Mypy gives confusing/misleading error message

Bug Report

Mypy reports error: Name "..." is not defined [name-defined] when using an instance attribute that was annotated.

To Reproduce

from inspect import Parameter


class ListElementDescriptor[T]:
    name: str
    item_type: type[T]

    @property
    def signature_parameter(self) -> Parameter:
        return Parameter(name=self.name, kind=Parameter.KEYWORD_ONLY, annotation=list[self.item_type])

Expected Behavior

Definitely not an error that self.item_type is not defined. I suspect mypy tries to to convey a different error, maybe related to using variables for type parameters in generics, though I disagree with that as well since list[] is not used here in a typing context to specify a type, but is used as a value.

Actual Behavior

typing-7.py:11: error: Name "self.item_type" is not defined  [name-defined]
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: mypy 1.12.0+dev.6a0657e5959ba1777c4d427f8f355d499035d145 (compiled: no)
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files):

[tool.mypy]
enable_incomplete_feature = "NewGenericSyntax"
disable_bytearray_promotion = true
disable_memoryview_promotion = true
check_untyped_defs = true
warn_unreachable = true
warn_redundant_casts = true
warn_unused_ignores = true

• Python version used: 3.12

まず、提供された ListElementDescriptor の例を mypy 1.12.0+dev.6a0657e5959ba1777c4d427f8f355d499035d145 と、示されている Python 3.12 の設定で実行します。list[self.item_type] に対する診断を追跡し、self.item_type が未定義だと主張するのではなく、報告される問題が正確になるよう更新します。再現手順をもう一度実行して、誤解を招く name-defined エラーがなくなったことを確認します。