Array range indexes don't work in const eval

[LLFourn]

I haven't been able to find any issue dealing with this. It seems that min_const_fn stabilised array indexes but not ranges and ranges don't work.

I tried this code:

const a: [u8; 4] = [1, 2, 3, 4];
const b: &'static u8 = &a[1]; //fine
const c: &'static [u8] = &a[1..3]; //broken

pub fn main() {
    dbg!(b);
}

Error:

   Compiling playground v0.0.1 (/playground)
error[E0015]: calls in constants are limited to constant functions, tuple structs and tuple variants
 --> src/main.rs:3:27
  |
3 | const c: &'static [u8] = &a[1..3];
  |                           ^^^^^^^

Meta

$ rustc --version --verbose
rustc 1.46.0-nightly (118b50524 2020-06-06)
binary: rustc
commit-hash: 118b50524b79e565f017e08bce9b90a16c63634f
commit-date: 2020-06-06
host: x86_64-unknown-linux-gnu
release: 1.46.0-nightly
LLVM version: 10.0

[jonas-schievink]

Closing in favor of #67792 / #67794

[robertbastian]

Can this be reopened? Const indexing on array and slice was only implemented for single indices, but there doesn't seem to be a technical reason why this wouldn't work for ranges as well. Currently this requires dropping down to pointers and transmutes, which is pretty messy.

Const traits still haven't landed, and don't seem to be close.