mirror of https://github.com/rust-lang/rust
46 lines
1.0 KiB
Rust
46 lines
1.0 KiB
Rust
//@ check-pass
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//@ known-bug: #84591
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trait Subtrait<'a, 'b, R>: Supertrait<'a, 'b> {}
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trait Supertrait<'a, 'b> {
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fn convert<T: ?Sized>(x: &'a T) -> &'b T;
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}
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fn need_hrtb_subtrait<'a_, 'b_, S, T: ?Sized>(x: &'a_ T) -> &'b_ T
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where
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S: for<'a, 'b> Subtrait<'a, 'b, &'b &'a ()>,
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{
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need_hrtb_supertrait::<S, T>(x)
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// This call works and drops the implied bound `'a: 'b`
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// of the where-bound. This means the where-bound can
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// now be used to transmute any two lifetimes.
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}
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fn need_hrtb_supertrait<'a_, 'b_, S, T: ?Sized>(x: &'a_ T) -> &'b_ T
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where
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S: for<'a, 'b> Supertrait<'a, 'b>,
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{
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S::convert(x)
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}
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struct MyStruct;
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impl<'a: 'b, 'b> Supertrait<'a, 'b> for MyStruct {
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fn convert<T: ?Sized>(x: &'a T) -> &'b T {
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x
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}
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}
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impl<'a, 'b> Subtrait<'a, 'b, &'b &'a ()> for MyStruct {}
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fn extend_lifetime<'a, 'b, T: ?Sized>(x: &'a T) -> &'b T {
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need_hrtb_subtrait::<MyStruct, T>(x)
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}
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fn main() {
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let d;
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{
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let x = "Hello World".to_string();
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d = extend_lifetime(&x);
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}
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println!("{}", d);
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}
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