tests/ui/traits/trait-upcasting/illegal-upcast-from-impl.rs


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// revisions: current next
//[next] compile-flags: -Ztrait-solver=next

#![feature(trait_upcasting)]

trait Super {
    type Assoc;
}

trait Sub: Super {}

impl<T: ?Sized> Super for T {
    type Assoc = i32;
}

fn illegal(x: &dyn Sub<Assoc = ()>) -> &dyn Super<Assoc = i32> { x }
//~^ ERROR mismatched types

// Want to make sure that we can't "upcast" to a supertrait that has a different
// associated type that is instead provided by a blanket impl (and doesn't come
// from the object bounds).

fn main() {}