[PATCH 3 of 3 STABLE] rust: propagate Python exception raised from index_get_parents_checked()

[Yuya Nishihara]

On Tue, 30 Oct 2018 15:48:43 +0100, Georges Racinet wrote:
> On 10/29/2018 02:03 PM, Yuya Nishihara wrote:
> >> -	return rustlazyancestors_contains(self->iter, PyInt_AS_LONG(rev));
> >> +	res = rustlazyancestors_contains(self->iter, PyInt_AS_LONG(rev));
> >> +	if (PyErr_Occurred())
> >> +		return -1;
> >> +	return res;
> > Not that a proper fix is to make AncestorsIterator functions return
> > Result<_, GraphError>. I can send the patch for stable if it's preferred.
> Returning Result<_, GraphError> as much as possible is my intent indeed,
> but it wouldn't apply to next(), because the Iterator trait does not
> allow for that, unless we change the signature to an Iterator with Item
> = Result<Revision, GraphError>. I didn't dare to do that earlier, as it
> seemed to be too heavy.
> 
> That being said, I'm not sure how much of these errors (bad stoprev etc)
> we can get rid of from the start. The more serious case would be that of
> the corrupted index, though, in which a correct initialization can still
> give rise to errors later on.

Yes, that's the reason we need an iterator yielding Result type. We can't
guarantee that the index content is valid.