The symbolgraph is mostly platform agnostic, but not quite. APIs annotated with @available(iOS, unavailable) will appear in the symbolgraph with that annotation if the target is macOS, but if the target is iOS the API will not appear at all. This is a problem for users who want to generate bindings for both iOS and macOS.

A fix for this could be to generate symbolgraphs for both platforms and then merge them. That should be doable, if the only difference is whether the API appears.

If there are other divergences we'll need to consider how to handle them too.