Slightly adapted version of Nick Sieger's script to dump Ruby's exception hierarchy. If run with `bundle exec` or `rails console` the hierarchy will include all exception classes defined in any of the included gems as well. Therefore I found it necessary to determine the common ancestors of the Exception class at run-time rather than hard code t…

exception_hierarchy.rb

def class_hierarchy(root, exclude = [])
  common_ancestors = root.ancestors.drop(1)
  descendants = []
  tree = {}
  ObjectSpace.each_object(Class) do |cls|
    next unless cls.ancestors.include? root
    next if descendants.include? cls
    case exclude
    when Class, Array
      next unless (Array(exclude) & cls.ancestors).empty?
    when Regexp, String
      next if Regexp.compile(exclude).match(cls.to_s)
    end
    descendants << cls
    ancestors = cls.ancestors - common_ancestors
    ancestors.reverse.inject(tree) {|memo,klass| memo[klass] ||= {}}
  end
  tree
end

def print_tree(t, indent = 0)
  t.keys.sort_by(&:name).each do |k|
    puts "  " * indent + k.to_s
    print_tree(t[k], indent + 1)
  end
end
print_tree(class_hierarchy(Exception, /^Errno::/))