SONARJAVA-5754 : Increment and decrement operators (++/--) should not be used with floating point variables (#5371)

Author: rombirli

its/autoscan/src/test/resources/autoscan/diffs/diff_S8346.json

@@ -0,0 +1,6 @@
+{
+  "ruleKey": "S8346",
+  "hasTruePositives": true,
+  "falseNegatives": 0,
+  "falsePositives": 0
+}

its/ruling/src/test/resources/commons-beanutils/java-S8346.json

@@ -0,0 +1,5 @@
+{
+"commons-beanutils:commons-beanutils:src/main/java/org/apache/commons/beanutils2/MethodUtils.java": [
+1136
+]
+}

its/ruling/src/test/resources/sonar-server/java-S8346.json

@@ -0,0 +1,5 @@
+{
+"org.sonarsource.sonarqube:sonar-server:src/test/java/org/sonar/server/measure/ws/ComponentTreeSortTest.java": [
+85
+]
+}

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

@@ -0,0 +1,71 @@
+/*
+ * 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 java.util.Optional;
+import org.sonar.check.Rule;
+import org.sonar.plugins.java.api.IssuableSubscriptionVisitor;
+import org.sonar.plugins.java.api.semantic.Type;
+import org.sonar.plugins.java.api.semantic.Type.Primitives;
+import org.sonar.plugins.java.api.tree.IdentifierTree;
+import org.sonar.plugins.java.api.tree.Tree;
+import org.sonar.plugins.java.api.tree.UnaryExpressionTree;
+
+@Rule(key = "S8346")
+public class IncDecOnFloatingPointCheck extends IssuableSubscriptionVisitor {
+
+  @Override
+  public List<Tree.Kind> nodesToVisit() {
+    return List.of(
+      Tree.Kind.POSTFIX_INCREMENT,
+      Tree.Kind.PREFIX_INCREMENT,
+      Tree.Kind.POSTFIX_DECREMENT,
+      Tree.Kind.PREFIX_DECREMENT
+    );
+  }
+
+  @Override
+  public void visitNode(Tree tree) {
+    Optional.of(tree)
+      .filter(UnaryExpressionTree.class::isInstance)
+      .map(UnaryExpressionTree.class::cast)
+      .filter(unaryExpr ->
+        unaryExpr.expression() instanceof IdentifierTree identifierTree
+          && isFloatingPoint(identifierTree.symbolType())
+      )
+      .ifPresent(unaryExpr -> reportIssue(
+        unaryExpr,
+        "%s operator (%s) should not be used with floating point variables".formatted(
+          isIncrement(unaryExpr) ? "Increment" : "Decrement",
+          unaryExpr.operatorToken().text()
+        )
+      ));
+  }
+
+
+  private static boolean isFloatingPoint(Type type) {
+    return type.isPrimitive(Primitives.FLOAT) || type.isPrimitive(Primitives.DOUBLE);
+  }
+
+  private static boolean isIncrement(UnaryExpressionTree unaryExp) {
+    return unaryExp.is(
+      Tree.Kind.PREFIX_INCREMENT,
+      Tree.Kind.POSTFIX_INCREMENT
+    );
+  }
+}

java-checks/src/test/files/checks/IncDecOnFloatingPointCheck.java

@@ -0,0 +1,100 @@
+class A {
+  void specNonCompliantExamples() {
+    for (float i = 16_000_000; i < 17_000_000; i++) { // Noncompliant {{Increment operator (++) should not be used with floating point variables}}
+//                                             ^^^
+      // ...
+    }
+
+
+    float x = 0f;
+    double y = 1.0;
+
+    x++; // Noncompliant {{Increment operator (++) should not be used with floating point variables}}
+//  ^^^
+    y--; // Noncompliant {{Decrement operator (--) should not be used with floating point variables}}
+//  ^^^
+  }
+
+  void specCompliantExamples() {
+    for (int i = 16_000_000; i < 17_000_000; i++) { // Compliant
+      // ...
+    }
+
+    float x = 0f;
+    double y = 1.0;
+
+    x += 1.0; // Compliant
+    y -= 1.0; // Compliant
+  }
+
+  void floatIsNotCompliant() {
+    float y = 0.1f;
+    y++; // Noncompliant {{Increment operator (++) should not be used with floating point variables}}
+//  ^^^
+    ++y; // Noncompliant {{Increment operator (++) should not be used with floating point variables}}
+//  ^^^
+    y--; // Noncompliant {{Decrement operator (--) should not be used with floating point variables}}
+//  ^^^
+    --y; // Noncompliant {{Decrement operator (--) should not be used with floating point variables}}
+//  ^^^
+  }
+
+  void doubleIsNotCompliant() {
+    double y = 0.1;
+    y++; // Noncompliant {{Increment operator (++) should not be used with floating point variables}}
+//  ^^^
+    ++y; // Noncompliant {{Increment operator (++) should not be used with floating point variables}}
+//  ^^^
+    y--; // Noncompliant {{Decrement operator (--) should not be used with floating point variables}}
+//  ^^^
+    --y; // Noncompliant {{Decrement operator (--) should not be used with floating point variables}}
+//  ^^^
+  }
+
+  void intIsCompliant() {
+    int z = 0;
+    z++; // Compliant
+    ++z; // Compliant
+    z--; // Compliant
+    --z; // Compliant
+  }
+
+  void longIsCompliant() {
+    long w = 0L;
+    w++; // Compliant
+    ++w; // Compliant
+    w--; // Compliant
+    --w; // Compliant
+  }
+
+  void charIsCompliant() {
+    char c = 'a';
+    c++; // Compliant
+    ++c; // Compliant
+    c--; // Compliant
+    --c; // Compliant
+  }
+
+  void otherOperatorsNotAffected() {
+    float f = 1f;
+    // test unary operator -
+    float g = -f; // compliant
+    // test binary operators just in case
+    float h = f + 1f; // compliant
+  }
+
+  // variable shadowing test
+  private double d = 3.4;
+
+  void variableShadowingTestCompliant() {
+    for (int d = 0; d < 10; d++) { // Compliant
+    }
+  }
+  // variable shadowing test
+  private int i = 3;
+
+  void variableShadowingTestCompliant() {
+    for (float i = 0; i < 10; i++) { // Noncompliant {{Increment operator (++) should not be used with floating point variables}}
+    }
+  }
+}

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

@@ -0,0 +1,40 @@
+/*
+ * 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;
+
+class IncDecOnFloatingPointCheckTest {
+
+  @Test
+  void test() {
+    CheckVerifier.newVerifier()
+      .onFile("src/test/files/checks/IncDecOnFloatingPointCheck.java")
+      .withCheck(new IncDecOnFloatingPointCheck())
+      .verifyIssues();
+  }
+
+  @Test
+  void testNoSemantic() {
+    CheckVerifier.newVerifier()
+      .withoutSemantic()
+      .onFile("src/test/files/checks/IncDecOnFloatingPointCheck.java")
+      .withCheck(new IncDecOnFloatingPointCheck())
+      .verifyIssues();
+  }
+}

sonar-java-plugin/src/main/resources/org/sonar/l10n/java/rules/java/S8346.html

@@ -0,0 +1,43 @@
+<p>This rule raises an issue when increment (<code>++</code>) or decrement (<code>--</code>) operators are used with floating-point variables.</p>
+<h2>Why is this an issue?</h2>
+<p>Increment and decrement operators (<code>++</code> and <code>--</code>) shouldn’t be used with floating-point variables (like <code>float</code> or
+<code>double</code>). While the language allows it, the usage is not idiomatic, and most developers intuitively expect <code>x++</code> to apply to
+integer types. Using it on a float violates this common expectation and can lead to misleading code.</p>
+<h3>What is the potential impact?</h3>
+<p>Floating-point arithmetic has some non-intuitive properties, which can lead to unexpected bugs. For example, the following loop will not terminate.
+This happens because <code>float</code> has only 24 bits of precision (mantissa) and once a number gets large enough, adding <code>1.0</code> becomes
+insignificant and the increment operation does nothing:</p>
+<pre>
+for (float x = 16_000_000; x &lt; 17_000_000; x++) {
+  // ...
+}
+// The loop does not terminate
+</pre>
+<p>The problem would not occur if <code>int</code> is used instead of <code>float</code>, even though both types occupy 32 bits:</p>
+<pre>
+for (int x = 16_000_000; x &lt; 17_000_000; x++) {
+  // ...
+}
+// This loop terminates.
+</pre>
+<h2>How to fix it</h2>
+<p>Using the compound assignment operators (<code>+=</code> and <code>-=</code>) makes the intent clearer and avoids the surprising use of
+<code>++</code> and <code>--</code> on floating-point types.</p>
+<h3>Code examples</h3>
+<h4>Noncompliant code example</h4>
+<pre>
+float x = 0f;
+double y = 1.0;
+
+x++;
+y--;
+</pre>
+<h4>Compliant solution</h4>
+<pre>
+float x = 0f;
+double y = 1.0;
+
+x += 1.0;
+y -= 1.0;
+</pre>
+

sonar-java-plugin/src/main/resources/org/sonar/l10n/java/rules/java/S8346.json

@@ -0,0 +1,22 @@
+{
+  "title": "Increment and decrement operators (++\/--) should not be used with floating point variables",
+  "type": "CODE_SMELL",
+  "status": "ready",
+  "remediation": {
+    "func": "Constant\/Issue",
+    "constantCost": "5min"
+  },
+  "tags": [],
+  "defaultSeverity": "Major",
+  "ruleSpecification": "RSPEC-8346",
+  "sqKey": "S8346",
+  "scope": "All",
+  "quickfix": "targeted",
+  "code": {
+    "impacts": {
+      "MAINTAINABILITY": "HIGH",
+      "RELIABILITY": "MEDIUM"
+    },
+    "attribute": "CONVENTIONAL"
+  }
+}

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

@@ -516,6 +516,7 @@
     "S7479",
     "S7481",
     "S7482",
-    "S7629"
+    "S7629",
+    "S8346"
   ]
 }