hook: allow event = "" to overwrite previous values

Add the ability for empty events to clear previously set multivalue
variables, so the newly added "hook.*.event" behave like the other
multivalued keys.

Suggested-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: 10ne1

Documentation/config/hook.adoc

@@ -12,7 +12,9 @@ hook.<name>.event::
 	linkgit:githooks[5] for a complete list of hook events.) On the
 	specified event, the associated `hook.<name>.command` is executed.
 	This is a multi-valued key. To run `hook.<name>` on multiple
-	events, specify the key more than once. See linkgit:git-hook[1].
+	events, specify the key more than once. An empty value resets
+	the list of events, clearing any previously defined events for
+	`hook.<name>`. See linkgit:git-hook[1].
 
 hook.<name>.enabled::
 	Whether the hook `hook.<name>` is enabled. Defaults to `true`.

hook.c

@@ -147,18 +147,27 @@ static int hook_config_lookup_all(const char *key, const char *value,
 	hook_name = xmemdupz(name, name_len);
 
 	if (!strcmp(subkey, "event")) {
-		struct string_list *hooks =
-			strmap_get(&data->event_hooks, value);
+		if (!*value) {
+			/* Empty values reset previous events for this hook. */
+			struct hashmap_iter iter;
+			struct strmap_entry *e;
+
+			strmap_for_each_entry(&data->event_hooks, &iter, e)
+				unsorted_string_list_remove(e->value, hook_name);
+		} else {
+			struct string_list *hooks =
+				strmap_get(&data->event_hooks, value);
+
+			if (!hooks) {
+				hooks = xcalloc(1, sizeof(*hooks));
+				string_list_init_dup(hooks);
+				strmap_put(&data->event_hooks, value, hooks);
+			}
 
-		if (!hooks) {
-			hooks = xcalloc(1, sizeof(*hooks));
-			string_list_init_dup(hooks);
-			strmap_put(&data->event_hooks, value, hooks);
+			/* Re-insert if necessary to preserve last-seen order. */
+			unsorted_string_list_remove(hooks, hook_name);
+			string_list_append(hooks, hook_name);
 		}
-
-		/* Re-insert if necessary to preserve last-seen order. */
-		unsorted_string_list_remove(hooks, hook_name);
-		string_list_append(hooks, hook_name);
 	} else if (!strcmp(subkey, "command")) {
 		/* Store command overwriting the old value */
 		char *old = strmap_put(&data->commands, hook_name,

t/t1800-hook.sh

@@ -226,6 +226,18 @@ test_expect_success 'git hook list reorders on duplicate event declarations' '
 	test_cmp expected actual
 '
 
+test_expect_success 'git hook list: empty event value resets events' '
+	setup_hooks &&
+
+	# ghi is configured for pre-commit; reset it with an empty value
+	test_config hook.ghi.event "" --add &&
+
+	# only def should remain for pre-commit
+	echo "def" >expected &&
+	git hook list pre-commit >actual &&
+	test_cmp expected actual
+'
+
 test_expect_success 'hook can be configured for multiple events' '
 	setup_hooks &&