Hello, Swift community.
Feedback was light but positive. A couple of side issues came up during review:
First, some community members felt it wasn't clear how this proposal interacts with the idea of witness macros from the macros vision. The Language Steering Group believes witness macros are tied up with several major unresolved design questions around the future evolution of macros. We don't think SE-0407 closes any doors in that area — if we decide that witness macros as described in the vision are the right thing to do, this proposal will not be an obstacle.
Second, it is currently not possible to directly unit test extension macros, which will impact adopters of the features in this proposal. While the Language Steering Group sees this as a serious issue, it's an design and implementation issue for the swift-syntax library and its unit-testing features, which we do not consider to be covered by the evolution process. Therefore, we do not need to hold up the evolution review until this problem is solved.
Accordingly, SE-0407 has been accepted.
I'd like thank you all for participating in the evolution process.