[PATCH v2 2/2] ls-files: fix path used when recursing into submodules

[Jacob Keller <jacob.e.keller@intel.com>]

From: Jacob Keller <jacob.keller@gmail.com>

Don't assume that the current working directory is the root of the
repository. Correctly generate the path for the recursing child
processes by building it from the work_tree() root instead. Otherwise if
we run ls-files using --git-dir or --work-tree it will not work
correctly as it attempts to change directory into a potentially invalid
location. Best case, it doesn't exist and we produce an error. Worst
case we cd into the wrong location and unknown behavior occurs.

Add a new test which highlights this possibility.

Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
---
I'm not sure that I'm convinced by this method of solving the problem as
I suspect it has some corner cases (what about when run inside a
subdirectory? It seems to work for me but I'm not sure...) Additionally,
it felt weird that there's no helper function for creating a toplevel
relative path.

 builtin/ls-files.c                     |  5 ++++-
 t/t3007-ls-files-recurse-submodules.sh | 11 +++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/builtin/ls-files.c b/builtin/ls-files.c
index e9b3546ca053..a6c70dbe9ec8 100644
--- a/builtin/ls-files.c
+++ b/builtin/ls-files.c
@@ -203,6 +203,7 @@ static void show_gitlink(const struct cache_entry *ce)
 {
 	struct child_process cp = CHILD_PROCESS_INIT;
 	int status;
+	char *dir;
 
 	prepare_submodule_repo_env(&cp.env_array);
 	argv_array_push(&cp.env_array, GIT_DIR_ENVIRONMENT);
@@ -221,8 +222,10 @@ static void show_gitlink(const struct cache_entry *ce)
 	argv_array_pushv(&cp.args, submodule_options.argv);
 
 	cp.git_cmd = 1;
-	cp.dir = ce->name;
+	dir = mkpathdup("%s/%s", get_git_work_tree(), ce->name);
+	cp.dir = dir;
 	status = run_command(&cp);
+	free(dir);
 	if (status)
 		exit(status);
 }
diff --git a/t/t3007-ls-files-recurse-submodules.sh b/t/t3007-ls-files-recurse-submodules.sh
index c8030dd3299a..ebb956fd16cc 100755
--- a/t/t3007-ls-files-recurse-submodules.sh
+++ b/t/t3007-ls-files-recurse-submodules.sh
@@ -82,6 +82,17 @@ test_expect_success 'ls-files recurses more than 1 level' '
 	test_cmp expect actual
 '
 
+test_expect_success 'ls-files works with GIT_DIR' '
+	cat >expect <<-\EOF &&
+	.gitmodules
+	c
+	subsub/d
+	EOF
+
+	git --git-dir=submodule/.git ls-files --recurse-submodules >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success '--recurse-submodules and pathspecs setup' '
 	echo e >submodule/subsub/e.txt &&
 	git -C submodule/subsub add e.txt &&
-- 
2.12.2.776.gded3dc243c29.dirty