How do you compile an iOS «Metal» game in Xcode 6 with the target set to the iOS Simulator?
error: can't exec 'metal' (No such file or directory) Command metal failed with exit code 71
A «Metal» project cannot be compiled when the target is set to the iOS Simulator.
You have to connect a physical device and use that as your target when compiling the project.
As described in the answer on this issue: iOS 8 Metal templates are broken.
Update: As of Xcode
v6.0.1 «Metal» projects can be compiled and run on the iOS Simulator.