fix: Remove super calls from implicit enum constructors

Author: I-Al-Istannen

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

@@ -520,14 +520,41 @@ public <T> void visitCtCatchVariable(CtCatchVariable<T> e) {
 	@Override
 	public <T> void visitCtClass(CtClass<T> ctClass) {
 		if (child instanceof CtConstructor) {
-			ctClass.addConstructor((CtConstructor<T>) child);
+			CtConstructor<T> constructor = (CtConstructor<T>) child;
+			ctClass.addConstructor(constructor);
+			fixJdtEnumConstructorSuperCall(ctClass, constructor);
 		}
 		if (child instanceof CtAnonymousExecutable) {
 			ctClass.addAnonymousExecutable((CtAnonymousExecutable) child);
 		}
 		super.visitCtClass(ctClass);
 	}
 
+	private <T> void fixJdtEnumConstructorSuperCall(CtClass<T> ctClass, CtConstructor<T> constructor) {
+		// For some reason JDT inserts a `super()` call in implicit enum constructors.
+		// Explicit super calls are forbidden as java.lang.Enum subclasses are permitted by the JLS to delegate
+		// to the Enum constructor in whatever way they like.
+		// The constructor is implicit so this isn't *technically* illegal, but it doesn't really make much sense
+		// as explicit constructors can never contain such a call. Additionally, the Enum class from the standard
+		// library has a "String, int" constructor, rendering the parameterless supercall semantically invalid.
+		// We just remove the call to make it a bit more consistent.
+		// See https://github.com/INRIA/spoon/issues/4758 for more details.
+		if (!child.isImplicit() || !ctClass.isEnum() || !constructor.getParameters().isEmpty()) {
+			return;
+		}
+		if (constructor.getBody().getStatements().isEmpty()) {
+			return;
+		}
+		if (!(constructor.getBody().getStatement(0) instanceof CtInvocation)) {
+			return;
+		}
+
+		CtInvocation<?> superCall = constructor.getBody().getStatement(0);
+		if (superCall.getExecutable().getSimpleName().equals("<init>")) {
+			constructor.getBody().getStatements().remove(0);
+		}
+	}
+
 	@Override
 	public void visitCtTypeParameter(CtTypeParameter typeParameter) {
 		if (childJDT instanceof TypeReference && child instanceof CtTypeAccess) {

src/test/java/spoon/test/enums/EnumsTest.java

@@ -18,6 +18,7 @@
 
 import org.apache.commons.lang3.StringUtils;
 import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -28,17 +29,21 @@
 import spoon.reflect.CtModel;
 import spoon.reflect.code.CtBlock;
 import spoon.reflect.code.CtExpression;
+import spoon.reflect.code.CtInvocation;
 import spoon.reflect.code.CtNewClass;
 import spoon.reflect.code.CtStatement;
+import spoon.reflect.declaration.CtConstructor;
 import spoon.reflect.declaration.CtEnum;
 import spoon.reflect.declaration.CtEnumValue;
 import spoon.reflect.declaration.CtField;
 import spoon.reflect.declaration.CtMethod;
 import spoon.reflect.declaration.CtType;
 import spoon.reflect.declaration.ModifierKind;
 import spoon.reflect.factory.Factory;
+import spoon.reflect.reference.CtExecutableReference;
 import spoon.reflect.visitor.filter.TypeFilter;
 import spoon.support.reflect.CtExtendedModifier;
+import spoon.test.GitHubIssue;
 import spoon.test.SpoonTestHelpers;
 import spoon.test.annotation.AnnotationTest;
 import spoon.test.enums.testclasses.Burritos;
@@ -58,6 +63,7 @@
 
 import static org.hamcrest.CoreMatchers.hasItem;
 import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.CoreMatchers.not;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertSame;
@@ -264,6 +270,25 @@ void testLocalEnumExists() {
 		));
 	}
 
+	@GitHubIssue(issueNumber = 4758, fixed = true)
+	@DisplayName("Implicit enum constructors do not contain a super call")
+	void testImplicitEnumConstructorSuperCall() {
+		CtEnum<?> myEnum = (CtEnum<?>) Launcher.parseClass("enum Foo { CONSTANT; }");
+		CtConstructor<?> constructor = myEnum.getConstructors().iterator().next();
+
+		assertThat(constructor.isImplicit(), is(true));
+		
+		for (CtStatement statement : constructor.getBody().getStatements()) {
+			if (!(statement instanceof CtInvocation)) {
+				continue;
+			}
+			CtExecutableReference<?> executable = ((CtInvocation<?>) statement).getExecutable();
+			if (!executable.getDeclaringType().getQualifiedName().equals("java.lang.Enum")) {
+				continue;
+			}
+			assertThat(executable.getSimpleName(), not(is("<init>")));
+		}
+	}
 
 	static class NestedEnumTypeProvider implements ArgumentsProvider {
 		private final CtType<?> ctClass;