Rewrite crate with serde support from ground up

This commit completely rewrites this crate from the ground up,
supporting serde at the lowest levels as I believe serde support was
intended to do. This is a major change from the previous versions of
this crate, with a summary of changes being:

* Serialization directly to TOML is now supported without going through
  a `Value` first.

* Deserialization directly from TOML is now supported without going
  through a `Value`. Note that due to the TOML format some values still
  are buffered in intermediate memory, but overall this should be at a
  minimum now.

* The API of `Value` was overhauled to match the API of
  `serde_json::Value`. The changes here were to:

  * Add `is_*` accessors
  * Add `get` and `get_mut` for one-field lookups.
  * Implement panicking lookups through `Index`

  The old `index` methods are now gone in favor of `get` and `Index`
  implementations.

* A `Datetime` type has been added to represent a TOML datetime in a
  first-class fashion. Currently this type provides no accessors other
  than a `Display` implementation, but the idea is that this will grow
  support over time for decomposing the date.

* Support for the `rustc-serialize` crate has been dropped, that'll stay
  on the 0.2 and 0.1 release trains.

* This crate no longer supports the detection of unused fields, for that though
  you can use the `serde_ignored` crate on crates.io

1 files changed, 894 insertions, 0 deletions

diff --git a/src/value.rs b/src/value.rs
new file mode 100644
index 0000000..4769ef1
--- /dev/null
+++ b/src/value.rs
@@ -0,0 +1,894 @@
+//! Definition of a TOML value
+
+use std::collections::BTreeMap;
+use std::fmt;
+use std::ops;
+use std::str::FromStr;
+use std::vec;
+
+use serde::ser;
+use serde::de;
+
+pub use datetime::{Datetime, DatetimeParseError};
+use datetime::{DatetimeFromString, SERDE_STRUCT_FIELD_NAME};
+
+/// Representation of a TOML value.
+#[derive(PartialEq, Clone, Debug)]
+pub enum Value {
+    /// Represents a TOML string
+    String(String),
+    /// Represents a TOML integer
+    Integer(i64),
+    /// Represents a TOML float
+    Float(f64),
+    /// Represents a TOML boolean
+    Boolean(bool),
+    /// Represents a TOML datetime
+    Datetime(Datetime),
+    /// Represents a TOML array
+    Array(Array),
+    /// Represents a TOML table
+    Table(Table),
+}
+
+/// Type representing a TOML array, payload of the `Value::Array` variant
+pub type Array = Vec<Value>;
+
+/// Type representing a TOML table, payload of the `Value::Table` variant
+pub type Table = BTreeMap<String, Value>;
+
+impl Value {
+    /// Convert a `T` into `toml::Value` which is an enum that can represent
+    /// any valid TOML data.
+    ///
+    /// This conversion can fail if `T`'s implementation of `Serialize` decides to
+    /// fail, or if `T` contains a map with non-string keys.
+    pub fn try_from<T>(value: T) -> Result<Value, ::ser::Error>
+        where T: ser::Serialize,
+    {
+        value.serialize(Serializer)
+    }
+
+    /// Interpret a `toml::Value` as an instance of type `T`.
+    ///
+    /// This conversion can fail if the structure of the `Value` does not match the
+    /// structure expected by `T`, for example if `T` is a struct type but the
+    /// `Value` contains something other than a TOML table. It can also fail if the
+    /// structure is correct but `T`'s implementation of `Deserialize` decides that
+    /// something is wrong with the data, for example required struct fields are
+    /// missing from the TOML map or some number is too big to fit in the expected
+    /// primitive type.
+    pub fn try_into<T>(self) -> Result<T, ::de::Error>
+        where T: de::Deserialize,
+    {
+        de::Deserialize::deserialize(self)
+    }
+
+    /// Index into a TOML array or map. A string index can be used to access a
+    /// value in a map, and a usize index can be used to access an element of an
+    /// array.
+    ///
+    /// Returns `None` if the type of `self` does not match the type of the
+    /// index, for example if the index is a string and `self` is an array or a
+    /// number. Also returns `None` if the given key does not exist in the map
+    /// or the given index is not within the bounds of the array.
+    pub fn get<I: Index>(&self, index: I) -> Option<&Value> {
+        index.index(self)
+    }
+
+    /// Mutably index into a TOML array or map. A string index can be used to
+    /// access a value in a map, and a usize index can be used to access an
+    /// element of an array.
+    ///
+    /// Returns `None` if the type of `self` does not match the type of the
+    /// index, for example if the index is a string and `self` is an array or a
+    /// number. Also returns `None` if the given key does not exist in the map
+    /// or the given index is not within the bounds of the array.
+    pub fn get_mut<I: Index>(&mut self, index: I) -> Option<&mut Value> {
+        index.index_mut(self)
+    }
+
+    /// Extracts the integer value if it is an integer.
+    pub fn as_integer(&self) -> Option<i64> {
+        match *self { Value::Integer(i) => Some(i), _ => None }
+    }
+
+    /// Tests whether this value is an integer
+    pub fn is_integer(&self) -> bool {
+        self.as_integer().is_some()
+    }
+
+    /// Extracts the float value if it is a float.
+    pub fn as_float(&self) -> Option<f64> {
+        match *self { Value::Float(f) => Some(f), _ => None }
+    }
+
+    /// Tests whether this value is an float
+    pub fn is_float(&self) -> bool {
+        self.as_float().is_some()
+    }
+
+    /// Extracts the boolean value if it is a boolean.
+    pub fn as_bool(&self) -> Option<bool> {
+        match *self { Value::Boolean(b) => Some(b), _ => None }
+    }
+
+    /// Tests whether this value is an boolg
+    pub fn is_bool(&self) -> bool {
+        self.as_bool().is_some()
+    }
+
+    /// Extracts the string of this value if it is a string.
+    pub fn as_str(&self) -> Option<&str> {
+        match *self { Value::String(ref s) => Some(&**s), _ => None }
+    }
+
+    /// Tests if this value is a string
+    pub fn is_str(&self) -> bool {
+        self.as_str().is_some()
+    }
+
+    /// Extracts the datetime value if it is a datetime.
+    ///
+    /// Note that a parsed TOML value will only contain ISO 8601 dates. An
+    /// example date is:
+    ///
+    /// ```notrust
+    /// 1979-05-27T07:32:00Z
+    /// ```
+    pub fn as_datetime(&self) -> Option<&Datetime> {
+        match *self { Value::Datetime(ref s) => Some(s), _ => None }
+    }
+
+    /// Tests whether this value is an datetime
+    pub fn is_datetime(&self) -> bool {
+        self.as_datetime().is_some()
+    }
+
+    /// Extracts the array value if it is an array.
+    pub fn as_array(&self) -> Option<&Vec<Value>> {
+        match *self { Value::Array(ref s) => Some(s), _ => None }
+    }
+
+    /// Extracts the array value if it is an array.
+    pub fn as_array_mut(&mut self) -> Option<&mut Vec<Value>> {
+        match *self { Value::Array(ref mut s) => Some(s), _ => None }
+    }
+
+    /// Tests whether this value is an array
+    pub fn is_array(&self) -> bool {
+        self.as_array().is_some()
+    }
+
+    /// Extracts the table value if it is a table.
+    pub fn as_table(&self) -> Option<&Table> {
+        match *self { Value::Table(ref s) => Some(s), _ => None }
+    }
+
+    /// Extracts the table value if it is a table.
+    pub fn as_table_mut(&mut self) -> Option<&mut Table> {
+        match *self { Value::Table(ref mut s) => Some(s), _ => None }
+    }
+
+    /// Extracts the table value if it is a table.
+    pub fn is_table(&self) -> bool {
+        self.as_table().is_some()
+    }
+
+    /// Tests whether this and another value have the same type.
+    pub fn same_type(&self, other: &Value) -> bool {
+        match (self, other) {
+            (&Value::String(..), &Value::String(..)) |
+            (&Value::Integer(..), &Value::Integer(..)) |
+            (&Value::Float(..), &Value::Float(..)) |
+            (&Value::Boolean(..), &Value::Boolean(..)) |
+            (&Value::Datetime(..), &Value::Datetime(..)) |
+            (&Value::Array(..), &Value::Array(..)) |
+            (&Value::Table(..), &Value::Table(..)) => true,
+
+            _ => false,
+        }
+    }
+
+    /// Returns a human-readable representation of the type of this value.
+    pub fn type_str(&self) -> &'static str {
+        match *self {
+            Value::String(..) => "string",
+            Value::Integer(..) => "integer",
+            Value::Float(..) => "float",
+            Value::Boolean(..) => "boolean",
+            Value::Datetime(..) => "datetime",
+            Value::Array(..) => "array",
+            Value::Table(..) => "table",
+        }
+    }
+}
+
+impl<I> ops::Index<I> for Value where I: Index {
+    type Output = Value;
+
+    fn index(&self, index: I) -> &Value {
+        self.get(index).expect("index not found")
+    }
+}
+
+impl<I> ops::IndexMut<I> for Value where I: Index {
+    fn index_mut(&mut self, index: I) -> &mut Value {
+        self.get_mut(index).expect("index not found")
+    }
+}
+
+impl From<String> for Value {
+    fn from(val: String) -> Value {
+        Value::String(val)
+    }
+}
+
+impl From<i64> for Value {
+    fn from(val: i64) -> Value {
+        Value::Integer(val)
+    }
+}
+
+impl From<f64> for Value {
+    fn from(val: f64) -> Value {
+        Value::Float(val)
+    }
+}
+
+impl From<bool> for Value {
+    fn from(val: bool) -> Value {
+        Value::Boolean(val)
+    }
+}
+
+impl From<Array> for Value {
+    fn from(val: Array) -> Value {
+        Value::Array(val)
+    }
+}
+
+impl From<Table> for Value {
+    fn from(val: Table) -> Value {
+        Value::Table(val)
+    }
+}
+
+impl From<Datetime> for Value {
+    fn from(val: Datetime) -> Value {
+        Value::Datetime(val)
+    }
+}
+
+/// Types that can be used to index a `toml::Value`
+///
+/// Currently this is implemented for `usize` to index arrays and `str` to index
+/// tables.
+///
+/// This trait is sealed and not intended for implementation outside of the
+/// `toml` crate.
+pub trait Index: Sealed {
+    #[doc(hidden)]
+    fn index<'a>(&self, val: &'a Value) -> Option<&'a Value>;
+    #[doc(hidden)]
+    fn index_mut<'a>(&self, val: &'a mut Value) -> Option<&'a mut Value>;
+}
+
+/// An implementation detail that should not be implemented, this will change in
+/// the future and break code otherwise.
+#[doc(hidden)]
+pub trait Sealed {}
+impl Sealed for usize {}
+impl Sealed for str {}
+impl Sealed for String {}
+impl<'a, T: Sealed + ?Sized> Sealed for &'a T {}
+
+impl Index for usize {
+    fn index<'a>(&self, val: &'a Value) -> Option<&'a Value> {
+        match *val {
+            Value::Array(ref a) => a.get(*self),
+            _ => None,
+        }
+    }
+
+    fn index_mut<'a>(&self, val: &'a mut Value) -> Option<&'a mut Value> {
+        match *val {
+            Value::Array(ref mut a) => a.get_mut(*self),
+            _ => None,
+        }
+    }
+}
+
+impl Index for str {
+    fn index<'a>(&self, val: &'a Value) -> Option<&'a Value> {
+        match *val {
+            Value::Table(ref a) => a.get(self),
+            _ => None,
+        }
+    }
+
+    fn index_mut<'a>(&self, val: &'a mut Value) -> Option<&'a mut Value> {
+        match *val {
+            Value::Table(ref mut a) => a.get_mut(self),
+            _ => None,
+        }
+    }
+}
+
+impl Index for String {
+    fn index<'a>(&self, val: &'a Value) -> Option<&'a Value> {
+        self[..].index(val)
+    }
+
+    fn index_mut<'a>(&self, val: &'a mut Value) -> Option<&'a mut Value> {
+        self[..].index_mut(val)
+    }
+}
+
+impl<'s, T: ?Sized> Index for &'s T where T: Index {
+    fn index<'a>(&self, val: &'a Value) -> Option<&'a Value> {
+        (**self).index(val)
+    }
+
+    fn index_mut<'a>(&self, val: &'a mut Value) -> Option<&'a mut Value> {
+        (**self).index_mut(val)
+    }
+}
+
+impl fmt::Display for Value {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        ::ser::to_string(self).unwrap().fmt(f)
+    }
+}
+
+impl FromStr for Value {
+    type Err = ::de::Error;
+    fn from_str(s: &str) -> Result<Value, Self::Err> {
+        ::from_str(s)
+    }
+}
+
+impl ser::Serialize for Value {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+        where S: ser::Serializer
+    {
+        use serde::ser::SerializeMap;
+
+        match *self {
+            Value::String(ref s) => serializer.serialize_str(s),
+            Value::Integer(i) => serializer.serialize_i64(i),
+            Value::Float(f) => serializer.serialize_f64(f),
+            Value::Boolean(b) => serializer.serialize_bool(b),
+            Value::Datetime(ref s) => s.serialize(serializer),
+            Value::Array(ref a) => a.serialize(serializer),
+            Value::Table(ref t) => {
+                let mut map = serializer.serialize_map(Some(t.len()))?;
+                // Be sure to visit non-tables first (and also non
+                // array-of-tables) as all keys must be emitted first.
+                for (k, v) in t {
+                    if !v.is_array() && !v.is_table() {
+                        map.serialize_key(k)?;
+                        map.serialize_value(v)?;
+                    }
+                }
+                for (k, v) in t {
+                    if v.is_array() {
+                        map.serialize_key(k)?;
+                        map.serialize_value(v)?;
+                    }
+                }
+                for (k, v) in t {
+                    if v.is_table() {
+                        map.serialize_key(k)?;
+                        map.serialize_value(v)?;
+                    }
+                }
+                map.end()
+            }
+        }
+    }
+}
+
+impl de::Deserialize for Value {
+    fn deserialize<D>(deserializer: D) -> Result<Value, D::Error>
+        where D: de::Deserializer
+    {
+        struct ValueVisitor;
+
+        impl de::Visitor for ValueVisitor {
+            type Value = Value;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("any valid TOML value")
+            }
+
+            fn visit_bool<E>(self, value: bool) -> Result<Value, E> {
+                Ok(Value::Boolean(value))
+            }
+
+            fn visit_i64<E>(self, value: i64) -> Result<Value, E> {
+                Ok(Value::Integer(value))
+            }
+
+            fn visit_f64<E>(self, value: f64) -> Result<Value, E> {
+                Ok(Value::Float(value))
+            }
+
+            fn visit_str<E>(self, value: &str) -> Result<Value, E> {
+                Ok(Value::String(value.into()))
+            }
+
+            fn visit_string<E>(self, value: String) -> Result<Value, E> {
+                Ok(Value::String(value))
+            }
+
+            fn visit_some<D>(self, deserializer: D) -> Result<Value, D::Error>
+                where D: de::Deserializer,
+            {
+                de::Deserialize::deserialize(deserializer)
+            }
+
+            fn visit_seq<V>(self, visitor: V) -> Result<Value, V::Error>
+                where V: de::SeqVisitor
+            {
+                let values = de::impls::VecVisitor::new().visit_seq(visitor)?;
+                Ok(Value::Array(values))
+            }
+
+            fn visit_map<V>(self, mut visitor: V) -> Result<Value, V::Error>
+                where V: de::MapVisitor
+            {
+                let mut key = String::new();
+                let datetime = visitor.visit_key_seed(DatetimeOrTable {
+                    key: &mut key,
+                })?;
+                match datetime {
+                    Some(true) => {
+                        let date: DatetimeFromString = visitor.visit_value()?;
+                        return Ok(Value::Datetime(date.value))
+                    }
+                    None => return Ok(Value::Table(BTreeMap::new())),
+                    Some(false) => {}
+                }
+                let mut map = BTreeMap::new();
+                map.insert(key, visitor.visit_value()?);
+                while let Some(key) = visitor.visit_key()? {
+                    if map.contains_key(&key) {
+                        let msg = format!("duplicate key: `{}`", key);
+                        return Err(de::Error::custom(msg))
+                    }
+                    map.insert(key, visitor.visit_value()?);
+                }
+                Ok(Value::Table(map))
+            }
+        }
+
+        deserializer.deserialize(ValueVisitor)
+    }
+}
+
+impl de::Deserializer for Value {
+    type Error = ::de::Error;
+
+    fn deserialize<V>(self, visitor: V) -> Result<V::Value, ::de::Error>
+        where V: de::Visitor,
+    {
+        match self {
+            Value::Boolean(v) => visitor.visit_bool(v),
+            Value::Integer(n) => visitor.visit_i64(n),
+            Value::Float(n) => visitor.visit_f64(n),
+            Value::String(v) => visitor.visit_string(v),
+            Value::Datetime(v) => visitor.visit_string(v.to_string()),
+            Value::Array(v) => {
+                let len = v.len();
+                let mut deserializer = SeqDeserializer::new(v);
+                let seq = visitor.visit_seq(&mut deserializer)?;
+                let remaining = deserializer.iter.len();
+                if remaining == 0 {
+                    Ok(seq)
+                } else {
+                    Err(de::Error::invalid_length(len, &"fewer elements in array"))
+                }
+            }
+            Value::Table(v) => {
+                let len = v.len();
+                let mut deserializer = MapDeserializer::new(v);
+                let map = visitor.visit_map(&mut deserializer)?;
+                let remaining = deserializer.iter.len();
+                if remaining == 0 {
+                    Ok(map)
+                } else {
+                    Err(de::Error::invalid_length(len, &"fewer elements in map"))
+                }
+            }
+        }
+    }
+
+    // `None` is interpreted as a missing field so be sure to implement `Some`
+    // as a present field.
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, ::de::Error>
+        where V: de::Visitor
+    {
+        visitor.visit_some(self)
+    }
+
+    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 enum newtype_struct
+    }
+}
+
+struct SeqDeserializer {
+    iter: vec::IntoIter<Value>,
+}
+
+impl SeqDeserializer {
+    fn new(vec: Vec<Value>) -> Self {
+        SeqDeserializer {
+            iter: vec.into_iter(),
+        }
+    }
+}
+
+impl de::SeqVisitor for SeqDeserializer {
+    type Error = ::de::Error;
+
+    fn visit_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, ::de::Error>
+        where T: de::DeserializeSeed,
+    {
+        match self.iter.next() {
+            Some(value) => seed.deserialize(value).map(Some),
+            None => Ok(None),
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+struct MapDeserializer {
+    iter: <BTreeMap<String, Value> as IntoIterator>::IntoIter,
+    value: Option<(String, Value)>,
+}
+
+impl MapDeserializer {
+    fn new(map: BTreeMap<String, Value>) -> Self {
+        MapDeserializer {
+            iter: map.into_iter(),
+            value: None,
+        }
+    }
+}
+
+impl de::MapVisitor for MapDeserializer {
+    type Error = ::de::Error;
+
+    fn visit_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, ::de::Error>
+        where T: de::DeserializeSeed,
+    {
+        match self.iter.next() {
+            Some((key, value)) => {
+                self.value = Some((key.clone(), value));
+                seed.deserialize(Value::String(key)).map(Some)
+            }
+            None => Ok(None),
+        }
+    }
+
+    fn visit_value_seed<T>(&mut self, seed: T) -> Result<T::Value, ::de::Error>
+        where T: de::DeserializeSeed,
+    {
+        let (key, res) = match self.value.take() {
+            Some((key, value)) => (key, seed.deserialize(value)),
+            None => return Err(de::Error::custom("value is missing")),
+        };
+        res.map_err(|mut error| {
+            error.add_key_context(&key);
+            error
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+struct Serializer;
+
+impl ser::Serializer for Serializer {
+    type Ok = Value;
+    type Error = ::ser::Error;
+
+    type SerializeSeq = SerializeVec;
+    type SerializeTuple = ser::Impossible<Value, ::ser::Error>;
+    type SerializeTupleStruct = ser::Impossible<Value, ::ser::Error>;
+    type SerializeTupleVariant = ser::Impossible<Value, ::ser::Error>;
+    type SerializeMap = SerializeMap;
+    type SerializeStruct = SerializeMap;
+    type SerializeStructVariant = ser::Impossible<Value, ::ser::Error>;
+
+    fn serialize_bool(self, value: bool) -> Result<Value, ::ser::Error> {
+        Ok(Value::Boolean(value))
+    }
+
+    fn serialize_i8(self, value: i8) -> Result<Value, ::ser::Error> {
+        self.serialize_i64(value.into())
+    }
+
+    fn serialize_i16(self, value: i16) -> Result<Value, ::ser::Error> {
+        self.serialize_i64(value.into())
+    }
+
+    fn serialize_i32(self, value: i32) -> Result<Value, ::ser::Error> {
+        self.serialize_i64(value.into())
+    }
+
+    fn serialize_i64(self, value: i64) -> Result<Value, ::ser::Error> {
+        Ok(Value::Integer(value.into()))
+    }
+
+    fn serialize_u8(self, value: u8) -> Result<Value, ::ser::Error> {
+        self.serialize_i64(value.into())
+    }
+
+    fn serialize_u16(self, value: u16) -> Result<Value, ::ser::Error> {
+        self.serialize_i64(value.into())
+    }
+
+    fn serialize_u32(self, value: u32) -> Result<Value, ::ser::Error> {
+        self.serialize_i64(value.into())
+    }
+
+    fn serialize_u64(self, value: u64) -> Result<Value, ::ser::Error> {
+        if value <= i64::max_value() as u64 {
+            self.serialize_i64(value as i64)
+        } else {
+            Err(ser::Error::custom("u64 value was too large"))
+        }
+    }
+
+    fn serialize_f32(self, value: f32) -> Result<Value, ::ser::Error> {
+        self.serialize_f64(value.into())
+    }
+
+    fn serialize_f64(self, value: f64) -> Result<Value, ::ser::Error> {
+        Ok(Value::Float(value))
+    }
+
+    fn serialize_char(self, value: char) -> Result<Value, ::ser::Error> {
+        let mut s = String::new();
+        s.push(value);
+        self.serialize_str(&s)
+    }
+
+    fn serialize_str(self, value: &str) -> Result<Value, ::ser::Error> {
+        Ok(Value::String(value.to_owned()))
+    }
+
+    fn serialize_bytes(self, value: &[u8]) -> Result<Value, ::ser::Error> {
+        let vec = value.iter().map(|&b| Value::Integer(b.into())).collect();
+        Ok(Value::Array(vec))
+    }
+
+    fn serialize_unit(self) -> Result<Value, ::ser::Error> {
+        Err(::ser::Error::UnsupportedType)
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str)
+                             -> Result<Value, ::ser::Error> {
+        Err(::ser::Error::UnsupportedType)
+    }
+
+    fn serialize_unit_variant(self,
+                              _name: &'static str,
+                              _variant_index: usize,
+                              _variant: &'static str)
+                              -> Result<Value, ::ser::Error> {
+        Err(::ser::Error::UnsupportedType)
+    }
+
+    fn serialize_newtype_struct<T: ?Sized>(self,
+                                           _name: &'static str,
+                                           value: &T)
+                                           -> Result<Value, ::ser::Error>
+        where T: ser::Serialize,
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_newtype_variant<T: ?Sized>(self,
+                                            _name: &'static str,
+                                            _variant_index: usize,
+                                            _variant: &'static str,
+                                            _value: &T)
+                                            -> Result<Value, ::ser::Error>
+        where T: ser::Serialize,
+    {
+        Err(::ser::Error::UnsupportedType)
+    }
+
+    fn serialize_none(self) -> Result<Value, ::ser::Error> {
+        Err(::ser::Error::UnsupportedNone)
+    }
+
+    fn serialize_some<T: ?Sized>(self, value: &T) -> Result<Value, ::ser::Error>
+        where T: ser::Serialize,
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_seq(self, len: Option<usize>)
+                     -> Result<Self::SerializeSeq, ::ser::Error>
+    {
+        Ok(SerializeVec {
+            vec: Vec::with_capacity(len.unwrap_or(0))
+        })
+    }
+
+    fn serialize_seq_fixed_size(self, size: usize)
+                                -> Result<Self::SerializeSeq, ::ser::Error> {
+        self.serialize_seq(Some(size))
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple, ::ser::Error> {
+        Err(::ser::Error::UnsupportedType)
+    }
+
+    fn serialize_tuple_struct(self, _name: &'static str, _len: usize)
+                              -> Result<Self::SerializeTupleStruct, ::ser::Error> {
+        Err(::ser::Error::UnsupportedType)
+    }
+
+    fn serialize_tuple_variant(self,
+                               _name: &'static str,
+                               _variant_index: usize,
+                               _variant: &'static str,
+                               _len: usize)
+                               -> Result<Self::SerializeTupleVariant, ::ser::Error>
+    {
+        Err(::ser::Error::UnsupportedType)
+    }
+
+    fn serialize_map(self, _len: Option<usize>)
+                     -> Result<Self::SerializeMap, ::ser::Error>
+    {
+        Ok(SerializeMap {
+            map: BTreeMap::new(),
+            next_key: None,
+        })
+    }
+
+    fn serialize_struct(self, _name: &'static str, len: usize)
+                        -> Result<Self::SerializeStruct, ::ser::Error> {
+        self.serialize_map(Some(len))
+    }
+
+    fn serialize_struct_variant(self,
+                                _name: &'static str,
+                                _variant_index: usize,
+                                _variant: &'static str,
+                                _len: usize)
+                                -> Result<Self::SerializeStructVariant, ::ser::Error>
+    {
+        Err(::ser::Error::UnsupportedType)
+    }
+}
+
+struct SerializeVec {
+    vec: Vec<Value>,
+}
+
+struct SerializeMap {
+    map: BTreeMap<String, Value>,
+    next_key: Option<String>,
+}
+
+impl ser::SerializeSeq for SerializeVec {
+    type Ok = Value;
+    type Error = ::ser::Error;
+
+    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), ::ser::Error>
+        where T: ser::Serialize
+    {
+        self.vec.push(Value::try_from(value)?);
+        Ok(())
+    }
+
+    fn end(self) -> Result<Value, ::ser::Error> {
+        Ok(Value::Array(self.vec))
+    }
+}
+
+impl ser::SerializeMap for SerializeMap {
+    type Ok = Value;
+    type Error = ::ser::Error;
+
+    fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), ::ser::Error>
+        where T: ser::Serialize
+    {
+        match Value::try_from(key)? {
+            Value::String(s) => self.next_key = Some(s),
+            _ => return Err(::ser::Error::KeyNotString),
+        };
+        Ok(())
+    }
+
+    fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), ::ser::Error>
+        where T: ser::Serialize
+    {
+        let key = self.next_key.take();
+        let key = key.expect("serialize_value called before serialize_key");
+        match Value::try_from(value) {
+            Ok(value) => { self.map.insert(key, value); }
+            Err(::ser::Error::UnsupportedNone) => {}
+            Err(e) => return Err(e),
+        }
+        Ok(())
+    }
+
+    fn end(self) -> Result<Value, ::ser::Error> {
+        Ok(Value::Table(self.map))
+    }
+}
+
+impl ser::SerializeStruct for SerializeMap {
+    type Ok = Value;
+    type Error = ::ser::Error;
+
+    fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), ::ser::Error>
+        where T: ser::Serialize
+    {
+        try!(ser::SerializeMap::serialize_key(self, key));
+        ser::SerializeMap::serialize_value(self, value)
+    }
+
+    fn end(self) -> Result<Value, ::ser::Error> {
+        ser::SerializeMap::end(self)
+    }
+}
+
+struct DatetimeOrTable<'a> {
+    key: &'a mut String,
+}
+
+impl<'a> de::DeserializeSeed for DatetimeOrTable<'a> {
+    type Value = bool;
+
+    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+        where D: de::Deserializer
+    {
+        deserializer.deserialize(self)
+    }
+}
+
+impl<'a> de::Visitor for DatetimeOrTable<'a> {
+    type Value = bool;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("a string key")
+    }
+
+    fn visit_str<E>(self, s: &str) -> Result<bool, E>
+        where E: de::Error,
+    {
+        if s == SERDE_STRUCT_FIELD_NAME {
+            Ok(true)
+        } else {
+            self.key.push_str(s);
+            Ok(false)
+        }
+    }
+
+    fn visit_string<E>(self, s: String) -> Result<bool, E>
+        where E: de::Error,
+    {
+        if s == SERDE_STRUCT_FIELD_NAME {
+            Ok(true)
+        } else {
+            *self.key = s;
+            Ok(false)
+        }
+    }
+}