From 0ebf5bdf043a27fd3dfb7f92e0cb63d88954c44d Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Fri, 19 Apr 2024 03:47:29 +0200
Subject: Adding upstream version 115.8.0esr.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 third_party/rust/toml/src/datetime.rs |  544 ++++++++
 third_party/rust/toml/src/de.rs       | 2246 +++++++++++++++++++++++++++++++++
 third_party/rust/toml/src/lib.rs      |  176 +++
 third_party/rust/toml/src/macros.rs   |  459 +++++++
 third_party/rust/toml/src/map.rs      |  595 +++++++++
 third_party/rust/toml/src/ser.rs      | 1853 +++++++++++++++++++++++++++
 third_party/rust/toml/src/spanned.rs  |  166 +++
 third_party/rust/toml/src/tokens.rs   |  742 +++++++++++
 third_party/rust/toml/src/value.rs    | 1081 ++++++++++++++++
 9 files changed, 7862 insertions(+)
 create mode 100644 third_party/rust/toml/src/datetime.rs
 create mode 100644 third_party/rust/toml/src/de.rs
 create mode 100644 third_party/rust/toml/src/lib.rs
 create mode 100644 third_party/rust/toml/src/macros.rs
 create mode 100644 third_party/rust/toml/src/map.rs
 create mode 100644 third_party/rust/toml/src/ser.rs
 create mode 100644 third_party/rust/toml/src/spanned.rs
 create mode 100644 third_party/rust/toml/src/tokens.rs
 create mode 100644 third_party/rust/toml/src/value.rs

(limited to 'third_party/rust/toml/src')

diff --git a/third_party/rust/toml/src/datetime.rs b/third_party/rust/toml/src/datetime.rs
new file mode 100644
index 0000000000..e980e6abc0
--- /dev/null
+++ b/third_party/rust/toml/src/datetime.rs
@@ -0,0 +1,544 @@
+use std::error;
+use std::fmt;
+use std::str::{self, FromStr};
+
+use serde::{de, ser};
+
+/// A parsed TOML datetime value
+///
+/// This structure is intended to represent the datetime primitive type that can
+/// be encoded into TOML documents. This type is a parsed version that contains
+/// all metadata internally.
+///
+/// Currently this type is intentionally conservative and only supports
+/// `to_string` as an accessor. Over time though it's intended that it'll grow
+/// more support!
+///
+/// Note that if you're using `Deserialize` to deserialize a TOML document, you
+/// can use this as a placeholder for where you're expecting a datetime to be
+/// specified.
+///
+/// Also note though that while this type implements `Serialize` and
+/// `Deserialize` it's only recommended to use this type with the TOML format,
+/// otherwise encoded in other formats it may look a little odd.
+///
+/// Depending on how the option values are used, this struct will correspond
+/// with one of the following four datetimes from the [TOML v1.0.0 spec]:
+///
+/// | `date`    | `time`    | `offset`  | TOML type          |
+/// | --------- | --------- | --------- | ------------------ |
+/// | `Some(_)` | `Some(_)` | `Some(_)` | [Offset Date-Time] |
+/// | `Some(_)` | `Some(_)` | `None`    | [Local Date-Time]  |
+/// | `Some(_)` | `None`    | `None`    | [Local Date]       |
+/// | `None`    | `Some(_)` | `None`    | [Local Time]       |
+///
+/// **1. Offset Date-Time**: If all the optional values are used, `Datetime`
+/// corresponds to an [Offset Date-Time]. From the TOML v1.0.0 spec:
+///
+/// > To unambiguously represent a specific instant in time, you may use an
+/// > RFC 3339 formatted date-time with offset.
+/// >
+/// > ```toml
+/// > odt1 = 1979-05-27T07:32:00Z
+/// > odt2 = 1979-05-27T00:32:00-07:00
+/// > odt3 = 1979-05-27T00:32:00.999999-07:00
+/// > ```
+/// >
+/// > For the sake of readability, you may replace the T delimiter between date
+/// > and time with a space character (as permitted by RFC 3339 section 5.6).
+/// >
+/// > ```toml
+/// > odt4 = 1979-05-27 07:32:00Z
+/// > ```
+///
+/// **2. Local Date-Time**: If `date` and `time` are given but `offset` is
+/// `None`, `Datetime` corresponds to a [Local Date-Time]. From the spec:
+///
+/// > If you omit the offset from an RFC 3339 formatted date-time, it will
+/// > represent the given date-time without any relation to an offset or
+/// > timezone. It cannot be converted to an instant in time without additional
+/// > information. Conversion to an instant, if required, is implementation-
+/// > specific.
+/// >
+/// > ```toml
+/// > ldt1 = 1979-05-27T07:32:00
+/// > ldt2 = 1979-05-27T00:32:00.999999
+/// > ```
+///
+/// **3. Local Date**: If only `date` is given, `Datetime` corresponds to a
+/// [Local Date]; see the docs for [`Date`].
+///
+/// **4. Local Time**: If only `time` is given, `Datetime` corresponds to a
+/// [Local Time]; see the docs for [`Time`].
+///
+/// [TOML v1.0.0 spec]: https://toml.io/en/v1.0.0
+/// [Offset Date-Time]: https://toml.io/en/v1.0.0#offset-date-time
+/// [Local Date-Time]: https://toml.io/en/v1.0.0#local-date-time
+/// [Local Date]: https://toml.io/en/v1.0.0#local-date
+/// [Local Time]: https://toml.io/en/v1.0.0#local-time
+#[derive(PartialEq, Eq, Clone)]
+pub struct Datetime {
+    /// Optional date.
+    /// Required for: *Offset Date-Time*, *Local Date-Time*, *Local Date*.
+    pub date: Option<Date>,
+
+    /// Optional time.
+    /// Required for: *Offset Date-Time*, *Local Date-Time*, *Local Time*.
+    pub time: Option<Time>,
+
+    /// Optional offset.
+    /// Required for: *Offset Date-Time*.
+    pub offset: Option<Offset>,
+}
+
+/// Error returned from parsing a `Datetime` in the `FromStr` implementation.
+#[derive(Debug, Clone)]
+pub struct DatetimeParseError {
+    _private: (),
+}
+
+// Currently serde itself doesn't have a datetime type, so we map our `Datetime`
+// to a special valid in the serde data model. Namely one with these special
+// fields/struct names.
+//
+// In general the TOML encoder/decoder will catch this and not literally emit
+// these strings but rather emit datetimes as they're intended.
+pub const FIELD: &str = "$__toml_private_datetime";
+pub const NAME: &str = "$__toml_private_Datetime";
+
+/// A parsed TOML date value
+///
+/// May be part of a [`Datetime`]. Alone, `Date` corresponds to a [Local Date].
+/// From the TOML v1.0.0 spec:
+///
+/// > If you include only the date portion of an RFC 3339 formatted date-time,
+/// > it will represent that entire day without any relation to an offset or
+/// > timezone.
+/// >
+/// > ```toml
+/// > ld1 = 1979-05-27
+/// > ```
+///
+/// [Local Date]: https://toml.io/en/v1.0.0#local-date
+#[derive(PartialEq, Eq, Clone)]
+pub struct Date {
+    /// Year: four digits
+    pub year: u16,
+    /// Month: 1 to 12
+    pub month: u8,
+    /// Day: 1 to {28, 29, 30, 31} (based on month/year)
+    pub day: u8,
+}
+
+/// A parsed TOML time value
+///
+/// May be part of a [`Datetime`]. Alone, `Time` corresponds to a [Local Time].
+/// From the TOML v1.0.0 spec:
+///
+/// > If you include only the time portion of an RFC 3339 formatted date-time,
+/// > it will represent that time of day without any relation to a specific
+/// > day or any offset or timezone.
+/// >
+/// > ```toml
+/// > lt1 = 07:32:00
+/// > lt2 = 00:32:00.999999
+/// > ```
+/// >
+/// > Millisecond precision is required. Further precision of fractional
+/// > seconds is implementation-specific. If the value contains greater
+/// > precision than the implementation can support, the additional precision
+/// > must be truncated, not rounded.
+///
+/// [Local Time]: https://toml.io/en/v1.0.0#local-time
+#[derive(PartialEq, Eq, Clone)]
+pub struct Time {
+    /// Hour: 0 to 23
+    pub hour: u8,
+    /// Minute: 0 to 59
+    pub minute: u8,
+    /// Second: 0 to {58, 59, 60} (based on leap second rules)
+    pub second: u8,
+    /// Nanosecond: 0 to 999_999_999
+    pub nanosecond: u32,
+}
+
+/// A parsed TOML time offset
+///
+#[derive(PartialEq, Eq, Clone)]
+pub enum Offset {
+    /// > A suffix which, when applied to a time, denotes a UTC offset of 00:00;
+    /// > often spoken "Zulu" from the ICAO phonetic alphabet representation of
+    /// > the letter "Z". --- [RFC 3339 section 2]
+    ///
+    /// [RFC 3339 section 2]: https://datatracker.ietf.org/doc/html/rfc3339#section-2
+    Z,
+
+    /// Offset between local time and UTC
+    Custom {
+        /// Hours: -12 to +12
+        hours: i8,
+
+        /// Minutes: 0 to 59
+        minutes: u8,
+    },
+}
+
+impl fmt::Debug for Datetime {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
+impl fmt::Display for Datetime {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if let Some(ref date) = self.date {
+            write!(f, "{}", date)?;
+        }
+        if let Some(ref time) = self.time {
+            if self.date.is_some() {
+                write!(f, "T")?;
+            }
+            write!(f, "{}", time)?;
+        }
+        if let Some(ref offset) = self.offset {
+            write!(f, "{}", offset)?;
+        }
+        Ok(())
+    }
+}
+
+impl fmt::Display for Date {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:04}-{:02}-{:02}", self.year, self.month, self.day)
+    }
+}
+
+impl fmt::Display for Time {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:02}:{:02}:{:02}", self.hour, self.minute, self.second)?;
+        if self.nanosecond != 0 {
+            let s = format!("{:09}", self.nanosecond);
+            write!(f, ".{}", s.trim_end_matches('0'))?;
+        }
+        Ok(())
+    }
+}
+
+impl fmt::Display for Offset {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            Offset::Z => write!(f, "Z"),
+            Offset::Custom { hours, minutes } => write!(f, "{:+03}:{:02}", hours, minutes),
+        }
+    }
+}
+
+impl FromStr for Datetime {
+    type Err = DatetimeParseError;
+
+    fn from_str(date: &str) -> Result<Datetime, DatetimeParseError> {
+        // Accepted formats:
+        //
+        // 0000-00-00T00:00:00.00Z
+        // 0000-00-00T00:00:00.00
+        // 0000-00-00
+        // 00:00:00.00
+        if date.len() < 3 {
+            return Err(DatetimeParseError { _private: () });
+        }
+        let mut offset_allowed = true;
+        let mut chars = date.chars();
+
+        // First up, parse the full date if we can
+        let full_date = if chars.clone().nth(2) == Some(':') {
+            offset_allowed = false;
+            None
+        } else {
+            let y1 = u16::from(digit(&mut chars)?);
+            let y2 = u16::from(digit(&mut chars)?);
+            let y3 = u16::from(digit(&mut chars)?);
+            let y4 = u16::from(digit(&mut chars)?);
+
+            match chars.next() {
+                Some('-') => {}
+                _ => return Err(DatetimeParseError { _private: () }),
+            }
+
+            let m1 = digit(&mut chars)?;
+            let m2 = digit(&mut chars)?;
+
+            match chars.next() {
+                Some('-') => {}
+                _ => return Err(DatetimeParseError { _private: () }),
+            }
+
+            let d1 = digit(&mut chars)?;
+            let d2 = digit(&mut chars)?;
+
+            let date = Date {
+                year: y1 * 1000 + y2 * 100 + y3 * 10 + y4,
+                month: m1 * 10 + m2,
+                day: d1 * 10 + d2,
+            };
+
+            if date.month < 1 || date.month > 12 {
+                return Err(DatetimeParseError { _private: () });
+            }
+            if date.day < 1 || date.day > 31 {
+                return Err(DatetimeParseError { _private: () });
+            }
+
+            Some(date)
+        };
+
+        // Next parse the "partial-time" if available
+        let next = chars.clone().next();
+        let partial_time = if full_date.is_some()
+            && (next == Some('T') || next == Some('t') || next == Some(' '))
+        {
+            chars.next();
+            true
+        } else {
+            full_date.is_none()
+        };
+
+        let time = if partial_time {
+            let h1 = digit(&mut chars)?;
+            let h2 = digit(&mut chars)?;
+            match chars.next() {
+                Some(':') => {}
+                _ => return Err(DatetimeParseError { _private: () }),
+            }
+            let m1 = digit(&mut chars)?;
+            let m2 = digit(&mut chars)?;
+            match chars.next() {
+                Some(':') => {}
+                _ => return Err(DatetimeParseError { _private: () }),
+            }
+            let s1 = digit(&mut chars)?;
+            let s2 = digit(&mut chars)?;
+
+            let mut nanosecond = 0;
+            if chars.clone().next() == Some('.') {
+                chars.next();
+                let whole = chars.as_str();
+
+                let mut end = whole.len();
+                for (i, byte) in whole.bytes().enumerate() {
+                    match byte {
+                        b'0'..=b'9' => {
+                            if i < 9 {
+                                let p = 10_u32.pow(8 - i as u32);
+                                nanosecond += p * u32::from(byte - b'0');
+                            }
+                        }
+                        _ => {
+                            end = i;
+                            break;
+                        }
+                    }
+                }
+                if end == 0 {
+                    return Err(DatetimeParseError { _private: () });
+                }
+                chars = whole[end..].chars();
+            }
+
+            let time = Time {
+                hour: h1 * 10 + h2,
+                minute: m1 * 10 + m2,
+                second: s1 * 10 + s2,
+                nanosecond,
+            };
+
+            if time.hour > 24 {
+                return Err(DatetimeParseError { _private: () });
+            }
+            if time.minute > 59 {
+                return Err(DatetimeParseError { _private: () });
+            }
+            if time.second > 59 {
+                return Err(DatetimeParseError { _private: () });
+            }
+            if time.nanosecond > 999_999_999 {
+                return Err(DatetimeParseError { _private: () });
+            }
+
+            Some(time)
+        } else {
+            offset_allowed = false;
+            None
+        };
+
+        // And finally, parse the offset
+        let offset = if offset_allowed {
+            let next = chars.clone().next();
+            if next == Some('Z') || next == Some('z') {
+                chars.next();
+                Some(Offset::Z)
+            } else if next.is_none() {
+                None
+            } else {
+                let sign = match next {
+                    Some('+') => 1,
+                    Some('-') => -1,
+                    _ => return Err(DatetimeParseError { _private: () }),
+                };
+                chars.next();
+                let h1 = digit(&mut chars)? as i8;
+                let h2 = digit(&mut chars)? as i8;
+                match chars.next() {
+                    Some(':') => {}
+                    _ => return Err(DatetimeParseError { _private: () }),
+                }
+                let m1 = digit(&mut chars)?;
+                let m2 = digit(&mut chars)?;
+
+                Some(Offset::Custom {
+                    hours: sign * (h1 * 10 + h2),
+                    minutes: m1 * 10 + m2,
+                })
+            }
+        } else {
+            None
+        };
+
+        // Return an error if we didn't hit eof, otherwise return our parsed
+        // date
+        if chars.next().is_some() {
+            return Err(DatetimeParseError { _private: () });
+        }
+
+        Ok(Datetime {
+            date: full_date,
+            time,
+            offset,
+        })
+    }
+}
+
+fn digit(chars: &mut str::Chars<'_>) -> Result<u8, DatetimeParseError> {
+    match chars.next() {
+        Some(c) if ('0'..='9').contains(&c) => Ok(c as u8 - b'0'),
+        _ => Err(DatetimeParseError { _private: () }),
+    }
+}
+
+impl ser::Serialize for Datetime {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: ser::Serializer,
+    {
+        use serde::ser::SerializeStruct;
+
+        let mut s = serializer.serialize_struct(NAME, 1)?;
+        s.serialize_field(FIELD, &self.to_string())?;
+        s.end()
+    }
+}
+
+impl<'de> de::Deserialize<'de> for Datetime {
+    fn deserialize<D>(deserializer: D) -> Result<Datetime, D::Error>
+    where
+        D: de::Deserializer<'de>,
+    {
+        struct DatetimeVisitor;
+
+        impl<'de> de::Visitor<'de> for DatetimeVisitor {
+            type Value = Datetime;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+                formatter.write_str("a TOML datetime")
+            }
+
+            fn visit_map<V>(self, mut visitor: V) -> Result<Datetime, V::Error>
+            where
+                V: de::MapAccess<'de>,
+            {
+                let value = visitor.next_key::<DatetimeKey>()?;
+                if value.is_none() {
+                    return Err(de::Error::custom("datetime key not found"));
+                }
+                let v: DatetimeFromString = visitor.next_value()?;
+                Ok(v.value)
+            }
+        }
+
+        static FIELDS: [&str; 1] = [FIELD];
+        deserializer.deserialize_struct(NAME, &FIELDS, DatetimeVisitor)
+    }
+}
+
+struct DatetimeKey;
+
+impl<'de> de::Deserialize<'de> for DatetimeKey {
+    fn deserialize<D>(deserializer: D) -> Result<DatetimeKey, D::Error>
+    where
+        D: de::Deserializer<'de>,
+    {
+        struct FieldVisitor;
+
+        impl<'de> de::Visitor<'de> for FieldVisitor {
+            type Value = ();
+
+            fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+                formatter.write_str("a valid datetime field")
+            }
+
+            fn visit_str<E>(self, s: &str) -> Result<(), E>
+            where
+                E: de::Error,
+            {
+                if s == FIELD {
+                    Ok(())
+                } else {
+                    Err(de::Error::custom("expected field with custom name"))
+                }
+            }
+        }
+
+        deserializer.deserialize_identifier(FieldVisitor)?;
+        Ok(DatetimeKey)
+    }
+}
+
+pub struct DatetimeFromString {
+    pub value: Datetime,
+}
+
+impl<'de> de::Deserialize<'de> for DatetimeFromString {
+    fn deserialize<D>(deserializer: D) -> Result<DatetimeFromString, D::Error>
+    where
+        D: de::Deserializer<'de>,
+    {
+        struct Visitor;
+
+        impl<'de> de::Visitor<'de> for Visitor {
+            type Value = DatetimeFromString;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+                formatter.write_str("string containing a datetime")
+            }
+
+            fn visit_str<E>(self, s: &str) -> Result<DatetimeFromString, E>
+            where
+                E: de::Error,
+            {
+                match s.parse() {
+                    Ok(date) => Ok(DatetimeFromString { value: date }),
+                    Err(e) => Err(de::Error::custom(e)),
+                }
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
+    }
+}
+
+impl fmt::Display for DatetimeParseError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        "failed to parse datetime".fmt(f)
+    }
+}
+
+impl error::Error for DatetimeParseError {}
diff --git a/third_party/rust/toml/src/de.rs b/third_party/rust/toml/src/de.rs
new file mode 100644
index 0000000000..67b53156ac
--- /dev/null
+++ b/third_party/rust/toml/src/de.rs
@@ -0,0 +1,2246 @@
+//! Deserializing TOML into Rust structures.
+//!
+//! This module contains all the Serde support for deserializing TOML documents
+//! into Rust structures. Note that some top-level functions here are also
+//! provided at the top of the crate.
+
+use std::borrow::Cow;
+use std::collections::HashMap;
+use std::error;
+use std::f64;
+use std::fmt;
+use std::iter;
+use std::marker::PhantomData;
+use std::str;
+use std::vec;
+
+use serde::de;
+use serde::de::value::BorrowedStrDeserializer;
+use serde::de::IntoDeserializer;
+
+use crate::datetime;
+use crate::spanned;
+use crate::tokens::{Error as TokenError, Span, Token, Tokenizer};
+
+/// Type Alias for a TOML Table pair
+type TablePair<'a> = ((Span, Cow<'a, str>), Value<'a>);
+
+/// Deserializes a byte slice into a type.
+///
+/// This function will attempt to interpret `bytes` as UTF-8 data and then
+/// deserialize `T` from the TOML document provided.
+pub fn from_slice<'de, T>(bytes: &'de [u8]) -> Result<T, Error>
+where
+    T: de::Deserialize<'de>,
+{
+    match str::from_utf8(bytes) {
+        Ok(s) => from_str(s),
+        Err(e) => Err(Error::custom(None, e.to_string())),
+    }
+}
+
+/// Deserializes a string into a type.
+///
+/// This function will attempt to interpret `s` as a TOML document and
+/// deserialize `T` from the document.
+///
+/// # Examples
+///
+/// ```
+/// use serde_derive::Deserialize;
+///
+/// #[derive(Deserialize)]
+/// struct Config {
+///     title: String,
+///     owner: Owner,
+/// }
+///
+/// #[derive(Deserialize)]
+/// struct Owner {
+///     name: String,
+/// }
+///
+/// let config: Config = toml::from_str(r#"
+///     title = 'TOML Example'
+///
+///     [owner]
+///     name = 'Lisa'
+/// "#).unwrap();
+///
+/// assert_eq!(config.title, "TOML Example");
+/// assert_eq!(config.owner.name, "Lisa");
+/// ```
+pub fn from_str<'de, T>(s: &'de str) -> Result<T, Error>
+where
+    T: de::Deserialize<'de>,
+{
+    let mut d = Deserializer::new(s);
+    let ret = T::deserialize(&mut d)?;
+    d.end()?;
+    Ok(ret)
+}
+
+/// Errors that can occur when deserializing a type.
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub struct Error {
+    inner: Box<ErrorInner>,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+struct ErrorInner {
+    kind: ErrorKind,
+    line: Option<usize>,
+    col: usize,
+    at: Option<usize>,
+    message: String,
+    key: Vec<String>,
+}
+
+/// Errors that can occur when deserializing a type.
+#[derive(Debug, PartialEq, Eq, Clone)]
+#[non_exhaustive]
+enum ErrorKind {
+    /// EOF was reached when looking for a value
+    UnexpectedEof,
+
+    /// An invalid character not allowed in a string was found
+    InvalidCharInString(char),
+
+    /// An invalid character was found as an escape
+    InvalidEscape(char),
+
+    /// An invalid character was found in a hex escape
+    InvalidHexEscape(char),
+
+    /// An invalid escape value was specified in a hex escape in a string.
+    ///
+    /// Valid values are in the plane of unicode codepoints.
+    InvalidEscapeValue(u32),
+
+    /// A newline in a string was encountered when one was not allowed.
+    NewlineInString,
+
+    /// An unexpected character was encountered, typically when looking for a
+    /// value.
+    Unexpected(char),
+
+    /// An unterminated string was found where EOF was found before the ending
+    /// EOF mark.
+    UnterminatedString,
+
+    /// A newline was found in a table key.
+    NewlineInTableKey,
+
+    /// A number failed to parse
+    NumberInvalid,
+
+    /// A date or datetime was invalid
+    DateInvalid,
+
+    /// Wanted one sort of token, but found another.
+    Wanted {
+        /// Expected token type
+        expected: &'static str,
+        /// Actually found token type
+        found: &'static str,
+    },
+
+    /// A duplicate table definition was found.
+    DuplicateTable(String),
+
+    /// A previously defined table was redefined as an array.
+    RedefineAsArray,
+
+    /// An empty table key was found.
+    EmptyTableKey,
+
+    /// Multiline strings are not allowed for key
+    MultilineStringKey,
+
+    /// A custom error which could be generated when deserializing a particular
+    /// type.
+    Custom,
+
+    /// A tuple with a certain number of elements was expected but something
+    /// else was found.
+    ExpectedTuple(usize),
+
+    /// Expected table keys to be in increasing tuple index order, but something
+    /// else was found.
+    ExpectedTupleIndex {
+        /// Expected index.
+        expected: usize,
+        /// Key that was specified.
+        found: String,
+    },
+
+    /// An empty table was expected but entries were found
+    ExpectedEmptyTable,
+
+    /// Dotted key attempted to extend something that is not a table.
+    DottedKeyInvalidType,
+
+    /// An unexpected key was encountered.
+    ///
+    /// Used when deserializing a struct with a limited set of fields.
+    UnexpectedKeys {
+        /// The unexpected keys.
+        keys: Vec<String>,
+        /// Keys that may be specified.
+        available: &'static [&'static str],
+    },
+
+    /// Unquoted string was found when quoted one was expected
+    UnquotedString,
+}
+
+/// Deserialization implementation for TOML.
+pub struct Deserializer<'a> {
+    require_newline_after_table: bool,
+    allow_duplciate_after_longer_table: bool,
+    input: &'a str,
+    tokens: Tokenizer<'a>,
+}
+
+impl<'de, 'b> de::Deserializer<'de> for &'b mut Deserializer<'de> {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        let mut tables = self.tables()?;
+        let table_indices = build_table_indices(&tables);
+        let table_pindices = build_table_pindices(&tables);
+
+        let res = visitor.visit_map(MapVisitor {
+            values: Vec::new().into_iter().peekable(),
+            next_value: None,
+            depth: 0,
+            cur: 0,
+            cur_parent: 0,
+            max: tables.len(),
+            table_indices: &table_indices,
+            table_pindices: &table_pindices,
+            tables: &mut tables,
+            array: false,
+            de: self,
+        });
+        res.map_err(|mut err| {
+            // Errors originating from this library (toml), have an offset
+            // attached to them already. Other errors, like those originating
+            // from serde (like "missing field") or from a custom deserializer,
+            // do not have offsets on them. Here, we do a best guess at their
+            // location, by attributing them to the "current table" (the last
+            // item in `tables`).
+            err.fix_offset(|| tables.last().map(|table| table.at));
+            err.fix_linecol(|at| self.to_linecol(at));
+            err
+        })
+    }
+
+    // Called when the type to deserialize is an enum, as opposed to a field in the type.
+    fn deserialize_enum<V>(
+        self,
+        _name: &'static str,
+        _variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        let (value, name) = self.string_or_table()?;
+        match value.e {
+            E::String(val) => visitor.visit_enum(val.into_deserializer()),
+            E::InlineTable(values) => {
+                if values.len() != 1 {
+                    Err(Error::from_kind(
+                        Some(value.start),
+                        ErrorKind::Wanted {
+                            expected: "exactly 1 element",
+                            found: if values.is_empty() {
+                                "zero elements"
+                            } else {
+                                "more than 1 element"
+                            },
+                        },
+                    ))
+                } else {
+                    visitor.visit_enum(InlineTableDeserializer {
+                        values: values.into_iter(),
+                        next_value: None,
+                    })
+                }
+            }
+            E::DottedTable(_) => visitor.visit_enum(DottedTableDeserializer {
+                name: name.expect("Expected table header to be passed."),
+                value,
+            }),
+            e => Err(Error::from_kind(
+                Some(value.start),
+                ErrorKind::Wanted {
+                    expected: "string or table",
+                    found: e.type_name(),
+                },
+            )),
+        }
+    }
+
+    fn deserialize_struct<V>(
+        self,
+        name: &'static str,
+        fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if name == spanned::NAME && fields == [spanned::START, spanned::END, spanned::VALUE] {
+            let start = 0;
+            let end = self.input.len();
+
+            let res = visitor.visit_map(SpannedDeserializer {
+                phantom_data: PhantomData,
+                start: Some(start),
+                value: Some(self),
+                end: Some(end),
+            });
+            return res;
+        }
+
+        self.deserialize_any(visitor)
+    }
+
+    serde::forward_to_deserialize_any! {
+        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string seq
+        bytes byte_buf map unit newtype_struct
+        ignored_any unit_struct tuple_struct tuple option identifier
+    }
+}
+
+// Builds a datastructure that allows for efficient sublinear lookups.
+// The returned HashMap contains a mapping from table header (like [a.b.c])
+// to list of tables with that precise name. The tables are being identified
+// by their index in the passed slice. We use a list as the implementation
+// uses this data structure for arrays as well as tables,
+// so if any top level [[name]] array contains multiple entries,
+// there are multiple entries in the list.
+// The lookup is performed in the `SeqAccess` implementation of `MapVisitor`.
+// The lists are ordered, which we exploit in the search code by using
+// bisection.
+fn build_table_indices<'de>(tables: &[Table<'de>]) -> HashMap<Vec<Cow<'de, str>>, Vec<usize>> {
+    let mut res = HashMap::new();
+    for (i, table) in tables.iter().enumerate() {
+        let header = table.header.iter().map(|v| v.1.clone()).collect::<Vec<_>>();
+        res.entry(header).or_insert_with(Vec::new).push(i);
+    }
+    res
+}
+
+// Builds a datastructure that allows for efficient sublinear lookups.
+// The returned HashMap contains a mapping from table header (like [a.b.c])
+// to list of tables whose name at least starts with the specified
+// name. So searching for [a.b] would give both [a.b.c.d] as well as [a.b.e].
+// The tables are being identified by their index in the passed slice.
+//
+// A list is used for two reasons: First, the implementation also
+// stores arrays in the same data structure and any top level array
+// of size 2 or greater creates multiple entries in the list with the
+// same shared name. Second, there can be multiple tables sharing
+// the same prefix.
+//
+// The lookup is performed in the `MapAccess` implementation of `MapVisitor`.
+// The lists are ordered, which we exploit in the search code by using
+// bisection.
+fn build_table_pindices<'de>(tables: &[Table<'de>]) -> HashMap<Vec<Cow<'de, str>>, Vec<usize>> {
+    let mut res = HashMap::new();
+    for (i, table) in tables.iter().enumerate() {
+        let header = table.header.iter().map(|v| v.1.clone()).collect::<Vec<_>>();
+        for len in 0..=header.len() {
+            res.entry(header[..len].to_owned())
+                .or_insert_with(Vec::new)
+                .push(i);
+        }
+    }
+    res
+}
+
+fn headers_equal<'a, 'b>(hdr_a: &[(Span, Cow<'a, str>)], hdr_b: &[(Span, Cow<'b, str>)]) -> bool {
+    if hdr_a.len() != hdr_b.len() {
+        return false;
+    }
+    hdr_a.iter().zip(hdr_b.iter()).all(|(h1, h2)| h1.1 == h2.1)
+}
+
+struct Table<'a> {
+    at: usize,
+    header: Vec<(Span, Cow<'a, str>)>,
+    values: Option<Vec<TablePair<'a>>>,
+    array: bool,
+}
+
+struct MapVisitor<'de, 'b> {
+    values: iter::Peekable<vec::IntoIter<TablePair<'de>>>,
+    next_value: Option<TablePair<'de>>,
+    depth: usize,
+    cur: usize,
+    cur_parent: usize,
+    max: usize,
+    table_indices: &'b HashMap<Vec<Cow<'de, str>>, Vec<usize>>,
+    table_pindices: &'b HashMap<Vec<Cow<'de, str>>, Vec<usize>>,
+    tables: &'b mut [Table<'de>],
+    array: bool,
+    de: &'b mut Deserializer<'de>,
+}
+
+impl<'de, 'b> de::MapAccess<'de> for MapVisitor<'de, 'b> {
+    type Error = Error;
+
+    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Error>
+    where
+        K: de::DeserializeSeed<'de>,
+    {
+        if self.cur_parent == self.max || self.cur == self.max {
+            return Ok(None);
+        }
+
+        loop {
+            assert!(self.next_value.is_none());
+            if let Some((key, value)) = self.values.next() {
+                let ret = seed.deserialize(StrDeserializer::spanned(key.clone()))?;
+                self.next_value = Some((key, value));
+                return Ok(Some(ret));
+            }
+
+            let next_table = {
+                let prefix_stripped = self.tables[self.cur_parent].header[..self.depth]
+                    .iter()
+                    .map(|v| v.1.clone())
+                    .collect::<Vec<_>>();
+                self.table_pindices
+                    .get(&prefix_stripped)
+                    .and_then(|entries| {
+                        let start = entries.binary_search(&self.cur).unwrap_or_else(|v| v);
+                        if start == entries.len() || entries[start] < self.cur {
+                            return None;
+                        }
+                        entries[start..]
+                            .iter()
+                            .filter_map(|i| if *i < self.max { Some(*i) } else { None })
+                            .map(|i| (i, &self.tables[i]))
+                            .find(|(_, table)| table.values.is_some())
+                            .map(|p| p.0)
+                    })
+            };
+
+            let pos = match next_table {
+                Some(pos) => pos,
+                None => return Ok(None),
+            };
+            self.cur = pos;
+
+            // Test to see if we're duplicating our parent's table, and if so
+            // then this is an error in the toml format
+            if self.cur_parent != pos {
+                if headers_equal(
+                    &self.tables[self.cur_parent].header,
+                    &self.tables[pos].header,
+                ) {
+                    let at = self.tables[pos].at;
+                    let name = self.tables[pos]
+                        .header
+                        .iter()
+                        .map(|k| k.1.to_owned())
+                        .collect::<Vec<_>>()
+                        .join(".");
+                    return Err(self.de.error(at, ErrorKind::DuplicateTable(name)));
+                }
+
+                // If we're here we know we should share the same prefix, and if
+                // the longer table was defined first then we want to narrow
+                // down our parent's length if possible to ensure that we catch
+                // duplicate tables defined afterwards.
+                if !self.de.allow_duplciate_after_longer_table {
+                    let parent_len = self.tables[self.cur_parent].header.len();
+                    let cur_len = self.tables[pos].header.len();
+                    if cur_len < parent_len {
+                        self.cur_parent = pos;
+                    }
+                }
+            }
+
+            let table = &mut self.tables[pos];
+
+            // If we're not yet at the appropriate depth for this table then we
+            // just next the next portion of its header and then continue
+            // decoding.
+            if self.depth != table.header.len() {
+                let key = &table.header[self.depth];
+                let key = seed.deserialize(StrDeserializer::spanned(key.clone()))?;
+                return Ok(Some(key));
+            }
+
+            // Rule out cases like:
+            //
+            //      [[foo.bar]]
+            //      [[foo]]
+            if table.array {
+                let kind = ErrorKind::RedefineAsArray;
+                return Err(self.de.error(table.at, kind));
+            }
+
+            self.values = table
+                .values
+                .take()
+                .expect("Unable to read table values")
+                .into_iter()
+                .peekable();
+        }
+    }
+
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Error>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        if let Some((k, v)) = self.next_value.take() {
+            match seed.deserialize(ValueDeserializer::new(v)) {
+                Ok(v) => return Ok(v),
+                Err(mut e) => {
+                    e.add_key_context(&k.1);
+                    return Err(e);
+                }
+            }
+        }
+
+        let array =
+            self.tables[self.cur].array && self.depth == self.tables[self.cur].header.len() - 1;
+        self.cur += 1;
+        let res = seed.deserialize(MapVisitor {
+            values: Vec::new().into_iter().peekable(),
+            next_value: None,
+            depth: self.depth + if array { 0 } else { 1 },
+            cur_parent: self.cur - 1,
+            cur: 0,
+            max: self.max,
+            array,
+            table_indices: self.table_indices,
+            table_pindices: self.table_pindices,
+            tables: &mut *self.tables,
+            de: &mut *self.de,
+        });
+        res.map_err(|mut e| {
+            e.add_key_context(&self.tables[self.cur - 1].header[self.depth].1);
+            e
+        })
+    }
+}
+
+impl<'de, 'b> de::SeqAccess<'de> for MapVisitor<'de, 'b> {
+    type Error = Error;
+
+    fn next_element_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Error>
+    where
+        K: de::DeserializeSeed<'de>,
+    {
+        assert!(self.next_value.is_none());
+        assert!(self.values.next().is_none());
+
+        if self.cur_parent == self.max {
+            return Ok(None);
+        }
+
+        let header_stripped = self.tables[self.cur_parent]
+            .header
+            .iter()
+            .map(|v| v.1.clone())
+            .collect::<Vec<_>>();
+        let start_idx = self.cur_parent + 1;
+        let next = self
+            .table_indices
+            .get(&header_stripped)
+            .and_then(|entries| {
+                let start = entries.binary_search(&start_idx).unwrap_or_else(|v| v);
+                if start == entries.len() || entries[start] < start_idx {
+                    return None;
+                }
+                entries[start..]
+                    .iter()
+                    .filter_map(|i| if *i < self.max { Some(*i) } else { None })
+                    .map(|i| (i, &self.tables[i]))
+                    .find(|(_, table)| table.array)
+                    .map(|p| p.0)
+            })
+            .unwrap_or(self.max);
+
+        let ret = seed.deserialize(MapVisitor {
+            values: self.tables[self.cur_parent]
+                .values
+                .take()
+                .expect("Unable to read table values")
+                .into_iter()
+                .peekable(),
+            next_value: None,
+            depth: self.depth + 1,
+            cur_parent: self.cur_parent,
+            max: next,
+            cur: 0,
+            array: false,
+            table_indices: self.table_indices,
+            table_pindices: self.table_pindices,
+            tables: self.tables,
+            de: self.de,
+        })?;
+        self.cur_parent = next;
+        Ok(Some(ret))
+    }
+}
+
+impl<'de, 'b> de::Deserializer<'de> for MapVisitor<'de, 'b> {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if self.array {
+            visitor.visit_seq(self)
+        } else {
+            visitor.visit_map(self)
+        }
+    }
+
+    // `None` is interpreted as a missing field so be sure to implement `Some`
+    // as a present field.
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_some(self)
+    }
+
+    fn deserialize_newtype_struct<V>(
+        self,
+        _name: &'static str,
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_newtype_struct(self)
+    }
+
+    fn deserialize_struct<V>(
+        mut self,
+        name: &'static str,
+        fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if name == spanned::NAME
+            && fields == [spanned::START, spanned::END, spanned::VALUE]
+            && !(self.array && self.values.peek().is_some())
+        {
+            // TODO we can't actually emit spans here for the *entire* table/array
+            // due to the format that toml uses. Setting the start and end to 0 is
+            // *detectable* (and no reasonable span would look like that),
+            // it would be better to expose this in the API via proper
+            // ADTs like Option<T>.
+            let start = 0;
+            let end = 0;
+
+            let res = visitor.visit_map(SpannedDeserializer {
+                phantom_data: PhantomData,
+                start: Some(start),
+                value: Some(self),
+                end: Some(end),
+            });
+            return res;
+        }
+
+        self.deserialize_any(visitor)
+    }
+
+    fn deserialize_enum<V>(
+        self,
+        _name: &'static str,
+        _variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if self.tables.len() != 1 {
+            return Err(Error::custom(
+                Some(self.cur),
+                "enum table must contain exactly one table".into(),
+            ));
+        }
+        let table = &mut self.tables[0];
+        let values = table.values.take().expect("table has no values?");
+        if table.header.is_empty() {
+            return Err(self.de.error(self.cur, ErrorKind::EmptyTableKey));
+        }
+        let name = table.header[table.header.len() - 1].1.to_owned();
+        visitor.visit_enum(DottedTableDeserializer {
+            name,
+            value: Value {
+                e: E::DottedTable(values),
+                start: 0,
+                end: 0,
+            },
+        })
+    }
+
+    serde::forward_to_deserialize_any! {
+        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string seq
+        bytes byte_buf map unit identifier
+        ignored_any unit_struct tuple_struct tuple
+    }
+}
+
+struct StrDeserializer<'a> {
+    span: Option<Span>,
+    key: Cow<'a, str>,
+}
+
+impl<'a> StrDeserializer<'a> {
+    fn spanned(inner: (Span, Cow<'a, str>)) -> StrDeserializer<'a> {
+        StrDeserializer {
+            span: Some(inner.0),
+            key: inner.1,
+        }
+    }
+    fn new(key: Cow<'a, str>) -> StrDeserializer<'a> {
+        StrDeserializer { span: None, key }
+    }
+}
+
+impl<'a> de::IntoDeserializer<'a, Error> for StrDeserializer<'a> {
+    type Deserializer = Self;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        self
+    }
+}
+
+impl<'de> de::Deserializer<'de> for StrDeserializer<'de> {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.key {
+            Cow::Borrowed(s) => visitor.visit_borrowed_str(s),
+            Cow::Owned(s) => visitor.visit_string(s),
+        }
+    }
+
+    fn deserialize_struct<V>(
+        self,
+        name: &'static str,
+        fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if name == spanned::NAME && fields == [spanned::START, spanned::END, spanned::VALUE] {
+            if let Some(span) = self.span {
+                return visitor.visit_map(SpannedDeserializer {
+                    phantom_data: PhantomData,
+                    start: Some(span.start),
+                    value: Some(StrDeserializer::new(self.key)),
+                    end: Some(span.end),
+                });
+            }
+        }
+        self.deserialize_any(visitor)
+    }
+
+    serde::forward_to_deserialize_any! {
+        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string seq
+        bytes byte_buf map option unit newtype_struct
+        ignored_any unit_struct tuple_struct tuple enum identifier
+    }
+}
+
+struct ValueDeserializer<'a> {
+    value: Value<'a>,
+    validate_struct_keys: bool,
+}
+
+impl<'a> ValueDeserializer<'a> {
+    fn new(value: Value<'a>) -> ValueDeserializer<'a> {
+        ValueDeserializer {
+            value,
+            validate_struct_keys: false,
+        }
+    }
+
+    fn with_struct_key_validation(mut self) -> Self {
+        self.validate_struct_keys = true;
+        self
+    }
+}
+
+impl<'de> de::Deserializer<'de> for ValueDeserializer<'de> {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        let start = self.value.start;
+        let res = match self.value.e {
+            E::Integer(i) => visitor.visit_i64(i),
+            E::Boolean(b) => visitor.visit_bool(b),
+            E::Float(f) => visitor.visit_f64(f),
+            E::String(Cow::Borrowed(s)) => visitor.visit_borrowed_str(s),
+            E::String(Cow::Owned(s)) => visitor.visit_string(s),
+            E::Datetime(s) => visitor.visit_map(DatetimeDeserializer {
+                date: s,
+                visited: false,
+            }),
+            E::Array(values) => {
+                let mut s = de::value::SeqDeserializer::new(values.into_iter());
+                let ret = visitor.visit_seq(&mut s)?;
+                s.end()?;
+                Ok(ret)
+            }
+            E::InlineTable(values) | E::DottedTable(values) => {
+                visitor.visit_map(InlineTableDeserializer {
+                    values: values.into_iter(),
+                    next_value: None,
+                })
+            }
+        };
+        res.map_err(|mut err| {
+            // Attribute the error to whatever value returned the error.
+            err.fix_offset(|| Some(start));
+            err
+        })
+    }
+
+    fn deserialize_struct<V>(
+        self,
+        name: &'static str,
+        fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if name == datetime::NAME && fields == [datetime::FIELD] {
+            if let E::Datetime(s) = self.value.e {
+                return visitor.visit_map(DatetimeDeserializer {
+                    date: s,
+                    visited: false,
+                });
+            }
+        }
+
+        if self.validate_struct_keys {
+            match self.value.e {
+                E::InlineTable(ref values) | E::DottedTable(ref values) => {
+                    let extra_fields = values
+                        .iter()
+                        .filter_map(|key_value| {
+                            let (ref key, ref _val) = *key_value;
+                            if !fields.contains(&&*(key.1)) {
+                                Some(key.clone())
+                            } else {
+                                None
+                            }
+                        })
+                        .collect::<Vec<_>>();
+
+                    if !extra_fields.is_empty() {
+                        return Err(Error::from_kind(
+                            Some(self.value.start),
+                            ErrorKind::UnexpectedKeys {
+                                keys: extra_fields
+                                    .iter()
+                                    .map(|k| k.1.to_string())
+                                    .collect::<Vec<_>>(),
+                                available: fields,
+                            },
+                        ));
+                    }
+                }
+                _ => {}
+            }
+        }
+
+        if name == spanned::NAME && fields == [spanned::START, spanned::END, spanned::VALUE] {
+            let start = self.value.start;
+            let end = self.value.end;
+
+            return visitor.visit_map(SpannedDeserializer {
+                phantom_data: PhantomData,
+                start: Some(start),
+                value: Some(self.value),
+                end: Some(end),
+            });
+        }
+
+        self.deserialize_any(visitor)
+    }
+
+    // `None` is interpreted as a missing field so be sure to implement `Some`
+    // as a present field.
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_some(self)
+    }
+
+    fn deserialize_enum<V>(
+        self,
+        _name: &'static str,
+        _variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value.e {
+            E::String(val) => visitor.visit_enum(val.into_deserializer()),
+            E::InlineTable(values) => {
+                if values.len() != 1 {
+                    Err(Error::from_kind(
+                        Some(self.value.start),
+                        ErrorKind::Wanted {
+                            expected: "exactly 1 element",
+                            found: if values.is_empty() {
+                                "zero elements"
+                            } else {
+                                "more than 1 element"
+                            },
+                        },
+                    ))
+                } else {
+                    visitor.visit_enum(InlineTableDeserializer {
+                        values: values.into_iter(),
+                        next_value: None,
+                    })
+                }
+            }
+            e => Err(Error::from_kind(
+                Some(self.value.start),
+                ErrorKind::Wanted {
+                    expected: "string or inline table",
+                    found: e.type_name(),
+                },
+            )),
+        }
+    }
+
+    fn deserialize_newtype_struct<V>(
+        self,
+        _name: &'static str,
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_newtype_struct(self)
+    }
+
+    serde::forward_to_deserialize_any! {
+        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string seq
+        bytes byte_buf map unit identifier
+        ignored_any unit_struct tuple_struct tuple
+    }
+}
+
+impl<'de, 'b> de::IntoDeserializer<'de, Error> for MapVisitor<'de, 'b> {
+    type Deserializer = MapVisitor<'de, 'b>;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        self
+    }
+}
+
+impl<'de, 'b> de::IntoDeserializer<'de, Error> for &'b mut Deserializer<'de> {
+    type Deserializer = Self;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        self
+    }
+}
+
+impl<'de> de::IntoDeserializer<'de, Error> for Value<'de> {
+    type Deserializer = ValueDeserializer<'de>;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        ValueDeserializer::new(self)
+    }
+}
+
+struct SpannedDeserializer<'de, T: de::IntoDeserializer<'de, Error>> {
+    phantom_data: PhantomData<&'de ()>,
+    start: Option<usize>,
+    end: Option<usize>,
+    value: Option<T>,
+}
+
+impl<'de, T> de::MapAccess<'de> for SpannedDeserializer<'de, T>
+where
+    T: de::IntoDeserializer<'de, Error>,
+{
+    type Error = Error;
+
+    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Error>
+    where
+        K: de::DeserializeSeed<'de>,
+    {
+        if self.start.is_some() {
+            seed.deserialize(BorrowedStrDeserializer::new(spanned::START))
+                .map(Some)
+        } else if self.end.is_some() {
+            seed.deserialize(BorrowedStrDeserializer::new(spanned::END))
+                .map(Some)
+        } else if self.value.is_some() {
+            seed.deserialize(BorrowedStrDeserializer::new(spanned::VALUE))
+                .map(Some)
+        } else {
+            Ok(None)
+        }
+    }
+
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Error>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        if let Some(start) = self.start.take() {
+            seed.deserialize(start.into_deserializer())
+        } else if let Some(end) = self.end.take() {
+            seed.deserialize(end.into_deserializer())
+        } else if let Some(value) = self.value.take() {
+            seed.deserialize(value.into_deserializer())
+        } else {
+            panic!("next_value_seed called before next_key_seed")
+        }
+    }
+}
+
+struct DatetimeDeserializer<'a> {
+    visited: bool,
+    date: &'a str,
+}
+
+impl<'de> de::MapAccess<'de> for DatetimeDeserializer<'de> {
+    type Error = Error;
+
+    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Error>
+    where
+        K: de::DeserializeSeed<'de>,
+    {
+        if self.visited {
+            return Ok(None);
+        }
+        self.visited = true;
+        seed.deserialize(DatetimeFieldDeserializer).map(Some)
+    }
+
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Error>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        seed.deserialize(StrDeserializer::new(self.date.into()))
+    }
+}
+
+struct DatetimeFieldDeserializer;
+
+impl<'de> de::Deserializer<'de> for DatetimeFieldDeserializer {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_borrowed_str(datetime::FIELD)
+    }
+
+    serde::forward_to_deserialize_any! {
+        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string seq
+        bytes byte_buf map struct option unit newtype_struct
+        ignored_any unit_struct tuple_struct tuple enum identifier
+    }
+}
+
+struct DottedTableDeserializer<'a> {
+    name: Cow<'a, str>,
+    value: Value<'a>,
+}
+
+impl<'de> de::EnumAccess<'de> for DottedTableDeserializer<'de> {
+    type Error = Error;
+    type Variant = TableEnumDeserializer<'de>;
+
+    fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self::Variant), Self::Error>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        let (name, value) = (self.name, self.value);
+        seed.deserialize(StrDeserializer::new(name))
+            .map(|val| (val, TableEnumDeserializer { value }))
+    }
+}
+
+struct InlineTableDeserializer<'a> {
+    values: vec::IntoIter<TablePair<'a>>,
+    next_value: Option<Value<'a>>,
+}
+
+impl<'de> de::MapAccess<'de> for InlineTableDeserializer<'de> {
+    type Error = Error;
+
+    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Error>
+    where
+        K: de::DeserializeSeed<'de>,
+    {
+        let (key, value) = match self.values.next() {
+            Some(pair) => pair,
+            None => return Ok(None),
+        };
+        self.next_value = Some(value);
+        seed.deserialize(StrDeserializer::spanned(key)).map(Some)
+    }
+
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Error>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        let value = self.next_value.take().expect("Unable to read table values");
+        seed.deserialize(ValueDeserializer::new(value))
+    }
+}
+
+impl<'de> de::EnumAccess<'de> for InlineTableDeserializer<'de> {
+    type Error = Error;
+    type Variant = TableEnumDeserializer<'de>;
+
+    fn variant_seed<V>(mut self, seed: V) -> Result<(V::Value, Self::Variant), Self::Error>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        let (key, value) = match self.values.next() {
+            Some(pair) => pair,
+            None => {
+                return Err(Error::from_kind(
+                    None, // FIXME: How do we get an offset here?
+                    ErrorKind::Wanted {
+                        expected: "table with exactly 1 entry",
+                        found: "empty table",
+                    },
+                ));
+            }
+        };
+
+        seed.deserialize(StrDeserializer::new(key.1))
+            .map(|val| (val, TableEnumDeserializer { value }))
+    }
+}
+
+/// Deserializes table values into enum variants.
+struct TableEnumDeserializer<'a> {
+    value: Value<'a>,
+}
+
+impl<'de> de::VariantAccess<'de> for TableEnumDeserializer<'de> {
+    type Error = Error;
+
+    fn unit_variant(self) -> Result<(), Self::Error> {
+        match self.value.e {
+            E::InlineTable(values) | E::DottedTable(values) => {
+                if values.is_empty() {
+                    Ok(())
+                } else {
+                    Err(Error::from_kind(
+                        Some(self.value.start),
+                        ErrorKind::ExpectedEmptyTable,
+                    ))
+                }
+            }
+            e => Err(Error::from_kind(
+                Some(self.value.start),
+                ErrorKind::Wanted {
+                    expected: "table",
+                    found: e.type_name(),
+                },
+            )),
+        }
+    }
+
+    fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value, Self::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        seed.deserialize(ValueDeserializer::new(self.value))
+    }
+
+    fn tuple_variant<V>(self, len: usize, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value.e {
+            E::InlineTable(values) | E::DottedTable(values) => {
+                let tuple_values = values
+                    .into_iter()
+                    .enumerate()
+                    .map(|(index, (key, value))| match key.1.parse::<usize>() {
+                        Ok(key_index) if key_index == index => Ok(value),
+                        Ok(_) | Err(_) => Err(Error::from_kind(
+                            Some(key.0.start),
+                            ErrorKind::ExpectedTupleIndex {
+                                expected: index,
+                                found: key.1.to_string(),
+                            },
+                        )),
+                    })
+                    // Fold all values into a `Vec`, or return the first error.
+                    .fold(Ok(Vec::with_capacity(len)), |result, value_result| {
+                        result.and_then(move |mut tuple_values| match value_result {
+                            Ok(value) => {
+                                tuple_values.push(value);
+                                Ok(tuple_values)
+                            }
+                            // `Result<de::Value, Self::Error>` to `Result<Vec<_>, Self::Error>`
+                            Err(e) => Err(e),
+                        })
+                    })?;
+
+                if tuple_values.len() == len {
+                    de::Deserializer::deserialize_seq(
+                        ValueDeserializer::new(Value {
+                            e: E::Array(tuple_values),
+                            start: self.value.start,
+                            end: self.value.end,
+                        }),
+                        visitor,
+                    )
+                } else {
+                    Err(Error::from_kind(
+                        Some(self.value.start),
+                        ErrorKind::ExpectedTuple(len),
+                    ))
+                }
+            }
+            e => Err(Error::from_kind(
+                Some(self.value.start),
+                ErrorKind::Wanted {
+                    expected: "table",
+                    found: e.type_name(),
+                },
+            )),
+        }
+    }
+
+    fn struct_variant<V>(
+        self,
+        fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        de::Deserializer::deserialize_struct(
+            ValueDeserializer::new(self.value).with_struct_key_validation(),
+            "", // TODO: this should be the variant name
+            fields,
+            visitor,
+        )
+    }
+}
+
+impl<'a> Deserializer<'a> {
+    /// Creates a new deserializer which will be deserializing the string
+    /// provided.
+    pub fn new(input: &'a str) -> Deserializer<'a> {
+        Deserializer {
+            tokens: Tokenizer::new(input),
+            input,
+            require_newline_after_table: true,
+            allow_duplciate_after_longer_table: false,
+        }
+    }
+
+    #[doc(hidden)]
+    #[deprecated(since = "0.5.11")]
+    pub fn end(&mut self) -> Result<(), Error> {
+        Ok(())
+    }
+
+    #[doc(hidden)]
+    #[deprecated(since = "0.5.11")]
+    pub fn set_require_newline_after_table(&mut self, require: bool) {
+        self.require_newline_after_table = require;
+    }
+
+    #[doc(hidden)]
+    #[deprecated(since = "0.5.11")]
+    pub fn set_allow_duplicate_after_longer_table(&mut self, allow: bool) {
+        self.allow_duplciate_after_longer_table = allow;
+    }
+
+    fn tables(&mut self) -> Result<Vec<Table<'a>>, Error> {
+        let mut tables = Vec::new();
+        let mut cur_table = Table {
+            at: 0,
+            header: Vec::new(),
+            values: None,
+            array: false,
+        };
+
+        while let Some(line) = self.line()? {
+            match line {
+                Line::Table {
+                    at,
+                    mut header,
+                    array,
+                } => {
+                    if !cur_table.header.is_empty() || cur_table.values.is_some() {
+                        tables.push(cur_table);
+                    }
+                    cur_table = Table {
+                        at,
+                        header: Vec::new(),
+                        values: Some(Vec::new()),
+                        array,
+                    };
+                    loop {
+                        let part = header.next().map_err(|e| self.token_error(e));
+                        match part? {
+                            Some(part) => cur_table.header.push(part),
+                            None => break,
+                        }
+                    }
+                }
+                Line::KeyValue(key, value) => {
+                    if cur_table.values.is_none() {
+                        cur_table.values = Some(Vec::new());
+                    }
+                    self.add_dotted_key(key, value, cur_table.values.as_mut().unwrap())?;
+                }
+            }
+        }
+        if !cur_table.header.is_empty() || cur_table.values.is_some() {
+            tables.push(cur_table);
+        }
+        Ok(tables)
+    }
+
+    fn line(&mut self) -> Result<Option<Line<'a>>, Error> {
+        loop {
+            self.eat_whitespace()?;
+            if self.eat_comment()? {
+                continue;
+            }
+            if self.eat(Token::Newline)? {
+                continue;
+            }
+            break;
+        }
+
+        match self.peek()? {
+            Some((_, Token::LeftBracket)) => self.table_header().map(Some),
+            Some(_) => self.key_value().map(Some),
+            None => Ok(None),
+        }
+    }
+
+    fn table_header(&mut self) -> Result<Line<'a>, Error> {
+        let start = self.tokens.current();
+        self.expect(Token::LeftBracket)?;
+        let array = self.eat(Token::LeftBracket)?;
+        let ret = Header::new(self.tokens.clone(), array, self.require_newline_after_table);
+        if self.require_newline_after_table {
+            self.tokens.skip_to_newline();
+        } else {
+            loop {
+                match self.next()? {
+                    Some((_, Token::RightBracket)) => {
+                        if array {
+                            self.eat(Token::RightBracket)?;
+                        }
+                        break;
+                    }
+                    Some((_, Token::Newline)) | None => break,
+                    _ => {}
+                }
+            }
+            self.eat_whitespace()?;
+        }
+        Ok(Line::Table {
+            at: start,
+            header: ret,
+            array,
+        })
+    }
+
+    fn key_value(&mut self) -> Result<Line<'a>, Error> {
+        let key = self.dotted_key()?;
+        self.eat_whitespace()?;
+        self.expect(Token::Equals)?;
+        self.eat_whitespace()?;
+
+        let value = self.value()?;
+        self.eat_whitespace()?;
+        if !self.eat_comment()? {
+            self.eat_newline_or_eof()?;
+        }
+
+        Ok(Line::KeyValue(key, value))
+    }
+
+    fn value(&mut self) -> Result<Value<'a>, Error> {
+        let at = self.tokens.current();
+        let value = match self.next()? {
+            Some((Span { start, end }, Token::String { val, .. })) => Value {
+                e: E::String(val),
+                start,
+                end,
+            },
+            Some((Span { start, end }, Token::Keylike("true"))) => Value {
+                e: E::Boolean(true),
+                start,
+                end,
+            },
+            Some((Span { start, end }, Token::Keylike("false"))) => Value {
+                e: E::Boolean(false),
+                start,
+                end,
+            },
+            Some((span, Token::Keylike(key))) => self.parse_keylike(at, span, key)?,
+            Some((span, Token::Plus)) => self.number_leading_plus(span)?,
+            Some((Span { start, .. }, Token::LeftBrace)) => {
+                self.inline_table().map(|(Span { end, .. }, table)| Value {
+                    e: E::InlineTable(table),
+                    start,
+                    end,
+                })?
+            }
+            Some((Span { start, .. }, Token::LeftBracket)) => {
+                self.array().map(|(Span { end, .. }, array)| Value {
+                    e: E::Array(array),
+                    start,
+                    end,
+                })?
+            }
+            Some(token) => {
+                return Err(self.error(
+                    at,
+                    ErrorKind::Wanted {
+                        expected: "a value",
+                        found: token.1.describe(),
+                    },
+                ));
+            }
+            None => return Err(self.eof()),
+        };
+        Ok(value)
+    }
+
+    fn parse_keylike(&mut self, at: usize, span: Span, key: &'a str) -> Result<Value<'a>, Error> {
+        if key == "inf" || key == "nan" {
+            return self.number_or_date(span, key);
+        }
+
+        let first_char = key.chars().next().expect("key should not be empty here");
+        match first_char {
+            '-' | '0'..='9' => self.number_or_date(span, key),
+            _ => Err(self.error(at, ErrorKind::UnquotedString)),
+        }
+    }
+
+    fn number_or_date(&mut self, span: Span, s: &'a str) -> Result<Value<'a>, Error> {
+        if s.contains('T')
+            || s.contains('t')
+            || (s.len() > 1 && s[1..].contains('-') && !s.contains("e-") && !s.contains("E-"))
+        {
+            self.datetime(span, s, false)
+                .map(|(Span { start, end }, d)| Value {
+                    e: E::Datetime(d),
+                    start,
+                    end,
+                })
+        } else if self.eat(Token::Colon)? {
+            self.datetime(span, s, true)
+                .map(|(Span { start, end }, d)| Value {
+                    e: E::Datetime(d),
+                    start,
+                    end,
+                })
+        } else {
+            self.number(span, s)
+        }
+    }
+
+    /// Returns a string or table value type.
+    ///
+    /// Used to deserialize enums. Unit enums may be represented as a string or a table, all other
+    /// structures (tuple, newtype, struct) must be represented as a table.
+    fn string_or_table(&mut self) -> Result<(Value<'a>, Option<Cow<'a, str>>), Error> {
+        match self.peek()? {
+            Some((span, Token::LeftBracket)) => {
+                let tables = self.tables()?;
+                if tables.len() != 1 {
+                    return Err(Error::from_kind(
+                        Some(span.start),
+                        ErrorKind::Wanted {
+                            expected: "exactly 1 table",
+                            found: if tables.is_empty() {
+                                "zero tables"
+                            } else {
+                                "more than 1 table"
+                            },
+                        },
+                    ));
+                }
+
+                let table = tables
+                    .into_iter()
+                    .next()
+                    .expect("Expected exactly one table");
+                let header = table
+                    .header
+                    .last()
+                    .expect("Expected at least one header value for table.");
+
+                let start = table.at;
+                let end = table
+                    .values
+                    .as_ref()
+                    .and_then(|values| values.last())
+                    .map(|&(_, ref val)| val.end)
+                    .unwrap_or_else(|| header.1.len());
+                Ok((
+                    Value {
+                        e: E::DottedTable(table.values.unwrap_or_default()),
+                        start,
+                        end,
+                    },
+                    Some(header.1.clone()),
+                ))
+            }
+            Some(_) => self.value().map(|val| (val, None)),
+            None => Err(self.eof()),
+        }
+    }
+
+    fn number(&mut self, Span { start, end }: Span, s: &'a str) -> Result<Value<'a>, Error> {
+        let to_integer = |f| Value {
+            e: E::Integer(f),
+            start,
+            end,
+        };
+        if let Some(value) = s.strip_prefix("0x") {
+            self.integer(value, 16).map(to_integer)
+        } else if let Some(value) = s.strip_prefix("0o") {
+            self.integer(value, 8).map(to_integer)
+        } else if let Some(value) = s.strip_prefix("0b") {
+            self.integer(value, 2).map(to_integer)
+        } else if s.contains('e') || s.contains('E') {
+            self.float(s, None).map(|f| Value {
+                e: E::Float(f),
+                start,
+                end,
+            })
+        } else if self.eat(Token::Period)? {
+            let at = self.tokens.current();
+            match self.next()? {
+                Some((Span { start, end }, Token::Keylike(after))) => {
+                    self.float(s, Some(after)).map(|f| Value {
+                        e: E::Float(f),
+                        start,
+                        end,
+                    })
+                }
+                _ => Err(self.error(at, ErrorKind::NumberInvalid)),
+            }
+        } else if s == "inf" {
+            Ok(Value {
+                e: E::Float(f64::INFINITY),
+                start,
+                end,
+            })
+        } else if s == "-inf" {
+            Ok(Value {
+                e: E::Float(f64::NEG_INFINITY),
+                start,
+                end,
+            })
+        } else if s == "nan" {
+            Ok(Value {
+                e: E::Float(f64::NAN),
+                start,
+                end,
+            })
+        } else if s == "-nan" {
+            Ok(Value {
+                e: E::Float(-f64::NAN),
+                start,
+                end,
+            })
+        } else {
+            self.integer(s, 10).map(to_integer)
+        }
+    }
+
+    fn number_leading_plus(&mut self, Span { start, .. }: Span) -> Result<Value<'a>, Error> {
+        let start_token = self.tokens.current();
+        match self.next()? {
+            Some((Span { end, .. }, Token::Keylike(s))) => self.number(Span { start, end }, s),
+            _ => Err(self.error(start_token, ErrorKind::NumberInvalid)),
+        }
+    }
+
+    fn integer(&self, s: &'a str, radix: u32) -> Result<i64, Error> {
+        let allow_sign = radix == 10;
+        let allow_leading_zeros = radix != 10;
+        let (prefix, suffix) = self.parse_integer(s, allow_sign, allow_leading_zeros, radix)?;
+        let start = self.tokens.substr_offset(s);
+        if !suffix.is_empty() {
+            return Err(self.error(start, ErrorKind::NumberInvalid));
+        }
+        i64::from_str_radix(prefix.replace('_', "").trim_start_matches('+'), radix)
+            .map_err(|_e| self.error(start, ErrorKind::NumberInvalid))
+    }
+
+    fn parse_integer(
+        &self,
+        s: &'a str,
+        allow_sign: bool,
+        allow_leading_zeros: bool,
+        radix: u32,
+    ) -> Result<(&'a str, &'a str), Error> {
+        let start = self.tokens.substr_offset(s);
+
+        let mut first = true;
+        let mut first_zero = false;
+        let mut underscore = false;
+        let mut end = s.len();
+        for (i, c) in s.char_indices() {
+            let at = i + start;
+            if i == 0 && (c == '+' || c == '-') && allow_sign {
+                continue;
+            }
+
+            if c == '0' && first {
+                first_zero = true;
+            } else if c.is_digit(radix) {
+                if !first && first_zero && !allow_leading_zeros {
+                    return Err(self.error(at, ErrorKind::NumberInvalid));
+                }
+                underscore = false;
+            } else if c == '_' && first {
+                return Err(self.error(at, ErrorKind::NumberInvalid));
+            } else if c == '_' && !underscore {
+                underscore = true;
+            } else {
+                end = i;
+                break;
+            }
+            first = false;
+        }
+        if first || underscore {
+            return Err(self.error(start, ErrorKind::NumberInvalid));
+        }
+        Ok((&s[..end], &s[end..]))
+    }
+
+    fn float(&mut self, s: &'a str, after_decimal: Option<&'a str>) -> Result<f64, Error> {
+        let (integral, mut suffix) = self.parse_integer(s, true, false, 10)?;
+        let start = self.tokens.substr_offset(integral);
+
+        let mut fraction = None;
+        if let Some(after) = after_decimal {
+            if !suffix.is_empty() {
+                return Err(self.error(start, ErrorKind::NumberInvalid));
+            }
+            let (a, b) = self.parse_integer(after, false, true, 10)?;
+            fraction = Some(a);
+            suffix = b;
+        }
+
+        let mut exponent = None;
+        if suffix.starts_with('e') || suffix.starts_with('E') {
+            let (a, b) = if suffix.len() == 1 {
+                self.eat(Token::Plus)?;
+                match self.next()? {
+                    Some((_, Token::Keylike(s))) => self.parse_integer(s, false, true, 10)?,
+                    _ => return Err(self.error(start, ErrorKind::NumberInvalid)),
+                }
+            } else {
+                self.parse_integer(&suffix[1..], true, true, 10)?
+            };
+            if !b.is_empty() {
+                return Err(self.error(start, ErrorKind::NumberInvalid));
+            }
+            exponent = Some(a);
+        } else if !suffix.is_empty() {
+            return Err(self.error(start, ErrorKind::NumberInvalid));
+        }
+
+        let mut number = integral
+            .trim_start_matches('+')
+            .chars()
+            .filter(|c| *c != '_')
+            .collect::<String>();
+        if let Some(fraction) = fraction {
+            number.push('.');
+            number.extend(fraction.chars().filter(|c| *c != '_'));
+        }
+        if let Some(exponent) = exponent {
+            number.push('E');
+            number.extend(exponent.chars().filter(|c| *c != '_'));
+        }
+        number
+            .parse()
+            .map_err(|_e| self.error(start, ErrorKind::NumberInvalid))
+            .and_then(|n: f64| {
+                if n.is_finite() {
+                    Ok(n)
+                } else {
+                    Err(self.error(start, ErrorKind::NumberInvalid))
+                }
+            })
+    }
+
+    fn datetime(
+        &mut self,
+        mut span: Span,
+        date: &'a str,
+        colon_eaten: bool,
+    ) -> Result<(Span, &'a str), Error> {
+        let start = self.tokens.substr_offset(date);
+
+        // Check for space separated date and time.
+        let mut lookahead = self.tokens.clone();
+        if let Ok(Some((_, Token::Whitespace(" ")))) = lookahead.next() {
+            // Check if hour follows.
+            if let Ok(Some((_, Token::Keylike(_)))) = lookahead.next() {
+                self.next()?; // skip space
+                self.next()?; // skip keylike hour
+            }
+        }
+
+        if colon_eaten || self.eat(Token::Colon)? {
+            // minutes
+            match self.next()? {
+                Some((_, Token::Keylike(_))) => {}
+                _ => return Err(self.error(start, ErrorKind::DateInvalid)),
+            }
+            // Seconds
+            self.expect(Token::Colon)?;
+            match self.next()? {
+                Some((Span { end, .. }, Token::Keylike(_))) => {
+                    span.end = end;
+                }
+                _ => return Err(self.error(start, ErrorKind::DateInvalid)),
+            }
+            // Fractional seconds
+            if self.eat(Token::Period)? {
+                match self.next()? {
+                    Some((Span { end, .. }, Token::Keylike(_))) => {
+                        span.end = end;
+                    }
+                    _ => return Err(self.error(start, ErrorKind::DateInvalid)),
+                }
+            }
+
+            // offset
+            if self.eat(Token::Plus)? {
+                match self.next()? {
+                    Some((Span { end, .. }, Token::Keylike(_))) => {
+                        span.end = end;
+                    }
+                    _ => return Err(self.error(start, ErrorKind::DateInvalid)),
+                }
+            }
+            if self.eat(Token::Colon)? {
+                match self.next()? {
+                    Some((Span { end, .. }, Token::Keylike(_))) => {
+                        span.end = end;
+                    }
+                    _ => return Err(self.error(start, ErrorKind::DateInvalid)),
+                }
+            }
+        }
+
+        let end = self.tokens.current();
+        Ok((span, &self.tokens.input()[start..end]))
+    }
+
+    // TODO(#140): shouldn't buffer up this entire table in memory, it'd be
+    // great to defer parsing everything until later.
+    fn inline_table(&mut self) -> Result<(Span, Vec<TablePair<'a>>), Error> {
+        let mut ret = Vec::new();
+        self.eat_whitespace()?;
+        if let Some(span) = self.eat_spanned(Token::RightBrace)? {
+            return Ok((span, ret));
+        }
+        loop {
+            let key = self.dotted_key()?;
+            self.eat_whitespace()?;
+            self.expect(Token::Equals)?;
+            self.eat_whitespace()?;
+            let value = self.value()?;
+            self.add_dotted_key(key, value, &mut ret)?;
+
+            self.eat_whitespace()?;
+            if let Some(span) = self.eat_spanned(Token::RightBrace)? {
+                return Ok((span, ret));
+            }
+            self.expect(Token::Comma)?;
+            self.eat_whitespace()?;
+        }
+    }
+
+    // TODO(#140): shouldn't buffer up this entire array in memory, it'd be
+    // great to defer parsing everything until later.
+    fn array(&mut self) -> Result<(Span, Vec<Value<'a>>), Error> {
+        let mut ret = Vec::new();
+
+        let intermediate = |me: &mut Deserializer<'_>| {
+            loop {
+                me.eat_whitespace()?;
+                if !me.eat(Token::Newline)? && !me.eat_comment()? {
+                    break;
+                }
+            }
+            Ok(())
+        };
+
+        loop {
+            intermediate(self)?;
+            if let Some(span) = self.eat_spanned(Token::RightBracket)? {
+                return Ok((span, ret));
+            }
+            let value = self.value()?;
+            ret.push(value);
+            intermediate(self)?;
+            if !self.eat(Token::Comma)? {
+                break;
+            }
+        }
+        intermediate(self)?;
+        let span = self.expect_spanned(Token::RightBracket)?;
+        Ok((span, ret))
+    }
+
+    fn table_key(&mut self) -> Result<(Span, Cow<'a, str>), Error> {
+        self.tokens.table_key().map_err(|e| self.token_error(e))
+    }
+
+    fn dotted_key(&mut self) -> Result<Vec<(Span, Cow<'a, str>)>, Error> {
+        let mut result = vec![self.table_key()?];
+        self.eat_whitespace()?;
+        while self.eat(Token::Period)? {
+            self.eat_whitespace()?;
+            result.push(self.table_key()?);
+            self.eat_whitespace()?;
+        }
+        Ok(result)
+    }
+
+    /// Stores a value in the appropriate hierarchical structure positioned based on the dotted key.
+    ///
+    /// Given the following definition: `multi.part.key = "value"`, `multi` and `part` are
+    /// intermediate parts which are mapped to the relevant fields in the deserialized type's data
+    /// hierarchy.
+    ///
+    /// # Parameters
+    ///
+    /// * `key_parts`: Each segment of the dotted key, e.g. `part.one` maps to
+    ///                `vec![Cow::Borrowed("part"), Cow::Borrowed("one")].`
+    /// * `value`: The parsed value.
+    /// * `values`: The `Vec` to store the value in.
+    fn add_dotted_key(
+        &self,
+        mut key_parts: Vec<(Span, Cow<'a, str>)>,
+        value: Value<'a>,
+        values: &mut Vec<TablePair<'a>>,
+    ) -> Result<(), Error> {
+        let key = key_parts.remove(0);
+        if key_parts.is_empty() {
+            values.push((key, value));
+            return Ok(());
+        }
+        match values.iter_mut().find(|&&mut (ref k, _)| *k.1 == key.1) {
+            Some(&mut (
+                _,
+                Value {
+                    e: E::DottedTable(ref mut v),
+                    ..
+                },
+            )) => {
+                return self.add_dotted_key(key_parts, value, v);
+            }
+            Some(&mut (_, Value { start, .. })) => {
+                return Err(self.error(start, ErrorKind::DottedKeyInvalidType));
+            }
+            None => {}
+        }
+        // The start/end value is somewhat misleading here.
+        let table_values = Value {
+            e: E::DottedTable(Vec::new()),
+            start: value.start,
+            end: value.end,
+        };
+        values.push((key, table_values));
+        let last_i = values.len() - 1;
+        if let (
+            _,
+            Value {
+                e: E::DottedTable(ref mut v),
+                ..
+            },
+        ) = values[last_i]
+        {
+            self.add_dotted_key(key_parts, value, v)?;
+        }
+        Ok(())
+    }
+
+    fn eat_whitespace(&mut self) -> Result<(), Error> {
+        self.tokens
+            .eat_whitespace()
+            .map_err(|e| self.token_error(e))
+    }
+
+    fn eat_comment(&mut self) -> Result<bool, Error> {
+        self.tokens.eat_comment().map_err(|e| self.token_error(e))
+    }
+
+    fn eat_newline_or_eof(&mut self) -> Result<(), Error> {
+        self.tokens
+            .eat_newline_or_eof()
+            .map_err(|e| self.token_error(e))
+    }
+
+    fn eat(&mut self, expected: Token<'a>) -> Result<bool, Error> {
+        self.tokens.eat(expected).map_err(|e| self.token_error(e))
+    }
+
+    fn eat_spanned(&mut self, expected: Token<'a>) -> Result<Option<Span>, Error> {
+        self.tokens
+            .eat_spanned(expected)
+            .map_err(|e| self.token_error(e))
+    }
+
+    fn expect(&mut self, expected: Token<'a>) -> Result<(), Error> {
+        self.tokens
+            .expect(expected)
+            .map_err(|e| self.token_error(e))
+    }
+
+    fn expect_spanned(&mut self, expected: Token<'a>) -> Result<Span, Error> {
+        self.tokens
+            .expect_spanned(expected)
+            .map_err(|e| self.token_error(e))
+    }
+
+    fn next(&mut self) -> Result<Option<(Span, Token<'a>)>, Error> {
+        self.tokens.next().map_err(|e| self.token_error(e))
+    }
+
+    fn peek(&mut self) -> Result<Option<(Span, Token<'a>)>, Error> {
+        self.tokens.peek().map_err(|e| self.token_error(e))
+    }
+
+    fn eof(&self) -> Error {
+        self.error(self.input.len(), ErrorKind::UnexpectedEof)
+    }
+
+    fn token_error(&self, error: TokenError) -> Error {
+        match error {
+            TokenError::InvalidCharInString(at, ch) => {
+                self.error(at, ErrorKind::InvalidCharInString(ch))
+            }
+            TokenError::InvalidEscape(at, ch) => self.error(at, ErrorKind::InvalidEscape(ch)),
+            TokenError::InvalidEscapeValue(at, v) => {
+                self.error(at, ErrorKind::InvalidEscapeValue(v))
+            }
+            TokenError::InvalidHexEscape(at, ch) => self.error(at, ErrorKind::InvalidHexEscape(ch)),
+            TokenError::NewlineInString(at) => self.error(at, ErrorKind::NewlineInString),
+            TokenError::Unexpected(at, ch) => self.error(at, ErrorKind::Unexpected(ch)),
+            TokenError::UnterminatedString(at) => self.error(at, ErrorKind::UnterminatedString),
+            TokenError::NewlineInTableKey(at) => self.error(at, ErrorKind::NewlineInTableKey),
+            TokenError::Wanted {
+                at,
+                expected,
+                found,
+            } => self.error(at, ErrorKind::Wanted { expected, found }),
+            TokenError::MultilineStringKey(at) => self.error(at, ErrorKind::MultilineStringKey),
+        }
+    }
+
+    fn error(&self, at: usize, kind: ErrorKind) -> Error {
+        let mut err = Error::from_kind(Some(at), kind);
+        err.fix_linecol(|at| self.to_linecol(at));
+        err
+    }
+
+    /// Converts a byte offset from an error message to a (line, column) pair
+    ///
+    /// All indexes are 0-based.
+    fn to_linecol(&self, offset: usize) -> (usize, usize) {
+        let mut cur = 0;
+        // Use split_terminator instead of lines so that if there is a `\r`,
+        // it is included in the offset calculation. The `+1` values below
+        // account for the `\n`.
+        for (i, line) in self.input.split_terminator('\n').enumerate() {
+            if cur + line.len() + 1 > offset {
+                return (i, offset - cur);
+            }
+            cur += line.len() + 1;
+        }
+        (self.input.lines().count(), 0)
+    }
+}
+
+impl Error {
+    /// Produces a (line, column) pair of the position of the error if available
+    ///
+    /// All indexes are 0-based.
+    pub fn line_col(&self) -> Option<(usize, usize)> {
+        self.inner.line.map(|line| (line, self.inner.col))
+    }
+
+    fn from_kind(at: Option<usize>, kind: ErrorKind) -> Error {
+        Error {
+            inner: Box::new(ErrorInner {
+                kind,
+                line: None,
+                col: 0,
+                at,
+                message: String::new(),
+                key: Vec::new(),
+            }),
+        }
+    }
+
+    fn custom(at: Option<usize>, s: String) -> Error {
+        Error {
+            inner: Box::new(ErrorInner {
+                kind: ErrorKind::Custom,
+                line: None,
+                col: 0,
+                at,
+                message: s,
+                key: Vec::new(),
+            }),
+        }
+    }
+
+    pub(crate) fn add_key_context(&mut self, key: &str) {
+        self.inner.key.insert(0, key.to_string());
+    }
+
+    fn fix_offset<F>(&mut self, f: F)
+    where
+        F: FnOnce() -> Option<usize>,
+    {
+        // An existing offset is always better positioned than anything we
+        // might want to add later.
+        if self.inner.at.is_none() {
+            self.inner.at = f();
+        }
+    }
+
+    fn fix_linecol<F>(&mut self, f: F)
+    where
+        F: FnOnce(usize) -> (usize, usize),
+    {
+        if let Some(at) = self.inner.at {
+            let (line, col) = f(at);
+            self.inner.line = Some(line);
+            self.inner.col = col;
+        }
+    }
+}
+
+impl std::convert::From<Error> for std::io::Error {
+    fn from(e: Error) -> Self {
+        std::io::Error::new(std::io::ErrorKind::InvalidData, e.to_string())
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match &self.inner.kind {
+            ErrorKind::UnexpectedEof => "unexpected eof encountered".fmt(f)?,
+            ErrorKind::InvalidCharInString(c) => write!(
+                f,
+                "invalid character in string: `{}`",
+                c.escape_default().collect::<String>()
+            )?,
+            ErrorKind::InvalidEscape(c) => write!(
+                f,
+                "invalid escape character in string: `{}`",
+                c.escape_default().collect::<String>()
+            )?,
+            ErrorKind::InvalidHexEscape(c) => write!(
+                f,
+                "invalid hex escape character in string: `{}`",
+                c.escape_default().collect::<String>()
+            )?,
+            ErrorKind::InvalidEscapeValue(c) => write!(f, "invalid escape value: `{}`", c)?,
+            ErrorKind::NewlineInString => "newline in string found".fmt(f)?,
+            ErrorKind::Unexpected(ch) => write!(
+                f,
+                "unexpected character found: `{}`",
+                ch.escape_default().collect::<String>()
+            )?,
+            ErrorKind::UnterminatedString => "unterminated string".fmt(f)?,
+            ErrorKind::NewlineInTableKey => "found newline in table key".fmt(f)?,
+            ErrorKind::Wanted { expected, found } => {
+                write!(f, "expected {}, found {}", expected, found)?
+            }
+            ErrorKind::NumberInvalid => "invalid number".fmt(f)?,
+            ErrorKind::DateInvalid => "invalid date".fmt(f)?,
+            ErrorKind::DuplicateTable(ref s) => {
+                write!(f, "redefinition of table `{}`", s)?;
+            }
+            ErrorKind::RedefineAsArray => "table redefined as array".fmt(f)?,
+            ErrorKind::EmptyTableKey => "empty table key found".fmt(f)?,
+            ErrorKind::MultilineStringKey => "multiline strings are not allowed for key".fmt(f)?,
+            ErrorKind::Custom => self.inner.message.fmt(f)?,
+            ErrorKind::ExpectedTuple(l) => write!(f, "expected table with length {}", l)?,
+            ErrorKind::ExpectedTupleIndex {
+                expected,
+                ref found,
+            } => write!(f, "expected table key `{}`, but was `{}`", expected, found)?,
+            ErrorKind::ExpectedEmptyTable => "expected empty table".fmt(f)?,
+            ErrorKind::DottedKeyInvalidType => {
+                "dotted key attempted to extend non-table type".fmt(f)?
+            }
+            ErrorKind::UnexpectedKeys {
+                ref keys,
+                available,
+            } => write!(
+                f,
+                "unexpected keys in table: `{:?}`, available keys: `{:?}`",
+                keys, available
+            )?,
+            ErrorKind::UnquotedString => write!(
+                f,
+                "invalid TOML value, did you mean to use a quoted string?"
+            )?,
+        }
+
+        if !self.inner.key.is_empty() {
+            write!(f, " for key `")?;
+            for (i, k) in self.inner.key.iter().enumerate() {
+                if i > 0 {
+                    write!(f, ".")?;
+                }
+                write!(f, "{}", k)?;
+            }
+            write!(f, "`")?;
+        }
+
+        if let Some(line) = self.inner.line {
+            write!(f, " at line {} column {}", line + 1, self.inner.col + 1)?;
+        }
+
+        Ok(())
+    }
+}
+
+impl error::Error for Error {}
+
+impl de::Error for Error {
+    fn custom<T: fmt::Display>(msg: T) -> Error {
+        Error::custom(None, msg.to_string())
+    }
+}
+
+enum Line<'a> {
+    Table {
+        at: usize,
+        header: Header<'a>,
+        array: bool,
+    },
+    KeyValue(Vec<(Span, Cow<'a, str>)>, Value<'a>),
+}
+
+struct Header<'a> {
+    first: bool,
+    array: bool,
+    require_newline_after_table: bool,
+    tokens: Tokenizer<'a>,
+}
+
+impl<'a> Header<'a> {
+    fn new(tokens: Tokenizer<'a>, array: bool, require_newline_after_table: bool) -> Header<'a> {
+        Header {
+            first: true,
+            array,
+            tokens,
+            require_newline_after_table,
+        }
+    }
+
+    fn next(&mut self) -> Result<Option<(Span, Cow<'a, str>)>, TokenError> {
+        self.tokens.eat_whitespace()?;
+
+        if self.first || self.tokens.eat(Token::Period)? {
+            self.first = false;
+            self.tokens.eat_whitespace()?;
+            self.tokens.table_key().map(Some)
+        } else {
+            self.tokens.expect(Token::RightBracket)?;
+            if self.array {
+                self.tokens.expect(Token::RightBracket)?;
+            }
+
+            self.tokens.eat_whitespace()?;
+            if self.require_newline_after_table && !self.tokens.eat_comment()? {
+                self.tokens.eat_newline_or_eof()?;
+            }
+            Ok(None)
+        }
+    }
+}
+
+#[derive(Debug)]
+struct Value<'a> {
+    e: E<'a>,
+    start: usize,
+    end: usize,
+}
+
+#[derive(Debug)]
+enum E<'a> {
+    Integer(i64),
+    Float(f64),
+    Boolean(bool),
+    String(Cow<'a, str>),
+    Datetime(&'a str),
+    Array(Vec<Value<'a>>),
+    InlineTable(Vec<TablePair<'a>>),
+    DottedTable(Vec<TablePair<'a>>),
+}
+
+impl<'a> E<'a> {
+    fn type_name(&self) -> &'static str {
+        match *self {
+            E::String(..) => "string",
+            E::Integer(..) => "integer",
+            E::Float(..) => "float",
+            E::Boolean(..) => "boolean",
+            E::Datetime(..) => "datetime",
+            E::Array(..) => "array",
+            E::InlineTable(..) => "inline table",
+            E::DottedTable(..) => "dotted table",
+        }
+    }
+}
diff --git a/third_party/rust/toml/src/lib.rs b/third_party/rust/toml/src/lib.rs
new file mode 100644
index 0000000000..b20b42d2df
--- /dev/null
+++ b/third_party/rust/toml/src/lib.rs
@@ -0,0 +1,176 @@
+//! A [serde]-compatible [TOML]-parsing library
+//!
+//! TOML itself is a simple, ergonomic, and readable configuration format:
+//!
+//! ```toml
+//! [package]
+//! name = "toml"
+//! version = "0.4.2"
+//! authors = ["Alex Crichton <alex@alexcrichton.com>"]
+//!
+//! [dependencies]
+//! serde = "1.0"
+//! ```
+//!
+//! The TOML format tends to be relatively common throughout the Rust community
+//! for configuration, notably being used by [Cargo], Rust's package manager.
+//!
+//! ## TOML values
+//!
+//! A value in TOML is represented with the [`Value`] enum in this crate:
+//!
+//! ```rust,ignore
+//! pub enum Value {
+//!     String(String),
+//!     Integer(i64),
+//!     Float(f64),
+//!     Boolean(bool),
+//!     Datetime(Datetime),
+//!     Array(Array),
+//!     Table(Table),
+//! }
+//! ```
+//!
+//! TOML is similar to JSON with the notable addition of a [`Datetime`]
+//! type. In general, TOML and JSON are interchangeable in terms of
+//! formats.
+//!
+//! ## Parsing TOML
+//!
+//! The easiest way to parse a TOML document is via the [`Value`] type:
+//!
+//! ```rust
+//! use toml::Value;
+//!
+//! let value = "foo = 'bar'".parse::<Value>().unwrap();
+//!
+//! assert_eq!(value["foo"].as_str(), Some("bar"));
+//! ```
+//!
+//! The [`Value`] type implements a number of convenience methods and
+//! traits; the example above uses [`FromStr`] to parse a [`str`] into a
+//! [`Value`].
+//!
+//! ## Deserialization and Serialization
+//!
+//! This crate supports [`serde`] 1.0 with a number of
+//! implementations of the `Deserialize`, `Serialize`, `Deserializer`, and
+//! `Serializer` traits. Namely, you'll find:
+//!
+//! * `Deserialize for Value`
+//! * `Serialize for Value`
+//! * `Deserialize for Datetime`
+//! * `Serialize for Datetime`
+//! * `Deserializer for de::Deserializer`
+//! * `Serializer for ser::Serializer`
+//! * `Deserializer for Value`
+//!
+//! This means that you can use Serde to deserialize/serialize the
+//! [`Value`] type as well as the [`Datetime`] type in this crate. You can also
+//! use the [`Deserializer`], [`Serializer`], or [`Value`] type itself to act as
+//! a deserializer/serializer for arbitrary types.
+//!
+//! An example of deserializing with TOML is:
+//!
+//! ```rust
+//! use serde_derive::Deserialize;
+//!
+//! #[derive(Deserialize)]
+//! struct Config {
+//!     ip: String,
+//!     port: Option<u16>,
+//!     keys: Keys,
+//! }
+//!
+//! #[derive(Deserialize)]
+//! struct Keys {
+//!     github: String,
+//!     travis: Option<String>,
+//! }
+//!
+//! fn main() {
+//!     let config: Config = toml::from_str(r#"
+//!         ip = '127.0.0.1'
+//!
+//!         [keys]
+//!         github = 'xxxxxxxxxxxxxxxxx'
+//!         travis = 'yyyyyyyyyyyyyyyyy'
+//!     "#).unwrap();
+//!
+//!     assert_eq!(config.ip, "127.0.0.1");
+//!     assert_eq!(config.port, None);
+//!     assert_eq!(config.keys.github, "xxxxxxxxxxxxxxxxx");
+//!     assert_eq!(config.keys.travis.as_ref().unwrap(), "yyyyyyyyyyyyyyyyy");
+//! }
+//! ```
+//!
+//! You can serialize types in a similar fashion:
+//!
+//! ```rust
+//! use serde_derive::Serialize;
+//!
+//! #[derive(Serialize)]
+//! struct Config {
+//!     ip: String,
+//!     port: Option<u16>,
+//!     keys: Keys,
+//! }
+//!
+//! #[derive(Serialize)]
+//! struct Keys {
+//!     github: String,
+//!     travis: Option<String>,
+//! }
+//!
+//! fn main() {
+//!     let config = Config {
+//!         ip: "127.0.0.1".to_string(),
+//!         port: None,
+//!         keys: Keys {
+//!             github: "xxxxxxxxxxxxxxxxx".to_string(),
+//!             travis: Some("yyyyyyyyyyyyyyyyy".to_string()),
+//!         },
+//!     };
+//!
+//!     let toml = toml::to_string(&config).unwrap();
+//! }
+//! ```
+//!
+//! [TOML]: https://github.com/toml-lang/toml
+//! [Cargo]: https://crates.io/
+//! [`serde`]: https://serde.rs/
+//! [serde]: https://serde.rs/
+
+#![deny(missing_docs)]
+#![warn(rust_2018_idioms)]
+// Makes rustc abort compilation if there are any unsafe blocks in the crate.
+// Presence of this annotation is picked up by tools such as cargo-geiger
+// and lets them ensure that there is indeed no unsafe code as opposed to
+// something they couldn't detect (e.g. unsafe added via macro expansion, etc).
+#![forbid(unsafe_code)]
+
+pub mod map;
+pub mod value;
+#[doc(no_inline)]
+pub use crate::value::Value;
+mod datetime;
+
+pub mod ser;
+#[doc(no_inline)]
+pub use crate::ser::{to_string, to_string_pretty, to_vec, Serializer};
+pub mod de;
+#[doc(no_inline)]
+pub use crate::de::{from_slice, from_str, Deserializer};
+mod tokens;
+
+#[doc(hidden)]
+pub mod macros;
+
+mod spanned;
+pub use crate::spanned::Spanned;
+
+// Just for rustdoc
+#[allow(unused_imports)]
+use crate::datetime::Datetime;
+#[allow(unused_imports)]
+use core::str::FromStr;
diff --git a/third_party/rust/toml/src/macros.rs b/third_party/rust/toml/src/macros.rs
new file mode 100644
index 0000000000..19b2ce2286
--- /dev/null
+++ b/third_party/rust/toml/src/macros.rs
@@ -0,0 +1,459 @@
+pub use serde::de::{Deserialize, IntoDeserializer};
+
+use crate::value::{Array, Table, Value};
+
+/// Construct a [`toml::Value`] from TOML syntax.
+///
+/// [`toml::Value`]: value/enum.Value.html
+///
+/// ```rust
+/// let cargo_toml = toml::toml! {
+///     [package]
+///     name = "toml"
+///     version = "0.4.5"
+///     authors = ["Alex Crichton <alex@alexcrichton.com>"]
+///
+///     [badges]
+///     travis-ci = { repository = "alexcrichton/toml-rs" }
+///
+///     [dependencies]
+///     serde = "1.0"
+///
+///     [dev-dependencies]
+///     serde_derive = "1.0"
+///     serde_json = "1.0"
+/// };
+///
+/// println!("{:#?}", cargo_toml);
+/// ```
+#[macro_export]
+macro_rules! toml {
+    ($($toml:tt)+) => {{
+        let table = $crate::value::Table::new();
+        let mut root = $crate::Value::Table(table);
+        $crate::toml_internal!(@toplevel root [] $($toml)+);
+        root
+    }};
+}
+
+// TT-muncher to parse TOML syntax into a toml::Value.
+//
+//    @toplevel -- Parse tokens outside of an inline table or inline array. In
+//                 this state, `[table headers]` and `[[array headers]]` are
+//                 allowed and `key = value` pairs are not separated by commas.
+//
+//    @topleveldatetime -- Helper to parse a Datetime from string and insert it
+//                 into a table, continuing in the @toplevel state.
+//
+//    @path -- Turn a path segment into a string. Segments that look like idents
+//                 are stringified, while quoted segments like `"cfg(windows)"`
+//                 are not.
+//
+//    @value -- Parse the value part of a `key = value` pair, which may be a
+//                 primitive or inline table or inline array.
+//
+//    @table -- Parse the contents of an inline table, returning them as a
+//                 toml::Value::Table.
+//
+//    @tabledatetime -- Helper to parse a Datetime from string and insert it
+//                 into a table, continuing in the @table state.
+//
+//    @array -- Parse the contents of an inline array, returning them as a
+//                 toml::Value::Array.
+//
+//    @arraydatetime -- Helper to parse a Datetime from string and push it into
+//                 an array, continuing in the @array state.
+//
+//    @trailingcomma -- Helper to append a comma to a sequence of tokens if the
+//                 sequence is non-empty and does not already end in a trailing
+//                 comma.
+//
+#[macro_export]
+#[doc(hidden)]
+macro_rules! toml_internal {
+    // Base case, no elements remaining.
+    (@toplevel $root:ident [$($path:tt)*]) => {};
+
+    // Parse negative number `key = -value`.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = - $v:tt $($rest:tt)*) => {
+        $crate::toml_internal!(@toplevel $root [$($path)*] $($($k)-+).+ = (-$v) $($rest)*);
+    };
+
+    // Parse positive number `key = +value`.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = + $v:tt $($rest:tt)*) => {
+        $crate::toml_internal!(@toplevel $root [$($path)*] $($($k)-+).+ = ($v) $($rest)*);
+    };
+
+    // Parse offset datetime `key = 1979-05-27T00:32:00.999999-07:00`.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = $yr:tt - $mo:tt - $dhr:tt : $min:tt : $sec:tt . $frac:tt - $tzh:tt : $tzm:tt $($rest:tt)*) => {
+        $crate::toml_internal!(@topleveldatetime $root [$($path)*] $($($k)-+).+ = ($yr - $mo - $dhr : $min : $sec . $frac - $tzh : $tzm) $($rest)*);
+    };
+    // Space instead of T.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = $yr:tt - $mo:tt - $day:tt $hr:tt : $min:tt : $sec:tt . $frac:tt - $tzh:tt : $tzm:tt $($rest:tt)*) => {
+        $crate::toml_internal!(@topleveldatetime $root [$($path)*] $($($k)-+).+ = ($yr - $mo - $day T $hr : $min : $sec . $frac - $tzh : $tzm) $($rest)*);
+    };
+
+    // Parse offset datetime `key = 1979-05-27T00:32:00-07:00`.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = $yr:tt - $mo:tt - $dhr:tt : $min:tt : $sec:tt - $tzh:tt : $tzm:tt $($rest:tt)*) => {
+        $crate::toml_internal!(@topleveldatetime $root [$($path)*] $($($k)-+).+ = ($yr - $mo - $dhr : $min : $sec - $tzh : $tzm) $($rest)*);
+    };
+    // Space instead of T.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = $yr:tt - $mo:tt - $day:tt $hr:tt : $min:tt : $sec:tt - $tzh:tt : $tzm:tt $($rest:tt)*) => {
+        $crate::toml_internal!(@topleveldatetime $root [$($path)*] $($($k)-+).+ = ($yr - $mo - $day T $hr : $min : $sec - $tzh : $tzm) $($rest)*);
+    };
+
+    // Parse local datetime `key = 1979-05-27T00:32:00.999999`.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = $yr:tt - $mo:tt - $dhr:tt : $min:tt : $sec:tt . $frac:tt $($rest:tt)*) => {
+        $crate::toml_internal!(@topleveldatetime $root [$($path)*] $($($k)-+).+ = ($yr - $mo - $dhr : $min : $sec . $frac) $($rest)*);
+    };
+    // Space instead of T.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = $yr:tt - $mo:tt - $day:tt $hr:tt : $min:tt : $sec:tt . $frac:tt $($rest:tt)*) => {
+        $crate::toml_internal!(@topleveldatetime $root [$($path)*] $($($k)-+).+ = ($yr - $mo - $day T $hr : $min : $sec . $frac) $($rest)*);
+    };
+
+    // Parse offset datetime `key = 1979-05-27T07:32:00Z` and local datetime `key = 1979-05-27T07:32:00`.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = $yr:tt - $mo:tt - $dhr:tt : $min:tt : $sec:tt $($rest:tt)*) => {
+        $crate::toml_internal!(@topleveldatetime $root [$($path)*] $($($k)-+).+ = ($yr - $mo - $dhr : $min : $sec) $($rest)*);
+    };
+    // Space instead of T.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = $yr:tt - $mo:tt - $day:tt $hr:tt : $min:tt : $sec:tt $($rest:tt)*) => {
+        $crate::toml_internal!(@topleveldatetime $root [$($path)*] $($($k)-+).+ = ($yr - $mo - $day T $hr : $min : $sec) $($rest)*);
+    };
+
+    // Parse local date `key = 1979-05-27`.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = $yr:tt - $mo:tt - $day:tt $($rest:tt)*) => {
+        $crate::toml_internal!(@topleveldatetime $root [$($path)*] $($($k)-+).+ = ($yr - $mo - $day) $($rest)*);
+    };
+
+    // Parse local time `key = 00:32:00.999999`.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = $hr:tt : $min:tt : $sec:tt . $frac:tt $($rest:tt)*) => {
+        $crate::toml_internal!(@topleveldatetime $root [$($path)*] $($($k)-+).+ = ($hr : $min : $sec . $frac) $($rest)*);
+    };
+
+    // Parse local time `key = 07:32:00`.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = $hr:tt : $min:tt : $sec:tt $($rest:tt)*) => {
+        $crate::toml_internal!(@topleveldatetime $root [$($path)*] $($($k)-+).+ = ($hr : $min : $sec) $($rest)*);
+    };
+
+    // Parse any other `key = value` including string, inline array, inline
+    // table, number, and boolean.
+    (@toplevel $root:ident [$($path:tt)*] $($($k:tt)-+).+ = $v:tt $($rest:tt)*) => {{
+        $crate::macros::insert_toml(
+            &mut $root,
+            &[$($path)* $(&concat!($("-", $crate::toml_internal!(@path $k),)+)[1..], )+],
+            $crate::toml_internal!(@value $v));
+        $crate::toml_internal!(@toplevel $root [$($path)*] $($rest)*);
+    }};
+
+    // Parse array header `[[bin]]`.
+    (@toplevel $root:ident $oldpath:tt [[$($($path:tt)-+).+]] $($rest:tt)*) => {
+        $crate::macros::push_toml(
+            &mut $root,
+            &[$(&concat!($("-", $crate::toml_internal!(@path $path),)+)[1..],)+]);
+        $crate::toml_internal!(@toplevel $root [$(&concat!($("-", $crate::toml_internal!(@path $path),)+)[1..],)+] $($rest)*);
+    };
+
+    // Parse table header `[patch.crates-io]`.
+    (@toplevel $root:ident $oldpath:tt [$($($path:tt)-+).+] $($rest:tt)*) => {
+        $crate::macros::insert_toml(
+            &mut $root,
+            &[$(&concat!($("-", $crate::toml_internal!(@path $path),)+)[1..],)+],
+            $crate::Value::Table($crate::value::Table::new()));
+        $crate::toml_internal!(@toplevel $root [$(&concat!($("-", $crate::toml_internal!(@path $path),)+)[1..],)+] $($rest)*);
+    };
+
+    // Parse datetime from string and insert into table.
+    (@topleveldatetime $root:ident [$($path:tt)*] $($($k:tt)-+).+ = ($($datetime:tt)+) $($rest:tt)*) => {
+        $crate::macros::insert_toml(
+            &mut $root,
+            &[$($path)* $(&concat!($("-", $crate::toml_internal!(@path $k),)+)[1..], )+],
+            $crate::Value::Datetime(concat!($(stringify!($datetime)),+).parse().unwrap()));
+        $crate::toml_internal!(@toplevel $root [$($path)*] $($rest)*);
+    };
+
+    // Turn a path segment into a string.
+    (@path $ident:ident) => {
+        stringify!($ident)
+    };
+
+    // For a path segment that is not an ident, expect that it is already a
+    // quoted string, like in `[target."cfg(windows)".dependencies]`.
+    (@path $quoted:tt) => {
+        $quoted
+    };
+
+    // Construct a Value from an inline table.
+    (@value { $($inline:tt)* }) => {{
+        let mut table = $crate::Value::Table($crate::value::Table::new());
+        $crate::toml_internal!(@trailingcomma (@table table) $($inline)*);
+        table
+    }};
+
+    // Construct a Value from an inline array.
+    (@value [ $($inline:tt)* ]) => {{
+        let mut array = $crate::value::Array::new();
+        $crate::toml_internal!(@trailingcomma (@array array) $($inline)*);
+        $crate::Value::Array(array)
+    }};
+
+    (@value (-nan)) => {
+        $crate::Value::Float(-::std::f64::NAN)
+    };
+
+    (@value (nan)) => {
+        $crate::Value::Float(::std::f64::NAN)
+    };
+
+    (@value nan) => {
+        $crate::Value::Float(::std::f64::NAN)
+    };
+
+    (@value (-inf)) => {
+        $crate::Value::Float(::std::f64::NEG_INFINITY)
+    };
+
+    (@value (inf)) => {
+        $crate::Value::Float(::std::f64::INFINITY)
+    };
+
+    (@value inf) => {
+        $crate::Value::Float(::std::f64::INFINITY)
+    };
+
+    // Construct a Value from any other type, probably string or boolean or number.
+    (@value $v:tt) => {{
+        // TODO: Implement this with something like serde_json::to_value instead.
+        let de = $crate::macros::IntoDeserializer::<$crate::de::Error>::into_deserializer($v);
+        <$crate::Value as $crate::macros::Deserialize>::deserialize(de).unwrap()
+    }};
+
+    // Base case of inline table.
+    (@table $root:ident) => {};
+
+    // Parse negative number `key = -value`.
+    (@table $root:ident $($($k:tt)-+).+ = - $v:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@table $root $($($k)-+).+ = (-$v) , $($rest)*);
+    };
+
+    // Parse positive number `key = +value`.
+    (@table $root:ident $($($k:tt)-+).+ = + $v:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@table $root $($($k)-+).+ = ($v) , $($rest)*);
+    };
+
+    // Parse offset datetime `key = 1979-05-27T00:32:00.999999-07:00`.
+    (@table $root:ident $($($k:tt)-+).+ = $yr:tt - $mo:tt - $dhr:tt : $min:tt : $sec:tt . $frac:tt - $tzh:tt : $tzm:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@tabledatetime $root $($($k)-+).+ = ($yr - $mo - $dhr : $min : $sec . $frac - $tzh : $tzm) $($rest)*);
+    };
+    // Space instead of T.
+    (@table $root:ident $($($k:tt)-+).+ = $yr:tt - $mo:tt - $day:tt $hr:tt : $min:tt : $sec:tt . $frac:tt - $tzh:tt : $tzm:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@tabledatetime $root $($($k)-+).+ = ($yr - $mo - $day T $hr : $min : $sec . $frac - $tzh : $tzm) $($rest)*);
+    };
+
+    // Parse offset datetime `key = 1979-05-27T00:32:00-07:00`.
+    (@table $root:ident $($($k:tt)-+).+ = $yr:tt - $mo:tt - $dhr:tt : $min:tt : $sec:tt - $tzh:tt : $tzm:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@tabledatetime $root $($($k)-+).+ = ($yr - $mo - $dhr : $min : $sec - $tzh : $tzm) $($rest)*);
+    };
+    // Space instead of T.
+    (@table $root:ident $($($k:tt)-+).+ = $yr:tt - $mo:tt - $day:tt $hr:tt : $min:tt : $sec:tt - $tzh:tt : $tzm:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@tabledatetime $root $($($k)-+).+ = ($yr - $mo - $day T $hr : $min : $sec - $tzh : $tzm) $($rest)*);
+    };
+
+    // Parse local datetime `key = 1979-05-27T00:32:00.999999`.
+    (@table $root:ident $($($k:tt)-+).+ = $yr:tt - $mo:tt - $dhr:tt : $min:tt : $sec:tt . $frac:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@tabledatetime $root $($($k)-+).+ = ($yr - $mo - $dhr : $min : $sec . $frac) $($rest)*);
+    };
+    // Space instead of T.
+    (@table $root:ident $($($k:tt)-+).+ = $yr:tt - $mo:tt - $day:tt $hr:tt : $min:tt : $sec:tt . $frac:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@tabledatetime $root $($($k)-+).+ = ($yr - $mo - $day T $hr : $min : $sec . $frac) $($rest)*);
+    };
+
+    // Parse offset datetime `key = 1979-05-27T07:32:00Z` and local datetime `key = 1979-05-27T07:32:00`.
+    (@table $root:ident $($($k:tt)-+).+ = $yr:tt - $mo:tt - $dhr:tt : $min:tt : $sec:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@tabledatetime $root $($($k)-+).+ = ($yr - $mo - $dhr : $min : $sec) $($rest)*);
+    };
+    // Space instead of T.
+    (@table $root:ident $($($k:tt)-+).+ = $yr:tt - $mo:tt - $day:tt $hr:tt : $min:tt : $sec:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@tabledatetime $root $($($k)-+).+ = ($yr - $mo - $day T $hr : $min : $sec) $($rest)*);
+    };
+
+    // Parse local date `key = 1979-05-27`.
+    (@table $root:ident $($($k:tt)-+).+ = $yr:tt - $mo:tt - $day:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@tabledatetime $root $($($k)-+).+ = ($yr - $mo - $day) $($rest)*);
+    };
+
+    // Parse local time `key = 00:32:00.999999`.
+    (@table $root:ident $($($k:tt)-+).+ = $hr:tt : $min:tt : $sec:tt . $frac:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@tabledatetime $root $($($k)-+).+ = ($hr : $min : $sec . $frac) $($rest)*);
+    };
+
+    // Parse local time `key = 07:32:00`.
+    (@table $root:ident $($($k:tt)-+).+ = $hr:tt : $min:tt : $sec:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@tabledatetime $root $($($k)-+).+ = ($hr : $min : $sec) $($rest)*);
+    };
+
+    // Parse any other type, probably string or boolean or number.
+    (@table $root:ident $($($k:tt)-+).+ = $v:tt , $($rest:tt)*) => {
+        $crate::macros::insert_toml(
+            &mut $root,
+            &[$(&concat!($("-", $crate::toml_internal!(@path $k),)+)[1..], )+],
+            $crate::toml_internal!(@value $v));
+        $crate::toml_internal!(@table $root $($rest)*);
+    };
+
+    // Parse a Datetime from string and continue in @table state.
+    (@tabledatetime $root:ident $($($k:tt)-+).+ = ($($datetime:tt)*) $($rest:tt)*) => {
+        $crate::macros::insert_toml(
+            &mut $root,
+            &[$(&concat!($("-", $crate::toml_internal!(@path $k),)+)[1..], )+],
+            $crate::Value::Datetime(concat!($(stringify!($datetime)),+).parse().unwrap()));
+        $crate::toml_internal!(@table $root $($rest)*);
+    };
+
+    // Base case of inline array.
+    (@array $root:ident) => {};
+
+    // Parse negative number `-value`.
+    (@array $root:ident - $v:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@array $root (-$v) , $($rest)*);
+    };
+
+    // Parse positive number `+value`.
+    (@array $root:ident + $v:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@array $root ($v) , $($rest)*);
+    };
+
+    // Parse offset datetime `1979-05-27T00:32:00.999999-07:00`.
+    (@array $root:ident $yr:tt - $mo:tt - $dhr:tt : $min:tt : $sec:tt . $frac:tt - $tzh:tt : $tzm:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@arraydatetime $root ($yr - $mo - $dhr : $min : $sec . $frac - $tzh : $tzm) $($rest)*);
+    };
+    // Space instead of T.
+    (@array $root:ident $yr:tt - $mo:tt - $day:tt $hr:tt : $min:tt : $sec:tt . $frac:tt - $tzh:tt : $tzm:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@arraydatetime $root ($yr - $mo - $day T $hr : $min : $sec . $frac - $tzh : $tzm) $($rest)*);
+    };
+
+    // Parse offset datetime `1979-05-27T00:32:00-07:00`.
+    (@array $root:ident $yr:tt - $mo:tt - $dhr:tt : $min:tt : $sec:tt - $tzh:tt : $tzm:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@arraydatetime $root ($yr - $mo - $dhr : $min : $sec - $tzh : $tzm) $($rest)*);
+    };
+    // Space instead of T.
+    (@array $root:ident $yr:tt - $mo:tt - $day:tt $hr:tt : $min:tt : $sec:tt - $tzh:tt : $tzm:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@arraydatetime $root ($yr - $mo - $day T $hr : $min : $sec - $tzh : $tzm) $($rest)*);
+    };
+
+    // Parse local datetime `1979-05-27T00:32:00.999999`.
+    (@array $root:ident $yr:tt - $mo:tt - $dhr:tt : $min:tt : $sec:tt . $frac:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@arraydatetime $root ($yr - $mo - $dhr : $min : $sec . $frac) $($rest)*);
+    };
+    // Space instead of T.
+    (@array $root:ident $yr:tt - $mo:tt - $day:tt $hr:tt : $min:tt : $sec:tt . $frac:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@arraydatetime $root ($yr - $mo - $day T $hr : $min : $sec . $frac) $($rest)*);
+    };
+
+    // Parse offset datetime `1979-05-27T07:32:00Z` and local datetime `1979-05-27T07:32:00`.
+    (@array $root:ident $yr:tt - $mo:tt - $dhr:tt : $min:tt : $sec:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@arraydatetime $root ($yr - $mo - $dhr : $min : $sec) $($rest)*);
+    };
+    // Space instead of T.
+    (@array $root:ident $yr:tt - $mo:tt - $day:tt $hr:tt : $min:tt : $sec:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@arraydatetime $root ($yr - $mo - $day T $hr : $min : $sec) $($rest)*);
+    };
+
+    // Parse local date `1979-05-27`.
+    (@array $root:ident $yr:tt - $mo:tt - $day:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@arraydatetime $root ($yr - $mo - $day) $($rest)*);
+    };
+
+    // Parse local time `00:32:00.999999`.
+    (@array $root:ident $hr:tt : $min:tt : $sec:tt . $frac:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@arraydatetime $root ($hr : $min : $sec . $frac) $($rest)*);
+    };
+
+    // Parse local time `07:32:00`.
+    (@array $root:ident $hr:tt : $min:tt : $sec:tt , $($rest:tt)*) => {
+        $crate::toml_internal!(@arraydatetime $root ($hr : $min : $sec) $($rest)*);
+    };
+
+    // Parse any other type, probably string or boolean or number.
+    (@array $root:ident $v:tt , $($rest:tt)*) => {
+        $root.push($crate::toml_internal!(@value $v));
+        $crate::toml_internal!(@array $root $($rest)*);
+    };
+
+    // Parse a Datetime from string and continue in @array state.
+    (@arraydatetime $root:ident ($($datetime:tt)*) $($rest:tt)*) => {
+        $root.push($crate::Value::Datetime(concat!($(stringify!($datetime)),+).parse().unwrap()));
+        $crate::toml_internal!(@array $root $($rest)*);
+    };
+
+    // No trailing comma required if the tokens are empty.
+    (@trailingcomma ($($args:tt)*)) => {
+        $crate::toml_internal!($($args)*);
+    };
+
+    // Tokens end with a trailing comma, do not append another one.
+    (@trailingcomma ($($args:tt)*) ,) => {
+        $crate::toml_internal!($($args)* ,);
+    };
+
+    // Tokens end with something other than comma, append a trailing comma.
+    (@trailingcomma ($($args:tt)*) $last:tt) => {
+        $crate::toml_internal!($($args)* $last ,);
+    };
+
+    // Not yet at the last token.
+    (@trailingcomma ($($args:tt)*) $first:tt $($rest:tt)+) => {
+        $crate::toml_internal!(@trailingcomma ($($args)* $first) $($rest)+);
+    };
+}
+
+// Called when parsing a `key = value` pair.
+// Inserts an entry into the table at the given path.
+pub fn insert_toml(root: &mut Value, path: &[&str], value: Value) {
+    *traverse(root, path) = value;
+}
+
+// Called when parsing an `[[array header]]`.
+// Pushes an empty table onto the array at the given path.
+pub fn push_toml(root: &mut Value, path: &[&str]) {
+    let target = traverse(root, path);
+    if !target.is_array() {
+        *target = Value::Array(Array::new());
+    }
+    target
+        .as_array_mut()
+        .unwrap()
+        .push(Value::Table(Table::new()));
+}
+
+fn traverse<'a>(root: &'a mut Value, path: &[&str]) -> &'a mut Value {
+    let mut cur = root;
+    for &key in path {
+        // Lexical lifetimes :D
+        let cur1 = cur;
+
+        // From the TOML spec:
+        //
+        // > Each double-bracketed sub-table will belong to the most recently
+        // > defined table element above it.
+        let cur2 = if cur1.is_array() {
+            cur1.as_array_mut().unwrap().last_mut().unwrap()
+        } else {
+            cur1
+        };
+
+        // We are about to index into this value, so it better be a table.
+        if !cur2.is_table() {
+            *cur2 = Value::Table(Table::new());
+        }
+
+        if !cur2.as_table().unwrap().contains_key(key) {
+            // Insert an empty table for the next loop iteration to point to.
+            let empty = Value::Table(Table::new());
+            cur2.as_table_mut().unwrap().insert(key.to_owned(), empty);
+        }
+
+        // Step into the current table.
+        cur = cur2.as_table_mut().unwrap().get_mut(key).unwrap();
+    }
+    cur
+}
diff --git a/third_party/rust/toml/src/map.rs b/third_party/rust/toml/src/map.rs
new file mode 100644
index 0000000000..d130a1d540
--- /dev/null
+++ b/third_party/rust/toml/src/map.rs
@@ -0,0 +1,595 @@
+// Copyright 2017 Serde Developers
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! A map of String to toml::Value.
+//!
+//! By default the map is backed by a [`BTreeMap`]. Enable the `preserve_order`
+//! feature of toml-rs to use [`LinkedHashMap`] instead.
+//!
+//! [`BTreeMap`]: https://doc.rust-lang.org/std/collections/struct.BTreeMap.html
+//! [`LinkedHashMap`]: https://docs.rs/linked-hash-map/*/linked_hash_map/struct.LinkedHashMap.html
+
+use crate::value::Value;
+use serde::{de, ser};
+use std::borrow::Borrow;
+use std::fmt::{self, Debug};
+use std::hash::Hash;
+use std::iter::FromIterator;
+use std::ops;
+
+#[cfg(not(feature = "preserve_order"))]
+use std::collections::{btree_map, BTreeMap};
+
+#[cfg(feature = "preserve_order")]
+use indexmap::{self, IndexMap};
+
+/// Represents a TOML key/value type.
+pub struct Map<K, V> {
+    map: MapImpl<K, V>,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type MapImpl<K, V> = BTreeMap<K, V>;
+#[cfg(feature = "preserve_order")]
+type MapImpl<K, V> = IndexMap<K, V>;
+
+impl Map<String, Value> {
+    /// Makes a new empty Map.
+    #[inline]
+    pub fn new() -> Self {
+        Map {
+            map: MapImpl::new(),
+        }
+    }
+
+    #[cfg(not(feature = "preserve_order"))]
+    /// Makes a new empty Map with the given initial capacity.
+    #[inline]
+    pub fn with_capacity(capacity: usize) -> Self {
+        // does not support with_capacity
+        let _ = capacity;
+        Map {
+            map: BTreeMap::new(),
+        }
+    }
+
+    #[cfg(feature = "preserve_order")]
+    /// Makes a new empty Map with the given initial capacity.
+    #[inline]
+    pub fn with_capacity(capacity: usize) -> Self {
+        Map {
+            map: IndexMap::with_capacity(capacity),
+        }
+    }
+
+    /// Clears the map, removing all values.
+    #[inline]
+    pub fn clear(&mut self) {
+        self.map.clear()
+    }
+
+    /// Returns a reference to the value corresponding to the key.
+    ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    #[inline]
+    pub fn get<Q: ?Sized>(&self, key: &Q) -> Option<&Value>
+    where
+        String: Borrow<Q>,
+        Q: Ord + Eq + Hash,
+    {
+        self.map.get(key)
+    }
+
+    /// Returns true if the map contains a value for the specified key.
+    ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    #[inline]
+    pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool
+    where
+        String: Borrow<Q>,
+        Q: Ord + Eq + Hash,
+    {
+        self.map.contains_key(key)
+    }
+
+    /// Returns a mutable reference to the value corresponding to the key.
+    ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    #[inline]
+    pub fn get_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<&mut Value>
+    where
+        String: Borrow<Q>,
+        Q: Ord + Eq + Hash,
+    {
+        self.map.get_mut(key)
+    }
+
+    /// Inserts a key-value pair into the map.
+    ///
+    /// If the map did not have this key present, `None` is returned.
+    ///
+    /// If the map did have this key present, the value is updated, and the old
+    /// value is returned. The key is not updated, though; this matters for
+    /// types that can be `==` without being identical.
+    #[inline]
+    pub fn insert(&mut self, k: String, v: Value) -> Option<Value> {
+        self.map.insert(k, v)
+    }
+
+    /// Removes a key from the map, returning the value at the key if the key
+    /// was previously in the map.
+    ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    #[inline]
+    pub fn remove<Q: ?Sized>(&mut self, key: &Q) -> Option<Value>
+    where
+        String: Borrow<Q>,
+        Q: Ord + Eq + Hash,
+    {
+        self.map.remove(key)
+    }
+
+    /// Gets the given key's corresponding entry in the map for in-place
+    /// manipulation.
+    pub fn entry<S>(&mut self, key: S) -> Entry<'_>
+    where
+        S: Into<String>,
+    {
+        #[cfg(feature = "preserve_order")]
+        use indexmap::map::Entry as EntryImpl;
+        #[cfg(not(feature = "preserve_order"))]
+        use std::collections::btree_map::Entry as EntryImpl;
+
+        match self.map.entry(key.into()) {
+            EntryImpl::Vacant(vacant) => Entry::Vacant(VacantEntry { vacant }),
+            EntryImpl::Occupied(occupied) => Entry::Occupied(OccupiedEntry { occupied }),
+        }
+    }
+
+    /// Returns the number of elements in the map.
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.map.len()
+    }
+
+    /// Returns true if the map contains no elements.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.map.is_empty()
+    }
+
+    /// Gets an iterator over the entries of the map.
+    #[inline]
+    pub fn iter(&self) -> Iter<'_> {
+        Iter {
+            iter: self.map.iter(),
+        }
+    }
+
+    /// Gets a mutable iterator over the entries of the map.
+    #[inline]
+    pub fn iter_mut(&mut self) -> IterMut<'_> {
+        IterMut {
+            iter: self.map.iter_mut(),
+        }
+    }
+
+    /// Gets an iterator over the keys of the map.
+    #[inline]
+    pub fn keys(&self) -> Keys<'_> {
+        Keys {
+            iter: self.map.keys(),
+        }
+    }
+
+    /// Gets an iterator over the values of the map.
+    #[inline]
+    pub fn values(&self) -> Values<'_> {
+        Values {
+            iter: self.map.values(),
+        }
+    }
+}
+
+impl Default for Map<String, Value> {
+    #[inline]
+    fn default() -> Self {
+        Map {
+            map: MapImpl::new(),
+        }
+    }
+}
+
+impl Clone for Map<String, Value> {
+    #[inline]
+    fn clone(&self) -> Self {
+        Map {
+            map: self.map.clone(),
+        }
+    }
+}
+
+impl PartialEq for Map<String, Value> {
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        self.map.eq(&other.map)
+    }
+}
+
+/// Access an element of this map. Panics if the given key is not present in the
+/// map.
+impl<'a, Q: ?Sized> ops::Index<&'a Q> for Map<String, Value>
+where
+    String: Borrow<Q>,
+    Q: Ord + Eq + Hash,
+{
+    type Output = Value;
+
+    fn index(&self, index: &Q) -> &Value {
+        self.map.index(index)
+    }
+}
+
+/// Mutably access an element of this map. Panics if the given key is not
+/// present in the map.
+impl<'a, Q: ?Sized> ops::IndexMut<&'a Q> for Map<String, Value>
+where
+    String: Borrow<Q>,
+    Q: Ord + Eq + Hash,
+{
+    fn index_mut(&mut self, index: &Q) -> &mut Value {
+        self.map.get_mut(index).expect("no entry found for key")
+    }
+}
+
+impl Debug for Map<String, Value> {
+    #[inline]
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
+        self.map.fmt(formatter)
+    }
+}
+
+impl ser::Serialize for Map<String, Value> {
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: ser::Serializer,
+    {
+        use serde::ser::SerializeMap;
+        let mut map = serializer.serialize_map(Some(self.len()))?;
+        for (k, v) in self {
+            map.serialize_key(k)?;
+            map.serialize_value(v)?;
+        }
+        map.end()
+    }
+}
+
+impl<'de> de::Deserialize<'de> for Map<String, Value> {
+    #[inline]
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: de::Deserializer<'de>,
+    {
+        struct Visitor;
+
+        impl<'de> de::Visitor<'de> for Visitor {
+            type Value = Map<String, Value>;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+                formatter.write_str("a map")
+            }
+
+            #[inline]
+            fn visit_unit<E>(self) -> Result<Self::Value, E>
+            where
+                E: de::Error,
+            {
+                Ok(Map::new())
+            }
+
+            #[inline]
+            fn visit_map<V>(self, mut visitor: V) -> Result<Self::Value, V::Error>
+            where
+                V: de::MapAccess<'de>,
+            {
+                let mut values = Map::new();
+
+                while let Some((key, value)) = visitor.next_entry()? {
+                    values.insert(key, value);
+                }
+
+                Ok(values)
+            }
+        }
+
+        deserializer.deserialize_map(Visitor)
+    }
+}
+
+impl FromIterator<(String, Value)> for Map<String, Value> {
+    fn from_iter<T>(iter: T) -> Self
+    where
+        T: IntoIterator<Item = (String, Value)>,
+    {
+        Map {
+            map: FromIterator::from_iter(iter),
+        }
+    }
+}
+
+impl Extend<(String, Value)> for Map<String, Value> {
+    fn extend<T>(&mut self, iter: T)
+    where
+        T: IntoIterator<Item = (String, Value)>,
+    {
+        self.map.extend(iter);
+    }
+}
+
+macro_rules! delegate_iterator {
+    (($name:ident $($generics:tt)*) => $item:ty) => {
+        impl $($generics)* Iterator for $name $($generics)* {
+            type Item = $item;
+            #[inline]
+            fn next(&mut self) -> Option<Self::Item> {
+                self.iter.next()
+            }
+            #[inline]
+            fn size_hint(&self) -> (usize, Option<usize>) {
+                self.iter.size_hint()
+            }
+        }
+
+        impl $($generics)* DoubleEndedIterator for $name $($generics)* {
+            #[inline]
+            fn next_back(&mut self) -> Option<Self::Item> {
+                self.iter.next_back()
+            }
+        }
+
+        impl $($generics)* ExactSizeIterator for $name $($generics)* {
+            #[inline]
+            fn len(&self) -> usize {
+                self.iter.len()
+            }
+        }
+    }
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+/// A view into a single entry in a map, which may either be vacant or occupied.
+/// This enum is constructed from the [`entry`] method on [`Map`].
+///
+/// [`entry`]: struct.Map.html#method.entry
+/// [`Map`]: struct.Map.html
+pub enum Entry<'a> {
+    /// A vacant Entry.
+    Vacant(VacantEntry<'a>),
+    /// An occupied Entry.
+    Occupied(OccupiedEntry<'a>),
+}
+
+/// A vacant Entry. It is part of the [`Entry`] enum.
+///
+/// [`Entry`]: enum.Entry.html
+pub struct VacantEntry<'a> {
+    vacant: VacantEntryImpl<'a>,
+}
+
+/// An occupied Entry. It is part of the [`Entry`] enum.
+///
+/// [`Entry`]: enum.Entry.html
+pub struct OccupiedEntry<'a> {
+    occupied: OccupiedEntryImpl<'a>,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type VacantEntryImpl<'a> = btree_map::VacantEntry<'a, String, Value>;
+#[cfg(feature = "preserve_order")]
+type VacantEntryImpl<'a> = indexmap::map::VacantEntry<'a, String, Value>;
+
+#[cfg(not(feature = "preserve_order"))]
+type OccupiedEntryImpl<'a> = btree_map::OccupiedEntry<'a, String, Value>;
+#[cfg(feature = "preserve_order")]
+type OccupiedEntryImpl<'a> = indexmap::map::OccupiedEntry<'a, String, Value>;
+
+impl<'a> Entry<'a> {
+    /// Returns a reference to this entry's key.
+    pub fn key(&self) -> &String {
+        match *self {
+            Entry::Vacant(ref e) => e.key(),
+            Entry::Occupied(ref e) => e.key(),
+        }
+    }
+
+    /// Ensures a value is in the entry by inserting the default if empty, and
+    /// returns a mutable reference to the value in the entry.
+    pub fn or_insert(self, default: Value) -> &'a mut Value {
+        match self {
+            Entry::Vacant(entry) => entry.insert(default),
+            Entry::Occupied(entry) => entry.into_mut(),
+        }
+    }
+
+    /// Ensures a value is in the entry by inserting the result of the default
+    /// function if empty, and returns a mutable reference to the value in the
+    /// entry.
+    pub fn or_insert_with<F>(self, default: F) -> &'a mut Value
+    where
+        F: FnOnce() -> Value,
+    {
+        match self {
+            Entry::Vacant(entry) => entry.insert(default()),
+            Entry::Occupied(entry) => entry.into_mut(),
+        }
+    }
+}
+
+impl<'a> VacantEntry<'a> {
+    /// Gets a reference to the key that would be used when inserting a value
+    /// through the VacantEntry.
+    #[inline]
+    pub fn key(&self) -> &String {
+        self.vacant.key()
+    }
+
+    /// Sets the value of the entry with the VacantEntry's key, and returns a
+    /// mutable reference to it.
+    #[inline]
+    pub fn insert(self, value: Value) -> &'a mut Value {
+        self.vacant.insert(value)
+    }
+}
+
+impl<'a> OccupiedEntry<'a> {
+    /// Gets a reference to the key in the entry.
+    #[inline]
+    pub fn key(&self) -> &String {
+        self.occupied.key()
+    }
+
+    /// Gets a reference to the value in the entry.
+    #[inline]
+    pub fn get(&self) -> &Value {
+        self.occupied.get()
+    }
+
+    /// Gets a mutable reference to the value in the entry.
+    #[inline]
+    pub fn get_mut(&mut self) -> &mut Value {
+        self.occupied.get_mut()
+    }
+
+    /// Converts the entry into a mutable reference to its value.
+    #[inline]
+    pub fn into_mut(self) -> &'a mut Value {
+        self.occupied.into_mut()
+    }
+
+    /// Sets the value of the entry with the `OccupiedEntry`'s key, and returns
+    /// the entry's old value.
+    #[inline]
+    pub fn insert(&mut self, value: Value) -> Value {
+        self.occupied.insert(value)
+    }
+
+    /// Takes the value of the entry out of the map, and returns it.
+    #[inline]
+    pub fn remove(self) -> Value {
+        self.occupied.remove()
+    }
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+impl<'a> IntoIterator for &'a Map<String, Value> {
+    type Item = (&'a String, &'a Value);
+    type IntoIter = Iter<'a>;
+    #[inline]
+    fn into_iter(self) -> Self::IntoIter {
+        Iter {
+            iter: self.map.iter(),
+        }
+    }
+}
+
+/// An iterator over a toml::Map's entries.
+pub struct Iter<'a> {
+    iter: IterImpl<'a>,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type IterImpl<'a> = btree_map::Iter<'a, String, Value>;
+#[cfg(feature = "preserve_order")]
+type IterImpl<'a> = indexmap::map::Iter<'a, String, Value>;
+
+delegate_iterator!((Iter<'a>) => (&'a String, &'a Value));
+
+//////////////////////////////////////////////////////////////////////////////
+
+impl<'a> IntoIterator for &'a mut Map<String, Value> {
+    type Item = (&'a String, &'a mut Value);
+    type IntoIter = IterMut<'a>;
+    #[inline]
+    fn into_iter(self) -> Self::IntoIter {
+        IterMut {
+            iter: self.map.iter_mut(),
+        }
+    }
+}
+
+/// A mutable iterator over a toml::Map's entries.
+pub struct IterMut<'a> {
+    iter: IterMutImpl<'a>,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type IterMutImpl<'a> = btree_map::IterMut<'a, String, Value>;
+#[cfg(feature = "preserve_order")]
+type IterMutImpl<'a> = indexmap::map::IterMut<'a, String, Value>;
+
+delegate_iterator!((IterMut<'a>) => (&'a String, &'a mut Value));
+
+//////////////////////////////////////////////////////////////////////////////
+
+impl IntoIterator for Map<String, Value> {
+    type Item = (String, Value);
+    type IntoIter = IntoIter;
+    #[inline]
+    fn into_iter(self) -> Self::IntoIter {
+        IntoIter {
+            iter: self.map.into_iter(),
+        }
+    }
+}
+
+/// An owning iterator over a toml::Map's entries.
+pub struct IntoIter {
+    iter: IntoIterImpl,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type IntoIterImpl = btree_map::IntoIter<String, Value>;
+#[cfg(feature = "preserve_order")]
+type IntoIterImpl = indexmap::map::IntoIter<String, Value>;
+
+delegate_iterator!((IntoIter) => (String, Value));
+
+//////////////////////////////////////////////////////////////////////////////
+
+/// An iterator over a toml::Map's keys.
+pub struct Keys<'a> {
+    iter: KeysImpl<'a>,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type KeysImpl<'a> = btree_map::Keys<'a, String, Value>;
+#[cfg(feature = "preserve_order")]
+type KeysImpl<'a> = indexmap::map::Keys<'a, String, Value>;
+
+delegate_iterator!((Keys<'a>) => &'a String);
+
+//////////////////////////////////////////////////////////////////////////////
+
+/// An iterator over a toml::Map's values.
+pub struct Values<'a> {
+    iter: ValuesImpl<'a>,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type ValuesImpl<'a> = btree_map::Values<'a, String, Value>;
+#[cfg(feature = "preserve_order")]
+type ValuesImpl<'a> = indexmap::map::Values<'a, String, Value>;
+
+delegate_iterator!((Values<'a>) => &'a Value);
diff --git a/third_party/rust/toml/src/ser.rs b/third_party/rust/toml/src/ser.rs
new file mode 100644
index 0000000000..ecee1a296b
--- /dev/null
+++ b/third_party/rust/toml/src/ser.rs
@@ -0,0 +1,1853 @@
+//! Serializing Rust structures into TOML.
+//!
+//! This module contains all the Serde support for serializing Rust structures
+//! into TOML documents (as strings). Note that some top-level functions here
+//! are also provided at the top of the crate.
+//!
+//! Note that the TOML format has a restriction that if a table itself contains
+//! tables, all keys with non-table values must be emitted first. This is
+//! typically easy to ensure happens when you're defining a `struct` as you can
+//! reorder the fields manually, but when working with maps (such as `BTreeMap`
+//! or `HashMap`) this can lead to serialization errors. In those situations you
+//! may use the `tables_last` function in this module like so:
+//!
+//! ```rust
+//! # use serde_derive::Serialize;
+//! # use std::collections::HashMap;
+//! #[derive(Serialize)]
+//! struct Manifest {
+//!     package: Package,
+//!     #[serde(serialize_with = "toml::ser::tables_last")]
+//!     dependencies: HashMap<String, Dependency>,
+//! }
+//! # type Package = String;
+//! # type Dependency = String;
+//! # fn main() {}
+//! ```
+
+use std::cell::Cell;
+use std::error;
+use std::fmt::{self, Write};
+use std::marker;
+use std::rc::Rc;
+
+use crate::datetime;
+use serde::ser;
+
+/// Serialize the given data structure as a TOML byte vector.
+///
+/// Serialization can fail if `T`'s implementation of `Serialize` decides to
+/// fail, if `T` contains a map with non-string keys, or if `T` attempts to
+/// serialize an unsupported datatype such as an enum, tuple, or tuple struct.
+pub fn to_vec<T: ?Sized>(value: &T) -> Result<Vec<u8>, Error>
+where
+    T: ser::Serialize,
+{
+    to_string(value).map(|e| e.into_bytes())
+}
+
+/// Serialize the given data structure as a String of TOML.
+///
+/// Serialization can fail if `T`'s implementation of `Serialize` decides to
+/// fail, if `T` contains a map with non-string keys, or if `T` attempts to
+/// serialize an unsupported datatype such as an enum, tuple, or tuple struct.
+///
+/// # Examples
+///
+/// ```
+/// use serde_derive::Serialize;
+///
+/// #[derive(Serialize)]
+/// struct Config {
+///     database: Database,
+/// }
+///
+/// #[derive(Serialize)]
+/// struct Database {
+///     ip: String,
+///     port: Vec<u16>,
+///     connection_max: u32,
+///     enabled: bool,
+/// }
+///
+/// let config = Config {
+///     database: Database {
+///         ip: "192.168.1.1".to_string(),
+///         port: vec![8001, 8002, 8003],
+///         connection_max: 5000,
+///         enabled: false,
+///     },
+/// };
+///
+/// let toml = toml::to_string(&config).unwrap();
+/// println!("{}", toml)
+/// ```
+pub fn to_string<T: ?Sized>(value: &T) -> Result<String, Error>
+where
+    T: ser::Serialize,
+{
+    let mut dst = String::with_capacity(128);
+    value.serialize(&mut Serializer::new(&mut dst))?;
+    Ok(dst)
+}
+
+/// Serialize the given data structure as a "pretty" String of TOML.
+///
+/// This is identical to `to_string` except the output string has a more
+/// "pretty" output. See `Serializer::pretty` for more details.
+pub fn to_string_pretty<T: ?Sized>(value: &T) -> Result<String, Error>
+where
+    T: ser::Serialize,
+{
+    let mut dst = String::with_capacity(128);
+    value.serialize(&mut Serializer::pretty(&mut dst))?;
+    Ok(dst)
+}
+
+/// Errors that can occur when serializing a type.
+#[derive(Debug, PartialEq, Eq, Clone)]
+#[non_exhaustive]
+pub enum Error {
+    /// Indicates that a Rust type was requested to be serialized but it was not
+    /// supported.
+    ///
+    /// Currently the TOML format does not support serializing types such as
+    /// enums, tuples and tuple structs.
+    UnsupportedType,
+
+    /// The key of all TOML maps must be strings, but serialization was
+    /// attempted where the key of a map was not a string.
+    KeyNotString,
+
+    /// An error that we never omit but keep for backwards compatibility
+    #[doc(hidden)]
+    KeyNewline,
+
+    /// An array had to be homogeneous, but now it is allowed to be heterogeneous.
+    #[doc(hidden)]
+    ArrayMixedType,
+
+    /// All values in a TOML table must be emitted before further tables are
+    /// emitted. If a value is emitted *after* a table then this error is
+    /// generated.
+    ValueAfterTable,
+
+    /// A serialized date was invalid.
+    DateInvalid,
+
+    /// A serialized number was invalid.
+    NumberInvalid,
+
+    /// None was attempted to be serialized, but it's not supported.
+    UnsupportedNone,
+
+    /// A custom error which could be generated when serializing a particular
+    /// type.
+    Custom(String),
+}
+
+#[derive(Debug, Default, Clone)]
+/// Internal place for holding array settings
+struct ArraySettings {
+    indent: usize,
+    trailing_comma: bool,
+}
+
+impl ArraySettings {
+    fn pretty() -> ArraySettings {
+        ArraySettings {
+            indent: 4,
+            trailing_comma: true,
+        }
+    }
+}
+
+#[derive(Debug, Default, Clone)]
+/// String settings
+struct StringSettings {
+    /// Whether to use literal strings when possible
+    literal: bool,
+}
+
+impl StringSettings {
+    fn pretty() -> StringSettings {
+        StringSettings { literal: true }
+    }
+}
+
+#[derive(Debug, Default, Clone)]
+/// Internal struct for holding serialization settings
+struct Settings {
+    array: Option<ArraySettings>,
+    string: Option<StringSettings>,
+}
+
+/// Serialization implementation for TOML.
+///
+/// This structure implements serialization support for TOML to serialize an
+/// arbitrary type to TOML. Note that the TOML format does not support all
+/// datatypes in Rust, such as enums, tuples, and tuple structs. These types
+/// will generate an error when serialized.
+///
+/// Currently a serializer always writes its output to an in-memory `String`,
+/// which is passed in when creating the serializer itself.
+pub struct Serializer<'a> {
+    dst: &'a mut String,
+    state: State<'a>,
+    settings: Rc<Settings>,
+}
+
+#[derive(Debug, Copy, Clone)]
+enum ArrayState {
+    Started,
+    StartedAsATable,
+}
+
+#[derive(Debug, Clone)]
+enum State<'a> {
+    Table {
+        key: &'a str,
+        parent: &'a State<'a>,
+        first: &'a Cell<bool>,
+        table_emitted: &'a Cell<bool>,
+    },
+    Array {
+        parent: &'a State<'a>,
+        first: &'a Cell<bool>,
+        type_: &'a Cell<Option<ArrayState>>,
+        len: Option<usize>,
+    },
+    End,
+}
+
+#[doc(hidden)]
+pub struct SerializeSeq<'a, 'b> {
+    ser: &'b mut Serializer<'a>,
+    first: Cell<bool>,
+    type_: Cell<Option<ArrayState>>,
+    len: Option<usize>,
+}
+
+#[doc(hidden)]
+pub enum SerializeTable<'a, 'b> {
+    Datetime(&'b mut Serializer<'a>),
+    Table {
+        ser: &'b mut Serializer<'a>,
+        key: String,
+        first: Cell<bool>,
+        table_emitted: Cell<bool>,
+    },
+}
+
+impl<'a> Serializer<'a> {
+    /// Creates a new serializer which will emit TOML into the buffer provided.
+    ///
+    /// The serializer can then be used to serialize a type after which the data
+    /// will be present in `dst`.
+    pub fn new(dst: &'a mut String) -> Serializer<'a> {
+        Serializer {
+            dst,
+            state: State::End,
+            settings: Rc::new(Settings::default()),
+        }
+    }
+
+    /// Instantiate a "pretty" formatter
+    ///
+    /// By default this will use:
+    ///
+    /// - pretty strings: strings with newlines will use the `'''` syntax. See
+    ///   `Serializer::pretty_string`
+    /// - pretty arrays: each item in arrays will be on a newline, have an indentation of 4 and
+    ///   have a trailing comma. See `Serializer::pretty_array`
+    pub fn pretty(dst: &'a mut String) -> Serializer<'a> {
+        Serializer {
+            dst,
+            state: State::End,
+            settings: Rc::new(Settings {
+                array: Some(ArraySettings::pretty()),
+                string: Some(StringSettings::pretty()),
+            }),
+        }
+    }
+
+    /// Enable or Disable pretty strings
+    ///
+    /// If enabled, literal strings will be used when possible and strings with
+    /// one or more newlines will use triple quotes (i.e.: `'''` or `"""`)
+    ///
+    /// # Examples
+    ///
+    /// Instead of:
+    ///
+    /// ```toml,ignore
+    /// single = "no newlines"
+    /// text = "\nfoo\nbar\n"
+    /// ```
+    ///
+    /// You will have:
+    ///
+    /// ```toml,ignore
+    /// single = 'no newlines'
+    /// text = '''
+    /// foo
+    /// bar
+    /// '''
+    /// ```
+    pub fn pretty_string(&mut self, value: bool) -> &mut Self {
+        Rc::get_mut(&mut self.settings).unwrap().string = if value {
+            Some(StringSettings::pretty())
+        } else {
+            None
+        };
+        self
+    }
+
+    /// Enable or Disable Literal strings for pretty strings
+    ///
+    /// If enabled, literal strings will be used when possible and strings with
+    /// one or more newlines will use triple quotes (i.e.: `'''` or `"""`)
+    ///
+    /// If disabled, literal strings will NEVER be used and strings with one or
+    /// more newlines will use `"""`
+    ///
+    /// # Examples
+    ///
+    /// Instead of:
+    ///
+    /// ```toml,ignore
+    /// single = "no newlines"
+    /// text = "\nfoo\nbar\n"
+    /// ```
+    ///
+    /// You will have:
+    ///
+    /// ```toml,ignore
+    /// single = "no newlines"
+    /// text = """
+    /// foo
+    /// bar
+    /// """
+    /// ```
+    pub fn pretty_string_literal(&mut self, value: bool) -> &mut Self {
+        let use_default = if let Some(ref mut s) = Rc::get_mut(&mut self.settings).unwrap().string {
+            s.literal = value;
+            false
+        } else {
+            true
+        };
+
+        if use_default {
+            let mut string = StringSettings::pretty();
+            string.literal = value;
+            Rc::get_mut(&mut self.settings).unwrap().string = Some(string);
+        }
+        self
+    }
+
+    /// Enable or Disable pretty arrays
+    ///
+    /// If enabled, arrays will always have each item on their own line.
+    ///
+    /// Some specific features can be controlled via other builder methods:
+    ///
+    /// - `Serializer::pretty_array_indent`: set the indent to a value other
+    ///   than 4.
+    /// - `Serializer::pretty_array_trailing_comma`: enable/disable the trailing
+    ///   comma on the last item.
+    ///
+    /// # Examples
+    ///
+    /// Instead of:
+    ///
+    /// ```toml,ignore
+    /// array = ["foo", "bar"]
+    /// ```
+    ///
+    /// You will have:
+    ///
+    /// ```toml,ignore
+    /// array = [
+    ///     "foo",
+    ///     "bar",
+    /// ]
+    /// ```
+    pub fn pretty_array(&mut self, value: bool) -> &mut Self {
+        Rc::get_mut(&mut self.settings).unwrap().array = if value {
+            Some(ArraySettings::pretty())
+        } else {
+            None
+        };
+        self
+    }
+
+    /// Set the indent for pretty arrays
+    ///
+    /// See `Serializer::pretty_array` for more details.
+    pub fn pretty_array_indent(&mut self, value: usize) -> &mut Self {
+        let use_default = if let Some(ref mut a) = Rc::get_mut(&mut self.settings).unwrap().array {
+            a.indent = value;
+            false
+        } else {
+            true
+        };
+
+        if use_default {
+            let mut array = ArraySettings::pretty();
+            array.indent = value;
+            Rc::get_mut(&mut self.settings).unwrap().array = Some(array);
+        }
+        self
+    }
+
+    /// Specify whether to use a trailing comma when serializing pretty arrays
+    ///
+    /// See `Serializer::pretty_array` for more details.
+    pub fn pretty_array_trailing_comma(&mut self, value: bool) -> &mut Self {
+        let use_default = if let Some(ref mut a) = Rc::get_mut(&mut self.settings).unwrap().array {
+            a.trailing_comma = value;
+            false
+        } else {
+            true
+        };
+
+        if use_default {
+            let mut array = ArraySettings::pretty();
+            array.trailing_comma = value;
+            Rc::get_mut(&mut self.settings).unwrap().array = Some(array);
+        }
+        self
+    }
+
+    fn display<T: fmt::Display>(&mut self, t: T, type_: ArrayState) -> Result<(), Error> {
+        self.emit_key(type_)?;
+        write!(self.dst, "{}", t).map_err(ser::Error::custom)?;
+        if let State::Table { .. } = self.state {
+            self.dst.push('\n');
+        }
+        Ok(())
+    }
+
+    fn emit_key(&mut self, type_: ArrayState) -> Result<(), Error> {
+        self.array_type(type_)?;
+        let state = self.state.clone();
+        self._emit_key(&state)
+    }
+
+    // recursive implementation of `emit_key` above
+    fn _emit_key(&mut self, state: &State<'_>) -> Result<(), Error> {
+        match *state {
+            State::End => Ok(()),
+            State::Array {
+                parent,
+                first,
+                type_,
+                len,
+            } => {
+                assert!(type_.get().is_some());
+                if first.get() {
+                    self._emit_key(parent)?;
+                }
+                self.emit_array(first, len)
+            }
+            State::Table {
+                parent,
+                first,
+                table_emitted,
+                key,
+            } => {
+                if table_emitted.get() {
+                    return Err(Error::ValueAfterTable);
+                }
+                if first.get() {
+                    self.emit_table_header(parent)?;
+                    first.set(false);
+                }
+                self.escape_key(key)?;
+                self.dst.push_str(" = ");
+                Ok(())
+            }
+        }
+    }
+
+    fn emit_array(&mut self, first: &Cell<bool>, len: Option<usize>) -> Result<(), Error> {
+        match (len, &self.settings.array) {
+            (Some(0..=1), _) | (_, &None) => {
+                if first.get() {
+                    self.dst.push('[')
+                } else {
+                    self.dst.push_str(", ")
+                }
+            }
+            (_, &Some(ref a)) => {
+                if first.get() {
+                    self.dst.push_str("[\n")
+                } else {
+                    self.dst.push_str(",\n")
+                }
+                for _ in 0..a.indent {
+                    self.dst.push(' ');
+                }
+            }
+        }
+        Ok(())
+    }
+
+    fn array_type(&mut self, type_: ArrayState) -> Result<(), Error> {
+        let prev = match self.state {
+            State::Array { type_, .. } => type_,
+            _ => return Ok(()),
+        };
+        if prev.get().is_none() {
+            prev.set(Some(type_));
+        }
+        Ok(())
+    }
+
+    fn escape_key(&mut self, key: &str) -> Result<(), Error> {
+        let ok = !key.is_empty()
+            && key
+                .chars()
+                .all(|c| matches!(c,'a'..='z' | 'A'..='Z' | '0'..='9' | '-' | '_'));
+        if ok {
+            write!(self.dst, "{}", key).map_err(ser::Error::custom)?;
+        } else {
+            self.emit_str(key, true)?;
+        }
+        Ok(())
+    }
+
+    fn emit_str(&mut self, value: &str, is_key: bool) -> Result<(), Error> {
+        #[derive(PartialEq)]
+        enum Type {
+            NewlineTripple,
+            OnelineTripple,
+            OnelineSingle,
+        }
+
+        enum Repr {
+            /// represent as a literal string (using '')
+            Literal(String, Type),
+            /// represent the std way (using "")
+            Std(Type),
+        }
+
+        fn do_pretty(value: &str) -> Repr {
+            // For doing pretty prints we store in a new String
+            // because there are too many cases where pretty cannot
+            // work. We need to determine:
+            // - if we are a "multi-line" pretty (if there are \n)
+            // - if ['''] appears if multi or ['] if single
+            // - if there are any invalid control characters
+            //
+            // Doing it any other way would require multiple passes
+            // to determine if a pretty string works or not.
+            let mut out = String::with_capacity(value.len() * 2);
+            let mut ty = Type::OnelineSingle;
+            // found consecutive single quotes
+            let mut max_found_singles = 0;
+            let mut found_singles = 0;
+            let mut can_be_pretty = true;
+
+            for ch in value.chars() {
+                if can_be_pretty {
+                    if ch == '\'' {
+                        found_singles += 1;
+                        if found_singles >= 3 {
+                            can_be_pretty = false;
+                        }
+                    } else {
+                        if found_singles > max_found_singles {
+                            max_found_singles = found_singles;
+                        }
+                        found_singles = 0
+                    }
+                    match ch {
+                        '\t' => {}
+                        '\n' => ty = Type::NewlineTripple,
+                        // Escape codes are needed if any ascii control
+                        // characters are present, including \b \f \r.
+                        c if c <= '\u{1f}' || c == '\u{7f}' => can_be_pretty = false,
+                        _ => {}
+                    }
+                    out.push(ch);
+                } else {
+                    // the string cannot be represented as pretty,
+                    // still check if it should be multiline
+                    if ch == '\n' {
+                        ty = Type::NewlineTripple;
+                    }
+                }
+            }
+            if can_be_pretty && found_singles > 0 && value.ends_with('\'') {
+                // We cannot escape the ending quote so we must use """
+                can_be_pretty = false;
+            }
+            if !can_be_pretty {
+                debug_assert!(ty != Type::OnelineTripple);
+                return Repr::Std(ty);
+            }
+            if found_singles > max_found_singles {
+                max_found_singles = found_singles;
+            }
+            debug_assert!(max_found_singles < 3);
+            if ty == Type::OnelineSingle && max_found_singles >= 1 {
+                // no newlines, but must use ''' because it has ' in it
+                ty = Type::OnelineTripple;
+            }
+            Repr::Literal(out, ty)
+        }
+
+        let repr = if !is_key && self.settings.string.is_some() {
+            match (&self.settings.string, do_pretty(value)) {
+                (&Some(StringSettings { literal: false, .. }), Repr::Literal(_, ty)) => {
+                    Repr::Std(ty)
+                }
+                (_, r) => r,
+            }
+        } else {
+            Repr::Std(Type::OnelineSingle)
+        };
+        match repr {
+            Repr::Literal(literal, ty) => {
+                // A pretty string
+                match ty {
+                    Type::NewlineTripple => self.dst.push_str("'''\n"),
+                    Type::OnelineTripple => self.dst.push_str("'''"),
+                    Type::OnelineSingle => self.dst.push('\''),
+                }
+                self.dst.push_str(&literal);
+                match ty {
+                    Type::OnelineSingle => self.dst.push('\''),
+                    _ => self.dst.push_str("'''"),
+                }
+            }
+            Repr::Std(ty) => {
+                match ty {
+                    Type::NewlineTripple => self.dst.push_str("\"\"\"\n"),
+                    // note: OnelineTripple can happen if do_pretty wants to do
+                    // '''it's one line'''
+                    // but settings.string.literal == false
+                    Type::OnelineSingle | Type::OnelineTripple => self.dst.push('"'),
+                }
+                for ch in value.chars() {
+                    match ch {
+                        '\u{8}' => self.dst.push_str("\\b"),
+                        '\u{9}' => self.dst.push_str("\\t"),
+                        '\u{a}' => match ty {
+                            Type::NewlineTripple => self.dst.push('\n'),
+                            Type::OnelineSingle => self.dst.push_str("\\n"),
+                            _ => unreachable!(),
+                        },
+                        '\u{c}' => self.dst.push_str("\\f"),
+                        '\u{d}' => self.dst.push_str("\\r"),
+                        '\u{22}' => self.dst.push_str("\\\""),
+                        '\u{5c}' => self.dst.push_str("\\\\"),
+                        c if c <= '\u{1f}' || c == '\u{7f}' => {
+                            write!(self.dst, "\\u{:04X}", ch as u32).map_err(ser::Error::custom)?;
+                        }
+                        ch => self.dst.push(ch),
+                    }
+                }
+                match ty {
+                    Type::NewlineTripple => self.dst.push_str("\"\"\""),
+                    Type::OnelineSingle | Type::OnelineTripple => self.dst.push('"'),
+                }
+            }
+        }
+        Ok(())
+    }
+
+    fn emit_table_header(&mut self, state: &State<'_>) -> Result<(), Error> {
+        let array_of_tables = match *state {
+            State::End => return Ok(()),
+            State::Array { .. } => true,
+            _ => false,
+        };
+
+        // Unlike [..]s, we can't omit [[..]] ancestors, so be sure to emit table
+        // headers for them.
+        let mut p = state;
+        if let State::Array { first, parent, .. } = *state {
+            if first.get() {
+                p = parent;
+            }
+        }
+        while let State::Table { first, parent, .. } = *p {
+            p = parent;
+            if !first.get() {
+                break;
+            }
+            if let State::Array {
+                parent: &State::Table { .. },
+                ..
+            } = *parent
+            {
+                self.emit_table_header(parent)?;
+                break;
+            }
+        }
+
+        match *state {
+            State::Table { first, .. } => {
+                if !first.get() {
+                    // Newline if we are a table that is not the first
+                    // table in the document.
+                    self.dst.push('\n');
+                }
+            }
+            State::Array { parent, first, .. } => {
+                if !first.get() {
+                    // Always newline if we are not the first item in the
+                    // table-array
+                    self.dst.push('\n');
+                } else if let State::Table { first, .. } = *parent {
+                    if !first.get() {
+                        // Newline if we are not the first item in the document
+                        self.dst.push('\n');
+                    }
+                }
+            }
+            _ => {}
+        }
+        self.dst.push('[');
+        if array_of_tables {
+            self.dst.push('[');
+        }
+        self.emit_key_part(state)?;
+        if array_of_tables {
+            self.dst.push(']');
+        }
+        self.dst.push_str("]\n");
+        Ok(())
+    }
+
+    fn emit_key_part(&mut self, key: &State<'_>) -> Result<bool, Error> {
+        match *key {
+            State::Array { parent, .. } => self.emit_key_part(parent),
+            State::End => Ok(true),
+            State::Table {
+                key,
+                parent,
+                table_emitted,
+                ..
+            } => {
+                table_emitted.set(true);
+                let first = self.emit_key_part(parent)?;
+                if !first {
+                    self.dst.push('.');
+                }
+                self.escape_key(key)?;
+                Ok(false)
+            }
+        }
+    }
+}
+
+macro_rules! serialize_float {
+    ($this:expr, $v:expr) => {{
+        $this.emit_key(ArrayState::Started)?;
+        match ($v.is_sign_negative(), $v.is_nan(), $v == 0.0) {
+            (true, true, _) => write!($this.dst, "-nan"),
+            (false, true, _) => write!($this.dst, "nan"),
+            (true, false, true) => write!($this.dst, "-0.0"),
+            (false, false, true) => write!($this.dst, "0.0"),
+            (_, false, false) => write!($this.dst, "{}", $v).and_then(|_| {
+                if $v % 1.0 == 0.0 {
+                    write!($this.dst, ".0")
+                } else {
+                    Ok(())
+                }
+            }),
+        }
+        .map_err(ser::Error::custom)?;
+
+        if let State::Table { .. } = $this.state {
+            $this.dst.push_str("\n");
+        }
+        return Ok(());
+    }};
+}
+
+impl<'a, 'b> ser::Serializer for &'b mut Serializer<'a> {
+    type Ok = ();
+    type Error = Error;
+    type SerializeSeq = SerializeSeq<'a, 'b>;
+    type SerializeTuple = SerializeSeq<'a, 'b>;
+    type SerializeTupleStruct = SerializeSeq<'a, 'b>;
+    type SerializeTupleVariant = SerializeSeq<'a, 'b>;
+    type SerializeMap = SerializeTable<'a, 'b>;
+    type SerializeStruct = SerializeTable<'a, 'b>;
+    type SerializeStructVariant = ser::Impossible<(), Error>;
+
+    fn serialize_bool(self, v: bool) -> Result<(), Self::Error> {
+        self.display(v, ArrayState::Started)
+    }
+
+    fn serialize_i8(self, v: i8) -> Result<(), Self::Error> {
+        self.display(v, ArrayState::Started)
+    }
+
+    fn serialize_i16(self, v: i16) -> Result<(), Self::Error> {
+        self.display(v, ArrayState::Started)
+    }
+
+    fn serialize_i32(self, v: i32) -> Result<(), Self::Error> {
+        self.display(v, ArrayState::Started)
+    }
+
+    fn serialize_i64(self, v: i64) -> Result<(), Self::Error> {
+        self.display(v, ArrayState::Started)
+    }
+
+    fn serialize_u8(self, v: u8) -> Result<(), Self::Error> {
+        self.display(v, ArrayState::Started)
+    }
+
+    fn serialize_u16(self, v: u16) -> Result<(), Self::Error> {
+        self.display(v, ArrayState::Started)
+    }
+
+    fn serialize_u32(self, v: u32) -> Result<(), Self::Error> {
+        self.display(v, ArrayState::Started)
+    }
+
+    fn serialize_u64(self, v: u64) -> Result<(), Self::Error> {
+        self.display(v, ArrayState::Started)
+    }
+
+    fn serialize_f32(self, v: f32) -> Result<(), Self::Error> {
+        serialize_float!(self, v)
+    }
+
+    fn serialize_f64(self, v: f64) -> Result<(), Self::Error> {
+        serialize_float!(self, v)
+    }
+
+    fn serialize_char(self, v: char) -> Result<(), Self::Error> {
+        let mut buf = [0; 4];
+        self.serialize_str(v.encode_utf8(&mut buf))
+    }
+
+    fn serialize_str(self, value: &str) -> Result<(), Self::Error> {
+        self.emit_key(ArrayState::Started)?;
+        self.emit_str(value, false)?;
+        if let State::Table { .. } = self.state {
+            self.dst.push('\n');
+        }
+        Ok(())
+    }
+
+    fn serialize_bytes(self, value: &[u8]) -> Result<(), Self::Error> {
+        use serde::ser::Serialize;
+        value.serialize(self)
+    }
+
+    fn serialize_none(self) -> Result<(), Self::Error> {
+        Err(Error::UnsupportedNone)
+    }
+
+    fn serialize_some<T: ?Sized>(self, value: &T) -> Result<(), Self::Error>
+    where
+        T: ser::Serialize,
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_unit(self) -> Result<(), Self::Error> {
+        Err(Error::UnsupportedType)
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<(), Self::Error> {
+        Err(Error::UnsupportedType)
+    }
+
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+    ) -> Result<(), Self::Error> {
+        self.serialize_str(variant)
+    }
+
+    fn serialize_newtype_struct<T: ?Sized>(
+        self,
+        _name: &'static str,
+        value: &T,
+    ) -> Result<(), Self::Error>
+    where
+        T: ser::Serialize,
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_newtype_variant<T: ?Sized>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _value: &T,
+    ) -> Result<(), Self::Error>
+    where
+        T: ser::Serialize,
+    {
+        Err(Error::UnsupportedType)
+    }
+
+    fn serialize_seq(self, len: Option<usize>) -> Result<Self::SerializeSeq, Self::Error> {
+        self.array_type(ArrayState::Started)?;
+        Ok(SerializeSeq {
+            ser: self,
+            first: Cell::new(true),
+            type_: Cell::new(None),
+            len,
+        })
+    }
+
+    fn serialize_tuple(self, len: usize) -> Result<Self::SerializeTuple, Self::Error> {
+        self.serialize_seq(Some(len))
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeTupleStruct, Self::Error> {
+        self.serialize_seq(Some(len))
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeTupleVariant, Self::Error> {
+        self.serialize_seq(Some(len))
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap, Self::Error> {
+        self.array_type(ArrayState::StartedAsATable)?;
+        Ok(SerializeTable::Table {
+            ser: self,
+            key: String::new(),
+            first: Cell::new(true),
+            table_emitted: Cell::new(false),
+        })
+    }
+
+    fn serialize_struct(
+        self,
+        name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStruct, Self::Error> {
+        if name == datetime::NAME {
+            self.array_type(ArrayState::Started)?;
+            Ok(SerializeTable::Datetime(self))
+        } else {
+            self.array_type(ArrayState::StartedAsATable)?;
+            Ok(SerializeTable::Table {
+                ser: self,
+                key: String::new(),
+                first: Cell::new(true),
+                table_emitted: Cell::new(false),
+            })
+        }
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant, Self::Error> {
+        Err(Error::UnsupportedType)
+    }
+}
+
+impl<'a, 'b> ser::SerializeSeq for SerializeSeq<'a, 'b> {
+    type Ok = ();
+    type Error = Error;
+
+    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    where
+        T: ser::Serialize,
+    {
+        value.serialize(&mut Serializer {
+            dst: &mut *self.ser.dst,
+            state: State::Array {
+                parent: &self.ser.state,
+                first: &self.first,
+                type_: &self.type_,
+                len: self.len,
+            },
+            settings: self.ser.settings.clone(),
+        })?;
+        self.first.set(false);
+        Ok(())
+    }
+
+    fn end(self) -> Result<(), Error> {
+        match self.type_.get() {
+            Some(ArrayState::StartedAsATable) => return Ok(()),
+            Some(ArrayState::Started) => match (self.len, &self.ser.settings.array) {
+                (Some(0..=1), _) | (_, &None) => {
+                    self.ser.dst.push(']');
+                }
+                (_, &Some(ref a)) => {
+                    if a.trailing_comma {
+                        self.ser.dst.push(',');
+                    }
+                    self.ser.dst.push_str("\n]");
+                }
+            },
+            None => {
+                assert!(self.first.get());
+                self.ser.emit_key(ArrayState::Started)?;
+                self.ser.dst.push_str("[]")
+            }
+        }
+        if let State::Table { .. } = self.ser.state {
+            self.ser.dst.push('\n');
+        }
+        Ok(())
+    }
+}
+
+impl<'a, 'b> ser::SerializeTuple for SerializeSeq<'a, 'b> {
+    type Ok = ();
+    type Error = Error;
+
+    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    where
+        T: ser::Serialize,
+    {
+        ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    fn end(self) -> Result<(), Error> {
+        ser::SerializeSeq::end(self)
+    }
+}
+
+impl<'a, 'b> ser::SerializeTupleVariant for SerializeSeq<'a, 'b> {
+    type Ok = ();
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    where
+        T: ser::Serialize,
+    {
+        ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    fn end(self) -> Result<(), Error> {
+        ser::SerializeSeq::end(self)
+    }
+}
+
+impl<'a, 'b> ser::SerializeTupleStruct for SerializeSeq<'a, 'b> {
+    type Ok = ();
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    where
+        T: ser::Serialize,
+    {
+        ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    fn end(self) -> Result<(), Error> {
+        ser::SerializeSeq::end(self)
+    }
+}
+
+impl<'a, 'b> ser::SerializeMap for SerializeTable<'a, 'b> {
+    type Ok = ();
+    type Error = Error;
+
+    fn serialize_key<T: ?Sized>(&mut self, input: &T) -> Result<(), Error>
+    where
+        T: ser::Serialize,
+    {
+        match *self {
+            SerializeTable::Datetime(_) => panic!(), // shouldn't be possible
+            SerializeTable::Table { ref mut key, .. } => {
+                key.truncate(0);
+                *key = input.serialize(StringExtractor)?;
+            }
+        }
+        Ok(())
+    }
+
+    fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
+    where
+        T: ser::Serialize,
+    {
+        match *self {
+            SerializeTable::Datetime(_) => panic!(), // shouldn't be possible
+            SerializeTable::Table {
+                ref mut ser,
+                ref key,
+                ref first,
+                ref table_emitted,
+                ..
+            } => {
+                let res = value.serialize(&mut Serializer {
+                    dst: &mut *ser.dst,
+                    state: State::Table {
+                        key,
+                        parent: &ser.state,
+                        first,
+                        table_emitted,
+                    },
+                    settings: ser.settings.clone(),
+                });
+                match res {
+                    Ok(()) => first.set(false),
+                    Err(Error::UnsupportedNone) => {}
+                    Err(e) => return Err(e),
+                }
+            }
+        }
+        Ok(())
+    }
+
+    fn end(self) -> Result<(), Error> {
+        match self {
+            SerializeTable::Datetime(_) => panic!(), // shouldn't be possible
+            SerializeTable::Table { ser, first, .. } => {
+                if first.get() {
+                    let state = ser.state.clone();
+                    ser.emit_table_header(&state)?;
+                }
+            }
+        }
+        Ok(())
+    }
+}
+
+impl<'a, 'b> ser::SerializeStruct for SerializeTable<'a, 'b> {
+    type Ok = ();
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), Error>
+    where
+        T: ser::Serialize,
+    {
+        match *self {
+            SerializeTable::Datetime(ref mut ser) => {
+                if key == datetime::FIELD {
+                    value.serialize(DateStrEmitter(*ser))?;
+                } else {
+                    return Err(Error::DateInvalid);
+                }
+            }
+            SerializeTable::Table {
+                ref mut ser,
+                ref first,
+                ref table_emitted,
+                ..
+            } => {
+                let res = value.serialize(&mut Serializer {
+                    dst: &mut *ser.dst,
+                    state: State::Table {
+                        key,
+                        parent: &ser.state,
+                        first,
+                        table_emitted,
+                    },
+                    settings: ser.settings.clone(),
+                });
+                match res {
+                    Ok(()) => first.set(false),
+                    Err(Error::UnsupportedNone) => {}
+                    Err(e) => return Err(e),
+                }
+            }
+        }
+        Ok(())
+    }
+
+    fn end(self) -> Result<(), Error> {
+        match self {
+            SerializeTable::Datetime(_) => {}
+            SerializeTable::Table { ser, first, .. } => {
+                if first.get() {
+                    let state = ser.state.clone();
+                    ser.emit_table_header(&state)?;
+                }
+            }
+        }
+        Ok(())
+    }
+}
+
+struct DateStrEmitter<'a, 'b>(&'b mut Serializer<'a>);
+
+impl<'a, 'b> ser::Serializer for DateStrEmitter<'a, 'b> {
+    type Ok = ();
+    type Error = Error;
+    type SerializeSeq = ser::Impossible<(), Error>;
+    type SerializeTuple = ser::Impossible<(), Error>;
+    type SerializeTupleStruct = ser::Impossible<(), Error>;
+    type SerializeTupleVariant = ser::Impossible<(), Error>;
+    type SerializeMap = ser::Impossible<(), Error>;
+    type SerializeStruct = ser::Impossible<(), Error>;
+    type SerializeStructVariant = ser::Impossible<(), Error>;
+
+    fn serialize_bool(self, _v: bool) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_i8(self, _v: i8) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_i16(self, _v: i16) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_i32(self, _v: i32) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_i64(self, _v: i64) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_u8(self, _v: u8) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_u16(self, _v: u16) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_u32(self, _v: u32) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_u64(self, _v: u64) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_f32(self, _v: f32) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_f64(self, _v: f64) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_char(self, _v: char) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_str(self, value: &str) -> Result<(), Self::Error> {
+        self.0.display(value, ArrayState::Started)?;
+        Ok(())
+    }
+
+    fn serialize_bytes(self, _value: &[u8]) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_none(self) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_some<T: ?Sized>(self, _value: &T) -> Result<(), Self::Error>
+    where
+        T: ser::Serialize,
+    {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_unit(self) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+    ) -> Result<(), Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_newtype_struct<T: ?Sized>(
+        self,
+        _name: &'static str,
+        _value: &T,
+    ) -> Result<(), Self::Error>
+    where
+        T: ser::Serialize,
+    {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_newtype_variant<T: ?Sized>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _value: &T,
+    ) -> Result<(), Self::Error>
+    where
+        T: ser::Serialize,
+    {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq, Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple, Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleStruct, Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleVariant, Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap, Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStruct, Self::Error> {
+        Err(Error::DateInvalid)
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant, Self::Error> {
+        Err(Error::DateInvalid)
+    }
+}
+
+struct StringExtractor;
+
+impl ser::Serializer for StringExtractor {
+    type Ok = String;
+    type Error = Error;
+    type SerializeSeq = ser::Impossible<String, Error>;
+    type SerializeTuple = ser::Impossible<String, Error>;
+    type SerializeTupleStruct = ser::Impossible<String, Error>;
+    type SerializeTupleVariant = ser::Impossible<String, Error>;
+    type SerializeMap = ser::Impossible<String, Error>;
+    type SerializeStruct = ser::Impossible<String, Error>;
+    type SerializeStructVariant = ser::Impossible<String, Error>;
+
+    fn serialize_bool(self, _v: bool) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_i8(self, _v: i8) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_i16(self, _v: i16) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_i32(self, _v: i32) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_i64(self, _v: i64) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_u8(self, _v: u8) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_u16(self, _v: u16) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_u32(self, _v: u32) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_u64(self, _v: u64) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_f32(self, _v: f32) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_f64(self, _v: f64) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_char(self, _v: char) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_str(self, value: &str) -> Result<String, Self::Error> {
+        Ok(value.to_string())
+    }
+
+    fn serialize_bytes(self, _value: &[u8]) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_none(self) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_some<T: ?Sized>(self, _value: &T) -> Result<String, Self::Error>
+    where
+        T: ser::Serialize,
+    {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_unit(self) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+    ) -> Result<String, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_newtype_struct<T: ?Sized>(
+        self,
+        _name: &'static str,
+        value: &T,
+    ) -> Result<String, Self::Error>
+    where
+        T: ser::Serialize,
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_newtype_variant<T: ?Sized>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _value: &T,
+    ) -> Result<String, Self::Error>
+    where
+        T: ser::Serialize,
+    {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleStruct, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleVariant, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStruct, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant, Self::Error> {
+        Err(Error::KeyNotString)
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            Error::UnsupportedType => "unsupported Rust type".fmt(f),
+            Error::KeyNotString => "map key was not a string".fmt(f),
+            Error::ValueAfterTable => "values must be emitted before tables".fmt(f),
+            Error::DateInvalid => "a serialized date was invalid".fmt(f),
+            Error::NumberInvalid => "a serialized number was invalid".fmt(f),
+            Error::UnsupportedNone => "unsupported None value".fmt(f),
+            Error::Custom(ref s) => s.fmt(f),
+            Error::KeyNewline => unreachable!(),
+            Error::ArrayMixedType => unreachable!(),
+        }
+    }
+}
+
+impl error::Error for Error {}
+
+impl ser::Error for Error {
+    fn custom<T: fmt::Display>(msg: T) -> Error {
+        Error::Custom(msg.to_string())
+    }
+}
+
+enum Category {
+    Primitive,
+    Array,
+    Table,
+}
+
+/// Convenience function to serialize items in a map in an order valid with
+/// TOML.
+///
+/// TOML carries the restriction that keys in a table must be serialized last if
+/// their value is a table itself. This isn't always easy to guarantee, so this
+/// helper can be used like so:
+///
+/// ```rust
+/// # use serde_derive::Serialize;
+/// # use std::collections::HashMap;
+/// #[derive(Serialize)]
+/// struct Manifest {
+///     package: Package,
+///     #[serde(serialize_with = "toml::ser::tables_last")]
+///     dependencies: HashMap<String, Dependency>,
+/// }
+/// # type Package = String;
+/// # type Dependency = String;
+/// # fn main() {}
+/// ```
+pub fn tables_last<'a, I, K, V, S>(data: &'a I, serializer: S) -> Result<S::Ok, S::Error>
+where
+    &'a I: IntoIterator<Item = (K, V)>,
+    K: ser::Serialize,
+    V: ser::Serialize,
+    S: ser::Serializer,
+{
+    use serde::ser::SerializeMap;
+
+    let mut map = serializer.serialize_map(None)?;
+    for (k, v) in data {
+        if let Category::Primitive = v.serialize(Categorize::new())? {
+            map.serialize_entry(&k, &v)?;
+        }
+    }
+    for (k, v) in data {
+        if let Category::Array = v.serialize(Categorize::new())? {
+            map.serialize_entry(&k, &v)?;
+        }
+    }
+    for (k, v) in data {
+        if let Category::Table = v.serialize(Categorize::new())? {
+            map.serialize_entry(&k, &v)?;
+        }
+    }
+    map.end()
+}
+
+struct Categorize<E>(marker::PhantomData<E>);
+
+impl<E> Categorize<E> {
+    fn new() -> Self {
+        Categorize(marker::PhantomData)
+    }
+}
+
+impl<E: ser::Error> ser::Serializer for Categorize<E> {
+    type Ok = Category;
+    type Error = E;
+    type SerializeSeq = Self;
+    type SerializeTuple = Self;
+    type SerializeTupleStruct = Self;
+    type SerializeTupleVariant = Self;
+    type SerializeMap = Self;
+    type SerializeStruct = Self;
+    type SerializeStructVariant = ser::Impossible<Category, E>;
+
+    fn serialize_bool(self, _: bool) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Primitive)
+    }
+
+    fn serialize_i8(self, _: i8) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Primitive)
+    }
+
+    fn serialize_i16(self, _: i16) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Primitive)
+    }
+
+    fn serialize_i32(self, _: i32) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Primitive)
+    }
+
+    fn serialize_i64(self, _: i64) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Primitive)
+    }
+
+    fn serialize_u8(self, _: u8) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Primitive)
+    }
+
+    fn serialize_u16(self, _: u16) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Primitive)
+    }
+
+    fn serialize_u32(self, _: u32) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Primitive)
+    }
+
+    fn serialize_u64(self, _: u64) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Primitive)
+    }
+
+    fn serialize_f32(self, _: f32) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Primitive)
+    }
+
+    fn serialize_f64(self, _: f64) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Primitive)
+    }
+
+    fn serialize_char(self, _: char) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Primitive)
+    }
+
+    fn serialize_str(self, _: &str) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Primitive)
+    }
+
+    fn serialize_bytes(self, _: &[u8]) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Array)
+    }
+
+    fn serialize_none(self) -> Result<Self::Ok, Self::Error> {
+        Err(ser::Error::custom("unsupported"))
+    }
+
+    fn serialize_some<T: ?Sized + ser::Serialize>(self, v: &T) -> Result<Self::Ok, Self::Error> {
+        v.serialize(self)
+    }
+
+    fn serialize_unit(self) -> Result<Self::Ok, Self::Error> {
+        Err(ser::Error::custom("unsupported"))
+    }
+
+    fn serialize_unit_struct(self, _: &'static str) -> Result<Self::Ok, Self::Error> {
+        Err(ser::Error::custom("unsupported"))
+    }
+
+    fn serialize_unit_variant(
+        self,
+        _: &'static str,
+        _: u32,
+        _: &'static str,
+    ) -> Result<Self::Ok, Self::Error> {
+        Err(ser::Error::custom("unsupported"))
+    }
+
+    fn serialize_newtype_struct<T: ?Sized + ser::Serialize>(
+        self,
+        _: &'static str,
+        v: &T,
+    ) -> Result<Self::Ok, Self::Error> {
+        v.serialize(self)
+    }
+
+    fn serialize_newtype_variant<T: ?Sized + ser::Serialize>(
+        self,
+        _: &'static str,
+        _: u32,
+        _: &'static str,
+        _: &T,
+    ) -> Result<Self::Ok, Self::Error> {
+        Err(ser::Error::custom("unsupported"))
+    }
+
+    fn serialize_seq(self, _: Option<usize>) -> Result<Self, Self::Error> {
+        Ok(self)
+    }
+
+    fn serialize_tuple(self, _: usize) -> Result<Self::SerializeTuple, Self::Error> {
+        Ok(self)
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _: &'static str,
+        _: usize,
+    ) -> Result<Self::SerializeTupleStruct, Self::Error> {
+        Ok(self)
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _: &'static str,
+        _: u32,
+        _: &'static str,
+        _: usize,
+    ) -> Result<Self::SerializeTupleVariant, Self::Error> {
+        Ok(self)
+    }
+
+    fn serialize_map(self, _: Option<usize>) -> Result<Self, Self::Error> {
+        Ok(self)
+    }
+
+    fn serialize_struct(self, _: &'static str, _: usize) -> Result<Self, Self::Error> {
+        Ok(self)
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _: &'static str,
+        _: u32,
+        _: &'static str,
+        _: usize,
+    ) -> Result<Self::SerializeStructVariant, Self::Error> {
+        Err(ser::Error::custom("unsupported"))
+    }
+}
+
+impl<E: ser::Error> ser::SerializeSeq for Categorize<E> {
+    type Ok = Category;
+    type Error = E;
+
+    fn serialize_element<T: ?Sized + ser::Serialize>(&mut self, _: &T) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Array)
+    }
+}
+
+impl<E: ser::Error> ser::SerializeTuple for Categorize<E> {
+    type Ok = Category;
+    type Error = E;
+
+    fn serialize_element<T: ?Sized + ser::Serialize>(&mut self, _: &T) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Array)
+    }
+}
+
+impl<E: ser::Error> ser::SerializeTupleVariant for Categorize<E> {
+    type Ok = Category;
+    type Error = E;
+
+    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self, _: &T) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Array)
+    }
+}
+
+impl<E: ser::Error> ser::SerializeTupleStruct for Categorize<E> {
+    type Ok = Category;
+    type Error = E;
+
+    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self, _: &T) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Array)
+    }
+}
+
+impl<E: ser::Error> ser::SerializeMap for Categorize<E> {
+    type Ok = Category;
+    type Error = E;
+
+    fn serialize_key<T: ?Sized + ser::Serialize>(&mut self, _: &T) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    fn serialize_value<T: ?Sized + ser::Serialize>(&mut self, _: &T) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Table)
+    }
+}
+
+impl<E: ser::Error> ser::SerializeStruct for Categorize<E> {
+    type Ok = Category;
+    type Error = E;
+
+    fn serialize_field<T: ?Sized>(&mut self, _: &'static str, _: &T) -> Result<(), Self::Error>
+    where
+        T: ser::Serialize,
+    {
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok, Self::Error> {
+        Ok(Category::Table)
+    }
+}
diff --git a/third_party/rust/toml/src/spanned.rs b/third_party/rust/toml/src/spanned.rs
new file mode 100644
index 0000000000..f90c5492d9
--- /dev/null
+++ b/third_party/rust/toml/src/spanned.rs
@@ -0,0 +1,166 @@
+use serde::{de, ser};
+use std::borrow::Borrow;
+use std::cmp::Ordering;
+use std::fmt;
+use std::hash::{Hash, Hasher};
+
+pub(crate) const NAME: &str = "$__toml_private_Spanned";
+pub(crate) const START: &str = "$__toml_private_start";
+pub(crate) const END: &str = "$__toml_private_end";
+pub(crate) const VALUE: &str = "$__toml_private_value";
+
+/// A spanned value, indicating the range at which it is defined in the source.
+///
+/// ```
+/// use serde_derive::Deserialize;
+/// use toml::Spanned;
+///
+/// #[derive(Deserialize)]
+/// struct Value {
+///     s: Spanned<String>,
+/// }
+///
+/// let t = "s = \"value\"\n";
+///
+/// let u: Value = toml::from_str(t).unwrap();
+///
+/// assert_eq!(u.s.start(), 4);
+/// assert_eq!(u.s.end(), 11);
+/// assert_eq!(u.s.get_ref(), "value");
+/// assert_eq!(u.s.into_inner(), String::from("value"));
+/// ```
+#[derive(Clone, Debug)]
+pub struct Spanned<T> {
+    /// The start range.
+    start: usize,
+    /// The end range (exclusive).
+    end: usize,
+    /// The spanned value.
+    value: T,
+}
+
+impl<T> Spanned<T> {
+    /// Access the start of the span of the contained value.
+    pub fn start(&self) -> usize {
+        self.start
+    }
+
+    /// Access the end of the span of the contained value.
+    pub fn end(&self) -> usize {
+        self.end
+    }
+
+    /// Get the span of the contained value.
+    pub fn span(&self) -> (usize, usize) {
+        (self.start, self.end)
+    }
+
+    /// Consumes the spanned value and returns the contained value.
+    pub fn into_inner(self) -> T {
+        self.value
+    }
+
+    /// Returns a reference to the contained value.
+    pub fn get_ref(&self) -> &T {
+        &self.value
+    }
+
+    /// Returns a mutable reference to the contained value.
+    pub fn get_mut(&mut self) -> &mut T {
+        &mut self.value
+    }
+}
+
+impl Borrow<str> for Spanned<String> {
+    fn borrow(&self) -> &str {
+        self.get_ref()
+    }
+}
+
+impl<T: PartialEq> PartialEq for Spanned<T> {
+    fn eq(&self, other: &Self) -> bool {
+        self.value.eq(&other.value)
+    }
+}
+
+impl<T: Eq> Eq for Spanned<T> {}
+
+impl<T: Hash> Hash for Spanned<T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.value.hash(state);
+    }
+}
+
+impl<T: PartialOrd> PartialOrd for Spanned<T> {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        self.value.partial_cmp(&other.value)
+    }
+}
+
+impl<T: Ord> Ord for Spanned<T> {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.value.cmp(&other.value)
+    }
+}
+
+impl<'de, T> de::Deserialize<'de> for Spanned<T>
+where
+    T: de::Deserialize<'de>,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Spanned<T>, D::Error>
+    where
+        D: de::Deserializer<'de>,
+    {
+        struct SpannedVisitor<T>(::std::marker::PhantomData<T>);
+
+        impl<'de, T> de::Visitor<'de> for SpannedVisitor<T>
+        where
+            T: de::Deserialize<'de>,
+        {
+            type Value = Spanned<T>;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+                formatter.write_str("a TOML spanned")
+            }
+
+            fn visit_map<V>(self, mut visitor: V) -> Result<Spanned<T>, V::Error>
+            where
+                V: de::MapAccess<'de>,
+            {
+                if visitor.next_key()? != Some(START) {
+                    return Err(de::Error::custom("spanned start key not found"));
+                }
+
+                let start: usize = visitor.next_value()?;
+
+                if visitor.next_key()? != Some(END) {
+                    return Err(de::Error::custom("spanned end key not found"));
+                }
+
+                let end: usize = visitor.next_value()?;
+
+                if visitor.next_key()? != Some(VALUE) {
+                    return Err(de::Error::custom("spanned value key not found"));
+                }
+
+                let value: T = visitor.next_value()?;
+
+                Ok(Spanned { start, end, value })
+            }
+        }
+
+        let visitor = SpannedVisitor(::std::marker::PhantomData);
+
+        static FIELDS: [&str; 3] = [START, END, VALUE];
+        deserializer.deserialize_struct(NAME, &FIELDS, visitor)
+    }
+}
+
+impl<T: ser::Serialize> ser::Serialize for Spanned<T> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: ser::Serializer,
+    {
+        self.value.serialize(serializer)
+    }
+}
diff --git a/third_party/rust/toml/src/tokens.rs b/third_party/rust/toml/src/tokens.rs
new file mode 100644
index 0000000000..ea1e7ebd83
--- /dev/null
+++ b/third_party/rust/toml/src/tokens.rs
@@ -0,0 +1,742 @@
+use std::borrow::Cow;
+use std::char;
+use std::str;
+use std::string;
+use std::string::String as StdString;
+
+use self::Token::*;
+
+/// A span, designating a range of bytes where a token is located.
+#[derive(Eq, PartialEq, Debug, Clone, Copy)]
+pub struct Span {
+    /// The start of the range.
+    pub start: usize,
+    /// The end of the range (exclusive).
+    pub end: usize,
+}
+
+impl From<Span> for (usize, usize) {
+    fn from(Span { start, end }: Span) -> (usize, usize) {
+        (start, end)
+    }
+}
+
+#[derive(Eq, PartialEq, Debug)]
+pub enum Token<'a> {
+    Whitespace(&'a str),
+    Newline,
+    Comment(&'a str),
+
+    Equals,
+    Period,
+    Comma,
+    Colon,
+    Plus,
+    LeftBrace,
+    RightBrace,
+    LeftBracket,
+    RightBracket,
+
+    Keylike(&'a str),
+    String {
+        src: &'a str,
+        val: Cow<'a, str>,
+        multiline: bool,
+    },
+}
+
+#[derive(Eq, PartialEq, Debug)]
+pub enum Error {
+    InvalidCharInString(usize, char),
+    InvalidEscape(usize, char),
+    InvalidHexEscape(usize, char),
+    InvalidEscapeValue(usize, u32),
+    NewlineInString(usize),
+    Unexpected(usize, char),
+    UnterminatedString(usize),
+    NewlineInTableKey(usize),
+    MultilineStringKey(usize),
+    Wanted {
+        at: usize,
+        expected: &'static str,
+        found: &'static str,
+    },
+}
+
+#[derive(Clone)]
+pub struct Tokenizer<'a> {
+    input: &'a str,
+    chars: CrlfFold<'a>,
+}
+
+#[derive(Clone)]
+struct CrlfFold<'a> {
+    chars: str::CharIndices<'a>,
+}
+
+#[derive(Debug)]
+enum MaybeString {
+    NotEscaped(usize),
+    Owned(string::String),
+}
+
+impl<'a> Tokenizer<'a> {
+    pub fn new(input: &'a str) -> Tokenizer<'a> {
+        let mut t = Tokenizer {
+            input,
+            chars: CrlfFold {
+                chars: input.char_indices(),
+            },
+        };
+        // Eat utf-8 BOM
+        t.eatc('\u{feff}');
+        t
+    }
+
+    pub fn next(&mut self) -> Result<Option<(Span, Token<'a>)>, Error> {
+        let (start, token) = match self.one() {
+            Some((start, '\n')) => (start, Newline),
+            Some((start, ' ')) => (start, self.whitespace_token(start)),
+            Some((start, '\t')) => (start, self.whitespace_token(start)),
+            Some((start, '#')) => (start, self.comment_token(start)),
+            Some((start, '=')) => (start, Equals),
+            Some((start, '.')) => (start, Period),
+            Some((start, ',')) => (start, Comma),
+            Some((start, ':')) => (start, Colon),
+            Some((start, '+')) => (start, Plus),
+            Some((start, '{')) => (start, LeftBrace),
+            Some((start, '}')) => (start, RightBrace),
+            Some((start, '[')) => (start, LeftBracket),
+            Some((start, ']')) => (start, RightBracket),
+            Some((start, '\'')) => {
+                return self
+                    .literal_string(start)
+                    .map(|t| Some((self.step_span(start), t)))
+            }
+            Some((start, '"')) => {
+                return self
+                    .basic_string(start)
+                    .map(|t| Some((self.step_span(start), t)))
+            }
+            Some((start, ch)) if is_keylike(ch) => (start, self.keylike(start)),
+
+            Some((start, ch)) => return Err(Error::Unexpected(start, ch)),
+            None => return Ok(None),
+        };
+
+        let span = self.step_span(start);
+        Ok(Some((span, token)))
+    }
+
+    pub fn peek(&mut self) -> Result<Option<(Span, Token<'a>)>, Error> {
+        self.clone().next()
+    }
+
+    pub fn eat(&mut self, expected: Token<'a>) -> Result<bool, Error> {
+        self.eat_spanned(expected).map(|s| s.is_some())
+    }
+
+    /// Eat a value, returning it's span if it was consumed.
+    pub fn eat_spanned(&mut self, expected: Token<'a>) -> Result<Option<Span>, Error> {
+        let span = match self.peek()? {
+            Some((span, ref found)) if expected == *found => span,
+            Some(_) => return Ok(None),
+            None => return Ok(None),
+        };
+
+        drop(self.next());
+        Ok(Some(span))
+    }
+
+    pub fn expect(&mut self, expected: Token<'a>) -> Result<(), Error> {
+        // ignore span
+        let _ = self.expect_spanned(expected)?;
+        Ok(())
+    }
+
+    /// Expect the given token returning its span.
+    pub fn expect_spanned(&mut self, expected: Token<'a>) -> Result<Span, Error> {
+        let current = self.current();
+        match self.next()? {
+            Some((span, found)) => {
+                if expected == found {
+                    Ok(span)
+                } else {
+                    Err(Error::Wanted {
+                        at: current,
+                        expected: expected.describe(),
+                        found: found.describe(),
+                    })
+                }
+            }
+            None => Err(Error::Wanted {
+                at: self.input.len(),
+                expected: expected.describe(),
+                found: "eof",
+            }),
+        }
+    }
+
+    pub fn table_key(&mut self) -> Result<(Span, Cow<'a, str>), Error> {
+        let current = self.current();
+        match self.next()? {
+            Some((span, Token::Keylike(k))) => Ok((span, k.into())),
+            Some((
+                span,
+                Token::String {
+                    src,
+                    val,
+                    multiline,
+                },
+            )) => {
+                let offset = self.substr_offset(src);
+                if multiline {
+                    return Err(Error::MultilineStringKey(offset));
+                }
+                match src.find('\n') {
+                    None => Ok((span, val)),
+                    Some(i) => Err(Error::NewlineInTableKey(offset + i)),
+                }
+            }
+            Some((_, other)) => Err(Error::Wanted {
+                at: current,
+                expected: "a table key",
+                found: other.describe(),
+            }),
+            None => Err(Error::Wanted {
+                at: self.input.len(),
+                expected: "a table key",
+                found: "eof",
+            }),
+        }
+    }
+
+    pub fn eat_whitespace(&mut self) -> Result<(), Error> {
+        while self.eatc(' ') || self.eatc('\t') {
+            // ...
+        }
+        Ok(())
+    }
+
+    pub fn eat_comment(&mut self) -> Result<bool, Error> {
+        if !self.eatc('#') {
+            return Ok(false);
+        }
+        drop(self.comment_token(0));
+        self.eat_newline_or_eof().map(|()| true)
+    }
+
+    pub fn eat_newline_or_eof(&mut self) -> Result<(), Error> {
+        let current = self.current();
+        match self.next()? {
+            None | Some((_, Token::Newline)) => Ok(()),
+            Some((_, other)) => Err(Error::Wanted {
+                at: current,
+                expected: "newline",
+                found: other.describe(),
+            }),
+        }
+    }
+
+    pub fn skip_to_newline(&mut self) {
+        loop {
+            match self.one() {
+                Some((_, '\n')) | None => break,
+                _ => {}
+            }
+        }
+    }
+
+    fn eatc(&mut self, ch: char) -> bool {
+        match self.chars.clone().next() {
+            Some((_, ch2)) if ch == ch2 => {
+                self.one();
+                true
+            }
+            _ => false,
+        }
+    }
+
+    pub fn current(&mut self) -> usize {
+        self.chars
+            .clone()
+            .next()
+            .map(|i| i.0)
+            .unwrap_or_else(|| self.input.len())
+    }
+
+    pub fn input(&self) -> &'a str {
+        self.input
+    }
+
+    fn whitespace_token(&mut self, start: usize) -> Token<'a> {
+        while self.eatc(' ') || self.eatc('\t') {
+            // ...
+        }
+        Whitespace(&self.input[start..self.current()])
+    }
+
+    fn comment_token(&mut self, start: usize) -> Token<'a> {
+        while let Some((_, ch)) = self.chars.clone().next() {
+            if ch != '\t' && !('\u{20}'..='\u{10ffff}').contains(&ch) {
+                break;
+            }
+            self.one();
+        }
+        Comment(&self.input[start..self.current()])
+    }
+
+    #[allow(clippy::type_complexity)]
+    fn read_string(
+        &mut self,
+        delim: char,
+        start: usize,
+        new_ch: &mut dyn FnMut(
+            &mut Tokenizer<'_>,
+            &mut MaybeString,
+            bool,
+            usize,
+            char,
+        ) -> Result<(), Error>,
+    ) -> Result<Token<'a>, Error> {
+        let mut multiline = false;
+        if self.eatc(delim) {
+            if self.eatc(delim) {
+                multiline = true;
+            } else {
+                return Ok(String {
+                    src: &self.input[start..start + 2],
+                    val: Cow::Borrowed(""),
+                    multiline: false,
+                });
+            }
+        }
+        let mut val = MaybeString::NotEscaped(self.current());
+        let mut n = 0;
+        'outer: loop {
+            n += 1;
+            match self.one() {
+                Some((i, '\n')) => {
+                    if multiline {
+                        if self.input.as_bytes()[i] == b'\r' {
+                            val.to_owned(&self.input[..i]);
+                        }
+                        if n == 1 {
+                            val = MaybeString::NotEscaped(self.current());
+                        } else {
+                            val.push('\n');
+                        }
+                        continue;
+                    } else {
+                        return Err(Error::NewlineInString(i));
+                    }
+                }
+                Some((mut i, ch)) if ch == delim => {
+                    if multiline {
+                        if !self.eatc(delim) {
+                            val.push(delim);
+                            continue 'outer;
+                        }
+                        if !self.eatc(delim) {
+                            val.push(delim);
+                            val.push(delim);
+                            continue 'outer;
+                        }
+                        if self.eatc(delim) {
+                            val.push(delim);
+                            i += 1;
+                        }
+                        if self.eatc(delim) {
+                            val.push(delim);
+                            i += 1;
+                        }
+                    }
+                    return Ok(String {
+                        src: &self.input[start..self.current()],
+                        val: val.into_cow(&self.input[..i]),
+                        multiline,
+                    });
+                }
+                Some((i, c)) => new_ch(self, &mut val, multiline, i, c)?,
+                None => return Err(Error::UnterminatedString(start)),
+            }
+        }
+    }
+
+    fn literal_string(&mut self, start: usize) -> Result<Token<'a>, Error> {
+        self.read_string('\'', start, &mut |_me, val, _multi, i, ch| {
+            if ch == '\u{09}' || (('\u{20}'..='\u{10ffff}').contains(&ch) && ch != '\u{7f}') {
+                val.push(ch);
+                Ok(())
+            } else {
+                Err(Error::InvalidCharInString(i, ch))
+            }
+        })
+    }
+
+    fn basic_string(&mut self, start: usize) -> Result<Token<'a>, Error> {
+        self.read_string('"', start, &mut |me, val, multi, i, ch| match ch {
+            '\\' => {
+                val.to_owned(&me.input[..i]);
+                match me.chars.next() {
+                    Some((_, '"')) => val.push('"'),
+                    Some((_, '\\')) => val.push('\\'),
+                    Some((_, 'b')) => val.push('\u{8}'),
+                    Some((_, 'f')) => val.push('\u{c}'),
+                    Some((_, 'n')) => val.push('\n'),
+                    Some((_, 'r')) => val.push('\r'),
+                    Some((_, 't')) => val.push('\t'),
+                    Some((i, c @ 'u')) | Some((i, c @ 'U')) => {
+                        let len = if c == 'u' { 4 } else { 8 };
+                        val.push(me.hex(start, i, len)?);
+                    }
+                    Some((i, c @ ' ')) | Some((i, c @ '\t')) | Some((i, c @ '\n')) if multi => {
+                        if c != '\n' {
+                            while let Some((_, ch)) = me.chars.clone().next() {
+                                match ch {
+                                    ' ' | '\t' => {
+                                        me.chars.next();
+                                        continue;
+                                    }
+                                    '\n' => {
+                                        me.chars.next();
+                                        break;
+                                    }
+                                    _ => return Err(Error::InvalidEscape(i, c)),
+                                }
+                            }
+                        }
+                        while let Some((_, ch)) = me.chars.clone().next() {
+                            match ch {
+                                ' ' | '\t' | '\n' => {
+                                    me.chars.next();
+                                }
+                                _ => break,
+                            }
+                        }
+                    }
+                    Some((i, c)) => return Err(Error::InvalidEscape(i, c)),
+                    None => return Err(Error::UnterminatedString(start)),
+                }
+                Ok(())
+            }
+            ch if ch == '\u{09}' || (('\u{20}'..='\u{10ffff}').contains(&ch) && ch != '\u{7f}') => {
+                val.push(ch);
+                Ok(())
+            }
+            _ => Err(Error::InvalidCharInString(i, ch)),
+        })
+    }
+
+    fn hex(&mut self, start: usize, i: usize, len: usize) -> Result<char, Error> {
+        let mut buf = StdString::with_capacity(len);
+        for _ in 0..len {
+            match self.one() {
+                Some((_, ch)) if ch as u32 <= 0x7F && ch.is_ascii_hexdigit() => buf.push(ch),
+                Some((i, ch)) => return Err(Error::InvalidHexEscape(i, ch)),
+                None => return Err(Error::UnterminatedString(start)),
+            }
+        }
+        let val = u32::from_str_radix(&buf, 16).unwrap();
+        match char::from_u32(val) {
+            Some(ch) => Ok(ch),
+            None => Err(Error::InvalidEscapeValue(i, val)),
+        }
+    }
+
+    fn keylike(&mut self, start: usize) -> Token<'a> {
+        while let Some((_, ch)) = self.peek_one() {
+            if !is_keylike(ch) {
+                break;
+            }
+            self.one();
+        }
+        Keylike(&self.input[start..self.current()])
+    }
+
+    pub fn substr_offset(&self, s: &'a str) -> usize {
+        assert!(s.len() <= self.input.len());
+        let a = self.input.as_ptr() as usize;
+        let b = s.as_ptr() as usize;
+        assert!(a <= b);
+        b - a
+    }
+
+    /// Calculate the span of a single character.
+    fn step_span(&mut self, start: usize) -> Span {
+        let end = self
+            .peek_one()
+            .map(|t| t.0)
+            .unwrap_or_else(|| self.input.len());
+        Span { start, end }
+    }
+
+    /// Peek one char without consuming it.
+    fn peek_one(&mut self) -> Option<(usize, char)> {
+        self.chars.clone().next()
+    }
+
+    /// Take one char.
+    pub fn one(&mut self) -> Option<(usize, char)> {
+        self.chars.next()
+    }
+}
+
+impl<'a> Iterator for CrlfFold<'a> {
+    type Item = (usize, char);
+
+    fn next(&mut self) -> Option<(usize, char)> {
+        self.chars.next().map(|(i, c)| {
+            if c == '\r' {
+                let mut attempt = self.chars.clone();
+                if let Some((_, '\n')) = attempt.next() {
+                    self.chars = attempt;
+                    return (i, '\n');
+                }
+            }
+            (i, c)
+        })
+    }
+}
+
+impl MaybeString {
+    fn push(&mut self, ch: char) {
+        match *self {
+            MaybeString::NotEscaped(..) => {}
+            MaybeString::Owned(ref mut s) => s.push(ch),
+        }
+    }
+
+    #[allow(clippy::wrong_self_convention)]
+    fn to_owned(&mut self, input: &str) {
+        match *self {
+            MaybeString::NotEscaped(start) => {
+                *self = MaybeString::Owned(input[start..].to_owned());
+            }
+            MaybeString::Owned(..) => {}
+        }
+    }
+
+    fn into_cow(self, input: &str) -> Cow<'_, str> {
+        match self {
+            MaybeString::NotEscaped(start) => Cow::Borrowed(&input[start..]),
+            MaybeString::Owned(s) => Cow::Owned(s),
+        }
+    }
+}
+
+fn is_keylike(ch: char) -> bool {
+    ('A'..='Z').contains(&ch)
+        || ('a'..='z').contains(&ch)
+        || ('0'..='9').contains(&ch)
+        || ch == '-'
+        || ch == '_'
+}
+
+impl<'a> Token<'a> {
+    pub fn describe(&self) -> &'static str {
+        match *self {
+            Token::Keylike(_) => "an identifier",
+            Token::Equals => "an equals",
+            Token::Period => "a period",
+            Token::Comment(_) => "a comment",
+            Token::Newline => "a newline",
+            Token::Whitespace(_) => "whitespace",
+            Token::Comma => "a comma",
+            Token::RightBrace => "a right brace",
+            Token::LeftBrace => "a left brace",
+            Token::RightBracket => "a right bracket",
+            Token::LeftBracket => "a left bracket",
+            Token::String { multiline, .. } => {
+                if multiline {
+                    "a multiline string"
+                } else {
+                    "a string"
+                }
+            }
+            Token::Colon => "a colon",
+            Token::Plus => "a plus",
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{Error, Token, Tokenizer};
+    use std::borrow::Cow;
+
+    fn err(input: &str, err: Error) {
+        let mut t = Tokenizer::new(input);
+        let token = t.next().unwrap_err();
+        assert_eq!(token, err);
+        assert!(t.next().unwrap().is_none());
+    }
+
+    #[test]
+    fn literal_strings() {
+        fn t(input: &str, val: &str, multiline: bool) {
+            let mut t = Tokenizer::new(input);
+            let (_, token) = t.next().unwrap().unwrap();
+            assert_eq!(
+                token,
+                Token::String {
+                    src: input,
+                    val: Cow::Borrowed(val),
+                    multiline,
+                }
+            );
+            assert!(t.next().unwrap().is_none());
+        }
+
+        t("''", "", false);
+        t("''''''", "", true);
+        t("'''\n'''", "", true);
+        t("'a'", "a", false);
+        t("'\"a'", "\"a", false);
+        t("''''a'''", "'a", true);
+        t("'''\n'a\n'''", "'a\n", true);
+        t("'''a\n'a\r\n'''", "a\n'a\n", true);
+    }
+
+    #[test]
+    fn basic_strings() {
+        fn t(input: &str, val: &str, multiline: bool) {
+            let mut t = Tokenizer::new(input);
+            let (_, token) = t.next().unwrap().unwrap();
+            assert_eq!(
+                token,
+                Token::String {
+                    src: input,
+                    val: Cow::Borrowed(val),
+                    multiline,
+                }
+            );
+            assert!(t.next().unwrap().is_none());
+        }
+
+        t(r#""""#, "", false);
+        t(r#""""""""#, "", true);
+        t(r#""a""#, "a", false);
+        t(r#""""a""""#, "a", true);
+        t(r#""\t""#, "\t", false);
+        t(r#""\u0000""#, "\0", false);
+        t(r#""\U00000000""#, "\0", false);
+        t(r#""\U000A0000""#, "\u{A0000}", false);
+        t(r#""\\t""#, "\\t", false);
+        t("\"\t\"", "\t", false);
+        t("\"\"\"\n\t\"\"\"", "\t", true);
+        t("\"\"\"\\\n\"\"\"", "", true);
+        t(
+            "\"\"\"\\\n     \t   \t  \\\r\n  \t \n  \t \r\n\"\"\"",
+            "",
+            true,
+        );
+        t(r#""\r""#, "\r", false);
+        t(r#""\n""#, "\n", false);
+        t(r#""\b""#, "\u{8}", false);
+        t(r#""a\fa""#, "a\u{c}a", false);
+        t(r#""\"a""#, "\"a", false);
+        t("\"\"\"\na\"\"\"", "a", true);
+        t("\"\"\"\n\"\"\"", "", true);
+        t(r#""""a\"""b""""#, "a\"\"\"b", true);
+        err(r#""\a"#, Error::InvalidEscape(2, 'a'));
+        err("\"\\\n", Error::InvalidEscape(2, '\n'));
+        err("\"\\\r\n", Error::InvalidEscape(2, '\n'));
+        err("\"\\", Error::UnterminatedString(0));
+        err("\"\u{0}", Error::InvalidCharInString(1, '\u{0}'));
+        err(r#""\U00""#, Error::InvalidHexEscape(5, '"'));
+        err(r#""\U00"#, Error::UnterminatedString(0));
+        err(r#""\uD800"#, Error::InvalidEscapeValue(2, 0xd800));
+        err(r#""\UFFFFFFFF"#, Error::InvalidEscapeValue(2, 0xffff_ffff));
+    }
+
+    #[test]
+    fn keylike() {
+        fn t(input: &str) {
+            let mut t = Tokenizer::new(input);
+            let (_, token) = t.next().unwrap().unwrap();
+            assert_eq!(token, Token::Keylike(input));
+            assert!(t.next().unwrap().is_none());
+        }
+        t("foo");
+        t("0bar");
+        t("bar0");
+        t("1234");
+        t("a-b");
+        t("a_B");
+        t("-_-");
+        t("___");
+    }
+
+    #[test]
+    fn all() {
+        fn t(input: &str, expected: &[((usize, usize), Token<'_>, &str)]) {
+            let mut tokens = Tokenizer::new(input);
+            let mut actual: Vec<((usize, usize), Token<'_>, &str)> = Vec::new();
+            while let Some((span, token)) = tokens.next().unwrap() {
+                actual.push((span.into(), token, &input[span.start..span.end]));
+            }
+            for (a, b) in actual.iter().zip(expected) {
+                assert_eq!(a, b);
+            }
+            assert_eq!(actual.len(), expected.len());
+        }
+
+        t(
+            " a ",
+            &[
+                ((0, 1), Token::Whitespace(" "), " "),
+                ((1, 2), Token::Keylike("a"), "a"),
+                ((2, 3), Token::Whitespace(" "), " "),
+            ],
+        );
+
+        t(
+            " a\t [[]] \t [] {} , . =\n# foo \r\n#foo \n ",
+            &[
+                ((0, 1), Token::Whitespace(" "), " "),
+                ((1, 2), Token::Keylike("a"), "a"),
+                ((2, 4), Token::Whitespace("\t "), "\t "),
+                ((4, 5), Token::LeftBracket, "["),
+                ((5, 6), Token::LeftBracket, "["),
+                ((6, 7), Token::RightBracket, "]"),
+                ((7, 8), Token::RightBracket, "]"),
+                ((8, 11), Token::Whitespace(" \t "), " \t "),
+                ((11, 12), Token::LeftBracket, "["),
+                ((12, 13), Token::RightBracket, "]"),
+                ((13, 14), Token::Whitespace(" "), " "),
+                ((14, 15), Token::LeftBrace, "{"),
+                ((15, 16), Token::RightBrace, "}"),
+                ((16, 17), Token::Whitespace(" "), " "),
+                ((17, 18), Token::Comma, ","),
+                ((18, 19), Token::Whitespace(" "), " "),
+                ((19, 20), Token::Period, "."),
+                ((20, 21), Token::Whitespace(" "), " "),
+                ((21, 22), Token::Equals, "="),
+                ((22, 23), Token::Newline, "\n"),
+                ((23, 29), Token::Comment("# foo "), "# foo "),
+                ((29, 31), Token::Newline, "\r\n"),
+                ((31, 36), Token::Comment("#foo "), "#foo "),
+                ((36, 37), Token::Newline, "\n"),
+                ((37, 38), Token::Whitespace(" "), " "),
+            ],
+        );
+    }
+
+    #[test]
+    fn bare_cr_bad() {
+        err("\r", Error::Unexpected(0, '\r'));
+        err("'\n", Error::NewlineInString(1));
+        err("'\u{0}", Error::InvalidCharInString(1, '\u{0}'));
+        err("'", Error::UnterminatedString(0));
+        err("\u{0}", Error::Unexpected(0, '\u{0}'));
+    }
+
+    #[test]
+    fn bad_comment() {
+        let mut t = Tokenizer::new("#\u{0}");
+        t.next().unwrap().unwrap();
+        assert_eq!(t.next(), Err(Error::Unexpected(1, '\u{0}')));
+        assert!(t.next().unwrap().is_none());
+    }
+}
diff --git a/third_party/rust/toml/src/value.rs b/third_party/rust/toml/src/value.rs
new file mode 100644
index 0000000000..1a1756d102
--- /dev/null
+++ b/third_party/rust/toml/src/value.rs
@@ -0,0 +1,1081 @@
+//! Definition of a TOML value
+
+use std::collections::{BTreeMap, HashMap};
+use std::fmt;
+use std::hash::Hash;
+use std::mem::discriminant;
+use std::ops;
+use std::str::FromStr;
+use std::vec;
+
+use serde::de;
+use serde::de::IntoDeserializer;
+use serde::ser;
+
+use crate::datetime::{self, DatetimeFromString};
+pub use crate::datetime::{Date, Datetime, DatetimeParseError, Offset, Time};
+
+pub use crate::map::{Entry, Map};
+
+/// Representation of a TOML value.
+#[derive(PartialEq, Clone, Debug)]
+pub enum Value {
+    /// Represents a TOML string
+    String(String),
+    /// Represents a TOML integer
+    Integer(i64),
+    /// Represents a TOML float
+    Float(f64),
+    /// Represents a TOML boolean
+    Boolean(bool),
+    /// Represents a TOML datetime
+    Datetime(Datetime),
+    /// Represents a TOML array
+    Array(Array),
+    /// Represents a TOML table
+    Table(Table),
+}
+
+/// Type representing a TOML array, payload of the `Value::Array` variant
+pub type Array = Vec<Value>;
+
+/// Type representing a TOML table, payload of the `Value::Table` variant.
+/// By default it is backed by a BTreeMap, enable the `preserve_order` feature
+/// to use a LinkedHashMap instead.
+pub type Table = Map<String, Value>;
+
+impl Value {
+    /// Convert a `T` into `toml::Value` which is an enum that can represent
+    /// any valid TOML data.
+    ///
+    /// This conversion can fail if `T`'s implementation of `Serialize` decides to
+    /// fail, or if `T` contains a map with non-string keys.
+    pub fn try_from<T>(value: T) -> Result<Value, crate::ser::Error>
+    where
+        T: ser::Serialize,
+    {
+        value.serialize(Serializer)
+    }
+
+    /// Interpret a `toml::Value` as an instance of type `T`.
+    ///
+    /// This conversion can fail if the structure of the `Value` does not match the
+    /// structure expected by `T`, for example if `T` is a struct type but the
+    /// `Value` contains something other than a TOML table. It can also fail if the
+    /// structure is correct but `T`'s implementation of `Deserialize` decides that
+    /// something is wrong with the data, for example required struct fields are
+    /// missing from the TOML map or some number is too big to fit in the expected
+    /// primitive type.
+    pub fn try_into<'de, T>(self) -> Result<T, crate::de::Error>
+    where
+        T: de::Deserialize<'de>,
+    {
+        de::Deserialize::deserialize(self)
+    }
+
+    /// Index into a TOML array or map. A string index can be used to access a
+    /// value in a map, and a usize index can be used to access an element of an
+    /// array.
+    ///
+    /// Returns `None` if the type of `self` does not match the type of the
+    /// index, for example if the index is a string and `self` is an array or a
+    /// number. Also returns `None` if the given key does not exist in the map
+    /// or the given index is not within the bounds of the array.
+    pub fn get<I: Index>(&self, index: I) -> Option<&Value> {
+        index.index(self)
+    }
+
+    /// Mutably index into a TOML array or map. A string index can be used to
+    /// access a value in a map, and a usize index can be used to access an
+    /// element of an array.
+    ///
+    /// Returns `None` if the type of `self` does not match the type of the
+    /// index, for example if the index is a string and `self` is an array or a
+    /// number. Also returns `None` if the given key does not exist in the map
+    /// or the given index is not within the bounds of the array.
+    pub fn get_mut<I: Index>(&mut self, index: I) -> Option<&mut Value> {
+        index.index_mut(self)
+    }
+
+    /// Extracts the integer value if it is an integer.
+    pub fn as_integer(&self) -> Option<i64> {
+        match *self {
+            Value::Integer(i) => Some(i),
+            _ => None,
+        }
+    }
+
+    /// Tests whether this value is an integer.
+    pub fn is_integer(&self) -> bool {
+        self.as_integer().is_some()
+    }
+
+    /// Extracts the float value if it is a float.
+    pub fn as_float(&self) -> Option<f64> {
+        match *self {
+            Value::Float(f) => Some(f),
+            _ => None,
+        }
+    }
+
+    /// Tests whether this value is a float.
+    pub fn is_float(&self) -> bool {
+        self.as_float().is_some()
+    }
+
+    /// Extracts the boolean value if it is a boolean.
+    pub fn as_bool(&self) -> Option<bool> {
+        match *self {
+            Value::Boolean(b) => Some(b),
+            _ => None,
+        }
+    }
+
+    /// Tests whether this value is a boolean.
+    pub fn is_bool(&self) -> bool {
+        self.as_bool().is_some()
+    }
+
+    /// Extracts the string of this value if it is a string.
+    pub fn as_str(&self) -> Option<&str> {
+        match *self {
+            Value::String(ref s) => Some(&**s),
+            _ => None,
+        }
+    }
+
+    /// Tests if this value is a string.
+    pub fn is_str(&self) -> bool {
+        self.as_str().is_some()
+    }
+
+    /// Extracts the datetime value if it is a datetime.
+    ///
+    /// Note that a parsed TOML value will only contain ISO 8601 dates. An
+    /// example date is:
+    ///
+    /// ```notrust
+    /// 1979-05-27T07:32:00Z
+    /// ```
+    pub fn as_datetime(&self) -> Option<&Datetime> {
+        match *self {
+            Value::Datetime(ref s) => Some(s),
+            _ => None,
+        }
+    }
+
+    /// Tests whether this value is a datetime.
+    pub fn is_datetime(&self) -> bool {
+        self.as_datetime().is_some()
+    }
+
+    /// Extracts the array value if it is an array.
+    pub fn as_array(&self) -> Option<&Vec<Value>> {
+        match *self {
+            Value::Array(ref s) => Some(s),
+            _ => None,
+        }
+    }
+
+    /// Extracts the array value if it is an array.
+    pub fn as_array_mut(&mut self) -> Option<&mut Vec<Value>> {
+        match *self {
+            Value::Array(ref mut s) => Some(s),
+            _ => None,
+        }
+    }
+
+    /// Tests whether this value is an array.
+    pub fn is_array(&self) -> bool {
+        self.as_array().is_some()
+    }
+
+    /// Extracts the table value if it is a table.
+    pub fn as_table(&self) -> Option<&Table> {
+        match *self {
+            Value::Table(ref s) => Some(s),
+            _ => None,
+        }
+    }
+
+    /// Extracts the table value if it is a table.
+    pub fn as_table_mut(&mut self) -> Option<&mut Table> {
+        match *self {
+            Value::Table(ref mut s) => Some(s),
+            _ => None,
+        }
+    }
+
+    /// Tests whether this value is a table.
+    pub fn is_table(&self) -> bool {
+        self.as_table().is_some()
+    }
+
+    /// Tests whether this and another value have the same type.
+    pub fn same_type(&self, other: &Value) -> bool {
+        discriminant(self) == discriminant(other)
+    }
+
+    /// Returns a human-readable representation of the type of this value.
+    pub fn type_str(&self) -> &'static str {
+        match *self {
+            Value::String(..) => "string",
+            Value::Integer(..) => "integer",
+            Value::Float(..) => "float",
+            Value::Boolean(..) => "boolean",
+            Value::Datetime(..) => "datetime",
+            Value::Array(..) => "array",
+            Value::Table(..) => "table",
+        }
+    }
+}
+
+impl<I> ops::Index<I> for Value
+where
+    I: Index,
+{
+    type Output = Value;
+
+    fn index(&self, index: I) -> &Value {
+        self.get(index).expect("index not found")
+    }
+}
+
+impl<I> ops::IndexMut<I> for Value
+where
+    I: Index,
+{
+    fn index_mut(&mut self, index: I) -> &mut Value {
+        self.get_mut(index).expect("index not found")
+    }
+}
+
+impl<'a> From<&'a str> for Value {
+    #[inline]
+    fn from(val: &'a str) -> Value {
+        Value::String(val.to_string())
+    }
+}
+
+impl<V: Into<Value>> From<Vec<V>> for Value {
+    fn from(val: Vec<V>) -> Value {
+        Value::Array(val.into_iter().map(|v| v.into()).collect())
+    }
+}
+
+impl<S: Into<String>, V: Into<Value>> From<BTreeMap<S, V>> for Value {
+    fn from(val: BTreeMap<S, V>) -> Value {
+        let table = val.into_iter().map(|(s, v)| (s.into(), v.into())).collect();
+
+        Value::Table(table)
+    }
+}
+
+impl<S: Into<String> + Hash + Eq, V: Into<Value>> From<HashMap<S, V>> for Value {
+    fn from(val: HashMap<S, V>) -> Value {
+        let table = val.into_iter().map(|(s, v)| (s.into(), v.into())).collect();
+
+        Value::Table(table)
+    }
+}
+
+macro_rules! impl_into_value {
+    ($variant:ident : $T:ty) => {
+        impl From<$T> for Value {
+            #[inline]
+            fn from(val: $T) -> Value {
+                Value::$variant(val.into())
+            }
+        }
+    };
+}
+
+impl_into_value!(String: String);
+impl_into_value!(Integer: i64);
+impl_into_value!(Integer: i32);
+impl_into_value!(Integer: i8);
+impl_into_value!(Integer: u8);
+impl_into_value!(Integer: u32);
+impl_into_value!(Float: f64);
+impl_into_value!(Float: f32);
+impl_into_value!(Boolean: bool);
+impl_into_value!(Datetime: Datetime);
+impl_into_value!(Table: Table);
+
+/// Types that can be used to index a `toml::Value`
+///
+/// Currently this is implemented for `usize` to index arrays and `str` to index
+/// tables.
+///
+/// This trait is sealed and not intended for implementation outside of the
+/// `toml` crate.
+pub trait Index: Sealed {
+    #[doc(hidden)]
+    fn index<'a>(&self, val: &'a Value) -> Option<&'a Value>;
+    #[doc(hidden)]
+    fn index_mut<'a>(&self, val: &'a mut Value) -> Option<&'a mut Value>;
+}
+
+/// An implementation detail that should not be implemented, this will change in
+/// the future and break code otherwise.
+#[doc(hidden)]
+pub trait Sealed {}
+impl Sealed for usize {}
+impl Sealed for str {}
+impl Sealed for String {}
+impl<'a, T: Sealed + ?Sized> Sealed for &'a T {}
+
+impl Index for usize {
+    fn index<'a>(&self, val: &'a Value) -> Option<&'a Value> {
+        match *val {
+            Value::Array(ref a) => a.get(*self),
+            _ => None,
+        }
+    }
+
+    fn index_mut<'a>(&self, val: &'a mut Value) -> Option<&'a mut Value> {
+        match *val {
+            Value::Array(ref mut a) => a.get_mut(*self),
+            _ => None,
+        }
+    }
+}
+
+impl Index for str {
+    fn index<'a>(&self, val: &'a Value) -> Option<&'a Value> {
+        match *val {
+            Value::Table(ref a) => a.get(self),
+            _ => None,
+        }
+    }
+
+    fn index_mut<'a>(&self, val: &'a mut Value) -> Option<&'a mut Value> {
+        match *val {
+            Value::Table(ref mut a) => a.get_mut(self),
+            _ => None,
+        }
+    }
+}
+
+impl Index for String {
+    fn index<'a>(&self, val: &'a Value) -> Option<&'a Value> {
+        self[..].index(val)
+    }
+
+    fn index_mut<'a>(&self, val: &'a mut Value) -> Option<&'a mut Value> {
+        self[..].index_mut(val)
+    }
+}
+
+impl<'s, T: ?Sized> Index for &'s T
+where
+    T: Index,
+{
+    fn index<'a>(&self, val: &'a Value) -> Option<&'a Value> {
+        (**self).index(val)
+    }
+
+    fn index_mut<'a>(&self, val: &'a mut Value) -> Option<&'a mut Value> {
+        (**self).index_mut(val)
+    }
+}
+
+impl fmt::Display for Value {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        crate::ser::to_string(self)
+            .expect("Unable to represent value as string")
+            .fmt(f)
+    }
+}
+
+impl FromStr for Value {
+    type Err = crate::de::Error;
+    fn from_str(s: &str) -> Result<Value, Self::Err> {
+        crate::from_str(s)
+    }
+}
+
+impl ser::Serialize for Value {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: ser::Serializer,
+    {
+        use serde::ser::SerializeMap;
+
+        match *self {
+            Value::String(ref s) => serializer.serialize_str(s),
+            Value::Integer(i) => serializer.serialize_i64(i),
+            Value::Float(f) => serializer.serialize_f64(f),
+            Value::Boolean(b) => serializer.serialize_bool(b),
+            Value::Datetime(ref s) => s.serialize(serializer),
+            Value::Array(ref a) => a.serialize(serializer),
+            Value::Table(ref t) => {
+                let mut map = serializer.serialize_map(Some(t.len()))?;
+                // Be sure to visit non-tables first (and also non
+                // array-of-tables) as all keys must be emitted first.
+                for (k, v) in t {
+                    if !v.is_table() && !v.is_array()
+                        || (v
+                            .as_array()
+                            .map(|a| !a.iter().any(|v| v.is_table()))
+                            .unwrap_or(false))
+                    {
+                        map.serialize_entry(k, v)?;
+                    }
+                }
+                for (k, v) in t {
+                    if v.as_array()
+                        .map(|a| a.iter().any(|v| v.is_table()))
+                        .unwrap_or(false)
+                    {
+                        map.serialize_entry(k, v)?;
+                    }
+                }
+                for (k, v) in t {
+                    if v.is_table() {
+                        map.serialize_entry(k, v)?;
+                    }
+                }
+                map.end()
+            }
+        }
+    }
+}
+
+impl<'de> de::Deserialize<'de> for Value {
+    fn deserialize<D>(deserializer: D) -> Result<Value, D::Error>
+    where
+        D: de::Deserializer<'de>,
+    {
+        struct ValueVisitor;
+
+        impl<'de> de::Visitor<'de> for ValueVisitor {
+            type Value = Value;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+                formatter.write_str("any valid TOML value")
+            }
+
+            fn visit_bool<E>(self, value: bool) -> Result<Value, E> {
+                Ok(Value::Boolean(value))
+            }
+
+            fn visit_i64<E>(self, value: i64) -> Result<Value, E> {
+                Ok(Value::Integer(value))
+            }
+
+            fn visit_u64<E: de::Error>(self, value: u64) -> Result<Value, E> {
+                if value <= i64::max_value() as u64 {
+                    Ok(Value::Integer(value as i64))
+                } else {
+                    Err(de::Error::custom("u64 value was too large"))
+                }
+            }
+
+            fn visit_u32<E>(self, value: u32) -> Result<Value, E> {
+                Ok(Value::Integer(value.into()))
+            }
+
+            fn visit_i32<E>(self, value: i32) -> Result<Value, E> {
+                Ok(Value::Integer(value.into()))
+            }
+
+            fn visit_f64<E>(self, value: f64) -> Result<Value, E> {
+                Ok(Value::Float(value))
+            }
+
+            fn visit_str<E>(self, value: &str) -> Result<Value, E> {
+                Ok(Value::String(value.into()))
+            }
+
+            fn visit_string<E>(self, value: String) -> Result<Value, E> {
+                Ok(Value::String(value))
+            }
+
+            fn visit_some<D>(self, deserializer: D) -> Result<Value, D::Error>
+            where
+                D: de::Deserializer<'de>,
+            {
+                de::Deserialize::deserialize(deserializer)
+            }
+
+            fn visit_seq<V>(self, mut visitor: V) -> Result<Value, V::Error>
+            where
+                V: de::SeqAccess<'de>,
+            {
+                let mut vec = Vec::new();
+                while let Some(elem) = visitor.next_element()? {
+                    vec.push(elem);
+                }
+                Ok(Value::Array(vec))
+            }
+
+            fn visit_map<V>(self, mut visitor: V) -> Result<Value, V::Error>
+            where
+                V: de::MapAccess<'de>,
+            {
+                let mut key = String::new();
+                let datetime = visitor.next_key_seed(DatetimeOrTable { key: &mut key })?;
+                match datetime {
+                    Some(true) => {
+                        let date: DatetimeFromString = visitor.next_value()?;
+                        return Ok(Value::Datetime(date.value));
+                    }
+                    None => return Ok(Value::Table(Map::new())),
+                    Some(false) => {}
+                }
+                let mut map = Map::new();
+                map.insert(key, visitor.next_value()?);
+                while let Some(key) = visitor.next_key::<String>()? {
+                    if let Entry::Vacant(vacant) = map.entry(&key) {
+                        vacant.insert(visitor.next_value()?);
+                    } else {
+                        let msg = format!("duplicate key: `{}`", key);
+                        return Err(de::Error::custom(msg));
+                    }
+                }
+                Ok(Value::Table(map))
+            }
+        }
+
+        deserializer.deserialize_any(ValueVisitor)
+    }
+}
+
+impl<'de> de::Deserializer<'de> for Value {
+    type Error = crate::de::Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, crate::de::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self {
+            Value::Boolean(v) => visitor.visit_bool(v),
+            Value::Integer(n) => visitor.visit_i64(n),
+            Value::Float(n) => visitor.visit_f64(n),
+            Value::String(v) => visitor.visit_string(v),
+            Value::Datetime(v) => visitor.visit_string(v.to_string()),
+            Value::Array(v) => {
+                let len = v.len();
+                let mut deserializer = SeqDeserializer::new(v);
+                let seq = visitor.visit_seq(&mut deserializer)?;
+                let remaining = deserializer.iter.len();
+                if remaining == 0 {
+                    Ok(seq)
+                } else {
+                    Err(de::Error::invalid_length(len, &"fewer elements in array"))
+                }
+            }
+            Value::Table(v) => {
+                let len = v.len();
+                let mut deserializer = MapDeserializer::new(v);
+                let map = visitor.visit_map(&mut deserializer)?;
+                let remaining = deserializer.iter.len();
+                if remaining == 0 {
+                    Ok(map)
+                } else {
+                    Err(de::Error::invalid_length(len, &"fewer elements in map"))
+                }
+            }
+        }
+    }
+
+    #[inline]
+    fn deserialize_enum<V>(
+        self,
+        _name: &str,
+        _variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, crate::de::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self {
+            Value::String(variant) => visitor.visit_enum(variant.into_deserializer()),
+            _ => Err(de::Error::invalid_type(
+                de::Unexpected::UnitVariant,
+                &"string only",
+            )),
+        }
+    }
+
+    // `None` is interpreted as a missing field so be sure to implement `Some`
+    // as a present field.
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, crate::de::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_some(self)
+    }
+
+    fn deserialize_newtype_struct<V>(
+        self,
+        _name: &'static str,
+        visitor: V,
+    ) -> Result<V::Value, crate::de::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_newtype_struct(self)
+    }
+
+    serde::forward_to_deserialize_any! {
+        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit seq
+        bytes byte_buf map unit_struct tuple_struct struct
+        tuple ignored_any identifier
+    }
+}
+
+struct SeqDeserializer {
+    iter: vec::IntoIter<Value>,
+}
+
+impl SeqDeserializer {
+    fn new(vec: Vec<Value>) -> Self {
+        SeqDeserializer {
+            iter: vec.into_iter(),
+        }
+    }
+}
+
+impl<'de> de::SeqAccess<'de> for SeqDeserializer {
+    type Error = crate::de::Error;
+
+    fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, crate::de::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        match self.iter.next() {
+            Some(value) => seed.deserialize(value).map(Some),
+            None => Ok(None),
+        }
+    }
+
+    fn size_hint(&self) -> Option<usize> {
+        match self.iter.size_hint() {
+            (lower, Some(upper)) if lower == upper => Some(upper),
+            _ => None,
+        }
+    }
+}
+
+struct MapDeserializer {
+    iter: <Map<String, Value> as IntoIterator>::IntoIter,
+    value: Option<(String, Value)>,
+}
+
+impl MapDeserializer {
+    fn new(map: Map<String, Value>) -> Self {
+        MapDeserializer {
+            iter: map.into_iter(),
+            value: None,
+        }
+    }
+}
+
+impl<'de> de::MapAccess<'de> for MapDeserializer {
+    type Error = crate::de::Error;
+
+    fn next_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, crate::de::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        match self.iter.next() {
+            Some((key, value)) => {
+                self.value = Some((key.clone(), value));
+                seed.deserialize(Value::String(key)).map(Some)
+            }
+            None => Ok(None),
+        }
+    }
+
+    fn next_value_seed<T>(&mut self, seed: T) -> Result<T::Value, crate::de::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        let (key, res) = match self.value.take() {
+            Some((key, value)) => (key, seed.deserialize(value)),
+            None => return Err(de::Error::custom("value is missing")),
+        };
+        res.map_err(|mut error| {
+            error.add_key_context(&key);
+            error
+        })
+    }
+
+    fn size_hint(&self) -> Option<usize> {
+        match self.iter.size_hint() {
+            (lower, Some(upper)) if lower == upper => Some(upper),
+            _ => None,
+        }
+    }
+}
+
+impl<'de> de::IntoDeserializer<'de, crate::de::Error> for Value {
+    type Deserializer = Self;
+
+    fn into_deserializer(self) -> Self {
+        self
+    }
+}
+
+struct Serializer;
+
+impl ser::Serializer for Serializer {
+    type Ok = Value;
+    type Error = crate::ser::Error;
+
+    type SerializeSeq = SerializeVec;
+    type SerializeTuple = SerializeVec;
+    type SerializeTupleStruct = SerializeVec;
+    type SerializeTupleVariant = SerializeVec;
+    type SerializeMap = SerializeMap;
+    type SerializeStruct = SerializeMap;
+    type SerializeStructVariant = ser::Impossible<Value, crate::ser::Error>;
+
+    fn serialize_bool(self, value: bool) -> Result<Value, crate::ser::Error> {
+        Ok(Value::Boolean(value))
+    }
+
+    fn serialize_i8(self, value: i8) -> Result<Value, crate::ser::Error> {
+        self.serialize_i64(value.into())
+    }
+
+    fn serialize_i16(self, value: i16) -> Result<Value, crate::ser::Error> {
+        self.serialize_i64(value.into())
+    }
+
+    fn serialize_i32(self, value: i32) -> Result<Value, crate::ser::Error> {
+        self.serialize_i64(value.into())
+    }
+
+    fn serialize_i64(self, value: i64) -> Result<Value, crate::ser::Error> {
+        Ok(Value::Integer(value))
+    }
+
+    fn serialize_u8(self, value: u8) -> Result<Value, crate::ser::Error> {
+        self.serialize_i64(value.into())
+    }
+
+    fn serialize_u16(self, value: u16) -> Result<Value, crate::ser::Error> {
+        self.serialize_i64(value.into())
+    }
+
+    fn serialize_u32(self, value: u32) -> Result<Value, crate::ser::Error> {
+        self.serialize_i64(value.into())
+    }
+
+    fn serialize_u64(self, value: u64) -> Result<Value, crate::ser::Error> {
+        if value <= i64::max_value() as u64 {
+            self.serialize_i64(value as i64)
+        } else {
+            Err(ser::Error::custom("u64 value was too large"))
+        }
+    }
+
+    fn serialize_f32(self, value: f32) -> Result<Value, crate::ser::Error> {
+        self.serialize_f64(value.into())
+    }
+
+    fn serialize_f64(self, value: f64) -> Result<Value, crate::ser::Error> {
+        Ok(Value::Float(value))
+    }
+
+    fn serialize_char(self, value: char) -> Result<Value, crate::ser::Error> {
+        let mut s = String::new();
+        s.push(value);
+        self.serialize_str(&s)
+    }
+
+    fn serialize_str(self, value: &str) -> Result<Value, crate::ser::Error> {
+        Ok(Value::String(value.to_owned()))
+    }
+
+    fn serialize_bytes(self, value: &[u8]) -> Result<Value, crate::ser::Error> {
+        let vec = value.iter().map(|&b| Value::Integer(b.into())).collect();
+        Ok(Value::Array(vec))
+    }
+
+    fn serialize_unit(self) -> Result<Value, crate::ser::Error> {
+        Err(crate::ser::Error::UnsupportedType)
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<Value, crate::ser::Error> {
+        Err(crate::ser::Error::UnsupportedType)
+    }
+
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+    ) -> Result<Value, crate::ser::Error> {
+        self.serialize_str(_variant)
+    }
+
+    fn serialize_newtype_struct<T: ?Sized>(
+        self,
+        _name: &'static str,
+        value: &T,
+    ) -> Result<Value, crate::ser::Error>
+    where
+        T: ser::Serialize,
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_newtype_variant<T: ?Sized>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _value: &T,
+    ) -> Result<Value, crate::ser::Error>
+    where
+        T: ser::Serialize,
+    {
+        Err(crate::ser::Error::UnsupportedType)
+    }
+
+    fn serialize_none(self) -> Result<Value, crate::ser::Error> {
+        Err(crate::ser::Error::UnsupportedNone)
+    }
+
+    fn serialize_some<T: ?Sized>(self, value: &T) -> Result<Value, crate::ser::Error>
+    where
+        T: ser::Serialize,
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_seq(self, len: Option<usize>) -> Result<Self::SerializeSeq, crate::ser::Error> {
+        Ok(SerializeVec {
+            vec: Vec::with_capacity(len.unwrap_or(0)),
+        })
+    }
+
+    fn serialize_tuple(self, len: usize) -> Result<Self::SerializeTuple, crate::ser::Error> {
+        self.serialize_seq(Some(len))
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeTupleStruct, crate::ser::Error> {
+        self.serialize_seq(Some(len))
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeTupleVariant, crate::ser::Error> {
+        self.serialize_seq(Some(len))
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap, crate::ser::Error> {
+        Ok(SerializeMap {
+            map: Map::new(),
+            next_key: None,
+        })
+    }
+
+    fn serialize_struct(
+        self,
+        _name: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeStruct, crate::ser::Error> {
+        self.serialize_map(Some(len))
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant, crate::ser::Error> {
+        Err(crate::ser::Error::UnsupportedType)
+    }
+}
+
+struct SerializeVec {
+    vec: Vec<Value>,
+}
+
+struct SerializeMap {
+    map: Map<String, Value>,
+    next_key: Option<String>,
+}
+
+impl ser::SerializeSeq for SerializeVec {
+    type Ok = Value;
+    type Error = crate::ser::Error;
+
+    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), crate::ser::Error>
+    where
+        T: ser::Serialize,
+    {
+        self.vec.push(Value::try_from(value)?);
+        Ok(())
+    }
+
+    fn end(self) -> Result<Value, crate::ser::Error> {
+        Ok(Value::Array(self.vec))
+    }
+}
+
+impl ser::SerializeTuple for SerializeVec {
+    type Ok = Value;
+    type Error = crate::ser::Error;
+
+    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), crate::ser::Error>
+    where
+        T: ser::Serialize,
+    {
+        ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    fn end(self) -> Result<Value, crate::ser::Error> {
+        ser::SerializeSeq::end(self)
+    }
+}
+
+impl ser::SerializeTupleStruct for SerializeVec {
+    type Ok = Value;
+    type Error = crate::ser::Error;
+
+    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), crate::ser::Error>
+    where
+        T: ser::Serialize,
+    {
+        ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    fn end(self) -> Result<Value, crate::ser::Error> {
+        ser::SerializeSeq::end(self)
+    }
+}
+
+impl ser::SerializeTupleVariant for SerializeVec {
+    type Ok = Value;
+    type Error = crate::ser::Error;
+
+    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), crate::ser::Error>
+    where
+        T: ser::Serialize,
+    {
+        ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    fn end(self) -> Result<Value, crate::ser::Error> {
+        ser::SerializeSeq::end(self)
+    }
+}
+
+impl ser::SerializeMap for SerializeMap {
+    type Ok = Value;
+    type Error = crate::ser::Error;
+
+    fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), crate::ser::Error>
+    where
+        T: ser::Serialize,
+    {
+        match Value::try_from(key)? {
+            Value::String(s) => self.next_key = Some(s),
+            _ => return Err(crate::ser::Error::KeyNotString),
+        };
+        Ok(())
+    }
+
+    fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), crate::ser::Error>
+    where
+        T: ser::Serialize,
+    {
+        let key = self.next_key.take();
+        let key = key.expect("serialize_value called before serialize_key");
+        match Value::try_from(value) {
+            Ok(value) => {
+                self.map.insert(key, value);
+            }
+            Err(crate::ser::Error::UnsupportedNone) => {}
+            Err(e) => return Err(e),
+        }
+        Ok(())
+    }
+
+    fn end(self) -> Result<Value, crate::ser::Error> {
+        Ok(Value::Table(self.map))
+    }
+}
+
+impl ser::SerializeStruct for SerializeMap {
+    type Ok = Value;
+    type Error = crate::ser::Error;
+
+    fn serialize_field<T: ?Sized>(
+        &mut self,
+        key: &'static str,
+        value: &T,
+    ) -> Result<(), crate::ser::Error>
+    where
+        T: ser::Serialize,
+    {
+        ser::SerializeMap::serialize_key(self, key)?;
+        ser::SerializeMap::serialize_value(self, value)
+    }
+
+    fn end(self) -> Result<Value, crate::ser::Error> {
+        ser::SerializeMap::end(self)
+    }
+}
+
+struct DatetimeOrTable<'a> {
+    key: &'a mut String,
+}
+
+impl<'a, 'de> de::DeserializeSeed<'de> for DatetimeOrTable<'a> {
+    type Value = bool;
+
+    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: de::Deserializer<'de>,
+    {
+        deserializer.deserialize_any(self)
+    }
+}
+
+impl<'a, 'de> de::Visitor<'de> for DatetimeOrTable<'a> {
+    type Value = bool;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        formatter.write_str("a string key")
+    }
+
+    fn visit_str<E>(self, s: &str) -> Result<bool, E>
+    where
+        E: de::Error,
+    {
+        if s == datetime::FIELD {
+            Ok(true)
+        } else {
+            self.key.push_str(s);
+            Ok(false)
+        }
+    }
+
+    fn visit_string<E>(self, s: String) -> Result<bool, E>
+    where
+        E: de::Error,
+    {
+        if s == datetime::FIELD {
+            Ok(true)
+        } else {
+            *self.key = s;
+            Ok(false)
+        }
+    }
+}
-- 
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