Function parseFormatString

ext/formatting.go:783–827

parseFormatString formats a string according to the string.format syntax, taking the clause implementations from the provided FormatCallback and the args from the given FormatList.

(formatStr string, callback formatStringInterpolator, list formatListArgs, locale string, maxPrecision int)

// parseFormatString formats a string according to the string.format syntax, taking the clause implementations
// from the provided FormatCallback and the args from the given FormatList.
func parseFormatString(formatStr string, callback formatStringInterpolator, list formatListArgs, locale string, maxPrecision int) (string, error) {
	i := 0
	argIndex := 0
	var builtStr strings.Builder
	for i < len(formatStr) {
		if formatStr[i] == '%' {
			if i+1 < len(formatStr) && formatStr[i+1] == '%' {
				err := builtStr.WriteByte('%')
				if err != nil {
					return "", fmt.Errorf("error writing format string: %w", err)
				}
				i += 2
				continue
			} else {
				argAny, err := list.Arg(int64(argIndex))
				if err != nil {
					return "", err
				}
				if i+1 >= len(formatStr) {
					return "", errors.New("unexpected end of string")
				}
				if int64(argIndex) >= list.Size() {
					return "", fmt.Errorf("index %d out of range", argIndex)
				}
				numRead, val, refErr := parseAndFormatClause(formatStr[i:], argAny, callback, list, locale, maxPrecision)
				if refErr != nil {
					return "", refErr
				}
				_, err = builtStr.WriteString(val)
				if err != nil {
					return "", fmt.Errorf("error writing format string: %w", err)
				}
				i += numRead
				argIndex++
			}
		} else {
			err := builtStr.WriteByte(formatStr[i])
			if err != nil {
				return "", fmt.Errorf("error writing format string: %w", err)
			}
			i++
		}
	}
	return builtStr.String(), nil
}

// parseAndFormatClause parses the format clause at the start of the given string with val, and returns
// how many characters were consumed and the substituted string form of val, or an error if one occurred.