FnMut inside Pin complains about DerefMut not implemented

[roblabla]

When calling an FnMut() from inside a Pin, Rust complains that DerefMut is not implemented:

struct MyFuture<F> {
    f: F,
}

impl<F, T> core::future::Future for MyFuture<F>
where
    F: FnMut() -> Option<T> + Unpin,
{
    type Output = T;
    fn poll(mut self: core::pin::Pin<&mut Self>, cx: &mut core::task::Context) -> core::task::Poll<T> {
        (self.f)();
        core::task::Poll::Pending
    }
}

This seemingly equivalent piece of code works properly with no errors:

struct MyFuture<F> {
    f: F,
}

impl<F, T> core::future::Future for MyFuture<F>
where
    F: FnMut() -> Option<T> + Unpin,
{
    type Output = T;
    fn poll(mut self: core::pin::Pin<&mut Self>, cx: &mut core::task::Context) -> core::task::Poll<T> {
        let x = &mut *self; // Work around weird bug.
        (x.f)();
        core::task::Poll::Pending
    }
}

[Mark-Simulacrum]

(&mut self.f)(); works too. Seems like probably we're not looking at DerefMut sufficiently or with the wrong ParamEnv perhaps?

[roblabla]

Spent a couple minutes writing a more self-contained reproducer: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=70745ec56da08ff7a8aeee8fbead6488

Testing it in godbolt reveals that even Rust 1.0.0 didn't like it

[paulkernfeld]

I just pasted the first snippet into the Rust Playground with Rust 1.46 and it compiles, so maybe this issue is now fixed?

[roblabla]

Indeed, this seems to be fixed.