code: public final boolean isNominalConstructor() {
      if (isConstructor() || isInterface()) {
        FunctionType fn = toMaybeFunctionType();
        if (fn == null) {
          return false;
        }
  
        // Programmer-defined constructors will have a link
        // back to the original function in the source tree.
        // Structural constructors will not.
        if (fn.getSource() != null) {
          return true;
        }
  
        // Native constructors are always nominal.
        return fn.isNativeObjectType();
      }
      return false;
    }
docs: Whether this type is the original constructor of a nominal type.
  Does not include structural constructors.