gh-140389: fixed touchpad horizontal scrolling in IDLE editor

Lib/idlelib/idle_test/test_tree.py

@@ -32,27 +32,39 @@ def test_init(self):
 class TestScrollEvent(unittest.TestCase):
 
     def test_wheel_event(self):
-        # Fake widget class containing `yview` only.
+        # Fake widget class containing `xview` and `yview` only.
         class _Widget:
-            def __init__(widget, *expected):
+            def __init__(widget, direction, *expected):
+                widget.state = state
                 widget.expected = expected
+            def xview(widget, *args):
+                self.assertEqual(widget.state&1, 1)
+                self.assertTupleEqual(widget.expected, args)
             def yview(widget, *args):
+                self.assertEqual(widget.state&1, 0)
                 self.assertTupleEqual(widget.expected, args)
         # Fake event class
         class _Event:
             pass
-        #        (type, delta, num, amount)
-        tests = ((EventType.MouseWheel, 120, -1, -5),
-                 (EventType.MouseWheel, -120, -1, 5),
-                 (EventType.ButtonPress, -1, 4, -5),
-                 (EventType.ButtonPress, -1, 5, 5))
+        #        (type, delta, num, state, amount)
+        # If the first bit of state is set, scroll horizontally
+        tests = ((EventType.MouseWheel, 120, -1, 0, -5),
+                 (EventType.MouseWheel, -120, -1, 0, 5),
+                 (EventType.ButtonPress, -1, 4, 0, -5),
+                 (EventType.ButtonPress, -1, 5, 0, 5),
+                 (EventType.MouseWheel, 120, -1, 1, -5),
+                 (EventType.MouseWheel, -120, -1, 1, 5),
+                 (EventType.ButtonPress, -1, 4, 1, -5),
+                 (EventType.ButtonPress, -1, 5, 1, 5))
 
         event = _Event()
-        for ty, delta, num, amount in tests:
+        for ty, delta, num, state, amount in tests:
             event.type = ty
             event.delta = delta
             event.num = num
-            res = tree.wheel_event(event, _Widget(SCROLL, amount, "units"))
+            event.state = state
+            res = tree.wheel_event(event,
+                                   _Widget(state, SCROLL, amount, "units"))
             self.assertEqual(res, "break")
 
 

Lib/idlelib/tree.py

@@ -65,19 +65,25 @@ def wheel_event(event, widget=None):
     Macs use wheel down (delta = 1*n) to scroll up, so positive
     delta means to scroll up on both systems.
 
+    On both Windows and X-11, if the first bit of event.state is
+    set, it means that we should scroll horizontally not vertically.
+
     X-11 sends Control-Button-4,5 events instead.
 
     The widget parameter is needed so browser label bindings can pass
     the underlying canvas.
 
-    This function depends on widget.yview to not be overridden by
-    a subclass.
+    This function depends on widget.xview/widget.yview to not be
+    overridden by a subclass.
     """
     up = {EventType.MouseWheel: event.delta > 0,
           EventType.ButtonPress: event.num == 4}
     lines = -5 if up[event.type] else 5
     widget = event.widget if widget is None else widget
-    widget.yview(SCROLL, lines, 'units')
+    if event.state&1: # If the first bit is set, scroll horizontally
+        widget.xview(SCROLL, lines, 'units')
+    else:
+        widget.yview(SCROLL, lines, 'units')
     return 'break'
 
 

Misc/ACKS

@@ -1942,6 +1942,7 @@ John Tromp
 Diane Trout
 Jason Trowbridge
 Steven Troxler
+Daniel Tsvetkov
 Brent Tubbs
 Anthony Tuininga
 Erno Tukia

Misc/NEWS.d/next/IDLE/2025-10-20-21-40-38.gh-issue-140389.vOs4uy.rst

@@ -0,0 +1 @@
+Fixed trackpad scrolling direction in :mod:`IDLE <idlelib>`