Fix permalinks for all markdown sources

config.rb

@@ -1,3 +1,5 @@
+require 'lib/gfm_ids.rb'
+
 activate :bh
 
 set :css_dir, 'stylesheets'
@@ -18,6 +20,7 @@
 set :markdown, { fenced_code_blocks: true, with_toc_data: true }
 set :markdown_engine, :redcarpet
 activate :rouge_syntax
+activate :gfm_ids
 
 page '/documentation/*', :layout => 'documentation'
 

lib/gfm_ids.rb

@@ -0,0 +1,30 @@
+require 'middleman-core'
+require 'nokogiri'
+
+
+# Updates IDs from Markdown headings to be GFM compatible
+class GFMIDs < Middleman::Extension
+  def initialize(app, options={})
+    super
+
+    app.after_render do |content, path, locs, template_class|
+      if template_class == Middleman::Renderers::RedcarpetTemplate
+        document = Nokogiri::HTML(content)
+
+        document.css('h1, h2, h3, h4, h5, h6').each do |node|
+          node.attributes['id'].value = node.content
+            .downcase
+            .gsub(/[^\p{Alnum} -]/, '')  # Remove non-alpha numeric characters
+            .tr(' ', '-')  # Replace spaces with dashes
+        end
+
+        document.to_s
+      else
+        nil
+      end
+    end
+  end
+end
+
+
+::Middleman::Extensions.register(:gfm_ids, GFMIDs)