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