Subject: bug#33163: Adding a " in c++-mode fills the whole file with red

From: Konstantin Kharlamov <[email-masked]>
Date: Sun, 28 Oct 2018 14:21:11 +0300

On 10/28/18 1:49 PM, Alan Mackenzie wrote:
> In article <[email-masked]> you wrote:
>> This long-standing problem appears occasionally, and only disappears if
>> you kill the buffer completely, then reopen the file. I never got to
>> report it because I never could find steps to reproduce it… until now
>> :) Nvm the non-sense code, I reduced testcase as far as I managed.
> 
>> # Steps to reproduce:
> 
>> 1. Save the following text in `test.cpp`
>>      int main() {
>>              puts(It's");
>>          auto foo = []()-> void {  };
>>              puts("It's");
>>      }
>> 2. Open `emacs -Q ./test.cpp`
>> 3. Now, the text lacks a quote in the first `puts(It's");`. Add it so
>> it looks like `puts("It's");`. Essentially, if you'd compile it with
>> g++, it lacks any syntax error besides `puts` being undeclared.
> 
>> # Expected
> 
>> The line with `auto foo…` is not red.
> 
>> # Actual
> 
>> The line with `auto foo…` (in particular) becomes red.
> 
> Thanks for taking the trouble to report this bug.  Thanks even more for
> condensing it down to a minimal test case.
> 
> The following patch should fix it.  Would you please apply the patch,
> recompile .../lisp/progmodes/cc-mode.el, load the new file in to your
> Emacs (or restart Emacs), then try it out on your real C++ code.  Then
> please let me know whether it's working or not, and if not, how it's
> going wrong.  Thanks!

Thank you for the quick patch! I tried to do some editing and 
navigating, and all seems well. More real testing I can only do on 
Monday, so I guess I'll reply somewhere on Monday evening.

> 
>> # Additional information
> 
>> Emacs version GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+
>> Version 3.22.30) of 2018-10-01, build with -flto.
> 
> 
> 
> diff -r 2f7029fa229d cc-mode.el
> --- a/cc-mode.el	Sun Oct 14 20:01:07 2018 +0000
> +++ b/cc-mode.el	Sun Oct 28 10:20:38 2018 +0000
> @@ -1216,21 +1216,21 @@
>         (if (eq beg-literal-type 'string)
>   	  (setq c-new-BEG (min (car beg-limits) c-new-BEG))))
>   
> -     ((< c-new-END (point-max))
> -      (goto-char (1+ c-new-END))	; might be a newline.
> +     ((< end (point-max))
> +      (goto-char (1+ end))	; might be a newline.
>         ;; In the following regexp, the initial \n caters for a newline getting
>         ;; joined to a preceding \ by the removal of what comes between.
>         (re-search-forward "[\n\r]?\\(\\\\\\(.\\|\n\\|\r\\)\\|[^\\\n\r]\\)*"
>   			 nil t)
>         ;; We're at an EOLL or point-max.
> -      (setq c-new-END (min (1+ (point)) (point-max)))
> -      (goto-char c-new-END)
> -      (if (equal (c-get-char-property (1- (point)) 'syntax-table) '(15))
> -	  (if (memq (char-before) '(?\n ?\r))
> +      (setq c-new-END (max c-new-END (min (1+ (point)) (point-max))))
> +      (if (equal (c-get-char-property (point) 'syntax-table) '(15))
> +	  (if (memq (char-after) '(?\n ?\r))
>   	      ;; Normally terminated invalid string.
> -	      (progn
> +	      (let ((eoll-1 (point)))
> +		(forward-char)
>   		(backward-sexp)
> -		(c-clear-char-property (1- c-new-END) 'syntax-table)
> +		(c-clear-char-property eoll-1 'syntax-table)
>   		(c-clear-char-property (point) 'syntax-table))
>   	    ;; Opening " at EOB.
>   	    (c-clear-char-property (1- (point)) 'syntax-table))
> @@ -1238,7 +1238,7 @@
>   	    ;; Opening " on last line of text (without EOL).
>   	    (c-clear-char-property (point) 'syntax-table))))
>   
> -     (t (goto-char c-new-END)
> +     (t (goto-char end)			; point-max
>   	(if (c-search-backward-char-property 'syntax-table '(15) c-new-BEG)
>   	    (c-clear-char-property (point) 'syntax-table))))
>   
> @@ -1327,9 +1327,9 @@
>   	     (while (progn
>   		      (setq s (parse-partial-sexp (point) c-new-END nil
>   						  nil s 'syntax-table))
> -		      (and (not (nth 3 s))
> -			   (< (point) c-new-END)
> -			   (not (memq (char-before) c-string-delims)))))
> +                      (and (< (point) c-new-END)
> +                           (or (not (nth 3 s))
> +                               (not (memq (char-before) c-string-delims))))))
>   	     ;; We're at the start of a string.
>   	     (memq (char-before) c-string-delims)))
>   	(if (c-unescaped-nls-in-string-p (1- (point)))
> 
>