Do not cache dynamic attachment styles

lib/paperclip/attachment.rb

@@ -64,7 +64,7 @@ def initialize name, instance, options = {}
     end
 
     def styles
-      unless @normalized_styles
+      if @styles.respond_to?(:call) || !@normalized_styles
         @normalized_styles = {}
         (@styles.respond_to?(:call) ? @styles.call(self) : @styles).each do |name, args|
           @normalized_styles[name] = Paperclip::Style.new(name, args.dup, self)

test/attachment_test.rb

@@ -287,6 +287,24 @@ def thumb; "-thumb"; end
       assert_equal "50x50#", @attachment.styles[:thumb][:geometry]
     end
   end
+
+  context "An attachment with conditional :styles that is a proc" do
+    setup do
+      rebuild_model :styles => lambda{ |attachment| attachment.instance.other == 'a' ? {:thumb => "50x50#"} : {:large => "400x400"} }
+
+      @dummy = Dummy.new(:other => 'a')
+    end
+
+    should "have the correct styles for the assigned instance values" do
+      assert_equal "50x50#", @dummy.avatar.styles[:thumb][:geometry]
+      assert_nil @dummy.avatar.styles[:large]
+
+      @dummy.other = 'b'
+
+      assert_equal "400x400", @dummy.avatar.styles[:large][:geometry]
+      assert_nil @dummy.avatar.styles[:thumb]
+    end
+  end
 
   context "An attachment with :url that is a proc" do
     setup do