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::ty::{self, Binder, Ty, TyCtxt, TypeFlags, flags::FlagComputation};
37 use std::collections::BTreeMap;
39 use crate::util::nodemap::FxHashSet;
41 /// This trait is implemented for every type that can be folded.
42 /// Basically, every type that has a corresponding method in `TypeFolder`.
44 /// To implement this conveniently, use the derive macro located in librustc_macros.
45 pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
46 fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self;
47 fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self {
48 self.super_fold_with(folder)
51 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool;
52 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
53 self.super_visit_with(visitor)
56 /// Returns `true` if `self` has any late-bound regions that are either
57 /// bound by `binder` or bound by some binder outside of `binder`.
58 /// If `binder` is `ty::INNERMOST`, this indicates whether
59 /// there are any late-bound regions that appear free.
60 fn has_vars_bound_at_or_above(&self, binder: ty::DebruijnIndex) -> bool {
61 self.visit_with(&mut HasEscapingVarsVisitor { outer_index: binder })
64 /// Returns `true` if this `self` has any regions that escape `binder` (and
65 /// hence are not bound by it).
66 fn has_vars_bound_above(&self, binder: ty::DebruijnIndex) -> bool {
67 self.has_vars_bound_at_or_above(binder.shifted_in(1))
70 fn has_escaping_bound_vars(&self) -> bool {
71 self.has_vars_bound_at_or_above(ty::INNERMOST)
74 fn has_type_flags(&self, flags: TypeFlags) -> bool {
75 self.visit_with(&mut HasTypeFlagsVisitor { flags })
77 fn has_projections(&self) -> bool {
78 self.has_type_flags(TypeFlags::HAS_PROJECTION)
80 fn references_error(&self) -> bool {
81 self.has_type_flags(TypeFlags::HAS_TY_ERR)
83 fn has_param_types(&self) -> bool {
84 self.has_type_flags(TypeFlags::HAS_PARAMS)
86 fn has_infer_types(&self) -> bool {
87 self.has_type_flags(TypeFlags::HAS_TY_INFER)
89 fn has_infer_consts(&self) -> bool {
90 self.has_type_flags(TypeFlags::HAS_CT_INFER)
92 fn has_local_value(&self) -> bool {
93 self.has_type_flags(TypeFlags::KEEP_IN_LOCAL_TCX)
95 fn needs_infer(&self) -> bool {
97 TypeFlags::HAS_TY_INFER | TypeFlags::HAS_RE_INFER | TypeFlags::HAS_CT_INFER
100 fn has_placeholders(&self) -> bool {
102 TypeFlags::HAS_RE_PLACEHOLDER |
103 TypeFlags::HAS_TY_PLACEHOLDER |
104 TypeFlags::HAS_CT_PLACEHOLDER
107 fn needs_subst(&self) -> bool {
108 self.has_type_flags(TypeFlags::NEEDS_SUBST)
110 fn has_re_placeholders(&self) -> bool {
111 self.has_type_flags(TypeFlags::HAS_RE_PLACEHOLDER)
113 fn has_closure_types(&self) -> bool {
114 self.has_type_flags(TypeFlags::HAS_TY_CLOSURE)
116 /// "Free" regions in this context means that it has any region
117 /// that is not (a) erased or (b) late-bound.
118 fn has_free_regions(&self) -> bool {
119 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
122 /// True if there are any un-erased free regions.
123 fn has_erasable_regions(&self) -> bool {
124 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
127 /// Indicates whether this value references only 'global'
128 /// generic parameters that are the same regardless of what fn we are
129 /// in. This is used for caching.
130 fn is_global(&self) -> bool {
131 !self.has_type_flags(TypeFlags::HAS_FREE_LOCAL_NAMES)
134 /// True if there are any late-bound regions
135 fn has_late_bound_regions(&self) -> bool {
136 self.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND)
139 /// A visitor that does not recurse into types, works like `fn walk_shallow` in `Ty`.
140 fn visit_tys_shallow(&self, visit: impl FnMut(Ty<'tcx>) -> bool) -> bool {
142 pub struct Visitor<F>(F);
144 impl<'tcx, F: FnMut(Ty<'tcx>) -> bool> TypeVisitor<'tcx> for Visitor<F> {
145 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
150 self.visit_with(&mut Visitor(visit))
154 /// The `TypeFolder` trait defines the actual *folding*. There is a
155 /// method defined for every foldable type. Each of these has a
156 /// default implementation that does an "identity" fold. Within each
157 /// identity fold, it should invoke `foo.fold_with(self)` to fold each
159 pub trait TypeFolder<'tcx>: Sized {
160 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
162 fn fold_binder<T>(&mut self, t: &Binder<T>) -> Binder<T>
163 where T : TypeFoldable<'tcx>
165 t.super_fold_with(self)
168 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
169 t.super_fold_with(self)
172 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
173 r.super_fold_with(self)
176 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
177 c.super_fold_with(self)
181 pub trait TypeVisitor<'tcx> : Sized {
182 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
183 t.super_visit_with(self)
186 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
187 t.super_visit_with(self)
190 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
191 r.super_visit_with(self)
194 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
195 c.super_visit_with(self)
199 ///////////////////////////////////////////////////////////////////////////
200 // Some sample folders
202 pub struct BottomUpFolder<'tcx, F, G, H>
204 F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
205 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
206 H: FnMut(&'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>,
208 pub tcx: TyCtxt<'tcx>,
214 impl<'tcx, F, G, H> TypeFolder<'tcx> for BottomUpFolder<'tcx, F, G, H>
216 F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
217 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
218 H: FnMut(&'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>,
220 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
224 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
225 let t = ty.super_fold_with(self);
229 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
230 let r = r.super_fold_with(self);
234 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
235 let ct = ct.super_fold_with(self);
240 ///////////////////////////////////////////////////////////////////////////
243 impl<'tcx> TyCtxt<'tcx> {
244 /// Collects the free and escaping regions in `value` into `region_set`. Returns
245 /// whether any late-bound regions were skipped
246 pub fn collect_regions<T>(self,
248 region_set: &mut FxHashSet<ty::Region<'tcx>>)
250 where T : TypeFoldable<'tcx>
252 let mut have_bound_regions = false;
253 self.fold_regions(value, &mut have_bound_regions, |r, d| {
254 region_set.insert(self.mk_region(r.shifted_out_to_binder(d)));
260 /// Folds the escaping and free regions in `value` using `f`, and
261 /// sets `skipped_regions` to true if any late-bound region was found
263 pub fn fold_regions<T>(
266 skipped_regions: &mut bool,
267 mut f: impl FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
270 T : TypeFoldable<'tcx>,
272 value.fold_with(&mut RegionFolder::new(self, skipped_regions, &mut f))
275 /// Invoke `callback` on every region appearing free in `value`.
276 pub fn for_each_free_region(
278 value: &impl TypeFoldable<'tcx>,
279 mut callback: impl FnMut(ty::Region<'tcx>),
281 self.any_free_region_meets(value, |r| {
287 /// Returns `true` if `callback` returns true for every region appearing free in `value`.
288 pub fn all_free_regions_meet(
290 value: &impl TypeFoldable<'tcx>,
291 mut callback: impl FnMut(ty::Region<'tcx>) -> bool,
293 !self.any_free_region_meets(value, |r| !callback(r))
296 /// Returns `true` if `callback` returns true for some region appearing free in `value`.
297 pub fn any_free_region_meets(
299 value: &impl TypeFoldable<'tcx>,
300 callback: impl FnMut(ty::Region<'tcx>) -> bool,
302 return value.visit_with(&mut RegionVisitor {
303 outer_index: ty::INNERMOST,
307 struct RegionVisitor<F> {
308 /// The index of a binder *just outside* the things we have
309 /// traversed. If we encounter a bound region bound by this
310 /// binder or one outer to it, it appears free. Example:
313 /// for<'a> fn(for<'b> fn(), T)
315 /// | | | | here, would be shifted in 1
316 /// | | | here, would be shifted in 2
317 /// | | here, would be `INNERMOST` shifted in by 1
318 /// | here, initially, binder would be `INNERMOST`
321 /// You see that, initially, *any* bound value is free,
322 /// because we've not traversed any binders. As we pass
323 /// through a binder, we shift the `outer_index` by 1 to
324 /// account for the new binder that encloses us.
325 outer_index: ty::DebruijnIndex,
329 impl<'tcx, F> TypeVisitor<'tcx> for RegionVisitor<F>
330 where F: FnMut(ty::Region<'tcx>) -> bool
332 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
333 self.outer_index.shift_in(1);
334 let result = t.skip_binder().visit_with(self);
335 self.outer_index.shift_out(1);
339 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
341 ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => {
342 false // ignore bound regions, keep visiting
344 _ => (self.callback)(r),
348 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
349 // We're only interested in types involving regions
350 if ty.flags.intersects(TypeFlags::HAS_FREE_REGIONS) {
351 ty.super_visit_with(self)
353 false // keep visiting
360 /// Folds over the substructure of a type, visiting its component
361 /// types and all regions that occur *free* within it.
363 /// That is, `Ty` can contain function or method types that bind
364 /// regions at the call site (`ReLateBound`), and occurrences of
365 /// regions (aka "lifetimes") that are bound within a type are not
366 /// visited by this folder; only regions that occur free will be
367 /// visited by `fld_r`.
369 pub struct RegionFolder<'a, 'tcx> {
371 skipped_regions: &'a mut bool,
373 /// Stores the index of a binder *just outside* the stuff we have
374 /// visited. So this begins as INNERMOST; when we pass through a
375 /// binder, it is incremented (via `shift_in`).
376 current_index: ty::DebruijnIndex,
378 /// Callback invokes for each free region. The `DebruijnIndex`
379 /// points to the binder *just outside* the ones we have passed
382 &'a mut (dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx> + 'a),
385 impl<'a, 'tcx> RegionFolder<'a, 'tcx> {
389 skipped_regions: &'a mut bool,
390 fold_region_fn: &'a mut dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
391 ) -> RegionFolder<'a, 'tcx> {
395 current_index: ty::INNERMOST,
401 impl<'a, 'tcx> TypeFolder<'tcx> for RegionFolder<'a, 'tcx> {
402 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
406 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
407 self.current_index.shift_in(1);
408 let t = t.super_fold_with(self);
409 self.current_index.shift_out(1);
413 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
415 ty::ReLateBound(debruijn, _) if debruijn < self.current_index => {
416 debug!("RegionFolder.fold_region({:?}) skipped bound region (current index={:?})",
417 r, self.current_index);
418 *self.skipped_regions = true;
422 debug!("RegionFolder.fold_region({:?}) folding free region (current_index={:?})",
423 r, self.current_index);
424 (self.fold_region_fn)(r, self.current_index)
430 ///////////////////////////////////////////////////////////////////////////
431 // Bound vars replacer
433 /// Replaces the escaping bound vars (late bound regions or bound types) in a type.
434 struct BoundVarReplacer<'a, 'tcx> {
437 /// As with `RegionFolder`, represents the index of a binder *just outside*
438 /// the ones we have visited.
439 current_index: ty::DebruijnIndex,
441 fld_r: &'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a),
442 fld_t: &'a mut (dyn FnMut(ty::BoundTy) -> Ty<'tcx> + 'a),
443 fld_c: &'a mut (dyn FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx> + 'a),
446 impl<'a, 'tcx> BoundVarReplacer<'a, 'tcx> {
447 fn new<F, G, H>(tcx: TyCtxt<'tcx>, fld_r: &'a mut F, fld_t: &'a mut G, fld_c: &'a mut H) -> Self
449 F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
450 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
451 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
455 current_index: ty::INNERMOST,
463 impl<'a, 'tcx> TypeFolder<'tcx> for BoundVarReplacer<'a, 'tcx> {
464 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
468 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
469 self.current_index.shift_in(1);
470 let t = t.super_fold_with(self);
471 self.current_index.shift_out(1);
475 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
477 ty::Bound(debruijn, bound_ty) => {
478 if debruijn == self.current_index {
479 let fld_t = &mut self.fld_t;
480 let ty = fld_t(bound_ty);
481 ty::fold::shift_vars(
484 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(
529 self.current_index.as_u32()
535 if !ct.has_vars_bound_at_or_above(self.current_index) {
536 // Nothing more to substitute.
539 ct.super_fold_with(self)
545 impl<'tcx> TyCtxt<'tcx> {
546 /// Replaces all regions bound by the given `Binder` with the
547 /// results returned by the closure; the closure is expected to
548 /// return a free region (relative to this binder), and hence the
549 /// binder is removed in the return type. The closure is invoked
550 /// once for each unique `BoundRegion`; multiple references to the
551 /// same `BoundRegion` will reuse the previous result. A map is
552 /// returned at the end with each bound region and the free region
553 /// that replaced it.
555 /// This method only replaces late bound regions and the result may still
556 /// contain escaping bound types.
557 pub fn replace_late_bound_regions<T, F>(
561 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
562 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
563 T: TypeFoldable<'tcx>
565 // identity for bound types and consts
566 let fld_t = |bound_ty| self.mk_ty(ty::Bound(ty::INNERMOST, bound_ty));
567 let fld_c = |bound_ct, ty| {
568 self.mk_const(ty::Const {
569 val: ty::ConstKind::Bound(ty::INNERMOST, bound_ct),
573 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t, fld_c)
576 /// Replaces all escaping bound vars. The `fld_r` closure replaces escaping
577 /// bound regions; the `fld_t` closure replaces escaping bound types and the `fld_c`
578 /// closure replaces escaping bound consts.
579 pub fn replace_escaping_bound_vars<T, F, G, H>(
585 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
586 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
587 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
588 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
589 T: TypeFoldable<'tcx>,
591 use rustc_data_structures::fx::FxHashMap;
593 let mut region_map = BTreeMap::new();
594 let mut type_map = FxHashMap::default();
595 let mut const_map = FxHashMap::default();
597 if !value.has_escaping_bound_vars() {
598 (value.clone(), region_map)
600 let mut real_fld_r = |br| {
601 *region_map.entry(br).or_insert_with(|| fld_r(br))
604 let mut real_fld_t = |bound_ty| {
605 *type_map.entry(bound_ty).or_insert_with(|| fld_t(bound_ty))
608 let mut real_fld_c = |bound_ct, ty| {
609 *const_map.entry(bound_ct).or_insert_with(|| fld_c(bound_ct, ty))
612 let mut replacer = BoundVarReplacer::new(
618 let result = value.fold_with(&mut replacer);
623 /// Replaces all types or regions bound by the given `Binder`. The `fld_r`
624 /// closure replaces bound regions while the `fld_t` closure replaces bound
626 pub fn replace_bound_vars<T, F, G, H>(
632 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
633 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
634 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
635 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
636 T: TypeFoldable<'tcx>
638 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t, fld_c)
641 /// Replaces any late-bound regions bound in `value` with
642 /// free variants attached to `all_outlive_scope`.
643 pub fn liberate_late_bound_regions<T>(
645 all_outlive_scope: DefId,
646 value: &ty::Binder<T>
648 where T: TypeFoldable<'tcx> {
649 self.replace_late_bound_regions(value, |br| {
650 self.mk_region(ty::ReFree(ty::FreeRegion {
651 scope: all_outlive_scope,
657 /// Returns a set of all late-bound regions that are constrained
658 /// by `value`, meaning that if we instantiate those LBR with
659 /// variables and equate `value` with something else, those
660 /// variables will also be equated.
661 pub fn collect_constrained_late_bound_regions<T>(&self, value: &Binder<T>)
662 -> FxHashSet<ty::BoundRegion>
663 where T : TypeFoldable<'tcx>
665 self.collect_late_bound_regions(value, true)
668 /// Returns a set of all late-bound regions that appear in `value` anywhere.
669 pub fn collect_referenced_late_bound_regions<T>(&self, value: &Binder<T>)
670 -> FxHashSet<ty::BoundRegion>
671 where T : TypeFoldable<'tcx>
673 self.collect_late_bound_regions(value, false)
676 fn collect_late_bound_regions<T>(&self, value: &Binder<T>, just_constraint: bool)
677 -> FxHashSet<ty::BoundRegion>
678 where T : TypeFoldable<'tcx>
680 let mut collector = LateBoundRegionsCollector::new(just_constraint);
681 let result = value.skip_binder().visit_with(&mut collector);
682 assert!(!result); // should never have stopped early
686 /// Replaces any late-bound regions bound in `value` with `'erased`. Useful in codegen but also
687 /// method lookup and a few other places where precise region relationships are not required.
688 pub fn erase_late_bound_regions<T>(self, value: &Binder<T>) -> T
689 where T : TypeFoldable<'tcx>
691 self.replace_late_bound_regions(value, |_| self.lifetimes.re_erased).0
694 /// Rewrite any late-bound regions so that they are anonymous. Region numbers are
695 /// assigned starting at 1 and increasing monotonically in the order traversed
696 /// by the fold operation.
698 /// The chief purpose of this function is to canonicalize regions so that two
699 /// `FnSig`s or `TraitRef`s which are equivalent up to region naming will become
700 /// structurally identical. For example, `for<'a, 'b> fn(&'a isize, &'b isize)` and
701 /// `for<'a, 'b> fn(&'b isize, &'a isize)` will become identical after anonymization.
702 pub fn anonymize_late_bound_regions<T>(self, sig: &Binder<T>) -> Binder<T>
703 where T : TypeFoldable<'tcx>,
706 Binder::bind(self.replace_late_bound_regions(sig, |_| {
708 self.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BrAnon(counter)))
713 ///////////////////////////////////////////////////////////////////////////
716 // Shifts the De Bruijn indices on all escaping bound vars by a
717 // fixed amount. Useful in substitution or when otherwise introducing
718 // a binding level that is not intended to capture the existing bound
719 // vars. See comment on `shift_vars_through_binders` method in
720 // `subst.rs` for more details.
727 struct Shifter<'tcx> {
729 current_index: ty::DebruijnIndex,
731 direction: Direction,
735 pub fn new(tcx: TyCtxt<'tcx>, amount: u32, direction: Direction) -> Self {
738 current_index: ty::INNERMOST,
745 impl TypeFolder<'tcx> for Shifter<'tcx> {
746 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
750 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
751 self.current_index.shift_in(1);
752 let t = t.super_fold_with(self);
753 self.current_index.shift_out(1);
757 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
759 ty::ReLateBound(debruijn, br) => {
760 if self.amount == 0 || debruijn < self.current_index {
763 let debruijn = match self.direction {
764 Direction::In => debruijn.shifted_in(self.amount),
766 assert!(debruijn.as_u32() >= self.amount);
767 debruijn.shifted_out(self.amount)
770 let shifted = ty::ReLateBound(debruijn, br);
771 self.tcx.mk_region(shifted)
778 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
780 ty::Bound(debruijn, bound_ty) => {
781 if self.amount == 0 || debruijn < self.current_index {
784 let debruijn = match self.direction {
785 Direction::In => debruijn.shifted_in(self.amount),
787 assert!(debruijn.as_u32() >= self.amount);
788 debruijn.shifted_out(self.amount)
792 ty::Bound(debruijn, bound_ty)
797 _ => ty.super_fold_with(self),
801 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
802 if let ty::Const { val: ty::ConstKind::Bound(debruijn, bound_ct), ty } = *ct {
803 if self.amount == 0 || debruijn < self.current_index {
806 let debruijn = match self.direction {
807 Direction::In => debruijn.shifted_in(self.amount),
809 assert!(debruijn.as_u32() >= self.amount);
810 debruijn.shifted_out(self.amount)
813 self.tcx.mk_const(ty::Const {
814 val: ty::ConstKind::Bound(debruijn, bound_ct),
819 ct.super_fold_with(self)
824 pub fn shift_region<'tcx>(
826 region: ty::Region<'tcx>,
828 ) -> ty::Region<'tcx> {
830 ty::ReLateBound(debruijn, br) if amount > 0 => {
831 tcx.mk_region(ty::ReLateBound(debruijn.shifted_in(amount), *br))
839 pub fn shift_vars<'tcx, T>(tcx: TyCtxt<'tcx>, value: &T, amount: u32) -> T
841 T: TypeFoldable<'tcx>,
843 debug!("shift_vars(value={:?}, amount={})",
846 value.fold_with(&mut Shifter::new(tcx, amount, Direction::In))
849 pub fn shift_out_vars<'tcx, T>(tcx: TyCtxt<'tcx>, value: &T, amount: u32) -> T
851 T: TypeFoldable<'tcx>,
853 debug!("shift_out_vars(value={:?}, amount={})",
856 value.fold_with(&mut Shifter::new(tcx, amount, Direction::Out))
859 /// An "escaping var" is a bound var whose binder is not part of `t`. A bound var can be a
860 /// bound region or a bound type.
862 /// So, for example, consider a type like the following, which has two binders:
864 /// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize))
865 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope
866 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope
868 /// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the
869 /// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner
870 /// fn type*, that type has an escaping region: `'a`.
872 /// Note that what I'm calling an "escaping var" is often just called a "free var". However,
873 /// we already use the term "free var". It refers to the regions or types that we use to represent
874 /// bound regions or type params on a fn definition while we are type checking its body.
876 /// To clarify, conceptually there is no particular difference between
877 /// an "escaping" var and a "free" var. However, there is a big
878 /// difference in practice. Basically, when "entering" a binding
879 /// level, one is generally required to do some sort of processing to
880 /// a bound var, such as replacing it with a fresh/placeholder
881 /// var, or making an entry in the environment to represent the
882 /// scope to which it is attached, etc. An escaping var represents
883 /// a bound var for which this processing has not yet been done.
884 struct HasEscapingVarsVisitor {
885 /// Anything bound by `outer_index` or "above" is escaping.
886 outer_index: ty::DebruijnIndex,
889 impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
890 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
891 self.outer_index.shift_in(1);
892 let result = t.super_visit_with(self);
893 self.outer_index.shift_out(1);
897 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
898 // If the outer-exclusive-binder is *strictly greater* than
899 // `outer_index`, that means that `t` contains some content
900 // bound at `outer_index` or above (because
901 // `outer_exclusive_binder` is always 1 higher than the
902 // content in `t`). Therefore, `t` has some escaping vars.
903 t.outer_exclusive_binder > self.outer_index
906 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
907 // If the region is bound by `outer_index` or anything outside
908 // of outer index, then it escapes the binders we have
910 r.bound_at_or_above_binder(self.outer_index)
913 fn visit_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> bool {
914 // we don't have a `visit_infer_const` callback, so we have to
915 // hook in here to catch this case (annoying...), but
916 // otherwise we do want to remember to visit the rest of the
917 // const, as it has types/regions embedded in a lot of other
920 ty::ConstKind::Bound(debruijn, _) if debruijn >= self.outer_index => true,
921 _ => ct.super_visit_with(self),
926 // FIXME: Optimize for checking for infer flags
927 struct HasTypeFlagsVisitor {
928 flags: ty::TypeFlags,
931 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
932 fn visit_ty(&mut self, t: Ty<'_>) -> bool {
933 debug!("HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}", t, t.flags, self.flags);
934 t.flags.intersects(self.flags)
937 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
938 let flags = r.type_flags();
939 debug!("HasTypeFlagsVisitor: r={:?} r.flags={:?} self.flags={:?}", r, flags, self.flags);
940 flags.intersects(self.flags)
943 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
944 let flags = FlagComputation::for_const(c);
945 debug!("HasTypeFlagsVisitor: c={:?} c.flags={:?} self.flags={:?}", c, flags, self.flags);
946 flags.intersects(self.flags)
950 /// Collects all the late-bound regions at the innermost binding level
952 struct LateBoundRegionsCollector {
953 current_index: ty::DebruijnIndex,
954 regions: FxHashSet<ty::BoundRegion>,
956 /// `true` if we only want regions that are known to be
957 /// "constrained" when you equate this type with another type. In
958 /// particular, if you have e.g., `&'a u32` and `&'b u32`, equating
959 /// them constraints `'a == 'b`. But if you have `<&'a u32 as
960 /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
961 /// types may mean that `'a` and `'b` don't appear in the results,
962 /// so they are not considered *constrained*.
963 just_constrained: bool,
966 impl LateBoundRegionsCollector {
967 fn new(just_constrained: bool) -> Self {
968 LateBoundRegionsCollector {
969 current_index: ty::INNERMOST,
970 regions: Default::default(),
976 impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
977 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
978 self.current_index.shift_in(1);
979 let result = t.super_visit_with(self);
980 self.current_index.shift_out(1);
984 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
985 // if we are only looking for "constrained" region, we have to
986 // ignore the inputs to a projection, as they may not appear
987 // in the normalized form
988 if self.just_constrained {
990 ty::Projection(..) | ty::Opaque(..) => { return false; }
995 t.super_visit_with(self)
998 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
999 if let ty::ReLateBound(debruijn, br) = *r {
1000 if debruijn == self.current_index {
1001 self.regions.insert(br);