swift

4327c734 - [Serialization] Attempt to load transitive impl-only dependencies on testable imports

[Serialization] Attempt to load transitive impl-only dependencies on testable imports Implementation-only dependencies may be referenced from internal decls. When that module is imported as @testable, clients see the internal decls and may fail accessing them if the transitive implementation-only dependencies are not loaded. Let's consider such transtive implementation-only dependencies as optional for @testable imports. As such, the compiler will attempt to load them for test targets, and won't fail if the dependency is missing. We can make these dependencies required for non-public imports, but it could be project breaking to do so for implementation-only dependencies. Considering them as optional is a decent compromise. rdar://79459263