Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

1 files changed, 2892 insertions, 0 deletions

diff --git a/vendor/serde/src/private/de.rs b/vendor/serde/src/private/de.rs
new file mode 100644
index 0000000..883e690
--- /dev/null
+++ b/vendor/serde/src/private/de.rs
@@ -0,0 +1,2892 @@
+use crate::lib::*;
+
+use crate::de::value::{BorrowedBytesDeserializer, BytesDeserializer};
+use crate::de::{
+    Deserialize, DeserializeSeed, Deserializer, EnumAccess, Error, IntoDeserializer, VariantAccess,
+    Visitor,
+};
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+use crate::de::{MapAccess, Unexpected};
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+pub use self::content::{
+    Content, ContentDeserializer, ContentRefDeserializer, EnumDeserializer,
+    InternallyTaggedUnitVisitor, TagContentOtherField, TagContentOtherFieldVisitor,
+    TagOrContentField, TagOrContentFieldVisitor, TaggedContentVisitor, UntaggedUnitVisitor,
+};
+
+pub use crate::seed::InPlaceSeed;
+
+/// If the missing field is of type `Option<T>` then treat is as `None`,
+/// otherwise it is an error.
+pub fn missing_field<'de, V, E>(field: &'static str) -> Result<V, E>
+where
+    V: Deserialize<'de>,
+    E: Error,
+{
+    struct MissingFieldDeserializer<E>(&'static str, PhantomData<E>);
+
+    impl<'de, E> Deserializer<'de> for MissingFieldDeserializer<E>
+    where
+        E: Error,
+    {
+        type Error = E;
+
+        fn deserialize_any<V>(self, _visitor: V) -> Result<V::Value, E>
+        where
+            V: Visitor<'de>,
+        {
+            Err(Error::missing_field(self.0))
+        }
+
+        fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, E>
+        where
+            V: Visitor<'de>,
+        {
+            visitor.visit_none()
+        }
+
+        forward_to_deserialize_any! {
+            bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+            bytes byte_buf unit unit_struct newtype_struct seq tuple
+            tuple_struct map struct enum identifier ignored_any
+        }
+    }
+
+    let deserializer = MissingFieldDeserializer(field, PhantomData);
+    Deserialize::deserialize(deserializer)
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+pub fn borrow_cow_str<'de: 'a, 'a, D, R>(deserializer: D) -> Result<R, D::Error>
+where
+    D: Deserializer<'de>,
+    R: From<Cow<'a, str>>,
+{
+    struct CowStrVisitor;
+
+    impl<'a> Visitor<'a> for CowStrVisitor {
+        type Value = Cow<'a, str>;
+
+        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            formatter.write_str("a string")
+        }
+
+        fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            Ok(Cow::Owned(v.to_owned()))
+        }
+
+        fn visit_borrowed_str<E>(self, v: &'a str) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            Ok(Cow::Borrowed(v))
+        }
+
+        fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            Ok(Cow::Owned(v))
+        }
+
+        fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            match str::from_utf8(v) {
+                Ok(s) => Ok(Cow::Owned(s.to_owned())),
+                Err(_) => Err(Error::invalid_value(Unexpected::Bytes(v), &self)),
+            }
+        }
+
+        fn visit_borrowed_bytes<E>(self, v: &'a [u8]) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            match str::from_utf8(v) {
+                Ok(s) => Ok(Cow::Borrowed(s)),
+                Err(_) => Err(Error::invalid_value(Unexpected::Bytes(v), &self)),
+            }
+        }
+
+        fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            match String::from_utf8(v) {
+                Ok(s) => Ok(Cow::Owned(s)),
+                Err(e) => Err(Error::invalid_value(
+                    Unexpected::Bytes(&e.into_bytes()),
+                    &self,
+                )),
+            }
+        }
+    }
+
+    deserializer.deserialize_str(CowStrVisitor).map(From::from)
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+pub fn borrow_cow_bytes<'de: 'a, 'a, D, R>(deserializer: D) -> Result<R, D::Error>
+where
+    D: Deserializer<'de>,
+    R: From<Cow<'a, [u8]>>,
+{
+    struct CowBytesVisitor;
+
+    impl<'a> Visitor<'a> for CowBytesVisitor {
+        type Value = Cow<'a, [u8]>;
+
+        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            formatter.write_str("a byte array")
+        }
+
+        fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            Ok(Cow::Owned(v.as_bytes().to_vec()))
+        }
+
+        fn visit_borrowed_str<E>(self, v: &'a str) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            Ok(Cow::Borrowed(v.as_bytes()))
+        }
+
+        fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            Ok(Cow::Owned(v.into_bytes()))
+        }
+
+        fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            Ok(Cow::Owned(v.to_vec()))
+        }
+
+        fn visit_borrowed_bytes<E>(self, v: &'a [u8]) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            Ok(Cow::Borrowed(v))
+        }
+
+        fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
+        where
+            E: Error,
+        {
+            Ok(Cow::Owned(v))
+        }
+    }
+
+    deserializer
+        .deserialize_bytes(CowBytesVisitor)
+        .map(From::from)
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+mod content {
+    // This module is private and nothing here should be used outside of
+    // generated code.
+    //
+    // We will iterate on the implementation for a few releases and only have to
+    // worry about backward compatibility for the `untagged` and `tag` attributes
+    // rather than for this entire mechanism.
+    //
+    // This issue is tracking making some of this stuff public:
+    // https://github.com/serde-rs/serde/issues/741
+
+    use crate::lib::*;
+
+    use crate::actually_private;
+    use crate::de::value::{MapDeserializer, SeqDeserializer};
+    use crate::de::{
+        self, size_hint, Deserialize, DeserializeSeed, Deserializer, EnumAccess, Expected,
+        IgnoredAny, MapAccess, SeqAccess, Unexpected, Visitor,
+    };
+
+    /// Used from generated code to buffer the contents of the Deserializer when
+    /// deserializing untagged enums and internally tagged enums.
+    ///
+    /// Not public API. Use serde-value instead.
+    #[derive(Debug, Clone)]
+    pub enum Content<'de> {
+        Bool(bool),
+
+        U8(u8),
+        U16(u16),
+        U32(u32),
+        U64(u64),
+
+        I8(i8),
+        I16(i16),
+        I32(i32),
+        I64(i64),
+
+        F32(f32),
+        F64(f64),
+
+        Char(char),
+        String(String),
+        Str(&'de str),
+        ByteBuf(Vec<u8>),
+        Bytes(&'de [u8]),
+
+        None,
+        Some(Box<Content<'de>>),
+
+        Unit,
+        Newtype(Box<Content<'de>>),
+        Seq(Vec<Content<'de>>),
+        Map(Vec<(Content<'de>, Content<'de>)>),
+    }
+
+    impl<'de> Content<'de> {
+        pub fn as_str(&self) -> Option<&str> {
+            match *self {
+                Content::Str(x) => Some(x),
+                Content::String(ref x) => Some(x),
+                Content::Bytes(x) => str::from_utf8(x).ok(),
+                Content::ByteBuf(ref x) => str::from_utf8(x).ok(),
+                _ => None,
+            }
+        }
+
+        #[cold]
+        fn unexpected(&self) -> Unexpected {
+            match *self {
+                Content::Bool(b) => Unexpected::Bool(b),
+                Content::U8(n) => Unexpected::Unsigned(n as u64),
+                Content::U16(n) => Unexpected::Unsigned(n as u64),
+                Content::U32(n) => Unexpected::Unsigned(n as u64),
+                Content::U64(n) => Unexpected::Unsigned(n),
+                Content::I8(n) => Unexpected::Signed(n as i64),
+                Content::I16(n) => Unexpected::Signed(n as i64),
+                Content::I32(n) => Unexpected::Signed(n as i64),
+                Content::I64(n) => Unexpected::Signed(n),
+                Content::F32(f) => Unexpected::Float(f as f64),
+                Content::F64(f) => Unexpected::Float(f),
+                Content::Char(c) => Unexpected::Char(c),
+                Content::String(ref s) => Unexpected::Str(s),
+                Content::Str(s) => Unexpected::Str(s),
+                Content::ByteBuf(ref b) => Unexpected::Bytes(b),
+                Content::Bytes(b) => Unexpected::Bytes(b),
+                Content::None | Content::Some(_) => Unexpected::Option,
+                Content::Unit => Unexpected::Unit,
+                Content::Newtype(_) => Unexpected::NewtypeStruct,
+                Content::Seq(_) => Unexpected::Seq,
+                Content::Map(_) => Unexpected::Map,
+            }
+        }
+    }
+
+    impl<'de> Deserialize<'de> for Content<'de> {
+        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            // Untagged and internally tagged enums are only supported in
+            // self-describing formats.
+            let visitor = ContentVisitor { value: PhantomData };
+            deserializer.__deserialize_content(actually_private::T, visitor)
+        }
+    }
+
+    impl<'de, E> de::IntoDeserializer<'de, E> for Content<'de>
+    where
+        E: de::Error,
+    {
+        type Deserializer = ContentDeserializer<'de, E>;
+
+        fn into_deserializer(self) -> Self::Deserializer {
+            ContentDeserializer::new(self)
+        }
+    }
+
+    struct ContentVisitor<'de> {
+        value: PhantomData<Content<'de>>,
+    }
+
+    impl<'de> ContentVisitor<'de> {
+        fn new() -> Self {
+            ContentVisitor { value: PhantomData }
+        }
+    }
+
+    impl<'de> Visitor<'de> for ContentVisitor<'de> {
+        type Value = Content<'de>;
+
+        fn expecting(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+            fmt.write_str("any value")
+        }
+
+        fn visit_bool<F>(self, value: bool) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::Bool(value))
+        }
+
+        fn visit_i8<F>(self, value: i8) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::I8(value))
+        }
+
+        fn visit_i16<F>(self, value: i16) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::I16(value))
+        }
+
+        fn visit_i32<F>(self, value: i32) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::I32(value))
+        }
+
+        fn visit_i64<F>(self, value: i64) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::I64(value))
+        }
+
+        fn visit_u8<F>(self, value: u8) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::U8(value))
+        }
+
+        fn visit_u16<F>(self, value: u16) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::U16(value))
+        }
+
+        fn visit_u32<F>(self, value: u32) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::U32(value))
+        }
+
+        fn visit_u64<F>(self, value: u64) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::U64(value))
+        }
+
+        fn visit_f32<F>(self, value: f32) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::F32(value))
+        }
+
+        fn visit_f64<F>(self, value: f64) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::F64(value))
+        }
+
+        fn visit_char<F>(self, value: char) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::Char(value))
+        }
+
+        fn visit_str<F>(self, value: &str) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::String(value.into()))
+        }
+
+        fn visit_borrowed_str<F>(self, value: &'de str) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::Str(value))
+        }
+
+        fn visit_string<F>(self, value: String) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::String(value))
+        }
+
+        fn visit_bytes<F>(self, value: &[u8]) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::ByteBuf(value.into()))
+        }
+
+        fn visit_borrowed_bytes<F>(self, value: &'de [u8]) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::Bytes(value))
+        }
+
+        fn visit_byte_buf<F>(self, value: Vec<u8>) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::ByteBuf(value))
+        }
+
+        fn visit_unit<F>(self) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::Unit)
+        }
+
+        fn visit_none<F>(self) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            Ok(Content::None)
+        }
+
+        fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            Deserialize::deserialize(deserializer).map(|v| Content::Some(Box::new(v)))
+        }
+
+        fn visit_newtype_struct<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            Deserialize::deserialize(deserializer).map(|v| Content::Newtype(Box::new(v)))
+        }
+
+        fn visit_seq<V>(self, mut visitor: V) -> Result<Self::Value, V::Error>
+        where
+            V: SeqAccess<'de>,
+        {
+            let mut vec =
+                Vec::<Content>::with_capacity(size_hint::cautious::<Content>(visitor.size_hint()));
+            while let Some(e) = tri!(visitor.next_element()) {
+                vec.push(e);
+            }
+            Ok(Content::Seq(vec))
+        }
+
+        fn visit_map<V>(self, mut visitor: V) -> Result<Self::Value, V::Error>
+        where
+            V: MapAccess<'de>,
+        {
+            let mut vec =
+                Vec::<(Content, Content)>::with_capacity(
+                    size_hint::cautious::<(Content, Content)>(visitor.size_hint()),
+                );
+            while let Some(kv) = tri!(visitor.next_entry()) {
+                vec.push(kv);
+            }
+            Ok(Content::Map(vec))
+        }
+
+        fn visit_enum<V>(self, _visitor: V) -> Result<Self::Value, V::Error>
+        where
+            V: EnumAccess<'de>,
+        {
+            Err(de::Error::custom(
+                "untagged and internally tagged enums do not support enum input",
+            ))
+        }
+    }
+
+    /// This is the type of the map keys in an internally tagged enum.
+    ///
+    /// Not public API.
+    pub enum TagOrContent<'de> {
+        Tag,
+        Content(Content<'de>),
+    }
+
+    struct TagOrContentVisitor<'de> {
+        name: &'static str,
+        value: PhantomData<TagOrContent<'de>>,
+    }
+
+    impl<'de> TagOrContentVisitor<'de> {
+        fn new(name: &'static str) -> Self {
+            TagOrContentVisitor {
+                name,
+                value: PhantomData,
+            }
+        }
+    }
+
+    impl<'de> DeserializeSeed<'de> for TagOrContentVisitor<'de> {
+        type Value = TagOrContent<'de>;
+
+        fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            // Internally tagged enums are only supported in self-describing
+            // formats.
+            deserializer.deserialize_any(self)
+        }
+    }
+
+    impl<'de> Visitor<'de> for TagOrContentVisitor<'de> {
+        type Value = TagOrContent<'de>;
+
+        fn expecting(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+            write!(fmt, "a type tag `{}` or any other value", self.name)
+        }
+
+        fn visit_bool<F>(self, value: bool) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_bool(value)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_i8<F>(self, value: i8) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_i8(value)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_i16<F>(self, value: i16) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_i16(value)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_i32<F>(self, value: i32) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_i32(value)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_i64<F>(self, value: i64) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_i64(value)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_u8<F>(self, value: u8) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_u8(value)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_u16<F>(self, value: u16) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_u16(value)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_u32<F>(self, value: u32) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_u32(value)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_u64<F>(self, value: u64) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_u64(value)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_f32<F>(self, value: f32) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_f32(value)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_f64<F>(self, value: f64) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_f64(value)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_char<F>(self, value: char) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_char(value)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_str<F>(self, value: &str) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            if value == self.name {
+                Ok(TagOrContent::Tag)
+            } else {
+                ContentVisitor::new()
+                    .visit_str(value)
+                    .map(TagOrContent::Content)
+            }
+        }
+
+        fn visit_borrowed_str<F>(self, value: &'de str) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            if value == self.name {
+                Ok(TagOrContent::Tag)
+            } else {
+                ContentVisitor::new()
+                    .visit_borrowed_str(value)
+                    .map(TagOrContent::Content)
+            }
+        }
+
+        fn visit_string<F>(self, value: String) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            if value == self.name {
+                Ok(TagOrContent::Tag)
+            } else {
+                ContentVisitor::new()
+                    .visit_string(value)
+                    .map(TagOrContent::Content)
+            }
+        }
+
+        fn visit_bytes<F>(self, value: &[u8]) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            if value == self.name.as_bytes() {
+                Ok(TagOrContent::Tag)
+            } else {
+                ContentVisitor::new()
+                    .visit_bytes(value)
+                    .map(TagOrContent::Content)
+            }
+        }
+
+        fn visit_borrowed_bytes<F>(self, value: &'de [u8]) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            if value == self.name.as_bytes() {
+                Ok(TagOrContent::Tag)
+            } else {
+                ContentVisitor::new()
+                    .visit_borrowed_bytes(value)
+                    .map(TagOrContent::Content)
+            }
+        }
+
+        fn visit_byte_buf<F>(self, value: Vec<u8>) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            if value == self.name.as_bytes() {
+                Ok(TagOrContent::Tag)
+            } else {
+                ContentVisitor::new()
+                    .visit_byte_buf(value)
+                    .map(TagOrContent::Content)
+            }
+        }
+
+        fn visit_unit<F>(self) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_unit()
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_none<F>(self) -> Result<Self::Value, F>
+        where
+            F: de::Error,
+        {
+            ContentVisitor::new()
+                .visit_none()
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            ContentVisitor::new()
+                .visit_some(deserializer)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_newtype_struct<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            ContentVisitor::new()
+                .visit_newtype_struct(deserializer)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_seq<V>(self, visitor: V) -> Result<Self::Value, V::Error>
+        where
+            V: SeqAccess<'de>,
+        {
+            ContentVisitor::new()
+                .visit_seq(visitor)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_map<V>(self, visitor: V) -> Result<Self::Value, V::Error>
+        where
+            V: MapAccess<'de>,
+        {
+            ContentVisitor::new()
+                .visit_map(visitor)
+                .map(TagOrContent::Content)
+        }
+
+        fn visit_enum<V>(self, visitor: V) -> Result<Self::Value, V::Error>
+        where
+            V: EnumAccess<'de>,
+        {
+            ContentVisitor::new()
+                .visit_enum(visitor)
+                .map(TagOrContent::Content)
+        }
+    }
+
+    /// Used by generated code to deserialize an internally tagged enum.
+    ///
+    /// Not public API.
+    pub struct TaggedContentVisitor<T> {
+        tag_name: &'static str,
+        expecting: &'static str,
+        value: PhantomData<T>,
+    }
+
+    impl<T> TaggedContentVisitor<T> {
+        /// Visitor for the content of an internally tagged enum with the given
+        /// tag name.
+        pub fn new(name: &'static str, expecting: &'static str) -> Self {
+            TaggedContentVisitor {
+                tag_name: name,
+                expecting,
+                value: PhantomData,
+            }
+        }
+    }
+
+    impl<'de, T> Visitor<'de> for TaggedContentVisitor<T>
+    where
+        T: Deserialize<'de>,
+    {
+        type Value = (T, Content<'de>);
+
+        fn expecting(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+            fmt.write_str(self.expecting)
+        }
+
+        fn visit_seq<S>(self, mut seq: S) -> Result<Self::Value, S::Error>
+        where
+            S: SeqAccess<'de>,
+        {
+            let tag = match tri!(seq.next_element()) {
+                Some(tag) => tag,
+                None => {
+                    return Err(de::Error::missing_field(self.tag_name));
+                }
+            };
+            let rest = de::value::SeqAccessDeserializer::new(seq);
+            Ok((tag, tri!(Content::deserialize(rest))))
+        }
+
+        fn visit_map<M>(self, mut map: M) -> Result<Self::Value, M::Error>
+        where
+            M: MapAccess<'de>,
+        {
+            let mut tag = None;
+            let mut vec = Vec::<(Content, Content)>::with_capacity(size_hint::cautious::<(
+                Content,
+                Content,
+            )>(map.size_hint()));
+            while let Some(k) = tri!(map.next_key_seed(TagOrContentVisitor::new(self.tag_name))) {
+                match k {
+                    TagOrContent::Tag => {
+                        if tag.is_some() {
+                            return Err(de::Error::duplicate_field(self.tag_name));
+                        }
+                        tag = Some(tri!(map.next_value()));
+                    }
+                    TagOrContent::Content(k) => {
+                        let v = tri!(map.next_value());
+                        vec.push((k, v));
+                    }
+                }
+            }
+            match tag {
+                None => Err(de::Error::missing_field(self.tag_name)),
+                Some(tag) => Ok((tag, Content::Map(vec))),
+            }
+        }
+    }
+
+    /// Used by generated code to deserialize an adjacently tagged enum.
+    ///
+    /// Not public API.
+    pub enum TagOrContentField {
+        Tag,
+        Content,
+    }
+
+    /// Not public API.
+    pub struct TagOrContentFieldVisitor {
+        pub tag: &'static str,
+        pub content: &'static str,
+    }
+
+    impl<'de> DeserializeSeed<'de> for TagOrContentFieldVisitor {
+        type Value = TagOrContentField;
+
+        fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            deserializer.deserialize_identifier(self)
+        }
+    }
+
+    impl<'de> Visitor<'de> for TagOrContentFieldVisitor {
+        type Value = TagOrContentField;
+
+        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            write!(formatter, "{:?} or {:?}", self.tag, self.content)
+        }
+
+        fn visit_u64<E>(self, field_index: u64) -> Result<Self::Value, E>
+        where
+            E: de::Error,
+        {
+            match field_index {
+                0 => Ok(TagOrContentField::Tag),
+                1 => Ok(TagOrContentField::Content),
+                _ => Err(de::Error::invalid_value(
+                    Unexpected::Unsigned(field_index),
+                    &self,
+                )),
+            }
+        }
+
+        fn visit_str<E>(self, field: &str) -> Result<Self::Value, E>
+        where
+            E: de::Error,
+        {
+            if field == self.tag {
+                Ok(TagOrContentField::Tag)
+            } else if field == self.content {
+                Ok(TagOrContentField::Content)
+            } else {
+                Err(de::Error::invalid_value(Unexpected::Str(field), &self))
+            }
+        }
+
+        fn visit_bytes<E>(self, field: &[u8]) -> Result<Self::Value, E>
+        where
+            E: de::Error,
+        {
+            if field == self.tag.as_bytes() {
+                Ok(TagOrContentField::Tag)
+            } else if field == self.content.as_bytes() {
+                Ok(TagOrContentField::Content)
+            } else {
+                Err(de::Error::invalid_value(Unexpected::Bytes(field), &self))
+            }
+        }
+    }
+
+    /// Used by generated code to deserialize an adjacently tagged enum when
+    /// ignoring unrelated fields is allowed.
+    ///
+    /// Not public API.
+    pub enum TagContentOtherField {
+        Tag,
+        Content,
+        Other,
+    }
+
+    /// Not public API.
+    pub struct TagContentOtherFieldVisitor {
+        pub tag: &'static str,
+        pub content: &'static str,
+    }
+
+    impl<'de> DeserializeSeed<'de> for TagContentOtherFieldVisitor {
+        type Value = TagContentOtherField;
+
+        fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            deserializer.deserialize_identifier(self)
+        }
+    }
+
+    impl<'de> Visitor<'de> for TagContentOtherFieldVisitor {
+        type Value = TagContentOtherField;
+
+        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            write!(
+                formatter,
+                "{:?}, {:?}, or other ignored fields",
+                self.tag, self.content
+            )
+        }
+
+        fn visit_u64<E>(self, field_index: u64) -> Result<Self::Value, E>
+        where
+            E: de::Error,
+        {
+            match field_index {
+                0 => Ok(TagContentOtherField::Tag),
+                1 => Ok(TagContentOtherField::Content),
+                _ => Ok(TagContentOtherField::Other),
+            }
+        }
+
+        fn visit_str<E>(self, field: &str) -> Result<Self::Value, E>
+        where
+            E: de::Error,
+        {
+            self.visit_bytes(field.as_bytes())
+        }
+
+        fn visit_bytes<E>(self, field: &[u8]) -> Result<Self::Value, E>
+        where
+            E: de::Error,
+        {
+            if field == self.tag.as_bytes() {
+                Ok(TagContentOtherField::Tag)
+            } else if field == self.content.as_bytes() {
+                Ok(TagContentOtherField::Content)
+            } else {
+                Ok(TagContentOtherField::Other)
+            }
+        }
+    }
+
+    /// Not public API
+    pub struct ContentDeserializer<'de, E> {
+        content: Content<'de>,
+        err: PhantomData<E>,
+    }
+
+    impl<'de, E> ContentDeserializer<'de, E>
+    where
+        E: de::Error,
+    {
+        #[cold]
+        fn invalid_type(self, exp: &Expected) -> E {
+            de::Error::invalid_type(self.content.unexpected(), exp)
+        }
+
+        fn deserialize_integer<V>(self, visitor: V) -> Result<V::Value, E>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::U8(v) => visitor.visit_u8(v),
+                Content::U16(v) => visitor.visit_u16(v),
+                Content::U32(v) => visitor.visit_u32(v),
+                Content::U64(v) => visitor.visit_u64(v),
+                Content::I8(v) => visitor.visit_i8(v),
+                Content::I16(v) => visitor.visit_i16(v),
+                Content::I32(v) => visitor.visit_i32(v),
+                Content::I64(v) => visitor.visit_i64(v),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_float<V>(self, visitor: V) -> Result<V::Value, E>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::F32(v) => visitor.visit_f32(v),
+                Content::F64(v) => visitor.visit_f64(v),
+                Content::U8(v) => visitor.visit_u8(v),
+                Content::U16(v) => visitor.visit_u16(v),
+                Content::U32(v) => visitor.visit_u32(v),
+                Content::U64(v) => visitor.visit_u64(v),
+                Content::I8(v) => visitor.visit_i8(v),
+                Content::I16(v) => visitor.visit_i16(v),
+                Content::I32(v) => visitor.visit_i32(v),
+                Content::I64(v) => visitor.visit_i64(v),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+    }
+
+    fn visit_content_seq<'de, V, E>(content: Vec<Content<'de>>, visitor: V) -> Result<V::Value, E>
+    where
+        V: Visitor<'de>,
+        E: de::Error,
+    {
+        let seq = content.into_iter().map(ContentDeserializer::new);
+        let mut seq_visitor = SeqDeserializer::new(seq);
+        let value = tri!(visitor.visit_seq(&mut seq_visitor));
+        tri!(seq_visitor.end());
+        Ok(value)
+    }
+
+    fn visit_content_map<'de, V, E>(
+        content: Vec<(Content<'de>, Content<'de>)>,
+        visitor: V,
+    ) -> Result<V::Value, E>
+    where
+        V: Visitor<'de>,
+        E: de::Error,
+    {
+        let map = content
+            .into_iter()
+            .map(|(k, v)| (ContentDeserializer::new(k), ContentDeserializer::new(v)));
+        let mut map_visitor = MapDeserializer::new(map);
+        let value = tri!(visitor.visit_map(&mut map_visitor));
+        tri!(map_visitor.end());
+        Ok(value)
+    }
+
+    /// Used when deserializing an internally tagged enum because the content
+    /// will be used exactly once.
+    impl<'de, E> Deserializer<'de> for ContentDeserializer<'de, E>
+    where
+        E: de::Error,
+    {
+        type Error = E;
+
+        fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::Bool(v) => visitor.visit_bool(v),
+                Content::U8(v) => visitor.visit_u8(v),
+                Content::U16(v) => visitor.visit_u16(v),
+                Content::U32(v) => visitor.visit_u32(v),
+                Content::U64(v) => visitor.visit_u64(v),
+                Content::I8(v) => visitor.visit_i8(v),
+                Content::I16(v) => visitor.visit_i16(v),
+                Content::I32(v) => visitor.visit_i32(v),
+                Content::I64(v) => visitor.visit_i64(v),
+                Content::F32(v) => visitor.visit_f32(v),
+                Content::F64(v) => visitor.visit_f64(v),
+                Content::Char(v) => visitor.visit_char(v),
+                Content::String(v) => visitor.visit_string(v),
+                Content::Str(v) => visitor.visit_borrowed_str(v),
+                Content::ByteBuf(v) => visitor.visit_byte_buf(v),
+                Content::Bytes(v) => visitor.visit_borrowed_bytes(v),
+                Content::Unit => visitor.visit_unit(),
+                Content::None => visitor.visit_none(),
+                Content::Some(v) => visitor.visit_some(ContentDeserializer::new(*v)),
+                Content::Newtype(v) => visitor.visit_newtype_struct(ContentDeserializer::new(*v)),
+                Content::Seq(v) => visit_content_seq(v, visitor),
+                Content::Map(v) => visit_content_map(v, visitor),
+            }
+        }
+
+        fn deserialize_bool<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::Bool(v) => visitor.visit_bool(v),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_i8<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_i16<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_i32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_i64<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_u8<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_u16<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_u32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_u64<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_f32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_float(visitor)
+        }
+
+        fn deserialize_f64<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_float(visitor)
+        }
+
+        fn deserialize_char<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::Char(v) => visitor.visit_char(v),
+                Content::String(v) => visitor.visit_string(v),
+                Content::Str(v) => visitor.visit_borrowed_str(v),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_str<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_string(visitor)
+        }
+
+        fn deserialize_string<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::String(v) => visitor.visit_string(v),
+                Content::Str(v) => visitor.visit_borrowed_str(v),
+                Content::ByteBuf(v) => visitor.visit_byte_buf(v),
+                Content::Bytes(v) => visitor.visit_borrowed_bytes(v),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_bytes<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_byte_buf(visitor)
+        }
+
+        fn deserialize_byte_buf<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::String(v) => visitor.visit_string(v),
+                Content::Str(v) => visitor.visit_borrowed_str(v),
+                Content::ByteBuf(v) => visitor.visit_byte_buf(v),
+                Content::Bytes(v) => visitor.visit_borrowed_bytes(v),
+                Content::Seq(v) => visit_content_seq(v, visitor),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::None => visitor.visit_none(),
+                Content::Some(v) => visitor.visit_some(ContentDeserializer::new(*v)),
+                Content::Unit => visitor.visit_unit(),
+                _ => visitor.visit_some(self),
+            }
+        }
+
+        fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::Unit => visitor.visit_unit(),
+
+                // Allow deserializing newtype variant containing unit.
+                //
+                //     #[derive(Deserialize)]
+                //     #[serde(tag = "result")]
+                //     enum Response<T> {
+                //         Success(T),
+                //     }
+                //
+                // We want {"result":"Success"} to deserialize into Response<()>.
+                Content::Map(ref v) if v.is_empty() => visitor.visit_unit(),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_unit_struct<V>(
+            self,
+            _name: &'static str,
+            visitor: V,
+        ) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                // As a special case, allow deserializing untagged newtype
+                // variant containing unit struct.
+                //
+                //     #[derive(Deserialize)]
+                //     struct Info;
+                //
+                //     #[derive(Deserialize)]
+                //     #[serde(tag = "topic")]
+                //     enum Message {
+                //         Info(Info),
+                //     }
+                //
+                // We want {"topic":"Info"} to deserialize even though
+                // ordinarily unit structs do not deserialize from empty map/seq.
+                Content::Map(ref v) if v.is_empty() => visitor.visit_unit(),
+                Content::Seq(ref v) if v.is_empty() => visitor.visit_unit(),
+                _ => self.deserialize_any(visitor),
+            }
+        }
+
+        fn deserialize_newtype_struct<V>(
+            self,
+            _name: &str,
+            visitor: V,
+        ) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::Newtype(v) => visitor.visit_newtype_struct(ContentDeserializer::new(*v)),
+                _ => visitor.visit_newtype_struct(self),
+            }
+        }
+
+        fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::Seq(v) => visit_content_seq(v, visitor),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_tuple<V>(self, _len: usize, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_seq(visitor)
+        }
+
+        fn deserialize_tuple_struct<V>(
+            self,
+            _name: &'static str,
+            _len: usize,
+            visitor: V,
+        ) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_seq(visitor)
+        }
+
+        fn deserialize_map<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::Map(v) => visit_content_map(v, visitor),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_struct<V>(
+            self,
+            _name: &'static str,
+            _fields: &'static [&'static str],
+            visitor: V,
+        ) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::Seq(v) => visit_content_seq(v, visitor),
+                Content::Map(v) => visit_content_map(v, visitor),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_enum<V>(
+            self,
+            _name: &str,
+            _variants: &'static [&'static str],
+            visitor: V,
+        ) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            let (variant, value) = match self.content {
+                Content::Map(value) => {
+                    let mut iter = value.into_iter();
+                    let (variant, value) = match iter.next() {
+                        Some(v) => v,
+                        None => {
+                            return Err(de::Error::invalid_value(
+                                de::Unexpected::Map,
+                                &"map with a single key",
+                            ));
+                        }
+                    };
+                    // enums are encoded in json as maps with a single key:value pair
+                    if iter.next().is_some() {
+                        return Err(de::Error::invalid_value(
+                            de::Unexpected::Map,
+                            &"map with a single key",
+                        ));
+                    }
+                    (variant, Some(value))
+                }
+                s @ Content::String(_) | s @ Content::Str(_) => (s, None),
+                other => {
+                    return Err(de::Error::invalid_type(
+                        other.unexpected(),
+                        &"string or map",
+                    ));
+                }
+            };
+
+            visitor.visit_enum(EnumDeserializer::new(variant, value))
+        }
+
+        fn deserialize_identifier<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.content {
+                Content::String(v) => visitor.visit_string(v),
+                Content::Str(v) => visitor.visit_borrowed_str(v),
+                Content::ByteBuf(v) => visitor.visit_byte_buf(v),
+                Content::Bytes(v) => visitor.visit_borrowed_bytes(v),
+                Content::U8(v) => visitor.visit_u8(v),
+                Content::U64(v) => visitor.visit_u64(v),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            drop(self);
+            visitor.visit_unit()
+        }
+
+        fn __deserialize_content<V>(
+            self,
+            _: actually_private::T,
+            visitor: V,
+        ) -> Result<Content<'de>, Self::Error>
+        where
+            V: Visitor<'de, Value = Content<'de>>,
+        {
+            let _ = visitor;
+            Ok(self.content)
+        }
+    }
+
+    impl<'de, E> ContentDeserializer<'de, E> {
+        /// private API, don't use
+        pub fn new(content: Content<'de>) -> Self {
+            ContentDeserializer {
+                content,
+                err: PhantomData,
+            }
+        }
+    }
+
+    pub struct EnumDeserializer<'de, E>
+    where
+        E: de::Error,
+    {
+        variant: Content<'de>,
+        value: Option<Content<'de>>,
+        err: PhantomData<E>,
+    }
+
+    impl<'de, E> EnumDeserializer<'de, E>
+    where
+        E: de::Error,
+    {
+        pub fn new(variant: Content<'de>, value: Option<Content<'de>>) -> EnumDeserializer<'de, E> {
+            EnumDeserializer {
+                variant,
+                value,
+                err: PhantomData,
+            }
+        }
+    }
+
+    impl<'de, E> de::EnumAccess<'de> for EnumDeserializer<'de, E>
+    where
+        E: de::Error,
+    {
+        type Error = E;
+        type Variant = VariantDeserializer<'de, Self::Error>;
+
+        fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self::Variant), E>
+        where
+            V: de::DeserializeSeed<'de>,
+        {
+            let visitor = VariantDeserializer {
+                value: self.value,
+                err: PhantomData,
+            };
+            seed.deserialize(ContentDeserializer::new(self.variant))
+                .map(|v| (v, visitor))
+        }
+    }
+
+    pub struct VariantDeserializer<'de, E>
+    where
+        E: de::Error,
+    {
+        value: Option<Content<'de>>,
+        err: PhantomData<E>,
+    }
+
+    impl<'de, E> de::VariantAccess<'de> for VariantDeserializer<'de, E>
+    where
+        E: de::Error,
+    {
+        type Error = E;
+
+        fn unit_variant(self) -> Result<(), E> {
+            match self.value {
+                Some(value) => de::Deserialize::deserialize(ContentDeserializer::new(value)),
+                None => Ok(()),
+            }
+        }
+
+        fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value, E>
+        where
+            T: de::DeserializeSeed<'de>,
+        {
+            match self.value {
+                Some(value) => seed.deserialize(ContentDeserializer::new(value)),
+                None => Err(de::Error::invalid_type(
+                    de::Unexpected::UnitVariant,
+                    &"newtype variant",
+                )),
+            }
+        }
+
+        fn tuple_variant<V>(self, _len: usize, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: de::Visitor<'de>,
+        {
+            match self.value {
+                Some(Content::Seq(v)) => {
+                    de::Deserializer::deserialize_any(SeqDeserializer::new(v.into_iter()), visitor)
+                }
+                Some(other) => Err(de::Error::invalid_type(
+                    other.unexpected(),
+                    &"tuple variant",
+                )),
+                None => Err(de::Error::invalid_type(
+                    de::Unexpected::UnitVariant,
+                    &"tuple variant",
+                )),
+            }
+        }
+
+        fn struct_variant<V>(
+            self,
+            _fields: &'static [&'static str],
+            visitor: V,
+        ) -> Result<V::Value, Self::Error>
+        where
+            V: de::Visitor<'de>,
+        {
+            match self.value {
+                Some(Content::Map(v)) => {
+                    de::Deserializer::deserialize_any(MapDeserializer::new(v.into_iter()), visitor)
+                }
+                Some(Content::Seq(v)) => {
+                    de::Deserializer::deserialize_any(SeqDeserializer::new(v.into_iter()), visitor)
+                }
+                Some(other) => Err(de::Error::invalid_type(
+                    other.unexpected(),
+                    &"struct variant",
+                )),
+                None => Err(de::Error::invalid_type(
+                    de::Unexpected::UnitVariant,
+                    &"struct variant",
+                )),
+            }
+        }
+    }
+
+    /// Not public API.
+    pub struct ContentRefDeserializer<'a, 'de: 'a, E> {
+        content: &'a Content<'de>,
+        err: PhantomData<E>,
+    }
+
+    impl<'a, 'de, E> ContentRefDeserializer<'a, 'de, E>
+    where
+        E: de::Error,
+    {
+        #[cold]
+        fn invalid_type(self, exp: &Expected) -> E {
+            de::Error::invalid_type(self.content.unexpected(), exp)
+        }
+
+        fn deserialize_integer<V>(self, visitor: V) -> Result<V::Value, E>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::U8(v) => visitor.visit_u8(v),
+                Content::U16(v) => visitor.visit_u16(v),
+                Content::U32(v) => visitor.visit_u32(v),
+                Content::U64(v) => visitor.visit_u64(v),
+                Content::I8(v) => visitor.visit_i8(v),
+                Content::I16(v) => visitor.visit_i16(v),
+                Content::I32(v) => visitor.visit_i32(v),
+                Content::I64(v) => visitor.visit_i64(v),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_float<V>(self, visitor: V) -> Result<V::Value, E>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::F32(v) => visitor.visit_f32(v),
+                Content::F64(v) => visitor.visit_f64(v),
+                Content::U8(v) => visitor.visit_u8(v),
+                Content::U16(v) => visitor.visit_u16(v),
+                Content::U32(v) => visitor.visit_u32(v),
+                Content::U64(v) => visitor.visit_u64(v),
+                Content::I8(v) => visitor.visit_i8(v),
+                Content::I16(v) => visitor.visit_i16(v),
+                Content::I32(v) => visitor.visit_i32(v),
+                Content::I64(v) => visitor.visit_i64(v),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+    }
+
+    fn visit_content_seq_ref<'a, 'de, V, E>(
+        content: &'a [Content<'de>],
+        visitor: V,
+    ) -> Result<V::Value, E>
+    where
+        V: Visitor<'de>,
+        E: de::Error,
+    {
+        let seq = content.iter().map(ContentRefDeserializer::new);
+        let mut seq_visitor = SeqDeserializer::new(seq);
+        let value = tri!(visitor.visit_seq(&mut seq_visitor));
+        tri!(seq_visitor.end());
+        Ok(value)
+    }
+
+    fn visit_content_map_ref<'a, 'de, V, E>(
+        content: &'a [(Content<'de>, Content<'de>)],
+        visitor: V,
+    ) -> Result<V::Value, E>
+    where
+        V: Visitor<'de>,
+        E: de::Error,
+    {
+        let map = content.iter().map(|(k, v)| {
+            (
+                ContentRefDeserializer::new(k),
+                ContentRefDeserializer::new(v),
+            )
+        });
+        let mut map_visitor = MapDeserializer::new(map);
+        let value = tri!(visitor.visit_map(&mut map_visitor));
+        tri!(map_visitor.end());
+        Ok(value)
+    }
+
+    /// Used when deserializing an untagged enum because the content may need
+    /// to be used more than once.
+    impl<'de, 'a, E> Deserializer<'de> for ContentRefDeserializer<'a, 'de, E>
+    where
+        E: de::Error,
+    {
+        type Error = E;
+
+        fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, E>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::Bool(v) => visitor.visit_bool(v),
+                Content::U8(v) => visitor.visit_u8(v),
+                Content::U16(v) => visitor.visit_u16(v),
+                Content::U32(v) => visitor.visit_u32(v),
+                Content::U64(v) => visitor.visit_u64(v),
+                Content::I8(v) => visitor.visit_i8(v),
+                Content::I16(v) => visitor.visit_i16(v),
+                Content::I32(v) => visitor.visit_i32(v),
+                Content::I64(v) => visitor.visit_i64(v),
+                Content::F32(v) => visitor.visit_f32(v),
+                Content::F64(v) => visitor.visit_f64(v),
+                Content::Char(v) => visitor.visit_char(v),
+                Content::String(ref v) => visitor.visit_str(v),
+                Content::Str(v) => visitor.visit_borrowed_str(v),
+                Content::ByteBuf(ref v) => visitor.visit_bytes(v),
+                Content::Bytes(v) => visitor.visit_borrowed_bytes(v),
+                Content::Unit => visitor.visit_unit(),
+                Content::None => visitor.visit_none(),
+                Content::Some(ref v) => visitor.visit_some(ContentRefDeserializer::new(v)),
+                Content::Newtype(ref v) => {
+                    visitor.visit_newtype_struct(ContentRefDeserializer::new(v))
+                }
+                Content::Seq(ref v) => visit_content_seq_ref(v, visitor),
+                Content::Map(ref v) => visit_content_map_ref(v, visitor),
+            }
+        }
+
+        fn deserialize_bool<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::Bool(v) => visitor.visit_bool(v),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_i8<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_i16<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_i32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_i64<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_u8<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_u16<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_u32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_u64<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_integer(visitor)
+        }
+
+        fn deserialize_f32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_float(visitor)
+        }
+
+        fn deserialize_f64<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_float(visitor)
+        }
+
+        fn deserialize_char<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::Char(v) => visitor.visit_char(v),
+                Content::String(ref v) => visitor.visit_str(v),
+                Content::Str(v) => visitor.visit_borrowed_str(v),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_str<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::String(ref v) => visitor.visit_str(v),
+                Content::Str(v) => visitor.visit_borrowed_str(v),
+                Content::ByteBuf(ref v) => visitor.visit_bytes(v),
+                Content::Bytes(v) => visitor.visit_borrowed_bytes(v),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_string<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_str(visitor)
+        }
+
+        fn deserialize_bytes<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::String(ref v) => visitor.visit_str(v),
+                Content::Str(v) => visitor.visit_borrowed_str(v),
+                Content::ByteBuf(ref v) => visitor.visit_bytes(v),
+                Content::Bytes(v) => visitor.visit_borrowed_bytes(v),
+                Content::Seq(ref v) => visit_content_seq_ref(v, visitor),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_byte_buf<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_bytes(visitor)
+        }
+
+        fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, E>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::None => visitor.visit_none(),
+                Content::Some(ref v) => visitor.visit_some(ContentRefDeserializer::new(v)),
+                Content::Unit => visitor.visit_unit(),
+                _ => visitor.visit_some(self),
+            }
+        }
+
+        fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::Unit => visitor.visit_unit(),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_unit_struct<V>(
+            self,
+            _name: &'static str,
+            visitor: V,
+        ) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_unit(visitor)
+        }
+
+        fn deserialize_newtype_struct<V>(self, _name: &str, visitor: V) -> Result<V::Value, E>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::Newtype(ref v) => {
+                    visitor.visit_newtype_struct(ContentRefDeserializer::new(v))
+                }
+                _ => visitor.visit_newtype_struct(self),
+            }
+        }
+
+        fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::Seq(ref v) => visit_content_seq_ref(v, visitor),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_tuple<V>(self, _len: usize, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_seq(visitor)
+        }
+
+        fn deserialize_tuple_struct<V>(
+            self,
+            _name: &'static str,
+            _len: usize,
+            visitor: V,
+        ) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_seq(visitor)
+        }
+
+        fn deserialize_map<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::Map(ref v) => visit_content_map_ref(v, visitor),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_struct<V>(
+            self,
+            _name: &'static str,
+            _fields: &'static [&'static str],
+            visitor: V,
+        ) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::Seq(ref v) => visit_content_seq_ref(v, visitor),
+                Content::Map(ref v) => visit_content_map_ref(v, visitor),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_enum<V>(
+            self,
+            _name: &str,
+            _variants: &'static [&'static str],
+            visitor: V,
+        ) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            let (variant, value) = match *self.content {
+                Content::Map(ref value) => {
+                    let mut iter = value.iter();
+                    let (variant, value) = match iter.next() {
+                        Some(v) => v,
+                        None => {
+                            return Err(de::Error::invalid_value(
+                                de::Unexpected::Map,
+                                &"map with a single key",
+                            ));
+                        }
+                    };
+                    // enums are encoded in json as maps with a single key:value pair
+                    if iter.next().is_some() {
+                        return Err(de::Error::invalid_value(
+                            de::Unexpected::Map,
+                            &"map with a single key",
+                        ));
+                    }
+                    (variant, Some(value))
+                }
+                ref s @ Content::String(_) | ref s @ Content::Str(_) => (s, None),
+                ref other => {
+                    return Err(de::Error::invalid_type(
+                        other.unexpected(),
+                        &"string or map",
+                    ));
+                }
+            };
+
+            visitor.visit_enum(EnumRefDeserializer {
+                variant,
+                value,
+                err: PhantomData,
+            })
+        }
+
+        fn deserialize_identifier<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            match *self.content {
+                Content::String(ref v) => visitor.visit_str(v),
+                Content::Str(v) => visitor.visit_borrowed_str(v),
+                Content::ByteBuf(ref v) => visitor.visit_bytes(v),
+                Content::Bytes(v) => visitor.visit_borrowed_bytes(v),
+                Content::U8(v) => visitor.visit_u8(v),
+                Content::U64(v) => visitor.visit_u64(v),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: Visitor<'de>,
+        {
+            visitor.visit_unit()
+        }
+
+        fn __deserialize_content<V>(
+            self,
+            _: actually_private::T,
+            visitor: V,
+        ) -> Result<Content<'de>, Self::Error>
+        where
+            V: Visitor<'de, Value = Content<'de>>,
+        {
+            let _ = visitor;
+            Ok(self.content.clone())
+        }
+    }
+
+    impl<'a, 'de, E> ContentRefDeserializer<'a, 'de, E> {
+        /// private API, don't use
+        pub fn new(content: &'a Content<'de>) -> Self {
+            ContentRefDeserializer {
+                content,
+                err: PhantomData,
+            }
+        }
+    }
+
+    impl<'a, 'de: 'a, E> Copy for ContentRefDeserializer<'a, 'de, E> {}
+
+    impl<'a, 'de: 'a, E> Clone for ContentRefDeserializer<'a, 'de, E> {
+        fn clone(&self) -> Self {
+            *self
+        }
+    }
+
+    struct EnumRefDeserializer<'a, 'de: 'a, E>
+    where
+        E: de::Error,
+    {
+        variant: &'a Content<'de>,
+        value: Option<&'a Content<'de>>,
+        err: PhantomData<E>,
+    }
+
+    impl<'de, 'a, E> de::EnumAccess<'de> for EnumRefDeserializer<'a, 'de, E>
+    where
+        E: de::Error,
+    {
+        type Error = E;
+        type Variant = VariantRefDeserializer<'a, 'de, Self::Error>;
+
+        fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self::Variant), Self::Error>
+        where
+            V: de::DeserializeSeed<'de>,
+        {
+            let visitor = VariantRefDeserializer {
+                value: self.value,
+                err: PhantomData,
+            };
+            seed.deserialize(ContentRefDeserializer::new(self.variant))
+                .map(|v| (v, visitor))
+        }
+    }
+
+    struct VariantRefDeserializer<'a, 'de: 'a, E>
+    where
+        E: de::Error,
+    {
+        value: Option<&'a Content<'de>>,
+        err: PhantomData<E>,
+    }
+
+    impl<'de, 'a, E> de::VariantAccess<'de> for VariantRefDeserializer<'a, 'de, E>
+    where
+        E: de::Error,
+    {
+        type Error = E;
+
+        fn unit_variant(self) -> Result<(), E> {
+            match self.value {
+                Some(value) => de::Deserialize::deserialize(ContentRefDeserializer::new(value)),
+                None => Ok(()),
+            }
+        }
+
+        fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value, E>
+        where
+            T: de::DeserializeSeed<'de>,
+        {
+            match self.value {
+                Some(value) => seed.deserialize(ContentRefDeserializer::new(value)),
+                None => Err(de::Error::invalid_type(
+                    de::Unexpected::UnitVariant,
+                    &"newtype variant",
+                )),
+            }
+        }
+
+        fn tuple_variant<V>(self, _len: usize, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: de::Visitor<'de>,
+        {
+            match self.value {
+                Some(Content::Seq(v)) => {
+                    de::Deserializer::deserialize_any(SeqRefDeserializer::new(v), visitor)
+                }
+                Some(other) => Err(de::Error::invalid_type(
+                    other.unexpected(),
+                    &"tuple variant",
+                )),
+                None => Err(de::Error::invalid_type(
+                    de::Unexpected::UnitVariant,
+                    &"tuple variant",
+                )),
+            }
+        }
+
+        fn struct_variant<V>(
+            self,
+            _fields: &'static [&'static str],
+            visitor: V,
+        ) -> Result<V::Value, Self::Error>
+        where
+            V: de::Visitor<'de>,
+        {
+            match self.value {
+                Some(Content::Map(v)) => {
+                    de::Deserializer::deserialize_any(MapRefDeserializer::new(v), visitor)
+                }
+                Some(Content::Seq(v)) => {
+                    de::Deserializer::deserialize_any(SeqRefDeserializer::new(v), visitor)
+                }
+                Some(other) => Err(de::Error::invalid_type(
+                    other.unexpected(),
+                    &"struct variant",
+                )),
+                None => Err(de::Error::invalid_type(
+                    de::Unexpected::UnitVariant,
+                    &"struct variant",
+                )),
+            }
+        }
+    }
+
+    struct SeqRefDeserializer<'a, 'de: 'a, E>
+    where
+        E: de::Error,
+    {
+        iter: <&'a [Content<'de>] as IntoIterator>::IntoIter,
+        err: PhantomData<E>,
+    }
+
+    impl<'a, 'de, E> SeqRefDeserializer<'a, 'de, E>
+    where
+        E: de::Error,
+    {
+        fn new(slice: &'a [Content<'de>]) -> Self {
+            SeqRefDeserializer {
+                iter: slice.iter(),
+                err: PhantomData,
+            }
+        }
+    }
+
+    impl<'de, 'a, E> de::Deserializer<'de> for SeqRefDeserializer<'a, 'de, E>
+    where
+        E: de::Error,
+    {
+        type Error = E;
+
+        #[inline]
+        fn deserialize_any<V>(mut self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: de::Visitor<'de>,
+        {
+            let len = self.iter.len();
+            if len == 0 {
+                visitor.visit_unit()
+            } else {
+                let ret = tri!(visitor.visit_seq(&mut self));
+                let remaining = self.iter.len();
+                if remaining == 0 {
+                    Ok(ret)
+                } else {
+                    Err(de::Error::invalid_length(len, &"fewer elements in array"))
+                }
+            }
+        }
+
+        forward_to_deserialize_any! {
+            bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+            bytes byte_buf option unit unit_struct newtype_struct seq tuple
+            tuple_struct map struct enum identifier ignored_any
+        }
+    }
+
+    impl<'de, 'a, E> de::SeqAccess<'de> for SeqRefDeserializer<'a, 'de, E>
+    where
+        E: de::Error,
+    {
+        type Error = E;
+
+        fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
+        where
+            T: de::DeserializeSeed<'de>,
+        {
+            match self.iter.next() {
+                Some(value) => seed
+                    .deserialize(ContentRefDeserializer::new(value))
+                    .map(Some),
+                None => Ok(None),
+            }
+        }
+
+        fn size_hint(&self) -> Option<usize> {
+            size_hint::from_bounds(&self.iter)
+        }
+    }
+
+    struct MapRefDeserializer<'a, 'de: 'a, E>
+    where
+        E: de::Error,
+    {
+        iter: <&'a [(Content<'de>, Content<'de>)] as IntoIterator>::IntoIter,
+        value: Option<&'a Content<'de>>,
+        err: PhantomData<E>,
+    }
+
+    impl<'a, 'de, E> MapRefDeserializer<'a, 'de, E>
+    where
+        E: de::Error,
+    {
+        fn new(map: &'a [(Content<'de>, Content<'de>)]) -> Self {
+            MapRefDeserializer {
+                iter: map.iter(),
+                value: None,
+                err: PhantomData,
+            }
+        }
+    }
+
+    impl<'de, 'a, E> de::MapAccess<'de> for MapRefDeserializer<'a, 'de, E>
+    where
+        E: de::Error,
+    {
+        type Error = E;
+
+        fn next_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
+        where
+            T: de::DeserializeSeed<'de>,
+        {
+            match self.iter.next() {
+                Some((key, value)) => {
+                    self.value = Some(value);
+                    seed.deserialize(ContentRefDeserializer::new(key)).map(Some)
+                }
+                None => Ok(None),
+            }
+        }
+
+        fn next_value_seed<T>(&mut self, seed: T) -> Result<T::Value, Self::Error>
+        where
+            T: de::DeserializeSeed<'de>,
+        {
+            match self.value.take() {
+                Some(value) => seed.deserialize(ContentRefDeserializer::new(value)),
+                None => Err(de::Error::custom("value is missing")),
+            }
+        }
+
+        fn size_hint(&self) -> Option<usize> {
+            size_hint::from_bounds(&self.iter)
+        }
+    }
+
+    impl<'de, 'a, E> de::Deserializer<'de> for MapRefDeserializer<'a, 'de, E>
+    where
+        E: de::Error,
+    {
+        type Error = E;
+
+        #[inline]
+        fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+        where
+            V: de::Visitor<'de>,
+        {
+            visitor.visit_map(self)
+        }
+
+        forward_to_deserialize_any! {
+            bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+            bytes byte_buf option unit unit_struct newtype_struct seq tuple
+            tuple_struct map struct enum identifier ignored_any
+        }
+    }
+
+    impl<'de, E> de::IntoDeserializer<'de, E> for ContentDeserializer<'de, E>
+    where
+        E: de::Error,
+    {
+        type Deserializer = Self;
+
+        fn into_deserializer(self) -> Self {
+            self
+        }
+    }
+
+    impl<'de, 'a, E> de::IntoDeserializer<'de, E> for ContentRefDeserializer<'a, 'de, E>
+    where
+        E: de::Error,
+    {
+        type Deserializer = Self;
+
+        fn into_deserializer(self) -> Self {
+            self
+        }
+    }
+
+    /// Visitor for deserializing an internally tagged unit variant.
+    ///
+    /// Not public API.
+    pub struct InternallyTaggedUnitVisitor<'a> {
+        type_name: &'a str,
+        variant_name: &'a str,
+    }
+
+    impl<'a> InternallyTaggedUnitVisitor<'a> {
+        /// Not public API.
+        pub fn new(type_name: &'a str, variant_name: &'a str) -> Self {
+            InternallyTaggedUnitVisitor {
+                type_name,
+                variant_name,
+            }
+        }
+    }
+
+    impl<'de, 'a> Visitor<'de> for InternallyTaggedUnitVisitor<'a> {
+        type Value = ();
+
+        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            write!(
+                formatter,
+                "unit variant {}::{}",
+                self.type_name, self.variant_name
+            )
+        }
+
+        fn visit_seq<S>(self, _: S) -> Result<(), S::Error>
+        where
+            S: SeqAccess<'de>,
+        {
+            Ok(())
+        }
+
+        fn visit_map<M>(self, mut access: M) -> Result<(), M::Error>
+        where
+            M: MapAccess<'de>,
+        {
+            while tri!(access.next_entry::<IgnoredAny, IgnoredAny>()).is_some() {}
+            Ok(())
+        }
+    }
+
+    /// Visitor for deserializing an untagged unit variant.
+    ///
+    /// Not public API.
+    pub struct UntaggedUnitVisitor<'a> {
+        type_name: &'a str,
+        variant_name: &'a str,
+    }
+
+    impl<'a> UntaggedUnitVisitor<'a> {
+        /// Not public API.
+        pub fn new(type_name: &'a str, variant_name: &'a str) -> Self {
+            UntaggedUnitVisitor {
+                type_name,
+                variant_name,
+            }
+        }
+    }
+
+    impl<'de, 'a> Visitor<'de> for UntaggedUnitVisitor<'a> {
+        type Value = ();
+
+        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            write!(
+                formatter,
+                "unit variant {}::{}",
+                self.type_name, self.variant_name
+            )
+        }
+
+        fn visit_unit<E>(self) -> Result<(), E>
+        where
+            E: de::Error,
+        {
+            Ok(())
+        }
+
+        fn visit_none<E>(self) -> Result<(), E>
+        where
+            E: de::Error,
+        {
+            Ok(())
+        }
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+// Like `IntoDeserializer` but also implemented for `&[u8]`. This is used for
+// the newtype fallthrough case of `field_identifier`.
+//
+//    #[derive(Deserialize)]
+//    #[serde(field_identifier)]
+//    enum F {
+//        A,
+//        B,
+//        Other(String), // deserialized using IdentifierDeserializer
+//    }
+pub trait IdentifierDeserializer<'de, E: Error> {
+    type Deserializer: Deserializer<'de, Error = E>;
+
+    fn from(self) -> Self::Deserializer;
+}
+
+pub struct Borrowed<'de, T: 'de + ?Sized>(pub &'de T);
+
+impl<'de, E> IdentifierDeserializer<'de, E> for u64
+where
+    E: Error,
+{
+    type Deserializer = <u64 as IntoDeserializer<'de, E>>::Deserializer;
+
+    fn from(self) -> Self::Deserializer {
+        self.into_deserializer()
+    }
+}
+
+pub struct StrDeserializer<'a, E> {
+    value: &'a str,
+    marker: PhantomData<E>,
+}
+
+impl<'de, 'a, E> Deserializer<'de> for StrDeserializer<'a, E>
+where
+    E: Error,
+{
+    type Error = E;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        visitor.visit_str(self.value)
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct enum identifier ignored_any
+    }
+}
+
+pub struct BorrowedStrDeserializer<'de, E> {
+    value: &'de str,
+    marker: PhantomData<E>,
+}
+
+impl<'de, E> Deserializer<'de> for BorrowedStrDeserializer<'de, E>
+where
+    E: Error,
+{
+    type Error = E;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        visitor.visit_borrowed_str(self.value)
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct enum identifier ignored_any
+    }
+}
+
+impl<'a, E> IdentifierDeserializer<'a, E> for &'a str
+where
+    E: Error,
+{
+    type Deserializer = StrDeserializer<'a, E>;
+
+    fn from(self) -> Self::Deserializer {
+        StrDeserializer {
+            value: self,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'de, E> IdentifierDeserializer<'de, E> for Borrowed<'de, str>
+where
+    E: Error,
+{
+    type Deserializer = BorrowedStrDeserializer<'de, E>;
+
+    fn from(self) -> Self::Deserializer {
+        BorrowedStrDeserializer {
+            value: self.0,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'a, E> IdentifierDeserializer<'a, E> for &'a [u8]
+where
+    E: Error,
+{
+    type Deserializer = BytesDeserializer<'a, E>;
+
+    fn from(self) -> Self::Deserializer {
+        BytesDeserializer::new(self)
+    }
+}
+
+impl<'de, E> IdentifierDeserializer<'de, E> for Borrowed<'de, [u8]>
+where
+    E: Error,
+{
+    type Deserializer = BorrowedBytesDeserializer<'de, E>;
+
+    fn from(self) -> Self::Deserializer {
+        BorrowedBytesDeserializer::new(self.0)
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+pub struct FlatMapDeserializer<'a, 'de: 'a, E>(
+    pub &'a mut Vec<Option<(Content<'de>, Content<'de>)>>,
+    pub PhantomData<E>,
+);
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'a, 'de, E> FlatMapDeserializer<'a, 'de, E>
+where
+    E: Error,
+{
+    fn deserialize_other<V>() -> Result<V, E> {
+        Err(Error::custom("can only flatten structs and maps"))
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+macro_rules! forward_to_deserialize_other {
+    ($($func:ident ($($arg:ty),*))*) => {
+        $(
+            fn $func<V>(self, $(_: $arg,)* _visitor: V) -> Result<V::Value, Self::Error>
+            where
+                V: Visitor<'de>,
+            {
+                Self::deserialize_other()
+            }
+        )*
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'a, 'de, E> Deserializer<'de> for FlatMapDeserializer<'a, 'de, E>
+where
+    E: Error,
+{
+    type Error = E;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_map(visitor)
+    }
+
+    fn deserialize_enum<V>(
+        self,
+        name: &'static str,
+        variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        for entry in self.0 {
+            if let Some((key, value)) = flat_map_take_entry(entry, variants) {
+                return visitor.visit_enum(EnumDeserializer::new(key, Some(value)));
+            }
+        }
+
+        Err(Error::custom(format_args!(
+            "no variant of enum {} found in flattened data",
+            name
+        )))
+    }
+
+    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        visitor.visit_map(FlatMapAccess {
+            iter: self.0.iter(),
+            pending_content: None,
+            _marker: PhantomData,
+        })
+    }
+
+    fn deserialize_struct<V>(
+        self,
+        _: &'static str,
+        fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        visitor.visit_map(FlatStructAccess {
+            iter: self.0.iter_mut(),
+            pending_content: None,
+            fields,
+            _marker: PhantomData,
+        })
+    }
+
+    fn deserialize_newtype_struct<V>(self, _name: &str, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        visitor.visit_newtype_struct(self)
+    }
+
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        match visitor.__private_visit_untagged_option(self) {
+            Ok(value) => Ok(value),
+            Err(()) => Self::deserialize_other(),
+        }
+    }
+
+    fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        visitor.visit_unit()
+    }
+
+    fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: Visitor<'de>,
+    {
+        visitor.visit_unit()
+    }
+
+    forward_to_deserialize_other! {
+        deserialize_bool()
+        deserialize_i8()
+        deserialize_i16()
+        deserialize_i32()
+        deserialize_i64()
+        deserialize_u8()
+        deserialize_u16()
+        deserialize_u32()
+        deserialize_u64()
+        deserialize_f32()
+        deserialize_f64()
+        deserialize_char()
+        deserialize_str()
+        deserialize_string()
+        deserialize_bytes()
+        deserialize_byte_buf()
+        deserialize_unit_struct(&'static str)
+        deserialize_seq()
+        deserialize_tuple(usize)
+        deserialize_tuple_struct(&'static str, usize)
+        deserialize_identifier()
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+struct FlatMapAccess<'a, 'de: 'a, E> {
+    iter: slice::Iter<'a, Option<(Content<'de>, Content<'de>)>>,
+    pending_content: Option<&'a Content<'de>>,
+    _marker: PhantomData<E>,
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'a, 'de, E> MapAccess<'de> for FlatMapAccess<'a, 'de, E>
+where
+    E: Error,
+{
+    type Error = E;
+
+    fn next_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        for item in &mut self.iter {
+            // Items in the vector are nulled out when used by a struct.
+            if let Some((ref key, ref content)) = *item {
+                // Do not take(), instead borrow this entry. The internally tagged
+                // enum does its own buffering so we can't tell whether this entry
+                // is going to be consumed. Borrowing here leaves the entry
+                // available for later flattened fields.
+                self.pending_content = Some(content);
+                return seed.deserialize(ContentRefDeserializer::new(key)).map(Some);
+            }
+        }
+        Ok(None)
+    }
+
+    fn next_value_seed<T>(&mut self, seed: T) -> Result<T::Value, Self::Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        match self.pending_content.take() {
+            Some(value) => seed.deserialize(ContentRefDeserializer::new(value)),
+            None => Err(Error::custom("value is missing")),
+        }
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+struct FlatStructAccess<'a, 'de: 'a, E> {
+    iter: slice::IterMut<'a, Option<(Content<'de>, Content<'de>)>>,
+    pending_content: Option<Content<'de>>,
+    fields: &'static [&'static str],
+    _marker: PhantomData<E>,
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'a, 'de, E> MapAccess<'de> for FlatStructAccess<'a, 'de, E>
+where
+    E: Error,
+{
+    type Error = E;
+
+    fn next_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        for entry in self.iter.by_ref() {
+            if let Some((key, content)) = flat_map_take_entry(entry, self.fields) {
+                self.pending_content = Some(content);
+                return seed.deserialize(ContentDeserializer::new(key)).map(Some);
+            }
+        }
+        Ok(None)
+    }
+
+    fn next_value_seed<T>(&mut self, seed: T) -> Result<T::Value, Self::Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        match self.pending_content.take() {
+            Some(value) => seed.deserialize(ContentDeserializer::new(value)),
+            None => Err(Error::custom("value is missing")),
+        }
+    }
+}
+
+/// Claims one key-value pair from a FlatMapDeserializer's field buffer if the
+/// field name matches any of the recognized ones.
+#[cfg(any(feature = "std", feature = "alloc"))]
+fn flat_map_take_entry<'de>(
+    entry: &mut Option<(Content<'de>, Content<'de>)>,
+    recognized: &[&str],
+) -> Option<(Content<'de>, Content<'de>)> {
+    // Entries in the FlatMapDeserializer buffer are nulled out as they get
+    // claimed for deserialization. We only use an entry if it is still present
+    // and if the field is one recognized by the current data structure.
+    let is_recognized = match entry {
+        None => false,
+        Some((k, _v)) => k.as_str().map_or(false, |name| recognized.contains(&name)),
+    };
+
+    if is_recognized {
+        entry.take()
+    } else {
+        None
+    }
+}
+
+pub struct AdjacentlyTaggedEnumVariantSeed<F> {
+    pub enum_name: &'static str,
+    pub variants: &'static [&'static str],
+    pub fields_enum: PhantomData<F>,
+}
+
+pub struct AdjacentlyTaggedEnumVariantVisitor<F> {
+    enum_name: &'static str,
+    fields_enum: PhantomData<F>,
+}
+
+impl<'de, F> Visitor<'de> for AdjacentlyTaggedEnumVariantVisitor<F>
+where
+    F: Deserialize<'de>,
+{
+    type Value = F;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        write!(formatter, "variant of enum {}", self.enum_name)
+    }
+
+    fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error>
+    where
+        A: EnumAccess<'de>,
+    {
+        let (variant, variant_access) = tri!(data.variant());
+        tri!(variant_access.unit_variant());
+        Ok(variant)
+    }
+}
+
+impl<'de, F> DeserializeSeed<'de> for AdjacentlyTaggedEnumVariantSeed<F>
+where
+    F: Deserialize<'de>,
+{
+    type Value = F;
+
+    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_enum(
+            self.enum_name,
+            self.variants,
+            AdjacentlyTaggedEnumVariantVisitor {
+                enum_name: self.enum_name,
+                fields_enum: PhantomData,
+            },
+        )
+    }
+}