Use associative type defaults in `{Layout,FnAbi}OfHelpers`.

This avoids some repetitive boilerplate code.

compiler/rustc_codegen_cranelift/src/common.rs

@@ -309,8 +309,6 @@ pub(crate) struct FunctionCx<'m, 'clif, 'tcx: 'm> {
 }
 
 impl<'tcx> LayoutOfHelpers<'tcx> for FunctionCx<'_, '_, 'tcx> {
-    type LayoutOfResult = TyAndLayout<'tcx>;
-
     #[inline]
     fn handle_layout_err(&self, err: LayoutError<'tcx>, span: Span, ty: Ty<'tcx>) -> ! {
         RevealAllLayoutCx(self.tcx).handle_layout_err(err, span, ty)
@@ -318,8 +316,6 @@ impl<'tcx> LayoutOfHelpers<'tcx> for FunctionCx<'_, '_, 'tcx> {
 }
 
 impl<'tcx> FnAbiOfHelpers<'tcx> for FunctionCx<'_, '_, 'tcx> {
-    type FnAbiOfResult = &'tcx FnAbi<'tcx, Ty<'tcx>>;
-
     #[inline]
     fn handle_fn_abi_err(
         &self,
@@ -450,8 +446,6 @@ impl<'tcx> FunctionCx<'_, '_, 'tcx> {
 pub(crate) struct RevealAllLayoutCx<'tcx>(pub(crate) TyCtxt<'tcx>);
 
 impl<'tcx> LayoutOfHelpers<'tcx> for RevealAllLayoutCx<'tcx> {
-    type LayoutOfResult = TyAndLayout<'tcx>;
-
     #[inline]
     fn handle_layout_err(&self, err: LayoutError<'tcx>, span: Span, ty: Ty<'tcx>) -> ! {
         if let LayoutError::SizeOverflow(_) | LayoutError::ReferencesError(_) = err {
@@ -466,8 +460,6 @@ impl<'tcx> LayoutOfHelpers<'tcx> for RevealAllLayoutCx<'tcx> {
 }
 
 impl<'tcx> FnAbiOfHelpers<'tcx> for RevealAllLayoutCx<'tcx> {
-    type FnAbiOfResult = &'tcx FnAbi<'tcx, Ty<'tcx>>;
-
     #[inline]
     fn handle_fn_abi_err(
         &self,

compiler/rustc_codegen_gcc/src/builder.rs

@@ -23,7 +23,6 @@ use rustc_middle::bug;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
 use rustc_middle::ty::layout::{
     FnAbiError, FnAbiOfHelpers, FnAbiRequest, HasParamEnv, HasTyCtxt, LayoutError, LayoutOfHelpers,
-    TyAndLayout,
 };
 use rustc_middle::ty::{Instance, ParamEnv, Ty, TyCtxt};
 use rustc_span::def_id::DefId;
@@ -473,8 +472,6 @@ impl HasDataLayout for Builder<'_, '_, '_> {
 }
 
 impl<'tcx> LayoutOfHelpers<'tcx> for Builder<'_, '_, 'tcx> {
-    type LayoutOfResult = TyAndLayout<'tcx>;
-
     #[inline]
     fn handle_layout_err(&self, err: LayoutError<'tcx>, span: Span, ty: Ty<'tcx>) -> ! {
         self.cx.handle_layout_err(err, span, ty)
@@ -482,8 +479,6 @@ impl<'tcx> LayoutOfHelpers<'tcx> for Builder<'_, '_, 'tcx> {
 }
 
 impl<'tcx> FnAbiOfHelpers<'tcx> for Builder<'_, '_, 'tcx> {
-    type FnAbiOfResult = &'tcx FnAbi<'tcx, Ty<'tcx>>;
-
     #[inline]
     fn handle_fn_abi_err(
         &self,

compiler/rustc_codegen_gcc/src/context.rs

@@ -12,13 +12,12 @@ use rustc_middle::mir::mono::CodegenUnit;
 use rustc_middle::span_bug;
 use rustc_middle::ty::layout::{
     FnAbiError, FnAbiOf, FnAbiOfHelpers, FnAbiRequest, HasParamEnv, HasTyCtxt, LayoutError,
-    LayoutOfHelpers, TyAndLayout,
+    LayoutOfHelpers,
 };
 use rustc_middle::ty::{self, Instance, ParamEnv, PolyExistentialTraitRef, Ty, TyCtxt};
 use rustc_session::Session;
 use rustc_span::source_map::respan;
 use rustc_span::{Span, DUMMY_SP};
-use rustc_target::abi::call::FnAbi;
 use rustc_target::abi::{HasDataLayout, PointeeInfo, Size, TargetDataLayout, VariantIdx};
 use rustc_target::spec::{HasTargetSpec, HasWasmCAbiOpt, Target, TlsModel, WasmCAbi};
 
@@ -572,8 +571,6 @@ impl<'gcc, 'tcx> HasWasmCAbiOpt for CodegenCx<'gcc, 'tcx> {
 }
 
 impl<'gcc, 'tcx> LayoutOfHelpers<'tcx> for CodegenCx<'gcc, 'tcx> {
-    type LayoutOfResult = TyAndLayout<'tcx>;
-
     #[inline]
     fn handle_layout_err(&self, err: LayoutError<'tcx>, span: Span, ty: Ty<'tcx>) -> ! {
         if let LayoutError::SizeOverflow(_) | LayoutError::ReferencesError(_) = err {
@@ -585,8 +582,6 @@ impl<'gcc, 'tcx> LayoutOfHelpers<'tcx> for CodegenCx<'gcc, 'tcx> {
 }
 
 impl<'gcc, 'tcx> FnAbiOfHelpers<'tcx> for CodegenCx<'gcc, 'tcx> {
-    type FnAbiOfResult = &'tcx FnAbi<'tcx, Ty<'tcx>>;
-
     #[inline]
     fn handle_fn_abi_err(
         &self,

compiler/rustc_codegen_llvm/src/builder.rs

@@ -93,8 +93,6 @@ impl HasTargetSpec for Builder<'_, '_, '_> {
 }
 
 impl<'tcx> LayoutOfHelpers<'tcx> for Builder<'_, '_, 'tcx> {
-    type LayoutOfResult = TyAndLayout<'tcx>;
-
     #[inline]
     fn handle_layout_err(&self, err: LayoutError<'tcx>, span: Span, ty: Ty<'tcx>) -> ! {
         self.cx.handle_layout_err(err, span, ty)
@@ -102,8 +100,6 @@ impl<'tcx> LayoutOfHelpers<'tcx> for Builder<'_, '_, 'tcx> {
 }
 
 impl<'tcx> FnAbiOfHelpers<'tcx> for Builder<'_, '_, 'tcx> {
-    type FnAbiOfResult = &'tcx FnAbi<'tcx, Ty<'tcx>>;
-
     #[inline]
     fn handle_fn_abi_err(
         &self,

compiler/rustc_codegen_llvm/src/context.rs

@@ -15,7 +15,6 @@ use rustc_middle::middle::codegen_fn_attrs::PatchableFunctionEntry;
 use rustc_middle::mir::mono::CodegenUnit;
 use rustc_middle::ty::layout::{
     FnAbiError, FnAbiOfHelpers, FnAbiRequest, HasParamEnv, LayoutError, LayoutOfHelpers,
-    TyAndLayout,
 };
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
 use rustc_middle::{bug, span_bug};
@@ -25,7 +24,6 @@ use rustc_session::config::{
 use rustc_session::Session;
 use rustc_span::source_map::Spanned;
 use rustc_span::{Span, DUMMY_SP};
-use rustc_target::abi::call::FnAbi;
 use rustc_target::abi::{HasDataLayout, TargetDataLayout, VariantIdx};
 use rustc_target::spec::{HasTargetSpec, RelocModel, SmallDataThresholdSupport, Target, TlsModel};
 use smallvec::SmallVec;
@@ -1158,8 +1156,6 @@ impl<'tcx, 'll> HasParamEnv<'tcx> for CodegenCx<'ll, 'tcx> {
 }
 
 impl<'tcx> LayoutOfHelpers<'tcx> for CodegenCx<'_, 'tcx> {
-    type LayoutOfResult = TyAndLayout<'tcx>;
-
     #[inline]
     fn handle_layout_err(&self, err: LayoutError<'tcx>, span: Span, ty: Ty<'tcx>) -> ! {
         if let LayoutError::SizeOverflow(_) | LayoutError::ReferencesError(_) = err {
@@ -1171,8 +1167,6 @@ impl<'tcx> LayoutOfHelpers<'tcx> for CodegenCx<'_, 'tcx> {
 }
 
 impl<'tcx> FnAbiOfHelpers<'tcx> for CodegenCx<'_, 'tcx> {
-    type FnAbiOfResult = &'tcx FnAbi<'tcx, Ty<'tcx>>;
-
     #[inline]
     fn handle_fn_abi_err(
         &self,

compiler/rustc_middle/src/lib.rs

@@ -33,6 +33,7 @@
 #![feature(allocator_api)]
 #![feature(array_windows)]
 #![feature(assert_matches)]
+#![feature(associated_type_defaults)]
 #![feature(box_as_ptr)]
 #![feature(box_patterns)]
 #![feature(closure_track_caller)]

compiler/rustc_middle/src/ty/layout.rs

@@ -634,7 +634,7 @@ pub type TyAndLayout<'tcx> = rustc_target::abi::TyAndLayout<'tcx, Ty<'tcx>>;
 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>>;
+    type LayoutOfResult: MaybeResult<TyAndLayout<'tcx>> = TyAndLayout<'tcx>;
 
     /// `Span` to use for `tcx.at(span)`, from `layout_of`.
     // FIXME(eddyb) perhaps make this mandatory to get contexts to track it better?
@@ -1259,7 +1259,7 @@ pub enum FnAbiRequest<'tcx> {
 pub trait FnAbiOfHelpers<'tcx>: LayoutOfHelpers<'tcx> {
     /// The `&FnAbi`-wrapping type (or `&FnAbi` itself), which will be
     /// returned from `fn_abi_of_*` (see also `handle_fn_abi_err`).
-    type FnAbiOfResult: MaybeResult<&'tcx FnAbi<'tcx, Ty<'tcx>>>;
+    type FnAbiOfResult: MaybeResult<&'tcx FnAbi<'tcx, Ty<'tcx>>> = &'tcx FnAbi<'tcx, Ty<'tcx>>;
 
     /// Helper used for `fn_abi_of_*`, to adapt `tcx.fn_abi_of_*(...)` into a
     /// `Self::FnAbiOfResult` (which does not need to be a `Result<...>`).

compiler/rustc_passes/src/layout_test.rs

@@ -2,7 +2,7 @@ use rustc_ast::Attribute;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::LocalDefId;
 use rustc_middle::span_bug;
-use rustc_middle::ty::layout::{HasParamEnv, HasTyCtxt, LayoutError, LayoutOfHelpers, TyAndLayout};
+use rustc_middle::ty::layout::{HasParamEnv, HasTyCtxt, LayoutError, LayoutOfHelpers};
 use rustc_middle::ty::{self, ParamEnv, Ty, TyCtxt};
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::sym;
@@ -139,8 +139,6 @@ struct UnwrapLayoutCx<'tcx> {
 }
 
 impl<'tcx> LayoutOfHelpers<'tcx> for UnwrapLayoutCx<'tcx> {
-    type LayoutOfResult = TyAndLayout<'tcx>;
-
     fn handle_layout_err(&self, err: LayoutError<'tcx>, span: Span, ty: Ty<'tcx>) -> ! {
         span_bug!(span, "`#[rustc_layout(..)]` test resulted in `layout_of({ty}) = Err({err})`",);
     }