Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

7 files changed, 7042 insertions, 0 deletions

diff --git a/vendor/serde/src/de/format.rs b/vendor/serde/src/de/format.rs
new file mode 100644
index 000000000..58ec0968d
--- /dev/null
+++ b/vendor/serde/src/de/format.rs
@@ -0,0 +1,30 @@
+use lib::fmt::{self, Write};
+use lib::str;
+
+pub struct Buf<'a> {
+    bytes: &'a mut [u8],
+    offset: usize,
+}
+
+impl<'a> Buf<'a> {
+    pub fn new(bytes: &'a mut [u8]) -> Self {
+        Buf { bytes, offset: 0 }
+    }
+
+    pub fn as_str(&self) -> &str {
+        let slice = &self.bytes[..self.offset];
+        unsafe { str::from_utf8_unchecked(slice) }
+    }
+}
+
+impl<'a> Write for Buf<'a> {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        if self.offset + s.len() > self.bytes.len() {
+            Err(fmt::Error)
+        } else {
+            self.bytes[self.offset..self.offset + s.len()].copy_from_slice(s.as_bytes());
+            self.offset += s.len();
+            Ok(())
+        }
+    }
+}
diff --git a/vendor/serde/src/de/ignored_any.rs b/vendor/serde/src/de/ignored_any.rs
new file mode 100644
index 000000000..1d50f5ec3
--- /dev/null
+++ b/vendor/serde/src/de/ignored_any.rs
@@ -0,0 +1,243 @@
+use lib::*;
+
+use de::{
+    Deserialize, Deserializer, EnumAccess, Error, MapAccess, SeqAccess, VariantAccess, Visitor,
+};
+
+/// An efficient way of discarding data from a deserializer.
+///
+/// Think of this like `serde_json::Value` in that it can be deserialized from
+/// any type, except that it does not store any information about the data that
+/// gets deserialized.
+///
+/// ```edition2018
+/// use std::fmt;
+/// use std::marker::PhantomData;
+///
+/// use serde::de::{
+///     self, Deserialize, DeserializeSeed, Deserializer, IgnoredAny, SeqAccess, Visitor,
+/// };
+///
+/// /// A seed that can be used to deserialize only the `n`th element of a sequence
+/// /// while efficiently discarding elements of any type before or after index `n`.
+/// ///
+/// /// For example to deserialize only the element at index 3:
+/// ///
+/// /// ```
+/// /// NthElement::new(3).deserialize(deserializer)
+/// /// ```
+/// pub struct NthElement<T> {
+///     n: usize,
+///     marker: PhantomData<T>,
+/// }
+///
+/// impl<T> NthElement<T> {
+///     pub fn new(n: usize) -> Self {
+///         NthElement {
+///             n: n,
+///             marker: PhantomData,
+///         }
+///     }
+/// }
+///
+/// impl<'de, T> Visitor<'de> for NthElement<T>
+/// where
+///     T: Deserialize<'de>,
+/// {
+///     type Value = T;
+///
+///     fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+///         write!(
+///             formatter,
+///             "a sequence in which we care about element {}",
+///             self.n
+///         )
+///     }
+///
+///     fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+///     where
+///         A: SeqAccess<'de>,
+///     {
+///         // Skip over the first `n` elements.
+///         for i in 0..self.n {
+///             // It is an error if the sequence ends before we get to element `n`.
+///             if seq.next_element::<IgnoredAny>()?.is_none() {
+///                 return Err(de::Error::invalid_length(i, &self));
+///             }
+///         }
+///
+///         // Deserialize the one we care about.
+///         let nth = match seq.next_element()? {
+///             Some(nth) => nth,
+///             None => {
+///                 return Err(de::Error::invalid_length(self.n, &self));
+///             }
+///         };
+///
+///         // Skip over any remaining elements in the sequence after `n`.
+///         while let Some(IgnoredAny) = seq.next_element()? {
+///             // ignore
+///         }
+///
+///         Ok(nth)
+///     }
+/// }
+///
+/// impl<'de, T> DeserializeSeed<'de> for NthElement<T>
+/// where
+///     T: Deserialize<'de>,
+/// {
+///     type Value = T;
+///
+///     fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+///     where
+///         D: Deserializer<'de>,
+///     {
+///         deserializer.deserialize_seq(self)
+///     }
+/// }
+///
+/// # fn example<'de, D>(deserializer: D) -> Result<(), D::Error>
+/// # where
+/// #     D: Deserializer<'de>,
+/// # {
+/// // Deserialize only the sequence element at index 3 from this deserializer.
+/// // The element at index 3 is required to be a string. Elements before and
+/// // after index 3 are allowed to be of any type.
+/// let s: String = NthElement::new(3).deserialize(deserializer)?;
+/// #     Ok(())
+/// # }
+/// ```
+#[derive(Copy, Clone, Debug, Default)]
+pub struct IgnoredAny;
+
+impl<'de> Visitor<'de> for IgnoredAny {
+    type Value = IgnoredAny;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("anything at all")
+    }
+
+    #[inline]
+    fn visit_bool<E>(self, x: bool) -> Result<Self::Value, E> {
+        let _ = x;
+        Ok(IgnoredAny)
+    }
+
+    #[inline]
+    fn visit_i64<E>(self, x: i64) -> Result<Self::Value, E> {
+        let _ = x;
+        Ok(IgnoredAny)
+    }
+
+    serde_if_integer128! {
+        #[inline]
+        fn visit_i128<E>(self, x: i128) -> Result<Self::Value, E> {
+            let _ = x;
+            Ok(IgnoredAny)
+        }
+    }
+
+    #[inline]
+    fn visit_u64<E>(self, x: u64) -> Result<Self::Value, E> {
+        let _ = x;
+        Ok(IgnoredAny)
+    }
+
+    serde_if_integer128! {
+        #[inline]
+        fn visit_u128<E>(self, x: u128) -> Result<Self::Value, E> {
+            let _ = x;
+            Ok(IgnoredAny)
+        }
+    }
+
+    #[inline]
+    fn visit_f64<E>(self, x: f64) -> Result<Self::Value, E> {
+        let _ = x;
+        Ok(IgnoredAny)
+    }
+
+    #[inline]
+    fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        let _ = s;
+        Ok(IgnoredAny)
+    }
+
+    #[inline]
+    fn visit_none<E>(self) -> Result<Self::Value, E> {
+        Ok(IgnoredAny)
+    }
+
+    #[inline]
+    fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        IgnoredAny::deserialize(deserializer)
+    }
+
+    #[inline]
+    fn visit_newtype_struct<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        IgnoredAny::deserialize(deserializer)
+    }
+
+    #[inline]
+    fn visit_unit<E>(self) -> Result<Self::Value, E> {
+        Ok(IgnoredAny)
+    }
+
+    #[inline]
+    fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+    where
+        A: SeqAccess<'de>,
+    {
+        while let Some(IgnoredAny) = try!(seq.next_element()) {
+            // Gobble
+        }
+        Ok(IgnoredAny)
+    }
+
+    #[inline]
+    fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
+    where
+        A: MapAccess<'de>,
+    {
+        while let Some((IgnoredAny, IgnoredAny)) = try!(map.next_entry()) {
+            // Gobble
+        }
+        Ok(IgnoredAny)
+    }
+
+    #[inline]
+    fn visit_bytes<E>(self, bytes: &[u8]) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        let _ = bytes;
+        Ok(IgnoredAny)
+    }
+
+    fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error>
+    where
+        A: EnumAccess<'de>,
+    {
+        data.variant::<IgnoredAny>()?.1.newtype_variant()
+    }
+}
+
+impl<'de> Deserialize<'de> for IgnoredAny {
+    #[inline]
+    fn deserialize<D>(deserializer: D) -> Result<IgnoredAny, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_ignored_any(IgnoredAny)
+    }
+}
diff --git a/vendor/serde/src/de/impls.rs b/vendor/serde/src/de/impls.rs
new file mode 100644
index 000000000..c2a56b4fc
--- /dev/null
+++ b/vendor/serde/src/de/impls.rs
@@ -0,0 +1,2725 @@
+use lib::*;
+
+use de::{
+    Deserialize, Deserializer, EnumAccess, Error, SeqAccess, Unexpected, VariantAccess, Visitor,
+};
+
+#[cfg(any(feature = "std", feature = "alloc", not(no_core_duration)))]
+use de::MapAccess;
+
+use seed::InPlaceSeed;
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+use __private::size_hint;
+
+////////////////////////////////////////////////////////////////////////////////
+
+struct UnitVisitor;
+
+impl<'de> Visitor<'de> for UnitVisitor {
+    type Value = ();
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("unit")
+    }
+
+    fn visit_unit<E>(self) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(())
+    }
+}
+
+impl<'de> Deserialize<'de> for () {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_unit(UnitVisitor)
+    }
+}
+
+#[cfg(feature = "unstable")]
+impl<'de> Deserialize<'de> for ! {
+    fn deserialize<D>(_deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        Err(Error::custom("cannot deserialize `!`"))
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+struct BoolVisitor;
+
+impl<'de> Visitor<'de> for BoolVisitor {
+    type Value = bool;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("a boolean")
+    }
+
+    fn visit_bool<E>(self, v: bool) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(v)
+    }
+}
+
+impl<'de> Deserialize<'de> for bool {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_bool(BoolVisitor)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+macro_rules! impl_deserialize_num {
+    ($primitive:ident, $nonzero:ident $(cfg($($cfg:tt)*))*, $deserialize:ident $($method:ident!($($val:ident : $visit:ident)*);)*) => {
+        impl_deserialize_num!($primitive, $deserialize $($method!($($val : $visit)*);)*);
+
+        #[cfg(all(not(no_num_nonzero), $($($cfg)*)*))]
+        impl<'de> Deserialize<'de> for num::$nonzero {
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                struct NonZeroVisitor;
+
+                impl<'de> Visitor<'de> for NonZeroVisitor {
+                    type Value = num::$nonzero;
+
+                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                        formatter.write_str(concat!("a nonzero ", stringify!($primitive)))
+                    }
+
+                    $($($method!(nonzero $primitive $val : $visit);)*)*
+                }
+
+                deserializer.$deserialize(NonZeroVisitor)
+            }
+        }
+    };
+
+    ($primitive:ident, $deserialize:ident $($method:ident!($($val:ident : $visit:ident)*);)*) => {
+        impl<'de> Deserialize<'de> for $primitive {
+            #[inline]
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                struct PrimitiveVisitor;
+
+                impl<'de> Visitor<'de> for PrimitiveVisitor {
+                    type Value = $primitive;
+
+                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                        formatter.write_str(stringify!($primitive))
+                    }
+
+                    $($($method!($val : $visit);)*)*
+                }
+
+                deserializer.$deserialize(PrimitiveVisitor)
+            }
+        }
+    };
+}
+
+macro_rules! num_self {
+    ($ty:ident : $visit:ident) => {
+        #[inline]
+        fn $visit<E>(self, v: $ty) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            Ok(v)
+        }
+    };
+
+    (nonzero $primitive:ident $ty:ident : $visit:ident) => {
+        fn $visit<E>(self, v: $ty) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            if let Some(nonzero) = Self::Value::new(v) {
+                Ok(nonzero)
+            } else {
+                Err(Error::invalid_value(Unexpected::Unsigned(0), &self))
+            }
+        }
+    };
+}
+
+macro_rules! num_as_self {
+    ($ty:ident : $visit:ident) => {
+        #[inline]
+        fn $visit<E>(self, v: $ty) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            Ok(v as Self::Value)
+        }
+    };
+
+    (nonzero $primitive:ident $ty:ident : $visit:ident) => {
+        fn $visit<E>(self, v: $ty) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            if let Some(nonzero) = Self::Value::new(v as $primitive) {
+                Ok(nonzero)
+            } else {
+                Err(Error::invalid_value(Unexpected::Unsigned(0), &self))
+            }
+        }
+    };
+}
+
+macro_rules! int_to_int {
+    ($ty:ident : $visit:ident) => {
+        #[inline]
+        fn $visit<E>(self, v: $ty) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            if Self::Value::min_value() as i64 <= v as i64
+                && v as i64 <= Self::Value::max_value() as i64
+            {
+                Ok(v as Self::Value)
+            } else {
+                Err(Error::invalid_value(Unexpected::Signed(v as i64), &self))
+            }
+        }
+    };
+
+    (nonzero $primitive:ident $ty:ident : $visit:ident) => {
+        fn $visit<E>(self, v: $ty) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            if $primitive::min_value() as i64 <= v as i64
+                && v as i64 <= $primitive::max_value() as i64
+            {
+                if let Some(nonzero) = Self::Value::new(v as $primitive) {
+                    return Ok(nonzero);
+                }
+            }
+            Err(Error::invalid_value(Unexpected::Signed(v as i64), &self))
+        }
+    };
+}
+
+macro_rules! int_to_uint {
+    ($ty:ident : $visit:ident) => {
+        #[inline]
+        fn $visit<E>(self, v: $ty) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            if 0 <= v && v as u64 <= Self::Value::max_value() as u64 {
+                Ok(v as Self::Value)
+            } else {
+                Err(Error::invalid_value(Unexpected::Signed(v as i64), &self))
+            }
+        }
+    };
+
+    (nonzero $primitive:ident $ty:ident : $visit:ident) => {
+        fn $visit<E>(self, v: $ty) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            if 0 < v && v as u64 <= $primitive::max_value() as u64 {
+                if let Some(nonzero) = Self::Value::new(v as $primitive) {
+                    return Ok(nonzero);
+                }
+            }
+            Err(Error::invalid_value(Unexpected::Signed(v as i64), &self))
+        }
+    };
+}
+
+macro_rules! uint_to_self {
+    ($ty:ident : $visit:ident) => {
+        #[inline]
+        fn $visit<E>(self, v: $ty) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            if v as u64 <= Self::Value::max_value() as u64 {
+                Ok(v as Self::Value)
+            } else {
+                Err(Error::invalid_value(Unexpected::Unsigned(v as u64), &self))
+            }
+        }
+    };
+
+    (nonzero $primitive:ident $ty:ident : $visit:ident) => {
+        fn $visit<E>(self, v: $ty) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            if v as u64 <= $primitive::max_value() as u64 {
+                if let Some(nonzero) = Self::Value::new(v as $primitive) {
+                    return Ok(nonzero);
+                }
+            }
+            Err(Error::invalid_value(Unexpected::Unsigned(v as u64), &self))
+        }
+    };
+}
+
+impl_deserialize_num! {
+    i8, NonZeroI8 cfg(not(no_num_nonzero_signed)), deserialize_i8
+    num_self!(i8:visit_i8);
+    int_to_int!(i16:visit_i16 i32:visit_i32 i64:visit_i64);
+    uint_to_self!(u8:visit_u8 u16:visit_u16 u32:visit_u32 u64:visit_u64);
+}
+
+impl_deserialize_num! {
+    i16, NonZeroI16 cfg(not(no_num_nonzero_signed)), deserialize_i16
+    num_self!(i16:visit_i16);
+    num_as_self!(i8:visit_i8);
+    int_to_int!(i32:visit_i32 i64:visit_i64);
+    uint_to_self!(u8:visit_u8 u16:visit_u16 u32:visit_u32 u64:visit_u64);
+}
+
+impl_deserialize_num! {
+    i32, NonZeroI32 cfg(not(no_num_nonzero_signed)), deserialize_i32
+    num_self!(i32:visit_i32);
+    num_as_self!(i8:visit_i8 i16:visit_i16);
+    int_to_int!(i64:visit_i64);
+    uint_to_self!(u8:visit_u8 u16:visit_u16 u32:visit_u32 u64:visit_u64);
+}
+
+impl_deserialize_num! {
+    i64, NonZeroI64 cfg(not(no_num_nonzero_signed)), deserialize_i64
+    num_self!(i64:visit_i64);
+    num_as_self!(i8:visit_i8 i16:visit_i16 i32:visit_i32);
+    uint_to_self!(u8:visit_u8 u16:visit_u16 u32:visit_u32 u64:visit_u64);
+}
+
+impl_deserialize_num! {
+    isize, NonZeroIsize cfg(not(no_num_nonzero_signed)), deserialize_i64
+    num_as_self!(i8:visit_i8 i16:visit_i16);
+    int_to_int!(i32:visit_i32 i64:visit_i64);
+    uint_to_self!(u8:visit_u8 u16:visit_u16 u32:visit_u32 u64:visit_u64);
+}
+
+impl_deserialize_num! {
+    u8, NonZeroU8, deserialize_u8
+    num_self!(u8:visit_u8);
+    int_to_uint!(i8:visit_i8 i16:visit_i16 i32:visit_i32 i64:visit_i64);
+    uint_to_self!(u16:visit_u16 u32:visit_u32 u64:visit_u64);
+}
+
+impl_deserialize_num! {
+    u16, NonZeroU16, deserialize_u16
+    num_self!(u16:visit_u16);
+    num_as_self!(u8:visit_u8);
+    int_to_uint!(i8:visit_i8 i16:visit_i16 i32:visit_i32 i64:visit_i64);
+    uint_to_self!(u32:visit_u32 u64:visit_u64);
+}
+
+impl_deserialize_num! {
+    u32, NonZeroU32, deserialize_u32
+    num_self!(u32:visit_u32);
+    num_as_self!(u8:visit_u8 u16:visit_u16);
+    int_to_uint!(i8:visit_i8 i16:visit_i16 i32:visit_i32 i64:visit_i64);
+    uint_to_self!(u64:visit_u64);
+}
+
+impl_deserialize_num! {
+    u64, NonZeroU64, deserialize_u64
+    num_self!(u64:visit_u64);
+    num_as_self!(u8:visit_u8 u16:visit_u16 u32:visit_u32);
+    int_to_uint!(i8:visit_i8 i16:visit_i16 i32:visit_i32 i64:visit_i64);
+}
+
+impl_deserialize_num! {
+    usize, NonZeroUsize, deserialize_u64
+    num_as_self!(u8:visit_u8 u16:visit_u16);
+    int_to_uint!(i8:visit_i8 i16:visit_i16 i32:visit_i32 i64:visit_i64);
+    uint_to_self!(u32:visit_u32 u64:visit_u64);
+}
+
+impl_deserialize_num! {
+    f32, deserialize_f32
+    num_self!(f32:visit_f32);
+    num_as_self!(f64:visit_f64);
+    num_as_self!(i8:visit_i8 i16:visit_i16 i32:visit_i32 i64:visit_i64);
+    num_as_self!(u8:visit_u8 u16:visit_u16 u32:visit_u32 u64:visit_u64);
+}
+
+impl_deserialize_num! {
+    f64, deserialize_f64
+    num_self!(f64:visit_f64);
+    num_as_self!(f32:visit_f32);
+    num_as_self!(i8:visit_i8 i16:visit_i16 i32:visit_i32 i64:visit_i64);
+    num_as_self!(u8:visit_u8 u16:visit_u16 u32:visit_u32 u64:visit_u64);
+}
+
+serde_if_integer128! {
+    macro_rules! num_128 {
+        ($ty:ident : $visit:ident) => {
+            fn $visit<E>(self, v: $ty) -> Result<Self::Value, E>
+            where
+                E: Error,
+            {
+                if v as i128 >= Self::Value::min_value() as i128
+                    && v as u128 <= Self::Value::max_value() as u128
+                {
+                    Ok(v as Self::Value)
+                } else {
+                    Err(Error::invalid_value(
+                        Unexpected::Other(stringify!($ty)),
+                        &self,
+                    ))
+                }
+            }
+        };
+
+        (nonzero $primitive:ident $ty:ident : $visit:ident) => {
+            fn $visit<E>(self, v: $ty) -> Result<Self::Value, E>
+            where
+                E: Error,
+            {
+                if v as i128 >= $primitive::min_value() as i128
+                    && v as u128 <= $primitive::max_value() as u128
+                {
+                    if let Some(nonzero) = Self::Value::new(v as $primitive) {
+                        Ok(nonzero)
+                    } else {
+                        Err(Error::invalid_value(Unexpected::Unsigned(0), &self))
+                    }
+                } else {
+                    Err(Error::invalid_value(
+                        Unexpected::Other(stringify!($ty)),
+                        &self,
+                    ))
+                }
+            }
+        };
+    }
+
+    impl_deserialize_num! {
+        i128, NonZeroI128 cfg(not(no_num_nonzero_signed)), deserialize_i128
+        num_self!(i128:visit_i128);
+        num_as_self!(i8:visit_i8 i16:visit_i16 i32:visit_i32 i64:visit_i64);
+        num_as_self!(u8:visit_u8 u16:visit_u16 u32:visit_u32 u64:visit_u64);
+        num_128!(u128:visit_u128);
+    }
+
+    impl_deserialize_num! {
+        u128, NonZeroU128, deserialize_u128
+        num_self!(u128:visit_u128);
+        num_as_self!(u8:visit_u8 u16:visit_u16 u32:visit_u32 u64:visit_u64);
+        int_to_uint!(i8:visit_i8 i16:visit_i16 i32:visit_i32 i64:visit_i64);
+        num_128!(i128:visit_i128);
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+struct CharVisitor;
+
+impl<'de> Visitor<'de> for CharVisitor {
+    type Value = char;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("a character")
+    }
+
+    #[inline]
+    fn visit_char<E>(self, v: char) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(v)
+    }
+
+    #[inline]
+    fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        let mut iter = v.chars();
+        match (iter.next(), iter.next()) {
+            (Some(c), None) => Ok(c),
+            _ => Err(Error::invalid_value(Unexpected::Str(v), &self)),
+        }
+    }
+}
+
+impl<'de> Deserialize<'de> for char {
+    #[inline]
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_char(CharVisitor)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+struct StringVisitor;
+#[cfg(any(feature = "std", feature = "alloc"))]
+struct StringInPlaceVisitor<'a>(&'a mut String);
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'de> Visitor<'de> for StringVisitor {
+    type Value = String;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("a string")
+    }
+
+    fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(v.to_owned())
+    }
+
+    fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(v)
+    }
+
+    fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        match str::from_utf8(v) {
+            Ok(s) => Ok(s.to_owned()),
+            Err(_) => Err(Error::invalid_value(Unexpected::Bytes(v), &self)),
+        }
+    }
+
+    fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        match String::from_utf8(v) {
+            Ok(s) => Ok(s),
+            Err(e) => Err(Error::invalid_value(
+                Unexpected::Bytes(&e.into_bytes()),
+                &self,
+            )),
+        }
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'a, 'de> Visitor<'de> for StringInPlaceVisitor<'a> {
+    type Value = ();
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("a string")
+    }
+
+    fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        self.0.clear();
+        self.0.push_str(v);
+        Ok(())
+    }
+
+    fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        *self.0 = v;
+        Ok(())
+    }
+
+    fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        match str::from_utf8(v) {
+            Ok(s) => {
+                self.0.clear();
+                self.0.push_str(s);
+                Ok(())
+            }
+            Err(_) => Err(Error::invalid_value(Unexpected::Bytes(v), &self)),
+        }
+    }
+
+    fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        match String::from_utf8(v) {
+            Ok(s) => {
+                *self.0 = s;
+                Ok(())
+            }
+            Err(e) => Err(Error::invalid_value(
+                Unexpected::Bytes(&e.into_bytes()),
+                &self,
+            )),
+        }
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'de> Deserialize<'de> for String {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_string(StringVisitor)
+    }
+
+    fn deserialize_in_place<D>(deserializer: D, place: &mut Self) -> Result<(), D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_string(StringInPlaceVisitor(place))
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+struct StrVisitor;
+
+impl<'a> Visitor<'a> for StrVisitor {
+    type Value = &'a str;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("a borrowed string")
+    }
+
+    fn visit_borrowed_str<E>(self, v: &'a str) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(v) // so easy
+    }
+
+    fn visit_borrowed_bytes<E>(self, v: &'a [u8]) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        str::from_utf8(v).map_err(|_| Error::invalid_value(Unexpected::Bytes(v), &self))
+    }
+}
+
+impl<'de: 'a, 'a> Deserialize<'de> for &'a str {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_str(StrVisitor)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+struct BytesVisitor;
+
+impl<'a> Visitor<'a> for BytesVisitor {
+    type Value = &'a [u8];
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("a borrowed byte array")
+    }
+
+    fn visit_borrowed_bytes<E>(self, v: &'a [u8]) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(v)
+    }
+
+    fn visit_borrowed_str<E>(self, v: &'a str) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(v.as_bytes())
+    }
+}
+
+impl<'de: 'a, 'a> Deserialize<'de> for &'a [u8] {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_bytes(BytesVisitor)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(feature = "std")]
+struct CStringVisitor;
+
+#[cfg(feature = "std")]
+impl<'de> Visitor<'de> for CStringVisitor {
+    type Value = CString;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("byte array")
+    }
+
+    fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+    where
+        A: SeqAccess<'de>,
+    {
+        let len = size_hint::cautious(seq.size_hint());
+        let mut values = Vec::with_capacity(len);
+
+        while let Some(value) = try!(seq.next_element()) {
+            values.push(value);
+        }
+
+        CString::new(values).map_err(Error::custom)
+    }
+
+    fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        CString::new(v).map_err(Error::custom)
+    }
+
+    fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        CString::new(v).map_err(Error::custom)
+    }
+
+    fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        CString::new(v).map_err(Error::custom)
+    }
+
+    fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        CString::new(v).map_err(Error::custom)
+    }
+}
+
+#[cfg(feature = "std")]
+impl<'de> Deserialize<'de> for CString {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_byte_buf(CStringVisitor)
+    }
+}
+
+macro_rules! forwarded_impl {
+    (
+        $(#[doc = $doc:tt])*
+        ( $($id: ident),* ), $ty: ty, $func: expr
+    ) => {
+        $(#[doc = $doc])*
+        impl<'de $(, $id : Deserialize<'de>,)*> Deserialize<'de> for $ty {
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                Deserialize::deserialize(deserializer).map($func)
+            }
+        }
+    }
+}
+
+#[cfg(all(feature = "std", not(no_de_boxed_c_str)))]
+forwarded_impl!((), Box<CStr>, CString::into_boxed_c_str);
+
+#[cfg(not(no_core_reverse))]
+forwarded_impl!((T), Reverse<T>, Reverse);
+
+////////////////////////////////////////////////////////////////////////////////
+
+struct OptionVisitor<T> {
+    marker: PhantomData<T>,
+}
+
+impl<'de, T> Visitor<'de> for OptionVisitor<T>
+where
+    T: Deserialize<'de>,
+{
+    type Value = Option<T>;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("option")
+    }
+
+    #[inline]
+    fn visit_unit<E>(self) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(None)
+    }
+
+    #[inline]
+    fn visit_none<E>(self) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(None)
+    }
+
+    #[inline]
+    fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        T::deserialize(deserializer).map(Some)
+    }
+
+    fn __private_visit_untagged_option<D>(self, deserializer: D) -> Result<Self::Value, ()>
+    where
+        D: Deserializer<'de>,
+    {
+        Ok(T::deserialize(deserializer).ok())
+    }
+}
+
+impl<'de, T> Deserialize<'de> for Option<T>
+where
+    T: Deserialize<'de>,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_option(OptionVisitor {
+            marker: PhantomData,
+        })
+    }
+
+    // The Some variant's repr is opaque, so we can't play cute tricks with its
+    // tag to have deserialize_in_place build the content in place unconditionally.
+    //
+    // FIXME: investigate whether branching on the old value being Some to
+    // deserialize_in_place the value is profitable (probably data-dependent?)
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+struct PhantomDataVisitor<T: ?Sized> {
+    marker: PhantomData<T>,
+}
+
+impl<'de, T: ?Sized> Visitor<'de> for PhantomDataVisitor<T> {
+    type Value = PhantomData<T>;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("unit")
+    }
+
+    #[inline]
+    fn visit_unit<E>(self) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(PhantomData)
+    }
+}
+
+impl<'de, T: ?Sized> Deserialize<'de> for PhantomData<T> {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let visitor = PhantomDataVisitor {
+            marker: PhantomData,
+        };
+        deserializer.deserialize_unit_struct("PhantomData", visitor)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+macro_rules! seq_impl {
+    (
+        $ty:ident < T $(: $tbound1:ident $(+ $tbound2:ident)*)* $(, $typaram:ident : $bound1:ident $(+ $bound2:ident)*)* >,
+        $access:ident,
+        $clear:expr,
+        $with_capacity:expr,
+        $reserve:expr,
+        $insert:expr
+    ) => {
+        impl<'de, T $(, $typaram)*> Deserialize<'de> for $ty<T $(, $typaram)*>
+        where
+            T: Deserialize<'de> $(+ $tbound1 $(+ $tbound2)*)*,
+            $($typaram: $bound1 $(+ $bound2)*,)*
+        {
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                struct SeqVisitor<T $(, $typaram)*> {
+                    marker: PhantomData<$ty<T $(, $typaram)*>>,
+                }
+
+                impl<'de, T $(, $typaram)*> Visitor<'de> for SeqVisitor<T $(, $typaram)*>
+                where
+                    T: Deserialize<'de> $(+ $tbound1 $(+ $tbound2)*)*,
+                    $($typaram: $bound1 $(+ $bound2)*,)*
+                {
+                    type Value = $ty<T $(, $typaram)*>;
+
+                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                        formatter.write_str("a sequence")
+                    }
+
+                    #[inline]
+                    fn visit_seq<A>(self, mut $access: A) -> Result<Self::Value, A::Error>
+                    where
+                        A: SeqAccess<'de>,
+                    {
+                        let mut values = $with_capacity;
+
+                        while let Some(value) = try!($access.next_element()) {
+                            $insert(&mut values, value);
+                        }
+
+                        Ok(values)
+                    }
+                }
+
+                let visitor = SeqVisitor { marker: PhantomData };
+                deserializer.deserialize_seq(visitor)
+            }
+
+            fn deserialize_in_place<D>(deserializer: D, place: &mut Self) -> Result<(), D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                struct SeqInPlaceVisitor<'a, T: 'a $(, $typaram: 'a)*>(&'a mut $ty<T $(, $typaram)*>);
+
+                impl<'a, 'de, T $(, $typaram)*> Visitor<'de> for SeqInPlaceVisitor<'a, T $(, $typaram)*>
+                where
+                    T: Deserialize<'de> $(+ $tbound1 $(+ $tbound2)*)*,
+                    $($typaram: $bound1 $(+ $bound2)*,)*
+                {
+                    type Value = ();
+
+                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                        formatter.write_str("a sequence")
+                    }
+
+                    #[inline]
+                    fn visit_seq<A>(mut self, mut $access: A) -> Result<Self::Value, A::Error>
+                    where
+                        A: SeqAccess<'de>,
+                    {
+                        $clear(&mut self.0);
+                        $reserve(&mut self.0, size_hint::cautious($access.size_hint()));
+
+                        // FIXME: try to overwrite old values here? (Vec, VecDeque, LinkedList)
+                        while let Some(value) = try!($access.next_element()) {
+                            $insert(&mut self.0, value);
+                        }
+
+                        Ok(())
+                    }
+                }
+
+                deserializer.deserialize_seq(SeqInPlaceVisitor(place))
+            }
+        }
+    }
+}
+
+// Dummy impl of reserve
+#[cfg(any(feature = "std", feature = "alloc"))]
+fn nop_reserve<T>(_seq: T, _n: usize) {}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+seq_impl!(
+    BinaryHeap<T: Ord>,
+    seq,
+    BinaryHeap::clear,
+    BinaryHeap::with_capacity(size_hint::cautious(seq.size_hint())),
+    BinaryHeap::reserve,
+    BinaryHeap::push
+);
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+seq_impl!(
+    BTreeSet<T: Eq + Ord>,
+    seq,
+    BTreeSet::clear,
+    BTreeSet::new(),
+    nop_reserve,
+    BTreeSet::insert
+);
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+seq_impl!(
+    LinkedList<T>,
+    seq,
+    LinkedList::clear,
+    LinkedList::new(),
+    nop_reserve,
+    LinkedList::push_back
+);
+
+#[cfg(feature = "std")]
+seq_impl!(
+    HashSet<T: Eq + Hash, S: BuildHasher + Default>,
+    seq,
+    HashSet::clear,
+    HashSet::with_capacity_and_hasher(size_hint::cautious(seq.size_hint()), S::default()),
+    HashSet::reserve,
+    HashSet::insert);
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+seq_impl!(
+    VecDeque<T>,
+    seq,
+    VecDeque::clear,
+    VecDeque::with_capacity(size_hint::cautious(seq.size_hint())),
+    VecDeque::reserve,
+    VecDeque::push_back
+);
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'de, T> Deserialize<'de> for Vec<T>
+where
+    T: Deserialize<'de>,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct VecVisitor<T> {
+            marker: PhantomData<T>,
+        }
+
+        impl<'de, T> Visitor<'de> for VecVisitor<T>
+        where
+            T: Deserialize<'de>,
+        {
+            type Value = Vec<T>;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("a sequence")
+            }
+
+            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+            where
+                A: SeqAccess<'de>,
+            {
+                let mut values = Vec::with_capacity(size_hint::cautious(seq.size_hint()));
+
+                while let Some(value) = try!(seq.next_element()) {
+                    values.push(value);
+                }
+
+                Ok(values)
+            }
+        }
+
+        let visitor = VecVisitor {
+            marker: PhantomData,
+        };
+        deserializer.deserialize_seq(visitor)
+    }
+
+    fn deserialize_in_place<D>(deserializer: D, place: &mut Self) -> Result<(), D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct VecInPlaceVisitor<'a, T: 'a>(&'a mut Vec<T>);
+
+        impl<'a, 'de, T> Visitor<'de> for VecInPlaceVisitor<'a, T>
+        where
+            T: Deserialize<'de>,
+        {
+            type Value = ();
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("a sequence")
+            }
+
+            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+            where
+                A: SeqAccess<'de>,
+            {
+                let hint = size_hint::cautious(seq.size_hint());
+                if let Some(additional) = hint.checked_sub(self.0.len()) {
+                    self.0.reserve(additional);
+                }
+
+                for i in 0..self.0.len() {
+                    let next = {
+                        let next_place = InPlaceSeed(&mut self.0[i]);
+                        try!(seq.next_element_seed(next_place))
+                    };
+                    if next.is_none() {
+                        self.0.truncate(i);
+                        return Ok(());
+                    }
+                }
+
+                while let Some(value) = try!(seq.next_element()) {
+                    self.0.push(value);
+                }
+
+                Ok(())
+            }
+        }
+
+        deserializer.deserialize_seq(VecInPlaceVisitor(place))
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+struct ArrayVisitor<A> {
+    marker: PhantomData<A>,
+}
+struct ArrayInPlaceVisitor<'a, A: 'a>(&'a mut A);
+
+impl<A> ArrayVisitor<A> {
+    fn new() -> Self {
+        ArrayVisitor {
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'de, T> Visitor<'de> for ArrayVisitor<[T; 0]> {
+    type Value = [T; 0];
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("an empty array")
+    }
+
+    #[inline]
+    fn visit_seq<A>(self, _: A) -> Result<Self::Value, A::Error>
+    where
+        A: SeqAccess<'de>,
+    {
+        Ok([])
+    }
+}
+
+// Does not require T: Deserialize<'de>.
+impl<'de, T> Deserialize<'de> for [T; 0] {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_tuple(0, ArrayVisitor::<[T; 0]>::new())
+    }
+}
+
+macro_rules! array_impls {
+    ($($len:expr => ($($n:tt)+))+) => {
+        $(
+            impl<'de, T> Visitor<'de> for ArrayVisitor<[T; $len]>
+            where
+                T: Deserialize<'de>,
+            {
+                type Value = [T; $len];
+
+                fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                    formatter.write_str(concat!("an array of length ", $len))
+                }
+
+                #[inline]
+                fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+                where
+                    A: SeqAccess<'de>,
+                {
+                    Ok([$(
+                        match try!(seq.next_element()) {
+                            Some(val) => val,
+                            None => return Err(Error::invalid_length($n, &self)),
+                        }
+                    ),+])
+                }
+            }
+
+            impl<'a, 'de, T> Visitor<'de> for ArrayInPlaceVisitor<'a, [T; $len]>
+            where
+                T: Deserialize<'de>,
+            {
+                type Value = ();
+
+                fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                    formatter.write_str(concat!("an array of length ", $len))
+                }
+
+                #[inline]
+                fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+                where
+                    A: SeqAccess<'de>,
+                {
+                    let mut fail_idx = None;
+                    for (idx, dest) in self.0[..].iter_mut().enumerate() {
+                        if try!(seq.next_element_seed(InPlaceSeed(dest))).is_none() {
+                            fail_idx = Some(idx);
+                            break;
+                        }
+                    }
+                    if let Some(idx) = fail_idx {
+                        return Err(Error::invalid_length(idx, &self));
+                    }
+                    Ok(())
+                }
+            }
+
+            impl<'de, T> Deserialize<'de> for [T; $len]
+            where
+                T: Deserialize<'de>,
+            {
+                fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+                where
+                    D: Deserializer<'de>,
+                {
+                    deserializer.deserialize_tuple($len, ArrayVisitor::<[T; $len]>::new())
+                }
+
+                fn deserialize_in_place<D>(deserializer: D, place: &mut Self) -> Result<(), D::Error>
+                where
+                    D: Deserializer<'de>,
+                {
+                    deserializer.deserialize_tuple($len, ArrayInPlaceVisitor(place))
+                }
+            }
+        )+
+    }
+}
+
+array_impls! {
+    1 => (0)
+    2 => (0 1)
+    3 => (0 1 2)
+    4 => (0 1 2 3)
+    5 => (0 1 2 3 4)
+    6 => (0 1 2 3 4 5)
+    7 => (0 1 2 3 4 5 6)
+    8 => (0 1 2 3 4 5 6 7)
+    9 => (0 1 2 3 4 5 6 7 8)
+    10 => (0 1 2 3 4 5 6 7 8 9)
+    11 => (0 1 2 3 4 5 6 7 8 9 10)
+    12 => (0 1 2 3 4 5 6 7 8 9 10 11)
+    13 => (0 1 2 3 4 5 6 7 8 9 10 11 12)
+    14 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13)
+    15 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14)
+    16 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15)
+    17 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16)
+    18 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17)
+    19 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18)
+    20 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19)
+    21 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20)
+    22 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21)
+    23 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22)
+    24 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23)
+    25 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24)
+    26 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25)
+    27 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26)
+    28 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27)
+    29 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28)
+    30 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29)
+    31 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30)
+    32 => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31)
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+macro_rules! tuple_impls {
+    ($($len:tt => ($($n:tt $name:ident)+))+) => {
+        $(
+            impl<'de, $($name: Deserialize<'de>),+> Deserialize<'de> for ($($name,)+) {
+                #[inline]
+                fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+                where
+                    D: Deserializer<'de>,
+                {
+                    struct TupleVisitor<$($name,)+> {
+                        marker: PhantomData<($($name,)+)>,
+                    }
+
+                    impl<'de, $($name: Deserialize<'de>),+> Visitor<'de> for TupleVisitor<$($name,)+> {
+                        type Value = ($($name,)+);
+
+                        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                            formatter.write_str(concat!("a tuple of size ", $len))
+                        }
+
+                        #[inline]
+                        #[allow(non_snake_case)]
+                        fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+                        where
+                            A: SeqAccess<'de>,
+                        {
+                            $(
+                                let $name = match try!(seq.next_element()) {
+                                    Some(value) => value,
+                                    None => return Err(Error::invalid_length($n, &self)),
+                                };
+                            )+
+
+                            Ok(($($name,)+))
+                        }
+                    }
+
+                    deserializer.deserialize_tuple($len, TupleVisitor { marker: PhantomData })
+                }
+
+                #[inline]
+                fn deserialize_in_place<D>(deserializer: D, place: &mut Self) -> Result<(), D::Error>
+                where
+                    D: Deserializer<'de>,
+                {
+                    struct TupleInPlaceVisitor<'a, $($name: 'a,)+>(&'a mut ($($name,)+));
+
+                    impl<'a, 'de, $($name: Deserialize<'de>),+> Visitor<'de> for TupleInPlaceVisitor<'a, $($name,)+> {
+                        type Value = ();
+
+                        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                            formatter.write_str(concat!("a tuple of size ", $len))
+                        }
+
+                        #[inline]
+                        #[allow(non_snake_case)]
+                        fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+                        where
+                            A: SeqAccess<'de>,
+                        {
+                            $(
+                                if try!(seq.next_element_seed(InPlaceSeed(&mut (self.0).$n))).is_none() {
+                                    return Err(Error::invalid_length($n, &self));
+                                }
+                            )+
+
+                            Ok(())
+                        }
+                    }
+
+                    deserializer.deserialize_tuple($len, TupleInPlaceVisitor(place))
+                }
+            }
+        )+
+    }
+}
+
+tuple_impls! {
+    1  => (0 T0)
+    2  => (0 T0 1 T1)
+    3  => (0 T0 1 T1 2 T2)
+    4  => (0 T0 1 T1 2 T2 3 T3)
+    5  => (0 T0 1 T1 2 T2 3 T3 4 T4)
+    6  => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5)
+    7  => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6)
+    8  => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7)
+    9  => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8)
+    10 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9)
+    11 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10)
+    12 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11)
+    13 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12)
+    14 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12 13 T13)
+    15 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12 13 T13 14 T14)
+    16 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12 13 T13 14 T14 15 T15)
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+macro_rules! map_impl {
+    (
+        $ty:ident < K $(: $kbound1:ident $(+ $kbound2:ident)*)*, V $(, $typaram:ident : $bound1:ident $(+ $bound2:ident)*)* >,
+        $access:ident,
+        $with_capacity:expr
+    ) => {
+        impl<'de, K, V $(, $typaram)*> Deserialize<'de> for $ty<K, V $(, $typaram)*>
+        where
+            K: Deserialize<'de> $(+ $kbound1 $(+ $kbound2)*)*,
+            V: Deserialize<'de>,
+            $($typaram: $bound1 $(+ $bound2)*),*
+        {
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                struct MapVisitor<K, V $(, $typaram)*> {
+                    marker: PhantomData<$ty<K, V $(, $typaram)*>>,
+                }
+
+                impl<'de, K, V $(, $typaram)*> Visitor<'de> for MapVisitor<K, V $(, $typaram)*>
+                where
+                    K: Deserialize<'de> $(+ $kbound1 $(+ $kbound2)*)*,
+                    V: Deserialize<'de>,
+                    $($typaram: $bound1 $(+ $bound2)*),*
+                {
+                    type Value = $ty<K, V $(, $typaram)*>;
+
+                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                        formatter.write_str("a map")
+                    }
+
+                    #[inline]
+                    fn visit_map<A>(self, mut $access: A) -> Result<Self::Value, A::Error>
+                    where
+                        A: MapAccess<'de>,
+                    {
+                        let mut values = $with_capacity;
+
+                        while let Some((key, value)) = try!($access.next_entry()) {
+                            values.insert(key, value);
+                        }
+
+                        Ok(values)
+                    }
+                }
+
+                let visitor = MapVisitor { marker: PhantomData };
+                deserializer.deserialize_map(visitor)
+            }
+        }
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+map_impl!(
+    BTreeMap<K: Ord, V>,
+    map,
+    BTreeMap::new());
+
+#[cfg(feature = "std")]
+map_impl!(
+    HashMap<K: Eq + Hash, V, S: BuildHasher + Default>,
+    map,
+    HashMap::with_capacity_and_hasher(size_hint::cautious(map.size_hint()), S::default()));
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(feature = "std")]
+macro_rules! parse_ip_impl {
+    ($expecting:tt $ty:ty; $size:tt) => {
+        impl<'de> Deserialize<'de> for $ty {
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                if deserializer.is_human_readable() {
+                    deserializer.deserialize_str(FromStrVisitor::new($expecting))
+                } else {
+                    <[u8; $size]>::deserialize(deserializer).map(<$ty>::from)
+                }
+            }
+        }
+    };
+}
+
+#[cfg(feature = "std")]
+macro_rules! variant_identifier {
+    (
+        $name_kind: ident ( $($variant: ident; $bytes: expr; $index: expr),* )
+        $expecting_message: expr,
+        $variants_name: ident
+    ) => {
+        enum $name_kind {
+            $( $variant ),*
+        }
+
+        static $variants_name: &'static [&'static str] = &[ $( stringify!($variant) ),*];
+
+        impl<'de> Deserialize<'de> for $name_kind {
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                struct KindVisitor;
+
+                impl<'de> Visitor<'de> for KindVisitor {
+                    type Value = $name_kind;
+
+                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                        formatter.write_str($expecting_message)
+                    }
+
+                    fn visit_u64<E>(self, value: u64) -> Result<Self::Value, E>
+                    where
+                        E: Error,
+                    {
+                        match value {
+                            $(
+                                $index => Ok($name_kind :: $variant),
+                            )*
+                            _ => Err(Error::invalid_value(Unexpected::Unsigned(value), &self),),
+                        }
+                    }
+
+                    fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
+                    where
+                        E: Error,
+                    {
+                        match value {
+                            $(
+                                stringify!($variant) => Ok($name_kind :: $variant),
+                            )*
+                            _ => Err(Error::unknown_variant(value, $variants_name)),
+                        }
+                    }
+
+                    fn visit_bytes<E>(self, value: &[u8]) -> Result<Self::Value, E>
+                    where
+                        E: Error,
+                    {
+                        match value {
+                            $(
+                                $bytes => Ok($name_kind :: $variant),
+                            )*
+                            _ => {
+                                match str::from_utf8(value) {
+                                    Ok(value) => Err(Error::unknown_variant(value, $variants_name)),
+                                    Err(_) => Err(Error::invalid_value(Unexpected::Bytes(value), &self)),
+                                }
+                            }
+                        }
+                    }
+                }
+
+                deserializer.deserialize_identifier(KindVisitor)
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+macro_rules! deserialize_enum {
+    (
+        $name: ident $name_kind: ident ( $($variant: ident; $bytes: expr; $index: expr),* )
+        $expecting_message: expr,
+        $deserializer: expr
+    ) => {
+        variant_identifier!{
+            $name_kind ( $($variant; $bytes; $index),* )
+            $expecting_message,
+            VARIANTS
+        }
+
+        struct EnumVisitor;
+        impl<'de> Visitor<'de> for EnumVisitor {
+            type Value = $name;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str(concat!("a ", stringify!($name)))
+            }
+
+
+            fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error>
+            where
+                A: EnumAccess<'de>,
+            {
+                match try!(data.variant()) {
+                    $(
+                        ($name_kind :: $variant, v) => v.newtype_variant().map($name :: $variant),
+                    )*
+                }
+            }
+        }
+        $deserializer.deserialize_enum(stringify!($name), VARIANTS, EnumVisitor)
+    }
+}
+
+#[cfg(feature = "std")]
+impl<'de> Deserialize<'de> for net::IpAddr {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        if deserializer.is_human_readable() {
+            deserializer.deserialize_str(FromStrVisitor::new("IP address"))
+        } else {
+            use lib::net::IpAddr;
+            deserialize_enum! {
+                IpAddr IpAddrKind (V4; b"V4"; 0, V6; b"V6"; 1)
+                "`V4` or `V6`",
+                deserializer
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+parse_ip_impl!("IPv4 address" net::Ipv4Addr; 4);
+
+#[cfg(feature = "std")]
+parse_ip_impl!("IPv6 address" net::Ipv6Addr; 16);
+
+#[cfg(feature = "std")]
+macro_rules! parse_socket_impl {
+    ($expecting:tt $ty:ty, $new:expr) => {
+        impl<'de> Deserialize<'de> for $ty {
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                if deserializer.is_human_readable() {
+                    deserializer.deserialize_str(FromStrVisitor::new($expecting))
+                } else {
+                    <(_, u16)>::deserialize(deserializer).map(|(ip, port)| $new(ip, port))
+                }
+            }
+        }
+    };
+}
+
+#[cfg(feature = "std")]
+impl<'de> Deserialize<'de> for net::SocketAddr {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        if deserializer.is_human_readable() {
+            deserializer.deserialize_str(FromStrVisitor::new("socket address"))
+        } else {
+            use lib::net::SocketAddr;
+            deserialize_enum! {
+                SocketAddr SocketAddrKind (V4; b"V4"; 0, V6; b"V6"; 1)
+                "`V4` or `V6`",
+                deserializer
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+parse_socket_impl!("IPv4 socket address" net::SocketAddrV4, net::SocketAddrV4::new);
+
+#[cfg(feature = "std")]
+parse_socket_impl!("IPv6 socket address" net::SocketAddrV6, |ip, port| net::SocketAddrV6::new(
+    ip, port, 0, 0
+));
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(feature = "std")]
+struct PathVisitor;
+
+#[cfg(feature = "std")]
+impl<'a> Visitor<'a> for PathVisitor {
+    type Value = &'a Path;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("a borrowed path")
+    }
+
+    fn visit_borrowed_str<E>(self, v: &'a str) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(v.as_ref())
+    }
+
+    fn visit_borrowed_bytes<E>(self, v: &'a [u8]) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        str::from_utf8(v)
+            .map(AsRef::as_ref)
+            .map_err(|_| Error::invalid_value(Unexpected::Bytes(v), &self))
+    }
+}
+
+#[cfg(feature = "std")]
+impl<'de: 'a, 'a> Deserialize<'de> for &'a Path {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_str(PathVisitor)
+    }
+}
+
+#[cfg(feature = "std")]
+struct PathBufVisitor;
+
+#[cfg(feature = "std")]
+impl<'de> Visitor<'de> for PathBufVisitor {
+    type Value = PathBuf;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("path string")
+    }
+
+    fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(From::from(v))
+    }
+
+    fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Ok(From::from(v))
+    }
+
+    fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        str::from_utf8(v)
+            .map(From::from)
+            .map_err(|_| Error::invalid_value(Unexpected::Bytes(v), &self))
+    }
+
+    fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        String::from_utf8(v)
+            .map(From::from)
+            .map_err(|e| Error::invalid_value(Unexpected::Bytes(&e.into_bytes()), &self))
+    }
+}
+
+#[cfg(feature = "std")]
+impl<'de> Deserialize<'de> for PathBuf {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_string(PathBufVisitor)
+    }
+}
+
+#[cfg(all(feature = "std", not(no_de_boxed_path)))]
+forwarded_impl!((), Box<Path>, PathBuf::into_boxed_path);
+
+////////////////////////////////////////////////////////////////////////////////
+
+// If this were outside of the serde crate, it would just use:
+//
+//    #[derive(Deserialize)]
+//    #[serde(variant_identifier)]
+#[cfg(all(feature = "std", any(unix, windows)))]
+variant_identifier! {
+    OsStringKind (Unix; b"Unix"; 0, Windows; b"Windows"; 1)
+    "`Unix` or `Windows`",
+    OSSTR_VARIANTS
+}
+
+#[cfg(all(feature = "std", any(unix, windows)))]
+struct OsStringVisitor;
+
+#[cfg(all(feature = "std", any(unix, windows)))]
+impl<'de> Visitor<'de> for OsStringVisitor {
+    type Value = OsString;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("os string")
+    }
+
+    #[cfg(unix)]
+    fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error>
+    where
+        A: EnumAccess<'de>,
+    {
+        use std::os::unix::ffi::OsStringExt;
+
+        match try!(data.variant()) {
+            (OsStringKind::Unix, v) => v.newtype_variant().map(OsString::from_vec),
+            (OsStringKind::Windows, _) => Err(Error::custom(
+                "cannot deserialize Windows OS string on Unix",
+            )),
+        }
+    }
+
+    #[cfg(windows)]
+    fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error>
+    where
+        A: EnumAccess<'de>,
+    {
+        use std::os::windows::ffi::OsStringExt;
+
+        match try!(data.variant()) {
+            (OsStringKind::Windows, v) => v
+                .newtype_variant::<Vec<u16>>()
+                .map(|vec| OsString::from_wide(&vec)),
+            (OsStringKind::Unix, _) => Err(Error::custom(
+                "cannot deserialize Unix OS string on Windows",
+            )),
+        }
+    }
+}
+
+#[cfg(all(feature = "std", any(unix, windows)))]
+impl<'de> Deserialize<'de> for OsString {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_enum("OsString", OSSTR_VARIANTS, OsStringVisitor)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+forwarded_impl!((T), Box<T>, Box::new);
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+forwarded_impl!((T), Box<[T]>, Vec::into_boxed_slice);
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+forwarded_impl!((), Box<str>, String::into_boxed_str);
+
+#[cfg(all(no_de_rc_dst, feature = "rc", any(feature = "std", feature = "alloc")))]
+forwarded_impl! {
+    /// This impl requires the [`"rc"`] Cargo feature of Serde.
+    ///
+    /// Deserializing a data structure containing `Arc` will not attempt to
+    /// deduplicate `Arc` references to the same data. Every deserialized `Arc`
+    /// will end up with a strong count of 1.
+    ///
+    /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+    (T), Arc<T>, Arc::new
+}
+
+#[cfg(all(no_de_rc_dst, feature = "rc", any(feature = "std", feature = "alloc")))]
+forwarded_impl! {
+    /// This impl requires the [`"rc"`] Cargo feature of Serde.
+    ///
+    /// Deserializing a data structure containing `Rc` will not attempt to
+    /// deduplicate `Rc` references to the same data. Every deserialized `Rc`
+    /// will end up with a strong count of 1.
+    ///
+    /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+    (T), Rc<T>, Rc::new
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'de, 'a, T: ?Sized> Deserialize<'de> for Cow<'a, T>
+where
+    T: ToOwned,
+    T::Owned: Deserialize<'de>,
+{
+    #[inline]
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        T::Owned::deserialize(deserializer).map(Cow::Owned)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// This impl requires the [`"rc"`] Cargo feature of Serde. The resulting
+/// `Weak<T>` has a reference count of 0 and cannot be upgraded.
+///
+/// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+#[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+impl<'de, T: ?Sized> Deserialize<'de> for RcWeak<T>
+where
+    T: Deserialize<'de>,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        try!(Option::<T>::deserialize(deserializer));
+        Ok(RcWeak::new())
+    }
+}
+
+/// This impl requires the [`"rc"`] Cargo feature of Serde. The resulting
+/// `Weak<T>` has a reference count of 0 and cannot be upgraded.
+///
+/// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+#[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+impl<'de, T: ?Sized> Deserialize<'de> for ArcWeak<T>
+where
+    T: Deserialize<'de>,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        try!(Option::<T>::deserialize(deserializer));
+        Ok(ArcWeak::new())
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(all(
+    not(no_de_rc_dst),
+    feature = "rc",
+    any(feature = "std", feature = "alloc")
+))]
+macro_rules! box_forwarded_impl {
+    (
+        $(#[doc = $doc:tt])*
+        $t:ident
+    ) => {
+        $(#[doc = $doc])*
+        impl<'de, T: ?Sized> Deserialize<'de> for $t<T>
+        where
+            Box<T>: Deserialize<'de>,
+        {
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                Box::deserialize(deserializer).map(Into::into)
+            }
+        }
+    };
+}
+
+#[cfg(all(
+    not(no_de_rc_dst),
+    feature = "rc",
+    any(feature = "std", feature = "alloc")
+))]
+box_forwarded_impl! {
+    /// This impl requires the [`"rc"`] Cargo feature of Serde.
+    ///
+    /// Deserializing a data structure containing `Rc` will not attempt to
+    /// deduplicate `Rc` references to the same data. Every deserialized `Rc`
+    /// will end up with a strong count of 1.
+    ///
+    /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+    Rc
+}
+
+#[cfg(all(
+    not(no_de_rc_dst),
+    feature = "rc",
+    any(feature = "std", feature = "alloc")
+))]
+box_forwarded_impl! {
+    /// This impl requires the [`"rc"`] Cargo feature of Serde.
+    ///
+    /// Deserializing a data structure containing `Arc` will not attempt to
+    /// deduplicate `Arc` references to the same data. Every deserialized `Arc`
+    /// will end up with a strong count of 1.
+    ///
+    /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+    Arc
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<'de, T> Deserialize<'de> for Cell<T>
+where
+    T: Deserialize<'de> + Copy,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        T::deserialize(deserializer).map(Cell::new)
+    }
+}
+
+forwarded_impl!((T), RefCell<T>, RefCell::new);
+
+#[cfg(feature = "std")]
+forwarded_impl!((T), Mutex<T>, Mutex::new);
+
+#[cfg(feature = "std")]
+forwarded_impl!((T), RwLock<T>, RwLock::new);
+
+////////////////////////////////////////////////////////////////////////////////
+
+// This is a cleaned-up version of the impl generated by:
+//
+//     #[derive(Deserialize)]
+//     #[serde(deny_unknown_fields)]
+//     struct Duration {
+//         secs: u64,
+//         nanos: u32,
+//     }
+#[cfg(any(feature = "std", not(no_core_duration)))]
+impl<'de> Deserialize<'de> for Duration {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        // If this were outside of the serde crate, it would just use:
+        //
+        //    #[derive(Deserialize)]
+        //    #[serde(field_identifier, rename_all = "lowercase")]
+        enum Field {
+            Secs,
+            Nanos,
+        }
+
+        impl<'de> Deserialize<'de> for Field {
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                struct FieldVisitor;
+
+                impl<'de> Visitor<'de> for FieldVisitor {
+                    type Value = Field;
+
+                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                        formatter.write_str("`secs` or `nanos`")
+                    }
+
+                    fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
+                    where
+                        E: Error,
+                    {
+                        match value {
+                            "secs" => Ok(Field::Secs),
+                            "nanos" => Ok(Field::Nanos),
+                            _ => Err(Error::unknown_field(value, FIELDS)),
+                        }
+                    }
+
+                    fn visit_bytes<E>(self, value: &[u8]) -> Result<Self::Value, E>
+                    where
+                        E: Error,
+                    {
+                        match value {
+                            b"secs" => Ok(Field::Secs),
+                            b"nanos" => Ok(Field::Nanos),
+                            _ => {
+                                let value = ::__private::from_utf8_lossy(value);
+                                Err(Error::unknown_field(&*value, FIELDS))
+                            }
+                        }
+                    }
+                }
+
+                deserializer.deserialize_identifier(FieldVisitor)
+            }
+        }
+
+        fn check_overflow<E>(secs: u64, nanos: u32) -> Result<(), E>
+        where
+            E: Error,
+        {
+            static NANOS_PER_SEC: u32 = 1_000_000_000;
+            match secs.checked_add((nanos / NANOS_PER_SEC) as u64) {
+                Some(_) => Ok(()),
+                None => Err(E::custom("overflow deserializing Duration")),
+            }
+        }
+
+        struct DurationVisitor;
+
+        impl<'de> Visitor<'de> for DurationVisitor {
+            type Value = Duration;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("struct Duration")
+            }
+
+            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+            where
+                A: SeqAccess<'de>,
+            {
+                let secs: u64 = match try!(seq.next_element()) {
+                    Some(value) => value,
+                    None => {
+                        return Err(Error::invalid_length(0, &self));
+                    }
+                };
+                let nanos: u32 = match try!(seq.next_element()) {
+                    Some(value) => value,
+                    None => {
+                        return Err(Error::invalid_length(1, &self));
+                    }
+                };
+                try!(check_overflow(secs, nanos));
+                Ok(Duration::new(secs, nanos))
+            }
+
+            fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
+            where
+                A: MapAccess<'de>,
+            {
+                let mut secs: Option<u64> = None;
+                let mut nanos: Option<u32> = None;
+                while let Some(key) = try!(map.next_key()) {
+                    match key {
+                        Field::Secs => {
+                            if secs.is_some() {
+                                return Err(<A::Error as Error>::duplicate_field("secs"));
+                            }
+                            secs = Some(try!(map.next_value()));
+                        }
+                        Field::Nanos => {
+                            if nanos.is_some() {
+                                return Err(<A::Error as Error>::duplicate_field("nanos"));
+                            }
+                            nanos = Some(try!(map.next_value()));
+                        }
+                    }
+                }
+                let secs = match secs {
+                    Some(secs) => secs,
+                    None => return Err(<A::Error as Error>::missing_field("secs")),
+                };
+                let nanos = match nanos {
+                    Some(nanos) => nanos,
+                    None => return Err(<A::Error as Error>::missing_field("nanos")),
+                };
+                try!(check_overflow(secs, nanos));
+                Ok(Duration::new(secs, nanos))
+            }
+        }
+
+        const FIELDS: &'static [&'static str] = &["secs", "nanos"];
+        deserializer.deserialize_struct("Duration", FIELDS, DurationVisitor)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(feature = "std")]
+impl<'de> Deserialize<'de> for SystemTime {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        // Reuse duration
+        enum Field {
+            Secs,
+            Nanos,
+        }
+
+        impl<'de> Deserialize<'de> for Field {
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                struct FieldVisitor;
+
+                impl<'de> Visitor<'de> for FieldVisitor {
+                    type Value = Field;
+
+                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                        formatter.write_str("`secs_since_epoch` or `nanos_since_epoch`")
+                    }
+
+                    fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
+                    where
+                        E: Error,
+                    {
+                        match value {
+                            "secs_since_epoch" => Ok(Field::Secs),
+                            "nanos_since_epoch" => Ok(Field::Nanos),
+                            _ => Err(Error::unknown_field(value, FIELDS)),
+                        }
+                    }
+
+                    fn visit_bytes<E>(self, value: &[u8]) -> Result<Self::Value, E>
+                    where
+                        E: Error,
+                    {
+                        match value {
+                            b"secs_since_epoch" => Ok(Field::Secs),
+                            b"nanos_since_epoch" => Ok(Field::Nanos),
+                            _ => {
+                                let value = String::from_utf8_lossy(value);
+                                Err(Error::unknown_field(&value, FIELDS))
+                            }
+                        }
+                    }
+                }
+
+                deserializer.deserialize_identifier(FieldVisitor)
+            }
+        }
+
+        fn check_overflow<E>(secs: u64, nanos: u32) -> Result<(), E>
+        where
+            E: Error,
+        {
+            static NANOS_PER_SEC: u32 = 1_000_000_000;
+            match secs.checked_add((nanos / NANOS_PER_SEC) as u64) {
+                Some(_) => Ok(()),
+                None => Err(E::custom("overflow deserializing SystemTime epoch offset")),
+            }
+        }
+
+        struct DurationVisitor;
+
+        impl<'de> Visitor<'de> for DurationVisitor {
+            type Value = Duration;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("struct SystemTime")
+            }
+
+            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+            where
+                A: SeqAccess<'de>,
+            {
+                let secs: u64 = match try!(seq.next_element()) {
+                    Some(value) => value,
+                    None => {
+                        return Err(Error::invalid_length(0, &self));
+                    }
+                };
+                let nanos: u32 = match try!(seq.next_element()) {
+                    Some(value) => value,
+                    None => {
+                        return Err(Error::invalid_length(1, &self));
+                    }
+                };
+                try!(check_overflow(secs, nanos));
+                Ok(Duration::new(secs, nanos))
+            }
+
+            fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
+            where
+                A: MapAccess<'de>,
+            {
+                let mut secs: Option<u64> = None;
+                let mut nanos: Option<u32> = None;
+                while let Some(key) = try!(map.next_key()) {
+                    match key {
+                        Field::Secs => {
+                            if secs.is_some() {
+                                return Err(<A::Error as Error>::duplicate_field(
+                                    "secs_since_epoch",
+                                ));
+                            }
+                            secs = Some(try!(map.next_value()));
+                        }
+                        Field::Nanos => {
+                            if nanos.is_some() {
+                                return Err(<A::Error as Error>::duplicate_field(
+                                    "nanos_since_epoch",
+                                ));
+                            }
+                            nanos = Some(try!(map.next_value()));
+                        }
+                    }
+                }
+                let secs = match secs {
+                    Some(secs) => secs,
+                    None => return Err(<A::Error as Error>::missing_field("secs_since_epoch")),
+                };
+                let nanos = match nanos {
+                    Some(nanos) => nanos,
+                    None => return Err(<A::Error as Error>::missing_field("nanos_since_epoch")),
+                };
+                try!(check_overflow(secs, nanos));
+                Ok(Duration::new(secs, nanos))
+            }
+        }
+
+        const FIELDS: &'static [&'static str] = &["secs_since_epoch", "nanos_since_epoch"];
+        let duration = try!(deserializer.deserialize_struct("SystemTime", FIELDS, DurationVisitor));
+        #[cfg(not(no_systemtime_checked_add))]
+        let ret = UNIX_EPOCH
+            .checked_add(duration)
+            .ok_or_else(|| D::Error::custom("overflow deserializing SystemTime"));
+        #[cfg(no_systemtime_checked_add)]
+        let ret = Ok(UNIX_EPOCH + duration);
+        ret
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+// Similar to:
+//
+//     #[derive(Deserialize)]
+//     #[serde(deny_unknown_fields)]
+//     struct Range {
+//         start: u64,
+//         end: u32,
+//     }
+impl<'de, Idx> Deserialize<'de> for Range<Idx>
+where
+    Idx: Deserialize<'de>,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let (start, end) = deserializer.deserialize_struct(
+            "Range",
+            range::FIELDS,
+            range::RangeVisitor {
+                expecting: "struct Range",
+                phantom: PhantomData,
+            },
+        )?;
+        Ok(start..end)
+    }
+}
+
+#[cfg(not(no_range_inclusive))]
+impl<'de, Idx> Deserialize<'de> for RangeInclusive<Idx>
+where
+    Idx: Deserialize<'de>,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let (start, end) = deserializer.deserialize_struct(
+            "RangeInclusive",
+            range::FIELDS,
+            range::RangeVisitor {
+                expecting: "struct RangeInclusive",
+                phantom: PhantomData,
+            },
+        )?;
+        Ok(RangeInclusive::new(start, end))
+    }
+}
+
+mod range {
+    use lib::*;
+
+    use de::{Deserialize, Deserializer, Error, MapAccess, SeqAccess, Visitor};
+
+    pub const FIELDS: &'static [&'static str] = &["start", "end"];
+
+    // If this were outside of the serde crate, it would just use:
+    //
+    //    #[derive(Deserialize)]
+    //    #[serde(field_identifier, rename_all = "lowercase")]
+    enum Field {
+        Start,
+        End,
+    }
+
+    impl<'de> Deserialize<'de> for Field {
+        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            struct FieldVisitor;
+
+            impl<'de> Visitor<'de> for FieldVisitor {
+                type Value = Field;
+
+                fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                    formatter.write_str("`start` or `end`")
+                }
+
+                fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
+                where
+                    E: Error,
+                {
+                    match value {
+                        "start" => Ok(Field::Start),
+                        "end" => Ok(Field::End),
+                        _ => Err(Error::unknown_field(value, FIELDS)),
+                    }
+                }
+
+                fn visit_bytes<E>(self, value: &[u8]) -> Result<Self::Value, E>
+                where
+                    E: Error,
+                {
+                    match value {
+                        b"start" => Ok(Field::Start),
+                        b"end" => Ok(Field::End),
+                        _ => {
+                            let value = ::__private::from_utf8_lossy(value);
+                            Err(Error::unknown_field(&*value, FIELDS))
+                        }
+                    }
+                }
+            }
+
+            deserializer.deserialize_identifier(FieldVisitor)
+        }
+    }
+
+    pub struct RangeVisitor<Idx> {
+        pub expecting: &'static str,
+        pub phantom: PhantomData<Idx>,
+    }
+
+    impl<'de, Idx> Visitor<'de> for RangeVisitor<Idx>
+    where
+        Idx: Deserialize<'de>,
+    {
+        type Value = (Idx, Idx);
+
+        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            formatter.write_str(self.expecting)
+        }
+
+        fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+        where
+            A: SeqAccess<'de>,
+        {
+            let start: Idx = match try!(seq.next_element()) {
+                Some(value) => value,
+                None => {
+                    return Err(Error::invalid_length(0, &self));
+                }
+            };
+            let end: Idx = match try!(seq.next_element()) {
+                Some(value) => value,
+                None => {
+                    return Err(Error::invalid_length(1, &self));
+                }
+            };
+            Ok((start, end))
+        }
+
+        fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
+        where
+            A: MapAccess<'de>,
+        {
+            let mut start: Option<Idx> = None;
+            let mut end: Option<Idx> = None;
+            while let Some(key) = try!(map.next_key()) {
+                match key {
+                    Field::Start => {
+                        if start.is_some() {
+                            return Err(<A::Error as Error>::duplicate_field("start"));
+                        }
+                        start = Some(try!(map.next_value()));
+                    }
+                    Field::End => {
+                        if end.is_some() {
+                            return Err(<A::Error as Error>::duplicate_field("end"));
+                        }
+                        end = Some(try!(map.next_value()));
+                    }
+                }
+            }
+            let start = match start {
+                Some(start) => start,
+                None => return Err(<A::Error as Error>::missing_field("start")),
+            };
+            let end = match end {
+                Some(end) => end,
+                None => return Err(<A::Error as Error>::missing_field("end")),
+            };
+            Ok((start, end))
+        }
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(any(not(no_ops_bound), all(feature = "std", not(no_collections_bound))))]
+impl<'de, T> Deserialize<'de> for Bound<T>
+where
+    T: Deserialize<'de>,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        enum Field {
+            Unbounded,
+            Included,
+            Excluded,
+        }
+
+        impl<'de> Deserialize<'de> for Field {
+            #[inline]
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                struct FieldVisitor;
+
+                impl<'de> Visitor<'de> for FieldVisitor {
+                    type Value = Field;
+
+                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                        formatter.write_str("`Unbounded`, `Included` or `Excluded`")
+                    }
+
+                    fn visit_u64<E>(self, value: u64) -> Result<Self::Value, E>
+                    where
+                        E: Error,
+                    {
+                        match value {
+                            0 => Ok(Field::Unbounded),
+                            1 => Ok(Field::Included),
+                            2 => Ok(Field::Excluded),
+                            _ => Err(Error::invalid_value(Unexpected::Unsigned(value), &self)),
+                        }
+                    }
+
+                    fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
+                    where
+                        E: Error,
+                    {
+                        match value {
+                            "Unbounded" => Ok(Field::Unbounded),
+                            "Included" => Ok(Field::Included),
+                            "Excluded" => Ok(Field::Excluded),
+                            _ => Err(Error::unknown_variant(value, VARIANTS)),
+                        }
+                    }
+
+                    fn visit_bytes<E>(self, value: &[u8]) -> Result<Self::Value, E>
+                    where
+                        E: Error,
+                    {
+                        match value {
+                            b"Unbounded" => Ok(Field::Unbounded),
+                            b"Included" => Ok(Field::Included),
+                            b"Excluded" => Ok(Field::Excluded),
+                            _ => match str::from_utf8(value) {
+                                Ok(value) => Err(Error::unknown_variant(value, VARIANTS)),
+                                Err(_) => {
+                                    Err(Error::invalid_value(Unexpected::Bytes(value), &self))
+                                }
+                            },
+                        }
+                    }
+                }
+
+                deserializer.deserialize_identifier(FieldVisitor)
+            }
+        }
+
+        struct BoundVisitor<T>(PhantomData<Bound<T>>);
+
+        impl<'de, T> Visitor<'de> for BoundVisitor<T>
+        where
+            T: Deserialize<'de>,
+        {
+            type Value = Bound<T>;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("enum Bound")
+            }
+
+            fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error>
+            where
+                A: EnumAccess<'de>,
+            {
+                match try!(data.variant()) {
+                    (Field::Unbounded, v) => v.unit_variant().map(|()| Bound::Unbounded),
+                    (Field::Included, v) => v.newtype_variant().map(Bound::Included),
+                    (Field::Excluded, v) => v.newtype_variant().map(Bound::Excluded),
+                }
+            }
+        }
+
+        const VARIANTS: &'static [&'static str] = &["Unbounded", "Included", "Excluded"];
+
+        deserializer.deserialize_enum("Bound", VARIANTS, BoundVisitor(PhantomData))
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<'de, T, E> Deserialize<'de> for Result<T, E>
+where
+    T: Deserialize<'de>,
+    E: Deserialize<'de>,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        // If this were outside of the serde crate, it would just use:
+        //
+        //    #[derive(Deserialize)]
+        //    #[serde(variant_identifier)]
+        enum Field {
+            Ok,
+            Err,
+        }
+
+        impl<'de> Deserialize<'de> for Field {
+            #[inline]
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                struct FieldVisitor;
+
+                impl<'de> Visitor<'de> for FieldVisitor {
+                    type Value = Field;
+
+                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                        formatter.write_str("`Ok` or `Err`")
+                    }
+
+                    fn visit_u64<E>(self, value: u64) -> Result<Self::Value, E>
+                    where
+                        E: Error,
+                    {
+                        match value {
+                            0 => Ok(Field::Ok),
+                            1 => Ok(Field::Err),
+                            _ => Err(Error::invalid_value(Unexpected::Unsigned(value), &self)),
+                        }
+                    }
+
+                    fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
+                    where
+                        E: Error,
+                    {
+                        match value {
+                            "Ok" => Ok(Field::Ok),
+                            "Err" => Ok(Field::Err),
+                            _ => Err(Error::unknown_variant(value, VARIANTS)),
+                        }
+                    }
+
+                    fn visit_bytes<E>(self, value: &[u8]) -> Result<Self::Value, E>
+                    where
+                        E: Error,
+                    {
+                        match value {
+                            b"Ok" => Ok(Field::Ok),
+                            b"Err" => Ok(Field::Err),
+                            _ => match str::from_utf8(value) {
+                                Ok(value) => Err(Error::unknown_variant(value, VARIANTS)),
+                                Err(_) => {
+                                    Err(Error::invalid_value(Unexpected::Bytes(value), &self))
+                                }
+                            },
+                        }
+                    }
+                }
+
+                deserializer.deserialize_identifier(FieldVisitor)
+            }
+        }
+
+        struct ResultVisitor<T, E>(PhantomData<Result<T, E>>);
+
+        impl<'de, T, E> Visitor<'de> for ResultVisitor<T, E>
+        where
+            T: Deserialize<'de>,
+            E: Deserialize<'de>,
+        {
+            type Value = Result<T, E>;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("enum Result")
+            }
+
+            fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error>
+            where
+                A: EnumAccess<'de>,
+            {
+                match try!(data.variant()) {
+                    (Field::Ok, v) => v.newtype_variant().map(Ok),
+                    (Field::Err, v) => v.newtype_variant().map(Err),
+                }
+            }
+        }
+
+        const VARIANTS: &'static [&'static str] = &["Ok", "Err"];
+
+        deserializer.deserialize_enum("Result", VARIANTS, ResultVisitor(PhantomData))
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<'de, T> Deserialize<'de> for Wrapping<T>
+where
+    T: Deserialize<'de>,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        Deserialize::deserialize(deserializer).map(Wrapping)
+    }
+}
+
+#[cfg(all(feature = "std", not(no_std_atomic)))]
+macro_rules! atomic_impl {
+    ($($ty:ident)*) => {
+        $(
+            impl<'de> Deserialize<'de> for $ty {
+                fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+                where
+                    D: Deserializer<'de>,
+                {
+                    Deserialize::deserialize(deserializer).map(Self::new)
+                }
+            }
+        )*
+    };
+}
+
+#[cfg(all(feature = "std", not(no_std_atomic)))]
+atomic_impl! {
+    AtomicBool
+    AtomicI8 AtomicI16 AtomicI32 AtomicIsize
+    AtomicU8 AtomicU16 AtomicU32 AtomicUsize
+}
+
+#[cfg(all(feature = "std", not(no_std_atomic64)))]
+atomic_impl! {
+    AtomicI64 AtomicU64
+}
+
+#[cfg(feature = "std")]
+struct FromStrVisitor<T> {
+    expecting: &'static str,
+    ty: PhantomData<T>,
+}
+
+#[cfg(feature = "std")]
+impl<T> FromStrVisitor<T> {
+    fn new(expecting: &'static str) -> Self {
+        FromStrVisitor {
+            expecting: expecting,
+            ty: PhantomData,
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl<'de, T> Visitor<'de> for FromStrVisitor<T>
+where
+    T: str::FromStr,
+    T::Err: fmt::Display,
+{
+    type Value = T;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str(self.expecting)
+    }
+
+    fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        s.parse().map_err(Error::custom)
+    }
+}
diff --git a/vendor/serde/src/de/mod.rs b/vendor/serde/src/de/mod.rs
new file mode 100644
index 000000000..6100815f7
--- /dev/null
+++ b/vendor/serde/src/de/mod.rs
@@ -0,0 +1,2300 @@
+//! Generic data structure deserialization framework.
+//!
+//! The two most important traits in this module are [`Deserialize`] and
+//! [`Deserializer`].
+//!
+//!  - **A type that implements `Deserialize` is a data structure** that can be
+//!    deserialized from any data format supported by Serde, and conversely
+//!  - **A type that implements `Deserializer` is a data format** that can
+//!    deserialize any data structure supported by Serde.
+//!
+//! # The Deserialize trait
+//!
+//! Serde provides [`Deserialize`] implementations for many Rust primitive and
+//! standard library types. The complete list is below. All of these can be
+//! deserialized using Serde out of the box.
+//!
+//! Additionally, Serde provides a procedural macro called [`serde_derive`] to
+//! automatically generate [`Deserialize`] implementations for structs and enums
+//! in your program. See the [derive section of the manual] for how to use this.
+//!
+//! In rare cases it may be necessary to implement [`Deserialize`] manually for
+//! some type in your program. See the [Implementing `Deserialize`] section of
+//! the manual for more about this.
+//!
+//! Third-party crates may provide [`Deserialize`] implementations for types
+//! that they expose. For example the [`linked-hash-map`] crate provides a
+//! [`LinkedHashMap<K, V>`] type that is deserializable by Serde because the
+//! crate provides an implementation of [`Deserialize`] for it.
+//!
+//! # The Deserializer trait
+//!
+//! [`Deserializer`] implementations are provided by third-party crates, for
+//! example [`serde_json`], [`serde_yaml`] and [`bincode`].
+//!
+//! A partial list of well-maintained formats is given on the [Serde
+//! website][data formats].
+//!
+//! # Implementations of Deserialize provided by Serde
+//!
+//! This is a slightly different set of types than what is supported for
+//! serialization. Some types can be serialized by Serde but not deserialized.
+//! One example is `OsStr`.
+//!
+//!  - **Primitive types**:
+//!    - bool
+//!    - i8, i16, i32, i64, i128, isize
+//!    - u8, u16, u32, u64, u128, usize
+//!    - f32, f64
+//!    - char
+//!  - **Compound types**:
+//!    - \[T; 0\] through \[T; 32\]
+//!    - tuples up to size 16
+//!  - **Common standard library types**:
+//!    - String
+//!    - Option\<T\>
+//!    - Result\<T, E\>
+//!    - PhantomData\<T\>
+//!  - **Wrapper types**:
+//!    - Box\<T\>
+//!    - Box\<\[T\]\>
+//!    - Box\<str\>
+//!    - Cow\<'a, T\>
+//!    - Cell\<T\>
+//!    - RefCell\<T\>
+//!    - Mutex\<T\>
+//!    - RwLock\<T\>
+//!    - Rc\<T\>&emsp;*(if* features = ["rc"] *is enabled)*
+//!    - Arc\<T\>&emsp;*(if* features = ["rc"] *is enabled)*
+//!  - **Collection types**:
+//!    - BTreeMap\<K, V\>
+//!    - BTreeSet\<T\>
+//!    - BinaryHeap\<T\>
+//!    - HashMap\<K, V, H\>
+//!    - HashSet\<T, H\>
+//!    - LinkedList\<T\>
+//!    - VecDeque\<T\>
+//!    - Vec\<T\>
+//!  - **Zero-copy types**:
+//!    - &str
+//!    - &\[u8\]
+//!  - **FFI types**:
+//!    - CString
+//!    - Box\<CStr\>
+//!    - OsString
+//!  - **Miscellaneous standard library types**:
+//!    - Duration
+//!    - SystemTime
+//!    - Path
+//!    - PathBuf
+//!    - Range\<T\>
+//!    - RangeInclusive\<T\>
+//!    - Bound\<T\>
+//!    - num::NonZero*
+//!    - `!` *(unstable)*
+//!  - **Net types**:
+//!    - IpAddr
+//!    - Ipv4Addr
+//!    - Ipv6Addr
+//!    - SocketAddr
+//!    - SocketAddrV4
+//!    - SocketAddrV6
+//!
+//! [Implementing `Deserialize`]: https://serde.rs/impl-deserialize.html
+//! [`Deserialize`]: ../trait.Deserialize.html
+//! [`Deserializer`]: ../trait.Deserializer.html
+//! [`LinkedHashMap<K, V>`]: https://docs.rs/linked-hash-map/*/linked_hash_map/struct.LinkedHashMap.html
+//! [`bincode`]: https://github.com/bincode-org/bincode
+//! [`linked-hash-map`]: https://crates.io/crates/linked-hash-map
+//! [`serde_derive`]: https://crates.io/crates/serde_derive
+//! [`serde_json`]: https://github.com/serde-rs/json
+//! [`serde_yaml`]: https://github.com/dtolnay/serde-yaml
+//! [derive section of the manual]: https://serde.rs/derive.html
+//! [data formats]: https://serde.rs/#data-formats
+
+use lib::*;
+
+////////////////////////////////////////////////////////////////////////////////
+
+pub mod value;
+
+#[cfg(not(no_integer128))]
+mod format;
+mod ignored_any;
+mod impls;
+mod utf8;
+
+pub use self::ignored_any::IgnoredAny;
+
+#[cfg(feature = "std")]
+#[doc(no_inline)]
+pub use std::error::Error as StdError;
+#[cfg(not(feature = "std"))]
+#[doc(no_inline)]
+pub use std_error::Error as StdError;
+
+////////////////////////////////////////////////////////////////////////////////
+
+macro_rules! declare_error_trait {
+    (Error: Sized $(+ $($supertrait:ident)::+)*) => {
+        /// The `Error` trait allows `Deserialize` implementations to create descriptive
+        /// error messages belonging to the `Deserializer` against which they are
+        /// currently running.
+        ///
+        /// Every `Deserializer` declares an `Error` type that encompasses both
+        /// general-purpose deserialization errors as well as errors specific to the
+        /// particular deserialization format. For example the `Error` type of
+        /// `serde_json` can represent errors like an invalid JSON escape sequence or an
+        /// unterminated string literal, in addition to the error cases that are part of
+        /// this trait.
+        ///
+        /// Most deserializers should only need to provide the `Error::custom` method
+        /// and inherit the default behavior for the other methods.
+        ///
+        /// # Example implementation
+        ///
+        /// The [example data format] presented on the website shows an error
+        /// type appropriate for a basic JSON data format.
+        ///
+        /// [example data format]: https://serde.rs/data-format.html
+        pub trait Error: Sized $(+ $($supertrait)::+)* {
+            /// Raised when there is general error when deserializing a type.
+            ///
+            /// The message should not be capitalized and should not end with a period.
+            ///
+            /// ```edition2018
+            /// # use std::str::FromStr;
+            /// #
+            /// # struct IpAddr;
+            /// #
+            /// # impl FromStr for IpAddr {
+            /// #     type Err = String;
+            /// #
+            /// #     fn from_str(_: &str) -> Result<Self, String> {
+            /// #         unimplemented!()
+            /// #     }
+            /// # }
+            /// #
+            /// use serde::de::{self, Deserialize, Deserializer};
+            ///
+            /// impl<'de> Deserialize<'de> for IpAddr {
+            ///     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            ///     where
+            ///         D: Deserializer<'de>,
+            ///     {
+            ///         let s = String::deserialize(deserializer)?;
+            ///         s.parse().map_err(de::Error::custom)
+            ///     }
+            /// }
+            /// ```
+            fn custom<T>(msg: T) -> Self
+            where
+                T: Display;
+
+            /// Raised when a `Deserialize` receives a type different from what it was
+            /// expecting.
+            ///
+            /// The `unexp` argument provides information about what type was received.
+            /// This is the type that was present in the input file or other source data
+            /// of the Deserializer.
+            ///
+            /// The `exp` argument provides information about what type was being
+            /// expected. This is the type that is written in the program.
+            ///
+            /// For example if we try to deserialize a String out of a JSON file
+            /// containing an integer, the unexpected type is the integer and the
+            /// expected type is the string.
+            #[cold]
+            fn invalid_type(unexp: Unexpected, exp: &Expected) -> Self {
+                Error::custom(format_args!("invalid type: {}, expected {}", unexp, exp))
+            }
+
+            /// Raised when a `Deserialize` receives a value of the right type but that
+            /// is wrong for some other reason.
+            ///
+            /// The `unexp` argument provides information about what value was received.
+            /// This is the value that was present in the input file or other source
+            /// data of the Deserializer.
+            ///
+            /// The `exp` argument provides information about what value was being
+            /// expected. This is the type that is written in the program.
+            ///
+            /// For example if we try to deserialize a String out of some binary data
+            /// that is not valid UTF-8, the unexpected value is the bytes and the
+            /// expected value is a string.
+            #[cold]
+            fn invalid_value(unexp: Unexpected, exp: &Expected) -> Self {
+                Error::custom(format_args!("invalid value: {}, expected {}", unexp, exp))
+            }
+
+            /// Raised when deserializing a sequence or map and the input data contains
+            /// too many or too few elements.
+            ///
+            /// The `len` argument is the number of elements encountered. The sequence
+            /// or map may have expected more arguments or fewer arguments.
+            ///
+            /// The `exp` argument provides information about what data was being
+            /// expected. For example `exp` might say that a tuple of size 6 was
+            /// expected.
+            #[cold]
+            fn invalid_length(len: usize, exp: &Expected) -> Self {
+                Error::custom(format_args!("invalid length {}, expected {}", len, exp))
+            }
+
+            /// Raised when a `Deserialize` enum type received a variant with an
+            /// unrecognized name.
+            #[cold]
+            fn unknown_variant(variant: &str, expected: &'static [&'static str]) -> Self {
+                if expected.is_empty() {
+                    Error::custom(format_args!(
+                        "unknown variant `{}`, there are no variants",
+                        variant
+                    ))
+                } else {
+                    Error::custom(format_args!(
+                        "unknown variant `{}`, expected {}",
+                        variant,
+                        OneOf { names: expected }
+                    ))
+                }
+            }
+
+            /// Raised when a `Deserialize` struct type received a field with an
+            /// unrecognized name.
+            #[cold]
+            fn unknown_field(field: &str, expected: &'static [&'static str]) -> Self {
+                if expected.is_empty() {
+                    Error::custom(format_args!(
+                        "unknown field `{}`, there are no fields",
+                        field
+                    ))
+                } else {
+                    Error::custom(format_args!(
+                        "unknown field `{}`, expected {}",
+                        field,
+                        OneOf { names: expected }
+                    ))
+                }
+            }
+
+            /// Raised when a `Deserialize` struct type expected to receive a required
+            /// field with a particular name but that field was not present in the
+            /// input.
+            #[cold]
+            fn missing_field(field: &'static str) -> Self {
+                Error::custom(format_args!("missing field `{}`", field))
+            }
+
+            /// Raised when a `Deserialize` struct type received more than one of the
+            /// same field.
+            #[cold]
+            fn duplicate_field(field: &'static str) -> Self {
+                Error::custom(format_args!("duplicate field `{}`", field))
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+declare_error_trait!(Error: Sized + StdError);
+
+#[cfg(not(feature = "std"))]
+declare_error_trait!(Error: Sized + Debug + Display);
+
+/// `Unexpected` represents an unexpected invocation of any one of the `Visitor`
+/// trait methods.
+///
+/// This is used as an argument to the `invalid_type`, `invalid_value`, and
+/// `invalid_length` methods of the `Error` trait to build error messages.
+///
+/// ```edition2018
+/// # use std::fmt;
+/// #
+/// # use serde::de::{self, Unexpected, Visitor};
+/// #
+/// # struct Example;
+/// #
+/// # impl<'de> Visitor<'de> for Example {
+/// #     type Value = ();
+/// #
+/// #     fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+/// #         write!(formatter, "definitely not a boolean")
+/// #     }
+/// #
+/// fn visit_bool<E>(self, v: bool) -> Result<Self::Value, E>
+/// where
+///     E: de::Error,
+/// {
+///     Err(de::Error::invalid_type(Unexpected::Bool(v), &self))
+/// }
+/// # }
+/// ```
+#[derive(Copy, Clone, PartialEq, Debug)]
+pub enum Unexpected<'a> {
+    /// The input contained a boolean value that was not expected.
+    Bool(bool),
+
+    /// The input contained an unsigned integer `u8`, `u16`, `u32` or `u64` that
+    /// was not expected.
+    Unsigned(u64),
+
+    /// The input contained a signed integer `i8`, `i16`, `i32` or `i64` that
+    /// was not expected.
+    Signed(i64),
+
+    /// The input contained a floating point `f32` or `f64` that was not
+    /// expected.
+    Float(f64),
+
+    /// The input contained a `char` that was not expected.
+    Char(char),
+
+    /// The input contained a `&str` or `String` that was not expected.
+    Str(&'a str),
+
+    /// The input contained a `&[u8]` or `Vec<u8>` that was not expected.
+    Bytes(&'a [u8]),
+
+    /// The input contained a unit `()` that was not expected.
+    Unit,
+
+    /// The input contained an `Option<T>` that was not expected.
+    Option,
+
+    /// The input contained a newtype struct that was not expected.
+    NewtypeStruct,
+
+    /// The input contained a sequence that was not expected.
+    Seq,
+
+    /// The input contained a map that was not expected.
+    Map,
+
+    /// The input contained an enum that was not expected.
+    Enum,
+
+    /// The input contained a unit variant that was not expected.
+    UnitVariant,
+
+    /// The input contained a newtype variant that was not expected.
+    NewtypeVariant,
+
+    /// The input contained a tuple variant that was not expected.
+    TupleVariant,
+
+    /// The input contained a struct variant that was not expected.
+    StructVariant,
+
+    /// A message stating what uncategorized thing the input contained that was
+    /// not expected.
+    ///
+    /// The message should be a noun or noun phrase, not capitalized and without
+    /// a period. An example message is "unoriginal superhero".
+    Other(&'a str),
+}
+
+impl<'a> fmt::Display for Unexpected<'a> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        use self::Unexpected::*;
+        match *self {
+            Bool(b) => write!(formatter, "boolean `{}`", b),
+            Unsigned(i) => write!(formatter, "integer `{}`", i),
+            Signed(i) => write!(formatter, "integer `{}`", i),
+            Float(f) => write!(formatter, "floating point `{}`", f),
+            Char(c) => write!(formatter, "character `{}`", c),
+            Str(s) => write!(formatter, "string {:?}", s),
+            Bytes(_) => write!(formatter, "byte array"),
+            Unit => write!(formatter, "unit value"),
+            Option => write!(formatter, "Option value"),
+            NewtypeStruct => write!(formatter, "newtype struct"),
+            Seq => write!(formatter, "sequence"),
+            Map => write!(formatter, "map"),
+            Enum => write!(formatter, "enum"),
+            UnitVariant => write!(formatter, "unit variant"),
+            NewtypeVariant => write!(formatter, "newtype variant"),
+            TupleVariant => write!(formatter, "tuple variant"),
+            StructVariant => write!(formatter, "struct variant"),
+            Other(other) => formatter.write_str(other),
+        }
+    }
+}
+
+/// `Expected` represents an explanation of what data a `Visitor` was expecting
+/// to receive.
+///
+/// This is used as an argument to the `invalid_type`, `invalid_value`, and
+/// `invalid_length` methods of the `Error` trait to build error messages. The
+/// message should be a noun or noun phrase that completes the sentence "This
+/// Visitor expects to receive ...", for example the message could be "an
+/// integer between 0 and 64". The message should not be capitalized and should
+/// not end with a period.
+///
+/// Within the context of a `Visitor` implementation, the `Visitor` itself
+/// (`&self`) is an implementation of this trait.
+///
+/// ```edition2018
+/// # use std::fmt;
+/// #
+/// # use serde::de::{self, Unexpected, Visitor};
+/// #
+/// # struct Example;
+/// #
+/// # impl<'de> Visitor<'de> for Example {
+/// #     type Value = ();
+/// #
+/// #     fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+/// #         write!(formatter, "definitely not a boolean")
+/// #     }
+/// #
+/// fn visit_bool<E>(self, v: bool) -> Result<Self::Value, E>
+/// where
+///     E: de::Error,
+/// {
+///     Err(de::Error::invalid_type(Unexpected::Bool(v), &self))
+/// }
+/// # }
+/// ```
+///
+/// Outside of a `Visitor`, `&"..."` can be used.
+///
+/// ```edition2018
+/// # use serde::de::{self, Unexpected};
+/// #
+/// # fn example<E>() -> Result<(), E>
+/// # where
+/// #     E: de::Error,
+/// # {
+/// #     let v = true;
+/// return Err(de::Error::invalid_type(Unexpected::Bool(v), &"a negative integer"));
+/// # }
+/// ```
+pub trait Expected {
+    /// Format an explanation of what data was being expected. Same signature as
+    /// the `Display` and `Debug` traits.
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result;
+}
+
+impl<'de, T> Expected for T
+where
+    T: Visitor<'de>,
+{
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        self.expecting(formatter)
+    }
+}
+
+impl<'a> Expected for &'a str {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str(self)
+    }
+}
+
+impl<'a> Display for Expected + 'a {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        Expected::fmt(self, formatter)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A **data structure** that can be deserialized from any data format supported
+/// by Serde.
+///
+/// Serde provides `Deserialize` implementations for many Rust primitive and
+/// standard library types. The complete list is [here][de]. All of these can
+/// be deserialized using Serde out of the box.
+///
+/// Additionally, Serde provides a procedural macro called `serde_derive` to
+/// automatically generate `Deserialize` implementations for structs and enums
+/// in your program. See the [derive section of the manual][derive] for how to
+/// use this.
+///
+/// In rare cases it may be necessary to implement `Deserialize` manually for
+/// some type in your program. See the [Implementing
+/// `Deserialize`][impl-deserialize] section of the manual for more about this.
+///
+/// Third-party crates may provide `Deserialize` implementations for types that
+/// they expose. For example the `linked-hash-map` crate provides a
+/// `LinkedHashMap<K, V>` type that is deserializable by Serde because the crate
+/// provides an implementation of `Deserialize` for it.
+///
+/// [de]: https://docs.serde.rs/serde/de/index.html
+/// [derive]: https://serde.rs/derive.html
+/// [impl-deserialize]: https://serde.rs/impl-deserialize.html
+///
+/// # Lifetime
+///
+/// The `'de` lifetime of this trait is the lifetime of data that may be
+/// borrowed by `Self` when deserialized. See the page [Understanding
+/// deserializer lifetimes] for a more detailed explanation of these lifetimes.
+///
+/// [Understanding deserializer lifetimes]: https://serde.rs/lifetimes.html
+pub trait Deserialize<'de>: Sized {
+    /// Deserialize this value from the given Serde deserializer.
+    ///
+    /// See the [Implementing `Deserialize`][impl-deserialize] section of the
+    /// manual for more information about how to implement this method.
+    ///
+    /// [impl-deserialize]: https://serde.rs/impl-deserialize.html
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>;
+
+    /// Deserializes a value into `self` from the given Deserializer.
+    ///
+    /// The purpose of this method is to allow the deserializer to reuse
+    /// resources and avoid copies. As such, if this method returns an error,
+    /// `self` will be in an indeterminate state where some parts of the struct
+    /// have been overwritten. Although whatever state that is will be
+    /// memory-safe.
+    ///
+    /// This is generally useful when repeatedly deserializing values that
+    /// are processed one at a time, where the value of `self` doesn't matter
+    /// when the next deserialization occurs.
+    ///
+    /// If you manually implement this, your recursive deserializations should
+    /// use `deserialize_in_place`.
+    ///
+    /// This method is stable and an official public API, but hidden from the
+    /// documentation because it is almost never what newbies are looking for.
+    /// Showing it in rustdoc would cause it to be featured more prominently
+    /// than it deserves.
+    #[doc(hidden)]
+    fn deserialize_in_place<D>(deserializer: D, place: &mut Self) -> Result<(), D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        // Default implementation just delegates to `deserialize` impl.
+        *place = Deserialize::deserialize(deserializer)?;
+        Ok(())
+    }
+}
+
+/// A data structure that can be deserialized without borrowing any data from
+/// the deserializer.
+///
+/// This is primarily useful for trait bounds on functions. For example a
+/// `from_str` function may be able to deserialize a data structure that borrows
+/// from the input string, but a `from_reader` function may only deserialize
+/// owned data.
+///
+/// ```edition2018
+/// # use serde::de::{Deserialize, DeserializeOwned};
+/// # use std::io::{Read, Result};
+/// #
+/// # trait Ignore {
+/// fn from_str<'a, T>(s: &'a str) -> Result<T>
+/// where
+///     T: Deserialize<'a>;
+///
+/// fn from_reader<R, T>(rdr: R) -> Result<T>
+/// where
+///     R: Read,
+///     T: DeserializeOwned;
+/// # }
+/// ```
+///
+/// # Lifetime
+///
+/// The relationship between `Deserialize` and `DeserializeOwned` in trait
+/// bounds is explained in more detail on the page [Understanding deserializer
+/// lifetimes].
+///
+/// [Understanding deserializer lifetimes]: https://serde.rs/lifetimes.html
+pub trait DeserializeOwned: for<'de> Deserialize<'de> {}
+impl<T> DeserializeOwned for T where T: for<'de> Deserialize<'de> {}
+
+/// `DeserializeSeed` is the stateful form of the `Deserialize` trait. If you
+/// ever find yourself looking for a way to pass data into a `Deserialize` impl,
+/// this trait is the way to do it.
+///
+/// As one example of stateful deserialization consider deserializing a JSON
+/// array into an existing buffer. Using the `Deserialize` trait we could
+/// deserialize a JSON array into a `Vec<T>` but it would be a freshly allocated
+/// `Vec<T>`; there is no way for `Deserialize` to reuse a previously allocated
+/// buffer. Using `DeserializeSeed` instead makes this possible as in the
+/// example code below.
+///
+/// The canonical API for stateless deserialization looks like this:
+///
+/// ```edition2018
+/// # use serde::Deserialize;
+/// #
+/// # enum Error {}
+/// #
+/// fn func<'de, T: Deserialize<'de>>() -> Result<T, Error>
+/// # {
+/// #     unimplemented!()
+/// # }
+/// ```
+///
+/// Adjusting an API like this to support stateful deserialization is a matter
+/// of accepting a seed as input:
+///
+/// ```edition2018
+/// # use serde::de::DeserializeSeed;
+/// #
+/// # enum Error {}
+/// #
+/// fn func_seed<'de, T: DeserializeSeed<'de>>(seed: T) -> Result<T::Value, Error>
+/// # {
+/// #     let _ = seed;
+/// #     unimplemented!()
+/// # }
+/// ```
+///
+/// In practice the majority of deserialization is stateless. An API expecting a
+/// seed can be appeased by passing `std::marker::PhantomData` as a seed in the
+/// case of stateless deserialization.
+///
+/// # Lifetime
+///
+/// The `'de` lifetime of this trait is the lifetime of data that may be
+/// borrowed by `Self::Value` when deserialized. See the page [Understanding
+/// deserializer lifetimes] for a more detailed explanation of these lifetimes.
+///
+/// [Understanding deserializer lifetimes]: https://serde.rs/lifetimes.html
+///
+/// # Example
+///
+/// Suppose we have JSON that looks like `[[1, 2], [3, 4, 5], [6]]` and we need
+/// to deserialize it into a flat representation like `vec![1, 2, 3, 4, 5, 6]`.
+/// Allocating a brand new `Vec<T>` for each subarray would be slow. Instead we
+/// would like to allocate a single `Vec<T>` and then deserialize each subarray
+/// into it. This requires stateful deserialization using the `DeserializeSeed`
+/// trait.
+///
+/// ```edition2018
+/// use std::fmt;
+/// use std::marker::PhantomData;
+///
+/// use serde::de::{Deserialize, DeserializeSeed, Deserializer, SeqAccess, Visitor};
+///
+/// // A DeserializeSeed implementation that uses stateful deserialization to
+/// // append array elements onto the end of an existing vector. The preexisting
+/// // state ("seed") in this case is the Vec<T>. The `deserialize` method of
+/// // `ExtendVec` will be traversing the inner arrays of the JSON input and
+/// // appending each integer into the existing Vec.
+/// struct ExtendVec<'a, T: 'a>(&'a mut Vec<T>);
+///
+/// impl<'de, 'a, T> DeserializeSeed<'de> for ExtendVec<'a, T>
+/// where
+///     T: Deserialize<'de>,
+/// {
+///     // The return type of the `deserialize` method. This implementation
+///     // appends onto an existing vector but does not create any new data
+///     // structure, so the return type is ().
+///     type Value = ();
+///
+///     fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+///     where
+///         D: Deserializer<'de>,
+///     {
+///         // Visitor implementation that will walk an inner array of the JSON
+///         // input.
+///         struct ExtendVecVisitor<'a, T: 'a>(&'a mut Vec<T>);
+///
+///         impl<'de, 'a, T> Visitor<'de> for ExtendVecVisitor<'a, T>
+///         where
+///             T: Deserialize<'de>,
+///         {
+///             type Value = ();
+///
+///             fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+///                 write!(formatter, "an array of integers")
+///             }
+///
+///             fn visit_seq<A>(self, mut seq: A) -> Result<(), A::Error>
+///             where
+///                 A: SeqAccess<'de>,
+///             {
+///                 // Decrease the number of reallocations if there are many elements
+///                 if let Some(size_hint) = seq.size_hint() {
+///                    self.0.reserve(size_hint);
+///                 }
+///
+///                 // Visit each element in the inner array and push it onto
+///                 // the existing vector.
+///                 while let Some(elem) = seq.next_element()? {
+///                     self.0.push(elem);
+///                 }
+///                 Ok(())
+///             }
+///         }
+///
+///         deserializer.deserialize_seq(ExtendVecVisitor(self.0))
+///     }
+/// }
+///
+/// // Visitor implementation that will walk the outer array of the JSON input.
+/// struct FlattenedVecVisitor<T>(PhantomData<T>);
+///
+/// impl<'de, T> Visitor<'de> for FlattenedVecVisitor<T>
+/// where
+///     T: Deserialize<'de>,
+/// {
+///     // This Visitor constructs a single Vec<T> to hold the flattened
+///     // contents of the inner arrays.
+///     type Value = Vec<T>;
+///
+///     fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+///         write!(formatter, "an array of arrays")
+///     }
+///
+///     fn visit_seq<A>(self, mut seq: A) -> Result<Vec<T>, A::Error>
+///     where
+///         A: SeqAccess<'de>,
+///     {
+///         // Create a single Vec to hold the flattened contents.
+///         let mut vec = Vec::new();
+///
+///         // Each iteration through this loop is one inner array.
+///         while let Some(()) = seq.next_element_seed(ExtendVec(&mut vec))? {
+///             // Nothing to do; inner array has been appended into `vec`.
+///         }
+///
+///         // Return the finished vec.
+///         Ok(vec)
+///     }
+/// }
+///
+/// # fn example<'de, D>(deserializer: D) -> Result<(), D::Error>
+/// # where
+/// #     D: Deserializer<'de>,
+/// # {
+/// let visitor = FlattenedVecVisitor(PhantomData);
+/// let flattened: Vec<u64> = deserializer.deserialize_seq(visitor)?;
+/// #     Ok(())
+/// # }
+/// ```
+pub trait DeserializeSeed<'de>: Sized {
+    /// The type produced by using this seed.
+    type Value;
+
+    /// Equivalent to the more common `Deserialize::deserialize` method, except
+    /// with some initial piece of data (the seed) passed in.
+    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: Deserializer<'de>;
+}
+
+impl<'de, T> DeserializeSeed<'de> for PhantomData<T>
+where
+    T: Deserialize<'de>,
+{
+    type Value = T;
+
+    #[inline]
+    fn deserialize<D>(self, deserializer: D) -> Result<T, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        T::deserialize(deserializer)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A **data format** that can deserialize any data structure supported by
+/// Serde.
+///
+/// The role of this trait is to define the deserialization half of the [Serde
+/// data model], which is a way to categorize every Rust data type into one of
+/// 29 possible types. Each method of the `Deserializer` trait corresponds to one
+/// of the types of the data model.
+///
+/// Implementations of `Deserialize` map themselves into this data model by
+/// passing to the `Deserializer` a `Visitor` implementation that can receive
+/// these various types.
+///
+/// The types that make up the Serde data model are:
+///
+///  - **14 primitive types**
+///    - bool
+///    - i8, i16, i32, i64, i128
+///    - u8, u16, u32, u64, u128
+///    - f32, f64
+///    - char
+///  - **string**
+///    - UTF-8 bytes with a length and no null terminator.
+///    - When serializing, all strings are handled equally. When deserializing,
+///      there are three flavors of strings: transient, owned, and borrowed.
+///  - **byte array** - \[u8\]
+///    - Similar to strings, during deserialization byte arrays can be
+///      transient, owned, or borrowed.
+///  - **option**
+///    - Either none or some value.
+///  - **unit**
+///    - The type of `()` in Rust. It represents an anonymous value containing
+///      no data.
+///  - **unit_struct**
+///    - For example `struct Unit` or `PhantomData<T>`. It represents a named
+///      value containing no data.
+///  - **unit_variant**
+///    - For example the `E::A` and `E::B` in `enum E { A, B }`.
+///  - **newtype_struct**
+///    - For example `struct Millimeters(u8)`.
+///  - **newtype_variant**
+///    - For example the `E::N` in `enum E { N(u8) }`.
+///  - **seq**
+///    - A variably sized heterogeneous sequence of values, for example `Vec<T>`
+///      or `HashSet<T>`. When serializing, the length may or may not be known
+///      before iterating through all the data. When deserializing, the length
+///      is determined by looking at the serialized data.
+///  - **tuple**
+///    - A statically sized heterogeneous sequence of values for which the
+///      length will be known at deserialization time without looking at the
+///      serialized data, for example `(u8,)` or `(String, u64, Vec<T>)` or
+///      `[u64; 10]`.
+///  - **tuple_struct**
+///    - A named tuple, for example `struct Rgb(u8, u8, u8)`.
+///  - **tuple_variant**
+///    - For example the `E::T` in `enum E { T(u8, u8) }`.
+///  - **map**
+///    - A heterogeneous key-value pairing, for example `BTreeMap<K, V>`.
+///  - **struct**
+///    - A heterogeneous key-value pairing in which the keys are strings and
+///      will be known at deserialization time without looking at the serialized
+///      data, for example `struct S { r: u8, g: u8, b: u8 }`.
+///  - **struct_variant**
+///    - For example the `E::S` in `enum E { S { r: u8, g: u8, b: u8 } }`.
+///
+/// The `Deserializer` trait supports two entry point styles which enables
+/// different kinds of deserialization.
+///
+/// 1. The `deserialize` method. Self-describing data formats like JSON are able
+///    to look at the serialized data and tell what it represents. For example
+///    the JSON deserializer may see an opening curly brace (`{`) and know that
+///    it is seeing a map. If the data format supports
+///    `Deserializer::deserialize_any`, it will drive the Visitor using whatever
+///    type it sees in the input. JSON uses this approach when deserializing
+///    `serde_json::Value` which is an enum that can represent any JSON
+///    document. Without knowing what is in a JSON document, we can deserialize
+///    it to `serde_json::Value` by going through
+///    `Deserializer::deserialize_any`.
+///
+/// 2. The various `deserialize_*` methods. Non-self-describing formats like
+///    Bincode need to be told what is in the input in order to deserialize it.
+///    The `deserialize_*` methods are hints to the deserializer for how to
+///    interpret the next piece of input. Non-self-describing formats are not
+///    able to deserialize something like `serde_json::Value` which relies on
+///    `Deserializer::deserialize_any`.
+///
+/// When implementing `Deserialize`, you should avoid relying on
+/// `Deserializer::deserialize_any` unless you need to be told by the
+/// Deserializer what type is in the input. Know that relying on
+/// `Deserializer::deserialize_any` means your data type will be able to
+/// deserialize from self-describing formats only, ruling out Bincode and many
+/// others.
+///
+/// [Serde data model]: https://serde.rs/data-model.html
+///
+/// # Lifetime
+///
+/// The `'de` lifetime of this trait is the lifetime of data that may be
+/// borrowed from the input when deserializing. See the page [Understanding
+/// deserializer lifetimes] for a more detailed explanation of these lifetimes.
+///
+/// [Understanding deserializer lifetimes]: https://serde.rs/lifetimes.html
+///
+/// # Example implementation
+///
+/// The [example data format] presented on the website contains example code for
+/// a basic JSON `Deserializer`.
+///
+/// [example data format]: https://serde.rs/data-format.html
+pub trait Deserializer<'de>: Sized {
+    /// The error type that can be returned if some error occurs during
+    /// deserialization.
+    type Error: Error;
+
+    /// Require the `Deserializer` to figure out how to drive the visitor based
+    /// on what data type is in the input.
+    ///
+    /// When implementing `Deserialize`, you should avoid relying on
+    /// `Deserializer::deserialize_any` unless you need to be told by the
+    /// Deserializer what type is in the input. Know that relying on
+    /// `Deserializer::deserialize_any` means your data type will be able to
+    /// deserialize from self-describing formats only, ruling out Bincode and
+    /// many others.
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a `bool` value.
+    fn deserialize_bool<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting an `i8` value.
+    fn deserialize_i8<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting an `i16` value.
+    fn deserialize_i16<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting an `i32` value.
+    fn deserialize_i32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting an `i64` value.
+    fn deserialize_i64<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    serde_if_integer128! {
+        /// Hint that the `Deserialize` type is expecting an `i128` value.
+        ///
+        /// This method is available only on Rust compiler versions >=1.26. The
+        /// default behavior unconditionally returns an error.
+        fn deserialize_i128<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>
+        {
+            let _ = visitor;
+            Err(Error::custom("i128 is not supported"))
+        }
+    }
+
+    /// Hint that the `Deserialize` type is expecting a `u8` value.
+    fn deserialize_u8<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a `u16` value.
+    fn deserialize_u16<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a `u32` value.
+    fn deserialize_u32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a `u64` value.
+    fn deserialize_u64<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    serde_if_integer128! {
+        /// Hint that the `Deserialize` type is expecting an `u128` value.
+        ///
+        /// This method is available only on Rust compiler versions >=1.26. The
+        /// default behavior unconditionally returns an error.
+        fn deserialize_u128<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>
+        {
+            let _ = visitor;
+            Err(Error::custom("u128 is not supported"))
+        }
+    }
+
+    /// Hint that the `Deserialize` type is expecting a `f32` value.
+    fn deserialize_f32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a `f64` value.
+    fn deserialize_f64<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a `char` value.
+    fn deserialize_char<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a string value and does
+    /// not benefit from taking ownership of buffered data owned by the
+    /// `Deserializer`.
+    ///
+    /// If the `Visitor` would benefit from taking ownership of `String` data,
+    /// indicate this to the `Deserializer` by using `deserialize_string`
+    /// instead.
+    fn deserialize_str<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a string value and would
+    /// benefit from taking ownership of buffered data owned by the
+    /// `Deserializer`.
+    ///
+    /// If the `Visitor` would not benefit from taking ownership of `String`
+    /// data, indicate that to the `Deserializer` by using `deserialize_str`
+    /// instead.
+    fn deserialize_string<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a byte array and does not
+    /// benefit from taking ownership of buffered data owned by the
+    /// `Deserializer`.
+    ///
+    /// If the `Visitor` would benefit from taking ownership of `Vec<u8>` data,
+    /// indicate this to the `Deserializer` by using `deserialize_byte_buf`
+    /// instead.
+    fn deserialize_bytes<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a byte array and would
+    /// benefit from taking ownership of buffered data owned by the
+    /// `Deserializer`.
+    ///
+    /// If the `Visitor` would not benefit from taking ownership of `Vec<u8>`
+    /// data, indicate that to the `Deserializer` by using `deserialize_bytes`
+    /// instead.
+    fn deserialize_byte_buf<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting an optional value.
+    ///
+    /// This allows deserializers that encode an optional value as a nullable
+    /// value to convert the null value into `None` and a regular value into
+    /// `Some(value)`.
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a unit value.
+    fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a unit struct with a
+    /// particular name.
+    fn deserialize_unit_struct<V>(
+        self,
+        name: &'static str,
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a newtype struct with a
+    /// particular name.
+    fn deserialize_newtype_struct<V>(
+        self,
+        name: &'static str,
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a sequence of values.
+    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a sequence of values and
+    /// knows how many values there are without looking at the serialized data.
+    fn deserialize_tuple<V>(self, len: usize, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a tuple struct with a
+    /// particular name and number of fields.
+    fn deserialize_tuple_struct<V>(
+        self,
+        name: &'static str,
+        len: usize,
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a map of key-value pairs.
+    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting a struct with a particular
+    /// name and fields.
+    fn deserialize_struct<V>(
+        self,
+        name: &'static str,
+        fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting an enum value with a
+    /// particular name and possible variants.
+    fn deserialize_enum<V>(
+        self,
+        name: &'static str,
+        variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type is expecting the name of a struct
+    /// field or the discriminant of an enum variant.
+    fn deserialize_identifier<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Hint that the `Deserialize` type needs to deserialize a value whose type
+    /// doesn't matter because it is ignored.
+    ///
+    /// Deserializers for non-self-describing formats may not support this mode.
+    fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Determine whether `Deserialize` implementations should expect to
+    /// deserialize their human-readable form.
+    ///
+    /// Some types have a human-readable form that may be somewhat expensive to
+    /// construct, as well as a binary form that is compact and efficient.
+    /// Generally text-based formats like JSON and YAML will prefer to use the
+    /// human-readable one and binary formats like Bincode will prefer the
+    /// compact one.
+    ///
+    /// ```edition2018
+    /// # use std::ops::Add;
+    /// # use std::str::FromStr;
+    /// #
+    /// # struct Timestamp;
+    /// #
+    /// # impl Timestamp {
+    /// #     const EPOCH: Timestamp = Timestamp;
+    /// # }
+    /// #
+    /// # impl FromStr for Timestamp {
+    /// #     type Err = String;
+    /// #     fn from_str(_: &str) -> Result<Self, Self::Err> {
+    /// #         unimplemented!()
+    /// #     }
+    /// # }
+    /// #
+    /// # struct Duration;
+    /// #
+    /// # impl Duration {
+    /// #     fn seconds(_: u64) -> Self { unimplemented!() }
+    /// # }
+    /// #
+    /// # impl Add<Duration> for Timestamp {
+    /// #     type Output = Timestamp;
+    /// #     fn add(self, _: Duration) -> Self::Output {
+    /// #         unimplemented!()
+    /// #     }
+    /// # }
+    /// #
+    /// use serde::de::{self, Deserialize, Deserializer};
+    ///
+    /// impl<'de> Deserialize<'de> for Timestamp {
+    ///     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    ///     where
+    ///         D: Deserializer<'de>,
+    ///     {
+    ///         if deserializer.is_human_readable() {
+    ///             // Deserialize from a human-readable string like "2015-05-15T17:01:00Z".
+    ///             let s = String::deserialize(deserializer)?;
+    ///             Timestamp::from_str(&s).map_err(de::Error::custom)
+    ///         } else {
+    ///             // Deserialize from a compact binary representation, seconds since
+    ///             // the Unix epoch.
+    ///             let n = u64::deserialize(deserializer)?;
+    ///             Ok(Timestamp::EPOCH + Duration::seconds(n))
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// The default implementation of this method returns `true`. Data formats
+    /// may override this to `false` to request a compact form for types that
+    /// support one. Note that modifying this method to change a format from
+    /// human-readable to compact or vice versa should be regarded as a breaking
+    /// change, as a value serialized in human-readable mode is not required to
+    /// deserialize from the same data in compact mode.
+    #[inline]
+    fn is_human_readable(&self) -> bool {
+        true
+    }
+
+    // Not public API.
+    #[cfg(all(not(no_serde_derive), any(feature = "std", feature = "alloc")))]
+    #[doc(hidden)]
+    fn __deserialize_content<V>(
+        self,
+        _: ::actually_private::T,
+        visitor: V,
+    ) -> Result<::private::de::Content<'de>, Self::Error>
+    where
+        V: Visitor<'de, Value = ::private::de::Content<'de>>,
+    {
+        self.deserialize_any(visitor)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// This trait represents a visitor that walks through a deserializer.
+///
+/// # Lifetime
+///
+/// The `'de` lifetime of this trait is the requirement for lifetime of data
+/// that may be borrowed by `Self::Value`. See the page [Understanding
+/// deserializer lifetimes] for a more detailed explanation of these lifetimes.
+///
+/// [Understanding deserializer lifetimes]: https://serde.rs/lifetimes.html
+///
+/// # Example
+///
+/// ```edition2018
+/// # use std::fmt;
+/// #
+/// # use serde::de::{self, Unexpected, Visitor};
+/// #
+/// /// A visitor that deserializes a long string - a string containing at least
+/// /// some minimum number of bytes.
+/// struct LongString {
+///     min: usize,
+/// }
+///
+/// impl<'de> Visitor<'de> for LongString {
+///     type Value = String;
+///
+///     fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+///         write!(formatter, "a string containing at least {} bytes", self.min)
+///     }
+///
+///     fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
+///     where
+///         E: de::Error,
+///     {
+///         if s.len() >= self.min {
+///             Ok(s.to_owned())
+///         } else {
+///             Err(de::Error::invalid_value(Unexpected::Str(s), &self))
+///         }
+///     }
+/// }
+/// ```
+pub trait Visitor<'de>: Sized {
+    /// The value produced by this visitor.
+    type Value;
+
+    /// Format a message stating what data this Visitor expects to receive.
+    ///
+    /// This is used in error messages. The message should complete the sentence
+    /// "This Visitor expects to receive ...", for example the message could be
+    /// "an integer between 0 and 64". The message should not be capitalized and
+    /// should not end with a period.
+    ///
+    /// ```edition2018
+    /// # use std::fmt;
+    /// #
+    /// # struct S {
+    /// #     max: usize,
+    /// # }
+    /// #
+    /// # impl<'de> serde::de::Visitor<'de> for S {
+    /// #     type Value = ();
+    /// #
+    /// fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///     write!(formatter, "an integer between 0 and {}", self.max)
+    /// }
+    /// # }
+    /// ```
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result;
+
+    /// The input contains a boolean.
+    ///
+    /// The default implementation fails with a type error.
+    fn visit_bool<E>(self, v: bool) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Err(Error::invalid_type(Unexpected::Bool(v), &self))
+    }
+
+    /// The input contains an `i8`.
+    ///
+    /// The default implementation forwards to [`visit_i64`].
+    ///
+    /// [`visit_i64`]: #method.visit_i64
+    fn visit_i8<E>(self, v: i8) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        self.visit_i64(v as i64)
+    }
+
+    /// The input contains an `i16`.
+    ///
+    /// The default implementation forwards to [`visit_i64`].
+    ///
+    /// [`visit_i64`]: #method.visit_i64
+    fn visit_i16<E>(self, v: i16) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        self.visit_i64(v as i64)
+    }
+
+    /// The input contains an `i32`.
+    ///
+    /// The default implementation forwards to [`visit_i64`].
+    ///
+    /// [`visit_i64`]: #method.visit_i64
+    fn visit_i32<E>(self, v: i32) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        self.visit_i64(v as i64)
+    }
+
+    /// The input contains an `i64`.
+    ///
+    /// The default implementation fails with a type error.
+    fn visit_i64<E>(self, v: i64) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Err(Error::invalid_type(Unexpected::Signed(v), &self))
+    }
+
+    serde_if_integer128! {
+        /// The input contains a `i128`.
+        ///
+        /// This method is available only on Rust compiler versions >=1.26. The
+        /// default implementation fails with a type error.
+        fn visit_i128<E>(self, v: i128) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            let mut buf = [0u8; 58];
+            let mut writer = format::Buf::new(&mut buf);
+            fmt::Write::write_fmt(&mut writer, format_args!("integer `{}` as i128", v)).unwrap();
+            Err(Error::invalid_type(Unexpected::Other(writer.as_str()), &self))
+        }
+    }
+
+    /// The input contains a `u8`.
+    ///
+    /// The default implementation forwards to [`visit_u64`].
+    ///
+    /// [`visit_u64`]: #method.visit_u64
+    fn visit_u8<E>(self, v: u8) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        self.visit_u64(v as u64)
+    }
+
+    /// The input contains a `u16`.
+    ///
+    /// The default implementation forwards to [`visit_u64`].
+    ///
+    /// [`visit_u64`]: #method.visit_u64
+    fn visit_u16<E>(self, v: u16) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        self.visit_u64(v as u64)
+    }
+
+    /// The input contains a `u32`.
+    ///
+    /// The default implementation forwards to [`visit_u64`].
+    ///
+    /// [`visit_u64`]: #method.visit_u64
+    fn visit_u32<E>(self, v: u32) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        self.visit_u64(v as u64)
+    }
+
+    /// The input contains a `u64`.
+    ///
+    /// The default implementation fails with a type error.
+    fn visit_u64<E>(self, v: u64) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Err(Error::invalid_type(Unexpected::Unsigned(v), &self))
+    }
+
+    serde_if_integer128! {
+        /// The input contains a `u128`.
+        ///
+        /// This method is available only on Rust compiler versions >=1.26. The
+        /// default implementation fails with a type error.
+        fn visit_u128<E>(self, v: u128) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            let mut buf = [0u8; 57];
+            let mut writer = format::Buf::new(&mut buf);
+            fmt::Write::write_fmt(&mut writer, format_args!("integer `{}` as u128", v)).unwrap();
+            Err(Error::invalid_type(Unexpected::Other(writer.as_str()), &self))
+        }
+    }
+
+    /// The input contains an `f32`.
+    ///
+    /// The default implementation forwards to [`visit_f64`].
+    ///
+    /// [`visit_f64`]: #method.visit_f64
+    fn visit_f32<E>(self, v: f32) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        self.visit_f64(v as f64)
+    }
+
+    /// The input contains an `f64`.
+    ///
+    /// The default implementation fails with a type error.
+    fn visit_f64<E>(self, v: f64) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Err(Error::invalid_type(Unexpected::Float(v), &self))
+    }
+
+    /// The input contains a `char`.
+    ///
+    /// The default implementation forwards to [`visit_str`] as a one-character
+    /// string.
+    ///
+    /// [`visit_str`]: #method.visit_str
+    #[inline]
+    fn visit_char<E>(self, v: char) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        self.visit_str(utf8::encode(v).as_str())
+    }
+
+    /// The input contains a string. The lifetime of the string is ephemeral and
+    /// it may be destroyed after this method returns.
+    ///
+    /// This method allows the `Deserializer` to avoid a copy by retaining
+    /// ownership of any buffered data. `Deserialize` implementations that do
+    /// not benefit from taking ownership of `String` data should indicate that
+    /// to the deserializer by using `Deserializer::deserialize_str` rather than
+    /// `Deserializer::deserialize_string`.
+    ///
+    /// It is never correct to implement `visit_string` without implementing
+    /// `visit_str`. Implement neither, both, or just `visit_str`.
+    fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Err(Error::invalid_type(Unexpected::Str(v), &self))
+    }
+
+    /// The input contains a string that lives at least as long as the
+    /// `Deserializer`.
+    ///
+    /// This enables zero-copy deserialization of strings in some formats. For
+    /// example JSON input containing the JSON string `"borrowed"` can be
+    /// deserialized with zero copying into a `&'a str` as long as the input
+    /// data outlives `'a`.
+    ///
+    /// The default implementation forwards to `visit_str`.
+    #[inline]
+    fn visit_borrowed_str<E>(self, v: &'de str) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        self.visit_str(v)
+    }
+
+    /// The input contains a string and ownership of the string is being given
+    /// to the `Visitor`.
+    ///
+    /// This method allows the `Visitor` to avoid a copy by taking ownership of
+    /// a string created by the `Deserializer`. `Deserialize` implementations
+    /// that benefit from taking ownership of `String` data should indicate that
+    /// to the deserializer by using `Deserializer::deserialize_string` rather
+    /// than `Deserializer::deserialize_str`, although not every deserializer
+    /// will honor such a request.
+    ///
+    /// It is never correct to implement `visit_string` without implementing
+    /// `visit_str`. Implement neither, both, or just `visit_str`.
+    ///
+    /// The default implementation forwards to `visit_str` and then drops the
+    /// `String`.
+    #[inline]
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        self.visit_str(&v)
+    }
+
+    /// The input contains a byte array. The lifetime of the byte array is
+    /// ephemeral and it may be destroyed after this method returns.
+    ///
+    /// This method allows the `Deserializer` to avoid a copy by retaining
+    /// ownership of any buffered data. `Deserialize` implementations that do
+    /// not benefit from taking ownership of `Vec<u8>` data should indicate that
+    /// to the deserializer by using `Deserializer::deserialize_bytes` rather
+    /// than `Deserializer::deserialize_byte_buf`.
+    ///
+    /// It is never correct to implement `visit_byte_buf` without implementing
+    /// `visit_bytes`. Implement neither, both, or just `visit_bytes`.
+    fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        let _ = v;
+        Err(Error::invalid_type(Unexpected::Bytes(v), &self))
+    }
+
+    /// The input contains a byte array that lives at least as long as the
+    /// `Deserializer`.
+    ///
+    /// This enables zero-copy deserialization of bytes in some formats. For
+    /// example Bincode data containing bytes can be deserialized with zero
+    /// copying into a `&'a [u8]` as long as the input data outlives `'a`.
+    ///
+    /// The default implementation forwards to `visit_bytes`.
+    #[inline]
+    fn visit_borrowed_bytes<E>(self, v: &'de [u8]) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        self.visit_bytes(v)
+    }
+
+    /// The input contains a byte array and ownership of the byte array is being
+    /// given to the `Visitor`.
+    ///
+    /// This method allows the `Visitor` to avoid a copy by taking ownership of
+    /// a byte buffer created by the `Deserializer`. `Deserialize`
+    /// implementations that benefit from taking ownership of `Vec<u8>` data
+    /// should indicate that to the deserializer by using
+    /// `Deserializer::deserialize_byte_buf` rather than
+    /// `Deserializer::deserialize_bytes`, although not every deserializer will
+    /// honor such a request.
+    ///
+    /// It is never correct to implement `visit_byte_buf` without implementing
+    /// `visit_bytes`. Implement neither, both, or just `visit_bytes`.
+    ///
+    /// The default implementation forwards to `visit_bytes` and then drops the
+    /// `Vec<u8>`.
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        self.visit_bytes(&v)
+    }
+
+    /// The input contains an optional that is absent.
+    ///
+    /// The default implementation fails with a type error.
+    fn visit_none<E>(self) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Err(Error::invalid_type(Unexpected::Option, &self))
+    }
+
+    /// The input contains an optional that is present.
+    ///
+    /// The default implementation fails with a type error.
+    fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let _ = deserializer;
+        Err(Error::invalid_type(Unexpected::Option, &self))
+    }
+
+    /// The input contains a unit `()`.
+    ///
+    /// The default implementation fails with a type error.
+    fn visit_unit<E>(self) -> Result<Self::Value, E>
+    where
+        E: Error,
+    {
+        Err(Error::invalid_type(Unexpected::Unit, &self))
+    }
+
+    /// The input contains a newtype struct.
+    ///
+    /// The content of the newtype struct may be read from the given
+    /// `Deserializer`.
+    ///
+    /// The default implementation fails with a type error.
+    fn visit_newtype_struct<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let _ = deserializer;
+        Err(Error::invalid_type(Unexpected::NewtypeStruct, &self))
+    }
+
+    /// The input contains a sequence of elements.
+    ///
+    /// The default implementation fails with a type error.
+    fn visit_seq<A>(self, seq: A) -> Result<Self::Value, A::Error>
+    where
+        A: SeqAccess<'de>,
+    {
+        let _ = seq;
+        Err(Error::invalid_type(Unexpected::Seq, &self))
+    }
+
+    /// The input contains a key-value map.
+    ///
+    /// The default implementation fails with a type error.
+    fn visit_map<A>(self, map: A) -> Result<Self::Value, A::Error>
+    where
+        A: MapAccess<'de>,
+    {
+        let _ = map;
+        Err(Error::invalid_type(Unexpected::Map, &self))
+    }
+
+    /// The input contains an enum.
+    ///
+    /// The default implementation fails with a type error.
+    fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error>
+    where
+        A: EnumAccess<'de>,
+    {
+        let _ = data;
+        Err(Error::invalid_type(Unexpected::Enum, &self))
+    }
+
+    // Used when deserializing a flattened Option field. Not public API.
+    #[doc(hidden)]
+    fn __private_visit_untagged_option<D>(self, _: D) -> Result<Self::Value, ()>
+    where
+        D: Deserializer<'de>,
+    {
+        Err(())
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// Provides a `Visitor` access to each element of a sequence in the input.
+///
+/// This is a trait that a `Deserializer` passes to a `Visitor` implementation,
+/// which deserializes each item in a sequence.
+///
+/// # Lifetime
+///
+/// The `'de` lifetime of this trait is the lifetime of data that may be
+/// borrowed by deserialized sequence elements. See the page [Understanding
+/// deserializer lifetimes] for a more detailed explanation of these lifetimes.
+///
+/// [Understanding deserializer lifetimes]: https://serde.rs/lifetimes.html
+///
+/// # Example implementation
+///
+/// The [example data format] presented on the website demonstrates an
+/// implementation of `SeqAccess` for a basic JSON data format.
+///
+/// [example data format]: https://serde.rs/data-format.html
+pub trait SeqAccess<'de> {
+    /// The error type that can be returned if some error occurs during
+    /// deserialization.
+    type Error: Error;
+
+    /// This returns `Ok(Some(value))` for the next value in the sequence, or
+    /// `Ok(None)` if there are no more remaining items.
+    ///
+    /// `Deserialize` implementations should typically use
+    /// `SeqAccess::next_element` instead.
+    fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
+    where
+        T: DeserializeSeed<'de>;
+
+    /// This returns `Ok(Some(value))` for the next value in the sequence, or
+    /// `Ok(None)` if there are no more remaining items.
+    ///
+    /// This method exists as a convenience for `Deserialize` implementations.
+    /// `SeqAccess` implementations should not override the default behavior.
+    #[inline]
+    fn next_element<T>(&mut self) -> Result<Option<T>, Self::Error>
+    where
+        T: Deserialize<'de>,
+    {
+        self.next_element_seed(PhantomData)
+    }
+
+    /// Returns the number of elements remaining in the sequence, if known.
+    #[inline]
+    fn size_hint(&self) -> Option<usize> {
+        None
+    }
+}
+
+impl<'de, 'a, A: ?Sized> SeqAccess<'de> for &'a mut A
+where
+    A: SeqAccess<'de>,
+{
+    type Error = A::Error;
+
+    #[inline]
+    fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        (**self).next_element_seed(seed)
+    }
+
+    #[inline]
+    fn next_element<T>(&mut self) -> Result<Option<T>, Self::Error>
+    where
+        T: Deserialize<'de>,
+    {
+        (**self).next_element()
+    }
+
+    #[inline]
+    fn size_hint(&self) -> Option<usize> {
+        (**self).size_hint()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// Provides a `Visitor` access to each entry of a map in the input.
+///
+/// This is a trait that a `Deserializer` passes to a `Visitor` implementation.
+///
+/// # Lifetime
+///
+/// The `'de` lifetime of this trait is the lifetime of data that may be
+/// borrowed by deserialized map entries. See the page [Understanding
+/// deserializer lifetimes] for a more detailed explanation of these lifetimes.
+///
+/// [Understanding deserializer lifetimes]: https://serde.rs/lifetimes.html
+///
+/// # Example implementation
+///
+/// The [example data format] presented on the website demonstrates an
+/// implementation of `MapAccess` for a basic JSON data format.
+///
+/// [example data format]: https://serde.rs/data-format.html
+pub trait MapAccess<'de> {
+    /// The error type that can be returned if some error occurs during
+    /// deserialization.
+    type Error: Error;
+
+    /// This returns `Ok(Some(key))` for the next key in the map, or `Ok(None)`
+    /// if there are no more remaining entries.
+    ///
+    /// `Deserialize` implementations should typically use
+    /// `MapAccess::next_key` or `MapAccess::next_entry` instead.
+    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Self::Error>
+    where
+        K: DeserializeSeed<'de>;
+
+    /// This returns a `Ok(value)` for the next value in the map.
+    ///
+    /// `Deserialize` implementations should typically use
+    /// `MapAccess::next_value` instead.
+    ///
+    /// # Panics
+    ///
+    /// Calling `next_value_seed` before `next_key_seed` is incorrect and is
+    /// allowed to panic or return bogus results.
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Self::Error>
+    where
+        V: DeserializeSeed<'de>;
+
+    /// This returns `Ok(Some((key, value)))` for the next (key-value) pair in
+    /// the map, or `Ok(None)` if there are no more remaining items.
+    ///
+    /// `MapAccess` implementations should override the default behavior if a
+    /// more efficient implementation is possible.
+    ///
+    /// `Deserialize` implementations should typically use
+    /// `MapAccess::next_entry` instead.
+    #[inline]
+    fn next_entry_seed<K, V>(
+        &mut self,
+        kseed: K,
+        vseed: V,
+    ) -> Result<Option<(K::Value, V::Value)>, Self::Error>
+    where
+        K: DeserializeSeed<'de>,
+        V: DeserializeSeed<'de>,
+    {
+        match try!(self.next_key_seed(kseed)) {
+            Some(key) => {
+                let value = try!(self.next_value_seed(vseed));
+                Ok(Some((key, value)))
+            }
+            None => Ok(None),
+        }
+    }
+
+    /// This returns `Ok(Some(key))` for the next key in the map, or `Ok(None)`
+    /// if there are no more remaining entries.
+    ///
+    /// This method exists as a convenience for `Deserialize` implementations.
+    /// `MapAccess` implementations should not override the default behavior.
+    #[inline]
+    fn next_key<K>(&mut self) -> Result<Option<K>, Self::Error>
+    where
+        K: Deserialize<'de>,
+    {
+        self.next_key_seed(PhantomData)
+    }
+
+    /// This returns a `Ok(value)` for the next value in the map.
+    ///
+    /// This method exists as a convenience for `Deserialize` implementations.
+    /// `MapAccess` implementations should not override the default behavior.
+    ///
+    /// # Panics
+    ///
+    /// Calling `next_value` before `next_key` is incorrect and is allowed to
+    /// panic or return bogus results.
+    #[inline]
+    fn next_value<V>(&mut self) -> Result<V, Self::Error>
+    where
+        V: Deserialize<'de>,
+    {
+        self.next_value_seed(PhantomData)
+    }
+
+    /// This returns `Ok(Some((key, value)))` for the next (key-value) pair in
+    /// the map, or `Ok(None)` if there are no more remaining items.
+    ///
+    /// This method exists as a convenience for `Deserialize` implementations.
+    /// `MapAccess` implementations should not override the default behavior.
+    #[inline]
+    fn next_entry<K, V>(&mut self) -> Result<Option<(K, V)>, Self::Error>
+    where
+        K: Deserialize<'de>,
+        V: Deserialize<'de>,
+    {
+        self.next_entry_seed(PhantomData, PhantomData)
+    }
+
+    /// Returns the number of entries remaining in the map, if known.
+    #[inline]
+    fn size_hint(&self) -> Option<usize> {
+        None
+    }
+}
+
+impl<'de, 'a, A: ?Sized> MapAccess<'de> for &'a mut A
+where
+    A: MapAccess<'de>,
+{
+    type Error = A::Error;
+
+    #[inline]
+    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Self::Error>
+    where
+        K: DeserializeSeed<'de>,
+    {
+        (**self).next_key_seed(seed)
+    }
+
+    #[inline]
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Self::Error>
+    where
+        V: DeserializeSeed<'de>,
+    {
+        (**self).next_value_seed(seed)
+    }
+
+    #[inline]
+    fn next_entry_seed<K, V>(
+        &mut self,
+        kseed: K,
+        vseed: V,
+    ) -> Result<Option<(K::Value, V::Value)>, Self::Error>
+    where
+        K: DeserializeSeed<'de>,
+        V: DeserializeSeed<'de>,
+    {
+        (**self).next_entry_seed(kseed, vseed)
+    }
+
+    #[inline]
+    fn next_entry<K, V>(&mut self) -> Result<Option<(K, V)>, Self::Error>
+    where
+        K: Deserialize<'de>,
+        V: Deserialize<'de>,
+    {
+        (**self).next_entry()
+    }
+
+    #[inline]
+    fn next_key<K>(&mut self) -> Result<Option<K>, Self::Error>
+    where
+        K: Deserialize<'de>,
+    {
+        (**self).next_key()
+    }
+
+    #[inline]
+    fn next_value<V>(&mut self) -> Result<V, Self::Error>
+    where
+        V: Deserialize<'de>,
+    {
+        (**self).next_value()
+    }
+
+    #[inline]
+    fn size_hint(&self) -> Option<usize> {
+        (**self).size_hint()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// Provides a `Visitor` access to the data of an enum in the input.
+///
+/// `EnumAccess` is created by the `Deserializer` and passed to the
+/// `Visitor` in order to identify which variant of an enum to deserialize.
+///
+/// # Lifetime
+///
+/// The `'de` lifetime of this trait is the lifetime of data that may be
+/// borrowed by the deserialized enum variant. See the page [Understanding
+/// deserializer lifetimes] for a more detailed explanation of these lifetimes.
+///
+/// [Understanding deserializer lifetimes]: https://serde.rs/lifetimes.html
+///
+/// # Example implementation
+///
+/// The [example data format] presented on the website demonstrates an
+/// implementation of `EnumAccess` for a basic JSON data format.
+///
+/// [example data format]: https://serde.rs/data-format.html
+pub trait EnumAccess<'de>: Sized {
+    /// The error type that can be returned if some error occurs during
+    /// deserialization.
+    type Error: Error;
+    /// The `Visitor` that will be used to deserialize the content of the enum
+    /// variant.
+    type Variant: VariantAccess<'de, Error = Self::Error>;
+
+    /// `variant` is called to identify which variant to deserialize.
+    ///
+    /// `Deserialize` implementations should typically use `EnumAccess::variant`
+    /// instead.
+    fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self::Variant), Self::Error>
+    where
+        V: DeserializeSeed<'de>;
+
+    /// `variant` is called to identify which variant to deserialize.
+    ///
+    /// This method exists as a convenience for `Deserialize` implementations.
+    /// `EnumAccess` implementations should not override the default behavior.
+    #[inline]
+    fn variant<V>(self) -> Result<(V, Self::Variant), Self::Error>
+    where
+        V: Deserialize<'de>,
+    {
+        self.variant_seed(PhantomData)
+    }
+}
+
+/// `VariantAccess` is a visitor that is created by the `Deserializer` and
+/// passed to the `Deserialize` to deserialize the content of a particular enum
+/// variant.
+///
+/// # Lifetime
+///
+/// The `'de` lifetime of this trait is the lifetime of data that may be
+/// borrowed by the deserialized enum variant. See the page [Understanding
+/// deserializer lifetimes] for a more detailed explanation of these lifetimes.
+///
+/// [Understanding deserializer lifetimes]: https://serde.rs/lifetimes.html
+///
+/// # Example implementation
+///
+/// The [example data format] presented on the website demonstrates an
+/// implementation of `VariantAccess` for a basic JSON data format.
+///
+/// [example data format]: https://serde.rs/data-format.html
+pub trait VariantAccess<'de>: Sized {
+    /// The error type that can be returned if some error occurs during
+    /// deserialization. Must match the error type of our `EnumAccess`.
+    type Error: Error;
+
+    /// Called when deserializing a variant with no values.
+    ///
+    /// If the data contains a different type of variant, the following
+    /// `invalid_type` error should be constructed:
+    ///
+    /// ```edition2018
+    /// # use serde::de::{self, value, DeserializeSeed, Visitor, VariantAccess, Unexpected};
+    /// #
+    /// # struct X;
+    /// #
+    /// # impl<'de> VariantAccess<'de> for X {
+    /// #     type Error = value::Error;
+    /// #
+    /// fn unit_variant(self) -> Result<(), Self::Error> {
+    ///     // What the data actually contained; suppose it is a tuple variant.
+    ///     let unexp = Unexpected::TupleVariant;
+    ///     Err(de::Error::invalid_type(unexp, &"unit variant"))
+    /// }
+    /// #
+    /// #     fn newtype_variant_seed<T>(self, _: T) -> Result<T::Value, Self::Error>
+    /// #     where
+    /// #         T: DeserializeSeed<'de>,
+    /// #     { unimplemented!() }
+    /// #
+    /// #     fn tuple_variant<V>(self, _: usize, _: V) -> Result<V::Value, Self::Error>
+    /// #     where
+    /// #         V: Visitor<'de>,
+    /// #     { unimplemented!() }
+    /// #
+    /// #     fn struct_variant<V>(self, _: &[&str], _: V) -> Result<V::Value, Self::Error>
+    /// #     where
+    /// #         V: Visitor<'de>,
+    /// #     { unimplemented!() }
+    /// # }
+    /// ```
+    fn unit_variant(self) -> Result<(), Self::Error>;
+
+    /// Called when deserializing a variant with a single value.
+    ///
+    /// `Deserialize` implementations should typically use
+    /// `VariantAccess::newtype_variant` instead.
+    ///
+    /// If the data contains a different type of variant, the following
+    /// `invalid_type` error should be constructed:
+    ///
+    /// ```edition2018
+    /// # use serde::de::{self, value, DeserializeSeed, Visitor, VariantAccess, Unexpected};
+    /// #
+    /// # struct X;
+    /// #
+    /// # impl<'de> VariantAccess<'de> for X {
+    /// #     type Error = value::Error;
+    /// #
+    /// #     fn unit_variant(self) -> Result<(), Self::Error> {
+    /// #         unimplemented!()
+    /// #     }
+    /// #
+    /// fn newtype_variant_seed<T>(self, _seed: T) -> Result<T::Value, Self::Error>
+    /// where
+    ///     T: DeserializeSeed<'de>,
+    /// {
+    ///     // What the data actually contained; suppose it is a unit variant.
+    ///     let unexp = Unexpected::UnitVariant;
+    ///     Err(de::Error::invalid_type(unexp, &"newtype variant"))
+    /// }
+    /// #
+    /// #     fn tuple_variant<V>(self, _: usize, _: V) -> Result<V::Value, Self::Error>
+    /// #     where
+    /// #         V: Visitor<'de>,
+    /// #     { unimplemented!() }
+    /// #
+    /// #     fn struct_variant<V>(self, _: &[&str], _: V) -> Result<V::Value, Self::Error>
+    /// #     where
+    /// #         V: Visitor<'de>,
+    /// #     { unimplemented!() }
+    /// # }
+    /// ```
+    fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value, Self::Error>
+    where
+        T: DeserializeSeed<'de>;
+
+    /// Called when deserializing a variant with a single value.
+    ///
+    /// This method exists as a convenience for `Deserialize` implementations.
+    /// `VariantAccess` implementations should not override the default
+    /// behavior.
+    #[inline]
+    fn newtype_variant<T>(self) -> Result<T, Self::Error>
+    where
+        T: Deserialize<'de>,
+    {
+        self.newtype_variant_seed(PhantomData)
+    }
+
+    /// Called when deserializing a tuple-like variant.
+    ///
+    /// The `len` is the number of fields expected in the tuple variant.
+    ///
+    /// If the data contains a different type of variant, the following
+    /// `invalid_type` error should be constructed:
+    ///
+    /// ```edition2018
+    /// # use serde::de::{self, value, DeserializeSeed, Visitor, VariantAccess, Unexpected};
+    /// #
+    /// # struct X;
+    /// #
+    /// # impl<'de> VariantAccess<'de> for X {
+    /// #     type Error = value::Error;
+    /// #
+    /// #     fn unit_variant(self) -> Result<(), Self::Error> {
+    /// #         unimplemented!()
+    /// #     }
+    /// #
+    /// #     fn newtype_variant_seed<T>(self, _: T) -> Result<T::Value, Self::Error>
+    /// #     where
+    /// #         T: DeserializeSeed<'de>,
+    /// #     { unimplemented!() }
+    /// #
+    /// fn tuple_variant<V>(
+    ///     self,
+    ///     _len: usize,
+    ///     _visitor: V,
+    /// ) -> Result<V::Value, Self::Error>
+    /// where
+    ///     V: Visitor<'de>,
+    /// {
+    ///     // What the data actually contained; suppose it is a unit variant.
+    ///     let unexp = Unexpected::UnitVariant;
+    ///     Err(de::Error::invalid_type(unexp, &"tuple variant"))
+    /// }
+    /// #
+    /// #     fn struct_variant<V>(self, _: &[&str], _: V) -> Result<V::Value, Self::Error>
+    /// #     where
+    /// #         V: Visitor<'de>,
+    /// #     { unimplemented!() }
+    /// # }
+    /// ```
+    fn tuple_variant<V>(self, len: usize, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+
+    /// Called when deserializing a struct-like variant.
+    ///
+    /// The `fields` are the names of the fields of the struct variant.
+    ///
+    /// If the data contains a different type of variant, the following
+    /// `invalid_type` error should be constructed:
+    ///
+    /// ```edition2018
+    /// # use serde::de::{self, value, DeserializeSeed, Visitor, VariantAccess, Unexpected};
+    /// #
+    /// # struct X;
+    /// #
+    /// # impl<'de> VariantAccess<'de> for X {
+    /// #     type Error = value::Error;
+    /// #
+    /// #     fn unit_variant(self) -> Result<(), Self::Error> {
+    /// #         unimplemented!()
+    /// #     }
+    /// #
+    /// #     fn newtype_variant_seed<T>(self, _: T) -> Result<T::Value, Self::Error>
+    /// #     where
+    /// #         T: DeserializeSeed<'de>,
+    /// #     { unimplemented!() }
+    /// #
+    /// #     fn tuple_variant<V>(self, _: usize, _: V) -> Result<V::Value, Self::Error>
+    /// #     where
+    /// #         V: Visitor<'de>,
+    /// #     { unimplemented!() }
+    /// #
+    /// fn struct_variant<V>(
+    ///     self,
+    ///     _fields: &'static [&'static str],
+    ///     _visitor: V,
+    /// ) -> Result<V::Value, Self::Error>
+    /// where
+    ///     V: Visitor<'de>,
+    /// {
+    ///     // What the data actually contained; suppose it is a unit variant.
+    ///     let unexp = Unexpected::UnitVariant;
+    ///     Err(de::Error::invalid_type(unexp, &"struct variant"))
+    /// }
+    /// # }
+    /// ```
+    fn struct_variant<V>(
+        self,
+        fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// Converts an existing value into a `Deserializer` from which other values can
+/// be deserialized.
+///
+/// # Lifetime
+///
+/// The `'de` lifetime of this trait is the lifetime of data that may be
+/// borrowed from the resulting `Deserializer`. See the page [Understanding
+/// deserializer lifetimes] for a more detailed explanation of these lifetimes.
+///
+/// [Understanding deserializer lifetimes]: https://serde.rs/lifetimes.html
+///
+/// # Example
+///
+/// ```edition2018
+/// use std::str::FromStr;
+/// use serde::Deserialize;
+/// use serde::de::{value, IntoDeserializer};
+///
+/// #[derive(Deserialize)]
+/// enum Setting {
+///     On,
+///     Off,
+/// }
+///
+/// impl FromStr for Setting {
+///     type Err = value::Error;
+///
+///     fn from_str(s: &str) -> Result<Self, Self::Err> {
+///         Self::deserialize(s.into_deserializer())
+///     }
+/// }
+/// ```
+pub trait IntoDeserializer<'de, E: Error = value::Error> {
+    /// The type of the deserializer being converted into.
+    type Deserializer: Deserializer<'de, Error = E>;
+
+    /// Convert this value into a deserializer.
+    fn into_deserializer(self) -> Self::Deserializer;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// Used in error messages.
+///
+/// - expected `a`
+/// - expected `a` or `b`
+/// - expected one of `a`, `b`, `c`
+///
+/// The slice of names must not be empty.
+struct OneOf {
+    names: &'static [&'static str],
+}
+
+impl Display for OneOf {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        match self.names.len() {
+            0 => panic!(), // special case elsewhere
+            1 => write!(formatter, "`{}`", self.names[0]),
+            2 => write!(formatter, "`{}` or `{}`", self.names[0], self.names[1]),
+            _ => {
+                try!(write!(formatter, "one of "));
+                for (i, alt) in self.names.iter().enumerate() {
+                    if i > 0 {
+                        try!(write!(formatter, ", "));
+                    }
+                    try!(write!(formatter, "`{}`", alt));
+                }
+                Ok(())
+            }
+        }
+    }
+}
diff --git a/vendor/serde/src/de/seed.rs b/vendor/serde/src/de/seed.rs
new file mode 100644
index 000000000..13b7ea461
--- /dev/null
+++ b/vendor/serde/src/de/seed.rs
@@ -0,0 +1,19 @@
+use de::{Deserialize, DeserializeSeed, Deserializer};
+
+/// A DeserializeSeed helper for implementing deserialize_in_place Visitors.
+///
+/// Wraps a mutable reference and calls deserialize_in_place on it.
+pub struct InPlaceSeed<'a, T: 'a>(pub &'a mut T);
+
+impl<'a, 'de, T> DeserializeSeed<'de> for InPlaceSeed<'a, T>
+where
+    T: Deserialize<'de>,
+{
+    type Value = ();
+    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        T::deserialize_in_place(deserializer, self.0)
+    }
+}
diff --git a/vendor/serde/src/de/utf8.rs b/vendor/serde/src/de/utf8.rs
new file mode 100644
index 000000000..576fd03cf
--- /dev/null
+++ b/vendor/serde/src/de/utf8.rs
@@ -0,0 +1,46 @@
+use lib::*;
+
+const TAG_CONT: u8 = 0b1000_0000;
+const TAG_TWO_B: u8 = 0b1100_0000;
+const TAG_THREE_B: u8 = 0b1110_0000;
+const TAG_FOUR_B: u8 = 0b1111_0000;
+const MAX_ONE_B: u32 = 0x80;
+const MAX_TWO_B: u32 = 0x800;
+const MAX_THREE_B: u32 = 0x10000;
+
+#[inline]
+pub fn encode(c: char) -> Encode {
+    let code = c as u32;
+    let mut buf = [0; 4];
+    let pos = if code < MAX_ONE_B {
+        buf[3] = code as u8;
+        3
+    } else if code < MAX_TWO_B {
+        buf[2] = (code >> 6 & 0x1F) as u8 | TAG_TWO_B;
+        buf[3] = (code & 0x3F) as u8 | TAG_CONT;
+        2
+    } else if code < MAX_THREE_B {
+        buf[1] = (code >> 12 & 0x0F) as u8 | TAG_THREE_B;
+        buf[2] = (code >> 6 & 0x3F) as u8 | TAG_CONT;
+        buf[3] = (code & 0x3F) as u8 | TAG_CONT;
+        1
+    } else {
+        buf[0] = (code >> 18 & 0x07) as u8 | TAG_FOUR_B;
+        buf[1] = (code >> 12 & 0x3F) as u8 | TAG_CONT;
+        buf[2] = (code >> 6 & 0x3F) as u8 | TAG_CONT;
+        buf[3] = (code & 0x3F) as u8 | TAG_CONT;
+        0
+    };
+    Encode { buf: buf, pos: pos }
+}
+
+pub struct Encode {
+    buf: [u8; 4],
+    pos: usize,
+}
+
+impl Encode {
+    pub fn as_str(&self) -> &str {
+        str::from_utf8(&self.buf[self.pos..]).unwrap()
+    }
+}
diff --git a/vendor/serde/src/de/value.rs b/vendor/serde/src/de/value.rs
new file mode 100644
index 000000000..e7afdd8d1
--- /dev/null
+++ b/vendor/serde/src/de/value.rs
@@ -0,0 +1,1679 @@
+//! Building blocks for deserializing basic values using the `IntoDeserializer`
+//! trait.
+//!
+//! ```edition2018
+//! use std::str::FromStr;
+//! use serde::Deserialize;
+//! use serde::de::{value, IntoDeserializer};
+//!
+//! #[derive(Deserialize)]
+//! enum Setting {
+//!     On,
+//!     Off,
+//! }
+//!
+//! impl FromStr for Setting {
+//!     type Err = value::Error;
+//!
+//!     fn from_str(s: &str) -> Result<Self, Self::Err> {
+//!         Self::deserialize(s.into_deserializer())
+//!     }
+//! }
+//! ```
+
+use lib::*;
+
+use self::private::{First, Second};
+use __private::size_hint;
+use de::{self, Deserializer, Expected, IntoDeserializer, SeqAccess, Visitor};
+use ser;
+
+////////////////////////////////////////////////////////////////////////////////
+
+// For structs that contain a PhantomData. We do not want the trait
+// bound `E: Clone` inferred by derive(Clone).
+macro_rules! impl_copy_clone {
+    ($ty:ident $(<$lifetime:tt>)*) => {
+        impl<$($lifetime,)* E> Copy for $ty<$($lifetime,)* E> {}
+
+        impl<$($lifetime,)* E> Clone for $ty<$($lifetime,)* E> {
+            fn clone(&self) -> Self {
+                *self
+            }
+        }
+    };
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A minimal representation of all possible errors that can occur using the
+/// `IntoDeserializer` trait.
+#[derive(Clone, PartialEq)]
+pub struct Error {
+    err: ErrorImpl,
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+type ErrorImpl = Box<str>;
+#[cfg(not(any(feature = "std", feature = "alloc")))]
+type ErrorImpl = ();
+
+impl de::Error for Error {
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cold]
+    fn custom<T>(msg: T) -> Self
+    where
+        T: Display,
+    {
+        Error {
+            err: msg.to_string().into_boxed_str(),
+        }
+    }
+
+    #[cfg(not(any(feature = "std", feature = "alloc")))]
+    #[cold]
+    fn custom<T>(msg: T) -> Self
+    where
+        T: Display,
+    {
+        let _ = msg;
+        Error { err: () }
+    }
+}
+
+impl ser::Error for Error {
+    #[cold]
+    fn custom<T>(msg: T) -> Self
+    where
+        T: Display,
+    {
+        de::Error::custom(msg)
+    }
+}
+
+impl Display for Error {
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str(&self.err)
+    }
+
+    #[cfg(not(any(feature = "std", feature = "alloc")))]
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("Serde deserialization error")
+    }
+}
+
+impl Debug for Error {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        let mut debug = formatter.debug_tuple("Error");
+        #[cfg(any(feature = "std", feature = "alloc"))]
+        debug.field(&self.err);
+        debug.finish()
+    }
+}
+
+#[cfg(feature = "std")]
+impl error::Error for Error {
+    fn description(&self) -> &str {
+        &self.err
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<'de, E> IntoDeserializer<'de, E> for ()
+where
+    E: de::Error,
+{
+    type Deserializer = UnitDeserializer<E>;
+
+    fn into_deserializer(self) -> UnitDeserializer<E> {
+        UnitDeserializer::new()
+    }
+}
+
+/// A deserializer holding a `()`.
+pub struct UnitDeserializer<E> {
+    marker: PhantomData<E>,
+}
+
+impl_copy_clone!(UnitDeserializer);
+
+impl<E> UnitDeserializer<E> {
+    #[allow(missing_docs)]
+    pub fn new() -> Self {
+        UnitDeserializer {
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'de, E> de::Deserializer<'de> for UnitDeserializer<E>
+where
+    E: de::Error,
+{
+    type Error = E;
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf unit unit_struct newtype_struct seq tuple tuple_struct
+        map struct enum identifier ignored_any
+    }
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_unit()
+    }
+
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_none()
+    }
+}
+
+impl<E> Debug for UnitDeserializer<E> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.debug_struct("UnitDeserializer").finish()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A deserializer that cannot be instantiated.
+#[cfg(feature = "unstable")]
+pub struct NeverDeserializer<E> {
+    never: !,
+    marker: PhantomData<E>,
+}
+
+#[cfg(feature = "unstable")]
+impl<'de, E> IntoDeserializer<'de, E> for !
+where
+    E: de::Error,
+{
+    type Deserializer = NeverDeserializer<E>;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        self
+    }
+}
+
+#[cfg(feature = "unstable")]
+impl<'de, E> de::Deserializer<'de> for NeverDeserializer<E>
+where
+    E: de::Error,
+{
+    type Error = E;
+
+    fn deserialize_any<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.never
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct enum identifier ignored_any
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+macro_rules! primitive_deserializer {
+    ($ty:ty, $doc:tt, $name:ident, $method:ident $($cast:tt)*) => {
+        #[doc = "A deserializer holding"]
+        #[doc = $doc]
+        pub struct $name<E> {
+            value: $ty,
+            marker: PhantomData<E>
+        }
+
+        impl_copy_clone!($name);
+
+        impl<'de, E> IntoDeserializer<'de, E> for $ty
+        where
+            E: de::Error,
+        {
+            type Deserializer = $name<E>;
+
+            fn into_deserializer(self) -> $name<E> {
+                $name::new(self)
+            }
+        }
+
+        impl<E> $name<E> {
+            #[allow(missing_docs)]
+            pub fn new(value: $ty) -> Self {
+                $name {
+                    value: value,
+                    marker: PhantomData,
+                }
+            }
+        }
+
+        impl<'de, E> de::Deserializer<'de> for $name<E>
+        where
+            E: de::Error,
+        {
+            type Error = E;
+
+            forward_to_deserialize_any! {
+                bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str
+                string bytes byte_buf option unit unit_struct newtype_struct seq
+                tuple tuple_struct map struct enum identifier ignored_any
+            }
+
+            fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+            where
+                V: de::Visitor<'de>,
+            {
+                visitor.$method(self.value $($cast)*)
+            }
+        }
+
+        impl<E> Debug for $name<E> {
+            fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter
+                    .debug_struct(stringify!($name))
+                    .field("value", &self.value)
+                    .finish()
+            }
+        }
+    }
+}
+
+primitive_deserializer!(bool, "a `bool`.", BoolDeserializer, visit_bool);
+primitive_deserializer!(i8, "an `i8`.", I8Deserializer, visit_i8);
+primitive_deserializer!(i16, "an `i16`.", I16Deserializer, visit_i16);
+primitive_deserializer!(i32, "an `i32`.", I32Deserializer, visit_i32);
+primitive_deserializer!(i64, "an `i64`.", I64Deserializer, visit_i64);
+primitive_deserializer!(isize, "an `isize`.", IsizeDeserializer, visit_i64 as i64);
+primitive_deserializer!(u8, "a `u8`.", U8Deserializer, visit_u8);
+primitive_deserializer!(u16, "a `u16`.", U16Deserializer, visit_u16);
+primitive_deserializer!(u64, "a `u64`.", U64Deserializer, visit_u64);
+primitive_deserializer!(usize, "a `usize`.", UsizeDeserializer, visit_u64 as u64);
+primitive_deserializer!(f32, "an `f32`.", F32Deserializer, visit_f32);
+primitive_deserializer!(f64, "an `f64`.", F64Deserializer, visit_f64);
+primitive_deserializer!(char, "a `char`.", CharDeserializer, visit_char);
+
+serde_if_integer128! {
+    primitive_deserializer!(i128, "an `i128`.", I128Deserializer, visit_i128);
+    primitive_deserializer!(u128, "a `u128`.", U128Deserializer, visit_u128);
+}
+
+/// A deserializer holding a `u32`.
+pub struct U32Deserializer<E> {
+    value: u32,
+    marker: PhantomData<E>,
+}
+
+impl_copy_clone!(U32Deserializer);
+
+impl<'de, E> IntoDeserializer<'de, E> for u32
+where
+    E: de::Error,
+{
+    type Deserializer = U32Deserializer<E>;
+
+    fn into_deserializer(self) -> U32Deserializer<E> {
+        U32Deserializer::new(self)
+    }
+}
+
+impl<E> U32Deserializer<E> {
+    #[allow(missing_docs)]
+    pub fn new(value: u32) -> Self {
+        U32Deserializer {
+            value: value,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'de, E> de::Deserializer<'de> for U32Deserializer<E>
+where
+    E: de::Error,
+{
+    type Error = E;
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct identifier ignored_any
+    }
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_u32(self.value)
+    }
+
+    fn deserialize_enum<V>(
+        self,
+        name: &str,
+        variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        let _ = name;
+        let _ = variants;
+        visitor.visit_enum(self)
+    }
+}
+
+impl<'de, E> de::EnumAccess<'de> for U32Deserializer<E>
+where
+    E: de::Error,
+{
+    type Error = E;
+    type Variant = private::UnitOnly<E>;
+
+    fn variant_seed<T>(self, seed: T) -> Result<(T::Value, Self::Variant), Self::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        seed.deserialize(self).map(private::unit_only)
+    }
+}
+
+impl<E> Debug for U32Deserializer<E> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter
+            .debug_struct("U32Deserializer")
+            .field("value", &self.value)
+            .finish()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A deserializer holding a `&str`.
+pub struct StrDeserializer<'a, E> {
+    value: &'a str,
+    marker: PhantomData<E>,
+}
+
+impl_copy_clone!(StrDeserializer<'de>);
+
+impl<'de, 'a, E> IntoDeserializer<'de, E> for &'a str
+where
+    E: de::Error,
+{
+    type Deserializer = StrDeserializer<'a, E>;
+
+    fn into_deserializer(self) -> StrDeserializer<'a, E> {
+        StrDeserializer::new(self)
+    }
+}
+
+impl<'a, E> StrDeserializer<'a, E> {
+    #[allow(missing_docs)]
+    pub fn new(value: &'a str) -> Self {
+        StrDeserializer {
+            value: value,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'de, 'a, E> de::Deserializer<'de> for StrDeserializer<'a, E>
+where
+    E: de::Error,
+{
+    type Error = E;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_str(self.value)
+    }
+
+    fn deserialize_enum<V>(
+        self,
+        name: &str,
+        variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        let _ = name;
+        let _ = variants;
+        visitor.visit_enum(self)
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct identifier ignored_any
+    }
+}
+
+impl<'de, 'a, E> de::EnumAccess<'de> for StrDeserializer<'a, E>
+where
+    E: de::Error,
+{
+    type Error = E;
+    type Variant = private::UnitOnly<E>;
+
+    fn variant_seed<T>(self, seed: T) -> Result<(T::Value, Self::Variant), Self::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        seed.deserialize(self).map(private::unit_only)
+    }
+}
+
+impl<'a, E> Debug for StrDeserializer<'a, E> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter
+            .debug_struct("StrDeserializer")
+            .field("value", &self.value)
+            .finish()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A deserializer holding a `&str` with a lifetime tied to another
+/// deserializer.
+pub struct BorrowedStrDeserializer<'de, E> {
+    value: &'de str,
+    marker: PhantomData<E>,
+}
+
+impl_copy_clone!(BorrowedStrDeserializer<'de>);
+
+impl<'de, E> BorrowedStrDeserializer<'de, E> {
+    /// Create a new borrowed deserializer from the given string.
+    pub fn new(value: &'de str) -> BorrowedStrDeserializer<'de, E> {
+        BorrowedStrDeserializer {
+            value: value,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'de, E> de::Deserializer<'de> for BorrowedStrDeserializer<'de, E>
+where
+    E: de::Error,
+{
+    type Error = E;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_borrowed_str(self.value)
+    }
+
+    fn deserialize_enum<V>(
+        self,
+        name: &str,
+        variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        let _ = name;
+        let _ = variants;
+        visitor.visit_enum(self)
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct identifier ignored_any
+    }
+}
+
+impl<'de, E> de::EnumAccess<'de> for BorrowedStrDeserializer<'de, E>
+where
+    E: de::Error,
+{
+    type Error = E;
+    type Variant = private::UnitOnly<E>;
+
+    fn variant_seed<T>(self, seed: T) -> Result<(T::Value, Self::Variant), Self::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        seed.deserialize(self).map(private::unit_only)
+    }
+}
+
+impl<'de, E> Debug for BorrowedStrDeserializer<'de, E> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter
+            .debug_struct("BorrowedStrDeserializer")
+            .field("value", &self.value)
+            .finish()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A deserializer holding a `String`.
+#[cfg(any(feature = "std", feature = "alloc"))]
+pub struct StringDeserializer<E> {
+    value: String,
+    marker: PhantomData<E>,
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<E> Clone for StringDeserializer<E> {
+    fn clone(&self) -> Self {
+        StringDeserializer {
+            value: self.value.clone(),
+            marker: PhantomData,
+        }
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'de, E> IntoDeserializer<'de, E> for String
+where
+    E: de::Error,
+{
+    type Deserializer = StringDeserializer<E>;
+
+    fn into_deserializer(self) -> StringDeserializer<E> {
+        StringDeserializer::new(self)
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<E> StringDeserializer<E> {
+    #[allow(missing_docs)]
+    pub fn new(value: String) -> Self {
+        StringDeserializer {
+            value: value,
+            marker: PhantomData,
+        }
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'de, E> de::Deserializer<'de> for StringDeserializer<E>
+where
+    E: de::Error,
+{
+    type Error = E;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_string(self.value)
+    }
+
+    fn deserialize_enum<V>(
+        self,
+        name: &str,
+        variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        let _ = name;
+        let _ = variants;
+        visitor.visit_enum(self)
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct identifier ignored_any
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'de, E> de::EnumAccess<'de> for StringDeserializer<E>
+where
+    E: de::Error,
+{
+    type Error = E;
+    type Variant = private::UnitOnly<E>;
+
+    fn variant_seed<T>(self, seed: T) -> Result<(T::Value, Self::Variant), Self::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        seed.deserialize(self).map(private::unit_only)
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<E> Debug for StringDeserializer<E> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter
+            .debug_struct("StringDeserializer")
+            .field("value", &self.value)
+            .finish()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A deserializer holding a `Cow<str>`.
+#[cfg(any(feature = "std", feature = "alloc"))]
+pub struct CowStrDeserializer<'a, E> {
+    value: Cow<'a, str>,
+    marker: PhantomData<E>,
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'a, E> Clone for CowStrDeserializer<'a, E> {
+    fn clone(&self) -> Self {
+        CowStrDeserializer {
+            value: self.value.clone(),
+            marker: PhantomData,
+        }
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'de, 'a, E> IntoDeserializer<'de, E> for Cow<'a, str>
+where
+    E: de::Error,
+{
+    type Deserializer = CowStrDeserializer<'a, E>;
+
+    fn into_deserializer(self) -> CowStrDeserializer<'a, E> {
+        CowStrDeserializer::new(self)
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'a, E> CowStrDeserializer<'a, E> {
+    #[allow(missing_docs)]
+    pub fn new(value: Cow<'a, str>) -> Self {
+        CowStrDeserializer {
+            value: value,
+            marker: PhantomData,
+        }
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'de, 'a, E> de::Deserializer<'de> for CowStrDeserializer<'a, E>
+where
+    E: de::Error,
+{
+    type Error = E;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            Cow::Borrowed(string) => visitor.visit_str(string),
+            Cow::Owned(string) => visitor.visit_string(string),
+        }
+    }
+
+    fn deserialize_enum<V>(
+        self,
+        name: &str,
+        variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        let _ = name;
+        let _ = variants;
+        visitor.visit_enum(self)
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct identifier ignored_any
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'de, 'a, E> de::EnumAccess<'de> for CowStrDeserializer<'a, E>
+where
+    E: de::Error,
+{
+    type Error = E;
+    type Variant = private::UnitOnly<E>;
+
+    fn variant_seed<T>(self, seed: T) -> Result<(T::Value, Self::Variant), Self::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        seed.deserialize(self).map(private::unit_only)
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'a, E> Debug for CowStrDeserializer<'a, E> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter
+            .debug_struct("CowStrDeserializer")
+            .field("value", &self.value)
+            .finish()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A deserializer holding a `&[u8]`. Always calls [`Visitor::visit_bytes`].
+pub struct BytesDeserializer<'a, E> {
+    value: &'a [u8],
+    marker: PhantomData<E>,
+}
+
+impl<'a, E> BytesDeserializer<'a, E> {
+    /// Create a new deserializer from the given bytes.
+    pub fn new(value: &'a [u8]) -> Self {
+        BytesDeserializer {
+            value: value,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl_copy_clone!(BytesDeserializer<'a>);
+
+impl<'de, 'a, E> IntoDeserializer<'de, E> for &'a [u8]
+where
+    E: de::Error,
+{
+    type Deserializer = BytesDeserializer<'a, E>;
+
+    fn into_deserializer(self) -> BytesDeserializer<'a, E> {
+        BytesDeserializer::new(self)
+    }
+}
+
+impl<'de, 'a, E> Deserializer<'de> for BytesDeserializer<'a, E>
+where
+    E: de::Error,
+{
+    type Error = E;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        visitor.visit_bytes(self.value)
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct enum identifier ignored_any
+    }
+}
+
+impl<'a, E> Debug for BytesDeserializer<'a, E> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter
+            .debug_struct("BytesDeserializer")
+            .field("value", &self.value)
+            .finish()
+    }
+}
+
+/// A deserializer holding a `&[u8]` with a lifetime tied to another
+/// deserializer. Always calls [`Visitor::visit_borrowed_bytes`].
+pub struct BorrowedBytesDeserializer<'de, E> {
+    value: &'de [u8],
+    marker: PhantomData<E>,
+}
+
+impl<'de, E> BorrowedBytesDeserializer<'de, E> {
+    /// Create a new borrowed deserializer from the given borrowed bytes.
+    pub fn new(value: &'de [u8]) -> Self {
+        BorrowedBytesDeserializer {
+            value: value,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl_copy_clone!(BorrowedBytesDeserializer<'de>);
+
+impl<'de, E> Deserializer<'de> for BorrowedBytesDeserializer<'de, E>
+where
+    E: de::Error,
+{
+    type Error = E;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        visitor.visit_borrowed_bytes(self.value)
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct enum identifier ignored_any
+    }
+}
+
+impl<'de, E> Debug for BorrowedBytesDeserializer<'de, E> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter
+            .debug_struct("BorrowedBytesDeserializer")
+            .field("value", &self.value)
+            .finish()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A deserializer that iterates over a sequence.
+#[derive(Clone)]
+pub struct SeqDeserializer<I, E> {
+    iter: iter::Fuse<I>,
+    count: usize,
+    marker: PhantomData<E>,
+}
+
+impl<I, E> SeqDeserializer<I, E>
+where
+    I: Iterator,
+{
+    /// Construct a new `SeqDeserializer<I, E>`.
+    pub fn new(iter: I) -> Self {
+        SeqDeserializer {
+            iter: iter.fuse(),
+            count: 0,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<I, E> SeqDeserializer<I, E>
+where
+    I: Iterator,
+    E: de::Error,
+{
+    /// Check for remaining elements after passing a `SeqDeserializer` to
+    /// `Visitor::visit_seq`.
+    pub fn end(self) -> Result<(), E> {
+        let remaining = self.iter.count();
+        if remaining == 0 {
+            Ok(())
+        } else {
+            // First argument is the number of elements in the data, second
+            // argument is the number of elements expected by the Deserialize.
+            Err(de::Error::invalid_length(
+                self.count + remaining,
+                &ExpectedInSeq(self.count),
+            ))
+        }
+    }
+}
+
+impl<'de, I, T, E> de::Deserializer<'de> for SeqDeserializer<I, E>
+where
+    I: Iterator<Item = T>,
+    T: IntoDeserializer<'de, E>,
+    E: de::Error,
+{
+    type Error = E;
+
+    fn deserialize_any<V>(mut self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        let v = try!(visitor.visit_seq(&mut self));
+        try!(self.end());
+        Ok(v)
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct enum identifier ignored_any
+    }
+}
+
+impl<'de, I, T, E> de::SeqAccess<'de> for SeqDeserializer<I, E>
+where
+    I: Iterator<Item = T>,
+    T: IntoDeserializer<'de, E>,
+    E: de::Error,
+{
+    type Error = E;
+
+    fn next_element_seed<V>(&mut self, seed: V) -> Result<Option<V::Value>, Self::Error>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        match self.iter.next() {
+            Some(value) => {
+                self.count += 1;
+                seed.deserialize(value.into_deserializer()).map(Some)
+            }
+            None => Ok(None),
+        }
+    }
+
+    fn size_hint(&self) -> Option<usize> {
+        size_hint::from_bounds(&self.iter)
+    }
+}
+
+struct ExpectedInSeq(usize);
+
+impl Expected for ExpectedInSeq {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        if self.0 == 1 {
+            write!(formatter, "1 element in sequence")
+        } else {
+            write!(formatter, "{} elements in sequence", self.0)
+        }
+    }
+}
+
+impl<I, E> Debug for SeqDeserializer<I, E>
+where
+    I: Debug,
+{
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter
+            .debug_struct("SeqDeserializer")
+            .field("iter", &self.iter)
+            .field("count", &self.count)
+            .finish()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'de, T, E> IntoDeserializer<'de, E> for Vec<T>
+where
+    T: IntoDeserializer<'de, E>,
+    E: de::Error,
+{
+    type Deserializer = SeqDeserializer<<Self as IntoIterator>::IntoIter, E>;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        SeqDeserializer::new(self.into_iter())
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'de, T, E> IntoDeserializer<'de, E> for BTreeSet<T>
+where
+    T: IntoDeserializer<'de, E> + Eq + Ord,
+    E: de::Error,
+{
+    type Deserializer = SeqDeserializer<<Self as IntoIterator>::IntoIter, E>;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        SeqDeserializer::new(self.into_iter())
+    }
+}
+
+#[cfg(feature = "std")]
+impl<'de, T, S, E> IntoDeserializer<'de, E> for HashSet<T, S>
+where
+    T: IntoDeserializer<'de, E> + Eq + Hash,
+    S: BuildHasher,
+    E: de::Error,
+{
+    type Deserializer = SeqDeserializer<<Self as IntoIterator>::IntoIter, E>;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        SeqDeserializer::new(self.into_iter())
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A deserializer holding a `SeqAccess`.
+#[derive(Clone, Debug)]
+pub struct SeqAccessDeserializer<A> {
+    seq: A,
+}
+
+impl<A> SeqAccessDeserializer<A> {
+    /// Construct a new `SeqAccessDeserializer<A>`.
+    pub fn new(seq: A) -> Self {
+        SeqAccessDeserializer { seq: seq }
+    }
+}
+
+impl<'de, A> de::Deserializer<'de> for SeqAccessDeserializer<A>
+where
+    A: de::SeqAccess<'de>,
+{
+    type Error = A::Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_seq(self.seq)
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct enum identifier ignored_any
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A deserializer that iterates over a map.
+pub struct MapDeserializer<'de, I, E>
+where
+    I: Iterator,
+    I::Item: private::Pair,
+{
+    iter: iter::Fuse<I>,
+    value: Option<Second<I::Item>>,
+    count: usize,
+    lifetime: PhantomData<&'de ()>,
+    error: PhantomData<E>,
+}
+
+impl<'de, I, E> MapDeserializer<'de, I, E>
+where
+    I: Iterator,
+    I::Item: private::Pair,
+{
+    /// Construct a new `MapDeserializer<I, E>`.
+    pub fn new(iter: I) -> Self {
+        MapDeserializer {
+            iter: iter.fuse(),
+            value: None,
+            count: 0,
+            lifetime: PhantomData,
+            error: PhantomData,
+        }
+    }
+}
+
+impl<'de, I, E> MapDeserializer<'de, I, E>
+where
+    I: Iterator,
+    I::Item: private::Pair,
+    E: de::Error,
+{
+    /// Check for remaining elements after passing a `MapDeserializer` to
+    /// `Visitor::visit_map`.
+    pub fn end(self) -> Result<(), E> {
+        let remaining = self.iter.count();
+        if remaining == 0 {
+            Ok(())
+        } else {
+            // First argument is the number of elements in the data, second
+            // argument is the number of elements expected by the Deserialize.
+            Err(de::Error::invalid_length(
+                self.count + remaining,
+                &ExpectedInMap(self.count),
+            ))
+        }
+    }
+}
+
+impl<'de, I, E> MapDeserializer<'de, I, E>
+where
+    I: Iterator,
+    I::Item: private::Pair,
+{
+    fn next_pair(&mut self) -> Option<(First<I::Item>, Second<I::Item>)> {
+        match self.iter.next() {
+            Some(kv) => {
+                self.count += 1;
+                Some(private::Pair::split(kv))
+            }
+            None => None,
+        }
+    }
+}
+
+impl<'de, I, E> de::Deserializer<'de> for MapDeserializer<'de, I, E>
+where
+    I: Iterator,
+    I::Item: private::Pair,
+    First<I::Item>: IntoDeserializer<'de, E>,
+    Second<I::Item>: IntoDeserializer<'de, E>,
+    E: de::Error,
+{
+    type Error = E;
+
+    fn deserialize_any<V>(mut self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        let value = try!(visitor.visit_map(&mut self));
+        try!(self.end());
+        Ok(value)
+    }
+
+    fn deserialize_seq<V>(mut self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        let value = try!(visitor.visit_seq(&mut self));
+        try!(self.end());
+        Ok(value)
+    }
+
+    fn deserialize_tuple<V>(self, len: usize, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        let _ = len;
+        self.deserialize_seq(visitor)
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct tuple_struct map
+        struct enum identifier ignored_any
+    }
+}
+
+impl<'de, I, E> de::MapAccess<'de> for MapDeserializer<'de, I, E>
+where
+    I: Iterator,
+    I::Item: private::Pair,
+    First<I::Item>: IntoDeserializer<'de, E>,
+    Second<I::Item>: IntoDeserializer<'de, E>,
+    E: de::Error,
+{
+    type Error = E;
+
+    fn next_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        match self.next_pair() {
+            Some((key, value)) => {
+                self.value = Some(value);
+                seed.deserialize(key.into_deserializer()).map(Some)
+            }
+            None => Ok(None),
+        }
+    }
+
+    fn next_value_seed<T>(&mut self, seed: T) -> Result<T::Value, Self::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        let value = self.value.take();
+        // Panic because this indicates a bug in the program rather than an
+        // expected failure.
+        let value = value.expect("MapAccess::next_value called before next_key");
+        seed.deserialize(value.into_deserializer())
+    }
+
+    fn next_entry_seed<TK, TV>(
+        &mut self,
+        kseed: TK,
+        vseed: TV,
+    ) -> Result<Option<(TK::Value, TV::Value)>, Self::Error>
+    where
+        TK: de::DeserializeSeed<'de>,
+        TV: de::DeserializeSeed<'de>,
+    {
+        match self.next_pair() {
+            Some((key, value)) => {
+                let key = try!(kseed.deserialize(key.into_deserializer()));
+                let value = try!(vseed.deserialize(value.into_deserializer()));
+                Ok(Some((key, value)))
+            }
+            None => Ok(None),
+        }
+    }
+
+    fn size_hint(&self) -> Option<usize> {
+        size_hint::from_bounds(&self.iter)
+    }
+}
+
+impl<'de, I, E> de::SeqAccess<'de> for MapDeserializer<'de, I, E>
+where
+    I: Iterator,
+    I::Item: private::Pair,
+    First<I::Item>: IntoDeserializer<'de, E>,
+    Second<I::Item>: IntoDeserializer<'de, E>,
+    E: de::Error,
+{
+    type Error = E;
+
+    fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        match self.next_pair() {
+            Some((k, v)) => {
+                let de = PairDeserializer(k, v, PhantomData);
+                seed.deserialize(de).map(Some)
+            }
+            None => Ok(None),
+        }
+    }
+
+    fn size_hint(&self) -> Option<usize> {
+        size_hint::from_bounds(&self.iter)
+    }
+}
+
+// Cannot #[derive(Clone)] because of the bound `Second<I::Item>: Clone`.
+impl<'de, I, E> Clone for MapDeserializer<'de, I, E>
+where
+    I: Iterator + Clone,
+    I::Item: private::Pair,
+    Second<I::Item>: Clone,
+{
+    fn clone(&self) -> Self {
+        MapDeserializer {
+            iter: self.iter.clone(),
+            value: self.value.clone(),
+            count: self.count,
+            lifetime: self.lifetime,
+            error: self.error,
+        }
+    }
+}
+
+impl<'de, I, E> Debug for MapDeserializer<'de, I, E>
+where
+    I: Iterator + Debug,
+    I::Item: private::Pair,
+    Second<I::Item>: Debug,
+{
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter
+            .debug_struct("MapDeserializer")
+            .field("iter", &self.iter)
+            .field("value", &self.value)
+            .field("count", &self.count)
+            .finish()
+    }
+}
+
+// Used in the `impl SeqAccess for MapDeserializer` to visit the map as a
+// sequence of pairs.
+struct PairDeserializer<A, B, E>(A, B, PhantomData<E>);
+
+impl<'de, A, B, E> de::Deserializer<'de> for PairDeserializer<A, B, E>
+where
+    A: IntoDeserializer<'de, E>,
+    B: IntoDeserializer<'de, E>,
+    E: de::Error,
+{
+    type Error = E;
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct tuple_struct map
+        struct enum identifier ignored_any
+    }
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_seq(visitor)
+    }
+
+    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        let mut pair_visitor = PairVisitor(Some(self.0), Some(self.1), PhantomData);
+        let pair = try!(visitor.visit_seq(&mut pair_visitor));
+        if pair_visitor.1.is_none() {
+            Ok(pair)
+        } else {
+            let remaining = pair_visitor.size_hint().unwrap();
+            // First argument is the number of elements in the data, second
+            // argument is the number of elements expected by the Deserialize.
+            Err(de::Error::invalid_length(2, &ExpectedInSeq(2 - remaining)))
+        }
+    }
+
+    fn deserialize_tuple<V>(self, len: usize, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if len == 2 {
+            self.deserialize_seq(visitor)
+        } else {
+            // First argument is the number of elements in the data, second
+            // argument is the number of elements expected by the Deserialize.
+            Err(de::Error::invalid_length(2, &ExpectedInSeq(len)))
+        }
+    }
+}
+
+struct PairVisitor<A, B, E>(Option<A>, Option<B>, PhantomData<E>);
+
+impl<'de, A, B, E> de::SeqAccess<'de> for PairVisitor<A, B, E>
+where
+    A: IntoDeserializer<'de, E>,
+    B: IntoDeserializer<'de, E>,
+    E: de::Error,
+{
+    type Error = E;
+
+    fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        if let Some(k) = self.0.take() {
+            seed.deserialize(k.into_deserializer()).map(Some)
+        } else if let Some(v) = self.1.take() {
+            seed.deserialize(v.into_deserializer()).map(Some)
+        } else {
+            Ok(None)
+        }
+    }
+
+    fn size_hint(&self) -> Option<usize> {
+        if self.0.is_some() {
+            Some(2)
+        } else if self.1.is_some() {
+            Some(1)
+        } else {
+            Some(0)
+        }
+    }
+}
+
+struct ExpectedInMap(usize);
+
+impl Expected for ExpectedInMap {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        if self.0 == 1 {
+            write!(formatter, "1 element in map")
+        } else {
+            write!(formatter, "{} elements in map", self.0)
+        }
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'de, K, V, E> IntoDeserializer<'de, E> for BTreeMap<K, V>
+where
+    K: IntoDeserializer<'de, E> + Eq + Ord,
+    V: IntoDeserializer<'de, E>,
+    E: de::Error,
+{
+    type Deserializer = MapDeserializer<'de, <Self as IntoIterator>::IntoIter, E>;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        MapDeserializer::new(self.into_iter())
+    }
+}
+
+#[cfg(feature = "std")]
+impl<'de, K, V, S, E> IntoDeserializer<'de, E> for HashMap<K, V, S>
+where
+    K: IntoDeserializer<'de, E> + Eq + Hash,
+    V: IntoDeserializer<'de, E>,
+    S: BuildHasher,
+    E: de::Error,
+{
+    type Deserializer = MapDeserializer<'de, <Self as IntoIterator>::IntoIter, E>;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        MapDeserializer::new(self.into_iter())
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A deserializer holding a `MapAccess`.
+#[derive(Clone, Debug)]
+pub struct MapAccessDeserializer<A> {
+    map: A,
+}
+
+impl<A> MapAccessDeserializer<A> {
+    /// Construct a new `MapAccessDeserializer<A>`.
+    pub fn new(map: A) -> Self {
+        MapAccessDeserializer { map: map }
+    }
+}
+
+impl<'de, A> de::Deserializer<'de> for MapAccessDeserializer<A>
+where
+    A: de::MapAccess<'de>,
+{
+    type Error = A::Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_map(self.map)
+    }
+
+    fn deserialize_enum<V>(
+        self,
+        _name: &str,
+        _variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_enum(self)
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct identifier ignored_any
+    }
+}
+
+impl<'de, A> de::EnumAccess<'de> for MapAccessDeserializer<A>
+where
+    A: de::MapAccess<'de>,
+{
+    type Error = A::Error;
+    type Variant = private::MapAsEnum<A>;
+
+    fn variant_seed<T>(mut self, seed: T) -> Result<(T::Value, Self::Variant), Self::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        match self.map.next_key_seed(seed)? {
+            Some(key) => Ok((key, private::map_as_enum(self.map))),
+            None => Err(de::Error::invalid_type(de::Unexpected::Map, &"enum")),
+        }
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+mod private {
+    use lib::*;
+
+    use de::{self, DeserializeSeed, Deserializer, MapAccess, Unexpected, VariantAccess, Visitor};
+
+    pub struct UnitOnly<E> {
+        marker: PhantomData<E>,
+    }
+
+    pub fn unit_only<T, E>(t: T) -> (T, UnitOnly<E>) {
+        (
+            t,
+            UnitOnly {
+                marker: PhantomData,
+            },
+        )
+    }
+
+    impl<'de, E> de::VariantAccess<'de> for UnitOnly<E>
+    where
+        E: de::Error,
+    {
+        type Error = E;
+
+        fn unit_variant(self) -> Result<(), Self::Error> {
+            Ok(())
+        }
+
+        fn newtype_variant_seed<T>(self, _seed: T) -> Result<T::Value, Self::Error>
+        where
+            T: de::DeserializeSeed<'de>,
+        {
+            Err(de::Error::invalid_type(
+                Unexpected::UnitVariant,
+                &"newtype variant",
+            ))
+        }
+
+        fn tuple_variant<V>(self, _len: usize, _visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: de::Visitor<'de>,
+        {
+            Err(de::Error::invalid_type(
+                Unexpected::UnitVariant,
+                &"tuple variant",
+            ))
+        }
+
+        fn struct_variant<V>(
+            self,
+            _fields: &'static [&'static str],
+            _visitor: V,
+        ) -> Result<V::Value, Self::Error>
+        where
+            V: de::Visitor<'de>,
+        {
+            Err(de::Error::invalid_type(
+                Unexpected::UnitVariant,
+                &"struct variant",
+            ))
+        }
+    }
+
+    pub struct MapAsEnum<A> {
+        map: A,
+    }
+
+    pub fn map_as_enum<A>(map: A) -> MapAsEnum<A> {
+        MapAsEnum { map: map }
+    }
+
+    impl<'de, A> VariantAccess<'de> for MapAsEnum<A>
+    where
+        A: MapAccess<'de>,
+    {
+        type Error = A::Error;
+
+        fn unit_variant(mut self) -> Result<(), Self::Error> {
+            self.map.next_value()
+        }
+
+        fn newtype_variant_seed<T>(mut self, seed: T) -> Result<T::Value, Self::Error>
+        where
+            T: DeserializeSeed<'de>,
+        {
+            self.map.next_value_seed(seed)
+        }
+
+        fn tuple_variant<V>(mut self, len: usize, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.map.next_value_seed(SeedTupleVariant {
+                len: len,
+                visitor: visitor,
+            })
+        }
+
+        fn struct_variant<V>(
+            mut self,
+            _fields: &'static [&'static str],
+            visitor: V,
+        ) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.map
+                .next_value_seed(SeedStructVariant { visitor: visitor })
+        }
+    }
+
+    struct SeedTupleVariant<V> {
+        len: usize,
+        visitor: V,
+    }
+
+    impl<'de, V> DeserializeSeed<'de> for SeedTupleVariant<V>
+    where
+        V: Visitor<'de>,
+    {
+        type Value = V::Value;
+
+        fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            deserializer.deserialize_tuple(self.len, self.visitor)
+        }
+    }
+
+    struct SeedStructVariant<V> {
+        visitor: V,
+    }
+
+    impl<'de, V> DeserializeSeed<'de> for SeedStructVariant<V>
+    where
+        V: Visitor<'de>,
+    {
+        type Value = V::Value;
+
+        fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            deserializer.deserialize_map(self.visitor)
+        }
+    }
+
+    /// Avoid having to restate the generic types on `MapDeserializer`. The
+    /// `Iterator::Item` contains enough information to figure out K and V.
+    pub trait Pair {
+        type First;
+        type Second;
+        fn split(self) -> (Self::First, Self::Second);
+    }
+
+    impl<A, B> Pair for (A, B) {
+        type First = A;
+        type Second = B;
+        fn split(self) -> (A, B) {
+            self
+        }
+    }
+
+    pub type First<T> = <T as Pair>::First;
+    pub type Second<T> = <T as Pair>::Second;
+}