quick fix for finding eponymous parents

middleman-core/lib/middleman-core/sitemap/extensions/traversal.rb

@@ -9,16 +9,23 @@ module Middleman
         # @return [Middleman::Sitemap::Resource, nil]
         def parent
           parts = path.split('/')
-          parts.pop if path.include?(app.index_file)
+          tail = parts.pop
+          is_index = (tail == app.index_file)
 
-          return nil if parts.length < 1
+          return nil if is_index && parts.length < 1
 
-          parts.pop
-          parts << app.index_file
+          test_expr = parts.join('\\/')
+          # A makeshift for eponymous reverse-lookup
+          found = store.resources.find { |candidate|
+              candidate.path =~ %r!^#{test_expr}(?:\.[a-zA-Z0-9]+|\/)$!
+          }
 
-          parent_path = '/' + parts.join('/')
-
-          store.find_resource_by_destination_path(parent_path)
+          if found
+            return found
+          else
+            parts.pop if is_index
+            return store.find_resource_by_destination_path("#{parts.join('/')}/#{app.index_file}")
+          end
         end
 
         # This resource's child resources