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:
6 //!
7 //! T.fold_with(F) --calls--> F.fold_T(T) --calls--> T.super_fold_with(F)
8 //!
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.)
15 //!
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()`.
19 //!
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
25 //! proper thing.
26 //!
27 //! A `TypeFoldable` T can also be visited by a `TypeVisitor` V using similar setup:
28 //!
29 //! T.visit_with(V) --calls--> V.visit_T(T) --calls--> T.super_visit_with(V).
30 //!
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::mir;
34 use crate::ty::{self, flags::FlagComputation, Binder, Ty, TyCtxt, TypeFlags};
35 use rustc_hir as hir;
36 use rustc_hir::def_id::DefId;
37
38 use rustc_data_structures::fx::FxHashSet;
39 use rustc_data_structures::sso::SsoHashSet;
40 use std::collections::BTreeMap;
41 use std::fmt;
42 use std::ops::ControlFlow;
43
44 /// This trait is implemented for every type that can be folded.
45 /// Basically, every type that has a corresponding method in `TypeFolder`.
46 ///
47 /// To implement this conveniently, use the derive macro located in `rustc_macros`.
48 pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
super_fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self49 fn super_fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self;
fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self50 fn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self {
51 self.super_fold_with(folder)
52 }
53
super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy>54 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy>;
visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy>55 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
56 self.super_visit_with(visitor)
57 }
58
59 /// Returns `true` if `self` has any late-bound regions that are either
60 /// bound by `binder` or bound by some binder outside of `binder`.
61 /// If `binder` is `ty::INNERMOST`, this indicates whether
62 /// there are any late-bound regions that appear free.
has_vars_bound_at_or_above(&self, binder: ty::DebruijnIndex) -> bool63 fn has_vars_bound_at_or_above(&self, binder: ty::DebruijnIndex) -> bool {
64 self.visit_with(&mut HasEscapingVarsVisitor { outer_index: binder }).is_break()
65 }
66
67 /// Returns `true` if this `self` has any regions that escape `binder` (and
68 /// hence are not bound by it).
has_vars_bound_above(&self, binder: ty::DebruijnIndex) -> bool69 fn has_vars_bound_above(&self, binder: ty::DebruijnIndex) -> bool {
70 self.has_vars_bound_at_or_above(binder.shifted_in(1))
71 }
72
has_escaping_bound_vars(&self) -> bool73 fn has_escaping_bound_vars(&self) -> bool {
74 self.has_vars_bound_at_or_above(ty::INNERMOST)
75 }
76
definitely_has_type_flags(&self, tcx: TyCtxt<'tcx>, flags: TypeFlags) -> bool77 fn definitely_has_type_flags(&self, tcx: TyCtxt<'tcx>, flags: TypeFlags) -> bool {
78 self.visit_with(&mut HasTypeFlagsVisitor { tcx: Some(tcx), flags }).break_value()
79 == Some(FoundFlags)
80 }
81
82 #[instrument(level = "trace")]
has_type_flags(&self, flags: TypeFlags) -> bool83 fn has_type_flags(&self, flags: TypeFlags) -> bool {
84 self.visit_with(&mut HasTypeFlagsVisitor { tcx: None, flags }).break_value()
85 == Some(FoundFlags)
86 }
has_projections(&self) -> bool87 fn has_projections(&self) -> bool {
88 self.has_type_flags(TypeFlags::HAS_PROJECTION)
89 }
has_opaque_types(&self) -> bool90 fn has_opaque_types(&self) -> bool {
91 self.has_type_flags(TypeFlags::HAS_TY_OPAQUE)
92 }
references_error(&self) -> bool93 fn references_error(&self) -> bool {
94 self.has_type_flags(TypeFlags::HAS_ERROR)
95 }
potentially_has_param_types_or_consts(&self) -> bool96 fn potentially_has_param_types_or_consts(&self) -> bool {
97 self.has_type_flags(
98 TypeFlags::HAS_KNOWN_TY_PARAM
99 | TypeFlags::HAS_KNOWN_CT_PARAM
100 | TypeFlags::HAS_UNKNOWN_DEFAULT_CONST_SUBSTS,
101 )
102 }
definitely_has_param_types_or_consts(&self, tcx: TyCtxt<'tcx>) -> bool103 fn definitely_has_param_types_or_consts(&self, tcx: TyCtxt<'tcx>) -> bool {
104 self.definitely_has_type_flags(
105 tcx,
106 TypeFlags::HAS_KNOWN_TY_PARAM | TypeFlags::HAS_KNOWN_CT_PARAM,
107 )
108 }
has_infer_regions(&self) -> bool109 fn has_infer_regions(&self) -> bool {
110 self.has_type_flags(TypeFlags::HAS_RE_INFER)
111 }
has_infer_types(&self) -> bool112 fn has_infer_types(&self) -> bool {
113 self.has_type_flags(TypeFlags::HAS_TY_INFER)
114 }
has_infer_types_or_consts(&self) -> bool115 fn has_infer_types_or_consts(&self) -> bool {
116 self.has_type_flags(TypeFlags::HAS_TY_INFER | TypeFlags::HAS_CT_INFER)
117 }
needs_infer(&self) -> bool118 fn needs_infer(&self) -> bool {
119 self.has_type_flags(TypeFlags::NEEDS_INFER)
120 }
has_placeholders(&self) -> bool121 fn has_placeholders(&self) -> bool {
122 self.has_type_flags(
123 TypeFlags::HAS_RE_PLACEHOLDER
124 | TypeFlags::HAS_TY_PLACEHOLDER
125 | TypeFlags::HAS_CT_PLACEHOLDER,
126 )
127 }
potentially_needs_subst(&self) -> bool128 fn potentially_needs_subst(&self) -> bool {
129 self.has_type_flags(
130 TypeFlags::KNOWN_NEEDS_SUBST | TypeFlags::HAS_UNKNOWN_DEFAULT_CONST_SUBSTS,
131 )
132 }
definitely_needs_subst(&self, tcx: TyCtxt<'tcx>) -> bool133 fn definitely_needs_subst(&self, tcx: TyCtxt<'tcx>) -> bool {
134 self.definitely_has_type_flags(tcx, TypeFlags::KNOWN_NEEDS_SUBST)
135 }
136 /// "Free" regions in this context means that it has any region
137 /// that is not (a) erased or (b) late-bound.
has_free_regions(&self, tcx: TyCtxt<'tcx>) -> bool138 fn has_free_regions(&self, tcx: TyCtxt<'tcx>) -> bool {
139 self.definitely_has_type_flags(tcx, TypeFlags::HAS_KNOWN_FREE_REGIONS)
140 }
141
has_erased_regions(&self) -> bool142 fn has_erased_regions(&self) -> bool {
143 self.has_type_flags(TypeFlags::HAS_RE_ERASED)
144 }
145
146 /// True if there are any un-erased free regions.
has_erasable_regions(&self, tcx: TyCtxt<'tcx>) -> bool147 fn has_erasable_regions(&self, tcx: TyCtxt<'tcx>) -> bool {
148 self.definitely_has_type_flags(tcx, TypeFlags::HAS_KNOWN_FREE_REGIONS)
149 }
150
151 /// Indicates whether this value definitely references only 'global'
152 /// generic parameters that are the same regardless of what fn we are
153 /// in. This is used for caching.
154 ///
155 /// Note that this function is pessimistic and may incorrectly return
156 /// `false`.
is_known_global(&self) -> bool157 fn is_known_global(&self) -> bool {
158 !self.has_type_flags(TypeFlags::HAS_POTENTIAL_FREE_LOCAL_NAMES)
159 }
160
161 /// Indicates whether this value references only 'global'
162 /// generic parameters that are the same regardless of what fn we are
163 /// in. This is used for caching.
is_global(&self, tcx: TyCtxt<'tcx>) -> bool164 fn is_global(&self, tcx: TyCtxt<'tcx>) -> bool {
165 !self.definitely_has_type_flags(tcx, TypeFlags::HAS_KNOWN_FREE_LOCAL_NAMES)
166 }
167
168 /// True if there are any late-bound regions
has_late_bound_regions(&self) -> bool169 fn has_late_bound_regions(&self) -> bool {
170 self.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND)
171 }
172
173 /// Indicates whether this value still has parameters/placeholders/inference variables
174 /// which could be replaced later, in a way that would change the results of `impl`
175 /// specialization.
still_further_specializable(&self) -> bool176 fn still_further_specializable(&self) -> bool {
177 self.has_type_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE)
178 }
179 }
180
181 impl TypeFoldable<'tcx> for hir::Constness {
super_fold_with<F: TypeFolder<'tcx>>(self, _: &mut F) -> Self182 fn super_fold_with<F: TypeFolder<'tcx>>(self, _: &mut F) -> Self {
183 self
184 }
super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> ControlFlow<V::BreakTy>185 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> ControlFlow<V::BreakTy> {
186 ControlFlow::CONTINUE
187 }
188 }
189
190 /// The `TypeFolder` trait defines the actual *folding*. There is a
191 /// method defined for every foldable type. Each of these has a
192 /// default implementation that does an "identity" fold. Within each
193 /// identity fold, it should invoke `foo.fold_with(self)` to fold each
194 /// sub-item.
195 pub trait TypeFolder<'tcx>: Sized {
tcx<'a>(&'a self) -> TyCtxt<'tcx>196 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
197
fold_binder<T>(&mut self, t: Binder<'tcx, T>) -> Binder<'tcx, T> where T: TypeFoldable<'tcx>,198 fn fold_binder<T>(&mut self, t: Binder<'tcx, T>) -> Binder<'tcx, T>
199 where
200 T: TypeFoldable<'tcx>,
201 {
202 t.super_fold_with(self)
203 }
204
fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx>205 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
206 t.super_fold_with(self)
207 }
208
fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx>209 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
210 r.super_fold_with(self)
211 }
212
fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>213 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
214 c.super_fold_with(self)
215 }
216
fold_predicate(&mut self, p: ty::Predicate<'tcx>) -> ty::Predicate<'tcx>217 fn fold_predicate(&mut self, p: ty::Predicate<'tcx>) -> ty::Predicate<'tcx> {
218 p.super_fold_with(self)
219 }
220
fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx>221 fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
222 bug!("most type folders should not be folding MIR datastructures: {:?}", c)
223 }
224 }
225
226 pub trait TypeVisitor<'tcx>: Sized {
227 type BreakTy = !;
228 /// Supplies the `tcx` for an unevaluated anonymous constant in case its default substs
229 /// are not yet supplied.
230 ///
231 /// Returning `None` for this method is only recommended if the `TypeVisitor`
232 /// does not care about default anon const substs, as it ignores generic parameters,
233 /// and fetching the default substs would cause a query cycle.
234 ///
235 /// For visitors which return `None` we completely skip the default substs in `ty::Unevaluated::super_visit_with`.
236 /// This means that incorrectly returning `None` can very quickly lead to ICE or other critical bugs, so be careful and
237 /// try to return an actual `tcx` if possible.
tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>>238 fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>>;
239
visit_binder<T: TypeFoldable<'tcx>>( &mut self, t: &Binder<'tcx, T>, ) -> ControlFlow<Self::BreakTy>240 fn visit_binder<T: TypeFoldable<'tcx>>(
241 &mut self,
242 t: &Binder<'tcx, T>,
243 ) -> ControlFlow<Self::BreakTy> {
244 t.super_visit_with(self)
245 }
246
visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy>247 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
248 t.super_visit_with(self)
249 }
250
visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy>251 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
252 r.super_visit_with(self)
253 }
254
visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy>255 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
256 c.super_visit_with(self)
257 }
258
visit_unevaluated_const(&mut self, uv: ty::Unevaluated<'tcx>) -> ControlFlow<Self::BreakTy>259 fn visit_unevaluated_const(&mut self, uv: ty::Unevaluated<'tcx>) -> ControlFlow<Self::BreakTy> {
260 uv.super_visit_with(self)
261 }
262
visit_predicate(&mut self, p: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy>263 fn visit_predicate(&mut self, p: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
264 p.super_visit_with(self)
265 }
266 }
267
268 ///////////////////////////////////////////////////////////////////////////
269 // Some sample folders
270
271 pub struct BottomUpFolder<'tcx, F, G, H>
272 where
273 F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
274 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
275 H: FnMut(&'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>,
276 {
277 pub tcx: TyCtxt<'tcx>,
278 pub ty_op: F,
279 pub lt_op: G,
280 pub ct_op: H,
281 }
282
283 impl<'tcx, F, G, H> TypeFolder<'tcx> for BottomUpFolder<'tcx, F, G, H>
284 where
285 F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
286 G: FnMut(ty::Region<'tcx>) -> ty::Region<'tcx>,
287 H: FnMut(&'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>,
288 {
tcx<'b>(&'b self) -> TyCtxt<'tcx>289 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
290 self.tcx
291 }
292
fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx>293 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
294 let t = ty.super_fold_with(self);
295 (self.ty_op)(t)
296 }
297
fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx>298 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
299 let r = r.super_fold_with(self);
300 (self.lt_op)(r)
301 }
302
fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>303 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
304 let ct = ct.super_fold_with(self);
305 (self.ct_op)(ct)
306 }
307 }
308
309 ///////////////////////////////////////////////////////////////////////////
310 // Region folder
311
312 impl<'tcx> TyCtxt<'tcx> {
313 /// Folds the escaping and free regions in `value` using `f`, and
314 /// sets `skipped_regions` to true if any late-bound region was found
315 /// and skipped.
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>,316 pub fn fold_regions<T>(
317 self,
318 value: T,
319 skipped_regions: &mut bool,
320 mut f: impl FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
321 ) -> T
322 where
323 T: TypeFoldable<'tcx>,
324 {
325 value.fold_with(&mut RegionFolder::new(self, skipped_regions, &mut f))
326 }
327
328 /// Invoke `callback` on every region appearing free in `value`.
for_each_free_region( self, value: &impl TypeFoldable<'tcx>, mut callback: impl FnMut(ty::Region<'tcx>), )329 pub fn for_each_free_region(
330 self,
331 value: &impl TypeFoldable<'tcx>,
332 mut callback: impl FnMut(ty::Region<'tcx>),
333 ) {
334 self.any_free_region_meets(value, |r| {
335 callback(r);
336 false
337 });
338 }
339
340 /// Returns `true` if `callback` returns true for every region appearing free in `value`.
all_free_regions_meet( self, value: &impl TypeFoldable<'tcx>, mut callback: impl FnMut(ty::Region<'tcx>) -> bool, ) -> bool341 pub fn all_free_regions_meet(
342 self,
343 value: &impl TypeFoldable<'tcx>,
344 mut callback: impl FnMut(ty::Region<'tcx>) -> bool,
345 ) -> bool {
346 !self.any_free_region_meets(value, |r| !callback(r))
347 }
348
349 /// Returns `true` if `callback` returns true for some region appearing free in `value`.
any_free_region_meets( self, value: &impl TypeFoldable<'tcx>, callback: impl FnMut(ty::Region<'tcx>) -> bool, ) -> bool350 pub fn any_free_region_meets(
351 self,
352 value: &impl TypeFoldable<'tcx>,
353 callback: impl FnMut(ty::Region<'tcx>) -> bool,
354 ) -> bool {
355 struct RegionVisitor<'tcx, F> {
356 tcx: TyCtxt<'tcx>,
357 /// The index of a binder *just outside* the things we have
358 /// traversed. If we encounter a bound region bound by this
359 /// binder or one outer to it, it appears free. Example:
360 ///
361 /// ```
362 /// for<'a> fn(for<'b> fn(), T)
363 /// ^ ^ ^ ^
364 /// | | | | here, would be shifted in 1
365 /// | | | here, would be shifted in 2
366 /// | | here, would be `INNERMOST` shifted in by 1
367 /// | here, initially, binder would be `INNERMOST`
368 /// ```
369 ///
370 /// You see that, initially, *any* bound value is free,
371 /// because we've not traversed any binders. As we pass
372 /// through a binder, we shift the `outer_index` by 1 to
373 /// account for the new binder that encloses us.
374 outer_index: ty::DebruijnIndex,
375 callback: F,
376 }
377
378 impl<'tcx, F> TypeVisitor<'tcx> for RegionVisitor<'tcx, F>
379 where
380 F: FnMut(ty::Region<'tcx>) -> bool,
381 {
382 type BreakTy = ();
383
384 fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
385 Some(self.tcx)
386 }
387
388 fn visit_binder<T: TypeFoldable<'tcx>>(
389 &mut self,
390 t: &Binder<'tcx, T>,
391 ) -> ControlFlow<Self::BreakTy> {
392 self.outer_index.shift_in(1);
393 let result = t.as_ref().skip_binder().visit_with(self);
394 self.outer_index.shift_out(1);
395 result
396 }
397
398 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
399 match *r {
400 ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => {
401 ControlFlow::CONTINUE
402 }
403 _ => {
404 if (self.callback)(r) {
405 ControlFlow::BREAK
406 } else {
407 ControlFlow::CONTINUE
408 }
409 }
410 }
411 }
412
413 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
414 // We're only interested in types involving regions
415 if ty.flags().intersects(TypeFlags::HAS_POTENTIAL_FREE_REGIONS) {
416 ty.super_visit_with(self)
417 } else {
418 ControlFlow::CONTINUE
419 }
420 }
421 }
422
423 value
424 .visit_with(&mut RegionVisitor { tcx: self, outer_index: ty::INNERMOST, callback })
425 .is_break()
426 }
427 }
428
429 /// Folds over the substructure of a type, visiting its component
430 /// types and all regions that occur *free* within it.
431 ///
432 /// That is, `Ty` can contain function or method types that bind
433 /// regions at the call site (`ReLateBound`), and occurrences of
434 /// regions (aka "lifetimes") that are bound within a type are not
435 /// visited by this folder; only regions that occur free will be
436 /// visited by `fld_r`.
437
438 pub struct RegionFolder<'a, 'tcx> {
439 tcx: TyCtxt<'tcx>,
440 skipped_regions: &'a mut bool,
441
442 /// Stores the index of a binder *just outside* the stuff we have
443 /// visited. So this begins as INNERMOST; when we pass through a
444 /// binder, it is incremented (via `shift_in`).
445 current_index: ty::DebruijnIndex,
446
447 /// Callback invokes for each free region. The `DebruijnIndex`
448 /// points to the binder *just outside* the ones we have passed
449 /// through.
450 fold_region_fn:
451 &'a mut (dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx> + 'a),
452 }
453
454 impl<'a, 'tcx> RegionFolder<'a, 'tcx> {
455 #[inline]
new( tcx: TyCtxt<'tcx>, skipped_regions: &'a mut bool, fold_region_fn: &'a mut dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>, ) -> RegionFolder<'a, 'tcx>456 pub fn new(
457 tcx: TyCtxt<'tcx>,
458 skipped_regions: &'a mut bool,
459 fold_region_fn: &'a mut dyn FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
460 ) -> RegionFolder<'a, 'tcx> {
461 RegionFolder { tcx, skipped_regions, current_index: ty::INNERMOST, fold_region_fn }
462 }
463 }
464
465 impl<'a, 'tcx> TypeFolder<'tcx> for RegionFolder<'a, 'tcx> {
tcx<'b>(&'b self) -> TyCtxt<'tcx>466 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
467 self.tcx
468 }
469
fold_binder<T: TypeFoldable<'tcx>>( &mut self, t: ty::Binder<'tcx, T>, ) -> ty::Binder<'tcx, T>470 fn fold_binder<T: TypeFoldable<'tcx>>(
471 &mut self,
472 t: ty::Binder<'tcx, T>,
473 ) -> ty::Binder<'tcx, T> {
474 self.current_index.shift_in(1);
475 let t = t.super_fold_with(self);
476 self.current_index.shift_out(1);
477 t
478 }
479
480 #[instrument(skip(self), level = "debug")]
fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx>481 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
482 match *r {
483 ty::ReLateBound(debruijn, _) if debruijn < self.current_index => {
484 debug!(?self.current_index, "skipped bound region");
485 *self.skipped_regions = true;
486 r
487 }
488 _ => {
489 debug!(?self.current_index, "folding free region");
490 (self.fold_region_fn)(r, self.current_index)
491 }
492 }
493 }
494 }
495
496 ///////////////////////////////////////////////////////////////////////////
497 // Bound vars replacer
498
499 /// Replaces the escaping bound vars (late bound regions or bound types) in a type.
500 struct BoundVarReplacer<'a, 'tcx> {
501 tcx: TyCtxt<'tcx>,
502
503 /// As with `RegionFolder`, represents the index of a binder *just outside*
504 /// the ones we have visited.
505 current_index: ty::DebruijnIndex,
506
507 fld_r: Option<&'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a)>,
508 fld_t: Option<&'a mut (dyn FnMut(ty::BoundTy) -> Ty<'tcx> + 'a)>,
509 fld_c: Option<&'a mut (dyn FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx> + 'a)>,
510 }
511
512 impl<'a, 'tcx> BoundVarReplacer<'a, 'tcx> {
new( tcx: TyCtxt<'tcx>, fld_r: Option<&'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a)>, fld_t: Option<&'a mut (dyn FnMut(ty::BoundTy) -> Ty<'tcx> + 'a)>, fld_c: Option<&'a mut (dyn FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx> + 'a)>, ) -> Self513 fn new(
514 tcx: TyCtxt<'tcx>,
515 fld_r: Option<&'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a)>,
516 fld_t: Option<&'a mut (dyn FnMut(ty::BoundTy) -> Ty<'tcx> + 'a)>,
517 fld_c: Option<&'a mut (dyn FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx> + 'a)>,
518 ) -> Self {
519 BoundVarReplacer { tcx, current_index: ty::INNERMOST, fld_r, fld_t, fld_c }
520 }
521 }
522
523 impl<'a, 'tcx> TypeFolder<'tcx> for BoundVarReplacer<'a, 'tcx> {
tcx<'b>(&'b self) -> TyCtxt<'tcx>524 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
525 self.tcx
526 }
527
fold_binder<T: TypeFoldable<'tcx>>( &mut self, t: ty::Binder<'tcx, T>, ) -> ty::Binder<'tcx, T>528 fn fold_binder<T: TypeFoldable<'tcx>>(
529 &mut self,
530 t: ty::Binder<'tcx, T>,
531 ) -> ty::Binder<'tcx, T> {
532 self.current_index.shift_in(1);
533 let t = t.super_fold_with(self);
534 self.current_index.shift_out(1);
535 t
536 }
537
fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx>538 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
539 match *t.kind() {
540 ty::Bound(debruijn, bound_ty) if debruijn == self.current_index => {
541 if let Some(fld_t) = self.fld_t.as_mut() {
542 let ty = fld_t(bound_ty);
543 return ty::fold::shift_vars(self.tcx, &ty, self.current_index.as_u32());
544 }
545 }
546 _ if t.has_vars_bound_at_or_above(self.current_index) => {
547 return t.super_fold_with(self);
548 }
549 _ => {}
550 }
551 t
552 }
553
fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx>554 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
555 match *r {
556 ty::ReLateBound(debruijn, br) if debruijn == self.current_index => {
557 if let Some(fld_r) = self.fld_r.as_mut() {
558 let region = fld_r(br);
559 return if let ty::ReLateBound(debruijn1, br) = *region {
560 // If the callback returns a late-bound region,
561 // that region should always use the INNERMOST
562 // debruijn index. Then we adjust it to the
563 // correct depth.
564 assert_eq!(debruijn1, ty::INNERMOST);
565 self.tcx.mk_region(ty::ReLateBound(debruijn, br))
566 } else {
567 region
568 };
569 }
570 }
571 _ => {}
572 }
573 r
574 }
575
fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>576 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
577 match *ct {
578 ty::Const { val: ty::ConstKind::Bound(debruijn, bound_const), ty }
579 if debruijn == self.current_index =>
580 {
581 if let Some(fld_c) = self.fld_c.as_mut() {
582 let ct = fld_c(bound_const, ty);
583 return ty::fold::shift_vars(self.tcx, &ct, self.current_index.as_u32());
584 }
585 }
586 _ if ct.has_vars_bound_at_or_above(self.current_index) => {
587 return ct.super_fold_with(self);
588 }
589 _ => {}
590 }
591 ct
592 }
593 }
594
595 impl<'tcx> TyCtxt<'tcx> {
596 /// Replaces all regions bound by the given `Binder` with the
597 /// results returned by the closure; the closure is expected to
598 /// return a free region (relative to this binder), and hence the
599 /// binder is removed in the return type. The closure is invoked
600 /// once for each unique `BoundRegionKind`; multiple references to the
601 /// same `BoundRegionKind` will reuse the previous result. A map is
602 /// returned at the end with each bound region and the free region
603 /// that replaced it.
604 ///
605 /// This method only replaces late bound regions and the result may still
606 /// contain escaping bound types.
replace_late_bound_regions<T, F>( self, value: Binder<'tcx, T>, mut fld_r: F, ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>) where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>, T: TypeFoldable<'tcx>,607 pub fn replace_late_bound_regions<T, F>(
608 self,
609 value: Binder<'tcx, T>,
610 mut fld_r: F,
611 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
612 where
613 F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
614 T: TypeFoldable<'tcx>,
615 {
616 let mut region_map = BTreeMap::new();
617 let mut real_fld_r =
618 |br: ty::BoundRegion| *region_map.entry(br).or_insert_with(|| fld_r(br));
619 let value = value.skip_binder();
620 let value = if !value.has_escaping_bound_vars() {
621 value
622 } else {
623 let mut replacer = BoundVarReplacer::new(self, Some(&mut real_fld_r), None, None);
624 value.fold_with(&mut replacer)
625 };
626 (value, region_map)
627 }
628
629 /// Replaces all escaping bound vars. The `fld_r` closure replaces escaping
630 /// bound regions; the `fld_t` closure replaces escaping bound types and the `fld_c`
631 /// closure replaces escaping bound consts.
replace_escaping_bound_vars<T, F, G, H>( self, value: T, mut fld_r: F, mut fld_t: G, mut fld_c: H, ) -> T where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>, G: FnMut(ty::BoundTy) -> Ty<'tcx>, H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>, T: TypeFoldable<'tcx>,632 pub fn replace_escaping_bound_vars<T, F, G, H>(
633 self,
634 value: T,
635 mut fld_r: F,
636 mut fld_t: G,
637 mut fld_c: H,
638 ) -> T
639 where
640 F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
641 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
642 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
643 T: TypeFoldable<'tcx>,
644 {
645 if !value.has_escaping_bound_vars() {
646 value
647 } else {
648 let mut replacer =
649 BoundVarReplacer::new(self, Some(&mut fld_r), Some(&mut fld_t), Some(&mut fld_c));
650 value.fold_with(&mut replacer)
651 }
652 }
653
654 /// Replaces all types or regions bound by the given `Binder`. The `fld_r`
655 /// closure replaces bound regions while the `fld_t` closure replaces bound
656 /// types.
replace_bound_vars<T, F, G, H>( self, value: Binder<'tcx, T>, mut fld_r: F, fld_t: G, fld_c: H, ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>) where F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>, G: FnMut(ty::BoundTy) -> Ty<'tcx>, H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>, T: TypeFoldable<'tcx>,657 pub fn replace_bound_vars<T, F, G, H>(
658 self,
659 value: Binder<'tcx, T>,
660 mut fld_r: F,
661 fld_t: G,
662 fld_c: H,
663 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
664 where
665 F: FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
666 G: FnMut(ty::BoundTy) -> Ty<'tcx>,
667 H: FnMut(ty::BoundVar, Ty<'tcx>) -> &'tcx ty::Const<'tcx>,
668 T: TypeFoldable<'tcx>,
669 {
670 let mut region_map = BTreeMap::new();
671 let real_fld_r = |br: ty::BoundRegion| *region_map.entry(br).or_insert_with(|| fld_r(br));
672 let value = self.replace_escaping_bound_vars(value.skip_binder(), real_fld_r, fld_t, fld_c);
673 (value, region_map)
674 }
675
676 /// Replaces any late-bound regions bound in `value` with
677 /// free variants attached to `all_outlive_scope`.
liberate_late_bound_regions<T>( self, all_outlive_scope: DefId, value: ty::Binder<'tcx, T>, ) -> T where T: TypeFoldable<'tcx>,678 pub fn liberate_late_bound_regions<T>(
679 self,
680 all_outlive_scope: DefId,
681 value: ty::Binder<'tcx, T>,
682 ) -> T
683 where
684 T: TypeFoldable<'tcx>,
685 {
686 self.replace_late_bound_regions(value, |br| {
687 self.mk_region(ty::ReFree(ty::FreeRegion {
688 scope: all_outlive_scope,
689 bound_region: br.kind,
690 }))
691 })
692 .0
693 }
694
shift_bound_var_indices<T>(self, bound_vars: usize, value: T) -> T where T: TypeFoldable<'tcx>,695 pub fn shift_bound_var_indices<T>(self, bound_vars: usize, value: T) -> T
696 where
697 T: TypeFoldable<'tcx>,
698 {
699 self.replace_escaping_bound_vars(
700 value,
701 |r| {
702 self.mk_region(ty::ReLateBound(
703 ty::INNERMOST,
704 ty::BoundRegion {
705 var: ty::BoundVar::from_usize(r.var.as_usize() + bound_vars),
706 kind: r.kind,
707 },
708 ))
709 },
710 |t| {
711 self.mk_ty(ty::Bound(
712 ty::INNERMOST,
713 ty::BoundTy {
714 var: ty::BoundVar::from_usize(t.var.as_usize() + bound_vars),
715 kind: t.kind,
716 },
717 ))
718 },
719 |c, ty| {
720 self.mk_const(ty::Const {
721 val: ty::ConstKind::Bound(
722 ty::INNERMOST,
723 ty::BoundVar::from_usize(c.as_usize() + bound_vars),
724 ),
725 ty,
726 })
727 },
728 )
729 }
730
731 /// Returns a set of all late-bound regions that are constrained
732 /// by `value`, meaning that if we instantiate those LBR with
733 /// variables and equate `value` with something else, those
734 /// variables will also be equated.
collect_constrained_late_bound_regions<T>( self, value: &Binder<'tcx, T>, ) -> FxHashSet<ty::BoundRegionKind> where T: TypeFoldable<'tcx>,735 pub fn collect_constrained_late_bound_regions<T>(
736 self,
737 value: &Binder<'tcx, T>,
738 ) -> FxHashSet<ty::BoundRegionKind>
739 where
740 T: TypeFoldable<'tcx>,
741 {
742 self.collect_late_bound_regions(value, true)
743 }
744
745 /// Returns a set of all late-bound regions that appear in `value` anywhere.
collect_referenced_late_bound_regions<T>( self, value: &Binder<'tcx, T>, ) -> FxHashSet<ty::BoundRegionKind> where T: TypeFoldable<'tcx>,746 pub fn collect_referenced_late_bound_regions<T>(
747 self,
748 value: &Binder<'tcx, T>,
749 ) -> FxHashSet<ty::BoundRegionKind>
750 where
751 T: TypeFoldable<'tcx>,
752 {
753 self.collect_late_bound_regions(value, false)
754 }
755
collect_late_bound_regions<T>( self, value: &Binder<'tcx, T>, just_constraint: bool, ) -> FxHashSet<ty::BoundRegionKind> where T: TypeFoldable<'tcx>,756 fn collect_late_bound_regions<T>(
757 self,
758 value: &Binder<'tcx, T>,
759 just_constraint: bool,
760 ) -> FxHashSet<ty::BoundRegionKind>
761 where
762 T: TypeFoldable<'tcx>,
763 {
764 let mut collector = LateBoundRegionsCollector::new(self, just_constraint);
765 let result = value.as_ref().skip_binder().visit_with(&mut collector);
766 assert!(result.is_continue()); // should never have stopped early
767 collector.regions
768 }
769
770 /// Replaces any late-bound regions bound in `value` with `'erased`. Useful in codegen but also
771 /// method lookup and a few other places where precise region relationships are not required.
erase_late_bound_regions<T>(self, value: Binder<'tcx, T>) -> T where T: TypeFoldable<'tcx>,772 pub fn erase_late_bound_regions<T>(self, value: Binder<'tcx, T>) -> T
773 where
774 T: TypeFoldable<'tcx>,
775 {
776 self.replace_late_bound_regions(value, |_| self.lifetimes.re_erased).0
777 }
778
779 /// Rewrite any late-bound regions so that they are anonymous. Region numbers are
780 /// assigned starting at 0 and increasing monotonically in the order traversed
781 /// by the fold operation.
782 ///
783 /// The chief purpose of this function is to canonicalize regions so that two
784 /// `FnSig`s or `TraitRef`s which are equivalent up to region naming will become
785 /// structurally identical. For example, `for<'a, 'b> fn(&'a isize, &'b isize)` and
786 /// `for<'a, 'b> fn(&'b isize, &'a isize)` will become identical after anonymization.
anonymize_late_bound_regions<T>(self, sig: Binder<'tcx, T>) -> Binder<'tcx, T> where T: TypeFoldable<'tcx>,787 pub fn anonymize_late_bound_regions<T>(self, sig: Binder<'tcx, T>) -> Binder<'tcx, T>
788 where
789 T: TypeFoldable<'tcx>,
790 {
791 let mut counter = 0;
792 let inner = self
793 .replace_late_bound_regions(sig, |_| {
794 let br = ty::BoundRegion {
795 var: ty::BoundVar::from_u32(counter),
796 kind: ty::BrAnon(counter),
797 };
798 let r = self.mk_region(ty::ReLateBound(ty::INNERMOST, br));
799 counter += 1;
800 r
801 })
802 .0;
803 let bound_vars = self.mk_bound_variable_kinds(
804 (0..counter).map(|i| ty::BoundVariableKind::Region(ty::BrAnon(i))),
805 );
806 Binder::bind_with_vars(inner, bound_vars)
807 }
808 }
809
810 pub struct ValidateBoundVars<'tcx> {
811 bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
812 binder_index: ty::DebruijnIndex,
813 // We may encounter the same variable at different levels of binding, so
814 // this can't just be `Ty`
815 visited: SsoHashSet<(ty::DebruijnIndex, Ty<'tcx>)>,
816 }
817
818 impl<'tcx> ValidateBoundVars<'tcx> {
new(bound_vars: &'tcx ty::List<ty::BoundVariableKind>) -> Self819 pub fn new(bound_vars: &'tcx ty::List<ty::BoundVariableKind>) -> Self {
820 ValidateBoundVars {
821 bound_vars,
822 binder_index: ty::INNERMOST,
823 visited: SsoHashSet::default(),
824 }
825 }
826 }
827
828 impl<'tcx> TypeVisitor<'tcx> for ValidateBoundVars<'tcx> {
829 type BreakTy = ();
830
tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>>831 fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
832 // Anonymous constants do not contain bound vars in their substs by default.
833 None
834 }
835
visit_binder<T: TypeFoldable<'tcx>>( &mut self, t: &Binder<'tcx, T>, ) -> ControlFlow<Self::BreakTy>836 fn visit_binder<T: TypeFoldable<'tcx>>(
837 &mut self,
838 t: &Binder<'tcx, T>,
839 ) -> ControlFlow<Self::BreakTy> {
840 self.binder_index.shift_in(1);
841 let result = t.super_visit_with(self);
842 self.binder_index.shift_out(1);
843 result
844 }
845
visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy>846 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
847 if t.outer_exclusive_binder < self.binder_index
848 || !self.visited.insert((self.binder_index, t))
849 {
850 return ControlFlow::BREAK;
851 }
852 match *t.kind() {
853 ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
854 if self.bound_vars.len() <= bound_ty.var.as_usize() {
855 bug!("Not enough bound vars: {:?} not found in {:?}", t, self.bound_vars);
856 }
857 let list_var = self.bound_vars[bound_ty.var.as_usize()];
858 match list_var {
859 ty::BoundVariableKind::Ty(kind) => {
860 if kind != bound_ty.kind {
861 bug!(
862 "Mismatched type kinds: {:?} doesn't var in list {:?}",
863 bound_ty.kind,
864 list_var
865 );
866 }
867 }
868 _ => {
869 bug!("Mismatched bound variable kinds! Expected type, found {:?}", list_var)
870 }
871 }
872 }
873
874 _ => (),
875 };
876
877 t.super_visit_with(self)
878 }
879
visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy>880 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
881 match r {
882 ty::ReLateBound(index, br) if *index == self.binder_index => {
883 if self.bound_vars.len() <= br.var.as_usize() {
884 bug!("Not enough bound vars: {:?} not found in {:?}", *br, self.bound_vars);
885 }
886 let list_var = self.bound_vars[br.var.as_usize()];
887 match list_var {
888 ty::BoundVariableKind::Region(kind) => {
889 if kind != br.kind {
890 bug!(
891 "Mismatched region kinds: {:?} doesn't match var ({:?}) in list ({:?})",
892 br.kind,
893 list_var,
894 self.bound_vars
895 );
896 }
897 }
898 _ => bug!(
899 "Mismatched bound variable kinds! Expected region, found {:?}",
900 list_var
901 ),
902 }
903 }
904
905 _ => (),
906 };
907
908 r.super_visit_with(self)
909 }
910 }
911
912 ///////////////////////////////////////////////////////////////////////////
913 // Shifter
914 //
915 // Shifts the De Bruijn indices on all escaping bound vars by a
916 // fixed amount. Useful in substitution or when otherwise introducing
917 // a binding level that is not intended to capture the existing bound
918 // vars. See comment on `shift_vars_through_binders` method in
919 // `subst.rs` for more details.
920
921 struct Shifter<'tcx> {
922 tcx: TyCtxt<'tcx>,
923 current_index: ty::DebruijnIndex,
924 amount: u32,
925 }
926
927 impl Shifter<'tcx> {
new(tcx: TyCtxt<'tcx>, amount: u32) -> Self928 pub fn new(tcx: TyCtxt<'tcx>, amount: u32) -> Self {
929 Shifter { tcx, current_index: ty::INNERMOST, amount }
930 }
931 }
932
933 impl TypeFolder<'tcx> for Shifter<'tcx> {
tcx<'b>(&'b self) -> TyCtxt<'tcx>934 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
935 self.tcx
936 }
937
fold_binder<T: TypeFoldable<'tcx>>( &mut self, t: ty::Binder<'tcx, T>, ) -> ty::Binder<'tcx, T>938 fn fold_binder<T: TypeFoldable<'tcx>>(
939 &mut self,
940 t: ty::Binder<'tcx, T>,
941 ) -> ty::Binder<'tcx, T> {
942 self.current_index.shift_in(1);
943 let t = t.super_fold_with(self);
944 self.current_index.shift_out(1);
945 t
946 }
947
fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx>948 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
949 match *r {
950 ty::ReLateBound(debruijn, br) => {
951 if self.amount == 0 || debruijn < self.current_index {
952 r
953 } else {
954 let debruijn = debruijn.shifted_in(self.amount);
955 let shifted = ty::ReLateBound(debruijn, br);
956 self.tcx.mk_region(shifted)
957 }
958 }
959 _ => r,
960 }
961 }
962
fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx>963 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
964 match *ty.kind() {
965 ty::Bound(debruijn, bound_ty) => {
966 if self.amount == 0 || debruijn < self.current_index {
967 ty
968 } else {
969 let debruijn = debruijn.shifted_in(self.amount);
970 self.tcx.mk_ty(ty::Bound(debruijn, bound_ty))
971 }
972 }
973
974 _ => ty.super_fold_with(self),
975 }
976 }
977
fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx>978 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
979 if let ty::Const { val: ty::ConstKind::Bound(debruijn, bound_ct), ty } = *ct {
980 if self.amount == 0 || debruijn < self.current_index {
981 ct
982 } else {
983 let debruijn = debruijn.shifted_in(self.amount);
984 self.tcx.mk_const(ty::Const { val: ty::ConstKind::Bound(debruijn, bound_ct), ty })
985 }
986 } else {
987 ct.super_fold_with(self)
988 }
989 }
990 }
991
shift_region<'tcx>( tcx: TyCtxt<'tcx>, region: ty::Region<'tcx>, amount: u32, ) -> ty::Region<'tcx>992 pub fn shift_region<'tcx>(
993 tcx: TyCtxt<'tcx>,
994 region: ty::Region<'tcx>,
995 amount: u32,
996 ) -> ty::Region<'tcx> {
997 match region {
998 ty::ReLateBound(debruijn, br) if amount > 0 => {
999 tcx.mk_region(ty::ReLateBound(debruijn.shifted_in(amount), *br))
1000 }
1001 _ => region,
1002 }
1003 }
1004
shift_vars<'tcx, T>(tcx: TyCtxt<'tcx>, value: T, amount: u32) -> T where T: TypeFoldable<'tcx>,1005 pub fn shift_vars<'tcx, T>(tcx: TyCtxt<'tcx>, value: T, amount: u32) -> T
1006 where
1007 T: TypeFoldable<'tcx>,
1008 {
1009 debug!("shift_vars(value={:?}, amount={})", value, amount);
1010
1011 value.fold_with(&mut Shifter::new(tcx, amount))
1012 }
1013
1014 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
1015 struct FoundEscapingVars;
1016
1017 /// An "escaping var" is a bound var whose binder is not part of `t`. A bound var can be a
1018 /// bound region or a bound type.
1019 ///
1020 /// So, for example, consider a type like the following, which has two binders:
1021 ///
1022 /// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize))
1023 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope
1024 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope
1025 ///
1026 /// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the
1027 /// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner
1028 /// fn type*, that type has an escaping region: `'a`.
1029 ///
1030 /// Note that what I'm calling an "escaping var" is often just called a "free var". However,
1031 /// we already use the term "free var". It refers to the regions or types that we use to represent
1032 /// bound regions or type params on a fn definition while we are type checking its body.
1033 ///
1034 /// To clarify, conceptually there is no particular difference between
1035 /// an "escaping" var and a "free" var. However, there is a big
1036 /// difference in practice. Basically, when "entering" a binding
1037 /// level, one is generally required to do some sort of processing to
1038 /// a bound var, such as replacing it with a fresh/placeholder
1039 /// var, or making an entry in the environment to represent the
1040 /// scope to which it is attached, etc. An escaping var represents
1041 /// a bound var for which this processing has not yet been done.
1042 struct HasEscapingVarsVisitor {
1043 /// Anything bound by `outer_index` or "above" is escaping.
1044 outer_index: ty::DebruijnIndex,
1045 }
1046
1047 impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
1048 type BreakTy = FoundEscapingVars;
1049
tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>>1050 fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
1051 // Anonymous constants do not contain bound vars in their substs by default.
1052 None
1053 }
1054
visit_binder<T: TypeFoldable<'tcx>>( &mut self, t: &Binder<'tcx, T>, ) -> ControlFlow<Self::BreakTy>1055 fn visit_binder<T: TypeFoldable<'tcx>>(
1056 &mut self,
1057 t: &Binder<'tcx, T>,
1058 ) -> ControlFlow<Self::BreakTy> {
1059 self.outer_index.shift_in(1);
1060 let result = t.super_visit_with(self);
1061 self.outer_index.shift_out(1);
1062 result
1063 }
1064
1065 #[inline]
visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy>1066 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1067 // If the outer-exclusive-binder is *strictly greater* than
1068 // `outer_index`, that means that `t` contains some content
1069 // bound at `outer_index` or above (because
1070 // `outer_exclusive_binder` is always 1 higher than the
1071 // content in `t`). Therefore, `t` has some escaping vars.
1072 if t.outer_exclusive_binder > self.outer_index {
1073 ControlFlow::Break(FoundEscapingVars)
1074 } else {
1075 ControlFlow::CONTINUE
1076 }
1077 }
1078
1079 #[inline]
visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy>1080 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
1081 // If the region is bound by `outer_index` or anything outside
1082 // of outer index, then it escapes the binders we have
1083 // visited.
1084 if r.bound_at_or_above_binder(self.outer_index) {
1085 ControlFlow::Break(FoundEscapingVars)
1086 } else {
1087 ControlFlow::CONTINUE
1088 }
1089 }
1090
visit_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy>1091 fn visit_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
1092 // we don't have a `visit_infer_const` callback, so we have to
1093 // hook in here to catch this case (annoying...), but
1094 // otherwise we do want to remember to visit the rest of the
1095 // const, as it has types/regions embedded in a lot of other
1096 // places.
1097 match ct.val {
1098 ty::ConstKind::Bound(debruijn, _) if debruijn >= self.outer_index => {
1099 ControlFlow::Break(FoundEscapingVars)
1100 }
1101 _ => ct.super_visit_with(self),
1102 }
1103 }
1104
1105 #[inline]
visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy>1106 fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
1107 if predicate.inner.outer_exclusive_binder > self.outer_index {
1108 ControlFlow::Break(FoundEscapingVars)
1109 } else {
1110 ControlFlow::CONTINUE
1111 }
1112 }
1113 }
1114
1115 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
1116 struct FoundFlags;
1117
1118 // FIXME: Optimize for checking for infer flags
1119 struct HasTypeFlagsVisitor<'tcx> {
1120 tcx: Option<TyCtxt<'tcx>>,
1121 flags: ty::TypeFlags,
1122 }
1123
1124 impl std::fmt::Debug for HasTypeFlagsVisitor<'tcx> {
fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result1125 fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
1126 self.flags.fmt(fmt)
1127 }
1128 }
1129
1130 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor<'tcx> {
1131 type BreakTy = FoundFlags;
tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>>1132 fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
1133 bug!("we shouldn't call this method as we manually look at ct substs");
1134 }
1135
1136 #[inline]
1137 #[instrument(level = "trace")]
visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy>1138 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1139 let flags = t.flags();
1140 trace!(t.flags=?t.flags());
1141 if flags.intersects(self.flags) {
1142 ControlFlow::Break(FoundFlags)
1143 } else {
1144 match flags.intersects(TypeFlags::HAS_UNKNOWN_DEFAULT_CONST_SUBSTS) {
1145 true if self.tcx.is_some() => UnknownConstSubstsVisitor::search(&self, t),
1146 _ => ControlFlow::CONTINUE,
1147 }
1148 }
1149 }
1150
1151 #[inline]
1152 #[instrument(skip(self), level = "trace")]
visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy>1153 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
1154 let flags = r.type_flags();
1155 trace!(r.flags=?flags);
1156 if flags.intersects(self.flags) {
1157 ControlFlow::Break(FoundFlags)
1158 } else {
1159 ControlFlow::CONTINUE
1160 }
1161 }
1162
1163 #[inline]
1164 #[instrument(level = "trace")]
visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy>1165 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
1166 let flags = FlagComputation::for_const(c);
1167 trace!(r.flags=?flags);
1168 if flags.intersects(self.flags) {
1169 ControlFlow::Break(FoundFlags)
1170 } else {
1171 match flags.intersects(TypeFlags::HAS_UNKNOWN_DEFAULT_CONST_SUBSTS) {
1172 true if self.tcx.is_some() => UnknownConstSubstsVisitor::search(&self, c),
1173 _ => ControlFlow::CONTINUE,
1174 }
1175 }
1176 }
1177
1178 #[inline]
1179 #[instrument(level = "trace")]
visit_unevaluated_const(&mut self, uv: ty::Unevaluated<'tcx>) -> ControlFlow<Self::BreakTy>1180 fn visit_unevaluated_const(&mut self, uv: ty::Unevaluated<'tcx>) -> ControlFlow<Self::BreakTy> {
1181 let flags = FlagComputation::for_unevaluated_const(uv);
1182 trace!(r.flags=?flags);
1183 if flags.intersects(self.flags) {
1184 ControlFlow::Break(FoundFlags)
1185 } else {
1186 match flags.intersects(TypeFlags::HAS_UNKNOWN_DEFAULT_CONST_SUBSTS) {
1187 true if self.tcx.is_some() => UnknownConstSubstsVisitor::search(&self, uv),
1188 _ => ControlFlow::CONTINUE,
1189 }
1190 }
1191 }
1192
1193 #[inline]
1194 #[instrument(level = "trace")]
visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy>1195 fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
1196 let flags = predicate.inner.flags;
1197 trace!(predicate.flags=?flags);
1198 if flags.intersects(self.flags) {
1199 ControlFlow::Break(FoundFlags)
1200 } else {
1201 match flags.intersects(TypeFlags::HAS_UNKNOWN_DEFAULT_CONST_SUBSTS) {
1202 true if self.tcx.is_some() => UnknownConstSubstsVisitor::search(&self, predicate),
1203 _ => ControlFlow::CONTINUE,
1204 }
1205 }
1206 }
1207 }
1208
1209 struct UnknownConstSubstsVisitor<'tcx> {
1210 tcx: TyCtxt<'tcx>,
1211 flags: ty::TypeFlags,
1212 }
1213
1214 impl<'tcx> UnknownConstSubstsVisitor<'tcx> {
1215 /// This is fairly cold and we don't want to
1216 /// bloat the size of the `HasTypeFlagsVisitor`.
1217 #[inline(never)]
search<T: TypeFoldable<'tcx>>( visitor: &HasTypeFlagsVisitor<'tcx>, v: T, ) -> ControlFlow<FoundFlags>1218 pub fn search<T: TypeFoldable<'tcx>>(
1219 visitor: &HasTypeFlagsVisitor<'tcx>,
1220 v: T,
1221 ) -> ControlFlow<FoundFlags> {
1222 if visitor.flags.intersects(TypeFlags::MAY_NEED_DEFAULT_CONST_SUBSTS) {
1223 v.super_visit_with(&mut UnknownConstSubstsVisitor {
1224 tcx: visitor.tcx.unwrap(),
1225 flags: visitor.flags,
1226 })
1227 } else {
1228 ControlFlow::CONTINUE
1229 }
1230 }
1231 }
1232
1233 impl<'tcx> TypeVisitor<'tcx> for UnknownConstSubstsVisitor<'tcx> {
1234 type BreakTy = FoundFlags;
tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>>1235 fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
1236 bug!("we shouldn't call this method as we manually look at ct substs");
1237 }
1238
visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy>1239 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1240 if t.flags().intersects(TypeFlags::HAS_UNKNOWN_DEFAULT_CONST_SUBSTS) {
1241 t.super_visit_with(self)
1242 } else {
1243 ControlFlow::CONTINUE
1244 }
1245 }
1246
1247 #[inline]
visit_unevaluated_const(&mut self, uv: ty::Unevaluated<'tcx>) -> ControlFlow<Self::BreakTy>1248 fn visit_unevaluated_const(&mut self, uv: ty::Unevaluated<'tcx>) -> ControlFlow<Self::BreakTy> {
1249 if uv.substs_.is_none() {
1250 self.tcx
1251 .default_anon_const_substs(uv.def.did)
1252 .visit_with(&mut HasTypeFlagsVisitor { tcx: Some(self.tcx), flags: self.flags })
1253 } else {
1254 ControlFlow::CONTINUE
1255 }
1256 }
1257
1258 #[inline]
visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy>1259 fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
1260 if predicate.inner.flags.intersects(TypeFlags::HAS_UNKNOWN_DEFAULT_CONST_SUBSTS) {
1261 predicate.super_visit_with(self)
1262 } else {
1263 ControlFlow::CONTINUE
1264 }
1265 }
1266 }
1267
1268 impl<'tcx> TyCtxt<'tcx> {
1269 /// This is a HACK(const_generics) and should probably not be needed.
1270 /// Might however be perf relevant, so who knows.
1271 ///
1272 /// FIXME(@lcnr): explain this function a bit more
expose_default_const_substs<T: TypeFoldable<'tcx>>(self, v: T) -> T1273 pub fn expose_default_const_substs<T: TypeFoldable<'tcx>>(self, v: T) -> T {
1274 v.fold_with(&mut ExposeDefaultConstSubstsFolder { tcx: self })
1275 }
1276 }
1277
1278 struct ExposeDefaultConstSubstsFolder<'tcx> {
1279 tcx: TyCtxt<'tcx>,
1280 }
1281
1282 impl<'tcx> TypeFolder<'tcx> for ExposeDefaultConstSubstsFolder<'tcx> {
tcx(&self) -> TyCtxt<'tcx>1283 fn tcx(&self) -> TyCtxt<'tcx> {
1284 self.tcx
1285 }
1286
fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx>1287 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1288 if ty.flags().intersects(TypeFlags::HAS_UNKNOWN_DEFAULT_CONST_SUBSTS) {
1289 ty.super_fold_with(self)
1290 } else {
1291 ty
1292 }
1293 }
1294
fold_predicate(&mut self, pred: ty::Predicate<'tcx>) -> ty::Predicate<'tcx>1295 fn fold_predicate(&mut self, pred: ty::Predicate<'tcx>) -> ty::Predicate<'tcx> {
1296 if pred.inner.flags.intersects(TypeFlags::HAS_UNKNOWN_DEFAULT_CONST_SUBSTS) {
1297 pred.super_fold_with(self)
1298 } else {
1299 pred
1300 }
1301 }
1302 }
1303
1304 /// Collects all the late-bound regions at the innermost binding level
1305 /// into a hash set.
1306 struct LateBoundRegionsCollector<'tcx> {
1307 tcx: TyCtxt<'tcx>,
1308 current_index: ty::DebruijnIndex,
1309 regions: FxHashSet<ty::BoundRegionKind>,
1310
1311 /// `true` if we only want regions that are known to be
1312 /// "constrained" when you equate this type with another type. In
1313 /// particular, if you have e.g., `&'a u32` and `&'b u32`, equating
1314 /// them constraints `'a == 'b`. But if you have `<&'a u32 as
1315 /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
1316 /// types may mean that `'a` and `'b` don't appear in the results,
1317 /// so they are not considered *constrained*.
1318 just_constrained: bool,
1319 }
1320
1321 impl LateBoundRegionsCollector<'tcx> {
new(tcx: TyCtxt<'tcx>, just_constrained: bool) -> Self1322 fn new(tcx: TyCtxt<'tcx>, just_constrained: bool) -> Self {
1323 LateBoundRegionsCollector {
1324 tcx,
1325 current_index: ty::INNERMOST,
1326 regions: Default::default(),
1327 just_constrained,
1328 }
1329 }
1330 }
1331
1332 impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector<'tcx> {
tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>>1333 fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
1334 Some(self.tcx)
1335 }
1336
visit_binder<T: TypeFoldable<'tcx>>( &mut self, t: &Binder<'tcx, T>, ) -> ControlFlow<Self::BreakTy>1337 fn visit_binder<T: TypeFoldable<'tcx>>(
1338 &mut self,
1339 t: &Binder<'tcx, T>,
1340 ) -> ControlFlow<Self::BreakTy> {
1341 self.current_index.shift_in(1);
1342 let result = t.super_visit_with(self);
1343 self.current_index.shift_out(1);
1344 result
1345 }
1346
visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy>1347 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1348 // if we are only looking for "constrained" region, we have to
1349 // ignore the inputs to a projection, as they may not appear
1350 // in the normalized form
1351 if self.just_constrained {
1352 if let ty::Projection(..) | ty::Opaque(..) = t.kind() {
1353 return ControlFlow::CONTINUE;
1354 }
1355 }
1356
1357 t.super_visit_with(self)
1358 }
1359
visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy>1360 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
1361 // if we are only looking for "constrained" region, we have to
1362 // ignore the inputs of an unevaluated const, as they may not appear
1363 // in the normalized form
1364 if self.just_constrained {
1365 if let ty::ConstKind::Unevaluated(..) = c.val {
1366 return ControlFlow::CONTINUE;
1367 }
1368 }
1369
1370 c.super_visit_with(self)
1371 }
1372
visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy>1373 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
1374 if let ty::ReLateBound(debruijn, br) = *r {
1375 if debruijn == self.current_index {
1376 self.regions.insert(br.kind);
1377 }
1378 }
1379 ControlFlow::CONTINUE
1380 }
1381 }
1382