mypy error for function returning TypeVar based on Type[T] argument

Question

I have a function that validates variable based on TypedDict declaration at runtime. I want it to perform validation, raise exception on error and set return type otherwise.

Essentially, I have this:

T = TypeVar("T")

def validated(data: Any, DataType: Type[T]) -> T:
    validate(data, DataType)  # this raises exception if data is not valid as T
    return data


class MyDataType(TypedDict):
    a: int
    b: str


d = validated(get_data(), MyDataType)
reveal_type(d)
d["a"] + 10
d["b"] + "suffix"

After validated call variable d should be typed as MyDataType, reveal_type(d) shows it. Hence the last two lines are type-safe. However, mypy complains:

temp.py:29: note: Revealed type is "temp.MyDataType"
temp.py:30: error: Unsupported operand types for + ("object" and "int")
temp.py:31: error: "object" has no attribute "lower"

What am I doing wrong?

UPD

I f I add explicit typing to d (d: MyDataType = validated(get_data(), MyDataType)) I get even more mysterious messages:

temp.py:28: error: Incompatible types in assignment (expression has type "MyDataType", variable has type "MyDataType")
temp.py:33: note: Revealed type is "TypedDict('temp.MyDataType', {'a': builtins.int, 'b': builtins.str})"

UPD 2

Seems like the same issue has already been reported: https://github.com/python/mypy/issues/12310

TL;DR: it's not a bug, TypedDict is not valid in this context (although the error message might have been clearer)

Software versions

• mypy: 0.950
• python: 3.9.12