Bug in impl FusedFuture for futures::future::Map

[Nemo157]

It doesn't correctly propagate the termination of the underlying future

use futures::future::FusedFuture;
use futures::future::FutureExt;

fn main() {
    assert!(futures::future::pending::<()>().is_terminated());
    assert!(futures::future::pending::<()>().map(|()| ()).is_terminated());
}

> cargo run
thread 'main' panicked at 'assertion failed: futures::future::pending::<()>().map(|()| ()).is_terminated()', src/main.rs:6:5

This should be delegating through to the inner future:

futures-rs/futures-util/src/future/future/map.rs

Line 34 in 32d970e

Map::Incomplete { .. } => false,

[taiki-e]

Right. Also some Fused{Future, Stream} impls, including Fuse, should have similar issues.
And, this is one of the reasons I'd like to remove Fused{Future, Stream} (#2111 (comment)).

[taiki-e]

As said in #2207 (comment), the current implementation is correct if the underlying types do not implement FusedFuture, but is incorrect if it is implemented.

Closing in favor of #2207, which propose the removal of FusedFuture.