Comment 2 for bug 1995236

Bother. There is a third problem, a scope issue of some sort.
The errors in ~/.xsession.error go away if "has_options" is moved from Xsession to its own file in Xsession.d

I don't see why sourceing it should make any difference, but it does.

$ cat /etc/X11/Xsession.d/00
has_option () {
  # Ensure that a later no-foo overrides an earlier foo
  if [ "$(echo "$OPTIONS" | grep -Eo "^(no-)?$1\>" | tail -n 1)" == "$1" ]; then
    return 0
  else
    return 1
  fi
}

Also I changed a "=" to "==", but that should be cosmetic.