FULL PRODUCT VERSION :
java version "1.8.0_60"
Java(TM) SE Runtime Environment (build 1.8.0_60-b27)
Java HotSpot(TM) 64-Bit Server VM (build 25.60-b23, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
6.1.7601

A DESCRIPTION OF THE PROBLEM :
The example code doesn't compile and fails with a type inference error. It does, however, compile just fine in Eclipse Mars.


ERROR MESSAGES/STACK TRACES THAT OCCUR :
method c in enum Q cannot be applied to given types;
        return c(f::e);
               ^
  required: Consumer<S<? super T#1>>
  found: f::e
  reason: cannot infer type-variable(s) T#1
    (argument mismatch; invalid method reference
      incompatible types: S<CAP#1> cannot be converted to S<? super CAP#2>)
  where T#1,T#2 are type-variables:
    T#1 extends Object declared in method <T#1>c(Consumer<S<? super T#1>>)
    T#2 extends Object declared in method <T#2>f(P<? extends T#2>)
  where CAP#1,CAP#2 are fresh type-variables:
    CAP#1 extends Object super: T#1 from capture of ? super T#1
    CAP#2 extends T#2 from capture of ? extends T#2

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
public enum Q {
    ;
    interface S<T> {
        
    }
    interface P<T> {
        void e(S<? super T> s);
    }
    
    static <T> P<T> c(Consumer<S<? super T>> c) {
        return null;
    }
    static <T> P<T> f(P<? extends T> f) {
        return c(f::e);
    }
}


---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Instead of method reference, use a full lambda:

return c(a -> f.e(a));