning: templates not found /home/anthony/share/git-core/templates
> remote: Counting objects: 214, done.
> remote: Total 214 (delta 0), reused 0 (delta 0), pack-reused 214
> Receiving objects: 100% (214/214), 25.89 KiB | 0 bytes/s, done.
> Resolving deltas: 100% (129/129), done.
> Checking connectivity... done.
> [master (root-commit) 5eb999d] foo
> ```
>
>
> * Bisect *
>
> ```
> $ git bisect good v2.5.0
> $ git bisect bad origin/master
> $ git bisect run ./test.sh
>
> ...
>
> d95138e695d99d32dcad528a2a7974f434c51e79 is the first bad commit
> commit d95138e695d99d32dcad528a2a7974f434c51e79
> Author: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
> Date:   Fri Jun 26 17:37:35 2015 +0700
>
>     setup: set env $GIT_WORK_TREE when work tree is set, like $GIT_DIR
>
>     In the test case, we run setup_git_dir_gently() the first time to read
>     $GIT_DIR/config so that we can resolve aliases. We'll enter
>     setup_discovered_git_dir() and may or may not call set_git_dir() near
>     the end of the function, depending on whether the detected git dir is
>     ".git" or not. This set_git_dir() will set env var $GIT_DIR.
>
>     For normal repo, git dir detected via setup_discovered_git_dir() will be
>     ".git", and set_git_dir() is not called. If .git file is used however,
>     the git dir can't be ".git" and set_git_dir() is called and $GIT_DIR
>     set. This is the key of this problem.
>
>     If we expand an alias (or autocorrect command names), then
>     setup_git_dir_gently() is run the second time. If $GIT_DIR is not set in
>     the first run, we run the same setup_discovered_git_dir() as before.
>     Nothing to see. If it is, however, we'll enter setup_explicit_git_dir()
>     this time.
>
>     This is where the "fun" is.  If $GIT_WORK_TREE is not set but
>     $GIT_DIR is, you are supposed to be at the root level of the
>     worktree.  But if you are in a subdir "foo/bar" (real worktree's top
>     is "foo"), this rule bites you: your detected worktree is now
>     "foo/bar", even though the first run correctly detected worktree as
>     "foo". You get "internal error: work tree has already been set" as a
>     result.
>
>     Bottom line is, when $GIT_DIR is set, $GIT_WORK_TREE should be set too
>     unless there's no work tree. But setting $GIT_WORK_TREE inside
>     set_git_dir() may backfire. We don't know at that point if work tree is
>     already configured by the caller. So set it when work tree is
>     detected. It does not harm if $GIT_WORK_TREE is set while $GIT_DIR is
>     not.
>
>     Reported-by: Bjørnar Snoksrud <snoksrud@gmail.com>
>     Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
>     Signed-off-by: Junio C Hamano <gitster@pobox.com>
>
> :100644 100644 9daa0ba4a36ced9f63541203e7bcc2ab9e1eae56
> 36fbba57fc83afd36d99bf5d4f3a1fc3feefba09 M    environment.c
> :040000 040000 1d7c4bf77e0fd49ca315271993cb69a8b055c3aa
> 145d85895cb6cb0810597e1854a7721ccfc8f457 M    t
> bisect run success
> ```
>
> Causing me a few headaches in
> https://github.com/pre-commit/pre-commit/issues/300
> I'm working around it in https://github.com/pre-commit/pre-commit/pull/301
>
> Thanks,
>
> Anthony
> --
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