Java 8 compiler bug?

[Oliver Gierke]

I've just found myself running into another (but apparently similar issue), again using types from JPA. Here's a Gist example:

public class Ambiguity {

	// JPA replica types

	interface Attribute<T, S> {}

	interface PluralAttribute<T, S, U> extends Attribute<T, S> {}

	interface SetAttribute<T, S> extends PluralAttribute<T, Set<S>, S> {}

	// User code

	static <A extends Attribute<T, S>, T, S> void path(A attribute) {}

	static <P extends PluralAttribute<T, ?, S>, T, S> void path(P attribute) {}

	// Call creating ambiguity with source/target 1.8, compiling fine with source/target 1.6

	public void bar(SetAttribute<String, String> attribute) {
		path(attribute);
	}
}

> Am 16.11.2016 um 01:45 schrieb Jonathan Gibbons <jonathan.gibbons at oracle.com>:
> 
> Thanks for the reduced test case.
> 
> -- Jon
> 
> On 11/15/2016 04:32 PM, Oliver Gierke wrote:
>> I wasn't sure whether any specialty of the types involved is causing the issue, that's why I kept the JPA dependency in the first place. But this piece of code shows the same characteristics:
>> 
>> public class Ambiguity {
>> 
>> 	public void foo(CriteriaBuilder builder) {
>> 
>> 		Expression<Object> objectExpression = null;
>> 		Expression<Collection<Object>> collectionOfObjectExpression = null;
>> 		builder.isNotMember(objectExpression, collectionOfObjectExpression);
>> 	}
>> 
>> 	interface Expression<T> {}
>> 
>> 	interface CriteriaBuilder {
>> 
>> 		<E, C extends Collection<E>> void isNotMember(E elem, Expression<C> collection);
>> 
>> 		<E, C extends Collection<E>> void isNotMember(Expression<E> elem, Expression<C> collection);
>> 	}
>> }
>> 
>>> Am 16.11.2016 um 00:54 schrieb Jonathan Gibbons <jonathan.gibbons at oracle.com>:
>>> 
>>> Can you simplify your example down to something that doesn't require us to download a zip file?
>>> 
>>> -- Jon
>>> 
>>> On 11/15/2016 03:49 PM, Oliver Gierke wrote:
>>>> Sorry, I forgot the link to the reproducing example:
>>>> 
>>>> https://dl.dropboxusercontent.com/u/25310722/compiler-ambiguity.zip
>>>> 
>>>>> Anfang der weitergeleiteten Nachricht:
>>>>> 
>>>>> Von: Oliver Gierke <ogierke at pivotal.io>
>>>>> Betreff: Java 8 compiler bug?
>>>>> Datum: 16. November 2016 um 00:46:02 MEZ
>>>>> An: compiler-dev at openjdk.java.net
>>>>> 
>>>>> 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
>>>>> 
>>>> --
>>>> /**
>>>>  * @author Oliver Gierke - Senior Software Engineer
>>>>  *
>>>>  * @param email ogierke at pivotal.io
>>>>  * @param phone +49-151-50465477
>>>>  * @param fax   +49-351-418898439
>>>>  * @param skype einsdreizehn
>>>>  * @see http://www.olivergierke.de
>>>>  */
>>>> 
>> --
>> /**
>>  * @author Oliver Gierke - Senior Software Engineer
>>  *
>>  * @param email ogierke at pivotal.io
>>  * @param phone +49-151-50465477
>>  * @param fax   +49-351-418898439
>>  * @param skype einsdreizehn
>>  * @see http://www.olivergierke.de
>>  */
>> 
> 

--
/**
 * @author Oliver Gierke - Senior Software Engineer
 *
 * @param email ogierke at pivotal.io
 * @param phone +49-151-50465477
 * @param fax   +49-351-418898439
 * @param skype einsdreizehn
 * @see http://www.olivergierke.de
 */

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