Fix #3952: Adding animated_gif tag to a ugoira post breaks the player.

app/models/post.rb

@@ -201,6 +201,14 @@ class Post < ApplicationRecord
       file_ext =~ /jpg|jpeg|gif|png/i
     end
 
+    def is_png?
+      file_ext =~ /png/i
+    end
+
+    def is_gif?
+      file_ext =~ /gif/i
+    end
+
     def is_flash?
       file_ext =~ /swf/i
     end
@@ -765,6 +773,14 @@ class Post < ApplicationRecord
         tags << "ugoira"
       end
 
+      if !is_gif?
+        tags -= ["animated_gif"]
+      end
+
+      if !is_png?
+        tags -= ["animated_png"]
+      end
+
       return tags
     end
 

test/unit/post_test.rb

@@ -1140,6 +1140,16 @@ class PostTest < ActiveSupport::TestCase
         end
       end
 
+      context "tagged with animated_gif or animated_png" do
+        should "remove the tag if not a gif or png" do
+          @post.update(tag_string: "tagme animated_gif")
+          assert_equal("tagme", @post.tag_string)
+
+          @post.update(tag_string: "tagme animated_png")
+          assert_equal("tagme", @post.tag_string)
+        end
+      end
+
       should "have an array representation of its tags" do
         post = FactoryBot.create(:post)
         post.reload