error[E0393]: the type parameter `Rhs` must be explicitly specified
  --> $DIR/issue-21950.rs:10:25
   |
LL | / trait Add<Rhs=Self> {
LL | |     type Output;
LL | | }
   | |_- type parameter `Rhs` must be specified for this
...
LL |       let x = &10 as &dyn Add;
   |                           ^^^ help: set the type parameter to the desired type: `Add<Rhs>`
   |
   = note: because of the default `Self` reference, type parameters must be specified on object types

error[E0191]: the value of the associated type `Output` (from trait `Add`) must be specified
  --> $DIR/issue-21950.rs:10:25
   |
LL |     type Output;
   |     ------------ `Output` defined here
...
LL |     let x = &10 as &dyn Add;
   |                         ^^^ help: specify the associated type: `Add<Output = Type>`

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0191, E0393.
For more information about an error, try `rustc --explain E0191`.