[PATCH v2 3/5] scalar: enable built-in FSMonitor on `register`

["Matthew John Cheetham via GitGitGadget" <gitgitgadget@gmail.com>]

From: Matthew John Cheetham <mjcheetham@outlook.com>

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).

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Matthew John Cheetham <mjcheetham@outlook.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Victoria Dye <vdye@github.com>
---
 contrib/scalar/scalar.c          | 21 +++++++++++++++++++++
 contrib/scalar/t/t9099-scalar.sh | 11 +++++++++++
 2 files changed, 32 insertions(+)

diff --git a/contrib/scalar/scalar.c b/contrib/scalar/scalar.c
index 6025cd71604..28d915ec006 100644
--- a/contrib/scalar/scalar.c
+++ b/contrib/scalar/scalar.c
@@ -7,6 +7,8 @@
 #include "parse-options.h"
 #include "config.h"
 #include "run-command.h"
+#include "simple-ipc.h"
+#include "fsmonitor-ipc.h"
 #include "refs.h"
 #include "dir.h"
 #include "packfile.h"
@@ -169,6 +171,12 @@ static int set_recommended_config(int reconfigure)
 		{ "core.autoCRLF", "false" },
 		{ "core.safeCRLF", "false" },
 		{ "fetch.showForcedUpdates", "false" },
+#ifdef HAVE_FSMONITOR_DAEMON_BACKEND
+		/*
+		 * Enable the built-in FSMonitor on supported platforms.
+		 */
+		{ "core.fsmonitor", "true" },
+#endif
 		{ NULL, NULL },
 	};
 	int i;
@@ -236,6 +244,16 @@ static int add_or_remove_enlistment(int add)
 		       "scalar.repo", the_repository->worktree, NULL);
 }
 
+static int start_fsmonitor_daemon(void)
+{
+	assert(fsmonitor_ipc__is_supported());
+
+	if (fsmonitor_ipc__get_state() != IPC_STATE__LISTENING)
+		return run_git("fsmonitor--daemon", "start", NULL);
+
+	return 0;
+}
+
 static int register_dir(void)
 {
 	if (add_or_remove_enlistment(1))
@@ -247,6 +265,9 @@ static int register_dir(void)
 	if (toggle_maintenance(1))
 		return error(_("could not turn on maintenance"));
 
+	if (fsmonitor_ipc__is_supported() && start_fsmonitor_daemon())
+		return error(_("could not start the FSMonitor daemon"));
+
 	return 0;
 }
 
diff --git a/contrib/scalar/t/t9099-scalar.sh b/contrib/scalar/t/t9099-scalar.sh
index 10b1172a8aa..526f64d001c 100755
--- a/contrib/scalar/t/t9099-scalar.sh
+++ b/contrib/scalar/t/t9099-scalar.sh
@@ -13,10 +13,21 @@ PATH=$PWD/..:$PATH
 GIT_TEST_MAINT_SCHEDULER="crontab:test-tool crontab ../cron.txt,launchctl:true,schtasks:true"
 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 &&
-- 
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