Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

15 files changed, 7082 insertions, 0 deletions

diff --git a/compiler/rustc_hir/src/arena.rs b/compiler/rustc_hir/src/arena.rs
new file mode 100644
index 000000000..44335b7f4
--- /dev/null
+++ b/compiler/rustc_hir/src/arena.rs
@@ -0,0 +1,55 @@
+/// This higher-order macro declares a list of types which can be allocated by `Arena`.
+///
+/// Specifying the `decode` modifier will add decode impls for `&T` and `&[T]`,
+/// where `T` is the type listed. These impls will appear in the implement_ty_decoder! macro.
+#[macro_export]
+macro_rules! arena_types {
+    ($macro:path) => (
+        $macro!([
+            // HIR types
+            [] hir_krate: rustc_hir::Crate<'tcx>,
+            [] arm: rustc_hir::Arm<'tcx>,
+            [] asm_operand: (rustc_hir::InlineAsmOperand<'tcx>, rustc_span::Span),
+            [] asm_template: rustc_ast::InlineAsmTemplatePiece,
+            [] attribute: rustc_ast::Attribute,
+            [] closure: rustc_hir::Closure<'tcx>,
+            [] block: rustc_hir::Block<'tcx>,
+            [] bare_fn_ty: rustc_hir::BareFnTy<'tcx>,
+            [] body: rustc_hir::Body<'tcx>,
+            [] generics: rustc_hir::Generics<'tcx>,
+            [] generic_arg: rustc_hir::GenericArg<'tcx>,
+            [] generic_args: rustc_hir::GenericArgs<'tcx>,
+            [] generic_bound: rustc_hir::GenericBound<'tcx>,
+            [] generic_param: rustc_hir::GenericParam<'tcx>,
+            [] expr: rustc_hir::Expr<'tcx>,
+            [] impl_: rustc_hir::Impl<'tcx>,
+            [] let_expr: rustc_hir::Let<'tcx>,
+            [] expr_field: rustc_hir::ExprField<'tcx>,
+            [] pat_field: rustc_hir::PatField<'tcx>,
+            [] fn_decl: rustc_hir::FnDecl<'tcx>,
+            [] foreign_item: rustc_hir::ForeignItem<'tcx>,
+            [] foreign_item_ref: rustc_hir::ForeignItemRef,
+            [] impl_item: rustc_hir::ImplItem<'tcx>,
+            [] impl_item_ref: rustc_hir::ImplItemRef,
+            [] item: rustc_hir::Item<'tcx>,
+            [] inline_asm: rustc_hir::InlineAsm<'tcx>,
+            [] local: rustc_hir::Local<'tcx>,
+            [] mod_: rustc_hir::Mod<'tcx>,
+            [] owner_info: rustc_hir::OwnerInfo<'tcx>,
+            [] param: rustc_hir::Param<'tcx>,
+            [] pat: rustc_hir::Pat<'tcx>,
+            [] path: rustc_hir::Path<'tcx>,
+            [] path_segment: rustc_hir::PathSegment<'tcx>,
+            [] poly_trait_ref: rustc_hir::PolyTraitRef<'tcx>,
+            [] qpath: rustc_hir::QPath<'tcx>,
+            [] stmt: rustc_hir::Stmt<'tcx>,
+            [] field_def: rustc_hir::FieldDef<'tcx>,
+            [] trait_item: rustc_hir::TraitItem<'tcx>,
+            [] trait_item_ref: rustc_hir::TraitItemRef,
+            [] ty: rustc_hir::Ty<'tcx>,
+            [] type_binding: rustc_hir::TypeBinding<'tcx>,
+            [] variant: rustc_hir::Variant<'tcx>,
+            [] where_predicate: rustc_hir::WherePredicate<'tcx>,
+        ]);
+    )
+}
diff --git a/compiler/rustc_hir/src/def.rs b/compiler/rustc_hir/src/def.rs
new file mode 100644
index 000000000..be5b7eccb
--- /dev/null
+++ b/compiler/rustc_hir/src/def.rs
@@ -0,0 +1,749 @@
+use crate::hir;
+
+use rustc_ast as ast;
+use rustc_ast::NodeId;
+use rustc_macros::HashStable_Generic;
+use rustc_span::def_id::{DefId, LocalDefId};
+use rustc_span::hygiene::MacroKind;
+use rustc_span::Symbol;
+
+use std::array::IntoIter;
+use std::fmt::Debug;
+
+/// Encodes if a `DefKind::Ctor` is the constructor of an enum variant or a struct.
+#[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
+#[derive(HashStable_Generic)]
+pub enum CtorOf {
+    /// This `DefKind::Ctor` is a synthesized constructor of a tuple or unit struct.
+    Struct,
+    /// This `DefKind::Ctor` is a synthesized constructor of a tuple or unit variant.
+    Variant,
+}
+
+/// What kind of constructor something is.
+#[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
+#[derive(HashStable_Generic)]
+pub enum CtorKind {
+    /// Constructor function automatically created by a tuple struct/variant.
+    Fn,
+    /// Constructor constant automatically created by a unit struct/variant.
+    Const,
+    /// Unusable name in value namespace created by a struct variant.
+    Fictive,
+}
+
+/// An attribute that is not a macro; e.g., `#[inline]` or `#[rustfmt::skip]`.
+#[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
+#[derive(HashStable_Generic)]
+pub enum NonMacroAttrKind {
+    /// Single-segment attribute defined by the language (`#[inline]`)
+    Builtin(Symbol),
+    /// Multi-segment custom attribute living in a "tool module" (`#[rustfmt::skip]`).
+    Tool,
+    /// Single-segment custom attribute registered by a derive macro (`#[serde(default)]`).
+    DeriveHelper,
+    /// Single-segment custom attribute registered by a derive macro
+    /// but used before that derive macro was expanded (deprecated).
+    DeriveHelperCompat,
+    /// Single-segment custom attribute registered with `#[register_attr]`.
+    Registered,
+}
+
+/// What kind of definition something is; e.g., `mod` vs `struct`.
+#[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
+#[derive(HashStable_Generic)]
+pub enum DefKind {
+    // Type namespace
+    Mod,
+    /// Refers to the struct itself, [`DefKind::Ctor`] refers to its constructor if it exists.
+    Struct,
+    Union,
+    Enum,
+    /// Refers to the variant itself, [`DefKind::Ctor`] refers to its constructor if it exists.
+    Variant,
+    Trait,
+    /// Type alias: `type Foo = Bar;`
+    TyAlias,
+    /// Type from an `extern` block.
+    ForeignTy,
+    /// Trait alias: `trait IntIterator = Iterator<Item = i32>;`
+    TraitAlias,
+    /// Associated type: `trait MyTrait { type Assoc; }`
+    AssocTy,
+    /// Type parameter: the `T` in `struct Vec<T> { ... }`
+    TyParam,
+
+    // Value namespace
+    Fn,
+    Const,
+    /// Constant generic parameter: `struct Foo<const N: usize> { ... }`
+    ConstParam,
+    Static(ast::Mutability),
+    /// Refers to the struct or enum variant's constructor.
+    ///
+    /// The reason `Ctor` exists in addition to [`DefKind::Struct`] and
+    /// [`DefKind::Variant`] is because structs and enum variants exist
+    /// in the *type* namespace, whereas struct and enum variant *constructors*
+    /// exist in the *value* namespace.
+    ///
+    /// You may wonder why enum variants exist in the type namespace as opposed
+    /// to the value namespace. Check out [RFC 2593] for intuition on why that is.
+    ///
+    /// [RFC 2593]: https://github.com/rust-lang/rfcs/pull/2593
+    Ctor(CtorOf, CtorKind),
+    /// Associated function: `impl MyStruct { fn associated() {} }`
+    /// or `trait Foo { fn associated() {} }`
+    AssocFn,
+    /// Associated constant: `trait MyTrait { const ASSOC: usize; }`
+    AssocConst,
+
+    // Macro namespace
+    Macro(MacroKind),
+
+    // Not namespaced (or they are, but we don't treat them so)
+    ExternCrate,
+    Use,
+    /// An `extern` block.
+    ForeignMod,
+    /// Anonymous constant, e.g. the `1 + 2` in `[u8; 1 + 2]`
+    AnonConst,
+    /// An inline constant, e.g. `const { 1 + 2 }`
+    InlineConst,
+    /// Opaque type, aka `impl Trait`.
+    OpaqueTy,
+    Field,
+    /// Lifetime parameter: the `'a` in `struct Foo<'a> { ... }`
+    LifetimeParam,
+    /// A use of `global_asm!`.
+    GlobalAsm,
+    Impl,
+    Closure,
+    Generator,
+}
+
+impl DefKind {
+    pub fn descr(self, def_id: DefId) -> &'static str {
+        match self {
+            DefKind::Fn => "function",
+            DefKind::Mod if def_id.is_crate_root() && !def_id.is_local() => "crate",
+            DefKind::Mod => "module",
+            DefKind::Static(..) => "static",
+            DefKind::Enum => "enum",
+            DefKind::Variant => "variant",
+            DefKind::Ctor(CtorOf::Variant, CtorKind::Fn) => "tuple variant",
+            DefKind::Ctor(CtorOf::Variant, CtorKind::Const) => "unit variant",
+            DefKind::Ctor(CtorOf::Variant, CtorKind::Fictive) => "struct variant",
+            DefKind::Struct => "struct",
+            DefKind::Ctor(CtorOf::Struct, CtorKind::Fn) => "tuple struct",
+            DefKind::Ctor(CtorOf::Struct, CtorKind::Const) => "unit struct",
+            DefKind::Ctor(CtorOf::Struct, CtorKind::Fictive) => {
+                panic!("impossible struct constructor")
+            }
+            DefKind::OpaqueTy => "opaque type",
+            DefKind::TyAlias => "type alias",
+            DefKind::TraitAlias => "trait alias",
+            DefKind::AssocTy => "associated type",
+            DefKind::Union => "union",
+            DefKind::Trait => "trait",
+            DefKind::ForeignTy => "foreign type",
+            DefKind::AssocFn => "associated function",
+            DefKind::Const => "constant",
+            DefKind::AssocConst => "associated constant",
+            DefKind::TyParam => "type parameter",
+            DefKind::ConstParam => "const parameter",
+            DefKind::Macro(macro_kind) => macro_kind.descr(),
+            DefKind::LifetimeParam => "lifetime parameter",
+            DefKind::Use => "import",
+            DefKind::ForeignMod => "foreign module",
+            DefKind::AnonConst => "constant expression",
+            DefKind::InlineConst => "inline constant",
+            DefKind::Field => "field",
+            DefKind::Impl => "implementation",
+            DefKind::Closure => "closure",
+            DefKind::Generator => "generator",
+            DefKind::ExternCrate => "extern crate",
+            DefKind::GlobalAsm => "global assembly block",
+        }
+    }
+
+    /// Gets an English article for the definition.
+    pub fn article(&self) -> &'static str {
+        match *self {
+            DefKind::AssocTy
+            | DefKind::AssocConst
+            | DefKind::AssocFn
+            | DefKind::Enum
+            | DefKind::OpaqueTy
+            | DefKind::Impl
+            | DefKind::Use
+            | DefKind::InlineConst
+            | DefKind::ExternCrate => "an",
+            DefKind::Macro(macro_kind) => macro_kind.article(),
+            _ => "a",
+        }
+    }
+
+    pub fn ns(&self) -> Option<Namespace> {
+        match self {
+            DefKind::Mod
+            | DefKind::Struct
+            | DefKind::Union
+            | DefKind::Enum
+            | DefKind::Variant
+            | DefKind::Trait
+            | DefKind::OpaqueTy
+            | DefKind::TyAlias
+            | DefKind::ForeignTy
+            | DefKind::TraitAlias
+            | DefKind::AssocTy
+            | DefKind::TyParam => Some(Namespace::TypeNS),
+
+            DefKind::Fn
+            | DefKind::Const
+            | DefKind::ConstParam
+            | DefKind::Static(..)
+            | DefKind::Ctor(..)
+            | DefKind::AssocFn
+            | DefKind::AssocConst => Some(Namespace::ValueNS),
+
+            DefKind::Macro(..) => Some(Namespace::MacroNS),
+
+            // Not namespaced.
+            DefKind::AnonConst
+            | DefKind::InlineConst
+            | DefKind::Field
+            | DefKind::LifetimeParam
+            | DefKind::ExternCrate
+            | DefKind::Closure
+            | DefKind::Generator
+            | DefKind::Use
+            | DefKind::ForeignMod
+            | DefKind::GlobalAsm
+            | DefKind::Impl => None,
+        }
+    }
+
+    #[inline]
+    pub fn is_fn_like(self) -> bool {
+        match self {
+            DefKind::Fn | DefKind::AssocFn | DefKind::Closure | DefKind::Generator => true,
+            _ => false,
+        }
+    }
+
+    /// Whether `query get_codegen_attrs` should be used with this definition.
+    pub fn has_codegen_attrs(self) -> bool {
+        match self {
+            DefKind::Fn
+            | DefKind::AssocFn
+            | DefKind::Ctor(..)
+            | DefKind::Closure
+            | DefKind::Generator
+            | DefKind::Static(_) => true,
+            DefKind::Mod
+            | DefKind::Struct
+            | DefKind::Union
+            | DefKind::Enum
+            | DefKind::Variant
+            | DefKind::Trait
+            | DefKind::TyAlias
+            | DefKind::ForeignTy
+            | DefKind::TraitAlias
+            | DefKind::AssocTy
+            | DefKind::Const
+            | DefKind::AssocConst
+            | DefKind::Macro(..)
+            | DefKind::Use
+            | DefKind::ForeignMod
+            | DefKind::OpaqueTy
+            | DefKind::Impl
+            | DefKind::Field
+            | DefKind::TyParam
+            | DefKind::ConstParam
+            | DefKind::LifetimeParam
+            | DefKind::AnonConst
+            | DefKind::InlineConst
+            | DefKind::GlobalAsm
+            | DefKind::ExternCrate => false,
+        }
+    }
+}
+
+/// The resolution of a path or export.
+///
+/// For every path or identifier in Rust, the compiler must determine
+/// what the path refers to. This process is called name resolution,
+/// and `Res` is the primary result of name resolution.
+///
+/// For example, everything prefixed with `/* Res */` in this example has
+/// an associated `Res`:
+///
+/// ```
+/// fn str_to_string(s: & /* Res */ str) -> /* Res */ String {
+///     /* Res */ String::from(/* Res */ s)
+/// }
+///
+/// /* Res */ str_to_string("hello");
+/// ```
+///
+/// The associated `Res`s will be:
+///
+/// - `str` will resolve to [`Res::PrimTy`];
+/// - `String` will resolve to [`Res::Def`], and the `Res` will include the [`DefId`]
+///   for `String` as defined in the standard library;
+/// - `String::from` will also resolve to [`Res::Def`], with the [`DefId`]
+///   pointing to `String::from`;
+/// - `s` will resolve to [`Res::Local`];
+/// - the call to `str_to_string` will resolve to [`Res::Def`], with the [`DefId`]
+///   pointing to the definition of `str_to_string` in the current crate.
+//
+#[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
+#[derive(HashStable_Generic)]
+pub enum Res<Id = hir::HirId> {
+    /// Definition having a unique ID (`DefId`), corresponds to something defined in user code.
+    ///
+    /// **Not bound to a specific namespace.**
+    Def(DefKind, DefId),
+
+    // Type namespace
+    /// A primitive type such as `i32` or `str`.
+    ///
+    /// **Belongs to the type namespace.**
+    PrimTy(hir::PrimTy),
+    /// The `Self` type, optionally with the [`DefId`] of the trait it belongs to and
+    /// optionally with the [`DefId`] of the item introducing the `Self` type alias.
+    ///
+    /// **Belongs to the type namespace.**
+    ///
+    /// Examples:
+    /// ```
+    /// struct Bar(Box<Self>);
+    /// // `Res::SelfTy { trait_: None, alias_of: Some(Bar) }`
+    ///
+    /// trait Foo {
+    ///     fn foo() -> Box<Self>;
+    ///     // `Res::SelfTy { trait_: Some(Foo), alias_of: None }`
+    /// }
+    ///
+    /// impl Bar {
+    ///     fn blah() {
+    ///         let _: Self;
+    ///         // `Res::SelfTy { trait_: None, alias_of: Some(::{impl#0}) }`
+    ///     }
+    /// }
+    ///
+    /// impl Foo for Bar {
+    ///     fn foo() -> Box<Self> {
+    ///     // `Res::SelfTy { trait_: Some(Foo), alias_of: Some(::{impl#1}) }`
+    ///         let _: Self;
+    ///         // `Res::SelfTy { trait_: Some(Foo), alias_of: Some(::{impl#1}) }`
+    ///
+    ///         todo!()
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// *See also [`Res::SelfCtor`].*
+    ///
+    /// -----
+    ///
+    /// HACK(min_const_generics): self types also have an optional requirement to **not** mention
+    /// any generic parameters to allow the following with `min_const_generics`:
+    /// ```
+    /// # struct Foo;
+    /// impl Foo { fn test() -> [u8; std::mem::size_of::<Self>()] { todo!() } }
+    ///
+    /// struct Bar([u8; baz::<Self>()]);
+    /// const fn baz<T>() -> usize { 10 }
+    /// ```
+    /// We do however allow `Self` in repeat expression even if it is generic to not break code
+    /// which already works on stable while causing the `const_evaluatable_unchecked` future compat lint:
+    /// ```
+    /// fn foo<T>() {
+    ///     let _bar = [1_u8; std::mem::size_of::<*mut T>()];
+    /// }
+    /// ```
+    // FIXME(generic_const_exprs): Remove this bodge once that feature is stable.
+    SelfTy {
+        /// The trait this `Self` is a generic arg for.
+        trait_: Option<DefId>,
+        /// The item introducing the `Self` type alias. Can be used in the `type_of` query
+        /// to get the underlying type. Additionally whether the `Self` type is disallowed
+        /// from mentioning generics (i.e. when used in an anonymous constant).
+        alias_to: Option<(DefId, bool)>,
+    },
+    /// A tool attribute module; e.g., the `rustfmt` in `#[rustfmt::skip]`.
+    ///
+    /// **Belongs to the type namespace.**
+    ToolMod,
+
+    // Value namespace
+    /// The `Self` constructor, along with the [`DefId`]
+    /// of the impl it is associated with.
+    ///
+    /// **Belongs to the value namespace.**
+    ///
+    /// *See also [`Res::SelfTy`].*
+    SelfCtor(DefId),
+    /// A local variable or function parameter.
+    ///
+    /// **Belongs to the value namespace.**
+    Local(Id),
+
+    // Macro namespace
+    /// An attribute that is *not* implemented via macro.
+    /// E.g., `#[inline]` and `#[rustfmt::skip]`, which are essentially directives,
+    /// as opposed to `#[test]`, which is a builtin macro.
+    ///
+    /// **Belongs to the macro namespace.**
+    NonMacroAttr(NonMacroAttrKind), // e.g., `#[inline]` or `#[rustfmt::skip]`
+
+    // All namespaces
+    /// Name resolution failed. We use a dummy `Res` variant so later phases
+    /// of the compiler won't crash and can instead report more errors.
+    ///
+    /// **Not bound to a specific namespace.**
+    Err,
+}
+
+/// The result of resolving a path before lowering to HIR,
+/// with "module" segments resolved and associated item
+/// segments deferred to type checking.
+/// `base_res` is the resolution of the resolved part of the
+/// path, `unresolved_segments` is the number of unresolved
+/// segments.
+///
+/// ```text
+/// module::Type::AssocX::AssocY::MethodOrAssocType
+/// ^~~~~~~~~~~~  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/// base_res      unresolved_segments = 3
+///
+/// <T as Trait>::AssocX::AssocY::MethodOrAssocType
+///       ^~~~~~~~~~~~~~  ^~~~~~~~~~~~~~~~~~~~~~~~~
+///       base_res        unresolved_segments = 2
+/// ```
+#[derive(Copy, Clone, Debug)]
+pub struct PartialRes {
+    base_res: Res<NodeId>,
+    unresolved_segments: usize,
+}
+
+impl PartialRes {
+    #[inline]
+    pub fn new(base_res: Res<NodeId>) -> Self {
+        PartialRes { base_res, unresolved_segments: 0 }
+    }
+
+    #[inline]
+    pub fn with_unresolved_segments(base_res: Res<NodeId>, mut unresolved_segments: usize) -> Self {
+        if base_res == Res::Err {
+            unresolved_segments = 0
+        }
+        PartialRes { base_res, unresolved_segments }
+    }
+
+    #[inline]
+    pub fn base_res(&self) -> Res<NodeId> {
+        self.base_res
+    }
+
+    #[inline]
+    pub fn unresolved_segments(&self) -> usize {
+        self.unresolved_segments
+    }
+}
+
+/// Different kinds of symbols can coexist even if they share the same textual name.
+/// Therefore, they each have a separate universe (known as a "namespace").
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+pub enum Namespace {
+    /// The type namespace includes `struct`s, `enum`s, `union`s, `trait`s, and `mod`s
+    /// (and, by extension, crates).
+    ///
+    /// Note that the type namespace includes other items; this is not an
+    /// exhaustive list.
+    TypeNS,
+    /// The value namespace includes `fn`s, `const`s, `static`s, and local variables (including function arguments).
+    ValueNS,
+    /// The macro namespace includes `macro_rules!` macros, declarative `macro`s,
+    /// procedural macros, attribute macros, `derive` macros, and non-macro attributes
+    /// like `#[inline]` and `#[rustfmt::skip]`.
+    MacroNS,
+}
+
+impl Namespace {
+    /// The English description of the namespace.
+    pub fn descr(self) -> &'static str {
+        match self {
+            Self::TypeNS => "type",
+            Self::ValueNS => "value",
+            Self::MacroNS => "macro",
+        }
+    }
+}
+
+/// Just a helper ‒ separate structure for each namespace.
+#[derive(Copy, Clone, Default, Debug)]
+pub struct PerNS<T> {
+    pub value_ns: T,
+    pub type_ns: T,
+    pub macro_ns: T,
+}
+
+impl<T> PerNS<T> {
+    pub fn map<U, F: FnMut(T) -> U>(self, mut f: F) -> PerNS<U> {
+        PerNS { value_ns: f(self.value_ns), type_ns: f(self.type_ns), macro_ns: f(self.macro_ns) }
+    }
+
+    pub fn into_iter(self) -> IntoIter<T, 3> {
+        [self.value_ns, self.type_ns, self.macro_ns].into_iter()
+    }
+
+    pub fn iter(&self) -> IntoIter<&T, 3> {
+        [&self.value_ns, &self.type_ns, &self.macro_ns].into_iter()
+    }
+}
+
+impl<T> ::std::ops::Index<Namespace> for PerNS<T> {
+    type Output = T;
+
+    fn index(&self, ns: Namespace) -> &T {
+        match ns {
+            Namespace::ValueNS => &self.value_ns,
+            Namespace::TypeNS => &self.type_ns,
+            Namespace::MacroNS => &self.macro_ns,
+        }
+    }
+}
+
+impl<T> ::std::ops::IndexMut<Namespace> for PerNS<T> {
+    fn index_mut(&mut self, ns: Namespace) -> &mut T {
+        match ns {
+            Namespace::ValueNS => &mut self.value_ns,
+            Namespace::TypeNS => &mut self.type_ns,
+            Namespace::MacroNS => &mut self.macro_ns,
+        }
+    }
+}
+
+impl<T> PerNS<Option<T>> {
+    /// Returns `true` if all the items in this collection are `None`.
+    pub fn is_empty(&self) -> bool {
+        self.type_ns.is_none() && self.value_ns.is_none() && self.macro_ns.is_none()
+    }
+
+    /// Returns an iterator over the items which are `Some`.
+    pub fn present_items(self) -> impl Iterator<Item = T> {
+        [self.type_ns, self.value_ns, self.macro_ns].into_iter().flatten()
+    }
+}
+
+impl CtorKind {
+    pub fn from_ast(vdata: &ast::VariantData) -> CtorKind {
+        match *vdata {
+            ast::VariantData::Tuple(..) => CtorKind::Fn,
+            ast::VariantData::Unit(..) => CtorKind::Const,
+            ast::VariantData::Struct(..) => CtorKind::Fictive,
+        }
+    }
+
+    pub fn from_hir(vdata: &hir::VariantData<'_>) -> CtorKind {
+        match *vdata {
+            hir::VariantData::Tuple(..) => CtorKind::Fn,
+            hir::VariantData::Unit(..) => CtorKind::Const,
+            hir::VariantData::Struct(..) => CtorKind::Fictive,
+        }
+    }
+}
+
+impl NonMacroAttrKind {
+    pub fn descr(self) -> &'static str {
+        match self {
+            NonMacroAttrKind::Builtin(..) => "built-in attribute",
+            NonMacroAttrKind::Tool => "tool attribute",
+            NonMacroAttrKind::DeriveHelper | NonMacroAttrKind::DeriveHelperCompat => {
+                "derive helper attribute"
+            }
+            NonMacroAttrKind::Registered => "explicitly registered attribute",
+        }
+    }
+
+    pub fn article(self) -> &'static str {
+        match self {
+            NonMacroAttrKind::Registered => "an",
+            _ => "a",
+        }
+    }
+
+    /// Users of some attributes cannot mark them as used, so they are considered always used.
+    pub fn is_used(self) -> bool {
+        match self {
+            NonMacroAttrKind::Tool
+            | NonMacroAttrKind::DeriveHelper
+            | NonMacroAttrKind::DeriveHelperCompat => true,
+            NonMacroAttrKind::Builtin(..) | NonMacroAttrKind::Registered => false,
+        }
+    }
+}
+
+impl<Id> Res<Id> {
+    /// Return the `DefId` of this `Def` if it has an ID, else panic.
+    pub fn def_id(&self) -> DefId
+    where
+        Id: Debug,
+    {
+        self.opt_def_id()
+            .unwrap_or_else(|| panic!("attempted .def_id() on invalid res: {:?}", self))
+    }
+
+    /// Return `Some(..)` with the `DefId` of this `Res` if it has a ID, else `None`.
+    pub fn opt_def_id(&self) -> Option<DefId> {
+        match *self {
+            Res::Def(_, id) => Some(id),
+
+            Res::Local(..)
+            | Res::PrimTy(..)
+            | Res::SelfTy { .. }
+            | Res::SelfCtor(..)
+            | Res::ToolMod
+            | Res::NonMacroAttr(..)
+            | Res::Err => None,
+        }
+    }
+
+    /// Return the `DefId` of this `Res` if it represents a module.
+    pub fn mod_def_id(&self) -> Option<DefId> {
+        match *self {
+            Res::Def(DefKind::Mod, id) => Some(id),
+            _ => None,
+        }
+    }
+
+    /// A human readable name for the res kind ("function", "module", etc.).
+    pub fn descr(&self) -> &'static str {
+        match *self {
+            Res::Def(kind, def_id) => kind.descr(def_id),
+            Res::SelfCtor(..) => "self constructor",
+            Res::PrimTy(..) => "builtin type",
+            Res::Local(..) => "local variable",
+            Res::SelfTy { .. } => "self type",
+            Res::ToolMod => "tool module",
+            Res::NonMacroAttr(attr_kind) => attr_kind.descr(),
+            Res::Err => "unresolved item",
+        }
+    }
+
+    /// Gets an English article for the `Res`.
+    pub fn article(&self) -> &'static str {
+        match *self {
+            Res::Def(kind, _) => kind.article(),
+            Res::NonMacroAttr(kind) => kind.article(),
+            Res::Err => "an",
+            _ => "a",
+        }
+    }
+
+    pub fn map_id<R>(self, mut map: impl FnMut(Id) -> R) -> Res<R> {
+        match self {
+            Res::Def(kind, id) => Res::Def(kind, id),
+            Res::SelfCtor(id) => Res::SelfCtor(id),
+            Res::PrimTy(id) => Res::PrimTy(id),
+            Res::Local(id) => Res::Local(map(id)),
+            Res::SelfTy { trait_, alias_to } => Res::SelfTy { trait_, alias_to },
+            Res::ToolMod => Res::ToolMod,
+            Res::NonMacroAttr(attr_kind) => Res::NonMacroAttr(attr_kind),
+            Res::Err => Res::Err,
+        }
+    }
+
+    pub fn apply_id<R, E>(self, mut map: impl FnMut(Id) -> Result<R, E>) -> Result<Res<R>, E> {
+        Ok(match self {
+            Res::Def(kind, id) => Res::Def(kind, id),
+            Res::SelfCtor(id) => Res::SelfCtor(id),
+            Res::PrimTy(id) => Res::PrimTy(id),
+            Res::Local(id) => Res::Local(map(id)?),
+            Res::SelfTy { trait_, alias_to } => Res::SelfTy { trait_, alias_to },
+            Res::ToolMod => Res::ToolMod,
+            Res::NonMacroAttr(attr_kind) => Res::NonMacroAttr(attr_kind),
+            Res::Err => Res::Err,
+        })
+    }
+
+    #[track_caller]
+    pub fn expect_non_local<OtherId>(self) -> Res<OtherId> {
+        self.map_id(
+            #[track_caller]
+            |_| panic!("unexpected `Res::Local`"),
+        )
+    }
+
+    pub fn macro_kind(self) -> Option<MacroKind> {
+        match self {
+            Res::Def(DefKind::Macro(kind), _) => Some(kind),
+            Res::NonMacroAttr(..) => Some(MacroKind::Attr),
+            _ => None,
+        }
+    }
+
+    /// Returns `None` if this is `Res::Err`
+    pub fn ns(&self) -> Option<Namespace> {
+        match self {
+            Res::Def(kind, ..) => kind.ns(),
+            Res::PrimTy(..) | Res::SelfTy { .. } | Res::ToolMod => Some(Namespace::TypeNS),
+            Res::SelfCtor(..) | Res::Local(..) => Some(Namespace::ValueNS),
+            Res::NonMacroAttr(..) => Some(Namespace::MacroNS),
+            Res::Err => None,
+        }
+    }
+
+    /// Always returns `true` if `self` is `Res::Err`
+    pub fn matches_ns(&self, ns: Namespace) -> bool {
+        self.ns().map_or(true, |actual_ns| actual_ns == ns)
+    }
+
+    /// Returns whether such a resolved path can occur in a tuple struct/variant pattern
+    pub fn expected_in_tuple_struct_pat(&self) -> bool {
+        matches!(self, Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) | Res::SelfCtor(..))
+    }
+
+    /// Returns whether such a resolved path can occur in a unit struct/variant pattern
+    pub fn expected_in_unit_struct_pat(&self) -> bool {
+        matches!(self, Res::Def(DefKind::Ctor(_, CtorKind::Const), _) | Res::SelfCtor(..))
+    }
+}
+
+/// Resolution for a lifetime appearing in a type.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub enum LifetimeRes {
+    /// Successfully linked the lifetime to a generic parameter.
+    Param {
+        /// Id of the generic parameter that introduced it.
+        param: LocalDefId,
+        /// Id of the introducing place. That can be:
+        /// - an item's id, for the item's generic parameters;
+        /// - a TraitRef's ref_id, identifying the `for<...>` binder;
+        /// - a BareFn type's id.
+        ///
+        /// This information is used for impl-trait lifetime captures, to know when to or not to
+        /// capture any given lifetime.
+        binder: NodeId,
+    },
+    /// Created a generic parameter for an anonymous lifetime.
+    Fresh {
+        /// Id of the generic parameter that introduced it.
+        ///
+        /// Creating the associated `LocalDefId` is the responsibility of lowering.
+        param: NodeId,
+        /// Id of the introducing place. See `Param`.
+        binder: NodeId,
+    },
+    /// This variant is used for anonymous lifetimes that we did not resolve during
+    /// late resolution.  Those lifetimes will be inferred by typechecking.
+    Infer,
+    /// Explicit `'static` lifetime.
+    Static,
+    /// Resolution failure.
+    Error,
+    /// HACK: This is used to recover the NodeId of an elided lifetime.
+    ElidedAnchor { start: NodeId, end: NodeId },
+}
diff --git a/compiler/rustc_hir/src/def_path_hash_map.rs b/compiler/rustc_hir/src/def_path_hash_map.rs
new file mode 100644
index 000000000..8bfb47af2
--- /dev/null
+++ b/compiler/rustc_hir/src/def_path_hash_map.rs
@@ -0,0 +1,37 @@
+use rustc_data_structures::fingerprint::Fingerprint;
+use rustc_span::def_id::{DefIndex, DefPathHash};
+
+#[derive(Clone, Default)]
+pub struct Config;
+
+impl odht::Config for Config {
+    type Key = DefPathHash;
+    type Value = DefIndex;
+
+    type EncodedKey = [u8; 16];
+    type EncodedValue = [u8; 4];
+
+    type H = odht::UnHashFn;
+
+    #[inline]
+    fn encode_key(k: &DefPathHash) -> [u8; 16] {
+        k.0.to_le_bytes()
+    }
+
+    #[inline]
+    fn encode_value(v: &DefIndex) -> [u8; 4] {
+        v.as_u32().to_le_bytes()
+    }
+
+    #[inline]
+    fn decode_key(k: &[u8; 16]) -> DefPathHash {
+        DefPathHash(Fingerprint::from_le_bytes(*k))
+    }
+
+    #[inline]
+    fn decode_value(v: &[u8; 4]) -> DefIndex {
+        DefIndex::from_u32(u32::from_le_bytes(*v))
+    }
+}
+
+pub type DefPathHashMap = odht::HashTableOwned<Config>;
diff --git a/compiler/rustc_hir/src/definitions.rs b/compiler/rustc_hir/src/definitions.rs
new file mode 100644
index 000000000..c2c551e78
--- /dev/null
+++ b/compiler/rustc_hir/src/definitions.rs
@@ -0,0 +1,440 @@
+//! For each definition, we track the following data. A definition
+//! here is defined somewhat circularly as "something with a `DefId`",
+//! but it generally corresponds to things like structs, enums, etc.
+//! There are also some rather random cases (like const initializer
+//! expressions) that are mostly just leftovers.
+
+pub use crate::def_id::DefPathHash;
+use crate::def_id::{CrateNum, DefIndex, LocalDefId, StableCrateId, CRATE_DEF_INDEX, LOCAL_CRATE};
+use crate::def_path_hash_map::DefPathHashMap;
+
+use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::stable_hasher::StableHasher;
+use rustc_index::vec::IndexVec;
+use rustc_span::symbol::{kw, sym, Symbol};
+
+use std::fmt::{self, Write};
+use std::hash::Hash;
+use tracing::debug;
+
+/// The `DefPathTable` maps `DefIndex`es to `DefKey`s and vice versa.
+/// Internally the `DefPathTable` holds a tree of `DefKey`s, where each `DefKey`
+/// stores the `DefIndex` of its parent.
+/// There is one `DefPathTable` for each crate.
+#[derive(Clone, Default, Debug)]
+pub struct DefPathTable {
+    index_to_key: IndexVec<DefIndex, DefKey>,
+    def_path_hashes: IndexVec<DefIndex, DefPathHash>,
+    def_path_hash_to_index: DefPathHashMap,
+}
+
+impl DefPathTable {
+    fn allocate(&mut self, key: DefKey, def_path_hash: DefPathHash) -> DefIndex {
+        let index = {
+            let index = DefIndex::from(self.index_to_key.len());
+            debug!("DefPathTable::insert() - {:?} <-> {:?}", key, index);
+            self.index_to_key.push(key);
+            index
+        };
+        self.def_path_hashes.push(def_path_hash);
+        debug_assert!(self.def_path_hashes.len() == self.index_to_key.len());
+
+        // Check for hash collisions of DefPathHashes. These should be
+        // exceedingly rare.
+        if let Some(existing) = self.def_path_hash_to_index.insert(&def_path_hash, &index) {
+            let def_path1 = DefPath::make(LOCAL_CRATE, existing, |idx| self.def_key(idx));
+            let def_path2 = DefPath::make(LOCAL_CRATE, index, |idx| self.def_key(idx));
+
+            // Continuing with colliding DefPathHashes can lead to correctness
+            // issues. We must abort compilation.
+            //
+            // The likelihood of such a collision is very small, so actually
+            // running into one could be indicative of a poor hash function
+            // being used.
+            //
+            // See the documentation for DefPathHash for more information.
+            panic!(
+                "found DefPathHash collision between {:?} and {:?}. \
+                    Compilation cannot continue.",
+                def_path1, def_path2
+            );
+        }
+
+        // Assert that all DefPathHashes correctly contain the local crate's
+        // StableCrateId
+        #[cfg(debug_assertions)]
+        if let Some(root) = self.def_path_hashes.get(CRATE_DEF_INDEX) {
+            assert!(def_path_hash.stable_crate_id() == root.stable_crate_id());
+        }
+
+        index
+    }
+
+    #[inline(always)]
+    pub fn def_key(&self, index: DefIndex) -> DefKey {
+        self.index_to_key[index]
+    }
+
+    #[inline(always)]
+    pub fn def_path_hash(&self, index: DefIndex) -> DefPathHash {
+        let hash = self.def_path_hashes[index];
+        debug!("def_path_hash({:?}) = {:?}", index, hash);
+        hash
+    }
+
+    pub fn enumerated_keys_and_path_hashes(
+        &self,
+    ) -> impl Iterator<Item = (DefIndex, &DefKey, &DefPathHash)> + ExactSizeIterator + '_ {
+        self.index_to_key
+            .iter_enumerated()
+            .map(move |(index, key)| (index, key, &self.def_path_hashes[index]))
+    }
+}
+
+/// The definition table containing node definitions.
+/// It holds the `DefPathTable` for `LocalDefId`s/`DefPath`s.
+/// It also stores mappings to convert `LocalDefId`s to/from `HirId`s.
+#[derive(Clone, Debug)]
+pub struct Definitions {
+    table: DefPathTable,
+    next_disambiguator: FxHashMap<(LocalDefId, DefPathData), u32>,
+
+    /// The [StableCrateId] of the local crate.
+    stable_crate_id: StableCrateId,
+}
+
+/// A unique identifier that we can use to lookup a definition
+/// precisely. It combines the index of the definition's parent (if
+/// any) with a `DisambiguatedDefPathData`.
+#[derive(Copy, Clone, PartialEq, Debug, Encodable, Decodable)]
+pub struct DefKey {
+    /// The parent path.
+    pub parent: Option<DefIndex>,
+
+    /// The identifier of this node.
+    pub disambiguated_data: DisambiguatedDefPathData,
+}
+
+impl DefKey {
+    pub(crate) fn compute_stable_hash(&self, parent: DefPathHash) -> DefPathHash {
+        let mut hasher = StableHasher::new();
+
+        parent.hash(&mut hasher);
+
+        let DisambiguatedDefPathData { ref data, disambiguator } = self.disambiguated_data;
+
+        std::mem::discriminant(data).hash(&mut hasher);
+        if let Some(name) = data.get_opt_name() {
+            // Get a stable hash by considering the symbol chars rather than
+            // the symbol index.
+            name.as_str().hash(&mut hasher);
+        }
+
+        disambiguator.hash(&mut hasher);
+
+        let local_hash: u64 = hasher.finish();
+
+        // Construct the new DefPathHash, making sure that the `crate_id`
+        // portion of the hash is properly copied from the parent. This way the
+        // `crate_id` part will be recursively propagated from the root to all
+        // DefPathHashes in this DefPathTable.
+        DefPathHash::new(parent.stable_crate_id(), local_hash)
+    }
+
+    #[inline]
+    pub fn get_opt_name(&self) -> Option<Symbol> {
+        self.disambiguated_data.data.get_opt_name()
+    }
+}
+
+/// A pair of `DefPathData` and an integer disambiguator. The integer is
+/// normally `0`, but in the event that there are multiple defs with the
+/// same `parent` and `data`, we use this field to disambiguate
+/// between them. This introduces some artificial ordering dependency
+/// but means that if you have, e.g., two impls for the same type in
+/// the same module, they do get distinct `DefId`s.
+#[derive(Copy, Clone, PartialEq, Debug, Encodable, Decodable)]
+pub struct DisambiguatedDefPathData {
+    pub data: DefPathData,
+    pub disambiguator: u32,
+}
+
+impl DisambiguatedDefPathData {
+    pub fn fmt_maybe_verbose(&self, writer: &mut impl Write, verbose: bool) -> fmt::Result {
+        match self.data.name() {
+            DefPathDataName::Named(name) => {
+                if verbose && self.disambiguator != 0 {
+                    write!(writer, "{}#{}", name, self.disambiguator)
+                } else {
+                    writer.write_str(name.as_str())
+                }
+            }
+            DefPathDataName::Anon { namespace } => {
+                write!(writer, "{{{}#{}}}", namespace, self.disambiguator)
+            }
+        }
+    }
+}
+
+impl fmt::Display for DisambiguatedDefPathData {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.fmt_maybe_verbose(f, true)
+    }
+}
+
+#[derive(Clone, Debug, Encodable, Decodable)]
+pub struct DefPath {
+    /// The path leading from the crate root to the item.
+    pub data: Vec<DisambiguatedDefPathData>,
+
+    /// The crate root this path is relative to.
+    pub krate: CrateNum,
+}
+
+impl DefPath {
+    pub fn make<FN>(krate: CrateNum, start_index: DefIndex, mut get_key: FN) -> DefPath
+    where
+        FN: FnMut(DefIndex) -> DefKey,
+    {
+        let mut data = vec![];
+        let mut index = Some(start_index);
+        loop {
+            debug!("DefPath::make: krate={:?} index={:?}", krate, index);
+            let p = index.unwrap();
+            let key = get_key(p);
+            debug!("DefPath::make: key={:?}", key);
+            match key.disambiguated_data.data {
+                DefPathData::CrateRoot => {
+                    assert!(key.parent.is_none());
+                    break;
+                }
+                _ => {
+                    data.push(key.disambiguated_data);
+                    index = key.parent;
+                }
+            }
+        }
+        data.reverse();
+        DefPath { data, krate }
+    }
+
+    /// Returns a string representation of the `DefPath` without
+    /// the crate-prefix. This method is useful if you don't have
+    /// a `TyCtxt` available.
+    pub fn to_string_no_crate_verbose(&self) -> String {
+        let mut s = String::with_capacity(self.data.len() * 16);
+
+        for component in &self.data {
+            write!(s, "::{}", component).unwrap();
+        }
+
+        s
+    }
+
+    /// Returns a filename-friendly string of the `DefPath`, without
+    /// the crate-prefix. This method is useful if you don't have
+    /// a `TyCtxt` available.
+    pub fn to_filename_friendly_no_crate(&self) -> String {
+        let mut s = String::with_capacity(self.data.len() * 16);
+
+        let mut opt_delimiter = None;
+        for component in &self.data {
+            s.extend(opt_delimiter);
+            opt_delimiter = Some('-');
+            write!(s, "{}", component).unwrap();
+        }
+
+        s
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, Encodable, Decodable)]
+pub enum DefPathData {
+    // Root: these should only be used for the root nodes, because
+    // they are treated specially by the `def_path` function.
+    /// The crate root (marker).
+    CrateRoot,
+
+    // Different kinds of items and item-like things:
+    /// An impl.
+    Impl,
+    /// An `extern` block.
+    ForeignMod,
+    /// A `use` item.
+    Use,
+    /// A global asm item.
+    GlobalAsm,
+    /// Something in the type namespace.
+    TypeNs(Symbol),
+    /// Something in the value namespace.
+    ValueNs(Symbol),
+    /// Something in the macro namespace.
+    MacroNs(Symbol),
+    /// Something in the lifetime namespace.
+    LifetimeNs(Symbol),
+    /// A closure expression.
+    ClosureExpr,
+
+    // Subportions of items:
+    /// Implicit constructor for a unit or tuple-like struct or enum variant.
+    Ctor,
+    /// A constant expression (see `{ast,hir}::AnonConst`).
+    AnonConst,
+    /// An `impl Trait` type node.
+    ImplTrait,
+}
+
+impl Definitions {
+    pub fn def_path_table(&self) -> &DefPathTable {
+        &self.table
+    }
+
+    /// Gets the number of definitions.
+    pub fn def_index_count(&self) -> usize {
+        self.table.index_to_key.len()
+    }
+
+    #[inline]
+    pub fn def_key(&self, id: LocalDefId) -> DefKey {
+        self.table.def_key(id.local_def_index)
+    }
+
+    #[inline(always)]
+    pub fn def_path_hash(&self, id: LocalDefId) -> DefPathHash {
+        self.table.def_path_hash(id.local_def_index)
+    }
+
+    /// Returns the path from the crate root to `index`. The root
+    /// nodes are not included in the path (i.e., this will be an
+    /// empty vector for the crate root). For an inlined item, this
+    /// will be the path of the item in the external crate (but the
+    /// path will begin with the path to the external crate).
+    pub fn def_path(&self, id: LocalDefId) -> DefPath {
+        DefPath::make(LOCAL_CRATE, id.local_def_index, |index| {
+            self.def_key(LocalDefId { local_def_index: index })
+        })
+    }
+
+    /// Adds a root definition (no parent) and a few other reserved definitions.
+    pub fn new(stable_crate_id: StableCrateId) -> Definitions {
+        let key = DefKey {
+            parent: None,
+            disambiguated_data: DisambiguatedDefPathData {
+                data: DefPathData::CrateRoot,
+                disambiguator: 0,
+            },
+        };
+
+        let parent_hash = DefPathHash::new(stable_crate_id, 0);
+        let def_path_hash = key.compute_stable_hash(parent_hash);
+
+        // Create the root definition.
+        let mut table = DefPathTable::default();
+        let root = LocalDefId { local_def_index: table.allocate(key, def_path_hash) };
+        assert_eq!(root.local_def_index, CRATE_DEF_INDEX);
+
+        Definitions { table, next_disambiguator: Default::default(), stable_crate_id }
+    }
+
+    /// Adds a definition with a parent definition.
+    pub fn create_def(&mut self, parent: LocalDefId, data: DefPathData) -> LocalDefId {
+        // We can't use `Debug` implementation for `LocalDefId` here, since it tries to acquire a
+        // reference to `Definitions` and we're already holding a mutable reference.
+        debug!(
+            "create_def(parent={}, data={data:?})",
+            self.def_path(parent).to_string_no_crate_verbose(),
+        );
+
+        // The root node must be created with `create_root_def()`.
+        assert!(data != DefPathData::CrateRoot);
+
+        // Find the next free disambiguator for this key.
+        let disambiguator = {
+            let next_disamb = self.next_disambiguator.entry((parent, data)).or_insert(0);
+            let disambiguator = *next_disamb;
+            *next_disamb = next_disamb.checked_add(1).expect("disambiguator overflow");
+            disambiguator
+        };
+        let key = DefKey {
+            parent: Some(parent.local_def_index),
+            disambiguated_data: DisambiguatedDefPathData { data, disambiguator },
+        };
+
+        let parent_hash = self.table.def_path_hash(parent.local_def_index);
+        let def_path_hash = key.compute_stable_hash(parent_hash);
+
+        debug!("create_def: after disambiguation, key = {:?}", key);
+
+        // Create the definition.
+        LocalDefId { local_def_index: self.table.allocate(key, def_path_hash) }
+    }
+
+    pub fn iter_local_def_id(&self) -> impl Iterator<Item = LocalDefId> + '_ {
+        self.table.def_path_hashes.indices().map(|local_def_index| LocalDefId { local_def_index })
+    }
+
+    #[inline(always)]
+    pub fn local_def_path_hash_to_def_id(
+        &self,
+        hash: DefPathHash,
+        err: &mut dyn FnMut() -> !,
+    ) -> LocalDefId {
+        debug_assert!(hash.stable_crate_id() == self.stable_crate_id);
+        self.table
+            .def_path_hash_to_index
+            .get(&hash)
+            .map(|local_def_index| LocalDefId { local_def_index })
+            .unwrap_or_else(|| err())
+    }
+
+    pub fn def_path_hash_to_def_index_map(&self) -> &DefPathHashMap {
+        &self.table.def_path_hash_to_index
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Debug)]
+pub enum DefPathDataName {
+    Named(Symbol),
+    Anon { namespace: Symbol },
+}
+
+impl DefPathData {
+    pub fn get_opt_name(&self) -> Option<Symbol> {
+        use self::DefPathData::*;
+        match *self {
+            TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name) => Some(name),
+
+            Impl | ForeignMod | CrateRoot | Use | GlobalAsm | ClosureExpr | Ctor | AnonConst
+            | ImplTrait => None,
+        }
+    }
+
+    pub fn name(&self) -> DefPathDataName {
+        use self::DefPathData::*;
+        match *self {
+            TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name) => {
+                DefPathDataName::Named(name)
+            }
+            // Note that this does not show up in user print-outs.
+            CrateRoot => DefPathDataName::Anon { namespace: kw::Crate },
+            Impl => DefPathDataName::Anon { namespace: kw::Impl },
+            ForeignMod => DefPathDataName::Anon { namespace: kw::Extern },
+            Use => DefPathDataName::Anon { namespace: kw::Use },
+            GlobalAsm => DefPathDataName::Anon { namespace: sym::global_asm },
+            ClosureExpr => DefPathDataName::Anon { namespace: sym::closure },
+            Ctor => DefPathDataName::Anon { namespace: sym::constructor },
+            AnonConst => DefPathDataName::Anon { namespace: sym::constant },
+            ImplTrait => DefPathDataName::Anon { namespace: sym::opaque },
+        }
+    }
+}
+
+impl fmt::Display for DefPathData {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.name() {
+            DefPathDataName::Named(name) => f.write_str(name.as_str()),
+            // FIXME(#70334): this will generate legacy {{closure}}, {{impl}}, etc
+            DefPathDataName::Anon { namespace } => write!(f, "{{{{{}}}}}", namespace),
+        }
+    }
+}
diff --git a/compiler/rustc_hir/src/diagnostic_items.rs b/compiler/rustc_hir/src/diagnostic_items.rs
new file mode 100644
index 000000000..243014b00
--- /dev/null
+++ b/compiler/rustc_hir/src/diagnostic_items.rs
@@ -0,0 +1,17 @@
+use crate::def_id::DefId;
+use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_span::Symbol;
+
+#[derive(Debug, Default)]
+pub struct DiagnosticItems {
+    pub id_to_name: FxHashMap<DefId, Symbol>,
+    pub name_to_id: FxHashMap<Symbol, DefId>,
+}
+
+impl<CTX: crate::HashStableContext> HashStable<CTX> for DiagnosticItems {
+    #[inline]
+    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
+        self.name_to_id.hash_stable(ctx, hasher);
+    }
+}
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
new file mode 100644
index 000000000..617433a98
--- /dev/null
+++ b/compiler/rustc_hir/src/hir.rs
@@ -0,0 +1,3506 @@
+use crate::def::{CtorKind, DefKind, Res};
+use crate::def_id::DefId;
+pub(crate) use crate::hir_id::{HirId, ItemLocalId};
+use crate::intravisit::FnKind;
+use crate::LangItem;
+
+use rustc_ast as ast;
+use rustc_ast::util::parser::ExprPrecedence;
+use rustc_ast::{Attribute, FloatTy, IntTy, Label, LitKind, TraitObjectSyntax, UintTy};
+pub use rustc_ast::{BorrowKind, ImplPolarity, IsAuto};
+pub use rustc_ast::{CaptureBy, Movability, Mutability};
+use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
+use rustc_data_structures::fingerprint::Fingerprint;
+use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::sorted_map::SortedMap;
+use rustc_error_messages::MultiSpan;
+use rustc_index::vec::IndexVec;
+use rustc_macros::HashStable_Generic;
+use rustc_span::hygiene::MacroKind;
+use rustc_span::source_map::Spanned;
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::{def_id::LocalDefId, BytePos, Span, DUMMY_SP};
+use rustc_target::asm::InlineAsmRegOrRegClass;
+use rustc_target::spec::abi::Abi;
+
+use smallvec::SmallVec;
+use std::fmt;
+
+#[derive(Debug, Copy, Clone, Encodable, HashStable_Generic)]
+pub struct Lifetime {
+    pub hir_id: HirId,
+    pub span: Span,
+
+    /// Either "`'a`", referring to a named lifetime definition,
+    /// or "``" (i.e., `kw::Empty`), for elision placeholders.
+    ///
+    /// HIR lowering inserts these placeholders in type paths that
+    /// refer to type definitions needing lifetime parameters,
+    /// `&T` and `&mut T`, and trait objects without `... + 'a`.
+    pub name: LifetimeName,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Encodable, Hash, Copy)]
+#[derive(HashStable_Generic)]
+pub enum ParamName {
+    /// Some user-given name like `T` or `'x`.
+    Plain(Ident),
+
+    /// Synthetic name generated when user elided a lifetime in an impl header.
+    ///
+    /// E.g., the lifetimes in cases like these:
+    /// ```ignore (fragment)
+    /// impl Foo for &u32
+    /// impl Foo<'_> for u32
+    /// ```
+    /// in that case, we rewrite to
+    /// ```ignore (fragment)
+    /// impl<'f> Foo for &'f u32
+    /// impl<'f> Foo<'f> for u32
+    /// ```
+    /// where `'f` is something like `Fresh(0)`. The indices are
+    /// unique per impl, but not necessarily continuous.
+    Fresh,
+
+    /// Indicates an illegal name was given and an error has been
+    /// reported (so we should squelch other derived errors). Occurs
+    /// when, e.g., `'_` is used in the wrong place.
+    Error,
+}
+
+impl ParamName {
+    pub fn ident(&self) -> Ident {
+        match *self {
+            ParamName::Plain(ident) => ident,
+            ParamName::Fresh | ParamName::Error => Ident::with_dummy_span(kw::UnderscoreLifetime),
+        }
+    }
+
+    pub fn normalize_to_macros_2_0(&self) -> ParamName {
+        match *self {
+            ParamName::Plain(ident) => ParamName::Plain(ident.normalize_to_macros_2_0()),
+            param_name => param_name,
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Encodable, Hash, Copy)]
+#[derive(HashStable_Generic)]
+pub enum LifetimeName {
+    /// User-given names or fresh (synthetic) names.
+    Param(LocalDefId, ParamName),
+
+    /// Implicit lifetime in a context like `dyn Foo`. This is
+    /// distinguished from implicit lifetimes elsewhere because the
+    /// lifetime that they default to must appear elsewhere within the
+    /// enclosing type.  This means that, in an `impl Trait` context, we
+    /// don't have to create a parameter for them. That is, `impl
+    /// Trait<Item = &u32>` expands to an opaque type like `type
+    /// Foo<'a> = impl Trait<Item = &'a u32>`, but `impl Trait<item =
+    /// dyn Bar>` expands to `type Foo = impl Trait<Item = dyn Bar +
+    /// 'static>`. The latter uses `ImplicitObjectLifetimeDefault` so
+    /// that surrounding code knows not to create a lifetime
+    /// parameter.
+    ImplicitObjectLifetimeDefault,
+
+    /// Indicates an error during lowering (usually `'_` in wrong place)
+    /// that was already reported.
+    Error,
+
+    /// User wrote an anonymous lifetime, either `'_` or nothing.
+    /// The semantics of this lifetime should be inferred by typechecking code.
+    Infer,
+
+    /// User wrote `'static`.
+    Static,
+}
+
+impl LifetimeName {
+    pub fn ident(&self) -> Ident {
+        match *self {
+            LifetimeName::ImplicitObjectLifetimeDefault | LifetimeName::Error => Ident::empty(),
+            LifetimeName::Infer => Ident::with_dummy_span(kw::UnderscoreLifetime),
+            LifetimeName::Static => Ident::with_dummy_span(kw::StaticLifetime),
+            LifetimeName::Param(_, param_name) => param_name.ident(),
+        }
+    }
+
+    pub fn is_anonymous(&self) -> bool {
+        match *self {
+            LifetimeName::ImplicitObjectLifetimeDefault
+            | LifetimeName::Infer
+            | LifetimeName::Param(_, ParamName::Fresh)
+            | LifetimeName::Error => true,
+            LifetimeName::Static | LifetimeName::Param(..) => false,
+        }
+    }
+
+    pub fn is_elided(&self) -> bool {
+        match self {
+            LifetimeName::ImplicitObjectLifetimeDefault | LifetimeName::Infer => true,
+
+            // It might seem surprising that `Fresh` counts as
+            // *not* elided -- but this is because, as far as the code
+            // in the compiler is concerned -- `Fresh` variants act
+            // equivalently to "some fresh name". They correspond to
+            // early-bound regions on an impl, in other words.
+            LifetimeName::Error | LifetimeName::Param(..) | LifetimeName::Static => false,
+        }
+    }
+
+    fn is_static(&self) -> bool {
+        self == &LifetimeName::Static
+    }
+
+    pub fn normalize_to_macros_2_0(&self) -> LifetimeName {
+        match *self {
+            LifetimeName::Param(def_id, param_name) => {
+                LifetimeName::Param(def_id, param_name.normalize_to_macros_2_0())
+            }
+            lifetime_name => lifetime_name,
+        }
+    }
+}
+
+impl fmt::Display for Lifetime {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.name.ident().fmt(f)
+    }
+}
+
+impl Lifetime {
+    pub fn is_elided(&self) -> bool {
+        self.name.is_elided()
+    }
+
+    pub fn is_static(&self) -> bool {
+        self.name.is_static()
+    }
+}
+
+/// A `Path` is essentially Rust's notion of a name; for instance,
+/// `std::cmp::PartialEq`. It's represented as a sequence of identifiers,
+/// along with a bunch of supporting information.
+#[derive(Debug, HashStable_Generic)]
+pub struct Path<'hir> {
+    pub span: Span,
+    /// The resolution for the path.
+    pub res: Res,
+    /// The segments in the path: the things separated by `::`.
+    pub segments: &'hir [PathSegment<'hir>],
+}
+
+impl Path<'_> {
+    pub fn is_global(&self) -> bool {
+        !self.segments.is_empty() && self.segments[0].ident.name == kw::PathRoot
+    }
+}
+
+/// A segment of a path: an identifier, an optional lifetime, and a set of
+/// types.
+#[derive(Debug, HashStable_Generic)]
+pub struct PathSegment<'hir> {
+    /// The identifier portion of this path segment.
+    pub ident: Ident,
+    // `id` and `res` are optional. We currently only use these in save-analysis,
+    // any path segments without these will not have save-analysis info and
+    // therefore will not have 'jump to def' in IDEs, but otherwise will not be
+    // affected. (In general, we don't bother to get the defs for synthesized
+    // segments, only for segments which have come from the AST).
+    pub hir_id: Option<HirId>,
+    pub res: Option<Res>,
+
+    /// Type/lifetime parameters attached to this path. They come in
+    /// two flavors: `Path<A,B,C>` and `Path(A,B) -> C`. Note that
+    /// this is more than just simple syntactic sugar; the use of
+    /// parens affects the region binding rules, so we preserve the
+    /// distinction.
+    pub args: Option<&'hir GenericArgs<'hir>>,
+
+    /// Whether to infer remaining type parameters, if any.
+    /// This only applies to expression and pattern paths, and
+    /// out of those only the segments with no type parameters
+    /// to begin with, e.g., `Vec::new` is `<Vec<..>>::new::<..>`.
+    pub infer_args: bool,
+}
+
+impl<'hir> PathSegment<'hir> {
+    /// Converts an identifier to the corresponding segment.
+    pub fn from_ident(ident: Ident) -> PathSegment<'hir> {
+        PathSegment { ident, hir_id: None, res: None, infer_args: true, args: None }
+    }
+
+    pub fn invalid() -> Self {
+        Self::from_ident(Ident::empty())
+    }
+
+    pub fn args(&self) -> &GenericArgs<'hir> {
+        if let Some(ref args) = self.args {
+            args
+        } else {
+            const DUMMY: &GenericArgs<'_> = &GenericArgs::none();
+            DUMMY
+        }
+    }
+}
+
+#[derive(Encodable, Debug, HashStable_Generic)]
+pub struct ConstArg {
+    pub value: AnonConst,
+    pub span: Span,
+}
+
+#[derive(Encodable, Debug, HashStable_Generic)]
+pub struct InferArg {
+    pub hir_id: HirId,
+    pub span: Span,
+}
+
+impl InferArg {
+    pub fn to_ty(&self) -> Ty<'_> {
+        Ty { kind: TyKind::Infer, span: self.span, hir_id: self.hir_id }
+    }
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub enum GenericArg<'hir> {
+    Lifetime(Lifetime),
+    Type(Ty<'hir>),
+    Const(ConstArg),
+    Infer(InferArg),
+}
+
+impl GenericArg<'_> {
+    pub fn span(&self) -> Span {
+        match self {
+            GenericArg::Lifetime(l) => l.span,
+            GenericArg::Type(t) => t.span,
+            GenericArg::Const(c) => c.span,
+            GenericArg::Infer(i) => i.span,
+        }
+    }
+
+    pub fn id(&self) -> HirId {
+        match self {
+            GenericArg::Lifetime(l) => l.hir_id,
+            GenericArg::Type(t) => t.hir_id,
+            GenericArg::Const(c) => c.value.hir_id,
+            GenericArg::Infer(i) => i.hir_id,
+        }
+    }
+
+    pub fn is_synthetic(&self) -> bool {
+        matches!(self, GenericArg::Lifetime(lifetime) if lifetime.name.ident() == Ident::empty())
+    }
+
+    pub fn descr(&self) -> &'static str {
+        match self {
+            GenericArg::Lifetime(_) => "lifetime",
+            GenericArg::Type(_) => "type",
+            GenericArg::Const(_) => "constant",
+            GenericArg::Infer(_) => "inferred",
+        }
+    }
+
+    pub fn to_ord(&self) -> ast::ParamKindOrd {
+        match self {
+            GenericArg::Lifetime(_) => ast::ParamKindOrd::Lifetime,
+            GenericArg::Type(_) => ast::ParamKindOrd::Type,
+            GenericArg::Const(_) => ast::ParamKindOrd::Const,
+            GenericArg::Infer(_) => ast::ParamKindOrd::Infer,
+        }
+    }
+
+    pub fn is_ty_or_const(&self) -> bool {
+        match self {
+            GenericArg::Lifetime(_) => false,
+            GenericArg::Type(_) | GenericArg::Const(_) | GenericArg::Infer(_) => true,
+        }
+    }
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub struct GenericArgs<'hir> {
+    /// The generic arguments for this path segment.
+    pub args: &'hir [GenericArg<'hir>],
+    /// Bindings (equality constraints) on associated types, if present.
+    /// E.g., `Foo<A = Bar>`.
+    pub bindings: &'hir [TypeBinding<'hir>],
+    /// Were arguments written in parenthesized form `Fn(T) -> U`?
+    /// This is required mostly for pretty-printing and diagnostics,
+    /// but also for changing lifetime elision rules to be "function-like".
+    pub parenthesized: bool,
+    /// The span encompassing arguments and the surrounding brackets `<>` or `()`
+    ///       Foo<A, B, AssocTy = D>           Fn(T, U, V) -> W
+    ///          ^^^^^^^^^^^^^^^^^^^             ^^^^^^^^^
+    /// Note that this may be:
+    /// - empty, if there are no generic brackets (but there may be hidden lifetimes)
+    /// - dummy, if this was generated while desugaring
+    pub span_ext: Span,
+}
+
+impl<'hir> GenericArgs<'hir> {
+    pub const fn none() -> Self {
+        Self { args: &[], bindings: &[], parenthesized: false, span_ext: DUMMY_SP }
+    }
+
+    pub fn inputs(&self) -> &[Ty<'hir>] {
+        if self.parenthesized {
+            for arg in self.args {
+                match arg {
+                    GenericArg::Lifetime(_) => {}
+                    GenericArg::Type(ref ty) => {
+                        if let TyKind::Tup(ref tys) = ty.kind {
+                            return tys;
+                        }
+                        break;
+                    }
+                    GenericArg::Const(_) => {}
+                    GenericArg::Infer(_) => {}
+                }
+            }
+        }
+        panic!("GenericArgs::inputs: not a `Fn(T) -> U`");
+    }
+
+    #[inline]
+    pub fn has_type_params(&self) -> bool {
+        self.args.iter().any(|arg| matches!(arg, GenericArg::Type(_)))
+    }
+
+    pub fn has_err(&self) -> bool {
+        self.args.iter().any(|arg| match arg {
+            GenericArg::Type(ty) => matches!(ty.kind, TyKind::Err),
+            _ => false,
+        }) || self.bindings.iter().any(|arg| match arg.kind {
+            TypeBindingKind::Equality { term: Term::Ty(ty) } => matches!(ty.kind, TyKind::Err),
+            _ => false,
+        })
+    }
+
+    #[inline]
+    pub fn num_type_params(&self) -> usize {
+        self.args.iter().filter(|arg| matches!(arg, GenericArg::Type(_))).count()
+    }
+
+    #[inline]
+    pub fn num_lifetime_params(&self) -> usize {
+        self.args.iter().filter(|arg| matches!(arg, GenericArg::Lifetime(_))).count()
+    }
+
+    #[inline]
+    pub fn has_lifetime_params(&self) -> bool {
+        self.args.iter().any(|arg| matches!(arg, GenericArg::Lifetime(_)))
+    }
+
+    #[inline]
+    pub fn num_generic_params(&self) -> usize {
+        self.args.iter().filter(|arg| !matches!(arg, GenericArg::Lifetime(_))).count()
+    }
+
+    /// The span encompassing the text inside the surrounding brackets.
+    /// It will also include bindings if they aren't in the form `-> Ret`
+    /// Returns `None` if the span is empty (e.g. no brackets) or dummy
+    pub fn span(&self) -> Option<Span> {
+        let span_ext = self.span_ext()?;
+        Some(span_ext.with_lo(span_ext.lo() + BytePos(1)).with_hi(span_ext.hi() - BytePos(1)))
+    }
+
+    /// Returns span encompassing arguments and their surrounding `<>` or `()`
+    pub fn span_ext(&self) -> Option<Span> {
+        Some(self.span_ext).filter(|span| !span.is_empty())
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.args.is_empty()
+    }
+}
+
+/// A modifier on a bound, currently this is only used for `?Sized`, where the
+/// modifier is `Maybe`. Negative bounds should also be handled here.
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Hash, Debug)]
+#[derive(HashStable_Generic)]
+pub enum TraitBoundModifier {
+    None,
+    Maybe,
+    MaybeConst,
+}
+
+/// The AST represents all type param bounds as types.
+/// `typeck::collect::compute_bounds` matches these against
+/// the "special" built-in traits (see `middle::lang_items`) and
+/// detects `Copy`, `Send` and `Sync`.
+#[derive(Clone, Debug, HashStable_Generic)]
+pub enum GenericBound<'hir> {
+    Trait(PolyTraitRef<'hir>, TraitBoundModifier),
+    // FIXME(davidtwco): Introduce `PolyTraitRef::LangItem`
+    LangItemTrait(LangItem, Span, HirId, &'hir GenericArgs<'hir>),
+    Outlives(Lifetime),
+}
+
+impl GenericBound<'_> {
+    pub fn trait_ref(&self) -> Option<&TraitRef<'_>> {
+        match self {
+            GenericBound::Trait(data, _) => Some(&data.trait_ref),
+            _ => None,
+        }
+    }
+
+    pub fn span(&self) -> Span {
+        match self {
+            GenericBound::Trait(t, ..) => t.span,
+            GenericBound::LangItemTrait(_, span, ..) => *span,
+            GenericBound::Outlives(l) => l.span,
+        }
+    }
+}
+
+pub type GenericBounds<'hir> = &'hir [GenericBound<'hir>];
+
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Debug, HashStable_Generic)]
+pub enum LifetimeParamKind {
+    // Indicates that the lifetime definition was explicitly declared (e.g., in
+    // `fn foo<'a>(x: &'a u8) -> &'a u8 { x }`).
+    Explicit,
+
+    // Indication that the lifetime was elided (e.g., in both cases in
+    // `fn foo(x: &u8) -> &'_ u8 { x }`).
+    Elided,
+
+    // Indication that the lifetime name was somehow in error.
+    Error,
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub enum GenericParamKind<'hir> {
+    /// A lifetime definition (e.g., `'a: 'b + 'c + 'd`).
+    Lifetime {
+        kind: LifetimeParamKind,
+    },
+    Type {
+        default: Option<&'hir Ty<'hir>>,
+        synthetic: bool,
+    },
+    Const {
+        ty: &'hir Ty<'hir>,
+        /// Optional default value for the const generic param
+        default: Option<AnonConst>,
+    },
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub struct GenericParam<'hir> {
+    pub hir_id: HirId,
+    pub name: ParamName,
+    pub span: Span,
+    pub pure_wrt_drop: bool,
+    pub kind: GenericParamKind<'hir>,
+    pub colon_span: Option<Span>,
+}
+
+impl<'hir> GenericParam<'hir> {
+    /// Synthetic type-parameters are inserted after normal ones.
+    /// In order for normal parameters to be able to refer to synthetic ones,
+    /// scans them first.
+    pub fn is_impl_trait(&self) -> bool {
+        matches!(self.kind, GenericParamKind::Type { synthetic: true, .. })
+    }
+
+    /// This can happen for `async fn`, e.g. `async fn f<'_>(&'_ self)`.
+    ///
+    /// See `lifetime_to_generic_param` in `rustc_ast_lowering` for more information.
+    pub fn is_elided_lifetime(&self) -> bool {
+        matches!(self.kind, GenericParamKind::Lifetime { kind: LifetimeParamKind::Elided })
+    }
+}
+
+#[derive(Default)]
+pub struct GenericParamCount {
+    pub lifetimes: usize,
+    pub types: usize,
+    pub consts: usize,
+    pub infer: usize,
+}
+
+/// Represents lifetimes and type parameters attached to a declaration
+/// of a function, enum, trait, etc.
+#[derive(Debug, HashStable_Generic)]
+pub struct Generics<'hir> {
+    pub params: &'hir [GenericParam<'hir>],
+    pub predicates: &'hir [WherePredicate<'hir>],
+    pub has_where_clause_predicates: bool,
+    pub where_clause_span: Span,
+    pub span: Span,
+}
+
+impl<'hir> Generics<'hir> {
+    pub const fn empty() -> &'hir Generics<'hir> {
+        const NOPE: Generics<'_> = Generics {
+            params: &[],
+            predicates: &[],
+            has_where_clause_predicates: false,
+            where_clause_span: DUMMY_SP,
+            span: DUMMY_SP,
+        };
+        &NOPE
+    }
+
+    pub fn get_named(&self, name: Symbol) -> Option<&GenericParam<'hir>> {
+        for param in self.params {
+            if name == param.name.ident().name {
+                return Some(param);
+            }
+        }
+        None
+    }
+
+    pub fn spans(&self) -> MultiSpan {
+        if self.params.is_empty() {
+            self.span.into()
+        } else {
+            self.params.iter().map(|p| p.span).collect::<Vec<Span>>().into()
+        }
+    }
+
+    /// If there are generic parameters, return where to introduce a new one.
+    pub fn span_for_param_suggestion(&self) -> Option<Span> {
+        if self.params.iter().any(|p| self.span.contains(p.span)) {
+            // `fn foo<A>(t: impl Trait)`
+            //          ^ suggest `, T: Trait` here
+            let span = self.span.with_lo(self.span.hi() - BytePos(1)).shrink_to_lo();
+            Some(span)
+        } else {
+            None
+        }
+    }
+
+    /// `Span` where further predicates would be suggested, accounting for trailing commas, like
+    ///  in `fn foo<T>(t: T) where T: Foo,` so we don't suggest two trailing commas.
+    pub fn tail_span_for_predicate_suggestion(&self) -> Span {
+        let end = self.where_clause_span.shrink_to_hi();
+        if self.has_where_clause_predicates {
+            self.predicates
+                .iter()
+                .filter(|p| p.in_where_clause())
+                .last()
+                .map_or(end, |p| p.span())
+                .shrink_to_hi()
+                .to(end)
+        } else {
+            end
+        }
+    }
+
+    pub fn add_where_or_trailing_comma(&self) -> &'static str {
+        if self.has_where_clause_predicates {
+            ","
+        } else if self.where_clause_span.is_empty() {
+            " where"
+        } else {
+            // No where clause predicates, but we have `where` token
+            ""
+        }
+    }
+
+    pub fn bounds_for_param(
+        &self,
+        param_def_id: LocalDefId,
+    ) -> impl Iterator<Item = &WhereBoundPredicate<'hir>> {
+        self.predicates.iter().filter_map(move |pred| match pred {
+            WherePredicate::BoundPredicate(bp) if bp.is_param_bound(param_def_id.to_def_id()) => {
+                Some(bp)
+            }
+            _ => None,
+        })
+    }
+
+    pub fn outlives_for_param(
+        &self,
+        param_def_id: LocalDefId,
+    ) -> impl Iterator<Item = &WhereRegionPredicate<'_>> {
+        self.predicates.iter().filter_map(move |pred| match pred {
+            WherePredicate::RegionPredicate(rp) if rp.is_param_bound(param_def_id) => Some(rp),
+            _ => None,
+        })
+    }
+
+    pub fn bounds_span_for_suggestions(&self, param_def_id: LocalDefId) -> Option<Span> {
+        self.bounds_for_param(param_def_id).flat_map(|bp| bp.bounds.iter().rev()).find_map(
+            |bound| {
+                // We include bounds that come from a `#[derive(_)]` but point at the user's code,
+                // as we use this method to get a span appropriate for suggestions.
+                let bs = bound.span();
+                if bs.can_be_used_for_suggestions() { Some(bs.shrink_to_hi()) } else { None }
+            },
+        )
+    }
+
+    pub fn span_for_predicate_removal(&self, pos: usize) -> Span {
+        let predicate = &self.predicates[pos];
+        let span = predicate.span();
+
+        if !predicate.in_where_clause() {
+            // <T: ?Sized, U>
+            //   ^^^^^^^^
+            return span;
+        }
+
+        // We need to find out which comma to remove.
+        if pos < self.predicates.len() - 1 {
+            let next_pred = &self.predicates[pos + 1];
+            if next_pred.in_where_clause() {
+                // where T: ?Sized, Foo: Bar,
+                //       ^^^^^^^^^^^
+                return span.until(next_pred.span());
+            }
+        }
+
+        if pos > 0 {
+            let prev_pred = &self.predicates[pos - 1];
+            if prev_pred.in_where_clause() {
+                // where Foo: Bar, T: ?Sized,
+                //               ^^^^^^^^^^^
+                return prev_pred.span().shrink_to_hi().to(span);
+            }
+        }
+
+        // This is the only predicate in the where clause.
+        // where T: ?Sized
+        // ^^^^^^^^^^^^^^^
+        self.where_clause_span
+    }
+
+    pub fn span_for_bound_removal(&self, predicate_pos: usize, bound_pos: usize) -> Span {
+        let predicate = &self.predicates[predicate_pos];
+        let bounds = predicate.bounds();
+
+        if bounds.len() == 1 {
+            return self.span_for_predicate_removal(predicate_pos);
+        }
+
+        let span = bounds[bound_pos].span();
+        if bound_pos == 0 {
+            // where T: ?Sized + Bar, Foo: Bar,
+            //          ^^^^^^^^^
+            span.to(bounds[1].span().shrink_to_lo())
+        } else {
+            // where T: Bar + ?Sized, Foo: Bar,
+            //             ^^^^^^^^^
+            bounds[bound_pos - 1].span().shrink_to_hi().to(span)
+        }
+    }
+}
+
+/// A single predicate in a where-clause.
+#[derive(Debug, HashStable_Generic)]
+pub enum WherePredicate<'hir> {
+    /// A type binding (e.g., `for<'c> Foo: Send + Clone + 'c`).
+    BoundPredicate(WhereBoundPredicate<'hir>),
+    /// A lifetime predicate (e.g., `'a: 'b + 'c`).
+    RegionPredicate(WhereRegionPredicate<'hir>),
+    /// An equality predicate (unsupported).
+    EqPredicate(WhereEqPredicate<'hir>),
+}
+
+impl<'hir> WherePredicate<'hir> {
+    pub fn span(&self) -> Span {
+        match self {
+            WherePredicate::BoundPredicate(p) => p.span,
+            WherePredicate::RegionPredicate(p) => p.span,
+            WherePredicate::EqPredicate(p) => p.span,
+        }
+    }
+
+    pub fn in_where_clause(&self) -> bool {
+        match self {
+            WherePredicate::BoundPredicate(p) => p.origin == PredicateOrigin::WhereClause,
+            WherePredicate::RegionPredicate(p) => p.in_where_clause,
+            WherePredicate::EqPredicate(_) => false,
+        }
+    }
+
+    pub fn bounds(&self) -> GenericBounds<'hir> {
+        match self {
+            WherePredicate::BoundPredicate(p) => p.bounds,
+            WherePredicate::RegionPredicate(p) => p.bounds,
+            WherePredicate::EqPredicate(_) => &[],
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, HashStable_Generic, PartialEq, Eq)]
+pub enum PredicateOrigin {
+    WhereClause,
+    GenericParam,
+    ImplTrait,
+}
+
+/// A type bound (e.g., `for<'c> Foo: Send + Clone + 'c`).
+#[derive(Debug, HashStable_Generic)]
+pub struct WhereBoundPredicate<'hir> {
+    pub span: Span,
+    /// Origin of the predicate.
+    pub origin: PredicateOrigin,
+    /// Any generics from a `for` binding.
+    pub bound_generic_params: &'hir [GenericParam<'hir>],
+    /// The type being bounded.
+    pub bounded_ty: &'hir Ty<'hir>,
+    /// Trait and lifetime bounds (e.g., `Clone + Send + 'static`).
+    pub bounds: GenericBounds<'hir>,
+}
+
+impl<'hir> WhereBoundPredicate<'hir> {
+    /// Returns `true` if `param_def_id` matches the `bounded_ty` of this predicate.
+    pub fn is_param_bound(&self, param_def_id: DefId) -> bool {
+        self.bounded_ty.as_generic_param().map_or(false, |(def_id, _)| def_id == param_def_id)
+    }
+}
+
+/// A lifetime predicate (e.g., `'a: 'b + 'c`).
+#[derive(Debug, HashStable_Generic)]
+pub struct WhereRegionPredicate<'hir> {
+    pub span: Span,
+    pub in_where_clause: bool,
+    pub lifetime: Lifetime,
+    pub bounds: GenericBounds<'hir>,
+}
+
+impl<'hir> WhereRegionPredicate<'hir> {
+    /// Returns `true` if `param_def_id` matches the `lifetime` of this predicate.
+    pub fn is_param_bound(&self, param_def_id: LocalDefId) -> bool {
+        match self.lifetime.name {
+            LifetimeName::Param(id, _) => id == param_def_id,
+            _ => false,
+        }
+    }
+}
+
+/// An equality predicate (e.g., `T = int`); currently unsupported.
+#[derive(Debug, HashStable_Generic)]
+pub struct WhereEqPredicate<'hir> {
+    pub hir_id: HirId,
+    pub span: Span,
+    pub lhs_ty: &'hir Ty<'hir>,
+    pub rhs_ty: &'hir Ty<'hir>,
+}
+
+/// HIR node coupled with its parent's id in the same HIR owner.
+///
+/// The parent is trash when the node is a HIR owner.
+#[derive(Clone, Debug)]
+pub struct ParentedNode<'tcx> {
+    pub parent: ItemLocalId,
+    pub node: Node<'tcx>,
+}
+
+/// Attributes owned by a HIR owner.
+#[derive(Debug)]
+pub struct AttributeMap<'tcx> {
+    pub map: SortedMap<ItemLocalId, &'tcx [Attribute]>,
+    pub hash: Fingerprint,
+}
+
+impl<'tcx> AttributeMap<'tcx> {
+    pub const EMPTY: &'static AttributeMap<'static> =
+        &AttributeMap { map: SortedMap::new(), hash: Fingerprint::ZERO };
+
+    #[inline]
+    pub fn get(&self, id: ItemLocalId) -> &'tcx [Attribute] {
+        self.map.get(&id).copied().unwrap_or(&[])
+    }
+}
+
+/// Map of all HIR nodes inside the current owner.
+/// These nodes are mapped by `ItemLocalId` alongside the index of their parent node.
+/// The HIR tree, including bodies, is pre-hashed.
+pub struct OwnerNodes<'tcx> {
+    /// Pre-computed hash of the full HIR.
+    pub hash_including_bodies: Fingerprint,
+    /// Pre-computed hash of the item signature, sithout recursing into the body.
+    pub hash_without_bodies: Fingerprint,
+    /// Full HIR for the current owner.
+    // The zeroth node's parent should never be accessed: the owner's parent is computed by the
+    // hir_owner_parent query.  It is set to `ItemLocalId::INVALID` to force an ICE if accidentally
+    // used.
+    pub nodes: IndexVec<ItemLocalId, Option<ParentedNode<'tcx>>>,
+    /// Content of local bodies.
+    pub bodies: SortedMap<ItemLocalId, &'tcx Body<'tcx>>,
+    /// Non-owning definitions contained in this owner.
+    pub local_id_to_def_id: SortedMap<ItemLocalId, LocalDefId>,
+}
+
+impl<'tcx> OwnerNodes<'tcx> {
+    pub fn node(&self) -> OwnerNode<'tcx> {
+        use rustc_index::vec::Idx;
+        let node = self.nodes[ItemLocalId::new(0)].as_ref().unwrap().node;
+        let node = node.as_owner().unwrap(); // Indexing must ensure it is an OwnerNode.
+        node
+    }
+}
+
+impl fmt::Debug for OwnerNodes<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("OwnerNodes")
+            .field("node", &self.nodes[ItemLocalId::from_u32(0)])
+            .field("bodies", &self.bodies)
+            .field("local_id_to_def_id", &self.local_id_to_def_id)
+            .field("hash_without_bodies", &self.hash_without_bodies)
+            .field("hash_including_bodies", &self.hash_including_bodies)
+            .finish()
+    }
+}
+
+/// Full information resulting from lowering an AST node.
+#[derive(Debug, HashStable_Generic)]
+pub struct OwnerInfo<'hir> {
+    /// Contents of the HIR.
+    pub nodes: OwnerNodes<'hir>,
+    /// Map from each nested owner to its parent's local id.
+    pub parenting: FxHashMap<LocalDefId, ItemLocalId>,
+    /// Collected attributes of the HIR nodes.
+    pub attrs: AttributeMap<'hir>,
+    /// Map indicating what traits are in scope for places where this
+    /// is relevant; generated by resolve.
+    pub trait_map: FxHashMap<ItemLocalId, Box<[TraitCandidate]>>,
+}
+
+impl<'tcx> OwnerInfo<'tcx> {
+    #[inline]
+    pub fn node(&self) -> OwnerNode<'tcx> {
+        self.nodes.node()
+    }
+}
+
+#[derive(Copy, Clone, Debug, HashStable_Generic)]
+pub enum MaybeOwner<T> {
+    Owner(T),
+    NonOwner(HirId),
+    /// Used as a placeholder for unused LocalDefId.
+    Phantom,
+}
+
+impl<T> MaybeOwner<T> {
+    pub fn as_owner(self) -> Option<T> {
+        match self {
+            MaybeOwner::Owner(i) => Some(i),
+            MaybeOwner::NonOwner(_) | MaybeOwner::Phantom => None,
+        }
+    }
+
+    pub fn map<U>(self, f: impl FnOnce(T) -> U) -> MaybeOwner<U> {
+        match self {
+            MaybeOwner::Owner(i) => MaybeOwner::Owner(f(i)),
+            MaybeOwner::NonOwner(hir_id) => MaybeOwner::NonOwner(hir_id),
+            MaybeOwner::Phantom => MaybeOwner::Phantom,
+        }
+    }
+
+    pub fn unwrap(self) -> T {
+        match self {
+            MaybeOwner::Owner(i) => i,
+            MaybeOwner::NonOwner(_) | MaybeOwner::Phantom => panic!("Not a HIR owner"),
+        }
+    }
+}
+
+/// The top-level data structure that stores the entire contents of
+/// the crate currently being compiled.
+///
+/// For more details, see the [rustc dev guide].
+///
+/// [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/hir.html
+#[derive(Debug)]
+pub struct Crate<'hir> {
+    pub owners: IndexVec<LocalDefId, MaybeOwner<&'hir OwnerInfo<'hir>>>,
+    pub hir_hash: Fingerprint,
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub struct Closure<'hir> {
+    pub binder: ClosureBinder,
+    pub capture_clause: CaptureBy,
+    pub bound_generic_params: &'hir [GenericParam<'hir>],
+    pub fn_decl: &'hir FnDecl<'hir>,
+    pub body: BodyId,
+    pub fn_decl_span: Span,
+    pub movability: Option<Movability>,
+}
+
+/// A block of statements `{ .. }`, which may have a label (in this case the
+/// `targeted_by_break` field will be `true`) and may be `unsafe` by means of
+/// the `rules` being anything but `DefaultBlock`.
+#[derive(Debug, HashStable_Generic)]
+pub struct Block<'hir> {
+    /// Statements in a block.
+    pub stmts: &'hir [Stmt<'hir>],
+    /// An expression at the end of the block
+    /// without a semicolon, if any.
+    pub expr: Option<&'hir Expr<'hir>>,
+    #[stable_hasher(ignore)]
+    pub hir_id: HirId,
+    /// Distinguishes between `unsafe { ... }` and `{ ... }`.
+    pub rules: BlockCheckMode,
+    pub span: Span,
+    /// If true, then there may exist `break 'a` values that aim to
+    /// break out of this block early.
+    /// Used by `'label: {}` blocks and by `try {}` blocks.
+    pub targeted_by_break: bool,
+}
+
+impl<'hir> Block<'hir> {
+    pub fn innermost_block(&self) -> &Block<'hir> {
+        let mut block = self;
+        while let Some(Expr { kind: ExprKind::Block(inner_block, _), .. }) = block.expr {
+            block = inner_block;
+        }
+        block
+    }
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub struct Pat<'hir> {
+    #[stable_hasher(ignore)]
+    pub hir_id: HirId,
+    pub kind: PatKind<'hir>,
+    pub span: Span,
+    // Whether to use default binding modes.
+    // At present, this is false only for destructuring assignment.
+    pub default_binding_modes: bool,
+}
+
+impl<'hir> Pat<'hir> {
+    // FIXME(#19596) this is a workaround, but there should be a better way
+    fn walk_short_(&self, it: &mut impl FnMut(&Pat<'hir>) -> bool) -> bool {
+        if !it(self) {
+            return false;
+        }
+
+        use PatKind::*;
+        match self.kind {
+            Wild | Lit(_) | Range(..) | Binding(.., None) | Path(_) => true,
+            Box(s) | Ref(s, _) | Binding(.., Some(s)) => s.walk_short_(it),
+            Struct(_, fields, _) => fields.iter().all(|field| field.pat.walk_short_(it)),
+            TupleStruct(_, s, _) | Tuple(s, _) | Or(s) => s.iter().all(|p| p.walk_short_(it)),
+            Slice(before, slice, after) => {
+                before.iter().chain(slice).chain(after.iter()).all(|p| p.walk_short_(it))
+            }
+        }
+    }
+
+    /// Walk the pattern in left-to-right order,
+    /// short circuiting (with `.all(..)`) if `false` is returned.
+    ///
+    /// Note that when visiting e.g. `Tuple(ps)`,
+    /// if visiting `ps[0]` returns `false`,
+    /// then `ps[1]` will not be visited.
+    pub fn walk_short(&self, mut it: impl FnMut(&Pat<'hir>) -> bool) -> bool {
+        self.walk_short_(&mut it)
+    }
+
+    // FIXME(#19596) this is a workaround, but there should be a better way
+    fn walk_(&self, it: &mut impl FnMut(&Pat<'hir>) -> bool) {
+        if !it(self) {
+            return;
+        }
+
+        use PatKind::*;
+        match self.kind {
+            Wild | Lit(_) | Range(..) | Binding(.., None) | Path(_) => {}
+            Box(s) | Ref(s, _) | Binding(.., Some(s)) => s.walk_(it),
+            Struct(_, fields, _) => fields.iter().for_each(|field| field.pat.walk_(it)),
+            TupleStruct(_, s, _) | Tuple(s, _) | Or(s) => s.iter().for_each(|p| p.walk_(it)),
+            Slice(before, slice, after) => {
+                before.iter().chain(slice).chain(after.iter()).for_each(|p| p.walk_(it))
+            }
+        }
+    }
+
+    /// Walk the pattern in left-to-right order.
+    ///
+    /// If `it(pat)` returns `false`, the children are not visited.
+    pub fn walk(&self, mut it: impl FnMut(&Pat<'hir>) -> bool) {
+        self.walk_(&mut it)
+    }
+
+    /// Walk the pattern in left-to-right order.
+    ///
+    /// If you always want to recurse, prefer this method over `walk`.
+    pub fn walk_always(&self, mut it: impl FnMut(&Pat<'_>)) {
+        self.walk(|p| {
+            it(p);
+            true
+        })
+    }
+}
+
+/// A single field in a struct pattern.
+///
+/// Patterns like the fields of Foo `{ x, ref y, ref mut z }`
+/// are treated the same as` x: x, y: ref y, z: ref mut z`,
+/// except `is_shorthand` is true.
+#[derive(Debug, HashStable_Generic)]
+pub struct PatField<'hir> {
+    #[stable_hasher(ignore)]
+    pub hir_id: HirId,
+    /// The identifier for the field.
+    pub ident: Ident,
+    /// The pattern the field is destructured to.
+    pub pat: &'hir Pat<'hir>,
+    pub is_shorthand: bool,
+    pub span: Span,
+}
+
+/// Explicit binding annotations given in the HIR for a binding. Note
+/// that this is not the final binding *mode* that we infer after type
+/// inference.
+#[derive(Copy, Clone, PartialEq, Encodable, Debug, HashStable_Generic)]
+pub enum BindingAnnotation {
+    /// No binding annotation given: this means that the final binding mode
+    /// will depend on whether we have skipped through a `&` reference
+    /// when matching. For example, the `x` in `Some(x)` will have binding
+    /// mode `None`; if you do `let Some(x) = &Some(22)`, it will
+    /// ultimately be inferred to be by-reference.
+    ///
+    /// Note that implicit reference skipping is not implemented yet (#42640).
+    Unannotated,
+
+    /// Annotated with `mut x` -- could be either ref or not, similar to `None`.
+    Mutable,
+
+    /// Annotated as `ref`, like `ref x`
+    Ref,
+
+    /// Annotated as `ref mut x`.
+    RefMut,
+}
+
+#[derive(Copy, Clone, PartialEq, Encodable, Debug, HashStable_Generic)]
+pub enum RangeEnd {
+    Included,
+    Excluded,
+}
+
+impl fmt::Display for RangeEnd {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(match self {
+            RangeEnd::Included => "..=",
+            RangeEnd::Excluded => "..",
+        })
+    }
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub enum PatKind<'hir> {
+    /// Represents a wildcard pattern (i.e., `_`).
+    Wild,
+
+    /// A fresh binding `ref mut binding @ OPT_SUBPATTERN`.
+    /// The `HirId` is the canonical ID for the variable being bound,
+    /// (e.g., in `Ok(x) | Err(x)`, both `x` use the same canonical ID),
+    /// which is the pattern ID of the first `x`.
+    Binding(BindingAnnotation, HirId, Ident, Option<&'hir Pat<'hir>>),
+
+    /// A struct or struct variant pattern (e.g., `Variant {x, y, ..}`).
+    /// The `bool` is `true` in the presence of a `..`.
+    Struct(QPath<'hir>, &'hir [PatField<'hir>], bool),
+
+    /// A tuple struct/variant pattern `Variant(x, y, .., z)`.
+    /// If the `..` pattern fragment is present, then `Option<usize>` denotes its position.
+    /// `0 <= position <= subpats.len()`
+    TupleStruct(QPath<'hir>, &'hir [Pat<'hir>], Option<usize>),
+
+    /// An or-pattern `A | B | C`.
+    /// Invariant: `pats.len() >= 2`.
+    Or(&'hir [Pat<'hir>]),
+
+    /// A path pattern for a unit struct/variant or a (maybe-associated) constant.
+    Path(QPath<'hir>),
+
+    /// A tuple pattern (e.g., `(a, b)`).
+    /// If the `..` pattern fragment is present, then `Option<usize>` denotes its position.
+    /// `0 <= position <= subpats.len()`
+    Tuple(&'hir [Pat<'hir>], Option<usize>),
+
+    /// A `box` pattern.
+    Box(&'hir Pat<'hir>),
+
+    /// A reference pattern (e.g., `&mut (a, b)`).
+    Ref(&'hir Pat<'hir>, Mutability),
+
+    /// A literal.
+    Lit(&'hir Expr<'hir>),
+
+    /// A range pattern (e.g., `1..=2` or `1..2`).
+    Range(Option<&'hir Expr<'hir>>, Option<&'hir Expr<'hir>>, RangeEnd),
+
+    /// A slice pattern, `[before_0, ..., before_n, (slice, after_0, ..., after_n)?]`.
+    ///
+    /// Here, `slice` is lowered from the syntax `($binding_mode $ident @)? ..`.
+    /// If `slice` exists, then `after` can be non-empty.
+    ///
+    /// The representation for e.g., `[a, b, .., c, d]` is:
+    /// ```ignore (illustrative)
+    /// PatKind::Slice([Binding(a), Binding(b)], Some(Wild), [Binding(c), Binding(d)])
+    /// ```
+    Slice(&'hir [Pat<'hir>], Option<&'hir Pat<'hir>>, &'hir [Pat<'hir>]),
+}
+
+#[derive(Copy, Clone, PartialEq, Encodable, Debug, HashStable_Generic)]
+pub enum BinOpKind {
+    /// The `+` operator (addition).
+    Add,
+    /// The `-` operator (subtraction).
+    Sub,
+    /// The `*` operator (multiplication).
+    Mul,
+    /// The `/` operator (division).
+    Div,
+    /// The `%` operator (modulus).
+    Rem,
+    /// The `&&` operator (logical and).
+    And,
+    /// The `||` operator (logical or).
+    Or,
+    /// The `^` operator (bitwise xor).
+    BitXor,
+    /// The `&` operator (bitwise and).
+    BitAnd,
+    /// The `|` operator (bitwise or).
+    BitOr,
+    /// The `<<` operator (shift left).
+    Shl,
+    /// The `>>` operator (shift right).
+    Shr,
+    /// The `==` operator (equality).
+    Eq,
+    /// The `<` operator (less than).
+    Lt,
+    /// The `<=` operator (less than or equal to).
+    Le,
+    /// The `!=` operator (not equal to).
+    Ne,
+    /// The `>=` operator (greater than or equal to).
+    Ge,
+    /// The `>` operator (greater than).
+    Gt,
+}
+
+impl BinOpKind {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            BinOpKind::Add => "+",
+            BinOpKind::Sub => "-",
+            BinOpKind::Mul => "*",
+            BinOpKind::Div => "/",
+            BinOpKind::Rem => "%",
+            BinOpKind::And => "&&",
+            BinOpKind::Or => "||",
+            BinOpKind::BitXor => "^",
+            BinOpKind::BitAnd => "&",
+            BinOpKind::BitOr => "|",
+            BinOpKind::Shl => "<<",
+            BinOpKind::Shr => ">>",
+            BinOpKind::Eq => "==",
+            BinOpKind::Lt => "<",
+            BinOpKind::Le => "<=",
+            BinOpKind::Ne => "!=",
+            BinOpKind::Ge => ">=",
+            BinOpKind::Gt => ">",
+        }
+    }
+
+    pub fn is_lazy(self) -> bool {
+        matches!(self, BinOpKind::And | BinOpKind::Or)
+    }
+
+    pub fn is_shift(self) -> bool {
+        matches!(self, BinOpKind::Shl | BinOpKind::Shr)
+    }
+
+    pub fn is_comparison(self) -> bool {
+        match self {
+            BinOpKind::Eq
+            | BinOpKind::Lt
+            | BinOpKind::Le
+            | BinOpKind::Ne
+            | BinOpKind::Gt
+            | BinOpKind::Ge => true,
+            BinOpKind::And
+            | BinOpKind::Or
+            | BinOpKind::Add
+            | BinOpKind::Sub
+            | BinOpKind::Mul
+            | BinOpKind::Div
+            | BinOpKind::Rem
+            | BinOpKind::BitXor
+            | BinOpKind::BitAnd
+            | BinOpKind::BitOr
+            | BinOpKind::Shl
+            | BinOpKind::Shr => false,
+        }
+    }
+
+    /// Returns `true` if the binary operator takes its arguments by value.
+    pub fn is_by_value(self) -> bool {
+        !self.is_comparison()
+    }
+}
+
+impl Into<ast::BinOpKind> for BinOpKind {
+    fn into(self) -> ast::BinOpKind {
+        match self {
+            BinOpKind::Add => ast::BinOpKind::Add,
+            BinOpKind::Sub => ast::BinOpKind::Sub,
+            BinOpKind::Mul => ast::BinOpKind::Mul,
+            BinOpKind::Div => ast::BinOpKind::Div,
+            BinOpKind::Rem => ast::BinOpKind::Rem,
+            BinOpKind::And => ast::BinOpKind::And,
+            BinOpKind::Or => ast::BinOpKind::Or,
+            BinOpKind::BitXor => ast::BinOpKind::BitXor,
+            BinOpKind::BitAnd => ast::BinOpKind::BitAnd,
+            BinOpKind::BitOr => ast::BinOpKind::BitOr,
+            BinOpKind::Shl => ast::BinOpKind::Shl,
+            BinOpKind::Shr => ast::BinOpKind::Shr,
+            BinOpKind::Eq => ast::BinOpKind::Eq,
+            BinOpKind::Lt => ast::BinOpKind::Lt,
+            BinOpKind::Le => ast::BinOpKind::Le,
+            BinOpKind::Ne => ast::BinOpKind::Ne,
+            BinOpKind::Ge => ast::BinOpKind::Ge,
+            BinOpKind::Gt => ast::BinOpKind::Gt,
+        }
+    }
+}
+
+pub type BinOp = Spanned<BinOpKind>;
+
+#[derive(Copy, Clone, PartialEq, Encodable, Debug, HashStable_Generic)]
+pub enum UnOp {
+    /// The `*` operator (dereferencing).
+    Deref,
+    /// The `!` operator (logical negation).
+    Not,
+    /// The `-` operator (negation).
+    Neg,
+}
+
+impl UnOp {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Self::Deref => "*",
+            Self::Not => "!",
+            Self::Neg => "-",
+        }
+    }
+
+    /// Returns `true` if the unary operator takes its argument by value.
+    pub fn is_by_value(self) -> bool {
+        matches!(self, Self::Neg | Self::Not)
+    }
+}
+
+/// A statement.
+#[derive(Debug, HashStable_Generic)]
+pub struct Stmt<'hir> {
+    pub hir_id: HirId,
+    pub kind: StmtKind<'hir>,
+    pub span: Span,
+}
+
+/// The contents of a statement.
+#[derive(Debug, HashStable_Generic)]
+pub enum StmtKind<'hir> {
+    /// A local (`let`) binding.
+    Local(&'hir Local<'hir>),
+
+    /// An item binding.
+    Item(ItemId),
+
+    /// An expression without a trailing semi-colon (must have unit type).
+    Expr(&'hir Expr<'hir>),
+
+    /// An expression with a trailing semi-colon (may have any type).
+    Semi(&'hir Expr<'hir>),
+}
+
+/// Represents a `let` statement (i.e., `let <pat>:<ty> = <expr>;`).
+#[derive(Debug, HashStable_Generic)]
+pub struct Local<'hir> {
+    pub pat: &'hir Pat<'hir>,
+    /// Type annotation, if any (otherwise the type will be inferred).
+    pub ty: Option<&'hir Ty<'hir>>,
+    /// Initializer expression to set the value, if any.
+    pub init: Option<&'hir Expr<'hir>>,
+    /// Else block for a `let...else` binding.
+    pub els: Option<&'hir Block<'hir>>,
+    pub hir_id: HirId,
+    pub span: Span,
+    /// Can be `ForLoopDesugar` if the `let` statement is part of a `for` loop
+    /// desugaring. Otherwise will be `Normal`.
+    pub source: LocalSource,
+}
+
+/// Represents a single arm of a `match` expression, e.g.
+/// `<pat> (if <guard>) => <body>`.
+#[derive(Debug, HashStable_Generic)]
+pub struct Arm<'hir> {
+    #[stable_hasher(ignore)]
+    pub hir_id: HirId,
+    pub span: Span,
+    /// If this pattern and the optional guard matches, then `body` is evaluated.
+    pub pat: &'hir Pat<'hir>,
+    /// Optional guard clause.
+    pub guard: Option<Guard<'hir>>,
+    /// The expression the arm evaluates to if this arm matches.
+    pub body: &'hir Expr<'hir>,
+}
+
+/// Represents a `let <pat>[: <ty>] = <expr>` expression (not a Local), occurring in an `if-let` or
+/// `let-else`, evaluating to a boolean. Typically the pattern is refutable.
+///
+/// In an if-let, imagine it as `if (let <pat> = <expr>) { ... }`; in a let-else, it is part of the
+/// desugaring to if-let. Only let-else supports the type annotation at present.
+#[derive(Debug, HashStable_Generic)]
+pub struct Let<'hir> {
+    pub hir_id: HirId,
+    pub span: Span,
+    pub pat: &'hir Pat<'hir>,
+    pub ty: Option<&'hir Ty<'hir>>,
+    pub init: &'hir Expr<'hir>,
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub enum Guard<'hir> {
+    If(&'hir Expr<'hir>),
+    IfLet(&'hir Let<'hir>),
+}
+
+impl<'hir> Guard<'hir> {
+    /// Returns the body of the guard
+    ///
+    /// In other words, returns the e in either of the following:
+    ///
+    /// - `if e`
+    /// - `if let x = e`
+    pub fn body(&self) -> &'hir Expr<'hir> {
+        match self {
+            Guard::If(e) | Guard::IfLet(Let { init: e, .. }) => e,
+        }
+    }
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub struct ExprField<'hir> {
+    #[stable_hasher(ignore)]
+    pub hir_id: HirId,
+    pub ident: Ident,
+    pub expr: &'hir Expr<'hir>,
+    pub span: Span,
+    pub is_shorthand: bool,
+}
+
+#[derive(Copy, Clone, PartialEq, Encodable, Debug, HashStable_Generic)]
+pub enum BlockCheckMode {
+    DefaultBlock,
+    UnsafeBlock(UnsafeSource),
+}
+
+#[derive(Copy, Clone, PartialEq, Encodable, Debug, HashStable_Generic)]
+pub enum UnsafeSource {
+    CompilerGenerated,
+    UserProvided,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
+pub struct BodyId {
+    pub hir_id: HirId,
+}
+
+/// The body of a function, closure, or constant value. In the case of
+/// a function, the body contains not only the function body itself
+/// (which is an expression), but also the argument patterns, since
+/// those are something that the caller doesn't really care about.
+///
+/// # Examples
+///
+/// ```
+/// fn foo((x, y): (u32, u32)) -> u32 {
+///     x + y
+/// }
+/// ```
+///
+/// Here, the `Body` associated with `foo()` would contain:
+///
+/// - an `params` array containing the `(x, y)` pattern
+/// - a `value` containing the `x + y` expression (maybe wrapped in a block)
+/// - `generator_kind` would be `None`
+///
+/// All bodies have an **owner**, which can be accessed via the HIR
+/// map using `body_owner_def_id()`.
+#[derive(Debug, HashStable_Generic)]
+pub struct Body<'hir> {
+    pub params: &'hir [Param<'hir>],
+    pub value: Expr<'hir>,
+    pub generator_kind: Option<GeneratorKind>,
+}
+
+impl<'hir> Body<'hir> {
+    pub fn id(&self) -> BodyId {
+        BodyId { hir_id: self.value.hir_id }
+    }
+
+    pub fn generator_kind(&self) -> Option<GeneratorKind> {
+        self.generator_kind
+    }
+}
+
+/// The type of source expression that caused this generator to be created.
+#[derive(Clone, PartialEq, PartialOrd, Eq, Hash, Debug, Copy)]
+#[derive(HashStable_Generic, Encodable, Decodable)]
+pub enum GeneratorKind {
+    /// An explicit `async` block or the body of an async function.
+    Async(AsyncGeneratorKind),
+
+    /// A generator literal created via a `yield` inside a closure.
+    Gen,
+}
+
+impl fmt::Display for GeneratorKind {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            GeneratorKind::Async(k) => fmt::Display::fmt(k, f),
+            GeneratorKind::Gen => f.write_str("generator"),
+        }
+    }
+}
+
+impl GeneratorKind {
+    pub fn descr(&self) -> &'static str {
+        match self {
+            GeneratorKind::Async(ask) => ask.descr(),
+            GeneratorKind::Gen => "generator",
+        }
+    }
+}
+
+/// In the case of a generator created as part of an async construct,
+/// which kind of async construct caused it to be created?
+///
+/// This helps error messages but is also used to drive coercions in
+/// type-checking (see #60424).
+#[derive(Clone, PartialEq, PartialOrd, Eq, Hash, Debug, Copy)]
+#[derive(HashStable_Generic, Encodable, Decodable)]
+pub enum AsyncGeneratorKind {
+    /// An explicit `async` block written by the user.
+    Block,
+
+    /// An explicit `async` closure written by the user.
+    Closure,
+
+    /// The `async` block generated as the body of an async function.
+    Fn,
+}
+
+impl fmt::Display for AsyncGeneratorKind {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(match self {
+            AsyncGeneratorKind::Block => "`async` block",
+            AsyncGeneratorKind::Closure => "`async` closure body",
+            AsyncGeneratorKind::Fn => "`async fn` body",
+        })
+    }
+}
+
+impl AsyncGeneratorKind {
+    pub fn descr(&self) -> &'static str {
+        match self {
+            AsyncGeneratorKind::Block => "`async` block",
+            AsyncGeneratorKind::Closure => "`async` closure body",
+            AsyncGeneratorKind::Fn => "`async fn` body",
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+pub enum BodyOwnerKind {
+    /// Functions and methods.
+    Fn,
+
+    /// Closures
+    Closure,
+
+    /// Constants and associated constants.
+    Const,
+
+    /// Initializer of a `static` item.
+    Static(Mutability),
+}
+
+impl BodyOwnerKind {
+    pub fn is_fn_or_closure(self) -> bool {
+        match self {
+            BodyOwnerKind::Fn | BodyOwnerKind::Closure => true,
+            BodyOwnerKind::Const | BodyOwnerKind::Static(_) => false,
+        }
+    }
+}
+
+/// The kind of an item that requires const-checking.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum ConstContext {
+    /// A `const fn`.
+    ConstFn,
+
+    /// A `static` or `static mut`.
+    Static(Mutability),
+
+    /// A `const`, associated `const`, or other const context.
+    ///
+    /// Other contexts include:
+    /// - Array length expressions
+    /// - Enum discriminants
+    /// - Const generics
+    ///
+    /// For the most part, other contexts are treated just like a regular `const`, so they are
+    /// lumped into the same category.
+    Const,
+}
+
+impl ConstContext {
+    /// A description of this const context that can appear between backticks in an error message.
+    ///
+    /// E.g. `const` or `static mut`.
+    pub fn keyword_name(self) -> &'static str {
+        match self {
+            Self::Const => "const",
+            Self::Static(Mutability::Not) => "static",
+            Self::Static(Mutability::Mut) => "static mut",
+            Self::ConstFn => "const fn",
+        }
+    }
+}
+
+/// A colloquial, trivially pluralizable description of this const context for use in error
+/// messages.
+impl fmt::Display for ConstContext {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            Self::Const => write!(f, "constant"),
+            Self::Static(_) => write!(f, "static"),
+            Self::ConstFn => write!(f, "constant function"),
+        }
+    }
+}
+
+// NOTE: `IntoDiagnosticArg` impl for `ConstContext` lives in `rustc_errors`
+// due to a cyclical dependency between hir that crate.
+
+/// A literal.
+pub type Lit = Spanned<LitKind>;
+
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Debug, HashStable_Generic)]
+pub enum ArrayLen {
+    Infer(HirId, Span),
+    Body(AnonConst),
+}
+
+impl ArrayLen {
+    pub fn hir_id(&self) -> HirId {
+        match self {
+            &ArrayLen::Infer(hir_id, _) | &ArrayLen::Body(AnonConst { hir_id, body: _ }) => hir_id,
+        }
+    }
+}
+
+/// A constant (expression) that's not an item or associated item,
+/// but needs its own `DefId` for type-checking, const-eval, etc.
+/// These are usually found nested inside types (e.g., array lengths)
+/// or expressions (e.g., repeat counts), and also used to define
+/// explicit discriminant values for enum variants.
+///
+/// You can check if this anon const is a default in a const param
+/// `const N: usize = { ... }` with `tcx.hir().opt_const_param_default_param_hir_id(..)`
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Debug, HashStable_Generic)]
+pub struct AnonConst {
+    pub hir_id: HirId,
+    pub body: BodyId,
+}
+
+/// An expression.
+#[derive(Debug)]
+pub struct Expr<'hir> {
+    pub hir_id: HirId,
+    pub kind: ExprKind<'hir>,
+    pub span: Span,
+}
+
+impl Expr<'_> {
+    pub fn precedence(&self) -> ExprPrecedence {
+        match self.kind {
+            ExprKind::Box(_) => ExprPrecedence::Box,
+            ExprKind::ConstBlock(_) => ExprPrecedence::ConstBlock,
+            ExprKind::Array(_) => ExprPrecedence::Array,
+            ExprKind::Call(..) => ExprPrecedence::Call,
+            ExprKind::MethodCall(..) => ExprPrecedence::MethodCall,
+            ExprKind::Tup(_) => ExprPrecedence::Tup,
+            ExprKind::Binary(op, ..) => ExprPrecedence::Binary(op.node.into()),
+            ExprKind::Unary(..) => ExprPrecedence::Unary,
+            ExprKind::Lit(_) => ExprPrecedence::Lit,
+            ExprKind::Type(..) | ExprKind::Cast(..) => ExprPrecedence::Cast,
+            ExprKind::DropTemps(ref expr, ..) => expr.precedence(),
+            ExprKind::If(..) => ExprPrecedence::If,
+            ExprKind::Let(..) => ExprPrecedence::Let,
+            ExprKind::Loop(..) => ExprPrecedence::Loop,
+            ExprKind::Match(..) => ExprPrecedence::Match,
+            ExprKind::Closure { .. } => ExprPrecedence::Closure,
+            ExprKind::Block(..) => ExprPrecedence::Block,
+            ExprKind::Assign(..) => ExprPrecedence::Assign,
+            ExprKind::AssignOp(..) => ExprPrecedence::AssignOp,
+            ExprKind::Field(..) => ExprPrecedence::Field,
+            ExprKind::Index(..) => ExprPrecedence::Index,
+            ExprKind::Path(..) => ExprPrecedence::Path,
+            ExprKind::AddrOf(..) => ExprPrecedence::AddrOf,
+            ExprKind::Break(..) => ExprPrecedence::Break,
+            ExprKind::Continue(..) => ExprPrecedence::Continue,
+            ExprKind::Ret(..) => ExprPrecedence::Ret,
+            ExprKind::InlineAsm(..) => ExprPrecedence::InlineAsm,
+            ExprKind::Struct(..) => ExprPrecedence::Struct,
+            ExprKind::Repeat(..) => ExprPrecedence::Repeat,
+            ExprKind::Yield(..) => ExprPrecedence::Yield,
+            ExprKind::Err => ExprPrecedence::Err,
+        }
+    }
+
+    // Whether this looks like a place expr, without checking for deref
+    // adjustments.
+    // This will return `true` in some potentially surprising cases such as
+    // `CONSTANT.field`.
+    pub fn is_syntactic_place_expr(&self) -> bool {
+        self.is_place_expr(|_| true)
+    }
+
+    /// Whether this is a place expression.
+    ///
+    /// `allow_projections_from` should return `true` if indexing a field or index expression based
+    /// on the given expression should be considered a place expression.
+    pub fn is_place_expr(&self, mut allow_projections_from: impl FnMut(&Self) -> bool) -> bool {
+        match self.kind {
+            ExprKind::Path(QPath::Resolved(_, ref path)) => {
+                matches!(path.res, Res::Local(..) | Res::Def(DefKind::Static(_), _) | Res::Err)
+            }
+
+            // Type ascription inherits its place expression kind from its
+            // operand. See:
+            // https://github.com/rust-lang/rfcs/blob/master/text/0803-type-ascription.md#type-ascription-and-temporaries
+            ExprKind::Type(ref e, _) => e.is_place_expr(allow_projections_from),
+
+            ExprKind::Unary(UnOp::Deref, _) => true,
+
+            ExprKind::Field(ref base, _) | ExprKind::Index(ref base, _) => {
+                allow_projections_from(base) || base.is_place_expr(allow_projections_from)
+            }
+
+            // Lang item paths cannot currently be local variables or statics.
+            ExprKind::Path(QPath::LangItem(..)) => false,
+
+            // Partially qualified paths in expressions can only legally
+            // refer to associated items which are always rvalues.
+            ExprKind::Path(QPath::TypeRelative(..))
+            | ExprKind::Call(..)
+            | ExprKind::MethodCall(..)
+            | ExprKind::Struct(..)
+            | ExprKind::Tup(..)
+            | ExprKind::If(..)
+            | ExprKind::Match(..)
+            | ExprKind::Closure { .. }
+            | ExprKind::Block(..)
+            | ExprKind::Repeat(..)
+            | ExprKind::Array(..)
+            | ExprKind::Break(..)
+            | ExprKind::Continue(..)
+            | ExprKind::Ret(..)
+            | ExprKind::Let(..)
+            | ExprKind::Loop(..)
+            | ExprKind::Assign(..)
+            | ExprKind::InlineAsm(..)
+            | ExprKind::AssignOp(..)
+            | ExprKind::Lit(_)
+            | ExprKind::ConstBlock(..)
+            | ExprKind::Unary(..)
+            | ExprKind::Box(..)
+            | ExprKind::AddrOf(..)
+            | ExprKind::Binary(..)
+            | ExprKind::Yield(..)
+            | ExprKind::Cast(..)
+            | ExprKind::DropTemps(..)
+            | ExprKind::Err => false,
+        }
+    }
+
+    /// If `Self.kind` is `ExprKind::DropTemps(expr)`, drill down until we get a non-`DropTemps`
+    /// `Expr`. This is used in suggestions to ignore this `ExprKind` as it is semantically
+    /// silent, only signaling the ownership system. By doing this, suggestions that check the
+    /// `ExprKind` of any given `Expr` for presentation don't have to care about `DropTemps`
+    /// beyond remembering to call this function before doing analysis on it.
+    pub fn peel_drop_temps(&self) -> &Self {
+        let mut expr = self;
+        while let ExprKind::DropTemps(inner) = &expr.kind {
+            expr = inner;
+        }
+        expr
+    }
+
+    pub fn peel_blocks(&self) -> &Self {
+        let mut expr = self;
+        while let ExprKind::Block(Block { expr: Some(inner), .. }, _) = &expr.kind {
+            expr = inner;
+        }
+        expr
+    }
+
+    pub fn can_have_side_effects(&self) -> bool {
+        match self.peel_drop_temps().kind {
+            ExprKind::Path(_) | ExprKind::Lit(_) => false,
+            ExprKind::Type(base, _)
+            | ExprKind::Unary(_, base)
+            | ExprKind::Field(base, _)
+            | ExprKind::Index(base, _)
+            | ExprKind::AddrOf(.., base)
+            | ExprKind::Cast(base, _) => {
+                // This isn't exactly true for `Index` and all `Unary`, but we are using this
+                // method exclusively for diagnostics and there's a *cultural* pressure against
+                // them being used only for its side-effects.
+                base.can_have_side_effects()
+            }
+            ExprKind::Struct(_, fields, init) => fields
+                .iter()
+                .map(|field| field.expr)
+                .chain(init.into_iter())
+                .all(|e| e.can_have_side_effects()),
+
+            ExprKind::Array(args)
+            | ExprKind::Tup(args)
+            | ExprKind::Call(
+                Expr {
+                    kind:
+                        ExprKind::Path(QPath::Resolved(
+                            None,
+                            Path { res: Res::Def(DefKind::Ctor(_, CtorKind::Fn), _), .. },
+                        )),
+                    ..
+                },
+                args,
+            ) => args.iter().all(|arg| arg.can_have_side_effects()),
+            ExprKind::If(..)
+            | ExprKind::Match(..)
+            | ExprKind::MethodCall(..)
+            | ExprKind::Call(..)
+            | ExprKind::Closure { .. }
+            | ExprKind::Block(..)
+            | ExprKind::Repeat(..)
+            | ExprKind::Break(..)
+            | ExprKind::Continue(..)
+            | ExprKind::Ret(..)
+            | ExprKind::Let(..)
+            | ExprKind::Loop(..)
+            | ExprKind::Assign(..)
+            | ExprKind::InlineAsm(..)
+            | ExprKind::AssignOp(..)
+            | ExprKind::ConstBlock(..)
+            | ExprKind::Box(..)
+            | ExprKind::Binary(..)
+            | ExprKind::Yield(..)
+            | ExprKind::DropTemps(..)
+            | ExprKind::Err => true,
+        }
+    }
+
+    // To a first-order approximation, is this a pattern
+    pub fn is_approximately_pattern(&self) -> bool {
+        match &self.kind {
+            ExprKind::Box(_)
+            | ExprKind::Array(_)
+            | ExprKind::Call(..)
+            | ExprKind::Tup(_)
+            | ExprKind::Lit(_)
+            | ExprKind::Path(_)
+            | ExprKind::Struct(..) => true,
+            _ => false,
+        }
+    }
+
+    pub fn method_ident(&self) -> Option<Ident> {
+        match self.kind {
+            ExprKind::MethodCall(receiver_method, ..) => Some(receiver_method.ident),
+            ExprKind::Unary(_, expr) | ExprKind::AddrOf(.., expr) => expr.method_ident(),
+            _ => None,
+        }
+    }
+}
+
+/// Checks if the specified expression is a built-in range literal.
+/// (See: `LoweringContext::lower_expr()`).
+pub fn is_range_literal(expr: &Expr<'_>) -> bool {
+    match expr.kind {
+        // All built-in range literals but `..=` and `..` desugar to `Struct`s.
+        ExprKind::Struct(ref qpath, _, _) => matches!(
+            **qpath,
+            QPath::LangItem(
+                LangItem::Range
+                    | LangItem::RangeTo
+                    | LangItem::RangeFrom
+                    | LangItem::RangeFull
+                    | LangItem::RangeToInclusive,
+                ..
+            )
+        ),
+
+        // `..=` desugars into `::std::ops::RangeInclusive::new(...)`.
+        ExprKind::Call(ref func, _) => {
+            matches!(func.kind, ExprKind::Path(QPath::LangItem(LangItem::RangeInclusiveNew, ..)))
+        }
+
+        _ => false,
+    }
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub enum ExprKind<'hir> {
+    /// A `box x` expression.
+    Box(&'hir Expr<'hir>),
+    /// Allow anonymous constants from an inline `const` block
+    ConstBlock(AnonConst),
+    /// An array (e.g., `[a, b, c, d]`).
+    Array(&'hir [Expr<'hir>]),
+    /// A function call.
+    ///
+    /// The first field resolves to the function itself (usually an `ExprKind::Path`),
+    /// and the second field is the list of arguments.
+    /// This also represents calling the constructor of
+    /// tuple-like ADTs such as tuple structs and enum variants.
+    Call(&'hir Expr<'hir>, &'hir [Expr<'hir>]),
+    /// A method call (e.g., `x.foo::<'static, Bar, Baz>(a, b, c, d)`).
+    ///
+    /// The `PathSegment` represents the method name and its generic arguments
+    /// (within the angle brackets).
+    /// The first element of the `&[Expr]` is the expression that evaluates
+    /// to the object on which the method is being called on (the receiver),
+    /// and the remaining elements are the rest of the arguments.
+    /// Thus, `x.foo::<Bar, Baz>(a, b, c, d)` is represented as
+    /// `ExprKind::MethodCall(PathSegment { foo, [Bar, Baz] }, [x, a, b, c, d], span)`.
+    /// The final `Span` represents the span of the function and arguments
+    /// (e.g. `foo::<Bar, Baz>(a, b, c, d)` in `x.foo::<Bar, Baz>(a, b, c, d)`
+    ///
+    /// To resolve the called method to a `DefId`, call [`type_dependent_def_id`] with
+    /// the `hir_id` of the `MethodCall` node itself.
+    ///
+    /// [`type_dependent_def_id`]: ../../rustc_middle/ty/struct.TypeckResults.html#method.type_dependent_def_id
+    MethodCall(&'hir PathSegment<'hir>, &'hir [Expr<'hir>], Span),
+    /// A tuple (e.g., `(a, b, c, d)`).
+    Tup(&'hir [Expr<'hir>]),
+    /// A binary operation (e.g., `a + b`, `a * b`).
+    Binary(BinOp, &'hir Expr<'hir>, &'hir Expr<'hir>),
+    /// A unary operation (e.g., `!x`, `*x`).
+    Unary(UnOp, &'hir Expr<'hir>),
+    /// A literal (e.g., `1`, `"foo"`).
+    Lit(Lit),
+    /// A cast (e.g., `foo as f64`).
+    Cast(&'hir Expr<'hir>, &'hir Ty<'hir>),
+    /// A type reference (e.g., `Foo`).
+    Type(&'hir Expr<'hir>, &'hir Ty<'hir>),
+    /// Wraps the expression in a terminating scope.
+    /// This makes it semantically equivalent to `{ let _t = expr; _t }`.
+    ///
+    /// This construct only exists to tweak the drop order in HIR lowering.
+    /// An example of that is the desugaring of `for` loops.
+    DropTemps(&'hir Expr<'hir>),
+    /// A `let $pat = $expr` expression.
+    ///
+    /// These are not `Local` and only occur as expressions.
+    /// The `let Some(x) = foo()` in `if let Some(x) = foo()` is an example of `Let(..)`.
+    Let(&'hir Let<'hir>),
+    /// An `if` block, with an optional else block.
+    ///
+    /// I.e., `if <expr> { <expr> } else { <expr> }`.
+    If(&'hir Expr<'hir>, &'hir Expr<'hir>, Option<&'hir Expr<'hir>>),
+    /// A conditionless loop (can be exited with `break`, `continue`, or `return`).
+    ///
+    /// I.e., `'label: loop { <block> }`.
+    ///
+    /// The `Span` is the loop header (`for x in y`/`while let pat = expr`).
+    Loop(&'hir Block<'hir>, Option<Label>, LoopSource, Span),
+    /// A `match` block, with a source that indicates whether or not it is
+    /// the result of a desugaring, and if so, which kind.
+    Match(&'hir Expr<'hir>, &'hir [Arm<'hir>], MatchSource),
+    /// A closure (e.g., `move |a, b, c| {a + b + c}`).
+    ///
+    /// The `Span` is the argument block `|...|`.
+    ///
+    /// This may also be a generator literal or an `async block` as indicated by the
+    /// `Option<Movability>`.
+    Closure(&'hir Closure<'hir>),
+    /// A block (e.g., `'label: { ... }`).
+    Block(&'hir Block<'hir>, Option<Label>),
+
+    /// An assignment (e.g., `a = foo()`).
+    Assign(&'hir Expr<'hir>, &'hir Expr<'hir>, Span),
+    /// An assignment with an operator.
+    ///
+    /// E.g., `a += 1`.
+    AssignOp(BinOp, &'hir Expr<'hir>, &'hir Expr<'hir>),
+    /// Access of a named (e.g., `obj.foo`) or unnamed (e.g., `obj.0`) struct or tuple field.
+    Field(&'hir Expr<'hir>, Ident),
+    /// An indexing operation (`foo[2]`).
+    Index(&'hir Expr<'hir>, &'hir Expr<'hir>),
+
+    /// Path to a definition, possibly containing lifetime or type parameters.
+    Path(QPath<'hir>),
+
+    /// A referencing operation (i.e., `&a` or `&mut a`).
+    AddrOf(BorrowKind, Mutability, &'hir Expr<'hir>),
+    /// A `break`, with an optional label to break.
+    Break(Destination, Option<&'hir Expr<'hir>>),
+    /// A `continue`, with an optional label.
+    Continue(Destination),
+    /// A `return`, with an optional value to be returned.
+    Ret(Option<&'hir Expr<'hir>>),
+
+    /// Inline assembly (from `asm!`), with its outputs and inputs.
+    InlineAsm(&'hir InlineAsm<'hir>),
+
+    /// A struct or struct-like variant literal expression.
+    ///
+    /// E.g., `Foo {x: 1, y: 2}`, or `Foo {x: 1, .. base}`,
+    /// where `base` is the `Option<Expr>`.
+    Struct(&'hir QPath<'hir>, &'hir [ExprField<'hir>], Option<&'hir Expr<'hir>>),
+
+    /// An array literal constructed from one repeated element.
+    ///
+    /// E.g., `[1; 5]`. The first expression is the element
+    /// to be repeated; the second is the number of times to repeat it.
+    Repeat(&'hir Expr<'hir>, ArrayLen),
+
+    /// A suspension point for generators (i.e., `yield <expr>`).
+    Yield(&'hir Expr<'hir>, YieldSource),
+
+    /// A placeholder for an expression that wasn't syntactically well formed in some way.
+    Err,
+}
+
+/// Represents an optionally `Self`-qualified value/type path or associated extension.
+///
+/// To resolve the path to a `DefId`, call [`qpath_res`].
+///
+/// [`qpath_res`]: ../../rustc_middle/ty/struct.TypeckResults.html#method.qpath_res
+#[derive(Debug, HashStable_Generic)]
+pub enum QPath<'hir> {
+    /// Path to a definition, optionally "fully-qualified" with a `Self`
+    /// type, if the path points to an associated item in a trait.
+    ///
+    /// E.g., an unqualified path like `Clone::clone` has `None` for `Self`,
+    /// while `<Vec<T> as Clone>::clone` has `Some(Vec<T>)` for `Self`,
+    /// even though they both have the same two-segment `Clone::clone` `Path`.
+    Resolved(Option<&'hir Ty<'hir>>, &'hir Path<'hir>),
+
+    /// Type-related paths (e.g., `<T>::default` or `<T>::Output`).
+    /// Will be resolved by type-checking to an associated item.
+    ///
+    /// UFCS source paths can desugar into this, with `Vec::new` turning into
+    /// `<Vec>::new`, and `T::X::Y::method` into `<<<T>::X>::Y>::method`,
+    /// the `X` and `Y` nodes each being a `TyKind::Path(QPath::TypeRelative(..))`.
+    TypeRelative(&'hir Ty<'hir>, &'hir PathSegment<'hir>),
+
+    /// Reference to a `#[lang = "foo"]` item. `HirId` of the inner expr.
+    LangItem(LangItem, Span, Option<HirId>),
+}
+
+impl<'hir> QPath<'hir> {
+    /// Returns the span of this `QPath`.
+    pub fn span(&self) -> Span {
+        match *self {
+            QPath::Resolved(_, path) => path.span,
+            QPath::TypeRelative(qself, ps) => qself.span.to(ps.ident.span),
+            QPath::LangItem(_, span, _) => span,
+        }
+    }
+
+    /// Returns the span of the qself of this `QPath`. For example, `()` in
+    /// `<() as Trait>::method`.
+    pub fn qself_span(&self) -> Span {
+        match *self {
+            QPath::Resolved(_, path) => path.span,
+            QPath::TypeRelative(qself, _) => qself.span,
+            QPath::LangItem(_, span, _) => span,
+        }
+    }
+
+    /// Returns the span of the last segment of this `QPath`. For example, `method` in
+    /// `<() as Trait>::method`.
+    pub fn last_segment_span(&self) -> Span {
+        match *self {
+            QPath::Resolved(_, path) => path.segments.last().unwrap().ident.span,
+            QPath::TypeRelative(_, segment) => segment.ident.span,
+            QPath::LangItem(_, span, _) => span,
+        }
+    }
+}
+
+/// Hints at the original code for a let statement.
+#[derive(Copy, Clone, Encodable, Debug, HashStable_Generic)]
+pub enum LocalSource {
+    /// A `match _ { .. }`.
+    Normal,
+    /// When lowering async functions, we create locals within the `async move` so that
+    /// all parameters are dropped after the future is polled.
+    ///
+    /// ```ignore (pseudo-Rust)
+    /// async fn foo(<pattern> @ x: Type) {
+    ///     async move {
+    ///         let <pattern> = x;
+    ///     }
+    /// }
+    /// ```
+    AsyncFn,
+    /// A desugared `<expr>.await`.
+    AwaitDesugar,
+    /// A desugared `expr = expr`, where the LHS is a tuple, struct or array.
+    /// The span is that of the `=` sign.
+    AssignDesugar(Span),
+}
+
+/// Hints at the original code for a `match _ { .. }`.
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Hash, Debug)]
+#[derive(HashStable_Generic)]
+pub enum MatchSource {
+    /// A `match _ { .. }`.
+    Normal,
+    /// A desugared `for _ in _ { .. }` loop.
+    ForLoopDesugar,
+    /// A desugared `?` operator.
+    TryDesugar,
+    /// A desugared `<expr>.await`.
+    AwaitDesugar,
+}
+
+impl MatchSource {
+    #[inline]
+    pub const fn name(self) -> &'static str {
+        use MatchSource::*;
+        match self {
+            Normal => "match",
+            ForLoopDesugar => "for",
+            TryDesugar => "?",
+            AwaitDesugar => ".await",
+        }
+    }
+}
+
+/// The loop type that yielded an `ExprKind::Loop`.
+#[derive(Copy, Clone, PartialEq, Encodable, Debug, HashStable_Generic)]
+pub enum LoopSource {
+    /// A `loop { .. }` loop.
+    Loop,
+    /// A `while _ { .. }` loop.
+    While,
+    /// A `for _ in _ { .. }` loop.
+    ForLoop,
+}
+
+impl LoopSource {
+    pub fn name(self) -> &'static str {
+        match self {
+            LoopSource::Loop => "loop",
+            LoopSource::While => "while",
+            LoopSource::ForLoop => "for",
+        }
+    }
+}
+
+#[derive(Copy, Clone, Encodable, Debug, HashStable_Generic)]
+pub enum LoopIdError {
+    OutsideLoopScope,
+    UnlabeledCfInWhileCondition,
+    UnresolvedLabel,
+}
+
+impl fmt::Display for LoopIdError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(match self {
+            LoopIdError::OutsideLoopScope => "not inside loop scope",
+            LoopIdError::UnlabeledCfInWhileCondition => {
+                "unlabeled control flow (break or continue) in while condition"
+            }
+            LoopIdError::UnresolvedLabel => "label not found",
+        })
+    }
+}
+
+#[derive(Copy, Clone, Encodable, Debug, HashStable_Generic)]
+pub struct Destination {
+    // This is `Some(_)` iff there is an explicit user-specified `label
+    pub label: Option<Label>,
+
+    // These errors are caught and then reported during the diagnostics pass in
+    // librustc_passes/loops.rs
+    pub target_id: Result<HirId, LoopIdError>,
+}
+
+/// The yield kind that caused an `ExprKind::Yield`.
+#[derive(Copy, Clone, PartialEq, Eq, Debug, Encodable, Decodable, HashStable_Generic)]
+pub enum YieldSource {
+    /// An `<expr>.await`.
+    Await { expr: Option<HirId> },
+    /// A plain `yield`.
+    Yield,
+}
+
+impl YieldSource {
+    pub fn is_await(&self) -> bool {
+        matches!(self, YieldSource::Await { .. })
+    }
+}
+
+impl fmt::Display for YieldSource {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(match self {
+            YieldSource::Await { .. } => "`await`",
+            YieldSource::Yield => "`yield`",
+        })
+    }
+}
+
+impl From<GeneratorKind> for YieldSource {
+    fn from(kind: GeneratorKind) -> Self {
+        match kind {
+            // Guess based on the kind of the current generator.
+            GeneratorKind::Gen => Self::Yield,
+            GeneratorKind::Async(_) => Self::Await { expr: None },
+        }
+    }
+}
+
+// N.B., if you change this, you'll probably want to change the corresponding
+// type structure in middle/ty.rs as well.
+#[derive(Debug, HashStable_Generic)]
+pub struct MutTy<'hir> {
+    pub ty: &'hir Ty<'hir>,
+    pub mutbl: Mutability,
+}
+
+/// Represents a function's signature in a trait declaration,
+/// trait implementation, or a free function.
+#[derive(Debug, HashStable_Generic)]
+pub struct FnSig<'hir> {
+    pub header: FnHeader,
+    pub decl: &'hir FnDecl<'hir>,
+    pub span: Span,
+}
+
+// The bodies for items are stored "out of line", in a separate
+// hashmap in the `Crate`. Here we just record the hir-id of the item
+// so it can fetched later.
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, HashStable_Generic)]
+pub struct TraitItemId {
+    pub def_id: LocalDefId,
+}
+
+impl TraitItemId {
+    #[inline]
+    pub fn hir_id(&self) -> HirId {
+        // Items are always HIR owners.
+        HirId::make_owner(self.def_id)
+    }
+}
+
+/// Represents an item declaration within a trait declaration,
+/// possibly including a default implementation. A trait item is
+/// either required (meaning it doesn't have an implementation, just a
+/// signature) or provided (meaning it has a default implementation).
+#[derive(Debug, HashStable_Generic)]
+pub struct TraitItem<'hir> {
+    pub ident: Ident,
+    pub def_id: LocalDefId,
+    pub generics: &'hir Generics<'hir>,
+    pub kind: TraitItemKind<'hir>,
+    pub span: Span,
+    pub defaultness: Defaultness,
+}
+
+impl TraitItem<'_> {
+    #[inline]
+    pub fn hir_id(&self) -> HirId {
+        // Items are always HIR owners.
+        HirId::make_owner(self.def_id)
+    }
+
+    pub fn trait_item_id(&self) -> TraitItemId {
+        TraitItemId { def_id: self.def_id }
+    }
+}
+
+/// Represents a trait method's body (or just argument names).
+#[derive(Encodable, Debug, HashStable_Generic)]
+pub enum TraitFn<'hir> {
+    /// No default body in the trait, just a signature.
+    Required(&'hir [Ident]),
+
+    /// Both signature and body are provided in the trait.
+    Provided(BodyId),
+}
+
+/// Represents a trait method or associated constant or type
+#[derive(Debug, HashStable_Generic)]
+pub enum TraitItemKind<'hir> {
+    /// An associated constant with an optional value (otherwise `impl`s must contain a value).
+    Const(&'hir Ty<'hir>, Option<BodyId>),
+    /// An associated function with an optional body.
+    Fn(FnSig<'hir>, TraitFn<'hir>),
+    /// An associated type with (possibly empty) bounds and optional concrete
+    /// type.
+    Type(GenericBounds<'hir>, Option<&'hir Ty<'hir>>),
+}
+
+// The bodies for items are stored "out of line", in a separate
+// hashmap in the `Crate`. Here we just record the hir-id of the item
+// so it can fetched later.
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, HashStable_Generic)]
+pub struct ImplItemId {
+    pub def_id: LocalDefId,
+}
+
+impl ImplItemId {
+    #[inline]
+    pub fn hir_id(&self) -> HirId {
+        // Items are always HIR owners.
+        HirId::make_owner(self.def_id)
+    }
+}
+
+/// Represents anything within an `impl` block.
+#[derive(Debug, HashStable_Generic)]
+pub struct ImplItem<'hir> {
+    pub ident: Ident,
+    pub def_id: LocalDefId,
+    pub generics: &'hir Generics<'hir>,
+    pub kind: ImplItemKind<'hir>,
+    pub defaultness: Defaultness,
+    pub span: Span,
+    pub vis_span: Span,
+}
+
+impl ImplItem<'_> {
+    #[inline]
+    pub fn hir_id(&self) -> HirId {
+        // Items are always HIR owners.
+        HirId::make_owner(self.def_id)
+    }
+
+    pub fn impl_item_id(&self) -> ImplItemId {
+        ImplItemId { def_id: self.def_id }
+    }
+}
+
+/// Represents various kinds of content within an `impl`.
+#[derive(Debug, HashStable_Generic)]
+pub enum ImplItemKind<'hir> {
+    /// An associated constant of the given type, set to the constant result
+    /// of the expression.
+    Const(&'hir Ty<'hir>, BodyId),
+    /// An associated function implementation with the given signature and body.
+    Fn(FnSig<'hir>, BodyId),
+    /// An associated type.
+    TyAlias(&'hir Ty<'hir>),
+}
+
+// The name of the associated type for `Fn` return types.
+pub const FN_OUTPUT_NAME: Symbol = sym::Output;
+
+/// Bind a type to an associated type (i.e., `A = Foo`).
+///
+/// Bindings like `A: Debug` are represented as a special type `A =
+/// $::Debug` that is understood by the astconv code.
+///
+/// FIXME(alexreg): why have a separate type for the binding case,
+/// wouldn't it be better to make the `ty` field an enum like the
+/// following?
+///
+/// ```ignore (pseudo-rust)
+/// enum TypeBindingKind {
+///    Equals(...),
+///    Binding(...),
+/// }
+/// ```
+#[derive(Debug, HashStable_Generic)]
+pub struct TypeBinding<'hir> {
+    pub hir_id: HirId,
+    pub ident: Ident,
+    pub gen_args: &'hir GenericArgs<'hir>,
+    pub kind: TypeBindingKind<'hir>,
+    pub span: Span,
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub enum Term<'hir> {
+    Ty(&'hir Ty<'hir>),
+    Const(AnonConst),
+}
+
+impl<'hir> From<&'hir Ty<'hir>> for Term<'hir> {
+    fn from(ty: &'hir Ty<'hir>) -> Self {
+        Term::Ty(ty)
+    }
+}
+
+impl<'hir> From<AnonConst> for Term<'hir> {
+    fn from(c: AnonConst) -> Self {
+        Term::Const(c)
+    }
+}
+
+// Represents the two kinds of type bindings.
+#[derive(Debug, HashStable_Generic)]
+pub enum TypeBindingKind<'hir> {
+    /// E.g., `Foo<Bar: Send>`.
+    Constraint { bounds: &'hir [GenericBound<'hir>] },
+    /// E.g., `Foo<Bar = ()>`, `Foo<Bar = ()>`
+    Equality { term: Term<'hir> },
+}
+
+impl TypeBinding<'_> {
+    pub fn ty(&self) -> &Ty<'_> {
+        match self.kind {
+            TypeBindingKind::Equality { term: Term::Ty(ref ty) } => ty,
+            _ => panic!("expected equality type binding for parenthesized generic args"),
+        }
+    }
+    pub fn opt_const(&self) -> Option<&'_ AnonConst> {
+        match self.kind {
+            TypeBindingKind::Equality { term: Term::Const(ref c) } => Some(c),
+            _ => None,
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct Ty<'hir> {
+    pub hir_id: HirId,
+    pub kind: TyKind<'hir>,
+    pub span: Span,
+}
+
+impl<'hir> Ty<'hir> {
+    /// Returns `true` if `param_def_id` matches the `bounded_ty` of this predicate.
+    pub fn as_generic_param(&self) -> Option<(DefId, Ident)> {
+        let TyKind::Path(QPath::Resolved(None, path)) = self.kind else {
+            return None;
+        };
+        let [segment] = &path.segments else {
+            return None;
+        };
+        match path.res {
+            Res::Def(DefKind::TyParam, def_id)
+            | Res::SelfTy { trait_: Some(def_id), alias_to: None } => Some((def_id, segment.ident)),
+            _ => None,
+        }
+    }
+}
+
+/// Not represented directly in the AST; referred to by name through a `ty_path`.
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
+#[derive(HashStable_Generic)]
+pub enum PrimTy {
+    Int(IntTy),
+    Uint(UintTy),
+    Float(FloatTy),
+    Str,
+    Bool,
+    Char,
+}
+
+impl PrimTy {
+    /// All of the primitive types
+    pub const ALL: [Self; 17] = [
+        // any changes here should also be reflected in `PrimTy::from_name`
+        Self::Int(IntTy::I8),
+        Self::Int(IntTy::I16),
+        Self::Int(IntTy::I32),
+        Self::Int(IntTy::I64),
+        Self::Int(IntTy::I128),
+        Self::Int(IntTy::Isize),
+        Self::Uint(UintTy::U8),
+        Self::Uint(UintTy::U16),
+        Self::Uint(UintTy::U32),
+        Self::Uint(UintTy::U64),
+        Self::Uint(UintTy::U128),
+        Self::Uint(UintTy::Usize),
+        Self::Float(FloatTy::F32),
+        Self::Float(FloatTy::F64),
+        Self::Bool,
+        Self::Char,
+        Self::Str,
+    ];
+
+    /// Like [`PrimTy::name`], but returns a &str instead of a symbol.
+    ///
+    /// Used by clippy.
+    pub fn name_str(self) -> &'static str {
+        match self {
+            PrimTy::Int(i) => i.name_str(),
+            PrimTy::Uint(u) => u.name_str(),
+            PrimTy::Float(f) => f.name_str(),
+            PrimTy::Str => "str",
+            PrimTy::Bool => "bool",
+            PrimTy::Char => "char",
+        }
+    }
+
+    pub fn name(self) -> Symbol {
+        match self {
+            PrimTy::Int(i) => i.name(),
+            PrimTy::Uint(u) => u.name(),
+            PrimTy::Float(f) => f.name(),
+            PrimTy::Str => sym::str,
+            PrimTy::Bool => sym::bool,
+            PrimTy::Char => sym::char,
+        }
+    }
+
+    /// Returns the matching `PrimTy` for a `Symbol` such as "str" or "i32".
+    /// Returns `None` if no matching type is found.
+    pub fn from_name(name: Symbol) -> Option<Self> {
+        let ty = match name {
+            // any changes here should also be reflected in `PrimTy::ALL`
+            sym::i8 => Self::Int(IntTy::I8),
+            sym::i16 => Self::Int(IntTy::I16),
+            sym::i32 => Self::Int(IntTy::I32),
+            sym::i64 => Self::Int(IntTy::I64),
+            sym::i128 => Self::Int(IntTy::I128),
+            sym::isize => Self::Int(IntTy::Isize),
+            sym::u8 => Self::Uint(UintTy::U8),
+            sym::u16 => Self::Uint(UintTy::U16),
+            sym::u32 => Self::Uint(UintTy::U32),
+            sym::u64 => Self::Uint(UintTy::U64),
+            sym::u128 => Self::Uint(UintTy::U128),
+            sym::usize => Self::Uint(UintTy::Usize),
+            sym::f32 => Self::Float(FloatTy::F32),
+            sym::f64 => Self::Float(FloatTy::F64),
+            sym::bool => Self::Bool,
+            sym::char => Self::Char,
+            sym::str => Self::Str,
+            _ => return None,
+        };
+        Some(ty)
+    }
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub struct BareFnTy<'hir> {
+    pub unsafety: Unsafety,
+    pub abi: Abi,
+    pub generic_params: &'hir [GenericParam<'hir>],
+    pub decl: &'hir FnDecl<'hir>,
+    pub param_names: &'hir [Ident],
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub struct OpaqueTy<'hir> {
+    pub generics: &'hir Generics<'hir>,
+    pub bounds: GenericBounds<'hir>,
+    pub origin: OpaqueTyOrigin,
+}
+
+/// From whence the opaque type came.
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, HashStable_Generic)]
+pub enum OpaqueTyOrigin {
+    /// `-> impl Trait`
+    FnReturn(LocalDefId),
+    /// `async fn`
+    AsyncFn(LocalDefId),
+    /// type aliases: `type Foo = impl Trait;`
+    TyAlias,
+}
+
+/// The various kinds of types recognized by the compiler.
+#[derive(Debug, HashStable_Generic)]
+pub enum TyKind<'hir> {
+    /// A variable length slice (i.e., `[T]`).
+    Slice(&'hir Ty<'hir>),
+    /// A fixed length array (i.e., `[T; n]`).
+    Array(&'hir Ty<'hir>, ArrayLen),
+    /// A raw pointer (i.e., `*const T` or `*mut T`).
+    Ptr(MutTy<'hir>),
+    /// A reference (i.e., `&'a T` or `&'a mut T`).
+    Rptr(Lifetime, MutTy<'hir>),
+    /// A bare function (e.g., `fn(usize) -> bool`).
+    BareFn(&'hir BareFnTy<'hir>),
+    /// The never type (`!`).
+    Never,
+    /// A tuple (`(A, B, C, D, ...)`).
+    Tup(&'hir [Ty<'hir>]),
+    /// A path to a type definition (`module::module::...::Type`), or an
+    /// associated type (e.g., `<Vec<T> as Trait>::Type` or `<T>::Target`).
+    ///
+    /// Type parameters may be stored in each `PathSegment`.
+    Path(QPath<'hir>),
+    /// An opaque type definition itself. This is only used for `impl Trait`.
+    ///
+    /// The generic argument list contains the lifetimes (and in the future
+    /// possibly parameters) that are actually bound on the `impl Trait`.
+    OpaqueDef(ItemId, &'hir [GenericArg<'hir>]),
+    /// A trait object type `Bound1 + Bound2 + Bound3`
+    /// where `Bound` is a trait or a lifetime.
+    TraitObject(&'hir [PolyTraitRef<'hir>], Lifetime, TraitObjectSyntax),
+    /// Unused for now.
+    Typeof(AnonConst),
+    /// `TyKind::Infer` means the type should be inferred instead of it having been
+    /// specified. This can appear anywhere in a type.
+    Infer,
+    /// Placeholder for a type that has failed to be defined.
+    Err,
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub enum InlineAsmOperand<'hir> {
+    In {
+        reg: InlineAsmRegOrRegClass,
+        expr: Expr<'hir>,
+    },
+    Out {
+        reg: InlineAsmRegOrRegClass,
+        late: bool,
+        expr: Option<Expr<'hir>>,
+    },
+    InOut {
+        reg: InlineAsmRegOrRegClass,
+        late: bool,
+        expr: Expr<'hir>,
+    },
+    SplitInOut {
+        reg: InlineAsmRegOrRegClass,
+        late: bool,
+        in_expr: Expr<'hir>,
+        out_expr: Option<Expr<'hir>>,
+    },
+    Const {
+        anon_const: AnonConst,
+    },
+    SymFn {
+        anon_const: AnonConst,
+    },
+    SymStatic {
+        path: QPath<'hir>,
+        def_id: DefId,
+    },
+}
+
+impl<'hir> InlineAsmOperand<'hir> {
+    pub fn reg(&self) -> Option<InlineAsmRegOrRegClass> {
+        match *self {
+            Self::In { reg, .. }
+            | Self::Out { reg, .. }
+            | Self::InOut { reg, .. }
+            | Self::SplitInOut { reg, .. } => Some(reg),
+            Self::Const { .. } | Self::SymFn { .. } | Self::SymStatic { .. } => None,
+        }
+    }
+
+    pub fn is_clobber(&self) -> bool {
+        matches!(
+            self,
+            InlineAsmOperand::Out { reg: InlineAsmRegOrRegClass::Reg(_), late: _, expr: None }
+        )
+    }
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub struct InlineAsm<'hir> {
+    pub template: &'hir [InlineAsmTemplatePiece],
+    pub template_strs: &'hir [(Symbol, Option<Symbol>, Span)],
+    pub operands: &'hir [(InlineAsmOperand<'hir>, Span)],
+    pub options: InlineAsmOptions,
+    pub line_spans: &'hir [Span],
+}
+
+/// Represents a parameter in a function header.
+#[derive(Debug, HashStable_Generic)]
+pub struct Param<'hir> {
+    pub hir_id: HirId,
+    pub pat: &'hir Pat<'hir>,
+    pub ty_span: Span,
+    pub span: Span,
+}
+
+/// Represents the header (not the body) of a function declaration.
+#[derive(Debug, HashStable_Generic)]
+pub struct FnDecl<'hir> {
+    /// The types of the function's parameters.
+    ///
+    /// Additional argument data is stored in the function's [body](Body::params).
+    pub inputs: &'hir [Ty<'hir>],
+    pub output: FnRetTy<'hir>,
+    pub c_variadic: bool,
+    /// Does the function have an implicit self?
+    pub implicit_self: ImplicitSelfKind,
+}
+
+/// Represents what type of implicit self a function has, if any.
+#[derive(Copy, Clone, Encodable, Decodable, Debug, HashStable_Generic)]
+pub enum ImplicitSelfKind {
+    /// Represents a `fn x(self);`.
+    Imm,
+    /// Represents a `fn x(mut self);`.
+    Mut,
+    /// Represents a `fn x(&self);`.
+    ImmRef,
+    /// Represents a `fn x(&mut self);`.
+    MutRef,
+    /// Represents when a function does not have a self argument or
+    /// when a function has a `self: X` argument.
+    None,
+}
+
+impl ImplicitSelfKind {
+    /// Does this represent an implicit self?
+    pub fn has_implicit_self(&self) -> bool {
+        !matches!(*self, ImplicitSelfKind::None)
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Encodable, Decodable, Debug)]
+#[derive(HashStable_Generic)]
+pub enum IsAsync {
+    Async,
+    NotAsync,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, Encodable, Decodable, HashStable_Generic)]
+pub enum Defaultness {
+    Default { has_value: bool },
+    Final,
+}
+
+impl Defaultness {
+    pub fn has_value(&self) -> bool {
+        match *self {
+            Defaultness::Default { has_value } => has_value,
+            Defaultness::Final => true,
+        }
+    }
+
+    pub fn is_final(&self) -> bool {
+        *self == Defaultness::Final
+    }
+
+    pub fn is_default(&self) -> bool {
+        matches!(*self, Defaultness::Default { .. })
+    }
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub enum FnRetTy<'hir> {
+    /// Return type is not specified.
+    ///
+    /// Functions default to `()` and
+    /// closures default to inference. Span points to where return
+    /// type would be inserted.
+    DefaultReturn(Span),
+    /// Everything else.
+    Return(&'hir Ty<'hir>),
+}
+
+impl FnRetTy<'_> {
+    #[inline]
+    pub fn span(&self) -> Span {
+        match *self {
+            Self::DefaultReturn(span) => span,
+            Self::Return(ref ty) => ty.span,
+        }
+    }
+}
+
+/// Represents `for<...>` binder before a closure
+#[derive(Copy, Clone, Debug, HashStable_Generic)]
+pub enum ClosureBinder {
+    /// Binder is not specified.
+    Default,
+    /// Binder is specified.
+    ///
+    /// Span points to the whole `for<...>`.
+    For { span: Span },
+}
+
+#[derive(Encodable, Debug, HashStable_Generic)]
+pub struct Mod<'hir> {
+    pub spans: ModSpans,
+    pub item_ids: &'hir [ItemId],
+}
+
+#[derive(Copy, Clone, Debug, HashStable_Generic, Encodable)]
+pub struct ModSpans {
+    /// A span from the first token past `{` to the last token until `}`.
+    /// For `mod foo;`, the inner span ranges from the first token
+    /// to the last token in the external file.
+    pub inner_span: Span,
+    pub inject_use_span: Span,
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub struct EnumDef<'hir> {
+    pub variants: &'hir [Variant<'hir>],
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub struct Variant<'hir> {
+    /// Name of the variant.
+    pub ident: Ident,
+    /// Id of the variant (not the constructor, see `VariantData::ctor_hir_id()`).
+    pub id: HirId,
+    /// Fields and constructor id of the variant.
+    pub data: VariantData<'hir>,
+    /// Explicit discriminant (e.g., `Foo = 1`).
+    pub disr_expr: Option<AnonConst>,
+    /// Span
+    pub span: Span,
+}
+
+#[derive(Copy, Clone, PartialEq, Encodable, Debug, HashStable_Generic)]
+pub enum UseKind {
+    /// One import, e.g., `use foo::bar` or `use foo::bar as baz`.
+    /// Also produced for each element of a list `use`, e.g.
+    /// `use foo::{a, b}` lowers to `use foo::a; use foo::b;`.
+    Single,
+
+    /// Glob import, e.g., `use foo::*`.
+    Glob,
+
+    /// Degenerate list import, e.g., `use foo::{a, b}` produces
+    /// an additional `use foo::{}` for performing checks such as
+    /// unstable feature gating. May be removed in the future.
+    ListStem,
+}
+
+/// References to traits in impls.
+///
+/// `resolve` maps each `TraitRef`'s `ref_id` to its defining trait; that's all
+/// that the `ref_id` is for. Note that `ref_id`'s value is not the `HirId` of the
+/// trait being referred to but just a unique `HirId` that serves as a key
+/// within the resolution map.
+#[derive(Clone, Debug, HashStable_Generic)]
+pub struct TraitRef<'hir> {
+    pub path: &'hir Path<'hir>,
+    // Don't hash the `ref_id`. It is tracked via the thing it is used to access.
+    #[stable_hasher(ignore)]
+    pub hir_ref_id: HirId,
+}
+
+impl TraitRef<'_> {
+    /// Gets the `DefId` of the referenced trait. It _must_ actually be a trait or trait alias.
+    pub fn trait_def_id(&self) -> Option<DefId> {
+        match self.path.res {
+            Res::Def(DefKind::Trait | DefKind::TraitAlias, did) => Some(did),
+            Res::Err => None,
+            _ => unreachable!(),
+        }
+    }
+}
+
+#[derive(Clone, Debug, HashStable_Generic)]
+pub struct PolyTraitRef<'hir> {
+    /// The `'a` in `for<'a> Foo<&'a T>`.
+    pub bound_generic_params: &'hir [GenericParam<'hir>],
+
+    /// The `Foo<&'a T>` in `for<'a> Foo<&'a T>`.
+    pub trait_ref: TraitRef<'hir>,
+
+    pub span: Span,
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub struct FieldDef<'hir> {
+    pub span: Span,
+    pub vis_span: Span,
+    pub ident: Ident,
+    pub hir_id: HirId,
+    pub ty: &'hir Ty<'hir>,
+}
+
+impl FieldDef<'_> {
+    // Still necessary in couple of places
+    pub fn is_positional(&self) -> bool {
+        let first = self.ident.as_str().as_bytes()[0];
+        (b'0'..=b'9').contains(&first)
+    }
+}
+
+/// Fields and constructor IDs of enum variants and structs.
+#[derive(Debug, HashStable_Generic)]
+pub enum VariantData<'hir> {
+    /// A struct variant.
+    ///
+    /// E.g., `Bar { .. }` as in `enum Foo { Bar { .. } }`.
+    Struct(&'hir [FieldDef<'hir>], /* recovered */ bool),
+    /// A tuple variant.
+    ///
+    /// E.g., `Bar(..)` as in `enum Foo { Bar(..) }`.
+    Tuple(&'hir [FieldDef<'hir>], HirId),
+    /// A unit variant.
+    ///
+    /// E.g., `Bar = ..` as in `enum Foo { Bar = .. }`.
+    Unit(HirId),
+}
+
+impl<'hir> VariantData<'hir> {
+    /// Return the fields of this variant.
+    pub fn fields(&self) -> &'hir [FieldDef<'hir>] {
+        match *self {
+            VariantData::Struct(ref fields, ..) | VariantData::Tuple(ref fields, ..) => fields,
+            _ => &[],
+        }
+    }
+
+    /// Return the `HirId` of this variant's constructor, if it has one.
+    pub fn ctor_hir_id(&self) -> Option<HirId> {
+        match *self {
+            VariantData::Struct(_, _) => None,
+            VariantData::Tuple(_, hir_id) | VariantData::Unit(hir_id) => Some(hir_id),
+        }
+    }
+}
+
+// The bodies for items are stored "out of line", in a separate
+// hashmap in the `Crate`. Here we just record the hir-id of the item
+// so it can fetched later.
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, Hash, HashStable_Generic)]
+pub struct ItemId {
+    pub def_id: LocalDefId,
+}
+
+impl ItemId {
+    #[inline]
+    pub fn hir_id(&self) -> HirId {
+        // Items are always HIR owners.
+        HirId::make_owner(self.def_id)
+    }
+}
+
+/// An item
+///
+/// The name might be a dummy name in case of anonymous items
+#[derive(Debug, HashStable_Generic)]
+pub struct Item<'hir> {
+    pub ident: Ident,
+    pub def_id: LocalDefId,
+    pub kind: ItemKind<'hir>,
+    pub span: Span,
+    pub vis_span: Span,
+}
+
+impl Item<'_> {
+    #[inline]
+    pub fn hir_id(&self) -> HirId {
+        // Items are always HIR owners.
+        HirId::make_owner(self.def_id)
+    }
+
+    pub fn item_id(&self) -> ItemId {
+        ItemId { def_id: self.def_id }
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+#[derive(Encodable, Decodable, HashStable_Generic)]
+pub enum Unsafety {
+    Unsafe,
+    Normal,
+}
+
+impl Unsafety {
+    pub fn prefix_str(&self) -> &'static str {
+        match self {
+            Self::Unsafe => "unsafe ",
+            Self::Normal => "",
+        }
+    }
+}
+
+impl fmt::Display for Unsafety {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(match *self {
+            Self::Unsafe => "unsafe",
+            Self::Normal => "normal",
+        })
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+#[derive(Encodable, Decodable, HashStable_Generic)]
+pub enum Constness {
+    Const,
+    NotConst,
+}
+
+impl fmt::Display for Constness {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(match *self {
+            Self::Const => "const",
+            Self::NotConst => "non-const",
+        })
+    }
+}
+
+#[derive(Copy, Clone, Encodable, Debug, HashStable_Generic)]
+pub struct FnHeader {
+    pub unsafety: Unsafety,
+    pub constness: Constness,
+    pub asyncness: IsAsync,
+    pub abi: Abi,
+}
+
+impl FnHeader {
+    pub fn is_async(&self) -> bool {
+        matches!(&self.asyncness, IsAsync::Async)
+    }
+
+    pub fn is_const(&self) -> bool {
+        matches!(&self.constness, Constness::Const)
+    }
+
+    pub fn is_unsafe(&self) -> bool {
+        matches!(&self.unsafety, Unsafety::Unsafe)
+    }
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub enum ItemKind<'hir> {
+    /// An `extern crate` item, with optional *original* crate name if the crate was renamed.
+    ///
+    /// E.g., `extern crate foo` or `extern crate foo_bar as foo`.
+    ExternCrate(Option<Symbol>),
+
+    /// `use foo::bar::*;` or `use foo::bar::baz as quux;`
+    ///
+    /// or just
+    ///
+    /// `use foo::bar::baz;` (with `as baz` implicitly on the right).
+    Use(&'hir Path<'hir>, UseKind),
+
+    /// A `static` item.
+    Static(&'hir Ty<'hir>, Mutability, BodyId),
+    /// A `const` item.
+    Const(&'hir Ty<'hir>, BodyId),
+    /// A function declaration.
+    Fn(FnSig<'hir>, &'hir Generics<'hir>, BodyId),
+    /// A MBE macro definition (`macro_rules!` or `macro`).
+    Macro(ast::MacroDef, MacroKind),
+    /// A module.
+    Mod(Mod<'hir>),
+    /// An external module, e.g. `extern { .. }`.
+    ForeignMod { abi: Abi, items: &'hir [ForeignItemRef] },
+    /// Module-level inline assembly (from `global_asm!`).
+    GlobalAsm(&'hir InlineAsm<'hir>),
+    /// A type alias, e.g., `type Foo = Bar<u8>`.
+    TyAlias(&'hir Ty<'hir>, &'hir Generics<'hir>),
+    /// An opaque `impl Trait` type alias, e.g., `type Foo = impl Bar;`.
+    OpaqueTy(OpaqueTy<'hir>),
+    /// An enum definition, e.g., `enum Foo<A, B> {C<A>, D<B>}`.
+    Enum(EnumDef<'hir>, &'hir Generics<'hir>),
+    /// A struct definition, e.g., `struct Foo<A> {x: A}`.
+    Struct(VariantData<'hir>, &'hir Generics<'hir>),
+    /// A union definition, e.g., `union Foo<A, B> {x: A, y: B}`.
+    Union(VariantData<'hir>, &'hir Generics<'hir>),
+    /// A trait definition.
+    Trait(IsAuto, Unsafety, &'hir Generics<'hir>, GenericBounds<'hir>, &'hir [TraitItemRef]),
+    /// A trait alias.
+    TraitAlias(&'hir Generics<'hir>, GenericBounds<'hir>),
+
+    /// An implementation, e.g., `impl<A> Trait for Foo { .. }`.
+    Impl(&'hir Impl<'hir>),
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub struct Impl<'hir> {
+    pub unsafety: Unsafety,
+    pub polarity: ImplPolarity,
+    pub defaultness: Defaultness,
+    // We do not put a `Span` in `Defaultness` because it breaks foreign crate metadata
+    // decoding as `Span`s cannot be decoded when a `Session` is not available.
+    pub defaultness_span: Option<Span>,
+    pub constness: Constness,
+    pub generics: &'hir Generics<'hir>,
+
+    /// The trait being implemented, if any.
+    pub of_trait: Option<TraitRef<'hir>>,
+
+    pub self_ty: &'hir Ty<'hir>,
+    pub items: &'hir [ImplItemRef],
+}
+
+impl ItemKind<'_> {
+    pub fn generics(&self) -> Option<&Generics<'_>> {
+        Some(match *self {
+            ItemKind::Fn(_, ref generics, _)
+            | ItemKind::TyAlias(_, ref generics)
+            | ItemKind::OpaqueTy(OpaqueTy { ref generics, .. })
+            | ItemKind::Enum(_, ref generics)
+            | ItemKind::Struct(_, ref generics)
+            | ItemKind::Union(_, ref generics)
+            | ItemKind::Trait(_, _, ref generics, _, _)
+            | ItemKind::TraitAlias(ref generics, _)
+            | ItemKind::Impl(Impl { ref generics, .. }) => generics,
+            _ => return None,
+        })
+    }
+
+    pub fn descr(&self) -> &'static str {
+        match self {
+            ItemKind::ExternCrate(..) => "extern crate",
+            ItemKind::Use(..) => "`use` import",
+            ItemKind::Static(..) => "static item",
+            ItemKind::Const(..) => "constant item",
+            ItemKind::Fn(..) => "function",
+            ItemKind::Macro(..) => "macro",
+            ItemKind::Mod(..) => "module",
+            ItemKind::ForeignMod { .. } => "extern block",
+            ItemKind::GlobalAsm(..) => "global asm item",
+            ItemKind::TyAlias(..) => "type alias",
+            ItemKind::OpaqueTy(..) => "opaque type",
+            ItemKind::Enum(..) => "enum",
+            ItemKind::Struct(..) => "struct",
+            ItemKind::Union(..) => "union",
+            ItemKind::Trait(..) => "trait",
+            ItemKind::TraitAlias(..) => "trait alias",
+            ItemKind::Impl(..) => "implementation",
+        }
+    }
+}
+
+/// A reference from an trait to one of its associated items. This
+/// contains the item's id, naturally, but also the item's name and
+/// some other high-level details (like whether it is an associated
+/// type or method, and whether it is public). This allows other
+/// passes to find the impl they want without loading the ID (which
+/// means fewer edges in the incremental compilation graph).
+#[derive(Encodable, Debug, HashStable_Generic)]
+pub struct TraitItemRef {
+    pub id: TraitItemId,
+    pub ident: Ident,
+    pub kind: AssocItemKind,
+    pub span: Span,
+}
+
+/// A reference from an impl to one of its associated items. This
+/// contains the item's ID, naturally, but also the item's name and
+/// some other high-level details (like whether it is an associated
+/// type or method, and whether it is public). This allows other
+/// passes to find the impl they want without loading the ID (which
+/// means fewer edges in the incremental compilation graph).
+#[derive(Debug, HashStable_Generic)]
+pub struct ImplItemRef {
+    pub id: ImplItemId,
+    pub ident: Ident,
+    pub kind: AssocItemKind,
+    pub span: Span,
+    /// When we are in a trait impl, link to the trait-item's id.
+    pub trait_item_def_id: Option<DefId>,
+}
+
+#[derive(Copy, Clone, PartialEq, Encodable, Debug, HashStable_Generic)]
+pub enum AssocItemKind {
+    Const,
+    Fn { has_self: bool },
+    Type,
+}
+
+// The bodies for items are stored "out of line", in a separate
+// hashmap in the `Crate`. Here we just record the hir-id of the item
+// so it can fetched later.
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, HashStable_Generic)]
+pub struct ForeignItemId {
+    pub def_id: LocalDefId,
+}
+
+impl ForeignItemId {
+    #[inline]
+    pub fn hir_id(&self) -> HirId {
+        // Items are always HIR owners.
+        HirId::make_owner(self.def_id)
+    }
+}
+
+/// A reference from a foreign block to one of its items. This
+/// contains the item's ID, naturally, but also the item's name and
+/// some other high-level details (like whether it is an associated
+/// type or method, and whether it is public). This allows other
+/// passes to find the impl they want without loading the ID (which
+/// means fewer edges in the incremental compilation graph).
+#[derive(Debug, HashStable_Generic)]
+pub struct ForeignItemRef {
+    pub id: ForeignItemId,
+    pub ident: Ident,
+    pub span: Span,
+}
+
+#[derive(Debug, HashStable_Generic)]
+pub struct ForeignItem<'hir> {
+    pub ident: Ident,
+    pub kind: ForeignItemKind<'hir>,
+    pub def_id: LocalDefId,
+    pub span: Span,
+    pub vis_span: Span,
+}
+
+impl ForeignItem<'_> {
+    #[inline]
+    pub fn hir_id(&self) -> HirId {
+        // Items are always HIR owners.
+        HirId::make_owner(self.def_id)
+    }
+
+    pub fn foreign_item_id(&self) -> ForeignItemId {
+        ForeignItemId { def_id: self.def_id }
+    }
+}
+
+/// An item within an `extern` block.
+#[derive(Debug, HashStable_Generic)]
+pub enum ForeignItemKind<'hir> {
+    /// A foreign function.
+    Fn(&'hir FnDecl<'hir>, &'hir [Ident], &'hir Generics<'hir>),
+    /// A foreign static item (`static ext: u8`).
+    Static(&'hir Ty<'hir>, Mutability),
+    /// A foreign type.
+    Type,
+}
+
+/// A variable captured by a closure.
+#[derive(Debug, Copy, Clone, Encodable, HashStable_Generic)]
+pub struct Upvar {
+    // First span where it is accessed (there can be multiple).
+    pub span: Span,
+}
+
+// The TraitCandidate's import_ids is empty if the trait is defined in the same module, and
+// has length > 0 if the trait is found through an chain of imports, starting with the
+// import/use statement in the scope where the trait is used.
+#[derive(Encodable, Decodable, Clone, Debug, HashStable_Generic)]
+pub struct TraitCandidate {
+    pub def_id: DefId,
+    pub import_ids: SmallVec<[LocalDefId; 1]>,
+}
+
+#[derive(Copy, Clone, Debug, HashStable_Generic)]
+pub enum OwnerNode<'hir> {
+    Item(&'hir Item<'hir>),
+    ForeignItem(&'hir ForeignItem<'hir>),
+    TraitItem(&'hir TraitItem<'hir>),
+    ImplItem(&'hir ImplItem<'hir>),
+    Crate(&'hir Mod<'hir>),
+}
+
+impl<'hir> OwnerNode<'hir> {
+    pub fn ident(&self) -> Option<Ident> {
+        match self {
+            OwnerNode::Item(Item { ident, .. })
+            | OwnerNode::ForeignItem(ForeignItem { ident, .. })
+            | OwnerNode::ImplItem(ImplItem { ident, .. })
+            | OwnerNode::TraitItem(TraitItem { ident, .. }) => Some(*ident),
+            OwnerNode::Crate(..) => None,
+        }
+    }
+
+    pub fn span(&self) -> Span {
+        match self {
+            OwnerNode::Item(Item { span, .. })
+            | OwnerNode::ForeignItem(ForeignItem { span, .. })
+            | OwnerNode::ImplItem(ImplItem { span, .. })
+            | OwnerNode::TraitItem(TraitItem { span, .. }) => *span,
+            OwnerNode::Crate(Mod { spans: ModSpans { inner_span, .. }, .. }) => *inner_span,
+        }
+    }
+
+    pub fn fn_decl(&self) -> Option<&FnDecl<'hir>> {
+        match self {
+            OwnerNode::TraitItem(TraitItem { kind: TraitItemKind::Fn(fn_sig, _), .. })
+            | OwnerNode::ImplItem(ImplItem { kind: ImplItemKind::Fn(fn_sig, _), .. })
+            | OwnerNode::Item(Item { kind: ItemKind::Fn(fn_sig, _, _), .. }) => Some(fn_sig.decl),
+            OwnerNode::ForeignItem(ForeignItem {
+                kind: ForeignItemKind::Fn(fn_decl, _, _),
+                ..
+            }) => Some(fn_decl),
+            _ => None,
+        }
+    }
+
+    pub fn body_id(&self) -> Option<BodyId> {
+        match self {
+            OwnerNode::TraitItem(TraitItem {
+                kind: TraitItemKind::Fn(_, TraitFn::Provided(body_id)),
+                ..
+            })
+            | OwnerNode::ImplItem(ImplItem { kind: ImplItemKind::Fn(_, body_id), .. })
+            | OwnerNode::Item(Item { kind: ItemKind::Fn(.., body_id), .. }) => Some(*body_id),
+            _ => None,
+        }
+    }
+
+    pub fn generics(self) -> Option<&'hir Generics<'hir>> {
+        Node::generics(self.into())
+    }
+
+    pub fn def_id(self) -> LocalDefId {
+        match self {
+            OwnerNode::Item(Item { def_id, .. })
+            | OwnerNode::TraitItem(TraitItem { def_id, .. })
+            | OwnerNode::ImplItem(ImplItem { def_id, .. })
+            | OwnerNode::ForeignItem(ForeignItem { def_id, .. }) => *def_id,
+            OwnerNode::Crate(..) => crate::CRATE_HIR_ID.owner,
+        }
+    }
+
+    pub fn expect_item(self) -> &'hir Item<'hir> {
+        match self {
+            OwnerNode::Item(n) => n,
+            _ => panic!(),
+        }
+    }
+
+    pub fn expect_foreign_item(self) -> &'hir ForeignItem<'hir> {
+        match self {
+            OwnerNode::ForeignItem(n) => n,
+            _ => panic!(),
+        }
+    }
+
+    pub fn expect_impl_item(self) -> &'hir ImplItem<'hir> {
+        match self {
+            OwnerNode::ImplItem(n) => n,
+            _ => panic!(),
+        }
+    }
+
+    pub fn expect_trait_item(self) -> &'hir TraitItem<'hir> {
+        match self {
+            OwnerNode::TraitItem(n) => n,
+            _ => panic!(),
+        }
+    }
+}
+
+impl<'hir> Into<OwnerNode<'hir>> for &'hir Item<'hir> {
+    fn into(self) -> OwnerNode<'hir> {
+        OwnerNode::Item(self)
+    }
+}
+
+impl<'hir> Into<OwnerNode<'hir>> for &'hir ForeignItem<'hir> {
+    fn into(self) -> OwnerNode<'hir> {
+        OwnerNode::ForeignItem(self)
+    }
+}
+
+impl<'hir> Into<OwnerNode<'hir>> for &'hir ImplItem<'hir> {
+    fn into(self) -> OwnerNode<'hir> {
+        OwnerNode::ImplItem(self)
+    }
+}
+
+impl<'hir> Into<OwnerNode<'hir>> for &'hir TraitItem<'hir> {
+    fn into(self) -> OwnerNode<'hir> {
+        OwnerNode::TraitItem(self)
+    }
+}
+
+impl<'hir> Into<Node<'hir>> for OwnerNode<'hir> {
+    fn into(self) -> Node<'hir> {
+        match self {
+            OwnerNode::Item(n) => Node::Item(n),
+            OwnerNode::ForeignItem(n) => Node::ForeignItem(n),
+            OwnerNode::ImplItem(n) => Node::ImplItem(n),
+            OwnerNode::TraitItem(n) => Node::TraitItem(n),
+            OwnerNode::Crate(n) => Node::Crate(n),
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, HashStable_Generic)]
+pub enum Node<'hir> {
+    Param(&'hir Param<'hir>),
+    Item(&'hir Item<'hir>),
+    ForeignItem(&'hir ForeignItem<'hir>),
+    TraitItem(&'hir TraitItem<'hir>),
+    ImplItem(&'hir ImplItem<'hir>),
+    Variant(&'hir Variant<'hir>),
+    Field(&'hir FieldDef<'hir>),
+    AnonConst(&'hir AnonConst),
+    Expr(&'hir Expr<'hir>),
+    Stmt(&'hir Stmt<'hir>),
+    PathSegment(&'hir PathSegment<'hir>),
+    Ty(&'hir Ty<'hir>),
+    TypeBinding(&'hir TypeBinding<'hir>),
+    TraitRef(&'hir TraitRef<'hir>),
+    Pat(&'hir Pat<'hir>),
+    Arm(&'hir Arm<'hir>),
+    Block(&'hir Block<'hir>),
+    Local(&'hir Local<'hir>),
+
+    /// `Ctor` refers to the constructor of an enum variant or struct. Only tuple or unit variants
+    /// with synthesized constructors.
+    Ctor(&'hir VariantData<'hir>),
+
+    Lifetime(&'hir Lifetime),
+    GenericParam(&'hir GenericParam<'hir>),
+
+    Crate(&'hir Mod<'hir>),
+
+    Infer(&'hir InferArg),
+}
+
+impl<'hir> Node<'hir> {
+    /// Get the identifier of this `Node`, if applicable.
+    ///
+    /// # Edge cases
+    ///
+    /// Calling `.ident()` on a [`Node::Ctor`] will return `None`
+    /// because `Ctor`s do not have identifiers themselves.
+    /// Instead, call `.ident()` on the parent struct/variant, like so:
+    ///
+    /// ```ignore (illustrative)
+    /// ctor
+    ///     .ctor_hir_id()
+    ///     .and_then(|ctor_id| tcx.hir().find(tcx.hir().get_parent_node(ctor_id)))
+    ///     .and_then(|parent| parent.ident())
+    /// ```
+    pub fn ident(&self) -> Option<Ident> {
+        match self {
+            Node::TraitItem(TraitItem { ident, .. })
+            | Node::ImplItem(ImplItem { ident, .. })
+            | Node::ForeignItem(ForeignItem { ident, .. })
+            | Node::Field(FieldDef { ident, .. })
+            | Node::Variant(Variant { ident, .. })
+            | Node::Item(Item { ident, .. })
+            | Node::PathSegment(PathSegment { ident, .. }) => Some(*ident),
+            Node::Lifetime(lt) => Some(lt.name.ident()),
+            Node::GenericParam(p) => Some(p.name.ident()),
+            Node::TypeBinding(b) => Some(b.ident),
+            Node::Param(..)
+            | Node::AnonConst(..)
+            | Node::Expr(..)
+            | Node::Stmt(..)
+            | Node::Block(..)
+            | Node::Ctor(..)
+            | Node::Pat(..)
+            | Node::Arm(..)
+            | Node::Local(..)
+            | Node::Crate(..)
+            | Node::Ty(..)
+            | Node::TraitRef(..)
+            | Node::Infer(..) => None,
+        }
+    }
+
+    pub fn fn_decl(&self) -> Option<&'hir FnDecl<'hir>> {
+        match self {
+            Node::TraitItem(TraitItem { kind: TraitItemKind::Fn(fn_sig, _), .. })
+            | Node::ImplItem(ImplItem { kind: ImplItemKind::Fn(fn_sig, _), .. })
+            | Node::Item(Item { kind: ItemKind::Fn(fn_sig, _, _), .. }) => Some(fn_sig.decl),
+            Node::ForeignItem(ForeignItem { kind: ForeignItemKind::Fn(fn_decl, _, _), .. }) => {
+                Some(fn_decl)
+            }
+            _ => None,
+        }
+    }
+
+    pub fn fn_sig(&self) -> Option<&'hir FnSig<'hir>> {
+        match self {
+            Node::TraitItem(TraitItem { kind: TraitItemKind::Fn(fn_sig, _), .. })
+            | Node::ImplItem(ImplItem { kind: ImplItemKind::Fn(fn_sig, _), .. })
+            | Node::Item(Item { kind: ItemKind::Fn(fn_sig, _, _), .. }) => Some(fn_sig),
+            _ => None,
+        }
+    }
+
+    pub fn body_id(&self) -> Option<BodyId> {
+        match self {
+            Node::TraitItem(TraitItem {
+                kind: TraitItemKind::Fn(_, TraitFn::Provided(body_id)),
+                ..
+            })
+            | Node::ImplItem(ImplItem { kind: ImplItemKind::Fn(_, body_id), .. })
+            | Node::Item(Item { kind: ItemKind::Fn(.., body_id), .. }) => Some(*body_id),
+            _ => None,
+        }
+    }
+
+    pub fn generics(self) -> Option<&'hir Generics<'hir>> {
+        match self {
+            Node::ForeignItem(ForeignItem {
+                kind: ForeignItemKind::Fn(_, _, generics), ..
+            })
+            | Node::TraitItem(TraitItem { generics, .. })
+            | Node::ImplItem(ImplItem { generics, .. }) => Some(generics),
+            Node::Item(item) => item.kind.generics(),
+            _ => None,
+        }
+    }
+
+    pub fn as_owner(self) -> Option<OwnerNode<'hir>> {
+        match self {
+            Node::Item(i) => Some(OwnerNode::Item(i)),
+            Node::ForeignItem(i) => Some(OwnerNode::ForeignItem(i)),
+            Node::TraitItem(i) => Some(OwnerNode::TraitItem(i)),
+            Node::ImplItem(i) => Some(OwnerNode::ImplItem(i)),
+            Node::Crate(i) => Some(OwnerNode::Crate(i)),
+            _ => None,
+        }
+    }
+
+    pub fn fn_kind(self) -> Option<FnKind<'hir>> {
+        match self {
+            Node::Item(i) => match i.kind {
+                ItemKind::Fn(ref sig, ref generics, _) => {
+                    Some(FnKind::ItemFn(i.ident, generics, sig.header))
+                }
+                _ => None,
+            },
+            Node::TraitItem(ti) => match ti.kind {
+                TraitItemKind::Fn(ref sig, TraitFn::Provided(_)) => {
+                    Some(FnKind::Method(ti.ident, sig))
+                }
+                _ => None,
+            },
+            Node::ImplItem(ii) => match ii.kind {
+                ImplItemKind::Fn(ref sig, _) => Some(FnKind::Method(ii.ident, sig)),
+                _ => None,
+            },
+            Node::Expr(e) => match e.kind {
+                ExprKind::Closure { .. } => Some(FnKind::Closure),
+                _ => None,
+            },
+            _ => None,
+        }
+    }
+
+    /// Get the fields for the tuple-constructor,
+    /// if this node is a tuple constructor, otherwise None
+    pub fn tuple_fields(&self) -> Option<&'hir [FieldDef<'hir>]> {
+        if let Node::Ctor(&VariantData::Tuple(fields, _)) = self { Some(fields) } else { None }
+    }
+}
+
+// Some nodes are used a lot. Make sure they don't unintentionally get bigger.
+#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
+mod size_asserts {
+    use super::*;
+    // These are in alphabetical order, which is easy to maintain.
+    rustc_data_structures::static_assert_size!(Block<'static>, 48);
+    rustc_data_structures::static_assert_size!(Expr<'static>, 56);
+    rustc_data_structures::static_assert_size!(ForeignItem<'static>, 72);
+    rustc_data_structures::static_assert_size!(GenericBound<'_>, 48);
+    rustc_data_structures::static_assert_size!(Generics<'static>, 56);
+    rustc_data_structures::static_assert_size!(ImplItem<'static>, 88);
+    rustc_data_structures::static_assert_size!(Impl<'static>, 80);
+    rustc_data_structures::static_assert_size!(Item<'static>, 80);
+    rustc_data_structures::static_assert_size!(Pat<'static>, 88);
+    rustc_data_structures::static_assert_size!(QPath<'static>, 24);
+    rustc_data_structures::static_assert_size!(TraitItem<'static>, 96);
+    rustc_data_structures::static_assert_size!(Ty<'static>, 72);
+}
diff --git a/compiler/rustc_hir/src/hir_id.rs b/compiler/rustc_hir/src/hir_id.rs
new file mode 100644
index 000000000..346ac9e96
--- /dev/null
+++ b/compiler/rustc_hir/src/hir_id.rs
@@ -0,0 +1,89 @@
+use crate::def_id::{LocalDefId, CRATE_DEF_ID};
+use std::fmt;
+
+/// Uniquely identifies a node in the HIR of the current crate. It is
+/// composed of the `owner`, which is the `LocalDefId` of the directly enclosing
+/// `hir::Item`, `hir::TraitItem`, or `hir::ImplItem` (i.e., the closest "item-like"),
+/// and the `local_id` which is unique within the given owner.
+///
+/// This two-level structure makes for more stable values: One can move an item
+/// around within the source code, or add or remove stuff before it, without
+/// the `local_id` part of the `HirId` changing, which is a very useful property in
+/// incremental compilation where we have to persist things through changes to
+/// the code base.
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(Encodable, Decodable, HashStable_Generic)]
+#[rustc_pass_by_value]
+pub struct HirId {
+    pub owner: LocalDefId,
+    pub local_id: ItemLocalId,
+}
+
+impl HirId {
+    #[inline]
+    pub fn expect_owner(self) -> LocalDefId {
+        assert_eq!(self.local_id.index(), 0);
+        self.owner
+    }
+
+    #[inline]
+    pub fn as_owner(self) -> Option<LocalDefId> {
+        if self.local_id.index() == 0 { Some(self.owner) } else { None }
+    }
+
+    #[inline]
+    pub fn is_owner(self) -> bool {
+        self.local_id.index() == 0
+    }
+
+    #[inline]
+    pub fn make_owner(owner: LocalDefId) -> Self {
+        Self { owner, local_id: ItemLocalId::from_u32(0) }
+    }
+
+    pub fn index(self) -> (usize, usize) {
+        (rustc_index::vec::Idx::index(self.owner), rustc_index::vec::Idx::index(self.local_id))
+    }
+}
+
+impl fmt::Display for HirId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:?}", self)
+    }
+}
+
+impl Ord for HirId {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        (self.index()).cmp(&(other.index()))
+    }
+}
+
+impl PartialOrd for HirId {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(&other))
+    }
+}
+
+rustc_data_structures::define_id_collections!(HirIdMap, HirIdSet, HirId);
+rustc_data_structures::define_id_collections!(ItemLocalMap, ItemLocalSet, ItemLocalId);
+
+rustc_index::newtype_index! {
+    /// An `ItemLocalId` uniquely identifies something within a given "item-like";
+    /// that is, within a `hir::Item`, `hir::TraitItem`, or `hir::ImplItem`. There is no
+    /// guarantee that the numerical value of a given `ItemLocalId` corresponds to
+    /// the node's position within the owning item in any way, but there is a
+    /// guarantee that the `LocalItemId`s within an owner occupy a dense range of
+    /// integers starting at zero, so a mapping that maps all or most nodes within
+    /// an "item-like" to something else can be implemented by a `Vec` instead of a
+    /// tree or hash map.
+    #[derive(HashStable_Generic)]
+    pub struct ItemLocalId { .. }
+}
+
+impl ItemLocalId {
+    /// Signal local id which should never be used.
+    pub const INVALID: ItemLocalId = ItemLocalId::MAX;
+}
+
+/// The `HirId` corresponding to `CRATE_NODE_ID` and `CRATE_DEF_ID`.
+pub const CRATE_HIR_ID: HirId = HirId { owner: CRATE_DEF_ID, local_id: ItemLocalId::from_u32(0) };
diff --git a/compiler/rustc_hir/src/intravisit.rs b/compiler/rustc_hir/src/intravisit.rs
new file mode 100644
index 000000000..e676acebe
--- /dev/null
+++ b/compiler/rustc_hir/src/intravisit.rs
@@ -0,0 +1,1232 @@
+//! HIR walker for walking the contents of nodes.
+//!
+//! Here are the three available patterns for the visitor strategy,
+//! in roughly the order of desirability:
+//!
+//! 1. **Shallow visit**: Get a simple callback for every item (or item-like thing) in the HIR.
+//!    - Example: find all items with a `#[foo]` attribute on them.
+//!    - How: Use the `hir_crate_items` or `hir_module_items` query to traverse over item-like ids
+//!       (ItemId, TraitItemId, etc.) and use tcx.def_kind and `tcx.hir().item*(id)` to filter and
+//!       access actual item-like thing, respectively.
+//!    - Pro: Efficient; just walks the lists of item ids and gives users control whether to access
+//!       the hir_owners themselves or not.
+//!    - Con: Don't get information about nesting
+//!    - Con: Don't have methods for specific bits of HIR, like "on
+//!      every expr, do this".
+//! 2. **Deep visit**: Want to scan for specific kinds of HIR nodes within
+//!    an item, but don't care about how item-like things are nested
+//!    within one another.
+//!    - Example: Examine each expression to look for its type and do some check or other.
+//!    - How: Implement `intravisit::Visitor` and override the `NestedFilter` type to
+//!      `nested_filter::OnlyBodies` (and implement `nested_visit_map`), and use
+//!      `tcx.hir().visit_all_item_likes_in_crate(&mut visitor)`. Within your
+//!      `intravisit::Visitor` impl, implement methods like `visit_expr()` (don't forget to invoke
+//!      `intravisit::walk_expr()` to keep walking the subparts).
+//!    - Pro: Visitor methods for any kind of HIR node, not just item-like things.
+//!    - Pro: Integrates well into dependency tracking.
+//!    - Con: Don't get information about nesting between items
+//! 3. **Nested visit**: Want to visit the whole HIR and you care about the nesting between
+//!    item-like things.
+//!    - Example: Lifetime resolution, which wants to bring lifetimes declared on the
+//!      impl into scope while visiting the impl-items, and then back out again.
+//!    - How: Implement `intravisit::Visitor` and override the `NestedFilter` type to
+//!      `nested_filter::All` (and implement `nested_visit_map`). Walk your crate with
+//!      `tcx.hir().walk_toplevel_module(visitor)` invoked on `tcx.hir().krate()`.
+//!    - Pro: Visitor methods for any kind of HIR node, not just item-like things.
+//!    - Pro: Preserves nesting information
+//!    - Con: Does not integrate well into dependency tracking.
+//!
+//! If you have decided to use this visitor, here are some general
+//! notes on how to do so:
+//!
+//! Each overridden visit method has full control over what
+//! happens with its node, it can do its own traversal of the node's children,
+//! call `intravisit::walk_*` to apply the default traversal algorithm, or prevent
+//! deeper traversal by doing nothing.
+//!
+//! When visiting the HIR, the contents of nested items are NOT visited
+//! by default. This is different from the AST visitor, which does a deep walk.
+//! Hence this module is called `intravisit`; see the method `visit_nested_item`
+//! for more details.
+//!
+//! Note: it is an important invariant that the default visitor walks
+//! the body of a function in "execution order" - more concretely, if
+//! we consider the reverse post-order (RPO) of the CFG implied by the HIR,
+//! then a pre-order traversal of the HIR is consistent with the CFG RPO
+//! on the *initial CFG point* of each HIR node, while a post-order traversal
+//! of the HIR is consistent with the CFG RPO on each *final CFG point* of
+//! each CFG node.
+//!
+//! One thing that follows is that if HIR node A always starts/ends executing
+//! before HIR node B, then A appears in traversal pre/postorder before B,
+//! respectively. (This follows from RPO respecting CFG domination).
+//!
+//! This order consistency is required in a few places in rustc, for
+//! example generator inference, and possibly also HIR borrowck.
+
+use crate::hir::*;
+use rustc_ast::walk_list;
+use rustc_ast::{Attribute, Label};
+use rustc_span::symbol::{Ident, Symbol};
+use rustc_span::Span;
+
+pub trait IntoVisitor<'hir> {
+    type Visitor: Visitor<'hir>;
+    fn into_visitor(&self) -> Self::Visitor;
+}
+
+#[derive(Copy, Clone, Debug)]
+pub enum FnKind<'a> {
+    /// `#[xxx] pub async/const/extern "Abi" fn foo()`
+    ItemFn(Ident, &'a Generics<'a>, FnHeader),
+
+    /// `fn foo(&self)`
+    Method(Ident, &'a FnSig<'a>),
+
+    /// `|x, y| {}`
+    Closure,
+}
+
+impl<'a> FnKind<'a> {
+    pub fn header(&self) -> Option<&FnHeader> {
+        match *self {
+            FnKind::ItemFn(_, _, ref header) => Some(header),
+            FnKind::Method(_, ref sig) => Some(&sig.header),
+            FnKind::Closure => None,
+        }
+    }
+
+    pub fn constness(self) -> Constness {
+        self.header().map_or(Constness::NotConst, |header| header.constness)
+    }
+
+    pub fn asyncness(self) -> IsAsync {
+        self.header().map_or(IsAsync::NotAsync, |header| header.asyncness)
+    }
+}
+
+/// An abstract representation of the HIR `rustc_middle::hir::map::Map`.
+pub trait Map<'hir> {
+    /// Retrieves the `Node` corresponding to `id`, returning `None` if cannot be found.
+    fn find(&self, hir_id: HirId) -> Option<Node<'hir>>;
+    fn body(&self, id: BodyId) -> &'hir Body<'hir>;
+    fn item(&self, id: ItemId) -> &'hir Item<'hir>;
+    fn trait_item(&self, id: TraitItemId) -> &'hir TraitItem<'hir>;
+    fn impl_item(&self, id: ImplItemId) -> &'hir ImplItem<'hir>;
+    fn foreign_item(&self, id: ForeignItemId) -> &'hir ForeignItem<'hir>;
+}
+
+// Used when no map is actually available, forcing manual implementation of nested visitors.
+impl<'hir> Map<'hir> for ! {
+    fn find(&self, _: HirId) -> Option<Node<'hir>> {
+        *self;
+    }
+    fn body(&self, _: BodyId) -> &'hir Body<'hir> {
+        *self;
+    }
+    fn item(&self, _: ItemId) -> &'hir Item<'hir> {
+        *self;
+    }
+    fn trait_item(&self, _: TraitItemId) -> &'hir TraitItem<'hir> {
+        *self;
+    }
+    fn impl_item(&self, _: ImplItemId) -> &'hir ImplItem<'hir> {
+        *self;
+    }
+    fn foreign_item(&self, _: ForeignItemId) -> &'hir ForeignItem<'hir> {
+        *self;
+    }
+}
+
+pub mod nested_filter {
+    use super::Map;
+
+    /// Specifies what nested things a visitor wants to visit. By "nested
+    /// things", we are referring to bits of HIR that are not directly embedded
+    /// within one another but rather indirectly, through a table in the crate.
+    /// This is done to control dependencies during incremental compilation: the
+    /// non-inline bits of HIR can be tracked and hashed separately.
+    ///
+    /// The most common choice is `OnlyBodies`, which will cause the visitor to
+    /// visit fn bodies for fns that it encounters, and closure bodies, but
+    /// skip over nested item-like things.
+    ///
+    /// See the comments on `ItemLikeVisitor` for more details on the overall
+    /// visit strategy.
+    pub trait NestedFilter<'hir> {
+        type Map: Map<'hir>;
+
+        /// Whether the visitor visits nested "item-like" things.
+        /// E.g., item, impl-item.
+        const INTER: bool;
+        /// Whether the visitor visits "intra item-like" things.
+        /// E.g., function body, closure, `AnonConst`
+        const INTRA: bool;
+    }
+
+    /// Do not visit any nested things. When you add a new
+    /// "non-nested" thing, you will want to audit such uses to see if
+    /// they remain valid.
+    ///
+    /// Use this if you are only walking some particular kind of tree
+    /// (i.e., a type, or fn signature) and you don't want to thread a
+    /// HIR map around.
+    pub struct None(());
+    impl NestedFilter<'_> for None {
+        type Map = !;
+        const INTER: bool = false;
+        const INTRA: bool = false;
+    }
+}
+
+use nested_filter::NestedFilter;
+
+/// Each method of the Visitor trait is a hook to be potentially
+/// overridden. Each method's default implementation recursively visits
+/// the substructure of the input via the corresponding `walk` method;
+/// e.g., the `visit_mod` method by default calls `intravisit::walk_mod`.
+///
+/// Note that this visitor does NOT visit nested items by default
+/// (this is why the module is called `intravisit`, to distinguish it
+/// from the AST's `visit` module, which acts differently). If you
+/// simply want to visit all items in the crate in some order, you
+/// should call `tcx.hir().visit_all_item_likes_in_crate`. Otherwise, see the comment
+/// on `visit_nested_item` for details on how to visit nested items.
+///
+/// If you want to ensure that your code handles every variant
+/// explicitly, you need to override each method. (And you also need
+/// to monitor future changes to `Visitor` in case a new method with a
+/// new default implementation gets introduced.)
+pub trait Visitor<'v>: Sized {
+    // this type should not be overridden, it exists for convenient usage as `Self::Map`
+    type Map: Map<'v> = <Self::NestedFilter as NestedFilter<'v>>::Map;
+
+    ///////////////////////////////////////////////////////////////////////////
+    // Nested items.
+
+    /// Override this type to control which nested HIR are visited; see
+    /// [`NestedFilter`] for details. If you override this type, you
+    /// must also override [`nested_visit_map`](Self::nested_visit_map).
+    ///
+    /// **If for some reason you want the nested behavior, but don't
+    /// have a `Map` at your disposal:** then override the
+    /// `visit_nested_XXX` methods. If a new `visit_nested_XXX` variant is
+    /// added in the future, it will cause a panic which can be detected
+    /// and fixed appropriately.
+    type NestedFilter: NestedFilter<'v> = nested_filter::None;
+
+    /// If `type NestedFilter` is set to visit nested items, this method
+    /// must also be overridden to provide a map to retrieve nested items.
+    fn nested_visit_map(&mut self) -> Self::Map {
+        panic!(
+            "nested_visit_map must be implemented or consider using \
+            `type NestedFilter = nested_filter::None` (the default)"
+        );
+    }
+
+    /// Invoked when a nested item is encountered. By default, when
+    /// `Self::NestedFilter` is `nested_filter::None`, this method does
+    /// nothing. **You probably don't want to override this method** --
+    /// instead, override [`Self::NestedFilter`] or use the "shallow" or
+    /// "deep" visit patterns described on
+    /// `itemlikevisit::ItemLikeVisitor`. The only reason to override
+    /// this method is if you want a nested pattern but cannot supply a
+    /// [`Map`]; see `nested_visit_map` for advice.
+    fn visit_nested_item(&mut self, id: ItemId) {
+        if Self::NestedFilter::INTER {
+            let item = self.nested_visit_map().item(id);
+            self.visit_item(item);
+        }
+    }
+
+    /// Like `visit_nested_item()`, but for trait items. See
+    /// `visit_nested_item()` for advice on when to override this
+    /// method.
+    fn visit_nested_trait_item(&mut self, id: TraitItemId) {
+        if Self::NestedFilter::INTER {
+            let item = self.nested_visit_map().trait_item(id);
+            self.visit_trait_item(item);
+        }
+    }
+
+    /// Like `visit_nested_item()`, but for impl items. See
+    /// `visit_nested_item()` for advice on when to override this
+    /// method.
+    fn visit_nested_impl_item(&mut self, id: ImplItemId) {
+        if Self::NestedFilter::INTER {
+            let item = self.nested_visit_map().impl_item(id);
+            self.visit_impl_item(item);
+        }
+    }
+
+    /// Like `visit_nested_item()`, but for foreign items. See
+    /// `visit_nested_item()` for advice on when to override this
+    /// method.
+    fn visit_nested_foreign_item(&mut self, id: ForeignItemId) {
+        if Self::NestedFilter::INTER {
+            let item = self.nested_visit_map().foreign_item(id);
+            self.visit_foreign_item(item);
+        }
+    }
+
+    /// Invoked to visit the body of a function, method or closure. Like
+    /// `visit_nested_item`, does nothing by default unless you override
+    /// `Self::NestedFilter`.
+    fn visit_nested_body(&mut self, id: BodyId) {
+        if Self::NestedFilter::INTRA {
+            let body = self.nested_visit_map().body(id);
+            self.visit_body(body);
+        }
+    }
+
+    fn visit_param(&mut self, param: &'v Param<'v>) {
+        walk_param(self, param)
+    }
+
+    /// Visits the top-level item and (optionally) nested items / impl items. See
+    /// `visit_nested_item` for details.
+    fn visit_item(&mut self, i: &'v Item<'v>) {
+        walk_item(self, i)
+    }
+
+    fn visit_body(&mut self, b: &'v Body<'v>) {
+        walk_body(self, b);
+    }
+
+    ///////////////////////////////////////////////////////////////////////////
+
+    fn visit_id(&mut self, _hir_id: HirId) {
+        // Nothing to do.
+    }
+    fn visit_name(&mut self, _span: Span, _name: Symbol) {
+        // Nothing to do.
+    }
+    fn visit_ident(&mut self, ident: Ident) {
+        walk_ident(self, ident)
+    }
+    fn visit_mod(&mut self, m: &'v Mod<'v>, _s: Span, n: HirId) {
+        walk_mod(self, m, n)
+    }
+    fn visit_foreign_item(&mut self, i: &'v ForeignItem<'v>) {
+        walk_foreign_item(self, i)
+    }
+    fn visit_local(&mut self, l: &'v Local<'v>) {
+        walk_local(self, l)
+    }
+    fn visit_block(&mut self, b: &'v Block<'v>) {
+        walk_block(self, b)
+    }
+    fn visit_stmt(&mut self, s: &'v Stmt<'v>) {
+        walk_stmt(self, s)
+    }
+    fn visit_arm(&mut self, a: &'v Arm<'v>) {
+        walk_arm(self, a)
+    }
+    fn visit_pat(&mut self, p: &'v Pat<'v>) {
+        walk_pat(self, p)
+    }
+    fn visit_array_length(&mut self, len: &'v ArrayLen) {
+        walk_array_len(self, len)
+    }
+    fn visit_anon_const(&mut self, c: &'v AnonConst) {
+        walk_anon_const(self, c)
+    }
+    fn visit_expr(&mut self, ex: &'v Expr<'v>) {
+        walk_expr(self, ex)
+    }
+    fn visit_let_expr(&mut self, lex: &'v Let<'v>) {
+        walk_let_expr(self, lex)
+    }
+    fn visit_ty(&mut self, t: &'v Ty<'v>) {
+        walk_ty(self, t)
+    }
+    fn visit_generic_param(&mut self, p: &'v GenericParam<'v>) {
+        walk_generic_param(self, p)
+    }
+    fn visit_const_param_default(&mut self, _param: HirId, ct: &'v AnonConst) {
+        walk_const_param_default(self, ct)
+    }
+    fn visit_generics(&mut self, g: &'v Generics<'v>) {
+        walk_generics(self, g)
+    }
+    fn visit_where_predicate(&mut self, predicate: &'v WherePredicate<'v>) {
+        walk_where_predicate(self, predicate)
+    }
+    fn visit_fn_decl(&mut self, fd: &'v FnDecl<'v>) {
+        walk_fn_decl(self, fd)
+    }
+    fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v FnDecl<'v>, b: BodyId, s: Span, id: HirId) {
+        walk_fn(self, fk, fd, b, s, id)
+    }
+    fn visit_use(&mut self, path: &'v Path<'v>, hir_id: HirId) {
+        walk_use(self, path, hir_id)
+    }
+    fn visit_trait_item(&mut self, ti: &'v TraitItem<'v>) {
+        walk_trait_item(self, ti)
+    }
+    fn visit_trait_item_ref(&mut self, ii: &'v TraitItemRef) {
+        walk_trait_item_ref(self, ii)
+    }
+    fn visit_impl_item(&mut self, ii: &'v ImplItem<'v>) {
+        walk_impl_item(self, ii)
+    }
+    fn visit_foreign_item_ref(&mut self, ii: &'v ForeignItemRef) {
+        walk_foreign_item_ref(self, ii)
+    }
+    fn visit_impl_item_ref(&mut self, ii: &'v ImplItemRef) {
+        walk_impl_item_ref(self, ii)
+    }
+    fn visit_trait_ref(&mut self, t: &'v TraitRef<'v>) {
+        walk_trait_ref(self, t)
+    }
+    fn visit_param_bound(&mut self, bounds: &'v GenericBound<'v>) {
+        walk_param_bound(self, bounds)
+    }
+    fn visit_poly_trait_ref(&mut self, t: &'v PolyTraitRef<'v>, m: TraitBoundModifier) {
+        walk_poly_trait_ref(self, t, m)
+    }
+    fn visit_variant_data(
+        &mut self,
+        s: &'v VariantData<'v>,
+        _: Symbol,
+        _: &'v Generics<'v>,
+        _parent_id: HirId,
+        _: Span,
+    ) {
+        walk_struct_def(self, s)
+    }
+    fn visit_field_def(&mut self, s: &'v FieldDef<'v>) {
+        walk_field_def(self, s)
+    }
+    fn visit_enum_def(
+        &mut self,
+        enum_definition: &'v EnumDef<'v>,
+        generics: &'v Generics<'v>,
+        item_id: HirId,
+        _: Span,
+    ) {
+        walk_enum_def(self, enum_definition, generics, item_id)
+    }
+    fn visit_variant(&mut self, v: &'v Variant<'v>, g: &'v Generics<'v>, item_id: HirId) {
+        walk_variant(self, v, g, item_id)
+    }
+    fn visit_label(&mut self, label: &'v Label) {
+        walk_label(self, label)
+    }
+    fn visit_infer(&mut self, inf: &'v InferArg) {
+        walk_inf(self, inf);
+    }
+    fn visit_generic_arg(&mut self, generic_arg: &'v GenericArg<'v>) {
+        match generic_arg {
+            GenericArg::Lifetime(lt) => self.visit_lifetime(lt),
+            GenericArg::Type(ty) => self.visit_ty(ty),
+            GenericArg::Const(ct) => self.visit_anon_const(&ct.value),
+            GenericArg::Infer(inf) => self.visit_infer(inf),
+        }
+    }
+    fn visit_lifetime(&mut self, lifetime: &'v Lifetime) {
+        walk_lifetime(self, lifetime)
+    }
+    fn visit_qpath(&mut self, qpath: &'v QPath<'v>, id: HirId, span: Span) {
+        walk_qpath(self, qpath, id, span)
+    }
+    fn visit_path(&mut self, path: &'v Path<'v>, _id: HirId) {
+        walk_path(self, path)
+    }
+    fn visit_path_segment(&mut self, path_span: Span, path_segment: &'v PathSegment<'v>) {
+        walk_path_segment(self, path_span, path_segment)
+    }
+    fn visit_generic_args(&mut self, path_span: Span, generic_args: &'v GenericArgs<'v>) {
+        walk_generic_args(self, path_span, generic_args)
+    }
+    fn visit_assoc_type_binding(&mut self, type_binding: &'v TypeBinding<'v>) {
+        walk_assoc_type_binding(self, type_binding)
+    }
+    fn visit_attribute(&mut self, _attr: &'v Attribute) {}
+    fn visit_associated_item_kind(&mut self, kind: &'v AssocItemKind) {
+        walk_associated_item_kind(self, kind);
+    }
+    fn visit_defaultness(&mut self, defaultness: &'v Defaultness) {
+        walk_defaultness(self, defaultness);
+    }
+    fn visit_inline_asm(&mut self, asm: &'v InlineAsm<'v>, id: HirId) {
+        walk_inline_asm(self, asm, id);
+    }
+}
+
+pub fn walk_mod<'v, V: Visitor<'v>>(visitor: &mut V, module: &'v Mod<'v>, mod_hir_id: HirId) {
+    visitor.visit_id(mod_hir_id);
+    for &item_id in module.item_ids {
+        visitor.visit_nested_item(item_id);
+    }
+}
+
+pub fn walk_body<'v, V: Visitor<'v>>(visitor: &mut V, body: &'v Body<'v>) {
+    walk_list!(visitor, visit_param, body.params);
+    visitor.visit_expr(&body.value);
+}
+
+pub fn walk_local<'v, V: Visitor<'v>>(visitor: &mut V, local: &'v Local<'v>) {
+    // Intentionally visiting the expr first - the initialization expr
+    // dominates the local's definition.
+    walk_list!(visitor, visit_expr, &local.init);
+    visitor.visit_id(local.hir_id);
+    visitor.visit_pat(&local.pat);
+    if let Some(els) = local.els {
+        visitor.visit_block(els);
+    }
+    walk_list!(visitor, visit_ty, &local.ty);
+}
+
+pub fn walk_ident<'v, V: Visitor<'v>>(visitor: &mut V, ident: Ident) {
+    visitor.visit_name(ident.span, ident.name);
+}
+
+pub fn walk_label<'v, V: Visitor<'v>>(visitor: &mut V, label: &'v Label) {
+    visitor.visit_ident(label.ident);
+}
+
+pub fn walk_lifetime<'v, V: Visitor<'v>>(visitor: &mut V, lifetime: &'v Lifetime) {
+    visitor.visit_id(lifetime.hir_id);
+    match lifetime.name {
+        LifetimeName::Param(_, ParamName::Plain(ident)) => {
+            visitor.visit_ident(ident);
+        }
+        LifetimeName::Param(_, ParamName::Fresh)
+        | LifetimeName::Param(_, ParamName::Error)
+        | LifetimeName::Static
+        | LifetimeName::Error
+        | LifetimeName::ImplicitObjectLifetimeDefault
+        | LifetimeName::Infer => {}
+    }
+}
+
+pub fn walk_poly_trait_ref<'v, V: Visitor<'v>>(
+    visitor: &mut V,
+    trait_ref: &'v PolyTraitRef<'v>,
+    _modifier: TraitBoundModifier,
+) {
+    walk_list!(visitor, visit_generic_param, trait_ref.bound_generic_params);
+    visitor.visit_trait_ref(&trait_ref.trait_ref);
+}
+
+pub fn walk_trait_ref<'v, V: Visitor<'v>>(visitor: &mut V, trait_ref: &'v TraitRef<'v>) {
+    visitor.visit_id(trait_ref.hir_ref_id);
+    visitor.visit_path(&trait_ref.path, trait_ref.hir_ref_id)
+}
+
+pub fn walk_param<'v, V: Visitor<'v>>(visitor: &mut V, param: &'v Param<'v>) {
+    visitor.visit_id(param.hir_id);
+    visitor.visit_pat(&param.pat);
+}
+
+pub fn walk_item<'v, V: Visitor<'v>>(visitor: &mut V, item: &'v Item<'v>) {
+    visitor.visit_ident(item.ident);
+    match item.kind {
+        ItemKind::ExternCrate(orig_name) => {
+            visitor.visit_id(item.hir_id());
+            if let Some(orig_name) = orig_name {
+                visitor.visit_name(item.span, orig_name);
+            }
+        }
+        ItemKind::Use(ref path, _) => {
+            visitor.visit_use(path, item.hir_id());
+        }
+        ItemKind::Static(ref typ, _, body) | ItemKind::Const(ref typ, body) => {
+            visitor.visit_id(item.hir_id());
+            visitor.visit_ty(typ);
+            visitor.visit_nested_body(body);
+        }
+        ItemKind::Fn(ref sig, ref generics, body_id) => visitor.visit_fn(
+            FnKind::ItemFn(item.ident, generics, sig.header),
+            &sig.decl,
+            body_id,
+            item.span,
+            item.hir_id(),
+        ),
+        ItemKind::Macro(..) => {
+            visitor.visit_id(item.hir_id());
+        }
+        ItemKind::Mod(ref module) => {
+            // `visit_mod()` takes care of visiting the `Item`'s `HirId`.
+            visitor.visit_mod(module, item.span, item.hir_id())
+        }
+        ItemKind::ForeignMod { abi: _, items } => {
+            visitor.visit_id(item.hir_id());
+            walk_list!(visitor, visit_foreign_item_ref, items);
+        }
+        ItemKind::GlobalAsm(asm) => {
+            visitor.visit_id(item.hir_id());
+            visitor.visit_inline_asm(asm, item.hir_id());
+        }
+        ItemKind::TyAlias(ref ty, ref generics) => {
+            visitor.visit_id(item.hir_id());
+            visitor.visit_ty(ty);
+            visitor.visit_generics(generics)
+        }
+        ItemKind::OpaqueTy(OpaqueTy { ref generics, bounds, .. }) => {
+            visitor.visit_id(item.hir_id());
+            walk_generics(visitor, generics);
+            walk_list!(visitor, visit_param_bound, bounds);
+        }
+        ItemKind::Enum(ref enum_definition, ref generics) => {
+            visitor.visit_generics(generics);
+            // `visit_enum_def()` takes care of visiting the `Item`'s `HirId`.
+            visitor.visit_enum_def(enum_definition, generics, item.hir_id(), item.span)
+        }
+        ItemKind::Impl(Impl {
+            unsafety: _,
+            defaultness: _,
+            polarity: _,
+            constness: _,
+            defaultness_span: _,
+            ref generics,
+            ref of_trait,
+            ref self_ty,
+            items,
+        }) => {
+            visitor.visit_id(item.hir_id());
+            visitor.visit_generics(generics);
+            walk_list!(visitor, visit_trait_ref, of_trait);
+            visitor.visit_ty(self_ty);
+            walk_list!(visitor, visit_impl_item_ref, *items);
+        }
+        ItemKind::Struct(ref struct_definition, ref generics)
+        | ItemKind::Union(ref struct_definition, ref generics) => {
+            visitor.visit_generics(generics);
+            visitor.visit_id(item.hir_id());
+            visitor.visit_variant_data(
+                struct_definition,
+                item.ident.name,
+                generics,
+                item.hir_id(),
+                item.span,
+            );
+        }
+        ItemKind::Trait(.., ref generics, bounds, trait_item_refs) => {
+            visitor.visit_id(item.hir_id());
+            visitor.visit_generics(generics);
+            walk_list!(visitor, visit_param_bound, bounds);
+            walk_list!(visitor, visit_trait_item_ref, trait_item_refs);
+        }
+        ItemKind::TraitAlias(ref generics, bounds) => {
+            visitor.visit_id(item.hir_id());
+            visitor.visit_generics(generics);
+            walk_list!(visitor, visit_param_bound, bounds);
+        }
+    }
+}
+
+pub fn walk_inline_asm<'v, V: Visitor<'v>>(visitor: &mut V, asm: &'v InlineAsm<'v>, id: HirId) {
+    for (op, op_sp) in asm.operands {
+        match op {
+            InlineAsmOperand::In { expr, .. } | InlineAsmOperand::InOut { expr, .. } => {
+                visitor.visit_expr(expr)
+            }
+            InlineAsmOperand::Out { expr, .. } => {
+                if let Some(expr) = expr {
+                    visitor.visit_expr(expr);
+                }
+            }
+            InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
+                visitor.visit_expr(in_expr);
+                if let Some(out_expr) = out_expr {
+                    visitor.visit_expr(out_expr);
+                }
+            }
+            InlineAsmOperand::Const { anon_const, .. }
+            | InlineAsmOperand::SymFn { anon_const, .. } => visitor.visit_anon_const(anon_const),
+            InlineAsmOperand::SymStatic { path, .. } => visitor.visit_qpath(path, id, *op_sp),
+        }
+    }
+}
+
+pub fn walk_use<'v, V: Visitor<'v>>(visitor: &mut V, path: &'v Path<'v>, hir_id: HirId) {
+    visitor.visit_id(hir_id);
+    visitor.visit_path(path, hir_id);
+}
+
+pub fn walk_enum_def<'v, V: Visitor<'v>>(
+    visitor: &mut V,
+    enum_definition: &'v EnumDef<'v>,
+    generics: &'v Generics<'v>,
+    item_id: HirId,
+) {
+    visitor.visit_id(item_id);
+    walk_list!(visitor, visit_variant, enum_definition.variants, generics, item_id);
+}
+
+pub fn walk_variant<'v, V: Visitor<'v>>(
+    visitor: &mut V,
+    variant: &'v Variant<'v>,
+    generics: &'v Generics<'v>,
+    parent_item_id: HirId,
+) {
+    visitor.visit_ident(variant.ident);
+    visitor.visit_id(variant.id);
+    visitor.visit_variant_data(
+        &variant.data,
+        variant.ident.name,
+        generics,
+        parent_item_id,
+        variant.span,
+    );
+    walk_list!(visitor, visit_anon_const, &variant.disr_expr);
+}
+
+pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty<'v>) {
+    visitor.visit_id(typ.hir_id);
+
+    match typ.kind {
+        TyKind::Slice(ref ty) => visitor.visit_ty(ty),
+        TyKind::Ptr(ref mutable_type) => visitor.visit_ty(&mutable_type.ty),
+        TyKind::Rptr(ref lifetime, ref mutable_type) => {
+            visitor.visit_lifetime(lifetime);
+            visitor.visit_ty(&mutable_type.ty)
+        }
+        TyKind::Never => {}
+        TyKind::Tup(tuple_element_types) => {
+            walk_list!(visitor, visit_ty, tuple_element_types);
+        }
+        TyKind::BareFn(ref function_declaration) => {
+            walk_list!(visitor, visit_generic_param, function_declaration.generic_params);
+            visitor.visit_fn_decl(&function_declaration.decl);
+        }
+        TyKind::Path(ref qpath) => {
+            visitor.visit_qpath(qpath, typ.hir_id, typ.span);
+        }
+        TyKind::OpaqueDef(item_id, lifetimes) => {
+            visitor.visit_nested_item(item_id);
+            walk_list!(visitor, visit_generic_arg, lifetimes);
+        }
+        TyKind::Array(ref ty, ref length) => {
+            visitor.visit_ty(ty);
+            visitor.visit_array_length(length)
+        }
+        TyKind::TraitObject(bounds, ref lifetime, _syntax) => {
+            for bound in bounds {
+                visitor.visit_poly_trait_ref(bound, TraitBoundModifier::None);
+            }
+            visitor.visit_lifetime(lifetime);
+        }
+        TyKind::Typeof(ref expression) => visitor.visit_anon_const(expression),
+        TyKind::Infer | TyKind::Err => {}
+    }
+}
+
+pub fn walk_inf<'v, V: Visitor<'v>>(visitor: &mut V, inf: &'v InferArg) {
+    visitor.visit_id(inf.hir_id);
+}
+
+pub fn walk_qpath<'v, V: Visitor<'v>>(
+    visitor: &mut V,
+    qpath: &'v QPath<'v>,
+    id: HirId,
+    span: Span,
+) {
+    match *qpath {
+        QPath::Resolved(ref maybe_qself, ref path) => {
+            walk_list!(visitor, visit_ty, maybe_qself);
+            visitor.visit_path(path, id)
+        }
+        QPath::TypeRelative(ref qself, ref segment) => {
+            visitor.visit_ty(qself);
+            visitor.visit_path_segment(span, segment);
+        }
+        QPath::LangItem(..) => {}
+    }
+}
+
+pub fn walk_path<'v, V: Visitor<'v>>(visitor: &mut V, path: &'v Path<'v>) {
+    for segment in path.segments {
+        visitor.visit_path_segment(path.span, segment);
+    }
+}
+
+pub fn walk_path_segment<'v, V: Visitor<'v>>(
+    visitor: &mut V,
+    path_span: Span,
+    segment: &'v PathSegment<'v>,
+) {
+    visitor.visit_ident(segment.ident);
+    walk_list!(visitor, visit_id, segment.hir_id);
+    if let Some(ref args) = segment.args {
+        visitor.visit_generic_args(path_span, args);
+    }
+}
+
+pub fn walk_generic_args<'v, V: Visitor<'v>>(
+    visitor: &mut V,
+    _path_span: Span,
+    generic_args: &'v GenericArgs<'v>,
+) {
+    walk_list!(visitor, visit_generic_arg, generic_args.args);
+    walk_list!(visitor, visit_assoc_type_binding, generic_args.bindings);
+}
+
+pub fn walk_assoc_type_binding<'v, V: Visitor<'v>>(
+    visitor: &mut V,
+    type_binding: &'v TypeBinding<'v>,
+) {
+    visitor.visit_id(type_binding.hir_id);
+    visitor.visit_ident(type_binding.ident);
+    visitor.visit_generic_args(type_binding.span, type_binding.gen_args);
+    match type_binding.kind {
+        TypeBindingKind::Equality { ref term } => match term {
+            Term::Ty(ref ty) => visitor.visit_ty(ty),
+            Term::Const(ref c) => visitor.visit_anon_const(c),
+        },
+        TypeBindingKind::Constraint { bounds } => walk_list!(visitor, visit_param_bound, bounds),
+    }
+}
+
+pub fn walk_pat<'v, V: Visitor<'v>>(visitor: &mut V, pattern: &'v Pat<'v>) {
+    visitor.visit_id(pattern.hir_id);
+    match pattern.kind {
+        PatKind::TupleStruct(ref qpath, children, _) => {
+            visitor.visit_qpath(qpath, pattern.hir_id, pattern.span);
+            walk_list!(visitor, visit_pat, children);
+        }
+        PatKind::Path(ref qpath) => {
+            visitor.visit_qpath(qpath, pattern.hir_id, pattern.span);
+        }
+        PatKind::Struct(ref qpath, fields, _) => {
+            visitor.visit_qpath(qpath, pattern.hir_id, pattern.span);
+            for field in fields {
+                visitor.visit_id(field.hir_id);
+                visitor.visit_ident(field.ident);
+                visitor.visit_pat(&field.pat)
+            }
+        }
+        PatKind::Or(pats) => walk_list!(visitor, visit_pat, pats),
+        PatKind::Tuple(tuple_elements, _) => {
+            walk_list!(visitor, visit_pat, tuple_elements);
+        }
+        PatKind::Box(ref subpattern) | PatKind::Ref(ref subpattern, _) => {
+            visitor.visit_pat(subpattern)
+        }
+        PatKind::Binding(_, _hir_id, ident, ref optional_subpattern) => {
+            visitor.visit_ident(ident);
+            walk_list!(visitor, visit_pat, optional_subpattern);
+        }
+        PatKind::Lit(ref expression) => visitor.visit_expr(expression),
+        PatKind::Range(ref lower_bound, ref upper_bound, _) => {
+            walk_list!(visitor, visit_expr, lower_bound);
+            walk_list!(visitor, visit_expr, upper_bound);
+        }
+        PatKind::Wild => (),
+        PatKind::Slice(prepatterns, ref slice_pattern, postpatterns) => {
+            walk_list!(visitor, visit_pat, prepatterns);
+            walk_list!(visitor, visit_pat, slice_pattern);
+            walk_list!(visitor, visit_pat, postpatterns);
+        }
+    }
+}
+
+pub fn walk_foreign_item<'v, V: Visitor<'v>>(visitor: &mut V, foreign_item: &'v ForeignItem<'v>) {
+    visitor.visit_id(foreign_item.hir_id());
+    visitor.visit_ident(foreign_item.ident);
+
+    match foreign_item.kind {
+        ForeignItemKind::Fn(ref function_declaration, param_names, ref generics) => {
+            visitor.visit_generics(generics);
+            visitor.visit_fn_decl(function_declaration);
+            for &param_name in param_names {
+                visitor.visit_ident(param_name);
+            }
+        }
+        ForeignItemKind::Static(ref typ, _) => visitor.visit_ty(typ),
+        ForeignItemKind::Type => (),
+    }
+}
+
+pub fn walk_param_bound<'v, V: Visitor<'v>>(visitor: &mut V, bound: &'v GenericBound<'v>) {
+    match *bound {
+        GenericBound::Trait(ref typ, modifier) => {
+            visitor.visit_poly_trait_ref(typ, modifier);
+        }
+        GenericBound::LangItemTrait(_, span, hir_id, args) => {
+            visitor.visit_id(hir_id);
+            visitor.visit_generic_args(span, args);
+        }
+        GenericBound::Outlives(ref lifetime) => visitor.visit_lifetime(lifetime),
+    }
+}
+
+pub fn walk_generic_param<'v, V: Visitor<'v>>(visitor: &mut V, param: &'v GenericParam<'v>) {
+    visitor.visit_id(param.hir_id);
+    match param.name {
+        ParamName::Plain(ident) => visitor.visit_ident(ident),
+        ParamName::Error | ParamName::Fresh => {}
+    }
+    match param.kind {
+        GenericParamKind::Lifetime { .. } => {}
+        GenericParamKind::Type { ref default, .. } => walk_list!(visitor, visit_ty, default),
+        GenericParamKind::Const { ref ty, ref default } => {
+            visitor.visit_ty(ty);
+            if let Some(ref default) = default {
+                visitor.visit_const_param_default(param.hir_id, default);
+            }
+        }
+    }
+}
+
+pub fn walk_const_param_default<'v, V: Visitor<'v>>(visitor: &mut V, ct: &'v AnonConst) {
+    visitor.visit_anon_const(ct)
+}
+
+pub fn walk_generics<'v, V: Visitor<'v>>(visitor: &mut V, generics: &'v Generics<'v>) {
+    walk_list!(visitor, visit_generic_param, generics.params);
+    walk_list!(visitor, visit_where_predicate, generics.predicates);
+}
+
+pub fn walk_where_predicate<'v, V: Visitor<'v>>(
+    visitor: &mut V,
+    predicate: &'v WherePredicate<'v>,
+) {
+    match *predicate {
+        WherePredicate::BoundPredicate(WhereBoundPredicate {
+            ref bounded_ty,
+            bounds,
+            bound_generic_params,
+            ..
+        }) => {
+            visitor.visit_ty(bounded_ty);
+            walk_list!(visitor, visit_param_bound, bounds);
+            walk_list!(visitor, visit_generic_param, bound_generic_params);
+        }
+        WherePredicate::RegionPredicate(WhereRegionPredicate { ref lifetime, bounds, .. }) => {
+            visitor.visit_lifetime(lifetime);
+            walk_list!(visitor, visit_param_bound, bounds);
+        }
+        WherePredicate::EqPredicate(WhereEqPredicate {
+            hir_id, ref lhs_ty, ref rhs_ty, ..
+        }) => {
+            visitor.visit_id(hir_id);
+            visitor.visit_ty(lhs_ty);
+            visitor.visit_ty(rhs_ty);
+        }
+    }
+}
+
+pub fn walk_fn_ret_ty<'v, V: Visitor<'v>>(visitor: &mut V, ret_ty: &'v FnRetTy<'v>) {
+    if let FnRetTy::Return(ref output_ty) = *ret_ty {
+        visitor.visit_ty(output_ty)
+    }
+}
+
+pub fn walk_fn_decl<'v, V: Visitor<'v>>(visitor: &mut V, function_declaration: &'v FnDecl<'v>) {
+    for ty in function_declaration.inputs {
+        visitor.visit_ty(ty)
+    }
+    walk_fn_ret_ty(visitor, &function_declaration.output)
+}
+
+pub fn walk_fn_kind<'v, V: Visitor<'v>>(visitor: &mut V, function_kind: FnKind<'v>) {
+    match function_kind {
+        FnKind::ItemFn(_, generics, ..) => {
+            visitor.visit_generics(generics);
+        }
+        FnKind::Closure | FnKind::Method(..) => {}
+    }
+}
+
+pub fn walk_fn<'v, V: Visitor<'v>>(
+    visitor: &mut V,
+    function_kind: FnKind<'v>,
+    function_declaration: &'v FnDecl<'v>,
+    body_id: BodyId,
+    _span: Span,
+    id: HirId,
+) {
+    visitor.visit_id(id);
+    visitor.visit_fn_decl(function_declaration);
+    walk_fn_kind(visitor, function_kind);
+    visitor.visit_nested_body(body_id)
+}
+
+pub fn walk_trait_item<'v, V: Visitor<'v>>(visitor: &mut V, trait_item: &'v TraitItem<'v>) {
+    // N.B., deliberately force a compilation error if/when new fields are added.
+    let TraitItem { ident, generics, ref defaultness, ref kind, span, def_id: _ } = *trait_item;
+    let hir_id = trait_item.hir_id();
+    visitor.visit_ident(ident);
+    visitor.visit_generics(&generics);
+    visitor.visit_defaultness(&defaultness);
+    match *kind {
+        TraitItemKind::Const(ref ty, default) => {
+            visitor.visit_id(hir_id);
+            visitor.visit_ty(ty);
+            walk_list!(visitor, visit_nested_body, default);
+        }
+        TraitItemKind::Fn(ref sig, TraitFn::Required(param_names)) => {
+            visitor.visit_id(hir_id);
+            visitor.visit_fn_decl(&sig.decl);
+            for &param_name in param_names {
+                visitor.visit_ident(param_name);
+            }
+        }
+        TraitItemKind::Fn(ref sig, TraitFn::Provided(body_id)) => {
+            visitor.visit_fn(FnKind::Method(ident, sig), &sig.decl, body_id, span, hir_id);
+        }
+        TraitItemKind::Type(bounds, ref default) => {
+            visitor.visit_id(hir_id);
+            walk_list!(visitor, visit_param_bound, bounds);
+            walk_list!(visitor, visit_ty, default);
+        }
+    }
+}
+
+pub fn walk_trait_item_ref<'v, V: Visitor<'v>>(visitor: &mut V, trait_item_ref: &'v TraitItemRef) {
+    // N.B., deliberately force a compilation error if/when new fields are added.
+    let TraitItemRef { id, ident, ref kind, span: _ } = *trait_item_ref;
+    visitor.visit_nested_trait_item(id);
+    visitor.visit_ident(ident);
+    visitor.visit_associated_item_kind(kind);
+}
+
+pub fn walk_impl_item<'v, V: Visitor<'v>>(visitor: &mut V, impl_item: &'v ImplItem<'v>) {
+    // N.B., deliberately force a compilation error if/when new fields are added.
+    let ImplItem {
+        def_id: _,
+        ident,
+        ref generics,
+        ref kind,
+        ref defaultness,
+        span: _,
+        vis_span: _,
+    } = *impl_item;
+
+    visitor.visit_ident(ident);
+    visitor.visit_generics(generics);
+    visitor.visit_defaultness(defaultness);
+    match *kind {
+        ImplItemKind::Const(ref ty, body) => {
+            visitor.visit_id(impl_item.hir_id());
+            visitor.visit_ty(ty);
+            visitor.visit_nested_body(body);
+        }
+        ImplItemKind::Fn(ref sig, body_id) => {
+            visitor.visit_fn(
+                FnKind::Method(impl_item.ident, sig),
+                &sig.decl,
+                body_id,
+                impl_item.span,
+                impl_item.hir_id(),
+            );
+        }
+        ImplItemKind::TyAlias(ref ty) => {
+            visitor.visit_id(impl_item.hir_id());
+            visitor.visit_ty(ty);
+        }
+    }
+}
+
+pub fn walk_foreign_item_ref<'v, V: Visitor<'v>>(
+    visitor: &mut V,
+    foreign_item_ref: &'v ForeignItemRef,
+) {
+    // N.B., deliberately force a compilation error if/when new fields are added.
+    let ForeignItemRef { id, ident, span: _ } = *foreign_item_ref;
+    visitor.visit_nested_foreign_item(id);
+    visitor.visit_ident(ident);
+}
+
+pub fn walk_impl_item_ref<'v, V: Visitor<'v>>(visitor: &mut V, impl_item_ref: &'v ImplItemRef) {
+    // N.B., deliberately force a compilation error if/when new fields are added.
+    let ImplItemRef { id, ident, ref kind, span: _, trait_item_def_id: _ } = *impl_item_ref;
+    visitor.visit_nested_impl_item(id);
+    visitor.visit_ident(ident);
+    visitor.visit_associated_item_kind(kind);
+}
+
+pub fn walk_struct_def<'v, V: Visitor<'v>>(
+    visitor: &mut V,
+    struct_definition: &'v VariantData<'v>,
+) {
+    walk_list!(visitor, visit_id, struct_definition.ctor_hir_id());
+    walk_list!(visitor, visit_field_def, struct_definition.fields());
+}
+
+pub fn walk_field_def<'v, V: Visitor<'v>>(visitor: &mut V, field: &'v FieldDef<'v>) {
+    visitor.visit_id(field.hir_id);
+    visitor.visit_ident(field.ident);
+    visitor.visit_ty(&field.ty);
+}
+
+pub fn walk_block<'v, V: Visitor<'v>>(visitor: &mut V, block: &'v Block<'v>) {
+    visitor.visit_id(block.hir_id);
+    walk_list!(visitor, visit_stmt, block.stmts);
+    walk_list!(visitor, visit_expr, &block.expr);
+}
+
+pub fn walk_stmt<'v, V: Visitor<'v>>(visitor: &mut V, statement: &'v Stmt<'v>) {
+    visitor.visit_id(statement.hir_id);
+    match statement.kind {
+        StmtKind::Local(ref local) => visitor.visit_local(local),
+        StmtKind::Item(item) => visitor.visit_nested_item(item),
+        StmtKind::Expr(ref expression) | StmtKind::Semi(ref expression) => {
+            visitor.visit_expr(expression)
+        }
+    }
+}
+
+pub fn walk_array_len<'v, V: Visitor<'v>>(visitor: &mut V, len: &'v ArrayLen) {
+    match len {
+        &ArrayLen::Infer(hir_id, _span) => visitor.visit_id(hir_id),
+        ArrayLen::Body(c) => visitor.visit_anon_const(c),
+    }
+}
+
+pub fn walk_anon_const<'v, V: Visitor<'v>>(visitor: &mut V, constant: &'v AnonConst) {
+    visitor.visit_id(constant.hir_id);
+    visitor.visit_nested_body(constant.body);
+}
+
+pub fn walk_let_expr<'v, V: Visitor<'v>>(visitor: &mut V, let_expr: &'v Let<'v>) {
+    // match the visit order in walk_local
+    visitor.visit_expr(let_expr.init);
+    visitor.visit_id(let_expr.hir_id);
+    visitor.visit_pat(let_expr.pat);
+    walk_list!(visitor, visit_ty, let_expr.ty);
+}
+
+pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>) {
+    visitor.visit_id(expression.hir_id);
+    match expression.kind {
+        ExprKind::Box(ref subexpression) => visitor.visit_expr(subexpression),
+        ExprKind::Array(subexpressions) => {
+            walk_list!(visitor, visit_expr, subexpressions);
+        }
+        ExprKind::ConstBlock(ref anon_const) => visitor.visit_anon_const(anon_const),
+        ExprKind::Repeat(ref element, ref count) => {
+            visitor.visit_expr(element);
+            visitor.visit_array_length(count)
+        }
+        ExprKind::Struct(ref qpath, fields, ref optional_base) => {
+            visitor.visit_qpath(qpath, expression.hir_id, expression.span);
+            for field in fields {
+                visitor.visit_id(field.hir_id);
+                visitor.visit_ident(field.ident);
+                visitor.visit_expr(&field.expr)
+            }
+            walk_list!(visitor, visit_expr, optional_base);
+        }
+        ExprKind::Tup(subexpressions) => {
+            walk_list!(visitor, visit_expr, subexpressions);
+        }
+        ExprKind::Call(ref callee_expression, arguments) => {
+            visitor.visit_expr(callee_expression);
+            walk_list!(visitor, visit_expr, arguments);
+        }
+        ExprKind::MethodCall(ref segment, arguments, _) => {
+            visitor.visit_path_segment(expression.span, segment);
+            walk_list!(visitor, visit_expr, arguments);
+        }
+        ExprKind::Binary(_, ref left_expression, ref right_expression) => {
+            visitor.visit_expr(left_expression);
+            visitor.visit_expr(right_expression)
+        }
+        ExprKind::AddrOf(_, _, ref subexpression) | ExprKind::Unary(_, ref subexpression) => {
+            visitor.visit_expr(subexpression)
+        }
+        ExprKind::Cast(ref subexpression, ref typ) | ExprKind::Type(ref subexpression, ref typ) => {
+            visitor.visit_expr(subexpression);
+            visitor.visit_ty(typ)
+        }
+        ExprKind::DropTemps(ref subexpression) => {
+            visitor.visit_expr(subexpression);
+        }
+        ExprKind::Let(ref let_expr) => visitor.visit_let_expr(let_expr),
+        ExprKind::If(ref cond, ref then, ref else_opt) => {
+            visitor.visit_expr(cond);
+            visitor.visit_expr(then);
+            walk_list!(visitor, visit_expr, else_opt);
+        }
+        ExprKind::Loop(ref block, ref opt_label, _, _) => {
+            walk_list!(visitor, visit_label, opt_label);
+            visitor.visit_block(block);
+        }
+        ExprKind::Match(ref subexpression, arms, _) => {
+            visitor.visit_expr(subexpression);
+            walk_list!(visitor, visit_arm, arms);
+        }
+        ExprKind::Closure(&Closure {
+            binder: _,
+            bound_generic_params,
+            fn_decl,
+            body,
+            capture_clause: _,
+            fn_decl_span: _,
+            movability: _,
+        }) => {
+            walk_list!(visitor, visit_generic_param, bound_generic_params);
+            visitor.visit_fn(FnKind::Closure, fn_decl, body, expression.span, expression.hir_id)
+        }
+        ExprKind::Block(ref block, ref opt_label) => {
+            walk_list!(visitor, visit_label, opt_label);
+            visitor.visit_block(block);
+        }
+        ExprKind::Assign(ref lhs, ref rhs, _) => {
+            visitor.visit_expr(rhs);
+            visitor.visit_expr(lhs)
+        }
+        ExprKind::AssignOp(_, ref left_expression, ref right_expression) => {
+            visitor.visit_expr(right_expression);
+            visitor.visit_expr(left_expression);
+        }
+        ExprKind::Field(ref subexpression, ident) => {
+            visitor.visit_expr(subexpression);
+            visitor.visit_ident(ident);
+        }
+        ExprKind::Index(ref main_expression, ref index_expression) => {
+            visitor.visit_expr(main_expression);
+            visitor.visit_expr(index_expression)
+        }
+        ExprKind::Path(ref qpath) => {
+            visitor.visit_qpath(qpath, expression.hir_id, expression.span);
+        }
+        ExprKind::Break(ref destination, ref opt_expr) => {
+            walk_list!(visitor, visit_label, &destination.label);
+            walk_list!(visitor, visit_expr, opt_expr);
+        }
+        ExprKind::Continue(ref destination) => {
+            walk_list!(visitor, visit_label, &destination.label);
+        }
+        ExprKind::Ret(ref optional_expression) => {
+            walk_list!(visitor, visit_expr, optional_expression);
+        }
+        ExprKind::InlineAsm(ref asm) => {
+            visitor.visit_inline_asm(asm, expression.hir_id);
+        }
+        ExprKind::Yield(ref subexpression, _) => {
+            visitor.visit_expr(subexpression);
+        }
+        ExprKind::Lit(_) | ExprKind::Err => {}
+    }
+}
+
+pub fn walk_arm<'v, V: Visitor<'v>>(visitor: &mut V, arm: &'v Arm<'v>) {
+    visitor.visit_id(arm.hir_id);
+    visitor.visit_pat(&arm.pat);
+    if let Some(ref g) = arm.guard {
+        match g {
+            Guard::If(ref e) => visitor.visit_expr(e),
+            Guard::IfLet(ref l) => {
+                visitor.visit_let_expr(l);
+            }
+        }
+    }
+    visitor.visit_expr(&arm.body);
+}
+
+pub fn walk_associated_item_kind<'v, V: Visitor<'v>>(_: &mut V, _: &'v AssocItemKind) {
+    // No visitable content here: this fn exists so you can call it if
+    // the right thing to do, should content be added in the future,
+    // would be to walk it.
+}
+
+pub fn walk_defaultness<'v, V: Visitor<'v>>(_: &mut V, _: &'v Defaultness) {
+    // No visitable content here: this fn exists so you can call it if
+    // the right thing to do, should content be added in the future,
+    // would be to walk it.
+}
diff --git a/compiler/rustc_hir/src/lang_items.rs b/compiler/rustc_hir/src/lang_items.rs
new file mode 100644
index 000000000..c337be12a
--- /dev/null
+++ b/compiler/rustc_hir/src/lang_items.rs
@@ -0,0 +1,339 @@
+//! Defines language items.
+//!
+//! Language items are items that represent concepts intrinsic to the language
+//! itself. Examples are:
+//!
+//! * Traits that specify "kinds"; e.g., `Sync`, `Send`.
+//! * Traits that represent operators; e.g., `Add`, `Sub`, `Index`.
+//! * Functions called by the compiler itself.
+
+use crate::def_id::DefId;
+use crate::{MethodKind, Target};
+
+use rustc_ast as ast;
+use rustc_data_structures::fx::FxIndexMap;
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_macros::HashStable_Generic;
+use rustc_span::symbol::{kw, sym, Symbol};
+use rustc_span::Span;
+
+use std::sync::LazyLock;
+
+pub enum LangItemGroup {
+    Op,
+    Fn,
+}
+
+const NUM_GROUPS: usize = 2;
+
+macro_rules! expand_group {
+    () => {
+        None
+    };
+    ($group:expr) => {
+        Some($group)
+    };
+}
+
+// The actual lang items defined come at the end of this file in one handy table.
+// So you probably just want to nip down to the end.
+macro_rules! language_item_table {
+    (
+        $( $(#[$attr:meta])* $variant:ident $($group:expr)?, $module:ident :: $name:ident, $method:ident, $target:expr, $generics:expr; )*
+    ) => {
+
+        enum_from_u32! {
+            /// A representation of all the valid language items in Rust.
+            #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, Encodable, Decodable)]
+            pub enum LangItem {
+                $(
+                    #[doc = concat!("The `", stringify!($name), "` lang item.")]
+                    ///
+                    $(#[$attr])*
+                    $variant,
+                )*
+            }
+        }
+
+        impl LangItem {
+            /// Returns the `name` symbol in `#[lang = "$name"]`.
+            /// For example, [`LangItem::PartialEq`]`.name()`
+            /// would result in [`sym::eq`] since it is `#[lang = "eq"]`.
+            pub fn name(self) -> Symbol {
+                match self {
+                    $( LangItem::$variant => $module::$name, )*
+                }
+            }
+
+            /// The [group](LangItemGroup) that this lang item belongs to,
+            /// or `None` if it doesn't belong to a group.
+            pub fn group(self) -> Option<LangItemGroup> {
+                use LangItemGroup::*;
+                match self {
+                    $( LangItem::$variant => expand_group!($($group)*), )*
+                }
+            }
+
+            pub fn required_generics(&self) -> GenericRequirement {
+                match self {
+                    $( LangItem::$variant => $generics, )*
+                }
+            }
+        }
+
+        /// All of the language items, defined or not.
+        /// Defined lang items can come from the current crate or its dependencies.
+        #[derive(HashStable_Generic, Debug)]
+        pub struct LanguageItems {
+            /// Mappings from lang items to their possibly found [`DefId`]s.
+            /// The index corresponds to the order in [`LangItem`].
+            pub items: Vec<Option<DefId>>,
+            /// Lang items that were not found during collection.
+            pub missing: Vec<LangItem>,
+            /// Mapping from [`LangItemGroup`] discriminants to all
+            /// [`DefId`]s of lang items in that group.
+            pub groups: [Vec<DefId>; NUM_GROUPS],
+        }
+
+        impl LanguageItems {
+            /// Construct an empty collection of lang items and no missing ones.
+            pub fn new() -> Self {
+                fn init_none(_: LangItem) -> Option<DefId> { None }
+                const EMPTY: Vec<DefId> = Vec::new();
+
+                Self {
+                    items: vec![$(init_none(LangItem::$variant)),*],
+                    missing: Vec::new(),
+                    groups: [EMPTY; NUM_GROUPS],
+                }
+            }
+
+            /// Returns the mappings to the possibly found `DefId`s for each lang item.
+            pub fn items(&self) -> &[Option<DefId>] {
+                &*self.items
+            }
+
+            /// Requires that a given `LangItem` was bound and returns the corresponding `DefId`.
+            /// If it wasn't bound, e.g. due to a missing `#[lang = "<it.name()>"]`,
+            /// returns an error message as a string.
+            pub fn require(&self, it: LangItem) -> Result<DefId, String> {
+                self.items[it as usize].ok_or_else(|| format!("requires `{}` lang_item", it.name()))
+            }
+
+            /// Returns the [`DefId`]s of all lang items in a group.
+            pub fn group(&self, group: LangItemGroup) -> &[DefId] {
+                self.groups[group as usize].as_ref()
+            }
+
+            $(
+                #[doc = concat!("Returns the [`DefId`] of the `", stringify!($name), "` lang item if it is defined.")]
+                pub fn $method(&self) -> Option<DefId> {
+                    self.items[LangItem::$variant as usize]
+                }
+            )*
+        }
+
+        /// A mapping from the name of the lang item to its order and the form it must be of.
+        pub static ITEM_REFS: LazyLock<FxIndexMap<Symbol, (usize, Target)>> = LazyLock::new(|| {
+            let mut item_refs = FxIndexMap::default();
+            $( item_refs.insert($module::$name, (LangItem::$variant as usize, $target)); )*
+            item_refs
+        });
+
+// End of the macro
+    }
+}
+
+impl<CTX> HashStable<CTX> for LangItem {
+    fn hash_stable(&self, _: &mut CTX, hasher: &mut StableHasher) {
+        ::std::hash::Hash::hash(self, hasher);
+    }
+}
+
+/// Extracts the first `lang = "$name"` out of a list of attributes.
+/// The attributes `#[panic_handler]` and `#[alloc_error_handler]`
+/// are also extracted out when found.
+pub fn extract(attrs: &[ast::Attribute]) -> Option<(Symbol, Span)> {
+    attrs.iter().find_map(|attr| {
+        Some(match attr {
+            _ if attr.has_name(sym::lang) => (attr.value_str()?, attr.span),
+            _ if attr.has_name(sym::panic_handler) => (sym::panic_impl, attr.span),
+            _ if attr.has_name(sym::alloc_error_handler) => (sym::oom, attr.span),
+            _ => return None,
+        })
+    })
+}
+
+language_item_table! {
+//  Variant name,            Name,                     Method name,                Target                  Generic requirements;
+    Sized,                   sym::sized,               sized_trait,                Target::Trait,          GenericRequirement::Exact(0);
+    Unsize,                  sym::unsize,              unsize_trait,               Target::Trait,          GenericRequirement::Minimum(1);
+    /// Trait injected by `#[derive(PartialEq)]`, (i.e. "Partial EQ").
+    StructuralPeq,           sym::structural_peq,      structural_peq_trait,       Target::Trait,          GenericRequirement::None;
+    /// Trait injected by `#[derive(Eq)]`, (i.e. "Total EQ"; no, I will not apologize).
+    StructuralTeq,           sym::structural_teq,      structural_teq_trait,       Target::Trait,          GenericRequirement::None;
+    Copy,                    sym::copy,                copy_trait,                 Target::Trait,          GenericRequirement::Exact(0);
+    Clone,                   sym::clone,               clone_trait,                Target::Trait,          GenericRequirement::None;
+    Sync,                    sym::sync,                sync_trait,                 Target::Trait,          GenericRequirement::Exact(0);
+    DiscriminantKind,        sym::discriminant_kind,   discriminant_kind_trait,    Target::Trait,          GenericRequirement::None;
+    /// The associated item of the [`DiscriminantKind`] trait.
+    Discriminant,            sym::discriminant_type,   discriminant_type,          Target::AssocTy,        GenericRequirement::None;
+
+    PointeeTrait,            sym::pointee_trait,       pointee_trait,              Target::Trait,          GenericRequirement::None;
+    Metadata,                sym::metadata_type,       metadata_type,              Target::AssocTy,        GenericRequirement::None;
+    DynMetadata,             sym::dyn_metadata,        dyn_metadata,               Target::Struct,         GenericRequirement::None;
+
+    Freeze,                  sym::freeze,              freeze_trait,               Target::Trait,          GenericRequirement::Exact(0);
+
+    Drop,                    sym::drop,                drop_trait,                 Target::Trait,          GenericRequirement::None;
+    Destruct,                sym::destruct,            destruct_trait,             Target::Trait,          GenericRequirement::None;
+
+    CoerceUnsized,           sym::coerce_unsized,      coerce_unsized_trait,       Target::Trait,          GenericRequirement::Minimum(1);
+    DispatchFromDyn,         sym::dispatch_from_dyn,   dispatch_from_dyn_trait,    Target::Trait,          GenericRequirement::Minimum(1);
+
+    // language items relating to transmutability
+    TransmuteTrait,          sym::transmute_trait,     transmute_trait,            Target::Trait,          GenericRequirement::Exact(6);
+
+    Add(Op),                 sym::add,                 add_trait,                  Target::Trait,          GenericRequirement::Exact(1);
+    Sub(Op),                 sym::sub,                 sub_trait,                  Target::Trait,          GenericRequirement::Exact(1);
+    Mul(Op),                 sym::mul,                 mul_trait,                  Target::Trait,          GenericRequirement::Exact(1);
+    Div(Op),                 sym::div,                 div_trait,                  Target::Trait,          GenericRequirement::Exact(1);
+    Rem(Op),                 sym::rem,                 rem_trait,                  Target::Trait,          GenericRequirement::Exact(1);
+    Neg(Op),                 sym::neg,                 neg_trait,                  Target::Trait,          GenericRequirement::Exact(0);
+    Not(Op),                 sym::not,                 not_trait,                  Target::Trait,          GenericRequirement::Exact(0);
+    BitXor(Op),              sym::bitxor,              bitxor_trait,               Target::Trait,          GenericRequirement::Exact(1);
+    BitAnd(Op),              sym::bitand,              bitand_trait,               Target::Trait,          GenericRequirement::Exact(1);
+    BitOr(Op),               sym::bitor,               bitor_trait,                Target::Trait,          GenericRequirement::Exact(1);
+    Shl(Op),                 sym::shl,                 shl_trait,                  Target::Trait,          GenericRequirement::Exact(1);
+    Shr(Op),                 sym::shr,                 shr_trait,                  Target::Trait,          GenericRequirement::Exact(1);
+    AddAssign(Op),           sym::add_assign,          add_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
+    SubAssign(Op),           sym::sub_assign,          sub_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
+    MulAssign(Op),           sym::mul_assign,          mul_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
+    DivAssign(Op),           sym::div_assign,          div_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
+    RemAssign(Op),           sym::rem_assign,          rem_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
+    BitXorAssign(Op),        sym::bitxor_assign,       bitxor_assign_trait,        Target::Trait,          GenericRequirement::Exact(1);
+    BitAndAssign(Op),        sym::bitand_assign,       bitand_assign_trait,        Target::Trait,          GenericRequirement::Exact(1);
+    BitOrAssign(Op),         sym::bitor_assign,        bitor_assign_trait,         Target::Trait,          GenericRequirement::Exact(1);
+    ShlAssign(Op),           sym::shl_assign,          shl_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
+    ShrAssign(Op),           sym::shr_assign,          shr_assign_trait,           Target::Trait,          GenericRequirement::Exact(1);
+    Index(Op),               sym::index,               index_trait,                Target::Trait,          GenericRequirement::Exact(1);
+    IndexMut(Op),            sym::index_mut,           index_mut_trait,            Target::Trait,          GenericRequirement::Exact(1);
+
+    UnsafeCell,              sym::unsafe_cell,         unsafe_cell_type,           Target::Struct,         GenericRequirement::None;
+    VaList,                  sym::va_list,             va_list,                    Target::Struct,         GenericRequirement::None;
+
+    Deref,                   sym::deref,               deref_trait,                Target::Trait,          GenericRequirement::Exact(0);
+    DerefMut,                sym::deref_mut,           deref_mut_trait,            Target::Trait,          GenericRequirement::Exact(0);
+    DerefTarget,             sym::deref_target,        deref_target,               Target::AssocTy,        GenericRequirement::None;
+    Receiver,                sym::receiver,            receiver_trait,             Target::Trait,          GenericRequirement::None;
+
+    Fn(Fn),                  kw::Fn,                   fn_trait,                   Target::Trait,          GenericRequirement::Exact(1);
+    FnMut(Fn),               sym::fn_mut,              fn_mut_trait,               Target::Trait,          GenericRequirement::Exact(1);
+    FnOnce(Fn),              sym::fn_once,             fn_once_trait,              Target::Trait,          GenericRequirement::Exact(1);
+
+    FnOnceOutput,            sym::fn_once_output,      fn_once_output,             Target::AssocTy,        GenericRequirement::None;
+
+    Future,                  sym::future_trait,        future_trait,               Target::Trait,          GenericRequirement::Exact(0);
+    GeneratorState,          sym::generator_state,     gen_state,                  Target::Enum,           GenericRequirement::None;
+    Generator,               sym::generator,           gen_trait,                  Target::Trait,          GenericRequirement::Minimum(1);
+    GeneratorReturn,         sym::generator_return,    generator_return,           Target::AssocTy,        GenericRequirement::None;
+    Unpin,                   sym::unpin,               unpin_trait,                Target::Trait,          GenericRequirement::None;
+    Pin,                     sym::pin,                 pin_type,                   Target::Struct,         GenericRequirement::None;
+
+    PartialEq(Op),           sym::eq,                  eq_trait,                   Target::Trait,          GenericRequirement::Exact(1);
+    PartialOrd(Op),          sym::partial_ord,         partial_ord_trait,          Target::Trait,          GenericRequirement::Exact(1);
+
+    // A number of panic-related lang items. The `panic` item corresponds to divide-by-zero and
+    // various panic cases with `match`. The `panic_bounds_check` item is for indexing arrays.
+    //
+    // The `begin_unwind` lang item has a predefined symbol name and is sort of a "weak lang item"
+    // in the sense that a crate is not required to have it defined to use it, but a final product
+    // is required to define it somewhere. Additionally, there are restrictions on crates that use
+    // a weak lang item, but do not have it defined.
+    Panic,                   sym::panic,               panic_fn,                   Target::Fn,             GenericRequirement::Exact(0);
+    PanicFmt,                sym::panic_fmt,           panic_fmt,                  Target::Fn,             GenericRequirement::None;
+    PanicDisplay,            sym::panic_display,       panic_display,              Target::Fn,             GenericRequirement::None;
+    ConstPanicFmt,           sym::const_panic_fmt,     const_panic_fmt,            Target::Fn,             GenericRequirement::None;
+    PanicBoundsCheck,        sym::panic_bounds_check,  panic_bounds_check_fn,      Target::Fn,             GenericRequirement::Exact(0);
+    PanicInfo,               sym::panic_info,          panic_info,                 Target::Struct,         GenericRequirement::None;
+    PanicLocation,           sym::panic_location,      panic_location,             Target::Struct,         GenericRequirement::None;
+    PanicImpl,               sym::panic_impl,          panic_impl,                 Target::Fn,             GenericRequirement::None;
+    PanicNoUnwind,           sym::panic_no_unwind,     panic_no_unwind,            Target::Fn,             GenericRequirement::Exact(0);
+    /// libstd panic entry point. Necessary for const eval to be able to catch it
+    BeginPanic,              sym::begin_panic,         begin_panic_fn,             Target::Fn,             GenericRequirement::None;
+
+    ExchangeMalloc,          sym::exchange_malloc,     exchange_malloc_fn,         Target::Fn,             GenericRequirement::None;
+    BoxFree,                 sym::box_free,            box_free_fn,                Target::Fn,             GenericRequirement::Minimum(1);
+    DropInPlace,             sym::drop_in_place,       drop_in_place_fn,           Target::Fn,             GenericRequirement::Minimum(1);
+    Oom,                     sym::oom,                 oom,                        Target::Fn,             GenericRequirement::None;
+    AllocLayout,             sym::alloc_layout,        alloc_layout,               Target::Struct,         GenericRequirement::None;
+    ConstEvalSelect,         sym::const_eval_select,   const_eval_select,          Target::Fn,             GenericRequirement::Exact(4);
+    ConstConstEvalSelect,    sym::const_eval_select_ct,const_eval_select_ct,       Target::Fn,             GenericRequirement::Exact(4);
+
+    Start,                   sym::start,               start_fn,                   Target::Fn,             GenericRequirement::Exact(1);
+
+    EhPersonality,           sym::eh_personality,      eh_personality,             Target::Fn,             GenericRequirement::None;
+    EhCatchTypeinfo,         sym::eh_catch_typeinfo,   eh_catch_typeinfo,          Target::Static,         GenericRequirement::None;
+
+    OwnedBox,                sym::owned_box,           owned_box,                  Target::Struct,         GenericRequirement::Minimum(1);
+
+    PhantomData,             sym::phantom_data,        phantom_data,               Target::Struct,         GenericRequirement::Exact(1);
+
+    ManuallyDrop,            sym::manually_drop,       manually_drop,              Target::Struct,         GenericRequirement::None;
+
+    MaybeUninit,             sym::maybe_uninit,        maybe_uninit,               Target::Union,          GenericRequirement::None;
+
+    /// Align offset for stride != 1; must not panic.
+    AlignOffset,             sym::align_offset,        align_offset_fn,            Target::Fn,             GenericRequirement::None;
+
+    Termination,             sym::termination,         termination,                Target::Trait,          GenericRequirement::None;
+
+    Try,                     sym::Try,                 try_trait,                  Target::Trait,          GenericRequirement::None;
+
+    SliceLen,                sym::slice_len_fn,        slice_len_fn,               Target::Method(MethodKind::Inherent), GenericRequirement::None;
+
+    // Language items from AST lowering
+    TryTraitFromResidual,    sym::from_residual,       from_residual_fn,           Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
+    TryTraitFromOutput,      sym::from_output,         from_output_fn,             Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
+    TryTraitBranch,          sym::branch,              branch_fn,                  Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
+    TryTraitFromYeet,        sym::from_yeet,           from_yeet_fn,               Target::Fn,             GenericRequirement::None;
+
+    PollReady,               sym::Ready,               poll_ready_variant,         Target::Variant,        GenericRequirement::None;
+    PollPending,             sym::Pending,             poll_pending_variant,       Target::Variant,        GenericRequirement::None;
+
+    FromGenerator,           sym::from_generator,      from_generator_fn,          Target::Fn,             GenericRequirement::None;
+    GetContext,              sym::get_context,         get_context_fn,             Target::Fn,             GenericRequirement::None;
+
+    FuturePoll,              sym::poll,                future_poll_fn,             Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
+
+    FromFrom,                sym::from,                from_fn,                    Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
+
+    OptionSome,              sym::Some,                option_some_variant,        Target::Variant,        GenericRequirement::None;
+    OptionNone,              sym::None,                option_none_variant,        Target::Variant,        GenericRequirement::None;
+
+    ResultOk,                sym::Ok,                  result_ok_variant,          Target::Variant,        GenericRequirement::None;
+    ResultErr,               sym::Err,                 result_err_variant,         Target::Variant,        GenericRequirement::None;
+
+    ControlFlowContinue,     sym::Continue,            cf_continue_variant,        Target::Variant,        GenericRequirement::None;
+    ControlFlowBreak,        sym::Break,               cf_break_variant,           Target::Variant,        GenericRequirement::None;
+
+    IntoFutureIntoFuture,    sym::into_future,         into_future_fn,             Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
+    IntoIterIntoIter,        sym::into_iter,           into_iter_fn,               Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
+    IteratorNext,            sym::next,                next_fn,                    Target::Method(MethodKind::Trait { body: false}), GenericRequirement::None;
+
+    PinNewUnchecked,         sym::new_unchecked,       new_unchecked_fn,           Target::Method(MethodKind::Inherent), GenericRequirement::None;
+
+    RangeFrom,               sym::RangeFrom,           range_from_struct,          Target::Struct,         GenericRequirement::None;
+    RangeFull,               sym::RangeFull,           range_full_struct,          Target::Struct,         GenericRequirement::None;
+    RangeInclusiveStruct,    sym::RangeInclusive,      range_inclusive_struct,     Target::Struct,         GenericRequirement::None;
+    RangeInclusiveNew,       sym::range_inclusive_new, range_inclusive_new_method, Target::Method(MethodKind::Inherent), GenericRequirement::None;
+    Range,                   sym::Range,               range_struct,               Target::Struct,         GenericRequirement::None;
+    RangeToInclusive,        sym::RangeToInclusive,    range_to_inclusive_struct,  Target::Struct,         GenericRequirement::None;
+    RangeTo,                 sym::RangeTo,             range_to_struct,            Target::Struct,         GenericRequirement::None;
+}
+
+pub enum GenericRequirement {
+    None,
+    Minimum(usize),
+    Exact(usize),
+}
diff --git a/compiler/rustc_hir/src/lib.rs b/compiler/rustc_hir/src/lib.rs
new file mode 100644
index 000000000..0f9e6fa7b
--- /dev/null
+++ b/compiler/rustc_hir/src/lib.rs
@@ -0,0 +1,47 @@
+//! HIR datatypes. See the [rustc dev guide] for more info.
+//!
+//! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/hir.html
+
+#![feature(associated_type_defaults)]
+#![feature(closure_track_caller)]
+#![feature(const_btree_new)]
+#![feature(let_else)]
+#![feature(once_cell)]
+#![feature(min_specialization)]
+#![feature(never_type)]
+#![feature(rustc_attrs)]
+#![recursion_limit = "256"]
+
+#[macro_use]
+extern crate rustc_macros;
+
+#[macro_use]
+extern crate rustc_data_structures;
+
+extern crate self as rustc_hir;
+
+mod arena;
+pub mod def;
+pub mod def_path_hash_map;
+pub mod definitions;
+pub mod diagnostic_items;
+pub use rustc_span::def_id;
+mod hir;
+pub mod hir_id;
+pub mod intravisit;
+pub mod lang_items;
+pub mod pat_util;
+mod stable_hash_impls;
+mod target;
+pub mod weak_lang_items;
+
+#[cfg(test)]
+mod tests;
+
+pub use hir::*;
+pub use hir_id::*;
+pub use lang_items::{LangItem, LanguageItems};
+pub use stable_hash_impls::HashStableContext;
+pub use target::{MethodKind, Target};
+
+arena_types!(rustc_arena::declare_arena);
diff --git a/compiler/rustc_hir/src/pat_util.rs b/compiler/rustc_hir/src/pat_util.rs
new file mode 100644
index 000000000..93112199b
--- /dev/null
+++ b/compiler/rustc_hir/src/pat_util.rs
@@ -0,0 +1,157 @@
+use crate::def::{CtorOf, DefKind, Res};
+use crate::def_id::DefId;
+use crate::hir::{self, HirId, PatKind};
+use rustc_data_structures::fx::FxHashSet;
+use rustc_span::hygiene::DesugaringKind;
+use rustc_span::symbol::Ident;
+use rustc_span::Span;
+
+use std::iter::{Enumerate, ExactSizeIterator};
+
+pub struct EnumerateAndAdjust<I> {
+    enumerate: Enumerate<I>,
+    gap_pos: usize,
+    gap_len: usize,
+}
+
+impl<I> Iterator for EnumerateAndAdjust<I>
+where
+    I: Iterator,
+{
+    type Item = (usize, <I as Iterator>::Item);
+
+    fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
+        self.enumerate
+            .next()
+            .map(|(i, elem)| (if i < self.gap_pos { i } else { i + self.gap_len }, elem))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.enumerate.size_hint()
+    }
+}
+
+pub trait EnumerateAndAdjustIterator {
+    fn enumerate_and_adjust(
+        self,
+        expected_len: usize,
+        gap_pos: Option<usize>,
+    ) -> EnumerateAndAdjust<Self>
+    where
+        Self: Sized;
+}
+
+impl<T: ExactSizeIterator> EnumerateAndAdjustIterator for T {
+    fn enumerate_and_adjust(
+        self,
+        expected_len: usize,
+        gap_pos: Option<usize>,
+    ) -> EnumerateAndAdjust<Self>
+    where
+        Self: Sized,
+    {
+        let actual_len = self.len();
+        EnumerateAndAdjust {
+            enumerate: self.enumerate(),
+            gap_pos: gap_pos.unwrap_or(expected_len),
+            gap_len: expected_len - actual_len,
+        }
+    }
+}
+
+impl hir::Pat<'_> {
+    /// Call `f` on every "binding" in a pattern, e.g., on `a` in
+    /// `match foo() { Some(a) => (), None => () }`
+    pub fn each_binding(&self, mut f: impl FnMut(hir::BindingAnnotation, HirId, Span, Ident)) {
+        self.walk_always(|p| {
+            if let PatKind::Binding(binding_mode, _, ident, _) = p.kind {
+                f(binding_mode, p.hir_id, p.span, ident);
+            }
+        });
+    }
+
+    /// Call `f` on every "binding" in a pattern, e.g., on `a` in
+    /// `match foo() { Some(a) => (), None => () }`.
+    ///
+    /// When encountering an or-pattern `p_0 | ... | p_n` only `p_0` will be visited.
+    pub fn each_binding_or_first(
+        &self,
+        f: &mut impl FnMut(hir::BindingAnnotation, HirId, Span, Ident),
+    ) {
+        self.walk(|p| match &p.kind {
+            PatKind::Or(ps) => {
+                ps[0].each_binding_or_first(f);
+                false
+            }
+            PatKind::Binding(bm, _, ident, _) => {
+                f(*bm, p.hir_id, p.span, *ident);
+                true
+            }
+            _ => true,
+        })
+    }
+
+    pub fn simple_ident(&self) -> Option<Ident> {
+        match self.kind {
+            PatKind::Binding(
+                hir::BindingAnnotation::Unannotated | hir::BindingAnnotation::Mutable,
+                _,
+                ident,
+                None,
+            ) => Some(ident),
+            _ => None,
+        }
+    }
+
+    /// Returns variants that are necessary to exist for the pattern to match.
+    pub fn necessary_variants(&self) -> Vec<DefId> {
+        let mut variants = vec![];
+        self.walk(|p| match &p.kind {
+            PatKind::Or(_) => false,
+            PatKind::Path(hir::QPath::Resolved(_, path))
+            | PatKind::TupleStruct(hir::QPath::Resolved(_, path), ..)
+            | PatKind::Struct(hir::QPath::Resolved(_, path), ..) => {
+                if let Res::Def(DefKind::Variant | DefKind::Ctor(CtorOf::Variant, ..), id) =
+                    path.res
+                {
+                    variants.push(id);
+                }
+                true
+            }
+            _ => true,
+        });
+        // We remove duplicates by inserting into a `FxHashSet` to avoid re-ordering
+        // the bounds
+        let mut duplicates = FxHashSet::default();
+        variants.retain(|def_id| duplicates.insert(*def_id));
+        variants
+    }
+
+    /// Checks if the pattern contains any `ref` or `ref mut` bindings, and if
+    /// yes whether it contains mutable or just immutables ones.
+    //
+    // FIXME(tschottdorf): this is problematic as the HIR is being scraped, but
+    // ref bindings are be implicit after #42640 (default match binding modes). See issue #44848.
+    pub fn contains_explicit_ref_binding(&self) -> Option<hir::Mutability> {
+        let mut result = None;
+        self.each_binding(|annotation, _, _, _| match annotation {
+            hir::BindingAnnotation::Ref => match result {
+                None | Some(hir::Mutability::Not) => result = Some(hir::Mutability::Not),
+                _ => {}
+            },
+            hir::BindingAnnotation::RefMut => result = Some(hir::Mutability::Mut),
+            _ => {}
+        });
+        result
+    }
+
+    /// If the pattern is `Some(<pat>)` from a desugared for loop, returns the inner pattern
+    pub fn for_loop_some(&self) -> Option<&Self> {
+        if self.span.desugaring_kind() == Some(DesugaringKind::ForLoop) {
+            if let hir::PatKind::Struct(_, [pat_field], _) = self.kind {
+                return Some(pat_field.pat);
+            }
+        }
+        None
+    }
+}
diff --git a/compiler/rustc_hir/src/stable_hash_impls.rs b/compiler/rustc_hir/src/stable_hash_impls.rs
new file mode 100644
index 000000000..8ccd59e8e
--- /dev/null
+++ b/compiler/rustc_hir/src/stable_hash_impls.rs
@@ -0,0 +1,143 @@
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
+
+use crate::hir::{
+    AttributeMap, BodyId, Crate, Expr, ForeignItemId, ImplItemId, ItemId, OwnerNodes, TraitItemId,
+    Ty,
+};
+use crate::hir_id::{HirId, ItemLocalId};
+use rustc_span::def_id::DefPathHash;
+
+/// Requirements for a `StableHashingContext` to be used in this crate.
+/// This is a hack to allow using the `HashStable_Generic` derive macro
+/// instead of implementing everything in `rustc_middle`.
+pub trait HashStableContext:
+    rustc_ast::HashStableContext + rustc_target::HashStableContext
+{
+    fn hash_body_id(&mut self, _: BodyId, hasher: &mut StableHasher);
+    fn hash_hir_expr(&mut self, _: &Expr<'_>, hasher: &mut StableHasher);
+    fn hash_hir_ty(&mut self, _: &Ty<'_>, hasher: &mut StableHasher);
+}
+
+impl<HirCtx: crate::HashStableContext> ToStableHashKey<HirCtx> for HirId {
+    type KeyType = (DefPathHash, ItemLocalId);
+
+    #[inline]
+    fn to_stable_hash_key(&self, hcx: &HirCtx) -> (DefPathHash, ItemLocalId) {
+        let def_path_hash = self.owner.to_stable_hash_key(hcx);
+        (def_path_hash, self.local_id)
+    }
+}
+
+impl<HirCtx: crate::HashStableContext> ToStableHashKey<HirCtx> for ItemLocalId {
+    type KeyType = ItemLocalId;
+
+    #[inline]
+    fn to_stable_hash_key(&self, _: &HirCtx) -> ItemLocalId {
+        *self
+    }
+}
+
+impl<HirCtx: crate::HashStableContext> ToStableHashKey<HirCtx> for BodyId {
+    type KeyType = (DefPathHash, ItemLocalId);
+
+    #[inline]
+    fn to_stable_hash_key(&self, hcx: &HirCtx) -> (DefPathHash, ItemLocalId) {
+        let BodyId { hir_id } = *self;
+        hir_id.to_stable_hash_key(hcx)
+    }
+}
+
+impl<HirCtx: crate::HashStableContext> ToStableHashKey<HirCtx> for ItemId {
+    type KeyType = DefPathHash;
+
+    #[inline]
+    fn to_stable_hash_key(&self, hcx: &HirCtx) -> DefPathHash {
+        self.def_id.to_stable_hash_key(hcx)
+    }
+}
+
+impl<HirCtx: crate::HashStableContext> ToStableHashKey<HirCtx> for TraitItemId {
+    type KeyType = DefPathHash;
+
+    #[inline]
+    fn to_stable_hash_key(&self, hcx: &HirCtx) -> DefPathHash {
+        self.def_id.to_stable_hash_key(hcx)
+    }
+}
+
+impl<HirCtx: crate::HashStableContext> ToStableHashKey<HirCtx> for ImplItemId {
+    type KeyType = DefPathHash;
+
+    #[inline]
+    fn to_stable_hash_key(&self, hcx: &HirCtx) -> DefPathHash {
+        self.def_id.to_stable_hash_key(hcx)
+    }
+}
+
+impl<HirCtx: crate::HashStableContext> ToStableHashKey<HirCtx> for ForeignItemId {
+    type KeyType = DefPathHash;
+
+    #[inline]
+    fn to_stable_hash_key(&self, hcx: &HirCtx) -> DefPathHash {
+        self.def_id.to_stable_hash_key(hcx)
+    }
+}
+
+impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for BodyId {
+    fn hash_stable(&self, hcx: &mut HirCtx, hasher: &mut StableHasher) {
+        hcx.hash_body_id(*self, hasher)
+    }
+}
+
+// The following implementations of HashStable for `ItemId`, `TraitItemId`, and
+// `ImplItemId` deserve special attention. Normally we do not hash `NodeId`s within
+// the HIR, since they just signify a HIR nodes own path. But `ItemId` et al
+// are used when another item in the HIR is *referenced* and we certainly
+// want to pick up on a reference changing its target, so we hash the NodeIds
+// in "DefPath Mode".
+
+impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for Expr<'_> {
+    fn hash_stable(&self, hcx: &mut HirCtx, hasher: &mut StableHasher) {
+        hcx.hash_hir_expr(self, hasher)
+    }
+}
+
+impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for Ty<'_> {
+    fn hash_stable(&self, hcx: &mut HirCtx, hasher: &mut StableHasher) {
+        hcx.hash_hir_ty(self, hasher)
+    }
+}
+
+impl<'tcx, HirCtx: crate::HashStableContext> HashStable<HirCtx> for OwnerNodes<'tcx> {
+    fn hash_stable(&self, hcx: &mut HirCtx, hasher: &mut StableHasher) {
+        // We ignore the `nodes` and `bodies` fields since these refer to information included in
+        // `hash` which is hashed in the collector and used for the crate hash.
+        // `local_id_to_def_id` is also ignored because is dependent on the body, then just hashing
+        // the body satisfies the condition of two nodes being different have different
+        // `hash_stable` results.
+        let OwnerNodes {
+            hash_including_bodies,
+            hash_without_bodies: _,
+            nodes: _,
+            bodies: _,
+            local_id_to_def_id: _,
+        } = *self;
+        hash_including_bodies.hash_stable(hcx, hasher);
+    }
+}
+
+impl<'tcx, HirCtx: crate::HashStableContext> HashStable<HirCtx> for AttributeMap<'tcx> {
+    fn hash_stable(&self, hcx: &mut HirCtx, hasher: &mut StableHasher) {
+        // We ignore the `map` since it refers to information included in `hash` which is hashed in
+        // the collector and used for the crate hash.
+        let AttributeMap { hash, map: _ } = *self;
+        hash.hash_stable(hcx, hasher);
+    }
+}
+
+impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for Crate<'_> {
+    fn hash_stable(&self, hcx: &mut HirCtx, hasher: &mut StableHasher) {
+        let Crate { owners: _, hir_hash } = self;
+        hir_hash.hash_stable(hcx, hasher)
+    }
+}
diff --git a/compiler/rustc_hir/src/target.rs b/compiler/rustc_hir/src/target.rs
new file mode 100644
index 000000000..6236dea10
--- /dev/null
+++ b/compiler/rustc_hir/src/target.rs
@@ -0,0 +1,188 @@
+//! This module implements some validity checks for attributes.
+//! In particular it verifies that `#[inline]` and `#[repr]` attributes are
+//! attached to items that actually support them and if there are
+//! conflicts between multiple such attributes attached to the same
+//! item.
+
+use crate::hir;
+use crate::{Item, ItemKind, TraitItem, TraitItemKind};
+
+use crate::def::DefKind;
+use std::fmt::{self, Display};
+
+#[derive(Copy, Clone, PartialEq, Debug)]
+pub enum GenericParamKind {
+    Type,
+    Lifetime,
+    Const,
+}
+
+#[derive(Copy, Clone, PartialEq, Debug)]
+pub enum MethodKind {
+    Trait { body: bool },
+    Inherent,
+}
+
+#[derive(Copy, Clone, PartialEq, Debug)]
+pub enum Target {
+    ExternCrate,
+    Use,
+    Static,
+    Const,
+    Fn,
+    Closure,
+    Mod,
+    ForeignMod,
+    GlobalAsm,
+    TyAlias,
+    OpaqueTy,
+    Enum,
+    Variant,
+    Struct,
+    Field,
+    Union,
+    Trait,
+    TraitAlias,
+    Impl,
+    Expression,
+    Statement,
+    Arm,
+    AssocConst,
+    Method(MethodKind),
+    AssocTy,
+    ForeignFn,
+    ForeignStatic,
+    ForeignTy,
+    GenericParam(GenericParamKind),
+    MacroDef,
+    Param,
+}
+
+impl Display for Target {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", Self::name(*self))
+    }
+}
+
+impl Target {
+    pub fn from_item(item: &Item<'_>) -> Target {
+        match item.kind {
+            ItemKind::ExternCrate(..) => Target::ExternCrate,
+            ItemKind::Use(..) => Target::Use,
+            ItemKind::Static(..) => Target::Static,
+            ItemKind::Const(..) => Target::Const,
+            ItemKind::Fn(..) => Target::Fn,
+            ItemKind::Macro(..) => Target::MacroDef,
+            ItemKind::Mod(..) => Target::Mod,
+            ItemKind::ForeignMod { .. } => Target::ForeignMod,
+            ItemKind::GlobalAsm(..) => Target::GlobalAsm,
+            ItemKind::TyAlias(..) => Target::TyAlias,
+            ItemKind::OpaqueTy(..) => Target::OpaqueTy,
+            ItemKind::Enum(..) => Target::Enum,
+            ItemKind::Struct(..) => Target::Struct,
+            ItemKind::Union(..) => Target::Union,
+            ItemKind::Trait(..) => Target::Trait,
+            ItemKind::TraitAlias(..) => Target::TraitAlias,
+            ItemKind::Impl { .. } => Target::Impl,
+        }
+    }
+
+    // FIXME: For now, should only be used with def_kinds from ItemIds
+    pub fn from_def_kind(def_kind: DefKind) -> Target {
+        match def_kind {
+            DefKind::ExternCrate => Target::ExternCrate,
+            DefKind::Use => Target::Use,
+            DefKind::Static(..) => Target::Static,
+            DefKind::Const => Target::Const,
+            DefKind::Fn => Target::Fn,
+            DefKind::Macro(..) => Target::MacroDef,
+            DefKind::Mod => Target::Mod,
+            DefKind::ForeignMod => Target::ForeignMod,
+            DefKind::GlobalAsm => Target::GlobalAsm,
+            DefKind::TyAlias => Target::TyAlias,
+            DefKind::OpaqueTy => Target::OpaqueTy,
+            DefKind::Enum => Target::Enum,
+            DefKind::Struct => Target::Struct,
+            DefKind::Union => Target::Union,
+            DefKind::Trait => Target::Trait,
+            DefKind::TraitAlias => Target::TraitAlias,
+            DefKind::Impl => Target::Impl,
+            _ => panic!("impossible case reached"),
+        }
+    }
+
+    pub fn from_trait_item(trait_item: &TraitItem<'_>) -> Target {
+        match trait_item.kind {
+            TraitItemKind::Const(..) => Target::AssocConst,
+            TraitItemKind::Fn(_, hir::TraitFn::Required(_)) => {
+                Target::Method(MethodKind::Trait { body: false })
+            }
+            TraitItemKind::Fn(_, hir::TraitFn::Provided(_)) => {
+                Target::Method(MethodKind::Trait { body: true })
+            }
+            TraitItemKind::Type(..) => Target::AssocTy,
+        }
+    }
+
+    pub fn from_foreign_item(foreign_item: &hir::ForeignItem<'_>) -> Target {
+        match foreign_item.kind {
+            hir::ForeignItemKind::Fn(..) => Target::ForeignFn,
+            hir::ForeignItemKind::Static(..) => Target::ForeignStatic,
+            hir::ForeignItemKind::Type => Target::ForeignTy,
+        }
+    }
+
+    pub fn from_generic_param(generic_param: &hir::GenericParam<'_>) -> Target {
+        match generic_param.kind {
+            hir::GenericParamKind::Type { .. } => Target::GenericParam(GenericParamKind::Type),
+            hir::GenericParamKind::Lifetime { .. } => {
+                Target::GenericParam(GenericParamKind::Lifetime)
+            }
+            hir::GenericParamKind::Const { .. } => Target::GenericParam(GenericParamKind::Const),
+        }
+    }
+
+    pub fn name(self) -> &'static str {
+        match self {
+            Target::ExternCrate => "extern crate",
+            Target::Use => "use",
+            Target::Static => "static item",
+            Target::Const => "constant item",
+            Target::Fn => "function",
+            Target::Closure => "closure",
+            Target::Mod => "module",
+            Target::ForeignMod => "foreign module",
+            Target::GlobalAsm => "global asm",
+            Target::TyAlias => "type alias",
+            Target::OpaqueTy => "opaque type",
+            Target::Enum => "enum",
+            Target::Variant => "enum variant",
+            Target::Struct => "struct",
+            Target::Field => "struct field",
+            Target::Union => "union",
+            Target::Trait => "trait",
+            Target::TraitAlias => "trait alias",
+            Target::Impl => "implementation block",
+            Target::Expression => "expression",
+            Target::Statement => "statement",
+            Target::Arm => "match arm",
+            Target::AssocConst => "associated const",
+            Target::Method(kind) => match kind {
+                MethodKind::Inherent => "inherent method",
+                MethodKind::Trait { body: false } => "required trait method",
+                MethodKind::Trait { body: true } => "provided trait method",
+            },
+            Target::AssocTy => "associated type",
+            Target::ForeignFn => "foreign function",
+            Target::ForeignStatic => "foreign static item",
+            Target::ForeignTy => "foreign type",
+            Target::GenericParam(kind) => match kind {
+                GenericParamKind::Type => "type parameter",
+                GenericParamKind::Lifetime => "lifetime parameter",
+                GenericParamKind::Const => "const parameter",
+            },
+            Target::MacroDef => "macro def",
+            Target::Param => "function param",
+        }
+    }
+}
diff --git a/compiler/rustc_hir/src/tests.rs b/compiler/rustc_hir/src/tests.rs
new file mode 100644
index 000000000..4636d5152
--- /dev/null
+++ b/compiler/rustc_hir/src/tests.rs
@@ -0,0 +1,36 @@
+use crate::definitions::{DefKey, DefPathData, DisambiguatedDefPathData};
+use rustc_span::def_id::{DefPathHash, StableCrateId};
+
+#[test]
+fn def_path_hash_depends_on_crate_id() {
+    // This test makes sure that *both* halves of a DefPathHash depend on
+    // the crate-id of the defining crate. This is a desirable property
+    // because the crate-id can be more easily changed than the DefPath
+    // of an item, so, in the case of a crate-local DefPathHash collision,
+    // the user can simply "role the dice again" for all DefPathHashes in
+    // the crate by changing the crate disambiguator (e.g. via bumping the
+    // crate's version number).
+
+    let id0 = StableCrateId::new("foo", false, vec!["1".to_string()]);
+    let id1 = StableCrateId::new("foo", false, vec!["2".to_string()]);
+
+    let h0 = mk_test_hash(id0);
+    let h1 = mk_test_hash(id1);
+
+    assert_ne!(h0.stable_crate_id(), h1.stable_crate_id());
+    assert_ne!(h0.local_hash(), h1.local_hash());
+
+    fn mk_test_hash(stable_crate_id: StableCrateId) -> DefPathHash {
+        let parent_hash = DefPathHash::new(stable_crate_id, 0);
+
+        let key = DefKey {
+            parent: None,
+            disambiguated_data: DisambiguatedDefPathData {
+                data: DefPathData::CrateRoot,
+                disambiguator: 0,
+            },
+        };
+
+        key.compute_stable_hash(parent_hash)
+    }
+}
diff --git a/compiler/rustc_hir/src/weak_lang_items.rs b/compiler/rustc_hir/src/weak_lang_items.rs
new file mode 100644
index 000000000..b6a85c047
--- /dev/null
+++ b/compiler/rustc_hir/src/weak_lang_items.rs
@@ -0,0 +1,47 @@
+//! Validity checking for weak lang items
+
+use crate::def_id::DefId;
+use crate::{lang_items, LangItem, LanguageItems};
+
+use rustc_ast as ast;
+use rustc_data_structures::fx::FxIndexMap;
+use rustc_span::symbol::{sym, Symbol};
+
+use std::sync::LazyLock;
+
+macro_rules! weak_lang_items {
+    ($($name:ident, $item:ident, $sym:ident;)*) => (
+
+pub static WEAK_ITEMS_REFS: LazyLock<FxIndexMap<Symbol, LangItem>> = LazyLock::new(|| {
+    let mut map = FxIndexMap::default();
+    $(map.insert(sym::$name, LangItem::$item);)*
+    map
+});
+
+pub fn link_name(attrs: &[ast::Attribute]) -> Option<Symbol>
+{
+    lang_items::extract(attrs).and_then(|(name, _)| {
+        $(if name == sym::$name {
+            Some(sym::$sym)
+        } else)* {
+            None
+        }
+    })
+}
+
+impl LanguageItems {
+    pub fn is_weak_lang_item(&self, item_def_id: DefId) -> bool {
+        let did = Some(item_def_id);
+
+        $(self.$name() == did)||*
+    }
+}
+
+) }
+
+weak_lang_items! {
+    panic_impl,         PanicImpl,          rust_begin_unwind;
+    eh_personality,     EhPersonality,      rust_eh_personality;
+    eh_catch_typeinfo,  EhCatchTypeinfo,    rust_eh_catch_typeinfo;
+    oom,                Oom,                rust_oom;
+}