Type hint linting

[JustinDrake]

It should be possibly to lint the pyspec type hints. See here:

You can run mypy/a linter on the output pyspec file

[hwwhww]

I've tried to add mypy tests - however, the current SSZType + globals() style type definition is quite incompatible with mypy...

I'd say we can solve it with py-ssz. :p

[djrtwo]

We can at least mypy and lint the beacon chain pyspec in CI

[hwwhww]

Appy mypy type hinting check with the current spec:

mypy --follow-imports=silent --warn-unused-ignores --ignore-missing-imports --check-untyped-defs --disallow-incomplete-defs --disallow-any-generics -p eth2spec

Result:
https://gist.github.com/hwwhww/d000591903690fe9cc4a5eb8a09ee4a9

As I can see the problem is that the def SSZType + class SSZObject tricks are in runtime:

https://github.com/ethereum/eth2.0-specs/blob/f57d6fa28e151570e9c94807e6729a679fc7b1cf/test_libs/pyspec/eth2spec/utils/minimal_ssz.py#L10-L38

For example:

Fork = SSZType({
    # Previous fork version
    'previous_version': 'bytes4',
    # Current fork version
    'current_version': 'bytes4',
    # Fork epoch number
    'epoch': 'uint64',
})

And the type checker cannot see functions defined at runtime.

On the other hand, py-ssz defines a container as a ssz.sedes.Serializable subclass:

class Fork(ssz.Serializable):

    fields = [
        # Previous fork version
        ('previous_version', bytes4),
        # Current fork version
        ('current_version', bytes4),
        # Fork epoch number
        ('epoch', uint64)
    ]

    def __init__(self,
                 previous_version: bytes,
                 current_version: bytes,
                 epoch: Epoch) -> None:
        super().__init__(
            previous_version=previous_version,
            current_version=current_version,
            epoch=epoch,
        )

• the fields are knowable to type checkers.
• The __init__ function rewriting is for type hinting in object initialization.

---

/cc @protolambda @dankrad

[JustinDrake]

@hwwhww: What is the status of this with the new SSZ typing?

[hwwhww]

@JustinDrake I was testing on the early version of the new SSZ, I will start to test on the dev branch now.