A project I help maintain has had a report that it fails to compile with GCC 9
https://github.com/wahern/cqueues/issues/212#issuecomment-461693111
I've attached a minimal reproduction of the issue.
Trying to compile it results in:
: In function 'main':
:46:15: error: lvalue required as unary '&' operand
46 | void *x = &quietinit((struct bar){ 0, .a = 0 });
| ^
Compiler returned: 1
/*
* C O M P I L E R A N N O T A T I O N S
*
* GCC with -Wextra, and clang by default, complain about overrides in
* initializer lists. Overriding previous member initializers is well
* defined behavior in C. We rely on this behavior to define default,
* overrideable member values when instantiating configuration objects.
*
* quietinit() guards a compound literal expression with pragmas to
* silence these shrill warnings. This alleviates the burden of requiring
* third-party projects to adjust their compiler flags.
*
* NOTE: If you take the address of the compound literal, take the address
* of the transformed expression, otherwise the compound literal lifetime is
* tied to the scope of the GCC statement expression.
*
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
#if defined __clang__
#define PRAGMA_PUSH _Pragma("clang diagnostic push")
#define PRAGMA_QUIET _Pragma("clang diagnostic ignored \"-Winitializer-overrides\"")
#define PRAGMA_POP _Pragma("clang diagnostic pop")
#define quietinit(...) \
PRAGMA_PUSH PRAGMA_QUIET __VA_ARGS__ PRAGMA_POP
#elif (__GNUC__ == 4 && __GNUC_MINOR__ >= 6) || __GNUC__ > 4
#define PRAGMA_PUSH _Pragma("GCC diagnostic push")
#define PRAGMA_QUIET _Pragma("GCC diagnostic ignored \"-Woverride-init\"")
#define PRAGMA_POP _Pragma("GCC diagnostic pop")
/* GCC parses the _Pragma operator less elegantly than clang. */
#define quietinit(...) \
__extension__ ({ PRAGMA_PUSH PRAGMA_QUIET __VA_ARGS__; PRAGMA_POP })
#else
#define PRAGMA_PUSH
#define PRAGMA_QUIET
#define PRAGMA_POP
#define quietinit(...) __VA_ARGS__
#endif
struct bar {
int a;
};
int main() {
void *x = &quietinit((struct bar){ 0, .a = 0 });
}
