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_data_structures::sync::Lrc;
30 use rustc_macros::HashStable;
32 use syntax_pos::{Span, DUMMY_SP};
33 use crate::ty::subst::{InternalSubsts, SubstsRef};
34 use crate::ty::{self, AdtKind, List, Ty, TyCtxt, GenericParamDefKind, ToPredicate};
35 use crate::ty::error::{ExpectedFound, TypeError};
36 use crate::ty::fold::{TypeFolder, TypeFoldable, TypeVisitor};
37 use crate::util::common::ErrorReported;
42 pub use self::SelectionError::*;
43 pub use self::FulfillmentErrorCode::*;
44 pub use self::Vtable::*;
45 pub use self::ObligationCauseCode::*;
47 pub use self::coherence::{add_placeholder_note, orphan_check, overlapping_impls};
48 pub use self::coherence::{OrphanCheckErr, OverlapResult};
49 pub use self::fulfill::{FulfillmentContext, PendingPredicateObligation};
50 pub use self::project::MismatchedProjectionTypes;
51 pub use self::project::{normalize, normalize_projection_type, poly_project_and_unify_type};
52 pub use self::project::{ProjectionCache, ProjectionCacheSnapshot, Reveal, Normalized};
53 pub use self::object_safety::ObjectSafetyViolation;
54 pub use self::object_safety::MethodViolationCode;
55 pub use self::on_unimplemented::{OnUnimplementedDirective, OnUnimplementedNote};
56 pub use self::select::{EvaluationCache, SelectionContext, SelectionCache};
57 pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
58 pub use self::specialize::{OverlapError, specialization_graph, translate_substs};
59 pub use self::specialize::find_associated_item;
60 pub use self::specialize::specialization_graph::FutureCompatOverlapError;
61 pub use self::specialize::specialization_graph::FutureCompatOverlapErrorKind;
62 pub use self::engine::{TraitEngine, TraitEngineExt};
63 pub use self::util::{elaborate_predicates, elaborate_trait_ref, elaborate_trait_refs};
64 pub use self::util::{supertraits, supertrait_def_ids, transitive_bounds,
65 Supertraits, SupertraitDefIds};
67 pub use self::chalk_fulfill::{
68 CanonicalGoal as ChalkCanonicalGoal,
69 FulfillmentContext as ChalkFulfillmentContext
72 pub use self::ObligationCauseCode::*;
73 pub use self::FulfillmentErrorCode::*;
74 pub use self::SelectionError::*;
75 pub use self::Vtable::*;
77 /// Whether to enable bug compatibility with issue #43355.
78 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
79 pub enum IntercrateMode {
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.
91 // Canonicalized queries get dummy spans and hence
92 // must generally propagate errors to
93 // pre-canonicalization callsites.
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 /// The reason we have to prove this thing.
106 pub cause: ObligationCause<'tcx>,
108 /// The environment in which we should prove this thing.
109 pub param_env: ty::ParamEnv<'tcx>,
111 /// The thing we are trying to prove.
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,
122 pub type PredicateObligation<'tcx> = Obligation<'tcx, ty::Predicate<'tcx>>;
123 pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;
125 /// The reason why we incurred this obligation; used for error reporting.
126 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
127 pub struct ObligationCause<'tcx> {
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
136 pub body_id: hir::HirId,
138 pub code: ObligationCauseCode<'tcx>
141 impl<'tcx> ObligationCause<'tcx> {
142 pub fn span<'a, 'gcx>(&self, tcx: &TyCtxt<'a, 'gcx, 'tcx>) -> Span {
144 ObligationCauseCode::CompareImplMethodObligation { .. } |
145 ObligationCauseCode::MainFunctionType |
146 ObligationCauseCode::StartFunctionType => {
147 tcx.sess.source_map().def_span(self.span)
149 ObligationCauseCode::MatchExpressionArm { arm_span, .. } => arm_span,
155 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
156 pub enum ObligationCauseCode<'tcx> {
157 /// Not well classified or should be obvious from the span.
160 /// A slice or array is WF only if `T: Sized`.
163 /// A tuple is WF only if its middle elements are `Sized`.
166 /// This is the trait reference from the given projection.
167 ProjectionWf(ty::ProjectionTy<'tcx>),
169 /// In an impl of trait `X` for type `Y`, type `Y` must
170 /// also implement all supertraits of `X`.
171 ItemObligation(DefId),
173 /// A type like `&'a T` is WF only if `T: 'a`.
174 ReferenceOutlivesReferent(Ty<'tcx>),
176 /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
177 ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
179 /// Obligation incurred due to an object cast.
180 ObjectCastObligation(/* Object type */ Ty<'tcx>),
182 // Various cases where expressions must be sized/copy/etc:
183 /// L = X implies that L is Sized
185 /// (x1, .., xn) must be Sized
186 TupleInitializerSized,
187 /// S { ... } must be Sized
188 StructInitializerSized,
189 /// Type of each variable must be Sized
190 VariableType(ast::NodeId),
191 /// Argument type must be Sized
193 /// Return type must be Sized
195 /// Yield type must be Sized
197 /// [T,..n] --> T must be Copy
200 /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
201 FieldSized { adt_kind: AdtKind, last: bool },
203 /// Constant expressions must be sized.
206 /// static items must have `Sync` type
209 BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
211 ImplDerivedObligation(DerivedObligationCause<'tcx>),
213 /// error derived when matching traits/impls; see ObligationCause for more details
214 CompareImplMethodObligation {
215 item_name: ast::Name,
216 impl_item_def_id: DefId,
217 trait_item_def_id: DefId,
220 /// Checking that this expression can be assigned where it needs to be
221 // FIXME(eddyb) #11161 is the original Expr required?
224 /// Computing common supertype in the arms of a match expression
227 source: hir::MatchSource,
228 prior_arms: Vec<Span>,
232 /// Computing common supertype in the pattern guard for the arms of a match expression
233 MatchExpressionArmPattern { span: Span, ty: Ty<'tcx> },
235 /// Computing common supertype in an if expression
239 semicolon: Option<Span>,
242 /// Computing common supertype of an if expression with no else counter-part
243 IfExpressionWithNoElse,
245 /// `main` has wrong type
248 /// `start` has wrong type
251 /// intrinsic has wrong type
257 /// `return` with no expression
260 /// `return` with an expression
261 ReturnType(hir::HirId),
263 /// Block implicit return
264 BlockTailExpression(hir::HirId),
266 /// #[feature(trivial_bounds)] is not enabled
270 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
271 pub struct DerivedObligationCause<'tcx> {
272 /// The trait reference of the parent obligation that led to the
273 /// current obligation. Note that only trait obligations lead to
274 /// derived obligations, so we just store the trait reference here
276 parent_trait_ref: ty::PolyTraitRef<'tcx>,
278 /// The parent trait had this cause.
279 parent_code: Rc<ObligationCauseCode<'tcx>>
282 pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
283 pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
284 pub type TraitObligations<'tcx> = Vec<TraitObligation<'tcx>>;
286 /// The following types:
294 /// * `InEnvironment`,
295 /// are used for representing the trait system in the form of
296 /// logic programming clauses. They are part of the interface
297 /// for the chalk SLG solver.
298 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
299 pub enum WhereClause<'tcx> {
300 Implemented(ty::TraitPredicate<'tcx>),
301 ProjectionEq(ty::ProjectionPredicate<'tcx>),
302 RegionOutlives(ty::RegionOutlivesPredicate<'tcx>),
303 TypeOutlives(ty::TypeOutlivesPredicate<'tcx>),
306 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
307 pub enum WellFormed<'tcx> {
308 Trait(ty::TraitPredicate<'tcx>),
312 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
313 pub enum FromEnv<'tcx> {
314 Trait(ty::TraitPredicate<'tcx>),
318 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
319 pub enum DomainGoal<'tcx> {
320 Holds(WhereClause<'tcx>),
321 WellFormed(WellFormed<'tcx>),
322 FromEnv(FromEnv<'tcx>),
323 Normalize(ty::ProjectionPredicate<'tcx>),
326 pub type PolyDomainGoal<'tcx> = ty::Binder<DomainGoal<'tcx>>;
328 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
329 pub enum QuantifierKind {
334 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
335 pub enum GoalKind<'tcx> {
336 Implies(Clauses<'tcx>, Goal<'tcx>),
337 And(Goal<'tcx>, Goal<'tcx>),
339 DomainGoal(DomainGoal<'tcx>),
340 Quantified(QuantifierKind, ty::Binder<Goal<'tcx>>),
341 Subtype(Ty<'tcx>, Ty<'tcx>),
345 pub type Goal<'tcx> = &'tcx GoalKind<'tcx>;
347 pub type Goals<'tcx> = &'tcx List<Goal<'tcx>>;
349 impl<'tcx> DomainGoal<'tcx> {
350 pub fn into_goal(self) -> GoalKind<'tcx> {
351 GoalKind::DomainGoal(self)
354 pub fn into_program_clause(self) -> ProgramClause<'tcx> {
357 hypotheses: ty::List::empty(),
358 category: ProgramClauseCategory::Other,
363 impl<'tcx> GoalKind<'tcx> {
364 pub fn from_poly_domain_goal<'a, 'gcx>(
365 domain_goal: PolyDomainGoal<'tcx>,
366 tcx: TyCtxt<'a, 'gcx, 'tcx>,
367 ) -> GoalKind<'tcx> {
368 match domain_goal.no_bound_vars() {
369 Some(p) => p.into_goal(),
370 None => GoalKind::Quantified(
371 QuantifierKind::Universal,
372 domain_goal.map_bound(|p| tcx.mk_goal(p.into_goal()))
378 /// This matches the definition from Page 7 of "A Proof Procedure for the Logic of Hereditary
379 /// Harrop Formulas".
380 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
381 pub enum Clause<'tcx> {
382 Implies(ProgramClause<'tcx>),
383 ForAll(ty::Binder<ProgramClause<'tcx>>),
387 pub fn category(self) -> ProgramClauseCategory {
389 Clause::Implies(clause) => clause.category,
390 Clause::ForAll(clause) => clause.skip_binder().category,
395 /// Multiple clauses.
396 pub type Clauses<'tcx> = &'tcx List<Clause<'tcx>>;
398 /// A "program clause" has the form `D :- G1, ..., Gn`. It is saying
399 /// that the domain goal `D` is true if `G1...Gn` are provable. This
400 /// is equivalent to the implication `G1..Gn => D`; we usually write
401 /// it with the reverse implication operator `:-` to emphasize the way
402 /// that programs are actually solved (via backchaining, which starts
403 /// with the goal to solve and proceeds from there).
404 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
405 pub struct ProgramClause<'tcx> {
406 /// This goal will be considered true ...
407 pub goal: DomainGoal<'tcx>,
409 /// ... if we can prove these hypotheses (there may be no hypotheses at all):
410 pub hypotheses: Goals<'tcx>,
412 /// Useful for filtering clauses.
413 pub category: ProgramClauseCategory,
416 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
417 pub enum ProgramClauseCategory {
423 /// A set of clauses that we assume to be true.
424 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
425 pub struct Environment<'tcx> {
426 pub clauses: Clauses<'tcx>,
429 impl Environment<'tcx> {
430 pub fn with<G>(self, goal: G) -> InEnvironment<'tcx, G> {
438 /// Something (usually a goal), along with an environment.
439 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
440 pub struct InEnvironment<'tcx, G> {
441 pub environment: Environment<'tcx>,
445 pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
447 #[derive(Clone,Debug)]
448 pub enum SelectionError<'tcx> {
450 OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
451 ty::PolyTraitRef<'tcx>,
452 ty::error::TypeError<'tcx>),
453 TraitNotObjectSafe(DefId),
454 ConstEvalFailure(ErrorHandled),
458 pub struct FulfillmentError<'tcx> {
459 pub obligation: PredicateObligation<'tcx>,
460 pub code: FulfillmentErrorCode<'tcx>
464 pub enum FulfillmentErrorCode<'tcx> {
465 CodeSelectionError(SelectionError<'tcx>),
466 CodeProjectionError(MismatchedProjectionTypes<'tcx>),
467 CodeSubtypeError(ExpectedFound<Ty<'tcx>>,
468 TypeError<'tcx>), // always comes from a SubtypePredicate
472 /// When performing resolution, it is typically the case that there
473 /// can be one of three outcomes:
475 /// - `Ok(Some(r))`: success occurred with result `r`
476 /// - `Ok(None)`: could not definitely determine anything, usually due
477 /// to inconclusive type inference.
478 /// - `Err(e)`: error `e` occurred
479 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
481 /// Given the successful resolution of an obligation, the `Vtable`
482 /// indicates where the vtable comes from. Note that while we call this
483 /// a "vtable", it does not necessarily indicate dynamic dispatch at
484 /// runtime. `Vtable` instances just tell the compiler where to find
485 /// methods, but in generic code those methods are typically statically
486 /// dispatched -- only when an object is constructed is a `Vtable`
487 /// instance reified into an actual vtable.
489 /// For example, the vtable may be tied to a specific impl (case A),
490 /// or it may be relative to some bound that is in scope (case B).
493 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
494 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
495 /// impl Clone for int { ... } // Impl_3
497 /// fn foo<T:Clone>(concrete: Option<Box<int>>,
499 /// mixed: Option<T>) {
501 /// // Case A: Vtable points at a specific impl. Only possible when
502 /// // type is concretely known. If the impl itself has bounded
503 /// // type parameters, Vtable will carry resolutions for those as well:
504 /// concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
506 /// // Case B: Vtable must be provided by caller. This applies when
507 /// // type is a type parameter.
508 /// param.clone(); // VtableParam
510 /// // Case C: A mix of cases A and B.
511 /// mixed.clone(); // Vtable(Impl_1, [VtableParam])
515 /// ### The type parameter `N`
517 /// See explanation on `VtableImplData`.
518 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
519 pub enum Vtable<'tcx, N> {
520 /// Vtable identifying a particular impl.
521 VtableImpl(VtableImplData<'tcx, N>),
523 /// Vtable for auto trait implementations.
524 /// This carries the information and nested obligations with regards
525 /// to an auto implementation for a trait `Trait`. The nested obligations
526 /// ensure the trait implementation holds for all the constituent types.
527 VtableAutoImpl(VtableAutoImplData<N>),
529 /// Successful resolution to an obligation provided by the caller
530 /// for some type parameter. The `Vec<N>` represents the
531 /// obligations incurred from normalizing the where-clause (if
535 /// Virtual calls through an object.
536 VtableObject(VtableObjectData<'tcx, N>),
538 /// Successful resolution for a builtin trait.
539 VtableBuiltin(VtableBuiltinData<N>),
541 /// Vtable automatically generated for a closure. The `DefId` is the ID
542 /// of the closure expression. This is a `VtableImpl` in spirit, but the
543 /// impl is generated by the compiler and does not appear in the source.
544 VtableClosure(VtableClosureData<'tcx, N>),
546 /// Same as above, but for a function pointer type with the given signature.
547 VtableFnPointer(VtableFnPointerData<'tcx, N>),
549 /// Vtable automatically generated for a generator.
550 VtableGenerator(VtableGeneratorData<'tcx, N>),
552 /// Vtable for a trait alias.
553 VtableTraitAlias(VtableTraitAliasData<'tcx, N>),
556 /// Identifies a particular impl in the source, along with a set of
557 /// substitutions from the impl's type/lifetime parameters. The
558 /// `nested` vector corresponds to the nested obligations attached to
559 /// the impl's type parameters.
561 /// The type parameter `N` indicates the type used for "nested
562 /// obligations" that are required by the impl. During type check, this
563 /// is `Obligation`, as one might expect. During codegen, however, this
564 /// is `()`, because codegen only requires a shallow resolution of an
565 /// impl, and nested obligations are satisfied later.
566 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
567 pub struct VtableImplData<'tcx, N> {
568 pub impl_def_id: DefId,
569 pub substs: SubstsRef<'tcx>,
573 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
574 pub struct VtableGeneratorData<'tcx, N> {
575 pub generator_def_id: DefId,
576 pub substs: ty::GeneratorSubsts<'tcx>,
577 /// Nested obligations. This can be non-empty if the generator
578 /// signature contains associated types.
582 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
583 pub struct VtableClosureData<'tcx, N> {
584 pub closure_def_id: DefId,
585 pub substs: ty::ClosureSubsts<'tcx>,
586 /// Nested obligations. This can be non-empty if the closure
587 /// signature contains associated types.
591 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
592 pub struct VtableAutoImplData<N> {
593 pub trait_def_id: DefId,
597 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
598 pub struct VtableBuiltinData<N> {
602 /// A vtable for some object-safe trait `Foo` automatically derived
603 /// for the object type `Foo`.
604 #[derive(PartialEq, Eq, Clone, RustcEncodable, RustcDecodable, HashStable)]
605 pub struct VtableObjectData<'tcx, N> {
606 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
607 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
609 /// The vtable is formed by concatenating together the method lists of
610 /// the base object trait and all supertraits; this is the start of
611 /// `upcast_trait_ref`'s methods in that vtable.
612 pub vtable_base: usize,
617 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
618 pub struct VtableFnPointerData<'tcx, N> {
623 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
624 pub struct VtableTraitAliasData<'tcx, N> {
625 pub alias_def_id: DefId,
626 pub substs: SubstsRef<'tcx>,
630 /// Creates predicate obligations from the generic bounds.
631 pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
632 param_env: ty::ParamEnv<'tcx>,
633 generic_bounds: &ty::InstantiatedPredicates<'tcx>)
634 -> PredicateObligations<'tcx>
636 util::predicates_for_generics(cause, 0, param_env, generic_bounds)
639 /// Determines whether the type `ty` is known to meet `bound` and
640 /// returns true if so. Returns false if `ty` either does not meet
641 /// `bound` or is not known to meet bound (note that this is
642 /// conservative towards *no impl*, which is the opposite of the
643 /// `evaluate` methods).
644 pub fn type_known_to_meet_bound_modulo_regions<'a, 'gcx, 'tcx>(
645 infcx: &InferCtxt<'a, 'gcx, 'tcx>,
646 param_env: ty::ParamEnv<'tcx>,
651 debug!("type_known_to_meet_bound_modulo_regions(ty={:?}, bound={:?})",
653 infcx.tcx.item_path_str(def_id));
655 let trait_ref = ty::TraitRef {
657 substs: infcx.tcx.mk_substs_trait(ty, &[]),
659 let obligation = Obligation {
661 cause: ObligationCause::misc(span, hir::DUMMY_HIR_ID),
663 predicate: trait_ref.to_predicate(),
666 let result = infcx.predicate_must_hold_modulo_regions(&obligation);
667 debug!("type_known_to_meet_ty={:?} bound={} => {:?}",
668 ty, infcx.tcx.item_path_str(def_id), result);
670 if result && (ty.has_infer_types() || ty.has_closure_types()) {
671 // Because of inference "guessing", selection can sometimes claim
672 // to succeed while the success requires a guess. To ensure
673 // this function's result remains infallible, we must confirm
674 // that guess. While imperfect, I believe this is sound.
676 // The handling of regions in this area of the code is terrible,
677 // see issue #29149. We should be able to improve on this with
679 let mut fulfill_cx = FulfillmentContext::new_ignoring_regions();
681 // We can use a dummy node-id here because we won't pay any mind
682 // to region obligations that arise (there shouldn't really be any
684 let cause = ObligationCause::misc(span, hir::DUMMY_HIR_ID);
686 fulfill_cx.register_bound(infcx, param_env, ty, def_id, cause);
688 // Note: we only assume something is `Copy` if we can
689 // *definitively* show that it implements `Copy`. Otherwise,
690 // assume it is move; linear is always ok.
691 match fulfill_cx.select_all_or_error(infcx) {
693 debug!("type_known_to_meet_bound_modulo_regions: ty={:?} bound={} success",
695 infcx.tcx.item_path_str(def_id));
699 debug!("type_known_to_meet_bound_modulo_regions: ty={:?} bound={} errors={:?}",
701 infcx.tcx.item_path_str(def_id),
711 fn do_normalize_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
712 region_context: DefId,
713 cause: ObligationCause<'tcx>,
714 elaborated_env: ty::ParamEnv<'tcx>,
715 predicates: Vec<ty::Predicate<'tcx>>)
716 -> Result<Vec<ty::Predicate<'tcx>>, ErrorReported>
719 "do_normalize_predicates(predicates={:?}, region_context={:?}, cause={:?})",
724 let span = cause.span;
725 tcx.infer_ctxt().enter(|infcx| {
726 // FIXME. We should really... do something with these region
727 // obligations. But this call just continues the older
728 // behavior (i.e., doesn't cause any new bugs), and it would
729 // take some further refactoring to actually solve them. In
730 // particular, we would have to handle implied bounds
731 // properly, and that code is currently largely confined to
732 // regionck (though I made some efforts to extract it
735 // @arielby: In any case, these obligations are checked
736 // by wfcheck anyway, so I'm not sure we have to check
737 // them here too, and we will remove this function when
738 // we move over to lazy normalization *anyway*.
739 let fulfill_cx = FulfillmentContext::new_ignoring_regions();
740 let predicates = match fully_normalize(
747 Ok(predicates) => predicates,
749 infcx.report_fulfillment_errors(&errors, None, false);
750 return Err(ErrorReported)
754 debug!("do_normalize_predictes: normalized predicates = {:?}", predicates);
756 let region_scope_tree = region::ScopeTree::default();
758 // We can use the `elaborated_env` here; the region code only
759 // cares about declarations like `'a: 'b`.
760 let outlives_env = OutlivesEnvironment::new(elaborated_env);
762 infcx.resolve_regions_and_report_errors(
766 SuppressRegionErrors::default(),
769 let predicates = match infcx.fully_resolve(&predicates) {
770 Ok(predicates) => predicates,
772 // If we encounter a fixup error, it means that some type
773 // variable wound up unconstrained. I actually don't know
774 // if this can happen, and I certainly don't expect it to
775 // happen often, but if it did happen it probably
776 // represents a legitimate failure due to some kind of
777 // unconstrained variable, and it seems better not to ICE,
778 // all things considered.
779 tcx.sess.span_err(span, &fixup_err.to_string());
780 return Err(ErrorReported)
784 match tcx.lift_to_global(&predicates) {
785 Some(predicates) => Ok(predicates),
787 // FIXME: shouldn't we, you know, actually report an error here? or an ICE?
794 // FIXME: this is gonna need to be removed ...
795 /// Normalizes the parameter environment, reporting errors if they occur.
796 pub fn normalize_param_env_or_error<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
797 region_context: DefId,
798 unnormalized_env: ty::ParamEnv<'tcx>,
799 cause: ObligationCause<'tcx>)
800 -> ty::ParamEnv<'tcx>
802 // I'm not wild about reporting errors here; I'd prefer to
803 // have the errors get reported at a defined place (e.g.,
804 // during typeck). Instead I have all parameter
805 // environments, in effect, going through this function
806 // and hence potentially reporting errors. This ensures of
807 // course that we never forget to normalize (the
808 // alternative seemed like it would involve a lot of
809 // manual invocations of this fn -- and then we'd have to
810 // deal with the errors at each of those sites).
812 // In any case, in practice, typeck constructs all the
813 // parameter environments once for every fn as it goes,
814 // and errors will get reported then; so after typeck we
815 // can be sure that no errors should occur.
817 debug!("normalize_param_env_or_error(region_context={:?}, unnormalized_env={:?}, cause={:?})",
818 region_context, unnormalized_env, cause);
820 let mut predicates: Vec<_> =
821 util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec())
824 debug!("normalize_param_env_or_error: elaborated-predicates={:?}",
827 let elaborated_env = ty::ParamEnv::new(
828 tcx.intern_predicates(&predicates),
829 unnormalized_env.reveal,
830 unnormalized_env.def_id
833 // HACK: we are trying to normalize the param-env inside *itself*. The problem is that
834 // normalization expects its param-env to be already normalized, which means we have
837 // The way we handle this is by normalizing the param-env inside an unnormalized version
838 // of the param-env, which means that if the param-env contains unnormalized projections,
839 // we'll have some normalization failures. This is unfortunate.
841 // Lazy normalization would basically handle this by treating just the
842 // normalizing-a-trait-ref-requires-itself cycles as evaluation failures.
844 // Inferred outlives bounds can create a lot of `TypeOutlives` predicates for associated
845 // types, so to make the situation less bad, we normalize all the predicates *but*
846 // the `TypeOutlives` predicates first inside the unnormalized parameter environment, and
847 // then we normalize the `TypeOutlives` bounds inside the normalized parameter environment.
849 // This works fairly well because trait matching does not actually care about param-env
850 // TypeOutlives predicates - these are normally used by regionck.
851 let outlives_predicates: Vec<_> = predicates.drain_filter(|predicate| {
853 ty::Predicate::TypeOutlives(..) => true,
858 debug!("normalize_param_env_or_error: predicates=(non-outlives={:?}, outlives={:?})",
859 predicates, outlives_predicates);
860 let non_outlives_predicates =
861 match do_normalize_predicates(tcx, region_context, cause.clone(),
862 elaborated_env, predicates) {
863 Ok(predicates) => predicates,
864 // An unnormalized env is better than nothing.
865 Err(ErrorReported) => {
866 debug!("normalize_param_env_or_error: errored resolving non-outlives predicates");
867 return elaborated_env
871 debug!("normalize_param_env_or_error: non-outlives predicates={:?}", non_outlives_predicates);
873 // Not sure whether it is better to include the unnormalized TypeOutlives predicates
874 // here. I believe they should not matter, because we are ignoring TypeOutlives param-env
875 // predicates here anyway. Keeping them here anyway because it seems safer.
876 let outlives_env: Vec<_> =
877 non_outlives_predicates.iter().chain(&outlives_predicates).cloned().collect();
878 let outlives_env = ty::ParamEnv::new(
879 tcx.intern_predicates(&outlives_env),
880 unnormalized_env.reveal,
883 let outlives_predicates =
884 match do_normalize_predicates(tcx, region_context, cause,
885 outlives_env, outlives_predicates) {
886 Ok(predicates) => predicates,
887 // An unnormalized env is better than nothing.
888 Err(ErrorReported) => {
889 debug!("normalize_param_env_or_error: errored resolving outlives predicates");
890 return elaborated_env
893 debug!("normalize_param_env_or_error: outlives predicates={:?}", outlives_predicates);
895 let mut predicates = non_outlives_predicates;
896 predicates.extend(outlives_predicates);
897 debug!("normalize_param_env_or_error: final predicates={:?}", predicates);
899 tcx.intern_predicates(&predicates),
900 unnormalized_env.reveal,
901 unnormalized_env.def_id
905 pub fn fully_normalize<'a, 'gcx, 'tcx, T>(
906 infcx: &InferCtxt<'a, 'gcx, 'tcx>,
907 mut fulfill_cx: FulfillmentContext<'tcx>,
908 cause: ObligationCause<'tcx>,
909 param_env: ty::ParamEnv<'tcx>,
911 -> Result<T, Vec<FulfillmentError<'tcx>>>
912 where T : TypeFoldable<'tcx>
914 debug!("fully_normalize_with_fulfillcx(value={:?})", value);
915 let selcx = &mut SelectionContext::new(infcx);
916 let Normalized { value: normalized_value, obligations } =
917 project::normalize(selcx, param_env, cause, value);
918 debug!("fully_normalize: normalized_value={:?} obligations={:?}",
921 for obligation in obligations {
922 fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
925 debug!("fully_normalize: select_all_or_error start");
926 fulfill_cx.select_all_or_error(infcx)?;
927 debug!("fully_normalize: select_all_or_error complete");
928 let resolved_value = infcx.resolve_type_vars_if_possible(&normalized_value);
929 debug!("fully_normalize: resolved_value={:?}", resolved_value);
933 /// Normalizes the predicates and checks whether they hold in an empty
934 /// environment. If this returns false, then either normalize
935 /// encountered an error or one of the predicates did not hold. Used
936 /// when creating vtables to check for unsatisfiable methods.
937 fn normalize_and_test_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
938 predicates: Vec<ty::Predicate<'tcx>>)
941 debug!("normalize_and_test_predicates(predicates={:?})",
944 let result = tcx.infer_ctxt().enter(|infcx| {
945 let param_env = ty::ParamEnv::reveal_all();
946 let mut selcx = SelectionContext::new(&infcx);
947 let mut fulfill_cx = FulfillmentContext::new();
948 let cause = ObligationCause::dummy();
949 let Normalized { value: predicates, obligations } =
950 normalize(&mut selcx, param_env, cause.clone(), &predicates);
951 for obligation in obligations {
952 fulfill_cx.register_predicate_obligation(&infcx, obligation);
954 for predicate in predicates {
955 let obligation = Obligation::new(cause.clone(), param_env, predicate);
956 fulfill_cx.register_predicate_obligation(&infcx, obligation);
959 fulfill_cx.select_all_or_error(&infcx).is_ok()
961 debug!("normalize_and_test_predicates(predicates={:?}) = {:?}",
966 fn substitute_normalize_and_test_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
967 key: (DefId, SubstsRef<'tcx>))
970 debug!("substitute_normalize_and_test_predicates(key={:?})",
973 let predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates;
974 let result = normalize_and_test_predicates(tcx, predicates);
976 debug!("substitute_normalize_and_test_predicates(key={:?}) = {:?}",
981 /// Given a trait `trait_ref`, iterates the vtable entries
982 /// that come from `trait_ref`, including its supertraits.
983 #[inline] // FIXME(#35870): avoid closures being unexported due to `impl Trait`.
984 fn vtable_methods<'a, 'tcx>(
985 tcx: TyCtxt<'a, 'tcx, 'tcx>,
986 trait_ref: ty::PolyTraitRef<'tcx>)
987 -> Lrc<Vec<Option<(DefId, SubstsRef<'tcx>)>>>
989 debug!("vtable_methods({:?})", trait_ref);
992 supertraits(tcx, trait_ref).flat_map(move |trait_ref| {
993 let trait_methods = tcx.associated_items(trait_ref.def_id())
994 .filter(|item| item.kind == ty::AssociatedKind::Method);
996 // Now list each method's DefId and InternalSubsts (for within its trait).
997 // If the method can never be called from this object, produce None.
998 trait_methods.map(move |trait_method| {
999 debug!("vtable_methods: trait_method={:?}", trait_method);
1000 let def_id = trait_method.def_id;
1002 // Some methods cannot be called on an object; skip those.
1003 if !tcx.is_vtable_safe_method(trait_ref.def_id(), &trait_method) {
1004 debug!("vtable_methods: not vtable safe");
1008 // the method may have some early-bound lifetimes, add
1009 // regions for those
1010 let substs = trait_ref.map_bound(|trait_ref|
1011 InternalSubsts::for_item(tcx, def_id, |param, _|
1013 GenericParamDefKind::Lifetime => tcx.types.re_erased.into(),
1014 GenericParamDefKind::Type { .. } |
1015 GenericParamDefKind::Const => {
1016 trait_ref.substs[param.index as usize]
1022 // the trait type may have higher-ranked lifetimes in it;
1023 // so erase them if they appear, so that we get the type
1024 // at some particular call site
1025 let substs = tcx.normalize_erasing_late_bound_regions(
1026 ty::ParamEnv::reveal_all(),
1030 // It's possible that the method relies on where clauses that
1031 // do not hold for this particular set of type parameters.
1032 // Note that this method could then never be called, so we
1033 // do not want to try and codegen it, in that case (see #23435).
1034 let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
1035 if !normalize_and_test_predicates(tcx, predicates.predicates) {
1036 debug!("vtable_methods: predicates do not hold");
1040 Some((def_id, substs))
1046 impl<'tcx,O> Obligation<'tcx,O> {
1047 pub fn new(cause: ObligationCause<'tcx>,
1048 param_env: ty::ParamEnv<'tcx>,
1050 -> Obligation<'tcx, O>
1052 Obligation { cause, param_env, recursion_depth: 0, predicate }
1055 fn with_depth(cause: ObligationCause<'tcx>,
1056 recursion_depth: usize,
1057 param_env: ty::ParamEnv<'tcx>,
1059 -> Obligation<'tcx, O>
1061 Obligation { cause, param_env, recursion_depth, predicate }
1064 pub fn misc(span: Span,
1065 body_id: hir::HirId,
1066 param_env: ty::ParamEnv<'tcx>,
1068 -> Obligation<'tcx, O> {
1069 Obligation::new(ObligationCause::misc(span, body_id), param_env, trait_ref)
1072 pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
1073 Obligation { cause: self.cause.clone(),
1074 param_env: self.param_env,
1075 recursion_depth: self.recursion_depth,
1080 impl<'tcx> ObligationCause<'tcx> {
1082 pub fn new(span: Span,
1083 body_id: hir::HirId,
1084 code: ObligationCauseCode<'tcx>)
1085 -> ObligationCause<'tcx> {
1086 ObligationCause { span, body_id, code }
1089 pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> {
1090 ObligationCause { span, body_id, code: MiscObligation }
1093 pub fn dummy() -> ObligationCause<'tcx> {
1094 ObligationCause { span: DUMMY_SP, body_id: hir::CRATE_HIR_ID, code: MiscObligation }
1098 impl<'tcx, N> Vtable<'tcx, N> {
1099 pub fn nested_obligations(self) -> Vec<N> {
1101 VtableImpl(i) => i.nested,
1102 VtableParam(n) => n,
1103 VtableBuiltin(i) => i.nested,
1104 VtableAutoImpl(d) => d.nested,
1105 VtableClosure(c) => c.nested,
1106 VtableGenerator(c) => c.nested,
1107 VtableObject(d) => d.nested,
1108 VtableFnPointer(d) => d.nested,
1109 VtableTraitAlias(d) => d.nested,
1113 pub fn map<M, F>(self, f: F) -> Vtable<'tcx, M> where F: FnMut(N) -> M {
1115 VtableImpl(i) => VtableImpl(VtableImplData {
1116 impl_def_id: i.impl_def_id,
1118 nested: i.nested.into_iter().map(f).collect(),
1120 VtableParam(n) => VtableParam(n.into_iter().map(f).collect()),
1121 VtableBuiltin(i) => VtableBuiltin(VtableBuiltinData {
1122 nested: i.nested.into_iter().map(f).collect(),
1124 VtableObject(o) => VtableObject(VtableObjectData {
1125 upcast_trait_ref: o.upcast_trait_ref,
1126 vtable_base: o.vtable_base,
1127 nested: o.nested.into_iter().map(f).collect(),
1129 VtableAutoImpl(d) => VtableAutoImpl(VtableAutoImplData {
1130 trait_def_id: d.trait_def_id,
1131 nested: d.nested.into_iter().map(f).collect(),
1133 VtableClosure(c) => VtableClosure(VtableClosureData {
1134 closure_def_id: c.closure_def_id,
1136 nested: c.nested.into_iter().map(f).collect(),
1138 VtableGenerator(c) => VtableGenerator(VtableGeneratorData {
1139 generator_def_id: c.generator_def_id,
1141 nested: c.nested.into_iter().map(f).collect(),
1143 VtableFnPointer(p) => VtableFnPointer(VtableFnPointerData {
1145 nested: p.nested.into_iter().map(f).collect(),
1147 VtableTraitAlias(d) => VtableTraitAlias(VtableTraitAliasData {
1148 alias_def_id: d.alias_def_id,
1150 nested: d.nested.into_iter().map(f).collect(),
1156 impl<'tcx> FulfillmentError<'tcx> {
1157 fn new(obligation: PredicateObligation<'tcx>,
1158 code: FulfillmentErrorCode<'tcx>)
1159 -> FulfillmentError<'tcx>
1161 FulfillmentError { obligation: obligation, code: code }
1165 impl<'tcx> TraitObligation<'tcx> {
1166 fn self_ty(&self) -> ty::Binder<Ty<'tcx>> {
1167 self.predicate.map_bound(|p| p.self_ty())
1171 pub fn provide(providers: &mut ty::query::Providers<'_>) {
1172 *providers = ty::query::Providers {
1173 is_object_safe: object_safety::is_object_safe_provider,
1174 specialization_graph_of: specialize::specialization_graph_provider,
1175 specializes: specialize::specializes,
1176 codegen_fulfill_obligation: codegen::codegen_fulfill_obligation,
1178 substitute_normalize_and_test_predicates,
1183 pub trait ExClauseFold<'tcx>
1185 Self: chalk_engine::context::Context + Clone,
1187 fn fold_ex_clause_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(
1188 ex_clause: &chalk_engine::ExClause<Self>,
1190 ) -> chalk_engine::ExClause<Self>;
1192 fn visit_ex_clause_with<'gcx: 'tcx, V: TypeVisitor<'tcx>>(
1193 ex_clause: &chalk_engine::ExClause<Self>,
1198 pub trait ChalkContextLift<'tcx>
1200 Self: chalk_engine::context::Context + Clone,
1202 type LiftedExClause: Debug + 'tcx;
1203 type LiftedDelayedLiteral: Debug + 'tcx;
1204 type LiftedLiteral: Debug + 'tcx;
1206 fn lift_ex_clause_to_tcx<'a, 'gcx>(
1207 ex_clause: &chalk_engine::ExClause<Self>,
1208 tcx: TyCtxt<'a, 'gcx, 'tcx>,
1209 ) -> Option<Self::LiftedExClause>;
1211 fn lift_delayed_literal_to_tcx<'a, 'gcx>(
1212 ex_clause: &chalk_engine::DelayedLiteral<Self>,
1213 tcx: TyCtxt<'a, 'gcx, 'tcx>,
1214 ) -> Option<Self::LiftedDelayedLiteral>;
1216 fn lift_literal_to_tcx<'a, 'gcx>(
1217 ex_clause: &chalk_engine::Literal<Self>,
1218 tcx: TyCtxt<'a, 'gcx, 'tcx>,
1219 ) -> Option<Self::LiftedLiteral>;