A controller moving focus between tabs trips a fail-fast in WinUI's TabView::OnListViewGettingFocus. Add a GettingFocus handler on the TabViewItem that cancels that gamepad focus move before it reaches the framework handler.

Author: phil-scott-78

.github/actions/spelling/allow/microsoft.txt

@@ -78,4 +78,5 @@ wtl
 wtt
 wttlog
 Xamarin
+XBOX
 xfgcheck

src/cascadia/TerminalApp/Tab.cpp

@@ -162,6 +162,40 @@ namespace winrt::TerminalApp::implementation
             }
         });
 
+        // BODGY: Work around a fail-fast crash in WinUI 2's TabView. When a
+        // game controller (e.g. an XBOX controller's d-pad/stick) moves focus
+        // Up or Down between two TabViewItems, MUX's TabView::OnListViewGettingFocus
+        // runs a GameController-only code path that calls
+        // DispatcherQueue.TryEnqueue, which fails with E_INVALIDARG. That
+        // unhandled error inside a GettingFocus callback makes XAML fail-fast,
+        // and the whole window vanishes. See
+        // microsoft-ui-xaml/blob/840c6cd4ac9d16d9aa99b24f0bd43997fe21bef8/dev/TabView/TabView.cpp#L246
+        //
+        // This GettingFocus handler is on the TabViewItem, which is closer to
+        // the focus source than the TabViewListView that MUX's handler lives
+        // on, so it runs first. Marking the event Handled - and cancelling the
+        // focus move, which is exactly what MUX itself does for the keyboard
+        // case - preempts MUX's broken handler. Keyboard navigation is left
+        // untouched; MUX handles that path safely.
+        TabViewItem().GettingFocus([](auto&&, const winrt::WUX::Input::GettingFocusEventArgs& args) {
+            const auto direction{ args.Direction() };
+            if (direction != winrt::WUX::Input::FocusNavigationDirection::Up &&
+                direction != winrt::WUX::Input::FocusNavigationDirection::Down)
+            {
+                return;
+            }
+            if (args.InputDevice() != winrt::WUX::Input::FocusInputDeviceKind::GameController)
+            {
+                return;
+            }
+            if (args.OldFocusedElement().try_as<winrt::MUX::Controls::TabViewItem>() &&
+                args.NewFocusedElement().try_as<winrt::MUX::Controls::TabViewItem>())
+            {
+                args.Cancel(true);
+                args.Handled(true);
+            }
+        });
+
         UpdateTitle();
         _RecalculateAndApplyTabColor();
     }