bjoernager/rust
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Use delayed error handling for Encodable and Encoder infallible.

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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 2022-06-07 13:30:45 +10:00
parent 582b9cbc45
commit 1acbe7573d
45 changed files with 611 additions and 682 deletions
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22
compiler/rustc_macros/src/serialize.rs
View file

@ -146,21 +146,17 @@ fn encodable_body(
.map(|binding| {
let bind_ident = &binding.binding;
let result = quote! {
match ::rustc_serialize::Encodable::<#encoder_ty>::encode(
::rustc_serialize::Encodable::<#encoder_ty>::encode(
#bind_ident,
__encoder,
) {
::std::result::Result::Ok(()) => (),
::std::result::Result::Err(__err)
=> return ::std::result::Result::Err(__err),
}
);
};
result
})
.collect::<TokenStream>()
});
quote! {
::std::result::Result::Ok(match *self { #encode_inner })
match *self { #encode_inner }
}
}
_ => {
@ -172,14 +168,10 @@ fn encodable_body(
.map(|binding| {
let bind_ident = &binding.binding;
let result = quote! {
match ::rustc_serialize::Encodable::<#encoder_ty>::encode(
::rustc_serialize::Encodable::<#encoder_ty>::encode(
#bind_ident,
__encoder,
) {
::std::result::Result::Ok(()) => (),
::std::result::Result::Err(__err)
=> return ::std::result::Result::Err(__err),
}
);
};
result
})
@ -190,7 +182,7 @@ fn encodable_body(
::rustc_serialize::Encoder::emit_enum_variant(
__encoder,
#variant_idx,
|__encoder| { ::std::result::Result::Ok({ #encode_fields }) }
|__encoder| { #encode_fields }
)
}
} else {
@ -223,7 +215,7 @@ fn encodable_body(
fn encode(
&self,
__encoder: &mut #encoder_ty,
) -> ::std::result::Result<(), <#encoder_ty as ::rustc_serialize::Encoder>::Error> {
) {
#lints
#encode_body
}