[ER] Warn against unused braces for const value argument

[leonardo-m]

#![allow(dead_code)]
struct Foo<const N: usize> {
    data: [u32; N],
}
impl<const N: usize> Foo<{ N }> {
}
fn main() {}

Gives no warnings, but I expected a warning like:

warning: unnecessary braces around const value
 --> ...\test.rs:5:26
  |
5 | impl<const N: usize> Foo<{ N }> {
  |                          ^^^^^ help: remove these braces
  |
  = note: `#[warn(unused_braces)]` on by default

[osa1]

Apparently this is a known issue:

rust/compiler/rustc_lint/src/unused.rs

Line 991 in eb95ace

// FIXME(const_generics): handle paths when #67075 is fixed.

blocked on #67075.

[leonardo-m]

So do you suggest to close this issue down? Or do we keep this open to keep better memory of this little problem?

[osa1]

I couldn't find an open issue for this FIXME so I think we can use this one as the tracking issue.