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

[Zhang Haijun]

I find that I had too little time editing c/c++ source files recently. Because 
our project switched to golang.

So I didn’t test this patch too much. I just applied the patch and tested iedit 
with some c++ files and the lag disappeared.


> 在 2019年4月20日，上午10:44，张海君 <ccsmile2008@outlook.com> 写道：
> 
> 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
>