UI/Qt: Forward native window container focus events to the host

The view's Vulkan window container becomes its focus proxy while
visible. showing it moves keyboard focus onto the container and the
view reports a focus loss to WebContent.

On Wayland, the embedded window never receives keyboard focus, meaning
focus was never reported back, so the text caret stopped appearing in
editable content.

Author: tcl3

Tests/UI/Qt/TestNativeWindowContainerFocus.cpp

@@ -46,6 +46,19 @@ struct TestWindow {
     QWidget& sibling;
 };
 
+class FocusEventRecorder final : public QObject {
+public:
+    QEvent::Type last_focus_event { QEvent::None };
+
+private:
+    virtual bool eventFilter(QObject*, QEvent* event) override
+    {
+        if (event->type() == QEvent::FocusIn || event->type() == QEvent::FocusOut)
+            last_focus_event = event->type();
+        return false;
+    }
+};
+
 }
 
 TEST_CASE(focus_proxy_follows_container_visibility)
@@ -98,6 +111,33 @@ TEST_CASE(focus_is_not_stolen_from_other_widgets)
     EXPECT_EQ(QApplication::focusWidget(), &widgets.sibling);
 }
 
+TEST_CASE(container_focus_events_are_forwarded_to_the_host)
+{
+    application();
+    TestWindow widgets;
+    Ladybird::install_native_window_container_focus_forwarding(widgets.host, widgets.container);
+
+    FocusEventRecorder recorder;
+    widgets.host.installEventFilter(&recorder);
+
+    widgets.host.setFocus();
+    QApplication::processEvents();
+
+    Ladybird::set_native_window_container_visible(widgets.host, widgets.container, true);
+    EXPECT_EQ(QApplication::focusWidget(), &widgets.container);
+    EXPECT_EQ(recorder.last_focus_event, QEvent::FocusIn);
+
+    widgets.sibling.setFocus();
+    EXPECT_EQ(recorder.last_focus_event, QEvent::FocusOut);
+
+    widgets.container.setFocus();
+    EXPECT_EQ(recorder.last_focus_event, QEvent::FocusIn);
+
+    Ladybird::set_native_window_container_visible(widgets.host, widgets.container, false);
+    EXPECT_EQ(QApplication::focusWidget(), &widgets.host);
+    EXPECT_EQ(recorder.last_focus_event, QEvent::FocusIn);
+}
+
 TEST_CASE(visibility_changes_are_idempotent)
 {
     application();

UI/Qt/NativeWindowContainer.cpp

@@ -6,10 +6,37 @@
 
 #include <UI/Qt/NativeWindowContainer.h>
 
+#include <QCoreApplication>
+#include <QFocusEvent>
 #include <QWidget>
 
 namespace Ladybird {
 
+namespace {
+
+class FocusEventForwarder final : public QObject {
+public:
+    FocusEventForwarder(QWidget& host, QWidget& container)
+        : QObject(&container)
+        , m_host(host)
+    {
+    }
+
+private:
+    virtual bool eventFilter(QObject*, QEvent* event) override
+    {
+        if (event->type() == QEvent::FocusIn || event->type() == QEvent::FocusOut) {
+            QFocusEvent forwarded_event { event->type(), static_cast<QFocusEvent*>(event)->reason() };
+            QCoreApplication::sendEvent(&m_host, &forwarded_event);
+        }
+        return false;
+    }
+
+    QWidget& m_host;
+};
+
+}
+
 void set_native_window_container_visible(QWidget& host, QWidget& container, bool visible)
 {
     if (container.isVisible() == visible)
@@ -31,4 +58,9 @@ void set_native_window_container_visible(QWidget& host, QWidget& container, bool
     }
 }
 
+void install_native_window_container_focus_forwarding(QWidget& host, QWidget& container)
+{
+    container.installEventFilter(new FocusEventForwarder(host, container));
+}
+
 }

UI/Qt/NativeWindowContainer.h

@@ -14,4 +14,6 @@ namespace Ladybird {
 // consistent: The container is the host's focus proxy only while it's visible.
 void set_native_window_container_visible(QWidget& host, QWidget& container, bool visible);
 
+void install_native_window_container_focus_forwarding(QWidget& host, QWidget& container);
+
 }

UI/Qt/WebContentViewLinux.cpp

@@ -906,6 +906,7 @@ void WebContentView::create_vulkan_window()
     m_vulkan_window_container->setMouseTracking(true);
     m_vulkan_window_container->setGeometry(rect());
     m_vulkan_window_container->hide();
+    install_native_window_container_focus_forwarding(*this, *m_vulkan_window_container);
 }
 
 void WebContentView::set_vulkan_window_container_visible(bool visible)