bug#13891: 24.3.50; highlight-regexp incorrectly retains partial state after buffer reversion

[Jambunathan K <kjambunathan@gmail.com>]

Stefan Monnier <monnier@IRO.UMontreal.CA> writes:

>> I noticed two things that show that partial highlight-regexp state
>> lingers after calling revert-buffer, see items 9 and 12.  After buffer
>
> I've installed the patch below which should fix those problems.

(This is not a comment on the patch you have put in, but my initial
thoughts as I investigated the bug.)

I have a feeling that your fix is "inconsistent" with having
`hi-lock-interactive-patterns' as `permanent-local'.

`hi-lock-interactive-patterns' is marked as `permanent-local'.  So the
original intention is clearly to *retain* the highlighting across the
reverts and change of major modes.  With `global-hi-lock-mode' ON, you
will notice that highlighting will be retained across reverts.

When M-s h r is used, hi-lock-mode is turned on automatically.  But
after revert, the hi-lock-mode (being a minor mode) never gets turned
back again.

I was thinking of fix along the lines of 

1. If `hi-lock-interactive-patterns' is non-nil, turn on hi-lock-mode.

2. I think `font-lock-fontify-buffer' should be added to
   `hi-lock-font-lock-hook'.  For some reason, `hi-lock-font-lock-hook'
   doesn't get called at all (even though it is added to the
   `font-lock-mode-hook'.)  

   Problem area: `font-lock-mode-hook' is not documented and I really
   don't when it is getting called.

>
>
>         Stefan
>
>
> === modified file 'lisp/hi-lock.el'
> --- lisp/hi-lock.el	2013-03-08 04:18:16 +0000
> +++ lisp/hi-lock.el	2013-03-31 13:31:41 +0000
> @@ -389,7 +389,9 @@
>  	(define-key-after menu-bar-edit-menu [hi-lock]
>  	  (cons "Regexp Highlighting" hi-lock-menu))
>  	(hi-lock-find-patterns)
> -	(add-hook 'font-lock-mode-hook 'hi-lock-font-lock-hook nil t))
> +        (add-hook 'font-lock-mode-hook 'hi-lock-font-lock-hook nil t)
> +        ;; Remove regexps from font-lock-keywords (bug#13891).
> +	(add-hook 'change-major-mode-hook (lambda () (hi-lock-mode -1)) nil t))
>      ;; Turned off.
>      (when (or hi-lock-interactive-patterns
>  	      hi-lock-file-patterns)