I ran into some issues setting up a new Swift 4 project from Swift Package Manager. Specifically, my main.swift file couldn’t import the dependencies I specified in my Package.swift file. It turns out, you have to import your dependencies in the root dependencies: section, then refer to them by module name in the targets() portion of the package.
Omitting the declaration in your target means the module won’t be available to your app and your import statements will generate compiler errors for nonexistent modules.