Fix all the errors to get our tests green on Rails 5.1.

lib/topic_query.rb

@@ -266,9 +266,7 @@ class TopicQuery
 
   def list_category_topic_ids(category)
     query = default_results(category: category.id)
-    pinned_ids = query.where('pinned_at IS NOT NULL AND category_id = ?', category.id)
-      .limit(nil)
-      .order('pinned_at DESC').pluck(:id)
+    pinned_ids = query.where('pinned_at IS NOT NULL AND category_id = ?', category.id).limit(nil).order('pinned_at DESC').pluck(:id)
     non_pinned_ids = query.where('pinned_at IS NULL OR category_id <> ?', category.id).pluck(:id)
     (pinned_ids + non_pinned_ids)
   end
@@ -311,7 +309,7 @@ class TopicQuery
     if page == 0
       (pinned_topics + unpinned_topics)[0...limit] if limit
     else
-      offset = (page * per_page) - pinned_topics.count
+      offset = (page * per_page) - pinned_topics.length
       offset = 0 unless offset > 0
       unpinned_topics.offset(offset).to_a
     end
@@ -559,7 +557,7 @@ class TopicQuery
           end
         elsif @options[:no_tags]
           # the following will do: ("topics"."id" NOT IN (SELECT DISTINCT "topic_tags"."topic_id" FROM "topic_tags"))
-          result = result.where.not(id: TopicTag.select(:topic_id).uniq)
+          result = result.where.not(id: TopicTag.distinct.pluck(:topic_id))
         end
       end
 
@@ -576,7 +574,6 @@ class TopicQuery
       end
 
       result = result.limit(options[:per_page]) unless options[:limit] == false
-
       result = result.visible if options[:visible]
       result = result.where.not(topics: { id: options[:except_topic_ids] }).references(:topics) if options[:except_topic_ids]