Info-file-supports-index-cookies is a compiled Lisp function in `info.el'.

(Info-file-supports-index-cookies &optional FILE)

Return non-nil value if FILE supports Info index cookies.
Info index cookies were first introduced in 4.7, and all later
makeinfo versions output them in index nodes, so we can rely
solely on the makeinfo version. This function caches the information
in `Info-file-supports-index-cookies-list'.