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lazy_loadable.rb
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lazy_loadable.rb
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# frozen_string_literal: true
module I18n
module Backend
# Backend that lazy loads translations based on the current locale. This
# implementation avoids loading all translations up front. Instead, it only
# loads the translations that belong to the current locale. This offers a
# performance incentive in local development and test environments for
# applications with many translations for many different locales. It's
# particularly useful when the application only refers to a single locales'
# translations at a time (ex. A Rails workload). The implementation
# identifies which translation files from the load path belong to the
# current locale by pattern matching against their path name.
#
# Specifically, a translation file is considered to belong to a locale if:
# a) the filename is in the I18n load path
# b) the filename ends in a supported extension (ie. .yml, .json, .po, .rb)
# c) the filename starts with the locale identifier
# d) the locale identifier and optional proceeding text is separated by an underscore, ie. "_".
#
# Examples:
# Valid files that will be selected by this backend:
#
# "files/locales/en_translation.yml" (Selected for locale "en")
# "files/locales/fr.po" (Selected for locale "fr")
#
# Invalid files that won't be selected by this backend:
#
# "files/locales/translation-file"
# "files/locales/en-translation.unsupported"
# "files/locales/french/translation.yml"
# "files/locales/fr/translation.yml"
#
# The implementation uses this assumption to defer the loading of
# translation files until the current locale actually requires them.
#
# The backend has two working modes: lazy_load and eager_load.
#
# Note: This backend should only be enabled in test environments!
# When the mode is set to false, the backend behaves exactly like the
# Simple backend, with an additional check that the paths being loaded
# abide by the format. If paths can't be matched to the format, an error is raised.
#
# You can configure lazy loaded backends through the initializer or backends
# accessor:
#
# # In test environments
#
# I18n.backend = I18n::Backend::LazyLoadable.new(lazy_load: true)
#
# # In other environments, such as production and CI
#
# I18n.backend = I18n::Backend::LazyLoadable.new(lazy_load: false) # default
#
class LocaleExtractor
class << self
def locale_from_path(path)
name = File.basename(path, ".*")
locale = name.split("_").first
locale.to_sym unless locale.nil?
end
end
end
class LazyLoadable < Simple
def initialize(lazy_load: false)
@lazy_load = lazy_load
end
# Returns whether the current locale is initialized.
def initialized?
if lazy_load?
initialized_locales[I18n.locale]
else
super
end
end
# Clean up translations and uninitialize all locales.
def reload!
if lazy_load?
@initialized_locales = nil
@translations = nil
else
super
end
end
# Eager loading is not supported in the lazy context.
def eager_load!
if lazy_load?
raise UnsupportedMethod.new(__method__, self.class)
else
super
end
end
# Parse the load path and extract all locales.
def available_locales
if lazy_load?
I18n.load_path.map { |path| LocaleExtractor.locale_from_path(path) }
else
super
end
end
def lookup(locale, key, scope = [], options = EMPTY_HASH)
if lazy_load?
I18n.with_locale(locale) do
super
end
else
super
end
end
protected
# Load translations from files that belong to the current locale.
def init_translations
file_errors = if lazy_load?
initialized_locales[I18n.locale] = true
load_translations_and_collect_file_errors(filenames_for_current_locale)
else
@initialized = true
load_translations_and_collect_file_errors(I18n.load_path)
end
raise InvalidFilenames.new(file_errors) unless file_errors.empty?
end
def initialized_locales
@initialized_locales ||= Hash.new(false)
end
private
def lazy_load?
@lazy_load
end
class FilenameIncorrect < StandardError
def initialize(file, expected_locale, unexpected_locales)
super "#{file} can only load translations for \"#{expected_locale}\". Found translations for: #{unexpected_locales}."
end
end
# Loads each file supplied and asserts that the file only loads
# translations as expected by the name. The method returns a list of
# errors corresponding to offending files.
def load_translations_and_collect_file_errors(files)
errors = []
load_translations(files) do |file, loaded_translations|
assert_file_named_correctly!(file, loaded_translations)
rescue FilenameIncorrect => e
errors << e
end
errors
end
# Select all files from I18n load path that belong to current locale.
# These files must start with the locale identifier (ie. "en", "pt-BR"),
# followed by an "_" demarcation to separate proceeding text.
def filenames_for_current_locale
I18n.load_path.flatten.select do |path|
LocaleExtractor.locale_from_path(path) == I18n.locale
end
end
# Checks if a filename is named in correspondence to the translations it loaded.
# The locale extracted from the path must be the single locale loaded in the translations.
def assert_file_named_correctly!(file, translations)
loaded_locales = translations.keys.map(&:to_sym)
expected_locale = LocaleExtractor.locale_from_path(file)
unexpected_locales = loaded_locales.reject { |locale| locale == expected_locale }
raise FilenameIncorrect.new(file, expected_locale, unexpected_locales) unless unexpected_locales.empty?
end
end
end
end