Add integration test for '--release N' compiler option

Relates to #70

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

tests/features198/compiler_release/Buffers.java

@@ -0,0 +1,20 @@
+import java.nio.Buffer;
+import java.nio.ByteBuffer;
+
+public class Buffers {
+  /**
+   * Running this method will fail during runtime on JDK 8, if compiled on JDK 9+ with {@code -source 8 -target 8},
+   * because the API has changed: In JDK 8 there was only {@code Buffer.flip()}, but since JDK 9 it is overloaded by
+   * {@code ByteBuffer.flip()}.
+   * <p>
+   * Therefore, it is imperative to compile against the old API, using the correct boot classpath. On JDK 9+, the
+   * canonical way to do this is to use {@code --release 8}, because the JDK contains a compatibility layer exactly for
+   * this purpose.
+   * <p>
+   * If incorrectly compiled against JDK 9+ API, this will fail with:
+   * <pre>{@code java.lang.NoSuchMethodError: java.nio.ByteBuffer.flip()Ljava/nio/ByteBuffer; }</pre>
+   */
+  public static Buffer flip(ByteBuffer buffer) {
+    return buffer.flip();
+  }
+}

tests/src/test/java/org/aspectj/systemtest/ajc198/AllTestsAspectJ198.java

@@ -18,6 +18,9 @@ public class AllTestsAspectJ198 {
 
 	public static Test suite() {
 		TestSuite suite = new TestSuite("AspectJ 1.9.8 tests");
+		if (LangUtil.is9VMOrGreater()) {
+			suite.addTest(org.aspectj.systemtest.ajc198.CompileWithReleaseTests.suite());
+		}
 		if (LangUtil.is17VMOrGreater()) {
 			suite.addTest(SanityTestsJava17.suite());
 			suite.addTest(Ajc198TestsJava.suite());

tests/src/test/java/org/aspectj/systemtest/ajc198/CompileWithReleaseTests.java

@@ -0,0 +1,73 @@
+/*******************************************************************************
+ * 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.systemtest.ajc198;
+
+import junit.framework.Test;
+import org.aspectj.apache.bcel.Constants;
+import org.aspectj.apache.bcel.classfile.JavaClass;
+import org.aspectj.apache.bcel.classfile.Method;
+import org.aspectj.testing.XMLBasedAjcTestCase;
+import org.aspectj.testing.XMLBasedAjcTestCaseForJava9OrLater;
+
+import java.util.Objects;
+
+/**
+ * @author Alexander Kriegisch
+ */
+public class CompileWithReleaseTests extends XMLBasedAjcTestCaseForJava9OrLater {
+
+  /**
+   * In order to avoid a complicated test involving two different JDKs (9+ for compilation, 8 for runtime), we inspect
+   * the byte code of test class {@code Buffers} with BCEL, simply grepping on the disassembled byte code. If compiled
+   * correctly with {@code --release 8}, the byte code should contain the equivalent of a {@code Buffer.flip()} call,
+   * not a {@code ByteBuffer.flip()} one.
+   */
+  public void testCompileToOlderJDKRelease() {
+    runTest("compile to older JDK release");
+
+    // Check compiled byte code version
+    String className = "Buffers";
+    checkVersion(className, Constants.MAJOR_1_8, Constants.MINOR_1_8);
+
+    // Disassemble method and check if Java 8 API is used as expected
+    JavaClass javaClass;
+    try {
+      javaClass = getClassFrom(ajc.getSandboxDirectory(), className);
+    }
+    catch (ClassNotFoundException e) {
+      throw new IllegalStateException("Cannot find class " + className, e);
+    }
+    Method method = Objects.requireNonNull(getMethodFromClass(javaClass, "flip"));
+    String disassembledMethod = method.getCode().toString();
+
+    final String JAVA8_API_CALL = "invokevirtual\tjava.nio.ByteBuffer.flip ()Ljava/nio/Buffer;";
+    final String JAVA9_API_CALL = "invokevirtual\tjava.nio.ByteBuffer.flip ()Ljava/nio/ByteBuffer;";
+    if (disassembledMethod.contains(JAVA9_API_CALL))
+      fail(
+        "Class '" + className + "' was compiled against Java 9+ API. " +
+        "There seems to be a problem with the '--release' compiler option.\n" +
+        "Disassembled method:\n" + disassembledMethod
+      );
+    else if (!disassembledMethod.contains(JAVA8_API_CALL))
+      fail(
+        "Cannot determine if class '" + className + "' was compiled against Java 8 or 9+ API. " +
+        "This should never happen.\n" +
+        "Disassembled method:\n" + disassembledMethod
+      );
+  }
+
+  public static Test suite() {
+    return XMLBasedAjcTestCase.loadSuite(CompileWithReleaseTests.class);
+  }
+
+  @Override
+  protected java.net.URL getSpecFile() {
+    return getClassResource("ajc198.xml");
+  }
+
+}

tests/src/test/resources/org/aspectj/systemtest/ajc198/ajc198.xml

@@ -32,4 +32,9 @@
 	</ajc-test>
 -->
 
+	<!-- Javac/ECJ 9+ compiler option, but belated implementation in AJC 1.9.7 -->
+	<ajc-test dir="features198/compiler_release" vm="9" title="compile to older JDK release">
+		<compile files="Buffers.java" options="--release 8"/>
+	</ajc-test>
+
 </suite>