abusing defer evaluation for tracing https://go.dev/play/p/l9b03ugEgF0 https://go.dev/doc/effective_go#defer

main.go

package main

import (
	"fmt"
	"runtime"
)

func trace() func() {
	pc, file, line, _ := runtime.Caller(1)
	fmt.Printf("%s:%d enter %s\n", file, line, runtime.FuncForPC(pc).Name())
	return func() {
		pc, file, line, _ := runtime.Caller(1)
		fmt.Printf("%s:%d exit  %s\n", file, line, runtime.FuncForPC(pc).Name())
	}
}

func foo() {
	defer trace()()
	fmt.Println("lol")
}

func main() {
	foo()
}