1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Trait Resolution. See [rustc guide] for more info on how this works.
13 //! [rustc guide]: https://rust-lang-nursery.github.io/rustc-guide/trait-resolution.html
15 pub use self::SelectionError::*;
16 pub use self::FulfillmentErrorCode::*;
17 pub use self::Vtable::*;
18 pub use self::ObligationCauseCode::*;
22 use hir::def_id::DefId;
23 use infer::outlives::env::OutlivesEnvironment;
25 use middle::const_val::ConstEvalErr;
26 use ty::subst::Substs;
27 use ty::{self, AdtKind, Slice, Ty, TyCtxt, GenericParamDefKind, ToPredicate};
28 use ty::error::{ExpectedFound, TypeError};
29 use ty::fold::{TypeFolder, TypeFoldable, TypeVisitor};
30 use infer::canonical::{Canonical, Canonicalize};
31 use infer::{InferCtxt};
33 use rustc_data_structures::sync::Lrc;
37 use syntax_pos::{Span, DUMMY_SP};
39 pub use self::coherence::{orphan_check, overlapping_impls, OrphanCheckErr, OverlapResult};
40 pub use self::fulfill::{FulfillmentContext, PendingPredicateObligation};
41 pub use self::project::MismatchedProjectionTypes;
42 pub use self::project::{normalize, normalize_projection_type, poly_project_and_unify_type};
43 pub use self::project::{ProjectionCache, ProjectionCacheSnapshot, Reveal, Normalized};
44 pub use self::object_safety::ObjectSafetyViolation;
45 pub use self::object_safety::MethodViolationCode;
46 pub use self::on_unimplemented::{OnUnimplementedDirective, OnUnimplementedNote};
47 pub use self::select::{EvaluationCache, SelectionContext, SelectionCache};
48 pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
49 pub use self::specialize::{OverlapError, specialization_graph, translate_substs};
50 pub use self::specialize::{SpecializesCache, find_associated_item};
51 pub use self::engine::TraitEngine;
52 pub use self::util::elaborate_predicates;
53 pub use self::util::supertraits;
54 pub use self::util::Supertraits;
55 pub use self::util::supertrait_def_ids;
56 pub use self::util::SupertraitDefIds;
57 pub use self::util::transitive_bounds;
62 pub mod error_reporting;
76 // Whether to enable bug compatibility with issue #43355
77 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
78 pub enum IntercrateMode {
83 // The mode that trait queries run in
84 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
85 pub enum TraitQueryMode {
86 // Standard/un-canonicalized queries get accurate
87 // spans etc. passed in and hence can do reasonable
88 // error reporting on their own.
90 // Canonicalized queries get dummy spans and hence
91 // must generally propagate errors to
92 // pre-canonicalization callsites.
96 /// An `Obligation` represents some trait reference (e.g. `int:Eq`) for
97 /// which the vtable must be found. The process of finding a vtable is
98 /// called "resolving" the `Obligation`. This process consists of
99 /// either identifying an `impl` (e.g., `impl Eq for int`) that
100 /// provides the required vtable, or else finding a bound that is in
101 /// scope. The eventual result is usually a `Selection` (defined below).
102 #[derive(Clone, PartialEq, Eq, Hash)]
103 pub struct Obligation<'tcx, T> {
104 /// Why do we have to prove this thing?
105 pub cause: ObligationCause<'tcx>,
107 /// In which environment should we prove this thing?
108 pub param_env: ty::ParamEnv<'tcx>,
110 /// What are we trying to prove?
113 /// If we started proving this as a result of trying to prove
114 /// something else, track the total depth to ensure termination.
115 /// If this goes over a certain threshold, we abort compilation --
116 /// in such cases, we can not say whether or not the predicate
117 /// holds for certain. Stupid halting problem. Such a drag.
118 pub recursion_depth: usize,
121 pub type PredicateObligation<'tcx> = Obligation<'tcx, ty::Predicate<'tcx>>;
122 pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;
124 /// Why did we incur this obligation? Used for error reporting.
125 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
126 pub struct ObligationCause<'tcx> {
129 // The id of the fn body that triggered this obligation. This is
130 // used for region obligations to determine the precise
131 // environment in which the region obligation should be evaluated
132 // (in particular, closures can add new assumptions). See the
133 // field `region_obligations` of the `FulfillmentContext` for more
135 pub body_id: ast::NodeId,
137 pub code: ObligationCauseCode<'tcx>
140 impl<'tcx> ObligationCause<'tcx> {
141 pub fn span<'a, 'gcx>(&self, tcx: &TyCtxt<'a, 'gcx, 'tcx>) -> Span {
143 ObligationCauseCode::CompareImplMethodObligation { .. } |
144 ObligationCauseCode::MainFunctionType |
145 ObligationCauseCode::StartFunctionType => {
146 tcx.sess.codemap().def_span(self.span)
153 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
154 pub enum ObligationCauseCode<'tcx> {
155 /// Not well classified or should be obvious from span.
158 /// A slice or array is WF only if `T: Sized`
161 /// A tuple is WF only if its middle elements are Sized
164 /// This is the trait reference from the given projection
165 ProjectionWf(ty::ProjectionTy<'tcx>),
167 /// In an impl of trait X for type Y, type Y must
168 /// also implement all supertraits of X.
169 ItemObligation(DefId),
171 /// A type like `&'a T` is WF only if `T: 'a`.
172 ReferenceOutlivesReferent(Ty<'tcx>),
174 /// A type like `Box<Foo<'a> + 'b>` is WF only if `'b: 'a`.
175 ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
177 /// Obligation incurred due to an object cast.
178 ObjectCastObligation(/* Object type */ Ty<'tcx>),
180 // Various cases where expressions must be sized/copy/etc:
181 /// L = X implies that L is Sized
183 /// (x1, .., xn) must be Sized
184 TupleInitializerSized,
185 /// S { ... } must be Sized
186 StructInitializerSized,
187 /// Type of each variable must be Sized
188 VariableType(ast::NodeId),
189 /// Return type must be Sized
191 /// Yield type must be Sized
193 /// [T,..n] --> T must be Copy
196 /// Types of fields (other than the last) in a struct must be sized.
199 /// Constant expressions must be sized.
202 /// static items must have `Sync` type
205 BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
207 ImplDerivedObligation(DerivedObligationCause<'tcx>),
209 /// error derived when matching traits/impls; see ObligationCause for more details
210 CompareImplMethodObligation {
211 item_name: ast::Name,
212 impl_item_def_id: DefId,
213 trait_item_def_id: DefId,
216 /// Checking that this expression can be assigned where it needs to be
217 // FIXME(eddyb) #11161 is the original Expr required?
220 /// Computing common supertype in the arms of a match expression
221 MatchExpressionArm { arm_span: Span,
222 source: hir::MatchSource },
224 /// Computing common supertype in an if expression
227 /// Computing common supertype of an if expression with no else counter-part
228 IfExpressionWithNoElse,
230 /// `main` has wrong type
233 /// `start` has wrong type
236 /// intrinsic has wrong type
242 /// `return` with no expression
245 /// `return` with an expression
246 ReturnType(ast::NodeId),
248 /// Block implicit return
249 BlockTailExpression(ast::NodeId),
251 /// #[feature(trivial_bounds)] is not enabled
255 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
256 pub struct DerivedObligationCause<'tcx> {
257 /// The trait reference of the parent obligation that led to the
258 /// current obligation. Note that only trait obligations lead to
259 /// derived obligations, so we just store the trait reference here
261 parent_trait_ref: ty::PolyTraitRef<'tcx>,
263 /// The parent trait had this cause
264 parent_code: Rc<ObligationCauseCode<'tcx>>
267 pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
268 pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
269 pub type TraitObligations<'tcx> = Vec<TraitObligation<'tcx>>;
271 /// The following types:
272 /// * `WhereClauseAtom`
276 /// are used for representing the trait system in the form of
277 /// logic programming clauses. They are part of the interface
278 /// for the chalk SLG solver.
279 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
280 pub enum WhereClauseAtom<'tcx> {
281 Implemented(ty::TraitPredicate<'tcx>),
282 ProjectionEq(ty::ProjectionPredicate<'tcx>),
285 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
286 pub enum DomainGoal<'tcx> {
287 Holds(WhereClauseAtom<'tcx>),
288 WellFormed(WhereClauseAtom<'tcx>),
289 FromEnv(WhereClauseAtom<'tcx>),
290 WellFormedTy(Ty<'tcx>),
291 Normalize(ty::ProjectionPredicate<'tcx>),
293 RegionOutlives(ty::RegionOutlivesPredicate<'tcx>),
294 TypeOutlives(ty::TypeOutlivesPredicate<'tcx>),
297 pub type PolyDomainGoal<'tcx> = ty::Binder<DomainGoal<'tcx>>;
299 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
300 pub enum QuantifierKind {
305 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
306 pub enum Goal<'tcx> {
307 Implies(Clauses<'tcx>, &'tcx Goal<'tcx>),
308 And(&'tcx Goal<'tcx>, &'tcx Goal<'tcx>),
309 Not(&'tcx Goal<'tcx>),
310 DomainGoal(DomainGoal<'tcx>),
311 Quantified(QuantifierKind, ty::Binder<&'tcx Goal<'tcx>>),
315 pub type Goals<'tcx> = &'tcx Slice<Goal<'tcx>>;
317 impl<'tcx> Goal<'tcx> {
318 pub fn from_poly_domain_goal<'a>(
319 domain_goal: PolyDomainGoal<'tcx>,
320 tcx: TyCtxt<'a, 'tcx, 'tcx>,
322 match domain_goal.no_late_bound_regions() {
324 None => Goal::Quantified(
325 QuantifierKind::Universal,
326 domain_goal.map_bound(|p| tcx.mk_goal(Goal::from(p)))
332 impl<'tcx> From<DomainGoal<'tcx>> for Goal<'tcx> {
333 fn from(domain_goal: DomainGoal<'tcx>) -> Self {
334 Goal::DomainGoal(domain_goal)
338 /// This matches the definition from Page 7 of "A Proof Procedure for the Logic of Hereditary
339 /// Harrop Formulas".
340 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
341 pub enum Clause<'tcx> {
342 Implies(ProgramClause<'tcx>),
343 ForAll(ty::Binder<ProgramClause<'tcx>>),
346 /// Multiple clauses.
347 pub type Clauses<'tcx> = &'tcx Slice<Clause<'tcx>>;
349 /// A "program clause" has the form `D :- G1, ..., Gn`. It is saying
350 /// that the domain goal `D` is true if `G1...Gn` are provable. This
351 /// is equivalent to the implication `G1..Gn => D`; we usually write
352 /// it with the reverse implication operator `:-` to emphasize the way
353 /// that programs are actually solved (via backchaining, which starts
354 /// with the goal to solve and proceeds from there).
355 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
356 pub struct ProgramClause<'tcx> {
357 /// This goal will be considered true...
358 pub goal: DomainGoal<'tcx>,
360 /// ...if we can prove these hypotheses (there may be no hypotheses at all):
361 pub hypotheses: Goals<'tcx>,
364 pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
366 #[derive(Clone,Debug)]
367 pub enum SelectionError<'tcx> {
369 OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
370 ty::PolyTraitRef<'tcx>,
371 ty::error::TypeError<'tcx>),
372 TraitNotObjectSafe(DefId),
373 ConstEvalFailure(ConstEvalErr<'tcx>),
377 pub struct FulfillmentError<'tcx> {
378 pub obligation: PredicateObligation<'tcx>,
379 pub code: FulfillmentErrorCode<'tcx>
383 pub enum FulfillmentErrorCode<'tcx> {
384 CodeSelectionError(SelectionError<'tcx>),
385 CodeProjectionError(MismatchedProjectionTypes<'tcx>),
386 CodeSubtypeError(ExpectedFound<Ty<'tcx>>,
387 TypeError<'tcx>), // always comes from a SubtypePredicate
391 /// When performing resolution, it is typically the case that there
392 /// can be one of three outcomes:
394 /// - `Ok(Some(r))`: success occurred with result `r`
395 /// - `Ok(None)`: could not definitely determine anything, usually due
396 /// to inconclusive type inference.
397 /// - `Err(e)`: error `e` occurred
398 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
400 /// Given the successful resolution of an obligation, the `Vtable`
401 /// indicates where the vtable comes from. Note that while we call this
402 /// a "vtable", it does not necessarily indicate dynamic dispatch at
403 /// runtime. `Vtable` instances just tell the compiler where to find
404 /// methods, but in generic code those methods are typically statically
405 /// dispatched -- only when an object is constructed is a `Vtable`
406 /// instance reified into an actual vtable.
408 /// For example, the vtable may be tied to a specific impl (case A),
409 /// or it may be relative to some bound that is in scope (case B).
413 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
414 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
415 /// impl Clone for int { ... } // Impl_3
417 /// fn foo<T:Clone>(concrete: Option<Box<int>>,
419 /// mixed: Option<T>) {
421 /// // Case A: Vtable points at a specific impl. Only possible when
422 /// // type is concretely known. If the impl itself has bounded
423 /// // type parameters, Vtable will carry resolutions for those as well:
424 /// concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
426 /// // Case B: Vtable must be provided by caller. This applies when
427 /// // type is a type parameter.
428 /// param.clone(); // VtableParam
430 /// // Case C: A mix of cases A and B.
431 /// mixed.clone(); // Vtable(Impl_1, [VtableParam])
435 /// ### The type parameter `N`
437 /// See explanation on `VtableImplData`.
438 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
439 pub enum Vtable<'tcx, N> {
440 /// Vtable identifying a particular impl.
441 VtableImpl(VtableImplData<'tcx, N>),
443 /// Vtable for auto trait implementations
444 /// This carries the information and nested obligations with regards
445 /// to an auto implementation for a trait `Trait`. The nested obligations
446 /// ensure the trait implementation holds for all the constituent types.
447 VtableAutoImpl(VtableAutoImplData<N>),
449 /// Successful resolution to an obligation provided by the caller
450 /// for some type parameter. The `Vec<N>` represents the
451 /// obligations incurred from normalizing the where-clause (if
455 /// Virtual calls through an object
456 VtableObject(VtableObjectData<'tcx, N>),
458 /// Successful resolution for a builtin trait.
459 VtableBuiltin(VtableBuiltinData<N>),
461 /// Vtable automatically generated for a closure. The def ID is the ID
462 /// of the closure expression. This is a `VtableImpl` in spirit, but the
463 /// impl is generated by the compiler and does not appear in the source.
464 VtableClosure(VtableClosureData<'tcx, N>),
466 /// Same as above, but for a fn pointer type with the given signature.
467 VtableFnPointer(VtableFnPointerData<'tcx, N>),
469 /// Vtable automatically generated for a generator
470 VtableGenerator(VtableGeneratorData<'tcx, N>),
473 /// Identifies a particular impl in the source, along with a set of
474 /// substitutions from the impl's type/lifetime parameters. The
475 /// `nested` vector corresponds to the nested obligations attached to
476 /// the impl's type parameters.
478 /// The type parameter `N` indicates the type used for "nested
479 /// obligations" that are required by the impl. During type check, this
480 /// is `Obligation`, as one might expect. During codegen, however, this
481 /// is `()`, because codegen only requires a shallow resolution of an
482 /// impl, and nested obligations are satisfied later.
483 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
484 pub struct VtableImplData<'tcx, N> {
485 pub impl_def_id: DefId,
486 pub substs: &'tcx Substs<'tcx>,
490 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
491 pub struct VtableGeneratorData<'tcx, N> {
492 pub generator_def_id: DefId,
493 pub substs: ty::GeneratorSubsts<'tcx>,
494 /// Nested obligations. This can be non-empty if the generator
495 /// signature contains associated types.
499 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
500 pub struct VtableClosureData<'tcx, N> {
501 pub closure_def_id: DefId,
502 pub substs: ty::ClosureSubsts<'tcx>,
503 /// Nested obligations. This can be non-empty if the closure
504 /// signature contains associated types.
508 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
509 pub struct VtableAutoImplData<N> {
510 pub trait_def_id: DefId,
514 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
515 pub struct VtableBuiltinData<N> {
519 /// A vtable for some object-safe trait `Foo` automatically derived
520 /// for the object type `Foo`.
521 #[derive(PartialEq, Eq, Clone, RustcEncodable, RustcDecodable)]
522 pub struct VtableObjectData<'tcx, N> {
523 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
524 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
526 /// The vtable is formed by concatenating together the method lists of
527 /// the base object trait and all supertraits; this is the start of
528 /// `upcast_trait_ref`'s methods in that vtable.
529 pub vtable_base: usize,
534 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable)]
535 pub struct VtableFnPointerData<'tcx, N> {
540 /// Creates predicate obligations from the generic bounds.
541 pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
542 param_env: ty::ParamEnv<'tcx>,
543 generic_bounds: &ty::InstantiatedPredicates<'tcx>)
544 -> PredicateObligations<'tcx>
546 util::predicates_for_generics(cause, 0, param_env, generic_bounds)
549 /// Determines whether the type `ty` is known to meet `bound` and
550 /// returns true if so. Returns false if `ty` either does not meet
551 /// `bound` or is not known to meet bound (note that this is
552 /// conservative towards *no impl*, which is the opposite of the
553 /// `evaluate` methods).
554 pub fn type_known_to_meet_bound<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
555 param_env: ty::ParamEnv<'tcx>,
561 debug!("type_known_to_meet_bound(ty={:?}, bound={:?})",
563 infcx.tcx.item_path_str(def_id));
565 let trait_ref = ty::TraitRef {
567 substs: infcx.tcx.mk_substs_trait(ty, &[]),
569 let obligation = Obligation {
571 cause: ObligationCause::misc(span, ast::DUMMY_NODE_ID),
573 predicate: trait_ref.to_predicate(),
576 let result = infcx.predicate_must_hold(&obligation);
577 debug!("type_known_to_meet_ty={:?} bound={} => {:?}",
578 ty, infcx.tcx.item_path_str(def_id), result);
580 if result && (ty.has_infer_types() || ty.has_closure_types()) {
581 // Because of inference "guessing", selection can sometimes claim
582 // to succeed while the success requires a guess. To ensure
583 // this function's result remains infallible, we must confirm
584 // that guess. While imperfect, I believe this is sound.
586 // The handling of regions in this area of the code is terrible,
587 // see issue #29149. We should be able to improve on this with
589 let mut fulfill_cx = FulfillmentContext::new_ignoring_regions();
591 // We can use a dummy node-id here because we won't pay any mind
592 // to region obligations that arise (there shouldn't really be any
594 let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
596 fulfill_cx.register_bound(infcx, param_env, ty, def_id, cause);
598 // Note: we only assume something is `Copy` if we can
599 // *definitively* show that it implements `Copy`. Otherwise,
600 // assume it is move; linear is always ok.
601 match fulfill_cx.select_all_or_error(infcx) {
603 debug!("type_known_to_meet_bound: ty={:?} bound={} success",
605 infcx.tcx.item_path_str(def_id));
609 debug!("type_known_to_meet_bound: ty={:?} bound={} errors={:?}",
611 infcx.tcx.item_path_str(def_id),
621 // FIXME: this is gonna need to be removed ...
622 /// Normalizes the parameter environment, reporting errors if they occur.
623 pub fn normalize_param_env_or_error<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
624 region_context: DefId,
625 unnormalized_env: ty::ParamEnv<'tcx>,
626 cause: ObligationCause<'tcx>)
627 -> ty::ParamEnv<'tcx>
629 // I'm not wild about reporting errors here; I'd prefer to
630 // have the errors get reported at a defined place (e.g.,
631 // during typeck). Instead I have all parameter
632 // environments, in effect, going through this function
633 // and hence potentially reporting errors. This ensurse of
634 // course that we never forget to normalize (the
635 // alternative seemed like it would involve a lot of
636 // manual invocations of this fn -- and then we'd have to
637 // deal with the errors at each of those sites).
639 // In any case, in practice, typeck constructs all the
640 // parameter environments once for every fn as it goes,
641 // and errors will get reported then; so after typeck we
642 // can be sure that no errors should occur.
644 let span = cause.span;
646 debug!("normalize_param_env_or_error(unnormalized_env={:?})",
649 let predicates: Vec<_> =
650 util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec())
651 .filter(|p| !p.is_global() || p.has_late_bound_regions()) // (*)
654 // (*) FIXME(#50825) This shouldn't be needed.
655 // Removing the bounds here stopped them from being prefered in selection.
656 // See the issue-50825 ui tests for examples
658 debug!("normalize_param_env_or_error: elaborated-predicates={:?}",
661 let elaborated_env = ty::ParamEnv::new(tcx.intern_predicates(&predicates),
662 unnormalized_env.reveal);
664 tcx.infer_ctxt().enter(|infcx| {
665 // FIXME. We should really... do something with these region
666 // obligations. But this call just continues the older
667 // behavior (i.e., doesn't cause any new bugs), and it would
668 // take some further refactoring to actually solve them. In
669 // particular, we would have to handle implied bounds
670 // properly, and that code is currently largely confined to
671 // regionck (though I made some efforts to extract it
674 // @arielby: In any case, these obligations are checked
675 // by wfcheck anyway, so I'm not sure we have to check
676 // them here too, and we will remove this function when
677 // we move over to lazy normalization *anyway*.
678 let fulfill_cx = FulfillmentContext::new_ignoring_regions();
680 let predicates = match fully_normalize(
685 // You would really want to pass infcx.param_env.caller_bounds here,
686 // but that is an interned slice, and fully_normalize takes &T and returns T, so
687 // without further refactoring, a slice can't be used. Luckily, we still have the
688 // predicate vector from which we created the ParamEnv in infcx, so we
689 // can pass that instead. It's roundabout and a bit brittle, but this code path
690 // ought to be refactored anyway, and until then it saves us from having to copy.
693 Ok(predicates) => predicates,
695 infcx.report_fulfillment_errors(&errors, None, false);
696 // An unnormalized env is better than nothing.
697 return elaborated_env;
701 debug!("normalize_param_env_or_error: normalized predicates={:?}",
704 let region_scope_tree = region::ScopeTree::default();
706 // We can use the `elaborated_env` here; the region code only
707 // cares about declarations like `'a: 'b`.
708 let outlives_env = OutlivesEnvironment::new(elaborated_env);
710 infcx.resolve_regions_and_report_errors(region_context, ®ion_scope_tree, &outlives_env);
712 let predicates = match infcx.fully_resolve(&predicates) {
713 Ok(predicates) => predicates,
715 // If we encounter a fixup error, it means that some type
716 // variable wound up unconstrained. I actually don't know
717 // if this can happen, and I certainly don't expect it to
718 // happen often, but if it did happen it probably
719 // represents a legitimate failure due to some kind of
720 // unconstrained variable, and it seems better not to ICE,
721 // all things considered.
722 tcx.sess.span_err(span, &fixup_err.to_string());
723 // An unnormalized env is better than nothing.
724 return elaborated_env;
728 let predicates = match tcx.lift_to_global(&predicates) {
729 Some(predicates) => predicates,
730 None => return elaborated_env,
733 debug!("normalize_param_env_or_error: resolved predicates={:?}",
736 ty::ParamEnv::new(tcx.intern_predicates(&predicates), unnormalized_env.reveal)
740 pub fn fully_normalize<'a, 'gcx, 'tcx, T>(
741 infcx: &InferCtxt<'a, 'gcx, 'tcx>,
742 mut fulfill_cx: FulfillmentContext<'tcx>,
743 cause: ObligationCause<'tcx>,
744 param_env: ty::ParamEnv<'tcx>,
746 -> Result<T, Vec<FulfillmentError<'tcx>>>
747 where T : TypeFoldable<'tcx>
749 debug!("fully_normalize_with_fulfillcx(value={:?})", value);
750 let selcx = &mut SelectionContext::new(infcx);
751 let Normalized { value: normalized_value, obligations } =
752 project::normalize(selcx, param_env, cause, value);
753 debug!("fully_normalize: normalized_value={:?} obligations={:?}",
756 for obligation in obligations {
757 fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
760 debug!("fully_normalize: select_all_or_error start");
761 fulfill_cx.select_all_or_error(infcx)?;
762 debug!("fully_normalize: select_all_or_error complete");
763 let resolved_value = infcx.resolve_type_vars_if_possible(&normalized_value);
764 debug!("fully_normalize: resolved_value={:?}", resolved_value);
768 /// Normalizes the predicates and checks whether they hold in an empty
769 /// environment. If this returns false, then either normalize
770 /// encountered an error or one of the predicates did not hold. Used
771 /// when creating vtables to check for unsatisfiable methods.
772 fn normalize_and_test_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
773 predicates: Vec<ty::Predicate<'tcx>>)
776 debug!("normalize_and_test_predicates(predicates={:?})",
779 let result = tcx.infer_ctxt().enter(|infcx| {
780 let param_env = ty::ParamEnv::reveal_all();
781 let mut selcx = SelectionContext::new(&infcx);
782 let mut fulfill_cx = FulfillmentContext::new();
783 let cause = ObligationCause::dummy();
784 let Normalized { value: predicates, obligations } =
785 normalize(&mut selcx, param_env, cause.clone(), &predicates);
786 for obligation in obligations {
787 fulfill_cx.register_predicate_obligation(&infcx, obligation);
789 for predicate in predicates {
790 let obligation = Obligation::new(cause.clone(), param_env, predicate);
791 fulfill_cx.register_predicate_obligation(&infcx, obligation);
794 fulfill_cx.select_all_or_error(&infcx).is_ok()
796 debug!("normalize_and_test_predicates(predicates={:?}) = {:?}",
801 fn substitute_normalize_and_test_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
802 key: (DefId, &'tcx Substs<'tcx>))
805 use ty::subst::Subst;
806 debug!("substitute_normalize_and_test_predicates(key={:?})",
809 let predicates = tcx.predicates_of(key.0).predicates.subst(tcx, key.1);
810 let result = normalize_and_test_predicates(tcx, predicates);
812 debug!("substitute_normalize_and_test_predicates(key={:?}) = {:?}",
817 /// Given a trait `trait_ref`, iterates the vtable entries
818 /// that come from `trait_ref`, including its supertraits.
819 #[inline] // FIXME(#35870) Avoid closures being unexported due to impl Trait.
820 fn vtable_methods<'a, 'tcx>(
821 tcx: TyCtxt<'a, 'tcx, 'tcx>,
822 trait_ref: ty::PolyTraitRef<'tcx>)
823 -> Lrc<Vec<Option<(DefId, &'tcx Substs<'tcx>)>>>
825 debug!("vtable_methods({:?})", trait_ref);
828 supertraits(tcx, trait_ref).flat_map(move |trait_ref| {
829 let trait_methods = tcx.associated_items(trait_ref.def_id())
830 .filter(|item| item.kind == ty::AssociatedKind::Method);
832 // Now list each method's DefId and Substs (for within its trait).
833 // If the method can never be called from this object, produce None.
834 trait_methods.map(move |trait_method| {
835 debug!("vtable_methods: trait_method={:?}", trait_method);
836 let def_id = trait_method.def_id;
838 // Some methods cannot be called on an object; skip those.
839 if !tcx.is_vtable_safe_method(trait_ref.def_id(), &trait_method) {
840 debug!("vtable_methods: not vtable safe");
844 // the method may have some early-bound lifetimes, add
846 let substs = trait_ref.map_bound(|trait_ref| {
847 Substs::for_item(tcx, def_id, |param, _| {
849 GenericParamDefKind::Lifetime => tcx.types.re_erased.into(),
850 GenericParamDefKind::Type {..} => {
851 trait_ref.substs[param.index as usize]
857 // the trait type may have higher-ranked lifetimes in it;
858 // so erase them if they appear, so that we get the type
859 // at some particular call site
860 let substs = tcx.normalize_erasing_late_bound_regions(
861 ty::ParamEnv::reveal_all(),
865 // It's possible that the method relies on where clauses that
866 // do not hold for this particular set of type parameters.
867 // Note that this method could then never be called, so we
868 // do not want to try and codegen it, in that case (see #23435).
869 let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
870 if !normalize_and_test_predicates(tcx, predicates.predicates) {
871 debug!("vtable_methods: predicates do not hold");
875 Some((def_id, substs))
881 impl<'tcx,O> Obligation<'tcx,O> {
882 pub fn new(cause: ObligationCause<'tcx>,
883 param_env: ty::ParamEnv<'tcx>,
885 -> Obligation<'tcx, O>
887 Obligation { cause, param_env, recursion_depth: 0, predicate }
890 fn with_depth(cause: ObligationCause<'tcx>,
891 recursion_depth: usize,
892 param_env: ty::ParamEnv<'tcx>,
894 -> Obligation<'tcx, O>
896 Obligation { cause, param_env, recursion_depth, predicate }
899 pub fn misc(span: Span,
900 body_id: ast::NodeId,
901 param_env: ty::ParamEnv<'tcx>,
903 -> Obligation<'tcx, O> {
904 Obligation::new(ObligationCause::misc(span, body_id), param_env, trait_ref)
907 pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
908 Obligation { cause: self.cause.clone(),
909 param_env: self.param_env,
910 recursion_depth: self.recursion_depth,
915 impl<'tcx> ObligationCause<'tcx> {
916 pub fn new(span: Span,
917 body_id: ast::NodeId,
918 code: ObligationCauseCode<'tcx>)
919 -> ObligationCause<'tcx> {
920 ObligationCause { span: span, body_id: body_id, code: code }
923 pub fn misc(span: Span, body_id: ast::NodeId) -> ObligationCause<'tcx> {
924 ObligationCause { span: span, body_id: body_id, code: MiscObligation }
927 pub fn dummy() -> ObligationCause<'tcx> {
928 ObligationCause { span: DUMMY_SP, body_id: ast::CRATE_NODE_ID, code: MiscObligation }
932 impl<'tcx, N> Vtable<'tcx, N> {
933 pub fn nested_obligations(self) -> Vec<N> {
935 VtableImpl(i) => i.nested,
937 VtableBuiltin(i) => i.nested,
938 VtableAutoImpl(d) => d.nested,
939 VtableClosure(c) => c.nested,
940 VtableGenerator(c) => c.nested,
941 VtableObject(d) => d.nested,
942 VtableFnPointer(d) => d.nested,
946 pub fn map<M, F>(self, f: F) -> Vtable<'tcx, M> where F: FnMut(N) -> M {
948 VtableImpl(i) => VtableImpl(VtableImplData {
949 impl_def_id: i.impl_def_id,
951 nested: i.nested.into_iter().map(f).collect(),
953 VtableParam(n) => VtableParam(n.into_iter().map(f).collect()),
954 VtableBuiltin(i) => VtableBuiltin(VtableBuiltinData {
955 nested: i.nested.into_iter().map(f).collect(),
957 VtableObject(o) => VtableObject(VtableObjectData {
958 upcast_trait_ref: o.upcast_trait_ref,
959 vtable_base: o.vtable_base,
960 nested: o.nested.into_iter().map(f).collect(),
962 VtableAutoImpl(d) => VtableAutoImpl(VtableAutoImplData {
963 trait_def_id: d.trait_def_id,
964 nested: d.nested.into_iter().map(f).collect(),
966 VtableFnPointer(p) => VtableFnPointer(VtableFnPointerData {
968 nested: p.nested.into_iter().map(f).collect(),
970 VtableGenerator(c) => VtableGenerator(VtableGeneratorData {
971 generator_def_id: c.generator_def_id,
973 nested: c.nested.into_iter().map(f).collect(),
975 VtableClosure(c) => VtableClosure(VtableClosureData {
976 closure_def_id: c.closure_def_id,
978 nested: c.nested.into_iter().map(f).collect(),
984 impl<'tcx> FulfillmentError<'tcx> {
985 fn new(obligation: PredicateObligation<'tcx>,
986 code: FulfillmentErrorCode<'tcx>)
987 -> FulfillmentError<'tcx>
989 FulfillmentError { obligation: obligation, code: code }
993 impl<'tcx> TraitObligation<'tcx> {
994 fn self_ty(&self) -> ty::Binder<Ty<'tcx>> {
995 self.predicate.map_bound(|p| p.self_ty())
999 pub fn provide(providers: &mut ty::maps::Providers) {
1000 *providers = ty::maps::Providers {
1001 is_object_safe: object_safety::is_object_safe_provider,
1002 specialization_graph_of: specialize::specialization_graph_provider,
1003 specializes: specialize::specializes,
1004 codegen_fulfill_obligation: codegen::codegen_fulfill_obligation,
1006 substitute_normalize_and_test_predicates,
1011 impl<'gcx: 'tcx, 'tcx> Canonicalize<'gcx, 'tcx> for ty::ParamEnvAnd<'tcx, Goal<'tcx>> {
1012 // we ought to intern this, but I'm too lazy just now
1013 type Canonicalized = Canonical<'gcx, ty::ParamEnvAnd<'gcx, Goal<'gcx>>>;
1016 _gcx: TyCtxt<'_, 'gcx, 'gcx>,
1017 value: Canonical<'gcx, Self::Lifted>,
1018 ) -> Self::Canonicalized {
1023 pub trait ExClauseFold<'tcx>
1025 Self: chalk_engine::context::Context + Clone,
1027 fn fold_ex_clause_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(
1028 ex_clause: &chalk_engine::ExClause<Self>,
1030 ) -> chalk_engine::ExClause<Self>;
1032 fn visit_ex_clause_with<'gcx: 'tcx, V: TypeVisitor<'tcx>>(
1033 ex_clause: &chalk_engine::ExClause<Self>,
1038 pub trait ExClauseLift<'tcx>
1040 Self: chalk_engine::context::Context + Clone,
1042 type LiftedExClause: Debug + 'tcx;
1044 fn lift_ex_clause_to_tcx<'a, 'gcx>(
1045 ex_clause: &chalk_engine::ExClause<Self>,
1046 tcx: TyCtxt<'a, 'gcx, 'tcx>,
1047 ) -> Option<Self::LiftedExClause>;
1050 impl<'gcx: 'tcx, 'tcx, C> Canonicalize<'gcx, 'tcx> for chalk_engine::ExClause<C>
1052 C: chalk_engine::context::Context + Clone,
1053 C: ExClauseLift<'gcx> + ExClauseFold<'tcx>,
1054 C::Substitution: Clone,
1055 C::RegionConstraint: Clone,
1057 type Canonicalized = Canonical<'gcx, C::LiftedExClause>;
1060 _gcx: TyCtxt<'_, 'gcx, 'gcx>,
1061 value: Canonical<'gcx, Self::Lifted>,
1062 ) -> Self::Canonicalized {