ty::layout: split `LayoutOf` into required and (blanket) provided halves.

compiler/rustc_codegen_cranelift/src/common.rs

 use rustc_index::vec::IndexVec;
-use rustc_middle::ty::layout::LayoutError;
+use rustc_middle::ty::layout::{LayoutError, LayoutOfHelpers};
 use rustc_middle::ty::SymbolName;
 use rustc_target::abi::call::FnAbi;
 use rustc_target::abi::{Integer, Primitive};
@@ -257,7 +257,7 @@ pub(crate) struct FunctionCx<'m, 'clif, 'tcx: 'm> {
     pub(crate) inline_asm_index: u32,
 }
 
-impl<'tcx> LayoutOf<'tcx> for FunctionCx<'_, '_, 'tcx> {
+impl<'tcx> LayoutOfHelpers<'tcx> for FunctionCx<'_, '_, 'tcx> {
     type LayoutOfResult = TyAndLayout<'tcx>;
 
     #[inline]
@@ -365,7 +365,7 @@ pub(crate) fn anonymous_str(&mut self, msg: &str) -> Value {
 
 pub(crate) struct RevealAllLayoutCx<'tcx>(pub(crate) TyCtxt<'tcx>);
 
-impl<'tcx> LayoutOf<'tcx> for RevealAllLayoutCx<'tcx> {
+impl<'tcx> LayoutOfHelpers<'tcx> for RevealAllLayoutCx<'tcx> {
     type LayoutOfResult = TyAndLayout<'tcx>;
 
     #[inline]

compiler/rustc_codegen_llvm/src/builder.rs

@@ -15,7 +15,7 @@
 use rustc_codegen_ssa::MemFlags;
 use rustc_data_structures::small_c_str::SmallCStr;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::layout::{LayoutError, LayoutOf, TyAndLayout};
+use rustc_middle::ty::layout::{LayoutError, LayoutOfHelpers, TyAndLayout};
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::Span;
 use rustc_target::abi::{self, Align, Size};
@@ -88,7 +88,7 @@ fn target_spec(&self) -> &Target {
     }
 }
 
-impl LayoutOf<'tcx> for Builder<'_, '_, 'tcx> {
+impl LayoutOfHelpers<'tcx> for Builder<'_, '_, 'tcx> {
     type LayoutOfResult = TyAndLayout<'tcx>;
 
     #[inline]

compiler/rustc_codegen_llvm/src/context.rs

@@ -15,7 +15,7 @@
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::small_c_str::SmallCStr;
 use rustc_middle::mir::mono::CodegenUnit;
-use rustc_middle::ty::layout::{HasParamEnv, LayoutError, LayoutOf, TyAndLayout};
+use rustc_middle::ty::layout::{HasParamEnv, LayoutError, LayoutOfHelpers, TyAndLayout};
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
 use rustc_middle::{bug, span_bug};
 use rustc_session::config::{CFGuard, CrateType, DebugInfo};
@@ -835,7 +835,7 @@ fn tcx(&self) -> TyCtxt<'tcx> {
     }
 }
 
-impl LayoutOf<'tcx> for CodegenCx<'ll, 'tcx> {
+impl LayoutOfHelpers<'tcx> for CodegenCx<'ll, 'tcx> {
     type LayoutOfResult = TyAndLayout<'tcx>;
 
     #[inline]

compiler/rustc_lint/src/context.rs

@@ -31,7 +31,7 @@
 use rustc_middle::lint::LintDiagnosticBuilder;
 use rustc_middle::middle::privacy::AccessLevels;
 use rustc_middle::middle::stability;
-use rustc_middle::ty::layout::{LayoutError, LayoutOf, 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;
@@ -1080,7 +1080,7 @@ fn param_env(&self) -> ty::ParamEnv<'tcx> {
     }
 }
 
-impl<'tcx> LayoutOf<'tcx> for LateContext<'tcx> {
+impl<'tcx> LayoutOfHelpers<'tcx> for LateContext<'tcx> {
     type LayoutOfResult = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
 
     #[inline]

compiler/rustc_middle/src/ty/layout.rs

@@ -2093,8 +2093,9 @@ fn to_result(self) -> Result<T, Self::Error> {
 
 pub type TyAndLayout<'tcx> = rustc_target::abi::TyAndLayout<'tcx, Ty<'tcx>>;
 
-/// Trait for contexts that can compute layouts of types.
-pub trait LayoutOf<'tcx>: HasDataLayout + HasTyCtxt<'tcx> + HasParamEnv<'tcx> {
+/// Trait for contexts that want to be able to compute layouts of types.
+/// This automatically gives access to `LayoutOf`, through a blanket `impl`.
+pub trait LayoutOfHelpers<'tcx>: HasDataLayout + HasTyCtxt<'tcx> + HasParamEnv<'tcx> {
     /// The `TyAndLayout`-wrapping type (or `TyAndLayout` itself), which will be
     /// returned from `layout_of` (see also `handle_layout_err`).
     type LayoutOfResult: MaybeResult<TyAndLayout<'tcx>>;
@@ -2119,7 +2120,10 @@ fn handle_layout_err(
         span: Span,
         ty: Ty<'tcx>,
     ) -> <Self::LayoutOfResult as MaybeResult<TyAndLayout<'tcx>>>::Error;
+}
 
+/// Blanket extension trait for contexts that can compute layouts of types.
+pub trait LayoutOf<'tcx>: LayoutOfHelpers<'tcx> {
     /// Computes the layout of a type. Note that this implicitly
     /// executes in "reveal all" mode, and will normalize the input type.
     #[inline]
@@ -2143,7 +2147,9 @@ fn spanned_layout_of(&self, ty: Ty<'tcx>, span: Span) -> Self::LayoutOfResult {
     }
 }
 
-impl LayoutOf<'tcx> for LayoutCx<'tcx, TyCtxt<'tcx>> {
+impl<C: LayoutOfHelpers<'tcx>> LayoutOf<'tcx> for C {}
+
+impl LayoutOfHelpers<'tcx> for LayoutCx<'tcx, TyCtxt<'tcx>> {
     type LayoutOfResult = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
 
     #[inline]
@@ -2152,7 +2158,7 @@ fn handle_layout_err(&self, err: LayoutError<'tcx>, _: Span, _: Ty<'tcx>) -> Lay
     }
 }
 
-impl LayoutOf<'tcx> for LayoutCx<'tcx, ty::query::TyCtxtAt<'tcx>> {
+impl LayoutOfHelpers<'tcx> for LayoutCx<'tcx, ty::query::TyCtxtAt<'tcx>> {
     type LayoutOfResult = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
 
     #[inline]

compiler/rustc_mir/src/interpret/eval_context.rs

@@ -8,7 +8,7 @@
 use rustc_macros::HashStable;
 use rustc_middle::ich::StableHashingContext;
 use rustc_middle::mir;
-use rustc_middle::ty::layout::{self, LayoutError, LayoutOf, TyAndLayout};
+use rustc_middle::ty::layout::{self, LayoutError, LayoutOf, LayoutOfHelpers, TyAndLayout};
 use rustc_middle::ty::{
     self, query::TyCtxtAt, subst::SubstsRef, ParamEnv, Ty, TyCtxt, TypeFoldable,
 };
@@ -312,7 +312,7 @@ fn param_env(&self) -> ty::ParamEnv<'tcx> {
     }
 }
 
-impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> LayoutOf<'tcx> for InterpCx<'mir, 'tcx, M> {
+impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> LayoutOfHelpers<'tcx> for InterpCx<'mir, 'tcx, M> {
     type LayoutOfResult = InterpResult<'tcx, TyAndLayout<'tcx>>;
 
     #[inline]

compiler/rustc_mir/src/transform/const_prop.rs

@@ -17,7 +17,7 @@
     Location, Operand, Place, Rvalue, SourceInfo, SourceScope, SourceScopeData, Statement,
     StatementKind, Terminator, TerminatorKind, UnOp, RETURN_PLACE,
 };
-use rustc_middle::ty::layout::{LayoutError, LayoutOf, TyAndLayout};
+use rustc_middle::ty::layout::{LayoutError, LayoutOf, LayoutOfHelpers, TyAndLayout};
 use rustc_middle::ty::subst::{InternalSubsts, Subst};
 use rustc_middle::ty::{
     self, ConstInt, ConstKind, Instance, ParamEnv, ScalarInt, Ty, TyCtxt, TypeFoldable,
@@ -330,7 +330,7 @@ struct ConstPropagator<'mir, 'tcx> {
     source_info: Option<SourceInfo>,
 }
 
-impl<'mir, 'tcx> LayoutOf<'tcx> for ConstPropagator<'mir, 'tcx> {
+impl<'mir, 'tcx> LayoutOfHelpers<'tcx> for ConstPropagator<'mir, 'tcx> {
     type LayoutOfResult = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
 
     #[inline]

compiler/rustc_passes/src/layout_test.rs

@@ -3,7 +3,7 @@
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
 use rustc_hir::ItemKind;
-use rustc_middle::ty::layout::{HasParamEnv, HasTyCtxt, LayoutError, LayoutOf, TyAndLayout};
+use rustc_middle::ty::layout::{HasParamEnv, HasTyCtxt, LayoutError, LayoutOfHelpers, TyAndLayout};
 use rustc_middle::ty::{ParamEnv, Ty, TyCtxt};
 use rustc_span::symbol::sym;
 use rustc_span::Span;
@@ -114,7 +114,7 @@ struct UnwrapLayoutCx<'tcx> {
     param_env: ParamEnv<'tcx>,
 }
 
-impl LayoutOf<'tcx> for UnwrapLayoutCx<'tcx> {
+impl LayoutOfHelpers<'tcx> for UnwrapLayoutCx<'tcx> {
     type LayoutOfResult = TyAndLayout<'tcx>;
 
     fn handle_layout_err(&self, err: LayoutError<'tcx>, span: Span, ty: Ty<'tcx>) -> ! {