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//@ compile-flags: -Znext-solver
//@ check-pass
#![feature(rustc_attrs)]
#[rustc_coinductive]
trait Trait<T> {}
impl<'a, 'b, T> Trait<T> for (&'a (), &'b ())
where
'b: 'a,
&'a (): Trait<T>,
{}
impl Trait<i32> for &'static () {}
impl<'a> Trait<u32> for &'a ()
where
for<'b> (&'a (), &'b ()): Trait<u32>,
{}
fn impls_trait<T: Trait<U>, U>() {}
fn main() {
// This infers to `impls_trait::<(&'static (), &'static ()), i32>();`
//
// In the first attempt we have 2 candidates for `&'a (): Trait<_>`
// and we get ambiguity. The result is therefore ambiguity with a `'b: 'a`
// constraint. The next attempt then uses that provisional result when
// trying to apply `impl<'a> Trait<u32> for &'a ()`. This means we get a
// `for<'b> 'b: 'a` bound which fails the leak check. Because of this we
// end up with a single impl for `&'a (): Trait<_>` which infers `_` to `i32`
// and succeeds.
impls_trait::<(&(), &()), _>();
}
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