79 lines
1.5 KiB
Rust
79 lines
1.5 KiB
Rust
// run-pass
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// Regression test for issue #47139:
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//
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// Coherence was encountering an (unnecessary) overflow trying to
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// decide if the two impls of dummy overlap.
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//
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// The overflow went something like:
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//
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// - `&'a ?T: Insertable` ?
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// - let ?T = Option<?U> ?
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// - `Option<?U>: Insertable` ?
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// - `Option<&'a ?U>: Insertable` ?
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// - `&'a ?U: Insertable` ?
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//
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// While somewhere in the middle, a projection would occur, which
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// broke cycle detection.
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//
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// It turned out that this cycle was being kicked off due to some
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// extended diagnostic attempts in coherence, so removing those
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// sidestepped the issue for now.
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#![allow(dead_code)]
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pub trait Insertable {
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type Values;
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fn values(self) -> Self::Values;
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}
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impl<T> Insertable for Option<T>
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where
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T: Insertable,
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T::Values: Default,
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{
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type Values = T::Values;
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fn values(self) -> Self::Values {
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self.map(Insertable::values).unwrap_or_default()
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}
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}
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impl<'a, T> Insertable for &'a Option<T>
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where
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Option<&'a T>: Insertable,
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{
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type Values = <Option<&'a T> as Insertable>::Values;
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fn values(self) -> Self::Values {
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self.as_ref().values()
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}
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}
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impl<'a, T> Insertable for &'a [T]
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{
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type Values = Self;
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fn values(self) -> Self::Values {
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self
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}
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}
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trait Unimplemented { }
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trait Dummy { }
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struct Foo<T> { t: T }
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impl<'a, U> Dummy for Foo<&'a U>
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where &'a U: Insertable
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{
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}
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impl<T> Dummy for T
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where T: Unimplemented
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{ }
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fn main() {
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}
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