status: advise to consider use of -u when read_directory takes too long

Introduce advice.statusUoption to suggest considering use of -u to
strike different trade-off when it took more than 2 seconds to
enumerate untracked/ignored files.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -163,6 +163,10 @@ advice.*::
 		state in the output of linkgit:git-status[1] and in
 		the template shown when writing commit messages in
 		linkgit:git-commit[1].
+	statusUoption::
+		Advise to consider using the `-u` option to linkgit:git-status[1]
+		when the command takes more than 2 seconds to enumerate untracked
+		files.
 	commitBeforeMerge::
 		Advice shown when linkgit:git-merge[1] refuses to
 		merge to avoid overwriting local changes.

advice.c

@@ -5,6 +5,7 @@ int advice_push_non_ff_current = 1;
 int advice_push_non_ff_default = 1;
 int advice_push_non_ff_matching = 1;
 int advice_status_hints = 1;
+int advice_status_u_option = 1;
 int advice_commit_before_merge = 1;
 int advice_resolve_conflict = 1;
 int advice_implicit_identity = 1;
@@ -19,6 +20,7 @@ static struct {
 	{ "pushnonffdefault", &advice_push_non_ff_default },
 	{ "pushnonffmatching", &advice_push_non_ff_matching },
 	{ "statushints", &advice_status_hints },
+	{ "statusuoption", &advice_status_u_option },
 	{ "commitbeforemerge", &advice_commit_before_merge },
 	{ "resolveconflict", &advice_resolve_conflict },
 	{ "implicitidentity", &advice_implicit_identity },

advice.h

@@ -8,6 +8,7 @@ extern int advice_push_non_ff_current;
 extern int advice_push_non_ff_default;
 extern int advice_push_non_ff_matching;
 extern int advice_status_hints;
+extern int advice_status_u_option;
 extern int advice_commit_before_merge;
 extern int advice_resolve_conflict;
 extern int advice_implicit_identity;

t/t7060-wtstatus.sh

@@ -5,6 +5,7 @@ test_description='basic work tree status reporting'
 . ./test-lib.sh
 
 test_expect_success setup '
+	git config --global advice.statusuoption false &&
 	test_commit A &&
 	test_commit B oneside added &&
 	git checkout A^0 &&

t/t7508-status.sh

@@ -8,6 +8,7 @@ test_description='git status'
 . ./test-lib.sh
 
 test_expect_success 'status -h in broken repository' '
+	git config --global advice.statusuoption false &&
 	mkdir broken &&
 	test_when_finished "rm -fr broken" &&
 	(

t/t7512-status-help.sh

@@ -14,6 +14,7 @@ test_description='git status advices'
 set_fake_editor
 
 test_expect_success 'prepare for conflicts' '
+	git config --global advice.statusuoption false &&
 	test_commit init main.txt init &&
 	git branch conflicts &&
 	test_commit on_master main.txt on_master &&

wt-status.c

@@ -496,9 +496,14 @@ static void wt_status_collect_untracked(struct wt_status *s)
 {
 	int i;
 	struct dir_struct dir;
+	struct timeval t_begin;
 
 	if (!s->show_untracked_files)
 		return;
+
+	if (advice_status_u_option)
+		gettimeofday(&t_begin, NULL);
+
 	memset(&dir, 0, sizeof(dir));
 	if (s->show_untracked_files != SHOW_ALL_UNTRACKED_FILES)
 		dir.flags |=
@@ -528,6 +533,14 @@ static void wt_status_collect_untracked(struct wt_status *s)
 	}
 
 	free(dir.entries);
+
+	if (advice_status_u_option) {
+		struct timeval t_end;
+		gettimeofday(&t_end, NULL);
+		s->untracked_in_ms =
+			(uint64_t)t_end.tv_sec * 1000 + t_end.tv_usec / 1000 -
+			((uint64_t)t_begin.tv_sec * 1000 + t_begin.tv_usec / 1000);
+	}
 }
 
 void wt_status_collect(struct wt_status *s)
@@ -1011,6 +1024,18 @@ void wt_status_print(struct wt_status *s)
 		wt_status_print_other(s, &s->untracked, _("Untracked files"), "add");
 		if (s->show_ignored_files)
 			wt_status_print_other(s, &s->ignored, _("Ignored files"), "add -f");
+		if (advice_status_u_option && 2000 < s->untracked_in_ms) {
+			status_printf_ln(s, GIT_COLOR_NORMAL, "");
+			status_printf_ln(s, GIT_COLOR_NORMAL,
+				 _("It took %.2f seconds to enumerate untracked files."
+				   "  'status -uno'"),
+				 s->untracked_in_ms / 1000.0);
+			status_printf_ln(s, GIT_COLOR_NORMAL,
+				 _("may speed it up, but you have to be careful not"
+				   " to forget to add"));
+			status_printf_ln(s, GIT_COLOR_NORMAL,
+				 _("new files yourself (see 'git help status')."));
+		}
 	} else if (s->commitable)
 		status_printf_ln(s, GIT_COLOR_NORMAL, _("Untracked files not listed%s"),
 			advice_status_hints

wt-status.h

@@ -69,6 +69,7 @@ struct wt_status {
 	struct string_list change;
 	struct string_list untracked;
 	struct string_list ignored;
+	uint32_t untracked_in_ms;
 };
 
 struct wt_status_state {