Fix handling of default cases in arrow switches

And consolidate some reflective workarounds for switch API changes.

Fixes #4266

PiperOrigin-RevId: 609484284

Author: cushon

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

@@ -21,6 +21,7 @@
 import static com.google.common.base.Verify.verify;
 import static com.google.common.collect.ImmutableList.toImmutableList;
 import static com.google.common.collect.ImmutableSet.toImmutableSet;
+import static com.google.common.collect.Iterables.getOnlyElement;
 import static com.google.common.collect.Streams.stream;
 import static com.google.errorprone.matchers.JUnitMatchers.JUNIT4_RUN_WITH_ANNOTATION;
 import static com.google.errorprone.matchers.Matchers.isSubtypeOf;
@@ -2754,5 +2755,80 @@ private static boolean hasMatchingMethods(
     return false;
   }
 
+  private static final Method CASE_TREE_GET_LABELS = getCaseTreeGetLabelsMethod();
+
+  @Nullable
+  private static Method getCaseTreeGetLabelsMethod() {
+    try {
+      return CaseTree.class.getMethod("getLabels");
+    } catch (NoSuchMethodException e) {
+      return null;
+    }
+  }
+
+  @SuppressWarnings("unchecked") // reflection
+  private static List<? extends Tree> getCaseLabels(CaseTree caseTree) {
+    if (CASE_TREE_GET_LABELS == null) {
+      return ImmutableList.of();
+    }
+    try {
+      return (List<? extends Tree>) CASE_TREE_GET_LABELS.invoke(caseTree);
+    } catch (ReflectiveOperationException e) {
+      throw new LinkageError(e.getMessage(), e);
+    }
+  }
+
+  // getExpression() is being used for compatibility with earlier JDK versions
+  @SuppressWarnings("deprecation")
+  public static Optional<? extends CaseTree> getSwitchDefault(SwitchTree switchTree) {
+    return switchTree.getCases().stream()
+        .filter(
+            (CaseTree c) -> {
+              if (c.getExpression() != null) {
+                return false;
+              }
+              List<? extends Tree> labels = getCaseLabels(c);
+              return labels.isEmpty()
+                  || (labels.size() == 1
+                      && getOnlyElement(labels).getKind().name().equals("DEFAULT_CASE_LABEL"));
+            })
+        .findFirst();
+  }
+
+  private static final Method CASE_TREE_GET_EXPRESSIONS = getCaseTreeGetExpressionsMethod();
+
+  @Nullable
+  private static Method getCaseTreeGetExpressionsMethod() {
+    try {
+      return CaseTree.class.getMethod("getExpressions");
+    } catch (NoSuchMethodException e) {
+      return null;
+    }
+  }
+
+  /**
+   * Retrieves a stream containing all case expressions, in order, for a given {@code CaseTree}.
+   * This method acts as a facade to the {@code CaseTree.getExpressions()} API, falling back to
+   * legacy APIs when necessary.
+   */
+  @SuppressWarnings({
+    "deprecation", // getExpression() is being used for compatibility with earlier JDK versions
+    "unchecked", // reflection
+  })
+  public static Stream<? extends ExpressionTree> getCaseExpressions(CaseTree caseTree) {
+    if (!RuntimeVersion.isAtLeast12()) {
+      // "default" case gives an empty stream
+      return Stream.ofNullable(caseTree.getExpression());
+    }
+    if (CASE_TREE_GET_EXPRESSIONS == null) {
+      return Stream.empty();
+    }
+    try {
+      return ((List<? extends ExpressionTree>) CASE_TREE_GET_EXPRESSIONS.invoke(caseTree)).stream();
+    } catch (ReflectiveOperationException e) {
+      throw new LinkageError(e.getMessage(), e);
+    }
+  }
+
   private ASTHelpers() {}
 }

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

@@ -26,16 +26,11 @@
 import com.google.errorprone.bugpatterns.BugChecker.SwitchTreeMatcher;
 import com.google.errorprone.matchers.Description;
 import com.google.errorprone.util.ASTHelpers;
-import com.google.errorprone.util.RuntimeVersion;
-import com.sun.source.tree.CaseTree;
-import com.sun.source.tree.ExpressionTree;
 import com.sun.source.tree.IdentifierTree;
 import com.sun.source.tree.SwitchTree;
 import com.sun.tools.javac.code.Type;
-import java.util.List;
 import java.util.Set;
 import java.util.stream.Collectors;
-import java.util.stream.Stream;
 import javax.lang.model.element.ElementKind;
 
 /** A {@link BugChecker}; see the associated {@link BugPattern} annotation for details. */
@@ -58,7 +53,7 @@ public Description matchSwitch(SwitchTree tree, VisitorState state) {
     }
     ImmutableSet<String> handled =
         tree.getCases().stream()
-            .flatMap(MissingCasesInEnumSwitch::getExpressions)
+            .flatMap(ASTHelpers::getCaseExpressions)
             .filter(IdentifierTree.class::isInstance)
             .map(e -> ((IdentifierTree) e).getName().toString())
             .collect(toImmutableSet());
@@ -93,19 +88,4 @@ private static String buildMessage(Set<String> unhandled) {
     }
     return message.toString();
   }
-
-  @SuppressWarnings("unchecked")
-  private static Stream<? extends ExpressionTree> getExpressions(CaseTree caseTree) {
-    try {
-      if (RuntimeVersion.isAtLeast12()) {
-        return ((List<? extends ExpressionTree>)
-                CaseTree.class.getMethod("getExpressions").invoke(caseTree))
-            .stream();
-      } else {
-        return Stream.of(caseTree.getExpression());
-      }
-    } catch (ReflectiveOperationException e) {
-      throw new LinkageError(e.getMessage(), e);
-    }
-  }
 }

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

@@ -19,6 +19,7 @@
 import static com.google.common.collect.Iterables.getLast;
 import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
 import static com.google.errorprone.matchers.Description.NO_MATCH;
+import static com.google.errorprone.util.ASTHelpers.getSwitchDefault;
 
 import com.google.common.collect.Iterables;
 import com.google.errorprone.BugPattern;
@@ -52,8 +53,7 @@ public Description matchSwitch(SwitchTree tree, VisitorState state) {
       // by MissingCasesInEnumSwitch
       return NO_MATCH;
     }
-    Optional<? extends CaseTree> maybeDefault =
-        tree.getCases().stream().filter(c -> c.getExpression() == null).findFirst();
+    Optional<? extends CaseTree> maybeDefault = getSwitchDefault(tree);
     if (!maybeDefault.isPresent()) {
       Description.Builder description = buildDescription(tree);
       if (!tree.getCases().isEmpty()) {

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

@@ -22,6 +22,7 @@
 import static com.google.common.collect.Iterables.getOnlyElement;
 import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
 import static com.google.errorprone.matchers.Description.NO_MATCH;
+import static com.google.errorprone.util.ASTHelpers.getCaseExpressions;
 import static com.google.errorprone.util.ASTHelpers.getStartPosition;
 import static com.google.errorprone.util.ASTHelpers.getSymbol;
 import static com.sun.source.tree.Tree.Kind.BLOCK;
@@ -45,7 +46,6 @@
 import com.google.errorprone.matchers.Matchers;
 import com.google.errorprone.util.ASTHelpers;
 import com.google.errorprone.util.Reachability;
-import com.google.errorprone.util.RuntimeVersion;
 import com.google.errorprone.util.SourceVersion;
 import com.sun.source.tree.AssignmentTree;
 import com.sun.source.tree.BlockTree;
@@ -77,7 +77,6 @@
 import java.util.Optional;
 import java.util.Set;
 import java.util.regex.Pattern;
-import java.util.stream.Stream;
 import javax.inject.Inject;
 import javax.lang.model.element.ElementKind;
 
@@ -206,11 +205,11 @@ private static AnalysisResult analyzeSwitchTree(SwitchTree switchTree, VisitorSt
     // One-pass scan through each case in switch
     for (int caseIndex = 0; caseIndex < cases.size(); caseIndex++) {
       CaseTree caseTree = cases.get(caseIndex);
-      boolean isDefaultCase = (getExpressions(caseTree).count() == 0);
+      boolean isDefaultCase = (getCaseExpressions(caseTree).count() == 0);
       hasDefaultCase |= isDefaultCase;
       // Accumulate enum values included in this case
       handledEnumValues.addAll(
-          getExpressions(caseTree)
+          getCaseExpressions(caseTree)
               .filter(IdentifierTree.class::isInstance)
               .map(expressionTree -> ((IdentifierTree) expressionTree).getName().toString())
               .collect(toImmutableSet()));
@@ -954,30 +953,7 @@ private static String removeFallThruLines(String comments) {
 
   /** Prints source for all expressions in a given {@code case}, separated by commas. */
   private static String printCaseExpressions(CaseTree caseTree, VisitorState state) {
-    return getExpressions(caseTree).map(state::getSourceForNode).collect(joining(", "));
-  }
-
-  /**
-   * Retrieves a stream containing all case expressions, in order, for a given {@code CaseTree}.
-   * This method acts as a facade to the {@code CaseTree.getExpressions()} API, falling back to
-   * legacy APIs when necessary.
-   */
-  @SuppressWarnings("unchecked")
-  private static Stream<? extends ExpressionTree> getExpressions(CaseTree caseTree) {
-    try {
-      if (RuntimeVersion.isAtLeast12()) {
-        return ((List<? extends ExpressionTree>)
-                CaseTree.class.getMethod("getExpressions").invoke(caseTree))
-            .stream();
-      } else {
-        // "default" case gives an empty stream
-        return caseTree.getExpression() == null
-            ? Stream.empty()
-            : Stream.of(caseTree.getExpression());
-      }
-    } catch (ReflectiveOperationException e) {
-      throw new LinkageError(e.getMessage(), e);
-    }
+    return getCaseExpressions(caseTree).map(state::getSourceForNode).collect(joining(", "));
   }
 
   /**

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

@@ -20,6 +20,7 @@
 import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
 import static com.google.errorprone.matchers.Description.NO_MATCH;
 import static com.google.errorprone.util.ASTHelpers.getStartPosition;
+import static com.google.errorprone.util.ASTHelpers.getSwitchDefault;
 
 import com.google.errorprone.BugPattern;
 import com.google.errorprone.VisitorState;
@@ -44,8 +45,7 @@ public class SwitchDefault extends BugChecker implements SwitchTreeMatcher {
 
   @Override
   public Description matchSwitch(SwitchTree tree, VisitorState state) {
-    Optional<? extends CaseTree> maybeDefault =
-        tree.getCases().stream().filter(c -> c.getExpression() == null).findAny();
+    Optional<? extends CaseTree> maybeDefault = getSwitchDefault(tree);
     if (!maybeDefault.isPresent()) {
       return NO_MATCH;
     }

core/src/test/java/com/google/errorprone/bugpatterns/SwitchDefaultTest.java

@@ -291,4 +291,27 @@ public void newNotation_changeOrder() {
             "}")
         .doTest();
   }
+
+  @Test
+  public void arrowSwitch_noDefault() {
+    assumeTrue(RuntimeVersion.isAtLeast21());
+    compilationHelper
+        .addSourceLines(
+            "Foo.java", //
+            "sealed interface Foo {",
+            "  final class Bar implements Foo {}",
+            "  final class Baz implements Foo {}",
+            "}")
+        .addSourceLines(
+            "Test.java",
+            "class Test {",
+            "  void f(Foo i) {",
+            "    switch (i) {",
+            "      case Foo.Bar bar -> {}",
+            "      case Foo.Baz baz -> {}",
+            "    }",
+            "  }",
+            "}")
+        .doTest();
+  }
 }