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

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

1 files changed, 3506 insertions, 0 deletions

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);
+}