StatementSwitchToExpressionSwitch: only trigger on compatible target …

…versions

This change introduces a `SourceVersion` utility class, analogous to the
existing `RuntimeVersion` class. The new class tells whether selected language
features are available for the source version used by the compiler.

The new utility class is used to make sure that
`StatementSwitchToExpressionSwitch` flags statement switches only if the source
version supports expression switches, irrespective of whether the current
runtime supports such switch types. Concretely this makes the check compatible
with projects that target JDK 11, yet support building with JDK 17.

Fixes #3646

FUTURE_COPYBARA_INTEGRATE_REVIEW=#3646 from PicnicSupermarket:bugfix/dont-suggest-switch-expressions-pre-jdk14 641c9dc
PiperOrigin-RevId: 498755371

check_api/src/main/java/com/google/errorprone/util/RuntimeVersion.java

@@ -16,7 +16,15 @@
 
 package com.google.errorprone.util;
 
-/** JDK version string utilities. */
+/**
+ * JDK runtime version utilities.
+ *
+ * <p>These methods are generally used when deciding which method to call reflectively. Bug checkers
+ * that rely on support for specific source code constructs should consult {@link SourceVersion}
+ * instead.
+ *
+ * @see SourceVersion
+ */
 public final class RuntimeVersion {
 
   private static final int FEATURE = Runtime.version().feature();

check_api/src/main/java/com/google/errorprone/util/SourceVersion.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2023 The Error Prone 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.errorprone.util;
+
+import com.sun.tools.javac.code.Source;
+import com.sun.tools.javac.util.Context;
+
+/**
+ * JDK source version utilities.
+ *
+ * @see RuntimeVersion
+ */
+public final class SourceVersion {
+  /** Returns true if the compiler source version level supports switch expressions. */
+  public static boolean supportsSwitchExpressions(Context context) {
+    return sourceIsAtLeast(context, "14");
+  }
+
+  /** Returns true if the compiler source version level supports text blocks. */
+  public static boolean supportsTextBlocks(Context context) {
+    return sourceIsAtLeast(context, "15");
+  }
+
+  private static boolean sourceIsAtLeast(Context context, String versionString) {
+    Source lowerBound = Source.lookup(versionString);
+    return lowerBound != null && Source.instance(context).compareTo(lowerBound) >= 0;
+  }
+
+  private SourceVersion() {}
+}

check_api/src/test/java/com/google/errorprone/util/SourceVersionTest.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2023 The Error Prone 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.errorprone.util;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.sun.tools.javac.main.Option;
+import com.sun.tools.javac.util.Context;
+import com.sun.tools.javac.util.Options;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class SourceVersionTest {
+  @Test
+  public void supportsSwitchExpressions_notSupported() {
+    Context context = contextWithSourceVersion("13");
+
+    assertThat(SourceVersion.supportsSwitchExpressions(context)).isFalse();
+  }
+
+  @Test
+  public void supportsSwitchExpressions_conditionallySupported() {
+    Context context = contextWithSourceVersion("14");
+
+    assertThat(SourceVersion.supportsSwitchExpressions(context))
+        .isEqualTo(RuntimeVersion.isAtLeast14());
+  }
+
+  @Test
+  public void supportsTextBlocks_notSupported() {
+    Context context = contextWithSourceVersion("14");
+
+    assertThat(SourceVersion.supportsTextBlocks(context)).isFalse();
+  }
+
+  @Test
+  public void supportsTextBlocks_conditionallySupported() {
+    Context context = contextWithSourceVersion("15");
+
+    assertThat(SourceVersion.supportsTextBlocks(context)).isEqualTo(RuntimeVersion.isAtLeast15());
+  }
+
+  private static Context contextWithSourceVersion(String versionString) {
+    Context context = new Context();
+
+    Options options = Options.instance(context);
+    options.put(Option.SOURCE, versionString);
+
+    return context;
+  }
+}

core/src/main/java/com/google/errorprone/bugpatterns/StatementSwitchToExpressionSwitch.java

@@ -39,6 +39,7 @@
 import com.google.errorprone.matchers.Description;
 import com.google.errorprone.util.Reachability;
 import com.google.errorprone.util.RuntimeVersion;
+import com.google.errorprone.util.SourceVersion;
 import com.sun.source.tree.BreakTree;
 import com.sun.source.tree.CaseTree;
 import com.sun.source.tree.ExpressionTree;
@@ -85,8 +86,7 @@ public StatementSwitchToExpressionSwitch(ErrorProneFlags flags) {
 
   @Override
   public Description matchSwitch(SwitchTree switchTree, VisitorState state) {
-    // Expression switches finalized in Java 14
-    if (!RuntimeVersion.isAtLeast14()) {
+    if (!SourceVersion.supportsSwitchExpressions(state.context)) {
       return NO_MATCH;
     }