// compile-flags: -Z mir-opt-level=3 #![feature(type_alias_impl_trait, rustc_attrs)] use std::marker::PhantomData; trait MyIndex<T> { type O; fn my_index(self) -> Self::O; } trait MyFrom<T>: Sized { type Error; fn my_from(value: T) -> Result<Self, Self::Error>; } trait F {} impl F for () {} type DummyT<T> = impl F; fn _dummy_t<T>() -> DummyT<T> {} struct Phantom1<T>(PhantomData<T>); struct Phantom2<T>(PhantomData<T>); struct Scope<T>(Phantom2<DummyT<T>>); impl<T> Scope<T> { fn new() -> Self { unimplemented!() } } impl<T> MyFrom<Phantom2<T>> for Phantom1<T> { type Error = (); fn my_from(_: Phantom2<T>) -> Result<Self, Self::Error> { unimplemented!() } } impl<T: MyFrom<Phantom2<DummyT<U>>>, U> MyIndex<Phantom1<T>> for Scope<U> { type O = T; fn my_index(self) -> Self::O { MyFrom::my_from(self.0).ok().unwrap() } } #[rustc_error] fn main() { //~^ ERROR let _pos: Phantom1<DummyT<()>> = Scope::new().my_index(); }