That was helpful, especially realizing that part of the problem (at least as you see it) is that the "linking" is unidirectional. Function definitions/calls ar

That was helpful, especially realizing that part of the problem (at least as you see it) is that the "linking" is unidirectional. Function definitions/calls are also unidirectionally linked. You can see at the call site which function is called, but you can't see at the function definition the references. But unlike a function, which might be called from many places, it really should be the case that a file is `include`d exactly once.