compiler/rustc_error_codes/src/error_codes/E0705.md

   1 A `#![feature]` attribute was declared for a feature that is stable in the
   2 current edition, but not in all editions.
   3
   4 Erroneous code example:
   5
   6 ```ignore (limited to a warning during 2018 edition development)
   7 #![feature(rust_2018_preview)]
   8 #![feature(test_2018_feature)] // error: the feature
   9                                // `test_2018_feature` is
  10                                // included in the Rust 2018 edition
  11 ```