touchr() { test "$1" -nt "$2" && echo touch -r ${1@Q} ${2@Q}; }
propagate-date () { find ${1:?} -depth -type d | grep -v -e /[.][a-z] -e /tmp | while read d; do ls -t "$d" | { read r; touchr "$d/$r" "$d"; }; done; }

propagate-date ext | dash