ActionMailer should respect content type when choosing layouts

Signed-off-by: Pratik Naik <pratiknaik@gmail.com>

actionmailer/lib/action_mailer/base.rb

@@ -549,7 +549,12 @@ def initialize_defaults(method_name)
       end
 
       def render_message(method_name, body)
+        if method_name.respond_to?(:content_type)
+          @current_template_content_type = method_name.content_type
+        end
         render :file => method_name, :body => body
+      ensure
+        @current_template_content_type = nil
       end
 
       def render(opts)
@@ -568,7 +573,11 @@ def render(opts)
       end
 
       def default_template_format
-        :html
+        if @current_template_content_type
+          Mime::Type.lookup(@current_template_content_type).to_sym
+        else
+          :html
+        end
       end
 
       def candidate_for_layout?(options)
@@ -588,7 +597,9 @@ def template_path
       end
 
       def initialize_template_class(assigns)
-        ActionView::Base.new(view_paths, assigns, self)
+        template = ActionView::Base.new(view_paths, assigns, self)
+        template.template_format = default_template_format
+        template
       end
 
       def sort_parts(parts, order = [])

actionmailer/test/fixtures/auto_layout_mailer/multipart.text.html.erb

@@ -0,0 +1 @@
+text/html multipart

actionmailer/test/fixtures/auto_layout_mailer/multipart.text.plain.erb

@@ -0,0 +1 @@
+text/plain multipart

actionmailer/test/fixtures/layouts/auto_layout_mailer.text.erb

@@ -0,0 +1 @@
+text/plain layout - <%= yield %>

actionmailer/test/mail_layout_test.rb

@@ -20,6 +20,12 @@ def nolayout(recipient)
     from       "tester@example.com"
     body       render(:inline => "Hello, <%= @world %>", :layout => false, :body => { :world => "Earth" })
   end
+
+  def multipart(recipient)
+    recipients recipient
+    subject    "You have a mail"
+    from       "tester@example.com"
+  end
 end
 
 class ExplicitLayoutMailer < ActionMailer::Base
@@ -56,6 +62,17 @@ def test_should_pickup_default_layout
     assert_equal "Hello from layout Inside", mail.body.strip
   end
 
+  def test_should_pickup_multipart_layout
+    mail = AutoLayoutMailer.create_multipart(@recipient)
+    assert_equal 2, mail.parts.size
+
+    assert_equal 'text/plain', mail.parts.first.content_type
+    assert_equal "text/plain layout - text/plain multipart", mail.parts.first.body
+
+    assert_equal 'text/html', mail.parts.last.content_type
+    assert_equal "Hello from layout text/html multipart", mail.parts.last.body
+  end
+
   def test_should_pickup_layout_given_to_render
     mail = AutoLayoutMailer.create_spam(@recipient)
     assert_equal "Spammer layout Hello, Earth", mail.body.strip