Fix issue #2374 Comments of added Nodes are ignored in LexicalPreserv…

javaparser-core-testing/src/test/java/com/github/javaparser/printer/lexicalpreservation/Issue2374Test.java

@@ -0,0 +1,38 @@
+package com.github.javaparser.printer.lexicalpreservation;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.Optional;
+
+import org.junit.jupiter.api.Test;
+
+import com.github.javaparser.StaticJavaParser;
+import com.github.javaparser.ast.CompilationUnit;
+import com.github.javaparser.ast.body.MethodDeclaration;
+import com.github.javaparser.ast.stmt.Statement;
+
+public class Issue2374Test {
+
+    @Test
+    public void test() {
+        String lineComment = "Example comment";
+        CompilationUnit cu = StaticJavaParser.parse(
+                "public class Bar {\n" + 
+                "    public void foo() {\n" + 
+                "        System.out.print(\"Hello\");\n" + 
+                "    }\n" + 
+                "}"
+                );
+        LexicalPreservingPrinter.setup(cu); 
+        // contruct a statement with a comment
+        Statement stmt = StaticJavaParser.parseStatement("System.out.println(\"World!\");");
+        stmt.setLineComment(lineComment);
+        // add the statement to the ast
+        Optional<MethodDeclaration> md = cu.findFirst(MethodDeclaration.class);
+        md.get().getBody().get().addStatement(stmt);
+        // print the result from LexicalPreservingPrinter
+        String result = LexicalPreservingPrinter.print(cu);
+        // verify that the LexicalPreservingPrinter don't forget the comment
+        assertTrue(result.contains(lineComment));
+    }
+}

javaparser-core/src/main/java/com/github/javaparser/printer/lexicalpreservation/LexicalDifferenceCalculator.java

@@ -1,16 +1,19 @@
 package com.github.javaparser.printer.lexicalpreservation;
 
 import com.github.javaparser.GeneratedJavaParserConstants;
+import com.github.javaparser.JavaToken.Kind;
 import com.github.javaparser.ast.Modifier;
 import com.github.javaparser.ast.Node;
 import com.github.javaparser.ast.NodeList;
 import com.github.javaparser.ast.expr.StringLiteralExpr;
 import com.github.javaparser.ast.observer.ObservableProperty;
+import com.github.javaparser.ast.stmt.ExpressionStmt;
 import com.github.javaparser.printer.ConcreteSyntaxModel;
 import com.github.javaparser.printer.Printable;
 import com.github.javaparser.printer.SourcePrinter;
 import com.github.javaparser.printer.concretesyntaxmodel.*;
 import com.github.javaparser.printer.lexicalpreservation.changes.*;
+import com.github.javaparser.utils.Utils;
 
 import java.util.*;
 
@@ -146,6 +149,19 @@ private void calculatedSyntaxModelForNode(CsmElement csm, Node node, List<CsmEle
                 child = csmSingleReference.getProperty().getValueAsSingleReference(node);
             }
             if (child != null) {
+                // fix issue #2374
+                // Add node comment if needed (it's not very elegant but it works)
+                // We need to be sure that the node is an ExpressionStmt because we can meet
+                // this class definition
+                // a line comment <This is my class, with my comment> followed by
+                // class A {}
+                // In this case keyworld [class] is considered as a token and [A] is a child element
+                // So if we don't care that the node is an ExpressionStmt we could try to generate a wrong definition
+                // like this [class // This is my class, with my comment A {}]
+                if (node.getComment().isPresent() && node instanceof ExpressionStmt) {
+                    elements.add(new CsmChild(node.getComment().get()));
+                    elements.add(new CsmToken(Kind.EOF.getKind(), Utils.EOL));
+                }
                 elements.add(new CsmChild(child));
             }
         } else if (csm instanceof CsmNone) {