Java 8 compiler bug?

[Oliver Gierke]

Hi all,

I just ran in this code compiling fine with a JDK 8 if I define a compilation source and target of 1.6, but not if I define both values of 1.8.

public class Ambiguity {

	public void foo(CriteriaBuilder builder) {

		Expression<Object> objectExpression = null;
		Expression<Collection<Object>> collectionOfObjectExpression = null;
		builder.isNotMember(objectExpression, collectionOfObjectExpression);
		//      ^^^^^^^^^^^ - ambiguous
	}
}

CriteriaBuilder and all other types come from JPA. The method in question has two overloads:

<E, C extends Collection<E>> Predicate isNotMember(Expression<E> elem, Expression<C> collection);
<E, C extends Collection<E>> Predicate isNotMember(E elem, Expression<C> collection);

I fail to understand why the second method is even considered as that create a contradiction between the bound values of E (Expression<…>) and C (Collection<Object>).

I've prepared an example here [0]. Steps to reproduce:

1. Unzip
2. Run mvn clean compile -> fails
3. Change java.version property in pom.xml to 1.6
4. Run mvn clean compile -> succeeds

$ java -version
java version "1.8.0_112"
Java(TM) SE Runtime Environment (build 1.8.0_112-b16)
Java HotSpot(TM) 64-Bit Server VM (build 25.112-b16, mixed mode)

Is that a known issue, something I oversee or should I create a ticket for that?

Cheers,
Ollie

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