Re: bug in hi-lock?

[Dale Schaafsma <daleschaafsma@gmail.com>]

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Hi Alan,
  Thanks for the workaround...yep that works like a charm.
  Glad that it is fixed in emacs 23...I'll have to give that a whirl
sometime soon.
Thanks again,
 Dale

On Thu, May 21, 2009 at 2:02 PM, Alan Mackenzie <acm@muc.de> wrote:

> Hi, Dale!
>
> On Wed, May 20, 2009 at 11:32:08AM -0500, Dale Schaafsma wrote:
> > Hi Alan,
> >   I've attached a small text file...my regex is foo...and I just hit
> return
> > to take the default color of hi-yellow.
> >   Thanks for the compliment on the bug report (I do write&debug software
> so
> > I've tried to be specific!)...should I send this message to the address
> > below?
>
> Thanks for the file.  It was ideal.
>
> Now, take a deep, deep, breath.  This is what's happening:
>
> The bug, (switching hi-lock-mode off) has nothing to do with
> global-hi-lock-mode, it also happens when you manually switch on
> hi-lock-mode.
>
> The bug happens only the first time you do C-x w h inside a buffer.  If
> you then switch hi-lock-mode on again manually, it stays on.
>
> The bug happens only in major modes which don't have any font-lock
> keywords defined.  Text mode is one such mode.
>
> The bug happens only in major modes which don't have font-lock-keywords
> defined.  Text mode is one such mode.
>
> This is the sequence of events in foo.text:
>
> (i) C-x w h foo filters through to ...
> (ii) hi-lock-set-pattern which calls ...
> (iii) font-lock-add-keywords.  This function notices that
>  font-lock-keywords is nil (more or less), and thus decides that, and I
>  quote:
>
>     ;; The major mode has not set any keywords, so when we enabled
>     ;; font-lock-mode it only enabled the font-core.el part, not the
>     ;; font-lock-mode-internal.  Try again.
>
> (iv) font-lock-add-keywords, rather than carefully and conservatively
>  performing the remaining initialisation, brutally and recursively
>  power cycles font-lock mode thusly:
>
>           (font-lock-mode -1)
>           (set (make-local-variable 'font-lock-defaults) '(nil t))
>           (font-lock-mode 1))
>
> (v) The first of these invocations runs a hook called (something like)
>  `font-lock-mode-off-hook' whose value is `hi-lock-font-lock-hook'.
> (vi) hi-lock-font-lock-hook, on being told that font-lock-mode has been
>  switched off invokes `(hi-lock-mode -1)'.
>
> If I were to assign guilt for this bug, it would be to the scrappy way
> font-lock-mode is power cycled.
>
> However: The good news is that the bug has been fixed for Emacs 23 (I'm
> not sure how, but I vaguely remember complaining about something similar
> ~2 years ago, and something got fixed).
>
> How about a workaround?  I haven't tested this, but something like this
> function:
>
> (defun ds-protect-hl ()
>  "Prevent Font Lock Mode switching off hi-lock-mode at first use."
>  (make-local-variable 'font-lock-defaults)
>  (unless font-lock-defaults
>    (if font-lock-mode
>        (progn
>          (font-lock-mode -1)
>          (setq font-lock-defaults) '(nil t))
>          (font-lock-mode 1))
>      (setq font-lock-defaults '(nil t)))))
>
> , if placed on an appropriate hook (?after-change-major-mode-hook,
> perhaps) might do the job.  On the other hand, it might also screw up
> font-lock-mode.
>
> [Note: that's just an idea, not a working function.]
>
> --
> Alan Mackenzie (Nuremberg, Germany).
>

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