duplicates:

• SR-7965 Xcode Project generated by SwiftPM 4.2 can't build when package depends on Yams

Issue Description:

We started trying to upgrade the Point-Free repo (https://github.com/pointfreeco/pointfreeco) to Xcode 10 and Swift 4.2 but hit some snags using SPM.

Swiftx (https://github.com/typelift/Swiftx) uses #if SWIFT_PACKAGE to handle their own upstream import of Operadics (https://github.com/typelift/Operadics). I filed a bug with them documenting steps to reproduce here: typelift/Swiftx#73

Per convo with @aciidb0mb3r on Slack, this may be a regression in SPM.

Recap:

1. Use xcode-select with the Xcode 10 beta

2. Use swift package generate-xcodeproj with a project that depends on Swiftx, e.g. https://github.com/bkase/DoctorPretty

3. Try to build said project

This seems to fail because import Operadics, guarded behind #if SWIFT_PACKAGE, doesn't execute.