Conditional operator does not typecheck

[Michael Tautschnig]

While building your package using our research compiler infrastructure we noticed that the condition operator resulting from expansion of katze_object_assign of katze/katze-utils.h does not typecheck:

The return type of g_object_unref is void, but lvalue may be of an abitrary pointer type. Yet the C standard requires that the second and third argument of the conditional operator ?: are both void or compatible pointer types (there are several other cases, see 6.5.15 of the C Standard). Failing this, the compiler may produce arbitrary code.

The best way to fix this is likely changing

#define katze_object_assign(lvalue, rvalue) \
    lvalue = ((lvalue ? g_object_unref (lvalue) : lvalue), rvalue)

to

#define katze_object_assign(lvalue, rvalue) \
    lvalue = ((lvalue ? g_object_unref (lvalue) : (void)0), rvalue)

as the returned value is always rvalue anyway.

Best,
Michael

[Cris Dywan (kalikiana)]

I'm not sure that I see the practical consequence, but given it's a trivial fix, why not. Thanks!