StructureGuard

StructureGuard is a Roslyn-based architectural guard for C# projects. It allows you to define and enforce dependency rules between different layers or vertical slices of your application using namespaces, rather than relying solely on assembly (DLL) boundaries.

Why StructureGuard?

• Guard Vertical Slices: While layered architecture is often captured via different projects, guarding vertical slices within a single project is challenging. StructureGuard uses namespaces as the primary boundary.
• DLLs are for deployment: If you do not intend to deploy components independently, splitting your application into numerous projects/DLLs can lead to unnecessary complexity and slower build times.
• Namespaces as first-class citizens: Namespaces are more flexible and descriptive than assembly boundaries for defining internal structure.
• Shift-Left Feedback: Unlike unit tests (like NetArchTest) that run after compilation, StructureGuard provides real-time feedback directly in your IDE and fails the build during compilation if a rule is violated.

How it works

Create a "Analyzer" project in your solution in which you define your architectural rules. This project must reference StructureGuard and implements a class inheriting from SliceAnalyzer. For the analyser to work in your code, your project must reference this Analyzer project.

1. Create your Analyzer Project

Create a new netstandard2.0 class library project (e.g., MyProject.Analyzer).

Add a reference to the StructureGuard library. (use Nuget once a version is available there)

2. Configure your Rules

1. Using mermaid

---
title: Clean architecture
namespace: CleanArchitecture
---
graph TD
    Infrastructure --> Domain
    Infrastructure --> Application
    Presentation --> Application
    Presentation --> Domain
    Application --> Domain

Loading

2. Using C# code

Create a class that inherits from SliceAnalyzer and override OnInitialize to define your root namespace and permitted dependencies.

using System.Collections.Generic;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.Diagnostics;
using StructureGuard;

namespace MyProject.Analyzer
{
    [DiagnosticAnalyzer(LanguageNames.CSharp)]
    public class MyStructureGuard : SliceAnalyzer
    {
        protected override void OnInitialize(AnalysisContext context)
        {
            // The base namespace of your application
            RootNameSpace = "MyProject.App";

            // Define allowed dependencies between namespaces
            // Format: new Dependency(fromLayer, toLayer)
            PermittedDependencies = new List<Dependency>()
            {
                // Infrastructure can depend on Domain
                new Dependency(new Layer("Infrastructure"), new Layer("Domain")),
                
                // Web can depend on both Infrastructure and Domain
                new Dependency(new Layer("Web"), new Layer("Infrastructure")),
                new Dependency(new Layer("Web"), new Layer("Domain")),
            };

            base.OnInitialize(context);
        }
    }
}

3. Apply to your Target Project

In your main application project (.csproj), add a reference to your Analyzer project using OutputItemType="Analyzer" and ReferenceOutputAssembly="false".

<ItemGroup>
  <ProjectReference Include="..\MyProject.Analyzer\MyProject.Analyzer.csproj" 
                    OutputItemType="Analyzer" 
                    ReferenceOutputAssembly="false" />
</ItemGroup>

Rule Enforcement

Once configured, the analyzer will monitor your code. If you try to use a type from a namespace that isn't explicitly permitted for your current namespace, you will see a compiler error (STR001) in your IDE.

For example, if Domain tries to reference Infrastructure but no such dependency is defined in PermittedDependencies, a violation is reported.

Layer Matching

StructureGuard matches layers based on the namespace structure under your RootNameSpace.

If RootNameSpace is MyProject.App:

• A class in MyProject.App.Domain.Models is considered part of the Domain layer.
• A class in MyProject.App.Infrastructure.Data is considered part of the Infrastructure layer.