audit popover and dialog

crates/core/tests/popover.rs

@@ -45,6 +45,7 @@ impl Render for Harness {
                     })
                     .trigger(|_, _| {
                         div()
+                            .debug_selector(|| "popover-trigger".to_string())
                             .w(px(100.))
                             .h(px(32.))
                             .bg(rgba(0x000000ff))
@@ -188,3 +189,26 @@ fn clicking_another_control_dismisses_and_reaches_it() {
     assert_eq!(*changes.borrow(), vec![false]);
     assert_eq!(*clicks.borrow(), 1);
 }
+
+/// The panel hangs one spacing unit below the trigger: the anchor gap is
+/// theme-owned, and rides the anchored element so the window-edge clamp
+/// stays intact.
+#[test]
+fn the_panel_hangs_one_spacing_unit_below_the_trigger() {
+    let (cx, mut visual, _window, _changes, _clicks) = popover_window(true);
+
+    let trigger = visual
+        .debug_bounds("popover-trigger")
+        .expect("trigger rendered");
+    let panel = visual
+        .debug_bounds("popover-panel")
+        .expect("panel rendered");
+
+    let expected = cx.update(|cx| Theme::global(cx).spacing.unit);
+    let gap = panel.top() - trigger.bottom();
+    // Painted bounds are snapped to device pixels; allow half a pixel.
+    assert!(
+        (gap - expected).abs() <= px(0.5),
+        "the anchor gap is {gap:?}, expected {expected:?}"
+    );
+}