cfg(false) where where

[matthiaskrgr]

probably minor

The following code

#![feature(extern_types)]
fn main() {}
#[cfg(false)]
extern "C" {
    type A<T: Ord> where where T: 'static;
}

Compiled successfully ( with --crate-type=lib --cap-lints=warn):

warning: function `main` is never used
 --> ./a.rs:2:4
  |
2 | fn main() {}
  |    ^^^^
  |
  = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default

warning: 1 warning emitted

However rasur was found to have errors (-e 2015):

error: found `where` but expected `;`
 --> ./a.rs:5:26
  |
5 |     type A<T: Ord> where where T: 'static;
  |                          ^^^^^ unexpected token

[fmease]

Lol, that's amazing! I wonder if we should consider this a bug in rustc 🤔 I know that type aliases can have two where-clauses, one before its optional body = $ty and one after it (e.g., type X where (): Copy = () where (): Copy; or type X where = () where;) and in your snippet there's simply no body in between the two clauses.

While that does sound like accepting type X where where; is a logical consequence and all fine & dandy, rustc actually does explicitly reject "duplicate where-clauses" … except in this case. So it rejects type X where i32: Copy where String: Clone; as "duplicate" but it accepts type X where where;. That feels a bit contradictory to me. I'll think about it some more and then open a r-l/r issue and/or PR for this.

[essence-groove]

This is only a parser (hobby)