Given the following code...

class T{};

void f()
{
    UNDEFINED_MACRO (T);
}

https://godbolt.org/z/5WjGM4KE6

we might expect an error regarding the undeclared identifier UNDEFINED_MACRO however, in this specific case we get 'T' does not refer to a value.

If we change the code to so that it passes a variable instead of a type, for example...

void f()
{
    int i;
    UNDEFINED_MACRO (i);
}

https://godbolt.org/z/YT1GGPG4Y

then the error is the more expected use of undeclared identifier 'UNDEFINED_MACRO'.

gcc and MSVC both appear to error as we might expect in this scenario.

I've tested this using trunk on CompilerExplorer as linked above.