from __future__ import annotations

from typing import Callable

from mypy.plugin import AttributeContext, Plugin

from mypy.types import AnyType, Type, TypeOfAny

class AttrPlugin(Plugin):

def get_attribute_hook(self, fullname: str) -> Callable[[AttributeContext], Type] | None:

if fullname == "m.Magic.magic_field":

return magic_field_callback

if fullname == "m.Magic.nonexistent_field":

return nonexistent_field_callback

if fullname == "m.Magic.no_assignment_field":

return no_assignment_field_callback

return None

def magic_field_callback(ctx: AttributeContext) -> Type:

return ctx.api.named_generic_type("builtins.str", [])

def nonexistent_field_callback(ctx: AttributeContext) -> Type:

ctx.api.fail("Field does not exist", ctx.context)

return AnyType(TypeOfAny.from_error)

def no_assignment_field_callback(ctx: AttributeContext) -> Type:

if ctx.is_lvalue:

ctx.api.fail(f"Cannot assign to field", ctx.context)

return AnyType(TypeOfAny.from_error)

return ctx.default_attr_type

def plugin(version: str) -> type[AttrPlugin]:

return AttrPlugin