DB: Add `users.bot_type` and index it

Stop using `users.support_bot` which we will remove in a upcoming
release.

db/schema.rb

@@ -3243,8 +3243,10 @@ ActiveRecord::Schema.define(version: 20190404231137) do
     t.string "commit_email"
     t.integer "group_view"
     t.integer "managing_group_id"
+    t.integer "bot_type", limit: 2
     t.index ["accepted_term_id"], name: "index_users_on_accepted_term_id", using: :btree
     t.index ["admin"], name: "index_users_on_admin", using: :btree
+    t.index ["bot_type"], name: "index_users_on_bot_type", using: :btree
     t.index ["confirmation_token"], name: "index_users_on_confirmation_token", unique: true, using: :btree
     t.index ["created_at"], name: "index_users_on_created_at", using: :btree
     t.index ["email"], name: "index_users_on_email", unique: true, using: :btree
@@ -3258,6 +3260,7 @@ ActiveRecord::Schema.define(version: 20190404231137) do
     t.index ["name"], name: "index_users_on_name_trigram", using: :gin, opclasses: {"name"=>"gin_trgm_ops"}
     t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true, using: :btree
     t.index ["state"], name: "index_users_on_state", using: :btree
+    t.index ["state"], name: "index_users_on_state_and_internal", where: "((ghost <> true) AND (bot_type IS NULL))", using: :btree
     t.index ["state"], name: "index_users_on_state_and_internal_attrs", where: "((ghost <> true) AND (support_bot <> true))", using: :btree
     t.index ["support_bot"], name: "index_users_on_support_bot", using: :btree
     t.index ["username"], name: "index_users_on_username", using: :btree

ee/db/migrate/20190401150745_add_users_bot_type.rb

+# frozen_string_literal: true
+
+class AddUsersBotType < ActiveRecord::Migration[5.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def change
+    change_table :users do |t|
+      t.integer :bot_type, limit: 2
+    end
+  end
+end

ee/db/migrate/20190401150746_index_users_bot_type.rb

+# frozen_string_literal: true
+
+class IndexUsersBotType < ActiveRecord::Migration[5.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  class User < ActiveRecord::Base
+    enum bot_type: { support_bot: 1 }
+  end
+
+  def up
+    add_concurrent_index :users, :bot_type
+    add_concurrent_index :users, :state,
+      name: internal_index,
+      where: 'ghost <> true AND bot_type IS NULL'
+
+    User
+      .where(support_bot: true)
+      .update_all(bot_type: User.bot_types[:support_bot])
+  end
+
+  def down
+    User
+      .where(bot_type: User.bot_types[:support_bot])
+      .update_all(support_bot: true)
+
+    remove_concurrent_index :users, :state, name: internal_index
+    remove_concurrent_index :users, :bot_type
+  end
+
+  private
+
+  def internal_index
+    'index_users_on_state_and_internal'
+  end
+end

ee/spec/migrations/index_users_bot_type_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('ee', 'db', 'migrate', '20190401150746_index_users_bot_type.rb')
+
+describe IndexUsersBotType, :migration do
+  BOT_TYPE = {
+    support_bot: 1
+  }.freeze
+
+  let(:migration) { described_class.new }
+  let(:users) { table(:users) }
+
+  let!(:user) { create_user(username: 'test') }
+
+  describe '#up' do
+    let!(:support_bot) do
+      create_user(username: 'support_bot', support_bot: true)
+    end
+
+    it 'converts support_bot column to enum and adds indexes' do
+      migration.up
+
+      expect(user.reload.bot_type).to be_nil
+      expect(support_bot.reload.support_bot).to eq(true)
+      expect(support_bot.reload.bot_type).to eq(BOT_TYPE[:support_bot])
+
+      expect(index_exists?(:bot_type)).to eq(true)
+      expect(index_exists?(:state, name: internal_index)).to eq(true)
+    end
+  end
+
+  describe '#down' do
+    let!(:support_bot) do
+      create_user(username: 'support_bot', bot_type: BOT_TYPE[:support_bot])
+    end
+
+    it 'converts support_bot column to enum and removes indexes' do
+      migration.down
+
+      expect(user.reload.support_bot).to be_nil
+      expect(support_bot.reload.support_bot).to eq(true)
+
+      expect(index_exists?(:bot_type)).to eq(false)
+      expect(index_exists?(:state, name: internal_index)).to eq(false)
+    end
+  end
+
+  private
+
+  def create_user(username:, **params)
+    users.create!(
+      email: "#{username}@example.com",
+      projects_limit: 0,
+      username: username,
+      **params
+    )
+  end
+
+  def index_exists?(column, options = {})
+    migration.index_exists?(:users, column, options)
+  end
+
+  def internal_index
+    'index_users_on_state_and_internal'
+  end
+end