> If the compiler supports "-E", there absolutely is some equivalent of the expanded text, with (somewhat limited) whitespace info available: if you insert whitespace into between "b" and the comma in "b,", then "-E" invocation will dutifully show it. Yes, multiple spaces are collapsed into one, but their presence/absence is tracked already.

Whitespace is significant in the preprocessor so of course it tracks whitespace. Whitespace isn’t dropped until phase 7 when pp-tokens are converted to C tokens.

As I said it’s not impossible, write the patch and see if GCC accepts it.