SW102: Forbidden namespace using

Overview

Rule ID: SW102
Category: Architecture
Severity: Warning
Status: Currently disabled

Description

This rule prevents using directives that import feature-internal namespaces from outside the feature. It works in conjunction with SW101 to enforce architectural boundaries, specifically catching explicit using statements that target internal namespaces.

When This Rule Triggers

The analyzer reports a diagnostic when:

• A using directive imports a feature's internal namespace
• The code using the directive is outside that feature

Why This Matters

Explicit Import Prevention

While SW101 flags direct type references, this rule catches the more explicit case of importing entire namespaces:

• Prevents accidental pollution of the namespace
• Makes violations more obvious during code review
• Catches problems at the import stage before actual usage
• Serves as an early warning system

How to Fix

Option 1: Remove the using directive

Delete the using statement that imports the internal namespace:

// ❌ WRONG
using Users.Internal;

public class OrderService
{
    // ...
}

// ✅ CORRECT
public class OrderService
{
    // ...
}

Option 2: Use only public APIs

Reference types through their public namespaces:

// ❌ WRONG
using Users.Internal;
using Users.Internal.Helpers;

// ✅ CORRECT
using Users;

public class OrderProcessor
{
    private readonly IUserService userService;
}

Option 3: Move within the feature

If the code needs access to internal implementations, move it into the feature:

// ❌ WRONG - Outside Users feature
// File: Orders/UserValidator.cs
using Users.Internal;

public class UserValidator { }

// ✅ CORRECT - Inside Users feature
// File: Users/UserValidator.cs
namespace Users;

public class UserValidator { }

Example

// File: Users/Internal/UserCache.cs
namespace Users.Internal;

internal class UserCache
{
    public User? Get(int id) { /* ... */ }
}

// File: Orders/OrderService.cs
namespace Orders;

// ⚠️ SW102 - Using statement targets internal namespace
using Users.Internal;  // ❌ Violation

public class OrderService
{
    private UserCache cache = new();
}

// ✅ CORRECT - Use public interface
using Users;

public class OrderService
{
    private readonly IUserService userService;
}

Difference from SW101

Rule	Detects	Catches
SW101	Direct type references to internal types	var user = new Users.Internal.UserHelper()
SW102	using directives importing internal namespaces	using Users.Internal;

Both rules work together to prevent unauthorized access to feature internals.

Configuration

This rule is currently disabled to avoid false positives. To enable it:

[*.cs]
dotnet_diagnostic.SW102.severity = warning

To treat violations as errors:

[*.cs]
dotnet_diagnostic.SW102.severity = error

Related Rules

• SW101 - Forbidden reference to feature-internal namespace

See Also

• SW101 documentation
• Clean Architecture principles
• Feature-driven development patterns