find unused columns: ignore one column at a time and see if tests still pass

01 ignore columns initializer.rb

class ActiveRecord::Base
  def self.columns
    super.reject do |column|
      "#{table_name}.#{column.name}" == ENV['IGNORE_COLUMN']
    end
  end
end

02 list columns.rb

#sequel
DB.tables.each { |table| DB[table].columns.each { |column| puts "#{table}.#{column}" } }

03 columns.rb

File.open('../unnecessary-columns.txt', 'w') do |file|
  file.sync = true
  ARGF.readlines.shuffle.each do |line|
    line.chomp!
    puts line
    file.puts line if system("IGNORE_COLUMN=#{line} bundle exec rspec spec --fail-fast")
  end
end

04 watch.sh

watch "cat unnecessary-columns.txt"