diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index e38572f609b31..c07ba88ae204d 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -2367,9 +2367,9 @@ impl Async {
     }
 
     /// In this case this is an `async` return, the `NodeId` for the generated `impl Trait` item.
-    pub fn opt_return_id(self) -> Option<NodeId> {
+    pub fn opt_return_id(self) -> Option<(NodeId, Span)> {
         match self {
-            Async::Yes { return_impl_trait_id, .. } => Some(return_impl_trait_id),
+            Async::Yes { return_impl_trait_id, span, .. } => Some((return_impl_trait_id, span)),
             Async::No => None,
         }
     }
diff --git a/compiler/rustc_ast_lowering/src/errors.rs b/compiler/rustc_ast_lowering/src/errors.rs
index 4adeaef9bbfa8..c87d0ca96570e 100644
--- a/compiler/rustc_ast_lowering/src/errors.rs
+++ b/compiler/rustc_ast_lowering/src/errors.rs
@@ -334,3 +334,14 @@ pub struct InclusiveRangeWithNoEnd {
     #[primary_span]
     pub span: Span,
 }
+
+#[derive(SessionDiagnostic, Clone, Copy)]
+#[diag(ast_lowering::trait_fn_async, code = "E0706")]
+#[note]
+#[note(ast_lowering::note2)]
+pub struct TraitFnAsync {
+    #[primary_span]
+    pub fn_span: Span,
+    #[label]
+    pub span: Span,
+}
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 6fa8d7f0fcdd9..79babbfd6d63c 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -851,7 +851,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
         let bound_generic_params = self.lower_lifetime_binder(closure_id, generic_params);
         // Lower outside new scope to preserve `is_in_loop_condition`.
-        let fn_decl = self.lower_fn_decl(decl, None, FnDeclKind::Closure, None);
+        let fn_decl = self.lower_fn_decl(decl, None, fn_decl_span, FnDeclKind::Closure, None);
 
         let c = self.arena.alloc(hir::Closure {
             binder: binder_clause,
@@ -955,7 +955,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // We need to lower the declaration outside the new scope, because we
         // have to conserve the state of being inside a loop condition for the
         // closure argument types.
-        let fn_decl = self.lower_fn_decl(&outer_decl, None, FnDeclKind::Closure, None);
+        let fn_decl =
+            self.lower_fn_decl(&outer_decl, None, fn_decl_span, FnDeclKind::Closure, None);
 
         let c = self.arena.alloc(hir::Closure {
             binder: binder_clause,
diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index f0717b51d4b18..21143fda5582f 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -267,7 +267,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     let mut itctx = ImplTraitContext::Universal;
                     let (generics, decl) = this.lower_generics(generics, id, &mut itctx, |this| {
                         let ret_id = asyncness.opt_return_id();
-                        this.lower_fn_decl(&decl, Some(id), FnDeclKind::Fn, ret_id)
+                        this.lower_fn_decl(&decl, Some(id), fn_sig_span, FnDeclKind::Fn, ret_id)
                     });
                     let sig = hir::FnSig {
                         decl,
@@ -659,7 +659,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         self.lower_generics(generics, i.id, &mut itctx, |this| {
                             (
                                 // Disallow `impl Trait` in foreign items.
-                                this.lower_fn_decl(fdec, None, FnDeclKind::ExternFn, None),
+                                this.lower_fn_decl(
+                                    fdec,
+                                    None,
+                                    sig.span,
+                                    FnDeclKind::ExternFn,
+                                    None,
+                                ),
                                 this.lower_fn_params_to_names(fdec),
                             )
                         });
@@ -769,9 +775,15 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 (hir::Generics::empty(), hir::TraitItemKind::Const(ty, body), body.is_some())
             }
             AssocItemKind::Fn(box Fn { ref sig, ref generics, body: None, .. }) => {
+                let asyncness = sig.header.asyncness;
                 let names = self.lower_fn_params_to_names(&sig.decl);
-                let (generics, sig) =
-                    self.lower_method_sig(generics, sig, i.id, FnDeclKind::Trait, None);
+                let (generics, sig) = self.lower_method_sig(
+                    generics,
+                    sig,
+                    i.id,
+                    FnDeclKind::Trait,
+                    asyncness.opt_return_id(),
+                );
                 (generics, hir::TraitItemKind::Fn(sig, hir::TraitFn::Required(names)), false)
             }
             AssocItemKind::Fn(box Fn { ref sig, ref generics, body: Some(ref body), .. }) => {
@@ -1238,12 +1250,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
         sig: &FnSig,
         id: NodeId,
         kind: FnDeclKind,
-        is_async: Option<NodeId>,
+        is_async: Option<(NodeId, Span)>,
     ) -> (&'hir hir::Generics<'hir>, hir::FnSig<'hir>) {
         let header = self.lower_fn_header(sig.header);
         let mut itctx = ImplTraitContext::Universal;
         let (generics, decl) = self.lower_generics(generics, id, &mut itctx, |this| {
-            this.lower_fn_decl(&sig.decl, Some(id), kind, is_async)
+            this.lower_fn_decl(&sig.decl, Some(id), sig.span, kind, is_async)
         });
         (generics, hir::FnSig { header, decl, span: self.lower_span(sig.span) })
     }
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index e7bbf7dbdec29..0028199f97a61 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -42,7 +42,7 @@
 #[macro_use]
 extern crate tracing;
 
-use crate::errors::{AssocTyParentheses, AssocTyParenthesesSub, MisplacedImplTrait};
+use crate::errors::{AssocTyParentheses, AssocTyParenthesesSub, MisplacedImplTrait, TraitFnAsync};
 
 use rustc_ast::ptr::P;
 use rustc_ast::visit;
@@ -235,6 +235,7 @@ enum ImplTraitContext {
     ReturnPositionOpaqueTy {
         /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
         origin: hir::OpaqueTyOrigin,
+        in_trait: bool,
     },
     /// Impl trait in type aliases.
     TypeAliasesOpaqueTy,
@@ -294,7 +295,7 @@ impl std::fmt::Display for ImplTraitPosition {
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, PartialEq, Eq)]
 enum FnDeclKind {
     Fn,
     Inherent,
@@ -306,9 +307,17 @@ enum FnDeclKind {
 }
 
 impl FnDeclKind {
-    fn impl_trait_return_allowed(&self) -> bool {
+    fn impl_trait_return_allowed(&self, tcx: TyCtxt<'_>) -> bool {
         match self {
             FnDeclKind::Fn | FnDeclKind::Inherent => true,
+            FnDeclKind::Impl if tcx.features().return_position_impl_trait_in_trait => true,
+            _ => false,
+        }
+    }
+
+    fn impl_trait_in_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
+        match self {
+            FnDeclKind::Trait if tcx.features().return_position_impl_trait_in_trait => true,
             _ => false,
         }
     }
@@ -1241,7 +1250,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     generic_params,
                     unsafety: self.lower_unsafety(f.unsafety),
                     abi: self.lower_extern(f.ext),
-                    decl: self.lower_fn_decl(&f.decl, None, FnDeclKind::Pointer, None),
+                    decl: self.lower_fn_decl(&f.decl, None, t.span, FnDeclKind::Pointer, None),
                     param_names: self.lower_fn_params_to_names(&f.decl),
                 }))
             }
@@ -1309,19 +1318,23 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             TyKind::ImplTrait(def_node_id, ref bounds) => {
                 let span = t.span;
                 match itctx {
-                    ImplTraitContext::ReturnPositionOpaqueTy { origin } => {
-                        self.lower_opaque_impl_trait(span, *origin, def_node_id, bounds, itctx)
-                    }
-                    ImplTraitContext::TypeAliasesOpaqueTy => {
-                        let mut nested_itctx = ImplTraitContext::TypeAliasesOpaqueTy;
-                        self.lower_opaque_impl_trait(
+                    ImplTraitContext::ReturnPositionOpaqueTy { origin, in_trait } => self
+                        .lower_opaque_impl_trait(
                             span,
-                            hir::OpaqueTyOrigin::TyAlias,
+                            *origin,
                             def_node_id,
                             bounds,
-                            &mut nested_itctx,
-                        )
-                    }
+                            *in_trait,
+                            itctx,
+                        ),
+                    ImplTraitContext::TypeAliasesOpaqueTy => self.lower_opaque_impl_trait(
+                        span,
+                        hir::OpaqueTyOrigin::TyAlias,
+                        def_node_id,
+                        bounds,
+                        false,
+                        &mut ImplTraitContext::TypeAliasesOpaqueTy,
+                    ),
                     ImplTraitContext::Universal => {
                         let span = t.span;
                         let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
@@ -1333,6 +1346,21 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         }
                         path
                     }
+                    ImplTraitContext::Disallowed(
+                        position @ (ImplTraitPosition::TraitReturn | ImplTraitPosition::ImplReturn),
+                    ) => {
+                        self.tcx
+                            .sess
+                            .create_feature_err(
+                                MisplacedImplTrait {
+                                    span: t.span,
+                                    position: DiagnosticArgFromDisplay(&position),
+                                },
+                                sym::return_position_impl_trait_in_trait,
+                            )
+                            .emit();
+                        hir::TyKind::Err
+                    }
                     ImplTraitContext::Disallowed(position) => {
                         self.tcx.sess.emit_err(MisplacedImplTrait {
                             span: t.span,
@@ -1391,6 +1419,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         origin: hir::OpaqueTyOrigin,
         opaque_ty_node_id: NodeId,
         bounds: &GenericBounds,
+        in_trait: bool,
         itctx: &mut ImplTraitContext,
     ) -> hir::TyKind<'hir> {
         // Make sure we know that some funky desugaring has been going on here.
@@ -1479,6 +1508,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     }),
                     bounds: hir_bounds,
                     origin,
+                    in_trait,
                 };
                 debug!(?opaque_ty_item);
 
@@ -1505,7 +1535,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         debug!(?lifetimes);
 
         // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
-        hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, lifetimes)
+        hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, lifetimes, in_trait)
     }
 
     /// Registers a new opaque type with the proper `NodeId`s and
@@ -1613,19 +1643,17 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
     //      given DefId, otherwise impl Trait is disallowed. Must be `Some` if
     //      `make_ret_async` is also `Some`.
-    // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
-    //      This guards against trait declarations and implementations where `impl Trait` is
-    //      disallowed.
     // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
     //      return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
-    //      return type `impl Trait` item.
+    //      return type `impl Trait` item, and the `Span` points to the `async` keyword.
     #[instrument(level = "debug", skip(self))]
     fn lower_fn_decl(
         &mut self,
         decl: &FnDecl,
         fn_node_id: Option<NodeId>,
+        fn_span: Span,
         kind: FnDeclKind,
-        make_ret_async: Option<NodeId>,
+        make_ret_async: Option<(NodeId, Span)>,
     ) -> &'hir hir::FnDecl<'hir> {
         let c_variadic = decl.c_variadic();
 
@@ -1656,20 +1684,63 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             }
         }));
 
-        let output = if let Some(ret_id) = make_ret_async {
-            self.lower_async_fn_ret_ty(
-                &decl.output,
-                fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
-                ret_id,
-            )
+        let output = if let Some((ret_id, span)) = make_ret_async {
+            match kind {
+                FnDeclKind::Trait => {
+                    if !kind.impl_trait_in_trait_allowed(self.tcx) {
+                        self.tcx
+                            .sess
+                            .create_feature_err(
+                                TraitFnAsync { fn_span, span },
+                                sym::return_position_impl_trait_in_trait,
+                            )
+                            .emit();
+                    }
+                    self.lower_async_fn_ret_ty(
+                        &decl.output,
+                        fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
+                        ret_id,
+                        true,
+                    )
+                }
+                _ => {
+                    if !kind.impl_trait_return_allowed(self.tcx) {
+                        if kind == FnDeclKind::Impl {
+                            self.tcx
+                                .sess
+                                .create_feature_err(
+                                    TraitFnAsync { fn_span, span },
+                                    sym::return_position_impl_trait_in_trait,
+                                )
+                                .emit();
+                        } else {
+                            self.tcx.sess.emit_err(TraitFnAsync { fn_span, span });
+                        }
+                    }
+                    self.lower_async_fn_ret_ty(
+                        &decl.output,
+                        fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
+                        ret_id,
+                        false,
+                    )
+                }
+            }
         } else {
             match decl.output {
                 FnRetTy::Ty(ref ty) => {
                     let mut context = match fn_node_id {
-                        Some(fn_node_id) if kind.impl_trait_return_allowed() => {
+                        Some(fn_node_id) if kind.impl_trait_return_allowed(self.tcx) => {
                             let fn_def_id = self.local_def_id(fn_node_id);
                             ImplTraitContext::ReturnPositionOpaqueTy {
                                 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
+                                in_trait: false,
+                            }
+                        }
+                        Some(fn_node_id) if kind.impl_trait_in_trait_allowed(self.tcx) => {
+                            let fn_def_id = self.local_def_id(fn_node_id);
+                            ImplTraitContext::ReturnPositionOpaqueTy {
+                                origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
+                                in_trait: true,
                             }
                         }
                         _ => ImplTraitContext::Disallowed(match kind {
@@ -1733,6 +1804,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         output: &FnRetTy,
         fn_node_id: NodeId,
         opaque_ty_node_id: NodeId,
+        in_trait: bool,
     ) -> hir::FnRetTy<'hir> {
         let span = output.span();
 
@@ -1859,8 +1931,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 //
                 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
                 // hence the elision takes place at the fn site.
-                let future_bound =
-                    this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span);
+                let future_bound = this.lower_async_fn_output_type_to_future_bound(
+                    output,
+                    span,
+                    ImplTraitContext::ReturnPositionOpaqueTy {
+                        origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
+                        in_trait,
+                    },
+                );
 
                 let generic_params = this.arena.alloc_from_iter(collected_lifetimes.iter().map(
                     |&(new_node_id, lifetime, _)| {
@@ -1898,6 +1976,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     }),
                     bounds: arena_vec![this; future_bound],
                     origin: hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
+                    in_trait,
                 };
 
                 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
@@ -1943,8 +2022,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         // Foo = impl Trait` is, internally, created as a child of the
         // async fn, so the *type parameters* are inherited.  It's
         // only the lifetime parameters that we must supply.
-        let opaque_ty_ref =
-            hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, generic_args);
+        let opaque_ty_ref = hir::TyKind::OpaqueDef(
+            hir::ItemId { def_id: opaque_ty_def_id },
+            generic_args,
+            in_trait,
+        );
         let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
         hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
     }
@@ -1953,8 +2035,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn lower_async_fn_output_type_to_future_bound(
         &mut self,
         output: &FnRetTy,
-        fn_def_id: LocalDefId,
         span: Span,
+        mut nested_impl_trait_context: ImplTraitContext,
     ) -> hir::GenericBound<'hir> {
         // Compute the `T` in `Future<Output = T>` from the return type.
         let output_ty = match output {
@@ -1962,10 +2044,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
                 // `impl Future` opaque type that `async fn` implicitly
                 // generates.
-                let mut context = ImplTraitContext::ReturnPositionOpaqueTy {
-                    origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
-                };
-                self.lower_ty(ty, &mut context)
+                self.lower_ty(ty, &mut nested_impl_trait_context)
             }
             FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
         };
diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index d6d8881a53a14..6c754f38d144b 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -290,12 +290,6 @@ impl<'a> AstValidator<'a> {
         }
     }
 
-    fn check_trait_fn_not_async(&self, fn_span: Span, asyncness: Async) {
-        if let Async::Yes { span, .. } = asyncness {
-            self.session.emit_err(TraitFnAsync { fn_span, span });
-        }
-    }
-
     fn check_trait_fn_not_const(&self, constness: Const) {
         if let Const::Yes(span) = constness {
             self.session.emit_err(TraitFnConst { span });
@@ -1596,7 +1590,6 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             self.invalid_visibility(&item.vis, None);
             if let AssocItemKind::Fn(box Fn { sig, .. }) = &item.kind {
                 self.check_trait_fn_not_const(sig.header.constness);
-                self.check_trait_fn_not_async(item.span, sig.header.asyncness);
             }
         }
 
diff --git a/compiler/rustc_ast_passes/src/errors.rs b/compiler/rustc_ast_passes/src/errors.rs
index 21467e5765198..4f3b09c587113 100644
--- a/compiler/rustc_ast_passes/src/errors.rs
+++ b/compiler/rustc_ast_passes/src/errors.rs
@@ -79,17 +79,6 @@ pub enum InvalidVisibilityNote {
     IndividualForeignItems,
 }
 
-#[derive(SessionDiagnostic)]
-#[diag(ast_passes::trait_fn_async, code = "E0706")]
-#[note]
-#[note(ast_passes::note2)]
-pub struct TraitFnAsync {
-    #[primary_span]
-    pub fn_span: Span,
-    #[label]
-    pub span: Span,
-}
-
 #[derive(SessionDiagnostic)]
 #[diag(ast_passes::trait_fn_const, code = "E0379")]
 pub struct TraitFnConst {
diff --git a/compiler/rustc_borrowck/src/diagnostics/region_name.rs b/compiler/rustc_borrowck/src/diagnostics/region_name.rs
index 75fde53b6cdec..0707ff5ed02a0 100644
--- a/compiler/rustc_borrowck/src/diagnostics/region_name.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/region_name.rs
@@ -772,7 +772,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
     fn get_future_inner_return_ty(&self, hir_ty: &'tcx hir::Ty<'tcx>) -> &'tcx hir::Ty<'tcx> {
         let hir = self.infcx.tcx.hir();
 
-        let hir::TyKind::OpaqueDef(id, _) = hir_ty.kind else {
+        let hir::TyKind::OpaqueDef(id, _, _) = hir_ty.kind else {
             span_bug!(
                 hir_ty.span,
                 "lowered return type of async fn is not OpaqueDef: {:?}",
diff --git a/compiler/rustc_borrowck/src/region_infer/mod.rs b/compiler/rustc_borrowck/src/region_infer/mod.rs
index 8dc9368a0b994..de70b17e44ccd 100644
--- a/compiler/rustc_borrowck/src/region_infer/mod.rs
+++ b/compiler/rustc_borrowck/src/region_infer/mod.rs
@@ -135,7 +135,6 @@ pub struct RegionInferenceContext<'tcx> {
 /// adds a new lower bound to the SCC it is analyzing: so you wind up
 /// with `'R: 'O` where `'R` is the pick-region and `'O` is the
 /// minimal viable option.
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd)]
 pub(crate) struct AppliedMemberConstraint {
     /// The SCC that was affected. (The "member region".)
     ///
diff --git a/compiler/rustc_error_messages/locales/en-US/ast_lowering.ftl b/compiler/rustc_error_messages/locales/en-US/ast_lowering.ftl
index f2790531aba44..c45e045b4dba0 100644
--- a/compiler/rustc_error_messages/locales/en-US/ast_lowering.ftl
+++ b/compiler/rustc_error_messages/locales/en-US/ast_lowering.ftl
@@ -131,3 +131,9 @@ ast_lowering_arbitrary_expression_in_pattern =
     arbitrary expressions aren't allowed in patterns
 
 ast_lowering_inclusive_range_with_no_end = inclusive range with no end
+
+ast_lowering_trait_fn_async =
+    functions in traits cannot be declared `async`
+    .label = `async` because of this
+    .note = `async` trait functions are not currently supported
+    .note2 = consider using the `async-trait` crate: https://crates.io/crates/async-trait
diff --git a/compiler/rustc_error_messages/locales/en-US/ast_passes.ftl b/compiler/rustc_error_messages/locales/en-US/ast_passes.ftl
index d7108e1e2de35..e5cd1142b20c8 100644
--- a/compiler/rustc_error_messages/locales/en-US/ast_passes.ftl
+++ b/compiler/rustc_error_messages/locales/en-US/ast_passes.ftl
@@ -26,12 +26,6 @@ ast_passes_invalid_visibility =
     .individual_impl_items = place qualifiers on individual impl items instead
     .individual_foreign_items = place qualifiers on individual foreign items instead
 
-ast_passes_trait_fn_async =
-    functions in traits cannot be declared `async`
-    .label = `async` because of this
-    .note = `async` trait functions are not currently supported
-    .note2 = consider using the `async-trait` crate: https://crates.io/crates/async-trait
-
 ast_passes_trait_fn_const =
     functions in traits cannot be declared const
     .label = functions in traits cannot be const
diff --git a/compiler/rustc_error_messages/locales/en-US/parser.ftl b/compiler/rustc_error_messages/locales/en-US/parser.ftl
index bc17754c56ae3..f74df3d9746ae 100644
--- a/compiler/rustc_error_messages/locales/en-US/parser.ftl
+++ b/compiler/rustc_error_messages/locales/en-US/parser.ftl
@@ -153,3 +153,6 @@ parser_left_arrow_operator = unexpected token: `<-`
 
 parser_remove_let = expected pattern, found `let`
     .suggestion = remove the unnecessary `let` keyword
+
+parser_use_eq_instead = unexpected `==`
+    .suggestion = try using `=` instead
diff --git a/compiler/rustc_error_messages/locales/en-US/session.ftl b/compiler/rustc_error_messages/locales/en-US/session.ftl
index 983e5cee8237d..d2a2958f62436 100644
--- a/compiler/rustc_error_messages/locales/en-US/session.ftl
+++ b/compiler/rustc_error_messages/locales/en-US/session.ftl
@@ -14,3 +14,45 @@ session_feature_diagnostic_for_issue =
 
 session_feature_diagnostic_help =
     add `#![feature({$feature})]` to the crate attributes to enable
+
+session_not_circumvent_feature = `-Zunleash-the-miri-inside-of-you` may not be used to circumvent feature gates, except when testing error paths in the CTFE engine
+
+session_profile_use_file_does_not_exist = file `{$path}` passed to `-C profile-use` does not exist.
+
+session_linker_plugin_lto_windows_not_supported = linker plugin based LTO is not supported together with `-C prefer-dynamic` when targeting Windows-like targets
+
+session_profile_sample_use_file_does_not_exist = file `{$path}` passed to `-C profile-sample-use` does not exist.
+
+session_target_requires_unwind_tables = target requires unwind tables, they cannot be disabled with `-C force-unwind-tables=no`
+
+session_sanitizer_not_supported = {$us} sanitizer is not supported for this target
+
+session_sanitizers_not_supported = {$us} sanitizers are not supported for this target
+
+session_cannot_mix_and_match_sanitizers = `-Zsanitizer={$first}` is incompatible with `-Zsanitizer={$second}`
+
+session_cannot_enable_crt_static_linux = sanitizer is incompatible with statically linked libc, disable it using `-C target-feature=-crt-static`
+
+session_sanitizer_cfi_enabled = `-Zsanitizer=cfi` requires `-Clto`
+
+session_unstable_virtual_function_elimination = `-Zvirtual-function-elimination` requires `-Clto`
+
+session_unsupported_dwarf_version = requested DWARF version {$dwarf_version} is greater than 5
+
+session_target_invalid_address_space = invalid address space `{$addr_space}` for `{$cause}` in "data-layout": {$err}
+
+session_target_invalid_bits = invalid {$kind} `{$bit}` for `{$cause}` in "data-layout": {$err}
+
+session_target_missing_alignment = missing alignment for `{$cause}` in "data-layout"
+
+session_target_invalid_alignment = invalid alignment for `{$cause}` in "data-layout": {$err}
+
+session_target_inconsistent_architecture = inconsistent target specification: "data-layout" claims architecture is {$dl}-endian, while "target-endian" is `{$target}`
+
+session_target_inconsistent_pointer_width = inconsistent target specification: "data-layout" claims pointers are {$pointer_size}-bit, while "target-pointer-width" is `{$target}`
+
+session_target_invalid_bits_size = {$err}
+
+session_target_stack_protector_not_supported = `-Z stack-protector={$stack_protector}` is not supported for target {$target_triple} and will be ignored
+
+session_split_debuginfo_unstable_platform = `-Csplit-debuginfo={$debuginfo}` is unstable on this platform
diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index a052aaee04756..a774b52c8a592 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -10,10 +10,11 @@ use rustc_lint_defs::{Applicability, LintExpectationId};
 use rustc_span::edition::LATEST_STABLE_EDITION;
 use rustc_span::symbol::{Ident, MacroRulesNormalizedIdent, Symbol};
 use rustc_span::{edition::Edition, Span, DUMMY_SP};
-use rustc_target::spec::PanicStrategy;
+use rustc_target::spec::{PanicStrategy, SplitDebuginfo, StackProtector, TargetTriple};
 use std::borrow::Cow;
 use std::fmt;
 use std::hash::{Hash, Hasher};
+use std::num::ParseIntError;
 use std::path::{Path, PathBuf};
 
 /// Error type for `Diagnostic`'s `suggestions` field, indicating that
@@ -91,6 +92,10 @@ into_diagnostic_arg_using_display!(
     Edition,
     Ident,
     MacroRulesNormalizedIdent,
+    ParseIntError,
+    StackProtector,
+    &TargetTriple,
+    SplitDebuginfo
 );
 
 impl IntoDiagnosticArg for bool {
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 513225e160645..3e02d2ebb7e3e 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -456,7 +456,7 @@ struct HandlerInner {
 }
 
 /// A key denoting where from a diagnostic was stashed.
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Hash)]
 pub enum StashKey {
     ItemNoType,
     UnderscoreForArrayLengths,
diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs
index f71b3d59e2c04..3b8032040e76c 100644
--- a/compiler/rustc_feature/src/active.rs
+++ b/compiler/rustc_feature/src/active.rs
@@ -487,6 +487,8 @@ declare_features! (
     (incomplete, repr128, "1.16.0", Some(56071), None),
     /// Allows `repr(simd)` and importing the various simd intrinsics.
     (active, repr_simd, "1.4.0", Some(27731), None),
+    /// Allows return-position `impl Trait` in traits.
+    (incomplete, return_position_impl_trait_in_trait, "CURRENT_RUSTC_VERSION", Some(91611), None),
     /// Allows `extern "rust-cold"`.
     (active, rust_cold_cc, "1.63.0", Some(97544), None),
     /// Allows the use of SIMD types in functions declared in `extern` blocks.
diff --git a/compiler/rustc_hir/src/def.rs b/compiler/rustc_hir/src/def.rs
index d5ac07f1e6315..e7c26bd726fbf 100644
--- a/compiler/rustc_hir/src/def.rs
+++ b/compiler/rustc_hir/src/def.rs
@@ -109,6 +109,8 @@ pub enum DefKind {
     InlineConst,
     /// Opaque type, aka `impl Trait`.
     OpaqueTy,
+    /// A return-position `impl Trait` in a trait definition
+    ImplTraitPlaceholder,
     Field,
     /// Lifetime parameter: the `'a` in `struct Foo<'a> { ... }`
     LifetimeParam,
@@ -138,6 +140,7 @@ impl DefKind {
                 panic!("impossible struct constructor")
             }
             DefKind::OpaqueTy => "opaque type",
+            DefKind::ImplTraitPlaceholder => "opaque type in trait",
             DefKind::TyAlias => "type alias",
             DefKind::TraitAlias => "trait alias",
             DefKind::AssocTy => "associated type",
@@ -217,7 +220,8 @@ impl DefKind {
             | DefKind::Use
             | DefKind::ForeignMod
             | DefKind::GlobalAsm
-            | DefKind::Impl => None,
+            | DefKind::Impl
+            | DefKind::ImplTraitPlaceholder => None,
         }
     }
 
@@ -254,6 +258,7 @@ impl DefKind {
             | DefKind::Use
             | DefKind::ForeignMod
             | DefKind::OpaqueTy
+            | DefKind::ImplTraitPlaceholder
             | DefKind::Impl
             | DefKind::Field
             | DefKind::TyParam
@@ -457,7 +462,7 @@ impl PartialRes {
 
 /// Different kinds of symbols can coexist even if they share the same textual name.
 /// Therefore, they each have a separate universe (known as a "namespace").
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 pub enum Namespace {
     /// The type namespace includes `struct`s, `enum`s, `union`s, `trait`s, and `mod`s
     /// (and, by extension, crates).
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index a668c0e95ce4b..69cf220a29231 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -2476,6 +2476,7 @@ pub struct OpaqueTy<'hir> {
     pub generics: &'hir Generics<'hir>,
     pub bounds: GenericBounds<'hir>,
     pub origin: OpaqueTyOrigin,
+    pub in_trait: bool,
 }
 
 /// From whence the opaque type came.
@@ -2515,7 +2516,9 @@ pub enum TyKind<'hir> {
     ///
     /// The generic argument list contains the lifetimes (and in the future
     /// possibly parameters) that are actually bound on the `impl Trait`.
-    OpaqueDef(ItemId, &'hir [GenericArg<'hir>]),
+    ///
+    /// The last parameter specifies whether this opaque appears in a trait definition.
+    OpaqueDef(ItemId, &'hir [GenericArg<'hir>], bool),
     /// A trait object type `Bound1 + Bound2 + Bound3`
     /// where `Bound` is a trait or a lifetime.
     TraitObject(&'hir [PolyTraitRef<'hir>], Lifetime, TraitObjectSyntax),
diff --git a/compiler/rustc_hir/src/intravisit.rs b/compiler/rustc_hir/src/intravisit.rs
index 20ec788463ac0..bf4ab06638bb1 100644
--- a/compiler/rustc_hir/src/intravisit.rs
+++ b/compiler/rustc_hir/src/intravisit.rs
@@ -670,7 +670,7 @@ pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty<'v>) {
         TyKind::Path(ref qpath) => {
             visitor.visit_qpath(qpath, typ.hir_id, typ.span);
         }
-        TyKind::OpaqueDef(item_id, lifetimes) => {
+        TyKind::OpaqueDef(item_id, lifetimes, _in_trait) => {
             visitor.visit_nested_item(item_id);
             walk_list!(visitor, visit_generic_arg, lifetimes);
         }
diff --git a/compiler/rustc_hir/src/target.rs b/compiler/rustc_hir/src/target.rs
index 78bfd7191dba9..5917d5e346e37 100644
--- a/compiler/rustc_hir/src/target.rs
+++ b/compiler/rustc_hir/src/target.rs
@@ -36,6 +36,7 @@ pub enum Target {
     GlobalAsm,
     TyAlias,
     OpaqueTy,
+    ImplTraitPlaceholder,
     Enum,
     Variant,
     Struct,
@@ -79,7 +80,13 @@ impl Target {
             ItemKind::ForeignMod { .. } => Target::ForeignMod,
             ItemKind::GlobalAsm(..) => Target::GlobalAsm,
             ItemKind::TyAlias(..) => Target::TyAlias,
-            ItemKind::OpaqueTy(..) => Target::OpaqueTy,
+            ItemKind::OpaqueTy(ref opaque) => {
+                if opaque.in_trait {
+                    Target::ImplTraitPlaceholder
+                } else {
+                    Target::OpaqueTy
+                }
+            }
             ItemKind::Enum(..) => Target::Enum,
             ItemKind::Struct(..) => Target::Struct,
             ItemKind::Union(..) => Target::Union,
@@ -103,6 +110,7 @@ impl Target {
             DefKind::GlobalAsm => Target::GlobalAsm,
             DefKind::TyAlias => Target::TyAlias,
             DefKind::OpaqueTy => Target::OpaqueTy,
+            DefKind::ImplTraitPlaceholder => Target::ImplTraitPlaceholder,
             DefKind::Enum => Target::Enum,
             DefKind::Struct => Target::Struct,
             DefKind::Union => Target::Union,
@@ -157,6 +165,7 @@ impl Target {
             Target::GlobalAsm => "global asm",
             Target::TyAlias => "type alias",
             Target::OpaqueTy => "opaque type",
+            Target::ImplTraitPlaceholder => "opaque type in trait",
             Target::Enum => "enum",
             Target::Variant => "enum variant",
             Target::Struct => "struct",
diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index 0196bd262179e..95a36dd8a56a5 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -61,6 +61,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::{pluralize, struct_span_err, Diagnostic, ErrorGuaranteed, IntoDiagnosticArg};
 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString, MultiSpan};
 use rustc_hir as hir;
+use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::Node;
@@ -1682,6 +1683,19 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                                 pos.col.to_usize() + 1,
                             )
                         }
+                        (true, ty::Projection(proj))
+                            if self.tcx.def_kind(proj.item_def_id)
+                                == DefKind::ImplTraitPlaceholder =>
+                        {
+                            let sm = self.tcx.sess.source_map();
+                            let pos = sm.lookup_char_pos(self.tcx.def_span(proj.item_def_id).lo());
+                            format!(
+                                " (trait associated opaque type at <{}:{}:{}>)",
+                                sm.filename_for_diagnostics(&pos.file.name),
+                                pos.line,
+                                pos.col.to_usize() + 1,
+                            )
+                        }
                         (true, _) => format!(" ({})", ty.sort_string(self.tcx)),
                         (false, _) => "".to_string(),
                     };
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
index f804569b0747e..b115ac8b3df95 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
@@ -300,7 +300,7 @@ pub fn suggest_new_region_bound(
             continue;
         }
         match fn_return.kind {
-            TyKind::OpaqueDef(item_id, _) => {
+            TyKind::OpaqueDef(item_id, _, _) => {
                 let item = tcx.hir().item(item_id);
                 let ItemKind::OpaqueTy(opaque) = &item.kind else {
                     return;
diff --git a/compiler/rustc_lexer/src/lib.rs b/compiler/rustc_lexer/src/lib.rs
index 178366f7d8045..a79c982649afc 100644
--- a/compiler/rustc_lexer/src/lib.rs
+++ b/compiler/rustc_lexer/src/lib.rs
@@ -141,7 +141,7 @@ pub enum TokenKind {
     Unknown,
 }
 
-#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum DocStyle {
     Outer,
     Inner,
diff --git a/compiler/rustc_lint/src/context.rs b/compiler/rustc_lint/src/context.rs
index 9a163cf207e97..7ca6ec5d96234 100644
--- a/compiler/rustc_lint/src/context.rs
+++ b/compiler/rustc_lint/src/context.rs
@@ -50,6 +50,10 @@ use std::cell::Cell;
 use std::iter;
 use std::slice;
 
+type EarlyLintPassFactory = dyn Fn() -> EarlyLintPassObject + sync::Send + sync::Sync;
+type LateLintPassFactory =
+    dyn for<'tcx> Fn(TyCtxt<'tcx>) -> LateLintPassObject<'tcx> + sync::Send + sync::Sync;
+
 /// Information about the registered lints.
 ///
 /// This is basically the subset of `Context` that we can
@@ -64,11 +68,11 @@ pub struct LintStore {
     /// interior mutability, we don't enforce this (and lints should, in theory,
     /// be compatible with being constructed more than once, though not
     /// necessarily in a sane manner. This is safe though.)
-    pub pre_expansion_passes: Vec<Box<dyn Fn() -> EarlyLintPassObject + sync::Send + sync::Sync>>,
-    pub early_passes: Vec<Box<dyn Fn() -> EarlyLintPassObject + sync::Send + sync::Sync>>,
-    pub late_passes: Vec<Box<dyn Fn() -> LateLintPassObject + sync::Send + sync::Sync>>,
+    pub pre_expansion_passes: Vec<Box<EarlyLintPassFactory>>,
+    pub early_passes: Vec<Box<EarlyLintPassFactory>>,
+    pub late_passes: Vec<Box<LateLintPassFactory>>,
     /// This is unique in that we construct them per-module, so not once.
-    pub late_module_passes: Vec<Box<dyn Fn() -> LateLintPassObject + sync::Send + sync::Sync>>,
+    pub late_module_passes: Vec<Box<LateLintPassFactory>>,
 
     /// Lints indexed by name.
     by_name: FxHashMap<String, TargetLint>,
@@ -186,14 +190,20 @@ impl LintStore {
 
     pub fn register_late_pass(
         &mut self,
-        pass: impl Fn() -> LateLintPassObject + 'static + sync::Send + sync::Sync,
+        pass: impl for<'tcx> Fn(TyCtxt<'tcx>) -> LateLintPassObject<'tcx>
+        + 'static
+        + sync::Send
+        + sync::Sync,
     ) {
         self.late_passes.push(Box::new(pass));
     }
 
     pub fn register_late_mod_pass(
         &mut self,
-        pass: impl Fn() -> LateLintPassObject + 'static + sync::Send + sync::Sync,
+        pass: impl for<'tcx> Fn(TyCtxt<'tcx>) -> LateLintPassObject<'tcx>
+        + 'static
+        + sync::Send
+        + sync::Sync,
     ) {
         self.late_module_passes.push(Box::new(pass));
     }
@@ -558,7 +568,7 @@ pub trait LintPassObject: Sized {}
 
 impl LintPassObject for EarlyLintPassObject {}
 
-impl LintPassObject for LateLintPassObject {}
+impl LintPassObject for LateLintPassObject<'_> {}
 
 pub trait LintContext: Sized {
     type PassObject: LintPassObject;
@@ -949,8 +959,8 @@ impl<'a> EarlyContext<'a> {
     }
 }
 
-impl LintContext for LateContext<'_> {
-    type PassObject = LateLintPassObject;
+impl<'tcx> LintContext for LateContext<'tcx> {
+    type PassObject = LateLintPassObject<'tcx>;
 
     /// Gets the overall compiler `Session` object.
     fn sess(&self) -> &Session {
diff --git a/compiler/rustc_lint/src/late.rs b/compiler/rustc_lint/src/late.rs
index 8a336844dc2fa..66dc3ed59a384 100644
--- a/compiler/rustc_lint/src/late.rs
+++ b/compiler/rustc_lint/src/late.rs
@@ -306,12 +306,12 @@ impl<'tcx, T: LateLintPass<'tcx>> hir_visit::Visitor<'tcx> for LateContextAndPas
     }
 }
 
-struct LateLintPassObjects<'a> {
-    lints: &'a mut [LateLintPassObject],
+struct LateLintPassObjects<'a, 'tcx> {
+    lints: &'a mut [LateLintPassObject<'tcx>],
 }
 
 #[allow(rustc::lint_pass_impl_without_macro)]
-impl LintPass for LateLintPassObjects<'_> {
+impl LintPass for LateLintPassObjects<'_, '_> {
     fn name(&self) -> &'static str {
         panic!()
     }
@@ -329,7 +329,7 @@ macro_rules! expand_late_lint_pass_impl_methods {
 
 macro_rules! late_lint_pass_impl {
     ([], [$hir:tt], $methods:tt) => {
-        impl<$hir> LateLintPass<$hir> for LateLintPassObjects<'_> {
+        impl<$hir> LateLintPass<$hir> for LateLintPassObjects<'_, $hir> {
             expand_late_lint_pass_impl_methods!([$hir], $methods);
         }
     };
@@ -382,7 +382,7 @@ pub fn late_lint_mod<'tcx, T: LateLintPass<'tcx>>(
     late_lint_mod_pass(tcx, module_def_id, builtin_lints);
 
     let mut passes: Vec<_> =
-        unerased_lint_store(tcx).late_module_passes.iter().map(|pass| (pass)()).collect();
+        unerased_lint_store(tcx).late_module_passes.iter().map(|pass| (pass)(tcx)).collect();
 
     if !passes.is_empty() {
         late_lint_mod_pass(tcx, module_def_id, LateLintPassObjects { lints: &mut passes[..] });
@@ -418,7 +418,8 @@ fn late_lint_pass_crate<'tcx, T: LateLintPass<'tcx>>(tcx: TyCtxt<'tcx>, pass: T)
 }
 
 fn late_lint_crate<'tcx, T: LateLintPass<'tcx>>(tcx: TyCtxt<'tcx>, builtin_lints: T) {
-    let mut passes = unerased_lint_store(tcx).late_passes.iter().map(|p| (p)()).collect::<Vec<_>>();
+    let mut passes =
+        unerased_lint_store(tcx).late_passes.iter().map(|p| (p)(tcx)).collect::<Vec<_>>();
 
     if !tcx.sess.opts.unstable_opts.no_interleave_lints {
         if !passes.is_empty() {
@@ -434,7 +435,7 @@ fn late_lint_crate<'tcx, T: LateLintPass<'tcx>>(tcx: TyCtxt<'tcx>, builtin_lints
         }
 
         let mut passes: Vec<_> =
-            unerased_lint_store(tcx).late_module_passes.iter().map(|pass| (pass)()).collect();
+            unerased_lint_store(tcx).late_module_passes.iter().map(|pass| (pass)(tcx)).collect();
 
         for pass in &mut passes {
             tcx.sess.prof.extra_verbose_generic_activity("run_late_module_lint", pass.name()).run(
diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index 370a75cf70069..e0e6f1a8c080c 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -260,26 +260,41 @@ fn register_builtins(store: &mut LintStore, no_interleave_lints: bool) {
         )
     }
 
-    macro_rules! register_pass {
+    macro_rules! register_early_pass {
         ($method:ident, $ty:ident, $constructor:expr) => {
             store.register_lints(&$ty::get_lints());
             store.$method(|| Box::new($constructor));
         };
     }
 
-    macro_rules! register_passes {
+    macro_rules! register_late_pass {
+        ($method:ident, $ty:ident, $constructor:expr) => {
+            store.register_lints(&$ty::get_lints());
+            store.$method(|_| Box::new($constructor));
+        };
+    }
+
+    macro_rules! register_early_passes {
+        ($method:ident, [$($passes:ident: $constructor:expr,)*]) => (
+            $(
+                register_early_pass!($method, $passes, $constructor);
+            )*
+        )
+    }
+
+    macro_rules! register_late_passes {
         ($method:ident, [$($passes:ident: $constructor:expr,)*]) => (
             $(
-                register_pass!($method, $passes, $constructor);
+                register_late_pass!($method, $passes, $constructor);
             )*
         )
     }
 
     if no_interleave_lints {
-        pre_expansion_lint_passes!(register_passes, register_pre_expansion_pass);
-        early_lint_passes!(register_passes, register_early_pass);
-        late_lint_passes!(register_passes, register_late_pass);
-        late_lint_mod_passes!(register_passes, register_late_mod_pass);
+        pre_expansion_lint_passes!(register_early_passes, register_pre_expansion_pass);
+        early_lint_passes!(register_early_passes, register_early_pass);
+        late_lint_passes!(register_late_passes, register_late_pass);
+        late_lint_mod_passes!(register_late_passes, register_late_mod_pass);
     } else {
         store.register_lints(&BuiltinCombinedPreExpansionLintPass::get_lints());
         store.register_lints(&BuiltinCombinedEarlyLintPass::get_lints());
@@ -510,19 +525,19 @@ fn register_internals(store: &mut LintStore) {
     store.register_lints(&LintPassImpl::get_lints());
     store.register_early_pass(|| Box::new(LintPassImpl));
     store.register_lints(&DefaultHashTypes::get_lints());
-    store.register_late_pass(|| Box::new(DefaultHashTypes));
+    store.register_late_pass(|_| Box::new(DefaultHashTypes));
     store.register_lints(&QueryStability::get_lints());
-    store.register_late_pass(|| Box::new(QueryStability));
+    store.register_late_pass(|_| Box::new(QueryStability));
     store.register_lints(&ExistingDocKeyword::get_lints());
-    store.register_late_pass(|| Box::new(ExistingDocKeyword));
+    store.register_late_pass(|_| Box::new(ExistingDocKeyword));
     store.register_lints(&TyTyKind::get_lints());
-    store.register_late_pass(|| Box::new(TyTyKind));
+    store.register_late_pass(|_| Box::new(TyTyKind));
     store.register_lints(&Diagnostics::get_lints());
-    store.register_late_pass(|| Box::new(Diagnostics));
+    store.register_late_pass(|_| Box::new(Diagnostics));
     store.register_lints(&BadOptAccess::get_lints());
-    store.register_late_pass(|| Box::new(BadOptAccess));
+    store.register_late_pass(|_| Box::new(BadOptAccess));
     store.register_lints(&PassByValue::get_lints());
-    store.register_late_pass(|| Box::new(PassByValue));
+    store.register_late_pass(|_| Box::new(PassByValue));
     // FIXME(davidtwco): deliberately do not include `UNTRANSLATABLE_DIAGNOSTIC` and
     // `DIAGNOSTIC_OUTSIDE_OF_IMPL` here because `-Wrustc::internal` is provided to every crate and
     // these lints will trigger all of the time - change this once migration to diagnostic structs
diff --git a/compiler/rustc_lint/src/passes.rs b/compiler/rustc_lint/src/passes.rs
index 90c554c2e040b..666e61b85acfc 100644
--- a/compiler/rustc_lint/src/passes.rs
+++ b/compiler/rustc_lint/src/passes.rs
@@ -244,4 +244,4 @@ macro_rules! declare_combined_early_lint_pass {
 
 /// A lint pass boxed up as a trait object.
 pub type EarlyLintPassObject = Box<dyn EarlyLintPass + sync::Send + 'static>;
-pub type LateLintPassObject = Box<dyn for<'tcx> LateLintPass<'tcx> + sync::Send + 'static>;
+pub type LateLintPassObject<'tcx> = Box<dyn LateLintPass<'tcx> + sync::Send + 'tcx>;
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index b807663b10fd0..f967ac9a4dc3e 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -847,6 +847,7 @@ fn should_encode_visibility(def_kind: DefKind) -> bool {
         | DefKind::Use
         | DefKind::ForeignMod
         | DefKind::OpaqueTy
+        | DefKind::ImplTraitPlaceholder
         | DefKind::Impl
         | DefKind::Field => true,
         DefKind::TyParam
@@ -879,6 +880,7 @@ fn should_encode_stability(def_kind: DefKind) -> bool {
         | DefKind::ForeignMod
         | DefKind::TyAlias
         | DefKind::OpaqueTy
+        | DefKind::ImplTraitPlaceholder
         | DefKind::Enum
         | DefKind::Union
         | DefKind::Impl
@@ -967,6 +969,7 @@ fn should_encode_variances(def_kind: DefKind) -> bool {
         | DefKind::ForeignMod
         | DefKind::TyAlias
         | DefKind::OpaqueTy
+        | DefKind::ImplTraitPlaceholder
         | DefKind::Impl
         | DefKind::Trait
         | DefKind::TraitAlias
@@ -1003,6 +1006,7 @@ fn should_encode_generics(def_kind: DefKind) -> bool {
         | DefKind::AnonConst
         | DefKind::InlineConst
         | DefKind::OpaqueTy
+        | DefKind::ImplTraitPlaceholder
         | DefKind::Impl
         | DefKind::Field
         | DefKind::TyParam
@@ -1032,6 +1036,7 @@ fn should_encode_type(tcx: TyCtxt<'_>, def_id: LocalDefId, def_kind: DefKind) ->
         | DefKind::Static(..)
         | DefKind::TyAlias
         | DefKind::OpaqueTy
+        | DefKind::ImplTraitPlaceholder
         | DefKind::ForeignTy
         | DefKind::Impl
         | DefKind::AssocFn
@@ -1081,6 +1086,7 @@ fn should_encode_const(def_kind: DefKind) -> bool {
         | DefKind::Static(..)
         | DefKind::TyAlias
         | DefKind::OpaqueTy
+        | DefKind::ImplTraitPlaceholder
         | DefKind::ForeignTy
         | DefKind::Impl
         | DefKind::AssocFn
diff --git a/compiler/rustc_metadata/src/rmeta/table.rs b/compiler/rustc_metadata/src/rmeta/table.rs
index d5f151f0ed8e5..e7c1abd126e04 100644
--- a/compiler/rustc_metadata/src/rmeta/table.rs
+++ b/compiler/rustc_metadata/src/rmeta/table.rs
@@ -90,6 +90,7 @@ fixed_size_enum! {
         ( AnonConst                                )
         ( InlineConst                              )
         ( OpaqueTy                                 )
+        ( ImplTraitPlaceholder                     )
         ( Field                                    )
         ( LifetimeParam                            )
         ( GlobalAsm                                )
diff --git a/compiler/rustc_middle/src/arena.rs b/compiler/rustc_middle/src/arena.rs
index 65d5f755f7248..9b1fedd0b533c 100644
--- a/compiler/rustc_middle/src/arena.rs
+++ b/compiler/rustc_middle/src/arena.rs
@@ -101,6 +101,8 @@ macro_rules! arena_types {
             [decode] impl_source: rustc_middle::traits::ImplSource<'tcx, ()>,
 
             [] dep_kind: rustc_middle::dep_graph::DepKindStruct<'tcx>,
+
+            [] trait_impl_trait_tys: rustc_data_structures::fx::FxHashMap<rustc_hir::def_id::DefId, rustc_middle::ty::Ty<'tcx>>,
         ]);
     )
 }
diff --git a/compiler/rustc_middle/src/hir/map/mod.rs b/compiler/rustc_middle/src/hir/map/mod.rs
index 6217bffb8f76c..5a65ec9a4765a 100644
--- a/compiler/rustc_middle/src/hir/map/mod.rs
+++ b/compiler/rustc_middle/src/hir/map/mod.rs
@@ -212,7 +212,13 @@ impl<'hir> Map<'hir> {
                 ItemKind::Fn(..) => DefKind::Fn,
                 ItemKind::Macro(_, macro_kind) => DefKind::Macro(macro_kind),
                 ItemKind::Mod(..) => DefKind::Mod,
-                ItemKind::OpaqueTy(..) => DefKind::OpaqueTy,
+                ItemKind::OpaqueTy(ref opaque) => {
+                    if opaque.in_trait {
+                        DefKind::ImplTraitPlaceholder
+                    } else {
+                        DefKind::OpaqueTy
+                    }
+                }
                 ItemKind::TyAlias(..) => DefKind::TyAlias,
                 ItemKind::Enum(..) => DefKind::Enum,
                 ItemKind::Struct(..) => DefKind::Struct,
@@ -1187,7 +1193,13 @@ fn hir_id_to_string(map: Map<'_>, id: HirId) -> String {
                 ItemKind::ForeignMod { .. } => "foreign mod",
                 ItemKind::GlobalAsm(..) => "global asm",
                 ItemKind::TyAlias(..) => "ty",
-                ItemKind::OpaqueTy(..) => "opaque type",
+                ItemKind::OpaqueTy(ref opaque) => {
+                    if opaque.in_trait {
+                        "opaque type in trait"
+                    } else {
+                        "opaque type"
+                    }
+                }
                 ItemKind::Enum(..) => "enum",
                 ItemKind::Struct(..) => "struct",
                 ItemKind::Union(..) => "union",
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
index e149535bec7b5..1f7643a76afe5 100644
--- a/compiler/rustc_middle/src/mir/syntax.rs
+++ b/compiler/rustc_middle/src/mir/syntax.rs
@@ -741,7 +741,7 @@ pub enum TerminatorKind<'tcx> {
 }
 
 /// Information about an assertion failure.
-#[derive(Clone, TyEncodable, TyDecodable, Hash, HashStable, PartialEq, PartialOrd)]
+#[derive(Clone, TyEncodable, TyDecodable, Hash, HashStable, PartialEq)]
 pub enum AssertKind<O> {
     BoundsCheck { len: O, index: O },
     Overflow(BinOp, O, O),
diff --git a/compiler/rustc_middle/src/mir/terminator.rs b/compiler/rustc_middle/src/mir/terminator.rs
index 9ccf5aea63ca8..02a9958525b22 100644
--- a/compiler/rustc_middle/src/mir/terminator.rs
+++ b/compiler/rustc_middle/src/mir/terminator.rs
@@ -14,7 +14,7 @@ use std::slice;
 
 pub use super::query::*;
 
-#[derive(Debug, Clone, TyEncodable, TyDecodable, Hash, HashStable, PartialEq, PartialOrd)]
+#[derive(Debug, Clone, TyEncodable, TyDecodable, Hash, HashStable, PartialEq)]
 pub struct SwitchTargets {
     /// Possible values. The locations to branch to in each case
     /// are found in the corresponding indices from the `targets` vector.
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 4478b45cf1437..adf479c423604 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -161,6 +161,13 @@ rustc_queries! {
         separate_provide_extern
     }
 
+    query compare_predicates_and_trait_impl_trait_tys(key: DefId)
+        -> Result<&'tcx FxHashMap<DefId, Ty<'tcx>>, ErrorGuaranteed>
+    {
+        desc { "better description please" }
+        separate_provide_extern
+    }
+
     query analysis(key: ()) -> Result<(), ErrorGuaranteed> {
         eval_always
         desc { "running analysis passes on this crate" }
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index c2e5decfc786e..53e91e48c24d0 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -1252,7 +1252,7 @@ impl<'tcx> TyCtxt<'tcx> {
         output_filenames: OutputFilenames,
     ) -> GlobalCtxt<'tcx> {
         let data_layout = TargetDataLayout::parse(&s.target).unwrap_or_else(|err| {
-            s.fatal(&err);
+            s.emit_fatal(err);
         });
         let interners = CtxtInterners::new(arena);
         let common_types = CommonTypes::new(
diff --git a/compiler/rustc_middle/src/ty/diagnostics.rs b/compiler/rustc_middle/src/ty/diagnostics.rs
index dd2f43210603a..d8ce96bad663e 100644
--- a/compiler/rustc_middle/src/ty/diagnostics.rs
+++ b/compiler/rustc_middle/src/ty/diagnostics.rs
@@ -396,7 +396,7 @@ impl<'v> hir::intravisit::Visitor<'v> for TraitObjectVisitor<'v> {
             ) => {
                 self.0.push(ty);
             }
-            hir::TyKind::OpaqueDef(item_id, _) => {
+            hir::TyKind::OpaqueDef(item_id, _, _) => {
                 self.0.push(ty);
                 let item = self.1.item(item_id);
                 hir::intravisit::walk_item(self, item);
diff --git a/compiler/rustc_middle/src/ty/error.rs b/compiler/rustc_middle/src/ty/error.rs
index da564c66a70e1..279c8c8d6d16d 100644
--- a/compiler/rustc_middle/src/ty/error.rs
+++ b/compiler/rustc_middle/src/ty/error.rs
@@ -2,6 +2,7 @@ use crate::traits::{ObligationCause, ObligationCauseCode};
 use crate::ty::diagnostics::suggest_constraining_type_param;
 use crate::ty::print::{FmtPrinter, Printer};
 use crate::ty::{self, BoundRegionKind, Region, Ty, TyCtxt};
+use hir::def::DefKind;
 use rustc_errors::Applicability::{MachineApplicable, MaybeIncorrect};
 use rustc_errors::{pluralize, Diagnostic, MultiSpan};
 use rustc_hir as hir;
@@ -538,7 +539,7 @@ impl<T> Trait<T> for X {
                             diag.span_label(p_span, "this type parameter");
                         }
                     }
-                    (ty::Projection(proj_ty), _) => {
+                    (ty::Projection(proj_ty), _) if self.def_kind(proj_ty.item_def_id) != DefKind::ImplTraitPlaceholder => {
                         self.expected_projection(
                             diag,
                             proj_ty,
@@ -547,7 +548,7 @@ impl<T> Trait<T> for X {
                             cause.code(),
                         );
                     }
-                    (_, ty::Projection(proj_ty)) => {
+                    (_, ty::Projection(proj_ty)) if self.def_kind(proj_ty.item_def_id) != DefKind::ImplTraitPlaceholder => {
                         let msg = format!(
                             "consider constraining the associated type `{}` to `{}`",
                             values.found, values.expected,
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 37136ff2ef5d3..70ad74ba52ac6 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -2471,6 +2471,14 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn is_const_default_method(self, def_id: DefId) -> bool {
         matches!(self.trait_of_item(def_id), Some(trait_id) if self.has_attr(trait_id, sym::const_trait))
     }
+
+    pub fn impl_trait_in_trait_parent(self, mut def_id: DefId) -> DefId {
+        while let def_kind = self.def_kind(def_id) && def_kind != DefKind::AssocFn {
+            debug_assert_eq!(def_kind, DefKind::ImplTraitPlaceholder);
+            def_id = self.parent(def_id);
+        }
+        def_id
+    }
 }
 
 /// Yields the parent function's `LocalDefId` if `def_id` is an `impl Trait` definition.
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 1ae3063dae4e7..f134e2cd1bc65 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -632,7 +632,13 @@ pub trait PrettyPrinter<'tcx>:
             ty::Foreign(def_id) => {
                 p!(print_def_path(def_id, &[]));
             }
-            ty::Projection(ref data) => p!(print(data)),
+            ty::Projection(ref data) => {
+                if self.tcx().def_kind(data.item_def_id) == DefKind::ImplTraitPlaceholder {
+                    return self.pretty_print_opaque_impl_type(data.item_def_id, data.substs);
+                } else {
+                    p!(print(data))
+                }
+            }
             ty::Placeholder(placeholder) => p!(write("Placeholder({:?})", placeholder)),
             ty::Opaque(def_id, substs) => {
                 // FIXME(eddyb) print this with `print_def_path`.
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 9fb91b5fe8700..c5c5d3473418c 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -11,6 +11,7 @@ use crate::ty::{
     TypeVisitor,
 };
 use crate::ty::{List, ParamEnv};
+use hir::def::DefKind;
 use polonius_engine::Atom;
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::intern::Interned;
@@ -1196,7 +1197,9 @@ pub struct ProjectionTy<'tcx> {
 
 impl<'tcx> ProjectionTy<'tcx> {
     pub fn trait_def_id(&self, tcx: TyCtxt<'tcx>) -> DefId {
-        tcx.parent(self.item_def_id)
+        let parent = tcx.parent(self.item_def_id);
+        assert_eq!(tcx.def_kind(parent), DefKind::Trait);
+        parent
     }
 
     /// Extracts the underlying trait reference and own substs from this projection.
diff --git a/compiler/rustc_middle/src/ty/util.rs b/compiler/rustc_middle/src/ty/util.rs
index a3837512bce26..0c73ae54bc31a 100644
--- a/compiler/rustc_middle/src/ty/util.rs
+++ b/compiler/rustc_middle/src/ty/util.rs
@@ -651,6 +651,13 @@ impl<'tcx> TyCtxt<'tcx> {
         ty::EarlyBinder(self.type_of(def_id))
     }
 
+    pub fn bound_trait_impl_trait_tys(
+        self,
+        def_id: DefId,
+    ) -> ty::EarlyBinder<Result<&'tcx FxHashMap<DefId, Ty<'tcx>>, ErrorGuaranteed>> {
+        ty::EarlyBinder(self.compare_predicates_and_trait_impl_trait_tys(def_id))
+    }
+
     pub fn bound_fn_sig(self, def_id: DefId) -> ty::EarlyBinder<ty::PolyFnSig<'tcx>> {
         ty::EarlyBinder(self.fn_sig(def_id))
     }
diff --git a/compiler/rustc_middle/src/ty/visit.rs b/compiler/rustc_middle/src/ty/visit.rs
index 5e042c3acfce2..5f8cb57820210 100644
--- a/compiler/rustc_middle/src/ty/visit.rs
+++ b/compiler/rustc_middle/src/ty/visit.rs
@@ -666,7 +666,7 @@ impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
         // ignore the inputs to a projection, as they may not appear
         // in the normalized form
         if self.just_constrained {
-            if let ty::Projection(..) = t.kind() {
+            if let ty::Projection(..) | ty::Opaque(..) = t.kind() {
                 return ControlFlow::CONTINUE;
             }
         }
diff --git a/compiler/rustc_monomorphize/src/polymorphize.rs b/compiler/rustc_monomorphize/src/polymorphize.rs
index af4b35db3bace..98156a94ec4b4 100644
--- a/compiler/rustc_monomorphize/src/polymorphize.rs
+++ b/compiler/rustc_monomorphize/src/polymorphize.rs
@@ -170,6 +170,7 @@ fn mark_used_by_default_parameters<'tcx>(
         | DefKind::AnonConst
         | DefKind::InlineConst
         | DefKind::OpaqueTy
+        | DefKind::ImplTraitPlaceholder
         | DefKind::Field
         | DefKind::LifetimeParam
         | DefKind::GlobalAsm
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index ad49227222b2c..be524db785bc0 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -713,6 +713,14 @@ pub(crate) struct RemoveLet {
     pub span: Span,
 }
 
+#[derive(SessionDiagnostic)]
+#[diag(parser::use_eq_instead)]
+pub(crate) struct UseEqInstead {
+    #[primary_span]
+    #[suggestion_short(applicability = "machine-applicable", code = "=")]
+    pub span: Span,
+}
+
 // SnapshotParser is used to create a snapshot of the parser
 // without causing duplicate errors being emitted when the `Parser`
 // is dropped.
@@ -957,6 +965,14 @@ impl<'a> Parser<'a> {
             }
         }
 
+        if self.token.kind == TokenKind::EqEq
+            && self.prev_token.is_ident()
+            && expected.iter().any(|tok| matches!(tok, TokenType::Token(TokenKind::Eq)))
+        {
+            // Likely typo: `=` → `==` in let expr or enum item
+            return Err(self.sess.create_err(UseEqInstead { span: self.token.span }));
+        }
+
         let expect = tokens_to_string(&expected);
         let actual = super::token_descr(&self.token);
         let (msg_exp, (label_sp, label_exp)) = if expected.len() > 1 {
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index d0b46aa2c4530..bb684e784c58a 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -661,6 +661,7 @@ impl CheckAttrVisitor<'_> {
             | Target::GlobalAsm
             | Target::TyAlias
             | Target::OpaqueTy
+            | Target::ImplTraitPlaceholder
             | Target::Enum
             | Target::Variant
             | Target::Struct
diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs
index 625c854ea77a5..2191e3befb8cf 100644
--- a/compiler/rustc_passes/src/dead.rs
+++ b/compiler/rustc_passes/src/dead.rs
@@ -450,7 +450,7 @@ impl<'tcx> Visitor<'tcx> for MarkSymbolVisitor<'tcx> {
     }
 
     fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
-        if let TyKind::OpaqueDef(item_id, _) = ty.kind {
+        if let TyKind::OpaqueDef(item_id, _, _) = ty.kind {
             let item = self.tcx.hir().item(item_id);
             intravisit::walk_item(self, item);
         }
diff --git a/compiler/rustc_privacy/src/lib.rs b/compiler/rustc_privacy/src/lib.rs
index b2966f0d21801..afd423dc5fa1a 100644
--- a/compiler/rustc_privacy/src/lib.rs
+++ b/compiler/rustc_privacy/src/lib.rs
@@ -596,6 +596,7 @@ impl<'tcx> EmbargoVisitor<'tcx> {
             | DefKind::ForeignTy
             | DefKind::Fn
             | DefKind::OpaqueTy
+            | DefKind::ImplTraitPlaceholder
             | DefKind::AssocFn
             | DefKind::Trait
             | DefKind::TyParam
@@ -706,12 +707,12 @@ impl<'tcx> Visitor<'tcx> for EmbargoVisitor<'tcx> {
             hir::ItemKind::Use(..) => {}
             // The interface is empty.
             hir::ItemKind::GlobalAsm(..) => {}
-            hir::ItemKind::OpaqueTy(..) => {
+            hir::ItemKind::OpaqueTy(ref opaque) => {
                 // HACK(jynelson): trying to infer the type of `impl trait` breaks `async-std` (and `pub async fn` in general)
                 // Since rustdoc never needs to do codegen and doesn't care about link-time reachability,
                 // mark this as unreachable.
                 // See https://github.com/rust-lang/rust/issues/75100
-                if !self.tcx.sess.opts.actually_rustdoc {
+                if !opaque.in_trait && !self.tcx.sess.opts.actually_rustdoc {
                     // FIXME: This is some serious pessimization intended to workaround deficiencies
                     // in the reachability pass (`middle/reachable.rs`). Types are marked as link-time
                     // reachable if they are returned via `impl Trait`, even from private functions.
@@ -2033,7 +2034,8 @@ fn local_visibility(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Visibility {
                 //   Visibility on them should have no effect, but to avoid the visibility
                 //   query failing on some items, we provide it for opaque types as well.
                 | Node::Item(hir::Item {
-                    kind: hir::ItemKind::Use(_, hir::UseKind::ListStem) | hir::ItemKind::OpaqueTy(..),
+                    kind: hir::ItemKind::Use(_, hir::UseKind::ListStem)
+                        | hir::ItemKind::OpaqueTy(..),
                     ..
                 }) => ty::Visibility::Restricted(tcx.parent_module(hir_id)),
                 // Visibilities of trait impl items are inherited from their traits
diff --git a/compiler/rustc_resolve/src/build_reduced_graph.rs b/compiler/rustc_resolve/src/build_reduced_graph.rs
index 9cb735b36856c..81b67b758f7e1 100644
--- a/compiler/rustc_resolve/src/build_reduced_graph.rs
+++ b/compiler/rustc_resolve/src/build_reduced_graph.rs
@@ -972,6 +972,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                 | DefKind::TyAlias
                 | DefKind::ForeignTy
                 | DefKind::OpaqueTy
+                | DefKind::ImplTraitPlaceholder
                 | DefKind::TraitAlias
                 | DefKind::AssocTy,
                 _,
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index b37feb15890ba..2d6e76c451bfa 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -851,7 +851,7 @@ impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
                         // We include all lifetime parameters, either named or "Fresh".
                         // The order of those parameters does not matter, as long as it is
                         // deterministic.
-                        if let Some(async_node_id) = async_node_id {
+                        if let Some((async_node_id, _)) = async_node_id {
                             let mut extra_lifetime_params = this
                                 .r
                                 .extra_lifetime_params_map
diff --git a/compiler/rustc_resolve/src/late/lifetimes.rs b/compiler/rustc_resolve/src/late/lifetimes.rs
index 101679aa6dc93..6ff56f9a89114 100644
--- a/compiler/rustc_resolve/src/late/lifetimes.rs
+++ b/compiler/rustc_resolve/src/late/lifetimes.rs
@@ -715,7 +715,7 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
                 };
                 self.with(scope, |this| this.visit_ty(&mt.ty));
             }
-            hir::TyKind::OpaqueDef(item_id, lifetimes) => {
+            hir::TyKind::OpaqueDef(item_id, lifetimes, _in_trait) => {
                 // Resolve the lifetimes in the bounds to the lifetime defs in the generics.
                 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
                 // `type MyAnonTy<'b> = impl MyTrait<'b>;`
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index f7b7313d1049d..749a78a7552ed 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -57,7 +57,7 @@ use rustc_span::{Span, DUMMY_SP};
 use smallvec::{smallvec, SmallVec};
 use std::cell::{Cell, RefCell};
 use std::collections::BTreeSet;
-use std::{cmp, fmt, ptr};
+use std::{fmt, ptr};
 
 use diagnostics::{ImportSuggestion, LabelSuggestion, Suggestion};
 use imports::{Import, ImportKind, ImportResolver, NameResolution};
@@ -163,7 +163,6 @@ enum ImplTraitContext {
     Universal(LocalDefId),
 }
 
-#[derive(Eq)]
 struct BindingError {
     name: Symbol,
     origin: BTreeSet<Span>,
@@ -171,24 +170,6 @@ struct BindingError {
     could_be_path: bool,
 }
 
-impl PartialOrd for BindingError {
-    fn partial_cmp(&self, other: &BindingError) -> Option<cmp::Ordering> {
-        Some(self.cmp(other))
-    }
-}
-
-impl PartialEq for BindingError {
-    fn eq(&self, other: &BindingError) -> bool {
-        self.name == other.name
-    }
-}
-
-impl Ord for BindingError {
-    fn cmp(&self, other: &BindingError) -> cmp::Ordering {
-        self.name.cmp(&other.name)
-    }
-}
-
 enum ResolutionError<'a> {
     /// Error E0401: can't use type or const parameters from outer function.
     GenericParamsFromOuterFunction(Res, HasGenericParams),
@@ -845,7 +826,7 @@ impl<'a> NameBinding<'a> {
     }
 }
 
-#[derive(Debug, Default, Clone)]
+#[derive(Default, Clone)]
 pub struct ExternPreludeEntry<'a> {
     extern_crate_item: Option<&'a NameBinding<'a>>,
     pub introduced_by_item: bool,
diff --git a/compiler/rustc_save_analysis/src/dump_visitor.rs b/compiler/rustc_save_analysis/src/dump_visitor.rs
index 6658892881d4b..94f222251d3dc 100644
--- a/compiler/rustc_save_analysis/src/dump_visitor.rs
+++ b/compiler/rustc_save_analysis/src/dump_visitor.rs
@@ -1321,7 +1321,7 @@ impl<'tcx> Visitor<'tcx> for DumpVisitor<'tcx> {
                         }),
                 }
             }
-            hir::TyKind::OpaqueDef(item_id, _) => {
+            hir::TyKind::OpaqueDef(item_id, _, _) => {
                 let item = self.tcx.hir().item(item_id);
                 self.nest_typeck_results(item_id.def_id, |v| v.visit_item(item));
             }
diff --git a/compiler/rustc_save_analysis/src/lib.rs b/compiler/rustc_save_analysis/src/lib.rs
index 89bca39512f52..ebe44a56449d3 100644
--- a/compiler/rustc_save_analysis/src/lib.rs
+++ b/compiler/rustc_save_analysis/src/lib.rs
@@ -685,6 +685,7 @@ impl<'tcx> SaveContext<'tcx> {
                 | HirDefKind::AssocTy
                 | HirDefKind::Trait
                 | HirDefKind::OpaqueTy
+                | HirDefKind::ImplTraitPlaceholder
                 | HirDefKind::TyParam,
                 def_id,
             ) => Some(Ref { kind: RefKind::Type, span, ref_id: id_from_def_id(def_id) }),
diff --git a/compiler/rustc_save_analysis/src/sig.rs b/compiler/rustc_save_analysis/src/sig.rs
index d1286c9b8b0df..bae1828cd182d 100644
--- a/compiler/rustc_save_analysis/src/sig.rs
+++ b/compiler/rustc_save_analysis/src/sig.rs
@@ -316,7 +316,7 @@ impl<'hir> Sig for hir::Ty<'hir> {
                 let text = format!("[{}; {}]", nested_ty.text, expr);
                 Ok(replace_text(nested_ty, text))
             }
-            hir::TyKind::OpaqueDef(item_id, _) => {
+            hir::TyKind::OpaqueDef(item_id, _, _) => {
                 let item = scx.tcx.hir().item(item_id);
                 item.make(offset, Some(item_id.hir_id()), scx)
             }
@@ -561,7 +561,13 @@ impl<'hir> Sig for hir::Item<'hir> {
             hir::ItemKind::ForeignMod { .. } => Err("extern mod"),
             hir::ItemKind::GlobalAsm(_) => Err("global asm"),
             hir::ItemKind::ExternCrate(_) => Err("extern crate"),
-            hir::ItemKind::OpaqueTy(..) => Err("opaque type"),
+            hir::ItemKind::OpaqueTy(ref opaque) => {
+                if opaque.in_trait {
+                    Err("opaque type in trait")
+                } else {
+                    Err("opaque type")
+                }
+            }
             // FIXME should implement this (e.g., pub use).
             hir::ItemKind::Use(..) => Err("import"),
         }
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 04bd685f19001..8bb3878fbbb47 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -898,7 +898,7 @@ fn default_configuration(sess: &Session) -> CrateConfig {
     let max_atomic_width = sess.target.max_atomic_width();
     let atomic_cas = sess.target.atomic_cas;
     let layout = TargetDataLayout::parse(&sess.target).unwrap_or_else(|err| {
-        sess.fatal(&err);
+        sess.emit_fatal(err);
     });
 
     let mut ret = CrateConfig::default();
diff --git a/compiler/rustc_session/src/errors.rs b/compiler/rustc_session/src/errors.rs
index 7252f1799dac1..3c93cfab183d2 100644
--- a/compiler/rustc_session/src/errors.rs
+++ b/compiler/rustc_session/src/errors.rs
@@ -1,10 +1,12 @@
 use std::num::NonZeroU32;
 
-use crate as rustc_session;
 use crate::cgu_reuse_tracker::CguReuse;
-use rustc_errors::MultiSpan;
+use crate::{self as rustc_session, SessionDiagnostic};
+use rustc_errors::{fluent, DiagnosticBuilder, Handler, MultiSpan};
 use rustc_macros::SessionDiagnostic;
 use rustc_span::{Span, Symbol};
+use rustc_target::abi::TargetDataLayoutErrors;
+use rustc_target::spec::{SplitDebuginfo, StackProtector, TargetTriple};
 
 #[derive(SessionDiagnostic)]
 #[diag(session::incorrect_cgu_reuse_type)]
@@ -43,3 +45,128 @@ pub struct FeatureDiagnosticForIssue {
 pub struct FeatureDiagnosticHelp {
     pub feature: Symbol,
 }
+
+impl SessionDiagnostic<'_, !> for TargetDataLayoutErrors<'_> {
+    fn into_diagnostic(self, sess: &Handler) -> DiagnosticBuilder<'_, !> {
+        let mut diag;
+        match self {
+            TargetDataLayoutErrors::InvalidAddressSpace { addr_space, err, cause } => {
+                diag = sess.struct_fatal(fluent::session::target_invalid_address_space);
+                diag.set_arg("addr_space", addr_space);
+                diag.set_arg("cause", cause);
+                diag.set_arg("err", err);
+                diag
+            }
+            TargetDataLayoutErrors::InvalidBits { kind, bit, cause, err } => {
+                diag = sess.struct_fatal(fluent::session::target_invalid_bits);
+                diag.set_arg("kind", kind);
+                diag.set_arg("bit", bit);
+                diag.set_arg("cause", cause);
+                diag.set_arg("err", err);
+                diag
+            }
+            TargetDataLayoutErrors::MissingAlignment { cause } => {
+                diag = sess.struct_fatal(fluent::session::target_missing_alignment);
+                diag.set_arg("cause", cause);
+                diag
+            }
+            TargetDataLayoutErrors::InvalidAlignment { cause, err } => {
+                diag = sess.struct_fatal(fluent::session::target_invalid_alignment);
+                diag.set_arg("cause", cause);
+                diag.set_arg("err", err);
+                diag
+            }
+            TargetDataLayoutErrors::InconsistentTargetArchitecture { dl, target } => {
+                diag = sess.struct_fatal(fluent::session::target_inconsistent_architecture);
+                diag.set_arg("dl", dl);
+                diag.set_arg("target", target);
+                diag
+            }
+            TargetDataLayoutErrors::InconsistentTargetPointerWidth { pointer_size, target } => {
+                diag = sess.struct_fatal(fluent::session::target_inconsistent_pointer_width);
+                diag.set_arg("pointer_size", pointer_size);
+                diag.set_arg("target", target);
+                diag
+            }
+            TargetDataLayoutErrors::InvalidBitsSize { err } => {
+                diag = sess.struct_fatal(fluent::session::target_invalid_bits_size);
+                diag.set_arg("err", err);
+                diag
+            }
+        }
+    }
+}
+
+#[derive(SessionDiagnostic)]
+#[diag(session::not_circumvent_feature)]
+pub struct NotCircumventFeature;
+
+#[derive(SessionDiagnostic)]
+#[diag(session::linker_plugin_lto_windows_not_supported)]
+pub struct LinkerPluginToWindowsNotSupported;
+
+#[derive(SessionDiagnostic)]
+#[diag(session::profile_use_file_does_not_exist)]
+pub struct ProfileUseFileDoesNotExist<'a> {
+    pub path: &'a std::path::Path,
+}
+
+#[derive(SessionDiagnostic)]
+#[diag(session::profile_sample_use_file_does_not_exist)]
+pub struct ProfileSampleUseFileDoesNotExist<'a> {
+    pub path: &'a std::path::Path,
+}
+
+#[derive(SessionDiagnostic)]
+#[diag(session::target_requires_unwind_tables)]
+pub struct TargetRequiresUnwindTables;
+
+#[derive(SessionDiagnostic)]
+#[diag(session::sanitizer_not_supported)]
+pub struct SanitizerNotSupported {
+    pub us: String,
+}
+
+#[derive(SessionDiagnostic)]
+#[diag(session::sanitizers_not_supported)]
+pub struct SanitizersNotSupported {
+    pub us: String,
+}
+
+#[derive(SessionDiagnostic)]
+#[diag(session::cannot_mix_and_match_sanitizers)]
+pub struct CannotMixAndMatchSanitizers {
+    pub first: String,
+    pub second: String,
+}
+
+#[derive(SessionDiagnostic)]
+#[diag(session::cannot_enable_crt_static_linux)]
+pub struct CannotEnableCrtStaticLinux;
+
+#[derive(SessionDiagnostic)]
+#[diag(session::sanitizer_cfi_enabled)]
+pub struct SanitizerCfiEnabled;
+
+#[derive(SessionDiagnostic)]
+#[diag(session::unstable_virtual_function_elimination)]
+pub struct UnstableVirtualFunctionElimination;
+
+#[derive(SessionDiagnostic)]
+#[diag(session::unsupported_dwarf_version)]
+pub struct UnsupportedDwarfVersion {
+    pub dwarf_version: u32,
+}
+
+#[derive(SessionDiagnostic)]
+#[diag(session::target_stack_protector_not_supported)]
+pub struct StackProtectorNotSupportedForTarget<'a> {
+    pub stack_protector: StackProtector,
+    pub target_triple: &'a TargetTriple,
+}
+
+#[derive(SessionDiagnostic)]
+#[diag(session::split_debuginfo_unstable_platform)]
+pub struct SplitDebugInfoUnstablePlatform {
+    pub debuginfo: SplitDebuginfo,
+}
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 557edad548c64..caf9d582ab099 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -2,6 +2,13 @@ use crate::cgu_reuse_tracker::CguReuseTracker;
 use crate::code_stats::CodeStats;
 pub use crate::code_stats::{DataTypeKind, FieldInfo, SizeKind, VariantInfo};
 use crate::config::{self, CrateType, InstrumentCoverage, OptLevel, OutputType, SwitchWithOptPath};
+use crate::errors::{
+    CannotEnableCrtStaticLinux, CannotMixAndMatchSanitizers, LinkerPluginToWindowsNotSupported,
+    NotCircumventFeature, ProfileSampleUseFileDoesNotExist, ProfileUseFileDoesNotExist,
+    SanitizerCfiEnabled, SanitizerNotSupported, SanitizersNotSupported,
+    SplitDebugInfoUnstablePlatform, StackProtectorNotSupportedForTarget,
+    TargetRequiresUnwindTables, UnstableVirtualFunctionElimination, UnsupportedDwarfVersion,
+};
 use crate::parse::{add_feature_diagnostics, ParseSess};
 use crate::search_paths::{PathKind, SearchPath};
 use crate::{filesearch, lint};
@@ -235,6 +242,9 @@ impl Session {
         if !unleashed_features.is_empty() {
             let mut must_err = false;
             // Create a diagnostic pointing at where things got unleashed.
+            // FIXME(#100717): needs eager translation/lists
+            #[allow(rustc::untranslatable_diagnostic)]
+            #[allow(rustc::diagnostic_outside_of_impl)]
             let mut diag = self.struct_warn("skipping const checks");
             for &(span, feature_gate) in unleashed_features.iter() {
                 // FIXME: `span_label` doesn't do anything, so we use "help" as a hack.
@@ -250,10 +260,7 @@ impl Session {
             // If we should err, make sure we did.
             if must_err && self.has_errors().is_none() {
                 // We have skipped a feature gate, and not run into other errors... reject.
-                self.err(
-                    "`-Zunleash-the-miri-inside-of-you` may not be used to circumvent feature \
-                     gates, except when testing error paths in the CTFE engine",
-                );
+                self.emit_err(NotCircumventFeature);
             }
         }
     }
@@ -534,9 +541,13 @@ impl Session {
             Err(ErrorGuaranteed::unchecked_claim_error_was_emitted())
         }
     }
+    #[allow(rustc::untranslatable_diagnostic)]
+    #[allow(rustc::diagnostic_outside_of_impl)]
     pub fn span_warn<S: Into<MultiSpan>>(&self, sp: S, msg: impl Into<DiagnosticMessage>) {
         self.diagnostic().span_warn(sp, msg)
     }
+    #[allow(rustc::untranslatable_diagnostic)]
+    #[allow(rustc::diagnostic_outside_of_impl)]
     pub fn span_warn_with_code<S: Into<MultiSpan>>(
         &self,
         sp: S,
@@ -585,6 +596,8 @@ impl Session {
     ) {
         self.diagnostic().span_note_without_error(sp, msg)
     }
+    #[allow(rustc::untranslatable_diagnostic)]
+    #[allow(rustc::diagnostic_outside_of_impl)]
     pub fn struct_note_without_error(
         &self,
         msg: impl Into<DiagnosticMessage>,
@@ -1469,40 +1482,28 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
         && sess.opts.cg.prefer_dynamic
         && sess.target.is_like_windows
     {
-        sess.err(
-            "Linker plugin based LTO is not supported together with \
-                  `-C prefer-dynamic` when targeting Windows-like targets",
-        );
+        sess.emit_err(LinkerPluginToWindowsNotSupported);
     }
 
     // Make sure that any given profiling data actually exists so LLVM can't
     // decide to silently skip PGO.
     if let Some(ref path) = sess.opts.cg.profile_use {
         if !path.exists() {
-            sess.err(&format!(
-                "File `{}` passed to `-C profile-use` does not exist.",
-                path.display()
-            ));
+            sess.emit_err(ProfileUseFileDoesNotExist { path });
         }
     }
 
     // Do the same for sample profile data.
     if let Some(ref path) = sess.opts.unstable_opts.profile_sample_use {
         if !path.exists() {
-            sess.err(&format!(
-                "File `{}` passed to `-C profile-sample-use` does not exist.",
-                path.display()
-            ));
+            sess.emit_err(ProfileSampleUseFileDoesNotExist { path });
         }
     }
 
     // Unwind tables cannot be disabled if the target requires them.
     if let Some(include_uwtables) = sess.opts.cg.force_unwind_tables {
         if sess.target.requires_uwtable && !include_uwtables {
-            sess.err(
-                "target requires unwind tables, they cannot be disabled with \
-                     `-C force-unwind-tables=no`.",
-            );
+            sess.emit_err(TargetRequiresUnwindTables);
         }
     }
 
@@ -1512,64 +1513,55 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
     match unsupported_sanitizers.into_iter().count() {
         0 => {}
         1 => {
-            sess.err(&format!(
-                "{} sanitizer is not supported for this target",
-                unsupported_sanitizers
-            ));
+            sess.emit_err(SanitizerNotSupported { us: unsupported_sanitizers.to_string() });
         }
         _ => {
-            sess.err(&format!(
-                "{} sanitizers are not supported for this target",
-                unsupported_sanitizers
-            ));
+            sess.emit_err(SanitizersNotSupported { us: unsupported_sanitizers.to_string() });
         }
     }
     // Cannot mix and match sanitizers.
     let mut sanitizer_iter = sess.opts.unstable_opts.sanitizer.into_iter();
     if let (Some(first), Some(second)) = (sanitizer_iter.next(), sanitizer_iter.next()) {
-        sess.err(&format!("`-Zsanitizer={first}` is incompatible with `-Zsanitizer={second}`"));
+        sess.emit_err(CannotMixAndMatchSanitizers {
+            first: first.to_string(),
+            second: second.to_string(),
+        });
     }
 
     // Cannot enable crt-static with sanitizers on Linux
     if sess.crt_static(None) && !sess.opts.unstable_opts.sanitizer.is_empty() {
-        sess.err(
-            "sanitizer is incompatible with statically linked libc, \
-                                disable it using `-C target-feature=-crt-static`",
-        );
+        sess.emit_err(CannotEnableCrtStaticLinux);
     }
 
     // LLVM CFI and VFE both require LTO.
     if sess.lto() != config::Lto::Fat {
         if sess.is_sanitizer_cfi_enabled() {
-            sess.err("`-Zsanitizer=cfi` requires `-Clto`");
+            sess.emit_err(SanitizerCfiEnabled);
         }
         if sess.opts.unstable_opts.virtual_function_elimination {
-            sess.err("`-Zvirtual-function-elimination` requires `-Clto`");
+            sess.emit_err(UnstableVirtualFunctionElimination);
         }
     }
 
     if sess.opts.unstable_opts.stack_protector != StackProtector::None {
         if !sess.target.options.supports_stack_protector {
-            sess.warn(&format!(
-                "`-Z stack-protector={}` is not supported for target {} and will be ignored",
-                sess.opts.unstable_opts.stack_protector, sess.opts.target_triple
-            ))
+            sess.emit_warning(StackProtectorNotSupportedForTarget {
+                stack_protector: sess.opts.unstable_opts.stack_protector,
+                target_triple: &sess.opts.target_triple,
+            });
         }
     }
 
     if let Some(dwarf_version) = sess.opts.unstable_opts.dwarf_version {
         if dwarf_version > 5 {
-            sess.err(&format!("requested DWARF version {} is greater than 5", dwarf_version));
+            sess.emit_err(UnsupportedDwarfVersion { dwarf_version });
         }
     }
 
     if !sess.target.options.supported_split_debuginfo.contains(&sess.split_debuginfo())
         && !sess.opts.unstable_opts.unstable_options
     {
-        sess.err(&format!(
-            "`-Csplit-debuginfo={}` is unstable on this platform",
-            sess.split_debuginfo()
-        ));
+        sess.emit_err(SplitDebugInfoUnstablePlatform { debuginfo: sess.split_debuginfo() });
     }
 }
 
@@ -1614,14 +1606,20 @@ fn early_error_handler(output: config::ErrorOutputType) -> rustc_errors::Handler
     rustc_errors::Handler::with_emitter(true, None, emitter)
 }
 
+#[allow(rustc::untranslatable_diagnostic)]
+#[allow(rustc::diagnostic_outside_of_impl)]
 pub fn early_error_no_abort(output: config::ErrorOutputType, msg: &str) -> ErrorGuaranteed {
     early_error_handler(output).struct_err(msg).emit()
 }
 
+#[allow(rustc::untranslatable_diagnostic)]
+#[allow(rustc::diagnostic_outside_of_impl)]
 pub fn early_error(output: config::ErrorOutputType, msg: &str) -> ! {
     early_error_handler(output).struct_fatal(msg).emit()
 }
 
+#[allow(rustc::untranslatable_diagnostic)]
+#[allow(rustc::diagnostic_outside_of_impl)]
 pub fn early_warn(output: config::ErrorOutputType, msg: &str) {
     early_error_handler(output).struct_warn(msg).emit()
 }
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 75b1dfc856ac7..4fd9e7407ce14 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -1183,6 +1183,7 @@ symbols! {
         require,
         residual,
         result,
+        return_position_impl_trait_in_trait,
         rhs,
         rintf32,
         rintf64,
diff --git a/compiler/rustc_target/src/abi/mod.rs b/compiler/rustc_target/src/abi/mod.rs
index bcaf209f84b65..ec334e5887ab7 100644
--- a/compiler/rustc_target/src/abi/mod.rs
+++ b/compiler/rustc_target/src/abi/mod.rs
@@ -7,7 +7,7 @@ use crate::spec::Target;
 use std::convert::{TryFrom, TryInto};
 use std::fmt;
 use std::iter::Step;
-use std::num::NonZeroUsize;
+use std::num::{NonZeroUsize, ParseIntError};
 use std::ops::{Add, AddAssign, Deref, Mul, RangeInclusive, Sub};
 use std::str::FromStr;
 
@@ -69,34 +69,46 @@ impl Default for TargetDataLayout {
     }
 }
 
+pub enum TargetDataLayoutErrors<'a> {
+    InvalidAddressSpace { addr_space: &'a str, cause: &'a str, err: ParseIntError },
+    InvalidBits { kind: &'a str, bit: &'a str, cause: &'a str, err: ParseIntError },
+    MissingAlignment { cause: &'a str },
+    InvalidAlignment { cause: &'a str, err: String },
+    InconsistentTargetArchitecture { dl: &'a str, target: &'a str },
+    InconsistentTargetPointerWidth { pointer_size: u64, target: u32 },
+    InvalidBitsSize { err: String },
+}
+
 impl TargetDataLayout {
-    pub fn parse(target: &Target) -> Result<TargetDataLayout, String> {
+    pub fn parse<'a>(target: &'a Target) -> Result<TargetDataLayout, TargetDataLayoutErrors<'a>> {
         // Parse an address space index from a string.
-        let parse_address_space = |s: &str, cause: &str| {
+        let parse_address_space = |s: &'a str, cause: &'a str| {
             s.parse::<u32>().map(AddressSpace).map_err(|err| {
-                format!("invalid address space `{}` for `{}` in \"data-layout\": {}", s, cause, err)
+                TargetDataLayoutErrors::InvalidAddressSpace { addr_space: s, cause, err }
             })
         };
 
         // Parse a bit count from a string.
-        let parse_bits = |s: &str, kind: &str, cause: &str| {
-            s.parse::<u64>().map_err(|err| {
-                format!("invalid {} `{}` for `{}` in \"data-layout\": {}", kind, s, cause, err)
+        let parse_bits = |s: &'a str, kind: &'a str, cause: &'a str| {
+            s.parse::<u64>().map_err(|err| TargetDataLayoutErrors::InvalidBits {
+                kind,
+                bit: s,
+                cause,
+                err,
             })
         };
 
         // Parse a size string.
-        let size = |s: &str, cause: &str| parse_bits(s, "size", cause).map(Size::from_bits);
+        let size = |s: &'a str, cause: &'a str| parse_bits(s, "size", cause).map(Size::from_bits);
 
         // Parse an alignment string.
-        let align = |s: &[&str], cause: &str| {
+        let align = |s: &[&'a str], cause: &'a str| {
             if s.is_empty() {
-                return Err(format!("missing alignment for `{}` in \"data-layout\"", cause));
+                return Err(TargetDataLayoutErrors::MissingAlignment { cause });
             }
             let align_from_bits = |bits| {
-                Align::from_bits(bits).map_err(|err| {
-                    format!("invalid alignment for `{}` in \"data-layout\": {}", cause, err)
-                })
+                Align::from_bits(bits)
+                    .map_err(|err| TargetDataLayoutErrors::InvalidAlignment { cause, err })
             };
             let abi = parse_bits(s[0], "alignment", cause)?;
             let pref = s.get(1).map_or(Ok(abi), |pref| parse_bits(pref, "alignment", cause))?;
@@ -158,25 +170,24 @@ impl TargetDataLayout {
 
         // Perform consistency checks against the Target information.
         if dl.endian != target.endian {
-            return Err(format!(
-                "inconsistent target specification: \"data-layout\" claims \
-                 architecture is {}-endian, while \"target-endian\" is `{}`",
-                dl.endian.as_str(),
-                target.endian.as_str(),
-            ));
+            return Err(TargetDataLayoutErrors::InconsistentTargetArchitecture {
+                dl: dl.endian.as_str(),
+                target: target.endian.as_str(),
+            });
         }
 
         let target_pointer_width: u64 = target.pointer_width.into();
         if dl.pointer_size.bits() != target_pointer_width {
-            return Err(format!(
-                "inconsistent target specification: \"data-layout\" claims \
-                 pointers are {}-bit, while \"target-pointer-width\" is `{}`",
-                dl.pointer_size.bits(),
-                target.pointer_width
-            ));
+            return Err(TargetDataLayoutErrors::InconsistentTargetPointerWidth {
+                pointer_size: dl.pointer_size.bits(),
+                target: target.pointer_width,
+            });
         }
 
-        dl.c_enum_min_size = Integer::from_size(Size::from_bits(target.c_enum_min_bits))?;
+        dl.c_enum_min_size = match Integer::from_size(Size::from_bits(target.c_enum_min_bits)) {
+            Ok(bits) => bits,
+            Err(err) => return Err(TargetDataLayoutErrors::InvalidBitsSize { err }),
+        };
 
         Ok(dl)
     }
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index 8a093bf4281cb..8a65262a00723 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -32,6 +32,7 @@ use rustc_middle::traits::select::OverflowError;
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
 use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::visit::{MaxUniverse, TypeVisitable};
+use rustc_middle::ty::DefIdTree;
 use rustc_middle::ty::{self, Term, ToPredicate, Ty, TyCtxt};
 use rustc_span::symbol::sym;
 
@@ -70,6 +71,8 @@ enum ProjectionCandidate<'tcx> {
 
     /// From an "impl" (or a "pseudo-impl" returned by select)
     Select(Selection<'tcx>),
+
+    ImplTraitInTrait(ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>>),
 }
 
 enum ProjectionCandidateSet<'tcx> {
@@ -1265,6 +1268,8 @@ fn project<'cx, 'tcx>(
 
     let mut candidates = ProjectionCandidateSet::None;
 
+    assemble_candidate_for_impl_trait_in_trait(selcx, obligation, &mut candidates);
+
     // Make sure that the following procedures are kept in order. ParamEnv
     // needs to be first because it has highest priority, and Select checks
     // the return value of push_candidate which assumes it's ran at last.
@@ -1303,6 +1308,48 @@ fn project<'cx, 'tcx>(
     }
 }
 
+/// If the predicate's item is an `ImplTraitPlaceholder`, we do a select on the
+/// corresponding trait ref. If this yields an `impl`, then we're able to project
+/// to a concrete type, since we have an `impl`'s method  to provide the RPITIT.
+fn assemble_candidate_for_impl_trait_in_trait<'cx, 'tcx>(
+    selcx: &mut SelectionContext<'cx, 'tcx>,
+    obligation: &ProjectionTyObligation<'tcx>,
+    candidate_set: &mut ProjectionCandidateSet<'tcx>,
+) {
+    let tcx = selcx.tcx();
+    if tcx.def_kind(obligation.predicate.item_def_id) == DefKind::ImplTraitPlaceholder {
+        let trait_fn_def_id = tcx.impl_trait_in_trait_parent(obligation.predicate.item_def_id);
+        let trait_def_id = tcx.parent(trait_fn_def_id);
+        let trait_substs =
+            obligation.predicate.substs.truncate_to(tcx, tcx.generics_of(trait_def_id));
+        // FIXME(named-returns): Binders
+        let trait_predicate =
+            ty::Binder::dummy(ty::TraitRef { def_id: trait_def_id, substs: trait_substs })
+                .to_poly_trait_predicate();
+
+        let _ =
+            selcx.infcx().commit_if_ok(|_| match selcx.select(&obligation.with(trait_predicate)) {
+                Ok(Some(super::ImplSource::UserDefined(data))) => {
+                    candidate_set.push_candidate(ProjectionCandidate::ImplTraitInTrait(data));
+                    Ok(())
+                }
+                Ok(None) => {
+                    candidate_set.mark_ambiguous();
+                    return Err(());
+                }
+                Ok(Some(_)) => {
+                    // Don't know enough about the impl to provide a useful signature
+                    return Err(());
+                }
+                Err(e) => {
+                    debug!(error = ?e, "selection error");
+                    candidate_set.mark_error(e);
+                    return Err(());
+                }
+            });
+    }
+}
+
 /// The first thing we have to do is scan through the parameter
 /// environment to see whether there are any projection predicates
 /// there that can answer this question.
@@ -1465,6 +1512,11 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
     obligation: &ProjectionTyObligation<'tcx>,
     candidate_set: &mut ProjectionCandidateSet<'tcx>,
 ) {
+    // Can't assemble candidate from impl for RPITIT
+    if selcx.tcx().def_kind(obligation.predicate.item_def_id) == DefKind::ImplTraitPlaceholder {
+        return;
+    }
+
     // If we are resolving `<T as TraitRef<...>>::Item == Type`,
     // start out by selecting the predicate `T as TraitRef<...>`:
     let poly_trait_ref = ty::Binder::dummy(obligation.predicate.trait_ref(selcx.tcx()));
@@ -1740,6 +1792,9 @@ fn confirm_candidate<'cx, 'tcx>(
         ProjectionCandidate::Select(impl_source) => {
             confirm_select_candidate(selcx, obligation, impl_source)
         }
+        ProjectionCandidate::ImplTraitInTrait(data) => {
+            confirm_impl_trait_in_trait_candidate(selcx, obligation, data)
+        }
     };
 
     // When checking for cycle during evaluation, we compare predicates with
@@ -2102,6 +2157,72 @@ fn confirm_impl_candidate<'cx, 'tcx>(
     }
 }
 
+fn confirm_impl_trait_in_trait_candidate<'tcx>(
+    selcx: &mut SelectionContext<'_, 'tcx>,
+    obligation: &ProjectionTyObligation<'tcx>,
+    data: ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>>,
+) -> Progress<'tcx> {
+    let tcx = selcx.tcx();
+    let mut obligations = data.nested;
+
+    let trait_fn_def_id = tcx.impl_trait_in_trait_parent(obligation.predicate.item_def_id);
+    let Ok(leaf_def) = assoc_def(selcx, data.impl_def_id, trait_fn_def_id) else {
+        return Progress { term: tcx.ty_error().into(), obligations };
+    };
+    if !leaf_def.item.defaultness(tcx).has_value() {
+        return Progress { term: tcx.ty_error().into(), obligations };
+    }
+
+    let impl_fn_def_id = leaf_def.item.def_id;
+    let impl_fn_substs = obligation.predicate.substs.rebase_onto(tcx, trait_fn_def_id, data.substs);
+
+    let cause = ObligationCause::new(
+        obligation.cause.span,
+        obligation.cause.body_id,
+        super::ItemObligation(impl_fn_def_id),
+    );
+    let predicates = normalize_with_depth_to(
+        selcx,
+        obligation.param_env,
+        cause.clone(),
+        obligation.recursion_depth + 1,
+        tcx.predicates_of(impl_fn_def_id).instantiate(tcx, impl_fn_substs),
+        &mut obligations,
+    );
+    obligations.extend(std::iter::zip(predicates.predicates, predicates.spans).map(
+        |(pred, span)| {
+            Obligation::with_depth(
+                ObligationCause::new(
+                    obligation.cause.span,
+                    obligation.cause.body_id,
+                    if span.is_dummy() {
+                        super::ItemObligation(impl_fn_def_id)
+                    } else {
+                        super::BindingObligation(impl_fn_def_id, span)
+                    },
+                ),
+                obligation.recursion_depth + 1,
+                obligation.param_env,
+                pred,
+            )
+        },
+    ));
+
+    let ty = super::normalize_to(
+        selcx,
+        obligation.param_env,
+        cause.clone(),
+        tcx.bound_trait_impl_trait_tys(impl_fn_def_id)
+            .map_bound(|tys| {
+                tys.map_or_else(|_| tcx.ty_error(), |tys| tys[&obligation.predicate.item_def_id])
+            })
+            .subst(tcx, impl_fn_substs),
+        &mut obligations,
+    );
+
+    Progress { term: ty.into(), obligations }
+}
+
 // Get obligations corresponding to the predicates from the where-clause of the
 // associated type itself.
 // Note: `feature(generic_associated_types)` is required to write such
diff --git a/compiler/rustc_ty_utils/src/implied_bounds.rs b/compiler/rustc_ty_utils/src/implied_bounds.rs
index a77ea440aaaea..f0d8c240ea588 100644
--- a/compiler/rustc_ty_utils/src/implied_bounds.rs
+++ b/compiler/rustc_ty_utils/src/implied_bounds.rs
@@ -51,6 +51,7 @@ fn assumed_wf_types<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx ty::List<Ty
         | DefKind::AnonConst
         | DefKind::InlineConst
         | DefKind::OpaqueTy
+        | DefKind::ImplTraitPlaceholder
         | DefKind::Field
         | DefKind::LifetimeParam
         | DefKind::GlobalAsm
diff --git a/compiler/rustc_typeck/src/astconv/mod.rs b/compiler/rustc_typeck/src/astconv/mod.rs
index 801063583e633..d9789d5aaf031 100644
--- a/compiler/rustc_typeck/src/astconv/mod.rs
+++ b/compiler/rustc_typeck/src/astconv/mod.rs
@@ -2360,7 +2360,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         let span = path.span;
         match path.res {
-            Res::Def(DefKind::OpaqueTy, did) => {
+            Res::Def(DefKind::OpaqueTy | DefKind::ImplTraitPlaceholder, did) => {
                 // Check for desugared `impl Trait`.
                 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
                 let item_segment = path.segments.split_last().unwrap();
@@ -2627,13 +2627,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
                 self.res_to_ty(opt_self_ty, path, false)
             }
-            hir::TyKind::OpaqueDef(item_id, lifetimes) => {
+            hir::TyKind::OpaqueDef(item_id, lifetimes, in_trait) => {
                 let opaque_ty = tcx.hir().item(item_id);
                 let def_id = item_id.def_id.to_def_id();
 
                 match opaque_ty.kind {
                     hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
-                        self.impl_trait_ty_to_ty(def_id, lifetimes, origin)
+                        self.impl_trait_ty_to_ty(def_id, lifetimes, origin, in_trait)
                     }
                     ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
                 }
@@ -2703,6 +2703,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         def_id: DefId,
         lifetimes: &[hir::GenericArg<'_>],
         origin: OpaqueTyOrigin,
+        in_trait: bool,
     ) -> Ty<'tcx> {
         debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
         let tcx = self.tcx();
@@ -2746,7 +2747,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         });
         debug!("impl_trait_ty_to_ty: substs={:?}", substs);
 
-        tcx.mk_opaque(def_id, substs)
+        if in_trait { tcx.mk_projection(def_id, substs) } else { tcx.mk_opaque(def_id, substs) }
     }
 
     pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
@@ -2940,8 +2941,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 // though we can easily give a hint that ought to be
                 // relevant.
                 err.note(
-                    "lifetimes appearing in an associated type are not considered constrained",
+                    "lifetimes appearing in an associated or opaque type are not considered constrained",
                 );
+                err.note("consider introducing a named lifetime parameter");
             }
 
             err.emit();
diff --git a/compiler/rustc_typeck/src/check/closure.rs b/compiler/rustc_typeck/src/check/closure.rs
index bc3fec6e7d66a..55cbaf71e7cfd 100644
--- a/compiler/rustc_typeck/src/check/closure.rs
+++ b/compiler/rustc_typeck/src/check/closure.rs
@@ -4,6 +4,7 @@ use super::{check_fn, Expectation, FnCtxt, GeneratorTypes};
 
 use crate::astconv::AstConv;
 use crate::rustc_middle::ty::subst::Subst;
+use hir::def::DefKind;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
@@ -680,9 +681,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 .map(|e| e.map_bound(|e| *e).transpose_tuple2())
                 .find_map(|(p, s)| get_future_output(p.subst(self.tcx, substs), s.0))?,
             ty::Error(_) => return None,
+            ty::Projection(proj)
+                if self.tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder =>
+            {
+                self.tcx
+                    .bound_explicit_item_bounds(proj.item_def_id)
+                    .transpose_iter()
+                    .map(|e| e.map_bound(|e| *e).transpose_tuple2())
+                    .find_map(|(p, s)| get_future_output(p.subst(self.tcx, proj.substs), s.0))?
+            }
             _ => span_bug!(
                 self.tcx.def_span(expr_def_id),
-                "async fn generator return type not an inference variable"
+                "async fn generator return type not an inference variable: {ret_ty}"
             ),
         };
 
diff --git a/compiler/rustc_typeck/src/check/compare_method.rs b/compiler/rustc_typeck/src/check/compare_method.rs
index b6bc244d2b144..a6c8dbb2555dd 100644
--- a/compiler/rustc_typeck/src/check/compare_method.rs
+++ b/compiler/rustc_typeck/src/check/compare_method.rs
@@ -1,18 +1,22 @@
 use super::potentially_plural_count;
 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
-use rustc_data_structures::fx::FxHashSet;
+use hir::def_id::DefId;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::intravisit;
 use rustc_hir::{GenericParamKind, ImplItemKind, TraitItemKind};
 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
+use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::infer::{self, TyCtxtInferExt};
 use rustc_infer::traits::util;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::subst::{InternalSubsts, Subst};
 use rustc_middle::ty::util::ExplicitSelf;
-use rustc_middle::ty::{self, DefIdTree};
+use rustc_middle::ty::{
+    self, DefIdTree, Ty, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitable,
+};
 use rustc_middle::ty::{GenericParamDefKind, ToPredicate, TyCtxt};
 use rustc_span::Span;
 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
@@ -64,10 +68,7 @@ pub(crate) fn compare_impl_method<'tcx>(
         return;
     }
 
-    if let Err(_) = compare_predicate_entailment(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
-    {
-        return;
-    }
+    tcx.ensure().compare_predicates_and_trait_impl_trait_tys(impl_m.def_id);
 }
 
 /// This function is best explained by example. Consider a trait:
@@ -136,13 +137,15 @@ pub(crate) fn compare_impl_method<'tcx>(
 ///
 /// Finally we register each of these predicates as an obligation and check that
 /// they hold.
-fn compare_predicate_entailment<'tcx>(
+pub(super) fn compare_predicates_and_trait_impl_trait_tys<'tcx>(
     tcx: TyCtxt<'tcx>,
-    impl_m: &ty::AssocItem,
-    impl_m_span: Span,
-    trait_m: &ty::AssocItem,
-    impl_trait_ref: ty::TraitRef<'tcx>,
-) -> Result<(), ErrorGuaranteed> {
+    def_id: DefId,
+) -> Result<&'tcx FxHashMap<DefId, Ty<'tcx>>, ErrorGuaranteed> {
+    let impl_m = tcx.opt_associated_item(def_id).unwrap();
+    let impl_m_span = tcx.def_span(def_id);
+    let trait_m = tcx.opt_associated_item(impl_m.trait_item_def_id.unwrap()).unwrap();
+    let impl_trait_ref = tcx.impl_trait_ref(impl_m.impl_container(tcx).unwrap()).unwrap();
+
     let trait_to_impl_substs = impl_trait_ref.substs;
 
     // This node-id should be used for the `body_id` field on each
@@ -161,6 +164,7 @@ fn compare_predicate_entailment<'tcx>(
             kind: impl_m.kind,
         },
     );
+    let return_span = tcx.hir().fn_decl_by_hir_id(impl_m_hir_id).unwrap().output.span();
 
     // Create mapping from impl to placeholder.
     let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
@@ -266,6 +270,13 @@ fn compare_predicate_entailment<'tcx>(
 
         let trait_sig = tcx.bound_fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs);
         let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, trait_sig);
+        let mut collector =
+            ImplTraitInTraitCollector::new(&ocx, return_span, param_env, impl_m_hir_id);
+        // FIXME(RPITIT): This should only be needed on the output type, but
+        // RPITIT placeholders shouldn't show up anywhere except for there,
+        // so I think this is fine.
+        let trait_sig = trait_sig.fold_with(&mut collector);
+
         // Next, add all inputs and output as well-formed tys. Importantly,
         // we have to do this before normalization, since the normalized ty may
         // not contain the input parameters. See issue #87748.
@@ -411,10 +422,115 @@ fn compare_predicate_entailment<'tcx>(
             &outlives_environment,
         );
 
-        Ok(())
+        let mut collected_tys = FxHashMap::default();
+        for (def_id, (ty, substs)) in collector.types {
+            match infcx.fully_resolve(ty) {
+                Ok(ty) => {
+                    // `ty` contains free regions that we created earlier while liberating the
+                    // trait fn signature.  However, projection normalization expects `ty` to
+                    // contains `def_id`'s early-bound regions.
+                    let id_substs = InternalSubsts::identity_for_item(tcx, def_id);
+                    debug!(?id_substs, ?substs);
+                    let map: FxHashMap<ty::GenericArg<'tcx>, ty::GenericArg<'tcx>> = substs
+                        .iter()
+                        .enumerate()
+                        .map(|(index, arg)| (arg, id_substs[index]))
+                        .collect();
+                    debug!(?map);
+
+                    let ty = tcx.fold_regions(ty, |region, _| {
+                        if let ty::ReFree(_) = region.kind() {
+                            map[&region.into()].expect_region()
+                        } else {
+                            region
+                        }
+                    });
+                    collected_tys.insert(def_id, ty);
+                }
+                Err(err) => {
+                    tcx.sess.delay_span_bug(
+                        return_span,
+                        format!("could not fully resolve: {ty} => {err:?}"),
+                    );
+                    collected_tys.insert(def_id, tcx.ty_error());
+                }
+            }
+        }
+
+        Ok(&*tcx.arena.alloc(collected_tys))
     })
 }
 
+struct ImplTraitInTraitCollector<'a, 'tcx> {
+    ocx: &'a ObligationCtxt<'a, 'tcx>,
+    types: FxHashMap<DefId, (Ty<'tcx>, ty::SubstsRef<'tcx>)>,
+    span: Span,
+    param_env: ty::ParamEnv<'tcx>,
+    body_id: hir::HirId,
+}
+
+impl<'a, 'tcx> ImplTraitInTraitCollector<'a, 'tcx> {
+    fn new(
+        ocx: &'a ObligationCtxt<'a, 'tcx>,
+        span: Span,
+        param_env: ty::ParamEnv<'tcx>,
+        body_id: hir::HirId,
+    ) -> Self {
+        ImplTraitInTraitCollector { ocx, types: FxHashMap::default(), span, param_env, body_id }
+    }
+}
+
+impl<'tcx> TypeFolder<'tcx> for ImplTraitInTraitCollector<'_, 'tcx> {
+    fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
+        self.ocx.infcx.tcx
+    }
+
+    fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
+        if let ty::Projection(proj) = ty.kind()
+            && self.tcx().def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder
+        {
+            if let Some((ty, _)) = self.types.get(&proj.item_def_id) {
+                return *ty;
+            }
+            //FIXME(RPITIT): Deny nested RPITIT in substs too
+            if proj.substs.has_escaping_bound_vars() {
+                bug!("FIXME(RPITIT): error here");
+            }
+            // Replace with infer var
+            let infer_ty = self.ocx.infcx.next_ty_var(TypeVariableOrigin {
+                span: self.span,
+                kind: TypeVariableOriginKind::MiscVariable,
+            });
+            self.types.insert(proj.item_def_id, (infer_ty, proj.substs));
+            // Recurse into bounds
+            for pred in self.tcx().bound_explicit_item_bounds(proj.item_def_id).transpose_iter() {
+                let pred_span = pred.0.1;
+
+                let pred = pred.map_bound(|(pred, _)| *pred).subst(self.tcx(), proj.substs);
+                let pred = pred.fold_with(self);
+                let pred = self.ocx.normalize(
+                    ObligationCause::misc(self.span, self.body_id),
+                    self.param_env,
+                    pred,
+                );
+
+                self.ocx.register_obligation(traits::Obligation::new(
+                    ObligationCause::new(
+                        self.span,
+                        self.body_id,
+                        ObligationCauseCode::BindingObligation(proj.item_def_id, pred_span),
+                    ),
+                    self.param_env,
+                    pred,
+                ));
+            }
+            infer_ty
+        } else {
+            ty.super_fold_with(self)
+        }
+    }
+}
+
 fn check_region_bounds_on_impl_item<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl_m: &ty::AssocItem,
diff --git a/compiler/rustc_typeck/src/check/mod.rs b/compiler/rustc_typeck/src/check/mod.rs
index 69eb34b5f802d..8811b38fc555a 100644
--- a/compiler/rustc_typeck/src/check/mod.rs
+++ b/compiler/rustc_typeck/src/check/mod.rs
@@ -132,6 +132,7 @@ use crate::require_c_abi_if_c_variadic;
 use crate::util::common::indenter;
 
 use self::coercion::DynamicCoerceMany;
+use self::compare_method::compare_predicates_and_trait_impl_trait_tys;
 use self::region::region_scope_tree;
 pub use self::Expectation::*;
 
@@ -249,6 +250,7 @@ pub fn provide(providers: &mut Providers) {
         used_trait_imports,
         check_mod_item_types,
         region_scope_tree,
+        compare_predicates_and_trait_impl_trait_tys,
         ..*providers
     };
 }
diff --git a/compiler/rustc_typeck/src/collect.rs b/compiler/rustc_typeck/src/collect.rs
index e70f728d7dcce..ceb5684fdf0a8 100644
--- a/compiler/rustc_typeck/src/collect.rs
+++ b/compiler/rustc_typeck/src/collect.rs
@@ -1585,8 +1585,16 @@ fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
             ItemKind::OpaqueTy(hir::OpaqueTy {
                 origin:
                     hir::OpaqueTyOrigin::FnReturn(fn_def_id) | hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
+                in_trait,
                 ..
-            }) => Some(fn_def_id.to_def_id()),
+            }) => {
+                if in_trait {
+                    assert!(matches!(tcx.def_kind(fn_def_id), DefKind::AssocFn))
+                } else {
+                    assert!(matches!(tcx.def_kind(fn_def_id), DefKind::AssocFn | DefKind::Fn))
+                }
+                Some(fn_def_id.to_def_id())
+            }
             ItemKind::OpaqueTy(hir::OpaqueTy { origin: hir::OpaqueTyOrigin::TyAlias, .. }) => {
                 let parent_id = tcx.hir().get_parent_item(hir_id);
                 assert_ne!(parent_id, CRATE_DEF_ID);
@@ -1787,7 +1795,7 @@ fn is_suggestable_infer_ty(ty: &hir::Ty<'_>) -> bool {
         }
         Tup(tys) => tys.iter().any(is_suggestable_infer_ty),
         Ptr(mut_ty) | Rptr(_, mut_ty) => is_suggestable_infer_ty(mut_ty.ty),
-        OpaqueDef(_, generic_args) => are_suggestable_generic_args(generic_args),
+        OpaqueDef(_, generic_args, _) => are_suggestable_generic_args(generic_args),
         Path(hir::QPath::TypeRelative(ty, segment)) => {
             is_suggestable_infer_ty(ty) || are_suggestable_generic_args(segment.args().args)
         }
diff --git a/compiler/rustc_typeck/src/collect/item_bounds.rs b/compiler/rustc_typeck/src/collect/item_bounds.rs
index 318e8f581f7c8..0d34a8bfee333 100644
--- a/compiler/rustc_typeck/src/collect/item_bounds.rs
+++ b/compiler/rustc_typeck/src/collect/item_bounds.rs
@@ -59,10 +59,15 @@ fn opaque_type_bounds<'tcx>(
     opaque_def_id: DefId,
     ast_bounds: &'tcx [hir::GenericBound<'tcx>],
     span: Span,
+    in_trait: bool,
 ) -> &'tcx [(ty::Predicate<'tcx>, Span)] {
     ty::print::with_no_queries!({
-        let item_ty =
-            tcx.mk_opaque(opaque_def_id, InternalSubsts::identity_for_item(tcx, opaque_def_id));
+        let substs = InternalSubsts::identity_for_item(tcx, opaque_def_id);
+        let item_ty = if in_trait {
+            tcx.mk_projection(opaque_def_id, substs)
+        } else {
+            tcx.mk_opaque(opaque_def_id, substs)
+        };
 
         let icx = ItemCtxt::new(tcx, opaque_def_id);
         let mut bounds = <dyn AstConv<'_>>::compute_bounds(&icx, item_ty, ast_bounds);
@@ -86,10 +91,10 @@ pub(super) fn explicit_item_bounds(
             ..
         }) => associated_type_bounds(tcx, def_id, bounds, *span),
         hir::Node::Item(hir::Item {
-            kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, .. }),
+            kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, in_trait, .. }),
             span,
             ..
-        }) => opaque_type_bounds(tcx, def_id, bounds, *span),
+        }) => opaque_type_bounds(tcx, def_id, bounds, *span, *in_trait),
         _ => bug!("item_bounds called on {:?}", def_id),
     }
 }
diff --git a/compiler/rustc_typeck/src/collect/type_of.rs b/compiler/rustc_typeck/src/collect/type_of.rs
index a0280ddca4bd8..a26e26cb38996 100644
--- a/compiler/rustc_typeck/src/collect/type_of.rs
+++ b/compiler/rustc_typeck/src/collect/type_of.rs
@@ -333,8 +333,12 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                     find_opaque_ty_constraints_for_tait(tcx, def_id)
                 }
                 // Opaque types desugared from `impl Trait`.
-                ItemKind::OpaqueTy(OpaqueTy { origin: hir::OpaqueTyOrigin::FnReturn(owner) | hir::OpaqueTyOrigin::AsyncFn(owner), .. }) => {
-                    find_opaque_ty_constraints_for_rpit(tcx, def_id, owner)
+                ItemKind::OpaqueTy(OpaqueTy { origin: hir::OpaqueTyOrigin::FnReturn(owner) | hir::OpaqueTyOrigin::AsyncFn(owner), in_trait, .. }) => {
+                    if in_trait {
+                        span_bug!(item.span, "impl-trait in trait has no default")
+                    } else {
+                        find_opaque_ty_constraints_for_rpit(tcx, def_id, owner)
+                    }
                 }
                 ItemKind::Trait(..)
                 | ItemKind::TraitAlias(..)
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index c2baea839f638..f9f6d518b549e 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -1492,7 +1492,7 @@ pub(crate) fn clean_ty<'tcx>(ty: &hir::Ty<'tcx>, cx: &mut DocContext<'tcx>) -> T
             Array(Box::new(clean_ty(ty, cx)), length)
         }
         TyKind::Tup(tys) => Tuple(tys.iter().map(|ty| clean_ty(ty, cx)).collect()),
-        TyKind::OpaqueDef(item_id, _) => {
+        TyKind::OpaqueDef(item_id, _, _) => {
             let item = cx.tcx.hir().item(item_id);
             if let hir::ItemKind::OpaqueTy(ref ty) = item.kind {
                 ImplTrait(ty.bounds.iter().filter_map(|x| clean_generic_bound(x, cx)).collect())
diff --git a/src/librustdoc/clean/utils.rs b/src/librustdoc/clean/utils.rs
index a9d511ae11e8b..395f213ca87c3 100644
--- a/src/librustdoc/clean/utils.rs
+++ b/src/librustdoc/clean/utils.rs
@@ -511,8 +511,8 @@ pub(crate) fn register_res(cx: &mut DocContext<'_>, res: Res) -> DefId {
         | Res::Err => return res.def_id(),
         Res::Def(
             TyParam | ConstParam | Ctor(..) | ExternCrate | Use | ForeignMod | AnonConst
-            | InlineConst | OpaqueTy | Field | LifetimeParam | GlobalAsm | Impl | Closure
-            | Generator,
+            | InlineConst | OpaqueTy | ImplTraitPlaceholder | Field | LifetimeParam | GlobalAsm
+            | Impl | Closure | Generator,
             id,
         ) => return id,
     };
diff --git a/src/librustdoc/formats/item_type.rs b/src/librustdoc/formats/item_type.rs
index 0a7ee2005915b..f21e60a64e005 100644
--- a/src/librustdoc/formats/item_type.rs
+++ b/src/librustdoc/formats/item_type.rs
@@ -135,6 +135,7 @@ impl From<DefKind> for ItemType {
             | DefKind::AnonConst
             | DefKind::InlineConst
             | DefKind::OpaqueTy
+            | DefKind::ImplTraitPlaceholder
             | DefKind::Field
             | DefKind::LifetimeParam
             | DefKind::GlobalAsm
diff --git a/src/librustdoc/passes/collect_intra_doc_links.rs b/src/librustdoc/passes/collect_intra_doc_links.rs
index c27f0ce18c141..cfd6ce402c28a 100644
--- a/src/librustdoc/passes/collect_intra_doc_links.rs
+++ b/src/librustdoc/passes/collect_intra_doc_links.rs
@@ -1805,8 +1805,8 @@ fn resolution_failure(
                                 }
                                 return;
                             }
-                            Trait | TyAlias | ForeignTy | OpaqueTy | TraitAlias | TyParam
-                            | Static(_) => "associated item",
+                            Trait | TyAlias | ForeignTy | OpaqueTy | ImplTraitPlaceholder
+                            | TraitAlias | TyParam | Static(_) => "associated item",
                             Impl | GlobalAsm => unreachable!("not a path"),
                         }
                     } else {
diff --git a/src/test/ui-fulldeps/auxiliary/issue-40001-plugin.rs b/src/test/ui-fulldeps/auxiliary/issue-40001-plugin.rs
index 802b867a301aa..03ad3ca826146 100644
--- a/src/test/ui-fulldeps/auxiliary/issue-40001-plugin.rs
+++ b/src/test/ui-fulldeps/auxiliary/issue-40001-plugin.rs
@@ -21,7 +21,7 @@ use rustc_span::source_map;
 #[no_mangle]
 fn __rustc_plugin_registrar(reg: &mut Registry) {
     reg.lint_store.register_lints(&[&MISSING_ALLOWED_ATTR]);
-    reg.lint_store.register_late_pass(|| Box::new(MissingAllowedAttrPass));
+    reg.lint_store.register_late_pass(|_| Box::new(MissingAllowedAttrPass));
 }
 
 declare_lint! {
diff --git a/src/test/ui-fulldeps/auxiliary/lint-for-crate-rpass.rs b/src/test/ui-fulldeps/auxiliary/lint-for-crate-rpass.rs
index bc153faa8925a..a3b570ad8c40c 100644
--- a/src/test/ui-fulldeps/auxiliary/lint-for-crate-rpass.rs
+++ b/src/test/ui-fulldeps/auxiliary/lint-for-crate-rpass.rs
@@ -74,7 +74,7 @@ fn __rustc_plugin_registrar(reg: &mut Registry) {
         &CRATE_NOT_GREY,
         &CRATE_NOT_GREEN,
     ]);
-    reg.lint_store.register_late_pass(|| Box::new(PassOkay));
-    reg.lint_store.register_late_pass(|| Box::new(PassRedBlue));
-    reg.lint_store.register_late_pass(|| Box::new(PassGreyGreen));
+    reg.lint_store.register_late_pass(|_| Box::new(PassOkay));
+    reg.lint_store.register_late_pass(|_| Box::new(PassRedBlue));
+    reg.lint_store.register_late_pass(|_| Box::new(PassGreyGreen));
 }
diff --git a/src/test/ui-fulldeps/auxiliary/lint-for-crate.rs b/src/test/ui-fulldeps/auxiliary/lint-for-crate.rs
index 29d0abfbe5388..0b1534939b778 100644
--- a/src/test/ui-fulldeps/auxiliary/lint-for-crate.rs
+++ b/src/test/ui-fulldeps/auxiliary/lint-for-crate.rs
@@ -39,5 +39,5 @@ impl<'tcx> LateLintPass<'tcx> for Pass {
 #[no_mangle]
 fn __rustc_plugin_registrar(reg: &mut Registry) {
     reg.lint_store.register_lints(&[&CRATE_NOT_OKAY]);
-    reg.lint_store.register_late_pass(|| Box::new(Pass));
+    reg.lint_store.register_late_pass(|_| Box::new(Pass));
 }
diff --git a/src/test/ui-fulldeps/auxiliary/lint-group-plugin-test.rs b/src/test/ui-fulldeps/auxiliary/lint-group-plugin-test.rs
index 691cfb97d9218..2d41b5f30e975 100644
--- a/src/test/ui-fulldeps/auxiliary/lint-group-plugin-test.rs
+++ b/src/test/ui-fulldeps/auxiliary/lint-group-plugin-test.rs
@@ -36,7 +36,7 @@ impl<'tcx> LateLintPass<'tcx> for Pass {
 #[no_mangle]
 fn __rustc_plugin_registrar(reg: &mut Registry) {
     reg.lint_store.register_lints(&[&TEST_LINT, &PLEASE_LINT]);
-    reg.lint_store.register_late_pass(|| Box::new(Pass));
+    reg.lint_store.register_late_pass(|_| Box::new(Pass));
     reg.lint_store.register_group(
         true,
         "lint_me",
diff --git a/src/test/ui/associated-types/issue-62200.rs b/src/test/ui/associated-types/issue-62200.rs
index 9d18690e96049..499bbd6b6fad2 100644
--- a/src/test/ui/associated-types/issue-62200.rs
+++ b/src/test/ui/associated-types/issue-62200.rs
@@ -10,6 +10,7 @@ impl T<'_> for S {
 
 fn foo(x: impl Fn(<S as T<'_>>::A) -> <S as T<'_>>::A) {}
 //~^ ERROR binding for associated type `Output` references an anonymous lifetime
-//~^^ NOTE lifetimes appearing in an associated type are not considered constrained
+//~| NOTE lifetimes appearing in an associated or opaque type are not considered constrained
+//~| NOTE consider introducing a named lifetime parameter
 
 fn main() {}
diff --git a/src/test/ui/associated-types/issue-62200.stderr b/src/test/ui/associated-types/issue-62200.stderr
index f14cd81fdfe1f..04f0728f58ea8 100644
--- a/src/test/ui/associated-types/issue-62200.stderr
+++ b/src/test/ui/associated-types/issue-62200.stderr
@@ -4,7 +4,8 @@ error[E0582]: binding for associated type `Output` references an anonymous lifet
 LL | fn foo(x: impl Fn(<S as T<'_>>::A) -> <S as T<'_>>::A) {}
    |                                       ^^^^^^^^^^^^^^^
    |
-   = note: lifetimes appearing in an associated type are not considered constrained
+   = note: lifetimes appearing in an associated or opaque type are not considered constrained
+   = note: consider introducing a named lifetime parameter
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/async-await/async-trait-fn.rs b/src/test/ui/async-await/async-trait-fn.rs
index e2062e82725c0..0ea685986db40 100644
--- a/src/test/ui/async-await/async-trait-fn.rs
+++ b/src/test/ui/async-await/async-trait-fn.rs
@@ -1,8 +1,11 @@
 // edition:2018
 trait T {
     async fn foo() {} //~ ERROR functions in traits cannot be declared `async`
+    //~^ ERROR mismatched types
     async fn bar(&self) {} //~ ERROR functions in traits cannot be declared `async`
+    //~^ ERROR mismatched types
     async fn baz() { //~ ERROR functions in traits cannot be declared `async`
+        //~^ ERROR mismatched types
         // Nested item must not ICE.
         fn a() {}
     }
diff --git a/src/test/ui/async-await/async-trait-fn.stderr b/src/test/ui/async-await/async-trait-fn.stderr
index 1eb8969a80d20..e5c584e31e815 100644
--- a/src/test/ui/async-await/async-trait-fn.stderr
+++ b/src/test/ui/async-await/async-trait-fn.stderr
@@ -2,40 +2,89 @@ error[E0706]: functions in traits cannot be declared `async`
   --> $DIR/async-trait-fn.rs:3:5
    |
 LL |     async fn foo() {}
-   |     -----^^^^^^^^^^^^
+   |     -----^^^^^^^^^
    |     |
    |     `async` because of this
    |
    = note: `async` trait functions are not currently supported
    = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
 
 error[E0706]: functions in traits cannot be declared `async`
-  --> $DIR/async-trait-fn.rs:4:5
+  --> $DIR/async-trait-fn.rs:5:5
    |
 LL |     async fn bar(&self) {}
-   |     -----^^^^^^^^^^^^^^^^^
+   |     -----^^^^^^^^^^^^^^
    |     |
    |     `async` because of this
    |
    = note: `async` trait functions are not currently supported
    = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
 
 error[E0706]: functions in traits cannot be declared `async`
-  --> $DIR/async-trait-fn.rs:5:5
+  --> $DIR/async-trait-fn.rs:7:5
+   |
+LL |     async fn baz() {
+   |     -----^^^^^^^^^
+   |     |
+   |     `async` because of this
+   |
+   = note: `async` trait functions are not currently supported
+   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
+
+error[E0308]: mismatched types
+  --> $DIR/async-trait-fn.rs:3:20
+   |
+LL |     async fn foo() {}
+   |                    ^^ expected associated type, found opaque type
+   |
+  ::: $SRC_DIR/core/src/future/mod.rs:LL:COL
+   |
+LL | pub const fn from_generator<T>(gen: T) -> impl Future<Output = T::Return>
+   |                                           ------------------------------- the found opaque type
+   |
+   = note: expected associated type `impl Future<Output = ()>` (trait associated opaque type at <$DIR/async-trait-fn.rs:3:20>)
+                  found opaque type `impl Future<Output = ()>` (opaque type at <$SRC_DIR/core/src/future/mod.rs:LL:COL>)
+
+error[E0308]: mismatched types
+  --> $DIR/async-trait-fn.rs:5:25
+   |
+LL |     async fn bar(&self) {}
+   |                         ^^ expected associated type, found opaque type
+   |
+  ::: $SRC_DIR/core/src/future/mod.rs:LL:COL
+   |
+LL | pub const fn from_generator<T>(gen: T) -> impl Future<Output = T::Return>
+   |                                           ------------------------------- the found opaque type
+   |
+   = note: expected associated type `impl Future<Output = ()>` (trait associated opaque type at <$DIR/async-trait-fn.rs:5:25>)
+                  found opaque type `impl Future<Output = ()>` (opaque type at <$SRC_DIR/core/src/future/mod.rs:LL:COL>)
+
+error[E0308]: mismatched types
+  --> $DIR/async-trait-fn.rs:7:20
    |
 LL |       async fn baz() {
-   |       ^----
-   |       |
-   |  _____`async` because of this
-   | |
+   |  ____________________^
+LL | |
 LL | |         // Nested item must not ICE.
 LL | |         fn a() {}
 LL | |     }
-   | |_____^
+   | |_____^ expected associated type, found opaque type
    |
-   = note: `async` trait functions are not currently supported
-   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
+  ::: $SRC_DIR/core/src/future/mod.rs:LL:COL
+   |
+LL |   pub const fn from_generator<T>(gen: T) -> impl Future<Output = T::Return>
+   |                                             ------------------------------- the found opaque type
+   |
+   = note: expected associated type `impl Future<Output = ()>` (trait associated opaque type at <$DIR/async-trait-fn.rs:7:20>)
+                  found opaque type `impl Future<Output = ()>` (opaque type at <$SRC_DIR/core/src/future/mod.rs:LL:COL>)
 
-error: aborting due to 3 previous errors
+error: aborting due to 6 previous errors
 
-For more information about this error, try `rustc --explain E0706`.
+Some errors have detailed explanations: E0308, E0706.
+For more information about an error, try `rustc --explain E0308`.
diff --git a/src/test/ui/async-await/edition-deny-async-fns-2015.rs b/src/test/ui/async-await/edition-deny-async-fns-2015.rs
index e5dc9c8a5fee8..22a61dcd25f98 100644
--- a/src/test/ui/async-await/edition-deny-async-fns-2015.rs
+++ b/src/test/ui/async-await/edition-deny-async-fns-2015.rs
@@ -16,7 +16,8 @@ impl Foo {
 
 trait Bar {
     async fn foo() {} //~ ERROR `async fn` is not permitted in Rust 2015
-                      //~^ ERROR functions in traits cannot be declared `async`
+    //~^ ERROR functions in traits cannot be declared `async`
+    //~| ERROR mismatched types
 }
 
 fn main() {
diff --git a/src/test/ui/async-await/edition-deny-async-fns-2015.stderr b/src/test/ui/async-await/edition-deny-async-fns-2015.stderr
index 35f9c581c7b21..8c2902d9b00d1 100644
--- a/src/test/ui/async-await/edition-deny-async-fns-2015.stderr
+++ b/src/test/ui/async-await/edition-deny-async-fns-2015.stderr
@@ -53,7 +53,7 @@ LL |     async fn foo() {}
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
 error[E0670]: `async fn` is not permitted in Rust 2015
-  --> $DIR/edition-deny-async-fns-2015.rs:36:9
+  --> $DIR/edition-deny-async-fns-2015.rs:37:9
    |
 LL |         async fn bar() {}
    |         ^^^^^ to use `async fn`, switch to Rust 2018 or later
@@ -62,7 +62,7 @@ LL |         async fn bar() {}
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
 error[E0670]: `async fn` is not permitted in Rust 2015
-  --> $DIR/edition-deny-async-fns-2015.rs:26:9
+  --> $DIR/edition-deny-async-fns-2015.rs:27:9
    |
 LL |         async fn foo() {}
    |         ^^^^^ to use `async fn`, switch to Rust 2018 or later
@@ -71,7 +71,7 @@ LL |         async fn foo() {}
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
 error[E0670]: `async fn` is not permitted in Rust 2015
-  --> $DIR/edition-deny-async-fns-2015.rs:31:13
+  --> $DIR/edition-deny-async-fns-2015.rs:32:13
    |
 LL |             async fn bar() {}
    |             ^^^^^ to use `async fn`, switch to Rust 2018 or later
@@ -83,14 +83,30 @@ error[E0706]: functions in traits cannot be declared `async`
   --> $DIR/edition-deny-async-fns-2015.rs:18:5
    |
 LL |     async fn foo() {}
-   |     -----^^^^^^^^^^^^
+   |     -----^^^^^^^^^
    |     |
    |     `async` because of this
    |
    = note: `async` trait functions are not currently supported
    = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
 
-error: aborting due to 10 previous errors
+error[E0308]: mismatched types
+  --> $DIR/edition-deny-async-fns-2015.rs:18:20
+   |
+LL |     async fn foo() {}
+   |                    ^^ expected associated type, found opaque type
+   |
+  ::: $SRC_DIR/core/src/future/mod.rs:LL:COL
+   |
+LL | pub const fn from_generator<T>(gen: T) -> impl Future<Output = T::Return>
+   |                                           ------------------------------- the found opaque type
+   |
+   = note: expected associated type `impl Future<Output = ()>` (trait associated opaque type at <$DIR/edition-deny-async-fns-2015.rs:18:20>)
+                  found opaque type `impl Future<Output = ()>` (opaque type at <$SRC_DIR/core/src/future/mod.rs:LL:COL>)
+
+error: aborting due to 11 previous errors
 
-Some errors have detailed explanations: E0670, E0706.
-For more information about an error, try `rustc --explain E0670`.
+Some errors have detailed explanations: E0308, E0670, E0706.
+For more information about an error, try `rustc --explain E0308`.
diff --git a/src/test/ui/async-await/issues/issue-95307.stderr b/src/test/ui/async-await/issues/issue-95307.stderr
index 29aebb719d66f..1c12f1e4862e8 100644
--- a/src/test/ui/async-await/issues/issue-95307.stderr
+++ b/src/test/ui/async-await/issues/issue-95307.stderr
@@ -8,6 +8,8 @@ LL |     async fn new() -> [u8; _];
    |
    = note: `async` trait functions are not currently supported
    = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
 
 error: in expressions, `_` can only be used on the left-hand side of an assignment
   --> $DIR/issue-95307.rs:7:28
diff --git a/src/test/ui/feature-gates/feature-gate-return_position_impl_trait_in_trait.rs b/src/test/ui/feature-gates/feature-gate-return_position_impl_trait_in_trait.rs
new file mode 100644
index 0000000000000..de7966c66b057
--- /dev/null
+++ b/src/test/ui/feature-gates/feature-gate-return_position_impl_trait_in_trait.rs
@@ -0,0 +1,5 @@
+trait Foo {
+    fn bar() -> impl Sized; //~ ERROR `impl Trait` only allowed in function and inherent method return types, not in trait method return
+}
+
+fn main() {}
diff --git a/src/test/ui/feature-gates/feature-gate-return_position_impl_trait_in_trait.stderr b/src/test/ui/feature-gates/feature-gate-return_position_impl_trait_in_trait.stderr
new file mode 100644
index 0000000000000..36177bbe15830
--- /dev/null
+++ b/src/test/ui/feature-gates/feature-gate-return_position_impl_trait_in_trait.stderr
@@ -0,0 +1,12 @@
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in trait method return
+  --> $DIR/feature-gate-return_position_impl_trait_in_trait.rs:2:17
+   |
+LL |     fn bar() -> impl Sized;
+   |                 ^^^^^^^^^^
+   |
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0562`.
diff --git a/src/test/ui/impl-trait/in-trait/deep-match-works.rs b/src/test/ui/impl-trait/in-trait/deep-match-works.rs
new file mode 100644
index 0000000000000..772da845ee1f7
--- /dev/null
+++ b/src/test/ui/impl-trait/in-trait/deep-match-works.rs
@@ -0,0 +1,16 @@
+// check-pass
+
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+struct Wrapper<T>(T);
+
+trait Foo {
+    fn bar() -> Wrapper<impl Sized>;
+}
+
+impl Foo for () {
+    fn bar() -> Wrapper<i32> { Wrapper(0) }
+}
+
+fn main() {}
diff --git a/src/test/ui/impl-trait/in-trait/deep-match.rs b/src/test/ui/impl-trait/in-trait/deep-match.rs
new file mode 100644
index 0000000000000..5a220bc3f198a
--- /dev/null
+++ b/src/test/ui/impl-trait/in-trait/deep-match.rs
@@ -0,0 +1,15 @@
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+struct Wrapper<T>(T);
+
+trait Foo {
+    fn bar() -> Wrapper<impl Sized>;
+}
+
+impl Foo for () {
+    fn bar() -> i32 { 0 }
+    //~^ ERROR method `bar` has an incompatible type for trait
+}
+
+fn main() {}
diff --git a/src/test/ui/impl-trait/in-trait/deep-match.stderr b/src/test/ui/impl-trait/in-trait/deep-match.stderr
new file mode 100644
index 0000000000000..af449869cb356
--- /dev/null
+++ b/src/test/ui/impl-trait/in-trait/deep-match.stderr
@@ -0,0 +1,20 @@
+error[E0053]: method `bar` has an incompatible type for trait
+  --> $DIR/deep-match.rs:11:17
+   |
+LL |     fn bar() -> i32 { 0 }
+   |                 ^^^
+   |                 |
+   |                 expected struct `Wrapper`, found `i32`
+   |                 help: change the output type to match the trait: `Wrapper<_>`
+   |
+note: type in trait
+  --> $DIR/deep-match.rs:7:17
+   |
+LL |     fn bar() -> Wrapper<impl Sized>;
+   |                 ^^^^^^^^^^^^^^^^^^^
+   = note: expected fn pointer `fn() -> Wrapper<_>`
+              found fn pointer `fn() -> i32`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0053`.
diff --git a/src/test/ui/impl-trait/in-trait/doesnt-satisfy.rs b/src/test/ui/impl-trait/in-trait/doesnt-satisfy.rs
new file mode 100644
index 0000000000000..bb4e0d44f3eff
--- /dev/null
+++ b/src/test/ui/impl-trait/in-trait/doesnt-satisfy.rs
@@ -0,0 +1,13 @@
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+trait Foo {
+    fn bar() -> impl std::fmt::Display;
+}
+
+impl Foo for () {
+    fn bar() -> () {}
+    //~^ ERROR `()` doesn't implement `std::fmt::Display`
+}
+
+fn main() {}
diff --git a/src/test/ui/impl-trait/in-trait/doesnt-satisfy.stderr b/src/test/ui/impl-trait/in-trait/doesnt-satisfy.stderr
new file mode 100644
index 0000000000000..aa5492d285ed6
--- /dev/null
+++ b/src/test/ui/impl-trait/in-trait/doesnt-satisfy.stderr
@@ -0,0 +1,17 @@
+error[E0277]: `()` doesn't implement `std::fmt::Display`
+  --> $DIR/doesnt-satisfy.rs:9:17
+   |
+LL |     fn bar() -> () {}
+   |                 ^^ `()` cannot be formatted with the default formatter
+   |
+   = help: the trait `std::fmt::Display` is not implemented for `()`
+   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
+note: required by a bound in `Foo::bar::{opaque#0}`
+  --> $DIR/doesnt-satisfy.rs:5:22
+   |
+LL |     fn bar() -> impl std::fmt::Display;
+   |                      ^^^^^^^^^^^^^^^^^ required by this bound in `Foo::bar::{opaque#0}`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/src/test/ui/impl-trait/in-trait/nested-rpitit.rs b/src/test/ui/impl-trait/in-trait/nested-rpitit.rs
new file mode 100644
index 0000000000000..65285e3a3ccaf
--- /dev/null
+++ b/src/test/ui/impl-trait/in-trait/nested-rpitit.rs
@@ -0,0 +1,32 @@
+// check-pass
+
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+use std::fmt::Display;
+use std::ops::Deref;
+
+trait Foo {
+    fn bar(self) -> impl Deref<Target = impl Display + ?Sized>;
+}
+
+struct A;
+
+impl Foo for A {
+    fn bar(self) -> &'static str {
+        "Hello, world"
+    }
+}
+
+struct B;
+
+impl Foo for B {
+    fn bar(self) -> Box<i32> {
+        Box::new(42)
+    }
+}
+
+fn main() {
+    println!("Message for you: {:?}", &*A.bar());
+    println!("Another for you: {:?}", &*B.bar());
+}
diff --git a/src/test/ui/impl-trait/in-trait/opaque-in-impl-is-opaque.rs b/src/test/ui/impl-trait/in-trait/opaque-in-impl-is-opaque.rs
new file mode 100644
index 0000000000000..3ac264e8ebac5
--- /dev/null
+++ b/src/test/ui/impl-trait/in-trait/opaque-in-impl-is-opaque.rs
@@ -0,0 +1,19 @@
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+use std::fmt::Display;
+
+trait Foo {
+    fn bar(&self) -> impl Display;
+}
+
+impl Foo for () {
+    fn bar(&self) -> impl Display {
+        "Hello, world"
+    }
+}
+
+fn main() {
+    let x: &str = ().bar();
+    //~^ ERROR mismatched types
+}
diff --git a/src/test/ui/impl-trait/in-trait/opaque-in-impl-is-opaque.stderr b/src/test/ui/impl-trait/in-trait/opaque-in-impl-is-opaque.stderr
new file mode 100644
index 0000000000000..15edda4834015
--- /dev/null
+++ b/src/test/ui/impl-trait/in-trait/opaque-in-impl-is-opaque.stderr
@@ -0,0 +1,17 @@
+error[E0308]: mismatched types
+  --> $DIR/opaque-in-impl-is-opaque.rs:17:19
+   |
+LL |     fn bar(&self) -> impl Display {
+   |                      ------------ the found opaque type
+...
+LL |     let x: &str = ().bar();
+   |            ----   ^^^^^^^^ expected `&str`, found opaque type
+   |            |
+   |            expected due to this
+   |
+   = note: expected reference `&str`
+            found opaque type `impl std::fmt::Display`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/impl-trait/in-trait/opaque-in-impl.rs b/src/test/ui/impl-trait/in-trait/opaque-in-impl.rs
new file mode 100644
index 0000000000000..2e06629699aad
--- /dev/null
+++ b/src/test/ui/impl-trait/in-trait/opaque-in-impl.rs
@@ -0,0 +1,48 @@
+// check-pass
+
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+use std::fmt::Debug;
+
+trait Foo {
+    fn foo(&self) -> impl Debug;
+}
+
+impl Foo for () {
+    fn foo(&self) -> impl Debug {
+        "Hello, world"
+    }
+}
+
+impl<T: Default + Debug> Foo for std::marker::PhantomData<T> {
+    fn foo(&self) -> impl Debug {
+        T::default()
+    }
+}
+
+trait Bar {
+    fn bar<T>(&self) -> impl Debug;
+}
+
+impl Bar for () {
+    fn bar<T>(&self) -> impl Debug {
+        format!("Hello with generic {}", std::any::type_name::<T>())
+    }
+}
+
+trait Baz {
+    fn baz(&self) -> impl Debug + '_;
+}
+
+impl Baz for String {
+    fn baz(&self) -> impl Debug + '_ {
+        (self,)
+    }
+}
+
+fn main() {
+    println!("{:?}", ().foo());
+    println!("{:?}", ().bar::<u64>());
+    println!("{:?}", "hi".to_string().baz());
+}
diff --git a/src/test/ui/impl-trait/in-trait/reveal.rs b/src/test/ui/impl-trait/in-trait/reveal.rs
new file mode 100644
index 0000000000000..d6ede1cc495c6
--- /dev/null
+++ b/src/test/ui/impl-trait/in-trait/reveal.rs
@@ -0,0 +1,18 @@
+// check-pass
+
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+trait Foo {
+    fn f() -> Box<impl Sized>;
+}
+
+impl Foo for () {
+    fn f() -> Box<String> {
+        Box::new(String::new())
+    }
+}
+
+fn main() {
+    let x: Box<String> = <() as Foo>::f();
+}
diff --git a/src/test/ui/impl-trait/in-trait/success.rs b/src/test/ui/impl-trait/in-trait/success.rs
new file mode 100644
index 0000000000000..4cbe682b46f73
--- /dev/null
+++ b/src/test/ui/impl-trait/in-trait/success.rs
@@ -0,0 +1,40 @@
+// check-pass
+
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+use std::fmt::Display;
+
+trait Foo {
+    fn bar(&self) -> impl Display;
+}
+
+impl Foo for i32 {
+    fn bar(&self) -> i32 {
+        *self
+    }
+}
+
+impl Foo for &'static str {
+    fn bar(&self) -> &'static str {
+        *self
+    }
+}
+
+struct Yay;
+
+impl Foo for Yay {
+    fn bar(&self) -> String {
+        String::from(":^)")
+    }
+}
+
+fn foo_generically<T: Foo>(t: T) {
+    println!("{}", t.bar());
+}
+
+fn main() {
+    println!("{}", "Hello, world.".bar());
+    println!("The answer is {}!", 42.bar());
+    foo_generically(Yay);
+}
diff --git a/src/test/ui/impl-trait/where-allowed.stderr b/src/test/ui/impl-trait/where-allowed.stderr
index 58a2f79efb4c6..9b346387d6106 100644
--- a/src/test/ui/impl-trait/where-allowed.stderr
+++ b/src/test/ui/impl-trait/where-allowed.stderr
@@ -162,12 +162,18 @@ error[E0562]: `impl Trait` only allowed in function and inherent method return t
    |
 LL |     fn in_return() -> impl Debug;
    |                       ^^^^^^^^^^
+   |
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
 
 error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `impl` method return
   --> $DIR/where-allowed.rs:125:34
    |
 LL |     fn in_trait_impl_return() -> impl Debug { () }
    |                                  ^^^^^^^^^^
+   |
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
 
 error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `extern fn` param
   --> $DIR/where-allowed.rs:138:33
diff --git a/src/test/ui/issues/issue-47511.stderr b/src/test/ui/issues/issue-47511.stderr
index 5b84f7ed62c3a..9998ee0e8d0c6 100644
--- a/src/test/ui/issues/issue-47511.stderr
+++ b/src/test/ui/issues/issue-47511.stderr
@@ -4,7 +4,8 @@ error[E0581]: return type references an anonymous lifetime, which is not constra
 LL | fn f(_: X) -> X {
    |               ^
    |
-   = note: lifetimes appearing in an associated type are not considered constrained
+   = note: lifetimes appearing in an associated or opaque type are not considered constrained
+   = note: consider introducing a named lifetime parameter
 
 error[E0581]: return type references lifetime `'a`, which is not constrained by the fn input types
   --> $DIR/issue-47511.rs:12:23
diff --git a/src/test/ui/parser/fn-header-semantic-fail.rs b/src/test/ui/parser/fn-header-semantic-fail.rs
index 8ff14fb1f304a..cf5d3dab4aada 100644
--- a/src/test/ui/parser/fn-header-semantic-fail.rs
+++ b/src/test/ui/parser/fn-header-semantic-fail.rs
@@ -27,7 +27,6 @@ fn main() {
     struct Y;
     impl X for Y {
         async fn ft1() {} //~ ERROR functions in traits cannot be declared `async`
-        //~^ ERROR has an incompatible type for trait
         unsafe fn ft2() {} // OK.
         const fn ft3() {} //~ ERROR functions in traits cannot be declared const
         extern "C" fn ft4() {}
@@ -36,7 +35,6 @@ fn main() {
         //~| ERROR functions in traits cannot be declared const
         //~| ERROR functions cannot be both `const` and `async`
         //~| ERROR cycle detected
-        //~| ERROR has an incompatible type for trait
     }
 
     impl Y {
diff --git a/src/test/ui/parser/fn-header-semantic-fail.stderr b/src/test/ui/parser/fn-header-semantic-fail.stderr
index bc51ba8b8c5c5..36304779df36f 100644
--- a/src/test/ui/parser/fn-header-semantic-fail.stderr
+++ b/src/test/ui/parser/fn-header-semantic-fail.stderr
@@ -7,17 +7,6 @@ LL |     const async unsafe extern "C" fn ff5() {}
    |     |     `async` because of this
    |     `const` because of this
 
-error[E0706]: functions in traits cannot be declared `async`
-  --> $DIR/fn-header-semantic-fail.rs:17:9
-   |
-LL |         async fn ft1();
-   |         -----^^^^^^^^^^
-   |         |
-   |         `async` because of this
-   |
-   = note: `async` trait functions are not currently supported
-   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
-
 error[E0379]: functions in traits cannot be declared const
   --> $DIR/fn-header-semantic-fail.rs:19:9
    |
@@ -30,17 +19,6 @@ error[E0379]: functions in traits cannot be declared const
 LL |         const async unsafe extern "C" fn ft5();
    |         ^^^^^ functions in traits cannot be const
 
-error[E0706]: functions in traits cannot be declared `async`
-  --> $DIR/fn-header-semantic-fail.rs:21:9
-   |
-LL |         const async unsafe extern "C" fn ft5();
-   |         ^^^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |               |
-   |               `async` because of this
-   |
-   = note: `async` trait functions are not currently supported
-   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
-
 error: functions cannot be both `const` and `async`
   --> $DIR/fn-header-semantic-fail.rs:21:9
    |
@@ -50,42 +28,20 @@ LL |         const async unsafe extern "C" fn ft5();
    |         |     `async` because of this
    |         `const` because of this
 
-error[E0706]: functions in traits cannot be declared `async`
-  --> $DIR/fn-header-semantic-fail.rs:29:9
-   |
-LL |         async fn ft1() {}
-   |         -----^^^^^^^^^^^^
-   |         |
-   |         `async` because of this
-   |
-   = note: `async` trait functions are not currently supported
-   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
-
 error[E0379]: functions in traits cannot be declared const
-  --> $DIR/fn-header-semantic-fail.rs:32:9
+  --> $DIR/fn-header-semantic-fail.rs:31:9
    |
 LL |         const fn ft3() {}
    |         ^^^^^ functions in traits cannot be const
 
 error[E0379]: functions in traits cannot be declared const
-  --> $DIR/fn-header-semantic-fail.rs:34:9
+  --> $DIR/fn-header-semantic-fail.rs:33:9
    |
 LL |         const async unsafe extern "C" fn ft5() {}
    |         ^^^^^ functions in traits cannot be const
 
-error[E0706]: functions in traits cannot be declared `async`
-  --> $DIR/fn-header-semantic-fail.rs:34:9
-   |
-LL |         const async unsafe extern "C" fn ft5() {}
-   |         ^^^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |               |
-   |               `async` because of this
-   |
-   = note: `async` trait functions are not currently supported
-   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
-
 error: functions cannot be both `const` and `async`
-  --> $DIR/fn-header-semantic-fail.rs:34:9
+  --> $DIR/fn-header-semantic-fail.rs:33:9
    |
 LL |         const async unsafe extern "C" fn ft5() {}
    |         ^^^^^-^^^^^------------------------------
@@ -94,7 +50,7 @@ LL |         const async unsafe extern "C" fn ft5() {}
    |         `const` because of this
 
 error: functions cannot be both `const` and `async`
-  --> $DIR/fn-header-semantic-fail.rs:47:9
+  --> $DIR/fn-header-semantic-fail.rs:45:9
    |
 LL |         const async unsafe extern "C" fn fi5() {}
    |         ^^^^^-^^^^^------------------------------
@@ -103,7 +59,7 @@ LL |         const async unsafe extern "C" fn fi5() {}
    |         `const` because of this
 
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:53:18
+  --> $DIR/fn-header-semantic-fail.rs:51:18
    |
 LL |     extern "C" {
    |     ---------- in this `extern` block
@@ -116,7 +72,7 @@ LL |         fn fe1();
    |         ~~
 
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:54:19
+  --> $DIR/fn-header-semantic-fail.rs:52:19
    |
 LL |     extern "C" {
    |     ---------- in this `extern` block
@@ -130,7 +86,7 @@ LL |         fn fe2();
    |         ~~
 
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:55:18
+  --> $DIR/fn-header-semantic-fail.rs:53:18
    |
 LL |     extern "C" {
    |     ---------- in this `extern` block
@@ -144,7 +100,7 @@ LL |         fn fe3();
    |         ~~
 
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:56:23
+  --> $DIR/fn-header-semantic-fail.rs:54:23
    |
 LL |     extern "C" {
    |     ---------- in this `extern` block
@@ -158,7 +114,7 @@ LL |         fn fe4();
    |         ~~
 
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/fn-header-semantic-fail.rs:57:42
+  --> $DIR/fn-header-semantic-fail.rs:55:42
    |
 LL |     extern "C" {
    |     ---------- in this `extern` block
@@ -172,7 +128,7 @@ LL |         fn fe5();
    |         ~~
 
 error: functions cannot be both `const` and `async`
-  --> $DIR/fn-header-semantic-fail.rs:57:9
+  --> $DIR/fn-header-semantic-fail.rs:55:9
    |
 LL |         const async unsafe extern "C" fn fe5();
    |         ^^^^^-^^^^^----------------------------
@@ -180,6 +136,58 @@ LL |         const async unsafe extern "C" fn fe5();
    |         |     `async` because of this
    |         `const` because of this
 
+error[E0706]: functions in traits cannot be declared `async`
+  --> $DIR/fn-header-semantic-fail.rs:17:9
+   |
+LL |         async fn ft1();
+   |         -----^^^^^^^^^^
+   |         |
+   |         `async` because of this
+   |
+   = note: `async` trait functions are not currently supported
+   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
+
+error[E0706]: functions in traits cannot be declared `async`
+  --> $DIR/fn-header-semantic-fail.rs:21:9
+   |
+LL |         const async unsafe extern "C" fn ft5();
+   |         ^^^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |               |
+   |               `async` because of this
+   |
+   = note: `async` trait functions are not currently supported
+   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
+
+error[E0706]: functions in traits cannot be declared `async`
+  --> $DIR/fn-header-semantic-fail.rs:29:9
+   |
+LL |         async fn ft1() {}
+   |         -----^^^^^^^^^
+   |         |
+   |         `async` because of this
+   |
+   = note: `async` trait functions are not currently supported
+   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
+
+error[E0706]: functions in traits cannot be declared `async`
+  --> $DIR/fn-header-semantic-fail.rs:33:9
+   |
+LL |         const async unsafe extern "C" fn ft5() {}
+   |         ^^^^^^-----^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |               |
+   |               `async` because of this
+   |
+   = note: `async` trait functions are not currently supported
+   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
+
 error[E0391]: cycle detected when computing type of `main::ff5::{opaque#0}`
   --> $DIR/fn-header-semantic-fail.rs:12:44
    |
@@ -216,60 +224,24 @@ LL | |     }
 LL | | }
    | |_^
 
-error[E0053]: method `ft1` has an incompatible type for trait
-  --> $DIR/fn-header-semantic-fail.rs:29:24
-   |
-LL |         async fn ft1() {}
-   |                        ^
-   |                        |
-   |                        checked the `Output` of this `async fn`, found opaque type
-   |                        expected `()`, found opaque type
-   |
-   = note: while checking the return type of the `async fn`
-note: type in trait
-  --> $DIR/fn-header-semantic-fail.rs:17:23
-   |
-LL |         async fn ft1();
-   |                       ^
-   = note: expected fn pointer `fn()`
-              found fn pointer `fn() -> impl Future<Output = ()>`
-
-error[E0053]: method `ft5` has an incompatible type for trait
-  --> $DIR/fn-header-semantic-fail.rs:34:48
-   |
-LL |         const async unsafe extern "C" fn ft5() {}
-   |                                                ^
-   |                                                |
-   |                                                checked the `Output` of this `async fn`, found opaque type
-   |                                                expected `()`, found opaque type
-   |
-   = note: while checking the return type of the `async fn`
-note: type in trait
-  --> $DIR/fn-header-semantic-fail.rs:21:47
-   |
-LL |         const async unsafe extern "C" fn ft5();
-   |                                               ^
-   = note: expected fn pointer `unsafe extern "C" fn()`
-              found fn pointer `unsafe extern "C" fn() -> impl Future<Output = ()>`
-
 error[E0391]: cycle detected when computing type of `main::<impl at $DIR/fn-header-semantic-fail.rs:28:5: 28:17>::ft5::{opaque#0}`
-  --> $DIR/fn-header-semantic-fail.rs:34:48
+  --> $DIR/fn-header-semantic-fail.rs:33:48
    |
 LL |         const async unsafe extern "C" fn ft5() {}
    |                                                ^
    |
 note: ...which requires borrow-checking `main::<impl at $DIR/fn-header-semantic-fail.rs:28:5: 28:17>::ft5`...
-  --> $DIR/fn-header-semantic-fail.rs:34:9
+  --> $DIR/fn-header-semantic-fail.rs:33:9
    |
 LL |         const async unsafe extern "C" fn ft5() {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 note: ...which requires processing `main::<impl at $DIR/fn-header-semantic-fail.rs:28:5: 28:17>::ft5`...
-  --> $DIR/fn-header-semantic-fail.rs:34:9
+  --> $DIR/fn-header-semantic-fail.rs:33:9
    |
 LL |         const async unsafe extern "C" fn ft5() {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 note: ...which requires const checking `main::<impl at $DIR/fn-header-semantic-fail.rs:28:5: 28:17>::ft5`...
-  --> $DIR/fn-header-semantic-fail.rs:34:9
+  --> $DIR/fn-header-semantic-fail.rs:33:9
    |
 LL |         const async unsafe extern "C" fn ft5() {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -288,30 +260,30 @@ LL | |     }
 LL | | }
    | |_^
 
-error[E0391]: cycle detected when computing type of `main::<impl at $DIR/fn-header-semantic-fail.rs:42:5: 42:11>::fi5::{opaque#0}`
-  --> $DIR/fn-header-semantic-fail.rs:47:48
+error[E0391]: cycle detected when computing type of `main::<impl at $DIR/fn-header-semantic-fail.rs:40:5: 40:11>::fi5::{opaque#0}`
+  --> $DIR/fn-header-semantic-fail.rs:45:48
    |
 LL |         const async unsafe extern "C" fn fi5() {}
    |                                                ^
    |
-note: ...which requires borrow-checking `main::<impl at $DIR/fn-header-semantic-fail.rs:42:5: 42:11>::fi5`...
-  --> $DIR/fn-header-semantic-fail.rs:47:9
+note: ...which requires borrow-checking `main::<impl at $DIR/fn-header-semantic-fail.rs:40:5: 40:11>::fi5`...
+  --> $DIR/fn-header-semantic-fail.rs:45:9
    |
 LL |         const async unsafe extern "C" fn fi5() {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires processing `main::<impl at $DIR/fn-header-semantic-fail.rs:42:5: 42:11>::fi5`...
-  --> $DIR/fn-header-semantic-fail.rs:47:9
+note: ...which requires processing `main::<impl at $DIR/fn-header-semantic-fail.rs:40:5: 40:11>::fi5`...
+  --> $DIR/fn-header-semantic-fail.rs:45:9
    |
 LL |         const async unsafe extern "C" fn fi5() {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: ...which requires const checking `main::<impl at $DIR/fn-header-semantic-fail.rs:42:5: 42:11>::fi5`...
-  --> $DIR/fn-header-semantic-fail.rs:47:9
+note: ...which requires const checking `main::<impl at $DIR/fn-header-semantic-fail.rs:40:5: 40:11>::fi5`...
+  --> $DIR/fn-header-semantic-fail.rs:45:9
    |
 LL |         const async unsafe extern "C" fn fi5() {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: ...which requires computing whether `impl core::future::future::Future<Output = ()>` is freeze...
    = note: ...which requires evaluating trait selection obligation `impl core::future::future::Future<Output = ()>: core::marker::Freeze`...
-   = note: ...which again requires computing type of `main::<impl at $DIR/fn-header-semantic-fail.rs:42:5: 42:11>::fi5::{opaque#0}`, completing the cycle
+   = note: ...which again requires computing type of `main::<impl at $DIR/fn-header-semantic-fail.rs:40:5: 40:11>::fi5::{opaque#0}`, completing the cycle
 note: cycle used when checking item types in top-level module
   --> $DIR/fn-header-semantic-fail.rs:5:1
    |
@@ -324,7 +296,7 @@ LL | |     }
 LL | | }
    | |_^
 
-error: aborting due to 23 previous errors
+error: aborting due to 21 previous errors
 
-Some errors have detailed explanations: E0053, E0379, E0391, E0706.
-For more information about an error, try `rustc --explain E0053`.
+Some errors have detailed explanations: E0379, E0391, E0706.
+For more information about an error, try `rustc --explain E0379`.
diff --git a/src/test/ui/parser/issue-101477-enum.fixed b/src/test/ui/parser/issue-101477-enum.fixed
new file mode 100644
index 0000000000000..1dfeae22aea2f
--- /dev/null
+++ b/src/test/ui/parser/issue-101477-enum.fixed
@@ -0,0 +1,10 @@
+// run-rustfix
+
+#[allow(dead_code)]
+enum Demo {
+    A = 1,
+    B = 2 //~ ERROR unexpected `==`
+    //~^ expected item, found `==`
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/issue-101477-enum.rs b/src/test/ui/parser/issue-101477-enum.rs
new file mode 100644
index 0000000000000..ea7051d69a4c7
--- /dev/null
+++ b/src/test/ui/parser/issue-101477-enum.rs
@@ -0,0 +1,10 @@
+// run-rustfix
+
+#[allow(dead_code)]
+enum Demo {
+    A = 1,
+    B == 2 //~ ERROR unexpected `==`
+    //~^ expected item, found `==`
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/issue-101477-enum.stderr b/src/test/ui/parser/issue-101477-enum.stderr
new file mode 100644
index 0000000000000..bffc881bdc84b
--- /dev/null
+++ b/src/test/ui/parser/issue-101477-enum.stderr
@@ -0,0 +1,14 @@
+error: unexpected `==`
+  --> $DIR/issue-101477-enum.rs:6:7
+   |
+LL |     B == 2
+   |       ^^ help: try using `=` instead
+
+error: expected item, found `==`
+  --> $DIR/issue-101477-enum.rs:6:7
+   |
+LL |     B == 2
+   |       ^^ expected item
+
+error: aborting due to 2 previous errors
+
diff --git a/src/test/ui/parser/issue-101477-let.fixed b/src/test/ui/parser/issue-101477-let.fixed
new file mode 100644
index 0000000000000..9989ad81524e1
--- /dev/null
+++ b/src/test/ui/parser/issue-101477-let.fixed
@@ -0,0 +1,6 @@
+// run-rustfix
+
+fn main() {
+    let x = 2; //~ ERROR unexpected `==`
+    println!("x: {}", x)
+}
diff --git a/src/test/ui/parser/issue-101477-let.rs b/src/test/ui/parser/issue-101477-let.rs
new file mode 100644
index 0000000000000..8b0e8bee1799d
--- /dev/null
+++ b/src/test/ui/parser/issue-101477-let.rs
@@ -0,0 +1,6 @@
+// run-rustfix
+
+fn main() {
+    let x == 2; //~ ERROR unexpected `==`
+    println!("x: {}", x)
+}
diff --git a/src/test/ui/parser/issue-101477-let.stderr b/src/test/ui/parser/issue-101477-let.stderr
new file mode 100644
index 0000000000000..1b30d4b17861a
--- /dev/null
+++ b/src/test/ui/parser/issue-101477-let.stderr
@@ -0,0 +1,8 @@
+error: unexpected `==`
+  --> $DIR/issue-101477-let.rs:4:11
+   |
+LL |     let x == 2;
+   |           ^^ help: try using `=` instead
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.rs b/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.rs
index aaf0f7eaef0dc..49462f52fb4c2 100644
--- a/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.rs
+++ b/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.rs
@@ -14,7 +14,6 @@ trait B {
 impl B for A {
     async fn associated(); //~ ERROR without body
     //~^ ERROR cannot be declared `async`
-    //~| ERROR has an incompatible type for trait
 }
 
 fn main() {}
diff --git a/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.stderr b/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.stderr
index d3214458eac13..55c3b66f1363d 100644
--- a/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.stderr
+++ b/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.stderr
@@ -14,17 +14,6 @@ LL |     async fn inherent();
    |                        |
    |                        help: provide a definition for the function: `{ <body> }`
 
-error[E0706]: functions in traits cannot be declared `async`
-  --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:11:5
-   |
-LL |     async fn associated();
-   |     -----^^^^^^^^^^^^^^^^^
-   |     |
-   |     `async` because of this
-   |
-   = note: `async` trait functions are not currently supported
-   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
-
 error: associated function in `impl` without body
   --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:15:5
    |
@@ -34,7 +23,7 @@ LL |     async fn associated();
    |                          help: provide a definition for the function: `{ <body> }`
 
 error[E0706]: functions in traits cannot be declared `async`
-  --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:15:5
+  --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:11:5
    |
 LL |     async fn associated();
    |     -----^^^^^^^^^^^^^^^^^
@@ -43,26 +32,22 @@ LL |     async fn associated();
    |
    = note: `async` trait functions are not currently supported
    = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
 
-error[E0053]: method `associated` has an incompatible type for trait
-  --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:15:26
+error[E0706]: functions in traits cannot be declared `async`
+  --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:15:5
    |
 LL |     async fn associated();
-   |                          ^
-   |                          |
-   |                          checked the `Output` of this `async fn`, found opaque type
-   |                          expected `()`, found opaque type
-   |
-   = note: while checking the return type of the `async fn`
-note: type in trait
-  --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:11:26
+   |     -----^^^^^^^^^^^^^^^^^
+   |     |
+   |     `async` because of this
    |
-LL |     async fn associated();
-   |                          ^
-   = note: expected fn pointer `fn()`
-              found fn pointer `fn() -> impl Future<Output = ()>`
+   = note: `async` trait functions are not currently supported
+   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
 
-error: aborting due to 6 previous errors
+error: aborting due to 5 previous errors
 
-Some errors have detailed explanations: E0053, E0706.
-For more information about an error, try `rustc --explain E0053`.
+For more information about this error, try `rustc --explain E0706`.
diff --git a/src/test/ui/span/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.rs b/src/test/ui/span/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.rs
index b280c8ab6e2b2..94f578af209a8 100644
--- a/src/test/ui/span/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.rs
+++ b/src/test/ui/span/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.rs
@@ -12,7 +12,8 @@ impl A {
 
 trait C{async fn new(val: T) {} //~ ERROR  `async fn` is not permitted in Rust 2015
 //~^ ERROR functions in traits cannot be declared `async`
-//~^^ ERROR cannot find type `T` in this scope
-//~^^^ WARN changes to closure capture in Rust 2021 will affect drop order [rust_2021_incompatible_closure_captures]
+//~| ERROR mismatched types
+//~| ERROR cannot find type `T` in this scope
+//~| WARN changes to closure capture in Rust 2021 will affect drop order [rust_2021_incompatible_closure_captures]
 
 //~ ERROR  this file contains an unclosed delimiter
diff --git a/src/test/ui/span/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.stderr b/src/test/ui/span/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.stderr
index 50de2322907ed..3814c568e72c1 100644
--- a/src/test/ui/span/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.stderr
+++ b/src/test/ui/span/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.stderr
@@ -1,5 +1,5 @@
 error: this file contains an unclosed delimiter
-  --> $DIR/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.rs:18:53
+  --> $DIR/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.rs:19:53
    |
 LL | trait C{async fn new(val: T) {}
    |        - unclosed delimiter
@@ -25,17 +25,6 @@ LL | trait C{async fn new(val: T) {}
    = help: pass `--edition 2021` to `rustc`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
-error[E0706]: functions in traits cannot be declared `async`
-  --> $DIR/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.rs:13:9
-   |
-LL | trait C{async fn new(val: T) {}
-   |         -----^^^^^^^^^^^^^^^^^^
-   |         |
-   |         `async` because of this
-   |
-   = note: `async` trait functions are not currently supported
-   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
-
 error[E0423]: expected function, found module `crate`
   --> $DIR/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.rs:9:5
    |
@@ -51,6 +40,19 @@ LL | pub struct A {}
 LL | trait C{async fn new(val: T) {}
    |                           ^ help: a struct with a similar name exists: `A`
 
+error[E0706]: functions in traits cannot be declared `async`
+  --> $DIR/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.rs:13:9
+   |
+LL | trait C{async fn new(val: T) {}
+   |         -----^^^^^^^^^^^^^^^
+   |         |
+   |         `async` because of this
+   |
+   = note: `async` trait functions are not currently supported
+   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable
+
 warning: changes to closure capture in Rust 2021 will affect drop order
   --> $DIR/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.rs:6:57
    |
@@ -72,6 +74,20 @@ help: add a dummy let to cause `path` to be fully captured
 LL |     async fn create(path: impl AsRef<std::path::Path>)  { let _ = &path;
    |                                                           ++++++++++++++
 
+error[E0308]: mismatched types
+  --> $DIR/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.rs:13:30
+   |
+LL | trait C{async fn new(val: T) {}
+   |                              ^^ expected associated type, found opaque type
+   |
+  ::: $SRC_DIR/core/src/future/mod.rs:LL:COL
+   |
+LL | pub const fn from_generator<T>(gen: T) -> impl Future<Output = T::Return>
+   |                                           ------------------------------- the found opaque type
+   |
+   = note: expected associated type `impl Future<Output = ()>` (trait associated opaque type at <$DIR/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.rs:13:30>)
+                  found opaque type `impl Future<Output = ()>` (opaque type at <$SRC_DIR/core/src/future/mod.rs:LL:COL>)
+
 warning: changes to closure capture in Rust 2021 will affect drop order
   --> $DIR/drop-location-span-error-rust-2021-incompatible-closure-captures-93117.rs:13:30
    |
@@ -87,7 +103,7 @@ help: add a dummy let to cause `val` to be fully captured
 LL | trait C{async fn new(val: T) { let _ = &val;}
    |                                +++++++++++++
 
-error: aborting due to 6 previous errors; 2 warnings emitted
+error: aborting due to 7 previous errors; 2 warnings emitted
 
-Some errors have detailed explanations: E0412, E0423, E0670, E0706.
-For more information about an error, try `rustc --explain E0412`.
+Some errors have detailed explanations: E0308, E0412, E0423, E0670, E0706.
+For more information about an error, try `rustc --explain E0308`.
diff --git a/src/test/ui/type-alias-impl-trait/constrain_inputs.rs b/src/test/ui/type-alias-impl-trait/constrain_inputs.rs
index c32174288ee68..03fb64b7b94d7 100644
--- a/src/test/ui/type-alias-impl-trait/constrain_inputs.rs
+++ b/src/test/ui/type-alias-impl-trait/constrain_inputs.rs
@@ -1,17 +1,33 @@
-// check-pass
-
 #![feature(type_alias_impl_trait)]
 
-mod foo {
+mod lifetime_params {
     type Ty<'a> = impl Sized;
     fn defining(s: &str) -> Ty<'_> { s }
     fn execute(ty: Ty<'_>) -> &str { todo!() }
+    //~^ ERROR return type references an anonymous lifetime, which is not constrained by the fn input types
+
+    type BadFnSig = fn(Ty<'_>) -> &str;
+    //~^ ERROR return type references an anonymous lifetime, which is not constrained by the fn input types
+    type BadTraitRef = dyn Fn(Ty<'_>) -> &str;
+    //~^ ERROR binding for associated type `Output` references an anonymous lifetime
 }
 
-mod bar {
+mod lifetime_params_2 {
     type Ty<'a> = impl FnOnce() -> &'a str;
     fn defining(s: &str) -> Ty<'_> { move || s }
     fn execute(ty: Ty<'_>) -> &str { ty() }
+    //~^ ERROR return type references an anonymous lifetime, which is not constrained by the fn input types
+}
+
+// regression test for https://github.com/rust-lang/rust/issues/97104
+mod type_params {
+    type Ty<T> = impl Sized;
+    fn define<T>(s: T) -> Ty<T> { s }
+
+    type BadFnSig = fn(Ty<&str>) -> &str;
+    //~^ ERROR return type references an anonymous lifetime, which is not constrained by the fn input types
+    type BadTraitRef = dyn Fn(Ty<&str>) -> &str;
+    //~^ ERROR binding for associated type `Output` references an anonymous lifetime
 }
 
 fn main() {}
diff --git a/src/test/ui/type-alias-impl-trait/constrain_inputs.stderr b/src/test/ui/type-alias-impl-trait/constrain_inputs.stderr
new file mode 100644
index 0000000000000..93953fd06d1fd
--- /dev/null
+++ b/src/test/ui/type-alias-impl-trait/constrain_inputs.stderr
@@ -0,0 +1,58 @@
+error[E0581]: return type references an anonymous lifetime, which is not constrained by the fn input types
+  --> $DIR/constrain_inputs.rs:6:31
+   |
+LL |     fn execute(ty: Ty<'_>) -> &str { todo!() }
+   |                               ^^^^
+   |
+   = note: lifetimes appearing in an associated or opaque type are not considered constrained
+   = note: consider introducing a named lifetime parameter
+
+error[E0581]: return type references an anonymous lifetime, which is not constrained by the fn input types
+  --> $DIR/constrain_inputs.rs:9:35
+   |
+LL |     type BadFnSig = fn(Ty<'_>) -> &str;
+   |                                   ^^^^
+   |
+   = note: lifetimes appearing in an associated or opaque type are not considered constrained
+   = note: consider introducing a named lifetime parameter
+
+error[E0582]: binding for associated type `Output` references an anonymous lifetime, which does not appear in the trait input types
+  --> $DIR/constrain_inputs.rs:11:42
+   |
+LL |     type BadTraitRef = dyn Fn(Ty<'_>) -> &str;
+   |                                          ^^^^
+   |
+   = note: lifetimes appearing in an associated or opaque type are not considered constrained
+   = note: consider introducing a named lifetime parameter
+
+error[E0581]: return type references an anonymous lifetime, which is not constrained by the fn input types
+  --> $DIR/constrain_inputs.rs:18:31
+   |
+LL |     fn execute(ty: Ty<'_>) -> &str { ty() }
+   |                               ^^^^
+   |
+   = note: lifetimes appearing in an associated or opaque type are not considered constrained
+   = note: consider introducing a named lifetime parameter
+
+error[E0581]: return type references an anonymous lifetime, which is not constrained by the fn input types
+  --> $DIR/constrain_inputs.rs:27:37
+   |
+LL |     type BadFnSig = fn(Ty<&str>) -> &str;
+   |                                     ^^^^
+   |
+   = note: lifetimes appearing in an associated or opaque type are not considered constrained
+   = note: consider introducing a named lifetime parameter
+
+error[E0582]: binding for associated type `Output` references an anonymous lifetime, which does not appear in the trait input types
+  --> $DIR/constrain_inputs.rs:29:44
+   |
+LL |     type BadTraitRef = dyn Fn(Ty<&str>) -> &str;
+   |                                            ^^^^
+   |
+   = note: lifetimes appearing in an associated or opaque type are not considered constrained
+   = note: consider introducing a named lifetime parameter
+
+error: aborting due to 6 previous errors
+
+Some errors have detailed explanations: E0581, E0582.
+For more information about an error, try `rustc --explain E0581`.
diff --git a/src/test/ui/type-alias-impl-trait/constrain_inputs_unsound.rs b/src/test/ui/type-alias-impl-trait/constrain_inputs_unsound.rs
new file mode 100644
index 0000000000000..3bae0f1730994
--- /dev/null
+++ b/src/test/ui/type-alias-impl-trait/constrain_inputs_unsound.rs
@@ -0,0 +1,31 @@
+#![feature(type_alias_impl_trait)]
+
+trait Static: 'static {}
+impl Static for () {}
+
+type Gal<T> = impl Static;
+fn _defining<T>() -> Gal<T> {}
+
+trait Callable<Arg> { type Output; }
+
+/// We can infer `<C as Callable<Arg>>::Output: 'static`,
+/// because we know `C: 'static` and `Arg: 'static`,
+fn box_str<C, Arg>(s: C::Output) -> Box<dyn AsRef<str> + 'static>
+where
+    Arg: Static,
+    C: ?Sized + Callable<Arg> + 'static,
+    C::Output: AsRef<str>,
+{
+    Box::new(s)
+}
+
+fn extend_lifetime(s: &str) -> Box<dyn AsRef<str> + 'static> {
+    type MalformedTy = dyn for<'a> Callable<Gal<&'a ()>, Output = &'a str>;
+    //~^ ERROR binding for associated type `Output` references lifetime `'a`
+    box_str::<MalformedTy, _>(s)
+}
+
+fn main() {
+    let extended = extend_lifetime(&String::from("hello"));
+    println!("{}", extended.as_ref().as_ref());
+}
diff --git a/src/test/ui/type-alias-impl-trait/constrain_inputs_unsound.stderr b/src/test/ui/type-alias-impl-trait/constrain_inputs_unsound.stderr
new file mode 100644
index 0000000000000..d5fc46cb1f596
--- /dev/null
+++ b/src/test/ui/type-alias-impl-trait/constrain_inputs_unsound.stderr
@@ -0,0 +1,9 @@
+error[E0582]: binding for associated type `Output` references lifetime `'a`, which does not appear in the trait input types
+  --> $DIR/constrain_inputs_unsound.rs:23:58
+   |
+LL |     type MalformedTy = dyn for<'a> Callable<Gal<&'a ()>, Output = &'a str>;
+   |                                                          ^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0582`.
diff --git a/src/tools/clippy/clippy_dev/src/new_lint.rs b/src/tools/clippy/clippy_dev/src/new_lint.rs
index be05e67d724df..331b76484b8a5 100644
--- a/src/tools/clippy/clippy_dev/src/new_lint.rs
+++ b/src/tools/clippy/clippy_dev/src/new_lint.rs
@@ -120,15 +120,17 @@ fn add_lint(lint: &LintData<'_>, enable_msrv: bool) -> io::Result<()> {
 
     let new_lint = if enable_msrv {
         format!(
-            "store.register_{lint_pass}_pass(move || Box::new({module_name}::{camel_name}::new(msrv)));\n    ",
+            "store.register_{lint_pass}_pass(move |{ctor_arg}| Box::new({module_name}::{camel_name}::new(msrv)));\n    ",
             lint_pass = lint.pass,
+            ctor_arg = if lint.pass == "late" { "_" } else { "" },
             module_name = lint.name,
             camel_name = to_camel_case(lint.name),
         )
     } else {
         format!(
-            "store.register_{lint_pass}_pass(|| Box::new({module_name}::{camel_name}));\n    ",
+            "store.register_{lint_pass}_pass(|{ctor_arg}| Box::new({module_name}::{camel_name}));\n    ",
             lint_pass = lint.pass,
+            ctor_arg = if lint.pass == "late" { "_" } else { "" },
             module_name = lint.name,
             camel_name = to_camel_case(lint.name),
         )
diff --git a/src/tools/clippy/clippy_lints/src/lib.rs b/src/tools/clippy/clippy_lints/src/lib.rs
index dfdaf90f09f48..c70aa79ac8dcf 100644
--- a/src/tools/clippy/clippy_lints/src/lib.rs
+++ b/src/tools/clippy/clippy_lints/src/lib.rs
@@ -523,7 +523,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     #[cfg(feature = "internal")]
     {
         if std::env::var("ENABLE_METADATA_COLLECTION").eq(&Ok("1".to_string())) {
-            store.register_late_pass(|| Box::new(utils::internal_lints::metadata_collector::MetadataCollector::new()));
+            store.register_late_pass(|_| Box::new(utils::internal_lints::metadata_collector::MetadataCollector::new()));
             return;
         }
     }
@@ -533,69 +533,69 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     {
         store.register_early_pass(|| Box::new(utils::internal_lints::ClippyLintsInternal));
         store.register_early_pass(|| Box::new(utils::internal_lints::ProduceIce));
-        store.register_late_pass(|| Box::new(utils::internal_lints::CollapsibleCalls));
-        store.register_late_pass(|| Box::new(utils::internal_lints::CompilerLintFunctions::new()));
-        store.register_late_pass(|| Box::new(utils::internal_lints::IfChainStyle));
-        store.register_late_pass(|| Box::new(utils::internal_lints::InvalidPaths));
-        store.register_late_pass(|| Box::new(utils::internal_lints::InterningDefinedSymbol::default()));
-        store.register_late_pass(|| Box::new(utils::internal_lints::LintWithoutLintPass::default()));
-        store.register_late_pass(|| Box::new(utils::internal_lints::MatchTypeOnDiagItem));
-        store.register_late_pass(|| Box::new(utils::internal_lints::OuterExpnDataPass));
-        store.register_late_pass(|| Box::new(utils::internal_lints::MsrvAttrImpl));
+        store.register_late_pass(|_| Box::new(utils::internal_lints::CollapsibleCalls));
+        store.register_late_pass(|_| Box::new(utils::internal_lints::CompilerLintFunctions::new()));
+        store.register_late_pass(|_| Box::new(utils::internal_lints::IfChainStyle));
+        store.register_late_pass(|_| Box::new(utils::internal_lints::InvalidPaths));
+        store.register_late_pass(|_| Box::new(utils::internal_lints::InterningDefinedSymbol::default()));
+        store.register_late_pass(|_| Box::new(utils::internal_lints::LintWithoutLintPass::default()));
+        store.register_late_pass(|_| Box::new(utils::internal_lints::MatchTypeOnDiagItem));
+        store.register_late_pass(|_| Box::new(utils::internal_lints::OuterExpnDataPass));
+        store.register_late_pass(|_| Box::new(utils::internal_lints::MsrvAttrImpl));
     }
 
     let arithmetic_allowed = conf.arithmetic_allowed.clone();
-    store.register_late_pass(move || Box::new(operators::arithmetic::Arithmetic::new(arithmetic_allowed.clone())));
-    store.register_late_pass(|| Box::new(utils::dump_hir::DumpHir));
-    store.register_late_pass(|| Box::new(utils::author::Author));
+    store.register_late_pass(move |_| Box::new(operators::arithmetic::Arithmetic::new(arithmetic_allowed.clone())));
+    store.register_late_pass(|_| Box::new(utils::dump_hir::DumpHir));
+    store.register_late_pass(|_| Box::new(utils::author::Author));
     let await_holding_invalid_types = conf.await_holding_invalid_types.clone();
-    store.register_late_pass(move || {
+    store.register_late_pass(move |_| {
         Box::new(await_holding_invalid::AwaitHolding::new(
             await_holding_invalid_types.clone(),
         ))
     });
-    store.register_late_pass(|| Box::new(serde_api::SerdeApi));
+    store.register_late_pass(|_| Box::new(serde_api::SerdeApi));
     let vec_box_size_threshold = conf.vec_box_size_threshold;
     let type_complexity_threshold = conf.type_complexity_threshold;
     let avoid_breaking_exported_api = conf.avoid_breaking_exported_api;
-    store.register_late_pass(move || {
+    store.register_late_pass(move |_| {
         Box::new(types::Types::new(
             vec_box_size_threshold,
             type_complexity_threshold,
             avoid_breaking_exported_api,
         ))
     });
-    store.register_late_pass(|| Box::new(booleans::NonminimalBool));
-    store.register_late_pass(|| Box::new(enum_clike::UnportableVariant));
-    store.register_late_pass(|| Box::new(float_literal::FloatLiteral));
-    store.register_late_pass(|| Box::new(ptr::Ptr));
-    store.register_late_pass(|| Box::new(needless_bool::NeedlessBool));
-    store.register_late_pass(|| Box::new(needless_bool::BoolComparison));
-    store.register_late_pass(|| Box::new(needless_for_each::NeedlessForEach));
-    store.register_late_pass(|| Box::new(misc::MiscLints));
-    store.register_late_pass(|| Box::new(eta_reduction::EtaReduction));
-    store.register_late_pass(|| Box::new(mut_mut::MutMut));
-    store.register_late_pass(|| Box::new(mut_reference::UnnecessaryMutPassed));
-    store.register_late_pass(|| Box::new(len_zero::LenZero));
-    store.register_late_pass(|| Box::new(attrs::Attributes));
-    store.register_late_pass(|| Box::new(blocks_in_if_conditions::BlocksInIfConditions));
-    store.register_late_pass(|| Box::new(unicode::Unicode));
-    store.register_late_pass(|| Box::new(uninit_vec::UninitVec));
-    store.register_late_pass(|| Box::new(unit_return_expecting_ord::UnitReturnExpectingOrd));
-    store.register_late_pass(|| Box::new(strings::StringAdd));
-    store.register_late_pass(|| Box::new(implicit_return::ImplicitReturn));
-    store.register_late_pass(|| Box::new(implicit_saturating_sub::ImplicitSaturatingSub));
-    store.register_late_pass(|| Box::new(default_numeric_fallback::DefaultNumericFallback));
-    store.register_late_pass(|| Box::new(inconsistent_struct_constructor::InconsistentStructConstructor));
-    store.register_late_pass(|| Box::new(non_octal_unix_permissions::NonOctalUnixPermissions));
+    store.register_late_pass(|_| Box::new(booleans::NonminimalBool));
+    store.register_late_pass(|_| Box::new(enum_clike::UnportableVariant));
+    store.register_late_pass(|_| Box::new(float_literal::FloatLiteral));
+    store.register_late_pass(|_| Box::new(ptr::Ptr));
+    store.register_late_pass(|_| Box::new(needless_bool::NeedlessBool));
+    store.register_late_pass(|_| Box::new(needless_bool::BoolComparison));
+    store.register_late_pass(|_| Box::new(needless_for_each::NeedlessForEach));
+    store.register_late_pass(|_| Box::new(misc::MiscLints));
+    store.register_late_pass(|_| Box::new(eta_reduction::EtaReduction));
+    store.register_late_pass(|_| Box::new(mut_mut::MutMut));
+    store.register_late_pass(|_| Box::new(mut_reference::UnnecessaryMutPassed));
+    store.register_late_pass(|_| Box::new(len_zero::LenZero));
+    store.register_late_pass(|_| Box::new(attrs::Attributes));
+    store.register_late_pass(|_| Box::new(blocks_in_if_conditions::BlocksInIfConditions));
+    store.register_late_pass(|_| Box::new(unicode::Unicode));
+    store.register_late_pass(|_| Box::new(uninit_vec::UninitVec));
+    store.register_late_pass(|_| Box::new(unit_return_expecting_ord::UnitReturnExpectingOrd));
+    store.register_late_pass(|_| Box::new(strings::StringAdd));
+    store.register_late_pass(|_| Box::new(implicit_return::ImplicitReturn));
+    store.register_late_pass(|_| Box::new(implicit_saturating_sub::ImplicitSaturatingSub));
+    store.register_late_pass(|_| Box::new(default_numeric_fallback::DefaultNumericFallback));
+    store.register_late_pass(|_| Box::new(inconsistent_struct_constructor::InconsistentStructConstructor));
+    store.register_late_pass(|_| Box::new(non_octal_unix_permissions::NonOctalUnixPermissions));
     store.register_early_pass(|| Box::new(unnecessary_self_imports::UnnecessarySelfImports));
 
     let msrv = read_msrv(conf, sess);
     let avoid_breaking_exported_api = conf.avoid_breaking_exported_api;
     let allow_expect_in_tests = conf.allow_expect_in_tests;
     let allow_unwrap_in_tests = conf.allow_unwrap_in_tests;
-    store.register_late_pass(move || Box::new(approx_const::ApproxConstant::new(msrv)));
-    store.register_late_pass(move || {
+    store.register_late_pass(move |_| Box::new(approx_const::ApproxConstant::new(msrv)));
+    store.register_late_pass(move |_| {
         Box::new(methods::Methods::new(
             avoid_breaking_exported_api,
             msrv,
@@ -603,74 +603,74 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
             allow_unwrap_in_tests,
         ))
     });
-    store.register_late_pass(move || Box::new(matches::Matches::new(msrv)));
+    store.register_late_pass(move |_| Box::new(matches::Matches::new(msrv)));
     store.register_early_pass(move || Box::new(manual_non_exhaustive::ManualNonExhaustiveStruct::new(msrv)));
-    store.register_late_pass(move || Box::new(manual_non_exhaustive::ManualNonExhaustiveEnum::new(msrv)));
-    store.register_late_pass(move || Box::new(manual_strip::ManualStrip::new(msrv)));
+    store.register_late_pass(move |_| Box::new(manual_non_exhaustive::ManualNonExhaustiveEnum::new(msrv)));
+    store.register_late_pass(move |_| Box::new(manual_strip::ManualStrip::new(msrv)));
     store.register_early_pass(move || Box::new(redundant_static_lifetimes::RedundantStaticLifetimes::new(msrv)));
     store.register_early_pass(move || Box::new(redundant_field_names::RedundantFieldNames::new(msrv)));
-    store.register_late_pass(move || Box::new(checked_conversions::CheckedConversions::new(msrv)));
-    store.register_late_pass(move || Box::new(mem_replace::MemReplace::new(msrv)));
-    store.register_late_pass(move || Box::new(ranges::Ranges::new(msrv)));
-    store.register_late_pass(move || Box::new(from_over_into::FromOverInto::new(msrv)));
-    store.register_late_pass(move || Box::new(use_self::UseSelf::new(msrv)));
-    store.register_late_pass(move || Box::new(missing_const_for_fn::MissingConstForFn::new(msrv)));
-    store.register_late_pass(move || Box::new(needless_question_mark::NeedlessQuestionMark));
-    store.register_late_pass(move || Box::new(casts::Casts::new(msrv)));
+    store.register_late_pass(move |_| Box::new(checked_conversions::CheckedConversions::new(msrv)));
+    store.register_late_pass(move |_| Box::new(mem_replace::MemReplace::new(msrv)));
+    store.register_late_pass(move |_| Box::new(ranges::Ranges::new(msrv)));
+    store.register_late_pass(move |_| Box::new(from_over_into::FromOverInto::new(msrv)));
+    store.register_late_pass(move |_| Box::new(use_self::UseSelf::new(msrv)));
+    store.register_late_pass(move |_| Box::new(missing_const_for_fn::MissingConstForFn::new(msrv)));
+    store.register_late_pass(move |_| Box::new(needless_question_mark::NeedlessQuestionMark));
+    store.register_late_pass(move |_| Box::new(casts::Casts::new(msrv)));
     store.register_early_pass(move || Box::new(unnested_or_patterns::UnnestedOrPatterns::new(msrv)));
-    store.register_late_pass(|| Box::new(size_of_in_element_count::SizeOfInElementCount));
-    store.register_late_pass(|| Box::new(same_name_method::SameNameMethod));
+    store.register_late_pass(|_| Box::new(size_of_in_element_count::SizeOfInElementCount));
+    store.register_late_pass(|_| Box::new(same_name_method::SameNameMethod));
     let max_suggested_slice_pattern_length = conf.max_suggested_slice_pattern_length;
-    store.register_late_pass(move || {
+    store.register_late_pass(move |_| {
         Box::new(index_refutable_slice::IndexRefutableSlice::new(
             max_suggested_slice_pattern_length,
             msrv,
         ))
     });
-    store.register_late_pass(|| Box::new(shadow::Shadow::default()));
-    store.register_late_pass(|| Box::new(unit_types::UnitTypes));
-    store.register_late_pass(|| Box::new(loops::Loops));
-    store.register_late_pass(|| Box::new(main_recursion::MainRecursion::default()));
-    store.register_late_pass(|| Box::new(lifetimes::Lifetimes));
-    store.register_late_pass(|| Box::new(entry::HashMapPass));
-    store.register_late_pass(|| Box::new(minmax::MinMaxPass));
-    store.register_late_pass(|| Box::new(zero_div_zero::ZeroDiv));
-    store.register_late_pass(|| Box::new(mutex_atomic::Mutex));
-    store.register_late_pass(|| Box::new(needless_update::NeedlessUpdate));
-    store.register_late_pass(|| Box::new(needless_borrowed_ref::NeedlessBorrowedRef));
-    store.register_late_pass(|| Box::new(borrow_deref_ref::BorrowDerefRef));
-    store.register_late_pass(|| Box::new(no_effect::NoEffect));
-    store.register_late_pass(|| Box::new(temporary_assignment::TemporaryAssignment));
-    store.register_late_pass(move || Box::new(transmute::Transmute::new(msrv)));
+    store.register_late_pass(|_| Box::new(shadow::Shadow::default()));
+    store.register_late_pass(|_| Box::new(unit_types::UnitTypes));
+    store.register_late_pass(|_| Box::new(loops::Loops));
+    store.register_late_pass(|_| Box::new(main_recursion::MainRecursion::default()));
+    store.register_late_pass(|_| Box::new(lifetimes::Lifetimes));
+    store.register_late_pass(|_| Box::new(entry::HashMapPass));
+    store.register_late_pass(|_| Box::new(minmax::MinMaxPass));
+    store.register_late_pass(|_| Box::new(zero_div_zero::ZeroDiv));
+    store.register_late_pass(|_| Box::new(mutex_atomic::Mutex));
+    store.register_late_pass(|_| Box::new(needless_update::NeedlessUpdate));
+    store.register_late_pass(|_| Box::new(needless_borrowed_ref::NeedlessBorrowedRef));
+    store.register_late_pass(|_| Box::new(borrow_deref_ref::BorrowDerefRef));
+    store.register_late_pass(|_| Box::new(no_effect::NoEffect));
+    store.register_late_pass(|_| Box::new(temporary_assignment::TemporaryAssignment));
+    store.register_late_pass(move |_| Box::new(transmute::Transmute::new(msrv)));
     let cognitive_complexity_threshold = conf.cognitive_complexity_threshold;
-    store.register_late_pass(move || {
+    store.register_late_pass(move |_| {
         Box::new(cognitive_complexity::CognitiveComplexity::new(
             cognitive_complexity_threshold,
         ))
     });
     let too_large_for_stack = conf.too_large_for_stack;
-    store.register_late_pass(move || Box::new(escape::BoxedLocal { too_large_for_stack }));
-    store.register_late_pass(move || Box::new(vec::UselessVec { too_large_for_stack }));
-    store.register_late_pass(|| Box::new(panic_unimplemented::PanicUnimplemented));
-    store.register_late_pass(|| Box::new(strings::StringLitAsBytes));
-    store.register_late_pass(|| Box::new(derive::Derive));
-    store.register_late_pass(|| Box::new(derivable_impls::DerivableImpls));
-    store.register_late_pass(|| Box::new(drop_forget_ref::DropForgetRef));
-    store.register_late_pass(|| Box::new(empty_enum::EmptyEnum));
-    store.register_late_pass(|| Box::new(invalid_upcast_comparisons::InvalidUpcastComparisons));
-    store.register_late_pass(|| Box::new(regex::Regex));
-    store.register_late_pass(|| Box::new(copies::CopyAndPaste));
-    store.register_late_pass(|| Box::new(copy_iterator::CopyIterator));
-    store.register_late_pass(|| Box::new(format::UselessFormat));
-    store.register_late_pass(|| Box::new(swap::Swap));
-    store.register_late_pass(|| Box::new(overflow_check_conditional::OverflowCheckConditional));
-    store.register_late_pass(|| Box::new(new_without_default::NewWithoutDefault::default()));
+    store.register_late_pass(move |_| Box::new(escape::BoxedLocal { too_large_for_stack }));
+    store.register_late_pass(move |_| Box::new(vec::UselessVec { too_large_for_stack }));
+    store.register_late_pass(|_| Box::new(panic_unimplemented::PanicUnimplemented));
+    store.register_late_pass(|_| Box::new(strings::StringLitAsBytes));
+    store.register_late_pass(|_| Box::new(derive::Derive));
+    store.register_late_pass(|_| Box::new(derivable_impls::DerivableImpls));
+    store.register_late_pass(|_| Box::new(drop_forget_ref::DropForgetRef));
+    store.register_late_pass(|_| Box::new(empty_enum::EmptyEnum));
+    store.register_late_pass(|_| Box::new(invalid_upcast_comparisons::InvalidUpcastComparisons));
+    store.register_late_pass(|_| Box::new(regex::Regex));
+    store.register_late_pass(|_| Box::new(copies::CopyAndPaste));
+    store.register_late_pass(|_| Box::new(copy_iterator::CopyIterator));
+    store.register_late_pass(|_| Box::new(format::UselessFormat));
+    store.register_late_pass(|_| Box::new(swap::Swap));
+    store.register_late_pass(|_| Box::new(overflow_check_conditional::OverflowCheckConditional));
+    store.register_late_pass(|_| Box::new(new_without_default::NewWithoutDefault::default()));
     let disallowed_names = conf.disallowed_names.iter().cloned().collect::<FxHashSet<_>>();
-    store.register_late_pass(move || Box::new(disallowed_names::DisallowedNames::new(disallowed_names.clone())));
+    store.register_late_pass(move |_| Box::new(disallowed_names::DisallowedNames::new(disallowed_names.clone())));
     let too_many_arguments_threshold = conf.too_many_arguments_threshold;
     let too_many_lines_threshold = conf.too_many_lines_threshold;
     let large_error_threshold = conf.large_error_threshold;
-    store.register_late_pass(move || {
+    store.register_late_pass(move |_| {
         Box::new(functions::Functions::new(
             too_many_arguments_threshold,
             too_many_lines_threshold,
@@ -678,73 +678,73 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         ))
     });
     let doc_valid_idents = conf.doc_valid_idents.iter().cloned().collect::<FxHashSet<_>>();
-    store.register_late_pass(move || Box::new(doc::DocMarkdown::new(doc_valid_idents.clone())));
-    store.register_late_pass(|| Box::new(neg_multiply::NegMultiply));
-    store.register_late_pass(|| Box::new(mem_forget::MemForget));
-    store.register_late_pass(|| Box::new(let_if_seq::LetIfSeq));
-    store.register_late_pass(|| Box::new(mixed_read_write_in_expression::EvalOrderDependence));
-    store.register_late_pass(|| Box::new(missing_doc::MissingDoc::new()));
-    store.register_late_pass(|| Box::new(missing_inline::MissingInline));
-    store.register_late_pass(move || Box::new(exhaustive_items::ExhaustiveItems));
-    store.register_late_pass(|| Box::new(match_result_ok::MatchResultOk));
-    store.register_late_pass(|| Box::new(partialeq_ne_impl::PartialEqNeImpl));
-    store.register_late_pass(|| Box::new(unused_io_amount::UnusedIoAmount));
+    store.register_late_pass(move |_| Box::new(doc::DocMarkdown::new(doc_valid_idents.clone())));
+    store.register_late_pass(|_| Box::new(neg_multiply::NegMultiply));
+    store.register_late_pass(|_| Box::new(mem_forget::MemForget));
+    store.register_late_pass(|_| Box::new(let_if_seq::LetIfSeq));
+    store.register_late_pass(|_| Box::new(mixed_read_write_in_expression::EvalOrderDependence));
+    store.register_late_pass(|_| Box::new(missing_doc::MissingDoc::new()));
+    store.register_late_pass(|_| Box::new(missing_inline::MissingInline));
+    store.register_late_pass(move |_| Box::new(exhaustive_items::ExhaustiveItems));
+    store.register_late_pass(|_| Box::new(match_result_ok::MatchResultOk));
+    store.register_late_pass(|_| Box::new(partialeq_ne_impl::PartialEqNeImpl));
+    store.register_late_pass(|_| Box::new(unused_io_amount::UnusedIoAmount));
     let enum_variant_size_threshold = conf.enum_variant_size_threshold;
-    store.register_late_pass(move || Box::new(large_enum_variant::LargeEnumVariant::new(enum_variant_size_threshold)));
-    store.register_late_pass(|| Box::new(explicit_write::ExplicitWrite));
-    store.register_late_pass(|| Box::new(needless_pass_by_value::NeedlessPassByValue));
+    store.register_late_pass(move |_| Box::new(large_enum_variant::LargeEnumVariant::new(enum_variant_size_threshold)));
+    store.register_late_pass(|_| Box::new(explicit_write::ExplicitWrite));
+    store.register_late_pass(|_| Box::new(needless_pass_by_value::NeedlessPassByValue));
     let pass_by_ref_or_value = pass_by_ref_or_value::PassByRefOrValue::new(
         conf.trivial_copy_size_limit,
         conf.pass_by_value_size_limit,
         conf.avoid_breaking_exported_api,
         &sess.target,
     );
-    store.register_late_pass(move || Box::new(pass_by_ref_or_value));
-    store.register_late_pass(|| Box::new(ref_option_ref::RefOptionRef));
-    store.register_late_pass(|| Box::new(infinite_iter::InfiniteIter));
-    store.register_late_pass(|| Box::new(inline_fn_without_body::InlineFnWithoutBody));
-    store.register_late_pass(|| Box::new(useless_conversion::UselessConversion::default()));
-    store.register_late_pass(|| Box::new(implicit_hasher::ImplicitHasher));
-    store.register_late_pass(|| Box::new(fallible_impl_from::FallibleImplFrom));
-    store.register_late_pass(|| Box::new(question_mark::QuestionMark));
+    store.register_late_pass(move |_| Box::new(pass_by_ref_or_value));
+    store.register_late_pass(|_| Box::new(ref_option_ref::RefOptionRef));
+    store.register_late_pass(|_| Box::new(infinite_iter::InfiniteIter));
+    store.register_late_pass(|_| Box::new(inline_fn_without_body::InlineFnWithoutBody));
+    store.register_late_pass(|_| Box::new(useless_conversion::UselessConversion::default()));
+    store.register_late_pass(|_| Box::new(implicit_hasher::ImplicitHasher));
+    store.register_late_pass(|_| Box::new(fallible_impl_from::FallibleImplFrom));
+    store.register_late_pass(|_| Box::new(question_mark::QuestionMark));
     store.register_early_pass(|| Box::new(suspicious_operation_groupings::SuspiciousOperationGroupings));
-    store.register_late_pass(|| Box::new(suspicious_trait_impl::SuspiciousImpl));
-    store.register_late_pass(|| Box::new(map_unit_fn::MapUnit));
-    store.register_late_pass(|| Box::new(inherent_impl::MultipleInherentImpl));
-    store.register_late_pass(|| Box::new(neg_cmp_op_on_partial_ord::NoNegCompOpForPartialOrd));
-    store.register_late_pass(|| Box::new(unwrap::Unwrap));
-    store.register_late_pass(|| Box::new(indexing_slicing::IndexingSlicing));
-    store.register_late_pass(|| Box::new(non_copy_const::NonCopyConst));
-    store.register_late_pass(|| Box::new(ptr_offset_with_cast::PtrOffsetWithCast));
-    store.register_late_pass(|| Box::new(redundant_clone::RedundantClone));
-    store.register_late_pass(|| Box::new(slow_vector_initialization::SlowVectorInit));
-    store.register_late_pass(move || Box::new(unnecessary_wraps::UnnecessaryWraps::new(avoid_breaking_exported_api)));
-    store.register_late_pass(|| Box::new(assertions_on_constants::AssertionsOnConstants));
-    store.register_late_pass(|| Box::new(assertions_on_result_states::AssertionsOnResultStates));
-    store.register_late_pass(|| Box::new(inherent_to_string::InherentToString));
+    store.register_late_pass(|_| Box::new(suspicious_trait_impl::SuspiciousImpl));
+    store.register_late_pass(|_| Box::new(map_unit_fn::MapUnit));
+    store.register_late_pass(|_| Box::new(inherent_impl::MultipleInherentImpl));
+    store.register_late_pass(|_| Box::new(neg_cmp_op_on_partial_ord::NoNegCompOpForPartialOrd));
+    store.register_late_pass(|_| Box::new(unwrap::Unwrap));
+    store.register_late_pass(|_| Box::new(indexing_slicing::IndexingSlicing));
+    store.register_late_pass(|_| Box::new(non_copy_const::NonCopyConst));
+    store.register_late_pass(|_| Box::new(ptr_offset_with_cast::PtrOffsetWithCast));
+    store.register_late_pass(|_| Box::new(redundant_clone::RedundantClone));
+    store.register_late_pass(|_| Box::new(slow_vector_initialization::SlowVectorInit));
+    store.register_late_pass(move |_| Box::new(unnecessary_wraps::UnnecessaryWraps::new(avoid_breaking_exported_api)));
+    store.register_late_pass(|_| Box::new(assertions_on_constants::AssertionsOnConstants));
+    store.register_late_pass(|_| Box::new(assertions_on_result_states::AssertionsOnResultStates));
+    store.register_late_pass(|_| Box::new(inherent_to_string::InherentToString));
     let max_trait_bounds = conf.max_trait_bounds;
-    store.register_late_pass(move || Box::new(trait_bounds::TraitBounds::new(max_trait_bounds)));
-    store.register_late_pass(|| Box::new(comparison_chain::ComparisonChain));
-    store.register_late_pass(|| Box::new(mut_key::MutableKeyType));
+    store.register_late_pass(move |_| Box::new(trait_bounds::TraitBounds::new(max_trait_bounds)));
+    store.register_late_pass(|_| Box::new(comparison_chain::ComparisonChain));
+    store.register_late_pass(|_| Box::new(mut_key::MutableKeyType));
     store.register_early_pass(|| Box::new(reference::DerefAddrOf));
     store.register_early_pass(|| Box::new(double_parens::DoubleParens));
-    store.register_late_pass(|| Box::new(format_impl::FormatImpl::new()));
+    store.register_late_pass(|_| Box::new(format_impl::FormatImpl::new()));
     store.register_early_pass(|| Box::new(unsafe_removed_from_name::UnsafeNameRemoval));
     store.register_early_pass(|| Box::new(else_if_without_else::ElseIfWithoutElse));
     store.register_early_pass(|| Box::new(int_plus_one::IntPlusOne));
     store.register_early_pass(|| Box::new(formatting::Formatting));
     store.register_early_pass(|| Box::new(misc_early::MiscEarlyLints));
     store.register_early_pass(|| Box::new(redundant_closure_call::RedundantClosureCall));
-    store.register_late_pass(|| Box::new(redundant_closure_call::RedundantClosureCall));
+    store.register_late_pass(|_| Box::new(redundant_closure_call::RedundantClosureCall));
     store.register_early_pass(|| Box::new(unused_unit::UnusedUnit));
-    store.register_late_pass(|| Box::new(returns::Return));
+    store.register_late_pass(|_| Box::new(returns::Return));
     store.register_early_pass(|| Box::new(collapsible_if::CollapsibleIf));
     store.register_early_pass(|| Box::new(items_after_statements::ItemsAfterStatements));
     store.register_early_pass(|| Box::new(precedence::Precedence));
-    store.register_late_pass(|| Box::new(needless_parens_on_range_literals::NeedlessParensOnRangeLiterals));
+    store.register_late_pass(|_| Box::new(needless_parens_on_range_literals::NeedlessParensOnRangeLiterals));
     store.register_early_pass(|| Box::new(needless_continue::NeedlessContinue));
     store.register_early_pass(|| Box::new(redundant_else::RedundantElse));
-    store.register_late_pass(|| Box::new(create_dir::CreateDir));
+    store.register_late_pass(|_| Box::new(create_dir::CreateDir));
     store.register_early_pass(|| Box::new(needless_arbitrary_self_type::NeedlessArbitrarySelfType));
     let literal_representation_lint_fraction_readability = conf.unreadable_literal_lint_fractions;
     store.register_early_pass(move || {
@@ -759,7 +759,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         ))
     });
     let enum_variant_name_threshold = conf.enum_variant_name_threshold;
-    store.register_late_pass(move || {
+    store.register_late_pass(move |_| {
         Box::new(enum_variants::EnumVariantNames::new(
             enum_variant_name_threshold,
             avoid_breaking_exported_api,
@@ -767,23 +767,23 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     });
     store.register_early_pass(|| Box::new(tabs_in_doc_comments::TabsInDocComments));
     let upper_case_acronyms_aggressive = conf.upper_case_acronyms_aggressive;
-    store.register_late_pass(move || {
+    store.register_late_pass(move |_| {
         Box::new(upper_case_acronyms::UpperCaseAcronyms::new(
             avoid_breaking_exported_api,
             upper_case_acronyms_aggressive,
         ))
     });
-    store.register_late_pass(|| Box::new(default::Default::default()));
-    store.register_late_pass(move || Box::new(unused_self::UnusedSelf::new(avoid_breaking_exported_api)));
-    store.register_late_pass(|| Box::new(mutable_debug_assertion::DebugAssertWithMutCall));
-    store.register_late_pass(|| Box::new(exit::Exit));
-    store.register_late_pass(|| Box::new(to_digit_is_some::ToDigitIsSome));
+    store.register_late_pass(|_| Box::new(default::Default::default()));
+    store.register_late_pass(move |_| Box::new(unused_self::UnusedSelf::new(avoid_breaking_exported_api)));
+    store.register_late_pass(|_| Box::new(mutable_debug_assertion::DebugAssertWithMutCall));
+    store.register_late_pass(|_| Box::new(exit::Exit));
+    store.register_late_pass(|_| Box::new(to_digit_is_some::ToDigitIsSome));
     let array_size_threshold = conf.array_size_threshold;
-    store.register_late_pass(move || Box::new(large_stack_arrays::LargeStackArrays::new(array_size_threshold)));
-    store.register_late_pass(move || Box::new(large_const_arrays::LargeConstArrays::new(array_size_threshold)));
-    store.register_late_pass(|| Box::new(floating_point_arithmetic::FloatingPointArithmetic));
+    store.register_late_pass(move |_| Box::new(large_stack_arrays::LargeStackArrays::new(array_size_threshold)));
+    store.register_late_pass(move |_| Box::new(large_const_arrays::LargeConstArrays::new(array_size_threshold)));
+    store.register_late_pass(|_| Box::new(floating_point_arithmetic::FloatingPointArithmetic));
     store.register_early_pass(|| Box::new(as_conversions::AsConversions));
-    store.register_late_pass(|| Box::new(let_underscore::LetUnderscore));
+    store.register_late_pass(|_| Box::new(let_underscore::LetUnderscore));
     store.register_early_pass(|| Box::new(single_component_path_imports::SingleComponentPathImports));
     let max_fn_params_bools = conf.max_fn_params_bools;
     let max_struct_bools = conf.max_struct_bools;
@@ -795,17 +795,17 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     });
     store.register_early_pass(|| Box::new(option_env_unwrap::OptionEnvUnwrap));
     let warn_on_all_wildcard_imports = conf.warn_on_all_wildcard_imports;
-    store.register_late_pass(move || Box::new(wildcard_imports::WildcardImports::new(warn_on_all_wildcard_imports)));
-    store.register_late_pass(|| Box::new(redundant_pub_crate::RedundantPubCrate::default()));
-    store.register_late_pass(|| Box::new(unnamed_address::UnnamedAddress));
-    store.register_late_pass(move || Box::new(dereference::Dereferencing::new(msrv)));
-    store.register_late_pass(|| Box::new(option_if_let_else::OptionIfLetElse));
-    store.register_late_pass(|| Box::new(future_not_send::FutureNotSend));
-    store.register_late_pass(|| Box::new(if_let_mutex::IfLetMutex));
-    store.register_late_pass(|| Box::new(if_not_else::IfNotElse));
-    store.register_late_pass(|| Box::new(equatable_if_let::PatternEquality));
-    store.register_late_pass(|| Box::new(manual_async_fn::ManualAsyncFn));
-    store.register_late_pass(|| Box::new(panic_in_result_fn::PanicInResultFn));
+    store.register_late_pass(move |_| Box::new(wildcard_imports::WildcardImports::new(warn_on_all_wildcard_imports)));
+    store.register_late_pass(|_| Box::new(redundant_pub_crate::RedundantPubCrate::default()));
+    store.register_late_pass(|_| Box::new(unnamed_address::UnnamedAddress));
+    store.register_late_pass(move |_| Box::new(dereference::Dereferencing::new(msrv)));
+    store.register_late_pass(|_| Box::new(option_if_let_else::OptionIfLetElse));
+    store.register_late_pass(|_| Box::new(future_not_send::FutureNotSend));
+    store.register_late_pass(|_| Box::new(if_let_mutex::IfLetMutex));
+    store.register_late_pass(|_| Box::new(if_not_else::IfNotElse));
+    store.register_late_pass(|_| Box::new(equatable_if_let::PatternEquality));
+    store.register_late_pass(|_| Box::new(manual_async_fn::ManualAsyncFn));
+    store.register_late_pass(|_| Box::new(panic_in_result_fn::PanicInResultFn));
     let single_char_binding_names_threshold = conf.single_char_binding_names_threshold;
     store.register_early_pass(move || {
         Box::new(non_expressive_names::NonExpressiveNames {
@@ -814,92 +814,92 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     });
     let macro_matcher = conf.standard_macro_braces.iter().cloned().collect::<FxHashSet<_>>();
     store.register_early_pass(move || Box::new(nonstandard_macro_braces::MacroBraces::new(&macro_matcher)));
-    store.register_late_pass(|| Box::new(macro_use::MacroUseImports::default()));
-    store.register_late_pass(|| Box::new(pattern_type_mismatch::PatternTypeMismatch));
-    store.register_late_pass(|| Box::new(unwrap_in_result::UnwrapInResult));
-    store.register_late_pass(|| Box::new(semicolon_if_nothing_returned::SemicolonIfNothingReturned));
-    store.register_late_pass(|| Box::new(async_yields_async::AsyncYieldsAsync));
+    store.register_late_pass(|_| Box::new(macro_use::MacroUseImports::default()));
+    store.register_late_pass(|_| Box::new(pattern_type_mismatch::PatternTypeMismatch));
+    store.register_late_pass(|_| Box::new(unwrap_in_result::UnwrapInResult));
+    store.register_late_pass(|_| Box::new(semicolon_if_nothing_returned::SemicolonIfNothingReturned));
+    store.register_late_pass(|_| Box::new(async_yields_async::AsyncYieldsAsync));
     let disallowed_methods = conf.disallowed_methods.clone();
-    store.register_late_pass(move || Box::new(disallowed_methods::DisallowedMethods::new(disallowed_methods.clone())));
+    store.register_late_pass(move |_| Box::new(disallowed_methods::DisallowedMethods::new(disallowed_methods.clone())));
     store.register_early_pass(|| Box::new(asm_syntax::InlineAsmX86AttSyntax));
     store.register_early_pass(|| Box::new(asm_syntax::InlineAsmX86IntelSyntax));
-    store.register_late_pass(|| Box::new(empty_drop::EmptyDrop));
-    store.register_late_pass(|| Box::new(strings::StrToString));
-    store.register_late_pass(|| Box::new(strings::StringToString));
-    store.register_late_pass(|| Box::new(zero_sized_map_values::ZeroSizedMapValues));
-    store.register_late_pass(|| Box::new(vec_init_then_push::VecInitThenPush::default()));
-    store.register_late_pass(|| Box::new(redundant_slicing::RedundantSlicing));
-    store.register_late_pass(|| Box::new(from_str_radix_10::FromStrRadix10));
-    store.register_late_pass(move || Box::new(if_then_some_else_none::IfThenSomeElseNone::new(msrv)));
-    store.register_late_pass(|| Box::new(bool_assert_comparison::BoolAssertComparison));
+    store.register_late_pass(|_| Box::new(empty_drop::EmptyDrop));
+    store.register_late_pass(|_| Box::new(strings::StrToString));
+    store.register_late_pass(|_| Box::new(strings::StringToString));
+    store.register_late_pass(|_| Box::new(zero_sized_map_values::ZeroSizedMapValues));
+    store.register_late_pass(|_| Box::new(vec_init_then_push::VecInitThenPush::default()));
+    store.register_late_pass(|_| Box::new(redundant_slicing::RedundantSlicing));
+    store.register_late_pass(|_| Box::new(from_str_radix_10::FromStrRadix10));
+    store.register_late_pass(move |_| Box::new(if_then_some_else_none::IfThenSomeElseNone::new(msrv)));
+    store.register_late_pass(|_| Box::new(bool_assert_comparison::BoolAssertComparison));
     store.register_early_pass(move || Box::new(module_style::ModStyle));
-    store.register_late_pass(|| Box::new(unused_async::UnusedAsync));
+    store.register_late_pass(|_| Box::new(unused_async::UnusedAsync));
     let disallowed_types = conf.disallowed_types.clone();
-    store.register_late_pass(move || Box::new(disallowed_types::DisallowedTypes::new(disallowed_types.clone())));
+    store.register_late_pass(move |_| Box::new(disallowed_types::DisallowedTypes::new(disallowed_types.clone())));
     let import_renames = conf.enforced_import_renames.clone();
-    store.register_late_pass(move || {
+    store.register_late_pass(move |_| {
         Box::new(missing_enforced_import_rename::ImportRename::new(
             import_renames.clone(),
         ))
     });
     let scripts = conf.allowed_scripts.clone();
     store.register_early_pass(move || Box::new(disallowed_script_idents::DisallowedScriptIdents::new(&scripts)));
-    store.register_late_pass(|| Box::new(strlen_on_c_strings::StrlenOnCStrings));
-    store.register_late_pass(move || Box::new(self_named_constructors::SelfNamedConstructors));
-    store.register_late_pass(move || Box::new(iter_not_returning_iterator::IterNotReturningIterator));
-    store.register_late_pass(move || Box::new(manual_assert::ManualAssert));
+    store.register_late_pass(|_| Box::new(strlen_on_c_strings::StrlenOnCStrings));
+    store.register_late_pass(move |_| Box::new(self_named_constructors::SelfNamedConstructors));
+    store.register_late_pass(move |_| Box::new(iter_not_returning_iterator::IterNotReturningIterator));
+    store.register_late_pass(move |_| Box::new(manual_assert::ManualAssert));
     let enable_raw_pointer_heuristic_for_send = conf.enable_raw_pointer_heuristic_for_send;
-    store.register_late_pass(move || {
+    store.register_late_pass(move |_| {
         Box::new(non_send_fields_in_send_ty::NonSendFieldInSendTy::new(
             enable_raw_pointer_heuristic_for_send,
         ))
     });
-    store.register_late_pass(move || Box::new(undocumented_unsafe_blocks::UndocumentedUnsafeBlocks));
-    store.register_late_pass(move || Box::new(format_args::FormatArgs));
-    store.register_late_pass(|| Box::new(trailing_empty_array::TrailingEmptyArray));
+    store.register_late_pass(move |_| Box::new(undocumented_unsafe_blocks::UndocumentedUnsafeBlocks));
+    store.register_late_pass(move |_| Box::new(format_args::FormatArgs));
+    store.register_late_pass(|_| Box::new(trailing_empty_array::TrailingEmptyArray));
     store.register_early_pass(|| Box::new(octal_escapes::OctalEscapes));
-    store.register_late_pass(|| Box::new(needless_late_init::NeedlessLateInit));
-    store.register_late_pass(|| Box::new(return_self_not_must_use::ReturnSelfNotMustUse));
-    store.register_late_pass(|| Box::new(init_numbered_fields::NumberedFields));
+    store.register_late_pass(|_| Box::new(needless_late_init::NeedlessLateInit));
+    store.register_late_pass(|_| Box::new(return_self_not_must_use::ReturnSelfNotMustUse));
+    store.register_late_pass(|_| Box::new(init_numbered_fields::NumberedFields));
     store.register_early_pass(|| Box::new(single_char_lifetime_names::SingleCharLifetimeNames));
-    store.register_late_pass(move || Box::new(manual_bits::ManualBits::new(msrv)));
-    store.register_late_pass(|| Box::new(default_union_representation::DefaultUnionRepresentation));
+    store.register_late_pass(move |_| Box::new(manual_bits::ManualBits::new(msrv)));
+    store.register_late_pass(|_| Box::new(default_union_representation::DefaultUnionRepresentation));
     store.register_early_pass(|| Box::new(doc_link_with_quotes::DocLinkWithQuotes));
-    store.register_late_pass(|| Box::new(only_used_in_recursion::OnlyUsedInRecursion::default()));
+    store.register_late_pass(|_| Box::new(only_used_in_recursion::OnlyUsedInRecursion::default()));
     let allow_dbg_in_tests = conf.allow_dbg_in_tests;
-    store.register_late_pass(move || Box::new(dbg_macro::DbgMacro::new(allow_dbg_in_tests)));
+    store.register_late_pass(move |_| Box::new(dbg_macro::DbgMacro::new(allow_dbg_in_tests)));
     let cargo_ignore_publish = conf.cargo_ignore_publish;
-    store.register_late_pass(move || {
+    store.register_late_pass(move |_| {
         Box::new(cargo::Cargo {
             ignore_publish: cargo_ignore_publish,
         })
     });
     store.register_early_pass(|| Box::new(crate_in_macro_def::CrateInMacroDef));
     store.register_early_pass(|| Box::new(empty_structs_with_brackets::EmptyStructsWithBrackets));
-    store.register_late_pass(|| Box::new(unnecessary_owned_empty_strings::UnnecessaryOwnedEmptyStrings));
+    store.register_late_pass(|_| Box::new(unnecessary_owned_empty_strings::UnnecessaryOwnedEmptyStrings));
     store.register_early_pass(|| Box::new(pub_use::PubUse));
-    store.register_late_pass(|| Box::new(format_push_string::FormatPushString));
+    store.register_late_pass(|_| Box::new(format_push_string::FormatPushString));
     let max_include_file_size = conf.max_include_file_size;
-    store.register_late_pass(move || Box::new(large_include_file::LargeIncludeFile::new(max_include_file_size)));
-    store.register_late_pass(|| Box::new(strings::TrimSplitWhitespace));
-    store.register_late_pass(|| Box::new(rc_clone_in_vec_init::RcCloneInVecInit));
+    store.register_late_pass(move |_| Box::new(large_include_file::LargeIncludeFile::new(max_include_file_size)));
+    store.register_late_pass(|_| Box::new(strings::TrimSplitWhitespace));
+    store.register_late_pass(|_| Box::new(rc_clone_in_vec_init::RcCloneInVecInit));
     store.register_early_pass(|| Box::new(duplicate_mod::DuplicateMod::default()));
     store.register_early_pass(|| Box::new(unused_rounding::UnusedRounding));
     store.register_early_pass(move || Box::new(almost_complete_letter_range::AlmostCompleteLetterRange::new(msrv)));
-    store.register_late_pass(|| Box::new(swap_ptr_to_ref::SwapPtrToRef));
-    store.register_late_pass(|| Box::new(mismatching_type_param_order::TypeParamMismatch));
-    store.register_late_pass(|| Box::new(read_zero_byte_vec::ReadZeroByteVec));
-    store.register_late_pass(|| Box::new(default_instead_of_iter_empty::DefaultIterEmpty));
-    store.register_late_pass(move || Box::new(manual_rem_euclid::ManualRemEuclid::new(msrv)));
-    store.register_late_pass(move || Box::new(manual_retain::ManualRetain::new(msrv)));
+    store.register_late_pass(|_| Box::new(swap_ptr_to_ref::SwapPtrToRef));
+    store.register_late_pass(|_| Box::new(mismatching_type_param_order::TypeParamMismatch));
+    store.register_late_pass(|_| Box::new(read_zero_byte_vec::ReadZeroByteVec));
+    store.register_late_pass(|_| Box::new(default_instead_of_iter_empty::DefaultIterEmpty));
+    store.register_late_pass(move |_| Box::new(manual_rem_euclid::ManualRemEuclid::new(msrv)));
+    store.register_late_pass(move |_| Box::new(manual_retain::ManualRetain::new(msrv)));
     let verbose_bit_mask_threshold = conf.verbose_bit_mask_threshold;
-    store.register_late_pass(move || Box::new(operators::Operators::new(verbose_bit_mask_threshold)));
-    store.register_late_pass(|| Box::new(invalid_utf8_in_unchecked::InvalidUtf8InUnchecked));
-    store.register_late_pass(|| Box::new(std_instead_of_core::StdReexports::default()));
-    store.register_late_pass(|| Box::new(manual_instant_elapsed::ManualInstantElapsed));
-    store.register_late_pass(|| Box::new(partialeq_to_none::PartialeqToNone));
-    store.register_late_pass(|| Box::new(manual_string_new::ManualStringNew));
-    store.register_late_pass(|| Box::new(unused_peekable::UnusedPeekable));
+    store.register_late_pass(move |_| Box::new(operators::Operators::new(verbose_bit_mask_threshold)));
+    store.register_late_pass(|_| Box::new(invalid_utf8_in_unchecked::InvalidUtf8InUnchecked));
+    store.register_late_pass(|_| Box::new(std_instead_of_core::StdReexports::default()));
+    store.register_late_pass(|_| Box::new(manual_instant_elapsed::ManualInstantElapsed));
+    store.register_late_pass(|_| Box::new(partialeq_to_none::PartialeqToNone));
+    store.register_late_pass(|_| Box::new(manual_string_new::ManualStringNew));
+    store.register_late_pass(|_| Box::new(unused_peekable::UnusedPeekable));
     store.register_early_pass(|| Box::new(multi_assignments::MultiAssignments));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
diff --git a/src/tools/clippy/clippy_lints/src/lifetimes.rs b/src/tools/clippy/clippy_lints/src/lifetimes.rs
index 573a7c016b8e8..5995675bd969c 100644
--- a/src/tools/clippy/clippy_lints/src/lifetimes.rs
+++ b/src/tools/clippy/clippy_lints/src/lifetimes.rs
@@ -441,7 +441,7 @@ impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
 
     fn visit_ty(&mut self, ty: &'tcx Ty<'_>) {
         match ty.kind {
-            TyKind::OpaqueDef(item, bounds) => {
+            TyKind::OpaqueDef(item, bounds, _) => {
                 let map = self.cx.tcx.hir();
                 let item = map.item(item);
                 let len = self.lts.len();
diff --git a/src/tools/clippy/clippy_lints/src/manual_async_fn.rs b/src/tools/clippy/clippy_lints/src/manual_async_fn.rs
index 2502c8f880ddc..754b0e78a148c 100644
--- a/src/tools/clippy/clippy_lints/src/manual_async_fn.rs
+++ b/src/tools/clippy/clippy_lints/src/manual_async_fn.rs
@@ -103,7 +103,7 @@ fn future_trait_ref<'tcx>(
     ty: &'tcx Ty<'tcx>,
 ) -> Option<(&'tcx TraitRef<'tcx>, Vec<LifetimeName>)> {
     if_chain! {
-        if let TyKind::OpaqueDef(item_id, bounds) = ty.kind;
+        if let TyKind::OpaqueDef(item_id, bounds, false) = ty.kind;
         let item = cx.tcx.hir().item(item_id);
         if let ItemKind::OpaqueTy(opaque) = &item.kind;
         if let Some(trait_ref) = opaque.bounds.iter().find_map(|bound| {
diff --git a/src/tools/clippy/clippy_utils/src/hir_utils.rs b/src/tools/clippy/clippy_utils/src/hir_utils.rs
index 57448f716d494..f972106168ade 100644
--- a/src/tools/clippy/clippy_utils/src/hir_utils.rs
+++ b/src/tools/clippy/clippy_utils/src/hir_utils.rs
@@ -987,8 +987,9 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
                 }
             },
             TyKind::Path(ref qpath) => self.hash_qpath(qpath),
-            TyKind::OpaqueDef(_, arg_list) => {
+            TyKind::OpaqueDef(_, arg_list, in_trait) => {
                 self.hash_generic_args(arg_list);
+                in_trait.hash(&mut self.s);
             },
             TyKind::TraitObject(_, lifetime, _) => {
                 self.hash_lifetime(*lifetime);