Modularize rustc-serialize support

* Add rustc-serialize as a default feature
* Make room for for serde support

.travis.yml

@@ -2,7 +2,9 @@ language: rust
 sudo: false
 script:
   - cargo build --verbose
+  - cargo build --verbose --no-default-features
   - cargo test --verbose
+  - cargo test --verbose --no-default-features
   - rustdoc --test README.md -L target
   - cargo doc --no-deps
 after_success: |

Cargo.toml

@@ -16,4 +16,10 @@ facilitate deserializing and serializing Rust structures.
 """
 
 [dependencies]
-rustc-serialize = "0.3.0"
+rustc-serialize = { optional = true, version = "0.3.0" }
+
+[features]
+default = ["rustc-serialize"]
+
+[dev-dependencies]
+rustc-serialize = "0.3"

src/decoder/mod.rs

@@ -0,0 +1,205 @@
+use std::error;
+use std::fmt;
+
+use Value;
+use self::DecodeErrorKind::*;
+
+#[cfg(feature = "rustc-serialize")] mod rustc_serialize;
+
+/// A structure to transform TOML values into Rust values.
+///
+/// This decoder implements the serialization `Decoder` interface, allowing
+/// `Decodable` types to be generated by this decoder. The input is any
+/// arbitrary TOML value.
+pub struct Decoder {
+    /// The TOML value left over after decoding. This can be used to inspect
+    /// whether fields were decoded or not.
+    pub toml: Option<Value>,
+    cur_field: Option<String>,
+}
+
+/// Description for errors which can occur while decoding a type.
+#[derive(PartialEq, Debug)]
+pub struct DecodeError {
+    /// Field that this error applies to.
+    pub field: Option<String>,
+    /// The type of error which occurred while decoding,
+    pub kind: DecodeErrorKind,
+}
+
+/// Enumeration of possible errors which can occur while decoding a structure.
+#[derive(PartialEq, Debug)]
+pub enum DecodeErrorKind {
+    /// An error flagged by the application, e.g. value out of range
+    ApplicationError(String),
+    /// A field was expected, but none was found.
+    ExpectedField(/* type */ Option<&'static str>),
+    /// A field was found, but it had the wrong type.
+    ExpectedType(/* expected */ &'static str, /* found */ &'static str),
+    /// The nth map key was expected, but none was found.
+    ExpectedMapKey(usize),
+    /// The nth map element was expected, but none was found.
+    ExpectedMapElement(usize),
+    /// An enum decoding was requested, but no variants were supplied
+    NoEnumVariants,
+    /// The unit type was being decoded, but a non-zero length string was found
+    NilTooLong,
+    /// There was an error with the syntactical structure of the TOML.
+    SyntaxError,
+    /// The end of the TOML input was reached too soon
+    EndOfStream,
+}
+
+/// Decodes a TOML value into a decodable type.
+///
+/// This function will consume the given TOML value and attempt to decode it
+/// into the type specified. If decoding fails, `None` will be returned. If a
+/// finer-grained error is desired, then it is recommended to use `Decodable`
+/// directly.
+#[cfg(feature = "rustc-serialize")]
+pub fn decode<T: ::rustc_serialize::Decodable>(toml: Value) -> Option<T> {
+    ::rustc_serialize::Decodable::decode(&mut Decoder::new(toml)).ok()
+}
+
+/// Decodes a TOML value into a decodable type.
+///
+/// This function will consume the given TOML value and attempt to decode it
+/// into the type specified. If decoding fails, `None` will be returned. If a
+/// finer-grained error is desired, then it is recommended to use `Decodable`
+/// directly.
+#[cfg(all(not(feature = "rustc-serialize"), feature = "serde"))]
+pub fn decode<T: ::serde::Deserialize>(toml: Value) -> Option<T> {
+    ::serde::Deserialize::deserialize(&mut Decoder::new(toml)).ok()
+}
+
+/// Decodes a string into a toml-encoded value.
+///
+/// This function will parse the given string into a TOML value, and then parse
+/// the TOML value into the desired type. If any error occurs `None` is return.
+///
+/// If more fine-grained errors are desired, these steps should be driven
+/// manually.
+#[cfg(feature = "rustc-serialize")]
+pub fn decode_str<T: ::rustc_serialize::Decodable>(s: &str) -> Option<T> {
+    ::Parser::new(s).parse().and_then(|t| decode(Value::Table(t)))
+}
+
+/// Decodes a string into a toml-encoded value.
+///
+/// This function will parse the given string into a TOML value, and then parse
+/// the TOML value into the desired type. If any error occurs `None` is return.
+///
+/// If more fine-grained errors are desired, these steps should be driven
+/// manually.
+#[cfg(all(not(feature = "rustc-serialize"), feature = "serde"))]
+pub fn decode_str<T: ::serde::Deserialize>(s: &str) -> Option<T> {
+    ::Parser::new(s).parse().and_then(|t| decode(Value::Table(t)))
+}
+
+impl Decoder {
+    /// Creates a new decoder, consuming the TOML value to decode.
+    ///
+    /// This decoder can be passed to the `Decodable` methods or driven
+    /// manually.
+    pub fn new(toml: Value) -> Decoder {
+        Decoder { toml: Some(toml), cur_field: None }
+    }
+
+    fn sub_decoder(&self, toml: Option<Value>, field: &str) -> Decoder {
+        Decoder {
+            toml: toml,
+            cur_field: if field.len() == 0 {
+                self.cur_field.clone()
+            } else {
+                match self.cur_field {
+                    None => Some(format!("{}", field)),
+                    Some(ref s) => Some(format!("{}.{}", s, field))
+                }
+            }
+        }
+    }
+
+    fn err(&self, kind: DecodeErrorKind) -> DecodeError {
+        DecodeError {
+            field: self.cur_field.clone(),
+            kind: kind,
+        }
+    }
+
+    fn mismatch(&self, expected: &'static str,
+                found: &Option<Value>) -> DecodeError{
+        match *found {
+            Some(ref val) => self.err(ExpectedType(expected, val.type_str())),
+            None => self.err(ExpectedField(Some(expected))),
+        }
+    }
+}
+
+impl fmt::Display for DecodeError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        try!(match self.kind {
+            ApplicationError(ref err) => {
+                write!(f, "{}", err)
+            }
+            ExpectedField(expected_type) => {
+                match expected_type {
+                    Some("table") => write!(f, "expected a section"),
+                    Some(e) => write!(f, "expected a value of type `{}`", e),
+                    None => write!(f, "expected a value"),
+                }
+            }
+            ExpectedType(expected, found) => {
+                fn humanize(s: &str) -> String {
+                    if s == "section" {
+                        format!("a section")
+                    } else {
+                        format!("a value of type `{}`", s)
+                    }
+                }
+                write!(f, "expected {}, but found {}",
+                       humanize(expected),
+                       humanize(found))
+            }
+            ExpectedMapKey(idx) => {
+                write!(f, "expected at least {} keys", idx + 1)
+            }
+            ExpectedMapElement(idx) => {
+                write!(f, "expected at least {} elements", idx + 1)
+            }
+            NoEnumVariants => {
+                write!(f, "expected an enum variant to decode to")
+            }
+            NilTooLong => {
+                write!(f, "expected 0-length string")
+            }
+            SyntaxError => {
+                write!(f, "syntax error")
+            }
+            EndOfStream => {
+                write!(f, "end of stream")
+            }
+        });
+        match self.field {
+            Some(ref s) => {
+                write!(f, " for the key `{}`", s)
+            }
+            None => Ok(())
+        }
+    }
+}
+
+impl error::Error for DecodeError {
+    fn description(&self) -> &str {
+        match self.kind {
+            ApplicationError(ref s) => &**s,
+            ExpectedField(..) => "expected a field",
+            ExpectedType(..) => "expected a type",
+            ExpectedMapKey(..) => "expected a map key",
+            ExpectedMapElement(..) => "expected a map element",
+            NoEnumVariants => "no enum variants to decode to",
+            NilTooLong => "nonzero length string representing nil",
+            SyntaxError => "syntax error",
+            EndOfStream => "end of stream",
+        }
+    }
+}

src/decoder/rustc_serialize.rs

@@ -0,0 +1,311 @@
+use rustc_serialize;
+use std::mem;
+
+use super::{Decoder, DecodeError};
+use super::DecodeErrorKind::*;
+use Value;
+
+impl rustc_serialize::Decoder for Decoder {
+    type Error = DecodeError;
+    fn read_nil(&mut self) -> Result<(), DecodeError> {
+        match self.toml {
+            Some(Value::String(ref s)) if s.len() == 0 => {}
+            Some(Value::String(..)) => return Err(self.err(NilTooLong)),
+            ref found => return Err(self.mismatch("string", found)),
+        }
+        self.toml.take();
+        Ok(())
+    }
+    fn read_usize(&mut self) -> Result<usize, DecodeError> {
+        self.read_i64().map(|i| i as usize)
+    }
+    fn read_u64(&mut self) -> Result<u64, DecodeError> {
+        self.read_i64().map(|i| i as u64)
+    }
+    fn read_u32(&mut self) -> Result<u32, DecodeError> {
+        self.read_i64().map(|i| i as u32)
+    }
+    fn read_u16(&mut self) -> Result<u16, DecodeError> {
+        self.read_i64().map(|i| i as u16)
+    }
+    fn read_u8(&mut self) -> Result<u8, DecodeError> {
+        self.read_i64().map(|i| i as u8)
+    }
+    fn read_isize(&mut self) -> Result<isize, DecodeError> {
+        self.read_i64().map(|i| i as isize)
+    }
+    fn read_i64(&mut self) -> Result<i64, DecodeError> {
+        match self.toml {
+            Some(Value::Integer(i)) => { self.toml.take(); Ok(i) }
+            ref found => Err(self.mismatch("integer", found)),
+        }
+    }
+    fn read_i32(&mut self) -> Result<i32, DecodeError> {
+        self.read_i64().map(|i| i as i32)
+    }
+    fn read_i16(&mut self) -> Result<i16, DecodeError> {
+        self.read_i64().map(|i| i as i16)
+    }
+    fn read_i8(&mut self) -> Result<i8, DecodeError> {
+        self.read_i64().map(|i| i as i8)
+    }
+    fn read_bool(&mut self) -> Result<bool, DecodeError> {
+        match self.toml {
+            Some(Value::Boolean(b)) => { self.toml.take(); Ok(b) }
+            ref found => Err(self.mismatch("bool", found)),
+        }
+    }
+    fn read_f64(&mut self) -> Result<f64, DecodeError> {
+        match self.toml {
+            Some(Value::Float(f)) => Ok(f),
+            ref found => Err(self.mismatch("float", found)),
+        }
+    }
+    fn read_f32(&mut self) -> Result<f32, DecodeError> {
+        self.read_f64().map(|f| f as f32)
+    }
+    fn read_char(&mut self) -> Result<char, DecodeError> {
+        let ch = match self.toml {
+            Some(Value::String(ref s)) if s.chars().count() == 1 =>
+                s.chars().next().unwrap(),
+            ref found => return Err(self.mismatch("string", found)),
+        };
+        self.toml.take();
+        Ok(ch)
+    }
+    fn read_str(&mut self) -> Result<String, DecodeError> {
+        match self.toml.take() {
+            Some(Value::String(s)) => Ok(s),
+            found => {
+                let err = Err(self.mismatch("string", &found));
+                self.toml = found;
+                err
+            }
+        }
+    }
+
+    // Compound types:
+    fn read_enum<T, F>(&mut self, _name: &str, f: F)
+        -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder) -> Result<T, DecodeError>
+    {
+        f(self)
+    }
+
+    fn read_enum_variant<T, F>(&mut self, names: &[&str], mut f: F)
+        -> Result<T, DecodeError>
+        where F: FnMut(&mut Decoder, usize) -> Result<T, DecodeError>
+    {
+        let mut first_error = None;
+        for i in 0..names.len() {
+            let mut d = self.sub_decoder(self.toml.clone(), "");
+            match f(&mut d, i) {
+                Ok(t) => { self.toml = d.toml; return Ok(t) }
+                Err(e) => {
+                    if first_error.is_none() {
+                        first_error = Some(e);
+                    }
+                }
+            }
+        }
+        Err(first_error.unwrap_or_else(|| self.err(NoEnumVariants)))
+    }
+    fn read_enum_variant_arg<T, F>(&mut self, _a_idx: usize, f: F)
+        -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder) -> Result<T, DecodeError>
+    {
+        f(self)
+    }
+
+    fn read_enum_struct_variant<T, F>(&mut self, _names: &[&str], _f: F)
+        -> Result<T, DecodeError>
+        where F: FnMut(&mut Decoder, usize) -> Result<T, DecodeError>
+    {
+        panic!()
+    }
+    fn read_enum_struct_variant_field<T, F>(&mut self,
+                                            _f_name: &str,
+                                            _f_idx: usize,
+                                            _f: F)
+        -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder) -> Result<T, DecodeError>
+    {
+        panic!()
+    }
+
+    fn read_struct<T, F>(&mut self, _s_name: &str, _len: usize, f: F)
+        -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder) -> Result<T, DecodeError>
+    {
+        match self.toml {
+            Some(Value::Table(..)) => {
+                let ret = try!(f(self));
+                match self.toml {
+                    Some(Value::Table(ref t)) if t.len() == 0 => {}
+                    _ => return Ok(ret)
+                }
+                self.toml.take();
+                Ok(ret)
+            }
+            ref found => Err(self.mismatch("table", found)),
+        }
+    }
+    fn read_struct_field<T, F>(&mut self, f_name: &str, _f_idx: usize, f: F)
+        -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder) -> Result<T, DecodeError>
+    {
+        let field = format!("{}", f_name);
+        let toml = match self.toml {
+            Some(Value::Table(ref mut table)) => {
+                table.remove(&field)
+                    .or_else(|| table.remove(&f_name.replace("_", "-")))
+            },
+            ref found => return Err(self.mismatch("table", found)),
+        };
+        let mut d = self.sub_decoder(toml, f_name);
+        let ret = try!(f(&mut d));
+        if let Some(value) = d.toml {
+            if let Some(Value::Table(ref mut table)) = self.toml {
+                table.insert(field, value);
+            }
+        }
+        Ok(ret)
+    }
+
+    fn read_tuple<T, F>(&mut self, tuple_len: usize, f: F)
+        -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder) -> Result<T, DecodeError>
+    {
+        self.read_seq(move |d, len| {
+            assert!(len == tuple_len,
+                    "expected tuple of length `{}`, found tuple \
+                         of length `{}`", tuple_len, len);
+            f(d)
+        })
+    }
+    fn read_tuple_arg<T, F>(&mut self, a_idx: usize, f: F)
+        -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder) -> Result<T, DecodeError>
+    {
+        self.read_seq_elt(a_idx, f)
+    }
+
+    fn read_tuple_struct<T, F>(&mut self, _s_name: &str, _len: usize, _f: F)
+        -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder) -> Result<T, DecodeError>
+    {
+        panic!()
+    }
+    fn read_tuple_struct_arg<T, F>(&mut self, _a_idx: usize, _f: F)
+        -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder) -> Result<T, DecodeError>
+    {
+        panic!()
+    }
+
+    // Specialized types:
+    fn read_option<T, F>(&mut self, mut f: F)
+        -> Result<T, DecodeError>
+        where F: FnMut(&mut Decoder, bool) -> Result<T, DecodeError>
+    {
+        match self.toml {
+            Some(..) => f(self, true),
+            None => f(self, false),
+        }
+    }
+
+    fn read_seq<T, F>(&mut self, f: F) -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder, usize) -> Result<T, DecodeError>
+    {
+        let len = match self.toml {
+            Some(Value::Array(ref arr)) => arr.len(),
+            None => 0,
+            ref found => return Err(self.mismatch("array", found)),
+        };
+        let ret = try!(f(self, len));
+        match self.toml {
+            Some(Value::Array(ref mut arr)) => {
+                arr.retain(|slot| slot.as_integer() != Some(0));
+                if arr.len() != 0 { return Ok(ret) }
+            }
+            _ => return Ok(ret)
+        }
+        self.toml.take();
+        Ok(ret)
+    }
+    fn read_seq_elt<T, F>(&mut self, idx: usize, f: F)
+        -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder) -> Result<T, DecodeError>
+    {
+        let toml = match self.toml {
+            Some(Value::Array(ref mut arr)) => {
+                mem::replace(&mut arr[idx], Value::Integer(0))
+            }
+            ref found => return Err(self.mismatch("array", found)),
+        };
+        let mut d = self.sub_decoder(Some(toml), "");
+        let ret = try!(f(&mut d));
+        match d.toml {
+            Some(toml) => match self.toml {
+                Some(Value::Array(ref mut arr)) => arr[idx] = toml,
+                _ => {}
+            },
+            _ => {}
+        }
+        Ok(ret)
+    }
+
+    fn read_map<T, F>(&mut self, f: F)
+        -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder, usize) -> Result<T, DecodeError>
+    {
+        let len = match self.toml {
+            Some(Value::Table(ref table)) => table.len(),
+            ref found => return Err(self.mismatch("table", found)),
+        };
+        let ret = try!(f(self, len));
+        self.toml.take();
+        Ok(ret)
+    }
+    fn read_map_elt_key<T, F>(&mut self, idx: usize, f: F)
+        -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder) -> Result<T, DecodeError>
+    {
+        match self.toml {
+            Some(Value::Table(ref table)) => {
+                match table.iter().skip(idx).next() {
+                    Some((key, _)) => {
+                        let val = Value::String(format!("{}", key));
+                        f(&mut self.sub_decoder(Some(val), &**key))
+                    }
+                    None => Err(self.err(ExpectedMapKey(idx))),
+                }
+            }
+            ref found => Err(self.mismatch("table", found)),
+        }
+    }
+    fn read_map_elt_val<T, F>(&mut self, idx: usize, f: F)
+        -> Result<T, DecodeError>
+        where F: FnOnce(&mut Decoder) -> Result<T, DecodeError>
+    {
+        match self.toml {
+            Some(Value::Table(ref table)) => {
+                match table.iter().skip(idx).next() {
+                    Some((_, value)) => {
+                        // XXX: this shouldn't clone
+                        f(&mut self.sub_decoder(Some(value.clone()), ""))
+                    }
+                    None => Err(self.err(ExpectedMapElement(idx))),
+                }
+            }
+            ref found => Err(self.mismatch("table", found)),
+        }
+    }
+
+    fn error(&mut self, err: &str) -> DecodeError {
+        DecodeError {
+            field: self.cur_field.clone(),
+            kind: ApplicationError(format!("{}", err))
+        }
+    }
+}

src/encoder/mod.rs

@@ -0,0 +1,210 @@
+use std::collections::BTreeMap;
+use std::error;
+use std::fmt;
+use std::mem;
+
+use {Value, Table};
+
+#[cfg(feature = "rustc-serialize")] mod rustc_serialize;
+
+/// A structure to transform Rust values into TOML values.
+///
+/// This encoder implements the serialization `Encoder` interface, allowing
+/// `Encodable` rust types to be fed into the encoder. The output of this
+/// encoder is a TOML `Table` structure. The resulting TOML can be stringified
+/// if necessary.
+///
+/// # Example
+///
+/// ```
+/// extern crate rustc_serialize;
+/// extern crate toml;
+///
+/// # fn main() {
+/// use toml::{Encoder, Value};
+/// use rustc_serialize::Encodable;
+///
+/// #[derive(RustcEncodable)]
+/// struct MyStruct { foo: isize, bar: String }
+/// let my_struct = MyStruct { foo: 4, bar: "hello!".to_string() };
+///
+/// let mut e = Encoder::new();
+/// my_struct.encode(&mut e).unwrap();
+///
+/// assert_eq!(e.toml.get(&"foo".to_string()), Some(&Value::Integer(4)))
+/// # }
+/// ```
+pub struct Encoder {
+    /// Output TOML that is emitted. The current version of this encoder forces
+    /// the top-level representation of a structure to be a table.
+    ///
+    /// This field can be used to extract the return value after feeding a value
+    /// into this `Encoder`.
+    pub toml: Table,
+    state: State,
+}
+
+/// Enumeration of errors which can occur while encoding a rust value into a
+/// TOML value.
+#[allow(missing_copy_implementations)]
+#[derive(Debug)]
+pub enum Error {
+    /// Indication that a key was needed when a value was emitted, but no key
+    /// was previously emitted.
+    NeedsKey,
+    /// Indication that a key was emitted, but not value was emitted.
+    NoValue,
+    /// Indicates that a map key was attempted to be emitted at an invalid
+    /// location.
+    InvalidMapKeyLocation,
+    /// Indicates that a type other than a string was attempted to be used as a
+    /// map key type.
+    InvalidMapKeyType,
+}
+
+#[derive(PartialEq)]
+enum State {
+    Start,
+    NextKey(String),
+    NextArray(Vec<Value>),
+    NextMapKey,
+}
+
+impl Encoder {
+    /// Constructs a new encoder which will emit to the given output stream.
+    pub fn new() -> Encoder {
+        Encoder { state: State::Start, toml: BTreeMap::new() }
+    }
+
+    fn emit_value(&mut self, v: Value) -> Result<(), Error> {
+        match mem::replace(&mut self.state, State::Start) {
+            State::NextKey(key) => { self.toml.insert(key, v); Ok(()) }
+            State::NextArray(mut vec) => {
+                // TODO: validate types
+                vec.push(v);
+                self.state = State::NextArray(vec);
+                Ok(())
+            }
+            State::NextMapKey => {
+                match v {
+                    Value::String(s) => { self.state = State::NextKey(s); Ok(()) }
+                    _ => Err(Error::InvalidMapKeyType)
+                }
+            }
+            _ => Err(Error::NeedsKey)
+        }
+    }
+
+    fn emit_none(&mut self) -> Result<(), Error> {
+        match mem::replace(&mut self.state, State::Start) {
+            State::Start => unreachable!(),
+            State::NextKey(_) => Ok(()),
+            State::NextArray(..) => panic!("how to encode None in an array?"),
+            State::NextMapKey => Err(Error::InvalidMapKeyLocation),
+        }
+    }
+
+    fn seq<F>(&mut self, f: F) -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        let old = mem::replace(&mut self.state, State::NextArray(Vec::new()));
+        try!(f(self));
+        match mem::replace(&mut self.state, old) {
+            State::NextArray(v) => self.emit_value(Value::Array(v)),
+            _ => unreachable!(),
+        }
+    }
+
+    fn table<F>(&mut self, f: F) -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        match mem::replace(&mut self.state, State::Start) {
+            State::NextKey(key) => {
+                let mut nested = Encoder::new();
+                try!(f(&mut nested));
+                self.toml.insert(key, Value::Table(nested.toml));
+                Ok(())
+            }
+            State::NextArray(mut arr) => {
+                let mut nested = Encoder::new();
+                try!(f(&mut nested));
+                arr.push(Value::Table(nested.toml));
+                self.state = State::NextArray(arr);
+                Ok(())
+            }
+            State::Start => f(self),
+            State::NextMapKey => Err(Error::InvalidMapKeyLocation),
+        }
+    }
+
+    fn table_key<F>(&mut self, f: F) -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        match mem::replace(&mut self.state, State::NextMapKey) {
+            State::Start => {}
+            _ => return Err(Error::InvalidMapKeyLocation),
+        }
+        try!(f(self));
+        match self.state {
+            State::NextKey(_) => Ok(()),
+            _ => Err(Error::InvalidMapKeyLocation),
+        }
+    }
+}
+
+/// Encodes an encodable value into a TOML value.
+///
+/// This function expects the type given to represent a TOML table in some form.
+/// If encoding encounters an error, then this function will fail the task.
+#[cfg(feature = "rustc-serialize")]
+pub fn encode<T: ::rustc_serialize::Encodable>(t: &T) -> Value {
+    let mut e = Encoder::new();
+    t.encode(&mut e).unwrap();
+    Value::Table(e.toml)
+}
+
+/// Encodes an encodable value into a TOML value.
+///
+/// This function expects the type given to represent a TOML table in some form.
+/// If encoding encounters an error, then this function will fail the task.
+#[cfg(all(not(feature = "rustc-serialize"), feature = "serde"))]
+pub fn encode<T: ::serde::Serialize>(t: &T) -> Value {
+    let mut e = Encoder::new();
+    t.deserialize(&mut e).unwrap();
+    Value::Table(e.toml)
+}
+
+/// Encodes an encodable value into a TOML string.
+///
+/// This function expects the type given to represent a TOML table in some form.
+/// If encoding encounters an error, then this function will fail the task.
+#[cfg(feature = "rustc-serialize")]
+pub fn encode_str<T: ::rustc_serialize::Encodable>(t: &T) -> String {
+    encode(t).to_string()
+}
+
+/// Encodes an encodable value into a TOML string.
+///
+/// This function expects the type given to represent a TOML table in some form.
+/// If encoding encounters an error, then this function will fail the task.
+#[cfg(all(not(feature = "rustc-serialize"), feature = "serde"))]
+pub fn encode_str<T: ::serde::Serialize>(t: &T) -> String {
+    encode(t).to_string()
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            Error::NeedsKey => write!(f, "need a key to encode"),
+            Error::NoValue => write!(f, "not value to emit for a previous key"),
+            Error::InvalidMapKeyLocation => write!(f, "a map cannot be emitted \
+                                                       at this location"),
+            Error::InvalidMapKeyType => write!(f, "only strings can be used as \
+                                                   key types"),
+        }
+    }
+}
+
+impl error::Error for Error {
+    fn description(&self) -> &str { "TOML encoding error" }
+}

src/encoder/rustc_serialize.rs

@@ -0,0 +1,689 @@
+use std::mem;
+
+use rustc_serialize;
+use Value;
+use super::{Encoder, Error, State};
+use super::Error::*;
+
+impl rustc_serialize::Encoder for Encoder {
+    type Error = Error;
+
+    fn emit_nil(&mut self) -> Result<(), Error> { Ok(()) }
+    fn emit_usize(&mut self, v: usize) -> Result<(), Error> {
+        self.emit_i64(v as i64)
+    }
+    fn emit_u8(&mut self, v: u8) -> Result<(), Error> {
+        self.emit_i64(v as i64)
+    }
+    fn emit_u16(&mut self, v: u16) -> Result<(), Error> {
+        self.emit_i64(v as i64)
+    }
+    fn emit_u32(&mut self, v: u32) -> Result<(), Error> {
+        self.emit_i64(v as i64)
+    }
+    fn emit_u64(&mut self, v: u64) -> Result<(), Error> {
+        self.emit_i64(v as i64)
+    }
+    fn emit_isize(&mut self, v: isize) -> Result<(), Error> {
+        self.emit_i64(v as i64)
+    }
+    fn emit_i8(&mut self, v: i8) -> Result<(), Error> {
+        self.emit_i64(v as i64)
+    }
+    fn emit_i16(&mut self, v: i16) -> Result<(), Error> {
+        self.emit_i64(v as i64)
+    }
+    fn emit_i32(&mut self, v: i32) -> Result<(), Error> {
+        self.emit_i64(v as i64)
+    }
+    fn emit_i64(&mut self, v: i64) -> Result<(), Error> {
+        self.emit_value(Value::Integer(v))
+    }
+    fn emit_bool(&mut self, v: bool) -> Result<(), Error> {
+        self.emit_value(Value::Boolean(v))
+    }
+    fn emit_f32(&mut self, v: f32) -> Result<(), Error> { self.emit_f64(v as f64) }
+    fn emit_f64(&mut self, v: f64) -> Result<(), Error> {
+        self.emit_value(Value::Float(v))
+    }
+    fn emit_char(&mut self, v: char) -> Result<(), Error> {
+        self.emit_str(&*format!("{}", v))
+    }
+    fn emit_str(&mut self, v: &str) -> Result<(), Error> {
+        self.emit_value(Value::String(format!("{}", v)))
+    }
+    fn emit_enum<F>(&mut self, _name: &str, f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        f(self)
+    }
+    fn emit_enum_variant<F>(&mut self, _v_name: &str, _v_id: usize,
+                            _len: usize, f: F) -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        f(self)
+    }
+    fn emit_enum_variant_arg<F>(&mut self, _a_idx: usize, f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        f(self)
+    }
+    fn emit_enum_struct_variant<F>(&mut self, _v_name: &str, _v_id: usize,
+                                   _len: usize,
+                                   _f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        panic!()
+    }
+    fn emit_enum_struct_variant_field<F>(&mut self,
+                                         _f_name: &str,
+                                         _f_idx: usize,
+                                         _f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        panic!()
+    }
+    fn emit_struct<F>(&mut self, _name: &str, _len: usize, f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        self.table(f)
+    }
+    fn emit_struct_field<F>(&mut self, f_name: &str, _f_idx: usize, f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        let old = mem::replace(&mut self.state,
+                               State::NextKey(format!("{}", f_name)));
+        try!(f(self));
+        if self.state != State::Start {
+            return Err(NoValue)
+        }
+        self.state = old;
+        Ok(())
+    }
+    fn emit_tuple<F>(&mut self, len: usize, f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        self.emit_seq(len, f)
+    }
+    fn emit_tuple_arg<F>(&mut self, idx: usize, f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        self.emit_seq_elt(idx, f)
+    }
+    fn emit_tuple_struct<F>(&mut self, _name: &str, _len: usize, _f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        unimplemented!()
+    }
+    fn emit_tuple_struct_arg<F>(&mut self, _f_idx: usize, _f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        unimplemented!()
+    }
+    fn emit_option<F>(&mut self, f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        f(self)
+    }
+    fn emit_option_none(&mut self) -> Result<(), Error> {
+        self.emit_none()
+    }
+    fn emit_option_some<F>(&mut self, f: F) -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        f(self)
+    }
+    fn emit_seq<F>(&mut self, _len: usize, f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        self.seq(f)
+    }
+    fn emit_seq_elt<F>(&mut self, _idx: usize, f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        f(self)
+    }
+    fn emit_map<F>(&mut self, len: usize, f: F)
+        -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        self.emit_struct("foo", len, f)
+    }
+    fn emit_map_elt_key<F>(&mut self, _idx: usize, f: F) -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        self.table_key(f)
+    }
+    fn emit_map_elt_val<F>(&mut self, _idx: usize, f: F) -> Result<(), Error>
+        where F: FnOnce(&mut Encoder) -> Result<(), Error>
+    {
+        f(self)
+    }
+}
+
+impl rustc_serialize::Encodable for Value {
+    fn encode<E>(&self, e: &mut E) -> Result<(), E::Error>
+        where E: rustc_serialize::Encoder
+    {
+        match *self {
+            Value::String(ref s) => e.emit_str(s),
+            Value::Integer(i) => e.emit_i64(i),
+            Value::Float(f) => e.emit_f64(f),
+            Value::Boolean(b) => e.emit_bool(b),
+            Value::Datetime(ref s) => e.emit_str(s),
+            Value::Array(ref a) => {
+                e.emit_seq(a.len(), |e| {
+                    for item in a {
+                        try!(item.encode(e));
+                    }
+                    Ok(())
+                })
+            }
+            Value::Table(ref t) => {
+                e.emit_map(t.len(), |e| {
+                    for (i, (key, value)) in t.iter().enumerate() {
+                        try!(e.emit_map_elt_key(i, |e| e.emit_str(key)));
+                        try!(e.emit_map_elt_val(i, |e| value.encode(e)));
+                    }
+                    Ok(())
+                })
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::{BTreeMap, HashSet};
+    use rustc_serialize::{self, Encodable, Decodable};
+
+    use {Encoder, Decoder, DecodeError};
+    use Value;
+    use Value::{Table, Integer, Array, Float};
+
+    macro_rules! encode( ($t:expr) => ({
+        let mut e = Encoder::new();
+        $t.encode(&mut e).unwrap();
+        e.toml
+    }) );
+
+    macro_rules! decode( ($t:expr) => ({
+        let mut d = Decoder::new($t);
+        Decodable::decode(&mut d).unwrap()
+    }) );
+
+    macro_rules! map( ($($k:ident, $v:expr),*) => ({
+        let mut _m = BTreeMap::new();
+        $(_m.insert(stringify!($k).to_string(), $v);)*
+        _m
+    }) );
+
+    #[test]
+    fn smoke() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: isize }
+
+        let v = Foo { a: 2 };
+        assert_eq!(encode!(v), map! { a, Integer(2) });
+        assert_eq!(v, decode!(Table(encode!(v))));
+    }
+
+    #[test]
+    fn smoke_hyphen() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a_b: isize }
+
+        let v = Foo { a_b: 2 };
+        assert_eq!(encode!(v), map! { a_b, Integer(2) });
+        assert_eq!(v, decode!(Table(encode!(v))));
+
+        let mut m = BTreeMap::new();
+        m.insert("a-b".to_string(), Integer(2));
+        assert_eq!(v, decode!(Table(encode!(v))));
+    }
+
+    #[test]
+    fn nested() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: isize, b: Bar }
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Bar { a: String }
+
+        let v = Foo { a: 2, b: Bar { a: "test".to_string() } };
+        assert_eq!(encode!(v),
+                   map! {
+                       a, Integer(2),
+                       b, Table(map! {
+                           a, Value::String("test".to_string())
+                       })
+                   });
+        assert_eq!(v, decode!(Table(encode!(v))));
+    }
+
+    #[test]
+    fn application_decode_error() {
+        #[derive(PartialEq, Debug)]
+        struct Range10(usize);
+        impl Decodable for Range10 {
+             fn decode<D: rustc_serialize::Decoder>(d: &mut D) -> Result<Range10, D::Error> {
+                 let x: usize = try!(Decodable::decode(d));
+                 if x > 10 {
+                     Err(d.error("Value out of range!"))
+                 } else {
+                     Ok(Range10(x))
+                 }
+             }
+        }
+        let mut d_good = Decoder::new(Integer(5));
+        let mut d_bad1 = Decoder::new(Value::String("not an isize".to_string()));
+        let mut d_bad2 = Decoder::new(Integer(11));
+
+        assert_eq!(Ok(Range10(5)), Decodable::decode(&mut d_good));
+
+        let err1: Result<Range10, _> = Decodable::decode(&mut d_bad1);
+        assert!(err1.is_err());
+        let err2: Result<Range10, _> = Decodable::decode(&mut d_bad2);
+        assert!(err2.is_err());
+    }
+
+    #[test]
+    fn array() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: Vec<isize> }
+
+        let v = Foo { a: vec![1, 2, 3, 4] };
+        assert_eq!(encode!(v),
+                   map! {
+                       a, Array(vec![
+                            Integer(1),
+                            Integer(2),
+                            Integer(3),
+                            Integer(4)
+                       ])
+                   });
+        assert_eq!(v, decode!(Table(encode!(v))));
+    }
+
+    #[test]
+    fn tuple() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: (isize, isize, isize, isize) }
+
+        let v = Foo { a: (1, 2, 3, 4) };
+        assert_eq!(encode!(v),
+                   map! {
+                       a, Array(vec![
+                            Integer(1),
+                            Integer(2),
+                            Integer(3),
+                            Integer(4)
+                       ])
+                   });
+        assert_eq!(v, decode!(Table(encode!(v))));
+    }
+
+    #[test]
+    fn inner_structs_with_options() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo {
+            a: Option<Box<Foo>>,
+            b: Bar,
+        }
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Bar {
+            a: String,
+            b: f64,
+        }
+
+        let v = Foo {
+            a: Some(Box::new(Foo {
+                a: None,
+                b: Bar { a: "foo".to_string(), b: 4.5 },
+            })),
+            b: Bar { a: "bar".to_string(), b: 1.0 },
+        };
+        assert_eq!(encode!(v),
+                   map! {
+                       a, Table(map! {
+                           b, Table(map! {
+                               a, Value::String("foo".to_string()),
+                               b, Float(4.5)
+                           })
+                       }),
+                       b, Table(map! {
+                           a, Value::String("bar".to_string()),
+                           b, Float(1.0)
+                       })
+                   });
+        assert_eq!(v, decode!(Table(encode!(v))));
+    }
+
+    #[test]
+    fn hashmap() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo {
+            map: BTreeMap<String, isize>,
+            set: HashSet<char>,
+        }
+
+        let v = Foo {
+            map: {
+                let mut m = BTreeMap::new();
+                m.insert("foo".to_string(), 10);
+                m.insert("bar".to_string(), 4);
+                m
+            },
+            set: {
+                let mut s = HashSet::new();
+                s.insert('a');
+                s
+            },
+        };
+        assert_eq!(encode!(v),
+            map! {
+                map, Table(map! {
+                    foo, Integer(10),
+                    bar, Integer(4)
+                }),
+                set, Array(vec![Value::String("a".to_string())])
+            }
+        );
+        assert_eq!(v, decode!(Table(encode!(v))));
+    }
+
+    #[test]
+    fn tuple_struct() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo(isize, String, f64);
+
+        let v = Foo(1, "foo".to_string(), 4.5);
+        assert_eq!(
+            encode!(v),
+            map! {
+                _field0, Integer(1),
+                _field1, Value::String("foo".to_string()),
+                _field2, Float(4.5)
+            }
+        );
+        assert_eq!(v, decode!(Table(encode!(v))));
+    }
+
+    #[test]
+    fn table_array() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: Vec<Bar>, }
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Bar { a: isize }
+
+        let v = Foo { a: vec![Bar { a: 1 }, Bar { a: 2 }] };
+        assert_eq!(
+            encode!(v),
+            map! {
+                a, Array(vec![
+                    Table(map!{ a, Integer(1) }),
+                    Table(map!{ a, Integer(2) }),
+                ])
+            }
+        );
+        assert_eq!(v, decode!(Table(encode!(v))));
+    }
+
+    #[test]
+    fn type_errors() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { bar: isize }
+
+        let mut d = Decoder::new(Table(map! {
+            bar, Float(1.0)
+        }));
+        let a: Result<Foo, DecodeError> = Decodable::decode(&mut d);
+        match a {
+            Ok(..) => panic!("should not have decoded"),
+            Err(e) => {
+                assert_eq!(format!("{}", e),
+                           "expected a value of type `integer`, but \
+                            found a value of type `float` for the key `bar`");
+            }
+        }
+    }
+
+    #[test]
+    fn missing_errors() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { bar: isize }
+
+        let mut d = Decoder::new(Table(map! {
+        }));
+        let a: Result<Foo, DecodeError> = Decodable::decode(&mut d);
+        match a {
+            Ok(..) => panic!("should not have decoded"),
+            Err(e) => {
+                assert_eq!(format!("{}", e),
+                           "expected a value of type `integer` for the key `bar`");
+            }
+        }
+    }
+
+    #[test]
+    fn parse_enum() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: E }
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        enum E {
+            Bar(isize),
+            Baz(f64),
+            Last(Foo2),
+        }
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo2 {
+            test: String,
+        }
+
+        let v = Foo { a: E::Bar(10) };
+        assert_eq!(
+            encode!(v),
+            map! { a, Integer(10) }
+        );
+        assert_eq!(v, decode!(Table(encode!(v))));
+
+        let v = Foo { a: E::Baz(10.2) };
+        assert_eq!(
+            encode!(v),
+            map! { a, Float(10.2) }
+        );
+        assert_eq!(v, decode!(Table(encode!(v))));
+
+        let v = Foo { a: E::Last(Foo2 { test: "test".to_string() }) };
+        assert_eq!(
+            encode!(v),
+            map! { a, Table(map! { test, Value::String("test".to_string()) }) }
+        );
+        assert_eq!(v, decode!(Table(encode!(v))));
+    }
+
+    #[test]
+    fn unused_fields() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: isize }
+
+        let v = Foo { a: 2 };
+        let mut d = Decoder::new(Table(map! {
+            a, Integer(2),
+            b, Integer(5)
+        }));
+        assert_eq!(v, Decodable::decode(&mut d).unwrap());
+
+        assert_eq!(d.toml, Some(Table(map! {
+            b, Integer(5)
+        })));
+    }
+
+    #[test]
+    fn unused_fields2() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: Bar }
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Bar { a: isize }
+
+        let v = Foo { a: Bar { a: 2 } };
+        let mut d = Decoder::new(Table(map! {
+            a, Table(map! {
+                a, Integer(2),
+                b, Integer(5)
+            })
+        }));
+        assert_eq!(v, Decodable::decode(&mut d).unwrap());
+
+        assert_eq!(d.toml, Some(Table(map! {
+            a, Table(map! {
+                b, Integer(5)
+            })
+        })));
+    }
+
+    #[test]
+    fn unused_fields3() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: Bar }
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Bar { a: isize }
+
+        let v = Foo { a: Bar { a: 2 } };
+        let mut d = Decoder::new(Table(map! {
+            a, Table(map! {
+                a, Integer(2)
+            })
+        }));
+        assert_eq!(v, Decodable::decode(&mut d).unwrap());
+
+        assert_eq!(d.toml, None);
+    }
+
+    #[test]
+    fn unused_fields4() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: BTreeMap<String, String> }
+
+        let v = Foo { a: map! { a, "foo".to_string() } };
+        let mut d = Decoder::new(Table(map! {
+            a, Table(map! {
+                a, Value::String("foo".to_string())
+            })
+        }));
+        assert_eq!(v, Decodable::decode(&mut d).unwrap());
+
+        assert_eq!(d.toml, None);
+    }
+
+    #[test]
+    fn unused_fields5() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: Vec<String> }
+
+        let v = Foo { a: vec!["a".to_string()] };
+        let mut d = Decoder::new(Table(map! {
+            a, Array(vec![Value::String("a".to_string())])
+        }));
+        assert_eq!(v, Decodable::decode(&mut d).unwrap());
+
+        assert_eq!(d.toml, None);
+    }
+
+    #[test]
+    fn unused_fields6() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: Option<Vec<String>> }
+
+        let v = Foo { a: Some(vec![]) };
+        let mut d = Decoder::new(Table(map! {
+            a, Array(vec![])
+        }));
+        assert_eq!(v, Decodable::decode(&mut d).unwrap());
+
+        assert_eq!(d.toml, None);
+    }
+
+    #[test]
+    fn unused_fields7() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: Vec<Bar> }
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Bar { a: isize }
+
+        let v = Foo { a: vec![Bar { a: 1 }] };
+        let mut d = Decoder::new(Table(map! {
+            a, Array(vec![Table(map! {
+                a, Integer(1),
+                b, Integer(2)
+            })])
+        }));
+        assert_eq!(v, Decodable::decode(&mut d).unwrap());
+
+        assert_eq!(d.toml, Some(Table(map! {
+            a, Array(vec![Table(map! {
+                b, Integer(2)
+            })])
+        })));
+    }
+
+    #[test]
+    fn empty_arrays() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: Vec<Bar> }
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Bar;
+
+        let v = Foo { a: vec![] };
+        let mut d = Decoder::new(Table(map! {}));
+        assert_eq!(v, Decodable::decode(&mut d).unwrap());
+    }
+
+    #[test]
+    fn empty_arrays2() {
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Foo { a: Option<Vec<Bar>> }
+        #[derive(RustcEncodable, RustcDecodable, PartialEq, Debug)]
+        struct Bar;
+
+        let v = Foo { a: None };
+        let mut d = Decoder::new(Table(map! {}));
+        assert_eq!(v, Decodable::decode(&mut d).unwrap());
+
+        let v = Foo { a: Some(vec![]) };
+        let mut d = Decoder::new(Table(map! {
+            a, Array(vec![])
+        }));
+        assert_eq!(v, Decodable::decode(&mut d).unwrap());
+    }
+
+    #[test]
+    fn round_trip() {
+        let toml = r#"
+              [test]
+              foo = "bar"
+
+              [[values]]
+              foo = "baz"
+
+              [[values]]
+              foo = "qux"
+        "#;
+
+        let value: Value = toml.parse().unwrap();
+        let val2 = ::encode_str(&value).parse().unwrap();
+        assert_eq!(value, val2);
+    }
+}

src/lib.rs

@@ -39,26 +39,25 @@
 #![deny(missing_docs)]
 #![cfg_attr(test, deny(warnings))]
 
-extern crate rustc_serialize;
+#[cfg(feature = "rustc-serialize")] extern crate rustc_serialize;
 
 use std::collections::BTreeMap;
 use std::str::FromStr;
 use std::string;
 
 pub use parser::{Parser, ParserError};
-pub use serialization::{Encoder, encode, encode_str};
-pub use serialization::{Decoder, decode, decode_str};
-pub use serialization::Error;
-pub use serialization::Error::{NeedsKey, NoValue};
-pub use serialization::Error::{InvalidMapKeyLocation, InvalidMapKeyType};
-pub use serialization::{DecodeError, DecodeErrorKind};
-pub use serialization::DecodeErrorKind::{ApplicationError, ExpectedField};
-pub use serialization::DecodeErrorKind::{ExpectedMapElement, ExpectedMapKey, NoEnumVariants};
-pub use serialization::DecodeErrorKind::{ExpectedType, NilTooLong};
+
+#[cfg(any(feature = "rustc-serialize", feature = "serde"))]
+pub use self::encoder::{Encoder, Error, encode, encode_str};
+#[cfg(any(feature = "rustc-serialize", feature = "serde"))]
+pub use self::decoder::{Decoder, DecodeError, DecodeErrorKind, decode, decode_str};
 
 mod parser;
 mod display;
-mod serialization;
+#[cfg(any(feature = "rustc-serialize", feature = "serde"))]
+mod encoder;
+#[cfg(any(feature = "rustc-serialize", feature = "serde"))]
+mod decoder;
 
 /// Representation of a TOML value.
 #[derive(PartialEq, Clone, Debug)]
@@ -203,37 +202,6 @@ impl Value {
     }
 }
 
-impl rustc_serialize::Encodable for Value {
-    fn encode<E>(&self, e: &mut E) -> Result<(), E::Error>
-        where E: rustc_serialize::Encoder
-    {
-        match *self {
-            Value::String(ref s) => e.emit_str(s),
-            Value::Integer(i) => e.emit_i64(i),
-            Value::Float(f) => e.emit_f64(f),
-            Value::Boolean(b) => e.emit_bool(b),
-            Value::Datetime(ref s) => e.emit_str(s),
-            Value::Array(ref a) => {
-                e.emit_seq(a.len(), |e| {
-                    for item in a {
-                        try!(item.encode(e));
-                    }
-                    Ok(())
-                })
-            }
-            Value::Table(ref t) => {
-                e.emit_map(t.len(), |e| {
-                    for (i, (key, value)) in t.iter().enumerate() {
-                        try!(e.emit_map_elt_key(i, |e| e.emit_str(key)));
-                        try!(e.emit_map_elt_val(i, |e| value.encode(e)));
-                    }
-                    Ok(())
-                })
-            }
-        }
-    }
-}
-
 impl FromStr for Value {
     type Err = Vec<ParserError>;
     fn from_str(s: &str) -> Result<Value, Vec<ParserError>> {
@@ -292,22 +260,4 @@ mod tests {
         let foo = value.lookup("values.str.foo");
         assert!(foo.is_none());
     }
-
-    #[test]
-    fn round_trip() {
-        let toml = r#"
-              [test]
-              foo = "bar"
-
-              [[values]]
-              foo = "baz"
-
-              [[values]]
-              foo = "qux"
-        "#;
-
-        let value: Value = toml.parse().unwrap();
-        let val2 = ::encode_str(&value).parse().unwrap();
-        assert_eq!(value, val2);
-    }
 }