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// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package xerrors
import (
"bytes"
"fmt"
"io"
"reflect"
"strconv"
)
// FormatError calls the FormatError method of f with an errors.Printer
// configured according to s and verb, and writes the result to s.
func FormatError(f Formatter, s fmt.State, verb rune) {
// Assuming this function is only called from the Format method, and given
// that FormatError takes precedence over Format, it cannot be called from
// any package that supports errors.Formatter. It is therefore safe to
// disregard that State may be a specific printer implementation and use one
// of our choice instead.
// limitations: does not support printing error as Go struct.
var (
sep = " " // separator before next error
p = &state{State: s}
direct = true
)
var err error = f
switch verb {
// Note that this switch must match the preference order
// for ordinary string printing (%#v before %+v, and so on).
case 'v':
if s.Flag('#') {
if stringer, ok := err.(fmt.GoStringer); ok {
io.WriteString(&p.buf, stringer.GoString())
goto exit
}
// proceed as if it were %v
} else if s.Flag('+') {
p.printDetail = true
sep = "\n - "
}
case 's':
case 'q', 'x', 'X':
// Use an intermediate buffer in the rare cases that precision,
// truncation, or one of the alternative verbs (q, x, and X) are
// specified.
direct = false
default:
p.buf.WriteString("%!")
p.buf.WriteRune(verb)
p.buf.WriteByte('(')
switch {
case err != nil:
p.buf.WriteString(reflect.TypeOf(f).String())
default:
p.buf.WriteString("<nil>")
}
p.buf.WriteByte(')')
io.Copy(s, &p.buf)
return
}
loop:
for {
switch v := err.(type) {
case Formatter:
err = v.FormatError((*printer)(p))
case fmt.Formatter:
v.Format(p, 'v')
break loop
default:
io.WriteString(&p.buf, v.Error())
break loop
}
if err == nil {
break
}
if p.needColon || !p.printDetail {
p.buf.WriteByte(':')
p.needColon = false
}
p.buf.WriteString(sep)
p.inDetail = false
p.needNewline = false
}
exit:
width, okW := s.Width()
prec, okP := s.Precision()
if !direct || (okW && width > 0) || okP {
// Construct format string from State s.
format := []byte{'%'}
if s.Flag('-') {
format = append(format, '-')
}
if s.Flag('+') {
format = append(format, '+')
}
if s.Flag(' ') {
format = append(format, ' ')
}
if okW {
format = strconv.AppendInt(format, int64(width), 10)
}
if okP {
format = append(format, '.')
format = strconv.AppendInt(format, int64(prec), 10)
}
format = append(format, string(verb)...)
fmt.Fprintf(s, string(format), p.buf.String())
} else {
io.Copy(s, &p.buf)
}
}
var detailSep = []byte("\n ")
// state tracks error printing state. It implements fmt.State.
type state struct {
fmt.State
buf bytes.Buffer
printDetail bool
inDetail bool
needColon bool
needNewline bool
}
func (s *state) Write(b []byte) (n int, err error) {
if s.printDetail {
if len(b) == 0 {
return 0, nil
}
if s.inDetail && s.needColon {
s.needNewline = true
if b[0] == '\n' {
b = b[1:]
}
}
k := 0
for i, c := range b {
if s.needNewline {
if s.inDetail && s.needColon {
s.buf.WriteByte(':')
s.needColon = false
}
s.buf.Write(detailSep)
s.needNewline = false
}
if c == '\n' {
s.buf.Write(b[k:i])
k = i + 1
s.needNewline = true
}
}
s.buf.Write(b[k:])
if !s.inDetail {
s.needColon = true
}
} else if !s.inDetail {
s.buf.Write(b)
}
return len(b), nil
}
// printer wraps a state to implement an xerrors.Printer.
type printer state
func (s *printer) Print(args ...interface{}) {
if !s.inDetail || s.printDetail {
fmt.Fprint((*state)(s), args...)
}
}
func (s *printer) Printf(format string, args ...interface{}) {
if !s.inDetail || s.printDetail {
fmt.Fprintf((*state)(s), format, args...)
}
}
func (s *printer) Detail() bool {
s.inDetail = true
return s.printDetail
}
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