Merge branch 'ar/parallel-hooks' into seen

* ar/parallel-hooks:
  hook: allow runtime enabling extensions.hookStdoutToStderr
  hook: introduce extensions.hookStdoutToStderr
  hook: add per-event jobs config
  hook: add -j/--jobs option to git hook run
  hook: mark non-parallelizable hooks
  hook: allow parallel hook execution
  hook: parse the hook.jobs config
  hook: refactor hook_config_cache from strmap to named struct
  config: add a repo_config_get_uint() helper
  repository: fix repo_init() memleak due to missing _clear()

Author: gitster

Documentation/config/extensions.adoc

@@ -116,6 +116,21 @@ The extension can be enabled automatically for new repositories by setting
 `init.defaultSubmodulePathConfig` to `true`, for example by running
 `git config --global init.defaultSubmodulePathConfig true`.
 
+hookStdoutToStderr:::
+	If enabled, the stdout of all hooks is redirected to stderr. This
+	enforces consistency, since by default most hooks already behave
+	this way, with pre-push being the only known exception.
++
+This is useful for parallel hook execution (see the `hook.jobs` config in
+linkgit:git-config[1]), as it allows the output of multiple hooks running
+in parallel to be grouped (de-interleaved) correctly.
++
+Defaults to disabled. When disabled, `hook.jobs` has no effect for pre-push
+hooks, which will always be run sequentially.
++
+The extension can also be enabled by setting `hook.forceStdoutToStderr`
+to `true` in the global configuration.
+
 worktreeConfig:::
 	If enabled, then worktrees will load config settings from the
 	`$GIT_DIR/config.worktree` file in addition to the

Documentation/config/hook.adoc

@@ -22,3 +22,52 @@ hook.<name>.enabled::
 	configuration. This is particularly useful when a hook is defined
 	in a system or global config file and needs to be disabled for a
 	specific repository. See linkgit:git-hook[1].
+
+hook.<name>.parallel::
+	Whether the hook `hook.<name>` may run in parallel with other hooks
+	for the same event. Defaults to `false`. Set to `true` only when the
+	hook script is safe to run concurrently with other hooks for the same
+	event. If any hook for an event does not have this set to `true`,
+	all hooks for that event run sequentially regardless of `hook.jobs`.
+	Only configured (named) hooks need to declare this. Traditional hooks
+	found in the hooks directory do not need to, and run in parallel when
+	the effective job count is greater than 1. See linkgit:git-hook[1].
+
+hook.<event>.jobs::
+	Specifies how many hooks can be run simultaneously for the `<event>`
+	hook event (e.g. `hook.post-receive.jobs = 4`). Overrides `hook.jobs`
+	for this specific event. The same parallelism restrictions apply: this
+	setting has no effect unless all configured hooks for the event have
+	`hook.<friendly-name>.parallel` set to `true`. Must be a positive int,
+	zero is rejected with a warning. See linkgit:git-hook[1].
++
+Note on naming: although this key resembles `hook.<friendly-name>.*`
+(a per-hook setting), `<event>` must be the event name, not a hook
+friendly name. The key component is stored literally and looked up by
+event name at runtime with no translation between the two namespaces.
+A key like `hook.my-hook.jobs` is stored under `"my-hook"` but the
+lookup at runtime uses the event name (e.g. `"post-receive"`), so
+`hook.my-hook.jobs` is silently ignored even when `my-hook` is
+registered for that event. Use `hook.post-receive.jobs` or any other
+valid event name when setting `hook.<event>.jobs`.
+
+hook.jobs::
+	Specifies how many hooks can be run simultaneously during parallelized
+	hook execution. If unspecified, defaults to 1 (serial execution).
+	Can be overridden on a per-event basis with `hook.<event>.jobs`.
+	Some hooks always run sequentially regardless of this setting because
+	git knows they cannot safely be parallelized: `applypatch-msg`,
+	`pre-commit`, `prepare-commit-msg`, `commit-msg`, `post-commit`,
+	`post-checkout`, and `push-to-checkout`.
++
+This setting has no effect unless all configured hooks for the event have
+`hook.<name>.parallel` set to `true`.
++
+This has no effect for hooks requiring separate output streams (like `pre-push`)
+unless `extensions.hookStdoutToStderr` is enabled.
+
+hook.forceStdoutToStderr::
+	A boolean that enables the `extensions.hookStdoutToStderr` behavior
+	(merging stdout to stderr for all hooks) globally. This effectively
+	forces all hooks to behave as if the extension was enabled, allowing
+	parallel execution for hooks like `pre-push`.

Documentation/git-hook.adoc

@@ -8,7 +8,8 @@ git-hook - Run git hooks
 SYNOPSIS
 --------
 [verse]
-'git hook' run [--ignore-missing] [--to-stdin=<path>] <hook-name> [-- <hook-args>]
+'git hook' run [--ignore-missing] [--to-stdin=<path>] [(-j|--jobs) <n>]
+	<hook-name> [-- <hook-args>]
 'git hook' list [-z] <hook-name>
 
 DESCRIPTION
@@ -134,6 +135,18 @@ OPTIONS
 -z::
 	Terminate "list" output lines with NUL instead of newlines.
 
+-j::
+--jobs::
+	Only valid for `run`.
++
+Specify how many hooks to run simultaneously. If this flag is not specified,
+the value of the `hook.jobs` config is used, see linkgit:git-config[1]. If
+neither is specified, defaults to 1 (serial execution). Some hooks always run
+sequentially regardless of this flag or the `hook.jobs` config, because git
+knows they cannot safely run in parallel: `applypatch-msg`, `pre-commit`,
+`prepare-commit-msg`, `commit-msg`, `post-commit`, `post-checkout`, and
+`push-to-checkout`.
+
 WRAPPERS
 --------
 
@@ -156,7 +169,8 @@ running:
 git hook run mywrapper-start-tests \
   # providing something to stdin
   --stdin some-tempfile-123 \
-  # execute hooks in serial
+  # execute multiple hooks in parallel
+  --jobs 3 \
   # plus some arguments of your own...
   -- \
   --testname bar \

builtin/am.c

@@ -490,9 +490,11 @@ static int run_applypatch_msg_hook(struct am_state *state)
 
 	assert(state->msg);
 
-	if (!state->no_verify)
-		ret = run_hooks_l(the_repository, "applypatch-msg",
-				  am_path(state, "final-commit"), NULL);
+	if (!state->no_verify) {
+		struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT_FORCE_SERIAL;
+		strvec_push(&opt.args, am_path(state, "final-commit"));
+		ret = run_hooks_opt(the_repository, "applypatch-msg", &opt);
+	}
 
 	if (!ret) {
 		FREE_AND_NULL(state->msg);

builtin/checkout.c

@@ -31,6 +31,7 @@
 #include "resolve-undo.h"
 #include "revision.h"
 #include "setup.h"
+#include "strvec.h"
 #include "submodule.h"
 #include "symlinks.h"
 #include "trace2.h"
@@ -123,13 +124,19 @@ static void branch_info_release(struct branch_info *info)
 static int post_checkout_hook(struct commit *old_commit, struct commit *new_commit,
 			      int changed)
 {
-	return run_hooks_l(the_repository, "post-checkout",
-			   oid_to_hex(old_commit ? &old_commit->object.oid : null_oid(the_hash_algo)),
-			   oid_to_hex(new_commit ? &new_commit->object.oid : null_oid(the_hash_algo)),
-			   changed ? "1" : "0", NULL);
-	/* "new_commit" can be NULL when checking out from the index before
-	   a commit exists. */
+	struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT_FORCE_SERIAL;
 
+	/*
+	 * "new_commit" can be NULL when checking out from the index before
+	 * a commit exists.
+	 */
+	strvec_pushl(&opt.args,
+		     oid_to_hex(old_commit ? &old_commit->object.oid : null_oid(the_hash_algo)),
+		     oid_to_hex(new_commit ? &new_commit->object.oid : null_oid(the_hash_algo)),
+		     changed ? "1" : "0",
+		     NULL);
+
+	return run_hooks_opt(the_repository, "post-checkout", &opt);
 }
 
 static int update_some(const struct object_id *oid, struct strbuf *base,

builtin/clone.c

@@ -647,6 +647,7 @@ static int checkout(int submodule_progress,
 	struct tree *tree;
 	struct tree_desc t;
 	int err = 0;
+	struct run_hooks_opt hook_opt = RUN_HOOKS_OPT_INIT_FORCE_SERIAL;
 
 	if (option_no_checkout)
 		return 0;
@@ -697,8 +698,9 @@ static int checkout(int submodule_progress,
 	if (write_locked_index(the_repository->index, &lock_file, COMMIT_LOCK))
 		die(_("unable to write new index file"));
 
-	err |= run_hooks_l(the_repository, "post-checkout", oid_to_hex(null_oid(the_hash_algo)),
-			   oid_to_hex(&oid), "1", NULL);
+	strvec_pushl(&hook_opt.args, oid_to_hex(null_oid(the_hash_algo)),
+		     oid_to_hex(&oid), "1", NULL);
+	err |= run_hooks_opt(the_repository, "post-checkout", &hook_opt);
 
 	if (!err && (option_recurse_submodules.nr > 0)) {
 		struct child_process cmd = CHILD_PROCESS_INIT;

builtin/hook.c

@@ -9,7 +9,8 @@
 #include "abspath.h"
 
 #define BUILTIN_HOOK_RUN_USAGE \
-	N_("git hook run [--ignore-missing] [--to-stdin=<path>] <hook-name> [-- <hook-args>]")
+	N_("git hook run [--ignore-missing] [--to-stdin=<path>] [(-j|--jobs) <n>]\n" \
+	   "<hook-name> [-- <hook-args>]")
 #define BUILTIN_HOOK_LIST_USAGE \
 	N_("git hook list [-z] <hook-name>")
 
@@ -97,6 +98,8 @@ static int run(int argc, const char **argv, const char *prefix,
 			 N_("silently ignore missing requested <hook-name>")),
 		OPT_STRING(0, "to-stdin", &opt.path_to_stdin, N_("path"),
 			   N_("file to read into hooks' stdin")),
+		OPT_UNSIGNED('j', "jobs", &opt.jobs,
+			    N_("run up to <n> hooks simultaneously")),
 		OPT_END(),
 	};
 	int ret;

builtin/receive-pack.c

@@ -1460,7 +1460,8 @@ static const char *push_to_checkout(unsigned char *hash,
 				    struct strvec *env,
 				    const char *work_tree)
 {
-	struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT;
+	struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT_FORCE_SERIAL;
+
 	opt.invoked_hook = invoked_hook;
 
 	strvec_pushf(env, "GIT_WORK_TREE=%s", absolute_path(work_tree));

builtin/worktree.c

@@ -609,7 +609,7 @@ static int add_worktree(const char *path, const char *refname,
 	 * is_junk is cleared, but do return appropriate code when hook fails.
 	 */
 	if (!ret && opts->checkout && !opts->orphan) {
-		struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT;
+		struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT_FORCE_SERIAL;
 
 		strvec_pushl(&opt.env, "GIT_DIR", "GIT_WORK_TREE", NULL);
 		strvec_pushl(&opt.args,

commit.c

@@ -1979,7 +1979,7 @@ size_t ignored_log_message_bytes(const char *buf, size_t len)
 int run_commit_hook(int editor_is_used, const char *index_file,
 		    int *invoked_hook, const char *name, ...)
 {
-	struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT;
+	struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT_FORCE_SERIAL;
 	va_list args;
 	const char *arg;