Getting a new error with latest snapshot version, this works with groovyc and was working as of 3-10-17 in groovy-eclipse. Seemed to break with the JDT patch commit.

Groovy:Could not find class for Transformation Processor com.company.transform.SerializableTransformation declared by com.company.transform.Serializable

Here's a slimmed down example

// POGO with error - SomePOGO.groovy
@serializable
class SomePOGO {
// fields
}

// annotation - Serializable.java
@retention(RetentionPolicy.RUNTIME)
@target(ElementType.TYPE)
@GroovyASTTransformationClass("com.company.transform.SerializableTransformation")
public @interface Serializable {
// implements serializable interface
}

// ast impl - SerializableTransformation.java
@GroovyASTTransformation(phase = CompilePhase.CANONICALIZATION)
public class SerializableTransformation implements ASTTransformation {

private static final String FIELD_NAME = "serialVersionUID";
private static final int FIELD_MODIFIERS = Opcodes.ACC_PRIVATE | Opcodes.ACC_STATIC | Opcodes.ACC_FINAL;
private static final ClassNode FIELD_TYPE = ClassHelper.long_TYPE;
private static final Long FIELD_VALUE = Long.valueOf(1);

@Override
public void visit(ASTNode[] nodes, SourceUnit source) {
	ClassNode classNode = (ClassNode) nodes[1];

	ClassNode serializable = ClassHelper.make(Serializable.class);

	if (!classNode.implementsInterface(serializable)) {
		classNode.addInterface(serializable);
	}

	classNode.addField(FIELD_NAME, FIELD_MODIFIERS, FIELD_TYPE, new ConstantExpression(FIELD_VALUE));
}

}