Invalid inferred toolchain? What?!
You’ve installed swiftenv on your shiny new Ubuntu system, obtained one of the Apple releases with swiftenv install, but when you run swift build you get error: invalid inferred toolchain. That’s no good.
Fortunately the fix is simple, you need to install clang:
sudo apt-get install clang-3.6 sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-3.6 100 sudo update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-3.6 100
In this example we’re using clang-3.6 but any version 3.6 or higher should be fine.