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e2750baf53
Provide `layout_of` automatically (given tcx + param_env + error handling). After #88337, there's no longer any uses of `LayoutOf` within `rustc_target` itself, so I realized I could move the trait to `rustc_middle::ty::layout` and redesign it a bit. This is similar to #88338 (and supersedes it), but at no ergonomic loss, since there's no funky `C: LayoutOf<Ty = Ty>` -> `Ty: TyAbiInterface<C>` generic `impl` chain, and each `LayoutOf` still corresponds to one `impl` (of `LayoutOfHelpers`) for the specific context. After this PR, this is what's needed to get `trait LayoutOf` (with the `layout_of` method) implemented on some context type: * `TyCtxt`, via `HasTyCtxt` * `ParamEnv`, via `HasParamEnv` * a way to transform `LayoutError`s into the desired error type * an error type of `!` can be paired with having `cx.layout_of(...)` return `TyAndLayout` *without* `Result<...>` around it, such as used by codegen * this is done through a new `LayoutOfHelpers` trait (and so is specifying the type of `cx.layout_of(...)`) When going through this path (and not bypassing it with a manual `impl` of `LayoutOf`), the end result is that only the error case can be customized, the query itself and the success paths are guaranteed to be uniform. (**EDIT**: just noticed that because of the supertrait relationship, you cannot actually implement `LayoutOf` yourself, the blanket `impl` fully covers all possible context types that could ever implement it) Part of the motivation for this shape of API is that I've been working on querifying `FnAbi::of_*`, and what I want/need to introduce for that looks a lot like the setup in this PR - in particular, it's harder to express the `FnAbi` methods in `rustc_target`, since they're much more tied to `rustc` concepts. r? `@nagisa` cc `@oli-obk` `@bjorn3` |
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Please read the rustc-dev-guide chapter on Backend Agnostic Codegen.