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 the Book for more.
13 pub use self::SelectionError::*;
14 pub use self::FulfillmentErrorCode::*;
15 pub use self::Vtable::*;
16 pub use self::ObligationCauseCode::*;
18 use dep_graph::DepNode;
19 use middle::def_id::DefId;
20 use middle::free_region::FreeRegionMap;
22 use middle::ty::{self, Ty, TypeFoldable};
23 use middle::ty::fast_reject;
24 use middle::infer::{self, fixup_err_to_string, InferCtxt};
28 use syntax::codemap::{Span, DUMMY_SP};
30 pub use self::error_reporting::TraitErrorKey;
31 pub use self::error_reporting::report_fulfillment_errors;
32 pub use self::error_reporting::report_overflow_error;
33 pub use self::error_reporting::report_selection_error;
34 pub use self::error_reporting::report_object_safety_error;
35 pub use self::coherence::orphan_check;
36 pub use self::coherence::overlapping_impls;
37 pub use self::coherence::OrphanCheckErr;
38 pub use self::fulfill::{FulfillmentContext, FulfilledPredicates, RegionObligation};
39 pub use self::project::MismatchedProjectionTypes;
40 pub use self::project::normalize;
41 pub use self::project::Normalized;
42 pub use self::object_safety::is_object_safe;
43 pub use self::object_safety::astconv_object_safety_violations;
44 pub use self::object_safety::object_safety_violations;
45 pub use self::object_safety::ObjectSafetyViolation;
46 pub use self::object_safety::MethodViolationCode;
47 pub use self::object_safety::is_vtable_safe_method;
48 pub use self::select::EvaluationCache;
49 pub use self::select::SelectionContext;
50 pub use self::select::SelectionCache;
51 pub use self::select::{MethodMatchResult, MethodMatched, MethodAmbiguous, MethodDidNotMatch};
52 pub use self::select::{MethodMatchedData}; // intentionally don't export variants
53 pub use self::util::elaborate_predicates;
54 pub use self::util::get_vtable_index_of_object_method;
55 pub use self::util::trait_ref_for_builtin_bound;
56 pub use self::util::predicate_for_trait_def;
57 pub use self::util::supertraits;
58 pub use self::util::Supertraits;
59 pub use self::util::supertrait_def_ids;
60 pub use self::util::SupertraitDefIds;
61 pub use self::util::transitive_bounds;
62 pub use self::util::upcast;
73 /// An `Obligation` represents some trait reference (e.g. `int:Eq`) for
74 /// which the vtable must be found. The process of finding a vtable is
75 /// called "resolving" the `Obligation`. This process consists of
76 /// either identifying an `impl` (e.g., `impl Eq for int`) that
77 /// provides the required vtable, or else finding a bound that is in
78 /// scope. The eventual result is usually a `Selection` (defined below).
79 #[derive(Clone, PartialEq, Eq)]
80 pub struct Obligation<'tcx, T> {
81 pub cause: ObligationCause<'tcx>,
82 pub recursion_depth: usize,
86 pub type PredicateObligation<'tcx> = Obligation<'tcx, ty::Predicate<'tcx>>;
87 pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;
89 /// Why did we incur this obligation? Used for error reporting.
90 #[derive(Clone, Debug, PartialEq, Eq)]
91 pub struct ObligationCause<'tcx> {
94 // The id of the fn body that triggered this obligation. This is
95 // used for region obligations to determine the precise
96 // environment in which the region obligation should be evaluated
97 // (in particular, closures can add new assumptions). See the
98 // field `region_obligations` of the `FulfillmentContext` for more
100 pub body_id: ast::NodeId,
102 pub code: ObligationCauseCode<'tcx>
105 #[derive(Clone, Debug, PartialEq, Eq)]
106 pub enum ObligationCauseCode<'tcx> {
107 /// Not well classified or should be obvious from span.
110 /// This is the trait reference from the given projection
113 /// This is the trait reference from the given projection
114 ProjectionWf(ty::ProjectionTy<'tcx>),
116 /// In an impl of trait X for type Y, type Y must
117 /// also implement all supertraits of X.
118 ItemObligation(DefId),
120 /// A type like `&'a T` is WF only if `T: 'a`.
121 ReferenceOutlivesReferent(Ty<'tcx>),
123 /// Obligation incurred due to an object cast.
124 ObjectCastObligation(/* Object type */ Ty<'tcx>),
126 /// Various cases where expressions must be sized/copy/etc:
127 AssignmentLhsSized, // L = X implies that L is Sized
128 StructInitializerSized, // S { ... } must be Sized
129 VariableType(ast::NodeId), // Type of each variable must be Sized
130 ReturnType, // Return type must be Sized
131 RepeatVec, // [T,..n] --> T must be Copy
133 // Captures of variable the given id by a closure (span is the
134 // span of the closure)
135 ClosureCapture(ast::NodeId, Span, ty::BuiltinBound),
137 // Types of fields (other than the last) in a struct must be sized.
140 // static items must have `Sync` type
143 BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
145 ImplDerivedObligation(DerivedObligationCause<'tcx>),
147 CompareImplMethodObligation,
150 #[derive(Clone, Debug, PartialEq, Eq)]
151 pub struct DerivedObligationCause<'tcx> {
152 /// The trait reference of the parent obligation that led to the
153 /// current obligation. Note that only trait obligations lead to
154 /// derived obligations, so we just store the trait reference here
156 parent_trait_ref: ty::PolyTraitRef<'tcx>,
158 /// The parent trait had this cause
159 parent_code: Rc<ObligationCauseCode<'tcx>>
162 pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
163 pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
164 pub type TraitObligations<'tcx> = Vec<TraitObligation<'tcx>>;
166 pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
168 #[derive(Clone,Debug)]
169 pub enum SelectionError<'tcx> {
171 OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
172 ty::PolyTraitRef<'tcx>,
173 ty::error::TypeError<'tcx>),
174 TraitNotObjectSafe(DefId),
177 pub struct FulfillmentError<'tcx> {
178 pub obligation: PredicateObligation<'tcx>,
179 pub code: FulfillmentErrorCode<'tcx>
183 pub enum FulfillmentErrorCode<'tcx> {
184 CodeSelectionError(SelectionError<'tcx>),
185 CodeProjectionError(MismatchedProjectionTypes<'tcx>),
189 /// When performing resolution, it is typically the case that there
190 /// can be one of three outcomes:
192 /// - `Ok(Some(r))`: success occurred with result `r`
193 /// - `Ok(None)`: could not definitely determine anything, usually due
194 /// to inconclusive type inference.
195 /// - `Err(e)`: error `e` occurred
196 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
198 /// Given the successful resolution of an obligation, the `Vtable`
199 /// indicates where the vtable comes from. Note that while we call this
200 /// a "vtable", it does not necessarily indicate dynamic dispatch at
201 /// runtime. `Vtable` instances just tell the compiler where to find
202 /// methods, but in generic code those methods are typically statically
203 /// dispatched -- only when an object is constructed is a `Vtable`
204 /// instance reified into an actual vtable.
206 /// For example, the vtable may be tied to a specific impl (case A),
207 /// or it may be relative to some bound that is in scope (case B).
211 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
212 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
213 /// impl Clone for int { ... } // Impl_3
215 /// fn foo<T:Clone>(concrete: Option<Box<int>>,
217 /// mixed: Option<T>) {
219 /// // Case A: Vtable points at a specific impl. Only possible when
220 /// // type is concretely known. If the impl itself has bounded
221 /// // type parameters, Vtable will carry resolutions for those as well:
222 /// concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
224 /// // Case B: Vtable must be provided by caller. This applies when
225 /// // type is a type parameter.
226 /// param.clone(); // VtableParam
228 /// // Case C: A mix of cases A and B.
229 /// mixed.clone(); // Vtable(Impl_1, [VtableParam])
233 /// ### The type parameter `N`
235 /// See explanation on `VtableImplData`.
237 pub enum Vtable<'tcx, N> {
238 /// Vtable identifying a particular impl.
239 VtableImpl(VtableImplData<'tcx, N>),
241 /// Vtable for default trait implementations
242 /// This carries the information and nested obligations with regards
243 /// to a default implementation for a trait `Trait`. The nested obligations
244 /// ensure the trait implementation holds for all the constituent types.
245 VtableDefaultImpl(VtableDefaultImplData<N>),
247 /// Successful resolution to an obligation provided by the caller
248 /// for some type parameter. The `Vec<N>` represents the
249 /// obligations incurred from normalizing the where-clause (if
253 /// Virtual calls through an object
254 VtableObject(VtableObjectData<'tcx>),
256 /// Successful resolution for a builtin trait.
257 VtableBuiltin(VtableBuiltinData<N>),
259 /// Vtable automatically generated for a closure. The def ID is the ID
260 /// of the closure expression. This is a `VtableImpl` in spirit, but the
261 /// impl is generated by the compiler and does not appear in the source.
262 VtableClosure(VtableClosureData<'tcx, N>),
264 /// Same as above, but for a fn pointer type with the given signature.
265 VtableFnPointer(ty::Ty<'tcx>),
268 /// Identifies a particular impl in the source, along with a set of
269 /// substitutions from the impl's type/lifetime parameters. The
270 /// `nested` vector corresponds to the nested obligations attached to
271 /// the impl's type parameters.
273 /// The type parameter `N` indicates the type used for "nested
274 /// obligations" that are required by the impl. During type check, this
275 /// is `Obligation`, as one might expect. During trans, however, this
276 /// is `()`, because trans only requires a shallow resolution of an
277 /// impl, and nested obligations are satisfied later.
278 #[derive(Clone, PartialEq, Eq)]
279 pub struct VtableImplData<'tcx, N> {
280 pub impl_def_id: DefId,
281 pub substs: subst::Substs<'tcx>,
285 #[derive(Clone, PartialEq, Eq)]
286 pub struct VtableClosureData<'tcx, N> {
287 pub closure_def_id: DefId,
288 pub substs: ty::ClosureSubsts<'tcx>,
289 /// Nested obligations. This can be non-empty if the closure
290 /// signature contains associated types.
295 pub struct VtableDefaultImplData<N> {
296 pub trait_def_id: DefId,
301 pub struct VtableBuiltinData<N> {
305 /// A vtable for some object-safe trait `Foo` automatically derived
306 /// for the object type `Foo`.
307 #[derive(PartialEq,Eq,Clone)]
308 pub struct VtableObjectData<'tcx> {
309 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
310 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
312 /// The vtable is formed by concatenating together the method lists of
313 /// the base object trait and all supertraits; this is the start of
314 /// `upcast_trait_ref`'s methods in that vtable.
315 pub vtable_base: usize
318 /// Creates predicate obligations from the generic bounds.
319 pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
320 generic_bounds: &ty::InstantiatedPredicates<'tcx>)
321 -> PredicateObligations<'tcx>
323 util::predicates_for_generics(cause, 0, generic_bounds)
326 /// Determines whether the type `ty` is known to meet `bound` and
327 /// returns true if so. Returns false if `ty` either does not meet
328 /// `bound` or is not known to meet bound (note that this is
329 /// conservative towards *no impl*, which is the opposite of the
330 /// `evaluate` methods).
331 pub fn type_known_to_meet_builtin_bound<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
333 bound: ty::BuiltinBound,
337 debug!("type_known_to_meet_builtin_bound(ty={:?}, bound={:?})",
341 let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
343 util::predicate_for_builtin_bound(infcx.tcx, cause, bound, 0, ty);
344 let obligation = match obligation {
346 Err(..) => return false
348 let result = SelectionContext::new(infcx)
349 .evaluate_obligation_conservatively(&obligation);
350 debug!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} => {:?}",
353 if result && (ty.has_infer_types() || ty.has_closure_types()) {
354 // Because of inference "guessing", selection can sometimes claim
355 // to succeed while the success requires a guess. To ensure
356 // this function's result remains infallible, we must confirm
357 // that guess. While imperfect, I believe this is sound.
359 let mut fulfill_cx = FulfillmentContext::new(false);
361 // We can use a dummy node-id here because we won't pay any mind
362 // to region obligations that arise (there shouldn't really be any
364 let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
366 fulfill_cx.register_builtin_bound(infcx, ty, bound, cause);
368 // Note: we only assume something is `Copy` if we can
369 // *definitively* show that it implements `Copy`. Otherwise,
370 // assume it is move; linear is always ok.
371 match fulfill_cx.select_all_or_error(infcx) {
373 debug!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} success",
379 debug!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} errors={:?}",
391 // FIXME: this is gonna need to be removed ...
392 /// Normalizes the parameter environment, reporting errors if they occur.
393 pub fn normalize_param_env_or_error<'a,'tcx>(unnormalized_env: ty::ParameterEnvironment<'a,'tcx>,
394 cause: ObligationCause<'tcx>)
395 -> ty::ParameterEnvironment<'a,'tcx>
397 // I'm not wild about reporting errors here; I'd prefer to
398 // have the errors get reported at a defined place (e.g.,
399 // during typeck). Instead I have all parameter
400 // environments, in effect, going through this function
401 // and hence potentially reporting errors. This ensurse of
402 // course that we never forget to normalize (the
403 // alternative seemed like it would involve a lot of
404 // manual invocations of this fn -- and then we'd have to
405 // deal with the errors at each of those sites).
407 // In any case, in practice, typeck constructs all the
408 // parameter environments once for every fn as it goes,
409 // and errors will get reported then; so after typeck we
410 // can be sure that no errors should occur.
412 let tcx = unnormalized_env.tcx;
413 let span = cause.span;
414 let body_id = cause.body_id;
416 debug!("normalize_param_env_or_error(unnormalized_env={:?})",
419 let predicates: Vec<_> =
420 util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.clone())
421 .filter(|p| !p.is_global()) // (*)
424 // (*) Any predicate like `i32: Trait<u32>` or whatever doesn't
425 // need to be in the *environment* to be proven, so screen those
426 // out. This is important for the soundness of inter-fn
427 // caching. Note though that we should probably check that these
428 // predicates hold at the point where the environment is
429 // constructed, but I am not currently doing so out of laziness.
432 debug!("normalize_param_env_or_error: elaborated-predicates={:?}",
435 let elaborated_env = unnormalized_env.with_caller_bounds(predicates);
437 let infcx = infer::new_infer_ctxt(tcx, &tcx.tables, Some(elaborated_env), false);
438 let predicates = match fully_normalize(&infcx, cause,
439 &infcx.parameter_environment.caller_bounds) {
440 Ok(predicates) => predicates,
442 report_fulfillment_errors(&infcx, &errors);
443 return infcx.parameter_environment; // an unnormalized env is better than nothing
447 let free_regions = FreeRegionMap::new();
448 infcx.resolve_regions_and_report_errors(&free_regions, body_id);
449 let predicates = match infcx.fully_resolve(&predicates) {
450 Ok(predicates) => predicates,
452 // If we encounter a fixup error, it means that some type
453 // variable wound up unconstrained. I actually don't know
454 // if this can happen, and I certainly don't expect it to
455 // happen often, but if it did happen it probably
456 // represents a legitimate failure due to some kind of
457 // unconstrained variable, and it seems better not to ICE,
458 // all things considered.
459 let err_msg = fixup_err_to_string(fixup_err);
460 tcx.sess.span_err(span, &err_msg);
461 return infcx.parameter_environment; // an unnormalized env is better than nothing
465 infcx.parameter_environment.with_caller_bounds(predicates)
468 pub fn fully_normalize<'a,'tcx,T>(infcx: &InferCtxt<'a,'tcx>,
469 cause: ObligationCause<'tcx>,
471 -> Result<T, Vec<FulfillmentError<'tcx>>>
472 where T : TypeFoldable<'tcx>
474 debug!("normalize_param_env(value={:?})", value);
476 let mut selcx = &mut SelectionContext::new(infcx);
477 // FIXME (@jroesch) ISSUE 26721
478 // I'm not sure if this is a bug or not, needs further investigation.
479 // It appears that by reusing the fulfillment_cx here we incur more
480 // obligations and later trip an asssertion on regionck.rs line 337.
482 // The two possibilities I see is:
483 // - normalization is not actually fully happening and we
484 // have a bug else where
485 // - we are adding a duplicate bound into the list causing
486 // its size to change.
488 // I think we should probably land this refactor and then come
489 // back to this is a follow-up patch.
490 let mut fulfill_cx = FulfillmentContext::new(false);
492 let Normalized { value: normalized_value, obligations } =
493 project::normalize(selcx, cause, value);
494 debug!("normalize_param_env: normalized_value={:?} obligations={:?}",
497 for obligation in obligations {
498 fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
501 try!(fulfill_cx.select_all_or_error(infcx));
502 let resolved_value = infcx.resolve_type_vars_if_possible(&normalized_value);
503 debug!("normalize_param_env: resolved_value={:?}", resolved_value);
507 impl<'tcx,O> Obligation<'tcx,O> {
508 pub fn new(cause: ObligationCause<'tcx>,
510 -> Obligation<'tcx, O>
512 Obligation { cause: cause,
514 predicate: trait_ref }
517 fn with_depth(cause: ObligationCause<'tcx>,
518 recursion_depth: usize,
520 -> Obligation<'tcx, O>
522 Obligation { cause: cause,
523 recursion_depth: recursion_depth,
524 predicate: trait_ref }
527 pub fn misc(span: Span, body_id: ast::NodeId, trait_ref: O) -> Obligation<'tcx, O> {
528 Obligation::new(ObligationCause::misc(span, body_id), trait_ref)
531 pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
532 Obligation { cause: self.cause.clone(),
533 recursion_depth: self.recursion_depth,
538 impl<'tcx> ObligationCause<'tcx> {
539 pub fn new(span: Span,
540 body_id: ast::NodeId,
541 code: ObligationCauseCode<'tcx>)
542 -> ObligationCause<'tcx> {
543 ObligationCause { span: span, body_id: body_id, code: code }
546 pub fn misc(span: Span, body_id: ast::NodeId) -> ObligationCause<'tcx> {
547 ObligationCause { span: span, body_id: body_id, code: MiscObligation }
550 pub fn dummy() -> ObligationCause<'tcx> {
551 ObligationCause { span: DUMMY_SP, body_id: 0, code: MiscObligation }
555 impl<'tcx, N> Vtable<'tcx, N> {
556 pub fn nested_obligations(self) -> Vec<N> {
558 VtableImpl(i) => i.nested,
560 VtableBuiltin(i) => i.nested,
561 VtableDefaultImpl(d) => d.nested,
562 VtableClosure(c) => c.nested,
563 VtableObject(_) | VtableFnPointer(..) => vec![]
567 pub fn map<M, F>(self, f: F) -> Vtable<'tcx, M> where F: FnMut(N) -> M {
569 VtableImpl(i) => VtableImpl(VtableImplData {
570 impl_def_id: i.impl_def_id,
572 nested: i.nested.into_iter().map(f).collect()
574 VtableParam(n) => VtableParam(n.into_iter().map(f).collect()),
575 VtableBuiltin(i) => VtableBuiltin(VtableBuiltinData {
576 nested: i.nested.into_iter().map(f).collect()
578 VtableObject(o) => VtableObject(o),
579 VtableDefaultImpl(d) => VtableDefaultImpl(VtableDefaultImplData {
580 trait_def_id: d.trait_def_id,
581 nested: d.nested.into_iter().map(f).collect()
583 VtableFnPointer(f) => VtableFnPointer(f),
584 VtableClosure(c) => VtableClosure(VtableClosureData {
585 closure_def_id: c.closure_def_id,
587 nested: c.nested.into_iter().map(f).collect(),
593 impl<'tcx> FulfillmentError<'tcx> {
594 fn new(obligation: PredicateObligation<'tcx>,
595 code: FulfillmentErrorCode<'tcx>)
596 -> FulfillmentError<'tcx>
598 FulfillmentError { obligation: obligation, code: code }
602 impl<'tcx> TraitObligation<'tcx> {
603 /// Creates the dep-node for selecting/evaluating this trait reference.
604 fn dep_node(&self, tcx: &ty::ctxt<'tcx>) -> DepNode {
606 fast_reject::simplify_type(tcx,
607 self.predicate.skip_binder().self_ty(), // (*)
610 // (*) skip_binder is ok because `simplify_type` doesn't care about regions
612 DepNode::TraitSelect(self.predicate.def_id(), simplified_ty)
615 fn self_ty(&self) -> ty::Binder<Ty<'tcx>> {
616 ty::Binder(self.predicate.skip_binder().self_ty())