Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

1 files changed, 1651 insertions, 0 deletions

diff --git a/vendor/syn/src/lit.rs b/vendor/syn/src/lit.rs
new file mode 100644
index 0000000..24524bb
--- /dev/null
+++ b/vendor/syn/src/lit.rs
@@ -0,0 +1,1651 @@
+#[cfg(feature = "parsing")]
+use crate::lookahead;
+#[cfg(feature = "parsing")]
+use crate::parse::{Parse, Parser};
+use crate::{Error, Result};
+use proc_macro2::{Ident, Literal, Span};
+#[cfg(feature = "parsing")]
+use proc_macro2::{TokenStream, TokenTree};
+use std::fmt::{self, Display};
+#[cfg(feature = "extra-traits")]
+use std::hash::{Hash, Hasher};
+use std::str::{self, FromStr};
+
+ast_enum_of_structs! {
+    /// A Rust literal such as a string or integer or boolean.
+    ///
+    /// # Syntax tree enum
+    ///
+    /// This type is a [syntax tree enum].
+    ///
+    /// [syntax tree enum]: crate::Expr#syntax-tree-enums
+    #[non_exhaustive]
+    pub enum Lit {
+        /// A UTF-8 string literal: `"foo"`.
+        Str(LitStr),
+
+        /// A byte string literal: `b"foo"`.
+        ByteStr(LitByteStr),
+
+        /// A byte literal: `b'f'`.
+        Byte(LitByte),
+
+        /// A character literal: `'a'`.
+        Char(LitChar),
+
+        /// An integer literal: `1` or `1u16`.
+        Int(LitInt),
+
+        /// A floating point literal: `1f64` or `1.0e10f64`.
+        ///
+        /// Must be finite. May not be infinite or NaN.
+        Float(LitFloat),
+
+        /// A boolean literal: `true` or `false`.
+        Bool(LitBool),
+
+        /// A raw token literal not interpreted by Syn.
+        Verbatim(Literal),
+    }
+}
+
+ast_struct! {
+    /// A UTF-8 string literal: `"foo"`.
+    pub struct LitStr {
+        repr: Box<LitRepr>,
+    }
+}
+
+ast_struct! {
+    /// A byte string literal: `b"foo"`.
+    pub struct LitByteStr {
+        repr: Box<LitRepr>,
+    }
+}
+
+ast_struct! {
+    /// A byte literal: `b'f'`.
+    pub struct LitByte {
+        repr: Box<LitRepr>,
+    }
+}
+
+ast_struct! {
+    /// A character literal: `'a'`.
+    pub struct LitChar {
+        repr: Box<LitRepr>,
+    }
+}
+
+struct LitRepr {
+    token: Literal,
+    suffix: Box<str>,
+}
+
+ast_struct! {
+    /// An integer literal: `1` or `1u16`.
+    pub struct LitInt {
+        repr: Box<LitIntRepr>,
+    }
+}
+
+struct LitIntRepr {
+    token: Literal,
+    digits: Box<str>,
+    suffix: Box<str>,
+}
+
+ast_struct! {
+    /// A floating point literal: `1f64` or `1.0e10f64`.
+    ///
+    /// Must be finite. May not be infinite or NaN.
+    pub struct LitFloat {
+        repr: Box<LitFloatRepr>,
+    }
+}
+
+struct LitFloatRepr {
+    token: Literal,
+    digits: Box<str>,
+    suffix: Box<str>,
+}
+
+ast_struct! {
+    /// A boolean literal: `true` or `false`.
+    pub struct LitBool {
+        pub value: bool,
+        pub span: Span,
+    }
+}
+
+impl LitStr {
+    pub fn new(value: &str, span: Span) -> Self {
+        let mut token = Literal::string(value);
+        token.set_span(span);
+        LitStr {
+            repr: Box::new(LitRepr {
+                token,
+                suffix: Box::<str>::default(),
+            }),
+        }
+    }
+
+    pub fn value(&self) -> String {
+        let repr = self.repr.token.to_string();
+        let (value, _suffix) = value::parse_lit_str(&repr);
+        String::from(value)
+    }
+
+    /// Parse a syntax tree node from the content of this string literal.
+    ///
+    /// All spans in the syntax tree will point to the span of this `LitStr`.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use syn::{Attribute, Error, Expr, Lit, Meta, Path, Result};
+    ///
+    /// // Parses the path from an attribute that looks like:
+    /// //
+    /// //     #[path = "a::b::c"]
+    /// //
+    /// // or returns `None` if the input is some other attribute.
+    /// fn get_path(attr: &Attribute) -> Result<Option<Path>> {
+    ///     if !attr.path().is_ident("path") {
+    ///         return Ok(None);
+    ///     }
+    ///
+    ///     if let Meta::NameValue(meta) = &attr.meta {
+    ///         if let Expr::Lit(expr) = &meta.value {
+    ///             if let Lit::Str(lit_str) = &expr.lit {
+    ///                 return lit_str.parse().map(Some);
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     let message = "expected #[path = \"...\"]";
+    ///     Err(Error::new_spanned(attr, message))
+    /// }
+    /// ```
+    #[cfg(feature = "parsing")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    pub fn parse<T: Parse>(&self) -> Result<T> {
+        self.parse_with(T::parse)
+    }
+
+    /// Invoke parser on the content of this string literal.
+    ///
+    /// All spans in the syntax tree will point to the span of this `LitStr`.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use proc_macro2::Span;
+    /// # use syn::{LitStr, Result};
+    /// #
+    /// # fn main() -> Result<()> {
+    /// #     let lit_str = LitStr::new("a::b::c", Span::call_site());
+    /// #
+    /// #     const IGNORE: &str = stringify! {
+    /// let lit_str: LitStr = /* ... */;
+    /// #     };
+    ///
+    /// // Parse a string literal like "a::b::c" into a Path, not allowing
+    /// // generic arguments on any of the path segments.
+    /// let basic_path = lit_str.parse_with(syn::Path::parse_mod_style)?;
+    /// #
+    /// #     Ok(())
+    /// # }
+    /// ```
+    #[cfg(feature = "parsing")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    pub fn parse_with<F: Parser>(&self, parser: F) -> Result<F::Output> {
+        use proc_macro2::Group;
+
+        // Token stream with every span replaced by the given one.
+        fn respan_token_stream(stream: TokenStream, span: Span) -> TokenStream {
+            stream
+                .into_iter()
+                .map(|token| respan_token_tree(token, span))
+                .collect()
+        }
+
+        // Token tree with every span replaced by the given one.
+        fn respan_token_tree(mut token: TokenTree, span: Span) -> TokenTree {
+            match &mut token {
+                TokenTree::Group(g) => {
+                    let stream = respan_token_stream(g.stream(), span);
+                    *g = Group::new(g.delimiter(), stream);
+                    g.set_span(span);
+                }
+                other => other.set_span(span),
+            }
+            token
+        }
+
+        // Parse string literal into a token stream with every span equal to the
+        // original literal's span.
+        let mut tokens = TokenStream::from_str(&self.value())?;
+        tokens = respan_token_stream(tokens, self.span());
+
+        let result = parser.parse2(tokens)?;
+
+        let suffix = self.suffix();
+        if !suffix.is_empty() {
+            return Err(Error::new(
+                self.span(),
+                format!("unexpected suffix `{}` on string literal", suffix),
+            ));
+        }
+
+        Ok(result)
+    }
+
+    pub fn span(&self) -> Span {
+        self.repr.token.span()
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        self.repr.token.set_span(span);
+    }
+
+    pub fn suffix(&self) -> &str {
+        &self.repr.suffix
+    }
+
+    pub fn token(&self) -> Literal {
+        self.repr.token.clone()
+    }
+}
+
+impl LitByteStr {
+    pub fn new(value: &[u8], span: Span) -> Self {
+        let mut token = Literal::byte_string(value);
+        token.set_span(span);
+        LitByteStr {
+            repr: Box::new(LitRepr {
+                token,
+                suffix: Box::<str>::default(),
+            }),
+        }
+    }
+
+    pub fn value(&self) -> Vec<u8> {
+        let repr = self.repr.token.to_string();
+        let (value, _suffix) = value::parse_lit_byte_str(&repr);
+        value
+    }
+
+    pub fn span(&self) -> Span {
+        self.repr.token.span()
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        self.repr.token.set_span(span);
+    }
+
+    pub fn suffix(&self) -> &str {
+        &self.repr.suffix
+    }
+
+    pub fn token(&self) -> Literal {
+        self.repr.token.clone()
+    }
+}
+
+impl LitByte {
+    pub fn new(value: u8, span: Span) -> Self {
+        let mut token = Literal::u8_suffixed(value);
+        token.set_span(span);
+        LitByte {
+            repr: Box::new(LitRepr {
+                token,
+                suffix: Box::<str>::default(),
+            }),
+        }
+    }
+
+    pub fn value(&self) -> u8 {
+        let repr = self.repr.token.to_string();
+        let (value, _suffix) = value::parse_lit_byte(&repr);
+        value
+    }
+
+    pub fn span(&self) -> Span {
+        self.repr.token.span()
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        self.repr.token.set_span(span);
+    }
+
+    pub fn suffix(&self) -> &str {
+        &self.repr.suffix
+    }
+
+    pub fn token(&self) -> Literal {
+        self.repr.token.clone()
+    }
+}
+
+impl LitChar {
+    pub fn new(value: char, span: Span) -> Self {
+        let mut token = Literal::character(value);
+        token.set_span(span);
+        LitChar {
+            repr: Box::new(LitRepr {
+                token,
+                suffix: Box::<str>::default(),
+            }),
+        }
+    }
+
+    pub fn value(&self) -> char {
+        let repr = self.repr.token.to_string();
+        let (value, _suffix) = value::parse_lit_char(&repr);
+        value
+    }
+
+    pub fn span(&self) -> Span {
+        self.repr.token.span()
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        self.repr.token.set_span(span);
+    }
+
+    pub fn suffix(&self) -> &str {
+        &self.repr.suffix
+    }
+
+    pub fn token(&self) -> Literal {
+        self.repr.token.clone()
+    }
+}
+
+impl LitInt {
+    pub fn new(repr: &str, span: Span) -> Self {
+        let (digits, suffix) = match value::parse_lit_int(repr) {
+            Some(parse) => parse,
+            None => panic!("Not an integer literal: `{}`", repr),
+        };
+
+        let mut token: Literal = repr.parse().unwrap();
+        token.set_span(span);
+        LitInt {
+            repr: Box::new(LitIntRepr {
+                token,
+                digits,
+                suffix,
+            }),
+        }
+    }
+
+    pub fn base10_digits(&self) -> &str {
+        &self.repr.digits
+    }
+
+    /// Parses the literal into a selected number type.
+    ///
+    /// This is equivalent to `lit.base10_digits().parse()` except that the
+    /// resulting errors will be correctly spanned to point to the literal token
+    /// in the macro input.
+    ///
+    /// ```
+    /// use syn::LitInt;
+    /// use syn::parse::{Parse, ParseStream, Result};
+    ///
+    /// struct Port {
+    ///     value: u16,
+    /// }
+    ///
+    /// impl Parse for Port {
+    ///     fn parse(input: ParseStream) -> Result<Self> {
+    ///         let lit: LitInt = input.parse()?;
+    ///         let value = lit.base10_parse::<u16>()?;
+    ///         Ok(Port { value })
+    ///     }
+    /// }
+    /// ```
+    pub fn base10_parse<N>(&self) -> Result<N>
+    where
+        N: FromStr,
+        N::Err: Display,
+    {
+        self.base10_digits()
+            .parse()
+            .map_err(|err| Error::new(self.span(), err))
+    }
+
+    pub fn suffix(&self) -> &str {
+        &self.repr.suffix
+    }
+
+    pub fn span(&self) -> Span {
+        self.repr.token.span()
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        self.repr.token.set_span(span);
+    }
+
+    pub fn token(&self) -> Literal {
+        self.repr.token.clone()
+    }
+}
+
+impl From<Literal> for LitInt {
+    fn from(token: Literal) -> Self {
+        let repr = token.to_string();
+        if let Some((digits, suffix)) = value::parse_lit_int(&repr) {
+            LitInt {
+                repr: Box::new(LitIntRepr {
+                    token,
+                    digits,
+                    suffix,
+                }),
+            }
+        } else {
+            panic!("Not an integer literal: `{}`", repr);
+        }
+    }
+}
+
+impl Display for LitInt {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        self.repr.token.fmt(formatter)
+    }
+}
+
+impl LitFloat {
+    pub fn new(repr: &str, span: Span) -> Self {
+        let (digits, suffix) = match value::parse_lit_float(repr) {
+            Some(parse) => parse,
+            None => panic!("Not a float literal: `{}`", repr),
+        };
+
+        let mut token: Literal = repr.parse().unwrap();
+        token.set_span(span);
+        LitFloat {
+            repr: Box::new(LitFloatRepr {
+                token,
+                digits,
+                suffix,
+            }),
+        }
+    }
+
+    pub fn base10_digits(&self) -> &str {
+        &self.repr.digits
+    }
+
+    pub fn base10_parse<N>(&self) -> Result<N>
+    where
+        N: FromStr,
+        N::Err: Display,
+    {
+        self.base10_digits()
+            .parse()
+            .map_err(|err| Error::new(self.span(), err))
+    }
+
+    pub fn suffix(&self) -> &str {
+        &self.repr.suffix
+    }
+
+    pub fn span(&self) -> Span {
+        self.repr.token.span()
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        self.repr.token.set_span(span);
+    }
+
+    pub fn token(&self) -> Literal {
+        self.repr.token.clone()
+    }
+}
+
+impl From<Literal> for LitFloat {
+    fn from(token: Literal) -> Self {
+        let repr = token.to_string();
+        if let Some((digits, suffix)) = value::parse_lit_float(&repr) {
+            LitFloat {
+                repr: Box::new(LitFloatRepr {
+                    token,
+                    digits,
+                    suffix,
+                }),
+            }
+        } else {
+            panic!("Not a float literal: `{}`", repr);
+        }
+    }
+}
+
+impl Display for LitFloat {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        self.repr.token.fmt(formatter)
+    }
+}
+
+impl LitBool {
+    pub fn new(value: bool, span: Span) -> Self {
+        LitBool { value, span }
+    }
+
+    pub fn value(&self) -> bool {
+        self.value
+    }
+
+    pub fn span(&self) -> Span {
+        self.span
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        self.span = span;
+    }
+
+    pub fn token(&self) -> Ident {
+        let s = if self.value { "true" } else { "false" };
+        Ident::new(s, self.span)
+    }
+}
+
+#[cfg(feature = "extra-traits")]
+mod debug_impls {
+    use super::*;
+    use std::fmt::{self, Debug};
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "extra-traits")))]
+    impl Debug for LitStr {
+        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            impl LitStr {
+                pub(crate) fn debug(
+                    &self,
+                    formatter: &mut fmt::Formatter,
+                    name: &str,
+                ) -> fmt::Result {
+                    formatter
+                        .debug_struct(name)
+                        .field("token", &format_args!("{}", self.repr.token))
+                        .finish()
+                }
+            }
+            self.debug(formatter, "LitStr")
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "extra-traits")))]
+    impl Debug for LitByteStr {
+        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            impl LitByteStr {
+                pub(crate) fn debug(
+                    &self,
+                    formatter: &mut fmt::Formatter,
+                    name: &str,
+                ) -> fmt::Result {
+                    formatter
+                        .debug_struct(name)
+                        .field("token", &format_args!("{}", self.repr.token))
+                        .finish()
+                }
+            }
+            self.debug(formatter, "LitByteStr")
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "extra-traits")))]
+    impl Debug for LitByte {
+        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            impl LitByte {
+                pub(crate) fn debug(
+                    &self,
+                    formatter: &mut fmt::Formatter,
+                    name: &str,
+                ) -> fmt::Result {
+                    formatter
+                        .debug_struct(name)
+                        .field("token", &format_args!("{}", self.repr.token))
+                        .finish()
+                }
+            }
+            self.debug(formatter, "LitByte")
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "extra-traits")))]
+    impl Debug for LitChar {
+        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            impl LitChar {
+                pub(crate) fn debug(
+                    &self,
+                    formatter: &mut fmt::Formatter,
+                    name: &str,
+                ) -> fmt::Result {
+                    formatter
+                        .debug_struct(name)
+                        .field("token", &format_args!("{}", self.repr.token))
+                        .finish()
+                }
+            }
+            self.debug(formatter, "LitChar")
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "extra-traits")))]
+    impl Debug for LitInt {
+        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            impl LitInt {
+                pub(crate) fn debug(
+                    &self,
+                    formatter: &mut fmt::Formatter,
+                    name: &str,
+                ) -> fmt::Result {
+                    formatter
+                        .debug_struct(name)
+                        .field("token", &format_args!("{}", self.repr.token))
+                        .finish()
+                }
+            }
+            self.debug(formatter, "LitInt")
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "extra-traits")))]
+    impl Debug for LitFloat {
+        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            impl LitFloat {
+                pub(crate) fn debug(
+                    &self,
+                    formatter: &mut fmt::Formatter,
+                    name: &str,
+                ) -> fmt::Result {
+                    formatter
+                        .debug_struct(name)
+                        .field("token", &format_args!("{}", self.repr.token))
+                        .finish()
+                }
+            }
+            self.debug(formatter, "LitFloat")
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "extra-traits")))]
+    impl Debug for LitBool {
+        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            impl LitBool {
+                pub(crate) fn debug(
+                    &self,
+                    formatter: &mut fmt::Formatter,
+                    name: &str,
+                ) -> fmt::Result {
+                    formatter
+                        .debug_struct(name)
+                        .field("value", &self.value)
+                        .finish()
+                }
+            }
+            self.debug(formatter, "LitBool")
+        }
+    }
+}
+
+#[cfg(feature = "clone-impls")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "clone-impls")))]
+impl Clone for LitRepr {
+    fn clone(&self) -> Self {
+        LitRepr {
+            token: self.token.clone(),
+            suffix: self.suffix.clone(),
+        }
+    }
+}
+
+#[cfg(feature = "clone-impls")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "clone-impls")))]
+impl Clone for LitIntRepr {
+    fn clone(&self) -> Self {
+        LitIntRepr {
+            token: self.token.clone(),
+            digits: self.digits.clone(),
+            suffix: self.suffix.clone(),
+        }
+    }
+}
+
+#[cfg(feature = "clone-impls")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "clone-impls")))]
+impl Clone for LitFloatRepr {
+    fn clone(&self) -> Self {
+        LitFloatRepr {
+            token: self.token.clone(),
+            digits: self.digits.clone(),
+            suffix: self.suffix.clone(),
+        }
+    }
+}
+
+macro_rules! lit_extra_traits {
+    ($ty:ident) => {
+        #[cfg(feature = "clone-impls")]
+        #[cfg_attr(doc_cfg, doc(cfg(feature = "clone-impls")))]
+        impl Clone for $ty {
+            fn clone(&self) -> Self {
+                $ty {
+                    repr: self.repr.clone(),
+                }
+            }
+        }
+
+        #[cfg(feature = "extra-traits")]
+        #[cfg_attr(doc_cfg, doc(cfg(feature = "extra-traits")))]
+        impl PartialEq for $ty {
+            fn eq(&self, other: &Self) -> bool {
+                self.repr.token.to_string() == other.repr.token.to_string()
+            }
+        }
+
+        #[cfg(feature = "extra-traits")]
+        #[cfg_attr(doc_cfg, doc(cfg(feature = "extra-traits")))]
+        impl Hash for $ty {
+            fn hash<H>(&self, state: &mut H)
+            where
+                H: Hasher,
+            {
+                self.repr.token.to_string().hash(state);
+            }
+        }
+
+        #[cfg(feature = "parsing")]
+        pub_if_not_doc! {
+            #[doc(hidden)]
+            #[allow(non_snake_case)]
+            pub fn $ty(marker: lookahead::TokenMarker) -> $ty {
+                match marker {}
+            }
+        }
+    };
+}
+
+lit_extra_traits!(LitStr);
+lit_extra_traits!(LitByteStr);
+lit_extra_traits!(LitByte);
+lit_extra_traits!(LitChar);
+lit_extra_traits!(LitInt);
+lit_extra_traits!(LitFloat);
+
+#[cfg(feature = "parsing")]
+pub_if_not_doc! {
+    #[doc(hidden)]
+    #[allow(non_snake_case)]
+    pub fn LitBool(marker: lookahead::TokenMarker) -> LitBool {
+        match marker {}
+    }
+}
+
+/// The style of a string literal, either plain quoted or a raw string like
+/// `r##"data"##`.
+#[doc(hidden)] // https://github.com/dtolnay/syn/issues/1566
+pub enum StrStyle {
+    /// An ordinary string like `"data"`.
+    Cooked,
+    /// A raw string like `r##"data"##`.
+    ///
+    /// The unsigned integer is the number of `#` symbols used.
+    Raw(usize),
+}
+
+#[cfg(feature = "parsing")]
+pub_if_not_doc! {
+    #[doc(hidden)]
+    #[allow(non_snake_case)]
+    pub fn Lit(marker: lookahead::TokenMarker) -> Lit {
+        match marker {}
+    }
+}
+
+#[cfg(feature = "parsing")]
+pub(crate) mod parsing {
+    use super::*;
+    use crate::buffer::Cursor;
+    use crate::parse::{Parse, ParseStream, Result};
+    use proc_macro2::Punct;
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    impl Parse for Lit {
+        fn parse(input: ParseStream) -> Result<Self> {
+            input.step(|cursor| {
+                if let Some((lit, rest)) = cursor.literal() {
+                    return Ok((Lit::new(lit), rest));
+                }
+
+                if let Some((ident, rest)) = cursor.ident() {
+                    let value = ident == "true";
+                    if value || ident == "false" {
+                        let lit_bool = LitBool {
+                            value,
+                            span: ident.span(),
+                        };
+                        return Ok((Lit::Bool(lit_bool), rest));
+                    }
+                }
+
+                if let Some((punct, rest)) = cursor.punct() {
+                    if punct.as_char() == '-' {
+                        if let Some((lit, rest)) = parse_negative_lit(punct, rest) {
+                            return Ok((lit, rest));
+                        }
+                    }
+                }
+
+                Err(cursor.error("expected literal"))
+            })
+        }
+    }
+
+    fn parse_negative_lit(neg: Punct, cursor: Cursor) -> Option<(Lit, Cursor)> {
+        let (lit, rest) = cursor.literal()?;
+
+        let mut span = neg.span();
+        span = span.join(lit.span()).unwrap_or(span);
+
+        let mut repr = lit.to_string();
+        repr.insert(0, '-');
+
+        if let Some((digits, suffix)) = value::parse_lit_int(&repr) {
+            let mut token: Literal = repr.parse().unwrap();
+            token.set_span(span);
+            return Some((
+                Lit::Int(LitInt {
+                    repr: Box::new(LitIntRepr {
+                        token,
+                        digits,
+                        suffix,
+                    }),
+                }),
+                rest,
+            ));
+        }
+
+        let (digits, suffix) = value::parse_lit_float(&repr)?;
+        let mut token: Literal = repr.parse().unwrap();
+        token.set_span(span);
+        Some((
+            Lit::Float(LitFloat {
+                repr: Box::new(LitFloatRepr {
+                    token,
+                    digits,
+                    suffix,
+                }),
+            }),
+            rest,
+        ))
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    impl Parse for LitStr {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let head = input.fork();
+            match input.parse() {
+                Ok(Lit::Str(lit)) => Ok(lit),
+                _ => Err(head.error("expected string literal")),
+            }
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    impl Parse for LitByteStr {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let head = input.fork();
+            match input.parse() {
+                Ok(Lit::ByteStr(lit)) => Ok(lit),
+                _ => Err(head.error("expected byte string literal")),
+            }
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    impl Parse for LitByte {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let head = input.fork();
+            match input.parse() {
+                Ok(Lit::Byte(lit)) => Ok(lit),
+                _ => Err(head.error("expected byte literal")),
+            }
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    impl Parse for LitChar {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let head = input.fork();
+            match input.parse() {
+                Ok(Lit::Char(lit)) => Ok(lit),
+                _ => Err(head.error("expected character literal")),
+            }
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    impl Parse for LitInt {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let head = input.fork();
+            match input.parse() {
+                Ok(Lit::Int(lit)) => Ok(lit),
+                _ => Err(head.error("expected integer literal")),
+            }
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    impl Parse for LitFloat {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let head = input.fork();
+            match input.parse() {
+                Ok(Lit::Float(lit)) => Ok(lit),
+                _ => Err(head.error("expected floating point literal")),
+            }
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    impl Parse for LitBool {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let head = input.fork();
+            match input.parse() {
+                Ok(Lit::Bool(lit)) => Ok(lit),
+                _ => Err(head.error("expected boolean literal")),
+            }
+        }
+    }
+}
+
+#[cfg(feature = "printing")]
+mod printing {
+    use super::*;
+    use proc_macro2::TokenStream;
+    use quote::{ToTokens, TokenStreamExt};
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
+    impl ToTokens for LitStr {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            self.repr.token.to_tokens(tokens);
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
+    impl ToTokens for LitByteStr {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            self.repr.token.to_tokens(tokens);
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
+    impl ToTokens for LitByte {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            self.repr.token.to_tokens(tokens);
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
+    impl ToTokens for LitChar {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            self.repr.token.to_tokens(tokens);
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
+    impl ToTokens for LitInt {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            self.repr.token.to_tokens(tokens);
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
+    impl ToTokens for LitFloat {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            self.repr.token.to_tokens(tokens);
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
+    impl ToTokens for LitBool {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            tokens.append(self.token());
+        }
+    }
+}
+
+mod value {
+    use super::*;
+    use crate::bigint::BigInt;
+    use std::char;
+    use std::ops::{Index, RangeFrom};
+
+    impl Lit {
+        /// Interpret a Syn literal from a proc-macro2 literal.
+        pub fn new(token: Literal) -> Self {
+            let repr = token.to_string();
+
+            match byte(&repr, 0) {
+                // "...", r"...", r#"..."#
+                b'"' | b'r' => {
+                    let (_, suffix) = parse_lit_str(&repr);
+                    return Lit::Str(LitStr {
+                        repr: Box::new(LitRepr { token, suffix }),
+                    });
+                }
+                b'b' => match byte(&repr, 1) {
+                    // b"...", br"...", br#"...#"
+                    b'"' | b'r' => {
+                        let (_, suffix) = parse_lit_byte_str(&repr);
+                        return Lit::ByteStr(LitByteStr {
+                            repr: Box::new(LitRepr { token, suffix }),
+                        });
+                    }
+                    // b'...'
+                    b'\'' => {
+                        let (_, suffix) = parse_lit_byte(&repr);
+                        return Lit::Byte(LitByte {
+                            repr: Box::new(LitRepr { token, suffix }),
+                        });
+                    }
+                    _ => {}
+                },
+                // '...'
+                b'\'' => {
+                    let (_, suffix) = parse_lit_char(&repr);
+                    return Lit::Char(LitChar {
+                        repr: Box::new(LitRepr { token, suffix }),
+                    });
+                }
+                b'0'..=b'9' | b'-' => {
+                    // 0, 123, 0xFF, 0o77, 0b11
+                    if let Some((digits, suffix)) = parse_lit_int(&repr) {
+                        return Lit::Int(LitInt {
+                            repr: Box::new(LitIntRepr {
+                                token,
+                                digits,
+                                suffix,
+                            }),
+                        });
+                    }
+                    // 1.0, 1e-1, 1e+1
+                    if let Some((digits, suffix)) = parse_lit_float(&repr) {
+                        return Lit::Float(LitFloat {
+                            repr: Box::new(LitFloatRepr {
+                                token,
+                                digits,
+                                suffix,
+                            }),
+                        });
+                    }
+                }
+                // true, false
+                b't' | b'f' => {
+                    if repr == "true" || repr == "false" {
+                        return Lit::Bool(LitBool {
+                            value: repr == "true",
+                            span: token.span(),
+                        });
+                    }
+                }
+                // c"...", cr"...", cr#"..."#
+                // TODO: add a Lit::CStr variant?
+                b'c' => return Lit::Verbatim(token),
+                b'(' if repr == "(/*ERROR*/)" => return Lit::Verbatim(token),
+                _ => {}
+            }
+
+            panic!("Unrecognized literal: `{}`", repr);
+        }
+
+        pub fn suffix(&self) -> &str {
+            match self {
+                Lit::Str(lit) => lit.suffix(),
+                Lit::ByteStr(lit) => lit.suffix(),
+                Lit::Byte(lit) => lit.suffix(),
+                Lit::Char(lit) => lit.suffix(),
+                Lit::Int(lit) => lit.suffix(),
+                Lit::Float(lit) => lit.suffix(),
+                Lit::Bool(_) | Lit::Verbatim(_) => "",
+            }
+        }
+
+        pub fn span(&self) -> Span {
+            match self {
+                Lit::Str(lit) => lit.span(),
+                Lit::ByteStr(lit) => lit.span(),
+                Lit::Byte(lit) => lit.span(),
+                Lit::Char(lit) => lit.span(),
+                Lit::Int(lit) => lit.span(),
+                Lit::Float(lit) => lit.span(),
+                Lit::Bool(lit) => lit.span,
+                Lit::Verbatim(lit) => lit.span(),
+            }
+        }
+
+        pub fn set_span(&mut self, span: Span) {
+            match self {
+                Lit::Str(lit) => lit.set_span(span),
+                Lit::ByteStr(lit) => lit.set_span(span),
+                Lit::Byte(lit) => lit.set_span(span),
+                Lit::Char(lit) => lit.set_span(span),
+                Lit::Int(lit) => lit.set_span(span),
+                Lit::Float(lit) => lit.set_span(span),
+                Lit::Bool(lit) => lit.span = span,
+                Lit::Verbatim(lit) => lit.set_span(span),
+            }
+        }
+    }
+
+    /// Get the byte at offset idx, or a default of `b'\0'` if we're looking
+    /// past the end of the input buffer.
+    pub(crate) fn byte<S: AsRef<[u8]> + ?Sized>(s: &S, idx: usize) -> u8 {
+        let s = s.as_ref();
+        if idx < s.len() {
+            s[idx]
+        } else {
+            0
+        }
+    }
+
+    fn next_chr(s: &str) -> char {
+        s.chars().next().unwrap_or('\0')
+    }
+
+    // Returns (content, suffix).
+    pub(crate) fn parse_lit_str(s: &str) -> (Box<str>, Box<str>) {
+        match byte(s, 0) {
+            b'"' => parse_lit_str_cooked(s),
+            b'r' => parse_lit_str_raw(s),
+            _ => unreachable!(),
+        }
+    }
+
+    // Clippy false positive
+    // https://github.com/rust-lang-nursery/rust-clippy/issues/2329
+    #[allow(clippy::needless_continue)]
+    fn parse_lit_str_cooked(mut s: &str) -> (Box<str>, Box<str>) {
+        assert_eq!(byte(s, 0), b'"');
+        s = &s[1..];
+
+        let mut content = String::new();
+        'outer: loop {
+            let ch = match byte(s, 0) {
+                b'"' => break,
+                b'\\' => {
+                    let b = byte(s, 1);
+                    s = &s[2..];
+                    match b {
+                        b'x' => {
+                            let (byte, rest) = backslash_x(s);
+                            s = rest;
+                            assert!(byte <= 0x7F, "Invalid \\x byte in string literal");
+                            char::from_u32(u32::from(byte)).unwrap()
+                        }
+                        b'u' => {
+                            let (chr, rest) = backslash_u(s);
+                            s = rest;
+                            chr
+                        }
+                        b'n' => '\n',
+                        b'r' => '\r',
+                        b't' => '\t',
+                        b'\\' => '\\',
+                        b'0' => '\0',
+                        b'\'' => '\'',
+                        b'"' => '"',
+                        b'\r' | b'\n' => loop {
+                            let b = byte(s, 0);
+                            match b {
+                                b' ' | b'\t' | b'\n' | b'\r' => s = &s[1..],
+                                _ => continue 'outer,
+                            }
+                        },
+                        b => panic!("unexpected byte {:?} after \\ character in byte literal", b),
+                    }
+                }
+                b'\r' => {
+                    assert_eq!(byte(s, 1), b'\n', "Bare CR not allowed in string");
+                    s = &s[2..];
+                    '\n'
+                }
+                _ => {
+                    let ch = next_chr(s);
+                    s = &s[ch.len_utf8()..];
+                    ch
+                }
+            };
+            content.push(ch);
+        }
+
+        assert!(s.starts_with('"'));
+        let content = content.into_boxed_str();
+        let suffix = s[1..].to_owned().into_boxed_str();
+        (content, suffix)
+    }
+
+    fn parse_lit_str_raw(mut s: &str) -> (Box<str>, Box<str>) {
+        assert_eq!(byte(s, 0), b'r');
+        s = &s[1..];
+
+        let mut pounds = 0;
+        while byte(s, pounds) == b'#' {
+            pounds += 1;
+        }
+        assert_eq!(byte(s, pounds), b'"');
+        let close = s.rfind('"').unwrap();
+        for end in s[close + 1..close + 1 + pounds].bytes() {
+            assert_eq!(end, b'#');
+        }
+
+        let content = s[pounds + 1..close].to_owned().into_boxed_str();
+        let suffix = s[close + 1 + pounds..].to_owned().into_boxed_str();
+        (content, suffix)
+    }
+
+    // Returns (content, suffix).
+    pub(crate) fn parse_lit_byte_str(s: &str) -> (Vec<u8>, Box<str>) {
+        assert_eq!(byte(s, 0), b'b');
+        match byte(s, 1) {
+            b'"' => parse_lit_byte_str_cooked(s),
+            b'r' => parse_lit_byte_str_raw(s),
+            _ => unreachable!(),
+        }
+    }
+
+    // Clippy false positive
+    // https://github.com/rust-lang-nursery/rust-clippy/issues/2329
+    #[allow(clippy::needless_continue)]
+    fn parse_lit_byte_str_cooked(mut s: &str) -> (Vec<u8>, Box<str>) {
+        assert_eq!(byte(s, 0), b'b');
+        assert_eq!(byte(s, 1), b'"');
+        s = &s[2..];
+
+        // We're going to want to have slices which don't respect codepoint boundaries.
+        let mut v = s.as_bytes();
+
+        let mut out = Vec::new();
+        'outer: loop {
+            let byte = match byte(v, 0) {
+                b'"' => break,
+                b'\\' => {
+                    let b = byte(v, 1);
+                    v = &v[2..];
+                    match b {
+                        b'x' => {
+                            let (b, rest) = backslash_x(v);
+                            v = rest;
+                            b
+                        }
+                        b'n' => b'\n',
+                        b'r' => b'\r',
+                        b't' => b'\t',
+                        b'\\' => b'\\',
+                        b'0' => b'\0',
+                        b'\'' => b'\'',
+                        b'"' => b'"',
+                        b'\r' | b'\n' => loop {
+                            let byte = byte(v, 0);
+                            if matches!(byte, b' ' | b'\t' | b'\n' | b'\r') {
+                                v = &v[1..];
+                            } else {
+                                continue 'outer;
+                            }
+                        },
+                        b => panic!("unexpected byte {:?} after \\ character in byte literal", b),
+                    }
+                }
+                b'\r' => {
+                    assert_eq!(byte(v, 1), b'\n', "Bare CR not allowed in string");
+                    v = &v[2..];
+                    b'\n'
+                }
+                b => {
+                    v = &v[1..];
+                    b
+                }
+            };
+            out.push(byte);
+        }
+
+        assert_eq!(byte(v, 0), b'"');
+        let suffix = s[s.len() - v.len() + 1..].to_owned().into_boxed_str();
+        (out, suffix)
+    }
+
+    fn parse_lit_byte_str_raw(s: &str) -> (Vec<u8>, Box<str>) {
+        assert_eq!(byte(s, 0), b'b');
+        let (value, suffix) = parse_lit_str_raw(&s[1..]);
+        (String::from(value).into_bytes(), suffix)
+    }
+
+    // Returns (value, suffix).
+    pub(crate) fn parse_lit_byte(s: &str) -> (u8, Box<str>) {
+        assert_eq!(byte(s, 0), b'b');
+        assert_eq!(byte(s, 1), b'\'');
+
+        // We're going to want to have slices which don't respect codepoint boundaries.
+        let mut v = s[2..].as_bytes();
+
+        let b = match byte(v, 0) {
+            b'\\' => {
+                let b = byte(v, 1);
+                v = &v[2..];
+                match b {
+                    b'x' => {
+                        let (b, rest) = backslash_x(v);
+                        v = rest;
+                        b
+                    }
+                    b'n' => b'\n',
+                    b'r' => b'\r',
+                    b't' => b'\t',
+                    b'\\' => b'\\',
+                    b'0' => b'\0',
+                    b'\'' => b'\'',
+                    b'"' => b'"',
+                    b => panic!("unexpected byte {:?} after \\ character in byte literal", b),
+                }
+            }
+            b => {
+                v = &v[1..];
+                b
+            }
+        };
+
+        assert_eq!(byte(v, 0), b'\'');
+        let suffix = s[s.len() - v.len() + 1..].to_owned().into_boxed_str();
+        (b, suffix)
+    }
+
+    // Returns (value, suffix).
+    pub(crate) fn parse_lit_char(mut s: &str) -> (char, Box<str>) {
+        assert_eq!(byte(s, 0), b'\'');
+        s = &s[1..];
+
+        let ch = match byte(s, 0) {
+            b'\\' => {
+                let b = byte(s, 1);
+                s = &s[2..];
+                match b {
+                    b'x' => {
+                        let (byte, rest) = backslash_x(s);
+                        s = rest;
+                        assert!(byte <= 0x80, "Invalid \\x byte in string literal");
+                        char::from_u32(u32::from(byte)).unwrap()
+                    }
+                    b'u' => {
+                        let (chr, rest) = backslash_u(s);
+                        s = rest;
+                        chr
+                    }
+                    b'n' => '\n',
+                    b'r' => '\r',
+                    b't' => '\t',
+                    b'\\' => '\\',
+                    b'0' => '\0',
+                    b'\'' => '\'',
+                    b'"' => '"',
+                    b => panic!("unexpected byte {:?} after \\ character in byte literal", b),
+                }
+            }
+            _ => {
+                let ch = next_chr(s);
+                s = &s[ch.len_utf8()..];
+                ch
+            }
+        };
+        assert_eq!(byte(s, 0), b'\'');
+        let suffix = s[1..].to_owned().into_boxed_str();
+        (ch, suffix)
+    }
+
+    fn backslash_x<S>(s: &S) -> (u8, &S)
+    where
+        S: Index<RangeFrom<usize>, Output = S> + AsRef<[u8]> + ?Sized,
+    {
+        let mut ch = 0;
+        let b0 = byte(s, 0);
+        let b1 = byte(s, 1);
+        ch += 0x10
+            * match b0 {
+                b'0'..=b'9' => b0 - b'0',
+                b'a'..=b'f' => 10 + (b0 - b'a'),
+                b'A'..=b'F' => 10 + (b0 - b'A'),
+                _ => panic!("unexpected non-hex character after \\x"),
+            };
+        ch += match b1 {
+            b'0'..=b'9' => b1 - b'0',
+            b'a'..=b'f' => 10 + (b1 - b'a'),
+            b'A'..=b'F' => 10 + (b1 - b'A'),
+            _ => panic!("unexpected non-hex character after \\x"),
+        };
+        (ch, &s[2..])
+    }
+
+    fn backslash_u(mut s: &str) -> (char, &str) {
+        if byte(s, 0) != b'{' {
+            panic!("{}", "expected { after \\u");
+        }
+        s = &s[1..];
+
+        let mut ch = 0;
+        let mut digits = 0;
+        loop {
+            let b = byte(s, 0);
+            let digit = match b {
+                b'0'..=b'9' => b - b'0',
+                b'a'..=b'f' => 10 + b - b'a',
+                b'A'..=b'F' => 10 + b - b'A',
+                b'_' if digits > 0 => {
+                    s = &s[1..];
+                    continue;
+                }
+                b'}' if digits == 0 => panic!("invalid empty unicode escape"),
+                b'}' => break,
+                _ => panic!("unexpected non-hex character after \\u"),
+            };
+            if digits == 6 {
+                panic!("overlong unicode escape (must have at most 6 hex digits)");
+            }
+            ch *= 0x10;
+            ch += u32::from(digit);
+            digits += 1;
+            s = &s[1..];
+        }
+        assert!(byte(s, 0) == b'}');
+        s = &s[1..];
+
+        if let Some(ch) = char::from_u32(ch) {
+            (ch, s)
+        } else {
+            panic!("character code {:x} is not a valid unicode character", ch);
+        }
+    }
+
+    // Returns base 10 digits and suffix.
+    pub(crate) fn parse_lit_int(mut s: &str) -> Option<(Box<str>, Box<str>)> {
+        let negative = byte(s, 0) == b'-';
+        if negative {
+            s = &s[1..];
+        }
+
+        let base = match (byte(s, 0), byte(s, 1)) {
+            (b'0', b'x') => {
+                s = &s[2..];
+                16
+            }
+            (b'0', b'o') => {
+                s = &s[2..];
+                8
+            }
+            (b'0', b'b') => {
+                s = &s[2..];
+                2
+            }
+            (b'0'..=b'9', _) => 10,
+            _ => return None,
+        };
+
+        let mut value = BigInt::new();
+        let mut has_digit = false;
+        'outer: loop {
+            let b = byte(s, 0);
+            let digit = match b {
+                b'0'..=b'9' => b - b'0',
+                b'a'..=b'f' if base > 10 => b - b'a' + 10,
+                b'A'..=b'F' if base > 10 => b - b'A' + 10,
+                b'_' => {
+                    s = &s[1..];
+                    continue;
+                }
+                // If looking at a floating point literal, we don't want to
+                // consider it an integer.
+                b'.' if base == 10 => return None,
+                b'e' | b'E' if base == 10 => {
+                    let mut has_exp = false;
+                    for (i, b) in s[1..].bytes().enumerate() {
+                        match b {
+                            b'_' => {}
+                            b'-' | b'+' => return None,
+                            b'0'..=b'9' => has_exp = true,
+                            _ => {
+                                let suffix = &s[1 + i..];
+                                if has_exp && crate::ident::xid_ok(suffix) {
+                                    return None;
+                                } else {
+                                    break 'outer;
+                                }
+                            }
+                        }
+                    }
+                    if has_exp {
+                        return None;
+                    } else {
+                        break;
+                    }
+                }
+                _ => break,
+            };
+
+            if digit >= base {
+                return None;
+            }
+
+            has_digit = true;
+            value *= base;
+            value += digit;
+            s = &s[1..];
+        }
+
+        if !has_digit {
+            return None;
+        }
+
+        let suffix = s;
+        if suffix.is_empty() || crate::ident::xid_ok(suffix) {
+            let mut repr = value.to_string();
+            if negative {
+                repr.insert(0, '-');
+            }
+            Some((repr.into_boxed_str(), suffix.to_owned().into_boxed_str()))
+        } else {
+            None
+        }
+    }
+
+    // Returns base 10 digits and suffix.
+    pub(crate) fn parse_lit_float(input: &str) -> Option<(Box<str>, Box<str>)> {
+        // Rust's floating point literals are very similar to the ones parsed by
+        // the standard library, except that rust's literals can contain
+        // ignorable underscores. Let's remove those underscores.
+
+        let mut bytes = input.to_owned().into_bytes();
+
+        let start = (*bytes.first()? == b'-') as usize;
+        match bytes.get(start)? {
+            b'0'..=b'9' => {}
+            _ => return None,
+        }
+
+        let mut read = start;
+        let mut write = start;
+        let mut has_dot = false;
+        let mut has_e = false;
+        let mut has_sign = false;
+        let mut has_exponent = false;
+        while read < bytes.len() {
+            match bytes[read] {
+                b'_' => {
+                    // Don't increase write
+                    read += 1;
+                    continue;
+                }
+                b'0'..=b'9' => {
+                    if has_e {
+                        has_exponent = true;
+                    }
+                    bytes[write] = bytes[read];
+                }
+                b'.' => {
+                    if has_e || has_dot {
+                        return None;
+                    }
+                    has_dot = true;
+                    bytes[write] = b'.';
+                }
+                b'e' | b'E' => {
+                    match bytes[read + 1..]
+                        .iter()
+                        .find(|b| **b != b'_')
+                        .unwrap_or(&b'\0')
+                    {
+                        b'-' | b'+' | b'0'..=b'9' => {}
+                        _ => break,
+                    }
+                    if has_e {
+                        if has_exponent {
+                            break;
+                        } else {
+                            return None;
+                        }
+                    }
+                    has_e = true;
+                    bytes[write] = b'e';
+                }
+                b'-' | b'+' => {
+                    if has_sign || has_exponent || !has_e {
+                        return None;
+                    }
+                    has_sign = true;
+                    if bytes[read] == b'-' {
+                        bytes[write] = bytes[read];
+                    } else {
+                        // Omit '+'
+                        read += 1;
+                        continue;
+                    }
+                }
+                _ => break,
+            }
+            read += 1;
+            write += 1;
+        }
+
+        if has_e && !has_exponent {
+            return None;
+        }
+
+        let mut digits = String::from_utf8(bytes).unwrap();
+        let suffix = digits.split_off(read);
+        digits.truncate(write);
+        if suffix.is_empty() || crate::ident::xid_ok(&suffix) {
+            Some((digits.into_boxed_str(), suffix.into_boxed_str()))
+        } else {
+            None
+        }
+    }
+}