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.
33 use crate::ty::{self, flags::FlagComputation, Binder, Ty, TyCtxt, TypeFlags};
35 use rustc_hir::def_id::DefId;
37 use rustc_data_structures::fx::FxHashSet;
38 use std::collections::BTreeMap;
40 use std::ops::ControlFlow;
42 /// This trait is implemented for every type that can be folded.
43 /// Basically, every type that has a corresponding method in `TypeFolder`.
45 /// To implement this conveniently, use the derive macro located in librustc_macros.
46 pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
47 fn super_fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self;
48 fn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self {
49 self.super_fold_with(folder)
52 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy>;
53 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
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 }).is_break()
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 }).break_value() == Some(FoundFlags)
78 fn has_projections(&self) -> bool {
79 self.has_type_flags(TypeFlags::HAS_PROJECTION)
81 fn has_opaque_types(&self) -> bool {
82 self.has_type_flags(TypeFlags::HAS_TY_OPAQUE)
84 fn references_error(&self) -> bool {
85 self.has_type_flags(TypeFlags::HAS_ERROR)
87 fn has_param_types_or_consts(&self) -> bool {
88 self.has_type_flags(TypeFlags::HAS_TY_PARAM | TypeFlags::HAS_CT_PARAM)
90 fn has_infer_regions(&self) -> bool {
91 self.has_type_flags(TypeFlags::HAS_RE_INFER)
93 fn has_infer_types(&self) -> bool {
94 self.has_type_flags(TypeFlags::HAS_TY_INFER)
96 fn has_infer_types_or_consts(&self) -> bool {
97 self.has_type_flags(TypeFlags::HAS_TY_INFER | TypeFlags::HAS_CT_INFER)
99 fn needs_infer(&self) -> bool {
100 self.has_type_flags(TypeFlags::NEEDS_INFER)
102 fn has_placeholders(&self) -> bool {
104 TypeFlags::HAS_RE_PLACEHOLDER
105 | TypeFlags::HAS_TY_PLACEHOLDER
106 | TypeFlags::HAS_CT_PLACEHOLDER,
109 fn needs_subst(&self) -> bool {
110 self.has_type_flags(TypeFlags::NEEDS_SUBST)
112 /// "Free" regions in this context means that it has any region
113 /// that is not (a) erased or (b) late-bound.
114 fn has_free_regions(&self) -> bool {
115 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
118 fn has_erased_regions(&self) -> bool {
119 self.has_type_flags(TypeFlags::HAS_RE_ERASED)
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 /// Indicates whether this value still has parameters/placeholders/inference variables
140 /// which could be replaced later, in a way that would change the results of `impl`
142 fn still_further_specializable(&self) -> bool {
143 self.has_type_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE)
147 impl TypeFoldable<'tcx> for hir::Constness {
148 fn super_fold_with<F: TypeFolder<'tcx>>(self, _: &mut F) -> Self {
151 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> ControlFlow<V::BreakTy> {
152 ControlFlow::CONTINUE
156 /// The `TypeFolder` trait defines the actual *folding*. There is a
157 /// method defined for every foldable type. Each of these has a
158 /// default implementation that does an "identity" fold. Within each
159 /// identity fold, it should invoke `foo.fold_with(self)` to fold each
161 pub trait TypeFolder<'tcx>: Sized {
162 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
164 fn fold_binder<T>(&mut self, t: Binder<T>) -> Binder<T>
166 T: TypeFoldable<'tcx>,
168 t.super_fold_with(self)
171 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
172 t.super_fold_with(self)
175 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
176 r.super_fold_with(self)
179 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
180 c.super_fold_with(self)
184 pub trait TypeVisitor<'tcx>: Sized {
187 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> ControlFlow<Self::BreakTy> {
188 t.super_visit_with(self)
191 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
192 t.super_visit_with(self)
195 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
196 r.super_visit_with(self)
199 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
200 c.super_visit_with(self)
203 fn visit_predicate(&mut self, p: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
204 p.super_visit_with(self)
208 ///////////////////////////////////////////////////////////////////////////
209 // Some sample folders
211 pub struct BottomUpFolder<'tcx, F, G, H>
213 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 pub tcx: TyCtxt<'tcx>,
223 impl<'tcx, F, G, H> TypeFolder<'tcx> for BottomUpFolder<'tcx, F, G, H>
225 F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
226 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
227 H: FnMut(&'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>,
229 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
233 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
234 let t = ty.super_fold_with(self);
238 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
239 let r = r.super_fold_with(self);
243 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
244 let ct = ct.super_fold_with(self);
249 ///////////////////////////////////////////////////////////////////////////
252 impl<'tcx> TyCtxt<'tcx> {
253 /// Folds the escaping and free regions in `value` using `f`, and
254 /// sets `skipped_regions` to true if any late-bound region was found
256 pub fn fold_regions<T>(
259 skipped_regions: &mut bool,
260 mut f: impl FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
263 T: TypeFoldable<'tcx>,
265 value.fold_with(&mut RegionFolder::new(self, skipped_regions, &mut f))
268 /// Invoke `callback` on every region appearing free in `value`.
269 pub fn for_each_free_region(
271 value: &impl TypeFoldable<'tcx>,
272 mut callback: impl FnMut(ty::Region<'tcx>),
274 self.any_free_region_meets(value, |r| {
280 /// Returns `true` if `callback` returns true for every region appearing free in `value`.
281 pub fn all_free_regions_meet(
283 value: &impl TypeFoldable<'tcx>,
284 mut callback: impl FnMut(ty::Region<'tcx>) -> bool,
286 !self.any_free_region_meets(value, |r| !callback(r))
289 /// Returns `true` if `callback` returns true for some region appearing free in `value`.
290 pub fn any_free_region_meets(
292 value: &impl TypeFoldable<'tcx>,
293 callback: impl FnMut(ty::Region<'tcx>) -> bool,
295 struct RegionVisitor<F> {
296 /// The index of a binder *just outside* the things we have
297 /// traversed. If we encounter a bound region bound by this
298 /// binder or one outer to it, it appears free. Example:
301 /// for<'a> fn(for<'b> fn(), T)
303 /// | | | | here, would be shifted in 1
304 /// | | | here, would be shifted in 2
305 /// | | here, would be `INNERMOST` shifted in by 1
306 /// | here, initially, binder would be `INNERMOST`
309 /// You see that, initially, *any* bound value is free,
310 /// because we've not traversed any binders. As we pass
311 /// through a binder, we shift the `outer_index` by 1 to
312 /// account for the new binder that encloses us.
313 outer_index: ty::DebruijnIndex,
317 impl<'tcx, F> TypeVisitor<'tcx> for RegionVisitor<F>
319 F: FnMut(ty::Region<'tcx>) -> bool,
323 fn visit_binder<T: TypeFoldable<'tcx>>(
326 ) -> ControlFlow<Self::BreakTy> {
327 self.outer_index.shift_in(1);
328 let result = t.as_ref().skip_binder().visit_with(self);
329 self.outer_index.shift_out(1);
333 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
335 ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => {
336 ControlFlow::CONTINUE
339 if (self.callback)(r) {
342 ControlFlow::CONTINUE
348 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
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 ControlFlow::CONTINUE
358 value.visit_with(&mut RegionVisitor { outer_index: ty::INNERMOST, callback }).is_break()
362 /// Folds over the substructure of a type, visiting its component
363 /// types and all regions that occur *free* within it.
365 /// That is, `Ty` can contain function or method types that bind
366 /// regions at the call site (`ReLateBound`), and occurrences of
367 /// regions (aka "lifetimes") that are bound within a type are not
368 /// visited by this folder; only regions that occur free will be
369 /// visited by `fld_r`.
371 pub struct RegionFolder<'a, 'tcx> {
373 skipped_regions: &'a mut bool,
375 /// Stores the index of a binder *just outside* the stuff we have
376 /// visited. So this begins as INNERMOST; when we pass through a
377 /// binder, it is incremented (via `shift_in`).
378 current_index: ty::DebruijnIndex,
380 /// Callback invokes for each free region. The `DebruijnIndex`
381 /// points to the binder *just outside* the ones we have passed
384 &'a mut (dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx> + 'a),
387 impl<'a, 'tcx> RegionFolder<'a, 'tcx> {
391 skipped_regions: &'a mut bool,
392 fold_region_fn: &'a mut dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
393 ) -> RegionFolder<'a, 'tcx> {
394 RegionFolder { tcx, skipped_regions, current_index: ty::INNERMOST, fold_region_fn }
398 impl<'a, 'tcx> TypeFolder<'tcx> for RegionFolder<'a, 'tcx> {
399 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
403 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: ty::Binder<T>) -> ty::Binder<T> {
404 self.current_index.shift_in(1);
405 let t = t.super_fold_with(self);
406 self.current_index.shift_out(1);
410 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
412 ty::ReLateBound(debruijn, _) if debruijn < self.current_index => {
414 "RegionFolder.fold_region({:?}) skipped bound region (current index={:?})",
415 r, self.current_index
417 *self.skipped_regions = true;
422 "RegionFolder.fold_region({:?}) folding free region (current_index={:?})",
423 r, self.current_index
425 (self.fold_region_fn)(r, self.current_index)
431 ///////////////////////////////////////////////////////////////////////////
432 // Bound vars replacer
434 /// Replaces the escaping bound vars (late bound regions or bound types) in a type.
435 struct BoundVarReplacer<'a, 'tcx> {
438 /// As with `RegionFolder`, represents the index of a binder *just outside*
439 /// the ones we have visited.
440 current_index: ty::DebruijnIndex,
442 fld_r: &'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a),
443 fld_t: &'a mut (dyn FnMut(ty::BoundTy) -> Ty<'tcx> + 'a),
444 fld_c: &'a mut (dyn FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx> + 'a),
447 impl<'a, 'tcx> BoundVarReplacer<'a, 'tcx> {
448 fn new<F, G, H>(tcx: TyCtxt<'tcx>, fld_r: &'a mut F, fld_t: &'a mut G, fld_c: &'a mut H) -> Self
450 F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
451 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
452 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
454 BoundVarReplacer { tcx, current_index: ty::INNERMOST, fld_r, fld_t, fld_c }
458 impl<'a, 'tcx> TypeFolder<'tcx> for BoundVarReplacer<'a, 'tcx> {
459 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
463 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: ty::Binder<T>) -> ty::Binder<T> {
464 self.current_index.shift_in(1);
465 let t = t.super_fold_with(self);
466 self.current_index.shift_out(1);
470 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
472 ty::Bound(debruijn, bound_ty) => {
473 if debruijn == self.current_index {
474 let fld_t = &mut self.fld_t;
475 let ty = fld_t(bound_ty);
476 ty::fold::shift_vars(self.tcx, &ty, self.current_index.as_u32())
482 if !t.has_vars_bound_at_or_above(self.current_index) {
483 // Nothing more to substitute.
486 t.super_fold_with(self)
492 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
494 ty::ReLateBound(debruijn, br) if debruijn == self.current_index => {
495 let fld_r = &mut self.fld_r;
496 let region = fld_r(br);
497 if let ty::ReLateBound(debruijn1, br) = *region {
498 // If the callback returns a late-bound region,
499 // that region should always use the INNERMOST
500 // debruijn index. Then we adjust it to the
502 assert_eq!(debruijn1, ty::INNERMOST);
503 self.tcx.mk_region(ty::ReLateBound(debruijn, br))
512 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
513 if let ty::Const { val: ty::ConstKind::Bound(debruijn, bound_const), ty } = *ct {
514 if debruijn == self.current_index {
515 let fld_c = &mut self.fld_c;
516 let ct = fld_c(bound_const, ty);
517 ty::fold::shift_vars(self.tcx, &ct, self.current_index.as_u32())
522 if !ct.has_vars_bound_at_or_above(self.current_index) {
523 // Nothing more to substitute.
526 ct.super_fold_with(self)
532 impl<'tcx> TyCtxt<'tcx> {
533 /// Replaces all regions bound by the given `Binder` with the
534 /// results returned by the closure; the closure is expected to
535 /// return a free region (relative to this binder), and hence the
536 /// binder is removed in the return type. The closure is invoked
537 /// once for each unique `BoundRegion`; multiple references to the
538 /// same `BoundRegion` will reuse the previous result. A map is
539 /// returned at the end with each bound region and the free region
540 /// that replaced it.
542 /// This method only replaces late bound regions and the result may still
543 /// contain escaping bound types.
544 pub fn replace_late_bound_regions<T, F>(
548 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
550 F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
551 T: TypeFoldable<'tcx>,
553 // identity for bound types and consts
554 let fld_t = |bound_ty| self.mk_ty(ty::Bound(ty::INNERMOST, bound_ty));
555 let fld_c = |bound_ct, ty| {
556 self.mk_const(ty::Const { val: ty::ConstKind::Bound(ty::INNERMOST, bound_ct), ty })
558 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t, fld_c)
561 /// Replaces all escaping bound vars. The `fld_r` closure replaces escaping
562 /// bound regions; the `fld_t` closure replaces escaping bound types and the `fld_c`
563 /// closure replaces escaping bound consts.
564 pub fn replace_escaping_bound_vars<T, F, G, H>(
570 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
572 F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
573 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
574 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
575 T: TypeFoldable<'tcx>,
577 use rustc_data_structures::fx::FxHashMap;
579 let mut region_map = BTreeMap::new();
580 let mut type_map = FxHashMap::default();
581 let mut const_map = FxHashMap::default();
583 if !value.has_escaping_bound_vars() {
584 (value.clone(), region_map)
586 let mut real_fld_r = |br| *region_map.entry(br).or_insert_with(|| fld_r(br));
589 |bound_ty| *type_map.entry(bound_ty).or_insert_with(|| fld_t(bound_ty));
592 |bound_ct, ty| *const_map.entry(bound_ct).or_insert_with(|| fld_c(bound_ct, ty));
595 BoundVarReplacer::new(self, &mut real_fld_r, &mut real_fld_t, &mut real_fld_c);
596 let result = value.fold_with(&mut replacer);
601 /// Replaces all types or regions bound by the given `Binder`. The `fld_r`
602 /// closure replaces bound regions while the `fld_t` closure replaces bound
604 pub fn replace_bound_vars<T, F, G, H>(
610 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
612 F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
613 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
614 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
615 T: TypeFoldable<'tcx>,
617 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t, fld_c)
620 /// Replaces any late-bound regions bound in `value` with
621 /// free variants attached to `all_outlive_scope`.
622 pub fn liberate_late_bound_regions<T>(self, all_outlive_scope: DefId, value: ty::Binder<T>) -> T
624 T: TypeFoldable<'tcx>,
626 self.replace_late_bound_regions(value, |br| {
627 self.mk_region(ty::ReFree(ty::FreeRegion {
628 scope: all_outlive_scope,
635 /// Returns a set of all late-bound regions that are constrained
636 /// by `value`, meaning that if we instantiate those LBR with
637 /// variables and equate `value` with something else, those
638 /// variables will also be equated.
639 pub fn collect_constrained_late_bound_regions<T>(
642 ) -> FxHashSet<ty::BoundRegion>
644 T: TypeFoldable<'tcx>,
646 self.collect_late_bound_regions(value, true)
649 /// Returns a set of all late-bound regions that appear in `value` anywhere.
650 pub fn collect_referenced_late_bound_regions<T>(
653 ) -> FxHashSet<ty::BoundRegion>
655 T: TypeFoldable<'tcx>,
657 self.collect_late_bound_regions(value, false)
660 fn collect_late_bound_regions<T>(
663 just_constraint: bool,
664 ) -> FxHashSet<ty::BoundRegion>
666 T: TypeFoldable<'tcx>,
668 let mut collector = LateBoundRegionsCollector::new(just_constraint);
669 let result = value.as_ref().skip_binder().visit_with(&mut collector);
670 assert!(result.is_continue()); // should never have stopped early
674 /// Replaces any late-bound regions bound in `value` with `'erased`. Useful in codegen but also
675 /// method lookup and a few other places where precise region relationships are not required.
676 pub fn erase_late_bound_regions<T>(self, value: Binder<T>) -> T
678 T: TypeFoldable<'tcx>,
680 self.replace_late_bound_regions(value, |_| self.lifetimes.re_erased).0
683 /// Rewrite any late-bound regions so that they are anonymous. Region numbers are
684 /// assigned starting at 0 and increasing monotonically in the order traversed
685 /// by the fold operation.
687 /// The chief purpose of this function is to canonicalize regions so that two
688 /// `FnSig`s or `TraitRef`s which are equivalent up to region naming will become
689 /// structurally identical. For example, `for<'a, 'b> fn(&'a isize, &'b isize)` and
690 /// `for<'a, 'b> fn(&'b isize, &'a isize)` will become identical after anonymization.
691 pub fn anonymize_late_bound_regions<T>(self, sig: Binder<T>) -> Binder<T>
693 T: TypeFoldable<'tcx>,
697 self.replace_late_bound_regions(sig, |_| {
698 let r = self.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BrAnon(counter)));
707 ///////////////////////////////////////////////////////////////////////////
710 // Shifts the De Bruijn indices on all escaping bound vars by a
711 // fixed amount. Useful in substitution or when otherwise introducing
712 // a binding level that is not intended to capture the existing bound
713 // vars. See comment on `shift_vars_through_binders` method in
714 // `subst.rs` for more details.
716 struct Shifter<'tcx> {
718 current_index: ty::DebruijnIndex,
723 pub fn new(tcx: TyCtxt<'tcx>, amount: u32) -> Self {
724 Shifter { tcx, current_index: ty::INNERMOST, amount }
728 impl TypeFolder<'tcx> for Shifter<'tcx> {
729 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
733 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: ty::Binder<T>) -> ty::Binder<T> {
734 self.current_index.shift_in(1);
735 let t = t.super_fold_with(self);
736 self.current_index.shift_out(1);
740 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
742 ty::ReLateBound(debruijn, br) => {
743 if self.amount == 0 || debruijn < self.current_index {
746 let debruijn = debruijn.shifted_in(self.amount);
747 let shifted = ty::ReLateBound(debruijn, br);
748 self.tcx.mk_region(shifted)
755 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
757 ty::Bound(debruijn, bound_ty) => {
758 if self.amount == 0 || debruijn < self.current_index {
761 let debruijn = debruijn.shifted_in(self.amount);
762 self.tcx.mk_ty(ty::Bound(debruijn, bound_ty))
766 _ => ty.super_fold_with(self),
770 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
771 if let ty::Const { val: ty::ConstKind::Bound(debruijn, bound_ct), ty } = *ct {
772 if self.amount == 0 || debruijn < self.current_index {
775 let debruijn = debruijn.shifted_in(self.amount);
776 self.tcx.mk_const(ty::Const { val: ty::ConstKind::Bound(debruijn, bound_ct), ty })
779 ct.super_fold_with(self)
784 pub fn shift_region<'tcx>(
786 region: ty::Region<'tcx>,
788 ) -> ty::Region<'tcx> {
790 ty::ReLateBound(debruijn, br) if amount > 0 => {
791 tcx.mk_region(ty::ReLateBound(debruijn.shifted_in(amount), *br))
797 pub fn shift_vars<'tcx, T>(tcx: TyCtxt<'tcx>, value: T, amount: u32) -> T
799 T: TypeFoldable<'tcx>,
801 debug!("shift_vars(value={:?}, amount={})", value, amount);
803 value.fold_with(&mut Shifter::new(tcx, amount))
806 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
807 struct FoundEscapingVars;
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 type BreakTy = FoundEscapingVars;
842 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> ControlFlow<Self::BreakTy> {
843 self.outer_index.shift_in(1);
844 let result = t.super_visit_with(self);
845 self.outer_index.shift_out(1);
849 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
850 // If the outer-exclusive-binder is *strictly greater* than
851 // `outer_index`, that means that `t` contains some content
852 // bound at `outer_index` or above (because
853 // `outer_exclusive_binder` is always 1 higher than the
854 // content in `t`). Therefore, `t` has some escaping vars.
855 if t.outer_exclusive_binder > self.outer_index {
856 ControlFlow::Break(FoundEscapingVars)
858 ControlFlow::CONTINUE
862 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
863 // If the region is bound by `outer_index` or anything outside
864 // of outer index, then it escapes the binders we have
866 if r.bound_at_or_above_binder(self.outer_index) {
867 ControlFlow::Break(FoundEscapingVars)
869 ControlFlow::CONTINUE
873 fn visit_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
874 // we don't have a `visit_infer_const` callback, so we have to
875 // hook in here to catch this case (annoying...), but
876 // otherwise we do want to remember to visit the rest of the
877 // const, as it has types/regions embedded in a lot of other
880 ty::ConstKind::Bound(debruijn, _) if debruijn >= self.outer_index => {
881 ControlFlow::Break(FoundEscapingVars)
883 _ => ct.super_visit_with(self),
887 fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
888 if predicate.inner.outer_exclusive_binder > self.outer_index {
889 ControlFlow::Break(FoundEscapingVars)
891 ControlFlow::CONTINUE
896 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
899 // FIXME: Optimize for checking for infer flags
900 struct HasTypeFlagsVisitor {
901 flags: ty::TypeFlags,
904 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
905 type BreakTy = FoundFlags;
907 fn visit_ty(&mut self, t: Ty<'_>) -> ControlFlow<Self::BreakTy> {
909 "HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}",
914 if t.flags().intersects(self.flags) {
915 ControlFlow::Break(FoundFlags)
917 ControlFlow::CONTINUE
921 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
922 let flags = r.type_flags();
923 debug!("HasTypeFlagsVisitor: r={:?} r.flags={:?} self.flags={:?}", r, flags, self.flags);
924 if flags.intersects(self.flags) {
925 ControlFlow::Break(FoundFlags)
927 ControlFlow::CONTINUE
931 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
932 let flags = FlagComputation::for_const(c);
933 debug!("HasTypeFlagsVisitor: c={:?} c.flags={:?} self.flags={:?}", c, flags, self.flags);
934 if flags.intersects(self.flags) {
935 ControlFlow::Break(FoundFlags)
937 ControlFlow::CONTINUE
941 fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
943 "HasTypeFlagsVisitor: predicate={:?} predicate.flags={:?} self.flags={:?}",
944 predicate, predicate.inner.flags, self.flags
946 if predicate.inner.flags.intersects(self.flags) {
947 ControlFlow::Break(FoundFlags)
949 ControlFlow::CONTINUE
954 /// Collects all the late-bound regions at the innermost binding level
956 struct LateBoundRegionsCollector {
957 current_index: ty::DebruijnIndex,
958 regions: FxHashSet<ty::BoundRegion>,
960 /// `true` if we only want regions that are known to be
961 /// "constrained" when you equate this type with another type. In
962 /// particular, if you have e.g., `&'a u32` and `&'b u32`, equating
963 /// them constraints `'a == 'b`. But if you have `<&'a u32 as
964 /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
965 /// types may mean that `'a` and `'b` don't appear in the results,
966 /// so they are not considered *constrained*.
967 just_constrained: bool,
970 impl LateBoundRegionsCollector {
971 fn new(just_constrained: bool) -> Self {
972 LateBoundRegionsCollector {
973 current_index: ty::INNERMOST,
974 regions: Default::default(),
980 impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
981 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> ControlFlow<Self::BreakTy> {
982 self.current_index.shift_in(1);
983 let result = t.super_visit_with(self);
984 self.current_index.shift_out(1);
988 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
989 // if we are only looking for "constrained" region, we have to
990 // ignore the inputs to a projection, as they may not appear
991 // in the normalized form
992 if self.just_constrained {
993 if let ty::Projection(..) | ty::Opaque(..) = t.kind() {
994 return ControlFlow::CONTINUE;
998 t.super_visit_with(self)
1001 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
1002 // if we are only looking for "constrained" region, we have to
1003 // ignore the inputs of an unevaluated const, as they may not appear
1004 // in the normalized form
1005 if self.just_constrained {
1006 if let ty::ConstKind::Unevaluated(..) = c.val {
1007 return ControlFlow::CONTINUE;
1011 c.super_visit_with(self)
1014 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
1015 if let ty::ReLateBound(debruijn, br) = *r {
1016 if debruijn == self.current_index {
1017 self.regions.insert(br);
1020 ControlFlow::CONTINUE