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