[GOOS:windows] skip 'windows does not use XDG_CACHE_HOME'
[GOOS:darwin]  skip 'darwin does not use XDG_CACHE_HOME'
[GOOS:ios]     skip 'ios does not use XDG_CACHE_HOME'
[GOOS:plan9]   skip 'plan9 does not use XDG_CACHE_HOME'

mkdir $WORK/gocache
mkdir $WORK/xdg
mkdir $WORK/home

# Set GOCACHE, XDG_CACHE_HOME, and HOME.
env GOCACHE=$WORK/gocache
env XDG_CACHE_HOME=$WORK/xdg
env HOME=$WORK/home

env GO111MODULE=off

# As of Go 1.12, the module cache is required.

# If none of the variables we use to locate GOCACHE are set, the cache is off
# and we cannot build.
env GOCACHE=
env XDG_CACHE_HOME=
env HOME=
[GOOS:plan9] env home=
[GOOS:windows] env LocalAppData=
! go build -o triv triv.go
stderr 'build cache is required, but could not be located: GOCACHE is not defined and .*'

		if dir == "" {
			return "", errors.New("$home is not defined")
		}
		dir += "/lib/cache"

	default: // Unix
		dir = Getenv("XDG_CACHE_HOME")
		if dir == "" {
			dir = Getenv("HOME")
			if dir == "" {
				return "", errors.New("neither $XDG_CACHE_HOME nor $HOME are defined")
			}
			dir += "/.cache"
		}
	}

	return dir, nil
}