fix threading issue (#3779)

* fix threading issue

* remote debug

* changelog

* version bump

* changelog

* docstring

* fix snapshot test

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## [0.42.2] - 2023-11-29
+
+### Fixed
+
+- Fixed NoWidget error https://github.com/Textualize/textual/pull/3779
+
 ## [0.43.1] - 2023-11-29
 
 ### Fixed
@@ -1465,6 +1471,7 @@ https://textual.textualize.io/blog/2022/11/08/version-040/#version-040
 - New handler system for messages that doesn't require inheritance
 - Improved traceback handling
 
+[0.43.2]: https://github.com/Textualize/textual/compare/v0.43.1...v0.43.2
 [0.43.1]: https://github.com/Textualize/textual/compare/v0.43.0...v0.43.1
 [0.43.0]: https://github.com/Textualize/textual/compare/v0.42.0...v0.43.0
 [0.42.0]: https://github.com/Textualize/textual/compare/v0.41.0...v0.42.0

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "textual"
-version = "0.43.1"
+version = "0.43.2"
 homepage = "https://github.com/Textualize/textual"
 repository = "https://github.com/Textualize/textual"
 documentation = "https://textual.textualize.io/"

src/textual/app.py

@@ -79,6 +79,7 @@
 from .dom import DOMNode
 from .driver import Driver
 from .drivers.headless_driver import HeadlessDriver
+from .errors import NoWidget
 from .features import FeatureFlag, parse_features
 from .file_monitor import FileMonitor
 from .geometry import Offset, Region, Size
@@ -444,6 +445,9 @@ def __init__(
         self._animate = self._animator.bind(self)
         self.mouse_position = Offset(0, 0)
 
+        self._mouse_down_widget: Widget | None = None
+        """The widget that was most recently mouse downed (used to create click events)."""
+
         self.cursor_position = Offset(0, 0)
         """The position of the terminal cursor in screen-space.
 
@@ -2671,7 +2675,7 @@ async def on_event(self, event: events.Event) -> None:
         # Handle input events that haven't been forwarded
         # If the event has been forwarded it may have bubbled up back to the App
         if isinstance(event, events.Compose):
-            screen = Screen(id=f"_default")
+            screen: Screen[Any] = Screen(id=f"_default")
             self._register(self, screen)
             self._screen_stack.append(screen)
             screen.post_message(events.ScreenResume())
@@ -2683,7 +2687,26 @@ async def on_event(self, event: events.Event) -> None:
             if isinstance(event, events.MouseEvent):
                 # Record current mouse position on App
                 self.mouse_position = Offset(event.x, event.y)
+
+                if isinstance(event, events.MouseDown):
+                    try:
+                        self._mouse_down_widget, _ = self.get_widget_at(
+                            event.x, event.y
+                        )
+                    except NoWidget:
+                        # Shouldn't occur, since at the very least this will find the Screen
+                        self._mouse_down_widget = None
+
                 self.screen._forward_event(event)
+
+                if isinstance(event, events.MouseUp):
+                    if self._mouse_down_widget is not None and (
+                        self.get_widget_at(event.x, event.y)[0]
+                        is self._mouse_down_widget
+                    ):
+                        click_event = events.Click.from_event(event)
+                        self.screen._forward_event(click_event)
+
             elif isinstance(event, events.Key):
                 if not await self.check_bindings(event.key, priority=True):
                     forward_target = self.focused or self.screen

src/textual/driver.py

@@ -9,7 +9,6 @@
 
 if TYPE_CHECKING:
     from .app import App
-    from .widget import Widget
 
 
 class Driver(ABC):
@@ -33,7 +32,6 @@ def __init__(
         self._debug = debug
         self._size = size
         self._loop = asyncio.get_running_loop()
-        self._mouse_down_widget: Widget | None = None
         self._down_buttons: list[int] = []
         self._last_move_event: events.MouseMove | None = None
 
@@ -58,17 +56,15 @@ def process_event(self, event: events.Event) -> None:
         Args:
             event: An event to send.
         """
+        # NOTE: This runs in a thread.
+        # Avoid calling methods on the app.
         event._set_sender(self._app)
         if isinstance(event, events.MouseDown):
-            self._mouse_down_widget = self._app.get_widget_at(event.x, event.y)[0]
             if event.button:
                 self._down_buttons.append(event.button)
         elif isinstance(event, events.MouseUp):
-            if event.button:
-                try:
-                    self._down_buttons.remove(event.button)
-                except ValueError:
-                    pass
+            if event.button and event.button in self._down_buttons:
+                self._down_buttons.remove(event.button)
         elif isinstance(event, events.MouseMove):
             if (
                 self._down_buttons
@@ -99,13 +95,6 @@ def process_event(self, event: events.Event) -> None:
 
         self.send_event(event)
 
-        if (
-            isinstance(event, events.MouseUp)
-            and self._app.get_widget_at(event.x, event.y)[0] is self._mouse_down_widget
-        ):
-            click_event = events.Click.from_event(event)
-            self.send_event(click_event)
-
     @abstractmethod
     def write(self, data: str) -> None:
         """Write data to the output device.

src/textual/pilot.py

@@ -323,12 +323,12 @@ async def _post_mouse_events(
             # Get the widget under the mouse before the event because the app might
             # react to the event and move things around. We override on each iteration
             # because we assume the final event in `events` is the actual event we care
-            # about and that all the preceeding events are just setup.
-            # E.g., the click event is preceeded by MouseDown/MouseUp to emulate how
+            # about and that all the preceding events are just setup.
+            # E.g., the click event is preceded by MouseDown/MouseUp to emulate how
             # the driver works and emits a click event.
             widget_at, _ = app.get_widget_at(*offset)
             event = mouse_event_cls(**message_arguments)
-            app.post_message(event)
+            app.screen._forward_event(event)
             await self.pause()
 
         return selector is None or widget_at is target_widget