log_with_caller.go

package main

import (
	"log"
	"runtime"
	"strings"
)

const (
	rootPath = "/path/to/project/root/"
)

func foo() {
	logWithCaller("test")
}

// Example output: 
// 2016/01/18 22:27:42 log_with_caller.go:14:foo test
func logWithCaller(str string) {
	pc, file, line, ok := runtime.Caller(1)
	if !ok {
		log.Println("ERROR: Failed to determine caller")
		return
	}

	fn := runtime.FuncForPC(pc)
	if fn == nil {
		log.Println("ERROR: Failed to find caller function")
		return
	}

	file = strings.Replace(file, rootPath, "", 1)
	fnName := strings.Split(fn.Name(), ".")[1]

	log.Printf("%s:%d:%s %s\n", file, line, fnName, str)
}

func main() {
	log.SetFlags(log.Ldate | log.Ltime)
	foo()
}