Really simple package to test if swift is figuring out which import libraries/modules can be set as weak-linked correctly or not.
In this test CryptoKit is imported but the code that uses it is wrapped in if #available so it should be weak linked.
See main.swift for details, but if run on macOS 10.14.6 it should run just fine; instead it fails with an error trying to load CryptoKit (which doesn't exist there).
Some disassembly may point to some kind of lazy protocol witness table cache accessors or something: