Add py.typed files

[NiklasRosenstein]

Fixes python-poetry/poetry#5099

This PR adds a py.typed file to mark the poetry-core source code as containing type hints.

Having poetry-core typed allows Poetry plugins to be more thoroughly type checked with Mypy.

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[finswimmer]

Hello @NiklasRosenstein,

thanks a lot for your contribution 👍

We would like to wait for this until we thoroughly type checked poetry-core itself with mypy to give you the best experience with it. 😃

fin swimmer

[NiklasRosenstein]

Hey @finswimmer,

Don't you think that having some wrong types is better than no types to check against?

It also opens up the opportunity for consumers of poetry-core to detect typing issues; see #270

[radoering]

We would like to wait for this until we thoroughly type checked poetry-core itself with mypy to give you the best experience with it. 😃

Maybe, we should rethink this? It could even help avoiding bugs in poetry. See python-poetry/poetry#5485 (comment)

I assume it does more good than evil.

[dimbleby]

I think on the whole this would be better in than not in

• we probably have made progress on the typechecking in this project since this MR was originally raised
• most remaining errors are probably mostly on internal methods and won't harm users of this library
• but anyway surely the only user of this library that counts is poetry itself, and if poetry would find it helpful to have typing here then that's the main thing

And if there are still mistakes then having a py.typed will encourage putting them right.

We could be still further ahead on the typechecking if the MRs that helped to progress this would be merged. python-poetry/poetry#5017 asks for community help, but poetry is slow to accept that help when it arrives. I added a list of open MRs that I know about at python-poetry/poetry#5017 (comment).

[radoering]

I suppose this can be closed because py.typed has already sneaked in via #331. 😉

[dimbleby]

py.typed has already sneaked in via #331.

I just noticed that myself! This was an accident, I'd been trying the effect of adding this and... well, I guess an empty file is an easy thing to miss in a diff.

Anyway, I came here to say that it had gone in accidentally but I reckon that it should stay anyway, happy to see that this was already the thought.