lib/nanoc/helpers/breadcrumbs.rb in nanoc-4.1.0 vs lib/nanoc/helpers/breadcrumbs.rb in nanoc-4.1.1

@@ -1,17 +1,27 @@
 module Nanoc::Helpers
   # Provides support for breadcrumbs, which allow the user to go up in the
   # page hierarchy.
   module Breadcrumbs
+    class CannotGetBreadcrumbsForNonLegacyItem < Nanoc::Int::Errors::Generic
+      def initialize(identifier)
+        super("You cannot build a breadcrumbs trail for an item that has a “full” identifier (#{identifier}). Doing so is only possible for items that have a legacy identifier.")
+      end
+    end
+
     # Creates a breadcrumb trail leading from the current item to its parent,
     # to its parent’s parent, etc, until the root item is reached. This
     # function does not require that each intermediate item exist; for
     # example, if there is no `/foo/` item, breadcrumbs for a `/foo/bar/` item
     # will contain a `nil` element.
     #
     # @return [Array] The breadcrumbs, starting with the root item and ending
     #   with the item itself
     def breadcrumbs_trail
+      unless @item.identifier.legacy?
+        raise CannotGetBreadcrumbsForNonLegacyItem.new(@item.identifier)
+      end
+
       trail      = []
       idx_start  = 0
 
       loop do
         idx = @item.identifier.to_s.index('/', idx_start)