E4011

Type parameters are not allowed on default implementation for traits.

Erroneous Example

pub(open) trait Stringer {
  stringify(Self) -> String
}

impl[T] Stringer with stringify(_self) { "hey" }

The example above uses a type parameter T on the default implementation of the Stringer trait, which is not allowed.

Suggestion

Remove the type parameter from the default implementation:

pub(open) trait Stringer {
  stringify(Self) -> String
}

impl Stringer with stringify(_self) { "hey" }