Note concrete type being coerced into object

compiler-errors · compiler-errors · commit 25fe474c3be1 · 2022-06-24T15:50:38.000-07:00
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -2217,9 +2217,10 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     err.span_note(tcx.def_span(item_def_id), &descr);
                 }
             }
-            ObligationCauseCode::ObjectCastObligation(_, object_ty) => {
+            ObligationCauseCode::ObjectCastObligation(concrete_ty, object_ty) => {
                 err.note(&format!(
-                    "required for the cast to the object type `{}`",
+                    "required for the cast from `{}` to the object type `{}`",
+                    self.ty_to_string(concrete_ty),
                     self.ty_to_string(object_ty)
                 ));
             }
diff --git a/src/test/ui/associated-type-bounds/assoc-type-eq-with-dyn-atb-fail.stderr b/src/test/ui/associated-type-bounds/assoc-type-eq-with-dyn-atb-fail.stderr
@@ -4,7 +4,7 @@ error[E0277]: the trait bound `String: Copy` is not satisfied
 LL |         Box::new(AssocNoCopy)
    |         ^^^^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `String`
    |
-   = note: required for the cast to the object type `dyn Bar<Assoc = <AssocNoCopy as Thing>::Out::{opaque#0}>`
+   = note: required for the cast from `AssocNoCopy` to the object type `dyn Bar<Assoc = <AssocNoCopy as Thing>::Out::{opaque#0}>`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/associated-types/associated-types-eq-3.stderr b/src/test/ui/associated-types/associated-types-eq-3.stderr
@@ -41,7 +41,7 @@ note: expected this to be `Bar`
    |
 LL |     type A = usize;
    |              ^^^^^
-   = note: required for the cast to the object type `dyn Foo<A = Bar>`
+   = note: required for the cast from `isize` to the object type `dyn Foo<A = Bar>`
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/associated-types/associated-types-overridden-binding-2.stderr b/src/test/ui/associated-types/associated-types-overridden-binding-2.stderr
@@ -4,7 +4,7 @@ error[E0271]: type mismatch resolving `<std::vec::IntoIter<u32> as Iterator>::It
 LL |     let _: &dyn I32Iterator<Item = u32> = &vec![42].into_iter();
    |                                           ^^^^^^^^^^^^^^^^^^^^^ expected `i32`, found `u32`
    |
-   = note: required for the cast to the object type `dyn Iterator<Item = u32, Item = i32>`
+   = note: required for the cast from `std::vec::IntoIter<u32>` to the object type `dyn Iterator<Item = u32, Item = i32>`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/associated-types/issue-65774-1.stderr b/src/test/ui/associated-types/issue-65774-1.stderr
@@ -23,7 +23,7 @@ note: required because of the requirements on the impl of `MyDisplay` for `&mut
    |
 LL | impl<'a, T: MyDisplay> MyDisplay for &'a mut T { }
    |                        ^^^^^^^^^     ^^^^^^^^^
-   = note: required for the cast to the object type `dyn MyDisplay`
+   = note: required for the cast from `&mut T` to the object type `dyn MyDisplay`
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/associated-types/issue-65774-2.stderr b/src/test/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 to the object type `dyn MyDisplay`
+   = note: required for the cast from `T` to the object type `dyn MyDisplay`
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/async-await/async-block-control-flow-static-semantics.stderr b/src/test/ui/async-await/async-block-control-flow-static-semantics.stderr
@@ -37,7 +37,7 @@ error[E0271]: type mismatch resolving `<impl Future<Output = u8> as Future>::Out
 LL |     let _: &dyn Future<Output = ()> = &block;
    |                                       ^^^^^^ expected `()`, found `u8`
    |
-   = note: required for the cast to the object type `dyn Future<Output = ()>`
+   = note: required for the cast from `impl Future<Output = u8>` to the object type `dyn Future<Output = ()>`
 
 error[E0308]: mismatched types
   --> $DIR/async-block-control-flow-static-semantics.rs:12:43
@@ -53,7 +53,7 @@ error[E0271]: type mismatch resolving `<impl Future<Output = u8> as Future>::Out
 LL |     let _: &dyn Future<Output = ()> = &block;
    |                                       ^^^^^^ expected `()`, found `u8`
    |
-   = note: required for the cast to the object type `dyn Future<Output = ()>`
+   = note: required for the cast from `impl Future<Output = u8>` to the object type `dyn Future<Output = ()>`
 
 error[E0308]: mismatched types
   --> $DIR/async-block-control-flow-static-semantics.rs:47:44
diff --git a/src/test/ui/async-await/issue-86507.stderr b/src/test/ui/async-await/issue-86507.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 to the object type `dyn Future<Output = ()> + Send`
+   = note: required for the cast from `impl Future<Output = ()>` to the object type `dyn Future<Output = ()> + Send`
 help: consider further restricting this bound
    |
 LL |     fn bar<'me, 'async_trait, T: Send + std::marker::Sync>(x: &'me T)
diff --git a/src/test/ui/coercion/coerce-issue-49593-box-never.nofallback.stderr b/src/test/ui/coercion/coerce-issue-49593-box-never.nofallback.stderr
@@ -4,15 +4,15 @@ 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 to the object type `dyn std::error::Error`
+   = note: required for the cast from `()` to the object type `dyn std::error::Error`
 
 error[E0277]: the trait bound `(): std::error::Error` is not satisfied
   --> $DIR/coerce-issue-49593-box-never.rs:23:49
    |
 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 to the object type `(dyn std::error::Error + 'static)`
+   = note: required for the cast from `()` to the object type `(dyn std::error::Error + 'static)`
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/const-generics/defaults/trait_objects_fail.stderr b/src/test/ui/const-generics/defaults/trait_objects_fail.stderr
@@ -7,7 +7,7 @@ LL |     foo(&10_u32);
    |     required by a bound introduced by this call
    |
    = help: the trait `Trait<2_u8>` is implemented for `u32`
-   = note: required for the cast to the object type `dyn Trait`
+   = note: required for the cast from `u32` to the object type `dyn Trait`
 
 error[E0277]: the trait bound `bool: Traitor<{_: u8}>` is not satisfied
   --> $DIR/trait_objects_fail.rs:28:9
@@ -18,7 +18,7 @@ LL |     bar(&true);
    |     required by a bound introduced by this call
    |
    = help: the trait `Traitor<2_u8, 3_u8>` is implemented for `bool`
-   = note: required for the cast to the object type `dyn Traitor<{_: u8}>`
+   = note: required for the cast from `bool` to the object type `dyn Traitor<{_: u8}>`
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/custom_test_frameworks/mismatch.stderr b/src/test/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 to the object type `dyn Testable`
+   = note: required for the cast from `TestDescAndFn` to the object type `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
diff --git a/src/test/ui/dst/dst-bad-coerce1.stderr b/src/test/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 to the object type `dyn Bar`
+   = note: required for the cast from `Foo` to the object type `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 to the object type `dyn Bar`
+   = note: required for the cast from `Foo` to the object type `dyn Bar`
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/dst/dst-object-from-unsized-type.stderr b/src/test/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 to the object type `dyn Foo`
+   = note: required for the cast from `T` to the object type `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 to the object type `dyn Foo`
+   = note: required for the cast from `T` to the object type `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 to the object type `dyn Foo`
+   = note: required for the cast from `str` to the object type `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 to the object type `dyn Foo`
+   = note: required for the cast from `[u8]` to the object type `dyn Foo`
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/generic-associated-types/issue-79422.extended.stderr b/src/test/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 to the object type `dyn MapLike<u8, u8, VRefCont = (dyn RefCont<'_, u8> + 'static)>`
+   = note: required for the cast from `BTreeMap<u8, u8>` to the object type `dyn MapLike<u8, u8, VRefCont = (dyn RefCont<'_, u8> + 'static)>`
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/issues/issue-14366.stderr b/src/test/ui/issues/issue-14366.stderr
@@ -5,7 +5,7 @@ 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 to the object type `dyn Any`
+   = note: required for the cast from `str` to the object type `dyn Any`
 help: consider borrowing the value, since `&str` can be coerced into `dyn Any`
    |
 LL |     let _x = &"test" as &dyn (::std::any::Any);
diff --git a/src/test/ui/issues/issue-22034.stderr b/src/test/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 to the object type `dyn Fn()`
+   = note: required for the cast from `()` to the object type `dyn Fn()`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issues/issue-22872.stderr b/src/test/ui/issues/issue-22872.stderr
@@ -10,7 +10,7 @@ note: required because of the requirements on the impl of `for<'b> Wrap<'b>` for
    |
 LL | impl<'b, P> Wrap<'b> for Wrapper<P>
    |             ^^^^^^^^     ^^^^^^^^^^
-   = note: required for the cast to the object type `dyn for<'b> Wrap<'b>`
+   = note: required for the cast from `Wrapper<P>` to the object type `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 {
diff --git a/src/test/ui/issues/issue-7013.stderr b/src/test/ui/issues/issue-7013.stderr
@@ -11,7 +11,7 @@ note: required because it appears within the type `B`
    |
 LL | struct B {
    |        ^
-   = note: required for the cast to the object type `dyn Foo + Send`
+   = note: required for the cast from `B` to the object type `dyn Foo + Send`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/kindck/kindck-impl-type-params.stderr b/src/test/ui/kindck/kindck-impl-type-params.stderr
@@ -9,7 +9,7 @@ note: required because of the requirements on the impl of `Gettable<T>` for `S<T
    |
 LL | impl<T: Send + Copy + 'static> Gettable<T> for S<T> {}
    |                                ^^^^^^^^^^^     ^^^^
-   = note: required for the cast to the object type `dyn Gettable<T>`
+   = note: required for the cast from `S<T>` to the object type `dyn Gettable<T>`
 help: consider restricting type parameter `T`
    |
 LL | fn f<T: std::marker::Send>(val: T) {
@@ -26,7 +26,7 @@ note: required because of the requirements on the impl of `Gettable<T>` for `S<T
    |
 LL | impl<T: Send + Copy + 'static> Gettable<T> for S<T> {}
    |                                ^^^^^^^^^^^     ^^^^
-   = note: required for the cast to the object type `dyn Gettable<T>`
+   = note: required for the cast from `S<T>` to the object type `dyn Gettable<T>`
 help: consider restricting type parameter `T`
    |
 LL | fn f<T: std::marker::Copy>(val: T) {
@@ -43,7 +43,7 @@ note: required because of the requirements on the impl of `Gettable<T>` for `S<T
    |
 LL | impl<T: Send + Copy + 'static> Gettable<T> for S<T> {}
    |                                ^^^^^^^^^^^     ^^^^
-   = note: required for the cast to the object type `dyn Gettable<T>`
+   = note: required for the cast from `S<T>` to the object type `dyn Gettable<T>`
 help: consider restricting type parameter `T`
    |
 LL | fn g<T: std::marker::Send>(val: T) {
@@ -60,7 +60,7 @@ note: required because of the requirements on the impl of `Gettable<T>` for `S<T
    |
 LL | impl<T: Send + Copy + 'static> Gettable<T> for S<T> {}
    |                                ^^^^^^^^^^^     ^^^^
-   = note: required for the cast to the object type `dyn Gettable<T>`
+   = note: required for the cast from `S<T>` to the object type `dyn Gettable<T>`
 help: consider restricting type parameter `T`
    |
 LL | fn g<T: std::marker::Copy>(val: T) {
@@ -78,7 +78,7 @@ note: required because of the requirements on the impl of `Gettable<String>` for
    |
 LL | impl<T: Send + Copy + 'static> Gettable<T> for S<T> {}
    |                                ^^^^^^^^^^^     ^^^^
-   = note: required for the cast to the object type `dyn Gettable<String>`
+   = note: required for the cast from `S<String>` to the object type `dyn Gettable<String>`
 
 error[E0277]: the trait bound `Foo: Copy` is not satisfied
   --> $DIR/kindck-impl-type-params.rs:43:37
@@ -92,7 +92,7 @@ note: required because of the requirements on the impl of `Gettable<Foo>` for `S
    |
 LL | impl<T: Send + Copy + 'static> Gettable<T> for S<T> {}
    |                                ^^^^^^^^^^^     ^^^^
-   = note: required for the cast to the object type `dyn Gettable<Foo>`
+   = note: required for the cast from `S<Foo>` to the object type `dyn Gettable<Foo>`
 help: consider annotating `Foo` with `#[derive(Copy)]`
    |
 LL |     #[derive(Copy)]
diff --git a/src/test/ui/mismatched_types/cast-rfc0401.stderr b/src/test/ui/mismatched_types/cast-rfc0401.stderr
@@ -220,7 +220,7 @@ LL |     let _ = fat_v as *const dyn Foo;
    |             ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[u8]`
-   = note: required for the cast to the object type `dyn Foo`
+   = note: required for the cast from `[u8]` to the object type `dyn Foo`
 help: consider borrowing the value, since `&[u8]` can be coerced into `dyn Foo`
    |
 LL |     let _ = &fat_v as *const dyn Foo;
@@ -233,7 +233,7 @@ LL |     let _ = a as *const dyn Foo;
    |             ^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
-   = note: required for the cast to the object type `dyn Foo`
+   = note: required for the cast from `str` to the object type `dyn Foo`
 help: consider borrowing the value, since `&str` can be coerced into `dyn Foo`
    |
 LL |     let _ = &a as *const dyn Foo;
diff --git a/src/test/ui/never_type/fallback-closure-wrap.fallback.stderr b/src/test/ui/never_type/fallback-closure-wrap.fallback.stderr
@@ -10,7 +10,7 @@ LL | |     }) as Box<dyn FnMut()>);
    |
    = note: expected unit type `()`
                    found type `!`
-   = note: required for the cast to the object type `dyn FnMut()`
+   = note: required for the cast from `[closure@$DIR/fallback-closure-wrap.rs:18:40: 21:6]` to the object type `dyn FnMut()`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/suggestions/derive-macro-missing-bounds.stderr b/src/test/ui/suggestions/derive-macro-missing-bounds.stderr
@@ -33,7 +33,7 @@ LL |     impl<T: Debug + Trait> Debug for Inner<T> {
    |                            ^^^^^     ^^^^^^^^
    = note: 1 redundant requirement hidden
    = note: required because of the requirements on the impl of `Debug` for `&c::Inner<T>`
-   = note: required for the cast to the object type `dyn Debug`
+   = note: required for the cast from `&c::Inner<T>` to the object type `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`
    |
@@ -55,7 +55,7 @@ LL |     impl<T> Debug for Inner<T> where T: Debug, T: Trait {
    |             ^^^^^     ^^^^^^^^
    = note: 1 redundant requirement hidden
    = note: required because of the requirements on the impl of `Debug` for `&d::Inner<T>`
-   = note: required for the cast to the object type `dyn Debug`
+   = note: required for the cast from `&d::Inner<T>` to the object type `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`
    |
@@ -77,7 +77,7 @@ LL |     impl<T> Debug for Inner<T> where T: Debug + Trait {
    |             ^^^^^     ^^^^^^^^
    = note: 1 redundant requirement hidden
    = note: required because of the requirements on the impl of `Debug` for `&e::Inner<T>`
-   = note: required for the cast to the object type `dyn Debug`
+   = note: required for the cast from `&e::Inner<T>` to the object type `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`
    |
@@ -99,7 +99,7 @@ LL |     impl<T: Debug> Debug for Inner<T> where T: Trait {
    |                    ^^^^^     ^^^^^^^^
    = note: 1 redundant requirement hidden
    = note: required because of the requirements on the impl of `Debug` for `&f::Inner<T>`
-   = note: required for the cast to the object type `dyn Debug`
+   = note: required for the cast from `&f::Inner<T>` to the object type `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`
    |
diff --git a/src/test/ui/suggestions/suggest-borrow-to-dyn-object.stderr b/src/test/ui/suggestions/suggest-borrow-to-dyn-object.stderr
@@ -8,7 +8,7 @@ LL |     check(s);
    |
    = help: within `OsStr`, the trait `Sized` is not implemented for `[u8]`
    = note: required because it appears within the type `OsStr`
-   = note: required for the cast to the object type `dyn AsRef<Path>`
+   = 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);
diff --git a/src/test/ui/traits/coercion-generic-bad.stderr b/src/test/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 to the object type `dyn Trait<isize>`
+   = note: required for the cast from `Struct` to the object type `dyn Trait<isize>`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/traits/map-types.stderr b/src/test/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 to the object type `dyn Map<usize, isize>`
+   = note: required for the cast from `Box<dyn Map<isize, isize>>` to the object type `dyn Map<usize, isize>`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/traits/trait-upcasting/type-checking-test-1.stderr b/src/test/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 to the object type `dyn Bar<_>`
+   = note: required for the cast from `&dyn Foo` to the object type `dyn Bar<_>`
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/traits/trait-upcasting/type-checking-test-2.stderr b/src/test/ui/traits/trait-upcasting/type-checking-test-2.stderr
diff --git a/src/test/ui/unsized/unsized-fn-param.stderr b/src/test/ui/unsized/unsized-fn-param.stderr

Original file line number	Diff line number	Diff line change
`@@ -2217,9 +2217,10 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {`
`2217`	`2217`	`err.span_note(tcx.def_span(item_def_id), &descr);`
`2218`	`2218`	`}`
`2219`	`2219`	`}`
`2220`		`- ObligationCauseCode::ObjectCastObligation(_, object_ty) => {`
	`2220`	`+ ObligationCauseCode::ObjectCastObligation(concrete_ty, object_ty) => {`
`2221`	`2221`	`err.note(&format!(`
`2222`		- "required for the cast to the object type `{}`",
	`2222`	+ "required for the cast from `{}` to the object type `{}`",
	`2223`	`+ self.ty_to_string(concrete_ty),`
`2223`	`2224`	`self.ty_to_string(object_ty)`
`2224`	`2225`	`));`
`2225`	`2226`	`}`
Original file line number	Diff line number	Diff line change
@@ -4,7 +4,7 @@ error[E0277]: the trait bound `String: Copy` is not satisfied
`4`	`4`	`LL \| Box::new(AssocNoCopy)`
`5`	`5`	\| ^^^^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `String`
`6`	`6`	`\|`
`7`		- = note: required for the cast to the object type `dyn Bar<Assoc = <AssocNoCopy as Thing>::Out::{opaque#0}>`
	`7`	+ = note: required for the cast from `AssocNoCopy` to the object type `dyn Bar<Assoc = <AssocNoCopy as Thing>::Out::{opaque#0}>`
`8`	`8`
`9`	`9`	`error: aborting due to previous error`
`10`	`10`
Original file line number	Diff line number	Diff line change
@@ -41,7 +41,7 @@ note: expected this to be `Bar`
`41`	`41`	`\|`
`42`	`42`	`LL \| type A = usize;`
`43`	`43`	`\| ^^^^^`
`44`		- = note: required for the cast to the object type `dyn Foo<A = Bar>`
	`44`	+ = note: required for the cast from `isize` to the object type `dyn Foo<A = Bar>`
`45`	`45`
`46`	`46`	`error: aborting due to 3 previous errors`
`47`	`47`
Original file line number	Diff line number	Diff line change
@@ -4,7 +4,7 @@ error[E0271]: type mismatch resolving `<std::vec::IntoIter<u32> as Iterator>::It
`4`	`4`	`LL \| let _: &dyn I32Iterator<Item = u32> = &vec![42].into_iter();`
`5`	`5`	\| ^^^^^^^^^^^^^^^^^^^^^ expected `i32`, found `u32`
`6`	`6`	`\|`
`7`		- = note: required for the cast to the object type `dyn Iterator<Item = u32, Item = i32>`
	`7`	+ = note: required for the cast from `std::vec::IntoIter<u32>` to the object type `dyn Iterator<Item = u32, Item = i32>`
`8`	`8`
`9`	`9`	`error: aborting due to previous error`
`10`	`10`
Original file line number	Diff line number	Diff line change
@@ -23,7 +23,7 @@ note: required because of the requirements on the impl of `MyDisplay` for `&mut
`23`	`23`	`\|`
`24`	`24`	`LL \| impl<'a, T: MyDisplay> MyDisplay for &'a mut T { }`
`25`	`25`	`\| ^^^^^^^^^ ^^^^^^^^^`
`26`		- = note: required for the cast to the object type `dyn MyDisplay`
	`26`	+ = note: required for the cast from `&mut T` to the object type `dyn MyDisplay`
`27`	`27`
`28`	`28`	`error: aborting due to 2 previous errors`
`29`	`29`
Original file line number	Diff line number	Diff line change
`@@ -18,7 +18,7 @@ LL \| writer.my_write(valref)`
`18`	`18`	\| ^^^^^^ the trait `MyDisplay` is not implemented for `T`
`19`	`19`	`\|`
`20`	`20`	= help: the trait `MyDisplay` is implemented for `&'a mut T`
`21`		- = note: required for the cast to the object type `dyn MyDisplay`
	`21`	+ = note: required for the cast from `T` to the object type `dyn MyDisplay`
`22`	`22`
`23`	`23`	`error: aborting due to 2 previous errors`
`24`	`24`
Original file line number	Diff line number	Diff line change
@@ -13,7 +13,7 @@ note: captured value is not `Send` because `&` references cannot be sent unless
`13`	`13`	`\|`
`14`	`14`	`LL \| let x = x;`
`15`	`15`	\| ^ has type `&T` which is not `Send`, because `T` is not `Sync`
`16`		- = note: required for the cast to the object type `dyn Future<Output = ()> + Send`
	`16`	+ = note: required for the cast from `impl Future<Output = ()>` to the object type `dyn Future<Output = ()> + Send`
`17`	`17`	`help: consider further restricting this bound`
`18`	`18`	`\|`
`19`	`19`	`LL \| fn bar<'me, 'async_trait, T: Send + std::marker::Sync>(x: &'me T)`
Original file line number	Diff line number	Diff line change
@@ -4,15 +4,15 @@ error[E0277]: the trait bound `(): std::error::Error` is not satisfied
`4`	`4`	`LL \| /* mut $0 is coerced to Box<dyn Error> here / Box::<_ /* ! */>::new(x)`
`5`	`5`	\| ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::error::Error` is not implemented for `()`
`6`	`6`	`\|`
`7`		- = note: required for the cast to the object type `dyn std::error::Error`
	`7`	+ = note: required for the cast from `()` to the object type `dyn std::error::Error`
`8`	`8`
`9`	`9`	error[E0277]: the trait bound `(): std::error::Error` is not satisfied
`10`	`10`	`--> $DIR/coerce-issue-49593-box-never.rs:23:49`
`11`	`11`	`\|`
`12`	`12`	`LL \| /* mut $0 is coerced to mut Error here / raw_ptr_box::<_ / ! */>(x)`
`13`	`13`	\| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::error::Error` is not implemented for `()`
`14`	`14`	`\|`
`15`		- = note: required for the cast to the object type `(dyn std::error::Error + 'static)`
	`15`	+ = note: required for the cast from `()` to the object type `(dyn std::error::Error + 'static)`
`16`	`16`
`17`	`17`	`error: aborting due to 2 previous errors`
`18`	`18`
Original file line number	Diff line number	Diff line change
`@@ -7,7 +7,7 @@ LL \| foo(&10_u32);`
`7`	`7`	`\| required by a bound introduced by this call`
`8`	`8`	`\|`
`9`	`9`	= help: the trait `Trait<2_u8>` is implemented for `u32`
`10`		- = note: required for the cast to the object type `dyn Trait`
	`10`	+ = note: required for the cast from `u32` to the object type `dyn Trait`
`11`	`11`
`12`	`12`	error[E0277]: the trait bound `bool: Traitor<{_: u8}>` is not satisfied
`13`	`13`	`--> $DIR/trait_objects_fail.rs:28:9`
`@@ -18,7 +18,7 @@ LL \| bar(&true);`
`18`	`18`	`\| required by a bound introduced by this call`
`19`	`19`	`\|`
`20`	`20`	= help: the trait `Traitor<2_u8, 3_u8>` is implemented for `bool`
`21`		- = note: required for the cast to the object type `dyn Traitor<{_: u8}>`
	`21`	+ = note: required for the cast from `bool` to the object type `dyn Traitor<{_: u8}>`
`22`	`22`
`23`	`23`	`error: aborting due to 2 previous errors`
`24`	`24`