Of course, a properly written source filter will insert #line statements, to keep the error messages in sync with the original file. Once you stack a second source filter on top of that, things become hairy, as then, that second source filter needs to understand #line hints as well, and parse them accordingly. Which is unlikely to be correct. I'm not sure if Filter::Simple implements that, but I found #line very handy when dealing with code generated from templates.

As Perl allows anonymous code structures, I tend to try to avoid code generation from templates and try to use as much anonymous code structures as possible, because then I get the Perl syntax check at initial compile time and not at template compile time, which may be in mid-flight already.