1. What version of Go are you using (go version)?
   go version devel +ad391c9 Sat Mar 26 12:12:04 2016 +0000 linux/amd64
2. What operating system and processor architecture are you using (go env)?
   GOARCH="amd64"
   GOBIN=""
   GOEXE=""
   GOHOSTARCH="amd64"
   GOHOSTOS="linux"
   GOOS="linux"
   GOPATH="/home/travis/gopath"
   GORACE=""
   GOROOT="/home/travis/.gimme/versions/go"
   GOTOOLDIR="/home/travis/.gimme/versions/go/pkg/tool/linux_amd64"
   CC="gcc"
   GOGCCFLAGS="-fPIC -m64 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build398857422=/tmp/go-build"
   CXX="g++"
   CGO_ENABLED="0"
3. What did you do?
   Ran CI tests on Go tip. Tests now fail on code that hasn't changed recently and still passes on Go 1.6. For example: https://travis-ci.org/mholt/caddy/builds/118687079
4. What did you expect to see?
   No errors
5. What did you see instead?

$ go vet ./...
caddy/config.go:194: function call copies lock value: sync.Once contains sync.Mutex
caddy/config_test.go:114: function call copies lock value: sync.Once contains sync.Mutex
caddy/config_test.go:115: function call copies lock value: sync.Once contains sync.Mutex

Relevant lines of code are:

onces[dir.name] = new(sync.Once)

map[string]*sync.Once{
    "dummy":  new(sync.Once),
    "dummy2": new(sync.Once),
}

Is new() really a function call that is copying a lock value?