Re: [PATCH] sequencer.c: set GIT_WORK_TREE in run_git_checkout

> On Tue, Jan 25, 2022 at 3:36 PM Glen Choo <chooglen@google.com> wrote:
>>
>> When rebasing in a subdirectory of a worktree, Git fails due to a dirty
>> worktree:
>>
>>   error: The following untracked working tree files would be overwritten
>> by merge:
>>           a/b/c
>>   Please move or remove them before you merge.
>>
>> This occurs because "git rebase" invokes a "git checkout" without
>> propagating the GIT_WORK_TREE environment variable, causing the worktree
>> to be assumed to be ".". This was not an issue until bc3ae46b42 (rebase:
>> do not attempt to remove startup_info->original_cwd, 2021-12-09), when
>> the .dir of the "git checkout" child process was changed such that it no
>> longer runs at the root of the worktree.
>>
>> Propagate GIT_WORK_TREE to the "git checkout" child process and test
>> that rebase in a subdirectory of a worktree succeeds.
>
> This is correct, but leaves the reader wondering why the failure to
> set GIT_WORK_TREE fails when in a non-primary worktree, but does not
> fail in the primary working tree.

> Here's how I described it in the patch I was about to send to the list:
>
> """
> In commit bc3ae46 ("rebase: do not attempt to remove
> startup_info->original_cwd", 2021-12-09), we wanted to allow the
> checkout subprocess to know which directory the parent process was
> running from, so that the subprocess could protect it.  However...
>
> When run from a non-main worktree, setup_git_directory() will note
> that the discovered git directory
> (/PATH/TO/.git/worktree/non-main-worktree) does not match
> DEFAULT_GIT_DIR_ENVIRONMENT (see setup_discovered_git_dir()), and
> decide to set GIT_DIR in the environment.  This matters because...
>
> Whenever git is run with the GIT_DIR environment variable set, and
> GIT_WORK_TREE not set, it presumes that '.' is the working tree.  So...
>
> This combination results in rebase failing when run from a subdirectory
> of a non-main worktree.  Fix it by also setting the GIT_WORK_TREE
> environment variable along with setting cmd.dir.
>
> A possibly more involved fix we could consider for later would be to
> make setup.c set GIT_WORK_TREE whenever (a) it discovers both the git
> directory and the working tree and (b) it decides to set GIT_DIR in the
> environment.  I did not attempt that here as such would be too big of a
> change for a 2.35.1 release.
> """
>
> (Another fix would also be making sequencer stop forking a "git
> checkout" subprocess; it should be able to call a library function,
> and then quit dropping and re-reading the index.  But that's also a
> much bigger change...)
>
>> Signed-off-by: Glen Choo <chooglen@google.com>
>> ---
>> Here is a fix for the bug I found in [1]. I didn't look through the rest
>> of the "preserve cwd" thread for other possible bugs pertaining to
>> worktrees, but I didn't find any during a cursory glance at sequencer.c.
>
> We'll need the same fix for stash due to 0fce211ccc ("stash: do not
> attempt to remove startup_info->original_cwd", 2021-12-09) -- in that
> case, though, it's calling git-clean rather than git-checkout.  But
> the same idea.