code: private String generatedBuilderSimpleName(TypeElement type) {
      String packageName = elements.getPackageOf(type).getQualifiedName().toString();
      String originalName = type.getQualifiedName().toString();
      checkState(originalName.startsWith(packageName + "."));
      String nameWithoutPackage = originalName.substring(packageName.length() + 1);
      return String.format(BUILDER_SIMPLE_NAME_TEMPLATE, nameWithoutPackage.replaceAll("\\.", "_"));
    }
docs: Returns the simple name of the builder class that should be generated for the given type.
  
  <p>This is simply the {@link #BUILDER_SIMPLE_NAME_TEMPLATE} with the original type name
  substituted in. (If the original type is nested, its enclosing classes will be included,
  separated with underscores, to ensure uniqueness.)