Dvc: Add type-hints

[lafrenierejm]

There are lots of type hints throughout dvc's codebase, but I couldn't find any mention of which type checker the hints are expected to pass against. I would propose mentioning it in the README and running the checker as part of the test suite.

[skshetry]

@lafrenierejm, we don't really use/have type-hints. We'd love to start using it, but so far, we haven't been able to get to it. The type-checks you are seeing are mostly for "documentation/autocompletion", we do not enforce it (yet).

[lafrenierejm]

We'd love to start using [a type checker], but so far, we haven't been able to get to it.

Are there any preferences about which type checker(s) is used? mypy [0] is the reference implementation, but there are also FOSS tools from Google, Facebook, and Microsoft that all promise better performance than mypy and various levels of strictness

--
Joseph LaFreniere

[skshetry]

@lafrenierejm, I'd say mypy, but don't really have any favourites. If it's easy to start with, let's say, pytype, we can totally go with that. I assume, it won't be difficult to migrate to "stricter" tools after we have considerable amounts of type-hints, compared to starting-out completely blank.

@lafrenierejm, are you interested in contributing?

[lafrenierejm]

@lafrenierejm, are you interested in contributing?

Yes, I am.

@lafrenierejm, I'd say mypy, but don't really have any favourites. If it's easy to start with, let's say, pytype, we can totally go with that.

Sure! Starting with pytype starts good.

I assume, it won't be difficult to migrate to "stricter" tools after we have considerable amounts of type-hints, compared to starting-out completely blank.

Correct, it should be fine.

[skshetry]

@lafrenierejm, wow, thanks for the interest.

Let's start small, with just simple "not-so strict" config and run those in Github Actions. And, we can expand to other modules thenafter.

If you need any help, please feel free to ask us here in the issue/PR or in the #dev-talk channel on Discord.

[skshetry]

Hi @lafrenierejm, I'll be repurposing this issue as for type checks, I guess that's fine.

[lafrenierejm]

@skshetry Yes, of course that's fine. I'm opening a PR now to run pytype during CI. The build is currently failing the type check, so I'll plan to continue pushing to the branch to resolve the type issues until the PR is suitable to merge.