Fix mouse-wheel scrolling in radio and checkbox lists

src/prompt_toolkit/widgets/base.py

@@ -17,7 +17,7 @@
 
 from collections.abc import Callable, Sequence
 from functools import partial
-from typing import Generic, TypeVar
+from typing import TYPE_CHECKING, Generic, TypeVar
 
 from prompt_toolkit.application.current import get_app
 from prompt_toolkit.auto_suggest import AutoSuggest, DynamicAutoSuggest
@@ -81,6 +81,9 @@
 
 from .toolbars import SearchToolbar
 
+if TYPE_CHECKING:
+    from prompt_toolkit.key_binding.key_bindings import NotImplementedOrNone
+
 __all__ = [
     "TextArea",
     "Label",
@@ -753,22 +756,28 @@ def __init__(
         else:
             self._selected_index = 0
 
+        def move_cursor_up() -> None:
+            self._selected_index = max(0, self._selected_index - 1)
+            if select_on_focus:
+                self._handle_enter()
+
+        def move_cursor_down() -> None:
+            self._selected_index = min(len(self.values) - 1, self._selected_index + 1)
+            if select_on_focus:
+                self._handle_enter()
+
         # Key bindings.
         kb = KeyBindings()
 
         @kb.add("up")
         @kb.add("k")  # Vi-like.
         def _up(event: E) -> None:
-            self._selected_index = max(0, self._selected_index - 1)
-            if select_on_focus:
-                self._handle_enter()
+            move_cursor_up()
 
         @kb.add("down")
         @kb.add("j")  # Vi-like.
         def _down(event: E) -> None:
-            self._selected_index = min(len(self.values) - 1, self._selected_index + 1)
-            if select_on_focus:
-                self._handle_enter()
+            move_cursor_down()
 
         @kb.add("pageup")
         def _pageup(event: E) -> None:
@@ -813,8 +822,16 @@ def _select_i(event: E, index: int = i) -> None:
                 if select_on_focus:
                     self._handle_enter()
 
+        # Let Window keep the cursor visible when scrolling with the mouse.
+        class DialogListControl(FormattedTextControl):
+            def move_cursor_up(self) -> None:
+                move_cursor_up()
+
+            def move_cursor_down(self) -> None:
+                move_cursor_down()
+
         # Control and window.
-        self.control = FormattedTextControl(
+        self.control = DialogListControl(
             self._get_text_fragments,
             key_bindings=kb,
             focusable=True,
@@ -844,14 +861,18 @@ def _handle_enter(self) -> None:
             self.current_value = self.values[self._selected_index][0]
 
     def _get_text_fragments(self) -> StyleAndTextTuples:
-        def mouse_handler(mouse_event: MouseEvent) -> None:
+        def mouse_handler(mouse_event: MouseEvent) -> NotImplementedOrNone:
             """
             Set `_selected_index` and `current_value` according to the y
             position of the mouse click event.
             """
             if mouse_event.event_type == MouseEventType.MOUSE_UP:
                 self._selected_index = mouse_event.position.y
                 self._handle_enter()
+                return None
+
+            # Let Window handle scrolling.
+            return NotImplemented
 
         result: StyleAndTextTuples = []
         for i, value in enumerate(self.values):

tests/test_widgets.py

@@ -1,8 +1,19 @@
 from __future__ import annotations
 
+import pytest
+
+from prompt_toolkit.application import Application
+from prompt_toolkit.application.current import set_app
+from prompt_toolkit.data_structures import Point
 from prompt_toolkit.formatted_text import fragment_list_to_text
-from prompt_toolkit.layout import to_window
-from prompt_toolkit.widgets import Button
+from prompt_toolkit.input import DummyInput
+from prompt_toolkit.layout import Layout, to_window
+from prompt_toolkit.layout.containers import HSplit
+from prompt_toolkit.layout.mouse_handlers import MouseHandlers
+from prompt_toolkit.layout.screen import Screen, WritePosition
+from prompt_toolkit.mouse_events import MouseButton, MouseEvent, MouseEventType
+from prompt_toolkit.output import DummyOutput
+from prompt_toolkit.widgets import Button, CheckboxList, RadioList
 
 
 def _to_text(button: Button) -> str:
@@ -18,3 +29,102 @@ def test_default_button():
 def test_custom_button():
     button = Button("Exit", left_symbol="[", right_symbol="]")
     assert _to_text(button) == "[   Exit   ]"
+
+
+def _render_list(app, widget):
+    """Render a short viewport, including the real screen-coordinate handlers."""
+    app.layout.update_parents_relations()
+    app.render_counter += 1
+    handlers = MouseHandlers()
+    widget.window.write_to_screen(
+        Screen(), handlers, WritePosition(0, 0, 20, 3), "", True, None
+    )
+    return handlers
+
+
+def _mouse_event(handlers, event_type):
+    return handlers.mouse_handlers[1][1](
+        MouseEvent(
+            Point(x=1, y=1),
+            event_type,
+            MouseButton.LEFT
+            if event_type == MouseEventType.MOUSE_UP
+            else MouseButton.NONE,
+            frozenset(),
+        )
+    )
+
+
+@pytest.mark.parametrize("widget_class", [RadioList, CheckboxList])
+@pytest.mark.parametrize("focused", [True, False])
+def test_dialog_list_mouse_wheel_scrolls(widget_class, focused):
+    widget = widget_class([(i, str(i)) for i in range(10)])
+    app = Application(layout=Layout(widget), input=DummyInput(), output=DummyOutput())
+    if not focused:
+        button = Button("Other")
+        app.layout = Layout(HSplit([widget, button]), focused_element=button)
+    current_value = widget.current_value
+    current_values = widget.current_values[:]
+
+    with set_app(app):
+        handlers = _render_list(app, widget)
+        for expected_scroll in [1, 2, 3, 4, 5, 6, 7, 7, 7]:
+            _mouse_event(handlers, MouseEventType.SCROLL_DOWN)
+            handlers = _render_list(app, widget)
+            assert widget.window.vertical_scroll == expected_scroll
+            assert 0 <= widget._selected_index < 10
+            assert widget.current_value == current_value
+            assert widget.current_values == current_values
+
+        for expected_scroll in [6, 5, 4, 3, 2, 1, 0, 0, 0]:
+            _mouse_event(handlers, MouseEventType.SCROLL_UP)
+            handlers = _render_list(app, widget)
+            assert widget.window.vertical_scroll == expected_scroll
+            assert 0 <= widget._selected_index < 10
+            assert widget.current_value == current_value
+            assert widget.current_values == current_values
+
+        # Screen coordinates must still select the correct item after scrolling.
+        for _ in range(2):
+            _mouse_event(handlers, MouseEventType.SCROLL_DOWN)
+            handlers = _render_list(app, widget)
+        _mouse_event(handlers, MouseEventType.MOUSE_UP)
+        assert widget._selected_index == 3
+        if isinstance(widget, CheckboxList):
+            assert widget.current_values == [3]
+            handlers = _render_list(app, widget)
+            _mouse_event(handlers, MouseEventType.MOUSE_UP)
+            assert widget.current_values == []
+        else:
+            assert widget.current_value == 3
+
+
+def test_radio_list_mouse_wheel_select_on_focus():
+    widget = RadioList(
+        [(i, str(i)) for i in range(10)], default=2, select_on_focus=True
+    )
+    app = Application(layout=Layout(widget), input=DummyInput(), output=DummyOutput())
+
+    with set_app(app):
+        handlers = _render_list(app, widget)
+        assert widget.window.vertical_scroll == 0
+        # Scrolling does not change selection while the cursor remains visible.
+        for expected_scroll in [1, 2]:
+            _mouse_event(handlers, MouseEventType.SCROLL_DOWN)
+            handlers = _render_list(app, widget)
+            assert widget.window.vertical_scroll == expected_scroll
+            assert widget.current_value == 2
+        # Once needed, move the cursor and honor select_on_focus.
+        _mouse_event(handlers, MouseEventType.SCROLL_DOWN)
+        handlers = _render_list(app, widget)
+        assert widget.window.vertical_scroll == 3
+        assert widget._selected_index == widget.current_value == 3
+        for expected_scroll in [2, 1]:
+            _mouse_event(handlers, MouseEventType.SCROLL_UP)
+            handlers = _render_list(app, widget)
+            assert widget.window.vertical_scroll == expected_scroll
+            assert widget.current_value == 3
+        _mouse_event(handlers, MouseEventType.SCROLL_UP)
+        _render_list(app, widget)
+        assert widget.window.vertical_scroll == 0
+        assert widget._selected_index == widget.current_value == 2