bb02cc47c4
This simplifies things, but requires making `CacheEncoder` non-generic. (This was previously merged as commit 4 in #94732 and then was reverted in #97905 because it caused a perf regression.)
470 lines
13 KiB
Rust
470 lines
13 KiB
Rust
//! Support code for encoding and decoding types.
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/*
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Core encoding and decoding interfaces.
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*/
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use std::borrow::Cow;
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use std::cell::{Cell, RefCell};
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use std::marker::PhantomData;
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use std::path;
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use std::rc::Rc;
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use std::sync::Arc;
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/// A note about error handling.
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///
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/// Encoders may be fallible, but in practice failure is rare and there are so
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/// many nested calls that typical Rust error handling (via `Result` and `?`)
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/// is pervasive and has non-trivial cost. Instead, impls of this trait must
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/// implement a delayed error handling strategy. If a failure occurs, they
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/// should record this internally, and all subsequent encoding operations can
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/// be processed or ignored, whichever is appropriate. Then they should provide
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/// a `finish` method that finishes up encoding. If the encoder is fallible,
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/// `finish` should return a `Result` that indicates success or failure.
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pub trait Encoder {
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// Primitive types:
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fn emit_usize(&mut self, v: usize);
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fn emit_u128(&mut self, v: u128);
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fn emit_u64(&mut self, v: u64);
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fn emit_u32(&mut self, v: u32);
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fn emit_u16(&mut self, v: u16);
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fn emit_u8(&mut self, v: u8);
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fn emit_isize(&mut self, v: isize);
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fn emit_i128(&mut self, v: i128);
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fn emit_i64(&mut self, v: i64);
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fn emit_i32(&mut self, v: i32);
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fn emit_i16(&mut self, v: i16);
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fn emit_i8(&mut self, v: i8);
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fn emit_bool(&mut self, v: bool);
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fn emit_f64(&mut self, v: f64);
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fn emit_f32(&mut self, v: f32);
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fn emit_char(&mut self, v: char);
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fn emit_str(&mut self, v: &str);
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fn emit_raw_bytes(&mut self, s: &[u8]);
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// Convenience for the derive macro:
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fn emit_enum_variant<F>(&mut self, v_id: usize, f: F)
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where
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F: FnOnce(&mut Self),
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{
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self.emit_usize(v_id);
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f(self);
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}
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// We put the field index in a const generic to allow the emit_usize to be
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// compiled into a more efficient form. In practice, the variant index is
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// known at compile-time, and that knowledge allows much more efficient
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// codegen than we'd otherwise get. LLVM isn't always able to make the
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// optimization that would otherwise be necessary here, likely due to the
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// multiple levels of inlining and const-prop that are needed.
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#[inline]
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fn emit_fieldless_enum_variant<const ID: usize>(&mut self) {
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self.emit_usize(ID)
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}
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}
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// Note: all the methods in this trait are infallible, which may be surprising.
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// They used to be fallible (i.e. return a `Result`) but many of the impls just
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// panicked when something went wrong, and for the cases that didn't the
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// top-level invocation would also just panic on failure. Switching to
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// infallibility made things faster and lots of code a little simpler and more
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// concise.
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pub trait Decoder {
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// Primitive types:
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fn read_usize(&mut self) -> usize;
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fn read_u128(&mut self) -> u128;
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fn read_u64(&mut self) -> u64;
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fn read_u32(&mut self) -> u32;
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fn read_u16(&mut self) -> u16;
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fn read_u8(&mut self) -> u8;
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fn read_isize(&mut self) -> isize;
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fn read_i128(&mut self) -> i128;
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fn read_i64(&mut self) -> i64;
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fn read_i32(&mut self) -> i32;
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fn read_i16(&mut self) -> i16;
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fn read_i8(&mut self) -> i8;
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fn read_bool(&mut self) -> bool;
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fn read_f64(&mut self) -> f64;
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fn read_f32(&mut self) -> f32;
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fn read_char(&mut self) -> char;
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fn read_str(&mut self) -> &str;
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fn read_raw_bytes(&mut self, len: usize) -> &[u8];
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}
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/// Trait for types that can be serialized
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///
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/// This can be implemented using the `Encodable`, `TyEncodable` and
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/// `MetadataEncodable` macros.
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///
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/// * `Encodable` should be used in crates that don't depend on
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/// `rustc_middle`.
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/// * `MetadataEncodable` is used in `rustc_metadata` for types that contain
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/// `rustc_metadata::rmeta::Lazy`.
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/// * `TyEncodable` should be used for types that are only serialized in crate
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/// metadata or the incremental cache. This is most types in `rustc_middle`.
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pub trait Encodable<S: Encoder> {
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fn encode(&self, s: &mut S);
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}
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/// Trait for types that can be deserialized
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///
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/// This can be implemented using the `Decodable`, `TyDecodable` and
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/// `MetadataDecodable` macros.
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///
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/// * `Decodable` should be used in crates that don't depend on
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/// `rustc_middle`.
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/// * `MetadataDecodable` is used in `rustc_metadata` for types that contain
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/// `rustc_metadata::rmeta::Lazy`.
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/// * `TyDecodable` should be used for types that are only serialized in crate
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/// metadata or the incremental cache. This is most types in `rustc_middle`.
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pub trait Decodable<D: Decoder>: Sized {
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fn decode(d: &mut D) -> Self;
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}
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macro_rules! direct_serialize_impls {
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($($ty:ident $emit_method:ident $read_method:ident),*) => {
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$(
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impl<S: Encoder> Encodable<S> for $ty {
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fn encode(&self, s: &mut S) {
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s.$emit_method(*self);
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}
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}
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impl<D: Decoder> Decodable<D> for $ty {
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fn decode(d: &mut D) -> $ty {
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d.$read_method()
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}
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}
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)*
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}
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}
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direct_serialize_impls! {
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usize emit_usize read_usize,
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u8 emit_u8 read_u8,
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u16 emit_u16 read_u16,
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u32 emit_u32 read_u32,
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u64 emit_u64 read_u64,
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u128 emit_u128 read_u128,
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isize emit_isize read_isize,
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i8 emit_i8 read_i8,
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i16 emit_i16 read_i16,
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i32 emit_i32 read_i32,
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i64 emit_i64 read_i64,
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i128 emit_i128 read_i128,
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f32 emit_f32 read_f32,
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f64 emit_f64 read_f64,
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bool emit_bool read_bool,
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char emit_char read_char
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}
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impl<S: Encoder, T: ?Sized> Encodable<S> for &T
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where
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T: Encodable<S>,
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{
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fn encode(&self, s: &mut S) {
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(**self).encode(s)
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}
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}
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impl<S: Encoder> Encodable<S> for ! {
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fn encode(&self, _s: &mut S) {
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unreachable!();
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}
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}
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impl<D: Decoder> Decodable<D> for ! {
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fn decode(_d: &mut D) -> ! {
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unreachable!()
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}
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}
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impl<S: Encoder> Encodable<S> for ::std::num::NonZeroU32 {
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fn encode(&self, s: &mut S) {
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s.emit_u32(self.get());
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}
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}
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impl<D: Decoder> Decodable<D> for ::std::num::NonZeroU32 {
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fn decode(d: &mut D) -> Self {
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::std::num::NonZeroU32::new(d.read_u32()).unwrap()
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}
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}
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impl<S: Encoder> Encodable<S> for str {
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fn encode(&self, s: &mut S) {
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s.emit_str(self);
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}
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}
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impl<S: Encoder> Encodable<S> for String {
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fn encode(&self, s: &mut S) {
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s.emit_str(&self[..]);
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}
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}
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impl<D: Decoder> Decodable<D> for String {
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fn decode(d: &mut D) -> String {
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d.read_str().to_owned()
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}
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}
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impl<S: Encoder> Encodable<S> for () {
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fn encode(&self, _s: &mut S) {}
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}
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impl<D: Decoder> Decodable<D> for () {
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fn decode(_: &mut D) -> () {}
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}
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impl<S: Encoder, T> Encodable<S> for PhantomData<T> {
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fn encode(&self, _s: &mut S) {}
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}
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impl<D: Decoder, T> Decodable<D> for PhantomData<T> {
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fn decode(_: &mut D) -> PhantomData<T> {
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PhantomData
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}
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}
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impl<D: Decoder, T: Decodable<D>> Decodable<D> for Box<[T]> {
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fn decode(d: &mut D) -> Box<[T]> {
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let v: Vec<T> = Decodable::decode(d);
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v.into_boxed_slice()
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}
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}
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impl<S: Encoder, T: Encodable<S>> Encodable<S> for Rc<T> {
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fn encode(&self, s: &mut S) {
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(**self).encode(s);
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}
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}
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impl<D: Decoder, T: Decodable<D>> Decodable<D> for Rc<T> {
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fn decode(d: &mut D) -> Rc<T> {
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Rc::new(Decodable::decode(d))
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}
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}
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impl<S: Encoder, T: Encodable<S>> Encodable<S> for [T] {
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default fn encode(&self, s: &mut S) {
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s.emit_usize(self.len());
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for e in self.iter() {
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e.encode(s);
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}
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}
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}
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impl<S: Encoder, T: Encodable<S>> Encodable<S> for Vec<T> {
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fn encode(&self, s: &mut S) {
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let slice: &[T] = self;
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slice.encode(s);
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}
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}
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impl<D: Decoder, T: Decodable<D>> Decodable<D> for Vec<T> {
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default fn decode(d: &mut D) -> Vec<T> {
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let len = d.read_usize();
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// SAFETY: we set the capacity in advance, only write elements, and
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// only set the length at the end once the writing has succeeded.
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let mut vec = Vec::with_capacity(len);
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unsafe {
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let ptr: *mut T = vec.as_mut_ptr();
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for i in 0..len {
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std::ptr::write(ptr.offset(i as isize), Decodable::decode(d));
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}
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vec.set_len(len);
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}
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vec
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}
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}
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impl<S: Encoder, T: Encodable<S>, const N: usize> Encodable<S> for [T; N] {
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fn encode(&self, s: &mut S) {
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let slice: &[T] = self;
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slice.encode(s);
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}
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}
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impl<D: Decoder, const N: usize> Decodable<D> for [u8; N] {
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fn decode(d: &mut D) -> [u8; N] {
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let len = d.read_usize();
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assert!(len == N);
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let mut v = [0u8; N];
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for i in 0..len {
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v[i] = Decodable::decode(d);
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}
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v
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}
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}
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impl<'a, S: Encoder, T: Encodable<S>> Encodable<S> for Cow<'a, [T]>
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where
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[T]: ToOwned<Owned = Vec<T>>,
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{
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fn encode(&self, s: &mut S) {
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let slice: &[T] = self;
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slice.encode(s);
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}
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}
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impl<D: Decoder, T: Decodable<D> + ToOwned> Decodable<D> for Cow<'static, [T]>
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where
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[T]: ToOwned<Owned = Vec<T>>,
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{
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fn decode(d: &mut D) -> Cow<'static, [T]> {
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let v: Vec<T> = Decodable::decode(d);
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Cow::Owned(v)
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}
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}
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impl<'a, S: Encoder> Encodable<S> for Cow<'a, str> {
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fn encode(&self, s: &mut S) {
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let val: &str = self;
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val.encode(s)
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}
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}
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impl<'a, D: Decoder> Decodable<D> for Cow<'a, str> {
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fn decode(d: &mut D) -> Cow<'static, str> {
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let v: String = Decodable::decode(d);
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Cow::Owned(v)
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}
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}
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impl<S: Encoder, T: Encodable<S>> Encodable<S> for Option<T> {
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fn encode(&self, s: &mut S) {
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match *self {
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None => s.emit_enum_variant(0, |_| {}),
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Some(ref v) => s.emit_enum_variant(1, |s| v.encode(s)),
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}
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}
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}
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impl<D: Decoder, T: Decodable<D>> Decodable<D> for Option<T> {
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fn decode(d: &mut D) -> Option<T> {
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match d.read_usize() {
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0 => None,
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1 => Some(Decodable::decode(d)),
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_ => panic!("Encountered invalid discriminant while decoding `Option`."),
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}
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}
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}
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impl<S: Encoder, T1: Encodable<S>, T2: Encodable<S>> Encodable<S> for Result<T1, T2> {
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fn encode(&self, s: &mut S) {
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match *self {
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Ok(ref v) => s.emit_enum_variant(0, |s| v.encode(s)),
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Err(ref v) => s.emit_enum_variant(1, |s| v.encode(s)),
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}
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}
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}
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impl<D: Decoder, T1: Decodable<D>, T2: Decodable<D>> Decodable<D> for Result<T1, T2> {
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fn decode(d: &mut D) -> Result<T1, T2> {
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match d.read_usize() {
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0 => Ok(T1::decode(d)),
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1 => Err(T2::decode(d)),
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_ => panic!("Encountered invalid discriminant while decoding `Result`."),
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}
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}
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}
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macro_rules! peel {
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($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
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}
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macro_rules! tuple {
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() => ();
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( $($name:ident,)+ ) => (
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impl<D: Decoder, $($name: Decodable<D>),+> Decodable<D> for ($($name,)+) {
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fn decode(d: &mut D) -> ($($name,)+) {
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($({ let element: $name = Decodable::decode(d); element },)+)
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}
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}
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impl<S: Encoder, $($name: Encodable<S>),+> Encodable<S> for ($($name,)+) {
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#[allow(non_snake_case)]
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fn encode(&self, s: &mut S) {
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let ($(ref $name,)+) = *self;
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$($name.encode(s);)+
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}
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}
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peel! { $($name,)+ }
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)
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}
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tuple! { T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, }
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impl<S: Encoder> Encodable<S> for path::Path {
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fn encode(&self, e: &mut S) {
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self.to_str().unwrap().encode(e);
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}
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}
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impl<S: Encoder> Encodable<S> for path::PathBuf {
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fn encode(&self, e: &mut S) {
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path::Path::encode(self, e);
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}
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}
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impl<D: Decoder> Decodable<D> for path::PathBuf {
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fn decode(d: &mut D) -> path::PathBuf {
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let bytes: String = Decodable::decode(d);
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path::PathBuf::from(bytes)
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}
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}
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impl<S: Encoder, T: Encodable<S> + Copy> Encodable<S> for Cell<T> {
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fn encode(&self, s: &mut S) {
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self.get().encode(s);
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}
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}
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impl<D: Decoder, T: Decodable<D> + Copy> Decodable<D> for Cell<T> {
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fn decode(d: &mut D) -> Cell<T> {
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Cell::new(Decodable::decode(d))
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}
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}
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// FIXME: #15036
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// Should use `try_borrow`, returning an
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// `encoder.error("attempting to Encode borrowed RefCell")`
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// from `encode` when `try_borrow` returns `None`.
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impl<S: Encoder, T: Encodable<S>> Encodable<S> for RefCell<T> {
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fn encode(&self, s: &mut S) {
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self.borrow().encode(s);
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}
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}
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impl<D: Decoder, T: Decodable<D>> Decodable<D> for RefCell<T> {
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fn decode(d: &mut D) -> RefCell<T> {
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RefCell::new(Decodable::decode(d))
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}
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}
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impl<S: Encoder, T: Encodable<S>> Encodable<S> for Arc<T> {
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fn encode(&self, s: &mut S) {
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(**self).encode(s);
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}
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}
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impl<D: Decoder, T: Decodable<D>> Decodable<D> for Arc<T> {
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fn decode(d: &mut D) -> Arc<T> {
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Arc::new(Decodable::decode(d))
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}
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}
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impl<S: Encoder, T: ?Sized + Encodable<S>> Encodable<S> for Box<T> {
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fn encode(&self, s: &mut S) {
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(**self).encode(s);
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}
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}
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impl<D: Decoder, T: Decodable<D>> Decodable<D> for Box<T> {
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fn decode(d: &mut D) -> Box<T> {
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Box::new(Decodable::decode(d))
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}
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}
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