rails--rails/actionpack/lib/action_view/renderable.rb

module ActionView
  module Renderable
    # NOTE: The template that this mixin is beening include into is frozen
    # So you can not set or modify any instance variables

    def self.included(base)
      @@mutex = Mutex.new
    end

    include ActiveSupport::Memoizable

    def handler
      Template.handler_class_for_extension(extension)
    end
    memorize :handler

    def compiled_source
      handler.new(nil).compile(self) if handler.compilable?
    end
    memorize :compiled_source

    def render(view, local_assigns = {})
      view._first_render ||= self
      view._last_render = self
      view.send(:evaluate_assigns)
      compile(local_assigns) if handler.compilable?
      handler.new(view).render(self, local_assigns)
    end

    def method(local_assigns)
      if local_assigns && local_assigns.any?
        local_assigns_keys = "locals_#{local_assigns.keys.map { |k| k.to_s }.sort.join('_')}"
      end
      ['_run', extension, method_segment, local_assigns_keys].compact.join('_').to_sym
    end

    private
      # Compile and evaluate the template's code
      def compile(local_assigns)
        render_symbol = method(local_assigns)

        @@mutex.synchronize do
          return false unless recompile?(render_symbol)

          locals_code = local_assigns.keys.map { |key| "#{key} = local_assigns[:#{key}];" }.join

          source = <<-end_src
            def #{render_symbol}(local_assigns)
              old_output_buffer = output_buffer;#{locals_code};#{compiled_source}
            ensure
              self.output_buffer = old_output_buffer
            end
          end_src

          begin
            file_name = respond_to?(:filename) ? filename : 'compiled-template'
            ActionView::Base::CompiledTemplates.module_eval(source, file_name, 0)
          rescue Exception => e # errors from template code
            if logger = ActionController::Base.logger
              logger.debug "ERROR: compiling #{render_symbol} RAISED #{e}"
              logger.debug "Function body: #{source}"
              logger.debug "Backtrace: #{e.backtrace.join("\n")}"
            end

            raise ActionView::TemplateError.new(self, {}, e)
          end
        end
      end

      # Method to check whether template compilation is necessary.
      # The template will be compiled if the file has not been compiled yet, or
      # if local_assigns has a new key, which isn't supported by the compiled code yet.
      def recompile?(symbol)
        meth = Base::CompiledTemplates.instance_method(template.method) rescue nil
        !(meth && Base.cache_template_loading)
      end
  end
end