How could Perl know this in the face of AUTOLOAD, run-time module loading, and symbol table manipulation?

It wouldn't be foolproof, but could the warning be somewhat like the "Name %s used only once" warnings with package variables? Example included for those who don't know what I'm talking about:

$ perl -wle '$foo = 1; print 5'
Name "main::foo" used only once: possible typo at -e line 1.
5
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