How to prevent the move from the invalid FileEditorProvider?

There's no API for that.

This can probably be implemented after getting a reference to corresponding JBTabs instance (using getTabAt(index).setEnabled(false) or setSelectionChangeHandler). But that instance is not exposed by EditorComposite. I'll add corresponding method to EditorComposite, but it will be available only in 'master' branch of IntelliJ platform (to be released as 2018.3 version).

YouTrack ticket, for reference - https://youtrack.jetbrains.com/issue/IDEA-195486.

Thanks, Dmitry Batrak.

How can I get a reference to a specific EditorComposite from com.intellij.openapi.fileEditor.FileEditor or com.intellij.openapi.fileEditor.FileEditorProvider?

Something like this?

@Override
public void deselectNotify() {
    AsyncResult<EditorWindow> activeEditorWindow = FileEditorManagerEx.getInstanceEx(project).getActiveWindow();
    activeEditorWindow.doWhenDone((Consumer<EditorWindow>) wnd -> {
        if (wnd == null) {
            return;
        }
        EditorWithProviderComposite fileComposite = wnd.findFileComposite(myFile);
        fileComposite.getTabAt(0).setEnabled(false);
    });
}

I don't think you'll be able to implement your logic in 'deselectNotify' - it's called when tab switching is already decided. You'll need to do that earlier.

FileEditorManager.getCurrentWindow and EditorWindow.findFileComposite or EditorWindow.getSelectedEditor can help you to get to EditorComposite instance.

Thanks!