Struct + Fn fulfills `Send`, but sugary version `|&: ...|` does not

[japaric]

STR

#![feature(unboxed_closures)]

use std::mem;
use std::ops::Fn;

// Unsugared closure
struct Closure(u8);

impl Fn<(u8,), u8> for Closure {
    extern "rust-call" fn call(&self, (y,): (u8,)) -> u8 {
        let &Closure(x) = self;

        x + y
    }
}

fn main() {
    let y = 0u8;
    let closure = |&: x| y + x;
    let unsugared_closure = Closure(y);

    // Check that both closures are capturing by value
    println!("{}", mem::size_of_val(&closure));  // prints 1
    println!("{}", mem::size_of_val(&unsugared_closure));  // prints 1

    spawn(proc() {
        let ok = unsugared_closure;
        let err = closure;
    })
}

Output

closure.rs:28:19: 28:26 error: cannot capture variable of type `closure`, which does not fulfill `'static+Send`, in a bounded closure [E0146]
closure.rs:28         let err = closure;
                                ^~~~~~~
closure.rs:28:19: 28:26 note: this closure's environment must satisfy `'static+Send`
closure.rs:28         let err = closure;
                                ^~~~~~~
error: aborting due to previous error

Version

rustc 0.12.0-pre (eff87bc9d 2014-08-17 13:11:06 +0000)

[bkoropoff]

The example code with appropriate changes now builds:

#![feature(unboxed_closures)]

use std::mem;

fn main() {
    let y = 0u8;
    let closure = move |&: x| y + x;

    // Check that both closures are capturing by value
    println!("{}", mem::size_of_val(&closure));  // prints 1

    spawn(proc() {
        let ok = closure;
    })
}

This issue just needs a test now.