I just converted one of my projects from Swift 2.3 to Swift 3 and eventhoug everything compiles fine and everything seem to be working I keep getting the following warning...
warning: target specifies SWIFT_VERSION = '2.3', but it is overridden by TOOLCHAINS = 'com.apple.dt.toolchain.XcodeDefault'
Command Line Tools:
It looks like the some of your dependencys may be specifying swift 2.3. So it is warning you that this may cause problems in the nex upcoming update. You also should check the setting for your project and make sure under project settings that the
compile-with-legacy-swift = NO.