git hook run: add an --ignore-missing flag

For certain one-shot hooks we'd like to optimistically run them, and
not complain if they don't exist.

This was already supported by the underlying hook.c library, but had
not been exposed via "git hook run". The command version of this will
be used by send-email in a subsequent commit.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Reviewed-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-hook.txt

@@ -8,7 +8,7 @@ git-hook - Run git hooks
 SYNOPSIS
 --------
 [verse]
-'git hook' run <hook-name> [-- <hook-args>]
+'git hook' run [--ignore-missing] <hook-name> [-- <hook-args>]
 
 DESCRIPTION
 -----------
@@ -28,6 +28,14 @@ Any positional arguments to the hook should be passed after a
 mandatory `--` (or `--end-of-options`, see linkgit:gitcli[7]). See
 linkgit:githooks[5] for arguments hooks might expect (if any).
 
+OPTIONS
+-------
+
+--ignore-missing::
+	Ignore any missing hook by quietly returning zero. Used for
+	tools that want to do a blind one-shot run of a hook that may
+	or may not be present.
+
 SEE ALSO
 --------
 linkgit:githooks[5]

builtin/hook.c

@@ -7,7 +7,7 @@
 #include "strvec.h"
 
 #define BUILTIN_HOOK_RUN_USAGE \
-	N_("git hook run <hook-name> [-- <hook-args>]")
+	N_("git hook run [--ignore-missing] <hook-name> [-- <hook-args>]")
 
 static const char * const builtin_hook_usage[] = {
 	BUILTIN_HOOK_RUN_USAGE,
@@ -23,8 +23,11 @@ static int run(int argc, const char **argv, const char *prefix)
 {
 	int i;
 	struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT;
+	int ignore_missing = 0;
 	const char *hook_name;
 	struct option run_options[] = {
+		OPT_BOOL(0, "ignore-missing", &ignore_missing,
+			 N_("silently ignore missing requested <hook-name>")),
 		OPT_END(),
 	};
 	int ret;
@@ -52,7 +55,8 @@ static int run(int argc, const char **argv, const char *prefix)
 	git_config(git_default_config, NULL);
 
 	hook_name = argv[0];
-	opt.error_if_missing = 1;
+	if (!ignore_missing)
+		opt.error_if_missing = 1;
 	ret = run_hooks_opt(hook_name, &opt);
 	if (ret < 0) /* error() return */
 		ret = 1;

t/t1800-hook.sh

@@ -21,6 +21,11 @@ test_expect_success 'git hook run: nonexistent hook' '
 	test_cmp stderr.expect stderr.actual
 '
 
+test_expect_success 'git hook run: nonexistent hook with --ignore-missing' '
+	git hook run --ignore-missing does-not-exist 2>stderr.actual &&
+	test_must_be_empty stderr.actual
+'
+
 test_expect_success 'git hook run: basic' '
 	write_script .git/hooks/test-hook <<-EOF &&
 	echo Test hook