Fix __exit__ return type of various context managers

docs/versionhistory.rst

@@ -11,6 +11,8 @@ This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
   (`#836 <https://github.com/agronholm/anyio/pull/836>`_; PR by @graingert)
 - Fixed ``AssertionError`` when using ``nest-asyncio``
   (`#840 <https://github.com/agronholm/anyio/issues/840>`_)
+- Fixed return type annotation of various context managers' ``__exit__`` method
+  (`#847 <https://github.com/agronholm/anyio/issues/847>`_; PR by @Enegg)
 
 **4.7.0**
 

src/anyio/_backends/_asyncio.py

@@ -485,7 +485,7 @@ def __exit__(
             # scope if necessary
             self._restart_cancellation_in_parent()
 
-            # We only swallow the exception iff it was an AnyIO CancelledError, either
+            # We only swallow the exception if it was an AnyIO CancelledError, either
             # directly as exc_val or inside an exception group and there are no cancelled
             # parent cancel scopes visible to us here
             if self._cancel_called and not self._parent_cancellation_is_visible_to_us:
@@ -2116,10 +2116,9 @@ def __exit__(
         exc_type: type[BaseException] | None,
         exc_val: BaseException | None,
         exc_tb: TracebackType | None,
-    ) -> bool | None:
+    ) -> None:
         for sig in self._handled_signals:
             self._loop.remove_signal_handler(sig)
-        return None
 
     def __aiter__(self) -> _SignalReceiver:
         return self

src/anyio/_backends/_trio.py

@@ -133,7 +133,6 @@ def __exit__(
         exc_val: BaseException | None,
         exc_tb: TracebackType | None,
     ) -> bool | None:
-        # https://github.com/python-trio/trio-typing/pull/79
         return self.__original.__exit__(exc_type, exc_val, exc_tb)
 
     def cancel(self) -> None:
@@ -186,9 +185,10 @@ async def __aexit__(
         exc_type: type[BaseException] | None,
         exc_val: BaseException | None,
         exc_tb: TracebackType | None,
-    ) -> bool | None:
+    ) -> bool:
         try:
-            return await self._nursery_manager.__aexit__(exc_type, exc_val, exc_tb)
+            # trio.Nursery.__exit__ returns bool; .open_nursery has wrong type
+            return await self._nursery_manager.__aexit__(exc_type, exc_val, exc_tb)  # type: ignore[return-value]
         except BaseExceptionGroup as exc:
             if not exc.split(trio.Cancelled)[1]:
                 raise trio.Cancelled._create() from exc

src/anyio/_core/_synchronization.py

@@ -728,6 +728,5 @@ def __exit__(
         exc_type: type[BaseException] | None,
         exc_val: BaseException | None,
         exc_tb: TracebackType | None,
-    ) -> bool | None:
+    ) -> None:
         self._guarded = False
-        return None