Description Stephan Herrmann 2015-05-05 14:02:42 EDT

This is a subset of bug 427423:

With compiler configured for null type annotations, and this code:

//---
package m7test;

import java.util.Set;
import java.util.function.*;
import java.util.stream.*;

import org.eclipse.jdt.annotation.NonNull;
public class StreamTest2 {
	void test(Stream<@NonNull String> s) {
		s.collect(new Collector<@NonNull String, Object, Integer>() {
			@Override
			public Supplier<Object> supplier() {
				return null;
			}
			@Override
			public BiConsumer<Object, String> accumulator() {
				return null;
			}
			@Override
			public BinaryOperator<Object> combiner() {
				return null;
			}
			@Override
			public Function<Object, Integer> finisher() {
				return null;
			}
			@Override
			public Set<java.util.stream.Collector.Characteristics> characteristics() {
				return null;
			}
		});
	}
}
//---

compiler correctly complains against the return type of accumulator():

The return type is incompatible with 'BiConsumer<Object,@NonNull String>' returned from Collector<String,Object,Integer>.accumulator() (mismatching null constraints)

The offered quick fix ("Change return type of accumulator(..) to '@NonNull'"), however, is wrong, producing
   public @NonNull BiConsumer<Object, String> accumulator()
instead of
   public BiConsumer<Object, @NonNull String> accumulator()


While bug 427423 is about more sophisticated quick fixes, that RFE isn't going to make it for Mars.

I should, however, try to suppress the quick fix when it is about to propose junk.