hooks: convert worktree 'post-checkout' hook to hook library

Move the running of the 'post-checkout' hook away from run-command.h
to the new hook.h library in builtin/worktree.c. For this special case
we need a change to the hook API to teach it to run the hook from a
given directory.

We cannot skip the "absolute_path" flag and just check if "dir" is
specified as we'd then fail to find our hook in the new dir we'd
chdir() to. We currently don't have a use-case for running a hook not
in our "base" repository at a given absolute path, so let's have "dir"
imply absolute_path(find_hook(hook_name)).

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

builtin/worktree.c

@@ -382,21 +382,17 @@ done:
 	 * is_junk is cleared, but do return appropriate code when hook fails.
 	 */
 	if (!ret && opts->checkout) {
-		const char *hook = find_hook("post-checkout");
-		if (hook) {
-			const char *env[] = { "GIT_DIR", "GIT_WORK_TREE", NULL };
-			struct child_process cp = CHILD_PROCESS_INIT;
-			cp.no_stdin = 1;
-			cp.stdout_to_stderr = 1;
-			cp.dir = path;
-			strvec_pushv(&cp.env_array, env);
-			cp.trace2_hook_name = "post-checkout";
-			strvec_pushl(&cp.args, absolute_path(hook),
-				     oid_to_hex(null_oid()),
-				     oid_to_hex(&commit->object.oid),
-				     "1", NULL);
-			ret = run_command(&cp);
-		}
+		struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT;
+
+		strvec_pushl(&opt.env, "GIT_DIR", "GIT_WORK_TREE", NULL);
+		strvec_pushl(&opt.args,
+			     oid_to_hex(null_oid()),
+			     oid_to_hex(&commit->object.oid),
+			     "1",
+			     NULL);
+		opt.dir = path;
+
+		ret = run_hooks_opt("post-checkout", &opt);
 	}
 
 	strvec_clear(&child_env);

hook.c

@@ -57,6 +57,7 @@ static int pick_next_hook(struct child_process *cp,
 	strvec_pushv(&cp->env_array, hook_cb->options->env.v);
 	cp->stdout_to_stderr = 1;
 	cp->trace2_hook_name = hook_cb->hook_name;
+	cp->dir = hook_cb->options->dir;
 
 	strvec_push(&cp->args, hook_path);
 	strvec_pushv(&cp->args, hook_cb->options->args.v);
@@ -109,6 +110,7 @@ static void run_hooks_opt_clear(struct run_hooks_opt *options)
 
 int run_hooks_opt(const char *hook_name, struct run_hooks_opt *options)
 {
+	struct strbuf abs_path = STRBUF_INIT;
 	struct hook_cb_data cb_data = {
 		.rc = 0,
 		.hook_name = hook_name,
@@ -130,6 +132,11 @@ int run_hooks_opt(const char *hook_name, struct run_hooks_opt *options)
 	}
 
 	cb_data.hook_path = hook_path;
+	if (options->dir) {
+		strbuf_add_absolute_path(&abs_path, hook_path);
+		cb_data.hook_path = abs_path.buf;
+	}
+
 	run_processes_parallel_tr2(jobs,
 				   pick_next_hook,
 				   notify_start_failure,
@@ -139,6 +146,7 @@ int run_hooks_opt(const char *hook_name, struct run_hooks_opt *options)
 				   hook_name);
 	ret = cb_data.rc;
 cleanup:
+	strbuf_release(&abs_path);
 	run_hooks_opt_clear(options);
 	return ret;
 }

hook.h

@@ -12,6 +12,12 @@ struct run_hooks_opt
 
 	/* Emit an error if the hook is missing */
 	unsigned int error_if_missing:1;
+
+	/**
+	 * An optional initial working directory for the hook,
+	 * translates to "struct child_process"'s "dir" member.
+	 */
+	const char *dir;
 };
 
 #define RUN_HOOKS_OPT_INIT { \