Report Caller location?

I am trying to refactor a number of things in our CMAKE code

As a RESULT - I have a number of ‘assert-like’ functions

for example,
assert_ENV_VAR_DEFINED( NAME OUTVAR )

This verifies that the NAMED env var exists
If not - it throws an error and exits.
If it does exist - the OUTVAR is set and we move on…

What I want to do is print the LOCATION of the CALLER

How can I print the location of the function caller?