code: Type unaryPromotion(Type t) {
          Type unboxed = types.unboxedTypeOrType(t);
          switch (unboxed.getTag()) {
              case BYTE:
              case SHORT:
              case CHAR:
                  return syms.intType;
              default:
                  return unboxed;
          }
      }
docs: Perform unary promotion of a type; this routine implements JLS 5.6.1.
  If the input type is not supported by unary promotion, it is returned unaltered.