Lint code that "indexes" generic pointers but doesn't special-case zero-sized types

Basically, it'd be nice to have a lint which checks unsafe code dealing with pointers that indexes them (either by from_raw_parts(...) or *ptr.offset(...)) which doesn't specifically special-case zero-sized types.

This could probably simplified to checking that functions that perform said indexing don't contain any mentions of mem::size_of or similar.

The main idea is that this would lint custom data structures similar to Vec and co. that will not work with zero-sized types. Obviously not a lint that I'd expect to come up very often, but people working in embedded code might run into a problem like this and it's good to point it out and require an #[allow(...)] that acknowledges the risks.

The issue names no files, tests, or entry points. Start by clarifying the intended lint scope for unsafe pointer indexing and zero-sized types, including which patterns count as a special case. Done would mean a defined lint that identifies affected custom data structures and requires an explicit allow when the risk is intentional.