We do. It's called a type checker. Every "formally verified" system is going to be partially verified. e.g. you might prove your sort procedure sorts, but did you prove its complexity? Under a cost model for integer compares or a cost model for page fetches? Or both? Multi-layer cache page fetch costs? How well you verify just depends on how well you decide to model the problem. Different type checkers have different modeling features.
This is a more useful perspective; it's not "we do/don't use formal methods," but instead "how can I more precisely model my domain?" Helpfully, if you model your domain well, code tends to be obvious/write itself.
This is a more useful perspective; it's not "we do/don't use formal methods," but instead "how can I more precisely model my domain?" Helpfully, if you model your domain well, code tends to be obvious/write itself.