Jekyll Plugin for Textual Inclusion in Data Files

read_data_file_with_liquid.rb

# Treat every _data file as liquid.
# This allows us to include YAML files in other YAML files.
module Jekyll
  # Monkey patch Jekyll::DataReader::read_data_file with our own implementation
  class DataReader
    def read_data_file_with_liquid(path)
      begin
        dir = File.dirname(path)
        filename = File.basename(path)

        # If there are multiple sites assume we're
        # the most recent since we're just starting up
        site = Jekyll.sites.last

        content = File.read(site.in_source_dir(dir, filename))
        template = Liquid::Template.parse(content)

        context = Liquid::Context.new({}, {}, { :site => site })
        rendered = template.render(context)

        # Write the post-liquid-rendered file to a temporary file.
        # read_data_file parses the name of the file to use as its
        # variable name in site.data so it's important to make the
        # temp file name match the original file name.
        Dir.mktmpdir do |tmp_dir|
          tmp_path = File.join(tmp_dir, filename)
          File.write(tmp_path, rendered)
          read_data_file_without_liquid(tmp_path)
        end
      rescue => e
        Jekyll.logger.warn(
          "[Liquid Data] Error parsing data files " +
          "for Liquid content at file #{path}: #{e.message}")
      end
    end

    # Make our function overwrite the existing read_data_file function
    # but keep the ability to still call back to the original
    alias_method :read_data_file_without_liquid, :read_data_file
    alias_method :read_data_file, :read_data_file_with_liquid
  end
end

# Only include the given file one time (in this call tree)
# Useful for files that include files that include the original file
module Jekyll
  module Tags
    class IncludeRelativeOnceTag < IncludeRelativeTag
      # Create a flag that indicates we're already 1 level
      # deep in the inclusion, and don't go any farther down
      SENTINEL = 'included_relative_once'
      def render(context)
        context.stack do
          unless context[SENTINEL]
            context[SENTINEL] = true
            super(context)
          end
        end
      end
    end
  end
end

Liquid::Template.register_tag("include_relative_once", Jekyll::Tags::IncludeRelativeOnceTag)

@dgopstein - Hey! I've been looking for a solution to this problem for ages and so far, this is the closest and best thing I've found. Thanks for putting this together and sharing it :)

I'm not a developer at all - I use Jekyll to write and manage my company's documentation. So while I dabble in Ruby, calling myself proficient would be generous. That being said, I hope you don't mind answering a few questions:

1. I see that this treats every file in _data as a Liquid file - is there a way to exclude files from being read this way? In my setup, I have a lot of data files that don't need this functionality, which is throwing a ton of errors when I start up the server.
2. Is there a way to read YAML that isn't in _data? In my case, I set up a collection that contains files with data about database schemas. This is the only place in my site that I'd like to use this.

Thanks :)