Set fallback locale for Mobility based on current store

core/app/models/concerns/spree/translatable_resource_slug.rb

@@ -4,12 +4,10 @@ module TranslatableResourceSlug
 
     included do
       def localized_slugs_for_store(store)
-        localized_slugs = Hash[translations.pluck(:locale, :slug)]
-        default_locale = store.default_locale
         supported_locales = store.supported_locales_list
 
         supported_locales.each_with_object({}) do |locale, hash|
-          hash[locale] = localized_slugs[locale] || localized_slugs[default_locale]
+          hash[locale] = I18n.with_locale(locale) { slug }
         end
       end
     end

core/app/models/spree/taxon.rb

@@ -13,6 +13,7 @@ class Taxon < Spree::Base
     extend FriendlyId
     friendly_id :permalink, slug_column: :permalink, use: :history
     before_validation :set_permalink, on: :create, if: :name
+    alias_attribute :slug, :permalink
 
     acts_as_nested_set dependent: :destroy
 
@@ -66,10 +67,12 @@ class Taxon < Spree::Base
 
       def set_permalink
         parent = translated_model.parent
+        name_with_fallback = name || translated_model.name
+
         if parent.present?
-          self.permalink = [parent.permalink, (permalink.blank? ? name.to_url : permalink.split('/').last)].join('/')
+          self.permalink = [parent.permalink, (permalink.blank? ? name_with_fallback.to_url : permalink.split('/').last)].join('/')
         else
-          self.permalink = name.to_url if permalink.blank?
+          self.permalink = name_with_fallback.to_url if permalink.blank?
         end
       end
     end

core/app/services/spree/locales/set_fallback_locale_for_store.rb

@@ -0,0 +1,16 @@
+module Spree
+  module Locales
+    class SetFallbackLocaleForStore
+      def call(store:)
+        store_default_locale = store.default_locale
+        fallbacks = store.supported_locales_list.each_with_object({}) do |locale, object|
+          object[locale] = [store_default_locale]
+        end
+
+        fallbacks_instance = I18n::Locale::Fallbacks.new(fallbacks)
+
+        Mobility.store_based_fallbacks = fallbacks_instance
+      end
+    end
+  end
+end

core/config/initializers/mobility.rb

@@ -8,11 +8,9 @@
     backend_reader
     query
     cache
-    fallbacks
+    store_based_fallbacks
     locale_accessors
     presence
     dirty
   end
-
-  config.defaults[:fallbacks] = true
 end

core/lib/mobility/plugins/store_based_fallbacks.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+require 'concurrent'
+require 'mobility'
+
+module Mobility
+  @store_based_fallbacks = Concurrent::ThreadLocalVar.new(I18n::Locale::Fallbacks.new)
+
+  class << self
+    def store_based_fallbacks
+      @store_based_fallbacks.value
+    end
+
+    def store_based_fallbacks=(value)
+      @store_based_fallbacks.value = value
+    end
+  end
+
+  module Plugins
+    module StoreBasedFallbacks
+      extend ::Mobility::Plugin
+
+      default true
+      requires :backend, include: :before
+
+      # Applies fallbacks plugin to attributes. Completely disables fallbacks
+      # on model if option is +false+.
+      included_hook do |_, backend_class|
+        unless options[:fallbacks] == false
+          backend_class.include(BackendInstanceMethods)
+        end
+      end
+
+      module BackendInstanceMethods
+        def read(locale, fallback: true, **kwargs)
+          return super(locale, **kwargs) if !fallback || kwargs[:locale]
+
+          locales = Mobility.store_based_fallbacks[locale]
+          locales.each do |fallback_locale|
+            value = super(fallback_locale, **kwargs)
+            return value if Util.present?(value)
+          end
+
+          super(locale, **kwargs)
+        end
+      end
+    end
+
+    register_plugin(:store_based_fallbacks, StoreBasedFallbacks)
+  end
+end

core/lib/spree/core/controller_helpers/locale.rb

@@ -6,6 +6,7 @@ module Locale
 
         included do
           before_action :set_locale
+          before_action :set_fallback_locale
 
           if defined?(helper_method)
             helper_method :supported_locales
@@ -21,6 +22,12 @@ def set_locale
           I18n.locale = current_locale
         end
 
+        def set_fallback_locale
+          return unless respond_to?(:current_store) && current_store.present?
+
+          Spree::Locales::SetFallbackLocaleForStore.new.call(store: current_store)
+        end
+
         def current_locale
           @current_locale ||= if user_locale?
                                 try_spree_current_user.selected_locale

core/lib/spree_core.rb

@@ -1,3 +1,4 @@
 require 'friendly_id/paranoia'
+require 'mobility/plugins/store_based_fallbacks'
 
 require 'spree/core'

core/spec/models/spree/product_spec.rb

@@ -924,6 +924,8 @@ def build_option_type_with_values(name, values)
     let(:product) { create(:product, stores: [store], slug: 'test_slug_en') }
     let!(:product_translation_fr) { product.translations.create(slug: 'test_slug_fr', locale: 'fr') }
 
+    before { Spree::Locales::SetFallbackLocaleForStore.new.call(store: store) }
+
     subject { product.localized_slugs_for_store(store) }
 
     context 'when there are slugs in locales not supported by the store' do

core/spec/models/spree/taxon_spec.rb

@@ -189,6 +189,8 @@
     let(:taxon) { create(:taxon, taxonomy: taxonomy, permalink: 'test_slug_en') }
     let!(:taxon_translation_fr) { taxon.translations.create(slug: 'test_slug_fr', locale: 'fr') }
 
+    before { Spree::Locales::SetFallbackLocaleForStore.new.call(store: store) }
+
     subject { taxon.localized_slugs_for_store(store) }
 
     context 'when there are slugs in locales not supported by the store' do

core/spec/services/spree/locales/set_fallback_locale_for_store_spec.rb

@@ -0,0 +1,37 @@
+require 'spec_helper'
+
+module Spree
+  describe Locales::SetFallbackLocaleForStore do
+    let(:command) { described_class.new }
+
+    describe '#call' do
+      let(:store) { create(:store, default_locale: 'pl', supported_locales: 'en,de,pl') }
+      let(:product) { create(:product, name: 'test') }
+
+      let(:name_en) { 'name en' }
+      let(:name_pl) { 'name pl' }
+
+      let!(:translation_en) { product.translations.find_or_create_by(locale: 'en') { |e| e.name = name_en } }
+      let!(:translation_pl) { product.translations.find_or_create_by(locale: 'pl') { |e| e.name = name_pl } }
+
+      before { command.call(store: store) }
+
+      context 'when translatable object does not have a translation in the requested locale' do
+        it 'sets mobility to retrieve value in the fallback locale' do
+          name = I18n.with_locale(:de) { product.name }
+          expect(name).to eq(name_pl)
+        end
+      end
+
+      context 'when translatable object has a translation in the requested locale' do
+        let(:name_de) { 'name de' }
+        let!(:translation_de) { product.translations.find_or_create_by(locale: 'de') { |e| e.name = name_de } }
+
+        it 'sets mobility to retrieve value directly' do
+          name = I18n.with_locale(:de) { product.name }
+          expect(name).to eq(name_de)
+        end
+      end
+    end
+  end
+end