wayland: Resize the client to last requested client size if decoration is destroyed

If the decoration is destroyed before the window is mapped, kwin can
respond with a configure event that has 0x0 size. New tests check that
problematic case.

BUG: 444962

autotests/integration/xdgshellclient_test.cpp

@@ -104,6 +104,8 @@ private Q_SLOTS:
     void testPointerInputTransform();
     void testReentrantSetFrameGeometry();
     void testDoubleMaximize();
+    void testMaximizeAndChangeDecorationModeAfterInitialCommit();
+    void testFullScreenAndChangeDecorationModeAfterInitialCommit();
 };
 
 void TestXdgShellClient::testXdgWindowReactive()
@@ -1837,5 +1839,51 @@ void TestXdgShellClient::testMaximizeFull()
     QVERIFY(Test::waitForWindowDestroyed(client));
 }
 
+void TestXdgShellClient::testMaximizeAndChangeDecorationModeAfterInitialCommit()
+{
+    // Ideally, the app would initialize the xdg-toplevel surface before the initial commit, but
+    // many don't do it. They initialize the surface after the first commit.
+    // This test verifies that the client will receive a configure event with correct size
+    // if an xdg-toplevel surface is set maximized and decoration mode changes after initial commit.
+
+    QScopedPointer<KWayland::Client::Surface> surface(Test::createSurface());
+    QScopedPointer<Test::XdgToplevel> shellSurface(Test::createXdgToplevelSurface(surface.data())); // will wait for the first configure event
+    QScopedPointer<Test::XdgToplevelDecorationV1> decoration(Test::createXdgToplevelDecorationV1(shellSurface.data()));
+    QSignalSpy toplevelConfigureRequestedSpy(shellSurface.data(), &Test::XdgToplevel::configureRequested);
+    QSignalSpy surfaceConfigureRequestedSpy(shellSurface->xdgSurface(), &Test::XdgSurface::configureRequested);
+
+    // Request maximized mode and set decoration mode, i.e. perform late initialization.
+    shellSurface->set_maximized();
+    decoration->set_mode(Test::XdgToplevelDecorationV1::mode_client_side);
+
+    // The compositor will respond with a new configure event, which should contain maximized state.
+    QVERIFY(surfaceConfigureRequestedSpy.wait());
+    QCOMPARE(toplevelConfigureRequestedSpy.last().at(0).value<QSize>(), QSize(1280, 1024));
+    QCOMPARE(toplevelConfigureRequestedSpy.last().at(1).value<Test::XdgToplevel::States>(), Test::XdgToplevel::State::Maximized);
+}
+
+void TestXdgShellClient::testFullScreenAndChangeDecorationModeAfterInitialCommit()
+{
+    // Ideally, the app would initialize the xdg-toplevel surface before the initial commit, but
+    // many don't do it. They initialize the surface after the first commit.
+    // This test verifies that the client will receive a configure event with correct size
+    // if an xdg-toplevel surface is set fullscreen and decoration mode changes after initial commit.
+
+    QScopedPointer<KWayland::Client::Surface> surface(Test::createSurface());
+    QScopedPointer<Test::XdgToplevel> shellSurface(Test::createXdgToplevelSurface(surface.data())); // will wait for the first configure event
+    QScopedPointer<Test::XdgToplevelDecorationV1> decoration(Test::createXdgToplevelDecorationV1(shellSurface.data()));
+    QSignalSpy toplevelConfigureRequestedSpy(shellSurface.data(), &Test::XdgToplevel::configureRequested);
+    QSignalSpy surfaceConfigureRequestedSpy(shellSurface->xdgSurface(), &Test::XdgSurface::configureRequested);
+
+    // Request fullscreen mode and set decoration mode, i.e. perform late initialization.
+    shellSurface->set_fullscreen(nullptr);
+    decoration->set_mode(Test::XdgToplevelDecorationV1::mode_client_side);
+
+    // The compositor will respond with a new configure event, which should contain fullscreen state.
+    QVERIFY(surfaceConfigureRequestedSpy.wait());
+    QCOMPARE(toplevelConfigureRequestedSpy.last().at(0).value<QSize>(), QSize(1280, 1024));
+    QCOMPARE(toplevelConfigureRequestedSpy.last().at(1).value<Test::XdgToplevel::States>(), Test::XdgToplevel::State::Fullscreen);
+}
+
 WAYLANDTEST_MAIN(TestXdgShellClient)
 #include "xdgshellclient_test.moc"

src/abstract_client.cpp

@@ -2337,8 +2337,9 @@ void AbstractClient::createDecoration(const QRect &oldGeometry)
 
 void AbstractClient::destroyDecoration()
 {
+    const QSize clientSize = frameSizeToClientSize(moveResizeGeometry().size());
     setDecoration(nullptr);
-    resize(implicitSize());
+    resize(clientSize);
 }
 
 void AbstractClient::setDecoration(KDecoration2::Decoration *decoration)