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 // `PredicateObligation` is used a lot. Make sure it doesn't unintentionally get bigger.
127 #[cfg(target_arch = "x86_64")]
128 static_assert_size!(PredicateObligation<'_>, 120);
130 /// The reason why we incurred this obligation; used for error reporting.
131 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
132 pub struct ObligationCause<'tcx> {
135 /// The ID of the fn body that triggered this obligation. This is
136 /// used for region obligations to determine the precise
137 /// environment in which the region obligation should be evaluated
138 /// (in particular, closures can add new assumptions). See the
139 /// field `region_obligations` of the `FulfillmentContext` for more
141 pub body_id: hir::HirId,
143 pub code: ObligationCauseCode<'tcx>
146 impl<'tcx> ObligationCause<'tcx> {
147 pub fn span(&self, tcx: TyCtxt<'tcx>) -> Span {
149 ObligationCauseCode::CompareImplMethodObligation { .. } |
150 ObligationCauseCode::MainFunctionType |
151 ObligationCauseCode::StartFunctionType => {
152 tcx.sess.source_map().def_span(self.span)
154 ObligationCauseCode::MatchExpressionArm(
155 box MatchExpressionArmCause { arm_span, .. }) => arm_span,
161 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
162 pub enum ObligationCauseCode<'tcx> {
163 /// Not well classified or should be obvious from the span.
166 /// A slice or array is WF only if `T: Sized`.
169 /// A tuple is WF only if its middle elements are `Sized`.
172 /// This is the trait reference from the given projection.
173 ProjectionWf(ty::ProjectionTy<'tcx>),
175 /// In an impl of trait `X` for type `Y`, type `Y` must
176 /// also implement all supertraits of `X`.
177 ItemObligation(DefId),
179 /// A type like `&'a T` is WF only if `T: 'a`.
180 ReferenceOutlivesReferent(Ty<'tcx>),
182 /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
183 ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
185 /// Obligation incurred due to an object cast.
186 ObjectCastObligation(/* Object type */ Ty<'tcx>),
188 // Various cases where expressions must be sized/copy/etc:
189 /// L = X implies that L is Sized
191 /// (x1, .., xn) must be Sized
192 TupleInitializerSized,
193 /// S { ... } must be Sized
194 StructInitializerSized,
195 /// Type of each variable must be Sized
196 VariableType(hir::HirId),
197 /// Argument type must be Sized
199 /// Return type must be Sized
201 /// Yield type must be Sized
203 /// [T,..n] --> T must be Copy
206 /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
207 FieldSized { adt_kind: AdtKind, last: bool },
209 /// Constant expressions must be sized.
212 /// static items must have `Sync` type
215 BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
217 ImplDerivedObligation(DerivedObligationCause<'tcx>),
219 /// error derived when matching traits/impls; see ObligationCause for more details
220 CompareImplMethodObligation {
221 item_name: ast::Name,
222 impl_item_def_id: DefId,
223 trait_item_def_id: DefId,
226 /// Checking that this expression can be assigned where it needs to be
227 // FIXME(eddyb) #11161 is the original Expr required?
230 /// Computing common supertype in the arms of a match expression
231 MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>),
233 /// Computing common supertype in the pattern guard for the arms of a match expression
234 MatchExpressionArmPattern { span: Span, ty: Ty<'tcx> },
236 /// Computing common supertype in an if expression
240 semicolon: Option<Span>,
243 /// Computing common supertype of an if expression with no else counter-part
244 IfExpressionWithNoElse,
246 /// `main` has wrong type
249 /// `start` has wrong type
252 /// intrinsic has wrong type
258 /// `return` with no expression
261 /// `return` with an expression
262 ReturnType(hir::HirId),
264 /// Block implicit return
265 BlockTailExpression(hir::HirId),
267 /// #[feature(trivial_bounds)] is not enabled
271 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
272 #[cfg(target_arch = "x86_64")]
273 static_assert_size!(ObligationCauseCode<'_>, 40);
275 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
276 pub struct MatchExpressionArmCause<'tcx> {
278 pub source: hir::MatchSource,
279 pub prior_arms: Vec<Span>,
280 pub last_ty: Ty<'tcx>,
281 pub discrim_hir_id: hir::HirId,
284 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
285 pub struct DerivedObligationCause<'tcx> {
286 /// The trait reference of the parent obligation that led to the
287 /// current obligation. Note that only trait obligations lead to
288 /// derived obligations, so we just store the trait reference here
290 parent_trait_ref: ty::PolyTraitRef<'tcx>,
292 /// The parent trait had this cause.
293 parent_code: Rc<ObligationCauseCode<'tcx>>
296 pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
297 pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
298 pub type TraitObligations<'tcx> = Vec<TraitObligation<'tcx>>;
300 /// The following types:
308 /// * `InEnvironment`,
309 /// are used for representing the trait system in the form of
310 /// logic programming clauses. They are part of the interface
311 /// for the chalk SLG solver.
312 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
313 pub enum WhereClause<'tcx> {
314 Implemented(ty::TraitPredicate<'tcx>),
315 ProjectionEq(ty::ProjectionPredicate<'tcx>),
316 RegionOutlives(ty::RegionOutlivesPredicate<'tcx>),
317 TypeOutlives(ty::TypeOutlivesPredicate<'tcx>),
320 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
321 pub enum WellFormed<'tcx> {
322 Trait(ty::TraitPredicate<'tcx>),
326 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
327 pub enum FromEnv<'tcx> {
328 Trait(ty::TraitPredicate<'tcx>),
332 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
333 pub enum DomainGoal<'tcx> {
334 Holds(WhereClause<'tcx>),
335 WellFormed(WellFormed<'tcx>),
336 FromEnv(FromEnv<'tcx>),
337 Normalize(ty::ProjectionPredicate<'tcx>),
340 pub type PolyDomainGoal<'tcx> = ty::Binder<DomainGoal<'tcx>>;
342 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
343 pub enum QuantifierKind {
348 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
349 pub enum GoalKind<'tcx> {
350 Implies(Clauses<'tcx>, Goal<'tcx>),
351 And(Goal<'tcx>, Goal<'tcx>),
353 DomainGoal(DomainGoal<'tcx>),
354 Quantified(QuantifierKind, ty::Binder<Goal<'tcx>>),
355 Subtype(Ty<'tcx>, Ty<'tcx>),
359 pub type Goal<'tcx> = &'tcx GoalKind<'tcx>;
361 pub type Goals<'tcx> = &'tcx List<Goal<'tcx>>;
363 impl<'tcx> DomainGoal<'tcx> {
364 pub fn into_goal(self) -> GoalKind<'tcx> {
365 GoalKind::DomainGoal(self)
368 pub fn into_program_clause(self) -> ProgramClause<'tcx> {
371 hypotheses: ty::List::empty(),
372 category: ProgramClauseCategory::Other,
377 impl<'tcx> GoalKind<'tcx> {
378 pub fn from_poly_domain_goal(
379 domain_goal: PolyDomainGoal<'tcx>,
381 ) -> GoalKind<'tcx> {
382 match domain_goal.no_bound_vars() {
383 Some(p) => p.into_goal(),
384 None => GoalKind::Quantified(
385 QuantifierKind::Universal,
386 domain_goal.map_bound(|p| tcx.mk_goal(p.into_goal()))
392 /// This matches the definition from Page 7 of "A Proof Procedure for the Logic of Hereditary
393 /// Harrop Formulas".
394 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
395 pub enum Clause<'tcx> {
396 Implies(ProgramClause<'tcx>),
397 ForAll(ty::Binder<ProgramClause<'tcx>>),
401 pub fn category(self) -> ProgramClauseCategory {
403 Clause::Implies(clause) => clause.category,
404 Clause::ForAll(clause) => clause.skip_binder().category,
409 /// Multiple clauses.
410 pub type Clauses<'tcx> = &'tcx List<Clause<'tcx>>;
412 /// A "program clause" has the form `D :- G1, ..., Gn`. It is saying
413 /// that the domain goal `D` is true if `G1...Gn` are provable. This
414 /// is equivalent to the implication `G1..Gn => D`; we usually write
415 /// it with the reverse implication operator `:-` to emphasize the way
416 /// that programs are actually solved (via backchaining, which starts
417 /// with the goal to solve and proceeds from there).
418 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
419 pub struct ProgramClause<'tcx> {
420 /// This goal will be considered true ...
421 pub goal: DomainGoal<'tcx>,
423 /// ... if we can prove these hypotheses (there may be no hypotheses at all):
424 pub hypotheses: Goals<'tcx>,
426 /// Useful for filtering clauses.
427 pub category: ProgramClauseCategory,
430 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
431 pub enum ProgramClauseCategory {
437 /// A set of clauses that we assume to be true.
438 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
439 pub struct Environment<'tcx> {
440 pub clauses: Clauses<'tcx>,
443 impl Environment<'tcx> {
444 pub fn with<G>(self, goal: G) -> InEnvironment<'tcx, G> {
452 /// Something (usually a goal), along with an environment.
453 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
454 pub struct InEnvironment<'tcx, G> {
455 pub environment: Environment<'tcx>,
459 pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
461 #[derive(Clone,Debug)]
462 pub enum SelectionError<'tcx> {
464 OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
465 ty::PolyTraitRef<'tcx>,
466 ty::error::TypeError<'tcx>),
467 TraitNotObjectSafe(DefId),
468 ConstEvalFailure(ErrorHandled),
472 EnumTypeFoldableImpl! {
473 impl<'tcx> TypeFoldable<'tcx> for SelectionError<'tcx> {
474 (SelectionError::Unimplemented),
475 (SelectionError::OutputTypeParameterMismatch)(a, b, c),
476 (SelectionError::TraitNotObjectSafe)(a),
477 (SelectionError::ConstEvalFailure)(a),
478 (SelectionError::Overflow),
482 pub struct FulfillmentError<'tcx> {
483 pub obligation: PredicateObligation<'tcx>,
484 pub code: FulfillmentErrorCode<'tcx>
488 pub enum FulfillmentErrorCode<'tcx> {
489 CodeSelectionError(SelectionError<'tcx>),
490 CodeProjectionError(MismatchedProjectionTypes<'tcx>),
491 CodeSubtypeError(ExpectedFound<Ty<'tcx>>,
492 TypeError<'tcx>), // always comes from a SubtypePredicate
496 /// When performing resolution, it is typically the case that there
497 /// can be one of three outcomes:
499 /// - `Ok(Some(r))`: success occurred with result `r`
500 /// - `Ok(None)`: could not definitely determine anything, usually due
501 /// to inconclusive type inference.
502 /// - `Err(e)`: error `e` occurred
503 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
505 /// Given the successful resolution of an obligation, the `Vtable`
506 /// indicates where the vtable comes from. Note that while we call this
507 /// a "vtable", it does not necessarily indicate dynamic dispatch at
508 /// runtime. `Vtable` instances just tell the compiler where to find
509 /// methods, but in generic code those methods are typically statically
510 /// dispatched -- only when an object is constructed is a `Vtable`
511 /// instance reified into an actual vtable.
513 /// For example, the vtable may be tied to a specific impl (case A),
514 /// or it may be relative to some bound that is in scope (case B).
517 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
518 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
519 /// impl Clone for int { ... } // Impl_3
521 /// fn foo<T:Clone>(concrete: Option<Box<int>>,
523 /// mixed: Option<T>) {
525 /// // Case A: Vtable points at a specific impl. Only possible when
526 /// // type is concretely known. If the impl itself has bounded
527 /// // type parameters, Vtable will carry resolutions for those as well:
528 /// concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
530 /// // Case B: Vtable must be provided by caller. This applies when
531 /// // type is a type parameter.
532 /// param.clone(); // VtableParam
534 /// // Case C: A mix of cases A and B.
535 /// mixed.clone(); // Vtable(Impl_1, [VtableParam])
539 /// ### The type parameter `N`
541 /// See explanation on `VtableImplData`.
542 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
543 pub enum Vtable<'tcx, N> {
544 /// Vtable identifying a particular impl.
545 VtableImpl(VtableImplData<'tcx, N>),
547 /// Vtable for auto trait implementations.
548 /// This carries the information and nested obligations with regards
549 /// to an auto implementation for a trait `Trait`. The nested obligations
550 /// ensure the trait implementation holds for all the constituent types.
551 VtableAutoImpl(VtableAutoImplData<N>),
553 /// Successful resolution to an obligation provided by the caller
554 /// for some type parameter. The `Vec<N>` represents the
555 /// obligations incurred from normalizing the where-clause (if
559 /// Virtual calls through an object.
560 VtableObject(VtableObjectData<'tcx, N>),
562 /// Successful resolution for a builtin trait.
563 VtableBuiltin(VtableBuiltinData<N>),
565 /// Vtable automatically generated for a closure. The `DefId` is the ID
566 /// of the closure expression. This is a `VtableImpl` in spirit, but the
567 /// impl is generated by the compiler and does not appear in the source.
568 VtableClosure(VtableClosureData<'tcx, N>),
570 /// Same as above, but for a function pointer type with the given signature.
571 VtableFnPointer(VtableFnPointerData<'tcx, N>),
573 /// Vtable automatically generated for a generator.
574 VtableGenerator(VtableGeneratorData<'tcx, N>),
576 /// Vtable for a trait alias.
577 VtableTraitAlias(VtableTraitAliasData<'tcx, N>),
580 /// Identifies a particular impl in the source, along with a set of
581 /// substitutions from the impl's type/lifetime parameters. The
582 /// `nested` vector corresponds to the nested obligations attached to
583 /// the impl's type parameters.
585 /// The type parameter `N` indicates the type used for "nested
586 /// obligations" that are required by the impl. During type check, this
587 /// is `Obligation`, as one might expect. During codegen, however, this
588 /// is `()`, because codegen only requires a shallow resolution of an
589 /// impl, and nested obligations are satisfied later.
590 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
591 pub struct VtableImplData<'tcx, N> {
592 pub impl_def_id: DefId,
593 pub substs: SubstsRef<'tcx>,
597 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
598 pub struct VtableGeneratorData<'tcx, N> {
599 pub generator_def_id: DefId,
600 pub substs: ty::GeneratorSubsts<'tcx>,
601 /// Nested obligations. This can be non-empty if the generator
602 /// signature contains associated types.
606 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
607 pub struct VtableClosureData<'tcx, N> {
608 pub closure_def_id: DefId,
609 pub substs: ty::ClosureSubsts<'tcx>,
610 /// Nested obligations. This can be non-empty if the closure
611 /// signature contains associated types.
615 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
616 pub struct VtableAutoImplData<N> {
617 pub trait_def_id: DefId,
621 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
622 pub struct VtableBuiltinData<N> {
626 /// A vtable for some object-safe trait `Foo` automatically derived
627 /// for the object type `Foo`.
628 #[derive(PartialEq, Eq, Clone, RustcEncodable, RustcDecodable, HashStable)]
629 pub struct VtableObjectData<'tcx, N> {
630 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
631 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
633 /// The vtable is formed by concatenating together the method lists of
634 /// the base object trait and all supertraits; this is the start of
635 /// `upcast_trait_ref`'s methods in that vtable.
636 pub vtable_base: usize,
641 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
642 pub struct VtableFnPointerData<'tcx, N> {
647 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
648 pub struct VtableTraitAliasData<'tcx, N> {
649 pub alias_def_id: DefId,
650 pub substs: SubstsRef<'tcx>,
654 /// Creates predicate obligations from the generic bounds.
655 pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
656 param_env: ty::ParamEnv<'tcx>,
657 generic_bounds: &ty::InstantiatedPredicates<'tcx>)
658 -> PredicateObligations<'tcx>
660 util::predicates_for_generics(cause, 0, param_env, generic_bounds)
663 /// Determines whether the type `ty` is known to meet `bound` and
664 /// returns true if so. Returns false if `ty` either does not meet
665 /// `bound` or is not known to meet bound (note that this is
666 /// conservative towards *no impl*, which is the opposite of the
667 /// `evaluate` methods).
668 pub fn type_known_to_meet_bound_modulo_regions<'a, 'tcx>(
669 infcx: &InferCtxt<'a, 'tcx>,
670 param_env: ty::ParamEnv<'tcx>,
675 debug!("type_known_to_meet_bound_modulo_regions(ty={:?}, bound={:?})",
677 infcx.tcx.def_path_str(def_id));
679 let trait_ref = ty::TraitRef {
681 substs: infcx.tcx.mk_substs_trait(ty, &[]),
683 let obligation = Obligation {
685 cause: ObligationCause::misc(span, hir::DUMMY_HIR_ID),
687 predicate: trait_ref.to_predicate(),
690 let result = infcx.predicate_must_hold_modulo_regions(&obligation);
691 debug!("type_known_to_meet_ty={:?} bound={} => {:?}",
692 ty, infcx.tcx.def_path_str(def_id), result);
694 if result && (ty.has_infer_types() || ty.has_closure_types()) {
695 // Because of inference "guessing", selection can sometimes claim
696 // to succeed while the success requires a guess. To ensure
697 // this function's result remains infallible, we must confirm
698 // that guess. While imperfect, I believe this is sound.
700 // The handling of regions in this area of the code is terrible,
701 // see issue #29149. We should be able to improve on this with
703 let mut fulfill_cx = FulfillmentContext::new_ignoring_regions();
705 // We can use a dummy node-id here because we won't pay any mind
706 // to region obligations that arise (there shouldn't really be any
708 let cause = ObligationCause::misc(span, hir::DUMMY_HIR_ID);
710 fulfill_cx.register_bound(infcx, param_env, ty, def_id, cause);
712 // Note: we only assume something is `Copy` if we can
713 // *definitively* show that it implements `Copy`. Otherwise,
714 // assume it is move; linear is always ok.
715 match fulfill_cx.select_all_or_error(infcx) {
717 debug!("type_known_to_meet_bound_modulo_regions: ty={:?} bound={} success",
719 infcx.tcx.def_path_str(def_id));
723 debug!("type_known_to_meet_bound_modulo_regions: ty={:?} bound={} errors={:?}",
725 infcx.tcx.def_path_str(def_id),
735 fn do_normalize_predicates<'tcx>(
737 region_context: DefId,
738 cause: ObligationCause<'tcx>,
739 elaborated_env: ty::ParamEnv<'tcx>,
740 predicates: Vec<ty::Predicate<'tcx>>,
741 ) -> Result<Vec<ty::Predicate<'tcx>>, ErrorReported> {
743 "do_normalize_predicates(predicates={:?}, region_context={:?}, cause={:?})",
748 let span = cause.span;
749 tcx.infer_ctxt().enter(|infcx| {
750 // FIXME. We should really... do something with these region
751 // obligations. But this call just continues the older
752 // behavior (i.e., doesn't cause any new bugs), and it would
753 // take some further refactoring to actually solve them. In
754 // particular, we would have to handle implied bounds
755 // properly, and that code is currently largely confined to
756 // regionck (though I made some efforts to extract it
759 // @arielby: In any case, these obligations are checked
760 // by wfcheck anyway, so I'm not sure we have to check
761 // them here too, and we will remove this function when
762 // we move over to lazy normalization *anyway*.
763 let fulfill_cx = FulfillmentContext::new_ignoring_regions();
764 let predicates = match fully_normalize(
771 Ok(predicates) => predicates,
773 infcx.report_fulfillment_errors(&errors, None, false);
774 return Err(ErrorReported)
778 debug!("do_normalize_predictes: normalized predicates = {:?}", predicates);
780 let region_scope_tree = region::ScopeTree::default();
782 // We can use the `elaborated_env` here; the region code only
783 // cares about declarations like `'a: 'b`.
784 let outlives_env = OutlivesEnvironment::new(elaborated_env);
786 infcx.resolve_regions_and_report_errors(
790 SuppressRegionErrors::default(),
793 let predicates = match infcx.fully_resolve(&predicates) {
794 Ok(predicates) => predicates,
796 // If we encounter a fixup error, it means that some type
797 // variable wound up unconstrained. I actually don't know
798 // if this can happen, and I certainly don't expect it to
799 // happen often, but if it did happen it probably
800 // represents a legitimate failure due to some kind of
801 // unconstrained variable, and it seems better not to ICE,
802 // all things considered.
803 tcx.sess.span_err(span, &fixup_err.to_string());
804 return Err(ErrorReported)
807 if predicates.has_local_value() {
808 // FIXME: shouldn't we, you know, actually report an error here? or an ICE?
816 // FIXME: this is gonna need to be removed ...
817 /// Normalizes the parameter environment, reporting errors if they occur.
818 pub fn normalize_param_env_or_error<'tcx>(
820 region_context: DefId,
821 unnormalized_env: ty::ParamEnv<'tcx>,
822 cause: ObligationCause<'tcx>,
823 ) -> ty::ParamEnv<'tcx> {
824 // I'm not wild about reporting errors here; I'd prefer to
825 // have the errors get reported at a defined place (e.g.,
826 // during typeck). Instead I have all parameter
827 // environments, in effect, going through this function
828 // and hence potentially reporting errors. This ensures of
829 // course that we never forget to normalize (the
830 // alternative seemed like it would involve a lot of
831 // manual invocations of this fn -- and then we'd have to
832 // deal with the errors at each of those sites).
834 // In any case, in practice, typeck constructs all the
835 // parameter environments once for every fn as it goes,
836 // and errors will get reported then; so after typeck we
837 // can be sure that no errors should occur.
839 debug!("normalize_param_env_or_error(region_context={:?}, unnormalized_env={:?}, cause={:?})",
840 region_context, unnormalized_env, cause);
842 let mut predicates: Vec<_> =
843 util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec())
846 debug!("normalize_param_env_or_error: elaborated-predicates={:?}",
849 let elaborated_env = ty::ParamEnv::new(
850 tcx.intern_predicates(&predicates),
851 unnormalized_env.reveal,
852 unnormalized_env.def_id
855 // HACK: we are trying to normalize the param-env inside *itself*. The problem is that
856 // normalization expects its param-env to be already normalized, which means we have
859 // The way we handle this is by normalizing the param-env inside an unnormalized version
860 // of the param-env, which means that if the param-env contains unnormalized projections,
861 // we'll have some normalization failures. This is unfortunate.
863 // Lazy normalization would basically handle this by treating just the
864 // normalizing-a-trait-ref-requires-itself cycles as evaluation failures.
866 // Inferred outlives bounds can create a lot of `TypeOutlives` predicates for associated
867 // types, so to make the situation less bad, we normalize all the predicates *but*
868 // the `TypeOutlives` predicates first inside the unnormalized parameter environment, and
869 // then we normalize the `TypeOutlives` bounds inside the normalized parameter environment.
871 // This works fairly well because trait matching does not actually care about param-env
872 // TypeOutlives predicates - these are normally used by regionck.
873 let outlives_predicates: Vec<_> = predicates.drain_filter(|predicate| {
875 ty::Predicate::TypeOutlives(..) => true,
880 debug!("normalize_param_env_or_error: predicates=(non-outlives={:?}, outlives={:?})",
881 predicates, outlives_predicates);
882 let non_outlives_predicates =
883 match do_normalize_predicates(tcx, region_context, cause.clone(),
884 elaborated_env, predicates) {
885 Ok(predicates) => predicates,
886 // An unnormalized env is better than nothing.
887 Err(ErrorReported) => {
888 debug!("normalize_param_env_or_error: errored resolving non-outlives predicates");
889 return elaborated_env
893 debug!("normalize_param_env_or_error: non-outlives predicates={:?}", non_outlives_predicates);
895 // Not sure whether it is better to include the unnormalized TypeOutlives predicates
896 // here. I believe they should not matter, because we are ignoring TypeOutlives param-env
897 // predicates here anyway. Keeping them here anyway because it seems safer.
898 let outlives_env: Vec<_> =
899 non_outlives_predicates.iter().chain(&outlives_predicates).cloned().collect();
900 let outlives_env = ty::ParamEnv::new(
901 tcx.intern_predicates(&outlives_env),
902 unnormalized_env.reveal,
905 let outlives_predicates =
906 match do_normalize_predicates(tcx, region_context, cause,
907 outlives_env, outlives_predicates) {
908 Ok(predicates) => predicates,
909 // An unnormalized env is better than nothing.
910 Err(ErrorReported) => {
911 debug!("normalize_param_env_or_error: errored resolving outlives predicates");
912 return elaborated_env
915 debug!("normalize_param_env_or_error: outlives predicates={:?}", outlives_predicates);
917 let mut predicates = non_outlives_predicates;
918 predicates.extend(outlives_predicates);
919 debug!("normalize_param_env_or_error: final predicates={:?}", predicates);
921 tcx.intern_predicates(&predicates),
922 unnormalized_env.reveal,
923 unnormalized_env.def_id
927 pub fn fully_normalize<'a, 'tcx, T>(
928 infcx: &InferCtxt<'a, 'tcx>,
929 mut fulfill_cx: FulfillmentContext<'tcx>,
930 cause: ObligationCause<'tcx>,
931 param_env: ty::ParamEnv<'tcx>,
933 ) -> Result<T, Vec<FulfillmentError<'tcx>>>
935 T: TypeFoldable<'tcx>,
937 debug!("fully_normalize_with_fulfillcx(value={:?})", value);
938 let selcx = &mut SelectionContext::new(infcx);
939 let Normalized { value: normalized_value, obligations } =
940 project::normalize(selcx, param_env, cause, value);
941 debug!("fully_normalize: normalized_value={:?} obligations={:?}",
944 for obligation in obligations {
945 fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
948 debug!("fully_normalize: select_all_or_error start");
949 fulfill_cx.select_all_or_error(infcx)?;
950 debug!("fully_normalize: select_all_or_error complete");
951 let resolved_value = infcx.resolve_vars_if_possible(&normalized_value);
952 debug!("fully_normalize: resolved_value={:?}", resolved_value);
956 /// Normalizes the predicates and checks whether they hold in an empty
957 /// environment. If this returns false, then either normalize
958 /// encountered an error or one of the predicates did not hold. Used
959 /// when creating vtables to check for unsatisfiable methods.
960 fn normalize_and_test_predicates<'tcx>(
962 predicates: Vec<ty::Predicate<'tcx>>,
964 debug!("normalize_and_test_predicates(predicates={:?})",
967 let result = tcx.infer_ctxt().enter(|infcx| {
968 let param_env = ty::ParamEnv::reveal_all();
969 let mut selcx = SelectionContext::new(&infcx);
970 let mut fulfill_cx = FulfillmentContext::new();
971 let cause = ObligationCause::dummy();
972 let Normalized { value: predicates, obligations } =
973 normalize(&mut selcx, param_env, cause.clone(), &predicates);
974 for obligation in obligations {
975 fulfill_cx.register_predicate_obligation(&infcx, obligation);
977 for predicate in predicates {
978 let obligation = Obligation::new(cause.clone(), param_env, predicate);
979 fulfill_cx.register_predicate_obligation(&infcx, obligation);
982 fulfill_cx.select_all_or_error(&infcx).is_ok()
984 debug!("normalize_and_test_predicates(predicates={:?}) = {:?}",
989 fn substitute_normalize_and_test_predicates<'tcx>(
991 key: (DefId, SubstsRef<'tcx>),
993 debug!("substitute_normalize_and_test_predicates(key={:?})",
996 let predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates;
997 let result = normalize_and_test_predicates(tcx, predicates);
999 debug!("substitute_normalize_and_test_predicates(key={:?}) = {:?}",
1004 /// Given a trait `trait_ref`, iterates the vtable entries
1005 /// that come from `trait_ref`, including its supertraits.
1006 #[inline] // FIXME(#35870): avoid closures being unexported due to `impl Trait`.
1007 fn vtable_methods<'tcx>(
1009 trait_ref: ty::PolyTraitRef<'tcx>,
1010 ) -> &'tcx [Option<(DefId, SubstsRef<'tcx>)>] {
1011 debug!("vtable_methods({:?})", trait_ref);
1013 tcx.arena.alloc_from_iter(
1014 supertraits(tcx, trait_ref).flat_map(move |trait_ref| {
1015 let trait_methods = tcx.associated_items(trait_ref.def_id())
1016 .filter(|item| item.kind == ty::AssocKind::Method);
1018 // Now list each method's DefId and InternalSubsts (for within its trait).
1019 // If the method can never be called from this object, produce None.
1020 trait_methods.map(move |trait_method| {
1021 debug!("vtable_methods: trait_method={:?}", trait_method);
1022 let def_id = trait_method.def_id;
1024 // Some methods cannot be called on an object; skip those.
1025 if !tcx.is_vtable_safe_method(trait_ref.def_id(), &trait_method) {
1026 debug!("vtable_methods: not vtable safe");
1030 // the method may have some early-bound lifetimes, add
1031 // regions for those
1032 let substs = trait_ref.map_bound(|trait_ref|
1033 InternalSubsts::for_item(tcx, def_id, |param, _|
1035 GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
1036 GenericParamDefKind::Type { .. } |
1037 GenericParamDefKind::Const => {
1038 trait_ref.substs[param.index as usize]
1044 // the trait type may have higher-ranked lifetimes in it;
1045 // so erase them if they appear, so that we get the type
1046 // at some particular call site
1047 let substs = tcx.normalize_erasing_late_bound_regions(
1048 ty::ParamEnv::reveal_all(),
1052 // It's possible that the method relies on where clauses that
1053 // do not hold for this particular set of type parameters.
1054 // Note that this method could then never be called, so we
1055 // do not want to try and codegen it, in that case (see #23435).
1056 let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
1057 if !normalize_and_test_predicates(tcx, predicates.predicates) {
1058 debug!("vtable_methods: predicates do not hold");
1062 Some((def_id, substs))
1068 impl<'tcx, O> Obligation<'tcx, O> {
1069 pub fn new(cause: ObligationCause<'tcx>,
1070 param_env: ty::ParamEnv<'tcx>,
1072 -> Obligation<'tcx, O>
1074 Obligation { cause, param_env, recursion_depth: 0, predicate }
1077 fn with_depth(cause: ObligationCause<'tcx>,
1078 recursion_depth: usize,
1079 param_env: ty::ParamEnv<'tcx>,
1081 -> Obligation<'tcx, O>
1083 Obligation { cause, param_env, recursion_depth, predicate }
1086 pub fn misc(span: Span,
1087 body_id: hir::HirId,
1088 param_env: ty::ParamEnv<'tcx>,
1090 -> Obligation<'tcx, O> {
1091 Obligation::new(ObligationCause::misc(span, body_id), param_env, trait_ref)
1094 pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
1095 Obligation { cause: self.cause.clone(),
1096 param_env: self.param_env,
1097 recursion_depth: self.recursion_depth,
1102 impl<'tcx> ObligationCause<'tcx> {
1104 pub fn new(span: Span,
1105 body_id: hir::HirId,
1106 code: ObligationCauseCode<'tcx>)
1107 -> ObligationCause<'tcx> {
1108 ObligationCause { span, body_id, code }
1111 pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> {
1112 ObligationCause { span, body_id, code: MiscObligation }
1115 pub fn dummy() -> ObligationCause<'tcx> {
1116 ObligationCause { span: DUMMY_SP, body_id: hir::CRATE_HIR_ID, code: MiscObligation }
1120 impl<'tcx, N> Vtable<'tcx, N> {
1121 pub fn nested_obligations(self) -> Vec<N> {
1123 VtableImpl(i) => i.nested,
1124 VtableParam(n) => n,
1125 VtableBuiltin(i) => i.nested,
1126 VtableAutoImpl(d) => d.nested,
1127 VtableClosure(c) => c.nested,
1128 VtableGenerator(c) => c.nested,
1129 VtableObject(d) => d.nested,
1130 VtableFnPointer(d) => d.nested,
1131 VtableTraitAlias(d) => d.nested,
1135 pub fn map<M, F>(self, f: F) -> Vtable<'tcx, M> where F: FnMut(N) -> M {
1137 VtableImpl(i) => VtableImpl(VtableImplData {
1138 impl_def_id: i.impl_def_id,
1140 nested: i.nested.into_iter().map(f).collect(),
1142 VtableParam(n) => VtableParam(n.into_iter().map(f).collect()),
1143 VtableBuiltin(i) => VtableBuiltin(VtableBuiltinData {
1144 nested: i.nested.into_iter().map(f).collect(),
1146 VtableObject(o) => VtableObject(VtableObjectData {
1147 upcast_trait_ref: o.upcast_trait_ref,
1148 vtable_base: o.vtable_base,
1149 nested: o.nested.into_iter().map(f).collect(),
1151 VtableAutoImpl(d) => VtableAutoImpl(VtableAutoImplData {
1152 trait_def_id: d.trait_def_id,
1153 nested: d.nested.into_iter().map(f).collect(),
1155 VtableClosure(c) => VtableClosure(VtableClosureData {
1156 closure_def_id: c.closure_def_id,
1158 nested: c.nested.into_iter().map(f).collect(),
1160 VtableGenerator(c) => VtableGenerator(VtableGeneratorData {
1161 generator_def_id: c.generator_def_id,
1163 nested: c.nested.into_iter().map(f).collect(),
1165 VtableFnPointer(p) => VtableFnPointer(VtableFnPointerData {
1167 nested: p.nested.into_iter().map(f).collect(),
1169 VtableTraitAlias(d) => VtableTraitAlias(VtableTraitAliasData {
1170 alias_def_id: d.alias_def_id,
1172 nested: d.nested.into_iter().map(f).collect(),
1178 impl<'tcx> FulfillmentError<'tcx> {
1179 fn new(obligation: PredicateObligation<'tcx>,
1180 code: FulfillmentErrorCode<'tcx>)
1181 -> FulfillmentError<'tcx>
1183 FulfillmentError { obligation: obligation, code: code }
1187 impl<'tcx> TraitObligation<'tcx> {
1188 fn self_ty(&self) -> ty::Binder<Ty<'tcx>> {
1189 self.predicate.map_bound(|p| p.self_ty())
1193 pub fn provide(providers: &mut ty::query::Providers<'_>) {
1194 *providers = ty::query::Providers {
1195 is_object_safe: object_safety::is_object_safe_provider,
1196 specialization_graph_of: specialize::specialization_graph_provider,
1197 specializes: specialize::specializes,
1198 codegen_fulfill_obligation: codegen::codegen_fulfill_obligation,
1200 substitute_normalize_and_test_predicates,
1205 pub trait ExClauseFold<'tcx>
1207 Self: chalk_engine::context::Context + Clone,
1209 fn fold_ex_clause_with<F: TypeFolder<'tcx>>(
1210 ex_clause: &chalk_engine::ExClause<Self>,
1212 ) -> chalk_engine::ExClause<Self>;
1214 fn visit_ex_clause_with<V: TypeVisitor<'tcx>>(
1215 ex_clause: &chalk_engine::ExClause<Self>,
1220 pub trait ChalkContextLift<'tcx>
1222 Self: chalk_engine::context::Context + Clone,
1224 type LiftedExClause: Debug + 'tcx;
1225 type LiftedDelayedLiteral: Debug + 'tcx;
1226 type LiftedLiteral: Debug + 'tcx;
1228 fn lift_ex_clause_to_tcx(
1229 ex_clause: &chalk_engine::ExClause<Self>,
1231 ) -> Option<Self::LiftedExClause>;
1233 fn lift_delayed_literal_to_tcx(
1234 ex_clause: &chalk_engine::DelayedLiteral<Self>,
1236 ) -> Option<Self::LiftedDelayedLiteral>;
1238 fn lift_literal_to_tcx(
1239 ex_clause: &chalk_engine::Literal<Self>,
1241 ) -> Option<Self::LiftedLiteral>;