func Errorf()

in fmt.go [36:79]
34 lines of code
13 McCabe index (conditional complexity)

func Errorf(format string, a ...interface{}) error {
	format = formatPlusW(format)
	// Support a ": %[wsv]" suffix, which works well with xerrors.Formatter.
	wrap := strings.HasSuffix(format, ": %w")
	idx, format2, ok := parsePercentW(format)
	percentWElsewhere := !wrap && idx >= 0
	if !percentWElsewhere && (wrap || strings.HasSuffix(format, ": %s") || strings.HasSuffix(format, ": %v")) {
		err := errorAt(a, len(a)-1)
		if err == nil {
			return &noWrapError{fmt.Sprintf(format, a...), nil, Caller(1)}
		}
		// TODO: this is not entirely correct. The error value could be
		// printed elsewhere in format if it mixes numbered with unnumbered
		// substitutions. With relatively small changes to doPrintf we can
		// have it optionally ignore extra arguments and pass the argument
		// list in its entirety.
		msg := fmt.Sprintf(format[:len(format)-len(": %s")], a[:len(a)-1]...)
		frame := Frame{}
		if internal.EnableTrace {
			frame = Caller(1)
		}
		if wrap {
			return &wrapError{msg, err, frame}
		}
		return &noWrapError{msg, err, frame}
	}
	// Support %w anywhere.
	// TODO: don't repeat the wrapped error's message when %w occurs in the middle.
	msg := fmt.Sprintf(format2, a...)
	if idx < 0 {
		return &noWrapError{msg, nil, Caller(1)}
	}
	err := errorAt(a, idx)
	if !ok || err == nil {
		// Too many %ws or argument of %w is not an error. Approximate the Go
		// 1.13 fmt.Errorf message.
		return &noWrapError{fmt.Sprintf("%sw(%s)", percentBangString, msg), nil, Caller(1)}
	}
	frame := Frame{}
	if internal.EnableTrace {
		frame = Caller(1)
	}
	return &wrapError{msg, err, frame}
}