#![feature(associated_type_defaults)] struct S<T = u8>(T); trait Tr<T = u8> { type A = (); } impl Tr<Self> for S {} // OK impl<T: Tr<Self>> Tr<T> for S {} // OK impl Tr for S where Self: Copy {} // OK impl Tr for S where S<Self>: Copy {} // OK impl Tr for S where Self::A: Copy {} // OK impl Tr for Self {} //~ ERROR `Self` is not valid in the self type of an impl block impl Tr for S<Self> {} //~ ERROR `Self` is not valid in the self type of an impl block impl Self {} //~ ERROR `Self` is not valid in the self type of an impl block impl S<Self> {} //~ ERROR `Self` is not valid in the self type of an impl block impl (Self, Self) {} //~ ERROR `Self` is not valid in the self type of an impl block impl Tr<Self::A> for S {} //~ ERROR cycle detected fn main() {}