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 `BoundRegionKind`; multiple references to the
538 /// same `BoundRegionKind` 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 let mut region_map
= BTreeMap
::new();
559 let real_fld_r
= |br
: ty
::BoundRegion
| *region_map
.entry(br
).or_insert_with(|| fld_r(br
));
560 let value
= self.replace_escaping_bound_vars(value
.skip_binder(), real_fld_r
, fld_t
, fld_c
);
564 /// Replaces all escaping bound vars. The `fld_r` closure replaces escaping
565 /// bound regions; the `fld_t` closure replaces escaping bound types and the `fld_c`
566 /// closure replaces escaping bound consts.
567 pub fn replace_escaping_bound_vars
<T
, F
, G
, H
>(
575 F
: FnMut(ty
::BoundRegion
) -> ty
::Region
<'tcx
>,
576 G
: FnMut(ty
::BoundTy
) -> Ty
<'tcx
>,
577 H
: FnMut(ty
::BoundVar
, Ty
<'tcx
>) -> &'tcx ty
::Const
<'tcx
>,
578 T
: TypeFoldable
<'tcx
>,
580 if !value
.has_escaping_bound_vars() {
583 let mut replacer
= BoundVarReplacer
::new(self, &mut fld_r
, &mut fld_t
, &mut fld_c
);
584 value
.fold_with(&mut replacer
)
588 /// Replaces all types or regions bound by the given `Binder`. The `fld_r`
589 /// closure replaces bound regions while the `fld_t` closure replaces bound
591 pub fn replace_bound_vars
<T
, F
, G
, H
>(
597 ) -> (T
, BTreeMap
<ty
::BoundRegion
, ty
::Region
<'tcx
>>)
599 F
: FnMut(ty
::BoundRegion
) -> ty
::Region
<'tcx
>,
600 G
: FnMut(ty
::BoundTy
) -> Ty
<'tcx
>,
601 H
: FnMut(ty
::BoundVar
, Ty
<'tcx
>) -> &'tcx ty
::Const
<'tcx
>,
602 T
: TypeFoldable
<'tcx
>,
604 let mut region_map
= BTreeMap
::new();
605 let real_fld_r
= |br
: ty
::BoundRegion
| *region_map
.entry(br
).or_insert_with(|| fld_r(br
));
606 let value
= self.replace_escaping_bound_vars(value
.skip_binder(), real_fld_r
, fld_t
, fld_c
);
610 /// Replaces any late-bound regions bound in `value` with
611 /// free variants attached to `all_outlive_scope`.
612 pub fn liberate_late_bound_regions
<T
>(self, all_outlive_scope
: DefId
, value
: ty
::Binder
<T
>) -> T
614 T
: TypeFoldable
<'tcx
>,
616 self.replace_late_bound_regions(value
, |br
| {
617 self.mk_region(ty
::ReFree(ty
::FreeRegion
{
618 scope
: all_outlive_scope
,
619 bound_region
: br
.kind
,
625 /// Returns a set of all late-bound regions that are constrained
626 /// by `value`, meaning that if we instantiate those LBR with
627 /// variables and equate `value` with something else, those
628 /// variables will also be equated.
629 pub fn collect_constrained_late_bound_regions
<T
>(
632 ) -> FxHashSet
<ty
::BoundRegionKind
>
634 T
: TypeFoldable
<'tcx
>,
636 self.collect_late_bound_regions(value
, true)
639 /// Returns a set of all late-bound regions that appear in `value` anywhere.
640 pub fn collect_referenced_late_bound_regions
<T
>(
643 ) -> FxHashSet
<ty
::BoundRegionKind
>
645 T
: TypeFoldable
<'tcx
>,
647 self.collect_late_bound_regions(value
, false)
650 fn collect_late_bound_regions
<T
>(
653 just_constraint
: bool
,
654 ) -> FxHashSet
<ty
::BoundRegionKind
>
656 T
: TypeFoldable
<'tcx
>,
658 let mut collector
= LateBoundRegionsCollector
::new(just_constraint
);
659 let result
= value
.as_ref().skip_binder().visit_with(&mut collector
);
660 assert
!(result
.is_continue()); // should never have stopped early
664 /// Replaces any late-bound regions bound in `value` with `'erased`. Useful in codegen but also
665 /// method lookup and a few other places where precise region relationships are not required.
666 pub fn erase_late_bound_regions
<T
>(self, value
: Binder
<T
>) -> T
668 T
: TypeFoldable
<'tcx
>,
670 self.replace_late_bound_regions(value
, |_
| self.lifetimes
.re_erased
).0
673 /// Rewrite any late-bound regions so that they are anonymous. Region numbers are
674 /// assigned starting at 0 and increasing monotonically in the order traversed
675 /// by the fold operation.
677 /// The chief purpose of this function is to canonicalize regions so that two
678 /// `FnSig`s or `TraitRef`s which are equivalent up to region naming will become
679 /// structurally identical. For example, `for<'a, 'b> fn(&'a isize, &'b isize)` and
680 /// `for<'a, 'b> fn(&'b isize, &'a isize)` will become identical after anonymization.
681 pub fn anonymize_late_bound_regions
<T
>(self, sig
: Binder
<T
>) -> Binder
<T
>
683 T
: TypeFoldable
<'tcx
>,
687 self.replace_late_bound_regions(sig
, |_
| {
688 let br
= ty
::BoundRegion { kind: ty::BrAnon(counter) }
;
689 let r
= self.mk_region(ty
::ReLateBound(ty
::INNERMOST
, br
));
698 ///////////////////////////////////////////////////////////////////////////
701 // Shifts the De Bruijn indices on all escaping bound vars by a
702 // fixed amount. Useful in substitution or when otherwise introducing
703 // a binding level that is not intended to capture the existing bound
704 // vars. See comment on `shift_vars_through_binders` method in
705 // `subst.rs` for more details.
707 struct Shifter
<'tcx
> {
709 current_index
: ty
::DebruijnIndex
,
714 pub fn new(tcx
: TyCtxt
<'tcx
>, amount
: u32) -> Self {
715 Shifter { tcx, current_index: ty::INNERMOST, amount }
719 impl TypeFolder
<'tcx
> for Shifter
<'tcx
> {
720 fn tcx
<'b
>(&'b
self) -> TyCtxt
<'tcx
> {
724 fn fold_binder
<T
: TypeFoldable
<'tcx
>>(&mut self, t
: ty
::Binder
<T
>) -> ty
::Binder
<T
> {
725 self.current_index
.shift_in(1);
726 let t
= t
.super_fold_with(self);
727 self.current_index
.shift_out(1);
731 fn fold_region(&mut self, r
: ty
::Region
<'tcx
>) -> ty
::Region
<'tcx
> {
733 ty
::ReLateBound(debruijn
, br
) => {
734 if self.amount
== 0 || debruijn
< self.current_index
{
737 let debruijn
= debruijn
.shifted_in(self.amount
);
738 let shifted
= ty
::ReLateBound(debruijn
, br
);
739 self.tcx
.mk_region(shifted
)
746 fn fold_ty(&mut self, ty
: Ty
<'tcx
>) -> Ty
<'tcx
> {
748 ty
::Bound(debruijn
, bound_ty
) => {
749 if self.amount
== 0 || debruijn
< self.current_index
{
752 let debruijn
= debruijn
.shifted_in(self.amount
);
753 self.tcx
.mk_ty(ty
::Bound(debruijn
, bound_ty
))
757 _
=> ty
.super_fold_with(self),
761 fn fold_const(&mut self, ct
: &'tcx ty
::Const
<'tcx
>) -> &'tcx ty
::Const
<'tcx
> {
762 if let ty
::Const { val: ty::ConstKind::Bound(debruijn, bound_ct), ty }
= *ct
{
763 if self.amount
== 0 || debruijn
< self.current_index
{
766 let debruijn
= debruijn
.shifted_in(self.amount
);
767 self.tcx
.mk_const(ty
::Const { val: ty::ConstKind::Bound(debruijn, bound_ct), ty }
)
770 ct
.super_fold_with(self)
775 pub fn shift_region
<'tcx
>(
777 region
: ty
::Region
<'tcx
>,
779 ) -> ty
::Region
<'tcx
> {
781 ty
::ReLateBound(debruijn
, br
) if amount
> 0 => {
782 tcx
.mk_region(ty
::ReLateBound(debruijn
.shifted_in(amount
), *br
))
788 pub fn shift_vars
<'tcx
, T
>(tcx
: TyCtxt
<'tcx
>, value
: T
, amount
: u32) -> T
790 T
: TypeFoldable
<'tcx
>,
792 debug
!("shift_vars(value={:?}, amount={})", value
, amount
);
794 value
.fold_with(&mut Shifter
::new(tcx
, amount
))
797 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
798 struct FoundEscapingVars
;
800 /// An "escaping var" is a bound var whose binder is not part of `t`. A bound var can be a
801 /// bound region or a bound type.
803 /// So, for example, consider a type like the following, which has two binders:
805 /// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize))
806 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope
807 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope
809 /// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the
810 /// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner
811 /// fn type*, that type has an escaping region: `'a`.
813 /// Note that what I'm calling an "escaping var" is often just called a "free var". However,
814 /// we already use the term "free var". It refers to the regions or types that we use to represent
815 /// bound regions or type params on a fn definition while we are type checking its body.
817 /// To clarify, conceptually there is no particular difference between
818 /// an "escaping" var and a "free" var. However, there is a big
819 /// difference in practice. Basically, when "entering" a binding
820 /// level, one is generally required to do some sort of processing to
821 /// a bound var, such as replacing it with a fresh/placeholder
822 /// var, or making an entry in the environment to represent the
823 /// scope to which it is attached, etc. An escaping var represents
824 /// a bound var for which this processing has not yet been done.
825 struct HasEscapingVarsVisitor
{
826 /// Anything bound by `outer_index` or "above" is escaping.
827 outer_index
: ty
::DebruijnIndex
,
830 impl<'tcx
> TypeVisitor
<'tcx
> for HasEscapingVarsVisitor
{
831 type BreakTy
= FoundEscapingVars
;
833 fn visit_binder
<T
: TypeFoldable
<'tcx
>>(&mut self, t
: &Binder
<T
>) -> ControlFlow
<Self::BreakTy
> {
834 self.outer_index
.shift_in(1);
835 let result
= t
.super_visit_with(self);
836 self.outer_index
.shift_out(1);
840 fn visit_ty(&mut self, t
: Ty
<'tcx
>) -> ControlFlow
<Self::BreakTy
> {
841 // If the outer-exclusive-binder is *strictly greater* than
842 // `outer_index`, that means that `t` contains some content
843 // bound at `outer_index` or above (because
844 // `outer_exclusive_binder` is always 1 higher than the
845 // content in `t`). Therefore, `t` has some escaping vars.
846 if t
.outer_exclusive_binder
> self.outer_index
{
847 ControlFlow
::Break(FoundEscapingVars
)
849 ControlFlow
::CONTINUE
853 fn visit_region(&mut self, r
: ty
::Region
<'tcx
>) -> ControlFlow
<Self::BreakTy
> {
854 // If the region is bound by `outer_index` or anything outside
855 // of outer index, then it escapes the binders we have
857 if r
.bound_at_or_above_binder(self.outer_index
) {
858 ControlFlow
::Break(FoundEscapingVars
)
860 ControlFlow
::CONTINUE
864 fn visit_const(&mut self, ct
: &'tcx ty
::Const
<'tcx
>) -> ControlFlow
<Self::BreakTy
> {
865 // we don't have a `visit_infer_const` callback, so we have to
866 // hook in here to catch this case (annoying...), but
867 // otherwise we do want to remember to visit the rest of the
868 // const, as it has types/regions embedded in a lot of other
871 ty
::ConstKind
::Bound(debruijn
, _
) if debruijn
>= self.outer_index
=> {
872 ControlFlow
::Break(FoundEscapingVars
)
874 _
=> ct
.super_visit_with(self),
878 fn visit_predicate(&mut self, predicate
: ty
::Predicate
<'tcx
>) -> ControlFlow
<Self::BreakTy
> {
879 if predicate
.inner
.outer_exclusive_binder
> self.outer_index
{
880 ControlFlow
::Break(FoundEscapingVars
)
882 ControlFlow
::CONTINUE
887 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
890 // FIXME: Optimize for checking for infer flags
891 struct HasTypeFlagsVisitor
{
892 flags
: ty
::TypeFlags
,
895 impl<'tcx
> TypeVisitor
<'tcx
> for HasTypeFlagsVisitor
{
896 type BreakTy
= FoundFlags
;
898 fn visit_ty(&mut self, t
: Ty
<'_
>) -> ControlFlow
<Self::BreakTy
> {
900 "HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}",
905 if t
.flags().intersects(self.flags
) {
906 ControlFlow
::Break(FoundFlags
)
908 ControlFlow
::CONTINUE
912 fn visit_region(&mut self, r
: ty
::Region
<'tcx
>) -> ControlFlow
<Self::BreakTy
> {
913 let flags
= r
.type_flags();
914 debug
!("HasTypeFlagsVisitor: r={:?} r.flags={:?} self.flags={:?}", r
, flags
, self.flags
);
915 if flags
.intersects(self.flags
) {
916 ControlFlow
::Break(FoundFlags
)
918 ControlFlow
::CONTINUE
922 fn visit_const(&mut self, c
: &'tcx ty
::Const
<'tcx
>) -> ControlFlow
<Self::BreakTy
> {
923 let flags
= FlagComputation
::for_const(c
);
924 debug
!("HasTypeFlagsVisitor: c={:?} c.flags={:?} self.flags={:?}", c
, flags
, self.flags
);
925 if flags
.intersects(self.flags
) {
926 ControlFlow
::Break(FoundFlags
)
928 ControlFlow
::CONTINUE
932 fn visit_predicate(&mut self, predicate
: ty
::Predicate
<'tcx
>) -> ControlFlow
<Self::BreakTy
> {
934 "HasTypeFlagsVisitor: predicate={:?} predicate.flags={:?} self.flags={:?}",
935 predicate
, predicate
.inner
.flags
, self.flags
937 if predicate
.inner
.flags
.intersects(self.flags
) {
938 ControlFlow
::Break(FoundFlags
)
940 ControlFlow
::CONTINUE
945 /// Collects all the late-bound regions at the innermost binding level
947 struct LateBoundRegionsCollector
{
948 current_index
: ty
::DebruijnIndex
,
949 regions
: FxHashSet
<ty
::BoundRegionKind
>,
951 /// `true` if we only want regions that are known to be
952 /// "constrained" when you equate this type with another type. In
953 /// particular, if you have e.g., `&'a u32` and `&'b u32`, equating
954 /// them constraints `'a == 'b`. But if you have `<&'a u32 as
955 /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
956 /// types may mean that `'a` and `'b` don't appear in the results,
957 /// so they are not considered *constrained*.
958 just_constrained
: bool
,
961 impl LateBoundRegionsCollector
{
962 fn new(just_constrained
: bool
) -> Self {
963 LateBoundRegionsCollector
{
964 current_index
: ty
::INNERMOST
,
965 regions
: Default
::default(),
971 impl<'tcx
> TypeVisitor
<'tcx
> for LateBoundRegionsCollector
{
972 fn visit_binder
<T
: TypeFoldable
<'tcx
>>(&mut self, t
: &Binder
<T
>) -> ControlFlow
<Self::BreakTy
> {
973 self.current_index
.shift_in(1);
974 let result
= t
.super_visit_with(self);
975 self.current_index
.shift_out(1);
979 fn visit_ty(&mut self, t
: Ty
<'tcx
>) -> ControlFlow
<Self::BreakTy
> {
980 // if we are only looking for "constrained" region, we have to
981 // ignore the inputs to a projection, as they may not appear
982 // in the normalized form
983 if self.just_constrained
{
984 if let ty
::Projection(..) | ty
::Opaque(..) = t
.kind() {
985 return ControlFlow
::CONTINUE
;
989 t
.super_visit_with(self)
992 fn visit_const(&mut self, c
: &'tcx ty
::Const
<'tcx
>) -> ControlFlow
<Self::BreakTy
> {
993 // if we are only looking for "constrained" region, we have to
994 // ignore the inputs of an unevaluated const, as they may not appear
995 // in the normalized form
996 if self.just_constrained
{
997 if let ty
::ConstKind
::Unevaluated(..) = c
.val
{
998 return ControlFlow
::CONTINUE
;
1002 c
.super_visit_with(self)
1005 fn visit_region(&mut self, r
: ty
::Region
<'tcx
>) -> ControlFlow
<Self::BreakTy
> {
1006 if let ty
::ReLateBound(debruijn
, br
) = *r
{
1007 if debruijn
== self.current_index
{
1008 self.regions
.insert(br
.kind
);
1011 ControlFlow
::CONTINUE