A problem with inline_const feature in ranges

As soon as I've seen the new inline_const feature, I've tried to find some use cases for it in my code, and I did find only very few of them, unfortunately, and one of the two uses cases could be reduced to this:

#![allow(incomplete_features)]
#![feature(inline_const)]
fn main() {
    const N: u32 = 10;
    let x: u32 = 3;

    match x {
        1 .. const { N - 1 } => {},
        _ => {},
    }
}

That gives errors:

error: expected one of `=>`, `if`, or `|`, found keyword `const`
 --> ...\temp.rs:9:14
  |
9 |         1 .. const { N - 1 } => {},
  |              ^^^^^ expected one of `=>`, `if`, or `|`

error[E0658]: half-open range patterns are unstable
 --> ...\temp.rs:9:9
  |
9 |         1 .. const { N - 1 } => {},
  |         ^^^^
  |
  = note: see issue #67264 <https://github.com/rust-lang/rust/issues/67264> for more information
  = help: add `#![feature(half_open_range_patterns)]` to the crate attributes to enable

So I am not sure if this is a bug report or an enhancement request.

Note that this does work in expressions (playground):

#![allow(incomplete_features)]
#![feature(inline_const)]
fn main() {
    const N: u32 = 10;

    let range = 1 .. const { N - 1 };
    println!("{:?}", range);
}

Support for ranges in patterns (1 .. const { 2 } or const { 1 } .. 2) needs to be added separately, to fn parse_pat_range_end and fn parse_pat_with_range_pat respectively.

Ohh I've just realized that we had this issue opened, I've fixed this in #78116.

Going to adjust description of the PR accordingly so it closes this issue when merged.

Rollup merge of rust-lang#78116 - spastorino:inline-const-in-range-pa…

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A problem with inline_const feature in ranges #78108

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A problem with inline_const feature in ranges #78108

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camelid commented on Oct 19, 2020

petrochenkov commented on Oct 19, 2020

spastorino commented on Oct 19, 2020

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