Rubyonrails 如何检测导致 Rake 中的弃用警告的原因

当我做bundle exec rake -T次(或bundle exec rake次)时，我会收到弃用警告:

Andrews-Air:nabu agrimm$ bundle exec rake --trace -T
[DEPRECATION] `last_comment` is deprecated.  Please use `last_description` instead.
[DEPRECATION] `last_comment` is deprecated.  Please use `last_description` instead.
[DEPRECATION] `last_comment` is deprecated.  Please use `last_description` instead.
[DEPRECATION] `last_comment` is deprecated.  Please use `last_description` instead.
[DEPRECATION] `last_comment` is deprecated.  Please use `last_description` instead.
[DEPRECATION] `last_comment` is deprecated.  Please use `last_description` instead.
[DEPRECATION] `last_comment` is deprecated.  Please use `last_description` instead.
[DEPRECATION] `last_comment` is deprecated.  Please use `last_description` instead.
[DEPRECATION] `last_comment` is deprecated.  Please use `last_description` instead.
[DEPRECATION] `last_comment` is deprecated.  Please use `last_description` instead.
rake about                               # List versions of all Rails frameworks and the environment
[snip]

虽然不是很相关，但这里有一个文件:

source 'https://rubygems.org'

gem 'rails', '~> 3.2.22.2'

gem 'mysql2'

group :assets do
  gem 'coffee-rails', '~> 3.2.1'
  gem 'compass-rails'

  gem 'therubyracer'
  gem 'libv8'

  gem 'uglifier', '>= 1.0.3'
end

gem 'jquery-rails'
gem 'haml-rails'
gem 'to-csv', :require => 'to_csv'
gem 'kaminari'
gem 'oai'
gem 'analytical'

gem 'country-select'
gem 'activeadmin'
gem 'sass-rails',  '~> 3.2.3'
gem 'meta_search', '>= 1.1.0.pre'

gem 'devise', '2.2.3'
gem 'cancancan', '~> 1.12.0'

gem 'squeel'
gem 'nilify_blanks'

gem 'sunspot_rails'
gem 'sunspot_solr'

gem 'unicorn'

gem 'ruby-filemagic'

gem 'capistrano'
gem 'capistrano-ext'
gem 'capistrano-unicorn'

gem 'rollbar', '~> 2.8.3'
gem 'newrelic_rpm'

gem 'progress_bar'
gem 'paper_trail', '~> 2'
gem 'quiet_assets'
gem 'roo', '~> 2.1.0'
gem 'roo-xls', :github => 'roo-rb/roo-xls', :ref => '0a5ef88'
gem 'streamio-ffmpeg'
gem 'rake'

gem 'rmagick'

gem 'whenever', :require => false

group :development, :test do
  gem 'turn', '~> 0.8.3', :require => false
  gem 'rspec-rails', '~> 2.0'
  gem 'sextant'
  gem 'thin'

  gem 'spring'
  gem 'spring-commands-rspec'

  gem 'pry'
  gem 'pry-rails'

  gem 'letter_opener'

  gem 'guard-bundler'
  gem 'guard-rails'
  gem 'guard-rspec'
  gem 'guard-sunspot'

  gem 'rb-inotify', :require => RUBY_PLATFORM.include?('linux') ? 'rb-inotify' : false
  gem 'rb-fsevent', :require => RUBY_PLATFORM.include?('darwin') ? 'rb-fsevent' : false
end

group :development do
  gem 'annotate'
  gem 'binding_of_caller'
  gem 'better_errors'
  gem 'rubocop'
end

group :test do
  gem 'capybara'
  gem 'poltergeist'
  gem 'factory_girl_rails'
  gem 'database_cleaner'
  gem 'email_spec'
  gem 'launchy'
end

做git grep -i last_comment表示它不在我的代码中——可能是在第三方的gem中.

我如何找出导致弃用警告的原因？