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

[Alan Mackenzie]

Hello, Eli.

On Tue, May 16, 2023 at 18:43:59 +0300, Eli Zaretskii wrote:
> > Date: Tue, 16 May 2023 10:57:40 +0000
> > From: Alan Mackenzie <acm@muc.de>

> > Hello, Emacs.

> > In the master branch:

> Is it different on emacs-29?

No, the bug has been there since ?2016, having been coded, almost
certainly, by me.  ;-(  The context in 2016 was making an escaped NL in
a C++ line comment continue the comment's fontification onto the next
line.  The (then) new variable comment-end-can-be-escaped configured the
effect of the backslash at EOL.

I have been assuming that it is too unimportant a bug to go into
emacs-29 at this late stage.

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

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

> Why not both?  IOW, please explain why char_quoted is not TRT here.

Because parse-partial-sexp is not scanning the backslash.  The scan
starts one character after the backslash, and the syntactic effect of
that backslash is not in the OLDSTATE argument to parse-partial-sexp.

-- 
Alan Mackenzie (Nuremberg, Germany)