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