Enable the built-in FSMonitor as an experimental feature

If `feature.experimental` and `feature.manyFiles` are set and the user
has not explicitly turned off the builtin FSMonitor, we now start
the built-in FSMonitor by default.

Only forcing it when UNSET matches the behavior of UPDATE_DEFAULT_BOOL()
used for other repo settings.

Signed-off-by: Johannes Schindelin <[email protected]>
Signed-off-by: Jeff Hostetler <[email protected]>

Author: dscho

repo-settings.c

@@ -2,13 +2,14 @@
 #include "config.h"
 #include "repository.h"
 #include "midx.h"
-#include "compat/fsmonitor/fsm-listen.h"
+#include "fsmonitor-ipc.h"
+#include "fsmonitor-settings.h"
 
 #define UPDATE_DEFAULT_BOOL(s,v) do { if (s == -1) { s = v; } } while(0)
 
 void prepare_repo_settings(struct repository *r)
 {
-	int value;
+	int value, feature_many_files = 0;
 	char *strval;
 
 	if (r->settings.initialized)
@@ -62,6 +63,7 @@ void prepare_repo_settings(struct repository *r)
 	UPDATE_DEFAULT_BOOL(r->settings.core_multi_pack_index, 1);
 
 	if (!repo_config_get_bool(r, "feature.manyfiles", &value) && value) {
+		feature_many_files = 1;
 		UPDATE_DEFAULT_BOOL(r->settings.index_version, 4);
 		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
 	}
@@ -70,9 +72,33 @@ void prepare_repo_settings(struct repository *r)
 		r->settings.fetch_write_commit_graph = value;
 	UPDATE_DEFAULT_BOOL(r->settings.fetch_write_commit_graph, 0);
 
-	if (!repo_config_get_bool(r, "feature.experimental", &value) && value)
+	if (!repo_config_get_bool(r, "feature.experimental", &value) && value) {
 		UPDATE_DEFAULT_BOOL(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_SKIPPING);
 
+		/*
+		 * Force enable the builtin FSMonitor (unless the repo
+		 * is incompatible or they've already selected it or
+		 * the hook version).  But only if they haven't
+		 * explicitly turned it off -- so only if our config
+		 * value is UNSET.
+		 *
+		 * lookup_fsmonitor_settings() and check_for_ipc() do
+		 * not distinguish between explicitly set FALSE and
+		 * UNSET, so we re-test for an UNSET config key here.
+		 *
+		 * I'm not sure I want to fix fsmonitor-settings.c to
+		 * have more than one _DISABLED state since our usage
+		 * here is only to support this experimental period
+		 * (and I don't want to overload the _reason field
+		 * because it describes incompabilities).
+		 */
+		if (feature_many_files &&
+		    fsmonitor_ipc__is_supported()  &&
+		    fsm_settings__get_mode(r) == FSMONITOR_MODE_DISABLED &&
+		    repo_config_get_bool(r, "core.usebuiltinfsmonitor", &value))
+			fsm_settings__set_ipc(r);
+	}
+
 	/* Hack for test programs like test-dump-untracked-cache */
 	if (ignore_untracked_cache_config)
 		r->settings.core_untracked_cache = UNTRACKED_CACHE_KEEP;