Issue #11973: Fix NPE on empty switch statements in VariableDeclarati…

…onUsageDistance

.ci/pitest-suppressions/pitest-coding-1-suppressions.xml

@@ -179,13 +179,4 @@
     <description>replaced call to com/puppycrawl/tools/checkstyle/api/DetailAST::getNextSibling with receiver</description>
     <lineContent>DetailAST exprBetweenBrackets = openingBracket.getNextSibling();</lineContent>
   </mutation>
-
-  <mutation unstable="false">
-    <sourceFile>VariableDeclarationUsageDistanceCheck.java</sourceFile>
-    <mutatedClass>com.puppycrawl.tools.checkstyle.checks.coding.VariableDeclarationUsageDistanceCheck</mutatedClass>
-    <mutatedMethod>lambda$getFirstCaseGroupOrSwitchRule$2</mutatedMethod>
-    <mutator>org.pitest.mutationtest.engine.gregor.mutators.experimental.NakedReceiverMutator</mutator>
-    <description>replaced call to com/puppycrawl/tools/checkstyle/api/DetailAST::findFirstToken with receiver</description>
-    <lineContent>.orElseGet(() -&gt; block.findFirstToken(TokenTypes.SWITCH_RULE));</lineContent>
-  </mutation>
 </suppressedMutations>

src/main/java/com/puppycrawl/tools/checkstyle/checks/coding/VariableDeclarationUsageDistanceCheck.java

@@ -814,13 +814,15 @@ private static DetailAST getFirstNodeInsideSwitchBlock(
                 new ArrayList<>();
 
         // Checking variable usage inside all CASE_GROUP and SWITCH_RULE ast's.
-        TokenUtil.forEachChild(block, currentNode.getType(), node -> {
-            final DetailAST lastNodeInCaseGroup =
-                node.getLastChild();
-            if (isChild(lastNodeInCaseGroup, variable)) {
-                variableUsageExpressions.add(lastNodeInCaseGroup);
-            }
-        });
+        if (currentNode != null) {
+            TokenUtil.forEachChild(block, currentNode.getType(), node -> {
+                final DetailAST lastNodeInCaseGroup =
+                    node.getLastChild();
+                if (isChild(lastNodeInCaseGroup, variable)) {
+                    variableUsageExpressions.add(lastNodeInCaseGroup);
+                }
+            });
+        }
 
         // If variable usage exists in several related blocks, then
         // firstNodeInsideBlock = null, otherwise if variable usage exists

src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/VariableDeclarationUsageDistanceCheckTest.java

@@ -314,6 +314,7 @@ public void testVariableDeclarationUsageDistanceSwitchExpressions2() throws Exce
             "78:17: " + getCheckMessage(MSG_KEY, "m", 3, maxDistance),
             "79:17: " + getCheckMessage(MSG_KEY, "n", 2, maxDistance),
             "100:17: " + getCheckMessage(MSG_KEY, "count", 3, maxDistance),
+            "110:9: " + getCheckMessage(MSG_KEY, "i", 2, maxDistance),
         };
 
         final String filename = "InputVariableDeclarationUsageDistanceCheckSwitchExpressions2.java";

src/test/resources-noncompilable/com/puppycrawl/tools/checkstyle/checks/coding/variabledeclarationusagedistance/InputVariableDeclarationUsageDistanceCheckSwitchExpressions2.java

@@ -105,4 +105,15 @@ public boolean equals(Object obj) {
         }
         return false;
     }
+
+    void issue11973() {
+        int i = -1; // violation 'Distance between.*'i'.*and.*first usage is 2, but allowed 1.'
+        int x = -1;
+        switch (i) {
+            case 1 -> {
+                x++;
+                i++;
+            }
+        }
+    }
 }

src/test/resources/com/puppycrawl/tools/checkstyle/checks/coding/variabledeclarationusagedistance/InputVariableDeclarationUsageDistanceGeneral2.java

@@ -63,4 +63,10 @@ void method() throws Exception {
             a.equals("");
         }
     }
+
+    void issue11973() {
+        int i = -1;
+        switch (i) {
+        }
+    }
 }