[PATCH] submodule.c: report the submodule that an error occurs in

[Stefan Beller <sbeller@google.com>]

When an error occurs in updating the working tree of a submodule in
submodule_move_head, tell the user which submodule the error occurred in.

The call to read-tree contains a super-prefix, such that the read-tree
will correctly report any path related issues, but some error messages
do not contain a path, for example:

  ~/gerrit$ git checkout --recurse-submodules origin/master
  ~/gerrit$ fatal: failed to unpack tree object 07672f31880ba80300b38492df9d0acfcd6ee00a

Give the hint which submodule has a problem.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c               | 2 +-
 t/lib-submodule-update.sh | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/submodule.c b/submodule.c
index 939d6870ecd..ebd092a14fd 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1668,7 +1668,7 @@ int submodule_move_head(const char *path,
 	argv_array_push(&cp.args, new_head ? new_head : empty_tree_oid_hex());
 
 	if (run_command(&cp)) {
-		ret = -1;
+		ret = error(_("Submodule '%s' could not be updated."), path);
 		goto out;
 	}
 
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 1f38a85371a..e27f5d8541d 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -781,7 +781,8 @@ test_submodule_recursing_with_args_common() {
 		(
 			cd submodule_update &&
 			git branch -t invalid_sub1 origin/invalid_sub1 &&
-			test_must_fail $command invalid_sub1 &&
+			test_must_fail $command invalid_sub1 2>err &&
+			grep sub1 err &&
 			test_superproject_content origin/add_sub1 &&
 			test_submodule_content sub1 origin/add_sub1
 		)
-- 
2.18.0.rc2.346.g013aa6912e-goog