Swift SourceKitService Crashed
Apple solve this crash Version: 6.1.1
What's New in Version 6.1.1
Includes SDKs for OS X 10.10 Yosemite, OS X 10.9 Mavericks, and iOS 8.1
• Fixes common causes of SourceKit crashes when working with Swift• Additional bug fixes and stability improvements
https://itunes.apple.com/us/app/xcode/id497799835?ls=1&mt=12
also you can solve this using delete your project from following path
~/Library/Developer/Xcode/DerivedData