Change flutter plugin by cli-tools make xcode lost code highlight and suggestion in swift files

Question

reproduce:

1. flutter create --org com.example --template=plugin --platforms=ios f_sof_ask
2. cd f_sof_ask;cd example
3. flutter build ios --no-codesign
4. cd ios; open ., open .workspace by Xcode
5. try to edit file "SwiftFSofAskPlugin.swift"

this is what I got

Build success, but Xcode seems suck and it is hard for me to edit swift code in Xcode.

Any suggestion?