Forward-referencing type application with type variable in a value expression in stubs emits confusing error

Bug Report, To Reproduce, & Actual Behaviour

In .pyi stub files, the spec mandates type-checkers to recognise forward references in annotation expressions without string-quoting. It is however silent about value expressions, but in mypy I've used symbols defined later in a stub file in a value context before without any issues, except recently when hitting the following example:

# stub.pyi
from typing_extensions import Generic, TypeVar

R = TypeVar("R")
T = TypeVar("T")

class A(Generic[R]):
    var = B[R]()  # E: "R" is a type variable and only valid in type context

class B(Generic[T]): ...

Expected Behavior

Either:

1. no errors, or
2. mypy doesn't support forward references in value contexts for stub files, and this emits a used-before-def error at B[R]().

Your Environment

• Mypy version used: 1.17
• Python version used: 3.11, 3.12

stub.pyi の再現ケースから始め、mypy が stub ファイル内の値式における前方参照をどのように処理するかを調べます。現在の診断結果を issue に記載された 2 つの期待される結果と比較します。B[R]() で動作が受け入れられるか、used-before-def として報告されれば完了です。