> a runtime impact we need to consider

No need to read the source lines from file.

caller(EXPR) gives you the subs name already as 4th return value.

See caller for details.

update

never mind, I just realized that you still want to parse the code where the call happens, because the error happens in the args-list there debug("x=$x y=$y");

That's pretty much as stable as a source filter.

Why not relying on Smart::Comments then?

YMMV