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!("unexpect 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             ty::Dynamic(predicates, region) => chalk_ir::TyKind::Dyn(chalk_ir::DynTy {
 330                 bounds: predicates.lower_into(interner),
 331                 lifetime: region.lower_into(interner),
 332             }),
 333             ty::Closure(def_id, substs) => {
 334                 chalk_ir::TyKind::Closure(chalk_ir::ClosureId(def_id), substs.lower_into(interner))
 335             }
 336             ty::Generator(def_id, substs, _) => chalk_ir::TyKind::Generator(
 337                 chalk_ir::GeneratorId(def_id),
 338                 substs.lower_into(interner),
 339             ),
 340             ty::GeneratorWitness(_) => unimplemented!(),
 341             ty::Never => chalk_ir::TyKind::Never,
 342             ty::Tuple(types) => {
 343                 chalk_ir::TyKind::Tuple(types.len(), types.as_substs().lower_into(interner))
 344             }
 345             ty::Projection(proj) => chalk_ir::TyKind::Alias(proj.lower_into(interner)),
 346             ty::Opaque(def_id, substs) => {
 347                 chalk_ir::TyKind::Alias(chalk_ir::AliasTy::Opaque(chalk_ir::OpaqueTy {
 348                     opaque_ty_id: chalk_ir::OpaqueTyId(def_id),
 349                     substitution: substs.lower_into(interner),
 350                 }))
 351             }
 352             // This should have been done eagerly prior to this, and all Params
 353             // should have been substituted to placeholders
 354             ty::Param(_) => panic!("Lowering Param when not expected."),
 355             ty::Bound(db, bound) => chalk_ir::TyKind::BoundVar(chalk_ir::BoundVar::new(
 356                 chalk_ir::DebruijnIndex::new(db.as_u32()),
 357                 bound.var.index(),
 358             )),
 359             ty::Placeholder(_placeholder) => {
 360                 chalk_ir::TyKind::Placeholder(chalk_ir::PlaceholderIndex {
 361                     ui: chalk_ir::UniverseIndex { counter: _placeholder.universe.as_usize() },
 362                     idx: _placeholder.name.as_usize(),
 363                 })
 364             }
 365             ty::Infer(_infer) => unimplemented!(),
 366             ty::Error(_) => chalk_ir::TyKind::Error,
 367         }
 368         .intern(interner)
 369     }
 370 }
 371
 372 impl<'tcx> LowerInto<'tcx, Ty<'tcx>> for &chalk_ir::Ty<RustInterner<'tcx>> {
 373     fn lower_into(self, interner: RustInterner<'tcx>) -> Ty<'tcx> {
 374         use chalk_ir::TyKind;
 375
 376         let kind = match self.kind(interner) {
 377             TyKind::Adt(struct_id, substitution) => {
 378                 ty::Adt(struct_id.0, substitution.lower_into(interner))
 379             }
 380             TyKind::Scalar(scalar) => match scalar {
 381                 chalk_ir::Scalar::Bool => ty::Bool,
 382                 chalk_ir::Scalar::Char => ty::Char,
 383                 chalk_ir::Scalar::Int(int_ty) => match int_ty {
 384                     chalk_ir::IntTy::Isize => ty::Int(ty::IntTy::Isize),
 385                     chalk_ir::IntTy::I8 => ty::Int(ty::IntTy::I8),
 386                     chalk_ir::IntTy::I16 => ty::Int(ty::IntTy::I16),
 387                     chalk_ir::IntTy::I32 => ty::Int(ty::IntTy::I32),
 388                     chalk_ir::IntTy::I64 => ty::Int(ty::IntTy::I64),
 389                     chalk_ir::IntTy::I128 => ty::Int(ty::IntTy::I128),
 390                 },
 391                 chalk_ir::Scalar::Uint(int_ty) => match int_ty {
 392                     chalk_ir::UintTy::Usize => ty::Uint(ty::UintTy::Usize),
 393                     chalk_ir::UintTy::U8 => ty::Uint(ty::UintTy::U8),
 394                     chalk_ir::UintTy::U16 => ty::Uint(ty::UintTy::U16),
 395                     chalk_ir::UintTy::U32 => ty::Uint(ty::UintTy::U32),
 396                     chalk_ir::UintTy::U64 => ty::Uint(ty::UintTy::U64),
 397                     chalk_ir::UintTy::U128 => ty::Uint(ty::UintTy::U128),
 398                 },
 399                 chalk_ir::Scalar::Float(float_ty) => match float_ty {
 400                     chalk_ir::FloatTy::F32 => ty::Float(ty::FloatTy::F32),
 401                     chalk_ir::FloatTy::F64 => ty::Float(ty::FloatTy::F64),
 402                 },
 403             },
 404             TyKind::Array(ty, c) => {
 405                 let ty = ty.lower_into(interner);
 406                 let c = c.lower_into(interner);
 407                 ty::Array(ty, c)
 408             }
 409             TyKind::FnDef(id, substitution) => ty::FnDef(id.0, substitution.lower_into(interner)),
 410             TyKind::Closure(closure, substitution) => {
 411                 ty::Closure(closure.0, substitution.lower_into(interner))
 412             }
 413             TyKind::Generator(..) => unimplemented!(),
 414             TyKind::GeneratorWitness(..) => unimplemented!(),
 415             TyKind::Never => ty::Never,
 416             TyKind::Tuple(_len, substitution) => {
 417                 ty::Tuple(substitution.lower_into(interner).try_as_type_list().unwrap())
 418             }
 419             TyKind::Slice(ty) => ty::Slice(ty.lower_into(interner)),
 420             TyKind::Raw(mutbl, ty) => ty::RawPtr(ty::TypeAndMut {
 421                 ty: ty.lower_into(interner),
 422                 mutbl: mutbl.lower_into(interner),
 423             }),
 424             TyKind::Ref(mutbl, lifetime, ty) => ty::Ref(
 425                 lifetime.lower_into(interner),
 426                 ty.lower_into(interner),
 427                 mutbl.lower_into(interner),
 428             ),
 429             TyKind::Str => ty::Str,
 430             TyKind::OpaqueType(opaque_ty, substitution) => {
 431                 ty::Opaque(opaque_ty.0, substitution.lower_into(interner))
 432             }
 433             TyKind::AssociatedType(assoc_ty, substitution) => ty::Projection(ty::ProjectionTy {
 434                 substs: substitution.lower_into(interner),
 435                 item_def_id: assoc_ty.0,
 436             }),
 437             TyKind::Foreign(def_id) => ty::Foreign(def_id.0),
 438             TyKind::Error => return interner.tcx.ty_error(),
 439             TyKind::Placeholder(placeholder) => ty::Placeholder(ty::Placeholder {
 440                 universe: ty::UniverseIndex::from_usize(placeholder.ui.counter),
 441                 name: ty::BoundVar::from_usize(placeholder.idx),
 442             }),
 443             TyKind::Alias(alias_ty) => match alias_ty {
 444                 chalk_ir::AliasTy::Projection(projection) => ty::Projection(ty::ProjectionTy {
 445                     item_def_id: projection.associated_ty_id.0,
 446                     substs: projection.substitution.lower_into(interner),
 447                 }),
 448                 chalk_ir::AliasTy::Opaque(opaque) => {
 449                     ty::Opaque(opaque.opaque_ty_id.0, opaque.substitution.lower_into(interner))
 450                 }
 451             },
 452             TyKind::Function(_quantified_ty) => unimplemented!(),
 453             TyKind::BoundVar(_bound) => ty::Bound(
 454                 ty::DebruijnIndex::from_usize(_bound.debruijn.depth() as usize),
 455                 ty::BoundTy {
 456                     var: ty::BoundVar::from_usize(_bound.index),
 457                     kind: ty::BoundTyKind::Anon,
 458                 },
 459             ),
 460             TyKind::InferenceVar(_, _) => unimplemented!(),
 461             TyKind::Dyn(_) => unimplemented!(),
 462         };
 463         interner.tcx.mk_ty(kind)
 464     }
 465 }
 466
 467 impl<'tcx> LowerInto<'tcx, chalk_ir::Lifetime<RustInterner<'tcx>>> for Region<'tcx> {
 468     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::Lifetime<RustInterner<'tcx>> {
 469         match *self {
 470             ty::ReEarlyBound(_) => {
 471                 panic!("Should have already been substituted.");
 472             }
 473             ty::ReLateBound(db, br) => chalk_ir::LifetimeData::BoundVar(chalk_ir::BoundVar::new(
 474                 chalk_ir::DebruijnIndex::new(db.as_u32()),
 475                 br.var.as_usize(),
 476             ))
 477             .intern(interner),
 478             ty::ReFree(_) => unimplemented!(),
 479             ty::ReStatic => chalk_ir::LifetimeData::Static.intern(interner),
 480             ty::ReVar(_) => unimplemented!(),
 481             ty::RePlaceholder(placeholder_region) => {
 482                 chalk_ir::LifetimeData::Placeholder(chalk_ir::PlaceholderIndex {
 483                     ui: chalk_ir::UniverseIndex { counter: placeholder_region.universe.index() },
 484                     idx: 0,
 485                 })
 486                 .intern(interner)
 487             }
 488             ty::ReEmpty(ui) => {
 489                 chalk_ir::LifetimeData::Empty(chalk_ir::UniverseIndex { counter: ui.index() })
 490                     .intern(interner)
 491             }
 492             ty::ReErased => chalk_ir::LifetimeData::Erased.intern(interner),
 493         }
 494     }
 495 }
 496
 497 impl<'tcx> LowerInto<'tcx, Region<'tcx>> for &chalk_ir::Lifetime<RustInterner<'tcx>> {
 498     fn lower_into(self, interner: RustInterner<'tcx>) -> Region<'tcx> {
 499         let kind = match self.data(interner) {
 500             chalk_ir::LifetimeData::BoundVar(var) => ty::ReLateBound(
 501                 ty::DebruijnIndex::from_u32(var.debruijn.depth()),
 502                 ty::BoundRegion {
 503                     var: ty::BoundVar::from_usize(var.index),
 504                     kind: ty::BrAnon(var.index as u32),
 505                 },
 506             ),
 507             chalk_ir::LifetimeData::InferenceVar(_var) => unimplemented!(),
 508             chalk_ir::LifetimeData::Placeholder(p) => ty::RePlaceholder(ty::Placeholder {
 509                 universe: ty::UniverseIndex::from_usize(p.ui.counter),
 510                 name: ty::BoundRegionKind::BrAnon(p.idx as u32),
 511             }),
 512             chalk_ir::LifetimeData::Static => return interner.tcx.lifetimes.re_static,
 513             chalk_ir::LifetimeData::Empty(ui) => {
 514                 ty::ReEmpty(ty::UniverseIndex::from_usize(ui.counter))
 515             }
 516             chalk_ir::LifetimeData::Erased => return interner.tcx.lifetimes.re_erased,
 517             chalk_ir::LifetimeData::Phantom(void, _) => match *void {},
 518         };
 519         interner.tcx.mk_region(kind)
 520     }
 521 }
 522
 523 impl<'tcx> LowerInto<'tcx, chalk_ir::Const<RustInterner<'tcx>>> for ty::Const<'tcx> {
 524     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::Const<RustInterner<'tcx>> {
 525         let ty = self.ty().lower_into(interner);
 526         let value = match self.kind() {
 527             ty::ConstKind::Value(val) => {
 528                 chalk_ir::ConstValue::Concrete(chalk_ir::ConcreteConst { interned: val })
 529             }
 530             ty::ConstKind::Bound(db, bound) => chalk_ir::ConstValue::BoundVar(
 531                 chalk_ir::BoundVar::new(chalk_ir::DebruijnIndex::new(db.as_u32()), bound.index()),
 532             ),
 533             _ => unimplemented!("Const not implemented. {:?}", self),
 534         };
 535         chalk_ir::ConstData { ty, value }.intern(interner)
 536     }
 537 }
 538
 539 impl<'tcx> LowerInto<'tcx, ty::Const<'tcx>> for &chalk_ir::Const<RustInterner<'tcx>> {
 540     fn lower_into(self, interner: RustInterner<'tcx>) -> ty::Const<'tcx> {
 541         let data = self.data(interner);
 542         let ty = data.ty.lower_into(interner);
 543         let kind = match data.value {
 544             chalk_ir::ConstValue::BoundVar(var) => ty::ConstKind::Bound(
 545                 ty::DebruijnIndex::from_u32(var.debruijn.depth()),
 546                 ty::BoundVar::from_u32(var.index as u32),
 547             ),
 548             chalk_ir::ConstValue::InferenceVar(_var) => unimplemented!(),
 549             chalk_ir::ConstValue::Placeholder(_p) => unimplemented!(),
 550             chalk_ir::ConstValue::Concrete(c) => ty::ConstKind::Value(c.interned),
 551         };
 552         interner.tcx.mk_const(ty::ConstS { ty, kind })
 553     }
 554 }
 555
 556 impl<'tcx> LowerInto<'tcx, chalk_ir::GenericArg<RustInterner<'tcx>>> for GenericArg<'tcx> {
 557     fn lower_into(self, interner: RustInterner<'tcx>) -> chalk_ir::GenericArg<RustInterner<'tcx>> {
 558         match self.unpack() {
 559             ty::subst::GenericArgKind::Type(ty) => {
 560                 chalk_ir::GenericArgData::Ty(ty.lower_into(interner))
 561             }
 562             ty::subst::GenericArgKind::Lifetime(lifetime) => {
 563                 chalk_ir::GenericArgData::Lifetime(lifetime.lower_into(interner))
 564             }
 565             ty::subst::GenericArgKind::Const(c) => {
 566                 chalk_ir::GenericArgData::Const(c.lower_into(interner))
 567             }
 568         }
 569         .intern(interner)
 570     }
 571 }
 572
 573 impl<'tcx> LowerInto<'tcx, ty::subst::GenericArg<'tcx>>
 574     for &chalk_ir::GenericArg<RustInterner<'tcx>>
 575 {
 576     fn lower_into(self, interner: RustInterner<'tcx>) -> ty::subst::GenericArg<'tcx> {
 577         match self.data(interner) {
 578             chalk_ir::GenericArgData::Ty(ty) => {
 579                 let t: Ty<'tcx> = ty.lower_into(interner);
 580                 t.into()
 581             }
 582             chalk_ir::GenericArgData::Lifetime(lifetime) => {
 583                 let r: Region<'tcx> = lifetime.lower_into(interner);
 584                 r.into()
 585             }
 586             chalk_ir::GenericArgData::Const(c) => {
 587                 let c: ty::Const<'tcx> = c.lower_into(interner);
 588                 c.into()
 589             }
 590         }
 591     }
 592 }
 593
 594 // We lower into an Option here since there are some predicates which Chalk
 595 // doesn't have a representation for yet (as a `WhereClause`), but are so common
 596 // that we just are accepting the unsoundness for now. The `Option` will
 597 // eventually be removed.
 598 impl<'tcx> LowerInto<'tcx, Option<chalk_ir::QuantifiedWhereClause<RustInterner<'tcx>>>>
 599     for ty::Predicate<'tcx>
 600 {
 601     fn lower_into(
 602         self,
 603         interner: RustInterner<'tcx>,
 604     ) -> Option<chalk_ir::QuantifiedWhereClause<RustInterner<'tcx>>> {
 605         let (predicate, binders, _named_regions) =
 606             collect_bound_vars(interner, interner.tcx, self.kind());
 607         let value = match predicate {
 608             ty::PredicateKind::Trait(predicate) => {
 609                 Some(chalk_ir::WhereClause::Implemented(predicate.trait_ref.lower_into(interner)))
 610             }
 611             ty::PredicateKind::RegionOutlives(predicate) => {
 612                 Some(chalk_ir::WhereClause::LifetimeOutlives(chalk_ir::LifetimeOutlives {
 613                     a: predicate.0.lower_into(interner),
 614                     b: predicate.1.lower_into(interner),
 615                 }))
 616             }
 617             ty::PredicateKind::TypeOutlives(predicate) => {
 618                 Some(chalk_ir::WhereClause::TypeOutlives(chalk_ir::TypeOutlives {
 619                     ty: predicate.0.lower_into(interner),
 620                     lifetime: predicate.1.lower_into(interner),
 621                 }))
 622             }
 623             ty::PredicateKind::Projection(predicate) => {
 624                 Some(chalk_ir::WhereClause::AliasEq(predicate.lower_into(interner)))
 625             }
 626             ty::PredicateKind::WellFormed(_ty) => None,
 627
 628             ty::PredicateKind::ObjectSafe(..)
 629             | ty::PredicateKind::ClosureKind(..)
 630             | ty::PredicateKind::Subtype(..)
 631             | ty::PredicateKind::Coerce(..)
 632             | ty::PredicateKind::ConstEvaluatable(..)
 633             | ty::PredicateKind::ConstEquate(..)
 634             | ty::PredicateKind::TypeWellFormedFromEnv(..) => {
 635                 bug!("unexpected predicate {}", &self)
 636             }
 637         };
 638         value.map(|value| chalk_ir::Binders::new(binders, value))
 639     }
 640 }
 641
 642 impl<'tcx> LowerInto<'tcx, chalk_ir::Binders<chalk_ir::QuantifiedWhereClauses<RustInterner<'tcx>>>>
 643     for &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>
 644 {
 645     fn lower_into(
 646         self,
 647         interner: RustInterner<'tcx>,
 648     ) -> chalk_ir::Binders<chalk_ir::QuantifiedWhereClauses<RustInterner<'tcx>>> {
 649         // `Self` has one binder:
 650         // Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>
 651         // The return type has two:
 652         // Binders<&[Binders<WhereClause<I>>]>
 653         // This means that any variables that are escaping `self` need to be
 654         // shifted in by one so that they are still escaping.
 655         let predicates = ty::fold::shift_vars(interner.tcx, self, 1);
 656
 657         let self_ty = interner.tcx.mk_ty(ty::Bound(
 658             // This is going to be wrapped in a binder
 659             ty::DebruijnIndex::from_usize(1),
 660             ty::BoundTy { var: ty::BoundVar::from_usize(0), kind: ty::BoundTyKind::Anon },
 661         ));
 662         let where_clauses = predicates.into_iter().map(|predicate| {
 663             let (predicate, binders, _named_regions) =
 664                 collect_bound_vars(interner, interner.tcx, predicate);
 665             match predicate {
 666                 ty::ExistentialPredicate::Trait(ty::ExistentialTraitRef { def_id, substs }) => {
 667                     chalk_ir::Binders::new(
 668                         binders.clone(),
 669                         chalk_ir::WhereClause::Implemented(chalk_ir::TraitRef {
 670                             trait_id: chalk_ir::TraitId(def_id),
 671                             substitution: interner
 672                                 .tcx
 673                                 .mk_substs_trait(self_ty, substs)
 674                                 .lower_into(interner),
 675                         }),
 676                     )
 677                 }
 678                 ty::ExistentialPredicate::Projection(predicate) => chalk_ir::Binders::new(
 679                     binders.clone(),
 680                     chalk_ir::WhereClause::AliasEq(chalk_ir::AliasEq {
 681                         alias: chalk_ir::AliasTy::Projection(chalk_ir::ProjectionTy {
 682                             associated_ty_id: chalk_ir::AssocTypeId(predicate.item_def_id),
 683                             substitution: interner
 684                                 .tcx
 685                                 .mk_substs_trait(self_ty, predicate.substs)
 686                                 .lower_into(interner),
 687                         }),
 688                         // FIXME(associated_const_equality): teach chalk about terms for alias eq.
 689                         ty: predicate.term.ty().unwrap().lower_into(interner),
 690                     }),
 691                 ),
 692                 ty::ExistentialPredicate::AutoTrait(def_id) => chalk_ir::Binders::new(
 693                     binders.clone(),
 694                     chalk_ir::WhereClause::Implemented(chalk_ir::TraitRef {
 695                         trait_id: chalk_ir::TraitId(def_id),
 696                         substitution: interner
 697                             .tcx
 698                             .mk_substs_trait(self_ty, &[])
 699                             .lower_into(interner),
 700                     }),
 701                 ),
 702             }
 703         });
 704
 705         // Binder for the bound variable representing the concrete underlying type.
 706         let existential_binder = chalk_ir::VariableKinds::from1(
 707             interner,
 708             chalk_ir::VariableKind::Ty(chalk_ir::TyVariableKind::General),
 709         );
 710         let value = chalk_ir::QuantifiedWhereClauses::from_iter(interner, where_clauses);
 711         chalk_ir::Binders::new(existential_binder, value)
 712     }
 713 }
 714
 715 impl<'tcx> LowerInto<'tcx, chalk_ir::FnSig<RustInterner<'tcx>>>
 716     for ty::Binder<'tcx, ty::FnSig<'tcx>>
 717 {
 718     fn lower_into(self, _interner: RustInterner<'_>) -> FnSig<RustInterner<'tcx>> {
 719         chalk_ir::FnSig {
 720             abi: self.abi(),
 721             safety: match self.unsafety() {
 722                 Unsafety::Normal => chalk_ir::Safety::Safe,
 723                 Unsafety::Unsafe => chalk_ir::Safety::Unsafe,
 724             },
 725             variadic: self.c_variadic(),
 726         }
 727     }
 728 }
 729
 730 // We lower into an Option here since there are some predicates which Chalk
 731 // doesn't have a representation for yet (as an `InlineBound`). The `Option` will
 732 // eventually be removed.
 733 impl<'tcx> LowerInto<'tcx, Option<chalk_solve::rust_ir::QuantifiedInlineBound<RustInterner<'tcx>>>>
 734     for ty::Predicate<'tcx>
 735 {
 736     fn lower_into(
 737         self,
 738         interner: RustInterner<'tcx>,
 739     ) -> Option<chalk_solve::rust_ir::QuantifiedInlineBound<RustInterner<'tcx>>> {
 740         let (predicate, binders, _named_regions) =
 741             collect_bound_vars(interner, interner.tcx, self.kind());
 742         match predicate {
 743             ty::PredicateKind::Trait(predicate) => Some(chalk_ir::Binders::new(
 744                 binders,
 745                 chalk_solve::rust_ir::InlineBound::TraitBound(
 746                     predicate.trait_ref.lower_into(interner),
 747                 ),
 748             )),
 749             ty::PredicateKind::Projection(predicate) => Some(chalk_ir::Binders::new(
 750                 binders,
 751                 chalk_solve::rust_ir::InlineBound::AliasEqBound(predicate.lower_into(interner)),
 752             )),
 753             ty::PredicateKind::TypeOutlives(_predicate) => None,
 754             ty::PredicateKind::WellFormed(_ty) => None,
 755
 756             ty::PredicateKind::RegionOutlives(..)
 757             | ty::PredicateKind::ObjectSafe(..)
 758             | ty::PredicateKind::ClosureKind(..)
 759             | ty::PredicateKind::Subtype(..)
 760             | ty::PredicateKind::Coerce(..)
 761             | ty::PredicateKind::ConstEvaluatable(..)
 762             | ty::PredicateKind::ConstEquate(..)
 763             | ty::PredicateKind::TypeWellFormedFromEnv(..) => {
 764                 bug!("unexpected predicate {}", &self)
 765             }
 766         }
 767     }
 768 }
 769
 770 impl<'tcx> LowerInto<'tcx, chalk_solve::rust_ir::TraitBound<RustInterner<'tcx>>>
 771     for ty::TraitRef<'tcx>
 772 {
 773     fn lower_into(
 774         self,
 775         interner: RustInterner<'tcx>,
 776     ) -> chalk_solve::rust_ir::TraitBound<RustInterner<'tcx>> {
 777         chalk_solve::rust_ir::TraitBound {
 778             trait_id: chalk_ir::TraitId(self.def_id),
 779             args_no_self: self.substs[1..].iter().map(|arg| arg.lower_into(interner)).collect(),
 780         }
 781     }
 782 }
 783
 784 impl<'tcx> LowerInto<'tcx, chalk_ir::Mutability> for ast::Mutability {
 785     fn lower_into(self, _interner: RustInterner<'tcx>) -> chalk_ir::Mutability {
 786         match self {
 787             rustc_ast::Mutability::Mut => chalk_ir::Mutability::Mut,
 788             rustc_ast::Mutability::Not => chalk_ir::Mutability::Not,
 789         }
 790     }
 791 }
 792
 793 impl<'tcx> LowerInto<'tcx, ast::Mutability> for chalk_ir::Mutability {
 794     fn lower_into(self, _interner: RustInterner<'tcx>) -> ast::Mutability {
 795         match self {
 796             chalk_ir::Mutability::Mut => ast::Mutability::Mut,
 797             chalk_ir::Mutability::Not => ast::Mutability::Not,
 798         }
 799     }
 800 }
 801
 802 impl<'tcx> LowerInto<'tcx, chalk_solve::rust_ir::Polarity> for ty::ImplPolarity {
 803     fn lower_into(self, _interner: RustInterner<'tcx>) -> chalk_solve::rust_ir::Polarity {
 804         match self {
 805             ty::ImplPolarity::Positive => chalk_solve::rust_ir::Polarity::Positive,
 806             ty::ImplPolarity::Negative => chalk_solve::rust_ir::Polarity::Negative,
 807             // FIXME(chalk) reservation impls
 808             ty::ImplPolarity::Reservation => chalk_solve::rust_ir::Polarity::Negative,
 809         }
 810     }
 811 }
 812 impl<'tcx> LowerInto<'tcx, chalk_ir::Variance> for ty::Variance {
 813     fn lower_into(self, _interner: RustInterner<'tcx>) -> chalk_ir::Variance {
 814         match self {
 815             ty::Variance::Covariant => chalk_ir::Variance::Covariant,
 816             ty::Variance::Invariant => chalk_ir::Variance::Invariant,
 817             ty::Variance::Contravariant => chalk_ir::Variance::Contravariant,
 818             ty::Variance::Bivariant => unimplemented!(),
 819         }
 820     }
 821 }
 822
 823 impl<'tcx> LowerInto<'tcx, chalk_solve::rust_ir::AliasEqBound<RustInterner<'tcx>>>
 824     for ty::ProjectionPredicate<'tcx>
 825 {
 826     fn lower_into(
 827         self,
 828         interner: RustInterner<'tcx>,
 829     ) -> chalk_solve::rust_ir::AliasEqBound<RustInterner<'tcx>> {
 830         let (trait_ref, own_substs) = self.projection_ty.trait_ref_and_own_substs(interner.tcx);
 831         chalk_solve::rust_ir::AliasEqBound {
 832             trait_bound: trait_ref.lower_into(interner),
 833             associated_ty_id: chalk_ir::AssocTypeId(self.projection_ty.item_def_id),
 834             parameters: own_substs.iter().map(|arg| arg.lower_into(interner)).collect(),
 835             value: self.term.ty().unwrap().lower_into(interner),
 836         }
 837     }
 838 }
 839
 840 /// To collect bound vars, we have to do two passes. In the first pass, we
 841 /// collect all `BoundRegionKind`s and `ty::Bound`s. In the second pass, we then
 842 /// replace `BrNamed` into `BrAnon`. The two separate passes are important,
 843 /// since we can only replace `BrNamed` with `BrAnon`s with indices *after* all
 844 /// "real" `BrAnon`s.
 845 ///
 846 /// It's important to note that because of prior substitution, we may have
 847 /// late-bound regions, even outside of fn contexts, since this is the best way
 848 /// to prep types for chalk lowering.
 849 pub(crate) fn collect_bound_vars<'tcx, T: TypeFoldable<'tcx>>(
 850     interner: RustInterner<'tcx>,
 851     tcx: TyCtxt<'tcx>,
 852     ty: Binder<'tcx, T>,
 853 ) -> (T, chalk_ir::VariableKinds<RustInterner<'tcx>>, BTreeMap<DefId, u32>) {
 854     let mut bound_vars_collector = BoundVarsCollector::new();
 855     ty.as_ref().skip_binder().visit_with(&mut bound_vars_collector);
 856     let mut parameters = bound_vars_collector.parameters;
 857     let named_parameters: BTreeMap<DefId, u32> = bound_vars_collector
 858         .named_parameters
 859         .into_iter()
 860         .enumerate()
 861         .map(|(i, def_id)| (def_id, (i + parameters.len()) as u32))
 862         .collect();
 863
 864     let mut bound_var_substitutor = NamedBoundVarSubstitutor::new(tcx, &named_parameters);
 865     let new_ty = ty.skip_binder().fold_with(&mut bound_var_substitutor);
 866
 867     for var in named_parameters.values() {
 868         parameters.insert(*var, chalk_ir::VariableKind::Lifetime);
 869     }
 870
 871     (0..parameters.len()).for_each(|i| {
 872         parameters
 873             .get(&(i as u32))
 874             .or_else(|| bug!("Skipped bound var index: parameters={:?}", parameters));
 875     });
 876
 877     let binders =
 878         chalk_ir::VariableKinds::from_iter(interner, parameters.into_iter().map(|(_, v)| v));
 879
 880     (new_ty, binders, named_parameters)
 881 }
 882
 883 pub(crate) struct BoundVarsCollector<'tcx> {
 884     binder_index: ty::DebruijnIndex,
 885     pub(crate) parameters: BTreeMap<u32, chalk_ir::VariableKind<RustInterner<'tcx>>>,
 886     pub(crate) named_parameters: Vec<DefId>,
 887 }
 888
 889 impl<'tcx> BoundVarsCollector<'tcx> {
 890     pub(crate) fn new() -> Self {
 891         BoundVarsCollector {
 892             binder_index: ty::INNERMOST,
 893             parameters: BTreeMap::new(),
 894             named_parameters: vec![],
 895         }
 896     }
 897 }
 898
 899 impl<'tcx> TypeVisitor<'tcx> for BoundVarsCollector<'tcx> {
 900     fn visit_binder<T: TypeVisitable<'tcx>>(
 901         &mut self,
 902         t: &Binder<'tcx, T>,
 903     ) -> ControlFlow<Self::BreakTy> {
 904         self.binder_index.shift_in(1);
 905         let result = t.super_visit_with(self);
 906         self.binder_index.shift_out(1);
 907         result
 908     }
 909
 910     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
 911         match *t.kind() {
 912             ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
 913                 match self.parameters.entry(bound_ty.var.as_u32()) {
 914                     Entry::Vacant(entry) => {
 915                         entry.insert(chalk_ir::VariableKind::Ty(chalk_ir::TyVariableKind::General));
 916                     }
 917                     Entry::Occupied(entry) => match entry.get() {
 918                         chalk_ir::VariableKind::Ty(_) => {}
 919                         _ => panic!(),
 920                     },
 921                 }
 922             }
 923
 924             _ => (),
 925         };
 926
 927         t.super_visit_with(self)
 928     }
 929
 930     fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<Self::BreakTy> {
 931         match *r {
 932             ty::ReLateBound(index, br) if index == self.binder_index => match br.kind {
 933                 ty::BoundRegionKind::BrNamed(def_id, _name) => {
 934                     if !self.named_parameters.iter().any(|d| *d == def_id) {
 935                         self.named_parameters.push(def_id);
 936                     }
 937                 }
 938
 939                 ty::BoundRegionKind::BrAnon(var) => match self.parameters.entry(var) {
 940                     Entry::Vacant(entry) => {
 941                         entry.insert(chalk_ir::VariableKind::Lifetime);
 942                     }
 943                     Entry::Occupied(entry) => match entry.get() {
 944                         chalk_ir::VariableKind::Lifetime => {}
 945                         _ => panic!(),
 946                     },
 947                 },
 948
 949                 ty::BoundRegionKind::BrEnv => unimplemented!(),
 950             },
 951
 952             ty::ReEarlyBound(_re) => {
 953                 // FIXME(chalk): jackh726 - I think we should always have already
 954                 // substituted away `ReEarlyBound`s for `ReLateBound`s, but need to confirm.
 955                 unimplemented!();
 956             }
 957
 958             _ => (),
 959         };
 960
 961         r.super_visit_with(self)
 962     }
 963 }
 964
 965 /// This is used to replace `BoundRegionKind::BrNamed` with `BoundRegionKind::BrAnon`.
 966 /// Note: we assume that we will always have room for more bound vars. (i.e. we
 967 /// won't ever hit the `u32` limit in `BrAnon`s).
 968 struct NamedBoundVarSubstitutor<'a, 'tcx> {
 969     tcx: TyCtxt<'tcx>,
 970     binder_index: ty::DebruijnIndex,
 971     named_parameters: &'a BTreeMap<DefId, u32>,
 972 }
 973
 974 impl<'a, 'tcx> NamedBoundVarSubstitutor<'a, 'tcx> {
 975     fn new(tcx: TyCtxt<'tcx>, named_parameters: &'a BTreeMap<DefId, u32>) -> Self {
 976         NamedBoundVarSubstitutor { tcx, binder_index: ty::INNERMOST, named_parameters }
 977     }
 978 }
 979
 980 impl<'a, 'tcx> TypeFolder<'tcx> for NamedBoundVarSubstitutor<'a, 'tcx> {
 981     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
 982         self.tcx
 983     }
 984
 985     fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: Binder<'tcx, T>) -> Binder<'tcx, T> {
 986         self.binder_index.shift_in(1);
 987         let result = t.super_fold_with(self);
 988         self.binder_index.shift_out(1);
 989         result
 990     }
 991
 992     fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
 993         match *r {
 994             ty::ReLateBound(index, br) if index == self.binder_index => match br.kind {
 995                 ty::BrNamed(def_id, _name) => match self.named_parameters.get(&def_id) {
 996                     Some(idx) => {
 997                         let new_br = ty::BoundRegion { var: br.var, kind: ty::BrAnon(*idx) };
 998                         return self.tcx.mk_region(ty::ReLateBound(index, new_br));
 999                     }
1000                     None => panic!("Missing `BrNamed`."),
1001                 },
1002                 ty::BrEnv => unimplemented!(),
1003                 ty::BrAnon(_) => {}
1004             },
1005             _ => (),
1006         };
1007
1008         r.super_fold_with(self)
1009     }
1010 }
1011
1012 /// Used to substitute `Param`s with placeholders. We do this since Chalk
1013 /// have a notion of `Param`s.
1014 pub(crate) struct ParamsSubstitutor<'tcx> {
1015     tcx: TyCtxt<'tcx>,
1016     binder_index: ty::DebruijnIndex,
1017     list: Vec<rustc_middle::ty::ParamTy>,
1018     next_ty_placeholder: usize,
1019     pub(crate) params: rustc_data_structures::fx::FxHashMap<usize, rustc_middle::ty::ParamTy>,
1020     pub(crate) named_regions: BTreeMap<DefId, u32>,
1021 }
1022
1023 impl<'tcx> ParamsSubstitutor<'tcx> {
1024     pub(crate) fn new(tcx: TyCtxt<'tcx>, next_ty_placeholder: usize) -> Self {
1025         ParamsSubstitutor {
1026             tcx,
1027             binder_index: ty::INNERMOST,
1028             list: vec![],
1029             next_ty_placeholder,
1030             params: rustc_data_structures::fx::FxHashMap::default(),
1031             named_regions: BTreeMap::default(),
1032         }
1033     }
1034 }
1035
1036 impl<'tcx> TypeFolder<'tcx> for ParamsSubstitutor<'tcx> {
1037     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1038         self.tcx
1039     }
1040
1041     fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: Binder<'tcx, T>) -> Binder<'tcx, T> {
1042         self.binder_index.shift_in(1);
1043         let result = t.super_fold_with(self);
1044         self.binder_index.shift_out(1);
1045         result
1046     }
1047
1048     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
1049         match *t.kind() {
1050             ty::Param(param) => match self.list.iter().position(|r| r == &param) {
1051                 Some(idx) => self.tcx.mk_ty(ty::Placeholder(ty::PlaceholderType {
1052                     universe: ty::UniverseIndex::from_usize(0),
1053                     name: ty::BoundVar::from_usize(idx),
1054                 })),
1055                 None => {
1056                     self.list.push(param);
1057                     let idx = self.list.len() - 1 + self.next_ty_placeholder;
1058                     self.params.insert(idx, param);
1059                     self.tcx.mk_ty(ty::Placeholder(ty::PlaceholderType {
1060                         universe: ty::UniverseIndex::from_usize(0),
1061                         name: ty::BoundVar::from_usize(idx),
1062                     }))
1063                 }
1064             },
1065             _ => t.super_fold_with(self),
1066         }
1067     }
1068
1069     fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
1070         match *r {
1071             // FIXME(chalk) - jackh726 - this currently isn't hit in any tests,
1072             // since canonicalization will already change these to canonical
1073             // variables (ty::ReLateBound).
1074             ty::ReEarlyBound(_re) => match self.named_regions.get(&_re.def_id) {
1075                 Some(idx) => {
1076                     let br = ty::BoundRegion {
1077                         var: ty::BoundVar::from_u32(*idx),
1078                         kind: ty::BrAnon(*idx),
1079                     };
1080                     self.tcx.mk_region(ty::ReLateBound(self.binder_index, br))
1081                 }
1082                 None => {
1083                     let idx = self.named_regions.len() as u32;
1084                     let br =
1085                         ty::BoundRegion { var: ty::BoundVar::from_u32(idx), kind: ty::BrAnon(idx) };
1086                     self.named_regions.insert(_re.def_id, idx);
1087                     self.tcx.mk_region(ty::ReLateBound(self.binder_index, br))
1088                 }
1089             },
1090
1091             _ => r.super_fold_with(self),
1092         }
1093     }
1094 }
1095
1096 pub(crate) struct ReverseParamsSubstitutor<'tcx> {
1097     tcx: TyCtxt<'tcx>,
1098     params: rustc_data_structures::fx::FxHashMap<usize, rustc_middle::ty::ParamTy>,
1099 }
1100
1101 impl<'tcx> ReverseParamsSubstitutor<'tcx> {
1102     pub(crate) fn new(
1103         tcx: TyCtxt<'tcx>,
1104         params: rustc_data_structures::fx::FxHashMap<usize, rustc_middle::ty::ParamTy>,
1105     ) -> Self {
1106         Self { tcx, params }
1107     }
1108 }
1109
1110 impl<'tcx> TypeFolder<'tcx> for ReverseParamsSubstitutor<'tcx> {
1111     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1112         self.tcx
1113     }
1114
1115     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
1116         match *t.kind() {
1117             ty::Placeholder(ty::PlaceholderType { universe: ty::UniverseIndex::ROOT, name }) => {
1118                 match self.params.get(&name.as_usize()) {
1119                     Some(param) => self.tcx.mk_ty(ty::Param(*param)),
1120                     None => t,
1121                 }
1122             }
1123
1124             _ => t.super_fold_with(self),
1125         }
1126     }
1127 }
1128
1129 /// Used to collect `Placeholder`s.
1130 pub(crate) struct PlaceholdersCollector {
1131     universe_index: ty::UniverseIndex,
1132     pub(crate) next_ty_placeholder: usize,
1133     pub(crate) next_anon_region_placeholder: u32,
1134 }
1135
1136 impl PlaceholdersCollector {
1137     pub(crate) fn new() -> Self {
1138         PlaceholdersCollector {
1139             universe_index: ty::UniverseIndex::ROOT,
1140             next_ty_placeholder: 0,
1141             next_anon_region_placeholder: 0,
1142         }
1143     }
1144 }
1145
1146 impl<'tcx> TypeVisitor<'tcx> for PlaceholdersCollector {
1147     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1148         match t.kind() {
1149             ty::Placeholder(p) if p.universe == self.universe_index => {
1150                 self.next_ty_placeholder = self.next_ty_placeholder.max(p.name.as_usize() + 1);
1151             }
1152
1153             _ => (),
1154         };
1155
1156         t.super_visit_with(self)
1157     }
1158
1159     fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<Self::BreakTy> {
1160         match *r {
1161             ty::RePlaceholder(p) if p.universe == self.universe_index => {
1162                 if let ty::BoundRegionKind::BrAnon(anon) = p.name {
1163                     self.next_anon_region_placeholder = self.next_anon_region_placeholder.max(anon);
1164                 }
1165             }
1166
1167             _ => (),
1168         };
1169
1170         r.super_visit_with(self)
1171     }
1172 }