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    //! A Serde ast, parsed from the Syn ast and ready to generate Rust code.

    use internals::attr;
    use internals::check;
    use internals::{Ctxt, Derive};
    use syn;
    use syn::punctuated::Punctuated;

    /// A source data structure annotated with `#[derive(Serialize)]` and/or `#[derive(Deserialize)]`,
    /// parsed into an internal representation.
    pub struct Container<'a> {
        /// The struct or enum name (without generics).
        pub ident: syn::Ident,
        /// Attributes on the structure, parsed for Serde.
        pub attrs: attr::Container,
        /// The contents of the struct or enum.
        pub data: Data<'a>,
        /// Any generics on the struct or enum.
        pub generics: &'a syn::Generics,
        /// Original input.
        pub original: &'a syn::DeriveInput,
    }

    /// The fields of a struct or enum.
    ///
    /// Analogous to `syn::Data`.
    pub enum Data<'a> {
        Enum(Vec<Variant<'a>>),
        Struct(Style, Vec<Field<'a>>),
    }

    /// A variant of an enum.
    pub struct Variant<'a> {
        pub ident: syn::Ident,
        pub attrs: attr::Variant,
        pub style: Style,
        pub fields: Vec<Field<'a>>,
        pub original: &'a syn::Variant,
    }

    /// A field of a struct.
    pub struct Field<'a> {
        pub member: syn::Member,
        pub attrs: attr::Field,
        pub ty: &'a syn::Type,
        pub original: &'a syn::Field,
    }

    #[derive(Copy, Clone)]
    pub enum Style {
        /// Named fields.
        Struct,
        /// Many unnamed fields.
        Tuple,
        /// One unnamed field.
        Newtype,
        /// No fields.
        Unit,
    }

    impl<'a> Container<'a> {
        /// Convert the raw Syn ast into a parsed container object, collecting errors in `cx`.
        pub fn from_ast(
            cx: &Ctxt,
            item: &'a syn::DeriveInput,
            derive: Derive,
        ) -> Option<Container<'a>> {
            let mut attrs = attr::Container::from_ast(cx, item);

            let mut data = match &item.data {
                syn::Data::Enum(data) => Data::Enum(enum_from_ast(cx, &data.variants, attrs.default())),
                syn::Data::Struct(data) => {
                    let (style, fields) = struct_from_ast(cx, &data.fields, None, attrs.default());
                    Data::Struct(style, fields)
                }
                syn::Data::Union(_) => {
                    cx.error_spanned_by(item, "Serde does not support derive for unions");
                    return None;
                }
            };

            let mut has_flatten = false;
            match &mut data {
                Data::Enum(variants) => {
                    for variant in variants {
                        variant.attrs.rename_by_rules(attrs.rename_all_rules());
                        for field in &mut variant.fields {
                            if field.attrs.flatten() {
                                has_flatten = true;
                            }
                            field
                                .attrs
                                .rename_by_rules(variant.attrs.rename_all_rules());
                        }
                    }
                }
                Data::Struct(_, fields) => {
                    for field in fields {
                        if field.attrs.flatten() {
                            has_flatten = true;
                        }
                        field.attrs.rename_by_rules(attrs.rename_all_rules());
                    }
                }
            }

            if has_flatten {
                attrs.mark_has_flatten();
            }

            let mut item = Container {
                ident: item.ident.clone(),
                attrs,
                data,
                generics: &item.generics,
                original: item,
            };
            check::check(cx, &mut item, derive);
            Some(item)
        }
    }

    impl<'a> Data<'a> {
        pub fn all_fields(&'a self) -> Box<Iterator<Item = &'a Field<'a>> + 'a> {
            match self {
                Data::Enum(variants) => {
                    Box::new(variants.iter().flat_map(|variant| variant.fields.iter()))
                }
                Data::Struct(_, fields) => Box::new(fields.iter()),
            }
        }

        pub fn has_getter(&self) -> bool {
            self.all_fields().any(|f| f.attrs.getter().is_some())
        }
    }

    fn enum_from_ast<'a>(
        cx: &Ctxt,
        variants: &'a Punctuated<syn::Variant, Token![,]>,
        container_default: &attr::Default,
    ) -> Vec<Variant<'a>> {
        variants
            .iter()
            .map(|variant| {
                let attrs = attr::Variant::from_ast(cx, variant);
                let (style, fields) =
                    struct_from_ast(cx, &variant.fields, Some(&attrs), container_default);
                Variant {
                    ident: variant.ident.clone(),
                    attrs,
                    style,
                    fields,
                    original: variant,
                }
            })
            .collect()
    }

    fn struct_from_ast<'a>(
        cx: &Ctxt,
        fields: &'a syn::Fields,
        attrs: Option<&attr::Variant>,
        container_default: &attr::Default,
    ) -> (Style, Vec<Field<'a>>) {
        match fields {
            syn::Fields::Named(fields) => (
                Style::Struct,
                fields_from_ast(cx, &fields.named, attrs, container_default),
            ),
            syn::Fields::Unnamed(fields) if fields.unnamed.len() == 1 => (
                Style::Newtype,
                fields_from_ast(cx, &fields.unnamed, attrs, container_default),
            ),
            syn::Fields::Unnamed(fields) => (
                Style::Tuple,
                fields_from_ast(cx, &fields.unnamed, attrs, container_default),
            ),
            syn::Fields::Unit => (Style::Unit, Vec::new()),
        }
    }

    fn fields_from_ast<'a>(
        cx: &Ctxt,
        fields: &'a Punctuated<syn::Field, Token![,]>,
        attrs: Option<&attr::Variant>,
        container_default: &attr::Default,
    ) -> Vec<Field<'a>> {
        fields
            .iter()
            .enumerate()
            .map(|(i, field)| Field {
                member: match &field.ident {
                    Some(ident) => syn::Member::Named(ident.clone()),
                    None => syn::Member::Unnamed(i.into()),
                },
                attrs: attr::Field::from_ast(cx, i, field, attrs, container_default),
                ty: &field.ty,
                original: field,
            })
            .collect()
    }