How to access custom attributes from implements section via reflection?

[n9]

I want to access information about nullable reference types (#29723). Some information seems to be hidden in custom attributes of implements section (not sure how it is called officially). How to access the following attribute via reflection?

.class private auto ansi beforefieldinit BarN
    extends [System.Private.CoreLib]System.Object
    implements .custom instance void System.Runtime.CompilerServices.NullableAttribute::.ctor(uint8[]) = (
        01 00 02 00 00 00 00 02 00 00
    )
    class IBar`1<string>

Context is here: RicoSuter/Namotion.Reflection#67.

[Joe4evr]

The entire point of #29723 is so that you don't have to do this in the first place. You should wait until that API is implemented and released, then you can query for the nullability information with normal reflection code.

[n9]

This won't return the custom attributes from implements section. Try it.

[huoyaoyuan]

You can see the PR #54985

[Joe4evr]

This won't return the custom attributes from implements section. Try it.

Then why does the PR use it successfully?

runtime/src/libraries/System.Private.CoreLib/src/System/Reflection/NullabilityInfoContext.cs

Line 37 in bfd9f1b

foreach (CustomAttributeData attribute in memberInfo.GetCustomAttributesData())

[n9]

@Joe4evr The line, you posted, access custom attributes from members, but not the attributes from the implements section from the question:

.class private auto ansi beforefieldinit BarN
    extends [System.Private.CoreLib]System.Object
    implements .custom instance void System.Runtime.CompilerServices.NullableAttribute::.ctor(uint8[]) = (
        01 00 02 00 00 00 00 02 00 00
    )
    class IBar`1<string>

The code in the linked issue is following:

interface IBar<T> { }

class Bar : IBar<string> { }
class BarN : IBar<string?> { }

[n9]

@huoyaoyuan What part of the PR resolves nullability of generic argument in BarN.