Can't compare unsafe function pointers

[jdm]

type JSPropertyOp = extern "C" fn();
type JSPropertyOp2 = extern "C" unsafe fn();

extern fn foo() {
}

fn main() {
    let bar: JSPropertyOp = foo;
    if bar == foo {
    }

    let bar: JSPropertyOp2 = foo;
    if bar == foo {
    }
}

yields

[jdm@rosencrantz rust-mozjs]$ rustc /tmp/unsafe.rs 
/tmp/unsafe.rs:13:8: 13:18 error: binary operation `==` cannot be applied to type `extern "C" unsafe fn()`
/tmp/unsafe.rs:13     if bar == foo {
                         ^~~~~~~~~~
error: aborting due to previous error

[huonw]

I wrote some code over in #14719, but @alexcrichton points out some edge cases that it would be good to properly spec. This can/should probably go through an RFC.

[steveklabnik]

I'm pulling a massive triage effort to get us ready for 1.0. As part of this, I'm moving stuff that's wishlist-like to the RFCs repo, as that's where major new things should get discussed/prioritized.

This issue has been moved to the RFCs repo: rust-lang/rfcs#718