Re: [PATCH 4/4] usage.c: add a non-fatal bug() function to go with BUG()

From: Junio C Hamano <gitster@pobox.com>
Date: Mar 28, 2021, 06:12 UTC
Message-ID: <xmqqh7kvolgn.fsf@gitster.g>
In-Reply-To: <patch-4.5-515d146cac8-20210328T022343Z-avarab@gmail.com>

Ævar Arnfjörð Bjarmason  <avarab@gmail.com> writes:

Show 8 quoted lines

> Add a bug() function that works like error() except the message is
> prefixed with "bug:" instead of "error:".
>
> The reason this is needed is for e.g. the fsck code. If we encounter
> what we'd consider a BUG() in the middle of fsck traversal we'd still
> like to try as hard as possible to go past that object and complete
> the fsck, instead of hard dying. A follow-up commit will introduce
> such a use in object-file.c.

Reading the description above, i.e. "to go past that object", the assumed use case seems to be to deal with a data error, not a program bug (which is where we use BUG()---e.g. one helper function in the fsck code detected that the caller wasn't careful enough to vet the data it has and called it with incoherent data). If we find a tree entry whose mode bits implies that the object recorded in the entry ought to be a blob, and later find out that the object turns out to be a tree, that is a corrupt repository and the code that detected is not buggy (and we shouldn't use BUG(), of course).

So, ... I am skeptical. If the code is prepared to handle breakage, we would not want to die, but then I am not sure why it has to be different from error().