Auto merge of #109130 - matthiaskrgr:rollup-dm3jza6, r=matthiaskrgr

Rollup of 9 pull requests

Successful merges:

 - #108722 (Support for Fuchsia RISC-V target)
 - #108880 (Remove tests/ui/impl-trait/in-trait/new-lowering-strategy in favor of using revisions on existing tests)
 - #108909 (Fix object safety checks for new RPITITs)
 - #108915 (Remove some direct calls to local_def_id_to_hir_id on diagnostics)
 - #108923 (Make fns from other crates with RPITIT work for -Zlower-impl-trait-in-trait-to-assoc-ty)
 - #109101 (Fall back to old metadata computation when type references errors)
 - #109105 (Don't ICE for late-bound consts across `AnonConstBoundary`)
 - #109110 (Don't codegen impossible to satisfy impls)
 - #109116 (Emit diagnostic when calling methods on the unit type in method chains)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_hir/src/definitions.rs

@@ -404,8 +404,12 @@ impl DefPathData {
         match *self {
             TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name) => Some(name),
 
+            // We use this name when collecting `ModChild`s.
+            // FIXME this could probably be removed with some refactoring to the name resolver.
+            ImplTraitAssocTy => Some(kw::Empty),
+
             Impl | ForeignMod | CrateRoot | Use | GlobalAsm | ClosureExpr | Ctor | AnonConst
-            | ImplTrait | ImplTraitAssocTy => None,
+            | ImplTrait => None,
         }
     }
 

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -1440,6 +1440,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                             tcx.associated_items(pred.def_id())
                                 .in_definition_order()
                                 .filter(|item| item.kind == ty::AssocKind::Type)
+                                .filter(|item| tcx.opt_rpitit_info(item.def_id).is_none())
                                 .map(|item| item.def_id),
                         );
                     }

compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs

@@ -1427,25 +1427,25 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
             if let ResolvedArg::LateBound(..) = def && crossed_anon_const {
                 let use_span = self.tcx.hir().span(hir_id);
                 let def_span = self.tcx.def_span(param_def_id);
-                match self.tcx.def_kind(param_def_id) {
+                let guar = match self.tcx.def_kind(param_def_id) {
                     DefKind::ConstParam => {
                         self.tcx.sess.emit_err(errors::CannotCaptureLateBoundInAnonConst::Const {
                             use_span,
                             def_span,
-                        });
+                        })
                     }
                     DefKind::TyParam => {
                         self.tcx.sess.emit_err(errors::CannotCaptureLateBoundInAnonConst::Type {
                             use_span,
                             def_span,
-                        });
+                        })
                     }
                     _ => unreachable!(),
-                }
+                };
-                return;
+                self.map.defs.insert(hir_id, ResolvedArg::Error(guar));
+            } else {
+                self.map.defs.insert(hir_id, def);
             }
-
-            self.map.defs.insert(hir_id, def);
             return;
         }
 

compiler/rustc_hir_typeck/src/demand.rs

@@ -83,7 +83,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self.annotate_expected_due_to_let_ty(err, expr, error);
         self.emit_type_mismatch_suggestions(err, expr, expr_ty, expected, expected_ty_expr, error);
         self.note_type_is_not_clone(err, expected, expr_ty, expr);
-        self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
+        self.note_internal_mutation_in_method(err, expr, Some(expected), expr_ty);
         self.check_for_range_as_method_call(err, expr, expr_ty, expected);
         self.check_for_binding_assigned_block_without_tail_expression(err, expr, expr_ty, expected);
         self.check_wrong_return_type_due_to_generic_arg(err, expr, expr_ty);

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -950,44 +950,75 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         &self,
         err: &mut Diagnostic,
         expr: &hir::Expr<'_>,
-        expected: Ty<'tcx>,
+        expected: Option<Ty<'tcx>>,
         found: Ty<'tcx>,
     ) {
         if found != self.tcx.types.unit {
             return;
         }
-        if let ExprKind::MethodCall(path_segment, rcvr, ..) = expr.kind {
+
-            if self
+        let ExprKind::MethodCall(path_segment, rcvr, ..) = expr.kind else {
-                .typeck_results
+            return;
+        };
+
+        let rcvr_has_the_expected_type = self
+            .typeck_results
+            .borrow()
+            .expr_ty_adjusted_opt(rcvr)
+            .and_then(|ty| expected.map(|expected_ty| expected_ty.peel_refs() == ty.peel_refs()))
+            .unwrap_or(false);
+
+        let prev_call_mutates_and_returns_unit = || {
+            self.typeck_results
                 .borrow()
-                .expr_ty_adjusted_opt(rcvr)
+                .type_dependent_def_id(expr.hir_id)
-                .map_or(true, |ty| expected.peel_refs() != ty.peel_refs())
+                .map(|def_id| self.tcx.fn_sig(def_id).skip_binder().skip_binder())
-            {
+                .and_then(|sig| sig.inputs_and_output.split_last())
-                return;
+                .map(|(output, inputs)| {
-            }
+                    output.is_unit()
-            let mut sp = MultiSpan::from_span(path_segment.ident.span);
+                        && inputs
-            sp.push_span_label(
+                            .get(0)
-                path_segment.ident.span,
+                            .and_then(|self_ty| self_ty.ref_mutability())
-                format!(
+                            .map_or(false, rustc_ast::Mutability::is_mut)
-                    "this call modifies {} in-place",
+                })
-                    match rcvr.kind {
+                .unwrap_or(false)
-                        ExprKind::Path(QPath::Resolved(
+        };
-                            None,
+
-                            hir::Path { segments: [segment], .. },
+        if !(rcvr_has_the_expected_type || prev_call_mutates_and_returns_unit()) {
-                        )) => format!("`{}`", segment.ident),
+            return;
-                        _ => "its receiver".to_string(),
+        }
-                    }
+
-                ),
+        let mut sp = MultiSpan::from_span(path_segment.ident.span);
-            );
+        sp.push_span_label(
+            path_segment.ident.span,
+            format!(
+                "this call modifies {} in-place",
+                match rcvr.kind {
+                    ExprKind::Path(QPath::Resolved(
+                        None,
+                        hir::Path { segments: [segment], .. },
+                    )) => format!("`{}`", segment.ident),
+                    _ => "its receiver".to_string(),
+                }
+            ),
+        );
+
+        let modifies_rcvr_note =
+            format!("method `{}` modifies its receiver in-place", path_segment.ident);
+        if rcvr_has_the_expected_type {
             sp.push_span_label(
                 rcvr.span,
                 "you probably want to use this value after calling the method...",
             );
+            err.span_note(sp, &modifies_rcvr_note);
+            err.note(&format!("...instead of the `()` output of method `{}`", path_segment.ident));
+        } else if let ExprKind::MethodCall(..) = rcvr.kind {
             err.span_note(
                 sp,
-                &format!("method `{}` modifies its receiver in-place", path_segment.ident),
+                modifies_rcvr_note.clone() + ", it is not meant to be used in method chains.",
             );
-            err.note(&format!("...instead of the `()` output of method `{}`", path_segment.ident));
+        } else {
+            err.span_note(sp, &modifies_rcvr_note);
         }
     }
 

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -416,6 +416,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 );
                 probe.is_ok()
             });
+
+            self.note_internal_mutation_in_method(
+                &mut err,
+                rcvr_expr,
+                expected.to_option(&self),
+                rcvr_ty,
+            );
         }
 
         let mut custom_span_label = false;

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1356,13 +1356,14 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         debug!("EncodeContext::encode_info_for_impl_item({:?})", def_id);
         let tcx = self.tcx;
 
-        let ast_item = self.tcx.hir().expect_impl_item(def_id.expect_local());
+        let defaultness = self.tcx.impl_defaultness(def_id.expect_local());
-        self.tables.impl_defaultness.set_some(def_id.index, ast_item.defaultness);
+        self.tables.impl_defaultness.set_some(def_id.index, defaultness);
         let impl_item = self.tcx.associated_item(def_id);
         self.tables.assoc_container.set_some(def_id.index, impl_item.container);
 
         match impl_item.kind {
             ty::AssocKind::Fn => {
+                let ast_item = self.tcx.hir().expect_impl_item(def_id.expect_local());
                 let hir::ImplItemKind::Fn(ref sig, body) = ast_item.kind else { bug!() };
                 self.tables.asyncness.set_some(def_id.index, sig.header.asyncness);
                 record_array!(self.tables.fn_arg_names[def_id] <- self.tcx.hir().body_param_names(body));

compiler/rustc_middle/src/hir/map/mod.rs

@@ -316,7 +316,7 @@ impl<'hir> Map<'hir> {
     /// Retrieves the `Node` corresponding to `id`, returning `None` if cannot be found.
     #[inline]
     pub fn find_by_def_id(self, id: LocalDefId) -> Option<Node<'hir>> {
-        self.find(self.local_def_id_to_hir_id(id))
+        self.find(self.tcx.opt_local_def_id_to_hir_id(id)?)
     }
 
     /// Retrieves the `Node` corresponding to `id`, panicking if it cannot be found.
@@ -333,7 +333,7 @@ impl<'hir> Map<'hir> {
     }
 
     pub fn get_if_local(self, id: DefId) -> Option<Node<'hir>> {
-        id.as_local().and_then(|id| self.find(self.local_def_id_to_hir_id(id)))
+        id.as_local().and_then(|id| self.find(self.tcx.opt_local_def_id_to_hir_id(id)?))
     }
 
     pub fn get_generics(self, id: LocalDefId) -> Option<&'hir Generics<'hir>> {

compiler/rustc_middle/src/ty/layout.rs

@@ -730,7 +730,11 @@ where
                         */
                     };
 
-                    let metadata = if let Some(metadata_def_id) = tcx.lang_items().metadata_type() {
+                    let metadata = if let Some(metadata_def_id) = tcx.lang_items().metadata_type()
+                        // Projection eagerly bails out when the pointee references errors,
+                        // fall back to structurally deducing metadata.
+                        && !pointee.references_error()
+                    {
                         let metadata = tcx.normalize_erasing_regions(
                             cx.param_env(),
                             tcx.mk_projection(metadata_def_id, [pointee]),

compiler/rustc_monomorphize/src/collector.rs

@@ -1326,6 +1326,21 @@ fn create_mono_items_for_default_impls<'tcx>(
         return;
     }
 
+    // Unlike 'lazy' monomorphization that begins by collecting items transitively
+    // called by `main` or other global items, when eagerly monomorphizing impl
+    // items, we never actually check that the predicates of this impl are satisfied
+    // in a empty reveal-all param env (i.e. with no assumptions).
+    //
+    // Even though this impl has no substitutions, because we don't consider higher-
+    // ranked predicates such as `for<'a> &'a mut [u8]: Copy` to be trivially false,
+    // we must now check that the impl has no impossible-to-satisfy predicates.
+    if tcx.subst_and_check_impossible_predicates((
+        item.owner_id.to_def_id(),
+        &InternalSubsts::identity_for_item(tcx, item.owner_id.to_def_id()),
+    )) {
+        return;
+    }
+
     let Some(trait_ref) = tcx.impl_trait_ref(item.owner_id) else {
         return;
     };

compiler/rustc_target/src/spec/mod.rs

@@ -1115,6 +1115,7 @@ supported_targets! {
     // FIXME(#106649): Remove aarch64-fuchsia in favor of aarch64-unknown-fuchsia
     ("aarch64-fuchsia", aarch64_fuchsia),
     ("aarch64-unknown-fuchsia", aarch64_unknown_fuchsia),
+    ("riscv64gc-unknown-fuchsia", riscv64gc_unknown_fuchsia),
     // FIXME(#106649): Remove x86_64-fuchsia in favor of x86_64-unknown-fuchsia
     ("x86_64-fuchsia", x86_64_fuchsia),
     ("x86_64-unknown-fuchsia", x86_64_unknown_fuchsia),

compiler/rustc_target/src/spec/riscv64gc_unknown_fuchsia.rs

@@ -0,0 +1,19 @@
+use crate::spec::{CodeModel, SanitizerSet, Target, TargetOptions};
+
+pub fn target() -> Target {
+    Target {
+        llvm_target: "riscv64gc-unknown-fuchsia".into(),
+        pointer_width: 64,
+        data_layout: "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128".into(),
+        arch: "riscv64".into(),
+        options: TargetOptions {
+            code_model: Some(CodeModel::Medium),
+            cpu: "generic-rv64".into(),
+            features: "+m,+a,+f,+d,+c".into(),
+            llvm_abiname: "lp64d".into(),
+            max_atomic_width: Some(64),
+            supported_sanitizers: SanitizerSet::SHADOWCALLSTACK,
+            ..super::fuchsia_base::opts()
+        },
+    }
+}

compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs

@@ -144,6 +144,10 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         trait_ref: ty::PolyTraitRef<'tcx>,
         obligation: &PredicateObligation<'tcx>,
     ) -> OnUnimplementedNote {
+        if self.tcx.opt_rpitit_info(obligation.cause.body_id.to_def_id()).is_some() {
+            return OnUnimplementedNote::default();
+        }
+
         let (def_id, substs) = self
             .impl_similar_to(trait_ref, obligation)
             .unwrap_or_else(|| (trait_ref.def_id(), trait_ref.skip_binder().substs));

compiler/rustc_trait_selection/src/traits/object_safety.rs

@@ -13,7 +13,6 @@ use super::{elaborate_predicates, elaborate_trait_ref};
 use crate::infer::TyCtxtInferExt;
 use crate::traits::query::evaluate_obligation::InferCtxtExt;
 use crate::traits::{self, Obligation, ObligationCause};
-use hir::def::DefKind;
 use rustc_errors::{DelayDm, FatalError, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
@@ -157,6 +156,7 @@ fn object_safety_violations_for_trait(
                 .in_definition_order()
                 .filter(|item| item.kind == ty::AssocKind::Type)
                 .filter(|item| !tcx.generics_of(item.def_id).params.is_empty())
+                .filter(|item| tcx.opt_rpitit_info(item.def_id).is_none())
                 .map(|item| {
                     let ident = item.ident(tcx);
                     ObjectSafetyViolation::GAT(ident.name, ident.span)
@@ -854,7 +854,7 @@ fn contains_illegal_self_type_reference<'tcx, T: TypeVisitable<TyCtxt<'tcx>>>(
                     }
                 }
                 ty::Alias(ty::Projection, ref data)
-                    if self.tcx.def_kind(data.def_id) == DefKind::ImplTraitPlaceholder =>
+                    if self.tcx.is_impl_trait_in_trait(data.def_id) =>
                 {
                     // We'll deny these later in their own pass
                     ControlFlow::Continue(())
@@ -921,7 +921,7 @@ pub fn contains_illegal_impl_trait_in_trait<'tcx>(
     ty.skip_binder().walk().find_map(|arg| {
         if let ty::GenericArgKind::Type(ty) = arg.unpack()
             && let ty::Alias(ty::Projection, proj) = ty.kind()
-            && tcx.def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder
+            && tcx.is_impl_trait_in_trait(proj.def_id)
         {
             Some(MethodViolationCode::ReferencesImplTraitInTrait(tcx.def_span(proj.def_id)))
         } else {

compiler/rustc_ty_utils/src/assoc.rs

@@ -328,6 +328,9 @@ fn impl_associated_item_for_impl_trait_in_trait(
     // `opt_local_def_id_to_hir_id` with `None`.
     impl_assoc_ty.opt_local_def_id_to_hir_id(None);
 
+    // Copy span of the opaque.
+    impl_assoc_ty.def_ident_span(Some(span));
+
     impl_assoc_ty.associated_item(ty::AssocItem {
         name: kw::Empty,
         kind: ty::AssocKind::Type,
@@ -342,6 +345,9 @@ fn impl_associated_item_for_impl_trait_in_trait(
     // extra predicates to assume.
     impl_assoc_ty.param_env(tcx.param_env(impl_fn_def_id));
 
+    // Copy visility of the containing function.
+    impl_assoc_ty.visibility(tcx.visibility(impl_fn_def_id));
+
     // Copy impl_defaultness of the containing function.
     impl_assoc_ty.impl_defaultness(tcx.impl_defaultness(impl_fn_def_id));
 

compiler/rustc_ty_utils/src/layout.rs

@@ -156,7 +156,11 @@ fn layout_of_uncached<'tcx>(
 
             let unsized_part = tcx.struct_tail_erasing_lifetimes(pointee, param_env);
 
-            let metadata = if let Some(metadata_def_id) = tcx.lang_items().metadata_type() {
+            let metadata = if let Some(metadata_def_id) = tcx.lang_items().metadata_type()
+                // Projection eagerly bails out when the pointee references errors,
+                // fall back to structurally deducing metadata.
+                && !pointee.references_error()
+            {
                 let metadata_ty = tcx.normalize_erasing_regions(
                     param_env,
                     tcx.mk_projection(metadata_def_id, [pointee]),

src/doc/rustc/src/platform-support.md

@@ -295,6 +295,7 @@ target | std | host | notes
 [`riscv32imac-unknown-xous-elf`](platform-support/riscv32imac-unknown-xous-elf.md) | ? |  | RISC-V Xous (RV32IMAC ISA)
 `riscv32imc-esp-espidf` | ✓ |  | RISC-V ESP-IDF
 `riscv64gc-unknown-freebsd` |   |   | RISC-V FreeBSD
+`riscv64gc-unknown-fuchsia` |   |   | RISC-V Fuchsia
 `riscv64gc-unknown-linux-musl` |   |   | RISC-V Linux (kernel 4.20, musl 1.2.0)
 [`riscv64gc-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | OpenBSD/riscv64
 `s390x-unknown-linux-musl` |  |  | S390x Linux (kernel 3.2, MUSL)

tests/ui/async-await/in-trait/async-associated-types.rs

@@ -1,5 +1,7 @@
 // check-pass
 // edition: 2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![feature(impl_trait_projections)]

tests/ui/async-await/in-trait/async-associated-types2.rs

@@ -1,5 +1,7 @@
 // check-pass
 // edition: 2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![feature(type_alias_impl_trait)]

tests/ui/async-await/in-trait/async-example-desugared-boxed-in-trait.current.stderr

@@ -1,11 +1,11 @@
 error[E0053]: method `foo` has an incompatible type for trait
-  --> $DIR/async-example-desugared-boxed-in-trait.rs:15:28
+  --> $DIR/async-example-desugared-boxed-in-trait.rs:17:28
    |
 LL |     async fn foo(&self) -> i32 {
    |                            ^^^ expected `Pin<Box<dyn Future<Output = i32>>>`, found future
    |
 note: type in trait
-  --> $DIR/async-example-desugared-boxed-in-trait.rs:11:22
+  --> $DIR/async-example-desugared-boxed-in-trait.rs:13:22
    |
 LL |     fn foo(&self) -> Pin<Box<dyn Future<Output = i32> + '_>>;
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

tests/ui/async-await/in-trait/async-example-desugared-boxed-in-trait.next.stderr

@@ -0,0 +1,17 @@
+error[E0053]: method `foo` has an incompatible type for trait
+  --> $DIR/async-example-desugared-boxed-in-trait.rs:17:28
+   |
+LL |     async fn foo(&self) -> i32 {
+   |                            ^^^ expected `Pin<Box<dyn Future<Output = i32>>>`, found future
+   |
+note: type in trait
+  --> $DIR/async-example-desugared-boxed-in-trait.rs:13:22
+   |
+LL |     fn foo(&self) -> Pin<Box<dyn Future<Output = i32> + '_>>;
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: expected signature `fn(&i32) -> Pin<Box<dyn Future<Output = i32>>>`
+              found signature `fn(&i32) -> impl Future<Output = i32>`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0053`.

tests/ui/async-await/in-trait/async-example-desugared-boxed-in-trait.rs

@@ -1,4 +1,6 @@
 // edition: 2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![feature(return_position_impl_trait_in_trait)]

tests/ui/async-await/in-trait/async-example-desugared-boxed.current.stderr

@@ -1,5 +1,5 @@
 error: method `foo` should be async because the method from the trait is async
-  --> $DIR/async-example-desugared-boxed.rs:15:5
+  --> $DIR/async-example-desugared-boxed.rs:17:5
    |
 LL |     async fn foo(&self) -> i32;
    |     --------------------------- required because the trait method is async

tests/ui/async-await/in-trait/async-example-desugared-boxed.next.stderr

@@ -0,0 +1,11 @@
+error: method `foo` should be async because the method from the trait is async
+  --> $DIR/async-example-desugared-boxed.rs:17:5
+   |
+LL |     async fn foo(&self) -> i32;
+   |     --------------------------- required because the trait method is async
+...
+LL |     fn foo(&self) -> Pin<Box<dyn Future<Output = i32> + '_>> {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+

tests/ui/async-await/in-trait/async-example-desugared-boxed.rs

@@ -1,4 +1,6 @@
 // edition: 2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![feature(return_position_impl_trait_in_trait)]

tests/ui/async-await/in-trait/async-example-desugared-extra.rs

@@ -1,5 +1,7 @@
 // check-pass
 // edition: 2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![feature(return_position_impl_trait_in_trait)]

tests/ui/async-await/in-trait/async-example-desugared-in-trait.rs

@@ -1,5 +1,7 @@
 // check-pass
 // edition: 2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![feature(return_position_impl_trait_in_trait)]

tests/ui/async-await/in-trait/async-example-desugared-manual.current.stderr

@@ -1,5 +1,5 @@
 error: method `foo` should be async because the method from the trait is async
-  --> $DIR/async-example-desugared-manual.rs:23:5
+  --> $DIR/async-example-desugared-manual.rs:25:5
    |
 LL |     async fn foo(&self) -> i32;
    |     --------------------------- required because the trait method is async

tests/ui/async-await/in-trait/async-example-desugared-manual.next.stderr

@@ -0,0 +1,11 @@
+error: method `foo` should be async because the method from the trait is async
+  --> $DIR/async-example-desugared-manual.rs:25:5
+   |
+LL |     async fn foo(&self) -> i32;
+   |     --------------------------- required because the trait method is async
+...
+LL |     fn foo(&self) -> MyFuture {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+

tests/ui/async-await/in-trait/async-example-desugared-manual.rs

@@ -1,4 +1,6 @@
 // edition: 2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![feature(return_position_impl_trait_in_trait)]

tests/ui/async-await/in-trait/async-example-desugared.rs

@@ -1,5 +1,7 @@
 // check-pass
 // edition: 2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![feature(return_position_impl_trait_in_trait)]

tests/ui/async-await/in-trait/async-recursive-generic.current.stderr

@@ -1,5 +1,5 @@
 error[E0733]: recursion in an `async fn` requires boxing
-  --> $DIR/async-recursive-generic.rs:11:48
+  --> $DIR/async-recursive-generic.rs:13:48
    |
 LL |     async fn foo_recursive(&self, n: usize) -> T {
    |                                                ^ recursive `async fn`

tests/ui/async-await/in-trait/async-recursive-generic.next.stderr

@@ -0,0 +1,12 @@
+error[E0733]: recursion in an `async fn` requires boxing
+  --> $DIR/async-recursive-generic.rs:13:48
+   |
+LL |     async fn foo_recursive(&self, n: usize) -> T {
+   |                                                ^ recursive `async fn`
+   |
+   = note: a recursive `async fn` must be rewritten to return a boxed `dyn Future`
+   = note: consider using the `async_recursion` crate: https://crates.io/crates/async_recursion
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0733`.

tests/ui/async-await/in-trait/async-recursive-generic.rs

@@ -1,4 +1,6 @@
 // edition: 2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![allow(incomplete_features)]

tests/ui/async-await/in-trait/async-recursive.current.stderr

@@ -1,5 +1,5 @@
 error[E0733]: recursion in an `async fn` requires boxing
-  --> $DIR/async-recursive.rs:11:48
+  --> $DIR/async-recursive.rs:13:48
    |
 LL |     async fn foo_recursive(&self, n: usize) -> i32 {
    |                                                ^^^ recursive `async fn`

tests/ui/async-await/in-trait/async-recursive.next.stderr

@@ -0,0 +1,12 @@
+error[E0733]: recursion in an `async fn` requires boxing
+  --> $DIR/async-recursive.rs:13:48
+   |
+LL |     async fn foo_recursive(&self, n: usize) -> i32 {
+   |                                                ^^^ recursive `async fn`
+   |
+   = note: a recursive `async fn` must be rewritten to return a boxed `dyn Future`
+   = note: consider using the `async_recursion` crate: https://crates.io/crates/async_recursion
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0733`.

tests/ui/async-await/in-trait/async-recursive.rs

@@ -1,4 +1,6 @@
 // edition: 2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![allow(incomplete_features)]

tests/ui/async-await/in-trait/bad-signatures.current.stderr

@@ -1,11 +1,11 @@
 error: expected identifier, found keyword `self`
-  --> $DIR/bad-signatures.rs:7:23
+  --> $DIR/bad-signatures.rs:9:23
    |
 LL |     async fn bar(&abc self);
    |                       ^^^^ expected identifier, found keyword
 
 error: expected one of `:`, `@`, or `|`, found keyword `self`
-  --> $DIR/bad-signatures.rs:7:23
+  --> $DIR/bad-signatures.rs:9:23
    |
 LL |     async fn bar(&abc self);
    |                  -----^^^^
@@ -14,7 +14,7 @@ LL |     async fn bar(&abc self);
    |                  help: declare the type after the parameter binding: `<identifier>: <type>`
 
 warning: the feature `async_fn_in_trait` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/bad-signatures.rs:3:12
+  --> $DIR/bad-signatures.rs:5:12
    |
 LL | #![feature(async_fn_in_trait)]
    |            ^^^^^^^^^^^^^^^^^

tests/ui/async-await/in-trait/bad-signatures.next.stderr

@@ -0,0 +1,26 @@
+error: expected identifier, found keyword `self`
+  --> $DIR/bad-signatures.rs:9:23
+   |
+LL |     async fn bar(&abc self);
+   |                       ^^^^ expected identifier, found keyword
+
+error: expected one of `:`, `@`, or `|`, found keyword `self`
+  --> $DIR/bad-signatures.rs:9:23
+   |
+LL |     async fn bar(&abc self);
+   |                  -----^^^^
+   |                  |    |
+   |                  |    expected one of `:`, `@`, or `|`
+   |                  help: declare the type after the parameter binding: `<identifier>: <type>`
+
+warning: the feature `async_fn_in_trait` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/bad-signatures.rs:5:12
+   |
+LL | #![feature(async_fn_in_trait)]
+   |            ^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error: aborting due to 2 previous errors; 1 warning emitted
+

tests/ui/async-await/in-trait/bad-signatures.rs

@@ -1,4 +1,6 @@
 // edition:2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 //~^ WARN the feature `async_fn_in_trait` is incomplete

tests/ui/async-await/in-trait/early-bound-1.rs

@@ -1,5 +1,7 @@
 // check-pass
 // edition:2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![allow(incomplete_features)]

tests/ui/async-await/in-trait/early-bound-2.rs

@@ -1,5 +1,7 @@
 // check-pass
 // edition:2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![allow(incomplete_features)]

tests/ui/async-await/in-trait/fn-not-async-err2.current.stderr

@@ -1,5 +1,5 @@
 error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `impl` method return types
-  --> $DIR/fn-not-async-err2.rs:13:22
+  --> $DIR/fn-not-async-err2.rs:15:22
    |
 LL |     fn foo(&self) -> impl Future<Output = i32> {
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^

tests/ui/async-await/in-trait/fn-not-async-err2.next.stderr

@@ -0,0 +1,12 @@
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `impl` method return types
+  --> $DIR/fn-not-async-err2.rs:15:22
+   |
+LL |     fn foo(&self) -> impl Future<Output = i32> {
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = 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`.

tests/ui/async-await/in-trait/fn-not-async-err2.rs

@@ -1,4 +1,6 @@
 // edition: 2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![allow(incomplete_features)]

tests/ui/async-await/in-trait/implied-bounds.rs

@@ -1,5 +1,7 @@
 // check-pass
 // edition: 2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![allow(incomplete_features)]

tests/ui/async-await/in-trait/issue-102138.rs

@@ -1,5 +1,7 @@
 // check-pass
 // edition:2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![allow(incomplete_features)]

tests/ui/async-await/in-trait/issue-102219.rs

@@ -1,6 +1,8 @@
 // compile-flags:--crate-type=lib
 // edition:2021
 // check-pass
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![allow(incomplete_features)]

tests/ui/async-await/in-trait/object-safety.current.stderr

@@ -1,5 +1,5 @@
 warning: the feature `async_fn_in_trait` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/object-safety.rs:3:12
+  --> $DIR/object-safety.rs:5:12
    |
 LL | #![feature(async_fn_in_trait)]
    |            ^^^^^^^^^^^^^^^^^
@@ -8,13 +8,13 @@ LL | #![feature(async_fn_in_trait)]
    = note: `#[warn(incomplete_features)]` on by default
 
 error[E0038]: the trait `Foo` cannot be made into an object
-  --> $DIR/object-safety.rs:11:12
+  --> $DIR/object-safety.rs:13:12
    |
 LL |     let x: &dyn Foo = todo!();
    |            ^^^^^^^^ `Foo` cannot be made into an object
    |
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
-  --> $DIR/object-safety.rs:7:14
+  --> $DIR/object-safety.rs:9:14
    |
 LL | trait Foo {
    |       --- this trait cannot be made into an object...

tests/ui/async-await/in-trait/object-safety.next.stderr

@@ -0,0 +1,27 @@
+warning: the feature `async_fn_in_trait` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/object-safety.rs:5:12
+   |
+LL | #![feature(async_fn_in_trait)]
+   |            ^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0038]: the trait `Foo` cannot be made into an object
+  --> $DIR/object-safety.rs:13:12
+   |
+LL |     let x: &dyn Foo = todo!();
+   |            ^^^^^^^^ `Foo` cannot be made into an object
+   |
+note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/object-safety.rs:9:14
+   |
+LL | trait Foo {
+   |       --- this trait cannot be made into an object...
+LL |     async fn foo(&self);
+   |              ^^^ ...because method `foo` is `async`
+   = help: consider moving `foo` to another trait
+
+error: aborting due to previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0038`.

tests/ui/async-await/in-trait/object-safety.rs

@@ -1,4 +1,6 @@
 // edition:2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 //~^ WARN the feature `async_fn_in_trait` is incomplete and may not be safe to use and/or cause compiler crashes

tests/ui/codegen/mono-impossible.rs

@@ -0,0 +1,13 @@
+// compile-flags: -Clink-dead-code=on --crate-type=lib
+// build-pass
+
+// Make sure that we don't monomorphize the impossible method `<() as Visit>::visit`,
+// which does not hold under a reveal-all param env.
+
+pub trait Visit {
+    fn visit() {}
+}
+
+pub trait Array<'a> {}
+
+impl Visit for () where (): for<'a> Array<'a> {}

tests/ui/impl-trait/in-trait/deep-match-works.rs

@@ -1,4 +1,6 @@
 // check-pass
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(return_position_impl_trait_in_trait)]
 #![allow(incomplete_features)]
@@ -10,7 +12,9 @@ trait Foo {
 }
 
 impl Foo for () {
-    fn bar() -> Wrapper<i32> { Wrapper(0) }
+    fn bar() -> Wrapper<i32> {
+        Wrapper(0)
+    }
 }
 
 fn main() {}

tests/ui/impl-trait/in-trait/deep-match.current.stderr

@@ -1,7 +1,7 @@
 error[E0053]: method `bar` has an incompatible return type for trait
-  --> $DIR/deep-match.rs:11:17
+  --> $DIR/deep-match.rs:14:17
    |
-LL |     fn bar() -> i32 { 0 }
+LL |     fn bar() -> i32 {
    |                 ^^^
    |                 |
    |                 expected `Wrapper<_>`, found `i32`

tests/ui/impl-trait/in-trait/deep-match.next.stderr

@@ -0,0 +1,15 @@
+error[E0053]: method `bar` has an incompatible return type for trait
+  --> $DIR/deep-match.rs:14:17
+   |
+LL |     fn bar() -> i32 {
+   |                 ^^^
+   |                 |
+   |                 expected `Wrapper<_>`, found `i32`
+   |                 return type in trait
+   |
+   = note: expected struct `Wrapper<_>`
+                found type `i32`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0053`.

tests/ui/impl-trait/in-trait/deep-match.rs

@@ -1,3 +1,6 @@
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
+
 #![feature(return_position_impl_trait_in_trait)]
 #![allow(incomplete_features)]
 
@@ -8,8 +11,10 @@ trait Foo {
 }
 
 impl Foo for () {
-    fn bar() -> i32 { 0 }
+    fn bar() -> i32 {
-    //~^ ERROR method `bar` has an incompatible return type for trait
+        //~^ ERROR method `bar` has an incompatible return type for trait
+        0
+    }
 }
 
 fn main() {}

tests/ui/impl-trait/in-trait/default-method-binder-shifting.current.stderr

@@ -1,5 +1,5 @@
 warning: the feature `return_position_impl_trait_in_trait` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/default-method-binder-shifting.rs:3:12
+  --> $DIR/default-method-binder-shifting.rs:5:12
    |
 LL | #![feature(return_position_impl_trait_in_trait)]
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

tests/ui/impl-trait/in-trait/default-method-binder-shifting.next.stderr

@@ -0,0 +1,11 @@
+warning: the feature `return_position_impl_trait_in_trait` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/default-method-binder-shifting.rs:5:12
+   |
+LL | #![feature(return_position_impl_trait_in_trait)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/impl-trait/in-trait/default-method-binder-shifting.rs

@@ -1,4 +1,6 @@
 // check-pass
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(return_position_impl_trait_in_trait)]
 //~^ WARN the feature `return_position_impl_trait_in_trait` is incomplete

tests/ui/impl-trait/in-trait/encode.rs

@@ -1,5 +1,7 @@
 // build-pass
 // compile-flags: --crate-type=lib
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(return_position_impl_trait_in_trait)]
 #![allow(incomplete_features)]

tests/ui/impl-trait/in-trait/foreign.rs

@@ -1,5 +1,7 @@
 // check-pass
 // aux-build: rpitit.rs
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 extern crate rpitit;
 

tests/ui/impl-trait/in-trait/issue-102140.current.stderr

@@ -1,5 +1,5 @@
 error[E0277]: the trait bound `&dyn MyTrait: MyTrait` is not satisfied
-  --> $DIR/issue-102140.rs:23:22
+  --> $DIR/issue-102140.rs:26:22
    |
 LL |         MyTrait::foo(&self)
    |         ------------ ^^^^^ the trait `MyTrait` is not implemented for `&dyn MyTrait`
@@ -13,7 +13,7 @@ LL +         MyTrait::foo(self)
    |
 
 error[E0277]: the trait bound `&dyn MyTrait: MyTrait` is not satisfied
-  --> $DIR/issue-102140.rs:23:9
+  --> $DIR/issue-102140.rs:26:9
    |
 LL |         MyTrait::foo(&self)
    |         ^^^^^^^^^^^^^^^^^^^ the trait `MyTrait` is not implemented for `&dyn MyTrait`
@@ -21,7 +21,7 @@ LL |         MyTrait::foo(&self)
    = help: the trait `MyTrait` is implemented for `Outer`
 
 error[E0277]: the trait bound `&dyn MyTrait: MyTrait` is not satisfied
-  --> $DIR/issue-102140.rs:23:9
+  --> $DIR/issue-102140.rs:26:9
    |
 LL |         MyTrait::foo(&self)
    |         ^^^^^^^^^^^^ the trait `MyTrait` is not implemented for `&dyn MyTrait`

tests/ui/impl-trait/in-trait/issue-102140.next.stderr

@@ -0,0 +1,33 @@
+error[E0277]: the trait bound `&dyn MyTrait: MyTrait` is not satisfied
+  --> $DIR/issue-102140.rs:26:22
+   |
+LL |         MyTrait::foo(&self)
+   |         ------------ ^^^^^ the trait `MyTrait` is not implemented for `&dyn MyTrait`
+   |         |
+   |         required by a bound introduced by this call
+   |
+help: consider removing the leading `&`-reference
+   |
+LL -         MyTrait::foo(&self)
+LL +         MyTrait::foo(self)
+   |
+
+error[E0277]: the trait bound `&dyn MyTrait: MyTrait` is not satisfied
+  --> $DIR/issue-102140.rs:26:9
+   |
+LL |         MyTrait::foo(&self)
+   |         ^^^^^^^^^^^^^^^^^^^ the trait `MyTrait` is not implemented for `&dyn MyTrait`
+   |
+   = help: the trait `MyTrait` is implemented for `Outer`
+
+error[E0277]: the trait bound `&dyn MyTrait: MyTrait` is not satisfied
+  --> $DIR/issue-102140.rs:26:9
+   |
+LL |         MyTrait::foo(&self)
+   |         ^^^^^^^^^^^^ the trait `MyTrait` is not implemented for `&dyn MyTrait`
+   |
+   = help: the trait `MyTrait` is implemented for `Outer`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/impl-trait/in-trait/issue-102140.rs

@@ -1,3 +1,6 @@
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
+
 #![feature(return_position_impl_trait_in_trait)]
 #![allow(incomplete_features)]
 

tests/ui/impl-trait/in-trait/new-lowering-strategy/simple-impl-trait.rs

@@ -1,17 +0,0 @@
-// check-pass
-// compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
-
-#![feature(return_position_impl_trait_in_trait)]
-#![allow(incomplete_features)]
-
-trait Foo {
-    fn foo() -> impl Sized;
-}
-
-impl Foo for String {
-    fn foo() -> i32 {
-        22
-    }
-}
-
-fn main() {}

tests/ui/impl-trait/in-trait/new-lowering-strategy/simple-trait.rs

@@ -1,11 +0,0 @@
-// check-pass
-// compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
-
-#![feature(return_position_impl_trait_in_trait)]
-#![allow(incomplete_features)]
-
-trait Foo {
-    fn foo() -> impl Sized;
-}
-
-fn main() {}

tests/ui/impl-trait/in-trait/object-safety.current.stderr

@@ -1,11 +1,26 @@
 error[E0038]: the trait `Foo` cannot be made into an object
-  --> $DIR/object-safety.rs:17:33
+  --> $DIR/object-safety.rs:20:33
    |
 LL |     let i = Box::new(42_u32) as Box<dyn Foo>;
    |                                 ^^^^^^^^^^^^ `Foo` cannot be made into an object
    |
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
-  --> $DIR/object-safety.rs:7:22
+  --> $DIR/object-safety.rs:10:22
+   |
+LL | trait Foo {
+   |       --- this trait cannot be made into an object...
+LL |     fn baz(&self) -> impl Debug;
+   |                      ^^^^^^^^^^ ...because method `baz` references an `impl Trait` type in its return type
+   = help: consider moving `baz` to another trait
+
+error[E0038]: the trait `Foo` cannot be made into an object
+  --> $DIR/object-safety.rs:23:13
+   |
+LL |     let s = i.baz();
+   |             ^^^^^^^ `Foo` cannot be made into an object
+   |
+note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/object-safety.rs:10:22
    |
 LL | trait Foo {
    |       --- this trait cannot be made into an object...
@@ -16,26 +31,11 @@ LL |     fn baz(&self) -> impl Debug;
 error[E0038]: the trait `Foo` cannot be made into an object
   --> $DIR/object-safety.rs:20:13
    |
-LL |     let s = i.baz();
-   |             ^^^^^^^ `Foo` cannot be made into an object
-   |
-note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
-  --> $DIR/object-safety.rs:7:22
-   |
-LL | trait Foo {
-   |       --- this trait cannot be made into an object...
-LL |     fn baz(&self) -> impl Debug;
-   |                      ^^^^^^^^^^ ...because method `baz` references an `impl Trait` type in its return type
-   = help: consider moving `baz` to another trait
-
-error[E0038]: the trait `Foo` cannot be made into an object
-  --> $DIR/object-safety.rs:17:13
-   |
 LL |     let i = Box::new(42_u32) as Box<dyn Foo>;
    |             ^^^^^^^^^^^^^^^^ `Foo` cannot be made into an object
    |
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
-  --> $DIR/object-safety.rs:7:22
+  --> $DIR/object-safety.rs:10:22
    |
 LL | trait Foo {
    |       --- this trait cannot be made into an object...

tests/ui/impl-trait/in-trait/object-safety.next.stderr

@@ -0,0 +1,50 @@
+error[E0038]: the trait `Foo` cannot be made into an object
+  --> $DIR/object-safety.rs:20:33
+   |
+LL |     let i = Box::new(42_u32) as Box<dyn Foo>;
+   |                                 ^^^^^^^^^^^^ `Foo` cannot be made into an object
+   |
+note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/object-safety.rs:10:22
+   |
+LL | trait Foo {
+   |       --- this trait cannot be made into an object...
+LL |     fn baz(&self) -> impl Debug;
+   |                      ^^^^^^^^^^ ...because method `baz` references an `impl Trait` type in its return type
+   = help: consider moving `baz` to another trait
+
+error[E0038]: the trait `Foo` cannot be made into an object
+  --> $DIR/object-safety.rs:23:13
+   |
+LL |     let s = i.baz();
+   |             ^^^^^^^ `Foo` cannot be made into an object
+   |
+note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/object-safety.rs:10:22
+   |
+LL | trait Foo {
+   |       --- this trait cannot be made into an object...
+LL |     fn baz(&self) -> impl Debug;
+   |                      ^^^^^^^^^^ ...because method `baz` references an `impl Trait` type in its return type
+   = help: consider moving `baz` to another trait
+
+error[E0038]: the trait `Foo` cannot be made into an object
+  --> $DIR/object-safety.rs:20:13
+   |
+LL |     let i = Box::new(42_u32) as Box<dyn Foo>;
+   |             ^^^^^^^^^^^^^^^^ `Foo` cannot be made into an object
+   |
+note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/object-safety.rs:10:22
+   |
+LL | trait Foo {
+   |       --- this trait cannot be made into an object...
+LL |     fn baz(&self) -> impl Debug;
+   |                      ^^^^^^^^^^ ...because method `baz` references an `impl Trait` type in its return type
+   = help: consider moving `baz` to another trait
+   = note: required for `Box<u32>` to implement `CoerceUnsized<Box<dyn Foo>>`
+   = note: required by cast to type `Box<dyn Foo>`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0038`.

tests/ui/impl-trait/in-trait/object-safety.rs

@@ -1,3 +1,6 @@
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
+
 #![feature(return_position_impl_trait_in_trait)]
 #![allow(incomplete_features)]
 

tests/ui/impl-trait/in-trait/opaque-in-impl-is-opaque.current.stderr

@@ -1,5 +1,5 @@
 error[E0308]: mismatched types
-  --> $DIR/opaque-in-impl-is-opaque.rs:17:19
+  --> $DIR/opaque-in-impl-is-opaque.rs:20:19
    |
 LL |     fn bar(&self) -> impl Display {
    |                      ------------ the found opaque type

tests/ui/impl-trait/in-trait/opaque-in-impl-is-opaque.next.stderr

@@ -0,0 +1,17 @@
+error[E0308]: mismatched types
+  --> $DIR/opaque-in-impl-is-opaque.rs:20:19
+   |
+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`.

tests/ui/impl-trait/in-trait/opaque-in-impl-is-opaque.rs

@@ -1,3 +1,6 @@
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
+
 #![feature(return_position_impl_trait_in_trait)]
 #![allow(incomplete_features)]
 

tests/ui/impl-trait/in-trait/reveal.rs

@@ -1,4 +1,6 @@
 // check-pass
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(return_position_impl_trait_in_trait)]
 #![allow(incomplete_features)]

tests/ui/impl-trait/in-trait/signature-mismatch.current.stderr

@@ -1,5 +1,5 @@
 error: `impl` item signature doesn't match `trait` item signature
-  --> $DIR/signature-mismatch.rs:15:5
+  --> $DIR/signature-mismatch.rs:17:5
    |
 LL |     fn async_fn(&self, buff: &[u8]) -> impl Future<Output = Vec<u8>>;
    |     ----------------------------------------------------------------- expected `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>> + '3`

tests/ui/impl-trait/in-trait/signature-mismatch.next.stderr

@@ -0,0 +1,16 @@
+error: `impl` item signature doesn't match `trait` item signature
+  --> $DIR/signature-mismatch.rs:17:5
+   |
+LL |     fn async_fn(&self, buff: &[u8]) -> impl Future<Output = Vec<u8>>;
+   |     ----------------------------------------------------------------- expected `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>> + '3`
+...
+LL |     fn async_fn<'a>(&self, buff: &'a [u8]) -> impl Future<Output = Vec<u8>> + 'a {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ found `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>> + '2`
+   |
+   = note: expected signature `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>> + '3`
+              found signature `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>> + '2`
+   = help: the lifetime requirements from the `impl` do not correspond to the requirements in the `trait`
+   = help: verify the lifetime relationships in the `trait` and `impl` between the `self` argument, the other inputs and its output
+
+error: aborting due to previous error
+

tests/ui/impl-trait/in-trait/signature-mismatch.rs

@@ -1,4 +1,6 @@
 // edition:2021
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(return_position_impl_trait_in_trait)]
 #![allow(incomplete_features)]

tests/ui/impl-trait/in-trait/specialization-substs-remap.rs

@@ -1,4 +1,6 @@
 // check-pass
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(specialization)]
 #![feature(return_position_impl_trait_in_trait)]

tests/ui/impl-trait/in-trait/success.rs

@@ -1,4 +1,6 @@
 // check-pass
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(return_position_impl_trait_in_trait)]
 #![allow(incomplete_features)]

tests/ui/layout/transmute-to-tail-with-err.rs

@@ -0,0 +1,8 @@
+trait Trait<T> {}
+
+struct Bar(Box<dyn Trait<T>>);
+//~^ ERROR cannot find type `T` in this scope
+
+fn main() {
+    let x: Bar = unsafe { std::mem::transmute(()) };
+}

tests/ui/layout/transmute-to-tail-with-err.stderr

@@ -0,0 +1,14 @@
+error[E0412]: cannot find type `T` in this scope
+  --> $DIR/transmute-to-tail-with-err.rs:3:26
+   |
+LL | struct Bar(Box<dyn Trait<T>>);
+   |                          ^ not found in this scope
+   |
+help: you might be missing a type parameter
+   |
+LL | struct Bar<T>(Box<dyn Trait<T>>);
+   |           +++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0412`.

tests/ui/suggestions/chain-method-call-mutation-in-place.rs

@@ -1,4 +1,8 @@
-fn main() {}
+fn main() {
+    let x: Vec<i32> = vec![1, 2, 3].into_iter().collect::<Vec<i32>>().sort_by_key(|i| i); //~ ERROR mismatched types
+    vec![1, 2, 3].into_iter().collect::<Vec<i32>>().sort_by_key(|i| i).sort(); //~ ERROR no method named `sort` found for unit type `()` in the current scope
+}
+
 fn foo(mut s: String) -> String {
     s.push_str("asdf") //~ ERROR mismatched types
 }

tests/ui/suggestions/chain-method-call-mutation-in-place.stderr

@@ -1,5 +1,33 @@
 error[E0308]: mismatched types
-  --> $DIR/chain-method-call-mutation-in-place.rs:3:5
+  --> $DIR/chain-method-call-mutation-in-place.rs:2:23
+   |
+LL |     let x: Vec<i32> = vec![1, 2, 3].into_iter().collect::<Vec<i32>>().sort_by_key(|i| i);
+   |            --------   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `Vec<i32>`, found `()`
+   |            |
+   |            expected due to this
+   |
+   = note: expected struct `Vec<i32>`
+           found unit type `()`
+note: method `sort_by_key` modifies its receiver in-place, it is not meant to be used in method chains.
+  --> $DIR/chain-method-call-mutation-in-place.rs:2:71
+   |
+LL |     let x: Vec<i32> = vec![1, 2, 3].into_iter().collect::<Vec<i32>>().sort_by_key(|i| i);
+   |                                                                       ^^^^^^^^^^^ this call modifies its receiver in-place
+
+error[E0599]: no method named `sort` found for unit type `()` in the current scope
+  --> $DIR/chain-method-call-mutation-in-place.rs:3:72
+   |
+LL |     vec![1, 2, 3].into_iter().collect::<Vec<i32>>().sort_by_key(|i| i).sort();
+   |                                                                        ^^^^ method not found in `()`
+   |
+note: method `sort_by_key` modifies its receiver in-place, it is not meant to be used in method chains.
+  --> $DIR/chain-method-call-mutation-in-place.rs:3:53
+   |
+LL |     vec![1, 2, 3].into_iter().collect::<Vec<i32>>().sort_by_key(|i| i).sort();
+   |                                                     ^^^^^^^^^^^ this call modifies its receiver in-place
+
+error[E0308]: mismatched types
+  --> $DIR/chain-method-call-mutation-in-place.rs:7:5
    |
 LL | fn foo(mut s: String) -> String {
    |                          ------ expected `String` because of return type
@@ -7,7 +35,7 @@ LL |     s.push_str("asdf")
    |     ^^^^^^^^^^^^^^^^^^ expected `String`, found `()`
    |
 note: method `push_str` modifies its receiver in-place
-  --> $DIR/chain-method-call-mutation-in-place.rs:3:7
+  --> $DIR/chain-method-call-mutation-in-place.rs:7:7
    |
 LL |     s.push_str("asdf")
    |     - ^^^^^^^^ this call modifies `s` in-place
@@ -15,6 +43,7 @@ LL |     s.push_str("asdf")
    |     you probably want to use this value after calling the method...
    = note: ...instead of the `()` output of method `push_str`
 
-error: aborting due to previous error
+error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0308`.
+Some errors have detailed explanations: E0308, E0599.
+For more information about an error, try `rustc --explain E0308`.

tests/ui/traits/non_lifetime_binders/capture-late-ct-in-anon.rs

@@ -0,0 +1,11 @@
+#![feature(non_lifetime_binders)]
+//~^ WARN the feature `non_lifetime_binders` is incomplete
+
+fn b()
+where
+    for<const C: usize> [(); C]: Copy,
+    //~^ ERROR cannot capture late-bound const parameter in a constant
+{
+}
+
+fn main() {}

tests/ui/traits/non_lifetime_binders/capture-late-ct-in-anon.stderr

@@ -0,0 +1,19 @@
+warning: the feature `non_lifetime_binders` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/capture-late-ct-in-anon.rs:1:12
+   |
+LL | #![feature(non_lifetime_binders)]
+   |            ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error: cannot capture late-bound const parameter in a constant
+  --> $DIR/capture-late-ct-in-anon.rs:6:30
+   |
+LL |     for<const C: usize> [(); C]: Copy,
+   |         --------------       ^
+   |         |
+   |         parameter defined here
+
+error: aborting due to previous error; 1 warning emitted
+