3 use self::CombineMapType::*;
8 InferCtxtUndoLogs, MiscVariable, RegionVariableOrigin, Rollback, Snapshot, SubregionOrigin,
11 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
12 use rustc_data_structures::sync::Lrc;
13 use rustc_data_structures::undo_log::UndoLogs;
14 use rustc_data_structures::unify as ut;
15 use rustc_data_structures::unify::UnifyKey;
16 use rustc_hir::def_id::DefId;
17 use rustc_index::vec::IndexVec;
18 use rustc_middle::ty::ReStatic;
19 use rustc_middle::ty::{self, Ty, TyCtxt};
20 use rustc_middle::ty::{ReLateBound, ReVar};
21 use rustc_middle::ty::{Region, RegionVid};
24 use std::collections::BTreeMap;
26 use std::{cmp, fmt, mem};
30 pub use rustc_middle::infer::MemberConstraint;
33 pub struct RegionConstraintStorage<'tcx> {
34 /// For each `RegionVid`, the corresponding `RegionVariableOrigin`.
35 var_infos: IndexVec<RegionVid, RegionVariableInfo>,
37 data: RegionConstraintData<'tcx>,
39 /// For a given pair of regions (R1, R2), maps to a region R3 that
40 /// is designated as their LUB (edges R1 <= R3 and R2 <= R3
41 /// exist). This prevents us from making many such regions.
42 lubs: CombineMap<'tcx>,
44 /// For a given pair of regions (R1, R2), maps to a region R3 that
45 /// is designated as their GLB (edges R3 <= R1 and R3 <= R2
46 /// exist). This prevents us from making many such regions.
47 glbs: CombineMap<'tcx>,
49 /// When we add a R1 == R2 constriant, we currently add (a) edges
50 /// R1 <= R2 and R2 <= R1 and (b) we unify the two regions in this
51 /// table. You can then call `opportunistic_resolve_var` early
52 /// which will map R1 and R2 to some common region (i.e., either
53 /// R1 or R2). This is important when fulfillment, dropck and other such
54 /// code is iterating to a fixed point, because otherwise we sometimes
55 /// would wind up with a fresh stream of region variables that have been
56 /// equated but appear distinct.
57 pub(super) unification_table: ut::UnificationTableStorage<ty::RegionVid>,
59 /// a flag set to true when we perform any unifications; this is used
60 /// to micro-optimize `take_and_reset_data`
61 any_unifications: bool,
64 pub struct RegionConstraintCollector<'a, 'tcx> {
65 storage: &'a mut RegionConstraintStorage<'tcx>,
66 undo_log: &'a mut InferCtxtUndoLogs<'tcx>,
69 impl std::ops::Deref for RegionConstraintCollector<'_, 'tcx> {
70 type Target = RegionConstraintStorage<'tcx>;
72 fn deref(&self) -> &RegionConstraintStorage<'tcx> {
77 impl std::ops::DerefMut for RegionConstraintCollector<'_, 'tcx> {
79 fn deref_mut(&mut self) -> &mut RegionConstraintStorage<'tcx> {
84 pub type VarInfos = IndexVec<RegionVid, RegionVariableInfo>;
86 /// The full set of region constraints gathered up by the collector.
87 /// Describes constraints between the region variables and other
88 /// regions, as well as other conditions that must be verified, or
89 /// assumptions that can be made.
90 #[derive(Debug, Default, Clone)]
91 pub struct RegionConstraintData<'tcx> {
92 /// Constraints of the form `A <= B`, where either `A` or `B` can
93 /// be a region variable (or neither, as it happens).
94 pub constraints: BTreeMap<Constraint<'tcx>, SubregionOrigin<'tcx>>,
96 /// Constraints of the form `R0 member of [R1, ..., Rn]`, meaning that
97 /// `R0` must be equal to one of the regions `R1..Rn`. These occur
98 /// with `impl Trait` quite frequently.
99 pub member_constraints: Vec<MemberConstraint<'tcx>>,
101 /// A "verify" is something that we need to verify after inference
102 /// is done, but which does not directly affect inference in any
105 /// An example is a `A <= B` where neither `A` nor `B` are
106 /// inference variables.
107 pub verifys: Vec<Verify<'tcx>>,
109 /// A "given" is a relationship that is known to hold. In
110 /// particular, we often know from closure fn signatures that a
111 /// particular free region must be a subregion of a region
114 /// foo.iter().filter(<'a> |x: &'a &'b T| ...)
116 /// In situations like this, `'b` is in fact a region variable
117 /// introduced by the call to `iter()`, and `'a` is a bound region
118 /// on the closure (as indicated by the `<'a>` prefix). If we are
119 /// naive, we wind up inferring that `'b` must be `'static`,
120 /// because we require that it be greater than `'a` and we do not
121 /// know what `'a` is precisely.
123 /// This hashmap is used to avoid that naive scenario. Basically
124 /// we record the fact that `'a <= 'b` is implied by the fn
125 /// signature, and then ignore the constraint when solving
126 /// equations. This is a bit of a hack but seems to work.
127 pub givens: FxHashSet<(Region<'tcx>, ty::RegionVid)>,
130 /// Represents a constraint that influences the inference process.
131 #[derive(Clone, Copy, PartialEq, Eq, Debug, PartialOrd, Ord)]
132 pub enum Constraint<'tcx> {
133 /// A region variable is a subregion of another.
134 VarSubVar(RegionVid, RegionVid),
136 /// A concrete region is a subregion of region variable.
137 RegSubVar(Region<'tcx>, RegionVid),
139 /// A region variable is a subregion of a concrete region. This does not
140 /// directly affect inference, but instead is checked after
141 /// inference is complete.
142 VarSubReg(RegionVid, Region<'tcx>),
144 /// A constraint where neither side is a variable. This does not
145 /// directly affect inference, but instead is checked after
146 /// inference is complete.
147 RegSubReg(Region<'tcx>, Region<'tcx>),
150 impl Constraint<'_> {
151 pub fn involves_placeholders(&self) -> bool {
153 Constraint::VarSubVar(_, _) => false,
154 Constraint::VarSubReg(_, r) | Constraint::RegSubVar(r, _) => r.is_placeholder(),
155 Constraint::RegSubReg(r, s) => r.is_placeholder() || s.is_placeholder(),
160 #[derive(Debug, Clone)]
161 pub struct Verify<'tcx> {
162 pub kind: GenericKind<'tcx>,
163 pub origin: SubregionOrigin<'tcx>,
164 pub region: Region<'tcx>,
165 pub bound: VerifyBound<'tcx>,
168 #[derive(Copy, Clone, PartialEq, Eq, Hash, TypeFoldable)]
169 pub enum GenericKind<'tcx> {
171 Projection(ty::ProjectionTy<'tcx>),
174 /// Describes the things that some `GenericKind` value `G` is known to
175 /// outlive. Each variant of `VerifyBound` can be thought of as a
178 /// fn(min: Region) -> bool { .. }
180 /// where `true` means that the region `min` meets that `G: min`.
181 /// (False means nothing.)
183 /// So, for example, if we have the type `T` and we have in scope that
184 /// `T: 'a` and `T: 'b`, then the verify bound might be:
186 /// fn(min: Region) -> bool {
187 /// ('a: min) || ('b: min)
190 /// This is described with a `AnyRegion('a, 'b)` node.
191 #[derive(Debug, Clone)]
192 pub enum VerifyBound<'tcx> {
193 /// Given a kind K and a bound B, expands to a function like the
194 /// following, where `G` is the generic for which this verify
195 /// bound was created:
198 /// fn(min) -> bool {
207 /// In other words, if the generic `G` that we are checking is
208 /// equal to `K`, then check the associated verify bound
209 /// (otherwise, false).
211 /// This is used when we have something in the environment that
212 /// may or may not be relevant, depending on the region inference
213 /// results. For example, we may have `where <T as
214 /// Trait<'a>>::Item: 'b` in our where-clauses. If we are
215 /// generating the verify-bound for `<T as Trait<'0>>::Item`, then
216 /// this where-clause is only relevant if `'0` winds up inferred
219 /// So we would compile to a verify-bound like
222 /// IfEq(<T as Trait<'a>>::Item, AnyRegion('a))
225 /// meaning, if the subject G is equal to `<T as Trait<'a>>::Item`
226 /// (after inference), and `'a: min`, then `G: min`.
227 IfEq(Ty<'tcx>, Box<VerifyBound<'tcx>>),
229 /// Given a region `R`, expands to the function:
232 /// fn(min) -> bool {
237 /// This is used when we can establish that `G: R` -- therefore,
238 /// if `R: min`, then by transitivity `G: min`.
239 OutlivedBy(Region<'tcx>),
241 /// Given a region `R`, true if it is `'empty`.
244 /// Given a set of bounds `B`, expands to the function:
247 /// fn(min) -> bool {
248 /// exists (b in B) { b(min) }
252 /// In other words, if we meet some bound in `B`, that suffices.
253 /// This is used when all the bounds in `B` are known to apply to `G`.
254 AnyBound(Vec<VerifyBound<'tcx>>),
256 /// Given a set of bounds `B`, expands to the function:
259 /// fn(min) -> bool {
260 /// forall (b in B) { b(min) }
264 /// In other words, if we meet *all* bounds in `B`, that suffices.
265 /// This is used when *some* bound in `B` is known to suffice, but
266 /// we don't know which.
267 AllBounds(Vec<VerifyBound<'tcx>>),
270 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
271 pub(crate) struct TwoRegions<'tcx> {
276 #[derive(Copy, Clone, PartialEq)]
277 pub(crate) enum UndoLog<'tcx> {
278 /// We added `RegionVid`.
281 /// We added the given `constraint`.
282 AddConstraint(Constraint<'tcx>),
284 /// We added the given `verify`.
287 /// We added the given `given`.
288 AddGiven(Region<'tcx>, ty::RegionVid),
290 /// We added a GLB/LUB "combination variable".
291 AddCombination(CombineMapType, TwoRegions<'tcx>),
294 #[derive(Copy, Clone, PartialEq)]
295 pub(crate) enum CombineMapType {
300 type CombineMap<'tcx> = FxHashMap<TwoRegions<'tcx>, RegionVid>;
302 #[derive(Debug, Clone, Copy)]
303 pub struct RegionVariableInfo {
304 pub origin: RegionVariableOrigin,
305 pub universe: ty::UniverseIndex,
308 pub struct RegionSnapshot {
309 any_unifications: bool,
312 /// When working with placeholder regions, we often wish to find all of
313 /// the regions that are either reachable from a placeholder region, or
314 /// which can reach a placeholder region, or both. We call such regions
315 /// *tainted* regions. This struct allows you to decide what set of
316 /// tainted regions you want.
318 pub struct TaintDirections {
323 impl TaintDirections {
324 pub fn incoming() -> Self {
325 TaintDirections { incoming: true, outgoing: false }
328 pub fn outgoing() -> Self {
329 TaintDirections { incoming: false, outgoing: true }
332 pub fn both() -> Self {
333 TaintDirections { incoming: true, outgoing: true }
337 impl<'tcx> RegionConstraintStorage<'tcx> {
338 pub fn new() -> Self {
343 pub(crate) fn with_log<'a>(
345 undo_log: &'a mut InferCtxtUndoLogs<'tcx>,
346 ) -> RegionConstraintCollector<'a, 'tcx> {
347 RegionConstraintCollector { storage: self, undo_log }
350 fn rollback_undo_entry(&mut self, undo_entry: UndoLog<'tcx>) {
353 self.var_infos.pop().unwrap();
354 assert_eq!(self.var_infos.len(), vid.index() as usize);
356 AddConstraint(ref constraint) => {
357 self.data.constraints.remove(constraint);
359 AddVerify(index) => {
360 self.data.verifys.pop();
361 assert_eq!(self.data.verifys.len(), index);
363 AddGiven(sub, sup) => {
364 self.data.givens.remove(&(sub, sup));
366 AddCombination(Glb, ref regions) => {
367 self.glbs.remove(regions);
369 AddCombination(Lub, ref regions) => {
370 self.lubs.remove(regions);
376 impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
377 pub fn num_region_vars(&self) -> usize {
381 pub fn region_constraint_data(&self) -> &RegionConstraintData<'tcx> {
385 /// Once all the constraints have been gathered, extract out the final data.
387 /// Not legal during a snapshot.
388 pub fn into_infos_and_data(self) -> (VarInfos, RegionConstraintData<'tcx>) {
389 assert!(!UndoLogs::<super::UndoLog<'_>>::in_snapshot(&self.undo_log));
390 (mem::take(&mut self.storage.var_infos), mem::take(&mut self.storage.data))
393 /// Takes (and clears) the current set of constraints. Note that
394 /// the set of variables remains intact, but all relationships
395 /// between them are reset. This is used during NLL checking to
396 /// grab the set of constraints that arose from a particular
399 /// We don't want to leak relationships between variables between
400 /// points because just because (say) `r1 == r2` was true at some
401 /// point P in the graph doesn't imply that it will be true at
402 /// some other point Q, in NLL.
404 /// Not legal during a snapshot.
405 pub fn take_and_reset_data(&mut self) -> RegionConstraintData<'tcx> {
406 assert!(!UndoLogs::<super::UndoLog<'_>>::in_snapshot(&self.undo_log));
408 // If you add a new field to `RegionConstraintCollector`, you
409 // should think carefully about whether it needs to be cleared
410 // or updated in some way.
411 let RegionConstraintStorage {
416 unification_table: _,
420 // Clear the tables of (lubs, glbs), so that we will create
421 // fresh regions if we do a LUB operation. As it happens,
422 // LUB/GLB are not performed by the MIR type-checker, which is
423 // the one that uses this method, but it's good to be correct.
427 let data = mem::take(data);
429 // Clear all unifications and recreate the variables a "now
430 // un-unified" state. Note that when we unify `a` and `b`, we
431 // also insert `a <= b` and a `b <= a` edges, so the
432 // `RegionConstraintData` contains the relationship here.
433 if *any_unifications {
434 *any_unifications = false;
435 self.unification_table()
436 .reset_unifications(|vid| unify_key::RegionVidKey { min_vid: vid });
442 pub fn data(&self) -> &RegionConstraintData<'tcx> {
446 pub fn start_snapshot(&mut self) -> RegionSnapshot {
447 debug!("RegionConstraintCollector: start_snapshot");
448 RegionSnapshot { any_unifications: self.any_unifications }
451 pub fn rollback_to(&mut self, snapshot: RegionSnapshot) {
452 debug!("RegionConstraintCollector: rollback_to({:?})", snapshot);
453 self.any_unifications = snapshot.any_unifications;
456 pub fn new_region_var(
458 universe: ty::UniverseIndex,
459 origin: RegionVariableOrigin,
461 let vid = self.var_infos.push(RegionVariableInfo { origin, universe });
463 let u_vid = self.unification_table().new_key(unify_key::RegionVidKey { min_vid: vid });
464 assert_eq!(vid, u_vid);
465 self.undo_log.push(AddVar(vid));
466 debug!("created new region variable {:?} in {:?} with origin {:?}", vid, universe, origin);
470 /// Returns the universe for the given variable.
471 pub fn var_universe(&self, vid: RegionVid) -> ty::UniverseIndex {
472 self.var_infos[vid].universe
475 /// Returns the origin for the given variable.
476 pub fn var_origin(&self, vid: RegionVid) -> RegionVariableOrigin {
477 self.var_infos[vid].origin
480 fn add_constraint(&mut self, constraint: Constraint<'tcx>, origin: SubregionOrigin<'tcx>) {
481 // cannot add constraints once regions are resolved
482 debug!("RegionConstraintCollector: add_constraint({:?})", constraint);
484 // never overwrite an existing (constraint, origin) - only insert one if it isn't
485 // present in the map yet. This prevents origins from outside the snapshot being
486 // replaced with "less informative" origins e.g., during calls to `can_eq`
487 let undo_log = &mut self.undo_log;
488 self.storage.data.constraints.entry(constraint).or_insert_with(|| {
489 undo_log.push(AddConstraint(constraint));
494 fn add_verify(&mut self, verify: Verify<'tcx>) {
495 // cannot add verifys once regions are resolved
496 debug!("RegionConstraintCollector: add_verify({:?})", verify);
498 // skip no-op cases known to be satisfied
499 if let VerifyBound::AllBounds(ref bs) = verify.bound {
505 let index = self.data.verifys.len();
506 self.data.verifys.push(verify);
507 self.undo_log.push(AddVerify(index));
510 pub fn add_given(&mut self, sub: Region<'tcx>, sup: ty::RegionVid) {
511 // cannot add givens once regions are resolved
512 if self.data.givens.insert((sub, sup)) {
513 debug!("add_given({:?} <= {:?})", sub, sup);
515 self.undo_log.push(AddGiven(sub, sup));
519 pub fn make_eqregion(
521 origin: SubregionOrigin<'tcx>,
526 // Eventually, it would be nice to add direct support for
528 self.make_subregion(origin.clone(), sub, sup);
529 self.make_subregion(origin, sup, sub);
531 if let (ty::ReVar(sub), ty::ReVar(sup)) = (*sub, *sup) {
532 debug!("make_eqregion: uniying {:?} with {:?}", sub, sup);
533 self.unification_table().union(sub, sup);
534 self.any_unifications = true;
539 pub fn member_constraint(
541 opaque_type_def_id: DefId,
542 definition_span: Span,
544 member_region: ty::Region<'tcx>,
545 choice_regions: &Lrc<Vec<ty::Region<'tcx>>>,
547 debug!("member_constraint({:?} in {:#?})", member_region, choice_regions);
549 if choice_regions.iter().any(|&r| r == member_region) {
553 self.data.member_constraints.push(MemberConstraint {
558 choice_regions: choice_regions.clone(),
562 pub fn make_subregion(
564 origin: SubregionOrigin<'tcx>,
568 // cannot add constraints once regions are resolved
570 "RegionConstraintCollector: make_subregion({:?}, {:?}) due to {:?}",
575 (&ReLateBound(..), _) | (_, &ReLateBound(..)) => {
576 span_bug!(origin.span(), "cannot relate bound region: {:?} <= {:?}", sub, sup);
579 // all regions are subregions of static, so we can ignore this
581 (&ReVar(sub_id), &ReVar(sup_id)) => {
582 self.add_constraint(Constraint::VarSubVar(sub_id, sup_id), origin);
584 (_, &ReVar(sup_id)) => {
585 self.add_constraint(Constraint::RegSubVar(sub, sup_id), origin);
587 (&ReVar(sub_id), _) => {
588 self.add_constraint(Constraint::VarSubReg(sub_id, sup), origin);
591 self.add_constraint(Constraint::RegSubReg(sub, sup), origin);
596 pub fn verify_generic_bound(
598 origin: SubregionOrigin<'tcx>,
599 kind: GenericKind<'tcx>,
601 bound: VerifyBound<'tcx>,
603 self.add_verify(Verify { kind, origin, region: sub, bound });
609 origin: SubregionOrigin<'tcx>,
613 // cannot add constraints once regions are resolved
614 debug!("RegionConstraintCollector: lub_regions({:?}, {:?})", a, b);
616 (r @ &ReStatic, _) | (_, r @ &ReStatic) => {
617 r // nothing lives longer than static
624 _ => self.combine_vars(tcx, Lub, a, b, origin),
631 origin: SubregionOrigin<'tcx>,
635 // cannot add constraints once regions are resolved
636 debug!("RegionConstraintCollector: glb_regions({:?}, {:?})", a, b);
638 (&ReStatic, r) | (r, &ReStatic) => {
639 r // static lives longer than everything else
646 _ => self.combine_vars(tcx, Glb, a, b, origin),
650 pub fn opportunistic_resolve_var(&mut self, rid: RegionVid) -> ty::RegionVid {
651 self.unification_table().probe_value(rid).min_vid
654 fn combine_map(&mut self, t: CombineMapType) -> &mut CombineMap<'tcx> {
656 Glb => &mut self.glbs,
657 Lub => &mut self.lubs,
667 origin: SubregionOrigin<'tcx>,
669 let vars = TwoRegions { a, b };
670 if let Some(&c) = self.combine_map(t).get(&vars) {
671 return tcx.mk_region(ReVar(c));
673 let a_universe = self.universe(a);
674 let b_universe = self.universe(b);
675 let c_universe = cmp::max(a_universe, b_universe);
676 let c = self.new_region_var(c_universe, MiscVariable(origin.span()));
677 self.combine_map(t).insert(vars, c);
678 self.undo_log.push(AddCombination(t, vars));
679 let new_r = tcx.mk_region(ReVar(c));
680 for &old_r in &[a, b] {
682 Glb => self.make_subregion(origin.clone(), new_r, old_r),
683 Lub => self.make_subregion(origin.clone(), old_r, new_r),
686 debug!("combine_vars() c={:?}", c);
690 pub fn universe(&self, region: Region<'tcx>) -> ty::UniverseIndex {
692 ty::ReStatic | ty::ReErased | ty::ReFree(..) | ty::ReEarlyBound(..) => {
693 ty::UniverseIndex::ROOT
695 ty::ReEmpty(ui) => ui,
696 ty::RePlaceholder(placeholder) => placeholder.universe,
697 ty::ReVar(vid) => self.var_universe(vid),
698 ty::ReLateBound(..) => bug!("universe(): encountered bound region {:?}", region),
702 pub fn vars_since_snapshot(
705 ) -> (Range<RegionVid>, Vec<RegionVariableOrigin>) {
706 let range = RegionVid::from_index(value_count as u32)
707 ..RegionVid::from_index(self.unification_table.len() as u32);
710 (range.start.index()..range.end.index())
711 .map(|index| self.var_infos[ty::RegionVid::from(index)].origin)
716 /// See `InferCtxt::region_constraints_added_in_snapshot`.
717 pub fn region_constraints_added_in_snapshot(&self, mark: &Snapshot<'tcx>) -> Option<bool> {
719 .region_constraints_in_snapshot(mark)
720 .map(|&elt| match elt {
721 AddConstraint(constraint) => Some(constraint.involves_placeholders()),
729 fn unification_table(&mut self) -> super::UnificationTable<'_, 'tcx, ty::RegionVid> {
730 ut::UnificationTable::with_log(&mut self.storage.unification_table, self.undo_log)
734 impl fmt::Debug for RegionSnapshot {
735 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
736 write!(f, "RegionSnapshot")
740 impl<'tcx> fmt::Debug for GenericKind<'tcx> {
741 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
743 GenericKind::Param(ref p) => write!(f, "{:?}", p),
744 GenericKind::Projection(ref p) => write!(f, "{:?}", p),
749 impl<'tcx> fmt::Display for GenericKind<'tcx> {
750 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
752 GenericKind::Param(ref p) => write!(f, "{}", p),
753 GenericKind::Projection(ref p) => write!(f, "{}", p),
758 impl<'tcx> GenericKind<'tcx> {
759 pub fn to_ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
761 GenericKind::Param(ref p) => p.to_ty(tcx),
762 GenericKind::Projection(ref p) => tcx.mk_projection(p.item_def_id, p.substs),
767 impl<'tcx> VerifyBound<'tcx> {
768 pub fn must_hold(&self) -> bool {
770 VerifyBound::IfEq(..) => false,
771 VerifyBound::OutlivedBy(ty::ReStatic) => true,
772 VerifyBound::OutlivedBy(_) => false,
773 VerifyBound::IsEmpty => false,
774 VerifyBound::AnyBound(bs) => bs.iter().any(|b| b.must_hold()),
775 VerifyBound::AllBounds(bs) => bs.iter().all(|b| b.must_hold()),
779 pub fn cannot_hold(&self) -> bool {
781 VerifyBound::IfEq(_, b) => b.cannot_hold(),
782 VerifyBound::IsEmpty => false,
783 VerifyBound::OutlivedBy(_) => false,
784 VerifyBound::AnyBound(bs) => bs.iter().all(|b| b.cannot_hold()),
785 VerifyBound::AllBounds(bs) => bs.iter().any(|b| b.cannot_hold()),
789 pub fn or(self, vb: VerifyBound<'tcx>) -> VerifyBound<'tcx> {
790 if self.must_hold() || vb.cannot_hold() {
792 } else if self.cannot_hold() || vb.must_hold() {
795 VerifyBound::AnyBound(vec![self, vb])
799 pub fn and(self, vb: VerifyBound<'tcx>) -> VerifyBound<'tcx> {
800 if self.must_hold() && vb.must_hold() {
802 } else if self.cannot_hold() && vb.cannot_hold() {
805 VerifyBound::AllBounds(vec![self, vb])
810 impl<'tcx> RegionConstraintData<'tcx> {
811 /// Returns `true` if this region constraint data contains no constraints, and `false`
813 pub fn is_empty(&self) -> bool {
814 let RegionConstraintData { constraints, member_constraints, verifys, givens } = self;
815 constraints.is_empty()
816 && member_constraints.is_empty()
817 && verifys.is_empty()
822 impl<'tcx> Rollback<UndoLog<'tcx>> for RegionConstraintStorage<'tcx> {
823 fn reverse(&mut self, undo: UndoLog<'tcx>) {
824 self.rollback_undo_entry(undo)