tests/ui/traits/next-solver/closure-inference-guidance.rs

//@ compile-flags: -Znext-solver
//@ check-pass

fn foo(i: isize) -> isize { i + 1 }

fn apply<A, F>(f: F, v: A) -> A where F: FnOnce(A) -> A { f(v) }

pub fn main() {
    let f = |i| foo(i);
    assert_eq!(apply(f, 2), 3);
}