CombBox: Don't change on scroll unless we have focus / not at all on cupertino

* ComboBox: Don't change on scroll uless we have focus

This is what native Windows combobox does.
Otherwise this causes problem when combobox are in scrollable

Fixes #5929

* ComboBox: Don't scroll at all with the wheel on Mac.

This is also Qt's behavior
https://doc.qt.io/qt-6/qstyle.html#:~:text=SH_ComboBox_AllowWheelScrolling

internal/compiler/widgets/common/combobox-base.slint

@@ -73,7 +73,8 @@ export component ComboBoxBase {
         root.update-current-value();
     }
 
-    private property <length> scroll-delta: 2px;
+    /// Minimum scroll delta so that the scroll wheel changes the value.
+    in property <length> scroll-delta: 2px;
 
     forward-focus: i-focus-scope;
 
@@ -109,6 +110,9 @@ export component ComboBoxBase {
             }
 
             scroll-event(event) => {
+                if (!root.has-focus) {
+                    return reject;
+                }
                 if (event.delta-y < -root.scroll-delta) {
                     root.move-selection-down();
                     return accept;

internal/compiler/widgets/cupertino/combobox.slint

@@ -47,6 +47,9 @@ export component ComboBox {
         width: 100%;
         height: 100%;
 
+        // Mac doesn't react on mouse wheel on the ComboBox.
+        scroll-delta: 1000000px;
+
         show-popup => {
             popup.show();
         }

tests/cases/widgets/combobox.slint

@@ -21,6 +21,10 @@ export component TestCase inherits Window {
         }
     }
 
+    public function unfocus() {
+        box.clear-focus();
+    }
+
     in-out property current-index <=> box.current-index;
     in-out property current-value <=> box.current-value;
     in-out property model <=> box.model;
@@ -32,9 +36,7 @@ export component TestCase inherits Window {
 
 ```rust
 use std::rc::Rc;
-use slint::platform::Key;
-use slint::SharedString;
-use slint::VecModel;
+use slint::{platform::WindowEvent, platform::Key, VecModel, SharedString, LogicalPosition};
 use i_slint_backend_testing::mock_elapsed_time;
 
 let instance = TestCase::new().unwrap();
@@ -167,6 +169,40 @@ assert_eq!(instance.get_output(), "");
 assert_eq!(instance.get_has_focus(), true);
 assert_eq!(combobox.accessible_expanded(), Some(false));
 
+// Scroll with the wheel
+let wheel_change_value = !module_path!().contains("cupertino");
+instance.set_output(Default::default());
+instance.window().dispatch_event(WindowEvent::PointerScrolled { position: LogicalPosition::new(100.0, 100.0), delta_x: 0.0, delta_y: 20.0 });
+if wheel_change_value {
+    assert_eq!(instance.get_current_value(), "Aaa");
+    assert_eq!(instance.get_current_index(), 0);
+    assert_eq!(instance.get_output(), "selected(Aaa,0)\n");
+} else {
+    assert_eq!(instance.get_current_value(), "Bbb");
+    assert_eq!(instance.get_current_index(), 1);
+    assert_eq!(instance.get_output(), "");
+}
+instance.window().dispatch_event(WindowEvent::PointerScrolled { position: LogicalPosition::new(100.0, 100.0), delta_x: 0.0, delta_y: -5.0 });
+assert_eq!(instance.get_has_focus(), true);
+assert_eq!(instance.get_current_value(), "Bbb");
+assert_eq!(instance.get_current_index(), 1);
+if wheel_change_value {
+    assert_eq!(instance.get_output(), "selected(Aaa,0)\nselected(Bbb,1)\n");
+}
+// When not having focus, do nothing
+instance.invoke_unfocus();
+instance.set_output(Default::default());
+assert_eq!(instance.get_has_focus(), false);
+instance.window().dispatch_event(WindowEvent::PointerScrolled { position: LogicalPosition::new(100.0, 100.0), delta_x: 0.0, delta_y: 20.0 });
+assert_eq!(instance.get_current_value(), "Bbb");
+assert_eq!(instance.get_current_index(), 1);
+instance.window().dispatch_event(WindowEvent::PointerScrolled { position: LogicalPosition::new(100.0, 100.0), delta_x: 0.0, delta_y: -5.0 });
+assert_eq!(instance.get_has_focus(), false);
+assert_eq!(instance.get_current_value(), "Bbb");
+assert_eq!(instance.get_current_index(), 1);
+assert_eq!(instance.get_output(), "");
+slint_testing::send_keyboard_string_sequence(&instance, "\t");
+assert_eq!(instance.get_has_focus(), true);
 
 // Set current-index to -1
 instance.set_current_index(-1);