Auto merge of #88499 - eddyb:layout-off, r=nagisa

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`

compiler/rustc_lint/src/builtin.rs

@@ -41,16 +41,17 @@ use rustc_hir::{ForeignItemKind, GenericParamKind, PatKind};
 use rustc_hir::{HirId, Node};
 use rustc_index::vec::Idx;
 use rustc_middle::lint::LintDiagnosticBuilder;
+use rustc_middle::ty::layout::{LayoutError, LayoutOf};
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::subst::{GenericArgKind, Subst};
 use rustc_middle::ty::Instance;
-use rustc_middle::ty::{self, layout::LayoutError, Ty, TyCtxt};
+use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_session::lint::{BuiltinLintDiagnostics, FutureIncompatibilityReason};
 use rustc_span::edition::Edition;
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{BytePos, InnerSpan, MultiSpan, Span};
-use rustc_target::abi::{LayoutOf, VariantIdx};
+use rustc_target::abi::VariantIdx;
 use rustc_trait_selection::traits::misc::can_type_implement_copy;
 
 use crate::nonstandard_style::{method_context, MethodLateContext};

compiler/rustc_lint/src/context.rs

@@ -31,7 +31,7 @@ use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
 use rustc_middle::lint::LintDiagnosticBuilder;
 use rustc_middle::middle::privacy::AccessLevels;
 use rustc_middle::middle::stability;
-use rustc_middle::ty::layout::{LayoutError, TyAndLayout};
+use rustc_middle::ty::layout::{LayoutError, LayoutOfHelpers, TyAndLayout};
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, print::Printer, subst::GenericArg, Ty, TyCtxt};
 use rustc_serialize::json::Json;
@@ -41,7 +41,7 @@ use rustc_session::Session;
 use rustc_session::SessionLintStore;
 use rustc_span::lev_distance::find_best_match_for_name;
 use rustc_span::{symbol::Symbol, MultiSpan, Span, DUMMY_SP};
-use rustc_target::abi::{self, LayoutOf};
+use rustc_target::abi;
 use tracing::debug;
 
 use std::cell::Cell;
@@ -1080,12 +1080,12 @@ impl<'tcx> ty::layout::HasParamEnv<'tcx> for LateContext<'tcx> {
     }
 }
 
-impl<'tcx> LayoutOf<'tcx> for LateContext<'tcx> {
-    type Ty = Ty<'tcx>;
-    type TyAndLayout = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
+impl<'tcx> LayoutOfHelpers<'tcx> for LateContext<'tcx> {
+    type LayoutOfResult = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
 
-    fn layout_of(&self, ty: Ty<'tcx>) -> Self::TyAndLayout {
-        self.tcx.layout_of(self.param_env.and(ty))
+    #[inline]
+    fn handle_layout_err(&self, err: LayoutError<'tcx>, _: Span, _: Ty<'tcx>) -> LayoutError<'tcx> {
+        err
     }
 }
 

compiler/rustc_lint/src/types.rs

@@ -6,14 +6,14 @@ use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::{is_range_literal, Expr, ExprKind, Node};
-use rustc_middle::ty::layout::{IntegerExt, SizeSkeleton};
+use rustc_middle::ty::layout::{IntegerExt, LayoutOf, SizeSkeleton};
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{self, AdtKind, DefIdTree, Ty, TyCtxt, TypeFoldable};
 use rustc_span::source_map;
 use rustc_span::symbol::sym;
 use rustc_span::{Span, Symbol, DUMMY_SP};
 use rustc_target::abi::Abi;
-use rustc_target::abi::{Integer, LayoutOf, TagEncoding, Variants};
+use rustc_target::abi::{Integer, TagEncoding, Variants};
 use rustc_target::spec::abi::Abi as SpecAbi;
 
 use if_chain::if_chain;