error[E0393]: the type parameter `T` must be explicitly specified
  --> $DIR/type-parameter-defaults-referencing-Self.rs:8:16
   |
LL | trait Foo<T=Self> {
   | ----------------- type parameter `T` must be specified for this
...
LL | fn foo(x: &dyn Foo) { }
   |                ^^^
   |
   = note: because the parameter default references `Self`, the parameter must be specified on the object type
help: set the type parameter to the desired type
   |
LL | fn foo(x: &dyn Foo<T>) { }
   |                   +++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0393`.