From 0c858b0a7bbbc051e428f7760701d736af592fdf Mon Sep 17 00:00:00 2001
From: Andreas Dangel <andreas.dangel@pmd-code.org>
Date: Fri, 4 Oct 2024 16:03:21 +0200
Subject: [PATCH] [java] SwitchStmtsShouldHaveDefault should ignore patterns

Fixes #4813
---
 docs/pages/release_notes.md                   |  2 +
 .../resources/category/java/bestpractices.xml |  6 ++
 .../xml/SwitchStmtsShouldHaveDefault.xml      | 75 +++++++++++++++++++
 3 files changed, 83 insertions(+)

diff --git a/docs/pages/release_notes.md b/docs/pages/release_notes.md
index 197b7a4aec..154ac73a28 100644
--- a/docs/pages/release_notes.md
+++ b/docs/pages/release_notes.md
@@ -32,6 +32,8 @@ The old rule names still work but are deprecated.
 ### 🐛 Fixed Issues
 * java
   * [#4532](https://github.com/pmd/pmd/issues/4532): \[java] Rule misnomer for JUnit* rules
+* java-bestpractices
+  * [#4813](https://github.com/pmd/pmd/issues/4813): \[java] SwitchStmtsShouldHaveDefault false positive with pattern matching
 * java-errorprone
   * [#5067](https://github.com/pmd/pmd/issues/5067): \[java] CloseResource: False positive for FileSystems.getDefault()
 
diff --git a/pmd-java/src/main/resources/category/java/bestpractices.xml b/pmd-java/src/main/resources/category/java/bestpractices.xml
index 03b23ad1ca..aa965d9f67 100644
--- a/pmd-java/src/main/resources/category/java/bestpractices.xml
+++ b/pmd-java/src/main/resources/category/java/bestpractices.xml
@@ -1168,12 +1168,18 @@ class SomeTestClass {
             easier to follow. This can be achieved by adding a `default` case, or,
             if the switch is on an enum type, by ensuring there is one switch branch
             for each enum constant.
+
+            This rule doesn't consider Switch Statements, that use Pattern Matching, since for these the
+            compiler already ensures that all cases are covered. The same is true for Switch Expressions,
+            which are also not considered by this rule.
         </description>
         <priority>3</priority>
         <properties>
             <property name="xpath">
                 <value><![CDATA[
                 //SwitchStatement[@DefaultCase = false() and @ExhaustiveEnumSwitch = false()]
+                    (: exclude type pattern tests - for these, the compiler will ensure exhaustiveness :)
+                    [not(*/SwitchLabel/TypePattern)]
             ]]></value>
             </property>
         </properties>
diff --git a/pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/bestpractices/xml/SwitchStmtsShouldHaveDefault.xml b/pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/bestpractices/xml/SwitchStmtsShouldHaveDefault.xml
index 758b97b43b..e28cfe5b9d 100644
--- a/pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/bestpractices/xml/SwitchStmtsShouldHaveDefault.xml
+++ b/pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/bestpractices/xml/SwitchStmtsShouldHaveDefault.xml
@@ -240,4 +240,79 @@ public enum GradeSystem {
 }
         ]]></code>
     </test-code>
+
+    <test-code>
+        <description>[java] SwitchStmtsShouldHaveDefault false positive with pattern matching #4813</description>
+        <expected-problems>0</expected-problems>
+        <code><![CDATA[
+public sealed interface AcceptableResult permits Success, Warning {
+    public String message();
+}
+public final class Success implements AcceptableResult {
+    @Override
+    public String message() {
+        return "Success!";
+    }
+}
+public abstract class Failure {
+    abstract public String message();
+}
+public non-sealed class Warning extends Failure implements AcceptableResult {
+    @Override
+    public String message() {
+        return "Oopsie";
+    }
+}
+public class ProviderWarning extends Warning {
+    @Override
+    public String message() {
+        return "Ohoh";
+    }
+}
+public class Example {
+    public void test(AcceptableResult result) {
+        switch (result) {
+            case Warning failure -> System.out.println("WARNING " + failure.message());
+            case Success success -> System.out.println(success.message());
+        }
+    }
+    public void test2(AcceptableResult result) {
+        switch (result) {
+            case ProviderWarning failure: System.out.println("Provider WARNING " + failure.message()); break;
+            case Warning failure: System.out.println("WARNING " + failure.message()); break;
+            case Success success: System.out.println(success.message()); break;
+        }
+    }
+    public void test3(AcceptableResult result) {
+        switch (result) {
+            case ProviderWarning failure -> System.out.println("Provider WARNING " + failure.message());
+            case Success success -> System.out.println(success.message());
+            default -> System.out.println("default case");
+        }
+    }
+}
+]]></code>
+    </test-code>
+
+    <test-code>
+        <description>[java] SwitchStmtsShouldHaveDefault false positive with pattern matching #4813, example 2</description>
+        <expected-problems>0</expected-problems>
+        <code><![CDATA[
+sealed interface S permits A, B {}
+final class A implements S {}
+sealed abstract class B implements S permits C, D {}
+final class C extends B {}
+final class D extends B {}
+public class Example2 {
+    static int testSealedExhaustive(S s) {
+        switch(s) {
+            case A a -> { return 1; }
+            case C c -> { return 2; }
+            case D d -> { return 3; }
+            // case B b -> { return 4; } // not explicitly necessary, but possible
+        }
+    }
+}
+]]></code>
+    </test-code>
 </test-data>