ref-filter: avoid backend filtering with --ignore-case

When for-each-ref is used with --ignore-case, we expect
match_name_as_path() to do a case-insensitive match. But
there's an extra layer of filtering that happens before we
even get there. Since commit cfe004a5a9 (ref-filter: limit
traversal to prefix, 2017-05-22), we feed the prefix to the
ref backend so that it can optimize the ref iteration.

There's no mechanism for us to tell the backend we're matching
case-insensitively.  Nor is there likely to be one anytime soon,
since the packed backend relies on binary-searching the sorted list
of refs. Let's just punt on this case. The extra filtering is an
optimization that we simply can't do. We'll still give the correct
answer via the filtering in match_name_as_path().

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ref-filter.c

@@ -1769,6 +1769,15 @@ static int for_each_fullref_in_pattern(struct ref_filter *filter,
 		return for_each_fullref_in("", cb, cb_data, broken);
 	}
 
+	if (filter->ignore_case) {
+		/*
+		 * we can't handle case-insensitive comparisons,
+		 * so just return everything and let the caller
+		 * sort it out.
+		 */
+		return for_each_fullref_in("", cb, cb_data, broken);
+	}
+
 	if (!filter->name_patterns[0]) {
 		/* no patterns; we have to look at everything */
 		return for_each_fullref_in("", cb, cb_data, broken);

t/t6300-for-each-ref.sh

@@ -795,7 +795,7 @@ test_expect_success ':remotename and :remoteref' '
 	)
 '
 
-test_expect_failure 'for-each-ref --ignore-case ignores case' '
+test_expect_success 'for-each-ref --ignore-case ignores case' '
 	>expect &&
 	git for-each-ref --format="%(refname)" refs/heads/MASTER >actual &&
 	test_cmp expect actual &&