Compilation extremely slow since macros adoption

Highlighting this for the folks coming in new to the thread since there's been quite a bit of activity, and I've had a couple of folks message me off-forums asking me about the team's response. This is my attempt at summarizing the key points (please correct me if I'm wrong).


  • The Language Steering Group is aware of the build-system issues causing pain for macro adopters.

  • No timeline for a fix as of Feb 20th, 2024.

My two cents for Swift developers considering adopting macros:

  • Be aware of the fact that you're adding ~38,000 LoC of Swift source code to your project. This cost is forwarded to anyone consuming your Swift packages.
  • Be aware of the fact that SPM currently fetches the entire git history of the SwiftSyntax repo. This is a separate but, in my view, not unrelated issue as it directly factors into the cost of adopting macros.
  • Just adding SwiftSyntax can potentially add up to 12 minutes to your build time on Xcode Cloud as noted by @Ignacio_Soto.

It's peculiar enough that a core language feature is tied to a still-maturing package manager riddled with performance/build-systems issues, but what I find extremely disappointing is that these issues aren't mentioned anywhere in any official documentation/release notes.

While it's great that we can discuss this here on the forums, I don't think we should expect this to serve as a discoverable resource on the serious issues blocking folks on the adoption of macros.

If the LSG is aware of these issues as issues hindering adoption, one would expect that awareness to be reflected somewhere other than a forums thread. Perhaps an update/addendum to the Developer Experience section of the Swift 5.9 Released blog post is warranted?

If not, I'd love to know if there's an appropriate documentation article/resource that I can PR to!