Support MouseScrollLeft and MouseScrollRight control sequences.

src/textual/_xterm_parser.py

@@ -100,9 +100,12 @@ class XTermParser(Parser[Message]):
             event_class: type[events.MouseEvent]
 
             if buttons & 64:
-                event_class = (
+                event_class = [
-                    events.MouseScrollDown if buttons & 1 else events.MouseScrollUp
+                    events.MouseScrollUp,
-                )
+                    events.MouseScrollDown,
+                    events.MouseScrollLeft,
+                    events.MouseScrollRight,
+                ][buttons & 3]
                 button = 0
             else:
                 button = (buttons + 1) & 3

src/textual/events.py

@@ -606,6 +606,24 @@ class MouseScrollUp(MouseEvent, bubble=True, verbose=True):
     """
 
 
+@rich.repr.auto
+class MouseScrollRight(MouseEvent, bubble=True, verbose=True):
+    """Sent when the mouse wheel is scrolled *right*.
+
+    - [X] Bubbles
+    - [X] Verbose
+    """
+
+
+@rich.repr.auto
+class MouseScrollLeft(MouseEvent, bubble=True, verbose=True):
+    """Sent when the mouse wheel is scrolled *left*.
+
+    - [X] Bubbles
+    - [X] Verbose
+    """
+
+
 class Click(MouseEvent, bubble=True):
     """Sent when a widget is clicked.
 

src/textual/widget.py

@@ -113,7 +113,12 @@ _JUSTIFY_MAP: dict[str, JustifyMethod] = {
 
 
 _MOUSE_EVENTS_DISALLOW_IF_DISABLED = (events.MouseEvent, events.Enter, events.Leave)
-_MOUSE_EVENTS_ALLOW_IF_DISABLED = (events.MouseScrollDown, events.MouseScrollUp)
+_MOUSE_EVENTS_ALLOW_IF_DISABLED = (
+    events.MouseScrollDown,
+    events.MouseScrollUp,
+    events.MouseScrollRight,
+    events.MouseScrollLeft,
+)
 
 
 @rich.repr.auto
@@ -4569,6 +4574,18 @@ class Widget(DOMNode):
                 if self._scroll_up_for_pointer(animate=False):
                     event.stop()
 
+    def _on_mouse_scroll_right(self, event: events.MouseScrollRight) -> None:
+        if self.allow_horizontal_scroll:
+            self.release_anchor()
+            if self._scroll_right_for_pointer(animate=False):
+                event.stop()
+
+    def _on_mouse_scroll_left(self, event: events.MouseScrollLeft) -> None:
+        if self.allow_horizontal_scroll:
+            self.release_anchor()
+            if self._scroll_left_for_pointer(animate=False):
+                event.stop()
+
     def _on_scroll_to(self, message: ScrollTo) -> None:
         if self._allow_scroll:
             self.release_anchor()

tests/test_xterm_parser.py

@@ -8,6 +8,8 @@ from textual.events import (
     MouseDown,
     MouseMove,
     MouseScrollDown,
+    MouseScrollLeft,
+    MouseScrollRight,
     MouseScrollUp,
     MouseUp,
     Paste,
@@ -283,6 +285,56 @@ def test_mouse_scroll_down(parser, sequence, shift, meta):
     assert event.meta is meta
 
 
+@pytest.mark.parametrize(
+    "sequence, shift, meta",
+    [
+        ("\x1b[<66;18;25M", False, False),
+        ("\x1b[<70;18;25M", True, False),
+        ("\x1b[<74;18;25M", False, True),
+    ],
+)
+def test_mouse_scroll_left(parser, sequence, shift, meta):
+    """Scrolling the mouse with and without modifiers held down.
+    We don't currently capture modifier keys in scroll events.
+    """
+    events = list(parser.feed(sequence))
+
+    assert len(events) == 1
+
+    event = events[0]
+
+    assert isinstance(event, MouseScrollLeft)
+    assert event.x == 17
+    assert event.y == 24
+    assert event.shift is shift
+    assert event.meta is meta
+
+
+@pytest.mark.parametrize(
+    "sequence, shift, meta",
+    [
+        ("\x1b[<67;18;25M", False, False),
+        ("\x1b[<71;18;25M", True, False),
+        ("\x1b[<75;18;25M", False, True),
+    ],
+)
+def test_mouse_scroll_right(parser, sequence, shift, meta):
+    """Scrolling the mouse with and without modifiers held down.
+    We don't currently capture modifier keys in scroll events.
+    """
+    events = list(parser.feed(sequence))
+
+    assert len(events) == 1
+
+    event = events[0]
+
+    assert isinstance(event, MouseScrollRight)
+    assert event.x == 17
+    assert event.y == 24
+    assert event.shift is shift
+    assert event.meta is meta
+
+
 def test_mouse_event_detected_but_info_not_parsed(parser):
     # I don't know if this can actually happen in reality, but
     # there's a branch in the code that allows for the possibility.