@Override
    public boolean equals(Object o) {
        if ( ! (o instanceof FieldSet other)) return false;
        if ( ! this.name.equals(other.name)) return false;
        if ( ! this.fieldNames.equals(other.fieldNames)) return false;
        return true;
    }
Use a random field in this to determine its properties. Any inconsistency will have been warned about on deploy.
container-search/src/main/java/com/yahoo/search/schema/FieldSet.java