[java] ImplicitSwitchFallThrough should consider switch expressions

Fixes #3362

docs/pages/release_notes.md

@@ -33,6 +33,7 @@ The old rule names still work but are deprecated.
 * java
   * [#4532](https://github.com/pmd/pmd/issues/4532): \[java] Rule misnomer for JUnit* rules
 * java-errorprone
+  * [#3362](https://github.com/pmd/pmd/issues/3362): \[java] ImplicitSwitchFallThrough should consider switch expressions
   * [#5067](https://github.com/pmd/pmd/issues/5067): \[java] CloseResource: False positive for FileSystems.getDefault()
 
 ### 🚨 API Changes

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/errorprone/ImplicitSwitchFallThroughRule.java

@@ -9,28 +9,40 @@ import java.util.regex.Pattern;
 import net.sourceforge.pmd.lang.ast.GenericToken;
 import net.sourceforge.pmd.lang.ast.impl.javacc.JavaccToken;
 import net.sourceforge.pmd.lang.java.ast.ASTSwitchBranch;
+import net.sourceforge.pmd.lang.java.ast.ASTSwitchExpression;
 import net.sourceforge.pmd.lang.java.ast.ASTSwitchFallthroughBranch;
+import net.sourceforge.pmd.lang.java.ast.ASTSwitchLike;
 import net.sourceforge.pmd.lang.java.ast.ASTSwitchStatement;
 import net.sourceforge.pmd.lang.java.ast.JavaNode;
 import net.sourceforge.pmd.lang.java.ast.internal.JavaAstUtils;
 import net.sourceforge.pmd.lang.java.rule.AbstractJavaRulechainRule;
 import net.sourceforge.pmd.lang.java.rule.internal.DataflowPass;
 import net.sourceforge.pmd.lang.java.rule.internal.DataflowPass.DataflowResult;
+import net.sourceforge.pmd.reporting.RuleContext;
 import net.sourceforge.pmd.util.OptionalBool;
 
 public class ImplicitSwitchFallThroughRule extends AbstractJavaRulechainRule {
 
-    //todo should consider switch exprs
-
     private static final Pattern IGNORED_COMMENT = Pattern.compile("/[/*].*\\bfalls?[ -]?thr(ough|u)\\b.*",
                                                                    Pattern.DOTALL | Pattern.CASE_INSENSITIVE);
 
     public ImplicitSwitchFallThroughRule() {
-        super(ASTSwitchStatement.class);
+        super(ASTSwitchStatement.class, ASTSwitchExpression.class);
     }
 
     @Override
     public Object visit(ASTSwitchStatement node, Object data) {
+        checkSwitchLike(node, asCtx(data));
+        return null;
+    }
+
+    @Override
+    public Object visit(ASTSwitchExpression node, Object data) {
+        checkSwitchLike(node, asCtx(data));
+        return null;
+    }
+
+    private void checkSwitchLike(ASTSwitchLike node, RuleContext ruleContext) {
         DataflowResult dataflow = DataflowPass.getDataflowResult(node.getRoot());
 
         for (ASTSwitchBranch branch : node.getBranches()) {
@@ -38,15 +50,14 @@ public class ImplicitSwitchFallThroughRule extends AbstractJavaRulechainRule {
                 ASTSwitchFallthroughBranch fallthrough = (ASTSwitchFallthroughBranch) branch;
                 OptionalBool bool = dataflow.switchBranchFallsThrough(branch);
                 if (bool != OptionalBool.NO
-                    && fallthrough.getStatements().nonEmpty()
-                    && !nextBranchHasComment(branch)) {
-                    asCtx(data).addViolation(branch.getNextBranch().getLabel());
+                        && fallthrough.getStatements().nonEmpty()
+                        && !nextBranchHasComment(branch)) {
+                    ruleContext.addViolation(branch.getNextBranch().getLabel());
                 }
             } else {
-                return null;
+                return;
             }
         }
-        return null;
     }
 
     boolean nextBranchHasComment(ASTSwitchBranch branch) {
@@ -62,5 +73,4 @@ public class ImplicitSwitchFallThroughRule extends AbstractJavaRulechainRule {
         }
         return false;
     }
-
 }

pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/errorprone/xml/ImplicitSwitchFallThrough.xml

@@ -581,4 +581,24 @@ public class Test {
 }
             ]]></code>
     </test-code>
+
+    <test-code>
+        <description>switch expression with one case, which is not empty</description>
+        <expected-problems>1</expected-problems>
+        <expected-linenumbers>6</expected-linenumbers>
+        <code><![CDATA[
+public class Foo {
+  public static void main(String[] args) {
+    int i = 1;
+    String result = switch(i) {
+      case 1: doSomething();
+      default: yield "default case fall through";
+    };
+    System.out.println(result);
+  }
+
+  private static void doSomething() {}
+}
+]]></code>
+    </test-code>
 </test-data>