fix: Print unqualified enum constants in switches pre Java 21 (#5636)

src/main/java/spoon/reflect/visitor/DefaultJavaPrettyPrinter.java

@@ -629,7 +629,7 @@ public <E> void visitCtCase(CtCase<E> caseStatement) {
 				if (caseExpression instanceof CtFieldAccess<E> fieldAccess) {
 					final CtFieldReference variable = ((CtFieldAccess) caseExpression).getVariable();
 					// In noclasspath mode, we don't have always the type of the declaring type.
-					if (fieldAccess.getTarget().isImplicit()
+					if ((fieldAccess.getTarget().isImplicit() || env.getComplianceLevel() < 21)
 							&& variable.getType() != null
 							&& variable.getDeclaringType() != null
 							&& variable.getType().getQualifiedName().equals(variable.getDeclaringType().getQualifiedName())) {

src/test/java/spoon/test/model/SwitchCaseTest.java

@@ -20,12 +20,14 @@
 import static spoon.testing.utils.ModelUtils.build;
 import static spoon.testing.utils.ModelUtils.createFactory;
 
+import java.nio.file.StandardCopyOption;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.stream.Collectors;
 
+import org.assertj.core.api.Assertions;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
@@ -60,8 +62,11 @@ private static String toSingleLineString(CtElement e) {
 		return e.toString().replace("\n", "").replace("\r", "");
 	}
 	private static CtModel createModelFromString(String code) {
+		return createModelFromString(code, 21);
+	}
+	private static CtModel createModelFromString(String code, int complianceLevel) {
 		Launcher launcher = new Launcher();
-		launcher.getEnvironment().setComplianceLevel(14);
+		launcher.getEnvironment().setComplianceLevel(complianceLevel);
 		launcher.getEnvironment().setNoClasspath(true);
 		launcher.addInputResource(new VirtualFile(code));
 		return launcher.buildModel();
@@ -121,6 +126,78 @@ public void testSwitchStatementOnAString() throws Exception {
 				assertEquals(String.class.getName(), aCase.getCaseExpression().getType().getTypeDeclaration().getQualifiedName());
 			}
 		}
+
+		@DisplayName("Switch over Enum with qualified names since Java 21")
+		@Test
+		public void testSwitchStatementOnAnEnum() {
+			CtModel model = createModelFromString(
+				"""
+					import java.nio.file.StandardCopyOption;
+					class C {
+						int m(StandardCopyOption option) {
+							return switch (option) {
+								case ATOMIC_MOVE -> 1;
+								case StandardCopyOption.COPY_ATTRIBUTES -> 2;
+								case java.nio.file.StandardCopyOption.REPLACE_EXISTING -> 3;
+							};
+						}
+					}
+					"""
+			);
+
+			CtSwitchExpression<?, ?> ctSwitch = model.getElements(new TypeFilter<CtSwitchExpression<?, ?>>(CtSwitchExpression.class)).get(0);
+
+			// Checks the selector is the enum.
+			assertEquals(StandardCopyOption.class.getName(), ctSwitch.getSelector().getType().getTypeDeclaration().getQualifiedName());
+
+			// Checks all cases are the matching enum constants.
+			var cases = ctSwitch.getCases();
+			List<String> expectedPrinterOutputForceFQP = List.of(
+				"case java.nio.file.StandardCopyOption.ATOMIC_MOVE ->",
+				"case java.nio.file.StandardCopyOption.COPY_ATTRIBUTES ->",
+				"case java.nio.file.StandardCopyOption.REPLACE_EXISTING ->"
+			);
+			List<String> expectedPrinterOutputForcePretty = List.of(
+				"case ATOMIC_MOVE ->",
+				"case StandardCopyOption.COPY_ATTRIBUTES ->",
+				"case StandardCopyOption.REPLACE_EXISTING ->"
+			);
+			for (int i = 0; i < cases.size(); i++) {
+				CtCase<?> aCase = cases.get(i);
+				// make sure all are qualified when using toString (printer with ForceFullyQualifiedProcessor)
+				Assertions.assertThat(aCase.toString()).contains(expectedPrinterOutputForceFQP.get(i));
+				// make sure the auto-import strips the package name but not the class name if not implicit
+				Assertions.assertThat(aCase.prettyprint()).contains(expectedPrinterOutputForcePretty.get(i));
+				assertEquals(StandardCopyOption.class.getName(), aCase.getCaseExpression().getType().getTypeDeclaration().getQualifiedName());
+			}
+		}
+
+		@DisplayName("Print switch on enum pre Java 21")
+		@Test
+		public void testSwitchStatementOnAnEnumPrintPre21() {
+			CtModel model = createModelFromString(
+				"""
+					import java.nio.file.StandardCopyOption;
+					class C {
+						int m(StandardCopyOption option) {
+							return switch (option) {
+								case ATOMIC_MOVE -> 1;
+								case COPY_ATTRIBUTES -> 2;
+								case REPLACE_EXISTING -> 3;
+							};
+						}
+					}
+					""",
+				20
+			);
+			CtSwitchExpression<?, ?> ctSwitch = model.getElements(new TypeFilter<CtSwitchExpression<?, ?>>(CtSwitchExpression.class)).get(0);
+			Assertions.assertThat(ctSwitch.toString()).contains(
+				"case ATOMIC_MOVE ->",
+				"case COPY_ATTRIBUTES ->",
+				"case REPLACE_EXISTING ->"
+			);
+		}
+
 		@DisplayName("Parent is set")
 		@Test
 		public void testParentInCaseExpressions() {