private String formatMethodList(ImmutableList<ExecutableElement> methods) {
    return methods.stream().map(this::formatMethodInList).collect(joining());
  }
An annotation processor that validates {@link
com.google.auto.value.extension.toprettystring.ToPrettyString} usage.
value/src/main/java/com/google/auto/value/extension/toprettystring/processor/ToPrettyStringValidator.java