`generics_defaults.py` mandates that type checkers should allow a class that raises `TypeError` at runtime

This test mandates that type checkers should allow classes that have ParamSpecs-with-defaults following TypeVarTuples: https://github.com/python/typing/blob/22d9392a5ead302cc02c47ecbbcf3aa40106fd9f/conformance/tests/generics_defaults.py#L191-L200

But these fail at runtime. Using Python 3.11 syntax:

% uvx python3.14       
Python 3.14.0 (main, Oct 10 2025, 12:54:13) [Clang 20.1.4 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from typing import *
>>> Ts = TypeVarTuple("Ts")
>>> P = ParamSpec("P", default=[int, str])
>>> class A(Generic[*Ts, P]): ...
... 
Traceback (most recent call last):
  File "<python-input-3>", line 1, in <module>
    class A(Generic[*Ts, P]): ...
            ~~~~~~~^^^^^^^^
  File "/Users/alexw/Library/Application Support/uv/python/cpython-3.14.0-macos-aarch64-none/lib/python3.14/typing.py", line 402, in inner
    return func(*args, **kwds)
  File "/Users/alexw/Library/Application Support/uv/python/cpython-3.14.0-macos-aarch64-none/lib/python3.14/typing.py", line 1157, in _generic_class_getitem
    return _GenericAlias(cls, args)
  File "/Users/alexw/Library/Application Support/uv/python/cpython-3.14.0-macos-aarch64-none/lib/python3.14/typing.py", line 1334, in __init__
    self.__parameters__ = _collect_type_parameters(
                          ~~~~~~~~~~~~~~~~~~~~~~~~^
        args,
        ^^^^^
        enforce_default_ordering=enforce_default_ordering,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/Users/alexw/Library/Application Support/uv/python/cpython-3.14.0-macos-aarch64-none/lib/python3.14/typing.py", line 291, in _collect_type_parameters
    raise TypeError('Type parameter with a default'
                    ' follows TypeVarTuple')
TypeError: Type parameter with a default follows TypeVarTuple

Using Python <=3.10 syntax:

>>> class B(Generic[Unpack[Ts], P]): ...
... 
Traceback (most recent call last):
  File "<python-input-4>", line 1, in <module>
    class B(Generic[Unpack[Ts], P]): ...
            ~~~~~~~^^^^^^^^^^^^^^^
  File "/Users/alexw/Library/Application Support/uv/python/cpython-3.14.0-macos-aarch64-none/lib/python3.14/typing.py", line 402, in inner
    return func(*args, **kwds)
  File "/Users/alexw/Library/Application Support/uv/python/cpython-3.14.0-macos-aarch64-none/lib/python3.14/typing.py", line 1157, in _generic_class_getitem
    return _GenericAlias(cls, args)
  File "/Users/alexw/Library/Application Support/uv/python/cpython-3.14.0-macos-aarch64-none/lib/python3.14/typing.py", line 1334, in __init__
    self.__parameters__ = _collect_type_parameters(
                          ~~~~~~~~~~~~~~~~~~~~~~~~^
        args,
        ^^^^^
        enforce_default_ordering=enforce_default_ordering,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/Users/alexw/Library/Application Support/uv/python/cpython-3.14.0-macos-aarch64-none/lib/python3.14/typing.py", line 291, in _collect_type_parameters
    raise TypeError('Type parameter with a default'
                    ' follows TypeVarTuple')
TypeError: Type parameter with a default follows TypeVarTuple

And using Python 3.13+ syntax:

>>> class C[*Ts, **P = [int, str]]: ...
... 
Traceback (most recent call last):
  File "<python-input-5>", line 1, in <module>
    class C[*Ts, **P = [int, str]]: ...
  File "<python-input-5>", line 1, in <generic parameters of C>
    class C[*Ts, **P = [int, str]]: ...
  File "/Users/alexw/Library/Application Support/uv/python/cpython-3.14.0-macos-aarch64-none/lib/python3.14/typing.py", line 1334, in __init__
    self.__parameters__ = _collect_type_parameters(
                          ~~~~~~~~~~~~~~~~~~~~~~~~^
        args,
        ^^^^^
        enforce_default_ordering=enforce_default_ordering,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/Users/alexw/Library/Application Support/uv/python/cpython-3.14.0-macos-aarch64-none/lib/python3.14/typing.py", line 291, in _collect_type_parameters
    raise TypeError('Type parameter with a default'
                    ' follows TypeVarTuple')
TypeError: Type parameter with a default follows TypeVarTuple

Since it seems that the tests are quoting the spec here, is this a bug in the runtime implementation of the typing module? Or should we update the spec and the conformance suite to allow type checkers to catch this runtime error?

conformance/tests/generics_defaults.py の191-200行から始め、その要件を typing 仕様と比較します。次に typing.py の _collect_type_parameters を調査し、引用されている Python 構文バージョン全体で例を再現します。完了条件は、runtime と仕様および conformance test のどちらが不整合なのかを判断し、選択した修正に対する回帰テストのカバレッジを追加することです。