error: constant values inside of type parameter defaults must not depend on generic parameters
  --> $DIR/param-in-ct-in-ty-param-default.rs:1:44
   |
LL | struct Foo<T, U = [u8; std::mem::size_of::<T>()]>(T, U);
   |                                            ^ the anonymous constant must not depend on the parameter `T`

error: aborting due to previous error