1 // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Generalized type folding mechanism. The setup is a bit convoluted
12 //! but allows for convenient usage. Let T be an instance of some
13 //! "foldable type" (one which implements `TypeFoldable`) and F be an
14 //! instance of a "folder" (a type which implements `TypeFolder`). Then
15 //! the setup is intended to be:
17 //! T.fold_with(F) --calls--> F.fold_T(T) --calls--> T.super_fold_with(F)
19 //! This way, when you define a new folder F, you can override
20 //! `fold_T()` to customize the behavior, and invoke `T.super_fold_with()`
21 //! to get the original behavior. Meanwhile, to actually fold
22 //! something, you can just write `T.fold_with(F)`, which is
23 //! convenient. (Note that `fold_with` will also transparently handle
24 //! things like a `Vec<T>` where T is foldable and so on.)
26 //! In this ideal setup, the only function that actually *does*
27 //! anything is `T.super_fold_with()`, which traverses the type `T`.
28 //! Moreover, `T.super_fold_with()` should only ever call `T.fold_with()`.
30 //! In some cases, we follow a degenerate pattern where we do not have
31 //! a `fold_T` method. Instead, `T.fold_with` traverses the structure directly.
32 //! This is suboptimal because the behavior cannot be overridden, but it's
33 //! much less work to implement. If you ever *do* need an override that
34 //! doesn't exist, it's not hard to convert the degenerate pattern into the
37 //! A `TypeFoldable` T can also be visited by a `TypeVisitor` V using similar setup:
38 //! T.visit_with(V) --calls--> V.visit_T(T) --calls--> T.super_visit_with(V).
39 //! These methods return true to indicate that the visitor has found what it is looking for
40 //! and does not need to visit anything else.
42 use mir::interpret::ConstValue;
43 use hir::def_id::DefId;
44 use ty::{self, Binder, Ty, TyCtxt, TypeFlags};
46 use std::collections::BTreeMap;
48 use util::nodemap::FxHashSet;
50 /// The TypeFoldable trait is implemented for every type that can be folded.
51 /// Basically, every type that has a corresponding method in TypeFolder.
53 /// To implement this conveniently, use the
54 /// `BraceStructTypeFoldableImpl` etc macros found in `macros.rs`.
55 pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
56 fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self;
57 fn fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
58 self.super_fold_with(folder)
61 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool;
62 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
63 self.super_visit_with(visitor)
66 /// True if `self` has any late-bound regions that are either
67 /// bound by `binder` or bound by some binder outside of `binder`.
68 /// If `binder` is `ty::INNERMOST`, this indicates whether
69 /// there are any late-bound regions that appear free.
70 fn has_vars_bound_at_or_above(&self, binder: ty::DebruijnIndex) -> bool {
71 self.visit_with(&mut HasEscapingVarsVisitor { outer_index: binder })
74 /// True if this `self` has any regions that escape `binder` (and
75 /// hence are not bound by it).
76 fn has_vars_bound_above(&self, binder: ty::DebruijnIndex) -> bool {
77 self.has_vars_bound_at_or_above(binder.shifted_in(1))
80 fn has_escaping_bound_vars(&self) -> bool {
81 self.has_vars_bound_at_or_above(ty::INNERMOST)
84 fn has_type_flags(&self, flags: TypeFlags) -> bool {
85 self.visit_with(&mut HasTypeFlagsVisitor { flags })
87 fn has_projections(&self) -> bool {
88 self.has_type_flags(TypeFlags::HAS_PROJECTION)
90 fn references_error(&self) -> bool {
91 self.has_type_flags(TypeFlags::HAS_TY_ERR)
93 fn has_param_types(&self) -> bool {
94 self.has_type_flags(TypeFlags::HAS_PARAMS)
96 fn has_self_ty(&self) -> bool {
97 self.has_type_flags(TypeFlags::HAS_SELF)
99 fn has_infer_types(&self) -> bool {
100 self.has_type_flags(TypeFlags::HAS_TY_INFER)
102 fn needs_infer(&self) -> bool {
103 self.has_type_flags(TypeFlags::HAS_TY_INFER | TypeFlags::HAS_RE_INFER)
105 fn has_placeholders(&self) -> bool {
106 self.has_type_flags(TypeFlags::HAS_RE_PLACEHOLDER | TypeFlags::HAS_TY_PLACEHOLDER)
108 fn needs_subst(&self) -> bool {
109 self.has_type_flags(TypeFlags::NEEDS_SUBST)
111 fn has_re_placeholders(&self) -> bool {
112 self.has_type_flags(TypeFlags::HAS_RE_PLACEHOLDER)
114 fn has_closure_types(&self) -> bool {
115 self.has_type_flags(TypeFlags::HAS_TY_CLOSURE)
117 /// "Free" regions in this context means that it has any region
118 /// that is not (a) erased or (b) late-bound.
119 fn has_free_regions(&self) -> bool {
120 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
123 /// True if there any any un-erased free regions.
124 fn has_erasable_regions(&self) -> bool {
125 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
128 /// Indicates whether this value references only 'global'
129 /// types/lifetimes that are the same regardless of what fn we are
130 /// in. This is used for caching.
131 fn is_global(&self) -> bool {
132 !self.has_type_flags(TypeFlags::HAS_FREE_LOCAL_NAMES)
135 /// True if there are any late-bound regions
136 fn has_late_bound_regions(&self) -> bool {
137 self.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND)
140 /// A visitor that does not recurse into types, works like `fn walk_shallow` in `Ty`.
141 fn visit_tys_shallow(&self, visit: impl FnMut(Ty<'tcx>) -> bool) -> bool {
143 pub struct Visitor<F>(F);
145 impl<'tcx, F: FnMut(Ty<'tcx>) -> bool> TypeVisitor<'tcx> for Visitor<F> {
146 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
151 self.visit_with(&mut Visitor(visit))
155 /// The TypeFolder trait defines the actual *folding*. There is a
156 /// method defined for every foldable type. Each of these has a
157 /// default implementation that does an "identity" fold. Within each
158 /// identity fold, it should invoke `foo.fold_with(self)` to fold each
160 pub trait TypeFolder<'gcx: 'tcx, 'tcx> : Sized {
161 fn tcx<'a>(&'a self) -> TyCtxt<'a, 'gcx, 'tcx>;
163 fn fold_binder<T>(&mut self, t: &Binder<T>) -> Binder<T>
164 where T : TypeFoldable<'tcx>
166 t.super_fold_with(self)
169 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
170 t.super_fold_with(self)
173 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
174 r.super_fold_with(self)
177 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
178 c.super_fold_with(self)
182 pub trait TypeVisitor<'tcx> : Sized {
183 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
184 t.super_visit_with(self)
187 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
188 t.super_visit_with(self)
191 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
192 r.super_visit_with(self)
195 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
196 c.super_visit_with(self)
200 ///////////////////////////////////////////////////////////////////////////
201 // Some sample folders
203 pub struct BottomUpFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a, F, G>
204 where F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
205 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
207 pub tcx: TyCtxt<'a, 'gcx, 'tcx>,
212 impl<'a, 'gcx, 'tcx, F, G> TypeFolder<'gcx, 'tcx> for BottomUpFolder<'a, 'gcx, 'tcx, F, G>
213 where F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
214 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
216 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
218 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
219 let t1 = ty.super_fold_with(self);
223 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
224 let r = r.super_fold_with(self);
229 ///////////////////////////////////////////////////////////////////////////
232 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
233 /// Collects the free and escaping regions in `value` into `region_set`. Returns
234 /// whether any late-bound regions were skipped
235 pub fn collect_regions<T>(self,
237 region_set: &mut FxHashSet<ty::Region<'tcx>>)
239 where T : TypeFoldable<'tcx>
241 let mut have_bound_regions = false;
242 self.fold_regions(value, &mut have_bound_regions, |r, d| {
243 region_set.insert(self.mk_region(r.shifted_out_to_binder(d)));
249 /// Folds the escaping and free regions in `value` using `f`, and
250 /// sets `skipped_regions` to true if any late-bound region was found
252 pub fn fold_regions<T>(
255 skipped_regions: &mut bool,
256 mut f: impl FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
259 T : TypeFoldable<'tcx>,
261 value.fold_with(&mut RegionFolder::new(self, skipped_regions, &mut f))
264 /// Invoke `callback` on every region appearing free in `value`.
265 pub fn for_each_free_region(
267 value: &impl TypeFoldable<'tcx>,
268 mut callback: impl FnMut(ty::Region<'tcx>),
270 self.any_free_region_meets(value, |r| {
276 /// True if `callback` returns true for every region appearing free in `value`.
277 pub fn all_free_regions_meet(
279 value: &impl TypeFoldable<'tcx>,
280 mut callback: impl FnMut(ty::Region<'tcx>) -> bool,
282 !self.any_free_region_meets(value, |r| !callback(r))
285 /// True if `callback` returns true for some region appearing free in `value`.
286 pub fn any_free_region_meets(
288 value: &impl TypeFoldable<'tcx>,
289 callback: impl FnMut(ty::Region<'tcx>) -> bool,
291 return value.visit_with(&mut RegionVisitor {
292 outer_index: ty::INNERMOST,
296 struct RegionVisitor<F> {
297 /// The index of a binder *just outside* the things we have
298 /// traversed. If we encounter a bound region bound by this
299 /// binder or one outer to it, it appears free. Example:
302 /// for<'a> fn(for<'b> fn(), T)
304 /// | | | | here, would be shifted in 1
305 /// | | | here, would be shifted in 2
306 /// | | here, would be INNERMOST shifted in by 1
307 /// | here, initially, binder would be INNERMOST
310 /// You see that, initially, *any* bound value is free,
311 /// because we've not traversed any binders. As we pass
312 /// through a binder, we shift the `outer_index` by 1 to
313 /// account for the new binder that encloses us.
314 outer_index: ty::DebruijnIndex,
318 impl<'tcx, F> TypeVisitor<'tcx> for RegionVisitor<F>
319 where F: FnMut(ty::Region<'tcx>) -> bool
321 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
322 self.outer_index.shift_in(1);
323 let result = t.skip_binder().visit_with(self);
324 self.outer_index.shift_out(1);
328 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
330 ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => {
331 false // ignore bound regions, keep visiting
333 _ => (self.callback)(r),
337 fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
338 // We're only interested in types involving regions
339 if ty.flags.intersects(TypeFlags::HAS_FREE_REGIONS) {
340 ty.super_visit_with(self)
342 false // keep visiting
349 /// Folds over the substructure of a type, visiting its component
350 /// types and all regions that occur *free* within it.
352 /// That is, `Ty` can contain function or method types that bind
353 /// regions at the call site (`ReLateBound`), and occurrences of
354 /// regions (aka "lifetimes") that are bound within a type are not
355 /// visited by this folder; only regions that occur free will be
356 /// visited by `fld_r`.
358 pub struct RegionFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
359 tcx: TyCtxt<'a, 'gcx, 'tcx>,
360 skipped_regions: &'a mut bool,
362 /// Stores the index of a binder *just outside* the stuff we have
363 /// visited. So this begins as INNERMOST; when we pass through a
364 /// binder, it is incremented (via `shift_in`).
365 current_index: ty::DebruijnIndex,
367 /// Callback invokes for each free region. The `DebruijnIndex`
368 /// points to the binder *just outside* the ones we have passed
370 fold_region_fn: &'a mut (dyn FnMut(
373 ) -> ty::Region<'tcx> + 'a),
376 impl<'a, 'gcx, 'tcx> RegionFolder<'a, 'gcx, 'tcx> {
379 tcx: TyCtxt<'a, 'gcx, 'tcx>,
380 skipped_regions: &'a mut bool,
381 fold_region_fn: &'a mut dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
382 ) -> RegionFolder<'a, 'gcx, 'tcx> {
386 current_index: ty::INNERMOST,
392 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionFolder<'a, 'gcx, 'tcx> {
393 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
395 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
396 self.current_index.shift_in(1);
397 let t = t.super_fold_with(self);
398 self.current_index.shift_out(1);
402 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
404 ty::ReLateBound(debruijn, _) if debruijn < self.current_index => {
405 debug!("RegionFolder.fold_region({:?}) skipped bound region (current index={:?})",
406 r, self.current_index);
407 *self.skipped_regions = true;
411 debug!("RegionFolder.fold_region({:?}) folding free region (current_index={:?})",
412 r, self.current_index);
413 (self.fold_region_fn)(r, self.current_index)
419 ///////////////////////////////////////////////////////////////////////////
420 // Bound vars replacer
422 /// Replaces the escaping bound vars (late bound regions or bound types) in a type.
423 struct BoundVarReplacer<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
424 tcx: TyCtxt<'a, 'gcx, 'tcx>,
426 /// As with `RegionFolder`, represents the index of a binder *just outside*
427 /// the ones we have visited.
428 current_index: ty::DebruijnIndex,
430 fld_r: &'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a),
431 fld_t: &'a mut (dyn FnMut(ty::BoundTy) -> ty::Ty<'tcx> + 'a),
434 impl<'a, 'gcx, 'tcx> BoundVarReplacer<'a, 'gcx, 'tcx> {
436 tcx: TyCtxt<'a, 'gcx, 'tcx>,
440 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
441 G: FnMut(ty::BoundTy) -> ty::Ty<'tcx>
445 current_index: ty::INNERMOST,
452 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for BoundVarReplacer<'a, 'gcx, 'tcx> {
453 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
455 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
456 self.current_index.shift_in(1);
457 let t = t.super_fold_with(self);
458 self.current_index.shift_out(1);
462 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
464 ty::Bound(debruijn, bound_ty) => {
465 if debruijn == self.current_index {
466 let fld_t = &mut self.fld_t;
467 let ty = fld_t(bound_ty);
468 ty::fold::shift_vars(
471 self.current_index.as_u32()
478 if !t.has_vars_bound_at_or_above(self.current_index) {
479 // Nothing more to substitute.
482 t.super_fold_with(self)
488 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
490 ty::ReLateBound(debruijn, br) if debruijn == self.current_index => {
491 let fld_r = &mut self.fld_r;
492 let region = fld_r(br);
493 if let ty::ReLateBound(debruijn1, br) = *region {
494 // If the callback returns a late-bound region,
495 // that region should always use the INNERMOST
496 // debruijn index. Then we adjust it to the
498 assert_eq!(debruijn1, ty::INNERMOST);
499 self.tcx.mk_region(ty::ReLateBound(debruijn, br))
509 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
510 /// Replace all regions bound by the given `Binder` with the
511 /// results returned by the closure; the closure is expected to
512 /// return a free region (relative to this binder), and hence the
513 /// binder is removed in the return type. The closure is invoked
514 /// once for each unique `BoundRegion`; multiple references to the
515 /// same `BoundRegion` will reuse the previous result. A map is
516 /// returned at the end with each bound region and the free region
517 /// that replaced it.
519 /// This method only replaces late bound regions and the result may still
520 /// contain escaping bound types.
521 pub fn replace_late_bound_regions<T, F>(
525 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
526 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
527 T: TypeFoldable<'tcx>
529 // identity for bound types
530 let fld_t = |bound_ty| self.mk_ty(ty::Bound(ty::INNERMOST, bound_ty));
531 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t)
534 /// Replace all escaping bound vars. The `fld_r` closure replaces escaping
535 /// bound regions while the `fld_t` closure replaces escaping bound types.
536 pub fn replace_escaping_bound_vars<T, F, G>(
541 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
542 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
543 G: FnMut(ty::BoundTy) -> ty::Ty<'tcx>,
544 T: TypeFoldable<'tcx>
546 let mut map = BTreeMap::new();
548 if !value.has_escaping_bound_vars() {
551 let mut real_fld_r = |br| {
552 *map.entry(br).or_insert_with(|| fld_r(br))
555 let mut replacer = BoundVarReplacer::new(self, &mut real_fld_r, &mut fld_t);
556 let result = value.fold_with(&mut replacer);
561 /// Replace all types or regions bound by the given `Binder`. The `fld_r`
562 /// closure replaces bound regions while the `fld_t` closure replaces bound
564 pub fn replace_bound_vars<T, F, G>(
569 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
570 where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
571 G: FnMut(ty::BoundTy) -> ty::Ty<'tcx>,
572 T: TypeFoldable<'tcx>
574 self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t)
577 /// Replace any late-bound regions bound in `value` with
578 /// free variants attached to `all_outlive_scope`.
579 pub fn liberate_late_bound_regions<T>(
581 all_outlive_scope: DefId,
582 value: &ty::Binder<T>
584 where T: TypeFoldable<'tcx> {
585 self.replace_late_bound_regions(value, |br| {
586 self.mk_region(ty::ReFree(ty::FreeRegion {
587 scope: all_outlive_scope,
593 /// Flattens multiple binding levels into one. So `for<'a> for<'b> Foo`
594 /// becomes `for<'a,'b> Foo`.
595 pub fn flatten_late_bound_regions<T>(self, bound2_value: &Binder<Binder<T>>)
597 where T: TypeFoldable<'tcx>
599 let bound0_value = bound2_value.skip_binder().skip_binder();
600 let value = self.fold_regions(bound0_value, &mut false, |region, current_depth| {
602 ty::ReLateBound(debruijn, br) => {
603 // We assume no regions bound *outside* of the
604 // binders in `bound2_value` (nmatsakis added in
605 // the course of this PR; seems like a reasonable
606 // sanity check though).
607 assert!(debruijn == current_depth);
608 self.mk_region(ty::ReLateBound(current_depth, br))
618 /// Returns a set of all late-bound regions that are constrained
619 /// by `value`, meaning that if we instantiate those LBR with
620 /// variables and equate `value` with something else, those
621 /// variables will also be equated.
622 pub fn collect_constrained_late_bound_regions<T>(&self, value: &Binder<T>)
623 -> FxHashSet<ty::BoundRegion>
624 where T : TypeFoldable<'tcx>
626 self.collect_late_bound_regions(value, true)
629 /// Returns a set of all late-bound regions that appear in `value` anywhere.
630 pub fn collect_referenced_late_bound_regions<T>(&self, value: &Binder<T>)
631 -> FxHashSet<ty::BoundRegion>
632 where T : TypeFoldable<'tcx>
634 self.collect_late_bound_regions(value, false)
637 fn collect_late_bound_regions<T>(&self, value: &Binder<T>, just_constraint: bool)
638 -> FxHashSet<ty::BoundRegion>
639 where T : TypeFoldable<'tcx>
641 let mut collector = LateBoundRegionsCollector::new(just_constraint);
642 let result = value.skip_binder().visit_with(&mut collector);
643 assert!(!result); // should never have stopped early
647 /// Replace any late-bound regions bound in `value` with `'erased`. Useful in codegen but also
648 /// method lookup and a few other places where precise region relationships are not required.
649 pub fn erase_late_bound_regions<T>(self, value: &Binder<T>) -> T
650 where T : TypeFoldable<'tcx>
652 self.replace_late_bound_regions(value, |_| self.types.re_erased).0
655 /// Rewrite any late-bound regions so that they are anonymous. Region numbers are
656 /// assigned starting at 1 and increasing monotonically in the order traversed
657 /// by the fold operation.
659 /// The chief purpose of this function is to canonicalize regions so that two
660 /// `FnSig`s or `TraitRef`s which are equivalent up to region naming will become
661 /// structurally identical. For example, `for<'a, 'b> fn(&'a isize, &'b isize)` and
662 /// `for<'a, 'b> fn(&'b isize, &'a isize)` will become identical after anonymization.
663 pub fn anonymize_late_bound_regions<T>(self, sig: &Binder<T>) -> Binder<T>
664 where T : TypeFoldable<'tcx>,
667 Binder::bind(self.replace_late_bound_regions(sig, |_| {
669 self.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BrAnon(counter)))
674 ///////////////////////////////////////////////////////////////////////////
677 // Shifts the De Bruijn indices on all escaping bound vars by a
678 // fixed amount. Useful in substitution or when otherwise introducing
679 // a binding level that is not intended to capture the existing bound
680 // vars. See comment on `shift_vars_through_binders` method in
681 // `subst.rs` for more details.
683 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
689 struct Shifter<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
690 tcx: TyCtxt<'a, 'gcx, 'tcx>,
691 current_index: ty::DebruijnIndex,
693 direction: Direction,
696 impl Shifter<'a, 'gcx, 'tcx> {
697 pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>, amount: u32, direction: Direction) -> Self {
700 current_index: ty::INNERMOST,
707 impl TypeFolder<'gcx, 'tcx> for Shifter<'a, 'gcx, 'tcx> {
708 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
710 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
711 self.current_index.shift_in(1);
712 let t = t.super_fold_with(self);
713 self.current_index.shift_out(1);
717 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
719 ty::ReLateBound(debruijn, br) => {
720 if self.amount == 0 || debruijn < self.current_index {
723 let debruijn = match self.direction {
724 Direction::In => debruijn.shifted_in(self.amount),
726 assert!(debruijn.as_u32() >= self.amount);
727 debruijn.shifted_out(self.amount)
730 let shifted = ty::ReLateBound(debruijn, br);
731 self.tcx.mk_region(shifted)
738 fn fold_ty(&mut self, ty: ty::Ty<'tcx>) -> ty::Ty<'tcx> {
740 ty::Bound(debruijn, bound_ty) => {
741 if self.amount == 0 || debruijn < self.current_index {
744 let debruijn = match self.direction {
745 Direction::In => debruijn.shifted_in(self.amount),
747 assert!(debruijn.as_u32() >= self.amount);
748 debruijn.shifted_out(self.amount)
752 ty::Bound(debruijn, bound_ty)
757 _ => ty.super_fold_with(self),
762 pub fn shift_region<'a, 'gcx, 'tcx>(
763 tcx: TyCtxt<'a, 'gcx, 'tcx>,
764 region: ty::Region<'tcx>,
766 ) -> ty::Region<'tcx> {
768 ty::ReLateBound(debruijn, br) if amount > 0 => {
769 tcx.mk_region(ty::ReLateBound(debruijn.shifted_in(amount), *br))
777 pub fn shift_vars<'a, 'gcx, 'tcx, T>(
778 tcx: TyCtxt<'a, 'gcx, 'tcx>,
781 ) -> T where T: TypeFoldable<'tcx> {
782 debug!("shift_vars(value={:?}, amount={})",
785 value.fold_with(&mut Shifter::new(tcx, amount, Direction::In))
788 pub fn shift_out_vars<'a, 'gcx, 'tcx, T>(
789 tcx: TyCtxt<'a, 'gcx, 'tcx>,
792 ) -> T where T: TypeFoldable<'tcx> {
793 debug!("shift_out_vars(value={:?}, amount={})",
796 value.fold_with(&mut Shifter::new(tcx, amount, Direction::Out))
799 /// An "escaping var" is a bound var whose binder is not part of `t`. A bound var can be a
800 /// bound region or a bound type.
802 /// So, for example, consider a type like the following, which has two binders:
804 /// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize))
805 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope
806 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope
808 /// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the
809 /// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner
810 /// fn type*, that type has an escaping region: `'a`.
812 /// Note that what I'm calling an "escaping var" is often just called a "free var". However,
813 /// we already use the term "free var". It refers to the regions or types that we use to represent
814 /// bound regions or type params on a fn definition while we are type checking its body.
816 /// To clarify, conceptually there is no particular difference between
817 /// an "escaping" var and a "free" var. However, there is a big
818 /// difference in practice. Basically, when "entering" a binding
819 /// level, one is generally required to do some sort of processing to
820 /// a bound var, such as replacing it with a fresh/placeholder
821 /// var, or making an entry in the environment to represent the
822 /// scope to which it is attached, etc. An escaping var represents
823 /// a bound var for which this processing has not yet been done.
824 struct HasEscapingVarsVisitor {
825 /// Anything bound by `outer_index` or "above" is escaping
826 outer_index: ty::DebruijnIndex,
829 impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
830 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
831 self.outer_index.shift_in(1);
832 let result = t.super_visit_with(self);
833 self.outer_index.shift_out(1);
837 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
838 // If the outer-exclusive-binder is *strictly greater* than
839 // `outer_index`, that means that `t` contains some content
840 // bound at `outer_index` or above (because
841 // `outer_exclusive_binder` is always 1 higher than the
842 // content in `t`). Therefore, `t` has some escaping vars.
843 t.outer_exclusive_binder > self.outer_index
846 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
847 // If the region is bound by `outer_index` or anything outside
848 // of outer index, then it escapes the binders we have
850 r.bound_at_or_above_binder(self.outer_index)
854 struct HasTypeFlagsVisitor {
855 flags: ty::TypeFlags,
858 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
859 fn visit_ty(&mut self, t: Ty<'_>) -> bool {
860 debug!("HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}", t, t.flags, self.flags);
861 t.flags.intersects(self.flags)
864 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
865 let flags = r.type_flags();
866 debug!("HasTypeFlagsVisitor: r={:?} r.flags={:?} self.flags={:?}", r, flags, self.flags);
867 flags.intersects(self.flags)
870 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
871 if let ConstValue::Unevaluated(..) = c.val {
872 let projection_flags = TypeFlags::HAS_NORMALIZABLE_PROJECTION |
873 TypeFlags::HAS_PROJECTION;
874 if projection_flags.intersects(self.flags) {
878 c.super_visit_with(self)
882 /// Collects all the late-bound regions at the innermost binding level
884 struct LateBoundRegionsCollector {
885 current_index: ty::DebruijnIndex,
886 regions: FxHashSet<ty::BoundRegion>,
888 /// If true, we only want regions that are known to be
889 /// "constrained" when you equate this type with another type. In
890 /// particular, if you have e.g. `&'a u32` and `&'b u32`, equating
891 /// them constraints `'a == 'b`. But if you have `<&'a u32 as
892 /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
893 /// types may mean that `'a` and `'b` don't appear in the results,
894 /// so they are not considered *constrained*.
895 just_constrained: bool,
898 impl LateBoundRegionsCollector {
899 fn new(just_constrained: bool) -> Self {
900 LateBoundRegionsCollector {
901 current_index: ty::INNERMOST,
902 regions: Default::default(),
908 impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
909 fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool {
910 self.current_index.shift_in(1);
911 let result = t.super_visit_with(self);
912 self.current_index.shift_out(1);
916 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
917 // if we are only looking for "constrained" region, we have to
918 // ignore the inputs to a projection, as they may not appear
919 // in the normalized form
920 if self.just_constrained {
922 ty::Projection(..) | ty::Opaque(..) => { return false; }
927 t.super_visit_with(self)
930 fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
931 if let ty::ReLateBound(debruijn, br) = *r {
932 if debruijn == self.current_index {
933 self.regions.insert(br);