SPM platform specific targets

[SDGGiesbrecht (Jeremy David Giesbrecht)]

A client package that asks for Frontend will not attempt to build or use XcodeSupport for Linux.

But when you do swift build for your own package, it will still build every target in the package.

It is only a conditional dependency, not a conditional target (which is a separate, sorely needed feature.)

For now, to support swift build you can either put #if !os(Linux) around every file in XcodeSupport, or you can do something like I described in this post:

SPM build fails for watchOS libraries

This is what I do: Since CI builds are from the command line, I simply have that environment variable set. On the rare occasion something fails only on watchOS, I comment out the if while I’m working and re‐open Xcode. It would be nice to have watchOS automatically evade tests in a similar way to how iOS evades executable targets. (Although even that seems to only work from the GUI and not command line invocations.) But as @NeoNacho said, those are the domain of Xcode, not SwiftPM.