error: expected path
 --> dev/main.rs:4:8
  |
4 |     #![async]
  |        ^^^^^

error: unexpected end of input, expected path segment
 --> dev/main.rs:5:13
  |
5 |     #![foo::]
  |             ^

error: expected identifier, found keyword `async`
 --> dev/main.rs:4:8
  |
4 |     #![async]
  |        ^^^^^

error: unexpected end of input, expected path segment after `::`
 --> dev/main.rs:5:13
  |
5 |     #![foo::]
  |             ^