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).