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<'_>, 112);
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 /// Like `ItemObligation`, but with extra detail on the source of the obligation.
180 BindingObligation(DefId, Span),
182 /// A type like `&'a T` is WF only if `T: 'a`.
183 ReferenceOutlivesReferent(Ty<'tcx>),
185 /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
186 ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
188 /// Obligation incurred due to an object cast.
189 ObjectCastObligation(/* Object type */ Ty<'tcx>),
191 // Various cases where expressions must be sized/copy/etc:
192 /// L = X implies that L is Sized
194 /// (x1, .., xn) must be Sized
195 TupleInitializerSized,
196 /// S { ... } must be Sized
197 StructInitializerSized,
198 /// Type of each variable must be Sized
199 VariableType(hir::HirId),
200 /// Argument type must be Sized
202 /// Return type must be Sized
204 /// Yield type must be Sized
206 /// [T,..n] --> T must be Copy
209 /// Types of fields (other than the last, except for packed structs) in a struct must be sized.
210 FieldSized { adt_kind: AdtKind, last: bool },
212 /// Constant expressions must be sized.
215 /// static items must have `Sync` type
218 BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
220 ImplDerivedObligation(DerivedObligationCause<'tcx>),
222 /// error derived when matching traits/impls; see ObligationCause for more details
223 CompareImplMethodObligation {
224 item_name: ast::Name,
225 impl_item_def_id: DefId,
226 trait_item_def_id: DefId,
229 /// Checking that this expression can be assigned where it needs to be
230 // FIXME(eddyb) #11161 is the original Expr required?
233 /// Computing common supertype in the arms of a match expression
234 MatchExpressionArm(Box<MatchExpressionArmCause<'tcx>>),
236 /// Computing common supertype in the pattern guard for the arms of a match expression
237 MatchExpressionArmPattern { span: Span, ty: Ty<'tcx> },
239 /// Computing common supertype in an if expression
240 IfExpression(Box<IfExpressionCause>),
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 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
271 #[cfg(target_arch = "x86_64")]
272 static_assert_size!(ObligationCauseCode<'_>, 32);
274 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
275 pub struct MatchExpressionArmCause<'tcx> {
277 pub source: hir::MatchSource,
278 pub prior_arms: Vec<Span>,
279 pub last_ty: Ty<'tcx>,
280 pub discrim_hir_id: hir::HirId,
283 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
284 pub struct IfExpressionCause {
286 pub outer: Option<Span>,
287 pub semicolon: Option<Span>,
290 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
291 pub struct DerivedObligationCause<'tcx> {
292 /// The trait reference of the parent obligation that led to the
293 /// current obligation. Note that only trait obligations lead to
294 /// derived obligations, so we just store the trait reference here
296 parent_trait_ref: ty::PolyTraitRef<'tcx>,
298 /// The parent trait had this cause.
299 parent_code: Rc<ObligationCauseCode<'tcx>>
302 pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
303 pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
304 pub type TraitObligations<'tcx> = Vec<TraitObligation<'tcx>>;
306 /// The following types:
314 /// * `InEnvironment`,
315 /// are used for representing the trait system in the form of
316 /// logic programming clauses. They are part of the interface
317 /// for the chalk SLG solver.
318 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
319 pub enum WhereClause<'tcx> {
320 Implemented(ty::TraitPredicate<'tcx>),
321 ProjectionEq(ty::ProjectionPredicate<'tcx>),
322 RegionOutlives(ty::RegionOutlivesPredicate<'tcx>),
323 TypeOutlives(ty::TypeOutlivesPredicate<'tcx>),
326 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
327 pub enum WellFormed<'tcx> {
328 Trait(ty::TraitPredicate<'tcx>),
332 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
333 pub enum FromEnv<'tcx> {
334 Trait(ty::TraitPredicate<'tcx>),
338 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable)]
339 pub enum DomainGoal<'tcx> {
340 Holds(WhereClause<'tcx>),
341 WellFormed(WellFormed<'tcx>),
342 FromEnv(FromEnv<'tcx>),
343 Normalize(ty::ProjectionPredicate<'tcx>),
346 pub type PolyDomainGoal<'tcx> = ty::Binder<DomainGoal<'tcx>>;
348 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
349 pub enum QuantifierKind {
354 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
355 pub enum GoalKind<'tcx> {
356 Implies(Clauses<'tcx>, Goal<'tcx>),
357 And(Goal<'tcx>, Goal<'tcx>),
359 DomainGoal(DomainGoal<'tcx>),
360 Quantified(QuantifierKind, ty::Binder<Goal<'tcx>>),
361 Subtype(Ty<'tcx>, Ty<'tcx>),
365 pub type Goal<'tcx> = &'tcx GoalKind<'tcx>;
367 pub type Goals<'tcx> = &'tcx List<Goal<'tcx>>;
369 impl<'tcx> DomainGoal<'tcx> {
370 pub fn into_goal(self) -> GoalKind<'tcx> {
371 GoalKind::DomainGoal(self)
374 pub fn into_program_clause(self) -> ProgramClause<'tcx> {
377 hypotheses: ty::List::empty(),
378 category: ProgramClauseCategory::Other,
383 impl<'tcx> GoalKind<'tcx> {
384 pub fn from_poly_domain_goal(
385 domain_goal: PolyDomainGoal<'tcx>,
387 ) -> GoalKind<'tcx> {
388 match domain_goal.no_bound_vars() {
389 Some(p) => p.into_goal(),
390 None => GoalKind::Quantified(
391 QuantifierKind::Universal,
392 domain_goal.map_bound(|p| tcx.mk_goal(p.into_goal()))
398 /// This matches the definition from Page 7 of "A Proof Procedure for the Logic of Hereditary
399 /// Harrop Formulas".
400 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
401 pub enum Clause<'tcx> {
402 Implies(ProgramClause<'tcx>),
403 ForAll(ty::Binder<ProgramClause<'tcx>>),
407 pub fn category(self) -> ProgramClauseCategory {
409 Clause::Implies(clause) => clause.category,
410 Clause::ForAll(clause) => clause.skip_binder().category,
415 /// Multiple clauses.
416 pub type Clauses<'tcx> = &'tcx List<Clause<'tcx>>;
418 /// A "program clause" has the form `D :- G1, ..., Gn`. It is saying
419 /// that the domain goal `D` is true if `G1...Gn` are provable. This
420 /// is equivalent to the implication `G1..Gn => D`; we usually write
421 /// it with the reverse implication operator `:-` to emphasize the way
422 /// that programs are actually solved (via backchaining, which starts
423 /// with the goal to solve and proceeds from there).
424 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
425 pub struct ProgramClause<'tcx> {
426 /// This goal will be considered true ...
427 pub goal: DomainGoal<'tcx>,
429 /// ... if we can prove these hypotheses (there may be no hypotheses at all):
430 pub hypotheses: Goals<'tcx>,
432 /// Useful for filtering clauses.
433 pub category: ProgramClauseCategory,
436 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
437 pub enum ProgramClauseCategory {
443 /// A set of clauses that we assume to be true.
444 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
445 pub struct Environment<'tcx> {
446 pub clauses: Clauses<'tcx>,
449 impl Environment<'tcx> {
450 pub fn with<G>(self, goal: G) -> InEnvironment<'tcx, G> {
458 /// Something (usually a goal), along with an environment.
459 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable)]
460 pub struct InEnvironment<'tcx, G> {
461 pub environment: Environment<'tcx>,
465 pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
467 #[derive(Clone,Debug)]
468 pub enum SelectionError<'tcx> {
470 OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
471 ty::PolyTraitRef<'tcx>,
472 ty::error::TypeError<'tcx>),
473 TraitNotObjectSafe(DefId),
474 ConstEvalFailure(ErrorHandled),
478 EnumTypeFoldableImpl! {
479 impl<'tcx> TypeFoldable<'tcx> for SelectionError<'tcx> {
480 (SelectionError::Unimplemented),
481 (SelectionError::OutputTypeParameterMismatch)(a, b, c),
482 (SelectionError::TraitNotObjectSafe)(a),
483 (SelectionError::ConstEvalFailure)(a),
484 (SelectionError::Overflow),
488 pub struct FulfillmentError<'tcx> {
489 pub obligation: PredicateObligation<'tcx>,
490 pub code: FulfillmentErrorCode<'tcx>,
491 /// Diagnostics only: we opportunistically change the `code.span` when we encounter an
492 /// obligation error caused by a call argument. When this is the case, we also signal that in
493 /// this field to ensure accuracy of suggestions.
494 pub points_at_arg_span: bool,
498 pub enum FulfillmentErrorCode<'tcx> {
499 CodeSelectionError(SelectionError<'tcx>),
500 CodeProjectionError(MismatchedProjectionTypes<'tcx>),
501 CodeSubtypeError(ExpectedFound<Ty<'tcx>>,
502 TypeError<'tcx>), // always comes from a SubtypePredicate
506 /// When performing resolution, it is typically the case that there
507 /// can be one of three outcomes:
509 /// - `Ok(Some(r))`: success occurred with result `r`
510 /// - `Ok(None)`: could not definitely determine anything, usually due
511 /// to inconclusive type inference.
512 /// - `Err(e)`: error `e` occurred
513 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
515 /// Given the successful resolution of an obligation, the `Vtable`
516 /// indicates where the vtable comes from. Note that while we call this
517 /// a "vtable", it does not necessarily indicate dynamic dispatch at
518 /// runtime. `Vtable` instances just tell the compiler where to find
519 /// methods, but in generic code those methods are typically statically
520 /// dispatched -- only when an object is constructed is a `Vtable`
521 /// instance reified into an actual vtable.
523 /// For example, the vtable may be tied to a specific impl (case A),
524 /// or it may be relative to some bound that is in scope (case B).
527 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
528 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
529 /// impl Clone for int { ... } // Impl_3
531 /// fn foo<T:Clone>(concrete: Option<Box<int>>,
533 /// mixed: Option<T>) {
535 /// // Case A: Vtable points at a specific impl. Only possible when
536 /// // type is concretely known. If the impl itself has bounded
537 /// // type parameters, Vtable will carry resolutions for those as well:
538 /// concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
540 /// // Case B: Vtable must be provided by caller. This applies when
541 /// // type is a type parameter.
542 /// param.clone(); // VtableParam
544 /// // Case C: A mix of cases A and B.
545 /// mixed.clone(); // Vtable(Impl_1, [VtableParam])
549 /// ### The type parameter `N`
551 /// See explanation on `VtableImplData`.
552 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
553 pub enum Vtable<'tcx, N> {
554 /// Vtable identifying a particular impl.
555 VtableImpl(VtableImplData<'tcx, N>),
557 /// Vtable for auto trait implementations.
558 /// This carries the information and nested obligations with regards
559 /// to an auto implementation for a trait `Trait`. The nested obligations
560 /// ensure the trait implementation holds for all the constituent types.
561 VtableAutoImpl(VtableAutoImplData<N>),
563 /// Successful resolution to an obligation provided by the caller
564 /// for some type parameter. The `Vec<N>` represents the
565 /// obligations incurred from normalizing the where-clause (if
569 /// Virtual calls through an object.
570 VtableObject(VtableObjectData<'tcx, N>),
572 /// Successful resolution for a builtin trait.
573 VtableBuiltin(VtableBuiltinData<N>),
575 /// Vtable automatically generated for a closure. The `DefId` is the ID
576 /// of the closure expression. This is a `VtableImpl` in spirit, but the
577 /// impl is generated by the compiler and does not appear in the source.
578 VtableClosure(VtableClosureData<'tcx, N>),
580 /// Same as above, but for a function pointer type with the given signature.
581 VtableFnPointer(VtableFnPointerData<'tcx, N>),
583 /// Vtable automatically generated for a generator.
584 VtableGenerator(VtableGeneratorData<'tcx, N>),
586 /// Vtable for a trait alias.
587 VtableTraitAlias(VtableTraitAliasData<'tcx, N>),
590 /// Identifies a particular impl in the source, along with a set of
591 /// substitutions from the impl's type/lifetime parameters. The
592 /// `nested` vector corresponds to the nested obligations attached to
593 /// the impl's type parameters.
595 /// The type parameter `N` indicates the type used for "nested
596 /// obligations" that are required by the impl. During type check, this
597 /// is `Obligation`, as one might expect. During codegen, however, this
598 /// is `()`, because codegen only requires a shallow resolution of an
599 /// impl, and nested obligations are satisfied later.
600 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
601 pub struct VtableImplData<'tcx, N> {
602 pub impl_def_id: DefId,
603 pub substs: SubstsRef<'tcx>,
607 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
608 pub struct VtableGeneratorData<'tcx, N> {
609 pub generator_def_id: DefId,
610 pub substs: ty::GeneratorSubsts<'tcx>,
611 /// Nested obligations. This can be non-empty if the generator
612 /// signature contains associated types.
616 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
617 pub struct VtableClosureData<'tcx, N> {
618 pub closure_def_id: DefId,
619 pub substs: ty::ClosureSubsts<'tcx>,
620 /// Nested obligations. This can be non-empty if the closure
621 /// signature contains associated types.
625 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
626 pub struct VtableAutoImplData<N> {
627 pub trait_def_id: DefId,
631 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
632 pub struct VtableBuiltinData<N> {
636 /// A vtable for some object-safe trait `Foo` automatically derived
637 /// for the object type `Foo`.
638 #[derive(PartialEq, Eq, Clone, RustcEncodable, RustcDecodable, HashStable)]
639 pub struct VtableObjectData<'tcx, N> {
640 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
641 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
643 /// The vtable is formed by concatenating together the method lists of
644 /// the base object trait and all supertraits; this is the start of
645 /// `upcast_trait_ref`'s methods in that vtable.
646 pub vtable_base: usize,
651 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
652 pub struct VtableFnPointerData<'tcx, N> {
657 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, HashStable)]
658 pub struct VtableTraitAliasData<'tcx, N> {
659 pub alias_def_id: DefId,
660 pub substs: SubstsRef<'tcx>,
664 /// Creates predicate obligations from the generic bounds.
665 pub fn predicates_for_generics<'tcx>(
666 cause: ObligationCause<'tcx>,
667 param_env: ty::ParamEnv<'tcx>,
668 generic_bounds: &ty::InstantiatedPredicates<'tcx>,
669 ) -> PredicateObligations<'tcx> {
670 util::predicates_for_generics(cause, 0, param_env, generic_bounds)
673 /// Determines whether the type `ty` is known to meet `bound` and
674 /// returns true if so. Returns false if `ty` either does not meet
675 /// `bound` or is not known to meet bound (note that this is
676 /// conservative towards *no impl*, which is the opposite of the
677 /// `evaluate` methods).
678 pub fn type_known_to_meet_bound_modulo_regions<'a, 'tcx>(
679 infcx: &InferCtxt<'a, 'tcx>,
680 param_env: ty::ParamEnv<'tcx>,
685 debug!("type_known_to_meet_bound_modulo_regions(ty={:?}, bound={:?})",
687 infcx.tcx.def_path_str(def_id));
689 let trait_ref = ty::TraitRef {
691 substs: infcx.tcx.mk_substs_trait(ty, &[]),
693 let obligation = Obligation {
695 cause: ObligationCause::misc(span, hir::DUMMY_HIR_ID),
697 predicate: trait_ref.to_predicate(),
700 let result = infcx.predicate_must_hold_modulo_regions(&obligation);
701 debug!("type_known_to_meet_ty={:?} bound={} => {:?}",
702 ty, infcx.tcx.def_path_str(def_id), result);
704 if result && (ty.has_infer_types() || ty.has_closure_types()) {
705 // Because of inference "guessing", selection can sometimes claim
706 // to succeed while the success requires a guess. To ensure
707 // this function's result remains infallible, we must confirm
708 // that guess. While imperfect, I believe this is sound.
710 // The handling of regions in this area of the code is terrible,
711 // see issue #29149. We should be able to improve on this with
713 let mut fulfill_cx = FulfillmentContext::new_ignoring_regions();
715 // We can use a dummy node-id here because we won't pay any mind
716 // to region obligations that arise (there shouldn't really be any
718 let cause = ObligationCause::misc(span, hir::DUMMY_HIR_ID);
720 fulfill_cx.register_bound(infcx, param_env, ty, def_id, cause);
722 // Note: we only assume something is `Copy` if we can
723 // *definitively* show that it implements `Copy`. Otherwise,
724 // assume it is move; linear is always ok.
725 match fulfill_cx.select_all_or_error(infcx) {
727 debug!("type_known_to_meet_bound_modulo_regions: ty={:?} bound={} success",
729 infcx.tcx.def_path_str(def_id));
733 debug!("type_known_to_meet_bound_modulo_regions: ty={:?} bound={} errors={:?}",
735 infcx.tcx.def_path_str(def_id),
745 fn do_normalize_predicates<'tcx>(
747 region_context: DefId,
748 cause: ObligationCause<'tcx>,
749 elaborated_env: ty::ParamEnv<'tcx>,
750 predicates: Vec<ty::Predicate<'tcx>>,
751 ) -> Result<Vec<ty::Predicate<'tcx>>, ErrorReported> {
753 "do_normalize_predicates(predicates={:?}, region_context={:?}, cause={:?})",
758 let span = cause.span;
759 tcx.infer_ctxt().enter(|infcx| {
760 // FIXME. We should really... do something with these region
761 // obligations. But this call just continues the older
762 // behavior (i.e., doesn't cause any new bugs), and it would
763 // take some further refactoring to actually solve them. In
764 // particular, we would have to handle implied bounds
765 // properly, and that code is currently largely confined to
766 // regionck (though I made some efforts to extract it
769 // @arielby: In any case, these obligations are checked
770 // by wfcheck anyway, so I'm not sure we have to check
771 // them here too, and we will remove this function when
772 // we move over to lazy normalization *anyway*.
773 let fulfill_cx = FulfillmentContext::new_ignoring_regions();
774 let predicates = match fully_normalize(
781 Ok(predicates) => predicates,
783 infcx.report_fulfillment_errors(&errors, None, false);
784 return Err(ErrorReported)
788 debug!("do_normalize_predictes: normalized predicates = {:?}", predicates);
790 let region_scope_tree = region::ScopeTree::default();
792 // We can use the `elaborated_env` here; the region code only
793 // cares about declarations like `'a: 'b`.
794 let outlives_env = OutlivesEnvironment::new(elaborated_env);
796 infcx.resolve_regions_and_report_errors(
800 SuppressRegionErrors::default(),
803 let predicates = match infcx.fully_resolve(&predicates) {
804 Ok(predicates) => predicates,
806 // If we encounter a fixup error, it means that some type
807 // variable wound up unconstrained. I actually don't know
808 // if this can happen, and I certainly don't expect it to
809 // happen often, but if it did happen it probably
810 // represents a legitimate failure due to some kind of
811 // unconstrained variable, and it seems better not to ICE,
812 // all things considered.
813 tcx.sess.span_err(span, &fixup_err.to_string());
814 return Err(ErrorReported)
817 if predicates.has_local_value() {
818 // FIXME: shouldn't we, you know, actually report an error here? or an ICE?
826 // FIXME: this is gonna need to be removed ...
827 /// Normalizes the parameter environment, reporting errors if they occur.
828 pub fn normalize_param_env_or_error<'tcx>(
830 region_context: DefId,
831 unnormalized_env: ty::ParamEnv<'tcx>,
832 cause: ObligationCause<'tcx>,
833 ) -> ty::ParamEnv<'tcx> {
834 // I'm not wild about reporting errors here; I'd prefer to
835 // have the errors get reported at a defined place (e.g.,
836 // during typeck). Instead I have all parameter
837 // environments, in effect, going through this function
838 // and hence potentially reporting errors. This ensures of
839 // course that we never forget to normalize (the
840 // alternative seemed like it would involve a lot of
841 // manual invocations of this fn -- and then we'd have to
842 // deal with the errors at each of those sites).
844 // In any case, in practice, typeck constructs all the
845 // parameter environments once for every fn as it goes,
846 // and errors will get reported then; so after typeck we
847 // can be sure that no errors should occur.
849 debug!("normalize_param_env_or_error(region_context={:?}, unnormalized_env={:?}, cause={:?})",
850 region_context, unnormalized_env, cause);
852 let mut predicates: Vec<_> =
853 util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec())
856 debug!("normalize_param_env_or_error: elaborated-predicates={:?}",
859 let elaborated_env = ty::ParamEnv::new(
860 tcx.intern_predicates(&predicates),
861 unnormalized_env.reveal,
862 unnormalized_env.def_id
865 // HACK: we are trying to normalize the param-env inside *itself*. The problem is that
866 // normalization expects its param-env to be already normalized, which means we have
869 // The way we handle this is by normalizing the param-env inside an unnormalized version
870 // of the param-env, which means that if the param-env contains unnormalized projections,
871 // we'll have some normalization failures. This is unfortunate.
873 // Lazy normalization would basically handle this by treating just the
874 // normalizing-a-trait-ref-requires-itself cycles as evaluation failures.
876 // Inferred outlives bounds can create a lot of `TypeOutlives` predicates for associated
877 // types, so to make the situation less bad, we normalize all the predicates *but*
878 // the `TypeOutlives` predicates first inside the unnormalized parameter environment, and
879 // then we normalize the `TypeOutlives` bounds inside the normalized parameter environment.
881 // This works fairly well because trait matching does not actually care about param-env
882 // TypeOutlives predicates - these are normally used by regionck.
883 let outlives_predicates: Vec<_> = predicates.drain_filter(|predicate| {
885 ty::Predicate::TypeOutlives(..) => true,
890 debug!("normalize_param_env_or_error: predicates=(non-outlives={:?}, outlives={:?})",
891 predicates, outlives_predicates);
892 let non_outlives_predicates =
893 match do_normalize_predicates(tcx, region_context, cause.clone(),
894 elaborated_env, predicates) {
895 Ok(predicates) => predicates,
896 // An unnormalized env is better than nothing.
897 Err(ErrorReported) => {
898 debug!("normalize_param_env_or_error: errored resolving non-outlives predicates");
899 return elaborated_env
903 debug!("normalize_param_env_or_error: non-outlives predicates={:?}", non_outlives_predicates);
905 // Not sure whether it is better to include the unnormalized TypeOutlives predicates
906 // here. I believe they should not matter, because we are ignoring TypeOutlives param-env
907 // predicates here anyway. Keeping them here anyway because it seems safer.
908 let outlives_env: Vec<_> =
909 non_outlives_predicates.iter().chain(&outlives_predicates).cloned().collect();
910 let outlives_env = ty::ParamEnv::new(
911 tcx.intern_predicates(&outlives_env),
912 unnormalized_env.reveal,
915 let outlives_predicates =
916 match do_normalize_predicates(tcx, region_context, cause,
917 outlives_env, outlives_predicates) {
918 Ok(predicates) => predicates,
919 // An unnormalized env is better than nothing.
920 Err(ErrorReported) => {
921 debug!("normalize_param_env_or_error: errored resolving outlives predicates");
922 return elaborated_env
925 debug!("normalize_param_env_or_error: outlives predicates={:?}", outlives_predicates);
927 let mut predicates = non_outlives_predicates;
928 predicates.extend(outlives_predicates);
929 debug!("normalize_param_env_or_error: final predicates={:?}", predicates);
931 tcx.intern_predicates(&predicates),
932 unnormalized_env.reveal,
933 unnormalized_env.def_id
937 pub fn fully_normalize<'a, 'tcx, T>(
938 infcx: &InferCtxt<'a, 'tcx>,
939 mut fulfill_cx: FulfillmentContext<'tcx>,
940 cause: ObligationCause<'tcx>,
941 param_env: ty::ParamEnv<'tcx>,
943 ) -> Result<T, Vec<FulfillmentError<'tcx>>>
945 T: TypeFoldable<'tcx>,
947 debug!("fully_normalize_with_fulfillcx(value={:?})", value);
948 let selcx = &mut SelectionContext::new(infcx);
949 let Normalized { value: normalized_value, obligations } =
950 project::normalize(selcx, param_env, cause, value);
951 debug!("fully_normalize: normalized_value={:?} obligations={:?}",
954 for obligation in obligations {
955 fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
958 debug!("fully_normalize: select_all_or_error start");
959 fulfill_cx.select_all_or_error(infcx)?;
960 debug!("fully_normalize: select_all_or_error complete");
961 let resolved_value = infcx.resolve_vars_if_possible(&normalized_value);
962 debug!("fully_normalize: resolved_value={:?}", resolved_value);
966 /// Normalizes the predicates and checks whether they hold in an empty
967 /// environment. If this returns false, then either normalize
968 /// encountered an error or one of the predicates did not hold. Used
969 /// when creating vtables to check for unsatisfiable methods.
970 fn normalize_and_test_predicates<'tcx>(
972 predicates: Vec<ty::Predicate<'tcx>>,
974 debug!("normalize_and_test_predicates(predicates={:?})",
977 let result = tcx.infer_ctxt().enter(|infcx| {
978 let param_env = ty::ParamEnv::reveal_all();
979 let mut selcx = SelectionContext::new(&infcx);
980 let mut fulfill_cx = FulfillmentContext::new();
981 let cause = ObligationCause::dummy();
982 let Normalized { value: predicates, obligations } =
983 normalize(&mut selcx, param_env, cause.clone(), &predicates);
984 for obligation in obligations {
985 fulfill_cx.register_predicate_obligation(&infcx, obligation);
987 for predicate in predicates {
988 let obligation = Obligation::new(cause.clone(), param_env, predicate);
989 fulfill_cx.register_predicate_obligation(&infcx, obligation);
992 fulfill_cx.select_all_or_error(&infcx).is_ok()
994 debug!("normalize_and_test_predicates(predicates={:?}) = {:?}",
999 fn substitute_normalize_and_test_predicates<'tcx>(
1001 key: (DefId, SubstsRef<'tcx>),
1003 debug!("substitute_normalize_and_test_predicates(key={:?})",
1006 let predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates;
1007 let result = normalize_and_test_predicates(tcx, predicates);
1009 debug!("substitute_normalize_and_test_predicates(key={:?}) = {:?}",
1014 /// Given a trait `trait_ref`, iterates the vtable entries
1015 /// that come from `trait_ref`, including its supertraits.
1016 #[inline] // FIXME(#35870): avoid closures being unexported due to `impl Trait`.
1017 fn vtable_methods<'tcx>(
1019 trait_ref: ty::PolyTraitRef<'tcx>,
1020 ) -> &'tcx [Option<(DefId, SubstsRef<'tcx>)>] {
1021 debug!("vtable_methods({:?})", trait_ref);
1023 tcx.arena.alloc_from_iter(
1024 supertraits(tcx, trait_ref).flat_map(move |trait_ref| {
1025 let trait_methods = tcx.associated_items(trait_ref.def_id())
1026 .filter(|item| item.kind == ty::AssocKind::Method);
1028 // Now list each method's DefId and InternalSubsts (for within its trait).
1029 // If the method can never be called from this object, produce None.
1030 trait_methods.map(move |trait_method| {
1031 debug!("vtable_methods: trait_method={:?}", trait_method);
1032 let def_id = trait_method.def_id;
1034 // Some methods cannot be called on an object; skip those.
1035 if !tcx.is_vtable_safe_method(trait_ref.def_id(), &trait_method) {
1036 debug!("vtable_methods: not vtable safe");
1040 // the method may have some early-bound lifetimes, add
1041 // regions for those
1042 let substs = trait_ref.map_bound(|trait_ref|
1043 InternalSubsts::for_item(tcx, def_id, |param, _|
1045 GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
1046 GenericParamDefKind::Type { .. } |
1047 GenericParamDefKind::Const => {
1048 trait_ref.substs[param.index as usize]
1054 // the trait type may have higher-ranked lifetimes in it;
1055 // so erase them if they appear, so that we get the type
1056 // at some particular call site
1057 let substs = tcx.normalize_erasing_late_bound_regions(
1058 ty::ParamEnv::reveal_all(),
1062 // It's possible that the method relies on where clauses that
1063 // do not hold for this particular set of type parameters.
1064 // Note that this method could then never be called, so we
1065 // do not want to try and codegen it, in that case (see #23435).
1066 let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
1067 if !normalize_and_test_predicates(tcx, predicates.predicates) {
1068 debug!("vtable_methods: predicates do not hold");
1072 Some((def_id, substs))
1078 impl<'tcx, O> Obligation<'tcx, O> {
1079 pub fn new(cause: ObligationCause<'tcx>,
1080 param_env: ty::ParamEnv<'tcx>,
1082 -> Obligation<'tcx, O>
1084 Obligation { cause, param_env, recursion_depth: 0, predicate }
1087 fn with_depth(cause: ObligationCause<'tcx>,
1088 recursion_depth: usize,
1089 param_env: ty::ParamEnv<'tcx>,
1091 -> Obligation<'tcx, O>
1093 Obligation { cause, param_env, recursion_depth, predicate }
1096 pub fn misc(span: Span,
1097 body_id: hir::HirId,
1098 param_env: ty::ParamEnv<'tcx>,
1100 -> Obligation<'tcx, O> {
1101 Obligation::new(ObligationCause::misc(span, body_id), param_env, trait_ref)
1104 pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
1105 Obligation { cause: self.cause.clone(),
1106 param_env: self.param_env,
1107 recursion_depth: self.recursion_depth,
1112 impl<'tcx> ObligationCause<'tcx> {
1114 pub fn new(span: Span,
1115 body_id: hir::HirId,
1116 code: ObligationCauseCode<'tcx>)
1117 -> ObligationCause<'tcx> {
1118 ObligationCause { span, body_id, code }
1121 pub fn misc(span: Span, body_id: hir::HirId) -> ObligationCause<'tcx> {
1122 ObligationCause { span, body_id, code: MiscObligation }
1125 pub fn dummy() -> ObligationCause<'tcx> {
1126 ObligationCause { span: DUMMY_SP, body_id: hir::CRATE_HIR_ID, code: MiscObligation }
1130 impl<'tcx, N> Vtable<'tcx, N> {
1131 pub fn nested_obligations(self) -> Vec<N> {
1133 VtableImpl(i) => i.nested,
1134 VtableParam(n) => n,
1135 VtableBuiltin(i) => i.nested,
1136 VtableAutoImpl(d) => d.nested,
1137 VtableClosure(c) => c.nested,
1138 VtableGenerator(c) => c.nested,
1139 VtableObject(d) => d.nested,
1140 VtableFnPointer(d) => d.nested,
1141 VtableTraitAlias(d) => d.nested,
1145 pub fn map<M, F>(self, f: F) -> Vtable<'tcx, M> where F: FnMut(N) -> M {
1147 VtableImpl(i) => VtableImpl(VtableImplData {
1148 impl_def_id: i.impl_def_id,
1150 nested: i.nested.into_iter().map(f).collect(),
1152 VtableParam(n) => VtableParam(n.into_iter().map(f).collect()),
1153 VtableBuiltin(i) => VtableBuiltin(VtableBuiltinData {
1154 nested: i.nested.into_iter().map(f).collect(),
1156 VtableObject(o) => VtableObject(VtableObjectData {
1157 upcast_trait_ref: o.upcast_trait_ref,
1158 vtable_base: o.vtable_base,
1159 nested: o.nested.into_iter().map(f).collect(),
1161 VtableAutoImpl(d) => VtableAutoImpl(VtableAutoImplData {
1162 trait_def_id: d.trait_def_id,
1163 nested: d.nested.into_iter().map(f).collect(),
1165 VtableClosure(c) => VtableClosure(VtableClosureData {
1166 closure_def_id: c.closure_def_id,
1168 nested: c.nested.into_iter().map(f).collect(),
1170 VtableGenerator(c) => VtableGenerator(VtableGeneratorData {
1171 generator_def_id: c.generator_def_id,
1173 nested: c.nested.into_iter().map(f).collect(),
1175 VtableFnPointer(p) => VtableFnPointer(VtableFnPointerData {
1177 nested: p.nested.into_iter().map(f).collect(),
1179 VtableTraitAlias(d) => VtableTraitAlias(VtableTraitAliasData {
1180 alias_def_id: d.alias_def_id,
1182 nested: d.nested.into_iter().map(f).collect(),
1188 impl<'tcx> FulfillmentError<'tcx> {
1189 fn new(obligation: PredicateObligation<'tcx>,
1190 code: FulfillmentErrorCode<'tcx>)
1191 -> FulfillmentError<'tcx>
1193 FulfillmentError { obligation: obligation, code: code, points_at_arg_span: false }
1197 impl<'tcx> TraitObligation<'tcx> {
1198 fn self_ty(&self) -> ty::Binder<Ty<'tcx>> {
1199 self.predicate.map_bound(|p| p.self_ty())
1203 pub fn provide(providers: &mut ty::query::Providers<'_>) {
1204 *providers = ty::query::Providers {
1205 is_object_safe: object_safety::is_object_safe_provider,
1206 specialization_graph_of: specialize::specialization_graph_provider,
1207 specializes: specialize::specializes,
1208 codegen_fulfill_obligation: codegen::codegen_fulfill_obligation,
1210 substitute_normalize_and_test_predicates,
1215 pub trait ExClauseFold<'tcx>
1217 Self: chalk_engine::context::Context + Clone,
1219 fn fold_ex_clause_with<F: TypeFolder<'tcx>>(
1220 ex_clause: &chalk_engine::ExClause<Self>,
1222 ) -> chalk_engine::ExClause<Self>;
1224 fn visit_ex_clause_with<V: TypeVisitor<'tcx>>(
1225 ex_clause: &chalk_engine::ExClause<Self>,
1230 pub trait ChalkContextLift<'tcx>
1232 Self: chalk_engine::context::Context + Clone,
1234 type LiftedExClause: Debug + 'tcx;
1235 type LiftedDelayedLiteral: Debug + 'tcx;
1236 type LiftedLiteral: Debug + 'tcx;
1238 fn lift_ex_clause_to_tcx(
1239 ex_clause: &chalk_engine::ExClause<Self>,
1241 ) -> Option<Self::LiftedExClause>;
1243 fn lift_delayed_literal_to_tcx(
1244 ex_clause: &chalk_engine::DelayedLiteral<Self>,
1246 ) -> Option<Self::LiftedDelayedLiteral>;
1248 fn lift_literal_to_tcx(
1249 ex_clause: &chalk_engine::Literal<Self>,
1251 ) -> Option<Self::LiftedLiteral>;