Fix erronious ButtonDown mouse event reporting.

After v0.38.0, I was seeing Input fields lose focus whenever the mouse
left the input field area (but without having clicked anywhere). This
was being caused because since the release Mouse ButtonDown events
trigger loss of focus. But I wasn't pressing any mouse buttons.

The erronious ButtonDown events were actually MouseMove events with
no keys held down. According to the docs for xterm escape sequences,
wher SGR (1006) mode is enabled, the encoded button value isn't always
incremented by 32 for move movements events. [1]

I believe the correct fix to this issue is to detect mouse movement
events with no button down by checking if the "pressed button" is 0.
Which appears to indicate that no mouse button is pressed (in this
specific case). Whereas, the button value will be set to 1 when left
click is pressed for example.

I'm not sure if this change is fully correct for terminals which don't
support SGR mode.

[1] https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h3-Extended-coordinates

Author: EricWF

CHANGELOG.md

@@ -252,6 +252,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Fixed CSS watcher crash if file becomes unreadable (even temporarily) https://github.com/Textualize/textual/pull/4079
 - Fixed display of keys when used in conjunction with other keys https://github.com/Textualize/textual/pull/3050
 - Fixed double detection of <kbd>Escape</kbd> on Windows https://github.com/Textualize/textual/issues/4038
+- Fixed erroneous mouse 'ButtonDown' reporting for mouse movement when any-event mode is enabled in xterm. https://github.com/Textualize/textual/pull/3647
+
 
 ## [0.47.1] - 2024-01-05
 

src/textual/_xterm_parser.py

@@ -73,13 +73,14 @@ def parse_mouse_code(self, code: str) -> events.Event | None:
                 )
                 button = 0
             else:
-                if buttons & 32:
+                button = (buttons + 1) & 3
+                # XTerm events for mouse movement can look like mouse button down events. But if there is no key pressed,
+                # it's a mouse move event.
+                if buttons & 32 or button == 0:
                     event_class = events.MouseMove
                 else:
                     event_class = events.MouseDown if state == "M" else events.MouseUp
 
-                button = (buttons + 1) & 3
-
             event = event_class(
                 x,
                 y,

tests/test_xterm_parser.py

@@ -218,6 +218,7 @@ def test_mouse_click(parser, sequence, event_type, shift, meta):
         ("\x1b[<35;15;38M", False, False, 0),  # Basic cursor movement
         ("\x1b[<39;15;38M", True, False, 0),  # Shift held down
         ("\x1b[<43;15;38M", False, True, 0),  # Meta held down
+        ("\x1b[<3;15;38M", False, False, 0),
     ],
 )
 def test_mouse_move(parser, sequence, shift, meta, button):