Demonstration of a weird bug in Ruby 1.9.

example.rb

module MyModule
  def some_method; super; end
end

class MyBaseClass; end

class MySubClass < MyBaseClass;
  include MyModule
end

# To trigger this bug, we must include the module in the base class after
# the module has already been included in the subclass.  If we move this line
# above the subclass declaration, this bug will not occur.
MyBaseClass.send(:include, MyModule)

MySubClass.new.some_method

ruby 1.8 output

➜ ruby --version
ruby 1.8.7 (2011-02-18 patchlevel 334) [i686-darwin10.6.0]
➜ ruby example.rb 
example.rb:2:in `some_method': super: no superclass method `some_method' for #<MySubClass:0x1001bc2d0> (NoMethodError)
	from example.rb:2:in `some_method'
	from example.rb:13

ruby 1.9 output

➜ ruby --version
ruby 1.9.2p180 (2011-02-18 revision 30909) [x86_64-darwin10.6.0]
➜ ruby example.rb 
example.rb:2: stack level too deep (SystemStackError)

UGH, just spent WAAAY too much time debugging this bug myself while upgrading some code to ruby 1.9.

As a note for those using rspec < 2.6, a workaround is to use the syck YAML parser instead of psych, which is a new default in ruby 1.9. If you can upgrade your rspec version, that's definitely the best way, as syck has issues of its own.

Oh yeah, it's apparently slated to be fixed in 1.9.4.

http://bugs.ruby-lang.org/issues/3351

Yuck!