Fix menu keyboard toggle for open submenus (#7957)

Summary
This PR fixes submenu keyboard parity: pressing Enter/Space on an
already-open submenu button now collapses that submenu (matching
top-level menu button behavior).

What changed
Updated submenu interaction logic to distinguish pointer primary clicks
from keyboard/accessibility-triggered clicks.
Kept pointer/touch behavior unchanged (submenu button clicks still don’t
auto-close submenu).
Added regression tests for:
keyboard open of nested submenu,
keyboard close (second Enter) of nested submenu,
pointer clicks on submenu button keeping submenu open.


Validation
cargo test -p egui_kittest --test regression_tests

Breaking changes
None. Behavior change is limited to keyboard/accessibility activation of
already-open submenu buttons.

* Closes <https://github.com/emilk/egui/issues/7926> 
* [ X ] I have followed the instructions in the PR template

---------

Co-authored-by: Lucas Meurer <hi@lucasmerlin.me>

crates/egui/src/containers/menu.rs

@@ -10,7 +10,7 @@
 
 use crate::style::StyleModifier;
 use crate::{
-    Button, Color32, Context, Frame, Id, InnerResponse, IntoAtoms, Layout, Popup,
+    Button, Color32, Context, Frame, Id, InnerResponse, IntoAtoms, Layout, PointerButton, Popup,
     PopupCloseBehavior, Response, Style, Ui, UiBuilder, UiKind, UiStack, UiStackInfo, Widget as _,
 };
 use emath::{Align, RectAlign, Vec2, vec2};
@@ -458,6 +458,7 @@ impl SubMenu {
 
         let is_any_open = open_item.is_some();
         let mut is_open = open_item == Some(id);
+        let was_open = is_open;
         let mut set_open = None;
 
         // We expand the button rect so there is no empty space where no menu is shown
@@ -470,9 +471,21 @@ impl SubMenu {
         // But since we check if no other menu is open, nothing should be able to cover the button
         let is_hovered = hover_pos.is_some_and(|pos| button_rect.contains(pos));
 
+        // `clicked` includes keyboard and accessibility click actions.
+        // We want Enter/Space to toggle an already open submenu, while pointer clicks should keep
+        // the submenu open (for touch and pointer interactions).
+        let clicked = button_response.clicked();
+        let clicked_by_pointer = button_response.clicked_by(PointerButton::Primary);
+        let clicked_by_keyboard_or_access = clicked && !clicked_by_pointer;
+
+        if ui.is_enabled() && is_open && clicked_by_keyboard_or_access {
+            set_open = Some(false);
+            is_open = false;
+        }
+
         // The clicked handler is there for accessibility (keyboard navigation)
         let should_open =
-            ui.is_enabled() && (button_response.clicked() || (is_hovered && !is_any_open));
+            ui.is_enabled() && ((!was_open && clicked) || (is_hovered && !is_any_open));
         if should_open {
             set_open = Some(true);
             is_open = true;

crates/egui_kittest/tests/regression_tests.rs

@@ -262,3 +262,101 @@ pub fn menus_should_close_even_if_submenu_disappears() {
         );
     }
 }
+
+fn keyboard_submenu_harness() -> Harness<'static, bool> {
+    Harness::builder()
+        .with_size(Vec2::new(400.0, 240.0))
+        .build_ui_state(
+            |ui, checked| {
+                egui::Panel::top("menu_bar").show_inside(ui, |ui| {
+                    egui::MenuBar::new().ui(ui, |ui| {
+                        ui.menu_button("X", |ui| {
+                            ui.menu_button("Y", |ui| {
+                                ui.checkbox(checked, "Goal");
+                            });
+                        });
+                    });
+                });
+            },
+            false,
+        )
+}
+
+#[test]
+pub fn keyboard_should_open_nested_submenu() {
+    let mut harness = keyboard_submenu_harness();
+
+    harness.get_by_label("X").focus();
+    harness.run();
+
+    harness.key_press(egui::Key::Enter);
+    harness.run();
+
+    harness.get_by_label_contains("Y").focus();
+    harness.run();
+
+    harness.key_press(egui::Key::Enter);
+    harness.run();
+
+    assert!(
+        harness.query_by_label("Goal").is_some(),
+        "Expected nested submenu to open via keyboard"
+    );
+}
+
+#[test]
+pub fn keyboard_should_close_nested_submenu_with_second_enter() {
+    let mut harness = keyboard_submenu_harness();
+
+    harness.get_by_label("X").focus();
+    harness.run();
+
+    harness.key_press(egui::Key::Enter);
+    harness.run();
+
+    harness.get_by_label_contains("Y").focus();
+    harness.run();
+
+    harness.key_press(egui::Key::Enter);
+    harness.run();
+
+    assert!(
+        harness.query_by_label("Goal").is_some(),
+        "Expected nested submenu to open before close attempt"
+    );
+
+    harness.get_by_label_contains("Y").focus();
+    harness.run();
+
+    harness.key_press(egui::Key::Enter);
+    harness.run();
+
+    assert!(
+        harness.query_by_label("Goal").is_none(),
+        "Expected nested submenu to close when pressing Enter again"
+    );
+}
+
+#[test]
+pub fn pointer_click_on_open_submenu_button_should_not_close_it() {
+    let mut harness = keyboard_submenu_harness();
+
+    harness.get_by_label("X").click();
+    harness.run();
+
+    harness.get_by_label_contains("Y").click();
+    harness.run();
+
+    assert!(
+        harness.query_by_label("Goal").is_some(),
+        "Expected submenu to remain open after pointer click on its button"
+    );
+
+    harness.get_by_label_contains("Y").click();
+    harness.run();
+
+    assert!(
+        harness.query_by_label("Goal").is_some(),
+        "Expected submenu to remain open on repeated pointer click"
+    );
+}