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    //! Extension traits to provide parsing methods on foreign types.
    //!
    //! *This module is available only if Syn is built with the `"parsing"` feature.*

    use crate::buffer::Cursor;
    use crate::parse::Peek;
    use crate::parse::{ParseStream, Result};
    use crate::sealed::lookahead;
    use crate::token::CustomToken;
    use proc_macro2::Ident;

    /// Additional methods for `Ident` not provided by proc-macro2 or libproc_macro.
    ///
    /// This trait is sealed and cannot be implemented for types outside of Syn. It
    /// is implemented only for `proc_macro2::Ident`.
    ///
    /// *This trait is available only if Syn is built with the `"parsing"` feature.*
    pub trait IdentExt: Sized + private::Sealed {
        /// Parses any identifier including keywords.
        ///
        /// This is useful when parsing macro input which allows Rust keywords as
        /// identifiers.
        ///
        /// # Example
        ///
        /// ```
        /// use syn::{Error, Ident, Result, Token};
        /// use syn::ext::IdentExt;
        /// use syn::parse::ParseStream;
        ///
        /// mod kw {
        ///     syn::custom_keyword!(name);
        /// }
        ///
        /// // Parses input that looks like `name = NAME` where `NAME` can be
        /// // any identifier.
        /// //
        /// // Examples:
        /// //
        /// //     name = anything
        /// //     name = impl
        /// fn parse_dsl(input: ParseStream) -> Result<Ident> {
        ///     input.parse::<kw::name>()?;
        ///     input.parse::<Token![=]>()?;
        ///     let name = input.call(Ident::parse_any)?;
        ///     Ok(name)
        /// }
        /// ```
        fn parse_any(input: ParseStream) -> Result<Self>;

        /// Peeks any identifier including keywords. Usage:
        /// `input.peek(Ident::peek_any)`
        ///
        /// This is different from `input.peek(Ident)` which only returns true in
        /// the case of an ident which is not a Rust keyword.
        #[allow(non_upper_case_globals)]
        const peek_any: private::PeekFn = private::PeekFn;

        /// Strips the raw marker `r#`, if any, from the beginning of an ident.
        ///
        ///   - unraw(`x`) = `x`
        ///   - unraw(`move`) = `move`
        ///   - unraw(`r#move`) = `move`
        ///
        /// # Example
        ///
        /// In the case of interop with other languages like Python that have a
        /// different set of keywords than Rust, we might come across macro input
        /// that involves raw identifiers to refer to ordinary variables in the
        /// other language with a name that happens to be a Rust keyword.
        ///
        /// The function below appends an identifier from the caller's input onto a
        /// fixed prefix. Without using `unraw()`, this would tend to produce
        /// invalid identifiers like `__pyo3_get_r#move`.
        ///
        /// ```
        /// use proc_macro2::Span;
        /// use syn::Ident;
        /// use syn::ext::IdentExt;
        ///
        /// fn ident_for_getter(variable: &Ident) -> Ident {
        ///     let getter = format!("__pyo3_get_{}", variable.unraw());
        ///     Ident::new(&getter, Span::call_site())
        /// }
        /// ```
        fn unraw(&self) -> Ident;
    }

    impl IdentExt for Ident {
        fn parse_any(input: ParseStream) -> Result<Self> {
            input.step(|cursor| match cursor.ident() {
                Some((ident, rest)) => Ok((ident, rest)),
                None => Err(cursor.error("expected ident")),
            })
        }

        fn unraw(&self) -> Ident {
            let string = self.to_string();
            if string.starts_with("r#") {
                Ident::new(&string[2..], self.span())
            } else {
                self.clone()
            }
        }
    }

    impl Peek for private::PeekFn {
        type Token = private::IdentAny;
    }

    impl CustomToken for private::IdentAny {
        fn peek(cursor: Cursor) -> bool {
            cursor.ident().is_some()
        }

        fn display() -> &'static str {
            "identifier"
        }
    }

    impl lookahead::Sealed for private::PeekFn {}

    mod private {
        use proc_macro2::Ident;

        pub trait Sealed {}

        impl Sealed for Ident {}

        pub struct PeekFn;
        pub struct IdentAny;

        impl Copy for PeekFn {}
        impl Clone for PeekFn {
            fn clone(&self) -> Self {
                *self
            }
        }
    }