A way to require (at compile-time) that variables be "declared"
(assigned a value) before use, like Perl's 'use strict'.
I think this would really help those who take Lua coding beyond "mere
scripting" and into "small-time software engineering". Being able to
catch typos and such at compile-time would really help for non-trivial
projects.
It has to be something that can be turned off, though, as there's no
reason to impede the speed of development when you really are "just
scripting" and don't need it.