ls-files: filter pathspec before lstat

In --deleted and --modified modes, show_files() calls lstat() for each
index entry before show_ce() applies the pathspec. prune_index() avoids
most of these calls for pathspecs with a common directory prefix, but
not for a top-level name or leading wildcard.

Match before lstat() to avoid accessing the worktree for entries that
cannot be shown. Treat this as a prefilter: do not update ps_matched,
and retain the match in show_ce() so --error-unmatch is satisfied only
by entries that the selected modes actually show.

Prefilter only a single pathspec item, bounding the added work for each
index entry. Applying match_pathspec() to multiple arguments can cost
more than the lstat() calls it avoids. In a synthetic repository with
10,000 clean files, passing every path to ls-files --modified increased
runtime from 112.5 ms to 494.1 ms when the prefilter was unconditional.

With $parent and $this exported as paths to binaries built from the
parent and this commit, on a repository with 881,290 index entries:

    hyperfine --warmup 0 --runs 3 \
        --command-name parent \
        '$parent -c core.fsmonitor=false ls-files --deleted -- README.md >/dev/null' \
        --command-name this-commit \
        '$this -c core.fsmonitor=false ls-files --deleted -- README.md >/dev/null'

reported means of 65.790 seconds for the parent and 4.987 seconds for
this commit.

Link: https://lore.kernel.org/r/xmqqfr2tnfk0.fsf@gitster.g
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/ls-files.c

@@ -453,6 +453,17 @@ static void show_files(struct repository *repo, struct dir_struct *dir)
 			continue;
 		if (ce_skip_worktree(ce))
 			continue;
+		/*
+		 * match_pathspec() is linear in pathspec.nr, so prefilter only
+		 * the single-pathspec case. Only entries shown by show_ce()
+		 * satisfy --error-unmatch.
+		 */
+		if (pathspec.nr == 1 &&
+		    !match_pathspec(repo->index, &pathspec, fullname.buf,
+				    fullname.len, max_prefix_len, NULL,
+				    S_ISDIR(ce->ce_mode) ||
+				    S_ISGITLINK(ce->ce_mode)))
+			continue;
 		stat_err = lstat(fullname.buf, &st);
 		if (stat_err && (errno != ENOENT && errno != ENOTDIR))
 			error_errno("cannot lstat '%s'", fullname.buf);

t/meson.build

@@ -1141,6 +1141,7 @@ benchmarks = [
   'perf/p1500-graph-walks.sh',
   'perf/p1501-rev-parse-oneline.sh',
   'perf/p2000-sparse-operations.sh',
+  'perf/p3010-ls-files.sh',
   'perf/p3400-rebase.sh',
   'perf/p3404-rebase-interactive.sh',
   'perf/p4000-diff-algorithms.sh',

t/perf/p3010-ls-files.sh

@@ -0,0 +1,31 @@
+#!/bin/sh
+
+test_description='Tests ls-files worktree performance'
+
+. ./perf-lib.sh
+
+test_perf_large_repo
+test_checkout_worktree
+
+test_expect_success 'select a zero-prefix pathspec' '
+	tracked_file=$(git ls-files | sed -n 1p) &&
+	test -n "$tracked_file" &&
+	pathspec="?${tracked_file#?}" &&
+	test_export pathspec
+'
+
+test_perf 'ls-files --deleted with pathspec' '
+	git -c core.fsmonitor=false ls-files --deleted \
+		-- "$pathspec" >/dev/null
+'
+
+test_perf 'ls-files --deleted with all-matching pathspec' '
+	git -c core.fsmonitor=false ls-files --deleted -- "*" >/dev/null
+'
+
+test_perf 'ls-files --modified with pathspec' '
+	git -c core.fsmonitor=false ls-files --modified \
+		-- "$pathspec" >/dev/null
+'
+
+test_done

t/t3010-ls-files-killed-modified.sh

@@ -124,4 +124,22 @@ test_expect_success 'validate git ls-files -m output.' '
 	test_cmp .expected .output
 '
 
+test_expect_success 'worktree modes honor wildcard pathspecs' '
+	cat >.expected <<-\EOF &&
+	path2/file2
+	path3/file3
+	EOF
+	git ls-files --deleted -- "path?/file?" >.output &&
+	test_cmp .expected .output &&
+
+	cat >.expected <<-\EOF &&
+	path7
+	path8
+	EOF
+	git ls-files --modified --error-unmatch -- "path[78]" >.output &&
+	test_cmp .expected .output &&
+
+	test_must_fail git ls-files --modified --error-unmatch -- path10
+'
+
 test_done