1 // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Generalized type folding mechanism. The setup is a bit convoluted
12 //! but allows for convenient usage. Let T be an instance of some
13 //! "foldable type" (one which implements `TypeFoldable`) and F be an
14 //! instance of a "folder" (a type which implements `TypeFolder`). Then
15 //! the setup is intended to be:
17 //! T.fold_with(F) --calls--> F.fold_T(T) --calls--> T.super_fold_with(F)
19 //! This way, when you define a new folder F, you can override
20 //! `fold_T()` to customize the behavior, and invoke `T.super_fold_with()`
21 //! to get the original behavior. Meanwhile, to actually fold
22 //! something, you can just write `T.fold_with(F)`, which is
23 //! convenient. (Note that `fold_with` will also transparently handle
24 //! things like a `Vec<T>` where T is foldable and so on.)
26 //! In this ideal setup, the only function that actually *does*
27 //! anything is `T.super_fold_with()`, which traverses the type `T`.
28 //! Moreover, `T.super_fold_with()` should only ever call `T.fold_with()`.
30 //! In some cases, we follow a degenerate pattern where we do not have
31 //! a `fold_T` method. Instead, `T.fold_with` traverses the structure directly.
32 //! This is suboptimal because the behavior cannot be overridden, but it's
33 //! much less work to implement. If you ever *do* need an override that
34 //! doesn't exist, it's not hard to convert the degenerate pattern into the
37 //! A `TypeFoldable` T can also be visited by a `TypeVisitor` V using similar setup:
38 //! T.visit_with(V) --calls--> V.visit_T(T) --calls--> T.super_visit_with(V).
39 //! These methods return true to indicate that the visitor has found what it is looking for
40 //! and does not need to visit anything else.
43 use ty::subst::Substs;
45 use ty::{self, Binder, Ty, TyCtxt, TypeFlags};
48 use util::nodemap::{FxHashMap, FxHashSet};
50 /// The TypeFoldable trait is implemented for every type that can be folded.
51 /// Basically, every type that has a corresponding method in TypeFolder.
52 pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
53 fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self;
54 fn fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
55 self.super_fold_with(folder)
58 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool;
59 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
60 self.super_visit_with(visitor)
63 fn has_regions_escaping_depth(&self, depth: u32) -> bool {
64 self.visit_with(&mut HasEscapingRegionsVisitor { depth: depth })
66 fn has_escaping_regions(&self) -> bool {
67 self.has_regions_escaping_depth(0)
70 fn has_type_flags(&self, flags: TypeFlags) -> bool {
71 self.visit_with(&mut HasTypeFlagsVisitor { flags: flags })
73 fn has_projection_types(&self) -> bool {
74 self.has_type_flags(TypeFlags::HAS_PROJECTION)
76 fn references_error(&self) -> bool {
77 self.has_type_flags(TypeFlags::HAS_TY_ERR)
79 fn has_param_types(&self) -> bool {
80 self.has_type_flags(TypeFlags::HAS_PARAMS)
82 fn has_self_ty(&self) -> bool {
83 self.has_type_flags(TypeFlags::HAS_SELF)
85 fn has_infer_types(&self) -> bool {
86 self.has_type_flags(TypeFlags::HAS_TY_INFER)
88 fn needs_infer(&self) -> bool {
89 self.has_type_flags(TypeFlags::HAS_TY_INFER | TypeFlags::HAS_RE_INFER)
91 fn needs_subst(&self) -> bool {
92 self.has_type_flags(TypeFlags::NEEDS_SUBST)
94 fn has_re_skol(&self) -> bool {
95 self.has_type_flags(TypeFlags::HAS_RE_SKOL)
97 fn has_closure_types(&self) -> bool {
98 self.has_type_flags(TypeFlags::HAS_TY_CLOSURE)
100 fn has_erasable_regions(&self) -> bool {
101 self.has_type_flags(TypeFlags::HAS_RE_EARLY_BOUND |
102 TypeFlags::HAS_RE_INFER |
103 TypeFlags::HAS_FREE_REGIONS)
105 fn is_normalized_for_trans(&self) -> bool {
106 !self.has_type_flags(TypeFlags::HAS_RE_EARLY_BOUND |
107 TypeFlags::HAS_RE_INFER |
108 TypeFlags::HAS_FREE_REGIONS |
109 TypeFlags::HAS_TY_INFER |
110 TypeFlags::HAS_PARAMS |
111 TypeFlags::HAS_NORMALIZABLE_PROJECTION |
112 TypeFlags::HAS_TY_ERR |
115 /// Indicates whether this value references only 'global'
116 /// types/lifetimes that are the same regardless of what fn we are
117 /// in. This is used for caching. Errs on the side of returning
119 fn is_global(&self) -> bool {
120 !self.has_type_flags(TypeFlags::HAS_LOCAL_NAMES)
124 /// The TypeFolder trait defines the actual *folding*. There is a
125 /// method defined for every foldable type. Each of these has a
126 /// default implementation that does an "identity" fold. Within each
127 /// identity fold, it should invoke `foo.fold_with(self)` to fold each
129 pub trait TypeFolder<'gcx: 'tcx, 'tcx> : Sized {
130 fn tcx<'a>(&'a self) -> TyCtxt<'a, 'gcx, 'tcx>;
132 fn fold_binder<T>(&mut self, t: &Binder<T>) -> Binder<T>
133 where T : TypeFoldable<'tcx>
135 t.super_fold_with(self)
138 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
139 t.super_fold_with(self)
142 fn fold_mt(&mut self, t: &ty::TypeAndMut<'tcx>) -> ty::TypeAndMut<'tcx> {
143 t.super_fold_with(self)
146 fn fold_impl_header(&mut self, imp: &ty::ImplHeader<'tcx>) -> ty::ImplHeader<'tcx> {
147 imp.super_fold_with(self)
150 fn fold_substs(&mut self,
151 substs: &'tcx Substs<'tcx>)
152 -> &'tcx Substs<'tcx> {
153 substs.super_fold_with(self)
156 fn fold_fn_sig(&mut self,
157 sig: &ty::FnSig<'tcx>)
159 sig.super_fold_with(self)
162 fn fold_region(&mut self, r: &'tcx ty::Region) -> &'tcx ty::Region {
163 r.super_fold_with(self)
166 fn fold_autoref(&mut self, ar: &adjustment::AutoBorrow<'tcx>)
167 -> adjustment::AutoBorrow<'tcx> {
168 ar.super_fold_with(self)
172 pub trait TypeVisitor<'tcx> : Sized {
173 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
174 t.super_visit_with(self)
177 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
178 t.super_visit_with(self)
181 fn visit_trait_ref(&mut self, trait_ref: ty::TraitRef<'tcx>) -> bool {
182 trait_ref.super_visit_with(self)
185 fn visit_region(&mut self, r: &'tcx ty::Region) -> bool {
186 r.super_visit_with(self)
190 ///////////////////////////////////////////////////////////////////////////
191 // Some sample folders
193 pub struct BottomUpFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a, F>
194 where F: FnMut(Ty<'tcx>) -> Ty<'tcx>
196 pub tcx: TyCtxt<'a, 'gcx, 'tcx>,
200 impl<'a, 'gcx, 'tcx, F> TypeFolder<'gcx, 'tcx> for BottomUpFolder<'a, 'gcx, 'tcx, F>
201 where F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
203 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
205 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
206 let t1 = ty.super_fold_with(self);
211 ///////////////////////////////////////////////////////////////////////////
214 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
215 /// Collects the free and escaping regions in `value` into `region_set`. Returns
216 /// whether any late-bound regions were skipped
217 pub fn collect_regions<T>(self,
219 region_set: &mut FxHashSet<&'tcx ty::Region>)
221 where T : TypeFoldable<'tcx>
223 let mut have_bound_regions = false;
224 self.fold_regions(value, &mut have_bound_regions, |r, d| {
225 region_set.insert(self.mk_region(r.from_depth(d)));
231 /// Folds the escaping and free regions in `value` using `f`, and
232 /// sets `skipped_regions` to true if any late-bound region was found
234 pub fn fold_regions<T,F>(self,
236 skipped_regions: &mut bool,
239 where F : FnMut(&'tcx ty::Region, u32) -> &'tcx ty::Region,
240 T : TypeFoldable<'tcx>,
242 value.fold_with(&mut RegionFolder::new(self, skipped_regions, &mut f))
246 /// Folds over the substructure of a type, visiting its component
247 /// types and all regions that occur *free* within it.
249 /// That is, `Ty` can contain function or method types that bind
250 /// regions at the call site (`ReLateBound`), and occurrences of
251 /// regions (aka "lifetimes") that are bound within a type are not
252 /// visited by this folder; only regions that occur free will be
253 /// visited by `fld_r`.
255 pub struct RegionFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
256 tcx: TyCtxt<'a, 'gcx, 'tcx>,
257 skipped_regions: &'a mut bool,
259 fld_r: &'a mut (FnMut(&'tcx ty::Region, u32) -> &'tcx ty::Region + 'a),
262 impl<'a, 'gcx, 'tcx> RegionFolder<'a, 'gcx, 'tcx> {
263 pub fn new<F>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
264 skipped_regions: &'a mut bool,
265 fld_r: &'a mut F) -> RegionFolder<'a, 'gcx, 'tcx>
266 where F : FnMut(&'tcx ty::Region, u32) -> &'tcx ty::Region
270 skipped_regions: skipped_regions,
277 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionFolder<'a, 'gcx, 'tcx> {
278 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
280 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
281 self.current_depth += 1;
282 let t = t.super_fold_with(self);
283 self.current_depth -= 1;
287 fn fold_region(&mut self, r: &'tcx ty::Region) -> &'tcx ty::Region {
289 ty::ReLateBound(debruijn, _) if debruijn.depth < self.current_depth => {
290 debug!("RegionFolder.fold_region({:?}) skipped bound region (current depth={})",
291 r, self.current_depth);
292 *self.skipped_regions = true;
296 debug!("RegionFolder.fold_region({:?}) folding free region (current_depth={})",
297 r, self.current_depth);
298 (self.fld_r)(r, self.current_depth)
304 ///////////////////////////////////////////////////////////////////////////
305 // Late-bound region replacer
307 // Replaces the escaping regions in a type.
309 struct RegionReplacer<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
310 tcx: TyCtxt<'a, 'gcx, 'tcx>,
312 fld_r: &'a mut (FnMut(ty::BoundRegion) -> &'tcx ty::Region + 'a),
313 map: FxHashMap<ty::BoundRegion, &'tcx ty::Region>
316 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
317 pub fn replace_late_bound_regions<T,F>(self,
320 -> (T, FxHashMap<ty::BoundRegion, &'tcx ty::Region>)
321 where F : FnMut(ty::BoundRegion) -> &'tcx ty::Region,
322 T : TypeFoldable<'tcx>,
324 let mut replacer = RegionReplacer::new(self, &mut f);
325 let result = value.skip_binder().fold_with(&mut replacer);
326 (result, replacer.map)
330 /// Replace any late-bound regions bound in `value` with free variants attached to scope-id
332 pub fn liberate_late_bound_regions<T>(self,
333 all_outlive_scope: region::CodeExtent,
336 where T : TypeFoldable<'tcx>
338 self.replace_late_bound_regions(value, |br| {
339 self.mk_region(ty::ReFree(ty::FreeRegion {
340 scope: all_outlive_scope,
346 /// Flattens two binding levels into one. So `for<'a> for<'b> Foo`
347 /// becomes `for<'a,'b> Foo`.
348 pub fn flatten_late_bound_regions<T>(self, bound2_value: &Binder<Binder<T>>)
350 where T: TypeFoldable<'tcx>
352 let bound0_value = bound2_value.skip_binder().skip_binder();
353 let value = self.fold_regions(bound0_value, &mut false,
354 |region, current_depth| {
356 ty::ReLateBound(debruijn, br) if debruijn.depth >= current_depth => {
357 // should be true if no escaping regions from bound2_value
358 assert!(debruijn.depth - current_depth <= 1);
359 self.mk_region(ty::ReLateBound(ty::DebruijnIndex::new(current_depth), br))
369 pub fn no_late_bound_regions<T>(self, value: &Binder<T>) -> Option<T>
370 where T : TypeFoldable<'tcx>
372 if value.0.has_escaping_regions() {
375 Some(value.0.clone())
379 /// Returns a set of all late-bound regions that are constrained
380 /// by `value`, meaning that if we instantiate those LBR with
381 /// variables and equate `value` with something else, those
382 /// variables will also be equated.
383 pub fn collect_constrained_late_bound_regions<T>(&self, value: &Binder<T>)
384 -> FxHashSet<ty::BoundRegion>
385 where T : TypeFoldable<'tcx>
387 self.collect_late_bound_regions(value, true)
390 /// Returns a set of all late-bound regions that appear in `value` anywhere.
391 pub fn collect_referenced_late_bound_regions<T>(&self, value: &Binder<T>)
392 -> FxHashSet<ty::BoundRegion>
393 where T : TypeFoldable<'tcx>
395 self.collect_late_bound_regions(value, false)
398 fn collect_late_bound_regions<T>(&self, value: &Binder<T>, just_constraint: bool)
399 -> FxHashSet<ty::BoundRegion>
400 where T : TypeFoldable<'tcx>
402 let mut collector = LateBoundRegionsCollector::new(just_constraint);
403 let result = value.skip_binder().visit_with(&mut collector);
404 assert!(!result); // should never have stopped early
408 /// Replace any late-bound regions bound in `value` with `'erased`. Useful in trans but also
409 /// method lookup and a few other places where precise region relationships are not required.
410 pub fn erase_late_bound_regions<T>(self, value: &Binder<T>) -> T
411 where T : TypeFoldable<'tcx>
413 self.replace_late_bound_regions(value, |_| self.types.re_erased).0
416 /// Rewrite any late-bound regions so that they are anonymous. Region numbers are
417 /// assigned starting at 1 and increasing monotonically in the order traversed
418 /// by the fold operation.
420 /// The chief purpose of this function is to canonicalize regions so that two
421 /// `FnSig`s or `TraitRef`s which are equivalent up to region naming will become
422 /// structurally identical. For example, `for<'a, 'b> fn(&'a isize, &'b isize)` and
423 /// `for<'a, 'b> fn(&'b isize, &'a isize)` will become identical after anonymization.
424 pub fn anonymize_late_bound_regions<T>(self, sig: &Binder<T>) -> Binder<T>
425 where T : TypeFoldable<'tcx>,
428 Binder(self.replace_late_bound_regions(sig, |_| {
430 self.mk_region(ty::ReLateBound(ty::DebruijnIndex::new(1), ty::BrAnon(counter)))
435 impl<'a, 'gcx, 'tcx> RegionReplacer<'a, 'gcx, 'tcx> {
436 fn new<F>(tcx: TyCtxt<'a, 'gcx, 'tcx>, fld_r: &'a mut F)
437 -> RegionReplacer<'a, 'gcx, 'tcx>
438 where F : FnMut(ty::BoundRegion) -> &'tcx ty::Region
449 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionReplacer<'a, 'gcx, 'tcx> {
450 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
452 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
453 self.current_depth += 1;
454 let t = t.super_fold_with(self);
455 self.current_depth -= 1;
459 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
460 if !t.has_regions_escaping_depth(self.current_depth-1) {
464 t.super_fold_with(self)
467 fn fold_region(&mut self, r:&'tcx ty::Region) -> &'tcx ty::Region {
469 ty::ReLateBound(debruijn, br) if debruijn.depth == self.current_depth => {
470 let fld_r = &mut self.fld_r;
471 let region = *self.map.entry(br).or_insert_with(|| fld_r(br));
472 if let ty::ReLateBound(debruijn1, br) = *region {
473 // If the callback returns a late-bound region,
474 // that region should always use depth 1. Then we
475 // adjust it to the correct depth.
476 assert_eq!(debruijn1.depth, 1);
477 self.tcx.mk_region(ty::ReLateBound(debruijn, br))
487 ///////////////////////////////////////////////////////////////////////////
490 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
491 /// Returns an equivalent value with all free regions removed (note
492 /// that late-bound regions remain, because they are important for
493 /// subtyping, but they are anonymized and normalized as well)..
494 pub fn erase_regions<T>(self, value: &T) -> T
495 where T : TypeFoldable<'tcx>
497 let value1 = value.fold_with(&mut RegionEraser(self));
498 debug!("erase_regions({:?}) = {:?}",
502 struct RegionEraser<'a, 'gcx: 'a+'tcx, 'tcx: 'a>(TyCtxt<'a, 'gcx, 'tcx>);
504 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionEraser<'a, 'gcx, 'tcx> {
505 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.0 }
507 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
508 if let Some(u) = self.tcx().normalized_cache.borrow().get(&ty).cloned() {
512 // FIXME(eddyb) should local contexts have a cache too?
513 if let Some(ty_lifted) = self.tcx().lift_to_global(&ty) {
514 let tcx = self.tcx().global_tcx();
515 let t_norm = ty_lifted.super_fold_with(&mut RegionEraser(tcx));
516 tcx.normalized_cache.borrow_mut().insert(ty_lifted, t_norm);
519 ty.super_fold_with(self)
523 fn fold_binder<T>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T>
524 where T : TypeFoldable<'tcx>
526 let u = self.tcx().anonymize_late_bound_regions(t);
527 u.super_fold_with(self)
530 fn fold_region(&mut self, r: &'tcx ty::Region) -> &'tcx ty::Region {
531 // because late-bound regions affect subtyping, we can't
532 // erase the bound/free distinction, but we can replace
533 // all free regions with 'erased.
535 // Note that we *CAN* replace early-bound regions -- the
536 // type system never "sees" those, they get substituted
537 // away. In trans, they will always be erased to 'erased
538 // whenever a substitution occurs.
540 ty::ReLateBound(..) => r,
541 _ => self.tcx().types.re_erased
548 ///////////////////////////////////////////////////////////////////////////
551 // Shifts the De Bruijn indices on all escaping bound regions by a
552 // fixed amount. Useful in substitution or when otherwise introducing
553 // a binding level that is not intended to capture the existing bound
554 // regions. See comment on `shift_regions_through_binders` method in
555 // `subst.rs` for more details.
557 pub fn shift_region(region: ty::Region, amount: u32) -> ty::Region {
559 ty::ReLateBound(debruijn, br) => {
560 ty::ReLateBound(debruijn.shifted(amount), br)
568 pub fn shift_region_ref<'a, 'gcx, 'tcx>(
569 tcx: TyCtxt<'a, 'gcx, 'tcx>,
570 region: &'tcx ty::Region,
575 &ty::ReLateBound(debruijn, br) if amount > 0 => {
576 tcx.mk_region(ty::ReLateBound(debruijn.shifted(amount), br))
584 pub fn shift_regions<'a, 'gcx, 'tcx, T>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
585 amount: u32, value: &T) -> T
586 where T: TypeFoldable<'tcx>
588 debug!("shift_regions(value={:?}, amount={})",
591 value.fold_with(&mut RegionFolder::new(tcx, &mut false, &mut |region, _current_depth| {
592 shift_region_ref(tcx, region, amount)
596 /// An "escaping region" is a bound region whose binder is not part of `t`.
598 /// So, for example, consider a type like the following, which has two binders:
600 /// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize))
601 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope
602 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope
604 /// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the
605 /// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner
606 /// fn type*, that type has an escaping region: `'a`.
608 /// Note that what I'm calling an "escaping region" is often just called a "free region". However,
609 /// we already use the term "free region". It refers to the regions that we use to represent bound
610 /// regions on a fn definition while we are typechecking its body.
612 /// To clarify, conceptually there is no particular difference between an "escaping" region and a
613 /// "free" region. However, there is a big difference in practice. Basically, when "entering" a
614 /// binding level, one is generally required to do some sort of processing to a bound region, such
615 /// as replacing it with a fresh/skolemized region, or making an entry in the environment to
616 /// represent the scope to which it is attached, etc. An escaping region represents a bound region
617 /// for which this processing has not yet been done.
618 struct HasEscapingRegionsVisitor {
622 impl<'tcx> TypeVisitor<'tcx> for HasEscapingRegionsVisitor {
623 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
625 let result = t.super_visit_with(self);
630 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
631 t.region_depth > self.depth
634 fn visit_region(&mut self, r: &'tcx ty::Region) -> bool {
635 r.escapes_depth(self.depth)
639 struct HasTypeFlagsVisitor {
640 flags: ty::TypeFlags,
643 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
644 fn visit_ty(&mut self, t: Ty) -> bool {
645 let flags = t.flags.get();
646 debug!("HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}", t, flags, self.flags);
647 flags.intersects(self.flags)
650 fn visit_region(&mut self, r: &'tcx ty::Region) -> bool {
651 let flags = r.type_flags();
652 debug!("HasTypeFlagsVisitor: r={:?} r.flags={:?} self.flags={:?}", r, flags, self.flags);
653 flags.intersects(self.flags)
657 /// Collects all the late-bound regions it finds into a hash set.
658 struct LateBoundRegionsCollector {
660 regions: FxHashSet<ty::BoundRegion>,
661 just_constrained: bool,
664 impl LateBoundRegionsCollector {
665 fn new(just_constrained: bool) -> Self {
666 LateBoundRegionsCollector {
668 regions: FxHashSet(),
669 just_constrained: just_constrained,
674 impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
675 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
676 self.current_depth += 1;
677 let result = t.super_visit_with(self);
678 self.current_depth -= 1;
682 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
683 // if we are only looking for "constrained" region, we have to
684 // ignore the inputs to a projection, as they may not appear
685 // in the normalized form
686 if self.just_constrained {
688 ty::TyProjection(..) | ty::TyAnon(..) => { return false; }
693 t.super_visit_with(self)
696 fn visit_region(&mut self, r: &'tcx ty::Region) -> bool {
698 ty::ReLateBound(debruijn, br) if debruijn.depth == self.current_depth => {
699 self.regions.insert(br);