[PATCH v2 1/1] submodule: fix 'submodule status' when called from a subdirectory

["Manish Goregaokar via GitGitGadget" <gitgitgadget@gmail.com>]

From: Manish Goregaokar <manishsmail@gmail.com>

When calling `git submodule status` while in a subdirectory, we are
incorrectly not detecting modified submodules and
thus reporting that all of the submodules are unchanged.

This is because the submodule helper is calling `diff-index` with the
submodule path assuming the path is relative to the current prefix
directory, however the submodule path used is actually relative to the root.

Always pass NULL as the `prefix` when running diff-files on the
submodule, to make sure the submodule's path is interpreted as relative
to the superproject's repository root.

Signed-off-by: Manish Goregaokar <manishsmail@gmail.com>
---
 builtin/submodule--helper.c |  3 ++-
 t/t7400-submodule-basic.sh  | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 909e77e802..eeea8dfa97 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -802,7 +802,8 @@ static void status_submodule(const char *path, const struct object_id *ce_oid,
 			 path, NULL);
 
 	git_config(git_diff_basic_config, NULL);
-	repo_init_revisions(the_repository, &rev, prefix);
+
+	repo_init_revisions(the_repository, &rev, NULL);
 	rev.abbrev = 0;
 	diff_files_args.argc = setup_revisions(diff_files_args.argc,
 					       diff_files_args.argv,
diff --git a/t/t7400-submodule-basic.sh b/t/t7400-submodule-basic.sh
index a208cb26e1..4545b47ca4 100755
--- a/t/t7400-submodule-basic.sh
+++ b/t/t7400-submodule-basic.sh
@@ -356,6 +356,25 @@ test_expect_success 'status should only print one line' '
 	test_line_count = 1 lines
 '
 
+test_expect_success 'status from subdirectory should have the same SHA1' '
+	test_when_finished "rmdir addtest/subdir" &&
+	(
+		cd addtest &&
+		git status > /tmp/foo &&
+		git submodule status | awk "{print \$1}" >expected &&
+		mkdir subdir &&
+		cd subdir &&
+		git submodule status | awk "{print \$1}" >../actual &&
+		test_cmp ../expected ../actual &&
+		git -C ../submod checkout @^ &&
+		git submodule status | awk "{print \$1}" >../actual2 &&
+		cd .. &&
+		git submodule status | awk "{print \$1}" >expected2 &&
+		test_cmp actual2 expected2 &&
+		test_must_fail test_cmp actual actual2
+	)
+'
+
 test_expect_success 'setup - fetch commit name from submodule' '
 	rev1=$(cd .subrepo && git rev-parse HEAD) &&
 	printf "rev1: %s\n" "$rev1" &&
-- 
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