non-&mut unboxed closures look for FnMut trait for direct call_once/call method call

[huonw]

#![feature(unboxed_closures, unboxed_closure_sugar)]

fn main() {
    let once_ = |: x| x;
    once_.call_once((0i, ));

    let mut_ = |&mut: x| x;
    mut_.call_once((0i, ));
}

<anon>:7:5: 7:28 error: failed to find an implementation of trait core::ops::FnMut<(int),int> for closure
<anon>:7     once_.call_once((0i, ));
             ^~~~~~~~~~~~~~~~~~~~~~~
<anon>:7:5: 7:28 error: failed to find an implementation of trait core::ops::FnMut<(int),int> for closure
<anon>:7     once_.call_once((0i, ));
             ^~~~~~~~~~~~~~~~~~~~~~~

It's particularly strange that the mut_.call_once form works (it's also a little strange that the error message is emitted twice.)

[huonw]

Oh, this fails for Fn & .call too:

#![feature(unboxed_closures, unboxed_closure_sugar)]

fn main() {
    let f = |&: x: int| x;
    f.call((1i,));
}

<anon>:5:5: 5:18 error: failed to find an implementation of trait core::ops::FnMut<(int),int> for closure
<anon>:5     f.call((1i,));
             ^~~~~~~~~~~~~
<anon>:5:5: 5:18 error: failed to find an implementation of trait core::ops::FnMut<(int),int> for closure
<anon>:5     f.call((1i,));
             ^~~~~~~~~~~~~

[jroesch]

Just leaving a comment here because I've run into this bug in the past few hours as well, and I am interested in its progress.