Check namespace of all MVC controllers in a solution

Program.cs

public static class Program
{
    private const string ControllerType = "System.Web.Mvc.Controller";

    public static void Main(string[] args)
    {
        MainAsync(args).Wait();
    }

    private static async Task MainAsync(string[] args)
    {
        var workspace = MSBuildWorkspace.Create();

        var solution = await workspace.OpenSolutionAsync(args[0]);

        foreach (var project in solution.Projects)
        {
            // Compile the project.
            var compilation = await project.GetCompilationAsync();

            // Get a symbol instance for the MVC controller type.
            var controllerBaseType = compilation.GetTypeByMetadataName(ControllerType);

            foreach (var document in project.Documents)
            {
                // Get all controllers in document.
                var controllerTypes = await document.GetControllerTypes(compilation, controllerBaseType);

                foreach (var controllerType in controllerTypes)
                {
                    // Check if controller has the correct namespace.
                    if (!controllerType.ContainingNamespace.Name.Equals("Controllers"))
                    {
                        // Do whatever...
                    }
                }
            }
        }
    }

    private static async Task<IEnumerable<INamedTypeSymbol>> GetControllerTypes(this Document document, Compilation compilation, INamedTypeSymbol controllerType)
    {
        var syntaxTree = await document.GetSyntaxTreeAsync();

        var semanticModel = compilation.GetSemanticModel(syntaxTree);

        var rootNode = await syntaxTree.GetRootAsync();

        return rootNode.DescendantNodes()
            .OfType<ClassDeclarationSyntax>()
            .Select(x => semanticModel.GetDeclaredSymbol(x))
            .Where(x => x.IsAssignableTo(controllerType));
    }

    private static bool IsAssignableTo(this ITypeSymbol symbol, ISymbol other)
    {
        if (symbol.Equals(other))
        {
            return true;
        }

        var baseType = symbol.BaseType;

        if (baseType == null)
        {
            return false;
        }

        return baseType.IsAssignableTo(other);
    }
}