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    use super::*;
    use crate::punctuated::Punctuated;

    ast_struct! {
        /// An enum variant.
        ///
        /// *This type is available only if Syn is built with the `"derive"` or `"full"`
        /// feature.*
        #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
        pub struct Variant {
            /// Attributes tagged on the variant.
            pub attrs: Vec<Attribute>,

            /// Name of the variant.
            pub ident: Ident,

            /// Content stored in the variant.
            pub fields: Fields,

            /// Explicit discriminant: `Variant = 1`
            pub discriminant: Option<(Token![=], Expr)>,
        }
    }

    ast_enum_of_structs! {
        /// Data stored within an enum variant or struct.
        ///
        /// *This type is available only if Syn is built with the `"derive"` or `"full"`
        /// feature.*
        ///
        /// # Syntax tree enum
        ///
        /// This type is a [syntax tree enum].
        ///
        /// [syntax tree enum]: Expr#syntax-tree-enums
        #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
        pub enum Fields {
            /// Named fields of a struct or struct variant such as `Point { x: f64,
            /// y: f64 }`.
            Named(FieldsNamed),

            /// Unnamed fields of a tuple struct or tuple variant such as `Some(T)`.
            Unnamed(FieldsUnnamed),

            /// Unit struct or unit variant such as `None`.
            Unit,
        }
    }

    ast_struct! {
        /// Named fields of a struct or struct variant such as `Point { x: f64,
        /// y: f64 }`.
        ///
        /// *This type is available only if Syn is built with the `"derive"` or
        /// `"full"` feature.*
        #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
        pub struct FieldsNamed {
            pub brace_token: token::Brace,
            pub named: Punctuated<Field, Token![,]>,
        }
    }

    ast_struct! {
        /// Unnamed fields of a tuple struct or tuple variant such as `Some(T)`.
        ///
        /// *This type is available only if Syn is built with the `"derive"` or
        /// `"full"` feature.*
        #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
        pub struct FieldsUnnamed {
            pub paren_token: token::Paren,
            pub unnamed: Punctuated<Field, Token![,]>,
        }
    }

    impl Fields {
        /// Get an iterator over the borrowed [`Field`] items in this object. This
        /// iterator can be used to iterate over a named or unnamed struct or
        /// variant's fields uniformly.
        pub fn iter(&self) -> punctuated::Iter<Field> {
            match self {
                Fields::Unit => crate::punctuated::empty_punctuated_iter(),
                Fields::Named(f) => f.named.iter(),
                Fields::Unnamed(f) => f.unnamed.iter(),
            }
        }

        /// Get an iterator over the mutably borrowed [`Field`] items in this
        /// object. This iterator can be used to iterate over a named or unnamed
        /// struct or variant's fields uniformly.
        pub fn iter_mut(&mut self) -> punctuated::IterMut<Field> {
            match self {
                Fields::Unit => crate::punctuated::empty_punctuated_iter_mut(),
                Fields::Named(f) => f.named.iter_mut(),
                Fields::Unnamed(f) => f.unnamed.iter_mut(),
            }
        }

        /// Returns the number of fields.
        pub fn len(&self) -> usize {
            match self {
                Fields::Unit => 0,
                Fields::Named(f) => f.named.len(),
                Fields::Unnamed(f) => f.unnamed.len(),
            }
        }

        /// Returns `true` if there are zero fields.
        pub fn is_empty(&self) -> bool {
            match self {
                Fields::Unit => true,
                Fields::Named(f) => f.named.is_empty(),
                Fields::Unnamed(f) => f.unnamed.is_empty(),
            }
        }
    }

    impl IntoIterator for Fields {
        type Item = Field;
        type IntoIter = punctuated::IntoIter<Field>;

        fn into_iter(self) -> Self::IntoIter {
            match self {
                Fields::Unit => Punctuated::<Field, ()>::new().into_iter(),
                Fields::Named(f) => f.named.into_iter(),
                Fields::Unnamed(f) => f.unnamed.into_iter(),
            }
        }
    }

    impl<'a> IntoIterator for &'a Fields {
        type Item = &'a Field;
        type IntoIter = punctuated::Iter<'a, Field>;

        fn into_iter(self) -> Self::IntoIter {
            self.iter()
        }
    }

    impl<'a> IntoIterator for &'a mut Fields {
        type Item = &'a mut Field;
        type IntoIter = punctuated::IterMut<'a, Field>;

        fn into_iter(self) -> Self::IntoIter {
            self.iter_mut()
        }
    }

    ast_struct! {
        /// A field of a struct or enum variant.
        ///
        /// *This type is available only if Syn is built with the `"derive"` or `"full"`
        /// feature.*
        #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
        pub struct Field {
            /// Attributes tagged on the field.
            pub attrs: Vec<Attribute>,

            /// Visibility of the field.
            pub vis: Visibility,

            /// Name of the field, if any.
            ///
            /// Fields of tuple structs have no names.
            pub ident: Option<Ident>,

            pub colon_token: Option<Token![:]>,

            /// Type of the field.
            pub ty: Type,
        }
    }

    ast_enum_of_structs! {
        /// The visibility level of an item: inherited or `pub` or
        /// `pub(restricted)`.
        ///
        /// *This type is available only if Syn is built with the `"derive"` or `"full"`
        /// feature.*
        ///
        /// # Syntax tree enum
        ///
        /// This type is a [syntax tree enum].
        ///
        /// [syntax tree enum]: Expr#syntax-tree-enums
        #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
        pub enum Visibility {
            /// A public visibility level: `pub`.
            Public(VisPublic),

            /// A crate-level visibility: `crate`.
            Crate(VisCrate),

            /// A visibility level restricted to some path: `pub(self)` or
            /// `pub(super)` or `pub(crate)` or `pub(in some::module)`.
            Restricted(VisRestricted),

            /// An inherited visibility, which usually means private.
            Inherited,
        }
    }

    ast_struct! {
        /// A public visibility level: `pub`.
        ///
        /// *This type is available only if Syn is built with the `"derive"` or
        /// `"full"` feature.*
        #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
        pub struct VisPublic {
            pub pub_token: Token![pub],
        }
    }

    ast_struct! {
        /// A crate-level visibility: `crate`.
        ///
        /// *This type is available only if Syn is built with the `"derive"` or
        /// `"full"` feature.*
        #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
        pub struct VisCrate {
            pub crate_token: Token![crate],
        }
    }

    ast_struct! {
        /// A visibility level restricted to some path: `pub(self)` or
        /// `pub(super)` or `pub(crate)` or `pub(in some::module)`.
        ///
        /// *This type is available only if Syn is built with the `"derive"` or
        /// `"full"` feature.*
        #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
        pub struct VisRestricted {
            pub pub_token: Token![pub],
            pub paren_token: token::Paren,
            pub in_token: Option<Token![in]>,
            pub path: Box<Path>,
        }
    }

    #[cfg(feature = "parsing")]
    pub mod parsing {
        use super::*;
        use crate::ext::IdentExt;
        use crate::parse::discouraged::Speculative;
        use crate::parse::{Parse, ParseStream, Result};

        #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
        impl Parse for Variant {
            fn parse(input: ParseStream) -> Result<Self> {
                let attrs = input.call(Attribute::parse_outer)?;
                let _visibility: Visibility = input.parse()?;
                let ident: Ident = input.parse()?;
                let fields = if input.peek(token::Brace) {
                    Fields::Named(input.parse()?)
                } else if input.peek(token::Paren) {
                    Fields::Unnamed(input.parse()?)
                } else {
                    Fields::Unit
                };
                let discriminant = if input.peek(Token![=]) {
                    let eq_token: Token![=] = input.parse()?;
                    let discriminant: Expr = input.parse()?;
                    Some((eq_token, discriminant))
                } else {
                    None
                };
                Ok(Variant {
                    attrs,
                    ident,
                    fields,
                    discriminant,
                })
            }
        }

        #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
        impl Parse for FieldsNamed {
            fn parse(input: ParseStream) -> Result<Self> {
                let content;
                Ok(FieldsNamed {
                    brace_token: braced!(content in input),
                    named: content.parse_terminated(Field::parse_named)?,
                })
            }
        }

        #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
        impl Parse for FieldsUnnamed {
            fn parse(input: ParseStream) -> Result<Self> {
                let content;
                Ok(FieldsUnnamed {
                    paren_token: parenthesized!(content in input),
                    unnamed: content.parse_terminated(Field::parse_unnamed)?,
                })
            }
        }

        impl Field {
            /// Parses a named (braced struct) field.
            #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
            pub fn parse_named(input: ParseStream) -> Result<Self> {
                Ok(Field {
                    attrs: input.call(Attribute::parse_outer)?,
                    vis: input.parse()?,
                    ident: Some(if input.peek(Token![_]) {
                        input.call(Ident::parse_any)
                    } else {
                        input.parse()
                    }?),
                    colon_token: Some(input.parse()?),
                    ty: input.parse()?,
                })
            }

            /// Parses an unnamed (tuple struct) field.
            #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
            pub fn parse_unnamed(input: ParseStream) -> Result<Self> {
                Ok(Field {
                    attrs: input.call(Attribute::parse_outer)?,
                    vis: input.parse()?,
                    ident: None,
                    colon_token: None,
                    ty: input.parse()?,
                })
            }
        }

        #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
        impl Parse for Visibility {
            fn parse(input: ParseStream) -> Result<Self> {
                // Recognize an empty None-delimited group, as produced by a $:vis
                // matcher that matched no tokens.
                if input.peek(token::Group) {
                    let ahead = input.fork();
                    let group = crate::group::parse_group(&ahead)?;
                    if group.content.is_empty() {
                        input.advance_to(&ahead);
                        return Ok(Visibility::Inherited);
                    }
                }

                if input.peek(Token![pub]) {
                    Self::parse_pub(input)
                } else if input.peek(Token![crate]) {
                    Self::parse_crate(input)
                } else {
                    Ok(Visibility::Inherited)
                }
            }
        }

        impl Visibility {
            fn parse_pub(input: ParseStream) -> Result<Self> {
                let pub_token = input.parse::<Token![pub]>()?;

                if input.peek(token::Paren) {
                    let ahead = input.fork();

                    let content;
                    let paren_token = parenthesized!(content in ahead);
                    if content.peek(Token![crate])
                        || content.peek(Token![self])
                        || content.peek(Token![super])
                    {
                        let path = content.call(Ident::parse_any)?;

                        // Ensure there are no additional tokens within `content`.
                        // Without explicitly checking, we may misinterpret a tuple
                        // field as a restricted visibility, causing a parse error.
                        // e.g. `pub (crate::A, crate::B)` (Issue #720).
                        if content.is_empty() {
                            input.advance_to(&ahead);
                            return Ok(Visibility::Restricted(VisRestricted {
                                pub_token,
                                paren_token,
                                in_token: None,
                                path: Box::new(Path::from(path)),
                            }));
                        }
                    } else if content.peek(Token![in]) {
                        let in_token: Token![in] = content.parse()?;
                        let path = content.call(Path::parse_mod_style)?;

                        input.advance_to(&ahead);
                        return Ok(Visibility::Restricted(VisRestricted {
                            pub_token,
                            paren_token,
                            in_token: Some(in_token),
                            path: Box::new(path),
                        }));
                    }
                }

                Ok(Visibility::Public(VisPublic { pub_token }))
            }

            fn parse_crate(input: ParseStream) -> Result<Self> {
                if input.peek2(Token![::]) {
                    Ok(Visibility::Inherited)
                } else {
                    Ok(Visibility::Crate(VisCrate {
                        crate_token: input.parse()?,
                    }))
                }
            }

            #[cfg(feature = "full")]
            pub(crate) fn is_some(&self) -> bool {
                match self {
                    Visibility::Inherited => false,
                    _ => true,
                }
            }
        }
    }

    #[cfg(feature = "printing")]
    mod printing {
        use super::*;
        use crate::print::TokensOrDefault;
        use proc_macro2::TokenStream;
        use quote::{ToTokens, TokenStreamExt};

        #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
        impl ToTokens for Variant {
            fn to_tokens(&self, tokens: &mut TokenStream) {
                tokens.append_all(&self.attrs);
                self.ident.to_tokens(tokens);
                self.fields.to_tokens(tokens);
                if let Some((eq_token, disc)) = &self.discriminant {
                    eq_token.to_tokens(tokens);
                    disc.to_tokens(tokens);
                }
            }
        }

        #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
        impl ToTokens for FieldsNamed {
            fn to_tokens(&self, tokens: &mut TokenStream) {
                self.brace_token.surround(tokens, |tokens| {
                    self.named.to_tokens(tokens);
                });
            }
        }

        #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
        impl ToTokens for FieldsUnnamed {
            fn to_tokens(&self, tokens: &mut TokenStream) {
                self.paren_token.surround(tokens, |tokens| {
                    self.unnamed.to_tokens(tokens);
                });
            }
        }

        #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
        impl ToTokens for Field {
            fn to_tokens(&self, tokens: &mut TokenStream) {
                tokens.append_all(&self.attrs);
                self.vis.to_tokens(tokens);
                if let Some(ident) = &self.ident {
                    ident.to_tokens(tokens);
                    TokensOrDefault(&self.colon_token).to_tokens(tokens);
                }
                self.ty.to_tokens(tokens);
            }
        }

        #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
        impl ToTokens for VisPublic {
            fn to_tokens(&self, tokens: &mut TokenStream) {
                self.pub_token.to_tokens(tokens);
            }
        }

        #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
        impl ToTokens for VisCrate {
            fn to_tokens(&self, tokens: &mut TokenStream) {
                self.crate_token.to_tokens(tokens);
            }
        }

        #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
        impl ToTokens for VisRestricted {
            fn to_tokens(&self, tokens: &mut TokenStream) {
                self.pub_token.to_tokens(tokens);
                self.paren_token.surround(tokens, |tokens| {
                    // TODO: If we have a path which is not "self" or "super" or
                    // "crate", automatically add the "in" token.
                    self.in_token.to_tokens(tokens);
                    self.path.to_tokens(tokens);
                });
            }
        }
    }