ADDITIONAL SYSTEM INFORMATION :
docker image of openjdk:8

A DESCRIPTION OF THE PROBLEM :
In case a filter method which is invoked in an unchecked manner, the collect(Collector col) fails to compile. For instance, given the attached code, the compiler will fail with this error: error: incompatible types: Object cannot be converted to Collection<Target>
                .collect( Collectors.toList());

even if the compiler is instructed to ignore the unchecked code warnings using the -Xlint:unchecked flag.

The code compiles fine (with the right warning) in the openjdk 10 branch.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
javac StreamBugCase.java

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
compiles with warnings
ACTUAL -
doesn't compile

---------- BEGIN SOURCE ----------
import java.util.Collection;
import java.util.stream.Collectors;

public class StreamBugCase
{
    Class clazz;
    Collection<Target> targets;

    public Collection<Target> getTargets()
    {
        Collection<Target> myTargets = targets.stream()
                .filter( t -> t.isApplicable( clazz ) )
                .collect( Collectors.toList() );
        return myTargets;
    }

    public interface Target
    {
        boolean isApplicable(Class<? extends MainType> clazz);
    }

    public interface MainType
    {
    }
}
---------- END SOURCE ----------

FREQUENCY : always