Make clear that this method discards arguments
Suppress ambiguous argument and grouped expression warnings
extend/fileutils: suppress discarded method definition warnings
Suppress uninitialized instance variable warnings
Remove circular require

Will this break anything? It shouldn't; Formula will always be loaded
before Tab anyway. But really there is a design problem here, Tab
shouldn't have any hardcoded references to Formula. I think this is
fixable, but callers of for_formula will need to be checked first.