Re: CC Mode - syntactical can of worms.

[Alan Mackenzie <acm@muc.de>]

Hi, Stefan!

On Thu, Jan 31, 2008 at 10:00:07AM -0500, Stefan Monnier wrote:
> > Hi, Emacs and CC Mode!
> > Following up from: [orium69@gmail.com: Bug in emacs 22.1.1 (cosmetic
> > bug)].

> > This bug was in C Mode, with the following source line:

> >     #warning for isn't a keyword here.

> > This fouls up the fontification, because the syntactic fontification
> > recognises the apostrophe as a string opener.  It can get pretty bad -
> > here is a syntactically correct C function:

> > 1   #warning for isn't a keyword here. (
> > 2   //#warning for isnt a keyword here.
> > 3   void foo (bar)
> > 4   {
> > 5   #error Brace yourself! }
> > 6       printf ("Hello, world!\n") ; /* the famous one liner! */
> > 7   }

> You forget other interesting constructs such as

>    #define HELLO }
>    #define WORLD )

>    void foo (WORLD
>    {
>      printf ("Hello\n"WORLD;
>    HELLO

Well, anybody who writes anything like this will get what she deserves.

> and of course, the more common ones like

>    #if foo
>    void foo (void)
>    {
>       size_t toto;
>    #else
>    int foo ()
>    {
>       unsigned toto;
>    #endif

Yes, this has been on my TODO list for a long time.  It shouldn't be that
difficult to fix.  I'm intending a fix in CC Mode 5.32.

> CC-mode's job is fundamentally impossible.

Hey, don't be like that!  ;-)  Yes, people can deliberately break it with
the likes of HELLO and WORLD, but the more modest aim of CC Mode, to deal
properly with anything reasonable, is doable.

I think I can fix this by setting a neutral syntax-table property on
anything obtrusive in a CPP construct.  Here's a first shot at doing
that:


;; Set syntax table properties on a CPP (logical) line, so that it becomes
;; "syntactically neutral".  This means that lines such as:
;;
;;     #warning for isn't a keyword.
;;                     ^
;; and
;;
;;     #define RBRACE }
;;                    ^
;; won't interact syntactically with the rest of the file.
(defun c-neutralize-CPP-line (beg end)
  (let (s)
    (while
	(progn
	  (setq s (parse-partial-sexp beg end -1))
	  (cond
	   ((< (nth 0 s) 0)		; found an unmated ),},]
	    (c-put-char-property (1- (point)) 'syntax-table '(1)) ; "punctuation".
	    t)
	   ((or (nth 3 s) (nth 4 s))	; In a string or comment.
	    (c-put-char-property (nth 8 s) 'syntax-table '(1))
	    t)
	   ((> (nth 0 s) 0)		; In a (,{,[
	    (c-put-char-property (nth 1 s) 'syntax-table '(1))
	    t)
	   (t nil))))))


>         Stefan

-- 
Alan Mackenzie (Nuremberg, Germany).