FIX: categories created by users who are deleted cannot be deleted

lib/user_destroyer.rb

@@ -42,6 +42,19 @@ class UserDestroyer
             b.record_match! if b
           end
           Post.with_deleted.where(user_id: user.id).update_all("user_id = NULL")
+
+          # If this user created categories, fix those up:
+          categories = Category.where(user_id: user.id).all
+          categories.each do |c|
+            c.user_id = Discourse.system_user.id
+            c.save!
+            if topic = Topic.with_deleted.where(id: c.topic_id).first
+              topic.try(:recover!)
+              topic.user_id = Discourse.system_user.id
+              topic.save!
+            end
+          end
+
           StaffActionLogger.new(@staff).log_user_deletion(user, opts.slice(:context))
           DiscourseHub.unregister_nickname(user.username) if SiteSetting.call_discourse_hub?
           MessageBus.publish "/file-change", ["refresh"], user_ids: [user.id]

spec/components/user_destroyer_spec.rb

@@ -238,6 +238,17 @@ describe UserDestroyer do
         UserDestroyer.new(@admin).destroy(@user, {block_ip: true})
       end
     end
+
+    context 'user created a category' do
+      let!(:category) { Fabricate(:category, user: @user) }
+
+      it "assigns the system user to the categories" do
+        UserDestroyer.new(@admin).destroy(@user, {delete_posts: true})
+        category.reload.user_id.should == Discourse.system_user.id
+        category.topic.should be_present
+        category.topic.user_id.should == Discourse.system_user.id
+      end
+    end
   end
 
 end