maintenance: make unregister idempotent

The 'git maintenance unregister' subcommand has a step that removes the
current repository from the multi-valued maitenance.repo config key.
This fails if the repository is not listed in that key. This makes
running 'git maintenance unregister' twice result in a failure in the
second instance.

Make this task idempotent, since the end result is the same in both
cases: maintenance will no longer run on this repository.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>

builtin/gc.c

@@ -1528,21 +1528,35 @@ static int maintenance_unregister(int argc, const char **argv, const char *prefi
 	struct option options[] = {
 		OPT_END(),
 	};
-	int rc;
+	const char *key = "maintenance.repo";
+	int rc = 0;
 	struct child_process config_unset = CHILD_PROCESS_INIT;
 	char *maintpath = get_maintpath();
+	int found = 0;
+	struct string_list_item *item;
+	const struct string_list *list = git_config_get_value_multi(key);
 
 	argc = parse_options(argc, argv, prefix, options,
 			     builtin_maintenance_unregister_usage, 0);
 	if (argc)
 		usage_with_options(builtin_maintenance_unregister_usage,
 				   options);
 
-	config_unset.git_cmd = 1;
-	strvec_pushl(&config_unset.args, "config", "--global", "--unset",
-		     "--fixed-value", "maintenance.repo", maintpath, NULL);
+	for_each_string_list_item(item, list) {
+		if (!strcmp(maintpath, item->string)) {
+			found = 1;
+			break;
+		}
+	}
+
+	if (found) {
+		config_unset.git_cmd = 1;
+		strvec_pushl(&config_unset.args, "config", "--global", "--unset",
+			     "--fixed-value", key, maintpath, NULL);
+
+		rc = run_command(&config_unset);
+	}
 
-	rc = run_command(&config_unset);
 	free(maintpath);
 	return rc;
 }

t/t7900-maintenance.sh

@@ -493,7 +493,10 @@ test_expect_success 'register and unregister' '
 
 	git maintenance unregister &&
 	git config --global --get-all maintenance.repo >actual &&
-	test_cmp before actual
+	test_cmp before actual &&
+
+	# Expect unregister to be idempotent.
+	git maintenance unregister
 '
 
 test_expect_success !MINGW 'register and unregister with regex metacharacters' '