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SONARJAVA-5454 Implement S7467: replace Unused exception parameter with the unnamed pattern (#5087)
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Lines changed: 334 additions & 1 deletion

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‎its/autoscan/src/test/resources/autoscan/diffs/diff_S7467.json‎

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{
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"ruleKey": "S7467",
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"hasTruePositives": true,
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"falseNegatives": 0,
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"falsePositives": 0
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}

‎java-checks-test-sources/default/src/main/java/checks/ReplaceUnusedExceptionParameterWithUnnamedPatternCheckSample.java‎

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package checks;
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import io.restassured.exception.PathException;
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import java.util.List;
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import java.util.function.Supplier;
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public class ReplaceUnusedExceptionParameterWithUnnamedPatternCheckSample {
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public void simpleNonCompliant() {
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List<String> elements = List.of();
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int value = 0;
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try {
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var elem = elements.get(10);
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value = Integer.parseInt(elem);
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} catch (NumberFormatException nfe) { // Noncompliant {{Replace "nfe" with an unnamed pattern.}}
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// ^^^
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// fix@qf1 {{Replace "nfe" with "_"}}
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// edit@qf1 [[sc=36;ec=39]] {{_}}
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System.err.println("Wrong number format");
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} catch (IndexOutOfBoundsException ioob) { // Noncompliant {{Replace "ioob" with an unnamed pattern.}}
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// ^^^^
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// fix@qf2 {{Replace "ioob" with "_"}}
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// edit@qf2 [[sc=40;ec=44]] {{_}}
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System.err.println("No such element");
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}
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}
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public void simpleCompliant() {
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List<String> elements = List.of();
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int value = 0;
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try {
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var elem = elements.get(10);
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value = Integer.parseInt(elem);
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} catch (NumberFormatException _) { // compliant
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System.err.println("Wrong number format");
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} catch (IndexOutOfBoundsException _) { // compliant
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System.err.println("No such element");
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}
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}
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public void severalExceptionNonCompliant() {
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try {
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} catch (NumberFormatException | IndexOutOfBoundsException e) { // Noncompliant
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} catch (PathException | ClassCastException e) { // Noncompliant
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}
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}
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public void severalExceptionCompliant() {
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try {
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} catch (NumberFormatException | IndexOutOfBoundsException _) { // compliant
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} catch ( PathException | ClassCastException _) { // compliant
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}
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}
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public void nestedExceptionNonCompliant() {
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try {
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} catch (IndexOutOfBoundsException e) { // Noncompliant
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try {
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} catch (NumberFormatException k) { // Noncompliant
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try {
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} catch (PathException _) {
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}
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}
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}
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}
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public void codeInsideCatchBlockNonCompliant() {
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try {
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} catch (Exception e) { // Noncompliant
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int x = 0;
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foo(new RuntimeException());
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e();
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}
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}
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public void useExceptionCompliant() {
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try {
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} catch (Exception e) {
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var x = e;
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}
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try {
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} catch (Exception e) {
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foo(e);
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}
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try {
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} catch (Exception e) {
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throw e;
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}
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try {
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} catch (Exception e) {
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throw new RuntimeException(e);
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}
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try {
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} catch (Exception e) {
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var s = e.getStackTrace();
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}
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try {
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} catch (Exception e) {
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Supplier<Integer> s =() -> {
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var x = e;
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return 0;
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};
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}
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}
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public void foo(Exception e) {
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}
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public void e(){}
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}

‎java-checks-test-sources/default/src/main/java/checks/ReplaceUnusedExceptionParameterWithUnnamedPatternCheckSampleJava21.java‎

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package checks;
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import java.util.List;
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public class ReplaceUnusedExceptionParameterWithUnnamedPatternCheckSampleJava21 {
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public void simpleUnUsedParameter() {
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List<String> elements = List.of();
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int value = 0;
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try {
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var elem = elements.get(10);
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value = Integer.parseInt(elem);
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} catch (NumberFormatException nfe) { // compliant java 21
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System.err.println("Wrong number format");
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} catch (IndexOutOfBoundsException ioob) { // compliant java 21
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System.err.println("No such element");
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}
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}
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}

‎java-checks/src/main/java/org/sonar/java/checks/ReplaceUnusedExceptionParameterWithUnnamedPatternCheck.java‎

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/*
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* SonarQube Java
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* Copyright (C) 2012-2025 SonarSource SA
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* mailto:info AT sonarsource DOT com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the Sonar Source-Available License Version 1, as published by SonarSource SA.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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* See the Sonar Source-Available License for more details.
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*
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* You should have received a copy of the Sonar Source-Available License
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* along with this program; if not, see https://sonarsource.com/license/ssal/
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*/
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package org.sonar.java.checks;
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import java.util.List;
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import org.sonar.check.Rule;
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import org.sonar.java.checks.helpers.QuickFixHelper;
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import org.sonar.java.reporting.JavaQuickFix;
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import org.sonar.java.reporting.JavaTextEdit;
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import org.sonar.plugins.java.api.IssuableSubscriptionVisitor;
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import org.sonar.plugins.java.api.JavaVersion;
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import org.sonar.plugins.java.api.JavaVersionAwareVisitor;
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import org.sonar.plugins.java.api.tree.CatchTree;
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import org.sonar.plugins.java.api.tree.IdentifierTree;
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import org.sonar.plugins.java.api.tree.Tree;
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import org.sonar.plugins.java.api.tree.VariableTree;
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@Rule(key = "S7467")
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public class ReplaceUnusedExceptionParameterWithUnnamedPatternCheck extends IssuableSubscriptionVisitor implements JavaVersionAwareVisitor {
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@Override
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public List<Tree.Kind> nodesToVisit() {
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return List.of(Tree.Kind.CATCH);
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}
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@Override
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public void visitNode(Tree tree) {
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CatchTree catchTree = (CatchTree) tree;
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VariableTree v = catchTree.parameter();
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IdentifierTree ident = v.simpleName();
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if (!ident.isUnnamedVariable() && v.symbol().usages().isEmpty()) {
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QuickFixHelper.newIssue(context)
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.forRule(this)
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.onTree(ident)
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.withMessage(String.format("Replace \"%s\" with an unnamed pattern.", ident.name()))
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.withQuickFix(() -> getQuickFix(ident))
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.report();
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}
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}
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@Override
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public boolean isCompatibleWithJavaVersion(JavaVersion version) {
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return version.isJava22Compatible();
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}
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private static JavaQuickFix getQuickFix(IdentifierTree ident) {
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return JavaQuickFix.newQuickFix(String.format("Replace \"%s\" with unnamed pattern \"_\"", ident.name()))
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.addTextEdit(JavaTextEdit.replaceTree(ident, "_"))
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.build();
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}
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}

‎java-checks/src/test/java/org/sonar/java/checks/ReplaceUnusedExceptionParameterWithUnnamedPatternCheckTest.java‎

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/*
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* SonarQube Java
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* Copyright (C) 2012-2025 SonarSource SA
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* mailto:info AT sonarsource DOT com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the Sonar Source-Available License Version 1, as published by SonarSource SA.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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* See the Sonar Source-Available License for more details.
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*
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* You should have received a copy of the Sonar Source-Available License
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* along with this program; if not, see https://sonarsource.com/license/ssal/
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*/
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package org.sonar.java.checks;
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import org.junit.jupiter.api.Test;
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import org.sonar.java.checks.verifier.CheckVerifier;
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import static org.sonar.java.checks.verifier.TestUtils.mainCodeSourcesPath;
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class ReplaceUnusedExceptionParameterWithUnnamedPatternCheckTest {
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@Test
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void test_java22() {
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CheckVerifier.newVerifier()
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.onFile(mainCodeSourcesPath("checks/ReplaceUnusedExceptionParameterWithUnnamedPatternCheckSample.java"))
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.withCheck(new ReplaceUnusedExceptionParameterWithUnnamedPatternCheck())
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.withJavaVersion(22)
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.verifyIssues();
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}
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@Test
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void test_java21() {
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CheckVerifier.newVerifier()
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.onFile(mainCodeSourcesPath("checks/ReplaceUnusedExceptionParameterWithUnnamedPatternCheckSampleJava21.java"))
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.withCheck(new ReplaceUnusedExceptionParameterWithUnnamedPatternCheck())
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.withJavaVersion(21)
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.verifyNoIssues();
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}
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@Test
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void test_without_semantics() {
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CheckVerifier.newVerifier()
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.onFile(mainCodeSourcesPath("checks/ReplaceUnusedExceptionParameterWithUnnamedPatternCheckSample.java"))
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.withCheck(new ReplaceUnusedExceptionParameterWithUnnamedPatternCheck())
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.withoutSemantic()
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.withJavaVersion(22)
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.verifyIssues();
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}
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}

‎sonar-java-plugin/src/main/resources/org/sonar/l10n/java/rules/java/S7467.html‎

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<h2>Why is this an issue?</h2>
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<p>Good exception management is key to keeping a consistent application state in the face of errors and unexpected behaviors. However, in some cases,
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the information carried by the exception is not as important as the exception bubbling up itself. In such cases, developers may want to explicitly
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indicate that they have no use for the exception parameter. Java 22 introduces the unnamed variable pattern <code>_</code> which allows developers to
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free the catch clause from an unnecessary exception parameter name.</p>
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<h2>How to fix it</h2>
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<p>Replace exception parameter name with unnamed variable pattern <code>_</code>.</p>
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<h3>Code examples</h3>
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<h4>Noncompliant code example</h4>
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<pre data-diff-id="1" data-diff-type="noncompliant">
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List&lt;String&gt; elements = // ...
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int value = 0;
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try {
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var elem = elements.get(idx);
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value = Integer.parseInt(elem);
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} catch (NumberFormatException nfe) { // Noncompliant
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System.err.println("Wrong number format");
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} catch (IndexOutOfBoundsException ioob) { // Noncompliant
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System.err.println("No such element");
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}
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</pre>
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<h4>Compliant solution</h4>
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<pre data-diff-id="1" data-diff-type="compliant">
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List&lt;String&gt; elements = // ...
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int value = 0;
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try {
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var elem = elements.get(idx);
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value = Integer.parseInt(elem);
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} catch (NumberFormatException _) {
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System.err.println("Wrong number format");
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} catch (IndexOutOfBoundsException _) {
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System.err.println("No such element");
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}
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</pre>
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<h2>Resources</h2>
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<h3>Documentation</h3>
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<ul>
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<li> OpenJDK - <a href="https://openjdk.org/jeps/456">JEP 456: Unnamed Variables &amp; Patterns</a> </li>
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</ul>
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‎sonar-java-plugin/src/main/resources/org/sonar/l10n/java/rules/java/S7467.json‎

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{
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"title": "Unused exception parameter should use the unnamed variable pattern",
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"type": "CODE_SMELL",
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"status": "ready",
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"remediation": {
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"func": "Constant\/Issue",
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"constantCost": "2min"
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},
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"tags": [
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"java22"
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],
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"defaultSeverity": "Minor",
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"ruleSpecification": "RSPEC-7467",
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"sqKey": "S7467",
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"scope": "All",
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"quickfix": "targeted",
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"code": {
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"impacts": {
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"MAINTAINABILITY": "LOW"
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},
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"attribute": "CLEAR"
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}
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}

‎sonar-java-plugin/src/main/resources/org/sonar/l10n/java/rules/java/Sonar_way_profile.json‎

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"S7190",
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"S7409",
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"S7435",
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"S7466"
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"S7466",
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"S7467"
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]
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}

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