Add Wrapf and formatting declarations

adaptor.go

@@ -0,0 +1,189 @@
+package errorx
+
+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
+}

errorx.go

@@ -59,3 +59,13 @@ type errorString struct {
 func (e *errorString) Error() string {
 	return e.s
 }
+
+func (e *errorString) Format(s fmt.State, v rune) {
+	FormatError(e, s, v)
+}
+
+func (e *errorString) FormatError(p Printer) (next error) {
+	p.Print(e.s)
+	e.frame.Format(p)
+	return nil
+}

format.go

@@ -0,0 +1,12 @@
+package errorx
+
+type Formatter interface {
+	error
+	FormatError(p Printer) (next error)
+}
+
+type Printer interface {
+	Print(args ...any)
+	Printf(format string, args ...any)
+	Detail() bool
+}

frame.go

@@ -21,6 +21,18 @@ func (f Frame) Location() (function, file string, line int) {
 	return fr.Function, fr.File, fr.Line
 }
 
+func (f Frame) Format(p Printer) {
+	if p.Detail() {
+		function, file, line := f.Location()
+		if function != "" {
+			p.Printf("%s\n    ", function)
+		}
+		if file != "" {
+			p.Printf("%s:%d\n", file, line)
+		}
+	}
+}
+
 func caller(skip int) Frame {
 	var s Frame
 	runtime.Callers(skip+1, s.frames[:])

wrap.go

@@ -0,0 +1,63 @@
+package errorx
+
+import "fmt"
+
+func Trace(err error) error {
+	if err == nil {
+		return nil
+	}
+
+	frame := Frame{}
+	if IsTracingEnabled() {
+		frame = caller(1)
+	}
+	return &wrapError{
+		err:   err,
+		frame: frame,
+	}
+}
+
+func Wrapf(err error, format string, a ...any) error {
+	if err == nil {
+		return nil
+	}
+
+	frame := Frame{}
+	if IsTracingEnabled() {
+		frame = caller(1)
+	}
+
+	msg := format
+	if a != nil {
+		msg = fmt.Sprintf(format, a...)
+	}
+	return &wrapError{
+		err:   err,
+		msg:   msg,
+		frame: frame,
+	}
+}
+
+type wrapError struct {
+	err   error
+	msg   string
+	frame Frame
+}
+
+func (e *wrapError) Error() string {
+	return fmt.Sprint(e)
+}
+
+func (e *wrapError) Format(s fmt.State, v rune) {
+	FormatError(e, s, v)
+}
+
+func (e *wrapError) FormatError(p Printer) (next error) {
+	p.Print(e.msg)
+	e.frame.Format(p)
+	return e.err
+}
+
+func (e *wrapError) Unwrap() error {
+	return e.err
+}