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    use crate::{IdentFragment, ToTokens, TokenStreamExt};
    use core::fmt;
    use core::iter;
    use core::ops::BitOr;

    pub use core::option::Option;
    pub use proc_macro2::*;
    pub use std::format;

    pub struct HasIterator; // True
    pub struct ThereIsNoIteratorInRepetition; // False

    impl BitOr<ThereIsNoIteratorInRepetition> for ThereIsNoIteratorInRepetition {
        type Output = ThereIsNoIteratorInRepetition;
        fn bitor(self, _rhs: ThereIsNoIteratorInRepetition) -> ThereIsNoIteratorInRepetition {
            ThereIsNoIteratorInRepetition
        }
    }

    impl BitOr<ThereIsNoIteratorInRepetition> for HasIterator {
        type Output = HasIterator;
        fn bitor(self, _rhs: ThereIsNoIteratorInRepetition) -> HasIterator {
            HasIterator
        }
    }

    impl BitOr<HasIterator> for ThereIsNoIteratorInRepetition {
        type Output = HasIterator;
        fn bitor(self, _rhs: HasIterator) -> HasIterator {
            HasIterator
        }
    }

    impl BitOr<HasIterator> for HasIterator {
        type Output = HasIterator;
        fn bitor(self, _rhs: HasIterator) -> HasIterator {
            HasIterator
        }
    }

    /// Extension traits used by the implementation of `quote!`. These are defined
    /// in separate traits, rather than as a single trait due to ambiguity issues.
    ///
    /// These traits expose a `quote_into_iter` method which should allow calling
    /// whichever impl happens to be applicable. Calling that method repeatedly on
    /// the returned value should be idempotent.
    pub mod ext {
        use super::RepInterp;
        use super::{HasIterator as HasIter, ThereIsNoIteratorInRepetition as DoesNotHaveIter};
        use crate::ToTokens;
        use core::slice;
        use std::collections::btree_set::{self, BTreeSet};

        /// Extension trait providing the `quote_into_iter` method on iterators.
        pub trait RepIteratorExt: Iterator + Sized {
            fn quote_into_iter(self) -> (Self, HasIter) {
                (self, HasIter)
            }
        }

        impl<T: Iterator> RepIteratorExt for T {}

        /// Extension trait providing the `quote_into_iter` method for
        /// non-iterable types. These types interpolate the same value in each
        /// iteration of the repetition.
        pub trait RepToTokensExt {
            /// Pretend to be an iterator for the purposes of `quote_into_iter`.
            /// This allows repeated calls to `quote_into_iter` to continue
            /// correctly returning DoesNotHaveIter.
            fn next(&self) -> Option<&Self> {
                Some(self)
            }

            fn quote_into_iter(&self) -> (&Self, DoesNotHaveIter) {
                (self, DoesNotHaveIter)
            }
        }

        impl<T: ToTokens + ?Sized> RepToTokensExt for T {}

        /// Extension trait providing the `quote_into_iter` method for types that
        /// can be referenced as an iterator.
        pub trait RepAsIteratorExt<'q> {
            type Iter: Iterator;

            fn quote_into_iter(&'q self) -> (Self::Iter, HasIter);
        }

        impl<'q, 'a, T: RepAsIteratorExt<'q> + ?Sized> RepAsIteratorExt<'q> for &'a T {
            type Iter = T::Iter;

            fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
                <T as RepAsIteratorExt>::quote_into_iter(*self)
            }
        }

        impl<'q, 'a, T: RepAsIteratorExt<'q> + ?Sized> RepAsIteratorExt<'q> for &'a mut T {
            type Iter = T::Iter;

            fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
                <T as RepAsIteratorExt>::quote_into_iter(*self)
            }
        }

        impl<'q, T: 'q> RepAsIteratorExt<'q> for [T] {
            type Iter = slice::Iter<'q, T>;

            fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
                (self.iter(), HasIter)
            }
        }

        impl<'q, T: 'q> RepAsIteratorExt<'q> for Vec<T> {
            type Iter = slice::Iter<'q, T>;

            fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
                (self.iter(), HasIter)
            }
        }

        impl<'q, T: 'q> RepAsIteratorExt<'q> for BTreeSet<T> {
            type Iter = btree_set::Iter<'q, T>;

            fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
                (self.iter(), HasIter)
            }
        }

        impl<'q, T: RepAsIteratorExt<'q>> RepAsIteratorExt<'q> for RepInterp<T> {
            type Iter = T::Iter;

            fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
                self.0.quote_into_iter()
            }
        }
    }

    // Helper type used within interpolations to allow for repeated binding names.
    // Implements the relevant traits, and exports a dummy `next()` method.
    #[derive(Copy, Clone)]
    pub struct RepInterp<T>(pub T);

    impl<T> RepInterp<T> {
        // This method is intended to look like `Iterator::next`, and is called when
        // a name is bound multiple times, as the previous binding will shadow the
        // original `Iterator` object. This allows us to avoid advancing the
        // iterator multiple times per iteration.
        pub fn next(self) -> Option<T> {
            Some(self.0)
        }
    }

    impl<T: Iterator> Iterator for RepInterp<T> {
        type Item = T::Item;

        fn next(&mut self) -> Option<Self::Item> {
            self.0.next()
        }
    }

    impl<T: ToTokens> ToTokens for RepInterp<T> {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.0.to_tokens(tokens);
        }
    }

    pub fn push_group(tokens: &mut TokenStream, delimiter: Delimiter, inner: TokenStream) {
        tokens.append(Group::new(delimiter, inner));
    }

    pub fn push_group_spanned(
        tokens: &mut TokenStream,
        span: Span,
        delimiter: Delimiter,
        inner: TokenStream,
    ) {
        let mut g = Group::new(delimiter, inner);
        g.set_span(span);
        tokens.append(g);
    }

    pub fn parse(tokens: &mut TokenStream, s: &str) {
        let s: TokenStream = s.parse().expect("invalid token stream");
        tokens.extend(iter::once(s));
    }

    pub fn parse_spanned(tokens: &mut TokenStream, span: Span, s: &str) {
        let s: TokenStream = s.parse().expect("invalid token stream");
        tokens.extend(s.into_iter().map(|t| respan_token_tree(t, span)));
    }

    // 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 = g
                    .stream()
                    .into_iter()
                    .map(|token| respan_token_tree(token, span))
                    .collect();
                *g = Group::new(g.delimiter(), stream);
                g.set_span(span);
            }
            other => other.set_span(span),
        }
        token
    }

    pub fn push_ident(tokens: &mut TokenStream, s: &str) {
        let span = Span::call_site();
        push_ident_spanned(tokens, span, s);
    }

    pub fn push_ident_spanned(tokens: &mut TokenStream, span: Span, s: &str) {
        tokens.append(ident_maybe_raw(s, span));
    }

    pub fn push_lifetime(tokens: &mut TokenStream, lifetime: &str) {
        struct Lifetime<'a> {
            name: &'a str,
            state: u8,
        }

        impl<'a> Iterator for Lifetime<'a> {
            type Item = TokenTree;

            fn next(&mut self) -> Option<Self::Item> {
                match self.state {
                    0 => {
                        self.state = 1;
                        Some(TokenTree::Punct(Punct::new('\'', Spacing::Joint)))
                    }
                    1 => {
                        self.state = 2;
                        Some(TokenTree::Ident(Ident::new(self.name, Span::call_site())))
                    }
                    _ => None,
                }
            }
        }

        tokens.extend(Lifetime {
            name: &lifetime[1..],
            state: 0,
        });
    }

    pub fn push_lifetime_spanned(tokens: &mut TokenStream, span: Span, lifetime: &str) {
        struct Lifetime<'a> {
            name: &'a str,
            span: Span,
            state: u8,
        }

        impl<'a> Iterator for Lifetime<'a> {
            type Item = TokenTree;

            fn next(&mut self) -> Option<Self::Item> {
                match self.state {
                    0 => {
                        self.state = 1;
                        let mut apostrophe = Punct::new('\'', Spacing::Joint);
                        apostrophe.set_span(self.span);
                        Some(TokenTree::Punct(apostrophe))
                    }
                    1 => {
                        self.state = 2;
                        Some(TokenTree::Ident(Ident::new(self.name, self.span)))
                    }
                    _ => None,
                }
            }
        }

        tokens.extend(Lifetime {
            name: &lifetime[1..],
            span,
            state: 0,
        });
    }

    macro_rules! push_punct {
        ($name:ident $spanned:ident $char1:tt) => {
            pub fn $name(tokens: &mut TokenStream) {
                tokens.append(Punct::new($char1, Spacing::Alone));
            }
            pub fn $spanned(tokens: &mut TokenStream, span: Span) {
                let mut punct = Punct::new($char1, Spacing::Alone);
                punct.set_span(span);
                tokens.append(punct);
            }
        };
        ($name:ident $spanned:ident $char1:tt $char2:tt) => {
            pub fn $name(tokens: &mut TokenStream) {
                tokens.append(Punct::new($char1, Spacing::Joint));
                tokens.append(Punct::new($char2, Spacing::Alone));
            }
            pub fn $spanned(tokens: &mut TokenStream, span: Span) {
                let mut punct = Punct::new($char1, Spacing::Joint);
                punct.set_span(span);
                tokens.append(punct);
                let mut punct = Punct::new($char2, Spacing::Alone);
                punct.set_span(span);
                tokens.append(punct);
            }
        };
        ($name:ident $spanned:ident $char1:tt $char2:tt $char3:tt) => {
            pub fn $name(tokens: &mut TokenStream) {
                tokens.append(Punct::new($char1, Spacing::Joint));
                tokens.append(Punct::new($char2, Spacing::Joint));
                tokens.append(Punct::new($char3, Spacing::Alone));
            }
            pub fn $spanned(tokens: &mut TokenStream, span: Span) {
                let mut punct = Punct::new($char1, Spacing::Joint);
                punct.set_span(span);
                tokens.append(punct);
                let mut punct = Punct::new($char2, Spacing::Joint);
                punct.set_span(span);
                tokens.append(punct);
                let mut punct = Punct::new($char3, Spacing::Alone);
                punct.set_span(span);
                tokens.append(punct);
            }
        };
    }

    push_punct!(push_add push_add_spanned '+');
    push_punct!(push_add_eq push_add_eq_spanned '+' '=');
    push_punct!(push_and push_and_spanned '&');
    push_punct!(push_and_and push_and_and_spanned '&' '&');
    push_punct!(push_and_eq push_and_eq_spanned '&' '=');
    push_punct!(push_at push_at_spanned '@');
    push_punct!(push_bang push_bang_spanned '!');
    push_punct!(push_caret push_caret_spanned '^');
    push_punct!(push_caret_eq push_caret_eq_spanned '^' '=');
    push_punct!(push_colon push_colon_spanned ':');
    push_punct!(push_colon2 push_colon2_spanned ':' ':');
    push_punct!(push_comma push_comma_spanned ',');
    push_punct!(push_div push_div_spanned '/');
    push_punct!(push_div_eq push_div_eq_spanned '/' '=');
    push_punct!(push_dot push_dot_spanned '.');
    push_punct!(push_dot2 push_dot2_spanned '.' '.');
    push_punct!(push_dot3 push_dot3_spanned '.' '.' '.');
    push_punct!(push_dot_dot_eq push_dot_dot_eq_spanned '.' '.' '=');
    push_punct!(push_eq push_eq_spanned '=');
    push_punct!(push_eq_eq push_eq_eq_spanned '=' '=');
    push_punct!(push_ge push_ge_spanned '>' '=');
    push_punct!(push_gt push_gt_spanned '>');
    push_punct!(push_le push_le_spanned '<' '=');
    push_punct!(push_lt push_lt_spanned '<');
    push_punct!(push_mul_eq push_mul_eq_spanned '*' '=');
    push_punct!(push_ne push_ne_spanned '!' '=');
    push_punct!(push_or push_or_spanned '|');
    push_punct!(push_or_eq push_or_eq_spanned '|' '=');
    push_punct!(push_or_or push_or_or_spanned '|' '|');
    push_punct!(push_pound push_pound_spanned '#');
    push_punct!(push_question push_question_spanned '?');
    push_punct!(push_rarrow push_rarrow_spanned '-' '>');
    push_punct!(push_larrow push_larrow_spanned '<' '-');
    push_punct!(push_rem push_rem_spanned '%');
    push_punct!(push_rem_eq push_rem_eq_spanned '%' '=');
    push_punct!(push_fat_arrow push_fat_arrow_spanned '=' '>');
    push_punct!(push_semi push_semi_spanned ';');
    push_punct!(push_shl push_shl_spanned '<' '<');
    push_punct!(push_shl_eq push_shl_eq_spanned '<' '<' '=');
    push_punct!(push_shr push_shr_spanned '>' '>');
    push_punct!(push_shr_eq push_shr_eq_spanned '>' '>' '=');
    push_punct!(push_star push_star_spanned '*');
    push_punct!(push_sub push_sub_spanned '-');
    push_punct!(push_sub_eq push_sub_eq_spanned '-' '=');

    pub fn push_underscore(tokens: &mut TokenStream) {
        push_underscore_spanned(tokens, Span::call_site());
    }

    pub fn push_underscore_spanned(tokens: &mut TokenStream, span: Span) {
        tokens.append(Ident::new("_", span));
    }

    // Helper method for constructing identifiers from the `format_ident!` macro,
    // handling `r#` prefixes.
    pub fn mk_ident(id: &str, span: Option<Span>) -> Ident {
        let span = span.unwrap_or_else(Span::call_site);
        ident_maybe_raw(id, span)
    }

    fn ident_maybe_raw(id: &str, span: Span) -> Ident {
        if id.starts_with("r#") {
            Ident::new_raw(&id[2..], span)
        } else {
            Ident::new(id, span)
        }
    }

    // Adapts from `IdentFragment` to `fmt::Display` for use by the `format_ident!`
    // macro, and exposes span information from these fragments.
    //
    // This struct also has forwarding implementations of the formatting traits
    // `Octal`, `LowerHex`, `UpperHex`, and `Binary` to allow for their use within
    // `format_ident!`.
    #[derive(Copy, Clone)]
    pub struct IdentFragmentAdapter<T: IdentFragment>(pub T);

    impl<T: IdentFragment> IdentFragmentAdapter<T> {
        pub fn span(&self) -> Option<Span> {
            self.0.span()
        }
    }

    impl<T: IdentFragment> fmt::Display for IdentFragmentAdapter<T> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            IdentFragment::fmt(&self.0, f)
        }
    }

    impl<T: IdentFragment + fmt::Octal> fmt::Octal for IdentFragmentAdapter<T> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Octal::fmt(&self.0, f)
        }
    }

    impl<T: IdentFragment + fmt::LowerHex> fmt::LowerHex for IdentFragmentAdapter<T> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::LowerHex::fmt(&self.0, f)
        }
    }

    impl<T: IdentFragment + fmt::UpperHex> fmt::UpperHex for IdentFragmentAdapter<T> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::UpperHex::fmt(&self.0, f)
        }
    }

    impl<T: IdentFragment + fmt::Binary> fmt::Binary for IdentFragmentAdapter<T> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Binary::fmt(&self.0, f)
        }
    }