[PATCH v3 04/19] refs.c: return error string from ref_update_reject_duplicates on failure

@@ -3393,6 +3393,7 @@ static int ref_update_compare(const void *r1, const void *r2)
 }
 
 static int ref_update_reject_duplicates(struct ref_update **updates, int n,
+					char **err,
 					enum action_on_err onerr)
 {
 	int i;

@@ -3400,6 +3401,11 @@ static int ref_update_reject_duplicates(struct ref_update **updates, int n,
 		if (!strcmp(updates[i - 1]->refname, updates[i]->refname)) {
 			const char *str =
 				"Multiple updates for ref '%s' not allowed.";
+			if (err) {
+				*err = xmalloc(PATH_MAX + 41);
+				snprintf(*err, PATH_MAX + 41, str,
+					 updates[i]->refname);
+			}
 			switch (onerr) {
 			case UPDATE_REFS_MSG_ON_ERR:
 				error(str, updates[i]->refname); break;

@@ -3433,7 +3439,7 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 
 	/* Copy, sort, and reject duplicate refs */
 	qsort(updates, n, sizeof(*updates), ref_update_compare);
-	ret = ref_update_reject_duplicates(updates, n, onerr);
+	ret = ref_update_reject_duplicates(updates, n, err, onerr);
 	if (ret)
 		goto cleanup;