Subject: Re: [RFC PATCH 2/4] fsck: support refs pointing to lazy objects

From: Junio C Hamano <[email-masked]>
Date: Thu, 27 Jul 2017 11:59:47 -0700

Jonathan Tan <[email-masked]> writes:

> Teach fsck to not treat refs with missing targets as an error when
> extensions.lazyobject is set.
>
> For the purposes of warning about no default refs, such refs are still
> treated as legitimate refs.
>
> Signed-off-by: Jonathan Tan <[email-masked]>
> ---
>  builtin/fsck.c         |  8 ++++++++
>  t/t0410-lazy-object.sh | 20 ++++++++++++++++++++
>  2 files changed, 28 insertions(+)
>
> diff --git a/builtin/fsck.c b/builtin/fsck.c
> index 1cfb8d98c..e29ff760b 100644
> --- a/builtin/fsck.c
> +++ b/builtin/fsck.c
> @@ -438,6 +438,14 @@ static int fsck_handle_ref(const char *refname, const struct object_id *oid,
>  
>  	obj = parse_object(oid);
>  	if (!obj) {
> +		if (repository_format_lazy_object) {
> +			/*
> +			 * Increment default_refs anyway, because this is a
> +			 * valid ref.
> +			 */
> +			default_refs++;
> +			return 0;
> +		}
>  		error("%s: invalid sha1 pointer %s", refname, oid_to_hex(oid));
>  		errors_found |= ERROR_REACHABLE;

At this point, do we know (or can we tell) if this is a missing
object or a file exists as a loose object but is corrupt?  If we
could, it would be nice to do this only for the former to avoid
sweeping a real corruption that is unrelated to the lazy fetch under
the rug.

> +test_expect_success 'fsck fails on lazy object pointed to by ref' '
> +	rm -rf repo &&
> +	test_create_repo repo &&
> +	test_commit -C repo 1 &&
> +
> +	A=$(git -C repo commit-tree -m a HEAD^{tree}) &&
> +
> +	# Reference $A only from ref, and delete it
> +	git -C repo branch mybranch "$A" &&
> +	delete_object repo "$A" &&
> +
> +	test_must_fail git -C repo fsck
> +'

And a new test that uses a helper different from delete_object
(perhaps call it corrupt_object?) can be used to make sure that we
complain in that case here.

> +test_expect_success '...but succeeds if lazyobject is set' '
> +	git -C repo config core.repositoryformatversion 1 &&
> +	git -C repo config extensions.lazyobject "arbitrary string" &&
> +	git -C repo fsck
> +'
> +
>  test_done