golang.org/x/net/trace重复错误

golang.org/x/net/trace 在整个$GOPATH中有重复的副本，包括其他项目的vendor目录中依赖了golang.org/x/net包。

错误提示

goroutine 1 [running]:
golang.org/x/net/trace.init.0()
	/Users/lcl/go/src/golang.org/x/net/trace/trace.go:123  0x17e

查看golang.org/x/net/trace/trace.go文件中的init()方法

// HTTP ServeMux paths.
const (
	debugRequestsPath = "/debug/requests"
	debugEventsPath   = "/debug/events"
)

...

func init() {
	_, pat := http.DefaultServeMux.Handler(&http.Request{URL: &url.URL{Path: debugRequestsPath}})
	if pat == debugRequestsPath {
		panic("/debug/requests is already registered. You may have two independent copies of "  
			"golang.org/x/net/trace in your binary, trying to maintain separate state. This may "  
			"involve a vendored copy of golang.org/x/net/trace.")
	}

	// TODO(jbd): Serve Traces from /debug/traces in the future?
	// There is no requirement for a request to be present to have traces.
	http.HandleFunc(debugRequestsPath, Traces)
	http.HandleFunc(debugEventsPath, Events)
}

1. 使用包管理工具govendor，用于将go build时的应用路径搜索调整成为当前项目目录/vendor目录方式 推荐
2. 在$GOPATH目录下只保留一份golang.org/x/net/trace，删除所有项目vendor目录中的golang.org/x/net/trace 不推荐
3. 独立工程目录，每个项目设置GOPATH 不推荐