pub(crate) fn consume_string_literal(

    source: &InputSource, iter: &mut TokenIter, buffer: &mut String

) -> Result<InputSpan, ParseError> {

    if Some(TokenKind::String) != iter.next() {

        return Err(ParseError::new_error_str_at_pos(source, iter.last_valid_pos(), "expected a string literal"));

    }

    buffer.clear();

    let span = iter.next_span();

    iter.consume();

    let text = source.section_at_span(span);

    if !text.is_ascii() {

        return Err(ParseError::new_error_str_at_span(source, span, "expected an ASCII string literal"));

    }

    debug_assert_eq!(text[0], b'"'); // here as kind of a reminder: the span includes the bounding quotation marks

    debug_assert_eq!(text[text.len() - 1], b'"');

    buffer.reserve(text.len() - 2);

    let mut was_escape = false;

    for idx in 1..text.len() - 1 {

        let cur = text[idx];

        if was_escape {

            let to_push = parse_escaped_character(source, span, cur)?;

            buffer.push(to_push);

        } else {

            buffer.push(cur as char);

        }

            was_escape = false;

        } else {

        }

    }

    debug_assert!(!was_escape); // because otherwise we couldn't have ended the string literal

    Ok(span)

}

fn parse_escaped_character(source: &InputSource, literal_span: InputSpan, v: u8) -> Result<char, ParseError> {

    let result = match v {

        b'r' => '\r',

        b'n' => '\n',

        b't' => '\t',

        b'0' => '\0',

        b'\\' => '\\',

        b'\'' => '\'',

        b'"' => '"',

        v => {

            let msg = if v.is_ascii_graphic() {

                format!("unsupported escape character '{}'", v as char)

            } else {

                format!("unsupported escape character with (unsigned) byte value {}", v)

            };

            return Err(ParseError::new_error_at_span(source, literal_span, msg))