Ruby's Error Tree

display-class-hierarchy-tree.rb

#!/usr/bin/env ruby

# A more general case of finding all of the classes in a hierarchy
#
# Inspired by Nick Sieger's excellent article
# http://blog.nicksieger.com/articles/2006/09/06/rubys-exception-hierarchy/
#
top_class             = Exception
prune_below           = [ SystemCallError ]
outer_modules_to_skip = %w[ Gem ]
tree                  = {}

ObjectSpace.each_object(Class) do |cls|
  next unless cls <= top_class
  next if prune_below.any? { |parent| cls < parent }

  outer_module = cls.name.split("::").first
  next if outer_modules_to_skip.include?(outer_module)

  ancestors = cls.ancestors.take_while { |a| a <= top_class }.reverse
  ancestors.inject(tree) { |memo, k| memo[k] ||= {} }
end

indent = 0
tree_printer = Proc.new do |t|
  t.keys.sort { |c1,c2| c1.name <=> c2.name }.each do |k|
    space = (' ' * indent); space ||= ''
    puts space + k.to_s
    indent += 2; tree_printer.(t[k]); indent -= 2
  end
end
tree_printer.(tree)

output.text

Exception
  MonitorMixin::ConditionVariable::Timeout
  NoMemoryError
  ScriptError
    LoadError
    NotImplementedError
    SyntaxError
  SecurityError
  SignalException
    Interrupt
  StandardError
    ArgumentError
    EncodingError
      Encoding::CompatibilityError
      Encoding::ConverterNotFoundError
      Encoding::InvalidByteSequenceError
      Encoding::UndefinedConversionError
    FiberError
    IOError
      EOFError
    IndexError
      KeyError
      StopIteration
    LocalJumpError
    Math::DomainError
    NameError
      NoMethodError
    RangeError
      FloatDomainError
    RegexpError
    RuntimeError
    SystemCallError
    ThreadError
    TypeError
    ZeroDivisionError
  SystemExit
  SystemStackError
  fatal