Allow field(0) projection as a no-op when target value is a PtrLocal #871
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Stevengre
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The change in #811 allows pointer casts between pointers to data and pointers to "transparent wrapper structs" containing one field with the same data. While the code tries to insert
field(0, _)projections when casting, this remediation falls short when the cast pointer is of a second degree, i.e., a pointer to a pointer.An example of this can be observed in
Iterator<_>::next, where a pointer**Tis cast to a pointer*NonNull<T>,NonNullbeing one of these "transparent wrapper structs".The proposed code change allows for a
field(0, _)projection to be treated as a No-Op when applied to a non-aggregate (nor union), specifically aPtrLocalfor the case ofnext().This fixes
iter.next()for cases whereSome(element)is returned. The case where it returnsNoneis a separate issue tested but not fixed here.