compiler/rustc_traits/src/chalk/lowering.rs

   1 //! Contains the logic to lower rustc types into Chalk types
   2 //!
   3 //! In many cases there is a 1:1 relationship between a rustc type and a Chalk type.
   4 //! For example, a `SubstsRef` maps almost directly to a `Substitution`. In some
   5 //! other cases, such as `Param`s, there is no Chalk type, so we have to handle
   6 //! accordingly.
   7 //!
   8 //! ## `Ty` lowering
   9 //! Much of the `Ty` lowering is 1:1 with Chalk. (Or will be eventually). A
  10 //! helpful table for what types lower to what can be found in the
  11 //! [Chalk book](https://rust-lang.github.io/chalk/book/types/rust_types.html).
  12 //! The most notable difference lies with `Param`s. To convert from rustc to
  13 //! Chalk, we eagerly and deeply convert `Param`s to placeholders (in goals) or
  14 //! bound variables (for clause generation through functions in `db`).
  15 //!
  16 //! ## `Region` lowering
  17 //! Regions are handled in rustc and Chalk is quite differently. In rustc, there
  18 //! is a difference between "early bound" and "late bound" regions, where only
  19 //! the late bound regions have a `DebruijnIndex`. Moreover, in Chalk all
  20 //! regions (Lifetimes) have an associated index. In rustc, only `BrAnon`s have
  21 //! an index, whereas `BrNamed` don't. In order to lower regions to Chalk, we
  22 //! convert all regions into `BrAnon` late-bound regions.
  23 //!
  24 //! ## `Const` lowering
  25 //! Chalk doesn't handle consts currently, so consts are currently lowered to
  26 //! an empty tuple.
  27 //!
  28 //! ## Bound variable collection
  29 //! Another difference between rustc and Chalk lies in the handling of binders.
  30 //! Chalk requires that we store the bound parameter kinds, whereas rustc does
  31 //! not. To lower anything wrapped in a `Binder`, we first deeply find any bound
  32 //! variables from the current `Binder`.
  33
  34 use rustc_ast::ast;
  35 use rustc_middle::traits::{ChalkEnvironmentAndGoal, ChalkRustInterner as RustInterner};
  36 use rustc_middle::ty::fold::TypeFolder;
  37 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, SubstsRef};
  38 use rustc_middle::ty::{self, Binder, Region, Ty, TyCtxt, TypeFoldable, TypeVisitor};
  39 use rustc_span::def_id::DefId;
  40
  41 use chalk_ir::{FnSig, ForeignDefId};
  42 use rustc_hir::Unsafety;
  43 use std::collections::btree_map::{BTreeMap, Entry};
  44 use std::ops::ControlFlow;
  45
  46 /// Essentially an `Into` with a `&RustInterner` parameter
  47 crate trait LowerInto<'tcx, T> {
  48     /// Lower a rustc construct (e.g., `ty::TraitPredicate`) to a chalk type, consuming `self`.
  49     fn lower_into(self, interner: RustInterner<'tcx>) -> T;
  50 }
  51
  52 impl<'tcx> LowerInto<'tcx, chalk_ir::Substitution<RustInterner<'tcx>>> for SubstsRef<'tcx> {
  53     fn lower_into(
  54         self,
  55         interner: RustInterner<'tcx>,
  56     ) -> chalk_ir::Substitution<RustInterner<'tcx>> {
  57         chalk_ir::Substitution::from_iter(interner, self.iter().map(|s| s.lower_into(interner)))
  58     }
  59 }
  60
  61 impl<'tcx> LowerInto<'tcx, SubstsRef<'tcx>> for &chalk_ir::Substitution<RustInterner<'tcx>> {
  62     fn lower_into(self, interner: RustInterner<'tcx>) -> SubstsRef<'tcx> {
  63         interner.tcx.mk_substs(self.iter(interner).map(|subst| subst.lower_into(interner)))
  64     }
  65 }
  66
  67 impl<'tcx> LowerInto<'tcx, chalk_ir::AliasTy<RustInterner<'tcx>>> for ty::ProjectionTy<'tcx> {
  68     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::AliasTy<RustInterner<'tcx>> {
  69         chalk_ir::AliasTy::Projection(chalk_ir::ProjectionTy {
  70             associated_ty_id: chalk_ir::AssocTypeId(self.item_def_id),
  71             substitution: self.substs.lower_into(interner),
  72         })
  73     }
  74 }
  75
  76 impl<'tcx> LowerInto<'tcx, chalk_ir::InEnvironment<chalk_ir::Goal<RustInterner<'tcx>>>>
  77     for ChalkEnvironmentAndGoal<'tcx>
  78 {
  79     fn lower_into(
  80         self,
  81         interner: RustInterner<'tcx>,
  82     ) -> chalk_ir::InEnvironment<chalk_ir::Goal<RustInterner<'tcx>>> {
  83         let clauses = self.environment.into_iter().map(|predicate| {
  84             let (predicate, binders, _named_regions) =
  85                 collect_bound_vars(interner, interner.tcx, predicate.kind());
  86             let consequence = match predicate {
  87                 ty::PredicateKind::TypeWellFormedFromEnv(ty) => {
  88                     chalk_ir::DomainGoal::FromEnv(chalk_ir::FromEnv::Ty(ty.lower_into(interner)))
  89                 }
  90                 ty::PredicateKind::Trait(predicate) => chalk_ir::DomainGoal::FromEnv(
  91                     chalk_ir::FromEnv::Trait(predicate.trait_ref.lower_into(interner)),
  92                 ),
  93                 ty::PredicateKind::RegionOutlives(predicate) => chalk_ir::DomainGoal::Holds(
  94                     chalk_ir::WhereClause::LifetimeOutlives(chalk_ir::LifetimeOutlives {
  95                         a: predicate.0.lower_into(interner),
  96                         b: predicate.1.lower_into(interner),
  97                     }),
  98                 ),
  99                 ty::PredicateKind::TypeOutlives(predicate) => chalk_ir::DomainGoal::Holds(
 100                     chalk_ir::WhereClause::TypeOutlives(chalk_ir::TypeOutlives {
 101                         ty: predicate.0.lower_into(interner),
 102                         lifetime: predicate.1.lower_into(interner),
 103                     }),
 104                 ),
 105                 ty::PredicateKind::Projection(predicate) => chalk_ir::DomainGoal::Holds(
 106                     chalk_ir::WhereClause::AliasEq(predicate.lower_into(interner)),
 107                 ),
 108                 ty::PredicateKind::WellFormed(..)
 109                 | ty::PredicateKind::ObjectSafe(..)
 110                 | ty::PredicateKind::ClosureKind(..)
 111                 | ty::PredicateKind::Subtype(..)
 112                 | ty::PredicateKind::Coerce(..)
 113                 | ty::PredicateKind::ConstEvaluatable(..)
 114                 | ty::PredicateKind::ConstEquate(..) => bug!("unexpected predicate {}", predicate),
 115             };
 116             let value = chalk_ir::ProgramClauseImplication {
 117                 consequence,
 118                 conditions: chalk_ir::Goals::empty(interner),
 119                 priority: chalk_ir::ClausePriority::High,
 120                 constraints: chalk_ir::Constraints::empty(interner),
 121             };
 122             chalk_ir::ProgramClauseData(chalk_ir::Binders::new(binders, value)).intern(interner)
 123         });
 124
 125         let goal: chalk_ir::GoalData<RustInterner<'tcx>> = self.goal.lower_into(interner);
 126         chalk_ir::InEnvironment {
 127             environment: chalk_ir::Environment {
 128                 clauses: chalk_ir::ProgramClauses::from_iter(interner, clauses),
 129             },
 130             goal: goal.intern(interner),
 131         }
 132     }
 133 }
 134
 135 impl<'tcx> LowerInto<'tcx, chalk_ir::GoalData<RustInterner<'tcx>>> for ty::Predicate<'tcx> {
 136     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::GoalData<RustInterner<'tcx>> {
 137         let (predicate, binders, _named_regions) =
 138             collect_bound_vars(interner, interner.tcx, self.kind());
 139
 140         let value = match predicate {
 141             ty::PredicateKind::Trait(predicate) => {
 142                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
 143                     chalk_ir::WhereClause::Implemented(predicate.trait_ref.lower_into(interner)),
 144                 ))
 145             }
 146             ty::PredicateKind::RegionOutlives(predicate) => {
 147                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
 148                     chalk_ir::WhereClause::LifetimeOutlives(chalk_ir::LifetimeOutlives {
 149                         a: predicate.0.lower_into(interner),
 150                         b: predicate.1.lower_into(interner),
 151                     }),
 152                 ))
 153             }
 154             ty::PredicateKind::TypeOutlives(predicate) => {
 155                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
 156                     chalk_ir::WhereClause::TypeOutlives(chalk_ir::TypeOutlives {
 157                         ty: predicate.0.lower_into(interner),
 158                         lifetime: predicate.1.lower_into(interner),
 159                     }),
 160                 ))
 161             }
 162             ty::PredicateKind::Projection(predicate) => {
 163                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
 164                     chalk_ir::WhereClause::AliasEq(predicate.lower_into(interner)),
 165                 ))
 166             }
 167             ty::PredicateKind::WellFormed(arg) => match arg.unpack() {
 168                 GenericArgKind::Type(ty) => match ty.kind() {
 169                     // FIXME(chalk): In Chalk, a placeholder is WellFormed if it
 170                     // `FromEnv`. However, when we "lower" Params, we don't update
 171                     // the environment.
 172                     ty::Placeholder(..) => {
 173                         chalk_ir::GoalData::All(chalk_ir::Goals::empty(interner))
 174                     }
 175
 176                     _ => chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::WellFormed(
 177                         chalk_ir::WellFormed::Ty(ty.lower_into(interner)),
 178                     )),
 179                 },
 180                 // FIXME(chalk): handle well formed consts
 181                 GenericArgKind::Const(..) => {
 182                     chalk_ir::GoalData::All(chalk_ir::Goals::empty(interner))
 183                 }
 184                 GenericArgKind::Lifetime(lt) => bug!("unexpect well formed predicate: {:?}", lt),
 185             },
 186
 187             ty::PredicateKind::ObjectSafe(t) => chalk_ir::GoalData::DomainGoal(
 188                 chalk_ir::DomainGoal::ObjectSafe(chalk_ir::TraitId(t)),
 189             ),
 190
 191             ty::PredicateKind::Subtype(ty::SubtypePredicate { a, b, a_is_expected: _ }) => {
 192                 chalk_ir::GoalData::SubtypeGoal(chalk_ir::SubtypeGoal {
 193                     a: a.lower_into(interner),
 194                     b: b.lower_into(interner),
 195                 })
 196             }
 197
 198             // FIXME(chalk): other predicates
 199             //
 200             // We can defer this, but ultimately we'll want to express
 201             // some of these in terms of chalk operations.
 202             ty::PredicateKind::ClosureKind(..)
 203             | ty::PredicateKind::Coerce(..)
 204             | ty::PredicateKind::ConstEvaluatable(..)
 205             | ty::PredicateKind::ConstEquate(..) => {
 206                 chalk_ir::GoalData::All(chalk_ir::Goals::empty(interner))
 207             }
 208             ty::PredicateKind::TypeWellFormedFromEnv(ty) => chalk_ir::GoalData::DomainGoal(
 209                 chalk_ir::DomainGoal::FromEnv(chalk_ir::FromEnv::Ty(ty.lower_into(interner))),
 210             ),
 211         };
 212
 213         chalk_ir::GoalData::Quantified(
 214             chalk_ir::QuantifierKind::ForAll,
 215             chalk_ir::Binders::new(binders, value.intern(interner)),
 216         )
 217     }
 218 }
 219
 220 impl<'tcx> LowerInto<'tcx, chalk_ir::TraitRef<RustInterner<'tcx>>>
 221     for rustc_middle::ty::TraitRef<'tcx>
 222 {
 223     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::TraitRef<RustInterner<'tcx>> {
 224         chalk_ir::TraitRef {
 225             trait_id: chalk_ir::TraitId(self.def_id),
 226             substitution: self.substs.lower_into(interner),
 227         }
 228     }
 229 }
 230
 231 impl<'tcx> LowerInto<'tcx, chalk_ir::AliasEq<RustInterner<'tcx>>>
 232     for rustc_middle::ty::ProjectionPredicate<'tcx>
 233 {
 234     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::AliasEq<RustInterner<'tcx>> {
 235         // FIXME(associated_const_equality): teach chalk about terms for alias eq.
 236         chalk_ir::AliasEq {
 237             ty: self.term.ty().unwrap().lower_into(interner),
 238             alias: self.projection_ty.lower_into(interner),
 239         }
 240     }
 241 }
 242
 243 /*
 244 // FIXME(...): Where do I add this to Chalk? I can't find it in the rustc repo anywhere.
 245 impl<'tcx> LowerInto<'tcx, chalk_ir::Term<RustInterner<'tcx>>> for rustc_middle::ty::Term<'tcx> {
 246   fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::Term<RustInterner<'tcx>> {
 247     match self {
 248       ty::Term::Ty(ty) => ty.lower_into(interner).into(),
 249       ty::Term::Const(c) => c.lower_into(interner).into(),
 250     }
 251   }
 252 }
 253 */
 254
 255 impl<'tcx> LowerInto<'tcx, chalk_ir::Ty<RustInterner<'tcx>>> for Ty<'tcx> {
 256     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::Ty<RustInterner<'tcx>> {
 257         let int = |i| chalk_ir::TyKind::Scalar(chalk_ir::Scalar::Int(i));
 258         let uint = |i| chalk_ir::TyKind::Scalar(chalk_ir::Scalar::Uint(i));
 259         let float = |f| chalk_ir::TyKind::Scalar(chalk_ir::Scalar::Float(f));
 260
 261         match *self.kind() {
 262             ty::Bool => chalk_ir::TyKind::Scalar(chalk_ir::Scalar::Bool),
 263             ty::Char => chalk_ir::TyKind::Scalar(chalk_ir::Scalar::Char),
 264             ty::Int(ty) => match ty {
 265                 ty::IntTy::Isize => int(chalk_ir::IntTy::Isize),
 266                 ty::IntTy::I8 => int(chalk_ir::IntTy::I8),
 267                 ty::IntTy::I16 => int(chalk_ir::IntTy::I16),
 268                 ty::IntTy::I32 => int(chalk_ir::IntTy::I32),
 269                 ty::IntTy::I64 => int(chalk_ir::IntTy::I64),
 270                 ty::IntTy::I128 => int(chalk_ir::IntTy::I128),
 271             },
 272             ty::Uint(ty) => match ty {
 273                 ty::UintTy::Usize => uint(chalk_ir::UintTy::Usize),
 274                 ty::UintTy::U8 => uint(chalk_ir::UintTy::U8),
 275                 ty::UintTy::U16 => uint(chalk_ir::UintTy::U16),
 276                 ty::UintTy::U32 => uint(chalk_ir::UintTy::U32),
 277                 ty::UintTy::U64 => uint(chalk_ir::UintTy::U64),
 278                 ty::UintTy::U128 => uint(chalk_ir::UintTy::U128),
 279             },
 280             ty::Float(ty) => match ty {
 281                 ty::FloatTy::F32 => float(chalk_ir::FloatTy::F32),
 282                 ty::FloatTy::F64 => float(chalk_ir::FloatTy::F64),
 283             },
 284             ty::Adt(def, substs) => {
 285                 chalk_ir::TyKind::Adt(chalk_ir::AdtId(def), substs.lower_into(interner))
 286             }
 287             ty::Foreign(def_id) => chalk_ir::TyKind::Foreign(ForeignDefId(def_id)),
 288             ty::Str => chalk_ir::TyKind::Str,
 289             ty::Array(ty, len) => {
 290                 chalk_ir::TyKind::Array(ty.lower_into(interner), len.lower_into(interner))
 291             }
 292             ty::Slice(ty) => chalk_ir::TyKind::Slice(ty.lower_into(interner)),
 293
 294             ty::RawPtr(ptr) => {
 295                 chalk_ir::TyKind::Raw(ptr.mutbl.lower_into(interner), ptr.ty.lower_into(interner))
 296             }
 297             ty::Ref(region, ty, mutability) => chalk_ir::TyKind::Ref(
 298                 mutability.lower_into(interner),
 299                 region.lower_into(interner),
 300                 ty.lower_into(interner),
 301             ),
 302             ty::FnDef(def_id, substs) => {
 303                 chalk_ir::TyKind::FnDef(chalk_ir::FnDefId(def_id), substs.lower_into(interner))
 304             }
 305             ty::FnPtr(sig) => {
 306                 let (inputs_and_outputs, binders, _named_regions) =
 307                     collect_bound_vars(interner, interner.tcx, sig.inputs_and_output());
 308                 chalk_ir::TyKind::Function(chalk_ir::FnPointer {
 309                     num_binders: binders.len(interner),
 310                     sig: sig.lower_into(interner),
 311                     substitution: chalk_ir::FnSubst(chalk_ir::Substitution::from_iter(
 312                         interner,
 313                         inputs_and_outputs.iter().map(|ty| {
 314                             chalk_ir::GenericArgData::Ty(ty.lower_into(interner)).intern(interner)
 315                         }),
 316                     )),
 317                 })
 318             }
 319             ty::Dynamic(predicates, region) => chalk_ir::TyKind::Dyn(chalk_ir::DynTy {
 320                 bounds: predicates.lower_into(interner),
 321                 lifetime: region.lower_into(interner),
 322             }),
 323             ty::Closure(def_id, substs) => {
 324                 chalk_ir::TyKind::Closure(chalk_ir::ClosureId(def_id), substs.lower_into(interner))
 325             }
 326             ty::Generator(def_id, substs, _) => chalk_ir::TyKind::Generator(
 327                 chalk_ir::GeneratorId(def_id),
 328                 substs.lower_into(interner),
 329             ),
 330             ty::GeneratorWitness(_) => unimplemented!(),
 331             ty::Never => chalk_ir::TyKind::Never,
 332             ty::Tuple(types) => {
 333                 chalk_ir::TyKind::Tuple(types.len(), types.as_substs().lower_into(interner))
 334             }
 335             ty::Projection(proj) => chalk_ir::TyKind::Alias(proj.lower_into(interner)),
 336             ty::Opaque(def_id, substs) => {
 337                 chalk_ir::TyKind::Alias(chalk_ir::AliasTy::Opaque(chalk_ir::OpaqueTy {
 338                     opaque_ty_id: chalk_ir::OpaqueTyId(def_id),
 339                     substitution: substs.lower_into(interner),
 340                 }))
 341             }
 342             // This should have been done eagerly prior to this, and all Params
 343             // should have been substituted to placeholders
 344             ty::Param(_) => panic!("Lowering Param when not expected."),
 345             ty::Bound(db, bound) => chalk_ir::TyKind::BoundVar(chalk_ir::BoundVar::new(
 346                 chalk_ir::DebruijnIndex::new(db.as_u32()),
 347                 bound.var.index(),
 348             )),
 349             ty::Placeholder(_placeholder) => {
 350                 chalk_ir::TyKind::Placeholder(chalk_ir::PlaceholderIndex {
 351                     ui: chalk_ir::UniverseIndex { counter: _placeholder.universe.as_usize() },
 352                     idx: _placeholder.name.as_usize(),
 353                 })
 354             }
 355             ty::Infer(_infer) => unimplemented!(),
 356             ty::Error(_) => chalk_ir::TyKind::Error,
 357         }
 358         .intern(interner)
 359     }
 360 }
 361
 362 impl<'tcx> LowerInto<'tcx, Ty<'tcx>> for &chalk_ir::Ty<RustInterner<'tcx>> {
 363     fn lower_into(self, interner: RustInterner<'tcx>) -> Ty<'tcx> {
 364         use chalk_ir::TyKind;
 365
 366         let kind = match self.kind(interner) {
 367             TyKind::Adt(struct_id, substitution) => {
 368                 ty::Adt(struct_id.0, substitution.lower_into(interner))
 369             }
 370             TyKind::Scalar(scalar) => match scalar {
 371                 chalk_ir::Scalar::Bool => ty::Bool,
 372                 chalk_ir::Scalar::Char => ty::Char,
 373                 chalk_ir::Scalar::Int(int_ty) => match int_ty {
 374                     chalk_ir::IntTy::Isize => ty::Int(ty::IntTy::Isize),
 375                     chalk_ir::IntTy::I8 => ty::Int(ty::IntTy::I8),
 376                     chalk_ir::IntTy::I16 => ty::Int(ty::IntTy::I16),
 377                     chalk_ir::IntTy::I32 => ty::Int(ty::IntTy::I32),
 378                     chalk_ir::IntTy::I64 => ty::Int(ty::IntTy::I64),
 379                     chalk_ir::IntTy::I128 => ty::Int(ty::IntTy::I128),
 380                 },
 381                 chalk_ir::Scalar::Uint(int_ty) => match int_ty {
 382                     chalk_ir::UintTy::Usize => ty::Uint(ty::UintTy::Usize),
 383                     chalk_ir::UintTy::U8 => ty::Uint(ty::UintTy::U8),
 384                     chalk_ir::UintTy::U16 => ty::Uint(ty::UintTy::U16),
 385                     chalk_ir::UintTy::U32 => ty::Uint(ty::UintTy::U32),
 386                     chalk_ir::UintTy::U64 => ty::Uint(ty::UintTy::U64),
 387                     chalk_ir::UintTy::U128 => ty::Uint(ty::UintTy::U128),
 388                 },
 389                 chalk_ir::Scalar::Float(float_ty) => match float_ty {
 390                     chalk_ir::FloatTy::F32 => ty::Float(ty::FloatTy::F32),
 391                     chalk_ir::FloatTy::F64 => ty::Float(ty::FloatTy::F64),
 392                 },
 393             },
 394             TyKind::Array(ty, c) => {
 395                 let ty = ty.lower_into(interner);
 396                 let c = c.lower_into(interner);
 397                 ty::Array(ty, c)
 398             }
 399             TyKind::FnDef(id, substitution) => ty::FnDef(id.0, substitution.lower_into(interner)),
 400             TyKind::Closure(closure, substitution) => {
 401                 ty::Closure(closure.0, substitution.lower_into(interner))
 402             }
 403             TyKind::Generator(..) => unimplemented!(),
 404             TyKind::GeneratorWitness(..) => unimplemented!(),
 405             TyKind::Never => ty::Never,
 406             TyKind::Tuple(_len, substitution) => {
 407                 ty::Tuple(substitution.lower_into(interner).try_as_type_list().unwrap())
 408             }
 409             TyKind::Slice(ty) => ty::Slice(ty.lower_into(interner)),
 410             TyKind::Raw(mutbl, ty) => ty::RawPtr(ty::TypeAndMut {
 411                 ty: ty.lower_into(interner),
 412                 mutbl: mutbl.lower_into(interner),
 413             }),
 414             TyKind::Ref(mutbl, lifetime, ty) => ty::Ref(
 415                 lifetime.lower_into(interner),
 416                 ty.lower_into(interner),
 417                 mutbl.lower_into(interner),
 418             ),
 419             TyKind::Str => ty::Str,
 420             TyKind::OpaqueType(opaque_ty, substitution) => {
 421                 ty::Opaque(opaque_ty.0, substitution.lower_into(interner))
 422             }
 423             TyKind::AssociatedType(assoc_ty, substitution) => ty::Projection(ty::ProjectionTy {
 424                 substs: substitution.lower_into(interner),
 425                 item_def_id: assoc_ty.0,
 426             }),
 427             TyKind::Foreign(def_id) => ty::Foreign(def_id.0),
 428             TyKind::Error => return interner.tcx.ty_error(),
 429             TyKind::Placeholder(placeholder) => ty::Placeholder(ty::Placeholder {
 430                 universe: ty::UniverseIndex::from_usize(placeholder.ui.counter),
 431                 name: ty::BoundVar::from_usize(placeholder.idx),
 432             }),
 433             TyKind::Alias(alias_ty) => match alias_ty {
 434                 chalk_ir::AliasTy::Projection(projection) => ty::Projection(ty::ProjectionTy {
 435                     item_def_id: projection.associated_ty_id.0,
 436                     substs: projection.substitution.lower_into(interner),
 437                 }),
 438                 chalk_ir::AliasTy::Opaque(opaque) => {
 439                     ty::Opaque(opaque.opaque_ty_id.0, opaque.substitution.lower_into(interner))
 440                 }
 441             },
 442             TyKind::Function(_quantified_ty) => unimplemented!(),
 443             TyKind::BoundVar(_bound) => ty::Bound(
 444                 ty::DebruijnIndex::from_usize(_bound.debruijn.depth() as usize),
 445                 ty::BoundTy {
 446                     var: ty::BoundVar::from_usize(_bound.index),
 447                     kind: ty::BoundTyKind::Anon,
 448                 },
 449             ),
 450             TyKind::InferenceVar(_, _) => unimplemented!(),
 451             TyKind::Dyn(_) => unimplemented!(),
 452         };
 453         interner.tcx.mk_ty(kind)
 454     }
 455 }
 456
 457 impl<'tcx> LowerInto<'tcx, chalk_ir::Lifetime<RustInterner<'tcx>>> for Region<'tcx> {
 458     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::Lifetime<RustInterner<'tcx>> {
 459         match *self {
 460             ty::ReEarlyBound(_) => {
 461                 panic!("Should have already been substituted.");
 462             }
 463             ty::ReLateBound(db, br) => chalk_ir::LifetimeData::BoundVar(chalk_ir::BoundVar::new(
 464                 chalk_ir::DebruijnIndex::new(db.as_u32()),
 465                 br.var.as_usize(),
 466             ))
 467             .intern(interner),
 468             ty::ReFree(_) => unimplemented!(),
 469             ty::ReStatic => chalk_ir::LifetimeData::Static.intern(interner),
 470             ty::ReVar(_) => unimplemented!(),
 471             ty::RePlaceholder(placeholder_region) => {
 472                 chalk_ir::LifetimeData::Placeholder(chalk_ir::PlaceholderIndex {
 473                     ui: chalk_ir::UniverseIndex { counter: placeholder_region.universe.index() },
 474                     idx: 0,
 475                 })
 476                 .intern(interner)
 477             }
 478             ty::ReEmpty(ui) => {
 479                 chalk_ir::LifetimeData::Empty(chalk_ir::UniverseIndex { counter: ui.index() })
 480                     .intern(interner)
 481             }
 482             ty::ReErased => chalk_ir::LifetimeData::Erased.intern(interner),
 483         }
 484     }
 485 }
 486
 487 impl<'tcx> LowerInto<'tcx, Region<'tcx>> for &chalk_ir::Lifetime<RustInterner<'tcx>> {
 488     fn lower_into(self, interner: RustInterner<'tcx>) -> Region<'tcx> {
 489         let kind = match self.data(interner) {
 490             chalk_ir::LifetimeData::BoundVar(var) => ty::ReLateBound(
 491                 ty::DebruijnIndex::from_u32(var.debruijn.depth()),
 492                 ty::BoundRegion {
 493                     var: ty::BoundVar::from_usize(var.index),
 494                     kind: ty::BrAnon(var.index as u32),
 495                 },
 496             ),
 497             chalk_ir::LifetimeData::InferenceVar(_var) => unimplemented!(),
 498             chalk_ir::LifetimeData::Placeholder(p) => ty::RePlaceholder(ty::Placeholder {
 499                 universe: ty::UniverseIndex::from_usize(p.ui.counter),
 500                 name: ty::BoundRegionKind::BrAnon(p.idx as u32),
 501             }),
 502             chalk_ir::LifetimeData::Static => return interner.tcx.lifetimes.re_static,
 503             chalk_ir::LifetimeData::Empty(ui) => {
 504                 ty::ReEmpty(ty::UniverseIndex::from_usize(ui.counter))
 505             }
 506             chalk_ir::LifetimeData::Erased => return interner.tcx.lifetimes.re_erased,
 507             chalk_ir::LifetimeData::Phantom(void, _) => match *void {},
 508         };
 509         interner.tcx.mk_region(kind)
 510     }
 511 }
 512
 513 impl<'tcx> LowerInto<'tcx, chalk_ir::Const<RustInterner<'tcx>>> for ty::Const<'tcx> {
 514     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::Const<RustInterner<'tcx>> {
 515         let ty = self.ty().lower_into(interner);
 516         let value = match self.val() {
 517             ty::ConstKind::Value(val) => {
 518                 chalk_ir::ConstValue::Concrete(chalk_ir::ConcreteConst { interned: val })
 519             }
 520             ty::ConstKind::Bound(db, bound) => chalk_ir::ConstValue::BoundVar(
 521                 chalk_ir::BoundVar::new(chalk_ir::DebruijnIndex::new(db.as_u32()), bound.index()),
 522             ),
 523             _ => unimplemented!("Const not implemented. {:?}", self),
 524         };
 525         chalk_ir::ConstData { ty, value }.intern(interner)
 526     }
 527 }
 528
 529 impl<'tcx> LowerInto<'tcx, ty::Const<'tcx>> for &chalk_ir::Const<RustInterner<'tcx>> {
 530     fn lower_into(self, interner: RustInterner<'tcx>) -> ty::Const<'tcx> {
 531         let data = self.data(interner);
 532         let ty = data.ty.lower_into(interner);
 533         let val = match data.value {
 534             chalk_ir::ConstValue::BoundVar(var) => ty::ConstKind::Bound(
 535                 ty::DebruijnIndex::from_u32(var.debruijn.depth()),
 536                 ty::BoundVar::from_u32(var.index as u32),
 537             ),
 538             chalk_ir::ConstValue::InferenceVar(_var) => unimplemented!(),
 539             chalk_ir::ConstValue::Placeholder(_p) => unimplemented!(),
 540             chalk_ir::ConstValue::Concrete(c) => ty::ConstKind::Value(c.interned),
 541         };
 542         interner.tcx.mk_const(ty::ConstS { ty, val })
 543     }
 544 }
 545
 546 impl<'tcx> LowerInto<'tcx, chalk_ir::GenericArg<RustInterner<'tcx>>> for GenericArg<'tcx> {
 547     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::GenericArg<RustInterner<'tcx>> {
 548         match self.unpack() {
 549             ty::subst::GenericArgKind::Type(ty) => {
 550                 chalk_ir::GenericArgData::Ty(ty.lower_into(interner))
 551             }
 552             ty::subst::GenericArgKind::Lifetime(lifetime) => {
 553                 chalk_ir::GenericArgData::Lifetime(lifetime.lower_into(interner))
 554             }
 555             ty::subst::GenericArgKind::Const(c) => {
 556                 chalk_ir::GenericArgData::Const(c.lower_into(interner))
 557             }
 558         }
 559         .intern(interner)
 560     }
 561 }
 562
 563 impl<'tcx> LowerInto<'tcx, ty::subst::GenericArg<'tcx>>
 564     for &chalk_ir::GenericArg<RustInterner<'tcx>>
 565 {
 566     fn lower_into(self, interner: RustInterner<'tcx>) -> ty::subst::GenericArg<'tcx> {
 567         match self.data(interner) {
 568             chalk_ir::GenericArgData::Ty(ty) => {
 569                 let t: Ty<'tcx> = ty.lower_into(interner);
 570                 t.into()
 571             }
 572             chalk_ir::GenericArgData::Lifetime(lifetime) => {
 573                 let r: Region<'tcx> = lifetime.lower_into(interner);
 574                 r.into()
 575             }
 576             chalk_ir::GenericArgData::Const(c) => {
 577                 let c: ty::Const<'tcx> = c.lower_into(interner);
 578                 c.into()
 579             }
 580         }
 581     }
 582 }
 583
 584 // We lower into an Option here since there are some predicates which Chalk
 585 // doesn't have a representation for yet (as a `WhereClause`), but are so common
 586 // that we just are accepting the unsoundness for now. The `Option` will
 587 // eventually be removed.
 588 impl<'tcx> LowerInto<'tcx, Option<chalk_ir::QuantifiedWhereClause<RustInterner<'tcx>>>>
 589     for ty::Predicate<'tcx>
 590 {
 591     fn lower_into(
 592         self,
 593         interner: RustInterner<'tcx>,
 594     ) -> Option<chalk_ir::QuantifiedWhereClause<RustInterner<'tcx>>> {
 595         let (predicate, binders, _named_regions) =
 596             collect_bound_vars(interner, interner.tcx, self.kind());
 597         let value = match predicate {
 598             ty::PredicateKind::Trait(predicate) => {
 599                 Some(chalk_ir::WhereClause::Implemented(predicate.trait_ref.lower_into(interner)))
 600             }
 601             ty::PredicateKind::RegionOutlives(predicate) => {
 602                 Some(chalk_ir::WhereClause::LifetimeOutlives(chalk_ir::LifetimeOutlives {
 603                     a: predicate.0.lower_into(interner),
 604                     b: predicate.1.lower_into(interner),
 605                 }))
 606             }
 607             ty::PredicateKind::TypeOutlives(predicate) => {
 608                 Some(chalk_ir::WhereClause::TypeOutlives(chalk_ir::TypeOutlives {
 609                     ty: predicate.0.lower_into(interner),
 610                     lifetime: predicate.1.lower_into(interner),
 611                 }))
 612             }
 613             ty::PredicateKind::Projection(predicate) => {
 614                 Some(chalk_ir::WhereClause::AliasEq(predicate.lower_into(interner)))
 615             }
 616             ty::PredicateKind::WellFormed(_ty) => None,
 617
 618             ty::PredicateKind::ObjectSafe(..)
 619             | ty::PredicateKind::ClosureKind(..)
 620             | ty::PredicateKind::Subtype(..)
 621             | ty::PredicateKind::Coerce(..)
 622             | ty::PredicateKind::ConstEvaluatable(..)
 623             | ty::PredicateKind::ConstEquate(..)
 624             | ty::PredicateKind::TypeWellFormedFromEnv(..) => {
 625                 bug!("unexpected predicate {}", &self)
 626             }
 627         };
 628         value.map(|value| chalk_ir::Binders::new(binders, value))
 629     }
 630 }
 631
 632 impl<'tcx> LowerInto<'tcx, chalk_ir::Binders<chalk_ir::QuantifiedWhereClauses<RustInterner<'tcx>>>>
 633     for &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>
 634 {
 635     fn lower_into(
 636         self,
 637         interner: RustInterner<'tcx>,
 638     ) -> chalk_ir::Binders<chalk_ir::QuantifiedWhereClauses<RustInterner<'tcx>>> {
 639         // `Self` has one binder:
 640         // Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>
 641         // The return type has two:
 642         // Binders<&[Binders<WhereClause<I>>]>
 643         // This means that any variables that are escaping `self` need to be
 644         // shifted in by one so that they are still escaping.
 645         let predicates = ty::fold::shift_vars(interner.tcx, self, 1);
 646
 647         let self_ty = interner.tcx.mk_ty(ty::Bound(
 648             // This is going to be wrapped in a binder
 649             ty::DebruijnIndex::from_usize(1),
 650             ty::BoundTy { var: ty::BoundVar::from_usize(0), kind: ty::BoundTyKind::Anon },
 651         ));
 652         let where_clauses = predicates.into_iter().map(|predicate| {
 653             let (predicate, binders, _named_regions) =
 654                 collect_bound_vars(interner, interner.tcx, predicate);
 655             match predicate {
 656                 ty::ExistentialPredicate::Trait(ty::ExistentialTraitRef { def_id, substs }) => {
 657                     chalk_ir::Binders::new(
 658                         binders.clone(),
 659                         chalk_ir::WhereClause::Implemented(chalk_ir::TraitRef {
 660                             trait_id: chalk_ir::TraitId(def_id),
 661                             substitution: interner
 662                                 .tcx
 663                                 .mk_substs_trait(self_ty, substs)
 664                                 .lower_into(interner),
 665                         }),
 666                     )
 667                 }
 668                 ty::ExistentialPredicate::Projection(predicate) => chalk_ir::Binders::new(
 669                     binders.clone(),
 670                     chalk_ir::WhereClause::AliasEq(chalk_ir::AliasEq {
 671                         alias: chalk_ir::AliasTy::Projection(chalk_ir::ProjectionTy {
 672                             associated_ty_id: chalk_ir::AssocTypeId(predicate.item_def_id),
 673                             substitution: interner
 674                                 .tcx
 675                                 .mk_substs_trait(self_ty, predicate.substs)
 676                                 .lower_into(interner),
 677                         }),
 678                         // FIXME(associated_const_equality): teach chalk about terms for alias eq.
 679                         ty: predicate.term.ty().unwrap().lower_into(interner),
 680                     }),
 681                 ),
 682                 ty::ExistentialPredicate::AutoTrait(def_id) => chalk_ir::Binders::new(
 683                     binders.clone(),
 684                     chalk_ir::WhereClause::Implemented(chalk_ir::TraitRef {
 685                         trait_id: chalk_ir::TraitId(def_id),
 686                         substitution: interner
 687                             .tcx
 688                             .mk_substs_trait(self_ty, &[])
 689                             .lower_into(interner),
 690                     }),
 691                 ),
 692             }
 693         });
 694
 695         // Binder for the bound variable representing the concrete underlying type.
 696         let existential_binder = chalk_ir::VariableKinds::from1(
 697             interner,
 698             chalk_ir::VariableKind::Ty(chalk_ir::TyVariableKind::General),
 699         );
 700         let value = chalk_ir::QuantifiedWhereClauses::from_iter(interner, where_clauses);
 701         chalk_ir::Binders::new(existential_binder, value)
 702     }
 703 }
 704
 705 impl<'tcx> LowerInto<'tcx, chalk_ir::FnSig<RustInterner<'tcx>>>
 706     for ty::Binder<'tcx, ty::FnSig<'tcx>>
 707 {
 708     fn lower_into(self, _interner: RustInterner<'_>) -> FnSig<RustInterner<'tcx>> {
 709         chalk_ir::FnSig {
 710             abi: self.abi(),
 711             safety: match self.unsafety() {
 712                 Unsafety::Normal => chalk_ir::Safety::Safe,
 713                 Unsafety::Unsafe => chalk_ir::Safety::Unsafe,
 714             },
 715             variadic: self.c_variadic(),
 716         }
 717     }
 718 }
 719
 720 // We lower into an Option here since there are some predicates which Chalk
 721 // doesn't have a representation for yet (as an `InlineBound`). The `Option` will
 722 // eventually be removed.
 723 impl<'tcx> LowerInto<'tcx, Option<chalk_solve::rust_ir::QuantifiedInlineBound<RustInterner<'tcx>>>>
 724     for ty::Predicate<'tcx>
 725 {
 726     fn lower_into(
 727         self,
 728         interner: RustInterner<'tcx>,
 729     ) -> Option<chalk_solve::rust_ir::QuantifiedInlineBound<RustInterner<'tcx>>> {
 730         let (predicate, binders, _named_regions) =
 731             collect_bound_vars(interner, interner.tcx, self.kind());
 732         match predicate {
 733             ty::PredicateKind::Trait(predicate) => Some(chalk_ir::Binders::new(
 734                 binders,
 735                 chalk_solve::rust_ir::InlineBound::TraitBound(
 736                     predicate.trait_ref.lower_into(interner),
 737                 ),
 738             )),
 739             ty::PredicateKind::Projection(predicate) => Some(chalk_ir::Binders::new(
 740                 binders,
 741                 chalk_solve::rust_ir::InlineBound::AliasEqBound(predicate.lower_into(interner)),
 742             )),
 743             ty::PredicateKind::TypeOutlives(_predicate) => None,
 744             ty::PredicateKind::WellFormed(_ty) => None,
 745
 746             ty::PredicateKind::RegionOutlives(..)
 747             | ty::PredicateKind::ObjectSafe(..)
 748             | ty::PredicateKind::ClosureKind(..)
 749             | ty::PredicateKind::Subtype(..)
 750             | ty::PredicateKind::Coerce(..)
 751             | ty::PredicateKind::ConstEvaluatable(..)
 752             | ty::PredicateKind::ConstEquate(..)
 753             | ty::PredicateKind::TypeWellFormedFromEnv(..) => {
 754                 bug!("unexpected predicate {}", &self)
 755             }
 756         }
 757     }
 758 }
 759
 760 impl<'tcx> LowerInto<'tcx, chalk_solve::rust_ir::TraitBound<RustInterner<'tcx>>>
 761     for ty::TraitRef<'tcx>
 762 {
 763     fn lower_into(
 764         self,
 765         interner: RustInterner<'tcx>,
 766     ) -> chalk_solve::rust_ir::TraitBound<RustInterner<'tcx>> {
 767         chalk_solve::rust_ir::TraitBound {
 768             trait_id: chalk_ir::TraitId(self.def_id),
 769             args_no_self: self.substs[1..].iter().map(|arg| arg.lower_into(interner)).collect(),
 770         }
 771     }
 772 }
 773
 774 impl<'tcx> LowerInto<'tcx, chalk_ir::Mutability> for ast::Mutability {
 775     fn lower_into(self, _interner: RustInterner<'tcx>) -> chalk_ir::Mutability {
 776         match self {
 777             rustc_ast::Mutability::Mut => chalk_ir::Mutability::Mut,
 778             rustc_ast::Mutability::Not => chalk_ir::Mutability::Not,
 779         }
 780     }
 781 }
 782
 783 impl<'tcx> LowerInto<'tcx, ast::Mutability> for chalk_ir::Mutability {
 784     fn lower_into(self, _interner: RustInterner<'tcx>) -> ast::Mutability {
 785         match self {
 786             chalk_ir::Mutability::Mut => ast::Mutability::Mut,
 787             chalk_ir::Mutability::Not => ast::Mutability::Not,
 788         }
 789     }
 790 }
 791
 792 impl<'tcx> LowerInto<'tcx, chalk_solve::rust_ir::Polarity> for ty::ImplPolarity {
 793     fn lower_into(self, _interner: RustInterner<'tcx>) -> chalk_solve::rust_ir::Polarity {
 794         match self {
 795             ty::ImplPolarity::Positive => chalk_solve::rust_ir::Polarity::Positive,
 796             ty::ImplPolarity::Negative => chalk_solve::rust_ir::Polarity::Negative,
 797             // FIXME(chalk) reservation impls
 798             ty::ImplPolarity::Reservation => chalk_solve::rust_ir::Polarity::Negative,
 799         }
 800     }
 801 }
 802 impl<'tcx> LowerInto<'tcx, chalk_ir::Variance> for ty::Variance {
 803     fn lower_into(self, _interner: RustInterner<'tcx>) -> chalk_ir::Variance {
 804         match self {
 805             ty::Variance::Covariant => chalk_ir::Variance::Covariant,
 806             ty::Variance::Invariant => chalk_ir::Variance::Invariant,
 807             ty::Variance::Contravariant => chalk_ir::Variance::Contravariant,
 808             ty::Variance::Bivariant => unimplemented!(),
 809         }
 810     }
 811 }
 812
 813 impl<'tcx> LowerInto<'tcx, chalk_solve::rust_ir::AliasEqBound<RustInterner<'tcx>>>
 814     for ty::ProjectionPredicate<'tcx>
 815 {
 816     fn lower_into(
 817         self,
 818         interner: RustInterner<'tcx>,
 819     ) -> chalk_solve::rust_ir::AliasEqBound<RustInterner<'tcx>> {
 820         let (trait_ref, own_substs) = self.projection_ty.trait_ref_and_own_substs(interner.tcx);
 821         chalk_solve::rust_ir::AliasEqBound {
 822             trait_bound: trait_ref.lower_into(interner),
 823             associated_ty_id: chalk_ir::AssocTypeId(self.projection_ty.item_def_id),
 824             parameters: own_substs.iter().map(|arg| arg.lower_into(interner)).collect(),
 825             value: self.term.ty().unwrap().lower_into(interner),
 826         }
 827     }
 828 }
 829
 830 /// To collect bound vars, we have to do two passes. In the first pass, we
 831 /// collect all `BoundRegionKind`s and `ty::Bound`s. In the second pass, we then
 832 /// replace `BrNamed` into `BrAnon`. The two separate passes are important,
 833 /// since we can only replace `BrNamed` with `BrAnon`s with indices *after* all
 834 /// "real" `BrAnon`s.
 835 ///
 836 /// It's important to note that because of prior substitution, we may have
 837 /// late-bound regions, even outside of fn contexts, since this is the best way
 838 /// to prep types for chalk lowering.
 839 crate fn collect_bound_vars<'tcx, T: TypeFoldable<'tcx>>(
 840     interner: RustInterner<'tcx>,
 841     tcx: TyCtxt<'tcx>,
 842     ty: Binder<'tcx, T>,
 843 ) -> (T, chalk_ir::VariableKinds<RustInterner<'tcx>>, BTreeMap<DefId, u32>) {
 844     let mut bound_vars_collector = BoundVarsCollector::new();
 845     ty.as_ref().skip_binder().visit_with(&mut bound_vars_collector);
 846     let mut parameters = bound_vars_collector.parameters;
 847     let named_parameters: BTreeMap<DefId, u32> = bound_vars_collector
 848         .named_parameters
 849         .into_iter()
 850         .enumerate()
 851         .map(|(i, def_id)| (def_id, (i + parameters.len()) as u32))
 852         .collect();
 853
 854     let mut bound_var_substitutor = NamedBoundVarSubstitutor::new(tcx, &named_parameters);
 855     let new_ty = ty.skip_binder().fold_with(&mut bound_var_substitutor);
 856
 857     for var in named_parameters.values() {
 858         parameters.insert(*var, chalk_ir::VariableKind::Lifetime);
 859     }
 860
 861     (0..parameters.len()).for_each(|i| {
 862         parameters
 863             .get(&(i as u32))
 864             .or_else(|| bug!("Skipped bound var index: parameters={:?}", parameters));
 865     });
 866
 867     let binders =
 868         chalk_ir::VariableKinds::from_iter(interner, parameters.into_iter().map(|(_, v)| v));
 869
 870     (new_ty, binders, named_parameters)
 871 }
 872
 873 crate struct BoundVarsCollector<'tcx> {
 874     binder_index: ty::DebruijnIndex,
 875     crate parameters: BTreeMap<u32, chalk_ir::VariableKind<RustInterner<'tcx>>>,
 876     crate named_parameters: Vec<DefId>,
 877 }
 878
 879 impl<'tcx> BoundVarsCollector<'tcx> {
 880     crate fn new() -> Self {
 881         BoundVarsCollector {
 882             binder_index: ty::INNERMOST,
 883             parameters: BTreeMap::new(),
 884             named_parameters: vec![],
 885         }
 886     }
 887 }
 888
 889 impl<'tcx> TypeVisitor<'tcx> for BoundVarsCollector<'tcx> {
 890     fn visit_binder<T: TypeFoldable<'tcx>>(
 891         &mut self,
 892         t: &Binder<'tcx, T>,
 893     ) -> ControlFlow<Self::BreakTy> {
 894         self.binder_index.shift_in(1);
 895         let result = t.super_visit_with(self);
 896         self.binder_index.shift_out(1);
 897         result
 898     }
 899
 900     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
 901         match *t.kind() {
 902             ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
 903                 match self.parameters.entry(bound_ty.var.as_u32()) {
 904                     Entry::Vacant(entry) => {
 905                         entry.insert(chalk_ir::VariableKind::Ty(chalk_ir::TyVariableKind::General));
 906                     }
 907                     Entry::Occupied(entry) => match entry.get() {
 908                         chalk_ir::VariableKind::Ty(_) => {}
 909                         _ => panic!(),
 910                     },
 911                 }
 912             }
 913
 914             _ => (),
 915         };
 916
 917         t.super_visit_with(self)
 918     }
 919
 920     fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<Self::BreakTy> {
 921         match *r {
 922             ty::ReLateBound(index, br) if index == self.binder_index => match br.kind {
 923                 ty::BoundRegionKind::BrNamed(def_id, _name) => {
 924                     if !self.named_parameters.iter().any(|d| *d == def_id) {
 925                         self.named_parameters.push(def_id);
 926                     }
 927                 }
 928
 929                 ty::BoundRegionKind::BrAnon(var) => match self.parameters.entry(var) {
 930                     Entry::Vacant(entry) => {
 931                         entry.insert(chalk_ir::VariableKind::Lifetime);
 932                     }
 933                     Entry::Occupied(entry) => match entry.get() {
 934                         chalk_ir::VariableKind::Lifetime => {}
 935                         _ => panic!(),
 936                     },
 937                 },
 938
 939                 ty::BoundRegionKind::BrEnv => unimplemented!(),
 940             },
 941
 942             ty::ReEarlyBound(_re) => {
 943                 // FIXME(chalk): jackh726 - I think we should always have already
 944                 // substituted away `ReEarlyBound`s for `ReLateBound`s, but need to confirm.
 945                 unimplemented!();
 946             }
 947
 948             _ => (),
 949         };
 950
 951         r.super_visit_with(self)
 952     }
 953 }
 954
 955 /// This is used to replace `BoundRegionKind::BrNamed` with `BoundRegionKind::BrAnon`.
 956 /// Note: we assume that we will always have room for more bound vars. (i.e. we
 957 /// won't ever hit the `u32` limit in `BrAnon`s).
 958 struct NamedBoundVarSubstitutor<'a, 'tcx> {
 959     tcx: TyCtxt<'tcx>,
 960     binder_index: ty::DebruijnIndex,
 961     named_parameters: &'a BTreeMap<DefId, u32>,
 962 }
 963
 964 impl<'a, 'tcx> NamedBoundVarSubstitutor<'a, 'tcx> {
 965     fn new(tcx: TyCtxt<'tcx>, named_parameters: &'a BTreeMap<DefId, u32>) -> Self {
 966         NamedBoundVarSubstitutor { tcx, binder_index: ty::INNERMOST, named_parameters }
 967     }
 968 }
 969
 970 impl<'a, 'tcx> TypeFolder<'tcx> for NamedBoundVarSubstitutor<'a, 'tcx> {
 971     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
 972         self.tcx
 973     }
 974
 975     fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: Binder<'tcx, T>) -> Binder<'tcx, T> {
 976         self.binder_index.shift_in(1);
 977         let result = t.super_fold_with(self);
 978         self.binder_index.shift_out(1);
 979         result
 980     }
 981
 982     fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
 983         match *r {
 984             ty::ReLateBound(index, br) if index == self.binder_index => match br.kind {
 985                 ty::BrNamed(def_id, _name) => match self.named_parameters.get(&def_id) {
 986                     Some(idx) => {
 987                         let new_br = ty::BoundRegion { var: br.var, kind: ty::BrAnon(*idx) };
 988                         return self.tcx.mk_region(ty::ReLateBound(index, new_br));
 989                     }
 990                     None => panic!("Missing `BrNamed`."),
 991                 },
 992                 ty::BrEnv => unimplemented!(),
 993                 ty::BrAnon(_) => {}
 994             },
 995             _ => (),
 996         };
 997
 998         r.super_fold_with(self)
 999     }
1000 }
1001
1002 /// Used to substitute `Param`s with placeholders. We do this since Chalk
1003 /// have a notion of `Param`s.
1004 crate struct ParamsSubstitutor<'tcx> {
1005     tcx: TyCtxt<'tcx>,
1006     binder_index: ty::DebruijnIndex,
1007     list: Vec<rustc_middle::ty::ParamTy>,
1008     next_ty_placeholder: usize,
1009     crate params: rustc_data_structures::fx::FxHashMap<usize, rustc_middle::ty::ParamTy>,
1010     crate named_regions: BTreeMap<DefId, u32>,
1011 }
1012
1013 impl<'tcx> ParamsSubstitutor<'tcx> {
1014     crate fn new(tcx: TyCtxt<'tcx>, next_ty_placeholder: usize) -> Self {
1015         ParamsSubstitutor {
1016             tcx,
1017             binder_index: ty::INNERMOST,
1018             list: vec![],
1019             next_ty_placeholder,
1020             params: rustc_data_structures::fx::FxHashMap::default(),
1021             named_regions: BTreeMap::default(),
1022         }
1023     }
1024 }
1025
1026 impl<'tcx> TypeFolder<'tcx> for ParamsSubstitutor<'tcx> {
1027     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1028         self.tcx
1029     }
1030
1031     fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: Binder<'tcx, T>) -> Binder<'tcx, T> {
1032         self.binder_index.shift_in(1);
1033         let result = t.super_fold_with(self);
1034         self.binder_index.shift_out(1);
1035         result
1036     }
1037
1038     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
1039         match *t.kind() {
1040             ty::Param(param) => match self.list.iter().position(|r| r == &param) {
1041                 Some(idx) => self.tcx.mk_ty(ty::Placeholder(ty::PlaceholderType {
1042                     universe: ty::UniverseIndex::from_usize(0),
1043                     name: ty::BoundVar::from_usize(idx),
1044                 })),
1045                 None => {
1046                     self.list.push(param);
1047                     let idx = self.list.len() - 1 + self.next_ty_placeholder;
1048                     self.params.insert(idx, param);
1049                     self.tcx.mk_ty(ty::Placeholder(ty::PlaceholderType {
1050                         universe: ty::UniverseIndex::from_usize(0),
1051                         name: ty::BoundVar::from_usize(idx),
1052                     }))
1053                 }
1054             },
1055             _ => t.super_fold_with(self),
1056         }
1057     }
1058
1059     fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
1060         match *r {
1061             // FIXME(chalk) - jackh726 - this currently isn't hit in any tests,
1062             // since canonicalization will already change these to canonical
1063             // variables (ty::ReLateBound).
1064             ty::ReEarlyBound(_re) => match self.named_regions.get(&_re.def_id) {
1065                 Some(idx) => {
1066                     let br = ty::BoundRegion {
1067                         var: ty::BoundVar::from_u32(*idx),
1068                         kind: ty::BrAnon(*idx),
1069                     };
1070                     self.tcx.mk_region(ty::ReLateBound(self.binder_index, br))
1071                 }
1072                 None => {
1073                     let idx = self.named_regions.len() as u32;
1074                     let br =
1075                         ty::BoundRegion { var: ty::BoundVar::from_u32(idx), kind: ty::BrAnon(idx) };
1076                     self.named_regions.insert(_re.def_id, idx);
1077                     self.tcx.mk_region(ty::ReLateBound(self.binder_index, br))
1078                 }
1079             },
1080
1081             _ => r.super_fold_with(self),
1082         }
1083     }
1084 }
1085
1086 crate struct ReverseParamsSubstitutor<'tcx> {
1087     tcx: TyCtxt<'tcx>,
1088     params: rustc_data_structures::fx::FxHashMap<usize, rustc_middle::ty::ParamTy>,
1089 }
1090
1091 impl<'tcx> ReverseParamsSubstitutor<'tcx> {
1092     crate fn new(
1093         tcx: TyCtxt<'tcx>,
1094         params: rustc_data_structures::fx::FxHashMap<usize, rustc_middle::ty::ParamTy>,
1095     ) -> Self {
1096         Self { tcx, params }
1097     }
1098 }
1099
1100 impl<'tcx> TypeFolder<'tcx> for ReverseParamsSubstitutor<'tcx> {
1101     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1102         self.tcx
1103     }
1104
1105     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
1106         match *t.kind() {
1107             ty::Placeholder(ty::PlaceholderType { universe: ty::UniverseIndex::ROOT, name }) => {
1108                 match self.params.get(&name.as_usize()) {
1109                     Some(param) => self.tcx.mk_ty(ty::Param(*param)),
1110                     None => t,
1111                 }
1112             }
1113
1114             _ => t.super_fold_with(self),
1115         }
1116     }
1117 }
1118
1119 /// Used to collect `Placeholder`s.
1120 crate struct PlaceholdersCollector {
1121     universe_index: ty::UniverseIndex,
1122     crate next_ty_placeholder: usize,
1123     crate next_anon_region_placeholder: u32,
1124 }
1125
1126 impl PlaceholdersCollector {
1127     crate fn new() -> Self {
1128         PlaceholdersCollector {
1129             universe_index: ty::UniverseIndex::ROOT,
1130             next_ty_placeholder: 0,
1131             next_anon_region_placeholder: 0,
1132         }
1133     }
1134 }
1135
1136 impl<'tcx> TypeVisitor<'tcx> for PlaceholdersCollector {
1137     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1138         match t.kind() {
1139             ty::Placeholder(p) if p.universe == self.universe_index => {
1140                 self.next_ty_placeholder = self.next_ty_placeholder.max(p.name.as_usize() + 1);
1141             }
1142
1143             _ => (),
1144         };
1145
1146         t.super_visit_with(self)
1147     }
1148
1149     fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<Self::BreakTy> {
1150         match *r {
1151             ty::RePlaceholder(p) if p.universe == self.universe_index => {
1152                 if let ty::BoundRegionKind::BrAnon(anon) = p.name {
1153                     self.next_anon_region_placeholder = self.next_anon_region_placeholder.max(anon);
1154                 }
1155             }
1156
1157             _ => (),
1158         };
1159
1160         r.super_visit_with(self)
1161     }
1162 }