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reproducing example for https://github.com/rust-lang/rust/issues/43132
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| fn main() { | |
| let b = mk::< | |
| Forward<(Box<Future<Error = u32>>,)>, | |
| >(); | |
| b.map_err(|_| ()).join(); | |
| } | |
| fn mk<T>() -> T { | |
| loop {} | |
| } | |
| impl<I: Future<Error = E>, E> Future for (I,) { | |
| type Error = E; | |
| } | |
| struct Forward<T: Future> { | |
| _a: T, | |
| } | |
| impl<T: Future> Future for Forward<T> | |
| where | |
| T::Error: From<u32>, | |
| { | |
| type Error = T::Error; | |
| } | |
| trait Future { | |
| type Error; | |
| fn map_err<F, E>(self, _: F) -> (Self, F) | |
| where | |
| F: FnOnce(Self::Error) -> E, | |
| Self: Sized, | |
| { | |
| loop {} | |
| } | |
| fn join(self) -> (MaybeDone<Self>, ()) | |
| where | |
| Self: Sized, | |
| { | |
| loop {} | |
| } | |
| } | |
| impl<S: ?Sized + Future> Future for Box<S> { | |
| type Error = S::Error; | |
| } | |
| enum MaybeDone<A: Future> { | |
| _Done(A::Error), | |
| } | |
| impl<U, A: Future, F> Future for (A, F) | |
| where | |
| F: FnOnce(A::Error) -> U, | |
| { | |
| type Error = U; | |
| } |
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