Possible regression involving inferred generic types

[cushon]

Forwarded from compiler-dev at Alex Buckley's suggestion. Original thread:
http://mail.openjdk.java.net/pipermail/compiler-dev/2013-October/007726.html


I found some cases where javac 8 behaviour diverges from javac 7, and I'm
interested in knowing whether this is a bug or an intentional change.

The following programs do not compile with the jdk8 javac. (I tried b111 and
954dd199d6ff). All of the programs compile with the jdk7 javac.

-------------------------------------------------------------------------------
import java.util.List;

class ReproOne {

  static class Baz<T> {
    public static List<Baz<Object>> getElements(Baz<Object> transcoder) {
      return null;
    }
  }

  private static void bar(Baz arg) {
    for (Baz element : Baz.getElements(arg)) {}
  }
}
-------------------------------------------------------------------------------
abstract class ReproTwo<T> {

  class Bar<E> {}

  T get(Bar<? extends T> arg1, Bar arg2) {
    return circularGet(arg2, arg2);
  }

  abstract T circularGet(final Bar<? extends T> arg1, final Bar<?> arg2);
}
-------------------------------------------------------------------------------
abstract class ReproThree<T, V> {

  class Binding<E> {}
  class ProviderBinding<E> extends Binding<E> {}

  abstract V visitOther(Binding<? extends T> binding);

  public V visitTwo(ProviderBinding<? extends T> providerBinding) {
    return visitOther((Binding) providerBinding);
  }
}
-------------------------------------------------------------------------------

javac output:

ReproOne.java:12: error: incompatible types: Object cannot be converted to
Baz
    for (Baz element : Baz.getElements(arg)) {}
                                      ^

ReproTwo.java:6: error: incompatible types: Object cannot be converted to T
    return circularGet(arg2, arg2);
                      ^
  where T is a type-variable:
    T extends Object declared in class ReproTwo

ReproThree.java:10: error: incompatible types: Object cannot be converted
to V
    return visitOther((Binding) providerBinding);
                     ^
  where V is a type-variable:
    V extends Object declared in class ReproThree