4 files changed, 47 insertions, 6 deletions
diff --git a/src/core/lombok/Builder.java b/src/core/lombok/Builder.java
index 7a965486..a0b8242f 100644
--- a/src/core/lombok/Builder.java
+++ b/src/core/lombok/Builder.java
@@ -107,6 +107,13 @@ import java.lang.annotation.Target;
 @Target({TYPE, METHOD, CONSTRUCTOR})
 @Retention(SOURCE)
 public @interface Builder {
+	/**
+	 * Marks a given field as being a 'constant' (initialized by the initializing expression during construction and not eligible to be modified as part of {@code @Builder}.
+	 */
+	@Target(FIELD)
+	@Retention(SOURCE)
+	public @interface Constant {}
+
 	/** Name of the method that creates a new builder instance. Default: {@code builder}. */
 	String builderMethodName() default "builder";
 	
diff --git a/src/core/lombok/javac/handlers/HandleBuilder.java b/src/core/lombok/javac/handlers/HandleBuilder.java
index 4c670433..5dde551d 100644
--- a/src/core/lombok/javac/handlers/HandleBuilder.java
+++ b/src/core/lombok/javac/handlers/HandleBuilder.java
@@ -139,12 +139,21 @@ public class HandleBuilder extends JavacAnnotationHandler<Builder> {
 			ListBuffer<JavacNode> allFields = new ListBuffer<JavacNode>();
 			@SuppressWarnings("deprecation")
 			boolean valuePresent = (hasAnnotation(lombok.Value.class, parent) || hasAnnotation(lombok.experimental.Value.class, parent));
-			for (JavacNode fieldNode : HandleConstructor.findAllFields(tdParent)) {
+			for (JavacNode fieldNode : HandleConstructor.findAllFields(tdParent, true)) {
 				JCVariableDecl fd = (JCVariableDecl) fieldNode.get();
-				// final fields with an initializer cannot be written to, so they can't be 'builderized'. Unfortunately presence of @Value makes
-				// non-final fields final, but @Value's handler hasn't done this yet, so we have to do this math ourselves.
-				// Value will only skip making a field final if it has an explicit @NonFinal annotation, so we check for that.
-				if (fd.init != null && valuePresent && !hasAnnotation(NonFinal.class, fieldNode)) continue;
+				boolean isFinal = (fd.mods.flags & Flags.FINAL) != 0 || (valuePresent && !hasAnnotation(NonFinal.class, fieldNode));
+				JavacNode isConstant = findAnnotation(Builder.Constant.class, fieldNode, true);
+				
+				if (fd.init != null && isFinal) {
+					if (isConstant != null) continue;
+				}
+				
+				if (isConstant != null) {
+					if (!isFinal && fd.init == null) isConstant.addWarning("@Builder.Constant doesn't do anything unless the field has an initializing expression (' = something;') and is final.");
+					else if (!isFinal) isConstant.addWarning("@Builder.Constant doesn't do anything unless the field is final.");
+					else if (fd.init == null) isConstant.addWarning("@Builder.Constant doesn't do anything unless the field has an initializing expression (' = something;').");
+				}
+				
 				BuilderFieldData bfd = new BuilderFieldData();
 				bfd.rawName = fd.name;
 				bfd.name = removePrefixFromField(fieldNode);
diff --git a/src/core/lombok/javac/handlers/HandleConstructor.java b/src/core/lombok/javac/handlers/HandleConstructor.java
index 4e90b639..be4af41c 100644
--- a/src/core/lombok/javac/handlers/HandleConstructor.java
+++ b/src/core/lombok/javac/handlers/HandleConstructor.java
@@ -151,6 +151,10 @@ public class HandleConstructor {
 	}
 	
 	public static List<JavacNode> findAllFields(JavacNode typeNode) {
+		return findAllFields(typeNode, false);
+	}
+	
+	public static List<JavacNode> findAllFields(JavacNode typeNode, boolean evenFinalInitialized) {
 		ListBuffer<JavacNode> fields = new ListBuffer<JavacNode>();
 		for (JavacNode child : typeNode.down()) {
 			if (child.getKind() != Kind.FIELD) continue;
@@ -162,7 +166,7 @@ public class HandleConstructor {
 			if ((fieldFlags & Flags.STATIC) != 0) continue;
 			//Skip initialized final fields
 			boolean isFinal = (fieldFlags & Flags.FINAL) != 0;
-			if (!isFinal || fieldDecl.init == null) fields.append(child);
+			if (evenFinalInitialized || !isFinal || fieldDecl.init == null) fields.append(child);
 		}
 		return fields.toList();
 	}
diff --git a/src/core/lombok/javac/handlers/JavacHandlerUtil.java b/src/core/lombok/javac/handlers/JavacHandlerUtil.java
index 56e666f7..6fa60aac 100644
--- a/src/core/lombok/javac/handlers/JavacHandlerUtil.java
+++ b/src/core/lombok/javac/handlers/JavacHandlerUtil.java
@@ -191,6 +191,27 @@ public class JavacHandlerUtil {
 		}
 	}
 	
+	static JavacNode findAnnotation(Class<? extends Annotation> type, JavacNode node, boolean delete) {
+		if (node == null) return null;
+		if (type == null) return null;
+		switch (node.getKind()) {
+		case ARGUMENT:
+		case FIELD:
+		case LOCAL:
+		case TYPE:
+		case METHOD:
+			for (JavacNode child : node.down()) {
+				if (annotationTypeMatches(type, child)) {
+					if (delete) deleteAnnotationIfNeccessary(child, type);
+					return child;
+				}
+			}
+			// intentional fallthrough
+		default:
+			return null;
+		}
+	}
+	
 	/**
 	 * Checks if the Annotation AST Node provided is likely to be an instance of the provided annotation type.
 	 *