build(ariadne): vendor serde crates

third_party/crates/proc-macro2-1.0.107/src/parse.rs

@@ -0,0 +1,991 @@
+use crate::fallback::{
+    self, is_ident_continue, is_ident_start, Group, Ident, LexError, Literal, Span, TokenStream,
+    TokenStreamBuilder,
+};
+use crate::{Delimiter, Punct, Spacing, TokenTree};
+use alloc::borrow::ToOwned as _;
+use alloc::string::ToString as _;
+use alloc::vec::Vec;
+use core::char;
+use core::str::{Bytes, CharIndices, Chars};
+
+#[derive(Copy, Clone, Eq, PartialEq)]
+pub(crate) struct Cursor<'a> {
+    pub(crate) rest: &'a str,
+    #[cfg(span_locations)]
+    pub(crate) off: u32,
+}
+
+impl<'a> Cursor<'a> {
+    pub(crate) fn advance(&self, bytes: usize) -> Cursor<'a> {
+        let (_front, rest) = self.rest.split_at(bytes);
+        Cursor {
+            rest,
+            #[cfg(span_locations)]
+            off: self.off + _front.chars().count() as u32,
+        }
+    }
+
+    pub(crate) fn starts_with(&self, s: &str) -> bool {
+        self.rest.starts_with(s)
+    }
+
+    pub(crate) fn starts_with_char(&self, ch: char) -> bool {
+        self.rest.starts_with(ch)
+    }
+
+    pub(crate) fn starts_with_fn<Pattern>(&self, f: Pattern) -> bool
+    where
+        Pattern: FnMut(char) -> bool,
+    {
+        self.rest.starts_with(f)
+    }
+
+    pub(crate) fn is_empty(&self) -> bool {
+        self.rest.is_empty()
+    }
+
+    fn len(&self) -> usize {
+        self.rest.len()
+    }
+
+    fn as_bytes(&self) -> &'a [u8] {
+        self.rest.as_bytes()
+    }
+
+    fn bytes(&self) -> Bytes<'a> {
+        self.rest.bytes()
+    }
+
+    fn chars(&self) -> Chars<'a> {
+        self.rest.chars()
+    }
+
+    fn char_indices(&self) -> CharIndices<'a> {
+        self.rest.char_indices()
+    }
+
+    fn parse(&self, tag: &str) -> Result<Cursor<'a>, Reject> {
+        if self.starts_with(tag) {
+            Ok(self.advance(tag.len()))
+        } else {
+            Err(Reject)
+        }
+    }
+}
+
+pub(crate) struct Reject;
+type PResult<'a, O> = Result<(Cursor<'a>, O), Reject>;
+
+fn skip_whitespace(input: Cursor) -> Cursor {
+    let mut s = input;
+
+    while !s.is_empty() {
+        let byte = s.as_bytes()[0];
+        if byte == b'/' {
+            if s.starts_with("//")
+                && (!s.starts_with("///") || s.starts_with("////"))
+                && !s.starts_with("//!")
+            {
+                let (cursor, _) = take_until_newline_or_eof(s);
+                s = cursor;
+                continue;
+            } else if s.starts_with("/**/") {
+                s = s.advance(4);
+                continue;
+            } else if s.starts_with("/*")
+                && (!s.starts_with("/**") || s.starts_with("/***"))
+                && !s.starts_with("/*!")
+            {
+                match block_comment(s) {
+                    Ok((rest, _)) => {
+                        s = rest;
+                        continue;
+                    }
+                    Err(Reject) => return s,
+                }
+            }
+        }
+        match byte {
+            b' ' | 0x09..=0x0d => {
+                s = s.advance(1);
+                continue;
+            }
+            b if b.is_ascii() => {}
+            _ => {
+                let ch = s.chars().next().unwrap();
+                if is_whitespace(ch) {
+                    s = s.advance(ch.len_utf8());
+                    continue;
+                }
+            }
+        }
+        return s;
+    }
+    s
+}
+
+fn block_comment(input: Cursor) -> PResult<&str> {
+    if !input.starts_with("/*") {
+        return Err(Reject);
+    }
+
+    let mut depth = 0usize;
+    let bytes = input.as_bytes();
+    let mut i = 0usize;
+    let upper = bytes.len() - 1;
+
+    while i < upper {
+        if bytes[i] == b'/' && bytes[i + 1] == b'*' {
+            depth += 1;
+            i += 1; // eat '*'
+        } else if bytes[i] == b'*' && bytes[i + 1] == b'/' {
+            depth -= 1;
+            if depth == 0 {
+                return Ok((input.advance(i + 2), &input.rest[..i + 2]));
+            }
+            i += 1; // eat '/'
+        }
+        i += 1;
+    }
+
+    Err(Reject)
+}
+
+fn is_whitespace(ch: char) -> bool {
+    // Rust treats left-to-right mark and right-to-left mark as whitespace
+    ch.is_whitespace() || ch == '\u{200e}' || ch == '\u{200f}'
+}
+
+fn word_break(input: Cursor) -> Result<Cursor, Reject> {
+    match input.chars().next() {
+        Some(ch) if is_ident_continue(ch) => Err(Reject),
+        Some(_) | None => Ok(input),
+    }
+}
+
+// Rustc's representation of a macro expansion error in expression position or
+// type position.
+const ERROR: &str = "(/*ERROR*/)";
+
+pub(crate) fn token_stream(mut input: Cursor) -> Result<TokenStream, LexError> {
+    let mut tokens = TokenStreamBuilder::new();
+    let mut stack = Vec::new();
+
+    loop {
+        input = skip_whitespace(input);
+
+        if let Ok((rest, ())) = doc_comment(input, &mut tokens) {
+            input = rest;
+            continue;
+        }
+
+        #[cfg(span_locations)]
+        let lo = input.off;
+
+        let Some(first) = input.bytes().next() else {
+            return match stack.last() {
+                None => Ok(tokens.build()),
+                #[cfg(span_locations)]
+                Some((lo, _frame)) => Err(LexError {
+                    span: Span { lo: *lo, hi: *lo },
+                }),
+                #[cfg(not(span_locations))]
+                Some(_frame) => Err(LexError { span: Span {} }),
+            };
+        };
+
+        if let Some(open_delimiter) = match first {
+            b'(' if !input.starts_with(ERROR) => Some(Delimiter::Parenthesis),
+            b'[' => Some(Delimiter::Bracket),
+            b'{' => Some(Delimiter::Brace),
+            _ => None,
+        } {
+            input = input.advance(1);
+            let frame = (open_delimiter, tokens);
+            #[cfg(span_locations)]
+            let frame = (lo, frame);
+            stack.push(frame);
+            tokens = TokenStreamBuilder::new();
+        } else if let Some(close_delimiter) = match first {
+            b')' => Some(Delimiter::Parenthesis),
+            b']' => Some(Delimiter::Bracket),
+            b'}' => Some(Delimiter::Brace),
+            _ => None,
+        } {
+            let Some(frame) = stack.pop() else {
+                return Err(lex_error(input));
+            };
+            #[cfg(span_locations)]
+            let (lo, frame) = frame;
+            let (open_delimiter, outer) = frame;
+            if open_delimiter != close_delimiter {
+                return Err(lex_error(input));
+            }
+            input = input.advance(1);
+            let mut g = Group::new(open_delimiter, tokens.build());
+            g.set_span(Span {
+                #[cfg(span_locations)]
+                lo,
+                #[cfg(span_locations)]
+                hi: input.off,
+            });
+            tokens = outer;
+            tokens.push_token_from_parser(TokenTree::Group(crate::Group::_new_fallback(g)));
+        } else {
+            let (rest, mut tt) = match leaf_token(input) {
+                Ok((rest, tt)) => (rest, tt),
+                Err(Reject) => return Err(lex_error(input)),
+            };
+            tt.set_span(crate::Span::_new_fallback(Span {
+                #[cfg(span_locations)]
+                lo,
+                #[cfg(span_locations)]
+                hi: rest.off,
+            }));
+            tokens.push_token_from_parser(tt);
+            input = rest;
+        }
+    }
+}
+
+fn lex_error(cursor: Cursor) -> LexError {
+    #[cfg(not(span_locations))]
+    let _ = cursor;
+    LexError {
+        span: Span {
+            #[cfg(span_locations)]
+            lo: cursor.off,
+            #[cfg(span_locations)]
+            hi: cursor.off,
+        },
+    }
+}
+
+fn leaf_token(input: Cursor) -> PResult<TokenTree> {
+    if let Ok((input, l)) = literal(input) {
+        // must be parsed before ident
+        Ok((input, TokenTree::Literal(crate::Literal::_new_fallback(l))))
+    } else if let Ok((input, p)) = punct(input) {
+        Ok((input, TokenTree::Punct(p)))
+    } else if let Ok((input, i)) = ident(input) {
+        Ok((input, TokenTree::Ident(i)))
+    } else if input.starts_with(ERROR) {
+        let rest = input.advance(ERROR.len());
+        let repr = crate::Literal::_new_fallback(Literal::_new(ERROR.to_owned()));
+        Ok((rest, TokenTree::Literal(repr)))
+    } else {
+        Err(Reject)
+    }
+}
+
+fn ident(input: Cursor) -> PResult<crate::Ident> {
+    if [
+        "r\"", "r#\"", "r##", "b\"", "b\'", "br\"", "br#", "c\"", "cr\"", "cr#",
+    ]
+    .iter()
+    .any(|prefix| input.starts_with(prefix))
+    {
+        Err(Reject)
+    } else {
+        ident_any(input)
+    }
+}
+
+fn ident_any(input: Cursor) -> PResult<crate::Ident> {
+    let raw = input.starts_with("r#");
+    let rest = input.advance((raw as usize) << 1);
+
+    let (rest, sym) = ident_not_raw(rest)?;
+
+    if !raw {
+        let ident =
+            crate::Ident::_new_fallback(Ident::new_unchecked(sym, fallback::Span::call_site()));
+        return Ok((rest, ident));
+    }
+
+    match sym {
+        "_" | "super" | "self" | "Self" | "crate" => return Err(Reject),
+        _ => {}
+    }
+
+    let ident =
+        crate::Ident::_new_fallback(Ident::new_raw_unchecked(sym, fallback::Span::call_site()));
+    Ok((rest, ident))
+}
+
+fn ident_not_raw(input: Cursor) -> PResult<&str> {
+    let mut chars = input.char_indices();
+
+    match chars.next() {
+        Some((_, ch)) if is_ident_start(ch) => {}
+        _ => return Err(Reject),
+    }
+
+    let mut end = input.len();
+    for (i, ch) in chars {
+        if !is_ident_continue(ch) {
+            end = i;
+            break;
+        }
+    }
+
+    Ok((input.advance(end), &input.rest[..end]))
+}
+
+pub(crate) fn literal(input: Cursor) -> PResult<Literal> {
+    let rest = literal_nocapture(input)?;
+    let end = input.len() - rest.len();
+    Ok((rest, Literal::_new(input.rest[..end].to_string())))
+}
+
+fn literal_nocapture(input: Cursor) -> Result<Cursor, Reject> {
+    if let Ok(ok) = string(input) {
+        Ok(ok)
+    } else if let Ok(ok) = byte_string(input) {
+        Ok(ok)
+    } else if let Ok(ok) = c_string(input) {
+        Ok(ok)
+    } else if let Ok(ok) = byte(input) {
+        Ok(ok)
+    } else if let Ok(ok) = character(input) {
+        Ok(ok)
+    } else if let Ok(ok) = float(input) {
+        Ok(ok)
+    } else if let Ok(ok) = int(input) {
+        Ok(ok)
+    } else {
+        Err(Reject)
+    }
+}
+
+fn literal_suffix(input: Cursor) -> Cursor {
+    match ident_not_raw(input) {
+        Ok((input, _)) => input,
+        Err(Reject) => input,
+    }
+}
+
+fn string(input: Cursor) -> Result<Cursor, Reject> {
+    if let Ok(input) = input.parse("\"") {
+        cooked_string(input)
+    } else if let Ok(input) = input.parse("r") {
+        raw_string(input)
+    } else {
+        Err(Reject)
+    }
+}
+
+fn cooked_string(mut input: Cursor) -> Result<Cursor, Reject> {
+    let mut chars = input.char_indices();
+
+    while let Some((i, ch)) = chars.next() {
+        match ch {
+            '"' => {
+                let input = input.advance(i + 1);
+                return Ok(literal_suffix(input));
+            }
+            '\r' => match chars.next() {
+                Some((_, '\n')) => {}
+                _ => break,
+            },
+            '\\' => match chars.next() {
+                Some((_, 'x')) => {
+                    backslash_x_char(&mut chars)?;
+                }
+                Some((_, 'n' | 'r' | 't' | '\\' | '\'' | '"' | '0')) => {}
+                Some((_, 'u')) => {
+                    backslash_u(&mut chars)?;
+                }
+                Some((newline, ch @ ('\n' | '\r'))) => {
+                    input = input.advance(newline + 1);
+                    trailing_backslash(&mut input, ch as u8)?;
+                    chars = input.char_indices();
+                }
+                _ => break,
+            },
+            _ch => {}
+        }
+    }
+    Err(Reject)
+}
+
+fn raw_string(input: Cursor) -> Result<Cursor, Reject> {
+    let (input, delimiter) = delimiter_of_raw_string(input)?;
+    let mut bytes = input.bytes().enumerate();
+    while let Some((i, byte)) = bytes.next() {
+        match byte {
+            b'"' if input.rest[i + 1..].starts_with(delimiter) => {
+                let rest = input.advance(i + 1 + delimiter.len());
+                return Ok(literal_suffix(rest));
+            }
+            b'\r' => match bytes.next() {
+                Some((_, b'\n')) => {}
+                _ => break,
+            },
+            _ => {}
+        }
+    }
+    Err(Reject)
+}
+
+fn byte_string(input: Cursor) -> Result<Cursor, Reject> {
+    if let Ok(input) = input.parse("b\"") {
+        cooked_byte_string(input)
+    } else if let Ok(input) = input.parse("br") {
+        raw_byte_string(input)
+    } else {
+        Err(Reject)
+    }
+}
+
+fn cooked_byte_string(mut input: Cursor) -> Result<Cursor, Reject> {
+    let mut bytes = input.bytes().enumerate();
+    while let Some((offset, b)) = bytes.next() {
+        match b {
+            b'"' => {
+                let input = input.advance(offset + 1);
+                return Ok(literal_suffix(input));
+            }
+            b'\r' => match bytes.next() {
+                Some((_, b'\n')) => {}
+                _ => break,
+            },
+            b'\\' => match bytes.next() {
+                Some((_, b'x')) => {
+                    backslash_x_byte(&mut bytes)?;
+                }
+                Some((_, b'n' | b'r' | b't' | b'\\' | b'0' | b'\'' | b'"')) => {}
+                Some((newline, b @ (b'\n' | b'\r'))) => {
+                    input = input.advance(newline + 1);
+                    trailing_backslash(&mut input, b)?;
+                    bytes = input.bytes().enumerate();
+                }
+                _ => break,
+            },
+            b if b.is_ascii() => {}
+            _ => break,
+        }
+    }
+    Err(Reject)
+}
+
+fn delimiter_of_raw_string(input: Cursor) -> PResult<&str> {
+    for (i, byte) in input.bytes().enumerate() {
+        match byte {
+            b'"' => {
+                if i > 255 {
+                    // https://github.com/rust-lang/rust/pull/95251
+                    return Err(Reject);
+                }
+                return Ok((input.advance(i + 1), &input.rest[..i]));
+            }
+            b'#' => {}
+            _ => break,
+        }
+    }
+    Err(Reject)
+}
+
+fn raw_byte_string(input: Cursor) -> Result<Cursor, Reject> {
+    let (input, delimiter) = delimiter_of_raw_string(input)?;
+    let mut bytes = input.bytes().enumerate();
+    while let Some((i, byte)) = bytes.next() {
+        match byte {
+            b'"' if input.rest[i + 1..].starts_with(delimiter) => {
+                let rest = input.advance(i + 1 + delimiter.len());
+                return Ok(literal_suffix(rest));
+            }
+            b'\r' => match bytes.next() {
+                Some((_, b'\n')) => {}
+                _ => break,
+            },
+            other => {
+                if !other.is_ascii() {
+                    break;
+                }
+            }
+        }
+    }
+    Err(Reject)
+}
+
+fn c_string(input: Cursor) -> Result<Cursor, Reject> {
+    if let Ok(input) = input.parse("c\"") {
+        cooked_c_string(input)
+    } else if let Ok(input) = input.parse("cr") {
+        raw_c_string(input)
+    } else {
+        Err(Reject)
+    }
+}
+
+fn raw_c_string(input: Cursor) -> Result<Cursor, Reject> {
+    let (input, delimiter) = delimiter_of_raw_string(input)?;
+    let mut bytes = input.bytes().enumerate();
+    while let Some((i, byte)) = bytes.next() {
+        match byte {
+            b'"' if input.rest[i + 1..].starts_with(delimiter) => {
+                let rest = input.advance(i + 1 + delimiter.len());
+                return Ok(literal_suffix(rest));
+            }
+            b'\r' => match bytes.next() {
+                Some((_, b'\n')) => {}
+                _ => break,
+            },
+            b'\0' => break,
+            _ => {}
+        }
+    }
+    Err(Reject)
+}
+
+fn cooked_c_string(mut input: Cursor) -> Result<Cursor, Reject> {
+    let mut chars = input.char_indices();
+
+    while let Some((i, ch)) = chars.next() {
+        match ch {
+            '"' => {
+                let input = input.advance(i + 1);
+                return Ok(literal_suffix(input));
+            }
+            '\r' => match chars.next() {
+                Some((_, '\n')) => {}
+                _ => break,
+            },
+            '\\' => match chars.next() {
+                Some((_, 'x')) => {
+                    backslash_x_nonzero(&mut chars)?;
+                }
+                Some((_, 'n' | 'r' | 't' | '\\' | '\'' | '"')) => {}
+                Some((_, 'u')) => {
+                    if backslash_u(&mut chars)? == '\0' {
+                        break;
+                    }
+                }
+                Some((newline, ch @ ('\n' | '\r'))) => {
+                    input = input.advance(newline + 1);
+                    trailing_backslash(&mut input, ch as u8)?;
+                    chars = input.char_indices();
+                }
+                _ => break,
+            },
+            '\0' => break,
+            _ch => {}
+        }
+    }
+    Err(Reject)
+}
+
+fn byte(input: Cursor) -> Result<Cursor, Reject> {
+    let input = input.parse("b'")?;
+    let mut bytes = input.bytes().enumerate();
+    let ok = match bytes.next().map(|(_, b)| b) {
+        Some(b'\\') => match bytes.next().map(|(_, b)| b) {
+            Some(b'x') => backslash_x_byte(&mut bytes).is_ok(),
+            Some(b'n' | b'r' | b't' | b'\\' | b'0' | b'\'' | b'"') => true,
+            _ => false,
+        },
+        b => b.is_some(),
+    };
+    if !ok {
+        return Err(Reject);
+    }
+    let (offset, _) = bytes.next().ok_or(Reject)?;
+    if !input.chars().as_str().is_char_boundary(offset) {
+        return Err(Reject);
+    }
+    let input = input.advance(offset).parse("'")?;
+    Ok(literal_suffix(input))
+}
+
+fn character(input: Cursor) -> Result<Cursor, Reject> {
+    let input = input.parse("'")?;
+    let mut chars = input.char_indices();
+    let ok = match chars.next().map(|(_, ch)| ch) {
+        Some('\\') => match chars.next().map(|(_, ch)| ch) {
+            Some('x') => backslash_x_char(&mut chars).is_ok(),
+            Some('u') => backslash_u(&mut chars).is_ok(),
+            Some('n' | 'r' | 't' | '\\' | '0' | '\'' | '"') => true,
+            _ => false,
+        },
+        ch => ch.is_some(),
+    };
+    if !ok {
+        return Err(Reject);
+    }
+    let (idx, _) = chars.next().ok_or(Reject)?;
+    let input = input.advance(idx).parse("'")?;
+    Ok(literal_suffix(input))
+}
+
+macro_rules! next_ch {
+    ($chars:ident @ $pat:pat) => {
+        match $chars.next() {
+            Some((_, ch)) => match ch {
+                $pat => ch,
+                _ => return Err(Reject),
+            },
+            None => return Err(Reject),
+        }
+    };
+}
+
+fn backslash_x_char<I>(chars: &mut I) -> Result<(), Reject>
+where
+    I: Iterator<Item = (usize, char)>,
+{
+    next_ch!(chars @ '0'..='7');
+    next_ch!(chars @ '0'..='9' | 'a'..='f' | 'A'..='F');
+    Ok(())
+}
+
+fn backslash_x_byte<I>(chars: &mut I) -> Result<(), Reject>
+where
+    I: Iterator<Item = (usize, u8)>,
+{
+    next_ch!(chars @ b'0'..=b'9' | b'a'..=b'f' | b'A'..=b'F');
+    next_ch!(chars @ b'0'..=b'9' | b'a'..=b'f' | b'A'..=b'F');
+    Ok(())
+}
+
+fn backslash_x_nonzero<I>(chars: &mut I) -> Result<(), Reject>
+where
+    I: Iterator<Item = (usize, char)>,
+{
+    let first = next_ch!(chars @ '0'..='9' | 'a'..='f' | 'A'..='F');
+    let second = next_ch!(chars @ '0'..='9' | 'a'..='f' | 'A'..='F');
+    if first == '0' && second == '0' {
+        Err(Reject)
+    } else {
+        Ok(())
+    }
+}
+
+fn backslash_u<I>(chars: &mut I) -> Result<char, Reject>
+where
+    I: Iterator<Item = (usize, char)>,
+{
+    next_ch!(chars @ '{');
+    let mut value = 0;
+    let mut len = 0;
+    for (_, ch) in chars {
+        let digit = match ch {
+            '0'..='9' => ch as u8 - b'0',
+            'a'..='f' => 10 + ch as u8 - b'a',
+            'A'..='F' => 10 + ch as u8 - b'A',
+            '_' if len > 0 => continue,
+            '}' if len > 0 => return char::from_u32(value).ok_or(Reject),
+            _ => break,
+        };
+        if len == 6 {
+            break;
+        }
+        value *= 0x10;
+        value += u32::from(digit);
+        len += 1;
+    }
+    Err(Reject)
+}
+
+fn trailing_backslash(input: &mut Cursor, mut last: u8) -> Result<(), Reject> {
+    let mut whitespace = input.bytes().enumerate();
+    loop {
+        if last == b'\r' && whitespace.next().map_or(true, |(_, b)| b != b'\n') {
+            return Err(Reject);
+        }
+        match whitespace.next() {
+            Some((_, b @ (b' ' | b'\t' | b'\n' | b'\r'))) => {
+                last = b;
+            }
+            Some((offset, _)) => {
+                *input = input.advance(offset);
+                return Ok(());
+            }
+            None => return Err(Reject),
+        }
+    }
+}
+
+fn float(input: Cursor) -> Result<Cursor, Reject> {
+    let mut rest = float_digits(input)?;
+    if let Some(ch) = rest.chars().next() {
+        if is_ident_start(ch) {
+            rest = ident_not_raw(rest)?.0;
+        }
+    }
+    word_break(rest)
+}
+
+fn float_digits(input: Cursor) -> Result<Cursor, Reject> {
+    let mut chars = input.chars().peekable();
+    match chars.next() {
+        Some(ch) if '0' <= ch && ch <= '9' => {}
+        _ => return Err(Reject),
+    }
+
+    let mut len = 1;
+    let mut has_dot = false;
+    let mut has_exp = false;
+    while let Some(&ch) = chars.peek() {
+        match ch {
+            '0'..='9' | '_' => {
+                chars.next();
+                len += 1;
+            }
+            '.' => {
+                if has_dot {
+                    break;
+                }
+                chars.next();
+                if chars
+                    .peek()
+                    .is_some_and(|&ch| ch == '.' || is_ident_start(ch))
+                {
+                    return Err(Reject);
+                }
+                len += 1;
+                has_dot = true;
+            }
+            'e' | 'E' => {
+                chars.next();
+                len += 1;
+                has_exp = true;
+                break;
+            }
+            _ => break,
+        }
+    }
+
+    if !(has_dot || has_exp) {
+        return Err(Reject);
+    }
+
+    if has_exp {
+        let token_before_exp = if has_dot {
+            Ok(input.advance(len - 1))
+        } else {
+            Err(Reject)
+        };
+        let mut has_sign = false;
+        let mut has_exp_value = false;
+        while let Some(&ch) = chars.peek() {
+            match ch {
+                '+' | '-' => {
+                    if has_exp_value {
+                        break;
+                    }
+                    if has_sign {
+                        return token_before_exp;
+                    }
+                    chars.next();
+                    len += 1;
+                    has_sign = true;
+                }
+                '0'..='9' => {
+                    chars.next();
+                    len += 1;
+                    has_exp_value = true;
+                }
+                '_' => {
+                    chars.next();
+                    len += 1;
+                }
+                _ => break,
+            }
+        }
+        if !has_exp_value {
+            return token_before_exp;
+        }
+    }
+
+    Ok(input.advance(len))
+}
+
+fn int(input: Cursor) -> Result<Cursor, Reject> {
+    let mut rest = digits(input)?;
+    if let Some(ch) = rest.chars().next() {
+        if is_ident_start(ch) {
+            rest = ident_not_raw(rest)?.0;
+        }
+    }
+    word_break(rest)
+}
+
+fn digits(mut input: Cursor) -> Result<Cursor, Reject> {
+    let base = if input.starts_with("0x") {
+        input = input.advance(2);
+        16
+    } else if input.starts_with("0o") {
+        input = input.advance(2);
+        8
+    } else if input.starts_with("0b") {
+        input = input.advance(2);
+        2
+    } else {
+        10
+    };
+
+    let mut len = 0;
+    let mut empty = true;
+    for b in input.bytes() {
+        match b {
+            b'0'..=b'9' => {
+                let digit = (b - b'0') as u64;
+                if digit >= base {
+                    return Err(Reject);
+                }
+            }
+            b'a'..=b'f' => {
+                let digit = 10 + (b - b'a') as u64;
+                if digit >= base {
+                    break;
+                }
+            }
+            b'A'..=b'F' => {
+                let digit = 10 + (b - b'A') as u64;
+                if digit >= base {
+                    break;
+                }
+            }
+            b'_' => {
+                if empty && base == 10 {
+                    return Err(Reject);
+                }
+                len += 1;
+                continue;
+            }
+            _ => break,
+        }
+        len += 1;
+        empty = false;
+    }
+    if empty {
+        Err(Reject)
+    } else {
+        Ok(input.advance(len))
+    }
+}
+
+fn punct(input: Cursor) -> PResult<Punct> {
+    let (rest, ch) = punct_char(input)?;
+    if ch == '\'' {
+        let (after_lifetime, _ident) = ident_any(rest)?;
+        if after_lifetime.starts_with_char('\'')
+            || (after_lifetime.starts_with_char('#') && !rest.starts_with("r#"))
+        {
+            Err(Reject)
+        } else {
+            Ok((rest, Punct::new('\'', Spacing::Joint)))
+        }
+    } else {
+        let kind = match punct_char(rest) {
+            Ok(_) => Spacing::Joint,
+            Err(Reject) => Spacing::Alone,
+        };
+        Ok((rest, Punct::new(ch, kind)))
+    }
+}
+
+fn punct_char(input: Cursor) -> PResult<char> {
+    if input.starts_with("//") || input.starts_with("/*") {
+        // Do not accept `/` of a comment as a punct.
+        return Err(Reject);
+    }
+
+    let mut chars = input.chars();
+    let Some(first) = chars.next() else {
+        return Err(Reject);
+    };
+    let recognized = "~!@#$%^&*-=+|;:,<.>/?'";
+    if recognized.contains(first) {
+        Ok((input.advance(first.len_utf8()), first))
+    } else {
+        Err(Reject)
+    }
+}
+
+fn doc_comment<'a>(input: Cursor<'a>, tokens: &mut TokenStreamBuilder) -> PResult<'a, ()> {
+    #[cfg(span_locations)]
+    let lo = input.off;
+    let (rest, (comment, inner)) = doc_comment_contents(input)?;
+    let fallback_span = Span {
+        #[cfg(span_locations)]
+        lo,
+        #[cfg(span_locations)]
+        hi: rest.off,
+    };
+    let span = crate::Span::_new_fallback(fallback_span);
+
+    let mut scan_for_bare_cr = comment;
+    while let Some(cr) = scan_for_bare_cr.find('\r') {
+        let rest = &scan_for_bare_cr[cr + 1..];
+        if !rest.starts_with('\n') {
+            return Err(Reject);
+        }
+        scan_for_bare_cr = rest;
+    }
+
+    let mut pound = Punct::new('#', Spacing::Alone);
+    pound.set_span(span);
+    tokens.push_token_from_parser(TokenTree::Punct(pound));
+
+    if inner {
+        let mut bang = Punct::new('!', Spacing::Alone);
+        bang.set_span(span);
+        tokens.push_token_from_parser(TokenTree::Punct(bang));
+    }
+
+    let doc_ident = crate::Ident::_new_fallback(Ident::new_unchecked("doc", fallback_span));
+    let mut equal = Punct::new('=', Spacing::Alone);
+    equal.set_span(span);
+    let mut literal = crate::Literal::_new_fallback(Literal::string(comment));
+    literal.set_span(span);
+    let mut bracketed = TokenStreamBuilder::with_capacity(3);
+    bracketed.push_token_from_parser(TokenTree::Ident(doc_ident));
+    bracketed.push_token_from_parser(TokenTree::Punct(equal));
+    bracketed.push_token_from_parser(TokenTree::Literal(literal));
+    let group = Group::new(Delimiter::Bracket, bracketed.build());
+    let mut group = crate::Group::_new_fallback(group);
+    group.set_span(span);
+    tokens.push_token_from_parser(TokenTree::Group(group));
+
+    Ok((rest, ()))
+}
+
+fn doc_comment_contents(input: Cursor) -> PResult<(&str, bool)> {
+    if input.starts_with("//!") {
+        let input = input.advance(3);
+        let (input, s) = take_until_newline_or_eof(input);
+        Ok((input, (s, true)))
+    } else if input.starts_with("/*!") {
+        let (input, s) = block_comment(input)?;
+        Ok((input, (&s[3..s.len() - 2], true)))
+    } else if input.starts_with("///") {
+        let input = input.advance(3);
+        if input.starts_with_char('/') {
+            return Err(Reject);
+        }
+        let (input, s) = take_until_newline_or_eof(input);
+        Ok((input, (s, false)))
+    } else if input.starts_with("/**") && !input.rest[3..].starts_with('*') {
+        let (input, s) = block_comment(input)?;
+        Ok((input, (&s[3..s.len() - 2], false)))
+    } else {
+        Err(Reject)
+    }
+}
+
+fn take_until_newline_or_eof(input: Cursor) -> (Cursor, &str) {
+    let chars = input.char_indices();
+
+    for (i, ch) in chars {
+        if ch == '\n' {
+            return (input.advance(i), &input.rest[..i]);
+        } else if ch == '\r' && input.rest[i + 1..].starts_with('\n') {
+            return (input.advance(i + 1), &input.rest[..i]);
+        }
+    }
+
+    (input.advance(input.len()), input.rest)
+}