error_inspect.go

package main

import (
	"fmt"

	"golang.org/x/xerrors"
)

type printer struct {
	values   []string
	function interface{}
	file     interface{}
	line     interface{}
}

var _ xerrors.Printer = &printer{}

func (p *printer) Print(args ...interface{}) {
}

func (p *printer) Printf(format string, args ...interface{}) {
	if format == "%s\n    " {
		p.function = args[0]
	}
	if format == "%s:%d\n" {
		p.file = args[0]
		p.line = args[1]
	}
}

func (p *printer) Detail() bool {
	return true
}

func err() error {
	return xerrors.Errorf("err")
}
func main() {
	err := xerrors.Errorf("test: %w", err())
	var printers []printer
	e := err
	for e != nil {
		if fmtr, ok := e.(xerrors.Formatter); ok {
			p := printer{}
			e = fmtr.FormatError(&p)
			printers = append(printers, p)
		} else {
			break
		}
	}
	for i, _ := range printers {
		fmt.Printf("function: %s, file: %s, line: %d\n", printers[i].function, printers[i].file, printers[i].line)
	}
	fmt.Printf("%+v\n", err)
}