FIX: wrongs counts on tags with deleted topics

app/models/tag.rb

@@ -12,7 +12,7 @@ class Tag < ActiveRecord::Base
   has_many :tag_group_memberships
   has_many :tag_groups, through: :tag_group_memberships
 
-  COUNT_ARG = "topic_tags.id"
+  COUNT_ARG = "topics.id"
 
   # Apply more activerecord filters to the tags_by_count_query, and then
   # fetch the result with .count(Tag::COUNT_ARG).
@@ -20,9 +20,9 @@ class Tag < ActiveRecord::Base
   # e.g., Tag.tags_by_count_query.where("topics.category_id = ?", category.id).count(Tag::COUNT_ARG)
   def self.tags_by_count_query(opts = {})
     q = Tag.joins("LEFT JOIN topic_tags ON tags.id = topic_tags.tag_id")
-      .joins("LEFT JOIN topics ON topics.id = topic_tags.topic_id")
+      .joins("LEFT JOIN topics ON topics.id = topic_tags.topic_id AND topics.deleted_at IS NULL")
       .group("tags.id, tags.name")
-      .order('count_topic_tags_id DESC')
+      .order('count_topics_id DESC')
     q = q.limit(opts[:limit]) if opts[:limit]
     q
   end

spec/models/tag_spec.rb

@@ -46,6 +46,17 @@ describe Tag do
         counts = described_class.tags_by_count_query.count(Tag::COUNT_ARG)
         expect(counts[unused.name]).to eq(0)
       end
+
+      it "doesn't include deleted topics in counts" do
+        deleted_topic_tag = Fabricate(:tag)
+        delete_topic = Fabricate(:topic)
+        post = Fabricate(:post, topic: delete_topic, user: delete_topic.user)
+        delete_topic.tags << deleted_topic_tag
+        PostDestroyer.new(Fabricate(:admin), post).destroy
+
+        counts = described_class.tags_by_count_query.count(Tag::COUNT_ARG)
+        expect(counts[deleted_topic_tag.name]).to eq(0)
+      end
     end
   end