Merge pull request #33574 from lsylvester/change-i18n-defaults-behaviour-to-match-i18n-1.1.0

update I18n fallbacks configuration to be compatible with i18n 1.1.0

1 files changed, 13 insertions, 1 deletions

diff --git a/activesupport/lib/active_support/i18n_railtie.rb b/activesupport/lib/active_support/i18n_railtie.rb
index 93bde57f6a..c07eb5b569 100644
--- a/activesupport/lib/active_support/i18n_railtie.rb
+++ b/activesupport/lib/active_support/i18n_railtie.rb
@@ -87,9 +87,21 @@ module I18n
         when Hash, Array
           Array.wrap(fallbacks)
         else # TrueClass
-          []
+          [I18n.default_locale]
         end
 
+      if args.empty? || args.first.is_a?(Hash)
+        ActiveSupport::Deprecation.warn(<<-MSG.squish)
+          Using I18n fallbacks with an empty `defaults` sets the defaults to
+          include the `default_locale`. This behavior will change in Rails 6.1.
+          If you desire the default local to be included in the defaults, please
+          explicitly configure it with `config.i18n.fallbacks.defaults =
+          [I18n.default_locale]` or `config.i18n.fallbacks = [I18n.default_locale,
+          {...}]`
+        MSG
+        args.unshift I18n.default_locale
+      end
+
       I18n.fallbacks = I18n::Locale::Fallbacks.new(*args)
     end