content.rs

// This module is doc(hidden) and nothing here should be used outside of
// generated code.
//
// We will iterate on the implementation for a few releases and only have to
// worry about backward compatibility for the `untagged` and `tag` attributes
// rather than for this entire mechanism.
//
// This issue is tracking making some of this stuff public:
// https://github.com/serde-rs/serde/issues/741

#![doc(hidden)]

use core::cmp;
use core::fmt;
use core::marker::PhantomData;

#[cfg(all(not(feature = "std"), feature = "collections"))]
use collections::{String, Vec};

#[cfg(all(feature = "alloc", not(feature = "std")))]
use alloc::boxed::Box;

use de::{self, Deserialize, DeserializeSeed, Deserializer, Visitor, SeqVisitor, MapVisitor,
         EnumVisitor, Unexpected};

/// Used from generated code to buffer the contents of the Deserializer when
/// deserializing untagged enums and internally tagged enums.
///
/// Not public API. Use serde-value instead.
#[derive(Debug)]
pub enum Content {
    Bool(bool),

    U8(u8),
    U16(u16),
    U32(u32),
    U64(u64),

    I8(i8),
    I16(i16),
    I32(i32),
    I64(i64),

    F32(f32),
    F64(f64),

    Char(char),
    String(String),
    Bytes(Vec<u8>),

    None,
    Some(Box<Content>),

    Unit,
    Newtype(Box<Content>),
    Seq(Vec<Content>),
    Map(Vec<(Content, Content)>),
}

impl Content {
    fn unexpected(&self) -> Unexpected {
        match *self {
            Content::Bool(b) => Unexpected::Bool(b),
            Content::U8(n) => Unexpected::Unsigned(n as u64),
            Content::U16(n) => Unexpected::Unsigned(n as u64),
            Content::U32(n) => Unexpected::Unsigned(n as u64),
            Content::U64(n) => Unexpected::Unsigned(n),
            Content::I8(n) => Unexpected::Signed(n as i64),
            Content::I16(n) => Unexpected::Signed(n as i64),
            Content::I32(n) => Unexpected::Signed(n as i64),
            Content::I64(n) => Unexpected::Signed(n),
            Content::F32(f) => Unexpected::Float(f as f64),
            Content::F64(f) => Unexpected::Float(f),
            Content::Char(c) => Unexpected::Char(c),
            Content::String(ref s) => Unexpected::Str(s),
            Content::Bytes(ref b) => Unexpected::Bytes(b),
            Content::None | Content::Some(_) => Unexpected::Option,
            Content::Unit => Unexpected::Unit,
            Content::Newtype(_) => Unexpected::NewtypeStruct,
            Content::Seq(_) => Unexpected::Seq,
            Content::Map(_) => Unexpected::Map,
        }
    }
}

impl Deserialize for Content {
    fn deserialize<D: Deserializer>(deserializer: D) -> Result<Self, D::Error> {
        // Untagged and internally tagged enums are only supported in
        // self-describing formats.
        deserializer.deserialize(ContentVisitor)
    }
}

struct ContentVisitor;

impl Visitor for ContentVisitor {
    type Value = Content;

    fn expecting(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.write_str("any value")
    }

    fn visit_bool<F>(self, value: bool) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::Bool(value))
    }

    fn visit_i8<F>(self, value: i8) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::I8(value))
    }

    fn visit_i16<F>(self, value: i16) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::I16(value))
    }

    fn visit_i32<F>(self, value: i32) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::I32(value))
    }

    fn visit_i64<F>(self, value: i64) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::I64(value))
    }

    fn visit_u8<F>(self, value: u8) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::U8(value))
    }

    fn visit_u16<F>(self, value: u16) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::U16(value))
    }

    fn visit_u32<F>(self, value: u32) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::U32(value))
    }

    fn visit_u64<F>(self, value: u64) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::U64(value))
    }

    fn visit_f32<F>(self, value: f32) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::F32(value))
    }

    fn visit_f64<F>(self, value: f64) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::F64(value))
    }

    fn visit_char<F>(self, value: char) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::Char(value))
    }

    fn visit_str<F>(self, value: &str) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::String(value.into()))
    }

    fn visit_string<F>(self, value: String) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::String(value))
    }

    fn visit_bytes<F>(self, value: &[u8]) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::Bytes(value.into()))
    }

    fn visit_byte_buf<F>(self, value: Vec<u8>) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::Bytes(value))
    }

    fn visit_unit<F>(self) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::Unit)
    }

    fn visit_none<F>(self) -> Result<Self::Value, F>
        where F: de::Error
    {
        Ok(Content::None)
    }

    fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
        where D: Deserializer
    {
        Deserialize::deserialize(deserializer).map(|v| Content::Some(Box::new(v)))
    }

    fn visit_newtype_struct<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
        where D: Deserializer
    {
        Deserialize::deserialize(deserializer).map(|v| Content::Newtype(Box::new(v)))
    }

    fn visit_seq<V>(self, mut visitor: V) -> Result<Self::Value, V::Error>
        where V: SeqVisitor
    {
        let mut vec = Vec::with_capacity(cmp::min(visitor.size_hint().0, 4096));
        while let Some(e) = try!(visitor.visit()) {
            vec.push(e);
        }
        Ok(Content::Seq(vec))
    }

    fn visit_map<V>(self, mut visitor: V) -> Result<Self::Value, V::Error>
        where V: MapVisitor
    {
        let mut vec = Vec::with_capacity(cmp::min(visitor.size_hint().0, 4096));
        while let Some(kv) = try!(visitor.visit()) {
            vec.push(kv);
        }
        Ok(Content::Map(vec))
    }

    fn visit_enum<V>(self, _visitor: V) -> Result<Self::Value, V::Error>
        where V: EnumVisitor
    {
        Err(de::Error::custom("untagged and internally tagged enums do not support enum input"))
    }
}

/// This is the type of the map keys in an internally tagged enum.
///
/// Not public API.
pub enum TagOrContent {
    Tag,
    Content(Content),
}

struct TagOrContentVisitor {
    name: &'static str,
}

impl TagOrContentVisitor {
    fn new(name: &'static str) -> Self {
        TagOrContentVisitor { name: name }
    }
}

impl DeserializeSeed for TagOrContentVisitor {
    type Value = TagOrContent;

    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
        where D: Deserializer
    {
        // Internally tagged enums are only supported in self-describing
        // formats.
        deserializer.deserialize(self)
    }
}

impl Visitor for TagOrContentVisitor {
    type Value = TagOrContent;

    fn expecting(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        write!(fmt, "a type tag `{}` or any other value", self.name)
    }

    fn visit_bool<F>(self, value: bool) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_bool(value).map(TagOrContent::Content)
    }

    fn visit_i8<F>(self, value: i8) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_i8(value).map(TagOrContent::Content)
    }

    fn visit_i16<F>(self, value: i16) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_i16(value).map(TagOrContent::Content)
    }

    fn visit_i32<F>(self, value: i32) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_i32(value).map(TagOrContent::Content)
    }

    fn visit_i64<F>(self, value: i64) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_i64(value).map(TagOrContent::Content)
    }

    fn visit_u8<F>(self, value: u8) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_u8(value).map(TagOrContent::Content)
    }

    fn visit_u16<F>(self, value: u16) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_u16(value).map(TagOrContent::Content)
    }

    fn visit_u32<F>(self, value: u32) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_u32(value).map(TagOrContent::Content)
    }

    fn visit_u64<F>(self, value: u64) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_u64(value).map(TagOrContent::Content)
    }

    fn visit_f32<F>(self, value: f32) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_f32(value).map(TagOrContent::Content)
    }

    fn visit_f64<F>(self, value: f64) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_f64(value).map(TagOrContent::Content)
    }

    fn visit_char<F>(self, value: char) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_char(value).map(TagOrContent::Content)
    }

    fn visit_str<F>(self, value: &str) -> Result<Self::Value, F>
        where F: de::Error
    {
        if value == self.name {
            Ok(TagOrContent::Tag)
        } else {
            ContentVisitor.visit_str(value).map(TagOrContent::Content)
        }
    }

    fn visit_string<F>(self, value: String) -> Result<Self::Value, F>
        where F: de::Error
    {
        if value == self.name {
            Ok(TagOrContent::Tag)
        } else {
            ContentVisitor.visit_string(value).map(TagOrContent::Content)
        }
    }

    fn visit_bytes<F>(self, value: &[u8]) -> Result<Self::Value, F>
        where F: de::Error
    {
        if value == self.name.as_bytes() {
            Ok(TagOrContent::Tag)
        } else {
            ContentVisitor.visit_bytes(value).map(TagOrContent::Content)
        }
    }

    fn visit_byte_buf<F>(self, value: Vec<u8>) -> Result<Self::Value, F>
        where F: de::Error
    {
        if value == self.name.as_bytes() {
            Ok(TagOrContent::Tag)
        } else {
            ContentVisitor.visit_byte_buf(value).map(TagOrContent::Content)
        }
    }

    fn visit_unit<F>(self) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_unit().map(TagOrContent::Content)
    }

    fn visit_none<F>(self) -> Result<Self::Value, F>
        where F: de::Error
    {
        ContentVisitor.visit_none().map(TagOrContent::Content)
    }

    fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
        where D: Deserializer
    {
        ContentVisitor.visit_some(deserializer).map(TagOrContent::Content)
    }

    fn visit_newtype_struct<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
        where D: Deserializer
    {
        ContentVisitor.visit_newtype_struct(deserializer).map(TagOrContent::Content)
    }

    fn visit_seq<V>(self, visitor: V) -> Result<Self::Value, V::Error>
        where V: SeqVisitor
    {
        ContentVisitor.visit_seq(visitor).map(TagOrContent::Content)
    }

    fn visit_map<V>(self, visitor: V) -> Result<Self::Value, V::Error>
        where V: MapVisitor
    {
        ContentVisitor.visit_map(visitor).map(TagOrContent::Content)
    }

    fn visit_enum<V>(self, visitor: V) -> Result<Self::Value, V::Error>
        where V: EnumVisitor
    {
        ContentVisitor.visit_enum(visitor).map(TagOrContent::Content)
    }
}

/// Used by generated code to deserialize an internally tagged enum.
///
/// Not public API.
pub struct TaggedContent<T> {
    pub tag: T,
    pub content: Content,
}

/// Not public API.
pub struct TaggedContentVisitor<T> {
    tag_name: &'static str,
    tag: PhantomData<T>,
}

impl<T> TaggedContentVisitor<T> {
    /// Visitor for the content of an internally tagged enum with the given tag
    /// name.
    pub fn new(name: &'static str) -> Self {
        TaggedContentVisitor {
            tag_name: name,
            tag: PhantomData,
        }
    }
}

impl<T> DeserializeSeed for TaggedContentVisitor<T>
    where T: Deserialize
{
    type Value = TaggedContent<T>;

    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
        where D: Deserializer
    {
        // Internally tagged enums are only supported in self-describing
        // formats.
        deserializer.deserialize(self)
    }
}

impl<T> Visitor for TaggedContentVisitor<T>
    where T: Deserialize
{
    type Value = TaggedContent<T>;

    fn expecting(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.write_str("any value")
    }

    fn visit_map<V>(self, mut visitor: V) -> Result<Self::Value, V::Error>
        where V: MapVisitor
    {
        let mut tag = None;
        let mut vec = Vec::with_capacity(cmp::min(visitor.size_hint().0, 4096));
        while let Some(k) = try!(visitor.visit_key_seed(TagOrContentVisitor::new(self.tag_name))) {
            match k {
                TagOrContent::Tag => {
                    if tag.is_some() {
                        return Err(de::Error::duplicate_field(self.tag_name));
                    }
                    tag = Some(try!(visitor.visit_value()));
                }
                TagOrContent::Content(k) => {
                    let v = try!(visitor.visit_value());
                    vec.push((k, v));
                }
            }
        }
        match tag {
            None => Err(de::Error::missing_field(self.tag_name)),
            Some(tag) => {
                Ok(TaggedContent {
                    tag: tag,
                    content: Content::Map(vec),
                })
            }
        }
    }
}

/// Used by generated code to deserialize an adjacently tagged enum.
///
/// Not public API.
pub enum TagOrContentField {
    Tag,
    Content,
}

/// Not public API.
pub struct TagOrContentFieldVisitor {
    pub tag: &'static str,
    pub content: &'static str,
}

impl DeserializeSeed for TagOrContentFieldVisitor {
    type Value = TagOrContentField;

    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
        where D: Deserializer
    {
        deserializer.deserialize_str(self)
    }
}

impl Visitor for TagOrContentFieldVisitor {
    type Value = TagOrContentField;

    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        write!(formatter, "{:?} or {:?}", self.tag, self.content)
    }

    fn visit_str<E>(self, field: &str) -> Result<Self::Value, E>
        where E: de::Error
    {
        if field == self.tag {
            Ok(TagOrContentField::Tag)
        } else if field == self.content {
            Ok(TagOrContentField::Content)
        } else {
            Err(de::Error::invalid_value(Unexpected::Str(field), &self))
        }
    }
}

/// Not public API
pub struct ContentDeserializer<E> {
    content: Content,
    err: PhantomData<E>,
}

/// Used when deserializing an internally tagged enum because the content will
/// be used exactly once.
impl<E> Deserializer for ContentDeserializer<E>
    where E: de::Error
{
    type Error = E;

    fn deserialize<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where V: Visitor
    {
        match self.content {
            Content::Bool(v) => visitor.visit_bool(v),
            Content::U8(v) => visitor.visit_u8(v),
            Content::U16(v) => visitor.visit_u16(v),
            Content::U32(v) => visitor.visit_u32(v),
            Content::U64(v) => visitor.visit_u64(v),
            Content::I8(v) => visitor.visit_i8(v),
            Content::I16(v) => visitor.visit_i16(v),
            Content::I32(v) => visitor.visit_i32(v),
            Content::I64(v) => visitor.visit_i64(v),
            Content::F32(v) => visitor.visit_f32(v),
            Content::F64(v) => visitor.visit_f64(v),
            Content::Char(v) => visitor.visit_char(v),
            Content::String(v) => visitor.visit_string(v),
            Content::Unit => visitor.visit_unit(),
            Content::None => visitor.visit_none(),
            Content::Some(v) => visitor.visit_some(ContentDeserializer::new(*v)),
            Content::Newtype(v) => visitor.visit_newtype_struct(ContentDeserializer::new(*v)),
            Content::Seq(v) => {
                let seq = v.into_iter().map(ContentDeserializer::new);
                let mut seq_visitor = de::value::SeqDeserializer::new(seq);
                let value = try!(visitor.visit_seq(&mut seq_visitor));
                try!(seq_visitor.end());
                Ok(value)
            }
            Content::Map(v) => {
                let map = v.into_iter()
                    .map(|(k, v)| (ContentDeserializer::new(k), ContentDeserializer::new(v)));
                let mut map_visitor = de::value::MapDeserializer::new(map);
                let value = try!(visitor.visit_map(&mut map_visitor));
                try!(map_visitor.end());
                Ok(value)
            }
            Content::Bytes(v) => visitor.visit_byte_buf(v),
        }
    }

    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where V: Visitor
    {
        match self.content {
            Content::None => visitor.visit_none(),
            Content::Some(v) => visitor.visit_some(ContentDeserializer::new(*v)),
            Content::Unit => visitor.visit_unit(),
            _ => visitor.visit_some(self),
        }
    }

    fn deserialize_newtype_struct<V>(self, _name: &str, visitor: V) -> Result<V::Value, Self::Error>
        where V: Visitor
    {
        visitor.visit_newtype_struct(self)
    }

    fn deserialize_enum<V>(self, _name: &str, _variants: &'static [&'static str], visitor: V) -> Result<V::Value, Self::Error>
        where V: Visitor,
    {
        let (variant, value) = match self.content {
            Content::Map(value) => {
                let mut iter = value.into_iter();
                let (variant, value) = match iter.next() {
                    Some(v) => v,
                    None => {
                        return Err(de::Error::invalid_value(de::Unexpected::Map, &"map with a single key"));
                    }
                };
                // enums are encoded in json as maps with a single key:value pair
                if iter.next().is_some() {
                    return Err(de::Error::invalid_value(de::Unexpected::Map, &"map with a single key"));
                }
                (variant, Some(value))
            }
            Content::String(variant) => (Content::String(variant), None),
            other => {
                return Err(de::Error::invalid_type(other.unexpected(), &"string or map"));
            }
        };

        visitor.visit_enum(EnumDeserializer {
            variant: variant,
            value: value,
            err: PhantomData,
        })
    }

    forward_to_deserialize! {
        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit seq
        seq_fixed_size bytes byte_buf map unit_struct tuple_struct struct
        struct_field tuple ignored_any
    }
}

impl<E> ContentDeserializer<E> {
    /// private API, don't use
    pub fn new(content: Content) -> Self {
        ContentDeserializer {
            content: content,
            err: PhantomData,
        }
    }
}

struct EnumDeserializer<E> where E: de::Error {
    variant: Content,
    value: Option<Content>,
    err: PhantomData<E>,
}

impl<E> de::EnumVisitor for EnumDeserializer<E> where E: de::Error {
    type Error = E;
    type Variant = VariantDeserializer<Self::Error>;

    fn visit_variant_seed<V>(self, seed: V) -> Result<(V::Value, VariantDeserializer<E>), Self::Error>
        where V: de::DeserializeSeed,
    {
        let visitor = VariantDeserializer { value: self.value, err: PhantomData, };
        seed.deserialize(ContentDeserializer::new(self.variant)).map(|v| (v, visitor))
    }
}

struct VariantDeserializer<E> where E: de::Error {
    value: Option<Content>,
    err: PhantomData<E>,
}

impl<E> de::VariantVisitor for VariantDeserializer<E> where E: de::Error {
    type Error = E;

    fn visit_unit(self) -> Result<(), E> {
        match self.value {
            Some(value) => de::Deserialize::deserialize(ContentDeserializer::new(value)),
            None => Ok(()),
        }
    }

    fn visit_newtype_seed<T>(self, seed: T) -> Result<T::Value, E>
        where T: de::DeserializeSeed
    {
        match self.value {
            Some(value) => seed.deserialize(ContentDeserializer::new(value)),
            None => Err(de::Error::invalid_type(de::Unexpected::UnitVariant, &"newtype variant")),
        }
    }

    fn visit_tuple<V>(
        self,
        _len: usize,
        visitor: V
    ) -> Result<V::Value, Self::Error>
        where V: de::Visitor
    {
        match self.value {
            Some(Content::Seq(v)) => {
                de::Deserializer::deserialize(SeqDeserializer::new(v), visitor)
            }
            Some(other) => Err(de::Error::invalid_type(other.unexpected(), &"tuple variant")),
            None => Err(de::Error::invalid_type(de::Unexpected::UnitVariant, &"tuple variant"))
        }
    }

    fn visit_struct<V>(
        self,
        _fields: &'static [&'static str],
        visitor: V
    ) -> Result<V::Value, Self::Error>
        where V: de::Visitor
    {
        match self.value {
            Some(Content::Map(v)) => {
                de::Deserializer::deserialize(MapDeserializer::new(v), visitor)
            }
            Some(other) => Err(de::Error::invalid_type(other.unexpected(), &"struct variant")),
            _ => Err(de::Error::invalid_type(de::Unexpected::UnitVariant, &"struct variant"))
        }
    }
}

struct SeqDeserializer<E> where E: de::Error {
    iter: <Vec<Content> as IntoIterator>::IntoIter,
    err: PhantomData<E>,
}

impl<E> SeqDeserializer<E> where E: de::Error {
    fn new(vec: Vec<Content>) -> Self {
        SeqDeserializer {
            iter: vec.into_iter(),
            err: PhantomData,
        }
    }
}

impl<E> de::Deserializer for SeqDeserializer<E> where E: de::Error {
    type Error = E;

    #[inline]
    fn deserialize<V>(mut self, visitor: V) -> Result<V::Value, Self::Error>
        where V: de::Visitor,
    {
        let len = self.iter.len();
        if len == 0 {
            visitor.visit_unit()
        } else {
            let ret = try!(visitor.visit_seq(&mut self));
            let remaining = self.iter.len();
            if remaining == 0 {
                Ok(ret)
            } else {
                Err(de::Error::invalid_length(len, &"fewer elements in array"))
            }
        }
    }

    forward_to_deserialize! {
        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
        seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
        tuple_struct struct struct_field tuple enum ignored_any
    }
}

impl<E> de::SeqVisitor for SeqDeserializer<E> where E: de::Error {
    type Error = E;

    fn visit_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
        where T: de::DeserializeSeed,
    {
        match self.iter.next() {
            Some(value) => seed.deserialize(ContentDeserializer::new(value)).map(Some),
            None => Ok(None),
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

struct MapDeserializer<E> where E: de::Error {
    iter: <Vec<(Content, Content)> as IntoIterator>::IntoIter,
    value: Option<Content>,
    err: PhantomData<E>,
}

impl<E> MapDeserializer<E> where E: de::Error {
    fn new(map: Vec<(Content, Content)>) -> Self {
        MapDeserializer {
            iter: map.into_iter(),
            value: None,
            err: PhantomData,
        }
    }
}

impl<E> de::MapVisitor for MapDeserializer<E> where E: de::Error {
    type Error = E;

    fn visit_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
        where T: de::DeserializeSeed,
    {
        match self.iter.next() {
            Some((key, value)) => {
                self.value = Some(value);
                seed.deserialize(ContentDeserializer::new(key)).map(Some)
            }
            None => Ok(None),
        }
    }

    fn visit_value_seed<T>(&mut self, seed: T) -> Result<T::Value, Self::Error>
        where T: de::DeserializeSeed,
    {
        match self.value.take() {
            Some(value) => seed.deserialize(ContentDeserializer::new(value)),
            None => Err(de::Error::custom("value is missing")),
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

impl<E> de::Deserializer for MapDeserializer<E> where E: de::Error {
    type Error = E;

    #[inline]
    fn deserialize<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where V: de::Visitor,
    {
        visitor.visit_map(self)
    }

    forward_to_deserialize! {
        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
        seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
        tuple_struct struct struct_field tuple enum ignored_any
    }
}


/// Not public API.
pub struct ContentRefDeserializer<'a, E> {
    content: &'a Content,
    err: PhantomData<E>,
}

/// Used when deserializing an untagged enum because the content may need to be
/// used more than once.
impl<'a, E> Deserializer for ContentRefDeserializer<'a, E>
    where E: de::Error
{
    type Error = E;

    fn deserialize<V>(self, visitor: V) -> Result<V::Value, E>
        where V: Visitor
    {
        match *self.content {
            Content::Bool(v) => visitor.visit_bool(v),
            Content::U8(v) => visitor.visit_u8(v),
            Content::U16(v) => visitor.visit_u16(v),
            Content::U32(v) => visitor.visit_u32(v),
            Content::U64(v) => visitor.visit_u64(v),
            Content::I8(v) => visitor.visit_i8(v),
            Content::I16(v) => visitor.visit_i16(v),
            Content::I32(v) => visitor.visit_i32(v),
            Content::I64(v) => visitor.visit_i64(v),
            Content::F32(v) => visitor.visit_f32(v),
            Content::F64(v) => visitor.visit_f64(v),
            Content::Char(v) => visitor.visit_char(v),
            Content::String(ref v) => visitor.visit_str(v),
            Content::Unit => visitor.visit_unit(),
            Content::None => visitor.visit_none(),
            Content::Some(ref v) => visitor.visit_some(ContentRefDeserializer::new(v)),
            Content::Newtype(ref v) => visitor.visit_newtype_struct(ContentRefDeserializer::new(v)),
            Content::Seq(ref v) => {
                let seq = v.into_iter().map(ContentRefDeserializer::new);
                let mut seq_visitor = de::value::SeqDeserializer::new(seq);
                let value = try!(visitor.visit_seq(&mut seq_visitor));
                try!(seq_visitor.end());
                Ok(value)
            }
            Content::Map(ref v) => {
                let map = v.into_iter().map(|&(ref k, ref v)| {
                    (ContentRefDeserializer::new(k), ContentRefDeserializer::new(v))
                });
                let mut map_visitor = de::value::MapDeserializer::new(map);
                let value = try!(visitor.visit_map(&mut map_visitor));
                try!(map_visitor.end());
                Ok(value)
            }
            Content::Bytes(ref v) => visitor.visit_bytes(v),
        }
    }

    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, E>
        where V: Visitor
    {
        match *self.content {
            Content::None => visitor.visit_none(),
            Content::Some(ref v) => visitor.visit_some(ContentRefDeserializer::new(v)),
            Content::Unit => visitor.visit_unit(),
            _ => visitor.visit_some(self),
        }
    }

    fn deserialize_newtype_struct<V>(self, _name: &str, visitor: V) -> Result<V::Value, E>
        where V: Visitor
    {
        visitor.visit_newtype_struct(self)
    }

    fn deserialize_enum<V>(self, _name: &str, _variants: &'static [&'static str], visitor: V) -> Result<V::Value, Self::Error>
        where V: Visitor,
    {
        let (variant, value) = match *self.content {
            Content::Map(ref value) => {
                let mut iter = value.into_iter();
                let &(ref variant, ref value) = match iter.next() {
                    Some(v) => v,
                    None => {
                        return Err(de::Error::invalid_value(de::Unexpected::Map, &"map with a single key"));
                    }
                };
                // enums are encoded in json as maps with a single key:value pair
                if iter.next().is_some() {
                    return Err(de::Error::invalid_value(de::Unexpected::Map, &"map with a single key"));
                }
                (variant, Some(value))
            }
            ref s @ Content::String(_) => (s, None),
            ref other => {
                return Err(de::Error::invalid_type(other.unexpected(), &"string or map"));
            }
        };

        visitor.visit_enum(EnumRefDeserializer {
            variant: variant,
            value: value,
            err: PhantomData,
        })
    }

    forward_to_deserialize! {
        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit seq
        seq_fixed_size bytes byte_buf map unit_struct tuple_struct struct
        struct_field tuple ignored_any
    }
}

impl<'a, E> ContentRefDeserializer<'a, E> {
    /// private API, don't use
    pub fn new(content: &'a Content) -> Self {
        ContentRefDeserializer {
            content: content,
            err: PhantomData,
        }
    }
}

struct EnumRefDeserializer<'a, E> where E: de::Error {
    variant: &'a Content,
    value: Option<&'a Content>,
    err: PhantomData<E>,
}

impl<'a, E> de::EnumVisitor for EnumRefDeserializer<'a, E> where E: de::Error {
    type Error = E;
    type Variant = VariantRefDeserializer<'a, Self::Error>;

    fn visit_variant_seed<V>(self, seed: V) -> Result<(V::Value, Self::Variant), Self::Error>
        where V: de::DeserializeSeed,
    {
        let visitor = VariantRefDeserializer { value: self.value, err: PhantomData, };
        seed.deserialize(ContentRefDeserializer::new(self.variant)).map(|v| (v, visitor))
    }
}

struct VariantRefDeserializer<'a, E> where E: de::Error {
    value: Option<&'a Content>,
    err: PhantomData<E>,
}

impl<'a, E> de::VariantVisitor for VariantRefDeserializer<'a, E> where E: de::Error {
    type Error = E;

    fn visit_unit(self) -> Result<(), E> {
        match self.value {
            Some(value) => de::Deserialize::deserialize(ContentRefDeserializer::new(value)),
            None => Ok(()),
        }
    }

    fn visit_newtype_seed<T>(self, seed: T) -> Result<T::Value, E>
        where T: de::DeserializeSeed
    {
        match self.value {
            Some(value) => seed.deserialize(ContentRefDeserializer::new(value)),
            None => Err(de::Error::invalid_type(de::Unexpected::UnitVariant, &"newtype variant")),
        }
    }

    fn visit_tuple<V>(
        self,
        _len: usize,
        visitor: V
    ) -> Result<V::Value, Self::Error>
        where V: de::Visitor
    {
        match self.value {
            Some(&Content::Seq(ref v)) => {
                de::Deserializer::deserialize(SeqRefDeserializer::new(v), visitor)
            }
            Some(other) => Err(de::Error::invalid_type(other.unexpected(), &"tuple variant")),
            None => Err(de::Error::invalid_type(de::Unexpected::UnitVariant, &"tuple variant"))
        }
    }

    fn visit_struct<V>(
        self,
        _fields: &'static [&'static str],
        visitor: V
    ) -> Result<V::Value, Self::Error>
        where V: de::Visitor
    {
        match self.value {
            Some(&Content::Map(ref v)) => {
                de::Deserializer::deserialize(MapRefDeserializer::new(v), visitor)
            }
            Some(other) => Err(de::Error::invalid_type(other.unexpected(), &"struct variant")),
            _ => Err(de::Error::invalid_type(de::Unexpected::UnitVariant, &"struct variant"))
        }
    }
}

struct SeqRefDeserializer<'a, E> where E: de::Error {
    iter: <&'a [Content] as IntoIterator>::IntoIter,
    err: PhantomData<E>,
}

impl<'a, E> SeqRefDeserializer<'a, E> where E: de::Error {
    fn new(vec: &'a [Content]) -> Self {
        SeqRefDeserializer {
            iter: vec.into_iter(),
            err: PhantomData,
        }
    }
}

impl<'a, E> de::Deserializer for SeqRefDeserializer<'a, E> where E: de::Error {
    type Error = E;

    #[inline]
    fn deserialize<V>(mut self, visitor: V) -> Result<V::Value, Self::Error>
        where V: de::Visitor,
    {
        let len = self.iter.len();
        if len == 0 {
            visitor.visit_unit()
        } else {
            let ret = try!(visitor.visit_seq(&mut self));
            let remaining = self.iter.len();
            if remaining == 0 {
                Ok(ret)
            } else {
                Err(de::Error::invalid_length(len, &"fewer elements in array"))
            }
        }
    }

    forward_to_deserialize! {
        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
        seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
        tuple_struct struct struct_field tuple enum ignored_any
    }
}

impl<'a, E> de::SeqVisitor for SeqRefDeserializer<'a, E> where E: de::Error {
    type Error = E;

    fn visit_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
        where T: de::DeserializeSeed,
    {
        match self.iter.next() {
            Some(value) => seed.deserialize(ContentRefDeserializer::new(value)).map(Some),
            None => Ok(None),
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

struct MapRefDeserializer<'a, E> where E: de::Error {
    iter: <&'a [(Content, Content)] as IntoIterator>::IntoIter,
    value: Option<&'a Content>,
    err: PhantomData<E>,
}

impl<'a, E> MapRefDeserializer<'a, E> where E: de::Error {
    fn new(map: &'a [(Content, Content)]) -> Self {
        MapRefDeserializer {
            iter: map.into_iter(),
            value: None,
            err: PhantomData,
        }
    }
}

impl<'a, E> de::MapVisitor for MapRefDeserializer<'a, E> where E: de::Error {
    type Error = E;

    fn visit_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
        where T: de::DeserializeSeed,
    {
        match self.iter.next() {
            Some(&(ref key, ref value)) => {
                self.value = Some(value);
                seed.deserialize(ContentRefDeserializer::new(key)).map(Some)
            }
            None => Ok(None),
        }
    }

    fn visit_value_seed<T>(&mut self, seed: T) -> Result<T::Value, Self::Error>
        where T: de::DeserializeSeed,
    {
        match self.value.take() {
            Some(value) => seed.deserialize(ContentRefDeserializer::new(value)),
            None => Err(de::Error::custom("value is missing")),
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

impl<'a, E> de::Deserializer for MapRefDeserializer<'a, E> where E: de::Error {
    type Error = E;

    #[inline]
    fn deserialize<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where V: de::Visitor,
    {
        visitor.visit_map(self)
    }

    forward_to_deserialize! {
        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
        seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
        tuple_struct struct struct_field tuple enum ignored_any
    }
}

impl<E> de::value::ValueDeserializer<E> for ContentDeserializer<E>
    where E: de::Error
{
    type Deserializer = Self;

    fn into_deserializer(self) -> Self {
        self
    }
}

impl<'a, E> de::value::ValueDeserializer<E> for ContentRefDeserializer<'a, E>
    where E: de::Error
{
    type Deserializer = Self;

    fn into_deserializer(self) -> Self {
        self
    }
}

/// Visitor for deserializing an internally tagged unit variant.
///
/// Not public API.
pub struct InternallyTaggedUnitVisitor<'a> {
    type_name: &'a str,
    variant_name: &'a str,
}

impl<'a> InternallyTaggedUnitVisitor<'a> {
    /// Not public API.
    pub fn new(type_name: &'a str, variant_name: &'a str) -> Self {
        InternallyTaggedUnitVisitor {
            type_name: type_name,
            variant_name: variant_name,
        }
    }
}

impl<'a> Visitor for InternallyTaggedUnitVisitor<'a> {
    type Value = ();

    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        write!(formatter, "unit variant {}::{}", self.type_name, self.variant_name)
    }

    fn visit_map<V>(self, _: V) -> Result<(), V::Error>
        where V: MapVisitor
    {
        Ok(())
    }
}

/// Visitor for deserializing an untagged unit variant.
///
/// Not public API.
pub struct UntaggedUnitVisitor<'a> {
    type_name: &'a str,
    variant_name: &'a str,
}

impl<'a> UntaggedUnitVisitor<'a> {
    /// Not public API.
    pub fn new(type_name: &'a str, variant_name: &'a str) -> Self {
        UntaggedUnitVisitor {
            type_name: type_name,
            variant_name: variant_name,
        }
    }
}

impl<'a> Visitor for UntaggedUnitVisitor<'a> {
    type Value = ();

    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        write!(formatter, "unit variant {}::{}", self.type_name, self.variant_name)
    }

    fn visit_unit<E>(self) -> Result<(), E>
        where E: de::Error
    {
        Ok(())
    }
}