After upgrading to Catalina, I encountered the error below. Seems Xcode was no longer available.
xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
Try the following in your terminal; otherwise, head to https://developer.apple.com/download/more/ and download Xcode manually.
xcode-select --install