(font-lock-mode 1) does not always force font-lock

[Hrvoje Niksic <hniksic@xemacs.org>]

I have code that needs to force fontification of a file loaded from
disk without affecting buffers visiting the file.  What I tried was:

(with-temp-buffer
  (insert-file-contents FILE)
  (let ((buffer-file-name FILE))  ; for normal-mode
    (normal-mode)
    (font-lock-mode 1)
    ;; Here the buffer should be fontified and font-lock-mode turned
    ;; on.
    font-lock-mode))

This returns nil because `(font-lock-mode 1)' does not force
font-lock, contrary to the docstring which, in GNU Emacs 21.2.1,
states:

    With arg, turn Font Lock mode off if and only if arg is a
    non-positive number; if arg is nil, toggle Font Lock mode;
    anything else turns Font Lock on.

I assume the problem is that the buffer is that the buffer in question
is temporary.  But `(font-lock-mode 1)' should IMHO still force
font-lock.  And if not, there should be a way to say, "yes, I know
what I'm doing and I really want to fontify this temporary buffer."

A workaround that works for me is to add:

  (unless font-lock-mode
    (font-lock-fontify-buffer))

but that kind of solution might not work elsewhere.