Running netbeans on a JVM1.5 is not a supported platform for lombok. Instead of an obscure error and no netbeans, you now get netbeans with no lombok, and a GUI warning box explaining what's wrong and how to fix it.

src/core/lombok/core/Agent.java

@@ -21,42 +21,118 @@
  */
 package lombok.core;
 
+import java.lang.instrument.ClassFileTransformer;
+import java.lang.instrument.IllegalClassFormatException;
 import java.lang.instrument.Instrumentation;
+import java.security.ProtectionDomain;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 
+import javax.swing.JOptionPane;
+import javax.swing.SwingUtilities;
+
 public abstract class Agent {
 	protected abstract void runAgent(String agentArgs, Instrumentation instrumentation, boolean injected) throws Exception;
 	
-	public static void agentmain(String agentArgs, Instrumentation instrumentation) throws Exception {
+	public static void agentmain(String agentArgs, Instrumentation instrumentation) throws Throwable {
 		runAgents(agentArgs, instrumentation, true);
 	}
 	
-	public static void premain(String agentArgs, Instrumentation instrumentation) throws Exception {
+	public static void premain(String agentArgs, Instrumentation instrumentation) throws Throwable {
 		runAgents(agentArgs, instrumentation, false);
 	}
 	
-	private static final List<String> AGENT_NAMES = Collections.unmodifiableList(Arrays.asList(
-			"lombok.netbeans.agent.NetbeansPatcher",
-			"lombok.eclipse.agent.EclipsePatcher"
-			));
+	private static final List<AgentInfo> AGENTS = Collections.unmodifiableList(Arrays.asList(
+			new NetbeansPatcherInfo(),
+			new EclipsePatcherInfo()
+	));
 	
-	private static void runAgents(String agentArgs, Instrumentation instrumentation, boolean injected) throws Exception {
-		for (String agentName : AGENT_NAMES) {
+	private static void runAgents(String agentArgs, Instrumentation instrumentation, boolean injected) throws Throwable {
+		for (AgentInfo info : AGENTS) {
 			try {
-				Class<?> agentClass = Class.forName(agentName);
+				Class<?> agentClass = Class.forName(info.className());
 				Agent agent = (Agent) agentClass.newInstance();
 				agent.runAgent(agentArgs, instrumentation, injected);
-			} catch (ClassNotFoundException e) {
-				//That's okay - this lombok evidently is a version with support for something stripped out.
-			} catch (ClassCastException e) {
-				throw new InternalError("Lombok bug. Class: " + agentName + " is not an implementation of lombok.core.Agent");
-			} catch (IllegalAccessException e) {
-				throw new InternalError("Lombok bug. Class: " + agentName + " is not public");
-			} catch (InstantiationException e) {
-				throw new InternalError("Lombok bug. Class: " + agentName + " is not concrete or has no public no-args constructor");
+			} catch (Throwable t) {
+				info.problem(t, instrumentation);
 			}
 		}
 	}
+	
+	private static abstract class AgentInfo {
+		abstract String className();
+		
+		/**
+		 * Called if an exception occurs while loading the agent represented by this AgentInfo object.
+		 * 
+		 * @param t The throwable.
+		 * @param instrumentation In case you want to take an alternative action.
+		 */
+		void problem(Throwable t, Instrumentation instrumentation) throws Throwable {
+			if (t instanceof ClassNotFoundException) {
+				//That's okay - this lombok evidently is a version with support for something stripped out.
+				return;
+			}
+			
+			if (t instanceof ClassCastException) {
+				throw new InternalError("Lombok bug. Class: " + className() + " is not an implementation of lombok.core.Agent");
+			}
+			
+			if (t instanceof IllegalAccessError) {
+				throw new InternalError("Lombok bug. Class: " + className() + " is not public");
+			}
+			
+			if (t instanceof InstantiationException) {
+				throw new InternalError("Lombok bug. Class: " + className() + " is not concrete or has no public no-args constructor");
+			}
+			
+			throw t;
+		}
+	}
+	
+	private static class NetbeansPatcherInfo extends AgentInfo {
+		@Override String className() {
+			return "lombok.netbeans.agent.NetbeansPatcher";
+		}
+		
+		@Override void problem(Throwable in, Instrumentation instrumentation) throws Throwable {
+			try {
+				super.problem(in, instrumentation);
+			} catch (InternalError ie) {
+				throw ie;
+			} catch (Throwable t) {
+				final String error;
+				
+				if (t instanceof UnsupportedClassVersionError) {
+					error = "Lombok only works on netbeans if you start netbeans using a 1.6 or higher JVM.\n" +
+							"Change your platform's default JVM, or edit etc/netbeans.conf\n" +
+							"and explicitly tell netbeans your 1.6 JVM's location.";
+				} else {
+					error = "Lombok disabled due to error: " + t;
+				}
+				
+				instrumentation.addTransformer(new ClassFileTransformer() {
+					@Override public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
+						if ("org/netbeans/modules/java/source/parsing/JavacParser".equals(className)) {
+							//If that class gets loaded, this is definitely a netbeans(-esque) environment, and thus we SHOULD tell the user that lombok is not in fact loaded.
+							SwingUtilities.invokeLater(new Runnable() {
+								@Override public void run() {
+									JOptionPane.showMessageDialog(null, error, "Lombok Disabled", JOptionPane.ERROR_MESSAGE);
+								}
+							});
+						}
+						
+						return null;
+					}
+				});
+			}
+		}
+	}
+	
+	private static class EclipsePatcherInfo extends AgentInfo {
+		@Override String className() {
+			return "lombok.eclipse.agent.EclipsePatcher";
+		}
+	}
 }