mv compiler to compiler/

1 files changed, 2288 insertions, 0 deletions

diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
new file mode 100644
index 00000000000..c1f354c7a15
--- /dev/null
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -0,0 +1,2288 @@
+//! This module contains `TyKind` and its major components.
+
+#![allow(rustc::usage_of_ty_tykind)]
+
+use self::InferTy::*;
+use self::TyKind::*;
+
+use crate::infer::canonical::Canonical;
+use crate::ty::subst::{GenericArg, InternalSubsts, Subst, SubstsRef};
+use crate::ty::{
+    self, AdtDef, DefIdTree, Discr, Ty, TyCtxt, TypeFlags, TypeFoldable, WithConstness,
+};
+use crate::ty::{DelaySpanBugEmitted, List, ParamEnv, TyS};
+use polonius_engine::Atom;
+use rustc_ast as ast;
+use rustc_data_structures::captures::Captures;
+use rustc_hir as hir;
+use rustc_hir::def_id::DefId;
+use rustc_index::vec::Idx;
+use rustc_macros::HashStable;
+use rustc_span::symbol::{kw, Ident, Symbol};
+use rustc_target::abi::VariantIdx;
+use rustc_target::spec::abi;
+use std::borrow::Cow;
+use std::cmp::Ordering;
+use std::marker::PhantomData;
+use std::ops::Range;
+use ty::util::IntTypeExt;
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, TyEncodable, TyDecodable)]
+#[derive(HashStable, TypeFoldable, Lift)]
+pub struct TypeAndMut<'tcx> {
+    pub ty: Ty<'tcx>,
+    pub mutbl: hir::Mutability,
+}
+
+#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, TyEncodable, TyDecodable, Copy)]
+#[derive(HashStable)]
+/// A "free" region `fr` can be interpreted as "some region
+/// at least as big as the scope `fr.scope`".
+pub struct FreeRegion {
+    pub scope: DefId,
+    pub bound_region: BoundRegion,
+}
+
+#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, TyEncodable, TyDecodable, Copy)]
+#[derive(HashStable)]
+pub enum BoundRegion {
+    /// An anonymous region parameter for a given fn (&T)
+    BrAnon(u32),
+
+    /// Named region parameters for functions (a in &'a T)
+    ///
+    /// The `DefId` is needed to distinguish free regions in
+    /// the event of shadowing.
+    BrNamed(DefId, Symbol),
+
+    /// Anonymous region for the implicit env pointer parameter
+    /// to a closure
+    BrEnv,
+}
+
+impl BoundRegion {
+    pub fn is_named(&self) -> bool {
+        match *self {
+            BoundRegion::BrNamed(_, name) => name != kw::UnderscoreLifetime,
+            _ => false,
+        }
+    }
+
+    /// When canonicalizing, we replace unbound inference variables and free
+    /// regions with anonymous late bound regions. This method asserts that
+    /// we have an anonymous late bound region, which hence may refer to
+    /// a canonical variable.
+    pub fn assert_bound_var(&self) -> BoundVar {
+        match *self {
+            BoundRegion::BrAnon(var) => BoundVar::from_u32(var),
+            _ => bug!("bound region is not anonymous"),
+        }
+    }
+}
+
+/// N.B., if you change this, you'll probably want to change the corresponding
+/// AST structure in `librustc_ast/ast.rs` as well.
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, TyEncodable, TyDecodable, Debug)]
+#[derive(HashStable)]
+#[rustc_diagnostic_item = "TyKind"]
+pub enum TyKind<'tcx> {
+    /// The primitive boolean type. Written as `bool`.
+    Bool,
+
+    /// The primitive character type; holds a Unicode scalar value
+    /// (a non-surrogate code point). Written as `char`.
+    Char,
+
+    /// A primitive signed integer type. For example, `i32`.
+    Int(ast::IntTy),
+
+    /// A primitive unsigned integer type. For example, `u32`.
+    Uint(ast::UintTy),
+
+    /// A primitive floating-point type. For example, `f64`.
+    Float(ast::FloatTy),
+
+    /// Structures, enumerations and unions.
+    ///
+    /// InternalSubsts here, possibly against intuition, *may* contain `Param`s.
+    /// That is, even after substitution it is possible that there are type
+    /// variables. This happens when the `Adt` corresponds to an ADT
+    /// definition and not a concrete use of it.
+    Adt(&'tcx AdtDef, SubstsRef<'tcx>),
+
+    /// An unsized FFI type that is opaque to Rust. Written as `extern type T`.
+    Foreign(DefId),
+
+    /// The pointee of a string slice. Written as `str`.
+    Str,
+
+    /// An array with the given length. Written as `[T; n]`.
+    Array(Ty<'tcx>, &'tcx ty::Const<'tcx>),
+
+    /// The pointee of an array slice. Written as `[T]`.
+    Slice(Ty<'tcx>),
+
+    /// A raw pointer. Written as `*mut T` or `*const T`
+    RawPtr(TypeAndMut<'tcx>),
+
+    /// A reference; a pointer with an associated lifetime. Written as
+    /// `&'a mut T` or `&'a T`.
+    Ref(Region<'tcx>, Ty<'tcx>, hir::Mutability),
+
+    /// The anonymous type of a function declaration/definition. Each
+    /// function has a unique type, which is output (for a function
+    /// named `foo` returning an `i32`) as `fn() -> i32 {foo}`.
+    ///
+    /// For example the type of `bar` here:
+    ///
+    /// ```rust
+    /// fn foo() -> i32 { 1 }
+    /// let bar = foo; // bar: fn() -> i32 {foo}
+    /// ```
+    FnDef(DefId, SubstsRef<'tcx>),
+
+    /// A pointer to a function. Written as `fn() -> i32`.
+    ///
+    /// For example the type of `bar` here:
+    ///
+    /// ```rust
+    /// fn foo() -> i32 { 1 }
+    /// let bar: fn() -> i32 = foo;
+    /// ```
+    FnPtr(PolyFnSig<'tcx>),
+
+    /// A trait, defined with `trait`.
+    Dynamic(Binder<&'tcx List<ExistentialPredicate<'tcx>>>, ty::Region<'tcx>),
+
+    /// The anonymous type of a closure. Used to represent the type of
+    /// `|a| a`.
+    Closure(DefId, SubstsRef<'tcx>),
+
+    /// The anonymous type of a generator. Used to represent the type of
+    /// `|a| yield a`.
+    Generator(DefId, SubstsRef<'tcx>, hir::Movability),
+
+    /// A type representin the types stored inside a generator.
+    /// This should only appear in GeneratorInteriors.
+    GeneratorWitness(Binder<&'tcx List<Ty<'tcx>>>),
+
+    /// The never type `!`
+    Never,
+
+    /// A tuple type. For example, `(i32, bool)`.
+    /// Use `TyS::tuple_fields` to iterate over the field types.
+    Tuple(SubstsRef<'tcx>),
+
+    /// The projection of an associated type. For example,
+    /// `<T as Trait<..>>::N`.
+    Projection(ProjectionTy<'tcx>),
+
+    /// Opaque (`impl Trait`) type found in a return type.
+    /// The `DefId` comes either from
+    /// * the `impl Trait` ast::Ty node,
+    /// * or the `type Foo = impl Trait` declaration
+    /// The substitutions are for the generics of the function in question.
+    /// After typeck, the concrete type can be found in the `types` map.
+    Opaque(DefId, SubstsRef<'tcx>),
+
+    /// A type parameter; for example, `T` in `fn f<T>(x: T) {}`.
+    Param(ParamTy),
+
+    /// Bound type variable, used only when preparing a trait query.
+    Bound(ty::DebruijnIndex, BoundTy),
+
+    /// A placeholder type - universally quantified higher-ranked type.
+    Placeholder(ty::PlaceholderType),
+
+    /// A type variable used during type checking.
+    Infer(InferTy),
+
+    /// A placeholder for a type which could not be computed; this is
+    /// propagated to avoid useless error messages.
+    Error(DelaySpanBugEmitted),
+}
+
+impl TyKind<'tcx> {
+    #[inline]
+    pub fn is_primitive(&self) -> bool {
+        match self {
+            Bool | Char | Int(_) | Uint(_) | Float(_) => true,
+            _ => false,
+        }
+    }
+}
+
+// `TyKind` is used a lot. Make sure it doesn't unintentionally get bigger.
+#[cfg(target_arch = "x86_64")]
+static_assert_size!(TyKind<'_>, 24);
+
+/// A closure can be modeled as a struct that looks like:
+///
+///     struct Closure<'l0...'li, T0...Tj, CK, CS, U>(...U);
+///
+/// where:
+///
+/// - 'l0...'li and T0...Tj are the generic parameters
+///   in scope on the function that defined the closure,
+/// - CK represents the *closure kind* (Fn vs FnMut vs FnOnce). This
+///   is rather hackily encoded via a scalar type. See
+///   `TyS::to_opt_closure_kind` for details.
+/// - CS represents the *closure signature*, representing as a `fn()`
+///   type. For example, `fn(u32, u32) -> u32` would mean that the closure
+///   implements `CK<(u32, u32), Output = u32>`, where `CK` is the trait
+///   specified above.
+/// - U is a type parameter representing the types of its upvars, tupled up
+///   (borrowed, if appropriate; that is, if an U field represents a by-ref upvar,
+///    and the up-var has the type `Foo`, then that field of U will be `&Foo`).
+///
+/// So, for example, given this function:
+///
+///     fn foo<'a, T>(data: &'a mut T) {
+///          do(|| data.count += 1)
+///     }
+///
+/// the type of the closure would be something like:
+///
+///     struct Closure<'a, T, U>(...U);
+///
+/// Note that the type of the upvar is not specified in the struct.
+/// You may wonder how the impl would then be able to use the upvar,
+/// if it doesn't know it's type? The answer is that the impl is
+/// (conceptually) not fully generic over Closure but rather tied to
+/// instances with the expected upvar types:
+///
+///     impl<'b, 'a, T> FnMut() for Closure<'a, T, (&'b mut &'a mut T,)> {
+///         ...
+///     }
+///
+/// You can see that the *impl* fully specified the type of the upvar
+/// and thus knows full well that `data` has type `&'b mut &'a mut T`.
+/// (Here, I am assuming that `data` is mut-borrowed.)
+///
+/// Now, the last question you may ask is: Why include the upvar types
+/// in an extra type parameter? The reason for this design is that the
+/// upvar types can reference lifetimes that are internal to the
+/// creating function. In my example above, for example, the lifetime
+/// `'b` represents the scope of the closure itself; this is some
+/// subset of `foo`, probably just the scope of the call to the to
+/// `do()`. If we just had the lifetime/type parameters from the
+/// enclosing function, we couldn't name this lifetime `'b`. Note that
+/// there can also be lifetimes in the types of the upvars themselves,
+/// if one of them happens to be a reference to something that the
+/// creating fn owns.
+///
+/// OK, you say, so why not create a more minimal set of parameters
+/// that just includes the extra lifetime parameters? The answer is
+/// primarily that it would be hard --- we don't know at the time when
+/// we create the closure type what the full types of the upvars are,
+/// nor do we know which are borrowed and which are not. In this
+/// design, we can just supply a fresh type parameter and figure that
+/// out later.
+///
+/// All right, you say, but why include the type parameters from the
+/// original function then? The answer is that codegen may need them
+/// when monomorphizing, and they may not appear in the upvars. A
+/// closure could capture no variables but still make use of some
+/// in-scope type parameter with a bound (e.g., if our example above
+/// had an extra `U: Default`, and the closure called `U::default()`).
+///
+/// There is another reason. This design (implicitly) prohibits
+/// closures from capturing themselves (except via a trait
+/// object). This simplifies closure inference considerably, since it
+/// means that when we infer the kind of a closure or its upvars, we
+/// don't have to handle cycles where the decisions we make for
+/// closure C wind up influencing the decisions we ought to make for
+/// closure C (which would then require fixed point iteration to
+/// handle). Plus it fixes an ICE. :P
+///
+/// ## Generators
+///
+/// Generators are handled similarly in `GeneratorSubsts`.  The set of
+/// type parameters is similar, but `CK` and `CS` are replaced by the
+/// following type parameters:
+///
+/// * `GS`: The generator's "resume type", which is the type of the
+///   argument passed to `resume`, and the type of `yield` expressions
+///   inside the generator.
+/// * `GY`: The "yield type", which is the type of values passed to
+///   `yield` inside the generator.
+/// * `GR`: The "return type", which is the type of value returned upon
+///   completion of the generator.
+/// * `GW`: The "generator witness".
+#[derive(Copy, Clone, Debug, TypeFoldable)]
+pub struct ClosureSubsts<'tcx> {
+    /// Lifetime and type parameters from the enclosing function,
+    /// concatenated with a tuple containing the types of the upvars.
+    ///
+    /// These are separated out because codegen wants to pass them around
+    /// when monomorphizing.
+    pub substs: SubstsRef<'tcx>,
+}
+
+/// Struct returned by `split()`.
+pub struct ClosureSubstsParts<'tcx, T> {
+    pub parent_substs: &'tcx [GenericArg<'tcx>],
+    pub closure_kind_ty: T,
+    pub closure_sig_as_fn_ptr_ty: T,
+    pub tupled_upvars_ty: T,
+}
+
+impl<'tcx> ClosureSubsts<'tcx> {
+    /// Construct `ClosureSubsts` from `ClosureSubstsParts`, containing `Substs`
+    /// for the closure parent, alongside additional closure-specific components.
+    pub fn new(
+        tcx: TyCtxt<'tcx>,
+        parts: ClosureSubstsParts<'tcx, Ty<'tcx>>,
+    ) -> ClosureSubsts<'tcx> {
+        ClosureSubsts {
+            substs: tcx.mk_substs(
+                parts.parent_substs.iter().copied().chain(
+                    [parts.closure_kind_ty, parts.closure_sig_as_fn_ptr_ty, parts.tupled_upvars_ty]
+                        .iter()
+                        .map(|&ty| ty.into()),
+                ),
+            ),
+        }
+    }
+
+    /// Divides the closure substs into their respective components.
+    /// The ordering assumed here must match that used by `ClosureSubsts::new` above.
+    fn split(self) -> ClosureSubstsParts<'tcx, GenericArg<'tcx>> {
+        match self.substs[..] {
+            [ref parent_substs @ .., closure_kind_ty, closure_sig_as_fn_ptr_ty, tupled_upvars_ty] => {
+                ClosureSubstsParts {
+                    parent_substs,
+                    closure_kind_ty,
+                    closure_sig_as_fn_ptr_ty,
+                    tupled_upvars_ty,
+                }
+            }
+            _ => bug!("closure substs missing synthetics"),
+        }
+    }
+
+    /// Returns `true` only if enough of the synthetic types are known to
+    /// allow using all of the methods on `ClosureSubsts` without panicking.
+    ///
+    /// Used primarily by `ty::print::pretty` to be able to handle closure
+    /// types that haven't had their synthetic types substituted in.
+    pub fn is_valid(self) -> bool {
+        self.substs.len() >= 3 && matches!(self.split().tupled_upvars_ty.expect_ty().kind, Tuple(_))
+    }
+
+    /// Returns the substitutions of the closure's parent.
+    pub fn parent_substs(self) -> &'tcx [GenericArg<'tcx>] {
+        self.split().parent_substs
+    }
+
+    #[inline]
+    pub fn upvar_tys(self) -> impl Iterator<Item = Ty<'tcx>> + 'tcx {
+        self.tupled_upvars_ty().tuple_fields()
+    }
+
+    /// Returns the tuple type representing the upvars for this closure.
+    #[inline]
+    pub fn tupled_upvars_ty(self) -> Ty<'tcx> {
+        self.split().tupled_upvars_ty.expect_ty()
+    }
+
+    /// Returns the closure kind for this closure; may return a type
+    /// variable during inference. To get the closure kind during
+    /// inference, use `infcx.closure_kind(substs)`.
+    pub fn kind_ty(self) -> Ty<'tcx> {
+        self.split().closure_kind_ty.expect_ty()
+    }
+
+    /// Returns the `fn` pointer type representing the closure signature for this
+    /// closure.
+    // FIXME(eddyb) this should be unnecessary, as the shallowly resolved
+    // type is known at the time of the creation of `ClosureSubsts`,
+    // see `rustc_typeck::check::closure`.
+    pub fn sig_as_fn_ptr_ty(self) -> Ty<'tcx> {
+        self.split().closure_sig_as_fn_ptr_ty.expect_ty()
+    }
+
+    /// Returns the closure kind for this closure; only usable outside
+    /// of an inference context, because in that context we know that
+    /// there are no type variables.
+    ///
+    /// If you have an inference context, use `infcx.closure_kind()`.
+    pub fn kind(self) -> ty::ClosureKind {
+        self.kind_ty().to_opt_closure_kind().unwrap()
+    }
+
+    /// Extracts the signature from the closure.
+    pub fn sig(self) -> ty::PolyFnSig<'tcx> {
+        let ty = self.sig_as_fn_ptr_ty();
+        match ty.kind {
+            ty::FnPtr(sig) => sig,
+            _ => bug!("closure_sig_as_fn_ptr_ty is not a fn-ptr: {:?}", ty.kind),
+        }
+    }
+}
+
+/// Similar to `ClosureSubsts`; see the above documentation for more.
+#[derive(Copy, Clone, Debug, TypeFoldable)]
+pub struct GeneratorSubsts<'tcx> {
+    pub substs: SubstsRef<'tcx>,
+}
+
+pub struct GeneratorSubstsParts<'tcx, T> {
+    pub parent_substs: &'tcx [GenericArg<'tcx>],
+    pub resume_ty: T,
+    pub yield_ty: T,
+    pub return_ty: T,
+    pub witness: T,
+    pub tupled_upvars_ty: T,
+}
+
+impl<'tcx> GeneratorSubsts<'tcx> {
+    /// Construct `GeneratorSubsts` from `GeneratorSubstsParts`, containing `Substs`
+    /// for the generator parent, alongside additional generator-specific components.
+    pub fn new(
+        tcx: TyCtxt<'tcx>,
+        parts: GeneratorSubstsParts<'tcx, Ty<'tcx>>,
+    ) -> GeneratorSubsts<'tcx> {
+        GeneratorSubsts {
+            substs: tcx.mk_substs(
+                parts.parent_substs.iter().copied().chain(
+                    [
+                        parts.resume_ty,
+                        parts.yield_ty,
+                        parts.return_ty,
+                        parts.witness,
+                        parts.tupled_upvars_ty,
+                    ]
+                    .iter()
+                    .map(|&ty| ty.into()),
+                ),
+            ),
+        }
+    }
+
+    /// Divides the generator substs into their respective components.
+    /// The ordering assumed here must match that used by `GeneratorSubsts::new` above.
+    fn split(self) -> GeneratorSubstsParts<'tcx, GenericArg<'tcx>> {
+        match self.substs[..] {
+            [ref parent_substs @ .., resume_ty, yield_ty, return_ty, witness, tupled_upvars_ty] => {
+                GeneratorSubstsParts {
+                    parent_substs,
+                    resume_ty,
+                    yield_ty,
+                    return_ty,
+                    witness,
+                    tupled_upvars_ty,
+                }
+            }
+            _ => bug!("generator substs missing synthetics"),
+        }
+    }
+
+    /// Returns `true` only if enough of the synthetic types are known to
+    /// allow using all of the methods on `GeneratorSubsts` without panicking.
+    ///
+    /// Used primarily by `ty::print::pretty` to be able to handle generator
+    /// types that haven't had their synthetic types substituted in.
+    pub fn is_valid(self) -> bool {
+        self.substs.len() >= 5 && matches!(self.split().tupled_upvars_ty.expect_ty().kind, Tuple(_))
+    }
+
+    /// Returns the substitutions of the generator's parent.
+    pub fn parent_substs(self) -> &'tcx [GenericArg<'tcx>] {
+        self.split().parent_substs
+    }
+
+    /// This describes the types that can be contained in a generator.
+    /// It will be a type variable initially and unified in the last stages of typeck of a body.
+    /// It contains a tuple of all the types that could end up on a generator frame.
+    /// The state transformation MIR pass may only produce layouts which mention types
+    /// in this tuple. Upvars are not counted here.
+    pub fn witness(self) -> Ty<'tcx> {
+        self.split().witness.expect_ty()
+    }
+
+    #[inline]
+    pub fn upvar_tys(self) -> impl Iterator<Item = Ty<'tcx>> + 'tcx {
+        self.tupled_upvars_ty().tuple_fields()
+    }
+
+    /// Returns the tuple type representing the upvars for this generator.
+    #[inline]
+    pub fn tupled_upvars_ty(self) -> Ty<'tcx> {
+        self.split().tupled_upvars_ty.expect_ty()
+    }
+
+    /// Returns the type representing the resume type of the generator.
+    pub fn resume_ty(self) -> Ty<'tcx> {
+        self.split().resume_ty.expect_ty()
+    }
+
+    /// Returns the type representing the yield type of the generator.
+    pub fn yield_ty(self) -> Ty<'tcx> {
+        self.split().yield_ty.expect_ty()
+    }
+
+    /// Returns the type representing the return type of the generator.
+    pub fn return_ty(self) -> Ty<'tcx> {
+        self.split().return_ty.expect_ty()
+    }
+
+    /// Returns the "generator signature", which consists of its yield
+    /// and return types.
+    ///
+    /// N.B., some bits of the code prefers to see this wrapped in a
+    /// binder, but it never contains bound regions. Probably this
+    /// function should be removed.
+    pub fn poly_sig(self) -> PolyGenSig<'tcx> {
+        ty::Binder::dummy(self.sig())
+    }
+
+    /// Returns the "generator signature", which consists of its resume, yield
+    /// and return types.
+    pub fn sig(self) -> GenSig<'tcx> {
+        ty::GenSig {
+            resume_ty: self.resume_ty(),
+            yield_ty: self.yield_ty(),
+            return_ty: self.return_ty(),
+        }
+    }
+}
+
+impl<'tcx> GeneratorSubsts<'tcx> {
+    /// Generator has not been resumed yet.
+    pub const UNRESUMED: usize = 0;
+    /// Generator has returned or is completed.
+    pub const RETURNED: usize = 1;
+    /// Generator has been poisoned.
+    pub const POISONED: usize = 2;
+
+    const UNRESUMED_NAME: &'static str = "Unresumed";
+    const RETURNED_NAME: &'static str = "Returned";
+    const POISONED_NAME: &'static str = "Panicked";
+
+    /// The valid variant indices of this generator.
+    #[inline]
+    pub fn variant_range(&self, def_id: DefId, tcx: TyCtxt<'tcx>) -> Range<VariantIdx> {
+        // FIXME requires optimized MIR
+        let num_variants = tcx.generator_layout(def_id).variant_fields.len();
+        VariantIdx::new(0)..VariantIdx::new(num_variants)
+    }
+
+    /// The discriminant for the given variant. Panics if the `variant_index` is
+    /// out of range.
+    #[inline]
+    pub fn discriminant_for_variant(
+        &self,
+        def_id: DefId,
+        tcx: TyCtxt<'tcx>,
+        variant_index: VariantIdx,
+    ) -> Discr<'tcx> {
+        // Generators don't support explicit discriminant values, so they are
+        // the same as the variant index.
+        assert!(self.variant_range(def_id, tcx).contains(&variant_index));
+        Discr { val: variant_index.as_usize() as u128, ty: self.discr_ty(tcx) }
+    }
+
+    /// The set of all discriminants for the generator, enumerated with their
+    /// variant indices.
+    #[inline]
+    pub fn discriminants(
+        self,
+        def_id: DefId,
+        tcx: TyCtxt<'tcx>,
+    ) -> impl Iterator<Item = (VariantIdx, Discr<'tcx>)> + Captures<'tcx> {
+        self.variant_range(def_id, tcx).map(move |index| {
+            (index, Discr { val: index.as_usize() as u128, ty: self.discr_ty(tcx) })
+        })
+    }
+
+    /// Calls `f` with a reference to the name of the enumerator for the given
+    /// variant `v`.
+    pub fn variant_name(v: VariantIdx) -> Cow<'static, str> {
+        match v.as_usize() {
+            Self::UNRESUMED => Cow::from(Self::UNRESUMED_NAME),
+            Self::RETURNED => Cow::from(Self::RETURNED_NAME),
+            Self::POISONED => Cow::from(Self::POISONED_NAME),
+            _ => Cow::from(format!("Suspend{}", v.as_usize() - 3)),
+        }
+    }
+
+    /// The type of the state discriminant used in the generator type.
+    #[inline]
+    pub fn discr_ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
+        tcx.types.u32
+    }
+
+    /// This returns the types of the MIR locals which had to be stored across suspension points.
+    /// It is calculated in rustc_mir::transform::generator::StateTransform.
+    /// All the types here must be in the tuple in GeneratorInterior.
+    ///
+    /// The locals are grouped by their variant number. Note that some locals may
+    /// be repeated in multiple variants.
+    #[inline]
+    pub fn state_tys(
+        self,
+        def_id: DefId,
+        tcx: TyCtxt<'tcx>,
+    ) -> impl Iterator<Item = impl Iterator<Item = Ty<'tcx>> + Captures<'tcx>> {
+        let layout = tcx.generator_layout(def_id);
+        layout.variant_fields.iter().map(move |variant| {
+            variant.iter().map(move |field| layout.field_tys[*field].subst(tcx, self.substs))
+        })
+    }
+
+    /// This is the types of the fields of a generator which are not stored in a
+    /// variant.
+    #[inline]
+    pub fn prefix_tys(self) -> impl Iterator<Item = Ty<'tcx>> {
+        self.upvar_tys()
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+pub enum UpvarSubsts<'tcx> {
+    Closure(SubstsRef<'tcx>),
+    Generator(SubstsRef<'tcx>),
+}
+
+impl<'tcx> UpvarSubsts<'tcx> {
+    #[inline]
+    pub fn upvar_tys(self) -> impl Iterator<Item = Ty<'tcx>> + 'tcx {
+        let tupled_upvars_ty = match self {
+            UpvarSubsts::Closure(substs) => substs.as_closure().split().tupled_upvars_ty,
+            UpvarSubsts::Generator(substs) => substs.as_generator().split().tupled_upvars_ty,
+        };
+        tupled_upvars_ty.expect_ty().tuple_fields()
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, PartialOrd, Ord, Eq, Hash, TyEncodable, TyDecodable)]
+#[derive(HashStable, TypeFoldable)]
+pub enum ExistentialPredicate<'tcx> {
+    /// E.g., `Iterator`.
+    Trait(ExistentialTraitRef<'tcx>),
+    /// E.g., `Iterator::Item = T`.
+    Projection(ExistentialProjection<'tcx>),
+    /// E.g., `Send`.
+    AutoTrait(DefId),
+}
+
+impl<'tcx> ExistentialPredicate<'tcx> {
+    /// Compares via an ordering that will not change if modules are reordered or other changes are
+    /// made to the tree. In particular, this ordering is preserved across incremental compilations.
+    pub fn stable_cmp(&self, tcx: TyCtxt<'tcx>, other: &Self) -> Ordering {
+        use self::ExistentialPredicate::*;
+        match (*self, *other) {
+            (Trait(_), Trait(_)) => Ordering::Equal,
+            (Projection(ref a), Projection(ref b)) => {
+                tcx.def_path_hash(a.item_def_id).cmp(&tcx.def_path_hash(b.item_def_id))
+            }
+            (AutoTrait(ref a), AutoTrait(ref b)) => {
+                tcx.trait_def(*a).def_path_hash.cmp(&tcx.trait_def(*b).def_path_hash)
+            }
+            (Trait(_), _) => Ordering::Less,
+            (Projection(_), Trait(_)) => Ordering::Greater,
+            (Projection(_), _) => Ordering::Less,
+            (AutoTrait(_), _) => Ordering::Greater,
+        }
+    }
+}
+
+impl<'tcx> Binder<ExistentialPredicate<'tcx>> {
+    pub fn with_self_ty(&self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> ty::Predicate<'tcx> {
+        use crate::ty::ToPredicate;
+        match self.skip_binder() {
+            ExistentialPredicate::Trait(tr) => {
+                Binder(tr).with_self_ty(tcx, self_ty).without_const().to_predicate(tcx)
+            }
+            ExistentialPredicate::Projection(p) => {
+                Binder(p.with_self_ty(tcx, self_ty)).to_predicate(tcx)
+            }
+            ExistentialPredicate::AutoTrait(did) => {
+                let trait_ref =
+                    Binder(ty::TraitRef { def_id: did, substs: tcx.mk_substs_trait(self_ty, &[]) });
+                trait_ref.without_const().to_predicate(tcx)
+            }
+        }
+    }
+}
+
+impl<'tcx> List<ExistentialPredicate<'tcx>> {
+    /// Returns the "principal `DefId`" of this set of existential predicates.
+    ///
+    /// A Rust trait object type consists (in addition to a lifetime bound)
+    /// of a set of trait bounds, which are separated into any number
+    /// of auto-trait bounds, and at most one non-auto-trait bound. The
+    /// non-auto-trait bound is called the "principal" of the trait
+    /// object.
+    ///
+    /// Only the principal can have methods or type parameters (because
+    /// auto traits can have neither of them). This is important, because
+    /// it means the auto traits can be treated as an unordered set (methods
+    /// would force an order for the vtable, while relating traits with
+    /// type parameters without knowing the order to relate them in is
+    /// a rather non-trivial task).
+    ///
+    /// For example, in the trait object `dyn fmt::Debug + Sync`, the
+    /// principal bound is `Some(fmt::Debug)`, while the auto-trait bounds
+    /// are the set `{Sync}`.
+    ///
+    /// It is also possible to have a "trivial" trait object that
+    /// consists only of auto traits, with no principal - for example,
+    /// `dyn Send + Sync`. In that case, the set of auto-trait bounds
+    /// is `{Send, Sync}`, while there is no principal. These trait objects
+    /// have a "trivial" vtable consisting of just the size, alignment,
+    /// and destructor.
+    pub fn principal(&self) -> Option<ExistentialTraitRef<'tcx>> {
+        match self[0] {
+            ExistentialPredicate::Trait(tr) => Some(tr),
+            _ => None,
+        }
+    }
+
+    pub fn principal_def_id(&self) -> Option<DefId> {
+        self.principal().map(|trait_ref| trait_ref.def_id)
+    }
+
+    #[inline]
+    pub fn projection_bounds<'a>(
+        &'a self,
+    ) -> impl Iterator<Item = ExistentialProjection<'tcx>> + 'a {
+        self.iter().filter_map(|predicate| match predicate {
+            ExistentialPredicate::Projection(projection) => Some(projection),
+            _ => None,
+        })
+    }
+
+    #[inline]
+    pub fn auto_traits<'a>(&'a self) -> impl Iterator<Item = DefId> + 'a {
+        self.iter().filter_map(|predicate| match predicate {
+            ExistentialPredicate::AutoTrait(did) => Some(did),
+            _ => None,
+        })
+    }
+}
+
+impl<'tcx> Binder<&'tcx List<ExistentialPredicate<'tcx>>> {
+    pub fn principal(&self) -> Option<ty::Binder<ExistentialTraitRef<'tcx>>> {
+        self.skip_binder().principal().map(Binder::bind)
+    }
+
+    pub fn principal_def_id(&self) -> Option<DefId> {
+        self.skip_binder().principal_def_id()
+    }
+
+    #[inline]
+    pub fn projection_bounds<'a>(
+        &'a self,
+    ) -> impl Iterator<Item = PolyExistentialProjection<'tcx>> + 'a {
+        self.skip_binder().projection_bounds().map(Binder::bind)
+    }
+
+    #[inline]
+    pub fn auto_traits<'a>(&'a self) -> impl Iterator<Item = DefId> + 'a {
+        self.skip_binder().auto_traits()
+    }
+
+    pub fn iter<'a>(
+        &'a self,
+    ) -> impl DoubleEndedIterator<Item = Binder<ExistentialPredicate<'tcx>>> + 'tcx {
+        self.skip_binder().iter().map(Binder::bind)
+    }
+}
+
+/// A complete reference to a trait. These take numerous guises in syntax,
+/// but perhaps the most recognizable form is in a where-clause:
+///
+///     T: Foo<U>
+///
+/// This would be represented by a trait-reference where the `DefId` is the
+/// `DefId` for the trait `Foo` and the substs define `T` as parameter 0,
+/// and `U` as parameter 1.
+///
+/// Trait references also appear in object types like `Foo<U>`, but in
+/// that case the `Self` parameter is absent from the substitutions.
+#[derive(Copy, Clone, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
+#[derive(HashStable, TypeFoldable)]
+pub struct TraitRef<'tcx> {
+    pub def_id: DefId,
+    pub substs: SubstsRef<'tcx>,
+}
+
+impl<'tcx> TraitRef<'tcx> {
+    pub fn new(def_id: DefId, substs: SubstsRef<'tcx>) -> TraitRef<'tcx> {
+        TraitRef { def_id, substs }
+    }
+
+    /// Returns a `TraitRef` of the form `P0: Foo<P1..Pn>` where `Pi`
+    /// are the parameters defined on trait.
+    pub fn identity(tcx: TyCtxt<'tcx>, def_id: DefId) -> TraitRef<'tcx> {
+        TraitRef { def_id, substs: InternalSubsts::identity_for_item(tcx, def_id) }
+    }
+
+    #[inline]
+    pub fn self_ty(&self) -> Ty<'tcx> {
+        self.substs.type_at(0)
+    }
+
+    pub fn from_method(
+        tcx: TyCtxt<'tcx>,
+        trait_id: DefId,
+        substs: SubstsRef<'tcx>,
+    ) -> ty::TraitRef<'tcx> {
+        let defs = tcx.generics_of(trait_id);
+
+        ty::TraitRef { def_id: trait_id, substs: tcx.intern_substs(&substs[..defs.params.len()]) }
+    }
+}
+
+pub type PolyTraitRef<'tcx> = Binder<TraitRef<'tcx>>;
+
+impl<'tcx> PolyTraitRef<'tcx> {
+    pub fn self_ty(&self) -> Binder<Ty<'tcx>> {
+        self.map_bound_ref(|tr| tr.self_ty())
+    }
+
+    pub fn def_id(&self) -> DefId {
+        self.skip_binder().def_id
+    }
+
+    pub fn to_poly_trait_predicate(&self) -> ty::PolyTraitPredicate<'tcx> {
+        // Note that we preserve binding levels
+        Binder(ty::TraitPredicate { trait_ref: self.skip_binder() })
+    }
+}
+
+/// An existential reference to a trait, where `Self` is erased.
+/// For example, the trait object `Trait<'a, 'b, X, Y>` is:
+///
+///     exists T. T: Trait<'a, 'b, X, Y>
+///
+/// The substitutions don't include the erased `Self`, only trait
+/// type and lifetime parameters (`[X, Y]` and `['a, 'b]` above).
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, TyEncodable, TyDecodable)]
+#[derive(HashStable, TypeFoldable)]
+pub struct ExistentialTraitRef<'tcx> {
+    pub def_id: DefId,
+    pub substs: SubstsRef<'tcx>,
+}
+
+impl<'tcx> ExistentialTraitRef<'tcx> {
+    pub fn erase_self_ty(
+        tcx: TyCtxt<'tcx>,
+        trait_ref: ty::TraitRef<'tcx>,
+    ) -> ty::ExistentialTraitRef<'tcx> {
+        // Assert there is a Self.
+        trait_ref.substs.type_at(0);
+
+        ty::ExistentialTraitRef {
+            def_id: trait_ref.def_id,
+            substs: tcx.intern_substs(&trait_ref.substs[1..]),
+        }
+    }
+
+    /// Object types don't have a self type specified. Therefore, when
+    /// we convert the principal trait-ref into a normal trait-ref,
+    /// you must give *some* self type. A common choice is `mk_err()`
+    /// or some placeholder type.
+    pub fn with_self_ty(&self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> ty::TraitRef<'tcx> {
+        // otherwise the escaping vars would be captured by the binder
+        // debug_assert!(!self_ty.has_escaping_bound_vars());
+
+        ty::TraitRef { def_id: self.def_id, substs: tcx.mk_substs_trait(self_ty, self.substs) }
+    }
+}
+
+pub type PolyExistentialTraitRef<'tcx> = Binder<ExistentialTraitRef<'tcx>>;
+
+impl<'tcx> PolyExistentialTraitRef<'tcx> {
+    pub fn def_id(&self) -> DefId {
+        self.skip_binder().def_id
+    }
+
+    /// Object types don't have a self type specified. Therefore, when
+    /// we convert the principal trait-ref into a normal trait-ref,
+    /// you must give *some* self type. A common choice is `mk_err()`
+    /// or some placeholder type.
+    pub fn with_self_ty(&self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> ty::PolyTraitRef<'tcx> {
+        self.map_bound(|trait_ref| trait_ref.with_self_ty(tcx, self_ty))
+    }
+}
+
+/// Binder is a binder for higher-ranked lifetimes or types. It is part of the
+/// compiler's representation for things like `for<'a> Fn(&'a isize)`
+/// (which would be represented by the type `PolyTraitRef ==
+/// Binder<TraitRef>`). Note that when we instantiate,
+/// erase, or otherwise "discharge" these bound vars, we change the
+/// type from `Binder<T>` to just `T` (see
+/// e.g., `liberate_late_bound_regions`).
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, TyEncodable, TyDecodable)]
+pub struct Binder<T>(T);
+
+impl<T> Binder<T> {
+    /// Wraps `value` in a binder, asserting that `value` does not
+    /// contain any bound vars that would be bound by the
+    /// binder. This is commonly used to 'inject' a value T into a
+    /// different binding level.
+    pub fn dummy<'tcx>(value: T) -> Binder<T>
+    where
+        T: TypeFoldable<'tcx>,
+    {
+        debug_assert!(!value.has_escaping_bound_vars());
+        Binder(value)
+    }
+
+    /// Wraps `value` in a binder, binding higher-ranked vars (if any).
+    pub fn bind(value: T) -> Binder<T> {
+        Binder(value)
+    }
+
+    /// Wraps `value` in a binder without actually binding any currently
+    /// unbound variables.
+    ///
+    /// Note that this will shift all debrujin indices of escaping bound variables
+    /// by 1 to avoid accidential captures.
+    pub fn wrap_nonbinding(tcx: TyCtxt<'tcx>, value: T) -> Binder<T>
+    where
+        T: TypeFoldable<'tcx>,
+    {
+        if value.has_escaping_bound_vars() {
+            Binder::bind(super::fold::shift_vars(tcx, &value, 1))
+        } else {
+            Binder::dummy(value)
+        }
+    }
+
+    /// Skips the binder and returns the "bound" value. This is a
+    /// risky thing to do because it's easy to get confused about
+    /// De Bruijn indices and the like. It is usually better to
+    /// discharge the binder using `no_bound_vars` or
+    /// `replace_late_bound_regions` or something like
+    /// that. `skip_binder` is only valid when you are either
+    /// extracting data that has nothing to do with bound vars, you
+    /// are doing some sort of test that does not involve bound
+    /// regions, or you are being very careful about your depth
+    /// accounting.
+    ///
+    /// Some examples where `skip_binder` is reasonable:
+    ///
+    /// - extracting the `DefId` from a PolyTraitRef;
+    /// - comparing the self type of a PolyTraitRef to see if it is equal to
+    ///   a type parameter `X`, since the type `X` does not reference any regions
+    pub fn skip_binder(self) -> T {
+        self.0
+    }
+
+    pub fn as_ref(&self) -> Binder<&T> {
+        Binder(&self.0)
+    }
+
+    pub fn map_bound_ref<F, U>(&self, f: F) -> Binder<U>
+    where
+        F: FnOnce(&T) -> U,
+    {
+        self.as_ref().map_bound(f)
+    }
+
+    pub fn map_bound<F, U>(self, f: F) -> Binder<U>
+    where
+        F: FnOnce(T) -> U,
+    {
+        Binder(f(self.0))
+    }
+
+    /// Unwraps and returns the value within, but only if it contains
+    /// no bound vars at all. (In other words, if this binder --
+    /// and indeed any enclosing binder -- doesn't bind anything at
+    /// all.) Otherwise, returns `None`.
+    ///
+    /// (One could imagine having a method that just unwraps a single
+    /// binder, but permits late-bound vars bound by enclosing
+    /// binders, but that would require adjusting the debruijn
+    /// indices, and given the shallow binding structure we often use,
+    /// would not be that useful.)
+    pub fn no_bound_vars<'tcx>(self) -> Option<T>
+    where
+        T: TypeFoldable<'tcx>,
+    {
+        if self.0.has_escaping_bound_vars() { None } else { Some(self.skip_binder()) }
+    }
+
+    /// Given two things that have the same binder level,
+    /// and an operation that wraps on their contents, executes the operation
+    /// and then wraps its result.
+    ///
+    /// `f` should consider bound regions at depth 1 to be free, and
+    /// anything it produces with bound regions at depth 1 will be
+    /// bound in the resulting return value.
+    pub fn fuse<U, F, R>(self, u: Binder<U>, f: F) -> Binder<R>
+    where
+        F: FnOnce(T, U) -> R,
+    {
+        Binder(f(self.0, u.0))
+    }
+
+    /// Splits the contents into two things that share the same binder
+    /// level as the original, returning two distinct binders.
+    ///
+    /// `f` should consider bound regions at depth 1 to be free, and
+    /// anything it produces with bound regions at depth 1 will be
+    /// bound in the resulting return values.
+    pub fn split<U, V, F>(self, f: F) -> (Binder<U>, Binder<V>)
+    where
+        F: FnOnce(T) -> (U, V),
+    {
+        let (u, v) = f(self.0);
+        (Binder(u), Binder(v))
+    }
+}
+
+impl<T> Binder<Option<T>> {
+    pub fn transpose(self) -> Option<Binder<T>> {
+        match self.0 {
+            Some(v) => Some(Binder(v)),
+            None => None,
+        }
+    }
+}
+
+/// Represents the projection of an associated type. In explicit UFCS
+/// form this would be written `<T as Trait<..>>::N`.
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, TyEncodable, TyDecodable)]
+#[derive(HashStable, TypeFoldable)]
+pub struct ProjectionTy<'tcx> {
+    /// The parameters of the associated item.
+    pub substs: SubstsRef<'tcx>,
+
+    /// The `DefId` of the `TraitItem` for the associated type `N`.
+    ///
+    /// Note that this is not the `DefId` of the `TraitRef` containing this
+    /// associated type, which is in `tcx.associated_item(item_def_id).container`.
+    pub item_def_id: DefId,
+}
+
+impl<'tcx> ProjectionTy<'tcx> {
+    /// Construct a `ProjectionTy` by searching the trait from `trait_ref` for the
+    /// associated item named `item_name`.
+    pub fn from_ref_and_name(
+        tcx: TyCtxt<'_>,
+        trait_ref: ty::TraitRef<'tcx>,
+        item_name: Ident,
+    ) -> ProjectionTy<'tcx> {
+        let item_def_id = tcx
+            .associated_items(trait_ref.def_id)
+            .find_by_name_and_kind(tcx, item_name, ty::AssocKind::Type, trait_ref.def_id)
+            .unwrap()
+            .def_id;
+
+        ProjectionTy { substs: trait_ref.substs, item_def_id }
+    }
+
+    /// Extracts the underlying trait reference from this projection.
+    /// For example, if this is a projection of `<T as Iterator>::Item`,
+    /// then this function would return a `T: Iterator` trait reference.
+    pub fn trait_ref(&self, tcx: TyCtxt<'tcx>) -> ty::TraitRef<'tcx> {
+        let def_id = tcx.associated_item(self.item_def_id).container.id();
+        ty::TraitRef { def_id, substs: self.substs.truncate_to(tcx, tcx.generics_of(def_id)) }
+    }
+
+    pub fn self_ty(&self) -> Ty<'tcx> {
+        self.substs.type_at(0)
+    }
+}
+
+#[derive(Copy, Clone, Debug, TypeFoldable)]
+pub struct GenSig<'tcx> {
+    pub resume_ty: Ty<'tcx>,
+    pub yield_ty: Ty<'tcx>,
+    pub return_ty: Ty<'tcx>,
+}
+
+pub type PolyGenSig<'tcx> = Binder<GenSig<'tcx>>;
+
+impl<'tcx> PolyGenSig<'tcx> {
+    pub fn resume_ty(&self) -> ty::Binder<Ty<'tcx>> {
+        self.map_bound_ref(|sig| sig.resume_ty)
+    }
+    pub fn yield_ty(&self) -> ty::Binder<Ty<'tcx>> {
+        self.map_bound_ref(|sig| sig.yield_ty)
+    }
+    pub fn return_ty(&self) -> ty::Binder<Ty<'tcx>> {
+        self.map_bound_ref(|sig| sig.return_ty)
+    }
+}
+
+/// Signature of a function type, which we have arbitrarily
+/// decided to use to refer to the input/output types.
+///
+/// - `inputs`: is the list of arguments and their modes.
+/// - `output`: is the return type.
+/// - `c_variadic`: indicates whether this is a C-variadic function.
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, TyEncodable, TyDecodable)]
+#[derive(HashStable, TypeFoldable)]
+pub struct FnSig<'tcx> {
+    pub inputs_and_output: &'tcx List<Ty<'tcx>>,
+    pub c_variadic: bool,
+    pub unsafety: hir::Unsafety,
+    pub abi: abi::Abi,
+}
+
+impl<'tcx> FnSig<'tcx> {
+    pub fn inputs(&self) -> &'tcx [Ty<'tcx>] {
+        &self.inputs_and_output[..self.inputs_and_output.len() - 1]
+    }
+
+    pub fn output(&self) -> Ty<'tcx> {
+        self.inputs_and_output[self.inputs_and_output.len() - 1]
+    }
+
+    // Creates a minimal `FnSig` to be used when encountering a `TyKind::Error` in a fallible
+    // method.
+    fn fake() -> FnSig<'tcx> {
+        FnSig {
+            inputs_and_output: List::empty(),
+            c_variadic: false,
+            unsafety: hir::Unsafety::Normal,
+            abi: abi::Abi::Rust,
+        }
+    }
+}
+
+pub type PolyFnSig<'tcx> = Binder<FnSig<'tcx>>;
+
+impl<'tcx> PolyFnSig<'tcx> {
+    #[inline]
+    pub fn inputs(&self) -> Binder<&'tcx [Ty<'tcx>]> {
+        self.map_bound_ref(|fn_sig| fn_sig.inputs())
+    }
+    #[inline]
+    pub fn input(&self, index: usize) -> ty::Binder<Ty<'tcx>> {
+        self.map_bound_ref(|fn_sig| fn_sig.inputs()[index])
+    }
+    pub fn inputs_and_output(&self) -> ty::Binder<&'tcx List<Ty<'tcx>>> {
+        self.map_bound_ref(|fn_sig| fn_sig.inputs_and_output)
+    }
+    #[inline]
+    pub fn output(&self) -> ty::Binder<Ty<'tcx>> {
+        self.map_bound_ref(|fn_sig| fn_sig.output())
+    }
+    pub fn c_variadic(&self) -> bool {
+        self.skip_binder().c_variadic
+    }
+    pub fn unsafety(&self) -> hir::Unsafety {
+        self.skip_binder().unsafety
+    }
+    pub fn abi(&self) -> abi::Abi {
+        self.skip_binder().abi
+    }
+}
+
+pub type CanonicalPolyFnSig<'tcx> = Canonical<'tcx, Binder<FnSig<'tcx>>>;
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, TyEncodable, TyDecodable)]
+#[derive(HashStable)]
+pub struct ParamTy {
+    pub index: u32,
+    pub name: Symbol,
+}
+
+impl<'tcx> ParamTy {
+    pub fn new(index: u32, name: Symbol) -> ParamTy {
+        ParamTy { index, name }
+    }
+
+    pub fn for_self() -> ParamTy {
+        ParamTy::new(0, kw::SelfUpper)
+    }
+
+    pub fn for_def(def: &ty::GenericParamDef) -> ParamTy {
+        ParamTy::new(def.index, def.name)
+    }
+
+    pub fn to_ty(self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
+        tcx.mk_ty_param(self.index, self.name)
+    }
+}
+
+#[derive(Copy, Clone, Hash, TyEncodable, TyDecodable, Eq, PartialEq, Ord, PartialOrd)]
+#[derive(HashStable)]
+pub struct ParamConst {
+    pub index: u32,
+    pub name: Symbol,
+}
+
+impl<'tcx> ParamConst {
+    pub fn new(index: u32, name: Symbol) -> ParamConst {
+        ParamConst { index, name }
+    }
+
+    pub fn for_def(def: &ty::GenericParamDef) -> ParamConst {
+        ParamConst::new(def.index, def.name)
+    }
+
+    pub fn to_const(self, tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> &'tcx ty::Const<'tcx> {
+        tcx.mk_const_param(self.index, self.name, ty)
+    }
+}
+
+rustc_index::newtype_index! {
+    /// A [De Bruijn index][dbi] is a standard means of representing
+    /// regions (and perhaps later types) in a higher-ranked setting. In
+    /// particular, imagine a type like this:
+    ///
+    ///     for<'a> fn(for<'b> fn(&'b isize, &'a isize), &'a char)
+    ///     ^          ^            |        |         |
+    ///     |          |            |        |         |
+    ///     |          +------------+ 0      |         |
+    ///     |                                |         |
+    ///     +--------------------------------+ 1       |
+    ///     |                                          |
+    ///     +------------------------------------------+ 0
+    ///
+    /// In this type, there are two binders (the outer fn and the inner
+    /// fn). We need to be able to determine, for any given region, which
+    /// fn type it is bound by, the inner or the outer one. There are
+    /// various ways you can do this, but a De Bruijn index is one of the
+    /// more convenient and has some nice properties. The basic idea is to
+    /// count the number of binders, inside out. Some examples should help
+    /// clarify what I mean.
+    ///
+    /// Let's start with the reference type `&'b isize` that is the first
+    /// argument to the inner function. This region `'b` is assigned a De
+    /// Bruijn index of 0, meaning "the innermost binder" (in this case, a
+    /// fn). The region `'a` that appears in the second argument type (`&'a
+    /// isize`) would then be assigned a De Bruijn index of 1, meaning "the
+    /// second-innermost binder". (These indices are written on the arrays
+    /// in the diagram).
+    ///
+    /// What is interesting is that De Bruijn index attached to a particular
+    /// variable will vary depending on where it appears. For example,
+    /// the final type `&'a char` also refers to the region `'a` declared on
+    /// the outermost fn. But this time, this reference is not nested within
+    /// any other binders (i.e., it is not an argument to the inner fn, but
+    /// rather the outer one). Therefore, in this case, it is assigned a
+    /// De Bruijn index of 0, because the innermost binder in that location
+    /// is the outer fn.
+    ///
+    /// [dbi]: https://en.wikipedia.org/wiki/De_Bruijn_index
+    #[derive(HashStable)]
+    pub struct DebruijnIndex {
+        DEBUG_FORMAT = "DebruijnIndex({})",
+        const INNERMOST = 0,
+    }
+}
+
+pub type Region<'tcx> = &'tcx RegionKind;
+
+/// Representation of regions. Note that the NLL checker uses a distinct
+/// representation of regions. For this reason, it internally replaces all the
+/// regions with inference variables -- the index of the variable is then used
+/// to index into internal NLL data structures. See `rustc_mir::borrow_check`
+/// module for more information.
+///
+/// ## The Region lattice within a given function
+///
+/// In general, the region lattice looks like
+///
+/// ```
+/// static ----------+-----...------+       (greatest)
+/// |                |              |
+/// early-bound and  |              |
+/// free regions     |              |
+/// |                |              |
+/// |                |              |
+/// empty(root)   placeholder(U1)   |
+/// |            /                  |
+/// |           /         placeholder(Un)
+/// empty(U1) --         /
+/// |                   /
+/// ...                /
+/// |                 /
+/// empty(Un) --------                      (smallest)
+/// ```
+///
+/// Early-bound/free regions are the named lifetimes in scope from the
+/// function declaration. They have relationships to one another
+/// determined based on the declared relationships from the
+/// function.
+///
+/// Note that inference variables and bound regions are not included
+/// in this diagram. In the case of inference variables, they should
+/// be inferred to some other region from the diagram.  In the case of
+/// bound regions, they are excluded because they don't make sense to
+/// include -- the diagram indicates the relationship between free
+/// regions.
+///
+/// ## Inference variables
+///
+/// During region inference, we sometimes create inference variables,
+/// represented as `ReVar`. These will be inferred by the code in
+/// `infer::lexical_region_resolve` to some free region from the
+/// lattice above (the minimal region that meets the
+/// constraints).
+///
+/// During NLL checking, where regions are defined differently, we
+/// also use `ReVar` -- in that case, the index is used to index into
+/// the NLL region checker's data structures. The variable may in fact
+/// represent either a free region or an inference variable, in that
+/// case.
+///
+/// ## Bound Regions
+///
+/// These are regions that are stored behind a binder and must be substituted
+/// with some concrete region before being used. There are two kind of
+/// bound regions: early-bound, which are bound in an item's `Generics`,
+/// and are substituted by a `InternalSubsts`, and late-bound, which are part of
+/// higher-ranked types (e.g., `for<'a> fn(&'a ())`), and are substituted by
+/// the likes of `liberate_late_bound_regions`. The distinction exists
+/// because higher-ranked lifetimes aren't supported in all places. See [1][2].
+///
+/// Unlike `Param`s, bound regions are not supposed to exist "in the wild"
+/// outside their binder, e.g., in types passed to type inference, and
+/// should first be substituted (by placeholder regions, free regions,
+/// or region variables).
+///
+/// ## Placeholder and Free Regions
+///
+/// One often wants to work with bound regions without knowing their precise
+/// identity. For example, when checking a function, the lifetime of a borrow
+/// can end up being assigned to some region parameter. In these cases,
+/// it must be ensured that bounds on the region can't be accidentally
+/// assumed without being checked.
+///
+/// To do this, we replace the bound regions with placeholder markers,
+/// which don't satisfy any relation not explicitly provided.
+///
+/// There are two kinds of placeholder regions in rustc: `ReFree` and
+/// `RePlaceholder`. When checking an item's body, `ReFree` is supposed
+/// to be used. These also support explicit bounds: both the internally-stored
+/// *scope*, which the region is assumed to outlive, as well as other
+/// relations stored in the `FreeRegionMap`. Note that these relations
+/// aren't checked when you `make_subregion` (or `eq_types`), only by
+/// `resolve_regions_and_report_errors`.
+///
+/// When working with higher-ranked types, some region relations aren't
+/// yet known, so you can't just call `resolve_regions_and_report_errors`.
+/// `RePlaceholder` is designed for this purpose. In these contexts,
+/// there's also the risk that some inference variable laying around will
+/// get unified with your placeholder region: if you want to check whether
+/// `for<'a> Foo<'_>: 'a`, and you substitute your bound region `'a`
+/// with a placeholder region `'%a`, the variable `'_` would just be
+/// instantiated to the placeholder region `'%a`, which is wrong because
+/// the inference variable is supposed to satisfy the relation
+/// *for every value of the placeholder region*. To ensure that doesn't
+/// happen, you can use `leak_check`. This is more clearly explained
+/// by the [rustc dev guide].
+///
+/// [1]: http://smallcultfollowing.com/babysteps/blog/2013/10/29/intermingled-parameter-lists/
+/// [2]: http://smallcultfollowing.com/babysteps/blog/2013/11/04/intermingled-parameter-lists/
+/// [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/hrtb.html
+#[derive(Clone, PartialEq, Eq, Hash, Copy, TyEncodable, TyDecodable, PartialOrd, Ord)]
+pub enum RegionKind {
+    /// Region bound in a type or fn declaration which will be
+    /// substituted 'early' -- that is, at the same time when type
+    /// parameters are substituted.
+    ReEarlyBound(EarlyBoundRegion),
+
+    /// Region bound in a function scope, which will be substituted when the
+    /// function is called.
+    ReLateBound(DebruijnIndex, BoundRegion),
+
+    /// When checking a function body, the types of all arguments and so forth
+    /// that refer to bound region parameters are modified to refer to free
+    /// region parameters.
+    ReFree(FreeRegion),
+
+    /// Static data that has an "infinite" lifetime. Top in the region lattice.
+    ReStatic,
+
+    /// A region variable. Should not exist after typeck.
+    ReVar(RegionVid),
+
+    /// A placeholder region -- basically, the higher-ranked version of `ReFree`.
+    /// Should not exist after typeck.
+    RePlaceholder(ty::PlaceholderRegion),
+
+    /// Empty lifetime is for data that is never accessed.  We tag the
+    /// empty lifetime with a universe -- the idea is that we don't
+    /// want `exists<'a> { forall<'b> { 'b: 'a } }` to be satisfiable.
+    /// Therefore, the `'empty` in a universe `U` is less than all
+    /// regions visible from `U`, but not less than regions not visible
+    /// from `U`.
+    ReEmpty(ty::UniverseIndex),
+
+    /// Erased region, used by trait selection, in MIR and during codegen.
+    ReErased,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Hash, TyEncodable, TyDecodable, Debug, PartialOrd, Ord)]
+pub struct EarlyBoundRegion {
+    pub def_id: DefId,
+    pub index: u32,
+    pub name: Symbol,
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, TyEncodable, TyDecodable)]
+pub struct TyVid {
+    pub index: u32,
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, TyEncodable, TyDecodable)]
+pub struct ConstVid<'tcx> {
+    pub index: u32,
+    pub phantom: PhantomData<&'tcx ()>,
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, TyEncodable, TyDecodable)]
+pub struct IntVid {
+    pub index: u32,
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, TyEncodable, TyDecodable)]
+pub struct FloatVid {
+    pub index: u32,
+}
+
+rustc_index::newtype_index! {
+    pub struct RegionVid {
+        DEBUG_FORMAT = custom,
+    }
+}
+
+impl Atom for RegionVid {
+    fn index(self) -> usize {
+        Idx::index(self)
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, TyEncodable, TyDecodable)]
+#[derive(HashStable)]
+pub enum InferTy {
+    TyVar(TyVid),
+    IntVar(IntVid),
+    FloatVar(FloatVid),
+
+    /// A `FreshTy` is one that is generated as a replacement for an
+    /// unbound type variable. This is convenient for caching etc. See
+    /// `infer::freshen` for more details.
+    FreshTy(u32),
+    FreshIntTy(u32),
+    FreshFloatTy(u32),
+}
+
+rustc_index::newtype_index! {
+    pub struct BoundVar { .. }
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, TyEncodable, TyDecodable)]
+#[derive(HashStable)]
+pub struct BoundTy {
+    pub var: BoundVar,
+    pub kind: BoundTyKind,
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, TyEncodable, TyDecodable)]
+#[derive(HashStable)]
+pub enum BoundTyKind {
+    Anon,
+    Param(Symbol),
+}
+
+impl From<BoundVar> for BoundTy {
+    fn from(var: BoundVar) -> Self {
+        BoundTy { var, kind: BoundTyKind::Anon }
+    }
+}
+
+/// A `ProjectionPredicate` for an `ExistentialTraitRef`.
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, TyEncodable, TyDecodable)]
+#[derive(HashStable, TypeFoldable)]
+pub struct ExistentialProjection<'tcx> {
+    pub item_def_id: DefId,
+    pub substs: SubstsRef<'tcx>,
+    pub ty: Ty<'tcx>,
+}
+
+pub type PolyExistentialProjection<'tcx> = Binder<ExistentialProjection<'tcx>>;
+
+impl<'tcx> ExistentialProjection<'tcx> {
+    /// Extracts the underlying existential trait reference from this projection.
+    /// For example, if this is a projection of `exists T. <T as Iterator>::Item == X`,
+    /// then this function would return a `exists T. T: Iterator` existential trait
+    /// reference.
+    pub fn trait_ref(&self, tcx: TyCtxt<'_>) -> ty::ExistentialTraitRef<'tcx> {
+        let def_id = tcx.associated_item(self.item_def_id).container.id();
+        ty::ExistentialTraitRef { def_id, substs: self.substs }
+    }
+
+    pub fn with_self_ty(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        self_ty: Ty<'tcx>,
+    ) -> ty::ProjectionPredicate<'tcx> {
+        // otherwise the escaping regions would be captured by the binders
+        debug_assert!(!self_ty.has_escaping_bound_vars());
+
+        ty::ProjectionPredicate {
+            projection_ty: ty::ProjectionTy {
+                item_def_id: self.item_def_id,
+                substs: tcx.mk_substs_trait(self_ty, self.substs),
+            },
+            ty: self.ty,
+        }
+    }
+}
+
+impl<'tcx> PolyExistentialProjection<'tcx> {
+    pub fn with_self_ty(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        self_ty: Ty<'tcx>,
+    ) -> ty::PolyProjectionPredicate<'tcx> {
+        self.map_bound(|p| p.with_self_ty(tcx, self_ty))
+    }
+
+    pub fn item_def_id(&self) -> DefId {
+        self.skip_binder().item_def_id
+    }
+}
+
+impl DebruijnIndex {
+    /// Returns the resulting index when this value is moved into
+    /// `amount` number of new binders. So, e.g., if you had
+    ///
+    ///    for<'a> fn(&'a x)
+    ///
+    /// and you wanted to change it to
+    ///
+    ///    for<'a> fn(for<'b> fn(&'a x))
+    ///
+    /// you would need to shift the index for `'a` into a new binder.
+    #[must_use]
+    pub fn shifted_in(self, amount: u32) -> DebruijnIndex {
+        DebruijnIndex::from_u32(self.as_u32() + amount)
+    }
+
+    /// Update this index in place by shifting it "in" through
+    /// `amount` number of binders.
+    pub fn shift_in(&mut self, amount: u32) {
+        *self = self.shifted_in(amount);
+    }
+
+    /// Returns the resulting index when this value is moved out from
+    /// `amount` number of new binders.
+    #[must_use]
+    pub fn shifted_out(self, amount: u32) -> DebruijnIndex {
+        DebruijnIndex::from_u32(self.as_u32() - amount)
+    }
+
+    /// Update in place by shifting out from `amount` binders.
+    pub fn shift_out(&mut self, amount: u32) {
+        *self = self.shifted_out(amount);
+    }
+
+    /// Adjusts any De Bruijn indices so as to make `to_binder` the
+    /// innermost binder. That is, if we have something bound at `to_binder`,
+    /// it will now be bound at INNERMOST. This is an appropriate thing to do
+    /// when moving a region out from inside binders:
+    ///
+    /// ```
+    ///             for<'a>   fn(for<'b>   for<'c>   fn(&'a u32), _)
+    /// // Binder:  D3           D2        D1            ^^
+    /// ```
+    ///
+    /// Here, the region `'a` would have the De Bruijn index D3,
+    /// because it is the bound 3 binders out. However, if we wanted
+    /// to refer to that region `'a` in the second argument (the `_`),
+    /// those two binders would not be in scope. In that case, we
+    /// might invoke `shift_out_to_binder(D3)`. This would adjust the
+    /// De Bruijn index of `'a` to D1 (the innermost binder).
+    ///
+    /// If we invoke `shift_out_to_binder` and the region is in fact
+    /// bound by one of the binders we are shifting out of, that is an
+    /// error (and should fail an assertion failure).
+    pub fn shifted_out_to_binder(self, to_binder: DebruijnIndex) -> Self {
+        self.shifted_out(to_binder.as_u32() - INNERMOST.as_u32())
+    }
+}
+
+/// Region utilities
+impl RegionKind {
+    /// Is this region named by the user?
+    pub fn has_name(&self) -> bool {
+        match *self {
+            RegionKind::ReEarlyBound(ebr) => ebr.has_name(),
+            RegionKind::ReLateBound(_, br) => br.is_named(),
+            RegionKind::ReFree(fr) => fr.bound_region.is_named(),
+            RegionKind::ReStatic => true,
+            RegionKind::ReVar(..) => false,
+            RegionKind::RePlaceholder(placeholder) => placeholder.name.is_named(),
+            RegionKind::ReEmpty(_) => false,
+            RegionKind::ReErased => false,
+        }
+    }
+
+    pub fn is_late_bound(&self) -> bool {
+        match *self {
+            ty::ReLateBound(..) => true,
+            _ => false,
+        }
+    }
+
+    pub fn is_placeholder(&self) -> bool {
+        match *self {
+            ty::RePlaceholder(..) => true,
+            _ => false,
+        }
+    }
+
+    pub fn bound_at_or_above_binder(&self, index: DebruijnIndex) -> bool {
+        match *self {
+            ty::ReLateBound(debruijn, _) => debruijn >= index,
+            _ => false,
+        }
+    }
+
+    /// Adjusts any De Bruijn indices so as to make `to_binder` the
+    /// innermost binder. That is, if we have something bound at `to_binder`,
+    /// it will now be bound at INNERMOST. This is an appropriate thing to do
+    /// when moving a region out from inside binders:
+    ///
+    /// ```
+    ///             for<'a>   fn(for<'b>   for<'c>   fn(&'a u32), _)
+    /// // Binder:  D3           D2        D1            ^^
+    /// ```
+    ///
+    /// Here, the region `'a` would have the De Bruijn index D3,
+    /// because it is the bound 3 binders out. However, if we wanted
+    /// to refer to that region `'a` in the second argument (the `_`),
+    /// those two binders would not be in scope. In that case, we
+    /// might invoke `shift_out_to_binder(D3)`. This would adjust the
+    /// De Bruijn index of `'a` to D1 (the innermost binder).
+    ///
+    /// If we invoke `shift_out_to_binder` and the region is in fact
+    /// bound by one of the binders we are shifting out of, that is an
+    /// error (and should fail an assertion failure).
+    pub fn shifted_out_to_binder(&self, to_binder: ty::DebruijnIndex) -> RegionKind {
+        match *self {
+            ty::ReLateBound(debruijn, r) => {
+                ty::ReLateBound(debruijn.shifted_out_to_binder(to_binder), r)
+            }
+            r => r,
+        }
+    }
+
+    pub fn type_flags(&self) -> TypeFlags {
+        let mut flags = TypeFlags::empty();
+
+        match *self {
+            ty::ReVar(..) => {
+                flags = flags | TypeFlags::HAS_FREE_REGIONS;
+                flags = flags | TypeFlags::HAS_FREE_LOCAL_REGIONS;
+                flags = flags | TypeFlags::HAS_RE_INFER;
+            }
+            ty::RePlaceholder(..) => {
+                flags = flags | TypeFlags::HAS_FREE_REGIONS;
+                flags = flags | TypeFlags::HAS_FREE_LOCAL_REGIONS;
+                flags = flags | TypeFlags::HAS_RE_PLACEHOLDER;
+            }
+            ty::ReEarlyBound(..) => {
+                flags = flags | TypeFlags::HAS_FREE_REGIONS;
+                flags = flags | TypeFlags::HAS_FREE_LOCAL_REGIONS;
+                flags = flags | TypeFlags::HAS_RE_PARAM;
+            }
+            ty::ReFree { .. } => {
+                flags = flags | TypeFlags::HAS_FREE_REGIONS;
+                flags = flags | TypeFlags::HAS_FREE_LOCAL_REGIONS;
+            }
+            ty::ReEmpty(_) | ty::ReStatic => {
+                flags = flags | TypeFlags::HAS_FREE_REGIONS;
+            }
+            ty::ReLateBound(..) => {
+                flags = flags | TypeFlags::HAS_RE_LATE_BOUND;
+            }
+            ty::ReErased => {
+                flags = flags | TypeFlags::HAS_RE_ERASED;
+            }
+        }
+
+        debug!("type_flags({:?}) = {:?}", self, flags);
+
+        flags
+    }
+
+    /// Given an early-bound or free region, returns the `DefId` where it was bound.
+    /// For example, consider the regions in this snippet of code:
+    ///
+    /// ```
+    /// impl<'a> Foo {
+    ///      ^^ -- early bound, declared on an impl
+    ///
+    ///     fn bar<'b, 'c>(x: &self, y: &'b u32, z: &'c u64) where 'static: 'c
+    ///            ^^  ^^     ^ anonymous, late-bound
+    ///            |   early-bound, appears in where-clauses
+    ///            late-bound, appears only in fn args
+    ///     {..}
+    /// }
+    /// ```
+    ///
+    /// Here, `free_region_binding_scope('a)` would return the `DefId`
+    /// of the impl, and for all the other highlighted regions, it
+    /// would return the `DefId` of the function. In other cases (not shown), this
+    /// function might return the `DefId` of a closure.
+    pub fn free_region_binding_scope(&self, tcx: TyCtxt<'_>) -> DefId {
+        match self {
+            ty::ReEarlyBound(br) => tcx.parent(br.def_id).unwrap(),
+            ty::ReFree(fr) => fr.scope,
+            _ => bug!("free_region_binding_scope invoked on inappropriate region: {:?}", self),
+        }
+    }
+}
+
+/// Type utilities
+impl<'tcx> TyS<'tcx> {
+    #[inline]
+    pub fn is_unit(&self) -> bool {
+        match self.kind {
+            Tuple(ref tys) => tys.is_empty(),
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_never(&self) -> bool {
+        match self.kind {
+            Never => true,
+            _ => false,
+        }
+    }
+
+    /// Checks whether a type is definitely uninhabited. This is
+    /// conservative: for some types that are uninhabited we return `false`,
+    /// but we only return `true` for types that are definitely uninhabited.
+    /// `ty.conservative_is_privately_uninhabited` implies that any value of type `ty`
+    /// will be `Abi::Uninhabited`. (Note that uninhabited types may have nonzero
+    /// size, to account for partial initialisation. See #49298 for details.)
+    pub fn conservative_is_privately_uninhabited(&self, tcx: TyCtxt<'tcx>) -> bool {
+        // FIXME(varkor): we can make this less conversative by substituting concrete
+        // type arguments.
+        match self.kind {
+            ty::Never => true,
+            ty::Adt(def, _) if def.is_union() => {
+                // For now, `union`s are never considered uninhabited.
+                false
+            }
+            ty::Adt(def, _) => {
+                // Any ADT is uninhabited if either:
+                // (a) It has no variants (i.e. an empty `enum`);
+                // (b) Each of its variants (a single one in the case of a `struct`) has at least
+                //     one uninhabited field.
+                def.variants.iter().all(|var| {
+                    var.fields.iter().any(|field| {
+                        tcx.type_of(field.did).conservative_is_privately_uninhabited(tcx)
+                    })
+                })
+            }
+            ty::Tuple(..) => {
+                self.tuple_fields().any(|ty| ty.conservative_is_privately_uninhabited(tcx))
+            }
+            ty::Array(ty, len) => {
+                match len.try_eval_usize(tcx, ParamEnv::empty()) {
+                    // If the array is definitely non-empty, it's uninhabited if
+                    // the type of its elements is uninhabited.
+                    Some(n) if n != 0 => ty.conservative_is_privately_uninhabited(tcx),
+                    _ => false,
+                }
+            }
+            ty::Ref(..) => {
+                // References to uninitialised memory is valid for any type, including
+                // uninhabited types, in unsafe code, so we treat all references as
+                // inhabited.
+                false
+            }
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_primitive(&self) -> bool {
+        self.kind.is_primitive()
+    }
+
+    #[inline]
+    pub fn is_ty_var(&self) -> bool {
+        match self.kind {
+            Infer(TyVar(_)) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_ty_infer(&self) -> bool {
+        match self.kind {
+            Infer(_) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_phantom_data(&self) -> bool {
+        if let Adt(def, _) = self.kind { def.is_phantom_data() } else { false }
+    }
+
+    #[inline]
+    pub fn is_bool(&self) -> bool {
+        self.kind == Bool
+    }
+
+    /// Returns `true` if this type is a `str`.
+    #[inline]
+    pub fn is_str(&self) -> bool {
+        self.kind == Str
+    }
+
+    #[inline]
+    pub fn is_param(&self, index: u32) -> bool {
+        match self.kind {
+            ty::Param(ref data) => data.index == index,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_slice(&self) -> bool {
+        match self.kind {
+            RawPtr(TypeAndMut { ty, .. }) | Ref(_, ty, _) => match ty.kind {
+                Slice(_) | Str => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_simd(&self) -> bool {
+        match self.kind {
+            Adt(def, _) => def.repr.simd(),
+            _ => false,
+        }
+    }
+
+    pub fn sequence_element_type(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
+        match self.kind {
+            Array(ty, _) | Slice(ty) => ty,
+            Str => tcx.mk_mach_uint(ast::UintTy::U8),
+            _ => bug!("`sequence_element_type` called on non-sequence value: {}", self),
+        }
+    }
+
+    pub fn simd_type(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
+        match self.kind {
+            Adt(def, substs) => def.non_enum_variant().fields[0].ty(tcx, substs),
+            _ => bug!("`simd_type` called on invalid type"),
+        }
+    }
+
+    pub fn simd_size(&self, _tcx: TyCtxt<'tcx>) -> u64 {
+        // Parameter currently unused, but probably needed in the future to
+        // allow `#[repr(simd)] struct Simd<T, const N: usize>([T; N]);`.
+        match self.kind {
+            Adt(def, _) => def.non_enum_variant().fields.len() as u64,
+            _ => bug!("`simd_size` called on invalid type"),
+        }
+    }
+
+    pub fn simd_size_and_type(&self, tcx: TyCtxt<'tcx>) -> (u64, Ty<'tcx>) {
+        match self.kind {
+            Adt(def, substs) => {
+                let variant = def.non_enum_variant();
+                (variant.fields.len() as u64, variant.fields[0].ty(tcx, substs))
+            }
+            _ => bug!("`simd_size_and_type` called on invalid type"),
+        }
+    }
+
+    #[inline]
+    pub fn is_region_ptr(&self) -> bool {
+        match self.kind {
+            Ref(..) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_mutable_ptr(&self) -> bool {
+        match self.kind {
+            RawPtr(TypeAndMut { mutbl: hir::Mutability::Mut, .. })
+            | Ref(_, _, hir::Mutability::Mut) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_unsafe_ptr(&self) -> bool {
+        match self.kind {
+            RawPtr(_) => true,
+            _ => false,
+        }
+    }
+
+    /// Tests if this is any kind of primitive pointer type (reference, raw pointer, fn pointer).
+    #[inline]
+    pub fn is_any_ptr(&self) -> bool {
+        self.is_region_ptr() || self.is_unsafe_ptr() || self.is_fn_ptr()
+    }
+
+    #[inline]
+    pub fn is_box(&self) -> bool {
+        match self.kind {
+            Adt(def, _) => def.is_box(),
+            _ => false,
+        }
+    }
+
+    /// Panics if called on any type other than `Box<T>`.
+    pub fn boxed_ty(&self) -> Ty<'tcx> {
+        match self.kind {
+            Adt(def, substs) if def.is_box() => substs.type_at(0),
+            _ => bug!("`boxed_ty` is called on non-box type {:?}", self),
+        }
+    }
+
+    /// A scalar type is one that denotes an atomic datum, with no sub-components.
+    /// (A RawPtr is scalar because it represents a non-managed pointer, so its
+    /// contents are abstract to rustc.)
+    #[inline]
+    pub fn is_scalar(&self) -> bool {
+        match self.kind {
+            Bool
+            | Char
+            | Int(_)
+            | Float(_)
+            | Uint(_)
+            | Infer(IntVar(_) | FloatVar(_))
+            | FnDef(..)
+            | FnPtr(_)
+            | RawPtr(_) => true,
+            _ => false,
+        }
+    }
+
+    /// Returns `true` if this type is a floating point type.
+    #[inline]
+    pub fn is_floating_point(&self) -> bool {
+        match self.kind {
+            Float(_) | Infer(FloatVar(_)) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_trait(&self) -> bool {
+        match self.kind {
+            Dynamic(..) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_enum(&self) -> bool {
+        match self.kind {
+            Adt(adt_def, _) => adt_def.is_enum(),
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_closure(&self) -> bool {
+        match self.kind {
+            Closure(..) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_generator(&self) -> bool {
+        match self.kind {
+            Generator(..) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_integral(&self) -> bool {
+        match self.kind {
+            Infer(IntVar(_)) | Int(_) | Uint(_) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_fresh_ty(&self) -> bool {
+        match self.kind {
+            Infer(FreshTy(_)) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_fresh(&self) -> bool {
+        match self.kind {
+            Infer(FreshTy(_)) => true,
+            Infer(FreshIntTy(_)) => true,
+            Infer(FreshFloatTy(_)) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_char(&self) -> bool {
+        match self.kind {
+            Char => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_numeric(&self) -> bool {
+        self.is_integral() || self.is_floating_point()
+    }
+
+    #[inline]
+    pub fn is_signed(&self) -> bool {
+        match self.kind {
+            Int(_) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_ptr_sized_integral(&self) -> bool {
+        match self.kind {
+            Int(ast::IntTy::Isize) | Uint(ast::UintTy::Usize) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_machine(&self) -> bool {
+        match self.kind {
+            Int(..) | Uint(..) | Float(..) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn has_concrete_skeleton(&self) -> bool {
+        match self.kind {
+            Param(_) | Infer(_) | Error(_) => false,
+            _ => true,
+        }
+    }
+
+    /// Returns the type and mutability of `*ty`.
+    ///
+    /// The parameter `explicit` indicates if this is an *explicit* dereference.
+    /// Some types -- notably unsafe ptrs -- can only be dereferenced explicitly.
+    pub fn builtin_deref(&self, explicit: bool) -> Option<TypeAndMut<'tcx>> {
+        match self.kind {
+            Adt(def, _) if def.is_box() => {
+                Some(TypeAndMut { ty: self.boxed_ty(), mutbl: hir::Mutability::Not })
+            }
+            Ref(_, ty, mutbl) => Some(TypeAndMut { ty, mutbl }),
+            RawPtr(mt) if explicit => Some(mt),
+            _ => None,
+        }
+    }
+
+    /// Returns the type of `ty[i]`.
+    pub fn builtin_index(&self) -> Option<Ty<'tcx>> {
+        match self.kind {
+            Array(ty, _) | Slice(ty) => Some(ty),
+            _ => None,
+        }
+    }
+
+    pub fn fn_sig(&self, tcx: TyCtxt<'tcx>) -> PolyFnSig<'tcx> {
+        match self.kind {
+            FnDef(def_id, substs) => tcx.fn_sig(def_id).subst(tcx, substs),
+            FnPtr(f) => f,
+            Error(_) => {
+                // ignore errors (#54954)
+                ty::Binder::dummy(FnSig::fake())
+            }
+            Closure(..) => bug!(
+                "to get the signature of a closure, use `substs.as_closure().sig()` not `fn_sig()`",
+            ),
+            _ => bug!("Ty::fn_sig() called on non-fn type: {:?}", self),
+        }
+    }
+
+    #[inline]
+    pub fn is_fn(&self) -> bool {
+        match self.kind {
+            FnDef(..) | FnPtr(_) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_fn_ptr(&self) -> bool {
+        match self.kind {
+            FnPtr(_) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn is_impl_trait(&self) -> bool {
+        match self.kind {
+            Opaque(..) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    pub fn ty_adt_def(&self) -> Option<&'tcx AdtDef> {
+        match self.kind {
+            Adt(adt, _) => Some(adt),
+            _ => None,
+        }
+    }
+
+    /// Iterates over tuple fields.
+    /// Panics when called on anything but a tuple.
+    pub fn tuple_fields(&self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> {
+        match self.kind {
+            Tuple(substs) => substs.iter().map(|field| field.expect_ty()),
+            _ => bug!("tuple_fields called on non-tuple"),
+        }
+    }
+
+    /// If the type contains variants, returns the valid range of variant indices.
+    //
+    // FIXME: This requires the optimized MIR in the case of generators.
+    #[inline]
+    pub fn variant_range(&self, tcx: TyCtxt<'tcx>) -> Option<Range<VariantIdx>> {
+        match self.kind {
+            TyKind::Adt(adt, _) => Some(adt.variant_range()),
+            TyKind::Generator(def_id, substs, _) => {
+                Some(substs.as_generator().variant_range(def_id, tcx))
+            }
+            _ => None,
+        }
+    }
+
+    /// If the type contains variants, returns the variant for `variant_index`.
+    /// Panics if `variant_index` is out of range.
+    //
+    // FIXME: This requires the optimized MIR in the case of generators.
+    #[inline]
+    pub fn discriminant_for_variant(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        variant_index: VariantIdx,
+    ) -> Option<Discr<'tcx>> {
+        match self.kind {
+            TyKind::Adt(adt, _) if adt.variants.is_empty() => {
+                bug!("discriminant_for_variant called on zero variant enum");
+            }
+            TyKind::Adt(adt, _) if adt.is_enum() => {
+                Some(adt.discriminant_for_variant(tcx, variant_index))
+            }
+            TyKind::Generator(def_id, substs, _) => {
+                Some(substs.as_generator().discriminant_for_variant(def_id, tcx, variant_index))
+            }
+            _ => None,
+        }
+    }
+
+    /// Returns the type of the discriminant of this type.
+    pub fn discriminant_ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
+        match self.kind {
+            ty::Adt(adt, _) if adt.is_enum() => adt.repr.discr_type().to_ty(tcx),
+            ty::Generator(_, substs, _) => substs.as_generator().discr_ty(tcx),
+            _ => {
+                // This can only be `0`, for now, so `u8` will suffice.
+                tcx.types.u8
+            }
+        }
+    }
+
+    /// When we create a closure, we record its kind (i.e., what trait
+    /// it implements) into its `ClosureSubsts` using a type
+    /// parameter. This is kind of a phantom type, except that the
+    /// most convenient thing for us to are the integral types. This
+    /// function converts such a special type into the closure
+    /// kind. To go the other way, use
+    /// `tcx.closure_kind_ty(closure_kind)`.
+    ///
+    /// Note that during type checking, we use an inference variable
+    /// to represent the closure kind, because it has not yet been
+    /// inferred. Once upvar inference (in `src/librustc_typeck/check/upvar.rs`)
+    /// is complete, that type variable will be unified.
+    pub fn to_opt_closure_kind(&self) -> Option<ty::ClosureKind> {
+        match self.kind {
+            Int(int_ty) => match int_ty {
+                ast::IntTy::I8 => Some(ty::ClosureKind::Fn),
+                ast::IntTy::I16 => Some(ty::ClosureKind::FnMut),
+                ast::IntTy::I32 => Some(ty::ClosureKind::FnOnce),
+                _ => bug!("cannot convert type `{:?}` to a closure kind", self),
+            },
+
+            // "Bound" types appear in canonical queries when the
+            // closure type is not yet known
+            Bound(..) | Infer(_) => None,
+
+            Error(_) => Some(ty::ClosureKind::Fn),
+
+            _ => bug!("cannot convert type `{:?}` to a closure kind", self),
+        }
+    }
+
+    /// Fast path helper for testing if a type is `Sized`.
+    ///
+    /// Returning true means the type is known to be sized. Returning
+    /// `false` means nothing -- could be sized, might not be.
+    pub fn is_trivially_sized(&self, tcx: TyCtxt<'tcx>) -> bool {
+        match self.kind {
+            ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
+            | ty::Uint(_)
+            | ty::Int(_)
+            | ty::Bool
+            | ty::Float(_)
+            | ty::FnDef(..)
+            | ty::FnPtr(_)
+            | ty::RawPtr(..)
+            | ty::Char
+            | ty::Ref(..)
+            | ty::Generator(..)
+            | ty::GeneratorWitness(..)
+            | ty::Array(..)
+            | ty::Closure(..)
+            | ty::Never
+            | ty::Error(_) => true,
+
+            ty::Str | ty::Slice(_) | ty::Dynamic(..) | ty::Foreign(..) => false,
+
+            ty::Tuple(tys) => tys.iter().all(|ty| ty.expect_ty().is_trivially_sized(tcx)),
+
+            ty::Adt(def, _substs) => def.sized_constraint(tcx).is_empty(),
+
+            ty::Projection(_) | ty::Param(_) | ty::Opaque(..) => false,
+
+            ty::Infer(ty::TyVar(_)) => false,
+
+            ty::Bound(..)
+            | ty::Placeholder(..)
+            | ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
+                bug!("`is_trivially_sized` applied to unexpected type: {:?}", self)
+            }
+        }
+    }
+
+    /// Is this a zero-sized type?
+    pub fn is_zst(&'tcx self, tcx: TyCtxt<'tcx>, did: DefId) -> bool {
+        tcx.layout_of(tcx.param_env(did).and(self)).map(|layout| layout.is_zst()).unwrap_or(false)
+    }
+}