make action and fragment caching of rails3 compatible with content_for

rails content_for caching

module ActionController

  class Metal
    attr_internal :cached_content_for
  end

  module Caching
    module Actions
      def _save_fragment(name, options)
        return unless caching_allowed?

        content = response_body
        content = content.join if content.is_a?(Array)
        content = cached_content_for.merge(:layout => content) if cached_content_for.is_a?(Hash)

        write_fragment(name, content, options)
      end
    end

    module Fragments
      def write_fragment_with_content_to_cache(key, content, options = nil)
        return_content = write_fragment_without_content_to_cache(key, content, options) 
        return_content.is_a?(Hash) ? return_content[:layout] : return_content
      end

      def read_fragment_with_content_to_cache(key, options = nil)
        result = read_fragment_without_content_to_cache(key, options)
        if (result.is_a?(Hash))
          result = result.dup if result.frozen?
          fragment = result.delete(:layout)
          self.cached_content_for = (self.cached_content_for || {}).merge(result)
          result = fragment
        end

        result.respond_to?(:html_safe) ? result.html_safe : result
      end

      alias_method_chain :write_fragment, :content_to_cache
      alias_method_chain :read_fragment, :content_to_cache
    end 
  end
end

module ActionView
  module Rendering
    # Added to support implementation of action caching
    def _render_template_with_cached_content_for(template, layout = nil, options = {})
      if controller.respond_to?('caching_allowed?') && controller.caching_allowed?
        controller.cached_content_for.each { |k, v| content_for(k, v) unless content_for?(k) } if controller.cached_content_for.is_a?(Hash)
        return_value = _render_template_without_cached_content_for(template, layout, options)
        controller.cached_content_for = content_to_cache
      elsif
        return_value = _render_template_without_cached_content_for(template, layout, options)
      end
      return_value
    end

    alias_method_chain :_render_template, :cached_content_for
  end

  module Helpers
    module CaptureHelper
      # Added to support implementation of fragment caching
      def cache_with_content_for #:nodoc:#
        @_subset_content_for = Hash.new { |h,k| h[k] = ActiveSupport::SafeBuffer.new }
        yield
      ensure
        @_subset_content_for = nil
      end

      # Added to support implementation of action caching
      def content_to_cache #:nodoc:#
        cache_this = @_subset_content_for || @_content_for.except(:layout)
        cache_this.dup.tap {|h| h.default = nil }
      end

      # Overwrite content_for to support fragment caching
      def content_for(name, content = nil, &block)
        content = capture(&block) if block_given?
        @_content_for[name] << content if content
        @_subset_content_for[name] << content if content && @_subset_content_for
        @_content_for[name] unless content
      end
    end
   
    module CacheHelper
      def fragment_for(name = {}, options = nil, &block) #:nodoc:
        if controller.fragment_exist?(name, options)
          fragment = controller.read_fragment(name, options)
          controller.cached_content_for.each { |k, v| content_for(k, v) unless content_for?(k) } if controller.cached_content_for.is_a?(Hash)
          fragment
        else
          pos = output_buffer.length
          hash_to_cache = nil
          cache_with_content_for do
            yield
            fragment = output_buffer.slice!(pos..-1)
            hash_to_cache = {:layout => fragment}.merge(content_to_cache)
          end
          controller.write_fragment(name, hash_to_cache, options)
        end
      end
    end 
  end
end

All right, I finally got this working on Rails 5.2 (which is the version I'm still on).

Here is my fork/patch , and a demo app that uses it.

Now to submit a merge request to rails (see feature proposal) ...

I've submitted a pull request here, in case you're interested: rails/rails#39600