41 lines
1.2 KiB
Rust
41 lines
1.2 KiB
Rust
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// check-pass
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// This test verifies that negative trait predicate cannot be satisfied from a
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// positive param-env candidate.
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// Negative coherence is one of the only places where we actually construct and
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// evaluate negative predicates. Specifically, when verifying whether the first
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// and second impls below overlap, we do not want to consider them disjoint,
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// otherwise the second impl would be missing an associated type `type Item`
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// which is provided by the first impl that it is specializing.
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#![feature(specialization)]
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//~^ WARN the feature `specialization` is incomplete
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#![feature(with_negative_coherence)]
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trait BoxIter {
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type Item;
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fn last(self) -> Option<Self::Item>;
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}
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impl<I: Iterator + ?Sized> BoxIter for Box<I> {
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type Item = I::Item;
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default fn last(self) -> Option<I::Item> {
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todo!()
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}
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}
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// When checking that this impl does/doesn't overlap the one above, we evaluate
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// a negative version of all of the where-clause predicates of the impl below.
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// For `I: !Iterator`, we should make sure that the param-env clause `I: Iterator`
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// from above doesn't satisfy this predicate.
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impl<I: Iterator> BoxIter for Box<I> {
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fn last(self) -> Option<I::Item> {
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(*self).last()
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}
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}
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fn main() {}
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