Merge branch 'rr/status-untracked-advice'

The advice message given by "git status" when it takes long time to
enumerate untracked paths has been updated.

* rr/status-untracked-advice:
  status: modernize git-status "slow untracked files" advice

Documentation/git-status.txt

@@ -457,6 +457,66 @@ during the write may conflict with other simultaneous processes, causing
 them to fail. Scripts running `status` in the background should consider
 using `git --no-optional-locks status` (see linkgit:git[1] for details).
 
+UNTRACKED FILES AND PERFORMANCE
+-------------------------------
+
+`git status` can be very slow in large worktrees if/when it
+needs to search for untracked files and directories. There are
+many configuration options available to speed this up by either
+avoiding the work or making use of cached results from previous
+Git commands. There is no single optimum set of settings right
+for everyone. We'll list a summary of the relevant options to help
+you, but before going into the list, you may want to run `git status`
+again, because your configuration may already be caching `git status`
+results, so it could be faster on subsequent runs.
+
+* The `--untracked-files=no` flag or the
+	`status.showUntrackedfiles=false` config (see above for both):
+	indicate that `git status` should not report untracked
+	files. This is the fastest option. `git status` will not list
+	the untracked files, so you need to be careful to remember if
+	you create any new files and manually `git add` them.
+
+* `advice.statusUoption=false` (see linkgit:git-config[1]):
+	setting this variable to `false` disables the warning message
+	given when enumerating untracked files takes more than 2
+	seconds.  In a large project, it may take longer and the user
+	may have already accepted the trade off (e.g. using "-uno" may
+	not be an acceptable option for the user), in which case, there
+	is no point issuing the warning message, and in such a case,
+	disabling the warning may be the best.
+
+* `core.untrackedCache=true` (see linkgit:git-update-index[1]):
+	enable the untracked cache feature and only search directories
+	that have been modified since the previous `git status` command.
+	Git remembers the set of untracked files within each directory
+	and assumes that if a directory has not been modified, then
+	the set of untracked files within has not changed.  This is much
+	faster than enumerating the contents of every directory, but still
+	not without cost, because Git still has to search for the set of
+	modified directories. The untracked cache is stored in the
+	`.git/index` file. The reduced cost of searching for untracked
+	files is offset slightly by the increased size of the index and
+	the cost of keeping it up-to-date. That reduced search time is
+	usually worth the additional size.
+
+* `core.untrackedCache=true` and `core.fsmonitor=true` or
+	`core.fsmonitor=<hook_command_pathname>` (see
+	linkgit:git-update-index[1]): enable both the untracked cache
+	and FSMonitor features and only search directories that have
+	been modified since the previous `git status` command.  This
+	is faster than using just the untracked cache alone because
+	Git can also avoid searching for modified directories.  Git
+	only has to enumerate the exact set of directories that have
+	changed recently. While the FSMonitor feature can be enabled
+	without the untracked cache, the benefits are greatly reduced
+	in that case.
+
+Note that after you turn on the untracked cache and/or FSMonitor
+features it may take a few `git status` commands for the various
+caches to warm up before you see improved command times.  This is
+normal.
+
 SEE ALSO
 --------
 linkgit:gitignore[5]

t/t7508-status.sh

@@ -1676,4 +1676,74 @@ test_expect_success 'racy timestamps will be fixed for dirty worktree' '
 	! test_is_magic_mtime .git/index
 '
 
+test_expect_success 'setup slow status advice' '
+	GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main git init slowstatus &&
+	(
+		cd slowstatus &&
+		cat >.gitignore <<-\EOF &&
+		/actual
+		/expected
+		/out
+		EOF
+		git add .gitignore &&
+		git commit -m "Add .gitignore" &&
+		git config advice.statusuoption true
+	)
+'
+
+test_expect_success 'slow status advice when core.untrackedCache and fsmonitor are unset' '
+	(
+		cd slowstatus &&
+		git config core.untrackedCache false &&
+		git config core.fsmonitor false &&
+		GIT_TEST_UF_DELAY_WARNING=1 git status >actual &&
+		cat >expected <<-\EOF &&
+		On branch main
+
+		It took 3.25 seconds to enumerate untracked files.
+		See '\''git help status'\'' for information on how to improve this.
+
+		nothing to commit, working tree clean
+		EOF
+		test_cmp expected actual
+	)
+'
+
+test_expect_success 'slow status advice when core.untrackedCache true, but not fsmonitor' '
+	(
+		cd slowstatus &&
+		git config core.untrackedCache true &&
+		git config core.fsmonitor false &&
+		GIT_TEST_UF_DELAY_WARNING=1 git status >actual &&
+		cat >expected <<-\EOF &&
+		On branch main
+
+		It took 3.25 seconds to enumerate untracked files.
+		See '\''git help status'\'' for information on how to improve this.
+
+		nothing to commit, working tree clean
+		EOF
+		test_cmp expected actual
+	)
+'
+
+test_expect_success 'slow status advice when core.untrackedCache true, and fsmonitor' '
+	(
+		cd slowstatus &&
+		git config core.untrackedCache true &&
+		git config core.fsmonitor true &&
+		GIT_TEST_UF_DELAY_WARNING=1 git status >actual &&
+		cat >expected <<-\EOF &&
+		On branch main
+
+		It took 3.25 seconds to enumerate untracked files,
+		but the results were cached, and subsequent runs may be faster.
+		See '\''git help status'\'' for information on how to improve this.
+
+		nothing to commit, working tree clean
+		EOF
+		test_cmp expected actual
+	)
+'
+
 test_done

wt-status.c

@@ -18,8 +18,10 @@
 #include "worktree.h"
 #include "lockfile.h"
 #include "sequencer.h"
+#include "fsmonitor-settings.h"
 
 #define AB_DELAY_WARNING_IN_MS (2 * 1000)
+#define UF_DELAY_WARNING_IN_MS (2 * 1000)
 
 static const char cut_line[] =
 "------------------------ >8 ------------------------\n";
@@ -1205,6 +1207,13 @@ static void wt_longstatus_print_tracking(struct wt_status *s)
 	strbuf_release(&sb);
 }
 
+static int uf_was_slow(struct wt_status *s)
+{
+	if (getenv("GIT_TEST_UF_DELAY_WARNING"))
+		s->untracked_in_ms = 3250;
+	return UF_DELAY_WARNING_IN_MS < s->untracked_in_ms;
+}
+
 static void show_merge_in_progress(struct wt_status *s,
 				   const char *color)
 {
@@ -1814,6 +1823,7 @@ static void wt_longstatus_print(struct wt_status *s)
 {
 	const char *branch_color = color(WT_STATUS_ONBRANCH, s);
 	const char *branch_status_color = color(WT_STATUS_HEADER, s);
+	enum fsmonitor_mode fsm_mode = fsm_settings__get_mode(s->repo);
 
 	if (s->branch) {
 		const char *on_what = _("On branch ");
@@ -1870,13 +1880,21 @@ static void wt_longstatus_print(struct wt_status *s)
 		wt_longstatus_print_other(s, &s->untracked, _("Untracked files"), "add");
 		if (s->show_ignored_mode)
 			wt_longstatus_print_other(s, &s->ignored, _("Ignored files"), "add -f");
-		if (advice_enabled(ADVICE_STATUS_U_OPTION) && 2000 < s->untracked_in_ms) {
+		if (advice_enabled(ADVICE_STATUS_U_OPTION) && uf_was_slow(s)) {
 			status_printf_ln(s, GIT_COLOR_NORMAL, "%s", "");
+			if (fsm_mode > FSMONITOR_MODE_DISABLED) {
+				status_printf_ln(s, GIT_COLOR_NORMAL,
+						_("It took %.2f seconds to enumerate untracked files,\n"
+						"but the results were cached, and subsequent runs may be faster."),
+						s->untracked_in_ms / 1000.0);
+			} else {
+				status_printf_ln(s, GIT_COLOR_NORMAL,
+						_("It took %.2f seconds to enumerate untracked files."),
+						s->untracked_in_ms / 1000.0);
+			}
 			status_printf_ln(s, GIT_COLOR_NORMAL,
-					 _("It took %.2f seconds to enumerate untracked files. 'status -uno'\n"
+					_("See 'git help status' for information on how to improve this."));
-					   "may speed it up, but you have to be careful not to forget to add\n"
+			status_printf_ln(s, GIT_COLOR_NORMAL, "%s", "");
-					   "new files yourself (see 'git help status')."),
-					 s->untracked_in_ms / 1000.0);
 		}
 	} else if (s->committable)
 		status_printf_ln(s, GIT_COLOR_NORMAL, _("Untracked files not listed%s"),