Cannot debug Swift module/framework embedded in Objective-C app

Question

Alternative titles (to aid searching)

• Cannot debug Swift 2.3 framework linked to an Objective-C app in Xcode 8
• error in auto-import: f

Answer 1

tl:dr

Add a user defined setting under "Build Settings" for your app target.

SWIFT_VERSION = 2.3

More Info

I'm unsure if this is an Xcode 8 bug or if it's Apple policy (to try an force developers to Swift 3.0?). But... by default Xcode 8 installs the Swift 3.0 versions of the standard Swift runtime libraries.

When it comes to debugging with LLDM the Swift 2.3 modules fail to load (in to the Swift 3.0 runtime).

Forcing the app to use Swift 2.3 (or legacy Swift as Apple call it), fixes the issue.

Swift apps have this setting exposed by Xcode but you have to manually add it for an Objective-C app.

Further Advice

Port your Swift 2.3 code to Swift 3.0 as soon as possible, Apple won't support 2.x for very long.