[GTK4] Clone instead of reusing objects on local clipbpard operations

When calling gdk_clipboard_read_value_async and related functions, if the
clipboard is owned locally it returns the instance that was placed on the
clipboard and avoid the serialization and deserialization.

This presents a problem for SWT because SWT has always returned a copy
(javaToNative/nativeToJava) of the object between the setContents and the
getContents.
For some objects, like String it may be ok to return the same instance since
String is immutable, but for others, such as ImageData or custom types a copy
definitely needs to be made to preserve the pre-existing behavior. However,
to maintain compatibility with the pre-existing implementations for even
String type Transfers that have returned a copy, we copy String types too in
this implementation.

(Includes removing invalid comment "Put a type on the clipboard and
ensure we don't match it" in the test_internalClone tests)

Part of #2126

Author: jonahgraham

bundles/org.eclipse.swt/Eclipse SWT Drag and Drop/gtk/org/eclipse/swt/dnd/ContentProviders.java

@@ -457,7 +457,8 @@ public Object getObject(long gvalue) {
 				// Object is from within app, so get contents from clipboard data
 				// Do not remove our reference to the object yet as it may be copied
 				// multiple times
-				return fromSourceId.data.get(transferKey(transfer));
+				Object object = fromSourceId.data.get(transferKey(transfer));
+				return clone(transfer, object);
 			} else {
 				// Object is from outside app or otherwise needed deserializing
 				// Remove our reference to it and return it
@@ -471,4 +472,39 @@ public Object getObject(long gvalue) {
 		// should have returned 0 in this case
 		return null;
 	}
+
+	/**
+	 * When calling gdk_clipboard_read_value_async and related functions, if the
+	 * clipboard is owned locally it returns the instance that was placed on the
+	 * clipboard and avoid the serialization and deserialization.
+	 *
+	 * This presents a problem for SWT because SWT has always returned a copy
+	 * (javaToNative/nativeToJava) of the object between the setContents and the
+	 * getContents.
+	 *
+	 * For some objects, like String it may be ok to return the same instance since
+	 * String is immutable, but for others, such as ImageData or custom types a copy
+	 * definitely needs to be made to preserve the pre-existing behavior. However,
+	 * to maintain compatibility with the pre-existing implementations for even
+	 * String type Transfers that have returned a copy, we copy String types too in
+	 * this implementation.
+	 */
+	private Object clone(Transfer transfer, Object object) {
+		TransferData td = new TransferData();
+		td.result = 0;
+		int[] typeIds = transfer.getTypeIds();
+		if (typeIds.length == 0 || typeIds[0] == 0) {
+			return null;
+		}
+		// Which type id we use doesn't matter, as long as it is the same in both
+		// directions
+		td.type = typeIds[0];
+		transfer.javaToNative(object, td);
+		if (td.result == 0 || td.pValue == 0 || td.length == 0) {
+			return null;
+		}
+		Object clonedObject = transfer.nativeToJava(td);
+		OS.g_free(td.pValue);
+		return clonedObject;
+	}
 }

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

@@ -13,6 +13,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -180,6 +181,7 @@ public void test_internalClone() throws Exception {
 		setContents(test);
 		MyType contents = getContents();
 		assertMyTypeEquals(test, contents);
+		assertNotSame(test, contents);
 	}
 
 	@Test

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

@@ -13,6 +13,7 @@
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -152,10 +153,10 @@ public void test_internalClone() throws Exception {
 		String[] fileList = getFileList();
 
 		openAndFocusShell(false);
-		// Put a type on the clipboard and ensure we don't match it
 		setContents(fileList);
 		String[] contents = getContents();
 		assertArrayEquals(fileList, contents);
+		assertNotSame(fileList, contents);
 	}
 
 	@Test

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

@@ -13,6 +13,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -122,6 +123,7 @@ public void test_internalClone() throws Exception {
 		setContents(test);
 		String contents = getContents();
 		assertEquals(test, contents);
+		assertNotSame(test, contents);
 	}
 
 	static Stream<Arguments> testData() {

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

@@ -14,6 +14,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -128,10 +129,10 @@ public void test_internalClone() throws Exception {
 		ImageData imageData = getImageData();
 
 		openAndFocusShell(false);
-		// Put a type on the clipboard and ensure we don't match it
 		setContents(imageData);
 		ImageData contents = getContents();
 		assertEquals(0, imageDataComparator().compare(imageData, contents));
+		assertNotSame(imageData, contents);
 	}
 
 	@Test

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

@@ -13,6 +13,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -118,6 +119,7 @@ public void test_internalClone() throws Exception {
 		setContents(test);
 		String contents = getContents();
 		assertEquals(test, contents);
+		assertNotSame(test, contents);
 	}
 
 	@Test

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

@@ -13,6 +13,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -126,6 +127,7 @@ public void test_internalClone(String name, String test) throws Exception {
 		setContents(test);
 		String contents = getContents();
 		assertEquals(test, contents);
+		assertNotSame(test, contents);
 	}
 
 	@ParameterizedTest(name = "{0}")

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

@@ -13,6 +13,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -128,6 +129,7 @@ public void test_internalClone() throws Exception {
 		setContents(test);
 		String contents = getContents();
 		assertEquals(test, contents);
+		assertNotSame(test, contents);
 	}
 
 	@Test