pack-objects: turn off bitmaps when we split packs

If a pack.packSizeLimit is set, we may split the pack data
across multiple packfiles. This means we cannot generate
.bitmap files, as they require that all of the reachable
objects are in the same pack. We check that condition when
we are generating the list of objects to pack (and disable
bitmaps if we are not packing everything), but we forgot to
update it when we notice that we needed to split (which
doesn't happen until the actual write phase).

The resulting bitmaps are quite bogus (they mention entries
that do not exist in the pack!) and can cause a fetch or
push to send insufficient objects.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -812,6 +812,7 @@ static void write_pack_file(void)
 			fixup_pack_header_footer(fd, sha1, pack_tmp_name,
 						 nr_written, sha1, offset);
 			close(fd);
+			write_bitmap_index = 0;
 		}
 
 		if (!pack_to_stdout) {

t/t5310-pack-bitmaps.sh

@@ -170,4 +170,13 @@ test_expect_success JGIT 'jgit can read our bitmaps' '
 	)
 '
 
+test_expect_success 'splitting packs does not generate bogus bitmaps' '
+	test-genrandom foo $((1024 * 1024)) >rand &&
+	git add rand &&
+	git commit -m "commit with big file" &&
+	git -c pack.packSizeLimit=500k repack -adb &&
+	git init --bare no-bitmaps.git &&
+	git -C no-bitmaps.git fetch .. HEAD
+'
+
 test_done