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    /// Formatting macro for constructing `Ident`s.
    ///
    /// <br>
    ///
    /// # Syntax
    ///
    /// Syntax is copied from the [`format!`] macro, supporting both positional and
    /// named arguments.
    ///
    /// Only a limited set of formatting traits are supported. The current mapping
    /// of format types to traits is:
    ///
    /// * `{}` ⇒ [`IdentFragment`]
    /// * `{:o}` ⇒ [`Octal`](std::fmt::Octal)
    /// * `{:x}` ⇒ [`LowerHex`](std::fmt::LowerHex)
    /// * `{:X}` ⇒ [`UpperHex`](std::fmt::UpperHex)
    /// * `{:b}` ⇒ [`Binary`](std::fmt::Binary)
    ///
    /// See [`std::fmt`] for more information.
    ///
    /// <br>
    ///
    /// # IdentFragment
    ///
    /// Unlike `format!`, this macro uses the [`IdentFragment`] formatting trait by
    /// default. This trait is like `Display`, with a few differences:
    ///
    /// * `IdentFragment` is only implemented for a limited set of types, such as
    ///    unsigned integers and strings.
    /// * [`Ident`] arguments will have their `r#` prefixes stripped, if present.
    ///
    /// [`IdentFragment`]: crate::IdentFragment
    /// [`Ident`]: proc_macro2::Ident
    ///
    /// <br>
    ///
    /// # Hygiene
    ///
    /// The [`Span`] of the first `Ident` argument is used as the span of the final
    /// identifier, falling back to [`Span::call_site`] when no identifiers are
    /// provided.
    ///
    /// ```
    /// # use quote::format_ident;
    /// # let ident = format_ident!("Ident");
    /// // If `ident` is an Ident, the span of `my_ident` will be inherited from it.
    /// let my_ident = format_ident!("My{}{}", ident, "IsCool");
    /// assert_eq!(my_ident, "MyIdentIsCool");
    /// ```
    ///
    /// Alternatively, the span can be overridden by passing the `span` named
    /// argument.
    ///
    /// ```
    /// # use quote::format_ident;
    /// # const IGNORE_TOKENS: &'static str = stringify! {
    /// let my_span = /* ... */;
    /// # };
    /// # let my_span = proc_macro2::Span::call_site();
    /// format_ident!("MyIdent", span = my_span);
    /// ```
    ///
    /// [`Span`]: proc_macro2::Span
    /// [`Span::call_site`]: proc_macro2::Span::call_site
    ///
    /// <p><br></p>
    ///
    /// # Panics
    ///
    /// This method will panic if the resulting formatted string is not a valid
    /// identifier.
    ///
    /// <br>
    ///
    /// # Examples
    ///
    /// Composing raw and non-raw identifiers:
    /// ```
    /// # use quote::format_ident;
    /// let my_ident = format_ident!("My{}", "Ident");
    /// assert_eq!(my_ident, "MyIdent");
    ///
    /// let raw = format_ident!("r#Raw");
    /// assert_eq!(raw, "r#Raw");
    ///
    /// let my_ident_raw = format_ident!("{}Is{}", my_ident, raw);
    /// assert_eq!(my_ident_raw, "MyIdentIsRaw");
    /// ```
    ///
    /// Integer formatting options:
    /// ```
    /// # use quote::format_ident;
    /// let num: u32 = 10;
    ///
    /// let decimal = format_ident!("Id_{}", num);
    /// assert_eq!(decimal, "Id_10");
    ///
    /// let octal = format_ident!("Id_{:o}", num);
    /// assert_eq!(octal, "Id_12");
    ///
    /// let binary = format_ident!("Id_{:b}", num);
    /// assert_eq!(binary, "Id_1010");
    ///
    /// let lower_hex = format_ident!("Id_{:x}", num);
    /// assert_eq!(lower_hex, "Id_a");
    ///
    /// let upper_hex = format_ident!("Id_{:X}", num);
    /// assert_eq!(upper_hex, "Id_A");
    /// ```
    #[macro_export]
    macro_rules! format_ident {
        ($fmt:expr) => {
            $crate::format_ident_impl!([
                $crate::__private::Option::None,
                $fmt
            ])
        };

        ($fmt:expr, $($rest:tt)*) => {
            $crate::format_ident_impl!([
                $crate::__private::Option::None,
                $fmt
            ] $($rest)*)
        };
    }

    #[macro_export]
    #[doc(hidden)]
    macro_rules! format_ident_impl {
        // Final state
        ([$span:expr, $($fmt:tt)*]) => {
            $crate::__private::mk_ident(
                &$crate::__private::format!($($fmt)*),
                $span,
            )
        };

        // Span argument
        ([$old:expr, $($fmt:tt)*] span = $span:expr) => {
            $crate::format_ident_impl!([$old, $($fmt)*] span = $span,)
        };
        ([$old:expr, $($fmt:tt)*] span = $span:expr, $($rest:tt)*) => {
            $crate::format_ident_impl!([
                $crate::__private::Option::Some::<$crate::__private::Span>($span),
                $($fmt)*
            ] $($rest)*)
        };

        // Named argument
        ([$span:expr, $($fmt:tt)*] $name:ident = $arg:expr) => {
            $crate::format_ident_impl!([$span, $($fmt)*] $name = $arg,)
        };
        ([$span:expr, $($fmt:tt)*] $name:ident = $arg:expr, $($rest:tt)*) => {
            match $crate::__private::IdentFragmentAdapter(&$arg) {
                arg => $crate::format_ident_impl!([$span.or(arg.span()), $($fmt)*, $name = arg] $($rest)*),
            }
        };

        // Positional argument
        ([$span:expr, $($fmt:tt)*] $arg:expr) => {
            $crate::format_ident_impl!([$span, $($fmt)*] $arg,)
        };
        ([$span:expr, $($fmt:tt)*] $arg:expr, $($rest:tt)*) => {
            match $crate::__private::IdentFragmentAdapter(&$arg) {
                arg => $crate::format_ident_impl!([$span.or(arg.span()), $($fmt)*, arg] $($rest)*),
            }
        };
    }