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Convert switch cases with returns to returned switch expression (#802)
* Convert switch cases with returns to returned switch expression * Early bit of polish * Convert switch if it's the last statement, not only statement * Use a more concise `visitBlock` * Update src/main/java/org/openrewrite/java/migrate/lang/SwitchCaseReturnsToSwitchExpression.java Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> * Some simplifications * Condense further * Further condense and reuse --------- Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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‎src/main/java/org/openrewrite/java/migrate/lang/SwitchCaseReturnsToSwitchExpression.java‎

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/*
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* Copyright 2025 the original author or authors.
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* <p>
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* Licensed under the Moderne Source Available License (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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* <p>
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* https://docs.moderne.io/licensing/moderne-source-available-license
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* <p>
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.openrewrite.java.migrate.lang;
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import lombok.EqualsAndHashCode;
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import lombok.Value;
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import org.jspecify.annotations.Nullable;
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import org.openrewrite.ExecutionContext;
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import org.openrewrite.Preconditions;
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import org.openrewrite.Recipe;
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import org.openrewrite.TreeVisitor;
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import org.openrewrite.internal.ListUtils;
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import org.openrewrite.java.JavaIsoVisitor;
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import org.openrewrite.java.search.UsesJavaVersion;
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import org.openrewrite.java.tree.*;
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import org.openrewrite.marker.Markers;
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import org.openrewrite.staticanalysis.groovy.GroovyFileChecker;
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import org.openrewrite.staticanalysis.kotlin.KotlinFileChecker;
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import java.util.List;
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import static org.openrewrite.Tree.randomId;
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@Value
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@EqualsAndHashCode(callSuper = false)
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public class SwitchCaseReturnsToSwitchExpression extends Recipe {
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@Override
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public String getDisplayName() {
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return "Convert switch cases where every case returns into a returned switch expression";
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}
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@Override
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public String getDescription() {
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return "Switch statements where each case returns a value can be converted to a switch expression that returns the value directly.";
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}
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@Override
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public TreeVisitor<?, ExecutionContext> getVisitor() {
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TreeVisitor<?, ExecutionContext> preconditions = Preconditions.and(
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new UsesJavaVersion<>(14),
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Preconditions.not(new KotlinFileChecker<>()),
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Preconditions.not(new GroovyFileChecker<>())
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);
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return Preconditions.check(preconditions, new JavaIsoVisitor<ExecutionContext>() {
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@Override
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public J.Block visitBlock(J.Block block, ExecutionContext ctx) {
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J.Block b = super.visitBlock(block, ctx);
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return b.withStatements(ListUtils.map(b.getStatements(), statement -> {
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if (statement instanceof J.Switch) {
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J.Switch sw = (J.Switch) statement;
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if (canConvertToSwitchExpression(sw)) {
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J.SwitchExpression switchExpression = convertToSwitchExpression(sw);
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return new J.Return(
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randomId(),
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sw.getPrefix(),
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Markers.EMPTY,
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switchExpression
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);
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}
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}
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return statement;
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}));
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}
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private boolean canConvertToSwitchExpression(J.Switch switchStatement) {
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for (Statement statement : switchStatement.getCases().getStatements()) {
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if (!(statement instanceof J.Case)) {
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return false;
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}
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J.Case caseStatement = (J.Case) statement;
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if (caseStatement.getBody() != null) {
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// Arrow case
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J body = caseStatement.getBody();
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if (body instanceof J.Block) {
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if (!isReturnCase(((J.Block) body).getStatements())) {
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return false;
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}
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} else if (!(body instanceof J.Return)) {
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return false;
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}
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} else {
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// Colon case
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if (!isReturnCase(caseStatement.getStatements())) {
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return false;
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}
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}
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}
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// We need either a default case or the switch to cover all possible values
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return SwitchUtils.coversAllPossibleValues(switchStatement);
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}
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private boolean isReturnCase(List<Statement> statements) {
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if (statements.size() != 1) {
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return false;
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}
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// Handle block containing a single return
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if (statements.get(0) instanceof J.Block) {
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return isReturnCase(((J.Block) statements.get(0)).getStatements());
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}
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// Direct return statement
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return statements.get(0) instanceof J.Return;
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}
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private J.SwitchExpression convertToSwitchExpression(J.Switch switchStatement) {
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JavaType returnType = extractReturnType(switchStatement);
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List<Statement> convertedCases = ListUtils.map(switchStatement.getCases().getStatements(), statement -> {
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J.Case caseStatement = (J.Case) statement;
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if (caseStatement.getBody() != null) {
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// Arrow case
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J body = caseStatement.getBody();
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if (body instanceof J.Block && ((J.Block) body).getStatements().size() == 1) {
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body = ((J.Block) body).getStatements().get(0);
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}
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if (body instanceof J.Return) {
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J.Return ret = (J.Return) body;
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if (ret.getExpression() != null) {
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return caseStatement.withBody(ret.getExpression());
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}
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}
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} else {
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// Colon case - convert to arrow case
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Expression returnExpression = extractReturnExpression(caseStatement.getStatements());
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if (returnExpression != null) {
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// When converting from colon to arrow syntax, we need to ensure proper spacing
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JContainer<J> caseLabels = caseStatement.getPadding().getCaseLabels();
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JContainer<J> updatedLabels = caseLabels.getPadding().withElements(
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ListUtils.mapLast(caseLabels.getPadding().getElements(),
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elem -> elem.withAfter(Space.SINGLE_SPACE)));
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return caseStatement
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.withStatements(null)
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.withBody(returnExpression.withPrefix(Space.SINGLE_SPACE))
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.withType(J.Case.Type.Rule)
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.getPadding()
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.withCaseLabels(updatedLabels);
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}
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}
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return caseStatement;
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});
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return new J.SwitchExpression(
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randomId(),
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Space.SINGLE_SPACE,
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Markers.EMPTY,
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switchStatement.getSelector(),
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switchStatement.getCases().withStatements(convertedCases),
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returnType
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);
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}
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private @Nullable JavaType extractReturnType(J.Switch switchStatement) {
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for (Statement statement : switchStatement.getCases().getStatements()) {
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J.Case caseStatement = (J.Case) statement;
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if (caseStatement.getBody() != null) {
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J body = caseStatement.getBody();
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if (body instanceof J.Block && ((J.Block) body).getStatements().size() == 1) {
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body = ((J.Block) body).getStatements().get(0);
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}
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if (body instanceof J.Return) {
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J.Return ret = (J.Return) body;
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if (ret.getExpression() != null && ret.getExpression().getType() != null) {
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return ret.getExpression().getType();
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}
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}
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} else {
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Expression returnExpression = extractReturnExpression(caseStatement.getStatements());
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if (returnExpression != null && returnExpression.getType() != null) {
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return returnExpression.getType();
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}
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}
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}
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return null;
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}
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private @Nullable Expression extractReturnExpression(List<Statement> statements) {
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if (statements.size() != 1) {
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return null;
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}
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// Handle block containing a single return
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if (statements.get(0) instanceof J.Block) {
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J.Block block = (J.Block) statements.get(0);
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if (block.getStatements().size() == 1 && block.getStatements().get(0) instanceof J.Return) {
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return ((J.Return) block.getStatements().get(0)).getExpression();
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}
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}
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// Direct return statement
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if (statements.get(0) instanceof J.Return) {
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return ((J.Return) statements.get(0)).getExpression();
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}
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return null;
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}
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});
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}
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}

‎src/main/resources/META-INF/rewrite/java-version-17.yml‎

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newVersion: 1.17.x
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- org.openrewrite.java.migrate.AddLombokMapstructBinding
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- org.openrewrite.java.migrate.lang.SwitchCaseAssignmentsToSwitchExpression
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- org.openrewrite.java.migrate.lang.SwitchCaseReturnsToSwitchExpression
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- org.openrewrite.java.migrate.lang.SwitchExpressionYieldToArrow
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---

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