review: feat: CloneMaker can be used to listen on cloning process

src/main/java/spoon/generating/CloneVisitorGenerator.java

@@ -77,6 +77,7 @@ public void process() {
 		final CtTypeReference<Object> cloneBuilder = factory.Type().createReference("spoon.support.visitor.clone.CloneBuilder");
 		final CtTypeAccess<Object> cloneBuilderType = factory.Code().createTypeAccess(cloneBuilder);
 		final CtVariableAccess<Object> builderFieldAccess = factory.Code().createVariableRead(factory.Field().createReference(target.getReference(), cloneBuilder, "builder"), false);
+		final CtVariableAccess<Object> cloneHelperFieldAccess = factory.Code().createVariableRead(factory.Field().createReference(target.getReference(), cloneBuilder, "cloneHelper"), false);
 		final CtFieldReference<Object> other = factory.Field().createReference((CtField) target.getField("other"));
 		final CtVariableAccess<Object> otherRead = factory.Code().createVariableRead(other, true);
 
@@ -138,7 +139,7 @@ private CtInvocation<?> createSetter(CtInvocation scanInvocation, CtVariableAcce
 				final CtExecutableReference<Object> setterRef = factory.Executable().createReference("void CtElement#set" + getterName.substring(3, getterName.length()) + "()");
 				final CtExecutableReference<Object> cloneRef = factory.Executable().createReference("CtElement spoon.support.visitor.equals.CloneHelper#clone()");
 				final CtInvocation<Object> cloneInv = factory.Code().createInvocation(null, cloneRef, getter);
-				cloneInv.setTarget(factory.Code().createTypeAccess(factory.Type().createReference("spoon.support.visitor.equals.CloneHelper")));
+				cloneInv.setTarget(cloneHelperFieldAccess);
 				return factory.Code().createInvocation(elementVarRead, setterRef, cloneInv);
 			}
 
@@ -515,6 +516,7 @@ public boolean matches(CtTypeReference reference) {
 			reference.setSimpleName(TARGET_CLONE_TYPE);
 			reference.setPackage(aPackage.getReference());
 		}
+		target.getConstructors().forEach(c -> c.addModifier(ModifierKind.PUBLIC));
 		return target;
 	}
 

src/main/java/spoon/generating/clone/CloneVisitorTemplate.java

@@ -19,16 +19,22 @@
 import spoon.reflect.declaration.CtElement;
 import spoon.reflect.visitor.CtScanner;
 import spoon.support.visitor.clone.CloneBuilder;
+import spoon.support.visitor.equals.CloneHelper;
 
 /**
  * Used to clone a given element.
  *
  * This class is generated automatically by the processor {@link spoon.generating.CloneVisitorGenerator}.
  */
 class CloneVisitorTemplate extends CtScanner {
+	private final CloneHelper cloneHelper;
 	private final CloneBuilder builder = new CloneBuilder();
 	private CtElement other;
 
+	CloneVisitorTemplate(CloneHelper cloneHelper) {
+		this.cloneHelper = cloneHelper;
+	}
+
 	public <T extends CtElement> T getClone() {
 		return (T) other;
 	}

src/main/java/spoon/support/DefaultCoreFactory.java

@@ -196,7 +196,7 @@ public DefaultCoreFactory() {
 	}
 
 	public <T extends CtElement> T clone(T object) {
-		return CloneHelper.clone(object);
+		return CloneHelper.INSTANCE.clone(object);
 	}
 
 	public <A extends Annotation> CtAnnotation<A> createAnnotation() {

src/main/java/spoon/support/compiler/jdt/JDTTreeBuilder.java

@@ -1026,7 +1026,6 @@ public boolean visit(ExplicitConstructorCall explicitConstructor, BlockScope sco
 		inv.setExecutable(references.getExecutableReference(explicitConstructor.binding));
 		CtTypeReference<?> declaringType = inv.getExecutable().getDeclaringType();
 		inv.getExecutable().setType(declaringType == null ? null : (CtTypeReference<Object>) declaringType.clone());
-
 		context.enter(inv, explicitConstructor);
 		return true;
 	}

src/main/java/spoon/support/reflect/declaration/CtElementImpl.java

@@ -476,6 +476,6 @@ public <E extends CtElement> E setComments(List<CtComment> comments) {
 
 	@Override
 	public CtElement clone() {
-		return CloneHelper.clone(this);
+		return CloneHelper.INSTANCE.clone(this);
 	}
 }

src/main/java/spoon/support/visitor/equals/CloneHelper.java

@@ -30,25 +30,37 @@
 import spoon.support.util.EmptyClearableSet;
 import spoon.support.visitor.clone.CloneVisitor;
 
-public final class CloneHelper {
-	public static <T extends CtElement> T clone(T element) {
-		final CloneVisitor cloneVisitor = new CloneVisitor();
+/**
+ * {@link CloneHelper} is responsible for creating clones of {@link CtElement} AST nodes including the whole subtree.
+ *
+ * By default, the same instance of {@link CloneHelper} is used for whole clonning process.
+ *
+ * However, by subclassing this class and overriding method {@link #clone(CtElement)},
+ * one can extend and/or modify the cloning behavior.
+ *
+ * For instance, one can listen to each call to clone and get each pair of `clone source` and `clone target`.
+ */
+public class CloneHelper {
+	public static final CloneHelper INSTANCE = new CloneHelper();
+
+	public <T extends CtElement> T clone(T element) {
+		final CloneVisitor cloneVisitor = new CloneVisitor(this);
 		cloneVisitor.scan(element);
 		return cloneVisitor.getClone();
 	}
 
-	public static <T extends CtElement> Collection<T> clone(Collection<T> elements) {
+	public <T extends CtElement> Collection<T> clone(Collection<T> elements) {
 		if (elements == null || elements.isEmpty()) {
 			return new ArrayList<>();
 		}
 		Collection<T> others = new ArrayList<>();
 		for (T element : elements) {
-			others.add(CloneHelper.clone(element));
+			others.add(clone(element));
 		}
 		return others;
 	}
 
-	public static <T extends CtElement> List<T> clone(List<T> elements) {
+	public <T extends CtElement> List<T> clone(List<T> elements) {
 		if (elements instanceof EmptyClearableList) {
 			return elements;
 		}
@@ -57,12 +69,12 @@ public static <T extends CtElement> List<T> clone(List<T> elements) {
 		}
 		List<T> others = new ArrayList<>();
 		for (T element : elements) {
-			others.add(CloneHelper.clone(element));
+			others.add(clone(element));
 		}
 		return others;
 	}
 
-	private static <T extends CtElement> Set<T> createRightSet(Set<T> elements) {
+	private <T extends CtElement> Set<T> createRightSet(Set<T> elements) {
 		try {
 			if (elements instanceof TreeSet) {
 				// we copy the set, incl its comparator
@@ -78,7 +90,7 @@ private static <T extends CtElement> Set<T> createRightSet(Set<T> elements) {
 		}
 	}
 
-	public static <T extends CtElement> Set<T> clone(Set<T> elements) {
+	public <T extends CtElement> Set<T> clone(Set<T> elements) {
 		if (elements instanceof EmptyClearableSet) {
 			return elements;
 		}
@@ -88,23 +100,19 @@ public static <T extends CtElement> Set<T> clone(Set<T> elements) {
 
 		Set<T> others = createRightSet(elements);
 		for (T element : elements) {
-			others.add(CloneHelper.clone(element));
+			others.add(clone(element));
 		}
 		return others;
 	}
 
-	public static <T extends CtElement> Map<String, T> clone(Map<String, T> elements) {
+	public <T extends CtElement> Map<String, T> clone(Map<String, T> elements) {
 		if (elements == null || elements.isEmpty()) {
 			return new HashMap<>();
 		}
 		Map<String, T> others = new HashMap<>();
 		for (Map.Entry<String, T> tEntry : elements.entrySet()) {
-			others.put(tEntry.getKey(), CloneHelper.clone(tEntry.getValue()));
+			others.put(tEntry.getKey(), clone(tEntry.getValue()));
 		}
 		return others;
 	}
-
-	private CloneHelper() {
-		throw new AssertionError("No instance.");
-	}
 }

src/test/java/spoon/reflect/ast/CloneTest.java

@@ -6,16 +6,27 @@
 import spoon.processing.AbstractProcessor;
 import spoon.reflect.code.CtConditional;
 import spoon.reflect.declaration.CtClass;
+import spoon.reflect.declaration.CtElement;
 import spoon.reflect.declaration.CtInterface;
 import spoon.reflect.declaration.CtMethod;
+import spoon.reflect.declaration.CtType;
+import spoon.reflect.factory.Factory;
 import spoon.reflect.visitor.CtScanner;
+import spoon.reflect.visitor.DefaultJavaPrettyPrinter;
+import spoon.reflect.visitor.PrinterHelper;
 import spoon.reflect.visitor.Query;
 import spoon.reflect.visitor.filter.TypeFilter;
+import spoon.support.visitor.equals.CloneHelper;
+import spoon.testing.utils.ModelUtils;
 
+import java.io.File;
+import java.io.PrintWriter;
+import java.io.StringWriter;
+import java.util.IdentityHashMap;
+import java.util.Map;
 import java.util.stream.Collectors;
 
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.*;
 
 public class CloneTest {
 	@Test
@@ -99,4 +110,42 @@ public void process(CtConditional<?> conditional) {
 		});
 		launcher.run();
 	}
+
+	@Test
+	public void testCloneListener() throws Exception {
+		// contract: it is possible to extend the cloning behavior
+
+		// in this example extension, a listener of cloning process gets access to origin node and cloned node
+		// we check the contract with some complicated class as target of cloning
+		Factory factory = ModelUtils.build(new File("./src/main/java/spoon/reflect/visitor/DefaultJavaPrettyPrinter.java"));
+		CtType<?> cloneSource = factory.Type().get(DefaultJavaPrettyPrinter.class);
+		class CloneListener extends CloneHelper {
+			Map<CtElement, CtElement> sourceToTarget = new IdentityHashMap<>();
+			@Override
+			public <T extends CtElement> T clone(T source) {
+				if (source == null) {
+					return null;
+				}
+				T target = super.clone(source);
+				onCloned(source, target);
+				return target;
+			}
+			private void onCloned(CtElement source, CtElement target) {
+				CtElement previousTarget = sourceToTarget.put(source, target);
+				assertNull(previousTarget);
+			}
+		}
+
+		CloneListener cl = new CloneListener();
+		CtType<?> cloneTarget = cl.clone(cloneSource);
+
+		cloneSource.filterChildren(null).forEach(sourceElement -> {
+			//contract: there exists cloned target for each visitable element
+			CtElement targetElement = cl.sourceToTarget.remove(sourceElement);
+			assertNotNull("Missing target for sourceElement\n" + sourceElement, targetElement);
+			assertEquals("Source and Target are not equal", sourceElement, targetElement);
+		});
+		//contract: each visitable elements was cloned exactly once.  No more no less.
+		assertTrue(cl.sourceToTarget.isEmpty());
+	}
 }