A DESCRIPTION OF THE PROBLEM :
javax.lang.model.element.ModuleElement#getDirectives returns duplicates

a example directive looks like this in the module-info

 provides javax.sound.midi.spi.MidiDeviceProvider with
        com.sun.media.sound.MidiInDeviceProvider,
        com.sun.media.sound.MidiOutDeviceProvider,
        com.sun.media.sound.RealTimeSequencerProvider,
        com.sun.media.sound.SoftProvider;

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
mvn clean install for the complete Project is all that is needed. Annotation processors are basically Compiler plugins. The Code in "processor" will get executed when "processed" gets build.


@SupportedSourceVersion(SourceVersion.RELEASE_11)
@SupportedAnnotationTypes("*")
public class Processor extends AbstractProcessor
{
   @Override
   public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv)
   {
      if (!roundEnv.processingOver())
      {
         return false;
      }

      ModuleElement javaDesktop = processingEnv.getElementUtils().getModuleElement("java.desktop");
      javaDesktop.getDirectives()
                 .stream()
                 .filter(directive -> directive.getKind().equals(ModuleElement.DirectiveKind.PROVIDES))
                 .map(ModuleElement.ProvidesDirective.class::cast)
                 .filter(providesDirective -> providesDirective.getService()
                                                               .getQualifiedName()
                                                               .toString()
                                                               .equals("javax.sound.midi.spi.MidiDeviceProvider"))
                 .forEach(providesDirective -> processingEnv.getMessager()
                                                            .printMessage(Diagnostic.Kind.MANDATORY_WARNING, providesDirective.toString()));

      return false;
   }
}

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
[WARNING] Provides[javax.sound.midi.spi.MidiDeviceProvider,com.sun.media.sound.MidiInDeviceProvider,com.sun.media.sound.MidiOutDeviceProvider,com.sun.media.sound.RealTimeSequencerProvider,com.sun.media.sound.SoftProvider]
ACTUAL -
[WARNING] Provides[javax.sound.midi.spi.MidiDeviceProvider,com.sun.media.sound.MidiInDeviceProvider]
[WARNING] Provides[javax.sound.midi.spi.MidiDeviceProvider,com.sun.media.sound.MidiInDeviceProvider,com.sun.media.sound.MidiOutDeviceProvider]
[WARNING] Provides[javax.sound.midi.spi.MidiDeviceProvider,com.sun.media.sound.MidiInDeviceProvider,com.sun.media.sound.MidiOutDeviceProvider,com.sun.media.sound.RealTimeSequencerProvider]
[WARNING] Provides[javax.sound.midi.spi.MidiDeviceProvider,com.sun.media.sound.MidiInDeviceProvider,com.sun.media.sound.MidiOutDeviceProvider,com.sun.media.sound.RealTimeSequencerProvider,com.sun.media.sound.SoftProvider]

---------- BEGIN SOURCE ----------
See attached zip file.

@SupportedSourceVersion(SourceVersion.RELEASE_11)
@SupportedAnnotationTypes("*")
public class Processor extends AbstractProcessor
{
   @Override
   public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv)
   {
      if (!roundEnv.processingOver())
      {
         return false;
      }

      ModuleElement javaDesktop = processingEnv.getElementUtils().getModuleElement("java.desktop");
      javaDesktop.getDirectives()
                 .stream()
                 .filter(directive -> directive.getKind().equals(ModuleElement.DirectiveKind.PROVIDES))
                 .map(ModuleElement.ProvidesDirective.class::cast)
                 .filter(providesDirective -> providesDirective.getService()
                                                               .getQualifiedName()
                                                               .toString()
                                                               .equals("javax.sound.midi.spi.MidiDeviceProvider"))
                 .forEach(providesDirective -> processingEnv.getMessager()
                                                            .printMessage(Diagnostic.Kind.MANDATORY_WARNING, providesDirective.toString()));

      return false;
   }
}
---------- END SOURCE ----------

FREQUENCY : always