Re: [PATCH 2/7] t: introduce tests for unexpected object types

> On Thu, Apr 04, 2019 at 08:37:44PM -0700, Taylor Blau wrote:
>
> > Let A be the object referenced with an unexpected type, and B be the
> > object doing the referencing. Do the following:
> >
> >   - test 'git rev-list --objects A B'. This causes A to be "cached", and
> >     presents the above scenario.
> >
> > Likewise, if we have a tree entry that claims to be a tree (for example)
> > but points to another object type (say, a blob), there are two ways we
> > might find out:
> >
> >   - when we call lookup_tree(), we might find that we've already seen
> >     the object referenced as another type, in which case we'd get NULL
> >
> >   - we call lookup_tree() successfully, but when we try to read the
> >     object, we find out it's something else.
> >
> > We should check that we behave sensibly in both cases (especially
> > because it is easy for a malicious actor to provoke one case or the
> > other).
>
> I think our pasting together of multiple commits adding the lone/seen
> cases ended up in some redundancy in the description. In particular, I'm
> not sure what the first paragraph/bullet quoted above is trying to say,
> as it corresponds to the second bullet in the later list.

> Maybe collapse them together like:
>
>   We might hit an unexpected type in two different ways (imagine we have
>   a tree entry that claims to be a tree but actually points to a blob):
>
>     - when we call lookup_tree(), we might find that we've already seen
>       the object referenced as a blob, in which case we'd get NULL. We
>       can exercise this with "git rev-list --objects $blob $tree", which
>       guarantees that the blob will have been parsed before we look in
>       the tree. These tests are marked as "seen" in the test script.
>
>     - we call lookup_tree() successfully, but when we try to read the
>       object, we find out it's something else. We construct our tests
>       such that $blob is not otherwise mentioned in $tree. These tests
>       are marked as "lone" in the script.