src/test/ui/impl-trait/bound-normalization-fail.rs

// compile-fail
// ignore-tidy-linelength
// edition:2018

#![feature(async_await)]
#![feature(impl_trait_in_bindings)]
//~^ WARNING the feature `impl_trait_in_bindings` is incomplete

// See issue 60414

// Reduction to `impl Trait`

struct Foo<T>(T);

trait FooLike { type Output; }

impl<T> FooLike for Foo<T> {
    type Output = T;
}

mod impl_trait {
    use super::*;

    trait Trait {
        type Assoc;
    }

    /// `T::Assoc` can't be normalized any further here.
    fn foo_fail<T: Trait>() -> impl FooLike<Output=T::Assoc> {
        //~^ ERROR: type mismatch
        Foo(())
    }
}

// Same with lifetimes in the trait

mod lifetimes {
    use super::*;

    trait Trait<'a> {
        type Assoc;
    }

    /// Missing bound constraining `Assoc`, `T::Assoc` can't be normalized further.
    fn foo2_fail<'a, T: Trait<'a>>() -> impl FooLike<Output=T::Assoc> {
    //~^ ERROR: type mismatch
    //~^^ ERROR `impl Trait` return type cannot contain a projection or `Self` that references lifetimes from a parent scope
        Foo(())
    }
}

fn main() {}