[PATCH 2/2] submodule.c: warn about missing submodule commit in recursive actions

[Stefan Beller <sbeller@google.com>]

By checking if a submodule commit exists before attempting the update
we can improve the error message from the
    error(_("Submodule '%s' could not be updated."), path);
to the new and more specific
    error(_("Submodule '%s' doesn't have commit '%s'"),
          path, oid_to_hex(new_oid));

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/submodule.c b/submodule.c
index da2ed8696f5..56104af1c7c 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1605,6 +1605,7 @@ int submodule_move_head(const char *path,
 	struct child_process cp = CHILD_PROCESS_INIT;
 	const struct submodule *sub;
 	int *error_code_ptr, error_code;
+	struct repository subrepo;
 
 	if (!is_submodule_active(the_repository, path))
 		return 0;
@@ -1627,6 +1628,13 @@ int submodule_move_head(const char *path,
 	if (!sub)
 		BUG("could not get submodule information for '%s'", path);
 
+	if (repo_submodule_init(&subrepo, the_repository, path) < 0)
+		warning(_("Could not get submodule repository for submodule 's'"), path);
+	else if (new_oid && !lookup_commit(subrepo, new_oid)) {
+		return error(_("Submodule '%s' doesn't have commit '%s'"),
+			     path, oid_to_hex(new_oid));
+	}
+
 	if (old_head && !(flags & SUBMODULE_MOVE_HEAD_FORCE)) {
 		/* Check if the submodule has a dirty index. */
 		if (submodule_has_dirty_index(sub))
-- 
2.19.0.rc2.392.g5ba43deb5a-goog