linktag.rb • 2015 Oct 21 • mahiwaga

I wrote a custom Liquid tag for writing standalone links with their associated metadata like so:

<a href="http://url" title="title • subtitle • date • author • site">title</a> • subtitle • date • author • site

…using this syntax:

{% link url: "url", title: "title", subtitle: "subtitle", date: "date", author: "author", site: "site" %}

All the parameters except for the URL and the title are optional (although you probably don’t need this tag if that’s all you’re going to use anyway.) You can also include variables instead of strings. And you can put Liquid tags inside the strings.

{% link url: post.url, title: post.title, date: post.date, author: post.author, site: site.title %}

{% link url: "url", title: "{{ post.title }} • {{ post.description }}", date: "date", site: site.title %}

Place the following file in the _plugins directory:

module Jekyll

  class LinkTag < Liquid::Tag
    include Jekyll::LiquidExtensions
        
    def initialize(tag_name, markup, tokens)
      super
      @attributes = { 'separator' => ' • ' }
      
      markup.scan(Liquid::TagAttributes) do |key, value|
        @attributes[key] = value
      end
    end

    def expression_parse(context, markup)
      case markup
      when /\A'(.*)'\z/m # Single quoted strings
        $1
      when /\A"(.*)"\z/m # Double quoted strings
        $1
      else
        lookup_variable(context, markup)
      end
    end
    
    def render(context)
      url = expression_parse(context, @attributes['url'])
      attribute_list = [@attributes['title'], @attributes['subtitle'], @attributes['date'], @attributes['author'], @attributes['site']].reject{ |attribute| attribute.nil? or attribute.empty? }
      attribute_list.map! { |attribute|
        Liquid::Template.parse(expression_parse(context, attribute)).render(context)
      }
      html = [%Q(<a href="#{url}" title="#{attribute_list.join(@attributes['separator'])}">#{attribute_list.first}</a>), attribute_list.drop(1)].join(@attributes['separator'])

    end
  end
end

Liquid::Template.register_tag('link', Jekyll::LinkTag)

At the very least, this can serve as an example of how to parse named tag parameters and how to pass variable names