indexer: do multiple passes over the delta list

Though unusual, a packfile may contain a delta whose base is a delta
that comes later. In order index such a packfile, we must not give up
on the first failure to resolve a delta, but keep it around.

If there is a pass which makes no progress, this indicates that the
packfile is broken, so fail accordingly.

src/indexer.c

@@ -594,20 +594,38 @@ static int resolve_deltas(git_indexer_stream *idx, git_transfer_progress *stats)
 {
 	unsigned int i;
 	struct delta_info *delta;
+	int progressed = 0;
 
+	while (idx->deltas.length > 0) {
+		progressed = 0;
 		git_vector_foreach(&idx->deltas, i, delta) {
 			git_rawobj obj;
 
 			idx->off = delta->delta_off;
 			if (git_packfile_unpack(&obj, idx->pack, &idx->off) < 0)
-			return -1;
+				continue;
 
 			if (hash_and_save(idx, &obj, delta->delta_off) < 0)
-			return -1;
+				continue;
 
 			git__free(obj.data);
 			stats->indexed_objects++;
+			progressed = 1;
 			do_progress_callback(idx, stats);
+
+			/*
+			 * Remove this delta from the list and
+			 * decrease i so we don't skip over the next
+			 * delta.
+			 */
+			git_vector_remove(&idx->deltas, i);
+			i--;
+		}
+
+		if (!progressed) {
+			giterr_set(GITERR_INDEXER, "the packfile is missing bases");
+			return -1;
+		}
 	}
 
 	return 0;

tests-clar/pack/indexer.c

+#include "clar_libgit2.h"
+#include "fileops.h"
+#include "hash.h"
+#include "iterator.h"
+#include "vector.h"
+#include "posix.h"
+
+/*
+ * This is a packfile with three objects. The second is a delta which
+ * depends on the third, which is also a delta.
+ */
+unsigned char out_of_order_pack[] = {
+  0x50, 0x41, 0x43, 0x4b, 0x00, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00, 0x03,
+  0x32, 0x78, 0x9c, 0x63, 0x67, 0x00, 0x00, 0x00, 0x10, 0x00, 0x08, 0x76,
+  0xe6, 0x8f, 0xe8, 0x12, 0x9b, 0x54, 0x6b, 0x10, 0x1a, 0xee, 0x95, 0x10,
+  0xc5, 0x32, 0x8e, 0x7f, 0x21, 0xca, 0x1d, 0x18, 0x78, 0x9c, 0x63, 0x62,
+  0x66, 0x4e, 0xcb, 0xcf, 0x07, 0x00, 0x02, 0xac, 0x01, 0x4d, 0x75, 0x01,
+  0xd7, 0x71, 0x36, 0x66, 0xf4, 0xde, 0x82, 0x27, 0x76, 0xc7, 0x62, 0x2c,
+  0x10, 0xf1, 0xb0, 0x7d, 0xe2, 0x80, 0xdc, 0x78, 0x9c, 0x63, 0x62, 0x62,
+  0x62, 0xb7, 0x03, 0x00, 0x00, 0x69, 0x00, 0x4c, 0xde, 0x7d, 0xaa, 0xe4,
+  0x19, 0x87, 0x58, 0x80, 0x61, 0x09, 0x9a, 0x33, 0xca, 0x7a, 0x31, 0x92,
+  0x6f, 0xae, 0x66, 0x75
+};
+unsigned int out_of_order_pack_len = 112;
+
+void test_pack_indexer__out_of_order(void)
+{
+	git_indexer_stream *idx;
+	git_transfer_progress stats;
+
+	cl_git_pass(git_indexer_stream_new(&idx, ".", NULL, NULL, NULL));
+	cl_git_pass(git_indexer_stream_add(idx, out_of_order_pack, out_of_order_pack_len, &stats));
+	cl_git_pass(git_indexer_stream_finalize(idx, &stats));
+
+	cl_assert_equal_i(stats.total_objects, 3);
+	cl_assert_equal_i(stats.received_objects, 3);
+	cl_assert_equal_i(stats.indexed_objects, 3);
+
+	git_indexer_stream_free(idx);
+}