Extend Chalk with support for well-known, builtin traits

[nikomatsakis]

This is a meta issue for the work of extending chalk to support the various built-in traits like Sized, Copy, and so forth.

• [x] Extend TraitDefn with concept of "well-known trait" identifier #356
• [x] Add basic support for the Sized trait https://github.com/rust-lang/chalk/issues/261
• [x] Add support for a built-in Copy trait
  • In particular, Copy has built-in well-formedness requirements required for soundness
• [x] Add support for a built-in Clone trait
  • Impls for tuples, closures are provided by rustc, at least
• [x] Add support for built-in Fn traits
• [x] Add support for built-in Unsize traits
• [x] Unpin
• [x] CoerceUnsized
• [ ] DispatchFromDyn
• [x] DiscriminantKind
• [ ] Generator

This issue has been assigned to @Areredify via this comment.

[basil-cow]

@rustbot claim

[nikomatsakis]

I would also say that this issue is fairly 'parallelizable', so if others want to pick up some aspects of it, that's not a problem. e.g. I think we could add code for Copy and the like. Maybe it's a good idea to break those out into separate issues and write-up some mentoring instructions?

[nikomatsakis]

Although they may be somewhat blocked on https://github.com/rust-lang/chalk/pull/371 -- having more details of Rust types would be useful.

[basil-cow]

So if someone wants to pick it up, I am done with Copy, Drop and Clone (as far as I understood Clone introduces no hard coded impls and/or wf checks?) modulo #371 of course, but it will be easy to address when it comes to it. Going to pick up Unsize next

[basil-cow]

Im already working on CoerceUnsized

[memoryleak47]

I'll try Unpin