__builtin_choose_expr is not evaluated in constant contexts

[medhefgo]

Bug type: Language Service

Describe the bug

• OS and Version: Arch Linux
• VS Code Version: 1.61.1
• C/C++ Extension Version: 1.7.0

The following code sample produces bogus warnings that neither gcc or clang produce when compiling. The macro is from systemd and is designed to give a compiler error if the expression cannot be evaluated at compile time.

#define ELEMENTSOF(x)                                                    \
        (__builtin_choose_expr(                                          \
                !__builtin_types_compatible_p(typeof(x), typeof(&*(x))), \
                sizeof(x)/sizeof((x)[0]),                                \
                (void)0))

int main(void) {
    int array1[1] = {};
    int array2[__builtin_choose_expr(1, 1, (void)0)] = {};
    int array3[ELEMENTSOF(array1)] = {};
    return 0;
}

variable may not be initialized and incomplete type is not allowed warnings for both array2 and array3 despite the fact that the expression is/must be evaluated at compile time (which is kind of the whole point of __builtin_choose_expr).

[Colengms]

Hi @medhefgo . Thanks for reporting this. I'm able to also reproduce the issue in VS, so I've opened an internal issue against VS.

[sean-mcmanus]

This is fixed with 1.10.3 (pre-release).

[sean-mcmanus]

But it's only fixed for gcc mode and not clang...so we either need to keep this open or create a new issue to track that case.

[sean-mcmanus]

The remaining bug with clang mode is being tracked by #9368