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::hir::def_id::DefId;
35 use crate::mir::interpret::ConstValue;
36 use crate::ty::{self, Binder, Ty, TyCtxt, TypeFlags, flags::FlagComputation};
38 use std::collections::BTreeMap;
40 use crate::util::nodemap::FxHashSet;
42 /// This trait is implemented for every type that can be folded.
43 /// Basically, every type that has a corresponding method in `TypeFolder`.
45 /// To implement this conveniently, use the
46 /// `BraceStructTypeFoldableImpl` etc macros found in `macros.rs`.
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 references_error(&self) -> bool {
83 self.has_type_flags(TypeFlags::HAS_TY_ERR)
85 fn has_param_types(&self) -> bool {
86 self.has_type_flags(TypeFlags::HAS_PARAMS)
88 fn has_infer_types(&self) -> bool {
89 self.has_type_flags(TypeFlags::HAS_TY_INFER)
91 fn has_infer_consts(&self) -> bool {
92 self.has_type_flags(TypeFlags::HAS_CT_INFER)
94 fn has_local_value(&self) -> bool {
95 self.has_type_flags(TypeFlags::KEEP_IN_LOCAL_TCX)
97 fn needs_infer(&self) -> bool {
99 TypeFlags::HAS_TY_INFER | TypeFlags::HAS_RE_INFER | TypeFlags::HAS_CT_INFER
102 fn has_placeholders(&self) -> bool {
104 TypeFlags::HAS_RE_PLACEHOLDER |
105 TypeFlags::HAS_TY_PLACEHOLDER |
106 TypeFlags::HAS_CT_PLACEHOLDER
109 fn needs_subst(&self) -> bool {
110 self.has_type_flags(TypeFlags::NEEDS_SUBST)
112 fn has_re_placeholders(&self) -> bool {
113 self.has_type_flags(TypeFlags::HAS_RE_PLACEHOLDER)
115 fn has_closure_types(&self) -> bool {
116 self.has_type_flags(TypeFlags::HAS_TY_CLOSURE)
118 /// "Free" regions in this context means that it has any region
119 /// that is not (a) erased or (b) late-bound.
120 fn has_free_regions(&self) -> bool {
121 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
124 /// True if there are any un-erased free regions.
125 fn has_erasable_regions(&self) -> bool {
126 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
129 /// Indicates whether this value references only 'global'
130 /// generic parameters that are the same regardless of what fn we are
131 /// in. This is used for caching.
132 fn is_global(&self) -> bool {
133 !self.has_type_flags(TypeFlags::HAS_FREE_LOCAL_NAMES)
136 /// True if there are any late-bound regions
137 fn has_late_bound_regions(&self) -> bool {
138 self.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND)
141 /// A visitor that does not recurse into types, works like `fn walk_shallow` in `Ty`.
142 fn visit_tys_shallow(&self, visit: impl FnMut(Ty<'tcx>) -> bool) -> bool {
144 pub struct Visitor<F>(F);
146 impl<'tcx, F: FnMut(Ty<'tcx>) -> bool> TypeVisitor<'tcx> for Visitor<F> {
147 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
152 self.visit_with(&mut Visitor(visit))
156 /// The `TypeFolder` trait defines the actual *folding*. There is a
157 /// method defined for every foldable type. Each of these has a
158 /// default implementation that does an "identity" fold. Within each
159 /// identity fold, it should invoke `foo.fold_with(self)` to fold each
161 pub trait TypeFolder<'tcx>: Sized {
162 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
164 fn fold_binder<T>(&mut self, t: &Binder<T>) -> Binder<T>
165 where T : TypeFoldable<'tcx>
167 t.super_fold_with(self)
170 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
171 t.super_fold_with(self)
174 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
175 r.super_fold_with(self)
178 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
179 c.super_fold_with(self)
183 pub trait TypeVisitor<'tcx> : Sized {
184 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
185 t.super_visit_with(self)
188 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
189 t.super_visit_with(self)
192 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
193 r.super_visit_with(self)
196 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
197 c.super_visit_with(self)
201 ///////////////////////////////////////////////////////////////////////////
202 // Some sample folders
204 pub struct BottomUpFolder<'tcx, F, G, H>
206 F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
207 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
208 H: FnMut(&'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>,
210 pub tcx: TyCtxt<'tcx>,
216 impl<'tcx, F, G, H> TypeFolder<'tcx> for BottomUpFolder<'tcx, F, G, H>
218 F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
219 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
220 H: FnMut(&'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>,
222 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
226 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
227 let t = ty.super_fold_with(self);
231 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
232 let r = r.super_fold_with(self);
236 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
237 let ct = ct.super_fold_with(self);
242 ///////////////////////////////////////////////////////////////////////////
245 impl<'tcx> TyCtxt<'tcx> {
246 /// Collects the free and escaping regions in `value` into `region_set`. Returns
247 /// whether any late-bound regions were skipped
248 pub fn collect_regions<T>(self,
250 region_set: &mut FxHashSet<ty::Region<'tcx>>)
252 where T : TypeFoldable<'tcx>
254 let mut have_bound_regions = false;
255 self.fold_regions(value, &mut have_bound_regions, |r, d| {
256 region_set.insert(self.mk_region(r.shifted_out_to_binder(d)));
262 /// Folds the escaping and free regions in `value` using `f`, and
263 /// sets `skipped_regions` to true if any late-bound region was found
265 pub fn fold_regions<T>(
268 skipped_regions: &mut bool,
269 mut f: impl FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
272 T : TypeFoldable<'tcx>,
274 value.fold_with(&mut RegionFolder::new(self, skipped_regions, &mut f))
277 /// Invoke `callback` on every region appearing free in `value`.
278 pub fn for_each_free_region(
280 value: &impl TypeFoldable<'tcx>,
281 mut callback: impl FnMut(ty::Region<'tcx>),
283 self.any_free_region_meets(value, |r| {
289 /// Returns `true` if `callback` returns true for every region appearing free in `value`.
290 pub fn all_free_regions_meet(
292 value: &impl TypeFoldable<'tcx>,
293 mut callback: impl FnMut(ty::Region<'tcx>) -> bool,
295 !self.any_free_region_meets(value, |r| !callback(r))
298 /// Returns `true` if `callback` returns true for some region appearing free in `value`.
299 pub fn any_free_region_meets(
301 value: &impl TypeFoldable<'tcx>,
302 callback: impl FnMut(ty::Region<'tcx>) -> bool,
304 return value.visit_with(&mut RegionVisitor {
305 outer_index: ty::INNERMOST,
309 struct RegionVisitor<F> {
310 /// The index of a binder *just outside* the things we have
311 /// traversed. If we encounter a bound region bound by this
312 /// binder or one outer to it, it appears free. Example:
315 /// for<'a> fn(for<'b> fn(), T)
317 /// | | | | here, would be shifted in 1
318 /// | | | here, would be shifted in 2
319 /// | | here, would be `INNERMOST` shifted in by 1
320 /// | here, initially, binder would be `INNERMOST`
323 /// You see that, initially, *any* bound value is free,
324 /// because we've not traversed any binders. As we pass
325 /// through a binder, we shift the `outer_index` by 1 to
326 /// account for the new binder that encloses us.
327 outer_index: ty::DebruijnIndex,
331 impl<'tcx, F> TypeVisitor<'tcx> for RegionVisitor<F>
332 where F: FnMut(ty::Region<'tcx>) -> bool
334 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
335 self.outer_index.shift_in(1);
336 let result = t.skip_binder().visit_with(self);
337 self.outer_index.shift_out(1);
341 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
343 ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => {
344 false // ignore bound regions, keep visiting
346 _ => (self.callback)(r),
350 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
351 // We're only interested in types involving regions
352 if ty.flags.intersects(TypeFlags::HAS_FREE_REGIONS) {
353 ty.super_visit_with(self)
355 false // keep visiting
362 /// Folds over the substructure of a type, visiting its component
363 /// types and all regions that occur *free* within it.
365 /// That is, `Ty` can contain function or method types that bind
366 /// regions at the call site (`ReLateBound`), and occurrences of
367 /// regions (aka "lifetimes") that are bound within a type are not
368 /// visited by this folder; only regions that occur free will be
369 /// visited by `fld_r`.
371 pub struct RegionFolder<'a, 'tcx> {
373 skipped_regions: &'a mut bool,
375 /// Stores the index of a binder *just outside* the stuff we have
376 /// visited. So this begins as INNERMOST; when we pass through a
377 /// binder, it is incremented (via `shift_in`).
378 current_index: ty::DebruijnIndex,
380 /// Callback invokes for each free region. The `DebruijnIndex`
381 /// points to the binder *just outside* the ones we have passed
384 &'a mut (dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx> + 'a),
387 impl<'a, 'tcx> RegionFolder<'a, 'tcx> {
391 skipped_regions: &'a mut bool,
392 fold_region_fn: &'a mut dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
393 ) -> RegionFolder<'a, 'tcx> {
397 current_index: ty::INNERMOST,
403 impl<'a, 'tcx> TypeFolder<'tcx> for RegionFolder<'a, 'tcx> {
404 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
408 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
409 self.current_index.shift_in(1);
410 let t = t.super_fold_with(self);
411 self.current_index.shift_out(1);
415 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
417 ty::ReLateBound(debruijn, _) if debruijn < self.current_index => {
418 debug!("RegionFolder.fold_region({:?}) skipped bound region (current index={:?})",
419 r, self.current_index);
420 *self.skipped_regions = true;
424 debug!("RegionFolder.fold_region({:?}) folding free region (current_index={:?})",
425 r, self.current_index);
426 (self.fold_region_fn)(r, self.current_index)
432 ///////////////////////////////////////////////////////////////////////////
433 // Bound vars replacer
435 /// Replaces the escaping bound vars (late bound regions or bound types) in a type.
436 struct BoundVarReplacer<'a, 'tcx> {
439 /// As with `RegionFolder`, represents the index of a binder *just outside*
440 /// the ones we have visited.
441 current_index: ty::DebruijnIndex,
443 fld_r: &'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a),
444 fld_t: &'a mut (dyn FnMut(ty::BoundTy) -> Ty<'tcx> + 'a),
445 fld_c: &'a mut (dyn FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx> + 'a),
448 impl<'a, 'tcx> BoundVarReplacer<'a, 'tcx> {
449 fn new<F, G, H>(tcx: TyCtxt<'tcx>, fld_r: &'a mut F, fld_t: &'a mut G, fld_c: &'a mut H) -> Self
451 F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
452 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
453 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
457 current_index: ty::INNERMOST,
465 impl<'a, 'tcx> TypeFolder<'tcx> for BoundVarReplacer<'a, 'tcx> {
466 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
470 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
471 self.current_index.shift_in(1);
472 let t = t.super_fold_with(self);
473 self.current_index.shift_out(1);
477 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
479 ty::Bound(debruijn, bound_ty) => {
480 if debruijn == self.current_index {
481 let fld_t = &mut self.fld_t;
482 let ty = fld_t(bound_ty);
483 ty::fold::shift_vars(
486 self.current_index.as_u32()
493 if !t.has_vars_bound_at_or_above(self.current_index) {
494 // Nothing more to substitute.
497 t.super_fold_with(self)
503 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
505 ty::ReLateBound(debruijn, br) if debruijn == self.current_index => {
506 let fld_r = &mut self.fld_r;
507 let region = fld_r(br);
508 if let ty::ReLateBound(debruijn1, br) = *region {
509 // If the callback returns a late-bound region,
510 // that region should always use the INNERMOST
511 // debruijn index. Then we adjust it to the
513 assert_eq!(debruijn1, ty::INNERMOST);
514 self.tcx.mk_region(ty::ReLateBound(debruijn, br))
523 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
525 val: ConstValue::Infer(ty::InferConst::Canonical(debruijn, bound_const)),
528 if debruijn == self.current_index {
529 let fld_c = &mut self.fld_c;
530 let ct = fld_c(bound_const, ty);
531 ty::fold::shift_vars(
534 self.current_index.as_u32()
540 if !ct.has_vars_bound_at_or_above(self.current_index) {
541 // Nothing more to substitute.
544 ct.super_fold_with(self)
550 impl<'tcx> TyCtxt<'tcx> {
551 /// Replaces all regions bound by the given `Binder` with the
552 /// results returned by the closure; the closure is expected to
553 /// return a free region (relative to this binder), and hence the
554 /// binder is removed in the return type. The closure is invoked
555 /// once for each unique `BoundRegion`; multiple references to the
556 /// same `BoundRegion` will reuse the previous result. A map is
557 /// returned at the end with each bound region and the free region
558 /// that replaced it.
560 /// This method only replaces late bound regions and the result may still
561 /// contain escaping bound types.
562 pub fn replace_late_bound_regions<T, F>(
566 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
567 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
568 T: TypeFoldable<'tcx>
570 // identity for bound types and consts
571 let fld_t = |bound_ty| self.mk_ty(ty::Bound(ty::INNERMOST, bound_ty));
572 let fld_c = |bound_ct, ty| {
573 self.mk_const_infer(ty::InferConst::Canonical(ty::INNERMOST, bound_ct), ty)
575 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t, fld_c)
578 /// Replaces all escaping bound vars. The `fld_r` closure replaces escaping
579 /// bound regions; the `fld_t` closure replaces escaping bound types and the `fld_c`
580 /// closure replaces escaping bound consts.
581 pub fn replace_escaping_bound_vars<T, F, G, H>(
587 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
588 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
589 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
590 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
591 T: TypeFoldable<'tcx>,
593 use rustc_data_structures::fx::FxHashMap;
595 let mut region_map = BTreeMap::new();
596 let mut type_map = FxHashMap::default();
597 let mut const_map = FxHashMap::default();
599 if !value.has_escaping_bound_vars() {
600 (value.clone(), region_map)
602 let mut real_fld_r = |br| {
603 *region_map.entry(br).or_insert_with(|| fld_r(br))
606 let mut real_fld_t = |bound_ty| {
607 *type_map.entry(bound_ty).or_insert_with(|| fld_t(bound_ty))
610 let mut real_fld_c = |bound_ct, ty| {
611 *const_map.entry(bound_ct).or_insert_with(|| fld_c(bound_ct, ty))
614 let mut replacer = BoundVarReplacer::new(
620 let result = value.fold_with(&mut replacer);
625 /// Replaces all types or regions bound by the given `Binder`. The `fld_r`
626 /// closure replaces bound regions while the `fld_t` closure replaces bound
628 pub fn replace_bound_vars<T, F, G, H>(
634 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
635 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
636 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
637 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
638 T: TypeFoldable<'tcx>
640 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t, fld_c)
643 /// Replaces any late-bound regions bound in `value` with
644 /// free variants attached to `all_outlive_scope`.
645 pub fn liberate_late_bound_regions<T>(
647 all_outlive_scope: DefId,
648 value: &ty::Binder<T>
650 where T: TypeFoldable<'tcx> {
651 self.replace_late_bound_regions(value, |br| {
652 self.mk_region(ty::ReFree(ty::FreeRegion {
653 scope: all_outlive_scope,
659 /// Returns a set of all late-bound regions that are constrained
660 /// by `value`, meaning that if we instantiate those LBR with
661 /// variables and equate `value` with something else, those
662 /// variables will also be equated.
663 pub fn collect_constrained_late_bound_regions<T>(&self, value: &Binder<T>)
664 -> FxHashSet<ty::BoundRegion>
665 where T : TypeFoldable<'tcx>
667 self.collect_late_bound_regions(value, true)
670 /// Returns a set of all late-bound regions that appear in `value` anywhere.
671 pub fn collect_referenced_late_bound_regions<T>(&self, value: &Binder<T>)
672 -> FxHashSet<ty::BoundRegion>
673 where T : TypeFoldable<'tcx>
675 self.collect_late_bound_regions(value, false)
678 fn collect_late_bound_regions<T>(&self, value: &Binder<T>, just_constraint: bool)
679 -> FxHashSet<ty::BoundRegion>
680 where T : TypeFoldable<'tcx>
682 let mut collector = LateBoundRegionsCollector::new(just_constraint);
683 let result = value.skip_binder().visit_with(&mut collector);
684 assert!(!result); // should never have stopped early
688 /// Replaces any late-bound regions bound in `value` with `'erased`. Useful in codegen but also
689 /// method lookup and a few other places where precise region relationships are not required.
690 pub fn erase_late_bound_regions<T>(self, value: &Binder<T>) -> T
691 where 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>
705 where T : TypeFoldable<'tcx>,
708 Binder::bind(self.replace_late_bound_regions(sig, |_| {
710 self.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BrAnon(counter)))
715 ///////////////////////////////////////////////////////////////////////////
718 // Shifts the De Bruijn indices on all escaping bound vars by a
719 // fixed amount. Useful in substitution or when otherwise introducing
720 // a binding level that is not intended to capture the existing bound
721 // vars. See comment on `shift_vars_through_binders` method in
722 // `subst.rs` for more details.
724 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
730 struct Shifter<'tcx> {
732 current_index: ty::DebruijnIndex,
734 direction: Direction,
738 pub fn new(tcx: TyCtxt<'tcx>, amount: u32, direction: Direction) -> Self {
741 current_index: ty::INNERMOST,
748 impl TypeFolder<'tcx> for Shifter<'tcx> {
749 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
753 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
754 self.current_index.shift_in(1);
755 let t = t.super_fold_with(self);
756 self.current_index.shift_out(1);
760 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
762 ty::ReLateBound(debruijn, br) => {
763 if self.amount == 0 || debruijn < self.current_index {
766 let debruijn = match self.direction {
767 Direction::In => debruijn.shifted_in(self.amount),
769 assert!(debruijn.as_u32() >= self.amount);
770 debruijn.shifted_out(self.amount)
773 let shifted = ty::ReLateBound(debruijn, br);
774 self.tcx.mk_region(shifted)
781 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
783 ty::Bound(debruijn, bound_ty) => {
784 if self.amount == 0 || debruijn < self.current_index {
787 let debruijn = match self.direction {
788 Direction::In => debruijn.shifted_in(self.amount),
790 assert!(debruijn.as_u32() >= self.amount);
791 debruijn.shifted_out(self.amount)
795 ty::Bound(debruijn, bound_ty)
800 _ => ty.super_fold_with(self),
804 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
806 val: ConstValue::Infer(ty::InferConst::Canonical(debruijn, bound_const)),
809 if self.amount == 0 || debruijn < self.current_index {
812 let debruijn = match self.direction {
813 Direction::In => debruijn.shifted_in(self.amount),
815 assert!(debruijn.as_u32() >= self.amount);
816 debruijn.shifted_out(self.amount)
819 self.tcx.mk_const_infer(ty::InferConst::Canonical(debruijn, bound_const), ty)
822 ct.super_fold_with(self)
827 pub fn shift_region<'tcx>(
829 region: ty::Region<'tcx>,
831 ) -> ty::Region<'tcx> {
833 ty::ReLateBound(debruijn, br) if amount > 0 => {
834 tcx.mk_region(ty::ReLateBound(debruijn.shifted_in(amount), *br))
842 pub fn shift_vars<'tcx, T>(tcx: TyCtxt<'tcx>, value: &T, amount: u32) -> T
844 T: TypeFoldable<'tcx>,
846 debug!("shift_vars(value={:?}, amount={})",
849 value.fold_with(&mut Shifter::new(tcx, amount, Direction::In))
852 pub fn shift_out_vars<'tcx, T>(tcx: TyCtxt<'tcx>, value: &T, amount: u32) -> T
854 T: TypeFoldable<'tcx>,
856 debug!("shift_out_vars(value={:?}, amount={})",
859 value.fold_with(&mut Shifter::new(tcx, amount, Direction::Out))
862 /// An "escaping var" is a bound var whose binder is not part of `t`. A bound var can be a
863 /// bound region or a bound type.
865 /// So, for example, consider a type like the following, which has two binders:
867 /// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize))
868 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope
869 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope
871 /// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the
872 /// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner
873 /// fn type*, that type has an escaping region: `'a`.
875 /// Note that what I'm calling an "escaping var" is often just called a "free var". However,
876 /// we already use the term "free var". It refers to the regions or types that we use to represent
877 /// bound regions or type params on a fn definition while we are type checking its body.
879 /// To clarify, conceptually there is no particular difference between
880 /// an "escaping" var and a "free" var. However, there is a big
881 /// difference in practice. Basically, when "entering" a binding
882 /// level, one is generally required to do some sort of processing to
883 /// a bound var, such as replacing it with a fresh/placeholder
884 /// var, or making an entry in the environment to represent the
885 /// scope to which it is attached, etc. An escaping var represents
886 /// a bound var for which this processing has not yet been done.
887 struct HasEscapingVarsVisitor {
888 /// Anything bound by `outer_index` or "above" is escaping.
889 outer_index: ty::DebruijnIndex,
892 impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
893 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
894 self.outer_index.shift_in(1);
895 let result = t.super_visit_with(self);
896 self.outer_index.shift_out(1);
900 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
901 // If the outer-exclusive-binder is *strictly greater* than
902 // `outer_index`, that means that `t` contains some content
903 // bound at `outer_index` or above (because
904 // `outer_exclusive_binder` is always 1 higher than the
905 // content in `t`). Therefore, `t` has some escaping vars.
906 t.outer_exclusive_binder > self.outer_index
909 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
910 // If the region is bound by `outer_index` or anything outside
911 // of outer index, then it escapes the binders we have
913 r.bound_at_or_above_binder(self.outer_index)
916 fn visit_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> bool {
917 // we don't have a `visit_infer_const` callback, so we have to
918 // hook in here to catch this case (annoying...), but
919 // otherwise we do want to remember to visit the rest of the
920 // const, as it has types/regions embedded in a lot of other
923 ConstValue::Infer(ty::InferConst::Canonical(debruijn, _))
924 if debruijn >= self.outer_index => true,
925 _ => ct.super_visit_with(self),
930 // FIXME: Optimize for checking for infer flags
931 struct HasTypeFlagsVisitor {
932 flags: ty::TypeFlags,
935 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
936 fn visit_ty(&mut self, t: Ty<'_>) -> bool {
937 debug!("HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}", t, t.flags, self.flags);
938 t.flags.intersects(self.flags)
941 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
942 let flags = r.type_flags();
943 debug!("HasTypeFlagsVisitor: r={:?} r.flags={:?} self.flags={:?}", r, flags, self.flags);
944 flags.intersects(self.flags)
947 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
948 let flags = FlagComputation::for_const(c);
949 debug!("HasTypeFlagsVisitor: c={:?} c.flags={:?} self.flags={:?}", c, flags, self.flags);
950 flags.intersects(self.flags)
954 /// Collects all the late-bound regions at the innermost binding level
956 struct LateBoundRegionsCollector {
957 current_index: ty::DebruijnIndex,
958 regions: FxHashSet<ty::BoundRegion>,
960 /// `true` if we only want regions that are known to be
961 /// "constrained" when you equate this type with another type. In
962 /// particular, if you have e.g., `&'a u32` and `&'b u32`, equating
963 /// them constraints `'a == 'b`. But if you have `<&'a u32 as
964 /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
965 /// types may mean that `'a` and `'b` don't appear in the results,
966 /// so they are not considered *constrained*.
967 just_constrained: bool,
970 impl LateBoundRegionsCollector {
971 fn new(just_constrained: bool) -> Self {
972 LateBoundRegionsCollector {
973 current_index: ty::INNERMOST,
974 regions: Default::default(),
980 impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
981 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
982 self.current_index.shift_in(1);
983 let result = t.super_visit_with(self);
984 self.current_index.shift_out(1);
988 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
989 // if we are only looking for "constrained" region, we have to
990 // ignore the inputs to a projection, as they may not appear
991 // in the normalized form
992 if self.just_constrained {
994 ty::Projection(..) | ty::Opaque(..) => { return false; }
999 t.super_visit_with(self)
1002 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
1003 if let ty::ReLateBound(debruijn, br) = *r {
1004 if debruijn == self.current_index {
1005 self.regions.insert(br);