Add support for guard clauses in Java 21 switch expressions

This PR adds support for `switch` statements where a `case` has a guard clause.

See Issue #983

Fixes #988

COPYBARA_INTEGRATE_REVIEW=google/google-java-format#988 from TheCK:master 4771486db7d8aab84eb4ecf8e68af2612d0c2b5c
PiperOrigin-RevId: 588913297

build.gradle

@@ -97,6 +97,6 @@ jdks {
 }
 
 javaVersions {
-    libraryTarget = 17
+    libraryTarget = 21
     runtime = 21
 }

core/src/main/java/com/google/googlejavaformat/java/java21/Java21InputAstVisitor.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2023 The google-java-format Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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 com.google.googlejavaformat.java.java21;
+
+import com.google.googlejavaformat.OpsBuilder;
+import com.google.googlejavaformat.java.java17.Java17InputAstVisitor;
+import com.sun.source.tree.CaseTree;
+import com.sun.source.tree.ExpressionTree;
+
+/**
+ * Extends {@link Java17InputAstVisitor} with support for AST nodes that were added or modified in
+ * Java 21.
+ */
+public class Java21InputAstVisitor extends Java17InputAstVisitor {
+
+  public Java21InputAstVisitor(OpsBuilder builder, int indentMultiplier) {
+    super(builder, indentMultiplier);
+  }
+
+  @Override
+  protected ExpressionTree getGuard(final CaseTree node) {
+    return node.getGuard();
+  }
+}

palantir-java-format/src/main/java/com/palantir/javaformat/java/Formatter.java

@@ -131,15 +131,10 @@ static JavaOutput format(
         OpsBuilder opsBuilder = new OpsBuilder(javaInput);
 
         JavaInputAstVisitor visitor;
-        if (getRuntimeVersion() >= 14) {
-            try {
-                visitor = Class.forName("com.palantir.javaformat.java.java14.Java14InputAstVisitor")
-                        .asSubclass(JavaInputAstVisitor.class)
-                        .getConstructor(OpsBuilder.class, int.class)
-                        .newInstance(opsBuilder, options.indentationMultiplier());
-            } catch (ReflectiveOperationException e) {
-                throw new RuntimeException(e.getMessage(), e);
-            }
+        if (getRuntimeVersion() >= 21) {
+            visitor = createVisitor("com.palantir.javaformat.java.java21.Java21InputAstVisitor", opsBuilder, options);
+        } else if (getRuntimeVersion() >= 14) {
+            visitor = createVisitor("com.palantir.javaformat.java.java14.Java14InputAstVisitor", opsBuilder, options);
         } else {
             visitor = new JavaInputAstVisitor(opsBuilder, options.indentationMultiplier());
         }
@@ -206,6 +201,18 @@ static int getRuntimeVersion() {
         return Runtime.version().feature();
     }
 
+    private static JavaInputAstVisitor createVisitor(
+            final String className, final OpsBuilder builder, final JavaFormatterOptions options) {
+        try {
+            return Class.forName(className)
+                    .asSubclass(JavaInputAstVisitor.class)
+                    .getConstructor(OpsBuilder.class, int.class)
+                    .newInstance(builder, options.indentationMultiplier());
+        } catch (ReflectiveOperationException e) {
+            throw new LinkageError(e.getMessage(), e);
+        }
+    }
+
     static boolean errorDiagnostic(Diagnostic<?> input) {
         if (input.getKind() != Diagnostic.Kind.ERROR) {
             return false;

palantir-java-format/src/main/java/com/palantir/javaformat/java/java14/Java14InputAstVisitor.java

@@ -31,6 +31,7 @@
 import com.sun.source.tree.CaseTree;
 import com.sun.source.tree.ClassTree;
 import com.sun.source.tree.CompilationUnitTree;
+import com.sun.source.tree.ExpressionTree;
 import com.sun.source.tree.InstanceOfTree;
 import com.sun.source.tree.LambdaExpressionTree;
 import com.sun.source.tree.ModifiersTree;
@@ -275,6 +276,15 @@ public Void visitCase(CaseTree node, Void unused) {
             }
             builder.close();
         }
+
+        final ExpressionTree guard = getGuard(node);
+        if (guard != null) {
+            builder.space();
+            token("when");
+            builder.space();
+            scan(guard, null);
+        }
+
         switch (node.getCaseKind()) {
             case STATEMENT:
                 token(":");
@@ -341,4 +351,8 @@ private static Object invoke(Method m, Object target) {
             throw new RuntimeException(e.getMessage(), e);
         }
     }
+
+    protected ExpressionTree getGuard(final CaseTree node) {
+        return null;
+    }
 }

palantir-java-format/src/main/java/com/palantir/javaformat/java/java21/Java21InputAstVisitor.java

@@ -0,0 +1,36 @@
+/*
+ * (c) Copyright 2024 Palantir Technologies Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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 com.palantir.javaformat.java.java21;
+
+import com.palantir.javaformat.OpsBuilder;
+import com.palantir.javaformat.java.java14.Java14InputAstVisitor;
+import com.sun.source.tree.CaseTree;
+import com.sun.source.tree.ExpressionTree;
+/**
+ * Extends {@link Java14InputAstVisitor} with support for AST nodes that were added or modified in
+ * Java 21.
+ */
+public class Java21InputAstVisitor extends Java14InputAstVisitor {
+    public Java21InputAstVisitor(OpsBuilder builder, int indentMultiplier) {
+        super(builder, indentMultiplier);
+    }
+
+    @Override
+    protected ExpressionTree getGuard(final CaseTree node) {
+        return node.getGuard();
+    }
+}

palantir-java-format/src/test/java/com/palantir/javaformat/java/FileBasedTests.java

@@ -50,6 +50,7 @@ public final class FileBasedTests {
                     .putAll(15, "I603")
                     .putAll(16, "I588")
                     .putAll(17, "I683", "I684", "I696")
+                    .putAll(21, "SwitchGuardClause")
                     .build();
 
     private final Class<?> testClass;

palantir-java-format/src/test/resources/com/palantir/javaformat/java/testdata/SwitchGuardClause.input

@@ -0,0 +1,9 @@
+class SwitchGuardClause {
+  boolean test(Object x) {
+    return switch (x) {
+      case String s when s.length() < 5 -> true;
+      case Integer i -> false;
+      default -> true;
+    };
+  }
+}

palantir-java-format/src/test/resources/com/palantir/javaformat/java/testdata/SwitchGuardClause.output

@@ -0,0 +1,9 @@
+class SwitchGuardClause {
+    boolean test(Object x) {
+        return switch (x) {
+            case String s when s.length() < 5 -> true;
+            case Integer i -> false;
+            default -> true;
+        };
+    }
+}