Rollup merge of rust-lang#153283 - LukeMathWalker:add-rkyv-support, r=aDotInTheVoid

feat(rustdoc-json): Add optional support for rkyv (de)serialization

## Motivation

The JSON documents produced by `rustdoc-json` are _big_. More often than not, tools need to access a small fraction of that output—e.g. a couple of types from a transitive dependency, or a subset of the fields on a given `rustdoc-json-types` type.

Using a binary (de)serialization format and a cache helps to drive down the performance cost of deserialization: you invoke `rustdoc-json` to get the JSON output you need, re-serialize it using a more perfomant format as target (e.g. `bincode` or `postcard`) and thus amortize the cost of future queries that hit the persistent cache rather than `rustdoc-json`.
This is _better_, but still not great: the deserialization cost for crates like `std` still shows up prominently in flamegraphs.

## An Alternative Approach: rkyv

`rkyv` provides a different opportunity: you avoid paying the deserialization cost _upfront_ thanks to [zero-copy deserialization](https://rkyv.org/zero-copy-deserialization.html).
You're often able to determine if you need a certain entry from the JSON document using the archived version of that type, thus incurring the full deserialization cost only for the subset of items you actually need ([example](LukeMathWalker/pavex@d067e7e)).

## The Change

This PR adds support for `rkyv` behind a feature flag (`rkyv_0_8`).
For most types, it's a straight-forward `derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize)` annotation. For co-recursive types, we need to adjust the generated bounds, using the techniques from [`rkyv`'s JSON example](https://github.com/rkyv/rkyv/blob/985b0230a0b9cb9fce4a4ee9facb6af148e27c8e/rkyv/examples/json_like_schema.rs).

I have added new round-trip tests to ensure `rkyv` works as expected.

r? @aDotInTheVoid

Author: JonathanBrouwer

Cargo.lock

@@ -376,12 +376,41 @@ version = "3.19.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "46c5e41b57b8bba42a04676d81cb89e9ee8e859a1a66f80a5a72e1cb76b34d43"
 
+[[package]]
+name = "bytecheck"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0caa33a2c0edca0419d15ac723dff03f1956f7978329b1e3b5fdaaaed9d3ca8b"
+dependencies = [
+ "bytecheck_derive",
+ "ptr_meta",
+ "rancor",
+ "simdutf8",
+]
+
+[[package]]
+name = "bytecheck_derive"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "89385e82b5d1821d2219e0b095efa2cc1f246cbf99080f3be46a1a85c0d392d9"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.110",
+]
+
 [[package]]
 name = "bytecount"
 version = "0.6.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "175812e0be2bccb6abe50bb8d566126198344f707e304f45c648fd8f2cc0365e"
 
+[[package]]
+name = "bytes"
+version = "1.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e748733b7cbc798e1434b6ac524f0c1ff2ab456fe201501e6497c8417a4fc33"
+
 [[package]]
 name = "camino"
 version = "1.2.1"
@@ -2476,6 +2505,26 @@ dependencies = [
 name = "miropt-test-tools"
 version = "0.1.0"
 
+[[package]]
+name = "munge"
+version = "0.4.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e17401f259eba956ca16491461b6e8f72913a0a114e39736ce404410f915a0c"
+dependencies = [
+ "munge_macro",
+]
+
+[[package]]
+name = "munge_macro"
+version = "0.4.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4568f25ccbd45ab5d5603dc34318c1ec56b117531781260002151b8530a9f931"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.110",
+]
+
 [[package]]
 name = "new_debug_unreachable"
 version = "1.0.6"
@@ -3047,6 +3096,26 @@ dependencies = [
  "cc",
 ]
 
+[[package]]
+name = "ptr_meta"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0b9a0cf95a1196af61d4f1cbdab967179516d9a4a4312af1f31948f8f6224a79"
+dependencies = [
+ "ptr_meta_derive",
+]
+
+[[package]]
+name = "ptr_meta_derive"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7347867d0a7e1208d93b46767be83e2b8f978c3dad35f775ac8d8847551d6fe1"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.110",
+]
+
 [[package]]
 name = "pulldown-cmark"
 version = "0.11.3"
@@ -3092,6 +3161,15 @@ version = "5.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "69cdb34c158ceb288df11e18b4bd39de994f6657d83847bdffdbd7f346754b0f"
 
+[[package]]
+name = "rancor"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a063ea72381527c2a0561da9c80000ef822bdd7c3241b1cc1b12100e3df081ee"
+dependencies = [
+ "ptr_meta",
+]
+
 [[package]]
 name = "rand"
 version = "0.8.5"
@@ -3275,6 +3353,15 @@ dependencies = [
 name = "remote-test-server"
 version = "0.1.0"
 
+[[package]]
+name = "rend"
+version = "0.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cadadef317c2f20755a64d7fdc48f9e7178ee6b0e1f7fce33fa60f1d68a276e6"
+dependencies = [
+ "bytecheck",
+]
+
 [[package]]
 name = "replace-version-placeholder"
 version = "0.1.0"
@@ -3283,6 +3370,36 @@ dependencies = [
  "walkdir",
 ]
 
+[[package]]
+name = "rkyv"
+version = "0.8.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1a30e631b7f4a03dee9056b8ef6982e8ba371dd5bedb74d3ec86df4499132c70"
+dependencies = [
+ "bytecheck",
+ "bytes",
+ "hashbrown 0.16.1",
+ "indexmap",
+ "munge",
+ "ptr_meta",
+ "rancor",
+ "rend",
+ "rkyv_derive",
+ "tinyvec",
+ "uuid",
+]
+
+[[package]]
+name = "rkyv_derive"
+version = "0.8.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8100bb34c0a1d0f907143db3149e6b4eea3c33b9ee8b189720168e818303986f"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.110",
+]
+
 [[package]]
 name = "run_make_support"
 version = "0.0.0"
@@ -4790,6 +4907,7 @@ name = "rustdoc-json-types"
 version = "0.1.0"
 dependencies = [
  "bincode",
+ "rkyv",
  "rustc-hash 2.1.1",
  "serde",
  "serde_derive",
@@ -5128,6 +5246,12 @@ version = "0.3.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d66dc143e6b11c1eddc06d5c423cfc97062865baf299914ab64caa38182078fe"
 
+[[package]]
+name = "simdutf8"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e3a9fe34e3e7a50316060351f37187a3f546bce95496156754b601a5fa71b76e"
+
 [[package]]
 name = "similar"
 version = "2.7.0"

src/bootstrap/src/core/build_steps/test.rs

@@ -3315,7 +3315,7 @@ impl Step for CrateRustdocJsonTypes {
             builder.kind,
             "src/rustdoc-json-types",
             SourceType::InTree,
-            &[],
+            &["rkyv_0_8".to_owned()],
         );
 
         // FIXME: this looks very wrong, libtest doesn't accept `-C` arguments and the quotes are fishy.

src/rustdoc-json-types/Cargo.toml

@@ -8,11 +8,13 @@ path = "lib.rs"
 
 [features]
 default = ["rustc-hash"]
+rkyv_0_8 = ["dep:rkyv"]
 
 [dependencies]
 serde = "1.0"
 serde_derive = "1.0"
 rustc-hash = { version = "2.0", optional = true }
+rkyv = { version = "0.8", optional = true }
 
 [dev-dependencies]
 serde_json = "1.0"