src/librustc/traits/mod.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Trait Resolution. See [rustc guide] for more info on how this works.
  12 //!
  13 //! [rustc guide]: https://rust-lang-nursery.github.io/rustc-guide/traits/resolution.html
  14
  15 pub use self::SelectionError::*;
  16 pub use self::FulfillmentErrorCode::*;
  17 pub use self::Vtable::*;
  18 pub use self::ObligationCauseCode::*;
  19
  20 use chalk_engine;
  21 use hir;
  22 use hir::def_id::DefId;
  23 use infer::SuppressRegionErrors;
  24 use infer::outlives::env::OutlivesEnvironment;
  25 use middle::region;
  26 use mir::interpret::ConstEvalErr;
  27 use ty::subst::Substs;
  28 use ty::{self, AdtKind, List, Ty, TyCtxt, GenericParamDefKind, ToPredicate};
  29 use ty::error::{ExpectedFound, TypeError};
  30 use ty::fold::{TypeFolder, TypeFoldable, TypeVisitor};
  31 use infer::{InferCtxt};
  32 use util::common::ErrorReported;
  33
  34 use rustc_data_structures::sync::Lrc;
  35 use std::fmt::Debug;
  36 use std::rc::Rc;
  37 use syntax::ast;
  38 use syntax_pos::{Span, DUMMY_SP};
  39
  40 pub use self::coherence::{orphan_check, overlapping_impls, OrphanCheckErr, OverlapResult};
  41 pub use self::fulfill::{FulfillmentContext, PendingPredicateObligation};
  42 pub use self::project::MismatchedProjectionTypes;
  43 pub use self::project::{normalize, normalize_projection_type, poly_project_and_unify_type};
  44 pub use self::project::{ProjectionCache, ProjectionCacheSnapshot, Reveal, Normalized};
  45 pub use self::object_safety::ObjectSafetyViolation;
  46 pub use self::object_safety::MethodViolationCode;
  47 pub use self::on_unimplemented::{OnUnimplementedDirective, OnUnimplementedNote};
  48 pub use self::select::{EvaluationCache, SelectionContext, SelectionCache};
  49 pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
  50 pub use self::specialize::{OverlapError, specialization_graph, translate_substs};
  51 pub use self::specialize::find_associated_item;
  52 pub use self::engine::{TraitEngine, TraitEngineExt};
  53 pub use self::util::elaborate_predicates;
  54 pub use self::util::supertraits;
  55 pub use self::util::Supertraits;
  56 pub use self::util::supertrait_def_ids;
  57 pub use self::util::SupertraitDefIds;
  58 pub use self::util::transitive_bounds;
  59
  60 #[allow(dead_code)]
  61 pub mod auto_trait;
  62 mod coherence;
  63 pub mod error_reporting;
  64 mod engine;
  65 mod fulfill;
  66 mod project;
  67 mod object_safety;
  68 mod on_unimplemented;
  69 mod select;
  70 mod specialize;
  71 mod structural_impls;
  72 pub mod codegen;
  73 mod util;
  74
  75 pub mod query;
  76
  77 // Whether to enable bug compatibility with issue #43355
  78 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
  79 pub enum IntercrateMode {
  80     Issue43355,
  81     Fixed
  82 }
  83
  84 // The mode that trait queries run in
  85 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
  86 pub enum TraitQueryMode {
  87     // Standard/un-canonicalized queries get accurate
  88     // spans etc. passed in and hence can do reasonable
  89     // error reporting on their own.
  90     Standard,
  91     // Canonicalized queries get dummy spans and hence
  92     // must generally propagate errors to
  93     // pre-canonicalization callsites.
  94     Canonical,
  95 }
  96
  97 /// An `Obligation` represents some trait reference (e.g. `int:Eq`) for
  98 /// which the vtable must be found.  The process of finding a vtable is
  99 /// called "resolving" the `Obligation`. This process consists of
 100 /// either identifying an `impl` (e.g., `impl Eq for int`) that
 101 /// provides the required vtable, or else finding a bound that is in
 102 /// scope. The eventual result is usually a `Selection` (defined below).
 103 #[derive(Clone, PartialEq, Eq, Hash)]
 104 pub struct Obligation<'tcx, T> {
 105     /// Why do we have to prove this thing?
 106     pub cause: ObligationCause<'tcx>,
 107
 108     /// In which environment should we prove this thing?
 109     pub param_env: ty::ParamEnv<'tcx>,
 110
 111     /// What are we trying to prove?
 112     pub predicate: T,
 113
 114     /// If we started proving this as a result of trying to prove
 115     /// something else, track the total depth to ensure termination.
 116     /// If this goes over a certain threshold, we abort compilation --
 117     /// in such cases, we can not say whether or not the predicate
 118     /// holds for certain. Stupid halting problem. Such a drag.
 119     pub recursion_depth: usize,
 120 }
 121
 122 pub type PredicateObligation<'tcx> = Obligation<'tcx, ty::Predicate<'tcx>>;
 123 pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;
 124
 125 /// Why did we incur this obligation? Used for error reporting.
 126 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 127 pub struct ObligationCause<'tcx> {
 128     pub span: Span,
 129
 130     // The id of the fn body that triggered this obligation. This is
 131     // used for region obligations to determine the precise
 132     // environment in which the region obligation should be evaluated
 133     // (in particular, closures can add new assumptions). See the
 134     // field `region_obligations` of the `FulfillmentContext` for more
 135     // information.
 136     pub body_id: ast::NodeId,
 137
 138     pub code: ObligationCauseCode<'tcx>
 139 }
 140
 141 impl<'tcx> ObligationCause<'tcx> {
 142     pub fn span<'a, 'gcx>(&self, tcx: &TyCtxt<'a, 'gcx, 'tcx>) -> Span {
 143         match self.code {
 144             ObligationCauseCode::CompareImplMethodObligation { .. } |
 145             ObligationCauseCode::MainFunctionType |
 146             ObligationCauseCode::StartFunctionType => {
 147                 tcx.sess.source_map().def_span(self.span)
 148             }
 149             _ => self.span,
 150         }
 151     }
 152 }
 153
 154 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 155 pub enum ObligationCauseCode<'tcx> {
 156     /// Not well classified or should be obvious from span.
 157     MiscObligation,
 158
 159     /// A slice or array is WF only if `T: Sized`
 160     SliceOrArrayElem,
 161
 162     /// A tuple is WF only if its middle elements are Sized
 163     TupleElem,
 164
 165     /// This is the trait reference from the given projection
 166     ProjectionWf(ty::ProjectionTy<'tcx>),
 167
 168     /// In an impl of trait X for type Y, type Y must
 169     /// also implement all supertraits of X.
 170     ItemObligation(DefId),
 171
 172     /// A type like `&'a T` is WF only if `T: 'a`.
 173     ReferenceOutlivesReferent(Ty<'tcx>),
 174
 175     /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
 176     ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
 177
 178     /// Obligation incurred due to an object cast.
 179     ObjectCastObligation(/* Object type */ Ty<'tcx>),
 180
 181     // Various cases where expressions must be sized/copy/etc:
 182     /// L = X implies that L is Sized
 183     AssignmentLhsSized,
 184     /// (x1, .., xn) must be Sized
 185     TupleInitializerSized,
 186     /// S { ... } must be Sized
 187     StructInitializerSized,
 188     /// Type of each variable must be Sized
 189     VariableType(ast::NodeId),
 190     /// Argument type must be Sized
 191     SizedArgumentType,
 192     /// Return type must be Sized
 193     SizedReturnType,
 194     /// Yield type must be Sized
 195     SizedYieldType,
 196     /// [T,..n] --> T must be Copy
 197     RepeatVec,
 198
 199     /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
 200     FieldSized { adt_kind: AdtKind, last: bool },
 201
 202     /// Constant expressions must be sized.
 203     ConstSized,
 204
 205     /// static items must have `Sync` type
 206     SharedStatic,
 207
 208     BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
 209
 210     ImplDerivedObligation(DerivedObligationCause<'tcx>),
 211
 212     /// error derived when matching traits/impls; see ObligationCause for more details
 213     CompareImplMethodObligation {
 214         item_name: ast::Name,
 215         impl_item_def_id: DefId,
 216         trait_item_def_id: DefId,
 217     },
 218
 219     /// Checking that this expression can be assigned where it needs to be
 220     // FIXME(eddyb) #11161 is the original Expr required?
 221     ExprAssignable,
 222
 223     /// Computing common supertype in the arms of a match expression
 224     MatchExpressionArm { arm_span: Span,
 225                          source: hir::MatchSource },
 226
 227     /// Computing common supertype in an if expression
 228     IfExpression,
 229
 230     /// Computing common supertype of an if expression with no else counter-part
 231     IfExpressionWithNoElse,
 232
 233     /// `main` has wrong type
 234     MainFunctionType,
 235
 236     /// `start` has wrong type
 237     StartFunctionType,
 238
 239     /// intrinsic has wrong type
 240     IntrinsicType,
 241
 242     /// method receiver
 243     MethodReceiver,
 244
 245     /// `return` with no expression
 246     ReturnNoExpression,
 247
 248     /// `return` with an expression
 249     ReturnType(ast::NodeId),
 250
 251     /// Block implicit return
 252     BlockTailExpression(ast::NodeId),
 253
 254     /// #[feature(trivial_bounds)] is not enabled
 255     TrivialBound,
 256 }
 257
 258 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 259 pub struct DerivedObligationCause<'tcx> {
 260     /// The trait reference of the parent obligation that led to the
 261     /// current obligation. Note that only trait obligations lead to
 262     /// derived obligations, so we just store the trait reference here
 263     /// directly.
 264     parent_trait_ref: ty::PolyTraitRef<'tcx>,
 265
 266     /// The parent trait had this cause
 267     parent_code: Rc<ObligationCauseCode<'tcx>>
 268 }
 269
 270 pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
 271 pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
 272 pub type TraitObligations<'tcx> = Vec<TraitObligation<'tcx>>;
 273
 274 /// The following types:
 275 /// * `WhereClause`
 276 /// * `WellFormed`
 277 /// * `FromEnv`
 278 /// * `DomainGoal`
 279 /// * `Goal`
 280 /// * `Clause`
 281 /// * `Environment`
 282 /// * `InEnvironment`
 283 /// are used for representing the trait system in the form of
 284 /// logic programming clauses. They are part of the interface
 285 /// for the chalk SLG solver.
 286 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
 287 pub enum WhereClause<'tcx> {
 288     Implemented(ty::TraitPredicate<'tcx>),
 289     ProjectionEq(ty::ProjectionPredicate<'tcx>),
 290     RegionOutlives(ty::RegionOutlivesPredicate<'tcx>),
 291     TypeOutlives(ty::TypeOutlivesPredicate<'tcx>),
 292 }
 293
 294 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
 295 pub enum WellFormed<'tcx> {
 296     Trait(ty::TraitPredicate<'tcx>),
 297     Ty(Ty<'tcx>),
 298 }
 299
 300 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
 301 pub enum FromEnv<'tcx> {
 302     Trait(ty::TraitPredicate<'tcx>),
 303     Ty(Ty<'tcx>),
 304 }
 305
 306 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
 307 pub enum DomainGoal<'tcx> {
 308     Holds(WhereClause<'tcx>),
 309     WellFormed(WellFormed<'tcx>),
 310     FromEnv(FromEnv<'tcx>),
 311     Normalize(ty::ProjectionPredicate<'tcx>),
 312 }
 313
 314 pub type PolyDomainGoal<'tcx> = ty::Binder<DomainGoal<'tcx>>;
 315
 316 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 317 pub enum QuantifierKind {
 318     Universal,
 319     Existential,
 320 }
 321
 322 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 323 pub enum GoalKind<'tcx> {
 324     Implies(Clauses<'tcx>, Goal<'tcx>),
 325     And(Goal<'tcx>, Goal<'tcx>),
 326     Not(Goal<'tcx>),
 327     DomainGoal(DomainGoal<'tcx>),
 328     Quantified(QuantifierKind, ty::Binder<Goal<'tcx>>),
 329     CannotProve,
 330 }
 331
 332 pub type Goal<'tcx> = &'tcx GoalKind<'tcx>;
 333
 334 pub type Goals<'tcx> = &'tcx List<Goal<'tcx>>;
 335
 336 impl<'tcx> DomainGoal<'tcx> {
 337     pub fn into_goal(self) -> GoalKind<'tcx> {
 338         GoalKind::DomainGoal(self)
 339     }
 340
 341     pub fn into_program_clause(self) -> ProgramClause<'tcx> {
 342         ProgramClause {
 343             goal: self,
 344             hypotheses: ty::List::empty(),
 345             category: ProgramClauseCategory::Other,
 346         }
 347     }
 348 }
 349
 350 impl<'tcx> GoalKind<'tcx> {
 351     pub fn from_poly_domain_goal<'a>(
 352         domain_goal: PolyDomainGoal<'tcx>,
 353         tcx: TyCtxt<'a, 'tcx, 'tcx>,
 354     ) -> GoalKind<'tcx> {
 355         match domain_goal.no_late_bound_regions() {
 356             Some(p) => p.into_goal(),
 357             None => GoalKind::Quantified(
 358                 QuantifierKind::Universal,
 359                 domain_goal.map_bound(|p| tcx.mk_goal(p.into_goal()))
 360             ),
 361         }
 362     }
 363 }
 364
 365 /// This matches the definition from Page 7 of "A Proof Procedure for the Logic of Hereditary
 366 /// Harrop Formulas".
 367 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 368 pub enum Clause<'tcx> {
 369     Implies(ProgramClause<'tcx>),
 370     ForAll(ty::Binder<ProgramClause<'tcx>>),
 371 }
 372
 373 impl Clause<'tcx> {
 374     pub fn category(self) -> ProgramClauseCategory {
 375         match self {
 376             Clause::Implies(clause) => clause.category,
 377             Clause::ForAll(clause) => clause.skip_binder().category,
 378         }
 379     }
 380 }
 381
 382 /// Multiple clauses.
 383 pub type Clauses<'tcx> = &'tcx List<Clause<'tcx>>;
 384
 385 /// A "program clause" has the form `D :- G1, ..., Gn`. It is saying
 386 /// that the domain goal `D` is true if `G1...Gn` are provable. This
 387 /// is equivalent to the implication `G1..Gn => D`; we usually write
 388 /// it with the reverse implication operator `:-` to emphasize the way
 389 /// that programs are actually solved (via backchaining, which starts
 390 /// with the goal to solve and proceeds from there).
 391 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 392 pub struct ProgramClause<'tcx> {
 393     /// This goal will be considered true...
 394     pub goal: DomainGoal<'tcx>,
 395
 396     /// ...if we can prove these hypotheses (there may be no hypotheses at all):
 397     pub hypotheses: Goals<'tcx>,
 398
 399     /// Useful for filtering clauses.
 400     pub category: ProgramClauseCategory,
 401 }
 402
 403 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 404 pub enum ProgramClauseCategory {
 405     ImpliedBound,
 406     WellFormed,
 407     Other,
 408 }
 409
 410 /// A set of clauses that we assume to be true.
 411 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 412 pub struct Environment<'tcx> {
 413     pub clauses: Clauses<'tcx>,
 414 }
 415
 416 impl Environment<'tcx> {
 417     pub fn with<G>(self, goal: G) -> InEnvironment<'tcx, G> {
 418         InEnvironment {
 419             environment: self,
 420             goal,
 421         }
 422     }
 423 }
 424
 425 /// Something (usually a goal), along with an environment.
 426 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 427 pub struct InEnvironment<'tcx, G> {
 428     pub environment: Environment<'tcx>,
 429     pub goal: G,
 430 }
 431
 432 pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
 433
 434 #[derive(Clone,Debug)]
 435 pub enum SelectionError<'tcx> {
 436     Unimplemented,
 437     OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
 438                                 ty::PolyTraitRef<'tcx>,
 439                                 ty::error::TypeError<'tcx>),
 440     TraitNotObjectSafe(DefId),
 441     ConstEvalFailure(Lrc<ConstEvalErr<'tcx>>),
 442     Overflow,
 443 }
 444
 445 pub struct FulfillmentError<'tcx> {
 446     pub obligation: PredicateObligation<'tcx>,
 447     pub code: FulfillmentErrorCode<'tcx>
 448 }
 449
 450 #[derive(Clone)]
 451 pub enum FulfillmentErrorCode<'tcx> {
 452     CodeSelectionError(SelectionError<'tcx>),
 453     CodeProjectionError(MismatchedProjectionTypes<'tcx>),
 454     CodeSubtypeError(ExpectedFound<Ty<'tcx>>,
 455                      TypeError<'tcx>), // always comes from a SubtypePredicate
 456     CodeAmbiguity,
 457 }
 458
 459 /// When performing resolution, it is typically the case that there
 460 /// can be one of three outcomes:
 461 ///
 462 /// - `Ok(Some(r))`: success occurred with result `r`
 463 /// - `Ok(None)`: could not definitely determine anything, usually due
 464 ///   to inconclusive type inference.
 465 /// - `Err(e)`: error `e` occurred
 466 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
 467
 468 /// Given the successful resolution of an obligation, the `Vtable`
 469 /// indicates where the vtable comes from. Note that while we call this
 470 /// a "vtable", it does not necessarily indicate dynamic dispatch at
 471 /// runtime. `Vtable` instances just tell the compiler where to find
 472 /// methods, but in generic code those methods are typically statically
 473 /// dispatched -- only when an object is constructed is a `Vtable`
 474 /// instance reified into an actual vtable.
 475 ///
 476 /// For example, the vtable may be tied to a specific impl (case A),
 477 /// or it may be relative to some bound that is in scope (case B).
 478 ///
 479 ///
 480 /// ```
 481 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
 482 /// impl<T:Clone> Clone<T> for Box<T> { ... }    // Impl_2
 483 /// impl Clone for int { ... }             // Impl_3
 484 ///
 485 /// fn foo<T:Clone>(concrete: Option<Box<int>>,
 486 ///                 param: T,
 487 ///                 mixed: Option<T>) {
 488 ///
 489 ///    // Case A: Vtable points at a specific impl. Only possible when
 490 ///    // type is concretely known. If the impl itself has bounded
 491 ///    // type parameters, Vtable will carry resolutions for those as well:
 492 ///    concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
 493 ///
 494 ///    // Case B: Vtable must be provided by caller. This applies when
 495 ///    // type is a type parameter.
 496 ///    param.clone();    // VtableParam
 497 ///
 498 ///    // Case C: A mix of cases A and B.
 499 ///    mixed.clone();    // Vtable(Impl_1, [VtableParam])
 500 /// }
 501 /// ```
 502 ///
 503 /// ### The type parameter `N`
 504 ///
 505 /// See explanation on `VtableImplData`.
 506 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
 507 pub enum Vtable<'tcx, N> {
 508     /// Vtable identifying a particular impl.
 509     VtableImpl(VtableImplData<'tcx, N>),
 510
 511     /// Vtable for auto trait implementations
 512     /// This carries the information and nested obligations with regards
 513     /// to an auto implementation for a trait `Trait`. The nested obligations
 514     /// ensure the trait implementation holds for all the constituent types.
 515     VtableAutoImpl(VtableAutoImplData<N>),
 516
 517     /// Successful resolution to an obligation provided by the caller
 518     /// for some type parameter. The `Vec<N>` represents the
 519     /// obligations incurred from normalizing the where-clause (if
 520     /// any).
 521     VtableParam(Vec<N>),
 522
 523     /// Virtual calls through an object
 524     VtableObject(VtableObjectData<'tcx, N>),
 525
 526     /// Successful resolution for a builtin trait.
 527     VtableBuiltin(VtableBuiltinData<N>),
 528
 529     /// Vtable automatically generated for a closure. The def ID is the ID
 530     /// of the closure expression. This is a `VtableImpl` in spirit, but the
 531     /// impl is generated by the compiler and does not appear in the source.
 532     VtableClosure(VtableClosureData<'tcx, N>),
 533
 534     /// Same as above, but for a fn pointer type with the given signature.
 535     VtableFnPointer(VtableFnPointerData<'tcx, N>),
 536
 537     /// Vtable automatically generated for a generator
 538     VtableGenerator(VtableGeneratorData<'tcx, N>),
 539 }
 540
 541 /// Identifies a particular impl in the source, along with a set of
 542 /// substitutions from the impl's type/lifetime parameters. The
 543 /// `nested` vector corresponds to the nested obligations attached to
 544 /// the impl's type parameters.
 545 ///
 546 /// The type parameter `N` indicates the type used for "nested
 547 /// obligations" that are required by the impl. During type check, this
 548 /// is `Obligation`, as one might expect. During codegen, however, this
 549 /// is `()`, because codegen only requires a shallow resolution of an
 550 /// impl, and nested obligations are satisfied later.
 551 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
 552 pub struct VtableImplData<'tcx, N> {
 553     pub impl_def_id: DefId,
 554     pub substs: &'tcx Substs<'tcx>,
 555     pub nested: Vec<N>
 556 }
 557
 558 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
 559 pub struct VtableGeneratorData<'tcx, N> {
 560     pub generator_def_id: DefId,
 561     pub substs: ty::GeneratorSubsts<'tcx>,
 562     /// Nested obligations. This can be non-empty if the generator
 563     /// signature contains associated types.
 564     pub nested: Vec<N>
 565 }
 566
 567 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
 568 pub struct VtableClosureData<'tcx, N> {
 569     pub closure_def_id: DefId,
 570     pub substs: ty::ClosureSubsts<'tcx>,
 571     /// Nested obligations. This can be non-empty if the closure
 572     /// signature contains associated types.
 573     pub nested: Vec<N>
 574 }
 575
 576 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
 577 pub struct VtableAutoImplData<N> {
 578     pub trait_def_id: DefId,
 579     pub nested: Vec<N>
 580 }
 581
 582 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
 583 pub struct VtableBuiltinData<N> {
 584     pub nested: Vec<N>
 585 }
 586
 587 /// A vtable for some object-safe trait `Foo` automatically derived
 588 /// for the object type `Foo`.
 589 #[derive(PartialEq, Eq, Clone, RustcEncodable, RustcDecodable)]
 590 pub struct VtableObjectData<'tcx, N> {
 591     /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
 592     pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
 593
 594     /// The vtable is formed by concatenating together the method lists of
 595     /// the base object trait and all supertraits; this is the start of
 596     /// `upcast_trait_ref`'s methods in that vtable.
 597     pub vtable_base: usize,
 598
 599     pub nested: Vec<N>,
 600 }
 601
 602 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
 603 pub struct VtableFnPointerData<'tcx, N> {
 604     pub fn_ty: Ty<'tcx>,
 605     pub nested: Vec<N>
 606 }
 607
 608 /// Creates predicate obligations from the generic bounds.
 609 pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
 610                                      param_env: ty::ParamEnv<'tcx>,
 611                                      generic_bounds: &ty::InstantiatedPredicates<'tcx>)
 612                                      -> PredicateObligations<'tcx>
 613 {
 614     util::predicates_for_generics(cause, 0, param_env, generic_bounds)
 615 }
 616
 617 /// Determines whether the type `ty` is known to meet `bound` and
 618 /// returns true if so. Returns false if `ty` either does not meet
 619 /// `bound` or is not known to meet bound (note that this is
 620 /// conservative towards *no impl*, which is the opposite of the
 621 /// `evaluate` methods).
 622 pub fn type_known_to_meet_bound<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
 623                                                 param_env: ty::ParamEnv<'tcx>,
 624                                                 ty: Ty<'tcx>,
 625                                                 def_id: DefId,
 626                                                 span: Span)
 627 -> bool
 628 {
 629     debug!("type_known_to_meet_bound(ty={:?}, bound={:?})",
 630            ty,
 631            infcx.tcx.item_path_str(def_id));
 632
 633     let trait_ref = ty::TraitRef {
 634         def_id,
 635         substs: infcx.tcx.mk_substs_trait(ty, &[]),
 636     };
 637     let obligation = Obligation {
 638         param_env,
 639         cause: ObligationCause::misc(span, ast::DUMMY_NODE_ID),
 640         recursion_depth: 0,
 641         predicate: trait_ref.to_predicate(),
 642     };
 643
 644     let result = infcx.predicate_must_hold(&obligation);
 645     debug!("type_known_to_meet_ty={:?} bound={} => {:?}",
 646            ty, infcx.tcx.item_path_str(def_id), result);
 647
 648     if result && (ty.has_infer_types() || ty.has_closure_types()) {
 649         // Because of inference "guessing", selection can sometimes claim
 650         // to succeed while the success requires a guess. To ensure
 651         // this function's result remains infallible, we must confirm
 652         // that guess. While imperfect, I believe this is sound.
 653
 654         // The handling of regions in this area of the code is terrible,
 655         // see issue #29149. We should be able to improve on this with
 656         // NLL.
 657         let mut fulfill_cx = FulfillmentContext::new_ignoring_regions();
 658
 659         // We can use a dummy node-id here because we won't pay any mind
 660         // to region obligations that arise (there shouldn't really be any
 661         // anyhow).
 662         let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
 663
 664         fulfill_cx.register_bound(infcx, param_env, ty, def_id, cause);
 665
 666         // Note: we only assume something is `Copy` if we can
 667         // *definitively* show that it implements `Copy`. Otherwise,
 668         // assume it is move; linear is always ok.
 669         match fulfill_cx.select_all_or_error(infcx) {
 670             Ok(()) => {
 671                 debug!("type_known_to_meet_bound: ty={:?} bound={} success",
 672                        ty,
 673                        infcx.tcx.item_path_str(def_id));
 674                 true
 675             }
 676             Err(e) => {
 677                 debug!("type_known_to_meet_bound: ty={:?} bound={} errors={:?}",
 678                        ty,
 679                        infcx.tcx.item_path_str(def_id),
 680                        e);
 681                 false
 682             }
 683         }
 684     } else {
 685         result
 686     }
 687 }
 688
 689 fn do_normalize_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 690                                      region_context: DefId,
 691                                      cause: ObligationCause<'tcx>,
 692                                      elaborated_env: ty::ParamEnv<'tcx>,
 693                                      predicates: Vec<ty::Predicate<'tcx>>)
 694                                      -> Result<Vec<ty::Predicate<'tcx>>, ErrorReported>
 695 {
 696     debug!("do_normalize_predicates({:?})", predicates);
 697     let span = cause.span;
 698     tcx.infer_ctxt().enter(|infcx| {
 699         // FIXME. We should really... do something with these region
 700         // obligations. But this call just continues the older
 701         // behavior (i.e., doesn't cause any new bugs), and it would
 702         // take some further refactoring to actually solve them. In
 703         // particular, we would have to handle implied bounds
 704         // properly, and that code is currently largely confined to
 705         // regionck (though I made some efforts to extract it
 706         // out). -nmatsakis
 707         //
 708         // @arielby: In any case, these obligations are checked
 709         // by wfcheck anyway, so I'm not sure we have to check
 710         // them here too, and we will remove this function when
 711         // we move over to lazy normalization *anyway*.
 712         let fulfill_cx = FulfillmentContext::new_ignoring_regions();
 713         let predicates = match fully_normalize(
 714             &infcx,
 715             fulfill_cx,
 716             cause,
 717             elaborated_env,
 718             &predicates,
 719         ) {
 720             Ok(predicates) => predicates,
 721             Err(errors) => {
 722                 infcx.report_fulfillment_errors(&errors, None, false);
 723                 return Err(ErrorReported)
 724             }
 725         };
 726
 727         debug!("do_normalize_predictes: normalized predicates = {:?}", predicates);
 728
 729         let region_scope_tree = region::ScopeTree::default();
 730
 731         // We can use the `elaborated_env` here; the region code only
 732         // cares about declarations like `'a: 'b`.
 733         let outlives_env = OutlivesEnvironment::new(elaborated_env);
 734
 735         infcx.resolve_regions_and_report_errors(
 736             region_context,
 737             &region_scope_tree,
 738             &outlives_env,
 739             SuppressRegionErrors::default(),
 740         );
 741
 742         let predicates = match infcx.fully_resolve(&predicates) {
 743             Ok(predicates) => predicates,
 744             Err(fixup_err) => {
 745                 // If we encounter a fixup error, it means that some type
 746                 // variable wound up unconstrained. I actually don't know
 747                 // if this can happen, and I certainly don't expect it to
 748                 // happen often, but if it did happen it probably
 749                 // represents a legitimate failure due to some kind of
 750                 // unconstrained variable, and it seems better not to ICE,
 751                 // all things considered.
 752                 tcx.sess.span_err(span, &fixup_err.to_string());
 753                 return Err(ErrorReported)
 754             }
 755         };
 756
 757         match tcx.lift_to_global(&predicates) {
 758             Some(predicates) => Ok(predicates),
 759             None => {
 760                 // FIXME: shouldn't we, you know, actually report an error here? or an ICE?
 761                 Err(ErrorReported)
 762             }
 763         }
 764     })
 765 }
 766
 767 // FIXME: this is gonna need to be removed ...
 768 /// Normalizes the parameter environment, reporting errors if they occur.
 769 pub fn normalize_param_env_or_error<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 770                                               region_context: DefId,
 771                                               unnormalized_env: ty::ParamEnv<'tcx>,
 772                                               cause: ObligationCause<'tcx>)
 773                                               -> ty::ParamEnv<'tcx>
 774 {
 775     // I'm not wild about reporting errors here; I'd prefer to
 776     // have the errors get reported at a defined place (e.g.,
 777     // during typeck). Instead I have all parameter
 778     // environments, in effect, going through this function
 779     // and hence potentially reporting errors. This ensures of
 780     // course that we never forget to normalize (the
 781     // alternative seemed like it would involve a lot of
 782     // manual invocations of this fn -- and then we'd have to
 783     // deal with the errors at each of those sites).
 784     //
 785     // In any case, in practice, typeck constructs all the
 786     // parameter environments once for every fn as it goes,
 787     // and errors will get reported then; so after typeck we
 788     // can be sure that no errors should occur.
 789
 790     debug!("normalize_param_env_or_error(region_context={:?}, unnormalized_env={:?}, cause={:?})",
 791            region_context, unnormalized_env, cause);
 792
 793     let mut predicates: Vec<_> =
 794         util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec())
 795             .collect();
 796
 797     debug!("normalize_param_env_or_error: elaborated-predicates={:?}",
 798            predicates);
 799
 800     let elaborated_env = ty::ParamEnv::new(tcx.intern_predicates(&predicates),
 801                                            unnormalized_env.reveal);
 802
 803     // HACK: we are trying to normalize the param-env inside *itself*. The problem is that
 804     // normalization expects its param-env to be already normalized, which means we have
 805     // a circularity.
 806     //
 807     // The way we handle this is by normalizing the param-env inside an unnormalized version
 808     // of the param-env, which means that if the param-env contains unnormalized projections,
 809     // we'll have some normalization failures. This is unfortunate.
 810     //
 811     // Lazy normalization would basically handle this by treating just the
 812     // normalizing-a-trait-ref-requires-itself cycles as evaluation failures.
 813     //
 814     // Inferred outlives bounds can create a lot of `TypeOutlives` predicates for associated
 815     // types, so to make the situation less bad, we normalize all the predicates *but*
 816     // the `TypeOutlives` predicates first inside the unnormalized parameter environment, and
 817     // then we normalize the `TypeOutlives` bounds inside the normalized parameter environment.
 818     //
 819     // This works fairly well because trait matching  does not actually care about param-env
 820     // TypeOutlives predicates - these are normally used by regionck.
 821     let outlives_predicates: Vec<_> = predicates.drain_filter(|predicate| {
 822         match predicate {
 823             ty::Predicate::TypeOutlives(..) => true,
 824             _ => false
 825         }
 826     }).collect();
 827
 828     debug!("normalize_param_env_or_error: predicates=(non-outlives={:?}, outlives={:?})",
 829            predicates, outlives_predicates);
 830     let non_outlives_predicates =
 831         match do_normalize_predicates(tcx, region_context, cause.clone(),
 832                                       elaborated_env, predicates) {
 833             Ok(predicates) => predicates,
 834             // An unnormalized env is better than nothing.
 835             Err(ErrorReported) => {
 836                 debug!("normalize_param_env_or_error: errored resolving non-outlives predicates");
 837                 return elaborated_env
 838             }
 839         };
 840
 841     debug!("normalize_param_env_or_error: non-outlives predicates={:?}", non_outlives_predicates);
 842
 843     // Not sure whether it is better to include the unnormalized TypeOutlives predicates
 844     // here. I believe they should not matter, because we are ignoring TypeOutlives param-env
 845     // predicates here anyway. Keeping them here anyway because it seems safer.
 846     let outlives_env: Vec<_> =
 847         non_outlives_predicates.iter().chain(&outlives_predicates).cloned().collect();
 848     let outlives_env = ty::ParamEnv::new(tcx.intern_predicates(&outlives_env),
 849                                          unnormalized_env.reveal);
 850     let outlives_predicates =
 851         match do_normalize_predicates(tcx, region_context, cause,
 852                                       outlives_env, outlives_predicates) {
 853             Ok(predicates) => predicates,
 854             // An unnormalized env is better than nothing.
 855             Err(ErrorReported) => {
 856                 debug!("normalize_param_env_or_error: errored resolving outlives predicates");
 857                 return elaborated_env
 858             }
 859         };
 860     debug!("normalize_param_env_or_error: outlives predicates={:?}", outlives_predicates);
 861
 862     let mut predicates = non_outlives_predicates;
 863     predicates.extend(outlives_predicates);
 864     debug!("normalize_param_env_or_error: final predicates={:?}", predicates);
 865     ty::ParamEnv::new(tcx.intern_predicates(&predicates), unnormalized_env.reveal)
 866 }
 867
 868 pub fn fully_normalize<'a, 'gcx, 'tcx, T>(
 869     infcx: &InferCtxt<'a, 'gcx, 'tcx>,
 870     mut fulfill_cx: FulfillmentContext<'tcx>,
 871     cause: ObligationCause<'tcx>,
 872     param_env: ty::ParamEnv<'tcx>,
 873     value: &T)
 874     -> Result<T, Vec<FulfillmentError<'tcx>>>
 875     where T : TypeFoldable<'tcx>
 876 {
 877     debug!("fully_normalize_with_fulfillcx(value={:?})", value);
 878     let selcx = &mut SelectionContext::new(infcx);
 879     let Normalized { value: normalized_value, obligations } =
 880         project::normalize(selcx, param_env, cause, value);
 881     debug!("fully_normalize: normalized_value={:?} obligations={:?}",
 882            normalized_value,
 883            obligations);
 884     for obligation in obligations {
 885         fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
 886     }
 887
 888     debug!("fully_normalize: select_all_or_error start");
 889     fulfill_cx.select_all_or_error(infcx)?;
 890     debug!("fully_normalize: select_all_or_error complete");
 891     let resolved_value = infcx.resolve_type_vars_if_possible(&normalized_value);
 892     debug!("fully_normalize: resolved_value={:?}", resolved_value);
 893     Ok(resolved_value)
 894 }
 895
 896 /// Normalizes the predicates and checks whether they hold in an empty
 897 /// environment. If this returns false, then either normalize
 898 /// encountered an error or one of the predicates did not hold. Used
 899 /// when creating vtables to check for unsatisfiable methods.
 900 fn normalize_and_test_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 901                                            predicates: Vec<ty::Predicate<'tcx>>)
 902                                            -> bool
 903 {
 904     debug!("normalize_and_test_predicates(predicates={:?})",
 905            predicates);
 906
 907     let result = tcx.infer_ctxt().enter(|infcx| {
 908         let param_env = ty::ParamEnv::reveal_all();
 909         let mut selcx = SelectionContext::new(&infcx);
 910         let mut fulfill_cx = FulfillmentContext::new();
 911         let cause = ObligationCause::dummy();
 912         let Normalized { value: predicates, obligations } =
 913             normalize(&mut selcx, param_env, cause.clone(), &predicates);
 914         for obligation in obligations {
 915             fulfill_cx.register_predicate_obligation(&infcx, obligation);
 916         }
 917         for predicate in predicates {
 918             let obligation = Obligation::new(cause.clone(), param_env, predicate);
 919             fulfill_cx.register_predicate_obligation(&infcx, obligation);
 920         }
 921
 922         fulfill_cx.select_all_or_error(&infcx).is_ok()
 923     });
 924     debug!("normalize_and_test_predicates(predicates={:?}) = {:?}",
 925            predicates, result);
 926     result
 927 }
 928
 929 fn substitute_normalize_and_test_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 930                                                       key: (DefId, &'tcx Substs<'tcx>))
 931                                                       -> bool
 932 {
 933     debug!("substitute_normalize_and_test_predicates(key={:?})",
 934            key);
 935
 936     let predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates;
 937     let result = normalize_and_test_predicates(tcx, predicates);
 938
 939     debug!("substitute_normalize_and_test_predicates(key={:?}) = {:?}",
 940            key, result);
 941     result
 942 }
 943
 944 /// Given a trait `trait_ref`, iterates the vtable entries
 945 /// that come from `trait_ref`, including its supertraits.
 946 #[inline] // FIXME(#35870) Avoid closures being unexported due to impl Trait.
 947 fn vtable_methods<'a, 'tcx>(
 948     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 949     trait_ref: ty::PolyTraitRef<'tcx>)
 950     -> Lrc<Vec<Option<(DefId, &'tcx Substs<'tcx>)>>>
 951 {
 952     debug!("vtable_methods({:?})", trait_ref);
 953
 954     Lrc::new(
 955         supertraits(tcx, trait_ref).flat_map(move |trait_ref| {
 956             let trait_methods = tcx.associated_items(trait_ref.def_id())
 957                 .filter(|item| item.kind == ty::AssociatedKind::Method);
 958
 959             // Now list each method's DefId and Substs (for within its trait).
 960             // If the method can never be called from this object, produce None.
 961             trait_methods.map(move |trait_method| {
 962                 debug!("vtable_methods: trait_method={:?}", trait_method);
 963                 let def_id = trait_method.def_id;
 964
 965                 // Some methods cannot be called on an object; skip those.
 966                 if !tcx.is_vtable_safe_method(trait_ref.def_id(), &trait_method) {
 967                     debug!("vtable_methods: not vtable safe");
 968                     return None;
 969                 }
 970
 971                 // the method may have some early-bound lifetimes, add
 972                 // regions for those
 973                 let substs = trait_ref.map_bound(|trait_ref|
 974                     Substs::for_item(tcx, def_id, |param, _|
 975                         match param.kind {
 976                             GenericParamDefKind::Lifetime => tcx.types.re_erased.into(),
 977                             GenericParamDefKind::Type {..} => {
 978                                 trait_ref.substs[param.index as usize]
 979                             }
 980                         }
 981                     )
 982                 );
 983
 984                 // the trait type may have higher-ranked lifetimes in it;
 985                 // so erase them if they appear, so that we get the type
 986                 // at some particular call site
 987                 let substs = tcx.normalize_erasing_late_bound_regions(
 988                     ty::ParamEnv::reveal_all(),
 989                     &substs
 990                 );
 991
 992                 // It's possible that the method relies on where clauses that
 993                 // do not hold for this particular set of type parameters.
 994                 // Note that this method could then never be called, so we
 995                 // do not want to try and codegen it, in that case (see #23435).
 996                 let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
 997                 if !normalize_and_test_predicates(tcx, predicates.predicates) {
 998                     debug!("vtable_methods: predicates do not hold");
 999                     return None;
1000                 }
1001
1002                 Some((def_id, substs))
1003             })
1004         }).collect()
1005     )
1006 }
1007
1008 impl<'tcx,O> Obligation<'tcx,O> {
1009     pub fn new(cause: ObligationCause<'tcx>,
1010                param_env: ty::ParamEnv<'tcx>,
1011                predicate: O)
1012                -> Obligation<'tcx, O>
1013     {
1014         Obligation { cause, param_env, recursion_depth: 0, predicate }
1015     }
1016
1017     fn with_depth(cause: ObligationCause<'tcx>,
1018                   recursion_depth: usize,
1019                   param_env: ty::ParamEnv<'tcx>,
1020                   predicate: O)
1021                   -> Obligation<'tcx, O>
1022     {
1023         Obligation { cause, param_env, recursion_depth, predicate }
1024     }
1025
1026     pub fn misc(span: Span,
1027                 body_id: ast::NodeId,
1028                 param_env: ty::ParamEnv<'tcx>,
1029                 trait_ref: O)
1030                 -> Obligation<'tcx, O> {
1031         Obligation::new(ObligationCause::misc(span, body_id), param_env, trait_ref)
1032     }
1033
1034     pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
1035         Obligation { cause: self.cause.clone(),
1036                      param_env: self.param_env,
1037                      recursion_depth: self.recursion_depth,
1038                      predicate: value }
1039     }
1040 }
1041
1042 impl<'tcx> ObligationCause<'tcx> {
1043     pub fn new(span: Span,
1044                body_id: ast::NodeId,
1045                code: ObligationCauseCode<'tcx>)
1046                -> ObligationCause<'tcx> {
1047         ObligationCause { span: span, body_id: body_id, code: code }
1048     }
1049
1050     pub fn misc(span: Span, body_id: ast::NodeId) -> ObligationCause<'tcx> {
1051         ObligationCause { span: span, body_id: body_id, code: MiscObligation }
1052     }
1053
1054     pub fn dummy() -> ObligationCause<'tcx> {
1055         ObligationCause { span: DUMMY_SP, body_id: ast::CRATE_NODE_ID, code: MiscObligation }
1056     }
1057 }
1058
1059 impl<'tcx, N> Vtable<'tcx, N> {
1060     pub fn nested_obligations(self) -> Vec<N> {
1061         match self {
1062             VtableImpl(i) => i.nested,
1063             VtableParam(n) => n,
1064             VtableBuiltin(i) => i.nested,
1065             VtableAutoImpl(d) => d.nested,
1066             VtableClosure(c) => c.nested,
1067             VtableGenerator(c) => c.nested,
1068             VtableObject(d) => d.nested,
1069             VtableFnPointer(d) => d.nested,
1070         }
1071     }
1072
1073     pub fn map<M, F>(self, f: F) -> Vtable<'tcx, M> where F: FnMut(N) -> M {
1074         match self {
1075             VtableImpl(i) => VtableImpl(VtableImplData {
1076                 impl_def_id: i.impl_def_id,
1077                 substs: i.substs,
1078                 nested: i.nested.into_iter().map(f).collect(),
1079             }),
1080             VtableParam(n) => VtableParam(n.into_iter().map(f).collect()),
1081             VtableBuiltin(i) => VtableBuiltin(VtableBuiltinData {
1082                 nested: i.nested.into_iter().map(f).collect(),
1083             }),
1084             VtableObject(o) => VtableObject(VtableObjectData {
1085                 upcast_trait_ref: o.upcast_trait_ref,
1086                 vtable_base: o.vtable_base,
1087                 nested: o.nested.into_iter().map(f).collect(),
1088             }),
1089             VtableAutoImpl(d) => VtableAutoImpl(VtableAutoImplData {
1090                 trait_def_id: d.trait_def_id,
1091                 nested: d.nested.into_iter().map(f).collect(),
1092             }),
1093             VtableFnPointer(p) => VtableFnPointer(VtableFnPointerData {
1094                 fn_ty: p.fn_ty,
1095                 nested: p.nested.into_iter().map(f).collect(),
1096             }),
1097             VtableGenerator(c) => VtableGenerator(VtableGeneratorData {
1098                 generator_def_id: c.generator_def_id,
1099                 substs: c.substs,
1100                 nested: c.nested.into_iter().map(f).collect(),
1101             }),
1102             VtableClosure(c) => VtableClosure(VtableClosureData {
1103                 closure_def_id: c.closure_def_id,
1104                 substs: c.substs,
1105                 nested: c.nested.into_iter().map(f).collect(),
1106             })
1107         }
1108     }
1109 }
1110
1111 impl<'tcx> FulfillmentError<'tcx> {
1112     fn new(obligation: PredicateObligation<'tcx>,
1113            code: FulfillmentErrorCode<'tcx>)
1114            -> FulfillmentError<'tcx>
1115     {
1116         FulfillmentError { obligation: obligation, code: code }
1117     }
1118 }
1119
1120 impl<'tcx> TraitObligation<'tcx> {
1121     fn self_ty(&self) -> ty::Binder<Ty<'tcx>> {
1122         self.predicate.map_bound(|p| p.self_ty())
1123     }
1124 }
1125
1126 pub fn provide(providers: &mut ty::query::Providers<'_>) {
1127     *providers = ty::query::Providers {
1128         is_object_safe: object_safety::is_object_safe_provider,
1129         specialization_graph_of: specialize::specialization_graph_provider,
1130         specializes: specialize::specializes,
1131         codegen_fulfill_obligation: codegen::codegen_fulfill_obligation,
1132         vtable_methods,
1133         substitute_normalize_and_test_predicates,
1134         ..*providers
1135     };
1136 }
1137
1138 pub trait ExClauseFold<'tcx>
1139 where
1140     Self: chalk_engine::context::Context + Clone,
1141 {
1142     fn fold_ex_clause_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(
1143         ex_clause: &chalk_engine::ExClause<Self>,
1144         folder: &mut F,
1145     ) -> chalk_engine::ExClause<Self>;
1146
1147     fn visit_ex_clause_with<'gcx: 'tcx, V: TypeVisitor<'tcx>>(
1148         ex_clause: &chalk_engine::ExClause<Self>,
1149         visitor: &mut V,
1150     ) -> bool;
1151 }
1152
1153 pub trait ExClauseLift<'tcx>
1154 where
1155     Self: chalk_engine::context::Context + Clone,
1156 {
1157     type LiftedExClause: Debug + 'tcx;
1158
1159     fn lift_ex_clause_to_tcx<'a, 'gcx>(
1160         ex_clause: &chalk_engine::ExClause<Self>,
1161         tcx: TyCtxt<'a, 'gcx, 'tcx>,
1162     ) -> Option<Self::LiftedExClause>;
1163 }