grammar org.xtext.example.mydsl.MyDsl with org.eclipse.xtext.common.Terminals

import "eclipse-org-site/xtext/common/JavaVMTypes" as jvmTypes 

generate myDsl "xtext-org-site/example/mydsl/MyDsl"

Model: (greetings+=Greeting | imports+=Import | goodbyes+=Goodbye)*;

Greeting: "Hello" name=ID;
Import: "import" importURI=STRING;
Goodbye: "Bye" ref=[Greeting] ;

public class MyDslGenerator implements IGenerator {

    @Override
    public void doGenerate(Resource resource, IFileSystemAccess fsa) {
        StringBuilder output = new StringBuilder();
        Iterator<?> it = resource.getAllContents();
        while (it.hasNext()) {
            Object o = it.next();
            if (o instanceof Greeting) {
                output.append("Hello " + ((Greeting) o).getName() + "\n");
            } else if (o instanceof Goodbye) {
                output.append("Goodbye " + ((Goodbye) o).getRef().getName() + "\n");
            }
        }
        fsa.generateFile(resource.getURI().lastSegment() + ".output", output);
    }
}

import "test2/test2.mydsl"

Hello aek

Bye aek 
Bye eak

    protected void runGenerator(String string) {
        ResourceSet set = resourceSetProvider.get();
        set.getResource(URI.createURI("src/test2/test2.mydsl"), true);

        Resource resource = set.getResource(URI.createURI(string), true);
        for (Resource r : set.getResources())
            System.out.println("loaded " + r.getURI());

        // validate the resource
        List<Issue> list = validator.validate(resource, CheckMode.ALL, CancelIndicator.NullImpl);
       
        if (!list.isEmpty()) {
            for (Issue issue : list) {
                System.err.println(issue);
            }
            System.exit(-1);
        }

        // configure and start the generator
        fileAccess.setOutputPath("src-gen/");
        generator.doGenerate(resource, fileAccess);

        System.out.println("Code generation finished");
    }

loaded src/test2/test2.mydsl
loaded src/test3.mydsl
ERROR:Couldn't resolve reference to Greeting 'eak'. (src/test3.mydsl line : 6)