Swift-DocC does parse @ extension files. If you compile documentation with A.symbols.json, A@B.symbols.json, and B.symbols.json, DocC will pick up the @ symbol graph file. However, you're right that this behavior isn't possible when building via Xcode or SwiftPM. We should still make sure that the workflow continues to work for other integrations of docc, though. Given that, I think we should make the behavior opt-in initially, and after some time (a few months, say), make it the default, as you're proposing. And yes, since these changes aren't for Swift 5.7 but the next release, we have some time :)