Error code E0203

Having duplicate relaxed default bounds is unsupported.

Erroneous code example:

#![allow(unused)]
fn main() {
struct Bad<T: ?Sized + ?Sized>{
    inner: T,
}
}

Here the type parameter T cannot have duplicate relaxed bounds for default trait Sized. This can be fixed by only using one relaxed bound:

#![allow(unused)]
fn main() {
struct Good<T: ?Sized>{
    inner: T
}
}