Preprocessor error on preprocessor-if in macro

[Oliver Parczyk]

While setting up cppcheck for a larger codebase (and working around my other problems) I've uncovered another issue, this time concering some... gymnastics using the preprocessor. It's not as contrived but I can't share the original.

I've condensed it into this example:

#define ADD_INT(x, y) x+y

int main() {
    return ADD_INT(1,
#if 1
    5
#else
    6
#endif
     );
}

cppcheck (both latest master and last release) give the following* error:

$ cppcheck preprocessorError.c 
Checking preprocessorError.c ...
preprocessorError.c:5:0: error: failed to expand 'ADD_INT', it is invalid to use a preprocessor directive as macro parameter [preprocessorErrorDirective]
#if 1
^

*: Perhaps interestingly, the build from master gives the error twice:

$ cppcheck preprocessorError.c 
Checking preprocessorError.c ...
preprocessorError.c:5:0: error: failed to expand 'ADD_INT', it is invalid to use a preprocessor directive as macro parameter [preprocessorErrorDirective]
#if 1
^
preprocessorError.c:5:1: error: failed to expand 'ADD_INT', it is invalid to use a preprocessor directive as macro parameter [preprocessorErrorDirective]
#if 1
^

Note that replacing #if 1 with #ifdef NOT_DEFINED doesn't change this behaviour.

both clang and gcc build this code just fine, their preprocessor output behaves as expected (I've removed a few blank lines):

$ cpp preprocessorError.c 
# 0 "preprocessorError.c"
# 0 "<built-in>"
# 0 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 0 "<command-line>" 2
# 1 "preprocessorError.c"

int main() {
 return 1 +5
   ;
}

[CHR]

See https://github.com/danmar/simplecpp/issues/328