class ActionView::Resolver::PathParser

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