error[E0277]: the size for values of type `dyn Trait` cannot be known at compilation time
  --> $DIR/unsized_coercion.rs:15:17
   |
LL |         let x = hello();
   |                 ^^^^^^^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `dyn Trait`

error[E0308]: mismatched types
  --> $DIR/unsized_coercion.rs:19:5
   |
LL | fn hello() -> Box<impl Trait> {
   |               ---------------
   |               |   |
   |               |   the expected opaque type
   |               expected `Box<impl Trait>` because of return type
...
LL |     Box::new(1u32)
   |     ^^^^^^^^^^^^^^ types differ
   |
   = note: expected struct `Box<impl Trait>`
              found struct `Box<u32>`

error[E0277]: the size for values of type `dyn Trait` cannot be known at compilation time
  --> $DIR/unsized_coercion.rs:12:1
   |
LL | fn hello() -> Box<impl Trait> {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `dyn Trait`

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0277, E0308.
For more information about an error, try `rustc --explain E0277`.