up = foo.north()
right = foo.east()
down = foo.south()
Personally, I don't even rely on normal autocomplete very much when I code because I feel like if I don't know what I'm trying to call, then I don't know the language or library well enough, and it's best to go look at the documentation.
As for mistakes, I've got a good enough sense for reading code in any language to know if something is obviously wrong with an algorithm. The mistakes Copilot makes aren't usually to do with language-specific syntax, they're typically algorithmic and therefore easy to spot in any language. This makes sense if you think about GPT-3's output for English: it tends to be syntactically correct, but often completely wrong about facts.
It helps that Rust's compiler is so picky and so helpful, because on the rare occasions when Copilot was completely wrong about the language the compiler could set me straight pretty quickly. Writing automated tests also helped and was made easy by Copilot. I could write a single test case showing how to use the API, and then just write function names to generate the rest of the tests (obviously I would sanity-check the assertions Copilot produced).
From what I've seen GTP3 works exceptionally well until it doesn't, which can be easily missed.
It is also great as a starting point for error messages, comments, etc.
I think the key is to still give a shit about the code you're writing.
As with everything I always do visual sanity checks.