Subject: bug#15251: 24.3.50; do-auto-fill "continues" comment from inside a string

From: Andreas Röhler <[email-masked]>
Date: Sun, 29 Sep 2013 15:12:57 +0200

Am 29.09.2013 05:59, schrieb Dmitry Gutov:
> Dmitry Gutov <[email-masked]> writes:
>
>> In certain conditions, if I press SPC, and a string on the current line
>> contains text matching `comment-start-skip', the filling is performed,
>> and the newly created line starts with a comment.
>>
>> Examples (point is at |, fill-column is 70):
>>
>> ruby-mode:
>>
>> aa = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa#{}a" a|
>>
>> press SPC =>
>>
>> aa = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa#{}a"
>>                                  #a
>>
>> js-mode:
>>
>> aa = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa//a" aa|
>>
>> press SPC =>
>>
>> aa = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa//a"
>> //aa
>
> I've tracked this to misbehaving `comment-beginning'. Since we start
> outside of string, and the comment char(s) are inside the string on the
> same line, the check comparing the face at point to
> `font-lock-string-face' doesn't work.
>
> And in ruby-mode's case, since interpolations use a different face, even
> putting a similar guard to check at `cs' won't help.
>
> As I see it, we either have to use `syntax-ppss' here, or trust
> font-lock. The latter means not skipping other checks even if
> `comment-end-skip' is defined and doesn't match at point, and also
> only trusting "let's assume ... if we're on the same line" when
> font-lock-mode is disabled.
>
> How does this change look? Seems to work fine.
>
> (As an aside, I'm having hard time understanding which search is
> supposed to have set the match data used by `(match-end 0)' there. Is it
> `comment-search-backward'? Or `(looking-at comment-end-skip)'?)
>
> === modified file 'lisp/newcomment.el'
> --- lisp/newcomment.el	2013-06-18 17:57:56 +0000
> +++ lisp/newcomment.el	2013-09-29 03:41:18 +0000
> @@ -526,12 +526,13 @@
>   	      (and
>   	       ;; For modes where comment-start and comment-end are the same,
>   	       ;; the search above may have found a `ce' rather than a `cs'.
> -	       (or (if comment-end-skip (not (looking-at comment-end-skip)))
> -		   ;; Maybe font-lock knows that it's a `cs'?
> +               (if comment-end-skip (not (looking-at comment-end-skip)))
> +	       (or ;; Maybe font-lock knows that it's a `cs'?
>   		   (eq (get-text-property (match-end 0) 'face)
>   		       'font-lock-comment-face)
> -		   (unless (eq (get-text-property (point) 'face)
> -			       'font-lock-comment-face)
> +		   (unless (or (eq (get-text-property (point) 'face)
> +                                   'font-lock-comment-face)
> +                               font-lock-mode)
>   		     ;; Let's assume it's a `cs' if we're on the same line.
>   		     (>= (line-end-position) pt)))
>   	       ;; Make sure that PT is not past the end of the comment.
>
>
>
>
>

Reading the face for detecting basic things like comment is terrible.
What did the author smoke when writing this ;)

BTW from my experience jumping to (nth 8 (syntax-ppss)) works well.