make Layout context management async (#730)

* make Layout context management async

* fix LayoutType

* changelog entry

Author: rmorshea

docs/source/about/changelog.rst

@@ -23,7 +23,9 @@ more info, see the :ref:`Contributor Guide <Creating a Changelog Entry>`.
 Unreleased
 ----------
 
-Nothing yet...
+Changed:
+
+- :pull:`730` - Layout context management is not async
 
 
 0.38.0-a2
@@ -444,7 +446,7 @@ See :ref:`Custom JavaScript Components` for details on the new interface.
 - Make docs section margins larger - :issue:`450`
 - Search broken in docs - :issue:`443`
 - Move src/idom/client out of Python package - :issue:`429`
-- Use composition instead of classes with Layout and LifeCycleHook  - :issue:`412`
+- Use composition instead of classes async with Layout and LifeCycleHook  - :issue:`412`
 - Remove Python language extension - :issue:`282`
 - Add keys to models so React doesn't complain of child arrays requiring them -
   :issue:`255`

docs/source/about/contributor-guide.rst

@@ -92,15 +92,15 @@ might look like:
 
     **Added**
 
-    - A really cool new feature - :pull:`123`
+    - :pull:`123` - A really cool new feature
 
     **Changed**
 
-    - The behavior of some existing feature - :pull:`456`
+    - :pull:`456` - The behavior of some existing feature
 
     **Fixed**
 
-    - Some really bad bug - :issue:`789`
+    - :issue:`789` - Some really bad bug
 
 .. note::
 

src/idom/core/layout.py

@@ -61,9 +61,6 @@ class LayoutEvent(NamedTuple):
     """A list of event data passed to the event handler."""
 
 
-_Self = TypeVar("_Self", bound="Layout")
-
-
 class Layout:
     """Responsible for "rendering" components. That is, turning them into VDOM."""
 
@@ -84,7 +81,7 @@ def __init__(self, root: "ComponentType") -> None:
             raise TypeError(f"Expected a ComponentType, not {type(root)!r}.")
         self.root = root
 
-    def __enter__(self: _Self) -> _Self:
+    async def __aenter__(self) -> Layout:
         # create attributes here to avoid access before entering context manager
         self._event_handlers: EventHandlerDict = {}
 
@@ -98,7 +95,7 @@ def __enter__(self: _Self) -> _Self:
 
         return self
 
-    def __exit__(self, *exc: Any) -> None:
+    async def __aexit__(self, *exc: Any) -> None:
         root_csid = self._root_life_cycle_state_id
         root_model_state = self._model_states_by_life_cycle_state_id[root_csid]
         self._unmount_model_states([root_model_state])

src/idom/core/serve.py

@@ -39,7 +39,7 @@ async def serve_json_patch(
     recv: RecvCoroutine,
 ) -> None:
     """Run a dispatch loop for a single view instance"""
-    with layout:
+    async with layout:
         try:
             async with create_task_group() as task_group:
                 task_group.start_soon(_single_outgoing_loop, layout, send)

src/idom/core/types.py

@@ -51,7 +51,6 @@ def should_render(self: _OwnType, new: _OwnType) -> bool:
         """Whether the new component instance should be rendered."""
 
 
-_Self = TypeVar("_Self")
 _Render = TypeVar("_Render", covariant=True)
 _Event = TypeVar("_Event", contravariant=True)
 
@@ -66,11 +65,14 @@ async def render(self) -> _Render:
     async def deliver(self, event: _Event) -> None:
         """Relay an event to its respective handler"""
 
-    def __enter__(self: _Self) -> _Self:
+    async def __aenter__(self) -> LayoutType[_Render, _Event]:
         """Prepare the layout for its first render"""
 
-    def __exit__(
-        self, exc_type: Type[Exception], exc_value: Exception, traceback: TracebackType
+    async def __aexit__(
+        self,
+        exc_type: Type[Exception],
+        exc_value: Exception,
+        traceback: TracebackType,
     ) -> Optional[bool]:
         """Clean up the view after its final render"""