More tests

tests/ui/impl-trait/unsized_coercion3.next.stderr

@@ -0,0 +1,9 @@
+error[E0271]: type mismatch resolving `impl Trait + ?Sized <: dyn Send`
+  --> $DIR/unsized_coercion3.rs:13:17
+   |
+LL |         let x = hello();
+   |                 ^^^^^^^ types differ
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0271`.

tests/ui/impl-trait/unsized_coercion3.old.stderr

@@ -0,0 +1,26 @@
+error: cannot check whether the hidden type of opaque type satisfies auto traits
+  --> $DIR/unsized_coercion3.rs:15:32
+   |
+LL |         let y: Box<dyn Send> = x;
+   |                                ^
+   |
+   = note: fetching the hidden types of an opaque inside of the defining scope is not supported. You can try moving the opaque type and the item that actually registers a hidden type into a new submodule
+note: opaque type is declared here
+  --> $DIR/unsized_coercion3.rs:11:19
+   |
+LL | fn hello() -> Box<impl Trait + ?Sized> {
+   |                   ^^^^^^^^^^^^^^^^^^^
+   = note: required for the cast from `Box<impl Trait + ?Sized>` to `Box<dyn Send>`
+
+error[E0277]: the size for values of type `impl Trait + ?Sized` cannot be known at compilation time
+  --> $DIR/unsized_coercion3.rs:15:32
+   |
+LL |         let y: Box<dyn Send> = x;
+   |                                ^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `impl Trait + ?Sized`
+   = note: required for the cast from `Box<impl Trait + ?Sized>` to `Box<dyn Send>`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/impl-trait/unsized_coercion3.rs

@@ -0,0 +1,22 @@
+//! This test checks that opaque types get unsized instead of
+//! constraining their hidden type to a trait object.
+
+//@ revisions: next old
+//@[next] compile-flags: -Znext-solver
+
+trait Trait {}
+
+impl Trait for u32 {}
+
+fn hello() -> Box<impl Trait + ?Sized> {
+    if true {
+        let x = hello();
+        //[next]~^ ERROR: type mismatch resolving `impl Trait + ?Sized <: dyn Send`
+        let y: Box<dyn Send> = x;
+        //[old]~^ ERROR: the size for values of type `impl Trait + ?Sized` cannot be know
+        //[old]~| ERROR: cannot check whether the hidden type of opaque type satisfies auto traits
+    }
+    Box::new(1u32)
+}
+
+fn main() {}

tests/ui/impl-trait/unsized_coercion4.rs

@@ -0,0 +1,20 @@
+//! This test checks that opaque types get unsized instead of
+//! constraining their hidden type to a trait object.
+
+//@ revisions: next old
+//@[next] compile-flags: -Znext-solver
+//@check-pass
+
+trait Trait {}
+
+impl Trait for u32 {}
+
+fn hello() -> Box<impl Trait + ?Sized> {
+    if true {
+        let x = hello() as Box<u32>;
+        let y: Box<dyn Send> = x;
+    }
+    Box::new(1u32)
+}
+
+fn main() {}

tests/ui/impl-trait/unsized_coercion5.old.stderr

@@ -0,0 +1,38 @@
+error[E0308]: mismatched types
+  --> $DIR/unsized_coercion5.rs:17:32
+   |
+LL |         let y: Box<dyn Send> = x as Box<dyn Trait + Send>;
+   |                -------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait `Send`, found trait `Trait + Send`
+   |                |
+   |                expected due to this
+   |
+   = note: expected struct `Box<dyn Send>`
+              found struct `Box<dyn Trait + Send>`
+
+error: cannot check whether the hidden type of opaque type satisfies auto traits
+  --> $DIR/unsized_coercion5.rs:17:32
+   |
+LL |         let y: Box<dyn Send> = x as Box<dyn Trait + Send>;
+   |                                ^
+   |
+   = note: fetching the hidden types of an opaque inside of the defining scope is not supported. You can try moving the opaque type and the item that actually registers a hidden type into a new submodule
+note: opaque type is declared here
+  --> $DIR/unsized_coercion5.rs:14:19
+   |
+LL | fn hello() -> Box<impl Trait + ?Sized> {
+   |                   ^^^^^^^^^^^^^^^^^^^
+   = note: required for the cast from `Box<impl Trait + ?Sized>` to `Box<dyn Trait + Send>`
+
+error[E0277]: the size for values of type `impl Trait + ?Sized` cannot be known at compilation time
+  --> $DIR/unsized_coercion5.rs:17:32
+   |
+LL |         let y: Box<dyn Send> = x as Box<dyn Trait + Send>;
+   |                                ^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `impl Trait + ?Sized`
+   = note: required for the cast from `Box<impl Trait + ?Sized>` to `Box<dyn Trait + Send>`
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0277, E0308.
+For more information about an error, try `rustc --explain E0277`.

tests/ui/impl-trait/unsized_coercion5.rs

@@ -0,0 +1,25 @@
+//! This test checks that opaque types get unsized instead of
+//! constraining their hidden type to a trait object.
+
+//@ revisions: next old
+//@[next] compile-flags: -Znext-solver
+//@[next] check-pass
+
+#![feature(trait_upcasting)]
+
+trait Trait {}
+
+impl Trait for u32 {}
+
+fn hello() -> Box<impl Trait + ?Sized> {
+    if true {
+        let x = hello();
+        let y: Box<dyn Send> = x as Box<dyn Trait + Send>;
+        //[old]~^ ERROR: the size for values of type `impl Trait + ?Sized` cannot be know
+        //[old]~| ERROR: mismatched types
+        //[old]~| ERROR: cannot check whether the hidden type of opaque type satisfies auto traits
+    }
+    Box::new(1u32)
+}
+
+fn main() {}