get_attribute_hook does not trigger for class attributes, get_base_class_hook cannot resolve class attr types

[FuegoFro]

Bug Report

I wasn't sure how to best phrase title and/or description for this, so edits/suggestions/renames are welcomed.

The get_attribute_hook plugin hook is not triggered for attributes/variables on classes. It seems to only trigger for attributes/variables on instances. Additionally, I seem to be unable to resolve types of class variables in the hook return by get_base_class_hook.

To Reproduce

Given the source file

from typing import Dict, TYPE_CHECKING, Tuple, cast


class Field:
    pass


class FieldBuilder:
    def with_name(self) -> 'FieldBuilder':
        return self

    # Imagine arbitrarily more builder methods

    def build(self) -> Field:
        return Field()


class BaseMeta(type):
    def __new__(mcs, name: str, bases: Tuple[type, ...], attrs: Dict[str, object]) -> 'BaseMeta':
        for key, val in attrs.items():
            if isinstance(val, FieldBuilder):
                attrs[key] = val.build()
        return cast(BaseMeta, type.__new__(mcs, name, bases, attrs))


class Base(metaclass=BaseMeta):
    pass


class Concrete(Base):
    foo = FieldBuilder().with_name()  # Can have arbitrary chain of builder methods
    bar = 1


if TYPE_CHECKING:
    reveal_type(Concrete.foo)  # Would like this to show up as type "Field"
    reveal_type(Concrete.bar)  # Would like this to show up as type "int"
print(type(Concrete.foo))
print(type(Concrete.bar))

and the plugin

from typing import Callable, Optional
from typing import Type as TypingType

from mypy.plugin import AttributeContext, ClassDefContext, Plugin
from mypy.types import Type as MypyType


class ExamplePlugin(Plugin):
    def get_attribute_hook(self, fullname: str) -> Optional[Callable[[AttributeContext], MypyType]]:
        print('ATTRIBUTE HOOK FOR', fullname)
        return None

    def get_base_class_hook(self, fullname: str) -> Optional[Callable[[ClassDefContext], None]]:
        if not fullname.endswith('.Base'):
            return None

        def hook(ctx: ClassDefContext) -> None:
            print('BASE CLASS HOOK FOR', fullname, ctx.cls.fullname)
            if ctx.cls.info.names['foo'].type is None:
                if ctx.api.final_iteration:
                    print('CANNOT DEFER ANY MORE', fullname)
                else:
                    print('DEFERRING', fullname)
                    ctx.api.defer()

        return hook

def plugin(_mypy_info: str) -> TypingType[Plugin]:
    return ExamplePlugin

Expected Behavior

I would expect that an ATTRIBUTE HOOK FOR line would be printed for the Concrete.foo and Concrete.bar accesses. Alternatively, I'd expect to be able to eventually get a non-None type for the foo attribute in the base class hook.

Actual Behavior

The ATTRIBUTE HOOK FOR is never printed for the Concrete.* accesses and we never get a non-None type for foo (we reach the final iteration).

If there's a way to accomplish the Would like this to show up as type comments with the existing plugin hook behaviors, that also works for me! Note, I've seen other plugins use the get_function_hook to modify the return type and therefore the type of the class var, but I didn't see a way to know that the result of the function would be stored in a class var, since I wouldn't want every builder method to be automatically converted.

Your Environment

• Mypy version used: mypy 0.800+dev.f220ce50725ed7f117832b9f03aed4d1a9508e00
• Mypy command-line flags: --show-traceback --warn-unused-configs --config-file <file>
• Mypy configuration options from mypy.ini (and other config files):

[mypy]
plugins = <my plugin>
strict = True

• Python version used: 3.7.6
• Operating system and version: macOS 10.15.7