[PATCH v14 12/21] update-index: enable/disable watchman support

@@ -18,6 +18,9 @@ each with a submodule, you might need four index-helpers.  (In practice,
 this is only worthwhile for large indexes, so only use it if you notice
 that git status is slow).
 
+If you want the index-helper to accelerate untracked file checking,
+run git update-index --watchman before using it.
+
 OPTIONS
 -------
 

@@ -19,6 +19,7 @@ SYNOPSIS
 	     [--ignore-submodules]
 	     [--[no-]split-index]
 	     [--[no-|test-|force-]untracked-cache]
+	     [--[no-]watchman]
 	     [--really-refresh] [--unresolve] [--again | -g]
 	     [--info-only] [--index-info]
 	     [-z] [--stdin] [--index-version <n>]

@@ -176,6 +177,11 @@ may not support it yet.
 --no-untracked-cache::
 	Enable or disable untracked cache feature. Please use
 	`--test-untracked-cache` before enabling it.
+
+--watchman::
+--no-watchman::
+	Enable or disable watchman support. This is, at present,
+	only useful with git index-helper.
 +
 These options take effect whatever the value of the `core.untrackedCache`
 configuration variable (see linkgit:git-config[1]). But a warning is

@@ -914,6 +914,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 {
 	int newfd, entries, has_errors = 0, nul_term_line = 0;
 	enum uc_mode untracked_cache = UC_UNSPECIFIED;
+	int use_watchman = -1;
 	int read_from_stdin = 0;
 	int prefix_length = prefix ? strlen(prefix) : 0;
 	int preferred_index_format = 0;

@@ -1012,6 +1013,8 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 			    N_("test if the filesystem supports untracked cache"), UC_TEST),
 		OPT_SET_INT(0, "force-untracked-cache", &untracked_cache,
 			    N_("enable untracked cache without testing the filesystem"), UC_FORCE),
+		OPT_BOOL(0, "watchman", &use_watchman,
+			N_("use or not use watchman to reduce refresh cost")),
 		OPT_END()
 	};
 

@@ -1149,6 +1152,18 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		die("Bug: bad untracked_cache value: %d", untracked_cache);
 	}
 
+	if (use_watchman > 0) {
+		the_index.last_update    = xstrdup("");
+		the_index.cache_changed |= WATCHMAN_CHANGED;
+#ifndef USE_WATCHMAN
+		warning(_("git was built without watchman support, so this "
+			  "command will probably not result in any speedup."));
+#endif
+	} else if (!use_watchman) {
+		the_index.last_update    = NULL;
+		the_index.cache_changed |= WATCHMAN_CHANGED;
+	}
+
 	if (active_cache_changed) {
 		if (newfd < 0) {
 			if (refresh_args.flags & REFRESH_QUIET)