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
::free_region
::FreeRegionMap
;
20 use middle
::ty
::{self, HasTypeFlags, Ty}
;
21 use middle
::ty_fold
::TypeFoldable
;
22 use middle
::infer
::{self, fixup_err_to_string, InferCtxt}
;
25 use syntax
::codemap
::{Span, DUMMY_SP}
;
27 pub use self::error_reporting
::report_fulfillment_errors
;
28 pub use self::error_reporting
::report_overflow_error
;
29 pub use self::error_reporting
::report_selection_error
;
30 pub use self::error_reporting
::suggest_new_overflow_limit
;
31 pub use self::coherence
::orphan_check
;
32 pub use self::coherence
::overlapping_impls
;
33 pub use self::coherence
::OrphanCheckErr
;
34 pub use self::fulfill
::{FulfillmentContext, FulfilledPredicates, RegionObligation}
;
35 pub use self::project
::MismatchedProjectionTypes
;
36 pub use self::project
::normalize
;
37 pub use self::project
::Normalized
;
38 pub use self::object_safety
::is_object_safe
;
39 pub use self::object_safety
::object_safety_violations
;
40 pub use self::object_safety
::ObjectSafetyViolation
;
41 pub use self::object_safety
::MethodViolationCode
;
42 pub use self::object_safety
::is_vtable_safe_method
;
43 pub use self::select
::SelectionContext
;
44 pub use self::select
::SelectionCache
;
45 pub use self::select
::{MethodMatchResult, MethodMatched, MethodAmbiguous, MethodDidNotMatch}
;
46 pub use self::select
::{MethodMatchedData}
; // intentionally don't export variants
47 pub use self::util
::elaborate_predicates
;
48 pub use self::util
::get_vtable_index_of_object_method
;
49 pub use self::util
::trait_ref_for_builtin_bound
;
50 pub use self::util
::predicate_for_trait_def
;
51 pub use self::util
::supertraits
;
52 pub use self::util
::Supertraits
;
53 pub use self::util
::supertrait_def_ids
;
54 pub use self::util
::SupertraitDefIds
;
55 pub use self::util
::transitive_bounds
;
56 pub use self::util
::upcast
;
66 /// An `Obligation` represents some trait reference (e.g. `int:Eq`) for
67 /// which the vtable must be found. The process of finding a vtable is
68 /// called "resolving" the `Obligation`. This process consists of
69 /// either identifying an `impl` (e.g., `impl Eq for int`) that
70 /// provides the required vtable, or else finding a bound that is in
71 /// scope. The eventual result is usually a `Selection` (defined below).
72 #[derive(Clone, PartialEq, Eq)]
73 pub struct Obligation
<'tcx
, T
> {
74 pub cause
: ObligationCause
<'tcx
>,
75 pub recursion_depth
: usize,
79 pub type PredicateObligation
<'tcx
> = Obligation
<'tcx
, ty
::Predicate
<'tcx
>>;
80 pub type TraitObligation
<'tcx
> = Obligation
<'tcx
, ty
::PolyTraitPredicate
<'tcx
>>;
82 /// Why did we incur this obligation? Used for error reporting.
83 #[derive(Clone, PartialEq, Eq)]
84 pub struct ObligationCause
<'tcx
> {
87 // The id of the fn body that triggered this obligation. This is
88 // used for region obligations to determine the precise
89 // environment in which the region obligation should be evaluated
90 // (in particular, closures can add new assumptions). See the
91 // field `region_obligations` of the `FulfillmentContext` for more
93 pub body_id
: ast
::NodeId
,
95 pub code
: ObligationCauseCode
<'tcx
>
98 #[derive(Clone, PartialEq, Eq)]
99 pub enum ObligationCauseCode
<'tcx
> {
100 /// Not well classified or should be obvious from span.
103 /// In an impl of trait X for type Y, type Y must
104 /// also implement all supertraits of X.
105 ItemObligation(ast
::DefId
),
107 /// Obligation incurred due to an object cast.
108 ObjectCastObligation(/* Object type */ Ty
<'tcx
>),
110 /// Various cases where expressions must be sized/copy/etc:
111 AssignmentLhsSized
, // L = X implies that L is Sized
112 StructInitializerSized
, // S { ... } must be Sized
113 VariableType(ast
::NodeId
), // Type of each variable must be Sized
114 ReturnType
, // Return type must be Sized
115 RepeatVec
, // [T,..n] --> T must be Copy
117 // Captures of variable the given id by a closure (span is the
118 // span of the closure)
119 ClosureCapture(ast
::NodeId
, Span
, ty
::BuiltinBound
),
121 // Types of fields (other than the last) in a struct must be sized.
124 // static items must have `Sync` type
128 BuiltinDerivedObligation(DerivedObligationCause
<'tcx
>),
130 ImplDerivedObligation(DerivedObligationCause
<'tcx
>),
132 CompareImplMethodObligation
,
135 #[derive(Clone, PartialEq, Eq)]
136 pub struct DerivedObligationCause
<'tcx
> {
137 /// The trait reference of the parent obligation that led to the
138 /// current obligation. Note that only trait obligations lead to
139 /// derived obligations, so we just store the trait reference here
141 parent_trait_ref
: ty
::PolyTraitRef
<'tcx
>,
143 /// The parent trait had this cause
144 parent_code
: Rc
<ObligationCauseCode
<'tcx
>>
147 pub type Obligations
<'tcx
, O
> = Vec
<Obligation
<'tcx
, O
>>;
148 pub type PredicateObligations
<'tcx
> = Vec
<PredicateObligation
<'tcx
>>;
149 pub type TraitObligations
<'tcx
> = Vec
<TraitObligation
<'tcx
>>;
151 pub type Selection
<'tcx
> = Vtable
<'tcx
, PredicateObligation
<'tcx
>>;
153 #[derive(Clone,Debug)]
154 pub enum SelectionError
<'tcx
> {
156 OutputTypeParameterMismatch(ty
::PolyTraitRef
<'tcx
>,
157 ty
::PolyTraitRef
<'tcx
>,
158 ty
::TypeError
<'tcx
>),
159 TraitNotObjectSafe(ast
::DefId
),
162 pub struct FulfillmentError
<'tcx
> {
163 pub obligation
: PredicateObligation
<'tcx
>,
164 pub code
: FulfillmentErrorCode
<'tcx
>
168 pub enum FulfillmentErrorCode
<'tcx
> {
169 CodeSelectionError(SelectionError
<'tcx
>),
170 CodeProjectionError(MismatchedProjectionTypes
<'tcx
>),
174 /// When performing resolution, it is typically the case that there
175 /// can be one of three outcomes:
177 /// - `Ok(Some(r))`: success occurred with result `r`
178 /// - `Ok(None)`: could not definitely determine anything, usually due
179 /// to inconclusive type inference.
180 /// - `Err(e)`: error `e` occurred
181 pub type SelectionResult
<'tcx
, T
> = Result
<Option
<T
>, SelectionError
<'tcx
>>;
183 /// Given the successful resolution of an obligation, the `Vtable`
184 /// indicates where the vtable comes from. Note that while we call this
185 /// a "vtable", it does not necessarily indicate dynamic dispatch at
186 /// runtime. `Vtable` instances just tell the compiler where to find
187 /// methods, but in generic code those methods are typically statically
188 /// dispatched -- only when an object is constructed is a `Vtable`
189 /// instance reified into an actual vtable.
191 /// For example, the vtable may be tied to a specific impl (case A),
192 /// or it may be relative to some bound that is in scope (case B).
196 /// impl<T:Clone> Clone<T> for Option<T> { ... } // Impl_1
197 /// impl<T:Clone> Clone<T> for Box<T> { ... } // Impl_2
198 /// impl Clone for int { ... } // Impl_3
200 /// fn foo<T:Clone>(concrete: Option<Box<int>>,
202 /// mixed: Option<T>) {
204 /// // Case A: Vtable points at a specific impl. Only possible when
205 /// // type is concretely known. If the impl itself has bounded
206 /// // type parameters, Vtable will carry resolutions for those as well:
207 /// concrete.clone(); // Vtable(Impl_1, [Vtable(Impl_2, [Vtable(Impl_3)])])
209 /// // Case B: Vtable must be provided by caller. This applies when
210 /// // type is a type parameter.
211 /// param.clone(); // VtableParam
213 /// // Case C: A mix of cases A and B.
214 /// mixed.clone(); // Vtable(Impl_1, [VtableParam])
218 /// ### The type parameter `N`
220 /// See explanation on `VtableImplData`.
222 pub enum Vtable
<'tcx
, N
> {
223 /// Vtable identifying a particular impl.
224 VtableImpl(VtableImplData
<'tcx
, N
>),
226 /// Vtable for default trait implementations
227 /// This carries the information and nested obligations with regards
228 /// to a default implementation for a trait `Trait`. The nested obligations
229 /// ensure the trait implementation holds for all the constituent types.
230 VtableDefaultImpl(VtableDefaultImplData
<N
>),
232 /// Successful resolution to an obligation provided by the caller
233 /// for some type parameter. The `Vec<N>` represents the
234 /// obligations incurred from normalizing the where-clause (if
238 /// Virtual calls through an object
239 VtableObject(VtableObjectData
<'tcx
>),
241 /// Successful resolution for a builtin trait.
242 VtableBuiltin(VtableBuiltinData
<N
>),
244 /// Vtable automatically generated for a closure. The def ID is the ID
245 /// of the closure expression. This is a `VtableImpl` in spirit, but the
246 /// impl is generated by the compiler and does not appear in the source.
247 VtableClosure(VtableClosureData
<'tcx
, N
>),
249 /// Same as above, but for a fn pointer type with the given signature.
250 VtableFnPointer(ty
::Ty
<'tcx
>),
253 /// Identifies a particular impl in the source, along with a set of
254 /// substitutions from the impl's type/lifetime parameters. The
255 /// `nested` vector corresponds to the nested obligations attached to
256 /// the impl's type parameters.
258 /// The type parameter `N` indicates the type used for "nested
259 /// obligations" that are required by the impl. During type check, this
260 /// is `Obligation`, as one might expect. During trans, however, this
261 /// is `()`, because trans only requires a shallow resolution of an
262 /// impl, and nested obligations are satisfied later.
263 #[derive(Clone, PartialEq, Eq)]
264 pub struct VtableImplData
<'tcx
, N
> {
265 pub impl_def_id
: ast
::DefId
,
266 pub substs
: subst
::Substs
<'tcx
>,
270 #[derive(Clone, PartialEq, Eq)]
271 pub struct VtableClosureData
<'tcx
, N
> {
272 pub closure_def_id
: ast
::DefId
,
273 pub substs
: ty
::ClosureSubsts
<'tcx
>,
274 /// Nested obligations. This can be non-empty if the closure
275 /// signature contains associated types.
280 pub struct VtableDefaultImplData
<N
> {
281 pub trait_def_id
: ast
::DefId
,
286 pub struct VtableBuiltinData
<N
> {
290 /// A vtable for some object-safe trait `Foo` automatically derived
291 /// for the object type `Foo`.
292 #[derive(PartialEq,Eq,Clone)]
293 pub struct VtableObjectData
<'tcx
> {
294 /// `Foo` upcast to the obligation trait. This will be some supertrait of `Foo`.
295 pub upcast_trait_ref
: ty
::PolyTraitRef
<'tcx
>,
297 /// The vtable is formed by concatenating together the method lists of
298 /// the base object trait and all supertraits; this is the start of
299 /// `upcast_trait_ref`'s methods in that vtable.
300 pub vtable_base
: usize
303 /// Creates predicate obligations from the generic bounds.
304 pub fn predicates_for_generics
<'tcx
>(cause
: ObligationCause
<'tcx
>,
305 generic_bounds
: &ty
::InstantiatedPredicates
<'tcx
>)
306 -> PredicateObligations
<'tcx
>
308 util
::predicates_for_generics(cause
, 0, generic_bounds
)
311 /// Determines whether the type `ty` is known to meet `bound` and
312 /// returns true if so. Returns false if `ty` either does not meet
313 /// `bound` or is not known to meet bound (note that this is
314 /// conservative towards *no impl*, which is the opposite of the
315 /// `evaluate` methods).
316 pub fn type_known_to_meet_builtin_bound
<'a
,'tcx
>(infcx
: &InferCtxt
<'a
,'tcx
>,
318 bound
: ty
::BuiltinBound
,
322 debug
!("type_known_to_meet_builtin_bound(ty={:?}, bound={:?})",
326 let mut fulfill_cx
= FulfillmentContext
::new(false);
328 // We can use a dummy node-id here because we won't pay any mind
329 // to region obligations that arise (there shouldn't really be any
331 let cause
= ObligationCause
::misc(span
, ast
::DUMMY_NODE_ID
);
333 fulfill_cx
.register_builtin_bound(infcx
, ty
, bound
, cause
);
335 // Note: we only assume something is `Copy` if we can
336 // *definitively* show that it implements `Copy`. Otherwise,
337 // assume it is move; linear is always ok.
338 match fulfill_cx
.select_all_or_error(infcx
) {
340 debug
!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} success",
346 debug
!("type_known_to_meet_builtin_bound: ty={:?} bound={:?} errors={:?}",
355 // FIXME: this is gonna need to be removed ...
356 /// Normalizes the parameter environment, reporting errors if they occur.
357 pub fn normalize_param_env_or_error
<'a
,'tcx
>(unnormalized_env
: ty
::ParameterEnvironment
<'a
,'tcx
>,
358 cause
: ObligationCause
<'tcx
>)
359 -> ty
::ParameterEnvironment
<'a
,'tcx
>
361 // I'm not wild about reporting errors here; I'd prefer to
362 // have the errors get reported at a defined place (e.g.,
363 // during typeck). Instead I have all parameter
364 // environments, in effect, going through this function
365 // and hence potentially reporting errors. This ensurse of
366 // course that we never forget to normalize (the
367 // alternative seemed like it would involve a lot of
368 // manual invocations of this fn -- and then we'd have to
369 // deal with the errors at each of those sites).
371 // In any case, in practice, typeck constructs all the
372 // parameter environments once for every fn as it goes,
373 // and errors will get reported then; so after typeck we
374 // can be sure that no errors should occur.
376 let tcx
= unnormalized_env
.tcx
;
377 let span
= cause
.span
;
378 let body_id
= cause
.body_id
;
380 debug
!("normalize_param_env_or_error(unnormalized_env={:?})",
383 let predicates
: Vec
<_
> =
384 util
::elaborate_predicates(tcx
, unnormalized_env
.caller_bounds
.clone())
385 .filter(|p
| !p
.is_global()) // (*)
388 // (*) Any predicate like `i32: Trait<u32>` or whatever doesn't
389 // need to be in the *environment* to be proven, so screen those
390 // out. This is important for the soundness of inter-fn
391 // caching. Note though that we should probably check that these
392 // predicates hold at the point where the environment is
393 // constructed, but I am not currently doing so out of laziness.
396 debug
!("normalize_param_env_or_error: elaborated-predicates={:?}",
399 let elaborated_env
= unnormalized_env
.with_caller_bounds(predicates
);
401 let infcx
= infer
::new_infer_ctxt(tcx
, &tcx
.tables
, Some(elaborated_env
), false);
402 let predicates
= match fully_normalize(&infcx
, cause
,
403 &infcx
.parameter_environment
.caller_bounds
) {
404 Ok(predicates
) => predicates
,
406 report_fulfillment_errors(&infcx
, &errors
);
407 return infcx
.parameter_environment
; // an unnormalized env is better than nothing
411 let free_regions
= FreeRegionMap
::new();
412 infcx
.resolve_regions_and_report_errors(&free_regions
, body_id
);
413 let predicates
= match infcx
.fully_resolve(&predicates
) {
414 Ok(predicates
) => predicates
,
416 // If we encounter a fixup error, it means that some type
417 // variable wound up unconstrained. I actually don't know
418 // if this can happen, and I certainly don't expect it to
419 // happen often, but if it did happen it probably
420 // represents a legitimate failure due to some kind of
421 // unconstrained variable, and it seems better not to ICE,
422 // all things considered.
423 let err_msg
= fixup_err_to_string(fixup_err
);
424 tcx
.sess
.span_err(span
, &err_msg
);
425 return infcx
.parameter_environment
; // an unnormalized env is better than nothing
429 infcx
.parameter_environment
.with_caller_bounds(predicates
)
432 pub fn fully_normalize
<'a
,'tcx
,T
>(infcx
: &InferCtxt
<'a
,'tcx
>,
433 cause
: ObligationCause
<'tcx
>,
435 -> Result
<T
, Vec
<FulfillmentError
<'tcx
>>>
436 where T
: TypeFoldable
<'tcx
> + HasTypeFlags
438 debug
!("normalize_param_env(value={:?})", value
);
440 let mut selcx
= &mut SelectionContext
::new(infcx
);
441 // FIXME (@jroesch) ISSUE 26721
442 // I'm not sure if this is a bug or not, needs further investigation.
443 // It appears that by reusing the fulfillment_cx here we incur more
444 // obligations and later trip an asssertion on regionck.rs line 337.
446 // The two possibilities I see is:
447 // - normalization is not actually fully happening and we
448 // have a bug else where
449 // - we are adding a duplicate bound into the list causing
450 // its size to change.
452 // I think we should probably land this refactor and then come
453 // back to this is a follow-up patch.
454 let mut fulfill_cx
= FulfillmentContext
::new(false);
456 let Normalized { value: normalized_value, obligations }
=
457 project
::normalize(selcx
, cause
, value
);
458 debug
!("normalize_param_env: normalized_value={:?} obligations={:?}",
461 for obligation
in obligations
{
462 fulfill_cx
.register_predicate_obligation(selcx
.infcx(), obligation
);
465 try
!(fulfill_cx
.select_all_or_error(infcx
));
466 let resolved_value
= infcx
.resolve_type_vars_if_possible(&normalized_value
);
467 debug
!("normalize_param_env: resolved_value={:?}", resolved_value
);
471 impl<'tcx
,O
> Obligation
<'tcx
,O
> {
472 pub fn new(cause
: ObligationCause
<'tcx
>,
474 -> Obligation
<'tcx
, O
>
476 Obligation
{ cause
: cause
,
478 predicate
: trait_ref
}
481 fn with_depth(cause
: ObligationCause
<'tcx
>,
482 recursion_depth
: usize,
484 -> Obligation
<'tcx
, O
>
486 Obligation
{ cause
: cause
,
487 recursion_depth
: recursion_depth
,
488 predicate
: trait_ref
}
491 pub fn misc(span
: Span
, body_id
: ast
::NodeId
, trait_ref
: O
) -> Obligation
<'tcx
, O
> {
492 Obligation
::new(ObligationCause
::misc(span
, body_id
), trait_ref
)
495 pub fn with
<P
>(&self, value
: P
) -> Obligation
<'tcx
,P
> {
496 Obligation
{ cause
: self.cause
.clone(),
497 recursion_depth
: self.recursion_depth
,
502 impl<'tcx
> ObligationCause
<'tcx
> {
503 pub fn new(span
: Span
,
504 body_id
: ast
::NodeId
,
505 code
: ObligationCauseCode
<'tcx
>)
506 -> ObligationCause
<'tcx
> {
507 ObligationCause { span: span, body_id: body_id, code: code }
510 pub fn misc(span
: Span
, body_id
: ast
::NodeId
) -> ObligationCause
<'tcx
> {
511 ObligationCause { span: span, body_id: body_id, code: MiscObligation }
514 pub fn dummy() -> ObligationCause
<'tcx
> {
515 ObligationCause { span: DUMMY_SP, body_id: 0, code: MiscObligation }
519 impl<'tcx
, N
> Vtable
<'tcx
, N
> {
520 pub fn nested_obligations(self) -> Vec
<N
> {
522 VtableImpl(i
) => i
.nested
,
524 VtableBuiltin(i
) => i
.nested
,
525 VtableDefaultImpl(d
) => d
.nested
,
526 VtableClosure(c
) => c
.nested
,
527 VtableObject(_
) | VtableFnPointer(..) => vec
![]
531 pub fn map
<M
, F
>(self, f
: F
) -> Vtable
<'tcx
, M
> where F
: FnMut(N
) -> M
{
533 VtableImpl(i
) => VtableImpl(VtableImplData
{
534 impl_def_id
: i
.impl_def_id
,
536 nested
: i
.nested
.into_iter().map(f
).collect()
538 VtableParam(n
) => VtableParam(n
.into_iter().map(f
).collect()),
539 VtableBuiltin(i
) => VtableBuiltin(VtableBuiltinData
{
540 nested
: i
.nested
.into_iter().map(f
).collect()
542 VtableObject(o
) => VtableObject(o
),
543 VtableDefaultImpl(d
) => VtableDefaultImpl(VtableDefaultImplData
{
544 trait_def_id
: d
.trait_def_id
,
545 nested
: d
.nested
.into_iter().map(f
).collect()
547 VtableFnPointer(f
) => VtableFnPointer(f
),
548 VtableClosure(c
) => VtableClosure(VtableClosureData
{
549 closure_def_id
: c
.closure_def_id
,
551 nested
: c
.nested
.into_iter().map(f
).collect(),
557 impl<'tcx
> FulfillmentError
<'tcx
> {
558 fn new(obligation
: PredicateObligation
<'tcx
>,
559 code
: FulfillmentErrorCode
<'tcx
>)
560 -> FulfillmentError
<'tcx
>
562 FulfillmentError { obligation: obligation, code: code }
566 impl<'tcx
> TraitObligation
<'tcx
> {
567 fn self_ty(&self) -> ty
::Binder
<Ty
<'tcx
>> {
568 ty
::Binder(self.predicate
.skip_binder().self_ty())