dev/airflow_mypy/plugin/outputs.py

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from __future__ import annotations

from collections.abc import Callable

from mypy.plugin import AttributeContext, MethodContext, Plugin
from mypy.types import AnyType, Type, TypeOfAny

OUTPUT_PROPERTIES = {
    "airflow.models.baseoperator.BaseOperator.output",
    "airflow.models.mappedoperator.MappedOperator.output",
    "airflow.sdk.bases.operator.BaseOperator.output",
    "airflow.sdk.definitions.mappedoperator.MappedOperator.output",
}

TASK_CALL_FUNCTIONS = {
    "airflow.decorators.base.Task.__call__",
    "airflow.sdk.bases.decorator.Task.__call__",
}


class OperatorOutputPlugin(Plugin):
    """Plugin to convert XComArg to the runtime type.

    This allows us to pass an *XComArg* to a downstream task, such as::

        @task
        def f(a: str) -> int:
            return len(a)


        f(op.output)  # "op" is an operator instance.
        f(g())  # "g" is a taskflow task.

    where the *a* argument of ``f`` should accept a *str* at runtime, but can be
    provided with an *XComArg* in the DAG.

    In the long run, it is probably a good idea to make *XComArg* a generic that
    carries information about the task's return type, and build the entire XCom
    mechanism into the type checker. But Python's type system is still limiting
    in this regard now, and (using the above example) we yet to have a good way
    to convert ``f``'s argument list from ``[str]`` to ``[XComArg[str] | str]``.
    Perhaps *ParamSpec* will be extended enough one day to accommodate this.
    """

    @staticmethod
    def _treat_as_any(context: AttributeContext | MethodContext) -> Type:
        """Pretend *XComArg* is actually *typing.Any*."""
        return AnyType(TypeOfAny.special_form, line=context.context.line, column=context.context.column)

    def get_attribute_hook(self, fullname: str) -> Callable[[AttributeContext], Type] | None:
        if fullname not in OUTPUT_PROPERTIES:
            return None
        return self._treat_as_any

    def get_method_hook(self, fullname: str) -> Callable[[MethodContext], Type] | None:
        if fullname not in TASK_CALL_FUNCTIONS:
            return None
        return self._treat_as_any


def plugin(version: str):
    return OperatorOutputPlugin