const fn is_int_char(c: char) -> bool {

    c.is_ascii_hexdigit() || c == '_'

}

const fn is_float_char(c: char) -> bool {

    c.is_ascii_digit() || matches!(c, 'e' | 'E' | '.' | '+' | '-' | '_')

}

pub fn is_ident_first_char(c: char) -> bool {

    c == '_' || is_xid_start(c)

}

pub fn is_ident_raw_char(c: char) -> bool {

    matches!(c, '.' | '+' | '-') | is_xid_continue(c)

}

pub const fn is_whitespace_char(c: char) -> bool {

    matches!(

        c,

}

    fn eq(&self, other: &Self) -> bool {

        self.cursor == other.cursor

    }

    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {

        self.cursor.partial_cmp(&other.cursor)

    }

    pub fn new(src: &'a str) -> SpannedResult<Self> {

        let mut parser = Parser {

            exts: Extensions::empty(),

            src,

            cursor: ParserCursor {

                cursor: 0,

                pre_ws_cursor: 0,

                last_ws_len: 0,

            },

        };

        parser.skip_ws().map_err(|e| parser.span_error(e))?;

            let attribute = parser.extensions().map_err(|e| parser.span_error(e))?;

            if attribute.is_empty() {

                break;

            }

            parser.exts |= attribute;

            parser.skip_ws().map_err(|e| parser.span_error(e))?;

        Ok(parser)

    }

    fn set_cursor(&mut self, cursor: ParserCursor) {

        self.cursor = cursor;

    }

    pub fn span_error(&self, code: Error) -> SpannedError {

        SpannedError {

            code,

            position: Position::from_src_end(&self.src[..self.cursor.cursor]),

        }

    }

    pub fn advance_bytes(&mut self, bytes: usize) {

        self.cursor.cursor += bytes;

    }

    pub fn next_char(&mut self) -> Result<char> {

        let c = self.peek_char_or_eof()?;

        self.cursor.cursor += c.len_utf8();

        Ok(c)

    }

    pub fn skip_next_char(&mut self) {

        std::mem::drop(self.next_char());

    }

    pub fn peek_char(&self) -> Option<char> {

        self.src().chars().next()

    }

    pub fn peek_char_or_eof(&self) -> Result<char> {

        self.peek_char().ok_or(Error::Eof)

    }

    pub fn check_char(&self, c: char) -> bool {

        self.src().starts_with(c)

    }

    pub fn check_str(&self, s: &str) -> bool {

        self.src().starts_with(s)

    }

    pub fn src(&self) -> &'a str {

        &self.src[self.cursor.cursor..]

    }

    pub fn pre_ws_src(&self) -> &'a str {

        &self.src[self.cursor.pre_ws_cursor..]

    }

    pub fn consume_str(&mut self, s: &str) -> bool {

        if self.check_str(s) {

            self.advance_bytes(s.len());

            true

            false

    }

    pub fn consume_char(&mut self, c: char) -> bool {

        if self.check_char(c) {

            self.advance_bytes(c.len_utf8());

            true

            false

    }

    fn consume_all(&mut self, all: &[&str]) -> Result<bool> {

        all.iter()

            .map(|elem| {

                if self.consume_str(elem) {

                    self.skip_ws()?;

                    Ok(true)

                    Ok(false)

            })

            .try_fold(true, |acc, x| x.map(|x| x && acc))

    }

    pub fn expect_char(&mut self, expected: char, error: Error) -> Result<()> {

        if self.consume_char(expected) {

            Ok(())

            Err(error)

    }

    pub fn next_chars_while_len(&self, condition: fn(char) -> bool) -> usize {

        self.next_chars_while_from_len(0, condition)

    }

    pub fn next_chars_while_from_len(&self, from: usize, condition: fn(char) -> bool) -> usize {

        self.src()[from..]

            .find(|c| !condition(c))

            .unwrap_or(self.src().len() - from)

    }

    fn parse_integer_digits<T: Num>(

        &mut self,

        s: &str,

        base: u8,

        f: fn(&mut T, u8) -> bool,

    ) -> Result<T> {

        let mut num_acc = T::from_u8(0);

        for (i, c) in s.char_indices() {

            if c == '_' {

                continue;

            }

            if num_acc.checked_mul_ext(base) {

                self.advance_bytes(s.len());

                return Err(Error::IntegerOutOfBounds);

            }

            let digit = Self::decode_hex(c)?;

            if digit >= base {

                self.advance_bytes(i);

                return Err(Error::InvalidIntegerDigit { digit: c, base });

            }

            if f(&mut num_acc, digit) {

                self.advance_bytes(s.len());

                return Err(Error::IntegerOutOfBounds);

            }

        self.advance_bytes(s.len());

        Ok(num_acc)

    }

    fn parse_integer<T: Num>(&mut self, sign: i8) -> Result<T> {

        let base = match () {

            () if self.consume_str("0b") => 2,

            () if self.consume_str("0o") => 8,

            () if self.consume_str("0x") => 16,

            () => 10,

        let num_bytes = self.next_chars_while_len(is_int_char);

        if num_bytes == 0 {

            return Err(Error::ExpectedInteger);

        }

        if self.check_char('_') {

            return Err(Error::UnderscoreAtBeginning);

        }

        let s = &self.src()[..num_bytes];

        if sign > 0 {

            self.parse_integer_digits(s, base, T::checked_add_ext)

            self.parse_integer_digits(s, base, T::checked_sub_ext)

    }

    pub fn integer<T: Integer>(&mut self) -> Result<T> {

        let src_backup = self.src();

        let is_negative = match self.peek_char_or_eof()? {

                self.skip_next_char();

                false

                self.skip_next_char();

                true

            'b' if self.consume_str("b'") => {

                let byte = match self.next_char()? {

                    '\\' => match self.parse_escape(EscapeEncoding::Binary, true)? {

                        EscapeCharacter::Ascii(b) => b,

                            return Err(Error::InvalidEscape(

                                "Unexpected Unicode escape in byte literal",

                            ))

                    b if b.is_ascii() => b as u8,

                    _ => return Err(Error::ExpectedByteLiteral),

                if !self.consume_char('\'') {

                    return Err(Error::ExpectedByteLiteral);

                }

                let bytes_ron = &src_backup[..src_backup.len() - self.src().len()];

                return T::try_from_parsed_integer(ParsedInteger::U8(byte), bytes_ron);

            _ => false,

        let sign = if is_negative { -1 } else { 1 };

        let num_bytes = self.next_chars_while_len(is_int_char);

        if self.src()[num_bytes..].starts_with(['i', 'u']) {

            let int_cursor = self.cursor;

            self.advance_bytes(num_bytes);

                let (res, suffix_bytes) = if self.consume_ident("i8") {

                    let suffix_bytes = self.src();

                    self.set_cursor(int_cursor);

                    (

                        self.parse_integer::<i8>(sign).map(ParsedInteger::I8),

                        suffix_bytes,

                    )

                } else if self.consume_ident("i16") {

                    let suffix_bytes = self.src();

                    self.set_cursor(int_cursor);

                    (

                        self.parse_integer::<i16>(sign).map(ParsedInteger::I16),

                        suffix_bytes,

                    )

                } else if self.consume_ident("i32") {

                    let suffix_bytes = self.src();

                    self.set_cursor(int_cursor);

                    (

                        self.parse_integer::<i32>(sign).map(ParsedInteger::I32),

                        suffix_bytes,

                    )

                } else if self.consume_ident("i64") {

                    let suffix_bytes = self.src();

                    self.set_cursor(int_cursor);

                    (

                        self.parse_integer::<i64>(sign).map(ParsedInteger::I64),

                        suffix_bytes,

                    )

                } else if self.consume_ident("u8") {

                    let suffix_bytes = self.src();

                    self.set_cursor(int_cursor);

                    (

                        self.parse_integer::<u8>(sign).map(ParsedInteger::U8),

                        suffix_bytes,

                    )

                } else if self.consume_ident("u16") {

                    let suffix_bytes = self.src();

                    self.set_cursor(int_cursor);

                    (

                        self.parse_integer::<u16>(sign).map(ParsedInteger::U16),

                        suffix_bytes,

                    )

                } else if self.consume_ident("u32") {

                    let suffix_bytes = self.src();

                    self.set_cursor(int_cursor);

                    (

                        self.parse_integer::<u32>(sign).map(ParsedInteger::U32),

                        suffix_bytes,

                    )

                } else if self.consume_ident("u64") {

                    let suffix_bytes = self.src();

                    self.set_cursor(int_cursor);

                    (

                        self.parse_integer::<u64>(sign).map(ParsedInteger::U64),

                        suffix_bytes,

                    )

                    if self.consume_ident("i128") {

                        let suffix_bytes = self.src();

                        self.set_cursor(int_cursor);

                        (

                            self.parse_integer::<i128>(sign).map(ParsedInteger::I128),

                            suffix_bytes,

                        )

                    } else if self.consume_ident("u128") {

                        let suffix_bytes = self.src();

                        self.set_cursor(int_cursor);

                        (

                            self.parse_integer::<u128>(sign).map(ParsedInteger::U128),

                            suffix_bytes,

                        )

                        break;

                        break;

                if !matches!(

                    &res,

                ) {

                    // Advance past the number suffix

                    self.skip_identifier();

                }

                let integer_ron = &src_backup[..src_backup.len() - suffix_bytes.len()];

                return res.and_then(|parsed| T::try_from_parsed_integer(parsed, integer_ron));

            self.set_cursor(int_cursor);

        }

        T::parse(self, sign)

    }

    pub fn any_number(&mut self) -> Result<Number> {

        if self.next_bytes_is_float() {

            return match self.float::<ParsedFloat>()? {

                ParsedFloat::F32(v) => Ok(Number::F32(v.into())),

                ParsedFloat::F64(v) => Ok(Number::F64(v.into())),

        }

        let backup_cursor = self.cursor;

        let (integer_err, integer_cursor) = match self.integer::<ParsedInteger>() {

            Ok(integer) => {

                return match integer {

                    ParsedInteger::I8(v) => Ok(Number::I8(v)),

                    ParsedInteger::I16(v) => Ok(Number::I16(v)),

                    ParsedInteger::I32(v) => Ok(Number::I32(v)),

                    ParsedInteger::I64(v) => Ok(Number::I64(v)),

                    ParsedInteger::I128(v) => Ok(Number::I128(v)),

                    ParsedInteger::U8(v) => Ok(Number::U8(v)),

                    ParsedInteger::U16(v) => Ok(Number::U16(v)),

                    ParsedInteger::U32(v) => Ok(Number::U32(v)),

                    ParsedInteger::U64(v) => Ok(Number::U64(v)),

                    ParsedInteger::U128(v) => Ok(Number::U128(v)),

            Err(err) => (err, self.cursor),

        };

        self.set_cursor(backup_cursor);

        // Fall-back to parse an out-of-range integer as a float

        match self.float::<ParsedFloat>() {

            Ok(ParsedFloat::F32(v)) if self.cursor >= integer_cursor => Ok(Number::F32(v.into())),

            Ok(ParsedFloat::F64(v)) if self.cursor >= integer_cursor => Ok(Number::F64(v.into())),

                self.set_cursor(integer_cursor);

                Err(integer_err)

    }

    pub fn bool(&mut self) -> Result<bool> {

        if self.consume_ident("true") {

            Ok(true)

        } else if self.consume_ident("false") {

            Ok(false)

            Err(Error::ExpectedBoolean)

    }

    pub fn char(&mut self) -> Result<char> {

        self.expect_char('\'', Error::ExpectedChar)?;

        let c = self.next_char()?;

        let c = if c == '\\' {

            match self.parse_escape(EscapeEncoding::Utf8, true)? {

                EscapeCharacter::Ascii(b) => char::from(b),

                EscapeCharacter::Utf8(c) => c,

            c

        self.expect_char('\'', Error::ExpectedChar)?;

        Ok(c)

    }

    pub fn comma(&mut self) -> Result<bool> {

        self.skip_ws()?;

        if self.consume_char(',') {

            self.skip_ws()?;

            Ok(true)

            Ok(false)

    }

    pub fn check_ident(&mut self, ident: &str) -> bool {

        self.check_str(ident) && !self.check_ident_other_char(ident.len())

    }

    fn check_ident_other_char(&self, index: usize) -> bool {

        self.src()[index..]

            .chars()

            .next()

            .map_or(false, is_xid_continue)

    }

    pub fn check_struct_type(

        &mut self,

        newtype: NewtypeMode,

        tuple: TupleMode,

    ) -> Result<StructType> {

        fn check_struct_type_inner(

            parser: &mut Parser,

            newtype: NewtypeMode,

            tuple: TupleMode,

        ) -> Result<StructType> {

            if matches!(newtype, NewtypeMode::NoParensMeanUnit) && !parser.consume_char('(') {

                return Ok(StructType::Unit);

            }

            parser.skip_ws()?;

            if matches!(newtype, NewtypeMode::NoParensMeanUnit) && parser.check_char(')') {

                return Ok(StructType::EmptyTuple);

            }

            if parser.skip_identifier().is_some() {

                parser.skip_ws()?;

                match parser.peek_char() {

                    Some(':') => return Ok(StructType::Named),

                        parser.skip_next_char();

                        parser.skip_ws()?;

                        if parser.check_char(')') {

                        }

                        // Definitely a tuple struct with more than one field

                        return Ok(StructType::NonNewtypeTuple);

                    Some(')') => return Ok(StructType::NewtypeTuple),

                    Some(_) | None => (),

            }

            if matches!(tuple, TupleMode::ImpreciseTupleOrNewtype) {

                return Ok(StructType::AnyTuple);

            }

            let mut braces = 1_usize;

            let mut more_than_one = false;

            while braces > 0 {

                parser.skip_ws()?;

                let cursor_backup = parser.cursor;

                if parser.char().is_err() {

                    parser.set_cursor(cursor_backup);

                }

                let cursor_backup = parser.cursor;

                match parser.string() {

                    Ok(_) => (),

                    Err(_) => parser.set_cursor(cursor_backup),

                let cursor_backup = parser.cursor;

                // we have already checked for strings, which subsume base64 byte strings

                match parser.byte_string_no_base64() {

                    Ok(_) => (),

                    Err(_) => parser.set_cursor(cursor_backup),

                let c = parser.next_char()?;

                if matches!(c, '(' | '[' | '{') {

                    braces += 1;

                } else if matches!(c, ')' | ']' | '}') {

                    braces -= 1;

                } else if c == ',' && braces == 1 {

                    parser.skip_ws()?;

                    more_than_one = !parser.check_char(')');

                    break;

                }

            if more_than_one {

                Ok(StructType::NonNewtypeTuple)

                Ok(StructType::NewtypeTuple)

        }

        let backup_cursor = self.cursor;

        let result = check_struct_type_inner(self, newtype, tuple);

        if result.is_ok() {

            // Revert the parser to before the struct type check

            self.set_cursor(backup_cursor);

        }

        result

    }

    pub fn consume_ident(&mut self, ident: &str) -> bool {

        if self.check_ident(ident) {

            self.advance_bytes(ident.len());

            true

            false

    }

    pub fn consume_struct_name(&mut self, ident: &'static str) -> Result<bool> {

        if self.check_ident("") {

            if self.exts.contains(Extensions::EXPLICIT_STRUCT_NAMES) {

                return Err(Error::ExpectedStructName(ident.to_string()));

            }

            return Ok(false);

        }

        let found_ident = match self.identifier() {

            Ok(maybe_ident) => maybe_ident,

            Err(Error::SuggestRawIdentifier(found_ident)) if found_ident == ident => {

                return Err(Error::SuggestRawIdentifier(found_ident))

            Err(_) => return Err(Error::ExpectedNamedStructLike(ident)),

        if ident.is_empty() {

            return Err(Error::ExpectedNamedStructLike(ident));

        }

        if found_ident != ident {

            return Err(Error::ExpectedDifferentStructName {

                expected: ident,

                found: String::from(found_ident),

            });

        }

        Ok(true)

    }

    fn extensions(&mut self) -> Result<Extensions> {

        if !self.check_char('#') {

            return Ok(Extensions::empty());

        }

        if !self.consume_all(&["#", "!", "[", "enable", "("])? {

            return Err(Error::ExpectedAttribute);

        }

        self.skip_ws()?;

        let mut extensions = Extensions::empty();

            let ident = self.identifier()?;

            let extension = Extensions::from_ident(ident)

                .ok_or_else(|| Error::NoSuchExtension(ident.into()))?;

            extensions |= extension;

            let comma = self.comma()?;

            if !comma && self.check_ident_other_char(0) {

                return Err(Error::ExpectedComma);

            }

            // If there's no comma, assume the list ended.

            // If there is, it might be a trailing one, thus we only

            // continue the loop if we get an ident char.

            if !comma || !self.check_ident_other_char(0) {

                break;

            }

        self.skip_ws()?;

        if self.consume_all(&[")", "]"])? {

            Ok(extensions)

            Err(Error::ExpectedAttributeEnd)

    }

    pub fn float<T: Float>(&mut self) -> Result<T> {

        for (literal, value_f32, value_f64) in &[

            ("inf", f32::INFINITY, f64::INFINITY),

            ("+inf", f32::INFINITY, f64::INFINITY),

            ("-inf", f32::NEG_INFINITY, f64::NEG_INFINITY),

            ("NaN", f32::NAN, f64::NAN),

            ("+NaN", f32::NAN, f64::NAN),

            ("-NaN", -f32::NAN, -f64::NAN),

        ] {

            if self.consume_ident(literal) {

                return T::parse(literal);

            }

            if let Some(suffix) = self.src().strip_prefix(literal) {

                if let Some(post_suffix) = suffix.strip_prefix(F32_SUFFIX) {

                    if !post_suffix.chars().next().map_or(false, is_xid_continue) {

                        let float_ron = &self.src()[..literal.len() + F32_SUFFIX.len()];

                        self.advance_bytes(literal.len() + F32_SUFFIX.len());

                        return T::try_from_parsed_float(ParsedFloat::F32(*value_f32), float_ron);

                    }

                }

                if let Some(post_suffix) = suffix.strip_prefix(F64_SUFFIX) {

                    if !post_suffix.chars().next().map_or(false, is_xid_continue) {

                        let float_ron = &self.src()[..literal.len() + F64_SUFFIX.len()];

                        self.advance_bytes(literal.len() + F64_SUFFIX.len());

                        return T::try_from_parsed_float(ParsedFloat::F64(*value_f64), float_ron);

                    }

                }

            }

        let num_bytes = self.next_chars_while_len(is_float_char);

        if num_bytes == 0 {

            return Err(Error::ExpectedFloat);

        }

        if self.check_char('_') {

            return Err(Error::UnderscoreAtBeginning);

        }

        let mut f = String::with_capacity(num_bytes);

        let mut allow_underscore = false;

        for (i, c) in self.src()[..num_bytes].char_indices() {

            match c {

                '_' if allow_underscore => continue,

                    self.advance_bytes(i);

                    return Err(Error::FloatUnderscore);

                '0'..='9' | 'e' | 'E' => allow_underscore = true,

                '.' => allow_underscore = false,

                _ => (),

            f.push(c);

        if self.src()[num_bytes..].starts_with('f') {

            let backup_cursor = self.cursor;

            self.advance_bytes(num_bytes);

                let res = if self.consume_ident(F32_SUFFIX) {

                    f32::from_str(&f).map(ParsedFloat::F32)

                } else if self.consume_ident(F64_SUFFIX) {

                    f64::from_str(&f).map(ParsedFloat::F64)

                    break;

                let parsed = if let Ok(parsed) = res {

                    parsed

                    self.set_cursor(backup_cursor);

                    return Err(Error::ExpectedFloat);

                let float_ron = &self.src[backup_cursor.cursor..self.cursor.cursor];

                return T::try_from_parsed_float(parsed, float_ron);

            self.set_cursor(backup_cursor);

        }

        let value = T::parse(&f)?;

        self.advance_bytes(num_bytes);

        Ok(value)

    }

    pub fn skip_identifier(&mut self) -> Option<&'a str> {

        #[allow(clippy::nonminimal_bool)]

        if self.check_str("b\"") // byte string

            || self.check_str("b'") // byte literal

            || self.check_str("br#") // raw byte string

            || self.check_str("br\"") // raw byte string

            || self.check_str("r\"") // raw string

            || self.check_str("r#\"") // raw string

            || self.check_str("r##") // raw string

            || false

            return None;

        }

        if self.check_str("r#") {

            let len = self.next_chars_while_from_len(2, is_ident_raw_char);

            if len > 0 {

                let ident = &self.src()[2..2 + len];

                self.advance_bytes(2 + len);

                return Some(ident);

            }

            return None;

        }

        if let Some(c) = self.peek_char() {

            if is_ident_first_char(c) {

                let len =

                    c.len_utf8() + self.next_chars_while_from_len(c.len_utf8(), is_xid_continue);

                let ident = &self.src()[..len];

                self.advance_bytes(len);

                return Some(ident);

            }

        }

        None

    }

    pub fn identifier(&mut self) -> Result<&'a str> {

        let first = self.peek_char_or_eof()?;

        if !is_ident_first_char(first) {

            if is_ident_raw_char(first) {

                let ident_bytes = self.next_chars_while_len(is_ident_raw_char);

                return Err(Error::SuggestRawIdentifier(

                    self.src()[..ident_bytes].into(),

                ));

            }

            return Err(Error::ExpectedIdentifier);

        }

        // If the next 2-3 bytes signify the start of a (raw) (byte) string

        //  literal, return an error.

        #[allow(clippy::nonminimal_bool)]

        if self.check_str("b\"") // byte string

            || self.check_str("b'") // byte literal

            || self.check_str("br#") // raw byte string

            || self.check_str("br\"") // raw byte string

            || self.check_str("r\"") // raw string

            || self.check_str("r#\"") // raw string

            || self.check_str("r##") // raw string

            || false

            return Err(Error::ExpectedIdentifier);

        }

        let length = if self.check_str("r#") {

            let cursor_backup = self.cursor;

            self.advance_bytes(2);

            if !matches!(self.peek_char(), Some(c) if is_ident_raw_char(c)) {

                self.set_cursor(cursor_backup);

                return Err(Error::ExpectedIdentifier);

            }

            self.next_chars_while_len(is_ident_raw_char)

        } else if first == 'r' {

            let std_ident_length = self.next_chars_while_len(is_xid_continue);

            let raw_ident_length = self.next_chars_while_len(is_ident_raw_char);

            if raw_ident_length > std_ident_length {

                return Err(Error::SuggestRawIdentifier(

                    self.src()[..raw_ident_length].into(),

                ));

            }

            std_ident_length

            let std_ident_length = first.len_utf8()

                + self.next_chars_while_from_len(first.len_utf8(), is_xid_continue);

            let raw_ident_length = self.next_chars_while_len(is_ident_raw_char);

            if raw_ident_length > std_ident_length {

                return Err(Error::SuggestRawIdentifier(

                    self.src()[..raw_ident_length].into(),

                ));

            }

            std_ident_length

        let ident = &self.src()[..length];

        self.advance_bytes(length);

        Ok(ident)

    }

    pub fn next_bytes_is_float(&mut self) -> bool {

        if let Some(c) = self.peek_char() {

            let skip = match c {

                '+' | '-' => 1,

                _ => 0,

            let valid_float_len = self.next_chars_while_from_len(skip, is_float_char);

            let valid_int_len = self.next_chars_while_from_len(skip, is_int_char);

            valid_float_len > valid_int_len

            false

    }

    pub fn skip_ws(&mut self) -> Result<()> {

        if (self.cursor.last_ws_len != WS_CURSOR_UNCLOSED_LINE)

            && ((self.cursor.pre_ws_cursor + self.cursor.last_ws_len) < self.cursor.cursor)

        {

            // the last whitespace is disjoint from this one, we need to track a new one

            self.cursor.pre_ws_cursor = self.cursor.cursor;

        }

        if self.src().is_empty() {

            return Ok(());

        }

            self.advance_bytes(self.next_chars_while_len(is_whitespace_char));

            match self.skip_comment()? {

                None => break,

                    self.cursor.last_ws_len = WS_CURSOR_UNCLOSED_LINE;

                    return Ok(());

                Some(Comment::ClosedLine | Comment::Block) => continue,

        self.cursor.last_ws_len = self.cursor.cursor - self.cursor.pre_ws_cursor;

        Ok(())

    }

    pub fn has_unclosed_line_comment(&self) -> bool {

        self.src().is_empty() && self.cursor.last_ws_len == WS_CURSOR_UNCLOSED_LINE

    }

    pub fn byte_string(&mut self) -> Result<ParsedByteStr<'a>> {

        fn expected_byte_string_found_base64(

            base64_str: &ParsedStr,

            byte_str: &ParsedByteStr,

        ) -> Error {

            let byte_str = match &byte_str {

                ParsedByteStr::Allocated(b) => b.as_slice(),

            .iter()

            .flat_map(|c| std::ascii::escape_default(*c))

            .map(char::from)

            .collect::<String>();

            let base64_str = match &base64_str {

                ParsedStr::Slice(s) => s,

            Error::InvalidValueForType {

                expected: format!("the Rusty byte string b\"{}\"", byte_str),

                found: format!("the ambiguous base64 string {:?}", base64_str),

            }

        }

        if self.consume_char('"') {

            let base64_str = self.escaped_string()?;

            let base64_result = ParsedByteStr::try_from_base64(&base64_str);

            if cfg!(not(test)) {

                base64_result.map_err(Error::Base64Error)

                match base64_result {

                    Ok(byte_str) => Err(expected_byte_string_found_base64(&base64_str, &byte_str)),

                    Err(_) => Err(Error::ExpectedByteString),

        } else if self.consume_char('r') {

            let base64_str = self.raw_string()?;

            let base64_result = ParsedByteStr::try_from_base64(&base64_str);

            if cfg!(not(test)) {

                base64_result.map_err(Error::Base64Error)

                match base64_result {

                    Ok(byte_str) => Err(expected_byte_string_found_base64(&base64_str, &byte_str)),

                    Err(_) => Err(Error::ExpectedByteString),

            self.byte_string_no_base64()

    }

    pub fn byte_string_no_base64(&mut self) -> Result<ParsedByteStr<'a>> {

        if self.consume_str("b\"") {

            self.escaped_byte_string()

        } else if self.consume_str("br") {

            self.raw_byte_string()

            Err(Error::ExpectedByteString)

    }

    fn escaped_byte_string(&mut self) -> Result<ParsedByteStr<'a>> {

        match self.escaped_byte_buf(EscapeEncoding::Binary) {

            Ok((bytes, advance)) => {

                self.advance_bytes(advance);

                Ok(bytes)

            Err(err) => Err(err),

    }

    fn raw_byte_string(&mut self) -> Result<ParsedByteStr<'a>> {

        match self.raw_byte_buf() {

            Ok((bytes, advance)) => {

                self.advance_bytes(advance);

                Ok(bytes)

            Err(Error::ExpectedString) => Err(Error::ExpectedByteString),

            Err(err) => Err(err),

    }

    pub fn string(&mut self) -> Result<ParsedStr<'a>> {

        if self.consume_char('"') {

            self.escaped_string()

        } else if self.consume_char('r') {

            self.raw_string()

            Err(Error::ExpectedString)

    }

    fn escaped_string(&mut self) -> Result<ParsedStr<'a>> {

        match self.escaped_byte_buf(EscapeEncoding::Utf8) {

            Ok((bytes, advance)) => {

                let string = ParsedStr::try_from_bytes(bytes).map_err(Error::from)?;

                self.advance_bytes(advance);

                Ok(string)

            Err(err) => Err(err),

    }

    fn raw_string(&mut self) -> Result<ParsedStr<'a>> {

        match self.raw_byte_buf() {

            Ok((bytes, advance)) => {

                let string = ParsedStr::try_from_bytes(bytes).map_err(Error::from)?;

                self.advance_bytes(advance);

                Ok(string)

            Err(err) => Err(err),

    }

    fn escaped_byte_buf(&mut self, encoding: EscapeEncoding) -> Result<(ParsedByteStr<'a>, usize)> {

        let str_end = self.src().find('"').ok_or(Error::ExpectedStringEnd)?;

        let escape = self.src()[..str_end].find('\\');

        if let Some(escape) = escape {

            let mut i = escape;

            let mut s = self.src().as_bytes()[..i].to_vec();

                self.advance_bytes(i + 1);

                match self.parse_escape(encoding, false)? {

                    EscapeCharacter::Ascii(c) => s.push(c),

                    EscapeCharacter::Utf8(c) => match c.len_utf8() {

                        1 => s.push(c as u8),

                        len => {

                            let start = s.len();

                            s.extend(std::iter::repeat(0).take(len));

                            c.encode_utf8(&mut s[start..]);

                        }

                let new_str_end = self.src().find('"').ok_or(Error::ExpectedStringEnd)?;

                let new_escape = self.src()[..new_str_end].find('\\');

                if let Some(new_escape) = new_escape {

                    s.extend_from_slice(&self.src().as_bytes()[..new_escape]);

                    i = new_escape;

                } else {

                    s.extend_from_slice(&self.src().as_bytes()[..new_str_end]);

                    // Advance to the end of the string + 1 for the `"`.

                    break Ok((ParsedByteStr::Allocated(s), new_str_end + 1));

            let s = &self.src().as_bytes()[..str_end];

            // Advance by the number of bytes of the string + 1 for the `"`.

            Ok((ParsedByteStr::Slice(s), str_end + 1))

    }

    fn raw_byte_buf(&mut self) -> Result<(ParsedByteStr<'a>, usize)> {

        let num_hashes = self.next_chars_while_len(|c| c == '#');

        let hashes = &self.src()[..num_hashes];

        self.advance_bytes(num_hashes);

        self.expect_char('"', Error::ExpectedString)?;

        let ending = ["\"", hashes].concat();

        let i = self.src().find(&ending).ok_or(Error::ExpectedStringEnd)?;

        let s = &self.src().as_bytes()[..i];

        // Advance by the number of bytes of the byte string

        // + `num_hashes` + 1 for the `"`.

        Ok((ParsedByteStr::Slice(s), i + num_hashes + 1))

    }

    fn decode_ascii_escape(&mut self) -> Result<u8> {

        let mut n = 0;

        for _ in 0..2 {

            n <<= 4;

            let byte = self.next_char()?;

            let decoded = Self::decode_hex(byte)?;

            n |= decoded;

        Ok(n)

    }

    fn decode_hex(c: char) -> Result<u8> {

        if !c.is_ascii() {

            return Err(Error::InvalidEscape("Non-hex digit found"));

        }

        // c is an ASCII character that can be losslessly cast to u8

        match c as u8 {

            c @ b'0'..=b'9' => Ok(c - b'0'),

            c @ b'a'..=b'f' => Ok(10 + c - b'a'),

            c @ b'A'..=b'F' => Ok(10 + c - b'A'),

            _ => Err(Error::InvalidEscape("Non-hex digit found")),

    }

    fn parse_escape(&mut self, encoding: EscapeEncoding, is_char: bool) -> Result<EscapeCharacter> {

        let c = match self.next_char()? {

            '\'' => EscapeCharacter::Ascii(b'\''),

            '"' => EscapeCharacter::Ascii(b'"'),

            '\\' => EscapeCharacter::Ascii(b'\\'),

            'n' => EscapeCharacter::Ascii(b'\n'),

            'r' => EscapeCharacter::Ascii(b'\r'),

            't' => EscapeCharacter::Ascii(b'\t'),

            '0' => EscapeCharacter::Ascii(b'\0'),

                let b: u8 = self.decode_ascii_escape()?;

                if let EscapeEncoding::Binary = encoding {

                    return Ok(EscapeCharacter::Ascii(b));

                }

                // Fast exit for ascii character in UTF-8 string

                let mut bytes = [b, 0, 0, 0];

                if let Ok(Some(c)) = from_utf8(&bytes[..=0]).map(|s| s.chars().next()) {

                    return Ok(EscapeCharacter::Utf8(c));

                }

                if is_char {

                    return Err(Error::InvalidEscape(

                        "Not a valid byte-escaped Unicode character",

                    ));

                }

                for i in 1..4 {

                    if !self.consume_str(r"\x") {

                        return Err(Error::InvalidEscape(

                            "Not a valid byte-escaped Unicode character",

                        ));

                    }

                    bytes[i] = self.decode_ascii_escape()?;

                    if let Ok(Some(c)) = from_utf8(&bytes[..=i]).map(|s| s.chars().next()) {

                        return Ok(EscapeCharacter::Utf8(c));

                    }

                return Err(Error::InvalidEscape(

                    "Not a valid byte-escaped Unicode character",

                ));

                self.expect_char('{', Error::InvalidEscape("Missing { in Unicode escape"))?;

                let mut bytes: u32 = 0;

                let mut num_digits = 0;

                while num_digits < 6 {

                    let byte = self.peek_char_or_eof()?;

                    if byte == '}' {

                        break;

                    }

                    self.skip_next_char();

                    num_digits += 1;

                    let byte = Self::decode_hex(byte)?;

                    bytes <<= 4;

                    bytes |= u32::from(byte);

                if num_digits == 0 {

                    return Err(Error::InvalidEscape(

                        "Expected 1-6 digits, got 0 digits in Unicode escape",

                    ));

                }

                self.expect_char(

                    '}',

                    Error::InvalidEscape("No } at the end of Unicode escape"),

                )?;

                let c = char_from_u32(bytes).ok_or(Error::InvalidEscape(

                    "Not a valid Unicode-escaped character",

                ))?;

                EscapeCharacter::Utf8(c)

            _ => return Err(Error::InvalidEscape("Unknown escape character")),

        Ok(c)

    }

    fn skip_comment(&mut self) -> Result<Option<Comment>> {

        if self.consume_char('/') {

            match self.next_char()? {

                    let bytes = self.next_chars_while_len(|c| c != '\n');

                    self.advance_bytes(bytes);

                    if self.src().is_empty() {

                        Ok(Some(Comment::UnclosedLine))

                        Ok(Some(Comment::ClosedLine))

                    let mut level = 1;

                    while level > 0 {

                        let bytes = self.next_chars_while_len(|c| !matches!(c, '/' | '*'));

                        if self.src().is_empty() {

                            return Err(Error::UnclosedBlockComment);

                        }