Const fn causes ICE in a pattern

[arielb1]

STR

#![feature(const_fn)]
const fn four() -> u32 { 4 }
const FOUR: u32 = four();
fn main() { match 4 { FOUR => {}, _ => unreachable!() }}

at the current version of play.rust-lang.org

ICE

error: internal compiler error: unexpected panic
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 'internal error: entered unreachable code', ../src/librustc/middle/const_eval.rs:327

playpen: application terminated with error code 101

[oli-obk]

The reason this is happening is because the code thinks four is an enum variant or a tuple struct.

The code around this is somewhat redundant and would probably better be solved by making enum variants const evaluable and adding a function that translates ConstVals to Constructor