Enable preview features

.github/workflows/ci.yml

@@ -18,5 +18,7 @@ jobs:
       uses: actions/setup-java@v1
       with:
         java-version: 13
+    - name: Gradle version
+      run: ./gradlew -version
     - name: Build with Gradle
       run: ./gradlew build

example/build.gradle

@@ -19,6 +19,11 @@ compileTestJava {
 
 test {
     doFirst {
+        def javaVersion = System.getProperty("java.version").tokenize(".").get(0).toInteger()
+        if (javaVersion != 13) {
+            throw new IllegalStateException("Must run build on Java 13 (system reported: ${javaVersion})")
+        }
+
         def java8home = System.getenv("JAVA_HOME_8")
         if (!java8home) {
             throw new IllegalStateException("JAVA_HOME_8 must be set")

example/src/main/java/com/example/JabelExample.java

@@ -63,4 +63,20 @@ public String innerPublic() {
             return outerPrivate();
         }
     }
+
+
+//    public void whenSwitchingOnOperationSquareMe_thenWillReturnSquare() {
+//        var me = 4;
+//        var operation = "squareMe";
+//        var result = switch (operation) {
+//            case "doubleMe" -> {
+//                yield me * 2;
+//            }
+//            case "squareMe" -> {
+//                yield me * me;
+//            }
+//            default -> me;
+//        };
+//
+//    }
 }

example/src/test/java/com/example/JabelExampleTest.java

@@ -7,17 +7,61 @@
 public class JabelExampleTest {
 
     @Test(expected = ClassNotFoundException.class)
-    public void isJava8() throws Exception {
+    public void isProbablyJava8() throws Exception {
         Class.forName("java.lang.StackWalker");
     }
 
     @Test
-    public void shouldWork() {
+    public void testRuntimeIsJava8() {
+        String jver = System.getProperty("java.version");
+        String needle = "1.8";
+        assertTrue("Java version expected: " + needle + " actual: " + jver, jver.startsWith(needle));
+    }
+
+    @Test
+    public void testPostJava8Features() {
         JabelExample jabelExample = new JabelExample();
 
         String result = jabelExample.run(new String[0]);
 
         assertTrue("'" + result + "' should start with 'idk '", result.startsWith("idk "));
+    }
+
+    @Test
+    public void testJava13PreviewFeatureTextBlocksJep355(){
+        String TEXT_BLOCK_JSON = """
+{
+    "name" : "Baeldung",
+    "website" : "https://www.%s.com/"
+}
+""";
+    }
 
+    /**
+     * JEP 354: Switch Expressions (Second Preview)
+     * https://openjdk.java.net/jeps/354
+     */
+    @Test
+    public void testJava13PreviewJep354() {
+        var me = 4;
+        var operation = "squareMe";
+        var result = switch (operation) {
+            case "doubleMe" -> {
+                yield me * 2;
+            }
+            case "squareMe" -> {
+                yield me * me;
+            }
+            default -> me;
+        };
+
+        assertEquals(16, result);
     }
+//
+//    @Test
+//    public void tgesd(){
+//        JabelExampleTest jabelExampleTest = new JabelExampleTest();
+//        jabelExampleTest.whenSwitchingOnOperationSquareMe_thenWillReturnSquare();
+//    }
+
 }

jabel-javac-plugin/src/main/java/com/github/bsideup/jabel/CheckSourceLevelAdvice.java

@@ -6,6 +6,12 @@
 
 public class CheckSourceLevelAdvice {
 
+    /**
+     * If the {@link com.sun.tools.javac.code.Source.Feature} is allowed in JDK8, make javac think it has the same
+     * characteristics as {@link Source.Feature.LAMBDA}
+     *
+     * @param feature
+     */
     @Advice.OnMethodEnter
     public static void checkSourceLevel(
             @Advice.Argument(value = 1, readOnly = false) Feature feature

jabel-javac-plugin/src/main/java/com/github/bsideup/jabel/IsPreviewAdvice.java

@@ -0,0 +1,25 @@
+package com.github.bsideup.jabel;
+
+import com.sun.tools.javac.code.Preview;
+import com.sun.tools.javac.code.Source;
+import net.bytebuddy.asm.Advice;
+
+public class IsPreviewAdvice {
+
+    static final boolean debug = false;
+
+    /**
+     * Force javac to think that no features are preview features - on {@link Preview#isPreview} exit, override the
+     * return value to always be false.
+     */
+    @Advice.OnMethodExit
+    static public boolean isPreview(Source.Feature feature) {
+        if (debug) {
+            /**
+             * Can't use {@link org.apache.maven.plugin.logging.Log} from instrumented javac classes.
+             */
+            System.out.println("Feature being set to NOT preview: " + feature);
+        }
+        return false;
+    }
+}

jabel-javac-plugin/src/main/java/com/github/bsideup/jabel/JabelJavacProcessor.java

@@ -1,11 +1,13 @@
 package com.github.bsideup.jabel;
 
+import com.sun.tools.javac.code.Preview;
 import com.sun.tools.javac.code.Source;
 import com.sun.tools.javac.parser.JavaTokenizer;
 import com.sun.tools.javac.parser.JavacParser;
 import net.bytebuddy.ByteBuddy;
 import net.bytebuddy.agent.ByteBuddyAgent;
 import net.bytebuddy.asm.Advice;
+import net.bytebuddy.asm.AsmVisitorWrapper.ForDeclaredMethods;
 import net.bytebuddy.dynamic.loading.ClassReloadingStrategy;
 
 import javax.annotation.processing.Completion;
@@ -61,21 +63,29 @@ public class JabelJavacProcessor implements Processor {
             .collect(Collectors.toSet());
 
     static {
-        ByteBuddyAgent.install();
+        // log that we've started, otherwise if there's certain types of errors, no output is seen at all from Jabel (e.g. errors compiling our code)
+        // helps for verifying Jabel is being picked up correctly from project settings
+        logInfo("Jabel static initialising ByteBuddy");
 
+        ByteBuddyAgent.install();
         ByteBuddy byteBuddy = new ByteBuddy();
 
-        for (Class<?> clazz : Arrays.asList(JavacParser.class, JavaTokenizer.class)) {
-            byteBuddy
-                    .redefine(clazz)
-                    .visit(
-                            Advice.to(CheckSourceLevelAdvice.class)
-                                    .on(named("checkSourceLevel").and(takesArguments(2)))
-                    )
-                    .make()
-                    .load(clazz.getClassLoader(), ClassReloadingStrategy.fromInstalledAgent());
-        }
+        sourceLevelCheck(byteBuddy);
+
+//        previewFeatureChecks(byteBuddy);
+
+        featureMinLevelChecks();
+
+        logInfo("Jabel ByteBuddy initialisation complete");
+    }
 
+    /**
+     * For all the features in {@link #ENABLED_FEATURES}, override the min JDK level, reducing it to 8
+     *
+     * @see #ENABLED_FEATURES
+     */
+    private static void featureMinLevelChecks() {
+        logInfo("Disabling feature min level checks");
         try {
             Field field = Source.Feature.class.getDeclaredField("minLevel");
             field.setAccessible(true);
@@ -91,14 +101,54 @@ public class JabelJavacProcessor implements Processor {
         }
     }
 
+    /**
+     * Intercept calls to {@link JavacParser#checkSourceLevel}
+     *
+     * @see JavacParser#checkSourceLevel
+     * @see JavaTokenizer#checkSourceLevel
+     * @see CheckSourceLevelAdvice
+     */
+    private static void sourceLevelCheck(ByteBuddy byteBuddy) {
+        logInfo("Disabling source level check");
+        for (Class<?> clazz : Arrays.asList(JavacParser.class, JavaTokenizer.class)) {
+            ForDeclaredMethods checkSourceLevelMethod = Advice.to(CheckSourceLevelAdvice.class)
+                    .on(named("checkSourceLevel").and(takesArguments(2)));
+            byteBuddy
+                    .redefine(clazz)
+                    .visit(checkSourceLevelMethod)
+                    .make()
+                    .load(clazz.getClassLoader(), ClassReloadingStrategy.fromInstalledAgent());
+        }
+    }
+
+    /**
+     * Intercept call return from {@link Preview#isPreview}
+     * 
+     * @see Preview#isPreview
+     * @see IsPreviewAdvice
+     */
+    private static void previewFeatureChecks(ByteBuddy byteBuddy) {
+        logInfo("Disabling preview feature flag checks");
+        Class<Preview> previewClass = Preview.class;
+        ForDeclaredMethods isPreviewMethod = Advice.to(IsPreviewAdvice.class).on(named("isPreview"));
+        byteBuddy.redefine(previewClass)
+                .visit(isPreviewMethod)
+                .make()
+                .load(previewClass.getClassLoader(), ClassReloadingStrategy.fromInstalledAgent());
+    }
+
+    static private void logInfo(String msg) {
+        System.out.println(msg);
+    }
+
     @Override
     public SourceVersion getSupportedSourceVersion() {
         return SourceVersion.RELEASE_8;
     }
 
     @Override
     public void init(ProcessingEnvironment processingEnv) {
-        System.out.println(
+        logInfo(
                 ENABLED_FEATURES.stream()
                         .map(Enum::name)
                         .collect(Collectors.joining(