code: public static void debugger(String fileName, int lineNumber) {
      logger.log(
          Level.WARNING,
          String.format(
              "Hit {debugger} statement at %s:%d. Put a breakpoint here to halt Soy rendering.",
              fileName, lineNumber),
          new Exception());
    }
docs: Every {@code debugger} statement will call this method. You can use conditional breakpoints
  here to easily stop execution at the right location.