Issue:

• FilesProvider fails to build using Swift 3.x (it's depending on the altered semantics of private in Swift 4.0)
• CocoaPods 1.4.0 apparently doesn't fully respect .swift-version files anymore; the replacement is using swift_version in the podspec DSL.
• Under some circumstances, Cocoapods 1.4.0 will select Swift 3.2 as the default Swift version, and apply that to the target build settings for FilesProvider.
• FilesProvider will then fail to build.

Solution:

Add s.swift_version = '4.0' to FilesProvider.podspec, and delete .swift-version