diff --git a/.gitignore b/.gitignore
index d6d8b99f6023c..b170dca88fa95 100644
--- a/.gitignore
+++ b/.gitignore
@@ -86,4 +86,13 @@ package.json
 ## Rustdoc GUI tests
 tests/rustdoc-gui/src/**.lock
 
+## direnv
+.envrc
+.direnv/
+
+## nix
+flake.nix
+flake.lock
+default.nix
+
 # Before adding new lines, see the comment at the top.
diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index 7bb3b2fa29095..1273b50dff816 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -286,7 +286,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
                                 parent: this.local_def_id(id),
                                 in_assoc_ty: false,
                             },
-                            fn_kind: None,
                         }),
                     },
                 );
@@ -983,7 +982,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
                                     parent: this.local_def_id(i.id),
                                     in_assoc_ty: true,
                                 },
-                                fn_kind: None,
                             });
                             hir::ImplItemKind::Type(ty)
                         }
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index c6cb7aa7dd5c2..9275308cccbce 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -288,12 +288,7 @@ enum ImplTraitContext {
     /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
     /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
     ///
-    OpaqueTy {
-        origin: hir::OpaqueTyOrigin,
-        /// Only used to change the lifetime capture rules, since
-        /// RPITIT captures all in scope, RPIT does not.
-        fn_kind: Option<FnDeclKind>,
-    },
+    OpaqueTy { origin: hir::OpaqueTyOrigin },
     /// `impl Trait` is unstably accepted in this position.
     FeatureGated(ImplTraitPosition, Symbol),
     /// `impl Trait` is not accepted in this position.
@@ -1404,14 +1399,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             TyKind::ImplTrait(def_node_id, bounds) => {
                 let span = t.span;
                 match itctx {
-                    ImplTraitContext::OpaqueTy { origin, fn_kind } => self.lower_opaque_impl_trait(
-                        span,
-                        origin,
-                        *def_node_id,
-                        bounds,
-                        fn_kind,
-                        itctx,
-                    ),
+                    ImplTraitContext::OpaqueTy { origin } => {
+                        self.lower_opaque_impl_trait(span, origin, *def_node_id, bounds, itctx)
+                    }
                     ImplTraitContext::Universal => {
                         if let Some(span) = bounds.iter().find_map(|bound| match *bound {
                             ast::GenericBound::Use(_, span) => Some(span),
@@ -1513,7 +1503,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         origin: hir::OpaqueTyOrigin,
         opaque_ty_node_id: NodeId,
         bounds: &GenericBounds,
-        fn_kind: Option<FnDeclKind>,
         itctx: ImplTraitContext,
     ) -> hir::TyKind<'hir> {
         // Make sure we know that some funky desugaring has been going on here.
@@ -1555,11 +1544,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         .map(|(ident, id, _)| Lifetime { id, ident })
                         .collect()
                 }
-                hir::OpaqueTyOrigin::FnReturn(..) => {
-                    if matches!(
-                        fn_kind.expect("expected RPITs to be lowered with a FnKind"),
-                        FnDeclKind::Impl | FnDeclKind::Trait
-                    ) || self.tcx.features().lifetime_capture_rules_2024
+                hir::OpaqueTyOrigin::FnReturn { in_trait_or_impl, .. } => {
+                    if in_trait_or_impl.is_some()
+                        || self.tcx.features().lifetime_capture_rules_2024
                         || span.at_least_rust_2024()
                     {
                         // return-position impl trait in trait was decided to capture all
@@ -1576,16 +1563,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         lifetime_collector::lifetimes_in_bounds(self.resolver, bounds)
                     }
                 }
-                hir::OpaqueTyOrigin::AsyncFn(..) => {
+                hir::OpaqueTyOrigin::AsyncFn { .. } => {
                     unreachable!("should be using `lower_async_fn_ret_ty`")
                 }
             }
         };
         debug!(?captured_lifetimes_to_duplicate);
 
-        match fn_kind {
-            // Deny `use<>` on RPITIT in trait/trait-impl for now.
-            Some(FnDeclKind::Trait | FnDeclKind::Impl) => {
+        // Feature gate for RPITIT + use<..>
+        match origin {
+            rustc_hir::OpaqueTyOrigin::FnReturn { in_trait_or_impl: Some(_), .. } => {
                 if let Some(span) = bounds.iter().find_map(|bound| match *bound {
                     ast::GenericBound::Use(_, span) => Some(span),
                     _ => None,
@@ -1593,20 +1580,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     self.tcx.dcx().emit_err(errors::NoPreciseCapturesOnRpitit { span });
                 }
             }
-            None
-            | Some(
-                FnDeclKind::Fn
-                | FnDeclKind::Inherent
-                | FnDeclKind::ExternFn
-                | FnDeclKind::Closure
-                | FnDeclKind::Pointer,
-            ) => {}
+            _ => {}
         }
 
         self.lower_opaque_inner(
             opaque_ty_node_id,
             origin,
-            matches!(fn_kind, Some(FnDeclKind::Trait)),
             captured_lifetimes_to_duplicate,
             span,
             opaque_ty_span,
@@ -1618,7 +1597,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         &mut self,
         opaque_ty_node_id: NodeId,
         origin: hir::OpaqueTyOrigin,
-        in_trait: bool,
         captured_lifetimes_to_duplicate: FxIndexSet<Lifetime>,
         span: Span,
         opaque_ty_span: Span,
@@ -1747,7 +1725,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 bounds,
                 origin,
                 lifetime_mapping,
-                in_trait,
             };
 
             // Generate an `type Foo = impl Trait;` declaration.
@@ -1776,7 +1753,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         hir::TyKind::OpaqueDef(
             hir::ItemId { owner_id: hir::OwnerId { def_id: opaque_ty_def_id } },
             generic_args,
-            in_trait,
         )
     }
 
@@ -1864,12 +1840,23 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             None => match &decl.output {
                 FnRetTy::Ty(ty) => {
                     let itctx = match kind {
-                        FnDeclKind::Fn
-                        | FnDeclKind::Inherent
-                        | FnDeclKind::Trait
-                        | FnDeclKind::Impl => ImplTraitContext::OpaqueTy {
-                            origin: hir::OpaqueTyOrigin::FnReturn(self.local_def_id(fn_node_id)),
-                            fn_kind: Some(kind),
+                        FnDeclKind::Fn | FnDeclKind::Inherent => ImplTraitContext::OpaqueTy {
+                            origin: hir::OpaqueTyOrigin::FnReturn {
+                                parent: self.local_def_id(fn_node_id),
+                                in_trait_or_impl: None,
+                            },
+                        },
+                        FnDeclKind::Trait => ImplTraitContext::OpaqueTy {
+                            origin: hir::OpaqueTyOrigin::FnReturn {
+                                parent: self.local_def_id(fn_node_id),
+                                in_trait_or_impl: Some(hir::RpitContext::Trait),
+                            },
+                        },
+                        FnDeclKind::Impl => ImplTraitContext::OpaqueTy {
+                            origin: hir::OpaqueTyOrigin::FnReturn {
+                                parent: self.local_def_id(fn_node_id),
+                                in_trait_or_impl: Some(hir::RpitContext::TraitImpl),
+                            },
                         },
                         FnDeclKind::ExternFn => {
                             ImplTraitContext::Disallowed(ImplTraitPosition::ExternFnReturn)
@@ -1951,10 +1938,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             .map(|(ident, id, _)| Lifetime { id, ident })
             .collect();
 
+        let in_trait_or_impl = match fn_kind {
+            FnDeclKind::Trait => Some(hir::RpitContext::Trait),
+            FnDeclKind::Impl => Some(hir::RpitContext::TraitImpl),
+            FnDeclKind::Fn | FnDeclKind::Inherent => None,
+            FnDeclKind::ExternFn | FnDeclKind::Closure | FnDeclKind::Pointer => unreachable!(),
+        };
+
         let opaque_ty_ref = self.lower_opaque_inner(
             opaque_ty_node_id,
-            hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
-            matches!(fn_kind, FnDeclKind::Trait),
+            hir::OpaqueTyOrigin::AsyncFn { parent: fn_def_id, in_trait_or_impl },
             captured_lifetimes,
             span,
             opaque_ty_span,
@@ -1964,8 +1957,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     coro,
                     opaque_ty_span,
                     ImplTraitContext::OpaqueTy {
-                        origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
-                        fn_kind: Some(fn_kind),
+                        origin: hir::OpaqueTyOrigin::FnReturn {
+                            parent: fn_def_id,
+                            in_trait_or_impl,
+                        },
                     },
                 );
                 arena_vec![this; bound]
diff --git a/compiler/rustc_borrowck/src/diagnostics/region_name.rs b/compiler/rustc_borrowck/src/diagnostics/region_name.rs
index 2f22e1532c196..d4598a1f582b6 100644
--- a/compiler/rustc_borrowck/src/diagnostics/region_name.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/region_name.rs
@@ -832,7 +832,7 @@ 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/opaque_types.rs b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
index 3cf21d4a36b83..2f90e91628141 100644
--- a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
+++ b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
@@ -503,8 +503,8 @@ impl<'tcx> LazyOpaqueTyEnv<'tcx> {
         let &Self { tcx, def_id, .. } = self;
         let origin = tcx.opaque_type_origin(def_id);
         let parent = match origin {
-            hir::OpaqueTyOrigin::FnReturn(parent)
-            | hir::OpaqueTyOrigin::AsyncFn(parent)
+            hir::OpaqueTyOrigin::FnReturn { parent, .. }
+            | hir::OpaqueTyOrigin::AsyncFn { parent, .. }
             | hir::OpaqueTyOrigin::TyAlias { parent, .. } => parent,
         };
         let param_env = tcx.param_env(parent);
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 71216023ecc33..f58ec22aea971 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -2632,7 +2632,7 @@ impl<'hir> Ty<'hir> {
             }
             TyKind::Tup(tys) => tys.iter().any(Self::is_suggestable_infer_ty),
             TyKind::Ptr(mut_ty) | TyKind::Ref(_, mut_ty) => mut_ty.ty.is_suggestable_infer_ty(),
-            TyKind::OpaqueDef(_, generic_args, _) => are_suggestable_generic_args(generic_args),
+            TyKind::OpaqueDef(_, generic_args) => are_suggestable_generic_args(generic_args),
             TyKind::Path(QPath::TypeRelative(ty, segment)) => {
                 ty.is_suggestable_infer_ty() || are_suggestable_generic_args(segment.args().args)
             }
@@ -2762,10 +2762,6 @@ pub struct OpaqueTy<'hir> {
     /// This mapping associated a captured lifetime (first parameter) with the new
     /// early-bound lifetime that was generated for the opaque.
     pub lifetime_mapping: &'hir [(&'hir Lifetime, LocalDefId)],
-    /// Whether the opaque is a return-position impl trait (or async future)
-    /// originating from a trait method. This makes it so that the opaque is
-    /// lowered as an associated type.
-    pub in_trait: bool,
 }
 
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
@@ -2802,13 +2798,29 @@ pub struct PreciseCapturingNonLifetimeArg {
     pub res: Res,
 }
 
+#[derive(Copy, Clone, PartialEq, Eq, Debug, HashStable_Generic)]
+pub enum RpitContext {
+    Trait,
+    TraitImpl,
+}
+
 /// From whence the opaque type came.
 #[derive(Copy, Clone, PartialEq, Eq, Debug, HashStable_Generic)]
 pub enum OpaqueTyOrigin {
     /// `-> impl Trait`
-    FnReturn(LocalDefId),
+    FnReturn {
+        /// The defining function.
+        parent: LocalDefId,
+        // Whether this is an RPITIT (return position impl trait in trait)
+        in_trait_or_impl: Option<RpitContext>,
+    },
     /// `async fn`
-    AsyncFn(LocalDefId),
+    AsyncFn {
+        /// The defining function.
+        parent: LocalDefId,
+        // Whether this is an AFIT (async fn in trait)
+        in_trait_or_impl: Option<RpitContext>,
+    },
     /// type aliases: `type Foo = impl Trait;`
     TyAlias {
         /// The type alias or associated type parent of the TAIT/ATPIT
@@ -2856,7 +2868,7 @@ pub enum TyKind<'hir> {
     /// possibly parameters) that are actually bound on the `impl Trait`.
     ///
     /// The last parameter specifies whether this opaque appears in a trait definition.
-    OpaqueDef(ItemId, &'hir [GenericArg<'hir>], bool),
+    OpaqueDef(ItemId, &'hir [GenericArg<'hir>]),
     /// A trait object type `Bound1 + Bound2 + Bound3`
     /// where `Bound` is a trait or a lifetime.
     TraitObject(
diff --git a/compiler/rustc_hir/src/intravisit.rs b/compiler/rustc_hir/src/intravisit.rs
index 4da3224578519..d0a8aaa85bb29 100644
--- a/compiler/rustc_hir/src/intravisit.rs
+++ b/compiler/rustc_hir/src/intravisit.rs
@@ -894,7 +894,7 @@ pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty<'v>) -> V::Resul
         TyKind::Path(ref qpath) => {
             try_visit!(visitor.visit_qpath(qpath, typ.hir_id, typ.span));
         }
-        TyKind::OpaqueDef(item_id, lifetimes, _in_trait) => {
+        TyKind::OpaqueDef(item_id, lifetimes) => {
             try_visit!(visitor.visit_nested_item(item_id));
             walk_list!(visitor, visit_generic_arg, lifetimes);
         }
diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
index d725772a5b369..312212232bcdc 100644
--- a/compiler/rustc_hir_analysis/src/check/check.rs
+++ b/compiler/rustc_hir_analysis/src/check/check.rs
@@ -336,9 +336,9 @@ fn check_opaque_meets_bounds<'tcx>(
     origin: &hir::OpaqueTyOrigin,
 ) -> Result<(), ErrorGuaranteed> {
     let defining_use_anchor = match *origin {
-        hir::OpaqueTyOrigin::FnReturn(did)
-        | hir::OpaqueTyOrigin::AsyncFn(did)
-        | hir::OpaqueTyOrigin::TyAlias { parent: did, .. } => did,
+        hir::OpaqueTyOrigin::FnReturn { parent, .. }
+        | hir::OpaqueTyOrigin::AsyncFn { parent, .. }
+        | hir::OpaqueTyOrigin::TyAlias { parent, .. } => parent,
     };
     let param_env = tcx.param_env(defining_use_anchor);
 
@@ -346,8 +346,8 @@ fn check_opaque_meets_bounds<'tcx>(
     let ocx = ObligationCtxt::new_with_diagnostics(&infcx);
 
     let args = match *origin {
-        hir::OpaqueTyOrigin::FnReturn(parent)
-        | hir::OpaqueTyOrigin::AsyncFn(parent)
+        hir::OpaqueTyOrigin::FnReturn { parent, .. }
+        | hir::OpaqueTyOrigin::AsyncFn { parent, .. }
         | hir::OpaqueTyOrigin::TyAlias { parent, .. } => GenericArgs::identity_for_item(
             tcx, parent,
         )
@@ -409,7 +409,7 @@ fn check_opaque_meets_bounds<'tcx>(
     let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
     ocx.resolve_regions_and_report_errors(defining_use_anchor, &outlives_env)?;
 
-    if let hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..) = origin {
+    if let hir::OpaqueTyOrigin::FnReturn { .. } | hir::OpaqueTyOrigin::AsyncFn { .. } = origin {
         // HACK: this should also fall through to the hidden type check below, but the original
         // implementation had a bug where equivalent lifetimes are not identical. This caused us
         // to reject existing stable code that is otherwise completely fine. The real fix is to
@@ -736,8 +736,8 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) {
             check_opaque_precise_captures(tcx, def_id);
 
             let origin = tcx.opaque_type_origin(def_id);
-            if let hir::OpaqueTyOrigin::FnReturn(fn_def_id)
-            | hir::OpaqueTyOrigin::AsyncFn(fn_def_id) = origin
+            if let hir::OpaqueTyOrigin::FnReturn { parent: fn_def_id, .. }
+            | hir::OpaqueTyOrigin::AsyncFn { parent: fn_def_id, .. } = origin
                 && let hir::Node::TraitItem(trait_item) = tcx.hir_node_by_def_id(fn_def_id)
                 && let (_, hir::TraitFn::Required(..)) = trait_item.expect_fn()
             {
diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item/refine.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item/refine.rs
index e07b587508a68..35c2b7e7ce2fb 100644
--- a/compiler/rustc_hir_analysis/src/check/compare_impl_item/refine.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_impl_item/refine.rs
@@ -94,8 +94,8 @@ pub(super) fn check_refining_return_position_impl_trait_in_trait<'tcx>(
         if !tcx.hir().get_if_local(impl_opaque.def_id).is_some_and(|node| {
             matches!(
                 node.expect_item().expect_opaque_ty().origin,
-                hir::OpaqueTyOrigin::AsyncFn(def_id)  | hir::OpaqueTyOrigin::FnReturn(def_id)
-                    if def_id == impl_m.def_id.expect_local()
+                hir::OpaqueTyOrigin::AsyncFn { parent, .. }  | hir::OpaqueTyOrigin::FnReturn { parent, .. }
+                    if parent == impl_m.def_id.expect_local()
             )
         }) {
             report_mismatched_rpitit_signature(
diff --git a/compiler/rustc_hir_analysis/src/collect/generics_of.rs b/compiler/rustc_hir_analysis/src/collect/generics_of.rs
index 0a8eef2006d5a..8ff9640a87489 100644
--- a/compiler/rustc_hir_analysis/src/collect/generics_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/generics_of.rs
@@ -210,11 +210,11 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
         Node::Item(item) => match item.kind {
             ItemKind::OpaqueTy(&hir::OpaqueTy {
                 origin:
-                    hir::OpaqueTyOrigin::FnReturn(fn_def_id) | hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
-                in_trait,
+                    hir::OpaqueTyOrigin::FnReturn { parent: fn_def_id, in_trait_or_impl }
+                    | hir::OpaqueTyOrigin::AsyncFn { parent: fn_def_id, in_trait_or_impl },
                 ..
             }) => {
-                if in_trait {
+                if in_trait_or_impl.is_some() {
                     assert_matches!(tcx.def_kind(fn_def_id), DefKind::AssocFn);
                 } else {
                     assert_matches!(tcx.def_kind(fn_def_id), DefKind::AssocFn | DefKind::Fn);
diff --git a/compiler/rustc_hir_analysis/src/collect/item_bounds.rs b/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
index f44b4728ad533..2418037ae962f 100644
--- a/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
+++ b/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
@@ -370,39 +370,47 @@ pub(super) fn explicit_item_bounds_with_filter(
             ..
         }) => associated_type_bounds(tcx, def_id, bounds, *span, filter),
         hir::Node::Item(hir::Item {
-            kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, in_trait: false, .. }),
+            kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, origin, .. }),
             span,
             ..
-        }) => {
-            let args = GenericArgs::identity_for_item(tcx, def_id);
-            let item_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);
-            let bounds = opaque_type_bounds(tcx, def_id, bounds, item_ty, *span, filter);
-            assert_only_contains_predicates_from(filter, bounds, item_ty);
-            bounds
-        }
-        // Since RPITITs are lowered as projections in `<dyn HirTyLowerer>::lower_ty`, when we're
-        // asking for the item bounds of the *opaques* in a trait's default method signature, we
-        // need to map these projections back to opaques.
-        hir::Node::Item(hir::Item {
-            kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, in_trait: true, origin, .. }),
-            span,
-            ..
-        }) => {
-            let (hir::OpaqueTyOrigin::FnReturn(fn_def_id)
-            | hir::OpaqueTyOrigin::AsyncFn(fn_def_id)) = *origin
-            else {
-                span_bug!(*span, "RPITIT cannot be a TAIT, but got origin {origin:?}");
-            };
-            let args = GenericArgs::identity_for_item(tcx, def_id);
-            let item_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);
-            let bounds = &*tcx.arena.alloc_slice(
-                &opaque_type_bounds(tcx, def_id, bounds, item_ty, *span, filter)
-                    .to_vec()
-                    .fold_with(&mut AssocTyToOpaque { tcx, fn_def_id: fn_def_id.to_def_id() }),
-            );
-            assert_only_contains_predicates_from(filter, bounds, item_ty);
-            bounds
-        }
+        }) => match origin {
+            // Since RPITITs are lowered as projections in `<dyn HirTyLowerer>::lower_ty`,
+            // when we're asking for the item bounds of the *opaques* in a trait's default
+            // method signature, we need to map these projections back to opaques.
+            rustc_hir::OpaqueTyOrigin::FnReturn {
+                parent,
+                in_trait_or_impl: Some(hir::RpitContext::Trait),
+            }
+            | rustc_hir::OpaqueTyOrigin::AsyncFn {
+                parent,
+                in_trait_or_impl: Some(hir::RpitContext::Trait),
+            } => {
+                let args = GenericArgs::identity_for_item(tcx, def_id);
+                let item_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);
+                let bounds = &*tcx.arena.alloc_slice(
+                    &opaque_type_bounds(tcx, def_id, bounds, item_ty, *span, filter)
+                        .to_vec()
+                        .fold_with(&mut AssocTyToOpaque { tcx, fn_def_id: parent.to_def_id() }),
+                );
+                assert_only_contains_predicates_from(filter, bounds, item_ty);
+                bounds
+            }
+            rustc_hir::OpaqueTyOrigin::FnReturn {
+                parent: _,
+                in_trait_or_impl: None | Some(hir::RpitContext::TraitImpl),
+            }
+            | rustc_hir::OpaqueTyOrigin::AsyncFn {
+                parent: _,
+                in_trait_or_impl: None | Some(hir::RpitContext::TraitImpl),
+            }
+            | rustc_hir::OpaqueTyOrigin::TyAlias { parent: _, .. } => {
+                let args = GenericArgs::identity_for_item(tcx, def_id);
+                let item_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);
+                let bounds = opaque_type_bounds(tcx, def_id, bounds, item_ty, *span, filter);
+                assert_only_contains_predicates_from(filter, bounds, item_ty);
+                bounds
+            }
+        },
         hir::Node::Item(hir::Item { kind: hir::ItemKind::TyAlias(..), .. }) => &[],
         _ => bug!("item_bounds called on {:?}", def_id),
     };
diff --git a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
index 9e9704622052f..33f6623edfdf3 100644
--- a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
@@ -332,7 +332,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
     // and the duplicated parameter, to ensure that they do not get out of sync.
     if let Node::Item(&Item { kind: ItemKind::OpaqueTy(..), .. }) = node {
         let opaque_ty_node = tcx.parent_hir_node(hir_id);
-        let Node::Ty(&hir::Ty { kind: TyKind::OpaqueDef(_, lifetimes, _), .. }) = opaque_ty_node
+        let Node::Ty(&hir::Ty { kind: TyKind::OpaqueDef(_, lifetimes), .. }) = opaque_ty_node
         else {
             bug!("unexpected {opaque_ty_node:?}")
         };
diff --git a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
index c9b949ad88d54..a15621bf28b9b 100644
--- a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
+++ b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
@@ -515,8 +515,8 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
             }
             hir::ItemKind::OpaqueTy(&hir::OpaqueTy {
                 origin:
-                    hir::OpaqueTyOrigin::FnReturn(parent)
-                    | hir::OpaqueTyOrigin::AsyncFn(parent)
+                    hir::OpaqueTyOrigin::FnReturn { parent, .. }
+                    | hir::OpaqueTyOrigin::AsyncFn { parent, .. }
                     | hir::OpaqueTyOrigin::TyAlias { parent, .. },
                 generics,
                 ..
@@ -689,7 +689,7 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
                 };
                 self.with(scope, |this| this.visit_ty(mt.ty));
             }
-            hir::TyKind::OpaqueDef(item_id, lifetimes, _in_trait) => {
+            hir::TyKind::OpaqueDef(item_id, lifetimes) => {
                 // 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_hir_analysis/src/collect/type_of.rs b/compiler/rustc_hir_analysis/src/collect/type_of.rs
index 48b5e87cbd033..3af4d1f5edad5 100644
--- a/compiler/rustc_hir_analysis/src/collect/type_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/type_of.rs
@@ -618,11 +618,13 @@ pub(super) fn type_of_opaque(
                 // Opaque types desugared from `impl Trait`.
                 ItemKind::OpaqueTy(&OpaqueTy {
                     origin:
-                        hir::OpaqueTyOrigin::FnReturn(owner) | hir::OpaqueTyOrigin::AsyncFn(owner),
-                    in_trait,
+                        hir::OpaqueTyOrigin::FnReturn { parent: owner, in_trait_or_impl }
+                        | hir::OpaqueTyOrigin::AsyncFn { parent: owner, in_trait_or_impl },
                     ..
                 }) => {
-                    if in_trait && !tcx.defaultness(owner).has_value() {
+                    if in_trait_or_impl == Some(hir::RpitContext::Trait)
+                        && !tcx.defaultness(owner).has_value()
+                    {
                         span_bug!(
                             tcx.def_span(def_id),
                             "tried to get type of this RPITIT with no definition"
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index 6dd3a06ef3773..95f83836d7573 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -2087,21 +2087,41 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.lower_ty(qself));
                 self.lower_path(opt_self_ty, path, hir_ty.hir_id, false)
             }
-            &hir::TyKind::OpaqueDef(item_id, lifetimes, in_trait) => {
+            &hir::TyKind::OpaqueDef(item_id, lifetimes) => {
                 let opaque_ty = tcx.hir().item(item_id);
 
                 match opaque_ty.kind {
-                    hir::ItemKind::OpaqueTy(&hir::OpaqueTy { .. }) => {
+                    hir::ItemKind::OpaqueTy(&hir::OpaqueTy { origin, .. }) => {
                         let local_def_id = item_id.owner_id.def_id;
                         // If this is an RPITIT and we are using the new RPITIT lowering scheme, we
                         // generate the def_id of an associated type for the trait and return as
                         // type a projection.
-                        let def_id = if in_trait {
-                            tcx.associated_type_for_impl_trait_in_trait(local_def_id).to_def_id()
-                        } else {
-                            local_def_id.to_def_id()
-                        };
-                        self.lower_opaque_ty(def_id, lifetimes, in_trait)
+                        match origin {
+                            hir::OpaqueTyOrigin::FnReturn {
+                                in_trait_or_impl: Some(hir::RpitContext::Trait),
+                                ..
+                            }
+                            | hir::OpaqueTyOrigin::AsyncFn {
+                                in_trait_or_impl: Some(hir::RpitContext::Trait),
+                                ..
+                            } => self.lower_opaque_ty(
+                                tcx.associated_type_for_impl_trait_in_trait(local_def_id)
+                                    .to_def_id(),
+                                lifetimes,
+                                true,
+                            ),
+                            hir::OpaqueTyOrigin::FnReturn {
+                                in_trait_or_impl: None | Some(hir::RpitContext::TraitImpl),
+                                ..
+                            }
+                            | hir::OpaqueTyOrigin::AsyncFn {
+                                in_trait_or_impl: None | Some(hir::RpitContext::TraitImpl),
+                                ..
+                            }
+                            | hir::OpaqueTyOrigin::TyAlias { .. } => {
+                                self.lower_opaque_ty(local_def_id.to_def_id(), lifetimes, false)
+                            }
+                        }
                     }
                     ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
                 }
diff --git a/compiler/rustc_hir_typeck/src/_match.rs b/compiler/rustc_hir_typeck/src/_match.rs
index bf8ed017cf703..2dbadf8198b3f 100644
--- a/compiler/rustc_hir_typeck/src/_match.rs
+++ b/compiler/rustc_hir_typeck/src/_match.rs
@@ -602,7 +602,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 .map(|(k, _)| (k.def_id, k.args))?,
             _ => return None,
         };
-        let hir::OpaqueTyOrigin::FnReturn(parent_def_id) = self.tcx.opaque_type_origin(def_id)
+        let hir::OpaqueTyOrigin::FnReturn { parent: parent_def_id, .. } =
+            self.tcx.opaque_type_origin(def_id)
         else {
             return None;
         };
diff --git a/compiler/rustc_hir_typeck/src/method/mod.rs b/compiler/rustc_hir_typeck/src/method/mod.rs
index 586b753f45493..3e9cb0ac2c80c 100644
--- a/compiler/rustc_hir_typeck/src/method/mod.rs
+++ b/compiler/rustc_hir_typeck/src/method/mod.rs
@@ -18,8 +18,8 @@ use rustc_middle::ty::{
     self, GenericArgs, GenericArgsRef, GenericParamDefKind, Ty, TypeVisitableExt,
 };
 use rustc_middle::{bug, span_bug};
-use rustc_span::Span;
 use rustc_span::symbol::Ident;
+use rustc_span::{ErrorGuaranteed, Span};
 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
 use rustc_trait_selection::traits::{self, NormalizeExt};
 use tracing::{debug, instrument};
@@ -46,17 +46,17 @@ pub(crate) struct MethodCallee<'tcx> {
 
 #[derive(Debug)]
 pub(crate) enum MethodError<'tcx> {
-    // Did not find an applicable method, but we did find various near-misses that may work.
+    /// Did not find an applicable method, but we did find various near-misses that may work.
     NoMatch(NoMatchData<'tcx>),
 
-    // Multiple methods might apply.
+    /// Multiple methods might apply.
     Ambiguity(Vec<CandidateSource>),
 
-    // Found an applicable method, but it is not visible. The third argument contains a list of
-    // not-in-scope traits which may work.
+    /// Found an applicable method, but it is not visible. The third argument contains a list of
+    /// not-in-scope traits which may work.
     PrivateMatch(DefKind, DefId, Vec<DefId>),
 
-    // Found a `Self: Sized` bound where `Self` is a trait object.
+    /// Found a `Self: Sized` bound where `Self` is a trait object.
     IllegalSizedBound {
         candidates: Vec<DefId>,
         needs_mut: bool,
@@ -64,8 +64,11 @@ pub(crate) enum MethodError<'tcx> {
         self_expr: &'tcx hir::Expr<'tcx>,
     },
 
-    // Found a match, but the return type is wrong
+    /// Found a match, but the return type is wrong
     BadReturnType,
+
+    /// Error has already been emitted, no need to emit another one.
+    ErrorReported(ErrorGuaranteed),
 }
 
 // Contains a list of static methods that may apply, a list of unsatisfied trait predicates which
@@ -120,6 +123,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             Err(PrivateMatch(..)) => false,
             Err(IllegalSizedBound { .. }) => true,
             Err(BadReturnType) => false,
+            Err(ErrorReported(_)) => false,
         }
     }
 
diff --git a/compiler/rustc_hir_typeck/src/method/probe.rs b/compiler/rustc_hir_typeck/src/method/probe.rs
index 371380e575dbc..3bb7070d61dfa 100644
--- a/compiler/rustc_hir_typeck/src/method/probe.rs
+++ b/compiler/rustc_hir_typeck/src/method/probe.rs
@@ -446,13 +446,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     _ => bug!("unexpected bad final type in method autoderef"),
                 };
                 self.demand_eqtype(span, ty, Ty::new_error(self.tcx, guar));
-                return Err(MethodError::NoMatch(NoMatchData {
-                    static_candidates: Vec::new(),
-                    unsatisfied_predicates: Vec::new(),
-                    out_of_scope_traits: Vec::new(),
-                    similar_candidate: None,
-                    mode,
-                }));
+                return Err(MethodError::ErrorReported(guar));
             }
         }
 
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index e03be4f43f73d..a37e9744293c3 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -229,20 +229,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         match error {
-            MethodError::NoMatch(mut no_match_data) => {
-                return self.report_no_match_method_error(
-                    span,
-                    rcvr_ty,
-                    item_name,
-                    call_id,
-                    source,
-                    args,
-                    sugg_span,
-                    &mut no_match_data,
-                    expected,
-                    trait_missing_method,
-                );
-            }
+            MethodError::NoMatch(mut no_match_data) => self.report_no_match_method_error(
+                span,
+                rcvr_ty,
+                item_name,
+                call_id,
+                source,
+                args,
+                sugg_span,
+                &mut no_match_data,
+                expected,
+                trait_missing_method,
+            ),
 
             MethodError::Ambiguity(mut sources) => {
                 let mut err = struct_span_code_err!(
@@ -263,7 +261,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     &mut sources,
                     Some(sugg_span),
                 );
-                return err.emit();
+                err.emit()
             }
 
             MethodError::PrivateMatch(kind, def_id, out_of_scope_traits) => {
@@ -284,7 +282,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     .unwrap_or_else(|| self.tcx.def_span(def_id));
                 err.span_label(sp, format!("private {kind} defined here"));
                 self.suggest_valid_traits(&mut err, item_name, out_of_scope_traits, true);
-                return err.emit();
+                err.emit()
             }
 
             MethodError::IllegalSizedBound { candidates, needs_mut, bound_span, self_expr } => {
@@ -383,9 +381,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         }
                     }
                 }
-                return err.emit();
+                err.emit()
             }
 
+            MethodError::ErrorReported(guar) => guar,
+
             MethodError::BadReturnType => bug!("no return type expectations but got BadReturnType"),
         }
     }
diff --git a/compiler/rustc_lint/src/impl_trait_overcaptures.rs b/compiler/rustc_lint/src/impl_trait_overcaptures.rs
index a073d16f634d8..5aeaad420699e 100644
--- a/compiler/rustc_lint/src/impl_trait_overcaptures.rs
+++ b/compiler/rustc_lint/src/impl_trait_overcaptures.rs
@@ -259,8 +259,8 @@ where
             // If it's owned by this function
             && let opaque =
                 self.tcx.hir_node_by_def_id(opaque_def_id).expect_item().expect_opaque_ty()
-            && let hir::OpaqueTyOrigin::FnReturn(parent_def_id) = opaque.origin
-            && parent_def_id == self.parent_def_id
+            && let hir::OpaqueTyOrigin::FnReturn { parent, .. } = opaque.origin
+            && parent == self.parent_def_id
         {
             let opaque_span = self.tcx.def_span(opaque_def_id);
             let new_capture_rules =
diff --git a/compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs b/compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs
index 83652bbf54631..342ebfa0b06cc 100644
--- a/compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs
+++ b/compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs
@@ -77,7 +77,7 @@ impl<'tcx> LateLintPass<'tcx> for OpaqueHiddenInferredBound {
         // That's because although we may have an opaque type on the function,
         // it won't have a hidden type, so proving predicates about it is
         // not really meaningful.
-        if let hir::OpaqueTyOrigin::FnReturn(method_def_id) = opaque.origin
+        if let hir::OpaqueTyOrigin::FnReturn { parent: method_def_id, .. } = opaque.origin
             && let hir::Node::TraitItem(trait_item) = cx.tcx.hir_node_by_def_id(method_def_id)
             && !trait_item.defaultness.has_value()
         {
@@ -103,7 +103,7 @@ impl<'tcx> LateLintPass<'tcx> for OpaqueHiddenInferredBound {
                     && cx.tcx.parent(opaque_ty.def_id) == def_id
                     && matches!(
                         opaque.origin,
-                        hir::OpaqueTyOrigin::FnReturn(_) | hir::OpaqueTyOrigin::AsyncFn(_)
+                        hir::OpaqueTyOrigin::FnReturn { .. } | hir::OpaqueTyOrigin::AsyncFn { .. }
                     )
                 {
                     return;
@@ -114,8 +114,10 @@ impl<'tcx> LateLintPass<'tcx> for OpaqueHiddenInferredBound {
                 // return type is well-formed in traits even when `Self` isn't sized.
                 if let ty::Param(param_ty) = *proj_term.kind()
                     && param_ty.name == kw::SelfUpper
-                    && matches!(opaque.origin, hir::OpaqueTyOrigin::AsyncFn(_))
-                    && opaque.in_trait
+                    && matches!(opaque.origin, hir::OpaqueTyOrigin::AsyncFn {
+                        in_trait_or_impl: Some(hir::RpitContext::Trait),
+                        ..
+                    })
                 {
                     return;
                 }
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index 5f756672b049e..610c682d3a461 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -1186,9 +1186,9 @@ fn should_encode_type(tcx: TyCtxt<'_>, def_id: LocalDefId, def_kind: DefKind) ->
 
         DefKind::OpaqueTy => {
             let origin = tcx.opaque_type_origin(def_id);
-            if let hir::OpaqueTyOrigin::FnReturn(fn_def_id)
-            | hir::OpaqueTyOrigin::AsyncFn(fn_def_id) = origin
-                && let hir::Node::TraitItem(trait_item) = tcx.hir_node_by_def_id(fn_def_id)
+            if let hir::OpaqueTyOrigin::FnReturn { parent, .. }
+            | hir::OpaqueTyOrigin::AsyncFn { parent, .. } = origin
+                && let hir::Node::TraitItem(trait_item) = tcx.hir_node_by_def_id(parent)
                 && let (_, hir::TraitFn::Required(..)) = trait_item.expect_fn()
             {
                 false
diff --git a/compiler/rustc_middle/src/hir/map/mod.rs b/compiler/rustc_middle/src/hir/map/mod.rs
index e11361a615f4c..72e6c96e6f646 100644
--- a/compiler/rustc_middle/src/hir/map/mod.rs
+++ b/compiler/rustc_middle/src/hir/map/mod.rs
@@ -1139,13 +1139,7 @@ fn hir_id_to_string(map: Map<'_>, id: HirId) -> String {
                 ItemKind::ForeignMod { .. } => "foreign mod",
                 ItemKind::GlobalAsm(..) => "global asm",
                 ItemKind::TyAlias(..) => "ty",
-                ItemKind::OpaqueTy(opaque) => {
-                    if opaque.in_trait {
-                        "opaque type in trait"
-                    } else {
-                        "opaque type"
-                    }
-                }
+                ItemKind::OpaqueTy(..) => "opaque type",
                 ItemKind::Enum(..) => "enum",
                 ItemKind::Struct(..) => "struct",
                 ItemKind::Union(..) => "union",
diff --git a/compiler/rustc_middle/src/ty/diagnostics.rs b/compiler/rustc_middle/src/ty/diagnostics.rs
index 992eb264163ba..d98e18c1b0c2e 100644
--- a/compiler/rustc_middle/src/ty/diagnostics.rs
+++ b/compiler/rustc_middle/src/ty/diagnostics.rs
@@ -510,7 +510,7 @@ 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_mir_transform/src/coverage/query.rs b/compiler/rustc_mir_transform/src/coverage/query.rs
index e65a5fdd5e7f1..df151f8cca35e 100644
--- a/compiler/rustc_mir_transform/src/coverage/query.rs
+++ b/compiler/rustc_mir_transform/src/coverage/query.rs
@@ -63,7 +63,8 @@ fn coverage_attr_on(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
             Some([item]) if item.has_name(sym::on) => return true,
             Some(_) | None => {
                 // Other possibilities should have been rejected by `rustc_parse::validate_attr`.
-                tcx.dcx().span_bug(attr.span, "unexpected value of coverage attribute");
+                // Use `span_delayed_bug` to avoid an ICE in failing builds (#127880).
+                tcx.dcx().span_delayed_bug(attr.span, "unexpected value of coverage attribute");
             }
         }
     }
diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs
index aa329fc546ecb..100f3e80603e5 100644
--- a/compiler/rustc_passes/src/dead.rs
+++ b/compiler/rustc_passes/src/dead.rs
@@ -656,7 +656,7 @@ 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 9094b00fbfb44..d00e7eff75212 100644
--- a/compiler/rustc_privacy/src/lib.rs
+++ b/compiler/rustc_privacy/src/lib.rs
@@ -637,17 +637,44 @@ impl<'tcx> Visitor<'tcx> for EmbargoVisitor<'tcx> {
     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
         if self.impl_trait_pass
             && let hir::ItemKind::OpaqueTy(opaque) = item.kind
-            && !opaque.in_trait
         {
-            // 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.
-            let pub_ev = EffectiveVisibility::from_vis(ty::Visibility::Public);
-            self.reach_through_impl_trait(item.owner_id.def_id, pub_ev)
-                .generics()
-                .predicates()
-                .ty();
-            return;
+            let should_visit = match opaque.origin {
+                hir::OpaqueTyOrigin::FnReturn {
+                    parent,
+                    in_trait_or_impl: Some(hir::RpitContext::Trait),
+                }
+                | hir::OpaqueTyOrigin::AsyncFn {
+                    parent,
+                    in_trait_or_impl: Some(hir::RpitContext::Trait),
+                } => match self.tcx.hir_node_by_def_id(parent).expect_trait_item().expect_fn().1 {
+                    hir::TraitFn::Required(_) => false,
+                    hir::TraitFn::Provided(..) => true,
+                },
+
+                // Always visit RPITs in functions that have definitions,
+                // and all TAITs.
+                hir::OpaqueTyOrigin::FnReturn {
+                    in_trait_or_impl: None | Some(hir::RpitContext::TraitImpl),
+                    ..
+                }
+                | hir::OpaqueTyOrigin::AsyncFn {
+                    in_trait_or_impl: None | Some(hir::RpitContext::TraitImpl),
+                    ..
+                }
+                | hir::OpaqueTyOrigin::TyAlias { .. } => true,
+            };
+
+            if should_visit {
+                // 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.
+                let pub_ev = EffectiveVisibility::from_vis(ty::Visibility::Public);
+                self.reach_through_impl_trait(item.owner_id.def_id, pub_ev)
+                    .generics()
+                    .predicates()
+                    .ty();
+                return;
+            }
         }
 
         // Update levels of nested things and mark all items
diff --git a/compiler/rustc_query_impl/src/lib.rs b/compiler/rustc_query_impl/src/lib.rs
index 69742bb49b1e8..df898e0587ff9 100644
--- a/compiler/rustc_query_impl/src/lib.rs
+++ b/compiler/rustc_query_impl/src/lib.rs
@@ -2,7 +2,7 @@
 
 // tidy-alphabetical-start
 #![allow(internal_features)]
-#![allow(rustc::potential_query_instability, unused_parens)]
+#![allow(unused_parens)]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(min_specialization)]
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/static_impl_trait.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/static_impl_trait.rs
index 4bde120cba9d0..31256bca55e93 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/static_impl_trait.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/static_impl_trait.rs
@@ -284,7 +284,7 @@ pub fn suggest_new_region_bound(
         }
         match fn_return.kind {
             // FIXME(precise_captures): Suggest adding to `use<...>` list instead.
-            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_trait_selection/src/error_reporting/infer/region.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/region.rs
index 41fe8a2bf2266..a2d717817db14 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/region.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/region.rs
@@ -857,7 +857,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             }
 
             fn visit_ty(&mut self, ty: &'hir hir::Ty<'hir>) {
-                let hir::TyKind::OpaqueDef(item_id, _, _) = ty.kind else {
+                let hir::TyKind::OpaqueDef(item_id, _) = ty.kind else {
                     return hir::intravisit::walk_ty(self, ty);
                 };
                 let opaque_ty = self.tcx.hir().item(item_id).expect_opaque_ty();
@@ -1271,7 +1271,7 @@ fn suggest_precise_capturing<'tcx>(
     let hir::OpaqueTy { bounds, origin, .. } =
         tcx.hir_node_by_def_id(opaque_def_id).expect_item().expect_opaque_ty();
 
-    let hir::OpaqueTyOrigin::FnReturn(fn_def_id) = *origin else {
+    let hir::OpaqueTyOrigin::FnReturn { parent: fn_def_id, .. } = *origin else {
         return;
     };
 
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
index 5af117a3f48c4..1889ecc7670ee 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
@@ -245,6 +245,9 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                                         span, "silent safe transmute error"
                                     );
                                 }
+                                GetSafeTransmuteErrorAndReason::Default => {
+                                    (err_msg, None)
+                                }
                                 GetSafeTransmuteErrorAndReason::Error {
                                     err_msg,
                                     safe_transmute_explanation,
@@ -2226,6 +2229,12 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
     ) -> GetSafeTransmuteErrorAndReason {
         use rustc_transmute::Answer;
 
+        // We don't assemble a transmutability candidate for types that are generic
+        // and we should have ambiguity for types that still have non-region infer.
+        if obligation.predicate.has_non_region_param() || obligation.has_non_region_infer() {
+            return GetSafeTransmuteErrorAndReason::Default;
+        }
+
         // Erase regions because layout code doesn't particularly care about regions.
         let trait_ref =
             self.tcx.erase_regions(self.tcx.instantiate_bound_regions_with_erased(trait_ref));
@@ -2248,6 +2257,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
 
         let dst = trait_ref.args.type_at(0);
         let src = trait_ref.args.type_at(1);
+
         let err_msg = format!("`{src}` cannot be safely transmuted into `{dst}`");
 
         match rustc_transmute::TransmuteTypeEnv::new(self.infcx).is_transmutable(
@@ -2630,7 +2640,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         def_id: DefId,
     ) -> ErrorGuaranteed {
         let name = match self.tcx.opaque_type_origin(def_id.expect_local()) {
-            hir::OpaqueTyOrigin::FnReturn(_) | hir::OpaqueTyOrigin::AsyncFn(_) => {
+            hir::OpaqueTyOrigin::FnReturn { .. } | hir::OpaqueTyOrigin::AsyncFn { .. } => {
                 "opaque type".to_string()
             }
             hir::OpaqueTyOrigin::TyAlias { .. } => {
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
index 109bae10b54cc..becc1acfb6641 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
@@ -43,6 +43,7 @@ pub struct ImplCandidate<'tcx> {
 
 enum GetSafeTransmuteErrorAndReason {
     Silent,
+    Default,
     Error { err_msg: String, safe_transmute_explanation: Option<String> },
 }
 
diff --git a/compiler/rustc_transmute/src/layout/tree.rs b/compiler/rustc_transmute/src/layout/tree.rs
index 6d5859a5a6563..17eddbfcd7f5e 100644
--- a/compiler/rustc_transmute/src/layout/tree.rs
+++ b/compiler/rustc_transmute/src/layout/tree.rs
@@ -195,10 +195,11 @@ pub(crate) mod rustc {
     impl<'tcx> From<&LayoutError<'tcx>> for Err {
         fn from(err: &LayoutError<'tcx>) -> Self {
             match err {
-                LayoutError::Unknown(..) | LayoutError::ReferencesError(..) => Self::UnknownLayout,
+                LayoutError::Unknown(..)
+                | LayoutError::ReferencesError(..)
+                | LayoutError::NormalizationFailure(..) => Self::UnknownLayout,
                 LayoutError::SizeOverflow(..) => Self::SizeOverflow,
                 LayoutError::Cycle(err) => Self::TypeError(*err),
-                err => unimplemented!("{:?}", err),
             }
         }
     }
diff --git a/compiler/rustc_ty_utils/src/assoc.rs b/compiler/rustc_ty_utils/src/assoc.rs
index 6726db8bb54df..e41f2c8ce4869 100644
--- a/compiler/rustc_ty_utils/src/assoc.rs
+++ b/compiler/rustc_ty_utils/src/assoc.rs
@@ -323,7 +323,7 @@ fn associated_types_for_impl_traits_in_associated_fn(
 
             impl<'tcx> Visitor<'tcx> for RPITVisitor<'tcx> {
                 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
-                    if let hir::TyKind::OpaqueDef(item_id, _, _) = ty.kind
+                    if let hir::TyKind::OpaqueDef(item_id, _) = ty.kind
                         && self.rpits.insert(item_id.owner_id.def_id)
                     {
                         let opaque_item =
@@ -379,7 +379,8 @@ fn associated_type_for_impl_trait_in_trait(
     tcx: TyCtxt<'_>,
     opaque_ty_def_id: LocalDefId,
 ) -> LocalDefId {
-    let (hir::OpaqueTyOrigin::FnReturn(fn_def_id) | hir::OpaqueTyOrigin::AsyncFn(fn_def_id)) =
+    let (hir::OpaqueTyOrigin::FnReturn { parent: fn_def_id, .. }
+    | hir::OpaqueTyOrigin::AsyncFn { parent: fn_def_id, .. }) =
         tcx.opaque_type_origin(opaque_ty_def_id)
     else {
         bug!("expected opaque for {opaque_ty_def_id:?}");
diff --git a/compiler/rustc_ty_utils/src/opaque_types.rs b/compiler/rustc_ty_utils/src/opaque_types.rs
index bac0d020d721b..7c4b4887b2d75 100644
--- a/compiler/rustc_ty_utils/src/opaque_types.rs
+++ b/compiler/rustc_ty_utils/src/opaque_types.rs
@@ -141,7 +141,8 @@ impl<'tcx> OpaqueTypeCollector<'tcx> {
         let origin = self.tcx.opaque_type_origin(alias_ty.def_id.expect_local());
         trace!(?origin);
         match origin {
-            rustc_hir::OpaqueTyOrigin::FnReturn(_) | rustc_hir::OpaqueTyOrigin::AsyncFn(_) => {}
+            rustc_hir::OpaqueTyOrigin::FnReturn { .. }
+            | rustc_hir::OpaqueTyOrigin::AsyncFn { .. } => {}
             rustc_hir::OpaqueTyOrigin::TyAlias { in_assoc_ty, .. } => {
                 if !in_assoc_ty && !self.check_tait_defining_scope(alias_ty.def_id.expect_local()) {
                     return;
diff --git a/library/alloc/src/collections/binary_heap/mod.rs b/library/alloc/src/collections/binary_heap/mod.rs
index 5e59abf54ee0f..59f10b09c73fd 100644
--- a/library/alloc/src/collections/binary_heap/mod.rs
+++ b/library/alloc/src/collections/binary_heap/mod.rs
@@ -374,7 +374,10 @@ impl<'a, T: Ord, A: Allocator> PeekMut<'a, T, A> {
             // the caller could've mutated the element. It is removed from the
             // heap on the next line and pop() is not sensitive to its value.
         }
-        this.heap.pop().unwrap()
+
+        // SAFETY: Have a `PeekMut` element proves that the associated binary heap being non-empty,
+        // so the `pop` operation will not fail.
+        unsafe { this.heap.pop().unwrap_unchecked() }
     }
 }
 
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 3d845cf878f4a..b79458eaa7890 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -1828,7 +1828,7 @@ pub(crate) fn clean_ty<'tcx>(ty: &hir::Ty<'tcx>, cx: &mut DocContext<'tcx>) -> T
             Array(Box::new(clean_ty(ty, cx)), length.into())
         }
         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(ty) = item.kind {
                 ImplTrait(ty.bounds.iter().filter_map(|x| clean_generic_bound(x, cx)).collect())
diff --git a/src/librustdoc/visit_ast.rs b/src/librustdoc/visit_ast.rs
index 2cf703f57c0b6..c44e5ecaba81c 100644
--- a/src/librustdoc/visit_ast.rs
+++ b/src/librustdoc/visit_ast.rs
@@ -515,7 +515,7 @@ impl<'a, 'tcx> RustdocVisitor<'a, 'tcx> {
                 self.add_to_current_mod(item, renamed, import_id);
             }
             hir::ItemKind::OpaqueTy(hir::OpaqueTy {
-                origin: hir::OpaqueTyOrigin::AsyncFn(_) | hir::OpaqueTyOrigin::FnReturn(_),
+                origin: hir::OpaqueTyOrigin::AsyncFn { .. } | hir::OpaqueTyOrigin::FnReturn { .. },
                 ..
             }) => {
                 // return-position impl traits are never nameable, and should never be documented.
diff --git a/src/tools/clippy/clippy_lints/src/extra_unused_type_parameters.rs b/src/tools/clippy/clippy_lints/src/extra_unused_type_parameters.rs
index 3b93d3ff93ed4..796af851bac0a 100644
--- a/src/tools/clippy/clippy_lints/src/extra_unused_type_parameters.rs
+++ b/src/tools/clippy/clippy_lints/src/extra_unused_type_parameters.rs
@@ -199,7 +199,7 @@ impl<'tcx> Visitor<'tcx> for TypeWalker<'_, 'tcx> {
     fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
         if let Some((def_id, _)) = t.peel_refs().as_generic_param() {
             self.ty_params.remove(&def_id);
-        } else if let TyKind::OpaqueDef(id, _, _) = t.kind {
+        } else if let TyKind::OpaqueDef(id, _) = t.kind {
             // Explicitly walk OpaqueDef. Normally `walk_ty` would do the job, but it calls
             // `visit_nested_item`, which checks that `Self::NestedFilter::INTER` is set. We're
             // using `OnlyBodies`, so the check ends up failing and the type isn't fully walked.
diff --git a/src/tools/clippy/clippy_lints/src/len_zero.rs b/src/tools/clippy/clippy_lints/src/len_zero.rs
index c88eb70384333..45346cd18a61b 100644
--- a/src/tools/clippy/clippy_lints/src/len_zero.rs
+++ b/src/tools/clippy/clippy_lints/src/len_zero.rs
@@ -313,7 +313,7 @@ fn extract_future_output<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<&
             kind: ItemKind::OpaqueTy(opaque),
             ..
         } = item
-        && let OpaqueTyOrigin::AsyncFn(_) = opaque.origin
+        && let OpaqueTyOrigin::AsyncFn { .. } = opaque.origin
         && let [GenericBound::Trait(trait_ref, _)] = &opaque.bounds
         && let Some(segment) = trait_ref.trait_ref.path.segments.last()
         && let Some(generic_args) = segment.args
diff --git a/src/tools/clippy/clippy_lints/src/lifetimes.rs b/src/tools/clippy/clippy_lints/src/lifetimes.rs
index 034cab7202523..5c37e73544577 100644
--- a/src/tools/clippy/clippy_lints/src/lifetimes.rs
+++ b/src/tools/clippy/clippy_lints/src/lifetimes.rs
@@ -420,7 +420,7 @@ impl<'tcx> Visitor<'tcx> for RefVisitor<'_, '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 fc3bba9e51232..7097c85156c34 100644
--- a/src/tools/clippy/clippy_lints/src/manual_async_fn.rs
+++ b/src/tools/clippy/clippy_lints/src/manual_async_fn.rs
@@ -105,7 +105,7 @@ fn future_trait_ref<'tcx>(
     cx: &LateContext<'tcx>,
     ty: &'tcx Ty<'tcx>,
 ) -> Option<(&'tcx TraitRef<'tcx>, Vec<LifetimeName>)> {
-    if let TyKind::OpaqueDef(item_id, bounds, false) = ty.kind
+    if let TyKind::OpaqueDef(item_id, bounds) = ty.kind
         && let item = cx.tcx.hir().item(item_id)
         && let ItemKind::OpaqueTy(opaque) = &item.kind
         && 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 06a5cb1a84f0c..a19c1555d166f 100644
--- a/src/tools/clippy/clippy_utils/src/hir_utils.rs
+++ b/src/tools/clippy/clippy_utils/src/hir_utils.rs
@@ -1126,9 +1126,8 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
                 }
             },
             TyKind::Path(ref qpath) => self.hash_qpath(qpath),
-            TyKind::OpaqueDef(_, arg_list, in_trait) => {
+            TyKind::OpaqueDef(_, arg_list) => {
                 self.hash_generic_args(arg_list);
-                in_trait.hash(&mut self.s);
             },
             TyKind::TraitObject(_, lifetime, _) => {
                 self.hash_lifetime(lifetime);
diff --git a/tests/codegen/binary-heap-peek-mut-pop-no-panic.rs b/tests/codegen/binary-heap-peek-mut-pop-no-panic.rs
new file mode 100644
index 0000000000000..9cf4f210e527a
--- /dev/null
+++ b/tests/codegen/binary-heap-peek-mut-pop-no-panic.rs
@@ -0,0 +1,13 @@
+//@ compile-flags: -O
+//@ ignore-debug
+#![crate_type = "lib"]
+
+use std::collections::binary_heap::PeekMut;
+
+// CHECK-LABEL: @peek_mut_pop
+#[no_mangle]
+pub fn peek_mut_pop(peek_mut: PeekMut<u32>) -> u32 {
+    // CHECK-NOT: panic
+    // CHECK-NOT: unwrap_failed
+    PeekMut::pop(peek_mut)
+}
diff --git a/tests/crashes/125881.rs b/tests/crashes/125881.rs
deleted file mode 100644
index a38f1891b61d9..0000000000000
--- a/tests/crashes/125881.rs
+++ /dev/null
@@ -1,8 +0,0 @@
-//@ known-bug: rust-lang/rust#125881
-#![crate_type = "lib"]
-#![feature(transmutability)]
-#![feature(unboxed_closures,effects)]
-
-const fn test() -> impl std::mem::TransmuteFrom() {
-    || {}
-}
diff --git a/tests/crashes/126377.rs b/tests/crashes/126377.rs
deleted file mode 100644
index f6727bcc0a494..0000000000000
--- a/tests/crashes/126377.rs
+++ /dev/null
@@ -1,29 +0,0 @@
-//@ known-bug: rust-lang/rust#126377
-
-#![feature(effects)]
-#![feature(generic_const_exprs)]
-
-mod assert {
-    use std::mem::{Assume, TransmuteFrom};
-
-    pub fn is_transmutable<
-        Src,
-        Dst,
-        const ASSUME_ALIGNMENT: bool,
-        const ASSUME_LIFETIMES: bool,
-        const ASSUME_SAFETY: bool,
-        const ASSUME_VALIDITY: bool,
-    >()
-    where
-        Dst: TransmuteFrom<
-            Src,
-            {  }
-        >,
-    {}
-}
-
-const fn from_options() -> Assume {
-    #[repr(C)] struct Src;
-    #[repr(C)] struct Dst;
-    assert::is_transmutable::<Src, Dst, {0u8}, false, false, false>();
-}
diff --git a/tests/crashes/127880.rs b/tests/crashes/127880.rs
deleted file mode 100644
index 6c625eac6914a..0000000000000
--- a/tests/crashes/127880.rs
+++ /dev/null
@@ -1,5 +0,0 @@
-//@ known-bug: #127880
-//@ compile-flags: -Cinstrument-coverage
-
-#[coverage]
-fn main() {}
diff --git a/tests/crashes/130413.rs b/tests/crashes/130413.rs
deleted file mode 100644
index 08435ac6450c0..0000000000000
--- a/tests/crashes/130413.rs
+++ /dev/null
@@ -1,17 +0,0 @@
-//@ known-bug: #130413
-
-#![feature(transmutability)]
-trait Aaa {
-    type Y;
-}
-
-trait Bbb {
-    type B: std::mem::TransmuteFrom<()>;
-}
-
-impl<T> Bbb for T
-where
-    T: Aaa,
-{
-    type B = T::Y;
-}
diff --git a/tests/ui/coverage-attr/bad-attr-ice.feat.stderr b/tests/ui/coverage-attr/bad-attr-ice.feat.stderr
new file mode 100644
index 0000000000000..9e3cd41c2777d
--- /dev/null
+++ b/tests/ui/coverage-attr/bad-attr-ice.feat.stderr
@@ -0,0 +1,15 @@
+error: malformed `coverage` attribute input
+  --> $DIR/bad-attr-ice.rs:10:1
+   |
+LL | #[coverage]
+   | ^^^^^^^^^^^
+   |
+help: the following are the possible correct uses
+   |
+LL | #[coverage(off)]
+   |
+LL | #[coverage(on)]
+   |
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/coverage-attr/bad-attr-ice.nofeat.stderr b/tests/ui/coverage-attr/bad-attr-ice.nofeat.stderr
new file mode 100644
index 0000000000000..d73636e158bae
--- /dev/null
+++ b/tests/ui/coverage-attr/bad-attr-ice.nofeat.stderr
@@ -0,0 +1,26 @@
+error: malformed `coverage` attribute input
+  --> $DIR/bad-attr-ice.rs:10:1
+   |
+LL | #[coverage]
+   | ^^^^^^^^^^^
+   |
+help: the following are the possible correct uses
+   |
+LL | #[coverage(off)]
+   |
+LL | #[coverage(on)]
+   |
+
+error[E0658]: the `#[coverage]` attribute is an experimental feature
+  --> $DIR/bad-attr-ice.rs:10:1
+   |
+LL | #[coverage]
+   | ^^^^^^^^^^^
+   |
+   = note: see issue #84605 <https://github.com/rust-lang/rust/issues/84605> for more information
+   = help: add `#![feature(coverage_attribute)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/coverage-attr/bad-attr-ice.rs b/tests/ui/coverage-attr/bad-attr-ice.rs
new file mode 100644
index 0000000000000..ae4d27d65ebd6
--- /dev/null
+++ b/tests/ui/coverage-attr/bad-attr-ice.rs
@@ -0,0 +1,16 @@
+#![cfg_attr(feat, feature(coverage_attribute))]
+//@ revisions: feat nofeat
+//@ compile-flags: -Cinstrument-coverage
+//@ needs-profiler-support
+
+// Malformed `#[coverage(..)]` attributes should not cause an ICE when built
+// with `-Cinstrument-coverage`.
+// Regression test for <https://github.com/rust-lang/rust/issues/127880>.
+
+#[coverage]
+//~^ ERROR malformed `coverage` attribute input
+//[nofeat]~| the `#[coverage]` attribute is an experimental feature
+fn main() {}
+
+// FIXME(#130766): When the `#[coverage(..)]` attribute is stabilized,
+// get rid of the revisions and just make this a normal test.
diff --git a/tests/ui/methods/dont-suggest-import-on-deref-err.rs b/tests/ui/methods/dont-suggest-import-on-deref-err.rs
new file mode 100644
index 0000000000000..c24ab7919824b
--- /dev/null
+++ b/tests/ui/methods/dont-suggest-import-on-deref-err.rs
@@ -0,0 +1,13 @@
+use std::clone::Clone;
+use std::ops::Deref;
+
+#[derive(Clone)]
+pub struct Foo {}
+
+impl Deref for Foo {}
+//~^ ERROR not all trait items implemented
+
+pub fn main() {
+    let f = Foo {};
+    let _ = f.clone();
+}
diff --git a/tests/ui/methods/dont-suggest-import-on-deref-err.stderr b/tests/ui/methods/dont-suggest-import-on-deref-err.stderr
new file mode 100644
index 0000000000000..20a63ff375d19
--- /dev/null
+++ b/tests/ui/methods/dont-suggest-import-on-deref-err.stderr
@@ -0,0 +1,12 @@
+error[E0046]: not all trait items implemented, missing: `Target`, `deref`
+  --> $DIR/dont-suggest-import-on-deref-err.rs:7:1
+   |
+LL | impl Deref for Foo {}
+   | ^^^^^^^^^^^^^^^^^^ missing `Target`, `deref` in implementation
+   |
+   = help: implement the missing item: `type Target = /* Type */;`
+   = help: implement the missing item: `fn deref(&self) -> &<Self as Deref>::Target { todo!() }`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0046`.
diff --git a/tests/ui/transmutability/assoc-bound.rs b/tests/ui/transmutability/assoc-bound.rs
new file mode 100644
index 0000000000000..e8a20b45cde34
--- /dev/null
+++ b/tests/ui/transmutability/assoc-bound.rs
@@ -0,0 +1,25 @@
+#![crate_type = "lib"]
+#![feature(transmutability)]
+
+trait A {
+    type AssocA;
+}
+
+trait B {
+    type AssocB: std::mem::TransmuteFrom<()>;
+}
+
+impl<T> B for (T, u8)
+where
+    T: A,
+{
+    type AssocB = T::AssocA; //~ERROR: the trait bound `<T as A>::AssocA: TransmuteFrom<(), Assume { alignment: false, lifetimes: false, safety: false, validity: false }>` is not satisfied [E0277]
+}
+
+
+impl<T> B for (T, u16)
+where
+    for<'a> &'a i32: A,
+{
+    type AssocB = <&'static i32 as A>::AssocA; //~ERROR: `()` cannot be safely transmuted into `<&i32 as A>::AssocA`
+}
diff --git a/tests/ui/transmutability/assoc-bound.stderr b/tests/ui/transmutability/assoc-bound.stderr
new file mode 100644
index 0000000000000..08d9089439645
--- /dev/null
+++ b/tests/ui/transmutability/assoc-bound.stderr
@@ -0,0 +1,31 @@
+error[E0277]: the trait bound `<T as A>::AssocA: TransmuteFrom<(), Assume { alignment: false, lifetimes: false, safety: false, validity: false }>` is not satisfied
+  --> $DIR/assoc-bound.rs:16:19
+   |
+LL |     type AssocB = T::AssocA;
+   |                   ^^^^^^^^^ the trait `TransmuteFrom<(), Assume { alignment: false, lifetimes: false, safety: false, validity: false }>` is not implemented for `<T as A>::AssocA`
+   |
+note: required by a bound in `B::AssocB`
+  --> $DIR/assoc-bound.rs:9:18
+   |
+LL |     type AssocB: std::mem::TransmuteFrom<()>;
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `B::AssocB`
+help: consider further restricting the associated type
+   |
+LL |     T: A, <T as A>::AssocA: TransmuteFrom<(), Assume { alignment: false, lifetimes: false, safety: false, validity: false }>
+   |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+error[E0277]: `()` cannot be safely transmuted into `<&i32 as A>::AssocA`
+  --> $DIR/assoc-bound.rs:24:19
+   |
+LL |     type AssocB = <&'static i32 as A>::AssocA;
+   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^ `<&i32 as A>::AssocA` has an unknown layout
+   |
+note: required by a bound in `B::AssocB`
+  --> $DIR/assoc-bound.rs:9:18
+   |
+LL |     type AssocB: std::mem::TransmuteFrom<()>;
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `B::AssocB`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.