class ActionView::Resolver::PathParser

def build_path_regex
  handlers = Regexp.union(Template::Handlers.extensions.map(&:to_s))
  formats = Regexp.union(Template::Types.symbols.map(&:to_s))
  available_locales = I18n.available_locales.map(&:to_s)
  regular_locales = [/[a-z]{2}(?:[-_][A-Z]{2})?/]
  locales = Regexp.union(available_locales + regular_locales)
  variants = "[^.]*"
  %r{
    \A
    (?:(?<prefix>.*)/)?
    (?<partial>_)?
    (?<action>.*?)
    (?:\.(?<locale>#{locales}))??
    (?:\.(?<format>#{formats}))??
    (?:\+(?<variant>#{variants}))??
    (?:\.(?<handler>#{handlers}))?
    \z
  }x
end