[BUG] Providing a hash to fallbacks with a default does not set I18n.fallbacks.defaults

[sergioisidoro]

Hello,

I'm not sure how to categorise this, as if a bug or a feature request, but certainly it is a bit of a missed expectation of how the fallback map / hash assignment worked :) And I'm leaving it here also as a reference for people to find.

What I tried to do

In a Rails environment:

language_fallbacks = {
  "en-US": [:en],
  "es-US": [:es, :en],
}

language_fallbacks.default = [:en]
...

config.i18n.fallbacks = language_fallbacks

What I expected to happen

I was expecting that providing a hash with default to I18n.fallbacks.map would automatically populate the I18n.fallbacks.defaults

What actually happened

I still got the Rails deprecation warning DEPRECATION WARNING: Using I18n fallbacks with an empty defaults sets the defaults to include the default_locale (...), meaning that fallbacks defaults was left empty.

And I needed to explicitly assign the defaults:

language_fallbacks = {
  "en-US": [:en],
  "es-US": [:es, :en],
}

language_fallbacks.default = [:en]
...

config.i18n.fallbacks.map = language_fallbacks
config.i18n.fallbacks.defaults = language_fallbacks.default

Versions of i18n, rails, and anything else you think is necessary

gem 'rails-i18n', '~> 6.0.0'
gem 'i18n', '1.8.5'

In rails 6.0