This command will fixed the issue that Xcode downloading too slow with SPM. Say you have a project name "hello", there is a Package.swift in it.
$ cd hello
$ xcodebuild -resolvePackageDependencies -scmProvider system
$ open Package.swift
This issue was because when using git, Xcode ignore the proxy setting by default.
Pre-request
You should have your proxy set, for me, I have
$ cat .bashrc
# proxy list
alias proxy='export all_proxy=socks5://127.0.0.1:7890'
alias unproxy='unset all_proxy'
# run
proxy
Xcode not follows system proxy settings to resolve SwiftPM dependencies