Ignore AssociatedSourceType on UnmanagedCallersOnly in CoreCLR

[Copilot]

CoreCLR rejected [UnmanagedCallersOnly] attributes containing the newer AssociatedSourceType named argument, throwing META_E_CA_UNKNOWN_ARGUMENT when setting up unmanaged callbacks. Assemblies valid for NativeAOT could therefore fail under CoreCLR.

• Runtime

  • Accept AssociatedSourceType in CoreCLR’s hand-written UnmanagedCallersOnlyAttribute parser.
  • Parse and ignore the value, matching the property’s NativeAOT-only semantics.

• Regression coverage

  • Add a CoreCLR interop test for an unmanaged function pointer call to a method annotated with:

    [UnmanagedCallersOnly(AssociatedSourceType = typeof(UnmanagedCallersOnlyBasicTest))]

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[MichalStrehovsky]

@copilot same problem with mono: * Assertion at /__w/1/s/src/mono/mono/metadata/marshal.c:3478, condition `is_ok (error)' not met, function:mono_marshal_set_callconv_from_unmanaged_callers_only_attribute, Binary format of the specified custom attribute was invalid. assembly: type:UnmanagedCallersOnlyBasicTest member:(null)

[Copilot]

@copilot this is a lot of new code in Mono. we only need this to support this narrow path with the existing limitations (e.g. multiple callconvs do not work). can you address the specific issu...

Addressed in 1ae3051. The broad Mono custom-attribute parser rewrite was removed; the Mono diff now only skips the narrow AssociatedSourceType-only attribute blob before falling back to the existing CallConvs decoder and its existing limitations.

[MichalStrehovsky]

@copilot is the bug on the Mono side in mono_reflection_create_custom_attr_data_args_noalloc? fix the bug there. you keep creating workarounds in the past few commits instead of fixing the bug.

[Copilot]

@copilot is the bug on the Mono side in mono_reflection_create_custom_attr_data_args_noalloc? fix the bug there. you keep creating workarounds in the past few commits instead of fixing the bug.

Addressed in af7862f. I removed the AssociatedSourceType blob workaround and fixed the decode path to call mono_reflection_create_custom_attr_data_args_noalloc with the attributed method's image, so System.Type named arguments resolve in the correct metadata context while preserving the existing CallConvs handling.