mu@xiaomudeMacBook-Pro ~ % swift --version
xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
mu@xiaomudeMacBook-Pro ~ % xcode-select --install
xcode-select: note: install requested for command line developer tools
mu@xiaomudeMacBook-Pro ~ % swift --version
Apple Swift version 5.1 (swiftlang-1100.0.270.13 clang-1100.0.33.7)
Target: x86_64-apple-darwin19.0.0