compiler/rustc_error_codes/src/error_codes/E0557.md

   1 A feature attribute named a feature that has been removed.
   2
   3 Erroneous code example:
   4
   5 ```compile_fail,E0557
   6 #![feature(managed_boxes)] // error: feature has been removed
   7 ```
   8
   9 Delete the offending feature attribute.