Use Sourcery to Generate bash script that will rewrite your source code to add final to all classes that have no inheritance

gistfile1.txt

#!/usr/bin/env bash
<% for type in types.classes { -%>
  <%_ if type.modifiers.map{ $0.name }.contains("final") || type.modifiers.map{ $0.name }.contains("open") || types.based[type.name].isEmpty == false { continue } -%>
<%_ _%>git grep -lz 'class <%= type.name %>' | xargs -0 perl -i'' -pE "s/class <%= type.name %>(?=\s|:)/final class <%= type.name %>/g"
<% } %>

// Run with Sourcery on your codebase and then execute generated code via bash :)

Nice one 🎉