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 middle::def_id::DefId;
19 use middle::free_region::FreeRegionMap;
21 use middle::ty::{self, HasTypeFlags, Ty};
22 use middle::ty::fold::TypeFoldable;
23 use middle::infer::{self, fixup_err_to_string, InferCtxt};
27 use syntax::codemap::{Span, DUMMY_SP};
29 pub use self::error_reporting::TraitErrorKey;
30 pub use self::error_reporting::report_fulfillment_errors;
31 pub use self::error_reporting::report_overflow_error;
32 pub use self::error_reporting::report_selection_error;
33 pub use self::error_reporting::report_object_safety_error;
34 pub use self::coherence::orphan_check;
35 pub use self::coherence::overlapping_impls;
36 pub use self::coherence::OrphanCheckErr;
37 pub use self::fulfill::{FulfillmentContext, FulfilledPredicates, RegionObligation};
38 pub use self::project::MismatchedProjectionTypes;
39 pub use self::project::normalize;
40 pub use self::project::Normalized;
41 pub use self::object_safety::is_object_safe;
42 pub use self::object_safety::astconv_object_safety_violations;
43 pub use self::object_safety::object_safety_violations;
44 pub use self::object_safety::ObjectSafetyViolation;
45 pub use self::object_safety::MethodViolationCode;
46 pub use self::object_safety::is_vtable_safe_method;
47 pub use self::select::EvaluationCache;
48 pub use self::select::SelectionContext;
49 pub use self::select::SelectionCache;
50 pub use self::select::{MethodMatchResult, MethodMatched, MethodAmbiguous, MethodDidNotMatch};
51 pub use self::select::{MethodMatchedData}; // intentionally don't export variants
52 pub use self::util::elaborate_predicates;
53 pub use self::util::get_vtable_index_of_object_method;
54 pub use self::util::trait_ref_for_builtin_bound;
55 pub use self::util::predicate_for_trait_def;
56 pub use self::util::supertraits;
57 pub use self::util::Supertraits;
58 pub use self::util::supertrait_def_ids;
59 pub use self::util::SupertraitDefIds;
60 pub use self::util::transitive_bounds;
61 pub use self::util::upcast;
72 /// An `Obligation` represents some trait reference (e.g. `int:Eq`) for
73 /// which the vtable must be found. The process of finding a vtable is
74 /// called "resolving" the `Obligation`. This process consists of
75 /// either identifying an `impl` (e.g., `impl Eq for int`) that
76 /// provides the required vtable, or else finding a bound that is in
77 /// scope. The eventual result is usually a `Selection` (defined below).
78 #[derive(Clone, PartialEq, Eq)]
79 pub struct Obligation<'tcx, T> {
80 pub cause: ObligationCause<'tcx>,
81 pub recursion_depth: usize,
85 pub type PredicateObligation<'tcx> = Obligation<'tcx, ty::Predicate<'tcx>>;
86 pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;
88 /// Why did we incur this obligation? Used for error reporting.
89 #[derive(Clone, Debug, PartialEq, Eq)]
90 pub struct ObligationCause<'tcx> {
93 // The id of the fn body that triggered this obligation. This is
94 // used for region obligations to determine the precise
95 // environment in which the region obligation should be evaluated
96 // (in particular, closures can add new assumptions). See the
97 // field `region_obligations` of the `FulfillmentContext` for more
99 pub body_id: ast::NodeId,
101 pub code: ObligationCauseCode<'tcx>
104 #[derive(Clone, Debug, PartialEq, Eq)]
105 pub enum ObligationCauseCode<'tcx> {
106 /// Not well classified or should be obvious from span.
109 /// This is the trait reference from the given projection
112 /// This is the trait reference from the given projection
113 ProjectionWf(ty::ProjectionTy<'tcx>),
115 /// In an impl of trait X for type Y, type Y must
116 /// also implement all supertraits of X.
117 ItemObligation(DefId),
119 /// A type like `&'a T` is WF only if `T: 'a`.
120 ReferenceOutlivesReferent(Ty<'tcx>),
122 /// Obligation incurred due to an object cast.
123 ObjectCastObligation(/* Object type */ Ty<'tcx>),
125 /// Various cases where expressions must be sized/copy/etc:
126 AssignmentLhsSized, // L = X implies that L is Sized
127 StructInitializerSized, // S { ... } must be Sized
128 VariableType(ast::NodeId), // Type of each variable must be Sized
129 ReturnType, // Return type must be Sized
130 RepeatVec, // [T,..n] --> T must be Copy
132 // Captures of variable the given id by a closure (span is the
133 // span of the closure)
134 ClosureCapture(ast::NodeId, Span, ty::BuiltinBound),
136 // Types of fields (other than the last) in a struct must be sized.
139 // static items must have `Sync` type
142 BuiltinDerivedObligation(DerivedObligationCause<'tcx>),
144 ImplDerivedObligation(DerivedObligationCause<'tcx>),
146 CompareImplMethodObligation,
149 #[derive(Clone, Debug, PartialEq, Eq)]
150 pub struct DerivedObligationCause<'tcx> {
151 /// The trait reference of the parent obligation that led to the
152 /// current obligation. Note that only trait obligations lead to
153 /// derived obligations, so we just store the trait reference here
155 parent_trait_ref: ty::PolyTraitRef<'tcx>,
157 /// The parent trait had this cause
158 parent_code: Rc<ObligationCauseCode<'tcx>>
161 pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
162 pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
163 pub type TraitObligations<'tcx> = Vec<TraitObligation<'tcx>>;
165 pub type Selection<'tcx> = Vtable<'tcx, PredicateObligation<'tcx>>;
167 #[derive(Clone,Debug)]
168 pub enum SelectionError<'tcx> {
170 OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
171 ty::PolyTraitRef<'tcx>,
172 ty::error::TypeError<'tcx>),
173 TraitNotObjectSafe(DefId),
176 pub struct FulfillmentError<'tcx> {
177 pub obligation: PredicateObligation<'tcx>,
178 pub code: FulfillmentErrorCode<'tcx>
182 pub enum FulfillmentErrorCode<'tcx> {
183 CodeSelectionError(SelectionError<'tcx>),
184 CodeProjectionError(MismatchedProjectionTypes<'tcx>),
188 /// When performing resolution, it is typically the case that there
189 /// can be one of three outcomes:
191 /// - `Ok(Some(r))`: success occurred with result `r`
192 /// - `Ok(None)`: could not definitely determine anything, usually due
193 /// to inconclusive type inference.
194 /// - `Err(e)`: error `e` occurred
195 pub type SelectionResult<'tcx, T> = Result<Option<T>, SelectionError<'tcx>>;
197 /// Given the successful resolution of an obligation, the `Vtable`
198 /// indicates where the vtable comes from. Note that while we call this
199 /// a "vtable", it does not necessarily indicate dynamic dispatch at
200 /// runtime. `Vtable` instances just tell the compiler where to find
201 /// methods, but in generic code those methods are typically statically
202 /// dispatched -- only when an object is constructed is a `Vtable`
203 /// instance reified into an actual vtable.
205 /// For example, the vtable may be tied to a specific impl (case A),
206 /// or it may be relative to some bound that is in scope (case B).
210 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
211 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
212 /// impl Clone for int { ... } // Impl_3
214 /// fn foo<T:Clone>(concrete: Option<Box<int>>,
216 /// mixed: Option<T>) {
218 /// // Case A: Vtable points at a specific impl. Only possible when
219 /// // type is concretely known. If the impl itself has bounded
220 /// // type parameters, Vtable will carry resolutions for those as well:
221 /// concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
223 /// // Case B: Vtable must be provided by caller. This applies when
224 /// // type is a type parameter.
225 /// param.clone(); // VtableParam
227 /// // Case C: A mix of cases A and B.
228 /// mixed.clone(); // Vtable(Impl_1, [VtableParam])
232 /// ### The type parameter `N`
234 /// See explanation on `VtableImplData`.
236 pub enum Vtable<'tcx, N> {
237 /// Vtable identifying a particular impl.
238 VtableImpl(VtableImplData<'tcx, N>),
240 /// Vtable for default trait implementations
241 /// This carries the information and nested obligations with regards
242 /// to a default implementation for a trait `Trait`. The nested obligations
243 /// ensure the trait implementation holds for all the constituent types.
244 VtableDefaultImpl(VtableDefaultImplData<N>),
246 /// Successful resolution to an obligation provided by the caller
247 /// for some type parameter. The `Vec<N>` represents the
248 /// obligations incurred from normalizing the where-clause (if
252 /// Virtual calls through an object
253 VtableObject(VtableObjectData<'tcx>),
255 /// Successful resolution for a builtin trait.
256 VtableBuiltin(VtableBuiltinData<N>),
258 /// Vtable automatically generated for a closure. The def ID is the ID
259 /// of the closure expression. This is a `VtableImpl` in spirit, but the
260 /// impl is generated by the compiler and does not appear in the source.
261 VtableClosure(VtableClosureData<'tcx, N>),
263 /// Same as above, but for a fn pointer type with the given signature.
264 VtableFnPointer(ty::Ty<'tcx>),
267 /// Identifies a particular impl in the source, along with a set of
268 /// substitutions from the impl's type/lifetime parameters. The
269 /// `nested` vector corresponds to the nested obligations attached to
270 /// the impl's type parameters.
272 /// The type parameter `N` indicates the type used for "nested
273 /// obligations" that are required by the impl. During type check, this
274 /// is `Obligation`, as one might expect. During trans, however, this
275 /// is `()`, because trans only requires a shallow resolution of an
276 /// impl, and nested obligations are satisfied later.
277 #[derive(Clone, PartialEq, Eq)]
278 pub struct VtableImplData<'tcx, N> {
279 pub impl_def_id: DefId,
280 pub substs: subst::Substs<'tcx>,
284 #[derive(Clone, PartialEq, Eq)]
285 pub struct VtableClosureData<'tcx, N> {
286 pub closure_def_id: DefId,
287 pub substs: ty::ClosureSubsts<'tcx>,
288 /// Nested obligations. This can be non-empty if the closure
289 /// signature contains associated types.
294 pub struct VtableDefaultImplData<N> {
295 pub trait_def_id: DefId,
300 pub struct VtableBuiltinData<N> {
304 /// A vtable for some object-safe trait `Foo` automatically derived
305 /// for the object type `Foo`.
306 #[derive(PartialEq,Eq,Clone)]
307 pub struct VtableObjectData<'tcx> {
308 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
309 pub upcast_trait_ref: ty::PolyTraitRef<'tcx>,
311 /// The vtable is formed by concatenating together the method lists of
312 /// the base object trait and all supertraits; this is the start of
313 /// `upcast_trait_ref`'s methods in that vtable.
314 pub vtable_base: usize
317 /// Creates predicate obligations from the generic bounds.
318 pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
319 generic_bounds: &ty::InstantiatedPredicates<'tcx>)
320 -> PredicateObligations<'tcx>
322 util::predicates_for_generics(cause, 0, generic_bounds)
325 /// Determines whether the type `ty` is known to meet `bound` and
326 /// returns true if so. Returns false if `ty` either does not meet
327 /// `bound` or is not known to meet bound (note that this is
328 /// conservative towards *no impl*, which is the opposite of the
329 /// `evaluate` methods).
330 pub fn type_known_to_meet_builtin_bound<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
332 bound: ty::BuiltinBound,
336 debug!("type_known_to_meet_builtin_bound(ty={:?}, bound={:?})",
340 let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
342 util::predicate_for_builtin_bound(infcx.tcx, cause, bound, 0, ty);
343 let obligation = match obligation {
345 Err(..) => return false
347 let result = SelectionContext::new(infcx)
348 .evaluate_obligation_conservatively(&obligation);
349 debug!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} => {:?}",
352 if result && (ty.has_infer_types() || ty.has_closure_types()) {
353 // Because of inference "guessing", selection can sometimes claim
354 // to succeed while the success requires a guess. To ensure
355 // this function's result remains infallible, we must confirm
356 // that guess. While imperfect, I believe this is sound.
358 let mut fulfill_cx = FulfillmentContext::new(false);
360 // We can use a dummy node-id here because we won't pay any mind
361 // to region obligations that arise (there shouldn't really be any
363 let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
365 fulfill_cx.register_builtin_bound(infcx, ty, bound, cause);
367 // Note: we only assume something is `Copy` if we can
368 // *definitively* show that it implements `Copy`. Otherwise,
369 // assume it is move; linear is always ok.
370 match fulfill_cx.select_all_or_error(infcx) {
372 debug!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} success",
378 debug!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} errors={:?}",
390 // FIXME: this is gonna need to be removed ...
391 /// Normalizes the parameter environment, reporting errors if they occur.
392 pub fn normalize_param_env_or_error<'a,'tcx>(unnormalized_env: ty::ParameterEnvironment<'a,'tcx>,
393 cause: ObligationCause<'tcx>)
394 -> ty::ParameterEnvironment<'a,'tcx>
396 // I'm not wild about reporting errors here; I'd prefer to
397 // have the errors get reported at a defined place (e.g.,
398 // during typeck). Instead I have all parameter
399 // environments, in effect, going through this function
400 // and hence potentially reporting errors. This ensurse of
401 // course that we never forget to normalize (the
402 // alternative seemed like it would involve a lot of
403 // manual invocations of this fn -- and then we'd have to
404 // deal with the errors at each of those sites).
406 // In any case, in practice, typeck constructs all the
407 // parameter environments once for every fn as it goes,
408 // and errors will get reported then; so after typeck we
409 // can be sure that no errors should occur.
411 let tcx = unnormalized_env.tcx;
412 let span = cause.span;
413 let body_id = cause.body_id;
415 debug!("normalize_param_env_or_error(unnormalized_env={:?})",
418 let predicates: Vec<_> =
419 util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.clone())
420 .filter(|p| !p.is_global()) // (*)
423 // (*) Any predicate like `i32: Trait<u32>` or whatever doesn't
424 // need to be in the *environment* to be proven, so screen those
425 // out. This is important for the soundness of inter-fn
426 // caching. Note though that we should probably check that these
427 // predicates hold at the point where the environment is
428 // constructed, but I am not currently doing so out of laziness.
431 debug!("normalize_param_env_or_error: elaborated-predicates={:?}",
434 let elaborated_env = unnormalized_env.with_caller_bounds(predicates);
436 let infcx = infer::new_infer_ctxt(tcx, &tcx.tables, Some(elaborated_env), false);
437 let predicates = match fully_normalize(&infcx, cause,
438 &infcx.parameter_environment.caller_bounds) {
439 Ok(predicates) => predicates,
441 report_fulfillment_errors(&infcx, &errors);
442 return infcx.parameter_environment; // an unnormalized env is better than nothing
446 let free_regions = FreeRegionMap::new();
447 infcx.resolve_regions_and_report_errors(&free_regions, body_id);
448 let predicates = match infcx.fully_resolve(&predicates) {
449 Ok(predicates) => predicates,
451 // If we encounter a fixup error, it means that some type
452 // variable wound up unconstrained. I actually don't know
453 // if this can happen, and I certainly don't expect it to
454 // happen often, but if it did happen it probably
455 // represents a legitimate failure due to some kind of
456 // unconstrained variable, and it seems better not to ICE,
457 // all things considered.
458 let err_msg = fixup_err_to_string(fixup_err);
459 tcx.sess.span_err(span, &err_msg);
460 return infcx.parameter_environment; // an unnormalized env is better than nothing
464 infcx.parameter_environment.with_caller_bounds(predicates)
467 pub fn fully_normalize<'a,'tcx,T>(infcx: &InferCtxt<'a,'tcx>,
468 cause: ObligationCause<'tcx>,
470 -> Result<T, Vec<FulfillmentError<'tcx>>>
471 where T : TypeFoldable<'tcx> + HasTypeFlags
473 debug!("normalize_param_env(value={:?})", value);
475 let mut selcx = &mut SelectionContext::new(infcx);
476 // FIXME (@jroesch) ISSUE 26721
477 // I'm not sure if this is a bug or not, needs further investigation.
478 // It appears that by reusing the fulfillment_cx here we incur more
479 // obligations and later trip an asssertion on regionck.rs line 337.
481 // The two possibilities I see is:
482 // - normalization is not actually fully happening and we
483 // have a bug else where
484 // - we are adding a duplicate bound into the list causing
485 // its size to change.
487 // I think we should probably land this refactor and then come
488 // back to this is a follow-up patch.
489 let mut fulfill_cx = FulfillmentContext::new(false);
491 let Normalized { value: normalized_value, obligations } =
492 project::normalize(selcx, cause, value);
493 debug!("normalize_param_env: normalized_value={:?} obligations={:?}",
496 for obligation in obligations {
497 fulfill_cx.register_predicate_obligation(selcx.infcx(), obligation);
500 try!(fulfill_cx.select_all_or_error(infcx));
501 let resolved_value = infcx.resolve_type_vars_if_possible(&normalized_value);
502 debug!("normalize_param_env: resolved_value={:?}", resolved_value);
506 impl<'tcx,O> Obligation<'tcx,O> {
507 pub fn new(cause: ObligationCause<'tcx>,
509 -> Obligation<'tcx, O>
511 Obligation { cause: cause,
513 predicate: trait_ref }
516 fn with_depth(cause: ObligationCause<'tcx>,
517 recursion_depth: usize,
519 -> Obligation<'tcx, O>
521 Obligation { cause: cause,
522 recursion_depth: recursion_depth,
523 predicate: trait_ref }
526 pub fn misc(span: Span, body_id: ast::NodeId, trait_ref: O) -> Obligation<'tcx, O> {
527 Obligation::new(ObligationCause::misc(span, body_id), trait_ref)
530 pub fn with<P>(&self, value: P) -> Obligation<'tcx,P> {
531 Obligation { cause: self.cause.clone(),
532 recursion_depth: self.recursion_depth,
537 impl<'tcx> ObligationCause<'tcx> {
538 pub fn new(span: Span,
539 body_id: ast::NodeId,
540 code: ObligationCauseCode<'tcx>)
541 -> ObligationCause<'tcx> {
542 ObligationCause { span: span, body_id: body_id, code: code }
545 pub fn misc(span: Span, body_id: ast::NodeId) -> ObligationCause<'tcx> {
546 ObligationCause { span: span, body_id: body_id, code: MiscObligation }
549 pub fn dummy() -> ObligationCause<'tcx> {
550 ObligationCause { span: DUMMY_SP, body_id: 0, code: MiscObligation }
554 impl<'tcx, N> Vtable<'tcx, N> {
555 pub fn nested_obligations(self) -> Vec<N> {
557 VtableImpl(i) => i.nested,
559 VtableBuiltin(i) => i.nested,
560 VtableDefaultImpl(d) => d.nested,
561 VtableClosure(c) => c.nested,
562 VtableObject(_) | VtableFnPointer(..) => vec![]
566 pub fn map<M, F>(self, f: F) -> Vtable<'tcx, M> where F: FnMut(N) -> M {
568 VtableImpl(i) => VtableImpl(VtableImplData {
569 impl_def_id: i.impl_def_id,
571 nested: i.nested.into_iter().map(f).collect()
573 VtableParam(n) => VtableParam(n.into_iter().map(f).collect()),
574 VtableBuiltin(i) => VtableBuiltin(VtableBuiltinData {
575 nested: i.nested.into_iter().map(f).collect()
577 VtableObject(o) => VtableObject(o),
578 VtableDefaultImpl(d) => VtableDefaultImpl(VtableDefaultImplData {
579 trait_def_id: d.trait_def_id,
580 nested: d.nested.into_iter().map(f).collect()
582 VtableFnPointer(f) => VtableFnPointer(f),
583 VtableClosure(c) => VtableClosure(VtableClosureData {
584 closure_def_id: c.closure_def_id,
586 nested: c.nested.into_iter().map(f).collect(),
592 impl<'tcx> FulfillmentError<'tcx> {
593 fn new(obligation: PredicateObligation<'tcx>,
594 code: FulfillmentErrorCode<'tcx>)
595 -> FulfillmentError<'tcx>
597 FulfillmentError { obligation: obligation, code: code }
601 impl<'tcx> TraitObligation<'tcx> {
602 fn self_ty(&self) -> ty::Binder<Ty<'tcx>> {
603 ty::Binder(self.predicate.skip_binder().self_ty())