mirror of https://github.com/rust-lang/rust
67 lines
1.5 KiB
Rust
67 lines
1.5 KiB
Rust
//@ run-pass
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// Test that we evaluate projection predicates to winnow out
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// candidates during trait selection and method resolution (#20296).
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// If we don't properly winnow out candidates based on the output type
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// `Target=[A]`, then the impl marked with `(*)` is seen to conflict
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// with all the others.
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//@ pretty-expanded FIXME #23616
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use std::marker::PhantomData;
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use std::ops::Deref;
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pub trait MyEq<U: ?Sized=Self> {
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fn eq(&self, u: &U) -> bool;
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}
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impl<A, B> MyEq<[B]> for [A]
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where A : MyEq<B>
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{
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fn eq(&self, other: &[B]) -> bool {
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self.len() == other.len() &&
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self.iter().zip(other).all(|(a, b)| MyEq::eq(a, b))
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}
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}
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// (*) This impl conflicts with everything unless the `Target=[A]`
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// constraint is considered.
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impl<'a, A, B, Lhs> MyEq<[B; 0]> for Lhs
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where A: MyEq<B>, Lhs: Deref<Target=[A]>
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{
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fn eq(&self, other: &[B; 0]) -> bool {
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MyEq::eq(&**self, other)
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}
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}
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struct DerefWithHelper<H, T> {
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pub helper: H,
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pub marker: PhantomData<T>,
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}
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trait Helper<T> {
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fn helper_borrow(&self) -> &T;
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}
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impl<T> Helper<T> for Option<T> {
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fn helper_borrow(&self) -> &T {
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self.as_ref().unwrap()
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}
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}
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impl<T, H: Helper<T>> Deref for DerefWithHelper<H, T> {
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type Target = T;
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fn deref(&self) -> &T {
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self.helper.helper_borrow()
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}
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}
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pub fn check<T: MyEq>(x: T, y: T) -> bool {
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let d: DerefWithHelper<Option<T>, T> = DerefWithHelper { helper: Some(x),
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marker: PhantomData };
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d.eq(&y)
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}
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pub fn main() {
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}
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