`package import of 'Foundation' was not used in package declarations` when also importing module `os`

[ahoppen]

Type checking the following file results in a warning package import of 'Foundation' was not used in package declarations despite NSObject actually being using in a declaration that is marked as package.

package import Foundation
import os  // os_log

package func foo(x: NSObject) {}

Interestingly, this issue does not occur if:

• os is not imported
• public instead of package declarations are used
• Date or NSString is used from Foundation instead of NSObject.