rustc_target: route LayoutOf through TyAbiInterface.
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Some changes occured to rustc_codegen_cranelift cc @bjorn3 Some changes occurred in src/tools/clippy. cc @rust-lang/clippy Some changes occured to the CTFE / Miri engine cc @rust-lang/miri |
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Closing as superseded by #88499, which doesn't have the ergonomic downsides. |
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Provide `layout_of` automatically (given tcx + param_env + error handling). After rust-lang#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 rust-lang#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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Provide `layout_of` automatically (given tcx + param_env + error handling). After rust-lang#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 rust-lang#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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Provide `layout_of` automatically (given tcx + param_env + error handling). After rust-lang#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 rust-lang#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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This is a bit strange (potentially an ergonomic disaster, especially around errors, see below), but I decided to try and use the
trait TyAbiInterfacefrom #88337 to provide a single implementation oflayout_of, tied toTy<'tcx>, and usable with any context that provides:TyCtxt, viaHasTyCtxtParamEnv, viaHasParamEnvLayoutErrors into the desired error type!can be paired with havingcx.layout_of(...)returnTyAndLayoutwithoutResult<...>around it, such as used by codegenIsLayoutCxtrait (and so is specifying the type ofcx.layout_of(...))Sadly, because of the generics involved, and Rust type-checking/inference limitations (mostly around autoderef and coercions), certain things that we took for granted change:
cx: &mut Cdoesn't autoderef incx.layout_of(...), if onlyC: LayoutOfimpls of the relevant traits on&mut _cx.layout_of(ty: &Ty)doesn't coerce&TytoTyTyAbiInterfaceon&Ty, but I decided to fix the callsites insteadI doubt this change can be landed in its initial state (or at all), but since I did get it to work, I wanted to put it up.