Document when items can be omitted from trait impls #1932
Description
The Reference says:
A trait implementation must define all non-default associated items declared by the implemented trait, may redefine default associated items defined by the implemented trait, and cannot define any other items.
However, the compiler accepts:
trait Tr { type Ty where Self: Sized; fn f() where Self: Sized; } trait A {} impl Tr for dyn A {}