compiler/rustc_serialize/src/serialize.rs - toolchain/rustc - Git at Google

 //! Support code for encoding and decoding types.

 /*
 Core encoding and decoding interfaces.
 */

 use std::borrow::Cow;
 use std::cell::{Cell, RefCell};
 use std::marker::PhantomData;
 use std::path;
 use std::rc::Rc;
 use std::sync::Arc;

 pub trait Encoder {
     type Error;

     // Primitive types:
     fn emit_unit(&mut self) -> Result<(), Self::Error>;
     fn emit_usize(&mut self, v: usize) -> Result<(), Self::Error>;
     fn emit_u128(&mut self, v: u128) -> Result<(), Self::Error>;
     fn emit_u64(&mut self, v: u64) -> Result<(), Self::Error>;
     fn emit_u32(&mut self, v: u32) -> Result<(), Self::Error>;
     fn emit_u16(&mut self, v: u16) -> Result<(), Self::Error>;
     fn emit_u8(&mut self, v: u8) -> Result<(), Self::Error>;
     fn emit_isize(&mut self, v: isize) -> Result<(), Self::Error>;
     fn emit_i128(&mut self, v: i128) -> Result<(), Self::Error>;
     fn emit_i64(&mut self, v: i64) -> Result<(), Self::Error>;
     fn emit_i32(&mut self, v: i32) -> Result<(), Self::Error>;
     fn emit_i16(&mut self, v: i16) -> Result<(), Self::Error>;
     fn emit_i8(&mut self, v: i8) -> Result<(), Self::Error>;
     fn emit_bool(&mut self, v: bool) -> Result<(), Self::Error>;
     fn emit_f64(&mut self, v: f64) -> Result<(), Self::Error>;
     fn emit_f32(&mut self, v: f32) -> Result<(), Self::Error>;
     fn emit_char(&mut self, v: char) -> Result<(), Self::Error>;
     fn emit_str(&mut self, v: &str) -> Result<(), Self::Error>;
     fn emit_raw_bytes(&mut self, s: &[u8]) -> Result<(), Self::Error>;

     // Compound types:
     #[inline]
     fn emit_enum<F>(&mut self, f: F) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         f(self)
     }

     fn emit_enum_variant<F>(
         &mut self,
         _v_name: &str,
         v_id: usize,
         _len: usize,
         f: F,
     ) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         self.emit_usize(v_id)?;
         f(self)
     }

     #[inline]
     fn emit_enum_variant_arg<F>(&mut self, _first: bool, f: F) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         f(self)
     }

     #[inline]
     fn emit_struct<F>(&mut self, _no_fields: bool, f: F) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         f(self)
     }

     #[inline]
     fn emit_struct_field<F>(&mut self, _f_name: &str, _first: bool, f: F) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         f(self)
     }

     #[inline]
     fn emit_tuple<F>(&mut self, _len: usize, f: F) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         f(self)
     }

     #[inline]
     fn emit_tuple_arg<F>(&mut self, _idx: usize, f: F) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         f(self)
     }

     // Specialized types:
     fn emit_option<F>(&mut self, f: F) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         self.emit_enum(f)
     }

     #[inline]
     fn emit_option_none(&mut self) -> Result<(), Self::Error> {
         self.emit_enum_variant("None", 0, 0, |_| Ok(()))
     }

     fn emit_option_some<F>(&mut self, f: F) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         self.emit_enum_variant("Some", 1, 1, f)
     }

     fn emit_seq<F>(&mut self, len: usize, f: F) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         self.emit_usize(len)?;
         f(self)
     }

     #[inline]
     fn emit_seq_elt<F>(&mut self, _idx: usize, f: F) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         f(self)
     }

     fn emit_map<F>(&mut self, len: usize, f: F) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         self.emit_usize(len)?;
         f(self)
     }

     #[inline]
     fn emit_map_elt_key<F>(&mut self, _idx: usize, f: F) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         f(self)
     }

     #[inline]
     fn emit_map_elt_val<F>(&mut self, f: F) -> Result<(), Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<(), Self::Error>,
     {
         f(self)
     }
 }

 pub trait Decoder {
     type Error;

     // Primitive types:
     fn read_nil(&mut self) -> Result<(), Self::Error>;
     fn read_usize(&mut self) -> Result<usize, Self::Error>;
     fn read_u128(&mut self) -> Result<u128, Self::Error>;
     fn read_u64(&mut self) -> Result<u64, Self::Error>;
     fn read_u32(&mut self) -> Result<u32, Self::Error>;
     fn read_u16(&mut self) -> Result<u16, Self::Error>;
     fn read_u8(&mut self) -> Result<u8, Self::Error>;
     fn read_isize(&mut self) -> Result<isize, Self::Error>;
     fn read_i128(&mut self) -> Result<i128, Self::Error>;
     fn read_i64(&mut self) -> Result<i64, Self::Error>;
     fn read_i32(&mut self) -> Result<i32, Self::Error>;
     fn read_i16(&mut self) -> Result<i16, Self::Error>;
     fn read_i8(&mut self) -> Result<i8, Self::Error>;
     fn read_bool(&mut self) -> Result<bool, Self::Error>;
     fn read_f64(&mut self) -> Result<f64, Self::Error>;
     fn read_f32(&mut self) -> Result<f32, Self::Error>;
     fn read_char(&mut self) -> Result<char, Self::Error>;
     fn read_str(&mut self) -> Result<Cow<'_, str>, Self::Error>;
     fn read_raw_bytes_into(&mut self, s: &mut [u8]) -> Result<(), Self::Error>;

     // Compound types:
     #[inline]
     fn read_enum<T, F>(&mut self, f: F) -> Result<T, Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<T, Self::Error>,
     {
         f(self)
     }

     #[inline]
     fn read_enum_variant<T, F>(&mut self, _names: &[&str], mut f: F) -> Result<T, Self::Error>
     where
         F: FnMut(&mut Self, usize) -> Result<T, Self::Error>,
     {
         let disr = self.read_usize()?;
         f(self, disr)
     }

     #[inline]
     fn read_enum_variant_arg<T, F>(&mut self, f: F) -> Result<T, Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<T, Self::Error>,
     {
         f(self)
     }

     #[inline]
     fn read_struct<T, F>(&mut self, f: F) -> Result<T, Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<T, Self::Error>,
     {
         f(self)
     }

     #[inline]
     fn read_struct_field<T, F>(&mut self, _f_name: &str, f: F) -> Result<T, Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<T, Self::Error>,
     {
         f(self)
     }

     #[inline]
     fn read_tuple<T, F>(&mut self, _len: usize, f: F) -> Result<T, Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<T, Self::Error>,
     {
         f(self)
     }

     #[inline]
     fn read_tuple_arg<T, F>(&mut self, f: F) -> Result<T, Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<T, Self::Error>,
     {
         f(self)
     }

     // Specialized types:
     fn read_option<T, F>(&mut self, mut f: F) -> Result<T, Self::Error>
     where
         F: FnMut(&mut Self, bool) -> Result<T, Self::Error>,
     {
         self.read_enum(move |this| {
             this.read_enum_variant(&["None", "Some"], move |this, idx| match idx {
                 0 => f(this, false),
                 1 => f(this, true),
                 _ => Err(this.error("read_option: expected 0 for None or 1 for Some")),
             })
         })
     }

     fn read_seq<T, F>(&mut self, f: F) -> Result<T, Self::Error>
     where
         F: FnOnce(&mut Self, usize) -> Result<T, Self::Error>,
     {
         let len = self.read_usize()?;
         f(self, len)
     }

     #[inline]
     fn read_seq_elt<T, F>(&mut self, f: F) -> Result<T, Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<T, Self::Error>,
     {
         f(self)
     }

     fn read_map<T, F>(&mut self, f: F) -> Result<T, Self::Error>
     where
         F: FnOnce(&mut Self, usize) -> Result<T, Self::Error>,
     {
         let len = self.read_usize()?;
         f(self, len)
     }

     #[inline]
     fn read_map_elt_key<T, F>(&mut self, f: F) -> Result<T, Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<T, Self::Error>,
     {
         f(self)
     }

     #[inline]
     fn read_map_elt_val<T, F>(&mut self, f: F) -> Result<T, Self::Error>
     where
         F: FnOnce(&mut Self) -> Result<T, Self::Error>,
     {
         f(self)
     }

     // Failure
     fn error(&mut self, err: &str) -> Self::Error;
 }

 /// Trait for types that can be serialized
 ///
 /// This can be implemented using the `Encodable`, `TyEncodable` and
 /// `MetadataEncodable` macros.
 ///
 /// * `Encodable` should be used in crates that don't depend on
 ///   `rustc_middle`.
 /// * `MetadataEncodable` is used in `rustc_metadata` for types that contain
 ///   `rustc_metadata::rmeta::Lazy`.
 /// * `TyEncodable` should be used for types that are only serialized in crate
 ///   metadata or the incremental cache. This is most types in `rustc_middle`.
 pub trait Encodable<S: Encoder> {
     fn encode(&self, s: &mut S) -> Result<(), S::Error>;
 }

 /// Trait for types that can be deserialized
 ///
 /// This can be implemented using the `Decodable`, `TyDecodable` and
 /// `MetadataDecodable` macros.
 ///
 /// * `Decodable` should be used in crates that don't depend on
 ///   `rustc_middle`.
 /// * `MetadataDecodable` is used in `rustc_metadata` for types that contain
 ///   `rustc_metadata::rmeta::Lazy`.
 /// * `TyDecodable` should be used for types that are only serialized in crate
 ///   metadata or the incremental cache. This is most types in `rustc_middle`.
 pub trait Decodable<D: Decoder>: Sized {
     fn decode(d: &mut D) -> Result<Self, D::Error>;
 }

 macro_rules! direct_serialize_impls {
     ($($ty:ident $emit_method:ident $read_method:ident),*) => {
         $(
             impl<S: Encoder> Encodable<S> for $ty {
                 fn encode(&self, s: &mut S) -> Result<(), S::Error> {
                     s.$emit_method(*self)
                 }
             }

             impl<D: Decoder> Decodable<D> for $ty {
                 fn decode(d: &mut D) -> Result<$ty, D::Error> {
                     d.$read_method()
                 }
             }
         )*
     }
 }

 direct_serialize_impls! {
     usize emit_usize read_usize,
     u8 emit_u8 read_u8,
     u16 emit_u16 read_u16,
     u32 emit_u32 read_u32,
     u64 emit_u64 read_u64,
     u128 emit_u128 read_u128,
     isize emit_isize read_isize,
     i8 emit_i8 read_i8,
     i16 emit_i16 read_i16,
     i32 emit_i32 read_i32,
     i64 emit_i64 read_i64,
     i128 emit_i128 read_i128,
     f32 emit_f32 read_f32,
     f64 emit_f64 read_f64,
     bool emit_bool read_bool,
     char emit_char read_char
 }

 impl<S: Encoder> Encodable<S> for ::std::num::NonZeroU32 {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         s.emit_u32(self.get())
     }
 }

 impl<D: Decoder> Decodable<D> for ::std::num::NonZeroU32 {
     fn decode(d: &mut D) -> Result<Self, D::Error> {
         d.read_u32().map(|d| ::std::num::NonZeroU32::new(d).unwrap())
     }
 }

 impl<S: Encoder> Encodable<S> for str {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         s.emit_str(self)
     }
 }

 impl<S: Encoder> Encodable<S> for &str {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         s.emit_str(self)
     }
 }

 impl<S: Encoder> Encodable<S> for String {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         s.emit_str(&self[..])
     }
 }

 impl<D: Decoder> Decodable<D> for String {
     fn decode(d: &mut D) -> Result<String, D::Error> {
         Ok(d.read_str()?.into_owned())
     }
 }

 impl<S: Encoder> Encodable<S> for () {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         s.emit_unit()
     }
 }

 impl<D: Decoder> Decodable<D> for () {
     fn decode(d: &mut D) -> Result<(), D::Error> {
         d.read_nil()
     }
 }

 impl<S: Encoder, T> Encodable<S> for PhantomData<T> {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         s.emit_unit()
     }
 }

 impl<D: Decoder, T> Decodable<D> for PhantomData<T> {
     fn decode(d: &mut D) -> Result<PhantomData<T>, D::Error> {
         d.read_nil()?;
         Ok(PhantomData)
     }
 }

 impl<D: Decoder, T: Decodable<D>> Decodable<D> for Box<[T]> {
     fn decode(d: &mut D) -> Result<Box<[T]>, D::Error> {
         let v: Vec<T> = Decodable::decode(d)?;
         Ok(v.into_boxed_slice())
     }
 }

 impl<S: Encoder, T: Encodable<S>> Encodable<S> for Rc<T> {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         (**self).encode(s)
     }
 }

 impl<D: Decoder, T: Decodable<D>> Decodable<D> for Rc<T> {
     fn decode(d: &mut D) -> Result<Rc<T>, D::Error> {
         Ok(Rc::new(Decodable::decode(d)?))
     }
 }

 impl<S: Encoder, T: Encodable<S>> Encodable<S> for [T] {
     default fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         s.emit_seq(self.len(), |s| {
             for (i, e) in self.iter().enumerate() {
                 s.emit_seq_elt(i, |s| e.encode(s))?
             }
             Ok(())
         })
     }
 }

 impl<S: Encoder, T: Encodable<S>> Encodable<S> for Vec<T> {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         let slice: &[T] = self;
         slice.encode(s)
     }
 }

 impl<D: Decoder, T: Decodable<D>> Decodable<D> for Vec<T> {
     default fn decode(d: &mut D) -> Result<Vec<T>, D::Error> {
         d.read_seq(|d, len| {
             let mut v = Vec::with_capacity(len);
             for _ in 0..len {
                 v.push(d.read_seq_elt(|d| Decodable::decode(d))?);
             }
             Ok(v)
         })
     }
 }

 impl<S: Encoder, T: Encodable<S>, const N: usize> Encodable<S> for [T; N] {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         let slice: &[T] = self;
         slice.encode(s)
     }
 }

 impl<D: Decoder, const N: usize> Decodable<D> for [u8; N] {
     fn decode(d: &mut D) -> Result<[u8; N], D::Error> {
         d.read_seq(|d, len| {
             assert!(len == N);
             let mut v = [0u8; N];
             for i in 0..len {
                 v[i] = d.read_seq_elt(|d| Decodable::decode(d))?;
             }
             Ok(v)
         })
     }
 }

 impl<'a, S: Encoder, T: Encodable<S>> Encodable<S> for Cow<'a, [T]>
 where
     [T]: ToOwned<Owned = Vec<T>>,
 {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         let slice: &[T] = self;
         slice.encode(s)
     }
 }

 impl<D: Decoder, T: Decodable<D> + ToOwned> Decodable<D> for Cow<'static, [T]>
 where
     [T]: ToOwned<Owned = Vec<T>>,
 {
     fn decode(d: &mut D) -> Result<Cow<'static, [T]>, D::Error> {
         let v: Vec<T> = Decodable::decode(d)?;
         Ok(Cow::Owned(v))
     }
 }

 impl<S: Encoder, T: Encodable<S>> Encodable<S> for Option<T> {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         s.emit_option(|s| match *self {
             None => s.emit_option_none(),
             Some(ref v) => s.emit_option_some(|s| v.encode(s)),
         })
     }
 }

 impl<D: Decoder, T: Decodable<D>> Decodable<D> for Option<T> {
     fn decode(d: &mut D) -> Result<Option<T>, D::Error> {
         d.read_option(|d, b| if b { Ok(Some(Decodable::decode(d)?)) } else { Ok(None) })
     }
 }

 impl<S: Encoder, T1: Encodable<S>, T2: Encodable<S>> Encodable<S> for Result<T1, T2> {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         s.emit_enum(|s| match *self {
             Ok(ref v) => {
                 s.emit_enum_variant("Ok", 0, 1, |s| s.emit_enum_variant_arg(true, |s| v.encode(s)))
             }
             Err(ref v) => {
                 s.emit_enum_variant("Err", 1, 1, |s| s.emit_enum_variant_arg(true, |s| v.encode(s)))
             }
         })
     }
 }

 impl<D: Decoder, T1: Decodable<D>, T2: Decodable<D>> Decodable<D> for Result<T1, T2> {
     fn decode(d: &mut D) -> Result<Result<T1, T2>, D::Error> {
         d.read_enum(|d| {
             d.read_enum_variant(&["Ok", "Err"], |d, disr| match disr {
                 0 => Ok(Ok(d.read_enum_variant_arg(|d| T1::decode(d))?)),
                 1 => Ok(Err(d.read_enum_variant_arg(|d| T2::decode(d))?)),
                 _ => {
                     panic!(
                         "Encountered invalid discriminant while \
                                 decoding `Result`."
                     );
                 }
             })
         })
     }
 }

 macro_rules! peel {
     ($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
 }

 /// Evaluates to the number of tokens passed to it.
 ///
 /// Logarithmic counting: every one or two recursive expansions, the number of
 /// tokens to count is divided by two, instead of being reduced by one.
 /// Therefore, the recursion depth is the binary logarithm of the number of
 /// tokens to count, and the expanded tree is likewise very small.
 macro_rules! count {
     ()                     => (0usize);
     ($one:tt)              => (1usize);
     ($($pairs:tt $_p:tt)*) => (count!($($pairs)*) << 1usize);
     ($odd:tt $($rest:tt)*) => (count!($($rest)*) | 1usize);
 }

 macro_rules! tuple {
     () => ();
     ( $($name:ident,)+ ) => (
         impl<D: Decoder, $($name: Decodable<D>),+> Decodable<D> for ($($name,)+) {
             #[allow(non_snake_case)]
             fn decode(d: &mut D) -> Result<($($name,)+), D::Error> {
                 let len: usize = count!($($name)+);
                 d.read_tuple(len, |d| {
                     let ret = ($(d.read_tuple_arg(|d| -> Result<$name, D::Error> {
                         Decodable::decode(d)
                     })?,)+);
                     Ok(ret)
                 })
             }
         }
         impl<S: Encoder, $($name: Encodable<S>),+> Encodable<S> for ($($name,)+) {
             #[allow(non_snake_case)]
             fn encode(&self, s: &mut S) -> Result<(), S::Error> {
                 let ($(ref $name,)+) = *self;
                 let mut n = 0;
                 $(let $name = $name; n += 1;)+
                 s.emit_tuple(n, |s| {
                     let mut i = 0;
                     $(s.emit_tuple_arg({ i+=1; i-1 }, |s| $name.encode(s))?;)+
                     Ok(())
                 })
             }
         }
         peel! { $($name,)+ }
     )
 }

 tuple! { T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, }

 impl<S: Encoder> Encodable<S> for path::Path {
     fn encode(&self, e: &mut S) -> Result<(), S::Error> {
         self.to_str().unwrap().encode(e)
     }
 }

 impl<S: Encoder> Encodable<S> for path::PathBuf {
     fn encode(&self, e: &mut S) -> Result<(), S::Error> {
         path::Path::encode(self, e)
     }
 }

 impl<D: Decoder> Decodable<D> for path::PathBuf {
     fn decode(d: &mut D) -> Result<path::PathBuf, D::Error> {
         let bytes: String = Decodable::decode(d)?;
         Ok(path::PathBuf::from(bytes))
     }
 }

 impl<S: Encoder, T: Encodable<S> + Copy> Encodable<S> for Cell<T> {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         self.get().encode(s)
     }
 }

 impl<D: Decoder, T: Decodable<D> + Copy> Decodable<D> for Cell<T> {
     fn decode(d: &mut D) -> Result<Cell<T>, D::Error> {
         Ok(Cell::new(Decodable::decode(d)?))
     }
 }

 // FIXME: #15036
 // Should use `try_borrow`, returning an
 // `encoder.error("attempting to Encode borrowed RefCell")`
 // from `encode` when `try_borrow` returns `None`.

 impl<S: Encoder, T: Encodable<S>> Encodable<S> for RefCell<T> {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         self.borrow().encode(s)
     }
 }

 impl<D: Decoder, T: Decodable<D>> Decodable<D> for RefCell<T> {
     fn decode(d: &mut D) -> Result<RefCell<T>, D::Error> {
         Ok(RefCell::new(Decodable::decode(d)?))
     }
 }

 impl<S: Encoder, T: Encodable<S>> Encodable<S> for Arc<T> {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         (**self).encode(s)
     }
 }

 impl<D: Decoder, T: Decodable<D>> Decodable<D> for Arc<T> {
     fn decode(d: &mut D) -> Result<Arc<T>, D::Error> {
         Ok(Arc::new(Decodable::decode(d)?))
     }
 }

 impl<S: Encoder, T: ?Sized + Encodable<S>> Encodable<S> for Box<T> {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         (**self).encode(s)
     }
 }
 impl<D: Decoder, T: Decodable<D>> Decodable<D> for Box<T> {
     fn decode(d: &mut D) -> Result<Box<T>, D::Error> {
         Ok(Box::new(Decodable::decode(d)?))
     }
 }
	//! Support code for encoding and decoding types.

	/*
	Core encoding and decoding interfaces.
	*/

	use std::borrow::Cow;
	use std::cell::{Cell, RefCell};
	use std::marker::PhantomData;
	use std::path;
	use std::rc::Rc;
	use std::sync::Arc;

	pub trait Encoder {
	type Error;

	// Primitive types:
	fn emit_unit(&mut self) -> Result<(), Self::Error>;
	fn emit_usize(&mut self, v: usize) -> Result<(), Self::Error>;
	fn emit_u128(&mut self, v: u128) -> Result<(), Self::Error>;
	fn emit_u64(&mut self, v: u64) -> Result<(), Self::Error>;
	fn emit_u32(&mut self, v: u32) -> Result<(), Self::Error>;
	fn emit_u16(&mut self, v: u16) -> Result<(), Self::Error>;
	fn emit_u8(&mut self, v: u8) -> Result<(), Self::Error>;
	fn emit_isize(&mut self, v: isize) -> Result<(), Self::Error>;
	fn emit_i128(&mut self, v: i128) -> Result<(), Self::Error>;
	fn emit_i64(&mut self, v: i64) -> Result<(), Self::Error>;
	fn emit_i32(&mut self, v: i32) -> Result<(), Self::Error>;
	fn emit_i16(&mut self, v: i16) -> Result<(), Self::Error>;
	fn emit_i8(&mut self, v: i8) -> Result<(), Self::Error>;
	fn emit_bool(&mut self, v: bool) -> Result<(), Self::Error>;
	fn emit_f64(&mut self, v: f64) -> Result<(), Self::Error>;
	fn emit_f32(&mut self, v: f32) -> Result<(), Self::Error>;
	fn emit_char(&mut self, v: char) -> Result<(), Self::Error>;
	fn emit_str(&mut self, v: &str) -> Result<(), Self::Error>;
	fn emit_raw_bytes(&mut self, s: &[u8]) -> Result<(), Self::Error>;

	// Compound types:
	#[inline]
	fn emit_enum<F>(&mut self, f: F) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	f(self)
	}

	fn emit_enum_variant<F>(
	&mut self,
	_v_name: &str,
	v_id: usize,
	_len: usize,
	f: F,
	) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	self.emit_usize(v_id)?;
	f(self)
	}

	#[inline]
	fn emit_enum_variant_arg<F>(&mut self, _first: bool, f: F) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	f(self)
	}

	#[inline]
	fn emit_struct<F>(&mut self, _no_fields: bool, f: F) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	f(self)
	}

	#[inline]
	fn emit_struct_field<F>(&mut self, _f_name: &str, _first: bool, f: F) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	f(self)
	}

	#[inline]
	fn emit_tuple<F>(&mut self, _len: usize, f: F) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	f(self)
	}

	#[inline]
	fn emit_tuple_arg<F>(&mut self, _idx: usize, f: F) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	f(self)
	}

	// Specialized types:
	fn emit_option<F>(&mut self, f: F) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	self.emit_enum(f)
	}

	#[inline]
	fn emit_option_none(&mut self) -> Result<(), Self::Error> {
	self.emit_enum_variant("None", 0, 0, \|_\| Ok(()))
	}

	fn emit_option_some<F>(&mut self, f: F) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	self.emit_enum_variant("Some", 1, 1, f)
	}

	fn emit_seq<F>(&mut self, len: usize, f: F) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	self.emit_usize(len)?;
	f(self)
	}

	#[inline]
	fn emit_seq_elt<F>(&mut self, _idx: usize, f: F) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	f(self)
	}

	fn emit_map<F>(&mut self, len: usize, f: F) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	self.emit_usize(len)?;
	f(self)
	}

	#[inline]
	fn emit_map_elt_key<F>(&mut self, _idx: usize, f: F) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	f(self)
	}

	#[inline]
	fn emit_map_elt_val<F>(&mut self, f: F) -> Result<(), Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<(), Self::Error>,
	{
	f(self)
	}
	}

	pub trait Decoder {
	type Error;

	// Primitive types:
	fn read_nil(&mut self) -> Result<(), Self::Error>;
	fn read_usize(&mut self) -> Result<usize, Self::Error>;
	fn read_u128(&mut self) -> Result<u128, Self::Error>;
	fn read_u64(&mut self) -> Result<u64, Self::Error>;
	fn read_u32(&mut self) -> Result<u32, Self::Error>;
	fn read_u16(&mut self) -> Result<u16, Self::Error>;
	fn read_u8(&mut self) -> Result<u8, Self::Error>;
	fn read_isize(&mut self) -> Result<isize, Self::Error>;
	fn read_i128(&mut self) -> Result<i128, Self::Error>;
	fn read_i64(&mut self) -> Result<i64, Self::Error>;
	fn read_i32(&mut self) -> Result<i32, Self::Error>;
	fn read_i16(&mut self) -> Result<i16, Self::Error>;
	fn read_i8(&mut self) -> Result<i8, Self::Error>;
	fn read_bool(&mut self) -> Result<bool, Self::Error>;
	fn read_f64(&mut self) -> Result<f64, Self::Error>;
	fn read_f32(&mut self) -> Result<f32, Self::Error>;
	fn read_char(&mut self) -> Result<char, Self::Error>;
	fn read_str(&mut self) -> Result<Cow<'_, str>, Self::Error>;
	fn read_raw_bytes_into(&mut self, s: &mut [u8]) -> Result<(), Self::Error>;

	// Compound types:
	#[inline]
	fn read_enum<T, F>(&mut self, f: F) -> Result<T, Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<T, Self::Error>,
	{
	f(self)
	}

	#[inline]
	fn read_enum_variant<T, F>(&mut self, _names: &[&str], mut f: F) -> Result<T, Self::Error>
	where
	F: FnMut(&mut Self, usize) -> Result<T, Self::Error>,
	{
	let disr = self.read_usize()?;
	f(self, disr)
	}

	#[inline]
	fn read_enum_variant_arg<T, F>(&mut self, f: F) -> Result<T, Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<T, Self::Error>,
	{
	f(self)
	}

	#[inline]
	fn read_struct<T, F>(&mut self, f: F) -> Result<T, Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<T, Self::Error>,
	{
	f(self)
	}

	#[inline]
	fn read_struct_field<T, F>(&mut self, _f_name: &str, f: F) -> Result<T, Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<T, Self::Error>,
	{
	f(self)
	}

	#[inline]
	fn read_tuple<T, F>(&mut self, _len: usize, f: F) -> Result<T, Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<T, Self::Error>,
	{
	f(self)
	}

	#[inline]
	fn read_tuple_arg<T, F>(&mut self, f: F) -> Result<T, Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<T, Self::Error>,
	{
	f(self)
	}

	// Specialized types:
	fn read_option<T, F>(&mut self, mut f: F) -> Result<T, Self::Error>
	where
	F: FnMut(&mut Self, bool) -> Result<T, Self::Error>,
	{
	self.read_enum(move \|this\| {
	this.read_enum_variant(&["None", "Some"], move \|this, idx\| match idx {
	0 => f(this, false),
	1 => f(this, true),
	_ => Err(this.error("read_option: expected 0 for None or 1 for Some")),
	})
	})
	}

	fn read_seq<T, F>(&mut self, f: F) -> Result<T, Self::Error>
	where
	F: FnOnce(&mut Self, usize) -> Result<T, Self::Error>,
	{
	let len = self.read_usize()?;
	f(self, len)
	}

	#[inline]
	fn read_seq_elt<T, F>(&mut self, f: F) -> Result<T, Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<T, Self::Error>,
	{
	f(self)
	}

	fn read_map<T, F>(&mut self, f: F) -> Result<T, Self::Error>
	where
	F: FnOnce(&mut Self, usize) -> Result<T, Self::Error>,
	{
	let len = self.read_usize()?;
	f(self, len)
	}

	#[inline]
	fn read_map_elt_key<T, F>(&mut self, f: F) -> Result<T, Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<T, Self::Error>,
	{
	f(self)
	}

	#[inline]
	fn read_map_elt_val<T, F>(&mut self, f: F) -> Result<T, Self::Error>
	where
	F: FnOnce(&mut Self) -> Result<T, Self::Error>,
	{
	f(self)
	}

	// Failure
	fn error(&mut self, err: &str) -> Self::Error;
	}

	/// Trait for types that can be serialized
	///
	/// This can be implemented using the `Encodable`, `TyEncodable` and
	/// `MetadataEncodable` macros.
	///
	/// * `Encodable` should be used in crates that don't depend on
	/// `rustc_middle`.
	/// * `MetadataEncodable` is used in `rustc_metadata` for types that contain
	/// `rustc_metadata::rmeta::Lazy`.
	/// * `TyEncodable` should be used for types that are only serialized in crate
	/// metadata or the incremental cache. This is most types in `rustc_middle`.
	pub trait Encodable<S: Encoder> {
	fn encode(&self, s: &mut S) -> Result<(), S::Error>;
	}

	/// Trait for types that can be deserialized
	///
	/// This can be implemented using the `Decodable`, `TyDecodable` and
	/// `MetadataDecodable` macros.
	///
	/// * `Decodable` should be used in crates that don't depend on
	/// `rustc_middle`.
	/// * `MetadataDecodable` is used in `rustc_metadata` for types that contain
	/// `rustc_metadata::rmeta::Lazy`.
	/// * `TyDecodable` should be used for types that are only serialized in crate
	/// metadata or the incremental cache. This is most types in `rustc_middle`.
	pub trait Decodable<D: Decoder>: Sized {
	fn decode(d: &mut D) -> Result<Self, D::Error>;
	}

	macro_rules! direct_serialize_impls {
	($($ty:ident $emit_method:ident $read_method:ident),*) => {
	$(
	impl<S: Encoder> Encodable<S> for $ty {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	s.$emit_method(*self)
	}
	}

	impl<D: Decoder> Decodable<D> for $ty {
	fn decode(d: &mut D) -> Result<$ty, D::Error> {
	d.$read_method()
	}
	}
	)*
	}
	}

	direct_serialize_impls! {
	usize emit_usize read_usize,
	u8 emit_u8 read_u8,
	u16 emit_u16 read_u16,
	u32 emit_u32 read_u32,
	u64 emit_u64 read_u64,
	u128 emit_u128 read_u128,
	isize emit_isize read_isize,
	i8 emit_i8 read_i8,
	i16 emit_i16 read_i16,
	i32 emit_i32 read_i32,
	i64 emit_i64 read_i64,
	i128 emit_i128 read_i128,
	f32 emit_f32 read_f32,
	f64 emit_f64 read_f64,
	bool emit_bool read_bool,
	char emit_char read_char
	}

	impl<S: Encoder> Encodable<S> for ::std::num::NonZeroU32 {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	s.emit_u32(self.get())
	}
	}

	impl<D: Decoder> Decodable<D> for ::std::num::NonZeroU32 {
	fn decode(d: &mut D) -> Result<Self, D::Error> {
	d.read_u32().map(\|d\| ::std::num::NonZeroU32::new(d).unwrap())
	}
	}

	impl<S: Encoder> Encodable<S> for str {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	s.emit_str(self)
	}
	}

	impl<S: Encoder> Encodable<S> for &str {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	s.emit_str(self)
	}
	}

	impl<S: Encoder> Encodable<S> for String {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	s.emit_str(&self[..])
	}
	}

	impl<D: Decoder> Decodable<D> for String {
	fn decode(d: &mut D) -> Result<String, D::Error> {
	Ok(d.read_str()?.into_owned())
	}
	}

	impl<S: Encoder> Encodable<S> for () {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	s.emit_unit()
	}
	}

	impl<D: Decoder> Decodable<D> for () {
	fn decode(d: &mut D) -> Result<(), D::Error> {
	d.read_nil()
	}
	}

	impl<S: Encoder, T> Encodable<S> for PhantomData<T> {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	s.emit_unit()
	}
	}

	impl<D: Decoder, T> Decodable<D> for PhantomData<T> {
	fn decode(d: &mut D) -> Result<PhantomData<T>, D::Error> {
	d.read_nil()?;
	Ok(PhantomData)
	}
	}

	impl<D: Decoder, T: Decodable<D>> Decodable<D> for Box<[T]> {
	fn decode(d: &mut D) -> Result<Box<[T]>, D::Error> {
	let v: Vec<T> = Decodable::decode(d)?;
	Ok(v.into_boxed_slice())
	}
	}

	impl<S: Encoder, T: Encodable<S>> Encodable<S> for Rc<T> {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	(**self).encode(s)
	}
	}

	impl<D: Decoder, T: Decodable<D>> Decodable<D> for Rc<T> {
	fn decode(d: &mut D) -> Result<Rc<T>, D::Error> {
	Ok(Rc::new(Decodable::decode(d)?))
	}
	}

	impl<S: Encoder, T: Encodable<S>> Encodable<S> for [T] {
	default fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	s.emit_seq(self.len(), \|s\| {
	for (i, e) in self.iter().enumerate() {
	s.emit_seq_elt(i, \|s\| e.encode(s))?
	}
	Ok(())
	})
	}
	}

	impl<S: Encoder, T: Encodable<S>> Encodable<S> for Vec<T> {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	let slice: &[T] = self;
	slice.encode(s)
	}
	}

	impl<D: Decoder, T: Decodable<D>> Decodable<D> for Vec<T> {
	default fn decode(d: &mut D) -> Result<Vec<T>, D::Error> {
	d.read_seq(\|d, len\| {
	let mut v = Vec::with_capacity(len);
	for _ in 0..len {
	v.push(d.read_seq_elt(\|d\| Decodable::decode(d))?);
	}
	Ok(v)
	})
	}
	}

	impl<S: Encoder, T: Encodable<S>, const N: usize> Encodable<S> for [T; N] {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	let slice: &[T] = self;
	slice.encode(s)
	}
	}

	impl<D: Decoder, const N: usize> Decodable<D> for [u8; N] {
	fn decode(d: &mut D) -> Result<[u8; N], D::Error> {
	d.read_seq(\|d, len\| {
	assert!(len == N);
	let mut v = [0u8; N];
	for i in 0..len {
	v[i] = d.read_seq_elt(\|d\| Decodable::decode(d))?;
	}
	Ok(v)
	})
	}
	}

	impl<'a, S: Encoder, T: Encodable<S>> Encodable<S> for Cow<'a, [T]>
	where
	[T]: ToOwned<Owned = Vec<T>>,
	{
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	let slice: &[T] = self;
	slice.encode(s)
	}
	}

	impl<D: Decoder, T: Decodable<D> + ToOwned> Decodable<D> for Cow<'static, [T]>
	where
	[T]: ToOwned<Owned = Vec<T>>,
	{
	fn decode(d: &mut D) -> Result<Cow<'static, [T]>, D::Error> {
	let v: Vec<T> = Decodable::decode(d)?;
	Ok(Cow::Owned(v))
	}
	}

	impl<S: Encoder, T: Encodable<S>> Encodable<S> for Option<T> {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	s.emit_option(\|s\| match *self {
	None => s.emit_option_none(),
	Some(ref v) => s.emit_option_some(\|s\| v.encode(s)),
	})
	}
	}

	impl<D: Decoder, T: Decodable<D>> Decodable<D> for Option<T> {
	fn decode(d: &mut D) -> Result<Option<T>, D::Error> {
	d.read_option(\|d, b\| if b { Ok(Some(Decodable::decode(d)?)) } else { Ok(None) })
	}
	}

	impl<S: Encoder, T1: Encodable<S>, T2: Encodable<S>> Encodable<S> for Result<T1, T2> {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	s.emit_enum(\|s\| match *self {
	Ok(ref v) => {
	s.emit_enum_variant("Ok", 0, 1, \|s\| s.emit_enum_variant_arg(true, \|s\| v.encode(s)))
	}
	Err(ref v) => {
	s.emit_enum_variant("Err", 1, 1, \|s\| s.emit_enum_variant_arg(true, \|s\| v.encode(s)))
	}
	})
	}
	}

	impl<D: Decoder, T1: Decodable<D>, T2: Decodable<D>> Decodable<D> for Result<T1, T2> {
	fn decode(d: &mut D) -> Result<Result<T1, T2>, D::Error> {
	d.read_enum(\|d\| {
	d.read_enum_variant(&["Ok", "Err"], \|d, disr\| match disr {
	0 => Ok(Ok(d.read_enum_variant_arg(\|d\| T1::decode(d))?)),
	1 => Ok(Err(d.read_enum_variant_arg(\|d\| T2::decode(d))?)),
	_ => {
	panic!(
	"Encountered invalid discriminant while \
	decoding `Result`."
	);
	}
	})
	})
	}
	}

	macro_rules! peel {
	($name:ident, $($other:ident,)) => (tuple! { $($other,) })
	}

	/// Evaluates to the number of tokens passed to it.
	///
	/// Logarithmic counting: every one or two recursive expansions, the number of
	/// tokens to count is divided by two, instead of being reduced by one.
	/// Therefore, the recursion depth is the binary logarithm of the number of
	/// tokens to count, and the expanded tree is likewise very small.
	macro_rules! count {
	() => (0usize);
	($one:tt) => (1usize);
	($($pairs:tt $_p:tt)) => (count!($($pairs)) << 1usize);
	($odd:tt $($rest:tt)) => (count!($($rest)) \| 1usize);
	}

	macro_rules! tuple {
	() => ();
	( $($name:ident,)+ ) => (
	impl<D: Decoder, $($name: Decodable<D>),+> Decodable<D> for ($($name,)+) {
	#[allow(non_snake_case)]
	fn decode(d: &mut D) -> Result<($($name,)+), D::Error> {
	let len: usize = count!($($name)+);
	d.read_tuple(len, \|d\| {
	let ret = ($(d.read_tuple_arg(\|d\| -> Result<$name, D::Error> {
	Decodable::decode(d)
	})?,)+);
	Ok(ret)
	})
	}
	}
	impl<S: Encoder, $($name: Encodable<S>),+> Encodable<S> for ($($name,)+) {
	#[allow(non_snake_case)]
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	let ($(ref $name,)+) = *self;
	let mut n = 0;
	$(let $name = $name; n += 1;)+
	s.emit_tuple(n, \|s\| {
	let mut i = 0;
	$(s.emit_tuple_arg({ i+=1; i-1 }, \|s\| $name.encode(s))?;)+
	Ok(())
	})
	}
	}
	peel! { $($name,)+ }
	)
	}

	tuple! { T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, }

	impl<S: Encoder> Encodable<S> for path::Path {
	fn encode(&self, e: &mut S) -> Result<(), S::Error> {
	self.to_str().unwrap().encode(e)
	}
	}

	impl<S: Encoder> Encodable<S> for path::PathBuf {
	fn encode(&self, e: &mut S) -> Result<(), S::Error> {
	path::Path::encode(self, e)
	}
	}

	impl<D: Decoder> Decodable<D> for path::PathBuf {
	fn decode(d: &mut D) -> Result<path::PathBuf, D::Error> {
	let bytes: String = Decodable::decode(d)?;
	Ok(path::PathBuf::from(bytes))
	}
	}

	impl<S: Encoder, T: Encodable<S> + Copy> Encodable<S> for Cell<T> {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	self.get().encode(s)
	}
	}

	impl<D: Decoder, T: Decodable<D> + Copy> Decodable<D> for Cell<T> {
	fn decode(d: &mut D) -> Result<Cell<T>, D::Error> {
	Ok(Cell::new(Decodable::decode(d)?))
	}
	}

	// FIXME: #15036
	// Should use `try_borrow`, returning an
	// `encoder.error("attempting to Encode borrowed RefCell")`
	// from `encode` when `try_borrow` returns `None`.

	impl<S: Encoder, T: Encodable<S>> Encodable<S> for RefCell<T> {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	self.borrow().encode(s)
	}
	}

	impl<D: Decoder, T: Decodable<D>> Decodable<D> for RefCell<T> {
	fn decode(d: &mut D) -> Result<RefCell<T>, D::Error> {
	Ok(RefCell::new(Decodable::decode(d)?))
	}
	}

	impl<S: Encoder, T: Encodable<S>> Encodable<S> for Arc<T> {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	(**self).encode(s)
	}
	}

	impl<D: Decoder, T: Decodable<D>> Decodable<D> for Arc<T> {
	fn decode(d: &mut D) -> Result<Arc<T>, D::Error> {
	Ok(Arc::new(Decodable::decode(d)?))
	}
	}

	impl<S: Encoder, T: ?Sized + Encodable<S>> Encodable<S> for Box<T> {
	fn encode(&self, s: &mut S) -> Result<(), S::Error> {
	(**self).encode(s)
	}
	}
	impl<D: Decoder, T: Decodable<D>> Decodable<D> for Box<T> {
	fn decode(d: &mut D) -> Result<Box<T>, D::Error> {
	Ok(Box::new(Decodable::decode(d)?))
	}
	}