Description Till Brychcy 2015-05-11 04:39:21 EDT

DESCRIPTION:
With Java8 TYPE_USE Annotations:

public abstract class GenericType<T extends @org.eclipse.jdt.annotation.NonNull Runnable> {
	abstract T get();
}
—
import static org.eclipse.jdt.annotation.DefaultLocation.*;
@org.eclipse.jdt.annotation.NonNullByDefault({ARRAY_CONTENTS,FIELD,PARAMETER,RETURN_TYPE,TYPE_ARGUMENT,TYPE_BOUND,TYPE_PARAMETER})
public class WildcardUsage {
	void fails(GenericType<?> p) {p.get().run();}
	void works(GenericType<@org.eclipse.jdt.annotation.NonNull ?> p) {p.get().run();}
}

Leads to the Error Message for them method „fails":
Null constraint mismatch: The type '?' is not a valid substitute for the type parameter 'T extends @NonNull Runnable'

As I understand the Wildcard operator, it should get the @NonNull from GenericType (just as it gets "extends Runnable")

As you can see, no possible value of DefaultLocation with NonNullByDefault at "Usage" fixes this.

Especially, if @NonNullByDefault with no args is used in GenericType, this error appears, because the default includes DefaultLocation.TYPE_BOUND,
which means that this problem is quite annoying.

Possible Workarounds:
- Add @NonNull in front of every single Wildcard usage, like in method „works“ 
- Remove DefaultLocation.TYPE_BOUND from the default value of NonNullByDefault. (which is what we do).