ICE: type mismatch comparing repeat and repeat

[arielb1]

STR

$ rustc --version
rustc 1.22.0-nightly (185cc5f26 2017-10-02)

const X: [u8; 1] = [0; 1];

fn main() {
    match &X {
        &X => println!("a"),
        _ => println!("b"),
    };
}

Expected Result

code compiles and runs

Actual Result

warning: unreachable pattern
 --> x.rs:6:9
  |
6 |         &X => println!("a"),
  |         ^^
  |
  = note: #[warn(unreachable_patterns)] on by default

error: internal compiler error: type mismatch comparing Aggregate(Repeat(Const { ty: u8, val: Integral(U8(0)) }, 1)) and Aggregate(Repeat(Const { ty: u8, val: Integral(U8(0)) }, 1))
 --> x.rs:6:10
  |
6 |         &X => println!("a"),
  |          ^

error: aborting due to previous error

[ysiraichi]

I think there is no one working on this issue yet, so can I work on this?
@nikomatsakis can you help me (it's my first time contributing to rust)?

[nikomatsakis]

@ysiraichi I agree nobody is working on this issue yet. =) I can try to leave a few tips. Maybe you can take some of these steps first.

It'd be good to know where the type error arises, first off. I'd run the compiler with RUST_BACKTRACE=1.

Second, the "unreachable pattern" message seems a bit strange. This no doubt arises -- in part -- because of the way that we handle constants in patterns. In short, the &X pattern will be internally expanded to &[0; 1] -- that is, the definition of the array is inlined. It's been a while since I looked at this code -- but I think that takes place in _match.rs somewhere?

cc @oli-obk -- have you been looking at this code lately? have any tips?

[oli-obk]

Yes I have touched this code very recently, it will be fixed by #46882