22 lines
661 B
Rust
22 lines
661 B
Rust
|
// compile-flags: -Znext-solver
|
||
|
|
// check-pass
|
||
|
|
|
||
|
|
fn map<T: Default, U, F: FnOnce(T) -> U>(f: F) {
|
||
|
|
f(T::default());
|
||
|
|
}
|
||
|
|
|
||
|
|
fn main() {
|
||
|
|
map::<i32, _ /* ?U */, _ /* ?F */>(|x| x.to_string());
|
||
|
|
// PREVIOUSLY when confirming the `map` call, we register:
|
||
|
|
//
|
||
|
|
// (1.) ?F: FnOnce<(i32,)>
|
||
|
|
// (2.) <?F as FnOnce<(i32,)>>::Output projects-to ?U
|
||
|
|
//
|
||
|
|
// While (1.) is ambiguous, (2.) immediately gets processed
|
||
|
|
// and we infer `?U := <?F as FnOnce<(i32,)>>::Output`.
|
||
|
|
//
|
||
|
|
// Thus, the only pending obligation that remains is (1.).
|
||
|
|
// Since it is a trait obligation, we don't use it to deduce
|
||
|
|
// the closure signature, and we fail!
|
||
|
|
}
|