rust/compiler/rustc_middle/src/traits
bors e4417cf020 Auto merge of #92268 - jswrenn:transmute, r=oli-obk
Initial implementation of transmutability trait.

*T'was the night before Christmas and all through the codebase, not a miri was stirring — no hint of `unsafe`!*

This PR provides an initial, **incomplete** implementation of *[MCP 411: Lang Item for Transmutability](https://github.com/rust-lang/compiler-team/issues/411)*. The `core::mem::BikeshedIntrinsicFrom` trait provided by this PR is implemented on-the-fly by the compiler for types `Src` and `Dst` when the bits of all possible values of type `Src` are safely reinterpretable as a value of type `Dst`.

What this PR provides is:
- [x] [support for transmutations involving primitives](https://github.com/jswrenn/rust/tree/transmute/src/test/ui/transmutability/primitives)
- [x] [support for transmutations involving arrays](https://github.com/jswrenn/rust/tree/transmute/src/test/ui/transmutability/arrays)
- [x] [support for transmutations involving structs](https://github.com/jswrenn/rust/tree/transmute/src/test/ui/transmutability/structs)
- [x] [support for transmutations involving enums](https://github.com/jswrenn/rust/tree/transmute/src/test/ui/transmutability/enums)
- [x] [support for transmutations involving unions](https://github.com/jswrenn/rust/tree/transmute/src/test/ui/transmutability/unions)
- [x] [support for weaker validity checks](https://github.com/jswrenn/rust/blob/transmute/src/test/ui/transmutability/unions/should_permit_intersecting_if_validity_is_assumed.rs) (i.e., `Assume::VALIDITY`)
- [x] visibility checking

What isn't yet implemented:
- [ ] transmutability options passed using the `Assume` struct
- [ ] [support for references](https://github.com/jswrenn/rust/blob/transmute/src/test/ui/transmutability/references.rs)
- [ ] smarter error messages

These features will be implemented in future PRs.
2022-08-02 21:17:31 +00:00
..
chalk.rs Add #[derive(TypeVisitable)] 2022-07-05 22:25:15 +01:00
mod.rs Combine redundant obligation cause codes 2022-07-24 19:35:53 +00:00
query.rs remove some manual hash stable impls 2022-07-29 12:48:28 +02:00
select.rs Initial (incomplete) implementation of transmutability trait. 2022-07-27 17:33:56 +00:00
specialization_graph.rs Store associated item defaultness in impl_defaultness. 2022-08-01 21:38:16 +02:00
structural_impls.rs Do if-expression obligation stuff less eagerly 2022-07-21 07:39:28 +00:00
util.rs Remove unused StableMap and StableSet types from rustc_data_structures 2022-07-20 13:11:39 +02:00