Avoid reading org.eclipse.swt.* properties too early

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Display.java

@@ -1211,6 +1211,14 @@ void createDisplay (DeviceData data) {
 		xDisplay = GTK.GTK4 ? 0 : GDK.gdk_x11_get_default_xdisplay();
 		// set GDK backend if we are on X11
 		System.setProperty("org.eclipse.swt.internal.gdk.backend", "x11");
+	} else if (OS.isWayland()) {
+		// only other option for backend is Wayland at the moment
+		System.setProperty("org.eclipse.swt.internal.gdk.backend", "wayland");
+	} else {
+		// unreachable at the moment since isWayland is defined as !isX11
+		// but if other items are added in the future this should be changed
+		// from unknown to real value.
+		System.setProperty("org.eclipse.swt.internal.gdk.backend", "unknown");
 	}
 	if (OS.SWT_DEBUG) Device.DEBUG = true;
 	if (!GTK.GTK4) {

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/SwtTestUtil.java

@@ -100,10 +100,49 @@ public class SwtTestUtil {
 	/** Useful if you want some tests not to run on Jenkins with user "genie.platform" */
 	public final static boolean isRunningOnContinousIntegration = isGTK && ("genie.platform".equalsIgnoreCase(System.getProperty("user.name")));
 
-	public final static boolean isX11 = isGTK
-			&& "x11".equals(System.getProperty("org.eclipse.swt.internal.gdk.backend"));
-	public final static boolean isGTK4 = isGTK
-			&& System.getProperty("org.eclipse.swt.internal.gtk.version", "").startsWith("4");
+	/**
+	 * Return whether running on x11. This is dynamically set at runtime and cannot
+	 * be accessed before the corresponding property is initialized in Display.
+	 *
+	 * <strong>Note:</strong> this method still must be called after the first
+	 * Display is created to be valid
+	 */
+	public final static boolean isX11() {
+		if (!isGTK) {
+			return false;
+		}
+		String backend = System.getProperty("org.eclipse.swt.internal.gdk.backend");
+
+		if ("x11".equals(backend)) {
+			return true;
+		} else if ("wayland".equals(backend)) {
+			return false;
+		}
+		fail("org.eclipse.swt.internal.gdk.backend System property is not set yet. Create a new Display before calling isX11");
+		throw new IllegalStateException("unreachable");
+	}
+
+	/**
+	 * Return whether running on GTK4. This is dynamically set at runtime and cannot
+	 * be accessed before the corresponding property is initialized in OS.
+	 *
+	 * <strong>Note:</strong> this method still must be called after the static
+	 * block of OS is run.
+	 */
+	public final static boolean isGTK4() {
+		if (!isGTK) {
+			return false;
+		}
+
+		String version = System.getProperty("org.eclipse.swt.internal.gtk.version", "");
+		if (version.startsWith("4")) {
+			return true;
+		} else if (!version.isBlank()) {
+			return false;
+		}
+		fail("org.eclipse.swt.internal.gtk.version System property is not set yet. Create a new Display (or otherwise access OS) before calling isGTK4");
+		throw new IllegalStateException("unreachable");
+	}
 
 	/**
 	 * The palette used by images. See {@link #getAllPixels(Image)} and {@link #createImage}

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_dnd_Clipboard.java

@@ -80,7 +80,7 @@ public void setUp() {
 	}
 
 	private void sleep() throws InterruptedException {
-		if (SwtTestUtil.isGTK4) {
+		if (SwtTestUtil.isGTK4()) {
 			/**
 			 * TODO remove all uses of sleep and change them to processEvents with the
 			 * suitable conditional, or entirely remove them
@@ -351,7 +351,7 @@ public void test_setContents() throws Exception {
 			String result = runOperationInThread(remote::getStringContents);
 			assertEquals(helloWorld, result);
 		} catch (Exception | AssertionError e) {
-			if (SwtTestUtil.isGTK4 && !SwtTestUtil.isX11) {
+			if (SwtTestUtil.isGTK4() && !SwtTestUtil.isX11()) {
 				// TODO make the code + test stable
 				throw new RuntimeException(
 						"This test is really unstable on wayland backend, at least with Ubuntu 25.04", e);

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_widgets_Display.java

@@ -1247,7 +1247,7 @@ public void test_setCursorLocationII(TestInfo info) {
 		display.setCursorLocation(location.x, location.y); // don't put cursor into a corner, since that could trigger special platform events
 		drainEventQueue(display, 150); // workaround for https://bugs.eclipse.org/492569
 		Point actual = display.getCursorLocation();
-		if (!BUG_492569 && SwtTestUtil.isX11) {
+		if (!BUG_492569 && SwtTestUtil.isX11()) {
 			if (!location.equals(actual)) {
 				Screenshots.takeScreenshot(getClass(), info.getDisplayName()); // Bug 528968 This call causes crash on Wayland.
 				fail("\nExpected:"+location.toString()+"  Actual:"+actual.toString());
@@ -1279,7 +1279,7 @@ public void test_setCursorLocationLorg_eclipse_swt_graphics_Point(TestInfo info)
 		}
 		drainEventQueue(display, 150); // workaround for https://bugs.eclipse.org/492569
 		Point actual = display.getCursorLocation();
-		if (!BUG_492569 && SwtTestUtil.isX11) {
+		if (!BUG_492569 && SwtTestUtil.isX11()) {
 			if (!location.equals(actual)) {
 				Screenshots.takeScreenshot(getClass(), info.getDisplayName()); // Bug 528968 This call causes crash on Wayland.
 				fail("\nExpected:"+location.toString()+"  Actual:"+actual.toString());

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_widgets_Shell.java

@@ -460,7 +460,7 @@ public void test_getImeInputMode() {
 @Test
 public void test_getLocation() {
 	//Setting location for Windows is not supported in GTK4
-	if (SwtTestUtil.isGTK4) {
+	if (SwtTestUtil.isGTK4()) {
 		return;
 	}
 	shell.setLocation(10,15);
@@ -656,7 +656,7 @@ public void test_setBoundsLorg_eclipse_swt_graphics_Rectangle() {
  */
 @Test
 public void test_activateEventSend() throws InterruptedException {
-	assumeTrue((SwtTestUtil.isGTK && SwtTestUtil.isX11) || SwtTestUtil.isGTK4,
+	assumeTrue((SwtTestUtil.isGTK && SwtTestUtil.isX11()) || SwtTestUtil.isGTK4(),
 			"Feature only works on GTK3 in x11 or GTK4 - https://bugs.eclipse.org/436841");
 
 	AtomicBoolean activateCalled = new AtomicBoolean();
@@ -708,7 +708,7 @@ public void test_activateEventSend() throws InterruptedException {
  */
 @Test
 public void test_setBounds() throws Exception {
-	if (SwtTestUtil.isX11) {
+	if (SwtTestUtil.isX11()) {
 		Rectangle bounds = new Rectangle(100, 200, 200, 200);
 		Rectangle bounds2 = new Rectangle(150, 250, 250, 250);
 
@@ -1037,7 +1037,7 @@ public void test_Issue450_NoShellActivateOnSetFocus() {
 @Override
 public void test_setLocationLorg_eclipse_swt_graphics_Point() {
 	//Setting location for Windows is not supported in GTK4
-	if (SwtTestUtil.isGTK4) {
+	if (SwtTestUtil.isGTK4()) {
 		return;
 	}
 	super.test_setLocationLorg_eclipse_swt_graphics_Point();
@@ -1047,7 +1047,7 @@ public void test_setLocationLorg_eclipse_swt_graphics_Point() {
 @Override
 public void test_setLocationII() {
 	//Setting location for Windows is not supported in GTK4
-	if (SwtTestUtil.isGTK4) {
+	if (SwtTestUtil.isGTK4()) {
 		return;
 	}
 	super.test_setLocationII();