SONARJAVA-5598 S3063: Fix additional FPs on charAt, methodRef, and arrays (#5202)

Author: tomasz-tylenda-sonarsource

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

@@ -50,6 +50,32 @@ public char[] usedGetChars() {
     return chars;
   }
 
+  public char usedChatAt() {
+    StringBuilder buf = new StringBuilder();
+    buf.append("Hello ");
+    buf.append("World!");
+    char c = buf.charAt(8);
+    return c;
+  }
+
+  public void usedInArray() {
+    StringBuilder buf = new StringBuilder();
+    buf.append("Hello");
+    buf.append("World!");
+    System.out.println("%s: %s".formatted(new Object[]{"Message", buf}));
+  }
+
+  public void usedInMethodReference() {
+    StringBuilder buf = new StringBuilder();
+    buf.append("Hello");
+    buf.append("World!");
+    myLog(buf::toString);
+  }
+
+  private void myLog(Supplier<String> messageSupplier) {
+    System.out.println(messageSupplier.get());
+  }
+
   public void unused() {
     StringBuilder sb = new StringBuilder(); // Noncompliant {{Consume or remove this unused StringBuilder}}
 //                ^^
@@ -124,6 +150,13 @@ private String unusedConstructorWithArgument() {
     return "Hello!";
   }
 
+  private String unusedConstructorAndAppend() {
+    // FN due to chained method, which we do not support.
+    StringBuilder sb = new StringBuilder().append("Hello");
+    sb.append("!");
+    return "Hello!";
+  }
+
   public void usedStringBufferTerminalMethod() {
     StringBuffer stringBuffer = new StringBuffer();
     stringBuffer.append("Hello");

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

@@ -22,13 +22,15 @@
 import javax.annotation.Nullable;
 import org.sonar.check.Rule;
 import org.sonar.java.ast.parser.ArgumentListTreeImpl;
+import org.sonar.java.ast.parser.InitializerListTreeImpl;
 import org.sonar.plugins.java.api.IssuableSubscriptionVisitor;
 import org.sonar.plugins.java.api.semantic.Symbol;
 import org.sonar.plugins.java.api.semantic.Type;
 import org.sonar.plugins.java.api.tree.AssignmentExpressionTree;
 import org.sonar.plugins.java.api.tree.BinaryExpressionTree;
 import org.sonar.plugins.java.api.tree.ExpressionTree;
 import org.sonar.plugins.java.api.tree.MemberSelectExpressionTree;
+import org.sonar.plugins.java.api.tree.MethodReferenceTree;
 import org.sonar.plugins.java.api.tree.NewClassTree;
 import org.sonar.plugins.java.api.tree.ReturnStatementTree;
 import org.sonar.plugins.java.api.tree.Tree;
@@ -39,7 +41,7 @@
  */
 @Rule(key = "S3063")
 public class UnusedStringBuilderCheck extends IssuableSubscriptionVisitor {
-  private static final Set<String> TERMINAL_METHODS = Set.of("getChars", "substring", "toString");
+  private static final Set<String> TERMINAL_METHODS = Set.of("charAt", "getChars", "substring", "toString");
 
   @Override
   public List<Tree.Kind> nodesToVisit() {
@@ -110,7 +112,9 @@ private static boolean isConsumed(Tree tree) {
           .filter(UnusedStringBuilderCheck::isConsumed)
           .isPresent();
       }
-    } else if (parent instanceof ReturnStatementTree || parent instanceof ArgumentListTreeImpl || parent instanceof BinaryExpressionTree) {
+    } else if (parent instanceof ReturnStatementTree || parent instanceof ArgumentListTreeImpl
+      || parent instanceof BinaryExpressionTree || parent instanceof MethodReferenceTree
+      || parent instanceof InitializerListTreeImpl) {
       return true;
     }
     return false;