src/librustc_traits/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_middle::traits::{
  35     ChalkEnvironmentAndGoal, ChalkEnvironmentClause, ChalkRustInterner as RustInterner,
  36 };
  37 use rustc_middle::ty::fold::TypeFolder;
  38 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, SubstsRef};
  39 use rustc_middle::ty::{
  40     self, Binder, BoundRegion, Region, RegionKind, Ty, TyCtxt, TyKind, TypeFoldable, TypeVisitor,
  41 };
  42 use rustc_span::def_id::DefId;
  43
  44 use std::collections::btree_map::{BTreeMap, Entry};
  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(interner, self.iter().map(|s| s.lower_into(interner)))
  58     }
  59 }
  60
  61 impl<'tcx> LowerInto<'tcx, chalk_ir::AliasTy<RustInterner<'tcx>>> for ty::ProjectionTy<'tcx> {
  62     fn lower_into(self, interner: &RustInterner<'tcx>) -> chalk_ir::AliasTy<RustInterner<'tcx>> {
  63         chalk_ir::AliasTy::Projection(chalk_ir::ProjectionTy {
  64             associated_ty_id: chalk_ir::AssocTypeId(self.item_def_id),
  65             substitution: self.substs.lower_into(interner),
  66         })
  67     }
  68 }
  69
  70 impl<'tcx> LowerInto<'tcx, chalk_ir::InEnvironment<chalk_ir::Goal<RustInterner<'tcx>>>>
  71     for ChalkEnvironmentAndGoal<'tcx>
  72 {
  73     fn lower_into(
  74         self,
  75         interner: &RustInterner<'tcx>,
  76     ) -> chalk_ir::InEnvironment<chalk_ir::Goal<RustInterner<'tcx>>> {
  77         let clauses = self.environment.into_iter().filter_map(|clause| match clause {
  78             ChalkEnvironmentClause::Predicate(predicate) => {
  79                 match predicate.kind() {
  80                     ty::PredicateKind::Trait(predicate, _) => {
  81                         let (predicate, binders, _named_regions) =
  82                             collect_bound_vars(interner, interner.tcx, predicate);
  83
  84                         Some(
  85                             chalk_ir::ProgramClauseData::ForAll(chalk_ir::Binders::new(
  86                                 binders,
  87                                 chalk_ir::ProgramClauseImplication {
  88                                     consequence: chalk_ir::DomainGoal::FromEnv(
  89                                         chalk_ir::FromEnv::Trait(
  90                                             predicate.trait_ref.lower_into(interner),
  91                                         ),
  92                                     ),
  93                                     conditions: chalk_ir::Goals::new(interner),
  94                                     priority: chalk_ir::ClausePriority::High,
  95                                 },
  96                             ))
  97                             .intern(interner),
  98                         )
  99                     }
 100                     ty::PredicateKind::RegionOutlives(predicate) => {
 101                         let (predicate, binders, _named_regions) =
 102                             collect_bound_vars(interner, interner.tcx, predicate);
 103
 104                         Some(
 105                             chalk_ir::ProgramClauseData::ForAll(chalk_ir::Binders::new(
 106                                 binders,
 107                                 chalk_ir::ProgramClauseImplication {
 108                                     consequence: chalk_ir::DomainGoal::Holds(
 109                                         chalk_ir::WhereClause::LifetimeOutlives(chalk_ir::LifetimeOutlives {
 110                                             a: predicate.0.lower_into(interner),
 111                                             b: predicate.1.lower_into(interner),
 112                                         })
 113                                     ),
 114                                     conditions: chalk_ir::Goals::new(interner),
 115                                     priority: chalk_ir::ClausePriority::High,
 116                                 },
 117                             ))
 118                             .intern(interner),
 119                         )
 120                     },
 121                     // FIXME(chalk): need to add TypeOutlives
 122                     ty::PredicateKind::TypeOutlives(_) => None,
 123                     ty::PredicateKind::Projection(predicate) => {
 124                         let (predicate, binders, _named_regions) =
 125                             collect_bound_vars(interner, interner.tcx, predicate);
 126
 127                         Some(
 128                             chalk_ir::ProgramClauseData::ForAll(chalk_ir::Binders::new(
 129                                 binders,
 130                                 chalk_ir::ProgramClauseImplication {
 131                                     consequence: chalk_ir::DomainGoal::Holds(
 132                                         chalk_ir::WhereClause::AliasEq(
 133                                             predicate.lower_into(interner),
 134                                         ),
 135                                     ),
 136                                     conditions: chalk_ir::Goals::new(interner),
 137                                     priority: chalk_ir::ClausePriority::High,
 138                                 },
 139                             ))
 140                             .intern(interner),
 141                         )
 142                     }
 143                     ty::PredicateKind::WellFormed(..)
 144                     | ty::PredicateKind::ObjectSafe(..)
 145                     | ty::PredicateKind::ClosureKind(..)
 146                     | ty::PredicateKind::Subtype(..)
 147                     | ty::PredicateKind::ConstEvaluatable(..)
 148                     | ty::PredicateKind::ConstEquate(..) => {
 149                         bug!("unexpected predicate {}", predicate)
 150                     }
 151                 }
 152             }
 153             ChalkEnvironmentClause::TypeFromEnv(ty) => Some(
 154                 chalk_ir::ProgramClauseData::Implies(chalk_ir::ProgramClauseImplication {
 155                     consequence: chalk_ir::DomainGoal::FromEnv(chalk_ir::FromEnv::Ty(
 156                         ty.lower_into(interner),
 157                     )),
 158                     conditions: chalk_ir::Goals::new(interner),
 159                     priority: chalk_ir::ClausePriority::High,
 160                 })
 161                 .intern(interner),
 162             ),
 163         });
 164
 165         let goal: chalk_ir::GoalData<RustInterner<'tcx>> = self.goal.lower_into(&interner);
 166         chalk_ir::InEnvironment {
 167             environment: chalk_ir::Environment {
 168                 clauses: chalk_ir::ProgramClauses::from(&interner, clauses),
 169             },
 170             goal: goal.intern(&interner),
 171         }
 172     }
 173 }
 174
 175 impl<'tcx> LowerInto<'tcx, chalk_ir::GoalData<RustInterner<'tcx>>> for ty::Predicate<'tcx> {
 176     fn lower_into(self, interner: &RustInterner<'tcx>) -> chalk_ir::GoalData<RustInterner<'tcx>> {
 177         match self.kind() {
 178             ty::PredicateKind::Trait(predicate, _) => predicate.lower_into(interner),
 179             ty::PredicateKind::RegionOutlives(predicate) => {
 180                 let (predicate, binders, _named_regions) =
 181                     collect_bound_vars(interner, interner.tcx, predicate);
 182
 183                 chalk_ir::GoalData::Quantified(
 184                     chalk_ir::QuantifierKind::ForAll,
 185                     chalk_ir::Binders::new(
 186                         binders,
 187                         chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
 188                             chalk_ir::WhereClause::LifetimeOutlives(chalk_ir::LifetimeOutlives {
 189                                 a: predicate.0.lower_into(interner),
 190                                 b: predicate.1.lower_into(interner),
 191                             })
 192                         )).intern(interner)
 193                     )
 194                 )
 195             }
 196             // FIXME(chalk): TypeOutlives
 197             ty::PredicateKind::TypeOutlives(_predicate) => {
 198                 chalk_ir::GoalData::All(chalk_ir::Goals::new(interner))
 199             }
 200             ty::PredicateKind::Projection(predicate) => predicate.lower_into(interner),
 201             ty::PredicateKind::WellFormed(arg) => match arg.unpack() {
 202                 GenericArgKind::Type(ty) => match ty.kind {
 203                     // FIXME(chalk): In Chalk, a placeholder is WellFormed if it
 204                     // `FromEnv`. However, when we "lower" Params, we don't update
 205                     // the environment.
 206                     ty::Placeholder(..) => chalk_ir::GoalData::All(chalk_ir::Goals::new(interner)),
 207
 208                     _ => chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::WellFormed(
 209                         chalk_ir::WellFormed::Ty(ty.lower_into(interner)),
 210                     )),
 211                 },
 212                 // FIXME(chalk): handle well formed consts
 213                 GenericArgKind::Const(..) => {
 214                     chalk_ir::GoalData::All(chalk_ir::Goals::new(interner))
 215                 }
 216                 GenericArgKind::Lifetime(lt) => bug!("unexpect well formed predicate: {:?}", lt),
 217             },
 218
 219             ty::PredicateKind::ObjectSafe(t) => {
 220                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::ObjectSafe(chalk_ir::TraitId(*t)))
 221             }
 222
 223             // FIXME(chalk): other predicates
 224             //
 225             // We can defer this, but ultimately we'll want to express
 226             // some of these in terms of chalk operations.
 227             ty::PredicateKind::ClosureKind(..)
 228             | ty::PredicateKind::Subtype(..)
 229             | ty::PredicateKind::ConstEvaluatable(..)
 230             | ty::PredicateKind::ConstEquate(..) => {
 231                 chalk_ir::GoalData::All(chalk_ir::Goals::new(interner))
 232             }
 233         }
 234     }
 235 }
 236
 237 impl<'tcx> LowerInto<'tcx, chalk_ir::TraitRef<RustInterner<'tcx>>>
 238     for rustc_middle::ty::TraitRef<'tcx>
 239 {
 240     fn lower_into(self, interner: &RustInterner<'tcx>) -> chalk_ir::TraitRef<RustInterner<'tcx>> {
 241         chalk_ir::TraitRef {
 242             trait_id: chalk_ir::TraitId(self.def_id),
 243             substitution: self.substs.lower_into(interner),
 244         }
 245     }
 246 }
 247
 248 impl<'tcx> LowerInto<'tcx, chalk_ir::GoalData<RustInterner<'tcx>>>
 249     for ty::PolyTraitPredicate<'tcx>
 250 {
 251     fn lower_into(self, interner: &RustInterner<'tcx>) -> chalk_ir::GoalData<RustInterner<'tcx>> {
 252         let (ty, binders, _named_regions) = collect_bound_vars(interner, interner.tcx, &self);
 253
 254         chalk_ir::GoalData::Quantified(
 255             chalk_ir::QuantifierKind::ForAll,
 256             chalk_ir::Binders::new(
 257                 binders,
 258                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
 259                     chalk_ir::WhereClause::Implemented(ty.trait_ref.lower_into(interner)),
 260                 ))
 261                 .intern(interner),
 262             ),
 263         )
 264     }
 265 }
 266
 267 impl<'tcx> LowerInto<'tcx, chalk_ir::AliasEq<RustInterner<'tcx>>>
 268     for rustc_middle::ty::ProjectionPredicate<'tcx>
 269 {
 270     fn lower_into(self, interner: &RustInterner<'tcx>) -> chalk_ir::AliasEq<RustInterner<'tcx>> {
 271         chalk_ir::AliasEq {
 272             ty: self.ty.lower_into(interner),
 273             alias: self.projection_ty.lower_into(interner),
 274         }
 275     }
 276 }
 277
 278 impl<'tcx> LowerInto<'tcx, chalk_ir::GoalData<RustInterner<'tcx>>>
 279     for ty::PolyProjectionPredicate<'tcx>
 280 {
 281     fn lower_into(self, interner: &RustInterner<'tcx>) -> chalk_ir::GoalData<RustInterner<'tcx>> {
 282         let (ty, binders, _named_regions) = collect_bound_vars(interner, interner.tcx, &self);
 283
 284         chalk_ir::GoalData::Quantified(
 285             chalk_ir::QuantifierKind::ForAll,
 286             chalk_ir::Binders::new(
 287                 binders,
 288                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
 289                     chalk_ir::WhereClause::AliasEq(ty.lower_into(interner)),
 290                 ))
 291                 .intern(interner),
 292             ),
 293         )
 294     }
 295 }
 296
 297 impl<'tcx> LowerInto<'tcx, chalk_ir::Ty<RustInterner<'tcx>>> for Ty<'tcx> {
 298     fn lower_into(self, interner: &RustInterner<'tcx>) -> chalk_ir::Ty<RustInterner<'tcx>> {
 299         use chalk_ir::TyData;
 300         use rustc_ast::ast;
 301         use TyKind::*;
 302
 303         let empty = || chalk_ir::Substitution::empty(interner);
 304         let struct_ty = |def_id| chalk_ir::TypeName::Adt(chalk_ir::AdtId(def_id));
 305         let apply = |name, substitution| {
 306             TyData::Apply(chalk_ir::ApplicationTy { name, substitution }).intern(interner)
 307         };
 308         let int = |i| apply(chalk_ir::TypeName::Scalar(chalk_ir::Scalar::Int(i)), empty());
 309         let uint = |i| apply(chalk_ir::TypeName::Scalar(chalk_ir::Scalar::Uint(i)), empty());
 310         let float = |f| apply(chalk_ir::TypeName::Scalar(chalk_ir::Scalar::Float(f)), empty());
 311
 312         match self.kind {
 313             Bool => apply(chalk_ir::TypeName::Scalar(chalk_ir::Scalar::Bool), empty()),
 314             Char => apply(chalk_ir::TypeName::Scalar(chalk_ir::Scalar::Char), empty()),
 315             Int(ty) => match ty {
 316                 ast::IntTy::Isize => int(chalk_ir::IntTy::Isize),
 317                 ast::IntTy::I8 => int(chalk_ir::IntTy::I8),
 318                 ast::IntTy::I16 => int(chalk_ir::IntTy::I16),
 319                 ast::IntTy::I32 => int(chalk_ir::IntTy::I32),
 320                 ast::IntTy::I64 => int(chalk_ir::IntTy::I64),
 321                 ast::IntTy::I128 => int(chalk_ir::IntTy::I128),
 322             },
 323             Uint(ty) => match ty {
 324                 ast::UintTy::Usize => uint(chalk_ir::UintTy::Usize),
 325                 ast::UintTy::U8 => uint(chalk_ir::UintTy::U8),
 326                 ast::UintTy::U16 => uint(chalk_ir::UintTy::U16),
 327                 ast::UintTy::U32 => uint(chalk_ir::UintTy::U32),
 328                 ast::UintTy::U64 => uint(chalk_ir::UintTy::U64),
 329                 ast::UintTy::U128 => uint(chalk_ir::UintTy::U128),
 330             },
 331             Float(ty) => match ty {
 332                 ast::FloatTy::F32 => float(chalk_ir::FloatTy::F32),
 333                 ast::FloatTy::F64 => float(chalk_ir::FloatTy::F64),
 334             },
 335             Adt(def, substs) => apply(struct_ty(def.did), substs.lower_into(interner)),
 336             Foreign(_def_id) => unimplemented!(),
 337             Str => apply(chalk_ir::TypeName::Str, empty()),
 338             Array(ty, _) => apply(
 339                 chalk_ir::TypeName::Array,
 340                 chalk_ir::Substitution::from(
 341                     interner,
 342                     &[
 343                         chalk_ir::GenericArgData::Ty(ty.lower_into(interner)).intern(interner),
 344                         chalk_ir::GenericArgData::Const(
 345                             chalk_ir::ConstData {
 346                                 ty: apply(chalk_ir::TypeName::Tuple(0), empty()),
 347                                 value: chalk_ir::ConstValue::Concrete(chalk_ir::ConcreteConst {
 348                                     interned: 0,
 349                                 }),
 350                             }
 351                             .intern(interner),
 352                         )
 353                         .intern(interner),
 354                     ],
 355                 ),
 356             ),
 357             Slice(ty) => apply(
 358                 chalk_ir::TypeName::Slice,
 359                 chalk_ir::Substitution::from1(
 360                     interner,
 361                     chalk_ir::GenericArgData::Ty(ty.lower_into(interner)).intern(interner),
 362                 ),
 363             ),
 364             RawPtr(ptr) => {
 365                 let name = match ptr.mutbl {
 366                     ast::Mutability::Mut => chalk_ir::TypeName::Raw(chalk_ir::Mutability::Mut),
 367                     ast::Mutability::Not => chalk_ir::TypeName::Raw(chalk_ir::Mutability::Not),
 368                 };
 369                 apply(name, chalk_ir::Substitution::from1(interner, ptr.ty.lower_into(interner)))
 370             }
 371             Ref(region, ty, mutability) => {
 372                 let name = match mutability {
 373                     ast::Mutability::Mut => chalk_ir::TypeName::Ref(chalk_ir::Mutability::Mut),
 374                     ast::Mutability::Not => chalk_ir::TypeName::Ref(chalk_ir::Mutability::Not),
 375                 };
 376                 apply(
 377                     name,
 378                     chalk_ir::Substitution::from(
 379                         interner,
 380                         &[
 381                             chalk_ir::GenericArgData::Lifetime(region.lower_into(interner))
 382                                 .intern(interner),
 383                             chalk_ir::GenericArgData::Ty(ty.lower_into(interner)).intern(interner),
 384                         ],
 385                     ),
 386                 )
 387             }
 388             FnDef(def_id, substs) => apply(
 389                 chalk_ir::TypeName::FnDef(chalk_ir::FnDefId(def_id)),
 390                 substs.lower_into(interner),
 391             ),
 392             FnPtr(sig) => {
 393                 let (inputs_and_outputs, binders, _named_regions) =
 394                     collect_bound_vars(interner, interner.tcx, &sig.inputs_and_output());
 395                 TyData::Function(chalk_ir::Fn {
 396                     num_binders: binders.len(interner),
 397                     substitution: chalk_ir::Substitution::from(
 398                         interner,
 399                         inputs_and_outputs.iter().map(|ty| {
 400                             chalk_ir::GenericArgData::Ty(ty.lower_into(interner)).intern(interner)
 401                         }),
 402                     ),
 403                 })
 404                 .intern(interner)
 405             }
 406             // FIXME(chalk): add region
 407             Dynamic(predicates, _region) => {
 408                 TyData::Dyn(chalk_ir::DynTy { bounds: predicates.lower_into(interner) })
 409                     .intern(interner)
 410             }
 411             Closure(_def_id, _) => unimplemented!(),
 412             Generator(_def_id, _substs, _) => unimplemented!(),
 413             GeneratorWitness(_) => unimplemented!(),
 414             Never => apply(chalk_ir::TypeName::Never, empty()),
 415             Tuple(substs) => {
 416                 apply(chalk_ir::TypeName::Tuple(substs.len()), substs.lower_into(interner))
 417             }
 418             Projection(proj) => TyData::Alias(proj.lower_into(interner)).intern(interner),
 419             Opaque(def_id, substs) => {
 420                 TyData::Alias(chalk_ir::AliasTy::Opaque(chalk_ir::OpaqueTy {
 421                     opaque_ty_id: chalk_ir::OpaqueTyId(def_id),
 422                     substitution: substs.lower_into(interner),
 423                 }))
 424                 .intern(interner)
 425             }
 426             // This should have been done eagerly prior to this, and all Params
 427             // should have been substituted to placeholders
 428             Param(_) => panic!("Lowering Param when not expected."),
 429             Bound(db, bound) => TyData::BoundVar(chalk_ir::BoundVar::new(
 430                 chalk_ir::DebruijnIndex::new(db.as_u32()),
 431                 bound.var.index(),
 432             ))
 433             .intern(interner),
 434             Placeholder(_placeholder) => TyData::Placeholder(chalk_ir::PlaceholderIndex {
 435                 ui: chalk_ir::UniverseIndex { counter: _placeholder.universe.as_usize() },
 436                 idx: _placeholder.name.as_usize(),
 437             })
 438             .intern(interner),
 439             Infer(_infer) => unimplemented!(),
 440             Error(_) => apply(chalk_ir::TypeName::Error, empty()),
 441         }
 442     }
 443 }
 444
 445 impl<'tcx> LowerInto<'tcx, chalk_ir::Lifetime<RustInterner<'tcx>>> for Region<'tcx> {
 446     fn lower_into(self, interner: &RustInterner<'tcx>) -> chalk_ir::Lifetime<RustInterner<'tcx>> {
 447         use rustc_middle::ty::RegionKind::*;
 448
 449         match self {
 450             ReEarlyBound(_) => {
 451                 panic!("Should have already been substituted.");
 452             }
 453             ReLateBound(db, br) => match br {
 454                 ty::BoundRegion::BrAnon(var) => {
 455                     chalk_ir::LifetimeData::BoundVar(chalk_ir::BoundVar::new(
 456                         chalk_ir::DebruijnIndex::new(db.as_u32()),
 457                         *var as usize,
 458                     ))
 459                     .intern(interner)
 460                 }
 461                 ty::BoundRegion::BrNamed(_def_id, _name) => unimplemented!(),
 462                 ty::BrEnv => unimplemented!(),
 463             },
 464             ReFree(_) => unimplemented!(),
 465             // FIXME(chalk): need to handle ReStatic
 466             ReStatic => unimplemented!(),
 467             ReVar(_) => unimplemented!(),
 468             RePlaceholder(placeholder_region) => {
 469                 chalk_ir::LifetimeData::Placeholder(chalk_ir::PlaceholderIndex {
 470                     ui: chalk_ir::UniverseIndex { counter: placeholder_region.universe.index() },
 471                     idx: 0,
 472                 })
 473                 .intern(interner)
 474             }
 475             ReEmpty(_) => unimplemented!(),
 476             // FIXME(chalk): need to handle ReErased
 477             ReErased => unimplemented!(),
 478         }
 479     }
 480 }
 481
 482 impl<'tcx> LowerInto<'tcx, chalk_ir::GenericArg<RustInterner<'tcx>>> for GenericArg<'tcx> {
 483     fn lower_into(self, interner: &RustInterner<'tcx>) -> chalk_ir::GenericArg<RustInterner<'tcx>> {
 484         match self.unpack() {
 485             ty::subst::GenericArgKind::Type(ty) => {
 486                 chalk_ir::GenericArgData::Ty(ty.lower_into(interner))
 487             }
 488             ty::subst::GenericArgKind::Lifetime(lifetime) => {
 489                 chalk_ir::GenericArgData::Lifetime(lifetime.lower_into(interner))
 490             }
 491             ty::subst::GenericArgKind::Const(_) => chalk_ir::GenericArgData::Ty(
 492                 chalk_ir::TyData::Apply(chalk_ir::ApplicationTy {
 493                     name: chalk_ir::TypeName::Tuple(0),
 494                     substitution: chalk_ir::Substitution::empty(interner),
 495                 })
 496                 .intern(interner),
 497             ),
 498         }
 499         .intern(interner)
 500     }
 501 }
 502
 503 // We lower into an Option here since there are some predicates which Chalk
 504 // doesn't have a representation for yet (as a `WhereClause`), but are so common
 505 // that we just are accepting the unsoundness for now. The `Option` will
 506 // eventually be removed.
 507 impl<'tcx> LowerInto<'tcx, Option<chalk_ir::QuantifiedWhereClause<RustInterner<'tcx>>>>
 508     for ty::Predicate<'tcx>
 509 {
 510     fn lower_into(
 511         self,
 512         interner: &RustInterner<'tcx>,
 513     ) -> Option<chalk_ir::QuantifiedWhereClause<RustInterner<'tcx>>> {
 514         match &self.kind() {
 515             ty::PredicateKind::Trait(predicate, _) => {
 516                 let (predicate, binders, _named_regions) =
 517                     collect_bound_vars(interner, interner.tcx, predicate);
 518
 519                 Some(chalk_ir::Binders::new(
 520                     binders,
 521                     chalk_ir::WhereClause::Implemented(predicate.trait_ref.lower_into(interner)),
 522                 ))
 523             }
 524             ty::PredicateKind::RegionOutlives(predicate) => {
 525                 let (predicate, binders, _named_regions) =
 526                     collect_bound_vars(interner, interner.tcx, predicate);
 527
 528                 Some(chalk_ir::Binders::new(
 529                     binders,
 530                     chalk_ir::WhereClause::LifetimeOutlives(chalk_ir::LifetimeOutlives {
 531                         a: predicate.0.lower_into(interner),
 532                         b: predicate.1.lower_into(interner),
 533                     }),
 534                 ))
 535
 536             },
 537             ty::PredicateKind::TypeOutlives(_predicate) => None,
 538             ty::PredicateKind::Projection(_predicate) => None,
 539             ty::PredicateKind::WellFormed(_ty) => None,
 540
 541             ty::PredicateKind::ObjectSafe(..)
 542             | ty::PredicateKind::ClosureKind(..)
 543             | ty::PredicateKind::Subtype(..)
 544             | ty::PredicateKind::ConstEvaluatable(..)
 545             | ty::PredicateKind::ConstEquate(..) => bug!("unexpected predicate {}", &self),
 546         }
 547     }
 548 }
 549
 550 impl<'tcx> LowerInto<'tcx, chalk_ir::Binders<chalk_ir::QuantifiedWhereClauses<RustInterner<'tcx>>>>
 551     for Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>
 552 {
 553     fn lower_into(
 554         self,
 555         interner: &RustInterner<'tcx>,
 556     ) -> chalk_ir::Binders<chalk_ir::QuantifiedWhereClauses<RustInterner<'tcx>>> {
 557         let (predicates, binders, _named_regions) =
 558             collect_bound_vars(interner, interner.tcx, &self);
 559         let where_clauses = predicates.into_iter().map(|predicate| match predicate {
 560             ty::ExistentialPredicate::Trait(ty::ExistentialTraitRef { def_id, substs }) => {
 561                 chalk_ir::Binders::new(
 562                     chalk_ir::VariableKinds::new(interner),
 563                     chalk_ir::WhereClause::Implemented(chalk_ir::TraitRef {
 564                         trait_id: chalk_ir::TraitId(*def_id),
 565                         substitution: substs.lower_into(interner),
 566                     }),
 567                 )
 568             }
 569             ty::ExistentialPredicate::Projection(_predicate) => unimplemented!(),
 570             ty::ExistentialPredicate::AutoTrait(def_id) => chalk_ir::Binders::new(
 571                 chalk_ir::VariableKinds::new(interner),
 572                 chalk_ir::WhereClause::Implemented(chalk_ir::TraitRef {
 573                     trait_id: chalk_ir::TraitId(*def_id),
 574                     substitution: chalk_ir::Substitution::empty(interner),
 575                 }),
 576             ),
 577         });
 578         let value = chalk_ir::QuantifiedWhereClauses::from(interner, where_clauses);
 579         chalk_ir::Binders::new(binders, value)
 580     }
 581 }
 582
 583 /// To collect bound vars, we have to do two passes. In the first pass, we
 584 /// collect all `BoundRegion`s and `ty::Bound`s. In the second pass, we then
 585 /// replace `BrNamed` into `BrAnon`. The two separate passes are important,
 586 /// since we can only replace `BrNamed` with `BrAnon`s with indices *after* all
 587 /// "real" `BrAnon`s.
 588 ///
 589 /// It's important to note that because of prior substitution, we may have
 590 /// late-bound regions, even outside of fn contexts, since this is the best way
 591 /// to prep types for chalk lowering.
 592 crate fn collect_bound_vars<'a, 'tcx, T: TypeFoldable<'tcx>>(
 593     interner: &RustInterner<'tcx>,
 594     tcx: TyCtxt<'tcx>,
 595     ty: &'a Binder<T>,
 596 ) -> (T, chalk_ir::VariableKinds<RustInterner<'tcx>>, BTreeMap<DefId, u32>) {
 597     let mut bound_vars_collector = BoundVarsCollector::new();
 598     ty.skip_binder().visit_with(&mut bound_vars_collector);
 599     let mut parameters = bound_vars_collector.parameters;
 600     let named_parameters: BTreeMap<DefId, u32> = bound_vars_collector
 601         .named_parameters
 602         .into_iter()
 603         .enumerate()
 604         .map(|(i, def_id)| (def_id, (i + parameters.len()) as u32))
 605         .collect();
 606
 607     let mut bound_var_substitutor = NamedBoundVarSubstitutor::new(tcx, &named_parameters);
 608     let new_ty = ty.skip_binder().fold_with(&mut bound_var_substitutor);
 609
 610     for var in named_parameters.values() {
 611         parameters.insert(*var, chalk_ir::VariableKind::Lifetime);
 612     }
 613
 614     (0..parameters.len()).for_each(|i| {
 615         parameters.get(&(i as u32)).expect("Skipped bound var index.");
 616     });
 617
 618     let binders = chalk_ir::VariableKinds::from(interner, parameters.into_iter().map(|(_, v)| v));
 619
 620     (new_ty, binders, named_parameters)
 621 }
 622
 623 crate struct BoundVarsCollector<'tcx> {
 624     binder_index: ty::DebruijnIndex,
 625     crate parameters: BTreeMap<u32, chalk_ir::VariableKind<RustInterner<'tcx>>>,
 626     crate named_parameters: Vec<DefId>,
 627 }
 628
 629 impl<'tcx> BoundVarsCollector<'tcx> {
 630     crate fn new() -> Self {
 631         BoundVarsCollector {
 632             binder_index: ty::INNERMOST,
 633             parameters: BTreeMap::new(),
 634             named_parameters: vec![],
 635         }
 636     }
 637 }
 638
 639 impl<'tcx> TypeVisitor<'tcx> for BoundVarsCollector<'tcx> {
 640     fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
 641         self.binder_index.shift_in(1);
 642         let result = t.super_visit_with(self);
 643         self.binder_index.shift_out(1);
 644         result
 645     }
 646
 647     fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
 648         match t.kind {
 649             ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
 650                 match self.parameters.entry(bound_ty.var.as_u32()) {
 651                     Entry::Vacant(entry) => {
 652                         entry.insert(chalk_ir::VariableKind::Ty(chalk_ir::TyKind::General));
 653                     }
 654                     Entry::Occupied(entry) => match entry.get() {
 655                         chalk_ir::VariableKind::Ty(_) => {}
 656                         _ => panic!(),
 657                     },
 658                 }
 659             }
 660
 661             _ => (),
 662         };
 663
 664         t.super_visit_with(self)
 665     }
 666
 667     fn visit_region(&mut self, r: Region<'tcx>) -> bool {
 668         match r {
 669             ty::ReLateBound(index, br) if *index == self.binder_index => match br {
 670                 ty::BoundRegion::BrNamed(def_id, _name) => {
 671                     if self.named_parameters.iter().find(|d| *d == def_id).is_none() {
 672                         self.named_parameters.push(*def_id);
 673                     }
 674                 }
 675
 676                 ty::BoundRegion::BrAnon(var) => match self.parameters.entry(*var) {
 677                     Entry::Vacant(entry) => {
 678                         entry.insert(chalk_ir::VariableKind::Lifetime);
 679                     }
 680                     Entry::Occupied(entry) => match entry.get() {
 681                         chalk_ir::VariableKind::Lifetime => {}
 682                         _ => panic!(),
 683                     },
 684                 },
 685
 686                 ty::BrEnv => unimplemented!(),
 687             },
 688
 689             ty::ReEarlyBound(_re) => {
 690                 // FIXME(chalk): jackh726 - I think we should always have already
 691                 // substituted away `ReEarlyBound`s for `ReLateBound`s, but need to confirm.
 692                 unimplemented!();
 693             }
 694
 695             _ => (),
 696         };
 697
 698         r.super_visit_with(self)
 699     }
 700 }
 701
 702 /// This is used to replace `BoundRegion::BrNamed` with `BoundRegion::BrAnon`.
 703 /// Note: we assume that we will always have room for more bound vars. (i.e. we
 704 /// won't ever hit the `u32` limit in `BrAnon`s).
 705 struct NamedBoundVarSubstitutor<'a, 'tcx> {
 706     tcx: TyCtxt<'tcx>,
 707     binder_index: ty::DebruijnIndex,
 708     named_parameters: &'a BTreeMap<DefId, u32>,
 709 }
 710
 711 impl<'a, 'tcx> NamedBoundVarSubstitutor<'a, 'tcx> {
 712     fn new(tcx: TyCtxt<'tcx>, named_parameters: &'a BTreeMap<DefId, u32>) -> Self {
 713         NamedBoundVarSubstitutor { tcx, binder_index: ty::INNERMOST, named_parameters }
 714     }
 715 }
 716
 717 impl<'a, 'tcx> TypeFolder<'tcx> for NamedBoundVarSubstitutor<'a, 'tcx> {
 718     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
 719         self.tcx
 720     }
 721
 722     fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> Binder<T> {
 723         self.binder_index.shift_in(1);
 724         let result = t.super_fold_with(self);
 725         self.binder_index.shift_out(1);
 726         result
 727     }
 728
 729     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
 730         t.super_fold_with(self)
 731     }
 732
 733     fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
 734         match r {
 735             ty::ReLateBound(index, br) if *index == self.binder_index => match br {
 736                 ty::BoundRegion::BrNamed(def_id, _name) => {
 737                     match self.named_parameters.get(def_id) {
 738                         Some(idx) => {
 739                             return self.tcx.mk_region(RegionKind::ReLateBound(
 740                                 *index,
 741                                 BoundRegion::BrAnon(*idx),
 742                             ));
 743                         }
 744                         None => panic!("Missing `BrNamed`."),
 745                     }
 746                 }
 747                 ty::BrEnv => unimplemented!(),
 748                 ty::BoundRegion::BrAnon(_) => {}
 749             },
 750             _ => (),
 751         };
 752
 753         r.super_fold_with(self)
 754     }
 755 }
 756
 757 /// Used to substitute `Param`s with placeholders. We do this since Chalk
 758 /// have a notion of `Param`s.
 759 crate struct ParamsSubstitutor<'tcx> {
 760     tcx: TyCtxt<'tcx>,
 761     binder_index: ty::DebruijnIndex,
 762     list: Vec<rustc_middle::ty::ParamTy>,
 763     crate params: rustc_data_structures::fx::FxHashMap<usize, rustc_middle::ty::ParamTy>,
 764     crate named_regions: BTreeMap<DefId, u32>,
 765 }
 766
 767 impl<'tcx> ParamsSubstitutor<'tcx> {
 768     crate fn new(tcx: TyCtxt<'tcx>) -> Self {
 769         ParamsSubstitutor {
 770             tcx,
 771             binder_index: ty::INNERMOST,
 772             list: vec![],
 773             params: rustc_data_structures::fx::FxHashMap::default(),
 774             named_regions: BTreeMap::default(),
 775         }
 776     }
 777 }
 778
 779 impl<'tcx> TypeFolder<'tcx> for ParamsSubstitutor<'tcx> {
 780     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
 781         self.tcx
 782     }
 783
 784     fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> Binder<T> {
 785         self.binder_index.shift_in(1);
 786         let result = t.super_fold_with(self);
 787         self.binder_index.shift_out(1);
 788         result
 789     }
 790
 791     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
 792         match t.kind {
 793             // FIXME(chalk): currently we convert params to placeholders starting at
 794             // index `0`. To support placeholders, we'll actually need to do a
 795             // first pass to collect placeholders. Then we can insert params after.
 796             ty::Placeholder(_) => unimplemented!(),
 797             ty::Param(param) => match self.list.iter().position(|r| r == &param) {
 798                 Some(_idx) => self.tcx.mk_ty(ty::Placeholder(ty::PlaceholderType {
 799                     universe: ty::UniverseIndex::from_usize(0),
 800                     name: ty::BoundVar::from_usize(_idx),
 801                 })),
 802                 None => {
 803                     self.list.push(param);
 804                     let idx = self.list.len() - 1;
 805                     self.params.insert(idx, param);
 806                     self.tcx.mk_ty(ty::Placeholder(ty::PlaceholderType {
 807                         universe: ty::UniverseIndex::from_usize(0),
 808                         name: ty::BoundVar::from_usize(idx),
 809                     }))
 810                 }
 811             },
 812
 813             _ => t.super_fold_with(self),
 814         }
 815     }
 816
 817     fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
 818         match r {
 819             // FIXME(chalk) - jackh726 - this currently isn't hit in any tests.
 820             // This covers any region variables in a goal, right?
 821             ty::ReEarlyBound(_re) => match self.named_regions.get(&_re.def_id) {
 822                 Some(idx) => self.tcx.mk_region(RegionKind::ReLateBound(
 823                     self.binder_index,
 824                     BoundRegion::BrAnon(*idx),
 825                 )),
 826                 None => {
 827                     let idx = self.named_regions.len() as u32;
 828                     self.named_regions.insert(_re.def_id, idx);
 829                     self.tcx.mk_region(RegionKind::ReLateBound(
 830                         self.binder_index,
 831                         BoundRegion::BrAnon(idx),
 832                     ))
 833                 }
 834             },
 835
 836             _ => r.super_fold_with(self),
 837         }
 838     }
 839 }