Ensure the underscore locale is included in i18n fallbacks

When a site has an underscore locale (e.g. "fr_BE") set as the default,
it is not included in the I18n fallbacks for non-default locales.

    I18n.fallbacks
    # => { :fr_BE => [:fr_BE, :"fr-BE", :fr],
    #      :nl_BE => [:nl_BE, :"fr-BE", :fr] }

    AlaveteliLocalization.with_locale(:fr_BE) { Globalize.fallbacks }
    # => [:fr_BE, :"fr-BE", :fr]
    AlaveteliLocalization.with_locale(:nl_BE) { Globalize.fallbacks }
    # => [:nl_BE, :"fr-BE", :fr]

In the example above, this means that a missing model translation when
using the "nl_BE" locale will **not** correctly fall back to the
translation for the default locale ("fr_BE").

This commit ensures that the default locale is always available in the
fallbacks for non-default locales. We try to add it before the
non-underscore version so that the regional translation is preferred,
with the non-regional fallback available as a last-ditch attempt to find
a useful translation.

Globalize model attributes fallbacks specs contributed by @gbp.

Fixes #5382
Fixes #5895

lib/alaveteli_localization.rb

@@ -80,9 +80,16 @@ def set_fast_gettext_locales(available, default)
     end
 
     def set_i18n_locales(available, default)
+      # Make all locales and their fallbacks available
       I18n.available_locales =
-        available.flat_map(&:self_and_parents).map(&:to_sym).uniq
+        available.flat_map(&:i18n_fallbacks).map(&:to_sym).uniq
 
+      # Configure the specific fallbacks for each locale
+      available.each do |locale|
+        I18n.fallbacks[locale.to_sym] = locale.i18n_fallbacks(default)
+      end
+
+      # Set the current locale as the default locale
       I18n.locale = I18n.default_locale = default.hyphenate.to_sym
     end
 

lib/alaveteli_localization/hyphenated_locale.rb

@@ -1,6 +1,12 @@
 class AlaveteliLocalization
   # Handle transformations of a hyphenated Locale identifier (e.g. "en-GB").
   class HyphenatedLocale < Locale
+    def self_and_parents
+      without_canonicalized = super
+      index = without_canonicalized.find_index(self) + 1
+      without_canonicalized.insert(index, canonicalize)
+    end
+
     private
 
     def split

lib/alaveteli_localization/locale.rb

@@ -49,13 +49,18 @@ def hyphenate
       self.class.parse(split.join('-'))
     end
 
-    # Note that self_and_parents only uses hyphenated locales
     def self_and_parents
       I18n::Locale::Tag::Simple.new(hyphenate).
         self_and_parents.
         map { |tag| self.class.parse(tag) }
     end
 
+    def i18n_fallbacks(default = nil)
+      default = self.class.parse(default) if default
+      (self_and_parents | Array(default&.i18n_fallbacks)).
+        compact.map(&:to_sym).uniq
+    end
+
     def to_s
       identifier
     end

lib/alaveteli_localization/underscorred_locale.rb

@@ -1,6 +1,10 @@
 class AlaveteliLocalization
   # Handle transformations of un anderscorred Locale identifier (e.g. "en_GB").
   class UnderscorredLocale < Locale
+    def self_and_parents
+      super.prepend(canonicalize)
+    end
+
     private
 
     def split

spec/lib/alaveteli_localization/hyphenated_locale_spec.rb

@@ -28,7 +28,34 @@
 
   describe '#self_and_parents' do
     subject { described_class.new(identifier).self_and_parents }
-    it { is_expected.to eq(%w[en-GB en]) }
+    it { is_expected.to eq(%w[en-GB en_GB en]) }
+  end
+
+  describe '#i18n_fallbacks' do
+    context 'without a default_locale' do
+      subject { described_class.new(identifier).i18n_fallbacks }
+      it { is_expected.to eq(%i[en-GB en_GB en]) }
+    end
+
+    context 'with a default_locale' do
+      subject { described_class.new(identifier).i18n_fallbacks('fr') }
+      it { is_expected.to eq(%i[en-GB en_GB en fr]) }
+    end
+
+    context 'with the default locale given to default_locale' do
+      subject { described_class.new(identifier).i18n_fallbacks(identifier) }
+      it { is_expected.to eq(%i[en-GB en_GB en]) }
+    end
+
+    context 'with a hyphenated default_locale' do
+      subject { described_class.new(identifier).i18n_fallbacks('fr-BE') }
+      it { is_expected.to eq(%i[en-GB en_GB en fr-BE fr_BE fr]) }
+    end
+
+    context 'with an underscorred default_locale' do
+      subject { described_class.new(identifier).i18n_fallbacks('fr_BE') }
+      it { is_expected.to eq(%i[en-GB en_GB en fr_BE fr-BE fr]) }
+    end
   end
 
   describe '#to_s' do

spec/lib/alaveteli_localization/locale_spec.rb

@@ -66,6 +66,33 @@
     it { is_expected.to eq(%w[en]) }
   end
 
+  describe '#i18n_fallbacks' do
+    context 'without a default_locale' do
+      subject { described_class.new('en').i18n_fallbacks }
+      it { is_expected.to eq(%i[en]) }
+    end
+
+    context 'with a default_locale' do
+      subject { described_class.new('en').i18n_fallbacks('fr') }
+      it { is_expected.to eq(%i[en fr]) }
+    end
+
+    context 'with the default locale given to default_locale' do
+      subject { described_class.new('en').i18n_fallbacks('en') }
+      it { is_expected.to eq(%i[en]) }
+    end
+
+    context 'with a hyphenated default_locale' do
+      subject { described_class.new('en').i18n_fallbacks('fr-BE') }
+      it { is_expected.to eq(%i[en fr-BE fr_BE fr]) }
+    end
+
+    context 'with an underscorred default_locale' do
+      subject { described_class.new('en').i18n_fallbacks('fr_BE') }
+      it { is_expected.to eq(%i[en fr_BE fr-BE fr]) }
+    end
+  end
+
   describe '#to_s' do
     subject { described_class.new('en').to_s }
     it { is_expected.to eq('en') }

spec/lib/alaveteli_localization/underscorred_locale_spec.rb

@@ -28,8 +28,34 @@
 
   describe '#self_and_parents' do
     subject { described_class.new(identifier).self_and_parents }
-    # Note that self_and_parents only uses hyphenated locales
-    it { is_expected.to eq(%w[en-GB en]) }
+    it { is_expected.to eq(%w[en_GB en-GB en]) }
+  end
+
+  describe '#i18n_fallbacks' do
+    context 'without a default_locale' do
+      subject { described_class.new(identifier).i18n_fallbacks }
+      it { is_expected.to eq(%i[en_GB en-GB en]) }
+    end
+
+    context 'with a default_locale' do
+      subject { described_class.new(identifier).i18n_fallbacks('fr') }
+      it { is_expected.to eq(%i[en_GB en-GB en fr]) }
+    end
+
+    context 'with the default locale given to default_locale' do
+      subject { described_class.new(identifier).i18n_fallbacks(identifier) }
+      it { is_expected.to eq(%i[en_GB en-GB en]) }
+    end
+
+    context 'with a hyphenated default_locale' do
+      subject { described_class.new(identifier).i18n_fallbacks('fr-BE') }
+      it { is_expected.to eq(%i[en_GB en-GB en fr-BE fr_BE fr]) }
+    end
+
+    context 'with an underscorred default_locale' do
+      subject { described_class.new(identifier).i18n_fallbacks('fr_BE') }
+      it { is_expected.to eq(%i[en_GB en-GB en fr_BE fr-BE fr]) }
+    end
   end
 
   describe '#to_s' do

spec/lib/alaveteli_localization_spec.rb

@@ -57,9 +57,55 @@
       end
 
       it 'sets I18n.available_locales' do
-        expect(I18n.available_locales).to eq(%i[en-GB en es])
+        expect(I18n.available_locales).to eq(%i[en_GB en-GB en es])
       end
 
+      it 'sets correct fallbacks when using an underscore default locale' do
+        AlaveteliLocalization.set_locales('en_RW rw', 'en_RW')
+        expect(I18n.fallbacks[:en_RW]).to eq(%i[en_RW en-RW en])
+        expect(I18n.fallbacks[:rw]).to eq(%i[rw en_RW en-RW en])
+      end
+    end
+
+    context 'when dealing with Globalize' do
+      it 'sets correct fallbacks when using an underscore default locale' do
+        AlaveteliLocalization.set_locales('en_RW rw', 'en_RW')
+        expect(Globalize.fallbacks(:en_RW)).to eq(%i[en_RW en-RW en])
+        expect(Globalize.fallbacks(:rw)).to eq(%i[rw en_RW en-RW en])
+      end
+    end
+
+    context 'Globalize model attributes fallbacks' do
+      before do
+        AlaveteliLocalization.set_locales('en_RW rw', 'en_RW')
+      end
+
+      let(:body_with_default_locale) do
+        AlaveteliLocalization.with_locale('en_RW') do
+          FactoryBot.create(:public_body, url_name: 'default')
+        end
+      end
+
+      let(:body_with_non_default_locale) do
+        AlaveteliLocalization.with_locale('rw') do
+          FactoryBot.create(:public_body, url_name: 'non_default')
+        end
+      end
+
+      context 'when using non-default locale' do
+        it 'falls back to the default locale attribute' do
+          AlaveteliLocalization.with_locale('rw') do
+            expect(body_with_default_locale.url_name).to eq 'default'
+          end
+        end
+
+        it 'returns the translated non-default locale attribute' do
+          AlaveteliLocalization.with_locale('rw') do
+            expect(body_with_non_default_locale.url_name).to eq 'non_default'
+          end
+        end
+
+      end
     end
 
     context 'when translating' do