この辺すね https://github.com/apple/swift-package-manager/blob/09efb063a6ae7f1175e56d51e3affbf95c79e4ab/Sources/PackagePlugin/Plugin.swift#L84-L107

1:31 PM

https://github.com/apple/swift-package-manager/blob/ad7b5ced3cf3af194c10faf4492a9b927f6222d9/Sources/Workspace/DefaultPluginScriptRunner.swift#L524-L532