1 // Copyright 2018 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 //! Support code for rustdoc and external tools . You really don't
12 //! want to be using this unless you need to.
16 use std::collections::hash_map::Entry;
17 use std::collections::VecDeque;
19 use infer::region_constraints::{Constraint, RegionConstraintData};
21 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
23 use ty::fold::TypeFolder;
24 use ty::{Region, RegionVid};
26 // FIXME(twk): this is obviously not nice to duplicate like that
27 #[derive(Eq, PartialEq, Hash, Copy, Clone, Debug)]
28 pub enum RegionTarget<'tcx> {
33 #[derive(Default, Debug, Clone)]
34 pub struct RegionDeps<'tcx> {
35 larger: FxHashSet<RegionTarget<'tcx>>,
36 smaller: FxHashSet<RegionTarget<'tcx>>,
39 pub enum AutoTraitResult<A> {
45 impl<A> AutoTraitResult<A> {
46 fn is_auto(&self) -> bool {
48 AutoTraitResult::PositiveImpl(_) | AutoTraitResult::NegativeImpl => true,
54 pub struct AutoTraitInfo<'cx> {
55 pub full_user_env: ty::ParamEnv<'cx>,
56 pub region_data: RegionConstraintData<'cx>,
57 pub names_map: FxHashSet<String>,
58 pub vid_to_region: FxHashMap<ty::RegionVid, ty::Region<'cx>>,
61 pub struct AutoTraitFinder<'a, 'tcx: 'a> {
62 tcx: &'a TyCtxt<'a, 'tcx, 'tcx>,
65 impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
66 pub fn new(tcx: &'a TyCtxt<'a, 'tcx, 'tcx>) -> Self {
67 AutoTraitFinder { tcx }
70 /// Make a best effort to determine whether and under which conditions an auto trait is
71 /// implemented for a type. For example, if you have
74 /// struct Foo<T> { data: Box<T> }
77 /// then this might return that Foo<T>: Send if T: Send (encoded in the AutoTraitResult type).
78 /// The analysis attempts to account for custom impls as well as other complex cases. This
79 /// result is intended for use by rustdoc and other such consumers.
81 /// (Note that due to the coinductive nature of Send, the full and correct result is actually
82 /// quite simple to generate. That is, when a type has no custom impl, it is Send iff its field
83 /// types are all Send. So, in our example, we might have that Foo<T>: Send if Box<T>: Send.
84 /// But this is often not the best way to present to the user.)
86 /// Warning: The API should be considered highly unstable, and it may be refactored or removed
88 pub fn find_auto_trait_generics<A>(
92 generics: &ty::Generics,
93 auto_trait_callback: impl for<'i> Fn(&InferCtxt<'_, 'tcx, 'i>, AutoTraitInfo<'i>) -> A,
94 ) -> AutoTraitResult<A> {
96 let ty = self.tcx.type_of(did);
98 let orig_params = tcx.param_env(did);
100 let trait_ref = ty::TraitRef {
102 substs: tcx.mk_substs_trait(ty, &[]),
105 let trait_pred = ty::Binder::bind(trait_ref);
107 let bail_out = tcx.infer_ctxt().enter(|infcx| {
108 let mut selcx = SelectionContext::with_negative(&infcx, true);
109 let result = selcx.select(&Obligation::new(
110 ObligationCause::dummy(),
112 trait_pred.to_poly_trait_predicate(),
116 Ok(Some(Vtable::VtableImpl(_))) => {
118 "find_auto_trait_generics(did={:?}, trait_did={:?}, generics={:?}): \
119 manual impl found, bailing out",
120 did, trait_did, generics
128 // If an explicit impl exists, it always takes priority over an auto impl
130 return AutoTraitResult::ExplicitImpl;
133 return tcx.infer_ctxt().enter(|mut infcx| {
134 let mut fresh_preds = FxHashSet::default();
136 // Due to the way projections are handled by SelectionContext, we need to run
137 // evaluate_predicates twice: once on the original param env, and once on the result of
138 // the first evaluate_predicates call.
140 // The problem is this: most of rustc, including SelectionContext and traits::project,
141 // are designed to work with a concrete usage of a type (e.g., Vec<u8>
142 // fn<T>() { Vec<T> }. This information will generally never change - given
143 // the 'T' in fn<T>() { ... }, we'll never know anything else about 'T'.
144 // If we're unable to prove that 'T' implements a particular trait, we're done -
145 // there's nothing left to do but error out.
147 // However, synthesizing an auto trait impl works differently. Here, we start out with
148 // a set of initial conditions - the ParamEnv of the struct/enum/union we're dealing
149 // with - and progressively discover the conditions we need to fulfill for it to
150 // implement a certain auto trait. This ends up breaking two assumptions made by trait
151 // selection and projection:
153 // * We can always cache the result of a particular trait selection for the lifetime of
155 // * Given a projection bound such as '<T as SomeTrait>::SomeItem = K', if 'T:
156 // SomeTrait' doesn't hold, then we don't need to care about the 'SomeItem = K'
158 // We fix the first assumption by manually clearing out all of the InferCtxt's caches
159 // in between calls to SelectionContext.select. This allows us to keep all of the
160 // intermediate types we create bound to the 'tcx lifetime, rather than needing to lift
161 // them between calls.
163 // We fix the second assumption by reprocessing the result of our first call to
164 // evaluate_predicates. Using the example of '<T as SomeTrait>::SomeItem = K', our first
165 // pass will pick up 'T: SomeTrait', but not 'SomeItem = K'. On our second pass,
166 // traits::project will see that 'T: SomeTrait' is in our ParamEnv, allowing
167 // SelectionContext to return it back to us.
169 let (new_env, user_env) = match self.evaluate_predicates(
180 None => return AutoTraitResult::NegativeImpl,
183 let (full_env, full_user_env) = self.evaluate_predicates(
192 ).unwrap_or_else(|| {
194 "Failed to fully process: {:?} {:?} {:?}",
195 ty, trait_did, orig_params
200 "find_auto_trait_generics(did={:?}, trait_did={:?}, generics={:?}): fulfilling \
202 did, trait_did, generics, full_env
204 infcx.clear_caches();
206 // At this point, we already have all of the bounds we need. FulfillmentContext is used
207 // to store all of the necessary region/lifetime bounds in the InferContext, as well as
208 // an additional sanity check.
209 let mut fulfill = FulfillmentContext::new();
210 fulfill.register_bound(
215 ObligationCause::misc(DUMMY_SP, ast::DUMMY_NODE_ID),
217 fulfill.select_all_or_error(&infcx).unwrap_or_else(|e| {
219 "Unable to fulfill trait {:?} for '{:?}': {:?}",
224 let names_map: FxHashSet<String> = generics
227 .filter_map(|param| match param.kind {
228 ty::GenericParamDefKind::Lifetime => Some(param.name.to_string()),
233 let body_id_map: FxHashMap<_, _> = infcx
237 .map(|&(id, _)| (id, vec![]))
240 infcx.process_registered_region_obligations(&body_id_map, None, full_env.clone());
242 let region_data = infcx
243 .borrow_region_constraints()
244 .region_constraint_data()
247 let vid_to_region = self.map_vid_to_region(®ion_data);
249 let info = AutoTraitInfo {
256 return AutoTraitResult::PositiveImpl(auto_trait_callback(&infcx, info));
261 impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
262 // The core logic responsible for computing the bounds for our synthesized impl.
264 // To calculate the bounds, we call SelectionContext.select in a loop. Like FulfillmentContext,
265 // we recursively select the nested obligations of predicates we encounter. However, whenever we
266 // encounter an UnimplementedError involving a type parameter, we add it to our ParamEnv. Since
267 // our goal is to determine when a particular type implements an auto trait, Unimplemented
268 // errors tell us what conditions need to be met.
270 // This method ends up working somewhat similarly to FulfillmentContext, but with a few key
271 // differences. FulfillmentContext works under the assumption that it's dealing with concrete
272 // user code. According, it considers all possible ways that a Predicate could be met - which
273 // isn't always what we want for a synthesized impl. For example, given the predicate 'T:
274 // Iterator', FulfillmentContext can end up reporting an Unimplemented error for T:
275 // IntoIterator - since there's an implementation of Iteratpr where T: IntoIterator,
276 // FulfillmentContext will drive SelectionContext to consider that impl before giving up. If we
277 // were to rely on FulfillmentContext's decision, we might end up synthesizing an impl like
279 // 'impl<T> Send for Foo<T> where T: IntoIterator'
281 // While it might be technically true that Foo implements Send where T: IntoIterator,
282 // the bound is overly restrictive - it's really only necessary that T: Iterator.
284 // For this reason, evaluate_predicates handles predicates with type variables specially. When
285 // we encounter an Unimplemented error for a bound such as 'T: Iterator', we immediately add it
286 // to our ParamEnv, and add it to our stack for recursive evaluation. When we later select it,
287 // we'll pick up any nested bounds, without ever inferring that 'T: IntoIterator' needs to
290 // One additional consideration is supertrait bounds. Normally, a ParamEnv is only ever
291 // constructed once for a given type. As part of the construction process, the ParamEnv will
292 // have any supertrait bounds normalized - e.g., if we have a type 'struct Foo<T: Copy>', the
293 // ParamEnv will contain 'T: Copy' and 'T: Clone', since 'Copy: Clone'. When we construct our
294 // own ParamEnv, we need to do this ourselves, through traits::elaborate_predicates, or else
295 // SelectionContext will choke on the missing predicates. However, this should never show up in
296 // the final synthesized generics: we don't want our generated docs page to contain something
297 // like 'T: Copy + Clone', as that's redundant. Therefore, we keep track of a separate
298 // 'user_env', which only holds the predicates that will actually be displayed to the user.
299 pub fn evaluate_predicates<'b, 'gcx, 'c>(
301 infcx: &InferCtxt<'b, 'tcx, 'c>,
305 param_env: ty::ParamEnv<'c>,
306 user_env: ty::ParamEnv<'c>,
307 fresh_preds: &mut FxHashSet<ty::Predicate<'c>>,
308 only_projections: bool,
309 ) -> Option<(ty::ParamEnv<'c>, ty::ParamEnv<'c>)> {
312 let mut select = SelectionContext::with_negative(&infcx, true);
314 let mut already_visited = FxHashSet::default();
315 let mut predicates = VecDeque::new();
316 predicates.push_back(ty::Binder::bind(ty::TraitPredicate {
317 trait_ref: ty::TraitRef {
319 substs: infcx.tcx.mk_substs_trait(ty, &[]),
323 let mut computed_preds: FxHashSet<_> = param_env.caller_bounds.iter().cloned().collect();
324 let mut user_computed_preds: FxHashSet<_> =
325 user_env.caller_bounds.iter().cloned().collect();
327 let mut new_env = param_env.clone();
328 let dummy_cause = ObligationCause::misc(DUMMY_SP, ast::DUMMY_NODE_ID);
330 while let Some(pred) = predicates.pop_front() {
331 infcx.clear_caches();
333 if !already_visited.insert(pred.clone()) {
337 // Call infcx.resolve_type_vars_if_possible to see if we can
338 // get rid of any inference variables.
339 let obligation = infcx.resolve_type_vars_if_possible(
340 &Obligation::new(dummy_cause.clone(), new_env, pred)
342 let result = select.select(&obligation);
345 &Ok(Some(ref vtable)) => {
346 // If we see an explicit negative impl (e.g., 'impl !Send for MyStruct'),
347 // we immediately bail out, since it's impossible for us to continue.
349 Vtable::VtableImpl(VtableImplData { impl_def_id, .. }) => {
350 // Blame tidy for the weird bracket placement
351 if infcx.tcx.impl_polarity(*impl_def_id) == hir::ImplPolarity::Negative
353 debug!("evaluate_nested_obligations: Found explicit negative impl\
354 {:?}, bailing out", impl_def_id);
361 let obligations = vtable.clone().nested_obligations().into_iter();
363 if !self.evaluate_nested_obligations(
366 &mut user_computed_preds,
376 &Err(SelectionError::Unimplemented) => {
377 if self.is_param_no_infer(pred.skip_binder().trait_ref.substs) {
378 already_visited.remove(&pred);
380 &mut user_computed_preds,
381 ty::Predicate::Trait(pred.clone()),
383 predicates.push_back(pred);
386 "evaluate_nested_obligations: Unimplemented found, bailing: \
390 pred.skip_binder().trait_ref.substs
395 _ => panic!("Unexpected error for '{:?}': {:?}", ty, result),
398 computed_preds.extend(user_computed_preds.iter().cloned());
399 let normalized_preds =
400 elaborate_predicates(tcx, computed_preds.clone().into_iter().collect());
401 new_env = ty::ParamEnv::new(tcx.mk_predicates(normalized_preds), param_env.reveal);
404 let final_user_env = ty::ParamEnv::new(
405 tcx.mk_predicates(user_computed_preds.into_iter()),
409 "evaluate_nested_obligations(ty_did={:?}, trait_did={:?}): succeeded with '{:?}' \
411 ty_did, trait_did, new_env, final_user_env
414 return Some((new_env, final_user_env));
417 // This method is designed to work around the following issue:
418 // When we compute auto trait bounds, we repeatedly call SelectionContext.select,
419 // progressively building a ParamEnv based on the results we get.
420 // However, our usage of SelectionContext differs from its normal use within the compiler,
421 // in that we capture and re-reprocess predicates from Unimplemented errors.
423 // This can lead to a corner case when dealing with region parameters.
424 // During our selection loop in evaluate_predicates, we might end up with
425 // two trait predicates that differ only in their region parameters:
426 // one containing a HRTB lifetime parameter, and one containing a 'normal'
427 // lifetime parameter. For example:
430 // T as MyTrait<'static>
432 // If we put both of these predicates in our computed ParamEnv, we'll
433 // confuse SelectionContext, since it will (correctly) view both as being applicable.
435 // To solve this, we pick the 'more strict' lifetime bound - i.e., the HRTB
436 // Our end goal is to generate a user-visible description of the conditions
437 // under which a type implements an auto trait. A trait predicate involving
438 // a HRTB means that the type needs to work with any choice of lifetime,
439 // not just one specific lifetime (e.g., 'static).
440 fn add_user_pred<'c>(
442 user_computed_preds: &mut FxHashSet<ty::Predicate<'c>>,
443 new_pred: ty::Predicate<'c>,
445 let mut should_add_new = true;
446 user_computed_preds.retain(|&old_pred| {
447 match (&new_pred, old_pred) {
448 (&ty::Predicate::Trait(new_trait), ty::Predicate::Trait(old_trait)) => {
449 if new_trait.def_id() == old_trait.def_id() {
450 let new_substs = new_trait.skip_binder().trait_ref.substs;
451 let old_substs = old_trait.skip_binder().trait_ref.substs;
453 if !new_substs.types().eq(old_substs.types()) {
454 // We can't compare lifetimes if the types are different,
455 // so skip checking old_pred
459 for (new_region, old_region) in
460 new_substs.regions().zip(old_substs.regions())
462 match (new_region, old_region) {
463 // If both predicates have an 'ReLateBound' (a HRTB) in the
464 // same spot, we do nothing
466 ty::RegionKind::ReLateBound(_, _),
467 ty::RegionKind::ReLateBound(_, _),
470 (ty::RegionKind::ReLateBound(_, _), _) |
471 (_, ty::RegionKind::ReVar(_)) => {
472 // One of these is true:
473 // The new predicate has a HRTB in a spot where the old
474 // predicate does not (if they both had a HRTB, the previous
475 // match arm would have executed). A HRBT is a 'stricter'
476 // bound than anything else, so we want to keep the newer
477 // predicate (with the HRBT) in place of the old predicate.
481 // The old predicate has a region variable where the new
482 // predicate has some other kind of region. An region
483 // variable isn't something we can actually display to a user,
484 // so we choose ther new predicate (which doesn't have a region
487 // In both cases, we want to remove the old predicate,
488 // from user_computed_preds, and replace it with the new
489 // one. Having both the old and the new
490 // predicate in a ParamEnv would confuse SelectionContext
492 // We're currently in the predicate passed to 'retain',
493 // so we return 'false' to remove the old predicate from
494 // user_computed_preds
497 (_, ty::RegionKind::ReLateBound(_, _)) |
498 (ty::RegionKind::ReVar(_), _) => {
499 // This is the opposite situation as the previous arm.
500 // One of these is true:
502 // The old predicate has a HRTB lifetime in a place where the
503 // new predicate does not.
507 // The new predicate has a region variable where the old
508 // predicate has some other type of region.
510 // We want to leave the old
511 // predicate in user_computed_preds, and skip adding
512 // new_pred to user_computed_params.
513 should_add_new = false
526 user_computed_preds.insert(new_pred);
530 pub fn region_name(&self, region: Region<'_>) -> Option<String> {
532 &ty::ReEarlyBound(r) => Some(r.name.to_string()),
537 pub fn get_lifetime(&self, region: Region<'_>,
538 names_map: &FxHashMap<String, String>) -> String {
539 self.region_name(region)
541 names_map.get(&name).unwrap_or_else(||
542 panic!("Missing lifetime with name {:?} for {:?}", name, region)
546 .unwrap_or_else(|| "'static".to_owned())
549 // This is very similar to handle_lifetimes. However, instead of matching ty::Region's
550 // to each other, we match ty::RegionVid's to ty::Region's
551 pub fn map_vid_to_region<'cx>(
553 regions: &RegionConstraintData<'cx>,
554 ) -> FxHashMap<ty::RegionVid, ty::Region<'cx>> {
555 let mut vid_map: FxHashMap<RegionTarget<'cx>, RegionDeps<'cx>> = FxHashMap::default();
556 let mut finished_map = FxHashMap::default();
558 for constraint in regions.constraints.keys() {
560 &Constraint::VarSubVar(r1, r2) => {
562 let deps1 = vid_map.entry(RegionTarget::RegionVid(r1)).or_default();
563 deps1.larger.insert(RegionTarget::RegionVid(r2));
566 let deps2 = vid_map.entry(RegionTarget::RegionVid(r2)).or_default();
567 deps2.smaller.insert(RegionTarget::RegionVid(r1));
569 &Constraint::RegSubVar(region, vid) => {
571 let deps1 = vid_map.entry(RegionTarget::Region(region)).or_default();
572 deps1.larger.insert(RegionTarget::RegionVid(vid));
575 let deps2 = vid_map.entry(RegionTarget::RegionVid(vid)).or_default();
576 deps2.smaller.insert(RegionTarget::Region(region));
578 &Constraint::VarSubReg(vid, region) => {
579 finished_map.insert(vid, region);
581 &Constraint::RegSubReg(r1, r2) => {
583 let deps1 = vid_map.entry(RegionTarget::Region(r1)).or_default();
584 deps1.larger.insert(RegionTarget::Region(r2));
587 let deps2 = vid_map.entry(RegionTarget::Region(r2)).or_default();
588 deps2.smaller.insert(RegionTarget::Region(r1));
593 while !vid_map.is_empty() {
594 let target = vid_map.keys().next().expect("Keys somehow empty").clone();
595 let deps = vid_map.remove(&target).expect("Entry somehow missing");
597 for smaller in deps.smaller.iter() {
598 for larger in deps.larger.iter() {
599 match (smaller, larger) {
600 (&RegionTarget::Region(_), &RegionTarget::Region(_)) => {
601 if let Entry::Occupied(v) = vid_map.entry(*smaller) {
602 let smaller_deps = v.into_mut();
603 smaller_deps.larger.insert(*larger);
604 smaller_deps.larger.remove(&target);
607 if let Entry::Occupied(v) = vid_map.entry(*larger) {
608 let larger_deps = v.into_mut();
609 larger_deps.smaller.insert(*smaller);
610 larger_deps.smaller.remove(&target);
613 (&RegionTarget::RegionVid(v1), &RegionTarget::Region(r1)) => {
614 finished_map.insert(v1, r1);
616 (&RegionTarget::Region(_), &RegionTarget::RegionVid(_)) => {
617 // Do nothing - we don't care about regions that are smaller than vids
619 (&RegionTarget::RegionVid(_), &RegionTarget::RegionVid(_)) => {
620 if let Entry::Occupied(v) = vid_map.entry(*smaller) {
621 let smaller_deps = v.into_mut();
622 smaller_deps.larger.insert(*larger);
623 smaller_deps.larger.remove(&target);
626 if let Entry::Occupied(v) = vid_map.entry(*larger) {
627 let larger_deps = v.into_mut();
628 larger_deps.smaller.insert(*smaller);
629 larger_deps.smaller.remove(&target);
639 fn is_param_no_infer(&self, substs: &Substs<'_>) -> bool {
640 return self.is_of_param(substs.type_at(0)) &&
641 !substs.types().any(|t| t.has_infer_types());
644 pub fn is_of_param(&self, ty: Ty<'_>) -> bool {
645 return match ty.sty {
646 ty::Param(_) => true,
647 ty::Projection(p) => self.is_of_param(p.self_ty()),
652 fn is_self_referential_projection(&self, p: ty::PolyProjectionPredicate<'_>) -> bool {
653 match p.ty().skip_binder().sty {
654 ty::Projection(proj) if proj == p.skip_binder().projection_ty => {
661 pub fn evaluate_nested_obligations<
666 T: Iterator<Item = Obligation<'cx, ty::Predicate<'cx>>>,
671 computed_preds: &'b mut FxHashSet<ty::Predicate<'cx>>,
672 fresh_preds: &'b mut FxHashSet<ty::Predicate<'cx>>,
673 predicates: &'b mut VecDeque<ty::PolyTraitPredicate<'cx>>,
674 select: &mut SelectionContext<'c, 'd, 'cx>,
675 only_projections: bool,
677 let dummy_cause = ObligationCause::misc(DUMMY_SP, ast::DUMMY_NODE_ID);
679 for (obligation, mut predicate) in nested
680 .map(|o| (o.clone(), o.predicate.clone()))
683 fresh_preds.insert(self.clean_pred(select.infcx(), predicate.clone()));
685 // Resolve any inference variables that we can, to help selection succeed
686 predicate = select.infcx().resolve_type_vars_if_possible(&predicate);
688 // We only add a predicate as a user-displayable bound if
689 // it involves a generic parameter, and doesn't contain
690 // any inference variables.
692 // Displaying a bound involving a concrete type (instead of a generic
693 // parameter) would be pointless, since it's always true
695 // Displaying an inference variable is impossible, since they're
696 // an internal compiler detail without a defined visual representation
698 // We check this by calling is_of_param on the relevant types
699 // from the various possible predicates
701 &ty::Predicate::Trait(ref p) => {
702 if self.is_param_no_infer(p.skip_binder().trait_ref.substs)
706 self.add_user_pred(computed_preds, predicate);
708 predicates.push_back(p.clone());
710 &ty::Predicate::Projection(p) => {
711 debug!("evaluate_nested_obligations: examining projection predicate {:?}",
714 // As described above, we only want to display
715 // bounds which include a generic parameter but don't include
716 // an inference variable.
717 // Additionally, we check if we've seen this predicate before,
718 // to avoid rendering duplicate bounds to the user.
719 if self.is_param_no_infer(p.skip_binder().projection_ty.substs)
720 && !p.ty().skip_binder().is_ty_infer()
722 debug!("evaluate_nested_obligations: adding projection predicate\
723 to computed_preds: {:?}", predicate);
725 // Under unusual circumstances, we can end up with a self-refeential
726 // projection predicate. For example:
727 // <T as MyType>::Value == <T as MyType>::Value
728 // Not only is displaying this to the user pointless,
729 // having it in the ParamEnv will cause an issue if we try to call
730 // poly_project_and_unify_type on the predicate, since this kind of
731 // predicate will normally never end up in a ParamEnv.
733 // For these reasons, we ignore these weird predicates,
734 // ensuring that we're able to properly synthesize an auto trait impl
735 if self.is_self_referential_projection(p) {
736 debug!("evaluate_nested_obligations: encountered a projection
737 predicate equating a type with itself! Skipping");
740 self.add_user_pred(computed_preds, predicate);
744 // We can only call poly_project_and_unify_type when our predicate's
745 // Ty is an inference variable - otherwise, there won't be anything to
747 if p.ty().skip_binder().is_ty_infer() {
748 debug!("Projecting and unifying projection predicate {:?}",
750 match poly_project_and_unify_type(select, &obligation.with(p.clone())) {
753 "evaluate_nested_obligations: Unable to unify predicate \
754 '{:?}' '{:?}', bailing out",
760 if !self.evaluate_nested_obligations(
762 v.clone().iter().cloned(),
773 panic!("Unexpected result when selecting {:?} {:?}", ty, obligation)
778 &ty::Predicate::RegionOutlives(ref binder) => {
781 .region_outlives_predicate(&dummy_cause, binder)
787 &ty::Predicate::TypeOutlives(ref binder) => {
789 binder.no_bound_vars(),
790 binder.map_bound_ref(|pred| pred.0).no_bound_vars(),
792 (None, Some(t_a)) => {
793 select.infcx().register_region_obligation_with_cause(
795 select.infcx().tcx.types.re_static,
799 (Some(ty::OutlivesPredicate(t_a, r_b)), _) => {
800 select.infcx().register_region_obligation_with_cause(
809 _ => panic!("Unexpected predicate {:?} {:?}", ty, predicate),
815 pub fn clean_pred<'c, 'd, 'cx>(
817 infcx: &InferCtxt<'c, 'd, 'cx>,
818 p: ty::Predicate<'cx>,
819 ) -> ty::Predicate<'cx> {
824 // Replaces all ReVars in a type with ty::Region's, using the provided map
825 pub struct RegionReplacer<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
826 vid_to_region: &'a FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
827 tcx: TyCtxt<'a, 'gcx, 'tcx>,
830 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionReplacer<'a, 'gcx, 'tcx> {
831 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> {
835 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
837 &ty::ReVar(vid) => self.vid_to_region.get(&vid).cloned(),
839 }).unwrap_or_else(|| r.super_fold_with(self))