format lookup for partials is derived from the format in which the template is being rendered

Closes rails#5025 part 2

Author: spastorino

actionmailer/lib/action_mailer/collector.rb

@@ -22,9 +22,9 @@ def any(*args, &block)
 
     def custom(mime, options={})
       options.reverse_merge!(:content_type => mime.to_s)
-      @context.freeze_formats([mime.to_sym])
+      @context.formats = [mime.to_sym]
       options[:body] = block_given? ? yield : @default_render.call
       @responses << options
     end
   end
-end
+end

actionpack/lib/action_controller/metal/mime_responds.rb

@@ -280,7 +280,7 @@ def retrieve_collector_from_mimes(mimes=nil, &block) #:nodoc:
 
       if format
         self.content_type ||= format.to_s
-        lookup_context.freeze_formats([format.to_sym])
+        lookup_context.formats = [format.to_sym]
         collector
       else
         head :not_acceptable

actionpack/lib/action_controller/metal/rendering.rb

@@ -14,7 +14,7 @@ def process_action(*) #:nodoc:
     def render(*args) #:nodoc:
       raise ::AbstractController::DoubleRenderError if response_body
       super
-      self.content_type ||= Mime[formats.first].to_s
+      self.content_type ||= Mime[lookup_context.rendered_format].to_s
       response_body
     end
 

actionpack/lib/action_view/lookup_context.rb

@@ -9,7 +9,7 @@ module ActionView
   # generate a key, given to view paths, used in the resolver cache lookup. Since
   # this key is generated just once during the request, it speeds up all cache accesses.
   class LookupContext #:nodoc:
-    attr_accessor :prefixes
+    attr_accessor :prefixes, :rendered_format
 
     mattr_accessor :fallbacks
     @@fallbacks = FallbackFileSystemResolver.instances
@@ -170,23 +170,15 @@ def normalize_name(name, prefixes) #:nodoc:
 
     def initialize(view_paths, details = {}, prefixes = [])
       @details, @details_key = {}, nil
-      @frozen_formats, @skip_default_locale = false, false
+      @skip_default_locale = false
       @cache = true
       @prefixes = prefixes
+      @rendered_format = nil
 
       self.view_paths = view_paths
       initialize_details(details)
     end
 
-    # Freeze the current formats in the lookup context. By freezing them, you are guaranteeing
-    # that next template lookups are not going to modify the formats. The controller can also
-    # use this, to ensure that formats won't be further modified (as it does in respond_to blocks).
-    def freeze_formats(formats, unless_frozen=false) #:nodoc:
-      return if unless_frozen && @frozen_formats
-      self.formats = formats
-      @frozen_formats = true
-    end
-
     # Override formats= to expand ["*/*"] values and automatically
     # add :html as fallback to :js.
     def formats=(values)

actionpack/lib/action_view/renderer/abstract_renderer.rb

@@ -1,7 +1,7 @@
 module ActionView
   class AbstractRenderer #:nodoc:
     delegate :find_template, :template_exists?, :with_fallbacks, :update_details,
-      :with_layout_format, :formats, :freeze_formats, :to => :@lookup_context
+      :with_layout_format, :formats, :to => :@lookup_context
 
     def initialize(lookup_context)
       @lookup_context = lookup_context

actionpack/lib/action_view/renderer/template_renderer.rb

@@ -6,7 +6,8 @@ def render(context, options)
       @view    = context
       @details = extract_details(options)
       template = determine_template(options)
-      freeze_formats(template.formats, true)
+      @lookup_context.rendered_format ||= template.formats.first
+      @lookup_context.formats = template.formats
       render_template(template, options[:layout], options[:locals])
     end
 

actionpack/lib/action_view/template.rb

@@ -159,17 +159,12 @@ def mime_type
     # virtual path set (true just for inline templates).
     def refresh(view)
       raise "A template needs to have a virtual path in order to be refreshed" unless @virtual_path
-      begin
-        lookup  = view.lookup_context
-        pieces  = @virtual_path.split("/")
-        name    = pieces.pop
-        partial = !!name.sub!(/^_/, "")
-        previous_formats, lookup.formats = lookup.formats, @formats
-        lookup.disable_cache do
-          lookup.find_template(name, [ pieces.join('/') ], partial, @locals)
-        end
-      ensure
-        lookup.formats = previous_formats
+      lookup  = view.lookup_context
+      pieces  = @virtual_path.split("/")
+      name    = pieces.pop
+      partial = !!name.sub!(/^_/, "")
+      lookup.disable_cache do
+        lookup.find_template(name, [ pieces.join('/') ], partial, @locals)
       end
     end
 

actionpack/lib/action_view/template/handlers/erb.rb

@@ -44,10 +44,6 @@ class ERB
         class_attribute :erb_trim_mode
         self.erb_trim_mode = '-'
 
-        # Default format used by ERB.
-        class_attribute :default_format
-        self.default_format = Mime::HTML
-
         # Default implementation used.
         class_attribute :erb_implementation
         self.erb_implementation = Erubis

actionpack/test/fixtures/test/one.html.erb

@@ -0,0 +1 @@
+<%= render :partial => "test/two" %> world

actionpack/test/template/lookup_context_test.rb

@@ -78,9 +78,9 @@ def teardown
   end
 
   test "found templates respects given formats if one cannot be found from template or handler" do
-    ActionView::Template::Handlers::ERB.expects(:default_format).returns(nil)
+    ActionView::Template::Handlers::Builder.expects(:default_format).returns(nil)
     @lookup_context.formats = [:text]
-    template = @lookup_context.find("hello_world", %w(test))
+    template = @lookup_context.find("hello", %w(test))
     assert_equal [:text], template.formats
   end