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 `self` 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 fn has_escaping_bound_vars(&self) -> bool {
82 self.has_vars_bound_at_or_above(ty::INNERMOST)
85 #[instrument(level = "trace", ret)]
86 fn has_type_flags(&self, flags: TypeFlags) -> bool {
87 self.visit_with(&mut HasTypeFlagsVisitor { flags }).break_value() == Some(FoundFlags)
89 fn has_projections(&self) -> bool {
90 self.has_type_flags(TypeFlags::HAS_PROJECTION)
92 fn has_opaque_types(&self) -> bool {
93 self.has_type_flags(TypeFlags::HAS_TY_OPAQUE)
95 fn references_error(&self) -> bool {
96 self.has_type_flags(TypeFlags::HAS_ERROR)
98 fn error_reported(&self) -> Result<(), ErrorGuaranteed> {
99 if self.references_error() {
100 if let Some(reported) = ty::tls::with(|tcx| tcx.sess.is_compilation_going_to_fail()) {
103 bug!("expect tcx.sess.is_compilation_going_to_fail return `Some`");
109 fn has_non_region_param(&self) -> bool {
110 self.has_type_flags(TypeFlags::NEEDS_SUBST - TypeFlags::HAS_RE_PARAM)
112 fn has_infer_regions(&self) -> bool {
113 self.has_type_flags(TypeFlags::HAS_RE_INFER)
115 fn has_infer_types(&self) -> bool {
116 self.has_type_flags(TypeFlags::HAS_TY_INFER)
118 fn has_non_region_infer(&self) -> bool {
119 self.has_type_flags(TypeFlags::NEEDS_INFER - TypeFlags::HAS_RE_INFER)
121 fn needs_infer(&self) -> bool {
122 self.has_type_flags(TypeFlags::NEEDS_INFER)
124 fn has_placeholders(&self) -> bool {
126 TypeFlags::HAS_RE_PLACEHOLDER
127 | TypeFlags::HAS_TY_PLACEHOLDER
128 | TypeFlags::HAS_CT_PLACEHOLDER,
131 fn needs_subst(&self) -> bool {
132 self.has_type_flags(TypeFlags::NEEDS_SUBST)
134 /// "Free" regions in this context means that it has any region
135 /// that is not (a) erased or (b) late-bound.
136 fn has_free_regions(&self) -> bool {
137 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
140 fn has_erased_regions(&self) -> bool {
141 self.has_type_flags(TypeFlags::HAS_RE_ERASED)
144 /// True if there are any un-erased free regions.
145 fn has_erasable_regions(&self) -> bool {
146 self.has_type_flags(TypeFlags::HAS_FREE_REGIONS)
149 /// Indicates whether this value references only 'global'
150 /// generic parameters that are the same regardless of what fn we are
151 /// in. This is used for caching.
152 fn is_global(&self) -> bool {
153 !self.has_type_flags(TypeFlags::HAS_FREE_LOCAL_NAMES)
156 /// True if there are any late-bound regions
157 fn has_late_bound_regions(&self) -> bool {
158 self.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND)
161 /// Indicates whether this value still has parameters/placeholders/inference variables
162 /// which could be replaced later, in a way that would change the results of `impl`
164 fn still_further_specializable(&self) -> bool {
165 self.has_type_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE)
169 pub trait TypeSuperVisitable<'tcx>: TypeVisitable<'tcx> {
170 /// Provides a default visit for a type of interest. This should only be
171 /// called within `TypeVisitor` methods, when a non-custom traversal is
172 /// desired for the value of the type of interest passed to that method.
173 /// For example, in `MyVisitor::visit_ty(ty)`, it is valid to call
174 /// `ty.super_visit_with(self)`, but any other visiting should be done
175 /// with `xyz.visit_with(self)`.
176 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy>;
179 /// This trait is implemented for every visiting traversal. There is a visit
180 /// method defined for every type of interest. Each such method has a default
181 /// that recurses into the type's fields in a non-custom fashion.
182 pub trait TypeVisitor<'tcx>: Sized {
185 fn visit_binder<T: TypeVisitable<'tcx>>(
188 ) -> ControlFlow<Self::BreakTy> {
189 t.super_visit_with(self)
192 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
193 t.super_visit_with(self)
196 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
197 r.super_visit_with(self)
200 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
201 c.super_visit_with(self)
204 fn visit_predicate(&mut self, p: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
205 p.super_visit_with(self)
209 ///////////////////////////////////////////////////////////////////////////
212 impl<'tcx> TyCtxt<'tcx> {
213 /// Invoke `callback` on every region appearing free in `value`.
214 pub fn for_each_free_region(
216 value: &impl TypeVisitable<'tcx>,
217 mut callback: impl FnMut(ty::Region<'tcx>),
219 self.any_free_region_meets(value, |r| {
225 /// Returns `true` if `callback` returns true for every region appearing free in `value`.
226 pub fn all_free_regions_meet(
228 value: &impl TypeVisitable<'tcx>,
229 mut callback: impl FnMut(ty::Region<'tcx>) -> bool,
231 !self.any_free_region_meets(value, |r| !callback(r))
234 /// Returns `true` if `callback` returns true for some region appearing free in `value`.
235 pub fn any_free_region_meets(
237 value: &impl TypeVisitable<'tcx>,
238 callback: impl FnMut(ty::Region<'tcx>) -> bool,
240 struct RegionVisitor<F> {
241 /// The index of a binder *just outside* the things we have
242 /// traversed. If we encounter a bound region bound by this
243 /// binder or one outer to it, it appears free. Example:
245 /// ```ignore (illustrative)
246 /// for<'a> fn(for<'b> fn(), T)
248 /// // | | | | here, would be shifted in 1
249 /// // | | | here, would be shifted in 2
250 /// // | | here, would be `INNERMOST` shifted in by 1
251 /// // | here, initially, binder would be `INNERMOST`
254 /// You see that, initially, *any* bound value is free,
255 /// because we've not traversed any binders. As we pass
256 /// through a binder, we shift the `outer_index` by 1 to
257 /// account for the new binder that encloses us.
258 outer_index: ty::DebruijnIndex,
262 impl<'tcx, F> TypeVisitor<'tcx> for RegionVisitor<F>
264 F: FnMut(ty::Region<'tcx>) -> bool,
268 fn visit_binder<T: TypeVisitable<'tcx>>(
271 ) -> ControlFlow<Self::BreakTy> {
272 self.outer_index.shift_in(1);
273 let result = t.super_visit_with(self);
274 self.outer_index.shift_out(1);
278 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
280 ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => {
281 ControlFlow::CONTINUE
284 if (self.callback)(r) {
287 ControlFlow::CONTINUE
293 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
294 // We're only interested in types involving regions
295 if ty.flags().intersects(TypeFlags::HAS_FREE_REGIONS) {
296 ty.super_visit_with(self)
298 ControlFlow::CONTINUE
303 value.visit_with(&mut RegionVisitor { outer_index: ty::INNERMOST, callback }).is_break()
306 /// Returns a set of all late-bound regions that are constrained
307 /// by `value`, meaning that if we instantiate those LBR with
308 /// variables and equate `value` with something else, those
309 /// variables will also be equated.
310 pub fn collect_constrained_late_bound_regions<T>(
312 value: &Binder<'tcx, T>,
313 ) -> FxHashSet<ty::BoundRegionKind>
315 T: TypeVisitable<'tcx>,
317 self.collect_late_bound_regions(value, true)
320 /// Returns a set of all late-bound regions that appear in `value` anywhere.
321 pub fn collect_referenced_late_bound_regions<T>(
323 value: &Binder<'tcx, T>,
324 ) -> FxHashSet<ty::BoundRegionKind>
326 T: TypeVisitable<'tcx>,
328 self.collect_late_bound_regions(value, false)
331 fn collect_late_bound_regions<T>(
333 value: &Binder<'tcx, T>,
334 just_constraint: bool,
335 ) -> FxHashSet<ty::BoundRegionKind>
337 T: TypeVisitable<'tcx>,
339 let mut collector = LateBoundRegionsCollector::new(just_constraint);
340 let result = value.as_ref().skip_binder().visit_with(&mut collector);
341 assert!(result.is_continue()); // should never have stopped early
346 pub struct ValidateBoundVars<'tcx> {
347 bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
348 binder_index: ty::DebruijnIndex,
349 // We may encounter the same variable at different levels of binding, so
350 // this can't just be `Ty`
351 visited: SsoHashSet<(ty::DebruijnIndex, Ty<'tcx>)>,
354 impl<'tcx> ValidateBoundVars<'tcx> {
355 pub fn new(bound_vars: &'tcx ty::List<ty::BoundVariableKind>) -> Self {
358 binder_index: ty::INNERMOST,
359 visited: SsoHashSet::default(),
364 impl<'tcx> TypeVisitor<'tcx> for ValidateBoundVars<'tcx> {
367 fn visit_binder<T: TypeVisitable<'tcx>>(
370 ) -> ControlFlow<Self::BreakTy> {
371 self.binder_index.shift_in(1);
372 let result = t.super_visit_with(self);
373 self.binder_index.shift_out(1);
377 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
378 if t.outer_exclusive_binder() < self.binder_index
379 || !self.visited.insert((self.binder_index, t))
381 return ControlFlow::BREAK;
384 ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
385 if self.bound_vars.len() <= bound_ty.var.as_usize() {
386 bug!("Not enough bound vars: {:?} not found in {:?}", t, self.bound_vars);
388 let list_var = self.bound_vars[bound_ty.var.as_usize()];
390 ty::BoundVariableKind::Ty(kind) => {
391 if kind != bound_ty.kind {
393 "Mismatched type kinds: {:?} doesn't var in list {:?}",
400 bug!("Mismatched bound variable kinds! Expected type, found {:?}", list_var)
408 t.super_visit_with(self)
411 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
413 ty::ReLateBound(index, br) if index == self.binder_index => {
414 if self.bound_vars.len() <= br.var.as_usize() {
415 bug!("Not enough bound vars: {:?} not found in {:?}", br, self.bound_vars);
417 let list_var = self.bound_vars[br.var.as_usize()];
419 ty::BoundVariableKind::Region(kind) => {
422 "Mismatched region kinds: {:?} doesn't match var ({:?}) in list ({:?})",
430 "Mismatched bound variable kinds! Expected region, found {:?}",
439 r.super_visit_with(self)
443 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
444 struct FoundEscapingVars;
446 /// An "escaping var" is a bound var whose binder is not part of `t`. A bound var can be a
447 /// bound region or a bound type.
449 /// So, for example, consider a type like the following, which has two binders:
451 /// for<'a> fn(x: for<'b> fn(&'a isize, &'b isize))
452 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ outer scope
453 /// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ inner scope
455 /// This type has *bound regions* (`'a`, `'b`), but it does not have escaping regions, because the
456 /// binders of both `'a` and `'b` are part of the type itself. However, if we consider the *inner
457 /// fn type*, that type has an escaping region: `'a`.
459 /// Note that what I'm calling an "escaping var" is often just called a "free var". However,
460 /// we already use the term "free var". It refers to the regions or types that we use to represent
461 /// bound regions or type params on a fn definition while we are type checking its body.
463 /// To clarify, conceptually there is no particular difference between
464 /// an "escaping" var and a "free" var. However, there is a big
465 /// difference in practice. Basically, when "entering" a binding
466 /// level, one is generally required to do some sort of processing to
467 /// a bound var, such as replacing it with a fresh/placeholder
468 /// var, or making an entry in the environment to represent the
469 /// scope to which it is attached, etc. An escaping var represents
470 /// a bound var for which this processing has not yet been done.
471 struct HasEscapingVarsVisitor {
472 /// Anything bound by `outer_index` or "above" is escaping.
473 outer_index: ty::DebruijnIndex,
476 impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
477 type BreakTy = FoundEscapingVars;
479 fn visit_binder<T: TypeVisitable<'tcx>>(
482 ) -> ControlFlow<Self::BreakTy> {
483 self.outer_index.shift_in(1);
484 let result = t.super_visit_with(self);
485 self.outer_index.shift_out(1);
490 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
491 // If the outer-exclusive-binder is *strictly greater* than
492 // `outer_index`, that means that `t` contains some content
493 // bound at `outer_index` or above (because
494 // `outer_exclusive_binder` is always 1 higher than the
495 // content in `t`). Therefore, `t` has some escaping vars.
496 if t.outer_exclusive_binder() > self.outer_index {
497 ControlFlow::Break(FoundEscapingVars)
499 ControlFlow::CONTINUE
504 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
505 // If the region is bound by `outer_index` or anything outside
506 // of outer index, then it escapes the binders we have
508 if r.bound_at_or_above_binder(self.outer_index) {
509 ControlFlow::Break(FoundEscapingVars)
511 ControlFlow::CONTINUE
515 fn visit_const(&mut self, ct: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
516 // we don't have a `visit_infer_const` callback, so we have to
517 // hook in here to catch this case (annoying...), but
518 // otherwise we do want to remember to visit the rest of the
519 // const, as it has types/regions embedded in a lot of other
522 ty::ConstKind::Bound(debruijn, _) if debruijn >= self.outer_index => {
523 ControlFlow::Break(FoundEscapingVars)
525 _ => ct.super_visit_with(self),
530 fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
531 if predicate.outer_exclusive_binder() > self.outer_index {
532 ControlFlow::Break(FoundEscapingVars)
534 ControlFlow::CONTINUE
539 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
542 // FIXME: Optimize for checking for infer flags
543 struct HasTypeFlagsVisitor {
544 flags: ty::TypeFlags,
547 impl std::fmt::Debug for HasTypeFlagsVisitor {
548 fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
553 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
554 type BreakTy = FoundFlags;
557 #[instrument(skip(self), level = "trace", ret)]
558 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
559 let flags = t.flags();
560 trace!(t.flags=?t.flags());
561 if flags.intersects(self.flags) {
562 ControlFlow::Break(FoundFlags)
564 ControlFlow::CONTINUE
569 #[instrument(skip(self), level = "trace", ret)]
570 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
571 let flags = r.type_flags();
572 trace!(r.flags=?flags);
573 if flags.intersects(self.flags) {
574 ControlFlow::Break(FoundFlags)
576 ControlFlow::CONTINUE
581 #[instrument(level = "trace", ret)]
582 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
583 let flags = FlagComputation::for_const(c);
584 trace!(r.flags=?flags);
585 if flags.intersects(self.flags) {
586 ControlFlow::Break(FoundFlags)
588 ControlFlow::CONTINUE
593 #[instrument(level = "trace", ret)]
594 fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
596 "HasTypeFlagsVisitor: predicate={:?} predicate.flags={:?} self.flags={:?}",
601 if predicate.flags().intersects(self.flags) {
602 ControlFlow::Break(FoundFlags)
604 ControlFlow::CONTINUE
609 /// Collects all the late-bound regions at the innermost binding level
611 struct LateBoundRegionsCollector {
612 current_index: ty::DebruijnIndex,
613 regions: FxHashSet<ty::BoundRegionKind>,
615 /// `true` if we only want regions that are known to be
616 /// "constrained" when you equate this type with another type. In
617 /// particular, if you have e.g., `&'a u32` and `&'b u32`, equating
618 /// them constraints `'a == 'b`. But if you have `<&'a u32 as
619 /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
620 /// types may mean that `'a` and `'b` don't appear in the results,
621 /// so they are not considered *constrained*.
622 just_constrained: bool,
625 impl LateBoundRegionsCollector {
626 fn new(just_constrained: bool) -> Self {
627 LateBoundRegionsCollector {
628 current_index: ty::INNERMOST,
629 regions: Default::default(),
635 impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
636 fn visit_binder<T: TypeVisitable<'tcx>>(
639 ) -> ControlFlow<Self::BreakTy> {
640 self.current_index.shift_in(1);
641 let result = t.super_visit_with(self);
642 self.current_index.shift_out(1);
646 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
647 // if we are only looking for "constrained" region, we have to
648 // ignore the inputs to a projection, as they may not appear
649 // in the normalized form
650 if self.just_constrained {
651 if let ty::Projection(..) | ty::Opaque(..) = t.kind() {
652 return ControlFlow::CONTINUE;
656 t.super_visit_with(self)
659 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
660 // if we are only looking for "constrained" region, we have to
661 // ignore the inputs of an unevaluated const, as they may not appear
662 // in the normalized form
663 if self.just_constrained {
664 if let ty::ConstKind::Unevaluated(..) = c.kind() {
665 return ControlFlow::CONTINUE;
669 c.super_visit_with(self)
672 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
673 if let ty::ReLateBound(debruijn, br) = *r {
674 if debruijn == self.current_index {
675 self.regions.insert(br.kind);
678 ControlFlow::CONTINUE
682 /// Finds the max universe present
683 pub struct MaxUniverse {
684 max_universe: ty::UniverseIndex,
688 pub fn new() -> Self {
689 MaxUniverse { max_universe: ty::UniverseIndex::ROOT }
692 pub fn max_universe(self) -> ty::UniverseIndex {
697 impl<'tcx> TypeVisitor<'tcx> for MaxUniverse {
698 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
699 if let ty::Placeholder(placeholder) = t.kind() {
700 self.max_universe = ty::UniverseIndex::from_u32(
701 self.max_universe.as_u32().max(placeholder.universe.as_u32()),
705 t.super_visit_with(self)
708 fn visit_const(&mut self, c: ty::consts::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
709 if let ty::ConstKind::Placeholder(placeholder) = c.kind() {
710 self.max_universe = ty::UniverseIndex::from_u32(
711 self.max_universe.as_u32().max(placeholder.universe.as_u32()),
715 c.super_visit_with(self)
718 fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
719 if let ty::RePlaceholder(placeholder) = *r {
720 self.max_universe = ty::UniverseIndex::from_u32(
721 self.max_universe.as_u32().max(placeholder.universe.as_u32()),
725 ControlFlow::CONTINUE