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    use core::fmt;
    use proc_macro2::{Ident, Span};
    use std::borrow::Cow;

    /// Specialized formatting trait used by `format_ident!`.
    ///
    /// [`Ident`] arguments formatted using this trait will have their `r#` prefix
    /// stripped, if present.
    ///
    /// See [`format_ident!`] for more information.
    pub trait IdentFragment {
        /// Format this value as an identifier fragment.
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result;

        /// Span associated with this `IdentFragment`.
        ///
        /// If non-`None`, may be inherited by formatted identifiers.
        fn span(&self) -> Option<Span> {
            None
        }
    }

    impl<T: IdentFragment + ?Sized> IdentFragment for &T {
        fn span(&self) -> Option<Span> {
            <T as IdentFragment>::span(*self)
        }

        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            IdentFragment::fmt(*self, f)
        }
    }

    impl<T: IdentFragment + ?Sized> IdentFragment for &mut T {
        fn span(&self) -> Option<Span> {
            <T as IdentFragment>::span(*self)
        }

        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            IdentFragment::fmt(*self, f)
        }
    }

    impl IdentFragment for Ident {
        fn span(&self) -> Option<Span> {
            Some(self.span())
        }

        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            let id = self.to_string();
            if id.starts_with("r#") {
                fmt::Display::fmt(&id[2..], f)
            } else {
                fmt::Display::fmt(&id[..], f)
            }
        }
    }

    impl<T> IdentFragment for Cow<'_, T>
    where
        T: IdentFragment + ToOwned + ?Sized,
    {
        fn span(&self) -> Option<Span> {
            T::span(self)
        }

        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            T::fmt(self, f)
        }
    }

    // Limited set of types which this is implemented for, as we want to avoid types
    // which will often include non-identifier characters in their `Display` impl.
    macro_rules! ident_fragment_display {
        ($($T:ty),*) => {
            $(
                impl IdentFragment for $T {
                    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                        fmt::Display::fmt(self, f)
                    }
                }
            )*
        };
    }

    ident_fragment_display!(bool, str, String, char);
    ident_fragment_display!(u8, u16, u32, u64, u128, usize);