Consolidate and rework CoercePointee and DispatchFromDyn errors

12 files changed, 69 insertions, 54 deletions

diff --git a/tests/ui/coercion/issue-26905.stderr b/tests/ui/coercion/issue-26905.stderr
index 86f6a14cd10..17387ae992b 100644
--- a/tests/ui/coercion/issue-26905.stderr
+++ b/tests/ui/coercion/issue-26905.stderr
@@ -1,11 +1,16 @@
-error[E0375]: implementing the trait `CoerceUnsized` requires multiple coercions
+error[E0375]: implementing `CoerceUnsized` does not allow multiple fields to be coerced
   --> $DIR/issue-26905.rs:16:40
    |
 LL | impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<MyRc<U>> for MyRc<T>{ }
-   |                                        ^^^^^^^^^^^^^^^^^^^^^^ requires multiple coercions
+   |                                        ^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: `CoerceUnsized` may only be implemented for a coercion between structures with one field being coerced
-   = note: currently, 2 fields need coercions: `_ptr` (`*const T` to `*const U`), `_boo` (`NotPhantomData<T>` to `NotPhantomData<U>`)
+note: the trait `CoerceUnsized` may only be implemented when a single field is being coerced
+  --> $DIR/issue-26905.rs:12:5
+   |
+LL |     _ptr: *const T,
+   |     ^^^^^^^^^^^^^^
+LL |     _boo: NotPhantomData<T>,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/error-codes/E0374.stderr b/tests/ui/error-codes/E0374.stderr
index 71eec4c16fd..95e6b95e0d5 100644
--- a/tests/ui/error-codes/E0374.stderr
+++ b/tests/ui/error-codes/E0374.stderr
@@ -6,7 +6,7 @@ LL | struct Foo<T: ?Sized> {
    |
    = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
 
-error[E0374]: the trait `CoerceUnsized` may only be implemented for a coercion between structures
+error[E0374]: implementing `CoerceUnsized` requires a field to be coerced
   --> $DIR/E0374.rs:8:1
    |
 LL | / impl<T, U> CoerceUnsized<Foo<U>> for Foo<T>
diff --git a/tests/ui/error-codes/E0375.stderr b/tests/ui/error-codes/E0375.stderr
index af720bd40e7..a797ba9d461 100644
--- a/tests/ui/error-codes/E0375.stderr
+++ b/tests/ui/error-codes/E0375.stderr
@@ -23,14 +23,19 @@ help: the `Box` type always has a statically known size and allocates its conten
 LL |     b: Box<T>,
    |        ++++ +
 
-error[E0375]: implementing the trait `CoerceUnsized` requires multiple coercions
+error[E0375]: implementing `CoerceUnsized` does not allow multiple fields to be coerced
   --> $DIR/E0375.rs:10:12
    |
 LL | impl<T, U> CoerceUnsized<Foo<U, T>> for Foo<T, U> {}
-   |            ^^^^^^^^^^^^^^^^^^^^^^^^ requires multiple coercions
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: `CoerceUnsized` may only be implemented for a coercion between structures with one field being coerced
-   = note: currently, 2 fields need coercions: `b` (`T` to `U`), `c` (`U` to `T`)
+note: the trait `CoerceUnsized` may only be implemented when a single field is being coerced
+  --> $DIR/E0375.rs:6:5
+   |
+LL |     b: T,
+   |     ^^^^
+LL |     c: U,
+   |     ^^^^
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/error-codes/E0376.rs b/tests/ui/error-codes/E0376.rs
deleted file mode 100644
index f092eb02c2b..00000000000
--- a/tests/ui/error-codes/E0376.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-#![feature(coerce_unsized)]
-use std::ops::CoerceUnsized;
-
-struct Foo<T: ?Sized> {
-    a: T,
-}
-
-impl<T, U> CoerceUnsized<U> for Foo<T> {} //~ ERROR E0376
-
-fn main() {}
diff --git a/tests/ui/error-codes/E0376.stderr b/tests/ui/error-codes/E0376.stderr
deleted file mode 100644
index 46668e05a42..00000000000
--- a/tests/ui/error-codes/E0376.stderr
+++ /dev/null
@@ -1,9 +0,0 @@
-error[E0376]: the trait `CoerceUnsized` may only be implemented for a coercion between structures
-  --> $DIR/E0376.rs:8:1
-   |
-LL | impl<T, U> CoerceUnsized<U> for Foo<T> {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0376`.
diff --git a/tests/ui/invalid_dispatch_from_dyn_impls.rs b/tests/ui/invalid_dispatch_from_dyn_impls.rs
index b7bc766fbe0..972465d7197 100644
--- a/tests/ui/invalid_dispatch_from_dyn_impls.rs
+++ b/tests/ui/invalid_dispatch_from_dyn_impls.rs
@@ -8,9 +8,10 @@ use std::{
 struct WrapperWithExtraField<T>(T, i32);
 
 impl<T, U> DispatchFromDyn<WrapperWithExtraField<U>> for WrapperWithExtraField<T>
+//~^ ERROR [E0378]
 where
     T: DispatchFromDyn<U>,
-{} //~^^^ ERROR [E0378]
+{}
 
 
 struct MultiplePointers<T: ?Sized>{
@@ -19,9 +20,10 @@ struct MultiplePointers<T: ?Sized>{
 }
 
 impl<T: ?Sized, U: ?Sized> DispatchFromDyn<MultiplePointers<U>> for MultiplePointers<T>
+//~^ implementing `DispatchFromDyn` does not allow multiple fields to be coerced
 where
     T: Unsize<U>,
-{} //~^^^ ERROR [E0378]
+{}
 
 
 struct NothingToCoerce<T: ?Sized> {
@@ -29,23 +31,25 @@ struct NothingToCoerce<T: ?Sized> {
 }
 
 impl<T: ?Sized, U: ?Sized> DispatchFromDyn<NothingToCoerce<T>> for NothingToCoerce<U> {}
-//~^ ERROR [E0378]
+//~^ ERROR implementing `DispatchFromDyn` requires a field to be coerced
 
 #[repr(C)]
 struct HasReprC<T: ?Sized>(Box<T>);
 
 impl<T: ?Sized, U: ?Sized> DispatchFromDyn<HasReprC<U>> for HasReprC<T>
+//~^ ERROR [E0378]
 where
     T: Unsize<U>,
-{} //~^^^ ERROR [E0378]
+{}
 
 #[repr(align(64))]
 struct OverAlignedZst;
 struct OverAligned<T: ?Sized>(Box<T>, OverAlignedZst);
 
 impl<T: ?Sized, U: ?Sized> DispatchFromDyn<OverAligned<U>> for OverAligned<T>
+//~^ ERROR [E0378]
     where
         T: Unsize<U>,
-{} //~^^^ ERROR [E0378]
+{}
 
 fn main() {}
diff --git a/tests/ui/invalid_dispatch_from_dyn_impls.stderr b/tests/ui/invalid_dispatch_from_dyn_impls.stderr
index 02718334c73..93ec6bbe089 100644
--- a/tests/ui/invalid_dispatch_from_dyn_impls.stderr
+++ b/tests/ui/invalid_dispatch_from_dyn_impls.stderr
@@ -2,25 +2,32 @@ error[E0378]: the trait `DispatchFromDyn` may only be implemented for structs co
   --> $DIR/invalid_dispatch_from_dyn_impls.rs:10:1
    |
 LL | / impl<T, U> DispatchFromDyn<WrapperWithExtraField<U>> for WrapperWithExtraField<T>
+LL | |
 LL | | where
 LL | |     T: DispatchFromDyn<U>,
    | |__________________________^
    |
    = note: extra field `1` of type `i32` is not allowed
 
-error[E0378]: implementing the `DispatchFromDyn` trait requires multiple coercions
-  --> $DIR/invalid_dispatch_from_dyn_impls.rs:21:1
+error[E0375]: implementing `DispatchFromDyn` does not allow multiple fields to be coerced
+  --> $DIR/invalid_dispatch_from_dyn_impls.rs:22:1
    |
 LL | / impl<T: ?Sized, U: ?Sized> DispatchFromDyn<MultiplePointers<U>> for MultiplePointers<T>
+LL | |
 LL | | where
 LL | |     T: Unsize<U>,
    | |_________________^
    |
-   = note: the trait `DispatchFromDyn` may only be implemented for a coercion between structures with a single field being coerced
-   = note: currently, 2 fields need coercions: `ptr1` (`*const T` to `*const U`), `ptr2` (`*const T` to `*const U`)
+note: the trait `DispatchFromDyn` may only be implemented when a single field is being coerced
+  --> $DIR/invalid_dispatch_from_dyn_impls.rs:18:5
+   |
+LL |     ptr1: *const T,
+   |     ^^^^^^^^^^^^^^
+LL |     ptr2: *const T,
+   |     ^^^^^^^^^^^^^^
 
-error[E0378]: the trait `DispatchFromDyn` may only be implemented for a coercion between structures
-  --> $DIR/invalid_dispatch_from_dyn_impls.rs:31:1
+error[E0374]: implementing `DispatchFromDyn` requires a field to be coerced
+  --> $DIR/invalid_dispatch_from_dyn_impls.rs:33:1
    |
 LL | impl<T: ?Sized, U: ?Sized> DispatchFromDyn<NothingToCoerce<T>> for NothingToCoerce<U> {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -28,17 +35,19 @@ LL | impl<T: ?Sized, U: ?Sized> DispatchFromDyn<NothingToCoerce<T>> for NothingT
    = note: expected a single field to be coerced, none found
 
 error[E0378]: structs implementing `DispatchFromDyn` may not have `#[repr(packed)]` or `#[repr(C)]`
-  --> $DIR/invalid_dispatch_from_dyn_impls.rs:37:1
+  --> $DIR/invalid_dispatch_from_dyn_impls.rs:39:1
    |
 LL | / impl<T: ?Sized, U: ?Sized> DispatchFromDyn<HasReprC<U>> for HasReprC<T>
+LL | |
 LL | | where
 LL | |     T: Unsize<U>,
    | |_________________^
 
 error[E0378]: the trait `DispatchFromDyn` may only be implemented for structs containing the field being coerced, ZST fields with 1 byte alignment that don't mention type/const generics, and nothing else
-  --> $DIR/invalid_dispatch_from_dyn_impls.rs:46:1
+  --> $DIR/invalid_dispatch_from_dyn_impls.rs:49:1
    |
 LL | / impl<T: ?Sized, U: ?Sized> DispatchFromDyn<OverAligned<U>> for OverAligned<T>
+LL | |
 LL | |     where
 LL | |         T: Unsize<U>,
    | |_____________________^
@@ -47,4 +56,5 @@ LL | |         T: Unsize<U>,
 
 error: aborting due to 5 previous errors
 
-For more information about this error, try `rustc --explain E0378`.
+Some errors have detailed explanations: E0374, E0375, E0378.
+For more information about an error, try `rustc --explain E0374`.
diff --git a/tests/ui/self/dispatch-from-dyn-zst-transmute-zst-nonzst.rs b/tests/ui/self/dispatch-from-dyn-zst-transmute-zst-nonzst.rs
index 71f198f7dc7..94b76fe9685 100644
--- a/tests/ui/self/dispatch-from-dyn-zst-transmute-zst-nonzst.rs
+++ b/tests/ui/self/dispatch-from-dyn-zst-transmute-zst-nonzst.rs
@@ -15,7 +15,7 @@ struct Dispatchable<T: ?Sized, Z> {
 }
 
 impl<T, U> DispatchFromDyn<Dispatchable<U, i32>> for Dispatchable<T, ()>
-//~^ ERROR implementing the `DispatchFromDyn` trait requires multiple coercions
+//~^ ERROR implementing `DispatchFromDyn` does not allow multiple fields to be coerced
 where
     T: Unsize<U> + ?Sized,
     U: ?Sized,
diff --git a/tests/ui/self/dispatch-from-dyn-zst-transmute-zst-nonzst.stderr b/tests/ui/self/dispatch-from-dyn-zst-transmute-zst-nonzst.stderr
index 1f13c51f679..91760b9e2ea 100644
--- a/tests/ui/self/dispatch-from-dyn-zst-transmute-zst-nonzst.stderr
+++ b/tests/ui/self/dispatch-from-dyn-zst-transmute-zst-nonzst.stderr
@@ -1,4 +1,4 @@
-error[E0378]: implementing the `DispatchFromDyn` trait requires multiple coercions
+error[E0375]: implementing `DispatchFromDyn` does not allow multiple fields to be coerced
   --> $DIR/dispatch-from-dyn-zst-transmute-zst-nonzst.rs:17:1
    |
 LL | / impl<T, U> DispatchFromDyn<Dispatchable<U, i32>> for Dispatchable<T, ()>
@@ -8,9 +8,14 @@ LL | |     T: Unsize<U> + ?Sized,
 LL | |     U: ?Sized,
    | |______________^
    |
-   = note: the trait `DispatchFromDyn` may only be implemented for a coercion between structures with a single field being coerced
-   = note: currently, 2 fields need coercions: `_ptr` (`Box<T>` to `Box<U>`), `z` (`()` to `i32`)
+note: the trait `DispatchFromDyn` may only be implemented when a single field is being coerced
+  --> $DIR/dispatch-from-dyn-zst-transmute-zst-nonzst.rs:13:5
+   |
+LL |     _ptr: Box<T>,
+   |     ^^^^^^^^^^^^
+LL |     z: Z,
+   |     ^^^^
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0378`.
+For more information about this error, try `rustc --explain E0375`.
diff --git a/tests/ui/self/dispatch-from-dyn-zst-transmute.rs b/tests/ui/self/dispatch-from-dyn-zst-transmute.rs
index 57c255b4d7b..967958ab486 100644
--- a/tests/ui/self/dispatch-from-dyn-zst-transmute.rs
+++ b/tests/ui/self/dispatch-from-dyn-zst-transmute.rs
@@ -15,7 +15,7 @@ struct Foo<'a, U: ?Sized> {
 }
 
 impl<'a, T, U> DispatchFromDyn<Foo<'a, U>> for Foo<'a, T>
-//~^ ERROR implementing the `DispatchFromDyn` trait requires multiple coercions
+//~^ ERROR implementing `DispatchFromDyn` does not allow multiple fields to be coerced
 where
     T: Unsize<U> + ?Sized,
     U: ?Sized {}
diff --git a/tests/ui/self/dispatch-from-dyn-zst-transmute.stderr b/tests/ui/self/dispatch-from-dyn-zst-transmute.stderr
index 5a8ae88b5f1..cc8be45e99d 100644
--- a/tests/ui/self/dispatch-from-dyn-zst-transmute.stderr
+++ b/tests/ui/self/dispatch-from-dyn-zst-transmute.stderr
@@ -1,4 +1,4 @@
-error[E0378]: implementing the `DispatchFromDyn` trait requires multiple coercions
+error[E0375]: implementing `DispatchFromDyn` does not allow multiple fields to be coerced
   --> $DIR/dispatch-from-dyn-zst-transmute.rs:17:1
    |
 LL | / impl<'a, T, U> DispatchFromDyn<Foo<'a, U>> for Foo<'a, T>
@@ -8,9 +8,14 @@ LL | |     T: Unsize<U> + ?Sized,
 LL | |     U: ?Sized {}
    | |_____________^
    |
-   = note: the trait `DispatchFromDyn` may only be implemented for a coercion between structures with a single field being coerced
-   = note: currently, 2 fields need coercions: `token` (`IsSendToken<T>` to `IsSendToken<U>`), `ptr` (`&'a T` to `&'a U`)
+note: the trait `DispatchFromDyn` may only be implemented when a single field is being coerced
+  --> $DIR/dispatch-from-dyn-zst-transmute.rs:13:5
+   |
+LL |     token: IsSendToken<U>,
+   |     ^^^^^^^^^^^^^^^^^^^^^
+LL |     ptr: &'a U,
+   |     ^^^^^^^^^^
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0378`.
+For more information about this error, try `rustc --explain E0375`.
diff --git a/tests/ui/traits/issue-78372.stderr b/tests/ui/traits/issue-78372.stderr
index d4dfba4f039..fbc60ce5d83 100644
--- a/tests/ui/traits/issue-78372.stderr
+++ b/tests/ui/traits/issue-78372.stderr
@@ -65,7 +65,7 @@ LL |     fn foo(self: Smaht<Self, T>);
    = note: type of `self` must be `Self` or a type that dereferences to it
    = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
-error[E0378]: the trait `DispatchFromDyn` may only be implemented for a coercion between structures
+error[E0377]: the trait `DispatchFromDyn` may only be implemented for a coercion between structures
   --> $DIR/issue-78372.rs:3:1
    |
 LL | impl<T> DispatchFromDyn<Smaht<U, MISC>> for T {}
@@ -73,5 +73,5 @@ LL | impl<T> DispatchFromDyn<Smaht<U, MISC>> for T {}
 
 error: aborting due to 7 previous errors
 
-Some errors have detailed explanations: E0307, E0378, E0412, E0658.
+Some errors have detailed explanations: E0307, E0377, E0412, E0658.
 For more information about an error, try `rustc --explain E0307`.