Mixing callsite assign and callsite source #126

Consider the following hypothetical assert function that mixes callsite_source and callsite assign syntax:

fn assert(
  bool assertion,
  char* callsite_source<file> unsafe file,
  char* callsite_source<function> unsafe scope,
  usize callsite_source<line> line,
  char *message = 0
) {
 ...
}

The compiler will yield the following compilation error:

[ERROR] call argument count mismatch
  --> /home/werle/repos/zzmodules/runtime-assert/tests/pass.zz:10:3
   |
10 |   assert(true);␊
   |   ^----^
   |
   = function '::runtime_assert::assert' is defined over 5 arguments, but you passed 4

when the message argument is not defined. Is this intended? The compiler will succeed in compilation when the message argument is given.