1 use super::universal_regions::UniversalRegions;
2 use crate::borrow_check::nll::constraints::graph::NormalConstraintGraph;
3 use crate::borrow_check::nll::constraints::{ConstraintSccIndex, ConstraintSet, OutlivesConstraint};
4 use crate::borrow_check::nll::region_infer::values::{
5 PlaceholderIndices, RegionElement, ToElementIndex
7 use crate::borrow_check::Upvar;
8 use crate::borrow_check::nll::type_check::free_region_relations::UniversalRegionRelations;
9 use crate::borrow_check::nll::type_check::Locations;
10 use rustc::hir::def_id::DefId;
11 use rustc::infer::canonical::QueryRegionConstraint;
12 use rustc::infer::region_constraints::{GenericKind, VarInfos, VerifyBound};
13 use rustc::infer::{InferCtxt, NLLRegionVariableOrigin, RegionVariableOrigin};
15 ClosureOutlivesRequirement, ClosureOutlivesSubject, ClosureRegionRequirements,
16 ConstraintCategory, Local, Location, Body,
18 use rustc::ty::{self, subst::SubstsRef, RegionVid, Ty, TyCtxt, TypeFoldable};
19 use rustc::util::common::{self, ErrorReported};
20 use rustc_data_structures::bit_set::BitSet;
21 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
22 use rustc_data_structures::graph::scc::Sccs;
23 use rustc_data_structures::indexed_vec::IndexVec;
24 use rustc_errors::{Diagnostic, DiagnosticBuilder};
31 crate use self::error_reporting::{RegionName, RegionNameSource};
34 use self::values::{LivenessValues, RegionValueElements, RegionValues};
36 use super::ToRegionVid;
38 pub struct RegionInferenceContext<'tcx> {
39 /// Contains the definition for every region variable. Region
40 /// variables are identified by their index (`RegionVid`). The
41 /// definition contains information about where the region came
42 /// from as well as its final inferred value.
43 definitions: IndexVec<RegionVid, RegionDefinition<'tcx>>,
45 /// The liveness constraints added to each region. For most
46 /// regions, these start out empty and steadily grow, though for
47 /// each universally quantified region R they start out containing
48 /// the entire CFG and `end(R)`.
49 liveness_constraints: LivenessValues<RegionVid>,
51 /// The outlives constraints computed by the type-check.
52 constraints: Rc<ConstraintSet>,
54 /// The constraint-set, but in graph form, making it easy to traverse
55 /// the constraints adjacent to a particular region. Used to construct
56 /// the SCC (see `constraint_sccs`) and for error reporting.
57 constraint_graph: Rc<NormalConstraintGraph>,
59 /// The SCC computed from `constraints` and the constraint graph. Used to
60 /// compute the values of each region.
61 constraint_sccs: Rc<Sccs<RegionVid, ConstraintSccIndex>>,
63 /// Map closure bounds to a `Span` that should be used for error reporting.
64 closure_bounds_mapping:
65 FxHashMap<Location, FxHashMap<(RegionVid, RegionVid), (ConstraintCategory, Span)>>,
67 /// Contains the minimum universe of any variable within the same
68 /// SCC. We will ensure that no SCC contains values that are not
69 /// visible from this index.
70 scc_universes: IndexVec<ConstraintSccIndex, ty::UniverseIndex>,
72 /// Contains a "representative" from each SCC. This will be the
73 /// minimal RegionVid belonging to that universe. It is used as a
74 /// kind of hacky way to manage checking outlives relationships,
75 /// since we can 'canonicalize' each region to the representative
76 /// of its SCC and be sure that -- if they have the same repr --
77 /// they *must* be equal (though not having the same repr does not
78 /// mean they are unequal).
79 scc_representatives: IndexVec<ConstraintSccIndex, ty::RegionVid>,
81 /// The final inferred values of the region variables; we compute
82 /// one value per SCC. To get the value for any given *region*,
83 /// you first find which scc it is a part of.
84 scc_values: RegionValues<ConstraintSccIndex>,
86 /// Type constraints that we check after solving.
87 type_tests: Vec<TypeTest<'tcx>>,
89 /// Information about the universally quantified regions in scope
91 universal_regions: Rc<UniversalRegions<'tcx>>,
93 /// Information about how the universally quantified regions in
94 /// scope on this function relate to one another.
95 universal_region_relations: Rc<UniversalRegionRelations<'tcx>>,
98 struct RegionDefinition<'tcx> {
99 /// What kind of variable is this -- a free region? existential
100 /// variable? etc. (See the `NLLRegionVariableOrigin` for more
102 origin: NLLRegionVariableOrigin,
104 /// Which universe is this region variable defined in? This is
105 /// most often `ty::UniverseIndex::ROOT`, but when we encounter
106 /// forall-quantifiers like `for<'a> { 'a = 'b }`, we would create
107 /// the variable for `'a` in a fresh universe that extends ROOT.
108 universe: ty::UniverseIndex,
110 /// If this is 'static or an early-bound region, then this is
111 /// `Some(X)` where `X` is the name of the region.
112 external_name: Option<ty::Region<'tcx>>,
115 /// N.B., the variants in `Cause` are intentionally ordered. Lower
116 /// values are preferred when it comes to error messages. Do not
117 /// reorder willy nilly.
118 #[derive(Copy, Clone, Debug, PartialOrd, Ord, PartialEq, Eq)]
119 pub(crate) enum Cause {
120 /// point inserted because Local was live at the given Location
121 LiveVar(Local, Location),
123 /// point inserted because Local was dropped at the given Location
124 DropVar(Local, Location),
127 /// A "type test" corresponds to an outlives constraint between a type
128 /// and a lifetime, like `T: 'x` or `<T as Foo>::Bar: 'x`. They are
129 /// translated from the `Verify` region constraints in the ordinary
130 /// inference context.
132 /// These sorts of constraints are handled differently than ordinary
133 /// constraints, at least at present. During type checking, the
134 /// `InferCtxt::process_registered_region_obligations` method will
135 /// attempt to convert a type test like `T: 'x` into an ordinary
136 /// outlives constraint when possible (for example, `&'a T: 'b` will
137 /// be converted into `'a: 'b` and registered as a `Constraint`).
139 /// In some cases, however, there are outlives relationships that are
140 /// not converted into a region constraint, but rather into one of
141 /// these "type tests". The distinction is that a type test does not
142 /// influence the inference result, but instead just examines the
143 /// values that we ultimately inferred for each region variable and
144 /// checks that they meet certain extra criteria. If not, an error
147 /// One reason for this is that these type tests typically boil down
148 /// to a check like `'a: 'x` where `'a` is a universally quantified
149 /// region -- and therefore not one whose value is really meant to be
150 /// *inferred*, precisely (this is not always the case: one can have a
151 /// type test like `<Foo as Trait<'?0>>::Bar: 'x`, where `'?0` is an
152 /// inference variable). Another reason is that these type tests can
153 /// involve *disjunction* -- that is, they can be satisfied in more
156 /// For more information about this translation, see
157 /// `InferCtxt::process_registered_region_obligations` and
158 /// `InferCtxt::type_must_outlive` in `rustc::infer::outlives`.
159 #[derive(Clone, Debug)]
160 pub struct TypeTest<'tcx> {
161 /// The type `T` that must outlive the region.
162 pub generic_kind: GenericKind<'tcx>,
164 /// The region `'x` that the type must outlive.
165 pub lower_bound: RegionVid,
167 /// Where did this constraint arise and why?
168 pub locations: Locations,
170 /// A test which, if met by the region `'x`, proves that this type
171 /// constraint is satisfied.
172 pub verify_bound: VerifyBound<'tcx>,
175 impl<'tcx> RegionInferenceContext<'tcx> {
176 /// Creates a new region inference context with a total of
177 /// `num_region_variables` valid inference variables; the first N
178 /// of those will be constant regions representing the free
179 /// regions defined in `universal_regions`.
181 /// The `outlives_constraints` and `type_tests` are an initial set
182 /// of constraints produced by the MIR type check.
185 universal_regions: Rc<UniversalRegions<'tcx>>,
186 placeholder_indices: Rc<PlaceholderIndices>,
187 universal_region_relations: Rc<UniversalRegionRelations<'tcx>>,
189 outlives_constraints: ConstraintSet,
190 closure_bounds_mapping: FxHashMap<
192 FxHashMap<(RegionVid, RegionVid), (ConstraintCategory, Span)>,
194 type_tests: Vec<TypeTest<'tcx>>,
195 liveness_constraints: LivenessValues<RegionVid>,
196 elements: &Rc<RegionValueElements>,
198 // Create a RegionDefinition for each inference variable.
199 let definitions: IndexVec<_, _> = var_infos
201 .map(|info| RegionDefinition::new(info.universe, info.origin))
204 let constraints = Rc::new(outlives_constraints); // freeze constraints
205 let constraint_graph = Rc::new(constraints.graph(definitions.len()));
206 let fr_static = universal_regions.fr_static;
207 let constraint_sccs = Rc::new(constraints.compute_sccs(&constraint_graph, fr_static));
210 RegionValues::new(elements, universal_regions.len(), &placeholder_indices);
212 for region in liveness_constraints.rows() {
213 let scc = constraint_sccs.scc(region);
214 scc_values.merge_liveness(scc, region, &liveness_constraints);
217 let scc_universes = Self::compute_scc_universes(&constraint_sccs, &definitions);
219 let scc_representatives = Self::compute_scc_representatives(&constraint_sccs, &definitions);
221 let mut result = Self {
223 liveness_constraints,
227 closure_bounds_mapping,
233 universal_region_relations,
236 result.init_free_and_bound_regions();
241 /// Each SCC is the combination of many region variables which
242 /// have been equated. Therefore, we can associate a universe with
243 /// each SCC which is minimum of all the universes of its
244 /// constituent regions -- this is because whatever value the SCC
245 /// takes on must be a value that each of the regions within the
246 /// SCC could have as well. This implies that the SCC must have
247 /// the minimum, or narrowest, universe.
248 fn compute_scc_universes(
249 constraints_scc: &Sccs<RegionVid, ConstraintSccIndex>,
250 definitions: &IndexVec<RegionVid, RegionDefinition<'tcx>>,
251 ) -> IndexVec<ConstraintSccIndex, ty::UniverseIndex> {
252 let num_sccs = constraints_scc.num_sccs();
253 let mut scc_universes = IndexVec::from_elem_n(ty::UniverseIndex::MAX, num_sccs);
255 for (region_vid, region_definition) in definitions.iter_enumerated() {
256 let scc = constraints_scc.scc(region_vid);
257 let scc_universe = &mut scc_universes[scc];
258 *scc_universe = ::std::cmp::min(*scc_universe, region_definition.universe);
261 debug!("compute_scc_universes: scc_universe = {:#?}", scc_universes);
266 /// For each SCC, we compute a unique `RegionVid` (in fact, the
267 /// minimal one that belongs to the SCC). See
268 /// `scc_representatives` field of `RegionInferenceContext` for
270 fn compute_scc_representatives(
271 constraints_scc: &Sccs<RegionVid, ConstraintSccIndex>,
272 definitions: &IndexVec<RegionVid, RegionDefinition<'tcx>>,
273 ) -> IndexVec<ConstraintSccIndex, ty::RegionVid> {
274 let num_sccs = constraints_scc.num_sccs();
275 let next_region_vid = definitions.next_index();
276 let mut scc_representatives = IndexVec::from_elem_n(next_region_vid, num_sccs);
278 for region_vid in definitions.indices() {
279 let scc = constraints_scc.scc(region_vid);
280 let prev_min = scc_representatives[scc];
281 scc_representatives[scc] = region_vid.min(prev_min);
287 /// Initializes the region variables for each universally
288 /// quantified region (lifetime parameter). The first N variables
289 /// always correspond to the regions appearing in the function
290 /// signature (both named and anonymous) and where-clauses. This
291 /// function iterates over those regions and initializes them with
296 /// fn foo<'a, 'b>(..) where 'a: 'b
298 /// would initialize two variables like so:
300 /// R0 = { CFG, R0 } // 'a
301 /// R1 = { CFG, R0, R1 } // 'b
303 /// Here, R0 represents `'a`, and it contains (a) the entire CFG
304 /// and (b) any universally quantified regions that it outlives,
305 /// which in this case is just itself. R1 (`'b`) in contrast also
306 /// outlives `'a` and hence contains R0 and R1.
307 fn init_free_and_bound_regions(&mut self) {
308 // Update the names (if any)
309 for (external_name, variable) in self.universal_regions.named_universal_regions() {
311 "init_universal_regions: region {:?} has external name {:?}",
312 variable, external_name
314 self.definitions[variable].external_name = Some(external_name);
317 for variable in self.definitions.indices() {
318 let scc = self.constraint_sccs.scc(variable);
320 match self.definitions[variable].origin {
321 NLLRegionVariableOrigin::FreeRegion => {
322 // For each free, universally quantified region X:
324 // Add all nodes in the CFG to liveness constraints
325 self.liveness_constraints.add_all_points(variable);
326 self.scc_values.add_all_points(scc);
328 // Add `end(X)` into the set for X.
329 self.scc_values.add_element(scc, variable);
332 NLLRegionVariableOrigin::Placeholder(placeholder) => {
333 // Each placeholder region is only visible from
334 // its universe `ui` and its extensions. So we
335 // can't just add it into `scc` unless the
336 // universe of the scc can name this region.
337 let scc_universe = self.scc_universes[scc];
338 if scc_universe.can_name(placeholder.universe) {
339 self.scc_values.add_element(scc, placeholder);
342 "init_free_and_bound_regions: placeholder {:?} is \
343 not compatible with universe {:?} of its SCC {:?}",
348 self.add_incompatible_universe(scc);
352 NLLRegionVariableOrigin::Existential => {
353 // For existential, regions, nothing to do.
359 /// Returns an iterator over all the region indices.
360 pub fn regions(&self) -> impl Iterator<Item = RegionVid> {
361 self.definitions.indices()
364 /// Given a universal region in scope on the MIR, returns the
365 /// corresponding index.
367 /// (Panics if `r` is not a registered universal region.)
368 pub fn to_region_vid(&self, r: ty::Region<'tcx>) -> RegionVid {
369 self.universal_regions.to_region_vid(r)
372 /// Adds annotations for `#[rustc_regions]`; see `UniversalRegions::annotate`.
373 crate fn annotate(&self, tcx: TyCtxt<'_, 'tcx>, err: &mut DiagnosticBuilder<'_>) {
374 self.universal_regions.annotate(tcx, err)
377 /// Returns `true` if the region `r` contains the point `p`.
379 /// Panics if called before `solve()` executes,
380 crate fn region_contains(&self, r: impl ToRegionVid, p: impl ToElementIndex) -> bool {
381 let scc = self.constraint_sccs.scc(r.to_region_vid());
382 self.scc_values.contains(scc, p)
385 /// Returns access to the value of `r` for debugging purposes.
386 crate fn region_value_str(&self, r: RegionVid) -> String {
387 let scc = self.constraint_sccs.scc(r.to_region_vid());
388 self.scc_values.region_value_str(scc)
391 /// Returns access to the value of `r` for debugging purposes.
392 crate fn region_universe(&self, r: RegionVid) -> ty::UniverseIndex {
393 let scc = self.constraint_sccs.scc(r.to_region_vid());
394 self.scc_universes[scc]
397 /// Performs region inference and report errors if we see any
398 /// unsatisfiable constraints. If this is a closure, returns the
399 /// region requirements to propagate to our creator, if any.
400 pub(super) fn solve<'gcx>(
402 infcx: &InferCtxt<'_, 'gcx, 'tcx>,
406 errors_buffer: &mut Vec<Diagnostic>,
407 ) -> Option<ClosureRegionRequirements<'gcx>> {
409 infcx.tcx.sess.time_extended(),
410 Some(infcx.tcx.sess),
411 &format!("solve_nll_region_constraints({:?})", mir_def_id),
412 || self.solve_inner(infcx, body, upvars, mir_def_id, errors_buffer),
416 fn solve_inner<'gcx>(
418 infcx: &InferCtxt<'_, 'gcx, 'tcx>,
422 errors_buffer: &mut Vec<Diagnostic>,
423 ) -> Option<ClosureRegionRequirements<'gcx>> {
424 self.propagate_constraints(body);
426 // If this is a closure, we can propagate unsatisfied
427 // `outlives_requirements` to our creator, so create a vector
428 // to store those. Otherwise, we'll pass in `None` to the
429 // functions below, which will trigger them to report errors
431 let mut outlives_requirements = if infcx.tcx.is_closure(mir_def_id) {
437 self.check_type_tests(
441 outlives_requirements.as_mut(),
445 self.check_universal_regions(
450 outlives_requirements.as_mut(),
454 let outlives_requirements = outlives_requirements.unwrap_or(vec![]);
456 if outlives_requirements.is_empty() {
459 let num_external_vids = self.universal_regions.num_global_and_external_regions();
460 Some(ClosureRegionRequirements {
462 outlives_requirements,
467 /// Propagate the region constraints: this will grow the values
468 /// for each region variable until all the constraints are
469 /// satisfied. Note that some values may grow **too** large to be
470 /// feasible, but we check this later.
471 fn propagate_constraints(&mut self, _body: &Body<'tcx>) {
472 debug!("propagate_constraints()");
474 debug!("propagate_constraints: constraints={:#?}", {
475 let mut constraints: Vec<_> = self.constraints.iter().collect();
479 .map(|c| (c, self.constraint_sccs.scc(c.sup), self.constraint_sccs.scc(c.sub)))
483 // To propagate constraints, we walk the DAG induced by the
484 // SCC. For each SCC, we visit its successors and compute
485 // their values, then we union all those values to get our
487 let visited = &mut BitSet::new_empty(self.constraint_sccs.num_sccs());
488 for scc_index in self.constraint_sccs.all_sccs() {
489 self.propagate_constraint_sccs_if_new(scc_index, visited);
494 fn propagate_constraint_sccs_if_new(
496 scc_a: ConstraintSccIndex,
497 visited: &mut BitSet<ConstraintSccIndex>,
499 if visited.insert(scc_a) {
500 self.propagate_constraint_sccs_new(scc_a, visited);
504 fn propagate_constraint_sccs_new(
506 scc_a: ConstraintSccIndex,
507 visited: &mut BitSet<ConstraintSccIndex>,
509 let constraint_sccs = self.constraint_sccs.clone();
511 // Walk each SCC `B` such that `A: B`...
512 for &scc_b in constraint_sccs.successors(scc_a) {
514 "propagate_constraint_sccs: scc_a = {:?} scc_b = {:?}",
518 // ...compute the value of `B`...
519 self.propagate_constraint_sccs_if_new(scc_b, visited);
521 // ...and add elements from `B` into `A`. One complication
522 // arises because of universes: If `B` contains something
523 // that `A` cannot name, then `A` can only contain `B` if
524 // it outlives static.
525 if self.universe_compatible(scc_b, scc_a) {
526 // `A` can name everything that is in `B`, so just
528 self.scc_values.add_region(scc_a, scc_b);
530 self.add_incompatible_universe(scc_a);
535 "propagate_constraint_sccs: scc_a = {:?} has value {:?}",
537 self.scc_values.region_value_str(scc_a),
541 /// Returns `true` if all the elements in the value of `scc_b` are nameable
542 /// in `scc_a`. Used during constraint propagation, and only once
543 /// the value of `scc_b` has been computed.
544 fn universe_compatible(&self, scc_b: ConstraintSccIndex, scc_a: ConstraintSccIndex) -> bool {
545 let universe_a = self.scc_universes[scc_a];
547 // Quick check: if scc_b's declared universe is a subset of
548 // scc_a's declared univese (typically, both are ROOT), then
549 // it cannot contain any problematic universe elements.
550 if universe_a.can_name(self.scc_universes[scc_b]) {
554 // Otherwise, we have to iterate over the universe elements in
555 // B's value, and check whether all of them are nameable
558 .placeholders_contained_in(scc_b)
559 .all(|p| universe_a.can_name(p.universe))
562 /// Extend `scc` so that it can outlive some placeholder region
563 /// from a universe it can't name; at present, the only way for
564 /// this to be true is if `scc` outlives `'static`. This is
565 /// actually stricter than necessary: ideally, we'd support bounds
566 /// like `for<'a: 'b`>` that might then allow us to approximate
567 /// `'a` with `'b` and not `'static`. But it will have to do for
569 fn add_incompatible_universe(&mut self, scc: ConstraintSccIndex) {
570 debug!("add_incompatible_universe(scc={:?})", scc);
572 let fr_static = self.universal_regions.fr_static;
573 self.scc_values.add_all_points(scc);
574 self.scc_values.add_element(scc, fr_static);
577 /// Once regions have been propagated, this method is used to see
578 /// whether the "type tests" produced by typeck were satisfied;
579 /// type tests encode type-outlives relationships like `T:
580 /// 'a`. See `TypeTest` for more details.
581 fn check_type_tests<'gcx>(
583 infcx: &InferCtxt<'_, 'gcx, 'tcx>,
586 mut propagated_outlives_requirements: Option<&mut Vec<ClosureOutlivesRequirement<'gcx>>>,
587 errors_buffer: &mut Vec<Diagnostic>,
591 // Sometimes we register equivalent type-tests that would
592 // result in basically the exact same error being reported to
593 // the user. Avoid that.
594 let mut deduplicate_errors = FxHashSet::default();
596 for type_test in &self.type_tests {
597 debug!("check_type_test: {:?}", type_test);
599 let generic_ty = type_test.generic_kind.to_ty(tcx);
600 if self.eval_verify_bound(
604 type_test.lower_bound,
605 &type_test.verify_bound,
610 if let Some(propagated_outlives_requirements) = &mut propagated_outlives_requirements {
611 if self.try_promote_type_test(
615 propagated_outlives_requirements,
621 // Type-test failed. Report the error.
623 // Try to convert the lower-bound region into something named we can print for the user.
624 let lower_bound_region = self.to_error_region(type_test.lower_bound);
626 // Skip duplicate-ish errors.
627 let type_test_span = type_test.locations.span(body);
628 let erased_generic_kind = tcx.erase_regions(&type_test.generic_kind);
629 if !deduplicate_errors.insert((
637 "check_type_test: reporting error for erased_generic_kind={:?}, \
638 lower_bound_region={:?}, \
639 type_test.locations={:?}",
640 erased_generic_kind, lower_bound_region, type_test.locations,
644 if let Some(lower_bound_region) = lower_bound_region {
645 let region_scope_tree = &tcx.region_scope_tree(mir_def_id);
647 .construct_generic_bound_failure(
651 type_test.generic_kind,
654 .buffer(errors_buffer);
656 // FIXME. We should handle this case better. It
657 // indicates that we have e.g., some region variable
658 // whose value is like `'a+'b` where `'a` and `'b` are
659 // distinct unrelated univesal regions that are not
660 // known to outlive one another. It'd be nice to have
661 // some examples where this arises to decide how best
662 // to report it; we could probably handle it by
663 // iterating over the universal regions and reporting
664 // an error that multiple bounds are required.
668 &format!("`{}` does not live long enough", type_test.generic_kind,),
670 .buffer(errors_buffer);
675 /// Converts a region inference variable into a `ty::Region` that
676 /// we can use for error reporting. If `r` is universally bound,
677 /// then we use the name that we have on record for it. If `r` is
678 /// existentially bound, then we check its inferred value and try
679 /// to find a good name from that. Returns `None` if we can't find
680 /// one (e.g., this is just some random part of the CFG).
681 pub fn to_error_region(&self, r: RegionVid) -> Option<ty::Region<'tcx>> {
682 self.to_error_region_vid(r).and_then(|r| self.definitions[r].external_name)
685 /// Returns the [RegionVid] corresponding to the region returned by
686 /// `to_error_region`.
687 pub fn to_error_region_vid(&self, r: RegionVid) -> Option<RegionVid> {
688 if self.universal_regions.is_universal_region(r) {
691 let r_scc = self.constraint_sccs.scc(r);
692 let upper_bound = self.universal_upper_bound(r);
693 if self.scc_values.contains(r_scc, upper_bound) {
694 self.to_error_region_vid(upper_bound)
701 /// Invoked when we have some type-test (e.g., `T: 'X`) that we cannot
702 /// prove to be satisfied. If this is a closure, we will attempt to
703 /// "promote" this type-test into our `ClosureRegionRequirements` and
704 /// hence pass it up the creator. To do this, we have to phrase the
705 /// type-test in terms of external free regions, as local free
706 /// regions are not nameable by the closure's creator.
708 /// Promotion works as follows: we first check that the type `T`
709 /// contains only regions that the creator knows about. If this is
710 /// true, then -- as a consequence -- we know that all regions in
711 /// the type `T` are free regions that outlive the closure body. If
712 /// false, then promotion fails.
714 /// Once we've promoted T, we have to "promote" `'X` to some region
715 /// that is "external" to the closure. Generally speaking, a region
716 /// may be the union of some points in the closure body as well as
717 /// various free lifetimes. We can ignore the points in the closure
718 /// body: if the type T can be expressed in terms of external regions,
719 /// we know it outlives the points in the closure body. That
720 /// just leaves the free regions.
722 /// The idea then is to lower the `T: 'X` constraint into multiple
723 /// bounds -- e.g., if `'X` is the union of two free lifetimes,
724 /// `'1` and `'2`, then we would create `T: '1` and `T: '2`.
725 fn try_promote_type_test<'gcx>(
727 infcx: &InferCtxt<'_, 'gcx, 'tcx>,
729 type_test: &TypeTest<'tcx>,
730 propagated_outlives_requirements: &mut Vec<ClosureOutlivesRequirement<'gcx>>,
741 let generic_ty = generic_kind.to_ty(tcx);
742 let subject = match self.try_promote_type_test_subject(infcx, generic_ty) {
744 None => return false,
747 // For each region outlived by lower_bound find a non-local,
748 // universal region (it may be the same region) and add it to
749 // `ClosureOutlivesRequirement`.
750 let r_scc = self.constraint_sccs.scc(*lower_bound);
751 for ur in self.scc_values.universal_regions_outlived_by(r_scc) {
752 // Check whether we can already prove that the "subject" outlives `ur`.
753 // If so, we don't have to propagate this requirement to our caller.
755 // To continue the example from the function, if we are trying to promote
756 // a requirement that `T: 'X`, and we know that `'X = '1 + '2` (i.e., the union
757 // `'1` and `'2`), then in this loop `ur` will be `'1` (and `'2`). So here
758 // we check whether `T: '1` is something we *can* prove. If so, no need
759 // to propagate that requirement.
761 // This is needed because -- particularly in the case
762 // where `ur` is a local bound -- we are sometimes in a
763 // position to prove things that our caller cannot. See
764 // #53570 for an example.
765 if self.eval_verify_bound(tcx, body, generic_ty, ur, &type_test.verify_bound) {
769 debug!("try_promote_type_test: ur={:?}", ur);
771 let non_local_ub = self.universal_region_relations.non_local_upper_bounds(&ur);
772 debug!("try_promote_type_test: non_local_ub={:?}", non_local_ub);
774 // This is slightly too conservative. To show T: '1, given `'2: '1`
775 // and `'3: '1` we only need to prove that T: '2 *or* T: '3, but to
776 // avoid potential non-determinism we approximate this by requiring
778 for &upper_bound in non_local_ub {
779 debug_assert!(self.universal_regions.is_universal_region(upper_bound));
780 debug_assert!(!self.universal_regions.is_local_free_region(upper_bound));
782 let requirement = ClosureOutlivesRequirement {
784 outlived_free_region: upper_bound,
785 blame_span: locations.span(body),
786 category: ConstraintCategory::Boring,
788 debug!("try_promote_type_test: pushing {:#?}", requirement);
789 propagated_outlives_requirements.push(requirement);
795 /// When we promote a type test `T: 'r`, we have to convert the
796 /// type `T` into something we can store in a query result (so
797 /// something allocated for `'gcx`). This is problematic if `ty`
798 /// contains regions. During the course of NLL region checking, we
799 /// will have replaced all of those regions with fresh inference
800 /// variables. To create a test subject, we want to replace those
801 /// inference variables with some region from the closure
802 /// signature -- this is not always possible, so this is a
803 /// fallible process. Presuming we do find a suitable region, we
804 /// will represent it with a `ReClosureBound`, which is a
805 /// `RegionKind` variant that can be allocated in the gcx.
806 fn try_promote_type_test_subject<'gcx>(
808 infcx: &InferCtxt<'_, 'gcx, 'tcx>,
810 ) -> Option<ClosureOutlivesSubject<'gcx>> {
812 let gcx = tcx.global_tcx();
814 debug!("try_promote_type_test_subject(ty = {:?})", ty);
816 let ty = tcx.fold_regions(&ty, &mut false, |r, _depth| {
817 let region_vid = self.to_region_vid(r);
819 // The challenge if this. We have some region variable `r`
820 // whose value is a set of CFG points and universal
821 // regions. We want to find if that set is *equivalent* to
822 // any of the named regions found in the closure.
824 // To do so, we compute the
825 // `non_local_universal_upper_bound`. This will be a
826 // non-local, universal region that is greater than `r`.
827 // However, it might not be *contained* within `r`, so
828 // then we further check whether this bound is contained
829 // in `r`. If so, we can say that `r` is equivalent to the
832 // Let's work through a few examples. For these, imagine
833 // that we have 3 non-local regions (I'll denote them as
834 // `'static`, `'a`, and `'b`, though of course in the code
835 // they would be represented with indices) where:
840 // First, let's assume that `r` is some existential
841 // variable with an inferred value `{'a, 'static}` (plus
842 // some CFG nodes). In this case, the non-local upper
843 // bound is `'static`, since that outlives `'a`. `'static`
844 // is also a member of `r` and hence we consider `r`
845 // equivalent to `'static` (and replace it with
848 // Now let's consider the inferred value `{'a, 'b}`. This
849 // means `r` is effectively `'a | 'b`. I'm not sure if
850 // this can come about, actually, but assuming it did, we
851 // would get a non-local upper bound of `'static`. Since
852 // `'static` is not contained in `r`, we would fail to
853 // find an equivalent.
854 let upper_bound = self.non_local_universal_upper_bound(region_vid);
855 if self.region_contains(region_vid, upper_bound) {
856 tcx.mk_region(ty::ReClosureBound(upper_bound))
858 // In the case of a failure, use a `ReVar`
859 // result. This will cause the `lift` later on to
864 debug!("try_promote_type_test_subject: folded ty = {:?}", ty);
866 // `lift` will only fail if we failed to promote some region.
867 let ty = gcx.lift(&ty)?;
869 Some(ClosureOutlivesSubject::Ty(ty))
872 /// Given some universal or existential region `r`, finds a
873 /// non-local, universal region `r+` that outlives `r` at entry to (and
874 /// exit from) the closure. In the worst case, this will be
877 /// This is used for two purposes. First, if we are propagated
878 /// some requirement `T: r`, we can use this method to enlarge `r`
879 /// to something we can encode for our creator (which only knows
880 /// about non-local, universal regions). It is also used when
881 /// encoding `T` as part of `try_promote_type_test_subject` (see
882 /// that fn for details).
884 /// This is based on the result `'y` of `universal_upper_bound`,
885 /// except that it converts further takes the non-local upper
886 /// bound of `'y`, so that the final result is non-local.
887 fn non_local_universal_upper_bound(&self, r: RegionVid) -> RegionVid {
889 "non_local_universal_upper_bound(r={:?}={})",
891 self.region_value_str(r)
894 let lub = self.universal_upper_bound(r);
896 // Grow further to get smallest universal region known to
898 let non_local_lub = self.universal_region_relations.non_local_upper_bound(lub);
901 "non_local_universal_upper_bound: non_local_lub={:?}",
908 /// Returns a universally quantified region that outlives the
909 /// value of `r` (`r` may be existentially or universally
912 /// Since `r` is (potentially) an existential region, it has some
913 /// value which may include (a) any number of points in the CFG
914 /// and (b) any number of `end('x)` elements of universally
915 /// quantified regions. To convert this into a single universal
916 /// region we do as follows:
918 /// - Ignore the CFG points in `'r`. All universally quantified regions
919 /// include the CFG anyhow.
920 /// - For each `end('x)` element in `'r`, compute the mutual LUB, yielding
922 fn universal_upper_bound(&self, r: RegionVid) -> RegionVid {
924 "universal_upper_bound(r={:?}={})",
926 self.region_value_str(r)
929 // Find the smallest universal region that contains all other
930 // universal regions within `region`.
931 let mut lub = self.universal_regions.fr_fn_body;
932 let r_scc = self.constraint_sccs.scc(r);
933 for ur in self.scc_values.universal_regions_outlived_by(r_scc) {
934 lub = self.universal_region_relations.postdom_upper_bound(lub, ur);
937 debug!("universal_upper_bound: r={:?} lub={:?}", r, lub);
942 /// Tests if `test` is true when applied to `lower_bound` at
944 fn eval_verify_bound(
946 tcx: TyCtxt<'_, 'tcx>,
948 generic_ty: Ty<'tcx>,
949 lower_bound: RegionVid,
950 verify_bound: &VerifyBound<'tcx>,
953 "eval_verify_bound(lower_bound={:?}, verify_bound={:?})",
954 lower_bound, verify_bound
958 VerifyBound::IfEq(test_ty, verify_bound1) => {
959 self.eval_if_eq(tcx, body, generic_ty, lower_bound, test_ty, verify_bound1)
962 VerifyBound::OutlivedBy(r) => {
963 let r_vid = self.to_region_vid(r);
964 self.eval_outlives(body, r_vid, lower_bound)
967 VerifyBound::AnyBound(verify_bounds) => verify_bounds.iter().any(|verify_bound| {
968 self.eval_verify_bound(tcx, body, generic_ty, lower_bound, verify_bound)
971 VerifyBound::AllBounds(verify_bounds) => verify_bounds.iter().all(|verify_bound| {
972 self.eval_verify_bound(tcx, body, generic_ty, lower_bound, verify_bound)
979 tcx: TyCtxt<'_, 'tcx>,
981 generic_ty: Ty<'tcx>,
982 lower_bound: RegionVid,
984 verify_bound: &VerifyBound<'tcx>,
986 let generic_ty_normalized = self.normalize_to_scc_representatives(tcx, generic_ty);
987 let test_ty_normalized = self.normalize_to_scc_representatives(tcx, test_ty);
988 if generic_ty_normalized == test_ty_normalized {
989 self.eval_verify_bound(tcx, body, generic_ty, lower_bound, verify_bound)
995 /// This is a conservative normalization procedure. It takes every
996 /// free region in `value` and replaces it with the
997 /// "representative" of its SCC (see `scc_representatives` field).
998 /// We are guaranteed that if two values normalize to the same
999 /// thing, then they are equal; this is a conservative check in
1000 /// that they could still be equal even if they normalize to
1001 /// different results. (For example, there might be two regions
1002 /// with the same value that are not in the same SCC).
1004 /// N.B., this is not an ideal approach and I would like to revisit
1005 /// it. However, it works pretty well in practice. In particular,
1006 /// this is needed to deal with projection outlives bounds like
1008 /// <T as Foo<'0>>::Item: '1
1010 /// In particular, this routine winds up being important when
1011 /// there are bounds like `where <T as Foo<'a>>::Item: 'b` in the
1012 /// environment. In this case, if we can show that `'0 == 'a`,
1013 /// and that `'b: '1`, then we know that the clause is
1014 /// satisfied. In such cases, particularly due to limitations of
1015 /// the trait solver =), we usually wind up with a where-clause like
1016 /// `T: Foo<'a>` in scope, which thus forces `'0 == 'a` to be added as
1017 /// a constraint, and thus ensures that they are in the same SCC.
1019 /// So why can't we do a more correct routine? Well, we could
1020 /// *almost* use the `relate_tys` code, but the way it is
1021 /// currently setup it creates inference variables to deal with
1022 /// higher-ranked things and so forth, and right now the inference
1023 /// context is not permitted to make more inference variables. So
1024 /// we use this kind of hacky solution.
1025 fn normalize_to_scc_representatives<T>(&self, tcx: TyCtxt<'_, 'tcx>, value: T) -> T
1027 T: TypeFoldable<'tcx>,
1029 tcx.fold_regions(&value, &mut false, |r, _db| {
1030 let vid = self.to_region_vid(r);
1031 let scc = self.constraint_sccs.scc(vid);
1032 let repr = self.scc_representatives[scc];
1033 tcx.mk_region(ty::ReVar(repr))
1037 // Evaluate whether `sup_region: sub_region @ point`.
1041 sup_region: RegionVid,
1042 sub_region: RegionVid,
1044 debug!("eval_outlives({:?}: {:?})", sup_region, sub_region);
1047 "eval_outlives: sup_region's value = {:?}",
1048 self.region_value_str(sup_region),
1051 "eval_outlives: sub_region's value = {:?}",
1052 self.region_value_str(sub_region),
1055 let sub_region_scc = self.constraint_sccs.scc(sub_region);
1056 let sup_region_scc = self.constraint_sccs.scc(sup_region);
1058 // Both the `sub_region` and `sup_region` consist of the union
1059 // of some number of universal regions (along with the union
1060 // of various points in the CFG; ignore those points for
1061 // now). Therefore, the sup-region outlives the sub-region if,
1062 // for each universal region R1 in the sub-region, there
1063 // exists some region R2 in the sup-region that outlives R1.
1064 let universal_outlives = self.scc_values
1065 .universal_regions_outlived_by(sub_region_scc)
1068 .universal_regions_outlived_by(sup_region_scc)
1069 .any(|r2| self.universal_region_relations.outlives(r2, r1))
1072 if !universal_outlives {
1076 // Now we have to compare all the points in the sub region and make
1077 // sure they exist in the sup region.
1079 if self.universal_regions.is_universal_region(sup_region) {
1080 // Micro-opt: universal regions contain all points.
1085 .contains_points(sup_region_scc, sub_region_scc)
1088 /// Once regions have been propagated, this method is used to see
1089 /// whether any of the constraints were too strong. In particular,
1090 /// we want to check for a case where a universally quantified
1091 /// region exceeded its bounds. Consider:
1093 /// fn foo<'a, 'b>(x: &'a u32) -> &'b u32 { x }
1095 /// In this case, returning `x` requires `&'a u32 <: &'b u32`
1096 /// and hence we establish (transitively) a constraint that
1097 /// `'a: 'b`. The `propagate_constraints` code above will
1098 /// therefore add `end('a)` into the region for `'b` -- but we
1099 /// have no evidence that `'b` outlives `'a`, so we want to report
1102 /// If `propagated_outlives_requirements` is `Some`, then we will
1103 /// push unsatisfied obligations into there. Otherwise, we'll
1104 /// report them as errors.
1105 fn check_universal_regions<'gcx>(
1107 infcx: &InferCtxt<'_, 'gcx, 'tcx>,
1111 mut propagated_outlives_requirements: Option<&mut Vec<ClosureOutlivesRequirement<'gcx>>>,
1112 errors_buffer: &mut Vec<Diagnostic>,
1114 for (fr, fr_definition) in self.definitions.iter_enumerated() {
1115 match fr_definition.origin {
1116 NLLRegionVariableOrigin::FreeRegion => {
1117 // Go through each of the universal regions `fr` and check that
1118 // they did not grow too large, accumulating any requirements
1119 // for our caller into the `outlives_requirements` vector.
1120 self.check_universal_region(
1126 &mut propagated_outlives_requirements,
1131 NLLRegionVariableOrigin::Placeholder(placeholder) => {
1132 self.check_bound_universal_region(infcx, body, mir_def_id, fr, placeholder);
1135 NLLRegionVariableOrigin::Existential => {
1136 // nothing to check here
1142 /// Checks the final value for the free region `fr` to see if it
1143 /// grew too large. In particular, examine what `end(X)` points
1144 /// wound up in `fr`'s final value; for each `end(X)` where `X !=
1145 /// fr`, we want to check that `fr: X`. If not, that's either an
1146 /// error, or something we have to propagate to our creator.
1148 /// Things that are to be propagated are accumulated into the
1149 /// `outlives_requirements` vector.
1150 fn check_universal_region<'gcx>(
1152 infcx: &InferCtxt<'_, 'gcx, 'tcx>,
1156 longer_fr: RegionVid,
1157 propagated_outlives_requirements: &mut Option<&mut Vec<ClosureOutlivesRequirement<'gcx>>>,
1158 errors_buffer: &mut Vec<Diagnostic>,
1160 debug!("check_universal_region(fr={:?})", longer_fr);
1162 let longer_fr_scc = self.constraint_sccs.scc(longer_fr);
1164 // Because this free region must be in the ROOT universe, we
1165 // know it cannot contain any bound universes.
1166 assert!(self.scc_universes[longer_fr_scc] == ty::UniverseIndex::ROOT);
1169 .placeholders_contained_in(longer_fr_scc)
1174 // Only check all of the relations for the main representative of each
1175 // SCC, otherwise just check that we outlive said representative. This
1176 // reduces the number of redundant relations propagated out of
1178 // Note that the representative will be a universal region if there is
1179 // one in this SCC, so we will always check the representative here.
1180 let representative = self.scc_representatives[longer_fr_scc];
1181 if representative != longer_fr {
1182 self.check_universal_region_relation(
1189 propagated_outlives_requirements,
1195 // Find every region `o` such that `fr: o`
1196 // (because `fr` includes `end(o)`).
1197 for shorter_fr in self.scc_values.universal_regions_outlived_by(longer_fr_scc) {
1198 if let Some(ErrorReported) = self.check_universal_region_relation(
1205 propagated_outlives_requirements,
1208 // continuing to iterate just reports more errors than necessary
1214 fn check_universal_region_relation(
1216 longer_fr: RegionVid,
1217 shorter_fr: RegionVid,
1218 infcx: &InferCtxt<'_, 'gcx, 'tcx>,
1222 propagated_outlives_requirements: &mut Option<&mut Vec<ClosureOutlivesRequirement<'gcx>>>,
1223 errors_buffer: &mut Vec<Diagnostic>,
1224 ) -> Option<ErrorReported> {
1225 // If it is known that `fr: o`, carry on.
1226 if self.universal_region_relations
1227 .outlives(longer_fr, shorter_fr)
1233 "check_universal_region_relation: fr={:?} does not outlive shorter_fr={:?}",
1234 longer_fr, shorter_fr,
1237 if let Some(propagated_outlives_requirements) = propagated_outlives_requirements {
1238 // Shrink `longer_fr` until we find a non-local region (if we do).
1239 // We'll call it `fr-` -- it's ever so slightly smaller than
1242 if let Some(fr_minus) = self
1243 .universal_region_relations
1244 .non_local_lower_bound(longer_fr)
1246 debug!("check_universal_region: fr_minus={:?}", fr_minus);
1248 let blame_span_category =
1249 self.find_outlives_blame_span(body, longer_fr, shorter_fr);
1251 // Grow `shorter_fr` until we find some non-local regions. (We
1252 // always will.) We'll call them `shorter_fr+` -- they're ever
1253 // so slightly larger than `shorter_fr`.
1254 let shorter_fr_plus = self.universal_region_relations
1255 .non_local_upper_bounds(&shorter_fr);
1257 "check_universal_region: shorter_fr_plus={:?}",
1260 for &&fr in &shorter_fr_plus {
1261 // Push the constraint `fr-: shorter_fr+`
1262 propagated_outlives_requirements.push(ClosureOutlivesRequirement {
1263 subject: ClosureOutlivesSubject::Region(fr_minus),
1264 outlived_free_region: fr,
1265 blame_span: blame_span_category.1,
1266 category: blame_span_category.0,
1273 // If we are not in a context where we can't propagate errors, or we
1274 // could not shrink `fr` to something smaller, then just report an
1277 // Note: in this case, we use the unapproximated regions to report the
1278 // error. This gives better error messages in some cases.
1279 self.report_error(body, upvars, infcx, mir_def_id, longer_fr, shorter_fr, errors_buffer);
1283 fn check_bound_universal_region<'gcx>(
1285 infcx: &InferCtxt<'_, 'gcx, 'tcx>,
1288 longer_fr: RegionVid,
1289 placeholder: ty::PlaceholderRegion,
1292 "check_bound_universal_region(fr={:?}, placeholder={:?})",
1293 longer_fr, placeholder,
1296 let longer_fr_scc = self.constraint_sccs.scc(longer_fr);
1298 "check_bound_universal_region: longer_fr_scc={:?}",
1302 // If we have some bound universal region `'a`, then the only
1303 // elements it can contain is itself -- we don't know anything
1305 let error_element = match {
1307 .elements_contained_in(longer_fr_scc)
1308 .find(|element| match element {
1309 RegionElement::Location(_) => true,
1310 RegionElement::RootUniversalRegion(_) => true,
1311 RegionElement::PlaceholderRegion(placeholder1) => placeholder != *placeholder1,
1317 debug!("check_bound_universal_region: error_element = {:?}", error_element);
1319 // Find the region that introduced this `error_element`.
1320 let error_region = match error_element {
1321 RegionElement::Location(l) => self.find_sub_region_live_at(longer_fr, l),
1322 RegionElement::RootUniversalRegion(r) => r,
1323 RegionElement::PlaceholderRegion(error_placeholder) => self.definitions
1325 .filter_map(|(r, definition)| match definition.origin {
1326 NLLRegionVariableOrigin::Placeholder(p) if p == error_placeholder => Some(r),
1333 // Find the code to blame for the fact that `longer_fr` outlives `error_fr`.
1334 let (_, span) = self.find_outlives_blame_span(body, longer_fr, error_region);
1336 // Obviously, this error message is far from satisfactory.
1337 // At present, though, it only appears in unit tests --
1338 // the AST-based checker uses a more conservative check,
1339 // so to even see this error, one must pass in a special
1341 let mut diag = infcx
1344 .struct_span_err(span, "higher-ranked subtype error");
1349 impl<'tcx> RegionDefinition<'tcx> {
1350 fn new(universe: ty::UniverseIndex, rv_origin: RegionVariableOrigin) -> Self {
1351 // Create a new region definition. Note that, for free
1352 // regions, the `external_name` field gets updated later in
1353 // `init_universal_regions`.
1355 let origin = match rv_origin {
1356 RegionVariableOrigin::NLL(origin) => origin,
1357 _ => NLLRegionVariableOrigin::Existential,
1363 external_name: None,
1368 pub trait ClosureRegionRequirementsExt<'gcx, 'tcx> {
1369 fn apply_requirements(
1371 tcx: TyCtxt<'gcx, 'tcx>,
1372 closure_def_id: DefId,
1373 closure_substs: SubstsRef<'tcx>,
1374 ) -> Vec<QueryRegionConstraint<'tcx>>;
1376 fn subst_closure_mapping<T>(
1378 tcx: TyCtxt<'gcx, 'tcx>,
1379 closure_mapping: &IndexVec<RegionVid, ty::Region<'tcx>>,
1383 T: TypeFoldable<'tcx>;
1386 impl<'gcx, 'tcx> ClosureRegionRequirementsExt<'gcx, 'tcx> for ClosureRegionRequirements<'gcx> {
1387 /// Given an instance T of the closure type, this method
1388 /// instantiates the "extra" requirements that we computed for the
1389 /// closure into the inference context. This has the effect of
1390 /// adding new outlives obligations to existing variables.
1392 /// As described on `ClosureRegionRequirements`, the extra
1393 /// requirements are expressed in terms of regionvids that index
1394 /// into the free regions that appear on the closure type. So, to
1395 /// do this, we first copy those regions out from the type T into
1396 /// a vector. Then we can just index into that vector to extract
1397 /// out the corresponding region from T and apply the
1399 fn apply_requirements(
1401 tcx: TyCtxt<'gcx, 'tcx>,
1402 closure_def_id: DefId,
1403 closure_substs: SubstsRef<'tcx>,
1404 ) -> Vec<QueryRegionConstraint<'tcx>> {
1406 "apply_requirements(closure_def_id={:?}, closure_substs={:?})",
1407 closure_def_id, closure_substs
1410 // Extract the values of the free regions in `closure_substs`
1411 // into a vector. These are the regions that we will be
1412 // relating to one another.
1413 let closure_mapping = &UniversalRegions::closure_mapping(
1416 self.num_external_vids,
1417 tcx.closure_base_def_id(closure_def_id),
1419 debug!("apply_requirements: closure_mapping={:?}", closure_mapping);
1421 // Create the predicates.
1422 self.outlives_requirements
1424 .map(|outlives_requirement| {
1425 let outlived_region = closure_mapping[outlives_requirement.outlived_free_region];
1427 match outlives_requirement.subject {
1428 ClosureOutlivesSubject::Region(region) => {
1429 let region = closure_mapping[region];
1431 "apply_requirements: region={:?} \
1432 outlived_region={:?} \
1433 outlives_requirement={:?}",
1434 region, outlived_region, outlives_requirement,
1436 ty::Binder::dummy(ty::OutlivesPredicate(region.into(), outlived_region))
1439 ClosureOutlivesSubject::Ty(ty) => {
1440 let ty = self.subst_closure_mapping(tcx, closure_mapping, &ty);
1442 "apply_requirements: ty={:?} \
1443 outlived_region={:?} \
1444 outlives_requirement={:?}",
1445 ty, outlived_region, outlives_requirement,
1447 ty::Binder::dummy(ty::OutlivesPredicate(ty.into(), outlived_region))
1454 fn subst_closure_mapping<T>(
1456 tcx: TyCtxt<'gcx, 'tcx>,
1457 closure_mapping: &IndexVec<RegionVid, ty::Region<'tcx>>,
1461 T: TypeFoldable<'tcx>,
1463 tcx.fold_regions(value, &mut false, |r, _depth| {
1464 if let ty::ReClosureBound(vid) = r {
1465 closure_mapping[*vid]
1468 "subst_closure_mapping: encountered non-closure bound free region {:?}",