Merge branch 'ds/ls-files-lazy-unsparse'

"git ls-files <pathspec>..." should not necessarily have to expand
the index fully if a sparsified directory is excluded by the
pathspec; the code is taught to expand the index on demand to avoid
this.

* ds/ls-files-lazy-unsparse:
  ls-files: conditionally leave index sparse

builtin/ls-files.c

@@ -414,14 +414,21 @@ static void show_files(struct repository *repo, struct dir_struct *dir)
 	if (!(show_cached || show_stage || show_deleted || show_modified))
 		return;
 
-	if (!show_sparse_dirs)
-		ensure_full_index(repo->index);
-
 	for (i = 0; i < repo->index->cache_nr; i++) {
 		const struct cache_entry *ce = repo->index->cache[i];
 		struct stat st;
 		int stat_err;
 
+		if (S_ISSPARSEDIR(ce->ce_mode) && !show_sparse_dirs) {
+			/*
+			 * This is the first time we've hit a sparse dir,
+			 * so expansion will leave the first 'i' entries
+			 * alone.
+			 */
+			ensure_full_index(repo->index);
+			ce = repo->index->cache[i];
+		}
+
 		construct_fullname(&fullname, repo, ce);
 
 		if ((dir->flags & DIR_SHOW_IGNORED) &&

t/t1092-sparse-checkout-compatibility.sh

@@ -1506,6 +1506,8 @@ test_expect_success 'sparse-index is not expanded' '
 	ensure_not_expanded reset --hard &&
 	ensure_not_expanded restore -s rename-out-to-out -- deep/deeper1 &&
 
+	ensure_not_expanded ls-files deep/deeper1 &&
+
 	echo >>sparse-index/README.md &&
 	ensure_not_expanded add -A &&
 	echo >>sparse-index/extra.txt &&
@@ -1607,6 +1609,17 @@ test_expect_success 'describe tested on all' '
 	test_all_match git describe --dirty
 '
 
+test_expect_success 'ls-files filtering and expansion' '
+	init_repos &&
+
+	# This filtering will hit a sparse directory midway
+	# through the iteration.
+	test_all_match git ls-files deep &&
+
+	# This pathspec will filter the index to only a sparse
+	# directory.
+	test_all_match git ls-files folder1
+'
 
 test_expect_success 'sparse-index is not expanded: describe' '
 	init_repos &&