chore: reduce component overhead (#3)

Reviewed-on: reya/gpui-native-kit#3

crates/core/tests/slider.rs

@@ -153,3 +153,132 @@ fn arrow_keys_step_the_value_while_focused() {
 
     assert_eq!(*changes.borrow(), vec![0.0, 10.0, 20.0, 10.0]);
 }
+
+struct TwoSliders {
+    changes_a: Rc<RefCell<Vec<f32>>>,
+    changes_b: Rc<RefCell<Vec<f32>>>,
+    value_a: f32,
+    value_b: f32,
+}
+
+impl Render for TwoSliders {
+    fn render(&mut self, _window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
+        let (changes_a, changes_b) = (self.changes_a.clone(), self.changes_b.clone());
+        div()
+            .size_full()
+            .child(
+                div().absolute().top_0().left_0().w(px(200.)).child(
+                    Slider::new("slider-a", self.value_a)
+                        .min(0.0)
+                        .max(100.0)
+                        .step(10.0)
+                        .on_change({
+                            let view = cx.entity();
+                            let changes_a = changes_a.clone();
+                            move |next, _, cx| {
+                                changes_a.borrow_mut().push(next);
+                                view.update(cx, |harness, cx| {
+                                    harness.value_a = next;
+                                    cx.notify();
+                                });
+                            }
+                        }),
+                ),
+            )
+            .child(
+                div().absolute().top(px(40.)).left_0().w(px(200.)).child(
+                    Slider::new("slider-b", self.value_b)
+                        .min(0.0)
+                        .max(100.0)
+                        .step(10.0)
+                        .on_change({
+                            let view = cx.entity();
+                            move |next, _, cx| {
+                                changes_b.borrow_mut().push(next);
+                                view.update(cx, |harness, cx| {
+                                    harness.value_b = next;
+                                    cx.notify();
+                                });
+                            }
+                        }),
+                ),
+            )
+    }
+}
+
+#[allow(clippy::type_complexity)]
+fn two_slider_window() -> (
+    VisualTestContext,
+    Rc<RefCell<Vec<f32>>>,
+    Rc<RefCell<Vec<f32>>>,
+) {
+    let mut cx = TestAppContext::single();
+    cx.update(Theme::init);
+    let changes_a = Rc::new(RefCell::new(Vec::new()));
+    let changes_b = Rc::new(RefCell::new(Vec::new()));
+    let (changes_a_for_window, changes_b_for_window) = (changes_a.clone(), changes_b.clone());
+    let window = cx.add_window(move |_, _| TwoSliders {
+        changes_a: changes_a_for_window,
+        changes_b: changes_b_for_window,
+        value_a: 0.0,
+        value_b: 0.0,
+    });
+    let window = window.into();
+    cx.update_window(window, |_, window, cx| {
+        window.draw(cx).clear(cx);
+    })
+    .unwrap();
+    (
+        VisualTestContext::from_window(window, &cx),
+        changes_a,
+        changes_b,
+    )
+}
+
+/// Dragging one slider must never drive a sibling slider: the drag flag is
+/// per instance, not shared keyed state.
+#[test]
+fn two_sliders_drag_independently() {
+    let (mut cx, changes_a, changes_b) = two_slider_window();
+
+    // Slider A occupies y 0..16, slider B starts at y 40.
+    cx.simulate_mouse_down(
+        point(px(100.), px(10.)),
+        MouseButton::Left,
+        Modifiers::default(),
+    );
+    cx.simulate_mouse_move(
+        point(px(120.), px(10.)),
+        MouseButton::Left,
+        Modifiers::default(),
+    );
+    cx.simulate_mouse_up(
+        point(px(120.), px(10.)),
+        MouseButton::Left,
+        Modifiers::default(),
+    );
+    assert_eq!(*changes_a.borrow(), vec![50.0, 60.0]);
+    assert!(changes_b.borrow().is_empty(), "A's drag leaked into B");
+
+    cx.simulate_mouse_down(
+        point(px(100.), px(50.)),
+        MouseButton::Left,
+        Modifiers::default(),
+    );
+    cx.simulate_mouse_move(
+        point(px(40.), px(50.)),
+        MouseButton::Left,
+        Modifiers::default(),
+    );
+    cx.simulate_mouse_up(
+        point(px(40.), px(50.)),
+        MouseButton::Left,
+        Modifiers::default(),
+    );
+    assert_eq!(*changes_b.borrow(), vec![50.0, 20.0]);
+    assert_eq!(
+        *changes_a.borrow(),
+        vec![50.0, 60.0],
+        "B's drag leaked into A"
+    );
+}