use cloned scanner to prevent concurrent access issues

Fixes eclipse-jdt#3424

org.eclipse.jdt.core.tests.model/src/org/eclipse/jdt/core/tests/dom/ASTVisitorTest.java

@@ -1375,6 +1375,25 @@ public void testCharacterLiteral() {
 		String result = this.b.toString();
 		assertTrue(result.equals("[(eCL'q''q'eCL)]")); //$NON-NLS-1$
 	}
+	public void testCharacterLiteralConcurrent() throws Exception {
+		CharacterLiteral x1 = this.ast.newCharacterLiteral();
+		x1.setCharValue('q');
+
+		ExecutorService executorService = Executors.newFixedThreadPool(10);
+		List<CompletableFuture<Void>> futures = new ArrayList<>();
+		for (int i = 0; i < 100; i++) {
+			CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
+				try {
+					x1.charValue();
+				} catch (Exception e) {
+					throw new RuntimeException(e);
+				}
+			}, executorService);
+			futures.add(future);
+		}
+		CompletableFuture.allOf(futures.toArray(new CompletableFuture[0])).get();
+		executorService.shutdown();
+	}
 	/** @deprecated using deprecated code */
 	public void testClassInstanceCreation() {
 		ClassInstanceCreation x1 = this.ast.newClassInstanceCreation();
@@ -2034,18 +2053,15 @@ public void testStringLiteral() {
 		assertTrue(result.equals("[(eSLHHeSL)]")); //$NON-NLS-1$
 	}
 	public void testStringLiteralConcurrent() throws Exception {
-		ASTParser parser = ASTParser.newParser(AST.JLS21);
-		parser.setSource("\"hello\\nworld\"".toCharArray());
-		parser.setKind(ASTParser.K_EXPRESSION);
-		ASTNode a = parser.createAST(null);
-		StringLiteral literal = (StringLiteral) a;
+		StringLiteral x1 = this.ast.newStringLiteral();
+		x1.setEscapedValue("\"hello\\nworld\""); //$NON-NLS-1$
 
 		ExecutorService executorService = Executors.newFixedThreadPool(10);
 		List<CompletableFuture<Void>> futures = new ArrayList<>();
 		for (int i = 0; i < 100; i++) {
 			CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
 				try {
-					literal.getLiteralValue();
+					x1.getLiteralValue();
 				} catch (Exception e) {
 					throw new RuntimeException(e);
 				}

org.eclipse.jdt.core/dom/org/eclipse/jdt/core/dom/AST.java

@@ -4003,4 +4003,28 @@ public boolean isPreviewEnabled() {
 	public static int getJLSLatest() {
 		return JLS_INTERNAL_Latest;
 	}
+
+	/**
+	 * Returns a new instance of the AST scanner with the same configuration. Since the scanner is
+	 * stateful, using a cloned copy in read methods on AST nodes (e.g. StringLiteral.getLiteralValue)
+	 * allows those read methods to be used concurrently
+	 *
+	 * @return new Scanner instance with the same config as AST.scanner
+	 * @since 3.41
+	 */
+	Scanner clonedScanner() {
+		Scanner astScanner = this.scanner;
+
+		return new Scanner(
+				astScanner.tokenizeComments,
+				astScanner.tokenizeWhiteSpace,
+				astScanner.checkNonExternalizedStringLiterals,
+				astScanner.sourceLevel,
+				astScanner.complianceLevel,
+				astScanner.taskTags,
+				astScanner.taskPriorities,
+				astScanner.isTaskCaseSensitive,
+				astScanner.previewEnabled);
+	}
+
 }

org.eclipse.jdt.core/dom/org/eclipse/jdt/core/dom/CharacterLiteral.java

@@ -205,7 +205,7 @@ void internalSetEscapedValue(String value) {
 	 * @exception IllegalArgumentException if the literal value cannot be converted
 	 */
 	public char charValue() {
-		Scanner scanner = this.ast.scanner;
+		Scanner scanner = this.ast.clonedScanner();
 		char[] source = this.escapedValue.toCharArray();
 		scanner.setSource(source);
 		scanner.resetTo(0, source.length);

org.eclipse.jdt.core/dom/org/eclipse/jdt/core/dom/StringLiteral.java

@@ -216,7 +216,7 @@ public String getLiteralValue() {
 			throw new IllegalArgumentException();
 		}
 
-		Scanner scanner = this.ast.scanner;
+		Scanner scanner = this.ast.clonedScanner();
 		char[] source = s.toCharArray();
 		scanner.setSource(source);
 		scanner.resetTo(0, source.length);