1 // Copyright 2012-2013 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 use hir
::def_id
::DefId
;
13 use ty
::subst
::Substs
;
15 use ty
::{self, ToPredicate, Ty, TyCtxt, TypeFoldable}
;
19 use middle
::lang_items
;
21 /// Returns the set of obligations needed to make `ty` well-formed.
22 /// If `ty` contains unresolved inference variables, this may include
23 /// further WF obligations. However, if `ty` IS an unresolved
24 /// inference variable, returns `None`, because we are not able to
25 /// make any progress at all. This is to prevent "livelock" where we
26 /// say "$0 is WF if $0 is WF".
27 pub fn obligations
<'a
, 'gcx
, 'tcx
>(infcx
: &InferCtxt
<'a
, 'gcx
, 'tcx
>,
28 param_env
: ty
::ParamEnv
<'tcx
>,
32 -> Option
<Vec
<traits
::PredicateObligation
<'tcx
>>>
34 let mut wf
= WfPredicates
{ infcx
: infcx
,
40 debug
!("wf::obligations({:?}, body_id={:?}) = {:?}", ty
, body_id
, wf
.out
);
41 let result
= wf
.normalize();
42 debug
!("wf::obligations({:?}, body_id={:?}) ~~> {:?}", ty
, body_id
, result
);
45 None
// no progress made, return None
49 /// Returns the obligations that make this trait reference
50 /// well-formed. For example, if there is a trait `Set` defined like
51 /// `trait Set<K:Eq>`, then the trait reference `Foo: Set<Bar>` is WF
53 pub fn trait_obligations
<'a
, 'gcx
, 'tcx
>(infcx
: &InferCtxt
<'a
, 'gcx
, 'tcx
>,
54 param_env
: ty
::ParamEnv
<'tcx
>,
56 trait_ref
: &ty
::TraitRef
<'tcx
>,
58 -> Vec
<traits
::PredicateObligation
<'tcx
>>
60 let mut wf
= WfPredicates { infcx, param_env, body_id, span, out: vec![] }
;
61 wf
.compute_trait_ref(trait_ref
);
65 pub fn predicate_obligations
<'a
, 'gcx
, 'tcx
>(infcx
: &InferCtxt
<'a
, 'gcx
, 'tcx
>,
66 param_env
: ty
::ParamEnv
<'tcx
>,
68 predicate
: &ty
::Predicate
<'tcx
>,
70 -> Vec
<traits
::PredicateObligation
<'tcx
>>
72 let mut wf
= WfPredicates { infcx, param_env, body_id, span, out: vec![] }
;
74 // (*) ok to skip binders, because wf code is prepared for it
76 ty
::Predicate
::Trait(ref t
) => {
77 wf
.compute_trait_ref(&t
.skip_binder().trait_ref
); // (*)
79 ty
::Predicate
::Equate(ref t
) => {
80 wf
.compute(t
.skip_binder().0);
81 wf
.compute(t
.skip_binder().1);
83 ty
::Predicate
::RegionOutlives(..) => {
85 ty
::Predicate
::TypeOutlives(ref t
) => {
86 wf
.compute(t
.skip_binder().0);
88 ty
::Predicate
::Projection(ref t
) => {
89 let t
= t
.skip_binder(); // (*)
90 wf
.compute_projection(t
.projection_ty
);
93 ty
::Predicate
::WellFormed(t
) => {
96 ty
::Predicate
::ObjectSafe(_
) => {
98 ty
::Predicate
::ClosureKind(..) => {
100 ty
::Predicate
::Subtype(ref data
) => {
101 wf
.compute(data
.skip_binder().a
); // (*)
102 wf
.compute(data
.skip_binder().b
); // (*)
109 struct WfPredicates
<'a
, 'gcx
: 'a
+'tcx
, 'tcx
: 'a
> {
110 infcx
: &'a InferCtxt
<'a
, 'gcx
, 'tcx
>,
111 param_env
: ty
::ParamEnv
<'tcx
>,
112 body_id
: ast
::NodeId
,
114 out
: Vec
<traits
::PredicateObligation
<'tcx
>>,
117 impl<'a
, 'gcx
, 'tcx
> WfPredicates
<'a
, 'gcx
, 'tcx
> {
118 fn cause(&mut self, code
: traits
::ObligationCauseCode
<'tcx
>) -> traits
::ObligationCause
<'tcx
> {
119 traits
::ObligationCause
::new(self.span
, self.body_id
, code
)
122 fn normalize(&mut self) -> Vec
<traits
::PredicateObligation
<'tcx
>> {
123 let cause
= self.cause(traits
::MiscObligation
);
124 let infcx
= &mut self.infcx
;
125 let param_env
= self.param_env
;
127 .inspect(|pred
| assert
!(!pred
.has_escaping_regions()))
129 let mut selcx
= traits
::SelectionContext
::new(infcx
);
130 let pred
= traits
::normalize(&mut selcx
, param_env
, cause
.clone(), pred
);
131 once(pred
.value
).chain(pred
.obligations
)
136 /// Pushes the obligations required for `trait_ref` to be WF into
138 fn compute_trait_ref(&mut self, trait_ref
: &ty
::TraitRef
<'tcx
>) {
139 let obligations
= self.nominal_obligations(trait_ref
.def_id
, trait_ref
.substs
);
140 self.out
.extend(obligations
);
142 let cause
= self.cause(traits
::MiscObligation
);
143 let param_env
= self.param_env
;
145 trait_ref
.substs
.types()
146 .filter(|ty
| !ty
.has_escaping_regions())
147 .map(|ty
| traits
::Obligation
::new(cause
.clone(),
149 ty
::Predicate
::WellFormed(ty
))));
152 /// Pushes the obligations required for `trait_ref::Item` to be WF
154 fn compute_projection(&mut self, data
: ty
::ProjectionTy
<'tcx
>) {
155 // A projection is well-formed if (a) the trait ref itself is
156 // WF and (b) the trait-ref holds. (It may also be
157 // normalizable and be WF that way.)
159 self.compute_trait_ref(&data
.trait_ref
);
161 if !data
.has_escaping_regions() {
162 let predicate
= data
.trait_ref
.to_predicate();
163 let cause
= self.cause(traits
::ProjectionWf(data
));
164 self.out
.push(traits
::Obligation
::new(cause
, self.param_env
, predicate
));
168 fn require_sized(&mut self, subty
: Ty
<'tcx
>, cause
: traits
::ObligationCauseCode
<'tcx
>) {
169 if !subty
.has_escaping_regions() {
170 let cause
= self.cause(cause
);
171 let trait_ref
= ty
::TraitRef
{
172 def_id
: self.infcx
.tcx
.require_lang_item(lang_items
::SizedTraitLangItem
),
173 substs
: self.infcx
.tcx
.mk_substs_trait(subty
, &[]),
175 self.out
.push(traits
::Obligation
::new(cause
, self.param_env
, trait_ref
.to_predicate()));
179 /// Push new obligations into `out`. Returns true if it was able
180 /// to generate all the predicates needed to validate that `ty0`
181 /// is WF. Returns false if `ty0` is an unresolved type variable,
182 /// in which case we are not able to simplify at all.
183 fn compute(&mut self, ty0
: Ty
<'tcx
>) -> bool
{
184 let mut subtys
= ty0
.walk();
185 let param_env
= self.param_env
;
186 while let Some(ty
) = subtys
.next() {
197 // WfScalar, WfParameter, etc
201 ty
::TyArray(subty
, _
) => {
202 self.require_sized(subty
, traits
::SliceOrArrayElem
);
205 ty
::TyTuple(ref tys
, _
) => {
206 if let Some((_last
, rest
)) = tys
.split_last() {
208 self.require_sized(elem
, traits
::TupleElem
);
214 // simple cases that are WF if their type args are WF
217 ty
::TyProjection(data
) => {
218 subtys
.skip_current_subtree(); // subtree handled by compute_projection
219 self.compute_projection(data
);
222 ty
::TyAdt(def
, substs
) => {
224 let obligations
= self.nominal_obligations(def
.did
, substs
);
225 self.out
.extend(obligations
);
228 ty
::TyRef(r
, mt
) => {
230 if !r
.has_escaping_regions() && !mt
.ty
.has_escaping_regions() {
231 let cause
= self.cause(traits
::ReferenceOutlivesReferent(ty
));
233 traits
::Obligation
::new(
236 ty
::Predicate
::TypeOutlives(
238 ty
::OutlivesPredicate(mt
.ty
, r
)))));
242 ty
::TyClosure(..) => {
243 // the types in a closure are always the types of
244 // local variables (or possibly references to local
245 // variables), we'll walk those.
247 // (Though, local variables are probably not
248 // needed, as they are separately checked w/r/t
252 ty
::TyFnDef(..) | ty
::TyFnPtr(_
) => {
253 // let the loop iterate into the argument/return
254 // types appearing in the fn signature
258 // all of the requirements on type parameters
259 // should've been checked by the instantiation
260 // of whatever returned this exact `impl Trait`.
263 ty
::TyDynamic(data
, r
) => {
266 // Here, we defer WF checking due to higher-ranked
267 // regions. This is perhaps not ideal.
268 self.from_object_ty(ty
, data
, r
);
270 // FIXME(#27579) RFC also considers adding trait
271 // obligations that don't refer to Self and
274 let cause
= self.cause(traits
::MiscObligation
);
275 let component_traits
=
276 data
.auto_traits().chain(data
.principal().map(|p
| p
.def_id()));
278 component_traits
.map(|did
| traits
::Obligation
::new(
281 ty
::Predicate
::ObjectSafe(did
)
286 // Inference variables are the complicated case, since we don't
287 // know what type they are. We do two things:
289 // 1. Check if they have been resolved, and if so proceed with
291 // 2. If not, check whether this is the type that we
292 // started with (ty0). In that case, we've made no
293 // progress at all, so return false. Otherwise,
294 // we've at least simplified things (i.e., we went
295 // from `Vec<$0>: WF` to `$0: WF`, so we can
296 // register a pending obligation and keep
297 // moving. (Goal is that an "inductive hypothesis"
298 // is satisfied to ensure termination.)
300 let ty
= self.infcx
.shallow_resolve(ty
);
301 if let ty
::TyInfer(_
) = ty
.sty
{ // not yet resolved...
302 if ty
== ty0
{ // ...this is the type we started from! no progress.
306 let cause
= self.cause(traits
::MiscObligation
);
307 self.out
.push( // ...not the type we started from, so we made progress.
308 traits
::Obligation
::new(cause
,
310 ty
::Predicate
::WellFormed(ty
)));
312 // Yes, resolved, proceed with the
313 // result. Should never return false because
314 // `ty` is not a TyInfer.
315 assert
!(self.compute(ty
));
321 // if we made it through that loop above, we made progress!
325 fn nominal_obligations(&mut self,
327 substs
: &Substs
<'tcx
>)
328 -> Vec
<traits
::PredicateObligation
<'tcx
>>
331 self.infcx
.tcx
.predicates_of(def_id
)
332 .instantiate(self.infcx
.tcx
, substs
);
333 let cause
= self.cause(traits
::ItemObligation(def_id
));
334 predicates
.predicates
336 .map(|pred
| traits
::Obligation
::new(cause
.clone(),
339 .filter(|pred
| !pred
.has_escaping_regions())
343 fn from_object_ty(&mut self, ty
: Ty
<'tcx
>,
344 data
: ty
::Binder
<&'tcx ty
::Slice
<ty
::ExistentialPredicate
<'tcx
>>>,
345 region
: ty
::Region
<'tcx
>) {
346 // Imagine a type like this:
349 // trait Bar<'c> : 'c { }
351 // &'b (Foo+'c+Bar<'d>)
354 // In this case, the following relationships must hold:
359 // The first conditions is due to the normal region pointer
360 // rules, which say that a reference cannot outlive its
363 // The final condition may be a bit surprising. In particular,
364 // you may expect that it would have been `'c <= 'd`, since
365 // usually lifetimes of outer things are conservative
366 // approximations for inner things. However, it works somewhat
367 // differently with trait objects: here the idea is that if the
368 // user specifies a region bound (`'c`, in this case) it is the
369 // "master bound" that *implies* that bounds from other traits are
370 // all met. (Remember that *all bounds* in a type like
371 // `Foo+Bar+Zed` must be met, not just one, hence if we write
372 // `Foo<'x>+Bar<'y>`, we know that the type outlives *both* 'x and
375 // Note: in fact we only permit builtin traits, not `Bar<'d>`, I
376 // am looking forward to the future here.
378 if !data
.has_escaping_regions() {
379 let implicit_bounds
=
380 object_region_bounds(self.infcx
.tcx
, data
);
382 let explicit_bound
= region
;
384 for implicit_bound
in implicit_bounds
{
385 let cause
= self.cause(traits
::ObjectTypeBound(ty
, explicit_bound
));
386 let outlives
= ty
::Binder(ty
::OutlivesPredicate(explicit_bound
, implicit_bound
));
387 self.out
.push(traits
::Obligation
::new(cause
,
389 outlives
.to_predicate()));
395 /// Given an object type like `SomeTrait+Send`, computes the lifetime
396 /// bounds that must hold on the elided self type. These are derived
397 /// from the declarations of `SomeTrait`, `Send`, and friends -- if
398 /// they declare `trait SomeTrait : 'static`, for example, then
399 /// `'static` would appear in the list. The hard work is done by
400 /// `ty::required_region_bounds`, see that for more information.
401 pub fn object_region_bounds
<'a
, 'gcx
, 'tcx
>(
402 tcx
: TyCtxt
<'a
, 'gcx
, 'tcx
>,
403 existential_predicates
: ty
::Binder
<&'tcx ty
::Slice
<ty
::ExistentialPredicate
<'tcx
>>>)
404 -> Vec
<ty
::Region
<'tcx
>>
406 // Since we don't actually *know* the self type for an object,
407 // this "open(err)" serves as a kind of dummy standin -- basically
408 // a skolemized type.
409 let open_ty
= tcx
.mk_infer(ty
::FreshTy(0));
411 let predicates
= existential_predicates
.iter().filter_map(|predicate
| {
412 if let ty
::ExistentialPredicate
::Projection(_
) = *predicate
.skip_binder() {
415 Some(predicate
.with_self_ty(tcx
, open_ty
))
419 tcx
.required_region_bounds(open_ty
, predicates
)