bug#43558: [PATCH]: Fix (forward-comment 1) when end delimiter is escaped.

[Michael Welsh Duggan]

Alan Mackenzie <acm@muc.de> writes:

> Hello, Mattias.
>
> On Wed, Sep 23, 2020 at 11:01:59 +0200, Mattias Engdegård wrote:
>> Sorry if I misunderstood, but since when do backslashes escape */ in C?
>
> Since forever, but only in the CC Mode test suite.  :-(
>
> I just tried it out with gcc, and it seems that \*/ does indeed end a
> block comment.  But an escaped newline doesn't end a line comment,
> instead continuing it to the next line.  So I got confused.  Thanks for
> pointing out the mistake.
>
> It seems that as well as the existing variable
> comment-end-can-be-escaped, we need a new one, say
> line-comment-end-can-be-escaped, too.  In C and C++ modes, these would
> be nil and t respectively.

But where does it say that backslashes escape */ in C++?  The C++ 14
standard (and it hasn't changed through C++ 20) says:

    2.7 Comments [lex.comment]
    
    The characters /* start a comment, which terminates with the
    characters */. These comments do not nest.  The characters // start
    a comment, which terminates immediately before the next new-line
    character. If there is a form-feed or a vertical-tab character in
    such a comment, only white-space characters shall appear between it
    and the new-line that terminates the comment; no diagnostic is
    required. [ Note: The comment characters //, /*, and */ have no
    special meaning within a // comment and are treated just like other
    characters. Similarly, the comment characters // and /* have no
    special meaning within a /* comment.  — end note ]

-- 
Michael Welsh Duggan
(md5i@md5i.com)