add: ignore outside the sparse-checkout in refresh()

Since b243012 (refresh_index(): add flag to ignore SKIP_WORKTREE
entries, 2021-04-08), 'git add --refresh <path>' will output a warning
message when the path is outside the sparse-checkout definition. The
implementation of this warning happened in parallel with the
sparse-index work to add ensure_full_index() calls throughout the
codebase.

Update this loop to have the proper logic that checks to see if the
pathspec is outside the sparse-checkout definition. This avoids the need
to expand the sparse directory entry and determine if the path is
tracked, untracked, or ignored. We simply avoid updating the stat()
information because there isn't even an entry that matches the path!

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>

Author: derrickstolee

builtin/add.c

@@ -192,13 +192,21 @@ static int refresh(int verbose, const struct pathspec *pathspec)
 	struct string_list only_match_skip_worktree = STRING_LIST_INIT_NODUP;
 	int flags = REFRESH_IGNORE_SKIP_WORKTREE |
 		    (verbose ? REFRESH_IN_PORCELAIN : REFRESH_QUIET);
+	struct pattern_list pl = { 0 };
+	int sparse_checkout_enabled = !get_sparse_checkout_patterns(&pl);
 
 	seen = xcalloc(pathspec->nr, 1);
 	refresh_index(&the_index, flags, pathspec, seen,
 		      _("Unstaged changes after refreshing the index:"));
 	for (i = 0; i < pathspec->nr; i++) {
 		if (!seen[i]) {
-			if (matches_skip_worktree(pathspec, i, &skip_worktree_seen)) {
+			const char *path = pathspec->items[i].original;
+			int dtype = DT_REG;
+
+			if (matches_skip_worktree(pathspec, i, &skip_worktree_seen) ||
+			    (sparse_checkout_enabled &&
+			     !path_matches_pattern_list(path, strlen(path), NULL,
+							&dtype, &pl, &the_index))) {
 				string_list_append(&only_match_skip_worktree,
 						   pathspec->items[i].original);
 			} else {

t/t1092-sparse-checkout-compatibility.sh

@@ -347,7 +347,7 @@ test_expect_success 'status/add: outside sparse cone' '
 	test_all_match git commit -m folder1/newer
 '
 
-test_expect_failure 'add: pathspec within sparse directory' '
+test_expect_success 'add: pathspec within sparse directory' '
 	init_repos &&
 
 	run_on_sparse mkdir folder1 &&
@@ -357,10 +357,6 @@ test_expect_failure 'add: pathspec within sparse directory' '
 	# This "git add folder1/a" fails with a warning
 	# in the sparse repos, differing from the full
 	# repo. This is intentional.
-	#
-	# However, in the sparse-index, folder1/a does not
-	# match any cache entry and fails with a different
-	# error message. This needs work.
 	test_sparse_match test_must_fail git add folder1/a &&
 	test_sparse_match test_must_fail git add --refresh folder1/a &&
 	test_all_match git status --porcelain=v2