Groovy - Add Class to script via AST transformations - groovy

Question

I'm currently creating a Groovy DSL that looks like the this:
types {
A "http://some.namespace.here"
B "..."
}
testMethod(A a, B b) { ... }
The user defines several types and some methods on these types. What I need to do is to create A and B as ClassNodes in the AST so that Groovy can find them.
To do so, I created the following AST transformation:
#GroovyASTTransformation(phase = CompilePhase.SEMANTIC_ANALYSIS)
class GenerateClassesTransformer implements ASTTransformation {
#Override
public void visit(ASTNode[] nodes, SourceUnit source) {
ClassNode a = createClass("A")
ClassNode b = createClass("b")
ModuleNode module = sourceUnit.getAST()
module.addClass(a)
module.addClass(b)
module.getClasses().each {
println "class: " + it
}
}
private ClassNode createClass(String className) {
new AstBuilder().buildFromSpec {
classNode(className, ClassNode.ACC_PUBLIC) {
classNode Object
interfaces { classNode GroovyObject }
mixins { }
}
}.first()
}
}
I then add the AST transformation to the Groovy shell:
CompilerConfiguration cc = new CompilerConfiguration();
cc.setScriptBaseClass("groovy.util.DelegatingScript");
cc.addCompilationCustomizers(new ASTTransformationCustomizer(new GenerateClassesTransformer()));
GroovyShell sh = new GroovyShell(loader, binding, cc);
// ...
When I run the code and do NOT reference A and B, everything works out fine. However, as soon as I use A and B, Groovy cannot find the classes (although they are on the AST). Instead, I get:
org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
C:\...\test.groovy: 23: unable to resolve class A
# line 23, column 6.
A a = null
^
Any help would be greatly appreciated!
Update: ClassLoader
I'm using a custom URLClassLoader, since I'm adding a couple of JARs to the classpath:
URL[] urls = this.getExtraJarUrls(); // read JARs from a directory relative to the DSL script
ClassLoader base = Launcher.class.getClassLoader();
loader = new URLClassLoader(urls, base);