Re: Fetching upstream remote fails if repo was a blobless clone

[Jeff King <peff@peff.net>]

On Sat, Aug 02, 2025 at 03:31:11PM -0400, Jeff King wrote:

> Doing this:
> 
> diff --git a/builtin/index-pack.c b/builtin/index-pack.c
> index 0a5c8a1ac8..e01cf7238b 100644
> --- a/builtin/index-pack.c
> +++ b/builtin/index-pack.c
> @@ -262,9 +262,14 @@ static unsigned check_object(struct object *obj)
>  		unsigned long size;
>  		int type = odb_read_object_info(the_repository->objects,
>  						&obj->oid, &size);
> -		if (type <= 0)
> +		if (type <= 0) {
> +			if (is_promisor_object(the_repository, &obj->oid)) {
> +				obj->flags |= FLAG_CHECKED;
> +				return 1;
> +			}
>  			die(_("did not receive expected object %s"),
>  			      oid_to_hex(&obj->oid));
> +		}
>  		if (type != obj->type)
>  			die(_("object %s: expected type %s, found %s"),
>  			    oid_to_hex(&obj->oid),
> 
> makes the problem go away. But I feel like I'm probably missing
> something (and that function is rather expensive to run, though maybe
> not so bad if the alternative is crashing).
> 
> +cc Jonathan Tan as the author of the code comment above for any wisdom.

And here is a minimal reproduction that doesn't depend on any other
repositories:

-- >8 --
# Server has two commits, with two blobs for file, old and new.
git init server
(
	cd server
	echo old >file
	git add .
	git commit -m old
	echo new >file
	git commit -am new

	git config uploadpack.allowfilter true
)

# The fork has built a new tree which mentions the old file.
git clone server fork
(
	cd fork
	git reset --hard HEAD^
	echo content >unrelated
	git add .
	git commit -m unrelated
)

# After our partial clone, we have the new blob (because we faulted it in to
# checkout), but not the old one (because it is buried in history).
git clone --no-local --filter=blob:none server repo
cd repo

# This will get the tree at the tip of the fork repo, which mentions old. When
# we fsck that tree, we'll see that it mentions the old blob, and expect to
# find it. But we won't due to the partial clone (though we could get it if we
# wanted from the server repo).
git -c transfer.fsckObjects=true fetch ../fork
-- >8 --

That fails with stock git now, like this:

  fatal: did not receive expected object 3367afdbbf91e638efe983616377c60477cc6612
  fatal: index-pack failed

but succeeds with the patch above.

-Peff