Cannot edit SPM package with a SwiftSyntax dependency

the swift-syntax package uses unsafe flags to speed up CI builds. as far as i can tell, these flags are never used in normal builds, but because swift-syntax’s Package.swift still passes the empty array to swiftSettings:, this causes the SPM to refuse to compile any downstream package while it is being edited. this means that a child package and a grandchild package cannot be developed in tandem, since the grandchild package can only observe changes in the child package after they have been pushed to a remote repository, and after updating the git commit hash in the grandchild package’s manifest.

PR: rewrite swiftSettings to avoid causing SPM build failures by kelvin13 · Pull Request #358 · apple/swift-syntax · GitHub