Unsoundness in MustCallChecker (and RLC) for functional interfaces

This example creates a Closeable functional interface and makes new instances of it in a few sneaky ways:

• normal inner class
• inline inner class
• anonymous class
• lambda expression
• method reference

// Test that the correct type is assigned to instantiations of functional
// interfaces.

import java.io.Closeable;
import org.checkerframework.checker.mustcall.qual.*;

public abstract class FunctionalInterfaces {

  @FunctionalInterface
  public interface Actor extends Closeable {
    void act();

    @Override
    default void close() {
    }
  }

  public static class ActorImpl implements Actor {
    @Override
    public void act() {
    }
  }

  public abstract void run(@MustCall({}) Actor a);

  public static void method() {
  }

  public void normalConstruction() {

    // :: error: (assignment)
    @MustCall({}) Actor a = new ActorImpl();

  }

  public void inlineClass() {

    class ActorImplInline implements Actor {
      @Override
      public void act() {
      }
    }

    // :: error: (assignment)
    @MustCall({}) Actor a = new ActorImplInline();

  }

  public void anonymousClass() {

    // :: error: (assignment)
    @MustCall({}) Actor a = new Actor() {
      public void act() {
      }
    };

  }

  public void lambda() {

    // :: error: (assignment)
    @MustCall({}) Actor a = () -> {
    };

  }

  public void methodRef() {

    // :: error: (assignment)
    @MustCall({}) Actor a = FunctionalInterfaces::method;

  }

}

I would expect all 5 cases would report an error, but only the first two do:

checker/tests/mustcall/FunctionalInterfaces.java:32: error: [assignment] incompatible types in assignment.
    @MustCall({}) Actor a = new ActorImpl();
                            ^
  found   : @MustCall("close") ActorImpl
  required: @MustCall Actor
checker/tests/mustcall/FunctionalInterfaces.java:45: error: [assignment] incompatible types in assignment.
    @MustCall({}) Actor a = new ActorImplInline();
                            ^
  found   : @MustCall FunctionalInterfaces.@MustCall("close") ActorImplInline
  required: @MustCall Actor
2 errors

I did my best to debug this one, but the problem actually seems to be in the "framework" part of the Checker Framework, and not in the Must Call Checker specifically---although I'm not quite knowledgeable enough to know for sure. It seems like new ClassName() is always assigned the correct type @MustCall({"close"}), but other ways of constructing an instance of the class do not get the right inherited annotations.

Start with checker/tests/mustcall/FunctionalInterfaces.java and run the reproducer, comparing normal, inline, anonymous, lambda, and method-reference construction. Trace how the framework and MustCallChecker/RLC assign inherited annotations; done means all five cases report the expected assignment error.