adress comments, removing redundant Generic, fixing open_memory_chann…

…el return type, and adding trio-typings class workaround to get type-checking on open_memory_channel by hiding it behind a TYPE_CHECKING guard

trio/_channel.py

@@ -10,6 +10,7 @@
     Generic,
     NoReturn,
     TypeVar,
+    TYPE_CHECKING,
 )
 
 import attr
@@ -38,8 +39,7 @@
 SelfT = TypeVar("SelfT")
 
 
-@generic_function
-def open_memory_channel(
+def _open_memory_channel(
     max_buffer_size: int,
 ) -> tuple[MemorySendChannel[T], MemoryReceiveChannel[T]]:
     """Open a channel for passing objects between tasks within a process.
@@ -99,11 +99,31 @@ def open_memory_channel(
         raise ValueError("max_buffer_size must be >= 0")
     state: MemoryChannelState[T] = MemoryChannelState(max_buffer_size)
     return (
-        MemorySendChannel._create(state),
-        MemoryReceiveChannel._create(state),
+        MemorySendChannel[T]._create(state),
+        MemoryReceiveChannel[T]._create(state),
     )
 
 
+# This workaround requires python3.9+, once older python versions are not supported
+# or there's a better way of achieving type-checking on a generic factory function,
+# it could replace the normal function header
+if TYPE_CHECKING:
+    # written as a class so you can say open_memory_channel[int](5)
+    class open_memory_channel(tuple[MemorySendChannel[T], MemoryReceiveChannel[T]]):
+        def __new__(  # type: ignore[misc]  # "must return a subtype"
+            cls, max_buffer_size: int
+        ) -> tuple[MemorySendChannel[T], MemoryReceiveChannel[T]]:
+            return _open_memory_channel(max_buffer_size)
+
+        def __init__(self, max_buffer_size: int):
+            ...
+
+else:
+    # apply the generic_function decorator to make open_memory_channel indexable
+    # so it's valid to say e.g. ``open_memory_channel[bytes](5)`` at runtime
+    open_memory_channel = generic_function(_open_memory_channel)
+
+
 @attr.s(frozen=True, slots=True)
 class MemoryChannelStats:
     current_buffer_used: int = attr.ib()
@@ -138,9 +158,7 @@ def statistics(self) -> MemoryChannelStats:
 
 
 @attr.s(eq=False, repr=False)
-class MemorySendChannel(
-    SendChannel[SendType], Generic[SendType], metaclass=NoPublicConstructor
-):
+class MemorySendChannel(SendChannel[SendType], metaclass=NoPublicConstructor):
     _state: MemoryChannelState[SendType] = attr.ib()
     _closed: bool = attr.ib(default=False)
     # This is just the tasks waiting on *this* object. As compared to
@@ -284,9 +302,7 @@ async def aclose(self) -> None:
 
 
 @attr.s(eq=False, repr=False)
-class MemoryReceiveChannel(
-    ReceiveChannel[ReceiveType], Generic[ReceiveType], metaclass=NoPublicConstructor
-):
+class MemoryReceiveChannel(ReceiveChannel[ReceiveType], metaclass=NoPublicConstructor):
     _state: MemoryChannelState[ReceiveType] = attr.ib()
     _closed: bool = attr.ib(default=False)
     _tasks: set[trio._core._run.Task] = attr.ib(factory=set)

trio/_core/_traps.py

@@ -64,7 +64,8 @@ class Abort(enum.Enum):
 class WaitTaskRescheduled:
     abort_func = attr.ib()
 
-RaiseCancelT = Callable[[], NoReturn] # TypeAlias
+
+RaiseCancelT = Callable[[], NoReturn]  # TypeAlias
 
 # Can this function be retyped to return something other than Any?
 async def wait_task_rescheduled(abort_func: Callable[[RaiseCancelT], Abort]) -> Any: