Missing plural keys: Extract plural_nodes method

Refs #309
Refs #310

lib/i18n/tasks/missing_keys.rb

@@ -59,12 +59,9 @@ def missing_used_forest(locales, _base = base_locale)
     def missing_plural_forest(locales, _base = base_locale)
       locales.each_with_object(empty_forest) do |locale, tree|
         next unless I18n.exists?(:'i18n.plural.keys', locale)
-
         required_keys = Set.new(I18n.t(:'i18n.plural.keys', locale: locale, resolve: false))
-
-        data[locale].leaves.map(&:parent).compact.uniq.each do |node|
+        plural_nodes data[locale] do |node|
           children = node.children
-          next unless plural_forms?(children)
           present_keys = Set.new(children.map { |c| c.key.to_sym })
           next if present_keys.superset?(required_keys)
           tree[node.full_key] = node.derive(
@@ -73,7 +70,6 @@ def missing_plural_forest(locales, _base = base_locale)
             data: node.data.merge(missing_keys: (required_keys - present_keys).to_a)
           )
         end
-
         tree.set_root_key!(locale, type: :missing_plural)
       end
     end

lib/i18n/tasks/plural_keys.rb

@@ -31,6 +31,20 @@ def depluralize_key(key, locale = base_locale)
     end
   end
 
+  # @param [::I18n::Tasks::Data::Tree::Traversal] tree
+  # @yieldparam node [::I18n::Tasks::Data::Tree::Node] plural node
+  def plural_nodes(tree)
+    return to_enum(:plural_nodes, tree) unless block_given?
+    visited = Set.new
+    tree.leaves.each do |node|
+      parent = node.parent
+      next if !parent || visited.include?(parent)
+      yield parent if plural_forms?(parent.children)
+      visited.add(parent)
+    end
+    self
+  end
+
   def plural_forms?(s)
     s.present? && s.all? { |node| node.leaf? && plural_suffix?(node.key) }
   end