Note base types of coercion

compiler/rustc_middle/src/traits/mod.rs

@@ -281,9 +281,6 @@ pub enum ObligationCauseCode<'tcx> {
     /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
     ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
 
-    /// Obligation incurred due to an object cast.
-    ObjectCastObligation(/* Concrete type */ Ty<'tcx>, /* Object type */ Ty<'tcx>),
-
     /// Obligation incurred due to a coercion.
     Coercion {
         source: Ty<'tcx>,

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

@@ -797,9 +797,17 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                             err.span_label(span, explanation);
                         }
 
-                        if let ObligationCauseCode::ObjectCastObligation(concrete_ty, obj_ty) = obligation.cause.code().peel_derives() &&
+                        if let ObligationCauseCode::Coercion { source, target } =
-                            Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
+                            *obligation.cause.code().peel_derives()
-                            self.suggest_borrowing_for_object_cast(&mut err, &root_obligation, *concrete_ty, *obj_ty);
+                        {
+                            if Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
+                                self.suggest_borrowing_for_object_cast(
+                                    &mut err,
+                                    &root_obligation,
+                                    source,
+                                    target,
+                                );
+                            }
                         }
 
                         let UnsatisfiedConst(unsatisfied_const) = self
@@ -1510,7 +1518,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         | ObligationCauseCode::BindingObligation(_, _)
                         | ObligationCauseCode::ExprItemObligation(..)
                         | ObligationCauseCode::ExprBindingObligation(..)
-                        | ObligationCauseCode::ObjectCastObligation(..)
+                        | ObligationCauseCode::Coercion { .. }
                         | ObligationCauseCode::OpaqueType
                 );
 

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

@@ -1442,8 +1442,9 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         err: &mut Diagnostic,
         obligation: &PredicateObligation<'tcx>,
         self_ty: Ty<'tcx>,
-        object_ty: Ty<'tcx>,
+        target_ty: Ty<'tcx>,
     ) {
+        let ty::Ref(_, object_ty, hir::Mutability::Not) = target_ty.kind() else { return; };
         let ty::Dynamic(predicates, _, ty::Dyn) = object_ty.kind() else { return; };
         let self_ref_ty = self.tcx.mk_imm_ref(self.tcx.lifetimes.re_erased, self_ty);
 
@@ -1458,7 +1459,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         err.span_suggestion(
             obligation.cause.span.shrink_to_lo(),
             format!(
-                "consider borrowing the value, since `&{self_ty}` can be coerced into `{object_ty}`"
+                "consider borrowing the value, since `&{self_ty}` can be coerced into `{target_ty}`"
             ),
             "&",
             Applicability::MaybeIncorrect,
@@ -2851,30 +2852,27 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     err.span_note(tcx.def_span(item_def_id), descr);
                 }
             }
-            ObligationCauseCode::ObjectCastObligation(concrete_ty, object_ty) => {
+            ObligationCauseCode::Coercion { source, target } => {
-                let (concrete_ty, concrete_file) =
+                let (source, source_file) =
-                    self.tcx.short_ty_string(self.resolve_vars_if_possible(concrete_ty));
+                    self.tcx.short_ty_string(self.resolve_vars_if_possible(source));
-                let (object_ty, object_file) =
+                let (target, target_file) =
-                    self.tcx.short_ty_string(self.resolve_vars_if_possible(object_ty));
+                    self.tcx.short_ty_string(self.resolve_vars_if_possible(target));
                 err.note(with_forced_trimmed_paths!(format!(
-                    "required for the cast from `{concrete_ty}` to the object type `{object_ty}`",
+                    "required for the cast from `{source}` to `{target}`",
                 )));
-                if let Some(file) = concrete_file {
+                if let Some(file) = source_file {
                     err.note(format!(
-                        "the full name for the casted type has been written to '{}'",
+                        "the full name for the source type has been written to '{}'",
                         file.display(),
                     ));
                 }
-                if let Some(file) = object_file {
+                if let Some(file) = target_file {
                     err.note(format!(
-                        "the full name for the object type has been written to '{}'",
+                        "the full name for the target type has been written to '{}'",
                         file.display(),
                     ));
                 }
             }
-            ObligationCauseCode::Coercion { source: _, target } => {
-                err.note(format!("required by cast to type `{}`", self.ty_to_string(target)));
-            }
             ObligationCauseCode::RepeatElementCopy { is_const_fn } => {
                 err.note(
                     "the `Copy` trait is required because this value will be copied for each element of the array",

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -29,9 +29,9 @@ use crate::traits::{
     ImplSourceAutoImplData, ImplSourceBuiltinData, ImplSourceClosureData,
     ImplSourceConstDestructData, ImplSourceFnPointerData, ImplSourceFutureData,
     ImplSourceGeneratorData, ImplSourceObjectData, ImplSourceTraitAliasData,
-    ImplSourceTraitUpcastingData, ImplSourceUserDefinedData, Normalized, ObjectCastObligation,
+    ImplSourceTraitUpcastingData, ImplSourceUserDefinedData, Normalized, Obligation,
-    Obligation, ObligationCause, OutputTypeParameterMismatch, PredicateObligation, Selection,
+    ObligationCause, OutputTypeParameterMismatch, PredicateObligation, Selection, SelectionError,
-    SelectionError, TraitNotObjectSafe, TraitObligation, Unimplemented,
+    TraitNotObjectSafe, TraitObligation, Unimplemented,
 };
 
 use super::BuiltinImplConditions;
@@ -905,16 +905,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     .map_err(|_| Unimplemented)?;
                 nested.extend(obligations);
 
-                // Register one obligation for 'a: 'b.
-                let cause = ObligationCause::new(
-                    obligation.cause.span,
-                    obligation.cause.body_id,
-                    ObjectCastObligation(source, target),
-                );
                 let outlives = ty::OutlivesPredicate(r_a, r_b);
                 nested.push(Obligation::with_depth(
                     tcx,
-                    cause,
+                    obligation.cause.clone(),
                     obligation.recursion_depth + 1,
                     obligation.param_env,
                     obligation.predicate.rebind(outlives),
@@ -1005,15 +999,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 nested.extend(obligations);
 
                 // Register one obligation for 'a: 'b.
-                let cause = ObligationCause::new(
-                    obligation.cause.span,
-                    obligation.cause.body_id,
-                    ObjectCastObligation(source, target),
-                );
                 let outlives = ty::OutlivesPredicate(r_a, r_b);
                 nested.push(Obligation::with_depth(
                     tcx,
-                    cause,
+                    obligation.cause.clone(),
                     obligation.recursion_depth + 1,
                     obligation.param_env,
                     obligation.predicate.rebind(outlives),
@@ -1027,16 +1016,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     return Err(TraitNotObjectSafe(did));
                 }
 
-                let cause = ObligationCause::new(
-                    obligation.cause.span,
-                    obligation.cause.body_id,
-                    ObjectCastObligation(source, target),
-                );
-
                 let predicate_to_obligation = |predicate| {
                     Obligation::with_depth(
                         tcx,
-                        cause.clone(),
+                        obligation.cause.clone(),
                         obligation.recursion_depth + 1,
                         obligation.param_env,
                         predicate,
@@ -1056,7 +1039,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 );
 
                 // We can only make objects from sized types.
-                let tr = ty::TraitRef::from_lang_item(tcx, LangItem::Sized, cause.span, [source]);
+                let tr = ty::TraitRef::from_lang_item(
+                    tcx,
+                    LangItem::Sized,
+                    obligation.cause.span,
+                    [source],
+                );
                 nested.push(predicate_to_obligation(tr.without_const().to_predicate(tcx)));
 
                 // If the type is `Foo + 'a`, ensure that the type

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -2647,14 +2647,19 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
         let predicates = predicates.instantiate_own(tcx, substs);
         let mut obligations = Vec::with_capacity(predicates.len());
         for (index, (predicate, span)) in predicates.into_iter().enumerate() {
-            let cause = cause.clone().derived_cause(parent_trait_pred, |derived| {
+            let cause =
+                if Some(parent_trait_pred.def_id()) == tcx.lang_items().coerce_unsized_trait() {
+                    cause.clone()
+                } else {
+                    cause.clone().derived_cause(parent_trait_pred, |derived| {
                         ImplDerivedObligation(Box::new(ImplDerivedObligationCause {
                             derived,
                             impl_or_alias_def_id: def_id,
                             impl_def_predicate_index: Some(index),
                             span,
                         }))
-            });
+                    })
+                };
             let predicate = normalize_with_depth_to(
                 self,
                 param_env,

tests/ui/associated-types/associated-types-eq-3.stderr

@@ -43,7 +43,7 @@ note: expected this to be `Bar`
    |
 LL |     type A = usize;
    |              ^^^^^
-   = note: required for the cast from `isize` to the object type `dyn Foo<A = Bar>`
+   = note: required for the cast from `&isize` to `&dyn Foo<A = Bar>`
 
 error: aborting due to 3 previous errors
 

tests/ui/associated-types/associated-types-overridden-binding-2.stderr

@@ -4,7 +4,7 @@ error[E0271]: expected `IntoIter<u32>` to be an iterator that yields `i32`, but
 LL |     let _: &dyn I32Iterator<Item = u32> = &vec![42].into_iter();
    |                                           ^^^^^^^^^^^^^^^^^^^^^ expected `i32`, found `u32`
    |
-   = note: required for the cast from `std::vec::IntoIter<u32>` to the object type `dyn Iterator<Item = u32, Item = i32>`
+   = note: required for the cast from `&std::vec::IntoIter<u32>` to `&dyn Iterator<Item = u32, Item = i32>`
 
 error: aborting due to previous error
 

tests/ui/associated-types/issue-65774-1.stderr

@@ -25,7 +25,7 @@ LL | impl<'a, T: MyDisplay> MyDisplay for &'a mut T { }
    |             ---------  ^^^^^^^^^     ^^^^^^^^^
    |             |
    |             unsatisfied trait bound introduced here
-   = note: required for the cast from `&mut T` to the object type `dyn MyDisplay`
+   = note: required for the cast from `&&mut T` to `&dyn MyDisplay`
 
 error: aborting due to 2 previous errors
 

tests/ui/associated-types/issue-65774-2.stderr

@@ -18,7 +18,7 @@ LL |         writer.my_write(valref)
    |                         ^^^^^^ the trait `MyDisplay` is not implemented for `T`
    |
    = help: the trait `MyDisplay` is implemented for `&'a mut T`
-   = note: required for the cast from `T` to the object type `dyn MyDisplay`
+   = note: required for the cast from `&mut T` to `&dyn MyDisplay`
 
 error: aborting due to 2 previous errors
 

tests/ui/async-await/async-block-control-flow-static-semantics.stderr

@@ -35,7 +35,7 @@ error[E0271]: expected `[async block@$DIR/async-block-control-flow-static-semant
 LL |     let _: &dyn Future<Output = ()> = &block;
    |                                       ^^^^^^ expected `()`, found `u8`
    |
-   = note: required for the cast from `[async block@$DIR/async-block-control-flow-static-semantics.rs:23:17: 25:6]` to the object type `dyn Future<Output = ()>`
+   = note: required for the cast from `&[async block@$DIR/async-block-control-flow-static-semantics.rs:23:17: 25:6]` to `&dyn Future<Output = ()>`
 
 error[E0308]: mismatched types
   --> $DIR/async-block-control-flow-static-semantics.rs:12:43
@@ -51,7 +51,7 @@ error[E0271]: expected `[async block@$DIR/async-block-control-flow-static-semant
 LL |     let _: &dyn Future<Output = ()> = &block;
    |                                       ^^^^^^ expected `()`, found `u8`
    |
-   = note: required for the cast from `[async block@$DIR/async-block-control-flow-static-semantics.rs:14:17: 16:6]` to the object type `dyn Future<Output = ()>`
+   = note: required for the cast from `&[async block@$DIR/async-block-control-flow-static-semantics.rs:14:17: 16:6]` to `&dyn Future<Output = ()>`
 
 error[E0308]: mismatched types
   --> $DIR/async-block-control-flow-static-semantics.rs:49:44

tests/ui/async-await/issue-86507.drop_tracking.stderr

@@ -13,7 +13,7 @@ note: captured value is not `Send` because `&` references cannot be sent unless
    |
 LL |                     let x = x;
    |                             ^ has type `&T` which is not `Send`, because `T` is not `Sync`
-   = note: required for the cast from `[async block@$DIR/issue-86507.rs:21:17: 23:18]` to the object type `dyn Future<Output = ()> + Send`
+   = note: required for the cast from `Pin<Box<[async block@$DIR/issue-86507.rs:21:17: 23:18]>>` to `Pin<Box<(dyn Future<Output = ()> + Send + 'async_trait)>>`
 help: consider further restricting this bound
    |
 LL |     fn bar<'me, 'async_trait, T: Send + std::marker::Sync>(x: &'me T)

tests/ui/async-await/issue-86507.drop_tracking_mir.stderr

@@ -13,7 +13,7 @@ note: captured value is not `Send` because `&` references cannot be sent unless
    |
 LL |                     let x = x;
    |                             ^ has type `&T` which is not `Send`, because `T` is not `Sync`
-   = note: required for the cast from `[async block@$DIR/issue-86507.rs:21:17: 23:18]` to the object type `dyn Future<Output = ()> + Send`
+   = note: required for the cast from `Pin<Box<[async block@$DIR/issue-86507.rs:21:17: 23:18]>>` to `Pin<Box<(dyn Future<Output = ()> + Send + 'async_trait)>>`
 help: consider further restricting this bound
    |
 LL |     fn bar<'me, 'async_trait, T: Send + std::marker::Sync>(x: &'me T)

tests/ui/async-await/issue-86507.no_drop_tracking.stderr

@@ -13,7 +13,7 @@ note: captured value is not `Send` because `&` references cannot be sent unless
    |
 LL |                     let x = x;
    |                             ^ has type `&T` which is not `Send`, because `T` is not `Sync`
-   = note: required for the cast from `[async block@$DIR/issue-86507.rs:21:17: 23:18]` to the object type `dyn Future<Output = ()> + Send`
+   = note: required for the cast from `Pin<Box<[async block@$DIR/issue-86507.rs:21:17: 23:18]>>` to `Pin<Box<(dyn Future<Output = ()> + Send + 'async_trait)>>`
 help: consider further restricting this bound
    |
 LL |     fn bar<'me, 'async_trait, T: Send + std::marker::Sync>(x: &'me T)

tests/ui/closure_context/issue-26046-fn-mut.stderr

@@ -9,7 +9,7 @@ LL |         num += 1;
 LL |     Box::new(closure)
    |     ----------------- the requirement to implement `Fn` derives from here
    |
-   = note: required for the cast from `[closure@$DIR/issue-26046-fn-mut.rs:4:19: 4:21]` to the object type `dyn Fn()`
+   = note: required for the cast from `Box<[closure@$DIR/issue-26046-fn-mut.rs:4:19: 4:21]>` to `Box<(dyn Fn() + 'static)>`
 
 error: aborting due to previous error
 

tests/ui/closure_context/issue-26046-fn-once.stderr

@@ -9,7 +9,7 @@ LL |         vec
 LL |     Box::new(closure)
    |     ----------------- the requirement to implement `Fn` derives from here
    |
-   = note: required for the cast from `[closure@$DIR/issue-26046-fn-once.rs:4:19: 4:26]` to the object type `dyn Fn() -> Vec<u8>`
+   = note: required for the cast from `Box<[closure@$DIR/issue-26046-fn-once.rs:4:19: 4:26]>` to `Box<(dyn Fn() -> Vec<u8> + 'static)>`
 
 error: aborting due to previous error
 

tests/ui/coercion/coerce-issue-49593-box-never-windows.nofallback.stderr

@@ -4,7 +4,7 @@ error[E0277]: the trait bound `(): std::error::Error` is not satisfied
 LL |     /* *mut $0 is coerced to Box<dyn Error> here */ Box::<_ /* ! */>::new(x)
    |                                                     ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::error::Error` is not implemented for `()`
    |
-   = note: required for the cast from `()` to the object type `dyn std::error::Error`
+   = note: required for the cast from `Box<()>` to `Box<(dyn std::error::Error + 'static)>`
 
 error[E0277]: the trait bound `(): std::error::Error` is not satisfied
   --> $DIR/coerce-issue-49593-box-never-windows.rs:23:49
@@ -12,7 +12,7 @@ error[E0277]: the trait bound `(): std::error::Error` is not satisfied
 LL |     /* *mut $0 is coerced to *mut Error here */ raw_ptr_box::<_ /* ! */>(x)
    |                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::error::Error` is not implemented for `()`
    |
-   = note: required for the cast from `()` to the object type `(dyn std::error::Error + 'static)`
+   = note: required for the cast from `*mut ()` to `*mut (dyn std::error::Error + 'static)`
 
 error: aborting due to 2 previous errors
 

tests/ui/coercion/coerce-issue-49593-box-never.nofallback.stderr

@@ -4,7 +4,7 @@ error[E0277]: the trait bound `(): std::error::Error` is not satisfied
 LL |     /* *mut $0 is coerced to Box<dyn Error> here */ Box::<_ /* ! */>::new(x)
    |                                                     ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::error::Error` is not implemented for `()`
    |
-   = note: required for the cast from `()` to the object type `dyn std::error::Error`
+   = note: required for the cast from `Box<()>` to `Box<(dyn std::error::Error + 'static)>`
 
 error[E0277]: the trait bound `(): std::error::Error` is not satisfied
   --> $DIR/coerce-issue-49593-box-never.rs:23:49
@@ -12,7 +12,7 @@ error[E0277]: the trait bound `(): std::error::Error` is not satisfied
 LL |     /* *mut $0 is coerced to *mut Error here */ raw_ptr_box::<_ /* ! */>(x)
    |                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::error::Error` is not implemented for `()`
    |
-   = note: required for the cast from `()` to the object type `(dyn std::error::Error + 'static)`
+   = note: required for the cast from `*mut ()` to `*mut (dyn std::error::Error + 'static)`
 
 error: aborting due to 2 previous errors
 

tests/ui/const-generics/defaults/trait_objects_fail.stderr

@@ -5,7 +5,7 @@ LL |     foo(&10_u32);
    |         ^^^^^^^ the trait `Trait` is not implemented for `u32`
    |
    = help: the trait `Trait<2>` is implemented for `u32`
-   = note: required for the cast from `u32` to the object type `dyn Trait`
+   = note: required for the cast from `&u32` to `&dyn Trait`
 
 error[E0277]: the trait bound `bool: Traitor<_>` is not satisfied
   --> $DIR/trait_objects_fail.rs:28:9
@@ -14,7 +14,7 @@ LL |     bar(&true);
    |         ^^^^^ the trait `Traitor<_>` is not implemented for `bool`
    |
    = help: the trait `Traitor<2, 3>` is implemented for `bool`
-   = note: required for the cast from `bool` to the object type `dyn Traitor<_>`
+   = note: required for the cast from `&bool` to `&dyn Traitor<_>`
 
 error: aborting due to 2 previous errors
 

tests/ui/custom_test_frameworks/mismatch.stderr

@@ -6,7 +6,7 @@ LL | #[test]
 LL | fn wrong_kind(){}
    | ^^^^^^^^^^^^^^^^^ the trait `Testable` is not implemented for `TestDescAndFn`
    |
-   = note: required for the cast from `TestDescAndFn` to the object type `dyn Testable`
+   = note: required for the cast from `&TestDescAndFn` to `&dyn Testable`
    = note: this error originates in the attribute macro `test` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error

tests/ui/diagnostic-width/E0271.stderr

@@ -15,8 +15,8 @@ note: expected this to be `Foo`
    |
 LL |     type Error = E;
    |                  ^
-   = note: required for the cast from `Result<Result<..., ...>, ...>` to the object type `dyn Future<Error = Foo>`
+   = note: required for the cast from `Box<Result<..., ...>>` to `Box<(dyn Future<Error = Foo> + 'static)>`
-   = note: the full name for the casted type has been written to '$TEST_BUILD_DIR/diagnostic-width/E0271/E0271.long-type-hash.txt'
+   = note: the full name for the source type has been written to '$TEST_BUILD_DIR/diagnostic-width/E0271/E0271.long-type-hash.txt'
 
 error: aborting due to previous error
 

tests/ui/dst/dst-bad-coerce1.stderr

@@ -15,7 +15,7 @@ error[E0277]: the trait bound `Foo: Bar` is not satisfied
 LL |     let f3: &Fat<dyn Bar> = f2;
    |                             ^^ the trait `Bar` is not implemented for `Foo`
    |
-   = note: required for the cast from `Foo` to the object type `dyn Bar`
+   = note: required for the cast from `&Fat<Foo>` to `&Fat<dyn Bar>`
 
 error[E0308]: mismatched types
   --> $DIR/dst-bad-coerce1.rs:28:27
@@ -34,7 +34,7 @@ error[E0277]: the trait bound `Foo: Bar` is not satisfied
 LL |     let f3: &(dyn Bar,) = f2;
    |                           ^^ the trait `Bar` is not implemented for `Foo`
    |
-   = note: required for the cast from `Foo` to the object type `dyn Bar`
+   = note: required for the cast from `&(Foo,)` to `&(dyn Bar,)`
 
 error: aborting due to 4 previous errors
 

tests/ui/dst/dst-object-from-unsized-type.stderr

@@ -6,7 +6,7 @@ LL | fn test1<T: ?Sized + Foo>(t: &T) {
 LL |     let u: &dyn Foo = t;
    |                       ^ doesn't have a size known at compile-time
    |
-   = note: required for the cast from `T` to the object type `dyn Foo`
+   = note: required for the cast from `&T` to `&dyn Foo`
 help: consider removing the `?Sized` bound to make the type parameter `Sized`
    |
 LL - fn test1<T: ?Sized + Foo>(t: &T) {
@@ -21,7 +21,7 @@ LL | fn test2<T: ?Sized + Foo>(t: &T) {
 LL |     let v: &dyn Foo = t as &dyn Foo;
    |                       ^ doesn't have a size known at compile-time
    |
-   = note: required for the cast from `T` to the object type `dyn Foo`
+   = note: required for the cast from `&T` to `&dyn Foo`
 help: consider removing the `?Sized` bound to make the type parameter `Sized`
    |
 LL - fn test2<T: ?Sized + Foo>(t: &T) {
@@ -35,7 +35,7 @@ LL |     let _: &[&dyn Foo] = &["hi"];
    |                            ^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
-   = note: required for the cast from `str` to the object type `dyn Foo`
+   = note: required for the cast from `&'static str` to `&dyn Foo`
 
 error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
   --> $DIR/dst-object-from-unsized-type.rs:23:23
@@ -44,7 +44,7 @@ LL |     let _: &dyn Foo = x as &dyn Foo;
    |                       ^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[u8]`
-   = note: required for the cast from `[u8]` to the object type `dyn Foo`
+   = note: required for the cast from `&[u8]` to `&dyn Foo`
 
 error: aborting due to 4 previous errors
 

tests/ui/feature-gates/feature-gate-dispatch-from-dyn-missing-impl.stderr

@@ -31,14 +31,7 @@ LL | trait Trait {
    |       ----- this trait cannot be made into an object...
 LL |     fn ptr(self: Ptr<Self>);
    |                  ^^^^^^^^^ ...because method `ptr`'s `self` parameter cannot be dispatched on
-note: required for `Ptr<{integer}>` to implement `CoerceUnsized<Ptr<dyn Trait>>`
+   = note: required for the cast from `Ptr<{integer}>` to `Ptr<dyn Trait>`
-  --> $DIR/feature-gate-dispatch-from-dyn-missing-impl.rs:20:40
-   |
-LL | impl<T: Unsize<U> + ?Sized, U: ?Sized> CoerceUnsized<Ptr<U>> for Ptr<T> {}
-   |         ---------                      ^^^^^^^^^^^^^^^^^^^^^     ^^^^^^
-   |         |
-   |         unsatisfied trait bound introduced here
-   = note: required by cast to type `Ptr<dyn Trait>`
 
 error: aborting due to 2 previous errors
 

tests/ui/generic-associated-types/issue-76535.base.stderr

@@ -43,8 +43,7 @@ LL | pub trait SuperTrait {
 LL |     type SubType<'a>: SubTrait where Self: 'a;
    |          ^^^^^^^ ...because it contains the generic associated type `SubType`
    = help: consider moving `SubType` to another trait
-   = note: required for `Box<SuperStruct>` to implement `CoerceUnsized<Box<dyn SuperTrait<SubType = SubStruct<'_>>>>`
+   = note: required for the cast from `Box<SuperStruct>` to `Box<dyn SuperTrait<SubType = SubStruct<'_>>>`
-   = note: required by cast to type `Box<dyn SuperTrait<SubType = SubStruct<'_>>>`
 
 error: aborting due to 3 previous errors
 

tests/ui/generic-associated-types/issue-79422.base.stderr

@@ -43,8 +43,7 @@ LL | trait MapLike<K, V> {
 LL |     type VRefCont<'a>: RefCont<'a, V> where Self: 'a;
    |          ^^^^^^^^ ...because it contains the generic associated type `VRefCont`
    = help: consider moving `VRefCont` to another trait
-   = note: required for `Box<BTreeMap<u8, u8>>` to implement `CoerceUnsized<Box<dyn MapLike<u8, u8, VRefCont = (dyn RefCont<'_, u8> + 'static)>>>`
+   = note: required for the cast from `Box<BTreeMap<u8, u8>>` to `Box<dyn MapLike<u8, u8, VRefCont = (dyn RefCont<'_, u8> + 'static)>>`
-   = note: required by cast to type `Box<dyn MapLike<u8, u8, VRefCont = (dyn RefCont<'_, u8> + 'static)>>`
 
 error: aborting due to 3 previous errors
 

tests/ui/generic-associated-types/issue-79422.extended.stderr

@@ -27,7 +27,7 @@ LL |     type VRefCont<'a> = &'a V where Self: 'a;
    |                         ^^^^^
    = note: expected trait object `(dyn RefCont<'_, u8> + 'static)`
                  found reference `&u8`
-   = note: required for the cast from `BTreeMap<u8, u8>` to the object type `dyn MapLike<u8, u8, VRefCont = (dyn RefCont<'_, u8> + 'static)>`
+   = note: required for the cast from `Box<BTreeMap<u8, u8>>` to `Box<dyn MapLike<u8, u8, VRefCont = (dyn RefCont<'_, u8> + 'static)>>`
 
 error: aborting due to 2 previous errors
 

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

@@ -42,8 +42,7 @@ LL | trait Foo {
 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 for the cast from `Box<u32>` to `Box<dyn Foo>`
-   = note: required by cast to type `Box<dyn Foo>`
 
 error: aborting due to 3 previous errors
 

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

@@ -42,8 +42,7 @@ LL | trait Foo {
 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 for the cast from `Box<u32>` to `Box<dyn Foo>`
-   = note: required by cast to type `Box<dyn Foo>`
 
 error: aborting due to 3 previous errors
 

tests/ui/issues/issue-14366.stderr

@@ -5,8 +5,8 @@ LL |     let _x = "test" as &dyn (::std::any::Any);
    |              ^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
-   = note: required for the cast from `str` to the object type `dyn Any`
+   = note: required for the cast from `&'static str` to `&(dyn Any + 'static)`
-help: consider borrowing the value, since `&str` can be coerced into `dyn Any`
+help: consider borrowing the value, since `&&'static str` can be coerced into `&(dyn Any + 'static)`
    |
 LL |     let _x = &"test" as &dyn (::std::any::Any);
    |              +

tests/ui/issues/issue-22034.stderr

@@ -6,7 +6,7 @@ LL |         &mut *(ptr as *mut dyn Fn())
    |
    = help: the trait `Fn<()>` is not implemented for `()`
    = note: wrap the `()` in a closure with no arguments: `|| { /* code */ }`
-   = note: required for the cast from `()` to the object type `dyn Fn()`
+   = note: required for the cast from `*mut ()` to `*mut dyn Fn()`
 
 error: aborting due to previous error
 

tests/ui/issues/issue-22872.stderr

@@ -13,7 +13,7 @@ LL | impl<'b, P> Wrap<'b> for Wrapper<P>
 LL | where P: Process<'b>,
 LL |       <P as Process<'b>>::Item: Iterator {
    |                                 -------- unsatisfied trait bound introduced here
-   = note: required for the cast from `Wrapper<P>` to the object type `dyn for<'b> Wrap<'b>`
+   = note: required for the cast from `Box<Wrapper<P>>` to `Box<dyn for<'b> Wrap<'b>>`
 help: consider further restricting the associated type
    |
 LL | fn push_process<P>(process: P) where P: Process<'static>, <P as Process<'_>>::Item: Iterator {

tests/ui/kindck/kindck-impl-type-params.stderr

@@ -11,7 +11,7 @@ LL | impl<T: Send + Copy + 'static> Gettable<T> for S<T> {}
    |         ----                   ^^^^^^^^^^^     ^^^^
    |         |
    |         unsatisfied trait bound introduced here
-   = note: required for the cast from `S<T>` to the object type `dyn Gettable<T>`
+   = note: required for the cast from `&S<T>` to `&dyn Gettable<T>`
 help: consider restricting type parameter `T`
    |
 LL | fn f<T: std::marker::Send>(val: T) {
@@ -30,7 +30,7 @@ LL | impl<T: Send + Copy + 'static> Gettable<T> for S<T> {}
    |                ----            ^^^^^^^^^^^     ^^^^
    |                |
    |                unsatisfied trait bound introduced here
-   = note: required for the cast from `S<T>` to the object type `dyn Gettable<T>`
+   = note: required for the cast from `&S<T>` to `&dyn Gettable<T>`
 help: consider restricting type parameter `T`
    |
 LL | fn f<T: std::marker::Copy>(val: T) {
@@ -49,7 +49,7 @@ LL | impl<T: Send + Copy + 'static> Gettable<T> for S<T> {}
    |         ----                   ^^^^^^^^^^^     ^^^^
    |         |
    |         unsatisfied trait bound introduced here
-   = note: required for the cast from `S<T>` to the object type `dyn Gettable<T>`
+   = note: required for the cast from `&S<T>` to `&dyn Gettable<T>`
 help: consider restricting type parameter `T`
    |
 LL | fn g<T: std::marker::Send>(val: T) {
@@ -68,7 +68,7 @@ LL | impl<T: Send + Copy + 'static> Gettable<T> for S<T> {}
    |                ----            ^^^^^^^^^^^     ^^^^
    |                |
    |                unsatisfied trait bound introduced here
-   = note: required for the cast from `S<T>` to the object type `dyn Gettable<T>`
+   = note: required for the cast from `&S<T>` to `&dyn Gettable<T>`
 help: consider restricting type parameter `T`
    |
 LL | fn g<T: std::marker::Copy>(val: T) {
@@ -88,7 +88,7 @@ LL | impl<T: Send + Copy + 'static> Gettable<T> for S<T> {}
    |                ----            ^^^^^^^^^^^     ^^^^
    |                |
    |                unsatisfied trait bound introduced here
-   = note: required for the cast from `S<String>` to the object type `dyn Gettable<String>`
+   = note: required for the cast from `Box<S<String>>` to `Box<dyn Gettable<String>>`
 
 error[E0277]: the trait bound `Foo: Copy` is not satisfied
   --> $DIR/kindck-impl-type-params.rs:43:37
@@ -104,7 +104,7 @@ LL | impl<T: Send + Copy + 'static> Gettable<T> for S<T> {}
    |                ----            ^^^^^^^^^^^     ^^^^
    |                |
    |                unsatisfied trait bound introduced here
-   = note: required for the cast from `S<Foo>` to the object type `dyn Gettable<Foo>`
+   = note: required for the cast from `Box<S<Foo>>` to `Box<dyn Gettable<Foo>>`
 help: consider annotating `Foo` with `#[derive(Copy)]`
    |
 LL +     #[derive(Copy)]

tests/ui/kindck/kindck-inherited-copy-bound.curr.stderr

@@ -46,8 +46,7 @@ LL | trait Foo : Copy {
    |       ---   ^^^^ ...because it requires `Self: Sized`
    |       |
    |       this trait cannot be made into an object...
-   = note: required for `&Box<{integer}>` to implement `CoerceUnsized<&dyn Foo>`
+   = note: required for the cast from `&Box<{integer}>` to `&dyn Foo`
-   = note: required by cast to type `&dyn Foo`
 
 error: aborting due to 3 previous errors
 

tests/ui/kindck/kindck-inherited-copy-bound.object_safe_for_dispatch.stderr

@@ -32,8 +32,7 @@ LL | trait Foo : Copy {
    |       ---   ^^^^ ...because it requires `Self: Sized`
    |       |
    |       this trait cannot be made into an object...
-   = note: required for `&Box<i32>` to implement `CoerceUnsized<&dyn Foo>`
+   = note: required for the cast from `&Box<i32>` to `&dyn Foo`
-   = note: required by cast to type `&dyn Foo`
 
 error: aborting due to 2 previous errors
 

tests/ui/mismatched_types/cast-rfc0401.stderr

@@ -220,11 +220,7 @@ LL |     let _ = fat_v as *const dyn Foo;
    |             ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[u8]`
-   = note: required for the cast from `[u8]` to the object type `dyn Foo`
+   = note: required for the cast from `*const [u8]` to `*const dyn Foo`
-help: consider borrowing the value, since `&[u8]` can be coerced into `dyn Foo`
-   |
-LL |     let _ = &fat_v as *const dyn Foo;
-   |             +
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
   --> $DIR/cast-rfc0401.rs:62:13
@@ -233,11 +229,7 @@ LL |     let _ = a as *const dyn Foo;
    |             ^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
-   = note: required for the cast from `str` to the object type `dyn Foo`
+   = note: required for the cast from `*const str` to `*const dyn Foo`
-help: consider borrowing the value, since `&str` can be coerced into `dyn Foo`
-   |
-LL |     let _ = &a as *const dyn Foo;
-   |             +
 
 error[E0606]: casting `&{float}` as `f32` is invalid
   --> $DIR/cast-rfc0401.rs:71:30

tests/ui/never_type/fallback-closure-wrap.fallback.stderr

@@ -10,7 +10,7 @@ LL | |     }) as Box<dyn FnMut()>);
    |
    = note: expected unit type `()`
                    found type `!`
-   = note: required for the cast from `[closure@$DIR/fallback-closure-wrap.rs:18:40: 18:47]` to the object type `dyn FnMut()`
+   = note: required for the cast from `Box<[closure@$DIR/fallback-closure-wrap.rs:18:40: 18:47]>` to `Box<dyn FnMut()>`
 
 error: aborting due to previous error
 

tests/ui/object-safety/issue-19538.stderr

@@ -29,8 +29,7 @@ LL |     fn foo<T>(&self, val: T);
 LL | trait Bar: Foo { }
    |       --- this trait cannot be made into an object...
    = help: consider moving `foo` to another trait
-   = note: required for `&mut Thing` to implement `CoerceUnsized<&mut dyn Bar>`
+   = note: required for the cast from `&mut Thing` to `&mut dyn Bar`
-   = note: required by cast to type `&mut dyn Bar`
 
 error: aborting due to 2 previous errors
 

tests/ui/object-safety/object-safety-associated-consts.object_safe_for_dispatch.stderr

@@ -12,8 +12,7 @@ LL | trait Bar {
 LL |     const X: usize;
    |           ^ ...because it contains this associated `const`
    = help: consider moving `X` to another trait
-   = note: required for `&T` to implement `CoerceUnsized<&dyn Bar>`
+   = note: required for the cast from `&T` to `&dyn Bar`
-   = note: required by cast to type `&dyn Bar`
 
 error: aborting due to previous error
 

tests/ui/object-safety/object-safety-generics.object_safe_for_dispatch.stderr

@@ -12,8 +12,7 @@ LL | trait Bar {
 LL |     fn bar<T>(&self, t: T);
    |        ^^^ ...because method `bar` has generic type parameters
    = help: consider moving `bar` to another trait
-   = note: required for `&T` to implement `CoerceUnsized<&dyn Bar>`
+   = note: required for the cast from `&T` to `&dyn Bar`
-   = note: required by cast to type `&dyn Bar`
 
 error[E0038]: the trait `Bar` cannot be made into an object
   --> $DIR/object-safety-generics.rs:26:5
@@ -29,8 +28,7 @@ LL | trait Bar {
 LL |     fn bar<T>(&self, t: T);
    |        ^^^ ...because method `bar` has generic type parameters
    = help: consider moving `bar` to another trait
-   = note: required for `&T` to implement `CoerceUnsized<&dyn Bar>`
+   = note: required for the cast from `&T` to `&dyn Bar`
-   = note: required by cast to type `&dyn Bar`
 
 error: aborting due to 2 previous errors
 

tests/ui/object-safety/object-safety-mentions-Self.object_safe_for_dispatch.stderr

@@ -12,8 +12,7 @@ LL | trait Bar {
 LL |     fn bar(&self, x: &Self);
    |                      ^^^^^ ...because method `bar` references the `Self` type in this parameter
    = help: consider moving `bar` to another trait
-   = note: required for `&T` to implement `CoerceUnsized<&dyn Bar>`
+   = note: required for the cast from `&T` to `&dyn Bar`
-   = note: required by cast to type `&dyn Bar`
 
 error[E0038]: the trait `Baz` cannot be made into an object
   --> $DIR/object-safety-mentions-Self.rs:30:5
@@ -29,8 +28,7 @@ LL | trait Baz {
 LL |     fn baz(&self) -> Self;
    |                      ^^^^ ...because method `baz` references the `Self` type in its return type
    = help: consider moving `baz` to another trait
-   = note: required for `&T` to implement `CoerceUnsized<&dyn Baz>`
+   = note: required for the cast from `&T` to `&dyn Baz`
-   = note: required by cast to type `&dyn Baz`
 
 error: aborting due to 2 previous errors
 

tests/ui/object-safety/object-safety-no-static.object_safe_for_dispatch.stderr

@@ -11,8 +11,7 @@ LL | trait Foo {
    |       --- this trait cannot be made into an object...
 LL |     fn foo() {}
    |        ^^^ ...because associated function `foo` has no `self` parameter
-   = note: required for `Box<Bar>` to implement `CoerceUnsized<Box<dyn Foo>>`
+   = note: required for the cast from `Box<Bar>` to `Box<dyn Foo>`
-   = note: required by cast to type `Box<dyn Foo>`
 help: consider turning `foo` into a method by giving it a `&self` argument
    |
 LL |     fn foo(&self) {}

tests/ui/object-safety/object-safety-sized-2.object_safe_for_dispatch.stderr

@@ -11,8 +11,7 @@ LL | trait Bar
    |       --- this trait cannot be made into an object...
 LL |     where Self : Sized
    |                  ^^^^^ ...because it requires `Self: Sized`
-   = note: required for `&T` to implement `CoerceUnsized<&dyn Bar>`
+   = note: required for the cast from `&T` to `&dyn Bar`
-   = note: required by cast to type `&dyn Bar`
 
 error: aborting due to previous error
 

tests/ui/object-safety/object-safety-sized.object_safe_for_dispatch.stderr

@@ -11,8 +11,7 @@ LL | trait Bar : Sized {
    |       ---   ^^^^^ ...because it requires `Self: Sized`
    |       |
    |       this trait cannot be made into an object...
-   = note: required for `&T` to implement `CoerceUnsized<&dyn Bar>`
+   = note: required for the cast from `&T` to `&dyn Bar`
-   = note: required by cast to type `&dyn Bar`
 
 error: aborting due to previous error
 

tests/ui/self/arbitrary-self-types-not-object-safe.curr.stderr

@@ -31,8 +31,7 @@ LL | trait Foo {
    |       --- this trait cannot be made into an object...
 LL |     fn foo(self: &Rc<Self>) -> usize;
    |                  ^^^^^^^^^ ...because method `foo`'s `self` parameter cannot be dispatched on
-   = note: required for `Rc<usize>` to implement `CoerceUnsized<Rc<dyn Foo>>`
+   = note: required for the cast from `Rc<usize>` to `Rc<dyn Foo>`
-   = note: required by cast to type `Rc<dyn Foo>`
 
 error: aborting due to 2 previous errors
 

tests/ui/self/arbitrary-self-types-not-object-safe.object_safe_for_dispatch.stderr

@@ -14,8 +14,7 @@ LL | trait Foo {
    |       --- this trait cannot be made into an object...
 LL |     fn foo(self: &Rc<Self>) -> usize;
    |                  ^^^^^^^^^ ...because method `foo`'s `self` parameter cannot be dispatched on
-   = note: required for `Rc<usize>` to implement `CoerceUnsized<Rc<dyn Foo>>`
+   = note: required for the cast from `Rc<usize>` to `Rc<dyn Foo>`
-   = note: required by cast to type `Rc<dyn Foo>`
 
 error: aborting due to previous error
 

tests/ui/suggestions/derive-macro-missing-bounds.stderr

@@ -36,7 +36,7 @@ LL |     impl<T: Debug + Trait> Debug for Inner<T> {
    |                     unsatisfied trait bound introduced here
    = note: 1 redundant requirement hidden
    = note: required for `&c::Inner<T>` to implement `Debug`
-   = note: required for the cast from `&c::Inner<T>` to the object type `dyn Debug`
+   = note: required for the cast from `&&c::Inner<T>` to `&dyn Debug`
    = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider restricting type parameter `T`
    |
@@ -58,7 +58,7 @@ LL |     impl<T> Debug for Inner<T> where T: Debug, T: Trait {
    |             ^^^^^     ^^^^^^^^                    ----- unsatisfied trait bound introduced here
    = note: 1 redundant requirement hidden
    = note: required for `&d::Inner<T>` to implement `Debug`
-   = note: required for the cast from `&d::Inner<T>` to the object type `dyn Debug`
+   = note: required for the cast from `&&d::Inner<T>` to `&dyn Debug`
    = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider restricting type parameter `T`
    |
@@ -80,7 +80,7 @@ LL |     impl<T> Debug for Inner<T> where T: Debug + Trait {
    |             ^^^^^     ^^^^^^^^                  ----- unsatisfied trait bound introduced here
    = note: 1 redundant requirement hidden
    = note: required for `&e::Inner<T>` to implement `Debug`
-   = note: required for the cast from `&e::Inner<T>` to the object type `dyn Debug`
+   = note: required for the cast from `&&e::Inner<T>` to `&dyn Debug`
    = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider restricting type parameter `T`
    |
@@ -102,7 +102,7 @@ LL |     impl<T: Debug> Debug for Inner<T> where T: Trait {
    |                    ^^^^^     ^^^^^^^^          ----- unsatisfied trait bound introduced here
    = note: 1 redundant requirement hidden
    = note: required for `&f::Inner<T>` to implement `Debug`
-   = note: required for the cast from `&f::Inner<T>` to the object type `dyn Debug`
+   = note: required for the cast from `&&f::Inner<T>` to `&dyn Debug`
    = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider restricting type parameter `T`
    |

tests/ui/suggestions/suggest-borrow-to-dyn-object.rs

@@ -1,16 +0,0 @@
-use std::ffi::{OsStr, OsString};
-use std::path::Path;
-
-fn check(p: &dyn AsRef<Path>) {
-    let m = std::fs::metadata(&p);
-    println!("{:?}", &m);
-}
-
-fn main() {
-    let s: OsString = ".".into();
-    let s: &OsStr = &s;
-    check(s);
-    //~^ ERROR the size for values of type `[u8]` cannot be known at compilation time
-    //~| HELP within `OsStr`, the trait `Sized` is not implemented for `[u8]`
-    //~| HELP consider borrowing the value, since `&OsStr` can be coerced into `dyn AsRef<Path>`
-}

tests/ui/suggestions/suggest-borrow-to-dyn-object.stderr

@@ -1,18 +0,0 @@
-error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
-  --> $DIR/suggest-borrow-to-dyn-object.rs:12:11
-   |
-LL |     check(s);
-   |           ^ doesn't have a size known at compile-time
-   |
-   = help: within `OsStr`, the trait `Sized` is not implemented for `[u8]`
-note: required because it appears within the type `OsStr`
-  --> $SRC_DIR/std/src/ffi/os_str.rs:LL:COL
-   = note: required for the cast from `OsStr` to the object type `dyn AsRef<Path>`
-help: consider borrowing the value, since `&OsStr` can be coerced into `dyn AsRef<Path>`
-   |
-LL |     check(&s);
-   |           +
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0277`.

tests/ui/traits/coercion-generic-bad.stderr

@@ -5,7 +5,7 @@ LL |     let s: Box<dyn Trait<isize>> = Box::new(Struct { person: "Fred" });
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Trait<isize>` is not implemented for `Struct`
    |
    = help: the trait `Trait<&'static str>` is implemented for `Struct`
-   = note: required for the cast from `Struct` to the object type `dyn Trait<isize>`
+   = note: required for the cast from `Box<Struct>` to `Box<dyn Trait<isize>>`
 
 error: aborting due to previous error
 

tests/ui/traits/issue-20692.stderr

@@ -27,8 +27,7 @@ LL | trait Array: Sized + Copy {}
    |       |      |
    |       |      ...because it requires `Self: Sized`
    |       this trait cannot be made into an object...
-   = note: required for `&T` to implement `CoerceUnsized<&dyn Array>`
+   = note: required for the cast from `&T` to `&dyn Array`
-   = note: required by cast to type `&dyn Array`
 
 error: aborting due to 2 previous errors
 

tests/ui/traits/issue-38604.stderr

@@ -25,8 +25,7 @@ LL | trait Foo where u32: Q<Self> {
    |       ---            ^^^^^^^ ...because it uses `Self` as a type parameter
    |       |
    |       this trait cannot be made into an object...
-   = note: required for `Box<()>` to implement `CoerceUnsized<Box<dyn Foo>>`
+   = note: required for the cast from `Box<()>` to `Box<dyn Foo>`
-   = note: required by cast to type `Box<dyn Foo>`
 
 error: aborting due to 2 previous errors
 

tests/ui/traits/issue-7013.stderr

@@ -12,7 +12,7 @@ note: required because it appears within the type `B`
    |
 LL | struct B {
    |        ^
-   = note: required for the cast from `B` to the object type `dyn Foo + Send`
+   = note: required for the cast from `Box<B>` to `Box<dyn Foo + Send>`
 
 error: aborting due to previous error
 

tests/ui/traits/map-types.stderr

@@ -5,7 +5,7 @@ LL |     let y: Box<dyn Map<usize, isize>> = Box::new(x);
    |                                         ^^^^^^^^^^^ the trait `Map<usize, isize>` is not implemented for `Box<dyn Map<isize, isize>>`
    |
    = help: the trait `Map<K, V>` is implemented for `HashMap<K, V>`
-   = note: required for the cast from `Box<dyn Map<isize, isize>>` to the object type `dyn Map<usize, isize>`
+   = note: required for the cast from `Box<Box<dyn Map<isize, isize>>>` to `Box<dyn Map<usize, isize>>`
 
 error: aborting due to previous error
 

tests/ui/traits/non_lifetime_binders/supertrait-object-safety.stderr

@@ -20,8 +20,7 @@ LL | trait Foo: for<T> Bar<T> {}
    |       ---  ^^^^^^^^^^^^^ ...because where clause cannot reference non-lifetime `for<...>` variables
    |       |
    |       this trait cannot be made into an object...
-   = note: required for `&()` to implement `CoerceUnsized<&dyn Foo>`
+   = note: required for the cast from `&()` to `&dyn Foo`
-   = note: required by cast to type `&dyn Foo`
 
 error[E0038]: the trait `Foo` cannot be made into an object
   --> $DIR/supertrait-object-safety.rs:19:12

tests/ui/traits/object/safety.stderr

@@ -11,8 +11,7 @@ LL | trait Tr {
    |       -- this trait cannot be made into an object...
 LL |     fn foo();
    |        ^^^ ...because associated function `foo` has no `self` parameter
-   = note: required for `&St` to implement `CoerceUnsized<&dyn Tr>`
+   = note: required for the cast from `&St` to `&dyn Tr`
-   = note: required by cast to type `&dyn Tr`
 help: consider turning `foo` into a method by giving it a `&self` argument
    |
 LL |     fn foo(&self);

tests/ui/traits/test-2.stderr

@@ -76,8 +76,7 @@ LL | trait bar { fn dup(&self) -> Self; fn blah<X>(&self); }
    |       this trait cannot be made into an object...
    = help: consider moving `dup` to another trait
    = help: consider moving `blah` to another trait
-   = note: required for `Box<{integer}>` to implement `CoerceUnsized<Box<dyn bar>>`
+   = note: required for the cast from `Box<{integer}>` to `Box<dyn bar>`
-   = note: required by cast to type `Box<dyn bar>`
 
 error: aborting due to 5 previous errors
 

tests/ui/traits/trait-upcasting/type-checking-test-1.stderr

@@ -15,7 +15,7 @@ error[E0277]: the trait bound `&dyn Foo: Bar<_>` is not satisfied
 LL |     let _ = x as &dyn Bar<_>; // Ambiguous
    |             ^ the trait `Bar<_>` is not implemented for `&dyn Foo`
    |
-   = note: required for the cast from `&dyn Foo` to the object type `dyn Bar<_>`
+   = note: required for the cast from `&&dyn Foo` to `&dyn Bar<_>`
 
 error: aborting due to 2 previous errors
 

tests/ui/traits/trait-upcasting/type-checking-test-2.stderr

@@ -15,7 +15,7 @@ error[E0277]: the trait bound `&dyn Foo<i32>: Bar<u32>` is not satisfied
 LL |     let _ = x as &dyn Bar<u32>; // Error
    |             ^ the trait `Bar<u32>` is not implemented for `&dyn Foo<i32>`
    |
-   = note: required for the cast from `&dyn Foo<i32>` to the object type `dyn Bar<u32>`
+   = note: required for the cast from `&&dyn Foo<i32>` to `&dyn Bar<u32>`
 
 error[E0605]: non-primitive cast: `&dyn Foo<u32>` as `&dyn Bar<_>`
   --> $DIR/type-checking-test-2.rs:25:13
@@ -34,7 +34,7 @@ error[E0277]: the trait bound `&dyn Foo<u32>: Bar<_>` is not satisfied
 LL |     let a = x as &dyn Bar<_>; // Ambiguous
    |             ^ the trait `Bar<_>` is not implemented for `&dyn Foo<u32>`
    |
-   = note: required for the cast from `&dyn Foo<u32>` to the object type `dyn Bar<_>`
+   = note: required for the cast from `&&dyn Foo<u32>` to `&dyn Bar<_>`
 
 error: aborting due to 4 previous errors
 

tests/ui/type-alias-impl-trait/issue-98604.stderr

@@ -4,7 +4,7 @@ error[E0271]: expected `test` to be a fn item that returns `Pin<Box<dyn Future<O
 LL |     Box::new(test) as AsyncFnPtr;
    |     ^^^^^^^^^^^^^^ expected `Pin<Box<dyn Future<Output = ()>>>`, found future
    |
-   = note: required for the cast from `fn() -> impl Future<Output = ()> {test}` to the object type `dyn Fn() -> Pin<Box<(dyn Future<Output = ()> + 'static)>>`
+   = note: required for the cast from `Box<fn() -> impl Future<Output = ()> {test}>` to `Box<(dyn Fn() -> Pin<Box<(dyn Future<Output = ()> + 'static)>> + 'static)>`
 
 error: aborting due to previous error
 

tests/ui/type-alias-impl-trait/issue-98608.stderr

@@ -9,7 +9,7 @@ LL |     let b: Box<dyn Fn() -> Box<u8>> = Box::new(hi);
    |
    = note:   expected struct `Box<u8>`
            found opaque type `impl Sized`
-   = note: required for the cast from `fn() -> impl Sized {hi}` to the object type `dyn Fn() -> Box<u8>`
+   = note: required for the cast from `Box<fn() -> impl Sized {hi}>` to `Box<dyn Fn() -> Box<u8>>`
 
 error: aborting due to previous error
 

tests/ui/type/issue-58355.stderr

@@ -6,7 +6,7 @@ LL |     x = Some(Box::new(callback));
    |
    = help: within `fn() -> dyn ToString`, the trait `Sized` is not implemented for `dyn ToString`
    = note: required because it appears within the type `fn() -> dyn ToString`
-   = note: required for the cast from `fn() -> dyn ToString` to the object type `dyn Fn() -> (dyn ToString + 'static)`
+   = note: required for the cast from `Box<fn() -> dyn ToString>` to `Box<dyn Fn() -> (dyn ToString + 'static)>`
 
 error: aborting due to previous error
 

tests/ui/unsized/unsized-fn-param.stderr

@@ -5,8 +5,8 @@ LL |     foo11("bar", &"baz");
    |           ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
-   = note: required for the cast from `str` to the object type `dyn AsRef<Path>`
+   = note: required for the cast from `&'static str` to `&dyn AsRef<Path>`
-help: consider borrowing the value, since `&str` can be coerced into `dyn AsRef<Path>`
+help: consider borrowing the value, since `&&'static str` can be coerced into `&dyn AsRef<Path>`
    |
 LL |     foo11(&"bar", &"baz");
    |           +
@@ -18,8 +18,8 @@ LL |     foo12(&"bar", "baz");
    |                   ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
-   = note: required for the cast from `str` to the object type `dyn AsRef<Path>`
+   = note: required for the cast from `&'static str` to `&dyn AsRef<Path>`
-help: consider borrowing the value, since `&str` can be coerced into `dyn AsRef<Path>`
+help: consider borrowing the value, since `&&'static str` can be coerced into `&dyn AsRef<Path>`
    |
 LL |     foo12(&"bar", &"baz");
    |                   +
@@ -31,8 +31,8 @@ LL |     foo21("bar", &"baz");
    |           ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
-   = note: required for the cast from `str` to the object type `dyn AsRef<str>`
+   = note: required for the cast from `&'static str` to `&dyn AsRef<str>`
-help: consider borrowing the value, since `&str` can be coerced into `dyn AsRef<str>`
+help: consider borrowing the value, since `&&'static str` can be coerced into `&dyn AsRef<str>`
    |
 LL |     foo21(&"bar", &"baz");
    |           +
@@ -44,8 +44,8 @@ LL |     foo22(&"bar", "baz");
    |                   ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
-   = note: required for the cast from `str` to the object type `dyn AsRef<str>`
+   = note: required for the cast from `&'static str` to `&dyn AsRef<str>`
-help: consider borrowing the value, since `&str` can be coerced into `dyn AsRef<str>`
+help: consider borrowing the value, since `&&'static str` can be coerced into `&dyn AsRef<str>`
    |
 LL |     foo22(&"bar", &"baz");
    |                   +

tests/ui/wf/wf-convert-unsafe-trait-obj-box.stderr

@@ -11,8 +11,7 @@ LL | trait Trait: Sized {}
    |       -----  ^^^^^ ...because it requires `Self: Sized`
    |       |
    |       this trait cannot be made into an object...
-   = note: required for `Box<S>` to implement `CoerceUnsized<Box<dyn Trait>>`
+   = note: required for the cast from `Box<S>` to `Box<dyn Trait>`
-   = note: required by cast to type `Box<dyn Trait>`
 
 error[E0038]: the trait `Trait` cannot be made into an object
   --> $DIR/wf-convert-unsafe-trait-obj-box.rs:17:15
@@ -27,8 +26,7 @@ LL | trait Trait: Sized {}
    |       -----  ^^^^^ ...because it requires `Self: Sized`
    |       |
    |       this trait cannot be made into an object...
-   = note: required for `Box<S>` to implement `CoerceUnsized<Box<dyn Trait>>`
+   = note: required for the cast from `Box<S>` to `Box<(dyn Trait + 'static)>`
-   = note: required by cast to type `Box<(dyn Trait + 'static)>`
 
 error[E0038]: the trait `Trait` cannot be made into an object
   --> $DIR/wf-convert-unsafe-trait-obj-box.rs:15:5
@@ -43,8 +41,7 @@ LL | trait Trait: Sized {}
    |       -----  ^^^^^ ...because it requires `Self: Sized`
    |       |
    |       this trait cannot be made into an object...
-   = note: required for `Box<S>` to implement `CoerceUnsized<Box<dyn Trait>>`
+   = note: required for the cast from `Box<S>` to `Box<dyn Trait>`
-   = note: required by cast to type `Box<dyn Trait>`
 
 error: aborting due to 3 previous errors
 

tests/ui/wf/wf-convert-unsafe-trait-obj.stderr

@@ -11,8 +11,7 @@ LL | trait Trait: Sized {}
    |       -----  ^^^^^ ...because it requires `Self: Sized`
    |       |
    |       this trait cannot be made into an object...
-   = note: required for `&S` to implement `CoerceUnsized<&dyn Trait>`
+   = note: required for the cast from `&S` to `&dyn Trait`
-   = note: required by cast to type `&dyn Trait`
 
 error[E0038]: the trait `Trait` cannot be made into an object
   --> $DIR/wf-convert-unsafe-trait-obj.rs:17:17
@@ -27,8 +26,7 @@ LL | trait Trait: Sized {}
    |       -----  ^^^^^ ...because it requires `Self: Sized`
    |       |
    |       this trait cannot be made into an object...
-   = note: required for `&S` to implement `CoerceUnsized<&dyn Trait>`
+   = note: required for the cast from `&S` to `&dyn Trait`
-   = note: required by cast to type `&dyn Trait`
 
 error[E0038]: the trait `Trait` cannot be made into an object
   --> $DIR/wf-convert-unsafe-trait-obj.rs:15:5
@@ -43,8 +41,7 @@ LL | trait Trait: Sized {}
    |       -----  ^^^^^ ...because it requires `Self: Sized`
    |       |
    |       this trait cannot be made into an object...
-   = note: required for `&S` to implement `CoerceUnsized<&dyn Trait>`
+   = note: required for the cast from `&S` to `&dyn Trait`
-   = note: required by cast to type `&dyn Trait`
 
 error: aborting due to 3 previous errors
 

tests/ui/wf/wf-unsafe-trait-obj-match.stderr

@@ -25,8 +25,7 @@ LL | trait Trait: Sized {}
    |       -----  ^^^^^ ...because it requires `Self: Sized`
    |       |
    |       this trait cannot be made into an object...
-   = note: required for `&S` to implement `CoerceUnsized<&dyn Trait>`
+   = note: required for the cast from `&S` to `&dyn Trait`
-   = note: required by cast to type `&dyn Trait`
 
 error[E0038]: the trait `Trait` cannot be made into an object
   --> $DIR/wf-unsafe-trait-obj-match.rs:25:25
@@ -45,8 +44,7 @@ LL | trait Trait: Sized {}
    |       -----  ^^^^^ ...because it requires `Self: Sized`
    |       |
    |       this trait cannot be made into an object...
-   = note: required for `&R` to implement `CoerceUnsized<&dyn Trait>`
+   = note: required for the cast from `&R` to `&dyn Trait`
-   = note: required by cast to type `&dyn Trait`
 
 error: aborting due to 3 previous errors