don't filter tags by taggable type

Due to performance reasons we cannot use the type filter on the tags.
The table for ActsAsTaggableOn is too big and too unoptimized, such that
the queries time out on production.

See the discussion
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/19740#note_120087938
for more info.

app/controllers/admin/runners_controller.rb

@@ -49,7 +49,7 @@ class Admin::RunnersController < Admin::ApplicationController
   end
   def tag_list
-    tags = Autocomplete::ActsAsTaggableOn::TagsFinder.new(taggable_type: Ci::Runner, params: params).execute
+    tags = Autocomplete::ActsAsTaggableOn::TagsFinder.new(params: params).execute
     render json: ActsAsTaggableOn::TagSerializer.new.represent(tags)
   end

app/finders/autocomplete/acts_as_taggable_on/tags_finder.rb

@@ -5,30 +5,19 @@ module Autocomplete
     class TagsFinder
       LIMIT = 20
-      def initialize(taggable_type:, params:)
-        @taggable_type = taggable_type
+      def initialize(params:)
         @params = params
       end
       def execute
         @tags = ::ActsAsTaggableOn::Tag.all
-        filter_by_taggable_type!
         search!
         limit!
         @tags
       end
-      def filter_by_taggable_type!
-        # rubocop: disable CodeReuse/ActiveRecord
-        @tags = @tags
-          .joins(:taggings)
-          .where(taggings: { taggable_type: @taggable_type.name })
-          .distinct
-        # rubocop: enable CodeReuse/ActiveRecord
-      end
-
       def search!
         search = @params[:search]

spec/finders/autocomplete/acts_as_taggable_on/tags_finder_spec.rb

@@ -6,10 +6,10 @@ describe Autocomplete::ActsAsTaggableOn::TagsFinder do
   describe '#execute' do
     context 'with empty params' do
       it 'returns all tags' do
-        create :ci_runner, tag_list: ['tag1']
-        create :ci_runner, tag_list: ['tag2']
-        tags = described_class.new(taggable_type: Ci::Runner, params: {}).execute.map(&:name)
+        ActsAsTaggableOn::Tag.create!(name: 'tag1')
+        ActsAsTaggableOn::Tag.create!(name: 'tag2')
+        tags = described_class.new(params: {}).execute.map(&:name)
         expect(tags).to match_array %w(tag1 tag2)
       end
@@ -18,10 +18,10 @@ describe Autocomplete::ActsAsTaggableOn::TagsFinder do
     context 'filter by search' do
       context 'with an empty search term' do
         it 'returns an empty collection' do
-          create :ci_runner, tag_list: ['tag1']
-          create :ci_runner, tag_list: ['tag2']
-          tags = described_class.new(taggable_type: Ci::Runner, params: { search: '' }).execute.map(&:name)
+          ActsAsTaggableOn::Tag.create!(name: 'tag1')
+          ActsAsTaggableOn::Tag.create!(name: 'tag2')
+          tags = described_class.new(params: { search: '' }).execute.map(&:name)
           expect(tags).to be_empty
         end
@@ -29,10 +29,10 @@ describe Autocomplete::ActsAsTaggableOn::TagsFinder do
       context 'with a search containing 2 characters' do
         it 'returns the tag that strictly matches the search term' do
-          create :ci_runner, tag_list: ['t1']
-          create :ci_runner, tag_list: ['t11']
-          tags = described_class.new(taggable_type: Ci::Runner, params: { search: 't1' }).execute.map(&:name)
+          ActsAsTaggableOn::Tag.create!(name: 't1')
+          ActsAsTaggableOn::Tag.create!(name: 't11')
+          tags = described_class.new(params: { search: 't1' }).execute.map(&:name)
           expect(tags).to match_array ['t1']
         end
@@ -40,10 +40,10 @@ describe Autocomplete::ActsAsTaggableOn::TagsFinder do
       context 'with a search containing 3 characters' do
         it 'returns the tag that partially matches the search term' do
-          create :ci_runner, tag_list: ['tag1']
-          create :ci_runner, tag_list: ['tag11']
-          tags = described_class.new(taggable_type: Ci::Runner, params: { search: 'ag1' }).execute.map(&:name)
+          ActsAsTaggableOn::Tag.create!(name: 'tag1')
+          ActsAsTaggableOn::Tag.create!(name: 'tag11')
+          tags = described_class.new(params: { search: 'ag1' }).execute.map(&:name)
           expect(tags).to match_array %w(tag1 tag11)
         end
@@ -54,10 +54,10 @@ describe Autocomplete::ActsAsTaggableOn::TagsFinder do
       it 'limits the result set by the limit constant' do
         stub_const("#{described_class}::LIMIT", 1)
-        create :ci_runner, tag_list: ['tag1']
-        create :ci_runner, tag_list: ['tag2']
-        tags = described_class.new(taggable_type: Ci::Runner, params: { search: 'tag' }).execute
+        ActsAsTaggableOn::Tag.create!(name: 'tag1')
+        ActsAsTaggableOn::Tag.create!(name: 'tag2')
+        tags = described_class.new(params: { search: 'tag' }).execute
         expect(tags.count).to eq 1
       end