Create templates with format=nil

actionmailer/lib/action_mailer/base.rb

@@ -973,10 +973,11 @@ def collect_responses_from_templates(headers)
         templates_name = headers[:template_name] || action_name
 
         each_template(Array(templates_path), templates_name).map do |template|
-          self.formats = [template.format]
+          format = template.format || self.formats.first
+          self.formats = [format]
           {
             body: render(template: template),
-            content_type: template.type.to_s
+            content_type: Mime[format].to_s
           }
         end
       end

actionview/lib/action_view/rendering.rb

@@ -118,7 +118,8 @@ def _render_template(options)
           renderer.render_to_object(context, options)
         end
 
-        @rendered_format = Template::Types[rendered_template.format]
+        rendered_format = rendered_template.format || lookup_context.formats.first
+        @rendered_format = Template::Types[rendered_format]
 
         rendered_template.body
       end

actionview/lib/action_view/template/resolver.rb

@@ -294,12 +294,12 @@ def extract_handler_and_format_and_variant(path, query_format)
           if handler.respond_to?(:default_format) # default_format can return nil
             handler.default_format
           else
-            query_format
+            nil
           end
         end
 
         # Template::Types[format] and handler.default_format can return nil
-        [handler, format || query_format, variant]
+        [handler, format, variant]
       end
   end
 

actionview/test/template/lookup_context_test.rb

@@ -121,11 +121,11 @@ def teardown
     assert_equal "Hello texty phone!", template.source
   end
 
-  test "found templates respects given formats if one cannot be found from template or handler" do
+  test "found templates have nil format if one cannot be found from template or handler" do
     assert_called(ActionView::Template::Handlers::Builder, :default_format, returns: nil) do
       @lookup_context.formats = [:text]
       template = @lookup_context.find("hello", %w(test))
-      assert_equal :text, template.format
+      assert_nil template.format
     end
   end
 

actionview/test/template/resolver_patterns_test.rb

@@ -19,7 +19,7 @@ def test_should_return_template_for_declared_path
     assert_equal 1, templates.size, "expected one template"
     assert_equal "Hello custom patterns!", templates.first.source
     assert_equal "custom_pattern/path",    templates.first.virtual_path
-    assert_equal :html,                    templates.first.format
+    assert_nil templates.first.format
   end
 
   def test_should_return_all_templates_when_ambiguous_pattern

actionview/test/template/testing/fixture_resolver_test.rb

@@ -15,6 +15,6 @@ def test_should_return_template_for_declared_path
     assert_equal 1, templates.size, "expected one template"
     assert_equal "this text",      templates.first.source
     assert_equal "arbitrary/path", templates.first.virtual_path
-    assert_equal :html,            templates.first.format
+    assert_nil templates.first.format
   end
 end