Consider this very simple code:

import java.util.*;

public class Test {
 private static class Foo<T> {
   public List<String> foo(List<String> param) {
     return param;
   }
 }

 public static void main(String[] args) {
   Foo f = new Foo();
   List<String> bar = f.foo(new ArrayList<String>());
 }
}

f is a member of the raw type Foo, and therefore as expected the code
produces a warning about an unchecked call to foo() when compiled with
-Xlint:unchecked.  What I don't understand, however, is why there is
also a warning about an unchecked conversion from java.util.List to
java.util.List<java.lang.String>.  Why is the compiler unable to
determine that foo does in fact return a List<String> and not a raw
List?  Or is the compiler output simply overstating the case?