Add wl_resource_get_client to lib

[m-col]

I used this for qtile/qtile#3663

Is there a more appropriate way to get access to this function, considering it isn't used by pywayland directly, or is this fine?

[flacjacket]

I'm fine with this. Is this something that we could wrap in a pywayland.server.Client and use something like wlroots.Ptr to compare this to the other client? We'd need to come up with a way to create a Client without it being created. If that makes things too hard, we can stick with this to get the functionality in and fix it up as we find better ways to structure this.

[m-col]

Something equivalent to this (though the construction could be moved to __init__ if we make its current arguments and creation optional)?:

    @classmethod
    def from_resource(cls, resource: Resource) -> Client:
        """Look up the corresponding wl_client for a wl_resource

        :param resource: The wl_resource
        :type resource: pywayland.protocol_core.Resource
        :returns:
            A `Client` instance.
        """
        client = Client.__new__()
        client._ptr = lib.wl_resource_get_client(res_ptr)
        client._display = None
        return client

That would be nice. Currently Client.__init__ creates a new wl_client, rather than allowing for representation of existing wl_clients, but that would be useful for cases like this.

[flacjacket]

Right, something like that!

[m-col]

Commit message for info on the updates:

This provides 2 alternative ways to construct Client instances:

- via the `from_resource` class method, from a wl_resource pointer. This
  accepts a pointer cdata rather than a `Resource` instance, as should
  be feasible to use this method without requiring an interface to
  implement the `Resource` generic for it. E.g. the layer shell protocol
  doesn't have a `Resource` class and this is fine; the requirement
  would disable usage of `Client.from_resource` from layer shell
  components.
- by passing `ptr=` to `Client` directly to represent an existing
  wl_client rather than creating a fresh one.

[m-col]

This is causing an interesting mypy error:

pywayland/server/client.py:157: error: Module has no attribute "wl_resource_get_client"; maybe "wl_resource_get_id", "wl_resource_get_version", or "wl_resource_get_user_data"?  [attr-defined]

The new C function added to the ffi lib isn't found by mypy so mypy is complaining about the absent attr. Any ideas how this can be resolved? Not sure I've seen this before with all of the ffi modules we use!

[flacjacket]

Right, you can add the stubs to pywayland/_ffi/lib.pyi.

[flacjacket]

Great!