The TUnit analyzer was incorrectly enforcing the required keyword for properties with data source attributes in all classes, including custom Attribute classes. This caused unnecessary compiler errors when creating custom attributes that use property injection.

Problem

When defining a custom attribute that inherits from System.Attribute with injected properties, the analyzer would flag TUnit0043 errors:

public class MyCustomAttribute : System.Attribute
{
    [ClassDataSource<string>]
    public string TestProperty { get; init; } // ❌ TUnit0043: Property must use `required` keyword
}

This was problematic because:

• Attribute classes have different initialization semantics than test classes
• The required keyword enforcement should only apply to test classes where property injection occurs during test execution
• Custom attributes need flexibility in their property definitions

Solution

Modified the TestDataAnalyzer.CheckPropertyAccessor() method to:

1. Check inheritance hierarchy: Added IsInAttributeClass() helper method that uses the existing IsOrInherits() extension to detect if a property's containing type inherits from System.Attribute

2. Skip enforcement for Attribute classes: When a property with data source attributes is in an Attribute class, the analyzer no longer reports TUnit0043

3. Maintain enforcement for test classes: Regular test classes continue to require the required keyword for proper property injection

After the fix

// ✅ No longer triggers TUnit0043
public class MyCustomAttribute : System.Attribute
{
    [ClassDataSource<string>]
    public string TestProperty { get; init; }
}

// ✅ Still correctly enforces required keyword
public class MyTestClass
{
    [ClassDataSource<string>]
    public required string TestProperty { get; init; } // Required for test classes
}

The fix correctly handles both direct inheritance (: System.Attribute) and indirect inheritance through base classes, ensuring robust detection of attribute classes.

Fixes #2980.

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