src/librustc_error_codes/error_codes/E0537.md

   1 An unknown predicate was used inside the `cfg` attribute.
   2
   3 Erroneous code example:
   4
   5 ```compile_fail,E0537
   6 #[cfg(unknown())] // error: invalid predicate `unknown`
   7 pub fn something() {}
   8
   9 pub fn main() {}
  10 ```
  11
  12 The `cfg` attribute supports only three kinds of predicates:
  13
  14  * any
  15  * all
  16  * not
  17
  18 Example:
  19
  20 ```
  21 #[cfg(not(target_os = "linux"))] // ok!
  22 pub fn something() {}
  23
  24 pub fn main() {}
  25 ```
  26
  27 For more information about the cfg attribute, read:
  28 https://doc.rust-lang.org/reference.html#conditional-compilation