Rollup merge of #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](https://github.com/LukeMathWalker/pavex/pull/574/changes/d067e7e0cfa38da5b0a3c8713b1c53beb0b29a5d)). ## 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
2026-04-26 13:01:27 +03:00 · 2026-03-10 22:44:05 +01:00
parent 86063080a5 1f05c768be
commit cf951bae87
5 changed files with 499 additions and 5 deletions
@@ -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"
@@ -3315,7 +3315,7 @@ fn run(self, builder: &Builder<'_>) {
            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.
@@ -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"
@@ -3,7 +3,11 @@
 //! These types are the public API exposed through the `--output-format json` flag. The [`Crate`]
 //! struct is the root of the JSON blob and all other items are contained within.
 //!
-//! We expose a `rustc-hash` feature that is disabled by default. This feature switches the
+//! # Feature Flags
+//!
+//! ## `rustc-hash`
+//!
+//! We expose a `rustc-hash` feature, disabled by default. This feature switches the
 //! [`std::collections::HashMap`] for [`rustc_hash::FxHashMap`] to improve the performance of said
 //! `HashMap` in specific situations.
 //!
@@ -12,8 +16,81 @@
 //! turning this feature on, as [`FxHashMap`][2] only concerns itself with hash speed, and may
 //! increase the number of collisions.
 //!
+//! ## `rkyv_0_8`
+//!
+//! We expose a `rkyv_0_8` feature, disabled by default. When enabled, it derives `rkyv`'s
+//! [`Archive`][3], [`Serialize`][4] and [`Deserialize`][5] traits for all types in this crate.
+//! Furthermore, it exposes the corresponding `Archived*` types (e.g. `ArchivedId` for [`Id`]).
+//!
+//! `rkyv` lets you works with JSON output without paying the deserialization cost _upfront_,
+//! thanks to [zero-copy deserialization][6].
+//! You can perform various types of analyses on the `Archived*` version of the relevant types,
+//! incurring the full deserialization cost only for the subset of items you actually need.
+//!
 //! [1]: https://rust-lang.zulipchat.com/#narrow/channel/266220-t-rustdoc/topic/rustc-hash.20and.20performance.20of.20rustdoc-types/near/474855731
 //! [2]: https://crates.io/crates/rustc-hash
+//! [3]: https://docs.rs/rkyv/0.8.15/rkyv/trait.Archive.html
+//! [4]: https://docs.rs/rkyv/0.8.15/rkyv/trait.Serialize.html
+//! [5]: https://docs.rs/rkyv/0.8.15/rkyv/trait.Deserialize.html
+//! [6]: https://rkyv.org/zero-copy-deserialization.html
+
+// # On `rkyv` Derives
+//
+// In most cases, it's enough to add `#[derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize)]`
+// on top of a type to derive the relevant `rkyv` traits.
+//
+// There are a few exceptions, though, where more complex macro options are required.
+// The following sections break down the patterns that are showcased by `rkyv'`s
+// [JSON schema example](https://github.com/rkyv/rkyv/blob/985b0230a0b9cb9fce4a4ee9facb6af148e27c8e/rkyv/examples/json_like_schema.rs).
+//
+// ## Recursive Types
+//
+// Let's look at the `Type` enum as an example. It stores a `Box<Type>` in its `Slice` variant.
+// A "vanilla" `rkyv` annotation will cause an overflow in the compiler when
+// building the crate, since the bounds generated by the macro will be self-referential and thus
+// trap the compiler into a never-ending loop.
+//
+// To prevent this issue, `#[rkyv(omit_bounds)]` must be added to the relevant field.
+//
+// ## Co-Recursive Types
+//
+// The same problem occurs if a type is co-recursive—i.e. it doesn't _directly_ store a pointer
+// to another instance of the same type, but one of its fields does, transitively.
+//
+// For example, let's look at `Path`:
+//
+// - `Path` has a field of type `Option<Box<GenericArgs>>`
+// - One of the variants in `GenericArgs` has a field of type `Vec<GenericArg>`
+// - One of the variants of `GenericArg` has a field of type `Type`
+// - `Type::ResolvedPath` stores a `Path` instance
+//
+// The same logic of the recursive case applies here: we must use `#[rkyv(omit_bounds)]` to break the cycle.
+//
+// ## Additional Bounds
+//
+// Whenever `#[rkyv(omit_bounds)]` is added to a field or variant, `rkyv` omits _all_ traits bounds for that
+// field in the generated impl. This may result in compilation errors due to insufficient bounds in the
+// generated code.
+//
+// To add _some_ bounds back, `rkyv` exposes four knobs:
+//
+// - `#[rkyv(archive_bounds(..))]` to add predicates to all generated impls
+// - `#[rkyv(serialize_bounds(..))]` to add predicates to just the `Serialize` impl
+// - `#[rkyv(deserialize_bounds(..))]` to add predicates to just the `Deserialize` impl
+// - `#[rkyv(bytecheck(bounds(..)))]` to add predicates to just the `CheckBytes` impl
+//
+// In particular, we use the following annotations in this crate:
+//
+// - `serialize_bounds(__S: rkyv::ser::Writer + rkyv::ser::Allocator, __S::Error: rkyv::rancor::Source)` for serializing
+//   variable-length types like `Vec<T>`. `rkyv`'s zero-copy format requires the serializer to be able
+//   to write bytes (`Writer`) and allocate scratch space (`Allocator`) for these types
+//   ([`rkyv`'s `Vec` impl bounds](https://docs.rs/rkyv/0.8.15/rkyv/trait.Serialize.html#impl-Serialize%3CS%3E-for-Vec%3CT%3E)).
+//   The `Error: Source` bound lets error types compose.
+// - `deserialize_bounds(__D::Error: rkyv::rancor::Source)` so that errors from deserializing fields behind
+//   `omit_bounds` (e.g. `Box<T>`, `Vec<T>`) can compose via the `Source` trait.
+// - `bytecheck(bounds(__C: rkyv::validation::ArchiveContext, __C::Error: rkyv::rancor::Source))` for validating
+//   archived data. Checking that bytes represent a valid archived value requires an `ArchiveContext` that tracks
+//   validation state (e.g. subtree ranges, to prevent overlapping/out-of-bounds archived data).

 #[cfg(not(feature = "rustc-hash"))]
 use std::collections::HashMap;
@@ -46,6 +123,8 @@
 /// about the language items in the local crate, as well as info about external items to allow
 /// tools to find or link to them.
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Crate {
    /// The id of the root [`Module`] item of the local crate.
    pub root: Id,
@@ -69,6 +148,8 @@ pub struct Crate {

 /// Information about a target
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Target {
    /// The target triple for which this documentation was generated
    pub triple: String,
@@ -99,6 +180,8 @@ pub struct Target {
 /// [1]: https://doc.rust-lang.org/stable/reference/attributes/codegen.html#the-target_feature-attribute
 /// [2]: https://doc.rust-lang.org/reference/conditional-compilation.html#target_feature
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct TargetFeature {
    /// The name of this target feature.
    pub name: String,
@@ -123,6 +206,8 @@ pub struct TargetFeature {

 /// Metadata of a crate, either the same crate on which `rustdoc` was invoked, or its dependency.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct ExternalCrate {
    /// The name of the crate.
    ///
@@ -140,6 +225,7 @@ pub struct ExternalCrate {
    ///
    /// This will typically be a `.rlib` or `.rmeta`. It can be used to determine which crate
    /// this was in terms of whatever build-system invoked rustc.
+    #[cfg_attr(feature = "rkyv_0_8", rkyv(with = rkyv::with::AsString))]
    pub path: PathBuf,
 }

@@ -150,6 +236,8 @@ pub struct ExternalCrate {
 /// question, or can be used by a tool that takes the json output of multiple crates to find
 /// the actual item definition with all the relevant info.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct ItemSummary {
    /// Can be used to look up the name and html_root_url of the crate this item came from in the
    /// `external_crates` map.
@@ -171,6 +259,8 @@ pub struct ItemSummary {
 /// The `Item` data type holds fields that can apply to any of these,
 /// and leaves kind-specific details (like function args or enum variants) to the `inner` field.
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Item {
    /// The unique identifier of this item. Can be used to find this item in various mappings.
    pub id: Id,
@@ -209,6 +299,8 @@ pub struct Item {
 }

 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 /// An attribute, e.g. `#[repr(C)]`
 ///
@@ -256,6 +348,8 @@ pub enum Attribute {
 }

 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 /// The contents of a `#[repr(...)]` attribute.
 ///
 /// Used in [`Attribute::Repr`].
@@ -275,6 +369,8 @@ pub struct AttributeRepr {
 }

 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 /// The kind of `#[repr]`.
 ///
@@ -294,8 +390,11 @@ pub enum ReprKind {

 /// A range of source code.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Span {
    /// The path to the source file for this span relative to the path `rustdoc` was invoked with.
+    #[cfg_attr(feature = "rkyv_0_8", rkyv(with = rkyv::with::AsString))]
    pub filename: PathBuf,
    /// One indexed Line and Column of the first character of the `Span`.
    pub begin: (usize, usize),
@@ -305,6 +404,8 @@ pub struct Span {

 /// Information about the deprecation of an [`Item`].
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Deprecation {
    /// Usually a version number when this [`Item`] first became deprecated.
    pub since: Option<String>,
@@ -314,6 +415,8 @@ pub struct Deprecation {

 /// Visibility of an [`Item`].
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 pub enum Visibility {
    /// Explicitly public visibility set with `pub`.
@@ -337,6 +440,8 @@ pub enum Visibility {

 /// Dynamic trait object type (`dyn Trait`).
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct DynTrait {
    /// All the traits implemented. One of them is the vtable, and the rest must be auto traits.
    pub traits: Vec<PolyTrait>,
@@ -352,6 +457,8 @@ pub struct DynTrait {

 /// A trait and potential HRTBs
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct PolyTrait {
    /// The path to the trait.
    #[serde(rename = "trait")]
@@ -371,6 +478,18 @@ pub struct PolyTrait {
 ///                    ^^^^^
 /// ```
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(serialize_bounds(
+    __S: rkyv::ser::Writer + rkyv::ser::Allocator,
+    __S::Error: rkyv::rancor::Source,
+)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(deserialize_bounds(
+    __D::Error: rkyv::rancor::Source,
+)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(bytecheck(bounds(
+    __C: rkyv::validation::ArchiveContext,
+))))]
 #[serde(rename_all = "snake_case")]
 pub enum GenericArgs {
    /// `<'a, 32, B: Copy, C = u32>`
@@ -387,8 +506,10 @@ pub enum GenericArgs {
    /// `Fn(A, B) -> C`
    Parenthesized {
        /// The input types, enclosed in parentheses.
+        #[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))]
        inputs: Vec<Type>,
        /// The output type provided after the `->`, if present.
+        #[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))]
        output: Option<Type>,
    },
    /// `T::method(..)`
@@ -399,6 +520,8 @@ pub enum GenericArgs {
 ///
 /// Part of [`GenericArgs`].
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 pub enum GenericArg {
    /// A lifetime argument.
@@ -429,6 +552,8 @@ pub enum GenericArg {

 /// A constant.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Constant {
    /// The stringified expression of this constant. Note that its mapping to the original
    /// source code is unstable and it's not guaranteed that it'll match the source code.
@@ -448,10 +573,24 @@ pub struct Constant {
 ///              ^^^^^^^^^^  ^^^^^^^^^^^^^^^
 /// ```
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(serialize_bounds(
+    __S: rkyv::ser::Writer + rkyv::ser::Allocator,
+    __S::Error: rkyv::rancor::Source,
+)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(deserialize_bounds(
+    __D::Error: rkyv::rancor::Source,
+)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(bytecheck(bounds(
+    __C: rkyv::validation::ArchiveContext,
+    <__C as rkyv::rancor::Fallible>::Error: rkyv::rancor::Source,
+))))]
 pub struct AssocItemConstraint {
    /// The name of the associated type/constant.
    pub name: String,
    /// Arguments provided to the associated type/constant.
+    #[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))]
    pub args: Option<Box<GenericArgs>>,
    /// The kind of bound applied to the associated type/constant.
    pub binding: AssocItemConstraintKind,
@@ -459,6 +598,8 @@ pub struct AssocItemConstraint {

 /// The way in which an associate type/constant is bound.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 pub enum AssocItemConstraintKind {
    /// The required value/type is specified exactly. e.g.
@@ -487,6 +628,8 @@ pub enum AssocItemConstraintKind {
 /// should treat them as opaque keys to lookup items, and avoid attempting
 /// to parse them, or otherwise depend on any implementation details.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash)))]
 // FIXME(aDotInTheVoid): Consider making this non-public in rustdoc-types.
 pub struct Id(pub u32);

@@ -494,6 +637,9 @@ pub enum AssocItemConstraintKind {
 ///
 /// Part of [`ItemSummary`].
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(compare(PartialEq)))]
 #[serde(rename_all = "snake_case")]
 pub enum ItemKind {
    /// A module declaration, e.g. `mod foo;` or `mod foo {}`
@@ -569,6 +715,8 @@ pub enum ItemKind {
 ///
 /// Part of [`Item`].
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 pub enum ItemEnum {
    /// A module declaration, e.g. `mod foo;` or `mod foo {}`
@@ -723,6 +871,8 @@ pub fn item_kind(&self) -> ItemKind {

 /// A module declaration, e.g. `mod foo;` or `mod foo {}`.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Module {
    /// Whether this is the root item of a crate.
    ///
@@ -738,6 +888,8 @@ pub struct Module {

 /// A `union`.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Union {
    /// The generic parameters and where clauses on this union.
    pub generics: Generics,
@@ -755,6 +907,8 @@ pub struct Union {

 /// A `struct`.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Struct {
    /// The kind of the struct (e.g. unit, tuple-like or struct-like) and the data specific to it,
    /// i.e. fields.
@@ -768,6 +922,8 @@ pub struct Struct {

 /// The kind of a [`Struct`] and the data specific to it, i.e. fields.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 pub enum StructKind {
    /// A struct with no fields and no parentheses.
@@ -805,6 +961,8 @@ pub enum StructKind {

 /// An `enum`.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Enum {
    /// Information about the type parameters and `where` clauses of the enum.
    pub generics: Generics,
@@ -820,6 +978,8 @@ pub struct Enum {

 /// A variant of an enum.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Variant {
    /// Whether the variant is plain, a tuple-like, or struct-like. Contains the fields.
    pub kind: VariantKind,
@@ -829,6 +989,8 @@ pub struct Variant {

 /// The kind of an [`Enum`] [`Variant`] and the data specific to it, i.e. fields.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 pub enum VariantKind {
    /// A variant with no parentheses
@@ -872,6 +1034,8 @@ pub enum VariantKind {

 /// The value that distinguishes a variant in an [`Enum`] from other variants.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Discriminant {
    /// The expression that produced the discriminant.
    ///
@@ -890,6 +1054,8 @@ pub struct Discriminant {

 /// A set of fundamental properties of a function.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct FunctionHeader {
    /// Is this function marked as `const`?
    pub is_const: bool,
@@ -910,6 +1076,8 @@ pub struct FunctionHeader {
 /// See the [Rustonomicon section](https://doc.rust-lang.org/nightly/nomicon/ffi.html#ffi-and-unwinding)
 /// on unwinding for more info.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub enum Abi {
    // We only have a concrete listing here for stable ABI's because there are so many
    // See rustc_ast_passes::feature_gate::PostExpansionVisitor::check_abi for the list
@@ -937,6 +1105,8 @@ pub enum Abi {

 /// A function declaration (including methods and other associated functions).
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Function {
    /// Information about the function signature, or declaration.
    pub sig: FunctionSignature,
@@ -950,6 +1120,8 @@ pub struct Function {

 /// Generic parameters accepted by an item and `where` clauses imposed on it and the parameters.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Generics {
    /// A list of generic parameter definitions (e.g. `<T: Clone + Hash, U: Copy>`).
    pub params: Vec<GenericParamDef>,
@@ -959,6 +1131,8 @@ pub struct Generics {

 /// One generic parameter accepted by an item.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct GenericParamDef {
    /// Name of the parameter.
    /// ```rust
@@ -973,6 +1147,18 @@ pub struct GenericParamDef {

 /// The kind of a [`GenericParamDef`].
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(serialize_bounds(
+    __S: rkyv::ser::Writer + rkyv::ser::Allocator,
+    __S::Error: rkyv::rancor::Source,
+)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(deserialize_bounds(
+    __D::Error: rkyv::rancor::Source,
+)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(bytecheck(bounds(
+    __C: rkyv::validation::ArchiveContext,
+))))]
 #[serde(rename_all = "snake_case")]
 pub enum GenericParamDefKind {
    /// Denotes a lifetime parameter.
@@ -995,6 +1181,7 @@ pub enum GenericParamDefKind {
        /// fn default2<T: Default>() -> [T; 2] where T: Clone { todo!() }
        /// //             ^^^^^^^
        /// ```
+        #[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))]
        bounds: Vec<GenericBound>,
        /// The default type for this parameter, if provided, e.g.
        ///
@@ -1002,6 +1189,7 @@ pub enum GenericParamDefKind {
        /// trait PartialEq<Rhs = Self> {}
        /// //                    ^^^^
        /// ```
+        #[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))]
        default: Option<Type>,
        /// This is normally `false`, which means that this generic parameter is
        /// declared in the Rust source text.
@@ -1033,6 +1221,7 @@ pub enum GenericParamDefKind {
    Const {
        /// The type of the constant as declared.
        #[serde(rename = "type")]
+        #[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))]
        type_: Type,
        /// The stringified expression for the default value, if provided. It's not guaranteed that
        /// it'll match the actual source code for the default value.
@@ -1046,6 +1235,8 @@ pub enum GenericParamDefKind {
 /// //                         ^^^^^^^^^^
 /// ```
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 pub enum WherePredicate {
    /// A type is expected to comply with a set of bounds
@@ -1092,6 +1283,8 @@ pub enum WherePredicate {

 /// Either a trait bound or a lifetime bound.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 pub enum GenericBound {
    /// A trait bound.
@@ -1122,6 +1315,8 @@ pub enum GenericBound {

 /// A set of modifiers applied to a trait.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 pub enum TraitBoundModifier {
    /// Marks the absence of a modifier.
@@ -1137,6 +1332,8 @@ pub enum TraitBoundModifier {

 /// One precise capturing argument. See [the rust reference](https://doc.rust-lang.org/reference/types/impl-trait.html#precise-capturing).
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 pub enum PreciseCapturingArg {
    /// A lifetime.
@@ -1154,6 +1351,8 @@ pub enum PreciseCapturingArg {
 /// Either a type or a constant, usually stored as the right-hand side of an equation in places like
 /// [`AssocItemConstraint`]
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 pub enum Term {
    /// A type.
@@ -1178,6 +1377,18 @@ pub enum Term {

 /// A type.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(serialize_bounds(
+    __S: rkyv::ser::Writer + rkyv::ser::Allocator,
+    __S::Error: rkyv::rancor::Source,
+)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(deserialize_bounds(
+    __D::Error: rkyv::rancor::Source,
+)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(bytecheck(bounds(
+    __C: rkyv::validation::ArchiveContext,
+))))]
 #[serde(rename_all = "snake_case")]
 pub enum Type {
    /// Structs, enums, unions and type aliases, e.g. `std::option::Option<u32>`
@@ -1189,15 +1400,16 @@ pub enum Type {
    /// Built-in numeric types (e.g. `u32`, `f32`), `bool`, `char`.
    Primitive(String),
    /// A function pointer type, e.g. `fn(u32) -> u32`, `extern "C" fn() -> *const u8`
-    FunctionPointer(Box<FunctionPointer>),
+    FunctionPointer(#[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))] Box<FunctionPointer>),
    /// A tuple type, e.g. `(String, u32, Box<usize>)`
-    Tuple(Vec<Type>),
+    Tuple(#[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))] Vec<Type>),
    /// An unsized slice type, e.g. `[u32]`.
-    Slice(Box<Type>),
+    Slice(#[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))] Box<Type>),
    /// An array type, e.g. `[u32; 15]`
    Array {
        /// The type of the contained element.
        #[serde(rename = "type")]
+        #[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))]
        type_: Box<Type>,
        /// The stringified expression that is the length of the array.
        ///
@@ -1210,6 +1422,7 @@ pub enum Type {
    Pat {
        /// The base type, e.g. the `u32` in `u32 is 1..`
        #[serde(rename = "type")]
+        #[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))]
        type_: Box<Type>,
        #[doc(hidden)]
        __pat_unstable_do_not_use: String,
@@ -1224,6 +1437,7 @@ pub enum Type {
        is_mutable: bool,
        /// The type of the pointee.
        #[serde(rename = "type")]
+        #[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))]
        type_: Box<Type>,
    },
    /// `&'a mut String`, `&str`, etc.
@@ -1234,6 +1448,7 @@ pub enum Type {
        is_mutable: bool,
        /// The type of the pointee, e.g. the `i32` in `&'a mut i32`
        #[serde(rename = "type")]
+        #[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))]
        type_: Box<Type>,
    },
    /// Associated types like `<Type as Trait>::Name` and `T::Item` where
@@ -1252,6 +1467,7 @@ pub enum Type {
        /// <core::slice::IterMut<'static, u32> as BetterIterator>::Item<'static>
        /// //                                                          ^^^^^^^^^
        /// ```
+        #[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))]
        args: Option<Box<GenericArgs>>,
        /// The type with which this type is associated.
        ///
@@ -1259,6 +1475,7 @@ pub enum Type {
        /// <core::array::IntoIter<u32, 42> as Iterator>::Item
        /// // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        /// ```
+        #[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))]
        self_type: Box<Type>,
        /// `None` iff this is an *inherent* associated type.
        #[serde(rename = "trait")]
@@ -1268,6 +1485,19 @@ pub enum Type {

 /// A type that has a simple path to it. This is the kind of type of structs, unions, enums, etc.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(serialize_bounds(
+    __S: rkyv::ser::Writer + rkyv::ser::Allocator,
+    __S::Error: rkyv::rancor::Source,
+)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(deserialize_bounds(
+    __D::Error: rkyv::rancor::Source,
+)))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(bytecheck(bounds(
+    __C: rkyv::validation::ArchiveContext,
+    <__C as rkyv::rancor::Fallible>::Error: rkyv::rancor::Source,
+))))]
 pub struct Path {
    /// The path of the type.
    ///
@@ -1291,11 +1521,14 @@ pub struct Path {
    /// std::borrow::Cow<'static, str>
    /// //              ^^^^^^^^^^^^^^
    /// ```
+    #[cfg_attr(feature = "rkyv_0_8", rkyv(omit_bounds))]
    pub args: Option<Box<GenericArgs>>,
 }

 /// A type that is a function pointer.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct FunctionPointer {
    /// The signature of the function.
    pub sig: FunctionSignature,
@@ -1312,6 +1545,8 @@ pub struct FunctionPointer {

 /// The signature of a function.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct FunctionSignature {
    /// List of argument names and their type.
    ///
@@ -1330,6 +1565,8 @@ pub struct FunctionSignature {

 /// A `trait` declaration.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Trait {
    /// Whether the trait is marked `auto` and is thus implemented automatically
    /// for all applicable types.
@@ -1354,6 +1591,8 @@ pub struct Trait {
 ///
 /// See [the tracking issue](https://github.com/rust-lang/rust/issues/41517)
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct TraitAlias {
    /// Information about the type parameters and `where` clauses of the alias.
    pub generics: Generics,
@@ -1363,6 +1602,8 @@ pub struct TraitAlias {

 /// An `impl` block.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Impl {
    /// Whether this impl is for an unsafe trait.
    pub is_unsafe: bool,
@@ -1401,6 +1642,8 @@ pub struct Impl {

 /// A `use` statement.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 pub struct Use {
    /// The full path being imported.
@@ -1419,6 +1662,8 @@ pub struct Use {

 /// A procedural macro.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct ProcMacro {
    /// How this macro is supposed to be called: `foo!()`, `#[foo]` or `#[derive(foo)]`
    pub kind: MacroKind,
@@ -1442,6 +1687,8 @@ pub struct ProcMacro {

 /// The way a [`ProcMacro`] is declared to be used.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 #[serde(rename_all = "snake_case")]
 pub enum MacroKind {
    /// A bang macro `foo!()`.
@@ -1454,6 +1701,8 @@ pub enum MacroKind {

 /// A type alias declaration, e.g. `type Pig = std::borrow::Cow<'static, str>;`
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct TypeAlias {
    /// The type referred to by this alias.
    #[serde(rename = "type")]
@@ -1464,6 +1713,8 @@ pub struct TypeAlias {

 /// A `static` declaration.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Static {
    /// The type of the static.
    #[serde(rename = "type")]
@@ -1494,6 +1745,8 @@ pub struct Static {

 /// A primitive type declaration. Declarations of this kind can only come from the core library.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[cfg_attr(feature = "rkyv_0_8", derive(rkyv::Archive, rkyv::Serialize, rkyv::Deserialize))]
+#[cfg_attr(feature = "rkyv_0_8", rkyv(derive(Debug)))]
 pub struct Primitive {
    /// The name of the type.
    pub name: String,
@@ -38,3 +38,118 @@ fn test_union_info_roundtrip() {
    let decoded: ItemEnum = bincode::deserialize(&encoded).unwrap();
    assert_eq!(u, decoded);
 }
+
+#[cfg(feature = "rkyv_0_8")]
+mod rkyv {
+    use std::fmt::Debug;
+
+    use rkyv::Archive;
+    use rkyv::api::high::{HighDeserializer, HighSerializer};
+    use rkyv::bytecheck::CheckBytes;
+    use rkyv::rancor::Strategy;
+    use rkyv::ser::allocator::ArenaHandle;
+    use rkyv::util::AlignedVec;
+    use rkyv::validation::Validator;
+    use rkyv::validation::archive::ArchiveValidator;
+    use rkyv::validation::shared::SharedValidator;
+
+    use crate::*;
+
+    #[test]
+    /// A test to exercise the (de)serialization roundtrip for a representative selection of types,
+    /// covering most of the rkyv-specific attributes we had to had.
+    fn test_rkyv_roundtrip() {
+        // Standard derives: a plain struct and union, mirroring the existing serde/bincode tests.
+        let s = ItemEnum::Struct(Struct {
+            generics: Generics { params: vec![], where_predicates: vec![] },
+            kind: StructKind::Plain { fields: vec![Id(1), Id(2)], has_stripped_fields: false },
+            impls: vec![Id(3)],
+        });
+        rkyv_roundtrip(&s);
+
+        let u = ItemEnum::Union(Union {
+            generics: Generics { params: vec![], where_predicates: vec![] },
+            has_stripped_fields: false,
+            fields: vec![Id(1)],
+            impls: vec![],
+        });
+        rkyv_roundtrip(&u);
+
+        // Extra trait derives, via rkyv(derive(PartialEq, Eq, PartialOrd, Ord, Hash)), on the archived type.
+        rkyv_roundtrip(&Id(99));
+
+        // Recursive cycle-breaking: `BorrowedRef` has omit_bounds on its `Box<Type>` field.
+        let ty = Type::BorrowedRef {
+            lifetime: Some("'a".to_string()),
+            is_mutable: false,
+            type_: Box::new(Type::Primitive("str".to_string())),
+        };
+        rkyv_roundtrip(&ty);
+
+        // `Slice` and `Tuple` are tuple-variant fields with omit_bounds on the unnamed field,
+        // which required special syntax (attribute inside the parentheses) to compile.
+        let ty = Type::Slice(Box::new(Type::Tuple(vec![
+            Type::Primitive("u32".to_string()),
+            Type::Generic("T".to_string()),
+        ])));
+        rkyv_roundtrip(&ty);
+
+        // `Path` has serialize_bounds/deserialize_bounds and omit_bounds on its `args` field.
+        // `GenericArgs::AngleBracketed` exercises the full recursive chain: `Path` -> `GenericArgs` -> `GenericArg` -> `Type`.
+        let path = Path {
+            path: "std::option::Option".to_string(),
+            id: Id(42),
+            args: Some(Box::new(GenericArgs::AngleBracketed {
+                args: vec![GenericArg::Type(Type::Primitive("u32".to_string()))],
+                constraints: vec![],
+            })),
+        };
+        rkyv_roundtrip(&path);
+
+        // `FunctionPointer` is a `Box<FunctionPointer>` behind `omit_bounds` in `Type`.
+        // It transitively contains `Type` via `FunctionSignature`, exercising the cycle from the other direction.
+        let fp = Type::FunctionPointer(Box::new(FunctionPointer {
+            sig: FunctionSignature {
+                inputs: vec![("x".to_string(), Type::Primitive("i32".to_string()))],
+                output: Some(Type::Primitive("bool".to_string())),
+                is_c_variadic: false,
+            },
+            generic_params: vec![],
+            header: FunctionHeader {
+                is_const: false,
+                is_unsafe: false,
+                is_async: false,
+                abi: Abi::Rust,
+            },
+        }));
+        rkyv_roundtrip(&fp);
+    }
+
+    /// A helper function for roundtrip testing of rkyv-powered deserialization.
+    fn rkyv_roundtrip<T>(value: &T)
+    where
+        T: PartialEq
+            + Debug
+            + Archive
+            + for<'a> rkyv::Serialize<
+                HighSerializer<AlignedVec, ArenaHandle<'a>, rkyv::rancor::Error>,
+            >,
+        T::Archived: rkyv::Deserialize<T, HighDeserializer<rkyv::rancor::Error>>
+            + Debug
+            + for<'a> CheckBytes<
+                Strategy<Validator<ArchiveValidator<'a>, SharedValidator>, rkyv::rancor::Error>,
+            >,
+    {
+        let bytes =
+            rkyv::api::high::to_bytes_in::<_, rkyv::rancor::Error>(value, AlignedVec::new())
+                .unwrap();
+        let archived = rkyv::api::high::access::<T::Archived, rkyv::rancor::Error>(&bytes)
+            .expect("Failed to access archived data");
+        let deserialized: T = rkyv::api::deserialize_using::<_, _, rkyv::rancor::Error>(
+            archived,
+            &mut rkyv::de::Pool::new(),
+        )
+        .unwrap();
+        assert_eq!(value, &deserialized);
+    }
+}