assert: add static_assert if using c11

[pwillem]

Contribution description

When using c11 the macro static_assert doesn't exist. This contribution adds the macro to RIOT's assert.h file.

Issues/PRs references

[miri64]

Ping @gebart, @kaspar030?

[miri64]

Change looks straight forward. However, my toolchain kung-fu isn't good enough to evaluate the value/impact of this change.

[kaspar030]

Wouldn't it make more sense to define

#if __STDC_VERSION__ >= 201112L && !defined __cplusplus
#define static_assert(...) _Static_assert(__VA_ARGS__)
#else
#define static_assert(...)
#endif

... so code compiles for both >=c11 and <c11 compilers?

[pwillem]

what do you think of

#if __STDC_VERSION__ >= 201112L && !defined __cplusplus
/**
 * @brief define c11 static_assert() macro
 */
#define static_assert _Static_assert
#else
#define static_assert(test, msg) assert(test)
#endif

so static asserts are mapped on normal asserts if you don't compile for c11?

[kaspar030]

I thought static asserts can be used at places where others can't, like at global level:

static_assert(sizeof(unsigned long) == 4);
void main() {...}

so defining to normal asserts would make that use case impossible.

[pwillem]

Yes you are right, I will change to your proposal

[pwillem]

I tested your proposal with

#include <assert.h>
int test;
static_assert(sizeof(test) == 4, "msg");
int main(void)
{
    return 0;
}

but when I compile for c99. I get

~/RIOT/tests/static/main.c:25:41: error: ISO C does not allow extra
;’ outside of a function [-Werror=pedantic]

So it seems that if you want to use this c11 feature you should compile your code with c11.

[pwillem]

@kaspar030 What do you want me todo?

[kaspar030]

can you try defining the non-c11 case to struct _static_assert_dummy?

that would turn a non-c11 call to "static_assert(...);" to a forward declaration, which can be in a file multiple times and doesn't have to be used.

[kaspar030]

(thanks for the nudge)

[pwillem]

I tested it and your proposal worked. OK to squash?

[kaspar030]

yes, please squash!

[kaspar030]

Seems like c++ has its own version of "static_assert".

Can you try applying https://gist.github.com/kaspar030/6a7b9d3b2a9e703603c514d32cbd5935?
It moves the else case within the "!defined(__cplusplus)```.

[kaspar030]

That seems to have done it. Please squash!

[kaspar030]

Thanks!