Use delayed error handling for Encodable and Encoder infallible.
There are two impls of the `Encoder` trait: `opaque::Encoder` and `opaque::FileEncoder`. The former encodes into memory and is infallible, the latter writes to file and is fallible. Currently, standard `Result`/`?`/`unwrap` error handling is used, but this is a bit verbose and has non-trivial cost, which is annoying given how rare failures are (especially in the infallible `opaque::Encoder` case). This commit changes how `Encoder` fallibility is handled. All the `emit_*` methods are now infallible. `opaque::Encoder` requires no great changes for this. `opaque::FileEncoder` now implements a delayed error handling strategy. If a failure occurs, it records this via the `res` field, and all subsequent encoding operations are skipped if `res` indicates an error has occurred. Once encoding is complete, the new `finish` method is called, which returns a `Result`. In other words, there is now a single `Result`-producing method instead of many of them. This has very little effect on how any file errors are reported if `opaque::FileEncoder` has any failures. Much of this commit is boring mechanical changes, removing `Result` return values and `?` or `unwrap` from expressions. The more interesting parts are as follows. - serialize.rs: The `Encoder` trait gains an `Ok` associated type. The `into_inner` method is changed into `finish`, which returns `Result<Vec<u8>, !>`. - opaque.rs: The `FileEncoder` adopts the delayed error handling strategy. Its `Ok` type is a `usize`, returning the number of bytes written, replacing previous uses of `FileEncoder::position`. - Various methods that take an encoder now consume it, rather than being passed a mutable reference, e.g. `serialize_query_result_cache`.
This commit is contained in:
Nicholas Nethercote
parent
582b9cbc45
commit
1acbe7573d
45 changed files with 611 additions and 682 deletions
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@ -11,36 +11,47 @@ 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 when `finish()` is
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/// called, an error result should be returned to indicate the failure. If no
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/// failures occurred, then `finish()` should return a success result.
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pub trait Encoder {
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type Error;
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type Ok;
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type Err;
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// Primitive types:
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fn emit_usize(&mut self, v: usize) -> Result<(), Self::Error>;
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fn emit_u128(&mut self, v: u128) -> Result<(), Self::Error>;
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fn emit_u64(&mut self, v: u64) -> Result<(), Self::Error>;
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fn emit_u32(&mut self, v: u32) -> Result<(), Self::Error>;
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fn emit_u16(&mut self, v: u16) -> Result<(), Self::Error>;
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fn emit_u8(&mut self, v: u8) -> Result<(), Self::Error>;
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fn emit_isize(&mut self, v: isize) -> Result<(), Self::Error>;
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fn emit_i128(&mut self, v: i128) -> Result<(), Self::Error>;
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fn emit_i64(&mut self, v: i64) -> Result<(), Self::Error>;
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fn emit_i32(&mut self, v: i32) -> Result<(), Self::Error>;
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fn emit_i16(&mut self, v: i16) -> Result<(), Self::Error>;
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fn emit_i8(&mut self, v: i8) -> Result<(), Self::Error>;
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fn emit_bool(&mut self, v: bool) -> Result<(), Self::Error>;
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fn emit_f64(&mut self, v: f64) -> Result<(), Self::Error>;
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fn emit_f32(&mut self, v: f32) -> Result<(), Self::Error>;
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fn emit_char(&mut self, v: char) -> Result<(), Self::Error>;
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fn emit_str(&mut self, v: &str) -> Result<(), Self::Error>;
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fn emit_raw_bytes(&mut self, s: &[u8]) -> Result<(), Self::Error>;
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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) -> Result<(), Self::Error>
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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) -> Result<(), Self::Error>,
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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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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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// 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) -> Result<(), Self::Error> {
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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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// Consume the encoder, getting the result.
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fn finish(self) -> Result<Self::Ok, Self::Err>;
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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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@ -95,7 +109,7 @@ pub trait Decoder {
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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) -> Result<(), S::Error>;
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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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@ -117,8 +131,8 @@ 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 $ty {
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fn encode(&self, s: &mut S) -> Result<(), S::Error> {
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s.$emit_method(*self)
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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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@ -138,12 +152,14 @@ direct_serialize_impls! {
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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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@ -154,14 +170,14 @@ 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) -> Result<(), S::Error> {
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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) -> Result<(), S::Error> {
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unreachable!()
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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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@ -172,8 +188,8 @@ impl<D: Decoder> Decodable<D> for ! {
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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) -> Result<(), S::Error> {
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s.emit_u32(self.get())
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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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@ -184,14 +200,14 @@ impl<D: Decoder> Decodable<D> for ::std::num::NonZeroU32 {
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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) -> Result<(), S::Error> {
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s.emit_str(self)
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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) -> Result<(), S::Error> {
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s.emit_str(&self[..])
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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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@ -202,9 +218,7 @@ impl<D: Decoder> Decodable<D> for String {
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}
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impl<S: Encoder> Encodable<S> for () {
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fn encode(&self, _s: &mut S) -> Result<(), S::Error> {
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Ok(())
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}
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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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@ -212,9 +226,7 @@ impl<D: Decoder> Decodable<D> for () {
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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) -> Result<(), S::Error> {
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Ok(())
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}
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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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@ -231,8 +243,8 @@ impl<D: Decoder, T: Decodable<D>> Decodable<D> for Box<[T]> {
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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) -> Result<(), S::Error> {
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(**self).encode(s)
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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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@ -243,19 +255,18 @@ impl<D: Decoder, T: Decodable<D>> Decodable<D> for Rc<T> {
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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) -> Result<(), S::Error> {
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s.emit_usize(self.len())?;
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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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e.encode(s);
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}
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Ok(())
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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) -> Result<(), S::Error> {
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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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slice.encode(s);
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}
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}
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@ -277,9 +288,9 @@ impl<D: Decoder, T: Decodable<D>> Decodable<D> for Vec<T> {
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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) -> Result<(), S::Error> {
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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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slice.encode(s);
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}
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}
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@ -299,9 +310,9 @@ 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) -> Result<(), S::Error> {
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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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slice.encode(s);
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}
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}
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@ -316,7 +327,7 @@ where
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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) -> Result<(), S::Error> {
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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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@ -330,9 +341,9 @@ impl<'a, D: Decoder> Decodable<D> for Cow<'a, str> {
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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) -> Result<(), S::Error> {
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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, |_| Ok(())),
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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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@ -349,7 +360,7 @@ impl<D: Decoder, T: Decodable<D>> Decodable<D> for Option<T> {
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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) -> Result<(), S::Error> {
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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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@ -381,10 +392,9 @@ macro_rules! tuple {
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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) -> Result<(), S::Error> {
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fn encode(&self, s: &mut S) {
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let ($(ref $name,)+) = *self;
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$($name.encode(s)?;)+
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Ok(())
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$($name.encode(s);)+
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}
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}
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peel! { $($name,)+ }
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@ -394,14 +404,14 @@ macro_rules! tuple {
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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) -> Result<(), S::Error> {
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self.to_str().unwrap().encode(e)
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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) -> Result<(), S::Error> {
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path::Path::encode(self, e)
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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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@ -413,8 +423,8 @@ impl<D: Decoder> Decodable<D> for path::PathBuf {
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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) -> Result<(), S::Error> {
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self.get().encode(s)
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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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@ -430,8 +440,8 @@ impl<D: Decoder, T: Decodable<D> + Copy> Decodable<D> for Cell<T> {
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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) -> Result<(), S::Error> {
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self.borrow().encode(s)
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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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@ -442,8 +452,8 @@ impl<D: Decoder, T: Decodable<D>> Decodable<D> for RefCell<T> {
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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) -> Result<(), S::Error> {
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(**self).encode(s)
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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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@ -454,8 +464,8 @@ impl<D: Decoder, T: Decodable<D>> Decodable<D> for Arc<T> {
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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) -> Result<(), S::Error> {
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(**self).encode(s)
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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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|
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Loading…
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Reference in a new issue