Add annotation for Widget

core/src/toga/widgets/base.py

@@ -1,12 +1,17 @@
 from __future__ import annotations
 
 from builtins import id as identifier
+from typing import NoReturn, Iterator, TYPE_CHECKING
 
 from travertino.node import Node
 
 from toga.platform import get_platform_factory
 from toga.style import Pack, TogaApplicator
 
+if TYPE_CHECKING:
+    from toga.app import App
+    from toga.window import Window
+
 
 class WidgetRegistry(dict):
     # WidgetRegistry is implemented as a subclass of dict, because it provides
@@ -16,26 +21,26 @@ class WidgetRegistry(dict):
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
 
-    def __setitem__(self, key, value):
+    def __setitem__(self, key: str, value: Widget) -> NoReturn:
         # We do not want to allow setting items directly but to use the "add"
         # method instead.
         raise RuntimeError("Widgets cannot be directly added to a registry")
 
-    def update(self, widgets: list[Widget]):
+    def update(self, widgets: list[Widget]) -> None:
         for widget in widgets:
             self.add(widget)
 
-    def add(self, widget: Widget):
+    def add(self, widget: Widget) -> None:
         if widget.id in self:
             # Prevent from adding the same widget twice
             # or adding 2 widgets with the same id
             raise KeyError(f"There is already a widget with the id {widget.id!r}")
         super().__setitem__(widget.id, widget)
 
-    def remove(self, id: str):
+    def remove(self, id: str) -> None:
         del self[id]
 
-    def __iter__(self):
+    def __iter__(self) -> Iterator[Widget]:
         return iter(self.values())
 
 
@@ -47,7 +52,7 @@ def __init__(
         self,
         id: str | None = None,
         style=None,
-    ):
+    ) -> None:
         """Create a base Toga widget.
 
         This is an abstract base class; it cannot be instantiated.
@@ -68,7 +73,7 @@ def __init__(
 
         self.factory = get_platform_factory()
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return f"<{self.__class__.__name__}:0x{identifier(self):x}>"
 
     @property
@@ -80,7 +85,7 @@ def id(self) -> str:
         return self._id
 
     @property
-    def tab_index(self):
+    def tab_index(self) -> int | None:
         """The position of the widget in the focus chain for the window.
 
         .. note::
@@ -91,10 +96,10 @@ def tab_index(self):
         return self._impl.get_tab_index()
 
     @tab_index.setter
-    def tab_index(self, tab_index):
+    def tab_index(self, tab_index: int) -> None:
         self._impl.set_tab_index(tab_index)
 
-    def add(self, *children: Widget):
+    def add(self, *children: Widget) -> None:
         """Add the provided widgets as children of this widget.
 
         If a child widget already has a parent, it will be re-parented as a
@@ -122,7 +127,7 @@ def add(self, *children: Widget):
         # Whatever layout we're a part of needs to be refreshed
         self.refresh()
 
-    def insert(self, index: int, child: Widget):
+    def insert(self, index: int, child: Widget) -> None:
         """Insert a widget as a child of this widget.
 
         If a child widget already has a parent, it will be re-parented as a
@@ -151,7 +156,7 @@ def insert(self, index: int, child: Widget):
         # Whatever layout we're a part of needs to be refreshed
         self.refresh()
 
-    def remove(self, *children: Widget):
+    def remove(self, *children: Widget) -> None:
         """Remove the provided widgets as children of this node.
 
         Any nominated child widget that is not a child of this widget will
@@ -178,7 +183,7 @@ def remove(self, *children: Widget):
         if removed:
             self.refresh()
 
-    def clear(self):
+    def clear(self) -> None:
         """Remove all child widgets of this node.
 
         Refreshes the widget after removal if any children were removed.
@@ -188,7 +193,7 @@ def clear(self):
         self.remove(*self.children)
 
     @property
-    def app(self):
+    def app(self) -> None:
         """The App to which this widget belongs.
 
         When setting the app for a widget, all children of this widget will be
@@ -199,7 +204,7 @@ def app(self):
         return self._app
 
     @app.setter
-    def app(self, app):
+    def app(self, app: App | None) -> None:
         # If the widget is already assigned to an app
         if self._app:
             if self._app == app:
@@ -219,7 +224,7 @@ def app(self, app):
             app.widgets.add(self)
 
     @property
-    def window(self):
+    def window(self) -> Window | None:
         """The window to which this widget belongs.
 
         When setting the window for a widget, all children of this widget will be
@@ -228,7 +233,7 @@ def window(self):
         return self._window
 
     @window.setter
-    def window(self, window):
+    def window(self, window: Window | None) -> None:
         # Remove the widget from the widget registry it is currently a part of
         if self.window is not None:
             self.window.widgets.remove(self.id)
@@ -249,15 +254,15 @@ def enabled(self) -> bool:
         return self._impl.get_enabled()
 
     @enabled.setter
-    def enabled(self, value):
+    def enabled(self, value: bool) -> None:
         self._impl.set_enabled(bool(value))
 
-    def refresh(self):
+    def refresh(self) -> None:
         self._impl.refresh()
 
         # Refresh the layout
         if self._root:
-            # We're not the root of the node heirarchy;
+            # We're not the root of the node hierarchy;
             # defer the refresh call to the root node.
             self._root.refresh()
         else:
@@ -267,11 +272,11 @@ def refresh(self):
                 super().refresh(self._impl.viewport)
                 self._impl.viewport.refreshed()
 
-    def refresh_sublayouts(self):
+    def refresh_sublayouts(self) -> None:
         for child in self.children:
             child.refresh_sublayouts()
 
-    def focus(self):
+    def focus(self) -> None:
         """Give this widget the input focus.
 
         This method is a no-op if the widget can't accept focus. The ability of a widget