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

    ast_struct! {
        /// Data structure sent to a `proc_macro_derive` macro.
        ///
        /// *This type is available only if Syn is built with the `"derive"` feature.*
        #[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
        pub struct DeriveInput {
            /// Attributes tagged on the whole struct or enum.
            pub attrs: Vec<Attribute>,

            /// Visibility of the struct or enum.
            pub vis: Visibility,

            /// Name of the struct or enum.
            pub ident: Ident,

            /// Generics required to complete the definition.
            pub generics: Generics,

            /// Data within the struct or enum.
            pub data: Data,
        }
    }

    ast_enum_of_structs! {
        /// The storage of a struct, enum or union data structure.
        ///
        /// *This type is available only if Syn is built with the `"derive"` feature.*
        ///
        /// # Syntax tree enum
        ///
        /// This type is a [syntax tree enum].
        ///
        /// [syntax tree enum]: Expr#syntax-tree-enums
        #[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
        pub enum Data {
            /// A struct input to a `proc_macro_derive` macro.
            Struct(DataStruct),

            /// An enum input to a `proc_macro_derive` macro.
            Enum(DataEnum),

            /// An untagged union input to a `proc_macro_derive` macro.
            Union(DataUnion),
        }

        do_not_generate_to_tokens
    }

    ast_struct! {
        /// A struct input to a `proc_macro_derive` macro.
        ///
        /// *This type is available only if Syn is built with the `"derive"`
        /// feature.*
        #[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
        pub struct DataStruct {
            pub struct_token: Token![struct],
            pub fields: Fields,
            pub semi_token: Option<Token![;]>,
        }
    }

    ast_struct! {
        /// An enum input to a `proc_macro_derive` macro.
        ///
        /// *This type is available only if Syn is built with the `"derive"`
        /// feature.*
        #[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
        pub struct DataEnum {
            pub enum_token: Token![enum],
            pub brace_token: token::Brace,
            pub variants: Punctuated<Variant, Token![,]>,
        }
    }

    ast_struct! {
        /// An untagged union input to a `proc_macro_derive` macro.
        ///
        /// *This type is available only if Syn is built with the `"derive"`
        /// feature.*
        #[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
        pub struct DataUnion {
            pub union_token: Token![union],
            pub fields: FieldsNamed,
        }
    }

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

        #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
        impl Parse for DeriveInput {
            fn parse(input: ParseStream) -> Result<Self> {
                let attrs = input.call(Attribute::parse_outer)?;
                let vis = input.parse::<Visibility>()?;

                let lookahead = input.lookahead1();
                if lookahead.peek(Token![struct]) {
                    let struct_token = input.parse::<Token![struct]>()?;
                    let ident = input.parse::<Ident>()?;
                    let generics = input.parse::<Generics>()?;
                    let (where_clause, fields, semi) = data_struct(input)?;
                    Ok(DeriveInput {
                        attrs,
                        vis,
                        ident,
                        generics: Generics {
                            where_clause,
                            ..generics
                        },
                        data: Data::Struct(DataStruct {
                            struct_token,
                            fields,
                            semi_token: semi,
                        }),
                    })
                } else if lookahead.peek(Token![enum]) {
                    let enum_token = input.parse::<Token![enum]>()?;
                    let ident = input.parse::<Ident>()?;
                    let generics = input.parse::<Generics>()?;
                    let (where_clause, brace, variants) = data_enum(input)?;
                    Ok(DeriveInput {
                        attrs,
                        vis,
                        ident,
                        generics: Generics {
                            where_clause,
                            ..generics
                        },
                        data: Data::Enum(DataEnum {
                            enum_token,
                            brace_token: brace,
                            variants,
                        }),
                    })
                } else if lookahead.peek(Token![union]) {
                    let union_token = input.parse::<Token![union]>()?;
                    let ident = input.parse::<Ident>()?;
                    let generics = input.parse::<Generics>()?;
                    let (where_clause, fields) = data_union(input)?;
                    Ok(DeriveInput {
                        attrs,
                        vis,
                        ident,
                        generics: Generics {
                            where_clause,
                            ..generics
                        },
                        data: Data::Union(DataUnion {
                            union_token,
                            fields,
                        }),
                    })
                } else {
                    Err(lookahead.error())
                }
            }
        }

        pub fn data_struct(
            input: ParseStream,
        ) -> Result<(Option<WhereClause>, Fields, Option<Token![;]>)> {
            let mut lookahead = input.lookahead1();
            let mut where_clause = None;
            if lookahead.peek(Token![where]) {
                where_clause = Some(input.parse()?);
                lookahead = input.lookahead1();
            }

            if where_clause.is_none() && lookahead.peek(token::Paren) {
                let fields = input.parse()?;

                lookahead = input.lookahead1();
                if lookahead.peek(Token![where]) {
                    where_clause = Some(input.parse()?);
                    lookahead = input.lookahead1();
                }

                if lookahead.peek(Token![;]) {
                    let semi = input.parse()?;
                    Ok((where_clause, Fields::Unnamed(fields), Some(semi)))
                } else {
                    Err(lookahead.error())
                }
            } else if lookahead.peek(token::Brace) {
                let fields = input.parse()?;
                Ok((where_clause, Fields::Named(fields), None))
            } else if lookahead.peek(Token![;]) {
                let semi = input.parse()?;
                Ok((where_clause, Fields::Unit, Some(semi)))
            } else {
                Err(lookahead.error())
            }
        }

        pub fn data_enum(
            input: ParseStream,
        ) -> Result<(
            Option<WhereClause>,
            token::Brace,
            Punctuated<Variant, Token![,]>,
        )> {
            let where_clause = input.parse()?;

            let content;
            let brace = braced!(content in input);
            let variants = content.parse_terminated(Variant::parse)?;

            Ok((where_clause, brace, variants))
        }

        pub fn data_union(input: ParseStream) -> Result<(Option<WhereClause>, FieldsNamed)> {
            let where_clause = input.parse()?;
            let fields = input.parse()?;
            Ok((where_clause, fields))
        }
    }

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

        #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
        impl ToTokens for DeriveInput {
            fn to_tokens(&self, tokens: &mut TokenStream) {
                for attr in self.attrs.outer() {
                    attr.to_tokens(tokens);
                }
                self.vis.to_tokens(tokens);
                match &self.data {
                    Data::Struct(d) => d.struct_token.to_tokens(tokens),
                    Data::Enum(d) => d.enum_token.to_tokens(tokens),
                    Data::Union(d) => d.union_token.to_tokens(tokens),
                }
                self.ident.to_tokens(tokens);
                self.generics.to_tokens(tokens);
                match &self.data {
                    Data::Struct(data) => match &data.fields {
                        Fields::Named(fields) => {
                            self.generics.where_clause.to_tokens(tokens);
                            fields.to_tokens(tokens);
                        }
                        Fields::Unnamed(fields) => {
                            fields.to_tokens(tokens);
                            self.generics.where_clause.to_tokens(tokens);
                            TokensOrDefault(&data.semi_token).to_tokens(tokens);
                        }
                        Fields::Unit => {
                            self.generics.where_clause.to_tokens(tokens);
                            TokensOrDefault(&data.semi_token).to_tokens(tokens);
                        }
                    },
                    Data::Enum(data) => {
                        self.generics.where_clause.to_tokens(tokens);
                        data.brace_token.surround(tokens, |tokens| {
                            data.variants.to_tokens(tokens);
                        });
                    }
                    Data::Union(data) => {
                        self.generics.where_clause.to_tokens(tokens);
                        data.fields.to_tokens(tokens);
                    }
                }
            }
        }
    }