GNU bug report logs - #63535
Master branch: Error in forw_comment (syntax.c) handling of escaped LFs

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Alan Mackenzie <acm <at> muc.de>
Subject: bug#63535: closed (Re: bug#63535: Master branch: Error in
 forw_comment (syntax.c) handling of escaped LFs)
Date: Mon, 22 May 2023 16:17:02 +0000

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Your bug report

#63535: Master branch: Error in forw_comment (syntax.c) handling of escaped LFs

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 63535 <at> debbugs.gnu.org.

-- 
63535: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=63535
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Alan Mackenzie <acm <at> muc.de>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: acm <at> muc.de, 63535-done <at> debbugs.gnu.org
Subject: Re: bug#63535: Master branch: Error in forw_comment (syntax.c)
 handling of escaped LFs
Date: Mon, 22 May 2023 16:16:49 +0000

Hello, Stefan.

On Mon, May 22, 2023 at 11:16:40 -0400, Stefan Monnier wrote:
> > I think the following patch is better.  Would you please have a look at
> > it, in the hope I haven't made any other silly mistakes.  Thanks!

> I don't see any silly mistake there, sorry.

Thanks!  I've committed the patch, and I'm closing the bug.

>         Stefan


> PS: It does remind me that we really should do ourselves a favor and get rid
> of the distinction between `Sescape` and `Scharquote`.
> IIRC there's a risk of backward incompatibility, so it has to be done
> progressively, but we should start the process.  E.g. first declare one of the
> two as obsolete, then emit a warning when we see it being used, ...

Yes.  I think Sescape should be the survivor.  I don't know if
Scharquote is used at all in Emacs code.

-- 
Alan Mackenzie (Nuremberg, Germany).

[Message part 3 (message/rfc822, inline)]

From: Alan Mackenzie <acm <at> muc.de>
To: bug-gnu-emacs <at> gnu.org
Subject: Master branch: Error in forw_comment (syntax.c) handling of escaped
 LFs
Date: Tue, 16 May 2023 10:57:40 +0000

Hello, Emacs.

In the master branch:

Consider the following C++ Mode buffer:

    // comment \
    comment line 2
    line_3();

..  The backslash at the end of line 1 extends the comment into line 2.

Put point at // on L1, and do:

    M-: (setq s (parse-partial-sexp (point) (+ (point) 9)))

..  s gets the parse state of the inside of the comment.

Now put point at EOL 1, between the backslash and the LF.  Do

    M-: (parse-partial-sexp (point) (point-max) nil nil s 'syntax-table)

..  This ought to leave point at BOL 2, since the syntax before the LF at
EOL 1 is that of a C++ comment, otherwise neutral.  Instead, it leaves
point wrongly at BOL 3.

#########################################################################

The reason for this bug is at L+42 of forw_comment (in syntax.c).  There
we have

   && !(comment_end_can_be_escaped && char_quoted (from, from_byte))

..  Checking char_quoted is wrong.  Instead the function should check the
current parse state.

-- 
Alan Mackenzie (Nuremberg, Germany).

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