[PATCH 04/23] fsmonitor: introduce `core.useBuiltinFSMonitor` to call the daemon via IPC

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

The `core.fsmonitor` setting is supposed to be set to a path pointing
to a script or executable that (via the Hook API) queries an fsmonitor
process such as watchman.

We are about to implement our own fsmonitor backend, and do not want
to spawn hook processes just to query it.  Let's use `Simple IPC` to
directly communicate with the daemon (and start it if necessary),
guarded by the brand-new `core.useBuiltinFSMonitor` toggle.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
---
 config.c        |  5 +++++
 fsmonitor.c     | 20 +++++++++++++++++---
 repo-settings.c |  3 +++
 repository.h    |  2 ++
 4 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/config.c b/config.c
index 955ff4f9461d..31f2cbaf6dfb 100644
--- a/config.c
+++ b/config.c
@@ -2515,6 +2515,11 @@ int git_config_get_max_percent_split_change(void)
 
 int repo_config_get_fsmonitor(struct repository *r)
 {
+	if (r->settings.use_builtin_fsmonitor > 0) {
+		core_fsmonitor = "(built-in daemon)";
+		return 1;
+	}
+
 	if (repo_config_get_pathname(r, "core.fsmonitor", &core_fsmonitor))
 		core_fsmonitor = getenv("GIT_TEST_FSMONITOR");
 
diff --git a/fsmonitor.c b/fsmonitor.c
index 9c9b2abc9414..d7e18fc8cd47 100644
--- a/fsmonitor.c
+++ b/fsmonitor.c
@@ -3,6 +3,7 @@
 #include "dir.h"
 #include "ewah/ewok.h"
 #include "fsmonitor.h"
+#include "fsmonitor-ipc.h"
 #include "run-command.h"
 #include "strbuf.h"
 
@@ -148,14 +149,27 @@ void write_fsmonitor_extension(struct strbuf *sb, struct index_state *istate)
 /*
  * Call the query-fsmonitor hook passing the last update token of the saved results.
  */
-static int query_fsmonitor(int version, const char *last_update, struct strbuf *query_result)
+static int query_fsmonitor(int version, struct index_state *istate, struct strbuf *query_result)
 {
+	struct repository *r = istate->repo ? istate->repo : the_repository;
+	const char *last_update = istate->fsmonitor_last_update;
 	struct child_process cp = CHILD_PROCESS_INIT;
 	int result;
 
 	if (!core_fsmonitor)
 		return -1;
 
+	if (r->settings.use_builtin_fsmonitor > 0) {
+#ifdef HAVE_FSMONITOR_DAEMON_BACKEND
+		return fsmonitor_ipc__send_query(last_update, query_result);
+#else
+		/* Fake a trivial response. */
+		warning(_("fsmonitor--daemon unavailable; falling back"));
+		strbuf_add(query_result, "/", 2);
+		return 0;
+#endif
+	}
+
 	strvec_push(&cp.args, core_fsmonitor);
 	strvec_pushf(&cp.args, "%d", version);
 	strvec_pushf(&cp.args, "%s", last_update);
@@ -263,7 +277,7 @@ void refresh_fsmonitor(struct index_state *istate)
 	if (istate->fsmonitor_last_update) {
 		if (hook_version == -1 || hook_version == HOOK_INTERFACE_VERSION2) {
 			query_success = !query_fsmonitor(HOOK_INTERFACE_VERSION2,
-				istate->fsmonitor_last_update, &query_result);
+				istate, &query_result);
 
 			if (query_success) {
 				if (hook_version < 0)
@@ -293,7 +307,7 @@ void refresh_fsmonitor(struct index_state *istate)
 
 		if (hook_version == HOOK_INTERFACE_VERSION1) {
 			query_success = !query_fsmonitor(HOOK_INTERFACE_VERSION1,
-				istate->fsmonitor_last_update, &query_result);
+				istate, &query_result);
 		}
 
 		trace_performance_since(last_update, "fsmonitor process '%s'", core_fsmonitor);
diff --git a/repo-settings.c b/repo-settings.c
index f7fff0f5ab83..93aab92ff164 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -58,6 +58,9 @@ void prepare_repo_settings(struct repository *r)
 		r->settings.core_multi_pack_index = value;
 	UPDATE_DEFAULT_BOOL(r->settings.core_multi_pack_index, 1);
 
+	if (!repo_config_get_bool(r, "core.usebuiltinfsmonitor", &value) && value)
+		r->settings.use_builtin_fsmonitor = 1;
+
 	if (!repo_config_get_bool(r, "feature.manyfiles", &value) && value) {
 		UPDATE_DEFAULT_BOOL(r->settings.index_version, 4);
 		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
diff --git a/repository.h b/repository.h
index b385ca3c94b6..7eeab871ac3e 100644
--- a/repository.h
+++ b/repository.h
@@ -41,6 +41,8 @@ struct repo_settings {
 	enum fetch_negotiation_setting fetch_negotiation_algorithm;
 
 	int core_multi_pack_index;
+
+	int use_builtin_fsmonitor;
 };
 
 struct repository {
-- 
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