Bring back AMo#i18n_key method

activemodel/lib/active_model/errors.rb

@@ -295,8 +295,8 @@ module ActiveModel
       type = options.delete(:message) if options[:message].is_a?(Symbol)
 
       defaults = @base.class.lookup_ancestors.map do |klass|
-        [ :"#{@base.class.i18n_scope}.errors.models.#{klass.model_name.underscore}.attributes.#{attribute}.#{type}",
-          :"#{@base.class.i18n_scope}.errors.models.#{klass.model_name.underscore}.#{type}" ]
+        [ :"#{@base.class.i18n_scope}.errors.models.#{klass.model_name.i18n_key}.attributes.#{attribute}.#{type}",
+          :"#{@base.class.i18n_scope}.errors.models.#{klass.model_name.i18n_key}.#{type}" ]
       end
 
       defaults << options.delete(:message)

activemodel/lib/active_model/naming.rb

@@ -4,7 +4,7 @@ require 'active_support/core_ext/module/introspection'
 
 module ActiveModel
   class Name < String
-    attr_reader :singular, :plural, :element, :collection, :partial_path, :route_key, :param_key
+    attr_reader :singular, :plural, :element, :collection, :partial_path, :route_key, :param_key, :i18n_key
     alias_method :cache_key, :collection
 
     def initialize(klass, namespace = nil)
@@ -20,6 +20,7 @@ module ActiveModel
       @partial_path = "#{@collection}/#{@element}".freeze
       @param_key = (namespace ? _singularize(@unnamespaced) : @singular).freeze
       @route_key = (namespace ? ActiveSupport::Inflector.pluralize(@param_key) : @plural).freeze
+      @i18n_key = self.underscore.to_sym
     end
 
     # Transform the model name into a more humane format, using I18n. By default,
@@ -33,7 +34,7 @@ module ActiveModel
                            @klass.respond_to?(:i18n_scope)
 
       defaults = @klass.lookup_ancestors.map do |klass|
-        klass.model_name.underscore.to_sym
+        klass.model_name.i18n_key
       end
 
       defaults << options[:default] if options[:default]
@@ -44,9 +45,10 @@ module ActiveModel
     end
 
     private
-      def _singularize(str)
-        ActiveSupport::Inflector.underscore(str).tr('/', '_')
-      end
+
+    def _singularize(string, replacement='_')
+      ActiveSupport::Inflector.underscore(string).tr('/', replacement)
+    end
   end
 
   # == Active Model Naming
@@ -62,6 +64,9 @@ module ActiveModel
   #   BookCover.model_name        # => "BookCover"
   #   BookCover.model_name.human  # => "Book cover"
   #
+  #   BookCover.model_name.i18n_key              # => "book_cover"
+  #   BookModule::BookCover.model_name.i18n_key  # => "book_module.book_cover"
+  #
   # Providing the functionality that ActiveModel::Naming provides in your object
   # is required to pass the Active Model Lint test.  So either extending the provided
   # method below, or rolling your own is required.

activemodel/lib/active_model/translation.rb

@@ -44,7 +44,7 @@ module ActiveModel
     # Specify +options+ with additional translating options.
     def human_attribute_name(attribute, options = {})
       defaults = lookup_ancestors.map do |klass|
-        :"#{self.i18n_scope}.attributes.#{klass.model_name.underscore}.#{attribute}"
+        :"#{self.i18n_scope}.attributes.#{klass.model_name.i18n_key}.#{attribute}"
       end
 
       defaults << :"attributes.#{attribute}"