| // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| //! Generalized type folding mechanism. The setup is a bit convoluted |
| //! but allows for convenient usage. Let T be an instance of some |
| //! "foldable type" (one which implements `TypeFoldable`) and F be an |
| //! instance of a "folder" (a type which implements `TypeFolder`). Then |
| //! the setup is intended to be: |
| //! |
| //! T.fold_with(F) --calls--> F.fold_T(T) --calls--> T.super_fold_with(F) |
| //! |
| //! This way, when you define a new folder F, you can override |
| //! `fold_T()` to customize the behavior, and invoke `T.super_fold_with()` |
| //! to get the original behavior. Meanwhile, to actually fold |
| //! something, you can just write `T.fold_with(F)`, which is |
| //! convenient. (Note that `fold_with` will also transparently handle |
| //! things like a `Vec<T>` where T is foldable and so on.) |
| //! |
| //! In this ideal setup, the only function that actually *does* |
| //! anything is `T.super_fold_with()`, which traverses the type `T`. |
| //! Moreover, `T.super_fold_with()` should only ever call `T.fold_with()`. |
| //! |
| //! In some cases, we follow a degenerate pattern where we do not have |
| //! a `fold_T` method. Instead, `T.fold_with` traverses the structure directly. |
| //! This is suboptimal because the behavior cannot be overridden, but it's |
| //! much less work to implement. If you ever *do* need an override that |
| //! doesn't exist, it's not hard to convert the degenerate pattern into the |
| //! proper thing. |
| //! |
| //! A `TypeFoldable` T can also be visited by a `TypeVisitor` V using similar setup: |
| //! T.visit_with(V) --calls--> V.visit_T(T) --calls--> T.super_visit_with(V). |
| //! These methods return true to indicate that the visitor has found what it is looking for |
| //! and does not need to visit anything else. |
| |
| use middle::const_val::ConstVal; |
| use hir::def_id::DefId; |
| use ty::{self, Binder, Ty, TyCtxt, TypeFlags}; |
| |
| use std::collections::BTreeMap; |
| use std::fmt; |
| use util::nodemap::FxHashSet; |
| |
| /// The TypeFoldable trait is implemented for every type that can be folded. |
| /// Basically, every type that has a corresponding method in TypeFolder. |
| /// |
| /// To implement this conveniently, use the |
| /// `BraceStructTypeFoldableImpl` etc macros found in `macros.rs`. |
| pub trait TypeFoldable<'tcx>: fmt::Debug + Clone { |
| fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self; |
| fn fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self { |
| self.super_fold_with(folder) |
| } |
| |
| fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool; |
| fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool { |
| self.super_visit_with(visitor) |
| } |
| |
| /// True if `self` has any late-bound regions that are either |
| /// bound by `binder` or bound by some binder outside of `binder`. |
| /// If `binder` is `ty::INNERMOST`, this indicates whether |
| /// there are any late-bound regions that appear free. |
| fn has_regions_bound_at_or_above(&self, binder: ty::DebruijnIndex) -> bool { |
| self.visit_with(&mut HasEscapingRegionsVisitor { outer_index: binder }) |
| } |
| |
| /// True if this `self` has any regions that escape `binder` (and |
| /// hence are not bound by it). |
| fn has_regions_bound_above(&self, binder: ty::DebruijnIndex) -> bool { |
| self.has_regions_bound_at_or_above(binder.shifted_in(1)) |
| } |
| |
| fn has_escaping_regions(&self) -> bool { |
| self.has_regions_bound_at_or_above(ty::INNERMOST) |
| } |
| |
| fn has_type_flags(&self, flags: TypeFlags) -> bool { |
| self.visit_with(&mut HasTypeFlagsVisitor { flags: flags }) |
| } |
| fn has_projections(&self) -> bool { |
| self.has_type_flags(TypeFlags::HAS_PROJECTION) |
| } |
| fn references_error(&self) -> bool { |
| self.has_type_flags(TypeFlags::HAS_TY_ERR) |
| } |
| fn has_param_types(&self) -> bool { |
| self.has_type_flags(TypeFlags::HAS_PARAMS) |
| } |
| fn has_self_ty(&self) -> bool { |
| self.has_type_flags(TypeFlags::HAS_SELF) |
| } |
| fn has_infer_types(&self) -> bool { |
| self.has_type_flags(TypeFlags::HAS_TY_INFER) |
| } |
| fn needs_infer(&self) -> bool { |
| self.has_type_flags(TypeFlags::HAS_TY_INFER | TypeFlags::HAS_RE_INFER) |
| } |
| fn has_skol(&self) -> bool { |
| self.has_type_flags(TypeFlags::HAS_RE_SKOL) |
| } |
| fn needs_subst(&self) -> bool { |
| self.has_type_flags(TypeFlags::NEEDS_SUBST) |
| } |
| fn has_re_skol(&self) -> bool { |
| self.has_type_flags(TypeFlags::HAS_RE_SKOL) |
| } |
| fn has_closure_types(&self) -> bool { |
| self.has_type_flags(TypeFlags::HAS_TY_CLOSURE) |
| } |
| /// "Free" regions in this context means that it has any region |
| /// that is not (a) erased or (b) late-bound. |
| fn has_free_regions(&self) -> bool { |
| self.has_type_flags(TypeFlags::HAS_FREE_REGIONS) |
| } |
| |
| /// True if there any any un-erased free regions. |
| fn has_erasable_regions(&self) -> bool { |
| self.has_type_flags(TypeFlags::HAS_FREE_REGIONS) |
| } |
| |
| /// Indicates whether this value references only 'global' |
| /// types/lifetimes that are the same regardless of what fn we are |
| /// in. This is used for caching. |
| fn is_global(&self) -> bool { |
| !self.has_type_flags(TypeFlags::HAS_FREE_LOCAL_NAMES) |
| } |
| |
| /// True if there are any late-bound regions |
| fn has_late_bound_regions(&self) -> bool { |
| self.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND) |
| } |
| } |
| |
| /// The TypeFolder trait defines the actual *folding*. There is a |
| /// method defined for every foldable type. Each of these has a |
| /// default implementation that does an "identity" fold. Within each |
| /// identity fold, it should invoke `foo.fold_with(self)` to fold each |
| /// sub-item. |
| pub trait TypeFolder<'gcx: 'tcx, 'tcx> : Sized { |
| fn tcx<'a>(&'a self) -> TyCtxt<'a, 'gcx, 'tcx>; |
| |
| fn fold_binder<T>(&mut self, t: &Binder<T>) -> Binder<T> |
| where T : TypeFoldable<'tcx> |
| { |
| t.super_fold_with(self) |
| } |
| |
| fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> { |
| t.super_fold_with(self) |
| } |
| |
| fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { |
| r.super_fold_with(self) |
| } |
| |
| fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> { |
| c.super_fold_with(self) |
| } |
| } |
| |
| pub trait TypeVisitor<'tcx> : Sized { |
| fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool { |
| t.super_visit_with(self) |
| } |
| |
| fn visit_ty(&mut self, t: Ty<'tcx>) -> bool { |
| t.super_visit_with(self) |
| } |
| |
| fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool { |
| r.super_visit_with(self) |
| } |
| |
| fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool { |
| c.super_visit_with(self) |
| } |
| } |
| |
| /////////////////////////////////////////////////////////////////////////// |
| // Some sample folders |
| |
| pub struct BottomUpFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a, F> |
| where F: FnMut(Ty<'tcx>) -> Ty<'tcx> |
| { |
| pub tcx: TyCtxt<'a, 'gcx, 'tcx>, |
| pub fldop: F, |
| } |
| |
| impl<'a, 'gcx, 'tcx, F> TypeFolder<'gcx, 'tcx> for BottomUpFolder<'a, 'gcx, 'tcx, F> |
| where F: FnMut(Ty<'tcx>) -> Ty<'tcx>, |
| { |
| fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx } |
| |
| fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { |
| let t1 = ty.super_fold_with(self); |
| (self.fldop)(t1) |
| } |
| } |
| |
| /////////////////////////////////////////////////////////////////////////// |
| // Region folder |
| |
| impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> { |
| /// Collects the free and escaping regions in `value` into `region_set`. Returns |
| /// whether any late-bound regions were skipped |
| pub fn collect_regions<T>(self, |
| value: &T, |
| region_set: &mut FxHashSet<ty::Region<'tcx>>) |
| -> bool |
| where T : TypeFoldable<'tcx> |
| { |
| let mut have_bound_regions = false; |
| self.fold_regions(value, &mut have_bound_regions, |r, d| { |
| region_set.insert(self.mk_region(r.shifted_out_to_binder(d))); |
| r |
| }); |
| have_bound_regions |
| } |
| |
| /// Folds the escaping and free regions in `value` using `f`, and |
| /// sets `skipped_regions` to true if any late-bound region was found |
| /// and skipped. |
| pub fn fold_regions<T>( |
| self, |
| value: &T, |
| skipped_regions: &mut bool, |
| mut f: impl FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>, |
| ) -> T |
| where |
| T : TypeFoldable<'tcx>, |
| { |
| value.fold_with(&mut RegionFolder::new(self, skipped_regions, &mut f)) |
| } |
| |
| pub fn for_each_free_region<T,F>(self, |
| value: &T, |
| callback: F) |
| where F: FnMut(ty::Region<'tcx>), |
| T: TypeFoldable<'tcx>, |
| { |
| value.visit_with(&mut RegionVisitor { |
| outer_index: ty::INNERMOST, |
| callback |
| }); |
| |
| struct RegionVisitor<F> { |
| /// The index of a binder *just outside* the things we have |
| /// traversed. If we encounter a bound region bound by this |
| /// binder or one outer to it, it appears free. Example: |
| /// |
| /// ``` |
| /// for<'a> fn(for<'b> fn(), T) |
| /// ^ ^ ^ ^ |
| /// | | | | here, would be shifted in 1 |
| /// | | | here, would be shifted in 2 |
| /// | | here, would be INNERMOST shifted in by 1 |
| /// | here, initially, binder would be INNERMOST |
| /// ``` |
| /// |
| /// You see that, initially, *any* bound value is free, |
| /// because we've not traversed any binders. As we pass |
| /// through a binder, we shift the `outer_index` by 1 to |
| /// account for the new binder that encloses us. |
| outer_index: ty::DebruijnIndex, |
| callback: F, |
| } |
| |
| impl<'tcx, F> TypeVisitor<'tcx> for RegionVisitor<F> |
| where F : FnMut(ty::Region<'tcx>) |
| { |
| fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool { |
| self.outer_index.shift_in(1); |
| t.skip_binder().visit_with(self); |
| self.outer_index.shift_out(1); |
| |
| false // keep visiting |
| } |
| |
| fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool { |
| match *r { |
| ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => { |
| /* ignore bound regions */ |
| } |
| _ => (self.callback)(r), |
| } |
| |
| false // keep visiting |
| } |
| } |
| } |
| } |
| |
| /// Folds over the substructure of a type, visiting its component |
| /// types and all regions that occur *free* within it. |
| /// |
| /// That is, `Ty` can contain function or method types that bind |
| /// regions at the call site (`ReLateBound`), and occurrences of |
| /// regions (aka "lifetimes") that are bound within a type are not |
| /// visited by this folder; only regions that occur free will be |
| /// visited by `fld_r`. |
| |
| pub struct RegionFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> { |
| tcx: TyCtxt<'a, 'gcx, 'tcx>, |
| skipped_regions: &'a mut bool, |
| |
| /// Stores the index of a binder *just outside* the stuff we have |
| /// visited. So this begins as INNERMOST; when we pass through a |
| /// binder, it is incremented (via `shift_in`). |
| current_index: ty::DebruijnIndex, |
| |
| /// Callback invokes for each free region. The `DebruijnIndex` |
| /// points to the binder *just outside* the ones we have passed |
| /// through. |
| fold_region_fn: &'a mut (dyn FnMut( |
| ty::Region<'tcx>, |
| ty::DebruijnIndex, |
| ) -> ty::Region<'tcx> + 'a), |
| } |
| |
| impl<'a, 'gcx, 'tcx> RegionFolder<'a, 'gcx, 'tcx> { |
| pub fn new( |
| tcx: TyCtxt<'a, 'gcx, 'tcx>, |
| skipped_regions: &'a mut bool, |
| fold_region_fn: &'a mut dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>, |
| ) -> RegionFolder<'a, 'gcx, 'tcx> { |
| RegionFolder { |
| tcx, |
| skipped_regions, |
| current_index: ty::INNERMOST, |
| fold_region_fn, |
| } |
| } |
| } |
| |
| impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionFolder<'a, 'gcx, 'tcx> { |
| fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx } |
| |
| fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> { |
| self.current_index.shift_in(1); |
| let t = t.super_fold_with(self); |
| self.current_index.shift_out(1); |
| t |
| } |
| |
| fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { |
| match *r { |
| ty::ReLateBound(debruijn, _) if debruijn < self.current_index => { |
| debug!("RegionFolder.fold_region({:?}) skipped bound region (current index={:?})", |
| r, self.current_index); |
| *self.skipped_regions = true; |
| r |
| } |
| _ => { |
| debug!("RegionFolder.fold_region({:?}) folding free region (current_index={:?})", |
| r, self.current_index); |
| (self.fold_region_fn)(r, self.current_index) |
| } |
| } |
| } |
| } |
| |
| /////////////////////////////////////////////////////////////////////////// |
| // Late-bound region replacer |
| |
| // Replaces the escaping regions in a type. |
| |
| struct RegionReplacer<'a, 'gcx: 'a+'tcx, 'tcx: 'a> { |
| tcx: TyCtxt<'a, 'gcx, 'tcx>, |
| |
| /// As with `RegionFolder`, represents the index of a binder *just outside* |
| /// the ones we have visited. |
| current_index: ty::DebruijnIndex, |
| |
| fld_r: &'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a), |
| map: BTreeMap<ty::BoundRegion, ty::Region<'tcx>> |
| } |
| |
| impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> { |
| /// Replace all regions bound by the given `Binder` with the |
| /// results returned by the closure; the closure is expected to |
| /// return a free region (relative to this binder), and hence the |
| /// binder is removed in the return type. The closure is invoked |
| /// once for each unique `BoundRegion`; multiple references to the |
| /// same `BoundRegion` will reuse the previous result. A map is |
| /// returned at the end with each bound region and the free region |
| /// that replaced it. |
| pub fn replace_late_bound_regions<T,F>(self, |
| value: &Binder<T>, |
| mut f: F) |
| -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>) |
| where F : FnMut(ty::BoundRegion) -> ty::Region<'tcx>, |
| T : TypeFoldable<'tcx>, |
| { |
| let mut replacer = RegionReplacer::new(self, &mut f); |
| let result = value.skip_binder().fold_with(&mut replacer); |
| (result, replacer.map) |
| } |
| |
| /// Replace any late-bound regions bound in `value` with |
| /// free variants attached to `all_outlive_scope`. |
| pub fn liberate_late_bound_regions<T>( |
| &self, |
| all_outlive_scope: DefId, |
| value: &ty::Binder<T> |
| ) -> T |
| where T: TypeFoldable<'tcx> { |
| self.replace_late_bound_regions(value, |br| { |
| self.mk_region(ty::ReFree(ty::FreeRegion { |
| scope: all_outlive_scope, |
| bound_region: br |
| })) |
| }).0 |
| } |
| |
| /// Flattens multiple binding levels into one. So `for<'a> for<'b> Foo` |
| /// becomes `for<'a,'b> Foo`. |
| pub fn flatten_late_bound_regions<T>(self, bound2_value: &Binder<Binder<T>>) |
| -> Binder<T> |
| where T: TypeFoldable<'tcx> |
| { |
| let bound0_value = bound2_value.skip_binder().skip_binder(); |
| let value = self.fold_regions(bound0_value, &mut false, |region, current_depth| { |
| match *region { |
| ty::ReLateBound(debruijn, br) => { |
| // We assume no regions bound *outside* of the |
| // binders in `bound2_value` (nmatsakis added in |
| // the course of this PR; seems like a reasonable |
| // sanity check though). |
| assert!(debruijn == current_depth); |
| self.mk_region(ty::ReLateBound(current_depth, br)) |
| } |
| _ => { |
| region |
| } |
| } |
| }); |
| Binder::bind(value) |
| } |
| |
| /// Returns a set of all late-bound regions that are constrained |
| /// by `value`, meaning that if we instantiate those LBR with |
| /// variables and equate `value` with something else, those |
| /// variables will also be equated. |
| pub fn collect_constrained_late_bound_regions<T>(&self, value: &Binder<T>) |
| -> FxHashSet<ty::BoundRegion> |
| where T : TypeFoldable<'tcx> |
| { |
| self.collect_late_bound_regions(value, true) |
| } |
| |
| /// Returns a set of all late-bound regions that appear in `value` anywhere. |
| pub fn collect_referenced_late_bound_regions<T>(&self, value: &Binder<T>) |
| -> FxHashSet<ty::BoundRegion> |
| where T : TypeFoldable<'tcx> |
| { |
| self.collect_late_bound_regions(value, false) |
| } |
| |
| fn collect_late_bound_regions<T>(&self, value: &Binder<T>, just_constraint: bool) |
| -> FxHashSet<ty::BoundRegion> |
| where T : TypeFoldable<'tcx> |
| { |
| let mut collector = LateBoundRegionsCollector::new(just_constraint); |
| let result = value.skip_binder().visit_with(&mut collector); |
| assert!(!result); // should never have stopped early |
| collector.regions |
| } |
| |
| /// Replace any late-bound regions bound in `value` with `'erased`. Useful in codegen but also |
| /// method lookup and a few other places where precise region relationships are not required. |
| pub fn erase_late_bound_regions<T>(self, value: &Binder<T>) -> T |
| where T : TypeFoldable<'tcx> |
| { |
| self.replace_late_bound_regions(value, |_| self.types.re_erased).0 |
| } |
| |
| /// Rewrite any late-bound regions so that they are anonymous. Region numbers are |
| /// assigned starting at 1 and increasing monotonically in the order traversed |
| /// by the fold operation. |
| /// |
| /// The chief purpose of this function is to canonicalize regions so that two |
| /// `FnSig`s or `TraitRef`s which are equivalent up to region naming will become |
| /// structurally identical. For example, `for<'a, 'b> fn(&'a isize, &'b isize)` and |
| /// `for<'a, 'b> fn(&'b isize, &'a isize)` will become identical after anonymization. |
| pub fn anonymize_late_bound_regions<T>(self, sig: &Binder<T>) -> Binder<T> |
| where T : TypeFoldable<'tcx>, |
| { |
| let mut counter = 0; |
| Binder::bind(self.replace_late_bound_regions(sig, |_| { |
| counter += 1; |
| self.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BrAnon(counter))) |
| }).0) |
| } |
| } |
| |
| impl<'a, 'gcx, 'tcx> RegionReplacer<'a, 'gcx, 'tcx> { |
| fn new<F>(tcx: TyCtxt<'a, 'gcx, 'tcx>, fld_r: &'a mut F) |
| -> RegionReplacer<'a, 'gcx, 'tcx> |
| where F : FnMut(ty::BoundRegion) -> ty::Region<'tcx> |
| { |
| RegionReplacer { |
| tcx, |
| current_index: ty::INNERMOST, |
| fld_r, |
| map: BTreeMap::default() |
| } |
| } |
| } |
| |
| impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionReplacer<'a, 'gcx, 'tcx> { |
| fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx } |
| |
| fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> { |
| self.current_index.shift_in(1); |
| let t = t.super_fold_with(self); |
| self.current_index.shift_out(1); |
| t |
| } |
| |
| fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> { |
| if !t.has_regions_bound_at_or_above(self.current_index) { |
| return t; |
| } |
| |
| t.super_fold_with(self) |
| } |
| |
| fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { |
| match *r { |
| ty::ReLateBound(debruijn, br) if debruijn == self.current_index => { |
| let fld_r = &mut self.fld_r; |
| let region = *self.map.entry(br).or_insert_with(|| fld_r(br)); |
| if let ty::ReLateBound(debruijn1, br) = *region { |
| // If the callback returns a late-bound region, |
| // that region should always use the INNERMOST |
| // debruijn index. Then we adjust it to the |
| // correct depth. |
| assert_eq!(debruijn1, ty::INNERMOST); |
| self.tcx.mk_region(ty::ReLateBound(debruijn, br)) |
| } else { |
| region |
| } |
| } |
| _ => r |
| } |
| } |
| } |
| |
| /////////////////////////////////////////////////////////////////////////// |
| // Region shifter |
| // |
| // Shifts the De Bruijn indices on all escaping bound regions by a |
| // fixed amount. Useful in substitution or when otherwise introducing |
| // a binding level that is not intended to capture the existing bound |
| // regions. See comment on `shift_regions_through_binders` method in |
| // `subst.rs` for more details. |
| |
| pub fn shift_region(region: ty::RegionKind, amount: u32) -> ty::RegionKind { |
| match region { |
| ty::ReLateBound(debruijn, br) => { |
| ty::ReLateBound(debruijn.shifted_in(amount), br) |
| } |
| _ => { |
| region |
| } |
| } |
| } |
| |
| pub fn shift_region_ref<'a, 'gcx, 'tcx>( |
| tcx: TyCtxt<'a, 'gcx, 'tcx>, |
| region: ty::Region<'tcx>, |
| amount: u32) |
| -> ty::Region<'tcx> |
| { |
| match region { |
| &ty::ReLateBound(debruijn, br) if amount > 0 => { |
| tcx.mk_region(ty::ReLateBound(debruijn.shifted_in(amount), br)) |
| } |
| _ => { |
| region |
| } |
| } |
| } |
| |
| pub fn shift_regions<'a, 'gcx, 'tcx, T>(tcx: TyCtxt<'a, 'gcx, 'tcx>, |
| amount: u32, |
| value: &T) -> T |
| where T: TypeFoldable<'tcx> |
| { |
| debug!("shift_regions(value={:?}, amount={})", |
| value, amount); |
| |
| value.fold_with(&mut RegionFolder::new(tcx, &mut false, &mut |region, _current_depth| { |
| shift_region_ref(tcx, region, amount) |
| })) |
| } |
| |
| /// An "escaping region" is a bound region whose binder is not part of `t`. |
| /// |
| /// So, for example, consider a type like the following, which has two binders: |
| /// |
| /// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize)) |
| /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope |
| /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope |
| /// |
| /// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the |
| /// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner |
| /// fn type*, that type has an escaping region: `'a`. |
| /// |
| /// Note that what I'm calling an "escaping region" is often just called a "free region". However, |
| /// we already use the term "free region". It refers to the regions that we use to represent bound |
| /// regions on a fn definition while we are typechecking its body. |
| /// |
| /// To clarify, conceptually there is no particular difference between an "escaping" region and a |
| /// "free" region. However, there is a big difference in practice. Basically, when "entering" a |
| /// binding level, one is generally required to do some sort of processing to a bound region, such |
| /// as replacing it with a fresh/skolemized region, or making an entry in the environment to |
| /// represent the scope to which it is attached, etc. An escaping region represents a bound region |
| /// for which this processing has not yet been done. |
| struct HasEscapingRegionsVisitor { |
| /// Anything bound by `outer_index` or "above" is escaping |
| outer_index: ty::DebruijnIndex, |
| } |
| |
| impl<'tcx> TypeVisitor<'tcx> for HasEscapingRegionsVisitor { |
| fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool { |
| self.outer_index.shift_in(1); |
| let result = t.super_visit_with(self); |
| self.outer_index.shift_out(1); |
| result |
| } |
| |
| fn visit_ty(&mut self, t: Ty<'tcx>) -> bool { |
| // If the outer-exclusive-binder is *strictly greater* than |
| // `outer_index`, that means that `t` contains some content |
| // bound at `outer_index` or above (because |
| // `outer_exclusive_binder` is always 1 higher than the |
| // content in `t`). Therefore, `t` has some escaping regions. |
| t.outer_exclusive_binder > self.outer_index |
| } |
| |
| fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool { |
| // If the region is bound by `outer_index` or anything outside |
| // of outer index, then it escapes the binders we have |
| // visited. |
| r.bound_at_or_above_binder(self.outer_index) |
| } |
| } |
| |
| struct HasTypeFlagsVisitor { |
| flags: ty::TypeFlags, |
| } |
| |
| impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor { |
| fn visit_ty(&mut self, t: Ty) -> bool { |
| debug!("HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}", t, t.flags, self.flags); |
| t.flags.intersects(self.flags) |
| } |
| |
| fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool { |
| let flags = r.type_flags(); |
| debug!("HasTypeFlagsVisitor: r={:?} r.flags={:?} self.flags={:?}", r, flags, self.flags); |
| flags.intersects(self.flags) |
| } |
| |
| fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool { |
| if let ConstVal::Unevaluated(..) = c.val { |
| let projection_flags = TypeFlags::HAS_NORMALIZABLE_PROJECTION | |
| TypeFlags::HAS_PROJECTION; |
| if projection_flags.intersects(self.flags) { |
| return true; |
| } |
| } |
| c.super_visit_with(self) |
| } |
| } |
| |
| /// Collects all the late-bound regions at the innermost binding level |
| /// into a hash set. |
| struct LateBoundRegionsCollector { |
| current_index: ty::DebruijnIndex, |
| regions: FxHashSet<ty::BoundRegion>, |
| |
| /// If true, we only want regions that are known to be |
| /// "constrained" when you equate this type with another type. In |
| /// partcular, if you have e.g. `&'a u32` and `&'b u32`, equating |
| /// them constraints `'a == 'b`. But if you have `<&'a u32 as |
| /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those |
| /// types may mean that `'a` and `'b` don't appear in the results, |
| /// so they are not considered *constrained*. |
| just_constrained: bool, |
| } |
| |
| impl LateBoundRegionsCollector { |
| fn new(just_constrained: bool) -> Self { |
| LateBoundRegionsCollector { |
| current_index: ty::INNERMOST, |
| regions: FxHashSet(), |
| just_constrained, |
| } |
| } |
| } |
| |
| impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector { |
| fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool { |
| self.current_index.shift_in(1); |
| let result = t.super_visit_with(self); |
| self.current_index.shift_out(1); |
| result |
| } |
| |
| fn visit_ty(&mut self, t: Ty<'tcx>) -> bool { |
| // if we are only looking for "constrained" region, we have to |
| // ignore the inputs to a projection, as they may not appear |
| // in the normalized form |
| if self.just_constrained { |
| match t.sty { |
| ty::TyProjection(..) | ty::TyAnon(..) => { return false; } |
| _ => { } |
| } |
| } |
| |
| t.super_visit_with(self) |
| } |
| |
| fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool { |
| match *r { |
| ty::ReLateBound(debruijn, br) if debruijn == self.current_index => { |
| self.regions.insert(br); |
| } |
| _ => { } |
| } |
| false |
| } |
| } |
