Ensure details are frozen after @details_keys lookup. The implementat…

…ion waits to freeze until the last required moment, to avoid duping hashes.

actionmailer/lib/action_mailer/base.rb

@@ -591,7 +591,7 @@ def collect_responses_and_parts_order(headers) #:nodoc:
       responses, parts_order = [], nil
 
       if block_given?
-        collector = ActionMailer::Collector.new(self) { render(action_name) }
+        collector = ActionMailer::Collector.new(lookup_context) { render(action_name) }
         yield(collector)
         parts_order = collector.responses.map { |r| r[:content_type] }
         responses  = collector.responses

actionmailer/lib/action_mailer/collector.rb

@@ -22,8 +22,7 @@ def any(*args, &block)
 
     def custom(mime, options={})
       options.reverse_merge!(:content_type => mime.to_s)
-      @context.formats = [mime.to_sym]
-      @context.formats.freeze
+      @context.freeze_formats([mime.to_sym])
       options[:body] = block_given? ? yield : @default_render.call
       @responses << options
     end

actionpack/lib/action_controller/metal/mime_responds.rb

@@ -262,8 +262,7 @@ def retrieve_response_from_mimes(mimes=nil, &block)
 
       if format = request.negotiate_mime(collector.order)
         self.content_type ||= format.to_s
-        self.formats = [format.to_sym]
-        self.formats.freeze
+        lookup_context.freeze_formats([format.to_sym])
         collector.response_for(format)
       else
         head :not_acceptable

actionpack/lib/action_view/lookup_context.rb

@@ -23,9 +23,12 @@ def #{name}
 
         def #{name}=(value)
           value = Array.wrap(value.presence || _#{name}_defaults)
-          @details_key = nil unless value == @details[:#{name}]
-          # Always set the value to handle frozen arrays
-          @details[:#{name}] = value
+
+          if value != @details[:#{name}]
+            @details_key = nil
+            @details = @details.dup if @details.frozen?
+            @details[:#{name}] = value.freeze
+          end
         end
       METHOD
     end
@@ -45,7 +48,7 @@ class DetailsKey #:nodoc:
       @details_keys = Hash.new
 
       def self.get(details)
-        @details_keys[details] ||= new
+        @details_keys[details.freeze] ||= new
       end
 
       def initialize
@@ -55,6 +58,7 @@ def initialize
 
     def initialize(view_paths, details = {})
       @details, @details_key = { :handlers => default_handlers }, nil
+      @frozen_formats = false
       self.view_paths = view_paths
       self.update_details(details, true)
     end
@@ -127,6 +131,15 @@ def details_key #:nodoc:
         @details_key ||= DetailsKey.get(@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
+
       # Overload formats= to reject [:"*/*"] values.
       def formats=(value)
         value = nil    if value == [:"*/*"]

actionpack/lib/action_view/render/rendering.rb

@@ -21,7 +21,7 @@ def render(options = {}, locals = {}, &block)
           _render_partial(options)
         else
           template = _determine_template(options)
-          _freeze_formats(template.formats)
+          lookup_context.freeze_formats(template.formats, true)
           _render_template(template, options[:layout], options)
         end
       when :update
@@ -62,14 +62,5 @@ def _render_template(template, layout = nil, options = {}) #:nodoc:
         content
       end
     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) #:nodoc:
-      return if self.formats.frozen?
-      self.formats = formats
-      self.formats.freeze
-    end
   end
 end