CA1421: Method uses runtime marshalling when DisableRuntimeMarshallingAttribute is applied

Property	Value
Rule ID	CA1421
Title	Method uses runtime marshalling when DisableRuntimeMarshallingAttribute is applied
Category	Interoperability
Fix is breaking or non-breaking	Non-breaking
Enabled by default in .NET 9	As suggestion

Cause

A method uses runtime marshalling, and runtime marshalling is explicitly disabled.

Rule description

If a method uses runtime marshalling when runtime marshalling is disabled, it can cause unexpected behavior differences at run time due to different expectations of a type's native layout.

How to fix violations

Enable runtime marshalling or use features like sizeof and pointers to ensure accurate results.

When to suppress warnings

Don't suppress a warning from this rule.

Example

The following code snippet shows a violation of CA1421:

using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

[assembly: DisableRuntimeMarshalling]

class C
{
    public void Test()
    {
        nint offset = Marshal.OffsetOf(typeof(ValueType), "field");
    }
}

struct ValueType
{
    int field;
}

Imports System.Runtime.CompilerServices
Imports System.Runtime.InteropServices

<Assembly: DisableRuntimeMarshalling>

Class C
    Shared Sub S1()
        Dim offset As IntPtr = Marshal.OffsetOf(GetType(ValueType), "field")
    End Sub
End Class

Structure ValueType
    Dim field As Integer
End Structure

To fix the violation, remove the DisableRuntimeMarshallingAttribute attribute on the assembly.