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, Ty, TypeFoldable}
;
22 use middle
::infer
::{self, fixup_err_to_string, InferCtxt}
;
26 use syntax
::codemap
::{Span, DUMMY_SP}
;
28 pub use self::error_reporting
::TraitErrorKey
;
29 pub use self::error_reporting
::recursive_type_with_infinite_size_error
;
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_overflow_error_cycle
;
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, GlobalFulfilledPredicates, 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();
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
));
438 let predicates
= match fully_normalize(&infcx
,
440 &infcx
.parameter_environment
.caller_bounds
) {
441 Ok(predicates
) => predicates
,
443 report_fulfillment_errors(&infcx
, &errors
);
444 return infcx
.parameter_environment
; // an unnormalized env is better than nothing
448 debug
!("normalize_param_env_or_error: normalized predicates={:?}",
451 let free_regions
= FreeRegionMap
::new();
452 infcx
.resolve_regions_and_report_errors(&free_regions
, body_id
);
453 let predicates
= match infcx
.fully_resolve(&predicates
) {
454 Ok(predicates
) => predicates
,
456 // If we encounter a fixup error, it means that some type
457 // variable wound up unconstrained. I actually don't know
458 // if this can happen, and I certainly don't expect it to
459 // happen often, but if it did happen it probably
460 // represents a legitimate failure due to some kind of
461 // unconstrained variable, and it seems better not to ICE,
462 // all things considered.
463 let err_msg
= fixup_err_to_string(fixup_err
);
464 tcx
.sess
.span_err(span
, &err_msg
);
465 return infcx
.parameter_environment
; // an unnormalized env is better than nothing
469 debug
!("normalize_param_env_or_error: resolved predicates={:?}",
472 infcx
.parameter_environment
.with_caller_bounds(predicates
)
475 pub fn fully_normalize
<'a
,'tcx
,T
>(infcx
: &InferCtxt
<'a
,'tcx
>,
476 cause
: ObligationCause
<'tcx
>,
478 -> Result
<T
, Vec
<FulfillmentError
<'tcx
>>>
479 where T
: TypeFoldable
<'tcx
>
481 debug
!("fully_normalize(value={:?})", value
);
483 let mut selcx
= &mut SelectionContext
::new(infcx
);
484 // FIXME (@jroesch) ISSUE 26721
485 // I'm not sure if this is a bug or not, needs further investigation.
486 // It appears that by reusing the fulfillment_cx here we incur more
487 // obligations and later trip an asssertion on regionck.rs line 337.
489 // The two possibilities I see is:
490 // - normalization is not actually fully happening and we
491 // have a bug else where
492 // - we are adding a duplicate bound into the list causing
493 // its size to change.
495 // I think we should probably land this refactor and then come
496 // back to this is a follow-up patch.
497 let mut fulfill_cx
= FulfillmentContext
::new();
499 let Normalized { value: normalized_value, obligations }
=
500 project
::normalize(selcx
, cause
, value
);
501 debug
!("fully_normalize: normalized_value={:?} obligations={:?}",
504 for obligation
in obligations
{
505 fulfill_cx
.register_predicate_obligation(selcx
.infcx(), obligation
);
508 debug
!("fully_normalize: select_all_or_error start");
509 match fulfill_cx
.select_all_or_error(infcx
) {
512 debug
!("fully_normalize: error={:?}", e
);
516 debug
!("fully_normalize: select_all_or_error complete");
517 let resolved_value
= infcx
.resolve_type_vars_if_possible(&normalized_value
);
518 debug
!("fully_normalize: resolved_value={:?}", resolved_value
);
522 impl<'tcx
,O
> Obligation
<'tcx
,O
> {
523 pub fn new(cause
: ObligationCause
<'tcx
>,
525 -> Obligation
<'tcx
, O
>
527 Obligation
{ cause
: cause
,
529 predicate
: trait_ref
}
532 fn with_depth(cause
: ObligationCause
<'tcx
>,
533 recursion_depth
: usize,
535 -> Obligation
<'tcx
, O
>
537 Obligation
{ cause
: cause
,
538 recursion_depth
: recursion_depth
,
539 predicate
: trait_ref
}
542 pub fn misc(span
: Span
, body_id
: ast
::NodeId
, trait_ref
: O
) -> Obligation
<'tcx
, O
> {
543 Obligation
::new(ObligationCause
::misc(span
, body_id
), trait_ref
)
546 pub fn with
<P
>(&self, value
: P
) -> Obligation
<'tcx
,P
> {
547 Obligation
{ cause
: self.cause
.clone(),
548 recursion_depth
: self.recursion_depth
,
553 impl<'tcx
> ObligationCause
<'tcx
> {
554 pub fn new(span
: Span
,
555 body_id
: ast
::NodeId
,
556 code
: ObligationCauseCode
<'tcx
>)
557 -> ObligationCause
<'tcx
> {
558 ObligationCause { span: span, body_id: body_id, code: code }
561 pub fn misc(span
: Span
, body_id
: ast
::NodeId
) -> ObligationCause
<'tcx
> {
562 ObligationCause { span: span, body_id: body_id, code: MiscObligation }
565 pub fn dummy() -> ObligationCause
<'tcx
> {
566 ObligationCause { span: DUMMY_SP, body_id: 0, code: MiscObligation }
570 impl<'tcx
, N
> Vtable
<'tcx
, N
> {
571 pub fn nested_obligations(self) -> Vec
<N
> {
573 VtableImpl(i
) => i
.nested
,
575 VtableBuiltin(i
) => i
.nested
,
576 VtableDefaultImpl(d
) => d
.nested
,
577 VtableClosure(c
) => c
.nested
,
578 VtableObject(_
) | VtableFnPointer(..) => vec
![]
582 pub fn map
<M
, F
>(self, f
: F
) -> Vtable
<'tcx
, M
> where F
: FnMut(N
) -> M
{
584 VtableImpl(i
) => VtableImpl(VtableImplData
{
585 impl_def_id
: i
.impl_def_id
,
587 nested
: i
.nested
.into_iter().map(f
).collect()
589 VtableParam(n
) => VtableParam(n
.into_iter().map(f
).collect()),
590 VtableBuiltin(i
) => VtableBuiltin(VtableBuiltinData
{
591 nested
: i
.nested
.into_iter().map(f
).collect()
593 VtableObject(o
) => VtableObject(o
),
594 VtableDefaultImpl(d
) => VtableDefaultImpl(VtableDefaultImplData
{
595 trait_def_id
: d
.trait_def_id
,
596 nested
: d
.nested
.into_iter().map(f
).collect()
598 VtableFnPointer(f
) => VtableFnPointer(f
),
599 VtableClosure(c
) => VtableClosure(VtableClosureData
{
600 closure_def_id
: c
.closure_def_id
,
602 nested
: c
.nested
.into_iter().map(f
).collect(),
608 impl<'tcx
> FulfillmentError
<'tcx
> {
609 fn new(obligation
: PredicateObligation
<'tcx
>,
610 code
: FulfillmentErrorCode
<'tcx
>)
611 -> FulfillmentError
<'tcx
>
613 FulfillmentError { obligation: obligation, code: code }
617 impl<'tcx
> TraitObligation
<'tcx
> {
618 fn self_ty(&self) -> ty
::Binder
<Ty
<'tcx
>> {
619 ty
::Binder(self.predicate
.skip_binder().self_ty())