1 //! Generalized type folding mechanism. The setup is a bit convoluted
2 //! but allows for convenient usage. Let T be an instance of some
3 //! "foldable type" (one which implements `TypeFoldable`) and F be an
4 //! instance of a "folder" (a type which implements `TypeFolder`). Then
5 //! the setup is intended to be:
7 //! T.fold_with(F) --calls--> F.fold_T(T) --calls--> T.super_fold_with(F)
9 //! This way, when you define a new folder F, you can override
10 //! `fold_T()` to customize the behavior, and invoke `T.super_fold_with()`
11 //! to get the original behavior. Meanwhile, to actually fold
12 //! something, you can just write `T.fold_with(F)`, which is
13 //! convenient. (Note that `fold_with` will also transparently handle
14 //! things like a `Vec<T>` where T is foldable and so on.)
16 //! In this ideal setup, the only function that actually *does*
17 //! anything is `T.super_fold_with()`, which traverses the type `T`.
18 //! Moreover, `T.super_fold_with()` should only ever call `T.fold_with()`.
20 //! In some cases, we follow a degenerate pattern where we do not have
21 //! a `fold_T` method. Instead, `T.fold_with` traverses the structure directly.
22 //! This is suboptimal because the behavior cannot be overridden, but it's
23 //! much less work to implement. If you ever *do* need an override that
24 //! doesn't exist, it's not hard to convert the degenerate pattern into the
27 //! A `TypeFoldable` T can also be visited by a `TypeVisitor` V using similar setup:
29 //! T.visit_with(V) --calls--> V.visit_T(T) --calls--> T.super_visit_with(V).
31 //! These methods return true to indicate that the visitor has found what it is
32 //! looking for, and does not need to visit anything else.
34 use crate::ty::structural_impls::PredicateVisitor;
35 use crate::ty::{self, flags::FlagComputation, Binder, Ty, TyCtxt, TypeFlags};
37 use rustc_hir::def_id::DefId;
39 use rustc_data_structures::fx::FxHashSet;
40 use std::collections::BTreeMap;
43 /// This trait is implemented for every type that can be folded.
44 /// Basically, every type that has a corresponding method in `TypeFolder`.
46 /// To implement this conveniently, use the derive macro located in librustc_macros.
47 pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
48 fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self;
49 fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self {
50 self.super_fold_with(folder)
53 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool;
54 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
55 self.super_visit_with(visitor)
58 /// Returns `true` if `self` has any late-bound regions that are either
59 /// bound by `binder` or bound by some binder outside of `binder`.
60 /// If `binder` is `ty::INNERMOST`, this indicates whether
61 /// there are any late-bound regions that appear free.
62 fn has_vars_bound_at_or_above(&self, binder: ty::DebruijnIndex) -> bool {
63 self.visit_with(&mut HasEscapingVarsVisitor { outer_index: binder })
66 /// Returns `true` if this `self` has any regions that escape `binder` (and
67 /// hence are not bound by it).
68 fn has_vars_bound_above(&self, binder: ty::DebruijnIndex) -> bool {
69 self.has_vars_bound_at_or_above(binder.shifted_in(1))
72 fn has_escaping_bound_vars(&self) -> bool {
73 self.has_vars_bound_at_or_above(ty::INNERMOST)
76 fn has_type_flags(&self, flags: TypeFlags) -> bool {
77 self.visit_with(&mut HasTypeFlagsVisitor { flags })
79 fn has_projections(&self) -> bool {
80 self.has_type_flags(TypeFlags::HAS_PROJECTION)
82 fn has_opaque_types(&self) -> bool {
83 self.has_type_flags(TypeFlags::HAS_TY_OPAQUE)
85 fn references_error(&self) -> bool {
86 self.has_type_flags(TypeFlags::HAS_ERROR)
88 fn has_param_types_or_consts(&self) -> bool {
89 self.has_type_flags(TypeFlags::HAS_TY_PARAM | TypeFlags::HAS_CT_PARAM)
91 fn has_infer_regions(&self) -> bool {
92 self.has_type_flags(TypeFlags::HAS_RE_INFER)
94 fn has_infer_types(&self) -> bool {
95 self.has_type_flags(TypeFlags::HAS_TY_INFER)
97 fn has_infer_types_or_consts(&self) -> bool {
98 self.has_type_flags(TypeFlags::HAS_TY_INFER | TypeFlags::HAS_CT_INFER)
100 fn has_infer_consts(&self) -> bool {
101 self.has_type_flags(TypeFlags::HAS_CT_INFER)
103 fn needs_infer(&self) -> bool {
104 self.has_type_flags(TypeFlags::NEEDS_INFER)
106 fn has_placeholders(&self) -> bool {
108 TypeFlags::HAS_RE_PLACEHOLDER
109 | TypeFlags::HAS_TY_PLACEHOLDER
110 | TypeFlags::HAS_CT_PLACEHOLDER,
113 fn needs_subst(&self) -> bool {
114 self.has_type_flags(TypeFlags::NEEDS_SUBST)
116 fn has_re_placeholders(&self) -> bool {
117 self.has_type_flags(TypeFlags::HAS_RE_PLACEHOLDER)
119 /// "Free" regions in this context means that it has any region
120 /// that is not (a) erased or (b) late-bound.
121 fn has_free_regions(&self) -> bool {
122 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
125 fn has_erased_regions(&self) -> bool {
126 self.has_type_flags(TypeFlags::HAS_RE_ERASED)
129 /// True if there are any un-erased free regions.
130 fn has_erasable_regions(&self) -> bool {
131 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
134 /// Indicates whether this value references only 'global'
135 /// generic parameters that are the same regardless of what fn we are
136 /// in. This is used for caching.
137 fn is_global(&self) -> bool {
138 !self.has_type_flags(TypeFlags::HAS_FREE_LOCAL_NAMES)
141 /// True if there are any late-bound regions
142 fn has_late_bound_regions(&self) -> bool {
143 self.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND)
146 /// Indicates whether this value still has parameters/placeholders/inference variables
147 /// which could be replaced later, in a way that would change the results of `impl`
149 fn still_further_specializable(&self) -> bool {
150 self.has_type_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE)
153 /// Does this value contain closures, generators or functions such that it may require
154 /// polymorphization?
155 fn may_polymorphize(&self) -> bool {
156 self.has_type_flags(TypeFlags::MAY_POLYMORPHIZE)
159 /// A visitor that does not recurse into types, works like `fn walk_shallow` in `Ty`.
160 fn visit_tys_shallow(&self, visit: impl FnMut(Ty<'tcx>) -> bool) -> bool {
161 pub struct Visitor<F>(F);
163 impl<'tcx, F: FnMut(Ty<'tcx>) -> bool> TypeVisitor<'tcx> for Visitor<F> {
164 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
169 self.visit_with(&mut Visitor(visit))
173 impl TypeFoldable<'tcx> for hir::Constness {
174 fn super_fold_with<F: TypeFolder<'tcx>>(&self, _: &mut F) -> Self {
177 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> bool {
182 /// The `TypeFolder` trait defines the actual *folding*. There is a
183 /// method defined for every foldable type. Each of these has a
184 /// default implementation that does an "identity" fold. Within each
185 /// identity fold, it should invoke `foo.fold_with(self)` to fold each
187 pub trait TypeFolder<'tcx>: Sized {
188 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
190 fn fold_binder<T>(&mut self, t: &Binder<T>) -> Binder<T>
192 T: TypeFoldable<'tcx>,
194 t.super_fold_with(self)
197 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
198 t.super_fold_with(self)
201 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
202 r.super_fold_with(self)
205 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
206 c.super_fold_with(self)
210 pub trait TypeVisitor<'tcx>: Sized {
211 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
212 t.super_visit_with(self)
215 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
216 t.super_visit_with(self)
219 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
220 r.super_visit_with(self)
223 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
224 c.super_visit_with(self)
228 ///////////////////////////////////////////////////////////////////////////
229 // Some sample folders
231 pub struct BottomUpFolder<'tcx, F, G, H>
233 F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
234 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
235 H: FnMut(&'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>,
237 pub tcx: TyCtxt<'tcx>,
243 impl<'tcx, F, G, H> TypeFolder<'tcx> for BottomUpFolder<'tcx, F, G, H>
245 F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
246 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
247 H: FnMut(&'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>,
249 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
253 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
254 let t = ty.super_fold_with(self);
258 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
259 let r = r.super_fold_with(self);
263 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
264 let ct = ct.super_fold_with(self);
269 ///////////////////////////////////////////////////////////////////////////
272 impl<'tcx> TyCtxt<'tcx> {
273 /// Folds the escaping and free regions in `value` using `f`, and
274 /// sets `skipped_regions` to true if any late-bound region was found
276 pub fn fold_regions<T>(
279 skipped_regions: &mut bool,
280 mut f: impl FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
283 T: TypeFoldable<'tcx>,
285 value.fold_with(&mut RegionFolder::new(self, skipped_regions, &mut f))
288 /// Invoke `callback` on every region appearing free in `value`.
289 pub fn for_each_free_region(
291 value: &impl TypeFoldable<'tcx>,
292 mut callback: impl FnMut(ty::Region<'tcx>),
294 self.any_free_region_meets(value, |r| {
300 /// Returns `true` if `callback` returns true for every region appearing free in `value`.
301 pub fn all_free_regions_meet(
303 value: &impl TypeFoldable<'tcx>,
304 mut callback: impl FnMut(ty::Region<'tcx>) -> bool,
306 !self.any_free_region_meets(value, |r| !callback(r))
309 /// Returns `true` if `callback` returns true for some region appearing free in `value`.
310 pub fn any_free_region_meets(
312 value: &impl TypeFoldable<'tcx>,
313 callback: impl FnMut(ty::Region<'tcx>) -> bool,
315 return value.visit_with(&mut RegionVisitor { outer_index: ty::INNERMOST, callback });
317 struct RegionVisitor<F> {
318 /// The index of a binder *just outside* the things we have
319 /// traversed. If we encounter a bound region bound by this
320 /// binder or one outer to it, it appears free. Example:
323 /// for<'a> fn(for<'b> fn(), T)
325 /// | | | | here, would be shifted in 1
326 /// | | | here, would be shifted in 2
327 /// | | here, would be `INNERMOST` shifted in by 1
328 /// | here, initially, binder would be `INNERMOST`
331 /// You see that, initially, *any* bound value is free,
332 /// because we've not traversed any binders. As we pass
333 /// through a binder, we shift the `outer_index` by 1 to
334 /// account for the new binder that encloses us.
335 outer_index: ty::DebruijnIndex,
339 impl<'tcx, F> TypeVisitor<'tcx> for RegionVisitor<F>
341 F: FnMut(ty::Region<'tcx>) -> bool,
343 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
344 self.outer_index.shift_in(1);
345 let result = t.as_ref().skip_binder().visit_with(self);
346 self.outer_index.shift_out(1);
350 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
352 ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => {
353 false // ignore bound regions, keep visiting
355 _ => (self.callback)(r),
359 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
360 // We're only interested in types involving regions
361 if ty.flags.intersects(TypeFlags::HAS_FREE_REGIONS) {
362 ty.super_visit_with(self)
364 false // keep visiting
371 /// Folds over the substructure of a type, visiting its component
372 /// types and all regions that occur *free* within it.
374 /// That is, `Ty` can contain function or method types that bind
375 /// regions at the call site (`ReLateBound`), and occurrences of
376 /// regions (aka "lifetimes") that are bound within a type are not
377 /// visited by this folder; only regions that occur free will be
378 /// visited by `fld_r`.
380 pub struct RegionFolder<'a, 'tcx> {
382 skipped_regions: &'a mut bool,
384 /// Stores the index of a binder *just outside* the stuff we have
385 /// visited. So this begins as INNERMOST; when we pass through a
386 /// binder, it is incremented (via `shift_in`).
387 current_index: ty::DebruijnIndex,
389 /// Callback invokes for each free region. The `DebruijnIndex`
390 /// points to the binder *just outside* the ones we have passed
393 &'a mut (dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx> + 'a),
396 impl<'a, 'tcx> RegionFolder<'a, 'tcx> {
400 skipped_regions: &'a mut bool,
401 fold_region_fn: &'a mut dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
402 ) -> RegionFolder<'a, 'tcx> {
403 RegionFolder { tcx, skipped_regions, current_index: ty::INNERMOST, fold_region_fn }
407 impl<'a, 'tcx> TypeFolder<'tcx> for RegionFolder<'a, 'tcx> {
408 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
412 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
413 self.current_index.shift_in(1);
414 let t = t.super_fold_with(self);
415 self.current_index.shift_out(1);
419 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
421 ty::ReLateBound(debruijn, _) if debruijn < self.current_index => {
423 "RegionFolder.fold_region({:?}) skipped bound region (current index={:?})",
424 r, self.current_index
426 *self.skipped_regions = true;
431 "RegionFolder.fold_region({:?}) folding free region (current_index={:?})",
432 r, self.current_index
434 (self.fold_region_fn)(r, self.current_index)
440 ///////////////////////////////////////////////////////////////////////////
441 // Bound vars replacer
443 /// Replaces the escaping bound vars (late bound regions or bound types) in a type.
444 struct BoundVarReplacer<'a, 'tcx> {
447 /// As with `RegionFolder`, represents the index of a binder *just outside*
448 /// the ones we have visited.
449 current_index: ty::DebruijnIndex,
451 fld_r: &'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a),
452 fld_t: &'a mut (dyn FnMut(ty::BoundTy) -> Ty<'tcx> + 'a),
453 fld_c: &'a mut (dyn FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx> + 'a),
456 impl<'a, 'tcx> BoundVarReplacer<'a, 'tcx> {
457 fn new<F, G, H>(tcx: TyCtxt<'tcx>, fld_r: &'a mut F, fld_t: &'a mut G, fld_c: &'a mut H) -> Self
459 F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
460 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
461 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
463 BoundVarReplacer { tcx, current_index: ty::INNERMOST, fld_r, fld_t, fld_c }
467 impl<'a, 'tcx> TypeFolder<'tcx> for BoundVarReplacer<'a, 'tcx> {
468 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
472 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
473 self.current_index.shift_in(1);
474 let t = t.super_fold_with(self);
475 self.current_index.shift_out(1);
479 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
481 ty::Bound(debruijn, bound_ty) => {
482 if debruijn == self.current_index {
483 let fld_t = &mut self.fld_t;
484 let ty = fld_t(bound_ty);
485 ty::fold::shift_vars(self.tcx, &ty, self.current_index.as_u32())
491 if !t.has_vars_bound_at_or_above(self.current_index) {
492 // Nothing more to substitute.
495 t.super_fold_with(self)
501 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
503 ty::ReLateBound(debruijn, br) if debruijn == self.current_index => {
504 let fld_r = &mut self.fld_r;
505 let region = fld_r(br);
506 if let ty::ReLateBound(debruijn1, br) = *region {
507 // If the callback returns a late-bound region,
508 // that region should always use the INNERMOST
509 // debruijn index. Then we adjust it to the
511 assert_eq!(debruijn1, ty::INNERMOST);
512 self.tcx.mk_region(ty::ReLateBound(debruijn, br))
521 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
522 if let ty::Const { val: ty::ConstKind::Bound(debruijn, bound_const), ty } = *ct {
523 if debruijn == self.current_index {
524 let fld_c = &mut self.fld_c;
525 let ct = fld_c(bound_const, ty);
526 ty::fold::shift_vars(self.tcx, &ct, self.current_index.as_u32())
531 if !ct.has_vars_bound_at_or_above(self.current_index) {
532 // Nothing more to substitute.
535 ct.super_fold_with(self)
541 impl<'tcx> TyCtxt<'tcx> {
542 /// Replaces all regions bound by the given `Binder` with the
543 /// results returned by the closure; the closure is expected to
544 /// return a free region (relative to this binder), and hence the
545 /// binder is removed in the return type. The closure is invoked
546 /// once for each unique `BoundRegion`; multiple references to the
547 /// same `BoundRegion` will reuse the previous result. A map is
548 /// returned at the end with each bound region and the free region
549 /// that replaced it.
551 /// This method only replaces late bound regions and the result may still
552 /// contain escaping bound types.
553 pub fn replace_late_bound_regions<T, F>(
557 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
559 F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
560 T: TypeFoldable<'tcx>,
562 // identity for bound types and consts
563 let fld_t = |bound_ty| self.mk_ty(ty::Bound(ty::INNERMOST, bound_ty));
564 let fld_c = |bound_ct, ty| {
565 self.mk_const(ty::Const { val: ty::ConstKind::Bound(ty::INNERMOST, bound_ct), ty })
567 self.replace_escaping_bound_vars(value.as_ref().skip_binder(), fld_r, fld_t, fld_c)
570 /// Replaces all escaping bound vars. The `fld_r` closure replaces escaping
571 /// bound regions; the `fld_t` closure replaces escaping bound types and the `fld_c`
572 /// closure replaces escaping bound consts.
573 pub fn replace_escaping_bound_vars<T, F, G, H>(
579 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
581 F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
582 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
583 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
584 T: TypeFoldable<'tcx>,
586 use rustc_data_structures::fx::FxHashMap;
588 let mut region_map = BTreeMap::new();
589 let mut type_map = FxHashMap::default();
590 let mut const_map = FxHashMap::default();
592 if !value.has_escaping_bound_vars() {
593 (value.clone(), region_map)
595 let mut real_fld_r = |br| *region_map.entry(br).or_insert_with(|| fld_r(br));
598 |bound_ty| *type_map.entry(bound_ty).or_insert_with(|| fld_t(bound_ty));
601 |bound_ct, ty| *const_map.entry(bound_ct).or_insert_with(|| fld_c(bound_ct, ty));
604 BoundVarReplacer::new(self, &mut real_fld_r, &mut real_fld_t, &mut real_fld_c);
605 let result = value.fold_with(&mut replacer);
610 /// Replaces all types or regions bound by the given `Binder`. The `fld_r`
611 /// closure replaces bound regions while the `fld_t` closure replaces bound
613 pub fn replace_bound_vars<T, F, G, H>(
619 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
621 F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
622 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
623 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
624 T: TypeFoldable<'tcx>,
626 self.replace_escaping_bound_vars(value.as_ref().skip_binder(), fld_r, fld_t, fld_c)
629 /// Replaces any late-bound regions bound in `value` with
630 /// free variants attached to `all_outlive_scope`.
631 pub fn liberate_late_bound_regions<T>(
633 all_outlive_scope: DefId,
634 value: &ty::Binder<T>,
637 T: TypeFoldable<'tcx>,
639 self.replace_late_bound_regions(value, |br| {
640 self.mk_region(ty::ReFree(ty::FreeRegion {
641 scope: all_outlive_scope,
648 /// Returns a set of all late-bound regions that are constrained
649 /// by `value`, meaning that if we instantiate those LBR with
650 /// variables and equate `value` with something else, those
651 /// variables will also be equated.
652 pub fn collect_constrained_late_bound_regions<T>(
655 ) -> FxHashSet<ty::BoundRegion>
657 T: TypeFoldable<'tcx>,
659 self.collect_late_bound_regions(value, true)
662 /// Returns a set of all late-bound regions that appear in `value` anywhere.
663 pub fn collect_referenced_late_bound_regions<T>(
666 ) -> FxHashSet<ty::BoundRegion>
668 T: TypeFoldable<'tcx>,
670 self.collect_late_bound_regions(value, false)
673 fn collect_late_bound_regions<T>(
676 just_constraint: bool,
677 ) -> FxHashSet<ty::BoundRegion>
679 T: TypeFoldable<'tcx>,
681 let mut collector = LateBoundRegionsCollector::new(just_constraint);
682 let result = value.as_ref().skip_binder().visit_with(&mut collector);
683 assert!(!result); // should never have stopped early
687 /// Replaces any late-bound regions bound in `value` with `'erased`. Useful in codegen but also
688 /// method lookup and a few other places where precise region relationships are not required.
689 pub fn erase_late_bound_regions<T>(self, value: &Binder<T>) -> T
691 T: TypeFoldable<'tcx>,
693 self.replace_late_bound_regions(value, |_| self.lifetimes.re_erased).0
696 /// Rewrite any late-bound regions so that they are anonymous. Region numbers are
697 /// assigned starting at 1 and increasing monotonically in the order traversed
698 /// by the fold operation.
700 /// The chief purpose of this function is to canonicalize regions so that two
701 /// `FnSig`s or `TraitRef`s which are equivalent up to region naming will become
702 /// structurally identical. For example, `for<'a, 'b> fn(&'a isize, &'b isize)` and
703 /// `for<'a, 'b> fn(&'b isize, &'a isize)` will become identical after anonymization.
704 pub fn anonymize_late_bound_regions<T>(self, sig: &Binder<T>) -> Binder<T>
706 T: TypeFoldable<'tcx>,
710 self.replace_late_bound_regions(sig, |_| {
712 self.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BrAnon(counter)))
719 ///////////////////////////////////////////////////////////////////////////
722 // Shifts the De Bruijn indices on all escaping bound vars by a
723 // fixed amount. Useful in substitution or when otherwise introducing
724 // a binding level that is not intended to capture the existing bound
725 // vars. See comment on `shift_vars_through_binders` method in
726 // `subst.rs` for more details.
733 struct Shifter<'tcx> {
735 current_index: ty::DebruijnIndex,
737 direction: Direction,
741 pub fn new(tcx: TyCtxt<'tcx>, amount: u32, direction: Direction) -> Self {
742 Shifter { tcx, current_index: ty::INNERMOST, amount, direction }
746 impl TypeFolder<'tcx> for Shifter<'tcx> {
747 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
751 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
752 self.current_index.shift_in(1);
753 let t = t.super_fold_with(self);
754 self.current_index.shift_out(1);
758 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
760 ty::ReLateBound(debruijn, br) => {
761 if self.amount == 0 || debruijn < self.current_index {
764 let debruijn = match self.direction {
765 Direction::In => debruijn.shifted_in(self.amount),
767 assert!(debruijn.as_u32() >= self.amount);
768 debruijn.shifted_out(self.amount)
771 let shifted = ty::ReLateBound(debruijn, br);
772 self.tcx.mk_region(shifted)
779 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
781 ty::Bound(debruijn, bound_ty) => {
782 if self.amount == 0 || debruijn < self.current_index {
785 let debruijn = match self.direction {
786 Direction::In => debruijn.shifted_in(self.amount),
788 assert!(debruijn.as_u32() >= self.amount);
789 debruijn.shifted_out(self.amount)
792 self.tcx.mk_ty(ty::Bound(debruijn, bound_ty))
796 _ => ty.super_fold_with(self),
800 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
801 if let ty::Const { val: ty::ConstKind::Bound(debruijn, bound_ct), ty } = *ct {
802 if self.amount == 0 || debruijn < self.current_index {
805 let debruijn = match self.direction {
806 Direction::In => debruijn.shifted_in(self.amount),
808 assert!(debruijn.as_u32() >= self.amount);
809 debruijn.shifted_out(self.amount)
812 self.tcx.mk_const(ty::Const { val: ty::ConstKind::Bound(debruijn, bound_ct), ty })
815 ct.super_fold_with(self)
820 pub fn shift_region<'tcx>(
822 region: ty::Region<'tcx>,
824 ) -> ty::Region<'tcx> {
826 ty::ReLateBound(debruijn, br) if amount > 0 => {
827 tcx.mk_region(ty::ReLateBound(debruijn.shifted_in(amount), *br))
833 pub fn shift_vars<'tcx, T>(tcx: TyCtxt<'tcx>, value: &T, amount: u32) -> T
835 T: TypeFoldable<'tcx>,
837 debug!("shift_vars(value={:?}, amount={})", value, amount);
839 value.fold_with(&mut Shifter::new(tcx, amount, Direction::In))
842 pub fn shift_out_vars<'tcx, T>(tcx: TyCtxt<'tcx>, value: &T, amount: u32) -> T
844 T: TypeFoldable<'tcx>,
846 debug!("shift_out_vars(value={:?}, amount={})", value, amount);
848 value.fold_with(&mut Shifter::new(tcx, amount, Direction::Out))
851 /// An "escaping var" is a bound var whose binder is not part of `t`. A bound var can be a
852 /// bound region or a bound type.
854 /// So, for example, consider a type like the following, which has two binders:
856 /// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize))
857 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope
858 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope
860 /// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the
861 /// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner
862 /// fn type*, that type has an escaping region: `'a`.
864 /// Note that what I'm calling an "escaping var" is often just called a "free var". However,
865 /// we already use the term "free var". It refers to the regions or types that we use to represent
866 /// bound regions or type params on a fn definition while we are type checking its body.
868 /// To clarify, conceptually there is no particular difference between
869 /// an "escaping" var and a "free" var. However, there is a big
870 /// difference in practice. Basically, when "entering" a binding
871 /// level, one is generally required to do some sort of processing to
872 /// a bound var, such as replacing it with a fresh/placeholder
873 /// var, or making an entry in the environment to represent the
874 /// scope to which it is attached, etc. An escaping var represents
875 /// a bound var for which this processing has not yet been done.
876 struct HasEscapingVarsVisitor {
877 /// Anything bound by `outer_index` or "above" is escaping.
878 outer_index: ty::DebruijnIndex,
881 impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
882 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
883 self.outer_index.shift_in(1);
884 let result = t.super_visit_with(self);
885 self.outer_index.shift_out(1);
889 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
890 // If the outer-exclusive-binder is *strictly greater* than
891 // `outer_index`, that means that `t` contains some content
892 // bound at `outer_index` or above (because
893 // `outer_exclusive_binder` is always 1 higher than the
894 // content in `t`). Therefore, `t` has some escaping vars.
895 t.outer_exclusive_binder > self.outer_index
898 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
899 // If the region is bound by `outer_index` or anything outside
900 // of outer index, then it escapes the binders we have
902 r.bound_at_or_above_binder(self.outer_index)
905 fn visit_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> bool {
906 // we don't have a `visit_infer_const` callback, so we have to
907 // hook in here to catch this case (annoying...), but
908 // otherwise we do want to remember to visit the rest of the
909 // const, as it has types/regions embedded in a lot of other
912 ty::ConstKind::Bound(debruijn, _) if debruijn >= self.outer_index => true,
913 _ => ct.super_visit_with(self),
918 impl<'tcx> PredicateVisitor<'tcx> for HasEscapingVarsVisitor {
919 fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> bool {
920 predicate.inner.outer_exclusive_binder > self.outer_index
924 // FIXME: Optimize for checking for infer flags
925 struct HasTypeFlagsVisitor {
926 flags: ty::TypeFlags,
929 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
930 fn visit_ty(&mut self, t: Ty<'_>) -> bool {
931 debug!("HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}", t, t.flags, self.flags);
932 t.flags.intersects(self.flags)
935 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
936 let flags = r.type_flags();
937 debug!("HasTypeFlagsVisitor: r={:?} r.flags={:?} self.flags={:?}", r, flags, self.flags);
938 flags.intersects(self.flags)
941 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
942 let flags = FlagComputation::for_const(c);
943 debug!("HasTypeFlagsVisitor: c={:?} c.flags={:?} self.flags={:?}", c, flags, self.flags);
944 flags.intersects(self.flags)
948 impl<'tcx> PredicateVisitor<'tcx> for HasTypeFlagsVisitor {
949 fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> bool {
951 "HasTypeFlagsVisitor: predicate={:?} predicate.flags={:?} self.flags={:?}",
952 predicate, predicate.inner.flags, self.flags
954 predicate.inner.flags.intersects(self.flags)
957 /// Collects all the late-bound regions at the innermost binding level
959 struct LateBoundRegionsCollector {
960 current_index: ty::DebruijnIndex,
961 regions: FxHashSet<ty::BoundRegion>,
963 /// `true` if we only want regions that are known to be
964 /// "constrained" when you equate this type with another type. In
965 /// particular, if you have e.g., `&'a u32` and `&'b u32`, equating
966 /// them constraints `'a == 'b`. But if you have `<&'a u32 as
967 /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
968 /// types may mean that `'a` and `'b` don't appear in the results,
969 /// so they are not considered *constrained*.
970 just_constrained: bool,
973 impl LateBoundRegionsCollector {
974 fn new(just_constrained: bool) -> Self {
975 LateBoundRegionsCollector {
976 current_index: ty::INNERMOST,
977 regions: Default::default(),
983 impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
984 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
985 self.current_index.shift_in(1);
986 let result = t.super_visit_with(self);
987 self.current_index.shift_out(1);
991 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
992 // if we are only looking for "constrained" region, we have to
993 // ignore the inputs to a projection, as they may not appear
994 // in the normalized form
995 if self.just_constrained {
996 if let ty::Projection(..) | ty::Opaque(..) = t.kind {
1001 t.super_visit_with(self)
1004 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
1005 // if we are only looking for "constrained" region, we have to
1006 // ignore the inputs of an unevaluated const, as they may not appear
1007 // in the normalized form
1008 if self.just_constrained {
1009 if let ty::ConstKind::Unevaluated(..) = c.val {
1014 c.super_visit_with(self)
1017 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
1018 if let ty::ReLateBound(debruijn, br) = *r {
1019 if debruijn == self.current_index {
1020 self.regions.insert(br);