Warnings and errors on specific positions works, sort of. Still missing something crucial to properly make javac generate the line + the ^^^^ indicators.

src/lombok/javac/HandlerLibrary.java

@@ -22,9 +22,6 @@ import lombok.core.TypeLibrary;
 import lombok.core.TypeResolver;
 import lombok.core.AnnotationValues.AnnotationValue;
 import lombok.core.AnnotationValues.AnnotationValueDecodeFail;
-import lombok.eclipse.Eclipse;
-import lombok.eclipse.EclipseAST;
-import lombok.eclipse.EclipseASTVisitor;
 
 import com.sun.tools.javac.tree.JCTree.JCAnnotation;
 import com.sun.tools.javac.tree.JCTree.JCAssign;
@@ -34,6 +31,8 @@ import com.sun.tools.javac.tree.JCTree.JCFieldAccess;
 import com.sun.tools.javac.tree.JCTree.JCIdent;
 import com.sun.tools.javac.tree.JCTree.JCLiteral;
 import com.sun.tools.javac.tree.JCTree.JCNewArray;
+import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
+import com.sun.tools.javac.util.JCDiagnostic.SimpleDiagnosticPosition;
 
 
 public class HandlerLibrary {
@@ -69,7 +68,7 @@ public class HandlerLibrary {
 			} else return null;
 		}
 		
-		public void handle(JavacAST.Node node) {
+		public void handle(final JavacAST.Node node) {
 			Map<String, AnnotationValue> values = new HashMap<String, AnnotationValue>();
 			JCAnnotation anno = (JCAnnotation) node.get();
 			List<JCExpression> arguments = anno.getArguments();
@@ -78,6 +77,7 @@ public class HandlerLibrary {
 				String name = m.getName();
 				List<String> raws = new ArrayList<String>();
 				List<Object> guesses = new ArrayList<Object>();
+				final List<DiagnosticPosition> positions = new ArrayList<DiagnosticPosition>();
 				
 				for ( JCExpression arg : arguments ) {
 					JCAssign assign = (JCAssign) arg;
@@ -89,17 +89,18 @@ public class HandlerLibrary {
 						for  ( JCExpression inner : elems ) {
 							raws.add(inner.toString());
 							guesses.add(calculateGuess(inner));
+							positions.add(new SimpleDiagnosticPosition(inner.pos));
 						}
 					} else {
 						raws.add(rhs.toString());
 						guesses.add(calculateGuess(rhs));
+						positions.add(new SimpleDiagnosticPosition(rhs.pos));
 					}
 				}
 				
 				values.put(name, new AnnotationValue(node, raws, guesses) {
 					@Override public void setError(String message, int valueIdx) {
-						//TODO
-						super.setError(message, valueIdx);
+						node.addError(message, positions.get(valueIdx));
 					}
 				});
 			}

src/lombok/javac/JavacAST.java

@@ -1,10 +1,13 @@
 package lombok.javac;
 
+import java.lang.reflect.Field;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 
 import javax.annotation.processing.Messager;
+import javax.tools.Diagnostic;
+import javax.tools.JavaFileObject;
 
 import lombok.core.AST;
 
@@ -22,21 +25,21 @@ import com.sun.tools.javac.tree.JCTree.JCImport;
 import com.sun.tools.javac.tree.JCTree.JCMethodDecl;
 import com.sun.tools.javac.tree.JCTree.JCStatement;
 import com.sun.tools.javac.tree.JCTree.JCVariableDecl;
+import com.sun.tools.javac.util.Log;
 import com.sun.tools.javac.util.Name;
+import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
 
 public class JavacAST extends AST<JCTree> {
-	private final Trees trees;
-	private final JavacProcessingEnvironment env;
 	private final Messager messager;
 	private final Name.Table nameTable;
 	private final TreeMaker treeMaker;
+	private final Log log;
 	
 	public JavacAST(Trees trees, JavacProcessingEnvironment env, JCCompilationUnit top) {
 		super(top.sourcefile == null ? null : top.sourcefile.toString());
 		setTop(buildCompilationUnit(top));
-		this.trees = trees;
-		this.env = env;
 		this.messager = env.getMessager();
+		this.log = Log.instance(env.getContext());
 		this.nameTable = Name.Table.instance(env.getContext());
 		this.treeMaker = TreeMaker.instance(env.getContext());
 	}
@@ -313,13 +316,69 @@ public class JavacAST extends AST<JCTree> {
 		}
 		
 		public void addError(String message) {
-			System.err.println("ERR: " + message);
-			//TODO
+			printMessage(Diagnostic.Kind.ERROR, message, this, null);
+		}
+		
+		public void addError(String message, DiagnosticPosition pos) {
+			printMessage(Diagnostic.Kind.ERROR, message, null, pos);
 		}
 		
 		public void addWarning(String message) {
-			System.err.println("WARN: " + message);
-			//TODO
+			printMessage(Diagnostic.Kind.WARNING, message, this, null);
+		}
+		
+		public void addWarning(String message, DiagnosticPosition pos) {
+			printMessage(Diagnostic.Kind.WARNING, message, null, pos);
+		}
+	}
+	
+	/** Supply either a position or a node (in that case, position of the node is used) */
+	private void printMessage(Diagnostic.Kind kind, String message, Node node, DiagnosticPosition pos) {
+		JavaFileObject oldSource = null;
+		JavaFileObject newSource = null;
+		JCTree astObject = node == null ? null : node.get();
+		JCCompilationUnit top = (JCCompilationUnit) top().get();
+		if (node != null) {
+			newSource = top.sourcefile;
+			if (newSource != null) {
+				oldSource = log.useSource(newSource);
+				pos = astObject.pos();
+			}
+		}
+		try {
+			switch (kind) {
+			case ERROR:
+				increaseErrorCount(messager);
+				boolean prev = log.multipleErrors;
+				log.multipleErrors = true;
+				try {
+					log.error(pos, "proc.messager", message);
+				} finally {
+					log.multipleErrors = prev;
+				}
+				break;
+			default:
+			case WARNING:
+				log.warning(pos, "proc.messager", message);
+				break;
+			}
+		} finally {
+			if (oldSource != null)
+				log.useSource(oldSource);
+		}
+	}
+	
+	private void increaseErrorCount(Messager messager) {
+		try {
+			Field f = messager.getClass().getDeclaredField("errorCount");
+			f.setAccessible(true);
+			if ( f.getType() == int.class ) {
+				int val = ((Number)f.get(messager)).intValue();
+				val++;
+				f.set(messager, val);
+			}
+		} catch ( Throwable t ) {
+			//Very unfortunate, but in most cases it still works fine, so we'll silently swallow it.
 		}
 	}