Convert switch expressions to arrows where possible

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

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

src/main/java/org/openrewrite/java/migrate/lang/SwitchExpressionYieldToArrow.java

@@ -0,0 +1,104 @@
+/*
+ * Copyright 2025 the original author or authors.
+ * <p>
+ * Licensed under the Moderne Source Available License (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * https://docs.moderne.io/licensing/moderne-source-available-license
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.openrewrite.java.migrate.lang;
+
+import lombok.EqualsAndHashCode;
+import lombok.Value;
+import org.openrewrite.ExecutionContext;
+import org.openrewrite.Preconditions;
+import org.openrewrite.Recipe;
+import org.openrewrite.TreeVisitor;
+import org.openrewrite.internal.ListUtils;
+import org.openrewrite.java.JavaIsoVisitor;
+import org.openrewrite.java.search.UsesJavaVersion;
+import org.openrewrite.java.tree.J;
+import org.openrewrite.java.tree.JContainer;
+import org.openrewrite.java.tree.Space;
+import org.openrewrite.java.tree.Statement;
+import org.openrewrite.staticanalysis.groovy.GroovyFileChecker;
+import org.openrewrite.staticanalysis.kotlin.KotlinFileChecker;
+
+import static java.util.Objects.requireNonNull;
+
+@Value
+@EqualsAndHashCode(callSuper = false)
+public class SwitchExpressionYieldToArrow extends Recipe {
+    @Override
+    public String getDisplayName() {
+        return "Convert switch expression yield to arrow";
+    }
+
+    @Override
+    public String getDescription() {
+        return "Convert switch expressions with colon cases and yield statements to arrow syntax.";
+    }
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getVisitor() {
+        TreeVisitor<?, ExecutionContext> preconditions = Preconditions.and(
+                new UsesJavaVersion<>(14),
+                Preconditions.not(new KotlinFileChecker<>()),
+                Preconditions.not(new GroovyFileChecker<>())
+        );
+        return Preconditions.check(preconditions, new JavaIsoVisitor<ExecutionContext>() {
+            @Override
+            public J.SwitchExpression visitSwitchExpression(J.SwitchExpression switchExpression, ExecutionContext ctx) {
+                J.SwitchExpression se = super.visitSwitchExpression(switchExpression, ctx);
+
+                // Check if this is a complex case (more than just a yield)
+                if (anythingOtherThanYield(se)) {
+                    return se;
+                }
+
+                return se.withCases(se.getCases().withStatements(ListUtils.map(se.getCases().getStatements(), statement -> {
+                    J.Case caseStatement = (J.Case) requireNonNull(statement);
+                    J.Yield yieldStatement = (J.Yield) caseStatement.getStatements().get(0);
+
+                    // Add space after the last case label to create space before arrow
+                    JContainer<J> caseLabels = caseStatement.getPadding().getCaseLabels();
+                    JContainer<J> updatedLabels = caseLabels.getPadding().withElements(
+                            ListUtils.mapLast(caseLabels.getPadding().getElements(),
+                                    elem -> elem.withAfter(Space.SINGLE_SPACE))
+                    );
+
+                    return caseStatement
+                            .withStatements(null)
+                            .withBody(yieldStatement.getValue().withPrefix(Space.SINGLE_SPACE))
+                            .withType(J.Case.Type.Rule)
+                            .getPadding()
+                            .withCaseLabels(updatedLabels);
+                })));
+            }
+
+            // For now, we only convert switch expressions that consist solely of yield statements
+            private boolean anythingOtherThanYield(J.SwitchExpression se) {
+                for (Statement statement : se.getCases().getStatements()) {
+                    if (!(statement instanceof J.Case)) {
+                        return true;
+                    }
+
+                    J.Case caseStatement = (J.Case) statement;
+                    if (caseStatement.getType() != J.Case.Type.Statement ||
+                            caseStatement.getStatements().size() != 1 ||
+                            !(caseStatement.getStatements().get(0) instanceof J.Yield)) {
+                        return true;
+                    }
+                }
+                return false;
+            }
+        });
+    }
+}

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

@@ -1025,31 +1025,34 @@ recipeName: org.openrewrite.java.migrate.UpgradePluginsForJava11
 examples:
 - description: ''
   sources:
+  - before: project
+    language: mavenProject
   - before: |
       <project>
         <groupId>com.mycompany.app</groupId>
         <artifactId>my-app</artifactId>
         <version>1</version>
-        <properties>
-          <wro4j.version>1.8.0</wro4j.version>
-        </properties>
         <build>
           <plugins>
             <plugin>
-              <groupId>ro.isdc.wro4j</groupId>
-              <artifactId>wro4j-maven-plugin</artifactId>
-              <version>${wro4j.version}</version>
+              <groupId>org.codehaus.mojo</groupId>
+              <artifactId>jaxb2-maven-plugin</artifactId>
+              <version>2.3.1</version>
             </plugin>
           </plugins>
         </build>
       </project>
-    after: |
+    path: pom.xml
+    language: xml
+- description: ''
+  sources:
+  - before: |
       <project>
         <groupId>com.mycompany.app</groupId>
         <artifactId>my-app</artifactId>
         <version>1</version>
         <properties>
-          <wro4j.version>1.10.1</wro4j.version>
+          <wro4j.version>1.8.0</wro4j.version>
         </properties>
         <build>
           <plugins>
@@ -1061,23 +1064,20 @@ examples:
           </plugins>
         </build>
       </project>
-    path: pom.xml
-    language: xml
-- description: ''
-  sources:
-  - before: project
-    language: mavenProject
-  - before: |
+    after: |
       <project>
         <groupId>com.mycompany.app</groupId>
         <artifactId>my-app</artifactId>
         <version>1</version>
+        <properties>
+          <wro4j.version>1.10.1</wro4j.version>
+        </properties>
         <build>
           <plugins>
             <plugin>
-              <groupId>org.codehaus.mojo</groupId>
-              <artifactId>jaxb2-maven-plugin</artifactId>
-              <version>2.3.1</version>
+              <groupId>ro.isdc.wro4j</groupId>
+              <artifactId>wro4j-maven-plugin</artifactId>
+              <version>${wro4j.version}</version>
             </plugin>
           </plugins>
         </build>
@@ -3338,25 +3338,6 @@ examples:
 type: specs.openrewrite.org/v1beta/example
 recipeName: org.openrewrite.java.migrate.guava.NoGuava
 examples:
-- description: ''
-  sources:
-  - before: |
-      import com.google.common.base.MoreObjects;
-
-      class A {
-          Object foo(Object obj) {
-              return MoreObjects.firstNonNull(obj, "default");
-          }
-      }
-    after: |
-      import java.util.Objects;
-
-      class A {
-          Object foo(Object obj) {
-              return Objects.requireNonNullElse(obj, "default");
-          }
-      }
-    language: java
 - description: ''
   sources:
   - before: |
@@ -3403,6 +3384,25 @@ examples:
           }
       }
     language: java
+- description: ''
+  sources:
+  - before: |
+      import com.google.common.base.MoreObjects;
+
+      class A {
+          Object foo(Object obj) {
+              return MoreObjects.firstNonNull(obj, "default");
+          }
+      }
+    after: |
+      import java.util.Objects;
+
+      class A {
+          Object foo(Object obj) {
+              return Objects.requireNonNullElse(obj, "default");
+          }
+      }
+    language: java
 ---
 type: specs.openrewrite.org/v1beta/example
 recipeName: org.openrewrite.java.migrate.guava.NoGuavaAtomicsNewReference
@@ -6235,7 +6235,7 @@ examples:
     language: java
 ---
 type: specs.openrewrite.org/v1beta/example
-recipeName: org.openrewrite.java.migrate.lang.SwitchCaseAssigningToSwitchExpression
+recipeName: org.openrewrite.java.migrate.lang.SwitchCaseAssignmentsToSwitchExpression
 examples:
 - description: ''
   sources:
@@ -6314,6 +6314,35 @@ examples:
     language: java
 ---
 type: specs.openrewrite.org/v1beta/example
+recipeName: org.openrewrite.java.migrate.lang.SwitchExpressionYieldToArrow
+examples:
+- description: ''
+  sources:
+  - before: |
+      class Test {
+          String format(String str) {
+              String formatted = switch (str) {
+                  case "foo": yield "Foo";
+                  case "bar": yield "Bar";
+                  case null, default: yield "unknown";
+              };
+              return formatted;
+          }
+      }
+    after: |
+      class Test {
+          String format(String str) {
+              String formatted = switch (str) {
+                  case "foo" -> "Foo";
+                  case "bar" -> "Bar";
+                  case null, default -> "unknown";
+              };
+              return formatted;
+          }
+      }
+    language: java
+---
+type: specs.openrewrite.org/v1beta/example
 recipeName: org.openrewrite.java.migrate.lang.ThreadStopUnsupported
 examples:
 - description: ''

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

@@ -60,6 +60,7 @@ recipeList:
       newVersion: 1.17.x
   - org.openrewrite.java.migrate.AddLombokMapstructBinding
   - org.openrewrite.java.migrate.lang.SwitchCaseAssignmentsToSwitchExpression
+  - org.openrewrite.java.migrate.lang.SwitchExpressionYieldToArrow
 
 ---
 type: specs.openrewrite.org/v1beta/recipe