Compiler error on impl with const generic

[imbrem]

Impls which are generic over a const parameter don't seem to work properly, generating a bunch of compiler errors

#![feature(const_generics)]

trait Fooable<const N : usize> {}

struct Foo<const N : usize>();

impl<const N : usize> Fooable<N> for Foo<N> {}

(Playground)

Errors:

   Compiling playground v0.0.1 (/playground)
warning: the feature `const_generics` is incomplete and may cause the compiler to crash
 --> src/lib.rs:1:12
  |
1 | #![feature(const_generics)]
  |            ^^^^^^^^^^^^^^

error[E0573]: expected type, found const parameter `N`
 --> src/lib.rs:7:31
  |
7 | impl<const N : usize> Fooable<N> for Foo<N> {}
  |                               ^ not a type

error[E0573]: expected type, found const parameter `N`
 --> src/lib.rs:7:42
  |
7 | impl<const N : usize> Fooable<N> for Foo<N> {}
  |                                          ^ not a type

error[E0107]: wrong number of const arguments: expected 1, found 0
 --> src/lib.rs:7:38
  |
7 | impl<const N : usize> Fooable<N> for Foo<N> {}
  |                                      ^^^^^^ expected 1 const argument

error[E0107]: wrong number of type arguments: expected 0, found 1
 --> src/lib.rs:7:42
  |
7 | impl<const N : usize> Fooable<N> for Foo<N> {}
  |                                          ^ unexpected type argument

error[E0107]: wrong number of const arguments: expected 1, found 0
 --> src/lib.rs:7:23
  |
7 | impl<const N : usize> Fooable<N> for Foo<N> {}
  |                       ^^^^^^^^^^ expected 1 const argument

error[E0107]: wrong number of type arguments: expected 0, found 1
 --> src/lib.rs:7:31
  |
7 | impl<const N : usize> Fooable<N> for Foo<N> {}
  |                               ^ unexpected type argument

error: aborting due to 6 previous errors

For more information about this error, try `rustc --explain E0107`.
error: Could not compile `playground`.

To learn more, run the command again with --verbose.

[varkor]

I've just created a catch-all issue for this: #60804. For now, you can get around it by surrounding const argument with curly brackets.