Re: [PATCH] fsck.c: fix bogus "empty tree" check

On Tue, 04 Mar 2008 03:21:16 -0800 Junio C Hamano wrote:

 * I've wasted a few hours tonight hunting for random breakages in "git
   push", the symptom of which is "fatal: unresolved deltas left after
   unpacking."  I was hoping this patch would fix it, but it seems that
   the problem is elsewhere.

   I'll revert the following two commits for now:

   d5ef408 (unpack-objects: prevent writing of inconsistent objects)
   28f72a0 (receive-pack: use strict mode for unpacking objects)

   as I have verified that running with receive.fsckobjects set to false
   fixes the issues for me, and the repository at the receiving end (both
   before and after the push) pass git-fsck without problems.  Needless to
   say, I am not a happy camper right now.

This part of commit d5ef408 changes is bogus:

The write_sha1_file() call here was calculating obj_list[nr].sha1; now
it is removed, but added_object() needs this value:

| static void added_object(unsigned nr, enum object_type type,
| 			 void *data, unsigned long size)
| {
| 	struct delta_info **p = &delta_list;
| 	struct delta_info *info;
|
| 	while ((info = *p) != NULL) {
| 		if (!hashcmp(info->base_sha1, obj_list[nr].sha1) ||
					      ^^^^^^^^^^^^^^^^^
| 		    info->base_offset == obj_list[nr].offset) {
| 			*p = info->next;
| 			p = &delta_list;
| 			resolve_delta(info->nr, type, data, size,
| 				      info->delta, info->size);
| 			free(info);
| 			continue;
| 		}
| 		p = &info->next;
| 	}
| }

However, I do not have time to create a proper test case for this.

+	if (!strict) {
+		if (write_sha1_file(buf, size, typename(type), obj_list[nr].sha1) < 0)
+			die("failed to write object");
+		free(buf);
+		obj_list[nr].obj = 0;
+	} else if (type == OBJ_BLOB) {
+		struct blob *blob;
+		if (write_sha1_file(buf, size, typename(type), obj_list[nr].sha1) < 0)
+			die("failed to write object");
+		free(buf);
+
+		blob = lookup_blob(obj_list[nr].sha1);
+		if (blob)
+			blob->object.flags |= FLAG_WRITTEN;
+		else
+			die("invalid blob object");
+		obj_list[nr].obj = 0;
+	} else {
+		struct object *obj;
+		int eaten;
+		hash_sha1_file(buf, size, typename(type), obj_list[nr].sha1);
+		obj = parse_object_buffer(obj_list[nr].sha1, type, size, buf, &eaten);
+		if (!obj)
+			die("invalid %s", typename(type));
+		/* buf is stored via add_object_buffer and in obj, if its a tree or commit */
+		add_object_buffer(obj, buf, size);
+		obj->flags |= FLAG_OPEN;
+		obj_list[nr].obj = obj;
+	}
 }

 static void resolve_delta(unsigned nr, enum object_type type,

The simplest way to fix this would be to duplicate the added_object()
call in all branches; invoking hash_sha1_file() unconditionally will
work too, but may be wasteful if we need to call write_sha1_file()
afterwards.