src/librustc_error_codes/error_codes/E0643.md

   1 This error indicates that there is a mismatch between generic parameters and
   2 impl Trait parameters in a trait declaration versus its impl.
   3
   4 ```compile_fail,E0643
   5 trait Foo {
   6     fn foo(&self, _: &impl Iterator);
   7 }
   8 impl Foo for () {
   9     fn foo<U: Iterator>(&self, _: &U) { } // error method `foo` has incompatible
  10                                           // signature for trait
  11 }
  12 ```