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SONARJAVA-5483 implement S7475: RemoveTypeFromUnusedPatternCheck (#5093)
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Lines changed: 327 additions & 1 deletion

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‎its/autoscan/src/test/resources/autoscan/diffs/diff_S7475.json‎

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{
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"ruleKey": "S7475",
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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/RemoveTypeFromUnusedPatternCheckSample.java‎

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package checks;
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import java.util.List;
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public class RemoveTypeFromUnusedPatternCheckSample {
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record Guest(String name, String email, String phoneNumber) {
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}
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record Bar(String a, int b){}
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record Foo(String a, Bar b){}
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void nonCompliantExamples(Object o) {
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if (o instanceof Guest(String name, String _, String phoneNumber)) { // Noncompliant
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}
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if(o instanceof Foo(String _, Bar b)){ // Noncompliant {{Remove unused type from unnamed pattern}}
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// ^^^^^^^^
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// fix@qf1 {{Remove unused type}}
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// edit@qf1 [[sc=25;ec=31]] {{}}
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if(b instanceof Bar(String a, int _)){} // Noncompliant {{Remove unused type from unnamed pattern}}
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}
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if(o instanceof Foo(String s, Bar(String _, int b))) { // Noncompliant
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}
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String s1 = switch (o) {
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case Guest(String name, String _, String phoneNumber) -> "Hello " + name + "!"; // Noncompliant
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default -> "Hello!";
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};
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String s2 = switch (o) {
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case Bar(String s, int _) when s.isEmpty() -> ""; // Noncompliant
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// ^^^^^
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// fix@qf1 {{Remove unused type}}
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// edit@qf1 [[sc=26;ec=29]] {{}}
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default -> "Hello!";
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};
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String s3 = switch (o) {
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case Foo(String s, Bar b) when b instanceof Bar(String v, int _) -> ""; // Noncompliant
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default -> "Hello!";
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};
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String s4 = switch (o) {
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case Foo(String s, Bar(String _, int b)) -> ""; // Noncompliant
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default -> "Hello!";
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};
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}
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record Primitives(double a, float b, int c, long d, float e, boolean g){}
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record ClassTypes(Object simple, List<Integer> parametrize, int[] array, List<List<Integer>> nested, List<?> wildcard){}
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record ParametrizeClass<A>(List<A> a){}
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void nonCompliantDifferentTypes(Object o){
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if(o instanceof Primitives(double _, float a, int b, long c, float d, boolean f)){} // Noncompliant
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// ^^^^^^^^
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if(o instanceof Primitives(double a, float _, int b, long c, float d, boolean f)){} // Noncompliant
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// ^^^^^^^
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if(o instanceof Primitives(double a, float b, int _, long c, float d, boolean f)){} // Noncompliant
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// ^^^^^
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if(o instanceof Primitives(double a, float b, int c, long _, float d, boolean f)){} // Noncompliant
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// ^^^^^^
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if(o instanceof Primitives(double a, float b, int c, long d, float _, boolean f)){} // Noncompliant
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// ^^^^^^^
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if(o instanceof Primitives(double a, float b, int c, long d, float e, boolean _)){} // Noncompliant
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// ^^^^^^^^^
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if(o instanceof ClassTypes(Object _, List<Integer> parametrize, int[] array, List<List<Integer>> nested, List<?> wildcard)){} // Noncompliant
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// ^^^^^^^^
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if(o instanceof ClassTypes(Object simple, List<Integer> _, int[] array, List<List<Integer>> nested, List<?> wildcard)){} // Noncompliant
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// ^^^^^^^^^^^^^^^
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if(o instanceof ClassTypes(Object simple, List<Integer> parametrize, int[] _, List<List<Integer>> nested, List<?> wildcard)){} // Noncompliant
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// ^^^^^^^
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if(o instanceof ClassTypes(Object simple, List<Integer> parametrize, int[] array, List<List<Integer>> _, List<?> wildcard)){} // Noncompliant
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// ^^^^^^^^^^^^^^^^^^^^^
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if(o instanceof ClassTypes(Object simple, List<Integer> parametrize, int[] array, List<List<Integer>> nested, List<?> _)){} // Noncompliant
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// ^^^^^^^^^
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if(o instanceof ParametrizeClass(var _)){} // Noncompliant
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// ^^^^^
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}
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void compliantExamples(Object o) {
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if (o instanceof Guest(String name, _, _)) { // compliant
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}
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if(o instanceof Foo(_, Bar b)){ // compliant
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if(b instanceof Bar(String a, _)){} // compliant
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}
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if(o instanceof Foo(String s, Bar(_, int b))) { // compliant
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}
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String s1 = switch (o) {
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case Guest(String name, _, _) -> "Hello " + name + "!"; // compliant
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default -> "Hello!";
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};
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String s2 = switch (o) {
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case Foo(String s, Bar(_, int b)) -> ""; // compliant
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default -> "Hello!";
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};
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}
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}

‎java-checks-test-sources/default/src/main/java/checks/RemoveTypeFromUnusedPatternCheck_Java21.java‎

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package checks;
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public class RemoveTypeFromUnusedPatternCheck_Java21 {
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record Guest(String name, String email, String phoneNumber) {
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}
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public void foo(Object o){
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if(o instanceof Guest(String name, String email, String phoneNumber)){} // compliant not java 22
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}
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}

‎java-checks/src/main/java/org/sonar/java/checks/RemoveTypeFromUnusedPatternCheck.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.InferedTypeTree;
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import org.sonar.plugins.java.api.tree.PatternTree;
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import org.sonar.plugins.java.api.tree.RecordPatternTree;
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import org.sonar.plugins.java.api.tree.Tree;
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import org.sonar.plugins.java.api.tree.TypePatternTree;
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import org.sonar.plugins.java.api.tree.TypeTree;
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import org.sonar.plugins.java.api.tree.VariableTree;
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@Rule(key = "S7475")
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public class RemoveTypeFromUnusedPatternCheck 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.RECORD_PATTERN);
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}
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@Override
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public void visitNode(Tree tree) {
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RecordPatternTree pattern = (RecordPatternTree) tree;
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for (PatternTree patternTree : pattern.patterns()) {
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if (patternTree instanceof TypePatternTree pat
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&& pat.patternVariable().simpleName().isUnnamedVariable()
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&& !typeIsMissing(pat.patternVariable())) {
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QuickFixHelper.newIssue(context)
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.forRule(this)
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.onTree(pat.patternVariable())
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.withMessage("Remove unused type from unnamed pattern")
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.withQuickFix(() -> getQuickFix(pat.patternVariable().type()))
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.report();
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}
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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(TypeTree tree) {
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return JavaQuickFix.newQuickFix("Remove unused type")
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.addTextEdit(JavaTextEdit.removeTree(tree))
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.build();
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}
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private static boolean typeIsMissing(VariableTree v) {
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return v.type() instanceof InferedTypeTree;
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}
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}

‎java-checks/src/test/java/org/sonar/java/checks/RemoveTypeFromUnusedPatternCheckTest.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 RemoveTypeFromUnusedPatternCheckTest {
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@Test
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void test() {
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CheckVerifier.newVerifier()
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.onFile(mainCodeSourcesPath("checks/RemoveTypeFromUnusedPatternCheckSample.java"))
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.withCheck(new RemoveTypeFromUnusedPatternCheck())
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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/RemoveTypeFromUnusedPatternCheck_Java21.java"))
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.withCheck(new RemoveTypeFromUnusedPatternCheck())
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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_semantic() {
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CheckVerifier.newVerifier()
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.onFile(mainCodeSourcesPath("checks/RemoveTypeFromUnusedPatternCheckSample.java"))
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.withCheck(new RemoveTypeFromUnusedPatternCheck())
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.withJavaVersion(22)
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.withoutSemantic()
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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/S7475.html‎

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<h2>Why is this an issue?</h2>
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<p>When using pattern matching on records, matching is done against the canonical constructor of the record. This implies listing all the components
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in the canonical constructor even if some are unused. To make the intent of not using the component clear, Java 22 introduced the unnamed variable
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pattern <code>_</code>.</p>
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<p>Because we can only pattern match against the canonical constructor, there is no need to disambiguate by specifying the types of its parameters.
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Therefore, the type of unused variables in pattern matching should be omitted, as it does not bring additional value.</p>
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<h2>How to fix it</h2>
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<p>Remove the type of the unused component.</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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record Guest(String name, String email, String phoneNumber) {}
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String greet(Object o) {
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if (o instanceof Guest(String name, String _, String _)) { // Noncompliant
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return "Hello " + name + "!";
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}
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return "Hello!";
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}
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String switchToGreet(Object o) {
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return switch (o) {
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case Guest(String name, String _, String _) -&gt; "Hello " + name + "!"; // Noncompliant
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default -&gt; "Hello!";
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};
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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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record Guest(String name, String email, String phoneNumber) {}
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String greet(Object o) {
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if (o instanceof Guest(String name, _, _)) {
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return "Hello " + name + "!";
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}
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return "Hello!";
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}
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String switchToGreet(Object o) {
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return switch (o) {
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case Guest(String name, _, _) -&gt; "Hello " + name + "!";
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default -&gt; "Hello!";
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};
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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> <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/S7475.json‎

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{
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"title": "Types of unused record components should be removed from pattern matching",
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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": "5min"
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},
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"tags": [
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"java22",
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"unused"
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],
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"defaultSeverity": "Info",
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"ruleSpecification": "RSPEC-7475",
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"sqKey": "S7475",
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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": "INFO"
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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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"S7409",
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"S7435",
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"S7466",
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"S7467"
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"S7467",
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"S7475"
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]
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}

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