commit: correctly respect skip-worktree bit

Commit b4d1690 (Teach Git to respect skip-worktree bit (reading part))
fails to make "git commit -- a b c" respect skip-worktree
(i.e. not committing paths that are skip-worktree). This is because
when the index is reset back to HEAD, all skip-worktree information is
gone.

This patch saves skip-worktree information in the string list of
committed paths, then reuse it later on to skip skip-worktree paths.

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

builtin-commit.c

@@ -164,11 +164,15 @@ static int list_paths(struct string_list *list, const char *with_tree,
 
 	for (i = 0; i < active_nr; i++) {
 		struct cache_entry *ce = active_cache[i];
+		struct string_list_item *item;
+
 		if (ce->ce_flags & CE_UPDATE)
 			continue;
 		if (!match_pathspec(pattern, ce->name, ce_namelen(ce), 0, m))
 			continue;
-		string_list_insert(ce->name, list);
+		item = string_list_insert(ce->name, list);
+		if (ce_skip_worktree(ce))
+			item->util = item; /* better a valid pointer than a fake one */
 	}
 
 	return report_path_error(m, pattern, prefix ? strlen(prefix) : 0);
@@ -180,10 +184,9 @@ static void add_remove_files(struct string_list *list)
 	for (i = 0; i < list->nr; i++) {
 		struct stat st;
 		struct string_list_item *p = &(list->items[i]);
-		int pos = index_name_pos(&the_index, p->string, strlen(p->string));
-		struct cache_entry *ce = pos < 0 ? NULL : active_cache[pos];
 
-		if (ce && ce_skip_worktree(ce))
+		/* p->util is skip-worktree */
+		if (p->util)
 			continue;
 
 		if (!lstat(p->string, &st)) {

t/t7011-skip-worktree-reading.sh

@@ -148,13 +148,13 @@ test_expect_success 'git-rm succeeds on skip-worktree absent entries' '
 	git rm 1
 '
 
-test_expect_failure 'commit on skip-worktree absent entries' '
+test_expect_success 'commit on skip-worktree absent entries' '
 	git reset &&
 	setup_absent &&
 	test_must_fail git commit -m null 1
 '
 
-test_expect_failure 'commit on skip-worktree dirty entries' '
+test_expect_success 'commit on skip-worktree dirty entries' '
 	git reset &&
 	setup_dirty &&
 	test_must_fail git commit -m null 1