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 /// The TypeFoldable 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<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self;
49 fn fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, '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_self_ty(&self) -> bool {
89 self.has_type_flags(TypeFlags::HAS_SELF)
91 fn has_infer_types(&self) -> bool {
92 self.has_type_flags(TypeFlags::HAS_TY_INFER)
94 fn needs_infer(&self) -> bool {
96 TypeFlags::HAS_TY_INFER | TypeFlags::HAS_RE_INFER | TypeFlags::HAS_CT_INFER
99 fn has_placeholders(&self) -> bool {
101 TypeFlags::HAS_RE_PLACEHOLDER |
102 TypeFlags::HAS_TY_PLACEHOLDER |
103 TypeFlags::HAS_CT_PLACEHOLDER
106 fn needs_subst(&self) -> bool {
107 self.has_type_flags(TypeFlags::NEEDS_SUBST)
109 fn has_re_placeholders(&self) -> bool {
110 self.has_type_flags(TypeFlags::HAS_RE_PLACEHOLDER)
112 fn has_closure_types(&self) -> bool {
113 self.has_type_flags(TypeFlags::HAS_TY_CLOSURE)
115 /// "Free" regions in this context means that it has any region
116 /// that is not (a) erased or (b) late-bound.
117 fn has_free_regions(&self) -> bool {
118 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
121 /// True if there are any un-erased free regions.
122 fn has_erasable_regions(&self) -> bool {
123 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
126 /// Indicates whether this value references only 'global'
127 /// generic parameters that are the same regardless of what fn we are
128 /// in. This is used for caching.
129 fn is_global(&self) -> bool {
130 !self.has_type_flags(TypeFlags::HAS_FREE_LOCAL_NAMES)
133 /// True if there are any late-bound regions
134 fn has_late_bound_regions(&self) -> bool {
135 self.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND)
138 /// A visitor that does not recurse into types, works like `fn walk_shallow` in `Ty`.
139 fn visit_tys_shallow(&self, visit: impl FnMut(Ty<'tcx>) -> bool) -> bool {
141 pub struct Visitor<F>(F);
143 impl<'tcx, F: FnMut(Ty<'tcx>) -> bool> TypeVisitor<'tcx> for Visitor<F> {
144 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
149 self.visit_with(&mut Visitor(visit))
153 /// The `TypeFolder` trait defines the actual *folding*. There is a
154 /// method defined for every foldable type. Each of these has a
155 /// default implementation that does an "identity" fold. Within each
156 /// identity fold, it should invoke `foo.fold_with(self)` to fold each
158 pub trait TypeFolder<'gcx: 'tcx, 'tcx> : Sized {
159 fn tcx<'a>(&'a self) -> TyCtxt<'a, 'gcx, 'tcx>;
161 fn fold_binder<T>(&mut self, t: &Binder<T>) -> Binder<T>
162 where T : TypeFoldable<'tcx>
164 t.super_fold_with(self)
167 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
168 t.super_fold_with(self)
171 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
172 r.super_fold_with(self)
175 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
176 c.super_fold_with(self)
180 pub trait TypeVisitor<'tcx> : Sized {
181 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
182 t.super_visit_with(self)
185 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
186 t.super_visit_with(self)
189 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
190 r.super_visit_with(self)
193 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
194 c.super_visit_with(self)
198 ///////////////////////////////////////////////////////////////////////////
199 // Some sample folders
201 pub struct BottomUpFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a, F, G, H>
202 where F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
203 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
204 H: FnMut(&'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>,
206 pub tcx: TyCtxt<'a, 'gcx, 'tcx>,
212 impl<'a, 'gcx, 'tcx, F, G, H> TypeFolder<'gcx, 'tcx> for BottomUpFolder<'a, 'gcx, 'tcx, F, G, H>
213 where F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
214 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
215 H: FnMut(&'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>,
217 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
219 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
220 let t = ty.super_fold_with(self);
224 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
225 let r = r.super_fold_with(self);
229 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
230 let ct = ct.super_fold_with(self);
235 ///////////////////////////////////////////////////////////////////////////
238 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
239 /// Collects the free and escaping regions in `value` into `region_set`. Returns
240 /// whether any late-bound regions were skipped
241 pub fn collect_regions<T>(self,
243 region_set: &mut FxHashSet<ty::Region<'tcx>>)
245 where T : TypeFoldable<'tcx>
247 let mut have_bound_regions = false;
248 self.fold_regions(value, &mut have_bound_regions, |r, d| {
249 region_set.insert(self.mk_region(r.shifted_out_to_binder(d)));
255 /// Folds the escaping and free regions in `value` using `f`, and
256 /// sets `skipped_regions` to true if any late-bound region was found
258 pub fn fold_regions<T>(
261 skipped_regions: &mut bool,
262 mut f: impl FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
265 T : TypeFoldable<'tcx>,
267 value.fold_with(&mut RegionFolder::new(self, skipped_regions, &mut f))
270 /// Invoke `callback` on every region appearing free in `value`.
271 pub fn for_each_free_region(
273 value: &impl TypeFoldable<'tcx>,
274 mut callback: impl FnMut(ty::Region<'tcx>),
276 self.any_free_region_meets(value, |r| {
282 /// Returns `true` if `callback` returns true for every region appearing free in `value`.
283 pub fn all_free_regions_meet(
285 value: &impl TypeFoldable<'tcx>,
286 mut callback: impl FnMut(ty::Region<'tcx>) -> bool,
288 !self.any_free_region_meets(value, |r| !callback(r))
291 /// Returns `true` if `callback` returns true for some region appearing free in `value`.
292 pub fn any_free_region_meets(
294 value: &impl TypeFoldable<'tcx>,
295 callback: impl FnMut(ty::Region<'tcx>) -> bool,
297 return value.visit_with(&mut RegionVisitor {
298 outer_index: ty::INNERMOST,
302 struct RegionVisitor<F> {
303 /// The index of a binder *just outside* the things we have
304 /// traversed. If we encounter a bound region bound by this
305 /// binder or one outer to it, it appears free. Example:
308 /// for<'a> fn(for<'b> fn(), T)
310 /// | | | | here, would be shifted in 1
311 /// | | | here, would be shifted in 2
312 /// | | here, would be `INNERMOST` shifted in by 1
313 /// | here, initially, binder would be `INNERMOST`
316 /// You see that, initially, *any* bound value is free,
317 /// because we've not traversed any binders. As we pass
318 /// through a binder, we shift the `outer_index` by 1 to
319 /// account for the new binder that encloses us.
320 outer_index: ty::DebruijnIndex,
324 impl<'tcx, F> TypeVisitor<'tcx> for RegionVisitor<F>
325 where F: FnMut(ty::Region<'tcx>) -> bool
327 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
328 self.outer_index.shift_in(1);
329 let result = t.skip_binder().visit_with(self);
330 self.outer_index.shift_out(1);
334 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
336 ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => {
337 false // ignore bound regions, keep visiting
339 _ => (self.callback)(r),
343 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
344 // We're only interested in types involving regions
345 if ty.flags.intersects(TypeFlags::HAS_FREE_REGIONS) {
346 ty.super_visit_with(self)
348 false // keep visiting
355 /// Folds over the substructure of a type, visiting its component
356 /// types and all regions that occur *free* within it.
358 /// That is, `Ty` can contain function or method types that bind
359 /// regions at the call site (`ReLateBound`), and occurrences of
360 /// regions (aka "lifetimes") that are bound within a type are not
361 /// visited by this folder; only regions that occur free will be
362 /// visited by `fld_r`.
364 pub struct RegionFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
365 tcx: TyCtxt<'a, 'gcx, 'tcx>,
366 skipped_regions: &'a mut bool,
368 /// Stores the index of a binder *just outside* the stuff we have
369 /// visited. So this begins as INNERMOST; when we pass through a
370 /// binder, it is incremented (via `shift_in`).
371 current_index: ty::DebruijnIndex,
373 /// Callback invokes for each free region. The `DebruijnIndex`
374 /// points to the binder *just outside* the ones we have passed
376 fold_region_fn: &'a mut (dyn FnMut(
379 ) -> ty::Region<'tcx> + 'a),
382 impl<'a, 'gcx, 'tcx> RegionFolder<'a, 'gcx, 'tcx> {
385 tcx: TyCtxt<'a, 'gcx, 'tcx>,
386 skipped_regions: &'a mut bool,
387 fold_region_fn: &'a mut dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
388 ) -> RegionFolder<'a, 'gcx, 'tcx> {
392 current_index: ty::INNERMOST,
398 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionFolder<'a, 'gcx, 'tcx> {
399 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
401 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
402 self.current_index.shift_in(1);
403 let t = t.super_fold_with(self);
404 self.current_index.shift_out(1);
408 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
410 ty::ReLateBound(debruijn, _) if debruijn < self.current_index => {
411 debug!("RegionFolder.fold_region({:?}) skipped bound region (current index={:?})",
412 r, self.current_index);
413 *self.skipped_regions = true;
417 debug!("RegionFolder.fold_region({:?}) folding free region (current_index={:?})",
418 r, self.current_index);
419 (self.fold_region_fn)(r, self.current_index)
425 ///////////////////////////////////////////////////////////////////////////
426 // Bound vars replacer
428 /// Replaces the escaping bound vars (late bound regions or bound types) in a type.
429 struct BoundVarReplacer<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
430 tcx: TyCtxt<'a, 'gcx, 'tcx>,
432 /// As with `RegionFolder`, represents the index of a binder *just outside*
433 /// the ones we have visited.
434 current_index: ty::DebruijnIndex,
436 fld_r: &'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a),
437 fld_t: &'a mut (dyn FnMut(ty::BoundTy) -> Ty<'tcx> + 'a),
438 fld_c: &'a mut (dyn FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx> + 'a),
441 impl<'a, 'gcx, 'tcx> BoundVarReplacer<'a, 'gcx, 'tcx> {
443 tcx: TyCtxt<'a, 'gcx, 'tcx>,
448 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
449 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
450 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
454 current_index: ty::INNERMOST,
462 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for BoundVarReplacer<'a, 'gcx, 'tcx> {
463 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
465 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
466 self.current_index.shift_in(1);
467 let t = t.super_fold_with(self);
468 self.current_index.shift_out(1);
472 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
474 ty::Bound(debruijn, bound_ty) => {
475 if debruijn == self.current_index {
476 let fld_t = &mut self.fld_t;
477 let ty = fld_t(bound_ty);
478 ty::fold::shift_vars(
481 self.current_index.as_u32()
488 if !t.has_vars_bound_at_or_above(self.current_index) {
489 // Nothing more to substitute.
492 t.super_fold_with(self)
498 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
500 ty::ReLateBound(debruijn, br) if debruijn == self.current_index => {
501 let fld_r = &mut self.fld_r;
502 let region = fld_r(br);
503 if let ty::ReLateBound(debruijn1, br) = *region {
504 // If the callback returns a late-bound region,
505 // that region should always use the INNERMOST
506 // debruijn index. Then we adjust it to the
508 assert_eq!(debruijn1, ty::INNERMOST);
509 self.tcx.mk_region(ty::ReLateBound(debruijn, br))
518 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
520 val: ConstValue::Infer(ty::InferConst::Canonical(debruijn, bound_const)),
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<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, '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_infer(ty::InferConst::Canonical(ty::INNERMOST, bound_ct), ty)
570 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t, fld_c)
573 /// Replaces all escaping bound vars. The `fld_r` closure replaces escaping
574 /// bound regions; the `fld_t` closure replaces escaping bound types and the `fld_c`
575 /// closure replaces escaping bound consts.
576 pub fn replace_escaping_bound_vars<T, F, G, H>(
582 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
583 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
584 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
585 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
586 T: TypeFoldable<'tcx>,
588 use rustc_data_structures::fx::FxHashMap;
590 let mut region_map = BTreeMap::new();
591 let mut type_map = FxHashMap::default();
592 let mut const_map = FxHashMap::default();
594 if !value.has_escaping_bound_vars() {
595 (value.clone(), region_map)
597 let mut real_fld_r = |br| {
598 *region_map.entry(br).or_insert_with(|| fld_r(br))
601 let mut real_fld_t = |bound_ty| {
602 *type_map.entry(bound_ty).or_insert_with(|| fld_t(bound_ty))
605 let mut real_fld_c = |bound_ct, ty| {
606 *const_map.entry(bound_ct).or_insert_with(|| fld_c(bound_ct, ty))
609 let mut replacer = BoundVarReplacer::new(
615 let result = value.fold_with(&mut replacer);
620 /// Replaces all types or regions bound by the given `Binder`. The `fld_r`
621 /// closure replaces bound regions while the `fld_t` closure replaces bound
623 pub fn replace_bound_vars<T, F, G, H>(
629 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
630 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
631 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
632 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
633 T: TypeFoldable<'tcx>
635 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t, fld_c)
638 /// Replaces any late-bound regions bound in `value` with
639 /// free variants attached to `all_outlive_scope`.
640 pub fn liberate_late_bound_regions<T>(
642 all_outlive_scope: DefId,
643 value: &ty::Binder<T>
645 where T: TypeFoldable<'tcx> {
646 self.replace_late_bound_regions(value, |br| {
647 self.mk_region(ty::ReFree(ty::FreeRegion {
648 scope: all_outlive_scope,
654 /// Returns a set of all late-bound regions that are constrained
655 /// by `value`, meaning that if we instantiate those LBR with
656 /// variables and equate `value` with something else, those
657 /// variables will also be equated.
658 pub fn collect_constrained_late_bound_regions<T>(&self, value: &Binder<T>)
659 -> FxHashSet<ty::BoundRegion>
660 where T : TypeFoldable<'tcx>
662 self.collect_late_bound_regions(value, true)
665 /// Returns a set of all late-bound regions that appear in `value` anywhere.
666 pub fn collect_referenced_late_bound_regions<T>(&self, value: &Binder<T>)
667 -> FxHashSet<ty::BoundRegion>
668 where T : TypeFoldable<'tcx>
670 self.collect_late_bound_regions(value, false)
673 fn collect_late_bound_regions<T>(&self, value: &Binder<T>, just_constraint: bool)
674 -> FxHashSet<ty::BoundRegion>
675 where T : TypeFoldable<'tcx>
677 let mut collector = LateBoundRegionsCollector::new(just_constraint);
678 let result = value.skip_binder().visit_with(&mut collector);
679 assert!(!result); // should never have stopped early
683 /// Replaces any late-bound regions bound in `value` with `'erased`. Useful in codegen but also
684 /// method lookup and a few other places where precise region relationships are not required.
685 pub fn erase_late_bound_regions<T>(self, value: &Binder<T>) -> T
686 where T : TypeFoldable<'tcx>
688 self.replace_late_bound_regions(value, |_| self.lifetimes.re_erased).0
691 /// Rewrite any late-bound regions so that they are anonymous. Region numbers are
692 /// assigned starting at 1 and increasing monotonically in the order traversed
693 /// by the fold operation.
695 /// The chief purpose of this function is to canonicalize regions so that two
696 /// `FnSig`s or `TraitRef`s which are equivalent up to region naming will become
697 /// structurally identical. For example, `for<'a, 'b> fn(&'a isize, &'b isize)` and
698 /// `for<'a, 'b> fn(&'b isize, &'a isize)` will become identical after anonymization.
699 pub fn anonymize_late_bound_regions<T>(self, sig: &Binder<T>) -> Binder<T>
700 where T : TypeFoldable<'tcx>,
703 Binder::bind(self.replace_late_bound_regions(sig, |_| {
705 self.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BrAnon(counter)))
710 ///////////////////////////////////////////////////////////////////////////
713 // Shifts the De Bruijn indices on all escaping bound vars by a
714 // fixed amount. Useful in substitution or when otherwise introducing
715 // a binding level that is not intended to capture the existing bound
716 // vars. See comment on `shift_vars_through_binders` method in
717 // `subst.rs` for more details.
719 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
725 struct Shifter<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
726 tcx: TyCtxt<'a, 'gcx, 'tcx>,
727 current_index: ty::DebruijnIndex,
729 direction: Direction,
732 impl Shifter<'a, 'gcx, 'tcx> {
733 pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>, amount: u32, direction: Direction) -> Self {
736 current_index: ty::INNERMOST,
743 impl TypeFolder<'gcx, 'tcx> for Shifter<'a, 'gcx, 'tcx> {
744 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
746 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
747 self.current_index.shift_in(1);
748 let t = t.super_fold_with(self);
749 self.current_index.shift_out(1);
753 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
755 ty::ReLateBound(debruijn, br) => {
756 if self.amount == 0 || debruijn < self.current_index {
759 let debruijn = match self.direction {
760 Direction::In => debruijn.shifted_in(self.amount),
762 assert!(debruijn.as_u32() >= self.amount);
763 debruijn.shifted_out(self.amount)
766 let shifted = ty::ReLateBound(debruijn, br);
767 self.tcx.mk_region(shifted)
774 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
776 ty::Bound(debruijn, bound_ty) => {
777 if self.amount == 0 || debruijn < self.current_index {
780 let debruijn = match self.direction {
781 Direction::In => debruijn.shifted_in(self.amount),
783 assert!(debruijn.as_u32() >= self.amount);
784 debruijn.shifted_out(self.amount)
788 ty::Bound(debruijn, bound_ty)
793 _ => ty.super_fold_with(self),
797 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
799 val: ConstValue::Infer(ty::InferConst::Canonical(debruijn, bound_const)),
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_infer(ty::InferConst::Canonical(debruijn, bound_const), ty)
815 ct.super_fold_with(self)
820 pub fn shift_region<'a, 'gcx, 'tcx>(
821 tcx: TyCtxt<'a, 'gcx, '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))
835 pub fn shift_vars<'a, 'gcx, 'tcx, T>(
836 tcx: TyCtxt<'a, 'gcx, 'tcx>,
839 ) -> T where T: TypeFoldable<'tcx> {
840 debug!("shift_vars(value={:?}, amount={})",
843 value.fold_with(&mut Shifter::new(tcx, amount, Direction::In))
846 pub fn shift_out_vars<'a, 'gcx, 'tcx, T>(
847 tcx: TyCtxt<'a, 'gcx, 'tcx>,
850 ) -> T where T: TypeFoldable<'tcx> {
851 debug!("shift_out_vars(value={:?}, amount={})",
854 value.fold_with(&mut Shifter::new(tcx, amount, Direction::Out))
857 /// An "escaping var" is a bound var whose binder is not part of `t`. A bound var can be a
858 /// bound region or a bound type.
860 /// So, for example, consider a type like the following, which has two binders:
862 /// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize))
863 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope
864 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope
866 /// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the
867 /// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner
868 /// fn type*, that type has an escaping region: `'a`.
870 /// Note that what I'm calling an "escaping var" is often just called a "free var". However,
871 /// we already use the term "free var". It refers to the regions or types that we use to represent
872 /// bound regions or type params on a fn definition while we are type checking its body.
874 /// To clarify, conceptually there is no particular difference between
875 /// an "escaping" var and a "free" var. However, there is a big
876 /// difference in practice. Basically, when "entering" a binding
877 /// level, one is generally required to do some sort of processing to
878 /// a bound var, such as replacing it with a fresh/placeholder
879 /// var, or making an entry in the environment to represent the
880 /// scope to which it is attached, etc. An escaping var represents
881 /// a bound var for which this processing has not yet been done.
882 struct HasEscapingVarsVisitor {
883 /// Anything bound by `outer_index` or "above" is escaping.
884 outer_index: ty::DebruijnIndex,
887 impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
888 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
889 self.outer_index.shift_in(1);
890 let result = t.super_visit_with(self);
891 self.outer_index.shift_out(1);
895 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
896 // If the outer-exclusive-binder is *strictly greater* than
897 // `outer_index`, that means that `t` contains some content
898 // bound at `outer_index` or above (because
899 // `outer_exclusive_binder` is always 1 higher than the
900 // content in `t`). Therefore, `t` has some escaping vars.
901 t.outer_exclusive_binder > self.outer_index
904 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
905 // If the region is bound by `outer_index` or anything outside
906 // of outer index, then it escapes the binders we have
908 r.bound_at_or_above_binder(self.outer_index)
911 fn visit_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> bool {
913 val: ConstValue::Infer(ty::InferConst::Canonical(debruijn, _)),
916 debruijn >= self.outer_index
923 struct HasTypeFlagsVisitor {
924 flags: ty::TypeFlags,
927 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
928 fn visit_ty(&mut self, t: Ty<'_>) -> bool {
929 debug!("HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}", t, t.flags, self.flags);
930 t.flags.intersects(self.flags)
933 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
934 let flags = r.type_flags();
935 debug!("HasTypeFlagsVisitor: r={:?} r.flags={:?} self.flags={:?}", r, flags, self.flags);
936 flags.intersects(self.flags)
939 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
940 let flags = FlagComputation::for_const(c);
941 debug!("HasTypeFlagsVisitor: c={:?} c.flags={:?} self.flags={:?}", c, flags, self.flags);
942 flags.intersects(self.flags)
946 /// Collects all the late-bound regions at the innermost binding level
948 struct LateBoundRegionsCollector {
949 current_index: ty::DebruijnIndex,
950 regions: FxHashSet<ty::BoundRegion>,
952 /// `true` if we only want regions that are known to be
953 /// "constrained" when you equate this type with another type. In
954 /// particular, if you have e.g., `&'a u32` and `&'b u32`, equating
955 /// them constraints `'a == 'b`. But if you have `<&'a u32 as
956 /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
957 /// types may mean that `'a` and `'b` don't appear in the results,
958 /// so they are not considered *constrained*.
959 just_constrained: bool,
962 impl LateBoundRegionsCollector {
963 fn new(just_constrained: bool) -> Self {
964 LateBoundRegionsCollector {
965 current_index: ty::INNERMOST,
966 regions: Default::default(),
972 impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
973 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
974 self.current_index.shift_in(1);
975 let result = t.super_visit_with(self);
976 self.current_index.shift_out(1);
980 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
981 // if we are only looking for "constrained" region, we have to
982 // ignore the inputs to a projection, as they may not appear
983 // in the normalized form
984 if self.just_constrained {
986 ty::Projection(..) | ty::Opaque(..) => { return false; }
991 t.super_visit_with(self)
994 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
995 if let ty::ReLateBound(debruijn, br) = *r {
996 if debruijn == self.current_index {
997 self.regions.insert(br);