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

The value of org.eclipse.swt.internal.gdk.backend is not set until
a display is created at least once since this value is assigned in
the Display constructor.

To be able to detect if Display has been created, set
"org.eclipse.swt.internal.gdk.backend" on wayland too.

A similar problem exists for org.eclipse.swt.internal.gtk.version
in relation to OS.

This is a fix for a regression caused by moving the setting of
org.eclipse.swt.internal.gdk.backend from OS to Display in
5d67ce6. That commit fixed
an unrelated bug, but sometimes bad initialization of isX11 is an
unintended side effect causing tests to be skipped or run in
unexpected ways since isX11 was not correct.

See for example #2592
for a test that was silently being skipped and had bitrotten as
a result.

Also removes comment on related code that didn't say anything beyond
what the code on the next line did.

Author: jonahgraham

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

@@ -1209,8 +1209,13 @@ void createDisplay (DeviceData data) {
 	themeDark = checkAndSetThemeDetails(themeName);
 	if (OS.isX11()) {
 		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()) {
+		System.setProperty("org.eclipse.swt.internal.gdk.backend", "wayland");
+	} else {
+		// 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();