Some features of Xtext-based editor don't work on files outside a project

I've written an Xtext-based plugin which works well when I open files inside one of the projects in my workspace; however, when I open a file outside the workspace (via File -> Open File...), some of the features don't work properly:

I get syntax coloring but I don't get syntax errors.
Quickfix options don't work, probably because context.getXtextDocument() returns null and I rely on it for my quickfix proposals.

There might be other things I'm missing, but most other features, such as content assist, definitions-on-hover, occurrence marking etc., work fine.

Is there a way I could make workspace-external source files behave the same as internal files? Alternatively, is there a workaround which will enable me to "trick" Xtext, somehow convincing it that the file is internal to the current project, for example by programmatically creating a link to it from the project?

This is a related question about the behavior with a workspace-external file, however I succeed in opening these files just fine, it's just that some features are not working.

Solution

As long a I know, currently there are no way to just make workspace-external source files behave the same as internal files.

Here is the workaround for broken validation:

In xxx.ui plugin, XxxUiModule.java add

public Class<? extends IResourceForEditorInputFactory> bindIResourceForEditorInputFactory() {
    return MyJavaClassPathResourceForIEditorInputFactory.class;
}

@Override
public Class<? extends IXtextEditorCallback> bindIXtextEditorCallback() {
    return MyNatureAddingEditorCallback.class;
}

Create MyJavaClassPathResourceForIEditorInputFactory.java

// Reenable validation
public class MyJavaClassPathResourceForIEditorInputFactory extends JavaClassPathResourceForIEditorInputFactory {

    @Override
    protected Resource createResource(java.net.URI uri) {
        XtextResource resource = (XtextResource) super.createResource(uri);
        resource.setValidationDisabled(false);
        return resource;
    }
}

Create MyNatureAddingEditorCallback.java

// With reenabled validation the syntax validation starts to work only after the first change made
// Run the validation manually to show the syntax errors straight away
// - CheckMode.ALL below should be probably changed to something else to improve the performance
public class MyNatureAddingEditorCallback extends NatureAddingEditorCallback {
    @Inject
    private IResourceValidator resourceValidator;
    @Inject 
    private MarkerCreator markerCreator;
    @Inject
    private MarkerTypeProvider markerTypeProvider;
    @Inject
    private IssueResolutionProvider issueResolutionProvider;

    @Override
    public void afterCreatePartControl(XtextEditor editor) {
        super.afterCreatePartControl(editor);
        validate(editor);
    }

    private void validate(XtextEditor xtextEditor) {
        if (xtextEditor == null) {
            return;
        }
        if (xtextEditor.getInternalSourceViewer() == null) {
            return;
        }
        IValidationIssueProcessor issueProcessor;
        IXtextDocument xtextDocument = xtextEditor.getDocument();
        IResource resource = xtextEditor.getResource();
        if(resource != null)
            issueProcessor = new MarkerIssueProcessor(resource, markerCreator, markerTypeProvider);
        else
            issueProcessor = new AnnotationIssueProcessor(xtextDocument, xtextEditor.getInternalSourceViewer().getAnnotationModel(), issueResolutionProvider);
        ValidationJob validationJob = new ValidationJob(resourceValidator, xtextDocument, issueProcessor,
                CheckMode.ALL); // Consider changing the CheckMode here
        validationJob.schedule();
    }
}

See also the corresponding bug report: https://bugs.eclipse.org/bugs/show_bug.cgi?id=388399