Add ActionView::Base.default_formats

default_formats array is used by LookupContext in order to allow
rendering templates when :formats option is not passed. Previously it
was always set to Mime::SET, which created dependency on Action Pack. In
order to remove this dependency, Mime::SET is used only if
ActionController is loaded.

actionpack/lib/action_dispatch.rb

@@ -101,3 +101,7 @@ module ActionDispatch
 end
 
 autoload :Mime, 'action_dispatch/http/mime_type'
+
+ActiveSupport.on_load(:action_view) do
+  ActionView::Base.default_formats ||= Mime::SET.symbols
+end

actionpack/lib/action_view/base.rb

@@ -146,6 +146,9 @@ module ActionView #:nodoc:
     cattr_accessor :prefix_partial_path_with_controller_namespace
     @@prefix_partial_path_with_controller_namespace = true
 
+    # Specify default_formats that can be rendered.
+    cattr_accessor :default_formats
+
     class_attribute :_routes
     class_attribute :logger
 

actionpack/lib/action_view/lookup_context.rb

@@ -43,7 +43,7 @@ module ActionView
     end
 
     register_detail(:locale)  { [I18n.locale, I18n.default_locale].uniq }
-    register_detail(:formats) { Mime::SET.symbols }
+    register_detail(:formats) { ActionView::Base.default_formats || [:html, :text, :js, :css,  :xml, :json] }
     register_detail(:handlers){ Template::Handlers.extensions }
 
     class DetailsKey #:nodoc:

actionpack/test/template/lookup_context_test.rb

@@ -11,6 +11,17 @@ class LookupContextTest < ActiveSupport::TestCase
     I18n.locale = :en
   end
 
+  test "allows to override default_formats with ActionView::Base.default_formats" do
+    begin
+      formats = ActionView::Base.default_formats
+      ActionView::Base.default_formats = [:foo, :bar]
+
+      assert_equal [:foo, :bar], ActionView::LookupContext.new([]).default_formats
+    ensure
+      ActionView::Base.default_formats = formats
+    end
+  end
+
   test "process view paths on initialization" do
     assert_kind_of ActionView::PathSet, @lookup_context.view_paths
   end