-wpedantic reports erroneous warning for parameters in EM_ASM_ blocks

[aaron-michaux]

Compiling the following code should work without warning. Even in pedantic mode.

#include <emscripten.h>

int main(int, char * *)
{
    int x = EM_ASM_INT({
            console.log('I received: ' + $0);
            return $0 + 1;
        }, 100);
    printf("%d\n", x);
    return 0;
}

However, emcc reports the following warning:

~ > emcc --version
emcc (Emscripten gcc/clang-like replacement) 1.38.8 (commit 1c100d9f8ad4e073b33d64aed2fdf91cbc355cb3)

~ > emcc -x c++ -std=c++17 -stdlib=libc++ -DTARGET="ariel.html" -Wall -Wextra -Wpedantic test.cpp 
test.cpp:7:42: warning: '$' in identifier [-Wdollar-in-identifier-extension]
            console.log('I received: ' + $0);
                                         ^
test.cpp:8:20: warning: '$' in identifier [-Wdollar-in-identifier-extension]
            return $0 + 1;
                   ^
2 warnings generated.

[kripken]

This is probably a side effect of how EM_ASM works - the C compiler does see that code. To avoid that, we'd need to do preprocessing ourselves before clang, which is trickier. But maybe there's another solution I'm missing.

[aaron-michaux]

I'm not sure of the moving parts, but maybe the $0 variable can be mangled as it is written out? Regardless, using the -Wno-dollar-in-identifier-extension switch turns off the warning, so perhaps the entire issue is -pedentic =).

[kripken]

Yeah, but mangling the $0 would need to be done before clang sees it - which would be a big change, I'm afraid.

Another option is to not use $N for those arguments, it could be _N for example. That would be a breaking change, unless we supported both - so none of the options is very appealing, sadly.

[aaron-michaux]

Suppose it would cause other problems with emcc supported both $N and _N. I think a lot of people use _ at the beginning of their variable names even though I believe it is reserved. Maybe __arg_N would be more obvious. I'm not sure I should be making a recommendation, but those are my thoughts.

[stale]

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