Fix the signatures of @(async)contextmanager

.github/workflows/mypy_primer.yml

@@ -55,6 +55,7 @@ jobs:
             --num-shards 4 --shard-index ${{ matrix.shard-index }} \
             --debug \
             --output concise \
+            --additional-flags="--enable-error-code deprecated" \
             | tee diff_${{ matrix.shard-index }}.txt
           ) || [ $? -eq 1 ]
       - if: ${{ matrix.shard-index == 0 }}

stdlib/contextlib.pyi

@@ -5,7 +5,7 @@ from abc import ABC, abstractmethod
 from collections.abc import AsyncGenerator, AsyncIterator, Awaitable, Callable, Generator, Iterator
 from types import TracebackType
 from typing import IO, Any, Generic, Protocol, TypeVar, overload, runtime_checkable
-from typing_extensions import ParamSpec, Self, TypeAlias
+from typing_extensions import ParamSpec, Self, TypeAlias, deprecated
 
 __all__ = [
     "contextmanager",
@@ -85,6 +85,12 @@ class _GeneratorContextManager(
         self, typ: type[BaseException] | None, value: BaseException | None, traceback: TracebackType | None
     ) -> bool | None: ...
 
+@overload
+def contextmanager(func: Callable[_P, Generator[_T_co, None, object]]) -> Callable[_P, _GeneratorContextManager[_T_co]]: ...
+@overload
+@deprecated(
+    "Annotating the return type as `-> Iterator[Foo]` with `@contextmanager` is deprecated. Use `-> Generator[Foo]` instead."
+)
 def contextmanager(func: Callable[_P, Iterator[_T_co]]) -> Callable[_P, _GeneratorContextManager[_T_co]]: ...
 
 if sys.version_info >= (3, 10):
@@ -111,6 +117,13 @@ else:
             self, typ: type[BaseException] | None, value: BaseException | None, traceback: TracebackType | None
         ) -> bool | None: ...
 
+@overload
+def asynccontextmanager(func: Callable[_P, AsyncGenerator[_T_co]]) -> Callable[_P, _AsyncGeneratorContextManager[_T_co]]: ...
+@overload
+@deprecated(
+    "Annotating the return type as `-> AsyncIterator[Foo]` with `@contextmanager` is deprecated. "
+    "Use `-> AsyncGenerator[Foo]` instead."
+)
 def asynccontextmanager(func: Callable[_P, AsyncIterator[_T_co]]) -> Callable[_P, _AsyncGeneratorContextManager[_T_co]]: ...
 
 class _SupportsClose(Protocol):