SONARJAVA-5430 Check Java version in case of foreach variable (#5091)

The quickfix will only work starting with Java 22.
We should not raise an issue before that.

Author: romainbrenguier

its/autoscan/src/test/resources/autoscan/diffs/diff_S1128.json

@@ -1,6 +1,6 @@
 {
   "ruleKey": "S1128",
   "hasTruePositives": true,
-  "falseNegatives": 36,
+  "falseNegatives": 33,
   "falsePositives": 0
 }

java-checks-test-sources/default/src/main/java/checks/unused/UnusedLocalVariableCheck.java

@@ -1,32 +1,12 @@
 package checks.unused;
 
-import org.hibernate.validator.internal.engine.validationcontext.ValidatorScopedContext;
-
-import java.util.Arrays;
-import java.util.List;
 import java.util.Queue;
 import java.util.function.BinaryOperator;
 import java.util.function.Function;
 import java.util.function.UnaryOperator;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
-class UnusedLocalVariable {
-  private UnusedLocalVariable() {
-  }
-
-  public static int count(int[] elements) {
-    int count = 0;
-    for (int element : elements) { // Noncompliant[[quickfixes=qf_ulv]]
-//           ^^^^^^^
-      // fix@qf_ulv {{Replace unused local variable with _}}
-      // edit@qf_ulv [[sc=10;ec=21]]{{var _}}
-      count++;
-    }
-    return count;
-  }
-}
-
 class UnusedLocalVariableCheck {
 
   int unusedField;
@@ -65,12 +45,6 @@ public void f(int unusedParameter, Object o) {
     } catch (Exception _) {
     }
 
-    for (int a : new int[]{0, 1, 2}) { // Noncompliant[[quickfixes=qf_f1]]
-//           ^
-      // fix@qf_f1 {{Replace unused local variable with _}}
-      // edit@qf_f1 [[sc=10;ec=15]]{{var _}}
-    }
-
     for (int i = 0; condition(); i++) { // Noncompliant
     }
 

java-checks-test-sources/default/src/main/java/checks/unused/UnusedLocalVariableCheck_java22.java

@@ -0,0 +1,24 @@
+package checks.unused;
+
+public class UnusedLocalVariableCheck_java22 {
+  private UnusedLocalVariableCheck_java22() {}
+
+  public static int count(int[] elements) {
+    int count = 0;
+    for (int element : elements) { // Noncompliant[[quickfixes=qf_ulv]]
+//           ^^^^^^^
+      // fix@qf_ulv {{Replace unused local variable with _}}
+      // edit@qf_ulv [[sc=10;ec=21]]{{var _}}
+      count++;
+    }
+
+    for (int a : new int[]{0, 1, 2}) { // Noncompliant[[quickfixes=qf_f1]]
+//           ^
+      // fix@qf_f1 {{Replace unused local variable with _}}
+      // edit@qf_f1 [[sc=10;ec=15]]{{var _}}
+      count++;
+    }
+
+    return count;
+  }
+}

java-checks/src/main/java/org/sonar/java/checks/unused/UnusedLocalVariableCheck.java

@@ -29,6 +29,7 @@
 import org.sonar.java.reporting.JavaQuickFix;
 import org.sonar.java.reporting.JavaTextEdit;
 import org.sonar.plugins.java.api.IssuableSubscriptionVisitor;
+import org.sonar.plugins.java.api.JavaVersion;
 import org.sonar.plugins.java.api.semantic.Symbol;
 import org.sonar.plugins.java.api.tree.AssignmentExpressionTree;
 import org.sonar.plugins.java.api.tree.CaseLabelTree;
@@ -75,7 +76,7 @@ public void leaveNode(Tree tree) {
       IdentifierTree simpleName = variable.simpleName();
       if (!simpleName.isUnnamedVariable()) {
         boolean unresolved = UNRESOLVED_IDENTIFIERS_AND_SWITCH_CASE_VISITOR.isUnresolved(simpleName.name());
-        if (!unresolved && isProperLocalVariable(variable) && isUnused(variable.symbol())) {
+        if (!unresolved && isProperLocalVariable(variable) && isUnused(variable.symbol()) && !isMandatoryForeachVariable(context.getJavaVersion(), variable)) {
           QuickFixHelper.newIssue(context)
             .forRule(this)
             .onTree(simpleName)
@@ -88,6 +89,14 @@ public void leaveNode(Tree tree) {
 
   }
 
+  /**
+   * Before Java 22 it was not possible to remove the variable in a foreach statement even it is unused.
+   * For instance in {@code for (String element : list) {}}, it is only since Java 22 that it can be rewritten {@code for (var _ : list) {}}.
+   */
+  private static boolean isMandatoryForeachVariable(JavaVersion javaVersion, VariableTree variable) {
+    return variable.parent() instanceof ForEachStatement && !javaVersion.isJava22Compatible();
+  }
+
   private static boolean isUnused(Symbol symbol) {
     return symbol.usages().stream().noneMatch(UnusedLocalVariableCheck::isRValue);
   }

java-checks/src/test/java/org/sonar/java/checks/unused/UnusedLocalVariableCheckTest.java

@@ -31,6 +31,25 @@ void test() {
       .verifyIssues();
   }
 
+  @Test
+  void test_java22() {
+    CheckVerifier.newVerifier()
+      .onFile(TestUtils.mainCodeSourcesPath("checks/unused/UnusedLocalVariableCheck_java22.java"))
+      .withCheck(new UnusedLocalVariableCheck())
+      .withJavaVersion(22)
+      .verifyIssues();
+  }
+
+  /** Check that issue that can only be acted upon with Java 22 are not raised for earlier versions. */
+  @Test
+  void test_java21() {
+    CheckVerifier.newVerifier()
+      .onFile(TestUtils.mainCodeSourcesPath("checks/unused/UnusedLocalVariableCheck_java22.java"))
+      .withCheck(new UnusedLocalVariableCheck())
+      .withJavaVersion(21)
+      .verifyNoIssues();
+  }
+
   @Test
   void test_non_compiling() {
     CheckVerifier.newVerifier()