class ActiveRecord::Associations::Builder::CollectionAssociation

def wrap_block_extension
  if block_extension
    @extension_module = mod = Module.new(&block_extension)
    silence_warnings do
      model.parent.const_set(extension_module_name, mod)
    end
    prev_scope = @scope
    if prev_scope
      @scope = proc { |owner| instance_exec(owner, &prev_scope).extending(mod) }
    else
      @scope = proc { extending(mod) }
    end
  end
end