Type annotations needed for closure with associated type

[camsteffen]

I tried this code:

use std::marker::PhantomData;

fn test_good() -> Builder<String> {
    // this compiles
    Builder::default().with_func(|s| drop(s))
}

fn test_bad() -> Builder<String> {
    // error[E0282]: type annotations needed
    Builder::default().with_func(|s| drop(s.len()))
}

#[derive(Default)]
pub struct Builder<Foo>(PhantomData<Foo>);

impl<Foo> Builder<Foo> {
    fn with_func(self, _: impl Fn(Foo)) -> Self {
        self
    }
}

I expect this to compile, but the test_bad function does not compile.

Meta

Rust Version: 1.86.0

[moxian]

See also #71713 which is very similar (not sure if it is an exact duplicate)

@rustbot label: +T-types +A-inference +A-closures -C-bug +C-enhancement -needs-triage