add _contextvars for proper naming (#12981)

On 3.9 and lower, the contextvars types call themselves builtins.*
which we can't and won't match. This improves naming fidelity for
3.10 and newer.

stdlib/@tests/stubtest_allowlists/common.txt

@@ -382,7 +382,7 @@ codecs.CodecInfo.streamreader
 codecs.CodecInfo.streamwriter
 
 collections.UserList.sort  # Runtime has *args but will error if any are supplied
-contextvars.Context.__init__  # C signature is broader than what is actually accepted
+_?contextvars.Context.__init__  # C signature is broader than what is actually accepted
 
 # The Dialect properties are initialized as None in Dialect but their values are enforced in _Dialect
 csv.Dialect.delimiter

stdlib/@tests/stubtest_allowlists/py311.txt

@@ -144,7 +144,6 @@ weakref.ProxyType.__reversed__  # Doesn't really exist
 # C signature is broader than what is actually accepted
 ast.ExtSlice.__new__
 ast.Index.__new__
-contextvars.Context.__init__
 
 # Undocumented implementation details
 cgi.FieldStorage.bufsize

stdlib/@tests/stubtest_allowlists/py312.txt

@@ -149,7 +149,6 @@ sys.last_exc
 # C signature is broader than what is actually accepted
 ast.ExtSlice.__new__
 ast.Index.__new__
-contextvars.Context.__init__
 
 # Treated an alias of a typing class in the stubs,
 # they are generic to type checkers anyway.

stdlib/@tests/stubtest_allowlists/py313.txt

@@ -125,7 +125,6 @@ sys.last_exc
 # C signature is broader than what is actually accepted
 ast.ExtSlice.__new__
 ast.Index.__new__
-contextvars.Context.__init__
 
 # Treated an alias of a typing class in the stubs,
 # they are generic to type checkers anyway.

stdlib/@tests/stubtest_allowlists/py38.txt

@@ -113,7 +113,7 @@ tkinter.Tcl
 tkinter.Tk.__init__
 
 # Exists at runtime, but missing from stubs
-contextvars.ContextVar.__class_getitem__
+_?contextvars.ContextVar.__class_getitem__
 datetime.datetime_CAPI
 dummy_threading.ExceptHookArgs
 dummy_threading.Lock

stdlib/VERSIONS

@@ -28,6 +28,7 @@ _codecs: 3.0-
 _collections_abc: 3.3-
 _compat_pickle: 3.1-
 _compression: 3.5-
+_contextvars: 3.7-
 _csv: 3.0-
 _ctypes: 3.0-
 _curses: 3.0-

stdlib/_contextvars.pyi

@@ -0,0 +1,61 @@
+import sys
+from collections.abc import Callable, Iterator, Mapping
+from typing import Any, ClassVar, Generic, TypeVar, final, overload
+from typing_extensions import ParamSpec
+
+if sys.version_info >= (3, 9):
+    from types import GenericAlias
+
+_T = TypeVar("_T")
+_D = TypeVar("_D")
+_P = ParamSpec("_P")
+
+@final
+class ContextVar(Generic[_T]):
+    @overload
+    def __init__(self, name: str) -> None: ...
+    @overload
+    def __init__(self, name: str, *, default: _T) -> None: ...
+    def __hash__(self) -> int: ...
+    @property
+    def name(self) -> str: ...
+    @overload
+    def get(self) -> _T: ...
+    @overload
+    def get(self, default: _T, /) -> _T: ...
+    @overload
+    def get(self, default: _D, /) -> _D | _T: ...
+    def set(self, value: _T, /) -> Token[_T]: ...
+    def reset(self, token: Token[_T], /) -> None: ...
+    if sys.version_info >= (3, 9):
+        def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
+
+@final
+class Token(Generic[_T]):
+    @property
+    def var(self) -> ContextVar[_T]: ...
+    @property
+    def old_value(self) -> Any: ...  # returns either _T or MISSING, but that's hard to express
+    MISSING: ClassVar[object]
+    if sys.version_info >= (3, 9):
+        def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
+
+def copy_context() -> Context: ...
+
+# It doesn't make sense to make this generic, because for most Contexts each ContextVar will have
+# a different value.
+@final
+class Context(Mapping[ContextVar[Any], Any]):
+    def __init__(self) -> None: ...
+    @overload
+    def get(self, key: ContextVar[_T], default: None = None, /) -> _T | None: ...
+    @overload
+    def get(self, key: ContextVar[_T], default: _T, /) -> _T: ...
+    @overload
+    def get(self, key: ContextVar[_T], default: _D, /) -> _T | _D: ...
+    def run(self, callable: Callable[_P, _T], *args: _P.args, **kwargs: _P.kwargs) -> _T: ...
+    def copy(self) -> Context: ...
+    def __getitem__(self, key: ContextVar[_T], /) -> _T: ...
+    def __iter__(self) -> Iterator[ContextVar[Any]]: ...
+    def __len__(self) -> int: ...
+    def __eq__(self, value: object, /) -> bool: ...

stdlib/contextvars.pyi

@@ -1,63 +1,3 @@
-import sys
-from collections.abc import Callable, Iterator, Mapping
-from typing import Any, ClassVar, Generic, TypeVar, final, overload
-from typing_extensions import ParamSpec
-
-if sys.version_info >= (3, 9):
-    from types import GenericAlias
+from _contextvars import Context as Context, ContextVar as ContextVar, Token as Token, copy_context as copy_context
 
 __all__ = ("Context", "ContextVar", "Token", "copy_context")
-
-_T = TypeVar("_T")
-_D = TypeVar("_D")
-_P = ParamSpec("_P")
-
-@final
-class ContextVar(Generic[_T]):
-    @overload
-    def __init__(self, name: str) -> None: ...
-    @overload
-    def __init__(self, name: str, *, default: _T) -> None: ...
-    def __hash__(self) -> int: ...
-    @property
-    def name(self) -> str: ...
-    @overload
-    def get(self) -> _T: ...
-    @overload
-    def get(self, default: _T, /) -> _T: ...
-    @overload
-    def get(self, default: _D, /) -> _D | _T: ...
-    def set(self, value: _T, /) -> Token[_T]: ...
-    def reset(self, token: Token[_T], /) -> None: ...
-    if sys.version_info >= (3, 9):
-        def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
-
-@final
-class Token(Generic[_T]):
-    @property
-    def var(self) -> ContextVar[_T]: ...
-    @property
-    def old_value(self) -> Any: ...  # returns either _T or MISSING, but that's hard to express
-    MISSING: ClassVar[object]
-    if sys.version_info >= (3, 9):
-        def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
-
-def copy_context() -> Context: ...
-
-# It doesn't make sense to make this generic, because for most Contexts each ContextVar will have
-# a different value.
-@final
-class Context(Mapping[ContextVar[Any], Any]):
-    def __init__(self) -> None: ...
-    @overload
-    def get(self, key: ContextVar[_T], default: None = None, /) -> _T | None: ...
-    @overload
-    def get(self, key: ContextVar[_T], default: _T, /) -> _T: ...
-    @overload
-    def get(self, key: ContextVar[_T], default: _D, /) -> _T | _D: ...
-    def run(self, callable: Callable[_P, _T], *args: _P.args, **kwargs: _P.kwargs) -> _T: ...
-    def copy(self) -> Context: ...
-    def __getitem__(self, key: ContextVar[_T], /) -> _T: ...
-    def __iter__(self) -> Iterator[ContextVar[Any]]: ...
-    def __len__(self) -> int: ...
-    def __eq__(self, value: object, /) -> bool: ...