[API Proposal]: Add support for skipping visibility checks with AssemblyBuilder.DefineDynamicAssembly

[MichalPetryka]

Background and motivation

DynamicMethod allows accessing non public elements with its restrictedSkipVisibility constructor parameter, but using AssemblyBuilder and emitting complete types this way does not provide such functionality.
Accessing such elements can be useful when working with runtime generation for example in serialization scenarios.
There exists a non documented IgnoreAccessChecksToAttribute attribute today, runtime users can't however rely on it being always supported due to being undocumented.

API Proposal

namespace System.Reflection.Emit;

public class AssemblyBuilder
{
    public static System.Reflection.Emit.AssemblyBuilder DefineDynamicAssembly(System.Reflection.AssemblyName name, System.Reflection.Emit.AssemblyBuilderAccess access, bool restrictedSkipVisibility);
    public static System.Reflection.Emit.AssemblyBuilder DefineDynamicAssembly(System.Reflection.AssemblyName name, System.Reflection.Emit.AssemblyBuilderAccess access, System.Collections.Generic.IEnumerable<System.Reflection.Emit.CustomAttributeBuilder>? assemblyAttributes, bool restrictedSkipVisibility);
}

API Usage

AssemblyName aName = new AssemblyName("DynamicAssemblyExample");
AssemblyBuilder ab = AssemblyBuilder.DefineDynamicAssembly(aName, AssemblyBuilderAccess.Run, true);
// emit module and types
TypeBuilder tb = ...
ConstructorInfo ctorOfSomeNonPublicTypeImplementingISomeInterface = ...

MethodBuilder meth = tb.DefineMethod(
            "MyMethod",
            MethodAttributes.Public,
            typeof(ISomeInterface),
            new Type[] {  });

ILGenerator methIL = meth.GetILGenerator();
methIL.Emit(OpCodes.Newobj, ctorOfSomeNonPublicTypeImplementingISomeInterface);
methIL.Emit(OpCodes.Ret);

Alternative Designs

Document and expose the hidden IgnoreAccessChecksToAttribute.

Risks

Accessing members that shouldn't be accessed, already possible with DynamicMethod though.

[ghost]

Tagging subscribers to this area: @dotnet/area-system-reflection-emit
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Background and motivation

DynamicMethod allows accessing non public elements with its restrictedSkipVisibility constructor parameter, but using AssemblyBuilder and emitting complete types this way does not provide such functionality.
Accessing such elements can be useful when working with runtime generation for example in serialization scenarios.
There exists a non documented IgnoreAccessChecksToAttribute attribute today, runtime users can't however rely on it being always supported due to being undocumented.

API Proposal

namespace System.Reflection.Emit;

public class AssemblyBuilder
{
    public static System.Reflection.Emit.AssemblyBuilder DefineDynamicAssembly(System.Reflection.AssemblyName name, System.Reflection.Emit.AssemblyBuilderAccess access, bool restrictedSkipVisibility);
public static System.Reflection.Emit.AssemblyBuilder DefineDynamicAssembly(System.Reflection.AssemblyName name, System.Reflection.Emit.AssemblyBuilderAccess access, System.Collections.Generic.IEnumerable<System.Reflection.Emit.CustomAttributeBuilder>? assemblyAttributes, bool restrictedSkipVisibility);
}

API Usage

AssemblyName aName = new AssemblyName("DynamicAssemblyExample");
AssemblyBuilder ab = AssemblyBuilder.DefineDynamicAssembly(aName, AssemblyBuilderAccess.Run, true);
// emit module and types
ConstructorInfo ctorOfSomeNonPublicTypeImplementingISomeInterface = ...

MethodBuilder meth = tb.DefineMethod(
            "MyMethod",
            MethodAttributes.Public,
            typeof(ISomeInterface),
            new Type[] {  });

ILGenerator methIL = meth.GetILGenerator();
methIL.Emit(OpCodes.Newobj, ctorOfSomeNonPublicTypeImplementingISomeInterface);
methIL.Emit(OpCodes.Ret);

Alternative Designs

Document and expose the hidden IgnoreAccessChecksToAttribute.

Risks

Accessing members that shouldn't be accessed, already possible with DynamicMethod though.

Author:	MichalPetryka
Assignees:	-
Labels:	api-suggestion, area-System.Reflection.Emit
Milestone:	-

[steveharter]

Since the compiler does not want to support this, this scenario is not supported by design.

Closing this issue in favor of #81741.

See also #37875

Currently the general supported mechanisms:

• Generating IL to call the method
• Use reflection (which has been made much faster in 7.0)