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//@ check-pass
//@ known-bug: #74629
// Should fail. The `0` and `1` impls overlap, violating coherence. Eg, with
// `T = Test, F = ()`, all bounds are true, making both impls applicable.
// `Test: Fold<Nil>`, `Test: Fold<()>` are true because of `2`.
// `Is<Test>: NotNil` is true because of `auto trait` and lack of negative impl.
#![feature(negative_impls)]
#![feature(auto_traits)]
struct Nil;
struct Cons<H>(H);
struct Test;
trait Fold<F> {}
impl<T, F> Fold<F> for Cons<T>
// 0
where
T: Fold<Nil>,
{
}
impl<T, F> Fold<F> for Cons<T>
// 1
where
T: Fold<F>,
private::Is<T>: private::NotNil,
{
}
impl<F> Fold<F> for Test {} // 2
mod private {
use crate::Nil;
pub struct Is<T>(T);
pub auto trait NotNil {}
impl !NotNil for Is<Nil> {}
}
fn main() {}
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