make erb engine configurable

lib/middleman.rb

@@ -73,6 +73,7 @@ module Middleman
     autoload :Sass,         "middleman/renderers/sass"
     autoload :Slim,         "middleman/renderers/slim"
     autoload :Markdown,     "middleman/renderers/markdown"
+    autoload :ERb,          "middleman/renderers/erb"
     autoload :CoffeeScript, "middleman/renderers/coffee_script"
     autoload :Liquid,       "middleman/renderers/liquid"
   end

lib/middleman/core_extensions/front_matter.rb

@@ -101,6 +101,9 @@ module Middleman::CoreExtensions::FrontMatter
   class ERBTemplate < ::Tilt::ERBTemplate
     include Middleman::CoreExtensions::FrontMatter::YamlAware
   end
+  class ErubisTemplate < ::Tilt::ErubisTemplate
+    include Middleman::CoreExtensions::FrontMatter::YamlAware
+  end
 
   class LiquidTemplate < ::Tilt::LiquidTemplate
     include Middleman::CoreExtensions::FrontMatter::YamlAware

lib/middleman/core_extensions/rendering.rb

@@ -11,6 +11,7 @@ module Middleman::CoreExtensions::Rendering
       app.register Middleman::Renderers::Haml
       app.register Middleman::Renderers::Sass
       app.register Middleman::Renderers::Markdown
+      app.register Middleman::Renderers::ERb
       app.register Middleman::Renderers::CoffeeScript
       app.register Middleman::Renderers::Liquid
     end

lib/middleman/renderers/erb.rb

@@ -0,0 +1,34 @@
+require "tilt"
+
+module Middleman::Renderers::ERb
+  class << self
+    def registered(app)
+      app.extend ClassMethods
+      
+      app.set :erb_engine, :erb
+      
+      if !app.respond_to? :erb_engine_prefix
+        app.set :erb_engine_prefix, ::Tilt
+      end
+      
+      app.after_configuration do
+        engine = app.settings.erb_engine
+        
+        if engine.is_a? Symbol
+          engine = app.tilt_template_from_symbol(engine)
+        end
+        
+        ::Tilt.prefer(engine)
+      end
+    end
+    alias :included :registered
+  end
+  
+  module ClassMethods
+    def tilt_template_from_symbol(engine)
+      engine = engine.to_s
+      engine = engine == "erb" ? "ERB" : engine.camelize
+      settings.erb_engine_prefix.const_get("#{engine}Template")
+    end
+  end
+end