1 //! A visiting traversal mechanism for complex data structures that contain type
4 //! This is a read-only traversal of the data structure.
6 //! This traversal has limited flexibility. Only a small number of "types of
7 //! interest" within the complex data structures can receive custom
8 //! visitation. These are the ones containing the most important type-related
9 //! information, such as `Ty`, `Predicate`, `Region`, and `Const`.
11 //! There are three groups of traits involved in each traversal.
12 //! - `TypeVisitable`. This is implemented once for many types, including:
13 //! - Types of interest, for which the methods delegate to the visitor.
14 //! - All other types, including generic containers like `Vec` and `Option`.
15 //! It defines a "skeleton" of how they should be visited.
16 //! - `TypeSuperVisitable`. This is implemented only for each type of interest,
17 //! and defines the visiting "skeleton" for these types.
18 //! - `TypeVisitor`. This is implemented for each visitor. This defines how
19 //! types of interest are visited.
21 //! This means each visit is a mixture of (a) generic visiting operations, and (b)
22 //! custom visit operations that are specific to the visitor.
23 //! - The `TypeVisitable` impls handle most of the traversal, and call into
24 //! `TypeVisitor` when they encounter a type of interest.
25 //! - A `TypeVisitor` may call into another `TypeVisitable` impl, because some of
26 //! the types of interest are recursive and can contain other types of interest.
27 //! - A `TypeVisitor` may also call into a `TypeSuperVisitable` impl, because each
28 //! visitor might provide custom handling only for some types of interest, or
29 //! only for some variants of each type of interest, and then use default
30 //! traversal for the remaining cases.
32 //! For example, if you have `struct S(Ty, U)` where `S: TypeVisitable` and `U:
33 //! TypeVisitable`, and an instance `s = S(ty, u)`, it would be visited like so:
35 //! s.visit_with(visitor) calls
36 //! - ty.visit_with(visitor) calls
37 //! - visitor.visit_ty(ty) may call
38 //! - ty.super_visit_with(visitor)
39 //! - u.visit_with(visitor)
41 use crate::ty::{self, flags::FlagComputation, Binder, Ty, TyCtxt, TypeFlags};
42 use rustc_errors::ErrorGuaranteed;
44 use rustc_data_structures::fx::FxHashSet;
45 use rustc_data_structures::sso::SsoHashSet;
47 use std::ops::ControlFlow;
49 /// This trait is implemented for every type that can be visited,
50 /// providing the skeleton of the traversal.
52 /// To implement this conveniently, use the derive macro located in
54 pub trait TypeVisitable<'tcx>: fmt::Debug + Clone {
55 /// The entry point for visiting. To visit a value `t` with a visitor `v`
56 /// call: `t.visit_with(v)`.
58 /// For most types, this just traverses the value, calling `visit_with` on
59 /// each field/element.
61 /// For types of interest (such as `Ty`), the implementation of this method
62 /// that calls a visitor method specifically for that type (such as
63 /// `V::visit_ty`). This is where control transfers from `TypeFoldable` to
65 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy>;
67 /// Returns `true` if `self` has any late-bound regions that are either
68 /// bound by `binder` or bound by some binder outside of `binder`.
69 /// If `binder` is `ty::INNERMOST`, this indicates whether
70 /// there are any late-bound regions that appear free.
71 fn has_vars_bound_at_or_above(&self, binder: ty::DebruijnIndex) -> bool {
72 self.visit_with(&mut HasEscapingVarsVisitor { outer_index: binder }).is_break()
75 /// Returns `true` if this type has any regions that escape `binder` (and
76 /// hence are not bound by it).
77 fn has_vars_bound_above(&self, binder: ty::DebruijnIndex) -> bool {
78 self.has_vars_bound_at_or_above(binder.shifted_in(1))
81 /// Return `true` if this type has regions that are not a part of the type.
82 /// For example, `for<'a> fn(&'a i32)` return `false`, while `fn(&'a i32)`
83 /// would return `true`. The latter can occur when traversing through the
86 /// See [`HasEscapingVarsVisitor`] for more information.
87 fn has_escaping_bound_vars(&self) -> bool {
88 self.has_vars_bound_at_or_above(ty::INNERMOST)
91 fn has_type_flags(&self, flags: TypeFlags) -> bool {
93 self.visit_with(&mut HasTypeFlagsVisitor { flags }).break_value() == Some(FoundFlags);
94 trace!(?self, ?flags, ?res, "has_type_flags");
97 fn has_projections(&self) -> bool {
98 self.has_type_flags(TypeFlags::HAS_PROJECTION)
100 fn has_opaque_types(&self) -> bool {
101 self.has_type_flags(TypeFlags::HAS_TY_OPAQUE)
103 fn references_error(&self) -> bool {
104 self.has_type_flags(TypeFlags::HAS_ERROR)
106 fn error_reported(&self) -> Result<(), ErrorGuaranteed> {
107 if self.references_error() {
108 if let Some(reported) = ty::tls::with(|tcx| tcx.sess.is_compilation_going_to_fail()) {
111 bug!("expect tcx.sess.is_compilation_going_to_fail return `Some`");
117 fn has_non_region_param(&self) -> bool {
118 self.has_type_flags(TypeFlags::NEEDS_SUBST - TypeFlags::HAS_RE_PARAM)
120 fn has_infer_regions(&self) -> bool {
121 self.has_type_flags(TypeFlags::HAS_RE_INFER)
123 fn has_infer_types(&self) -> bool {
124 self.has_type_flags(TypeFlags::HAS_TY_INFER)
126 fn has_non_region_infer(&self) -> bool {
127 self.has_type_flags(TypeFlags::NEEDS_INFER - TypeFlags::HAS_RE_INFER)
129 fn needs_infer(&self) -> bool {
130 self.has_type_flags(TypeFlags::NEEDS_INFER)
132 fn has_placeholders(&self) -> bool {
134 TypeFlags::HAS_RE_PLACEHOLDER
135 | TypeFlags::HAS_TY_PLACEHOLDER
136 | TypeFlags::HAS_CT_PLACEHOLDER,
139 fn needs_subst(&self) -> bool {
140 self.has_type_flags(TypeFlags::NEEDS_SUBST)
142 /// "Free" regions in this context means that it has any region
143 /// that is not (a) erased or (b) late-bound.
144 fn has_free_regions(&self) -> bool {
145 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
148 fn has_erased_regions(&self) -> bool {
149 self.has_type_flags(TypeFlags::HAS_RE_ERASED)
152 /// True if there are any un-erased free regions.
153 fn has_erasable_regions(&self) -> bool {
154 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
157 /// Indicates whether this value references only 'global'
158 /// generic parameters that are the same regardless of what fn we are
159 /// in. This is used for caching.
160 fn is_global(&self) -> bool {
161 !self.has_type_flags(TypeFlags::HAS_FREE_LOCAL_NAMES)
164 /// True if there are any late-bound regions
165 fn has_late_bound_regions(&self) -> bool {
166 self.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND)
169 /// Indicates whether this value still has parameters/placeholders/inference variables
170 /// which could be replaced later, in a way that would change the results of `impl`
172 fn still_further_specializable(&self) -> bool {
173 self.has_type_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE)
177 pub trait TypeSuperVisitable<'tcx>: TypeVisitable<'tcx> {
178 /// Provides a default visit for a type of interest. This should only be
179 /// called within `TypeVisitor` methods, when a non-custom traversal is
180 /// desired for the value of the type of interest passed to that method.
181 /// For example, in `MyVisitor::visit_ty(ty)`, it is valid to call
182 /// `ty.super_visit_with(self)`, but any other visiting should be done
183 /// with `xyz.visit_with(self)`.
184 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy>;
187 /// This trait is implemented for every visiting traversal. There is a visit
188 /// method defined for every type of interest. Each such method has a default
189 /// that recurses into the type's fields in a non-custom fashion.
190 pub trait TypeVisitor<'tcx>: Sized {
193 fn visit_binder<T: TypeVisitable<'tcx>>(
196 ) -> ControlFlow<Self::BreakTy> {
197 t.super_visit_with(self)
200 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
201 t.super_visit_with(self)
204 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
205 r.super_visit_with(self)
208 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
209 c.super_visit_with(self)
212 fn visit_predicate(&mut self, p: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
213 p.super_visit_with(self)
217 ///////////////////////////////////////////////////////////////////////////
220 impl<'tcx> TyCtxt<'tcx> {
221 /// Invoke `callback` on every region appearing free in `value`.
222 pub fn for_each_free_region(
224 value: &impl TypeVisitable<'tcx>,
225 mut callback: impl FnMut(ty::Region<'tcx>),
227 self.any_free_region_meets(value, |r| {
233 /// Returns `true` if `callback` returns true for every region appearing free in `value`.
234 pub fn all_free_regions_meet(
236 value: &impl TypeVisitable<'tcx>,
237 mut callback: impl FnMut(ty::Region<'tcx>) -> bool,
239 !self.any_free_region_meets(value, |r| !callback(r))
242 /// Returns `true` if `callback` returns true for some region appearing free in `value`.
243 pub fn any_free_region_meets(
245 value: &impl TypeVisitable<'tcx>,
246 callback: impl FnMut(ty::Region<'tcx>) -> bool,
248 struct RegionVisitor<F> {
249 /// The index of a binder *just outside* the things we have
250 /// traversed. If we encounter a bound region bound by this
251 /// binder or one outer to it, it appears free. Example:
253 /// ```ignore (illustrative)
254 /// for<'a> fn(for<'b> fn(), T)
256 /// // | | | | here, would be shifted in 1
257 /// // | | | here, would be shifted in 2
258 /// // | | here, would be `INNERMOST` shifted in by 1
259 /// // | here, initially, binder would be `INNERMOST`
262 /// You see that, initially, *any* bound value is free,
263 /// because we've not traversed any binders. As we pass
264 /// through a binder, we shift the `outer_index` by 1 to
265 /// account for the new binder that encloses us.
266 outer_index: ty::DebruijnIndex,
270 impl<'tcx, F> TypeVisitor<'tcx> for RegionVisitor<F>
272 F: FnMut(ty::Region<'tcx>) -> bool,
276 fn visit_binder<T: TypeVisitable<'tcx>>(
279 ) -> ControlFlow<Self::BreakTy> {
280 self.outer_index.shift_in(1);
281 let result = t.super_visit_with(self);
282 self.outer_index.shift_out(1);
286 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
288 ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => {
289 ControlFlow::CONTINUE
292 if (self.callback)(r) {
295 ControlFlow::CONTINUE
301 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
302 // We're only interested in types involving regions
303 if ty.flags().intersects(TypeFlags::HAS_FREE_REGIONS) {
304 ty.super_visit_with(self)
306 ControlFlow::CONTINUE
311 value.visit_with(&mut RegionVisitor { outer_index: ty::INNERMOST, callback }).is_break()
314 /// Returns a set of all late-bound regions that are constrained
315 /// by `value`, meaning that if we instantiate those LBR with
316 /// variables and equate `value` with something else, those
317 /// variables will also be equated.
318 pub fn collect_constrained_late_bound_regions<T>(
320 value: &Binder<'tcx, T>,
321 ) -> FxHashSet<ty::BoundRegionKind>
323 T: TypeVisitable<'tcx>,
325 self.collect_late_bound_regions(value, true)
328 /// Returns a set of all late-bound regions that appear in `value` anywhere.
329 pub fn collect_referenced_late_bound_regions<T>(
331 value: &Binder<'tcx, T>,
332 ) -> FxHashSet<ty::BoundRegionKind>
334 T: TypeVisitable<'tcx>,
336 self.collect_late_bound_regions(value, false)
339 fn collect_late_bound_regions<T>(
341 value: &Binder<'tcx, T>,
342 just_constraint: bool,
343 ) -> FxHashSet<ty::BoundRegionKind>
345 T: TypeVisitable<'tcx>,
347 let mut collector = LateBoundRegionsCollector::new(just_constraint);
348 let result = value.as_ref().skip_binder().visit_with(&mut collector);
349 assert!(result.is_continue()); // should never have stopped early
354 pub struct ValidateBoundVars<'tcx> {
355 bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
356 binder_index: ty::DebruijnIndex,
357 // We may encounter the same variable at different levels of binding, so
358 // this can't just be `Ty`
359 visited: SsoHashSet<(ty::DebruijnIndex, Ty<'tcx>)>,
362 impl<'tcx> ValidateBoundVars<'tcx> {
363 pub fn new(bound_vars: &'tcx ty::List<ty::BoundVariableKind>) -> Self {
366 binder_index: ty::INNERMOST,
367 visited: SsoHashSet::default(),
372 impl<'tcx> TypeVisitor<'tcx> for ValidateBoundVars<'tcx> {
375 fn visit_binder<T: TypeVisitable<'tcx>>(
378 ) -> ControlFlow<Self::BreakTy> {
379 self.binder_index.shift_in(1);
380 let result = t.super_visit_with(self);
381 self.binder_index.shift_out(1);
385 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
386 if t.outer_exclusive_binder() < self.binder_index
387 || !self.visited.insert((self.binder_index, t))
389 return ControlFlow::BREAK;
392 ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
393 if self.bound_vars.len() <= bound_ty.var.as_usize() {
394 bug!("Not enough bound vars: {:?} not found in {:?}", t, self.bound_vars);
396 let list_var = self.bound_vars[bound_ty.var.as_usize()];
398 ty::BoundVariableKind::Ty(kind) => {
399 if kind != bound_ty.kind {
401 "Mismatched type kinds: {:?} doesn't var in list {:?}",
408 bug!("Mismatched bound variable kinds! Expected type, found {:?}", list_var)
416 t.super_visit_with(self)
419 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
421 ty::ReLateBound(index, br) if index == self.binder_index => {
422 if self.bound_vars.len() <= br.var.as_usize() {
423 bug!("Not enough bound vars: {:?} not found in {:?}", br, self.bound_vars);
425 let list_var = self.bound_vars[br.var.as_usize()];
427 ty::BoundVariableKind::Region(kind) => {
430 "Mismatched region kinds: {:?} doesn't match var ({:?}) in list ({:?})",
438 "Mismatched bound variable kinds! Expected region, found {:?}",
447 r.super_visit_with(self)
451 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
452 struct FoundEscapingVars;
454 /// An "escaping var" is a bound var whose binder is not part of `t`. A bound var can be a
455 /// bound region or a bound type.
457 /// So, for example, consider a type like the following, which has two binders:
459 /// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize))
460 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope
461 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope
463 /// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the
464 /// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner
465 /// fn type*, that type has an escaping region: `'a`.
467 /// Note that what I'm calling an "escaping var" is often just called a "free var". However,
468 /// we already use the term "free var". It refers to the regions or types that we use to represent
469 /// bound regions or type params on a fn definition while we are type checking its body.
471 /// To clarify, conceptually there is no particular difference between
472 /// an "escaping" var and a "free" var. However, there is a big
473 /// difference in practice. Basically, when "entering" a binding
474 /// level, one is generally required to do some sort of processing to
475 /// a bound var, such as replacing it with a fresh/placeholder
476 /// var, or making an entry in the environment to represent the
477 /// scope to which it is attached, etc. An escaping var represents
478 /// a bound var for which this processing has not yet been done.
479 struct HasEscapingVarsVisitor {
480 /// Anything bound by `outer_index` or "above" is escaping.
481 outer_index: ty::DebruijnIndex,
484 impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
485 type BreakTy = FoundEscapingVars;
487 fn visit_binder<T: TypeVisitable<'tcx>>(
490 ) -> ControlFlow<Self::BreakTy> {
491 self.outer_index.shift_in(1);
492 let result = t.super_visit_with(self);
493 self.outer_index.shift_out(1);
498 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
499 // If the outer-exclusive-binder is *strictly greater* than
500 // `outer_index`, that means that `t` contains some content
501 // bound at `outer_index` or above (because
502 // `outer_exclusive_binder` is always 1 higher than the
503 // content in `t`). Therefore, `t` has some escaping vars.
504 if t.outer_exclusive_binder() > self.outer_index {
505 ControlFlow::Break(FoundEscapingVars)
507 ControlFlow::CONTINUE
512 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
513 // If the region is bound by `outer_index` or anything outside
514 // of outer index, then it escapes the binders we have
516 if r.bound_at_or_above_binder(self.outer_index) {
517 ControlFlow::Break(FoundEscapingVars)
519 ControlFlow::CONTINUE
523 fn visit_const(&mut self, ct: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
524 // we don't have a `visit_infer_const` callback, so we have to
525 // hook in here to catch this case (annoying...), but
526 // otherwise we do want to remember to visit the rest of the
527 // const, as it has types/regions embedded in a lot of other
530 ty::ConstKind::Bound(debruijn, _) if debruijn >= self.outer_index => {
531 ControlFlow::Break(FoundEscapingVars)
533 _ => ct.super_visit_with(self),
538 fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
539 if predicate.outer_exclusive_binder() > self.outer_index {
540 ControlFlow::Break(FoundEscapingVars)
542 ControlFlow::CONTINUE
547 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
550 // FIXME: Optimize for checking for infer flags
551 struct HasTypeFlagsVisitor {
552 flags: ty::TypeFlags,
555 impl std::fmt::Debug for HasTypeFlagsVisitor {
556 fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
561 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
562 type BreakTy = FoundFlags;
565 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
566 let flags = t.flags();
567 if flags.intersects(self.flags) {
568 ControlFlow::Break(FoundFlags)
570 ControlFlow::CONTINUE
575 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
576 let flags = r.type_flags();
577 if flags.intersects(self.flags) {
578 ControlFlow::Break(FoundFlags)
580 ControlFlow::CONTINUE
585 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
586 let flags = FlagComputation::for_const(c);
587 trace!(r.flags=?flags);
588 if flags.intersects(self.flags) {
589 ControlFlow::Break(FoundFlags)
591 ControlFlow::CONTINUE
596 fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
597 if predicate.flags().intersects(self.flags) {
598 ControlFlow::Break(FoundFlags)
600 ControlFlow::CONTINUE
605 /// Collects all the late-bound regions at the innermost binding level
607 struct LateBoundRegionsCollector {
608 current_index: ty::DebruijnIndex,
609 regions: FxHashSet<ty::BoundRegionKind>,
611 /// `true` if we only want regions that are known to be
612 /// "constrained" when you equate this type with another type. In
613 /// particular, if you have e.g., `&'a u32` and `&'b u32`, equating
614 /// them constraints `'a == 'b`. But if you have `<&'a u32 as
615 /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
616 /// types may mean that `'a` and `'b` don't appear in the results,
617 /// so they are not considered *constrained*.
618 just_constrained: bool,
621 impl LateBoundRegionsCollector {
622 fn new(just_constrained: bool) -> Self {
623 LateBoundRegionsCollector {
624 current_index: ty::INNERMOST,
625 regions: Default::default(),
631 impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
632 fn visit_binder<T: TypeVisitable<'tcx>>(
635 ) -> ControlFlow<Self::BreakTy> {
636 self.current_index.shift_in(1);
637 let result = t.super_visit_with(self);
638 self.current_index.shift_out(1);
642 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
643 // if we are only looking for "constrained" region, we have to
644 // ignore the inputs to a projection, as they may not appear
645 // in the normalized form
646 if self.just_constrained {
647 if let ty::Alias(..) = t.kind() {
648 return ControlFlow::CONTINUE;
652 t.super_visit_with(self)
655 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
656 // if we are only looking for "constrained" region, we have to
657 // ignore the inputs of an unevaluated const, as they may not appear
658 // in the normalized form
659 if self.just_constrained {
660 if let ty::ConstKind::Unevaluated(..) = c.kind() {
661 return ControlFlow::CONTINUE;
665 c.super_visit_with(self)
668 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
669 if let ty::ReLateBound(debruijn, br) = *r {
670 if debruijn == self.current_index {
671 self.regions.insert(br.kind);
674 ControlFlow::CONTINUE
678 /// Finds the max universe present
679 pub struct MaxUniverse {
680 max_universe: ty::UniverseIndex,
684 pub fn new() -> Self {
685 MaxUniverse { max_universe: ty::UniverseIndex::ROOT }
688 pub fn max_universe(self) -> ty::UniverseIndex {
693 impl<'tcx> TypeVisitor<'tcx> for MaxUniverse {
694 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
695 if let ty::Placeholder(placeholder) = t.kind() {
696 self.max_universe = ty::UniverseIndex::from_u32(
697 self.max_universe.as_u32().max(placeholder.universe.as_u32()),
701 t.super_visit_with(self)
704 fn visit_const(&mut self, c: ty::consts::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
705 if let ty::ConstKind::Placeholder(placeholder) = c.kind() {
706 self.max_universe = ty::UniverseIndex::from_u32(
707 self.max_universe.as_u32().max(placeholder.universe.as_u32()),
711 c.super_visit_with(self)
714 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
715 if let ty::RePlaceholder(placeholder) = *r {
716 self.max_universe = ty::UniverseIndex::from_u32(
717 self.max_universe.as_u32().max(placeholder.universe.as_u32()),
721 ControlFlow::CONTINUE