class_ancestors.rb

module A
  def func
    p 'A'
    super
  end
end

class B
  def func
    p 'B'
    super
  end
end

class C < B
  def func
    p 'C'
    super
  end
end

B.include A

p C.ancestors # [C, B, A, Object, Kernel, BasicObject]
C.new.func # "C", "B", "A", "no superclass method `func'"

module_missing_ancestors.rb

module A
  def func
    p 'A'
    super
  end
end

module B
  def func
    p 'B'
    super
  end
end

class C
  include B

  def func
    p 'C'
    super
  end
end

B.include A

p B.ancestors # [B, A]

# NOTE: A is missing!
p C.ancestors # [C, B, Object, Kernel, BasicObject]

C.new.func # "C", "B", "no superclass method `func'"

module_predictable_ancestors.rb

module A
  def func
    p 'A'
    super
  end
end

module B
  include A

  def func
    p 'B'
    super
  end
end

class C
  include B

  def func
    p 'C'
    super
  end
end

p B.ancestors # [B, A]
p C.ancestors # [C, B, A, Object, Kernel, BasicObject]
C.new.func # "C", "B", "A", "no superclass method `func'"