RE: Emacs-21.1: cwarn-mode doesn't highlight shift assignments >> =, <<=

[Broadey Kevin-BKB003]

Couldn't resist a bit of elisp hacking!  Here's a diff to highlight <<= and 
>>=.  It also highlights the whole of the operator rather than just the =.  
This makes it show up better IMHO.

I'm not entirely happy with the regexp.  I had to stick "[^!<>=]" at the 
beginning to stop the = in comparison operators being highlighted.  It works, 
but I think there should be a cleaner way to catch a plain assignment "=".


$ gdiff -u cwarn.el.orig cwarn.el
--- cwarn.el.orig Tue Dec  4 10:18:45 2001
+++ cwarn.el Tue Dec  4 10:44:13 2001
@@ -1,5 +1,9 @@
 ;;; cwarn.el --- highlight suspicious C and C++ constructions
 
+;; 4-Dec-01 kevin.broadey@motorola.com
+;; Add shift-assignment operators to list highlighted, and highlight
+;; the whole operator rather than just the "=".
+
 ;; Copyright (C) 1999, 2000 Free Software Foundation, Inc.
 
 ;; Author: Anders Lindgren <andersl@andersl.com>
@@ -394,7 +398,11 @@
   (let ((res nil))
     (while
  (progn
-   (setq res (re-search-forward "[^!<>=]\\(=\\)[^=]" limit t))
+   ;; the [^!<>=] at the beginning of the regexp is needed to stop the "=" in
+   ;; comparison operators == != <= >= being highlighted.  Is there a better
+   ;; way to anchor the regexp?
+   (setq res (re-search-forward "[^!<>=]\\(\\([-+*/%&^|]\\|<<\\|>>\\)?=\\)[^=]"
+           limit t))
    (and res
         (save-excursion
    (goto-char (match-beginning 1))

Here's my test file:-

void foo (void)
{
    /* assignment operators */

    if (a = b);

    if (a += b);

    if (a -= b);

    if (a *= b);

    if (a /= b);

    if (a &= b);

    if (a |= b);

    if (a ^= b);

    if (a <<= b);

    if (a >>= b);

    /* comparison operators */

    if (a == b);

    if (a != b);

    if (a <= b);

    if (a >= b);
}

-- 
Kevin

> -----Original Message-----
> From: Kevin Broadey [mailto:Kevin_Broadey-BKB003@email.mot.com]
> Sent: 04 December 2001 10:19
> To: bug-gnu-emacs@gnu.org
> Cc: andersl@andersl.com
> Subject: Emacs-21.1: cwarn-mode doesn't highlight shift 
> assignments >>=, <<=
> 
> 
> 
> In GNU Emacs 21.1.4 (sparc-sun-solaris2.7, Motif Version 2.1.0)
>  of 2001-11-30 on bah128
> configured using `configure  
> --prefix=/org/users/kevinbr/gnu/emacs-21.1 
> --exec-prefix=/org/users/kevinbr/gnu/emacs-21.1/SunOS 
> --with-x-toolkit=motif'
> Important settings:
>   value of $LC_ALL: nil
>   value of $LC_COLLATE: nil
>   value of $LC_CTYPE: nil
>   value of $LC_MESSAGES: nil
>   value of $LC_MONETARY: nil
>   value of $LC_NUMERIC: nil
>   value of $LC_TIME: nil
>   value of $LANG: nil
>   locale-coding-system: nil
>   default-enable-multibyte-characters: nil
> 
> cwarn-mode looks like a great idea.  I used to have this in my
> .emacs to guard against the same problem:-
> 
> (let ((c-font-lock-extras
>        '(
>        ;; assignment operators:
>        ("[-+*/%&^|]=" . font-lock-warning-face)       ; -= += 
> *= %= &= ^= |=
>        ("\\(>>\\|<<\\)=" . font-lock-warning-face)    ; <<= >>=
>        ("[<>!=]=" . 'default)                         ; <= >= != ==
>        ("=\\|\\+\\+\\|--" . font-lock-warning-face)   ; = ++ --
>        )))
>   (font-lock-add-keywords 'c-mode c-font-lock-extras)
>   (font-lock-add-keywords 'c++-mode c-font-lock-extras))
> 
> but cwarn is better as it only highlights the suspicious ones.
> 
> Unfortunately cwarn doesn't highlight the assigning shift operators
> "<<=" and ">>=".  Not a major problem, but it should do for
> completeness.  I guess it's difficult as you need to ignore "<=" and
> ">=".
> 
> One other suggestion - can you get it to highlight the whole of the
> operator rather than just the "="?
> 
> -- 
> Kevin Broadey
>