Duck.java

public interface Duck {
  @AutoImplement(Helper.class) // allowed at class or method level
  void shim(Bar someArg);
  @ManualImplement // to opt out in the case of class-level annotation, assumed by default otherwise
  void implementedByMixin();
}

Helper.java

public final class Helper {
  public static void shim(Minecraft minecraft, Bar someArg) {
    // do stuff
  }
}

Minecraft.java

public class Minecraft implements Duck{
  @Override
  public void shim(Bar someArg) {
    // filled in automatically
    Helper.shim(this, someArg);
  }
  // native for effect, probably wouldn't do it this way
  @Override
  public native void implementedByMixin();
}

MixinMinecraft.java

@Mixin(Minecraft.class)
public abstract class MixinMinecraft implements Shim {
  @Override
  public void implementedByMixin {/**/}
}

shimmagic.meta

magic/v1
[internal|exports] com/example/Duck