bug#39597: 27.0.60: M-x occur adds fontification to fundamental-mode

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@linkov.net>
> Date: Wed, 19 Feb 2020 00:49:12 +0200
> Cc: 39597@debbugs.gnu.org,
>  Kévin Le Gouguec <kevin.legouguec@gmail.com>
> 
> > diff --git a/lisp/font-lock.el b/lisp/font-lock.el
> > index 438511b647..bf045d9d7e 100644
> > --- a/lisp/font-lock.el
> > +++ b/lisp/font-lock.el
> > @@ -1139,9 +1139,10 @@ font-lock-ensure
> >    "Make sure the region BEG...END has been fontified.
> >  If the region is not specified, it defaults to the entire accessible
> >  portion of the buffer."
> > -  (font-lock-set-defaults)
> > -  (funcall font-lock-ensure-function
> > -           (or beg (point-min)) (or end (point-max))))
> > +  (when (font-lock-specified-p t)
> > +    (font-lock-set-defaults)
> > +    (funcall font-lock-ensure-function
> > +             (or beg (point-min)) (or end (point-max)))))
> >  
> >  (defun font-lock-default-fontify-buffer ()
> >    "Fontify the whole buffer using `font-lock-fontify-region-function'."
> 
> I confirm this fixes the problem reported by Kévin,
> so maybe this should be installed to emacs-27.

Doesn't sound serious enough to do this on the release branch.  We've
had this issue for quite some time, no?