1 //! Trait Resolution. See the [rustc guide] for more information on how this works.
3 //! [rustc guide]: https://rust-lang.github.io/rustc-guide/traits/resolution.html
9 pub mod error_reporting;
24 use crate::hir::def_id::DefId;
25 use crate::infer::{InferCtxt, SuppressRegionErrors};
26 use crate::infer::outlives::env::OutlivesEnvironment;
27 use crate::middle::region;
28 use crate::mir::interpret::ErrorHandled;
29 use rustc_macros::HashStable;
31 use syntax_pos::{Span, DUMMY_SP};
32 use crate::ty::subst::{InternalSubsts, SubstsRef};
33 use crate::ty::{self, AdtKind, List, Ty, TyCtxt, GenericParamDefKind, ToPredicate};
34 use crate::ty::error::{ExpectedFound, TypeError};
35 use crate::ty::fold::{TypeFolder, TypeFoldable, TypeVisitor};
36 use crate::util::common::ErrorReported;
41 pub use self::SelectionError::*;
42 pub use self::FulfillmentErrorCode::*;
43 pub use self::Vtable::*;
44 pub use self::ObligationCauseCode::*;
46 pub use self::coherence::{add_placeholder_note, orphan_check, overlapping_impls};
47 pub use self::coherence::{OrphanCheckErr, OverlapResult};
48 pub use self::fulfill::{FulfillmentContext, PendingPredicateObligation};
49 pub use self::project::MismatchedProjectionTypes;
50 pub use self::project::{normalize, normalize_projection_type, poly_project_and_unify_type};
51 pub use self::project::{ProjectionCache, ProjectionCacheSnapshot, Reveal, Normalized};
52 pub use self::object_safety::ObjectSafetyViolation;
53 pub use self::object_safety::MethodViolationCode;
54 pub use self::on_unimplemented::{OnUnimplementedDirective, OnUnimplementedNote};
55 pub use self::select::{EvaluationCache, SelectionContext, SelectionCache};
56 pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
57 pub use self::specialize::{OverlapError, specialization_graph, translate_substs};
58 pub use self::specialize::find_associated_item;
59 pub use self::specialize::specialization_graph::FutureCompatOverlapError;
60 pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind;
61 pub use self::engine::{TraitEngine, TraitEngineExt};
62 pub use self::util::{elaborate_predicates, elaborate_trait_ref, elaborate_trait_refs};
64 supertraits, supertrait_def_ids, transitive_bounds, Supertraits, SupertraitDefIds,
66 pub use self::util::{expand_trait_aliases, TraitAliasExpander};
68 pub use self::chalk_fulfill::{
69 CanonicalGoal as ChalkCanonicalGoal,
70 FulfillmentContext as ChalkFulfillmentContext
73 pub use self::ObligationCauseCode::*;
74 pub use self::FulfillmentErrorCode::*;
75 pub use self::SelectionError::*;
76 pub use self::Vtable::*;
78 /// Whether to enable bug compatibility with issue #43355.
79 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
80 pub enum IntercrateMode {
85 /// The mode that trait queries run in.
86 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
87 pub enum TraitQueryMode {
88 // Standard/un-canonicalized queries get accurate
89 // spans etc. passed in and hence can do reasonable
90 // error reporting on their own.
92 // Canonicalized queries get dummy spans and hence
93 // must generally propagate errors to
94 // pre-canonicalization callsites.
98 /// An `Obligation` represents some trait reference (e.g., `int: Eq`) for
99 /// which the vtable must be found. The process of finding a vtable is
100 /// called "resolving" the `Obligation`. This process consists of
101 /// either identifying an `impl` (e.g., `impl Eq for int`) that
102 /// provides the required vtable, or else finding a bound that is in
103 /// scope. The eventual result is usually a `Selection` (defined below).
104 #[derive(Clone, PartialEq, Eq, Hash)]
105 pub struct Obligation<'tcx, T> {
106 /// The reason we have to prove this thing.
107 pub cause: ObligationCause<'tcx>,
109 /// The environment in which we should prove this thing.
110 pub param_env: ty::ParamEnv<'tcx>,
112 /// The thing we are trying to prove.
115 /// If we started proving this as a result of trying to prove
116 /// something else, track the total depth to ensure termination.
117 /// If this goes over a certain threshold, we abort compilation --
118 /// in such cases, we can not say whether or not the predicate
119 /// holds for certain. Stupid halting problem; such a drag.
120 pub recursion_depth: usize,
123 pub type PredicateObligation<'tcx> = Obligation<'tcx, ty::Predicate<'tcx>>;
124 pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;
126 /// The reason why we incurred this obligation; used for error reporting.
127 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
128 pub struct ObligationCause<'tcx> {
131 /// The ID of the fn body that triggered this obligation. This is
132 /// used for region obligations to determine the precise
133 /// environment in which the region obligation should be evaluated
134 /// (in particular, closures can add new assumptions). See the
135 /// field `region_obligations` of the `FulfillmentContext` for more
137 pub body_id: hir::HirId,
139 pub code: ObligationCauseCode<'tcx>
142 impl<'tcx> ObligationCause<'tcx> {
143 pub fn span(&self, tcx: TyCtxt<'tcx>) -> Span {
145 ObligationCauseCode::CompareImplMethodObligation { .. } |
146 ObligationCauseCode::MainFunctionType |
147 ObligationCauseCode::StartFunctionType => {
148 tcx.sess.source_map().def_span(self.span)
150 ObligationCauseCode::MatchExpressionArm { arm_span, .. } => arm_span,
156 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
157 pub enum ObligationCauseCode<'tcx> {
158 /// Not well classified or should be obvious from the span.
161 /// A slice or array is WF only if `T: Sized`.
164 /// A tuple is WF only if its middle elements are `Sized`.
167 /// This is the trait reference from the given projection.
168 ProjectionWf(ty::ProjectionTy<'tcx>),
170 /// In an impl of trait `X` for type `Y`, type `Y` must
171 /// also implement all supertraits of `X`.
172 ItemObligation(DefId),
174 /// A type like `&'a T` is WF only if `T: 'a`.
175 ReferenceOutlivesReferent(Ty<'tcx>),
177 /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
178 ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
180 /// Obligation incurred due to an object cast.
181 ObjectCastObligation(/* Object type */ Ty<'tcx>),
183 // Various cases where expressions must be sized/copy/etc:
184 /// L = X implies that L is Sized
186 /// (x1, .., xn) must be Sized
187 TupleInitializerSized,
188 /// S { ... } must be Sized
189 StructInitializerSized,
190 /// Type of each variable must be Sized
191 VariableType(hir::HirId),
192 /// Argument type must be Sized
194 /// Return type must be Sized
196 /// Yield type must be Sized
198 /// [T,..n] --> T must be Copy
201 /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
202 FieldSized { adt_kind: AdtKind, last: bool },
204 /// Constant expressions must be sized.
207 /// static items must have `Sync` type
210 BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
212 ImplDerivedObligation(DerivedObligationCause<'tcx>),
214 /// error derived when matching traits/impls; see ObligationCause for more details
215 CompareImplMethodObligation {
216 item_name: ast::Name,
217 impl_item_def_id: DefId,
218 trait_item_def_id: DefId,
221 /// Checking that this expression can be assigned where it needs to be
222 // FIXME(eddyb) #11161 is the original Expr required?
225 /// Computing common supertype in the arms of a match expression
228 source: hir::MatchSource,
229 prior_arms: Vec<Span>,
231 discrim_hir_id: hir::HirId,
234 /// Computing common supertype in the pattern guard for the arms of a match expression
235 MatchExpressionArmPattern { span: Span, ty: Ty<'tcx> },
237 /// Computing common supertype in an if expression
241 semicolon: Option<Span>,
244 /// Computing common supertype of an if expression with no else counter-part
245 IfExpressionWithNoElse,
247 /// `main` has wrong type
250 /// `start` has wrong type
253 /// intrinsic has wrong type
259 /// `return` with no expression
262 /// `return` with an expression
263 ReturnType(hir::HirId),
265 /// Block implicit return
266 BlockTailExpression(hir::HirId),
268 /// #[feature(trivial_bounds)] is not enabled
272 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
273 pub struct DerivedObligationCause<'tcx> {
274 /// The trait reference of the parent obligation that led to the
275 /// current obligation. Note that only trait obligations lead to
276 /// derived obligations, so we just store the trait reference here
278 parent_trait_ref: ty::PolyTraitRef<'tcx>,
280 /// The parent trait had this cause.
281 parent_code: Rc<ObligationCauseCode<'tcx>>
284 pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
285 pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
286 pub type TraitObligations<'tcx> = Vec<TraitObligation<'tcx>>;
288 /// The following types:
296 /// * `InEnvironment`,
297 /// are used for representing the trait system in the form of
298 /// logic programming clauses. They are part of the interface
299 /// for the chalk SLG solver.
300 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
301 pub enum WhereClause<'tcx> {
302 Implemented(ty::TraitPredicate<'tcx>),
303 ProjectionEq(ty::ProjectionPredicate<'tcx>),
304 RegionOutlives(ty::RegionOutlivesPredicate<'tcx>),
305 TypeOutlives(ty::TypeOutlivesPredicate<'tcx>),
308 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
309 pub enum WellFormed<'tcx> {
310 Trait(ty::TraitPredicate<'tcx>),
314 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
315 pub enum FromEnv<'tcx> {
316 Trait(ty::TraitPredicate<'tcx>),
320 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
321 pub enum DomainGoal<'tcx> {
322 Holds(WhereClause<'tcx>),
323 WellFormed(WellFormed<'tcx>),
324 FromEnv(FromEnv<'tcx>),
325 Normalize(ty::ProjectionPredicate<'tcx>),
328 pub type PolyDomainGoal<'tcx> = ty::Binder<DomainGoal<'tcx>>;
330 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
331 pub enum QuantifierKind {
336 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
337 pub enum GoalKind<'tcx> {
338 Implies(Clauses<'tcx>, Goal<'tcx>),
339 And(Goal<'tcx>, Goal<'tcx>),
341 DomainGoal(DomainGoal<'tcx>),
342 Quantified(QuantifierKind, ty::Binder<Goal<'tcx>>),
343 Subtype(Ty<'tcx>, Ty<'tcx>),
347 pub type Goal<'tcx> = &'tcx GoalKind<'tcx>;
349 pub type Goals<'tcx> = &'tcx List<Goal<'tcx>>;
351 impl<'tcx> DomainGoal<'tcx> {
352 pub fn into_goal(self) -> GoalKind<'tcx> {
353 GoalKind::DomainGoal(self)
356 pub fn into_program_clause(self) -> ProgramClause<'tcx> {
359 hypotheses: ty::List::empty(),
360 category: ProgramClauseCategory::Other,
365 impl<'tcx> GoalKind<'tcx> {
366 pub fn from_poly_domain_goal(
367 domain_goal: PolyDomainGoal<'tcx>,
369 ) -> GoalKind<'tcx> {
370 match domain_goal.no_bound_vars() {
371 Some(p) => p.into_goal(),
372 None => GoalKind::Quantified(
373 QuantifierKind::Universal,
374 domain_goal.map_bound(|p| tcx.mk_goal(p.into_goal()))
380 /// This matches the definition from Page 7 of "A Proof Procedure for the Logic of Hereditary
381 /// Harrop Formulas".
382 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
383 pub enum Clause<'tcx> {
384 Implies(ProgramClause<'tcx>),
385 ForAll(ty::Binder<ProgramClause<'tcx>>),
389 pub fn category(self) -> ProgramClauseCategory {
391 Clause::Implies(clause) => clause.category,
392 Clause::ForAll(clause) => clause.skip_binder().category,
397 /// Multiple clauses.
398 pub type Clauses<'tcx> = &'tcx List<Clause<'tcx>>;
400 /// A "program clause" has the form `D :- G1, ..., Gn`. It is saying
401 /// that the domain goal `D` is true if `G1...Gn` are provable. This
402 /// is equivalent to the implication `G1..Gn => D`; we usually write
403 /// it with the reverse implication operator `:-` to emphasize the way
404 /// that programs are actually solved (via backchaining, which starts
405 /// with the goal to solve and proceeds from there).
406 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
407 pub struct ProgramClause<'tcx> {
408 /// This goal will be considered true ...
409 pub goal: DomainGoal<'tcx>,
411 /// ... if we can prove these hypotheses (there may be no hypotheses at all):
412 pub hypotheses: Goals<'tcx>,
414 /// Useful for filtering clauses.
415 pub category: ProgramClauseCategory,
418 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
419 pub enum ProgramClauseCategory {
425 /// A set of clauses that we assume to be true.
426 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
427 pub struct Environment<'tcx> {
428 pub clauses: Clauses<'tcx>,
431 impl Environment<'tcx> {
432 pub fn with<G>(self, goal: G) -> InEnvironment<'tcx, G> {
440 /// Something (usually a goal), along with an environment.
441 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
442 pub struct InEnvironment<'tcx, G> {
443 pub environment: Environment<'tcx>,
447 pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
449 #[derive(Clone,Debug)]
450 pub enum SelectionError<'tcx> {
452 OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
453 ty::PolyTraitRef<'tcx>,
454 ty::error::TypeError<'tcx>),
455 TraitNotObjectSafe(DefId),
456 ConstEvalFailure(ErrorHandled),
460 EnumTypeFoldableImpl! {
461 impl<'tcx> TypeFoldable<'tcx> for SelectionError<'tcx> {
462 (SelectionError::Unimplemented),
463 (SelectionError::OutputTypeParameterMismatch)(a, b, c),
464 (SelectionError::TraitNotObjectSafe)(a),
465 (SelectionError::ConstEvalFailure)(a),
466 (SelectionError::Overflow),
470 pub struct FulfillmentError<'tcx> {
471 pub obligation: PredicateObligation<'tcx>,
472 pub code: FulfillmentErrorCode<'tcx>
476 pub enum FulfillmentErrorCode<'tcx> {
477 CodeSelectionError(SelectionError<'tcx>),
478 CodeProjectionError(MismatchedProjectionTypes<'tcx>),
479 CodeSubtypeError(ExpectedFound<Ty<'tcx>>,
480 TypeError<'tcx>), // always comes from a SubtypePredicate
484 /// When performing resolution, it is typically the case that there
485 /// can be one of three outcomes:
487 /// - `Ok(Some(r))`: success occurred with result `r`
488 /// - `Ok(None)`: could not definitely determine anything, usually due
489 /// to inconclusive type inference.
490 /// - `Err(e)`: error `e` occurred
491 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
493 /// Given the successful resolution of an obligation, the `Vtable`
494 /// indicates where the vtable comes from. Note that while we call this
495 /// a "vtable", it does not necessarily indicate dynamic dispatch at
496 /// runtime. `Vtable` instances just tell the compiler where to find
497 /// methods, but in generic code those methods are typically statically
498 /// dispatched -- only when an object is constructed is a `Vtable`
499 /// instance reified into an actual vtable.
501 /// For example, the vtable may be tied to a specific impl (case A),
502 /// or it may be relative to some bound that is in scope (case B).
505 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
506 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
507 /// impl Clone for int { ... } // Impl_3
509 /// fn foo<T:Clone>(concrete: Option<Box<int>>,
511 /// mixed: Option<T>) {
513 /// // Case A: Vtable points at a specific impl. Only possible when
514 /// // type is concretely known. If the impl itself has bounded
515 /// // type parameters, Vtable will carry resolutions for those as well:
516 /// concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
518 /// // Case B: Vtable must be provided by caller. This applies when
519 /// // type is a type parameter.
520 /// param.clone(); // VtableParam
522 /// // Case C: A mix of cases A and B.
523 /// mixed.clone(); // Vtable(Impl_1, [VtableParam])
527 /// ### The type parameter `N`
529 /// See explanation on `VtableImplData`.
530 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
531 pub enum Vtable<'tcx, N> {
532 /// Vtable identifying a particular impl.
533 VtableImpl(VtableImplData<'tcx, N>),
535 /// Vtable for auto trait implementations.
536 /// This carries the information and nested obligations with regards
537 /// to an auto implementation for a trait `Trait`. The nested obligations
538 /// ensure the trait implementation holds for all the constituent types.
539 VtableAutoImpl(VtableAutoImplData<N>),
541 /// Successful resolution to an obligation provided by the caller
542 /// for some type parameter. The `Vec<N>` represents the
543 /// obligations incurred from normalizing the where-clause (if
547 /// Virtual calls through an object.
548 VtableObject(VtableObjectData<'tcx, N>),
550 /// Successful resolution for a builtin trait.
551 VtableBuiltin(VtableBuiltinData<N>),
553 /// Vtable automatically generated for a closure. The `DefId` is the ID
554 /// of the closure expression. This is a `VtableImpl` in spirit, but the
555 /// impl is generated by the compiler and does not appear in the source.
556 VtableClosure(VtableClosureData<'tcx, N>),
558 /// Same as above, but for a function pointer type with the given signature.
559 VtableFnPointer(VtableFnPointerData<'tcx, N>),
561 /// Vtable automatically generated for a generator.
562 VtableGenerator(VtableGeneratorData<'tcx, N>),
564 /// Vtable for a trait alias.
565 VtableTraitAlias(VtableTraitAliasData<'tcx, N>),
568 /// Identifies a particular impl in the source, along with a set of
569 /// substitutions from the impl's type/lifetime parameters. The
570 /// `nested` vector corresponds to the nested obligations attached to
571 /// the impl's type parameters.
573 /// The type parameter `N` indicates the type used for "nested
574 /// obligations" that are required by the impl. During type check, this
575 /// is `Obligation`, as one might expect. During codegen, however, this
576 /// is `()`, because codegen only requires a shallow resolution of an
577 /// impl, and nested obligations are satisfied later.
578 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
579 pub struct VtableImplData<'tcx, N> {
580 pub impl_def_id: DefId,
581 pub substs: SubstsRef<'tcx>,
585 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
586 pub struct VtableGeneratorData<'tcx, N> {
587 pub generator_def_id: DefId,
588 pub substs: ty::GeneratorSubsts<'tcx>,
589 /// Nested obligations. This can be non-empty if the generator
590 /// signature contains associated types.
594 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
595 pub struct VtableClosureData<'tcx, N> {
596 pub closure_def_id: DefId,
597 pub substs: ty::ClosureSubsts<'tcx>,
598 /// Nested obligations. This can be non-empty if the closure
599 /// signature contains associated types.
603 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
604 pub struct VtableAutoImplData<N> {
605 pub trait_def_id: DefId,
609 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
610 pub struct VtableBuiltinData<N> {
614 /// A vtable for some object-safe trait `Foo` automatically derived
615 /// for the object type `Foo`.
616 #[derive(PartialEq, Eq, Clone, RustcEncodable, RustcDecodable, HashStable)]
617 pub struct VtableObjectData<'tcx, N> {
618 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
619 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
621 /// The vtable is formed by concatenating together the method lists of
622 /// the base object trait and all supertraits; this is the start of
623 /// `upcast_trait_ref`'s methods in that vtable.
624 pub vtable_base: usize,
629 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
630 pub struct VtableFnPointerData<'tcx, N> {
635 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
636 pub struct VtableTraitAliasData<'tcx, N> {
637 pub alias_def_id: DefId,
638 pub substs: SubstsRef<'tcx>,
642 /// Creates predicate obligations from the generic bounds.
643 pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
644 param_env: ty::ParamEnv<'tcx>,
645 generic_bounds: &ty::InstantiatedPredicates<'tcx>)
646 -> PredicateObligations<'tcx>
648 util::predicates_for_generics(cause, 0, param_env, generic_bounds)
651 /// Determines whether the type `ty` is known to meet `bound` and
652 /// returns true if so. Returns false if `ty` either does not meet
653 /// `bound` or is not known to meet bound (note that this is
654 /// conservative towards *no impl*, which is the opposite of the
655 /// `evaluate` methods).
656 pub fn type_known_to_meet_bound_modulo_regions<'a, 'tcx>(
657 infcx: &InferCtxt<'a, 'tcx>,
658 param_env: ty::ParamEnv<'tcx>,
663 debug!("type_known_to_meet_bound_modulo_regions(ty={:?}, bound={:?})",
665 infcx.tcx.def_path_str(def_id));
667 let trait_ref = ty::TraitRef {
669 substs: infcx.tcx.mk_substs_trait(ty, &[]),
671 let obligation = Obligation {
673 cause: ObligationCause::misc(span, hir::DUMMY_HIR_ID),
675 predicate: trait_ref.to_predicate(),
678 let result = infcx.predicate_must_hold_modulo_regions(&obligation);
679 debug!("type_known_to_meet_ty={:?} bound={} => {:?}",
680 ty, infcx.tcx.def_path_str(def_id), result);
682 if result && (ty.has_infer_types() || ty.has_closure_types()) {
683 // Because of inference "guessing", selection can sometimes claim
684 // to succeed while the success requires a guess. To ensure
685 // this function's result remains infallible, we must confirm
686 // that guess. While imperfect, I believe this is sound.
688 // The handling of regions in this area of the code is terrible,
689 // see issue #29149. We should be able to improve on this with
691 let mut fulfill_cx = FulfillmentContext::new_ignoring_regions();
693 // We can use a dummy node-id here because we won't pay any mind
694 // to region obligations that arise (there shouldn't really be any
696 let cause = ObligationCause::misc(span, hir::DUMMY_HIR_ID);
698 fulfill_cx.register_bound(infcx, param_env, ty, def_id, cause);
700 // Note: we only assume something is `Copy` if we can
701 // *definitively* show that it implements `Copy`. Otherwise,
702 // assume it is move; linear is always ok.
703 match fulfill_cx.select_all_or_error(infcx) {
705 debug!("type_known_to_meet_bound_modulo_regions: ty={:?} bound={} success",
707 infcx.tcx.def_path_str(def_id));
711 debug!("type_known_to_meet_bound_modulo_regions: ty={:?} bound={} errors={:?}",
713 infcx.tcx.def_path_str(def_id),
723 fn do_normalize_predicates<'tcx>(
725 region_context: DefId,
726 cause: ObligationCause<'tcx>,
727 elaborated_env: ty::ParamEnv<'tcx>,
728 predicates: Vec<ty::Predicate<'tcx>>,
729 ) -> Result<Vec<ty::Predicate<'tcx>>, ErrorReported> {
731 "do_normalize_predicates(predicates={:?}, region_context={:?}, cause={:?})",
736 let span = cause.span;
737 tcx.infer_ctxt().enter(|infcx| {
738 // FIXME. We should really... do something with these region
739 // obligations. But this call just continues the older
740 // behavior (i.e., doesn't cause any new bugs), and it would
741 // take some further refactoring to actually solve them. In
742 // particular, we would have to handle implied bounds
743 // properly, and that code is currently largely confined to
744 // regionck (though I made some efforts to extract it
747 // @arielby: In any case, these obligations are checked
748 // by wfcheck anyway, so I'm not sure we have to check
749 // them here too, and we will remove this function when
750 // we move over to lazy normalization *anyway*.
751 let fulfill_cx = FulfillmentContext::new_ignoring_regions();
752 let predicates = match fully_normalize(
759 Ok(predicates) => predicates,
761 infcx.report_fulfillment_errors(&errors, None, false);
762 return Err(ErrorReported)
766 debug!("do_normalize_predictes: normalized predicates = {:?}", predicates);
768 let region_scope_tree = region::ScopeTree::default();
770 // We can use the `elaborated_env` here; the region code only
771 // cares about declarations like `'a: 'b`.
772 let outlives_env = OutlivesEnvironment::new(elaborated_env);
774 infcx.resolve_regions_and_report_errors(
778 SuppressRegionErrors::default(),
781 let predicates = match infcx.fully_resolve(&predicates) {
782 Ok(predicates) => predicates,
784 // If we encounter a fixup error, it means that some type
785 // variable wound up unconstrained. I actually don't know
786 // if this can happen, and I certainly don't expect it to
787 // happen often, but if it did happen it probably
788 // represents a legitimate failure due to some kind of
789 // unconstrained variable, and it seems better not to ICE,
790 // all things considered.
791 tcx.sess.span_err(span, &fixup_err.to_string());
792 return Err(ErrorReported)
795 if predicates.has_local_value() {
796 // FIXME: shouldn't we, you know, actually report an error here? or an ICE?
804 // FIXME: this is gonna need to be removed ...
805 /// Normalizes the parameter environment, reporting errors if they occur.
806 pub fn normalize_param_env_or_error<'tcx>(
808 region_context: DefId,
809 unnormalized_env: ty::ParamEnv<'tcx>,
810 cause: ObligationCause<'tcx>,
811 ) -> ty::ParamEnv<'tcx> {
812 // I'm not wild about reporting errors here; I'd prefer to
813 // have the errors get reported at a defined place (e.g.,
814 // during typeck). Instead I have all parameter
815 // environments, in effect, going through this function
816 // and hence potentially reporting errors. This ensures of
817 // course that we never forget to normalize (the
818 // alternative seemed like it would involve a lot of
819 // manual invocations of this fn -- and then we'd have to
820 // deal with the errors at each of those sites).
822 // In any case, in practice, typeck constructs all the
823 // parameter environments once for every fn as it goes,
824 // and errors will get reported then; so after typeck we
825 // can be sure that no errors should occur.
827 debug!("normalize_param_env_or_error(region_context={:?}, unnormalized_env={:?}, cause={:?})",
828 region_context, unnormalized_env, cause);
830 let mut predicates: Vec<_> =
831 util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec())
834 debug!("normalize_param_env_or_error: elaborated-predicates={:?}",
837 let elaborated_env = ty::ParamEnv::new(
838 tcx.intern_predicates(&predicates),
839 unnormalized_env.reveal,
840 unnormalized_env.def_id
843 // HACK: we are trying to normalize the param-env inside *itself*. The problem is that
844 // normalization expects its param-env to be already normalized, which means we have
847 // The way we handle this is by normalizing the param-env inside an unnormalized version
848 // of the param-env, which means that if the param-env contains unnormalized projections,
849 // we'll have some normalization failures. This is unfortunate.
851 // Lazy normalization would basically handle this by treating just the
852 // normalizing-a-trait-ref-requires-itself cycles as evaluation failures.
854 // Inferred outlives bounds can create a lot of `TypeOutlives` predicates for associated
855 // types, so to make the situation less bad, we normalize all the predicates *but*
856 // the `TypeOutlives` predicates first inside the unnormalized parameter environment, and
857 // then we normalize the `TypeOutlives` bounds inside the normalized parameter environment.
859 // This works fairly well because trait matching does not actually care about param-env
860 // TypeOutlives predicates - these are normally used by regionck.
861 let outlives_predicates: Vec<_> = predicates.drain_filter(|predicate| {
863 ty::Predicate::TypeOutlives(..) => true,
868 debug!("normalize_param_env_or_error: predicates=(non-outlives={:?}, outlives={:?})",
869 predicates, outlives_predicates);
870 let non_outlives_predicates =
871 match do_normalize_predicates(tcx, region_context, cause.clone(),
872 elaborated_env, predicates) {
873 Ok(predicates) => predicates,
874 // An unnormalized env is better than nothing.
875 Err(ErrorReported) => {
876 debug!("normalize_param_env_or_error: errored resolving non-outlives predicates");
877 return elaborated_env
881 debug!("normalize_param_env_or_error: non-outlives predicates={:?}", non_outlives_predicates);
883 // Not sure whether it is better to include the unnormalized TypeOutlives predicates
884 // here. I believe they should not matter, because we are ignoring TypeOutlives param-env
885 // predicates here anyway. Keeping them here anyway because it seems safer.
886 let outlives_env: Vec<_> =
887 non_outlives_predicates.iter().chain(&outlives_predicates).cloned().collect();
888 let outlives_env = ty::ParamEnv::new(
889 tcx.intern_predicates(&outlives_env),
890 unnormalized_env.reveal,
893 let outlives_predicates =
894 match do_normalize_predicates(tcx, region_context, cause,
895 outlives_env, outlives_predicates) {
896 Ok(predicates) => predicates,
897 // An unnormalized env is better than nothing.
898 Err(ErrorReported) => {
899 debug!("normalize_param_env_or_error: errored resolving outlives predicates");
900 return elaborated_env
903 debug!("normalize_param_env_or_error: outlives predicates={:?}", outlives_predicates);
905 let mut predicates = non_outlives_predicates;
906 predicates.extend(outlives_predicates);
907 debug!("normalize_param_env_or_error: final predicates={:?}", predicates);
909 tcx.intern_predicates(&predicates),
910 unnormalized_env.reveal,
911 unnormalized_env.def_id
915 pub fn fully_normalize<'a, 'tcx, T>(
916 infcx: &InferCtxt<'a, 'tcx>,
917 mut fulfill_cx: FulfillmentContext<'tcx>,
918 cause: ObligationCause<'tcx>,
919 param_env: ty::ParamEnv<'tcx>,
921 ) -> Result<T, Vec<FulfillmentError<'tcx>>>
923 T: TypeFoldable<'tcx>,
925 debug!("fully_normalize_with_fulfillcx(value={:?})", value);
926 let selcx = &mut SelectionContext::new(infcx);
927 let Normalized { value: normalized_value, obligations } =
928 project::normalize(selcx, param_env, cause, value);
929 debug!("fully_normalize: normalized_value={:?} obligations={:?}",
932 for obligation in obligations {
933 fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
936 debug!("fully_normalize: select_all_or_error start");
937 fulfill_cx.select_all_or_error(infcx)?;
938 debug!("fully_normalize: select_all_or_error complete");
939 let resolved_value = infcx.resolve_vars_if_possible(&normalized_value);
940 debug!("fully_normalize: resolved_value={:?}", resolved_value);
944 /// Normalizes the predicates and checks whether they hold in an empty
945 /// environment. If this returns false, then either normalize
946 /// encountered an error or one of the predicates did not hold. Used
947 /// when creating vtables to check for unsatisfiable methods.
948 fn normalize_and_test_predicates<'tcx>(
950 predicates: Vec<ty::Predicate<'tcx>>,
952 debug!("normalize_and_test_predicates(predicates={:?})",
955 let result = tcx.infer_ctxt().enter(|infcx| {
956 let param_env = ty::ParamEnv::reveal_all();
957 let mut selcx = SelectionContext::new(&infcx);
958 let mut fulfill_cx = FulfillmentContext::new();
959 let cause = ObligationCause::dummy();
960 let Normalized { value: predicates, obligations } =
961 normalize(&mut selcx, param_env, cause.clone(), &predicates);
962 for obligation in obligations {
963 fulfill_cx.register_predicate_obligation(&infcx, obligation);
965 for predicate in predicates {
966 let obligation = Obligation::new(cause.clone(), param_env, predicate);
967 fulfill_cx.register_predicate_obligation(&infcx, obligation);
970 fulfill_cx.select_all_or_error(&infcx).is_ok()
972 debug!("normalize_and_test_predicates(predicates={:?}) = {:?}",
977 fn substitute_normalize_and_test_predicates<'tcx>(
979 key: (DefId, SubstsRef<'tcx>),
981 debug!("substitute_normalize_and_test_predicates(key={:?})",
984 let predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates;
985 let result = normalize_and_test_predicates(tcx, predicates);
987 debug!("substitute_normalize_and_test_predicates(key={:?}) = {:?}",
992 /// Given a trait `trait_ref`, iterates the vtable entries
993 /// that come from `trait_ref`, including its supertraits.
994 #[inline] // FIXME(#35870): avoid closures being unexported due to `impl Trait`.
995 fn vtable_methods<'tcx>(
997 trait_ref: ty::PolyTraitRef<'tcx>,
998 ) -> &'tcx [Option<(DefId, SubstsRef<'tcx>)>] {
999 debug!("vtable_methods({:?})", trait_ref);
1001 tcx.arena.alloc_from_iter(
1002 supertraits(tcx, trait_ref).flat_map(move |trait_ref| {
1003 let trait_methods = tcx.associated_items(trait_ref.def_id())
1004 .filter(|item| item.kind == ty::AssocKind::Method);
1006 // Now list each method's DefId and InternalSubsts (for within its trait).
1007 // If the method can never be called from this object, produce None.
1008 trait_methods.map(move |trait_method| {
1009 debug!("vtable_methods: trait_method={:?}", trait_method);
1010 let def_id = trait_method.def_id;
1012 // Some methods cannot be called on an object; skip those.
1013 if !tcx.is_vtable_safe_method(trait_ref.def_id(), &trait_method) {
1014 debug!("vtable_methods: not vtable safe");
1018 // the method may have some early-bound lifetimes, add
1019 // regions for those
1020 let substs = trait_ref.map_bound(|trait_ref|
1021 InternalSubsts::for_item(tcx, def_id, |param, _|
1023 GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
1024 GenericParamDefKind::Type { .. } |
1025 GenericParamDefKind::Const => {
1026 trait_ref.substs[param.index as usize]
1032 // the trait type may have higher-ranked lifetimes in it;
1033 // so erase them if they appear, so that we get the type
1034 // at some particular call site
1035 let substs = tcx.normalize_erasing_late_bound_regions(
1036 ty::ParamEnv::reveal_all(),
1040 // It's possible that the method relies on where clauses that
1041 // do not hold for this particular set of type parameters.
1042 // Note that this method could then never be called, so we
1043 // do not want to try and codegen it, in that case (see #23435).
1044 let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
1045 if !normalize_and_test_predicates(tcx, predicates.predicates) {
1046 debug!("vtable_methods: predicates do not hold");
1050 Some((def_id, substs))
1056 impl<'tcx, O> Obligation<'tcx, O> {
1057 pub fn new(cause: ObligationCause<'tcx>,
1058 param_env: ty::ParamEnv<'tcx>,
1060 -> Obligation<'tcx, O>
1062 Obligation { cause, param_env, recursion_depth: 0, predicate }
1065 fn with_depth(cause: ObligationCause<'tcx>,
1066 recursion_depth: usize,
1067 param_env: ty::ParamEnv<'tcx>,
1069 -> Obligation<'tcx, O>
1071 Obligation { cause, param_env, recursion_depth, predicate }
1074 pub fn misc(span: Span,
1075 body_id: hir::HirId,
1076 param_env: ty::ParamEnv<'tcx>,
1078 -> Obligation<'tcx, O> {
1079 Obligation::new(ObligationCause::misc(span, body_id), param_env, trait_ref)
1082 pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
1083 Obligation { cause: self.cause.clone(),
1084 param_env: self.param_env,
1085 recursion_depth: self.recursion_depth,
1090 impl<'tcx> ObligationCause<'tcx> {
1092 pub fn new(span: Span,
1093 body_id: hir::HirId,
1094 code: ObligationCauseCode<'tcx>)
1095 -> ObligationCause<'tcx> {
1096 ObligationCause { span, body_id, code }
1099 pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> {
1100 ObligationCause { span, body_id, code: MiscObligation }
1103 pub fn dummy() -> ObligationCause<'tcx> {
1104 ObligationCause { span: DUMMY_SP, body_id: hir::CRATE_HIR_ID, code: MiscObligation }
1108 impl<'tcx, N> Vtable<'tcx, N> {
1109 pub fn nested_obligations(self) -> Vec<N> {
1111 VtableImpl(i) => i.nested,
1112 VtableParam(n) => n,
1113 VtableBuiltin(i) => i.nested,
1114 VtableAutoImpl(d) => d.nested,
1115 VtableClosure(c) => c.nested,
1116 VtableGenerator(c) => c.nested,
1117 VtableObject(d) => d.nested,
1118 VtableFnPointer(d) => d.nested,
1119 VtableTraitAlias(d) => d.nested,
1123 pub fn map<M, F>(self, f: F) -> Vtable<'tcx, M> where F: FnMut(N) -> M {
1125 VtableImpl(i) => VtableImpl(VtableImplData {
1126 impl_def_id: i.impl_def_id,
1128 nested: i.nested.into_iter().map(f).collect(),
1130 VtableParam(n) => VtableParam(n.into_iter().map(f).collect()),
1131 VtableBuiltin(i) => VtableBuiltin(VtableBuiltinData {
1132 nested: i.nested.into_iter().map(f).collect(),
1134 VtableObject(o) => VtableObject(VtableObjectData {
1135 upcast_trait_ref: o.upcast_trait_ref,
1136 vtable_base: o.vtable_base,
1137 nested: o.nested.into_iter().map(f).collect(),
1139 VtableAutoImpl(d) => VtableAutoImpl(VtableAutoImplData {
1140 trait_def_id: d.trait_def_id,
1141 nested: d.nested.into_iter().map(f).collect(),
1143 VtableClosure(c) => VtableClosure(VtableClosureData {
1144 closure_def_id: c.closure_def_id,
1146 nested: c.nested.into_iter().map(f).collect(),
1148 VtableGenerator(c) => VtableGenerator(VtableGeneratorData {
1149 generator_def_id: c.generator_def_id,
1151 nested: c.nested.into_iter().map(f).collect(),
1153 VtableFnPointer(p) => VtableFnPointer(VtableFnPointerData {
1155 nested: p.nested.into_iter().map(f).collect(),
1157 VtableTraitAlias(d) => VtableTraitAlias(VtableTraitAliasData {
1158 alias_def_id: d.alias_def_id,
1160 nested: d.nested.into_iter().map(f).collect(),
1166 impl<'tcx> FulfillmentError<'tcx> {
1167 fn new(obligation: PredicateObligation<'tcx>,
1168 code: FulfillmentErrorCode<'tcx>)
1169 -> FulfillmentError<'tcx>
1171 FulfillmentError { obligation: obligation, code: code }
1175 impl<'tcx> TraitObligation<'tcx> {
1176 fn self_ty(&self) -> ty::Binder<Ty<'tcx>> {
1177 self.predicate.map_bound(|p| p.self_ty())
1181 pub fn provide(providers: &mut ty::query::Providers<'_>) {
1182 *providers = ty::query::Providers {
1183 is_object_safe: object_safety::is_object_safe_provider,
1184 specialization_graph_of: specialize::specialization_graph_provider,
1185 specializes: specialize::specializes,
1186 codegen_fulfill_obligation: codegen::codegen_fulfill_obligation,
1188 substitute_normalize_and_test_predicates,
1193 pub trait ExClauseFold<'tcx>
1195 Self: chalk_engine::context::Context + Clone,
1197 fn fold_ex_clause_with<F: TypeFolder<'tcx>>(
1198 ex_clause: &chalk_engine::ExClause<Self>,
1200 ) -> chalk_engine::ExClause<Self>;
1202 fn visit_ex_clause_with<V: TypeVisitor<'tcx>>(
1203 ex_clause: &chalk_engine::ExClause<Self>,
1208 pub trait ChalkContextLift<'tcx>
1210 Self: chalk_engine::context::Context + Clone,
1212 type LiftedExClause: Debug + 'tcx;
1213 type LiftedDelayedLiteral: Debug + 'tcx;
1214 type LiftedLiteral: Debug + 'tcx;
1216 fn lift_ex_clause_to_tcx(
1217 ex_clause: &chalk_engine::ExClause<Self>,
1219 ) -> Option<Self::LiftedExClause>;
1221 fn lift_delayed_literal_to_tcx(
1222 ex_clause: &chalk_engine::DelayedLiteral<Self>,
1224 ) -> Option<Self::LiftedDelayedLiteral>;
1226 fn lift_literal_to_tcx(
1227 ex_clause: &chalk_engine::Literal<Self>,
1229 ) -> Option<Self::LiftedLiteral>;