feat: add dropdown menu component

crates/core/tests/menu.rs

@@ -138,18 +138,16 @@ fn rows_render_at_the_stated_menu_row_height() {
 fn arrow_navigation_skips_separators_and_disabled_items() {
     let (_cx, mut visual, _window, changes, activated) = menu_window(true);
 
-    // Selection starts on the first item; down moves to the next
-    // selectable item (Copy, past the separator), and enter activates it,
-    // closing the menu.
-    visual.simulate_keystrokes("down");
-    visual.simulate_keystrokes("enter");
+    // Nothing is highlighted when the menu opens; down arms the first
+    // selectable item, the next down crosses the separator to Copy, and
+    // enter activates it, closing the menu.
+    visual.simulate_keystrokes("down down enter");
     draw(&mut visual);
     assert_eq!(*activated.borrow(), vec!["copy"]);
     assert_eq!(*changes.borrow(), vec![false]);
 
-    // Reopen: the selection starts over on the first item, and end jumps
-    // straight to the last selectable item, over the separator and the
-    // disabled row.
+    // Reopen: pointer opens highlight nothing again, and end jumps straight
+    // to the last selectable item, over the separator and the disabled row.
     click(&mut visual, point(px(10.), px(16.)));
     draw(&mut visual);
     visual.simulate_keystrokes("end");
@@ -158,6 +156,18 @@ fn arrow_navigation_skips_separators_and_disabled_items() {
     assert_eq!(*changes.borrow(), vec![false, true, false]);
 }
 
+#[test]
+fn enter_without_navigation_activates_nothing() {
+    let (_cx, mut visual, _window, changes, activated) = menu_window(true);
+
+    // A pointer-opened menu arms no row, so enter cannot fire one and the
+    // menu stays open.
+    visual.simulate_keystrokes("enter");
+    draw(&mut visual);
+    assert!(activated.borrow().is_empty());
+    assert!(changes.borrow().is_empty(), "the menu stays open");
+}
+
 #[test]
 fn escape_dismisses_without_activating() {
     let (_cx, mut visual, _window, changes, activated) = menu_window(true);