Generate MouseUp events (#1968)

* Remove redundant import

* Generate a MouseUp event when dragging stops

* Update CHANGELOG.md

* Ensure button is propagated through to artificial MouseUp event

CHANGELOG.md

@@ -34,6 +34,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Fixed bug that prevented pilot from pressing some keys https://github.com/Textualize/textual/issues/1815
 - DataTable race condition that caused crash https://github.com/Textualize/textual/pull/1962
+- Fixed scrollbar getting "stuck" to cursor when cursor leaves window during drag https://github.com/Textualize/textual/pull/1968
 - DataTable crash when enter pressed when table is empty https://github.com/Textualize/textual/pull/1973
 
 ## [0.13.0] - 2023-03-02

src/textual/driver.py

@@ -6,6 +6,7 @@
 
 from . import _clock, events
 from ._types import MessageTarget
+from .events import MouseUp
 
 if TYPE_CHECKING:
     from rich.console import Console
@@ -26,6 +27,8 @@ def __init__(
         self._size = size
         self._loop = asyncio.get_running_loop()
         self._mouse_down_time = _clock.get_time_no_wait()
+        self._dragging = False
+        self._dragging_button = None
 
     @property
     def is_headless(self) -> bool:
@@ -41,6 +44,29 @@ def process_event(self, event: events.Event) -> None:
         """Performs some additional processing of events."""
         if isinstance(event, events.MouseDown):
             self._mouse_down_time = event.time
+        elif isinstance(event, events.MouseMove):
+            if event.button and not self._dragging:
+                self._dragging = True
+                self._dragging_button = event.button
+            elif self._dragging and self._dragging_button != event.button:
+                # Artificially generate a MouseUp event when we stop "dragging"
+                self.send_event(
+                    MouseUp(
+                        x=event.x,
+                        y=event.y,
+                        delta_x=event.delta_x,
+                        delta_y=event.delta_y,
+                        button=self._dragging_button,
+                        shift=event.shift,
+                        meta=event.meta,
+                        ctrl=event.ctrl,
+                        screen_x=event.screen_x,
+                        screen_y=event.screen_y,
+                        style=event.style,
+                    )
+                )
+                self._dragging = False
+                self._dragging_button = None
 
         self.send_event(event)
 

src/textual/drivers/linux_driver.py

@@ -17,7 +17,6 @@
 import rich.repr
 
 from .. import events, log
-from .._profile import timer
 from .._types import MessageTarget
 from .._xterm_parser import XTermParser
 from ..driver import Driver