object: apply skip_hash and discard_tree optimizations to unknown blobs too

parse_object_with_flags() has an optimization to skip parsing blobs if
PARSE_OBJECT_SKIP_HASH_CHECK is set and the object hasn't been seen
before or might be a blob but hasn't been parsed yet. The latter can
happen, for example, if add_tree_entries() walks a path that references
a blob object that hasn't been seen before: lookup_blob() marks the
referenced oid as being a blob, but does not provide any additional
information about it until it is parsed.

It's possible for an object to be created without even a type, such as
when prepare_revision_walk() uses mark_uninteresting() to mark all
promisor objects as uninteresting. These objects have obj->parsed ==
false and obj->type == OBJ_NONE.

The skip_hash optimization does not consider this kind of object, so
parse_object_with_flags() proceeds to fully parse the object to
determine its type.

Improve the optimization by applying it to OBJ_NONE objects as well as
OBJ_BLOB ones. Apply a similar fix for trees.

Fixes: 8db2dad ("parse_object(): check on-disk type of suspected blob")
Signed-off-by: Aaron Plattner <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: aaronp24

object.c

@@ -328,7 +328,7 @@ struct object *parse_object_with_flags(struct repository *r,
 			return &commit->object;
 	}
 
-	if ((!obj || obj->type == OBJ_BLOB) &&
+	if ((!obj || obj->type == OBJ_NONE || obj->type == OBJ_BLOB) &&
 	    odb_read_object_info(r->objects, oid, NULL) == OBJ_BLOB) {
 		if (!skip_hash && stream_object_signature(r, repl) < 0) {
 			error(_("hash mismatch %s"), oid_to_hex(oid));
@@ -344,7 +344,7 @@ struct object *parse_object_with_flags(struct repository *r,
 	 * have the on-disk object with the correct type.
 	 */
 	if (skip_hash && discard_tree &&
-	    (!obj || obj->type == OBJ_TREE) &&
+	    (!obj || obj->type == OBJ_NONE || obj->type == OBJ_TREE) &&
 	    odb_read_object_info(r->objects, oid, NULL) == OBJ_TREE) {
 		return &lookup_tree(r, oid)->object;
 	}