fully document rustdoc-json-types

1 files changed, 533 insertions, 52 deletions

diff --git a/src/rustdoc-json-types/lib.rs b/src/rustdoc-json-types/lib.rs
index 6fd23b60c8a..d15a59131cf 100644
--- a/src/rustdoc-json-types/lib.rs
+++ b/src/rustdoc-json-types/lib.rs
@@ -7,10 +7,16 @@ use rustc_hash::FxHashMap;
 use serde::{Deserialize, Serialize};
 use std::path::PathBuf;
 
-/// rustdoc format-version.
+/// The version of JSON output that this crate represents.
+///
+/// This integer is incremented with every breaking change to the API,
+/// and is returned along with the JSON blob as [`Crate::format_version`].
+/// Consuming code should assert that this value matches the format version(s) that it supports.
 pub const FORMAT_VERSION: u32 = 32;
 
-/// A `Crate` is the root of the emitted JSON blob. It contains all type/documentation information
+/// The root of the emitted JSON blob.
+///
+/// It contains all type/documentation information
 /// 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)]
@@ -33,13 +39,18 @@ pub struct Crate {
     pub format_version: u32,
 }
 
+/// Metadata of a crate, either the same crate on which `rustdoc` was invoked, or its dependency.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct ExternalCrate {
+    /// The name of the crate.
     pub name: String,
+    /// The root URL at which the crate's documentation lives.
     pub html_root_url: Option<String>,
 }
 
-/// For external (not defined in the local crate) items, you don't get the same level of
+/// Information about an external (not defined in the local crate) [`Item`].
+///
+/// For external items, you don't get the same level of
 /// information. This struct should contain enough to generate a link/reference to the item in
 /// 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.
@@ -60,6 +71,10 @@ pub struct ItemSummary {
     pub kind: ItemKind,
 }
 
+/// Anything that can hold documentation - modules, structs, enums, functions, traits, etc.
+///
+/// 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)]
 pub struct Item {
     /// The unique identifier of this item. Can be used to find this item in various mappings.
@@ -82,10 +97,13 @@ pub struct Item {
     pub links: FxHashMap<String, Id>,
     /// Stringified versions of the attributes on this item (e.g. `"#[inline]"`)
     pub attrs: Vec<String>,
+    /// Information about the item’s deprecation, if present.
     pub deprecation: Option<Deprecation>,
+    /// The type-specific fields describing this item.
     pub inner: ItemEnum,
 }
 
+/// A range of source code.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Span {
     /// The path to the source file for this span relative to the path `rustdoc` was invoked with.
@@ -96,28 +114,39 @@ pub struct Span {
     pub end: (usize, usize),
 }
 
+/// Information about the deprecation of an [`Item`].
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Deprecation {
+    /// Usually a version number when this [`Item`] first became deprecated.
     pub since: Option<String>,
+    /// The reason for deprecation and/or what alternatives to use.
     pub note: Option<String>,
 }
 
+/// Visibility of an [`Item`].
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum Visibility {
+    /// Explicitly public visibility set with `pub`.
     Public,
     /// For the most part items are private by default. The exceptions are associated items of
     /// public traits and variants of public enums.
     Default,
+    /// Explicitly crate-wide visibility set with `pub(crate)`
     Crate,
-    /// For `pub(in path)` visibility. `parent` is the module it's restricted to and `path` is how
-    /// that module was referenced (like `"super::super"` or `"crate::foo::bar"`).
+    /// For `pub(in path)` visibility.
     Restricted {
+        /// ID of the module to which this visibility restricts items.
         parent: Id,
+        /// The path with which [`parent`] was referenced
+        /// (like `super::super` or `crate::foo::bar`).
+        ///
+        /// [`parent`]: Visibility::Restricted::parent
         path: String,
     },
 }
 
+/// Dynamic trait object type (`dyn Trait`).
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct DynTrait {
     /// All the traits implemented. One of them is the vtable, and the rest must be auto traits.
@@ -132,64 +161,133 @@ pub struct DynTrait {
     pub lifetime: Option<String>,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 /// A trait and potential HRTBs
+#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct PolyTrait {
+    /// The path to the trait.
     #[serde(rename = "trait")]
     pub trait_: Path,
     /// Used for Higher-Rank Trait Bounds (HRTBs)
     /// ```text
     /// dyn for<'a> Fn() -> &'a i32"
     ///     ^^^^^^^
-    ///       |
-    ///       this part
     /// ```
     pub generic_params: Vec<GenericParamDef>,
 }
 
+/// A set of generic arguments provided to a path segment, e.g.
+///
+/// ```text
+/// std::option::Option::<u32>::None
+///                      ^^^^^
+/// ```
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum GenericArgs {
-    /// <'a, 32, B: Copy, C = u32>
-    AngleBracketed { args: Vec<GenericArg>, bindings: Vec<TypeBinding> },
-    /// Fn(A, B) -> C
-    Parenthesized { inputs: Vec<Type>, output: Option<Type> },
+    /// `<'a, 32, B: Copy, C = u32>`
+    AngleBracketed {
+        /// The list of each argument on this type.
+        /// ```text
+        /// <'a, 32, B: Copy, C = u32>
+        ///  ^^^^^^
+        /// ```
+        args: Vec<GenericArg>,
+        /// Associated type or constant bindings (e.g. `Item=i32` or `Item: Clone`) for this type.
+        bindings: Vec<TypeBinding>,
+    },
+    /// `Fn(A, B) -> C`
+    Parenthesized {
+        /// The input types, enclosed in parentheses.
+        inputs: Vec<Type>,
+        /// The output type provided after the `->`, if present.
+        output: Option<Type>,
+    },
 }
 
+/// One argument in a list of generic arguments to a path segment.
+///
+/// Part of [`GenericArgs`].
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum GenericArg {
+    /// A lifetime argument.
+    /// ```text
+    /// std::borrow::Cow<'static, str>
+    ///                  ^^^^^^^
+    /// ```
     Lifetime(String),
+    /// A type argument.
+    /// ```text
+    /// std::borrow::Cow<'static, str>
+    ///                           ^^^
+    /// ```
     Type(Type),
+    /// A constant as a generic argument.
+    /// ```text
+    /// core::array::IntoIter<u32, { 640 * 1024 }>
+    ///                            ^^^^^^^^^^^^^^
+    /// ```
     Const(Constant),
+    /// A generic argument that's explicitly set to be inferred.
+    /// ```text
+    /// std::vec::Vec::<_>::new()
+    ///                 ^
+    /// ```
     Infer,
 }
 
+/// A constant.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 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.
     pub expr: String,
+    /// The value of the evaluated expression for this constant, which is only computed for numeric
+    /// types.
     pub value: Option<String>,
+    /// Whether this constant is a bool, numeric, string, or char literal.
     pub is_literal: bool,
 }
 
+/// Describes a bound applied to an associated type/constant.
+///
+/// Example:
+/// ```text
+/// IntoIterator<Item = u32, IntoIter: Clone>
+///              ^^^^^^^^^^  ^^^^^^^^^^^^^^^
+/// ```
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct TypeBinding {
+    /// The name of the associated type/constant.
     pub name: String,
+    /// Arguments provided to the associated type/constant.
     pub args: GenericArgs,
+    /// The kind of bound applied to the associated type/constant.
     pub binding: TypeBindingKind,
 }
 
+/// The way in which an associate type/constant is bound.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum TypeBindingKind {
+    /// The required value/type is specified exactly. e.g.
+    /// ```text
+    /// Iterator<Item = u32, IntoIter: DoubleEndedIterator>
+    ///          ^^^^^^^^^^
+    /// ```
     Equality(Term),
+    /// The type is required to satisfy a set of bounds.
+    /// ```text
+    /// Iterator<Item = u32, IntoIter: DoubleEndedIterator>
+    ///                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+    /// ```
     Constraint(Vec<GenericBound>),
 }
 
 /// An opaque identifier for an item.
 ///
-/// It can be used to lookup in [Crate::index] or [Crate::paths] to resolve it
-/// to an [Item].
+/// It can be used to lookup in [`Crate::index`] or [`Crate::paths`] to resolve it
+/// to an [`Item`].
 ///
 /// Id's are only valid within a single JSON blob. They cannot be used to
 /// resolve references between the JSON output's for different crates.
@@ -201,115 +299,230 @@ pub enum TypeBindingKind {
 // FIXME(aDotInTheVoid): Consider making this non-public in rustdoc-types.
 pub struct Id(pub String);
 
+/// The fundamental kind of an item. Unlike [`ItemEnum`], this does not carry any aditional info.
+///
+/// Part of [`ItemSummary`].
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum ItemKind {
+    /// A module declaration, e.g. `mod foo;` or `mod foo {}`
     Module,
+    /// A crate imported via the `extern crate` syntax.
     ExternCrate,
+    /// An import of 1 or more items into scope, using the `use` keyword.
     Import,
+    /// A `struct` declaration.
     Struct,
+    /// A field of a struct.
     StructField,
+    /// A `union` declaration.
     Union,
+    /// An `enum` declaration.
     Enum,
+    /// A variant of a enum.
     Variant,
+    /// A function declaration, e.g. `fn f() {}`
     Function,
+    /// A type alias declaration, e.g. `type Pig = std::borrow::Cow<'static, str>;`
     TypeAlias,
     OpaqueTy,
+    /// The declaration of a constant, e.g. `const GREETING: &str = "Hi :3";`
     Constant,
+    /// A `trait` declaration.
     Trait,
+    /// A trait alias declaration, e.g. `trait Int = Add + Sub + Mul + Div;`
+    ///
+    /// See [the tracking issue](https://github.com/rust-lang/rust/issues/41517)
     TraitAlias,
+    /// An `impl` block.
     Impl,
+    /// A `static` declaration.
     Static,
+    /// `type`s from an `extern` block.
+    ///
+    /// See [the tracking issue](https://github.com/rust-lang/rust/issues/43467)
     ForeignType,
+    /// A macro declaration.
+    ///
+    /// Corresponds to either `ItemEnum::Macro(_)`
+    /// or `ItemEnum::ProcMacro(ProcMacro { kind: MacroKind::Bang })`
     Macro,
+    /// A procedural macro attribute.
+    ///
+    /// Corresponds to `ItemEnum::ProcMacro(ProcMacro { kind: MacroKind::Attr })`
     ProcAttribute,
+    /// A procedural macro usable in the `#[derive()]` attribute.
+    ///
+    /// Corresponds to `ItemEnum::ProcMacro(ProcMacro { kind: MacroKind::Derive })`
     ProcDerive,
+    /// An associated constant of a trait or a type.
     AssocConst,
+    /// An associated type of a trait or a type.
     AssocType,
+    /// A primitive type, e.g. `u32`.
+    ///
+    /// [`Item`]s of this kind only come from the core library.
     Primitive,
+    /// A keyword declaration.
+    ///
+    /// [`Item`]s of this kind only come from the come library and exist solely
+    /// to carry documentation for the respective keywords.
     Keyword,
 }
 
+/// Specific fields of an item.
+///
+/// Part of [`Item`].
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum ItemEnum {
+    /// A module declaration, e.g. `mod foo;` or `mod foo {}`
     Module(Module),
+    /// A crate imported via the `extern crate` syntax.
     ExternCrate {
+        /// The name of the imported crate.
         name: String,
+        /// If the crate is renamed, this is its name in the crate.
         rename: Option<String>,
     },
+    /// An import of 1 or more items into scope, using the `use` keyword.
     Import(Import),
 
+    /// A `union` declaration.
     Union(Union),
+    /// A `struct` declaration.
     Struct(Struct),
+    /// A field of a struct.
     StructField(Type),
+    /// An `enum` declaration.
     Enum(Enum),
+    /// A variant of a enum.
     Variant(Variant),
 
+    /// A function declaration (including methods and other associated functions)
     Function(Function),
 
+    /// A `trait` declaration.
     Trait(Trait),
+    /// A trait alias declaration, e.g. `trait Int = Add + Sub + Mul + Div;`
+    ///
+    /// See [the tracking issue](https://github.com/rust-lang/rust/issues/41517)
     TraitAlias(TraitAlias),
+    /// An `impl` block.
     Impl(Impl),
 
+    /// A type alias declaration, e.g. `type Pig = std::borrow::Cow<'static, str>;`
     TypeAlias(TypeAlias),
     OpaqueTy(OpaqueTy),
+    /// The declaration of a constant, e.g. `const GREETING: &str = "Hi :3";`
     Constant {
+        /// The type of the constant.
         #[serde(rename = "type")]
         type_: Type,
+        /// The declared constant itself.
         #[serde(rename = "const")]
         const_: Constant,
     },
 
+    /// A declaration of a `static`.
     Static(Static),
 
-    /// `type`s from an extern block
+    /// `type`s from an `extern` block.
+    ///
+    /// See [the tracking issue](https://github.com/rust-lang/rust/issues/43467)
     ForeignType,
 
-    /// Declarative macro_rules! macro
+    /// A macro_rules! declarative macro. Contains a single string with the source
+    /// representation of the macro with the patterns stripped.
     Macro(String),
+    /// A procedural macro.
     ProcMacro(ProcMacro),
 
+    /// A primitive type, e.g. `u32`.
+    ///
+    /// [`Item`]s of this kind only come from the core library.
     Primitive(Primitive),
 
+    /// An associated constant of a trait or a type.
     AssocConst {
+        /// The type of the constant.
         #[serde(rename = "type")]
         type_: Type,
-        /// e.g. `const X: usize = 5;`
+        /// The stringified expression for the default value, if provided, e.g.
+        /// ```rust
+        /// const X: usize = 640 * 1024;
+        /// //               ^^^^^^^^^^
+        /// ```
         default: Option<String>,
     },
+    /// An associated type of a trait or a type.
     AssocType {
+        /// The generic parameters and where clauses on ahis associated type.
         generics: Generics,
+        /// The bounds for this associated type. e.g.
+        /// ```rust
+        /// trait IntoIterator {
+        ///     type Item;
+        ///     type IntoIter: Iterator<Item = Self::Item>;
+        /// //                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+        /// }
+        /// ```
         bounds: Vec<GenericBound>,
-        /// e.g. `type X = usize;`
+        /// The default for this type, if provided, e.g.
+        /// ```rust
+        /// type X = usize;
+        /// //       ^^^^^
+        /// ```
         default: Option<Type>,
     },
 }
 
+/// A module declaration, e.g. `mod foo;` or `mod foo {}`.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Module {
+    /// Whether this is the root item of a crate.
+    ///
+    /// This item doesn't correspond to any construction in the source code and is generated by the
+    /// compiler.
     pub is_crate: bool,
+    /// [`Item`]s declared inside this module.
     pub items: Vec<Id>,
     /// If `true`, this module is not part of the public API, but it contains
     /// items that are re-exported as public API.
     pub is_stripped: bool,
 }
 
+/// A `union`.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Union {
+    /// The generic parameters and where clauses on this union.
     pub generics: Generics,
+    /// Whether any fields have been removed from the result, due to being private or hidden.
     pub fields_stripped: bool,
+    /// The list of fields in the union.
+    ///
+    /// All of the corresponding [`Item`]s are of kind [`ItemEnum::StructField`].
     pub fields: Vec<Id>,
+    /// All impls (both of traits and inherent) for this union.
+    ///
+    /// All of the corresponding [`Item`]s are of kind [`ItemEnum::Impl`].
     pub impls: Vec<Id>,
 }
 
+/// A `struct`.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 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.
     pub kind: StructKind,
+    /// The generic parameters and where clauses on this struct.
     pub generics: Generics,
+    /// All impls (both of traits and inherent) for this struct.
+    /// All of the corresponding [`Item`]s are of kind [`ItemEnum::Impl`].
     pub impls: Vec<Id>,
 }
 
+/// The kind of a [`Struct`] and the data specific to it, i.e. fields.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum StructKind {
@@ -321,13 +534,14 @@ pub enum StructKind {
     Unit,
     /// A struct with unnamed fields.
     ///
+    /// All [`Id`]'s will point to [`ItemEnum::StructField`].
+    /// Unlike most of JSON, private and `#[doc(hidden)]` fields will be given as `None`
+    /// instead of being omitted, because order matters.
+    ///
     /// ```rust
     /// pub struct TupleStruct(i32);
     /// pub struct EmptyTupleStruct();
     /// ```
-    ///
-    /// All [`Id`]'s will point to [`ItemEnum::StructField`]. Private and
-    /// `#[doc(hidden)]` fields will be given as `None`
     Tuple(Vec<Option<Id>>),
     /// A struct with named fields.
     ///
@@ -335,17 +549,32 @@ pub enum StructKind {
     /// pub struct PlainStruct { x: i32 }
     /// pub struct EmptyPlainStruct {}
     /// ```
-    Plain { fields: Vec<Id>, fields_stripped: bool },
+    Plain {
+        /// The list of fields in the struct.
+        ///
+        /// All of the corresponding [`Item`]s are of kind [`ItemEnum::StructField`].
+        fields: Vec<Id>,
+        /// Whether any fields have been removed from the result, due to being private or hidden.
+        fields_stripped: bool,
+    },
 }
 
+/// An `enum`.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Enum {
+    /// Information about the type parameters and `where` clauses of the enum.
     pub generics: Generics,
+    /// Whether any variants have been removed from the result, due to being private or hidden.
     pub variants_stripped: bool,
+    /// The list of variants in the enum.
+    ///
+    /// All of the corresponding [`Item`]s are of kind [`ItemEnum::Variant`]
     pub variants: Vec<Id>,
+    /// `impl`s for the enum.
     pub impls: Vec<Id>,
 }
 
+/// A variant of an enum.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Variant {
     /// Whether the variant is plain, a tuple-like, or struct-like. Contains the fields.
@@ -354,6 +583,7 @@ pub struct Variant {
     pub discriminant: Option<Discriminant>,
 }
 
+/// The kind of an [`Enum`] [`Variant`] and the data specific to it, i.e. fields.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum VariantKind {
@@ -368,7 +598,8 @@ pub enum VariantKind {
     Plain,
     /// A variant with unnamed fields.
     ///
-    /// Unlike most of json, `#[doc(hidden)]` fields will be given as `None`
+    /// All [`Id`]'s will point to [`ItemEnum::StructField`].
+    /// Unlike most of JSON, `#[doc(hidden)]` fields will be given as `None`
     /// instead of being omitted, because order matters.
     ///
     /// ```rust
@@ -386,9 +617,16 @@ pub enum VariantKind {
     ///     EmptyStructVariant {},
     /// }
     /// ```
-    Struct { fields: Vec<Id>, fields_stripped: bool },
+    Struct {
+        /// The list of variants in the enum.
+        /// All of the corresponding [`Item`]s are of kind [`ItemEnum::Variant`].
+        fields: Vec<Id>,
+        /// Whether any variants have been removed from the result, due to being private or hidden.
+        fields_stripped: bool,
+    },
 }
 
+/// The value that distinguishes a variant in an [`Enum`] from other variants.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Discriminant {
     /// The expression that produced the discriminant.
@@ -406,62 +644,123 @@ pub struct Discriminant {
     pub value: String,
 }
 
+/// A set of fundamental properties of a function.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Header {
+    /// Is this function marked as `const`?
     #[serde(rename = "const")]
     pub const_: bool,
+    /// Is this function unsafe?
     #[serde(rename = "unsafe")]
     pub unsafe_: bool,
+    /// Is this function async?
     #[serde(rename = "async")]
     pub async_: bool,
+    /// The ABI used by the function.
     pub abi: Abi,
 }
 
+/// The ABI (Application Binary Interface) used by a function.
+///
+/// If a variant has an `unwind` field, this means the ABI that it represents can be specified in 2
+/// ways: `extern "_"` and `extern "_-unwind"`, and a value of `true` for that field signifies the
+/// latter variant.
+///
+/// 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)]
 pub enum Abi {
     // We only have a concrete listing here for stable ABI's because their are so many
     // See rustc_ast_passes::feature_gate::PostExpansionVisitor::check_abi for the list
+    /// The default ABI, but that can also be written explicitly with `extern "Rust"`.
     Rust,
+    /// Can be specified as `extern "C"` or, as a shorthand, just `extern`.
     C { unwind: bool },
+    /// Can be specified as `extern "cdecl"`.
     Cdecl { unwind: bool },
+    /// Can be specified as `extern "stdcall"`.
     Stdcall { unwind: bool },
+    /// Can be specified as `extern "fastcall"`.
     Fastcall { unwind: bool },
+    /// Can be specified as `extern "aapcs"`.
     Aapcs { unwind: bool },
+    /// Can be specified as `extern "win64"`.
     Win64 { unwind: bool },
+    /// Can be specifed as `extern "sysv64"`.
     SysV64 { unwind: bool },
+    /// Can be specified as `extern "system"`.
     System { unwind: bool },
+    /// Any other ABI, including unstable ones.
     Other(String),
 }
 
-/// Represents a function (including methods and other associated functions)
+/// A function declaration (including methods and other associated functions).
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Function {
+    /// Information about the function signature, or declaration.
     pub decl: FnDecl,
+    /// Information about the function’s type parameters and `where` clauses.
     pub generics: Generics,
+    /// Information about core properties of the function, e.g. whether it's `const`, its ABI, etc.
     pub header: Header,
+    /// Whether the function has a body, i.e. an implementation.
     pub has_body: bool,
 }
 
+/// Generic parameters accepted by an item and `where` clauses imposed on it and the parameters.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Generics {
+    /// A list of generic parameter definitions (e.g. `<T: Clone + Hash, U: Copy>`).
     pub params: Vec<GenericParamDef>,
+    /// A list of where predicates (e.g. `where T: Iterator, T::Item: Copy`).
     pub where_predicates: Vec<WherePredicate>,
 }
 
+/// One generic parameter accepted by an item.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct GenericParamDef {
+    /// Name of the parameter.
+    /// ```rust
+    /// fn f<'resource, Resource>(x: &'resource Resource) {}
+    /// //    ^^^^^^^^  ^^^^^^^^
+    /// ```
     pub name: String,
+    /// The kind of the parameter and data specific to a particular parameter kind, e.g. type
+    /// bounds.
     pub kind: GenericParamDefKind,
 }
 
+/// The kind of a [`GenericParamDef`].
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum GenericParamDefKind {
+    /// Denotes a lifetime parameter.
     Lifetime {
+        /// Lifetimes that this lifetime parameter is required to outlive.
+        ///
+        /// ```rust
+        /// fn f<'a, 'b, 'resource: 'a + 'b>(a: &'a str, b: &'b str, res: &'resource str) {}
+        /// //                      ^^^^^^^
+        /// ```
         outlives: Vec<String>,
     },
+
+    /// Denotes a type parameter.
     Type {
+        /// Bounds applied directly to the type. Note that the bounds from `where` clauses
+        /// that constrain this parameter won't appear here.
+        ///
+        /// ```rust
+        /// fn default2<T: Default>() -> [T; 2] where T: Clone { todo!() }
+        /// //             ^^^^^^^
+        /// ```
         bounds: Vec<GenericBound>,
+        /// The default type for this parameter, if provided, e.g.
+        ///
+        /// ```rust
+        /// trait PartialEq<Rhs = Self> {}
+        /// //                    ^^^^
+        /// ```
         default: Option<Type>,
         /// This is normally `false`, which means that this generic parameter is
         /// declared in the Rust source text.
@@ -488,43 +787,75 @@ pub enum GenericParamDefKind {
         /// the Rust source text.
         synthetic: bool,
     },
+
+    /// Denotes a constant parameter.
     Const {
+        /// The type of the constant as declared.
         #[serde(rename = "type")]
         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.
         default: Option<String>,
     },
 }
 
+/// One `where` clause.
+/// ```rust
+/// fn default<T>() -> T where T: Default { T::default() }
+/// //                         ^^^^^^^^^^
+/// ```
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum WherePredicate {
+    /// A type is expected to comply with a set of bounds
     BoundPredicate {
+        /// The type that's being constrained.
+        ///
+        /// ```rust
+        /// fn f<T>(x: T) where for<'a> &'a T: Iterator {}
+        /// //                              ^
+        /// ```
         #[serde(rename = "type")]
         type_: Type,
+        /// The set of bounds that constrain the type.
+        ///
+        /// ```rust
+        /// fn f<T>(x: T) where for<'a> &'a T: Iterator {}
+        /// //                                 ^^^^^^^^
+        /// ```
         bounds: Vec<GenericBound>,
         /// Used for Higher-Rank Trait Bounds (HRTBs)
-        /// ```text
-        /// where for<'a> &'a T: Iterator,"
-        ///       ^^^^^^^
-        ///       |
-        ///       this part
+        /// ```rust
+        /// fn f<T>(x: T) where for<'a> &'a T: Iterator {}
+        /// //                  ^^^^^^^
         /// ```
         generic_params: Vec<GenericParamDef>,
     },
+
+    /// A lifetime is expected to outlive other lifetimes.
     LifetimePredicate {
+        /// The name of the lifetime.
         lifetime: String,
+        /// The lifetimes that must be encompassed by the lifetime.
         outlives: Vec<String>,
     },
+
+    /// A type must exactly equal another type.
     EqPredicate {
+        /// The left side of the equation.
         lhs: Type,
+        /// The right side of the equation.
         rhs: Term,
     },
 }
 
+/// Either a trait bound or a lifetime bound.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum GenericBound {
+    /// A trait bound.
     TraitBound {
+        /// The full path to the trait.
         #[serde(rename = "trait")]
         trait_: Path,
         /// Used for Higher-Rank Trait Bounds (HRTBs)
@@ -535,79 +866,142 @@ pub enum GenericBound {
         ///          this part
         /// ```
         generic_params: Vec<GenericParamDef>,
+        /// The context for which a trait is supposed to be used, e.g. `const
         modifier: TraitBoundModifier,
     },
+    /// A lifetime bound, e.g.
+    /// ```rust
+    /// fn f<'a, T>(x: &'a str, y: &T) where T: 'a {}
+    /// //                                     ^^^
+    /// ```
     Outlives(String),
     /// `use<'a, T>` precise-capturing bound syntax
     Use(Vec<String>),
 }
 
+/// A set of modifiers applied to a trait.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum TraitBoundModifier {
+    /// Marks the absence of a modifier.
     None,
+    /// Indicates that the trait bound relaxes a trait bound applied to a parameter by default,
+    /// e.g. `T: Sized?`, the `Sized` trait is required for all generic type parameters by default
+    /// unless specified otherwise with this modifier.
     Maybe,
+    /// Indicates that the trait bound must be applicable in both a run-time and a compile-time
+    /// context.
     MaybeConst,
 }
 
+/// Either a type or a constant, usually stored as the right-hand side of an equation in places like
+/// [`TypeBinding`]
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum Term {
+    /// A type.
+    ///
+    /// ```rust
+    /// fn f(x: impl IntoIterator<Item = u32>) {}
+    /// //                               ^^^
+    /// ```
     Type(Type),
+    /// A constant.
+    ///
+    /// ```ignore (incomplete feature in the snippet)
+    /// trait Foo {
+    ///     const BAR: usize;
+    /// }
+    ///
+    /// fn f(x: impl Foo<BAR = 42>) {}
+    /// //                     ^^
+    /// ```
     Constant(Constant),
 }
 
+/// A type.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum Type {
-    /// Structs, enums, and unions
+    /// Structs, enums, unions and type aliases, e.g. `std::option::Option<u32>`
     ResolvedPath(Path),
+    /// Dynamic trait object type (`dyn Trait`).
     DynTrait(DynTrait),
-    /// Parameterized types
+    /// Parameterized types. The contained string is the name of the parameter.
     Generic(String),
-    /// Built in numeric (i*, u*, f*) types, bool, and char
+    /// Built-in numeric types (e.g. `u32`, `f32`), `bool`, `char`.
     Primitive(String),
-    /// `extern "ABI" fn`
+    /// A function pointer type, e.g. `fn(u32) -> u32`, `extern "C" fn() -> *const u8`
     FunctionPointer(Box<FunctionPointer>),
-    /// `(String, u32, Box<usize>)`
+    /// A tuple type, e.g. `(String, u32, Box<usize>)`
     Tuple(Vec<Type>),
-    /// `[u32]`
+    /// An unsized slice type, e.g. `[u32]`.
     Slice(Box<Type>),
-    /// [u32; 15]
+    /// An array type, e.g. `[u32; 15]`
     Array {
+        /// The type of the contained element.
         #[serde(rename = "type")]
         type_: Box<Type>,
+        /// The stringified expression that is the length of the array.
+        ///
+        /// Keep in mind that it's not guaranteed to match the actual source code of the expression.
         len: String,
     },
-    /// `u32 is 1..`
+    /// A pattern type, e.g. `u32 is 1..`
+    ///
+    /// See [the tracking issue](https://github.com/rust-lang/rust/issues/123646)
     Pat {
+        /// The base type, e.g. the `u32` in `u32 is 1..`
         #[serde(rename = "type")]
         type_: Box<Type>,
         #[doc(hidden)]
         __pat_unstable_do_not_use: String,
     },
-    /// `impl TraitA + TraitB + ...`
+    /// An opaque type that satisfies a set of bounds, `impl TraitA + TraitB + ...`
     ImplTrait(Vec<GenericBound>),
-    /// `_`
+    /// A type that's left to be inferred, `_`
     Infer,
-    /// `*mut u32`, `*u8`, etc.
+    /// A raw pointer type, e.g. `*mut u32`, `*const u8`, etc.
     RawPointer {
+        /// This is `true` for `*mut _` and `false` for `*const _`.
         mutable: bool,
+        /// The type of the pointee.
         #[serde(rename = "type")]
         type_: Box<Type>,
     },
     /// `&'a mut String`, `&str`, etc.
     BorrowedRef {
+        /// The name of the lifetime of the reference, if provided.
         lifetime: Option<String>,
+        /// This is `true` for `&mut i32` and `false` for `&i32`
         mutable: bool,
+        /// The type of the pointee, e.g. the `i32` in `&'a mut i32`
         #[serde(rename = "type")]
         type_: Box<Type>,
     },
     /// Associated types like `<Type as Trait>::Name` and `T::Item` where
     /// `T: Iterator` or inherent associated types like `Struct::Name`.
     QualifiedPath {
+        /// The name of the associated type in the parent type.
+        ///
+        /// ```ignore (incomplete expresssion)
+        /// <core::array::IntoIter<u32, 42> as Iterator>::Item
+        /// //                                            ^^^^
+        /// ```
         name: String,
+        /// The generic arguments provided to the associated type.
+        ///
+        /// ```ignore (incomplete expression)
+        /// <core::slice::IterMut<'static, u32> as BetterIterator>::Item<'static>
+        /// //                                                          ^^^^^^^^^
+        /// ```
         args: Box<GenericArgs>,
+        /// The type with which this type is associated.
+        ///
+        /// ```ignore (incomplete expression)
+        /// <core::array::IntoIter<u32, 42> as Iterator>::Item
+        /// // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+        /// ```
         self_type: Box<Type>,
         /// `None` iff this is an *inherent* associated type.
         #[serde(rename = "trait")]
@@ -615,34 +1009,47 @@ 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)]
 pub struct Path {
+    /// The name of the type as declared, e.g. in
+    ///
+    /// ```rust
+    /// mod foo {
+    ///     struct Bar;
+    /// }
+    /// ```
+    ///
+    /// for `foo::Bar`, this field will be `Bar`.
     pub name: String,
+    /// The ID of the type.
     pub id: Id,
-    /// Generic arguments to the type
-    /// ```test
+    /// Generic arguments to the type.
+    ///
+    /// ```ignore (incomplete expression)
     /// std::borrow::Cow<'static, str>
-    ///                 ^^^^^^^^^^^^^^
-    ///                 |
-    ///                 this part
+    /// //              ^^^^^^^^^^^^^^
     /// ```
     pub args: Option<Box<GenericArgs>>,
 }
 
+/// A type that is a function pointer.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct FunctionPointer {
+    /// The signature of the function.
     pub decl: FnDecl,
     /// Used for Higher-Rank Trait Bounds (HRTBs)
-    /// ```text
-    /// for<'c> fn(val: &'c i32) -> i32
-    /// ^^^^^^^
-    ///       |
-    ///       this part
+    ///
+    /// ```ignore (incomplete expression)
+    ///    for<'c> fn(val: &'c i32) -> i32
+    /// // ^^^^^^^
     /// ```
     pub generic_params: Vec<GenericParamDef>,
+    /// The core properties of the function, such as the ABI it conforms to, whether it's unsafe, etc.
     pub header: Header,
 }
 
+/// The signature of a function.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct FnDecl {
     /// List of argument names and their type.
@@ -650,42 +1057,86 @@ pub struct FnDecl {
     /// Note that not all names will be valid identifiers, as some of
     /// them may be patterns.
     pub inputs: Vec<(String, Type)>,
+    /// The output type, if specified.
     pub output: Option<Type>,
+    /// Whether the function accepts an arbitrary amount of trailing arguments the C way.
+    ///
+    /// ```ignore (incomplete code)
+    /// fn printf(fmt: &str, ...);
+    /// ```
     pub c_variadic: bool,
 }
 
+/// A `trait` declaration.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Trait {
+    /// Whether the trait is marked `auto` and is thus implemented automatically
+    /// for all aplicable types.
     pub is_auto: bool,
+    /// Whether the trait is marked as `unsafe`.
     pub is_unsafe: bool,
+    /// Whether the trait is [object safe](https://doc.rust-lang.org/reference/items/traits.html#object-safety).
     pub is_object_safe: bool,
+    /// Associated [`Item`]s that can/must be implemented by the `impl` blocks.
     pub items: Vec<Id>,
+    /// Information about the type parameters and `where` clauses of the trait.
     pub generics: Generics,
+    /// Constraints that must be met by the implementor of the trait.
     pub bounds: Vec<GenericBound>,
+    /// The implementations of the trait.
     pub implementations: Vec<Id>,
 }
 
+/// A trait alias declaration, e.g. `trait Int = Add + Sub + Mul + Div;`
+///
+/// See [the tracking issue](https://github.com/rust-lang/rust/issues/41517)
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct TraitAlias {
+    /// Information about the type parameters and `where` clauses of the alias.
     pub generics: Generics,
+    /// The bounds that are associated with the alias.
     pub params: Vec<GenericBound>,
 }
 
+/// An `impl` block.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Impl {
+    /// Whether this impl is for an unsafe trait.
     pub is_unsafe: bool,
+    /// Information about the impl’s type parameters and `where` clauses.
     pub generics: Generics,
+    /// The list of the names of all the trait methods that weren't mentioned in this impl but
+    /// were provided by the trait itself.
+    ///
+    /// For example, for this impl of the [`PartialEq`] trait:
+    /// ```rust
+    /// struct Foo;
+    ///
+    /// impl PartialEq for Foo {
+    ///     fn eq(&self, other: &Self) -> bool { todo!() }
+    /// }
+    /// ```
+    /// This field will be `["ne"]`, as it has a default implementation defined for it.
     pub provided_trait_methods: Vec<String>,
+    /// The trait being implemented or `None` if the impl is inherent, which means
+    /// `impl Struct {}` as opposed to `impl Trait for Struct {}`.
     #[serde(rename = "trait")]
     pub trait_: Option<Path>,
+    /// The type that the impl block is for.
     #[serde(rename = "for")]
     pub for_: Type,
+    /// The list of associated items contained in this impl block.
     pub items: Vec<Id>,
+    /// Whether this is a negative impl (e.g. `!Sized` or `!Send`).
     pub negative: bool,
+    /// Whether this is an impl that’s implied by the compiler
+    /// (for autotraits, e.g. `Send` or `Sync`).
     pub synthetic: bool,
+    // FIXME: document this
     pub blanket_impl: Option<Type>,
 }
 
+/// A `use` statement.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub struct Import {
@@ -699,16 +1150,34 @@ pub struct Import {
     /// pub use i32 as my_i32;
     /// ```
     pub id: Option<Id>,
-    /// Whether this import uses a glob: `use source::*;`
+    /// Whether this statement is a wildcard `use`, e.g. `use source::*;`
     pub glob: bool,
 }
 
+/// A procedural macro.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct ProcMacro {
+    /// How this macro is supposed to be called: `foo!()`, `#[foo]` or `#[derive(foo)]`
     pub kind: MacroKind,
+    /// Helper attributes defined by a macro to be used inside it.
+    ///
+    /// Defined only for attribute & derive macros.
+    ///
+    /// E.g. the [`Default`] derive macro defines a `#[default]` helper attribute so that one can
+    /// do:
+    ///
+    /// ```rust
+    /// #[derive(Default)]
+    /// enum Option<T> {
+    ///     #[default]
+    ///     None,
+    ///     Some(T),
+    /// }
+    /// ```
     pub helpers: Vec<String>,
 }
 
+/// The way a [`ProcMacro`] is declared to be used.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum MacroKind {
@@ -720,10 +1189,13 @@ pub enum MacroKind {
     Derive,
 }
 
+/// A type alias declaration, e.g. `type Pig = std::borrow::Cow<'static, str>;`
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct TypeAlias {
+    /// The type referred to by this alias.
     #[serde(rename = "type")]
     pub type_: Type,
+    /// Information about the type parameters and `where` clauses of the alias.
     pub generics: Generics,
 }
 
@@ -733,17 +1205,26 @@ pub struct OpaqueTy {
     pub generics: Generics,
 }
 
+/// A `static` declaration.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Static {
+    /// The type of the static.
     #[serde(rename = "type")]
     pub type_: Type,
+    /// This is `true` for mutable statics, declared as `static mut X: T = f();`
     pub mutable: bool,
+    /// The stringified expression for the initial value.
+    ///
+    /// It's not guaranteed that it'll match the actual source code for the initial value.
     pub expr: String,
 }
 
+/// A primitive type declaration. Declarations of this kind can only come from the core library.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub struct Primitive {
+    /// The name of the type.
     pub name: String,
+    /// The implementations, inherent and of traits, on the primitive type.
     pub impls: Vec<Id>,
 }