Demonstrates the special `IgnoresAccessChecksToAttribute` of .NET 4.6+ and .NET Core 1.0+

IgnoresAccessChecksToAttributeDemo.cs

using System;
using System.Reflection;
using System.Reflection.Emit;

// Note that this is `internal` and regularly shouldn't be accessible from other assemblies:
internal sealed class Hellower
{
    internal void SayHello()
    {
        Console.WriteLine("Hello!");
    }
}

// The following code will implement this interface in a dynamic assembly such that it will call the above `SayHello` method:
public interface ITrigger
{
    void Do();
}

class Program
{
    static void Main()
    {
        var assemblyBuilder = AssemblyBuilder.DefineDynamicAssembly(new AssemblyName("DynamicAssembly"), AssemblyBuilderAccess.Run);
        var moduleBuilder = assemblyBuilder.DefineDynamicModule("DynamicAssembly");


        // class IgnoresAccessChecksToAttribute

        var attributeTypeBuilder = moduleBuilder.DefineType("System.Runtime.CompilerServices.IgnoresAccessChecksToAttribute", TypeAttributes.NotPublic | TypeAttributes.Sealed | TypeAttributes.Class, typeof(Attribute));

        var attributeTypeUsageAttrBuilder = new CustomAttributeBuilder(
            con: typeof(AttributeUsageAttribute).GetConstructor(new[] { typeof(AttributeTargets) }),
            constructorArgs: new object[] { AttributeTargets.Assembly },
            namedProperties: new[] { typeof(AttributeUsageAttribute).GetProperty("AllowMultiple") },
            propertyValues: new object[] { true });

        attributeTypeBuilder.SetCustomAttribute(attributeTypeUsageAttrBuilder);

        var attributeTypeFieldBuilder = attributeTypeBuilder.DefineField("assemblyName", typeof(string), FieldAttributes.Private | FieldAttributes.InitOnly);

        var attributeTypeCtorBuilder = attributeTypeBuilder.DefineConstructor(MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.RTSpecialName, CallingConventions.Standard | CallingConventions.HasThis, new[] { typeof(string) });
        var attributeTypeCtorIL = attributeTypeCtorBuilder.GetILGenerator();
        attributeTypeCtorIL.Emit(OpCodes.Ldarg_0);
        attributeTypeCtorIL.Emit(OpCodes.Ldarg_1);
        attributeTypeCtorIL.Emit(OpCodes.Ldfld, attributeTypeFieldBuilder);
        attributeTypeCtorIL.Emit(OpCodes.Ret);

        var attributeTypeGetterBuilder = attributeTypeBuilder.DefineMethod("get_AttributeName", MethodAttributes.Public | MethodAttributes.SpecialName, typeof(string), null);
        var attributeTypeGetterIL = attributeTypeGetterBuilder.GetILGenerator();
        attributeTypeGetterIL.Emit(OpCodes.Ldarg_0);
        attributeTypeGetterIL.Emit(OpCodes.Ldfld, attributeTypeFieldBuilder);
        attributeTypeGetterIL.Emit(OpCodes.Ret);

        var attributeTypePropertyBuilder = attributeTypeBuilder.DefineProperty("AttributeName", PropertyAttributes.None, typeof(string), null);
        attributeTypePropertyBuilder.SetGetMethod(attributeTypeGetterBuilder);

        var attributeType = attributeTypeBuilder.CreateTypeInfo().AsType();


        // [assembly: IgnoresAccessChecksToAttribute("ConsoleApp1")]

        // TODO: replace "ConsoleApp1" with the name of the project containing this code
        var assemblyAttrBuilder = new CustomAttributeBuilder(attributeType.GetConstructor(new[] { typeof(string) }), new object[] { "ConsoleApp1" });
        assemblyBuilder.SetCustomAttribute(assemblyAttrBuilder); // Try uncommenting this line and see the difference!


        // class Trigger : ITrigger

        var triggerTypeBuilder = moduleBuilder.DefineType("Trigger", TypeAttributes.Public | TypeAttributes.Sealed | TypeAttributes.Class);

        var doMethodBuilder = triggerTypeBuilder.DefineMethod("Do", MethodAttributes.Public | MethodAttributes.Virtual | MethodAttributes.ReuseSlot | MethodAttributes.HideBySig, CallingConventions.Standard | CallingConventions.HasThis, typeof(void), null);
        var doMethodIL = doMethodBuilder.GetILGenerator();
        doMethodIL.Emit(OpCodes.Newobj, typeof(Hellower).GetConstructor(Type.EmptyTypes));
        doMethodIL.EmitCall(OpCodes.Callvirt, typeof(Hellower).GetMethod("SayHello", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance), null);
        doMethodIL.Emit(OpCodes.Ret);

        triggerTypeBuilder.AddInterfaceImplementation(typeof(ITrigger));

        var triggerType = triggerTypeBuilder.CreateTypeInfo().AsType();

        var trigger = (ITrigger)Activator.CreateInstance(triggerType);

        trigger.Do();
    }
}