An attempt to load only necessary locales on the fly (#2169)

* Defer loading I18n YAML files until actually translating

* Load locale files for available locales only

lib/faker.rb

@@ -8,10 +8,27 @@
 
 Dir.glob(File.join(mydir, 'helpers', '*.rb')).sort.each { |file| require file }
 
-I18n.load_path += Dir[File.join(mydir, 'locales', '**/*.yml')]
-I18n.reload! if I18n.backend.initialized?
-
 module Faker
+  @i18n_loaded = nil
+
+  class << self
+    def load_i18n
+      return if @i18n_loaded
+
+      if I18n.available_locales&.any?
+        # We expect all locale .yml files to have the locale name in its filename
+        I18n.load_path += ::Dir[::File.join(__dir__, 'locales', "{#{I18n.available_locales.join(',')}}.yml")]
+        # Or to be located in a directory with the locale name
+        I18n.load_path += ::Dir[::File.join(__dir__, 'locales', "{#{I18n.available_locales.join(',')}}/*.yml")]
+      else
+        I18n.load_path += ::Dir[::File.join(__dir__, 'locales', '**/*.yml')]
+      end
+
+      I18n.reload! if I18n.backend.initialized?
+      @i18n_loaded = true
+    end
+  end
+
   class Config
     @locale = nil
     @random = nil
@@ -21,6 +38,8 @@ class << self
       attr_writer :random
 
       def locale
+        Faker.load_i18n
+
         # Because I18n.locale defaults to :en, if we don't have :en in our available_locales, errors will happen
         @locale || (I18n.available_locales.include?(I18n.locale) ? I18n.locale : I18n.available_locales.first)
       end
@@ -150,6 +169,8 @@ def parse(key)
       # Call I18n.translate with our configured locale if no
       # locale is specified
       def translate(*args, **opts)
+        Faker.load_i18n
+
         opts[:locale] ||= Faker::Config.locale
         opts[:raise] = true
         I18n.translate(*args, **opts)
@@ -166,6 +187,8 @@ def translate(*args, **opts)
 
       # Executes block with given locale set.
       def with_locale(tmp_locale = nil)
+        Faker.load_i18n
+
         current_locale = Faker::Config.own_locale
         Faker::Config.locale = tmp_locale
 

test/test_locale.rb

@@ -78,4 +78,19 @@ def test_regex
   def test_available_locales
     assert I18n.locale_available?('en-GB')
   end
+
+  def test_load_i18n
+    Faker.instance_variable_set :@i18n_loaded, nil
+    available_locales_was = I18n.available_locales
+
+    I18n.available_locales = %i[en ja id]
+    Faker.load_i18n
+    I18n.eager_load!
+
+    assert Faker.instance_variable_get(:@i18n_loaded)
+    assert_equal %i[en id ja], I18n.backend.translations.keys.sort
+  ensure
+    I18n.available_locales = available_locales_was
+    Faker.instance_variable_set :@i18n_loaded, nil
+  end
 end