c/6906: warn about asserts with side effects

[Matthias Klose <doko@klose.in-berlin.de>]

>Number:         6906
>Category:       c
>Synopsis:       warn about asserts with side effects
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    unassigned
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Sat Jun 01 16:36:00 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Anthony DeRobertis <asd@suespammers.org>
>Release:        3.1 (Debian) (Debian unstable)
>Organization:
The Debian Project
>Environment:
System: Debian GNU/Linux (unstable)
Architecture: i686
	
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Installed/Config-files/Unpacked/Failed-config/Half-installed
|/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
||/ Name           Version        Description
+++-==============-==============-============================================
ii  gcc-3.1        3.1-2          The GNU C compiler.
ii  binutils       2.12.90.0.7-1  The GNU assembler, linker and binary utiliti
ii  libc6          2.2.5-6        GNU C Library: Shared libraries and Timezone
host: i386-linux
configured with: /mnt/data/gcc-3.1/gcc-3.1-3.1ds2/src/configure -v --enable-languages=c,c++,java,f77,proto,objc,ada --prefix=/usr --mandir=$\(prefix\)/share/man --infodir=$\(prefix\)/share/info --with-gxx-include-dir=$\(prefix\)/include/g++-v3-3.1 --enable-shared --with-system-zlib --enable-long-long --enable-nls --without-included-gettext --enable-clocale=gnu --enable-threads=posix --enable-java-gc=boehm --enable-objc-gc i386-linux
>Description:
[ Reported to the Debian BTS as report #123468.
  Please CC 123468@bugs.debian.org on replies.
  Log of report can be found at http://bugs.debian.org/123468 ]

Anthony DeRobertis:
I realize this is probably implemented easily, but a warning about
asserts with obvious side effects would be nice. For example:

	assert(ptr = malloc(...))	/* programmer didn't understand/think about assert */
	assert(*ptr++)				/* ditto */

	assert(f())					/* very suspicious */

	assert(i = 1)				/* programmer made typo */

Some of these may be caught by other warnings (e.g., assignment in
conditional), at least on #undef NDEBUG builds. 

The problem with these is, of course, that everything works fine for the
debugging builds.[0] Then you do a release candidate build, and suddenly
everything breaks.

I wouldn't worry about:
	#ifndef NDEBUG
		...
		ptr++
		...
	#endif
btw, because that looks a lot more guilty to even a novice than
assert(), which looks like a function call.

[0] I'm not sure if assert is allowed to double-use its macro arguments
	or not. So its possible that the standard would allow some of the
	above to break, even on debugging builds.
>How-To-Repeat:
	
>Fix:
	
>Release-Note:
>Audit-Trail:
>Unformatted: