rev-list: fallback to non-bitmap traversal when filtering

The "--use-bitmap-index" option is usually aspirational: if we have
bitmaps and the request can be fulfilled more quickly using them we'll
do so, but otherwise fall back to a non-bitmap traversal.

The exception is object filtering, which explicitly dies if the two
options are combined. Let's convert this to the usual fallback behavior.
This is a minor convenience for now (since the caller can easily know
that --filter and --use-bitmap-index don't combine), but will become
much more useful as we start to support _some_ filters with bitmaps, but
not others.

The test infrastructure here is bigger than necessary for checking this
one small feature. But it will serve as the basis for more filtering
bitmap tests in future patches.

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

builtin/rev-list.c

@@ -521,8 +521,8 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix)
 	if (revs.show_notes)
 		die(_("rev-list does not support display of notes"));
 
-	if (filter_options.choice && use_bitmap_index)
-		die(_("cannot combine --use-bitmap-index with object filtering"));
+	if (filter_options.choice)
+		use_bitmap_index = 0;
 
 	save_commit_buffer = (revs.verbose_header ||
 			      revs.grep_filter.pattern_list ||

t/t6113-rev-list-bitmap-filters.sh

@@ -0,0 +1,24 @@
+#!/bin/sh
+
+test_description='rev-list combining bitmaps and filters'
+. ./test-lib.sh
+
+test_expect_success 'set up bitmapped repo' '
+	# one commit will have bitmaps, the other will not
+	test_commit one &&
+	git repack -adb &&
+	test_commit two
+'
+
+test_expect_success 'filters fallback to non-bitmap traversal' '
+	# use a path-based filter, since they are inherently incompatible with
+	# bitmaps (i.e., this test will never get confused by later code to
+	# combine the features)
+	filter=$(echo "!one" | git hash-object -w --stdin) &&
+	git rev-list --objects --filter=sparse:oid=$filter HEAD >expect &&
+	git rev-list --use-bitmap-index \
+		     --objects --filter=sparse:oid=$filter HEAD >actual &&
+	test_cmp expect actual
+'
+
+test_done