compiler/rustc_error_codes/src/error_codes/E0539.md

   1 An invalid meta-item was used inside an attribute.
   2
   3 Erroneous code example:
   4
   5 ```compile_fail,E0539
   6 #![feature(staged_api)]
   7 #![stable(since = "1.0.0", feature = "test")]
   8
   9 #[rustc_deprecated(reason)] // error!
  10 #[unstable(feature = "deprecated_fn", issue = "123")]
  11 fn deprecated() {}
  12
  13 #[unstable(feature = "unstable_struct", issue)] // error!
  14 struct Unstable;
  15
  16 #[rustc_const_unstable(feature)] // error!
  17 const fn unstable_fn() {}
  18
  19 #[stable(feature = "stable_struct", since)] // error!
  20 struct Stable;
  21
  22 #[rustc_const_stable(feature)] // error!
  23 const fn stable_fn() {}
  24 ```
  25
  26 Meta items are the key-value pairs inside of an attribute.
  27 To fix these issues you need to give required key-value pairs.
  28
  29 ```
  30 #![feature(staged_api)]
  31 #![stable(since = "1.0.0", feature = "test")]
  32
  33 #[rustc_deprecated(since = "1.39.0", reason = "reason")] // ok!
  34 #[unstable(feature = "deprecated_fn", issue = "123")]
  35 fn deprecated() {}
  36
  37 #[unstable(feature = "unstable_struct", issue = "123")] // ok!
  38 struct Unstable;
  39
  40 #[rustc_const_unstable(feature = "unstable_fn", issue = "124")] // ok!
  41 const fn unstable_fn() {}
  42
  43 #[stable(feature = "stable_struct", since = "1.39.0")] // ok!
  44 struct Stable;
  45
  46 #[rustc_const_stable(feature = "stable_fn", since = "1.39.0")] // ok!
  47 const fn stable_fn() {}
  48 ```