54 lines
1.4 KiB
Rust
54 lines
1.4 KiB
Rust
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// compile-flags: -Ztrait-solver=next
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#![feature(rustc_attrs)]
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// Check that we correctly rerun the trait solver for heads of cycles,
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// even if they are not the root.
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struct A<T: ?Sized>(*const T);
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struct B<T: ?Sized>(*const T);
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struct C<T: ?Sized>(*const T);
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#[rustc_coinductive]
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trait Trait<'a, 'b> {}
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trait NotImplemented {}
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impl<'a, 'b, T: ?Sized> Trait<'a, 'b> for A<T> where B<T>: Trait<'a, 'b> {}
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// With this the root of `B<T>` is `A<T>`, even if the other impl does
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// not have a cycle with `A<T>`. This candidate never applies because of
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// the `A<T>: NotImplemented` bound.
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impl<'a, 'b, T: ?Sized> Trait<'a, 'b> for B<T>
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where
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A<T>: Trait<'a, 'b>,
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A<T>: NotImplemented,
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{
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}
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// This impl directly requires 'b to be equal to 'static.
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//
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// Because of the coinductive cycle through `C<T>` it also requires
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// 'a to be 'static.
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impl<'a, T: ?Sized> Trait<'a, 'static> for B<T>
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where
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C<T>: Trait<'a, 'a>,
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{}
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// In the first iteration of `B<T>: Trait<'a, 'b>` we don't add any
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// constraints here, only after setting the provisional result to require
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// `'b == 'static` do we also add that constraint for `'a`.
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impl<'a, 'b, T: ?Sized> Trait<'a, 'b> for C<T>
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where
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B<T>: Trait<'a, 'b>,
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{}
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fn impls_trait<'a, 'b, T: Trait<'a, 'b> + ?Sized>() {}
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fn check<'a, T: ?Sized>() {
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impls_trait::<'a, 'static, A<T>>();
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//~^ ERROR lifetime may not live long enough
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}
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fn main() {
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check::<()>();
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}
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