I spent at least an hour a while ago trying to track down a bug that turned out to be caused by exactly this. I couldn't work out what was happening until I looked at the preprocessor output.
Unfortunately, the standard preprocessor output doesn't provide a convenient way to do this without a comment format. I guess you could use a do-nothing #pragma.
Eventually, I'm sure somebody will spin up some extension to clang to show you the complete evolution of a block of code and what other code contributed to that evolution.
For instance running it on the following code in the middle of a C source file:
#define BOGO_MAX(a, b) a > b ? a : b
int test()
{
return BOGO_MAX(3 + 4, 5);
}
int test()
{
return 3 + 4 > 5 ? 3 + 4: 5;
}That being said if I'm not sure if some code is being compiled I just add an "#error foo" and rebuild. Or even simpler I just type in some garbage to trigger a compilation error.