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::subst::{GenericArg, GenericArgKind, SubstsRef};
  37 use rustc_middle::ty::{
  38     self, Binder, Region, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitor,
  39 };
  40 use rustc_span::def_id::DefId;
  41
  42 use chalk_ir::{FnSig, ForeignDefId};
  43 use rustc_hir::Unsafety;
  44 use std::collections::btree_map::{BTreeMap, Entry};
  45 use std::ops::ControlFlow;
  46
  47 /// Essentially an `Into` with a `&RustInterner` parameter
  48 pub(crate) trait LowerInto<'tcx, T> {
  49     /// Lower a rustc construct (e.g., `ty::TraitPredicate`) to a chalk type, consuming `self`.
  50     fn lower_into(self, interner: RustInterner<'tcx>) -> T;
  51 }
  52
  53 impl<'tcx> LowerInto<'tcx, chalk_ir::Substitution<RustInterner<'tcx>>> for SubstsRef<'tcx> {
  54     fn lower_into(
  55         self,
  56         interner: RustInterner<'tcx>,
  57     ) -> chalk_ir::Substitution<RustInterner<'tcx>> {
  58         chalk_ir::Substitution::from_iter(interner, self.iter().map(|s| s.lower_into(interner)))
  59     }
  60 }
  61
  62 impl<'tcx> LowerInto<'tcx, SubstsRef<'tcx>> for &chalk_ir::Substitution<RustInterner<'tcx>> {
  63     fn lower_into(self, interner: RustInterner<'tcx>) -> SubstsRef<'tcx> {
  64         interner.tcx.mk_substs(self.iter(interner).map(|subst| subst.lower_into(interner)))
  65     }
  66 }
  67
  68 impl<'tcx> LowerInto<'tcx, chalk_ir::AliasTy<RustInterner<'tcx>>> for ty::ProjectionTy<'tcx> {
  69     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::AliasTy<RustInterner<'tcx>> {
  70         chalk_ir::AliasTy::Projection(chalk_ir::ProjectionTy {
  71             associated_ty_id: chalk_ir::AssocTypeId(self.item_def_id),
  72             substitution: self.substs.lower_into(interner),
  73         })
  74     }
  75 }
  76
  77 impl<'tcx> LowerInto<'tcx, chalk_ir::InEnvironment<chalk_ir::Goal<RustInterner<'tcx>>>>
  78     for ChalkEnvironmentAndGoal<'tcx>
  79 {
  80     fn lower_into(
  81         self,
  82         interner: RustInterner<'tcx>,
  83     ) -> chalk_ir::InEnvironment<chalk_ir::Goal<RustInterner<'tcx>>> {
  84         let clauses = self.environment.into_iter().map(|predicate| {
  85             let (predicate, binders, _named_regions) =
  86                 collect_bound_vars(interner, interner.tcx, predicate.kind());
  87             let consequence = match predicate {
  88                 ty::PredicateKind::TypeWellFormedFromEnv(ty) => {
  89                     chalk_ir::DomainGoal::FromEnv(chalk_ir::FromEnv::Ty(ty.lower_into(interner)))
  90                 }
  91                 ty::PredicateKind::Trait(predicate) => chalk_ir::DomainGoal::FromEnv(
  92                     chalk_ir::FromEnv::Trait(predicate.trait_ref.lower_into(interner)),
  93                 ),
  94                 ty::PredicateKind::RegionOutlives(predicate) => chalk_ir::DomainGoal::Holds(
  95                     chalk_ir::WhereClause::LifetimeOutlives(chalk_ir::LifetimeOutlives {
  96                         a: predicate.0.lower_into(interner),
  97                         b: predicate.1.lower_into(interner),
  98                     }),
  99                 ),
 100                 ty::PredicateKind::TypeOutlives(predicate) => chalk_ir::DomainGoal::Holds(
 101                     chalk_ir::WhereClause::TypeOutlives(chalk_ir::TypeOutlives {
 102                         ty: predicate.0.lower_into(interner),
 103                         lifetime: predicate.1.lower_into(interner),
 104                     }),
 105                 ),
 106                 ty::PredicateKind::Projection(predicate) => chalk_ir::DomainGoal::Holds(
 107                     chalk_ir::WhereClause::AliasEq(predicate.lower_into(interner)),
 108                 ),
 109                 ty::PredicateKind::WellFormed(arg) => match arg.unpack() {
 110                     ty::GenericArgKind::Type(ty) => chalk_ir::DomainGoal::WellFormed(
 111                         chalk_ir::WellFormed::Ty(ty.lower_into(interner)),
 112                     ),
 113                     // FIXME(chalk): we need to change `WellFormed` in Chalk to take a `GenericArg`
 114                     _ => chalk_ir::DomainGoal::WellFormed(chalk_ir::WellFormed::Ty(
 115                         interner.tcx.types.unit.lower_into(interner),
 116                     )),
 117                 },
 118                 ty::PredicateKind::ObjectSafe(..)
 119                 | ty::PredicateKind::ClosureKind(..)
 120                 | ty::PredicateKind::Subtype(..)
 121                 | ty::PredicateKind::Coerce(..)
 122                 | ty::PredicateKind::ConstEvaluatable(..)
 123                 | ty::PredicateKind::ConstEquate(..) => bug!("unexpected predicate {}", predicate),
 124             };
 125             let value = chalk_ir::ProgramClauseImplication {
 126                 consequence,
 127                 conditions: chalk_ir::Goals::empty(interner),
 128                 priority: chalk_ir::ClausePriority::High,
 129                 constraints: chalk_ir::Constraints::empty(interner),
 130             };
 131             chalk_ir::ProgramClauseData(chalk_ir::Binders::new(binders, value)).intern(interner)
 132         });
 133
 134         let goal: chalk_ir::GoalData<RustInterner<'tcx>> = self.goal.lower_into(interner);
 135         chalk_ir::InEnvironment {
 136             environment: chalk_ir::Environment {
 137                 clauses: chalk_ir::ProgramClauses::from_iter(interner, clauses),
 138             },
 139             goal: goal.intern(interner),
 140         }
 141     }
 142 }
 143
 144 impl<'tcx> LowerInto<'tcx, chalk_ir::GoalData<RustInterner<'tcx>>> for ty::Predicate<'tcx> {
 145     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::GoalData<RustInterner<'tcx>> {
 146         let (predicate, binders, _named_regions) =
 147             collect_bound_vars(interner, interner.tcx, self.kind());
 148
 149         let value = match predicate {
 150             ty::PredicateKind::Trait(predicate) => {
 151                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
 152                     chalk_ir::WhereClause::Implemented(predicate.trait_ref.lower_into(interner)),
 153                 ))
 154             }
 155             ty::PredicateKind::RegionOutlives(predicate) => {
 156                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
 157                     chalk_ir::WhereClause::LifetimeOutlives(chalk_ir::LifetimeOutlives {
 158                         a: predicate.0.lower_into(interner),
 159                         b: predicate.1.lower_into(interner),
 160                     }),
 161                 ))
 162             }
 163             ty::PredicateKind::TypeOutlives(predicate) => {
 164                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
 165                     chalk_ir::WhereClause::TypeOutlives(chalk_ir::TypeOutlives {
 166                         ty: predicate.0.lower_into(interner),
 167                         lifetime: predicate.1.lower_into(interner),
 168                     }),
 169                 ))
 170             }
 171             ty::PredicateKind::Projection(predicate) => {
 172                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
 173                     chalk_ir::WhereClause::AliasEq(predicate.lower_into(interner)),
 174                 ))
 175             }
 176             ty::PredicateKind::WellFormed(arg) => match arg.unpack() {
 177                 GenericArgKind::Type(ty) => match ty.kind() {
 178                     // FIXME(chalk): In Chalk, a placeholder is WellFormed if it
 179                     // `FromEnv`. However, when we "lower" Params, we don't update
 180                     // the environment.
 181                     ty::Placeholder(..) => {
 182                         chalk_ir::GoalData::All(chalk_ir::Goals::empty(interner))
 183                     }
 184
 185                     _ => chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::WellFormed(
 186                         chalk_ir::WellFormed::Ty(ty.lower_into(interner)),
 187                     )),
 188                 },
 189                 // FIXME(chalk): handle well formed consts
 190                 GenericArgKind::Const(..) => {
 191                     chalk_ir::GoalData::All(chalk_ir::Goals::empty(interner))
 192                 }
 193                 GenericArgKind::Lifetime(lt) => bug!("unexpect well formed predicate: {:?}", lt),
 194             },
 195
 196             ty::PredicateKind::ObjectSafe(t) => chalk_ir::GoalData::DomainGoal(
 197                 chalk_ir::DomainGoal::ObjectSafe(chalk_ir::TraitId(t)),
 198             ),
 199
 200             ty::PredicateKind::Subtype(ty::SubtypePredicate { a, b, a_is_expected: _ }) => {
 201                 chalk_ir::GoalData::SubtypeGoal(chalk_ir::SubtypeGoal {
 202                     a: a.lower_into(interner),
 203                     b: b.lower_into(interner),
 204                 })
 205             }
 206
 207             // FIXME(chalk): other predicates
 208             //
 209             // We can defer this, but ultimately we'll want to express
 210             // some of these in terms of chalk operations.
 211             ty::PredicateKind::ClosureKind(..)
 212             | ty::PredicateKind::Coerce(..)
 213             | ty::PredicateKind::ConstEvaluatable(..)
 214             | ty::PredicateKind::ConstEquate(..) => {
 215                 chalk_ir::GoalData::All(chalk_ir::Goals::empty(interner))
 216             }
 217             ty::PredicateKind::TypeWellFormedFromEnv(ty) => chalk_ir::GoalData::DomainGoal(
 218                 chalk_ir::DomainGoal::FromEnv(chalk_ir::FromEnv::Ty(ty.lower_into(interner))),
 219             ),
 220         };
 221
 222         chalk_ir::GoalData::Quantified(
 223             chalk_ir::QuantifierKind::ForAll,
 224             chalk_ir::Binders::new(binders, value.intern(interner)),
 225         )
 226     }
 227 }
 228
 229 impl<'tcx> LowerInto<'tcx, chalk_ir::TraitRef<RustInterner<'tcx>>>
 230     for rustc_middle::ty::TraitRef<'tcx>
 231 {
 232     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::TraitRef<RustInterner<'tcx>> {
 233         chalk_ir::TraitRef {
 234             trait_id: chalk_ir::TraitId(self.def_id),
 235             substitution: self.substs.lower_into(interner),
 236         }
 237     }
 238 }
 239
 240 impl<'tcx> LowerInto<'tcx, chalk_ir::AliasEq<RustInterner<'tcx>>>
 241     for rustc_middle::ty::ProjectionPredicate<'tcx>
 242 {
 243     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::AliasEq<RustInterner<'tcx>> {
 244         // FIXME(associated_const_equality): teach chalk about terms for alias eq.
 245         chalk_ir::AliasEq {
 246             ty: self.term.ty().unwrap().lower_into(interner),
 247             alias: self.projection_ty.lower_into(interner),
 248         }
 249     }
 250 }
 251
 252 /*
 253 // FIXME(...): Where do I add this to Chalk? I can't find it in the rustc repo anywhere.
 254 impl<'tcx> LowerInto<'tcx, chalk_ir::Term<RustInterner<'tcx>>> for rustc_middle::ty::Term<'tcx> {
 255   fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::Term<RustInterner<'tcx>> {
 256     match self {
 257       ty::Term::Ty(ty) => ty.lower_into(interner).into(),
 258       ty::Term::Const(c) => c.lower_into(interner).into(),
 259     }
 260   }
 261 }
 262 */
 263
 264 impl<'tcx> LowerInto<'tcx, chalk_ir::Ty<RustInterner<'tcx>>> for Ty<'tcx> {
 265     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::Ty<RustInterner<'tcx>> {
 266         let int = |i| chalk_ir::TyKind::Scalar(chalk_ir::Scalar::Int(i));
 267         let uint = |i| chalk_ir::TyKind::Scalar(chalk_ir::Scalar::Uint(i));
 268         let float = |f| chalk_ir::TyKind::Scalar(chalk_ir::Scalar::Float(f));
 269
 270         match *self.kind() {
 271             ty::Bool => chalk_ir::TyKind::Scalar(chalk_ir::Scalar::Bool),
 272             ty::Char => chalk_ir::TyKind::Scalar(chalk_ir::Scalar::Char),
 273             ty::Int(ty) => match ty {
 274                 ty::IntTy::Isize => int(chalk_ir::IntTy::Isize),
 275                 ty::IntTy::I8 => int(chalk_ir::IntTy::I8),
 276                 ty::IntTy::I16 => int(chalk_ir::IntTy::I16),
 277                 ty::IntTy::I32 => int(chalk_ir::IntTy::I32),
 278                 ty::IntTy::I64 => int(chalk_ir::IntTy::I64),
 279                 ty::IntTy::I128 => int(chalk_ir::IntTy::I128),
 280             },
 281             ty::Uint(ty) => match ty {
 282                 ty::UintTy::Usize => uint(chalk_ir::UintTy::Usize),
 283                 ty::UintTy::U8 => uint(chalk_ir::UintTy::U8),
 284                 ty::UintTy::U16 => uint(chalk_ir::UintTy::U16),
 285                 ty::UintTy::U32 => uint(chalk_ir::UintTy::U32),
 286                 ty::UintTy::U64 => uint(chalk_ir::UintTy::U64),
 287                 ty::UintTy::U128 => uint(chalk_ir::UintTy::U128),
 288             },
 289             ty::Float(ty) => match ty {
 290                 ty::FloatTy::F32 => float(chalk_ir::FloatTy::F32),
 291                 ty::FloatTy::F64 => float(chalk_ir::FloatTy::F64),
 292             },
 293             ty::Adt(def, substs) => {
 294                 chalk_ir::TyKind::Adt(chalk_ir::AdtId(def), substs.lower_into(interner))
 295             }
 296             ty::Foreign(def_id) => chalk_ir::TyKind::Foreign(ForeignDefId(def_id)),
 297             ty::Str => chalk_ir::TyKind::Str,
 298             ty::Array(ty, len) => {
 299                 chalk_ir::TyKind::Array(ty.lower_into(interner), len.lower_into(interner))
 300             }
 301             ty::Slice(ty) => chalk_ir::TyKind::Slice(ty.lower_into(interner)),
 302
 303             ty::RawPtr(ptr) => {
 304                 chalk_ir::TyKind::Raw(ptr.mutbl.lower_into(interner), ptr.ty.lower_into(interner))
 305             }
 306             ty::Ref(region, ty, mutability) => chalk_ir::TyKind::Ref(
 307                 mutability.lower_into(interner),
 308                 region.lower_into(interner),
 309                 ty.lower_into(interner),
 310             ),
 311             ty::FnDef(def_id, substs) => {
 312                 chalk_ir::TyKind::FnDef(chalk_ir::FnDefId(def_id), substs.lower_into(interner))
 313             }
 314             ty::FnPtr(sig) => {
 315                 let (inputs_and_outputs, binders, _named_regions) =
 316                     collect_bound_vars(interner, interner.tcx, sig.inputs_and_output());
 317                 chalk_ir::TyKind::Function(chalk_ir::FnPointer {
 318                     num_binders: binders.len(interner),
 319                     sig: sig.lower_into(interner),
 320                     substitution: chalk_ir::FnSubst(chalk_ir::Substitution::from_iter(
 321                         interner,
 322                         inputs_and_outputs.iter().map(|ty| {
 323                             chalk_ir::GenericArgData::Ty(ty.lower_into(interner)).intern(interner)
 324                         }),
 325                     )),
 326                 })
 327             }
 328             ty::Dynamic(predicates, region) => chalk_ir::TyKind::Dyn(chalk_ir::DynTy {
 329                 bounds: predicates.lower_into(interner),
 330                 lifetime: region.lower_into(interner),
 331             }),
 332             ty::Closure(def_id, substs) => {
 333                 chalk_ir::TyKind::Closure(chalk_ir::ClosureId(def_id), substs.lower_into(interner))
 334             }
 335             ty::Generator(def_id, substs, _) => chalk_ir::TyKind::Generator(
 336                 chalk_ir::GeneratorId(def_id),
 337                 substs.lower_into(interner),
 338             ),
 339             ty::GeneratorWitness(_) => unimplemented!(),
 340             ty::Never => chalk_ir::TyKind::Never,
 341             ty::Tuple(types) => {
 342                 chalk_ir::TyKind::Tuple(types.len(), types.as_substs().lower_into(interner))
 343             }
 344             ty::Projection(proj) => chalk_ir::TyKind::Alias(proj.lower_into(interner)),
 345             ty::Opaque(def_id, substs) => {
 346                 chalk_ir::TyKind::Alias(chalk_ir::AliasTy::Opaque(chalk_ir::OpaqueTy {
 347                     opaque_ty_id: chalk_ir::OpaqueTyId(def_id),
 348                     substitution: substs.lower_into(interner),
 349                 }))
 350             }
 351             // This should have been done eagerly prior to this, and all Params
 352             // should have been substituted to placeholders
 353             ty::Param(_) => panic!("Lowering Param when not expected."),
 354             ty::Bound(db, bound) => chalk_ir::TyKind::BoundVar(chalk_ir::BoundVar::new(
 355                 chalk_ir::DebruijnIndex::new(db.as_u32()),
 356                 bound.var.index(),
 357             )),
 358             ty::Placeholder(_placeholder) => {
 359                 chalk_ir::TyKind::Placeholder(chalk_ir::PlaceholderIndex {
 360                     ui: chalk_ir::UniverseIndex { counter: _placeholder.universe.as_usize() },
 361                     idx: _placeholder.name.as_usize(),
 362                 })
 363             }
 364             ty::Infer(_infer) => unimplemented!(),
 365             ty::Error(_) => chalk_ir::TyKind::Error,
 366         }
 367         .intern(interner)
 368     }
 369 }
 370
 371 impl<'tcx> LowerInto<'tcx, Ty<'tcx>> for &chalk_ir::Ty<RustInterner<'tcx>> {
 372     fn lower_into(self, interner: RustInterner<'tcx>) -> Ty<'tcx> {
 373         use chalk_ir::TyKind;
 374
 375         let kind = match self.kind(interner) {
 376             TyKind::Adt(struct_id, substitution) => {
 377                 ty::Adt(struct_id.0, substitution.lower_into(interner))
 378             }
 379             TyKind::Scalar(scalar) => match scalar {
 380                 chalk_ir::Scalar::Bool => ty::Bool,
 381                 chalk_ir::Scalar::Char => ty::Char,
 382                 chalk_ir::Scalar::Int(int_ty) => match int_ty {
 383                     chalk_ir::IntTy::Isize => ty::Int(ty::IntTy::Isize),
 384                     chalk_ir::IntTy::I8 => ty::Int(ty::IntTy::I8),
 385                     chalk_ir::IntTy::I16 => ty::Int(ty::IntTy::I16),
 386                     chalk_ir::IntTy::I32 => ty::Int(ty::IntTy::I32),
 387                     chalk_ir::IntTy::I64 => ty::Int(ty::IntTy::I64),
 388                     chalk_ir::IntTy::I128 => ty::Int(ty::IntTy::I128),
 389                 },
 390                 chalk_ir::Scalar::Uint(int_ty) => match int_ty {
 391                     chalk_ir::UintTy::Usize => ty::Uint(ty::UintTy::Usize),
 392                     chalk_ir::UintTy::U8 => ty::Uint(ty::UintTy::U8),
 393                     chalk_ir::UintTy::U16 => ty::Uint(ty::UintTy::U16),
 394                     chalk_ir::UintTy::U32 => ty::Uint(ty::UintTy::U32),
 395                     chalk_ir::UintTy::U64 => ty::Uint(ty::UintTy::U64),
 396                     chalk_ir::UintTy::U128 => ty::Uint(ty::UintTy::U128),
 397                 },
 398                 chalk_ir::Scalar::Float(float_ty) => match float_ty {
 399                     chalk_ir::FloatTy::F32 => ty::Float(ty::FloatTy::F32),
 400                     chalk_ir::FloatTy::F64 => ty::Float(ty::FloatTy::F64),
 401                 },
 402             },
 403             TyKind::Array(ty, c) => {
 404                 let ty = ty.lower_into(interner);
 405                 let c = c.lower_into(interner);
 406                 ty::Array(ty, c)
 407             }
 408             TyKind::FnDef(id, substitution) => ty::FnDef(id.0, substitution.lower_into(interner)),
 409             TyKind::Closure(closure, substitution) => {
 410                 ty::Closure(closure.0, substitution.lower_into(interner))
 411             }
 412             TyKind::Generator(..) => unimplemented!(),
 413             TyKind::GeneratorWitness(..) => unimplemented!(),
 414             TyKind::Never => ty::Never,
 415             TyKind::Tuple(_len, substitution) => {
 416                 ty::Tuple(substitution.lower_into(interner).try_as_type_list().unwrap())
 417             }
 418             TyKind::Slice(ty) => ty::Slice(ty.lower_into(interner)),
 419             TyKind::Raw(mutbl, ty) => ty::RawPtr(ty::TypeAndMut {
 420                 ty: ty.lower_into(interner),
 421                 mutbl: mutbl.lower_into(interner),
 422             }),
 423             TyKind::Ref(mutbl, lifetime, ty) => ty::Ref(
 424                 lifetime.lower_into(interner),
 425                 ty.lower_into(interner),
 426                 mutbl.lower_into(interner),
 427             ),
 428             TyKind::Str => ty::Str,
 429             TyKind::OpaqueType(opaque_ty, substitution) => {
 430                 ty::Opaque(opaque_ty.0, substitution.lower_into(interner))
 431             }
 432             TyKind::AssociatedType(assoc_ty, substitution) => ty::Projection(ty::ProjectionTy {
 433                 substs: substitution.lower_into(interner),
 434                 item_def_id: assoc_ty.0,
 435             }),
 436             TyKind::Foreign(def_id) => ty::Foreign(def_id.0),
 437             TyKind::Error => return interner.tcx.ty_error(),
 438             TyKind::Placeholder(placeholder) => ty::Placeholder(ty::Placeholder {
 439                 universe: ty::UniverseIndex::from_usize(placeholder.ui.counter),
 440                 name: ty::BoundVar::from_usize(placeholder.idx),
 441             }),
 442             TyKind::Alias(alias_ty) => match alias_ty {
 443                 chalk_ir::AliasTy::Projection(projection) => ty::Projection(ty::ProjectionTy {
 444                     item_def_id: projection.associated_ty_id.0,
 445                     substs: projection.substitution.lower_into(interner),
 446                 }),
 447                 chalk_ir::AliasTy::Opaque(opaque) => {
 448                     ty::Opaque(opaque.opaque_ty_id.0, opaque.substitution.lower_into(interner))
 449                 }
 450             },
 451             TyKind::Function(_quantified_ty) => unimplemented!(),
 452             TyKind::BoundVar(_bound) => ty::Bound(
 453                 ty::DebruijnIndex::from_usize(_bound.debruijn.depth() as usize),
 454                 ty::BoundTy {
 455                     var: ty::BoundVar::from_usize(_bound.index),
 456                     kind: ty::BoundTyKind::Anon,
 457                 },
 458             ),
 459             TyKind::InferenceVar(_, _) => unimplemented!(),
 460             TyKind::Dyn(_) => unimplemented!(),
 461         };
 462         interner.tcx.mk_ty(kind)
 463     }
 464 }
 465
 466 impl<'tcx> LowerInto<'tcx, chalk_ir::Lifetime<RustInterner<'tcx>>> for Region<'tcx> {
 467     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::Lifetime<RustInterner<'tcx>> {
 468         match *self {
 469             ty::ReEarlyBound(_) => {
 470                 panic!("Should have already been substituted.");
 471             }
 472             ty::ReLateBound(db, br) => chalk_ir::LifetimeData::BoundVar(chalk_ir::BoundVar::new(
 473                 chalk_ir::DebruijnIndex::new(db.as_u32()),
 474                 br.var.as_usize(),
 475             ))
 476             .intern(interner),
 477             ty::ReFree(_) => unimplemented!(),
 478             ty::ReStatic => chalk_ir::LifetimeData::Static.intern(interner),
 479             ty::ReVar(_) => unimplemented!(),
 480             ty::RePlaceholder(placeholder_region) => {
 481                 chalk_ir::LifetimeData::Placeholder(chalk_ir::PlaceholderIndex {
 482                     ui: chalk_ir::UniverseIndex { counter: placeholder_region.universe.index() },
 483                     idx: 0,
 484                 })
 485                 .intern(interner)
 486             }
 487             ty::ReEmpty(ui) => {
 488                 chalk_ir::LifetimeData::Empty(chalk_ir::UniverseIndex { counter: ui.index() })
 489                     .intern(interner)
 490             }
 491             ty::ReErased => chalk_ir::LifetimeData::Erased.intern(interner),
 492         }
 493     }
 494 }
 495
 496 impl<'tcx> LowerInto<'tcx, Region<'tcx>> for &chalk_ir::Lifetime<RustInterner<'tcx>> {
 497     fn lower_into(self, interner: RustInterner<'tcx>) -> Region<'tcx> {
 498         let kind = match self.data(interner) {
 499             chalk_ir::LifetimeData::BoundVar(var) => ty::ReLateBound(
 500                 ty::DebruijnIndex::from_u32(var.debruijn.depth()),
 501                 ty::BoundRegion {
 502                     var: ty::BoundVar::from_usize(var.index),
 503                     kind: ty::BrAnon(var.index as u32),
 504                 },
 505             ),
 506             chalk_ir::LifetimeData::InferenceVar(_var) => unimplemented!(),
 507             chalk_ir::LifetimeData::Placeholder(p) => ty::RePlaceholder(ty::Placeholder {
 508                 universe: ty::UniverseIndex::from_usize(p.ui.counter),
 509                 name: ty::BoundRegionKind::BrAnon(p.idx as u32),
 510             }),
 511             chalk_ir::LifetimeData::Static => return interner.tcx.lifetimes.re_static,
 512             chalk_ir::LifetimeData::Empty(ui) => {
 513                 ty::ReEmpty(ty::UniverseIndex::from_usize(ui.counter))
 514             }
 515             chalk_ir::LifetimeData::Erased => return interner.tcx.lifetimes.re_erased,
 516             chalk_ir::LifetimeData::Phantom(void, _) => match *void {},
 517         };
 518         interner.tcx.mk_region(kind)
 519     }
 520 }
 521
 522 impl<'tcx> LowerInto<'tcx, chalk_ir::Const<RustInterner<'tcx>>> for ty::Const<'tcx> {
 523     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::Const<RustInterner<'tcx>> {
 524         let ty = self.ty().lower_into(interner);
 525         let value = match self.kind() {
 526             ty::ConstKind::Value(val) => {
 527                 chalk_ir::ConstValue::Concrete(chalk_ir::ConcreteConst { interned: val })
 528             }
 529             ty::ConstKind::Bound(db, bound) => chalk_ir::ConstValue::BoundVar(
 530                 chalk_ir::BoundVar::new(chalk_ir::DebruijnIndex::new(db.as_u32()), bound.index()),
 531             ),
 532             _ => unimplemented!("Const not implemented. {:?}", self),
 533         };
 534         chalk_ir::ConstData { ty, value }.intern(interner)
 535     }
 536 }
 537
 538 impl<'tcx> LowerInto<'tcx, ty::Const<'tcx>> for &chalk_ir::Const<RustInterner<'tcx>> {
 539     fn lower_into(self, interner: RustInterner<'tcx>) -> ty::Const<'tcx> {
 540         let data = self.data(interner);
 541         let ty = data.ty.lower_into(interner);
 542         let kind = match data.value {
 543             chalk_ir::ConstValue::BoundVar(var) => ty::ConstKind::Bound(
 544                 ty::DebruijnIndex::from_u32(var.debruijn.depth()),
 545                 ty::BoundVar::from_u32(var.index as u32),
 546             ),
 547             chalk_ir::ConstValue::InferenceVar(_var) => unimplemented!(),
 548             chalk_ir::ConstValue::Placeholder(_p) => unimplemented!(),
 549             chalk_ir::ConstValue::Concrete(c) => ty::ConstKind::Value(c.interned),
 550         };
 551         interner.tcx.mk_const(ty::ConstS { ty, kind })
 552     }
 553 }
 554
 555 impl<'tcx> LowerInto<'tcx, chalk_ir::GenericArg<RustInterner<'tcx>>> for GenericArg<'tcx> {
 556     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::GenericArg<RustInterner<'tcx>> {
 557         match self.unpack() {
 558             ty::subst::GenericArgKind::Type(ty) => {
 559                 chalk_ir::GenericArgData::Ty(ty.lower_into(interner))
 560             }
 561             ty::subst::GenericArgKind::Lifetime(lifetime) => {
 562                 chalk_ir::GenericArgData::Lifetime(lifetime.lower_into(interner))
 563             }
 564             ty::subst::GenericArgKind::Const(c) => {
 565                 chalk_ir::GenericArgData::Const(c.lower_into(interner))
 566             }
 567         }
 568         .intern(interner)
 569     }
 570 }
 571
 572 impl<'tcx> LowerInto<'tcx, ty::subst::GenericArg<'tcx>>
 573     for &chalk_ir::GenericArg<RustInterner<'tcx>>
 574 {
 575     fn lower_into(self, interner: RustInterner<'tcx>) -> ty::subst::GenericArg<'tcx> {
 576         match self.data(interner) {
 577             chalk_ir::GenericArgData::Ty(ty) => {
 578                 let t: Ty<'tcx> = ty.lower_into(interner);
 579                 t.into()
 580             }
 581             chalk_ir::GenericArgData::Lifetime(lifetime) => {
 582                 let r: Region<'tcx> = lifetime.lower_into(interner);
 583                 r.into()
 584             }
 585             chalk_ir::GenericArgData::Const(c) => {
 586                 let c: ty::Const<'tcx> = c.lower_into(interner);
 587                 c.into()
 588             }
 589         }
 590     }
 591 }
 592
 593 // We lower into an Option here since there are some predicates which Chalk
 594 // doesn't have a representation for yet (as a `WhereClause`), but are so common
 595 // that we just are accepting the unsoundness for now. The `Option` will
 596 // eventually be removed.
 597 impl<'tcx> LowerInto<'tcx, Option<chalk_ir::QuantifiedWhereClause<RustInterner<'tcx>>>>
 598     for ty::Predicate<'tcx>
 599 {
 600     fn lower_into(
 601         self,
 602         interner: RustInterner<'tcx>,
 603     ) -> Option<chalk_ir::QuantifiedWhereClause<RustInterner<'tcx>>> {
 604         let (predicate, binders, _named_regions) =
 605             collect_bound_vars(interner, interner.tcx, self.kind());
 606         let value = match predicate {
 607             ty::PredicateKind::Trait(predicate) => {
 608                 Some(chalk_ir::WhereClause::Implemented(predicate.trait_ref.lower_into(interner)))
 609             }
 610             ty::PredicateKind::RegionOutlives(predicate) => {
 611                 Some(chalk_ir::WhereClause::LifetimeOutlives(chalk_ir::LifetimeOutlives {
 612                     a: predicate.0.lower_into(interner),
 613                     b: predicate.1.lower_into(interner),
 614                 }))
 615             }
 616             ty::PredicateKind::TypeOutlives(predicate) => {
 617                 Some(chalk_ir::WhereClause::TypeOutlives(chalk_ir::TypeOutlives {
 618                     ty: predicate.0.lower_into(interner),
 619                     lifetime: predicate.1.lower_into(interner),
 620                 }))
 621             }
 622             ty::PredicateKind::Projection(predicate) => {
 623                 Some(chalk_ir::WhereClause::AliasEq(predicate.lower_into(interner)))
 624             }
 625             ty::PredicateKind::WellFormed(_ty) => None,
 626
 627             ty::PredicateKind::ObjectSafe(..)
 628             | ty::PredicateKind::ClosureKind(..)
 629             | ty::PredicateKind::Subtype(..)
 630             | ty::PredicateKind::Coerce(..)
 631             | ty::PredicateKind::ConstEvaluatable(..)
 632             | ty::PredicateKind::ConstEquate(..)
 633             | ty::PredicateKind::TypeWellFormedFromEnv(..) => {
 634                 bug!("unexpected predicate {}", &self)
 635             }
 636         };
 637         value.map(|value| chalk_ir::Binders::new(binders, value))
 638     }
 639 }
 640
 641 impl<'tcx> LowerInto<'tcx, chalk_ir::Binders<chalk_ir::QuantifiedWhereClauses<RustInterner<'tcx>>>>
 642     for &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>
 643 {
 644     fn lower_into(
 645         self,
 646         interner: RustInterner<'tcx>,
 647     ) -> chalk_ir::Binders<chalk_ir::QuantifiedWhereClauses<RustInterner<'tcx>>> {
 648         // `Self` has one binder:
 649         // Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>
 650         // The return type has two:
 651         // Binders<&[Binders<WhereClause<I>>]>
 652         // This means that any variables that are escaping `self` need to be
 653         // shifted in by one so that they are still escaping.
 654         let predicates = ty::fold::shift_vars(interner.tcx, self, 1);
 655
 656         let self_ty = interner.tcx.mk_ty(ty::Bound(
 657             // This is going to be wrapped in a binder
 658             ty::DebruijnIndex::from_usize(1),
 659             ty::BoundTy { var: ty::BoundVar::from_usize(0), kind: ty::BoundTyKind::Anon },
 660         ));
 661         let where_clauses = predicates.into_iter().map(|predicate| {
 662             let (predicate, binders, _named_regions) =
 663                 collect_bound_vars(interner, interner.tcx, predicate);
 664             match predicate {
 665                 ty::ExistentialPredicate::Trait(ty::ExistentialTraitRef { def_id, substs }) => {
 666                     chalk_ir::Binders::new(
 667                         binders.clone(),
 668                         chalk_ir::WhereClause::Implemented(chalk_ir::TraitRef {
 669                             trait_id: chalk_ir::TraitId(def_id),
 670                             substitution: interner
 671                                 .tcx
 672                                 .mk_substs_trait(self_ty, substs)
 673                                 .lower_into(interner),
 674                         }),
 675                     )
 676                 }
 677                 ty::ExistentialPredicate::Projection(predicate) => chalk_ir::Binders::new(
 678                     binders.clone(),
 679                     chalk_ir::WhereClause::AliasEq(chalk_ir::AliasEq {
 680                         alias: chalk_ir::AliasTy::Projection(chalk_ir::ProjectionTy {
 681                             associated_ty_id: chalk_ir::AssocTypeId(predicate.item_def_id),
 682                             substitution: interner
 683                                 .tcx
 684                                 .mk_substs_trait(self_ty, predicate.substs)
 685                                 .lower_into(interner),
 686                         }),
 687                         // FIXME(associated_const_equality): teach chalk about terms for alias eq.
 688                         ty: predicate.term.ty().unwrap().lower_into(interner),
 689                     }),
 690                 ),
 691                 ty::ExistentialPredicate::AutoTrait(def_id) => chalk_ir::Binders::new(
 692                     binders.clone(),
 693                     chalk_ir::WhereClause::Implemented(chalk_ir::TraitRef {
 694                         trait_id: chalk_ir::TraitId(def_id),
 695                         substitution: interner
 696                             .tcx
 697                             .mk_substs_trait(self_ty, &[])
 698                             .lower_into(interner),
 699                     }),
 700                 ),
 701             }
 702         });
 703
 704         // Binder for the bound variable representing the concrete underlying type.
 705         let existential_binder = chalk_ir::VariableKinds::from1(
 706             interner,
 707             chalk_ir::VariableKind::Ty(chalk_ir::TyVariableKind::General),
 708         );
 709         let value = chalk_ir::QuantifiedWhereClauses::from_iter(interner, where_clauses);
 710         chalk_ir::Binders::new(existential_binder, value)
 711     }
 712 }
 713
 714 impl<'tcx> LowerInto<'tcx, chalk_ir::FnSig<RustInterner<'tcx>>>
 715     for ty::Binder<'tcx, ty::FnSig<'tcx>>
 716 {
 717     fn lower_into(self, _interner: RustInterner<'_>) -> FnSig<RustInterner<'tcx>> {
 718         chalk_ir::FnSig {
 719             abi: self.abi(),
 720             safety: match self.unsafety() {
 721                 Unsafety::Normal => chalk_ir::Safety::Safe,
 722                 Unsafety::Unsafe => chalk_ir::Safety::Unsafe,
 723             },
 724             variadic: self.c_variadic(),
 725         }
 726     }
 727 }
 728
 729 // We lower into an Option here since there are some predicates which Chalk
 730 // doesn't have a representation for yet (as an `InlineBound`). The `Option` will
 731 // eventually be removed.
 732 impl<'tcx> LowerInto<'tcx, Option<chalk_solve::rust_ir::QuantifiedInlineBound<RustInterner<'tcx>>>>
 733     for ty::Predicate<'tcx>
 734 {
 735     fn lower_into(
 736         self,
 737         interner: RustInterner<'tcx>,
 738     ) -> Option<chalk_solve::rust_ir::QuantifiedInlineBound<RustInterner<'tcx>>> {
 739         let (predicate, binders, _named_regions) =
 740             collect_bound_vars(interner, interner.tcx, self.kind());
 741         match predicate {
 742             ty::PredicateKind::Trait(predicate) => Some(chalk_ir::Binders::new(
 743                 binders,
 744                 chalk_solve::rust_ir::InlineBound::TraitBound(
 745                     predicate.trait_ref.lower_into(interner),
 746                 ),
 747             )),
 748             ty::PredicateKind::Projection(predicate) => Some(chalk_ir::Binders::new(
 749                 binders,
 750                 chalk_solve::rust_ir::InlineBound::AliasEqBound(predicate.lower_into(interner)),
 751             )),
 752             ty::PredicateKind::TypeOutlives(_predicate) => None,
 753             ty::PredicateKind::WellFormed(_ty) => None,
 754
 755             ty::PredicateKind::RegionOutlives(..)
 756             | ty::PredicateKind::ObjectSafe(..)
 757             | ty::PredicateKind::ClosureKind(..)
 758             | ty::PredicateKind::Subtype(..)
 759             | ty::PredicateKind::Coerce(..)
 760             | ty::PredicateKind::ConstEvaluatable(..)
 761             | ty::PredicateKind::ConstEquate(..)
 762             | ty::PredicateKind::TypeWellFormedFromEnv(..) => {
 763                 bug!("unexpected predicate {}", &self)
 764             }
 765         }
 766     }
 767 }
 768
 769 impl<'tcx> LowerInto<'tcx, chalk_solve::rust_ir::TraitBound<RustInterner<'tcx>>>
 770     for ty::TraitRef<'tcx>
 771 {
 772     fn lower_into(
 773         self,
 774         interner: RustInterner<'tcx>,
 775     ) -> chalk_solve::rust_ir::TraitBound<RustInterner<'tcx>> {
 776         chalk_solve::rust_ir::TraitBound {
 777             trait_id: chalk_ir::TraitId(self.def_id),
 778             args_no_self: self.substs[1..].iter().map(|arg| arg.lower_into(interner)).collect(),
 779         }
 780     }
 781 }
 782
 783 impl<'tcx> LowerInto<'tcx, chalk_ir::Mutability> for ast::Mutability {
 784     fn lower_into(self, _interner: RustInterner<'tcx>) -> chalk_ir::Mutability {
 785         match self {
 786             rustc_ast::Mutability::Mut => chalk_ir::Mutability::Mut,
 787             rustc_ast::Mutability::Not => chalk_ir::Mutability::Not,
 788         }
 789     }
 790 }
 791
 792 impl<'tcx> LowerInto<'tcx, ast::Mutability> for chalk_ir::Mutability {
 793     fn lower_into(self, _interner: RustInterner<'tcx>) -> ast::Mutability {
 794         match self {
 795             chalk_ir::Mutability::Mut => ast::Mutability::Mut,
 796             chalk_ir::Mutability::Not => ast::Mutability::Not,
 797         }
 798     }
 799 }
 800
 801 impl<'tcx> LowerInto<'tcx, chalk_solve::rust_ir::Polarity> for ty::ImplPolarity {
 802     fn lower_into(self, _interner: RustInterner<'tcx>) -> chalk_solve::rust_ir::Polarity {
 803         match self {
 804             ty::ImplPolarity::Positive => chalk_solve::rust_ir::Polarity::Positive,
 805             ty::ImplPolarity::Negative => chalk_solve::rust_ir::Polarity::Negative,
 806             // FIXME(chalk) reservation impls
 807             ty::ImplPolarity::Reservation => chalk_solve::rust_ir::Polarity::Negative,
 808         }
 809     }
 810 }
 811 impl<'tcx> LowerInto<'tcx, chalk_ir::Variance> for ty::Variance {
 812     fn lower_into(self, _interner: RustInterner<'tcx>) -> chalk_ir::Variance {
 813         match self {
 814             ty::Variance::Covariant => chalk_ir::Variance::Covariant,
 815             ty::Variance::Invariant => chalk_ir::Variance::Invariant,
 816             ty::Variance::Contravariant => chalk_ir::Variance::Contravariant,
 817             ty::Variance::Bivariant => unimplemented!(),
 818         }
 819     }
 820 }
 821
 822 impl<'tcx> LowerInto<'tcx, chalk_solve::rust_ir::AliasEqBound<RustInterner<'tcx>>>
 823     for ty::ProjectionPredicate<'tcx>
 824 {
 825     fn lower_into(
 826         self,
 827         interner: RustInterner<'tcx>,
 828     ) -> chalk_solve::rust_ir::AliasEqBound<RustInterner<'tcx>> {
 829         let (trait_ref, own_substs) = self.projection_ty.trait_ref_and_own_substs(interner.tcx);
 830         chalk_solve::rust_ir::AliasEqBound {
 831             trait_bound: trait_ref.lower_into(interner),
 832             associated_ty_id: chalk_ir::AssocTypeId(self.projection_ty.item_def_id),
 833             parameters: own_substs.iter().map(|arg| arg.lower_into(interner)).collect(),
 834             value: self.term.ty().unwrap().lower_into(interner),
 835         }
 836     }
 837 }
 838
 839 /// To collect bound vars, we have to do two passes. In the first pass, we
 840 /// collect all `BoundRegionKind`s and `ty::Bound`s. In the second pass, we then
 841 /// replace `BrNamed` into `BrAnon`. The two separate passes are important,
 842 /// since we can only replace `BrNamed` with `BrAnon`s with indices *after* all
 843 /// "real" `BrAnon`s.
 844 ///
 845 /// It's important to note that because of prior substitution, we may have
 846 /// late-bound regions, even outside of fn contexts, since this is the best way
 847 /// to prep types for chalk lowering.
 848 pub(crate) fn collect_bound_vars<'tcx, T: TypeFoldable<'tcx>>(
 849     interner: RustInterner<'tcx>,
 850     tcx: TyCtxt<'tcx>,
 851     ty: Binder<'tcx, T>,
 852 ) -> (T, chalk_ir::VariableKinds<RustInterner<'tcx>>, BTreeMap<DefId, u32>) {
 853     let mut bound_vars_collector = BoundVarsCollector::new();
 854     ty.as_ref().skip_binder().visit_with(&mut bound_vars_collector);
 855     let mut parameters = bound_vars_collector.parameters;
 856     let named_parameters: BTreeMap<DefId, u32> = bound_vars_collector
 857         .named_parameters
 858         .into_iter()
 859         .enumerate()
 860         .map(|(i, def_id)| (def_id, (i + parameters.len()) as u32))
 861         .collect();
 862
 863     let mut bound_var_substitutor = NamedBoundVarSubstitutor::new(tcx, &named_parameters);
 864     let new_ty = ty.skip_binder().fold_with(&mut bound_var_substitutor);
 865
 866     for var in named_parameters.values() {
 867         parameters.insert(*var, chalk_ir::VariableKind::Lifetime);
 868     }
 869
 870     (0..parameters.len()).for_each(|i| {
 871         parameters
 872             .get(&(i as u32))
 873             .or_else(|| bug!("Skipped bound var index: parameters={:?}", parameters));
 874     });
 875
 876     let binders =
 877         chalk_ir::VariableKinds::from_iter(interner, parameters.into_iter().map(|(_, v)| v));
 878
 879     (new_ty, binders, named_parameters)
 880 }
 881
 882 pub(crate) struct BoundVarsCollector<'tcx> {
 883     binder_index: ty::DebruijnIndex,
 884     pub(crate) parameters: BTreeMap<u32, chalk_ir::VariableKind<RustInterner<'tcx>>>,
 885     pub(crate) named_parameters: Vec<DefId>,
 886 }
 887
 888 impl<'tcx> BoundVarsCollector<'tcx> {
 889     pub(crate) fn new() -> Self {
 890         BoundVarsCollector {
 891             binder_index: ty::INNERMOST,
 892             parameters: BTreeMap::new(),
 893             named_parameters: vec![],
 894         }
 895     }
 896 }
 897
 898 impl<'tcx> TypeVisitor<'tcx> for BoundVarsCollector<'tcx> {
 899     fn visit_binder<T: TypeFoldable<'tcx>>(
 900         &mut self,
 901         t: &Binder<'tcx, T>,
 902     ) -> ControlFlow<Self::BreakTy> {
 903         self.binder_index.shift_in(1);
 904         let result = t.super_visit_with(self);
 905         self.binder_index.shift_out(1);
 906         result
 907     }
 908
 909     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
 910         match *t.kind() {
 911             ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
 912                 match self.parameters.entry(bound_ty.var.as_u32()) {
 913                     Entry::Vacant(entry) => {
 914                         entry.insert(chalk_ir::VariableKind::Ty(chalk_ir::TyVariableKind::General));
 915                     }
 916                     Entry::Occupied(entry) => match entry.get() {
 917                         chalk_ir::VariableKind::Ty(_) => {}
 918                         _ => panic!(),
 919                     },
 920                 }
 921             }
 922
 923             _ => (),
 924         };
 925
 926         t.super_visit_with(self)
 927     }
 928
 929     fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<Self::BreakTy> {
 930         match *r {
 931             ty::ReLateBound(index, br) if index == self.binder_index => match br.kind {
 932                 ty::BoundRegionKind::BrNamed(def_id, _name) => {
 933                     if !self.named_parameters.iter().any(|d| *d == def_id) {
 934                         self.named_parameters.push(def_id);
 935                     }
 936                 }
 937
 938                 ty::BoundRegionKind::BrAnon(var) => match self.parameters.entry(var) {
 939                     Entry::Vacant(entry) => {
 940                         entry.insert(chalk_ir::VariableKind::Lifetime);
 941                     }
 942                     Entry::Occupied(entry) => match entry.get() {
 943                         chalk_ir::VariableKind::Lifetime => {}
 944                         _ => panic!(),
 945                     },
 946                 },
 947
 948                 ty::BoundRegionKind::BrEnv => unimplemented!(),
 949             },
 950
 951             ty::ReEarlyBound(_re) => {
 952                 // FIXME(chalk): jackh726 - I think we should always have already
 953                 // substituted away `ReEarlyBound`s for `ReLateBound`s, but need to confirm.
 954                 unimplemented!();
 955             }
 956
 957             _ => (),
 958         };
 959
 960         r.super_visit_with(self)
 961     }
 962 }
 963
 964 /// This is used to replace `BoundRegionKind::BrNamed` with `BoundRegionKind::BrAnon`.
 965 /// Note: we assume that we will always have room for more bound vars. (i.e. we
 966 /// won't ever hit the `u32` limit in `BrAnon`s).
 967 struct NamedBoundVarSubstitutor<'a, 'tcx> {
 968     tcx: TyCtxt<'tcx>,
 969     binder_index: ty::DebruijnIndex,
 970     named_parameters: &'a BTreeMap<DefId, u32>,
 971 }
 972
 973 impl<'a, 'tcx> NamedBoundVarSubstitutor<'a, 'tcx> {
 974     fn new(tcx: TyCtxt<'tcx>, named_parameters: &'a BTreeMap<DefId, u32>) -> Self {
 975         NamedBoundVarSubstitutor { tcx, binder_index: ty::INNERMOST, named_parameters }
 976     }
 977 }
 978
 979 impl<'a, 'tcx> TypeFolder<'tcx> for NamedBoundVarSubstitutor<'a, 'tcx> {
 980     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
 981         self.tcx
 982     }
 983
 984     fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: Binder<'tcx, T>) -> Binder<'tcx, T> {
 985         self.binder_index.shift_in(1);
 986         let result = t.super_fold_with(self);
 987         self.binder_index.shift_out(1);
 988         result
 989     }
 990
 991     fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
 992         match *r {
 993             ty::ReLateBound(index, br) if index == self.binder_index => match br.kind {
 994                 ty::BrNamed(def_id, _name) => match self.named_parameters.get(&def_id) {
 995                     Some(idx) => {
 996                         let new_br = ty::BoundRegion { var: br.var, kind: ty::BrAnon(*idx) };
 997                         return self.tcx.mk_region(ty::ReLateBound(index, new_br));
 998                     }
 999                     None => panic!("Missing `BrNamed`."),
1000                 },
1001                 ty::BrEnv => unimplemented!(),
1002                 ty::BrAnon(_) => {}
1003             },
1004             _ => (),
1005         };
1006
1007         r.super_fold_with(self)
1008     }
1009 }
1010
1011 /// Used to substitute `Param`s with placeholders. We do this since Chalk
1012 /// have a notion of `Param`s.
1013 pub(crate) struct ParamsSubstitutor<'tcx> {
1014     tcx: TyCtxt<'tcx>,
1015     binder_index: ty::DebruijnIndex,
1016     list: Vec<rustc_middle::ty::ParamTy>,
1017     next_ty_placeholder: usize,
1018     pub(crate) params: rustc_data_structures::fx::FxHashMap<usize, rustc_middle::ty::ParamTy>,
1019     pub(crate) named_regions: BTreeMap<DefId, u32>,
1020 }
1021
1022 impl<'tcx> ParamsSubstitutor<'tcx> {
1023     pub(crate) fn new(tcx: TyCtxt<'tcx>, next_ty_placeholder: usize) -> Self {
1024         ParamsSubstitutor {
1025             tcx,
1026             binder_index: ty::INNERMOST,
1027             list: vec![],
1028             next_ty_placeholder,
1029             params: rustc_data_structures::fx::FxHashMap::default(),
1030             named_regions: BTreeMap::default(),
1031         }
1032     }
1033 }
1034
1035 impl<'tcx> TypeFolder<'tcx> for ParamsSubstitutor<'tcx> {
1036     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1037         self.tcx
1038     }
1039
1040     fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: Binder<'tcx, T>) -> Binder<'tcx, T> {
1041         self.binder_index.shift_in(1);
1042         let result = t.super_fold_with(self);
1043         self.binder_index.shift_out(1);
1044         result
1045     }
1046
1047     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
1048         match *t.kind() {
1049             ty::Param(param) => match self.list.iter().position(|r| r == &param) {
1050                 Some(idx) => self.tcx.mk_ty(ty::Placeholder(ty::PlaceholderType {
1051                     universe: ty::UniverseIndex::from_usize(0),
1052                     name: ty::BoundVar::from_usize(idx),
1053                 })),
1054                 None => {
1055                     self.list.push(param);
1056                     let idx = self.list.len() - 1 + self.next_ty_placeholder;
1057                     self.params.insert(idx, param);
1058                     self.tcx.mk_ty(ty::Placeholder(ty::PlaceholderType {
1059                         universe: ty::UniverseIndex::from_usize(0),
1060                         name: ty::BoundVar::from_usize(idx),
1061                     }))
1062                 }
1063             },
1064             _ => t.super_fold_with(self),
1065         }
1066     }
1067
1068     fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
1069         match *r {
1070             // FIXME(chalk) - jackh726 - this currently isn't hit in any tests,
1071             // since canonicalization will already change these to canonical
1072             // variables (ty::ReLateBound).
1073             ty::ReEarlyBound(_re) => match self.named_regions.get(&_re.def_id) {
1074                 Some(idx) => {
1075                     let br = ty::BoundRegion {
1076                         var: ty::BoundVar::from_u32(*idx),
1077                         kind: ty::BrAnon(*idx),
1078                     };
1079                     self.tcx.mk_region(ty::ReLateBound(self.binder_index, br))
1080                 }
1081                 None => {
1082                     let idx = self.named_regions.len() as u32;
1083                     let br =
1084                         ty::BoundRegion { var: ty::BoundVar::from_u32(idx), kind: ty::BrAnon(idx) };
1085                     self.named_regions.insert(_re.def_id, idx);
1086                     self.tcx.mk_region(ty::ReLateBound(self.binder_index, br))
1087                 }
1088             },
1089
1090             _ => r.super_fold_with(self),
1091         }
1092     }
1093 }
1094
1095 pub(crate) struct ReverseParamsSubstitutor<'tcx> {
1096     tcx: TyCtxt<'tcx>,
1097     params: rustc_data_structures::fx::FxHashMap<usize, rustc_middle::ty::ParamTy>,
1098 }
1099
1100 impl<'tcx> ReverseParamsSubstitutor<'tcx> {
1101     pub(crate) fn new(
1102         tcx: TyCtxt<'tcx>,
1103         params: rustc_data_structures::fx::FxHashMap<usize, rustc_middle::ty::ParamTy>,
1104     ) -> Self {
1105         Self { tcx, params }
1106     }
1107 }
1108
1109 impl<'tcx> TypeFolder<'tcx> for ReverseParamsSubstitutor<'tcx> {
1110     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1111         self.tcx
1112     }
1113
1114     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
1115         match *t.kind() {
1116             ty::Placeholder(ty::PlaceholderType { universe: ty::UniverseIndex::ROOT, name }) => {
1117                 match self.params.get(&name.as_usize()) {
1118                     Some(param) => self.tcx.mk_ty(ty::Param(*param)),
1119                     None => t,
1120                 }
1121             }
1122
1123             _ => t.super_fold_with(self),
1124         }
1125     }
1126 }
1127
1128 /// Used to collect `Placeholder`s.
1129 pub(crate) struct PlaceholdersCollector {
1130     universe_index: ty::UniverseIndex,
1131     pub(crate) next_ty_placeholder: usize,
1132     pub(crate) next_anon_region_placeholder: u32,
1133 }
1134
1135 impl PlaceholdersCollector {
1136     pub(crate) fn new() -> Self {
1137         PlaceholdersCollector {
1138             universe_index: ty::UniverseIndex::ROOT,
1139             next_ty_placeholder: 0,
1140             next_anon_region_placeholder: 0,
1141         }
1142     }
1143 }
1144
1145 impl<'tcx> TypeVisitor<'tcx> for PlaceholdersCollector {
1146     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1147         match t.kind() {
1148             ty::Placeholder(p) if p.universe == self.universe_index => {
1149                 self.next_ty_placeholder = self.next_ty_placeholder.max(p.name.as_usize() + 1);
1150             }
1151
1152             _ => (),
1153         };
1154
1155         t.super_visit_with(self)
1156     }
1157
1158     fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<Self::BreakTy> {
1159         match *r {
1160             ty::RePlaceholder(p) if p.universe == self.universe_index => {
1161                 if let ty::BoundRegionKind::BrAnon(anon) = p.name {
1162                     self.next_anon_region_placeholder = self.next_anon_region_placeholder.max(anon);
1163                 }
1164             }
1165
1166             _ => (),
1167         };
1168
1169         r.super_visit_with(self)
1170     }
1171 }