git: add --no-hooks global option

Git has several hooks which are executed during certain events as long
as those hooks are enabled in the hooks directory (possibly moved from
.git/hooks via the core.hooksPath config option). These are configured
by the user, or perhaps by tooling the user has agreed to, and are not
required to operate a Git repository.

In some situations, these hooks have poor performance and expert users
may want to skip the hooks as they don't seem to affect the current
situation. One example is a pre-commit hook that checks for certain
structures in the local changes, but expert users are likely to have
done the right thing in advance.

I have come across users who have disabled hooks themselves either by
deleting hooks (supported, safe) or setting 'core.hooksPath' to some
bogus path (seems unsafe). The supported process is painful to swap
between the hook-enabled scenario and the hook-disabled scenario.

To that end, add a new --no-hooks global option to allow users to
disable hooks quickly. This option is modeled similarly to the
--no-advice option in b79deeb (advice: add --no-advice global option,
2024-05-03). This uses a GIT_HOOKS environment variable to communicate
to subprocesses as well as making this a backwards-compatible way for
tools to signal that they want to disable hooks.

The critical piece is that all hooks pass through run_hooks_opt() where
a static int will evaluate the environment variable and store that the
variable is initialized for faster repeated runs.

Signed-off-by: Derrick Stolee <stolee@gmail.com>

Author: derrickstolee

Documentation/git.adoc

@@ -14,7 +14,7 @@ SYNOPSIS
     [-p | --paginate | -P | --no-pager] [--no-replace-objects] [--no-lazy-fetch]
     [--no-optional-locks] [--no-advice] [--bare] [--git-dir=<path>]
     [--work-tree=<path>] [--namespace=<name>] [--config-env=<name>=<envvar>]
-    <command> [<args>]
+    [--no-hooks] <command> [<args>]
 
 DESCRIPTION
 -----------
@@ -230,6 +230,12 @@ If you just want to run git as if it was started in `<path>` then use
 	linkgit:gitattributes[5]. This is equivalent to setting the
 	`GIT_ATTR_SOURCE` environment variable.
 
+--no-hooks::
+	Skip running local Git hooks, even if configured locally. Hooks
+	are an opt-in feature, so be sure that you know the impact of
+	ignoring hooks when running with this option. This is equivalent
+	to setting `GIT_HOOKS=0` environment variable.
+
 GIT COMMANDS
 ------------
 
@@ -771,6 +777,11 @@ for further details.
 	not set, Git will choose buffered or record-oriented flushing
 	based on whether stdout appears to be redirected to a file or not.
 
+`GIT_HOOKS`::
+	If this Boolean environment variable is set to false, then commands
+	will ignore any configured hooks as if the `--no-hooks` option was
+	provided.
+
 `GIT_TRACE`::
 	Enables general trace messages, e.g. alias expansion, built-in
 	command execution and external command execution.

environment.h

@@ -50,6 +50,12 @@
  */
 #define GIT_ADVICE_ENVIRONMENT "GIT_ADVICE"
 
+/*
+ * Environment variable used to propagate the --no-hooks global option to
+ * the hooks layer and to any child processes.
+ */
+#define GIT_HOOKS "GIT_HOOKS"
+
 /*
  * Environment variable used in handshaking the wire protocol.
  * Contains a colon ':' separated list of keys with optional values

git.c

@@ -41,7 +41,7 @@ const char git_usage_string[] =
 	   "           [-p | --paginate | -P | --no-pager] [--no-replace-objects] [--no-lazy-fetch]\n"
 	   "           [--no-optional-locks] [--no-advice] [--bare] [--git-dir=<path>]\n"
 	   "           [--work-tree=<path>] [--namespace=<name>] [--config-env=<name>=<envvar>]\n"
-	   "           <command> [<args>]");
+	   "           [--no-hooks] <command> [<args>]");
 
 const char git_more_info_string[] =
 	N_("'git help -a' and 'git help -g' list available subcommands and some\n"
@@ -349,6 +349,10 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			setenv(GIT_ADVICE_ENVIRONMENT, "0", 1);
 			if (envchanged)
 				*envchanged = 1;
+		} else if (!strcmp(cmd, "--no-hooks")) {
+			setenv(GIT_HOOKS, "0", 1);
+			if (envchanged)
+				*envchanged = 1;
 		} else {
 			fprintf(stderr, _("unknown option: %s\n"), cmd);
 			usage(git_usage_string);

hook.c

@@ -144,6 +144,13 @@ int run_hooks_opt(struct repository *r, const char *hook_name,
 
 		.data = &cb_data,
 	};
+	static int do_run_hooks = -1;
+
+	if (do_run_hooks < 0)
+		do_run_hooks = git_env_bool(GIT_HOOKS, 1);
+
+	if (!do_run_hooks)
+		return 0;
 
 	if (!options)
 		BUG("a struct run_hooks_opt must be provided to run_hooks");

t/t1350-config-hooks-path.sh

@@ -48,4 +48,38 @@ test_expect_success 'core.hooksPath=/dev/null' '
 	{ test /dev/null = "$value" || test nul = "$value"; }
 '
 
+test_expect_success '--no-hooks' '
+	rm -f actual &&
+	test_might_fail git config --unset core.hooksPath &&
+
+	write_script .git/hooks/pre-commit <<-\EOF &&
+	echo HOOK >>actual
+	EOF
+
+	echo HOOK >expect &&
+
+	git commit --allow-empty -m "A" &&
+	test_cmp expect actual &&
+
+	git --no-hooks commit --allow-empty -m "B" &&
+	test_cmp expect actual
+'
+
+test_expect_success 'GIT_HOOKS' '
+	rm -f actual &&
+	test_might_fail git config --unset core.hooksPath &&
+
+	write_script .git/hooks/pre-commit <<-\EOF &&
+	echo HOOK >>actual
+	EOF
+
+	echo HOOK >expect &&
+
+	GIT_HOOKS=1 git commit --allow-empty -m "A" &&
+	test_cmp expect actual &&
+
+	GIT_HOOKS=0 git commit --allow-empty -m "B" &&
+	test_cmp expect actual
+'
+
 test_done