How to determine configuration in Swift code using Swift Package Manager

Question

I'm creating an application using Swift Package Manager and I need to know the configuration of which the project was built under, i.e Debug or Release. I'm trying to stay away from using the .xcodeproj file. Please, someone let me know if this is possible. I'll paste a simple example below, but just know if there's a better way to handling configuration besides the code below, please submit as answer.

Example:

// main.swift

#if DEBUG
  print("Im in Debug!!")
#else
  print("Im in Release!!")
#endif

Answer 1

As of Swift 3.1, the Package Manager doesn't offer the option to customize build settings in the Package.swift file (this feature is part of the team's roadmap for Swift 4). However, you can use the -Xswiftc flag to pass custom build settings to the compiler when you invoke swift build or swift test.

To set the DEBUG flag in debug mode, invoke swift build like this:

swift build --configuration debug -Xswiftc "-D" -Xswiftc "DEBUG"

And for release builds you would do the usual:

swift build --configuration release

There is also -Xlinker and Xcc to pass flags to the linker and C compiler, respectively.