scalar: enable built-in FSMonitor on register

Using the built-in FSMonitor makes many common commands quite a bit
faster. So let's teach the `scalar register` command to enable the
built-in FSMonitor and kick-start the fsmonitor--daemon process (for
convenience).

For simplicity, we only support the built-in FSMonitor (and no external
file system monitor such as e.g. Watchman).

Signed-off-by: Matthew John Cheetham <mjcheetham@outlook.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

contrib/scalar/scalar.c

@@ -10,6 +10,8 @@
 #include "refs.h"
 #include "help.h"
 #include "dir.h"
+#include "simple-ipc.h"
+#include "fsmonitor-ipc.h"
 
 static void setup_enlistment_directory(int argc, const char **argv,
 				       const char * const *usagestr,
@@ -150,6 +152,12 @@ static int set_recommended_config(int reconfigure)
 		{ "maintenance.incremental-repack.enabled", "true" },
 		{ "maintenance.incremental-repack.auto", "0" },
 		{ "maintenance.incremental-repack.schedule", "daily" },
+#ifdef HAVE_FSMONITOR_DAEMON_BACKEND
+		/*
+		 * Enable the built-in FSMonitor on supported platforms.
+		 */
+		{ "core.useBuiltinFSMonitor", "true" },
+#endif
 		{ NULL, NULL },
 	};
 	int i;
@@ -220,6 +228,31 @@ static int add_or_remove_enlistment(int add)
 		       "scalar.repo", the_repository->worktree, NULL);
 }
 
+static int start_fsmonitor_daemon(void)
+{
+#ifdef HAVE_FSMONITOR_DAEMON_BACKEND
+	struct strbuf err = STRBUF_INIT;
+	struct child_process cp = CHILD_PROCESS_INIT;
+
+	cp.git_cmd = 1;
+	strvec_pushl(&cp.args, "fsmonitor--daemon", "start", NULL);
+	if (!pipe_command(&cp, NULL, 0, NULL, 0, &err, 0)) {
+		strbuf_release(&err);
+		return 0;
+	}
+
+	if (fsmonitor_ipc__get_state() != IPC_STATE__LISTENING) {
+		write_in_full(2, err.buf, err.len);
+		strbuf_release(&err);
+		return error(_("could not start the FSMonitor daemon"));
+	}
+
+	strbuf_release(&err);
+#endif
+
+	return 0;
+}
+
 static int register_dir(void)
 {
 	int res = add_or_remove_enlistment(1);
@@ -230,6 +263,9 @@ static int register_dir(void)
 	if (!res)
 		res = toggle_maintenance(1);
 
+	if (!res)
+		res = start_fsmonitor_daemon();
+
 	return res;
 }
 

contrib/scalar/t/t9099-scalar.sh

@@ -13,10 +13,21 @@ PATH=$(pwd)/..:$PATH
 GIT_TEST_MAINT_SCHEDULER="crontab:test-tool crontab ../cron.txt"
 export GIT_TEST_MAINT_SCHEDULER
 
+test_lazy_prereq BUILTIN_FSMONITOR '
+	git version --build-options | grep -q "feature:.*fsmonitor--daemon"
+'
+
 test_expect_success 'scalar shows a usage' '
 	test_expect_code 129 scalar -h
 '
 
+test_expect_success BUILTIN_FSMONITOR 'scalar register starts fsmon daemon' '
+	git init test/src &&
+	test_must_fail git -C test/src fsmonitor--daemon status &&
+	scalar register test/src &&
+	git -C test/src fsmonitor--daemon status
+'
+
 test_expect_success 'scalar unregister' '
 	git init vanish/src &&
 	scalar register vanish/src &&