Can you clarify? These MetadataTypedefs would still be applied to functions, so projections need to inspect an attribute and then unwrap values either way whether it's a different attribute or a single attribute with a property.

The .custom declaraction on, say, HANDLE, after this PR, may look something like:

.custom instance void [Windows.Win32.winmd]Windows.Win32.Foundation.Metadata.TypedefAttribute::.ctor(bool) = (
  01 00 01 00 00
)

A projection author wishing to ignore non-native typedefs will have fully parse the attribute, perhaps something like:

for each attribute in attributes
  if attribute == TypedefAttribute
    if attribute.valueType == bool && getBoolValue(attribute) != true
      continue;
    // ...

The proposed alternative eliminates a bunch of per-attribute work by simply using the type name:

for each attribute in attributes
  if attribute == MetadataTypedef
    continue;
  // ...

Ok. I'm fine with that to make the processing more efficient. Your earlier comment suggested maybe a different design altogether for the attribute and how it would be applied.

@mikebattista Oh didn't mean to imply that. Was just agreeing with your "Another option might be MetadataTypedef" 👍