[PATCH 1/2] worktree setup: return to original cwd if prefix is set NULL

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Commit a672ea6 (rehabilitate 'git index-pack' inside the object
store - 2008-10-20) worked around a fault in
setup_git_directory_gently(). When walking up from inside a git
repository, we will return NULL as prefix.

Prefix and cwd should be consistent. That is if cwd is moved, prefix
reflects that. If prefix is NULL, cwd is unmoved. In this case, to
retain current behavior, we move cwd back, with an eye on gitdir
because gitdir may be relative to cwd.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 setup.c             |    7 +++++++
 t/t1501-worktree.sh |   21 +++++++++++++++++++++
 2 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/setup.c b/setup.c
index 87c21f0..33eb253 100644
--- a/setup.c
+++ b/setup.c
@@ -413,6 +413,13 @@ const char *setup_git_directory_gently(int *nongit_ok)
 			if (!work_tree_env)
 				inside_work_tree = 0;
 			if (offset != len) {
+				/*
+				 * The returned prefix in this code path is NULL
+				 * chdir() back to match NULL prefix, i.e. unmoved cwd
+				 */
+				if (chdir(cwd))
+					die_errno("Cannot come back to cwd");
+
 				root_len = offset_1st_component(cwd);
 				cwd[offset > root_len ? offset : root_len] = '\0';
 				set_git_dir(cwd);
diff --git a/t/t1501-worktree.sh b/t/t1501-worktree.sh
index bd8b607..edd81ce 100755
--- a/t/t1501-worktree.sh
+++ b/t/t1501-worktree.sh
@@ -33,6 +33,27 @@ mkdir -p work/sub/dir || exit 1
 mkdir -p work2 || exit 1
 mv .git repo.git || exit 1
 
+cat >repo.git/objects/patch <<\EOF
+diff one one
+--- one
++++ one
+@@ -1 +1,2 @@
+ 1
++2
+EOF
+
+test_expect_success 'cwd is unchanged when prefix is NULL (from within a repo)' '
+	(
+		cd repo.git/objects &&
+		echo 1 > one &&
+		cp one expected &&
+		echo 2 >> expected &&
+		git apply patch &&
+		test_cmp expected one &&
+		rm one expected patch
+	)
+'
+
 say "core.worktree = relative path"
 GIT_DIR=repo.git
 GIT_CONFIG="$(pwd)"/$GIT_DIR/config
-- 
1.7.1.rc1.69.g24c2f7