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

module ActionView
  # NOTE: The template that this mixin is being included into is frozen
  # so you cannot set or modify any instance variables
  module Renderable #:nodoc:
    extend ActiveSupport::Memoizable

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

    def filename
      'compiled-template'
    end

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

    def compiled_source
      handler.call(self)
    end
    memoize :compiled_source

    def render(view, local_assigns = {})
      compile(local_assigns)

      stack = view.instance_variable_get(:@_render_stack)
      stack.push(self)

      # This is only used for TestResponse to set rendered_template
      unless is_a?(InlineTemplate) || view.instance_variable_get(:@_first_render)
        view.instance_variable_set(:@_first_render, self)
      end

      view.send(:_evaluate_assigns_and_ivars)
      view.send(:_set_controller_content_type, mime_type) if respond_to?(:mime_type)

      result = view.send(method_name(local_assigns), local_assigns) do |*names|
        ivar = :@_proc_for_layout
        if !view.instance_variable_defined?(:"@content_for_#{names.first}") && view.instance_variable_defined?(ivar) && (proc = view.instance_variable_get(ivar))
          view.capture(*names, &proc)
        elsif view.instance_variable_defined?(ivar = :"@content_for_#{names.first || :layout}")
          view.instance_variable_get(ivar)
        end
      end

      stack.pop
      result
    end

    def method_name(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 (if necessary)
      def compile(local_assigns)
        render_symbol = method_name(local_assigns)

        @@mutex.synchronize do
          if recompile?(render_symbol)
            compile!(render_symbol, local_assigns)
          end
        end
      end

      def compile!(render_symbol, local_assigns)
        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
          ActionView::Base::CompiledTemplates.module_eval(source, filename, 0)
        rescue Exception => e # errors from template code
          if logger = defined?(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

      # 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)
        !Base::CompiledTemplates.method_defined?(symbol) || !loaded?
      end
  end
end