そのままだと公開出来ない
/tmp/tmp.7NtbKdeUsR/Sources/Bar/Bar.swift:3:29: error: cannot use struct 'BarPrivate' here; it is an SPI imported from 'Foo' public func reExport(_: Foo.BarPrivate) { ^ Foo.BarPrivate:1:15: note: type declared here public struct BarPrivate { ^ /tmp/tmp.7NtbKdeUsR/Sources/Bar/Bar.swift:3:29: error: cannot use struct 'BarPrivate' here; it is an SPI imported from 'Foo' public func reExport(_: Foo.BarPrivate) { ^ Foo.BarPrivate:1:15: note: type declared here public struct BarPrivate { ^