bug#35316: 26.2; Emacs lags in c++-mode buffer when editing with iedit-mode on

[Zhang Haijun <ccsmile2008@outlook.com>]

I will try it for some days and give feedback.

> 在 2019年4月20日，上午12:20，Stefan Monnier <monnier@IRO.UMontreal.CA> 写道：
> 
>> Reproducing steps:
>> 1. emacs -Q
>> 2. Eval code: (add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/“))
>> 3. install the package iedit (version from melpa)
>> 4. open the attachment c++ file, and goto line 262 and column 17. cursor
>> will be on word “subsession"
>> 5. M-x narrow-to-defun
>> 6. M-x iedit-mode
>> 7. M-x widen
>> 8. You will see the lag when inputting chars.
> 
> This seems to be a good use case for my syntax-propertize patch.
> I just tried it on your test case and while there is still a slight slow
> down, it seemed to be much less problematic.
> 
> BEWARE: it likely introduces bugs.
> 
> 
>        Stefan
> 
> 
> diff --git a/lisp/progmodes/cc-mode.el b/lisp/progmodes/cc-mode.el
> index 49268c4482..31f5ecdfdb 100644
> --- a/lisp/progmodes/cc-mode.el
> +++ b/lisp/progmodes/cc-mode.el
> @@ -506,6 +506,8 @@ c-just-done-before-change
> ;; and `after-change-functions'.  Note that this variable is not set when
> ;; `c-before-change' is invoked by a change to text properties.
> 
> +(defvar c--use-syntax-propertize t)
> +
> (defun c-basic-common-init (mode default-style)
>   "Do the necessary initialization for the syntax handling routines
> and the line breaking/filling code.  Intended to be used by other
> @@ -648,12 +650,17 @@ c-basic-common-init
> 
>   ;; Install the functions that ensure that various internal caches
>   ;; don't become invalid due to buffer changes.
> -  (when (featurep 'xemacs)
> -    (make-local-hook 'before-change-functions)
> -    (make-local-hook 'after-change-functions))
> -  (add-hook 'before-change-functions 'c-before-change nil t)
> -  (setq c-just-done-before-change nil)
> -  (add-hook 'after-change-functions 'c-after-change nil t)
> +  (if c--use-syntax-propertize
> +      (setq-local syntax-propertize-function
> +		  (lambda (start end)
> +		    (c-before-change start (point-max))
> +		    (c-after-change start end (- end start))))
> +    (when (featurep 'xemacs)
> +      (make-local-hook 'before-change-functions)
> +      (make-local-hook 'after-change-functions))
> +    (add-hook 'before-change-functions 'c-before-change nil t)
> +    (setq c-just-done-before-change nil)
> +    (add-hook 'after-change-functions 'c-after-change nil t))
>   (when (boundp 'font-lock-extend-after-change-region-function)
>     (set (make-local-variable 'font-lock-extend-after-change-region-function)
>          'c-extend-after-change-region))) ; Currently (2009-05) used by all
> @@ -711,15 +718,17 @@ c-common-init
>     (widen)
>     (setq c-new-BEG (point-min))
>     (setq c-new-END (point-max))
> -    (save-excursion
> -      (let (before-change-functions after-change-functions)
> -	(mapc (lambda (fn)
> -		(funcall fn (point-min) (point-max)))
> -	      c-get-state-before-change-functions)
> -	(mapc (lambda (fn)
> -		(funcall fn (point-min) (point-max)
> -			 (- (point-max) (point-min))))
> -	      c-before-font-lock-functions))))
> +    (unless c--use-syntax-propertize
> +      (save-excursion
> +	(let (before-change-functions after-change-functions)
> +	  (mapc (lambda (fn)
> +		  (funcall fn (point-min) (point-max)))
> +		c-get-state-before-change-functions)
> +	  (mapc (lambda (fn)
> +		  (funcall fn (point-min) (point-max)
> +			   (- (point-max) (point-min))))
> +		c-before-font-lock-functions)
> +	  ))))
> 
>   (set (make-local-variable 'outline-regexp) "[^#\n\^M]")
>   (set (make-local-variable 'outline-level) 'c-outline-level)
> @@ -1954,6 +1963,12 @@ c-font-lock-fontify-region
>   ;;
>   ;; Type a space in the first blank line, and the fontification of the next
>   ;; line was fouled up by context fontification.
> +  (when c--use-syntax-propertize
> +    ;; This should also update c-new-END and c-new-BEG.
> +    (syntax-propertize end)
> +    ;; FIXME: Apparently `c-new-END' may be left unchanged to a stale value,
> +    ;; presumably when the buffer gets truncated.
> +    (if (> c-new-END (point-max)) (setq c-new-END (point-max))))
>   (let (new-beg new-end new-region case-fold-search)
>     (if (and c-in-after-change-fontification
> 	     (< beg c-new-END) (> end c-new-BEG))
> @@ -1992,7 +2007,8 @@ c-font-lock-fontify-region
> (defun c-after-font-lock-init ()
>   ;; Put on `font-lock-mode-hook'.  This function ensures our after-change
>   ;; function will get executed before the font-lock one.
> -  (when (memq #'c-after-change after-change-functions)
> +  (when (and c--use-syntax-propertize
> +	     (memq #'c-after-change after-change-functions))
>     (remove-hook 'after-change-functions #'c-after-change t)
>     (add-hook 'after-change-functions #'c-after-change nil t)))
> 
> @@ -2046,11 +2062,14 @@ c-extend-after-change-region
>   (when (eq font-lock-support-mode 'jit-lock-mode)
>     (save-restriction
>       (widen)
> +      ;; FIXME: This presumes that c-new-BEG and c-new-END have been set
> +      ;; I guess from the before-change-function.
>       (c-save-buffer-state () ; Protect the undo-list from put-text-property.
> 	(if (< c-new-BEG beg)
> 	    (put-text-property c-new-BEG beg 'fontified nil))
> 	(if (> c-new-END end)
> -	    (put-text-property end c-new-END 'fontified nil)))))
> +	    (put-text-property end (min c-new-END (point-max))
> +			       'fontified nil)))))
>   (cons c-new-BEG c-new-END))
> 
> ;; Emacs < 22 and XEmacs