public ImmutableDictionary <string, ImmutableArray <DiagnosticDescriptor> > GetDiagnosticDescriptors(Project projectOpt)
        {
            if (projectOpt == null)
            {
                return(_analyzerManager.GetHostDiagnosticDescriptorsPerReference());
            }

            return(_analyzerManager.GetDiagnosticDescriptorsPerReference(projectOpt));
        }