Add @type_check_only to stub-only private classes in stdlib (#14512)

stdlib/builtins.pyi

@@ -1340,6 +1340,9 @@ class property:
     def __set__(self, instance: Any, value: Any, /) -> None: ...
     def __delete__(self, instance: Any, /) -> None: ...
 
+# This class does not exist at runtime, but stubtest complains if it's marked as
+# @type_check_only because it has an alias that does exist at runtime. See mypy#19568.
+# @type_check_only
 @final
 class _NotImplementedType(Any):
     __call__: None
@@ -1513,7 +1516,7 @@ help: _sitebuiltins._Helper
 def hex(number: int | SupportsIndex, /) -> str: ...
 def id(obj: object, /) -> int: ...
 def input(prompt: object = "", /) -> str: ...
-
+@type_check_only
 class _GetItemIterable(Protocol[_T_co]):
     def __getitem__(self, i: int, /) -> _T_co: ...
 
@@ -1768,7 +1771,7 @@ def open(
     opener: _Opener | None = None,
 ) -> IO[Any]: ...
 def ord(c: str | bytes | bytearray, /) -> int: ...
-
+@type_check_only
 class _SupportsWriteAndFlush(SupportsWrite[_T_contra], SupportsFlush, Protocol[_T_contra]): ...
 
 @overload
@@ -1787,12 +1790,15 @@ def print(
 _E_contra = TypeVar("_E_contra", contravariant=True)
 _M_contra = TypeVar("_M_contra", contravariant=True)
 
+@type_check_only
 class _SupportsPow2(Protocol[_E_contra, _T_co]):
     def __pow__(self, other: _E_contra, /) -> _T_co: ...
 
+@type_check_only
 class _SupportsPow3NoneOnly(Protocol[_E_contra, _T_co]):
     def __pow__(self, other: _E_contra, modulo: None = None, /) -> _T_co: ...
 
+@type_check_only
 class _SupportsPow3(Protocol[_E_contra, _M_contra, _T_co]):
     def __pow__(self, other: _E_contra, modulo: _M_contra, /) -> _T_co: ...
 
@@ -1857,9 +1863,11 @@ def repr(obj: object, /) -> str: ...
 # and https://github.com/python/typeshed/pull/9151
 # on why we don't use `SupportsRound` from `typing.pyi`
 
+@type_check_only
 class _SupportsRound1(Protocol[_T_co]):
     def __round__(self) -> _T_co: ...
 
+@type_check_only
 class _SupportsRound2(Protocol[_T_co]):
     def __round__(self, ndigits: int, /) -> _T_co: ...
 
@@ -1881,6 +1889,7 @@ def sorted(iterable: Iterable[_T], /, *, key: Callable[[_T], SupportsRichCompari
 _AddableT1 = TypeVar("_AddableT1", bound=SupportsAdd[Any, Any])
 _AddableT2 = TypeVar("_AddableT2", bound=SupportsAdd[Any, Any])
 
+@type_check_only
 class _SupportsSumWithNoDefaultGiven(SupportsAdd[Any, Any], SupportsRAdd[int, Any], Protocol): ...
 
 _SupportsSumNoDefaultT = TypeVar("_SupportsSumNoDefaultT", bound=_SupportsSumWithNoDefaultGiven)