Prepare code, tests and docs for Java 18

- JDT Core dependency in pom.xml
- Constants.java
- LangUtil.java
- AjcTask.java
- messages_aspectj.properties

- XMLBasedAjcTestCaseForJava17Only.java
- XMLBasedAjcTestCaseForJava18*.java
- tests/bugs199
- tests/features199

- JavaVersionCompatibility.md
- README-199.html

- GitHub CI build

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

3 files changed, 70 insertions, 3 deletions

diff --git a/testing/src/test/java/org/aspectj/testing/XMLBasedAjcTestCaseForJava17Only.java b/testing/src/test/java/org/aspectj/testing/XMLBasedAjcTestCaseForJava17Only.java
index 0c351c69a..78941fcab 100644
--- a/testing/src/test/java/org/aspectj/testing/XMLBasedAjcTestCaseForJava17Only.java
+++ b/testing/src/test/java/org/aspectj/testing/XMLBasedAjcTestCaseForJava17Only.java
@@ -20,21 +20,21 @@ public abstract class XMLBasedAjcTestCaseForJava17Only extends XMLBasedAjcTestCa
 	@Override
 	public void setUp() throws Exception {
 		// Activate this block after upgrading to JDT Core Java 18
-		/*
 		throw new IllegalStateException(
 			"These tests need a Java 17 level AspectJ compiler " +
 				"(e.g. because they use version-specific preview features). " +
 				"This compiler does not support preview features of a previous version anymore."
 		);
-		*/
 		// Activate this block before upgrading to JDT Core Java 18
+		/*
 		if (!LangUtil.is17VMOrGreater() || LangUtil.is18VMOrGreater()) {
 			throw new IllegalStateException(
 				"These tests should be run on Java 17 only " +
 				"(e.g. because they use version-specific preview features)"
 			);
-		}
 		super.setUp();
+		}
+		*/
 	}
 
 }
diff --git a/testing/src/test/java/org/aspectj/testing/XMLBasedAjcTestCaseForJava18Only.java b/testing/src/test/java/org/aspectj/testing/XMLBasedAjcTestCaseForJava18Only.java
new file mode 100644
index 000000000..ba4d00605
--- /dev/null
+++ b/testing/src/test/java/org/aspectj/testing/XMLBasedAjcTestCaseForJava18Only.java
@@ -0,0 +1,40 @@
+/* *******************************************************************
+ * Copyright (c) 2021 Contributors
+ * All rights reserved.
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Public License v 2.0
+ * which accompanies this distribution and is available at
+ * https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.txt
+ * ******************************************************************/
+package org.aspectj.testing;
+
+import org.aspectj.util.LangUtil;
+
+/**
+ * Makes sure tests are running on the right level of JDK.
+ *
+ * @author Alexander Kriegisch
+ */
+public abstract class XMLBasedAjcTestCaseForJava18Only extends XMLBasedAjcTestCase {
+
+	@Override
+	public void setUp() throws Exception {
+		// Activate this block after upgrading to JDT Core Java 19
+		/*
+		throw new IllegalStateException(
+			"These tests need a Java 18 level AspectJ compiler " +
+				"(e.g. because they use version-specific preview features). " +
+				"This compiler does not support preview features of a previous version anymore."
+		);
+		*/
+		// Activate this block before upgrading to JDT Core Java 19
+		if (!LangUtil.is18VMOrGreater() || LangUtil.is19VMOrGreater()) {
+			throw new IllegalStateException(
+				"These tests should be run on Java 18 only " +
+				"(e.g. because they use version-specific preview features)"
+			);
+		}
+		super.setUp();
+	}
+
+}
diff --git a/testing/src/test/java/org/aspectj/testing/XMLBasedAjcTestCaseForJava18OrLater.java b/testing/src/test/java/org/aspectj/testing/XMLBasedAjcTestCaseForJava18OrLater.java
new file mode 100644
index 000000000..9b9efdd34
--- /dev/null
+++ b/testing/src/test/java/org/aspectj/testing/XMLBasedAjcTestCaseForJava18OrLater.java
@@ -0,0 +1,27 @@
+/* *******************************************************************
+ * Copyright (c) 2021 Contributors
+ * All rights reserved.
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Public License v 2.0
+ * which accompanies this distribution and is available at
+ * https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.txt
+ * ******************************************************************/
+package org.aspectj.testing;
+
+import org.aspectj.util.LangUtil;
+
+/**
+ * Makes sure tests are running on the right level of JDK.
+ *
+ * @author Alexander Kriegisch
+ */
+public abstract class XMLBasedAjcTestCaseForJava18OrLater extends XMLBasedAjcTestCase {
+
+	@Override
+	public void setUp() throws Exception {
+		if (!LangUtil.is18VMOrGreater())
+			throw new IllegalStateException("These tests should be run on Java 18 or later");
+		super.setUp();
+	}
+
+}