Issue #14506: False positive for UnusedLocalVariable

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

@@ -128,6 +128,21 @@ public class UnusedLocalVariableCheck extends AbstractCheck {
         TokenTypes.COMPACT_CTOR_DEF,
     };
 
+    /**
+     * An array of token types that indicate a variable is being used within
+     * an expression involving increment or decrement operators, or within a switch statement.
+     * When a token of one of these types is the parent of an expression, it indicates that the
+     * variable associated with the increment or decrement operation is being used.
+     * Ex:- TokenTypes.LITERAL_SWITCH: Indicates a switch statement. Variables used within the
+     * switch expression are considered to be used
+     */
+    private static final int[] INCREMENT_DECREMENT_VARIABLE_USAGE_TYPES = {
+        TokenTypes.ELIST,
+        TokenTypes.INDEX_OP,
+        TokenTypes.ASSIGN,
+        TokenTypes.LITERAL_SWITCH,
+    };
+
     /** Package separator. */
     private static final String PACKAGE_SEPARATOR = ".";
 
@@ -750,8 +765,7 @@ private static boolean isStandAloneIncrementOrDecrement(DetailAST identAst) {
      * @return true if variable nested in exprAst is used
      */
     private static boolean isIncrementOrDecrementVariableUsed(DetailAST exprAst) {
-        return TokenUtil.isOfType(exprAst.getParent(),
-                TokenTypes.ELIST, TokenTypes.INDEX_OP, TokenTypes.ASSIGN)
+        return TokenUtil.isOfType(exprAst.getParent(), INCREMENT_DECREMENT_VARIABLE_USAGE_TYPES)
                 && exprAst.getParent().getParent().getType() != TokenTypes.FOR_ITERATOR;
     }
 

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

@@ -360,6 +360,34 @@ public void testUnusedLocalVariableTernaryAndExpressions() throws Exception {
                 expected);
     }
 
+    @Test
+    public void testUnusedLocalVariableSwitchStatement() throws Exception {
+        final String[] expected = CommonUtil.EMPTY_STRING_ARRAY;
+        verifyWithInlineConfigParser(
+                getPath("InputUnusedLocalVariableSwitchStatement.java"),
+                expected);
+    }
+
+    @Test
+    public void testUnusedLocalVariableSwitchStatement2() throws Exception {
+        final String[] expected = {
+            "58:9: " + getCheckMessage(MSG_UNUSED_LOCAL_VARIABLE, "j"),
+        };
+        verifyWithInlineConfigParser(
+                getPath("InputUnusedLocalVariableSwitchStatement2.java"),
+                expected);
+    }
+
+    @Test
+    public void testUnusedLocalVariableSwitchExpression() throws Exception {
+        final String[] expected = {
+            "15:9: " + getCheckMessage(MSG_UNUSED_LOCAL_VARIABLE, "line2"),
+        };
+        verifyWithInlineConfigParser(
+                getNonCompilablePath("InputUnusedLocalVariableSwitchExpression.java"),
+                expected);
+    }
+
     @Test
     public void testClearStateVariables() throws Exception {
         final UnusedLocalVariableCheck check = new UnusedLocalVariableCheck();

src/test/resources-noncompilable/com/puppycrawl/tools/checkstyle/checks/coding/unusedlocalvariable/InputUnusedLocalVariableSwitchExpression.java

@@ -0,0 +1,44 @@
+/*
+UnusedLocalVariable
+
+*/
+
+//non-compiled with javac: Compilable with Java14
+package com.puppycrawl.tools.checkstyle.checks.coding.unusedlocalvariable;
+
+public class InputUnusedLocalVariableSwitchExpression {
+
+    public int complexSwitch(int input) {
+        int check = 8;
+        int something = 0;
+        int line = 1;
+        int line2 = 9; // violation 'Unused local variable 'line2''
+        return switch (check++) {
+            case 0 -> {
+                int x = 2;
+                line2++;
+                yield switch (x) {
+                    case 1 -> x++;
+                    case 2 -> x--;
+                    default -> 0;
+                };
+            }
+            case 1 -> {
+                int y = input * 2;
+                yield switch (++line) {
+                    case 2, 4 -> y / 2;
+                    case 6 -> y - 1;
+                    default -> -1;
+                };
+            }
+            case 2 -> {
+                int checks = switch (something++) {
+                    case 1 -> input/2;
+                    default -> input;
+                };
+                yield checks;
+            }
+            default -> 0;
+        };
+    }
+}

src/test/resources/com/puppycrawl/tools/checkstyle/checks/coding/unusedlocalvariable/InputUnusedLocalVariableSwitchStatement.java

@@ -0,0 +1,101 @@
+/*
+UnusedLocalVariable
+
+*/
+
+package com.puppycrawl.tools.checkstyle.checks.coding.unusedlocalvariable;
+
+public class InputUnusedLocalVariableSwitchStatement {
+    public void testParameters0() {
+
+        int i = 0;
+        switch (i++) {
+            default:
+            case 0:
+                System.out.println("one: ");
+                break;
+            case 1:
+                System.out.println("two: " );
+                break;
+        }
+
+    }
+
+    public void testParameters01() {
+        int i = 0;
+        switch (++i) {
+            default:
+            case 0:
+                System.out.println("one: ");
+                break;
+            case 1:
+                System.out.println("two: " );
+                break;
+        }
+
+    }
+
+    public void testParameters() {
+        String[] tests = { "one", "two" };
+        int i = 0;
+        for (String test : tests) {
+            switch (i++) {
+                default:
+                case 0:
+                    System.out.println("one: " + test);
+                    break;
+                case 1:
+                    System.out.println("two: " + test);
+                    break;
+            }
+        }
+    }
+
+    public void testParameters2() {
+        String[] tests = { "one", "two" };
+        int i = 0;
+        for (String test : tests) {
+            switch (++i) {
+                default:
+                case 0:
+                    System.out.println("one: " + test);
+                    break;
+                case 1:
+                    System.out.println("two: " + test);
+                    break;
+            }
+        }
+    }
+
+    public void testParameters3() {
+        String[] tests = { "one", "two" };
+        int i = 0;
+        for (String test : tests) {
+            switch (--i) {
+                default:
+                case 0:
+                    System.out.println("one: " + test);
+                    break;
+                case 1:
+                    System.out.println("two: " + test);
+                    break;
+            }
+        }
+    }
+
+    public void testParameters4() {
+        String[] tests = { "one", "two" };
+        int i = 0;
+        for (String test : tests) {
+            switch (i--) {
+                default:
+                case 0:
+                    System.out.println("one: " + test);
+                    break;
+                case 1:
+                    System.out.println("two: " + test);
+                    break;
+            }
+        }
+    }
+}

src/test/resources/com/puppycrawl/tools/checkstyle/checks/coding/unusedlocalvariable/InputUnusedLocalVariableSwitchStatement2.java

@@ -0,0 +1,104 @@
+/*
+UnusedLocalVariable
+
+*/
+
+package com.puppycrawl.tools.checkstyle.checks.coding.unusedlocalvariable;
+
+public class InputUnusedLocalVariableSwitchStatement2 {
+    public void testParameters0() {
+
+        int i = 0;
+        switch (i+1) {
+            default:
+            case 0:
+                System.out.println("one: ");
+                break;
+            case 1:
+                System.out.println("two: " );
+                break;
+        }
+
+    }
+
+    public void testParameters01() {
+        int i = 0;
+        switch (1+i) {
+            default:
+            case 0:
+                System.out.println("one: ");
+                break;
+            case 1:
+                System.out.println("two: " );
+                break;
+        }
+
+    }
+
+    public void testParameters() {
+        String[] tests = { "one", "two" };
+        int i = 0;
+        for (String test : tests) {
+            switch (i+1) {
+                default:
+                case 0:
+                    System.out.println("one: " + test);
+                    break;
+                case 1:
+                    System.out.println("two: " + test);
+                    break;
+            }
+        }
+    }
+
+    public void testParameters2() {
+        String[] tests = { "one", "two" };
+        int i = 0;
+        i++;
+        int j = 0; // violation 'Unused local variable 'j''
+        for (String test : tests) {
+            switch (i) {
+                default:
+                case 0:
+                    j++;
+                    System.out.println("one: " + test);
+                    break;
+                case 1:
+                    System.out.println("two: " + test);
+                    break;
+            }
+        }
+    }
+
+    public void testParameters4() {
+        int i = 2;
+        int j = 1;
+        switch (j) {
+            case 1:
+                System.out.println("j is 1");
+                break;
+            case 2:
+                System.out.println("j is 2");
+                System.out.println("i is: " + i);
+                break;
+            default:
+                System.out.println("j is something else");
+        }
+    }
+
+    public void testParameters5() {
+        int i = 2;
+        int j = 1;
+        switch (++j) {
+            case 1:
+                System.out.println("j is 1");
+                break;
+            case 2:
+                System.out.println("j is 2");
+                System.out.println("i is: " + ++i);
+                break;
+            default:
+                System.out.println("j is something else");
+        }
+    }
+}