1 // Copyright 2012-2014 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.
13 use self::CombineMapType::*;
17 use super::{MiscVariable, RegionVariableOrigin, SubregionOrigin};
19 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
20 use rustc_data_structures::indexed_vec::IndexVec;
21 use rustc_data_structures::unify as ut;
23 use ty::{self, Ty, TyCtxt};
24 use ty::{BrFresh, ReLateBound, ReVar};
25 use ty::{Region, RegionVid};
27 use std::collections::BTreeMap;
28 use std::{cmp, fmt, mem, u32};
33 pub struct RegionConstraintCollector<'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 /// Global counter used during the GLB algorithm to create unique
50 /// names for fresh bound regions
53 /// The undo log records actions that might later be undone.
55 /// Note: `num_open_snapshots` is used to track if we are actively
56 /// snapshotting. When the `start_snapshot()` method is called, we
57 /// increment `num_open_snapshots` to indicate that we are now actively
58 /// snapshotting. The reason for this is that otherwise we end up adding
59 /// entries for things like the lower bound on a variable and so forth,
60 /// which can never be rolled back.
61 undo_log: Vec<UndoLog<'tcx>>,
63 /// The number of open snapshots, i.e. those that haven't been committed or
65 num_open_snapshots: usize,
67 /// When we add a R1 == R2 constriant, we currently add (a) edges
68 /// R1 <= R2 and R2 <= R1 and (b) we unify the two regions in this
69 /// table. You can then call `opportunistic_resolve_var` early
70 /// which will map R1 and R2 to some common region (i.e., either
71 /// R1 or R2). This is important when dropck and other such code
72 /// is iterating to a fixed point, because otherwise we sometimes
73 /// would wind up with a fresh stream of region variables that
74 /// have been equated but appear distinct.
75 unification_table: ut::UnificationTable<ut::InPlace<ty::RegionVid>>,
77 /// a flag set to true when we perform any unifications; this is used
78 /// to micro-optimize `take_and_reset_data`
79 any_unifications: bool,
82 pub type VarInfos = IndexVec<RegionVid, RegionVariableInfo>;
84 /// The full set of region constraints gathered up by the collector.
85 /// Describes constraints between the region variables and other
86 /// regions, as well as other conditions that must be verified, or
87 /// assumptions that can be made.
88 #[derive(Debug, Default, Clone)]
89 pub struct RegionConstraintData<'tcx> {
90 /// Constraints of the form `A <= B`, where either `A` or `B` can
91 /// be a region variable (or neither, as it happens).
92 pub constraints: BTreeMap<Constraint<'tcx>, SubregionOrigin<'tcx>>,
94 /// A "verify" is something that we need to verify after inference
95 /// is done, but which does not directly affect inference in any
98 /// An example is a `A <= B` where neither `A` nor `B` are
99 /// inference variables.
100 pub verifys: Vec<Verify<'tcx>>,
102 /// A "given" is a relationship that is known to hold. In
103 /// particular, we often know from closure fn signatures that a
104 /// particular free region must be a subregion of a region
107 /// foo.iter().filter(<'a> |x: &'a &'b T| ...)
109 /// In situations like this, `'b` is in fact a region variable
110 /// introduced by the call to `iter()`, and `'a` is a bound region
111 /// on the closure (as indicated by the `<'a>` prefix). If we are
112 /// naive, we wind up inferring that `'b` must be `'static`,
113 /// because we require that it be greater than `'a` and we do not
114 /// know what `'a` is precisely.
116 /// This hashmap is used to avoid that naive scenario. Basically
117 /// we record the fact that `'a <= 'b` is implied by the fn
118 /// signature, and then ignore the constraint when solving
119 /// equations. This is a bit of a hack but seems to work.
120 pub givens: FxHashSet<(Region<'tcx>, ty::RegionVid)>,
123 /// A constraint that influences the inference process.
124 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
125 pub enum Constraint<'tcx> {
126 /// One region variable is subregion of another
127 VarSubVar(RegionVid, RegionVid),
129 /// Concrete region is subregion of region variable
130 RegSubVar(Region<'tcx>, RegionVid),
132 /// Region variable is subregion of concrete region. This does not
133 /// directly affect inference, but instead is checked after
134 /// inference is complete.
135 VarSubReg(RegionVid, Region<'tcx>),
137 /// A constraint where neither side is a variable. This does not
138 /// directly affect inference, but instead is checked after
139 /// inference is complete.
140 RegSubReg(Region<'tcx>, Region<'tcx>),
143 /// VerifyGenericBound(T, _, R, RS): The parameter type `T` (or
144 /// associated type) must outlive the region `R`. `T` is known to
145 /// outlive `RS`. Therefore verify that `R <= RS[i]` for some
146 /// `i`. Inference variables may be involved (but this verification
147 /// step doesn't influence inference).
148 #[derive(Debug, Clone)]
149 pub struct Verify<'tcx> {
150 pub kind: GenericKind<'tcx>,
151 pub origin: SubregionOrigin<'tcx>,
152 pub region: Region<'tcx>,
153 pub bound: VerifyBound<'tcx>,
156 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
157 pub enum GenericKind<'tcx> {
159 Projection(ty::ProjectionTy<'tcx>),
162 EnumTypeFoldableImpl! {
163 impl<'tcx> TypeFoldable<'tcx> for GenericKind<'tcx> {
164 (GenericKind::Param)(a),
165 (GenericKind::Projection)(a),
169 /// Describes the things that some `GenericKind` value G is known to
170 /// outlive. Each variant of `VerifyBound` can be thought of as a
173 /// fn(min: Region) -> bool { .. }
175 /// where `true` means that the region `min` meets that `G: min`.
176 /// (False means nothing.)
178 /// So, for example, if we have the type `T` and we have in scope that
179 /// `T: 'a` and `T: 'b`, then the verify bound might be:
181 /// fn(min: Region) -> bool {
182 /// ('a: min) || ('b: min)
185 /// This is described with a `AnyRegion('a, 'b)` node.
186 #[derive(Debug, Clone)]
187 pub enum VerifyBound<'tcx> {
188 /// Given a kind K and a bound B, expands to a function like the
189 /// following, where `G` is the generic for which this verify
190 /// bound was created:
192 /// fn(min) -> bool {
200 /// In other words, if the generic `G` that we are checking is
201 /// equal to `K`, then check the associated verify bound
202 /// (otherwise, false).
204 /// This is used when we have something in the environment that
205 /// may or may not be relevant, depending on the region inference
206 /// results. For example, we may have `where <T as
207 /// Trait<'a>>::Item: 'b` in our where clauses. If we are
208 /// generating the verify-bound for `<T as Trait<'0>>::Item`, then
209 /// this where-clause is only relevant if `'0` winds up inferred
212 /// So we would compile to a verify-bound like
214 /// IfEq(<T as Trait<'a>>::Item, AnyRegion('a))
216 /// meaning, if the subject G is equal to `<T as Trait<'a>>::Item`
217 /// (after inference), and `'a: min`, then `G: min`.
218 IfEq(Ty<'tcx>, Box<VerifyBound<'tcx>>),
220 /// Given a region `R`, expands to the function:
222 /// fn(min) -> bool {
226 /// This is used when we can establish that `G: R` -- therefore,
227 /// if `R: min`, then by transitivity `G: min`.
228 OutlivedBy(Region<'tcx>),
230 /// Given a set of bounds `B`, expands to the function:
232 /// fn(min) -> bool {
233 /// exists (b in B) { b(min) }
236 /// In other words, if we meet some bound in `B`, that suffices.
237 /// This is used when all the bounds in `B` are known to apply to
239 AnyBound(Vec<VerifyBound<'tcx>>),
241 /// Given a set of bounds `B`, expands to the function:
243 /// fn(min) -> bool {
244 /// forall (b in B) { b(min) }
247 /// In other words, if we meet *all* bounds in `B`, that suffices.
248 /// This is used when *some* bound in `B` is known to suffice, but
249 /// we don't know which.
250 AllBounds(Vec<VerifyBound<'tcx>>),
253 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
254 struct TwoRegions<'tcx> {
259 #[derive(Copy, Clone, PartialEq)]
261 /// We added `RegionVid`
264 /// We added the given `constraint`
265 AddConstraint(Constraint<'tcx>),
267 /// We added the given `verify`
270 /// We added the given `given`
271 AddGiven(Region<'tcx>, ty::RegionVid),
273 /// We added a GLB/LUB "combination variable"
274 AddCombination(CombineMapType, TwoRegions<'tcx>),
276 /// During skolemization, we sometimes purge entries from the undo
277 /// log in a kind of minisnapshot (unlike other snapshots, this
278 /// purging actually takes place *on success*). In that case, we
279 /// replace the corresponding entry with `Noop` so as to avoid the
280 /// need to do a bunch of swapping. (We can't use `swap_remove` as
281 /// the order of the vector is important.)
285 #[derive(Copy, Clone, PartialEq)]
286 enum CombineMapType {
291 type CombineMap<'tcx> = FxHashMap<TwoRegions<'tcx>, RegionVid>;
293 #[derive(Debug, Clone, Copy)]
294 pub struct RegionVariableInfo {
295 pub origin: RegionVariableOrigin,
296 pub universe: ty::UniverseIndex,
299 pub struct RegionSnapshot {
301 region_snapshot: ut::Snapshot<ut::InPlace<ty::RegionVid>>,
302 any_unifications: bool,
305 /// When working with placeholder regions, we often wish to find all of
306 /// the regions that are either reachable from a placeholder region, or
307 /// which can reach a placeholder region, or both. We call such regions
308 /// *tainted* regions. This struct allows you to decide what set of
309 /// tainted regions you want.
311 pub struct TaintDirections {
316 impl TaintDirections {
317 pub fn incoming() -> Self {
324 pub fn outgoing() -> Self {
331 pub fn both() -> Self {
339 impl<'tcx> RegionConstraintCollector<'tcx> {
340 pub fn new() -> Self {
344 pub fn num_region_vars(&self) -> usize {
348 pub fn region_constraint_data(&self) -> &RegionConstraintData<'tcx> {
352 /// Once all the constraints have been gathered, extract out the final data.
354 /// Not legal during a snapshot.
355 pub fn into_infos_and_data(self) -> (VarInfos, RegionConstraintData<'tcx>) {
356 assert!(!self.in_snapshot());
357 (self.var_infos, self.data)
360 /// Takes (and clears) the current set of constraints. Note that
361 /// the set of variables remains intact, but all relationships
362 /// between them are reset. This is used during NLL checking to
363 /// grab the set of constraints that arose from a particular
366 /// We don't want to leak relationships between variables between
367 /// points because just because (say) `r1 == r2` was true at some
368 /// point P in the graph doesn't imply that it will be true at
369 /// some other point Q, in NLL.
371 /// Not legal during a snapshot.
372 pub fn take_and_reset_data(&mut self) -> RegionConstraintData<'tcx> {
373 assert!(!self.in_snapshot());
375 // If you add a new field to `RegionConstraintCollector`, you
376 // should think carefully about whether it needs to be cleared
377 // or updated in some way.
378 let RegionConstraintCollector {
385 num_open_snapshots: _,
390 // Clear the tables of (lubs, glbs), so that we will create
391 // fresh regions if we do a LUB operation. As it happens,
392 // LUB/GLB are not performed by the MIR type-checker, which is
393 // the one that uses this method, but it's good to be correct.
397 // Clear all unifications and recreate the variables a "now
398 // un-unified" state. Note that when we unify `a` and `b`, we
399 // also insert `a <= b` and a `b <= a` edges, so the
400 // `RegionConstraintData` contains the relationship here.
401 if *any_unifications {
402 unification_table.reset_unifications(|vid| unify_key::RegionVidKey { min_vid: vid });
403 *any_unifications = false;
406 mem::replace(data, RegionConstraintData::default())
409 pub fn data(&self) -> &RegionConstraintData<'tcx> {
413 fn in_snapshot(&self) -> bool {
414 self.num_open_snapshots > 0
417 pub fn start_snapshot(&mut self) -> RegionSnapshot {
418 let length = self.undo_log.len();
419 debug!("RegionConstraintCollector: start_snapshot({})", length);
420 self.num_open_snapshots += 1;
423 region_snapshot: self.unification_table.snapshot(),
424 any_unifications: self.any_unifications,
428 fn assert_open_snapshot(&self, snapshot: &RegionSnapshot) {
429 assert!(self.undo_log.len() >= snapshot.length);
430 assert!(self.num_open_snapshots > 0);
433 pub fn commit(&mut self, snapshot: RegionSnapshot) {
434 debug!("RegionConstraintCollector: commit({})", snapshot.length);
435 self.assert_open_snapshot(&snapshot);
437 if self.num_open_snapshots == 1 {
438 // The root snapshot. It's safe to clear the undo log because
439 // there's no snapshot further out that we might need to roll back
441 assert!(snapshot.length == 0);
442 self.undo_log.clear();
445 self.num_open_snapshots -= 1;
447 self.unification_table.commit(snapshot.region_snapshot);
450 pub fn rollback_to(&mut self, snapshot: RegionSnapshot) {
451 debug!("RegionConstraintCollector: rollback_to({:?})", snapshot);
452 self.assert_open_snapshot(&snapshot);
454 while self.undo_log.len() > snapshot.length {
455 let undo_entry = self.undo_log.pop().unwrap();
456 self.rollback_undo_entry(undo_entry);
459 self.num_open_snapshots -= 1;
461 self.unification_table.rollback_to(snapshot.region_snapshot);
462 self.any_unifications = snapshot.any_unifications;
465 fn rollback_undo_entry(&mut self, undo_entry: UndoLog<'tcx>) {
468 // nothing to do here
471 self.var_infos.pop().unwrap();
472 assert_eq!(self.var_infos.len(), vid.index() as usize);
474 AddConstraint(ref constraint) => {
475 self.data.constraints.remove(constraint);
477 AddVerify(index) => {
478 self.data.verifys.pop();
479 assert_eq!(self.data.verifys.len(), index);
481 AddGiven(sub, sup) => {
482 self.data.givens.remove(&(sub, sup));
484 AddCombination(Glb, ref regions) => {
485 self.glbs.remove(regions);
487 AddCombination(Lub, ref regions) => {
488 self.lubs.remove(regions);
493 pub fn new_region_var(
495 universe: ty::UniverseIndex,
496 origin: RegionVariableOrigin,
498 let vid = self.var_infos.push(RegionVariableInfo { origin, universe });
500 let u_vid = self.unification_table
501 .new_key(unify_key::RegionVidKey { min_vid: vid });
502 assert_eq!(vid, u_vid);
503 if self.in_snapshot() {
504 self.undo_log.push(AddVar(vid));
507 "created new region variable {:?} with origin {:?}",
513 /// Returns the universe for the given variable.
514 pub fn var_universe(&self, vid: RegionVid) -> ty::UniverseIndex {
515 self.var_infos[vid].universe
518 /// Returns the origin for the given variable.
519 pub fn var_origin(&self, vid: RegionVid) -> RegionVariableOrigin {
520 self.var_infos[vid].origin
523 /// Removes all the edges to/from the placeholder regions that are
524 /// in `skols`. This is used after a higher-ranked operation
525 /// completes to remove all trace of the placeholder regions
526 /// created in that time.
527 pub fn pop_placeholders(&mut self, placeholders: &FxHashSet<ty::Region<'tcx>>) {
528 debug!("pop_placeholders(placeholders={:?})", placeholders);
530 assert!(self.in_snapshot());
532 let constraints_to_kill: Vec<usize> = self.undo_log
536 .filter(|&(_, undo_entry)| kill_constraint(placeholders, undo_entry))
537 .map(|(index, _)| index)
540 for index in constraints_to_kill {
541 let undo_entry = mem::replace(&mut self.undo_log[index], Purged);
542 self.rollback_undo_entry(undo_entry);
547 fn kill_constraint<'tcx>(
548 placeholders: &FxHashSet<ty::Region<'tcx>>,
549 undo_entry: &UndoLog<'tcx>,
552 &AddConstraint(Constraint::VarSubVar(..)) => false,
553 &AddConstraint(Constraint::RegSubVar(a, _)) => placeholders.contains(&a),
554 &AddConstraint(Constraint::VarSubReg(_, b)) => placeholders.contains(&b),
555 &AddConstraint(Constraint::RegSubReg(a, b)) => {
556 placeholders.contains(&a) || placeholders.contains(&b)
558 &AddGiven(..) => false,
559 &AddVerify(_) => false,
560 &AddCombination(_, ref two_regions) => {
561 placeholders.contains(&two_regions.a) || placeholders.contains(&two_regions.b)
563 &AddVar(..) | &Purged => false,
570 tcx: TyCtxt<'_, '_, 'tcx>,
571 debruijn: ty::DebruijnIndex,
573 // Creates a fresh bound variable for use in GLB computations.
574 // See discussion of GLB computation in the large comment at
575 // the top of this file for more details.
577 // This computation is potentially wrong in the face of
578 // rollover. It's conceivable, if unlikely, that one might
579 // wind up with accidental capture for nested functions in
580 // that case, if the outer function had bound regions created
581 // a very long time before and the inner function somehow
582 // wound up rolling over such that supposedly fresh
583 // identifiers were in fact shadowed. For now, we just assert
584 // that there is no rollover -- eventually we should try to be
585 // robust against this possibility, either by checking the set
586 // of bound identifiers that appear in a given expression and
587 // ensure that we generate one that is distinct, or by
588 // changing the representation of bound regions in a fn
591 let sc = self.bound_count;
592 self.bound_count = sc + 1;
594 if sc >= self.bound_count {
595 bug!("rollover in RegionInference new_bound()");
598 tcx.mk_region(ReLateBound(debruijn, BrFresh(sc)))
601 fn add_constraint(&mut self, constraint: Constraint<'tcx>, origin: SubregionOrigin<'tcx>) {
602 // cannot add constraints once regions are resolved
604 "RegionConstraintCollector: add_constraint({:?})",
608 // never overwrite an existing (constraint, origin) - only insert one if it isn't
609 // present in the map yet. This prevents origins from outside the snapshot being
610 // replaced with "less informative" origins e.g. during calls to `can_eq`
611 let in_snapshot = self.in_snapshot();
612 let undo_log = &mut self.undo_log;
613 self.data.constraints.entry(constraint).or_insert_with(|| {
615 undo_log.push(AddConstraint(constraint));
621 fn add_verify(&mut self, verify: Verify<'tcx>) {
622 // cannot add verifys once regions are resolved
623 debug!("RegionConstraintCollector: add_verify({:?})", verify);
625 // skip no-op cases known to be satisfied
626 if let VerifyBound::AllBounds(ref bs) = verify.bound {
632 let index = self.data.verifys.len();
633 self.data.verifys.push(verify);
634 if self.in_snapshot() {
635 self.undo_log.push(AddVerify(index));
639 pub fn add_given(&mut self, sub: Region<'tcx>, sup: ty::RegionVid) {
640 // cannot add givens once regions are resolved
641 if self.data.givens.insert((sub, sup)) {
642 debug!("add_given({:?} <= {:?})", sub, sup);
644 if self.in_snapshot() {
645 self.undo_log.push(AddGiven(sub, sup));
650 pub fn make_eqregion(
652 origin: SubregionOrigin<'tcx>,
657 // Eventually, it would be nice to add direct support for
659 self.make_subregion(origin.clone(), sub, sup);
660 self.make_subregion(origin, sup, sub);
662 if let (ty::ReVar(sub), ty::ReVar(sup)) = (*sub, *sup) {
663 self.unification_table.union(sub, sup);
664 self.any_unifications = true;
669 pub fn make_subregion(
671 origin: SubregionOrigin<'tcx>,
675 // cannot add constraints once regions are resolved
677 "RegionConstraintCollector: make_subregion({:?}, {:?}) due to {:?}",
682 (&ReLateBound(..), _) | (_, &ReLateBound(..)) => {
685 "cannot relate bound region: {:?} <= {:?}",
691 // all regions are subregions of static, so we can ignore this
693 (&ReVar(sub_id), &ReVar(sup_id)) => {
694 self.add_constraint(Constraint::VarSubVar(sub_id, sup_id), origin);
696 (_, &ReVar(sup_id)) => {
697 self.add_constraint(Constraint::RegSubVar(sub, sup_id), origin);
699 (&ReVar(sub_id), _) => {
700 self.add_constraint(Constraint::VarSubReg(sub_id, sup), origin);
703 self.add_constraint(Constraint::RegSubReg(sub, sup), origin);
708 /// See `Verify::VerifyGenericBound`
709 pub fn verify_generic_bound(
711 origin: SubregionOrigin<'tcx>,
712 kind: GenericKind<'tcx>,
714 bound: VerifyBound<'tcx>,
716 self.add_verify(Verify {
726 tcx: TyCtxt<'_, '_, 'tcx>,
727 origin: SubregionOrigin<'tcx>,
731 // cannot add constraints once regions are resolved
732 debug!("RegionConstraintCollector: lub_regions({:?}, {:?})", a, b);
734 (r @ &ReStatic, _) | (_, r @ &ReStatic) => {
735 r // nothing lives longer than static
742 _ => self.combine_vars(tcx, Lub, a, b, origin),
748 tcx: TyCtxt<'_, '_, 'tcx>,
749 origin: SubregionOrigin<'tcx>,
753 // cannot add constraints once regions are resolved
754 debug!("RegionConstraintCollector: glb_regions({:?}, {:?})", a, b);
756 (&ReStatic, r) | (r, &ReStatic) => {
757 r // static lives longer than everything else
764 _ => self.combine_vars(tcx, Glb, a, b, origin),
768 pub fn opportunistic_resolve_var(
770 tcx: TyCtxt<'_, '_, 'tcx>,
772 ) -> ty::Region<'tcx> {
773 let vid = self.unification_table.probe_value(rid).min_vid;
774 tcx.mk_region(ty::ReVar(vid))
777 fn combine_map(&mut self, t: CombineMapType) -> &mut CombineMap<'tcx> {
779 Glb => &mut self.glbs,
780 Lub => &mut self.lubs,
786 tcx: TyCtxt<'_, '_, 'tcx>,
790 origin: SubregionOrigin<'tcx>,
792 let vars = TwoRegions { a: a, b: b };
793 if let Some(&c) = self.combine_map(t).get(&vars) {
794 return tcx.mk_region(ReVar(c));
796 let a_universe = self.universe(a);
797 let b_universe = self.universe(b);
798 let c_universe = cmp::max(a_universe, b_universe);
799 let c = self.new_region_var(c_universe, MiscVariable(origin.span()));
800 self.combine_map(t).insert(vars, c);
801 if self.in_snapshot() {
802 self.undo_log.push(AddCombination(t, vars));
804 let new_r = tcx.mk_region(ReVar(c));
805 for &old_r in &[a, b] {
807 Glb => self.make_subregion(origin.clone(), new_r, old_r),
808 Lub => self.make_subregion(origin.clone(), old_r, new_r),
811 debug!("combine_vars() c={:?}", c);
815 fn universe(&self, region: Region<'tcx>) -> ty::UniverseIndex {
822 | ty::ReEarlyBound(..) => ty::UniverseIndex::ROOT,
823 ty::RePlaceholder(placeholder) => placeholder.universe,
824 ty::ReClosureBound(vid) | ty::ReVar(vid) => self.var_universe(vid),
825 ty::ReLateBound(..) => bug!("universe(): encountered bound region {:?}", region),
829 pub fn vars_created_since_snapshot(&self, mark: &RegionSnapshot) -> Vec<RegionVid> {
830 self.undo_log[mark.length..]
832 .filter_map(|&elt| match elt {
833 AddVar(vid) => Some(vid),
839 /// Computes all regions that have been related to `r0` since the
840 /// mark `mark` was made---`r0` itself will be the first
841 /// entry. The `directions` parameter controls what kind of
842 /// relations are considered. For example, one can say that only
843 /// "incoming" edges to `r0` are desired, in which case one will
844 /// get the set of regions `{r|r <= r0}`. This is used when
845 /// checking whether placeholder regions are being improperly
846 /// related to other regions.
849 tcx: TyCtxt<'_, '_, 'tcx>,
850 mark: &RegionSnapshot,
852 directions: TaintDirections,
853 ) -> FxHashSet<ty::Region<'tcx>> {
855 "tainted(mark={:?}, r0={:?}, directions={:?})",
859 // `result_set` acts as a worklist: we explore all outgoing
860 // edges and add any new regions we find to result_set. This
861 // is not a terribly efficient implementation.
862 let mut taint_set = taint::TaintSet::new(directions, r0);
863 taint_set.fixed_point(tcx, &self.undo_log[mark.length..], &self.data.verifys);
864 debug!("tainted: result={:?}", taint_set);
865 return taint_set.into_set();
869 impl fmt::Debug for RegionSnapshot {
870 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
871 write!(f, "RegionSnapshot(length={})", self.length)
875 impl<'tcx> fmt::Debug for GenericKind<'tcx> {
876 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
878 GenericKind::Param(ref p) => write!(f, "{:?}", p),
879 GenericKind::Projection(ref p) => write!(f, "{:?}", p),
884 impl<'tcx> fmt::Display for GenericKind<'tcx> {
885 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
887 GenericKind::Param(ref p) => write!(f, "{}", p),
888 GenericKind::Projection(ref p) => write!(f, "{}", p),
893 impl<'a, 'gcx, 'tcx> GenericKind<'tcx> {
894 pub fn to_ty(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Ty<'tcx> {
896 GenericKind::Param(ref p) => p.to_ty(tcx),
897 GenericKind::Projection(ref p) => tcx.mk_projection(p.item_def_id, p.substs),
902 impl<'a, 'gcx, 'tcx> VerifyBound<'tcx> {
903 pub fn must_hold(&self) -> bool {
905 VerifyBound::IfEq(..) => false,
906 VerifyBound::OutlivedBy(ty::ReStatic) => true,
907 VerifyBound::OutlivedBy(_) => false,
908 VerifyBound::AnyBound(bs) => bs.iter().any(|b| b.must_hold()),
909 VerifyBound::AllBounds(bs) => bs.iter().all(|b| b.must_hold()),
913 pub fn cannot_hold(&self) -> bool {
915 VerifyBound::IfEq(_, b) => b.cannot_hold(),
916 VerifyBound::OutlivedBy(ty::ReEmpty) => true,
917 VerifyBound::OutlivedBy(_) => false,
918 VerifyBound::AnyBound(bs) => bs.iter().all(|b| b.cannot_hold()),
919 VerifyBound::AllBounds(bs) => bs.iter().any(|b| b.cannot_hold()),
923 pub fn or(self, vb: VerifyBound<'tcx>) -> VerifyBound<'tcx> {
924 if self.must_hold() || vb.cannot_hold() {
926 } else if self.cannot_hold() || vb.must_hold() {
929 VerifyBound::AnyBound(vec![self, vb])
933 pub fn and(self, vb: VerifyBound<'tcx>) -> VerifyBound<'tcx> {
934 if self.must_hold() && vb.must_hold() {
936 } else if self.cannot_hold() && vb.cannot_hold() {
939 VerifyBound::AllBounds(vec![self, vb])
944 impl<'tcx> RegionConstraintData<'tcx> {
945 /// True if this region constraint data contains no constraints.
946 pub fn is_empty(&self) -> bool {
947 let RegionConstraintData {
952 constraints.is_empty() && verifys.is_empty() && givens.is_empty()