Adding upstream version 124.0.1.upstream/124.0.1

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

4 files changed, 3415 insertions, 0 deletions

diff --git a/third_party/rust/serde/src/ser/fmt.rs b/third_party/rust/serde/src/ser/fmt.rs
new file mode 100644
index 0000000000..0650ab6f12
--- /dev/null
+++ b/third_party/rust/serde/src/ser/fmt.rs
@@ -0,0 +1,170 @@
+use crate::lib::*;
+use crate::ser::{Error, Impossible, Serialize, Serializer};
+
+impl Error for fmt::Error {
+    fn custom<T: Display>(_msg: T) -> Self {
+        fmt::Error
+    }
+}
+
+macro_rules! fmt_primitives {
+    ($($f:ident: $t:ty,)*) => {
+        $(
+            fn $f(self, v: $t) -> fmt::Result {
+                Display::fmt(&v, self)
+            }
+        )*
+    };
+}
+
+/// ```edition2021
+/// use serde::ser::Serialize;
+/// use serde_derive::Serialize;
+/// use std::fmt::{self, Display};
+///
+/// #[derive(Serialize)]
+/// #[serde(rename_all = "kebab-case")]
+/// pub enum MessageType {
+///     StartRequest,
+///     EndRequest,
+/// }
+///
+/// impl Display for MessageType {
+///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+///         self.serialize(f)
+///     }
+/// }
+/// ```
+impl<'a, 'b> Serializer for &'a mut fmt::Formatter<'b> {
+    type Ok = ();
+    type Error = fmt::Error;
+    type SerializeSeq = Impossible<(), fmt::Error>;
+    type SerializeTuple = Impossible<(), fmt::Error>;
+    type SerializeTupleStruct = Impossible<(), fmt::Error>;
+    type SerializeTupleVariant = Impossible<(), fmt::Error>;
+    type SerializeMap = Impossible<(), fmt::Error>;
+    type SerializeStruct = Impossible<(), fmt::Error>;
+    type SerializeStructVariant = Impossible<(), fmt::Error>;
+
+    fmt_primitives! {
+        serialize_bool: bool,
+        serialize_i8: i8,
+        serialize_i16: i16,
+        serialize_i32: i32,
+        serialize_i64: i64,
+        serialize_i128: i128,
+        serialize_u8: u8,
+        serialize_u16: u16,
+        serialize_u32: u32,
+        serialize_u64: u64,
+        serialize_u128: u128,
+        serialize_f32: f32,
+        serialize_f64: f64,
+        serialize_char: char,
+        serialize_str: &str,
+        serialize_unit_struct: &'static str,
+    }
+
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+    ) -> fmt::Result {
+        Display::fmt(variant, self)
+    }
+
+    fn serialize_newtype_struct<T: ?Sized>(self, _name: &'static str, value: &T) -> fmt::Result
+    where
+        T: Serialize,
+    {
+        Serialize::serialize(value, self)
+    }
+
+    fn serialize_bytes(self, _v: &[u8]) -> fmt::Result {
+        Err(fmt::Error)
+    }
+
+    fn serialize_none(self) -> fmt::Result {
+        Err(fmt::Error)
+    }
+
+    fn serialize_some<T: ?Sized>(self, _value: &T) -> fmt::Result
+    where
+        T: Serialize,
+    {
+        Err(fmt::Error)
+    }
+
+    fn serialize_unit(self) -> fmt::Result {
+        Err(fmt::Error)
+    }
+
+    fn serialize_newtype_variant<T: ?Sized>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _value: &T,
+    ) -> fmt::Result
+    where
+        T: Serialize,
+    {
+        Err(fmt::Error)
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq, fmt::Error> {
+        Err(fmt::Error)
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple, fmt::Error> {
+        Err(fmt::Error)
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleStruct, fmt::Error> {
+        Err(fmt::Error)
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleVariant, fmt::Error> {
+        Err(fmt::Error)
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap, fmt::Error> {
+        Err(fmt::Error)
+    }
+
+    fn serialize_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStruct, fmt::Error> {
+        Err(fmt::Error)
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant, fmt::Error> {
+        Err(fmt::Error)
+    }
+
+    fn collect_str<T: ?Sized>(self, value: &T) -> fmt::Result
+    where
+        T: Display,
+    {
+        Display::fmt(value, self)
+    }
+}
diff --git a/third_party/rust/serde/src/ser/impls.rs b/third_party/rust/serde/src/ser/impls.rs
new file mode 100644
index 0000000000..8c70634af0
--- /dev/null
+++ b/third_party/rust/serde/src/ser/impls.rs
@@ -0,0 +1,1077 @@
+use crate::lib::*;
+
+use crate::ser::{Error, Serialize, SerializeTuple, Serializer};
+
+////////////////////////////////////////////////////////////////////////////////
+
+macro_rules! primitive_impl {
+    ($ty:ident, $method:ident $($cast:tt)*) => {
+        impl Serialize for $ty {
+            #[inline]
+            fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+            where
+                S: Serializer,
+            {
+                serializer.$method(*self $($cast)*)
+            }
+        }
+    }
+}
+
+primitive_impl!(bool, serialize_bool);
+primitive_impl!(isize, serialize_i64 as i64);
+primitive_impl!(i8, serialize_i8);
+primitive_impl!(i16, serialize_i16);
+primitive_impl!(i32, serialize_i32);
+primitive_impl!(i64, serialize_i64);
+primitive_impl!(i128, serialize_i128);
+primitive_impl!(usize, serialize_u64 as u64);
+primitive_impl!(u8, serialize_u8);
+primitive_impl!(u16, serialize_u16);
+primitive_impl!(u32, serialize_u32);
+primitive_impl!(u64, serialize_u64);
+primitive_impl!(u128, serialize_u128);
+primitive_impl!(f32, serialize_f32);
+primitive_impl!(f64, serialize_f64);
+primitive_impl!(char, serialize_char);
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl Serialize for str {
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        serializer.serialize_str(self)
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+impl Serialize for String {
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        serializer.serialize_str(self)
+    }
+}
+
+impl<'a> Serialize for fmt::Arguments<'a> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        serializer.collect_str(self)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(any(feature = "std", not(no_core_cstr)))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+impl Serialize for CStr {
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        serializer.serialize_bytes(self.to_bytes())
+    }
+}
+
+#[cfg(any(feature = "std", all(not(no_core_cstr), feature = "alloc")))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+impl Serialize for CString {
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        serializer.serialize_bytes(self.to_bytes())
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<T> Serialize for Option<T>
+where
+    T: Serialize,
+{
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match *self {
+            Some(ref value) => serializer.serialize_some(value),
+            None => serializer.serialize_none(),
+        }
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<T: ?Sized> Serialize for PhantomData<T> {
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        serializer.serialize_unit_struct("PhantomData")
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+// Does not require T: Serialize.
+impl<T> Serialize for [T; 0] {
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        tri!(serializer.serialize_tuple(0)).end()
+    }
+}
+
+macro_rules! array_impls {
+    ($($len:tt)+) => {
+        $(
+            impl<T> Serialize for [T; $len]
+            where
+                T: Serialize,
+            {
+                #[inline]
+                fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+                where
+                    S: Serializer,
+                {
+                    let mut seq = tri!(serializer.serialize_tuple($len));
+                    for e in self {
+                        tri!(seq.serialize_element(e));
+                    }
+                    seq.end()
+                }
+            }
+        )+
+    }
+}
+
+array_impls! {
+    01 02 03 04 05 06 07 08 09 10
+    11 12 13 14 15 16 17 18 19 20
+    21 22 23 24 25 26 27 28 29 30
+    31 32
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<T> Serialize for [T]
+where
+    T: Serialize,
+{
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        serializer.collect_seq(self)
+    }
+}
+
+#[cfg(not(no_relaxed_trait_bounds))]
+macro_rules! seq_impl {
+    (
+        $(#[$attr:meta])*
+        $ty:ident <T $(: $tbound1:ident $(+ $tbound2:ident)*)* $(, $typaram:ident : $bound:ident)*>
+    ) => {
+        $(#[$attr])*
+        impl<T $(, $typaram)*> Serialize for $ty<T $(, $typaram)*>
+        where
+            T: Serialize,
+        {
+            #[inline]
+            fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+            where
+                S: Serializer,
+            {
+                serializer.collect_seq(self)
+            }
+        }
+    }
+}
+
+#[cfg(no_relaxed_trait_bounds)]
+macro_rules! seq_impl {
+    (
+        $(#[$attr:meta])*
+        $ty:ident <T $(: $tbound1:ident $(+ $tbound2:ident)*)* $(, $typaram:ident : $bound:ident)*>
+    ) => {
+        $(#[$attr])*
+        impl<T $(, $typaram)*> Serialize for $ty<T $(, $typaram)*>
+        where
+            T: Serialize $(+ $tbound1 $(+ $tbound2)*)*,
+            $($typaram: $bound,)*
+        {
+            #[inline]
+            fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+            where
+                S: Serializer,
+            {
+                serializer.collect_seq(self)
+            }
+        }
+    }
+}
+
+seq_impl! {
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    BinaryHeap<T: Ord>
+}
+
+seq_impl! {
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    BTreeSet<T: Ord>
+}
+
+seq_impl! {
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    HashSet<T: Eq + Hash, H: BuildHasher>
+}
+
+seq_impl! {
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    LinkedList<T>
+}
+
+seq_impl! {
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    Vec<T>
+}
+
+seq_impl! {
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    VecDeque<T>
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<Idx> Serialize for Range<Idx>
+where
+    Idx: Serialize,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        use super::SerializeStruct;
+        let mut state = tri!(serializer.serialize_struct("Range", 2));
+        tri!(state.serialize_field("start", &self.start));
+        tri!(state.serialize_field("end", &self.end));
+        state.end()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<Idx> Serialize for RangeFrom<Idx>
+where
+    Idx: Serialize,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        use super::SerializeStruct;
+        let mut state = tri!(serializer.serialize_struct("RangeFrom", 1));
+        tri!(state.serialize_field("start", &self.start));
+        state.end()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<Idx> Serialize for RangeInclusive<Idx>
+where
+    Idx: Serialize,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        use super::SerializeStruct;
+        let mut state = tri!(serializer.serialize_struct("RangeInclusive", 2));
+        tri!(state.serialize_field("start", &self.start()));
+        tri!(state.serialize_field("end", &self.end()));
+        state.end()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<Idx> Serialize for RangeTo<Idx>
+where
+    Idx: Serialize,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        use super::SerializeStruct;
+        let mut state = tri!(serializer.serialize_struct("RangeTo", 1));
+        tri!(state.serialize_field("end", &self.end));
+        state.end()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<T> Serialize for Bound<T>
+where
+    T: Serialize,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match *self {
+            Bound::Unbounded => serializer.serialize_unit_variant("Bound", 0, "Unbounded"),
+            Bound::Included(ref value) => {
+                serializer.serialize_newtype_variant("Bound", 1, "Included", value)
+            }
+            Bound::Excluded(ref value) => {
+                serializer.serialize_newtype_variant("Bound", 2, "Excluded", value)
+            }
+        }
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl Serialize for () {
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        serializer.serialize_unit()
+    }
+}
+
+#[cfg(feature = "unstable")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "unstable")))]
+impl Serialize for ! {
+    fn serialize<S>(&self, _serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        *self
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+macro_rules! tuple_impls {
+    ($($len:expr => ($($n:tt $name:ident)+))+) => {
+        $(
+            impl<$($name),+> Serialize for ($($name,)+)
+            where
+                $($name: Serialize,)+
+            {
+                #[inline]
+                fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+                where
+                    S: Serializer,
+                {
+                    let mut tuple = tri!(serializer.serialize_tuple($len));
+                    $(
+                        tri!(tuple.serialize_element(&self.$n));
+                    )+
+                    tuple.end()
+                }
+            }
+        )+
+    }
+}
+
+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(not(no_relaxed_trait_bounds))]
+macro_rules! map_impl {
+    (
+        $(#[$attr:meta])*
+        $ty:ident <K $(: $kbound1:ident $(+ $kbound2:ident)*)*, V $(, $typaram:ident : $bound:ident)*>
+    ) => {
+        $(#[$attr])*
+        impl<K, V $(, $typaram)*> Serialize for $ty<K, V $(, $typaram)*>
+        where
+            K: Serialize,
+            V: Serialize,
+        {
+            #[inline]
+            fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+            where
+                S: Serializer,
+            {
+                serializer.collect_map(self)
+            }
+        }
+    }
+}
+
+#[cfg(no_relaxed_trait_bounds)]
+macro_rules! map_impl {
+    (
+        $(#[$attr:meta])*
+        $ty:ident <K $(: $kbound1:ident $(+ $kbound2:ident)*)*, V $(, $typaram:ident : $bound:ident)*>
+    ) => {
+        $(#[$attr])*
+        impl<K, V $(, $typaram)*> Serialize for $ty<K, V $(, $typaram)*>
+        where
+            K: Serialize $(+ $kbound1 $(+ $kbound2)*)*,
+            V: Serialize,
+            $($typaram: $bound,)*
+        {
+            #[inline]
+            fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+            where
+                S: Serializer,
+            {
+                serializer.collect_map(self)
+            }
+        }
+    }
+}
+
+map_impl! {
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    BTreeMap<K: Ord, V>
+}
+
+map_impl! {
+    #[cfg(feature = "std")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+    HashMap<K: Eq + Hash, V, H: BuildHasher>
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+macro_rules! deref_impl {
+    (
+        $(#[$attr:meta])*
+        <$($desc:tt)+
+    ) => {
+        $(#[$attr])*
+        impl <$($desc)+ {
+            #[inline]
+            fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+            where
+                S: Serializer,
+            {
+                (**self).serialize(serializer)
+            }
+        }
+    };
+}
+
+deref_impl! {
+    <'a, T: ?Sized> Serialize for &'a T where T: Serialize
+}
+
+deref_impl! {
+    <'a, T: ?Sized> Serialize for &'a mut T where T: Serialize
+}
+
+deref_impl! {
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    <T: ?Sized> Serialize for Box<T> where T: Serialize
+}
+
+deref_impl! {
+    /// This impl requires the [`"rc"`] Cargo feature of Serde.
+    ///
+    /// Serializing a data structure containing `Rc` will serialize a copy of
+    /// the contents of the `Rc` each time the `Rc` is referenced within the
+    /// data structure. Serialization will not attempt to deduplicate these
+    /// repeated data.
+    ///
+    /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+    #[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+    #[cfg_attr(doc_cfg, doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))))]
+    <T: ?Sized> Serialize for Rc<T> where T: Serialize
+}
+
+deref_impl! {
+    /// This impl requires the [`"rc"`] Cargo feature of Serde.
+    ///
+    /// Serializing a data structure containing `Arc` will serialize a copy of
+    /// the contents of the `Arc` each time the `Arc` is referenced within the
+    /// data structure. Serialization will not attempt to deduplicate these
+    /// repeated data.
+    ///
+    /// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+    #[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+    #[cfg_attr(doc_cfg, doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))))]
+    <T: ?Sized> Serialize for Arc<T> where T: Serialize
+}
+
+deref_impl! {
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "std", feature = "alloc"))))]
+    <'a, T: ?Sized> Serialize for Cow<'a, T> where T: Serialize + ToOwned
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// This impl requires the [`"rc"`] Cargo feature of Serde.
+///
+/// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+#[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+#[cfg_attr(
+    doc_cfg,
+    doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc"))))
+)]
+impl<T: ?Sized> Serialize for RcWeak<T>
+where
+    T: Serialize,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        self.upgrade().serialize(serializer)
+    }
+}
+
+/// This impl requires the [`"rc"`] Cargo feature of Serde.
+///
+/// [`"rc"`]: https://serde.rs/feature-flags.html#-features-rc
+#[cfg(all(feature = "rc", any(feature = "std", feature = "alloc")))]
+#[cfg_attr(
+    doc_cfg,
+    doc(cfg(all(feature = "rc", any(feature = "std", feature = "alloc"))))
+)]
+impl<T: ?Sized> Serialize for ArcWeak<T>
+where
+    T: Serialize,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        self.upgrade().serialize(serializer)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+macro_rules! nonzero_integers {
+    ($($T:ident,)+) => {
+        $(
+            impl Serialize for num::$T {
+                fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+                where
+                    S: Serializer,
+                {
+                    self.get().serialize(serializer)
+                }
+            }
+        )+
+    }
+}
+
+nonzero_integers! {
+    NonZeroU8,
+    NonZeroU16,
+    NonZeroU32,
+    NonZeroU64,
+    NonZeroU128,
+    NonZeroUsize,
+}
+
+#[cfg(not(no_num_nonzero_signed))]
+nonzero_integers! {
+    NonZeroI8,
+    NonZeroI16,
+    NonZeroI32,
+    NonZeroI64,
+    NonZeroI128,
+    NonZeroIsize,
+}
+
+impl<T> Serialize for Cell<T>
+where
+    T: Serialize + Copy,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        self.get().serialize(serializer)
+    }
+}
+
+impl<T: ?Sized> Serialize for RefCell<T>
+where
+    T: Serialize,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match self.try_borrow() {
+            Ok(value) => value.serialize(serializer),
+            Err(_) => Err(S::Error::custom("already mutably borrowed")),
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+impl<T: ?Sized> Serialize for Mutex<T>
+where
+    T: Serialize,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match self.lock() {
+            Ok(locked) => locked.serialize(serializer),
+            Err(_) => Err(S::Error::custom("lock poison error while serializing")),
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+impl<T: ?Sized> Serialize for RwLock<T>
+where
+    T: Serialize,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match self.read() {
+            Ok(locked) => locked.serialize(serializer),
+            Err(_) => Err(S::Error::custom("lock poison error while serializing")),
+        }
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<T, E> Serialize for Result<T, E>
+where
+    T: Serialize,
+    E: Serialize,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match *self {
+            Result::Ok(ref value) => serializer.serialize_newtype_variant("Result", 0, "Ok", value),
+            Result::Err(ref value) => {
+                serializer.serialize_newtype_variant("Result", 1, "Err", value)
+            }
+        }
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl Serialize for Duration {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        use super::SerializeStruct;
+        let mut state = tri!(serializer.serialize_struct("Duration", 2));
+        tri!(state.serialize_field("secs", &self.as_secs()));
+        tri!(state.serialize_field("nanos", &self.subsec_nanos()));
+        state.end()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+impl Serialize for SystemTime {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        use super::SerializeStruct;
+        let duration_since_epoch = match self.duration_since(UNIX_EPOCH) {
+            Ok(duration_since_epoch) => duration_since_epoch,
+            Err(_) => return Err(S::Error::custom("SystemTime must be later than UNIX_EPOCH")),
+        };
+        let mut state = tri!(serializer.serialize_struct("SystemTime", 2));
+        tri!(state.serialize_field("secs_since_epoch", &duration_since_epoch.as_secs()));
+        tri!(state.serialize_field("nanos_since_epoch", &duration_since_epoch.subsec_nanos()));
+        state.end()
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// Serialize a value that implements `Display` as a string, when that string is
+/// statically known to never have more than a constant `MAX_LEN` bytes.
+///
+/// Panics if the `Display` impl tries to write more than `MAX_LEN` bytes.
+#[cfg(feature = "std")]
+macro_rules! serialize_display_bounded_length {
+    ($value:expr, $max:expr, $serializer:expr) => {{
+        let mut buffer = [0u8; $max];
+        let remaining_len = {
+            let mut remaining = &mut buffer[..];
+            write!(remaining, "{}", $value).unwrap();
+            remaining.len()
+        };
+        let written_len = buffer.len() - remaining_len;
+        let written = &buffer[..written_len];
+
+        // write! only provides fmt::Formatter to Display implementations, which
+        // has methods write_str and write_char but no method to write arbitrary
+        // bytes. Therefore `written` must be valid UTF-8.
+        let written_str = str::from_utf8(written).expect("must be valid UTF-8");
+        $serializer.serialize_str(written_str)
+    }};
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+impl Serialize for net::IpAddr {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        if serializer.is_human_readable() {
+            match *self {
+                net::IpAddr::V4(ref a) => a.serialize(serializer),
+                net::IpAddr::V6(ref a) => a.serialize(serializer),
+            }
+        } else {
+            match *self {
+                net::IpAddr::V4(ref a) => {
+                    serializer.serialize_newtype_variant("IpAddr", 0, "V4", a)
+                }
+                net::IpAddr::V6(ref a) => {
+                    serializer.serialize_newtype_variant("IpAddr", 1, "V6", a)
+                }
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+const DEC_DIGITS_LUT: &[u8] = b"\
+      0001020304050607080910111213141516171819\
+      2021222324252627282930313233343536373839\
+      4041424344454647484950515253545556575859\
+      6061626364656667686970717273747576777879\
+      8081828384858687888990919293949596979899";
+
+#[cfg(feature = "std")]
+#[inline]
+fn format_u8(mut n: u8, out: &mut [u8]) -> usize {
+    if n >= 100 {
+        let d1 = ((n % 100) << 1) as usize;
+        n /= 100;
+        out[0] = b'0' + n;
+        out[1] = DEC_DIGITS_LUT[d1];
+        out[2] = DEC_DIGITS_LUT[d1 + 1];
+        3
+    } else if n >= 10 {
+        let d1 = (n << 1) as usize;
+        out[0] = DEC_DIGITS_LUT[d1];
+        out[1] = DEC_DIGITS_LUT[d1 + 1];
+        2
+    } else {
+        out[0] = b'0' + n;
+        1
+    }
+}
+
+#[cfg(feature = "std")]
+#[test]
+fn test_format_u8() {
+    let mut i = 0u8;
+
+    loop {
+        let mut buf = [0u8; 3];
+        let written = format_u8(i, &mut buf);
+        assert_eq!(i.to_string().as_bytes(), &buf[..written]);
+
+        match i.checked_add(1) {
+            Some(next) => i = next,
+            None => break,
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+impl Serialize for net::Ipv4Addr {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        if serializer.is_human_readable() {
+            const MAX_LEN: usize = 15;
+            debug_assert_eq!(MAX_LEN, "101.102.103.104".len());
+            let mut buf = [b'.'; MAX_LEN];
+            let mut written = format_u8(self.octets()[0], &mut buf);
+            for oct in &self.octets()[1..] {
+                // Skip over delimiters that we initialized buf with
+                written += format_u8(*oct, &mut buf[written + 1..]) + 1;
+            }
+            // Safety: We've only written ASCII bytes to the buffer, so it is valid UTF-8
+            let buf = unsafe { str::from_utf8_unchecked(&buf[..written]) };
+            serializer.serialize_str(buf)
+        } else {
+            self.octets().serialize(serializer)
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+impl Serialize for net::Ipv6Addr {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        if serializer.is_human_readable() {
+            const MAX_LEN: usize = 39;
+            debug_assert_eq!(MAX_LEN, "1001:1002:1003:1004:1005:1006:1007:1008".len());
+            serialize_display_bounded_length!(self, MAX_LEN, serializer)
+        } else {
+            self.octets().serialize(serializer)
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+impl Serialize for net::SocketAddr {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        if serializer.is_human_readable() {
+            match *self {
+                net::SocketAddr::V4(ref addr) => addr.serialize(serializer),
+                net::SocketAddr::V6(ref addr) => addr.serialize(serializer),
+            }
+        } else {
+            match *self {
+                net::SocketAddr::V4(ref addr) => {
+                    serializer.serialize_newtype_variant("SocketAddr", 0, "V4", addr)
+                }
+                net::SocketAddr::V6(ref addr) => {
+                    serializer.serialize_newtype_variant("SocketAddr", 1, "V6", addr)
+                }
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+impl Serialize for net::SocketAddrV4 {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        if serializer.is_human_readable() {
+            const MAX_LEN: usize = 21;
+            debug_assert_eq!(MAX_LEN, "101.102.103.104:65000".len());
+            serialize_display_bounded_length!(self, MAX_LEN, serializer)
+        } else {
+            (self.ip(), self.port()).serialize(serializer)
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+impl Serialize for net::SocketAddrV6 {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        if serializer.is_human_readable() {
+            const MAX_LEN: usize = 58;
+            debug_assert_eq!(
+                MAX_LEN,
+                "[1001:1002:1003:1004:1005:1006:1007:1008%4294967295]:65000".len()
+            );
+            serialize_display_bounded_length!(self, MAX_LEN, serializer)
+        } else {
+            (self.ip(), self.port()).serialize(serializer)
+        }
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+impl Serialize for Path {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match self.to_str() {
+            Some(s) => s.serialize(serializer),
+            None => Err(Error::custom("path contains invalid UTF-8 characters")),
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
+impl Serialize for PathBuf {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        self.as_path().serialize(serializer)
+    }
+}
+
+#[cfg(all(feature = "std", any(unix, windows)))]
+#[cfg_attr(doc_cfg, doc(cfg(all(feature = "std", any(unix, windows)))))]
+impl Serialize for OsStr {
+    #[cfg(unix)]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        use std::os::unix::ffi::OsStrExt;
+        serializer.serialize_newtype_variant("OsString", 0, "Unix", self.as_bytes())
+    }
+
+    #[cfg(windows)]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        use std::os::windows::ffi::OsStrExt;
+        let val = self.encode_wide().collect::<Vec<_>>();
+        serializer.serialize_newtype_variant("OsString", 1, "Windows", &val)
+    }
+}
+
+#[cfg(all(feature = "std", any(unix, windows)))]
+#[cfg_attr(doc_cfg, doc(cfg(all(feature = "std", any(unix, windows)))))]
+impl Serialize for OsString {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        self.as_os_str().serialize(serializer)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+impl<T> Serialize for Wrapping<T>
+where
+    T: Serialize,
+{
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        self.0.serialize(serializer)
+    }
+}
+
+impl<T> Serialize for Reverse<T>
+where
+    T: Serialize,
+{
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        self.0.serialize(serializer)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(all(feature = "std", not(no_std_atomic)))]
+macro_rules! atomic_impl {
+    ($($ty:ident $size:expr)*) => {
+        $(
+            #[cfg(any(no_target_has_atomic, target_has_atomic = $size))]
+            #[cfg_attr(doc_cfg, doc(cfg(all(feature = "std", target_has_atomic = $size))))]
+            impl Serialize for $ty {
+                fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+                where
+                    S: Serializer,
+                {
+                    // Matches the atomic ordering used in libcore for the Debug impl
+                    self.load(Ordering::Relaxed).serialize(serializer)
+                }
+            }
+        )*
+    }
+}
+
+#[cfg(all(feature = "std", not(no_std_atomic)))]
+atomic_impl! {
+    AtomicBool "8"
+    AtomicI8 "8"
+    AtomicI16 "16"
+    AtomicI32 "32"
+    AtomicIsize "ptr"
+    AtomicU8 "8"
+    AtomicU16 "16"
+    AtomicU32 "32"
+    AtomicUsize "ptr"
+}
+
+#[cfg(all(feature = "std", not(no_std_atomic64)))]
+atomic_impl! {
+    AtomicI64 "64"
+    AtomicU64 "64"
+}
diff --git a/third_party/rust/serde/src/ser/impossible.rs b/third_party/rust/serde/src/ser/impossible.rs
new file mode 100644
index 0000000000..479be94071
--- /dev/null
+++ b/third_party/rust/serde/src/ser/impossible.rs
@@ -0,0 +1,216 @@
+//! This module contains `Impossible` serializer and its implementations.
+
+use crate::lib::*;
+
+use crate::ser::{
+    self, Serialize, SerializeMap, SerializeSeq, SerializeStruct, SerializeStructVariant,
+    SerializeTuple, SerializeTupleStruct, SerializeTupleVariant,
+};
+
+/// Helper type for implementing a `Serializer` that does not support
+/// serializing one of the compound types.
+///
+/// This type cannot be instantiated, but implements every one of the traits
+/// corresponding to the [`Serializer`] compound types: [`SerializeSeq`],
+/// [`SerializeTuple`], [`SerializeTupleStruct`], [`SerializeTupleVariant`],
+/// [`SerializeMap`], [`SerializeStruct`], and [`SerializeStructVariant`].
+///
+/// ```edition2021
+/// # use serde::ser::{Serializer, Impossible};
+/// # use serde::__private::doc::Error;
+/// #
+/// # struct MySerializer;
+/// #
+/// impl Serializer for MySerializer {
+///     type Ok = ();
+///     type Error = Error;
+///
+///     type SerializeSeq = Impossible<(), Error>;
+///     /* other associated types */
+///
+///     /// This data format does not support serializing sequences.
+///     fn serialize_seq(self,
+///                      len: Option<usize>)
+///                      -> Result<Self::SerializeSeq, Error> {
+///         // Given Impossible cannot be instantiated, the only
+///         // thing we can do here is to return an error.
+/// #         stringify! {
+///         Err(...)
+/// #         };
+/// #         unimplemented!()
+///     }
+///
+///     /* other Serializer methods */
+/// #     serde::__serialize_unimplemented! {
+/// #         bool i8 i16 i32 i64 u8 u16 u32 u64 f32 f64 char str bytes none some
+/// #         unit unit_struct unit_variant newtype_struct newtype_variant
+/// #         tuple tuple_struct tuple_variant map struct struct_variant
+/// #     }
+/// }
+/// ```
+///
+/// [`Serializer`]: trait.Serializer.html
+/// [`SerializeSeq`]: trait.SerializeSeq.html
+/// [`SerializeTuple`]: trait.SerializeTuple.html
+/// [`SerializeTupleStruct`]: trait.SerializeTupleStruct.html
+/// [`SerializeTupleVariant`]: trait.SerializeTupleVariant.html
+/// [`SerializeMap`]: trait.SerializeMap.html
+/// [`SerializeStruct`]: trait.SerializeStruct.html
+/// [`SerializeStructVariant`]: trait.SerializeStructVariant.html
+pub struct Impossible<Ok, Error> {
+    void: Void,
+    ok: PhantomData<Ok>,
+    error: PhantomData<Error>,
+}
+
+enum Void {}
+
+impl<Ok, Error> SerializeSeq for Impossible<Ok, Error>
+where
+    Error: ser::Error,
+{
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    where
+        T: Serialize,
+    {
+        let _ = value;
+        match self.void {}
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        match self.void {}
+    }
+}
+
+impl<Ok, Error> SerializeTuple for Impossible<Ok, Error>
+where
+    Error: ser::Error,
+{
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    where
+        T: Serialize,
+    {
+        let _ = value;
+        match self.void {}
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        match self.void {}
+    }
+}
+
+impl<Ok, Error> SerializeTupleStruct for Impossible<Ok, Error>
+where
+    Error: ser::Error,
+{
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    where
+        T: Serialize,
+    {
+        let _ = value;
+        match self.void {}
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        match self.void {}
+    }
+}
+
+impl<Ok, Error> SerializeTupleVariant for Impossible<Ok, Error>
+where
+    Error: ser::Error,
+{
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    where
+        T: Serialize,
+    {
+        let _ = value;
+        match self.void {}
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        match self.void {}
+    }
+}
+
+impl<Ok, Error> SerializeMap for Impossible<Ok, Error>
+where
+    Error: ser::Error,
+{
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), Error>
+    where
+        T: Serialize,
+    {
+        let _ = key;
+        match self.void {}
+    }
+
+    fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    where
+        T: Serialize,
+    {
+        let _ = value;
+        match self.void {}
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        match self.void {}
+    }
+}
+
+impl<Ok, Error> SerializeStruct for Impossible<Ok, Error>
+where
+    Error: ser::Error,
+{
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), Error>
+    where
+        T: Serialize,
+    {
+        let _ = key;
+        let _ = value;
+        match self.void {}
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        match self.void {}
+    }
+}
+
+impl<Ok, Error> SerializeStructVariant for Impossible<Ok, Error>
+where
+    Error: ser::Error,
+{
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), Error>
+    where
+        T: Serialize,
+    {
+        let _ = key;
+        let _ = value;
+        match self.void {}
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        match self.void {}
+    }
+}
diff --git a/third_party/rust/serde/src/ser/mod.rs b/third_party/rust/serde/src/ser/mod.rs
new file mode 100644
index 0000000000..75c45140e2
--- /dev/null
+++ b/third_party/rust/serde/src/ser/mod.rs
@@ -0,0 +1,1952 @@
+//! Generic data structure serialization framework.
+//!
+//! The two most important traits in this module are [`Serialize`] and
+//! [`Serializer`].
+//!
+//!  - **A type that implements `Serialize` is a data structure** that can be
+//!    serialized to any data format supported by Serde, and conversely
+//!  - **A type that implements `Serializer` is a data format** that can
+//!    serialize any data structure supported by Serde.
+//!
+//! # The Serialize trait
+//!
+//! Serde provides [`Serialize`] implementations for many Rust primitive and
+//! standard library types. The complete list is below. All of these can be
+//! serialized using Serde out of the box.
+//!
+//! Additionally, Serde provides a procedural macro called [`serde_derive`] to
+//! automatically generate [`Serialize`] 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 [`Serialize`] manually for
+//! some type in your program. See the [Implementing `Serialize`] section of the
+//! manual for more about this.
+//!
+//! Third-party crates may provide [`Serialize`] implementations for types that
+//! they expose. For example the [`linked-hash-map`] crate provides a
+//! [`LinkedHashMap<K, V>`] type that is serializable by Serde because the crate
+//! provides an implementation of [`Serialize`] for it.
+//!
+//! # The Serializer trait
+//!
+//! [`Serializer`] implementations are provided by third-party crates, for
+//! example [`serde_json`], [`serde_yaml`] and [`postcard`].
+//!
+//! A partial list of well-maintained formats is given on the [Serde
+//! website][data formats].
+//!
+//! # Implementations of Serialize provided by Serde
+//!
+//!  - **Primitive types**:
+//!    - bool
+//!    - i8, i16, i32, i64, i128, isize
+//!    - u8, u16, u32, u64, u128, usize
+//!    - f32, f64
+//!    - char
+//!    - str
+//!    - &T and &mut T
+//!  - **Compound types**:
+//!    - \[T\]
+//!    - \[T; 0\] through \[T; 32\]
+//!    - tuples up to size 16
+//!  - **Common standard library types**:
+//!    - String
+//!    - Option\<T\>
+//!    - Result\<T, E\>
+//!    - PhantomData\<T\>
+//!  - **Wrapper types**:
+//!    - Box\<T\>
+//!    - 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\>
+//!  - **FFI types**:
+//!    - CStr
+//!    - CString
+//!    - OsStr
+//!    - 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 `Serialize`]: https://serde.rs/impl-serialize.html
+//! [`LinkedHashMap<K, V>`]: https://docs.rs/linked-hash-map/*/linked_hash_map/struct.LinkedHashMap.html
+//! [`Serialize`]: ../trait.Serialize.html
+//! [`Serializer`]: ../trait.Serializer.html
+//! [`postcard`]: https://github.com/jamesmunns/postcard
+//! [`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 crate::lib::*;
+
+mod fmt;
+mod impls;
+mod impossible;
+
+pub use self::impossible::Impossible;
+
+#[cfg(not(any(feature = "std", feature = "unstable")))]
+#[doc(no_inline)]
+pub use crate::std_error::Error as StdError;
+#[cfg(all(feature = "unstable", not(feature = "std")))]
+#[doc(no_inline)]
+pub use core::error::Error as StdError;
+#[cfg(feature = "std")]
+#[doc(no_inline)]
+pub use std::error::Error as StdError;
+
+////////////////////////////////////////////////////////////////////////////////
+
+macro_rules! declare_error_trait {
+    (Error: Sized $(+ $($supertrait:ident)::+)*) => {
+        /// Trait used by `Serialize` implementations to generically construct
+        /// errors belonging to the `Serializer` against which they are
+        /// currently running.
+        ///
+        /// # 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)::+)* {
+            /// Used when a [`Serialize`] implementation encounters any error
+            /// while serializing a type.
+            ///
+            /// The message should not be capitalized and should not end with a
+            /// period.
+            ///
+            /// For example, a filesystem [`Path`] may refuse to serialize
+            /// itself if it contains invalid UTF-8 data.
+            ///
+            /// ```edition2021
+            /// # struct Path;
+            /// #
+            /// # impl Path {
+            /// #     fn to_str(&self) -> Option<&str> {
+            /// #         unimplemented!()
+            /// #     }
+            /// # }
+            /// #
+            /// use serde::ser::{self, Serialize, Serializer};
+            ///
+            /// impl Serialize for Path {
+            ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+            ///     where
+            ///         S: Serializer,
+            ///     {
+            ///         match self.to_str() {
+            ///             Some(s) => serializer.serialize_str(s),
+            ///             None => Err(ser::Error::custom("path contains invalid UTF-8 characters")),
+            ///         }
+            ///     }
+            /// }
+            /// ```
+            ///
+            /// [`Path`]: https://doc.rust-lang.org/std/path/struct.Path.html
+            /// [`Serialize`]: ../trait.Serialize.html
+            fn custom<T>(msg: T) -> Self
+            where
+                T: Display;
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+declare_error_trait!(Error: Sized + StdError);
+
+#[cfg(not(feature = "std"))]
+declare_error_trait!(Error: Sized + Debug + Display);
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A **data structure** that can be serialized into any data format supported
+/// by Serde.
+///
+/// Serde provides `Serialize` implementations for many Rust primitive and
+/// standard library types. The complete list is [here][crate::ser]. All of
+/// these can be serialized using Serde out of the box.
+///
+/// Additionally, Serde provides a procedural macro called [`serde_derive`] to
+/// automatically generate `Serialize` 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 `Serialize` manually for some
+/// type in your program. See the [Implementing `Serialize`] section of the
+/// manual for more about this.
+///
+/// Third-party crates may provide `Serialize` implementations for types that
+/// they expose. For example the [`linked-hash-map`] crate provides a
+/// [`LinkedHashMap<K, V>`] type that is serializable by Serde because the crate
+/// provides an implementation of `Serialize` for it.
+///
+/// [Implementing `Serialize`]: https://serde.rs/impl-serialize.html
+/// [`LinkedHashMap<K, V>`]: https://docs.rs/linked-hash-map/*/linked_hash_map/struct.LinkedHashMap.html
+/// [`linked-hash-map`]: https://crates.io/crates/linked-hash-map
+/// [`serde_derive`]: https://crates.io/crates/serde_derive
+/// [derive section of the manual]: https://serde.rs/derive.html
+pub trait Serialize {
+    /// Serialize this value into the given Serde serializer.
+    ///
+    /// See the [Implementing `Serialize`] section of the manual for more
+    /// information about how to implement this method.
+    ///
+    /// ```edition2021
+    /// use serde::ser::{Serialize, SerializeStruct, Serializer};
+    ///
+    /// struct Person {
+    ///     name: String,
+    ///     age: u8,
+    ///     phones: Vec<String>,
+    /// }
+    ///
+    /// // This is what #[derive(Serialize)] would generate.
+    /// impl Serialize for Person {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         let mut s = serializer.serialize_struct("Person", 3)?;
+    ///         s.serialize_field("name", &self.name)?;
+    ///         s.serialize_field("age", &self.age)?;
+    ///         s.serialize_field("phones", &self.phones)?;
+    ///         s.end()
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [Implementing `Serialize`]: https://serde.rs/impl-serialize.html
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+/// A **data format** that can serialize any data structure supported by Serde.
+///
+/// The role of this trait is to define the serialization half of the [Serde
+/// data model], which is a way to categorize every Rust data structure into one
+/// of 29 possible types. Each method of the `Serializer` trait corresponds to
+/// one of the types of the data model.
+///
+/// Implementations of `Serialize` map themselves into this data model by
+/// invoking exactly one of the `Serializer` methods.
+///
+/// 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 } }`.
+///
+/// Many Serde serializers produce text or binary data as output, for example
+/// JSON or Postcard. This is not a requirement of the `Serializer` trait, and
+/// there are serializers that do not produce text or binary output. One example
+/// is the `serde_json::value::Serializer` (distinct from the main `serde_json`
+/// serializer) that produces a `serde_json::Value` data structure in memory as
+/// output.
+///
+/// [Serde data model]: https://serde.rs/data-model.html
+///
+/// # Example implementation
+///
+/// The [example data format] presented on the website contains example code for
+/// a basic JSON `Serializer`.
+///
+/// [example data format]: https://serde.rs/data-format.html
+pub trait Serializer: Sized {
+    /// The output type produced by this `Serializer` during successful
+    /// serialization. Most serializers that produce text or binary output
+    /// should set `Ok = ()` and serialize into an [`io::Write`] or buffer
+    /// contained within the `Serializer` instance. Serializers that build
+    /// in-memory data structures may be simplified by using `Ok` to propagate
+    /// the data structure around.
+    ///
+    /// [`io::Write`]: https://doc.rust-lang.org/std/io/trait.Write.html
+    type Ok;
+
+    /// The error type when some error occurs during serialization.
+    type Error: Error;
+
+    /// Type returned from [`serialize_seq`] for serializing the content of the
+    /// sequence.
+    ///
+    /// [`serialize_seq`]: #tymethod.serialize_seq
+    type SerializeSeq: SerializeSeq<Ok = Self::Ok, Error = Self::Error>;
+
+    /// Type returned from [`serialize_tuple`] for serializing the content of
+    /// the tuple.
+    ///
+    /// [`serialize_tuple`]: #tymethod.serialize_tuple
+    type SerializeTuple: SerializeTuple<Ok = Self::Ok, Error = Self::Error>;
+
+    /// Type returned from [`serialize_tuple_struct`] for serializing the
+    /// content of the tuple struct.
+    ///
+    /// [`serialize_tuple_struct`]: #tymethod.serialize_tuple_struct
+    type SerializeTupleStruct: SerializeTupleStruct<Ok = Self::Ok, Error = Self::Error>;
+
+    /// Type returned from [`serialize_tuple_variant`] for serializing the
+    /// content of the tuple variant.
+    ///
+    /// [`serialize_tuple_variant`]: #tymethod.serialize_tuple_variant
+    type SerializeTupleVariant: SerializeTupleVariant<Ok = Self::Ok, Error = Self::Error>;
+
+    /// Type returned from [`serialize_map`] for serializing the content of the
+    /// map.
+    ///
+    /// [`serialize_map`]: #tymethod.serialize_map
+    type SerializeMap: SerializeMap<Ok = Self::Ok, Error = Self::Error>;
+
+    /// Type returned from [`serialize_struct`] for serializing the content of
+    /// the struct.
+    ///
+    /// [`serialize_struct`]: #tymethod.serialize_struct
+    type SerializeStruct: SerializeStruct<Ok = Self::Ok, Error = Self::Error>;
+
+    /// Type returned from [`serialize_struct_variant`] for serializing the
+    /// content of the struct variant.
+    ///
+    /// [`serialize_struct_variant`]: #tymethod.serialize_struct_variant
+    type SerializeStructVariant: SerializeStructVariant<Ok = Self::Ok, Error = Self::Error>;
+
+    /// Serialize a `bool` value.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for bool {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_bool(*self)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_bool(self, v: bool) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize an `i8` value.
+    ///
+    /// If the format does not differentiate between `i8` and `i64`, a
+    /// reasonable implementation would be to cast the value to `i64` and
+    /// forward to `serialize_i64`.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for i8 {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_i8(*self)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_i8(self, v: i8) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize an `i16` value.
+    ///
+    /// If the format does not differentiate between `i16` and `i64`, a
+    /// reasonable implementation would be to cast the value to `i64` and
+    /// forward to `serialize_i64`.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for i16 {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_i16(*self)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_i16(self, v: i16) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize an `i32` value.
+    ///
+    /// If the format does not differentiate between `i32` and `i64`, a
+    /// reasonable implementation would be to cast the value to `i64` and
+    /// forward to `serialize_i64`.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for i32 {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_i32(*self)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_i32(self, v: i32) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize an `i64` value.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for i64 {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_i64(*self)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_i64(self, v: i64) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize an `i128` value.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for i128 {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_i128(*self)
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// The default behavior unconditionally returns an error.
+    fn serialize_i128(self, v: i128) -> Result<Self::Ok, Self::Error> {
+        let _ = v;
+        Err(Error::custom("i128 is not supported"))
+    }
+
+    /// Serialize a `u8` value.
+    ///
+    /// If the format does not differentiate between `u8` and `u64`, a
+    /// reasonable implementation would be to cast the value to `u64` and
+    /// forward to `serialize_u64`.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for u8 {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_u8(*self)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_u8(self, v: u8) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize a `u16` value.
+    ///
+    /// If the format does not differentiate between `u16` and `u64`, a
+    /// reasonable implementation would be to cast the value to `u64` and
+    /// forward to `serialize_u64`.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for u16 {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_u16(*self)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_u16(self, v: u16) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize a `u32` value.
+    ///
+    /// If the format does not differentiate between `u32` and `u64`, a
+    /// reasonable implementation would be to cast the value to `u64` and
+    /// forward to `serialize_u64`.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for u32 {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_u32(*self)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_u32(self, v: u32) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize a `u64` value.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for u64 {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_u64(*self)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_u64(self, v: u64) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize a `u128` value.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for u128 {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_u128(*self)
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// The default behavior unconditionally returns an error.
+    fn serialize_u128(self, v: u128) -> Result<Self::Ok, Self::Error> {
+        let _ = v;
+        Err(Error::custom("u128 is not supported"))
+    }
+
+    /// Serialize an `f32` value.
+    ///
+    /// If the format does not differentiate between `f32` and `f64`, a
+    /// reasonable implementation would be to cast the value to `f64` and
+    /// forward to `serialize_f64`.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for f32 {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_f32(*self)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_f32(self, v: f32) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize an `f64` value.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for f64 {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_f64(*self)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_f64(self, v: f64) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize a character.
+    ///
+    /// If the format does not support characters, it is reasonable to serialize
+    /// it as a single element `str` or a `u32`.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for char {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_char(*self)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_char(self, v: char) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize a `&str`.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for str {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_str(self)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_str(self, v: &str) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize a chunk of raw byte data.
+    ///
+    /// Enables serializers to serialize byte slices more compactly or more
+    /// efficiently than other types of slices. If no efficient implementation
+    /// is available, a reasonable implementation would be to forward to
+    /// `serialize_seq`. If forwarded, the implementation looks usually just
+    /// like this:
+    ///
+    /// ```edition2021
+    /// # use serde::ser::{Serializer, SerializeSeq};
+    /// # use serde::__private::doc::Error;
+    /// #
+    /// # struct MySerializer;
+    /// #
+    /// # impl Serializer for MySerializer {
+    /// #     type Ok = ();
+    /// #     type Error = Error;
+    /// #
+    /// fn serialize_bytes(self, v: &[u8]) -> Result<Self::Ok, Self::Error> {
+    ///     let mut seq = self.serialize_seq(Some(v.len()))?;
+    ///     for b in v {
+    ///         seq.serialize_element(b)?;
+    ///     }
+    ///     seq.end()
+    /// }
+    /// #
+    /// #     serde::__serialize_unimplemented! {
+    /// #         bool i8 i16 i32 i64 u8 u16 u32 u64 f32 f64 char str none some
+    /// #         unit unit_struct unit_variant newtype_struct newtype_variant
+    /// #         seq tuple tuple_struct tuple_variant map struct struct_variant
+    /// #     }
+    /// # }
+    /// ```
+    fn serialize_bytes(self, v: &[u8]) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize a [`None`] value.
+    ///
+    /// ```edition2021
+    /// # use serde::{Serialize, Serializer};
+    /// #
+    /// # enum Option<T> {
+    /// #     Some(T),
+    /// #     None,
+    /// # }
+    /// #
+    /// # use self::Option::{Some, None};
+    /// #
+    /// impl<T> Serialize for Option<T>
+    /// where
+    ///     T: Serialize,
+    /// {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         match *self {
+    ///             Some(ref value) => serializer.serialize_some(value),
+    ///             None => serializer.serialize_none(),
+    ///         }
+    ///     }
+    /// }
+    /// #
+    /// # fn main() {}
+    /// ```
+    ///
+    /// [`None`]: https://doc.rust-lang.org/std/option/enum.Option.html#variant.None
+    fn serialize_none(self) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize a [`Some(T)`] value.
+    ///
+    /// ```edition2021
+    /// # use serde::{Serialize, Serializer};
+    /// #
+    /// # enum Option<T> {
+    /// #     Some(T),
+    /// #     None,
+    /// # }
+    /// #
+    /// # use self::Option::{Some, None};
+    /// #
+    /// impl<T> Serialize for Option<T>
+    /// where
+    ///     T: Serialize,
+    /// {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         match *self {
+    ///             Some(ref value) => serializer.serialize_some(value),
+    ///             None => serializer.serialize_none(),
+    ///         }
+    ///     }
+    /// }
+    /// #
+    /// # fn main() {}
+    /// ```
+    ///
+    /// [`Some(T)`]: https://doc.rust-lang.org/std/option/enum.Option.html#variant.Some
+    fn serialize_some<T: ?Sized>(self, value: &T) -> Result<Self::Ok, Self::Error>
+    where
+        T: Serialize;
+
+    /// Serialize a `()` value.
+    ///
+    /// ```edition2021
+    /// # use serde::Serializer;
+    /// #
+    /// # serde::__private_serialize!();
+    /// #
+    /// impl Serialize for () {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_unit()
+    ///     }
+    /// }
+    /// ```
+    fn serialize_unit(self) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize a unit struct like `struct Unit` or `PhantomData<T>`.
+    ///
+    /// A reasonable implementation would be to forward to `serialize_unit`.
+    ///
+    /// ```edition2021
+    /// use serde::{Serialize, Serializer};
+    ///
+    /// struct Nothing;
+    ///
+    /// impl Serialize for Nothing {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_unit_struct("Nothing")
+    ///     }
+    /// }
+    /// ```
+    fn serialize_unit_struct(self, name: &'static str) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize a unit variant like `E::A` in `enum E { A, B }`.
+    ///
+    /// The `name` is the name of the enum, the `variant_index` is the index of
+    /// this variant within the enum, and the `variant` is the name of the
+    /// variant.
+    ///
+    /// ```edition2021
+    /// use serde::{Serialize, Serializer};
+    ///
+    /// enum E {
+    ///     A,
+    ///     B,
+    /// }
+    ///
+    /// impl Serialize for E {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         match *self {
+    ///             E::A => serializer.serialize_unit_variant("E", 0, "A"),
+    ///             E::B => serializer.serialize_unit_variant("E", 1, "B"),
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    fn serialize_unit_variant(
+        self,
+        name: &'static str,
+        variant_index: u32,
+        variant: &'static str,
+    ) -> Result<Self::Ok, Self::Error>;
+
+    /// Serialize a newtype struct like `struct Millimeters(u8)`.
+    ///
+    /// Serializers are encouraged to treat newtype structs as insignificant
+    /// wrappers around the data they contain. A reasonable implementation would
+    /// be to forward to `value.serialize(self)`.
+    ///
+    /// ```edition2021
+    /// use serde::{Serialize, Serializer};
+    ///
+    /// struct Millimeters(u8);
+    ///
+    /// impl Serialize for Millimeters {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.serialize_newtype_struct("Millimeters", &self.0)
+    ///     }
+    /// }
+    /// ```
+    fn serialize_newtype_struct<T: ?Sized>(
+        self,
+        name: &'static str,
+        value: &T,
+    ) -> Result<Self::Ok, Self::Error>
+    where
+        T: Serialize;
+
+    /// Serialize a newtype variant like `E::N` in `enum E { N(u8) }`.
+    ///
+    /// The `name` is the name of the enum, the `variant_index` is the index of
+    /// this variant within the enum, and the `variant` is the name of the
+    /// variant. The `value` is the data contained within this newtype variant.
+    ///
+    /// ```edition2021
+    /// use serde::{Serialize, Serializer};
+    ///
+    /// enum E {
+    ///     M(String),
+    ///     N(u8),
+    /// }
+    ///
+    /// impl Serialize for E {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         match *self {
+    ///             E::M(ref s) => serializer.serialize_newtype_variant("E", 0, "M", s),
+    ///             E::N(n) => serializer.serialize_newtype_variant("E", 1, "N", &n),
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    fn serialize_newtype_variant<T: ?Sized>(
+        self,
+        name: &'static str,
+        variant_index: u32,
+        variant: &'static str,
+        value: &T,
+    ) -> Result<Self::Ok, Self::Error>
+    where
+        T: Serialize;
+
+    /// Begin to serialize a variably sized sequence. This call must be
+    /// followed by zero or more calls to `serialize_element`, then a call to
+    /// `end`.
+    ///
+    /// The argument is the number of elements in the sequence, which may or may
+    /// not be computable before the sequence is iterated. Some serializers only
+    /// support sequences whose length is known up front.
+    ///
+    /// ```edition2021
+    /// # use std::marker::PhantomData;
+    /// #
+    /// # struct Vec<T>(PhantomData<T>);
+    /// #
+    /// # impl<T> Vec<T> {
+    /// #     fn len(&self) -> usize {
+    /// #         unimplemented!()
+    /// #     }
+    /// # }
+    /// #
+    /// # impl<'a, T> IntoIterator for &'a Vec<T> {
+    /// #     type Item = &'a T;
+    /// #     type IntoIter = Box<dyn Iterator<Item = &'a T>>;
+    /// #
+    /// #     fn into_iter(self) -> Self::IntoIter {
+    /// #         unimplemented!()
+    /// #     }
+    /// # }
+    /// #
+    /// use serde::ser::{Serialize, SerializeSeq, Serializer};
+    ///
+    /// impl<T> Serialize for Vec<T>
+    /// where
+    ///     T: Serialize,
+    /// {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         let mut seq = serializer.serialize_seq(Some(self.len()))?;
+    ///         for element in self {
+    ///             seq.serialize_element(element)?;
+    ///         }
+    ///         seq.end()
+    ///     }
+    /// }
+    /// ```
+    fn serialize_seq(self, len: Option<usize>) -> Result<Self::SerializeSeq, Self::Error>;
+
+    /// Begin to serialize a statically sized sequence whose length will be
+    /// known at deserialization time without looking at the serialized data.
+    /// This call must be followed by zero or more calls to `serialize_element`,
+    /// then a call to `end`.
+    ///
+    /// ```edition2021
+    /// use serde::ser::{Serialize, SerializeTuple, Serializer};
+    ///
+    /// # mod fool {
+    /// #     trait Serialize {}
+    /// impl<A, B, C> Serialize for (A, B, C)
+    /// #     {}
+    /// # }
+    /// #
+    /// # struct Tuple3<A, B, C>(A, B, C);
+    /// #
+    /// # impl<A, B, C> Serialize for Tuple3<A, B, C>
+    /// where
+    ///     A: Serialize,
+    ///     B: Serialize,
+    ///     C: Serialize,
+    /// {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         let mut tup = serializer.serialize_tuple(3)?;
+    ///         tup.serialize_element(&self.0)?;
+    ///         tup.serialize_element(&self.1)?;
+    ///         tup.serialize_element(&self.2)?;
+    ///         tup.end()
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// ```edition2021
+    /// use serde::ser::{Serialize, SerializeTuple, Serializer};
+    ///
+    /// const VRAM_SIZE: usize = 386;
+    /// struct Vram([u16; VRAM_SIZE]);
+    ///
+    /// impl Serialize for Vram {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         let mut seq = serializer.serialize_tuple(VRAM_SIZE)?;
+    ///         for element in &self.0[..] {
+    ///             seq.serialize_element(element)?;
+    ///         }
+    ///         seq.end()
+    ///     }
+    /// }
+    /// ```
+    fn serialize_tuple(self, len: usize) -> Result<Self::SerializeTuple, Self::Error>;
+
+    /// Begin to serialize a tuple struct like `struct Rgb(u8, u8, u8)`. This
+    /// call must be followed by zero or more calls to `serialize_field`, then a
+    /// call to `end`.
+    ///
+    /// The `name` is the name of the tuple struct and the `len` is the number
+    /// of data fields that will be serialized.
+    ///
+    /// ```edition2021
+    /// use serde::ser::{Serialize, SerializeTupleStruct, Serializer};
+    ///
+    /// struct Rgb(u8, u8, u8);
+    ///
+    /// impl Serialize for Rgb {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         let mut ts = serializer.serialize_tuple_struct("Rgb", 3)?;
+    ///         ts.serialize_field(&self.0)?;
+    ///         ts.serialize_field(&self.1)?;
+    ///         ts.serialize_field(&self.2)?;
+    ///         ts.end()
+    ///     }
+    /// }
+    /// ```
+    fn serialize_tuple_struct(
+        self,
+        name: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeTupleStruct, Self::Error>;
+
+    /// Begin to serialize a tuple variant like `E::T` in `enum E { T(u8, u8)
+    /// }`. This call must be followed by zero or more calls to
+    /// `serialize_field`, then a call to `end`.
+    ///
+    /// The `name` is the name of the enum, the `variant_index` is the index of
+    /// this variant within the enum, the `variant` is the name of the variant,
+    /// and the `len` is the number of data fields that will be serialized.
+    ///
+    /// ```edition2021
+    /// use serde::ser::{Serialize, SerializeTupleVariant, Serializer};
+    ///
+    /// enum E {
+    ///     T(u8, u8),
+    ///     U(String, u32, u32),
+    /// }
+    ///
+    /// impl Serialize for E {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         match *self {
+    ///             E::T(ref a, ref b) => {
+    ///                 let mut tv = serializer.serialize_tuple_variant("E", 0, "T", 2)?;
+    ///                 tv.serialize_field(a)?;
+    ///                 tv.serialize_field(b)?;
+    ///                 tv.end()
+    ///             }
+    ///             E::U(ref a, ref b, ref c) => {
+    ///                 let mut tv = serializer.serialize_tuple_variant("E", 1, "U", 3)?;
+    ///                 tv.serialize_field(a)?;
+    ///                 tv.serialize_field(b)?;
+    ///                 tv.serialize_field(c)?;
+    ///                 tv.end()
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    fn serialize_tuple_variant(
+        self,
+        name: &'static str,
+        variant_index: u32,
+        variant: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeTupleVariant, Self::Error>;
+
+    /// Begin to serialize a map. This call must be followed by zero or more
+    /// calls to `serialize_key` and `serialize_value`, then a call to `end`.
+    ///
+    /// The argument is the number of elements in the map, which may or may not
+    /// be computable before the map is iterated. Some serializers only support
+    /// maps whose length is known up front.
+    ///
+    /// ```edition2021
+    /// # use std::marker::PhantomData;
+    /// #
+    /// # struct HashMap<K, V>(PhantomData<K>, PhantomData<V>);
+    /// #
+    /// # impl<K, V> HashMap<K, V> {
+    /// #     fn len(&self) -> usize {
+    /// #         unimplemented!()
+    /// #     }
+    /// # }
+    /// #
+    /// # impl<'a, K, V> IntoIterator for &'a HashMap<K, V> {
+    /// #     type Item = (&'a K, &'a V);
+    /// #     type IntoIter = Box<dyn Iterator<Item = (&'a K, &'a V)>>;
+    /// #
+    /// #     fn into_iter(self) -> Self::IntoIter {
+    /// #         unimplemented!()
+    /// #     }
+    /// # }
+    /// #
+    /// use serde::ser::{Serialize, SerializeMap, Serializer};
+    ///
+    /// impl<K, V> Serialize for HashMap<K, V>
+    /// where
+    ///     K: Serialize,
+    ///     V: Serialize,
+    /// {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         let mut map = serializer.serialize_map(Some(self.len()))?;
+    ///         for (k, v) in self {
+    ///             map.serialize_entry(k, v)?;
+    ///         }
+    ///         map.end()
+    ///     }
+    /// }
+    /// ```
+    fn serialize_map(self, len: Option<usize>) -> Result<Self::SerializeMap, Self::Error>;
+
+    /// Begin to serialize a struct like `struct Rgb { r: u8, g: u8, b: u8 }`.
+    /// This call must be followed by zero or more calls to `serialize_field`,
+    /// then a call to `end`.
+    ///
+    /// The `name` is the name of the struct and the `len` is the number of
+    /// data fields that will be serialized.
+    ///
+    /// ```edition2021
+    /// use serde::ser::{Serialize, SerializeStruct, Serializer};
+    ///
+    /// struct Rgb {
+    ///     r: u8,
+    ///     g: u8,
+    ///     b: u8,
+    /// }
+    ///
+    /// impl Serialize for Rgb {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         let mut rgb = serializer.serialize_struct("Rgb", 3)?;
+    ///         rgb.serialize_field("r", &self.r)?;
+    ///         rgb.serialize_field("g", &self.g)?;
+    ///         rgb.serialize_field("b", &self.b)?;
+    ///         rgb.end()
+    ///     }
+    /// }
+    /// ```
+    fn serialize_struct(
+        self,
+        name: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeStruct, Self::Error>;
+
+    /// Begin to serialize a struct variant like `E::S` in `enum E { S { r: u8,
+    /// g: u8, b: u8 } }`. This call must be followed by zero or more calls to
+    /// `serialize_field`, then a call to `end`.
+    ///
+    /// The `name` is the name of the enum, the `variant_index` is the index of
+    /// this variant within the enum, the `variant` is the name of the variant,
+    /// and the `len` is the number of data fields that will be serialized.
+    ///
+    /// ```edition2021
+    /// use serde::ser::{Serialize, SerializeStructVariant, Serializer};
+    ///
+    /// enum E {
+    ///     S { r: u8, g: u8, b: u8 },
+    /// }
+    ///
+    /// impl Serialize for E {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         match *self {
+    ///             E::S {
+    ///                 ref r,
+    ///                 ref g,
+    ///                 ref b,
+    ///             } => {
+    ///                 let mut sv = serializer.serialize_struct_variant("E", 0, "S", 3)?;
+    ///                 sv.serialize_field("r", r)?;
+    ///                 sv.serialize_field("g", g)?;
+    ///                 sv.serialize_field("b", b)?;
+    ///                 sv.end()
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    fn serialize_struct_variant(
+        self,
+        name: &'static str,
+        variant_index: u32,
+        variant: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeStructVariant, Self::Error>;
+
+    /// Collect an iterator as a sequence.
+    ///
+    /// The default implementation serializes each item yielded by the iterator
+    /// using [`serialize_seq`]. Implementors should not need to override this
+    /// method.
+    ///
+    /// ```edition2021
+    /// use serde::{Serialize, Serializer};
+    ///
+    /// struct SecretlyOneHigher {
+    ///     data: Vec<i32>,
+    /// }
+    ///
+    /// impl Serialize for SecretlyOneHigher {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.collect_seq(self.data.iter().map(|x| x + 1))
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [`serialize_seq`]: #tymethod.serialize_seq
+    fn collect_seq<I>(self, iter: I) -> Result<Self::Ok, Self::Error>
+    where
+        I: IntoIterator,
+        <I as IntoIterator>::Item: Serialize,
+    {
+        let mut iter = iter.into_iter();
+        let mut serializer = tri!(self.serialize_seq(iterator_len_hint(&iter)));
+        tri!(iter.try_for_each(|item| serializer.serialize_element(&item)));
+        serializer.end()
+    }
+
+    /// Collect an iterator as a map.
+    ///
+    /// The default implementation serializes each pair yielded by the iterator
+    /// using [`serialize_map`]. Implementors should not need to override this
+    /// method.
+    ///
+    /// ```edition2021
+    /// use serde::{Serialize, Serializer};
+    /// use std::collections::BTreeSet;
+    ///
+    /// struct MapToUnit {
+    ///     keys: BTreeSet<i32>,
+    /// }
+    ///
+    /// // Serializes as a map in which the values are all unit.
+    /// impl Serialize for MapToUnit {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.collect_map(self.keys.iter().map(|k| (k, ())))
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [`serialize_map`]: #tymethod.serialize_map
+    fn collect_map<K, V, I>(self, iter: I) -> Result<Self::Ok, Self::Error>
+    where
+        K: Serialize,
+        V: Serialize,
+        I: IntoIterator<Item = (K, V)>,
+    {
+        let mut iter = iter.into_iter();
+        let mut serializer = tri!(self.serialize_map(iterator_len_hint(&iter)));
+        tri!(iter.try_for_each(|(key, value)| serializer.serialize_entry(&key, &value)));
+        serializer.end()
+    }
+
+    /// Serialize a string produced by an implementation of `Display`.
+    ///
+    /// The default implementation builds a heap-allocated [`String`] and
+    /// delegates to [`serialize_str`]. Serializers are encouraged to provide a
+    /// more efficient implementation if possible.
+    ///
+    /// ```edition2021
+    /// # struct DateTime;
+    /// #
+    /// # impl DateTime {
+    /// #     fn naive_local(&self) -> () { () }
+    /// #     fn offset(&self) -> () { () }
+    /// # }
+    /// #
+    /// use serde::{Serialize, Serializer};
+    ///
+    /// impl Serialize for DateTime {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.collect_str(&format_args!("{:?}{:?}", self.naive_local(), self.offset()))
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [`String`]: https://doc.rust-lang.org/std/string/struct.String.html
+    /// [`serialize_str`]: #tymethod.serialize_str
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    fn collect_str<T: ?Sized>(self, value: &T) -> Result<Self::Ok, Self::Error>
+    where
+        T: Display,
+    {
+        self.serialize_str(&value.to_string())
+    }
+
+    /// Serialize a string produced by an implementation of `Display`.
+    ///
+    /// Serializers that use `no_std` are required to provide an implementation
+    /// of this method. If no more sensible behavior is possible, the
+    /// implementation is expected to return an error.
+    ///
+    /// ```edition2021
+    /// # struct DateTime;
+    /// #
+    /// # impl DateTime {
+    /// #     fn naive_local(&self) -> () { () }
+    /// #     fn offset(&self) -> () { () }
+    /// # }
+    /// #
+    /// use serde::{Serialize, Serializer};
+    ///
+    /// impl Serialize for DateTime {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         serializer.collect_str(&format_args!("{:?}{:?}", self.naive_local(), self.offset()))
+    ///     }
+    /// }
+    /// ```
+    #[cfg(not(any(feature = "std", feature = "alloc")))]
+    fn collect_str<T: ?Sized>(self, value: &T) -> Result<Self::Ok, Self::Error>
+    where
+        T: Display;
+
+    /// Determine whether `Serialize` implementations should serialize in
+    /// 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 Postcard will prefer the
+    /// compact one.
+    ///
+    /// ```edition2021
+    /// # use std::fmt::{self, Display};
+    /// #
+    /// # struct Timestamp;
+    /// #
+    /// # impl Timestamp {
+    /// #     fn seconds_since_epoch(&self) -> u64 { unimplemented!() }
+    /// # }
+    /// #
+    /// # impl Display for Timestamp {
+    /// #     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    /// #         unimplemented!()
+    /// #     }
+    /// # }
+    /// #
+    /// use serde::{Serialize, Serializer};
+    ///
+    /// impl Serialize for Timestamp {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///     where
+    ///         S: Serializer,
+    ///     {
+    ///         if serializer.is_human_readable() {
+    ///             // Serialize to a human-readable string "2015-05-15T17:01:00Z".
+    ///             self.to_string().serialize(serializer)
+    ///         } else {
+    ///             // Serialize to a compact binary representation.
+    ///             self.seconds_since_epoch().serialize(serializer)
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// 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
+    }
+}
+
+/// Returned from `Serializer::serialize_seq`.
+///
+/// # Example use
+///
+/// ```edition2021
+/// # use std::marker::PhantomData;
+/// #
+/// # struct Vec<T>(PhantomData<T>);
+/// #
+/// # impl<T> Vec<T> {
+/// #     fn len(&self) -> usize {
+/// #         unimplemented!()
+/// #     }
+/// # }
+/// #
+/// # impl<'a, T> IntoIterator for &'a Vec<T> {
+/// #     type Item = &'a T;
+/// #     type IntoIter = Box<dyn Iterator<Item = &'a T>>;
+/// #     fn into_iter(self) -> Self::IntoIter {
+/// #         unimplemented!()
+/// #     }
+/// # }
+/// #
+/// use serde::ser::{Serialize, SerializeSeq, Serializer};
+///
+/// impl<T> Serialize for Vec<T>
+/// where
+///     T: Serialize,
+/// {
+///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+///     where
+///         S: Serializer,
+///     {
+///         let mut seq = serializer.serialize_seq(Some(self.len()))?;
+///         for element in self {
+///             seq.serialize_element(element)?;
+///         }
+///         seq.end()
+///     }
+/// }
+/// ```
+///
+/// # Example implementation
+///
+/// The [example data format] presented on the website demonstrates an
+/// implementation of `SerializeSeq` for a basic JSON data format.
+///
+/// [example data format]: https://serde.rs/data-format.html
+pub trait SerializeSeq {
+    /// Must match the `Ok` type of our `Serializer`.
+    type Ok;
+
+    /// Must match the `Error` type of our `Serializer`.
+    type Error: Error;
+
+    /// Serialize a sequence element.
+    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    where
+        T: Serialize;
+
+    /// Finish serializing a sequence.
+    fn end(self) -> Result<Self::Ok, Self::Error>;
+}
+
+/// Returned from `Serializer::serialize_tuple`.
+///
+/// # Example use
+///
+/// ```edition2021
+/// use serde::ser::{Serialize, SerializeTuple, Serializer};
+///
+/// # mod fool {
+/// #     trait Serialize {}
+/// impl<A, B, C> Serialize for (A, B, C)
+/// #     {}
+/// # }
+/// #
+/// # struct Tuple3<A, B, C>(A, B, C);
+/// #
+/// # impl<A, B, C> Serialize for Tuple3<A, B, C>
+/// where
+///     A: Serialize,
+///     B: Serialize,
+///     C: Serialize,
+/// {
+///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+///     where
+///         S: Serializer,
+///     {
+///         let mut tup = serializer.serialize_tuple(3)?;
+///         tup.serialize_element(&self.0)?;
+///         tup.serialize_element(&self.1)?;
+///         tup.serialize_element(&self.2)?;
+///         tup.end()
+///     }
+/// }
+/// ```
+///
+/// ```edition2021
+/// # use std::marker::PhantomData;
+/// #
+/// # struct Array<T>(PhantomData<T>);
+/// #
+/// # impl<T> Array<T> {
+/// #     fn len(&self) -> usize {
+/// #         unimplemented!()
+/// #     }
+/// # }
+/// #
+/// # impl<'a, T> IntoIterator for &'a Array<T> {
+/// #     type Item = &'a T;
+/// #     type IntoIter = Box<dyn Iterator<Item = &'a T>>;
+/// #     fn into_iter(self) -> Self::IntoIter {
+/// #         unimplemented!()
+/// #     }
+/// # }
+/// #
+/// use serde::ser::{Serialize, SerializeTuple, Serializer};
+///
+/// # mod fool {
+/// #     trait Serialize {}
+/// impl<T> Serialize for [T; 16]
+/// #     {}
+/// # }
+/// #
+/// # impl<T> Serialize for Array<T>
+/// where
+///     T: Serialize,
+/// {
+///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+///     where
+///         S: Serializer,
+///     {
+///         let mut seq = serializer.serialize_tuple(16)?;
+///         for element in self {
+///             seq.serialize_element(element)?;
+///         }
+///         seq.end()
+///     }
+/// }
+/// ```
+///
+/// # Example implementation
+///
+/// The [example data format] presented on the website demonstrates an
+/// implementation of `SerializeTuple` for a basic JSON data format.
+///
+/// [example data format]: https://serde.rs/data-format.html
+pub trait SerializeTuple {
+    /// Must match the `Ok` type of our `Serializer`.
+    type Ok;
+
+    /// Must match the `Error` type of our `Serializer`.
+    type Error: Error;
+
+    /// Serialize a tuple element.
+    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    where
+        T: Serialize;
+
+    /// Finish serializing a tuple.
+    fn end(self) -> Result<Self::Ok, Self::Error>;
+}
+
+/// Returned from `Serializer::serialize_tuple_struct`.
+///
+/// # Example use
+///
+/// ```edition2021
+/// use serde::ser::{Serialize, SerializeTupleStruct, Serializer};
+///
+/// struct Rgb(u8, u8, u8);
+///
+/// impl Serialize for Rgb {
+///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+///     where
+///         S: Serializer,
+///     {
+///         let mut ts = serializer.serialize_tuple_struct("Rgb", 3)?;
+///         ts.serialize_field(&self.0)?;
+///         ts.serialize_field(&self.1)?;
+///         ts.serialize_field(&self.2)?;
+///         ts.end()
+///     }
+/// }
+/// ```
+///
+/// # Example implementation
+///
+/// The [example data format] presented on the website demonstrates an
+/// implementation of `SerializeTupleStruct` for a basic JSON data format.
+///
+/// [example data format]: https://serde.rs/data-format.html
+pub trait SerializeTupleStruct {
+    /// Must match the `Ok` type of our `Serializer`.
+    type Ok;
+
+    /// Must match the `Error` type of our `Serializer`.
+    type Error: Error;
+
+    /// Serialize a tuple struct field.
+    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    where
+        T: Serialize;
+
+    /// Finish serializing a tuple struct.
+    fn end(self) -> Result<Self::Ok, Self::Error>;
+}
+
+/// Returned from `Serializer::serialize_tuple_variant`.
+///
+/// # Example use
+///
+/// ```edition2021
+/// use serde::ser::{Serialize, SerializeTupleVariant, Serializer};
+///
+/// enum E {
+///     T(u8, u8),
+///     U(String, u32, u32),
+/// }
+///
+/// impl Serialize for E {
+///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+///     where
+///         S: Serializer,
+///     {
+///         match *self {
+///             E::T(ref a, ref b) => {
+///                 let mut tv = serializer.serialize_tuple_variant("E", 0, "T", 2)?;
+///                 tv.serialize_field(a)?;
+///                 tv.serialize_field(b)?;
+///                 tv.end()
+///             }
+///             E::U(ref a, ref b, ref c) => {
+///                 let mut tv = serializer.serialize_tuple_variant("E", 1, "U", 3)?;
+///                 tv.serialize_field(a)?;
+///                 tv.serialize_field(b)?;
+///                 tv.serialize_field(c)?;
+///                 tv.end()
+///             }
+///         }
+///     }
+/// }
+/// ```
+///
+/// # Example implementation
+///
+/// The [example data format] presented on the website demonstrates an
+/// implementation of `SerializeTupleVariant` for a basic JSON data format.
+///
+/// [example data format]: https://serde.rs/data-format.html
+pub trait SerializeTupleVariant {
+    /// Must match the `Ok` type of our `Serializer`.
+    type Ok;
+
+    /// Must match the `Error` type of our `Serializer`.
+    type Error: Error;
+
+    /// Serialize a tuple variant field.
+    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    where
+        T: Serialize;
+
+    /// Finish serializing a tuple variant.
+    fn end(self) -> Result<Self::Ok, Self::Error>;
+}
+
+/// Returned from `Serializer::serialize_map`.
+///
+/// # Example use
+///
+/// ```edition2021
+/// # use std::marker::PhantomData;
+/// #
+/// # struct HashMap<K, V>(PhantomData<K>, PhantomData<V>);
+/// #
+/// # impl<K, V> HashMap<K, V> {
+/// #     fn len(&self) -> usize {
+/// #         unimplemented!()
+/// #     }
+/// # }
+/// #
+/// # impl<'a, K, V> IntoIterator for &'a HashMap<K, V> {
+/// #     type Item = (&'a K, &'a V);
+/// #     type IntoIter = Box<dyn Iterator<Item = (&'a K, &'a V)>>;
+/// #
+/// #     fn into_iter(self) -> Self::IntoIter {
+/// #         unimplemented!()
+/// #     }
+/// # }
+/// #
+/// use serde::ser::{Serialize, SerializeMap, Serializer};
+///
+/// impl<K, V> Serialize for HashMap<K, V>
+/// where
+///     K: Serialize,
+///     V: Serialize,
+/// {
+///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+///     where
+///         S: Serializer,
+///     {
+///         let mut map = serializer.serialize_map(Some(self.len()))?;
+///         for (k, v) in self {
+///             map.serialize_entry(k, v)?;
+///         }
+///         map.end()
+///     }
+/// }
+/// ```
+///
+/// # Example implementation
+///
+/// The [example data format] presented on the website demonstrates an
+/// implementation of `SerializeMap` for a basic JSON data format.
+///
+/// [example data format]: https://serde.rs/data-format.html
+pub trait SerializeMap {
+    /// Must match the `Ok` type of our `Serializer`.
+    type Ok;
+
+    /// Must match the `Error` type of our `Serializer`.
+    type Error: Error;
+
+    /// Serialize a map key.
+    ///
+    /// If possible, `Serialize` implementations are encouraged to use
+    /// `serialize_entry` instead as it may be implemented more efficiently in
+    /// some formats compared to a pair of calls to `serialize_key` and
+    /// `serialize_value`.
+    fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), Self::Error>
+    where
+        T: Serialize;
+
+    /// Serialize a map value.
+    ///
+    /// # Panics
+    ///
+    /// Calling `serialize_value` before `serialize_key` is incorrect and is
+    /// allowed to panic or produce bogus results.
+    fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    where
+        T: Serialize;
+
+    /// Serialize a map entry consisting of a key and a value.
+    ///
+    /// Some [`Serialize`] types are not able to hold a key and value in memory
+    /// at the same time so `SerializeMap` implementations are required to
+    /// support [`serialize_key`] and [`serialize_value`] individually. The
+    /// `serialize_entry` method allows serializers to optimize for the case
+    /// where key and value are both available. [`Serialize`] implementations
+    /// are encouraged to use `serialize_entry` if possible.
+    ///
+    /// The default implementation delegates to [`serialize_key`] and
+    /// [`serialize_value`]. This is appropriate for serializers that do not
+    /// care about performance or are not able to optimize `serialize_entry` any
+    /// better than this.
+    ///
+    /// [`Serialize`]: ../trait.Serialize.html
+    /// [`serialize_key`]: #tymethod.serialize_key
+    /// [`serialize_value`]: #tymethod.serialize_value
+    fn serialize_entry<K: ?Sized, V: ?Sized>(
+        &mut self,
+        key: &K,
+        value: &V,
+    ) -> Result<(), Self::Error>
+    where
+        K: Serialize,
+        V: Serialize,
+    {
+        tri!(self.serialize_key(key));
+        self.serialize_value(value)
+    }
+
+    /// Finish serializing a map.
+    fn end(self) -> Result<Self::Ok, Self::Error>;
+}
+
+/// Returned from `Serializer::serialize_struct`.
+///
+/// # Example use
+///
+/// ```edition2021
+/// use serde::ser::{Serialize, SerializeStruct, Serializer};
+///
+/// struct Rgb {
+///     r: u8,
+///     g: u8,
+///     b: u8,
+/// }
+///
+/// impl Serialize for Rgb {
+///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+///     where
+///         S: Serializer,
+///     {
+///         let mut rgb = serializer.serialize_struct("Rgb", 3)?;
+///         rgb.serialize_field("r", &self.r)?;
+///         rgb.serialize_field("g", &self.g)?;
+///         rgb.serialize_field("b", &self.b)?;
+///         rgb.end()
+///     }
+/// }
+/// ```
+///
+/// # Example implementation
+///
+/// The [example data format] presented on the website demonstrates an
+/// implementation of `SerializeStruct` for a basic JSON data format.
+///
+/// [example data format]: https://serde.rs/data-format.html
+pub trait SerializeStruct {
+    /// Must match the `Ok` type of our `Serializer`.
+    type Ok;
+
+    /// Must match the `Error` type of our `Serializer`.
+    type Error: Error;
+
+    /// Serialize a struct field.
+    fn serialize_field<T: ?Sized>(
+        &mut self,
+        key: &'static str,
+        value: &T,
+    ) -> Result<(), Self::Error>
+    where
+        T: Serialize;
+
+    /// Indicate that a struct field has been skipped.
+    #[inline]
+    fn skip_field(&mut self, key: &'static str) -> Result<(), Self::Error> {
+        let _ = key;
+        Ok(())
+    }
+
+    /// Finish serializing a struct.
+    fn end(self) -> Result<Self::Ok, Self::Error>;
+}
+
+/// Returned from `Serializer::serialize_struct_variant`.
+///
+/// # Example use
+///
+/// ```edition2021
+/// use serde::ser::{Serialize, SerializeStructVariant, Serializer};
+///
+/// enum E {
+///     S { r: u8, g: u8, b: u8 },
+/// }
+///
+/// impl Serialize for E {
+///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+///     where
+///         S: Serializer,
+///     {
+///         match *self {
+///             E::S {
+///                 ref r,
+///                 ref g,
+///                 ref b,
+///             } => {
+///                 let mut sv = serializer.serialize_struct_variant("E", 0, "S", 3)?;
+///                 sv.serialize_field("r", r)?;
+///                 sv.serialize_field("g", g)?;
+///                 sv.serialize_field("b", b)?;
+///                 sv.end()
+///             }
+///         }
+///     }
+/// }
+/// ```
+///
+/// # Example implementation
+///
+/// The [example data format] presented on the website demonstrates an
+/// implementation of `SerializeStructVariant` for a basic JSON data format.
+///
+/// [example data format]: https://serde.rs/data-format.html
+pub trait SerializeStructVariant {
+    /// Must match the `Ok` type of our `Serializer`.
+    type Ok;
+
+    /// Must match the `Error` type of our `Serializer`.
+    type Error: Error;
+
+    /// Serialize a struct variant field.
+    fn serialize_field<T: ?Sized>(
+        &mut self,
+        key: &'static str,
+        value: &T,
+    ) -> Result<(), Self::Error>
+    where
+        T: Serialize;
+
+    /// Indicate that a struct variant field has been skipped.
+    #[inline]
+    fn skip_field(&mut self, key: &'static str) -> Result<(), Self::Error> {
+        let _ = key;
+        Ok(())
+    }
+
+    /// Finish serializing a struct variant.
+    fn end(self) -> Result<Self::Ok, Self::Error>;
+}
+
+fn iterator_len_hint<I>(iter: &I) -> Option<usize>
+where
+    I: Iterator,
+{
+    match iter.size_hint() {
+        (lo, Some(hi)) if lo == hi => Some(lo),
+        _ => None,
+    }
+}