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 {
100 self.has_type_flags(TypeFlags::HAS_RE_PLACEHOLDER | TypeFlags::HAS_TY_PLACEHOLDER)
102 fn needs_subst(&self) -> bool {
103 self.has_type_flags(TypeFlags::NEEDS_SUBST)
105 fn has_re_placeholders(&self) -> bool {
106 self.has_type_flags(TypeFlags::HAS_RE_PLACEHOLDER)
108 fn has_closure_types(&self) -> bool {
109 self.has_type_flags(TypeFlags::HAS_TY_CLOSURE)
111 /// "Free" regions in this context means that it has any region
112 /// that is not (a) erased or (b) late-bound.
113 fn has_free_regions(&self) -> bool {
114 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
117 /// True if there are any un-erased free regions.
118 fn has_erasable_regions(&self) -> bool {
119 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
122 /// Indicates whether this value references only 'global'
123 /// generic parameters that are the same regardless of what fn we are
124 /// in. This is used for caching.
125 fn is_global(&self) -> bool {
126 !self.has_type_flags(TypeFlags::HAS_FREE_LOCAL_NAMES)
129 /// True if there are any late-bound regions
130 fn has_late_bound_regions(&self) -> bool {
131 self.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND)
134 /// A visitor that does not recurse into types, works like `fn walk_shallow` in `Ty`.
135 fn visit_tys_shallow(&self, visit: impl FnMut(Ty<'tcx>) -> bool) -> bool {
137 pub struct Visitor<F>(F);
139 impl<'tcx, F: FnMut(Ty<'tcx>) -> bool> TypeVisitor<'tcx> for Visitor<F> {
140 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
145 self.visit_with(&mut Visitor(visit))
149 /// The `TypeFolder` trait defines the actual *folding*. There is a
150 /// method defined for every foldable type. Each of these has a
151 /// default implementation that does an "identity" fold. Within each
152 /// identity fold, it should invoke `foo.fold_with(self)` to fold each
154 pub trait TypeFolder<'gcx: 'tcx, 'tcx> : Sized {
155 fn tcx<'a>(&'a self) -> TyCtxt<'a, 'gcx, 'tcx>;
157 fn fold_binder<T>(&mut self, t: &Binder<T>) -> Binder<T>
158 where T : TypeFoldable<'tcx>
160 t.super_fold_with(self)
163 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
164 t.super_fold_with(self)
167 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
168 r.super_fold_with(self)
171 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
172 c.super_fold_with(self)
176 pub trait TypeVisitor<'tcx> : Sized {
177 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
178 t.super_visit_with(self)
181 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
182 t.super_visit_with(self)
185 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
186 r.super_visit_with(self)
189 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
190 c.super_visit_with(self)
194 ///////////////////////////////////////////////////////////////////////////
195 // Some sample folders
197 pub struct BottomUpFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a, F, G, H>
198 where F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
199 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
200 H: FnMut(&'tcx ty::LazyConst<'tcx>) -> &'tcx ty::LazyConst<'tcx>,
202 pub tcx: TyCtxt<'a, 'gcx, 'tcx>,
208 impl<'a, 'gcx, 'tcx, F, G, H> TypeFolder<'gcx, 'tcx> for BottomUpFolder<'a, 'gcx, 'tcx, F, G, H>
209 where F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
210 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
211 H: FnMut(&'tcx ty::LazyConst<'tcx>) -> &'tcx ty::LazyConst<'tcx>,
213 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
215 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
216 let t = ty.super_fold_with(self);
220 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
221 let r = r.super_fold_with(self);
225 fn fold_const(&mut self, ct: &'tcx ty::LazyConst<'tcx>) -> &'tcx ty::LazyConst<'tcx> {
226 let ct = ct.super_fold_with(self);
231 ///////////////////////////////////////////////////////////////////////////
234 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
235 /// Collects the free and escaping regions in `value` into `region_set`. Returns
236 /// whether any late-bound regions were skipped
237 pub fn collect_regions<T>(self,
239 region_set: &mut FxHashSet<ty::Region<'tcx>>)
241 where T : TypeFoldable<'tcx>
243 let mut have_bound_regions = false;
244 self.fold_regions(value, &mut have_bound_regions, |r, d| {
245 region_set.insert(self.mk_region(r.shifted_out_to_binder(d)));
251 /// Folds the escaping and free regions in `value` using `f`, and
252 /// sets `skipped_regions` to true if any late-bound region was found
254 pub fn fold_regions<T>(
257 skipped_regions: &mut bool,
258 mut f: impl FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
261 T : TypeFoldable<'tcx>,
263 value.fold_with(&mut RegionFolder::new(self, skipped_regions, &mut f))
266 /// Invoke `callback` on every region appearing free in `value`.
267 pub fn for_each_free_region(
269 value: &impl TypeFoldable<'tcx>,
270 mut callback: impl FnMut(ty::Region<'tcx>),
272 self.any_free_region_meets(value, |r| {
278 /// Returns `true` if `callback` returns true for every region appearing free in `value`.
279 pub fn all_free_regions_meet(
281 value: &impl TypeFoldable<'tcx>,
282 mut callback: impl FnMut(ty::Region<'tcx>) -> bool,
284 !self.any_free_region_meets(value, |r| !callback(r))
287 /// Returns `true` if `callback` returns true for some region appearing free in `value`.
288 pub fn any_free_region_meets(
290 value: &impl TypeFoldable<'tcx>,
291 callback: impl FnMut(ty::Region<'tcx>) -> bool,
293 return value.visit_with(&mut RegionVisitor {
294 outer_index: ty::INNERMOST,
298 struct RegionVisitor<F> {
299 /// The index of a binder *just outside* the things we have
300 /// traversed. If we encounter a bound region bound by this
301 /// binder or one outer to it, it appears free. Example:
304 /// for<'a> fn(for<'b> fn(), T)
306 /// | | | | here, would be shifted in 1
307 /// | | | here, would be shifted in 2
308 /// | | here, would be `INNERMOST` shifted in by 1
309 /// | here, initially, binder would be `INNERMOST`
312 /// You see that, initially, *any* bound value is free,
313 /// because we've not traversed any binders. As we pass
314 /// through a binder, we shift the `outer_index` by 1 to
315 /// account for the new binder that encloses us.
316 outer_index: ty::DebruijnIndex,
320 impl<'tcx, F> TypeVisitor<'tcx> for RegionVisitor<F>
321 where F: FnMut(ty::Region<'tcx>) -> bool
323 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
324 self.outer_index.shift_in(1);
325 let result = t.skip_binder().visit_with(self);
326 self.outer_index.shift_out(1);
330 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
332 ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => {
333 false // ignore bound regions, keep visiting
335 _ => (self.callback)(r),
339 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
340 // We're only interested in types involving regions
341 if ty.flags.intersects(TypeFlags::HAS_FREE_REGIONS) {
342 ty.super_visit_with(self)
344 false // keep visiting
351 /// Folds over the substructure of a type, visiting its component
352 /// types and all regions that occur *free* within it.
354 /// That is, `Ty` can contain function or method types that bind
355 /// regions at the call site (`ReLateBound`), and occurrences of
356 /// regions (aka "lifetimes") that are bound within a type are not
357 /// visited by this folder; only regions that occur free will be
358 /// visited by `fld_r`.
360 pub struct RegionFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
361 tcx: TyCtxt<'a, 'gcx, 'tcx>,
362 skipped_regions: &'a mut bool,
364 /// Stores the index of a binder *just outside* the stuff we have
365 /// visited. So this begins as INNERMOST; when we pass through a
366 /// binder, it is incremented (via `shift_in`).
367 current_index: ty::DebruijnIndex,
369 /// Callback invokes for each free region. The `DebruijnIndex`
370 /// points to the binder *just outside* the ones we have passed
372 fold_region_fn: &'a mut (dyn FnMut(
375 ) -> ty::Region<'tcx> + 'a),
378 impl<'a, 'gcx, 'tcx> RegionFolder<'a, 'gcx, 'tcx> {
381 tcx: TyCtxt<'a, 'gcx, 'tcx>,
382 skipped_regions: &'a mut bool,
383 fold_region_fn: &'a mut dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
384 ) -> RegionFolder<'a, 'gcx, 'tcx> {
388 current_index: ty::INNERMOST,
394 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionFolder<'a, 'gcx, 'tcx> {
395 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
397 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
398 self.current_index.shift_in(1);
399 let t = t.super_fold_with(self);
400 self.current_index.shift_out(1);
404 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
406 ty::ReLateBound(debruijn, _) if debruijn < self.current_index => {
407 debug!("RegionFolder.fold_region({:?}) skipped bound region (current index={:?})",
408 r, self.current_index);
409 *self.skipped_regions = true;
413 debug!("RegionFolder.fold_region({:?}) folding free region (current_index={:?})",
414 r, self.current_index);
415 (self.fold_region_fn)(r, self.current_index)
421 ///////////////////////////////////////////////////////////////////////////
422 // Bound vars replacer
424 /// Replaces the escaping bound vars (late bound regions or bound types) in a type.
425 struct BoundVarReplacer<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
426 tcx: TyCtxt<'a, 'gcx, 'tcx>,
428 /// As with `RegionFolder`, represents the index of a binder *just outside*
429 /// the ones we have visited.
430 current_index: ty::DebruijnIndex,
432 fld_r: &'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a),
433 fld_t: &'a mut (dyn FnMut(ty::BoundTy) -> Ty<'tcx> + 'a),
436 impl<'a, 'gcx, 'tcx> BoundVarReplacer<'a, 'gcx, 'tcx> {
438 tcx: TyCtxt<'a, 'gcx, 'tcx>,
442 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
443 G: FnMut(ty::BoundTy) -> Ty<'tcx>
447 current_index: ty::INNERMOST,
454 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for BoundVarReplacer<'a, 'gcx, 'tcx> {
455 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
457 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
458 self.current_index.shift_in(1);
459 let t = t.super_fold_with(self);
460 self.current_index.shift_out(1);
464 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
466 ty::Bound(debruijn, bound_ty) => {
467 if debruijn == self.current_index {
468 let fld_t = &mut self.fld_t;
469 let ty = fld_t(bound_ty);
470 ty::fold::shift_vars(
473 self.current_index.as_u32()
480 if !t.has_vars_bound_at_or_above(self.current_index) {
481 // Nothing more to substitute.
484 t.super_fold_with(self)
490 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
492 ty::ReLateBound(debruijn, br) if debruijn == self.current_index => {
493 let fld_r = &mut self.fld_r;
494 let region = fld_r(br);
495 if let ty::ReLateBound(debruijn1, br) = *region {
496 // If the callback returns a late-bound region,
497 // that region should always use the INNERMOST
498 // debruijn index. Then we adjust it to the
500 assert_eq!(debruijn1, ty::INNERMOST);
501 self.tcx.mk_region(ty::ReLateBound(debruijn, br))
510 fn fold_const(&mut self, ct: &'tcx ty::LazyConst<'tcx>) -> &'tcx ty::LazyConst<'tcx> {
511 ct // FIXME(const_generics)
515 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
516 /// Replaces all regions bound by the given `Binder` with the
517 /// results returned by the closure; the closure is expected to
518 /// return a free region (relative to this binder), and hence the
519 /// binder is removed in the return type. The closure is invoked
520 /// once for each unique `BoundRegion`; multiple references to the
521 /// same `BoundRegion` will reuse the previous result. A map is
522 /// returned at the end with each bound region and the free region
523 /// that replaced it.
525 /// This method only replaces late bound regions and the result may still
526 /// contain escaping bound types.
527 pub fn replace_late_bound_regions<T, F>(
531 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
532 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
533 T: TypeFoldable<'tcx>
535 // identity for bound types
536 let fld_t = |bound_ty| self.mk_ty(ty::Bound(ty::INNERMOST, bound_ty));
537 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t)
540 /// Replaces all escaping bound vars. The `fld_r` closure replaces escaping
541 /// bound regions while the `fld_t` closure replaces escaping bound types.
542 pub fn replace_escaping_bound_vars<T, F, G>(
547 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
548 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
549 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
550 T: TypeFoldable<'tcx>
552 use rustc_data_structures::fx::FxHashMap;
554 let mut region_map = BTreeMap::new();
555 let mut type_map = FxHashMap::default();
557 if !value.has_escaping_bound_vars() {
558 (value.clone(), region_map)
560 let mut real_fld_r = |br| {
561 *region_map.entry(br).or_insert_with(|| fld_r(br))
564 let mut real_fld_t = |bound_ty| {
565 *type_map.entry(bound_ty).or_insert_with(|| fld_t(bound_ty))
568 let mut replacer = BoundVarReplacer::new(self, &mut real_fld_r, &mut real_fld_t);
569 let result = value.fold_with(&mut replacer);
574 /// Replaces all types or regions bound by the given `Binder`. The `fld_r`
575 /// closure replaces bound regions while the `fld_t` closure replaces bound
577 pub fn replace_bound_vars<T, F, G>(
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 T: TypeFoldable<'tcx>
587 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t)
590 /// Replaces any late-bound regions bound in `value` with
591 /// free variants attached to `all_outlive_scope`.
592 pub fn liberate_late_bound_regions<T>(
594 all_outlive_scope: DefId,
595 value: &ty::Binder<T>
597 where T: TypeFoldable<'tcx> {
598 self.replace_late_bound_regions(value, |br| {
599 self.mk_region(ty::ReFree(ty::FreeRegion {
600 scope: all_outlive_scope,
606 /// Returns a set of all late-bound regions that are constrained
607 /// by `value`, meaning that if we instantiate those LBR with
608 /// variables and equate `value` with something else, those
609 /// variables will also be equated.
610 pub fn collect_constrained_late_bound_regions<T>(&self, value: &Binder<T>)
611 -> FxHashSet<ty::BoundRegion>
612 where T : TypeFoldable<'tcx>
614 self.collect_late_bound_regions(value, true)
617 /// Returns a set of all late-bound regions that appear in `value` anywhere.
618 pub fn collect_referenced_late_bound_regions<T>(&self, value: &Binder<T>)
619 -> FxHashSet<ty::BoundRegion>
620 where T : TypeFoldable<'tcx>
622 self.collect_late_bound_regions(value, false)
625 fn collect_late_bound_regions<T>(&self, value: &Binder<T>, just_constraint: bool)
626 -> FxHashSet<ty::BoundRegion>
627 where T : TypeFoldable<'tcx>
629 let mut collector = LateBoundRegionsCollector::new(just_constraint);
630 let result = value.skip_binder().visit_with(&mut collector);
631 assert!(!result); // should never have stopped early
635 /// Replaces any late-bound regions bound in `value` with `'erased`. Useful in codegen but also
636 /// method lookup and a few other places where precise region relationships are not required.
637 pub fn erase_late_bound_regions<T>(self, value: &Binder<T>) -> T
638 where T : TypeFoldable<'tcx>
640 self.replace_late_bound_regions(value, |_| self.lifetimes.re_erased).0
643 /// Rewrite any late-bound regions so that they are anonymous. Region numbers are
644 /// assigned starting at 1 and increasing monotonically in the order traversed
645 /// by the fold operation.
647 /// The chief purpose of this function is to canonicalize regions so that two
648 /// `FnSig`s or `TraitRef`s which are equivalent up to region naming will become
649 /// structurally identical. For example, `for<'a, 'b> fn(&'a isize, &'b isize)` and
650 /// `for<'a, 'b> fn(&'b isize, &'a isize)` will become identical after anonymization.
651 pub fn anonymize_late_bound_regions<T>(self, sig: &Binder<T>) -> Binder<T>
652 where T : TypeFoldable<'tcx>,
655 Binder::bind(self.replace_late_bound_regions(sig, |_| {
657 self.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BrAnon(counter)))
662 ///////////////////////////////////////////////////////////////////////////
665 // Shifts the De Bruijn indices on all escaping bound vars by a
666 // fixed amount. Useful in substitution or when otherwise introducing
667 // a binding level that is not intended to capture the existing bound
668 // vars. See comment on `shift_vars_through_binders` method in
669 // `subst.rs` for more details.
671 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
677 struct Shifter<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
678 tcx: TyCtxt<'a, 'gcx, 'tcx>,
679 current_index: ty::DebruijnIndex,
681 direction: Direction,
684 impl Shifter<'a, 'gcx, 'tcx> {
685 pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>, amount: u32, direction: Direction) -> Self {
688 current_index: ty::INNERMOST,
695 impl TypeFolder<'gcx, 'tcx> for Shifter<'a, 'gcx, 'tcx> {
696 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
698 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
699 self.current_index.shift_in(1);
700 let t = t.super_fold_with(self);
701 self.current_index.shift_out(1);
705 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
707 ty::ReLateBound(debruijn, br) => {
708 if self.amount == 0 || debruijn < self.current_index {
711 let debruijn = match self.direction {
712 Direction::In => debruijn.shifted_in(self.amount),
714 assert!(debruijn.as_u32() >= self.amount);
715 debruijn.shifted_out(self.amount)
718 let shifted = ty::ReLateBound(debruijn, br);
719 self.tcx.mk_region(shifted)
726 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
728 ty::Bound(debruijn, bound_ty) => {
729 if self.amount == 0 || debruijn < self.current_index {
732 let debruijn = match self.direction {
733 Direction::In => debruijn.shifted_in(self.amount),
735 assert!(debruijn.as_u32() >= self.amount);
736 debruijn.shifted_out(self.amount)
740 ty::Bound(debruijn, bound_ty)
745 _ => ty.super_fold_with(self),
749 fn fold_const(&mut self, ct: &'tcx ty::LazyConst<'tcx>) -> &'tcx ty::LazyConst<'tcx> {
750 if let ty::LazyConst::Evaluated(ty::Const {
751 val: ConstValue::Infer(ty::InferConst::Canonical(debruijn, bound_const)),
754 if self.amount == 0 || debruijn < self.current_index {
757 let debruijn = match self.direction {
758 Direction::In => debruijn.shifted_in(self.amount),
760 assert!(debruijn.as_u32() >= self.amount);
761 debruijn.shifted_out(self.amount)
764 self.tcx.mk_const_infer(ty::InferConst::Canonical(debruijn, bound_const), ty)
767 ct.super_fold_with(self)
772 pub fn shift_region<'a, 'gcx, 'tcx>(
773 tcx: TyCtxt<'a, 'gcx, 'tcx>,
774 region: ty::Region<'tcx>,
776 ) -> ty::Region<'tcx> {
778 ty::ReLateBound(debruijn, br) if amount > 0 => {
779 tcx.mk_region(ty::ReLateBound(debruijn.shifted_in(amount), *br))
787 pub fn shift_vars<'a, 'gcx, 'tcx, T>(
788 tcx: TyCtxt<'a, 'gcx, 'tcx>,
791 ) -> T where T: TypeFoldable<'tcx> {
792 debug!("shift_vars(value={:?}, amount={})",
795 value.fold_with(&mut Shifter::new(tcx, amount, Direction::In))
798 pub fn shift_out_vars<'a, 'gcx, 'tcx, T>(
799 tcx: TyCtxt<'a, 'gcx, 'tcx>,
802 ) -> T where T: TypeFoldable<'tcx> {
803 debug!("shift_out_vars(value={:?}, amount={})",
806 value.fold_with(&mut Shifter::new(tcx, amount, Direction::Out))
809 /// An "escaping var" is a bound var whose binder is not part of `t`. A bound var can be a
810 /// bound region or a bound type.
812 /// So, for example, consider a type like the following, which has two binders:
814 /// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize))
815 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope
816 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope
818 /// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the
819 /// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner
820 /// fn type*, that type has an escaping region: `'a`.
822 /// Note that what I'm calling an "escaping var" is often just called a "free var". However,
823 /// we already use the term "free var". It refers to the regions or types that we use to represent
824 /// bound regions or type params on a fn definition while we are type checking its body.
826 /// To clarify, conceptually there is no particular difference between
827 /// an "escaping" var and a "free" var. However, there is a big
828 /// difference in practice. Basically, when "entering" a binding
829 /// level, one is generally required to do some sort of processing to
830 /// a bound var, such as replacing it with a fresh/placeholder
831 /// var, or making an entry in the environment to represent the
832 /// scope to which it is attached, etc. An escaping var represents
833 /// a bound var for which this processing has not yet been done.
834 struct HasEscapingVarsVisitor {
835 /// Anything bound by `outer_index` or "above" is escaping.
836 outer_index: ty::DebruijnIndex,
839 impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
840 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
841 self.outer_index.shift_in(1);
842 let result = t.super_visit_with(self);
843 self.outer_index.shift_out(1);
847 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
848 // If the outer-exclusive-binder is *strictly greater* than
849 // `outer_index`, that means that `t` contains some content
850 // bound at `outer_index` or above (because
851 // `outer_exclusive_binder` is always 1 higher than the
852 // content in `t`). Therefore, `t` has some escaping vars.
853 t.outer_exclusive_binder > self.outer_index
856 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
857 // If the region is bound by `outer_index` or anything outside
858 // of outer index, then it escapes the binders we have
860 r.bound_at_or_above_binder(self.outer_index)
863 fn visit_const(&mut self, ct: &'tcx ty::LazyConst<'tcx>) -> bool {
864 if let ty::LazyConst::Evaluated(ty::Const {
865 val: ConstValue::Infer(ty::InferConst::Canonical(debruijn, _)),
868 debruijn >= self.outer_index
875 struct HasTypeFlagsVisitor {
876 flags: ty::TypeFlags,
879 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
880 fn visit_ty(&mut self, t: Ty<'_>) -> bool {
881 debug!("HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}", t, t.flags, self.flags);
882 t.flags.intersects(self.flags)
885 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
886 let flags = r.type_flags();
887 debug!("HasTypeFlagsVisitor: r={:?} r.flags={:?} self.flags={:?}", r, flags, self.flags);
888 flags.intersects(self.flags)
891 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
892 let flags = FlagComputation::for_const(c);
893 debug!("HasTypeFlagsVisitor: c={:?} c.flags={:?} self.flags={:?}", c, flags, self.flags);
894 flags.intersects(self.flags) || c.super_visit_with(self)
898 /// Collects all the late-bound regions at the innermost binding level
900 struct LateBoundRegionsCollector {
901 current_index: ty::DebruijnIndex,
902 regions: FxHashSet<ty::BoundRegion>,
904 /// `true` if we only want regions that are known to be
905 /// "constrained" when you equate this type with another type. In
906 /// particular, if you have e.g., `&'a u32` and `&'b u32`, equating
907 /// them constraints `'a == 'b`. But if you have `<&'a u32 as
908 /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
909 /// types may mean that `'a` and `'b` don't appear in the results,
910 /// so they are not considered *constrained*.
911 just_constrained: bool,
914 impl LateBoundRegionsCollector {
915 fn new(just_constrained: bool) -> Self {
916 LateBoundRegionsCollector {
917 current_index: ty::INNERMOST,
918 regions: Default::default(),
924 impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
925 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
926 self.current_index.shift_in(1);
927 let result = t.super_visit_with(self);
928 self.current_index.shift_out(1);
932 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
933 // if we are only looking for "constrained" region, we have to
934 // ignore the inputs to a projection, as they may not appear
935 // in the normalized form
936 if self.just_constrained {
938 ty::Projection(..) | ty::Opaque(..) => { return false; }
943 t.super_visit_with(self)
946 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
947 if let ty::ReLateBound(debruijn, br) = *r {
948 if debruijn == self.current_index {
949 self.regions.insert(br);