bug#69431: 30.0.50; Strange fontificaion behavior

[Ihor Radchenko <yantar92@posteo.net>]

Andrea Corallo <acorallo@gnu.org> writes:

> I've applied the following:
>
>  (defun font-lock-set-defaults ()
> ...
> +    (when (string= (buffer-name) "test.org")
> +      (add-variable-watcher 'font-lock-keywords #'k-variable-watcher))
>
> Warm eln-cache (working fontification)
> ================
> For information about GNU Emacs and the GNU system, type C-h C-a.
> XXX set
>   backtrace()
>   k-variable-watcher(font-lock-keywords ... set #<buffer test.org>)
>   normal-mode(t)
>
> XXX set
>   backtrace()
>   k-variable-watcher(font-lock-keywords ... set #<buffer test.org>)
> ...
>   jit-lock-function(1)
>
> Empty eln-cache (fontification broken):
> ================
> For information about GNU Emacs and the GNU system, type C-h C-a.
> XXX makunbound
>   backtrace()
>   k-variable-watcher(font-lock-keywords nil makunbound #<buffer test.org>)
>   kill-local-variable(font-lock-keywords)
>   org-set-font-lock-defaults()
>   org-mode()
> ...
> XXX set
>   backtrace()
>   k-variable-watcher(font-lock-keywords (t nil) set nil)
> ...
>   jit-lock-function(1)
>
> ================
>
> So from what I see in the non working example 'font-lock-keywords' is
> cleared at the end of 'org-set-font-lock-defaults' which does
> '(kill-local-variable 'font-lock-keywords)'.
>
> Now why this is not happening in the working example I'm not sure ATM,
> ('org-set-font-lock-defaults' is not even called there AFAICS).

I am pretty sure that it does get called, but before your variable
watcher becomes active.

I suspect that font-lock is dumped to Emacs.
Maybe related to bug#66741.

-- 
Ihor Radchenko // yantar92,
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