experimental app getter

src/textual/getters.py

@@ -5,12 +5,53 @@ Descriptors to define properties on your widget, screen, or App.
 
 from __future__ import annotations
 
-from typing import Generic, overload
+from typing import TYPE_CHECKING, Generic, TypeVar, overload
 
+from textual._context import NoActiveAppError, active_app
 from textual.css.query import NoMatches, QueryType, WrongType
-from textual.dom import DOMNode
 from textual.widget import Widget
 
+if TYPE_CHECKING:
+    from textual.app import App
+    from textual.dom import DOMNode
+    from textual.message_pump import MessagePump
+
+
+AppType = TypeVar("AppType", bound="App")
+
+
+class app(Generic[AppType]):
+    """Create a property to return the active app.
+
+    Example:
+        ```python
+        class MyWidget(Widget):
+            app = getters.app(MyApp)
+        ```
+
+    Args:
+        app_type: The app class.
+    """
+
+    def __init__(self, app_type: type[AppType]) -> None:
+        self._app_type = app_type
+
+    def __get__(self, obj: MessagePump, obj_type: type[MessagePump]) -> AppType:
+        try:
+            app = active_app.get()
+        except LookupError:
+            from textual.app import App
+
+            node: MessagePump | None = obj
+            while not isinstance(node, App):
+                if node is None:
+                    raise NoActiveAppError()
+                node = node._parent
+            app = node
+
+        assert isinstance(app, self._app_type)
+        return app
+
 
 class query_one(Generic[QueryType]):
     """Create a query one property.
@@ -45,7 +86,7 @@ class query_one(Generic[QueryType]):
     """
 
     selector: str
-    expect_type: type[Widget]
+    expect_type: type["Widget"]
 
     @overload
     def __init__(self, selector: str) -> None:
@@ -72,6 +113,8 @@ class query_one(Generic[QueryType]):
         expect_type: type[QueryType] | None = None,
     ) -> None:
         if expect_type is None:
+            from textual.widget import Widget
+
             self.expect_type = Widget
         else:
             self.expect_type = expect_type

src/textual/message_pump.py

@@ -227,29 +227,35 @@ class MessagePump(metaclass=_MessagePumpMeta):
         """Is this a root node (i.e. the App)?"""
         return False
 
-    @property
-    def app(self) -> "App[object]":
-        """
-        Get the current app.
+    if TYPE_CHECKING:
+        from textual import getters
 
-        Returns:
-            The current app.
+        app = getters.app(App)
+    else:
 
-        Raises:
-            NoActiveAppError: if no active app could be found for the current asyncio context
-        """
-        try:
-            return active_app.get()
-        except LookupError:
-            from textual.app import App
+        @property
+        def app(self) -> "App[object]":
+            """
+            Get the current app.
 
-            node: MessagePump | None = self
-            while not isinstance(node, App):
-                if node is None:
-                    raise NoActiveAppError()
-                node = node._parent
+            Returns:
+                The current app.
 
-            return node
+            Raises:
+                NoActiveAppError: if no active app could be found for the current asyncio context
+            """
+            try:
+                return active_app.get()
+            except LookupError:
+                from textual.app import App
+
+                node: MessagePump | None = self
+                while not isinstance(node, App):
+                    if node is None:
+                        raise NoActiveAppError()
+                    node = node._parent
+
+                return node
 
     @property
     def is_attached(self) -> bool:

src/textual/widgets/_text_area.py

@@ -662,6 +662,11 @@ TextArea {
         self._line_cache.clear()
         super().notify_style_update()
 
+    def update_suggestion(self) -> None:
+        """A hook called after edits, to allow subclasses to update the
+        [`suggestion`][textual.widgets.TextArea.suggestion] attribute.
+        """
+
     def check_consume_key(self, key: str, character: str | None = None) -> bool:
         """Check if the widget may consume the given key.
 
@@ -1534,7 +1539,10 @@ TextArea {
             Data relating to the edit that may be useful. The data returned
             may be different depending on the edit performed.
         """
-        self.suggestion = ""
+        if self.suggestion.startswith(edit.text):
+            self.suggestion = self.suggestion[len(edit.text) :]
+        else:
+            self.suggestion = ""
         old_gutter_width = self.gutter_width
         result = edit.do(self)
         self.history.record(edit)
@@ -1553,6 +1561,7 @@ TextArea {
         edit.after(self)
         self._build_highlight_map()
         self.post_message(self.Changed(self))
+        self.update_suggestion()
         return result
 
     def undo(self) -> None:

tests/test_getters.py

@@ -43,3 +43,19 @@ async def test_getters() -> None:
 
         with pytest.raises(NoMatches):
             app.label2_missing
+
+
+async def test_app_getter() -> None:
+
+    class MyApp(App):
+        def compose(self) -> ComposeResult:
+            my_widget = MyWidget()
+            my_widget.app
+            yield my_widget
+
+    class MyWidget(Widget):
+        app = getters.app(MyApp)
+
+    app = MyApp()
+    async with app.run_test():
+        assert isinstance(app.query_one(MyWidget).app, MyApp)