multi-pack-index: verify oid lookup order

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

midx.c

@@ -959,5 +959,16 @@ int verify_midx_file(const char *object_dir)
 				    i, oid_fanout1, oid_fanout2, i + 1);
 	}
 
+	for (i = 0; i < m->num_objects - 1; i++) {
+		struct object_id oid1, oid2;
+
+		nth_midxed_object_oid(&oid1, m, i);
+		nth_midxed_object_oid(&oid2, m, i + 1);
+
+		if (oidcmp(&oid1, &oid2) >= 0)
+			midx_report(_("oid lookup out of order: oid[%d] = %s >= %s = oid[%d]"),
+				    i, oid_to_hex(&oid1), oid_to_hex(&oid2), i + 1);
+	}
+
 	return verify_midx_error;
 }

t/t5319-multi-pack-index.sh

@@ -175,6 +175,7 @@ test_expect_success 'verify bad signature' '
 		"multi-pack-index signature"
 '
 
+HASH_LEN=20
 MIDX_BYTE_VERSION=4
 MIDX_BYTE_OID_VERSION=5
 MIDX_BYTE_CHUNK_COUNT=6
@@ -189,6 +190,8 @@ MIDX_BYTE_PACKNAME_ORDER=$(($MIDX_OFFSET_PACKNAMES + 2))
 MIDX_OFFSET_OID_FANOUT=$(($MIDX_OFFSET_PACKNAMES + 652))
 MIDX_OID_FANOUT_WIDTH=4
 MIDX_BYTE_OID_FANOUT_ORDER=$((MIDX_OFFSET_OID_FANOUT + 250 * $MIDX_OID_FANOUT_WIDTH + 1))
+MIDX_OFFSET_OID_LOOKUP=$(($MIDX_OFFSET_OID_FANOUT + 256 * $MIDX_OID_FANOUT_WIDTH))
+MIDX_BYTE_OID_LOOKUP=$(($MIDX_OFFSET_OID_LOOKUP + 16 * $HASH_LEN))
 
 test_expect_success 'verify bad version' '
 	corrupt_midx_and_verify $MIDX_BYTE_VERSION "\00" $objdir \
@@ -235,6 +238,11 @@ test_expect_success 'verify oid fanout out of order' '
 		"oid fanout out of order"
 '
 
+test_expect_success 'verify oid lookup out of order' '
+	corrupt_midx_and_verify $MIDX_BYTE_OID_LOOKUP "\00" $objdir \
+		"oid lookup out of order"
+'
+
 test_expect_success 'repack removes multi-pack-index' '
 	test_path_is_file $objdir/pack/multi-pack-index &&
 	git repack -adf &&