Using Redcarpet and Middleman Syntax for Markdown and HAML files

config.rb

class CustomMarkdown < Middleman::Extension
  $markdown_options = {
    autolink:           true,
    fenced_code_blocks: true,
    no_intra_emphasis:  true,
    strikethrough:      true,
    tables:             true,
    hard_wrap:          true,
    with_toc_data:      true
  }
  
  # Markdown files
  def initialize(app, options_hash={}, &block)
    super
    app.set :markdown_engine, :redcarpet
    app.set :markdown, $markdown_options
  end

  # HAML Markdown filter
  module Haml::Filters
    remove_filter("Markdown")

    module Markdown
      include Haml::Filters::Base

      def render text
        markdown.render text
      end

      class MarkdownRenderer < Redcarpet::Render::HTML
        def block_code(code, language)
          Middleman::Syntax::Highlighter.highlight(code.force_encoding("UTF-8"), language)
        end
      end

      private

      def markdown
        @markdown ||= Redcarpet::Markdown.new MarkdownRenderer.new($markdown_options), $markdown_options
      end
    end
  end

  # TOC helper
  helpers do
    # Based on https://github.com/vmg/redcarpet/pull/186#issuecomment-22783188
    def toc(page)
      html_toc = Redcarpet::Markdown.new(Redcarpet::Render::HTML_TOC)
      file = ::File.read(page.source_file)

      # remove YAML frontmatter
      file = file.gsub(/^(---\s*\n.*?\n?)^(---\s*$\n?)/m,'')
  
      # quick fix for HAML: remove :markdown filter and indentation
      file = file.gsub(/:markdown\n/,'')
      file = file.gsub(/\t/,'')

      html_toc.render file
    end
  end
end

::Middleman::Extensions.register(:custom_markdown, CustomMarkdown)

activate :custom_markdown
activate :syntax, :line_numbers => true