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>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#63535: closed (Master branch: Error in forw_comment
 (syntax.c) handling of escaped LFs)
Date: Mon, 22 May 2023 16:17:01 +0000

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Your message dated Mon, 22 May 2023 16:16:49 +0000
with message-id <ZGuVcSfR-JEgVb7g <at> ACM>
and subject line Re: bug#63535: Master branch: Error in forw_comment (syntax.c) handling of escaped LFs
has caused the debbugs.gnu.org bug report #63535,
regarding Master branch: Error in forw_comment (syntax.c) handling of escaped LFs
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


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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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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).

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