Overriding "respond_to?" in java fails to be recognized

[HoneyryderChuck]

Coming these issues in the protobuf project (environment details inside).

Is this something that the jruby team can help unblock?

[JasonLunn]

Moving description of the issue originally captured in protocolbuffers/protobuf#9668 here.

JRuby Version: 9.3.3.0

Given a JRuby class defined in Java e.g.

import org.jruby.anno.JRubyMethod;
import org.jruby.anno.JRubyClass;
import org.jruby.RubyObject;
import org.jruby.Ruby;
import org.jruby.RubyClass;
import org.jruby.RubyModule;
import org.jruby.runtime.Helpers;
import org.jruby.runtime.Block;
import org.jruby.runtime.builtin.IRubyObject;
import org.jruby.runtime.ThreadContext;
import org.jruby.runtime.ObjectAllocator;
import org.jruby.runtime.load.BasicLibraryService;

public class RespondToJavaService implements BasicLibraryService  {

  @Override
  public boolean basicLoad(Ruby ruby) throws IOException {
    ruby.defineModule("Foo").defineClassUnder("Bar", ruby.getObject(), new ObjectAllocator() {
      @Override
      public IRubyObject allocate(Ruby runtime, RubyClass klazz) {
        return new RespondTo(runtime, klazz);
      }
    }).defineAnnotatedMethods(RespondTo.class);
    return true;
  }

  @JRubyClass(name = "RespondTo")
  public static class RespondTo extends RubyObject {

    public RespondTo(Ruby runtime, RubyClass klazz) {
      super(runtime, klazz);
    }

    @JRubyMethod(name = "respond_to?", required = 1, optional = 1)
    public IRubyObject respondTo(ThreadContext context, IRubyObject[] args) {
      System.err.println("Custom repond_to? got called!");
      return Helpers.invokeSuper(context, this, metaClass, "respond_to?", args, Block.NULL_BLOCK);
    }
  }
}

The same behavior is observed when binding a static method:

import java.io.IOException;

import org.jruby.anno.JRubyMethod;
import org.jruby.anno.JRubyClass;
import org.jruby.RubyObject;
import org.jruby.Ruby;
import org.jruby.RubyClass;
import org.jruby.RubyModule;
import org.jruby.runtime.Helpers;
import org.jruby.runtime.Block;
import org.jruby.runtime.builtin.IRubyObject;
import org.jruby.runtime.ThreadContext;
import org.jruby.runtime.ObjectAllocator;
import org.jruby.runtime.load.BasicLibraryService;

public class RespondToJavaService implements BasicLibraryService  {

  @Override
  public boolean basicLoad(Ruby ruby) throws IOException {
    ruby.defineModule("Foo").defineClassUnder("Bar", ruby.getObject(), new ObjectAllocator() {
      @Override
      public IRubyObject allocate(Ruby runtime, RubyClass klazz) {
        return new RespondTo(runtime, klazz);
      }
    }).defineAnnotatedMethods(RespondTo.class);
    return true;
  }

  @JRubyClass(name = "RespondTo")
  public static class RespondTo extends RubyObject {

    public RespondTo(Ruby runtime, RubyClass klazz) {
      super(runtime, klazz);
    }

    @JRubyMethod(name = "respond_to?", required = 1, optional = 1)
    public static IRubyObject respondTo(ThreadContext context, IRubyObject self, IRubyObject[] args) {
      System.err.println("Custom repond_to? got called!");
      String methodName = args[0].asJavaString();
      return self.getMetaClass().respondsToMethod(methodName, true) ? context.runtime.getTrue() : context.runtime.getFalse();
    }
  }
}

*** What did you expect to see
jruby -r ./respond_to_java.jar -e 'Foo::Bar.new.respond_to? :baz' should emit Custom repond_to? got called!

*** What did you see instead?
jruby -r ./respond_to_java.jar -e 'Foo::Bar.new.respond_to? :baz' emits nothing on the first example, but works on the second example, except if jruby is invoked with -X-C.
jruby -r ./respond_to_java.jar -e 'Foo::Bar.new.respond_to? :baz, :beep' does emit Custom repond_to? got called!
Invocations with more than 2 or fewer than 1 arguments raise ArgumentErrors as expected.

[JasonLunn]

@headius suggested the following workaround that explicitly sets isBuiltin to false on the method, and for now that works for me regardless of whether -X-C is passed to the JRuby CLI:

import java.io.IOException;

import org.jruby.anno.JRubyMethod;
import org.jruby.anno.JRubyClass;
import org.jruby.RubyObject;
import org.jruby.Ruby;
import org.jruby.RubyClass;
import org.jruby.RubyModule;
import org.jruby.runtime.Helpers;
import org.jruby.runtime.Block;
import org.jruby.runtime.builtin.IRubyObject;
import org.jruby.runtime.ThreadContext;
import org.jruby.runtime.ObjectAllocator;
import org.jruby.runtime.load.BasicLibraryService;

public class RespondToJavaService implements BasicLibraryService  {

  @Override
  public boolean basicLoad(Ruby ruby) throws IOException {
    RubyClass bar = ruby.defineModule("Foo").defineClassUnder("Bar", ruby.getObject(), new ObjectAllocator() {
      @Override
      public IRubyObject allocate(Ruby runtime, RubyClass klazz) {
        return new RespondTo(runtime, klazz);
      }
    });
    bar.defineAnnotatedMethods(RespondTo.class);
    bar.searchMethod("respond_to?").setIsBuiltin(false);

    return true;
  }

  @JRubyClass(name = "RespondTo")
  public static class RespondTo extends RubyObject {

    public RespondTo(Ruby runtime, RubyClass klazz) {
      super(runtime, klazz);
    }

    @JRubyMethod(name = "respond_to?", required = 1, optional = 1)
    public IRubyObject respondTo(ThreadContext context, IRubyObject[] args) {
      System.err.println("Custom repond_to? got called!");
      return Helpers.invokeSuper(context, this, metaClass, "respond_to?", args, Block.NULL_BLOCK);
    }
  }
}

[headius]

This should be fixed by #7156 for JRuby 9.3.5 and future versions.

[headius]

Perhaps someone could contribute a test case for this and method_missing and perhaps other Object/Kernel methods that could be overridden in Java? Help prevent us breaking user-custom versions of these methods in the future!