I am having resource issues when building a project too. swig-frontend and sourceKitControl grown in the 10s of GBs. I found some methods in my application which are harmless but cause the memory to balloon. e.g. 2 .onReceive() methods back to back in SwiftUI. At the moment the best I can recommend is to occasionally restart, kill the processes and try commenting out any newly add code that may be contributing...

Check Activity Monitor for swift-frontend or SourceKitService. They could be in the 10s of GB's (memory) which could be slowing your machine right down. Try killing them.

After 1 minute of testing I saw the process list 42gb

Following on from @alpsoy suggestion that this bug isn't present in Xcode 12.5.1 I've recreated the bug project. I can confirm that on Xcode 12.5.1 neither SourceKitService nor swift-frontend show the same memory bug. https://github.com/Func-Main/BugTester12

Haas anyone confirmed if this is an issue on Monterey? Maybe that could help...

I've tried  Xcode 13.1 RC and I confirm this bug is still present. Only option for me to reliably develop SwiftUI at the moment is to use Xcode 12. I tried the latest Xcode 13 Beta before GM and this issue was present.

I can confirm the issue I originally posted is still present in Xcode 13.2

Ha, although I don't think a 64gb max will save you from this. I have exactly that machine sat in it's box because of this bug. I need Xcode 12 and can't use Monterey yet 😢