rust/tests/ui/specialization/specialization-default-items-drop-coherence.rs

// revisions: classic coherence next
//[next] compile-flags: -Ztrait-solver=next
//[coherence] compile-flags: -Ztrait-solver=next-coherence
//[classic] check-pass
//[classic] known-bug: #105782

// Should fail. Default items completely drop candidates instead of ambiguity,
// which is unsound during coherence, since coherence requires completeness.

#![feature(specialization)]
#![allow(incomplete_features)]

trait Default {
   type Id;
}

impl<T> Default for T {
   default type Id = T;
}

trait Overlap {
   type Assoc;
}

impl Overlap for u32 {
   type Assoc = usize;
}

impl Overlap for <u32 as Default>::Id {
   //[coherence]~^ ERROR conflicting implementations of trait `Overlap` for type `u32`
   //[next]~^^ ERROR conflicting implementations of trait `Overlap` for type `u32`
   type Assoc = Box<usize>;
}

fn main() {}