[PATCH v3 03/19] refs.c: make ref_transaction_commit return an error string

@@ -367,7 +367,7 @@ int cmd_update_ref(int argc, const char **argv, const char *prefix)
 		if (end_null)
 			line_termination = '\0';
 		update_refs_stdin();
-		ret = ref_transaction_commit(transaction, msg,
+		ret = ref_transaction_commit(transaction, msg, NULL,
 					     UPDATE_REFS_DIE_ON_ERR);
 		return ret;
 	}

@@ -3414,7 +3414,8 @@ static int ref_update_reject_duplicates(struct ref_update **updates, int n,
 }
 
 int ref_transaction_commit(struct ref_transaction *transaction,
-			   const char *msg, enum action_on_err onerr)
+			   const char *msg, char **err,
+			   enum action_on_err onerr)
 {
 	int ret = 0, delnum = 0, i;
 	const char **delnames;

@@ -3424,6 +3425,9 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 	if (!n)
 		return 0;
 
+	if (err)
+		*err = NULL;
+
 	/* Allocate work space */
 	delnames = xmalloc(sizeof(*delnames) * n);
 

@@ -3443,6 +3447,12 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 					       update->flags,
 					       &update->type, onerr);
 		if (!update->lock) {
+			if (err) {
+				const char *str = "Cannot lock the ref '%s'.";
+				*err = xmalloc(PATH_MAX + 24);
+				snprintf(*err, PATH_MAX + 24, str,
+					 update->refname);
+			}
 			ret = 1;
 			goto cleanup;
 		}

@@ -268,9 +268,12 @@ void ref_transaction_delete(struct ref_transaction *transaction,
  * Commit all of the changes that have been queued in transaction, as
  * atomically as possible.  Return a nonzero value if there is a
  * problem.  The ref_transaction is freed by this function.
+ * If error is non-NULL it will return an error string that describes
+ * why a commit failed. This string must be free()ed by the caller.
  */
 int ref_transaction_commit(struct ref_transaction *transaction,
-			   const char *msg, enum action_on_err onerr);
+			   const char *msg, char **err,
+			   enum action_on_err onerr);
 
 /** Lock a ref and then write its file */
 int update_ref(const char *action, const char *refname,