You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: postgresql@12.rb
    path of file: ./repos/homebrew-core/Formula/p
    
    the code of the file until where you have to start completion: class PostgresqlAT12 < Formula
  desc "Object-relational database system"
    
  def post_install
    (var/"log").mkpath
    postgresql_datadir.mkpath

    # Don't initialize database, it clashes when testing other PostgreSQL versions.
    return if ENV["HOMEBREW_GITHUB_ACTIONS"]

    system "#{bin}/initdb", "--locale=C", "-E", "UTF-8", postgresql_datadir unless pg_version_exists?
  end