[NativeAOT] Unexpected behaviour of GetCustomAttribute in reflection-free mode

[tomvanenckevort]

I'm trying to build an app that uses a third-party library with Native AOT in reflection free mode (IlcDisableReflection set to true).
Since that library uses the GetCustomAttribute method in a few places I turned on shimming for the attributes (Switch.System.Reflection.Disabled.DoNotThrowForAttributes set to true).
Since that shims GetCustomAttributes to return an empty array, I assumed that GetCustomAttribute would return null (as it normally calls GetCustomAttributes internally and returns the first matching attribute or null if not found).

However, instead I get a Reflection_Disabled exception as it seems to be calling the RuntimeTypeInfo.GetAttributeFlagsImpl method first. Here's the final part of the stacktrace:

   at Internal.Reflection.RuntimeTypeInfo.GetAttributeFlagsImpl() + 0x33
   at Internal.Reflection.Extensions.NonPortable.CustomAttributeSearcher`1.GetMatchingCustomAttributes(E, Type, Boolean, Boolean) + 0xa1
   at Internal.Reflection.Extensions.NonPortable.CustomAttributeInheritanceRules.GetMatchingCustomAttributes(MemberInfo, Type, Boolean, Boolean) + 0x50
   at System.Reflection.CustomAttributeExtensions.GetCustomAttribute[T](MemberInfo) + 0x2d

Is there a particular reason why it would take this path?
Or is it the case that Native AOT needs a similar override to GetCustomAttributes for GetCustomAttribute that will return null when no reflection is used and the DoNotThrowForAttributes setting is turned on?

[MichalStrehovsky]

This will be fixed when dotnet/runtime#67193 is fixed. We could introduce yet another shim for this (we can compute some of the AttributeFlags, but not all), but I think it will be better to look into dotnet/runtime#67193 at some point.