ICE with mut reference in `static mut`

[eefriedman]

Testcase:

static mut TEST: [isize; 1] = [1];
static mut TEST2: &'static mut [isize] = unsafe { &mut TEST };
fn main() {
    println!("{}", unsafe { TEST2[0] });
}

Produces:

<anon>:2:56: 2:60 error: internal compiler error: expected a const, fn, struct, or variant def
<anon>:2 static mut TEST2: &'static mut [isize] = unsafe { &mut TEST };
                                                                ^~~~
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
note: run with `RUST_BACKTRACE=1` for a backtrace
thread 'rustc' panicked at 'Box<Any>', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/libsyntax/diagnostic.rs:176

[arielb1]

I think the original intent was to allow references to slices &mut [1,2,3].

[arielb1]

What level of this should be allowed? We don't borrowck statics, so you can do (&mut A, &mut A).

[eefriedman]

I would figure if someone is willing to use unsafe blocks to build a static mut variable, we should just let them shoot themselves in the foot. You can construct a static mut variable containing (&mut A, &mut A) at runtime anyway.

[apasel422]

Triage: Still an issue.

[steveklabnik]

This ICE seems to be fixed on

rustc 1.12.0-nightly (b30eff7ba 2016-08-05)

I have a hunch that this is due to MIR being turned on, though I'm not sure. Please let me know if this still ICEs for you, but closing for now 🎊