SONARJAVA-6104 S8469 Use IO.readln(String prompt) instead of IO.print(Object obj) followed by IO.readln() (#5491)

Author: aurelien-coet-sonarsource

its/autoscan/src/test/java/org/sonar/java/it/AutoScanTest.java

@@ -199,7 +199,7 @@ public void javaCheckTestSources() throws Exception {
     softly.assertThat(newDiffs).containsExactlyInAnyOrderElementsOf(knownDiffs.values());
     softly.assertThat(newTotal).isEqualTo(knownTotal);
     softly.assertThat(rulesCausingFPs).hasSize(10);
-    softly.assertThat(rulesNotReporting).hasSize(19);
+    softly.assertThat(rulesNotReporting).hasSize(20);
 
     /**
      * 4. Check total number of differences (FPs + FNs)

its/autoscan/src/test/resources/autoscan/autoscan-diff-by-rules.json

@@ -2902,5 +2902,11 @@
     "hasTruePositives": true,
     "falseNegatives": 0,
     "falsePositives": 0
+  },
+  {
+    "ruleKey": "S8469",
+    "hasTruePositives": false,
+    "falseNegatives": 0,
+    "falsePositives": 0
   }
 ]

its/autoscan/src/test/resources/autoscan/diffs/diff_S8469.json

@@ -0,0 +1,6 @@
+{
+  "ruleKey": "S8469",
+  "hasTruePositives": false,
+  "falseNegatives": 0,
+  "falsePositives": 0
+}

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

@@ -0,0 +1,38 @@
+package checks;
+
+public class ReadlnWithPromptCheckSample {
+
+  private static final String text = IO.readln("Enter your name: "); // Compliant
+
+  void nonCompliant() {
+    IO.print("Enter your name: ");
+    String name = IO.readln(); // Noncompliant {{Use "IO.readln(String prompt)" instead of separate "IO.print(Object obj)" and "IO.readln()" calls.}}
+//                ^^^^^^^^^^^
+    IO.print(name);
+
+    IO.println("Enter your age: ");
+    String age = IO.readln(); // Noncompliant {{Use "IO.readln(String prompt)" instead of separate "IO.println(Object obj)" and "IO.readln()" calls.}}
+//               ^^^^^^^^^^^
+    IO.print(age);
+
+    IO.print("Enter city: ");
+    IO.readln(); // Noncompliant {{Use "IO.readln(String prompt)" instead of separate "IO.print(Object obj)" and "IO.readln()" calls.}}
+//  ^^^^^^^^^^^
+  }
+
+  void compliant() {
+    IO.readln(); // Compliant
+
+    String name = IO.readln("Enter your name: "); // Compliant
+
+    IO.println("Welcome!");
+    String input = IO.readln("Please state your name:"); // Compliant
+
+    IO.println();
+    IO.readln(); // Compliant
+
+    IO.print("Enter email: ");
+    int x = 5;
+    String email = IO.readln(); // Compliant
+  }
+}

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

@@ -0,0 +1,83 @@
+/*
+ * SonarQube Java
+ * Copyright (C) 2012-2025 SonarSource Sàrl
+ * mailto:info AT sonarsource DOT com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the Sonar Source-Available License Version 1, as published by SonarSource SA.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the Sonar Source-Available License for more details.
+ *
+ * You should have received a copy of the Sonar Source-Available License
+ * along with this program; if not, see https://sonarsource.com/license/ssal/
+ */
+package org.sonar.java.checks;
+
+import java.util.List;
+import org.sonar.check.Rule;
+import org.sonar.java.checks.methods.AbstractMethodDetection;
+import org.sonar.plugins.java.api.JavaVersion;
+import org.sonar.plugins.java.api.JavaVersionAwareVisitor;
+import org.sonar.plugins.java.api.semantic.MethodMatchers;
+import org.sonar.plugins.java.api.tree.BlockTree;
+import org.sonar.plugins.java.api.tree.ExpressionStatementTree;
+import org.sonar.plugins.java.api.tree.MethodInvocationTree;
+import org.sonar.plugins.java.api.tree.StatementTree;
+import org.sonar.plugins.java.api.tree.Tree;
+
+@Rule(key = "S8469")
+public class ReadlnWithPromptCheck extends AbstractMethodDetection implements JavaVersionAwareVisitor {
+
+  private static final String MESSAGE = "Use \"IO.readln(String prompt)\" instead of separate \"IO.%s(Object obj)\" and \"IO.readln()\" calls.";
+
+  private static final MethodMatchers PRINT_MATCHERS = MethodMatchers.create()
+    .ofTypes("java.lang.IO")
+    .names("print", "println")
+    .addParametersMatcher("java.lang.Object")
+    .build();
+
+  private static final MethodMatchers READLN_MATCHER = MethodMatchers.create()
+    .ofTypes("java.lang.IO")
+    .names("readln")
+    .addWithoutParametersMatcher()
+    .build();
+
+  @Override
+  public boolean isCompatibleWithJavaVersion(JavaVersion version) {
+    return version.isJava25Compatible();
+  }
+
+  @Override
+  protected MethodMatchers getMethodInvocationMatchers() {
+    return READLN_MATCHER;
+  }
+
+  @Override
+  protected void onMethodInvocationFound(MethodInvocationTree mit) {
+    Tree parent = mit.parent();
+    Tree grandParent = parent.parent();
+    if (grandParent == null || !grandParent.is(Tree.Kind.BLOCK)) {
+      return;
+    }
+
+    BlockTree block = (BlockTree) grandParent;
+    List<StatementTree> statements = block.body();
+
+    int currentIndex = statements.indexOf(parent);
+    if (currentIndex <= 0) {
+      return;
+    }
+
+    StatementTree previousStatement = statements.get(currentIndex - 1);
+    if (previousStatement instanceof ExpressionStatementTree exprStmt
+      && exprStmt.expression() instanceof MethodInvocationTree previousCall
+      && PRINT_MATCHERS.matches(previousCall)) {
+      String message = String.format(MESSAGE, previousCall.methodSymbol().name());
+      reportIssue(mit, message);
+    }
+  }
+
+}

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

@@ -0,0 +1,44 @@
+/*
+ * SonarQube Java
+ * Copyright (C) 2012-2025 SonarSource Sàrl
+ * mailto:info AT sonarsource DOT com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the Sonar Source-Available License Version 1, as published by SonarSource SA.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the Sonar Source-Available License for more details.
+ *
+ * You should have received a copy of the Sonar Source-Available License
+ * along with this program; if not, see https://sonarsource.com/license/ssal/
+ */
+package org.sonar.java.checks;
+
+import org.junit.jupiter.api.Test;
+import org.sonar.java.checks.verifier.CheckVerifier;
+
+import static org.sonar.java.checks.verifier.TestUtils.mainCodeSourcesPath;
+
+class ReadlnWithPromptCheckTest {
+
+  @Test
+  void test() {
+    CheckVerifier.newVerifier()
+      .onFile(mainCodeSourcesPath("checks/ReadlnWithPromptCheckSample.java"))
+      .withCheck(new ReadlnWithPromptCheck())
+      .withJavaVersion(25)
+      .verifyIssues();
+  }
+
+  @Test
+  void test_java24() {
+    CheckVerifier.newVerifier()
+      .onFile(mainCodeSourcesPath("checks/ReadlnWithPromptCheckSample.java"))
+      .withCheck(new ReadlnWithPromptCheck())
+      .withJavaVersion(24)
+      .verifyNoIssues();
+  }
+
+}

sonar-java-plugin/src/main/resources/org/sonar/l10n/java/rules/java/S8469.html

@@ -0,0 +1,36 @@
+<p>The <code>java.io.IO</code> class in Java 25+ (introduced via JEP 512) provides a simplified interface for console interaction. It is common to see
+code that prints a message to the console using <code>IO.print(Object obj)</code> or <code>IO.println(Object obj)</code> and then immediately calls
+<code>IO.readln()</code> to wait for user input. This sequence should be replaced with the single call <code>IO.readln(String prompt)</code>.</p>
+<h2>Why is this an issue?</h2>
+<p>Using the prompt-aware overload is more idiomatic, reduces boilerplate, and explicitly links the prompt text to the input request in a single
+operation.</p>
+<h2>How to fix it</h2>
+<p>Remove calls to <code>IO.print(Object obj)</code> or <code>IO.println(Object obj)</code> directly followed <code>IO.readln()</code> with a single
+call to <code>IO.readln(String prompt)</code>.</p>
+<h3>Code examples</h3>
+<h4>Noncompliant code example</h4>
+<pre data-diff-id="1" data-diff-type="noncompliant">
+// Compact source file
+void main() {
+    // Non-compliant: manual prompt followed by readln() with no arguments
+    IO.print("Please enter your username: ");
+    String user = IO.readln();
+    IO.println("Welcome, " + user);
+}
+</pre>
+<h4>Compliant solution</h4>
+<pre data-diff-id="1" data-diff-type="compliant">
+// Compact source file
+void main() {
+    // Compliant: The prompt is directly passed to the readln method
+    String user = IO.readln("Please enter your username: ");
+    IO.println("Welcome, " + user);
+}
+</pre>
+<h2>Resources</h2>
+<h3>Documentation</h3>
+<ul>
+  <li><a href="https://openjdk.org/jeps/512">OpenJDK - JEP 512</a></li>
+  <li><a href="https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/IO.html">Java 25 API Documentation - java.io.IO</a></li>
+</ul>
+

sonar-java-plugin/src/main/resources/org/sonar/l10n/java/rules/java/S8469.json

@@ -0,0 +1,21 @@
+{
+  "title": "Prefer \"IO.readln(String prompt)\" rather than \"IO.print(Object obj)\" or \"IO.println(Object obj)\" followed by \"IO.readln()\"",
+  "type": "CODE_SMELL",
+  "status": "ready",
+  "remediation": {
+    "func": "Constant\/Issue",
+    "constantCost": "5min"
+  },
+  "tags": [],
+  "defaultSeverity": "Minor",
+  "ruleSpecification": "RSPEC-8469",
+  "sqKey": "S8469",
+  "scope": "All",
+  "quickfix": "unknown",
+  "code": {
+    "impacts": {
+      "MAINTAINABILITY": "LOW"
+    },
+    "attribute": "CONVENTIONAL"
+  }
+}

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

@@ -526,6 +526,7 @@
     "S8446",
     "S8447",
     "S8450",
-    "S8465"
+    "S8465",
+    "S8469"
   ]
 }