[PATCH] assert.h: allow gcc to detect assert(a = 1) errors

[Zack Weinberg]

On Wed, Nov 23, 2016 at 9:21 PM, Jim Meyering <jim@meyering.net> wrote:
[...]

Not commenting on anything else, but...

> We *do* need that __STRICT_ANSI__ disjunct.
> Otherwise, this would evoke no warning:
>
>   $ gcc -isystem. -I. -Werror=pedantic k.c
>   In file included from k.c:1:0:
>   k.c: In function ‘main’:
>   k.c:2:23: warning: ISO C forbids braced-groups within expressions [-Wpedantic]
>    int main() { assert ( ({1;}) ); return 0; }

... Would you please file a feature-request with the gcc people asking
for something that turns __extension__ back off?  It would be nice to
be able to get this right even in __STRICT_ANSI__ mode.  I'm imagining
that your macro could look like

    #define assert(expr) \
        __extension__ ({ \
            if (__noextension__ (expr)) \
               ; \
            else
               __assert_failed (...); \
            (void)0; \
       })

(Make clear that the parentheses in __noextension__(...) need to not
count for the purpose of -Wparentheses.)

zw