[PATCH] sequencer.c: set GIT_WORK_TREE in run_git_checkout

[Glen Choo <chooglen@google.com>]

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.

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.

I'm also not sure if this is the idiomatic way to do it since, I assume,
we'd always want to propagate GIT_WORK_TREE, but this is identical to
how do_exec() sets GIT_WORK_TREE in the same file (perhaps this is
something that should be refactored).

[1] https://lore.kernel.org/git/kl6lilu71rzl.fsf@chooglen-macbookpro.roam.corp.google.com

 sequencer.c       |  2 ++
 t/t3400-rebase.sh | 29 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/sequencer.c b/sequencer.c
index 83f257e7fa..e193dcf846 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4233,6 +4233,8 @@ static int run_git_checkout(struct repository *r, struct replay_opts *opts,
 	strvec_push(&cmd.args, "checkout");
 	strvec_push(&cmd.args, commit);
 	strvec_pushf(&cmd.env_array, GIT_REFLOG_ACTION "=%s", action);
+	strvec_pushf(&cmd.env_array, "GIT_WORK_TREE=%s",
+		     absolute_path(get_git_work_tree()));
 
 	if (opts->verbose)
 		ret = run_command(&cmd);
diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index 23dbd3c82e..8b8b66538b 100755
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -416,4 +416,33 @@ test_expect_success MINGW,SYMLINKS_WINDOWS 'rebase when .git/logs is a symlink'
 	mv actual_logs .git/logs
 '
 
+test_expect_success 'rebase when inside worktree subdirectory' '
+	git init main-wt &&
+	(
+		cd main-wt &&
+		git commit --allow-empty -m "initial" &&
+		# create commit with foo/bar/baz
+		mkdir -p foo/bar &&
+		touch foo/bar/baz &&
+		git add foo/bar/baz &&
+		git commit -m "add foo/bar/baz" &&
+		# create commit with a/b/c
+		mkdir -p a/b &&
+		touch a/b/c &&
+		git add a/b/c &&
+		git commit -m "add a/b/c" &&
+		# create another branch for our other worktree
+		git branch other &&
+		git worktree add ../other-wt other &&
+		(
+			cd ../other-wt &&
+			mkdir -p random/dir &&
+			(
+				cd random/dir &&
+				git rebase --onto HEAD^^ HEAD^  # drops the HEAD^ commit
+			)
+		)
+	)
+'
+
 test_done

base-commit: bc3ae46b420f58dfe2bfd87714dca096a043d554
-- 
2.33.GIT