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};
37 use std::collections::BTreeMap;
39 use crate::util::nodemap::FxHashSet;
41 /// The TypeFoldable 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
45 /// `BraceStructTypeFoldableImpl` etc macros found in `macros.rs`.
46 pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
47 fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self;
48 fn fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
49 self.super_fold_with(folder)
52 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool;
53 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
54 self.super_visit_with(visitor)
57 /// Returns `true` if `self` has any late-bound regions that are either
58 /// bound by `binder` or bound by some binder outside of `binder`.
59 /// If `binder` is `ty::INNERMOST`, this indicates whether
60 /// there are any late-bound regions that appear free.
61 fn has_vars_bound_at_or_above(&self, binder: ty::DebruijnIndex) -> bool {
62 self.visit_with(&mut HasEscapingVarsVisitor { outer_index: binder })
65 /// Returns `true` if this `self` has any regions that escape `binder` (and
66 /// hence are not bound by it).
67 fn has_vars_bound_above(&self, binder: ty::DebruijnIndex) -> bool {
68 self.has_vars_bound_at_or_above(binder.shifted_in(1))
71 fn has_escaping_bound_vars(&self) -> bool {
72 self.has_vars_bound_at_or_above(ty::INNERMOST)
75 fn has_type_flags(&self, flags: TypeFlags) -> bool {
76 self.visit_with(&mut HasTypeFlagsVisitor { flags })
78 fn has_projections(&self) -> bool {
79 self.has_type_flags(TypeFlags::HAS_PROJECTION)
81 fn references_error(&self) -> bool {
82 self.has_type_flags(TypeFlags::HAS_TY_ERR)
84 fn has_param_types(&self) -> bool {
85 self.has_type_flags(TypeFlags::HAS_PARAMS)
87 fn has_self_ty(&self) -> bool {
88 self.has_type_flags(TypeFlags::HAS_SELF)
90 fn has_infer_types(&self) -> bool {
91 self.has_type_flags(TypeFlags::HAS_TY_INFER)
93 fn needs_infer(&self) -> bool {
94 self.has_type_flags(TypeFlags::HAS_TY_INFER | TypeFlags::HAS_RE_INFER)
96 fn has_placeholders(&self) -> bool {
97 self.has_type_flags(TypeFlags::HAS_RE_PLACEHOLDER | TypeFlags::HAS_TY_PLACEHOLDER)
99 fn needs_subst(&self) -> bool {
100 self.has_type_flags(TypeFlags::NEEDS_SUBST)
102 fn has_re_placeholders(&self) -> bool {
103 self.has_type_flags(TypeFlags::HAS_RE_PLACEHOLDER)
105 fn has_closure_types(&self) -> bool {
106 self.has_type_flags(TypeFlags::HAS_TY_CLOSURE)
108 /// "Free" regions in this context means that it has any region
109 /// that is not (a) erased or (b) late-bound.
110 fn has_free_regions(&self) -> bool {
111 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
114 /// True if there are any un-erased free regions.
115 fn has_erasable_regions(&self) -> bool {
116 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
119 /// Indicates whether this value references only 'global'
120 /// types/lifetimes that are the same regardless of what fn we are
121 /// in. This is used for caching.
122 fn is_global(&self) -> bool {
123 !self.has_type_flags(TypeFlags::HAS_FREE_LOCAL_NAMES)
126 /// True if there are any late-bound regions
127 fn has_late_bound_regions(&self) -> bool {
128 self.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND)
131 /// A visitor that does not recurse into types, works like `fn walk_shallow` in `Ty`.
132 fn visit_tys_shallow(&self, visit: impl FnMut(Ty<'tcx>) -> bool) -> bool {
134 pub struct Visitor<F>(F);
136 impl<'tcx, F: FnMut(Ty<'tcx>) -> bool> TypeVisitor<'tcx> for Visitor<F> {
137 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
142 self.visit_with(&mut Visitor(visit))
146 /// The `TypeFolder` trait defines the actual *folding*. There is a
147 /// method defined for every foldable type. Each of these has a
148 /// default implementation that does an "identity" fold. Within each
149 /// identity fold, it should invoke `foo.fold_with(self)` to fold each
151 pub trait TypeFolder<'gcx: 'tcx, 'tcx> : Sized {
152 fn tcx<'a>(&'a self) -> TyCtxt<'a, 'gcx, 'tcx>;
154 fn fold_binder<T>(&mut self, t: &Binder<T>) -> Binder<T>
155 where T : TypeFoldable<'tcx>
157 t.super_fold_with(self)
160 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
161 t.super_fold_with(self)
164 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
165 r.super_fold_with(self)
168 fn fold_const(&mut self, c: &'tcx ty::LazyConst<'tcx>) -> &'tcx ty::LazyConst<'tcx> {
169 c.super_fold_with(self)
173 pub trait TypeVisitor<'tcx> : Sized {
174 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
175 t.super_visit_with(self)
178 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
179 t.super_visit_with(self)
182 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
183 r.super_visit_with(self)
186 fn visit_const(&mut self, c: &'tcx ty::LazyConst<'tcx>) -> bool {
187 c.super_visit_with(self)
191 ///////////////////////////////////////////////////////////////////////////
192 // Some sample folders
194 pub struct BottomUpFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a, F, G>
195 where F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
196 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
198 pub tcx: TyCtxt<'a, 'gcx, 'tcx>,
203 impl<'a, 'gcx, 'tcx, F, G> TypeFolder<'gcx, 'tcx> for BottomUpFolder<'a, 'gcx, 'tcx, F, G>
204 where F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
205 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
207 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
209 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
210 let t1 = ty.super_fold_with(self);
214 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
215 let r = r.super_fold_with(self);
220 ///////////////////////////////////////////////////////////////////////////
223 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
224 /// Collects the free and escaping regions in `value` into `region_set`. Returns
225 /// whether any late-bound regions were skipped
226 pub fn collect_regions<T>(self,
228 region_set: &mut FxHashSet<ty::Region<'tcx>>)
230 where T : TypeFoldable<'tcx>
232 let mut have_bound_regions = false;
233 self.fold_regions(value, &mut have_bound_regions, |r, d| {
234 region_set.insert(self.mk_region(r.shifted_out_to_binder(d)));
240 /// Folds the escaping and free regions in `value` using `f`, and
241 /// sets `skipped_regions` to true if any late-bound region was found
243 pub fn fold_regions<T>(
246 skipped_regions: &mut bool,
247 mut f: impl FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
250 T : TypeFoldable<'tcx>,
252 value.fold_with(&mut RegionFolder::new(self, skipped_regions, &mut f))
255 /// Invoke `callback` on every region appearing free in `value`.
256 pub fn for_each_free_region(
258 value: &impl TypeFoldable<'tcx>,
259 mut callback: impl FnMut(ty::Region<'tcx>),
261 self.any_free_region_meets(value, |r| {
267 /// Returns `true` if `callback` returns true for every region appearing free in `value`.
268 pub fn all_free_regions_meet(
270 value: &impl TypeFoldable<'tcx>,
271 mut callback: impl FnMut(ty::Region<'tcx>) -> bool,
273 !self.any_free_region_meets(value, |r| !callback(r))
276 /// Returns `true` if `callback` returns true for some region appearing free in `value`.
277 pub fn any_free_region_meets(
279 value: &impl TypeFoldable<'tcx>,
280 callback: impl FnMut(ty::Region<'tcx>) -> bool,
282 return value.visit_with(&mut RegionVisitor {
283 outer_index: ty::INNERMOST,
287 struct RegionVisitor<F> {
288 /// The index of a binder *just outside* the things we have
289 /// traversed. If we encounter a bound region bound by this
290 /// binder or one outer to it, it appears free. Example:
293 /// for<'a> fn(for<'b> fn(), T)
295 /// | | | | here, would be shifted in 1
296 /// | | | here, would be shifted in 2
297 /// | | here, would be `INNERMOST` shifted in by 1
298 /// | here, initially, binder would be `INNERMOST`
301 /// You see that, initially, *any* bound value is free,
302 /// because we've not traversed any binders. As we pass
303 /// through a binder, we shift the `outer_index` by 1 to
304 /// account for the new binder that encloses us.
305 outer_index: ty::DebruijnIndex,
309 impl<'tcx, F> TypeVisitor<'tcx> for RegionVisitor<F>
310 where F: FnMut(ty::Region<'tcx>) -> bool
312 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
313 self.outer_index.shift_in(1);
314 let result = t.skip_binder().visit_with(self);
315 self.outer_index.shift_out(1);
319 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
321 ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => {
322 false // ignore bound regions, keep visiting
324 _ => (self.callback)(r),
328 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
329 // We're only interested in types involving regions
330 if ty.flags.intersects(TypeFlags::HAS_FREE_REGIONS) {
331 ty.super_visit_with(self)
333 false // keep visiting
340 /// Folds over the substructure of a type, visiting its component
341 /// types and all regions that occur *free* within it.
343 /// That is, `Ty` can contain function or method types that bind
344 /// regions at the call site (`ReLateBound`), and occurrences of
345 /// regions (aka "lifetimes") that are bound within a type are not
346 /// visited by this folder; only regions that occur free will be
347 /// visited by `fld_r`.
349 pub struct RegionFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
350 tcx: TyCtxt<'a, 'gcx, 'tcx>,
351 skipped_regions: &'a mut bool,
353 /// Stores the index of a binder *just outside* the stuff we have
354 /// visited. So this begins as INNERMOST; when we pass through a
355 /// binder, it is incremented (via `shift_in`).
356 current_index: ty::DebruijnIndex,
358 /// Callback invokes for each free region. The `DebruijnIndex`
359 /// points to the binder *just outside* the ones we have passed
361 fold_region_fn: &'a mut (dyn FnMut(
364 ) -> ty::Region<'tcx> + 'a),
367 impl<'a, 'gcx, 'tcx> RegionFolder<'a, 'gcx, 'tcx> {
370 tcx: TyCtxt<'a, 'gcx, 'tcx>,
371 skipped_regions: &'a mut bool,
372 fold_region_fn: &'a mut dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
373 ) -> RegionFolder<'a, 'gcx, 'tcx> {
377 current_index: ty::INNERMOST,
383 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionFolder<'a, 'gcx, 'tcx> {
384 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
386 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
387 self.current_index.shift_in(1);
388 let t = t.super_fold_with(self);
389 self.current_index.shift_out(1);
393 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
395 ty::ReLateBound(debruijn, _) if debruijn < self.current_index => {
396 debug!("RegionFolder.fold_region({:?}) skipped bound region (current index={:?})",
397 r, self.current_index);
398 *self.skipped_regions = true;
402 debug!("RegionFolder.fold_region({:?}) folding free region (current_index={:?})",
403 r, self.current_index);
404 (self.fold_region_fn)(r, self.current_index)
410 ///////////////////////////////////////////////////////////////////////////
411 // Bound vars replacer
413 /// Replaces the escaping bound vars (late bound regions or bound types) in a type.
414 struct BoundVarReplacer<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
415 tcx: TyCtxt<'a, 'gcx, 'tcx>,
417 /// As with `RegionFolder`, represents the index of a binder *just outside*
418 /// the ones we have visited.
419 current_index: ty::DebruijnIndex,
421 fld_r: &'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a),
422 fld_t: &'a mut (dyn FnMut(ty::BoundTy) -> ty::Ty<'tcx> + 'a),
425 impl<'a, 'gcx, 'tcx> BoundVarReplacer<'a, 'gcx, 'tcx> {
427 tcx: TyCtxt<'a, 'gcx, 'tcx>,
431 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
432 G: FnMut(ty::BoundTy) -> ty::Ty<'tcx>
436 current_index: ty::INNERMOST,
443 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for BoundVarReplacer<'a, 'gcx, 'tcx> {
444 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
446 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
447 self.current_index.shift_in(1);
448 let t = t.super_fold_with(self);
449 self.current_index.shift_out(1);
453 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
455 ty::Bound(debruijn, bound_ty) => {
456 if debruijn == self.current_index {
457 let fld_t = &mut self.fld_t;
458 let ty = fld_t(bound_ty);
459 ty::fold::shift_vars(
462 self.current_index.as_u32()
469 if !t.has_vars_bound_at_or_above(self.current_index) {
470 // Nothing more to substitute.
473 t.super_fold_with(self)
479 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
481 ty::ReLateBound(debruijn, br) if debruijn == self.current_index => {
482 let fld_r = &mut self.fld_r;
483 let region = fld_r(br);
484 if let ty::ReLateBound(debruijn1, br) = *region {
485 // If the callback returns a late-bound region,
486 // that region should always use the INNERMOST
487 // debruijn index. Then we adjust it to the
489 assert_eq!(debruijn1, ty::INNERMOST);
490 self.tcx.mk_region(ty::ReLateBound(debruijn, br))
500 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
501 /// Replaces all regions bound by the given `Binder` with the
502 /// results returned by the closure; the closure is expected to
503 /// return a free region (relative to this binder), and hence the
504 /// binder is removed in the return type. The closure is invoked
505 /// once for each unique `BoundRegion`; multiple references to the
506 /// same `BoundRegion` will reuse the previous result. A map is
507 /// returned at the end with each bound region and the free region
508 /// that replaced it.
510 /// This method only replaces late bound regions and the result may still
511 /// contain escaping bound types.
512 pub fn replace_late_bound_regions<T, F>(
516 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
517 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
518 T: TypeFoldable<'tcx>
520 // identity for bound types
521 let fld_t = |bound_ty| self.mk_ty(ty::Bound(ty::INNERMOST, bound_ty));
522 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t)
525 /// Replaces all escaping bound vars. The `fld_r` closure replaces escaping
526 /// bound regions while the `fld_t` closure replaces escaping bound types.
527 pub fn replace_escaping_bound_vars<T, F, G>(
532 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
533 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
534 G: FnMut(ty::BoundTy) -> ty::Ty<'tcx>,
535 T: TypeFoldable<'tcx>
537 use rustc_data_structures::fx::FxHashMap;
539 let mut region_map = BTreeMap::new();
540 let mut type_map = FxHashMap::default();
542 if !value.has_escaping_bound_vars() {
543 (value.clone(), region_map)
545 let mut real_fld_r = |br| {
546 *region_map.entry(br).or_insert_with(|| fld_r(br))
549 let mut real_fld_t = |bound_ty| {
550 *type_map.entry(bound_ty).or_insert_with(|| fld_t(bound_ty))
553 let mut replacer = BoundVarReplacer::new(self, &mut real_fld_r, &mut real_fld_t);
554 let result = value.fold_with(&mut replacer);
559 /// Replaces all types or regions bound by the given `Binder`. The `fld_r`
560 /// closure replaces bound regions while the `fld_t` closure replaces bound
562 pub fn replace_bound_vars<T, F, G>(
567 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
568 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
569 G: FnMut(ty::BoundTy) -> ty::Ty<'tcx>,
570 T: TypeFoldable<'tcx>
572 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t)
575 /// Replaces any late-bound regions bound in `value` with
576 /// free variants attached to `all_outlive_scope`.
577 pub fn liberate_late_bound_regions<T>(
579 all_outlive_scope: DefId,
580 value: &ty::Binder<T>
582 where T: TypeFoldable<'tcx> {
583 self.replace_late_bound_regions(value, |br| {
584 self.mk_region(ty::ReFree(ty::FreeRegion {
585 scope: all_outlive_scope,
591 /// Returns a set of all late-bound regions that are constrained
592 /// by `value`, meaning that if we instantiate those LBR with
593 /// variables and equate `value` with something else, those
594 /// variables will also be equated.
595 pub fn collect_constrained_late_bound_regions<T>(&self, value: &Binder<T>)
596 -> FxHashSet<ty::BoundRegion>
597 where T : TypeFoldable<'tcx>
599 self.collect_late_bound_regions(value, true)
602 /// Returns a set of all late-bound regions that appear in `value` anywhere.
603 pub fn collect_referenced_late_bound_regions<T>(&self, value: &Binder<T>)
604 -> FxHashSet<ty::BoundRegion>
605 where T : TypeFoldable<'tcx>
607 self.collect_late_bound_regions(value, false)
610 fn collect_late_bound_regions<T>(&self, value: &Binder<T>, just_constraint: bool)
611 -> FxHashSet<ty::BoundRegion>
612 where T : TypeFoldable<'tcx>
614 let mut collector = LateBoundRegionsCollector::new(just_constraint);
615 let result = value.skip_binder().visit_with(&mut collector);
616 assert!(!result); // should never have stopped early
620 /// Replaces any late-bound regions bound in `value` with `'erased`. Useful in codegen but also
621 /// method lookup and a few other places where precise region relationships are not required.
622 pub fn erase_late_bound_regions<T>(self, value: &Binder<T>) -> T
623 where T : TypeFoldable<'tcx>
625 self.replace_late_bound_regions(value, |_| self.types.re_erased).0
628 /// Rewrite any late-bound regions so that they are anonymous. Region numbers are
629 /// assigned starting at 1 and increasing monotonically in the order traversed
630 /// by the fold operation.
632 /// The chief purpose of this function is to canonicalize regions so that two
633 /// `FnSig`s or `TraitRef`s which are equivalent up to region naming will become
634 /// structurally identical. For example, `for<'a, 'b> fn(&'a isize, &'b isize)` and
635 /// `for<'a, 'b> fn(&'b isize, &'a isize)` will become identical after anonymization.
636 pub fn anonymize_late_bound_regions<T>(self, sig: &Binder<T>) -> Binder<T>
637 where T : TypeFoldable<'tcx>,
640 Binder::bind(self.replace_late_bound_regions(sig, |_| {
642 self.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BrAnon(counter)))
647 ///////////////////////////////////////////////////////////////////////////
650 // Shifts the De Bruijn indices on all escaping bound vars by a
651 // fixed amount. Useful in substitution or when otherwise introducing
652 // a binding level that is not intended to capture the existing bound
653 // vars. See comment on `shift_vars_through_binders` method in
654 // `subst.rs` for more details.
656 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
662 struct Shifter<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
663 tcx: TyCtxt<'a, 'gcx, 'tcx>,
664 current_index: ty::DebruijnIndex,
666 direction: Direction,
669 impl Shifter<'a, 'gcx, 'tcx> {
670 pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>, amount: u32, direction: Direction) -> Self {
673 current_index: ty::INNERMOST,
680 impl TypeFolder<'gcx, 'tcx> for Shifter<'a, 'gcx, 'tcx> {
681 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
683 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
684 self.current_index.shift_in(1);
685 let t = t.super_fold_with(self);
686 self.current_index.shift_out(1);
690 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
692 ty::ReLateBound(debruijn, br) => {
693 if self.amount == 0 || debruijn < self.current_index {
696 let debruijn = match self.direction {
697 Direction::In => debruijn.shifted_in(self.amount),
699 assert!(debruijn.as_u32() >= self.amount);
700 debruijn.shifted_out(self.amount)
703 let shifted = ty::ReLateBound(debruijn, br);
704 self.tcx.mk_region(shifted)
711 fn fold_ty(&mut self, ty: ty::Ty<'tcx>) -> ty::Ty<'tcx> {
713 ty::Bound(debruijn, bound_ty) => {
714 if self.amount == 0 || debruijn < self.current_index {
717 let debruijn = match self.direction {
718 Direction::In => debruijn.shifted_in(self.amount),
720 assert!(debruijn.as_u32() >= self.amount);
721 debruijn.shifted_out(self.amount)
725 ty::Bound(debruijn, bound_ty)
730 _ => ty.super_fold_with(self),
735 pub fn shift_region<'a, 'gcx, 'tcx>(
736 tcx: TyCtxt<'a, 'gcx, 'tcx>,
737 region: ty::Region<'tcx>,
739 ) -> ty::Region<'tcx> {
741 ty::ReLateBound(debruijn, br) if amount > 0 => {
742 tcx.mk_region(ty::ReLateBound(debruijn.shifted_in(amount), *br))
750 pub fn shift_vars<'a, 'gcx, 'tcx, T>(
751 tcx: TyCtxt<'a, 'gcx, 'tcx>,
754 ) -> T where T: TypeFoldable<'tcx> {
755 debug!("shift_vars(value={:?}, amount={})",
758 value.fold_with(&mut Shifter::new(tcx, amount, Direction::In))
761 pub fn shift_out_vars<'a, 'gcx, 'tcx, T>(
762 tcx: TyCtxt<'a, 'gcx, 'tcx>,
765 ) -> T where T: TypeFoldable<'tcx> {
766 debug!("shift_out_vars(value={:?}, amount={})",
769 value.fold_with(&mut Shifter::new(tcx, amount, Direction::Out))
772 /// An "escaping var" is a bound var whose binder is not part of `t`. A bound var can be a
773 /// bound region or a bound type.
775 /// So, for example, consider a type like the following, which has two binders:
777 /// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize))
778 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope
779 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope
781 /// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the
782 /// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner
783 /// fn type*, that type has an escaping region: `'a`.
785 /// Note that what I'm calling an "escaping var" is often just called a "free var". However,
786 /// we already use the term "free var". It refers to the regions or types that we use to represent
787 /// bound regions or type params on a fn definition while we are type checking its body.
789 /// To clarify, conceptually there is no particular difference between
790 /// an "escaping" var and a "free" var. However, there is a big
791 /// difference in practice. Basically, when "entering" a binding
792 /// level, one is generally required to do some sort of processing to
793 /// a bound var, such as replacing it with a fresh/placeholder
794 /// var, or making an entry in the environment to represent the
795 /// scope to which it is attached, etc. An escaping var represents
796 /// a bound var for which this processing has not yet been done.
797 struct HasEscapingVarsVisitor {
798 /// Anything bound by `outer_index` or "above" is escaping.
799 outer_index: ty::DebruijnIndex,
802 impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
803 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
804 self.outer_index.shift_in(1);
805 let result = t.super_visit_with(self);
806 self.outer_index.shift_out(1);
810 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
811 // If the outer-exclusive-binder is *strictly greater* than
812 // `outer_index`, that means that `t` contains some content
813 // bound at `outer_index` or above (because
814 // `outer_exclusive_binder` is always 1 higher than the
815 // content in `t`). Therefore, `t` has some escaping vars.
816 t.outer_exclusive_binder > self.outer_index
819 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
820 // If the region is bound by `outer_index` or anything outside
821 // of outer index, then it escapes the binders we have
823 r.bound_at_or_above_binder(self.outer_index)
827 struct HasTypeFlagsVisitor {
828 flags: ty::TypeFlags,
831 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
832 fn visit_ty(&mut self, t: Ty<'_>) -> bool {
833 debug!("HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}", t, t.flags, self.flags);
834 t.flags.intersects(self.flags)
837 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
838 let flags = r.type_flags();
839 debug!("HasTypeFlagsVisitor: r={:?} r.flags={:?} self.flags={:?}", r, flags, self.flags);
840 flags.intersects(self.flags)
843 fn visit_const(&mut self, c: &'tcx ty::LazyConst<'tcx>) -> bool {
844 if let ty::LazyConst::Unevaluated(..) = c {
845 let projection_flags = TypeFlags::HAS_NORMALIZABLE_PROJECTION |
846 TypeFlags::HAS_PROJECTION;
847 if projection_flags.intersects(self.flags) {
851 c.super_visit_with(self)
855 /// Collects all the late-bound regions at the innermost binding level
857 struct LateBoundRegionsCollector {
858 current_index: ty::DebruijnIndex,
859 regions: FxHashSet<ty::BoundRegion>,
861 /// `true` if we only want regions that are known to be
862 /// "constrained" when you equate this type with another type. In
863 /// particular, if you have e.g., `&'a u32` and `&'b u32`, equating
864 /// them constraints `'a == 'b`. But if you have `<&'a u32 as
865 /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
866 /// types may mean that `'a` and `'b` don't appear in the results,
867 /// so they are not considered *constrained*.
868 just_constrained: bool,
871 impl LateBoundRegionsCollector {
872 fn new(just_constrained: bool) -> Self {
873 LateBoundRegionsCollector {
874 current_index: ty::INNERMOST,
875 regions: Default::default(),
881 impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
882 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
883 self.current_index.shift_in(1);
884 let result = t.super_visit_with(self);
885 self.current_index.shift_out(1);
889 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
890 // if we are only looking for "constrained" region, we have to
891 // ignore the inputs to a projection, as they may not appear
892 // in the normalized form
893 if self.just_constrained {
895 ty::Projection(..) | ty::Opaque(..) => { return false; }
900 t.super_visit_with(self)
903 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
904 if let ty::ReLateBound(debruijn, br) = *r {
905 if debruijn == self.current_index {
906 self.regions.insert(br);