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Convert switch expressions to arrows where possible (#801)
* Convert switches to switch expressions with arrows where possible * Apply best practices * Minimize SwitchExpressionYieldToArrow * Convert yield to arrows after `SwitchCaseAssignmentsToSwitchExpression` * Separate out `SwitchCaseReturnsToSwitchExpression` * Verify we do not yet convert empty cases * Apply suggestions from code review
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-63
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6 files changed

+398
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‎src/main/java/org/openrewrite/java/migrate/lang/SwitchCaseAssignmentsToSwitchExpression.java‎

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@@ -70,6 +70,7 @@ public J.Block visitBlock(J.Block originalBlock, ExecutionContext ctx) {
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return block.withStatements(ListUtils.map(block.getStatements(), (index, statement) -> {
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if (statement == originalSwitch.getAndSet(null)) {
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doAfterVisit(new InlineVariable().getVisitor());
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doAfterVisit(new SwitchExpressionYieldToArrow().getVisitor());
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// We've already converted the switch/assignments to an assignment with a switch expression.
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return null;
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}

‎src/main/java/org/openrewrite/java/migrate/lang/SwitchExpressionYieldToArrow.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.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.J;
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import org.openrewrite.java.tree.JContainer;
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import org.openrewrite.java.tree.Space;
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import org.openrewrite.java.tree.Statement;
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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 static java.util.Objects.requireNonNull;
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@Value
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@EqualsAndHashCode(callSuper = false)
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public class SwitchExpressionYieldToArrow extends Recipe {
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@Override
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public String getDisplayName() {
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return "Convert switch expression yield to arrow";
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}
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@Override
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public String getDescription() {
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return "Convert switch expressions with colon cases and yield statements to arrow syntax.";
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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.SwitchExpression visitSwitchExpression(J.SwitchExpression switchExpression, ExecutionContext ctx) {
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J.SwitchExpression se = super.visitSwitchExpression(switchExpression, ctx);
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// Check if this is a complex case (more than just a yield)
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if (anythingOtherThanYield(se)) {
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return se;
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}
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return se.withCases(se.getCases().withStatements(ListUtils.map(se.getCases().getStatements(), statement -> {
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J.Case caseStatement = (J.Case) requireNonNull(statement);
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J.Yield yieldStatement = (J.Yield) caseStatement.getStatements().get(0);
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// Add space after the last case label to create space before arrow
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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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);
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return caseStatement
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.withStatements(null)
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.withBody(yieldStatement.getValue().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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// For now, we only convert switch expressions that consist solely of yield statements
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private boolean anythingOtherThanYield(J.SwitchExpression se) {
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for (Statement statement : se.getCases().getStatements()) {
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if (!(statement instanceof J.Case)) {
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return true;
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}
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J.Case caseStatement = (J.Case) statement;
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if (caseStatement.getType() != J.Case.Type.Statement ||
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caseStatement.getStatements().size() != 1 ||
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!(caseStatement.getStatements().get(0) instanceof J.Yield)) {
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return true;
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}
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}
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return false;
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}
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});
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}
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}

‎src/main/resources/META-INF/rewrite/examples.yml‎

Lines changed: 67 additions & 38 deletions
Original file line numberDiff line numberDiff line change
@@ -1025,31 +1025,34 @@ recipeName: org.openrewrite.java.migrate.UpgradePluginsForJava11
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examples:
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- description: ''
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sources:
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- before: project
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language: mavenProject
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- before: |
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<project>
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<groupId>com.mycompany.app</groupId>
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<artifactId>my-app</artifactId>
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<version>1</version>
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<properties>
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<wro4j.version>1.8.0</wro4j.version>
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</properties>
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<build>
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<plugins>
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<plugin>
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<groupId>ro.isdc.wro4j</groupId>
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<artifactId>wro4j-maven-plugin</artifactId>
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<version>${wro4j.version}</version>
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<groupId>org.codehaus.mojo</groupId>
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<artifactId>jaxb2-maven-plugin</artifactId>
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<version>2.3.1</version>
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</plugin>
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</plugins>
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</build>
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</project>
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after: |
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path: pom.xml
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language: xml
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- description: ''
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sources:
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- before: |
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<project>
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<groupId>com.mycompany.app</groupId>
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<artifactId>my-app</artifactId>
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<version>1</version>
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<properties>
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<wro4j.version>1.10.1</wro4j.version>
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<wro4j.version>1.8.0</wro4j.version>
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</properties>
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<build>
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<plugins>
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</plugins>
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</build>
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</project>
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path: pom.xml
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language: xml
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- description: ''
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sources:
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- before: project
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language: mavenProject
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- before: |
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after: |
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<project>
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<groupId>com.mycompany.app</groupId>
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<artifactId>my-app</artifactId>
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<version>1</version>
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<properties>
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<wro4j.version>1.10.1</wro4j.version>
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</properties>
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<build>
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<plugins>
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<plugin>
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<groupId>org.codehaus.mojo</groupId>
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<artifactId>jaxb2-maven-plugin</artifactId>
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<version>2.3.1</version>
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<groupId>ro.isdc.wro4j</groupId>
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<artifactId>wro4j-maven-plugin</artifactId>
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<version>${wro4j.version}</version>
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</plugin>
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</plugins>
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</build>
@@ -3338,25 +3338,6 @@ examples:
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type: specs.openrewrite.org/v1beta/example
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recipeName: org.openrewrite.java.migrate.guava.NoGuava
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examples:
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- description: ''
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sources:
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- before: |
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import com.google.common.base.MoreObjects;
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class A {
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Object foo(Object obj) {
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return MoreObjects.firstNonNull(obj, "default");
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}
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}
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after: |
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import java.util.Objects;
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class A {
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Object foo(Object obj) {
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return Objects.requireNonNullElse(obj, "default");
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}
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}
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language: java
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- description: ''
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sources:
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- before: |
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}
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}
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language: java
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- description: ''
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sources:
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- before: |
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import com.google.common.base.MoreObjects;
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class A {
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Object foo(Object obj) {
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return MoreObjects.firstNonNull(obj, "default");
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}
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}
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after: |
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import java.util.Objects;
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class A {
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Object foo(Object obj) {
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return Objects.requireNonNullElse(obj, "default");
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}
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}
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language: java
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---
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type: specs.openrewrite.org/v1beta/example
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recipeName: org.openrewrite.java.migrate.guava.NoGuavaAtomicsNewReference
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language: java
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---
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type: specs.openrewrite.org/v1beta/example
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recipeName: org.openrewrite.java.migrate.lang.SwitchCaseAssigningToSwitchExpression
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recipeName: org.openrewrite.java.migrate.lang.SwitchCaseAssignmentsToSwitchExpression
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examples:
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- description: ''
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sources:
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language: java
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---
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type: specs.openrewrite.org/v1beta/example
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recipeName: org.openrewrite.java.migrate.lang.SwitchExpressionYieldToArrow
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examples:
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- description: ''
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sources:
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- before: |
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class Test {
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String format(String str) {
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String formatted = switch (str) {
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case "foo": yield "Foo";
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case "bar": yield "Bar";
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case null, default: yield "unknown";
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};
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return formatted;
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}
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}
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after: |
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class Test {
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String format(String str) {
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String formatted = switch (str) {
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case "foo" -> "Foo";
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case "bar" -> "Bar";
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case null, default -> "unknown";
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};
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return formatted;
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}
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}
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language: java
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---
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type: specs.openrewrite.org/v1beta/example
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recipeName: org.openrewrite.java.migrate.lang.ThreadStopUnsupported
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examples:
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- description: ''

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

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@@ -60,6 +60,7 @@ recipeList:
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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.SwitchExpressionYieldToArrow
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---
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type: specs.openrewrite.org/v1beta/recipe

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