Re: [PATCH 2/3] upload-pack: skip parse-object re-hashing of "want" objects

On Wed, Sep 07, 2022 at 10:45:39AM -0400, Derrick Stolee wrote:

After writing this, it was bothering me that 'rev-list --verify' should
be checking for corruption throughout the history, not just at the tips.

This is done via the condition in builtin/rev-list.c:finish_object():

static int finish_object(struct object *obj, const char *name, void *cb_data)
{
	struct rev_list_info *info = cb_data;
	if (oid_object_info_extended(the_repository, &obj->oid, NULL, 0) < 0) {
		finish_object__ma(obj);
		return 1;
	}
	if (info->revs->verify_objects && !obj->parsed && obj->type != OBJ_COMMIT)
		parse_object(the_repository, &obj->oid);
	return 0;
}

So this call is the one that is used most-often by the rev-list command,
but isn't necessary to update for the purpose of our desired speedup. This
is another place where we would want to use read_object_file(). (It may even
be the _only_ place, since finish_object() should be called even for the
tip objects.)

Yeah, I think this is the only place. At least, if you remove the hash
check entirely, then this parse_object() is the only spots that causes a
problem (via the existing test in t1450).

In case you think it is valuable to ensure we test both cases ("tip" and
"not tip") I modified your test to have a third commit and test two rev-list
calls:

I don't think it's important to test here, as we know we just touched
the tip code here. But also, that existing "rev-list --verify-objects"
test in t1450 is covering that case: it corrupts a blob that is
reachable from an otherwise good commit/tree.

We should also have tip and non-tip tests for commits, but I posted
those in a separate series. ;)

-Peff