Fetching https://github.com/thebrowsercompany/swift-windowsappsdk from cache
Fetched https://github.com/thebrowsercompany/swift-windowsappsdk from cache (0.93s)
Fetching https://github.com/thebrowsercompany/swift-windowsfoundation from cache
Fetched https://github.com/thebrowsercompany/swift-windowsfoundation from cache (0.88s)
Fetching https://github.com/thebrowsercompany/swift-winui from cache
Fetched https://github.com/thebrowsercompany/swift-winui from cache (0.90s)
Fetching https://github.com/thebrowsercompany/swift-cwinrt from cache
Fetched https://github.com/thebrowsercompany/swift-cwinrt from cache (0.89s)
Fetching https://github.com/thebrowsercompany/swift-uwp from cache
Fetched https://github.com/thebrowsercompany/swift-uwp from cache (0.88s)
Creating working copy for https://github.com/thebrowsercompany/swift-winui
Working copy of https://github.com/thebrowsercompany/swift-winui resolved at main (4c246a1)
Creating working copy for https://github.com/thebrowsercompany/swift-windowsfoundation
Working copy of https://github.com/thebrowsercompany/swift-windowsfoundation resolved at main (ba7a8b5)
Creating working copy for https://github.com/thebrowsercompany/swift-cwinrt
Working copy of https://github.com/thebrowsercompany/swift-cwinrt resolved at main (ad451d3)
Creating working copy for https://github.com/thebrowsercompany/swift-windowsappsdk
Working copy of https://github.com/thebrowsercompany/swift-windowsappsdk resolved at main (8d094d4)
Creating working copy for https://github.com/thebrowsercompany/swift-uwp
Working copy of https://github.com/thebrowsercompany/swift-uwp resolved at main (cfad0a4)
error: 'windows-samples': target at 'C:\Users\Simon\Projects\swift\windows-samples\WinUI3AnimationsPreview' contains mixed language source files; feature not supported
Actually this looks like it was caused by leftover build artifacts from when CMake was in use. For those who may run into this issue, delete all the build and .build folders and try again.
I'm running https://github.com/thebrowsercompany/swift-build/releases/tag/20240307.1