1 pub use self::freshen::TypeFreshener;
2 pub use self::lexical_region_resolve::RegionResolutionError;
3 pub use self::LateBoundRegionConversionTime::*;
4 pub use self::RegionVariableOrigin::*;
5 pub use self::SubregionOrigin::*;
6 pub use self::ValuePairs::*;
8 use self::opaque_types::OpaqueTypeStorage;
9 pub(crate) use self::undo_log::{InferCtxtUndoLogs, Snapshot, UndoLog};
11 use crate::traits::{self, ObligationCause, PredicateObligations, TraitEngine, TraitEngineExt};
13 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
14 use rustc_data_structures::sync::Lrc;
15 use rustc_data_structures::undo_log::Rollback;
16 use rustc_data_structures::unify as ut;
17 use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed};
18 use rustc_hir::def_id::{DefId, LocalDefId};
19 use rustc_middle::infer::canonical::{Canonical, CanonicalVarValues};
20 use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue};
21 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind, ToType};
22 use rustc_middle::mir::interpret::{ErrorHandled, EvalToValTreeResult};
23 use rustc_middle::traits::select;
24 use rustc_middle::ty::abstract_const::{AbstractConst, FailureKind};
25 use rustc_middle::ty::error::{ExpectedFound, TypeError};
26 use rustc_middle::ty::fold::BoundVarReplacerDelegate;
27 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
28 use rustc_middle::ty::relate::RelateResult;
29 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, SubstsRef};
30 use rustc_middle::ty::visit::TypeVisitable;
31 pub use rustc_middle::ty::IntVarValue;
32 use rustc_middle::ty::{self, GenericParamDefKind, InferConst, Ty, TyCtxt};
33 use rustc_middle::ty::{ConstVid, FloatVid, IntVid, TyVid};
34 use rustc_span::symbol::Symbol;
35 use rustc_span::{Span, DUMMY_SP};
37 use std::cell::{Cell, Ref, RefCell};
40 use self::combine::CombineFields;
41 use self::free_regions::RegionRelations;
42 use self::lexical_region_resolve::LexicalRegionResolutions;
43 use self::outlives::env::OutlivesEnvironment;
44 use self::region_constraints::{GenericKind, RegionConstraintData, VarInfos, VerifyBound};
45 use self::region_constraints::{
46 RegionConstraintCollector, RegionConstraintStorage, RegionSnapshot,
48 use self::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
54 pub mod error_reporting;
61 mod lexical_region_resolve;
67 pub mod region_constraints;
70 pub mod type_variable;
75 pub struct InferOk<'tcx, T> {
77 pub obligations: PredicateObligations<'tcx>,
79 pub type InferResult<'tcx, T> = Result<InferOk<'tcx, T>, TypeError<'tcx>>;
81 pub type Bound<T> = Option<T>;
82 pub type UnitResult<'tcx> = RelateResult<'tcx, ()>; // "unify result"
83 pub type FixupResult<'tcx, T> = Result<T, FixupError<'tcx>>; // "fixup result"
85 pub(crate) type UnificationTable<'a, 'tcx, T> = ut::UnificationTable<
86 ut::InPlace<T, &'a mut ut::UnificationStorage<T>, &'a mut InferCtxtUndoLogs<'tcx>>,
89 /// This type contains all the things within `InferCtxt` that sit within a
90 /// `RefCell` and are involved with taking/rolling back snapshots. Snapshot
91 /// operations are hot enough that we want only one call to `borrow_mut` per
92 /// call to `start_snapshot` and `rollback_to`.
94 pub struct InferCtxtInner<'tcx> {
95 /// Cache for projections. This cache is snapshotted along with the infcx.
97 /// Public so that `traits::project` can use it.
98 pub projection_cache: traits::ProjectionCacheStorage<'tcx>,
100 /// We instantiate `UnificationTable` with `bounds<Ty>` because the types
101 /// that might instantiate a general type variable have an order,
102 /// represented by its upper and lower bounds.
103 type_variable_storage: type_variable::TypeVariableStorage<'tcx>,
105 /// Map from const parameter variable to the kind of const it represents.
106 const_unification_storage: ut::UnificationTableStorage<ty::ConstVid<'tcx>>,
108 /// Map from integral variable to the kind of integer it represents.
109 int_unification_storage: ut::UnificationTableStorage<ty::IntVid>,
111 /// Map from floating variable to the kind of float it represents.
112 float_unification_storage: ut::UnificationTableStorage<ty::FloatVid>,
114 /// Tracks the set of region variables and the constraints between them.
115 /// This is initially `Some(_)` but when
116 /// `resolve_regions_and_report_errors` is invoked, this gets set to `None`
117 /// -- further attempts to perform unification, etc., may fail if new
118 /// region constraints would've been added.
119 region_constraint_storage: Option<RegionConstraintStorage<'tcx>>,
121 /// A set of constraints that regionck must validate. Each
122 /// constraint has the form `T:'a`, meaning "some type `T` must
123 /// outlive the lifetime 'a". These constraints derive from
124 /// instantiated type parameters. So if you had a struct defined
126 /// ```ignore (illustrative)
127 /// struct Foo<T:'static> { ... }
129 /// then in some expression `let x = Foo { ... }` it will
130 /// instantiate the type parameter `T` with a fresh type `$0`. At
131 /// the same time, it will record a region obligation of
132 /// `$0:'static`. This will get checked later by regionck. (We
133 /// can't generally check these things right away because we have
134 /// to wait until types are resolved.)
136 /// These are stored in a map keyed to the id of the innermost
137 /// enclosing fn body / static initializer expression. This is
138 /// because the location where the obligation was incurred can be
139 /// relevant with respect to which sublifetime assumptions are in
140 /// place. The reason that we store under the fn-id, and not
141 /// something more fine-grained, is so that it is easier for
142 /// regionck to be sure that it has found *all* the region
143 /// obligations (otherwise, it's easy to fail to walk to a
144 /// particular node-id).
146 /// Before running `resolve_regions_and_report_errors`, the creator
147 /// of the inference context is expected to invoke
148 /// [`InferCtxt::process_registered_region_obligations`]
149 /// for each body-id in this map, which will process the
150 /// obligations within. This is expected to be done 'late enough'
151 /// that all type inference variables have been bound and so forth.
152 region_obligations: Vec<RegionObligation<'tcx>>,
154 undo_log: InferCtxtUndoLogs<'tcx>,
156 /// Caches for opaque type inference.
157 pub opaque_type_storage: OpaqueTypeStorage<'tcx>,
160 impl<'tcx> InferCtxtInner<'tcx> {
161 fn new() -> InferCtxtInner<'tcx> {
163 projection_cache: Default::default(),
164 type_variable_storage: type_variable::TypeVariableStorage::new(),
165 undo_log: InferCtxtUndoLogs::default(),
166 const_unification_storage: ut::UnificationTableStorage::new(),
167 int_unification_storage: ut::UnificationTableStorage::new(),
168 float_unification_storage: ut::UnificationTableStorage::new(),
169 region_constraint_storage: Some(RegionConstraintStorage::new()),
170 region_obligations: vec![],
171 opaque_type_storage: Default::default(),
176 pub fn region_obligations(&self) -> &[RegionObligation<'tcx>] {
177 &self.region_obligations
181 pub fn projection_cache(&mut self) -> traits::ProjectionCache<'_, 'tcx> {
182 self.projection_cache.with_log(&mut self.undo_log)
186 fn type_variables(&mut self) -> type_variable::TypeVariableTable<'_, 'tcx> {
187 self.type_variable_storage.with_log(&mut self.undo_log)
191 pub fn opaque_types(&mut self) -> opaque_types::OpaqueTypeTable<'_, 'tcx> {
192 self.opaque_type_storage.with_log(&mut self.undo_log)
196 fn int_unification_table(
198 ) -> ut::UnificationTable<
201 &mut ut::UnificationStorage<ty::IntVid>,
202 &mut InferCtxtUndoLogs<'tcx>,
205 self.int_unification_storage.with_log(&mut self.undo_log)
209 fn float_unification_table(
211 ) -> ut::UnificationTable<
214 &mut ut::UnificationStorage<ty::FloatVid>,
215 &mut InferCtxtUndoLogs<'tcx>,
218 self.float_unification_storage.with_log(&mut self.undo_log)
222 fn const_unification_table(
224 ) -> ut::UnificationTable<
227 &mut ut::UnificationStorage<ty::ConstVid<'tcx>>,
228 &mut InferCtxtUndoLogs<'tcx>,
231 self.const_unification_storage.with_log(&mut self.undo_log)
235 pub fn unwrap_region_constraints(&mut self) -> RegionConstraintCollector<'_, 'tcx> {
236 self.region_constraint_storage
238 .expect("region constraints already solved")
239 .with_log(&mut self.undo_log)
243 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
244 pub enum DefiningAnchor {
245 /// `DefId` of the item.
247 /// When opaque types are not resolved, we `Bubble` up, meaning
248 /// return the opaque/hidden type pair from query, for caller of query to handle it.
250 /// Used to catch type mismatch errors when handling opaque types.
254 pub struct InferCtxt<'a, 'tcx> {
255 pub tcx: TyCtxt<'tcx>,
257 /// The `DefId` of the item in whose context we are performing inference or typeck.
258 /// It is used to check whether an opaque type use is a defining use.
260 /// If it is `DefiningAnchor::Bubble`, we can't resolve opaque types here and need to bubble up
261 /// the obligation. This frequently happens for
262 /// short lived InferCtxt within queries. The opaque type obligations are forwarded
263 /// to the outside until the end up in an `InferCtxt` for typeck or borrowck.
265 /// It is default value is `DefiningAnchor::Error`, this way it is easier to catch errors that
266 /// might come up during inference or typeck.
267 pub defining_use_anchor: DefiningAnchor,
269 /// Whether this inference context should care about region obligations in
270 /// the root universe. Most notably, this is used during hir typeck as region
271 /// solving is left to borrowck instead.
272 pub considering_regions: bool,
274 /// During type-checking/inference of a body, `in_progress_typeck_results`
275 /// contains a reference to the typeck results being built up, which are
276 /// used for reading closure kinds/signatures as they are inferred,
277 /// and for error reporting logic to read arbitrary node types.
278 pub in_progress_typeck_results: Option<&'a RefCell<ty::TypeckResults<'tcx>>>,
280 pub inner: RefCell<InferCtxtInner<'tcx>>,
282 /// If set, this flag causes us to skip the 'leak check' during
283 /// higher-ranked subtyping operations. This flag is a temporary one used
284 /// to manage the removal of the leak-check: for the time being, we still run the
285 /// leak-check, but we issue warnings. This flag can only be set to true
286 /// when entering a snapshot.
287 skip_leak_check: Cell<bool>,
289 /// Once region inference is done, the values for each variable.
290 lexical_region_resolutions: RefCell<Option<LexicalRegionResolutions<'tcx>>>,
292 /// Caches the results of trait selection. This cache is used
293 /// for things that have to do with the parameters in scope.
294 pub selection_cache: select::SelectionCache<'tcx>,
296 /// Caches the results of trait evaluation.
297 pub evaluation_cache: select::EvaluationCache<'tcx>,
299 /// the set of predicates on which errors have been reported, to
300 /// avoid reporting the same error twice.
301 pub reported_trait_errors: RefCell<FxHashMap<Span, Vec<ty::Predicate<'tcx>>>>,
303 pub reported_closure_mismatch: RefCell<FxHashSet<(Span, Option<Span>)>>,
305 /// When an error occurs, we want to avoid reporting "derived"
306 /// errors that are due to this original failure. Normally, we
307 /// handle this with the `err_count_on_creation` count, which
308 /// basically just tracks how many errors were reported when we
309 /// started type-checking a fn and checks to see if any new errors
310 /// have been reported since then. Not great, but it works.
312 /// However, when errors originated in other passes -- notably
313 /// resolve -- this heuristic breaks down. Therefore, we have this
314 /// auxiliary flag that one can set whenever one creates a
315 /// type-error that is due to an error in a prior pass.
317 /// Don't read this flag directly, call `is_tainted_by_errors()`
318 /// and `set_tainted_by_errors()`.
319 tainted_by_errors: Cell<Option<ErrorGuaranteed>>,
321 /// Track how many errors were reported when this infcx is created.
322 /// If the number of errors increases, that's also a sign (line
323 /// `tainted_by_errors`) to avoid reporting certain kinds of errors.
324 // FIXME(matthewjasper) Merge into `tainted_by_errors`
325 err_count_on_creation: usize,
327 /// This flag is true while there is an active snapshot.
328 in_snapshot: Cell<bool>,
330 /// What is the innermost universe we have created? Starts out as
331 /// `UniverseIndex::root()` but grows from there as we enter
332 /// universal quantifiers.
334 /// N.B., at present, we exclude the universal quantifiers on the
335 /// item we are type-checking, and just consider those names as
336 /// part of the root universe. So this would only get incremented
337 /// when we enter into a higher-ranked (`for<..>`) type or trait
339 universe: Cell<ty::UniverseIndex>,
341 normalize_fn_sig_for_diagnostic:
342 Option<Lrc<dyn Fn(&InferCtxt<'_, 'tcx>, ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx>>>,
345 /// See the `error_reporting` module for more details.
346 #[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable, TypeVisitable)]
347 pub enum ValuePairs<'tcx> {
348 Regions(ExpectedFound<ty::Region<'tcx>>),
349 Terms(ExpectedFound<ty::Term<'tcx>>),
350 TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>),
351 PolyTraitRefs(ExpectedFound<ty::PolyTraitRef<'tcx>>),
354 impl<'tcx> ValuePairs<'tcx> {
355 pub fn ty(&self) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
356 if let ValuePairs::Terms(ExpectedFound {
357 expected: ty::Term::Ty(expected),
358 found: ty::Term::Ty(found),
361 Some((*expected, *found))
368 /// The trace designates the path through inference that we took to
369 /// encounter an error or subtyping constraint.
371 /// See the `error_reporting` module for more details.
372 #[derive(Clone, Debug)]
373 pub struct TypeTrace<'tcx> {
374 pub cause: ObligationCause<'tcx>,
375 pub values: ValuePairs<'tcx>,
378 /// The origin of a `r1 <= r2` constraint.
380 /// See `error_reporting` module for more details
381 #[derive(Clone, Debug)]
382 pub enum SubregionOrigin<'tcx> {
383 /// Arose from a subtyping relation
384 Subtype(Box<TypeTrace<'tcx>>),
386 /// When casting `&'a T` to an `&'b Trait` object,
387 /// relating `'a` to `'b`
388 RelateObjectBound(Span),
390 /// Some type parameter was instantiated with the given type,
391 /// and that type must outlive some region.
392 RelateParamBound(Span, Ty<'tcx>, Option<Span>),
394 /// The given region parameter was instantiated with a region
395 /// that must outlive some other region.
396 RelateRegionParamBound(Span),
398 /// Creating a pointer `b` to contents of another reference
401 /// Creating a pointer `b` to contents of an upvar
402 ReborrowUpvar(Span, ty::UpvarId),
404 /// Data with type `Ty<'tcx>` was borrowed
405 DataBorrowed(Ty<'tcx>, Span),
407 /// (&'a &'b T) where a >= b
408 ReferenceOutlivesReferent(Ty<'tcx>, Span),
410 /// Comparing the signature and requirements of an impl method against
411 /// the containing trait.
412 CompareImplItemObligation { span: Span, impl_item_def_id: LocalDefId, trait_item_def_id: DefId },
414 /// Checking that the bounds of a trait's associated type hold for a given impl
415 CheckAssociatedTypeBounds {
416 parent: Box<SubregionOrigin<'tcx>>,
417 impl_item_def_id: LocalDefId,
418 trait_item_def_id: DefId,
422 // `SubregionOrigin` is used a lot. Make sure it doesn't unintentionally get bigger.
423 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
424 static_assert_size!(SubregionOrigin<'_>, 32);
426 /// Times when we replace late-bound regions with variables:
427 #[derive(Clone, Copy, Debug)]
428 pub enum LateBoundRegionConversionTime {
429 /// when a fn is called
432 /// when two higher-ranked types are compared
435 /// when projecting an associated type
436 AssocTypeProjection(DefId),
439 /// Reasons to create a region inference variable
441 /// See `error_reporting` module for more details
442 #[derive(Copy, Clone, Debug)]
443 pub enum RegionVariableOrigin {
444 /// Region variables created for ill-categorized reasons,
445 /// mostly indicates places in need of refactoring
448 /// Regions created by a `&P` or `[...]` pattern
451 /// Regions created by `&` operator
454 /// Regions created as part of an autoref of a method receiver
457 /// Regions created as part of an automatic coercion
460 /// Region variables created as the values for early-bound regions
461 EarlyBoundRegion(Span, Symbol),
463 /// Region variables created for bound regions
464 /// in a function or method that is called
465 LateBoundRegion(Span, ty::BoundRegionKind, LateBoundRegionConversionTime),
467 UpvarRegion(ty::UpvarId, Span),
469 /// This origin is used for the inference variables that we create
470 /// during NLL region processing.
471 Nll(NllRegionVariableOrigin),
474 #[derive(Copy, Clone, Debug)]
475 pub enum NllRegionVariableOrigin {
476 /// During NLL region processing, we create variables for free
477 /// regions that we encounter in the function signature and
478 /// elsewhere. This origin indices we've got one of those.
481 /// "Universal" instantiation of a higher-ranked region (e.g.,
482 /// from a `for<'a> T` binder). Meant to represent "any region".
483 Placeholder(ty::PlaceholderRegion),
486 /// If this is true, then this variable was created to represent a lifetime
487 /// bound in a `for` binder. For example, it might have been created to
488 /// represent the lifetime `'a` in a type like `for<'a> fn(&'a u32)`.
489 /// Such variables are created when we are trying to figure out if there
490 /// is any valid instantiation of `'a` that could fit into some scenario.
492 /// This is used to inform error reporting: in the case that we are trying to
493 /// determine whether there is any valid instantiation of a `'a` variable that meets
494 /// some constraint C, we want to blame the "source" of that `for` type,
495 /// rather than blaming the source of the constraint C.
500 // FIXME(eddyb) investigate overlap between this and `TyOrConstInferVar`.
501 #[derive(Copy, Clone, Debug)]
502 pub enum FixupError<'tcx> {
503 UnresolvedIntTy(IntVid),
504 UnresolvedFloatTy(FloatVid),
506 UnresolvedConst(ConstVid<'tcx>),
509 /// See the `region_obligations` field for more information.
510 #[derive(Clone, Debug)]
511 pub struct RegionObligation<'tcx> {
512 pub sub_region: ty::Region<'tcx>,
513 pub sup_type: Ty<'tcx>,
514 pub origin: SubregionOrigin<'tcx>,
517 impl<'tcx> fmt::Display for FixupError<'tcx> {
518 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
519 use self::FixupError::*;
522 UnresolvedIntTy(_) => write!(
524 "cannot determine the type of this integer; \
525 add a suffix to specify the type explicitly"
527 UnresolvedFloatTy(_) => write!(
529 "cannot determine the type of this number; \
530 add a suffix to specify the type explicitly"
532 UnresolvedTy(_) => write!(f, "unconstrained type"),
533 UnresolvedConst(_) => write!(f, "unconstrained const value"),
538 /// A temporary returned by `tcx.infer_ctxt()`. This is necessary
539 /// for multiple `InferCtxt` to share the same `in_progress_typeck_results`
540 /// without using `Rc` or something similar.
541 pub struct InferCtxtBuilder<'tcx> {
543 defining_use_anchor: DefiningAnchor,
544 considering_regions: bool,
545 fresh_typeck_results: Option<RefCell<ty::TypeckResults<'tcx>>>,
546 normalize_fn_sig_for_diagnostic:
547 Option<Lrc<dyn Fn(&InferCtxt<'_, 'tcx>, ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx>>>,
550 pub trait TyCtxtInferExt<'tcx> {
551 fn infer_ctxt(self) -> InferCtxtBuilder<'tcx>;
554 impl<'tcx> TyCtxtInferExt<'tcx> for TyCtxt<'tcx> {
555 fn infer_ctxt(self) -> InferCtxtBuilder<'tcx> {
558 defining_use_anchor: DefiningAnchor::Error,
559 considering_regions: true,
560 fresh_typeck_results: None,
561 normalize_fn_sig_for_diagnostic: None,
566 impl<'tcx> InferCtxtBuilder<'tcx> {
567 /// Used only by `rustc_typeck` during body type-checking/inference,
568 /// will initialize `in_progress_typeck_results` with fresh `TypeckResults`.
569 /// Will also change the scope for opaque type defining use checks to the given owner.
570 pub fn with_fresh_in_progress_typeck_results(mut self, table_owner: LocalDefId) -> Self {
571 self.fresh_typeck_results = Some(RefCell::new(ty::TypeckResults::new(table_owner)));
572 self.with_opaque_type_inference(DefiningAnchor::Bind(table_owner))
575 /// Whenever the `InferCtxt` should be able to handle defining uses of opaque types,
576 /// you need to call this function. Otherwise the opaque type will be treated opaquely.
578 /// It is only meant to be called in two places, for typeck
579 /// (via `with_fresh_in_progress_typeck_results`) and for the inference context used
581 pub fn with_opaque_type_inference(mut self, defining_use_anchor: DefiningAnchor) -> Self {
582 self.defining_use_anchor = defining_use_anchor;
586 pub fn ignoring_regions(mut self) -> Self {
587 self.considering_regions = false;
591 pub fn with_normalize_fn_sig_for_diagnostic(
593 fun: Lrc<dyn Fn(&InferCtxt<'_, 'tcx>, ty::PolyFnSig<'tcx>) -> ty::PolyFnSig<'tcx>>,
595 self.normalize_fn_sig_for_diagnostic = Some(fun);
599 /// Given a canonical value `C` as a starting point, create an
600 /// inference context that contains each of the bound values
601 /// within instantiated as a fresh variable. The `f` closure is
602 /// invoked with the new infcx, along with the instantiated value
603 /// `V` and a substitution `S`. This substitution `S` maps from
604 /// the bound values in `C` to their instantiated values in `V`
605 /// (in other words, `S(C) = V`).
606 pub fn enter_with_canonical<T, R>(
609 canonical: &Canonical<'tcx, T>,
610 f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>, T, CanonicalVarValues<'tcx>) -> R,
613 T: TypeFoldable<'tcx>,
617 infcx.instantiate_canonical_with_fresh_inference_vars(span, canonical);
618 f(infcx, value, subst)
622 pub fn enter<R>(&mut self, f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>) -> R) -> R {
623 let InferCtxtBuilder {
627 ref fresh_typeck_results,
628 ref normalize_fn_sig_for_diagnostic,
630 let in_progress_typeck_results = fresh_typeck_results.as_ref();
635 in_progress_typeck_results,
636 inner: RefCell::new(InferCtxtInner::new()),
637 lexical_region_resolutions: RefCell::new(None),
638 selection_cache: Default::default(),
639 evaluation_cache: Default::default(),
640 reported_trait_errors: Default::default(),
641 reported_closure_mismatch: Default::default(),
642 tainted_by_errors: Cell::new(None),
643 err_count_on_creation: tcx.sess.err_count(),
644 in_snapshot: Cell::new(false),
645 skip_leak_check: Cell::new(false),
646 universe: Cell::new(ty::UniverseIndex::ROOT),
647 normalize_fn_sig_for_diagnostic: normalize_fn_sig_for_diagnostic
654 impl<'tcx, T> InferOk<'tcx, T> {
655 pub fn unit(self) -> InferOk<'tcx, ()> {
656 InferOk { value: (), obligations: self.obligations }
659 /// Extracts `value`, registering any obligations into `fulfill_cx`.
660 pub fn into_value_registering_obligations(
662 infcx: &InferCtxt<'_, 'tcx>,
663 fulfill_cx: &mut dyn TraitEngine<'tcx>,
665 let InferOk { value, obligations } = self;
666 fulfill_cx.register_predicate_obligations(infcx, obligations);
671 impl<'tcx> InferOk<'tcx, ()> {
672 pub fn into_obligations(self) -> PredicateObligations<'tcx> {
677 #[must_use = "once you start a snapshot, you should always consume it"]
678 pub struct CombinedSnapshot<'a, 'tcx> {
679 undo_snapshot: Snapshot<'tcx>,
680 region_constraints_snapshot: RegionSnapshot,
681 universe: ty::UniverseIndex,
682 was_in_snapshot: bool,
683 _in_progress_typeck_results: Option<Ref<'a, ty::TypeckResults<'tcx>>>,
686 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
687 /// calls `tcx.try_unify_abstract_consts` after
688 /// canonicalizing the consts.
689 #[instrument(skip(self), level = "debug")]
690 pub fn try_unify_abstract_consts(
692 a: ty::Unevaluated<'tcx, ()>,
693 b: ty::Unevaluated<'tcx, ()>,
694 param_env: ty::ParamEnv<'tcx>,
696 // Reject any attempt to unify two unevaluated constants that contain inference
697 // variables, since inference variables in queries lead to ICEs.
698 if a.substs.has_infer_types_or_consts()
699 || b.substs.has_infer_types_or_consts()
700 || param_env.has_infer_types_or_consts()
702 debug!("a or b or param_env contain infer vars in its substs -> cannot unify");
706 let param_env_and = param_env.and((a, b));
707 let erased = self.tcx.erase_regions(param_env_and);
708 debug!("after erase_regions: {:?}", erased);
710 self.tcx.try_unify_abstract_consts(erased)
713 pub fn is_in_snapshot(&self) -> bool {
714 self.in_snapshot.get()
717 pub fn freshen<T: TypeFoldable<'tcx>>(&self, t: T) -> T {
718 t.fold_with(&mut self.freshener())
721 /// Returns the origin of the type variable identified by `vid`, or `None`
722 /// if this is not a type variable.
724 /// No attempt is made to resolve `ty`.
725 pub fn type_var_origin(&'a self, ty: Ty<'tcx>) -> Option<TypeVariableOrigin> {
727 ty::Infer(ty::TyVar(vid)) => {
728 Some(*self.inner.borrow_mut().type_variables().var_origin(vid))
734 pub fn freshener<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
735 freshen::TypeFreshener::new(self, false)
738 /// Like `freshener`, but does not replace `'static` regions.
739 pub fn freshener_keep_static<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
740 freshen::TypeFreshener::new(self, true)
743 pub fn unsolved_variables(&self) -> Vec<Ty<'tcx>> {
744 let mut inner = self.inner.borrow_mut();
745 let mut vars: Vec<Ty<'_>> = inner
747 .unsolved_variables()
749 .map(|t| self.tcx.mk_ty_var(t))
752 (0..inner.int_unification_table().len())
753 .map(|i| ty::IntVid { index: i as u32 })
754 .filter(|&vid| inner.int_unification_table().probe_value(vid).is_none())
755 .map(|v| self.tcx.mk_int_var(v)),
758 (0..inner.float_unification_table().len())
759 .map(|i| ty::FloatVid { index: i as u32 })
760 .filter(|&vid| inner.float_unification_table().probe_value(vid).is_none())
761 .map(|v| self.tcx.mk_float_var(v)),
768 trace: TypeTrace<'tcx>,
769 param_env: ty::ParamEnv<'tcx>,
770 define_opaque_types: bool,
771 ) -> CombineFields<'a, 'tcx> {
777 obligations: PredicateObligations::new(),
782 /// Clear the "currently in a snapshot" flag, invoke the closure,
783 /// then restore the flag to its original value. This flag is a
784 /// debugging measure designed to detect cases where we start a
785 /// snapshot, create type variables, and register obligations
786 /// which may involve those type variables in the fulfillment cx,
787 /// potentially leaving "dangling type variables" behind.
788 /// In such cases, an assertion will fail when attempting to
789 /// register obligations, within a snapshot. Very useful, much
790 /// better than grovelling through megabytes of `RUSTC_LOG` output.
792 /// HOWEVER, in some cases the flag is unhelpful. In particular, we
793 /// sometimes create a "mini-fulfilment-cx" in which we enroll
794 /// obligations. As long as this fulfillment cx is fully drained
795 /// before we return, this is not a problem, as there won't be any
796 /// escaping obligations in the main cx. In those cases, you can
797 /// use this function.
798 pub fn save_and_restore_in_snapshot_flag<F, R>(&self, func: F) -> R
800 F: FnOnce(&Self) -> R,
802 let flag = self.in_snapshot.replace(false);
803 let result = func(self);
804 self.in_snapshot.set(flag);
808 fn start_snapshot(&self) -> CombinedSnapshot<'a, 'tcx> {
809 debug!("start_snapshot()");
811 let in_snapshot = self.in_snapshot.replace(true);
813 let mut inner = self.inner.borrow_mut();
816 undo_snapshot: inner.undo_log.start_snapshot(),
817 region_constraints_snapshot: inner.unwrap_region_constraints().start_snapshot(),
818 universe: self.universe(),
819 was_in_snapshot: in_snapshot,
820 // Borrow typeck results "in progress" (i.e., during typeck)
821 // to ban writes from within a snapshot to them.
822 _in_progress_typeck_results: self
823 .in_progress_typeck_results
824 .map(|typeck_results| typeck_results.borrow()),
828 #[instrument(skip(self, snapshot), level = "debug")]
829 fn rollback_to(&self, cause: &str, snapshot: CombinedSnapshot<'a, 'tcx>) {
830 let CombinedSnapshot {
832 region_constraints_snapshot,
835 _in_progress_typeck_results,
838 self.in_snapshot.set(was_in_snapshot);
839 self.universe.set(universe);
841 let mut inner = self.inner.borrow_mut();
842 inner.rollback_to(undo_snapshot);
843 inner.unwrap_region_constraints().rollback_to(region_constraints_snapshot);
846 #[instrument(skip(self, snapshot), level = "debug")]
847 fn commit_from(&self, snapshot: CombinedSnapshot<'a, 'tcx>) {
848 let CombinedSnapshot {
850 region_constraints_snapshot: _,
853 _in_progress_typeck_results,
856 self.in_snapshot.set(was_in_snapshot);
858 self.inner.borrow_mut().commit(undo_snapshot);
861 /// Execute `f` and commit the bindings if closure `f` returns `Ok(_)`.
862 #[instrument(skip(self, f), level = "debug")]
863 pub fn commit_if_ok<T, E, F>(&self, f: F) -> Result<T, E>
865 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> Result<T, E>,
867 let snapshot = self.start_snapshot();
868 let r = f(&snapshot);
869 debug!("commit_if_ok() -- r.is_ok() = {}", r.is_ok());
872 self.commit_from(snapshot);
875 self.rollback_to("commit_if_ok -- error", snapshot);
881 /// Execute `f` then unroll any bindings it creates.
882 #[instrument(skip(self, f), level = "debug")]
883 pub fn probe<R, F>(&self, f: F) -> R
885 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
887 let snapshot = self.start_snapshot();
888 let r = f(&snapshot);
889 self.rollback_to("probe", snapshot);
893 /// If `should_skip` is true, then execute `f` then unroll any bindings it creates.
894 #[instrument(skip(self, f), level = "debug")]
895 pub fn probe_maybe_skip_leak_check<R, F>(&self, should_skip: bool, f: F) -> R
897 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
899 let snapshot = self.start_snapshot();
900 let was_skip_leak_check = self.skip_leak_check.get();
902 self.skip_leak_check.set(true);
904 let r = f(&snapshot);
905 self.rollback_to("probe", snapshot);
906 self.skip_leak_check.set(was_skip_leak_check);
910 /// Scan the constraints produced since `snapshot` began and returns:
912 /// - `None` -- if none of them involve "region outlives" constraints
913 /// - `Some(true)` -- if there are `'a: 'b` constraints where `'a` or `'b` is a placeholder
914 /// - `Some(false)` -- if there are `'a: 'b` constraints but none involve placeholders
915 pub fn region_constraints_added_in_snapshot(
917 snapshot: &CombinedSnapshot<'a, 'tcx>,
921 .unwrap_region_constraints()
922 .region_constraints_added_in_snapshot(&snapshot.undo_snapshot)
925 pub fn opaque_types_added_in_snapshot(&self, snapshot: &CombinedSnapshot<'a, 'tcx>) -> bool {
926 self.inner.borrow().undo_log.opaque_types_in_snapshot(&snapshot.undo_snapshot)
929 pub fn add_given(&self, sub: ty::Region<'tcx>, sup: ty::RegionVid) {
930 self.inner.borrow_mut().unwrap_region_constraints().add_given(sub, sup);
933 pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
935 T: at::ToTrace<'tcx>,
937 let origin = &ObligationCause::dummy();
939 self.at(origin, param_env).sub(a, b).map(|InferOk { obligations: _, .. }| {
940 // Ignore obligations, since we are unrolling
941 // everything anyway.
946 pub fn can_eq<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
948 T: at::ToTrace<'tcx>,
950 let origin = &ObligationCause::dummy();
952 self.at(origin, param_env).eq(a, b).map(|InferOk { obligations: _, .. }| {
953 // Ignore obligations, since we are unrolling
954 // everything anyway.
959 #[instrument(skip(self), level = "debug")]
962 origin: SubregionOrigin<'tcx>,
966 self.inner.borrow_mut().unwrap_region_constraints().make_subregion(origin, a, b);
969 /// Require that the region `r` be equal to one of the regions in
970 /// the set `regions`.
971 #[instrument(skip(self), level = "debug")]
972 pub fn member_constraint(
974 key: ty::OpaqueTypeKey<'tcx>,
975 definition_span: Span,
977 region: ty::Region<'tcx>,
978 in_regions: &Lrc<Vec<ty::Region<'tcx>>>,
980 self.inner.borrow_mut().unwrap_region_constraints().member_constraint(
989 /// Processes a `Coerce` predicate from the fulfillment context.
990 /// This is NOT the preferred way to handle coercion, which is to
991 /// invoke `FnCtxt::coerce` or a similar method (see `coercion.rs`).
993 /// This method here is actually a fallback that winds up being
994 /// invoked when `FnCtxt::coerce` encounters unresolved type variables
995 /// and records a coercion predicate. Presently, this method is equivalent
996 /// to `subtype_predicate` -- that is, "coercing" `a` to `b` winds up
997 /// actually requiring `a <: b`. This is of course a valid coercion,
998 /// but it's not as flexible as `FnCtxt::coerce` would be.
1000 /// (We may refactor this in the future, but there are a number of
1001 /// practical obstacles. Among other things, `FnCtxt::coerce` presently
1002 /// records adjustments that are required on the HIR in order to perform
1003 /// the coercion, and we don't currently have a way to manage that.)
1004 pub fn coerce_predicate(
1006 cause: &ObligationCause<'tcx>,
1007 param_env: ty::ParamEnv<'tcx>,
1008 predicate: ty::PolyCoercePredicate<'tcx>,
1009 ) -> Option<InferResult<'tcx, ()>> {
1010 let subtype_predicate = predicate.map_bound(|p| ty::SubtypePredicate {
1011 a_is_expected: false, // when coercing from `a` to `b`, `b` is expected
1015 self.subtype_predicate(cause, param_env, subtype_predicate)
1018 pub fn subtype_predicate(
1020 cause: &ObligationCause<'tcx>,
1021 param_env: ty::ParamEnv<'tcx>,
1022 predicate: ty::PolySubtypePredicate<'tcx>,
1023 ) -> Option<InferResult<'tcx, ()>> {
1024 // Check for two unresolved inference variables, in which case we can
1025 // make no progress. This is partly a micro-optimization, but it's
1026 // also an opportunity to "sub-unify" the variables. This isn't
1027 // *necessary* to prevent cycles, because they would eventually be sub-unified
1028 // anyhow during generalization, but it helps with diagnostics (we can detect
1029 // earlier that they are sub-unified).
1031 // Note that we can just skip the binders here because
1032 // type variables can't (at present, at
1033 // least) capture any of the things bound by this binder.
1035 // Note that this sub here is not just for diagnostics - it has semantic
1037 let r_a = self.shallow_resolve(predicate.skip_binder().a);
1038 let r_b = self.shallow_resolve(predicate.skip_binder().b);
1039 match (r_a.kind(), r_b.kind()) {
1040 (&ty::Infer(ty::TyVar(a_vid)), &ty::Infer(ty::TyVar(b_vid))) => {
1041 self.inner.borrow_mut().type_variables().sub(a_vid, b_vid);
1047 Some(self.commit_if_ok(|_snapshot| {
1048 let ty::SubtypePredicate { a_is_expected, a, b } =
1049 self.replace_bound_vars_with_placeholders(predicate);
1051 let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?;
1057 pub fn region_outlives_predicate(
1059 cause: &traits::ObligationCause<'tcx>,
1060 predicate: ty::PolyRegionOutlivesPredicate<'tcx>,
1062 let ty::OutlivesPredicate(r_a, r_b) = self.replace_bound_vars_with_placeholders(predicate);
1064 SubregionOrigin::from_obligation_cause(cause, || RelateRegionParamBound(cause.span));
1065 self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
1068 /// Number of type variables created so far.
1069 pub fn num_ty_vars(&self) -> usize {
1070 self.inner.borrow_mut().type_variables().num_vars()
1073 pub fn next_ty_var_id(&self, origin: TypeVariableOrigin) -> TyVid {
1074 self.inner.borrow_mut().type_variables().new_var(self.universe(), origin)
1077 pub fn next_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
1078 self.tcx.mk_ty_var(self.next_ty_var_id(origin))
1081 pub fn next_ty_var_id_in_universe(
1083 origin: TypeVariableOrigin,
1084 universe: ty::UniverseIndex,
1086 self.inner.borrow_mut().type_variables().new_var(universe, origin)
1089 pub fn next_ty_var_in_universe(
1091 origin: TypeVariableOrigin,
1092 universe: ty::UniverseIndex,
1094 let vid = self.next_ty_var_id_in_universe(origin, universe);
1095 self.tcx.mk_ty_var(vid)
1098 pub fn next_const_var(&self, ty: Ty<'tcx>, origin: ConstVariableOrigin) -> ty::Const<'tcx> {
1099 self.tcx.mk_const_var(self.next_const_var_id(origin), ty)
1102 pub fn next_const_var_in_universe(
1105 origin: ConstVariableOrigin,
1106 universe: ty::UniverseIndex,
1107 ) -> ty::Const<'tcx> {
1111 .const_unification_table()
1112 .new_key(ConstVarValue { origin, val: ConstVariableValue::Unknown { universe } });
1113 self.tcx.mk_const_var(vid, ty)
1116 pub fn next_const_var_id(&self, origin: ConstVariableOrigin) -> ConstVid<'tcx> {
1117 self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue {
1119 val: ConstVariableValue::Unknown { universe: self.universe() },
1123 fn next_int_var_id(&self) -> IntVid {
1124 self.inner.borrow_mut().int_unification_table().new_key(None)
1127 pub fn next_int_var(&self) -> Ty<'tcx> {
1128 self.tcx.mk_int_var(self.next_int_var_id())
1131 fn next_float_var_id(&self) -> FloatVid {
1132 self.inner.borrow_mut().float_unification_table().new_key(None)
1135 pub fn next_float_var(&self) -> Ty<'tcx> {
1136 self.tcx.mk_float_var(self.next_float_var_id())
1139 /// Creates a fresh region variable with the next available index.
1140 /// The variable will be created in the maximum universe created
1141 /// thus far, allowing it to name any region created thus far.
1142 pub fn next_region_var(&self, origin: RegionVariableOrigin) -> ty::Region<'tcx> {
1143 self.next_region_var_in_universe(origin, self.universe())
1146 /// Creates a fresh region variable with the next available index
1147 /// in the given universe; typically, you can use
1148 /// `next_region_var` and just use the maximal universe.
1149 pub fn next_region_var_in_universe(
1151 origin: RegionVariableOrigin,
1152 universe: ty::UniverseIndex,
1153 ) -> ty::Region<'tcx> {
1155 self.inner.borrow_mut().unwrap_region_constraints().new_region_var(universe, origin);
1156 self.tcx.mk_region(ty::ReVar(region_var))
1159 /// Return the universe that the region `r` was created in. For
1160 /// most regions (e.g., `'static`, named regions from the user,
1161 /// etc) this is the root universe U0. For inference variables or
1162 /// placeholders, however, it will return the universe which which
1163 /// they are associated.
1164 pub fn universe_of_region(&self, r: ty::Region<'tcx>) -> ty::UniverseIndex {
1165 self.inner.borrow_mut().unwrap_region_constraints().universe(r)
1168 /// Number of region variables created so far.
1169 pub fn num_region_vars(&self) -> usize {
1170 self.inner.borrow_mut().unwrap_region_constraints().num_region_vars()
1173 /// Just a convenient wrapper of `next_region_var` for using during NLL.
1174 pub fn next_nll_region_var(&self, origin: NllRegionVariableOrigin) -> ty::Region<'tcx> {
1175 self.next_region_var(RegionVariableOrigin::Nll(origin))
1178 /// Just a convenient wrapper of `next_region_var` for using during NLL.
1179 pub fn next_nll_region_var_in_universe(
1181 origin: NllRegionVariableOrigin,
1182 universe: ty::UniverseIndex,
1183 ) -> ty::Region<'tcx> {
1184 self.next_region_var_in_universe(RegionVariableOrigin::Nll(origin), universe)
1187 pub fn var_for_def(&self, span: Span, param: &ty::GenericParamDef) -> GenericArg<'tcx> {
1189 GenericParamDefKind::Lifetime => {
1190 // Create a region inference variable for the given
1191 // region parameter definition.
1192 self.next_region_var(EarlyBoundRegion(span, param.name)).into()
1194 GenericParamDefKind::Type { .. } => {
1195 // Create a type inference variable for the given
1196 // type parameter definition. The substitutions are
1197 // for actual parameters that may be referred to by
1198 // the default of this type parameter, if it exists.
1199 // e.g., `struct Foo<A, B, C = (A, B)>(...);` when
1200 // used in a path such as `Foo::<T, U>::new()` will
1201 // use an inference variable for `C` with `[T, U]`
1202 // as the substitutions for the default, `(T, U)`.
1203 let ty_var_id = self.inner.borrow_mut().type_variables().new_var(
1205 TypeVariableOrigin {
1206 kind: TypeVariableOriginKind::TypeParameterDefinition(
1214 self.tcx.mk_ty_var(ty_var_id).into()
1216 GenericParamDefKind::Const { .. } => {
1217 let origin = ConstVariableOrigin {
1218 kind: ConstVariableOriginKind::ConstParameterDefinition(
1225 self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue {
1227 val: ConstVariableValue::Unknown { universe: self.universe() },
1229 self.tcx.mk_const_var(const_var_id, self.tcx.type_of(param.def_id)).into()
1234 /// Given a set of generics defined on a type or impl, returns a substitution mapping each
1235 /// type/region parameter to a fresh inference variable.
1236 pub fn fresh_substs_for_item(&self, span: Span, def_id: DefId) -> SubstsRef<'tcx> {
1237 InternalSubsts::for_item(self.tcx, def_id, |param, _| self.var_for_def(span, param))
1240 /// Returns `true` if errors have been reported since this infcx was
1241 /// created. This is sometimes used as a heuristic to skip
1242 /// reporting errors that often occur as a result of earlier
1243 /// errors, but where it's hard to be 100% sure (e.g., unresolved
1244 /// inference variables, regionck errors).
1245 pub fn is_tainted_by_errors(&self) -> bool {
1247 "is_tainted_by_errors(err_count={}, err_count_on_creation={}, \
1248 tainted_by_errors={})",
1249 self.tcx.sess.err_count(),
1250 self.err_count_on_creation,
1251 self.tainted_by_errors.get().is_some()
1254 if self.tcx.sess.err_count() > self.err_count_on_creation {
1255 return true; // errors reported since this infcx was made
1257 self.tainted_by_errors.get().is_some()
1260 /// Set the "tainted by errors" flag to true. We call this when we
1261 /// observe an error from a prior pass.
1262 pub fn set_tainted_by_errors(&self) {
1263 debug!("set_tainted_by_errors()");
1264 self.tainted_by_errors.set(Some(
1265 self.tcx.sess.delay_span_bug(DUMMY_SP, "`InferCtxt` incorrectly tainted by errors"),
1269 pub fn skip_region_resolution(&self) {
1270 let (var_infos, _) = {
1271 let mut inner = self.inner.borrow_mut();
1272 let inner = &mut *inner;
1273 // Note: `inner.region_obligations` may not be empty, because we
1274 // didn't necessarily call `process_registered_region_obligations`.
1275 // This is okay, because that doesn't introduce new vars.
1277 .region_constraint_storage
1279 .expect("regions already resolved")
1280 .with_log(&mut inner.undo_log)
1281 .into_infos_and_data()
1284 let lexical_region_resolutions = LexicalRegionResolutions {
1285 values: rustc_index::vec::IndexVec::from_elem_n(
1286 crate::infer::lexical_region_resolve::VarValue::Value(self.tcx.lifetimes.re_erased),
1291 let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions));
1292 assert!(old_value.is_none());
1295 /// Process the region constraints and return any any errors that
1296 /// result. After this, no more unification operations should be
1297 /// done -- or the compiler will panic -- but it is legal to use
1298 /// `resolve_vars_if_possible` as well as `fully_resolve`.
1299 pub fn resolve_regions(
1301 outlives_env: &OutlivesEnvironment<'tcx>,
1302 ) -> Vec<RegionResolutionError<'tcx>> {
1303 let (var_infos, data) = {
1304 let mut inner = self.inner.borrow_mut();
1305 let inner = &mut *inner;
1307 self.is_tainted_by_errors() || inner.region_obligations.is_empty(),
1308 "region_obligations not empty: {:#?}",
1309 inner.region_obligations
1312 .region_constraint_storage
1314 .expect("regions already resolved")
1315 .with_log(&mut inner.undo_log)
1316 .into_infos_and_data()
1319 let region_rels = &RegionRelations::new(self.tcx, outlives_env.free_region_map());
1321 let (lexical_region_resolutions, errors) =
1322 lexical_region_resolve::resolve(outlives_env.param_env, region_rels, var_infos, data);
1324 let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions));
1325 assert!(old_value.is_none());
1330 /// Process the region constraints and report any errors that
1331 /// result. After this, no more unification operations should be
1332 /// done -- or the compiler will panic -- but it is legal to use
1333 /// `resolve_vars_if_possible` as well as `fully_resolve`.
1335 /// Make sure to call [`InferCtxt::process_registered_region_obligations`]
1336 /// first, or preferably use [`InferCtxt::check_region_obligations_and_report_errors`]
1337 /// to do both of these operations together.
1338 pub fn resolve_regions_and_report_errors(
1340 generic_param_scope: LocalDefId,
1341 outlives_env: &OutlivesEnvironment<'tcx>,
1343 let errors = self.resolve_regions(outlives_env);
1345 if !self.is_tainted_by_errors() {
1346 // As a heuristic, just skip reporting region errors
1347 // altogether if other errors have been reported while
1348 // this infcx was in use. This is totally hokey but
1349 // otherwise we have a hard time separating legit region
1350 // errors from silly ones.
1351 self.report_region_errors(generic_param_scope, &errors);
1355 /// Obtains (and clears) the current set of region
1356 /// constraints. The inference context is still usable: further
1357 /// unifications will simply add new constraints.
1359 /// This method is not meant to be used with normal lexical region
1360 /// resolution. Rather, it is used in the NLL mode as a kind of
1361 /// interim hack: basically we run normal type-check and generate
1362 /// region constraints as normal, but then we take them and
1363 /// translate them into the form that the NLL solver
1364 /// understands. See the NLL module for mode details.
1365 pub fn take_and_reset_region_constraints(&self) -> RegionConstraintData<'tcx> {
1367 self.inner.borrow().region_obligations.is_empty(),
1368 "region_obligations not empty: {:#?}",
1369 self.inner.borrow().region_obligations
1372 self.inner.borrow_mut().unwrap_region_constraints().take_and_reset_data()
1375 /// Gives temporary access to the region constraint data.
1376 pub fn with_region_constraints<R>(
1378 op: impl FnOnce(&RegionConstraintData<'tcx>) -> R,
1380 let mut inner = self.inner.borrow_mut();
1381 op(inner.unwrap_region_constraints().data())
1384 pub fn region_var_origin(&self, vid: ty::RegionVid) -> RegionVariableOrigin {
1385 let mut inner = self.inner.borrow_mut();
1386 let inner = &mut *inner;
1388 .region_constraint_storage
1390 .expect("regions already resolved")
1391 .with_log(&mut inner.undo_log)
1395 /// Takes ownership of the list of variable regions. This implies
1396 /// that all the region constraints have already been taken, and
1397 /// hence that `resolve_regions_and_report_errors` can never be
1398 /// called. This is used only during NLL processing to "hand off" ownership
1399 /// of the set of region variables into the NLL region context.
1400 pub fn take_region_var_origins(&self) -> VarInfos {
1401 let mut inner = self.inner.borrow_mut();
1402 let (var_infos, data) = inner
1403 .region_constraint_storage
1405 .expect("regions already resolved")
1406 .with_log(&mut inner.undo_log)
1407 .into_infos_and_data();
1408 assert!(data.is_empty());
1412 pub fn ty_to_string(&self, t: Ty<'tcx>) -> String {
1413 self.resolve_vars_if_possible(t).to_string()
1416 /// If `TyVar(vid)` resolves to a type, return that type. Else, return the
1417 /// universe index of `TyVar(vid)`.
1418 pub fn probe_ty_var(&self, vid: TyVid) -> Result<Ty<'tcx>, ty::UniverseIndex> {
1419 use self::type_variable::TypeVariableValue;
1421 match self.inner.borrow_mut().type_variables().probe(vid) {
1422 TypeVariableValue::Known { value } => Ok(value),
1423 TypeVariableValue::Unknown { universe } => Err(universe),
1427 /// Resolve any type variables found in `value` -- but only one
1428 /// level. So, if the variable `?X` is bound to some type
1429 /// `Foo<?Y>`, then this would return `Foo<?Y>` (but `?Y` may
1430 /// itself be bound to a type).
1432 /// Useful when you only need to inspect the outermost level of
1433 /// the type and don't care about nested types (or perhaps you
1434 /// will be resolving them as well, e.g. in a loop).
1435 pub fn shallow_resolve<T>(&self, value: T) -> T
1437 T: TypeFoldable<'tcx>,
1439 value.fold_with(&mut ShallowResolver { infcx: self })
1442 pub fn root_var(&self, var: ty::TyVid) -> ty::TyVid {
1443 self.inner.borrow_mut().type_variables().root_var(var)
1446 /// Where possible, replaces type/const variables in
1447 /// `value` with their final value. Note that region variables
1448 /// are unaffected. If a type/const variable has not been unified, it
1449 /// is left as is. This is an idempotent operation that does
1450 /// not affect inference state in any way and so you can do it
1452 pub fn resolve_vars_if_possible<T>(&self, value: T) -> T
1454 T: TypeFoldable<'tcx>,
1456 if !value.needs_infer() {
1457 return value; // Avoid duplicated subst-folding.
1459 let mut r = resolve::OpportunisticVarResolver::new(self);
1460 value.fold_with(&mut r)
1463 pub fn resolve_numeric_literals_with_default<T>(&self, value: T) -> T
1465 T: TypeFoldable<'tcx>,
1467 if !value.needs_infer() {
1468 return value; // Avoid duplicated subst-folding.
1470 let mut r = InferenceLiteralEraser { tcx: self.tcx };
1471 value.fold_with(&mut r)
1474 /// Returns the first unresolved variable contained in `T`. In the
1475 /// process of visiting `T`, this will resolve (where possible)
1476 /// type variables in `T`, but it never constructs the final,
1477 /// resolved type, so it's more efficient than
1478 /// `resolve_vars_if_possible()`.
1479 pub fn unresolved_type_vars<T>(&self, value: &T) -> Option<(Ty<'tcx>, Option<Span>)>
1481 T: TypeVisitable<'tcx>,
1483 value.visit_with(&mut resolve::UnresolvedTypeFinder::new(self)).break_value()
1486 pub fn probe_const_var(
1488 vid: ty::ConstVid<'tcx>,
1489 ) -> Result<ty::Const<'tcx>, ty::UniverseIndex> {
1490 match self.inner.borrow_mut().const_unification_table().probe_value(vid).val {
1491 ConstVariableValue::Known { value } => Ok(value),
1492 ConstVariableValue::Unknown { universe } => Err(universe),
1496 pub fn fully_resolve<T: TypeFoldable<'tcx>>(&self, value: T) -> FixupResult<'tcx, T> {
1498 * Attempts to resolve all type/region/const variables in
1499 * `value`. Region inference must have been run already (e.g.,
1500 * by calling `resolve_regions_and_report_errors`). If some
1501 * variable was never unified, an `Err` results.
1503 * This method is idempotent, but it not typically not invoked
1504 * except during the writeback phase.
1507 resolve::fully_resolve(self, value)
1510 // [Note-Type-error-reporting]
1511 // An invariant is that anytime the expected or actual type is Error (the special
1512 // error type, meaning that an error occurred when typechecking this expression),
1513 // this is a derived error. The error cascaded from another error (that was already
1514 // reported), so it's not useful to display it to the user.
1515 // The following methods implement this logic.
1516 // They check if either the actual or expected type is Error, and don't print the error
1517 // in this case. The typechecker should only ever report type errors involving mismatched
1518 // types using one of these methods, and should not call span_err directly for such
1521 pub fn type_error_struct_with_diag<M>(
1525 actual_ty: Ty<'tcx>,
1526 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>
1528 M: FnOnce(String) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>,
1530 let actual_ty = self.resolve_vars_if_possible(actual_ty);
1531 debug!("type_error_struct_with_diag({:?}, {:?})", sp, actual_ty);
1533 let mut err = mk_diag(self.ty_to_string(actual_ty));
1535 // Don't report an error if actual type is `Error`.
1536 if actual_ty.references_error() {
1537 err.downgrade_to_delayed_bug();
1543 pub fn report_mismatched_types(
1545 cause: &ObligationCause<'tcx>,
1548 err: TypeError<'tcx>,
1549 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1550 self.report_and_explain_type_error(TypeTrace::types(cause, true, expected, actual), err)
1553 pub fn report_mismatched_consts(
1555 cause: &ObligationCause<'tcx>,
1556 expected: ty::Const<'tcx>,
1557 actual: ty::Const<'tcx>,
1558 err: TypeError<'tcx>,
1559 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1560 self.report_and_explain_type_error(TypeTrace::consts(cause, true, expected, actual), err)
1563 pub fn replace_bound_vars_with_fresh_vars<T>(
1566 lbrct: LateBoundRegionConversionTime,
1567 value: ty::Binder<'tcx, T>,
1570 T: TypeFoldable<'tcx> + Copy,
1572 if let Some(inner) = value.no_bound_vars() {
1576 struct ToFreshVars<'a, 'tcx> {
1577 infcx: &'a InferCtxt<'a, 'tcx>,
1579 lbrct: LateBoundRegionConversionTime,
1580 map: FxHashMap<ty::BoundVar, ty::GenericArg<'tcx>>,
1583 impl<'tcx> BoundVarReplacerDelegate<'tcx> for ToFreshVars<'_, 'tcx> {
1584 fn replace_region(&mut self, br: ty::BoundRegion) -> ty::Region<'tcx> {
1587 .or_insert_with(|| {
1589 .next_region_var(LateBoundRegion(self.span, br.kind, self.lbrct))
1594 fn replace_ty(&mut self, bt: ty::BoundTy) -> Ty<'tcx> {
1597 .or_insert_with(|| {
1599 .next_ty_var(TypeVariableOrigin {
1600 kind: TypeVariableOriginKind::MiscVariable,
1607 fn replace_const(&mut self, bv: ty::BoundVar, ty: Ty<'tcx>) -> ty::Const<'tcx> {
1610 .or_insert_with(|| {
1614 ConstVariableOrigin {
1615 kind: ConstVariableOriginKind::MiscVariable,
1624 let delegate = ToFreshVars { infcx: self, span, lbrct, map: Default::default() };
1625 self.tcx.replace_bound_vars_uncached(value, delegate)
1628 /// See the [`region_constraints::RegionConstraintCollector::verify_generic_bound`] method.
1629 pub fn verify_generic_bound(
1631 origin: SubregionOrigin<'tcx>,
1632 kind: GenericKind<'tcx>,
1633 a: ty::Region<'tcx>,
1634 bound: VerifyBound<'tcx>,
1636 debug!("verify_generic_bound({:?}, {:?} <: {:?})", kind, a, bound);
1640 .unwrap_region_constraints()
1641 .verify_generic_bound(origin, kind, a, bound);
1644 /// Obtains the latest type of the given closure; this may be a
1645 /// closure in the current function, in which case its
1646 /// `ClosureKind` may not yet be known.
1647 pub fn closure_kind(&self, closure_substs: SubstsRef<'tcx>) -> Option<ty::ClosureKind> {
1648 let closure_kind_ty = closure_substs.as_closure().kind_ty();
1649 let closure_kind_ty = self.shallow_resolve(closure_kind_ty);
1650 closure_kind_ty.to_opt_closure_kind()
1653 /// Clears the selection, evaluation, and projection caches. This is useful when
1654 /// repeatedly attempting to select an `Obligation` while changing only
1655 /// its `ParamEnv`, since `FulfillmentContext` doesn't use probing.
1656 pub fn clear_caches(&self) {
1657 self.selection_cache.clear();
1658 self.evaluation_cache.clear();
1659 self.inner.borrow_mut().projection_cache().clear();
1662 pub fn universe(&self) -> ty::UniverseIndex {
1666 /// Creates and return a fresh universe that extends all previous
1667 /// universes. Updates `self.universe` to that new universe.
1668 pub fn create_next_universe(&self) -> ty::UniverseIndex {
1669 let u = self.universe.get().next_universe();
1670 self.universe.set(u);
1674 pub fn try_const_eval_resolve(
1676 param_env: ty::ParamEnv<'tcx>,
1677 unevaluated: ty::Unevaluated<'tcx>,
1680 ) -> Result<ty::Const<'tcx>, ErrorHandled> {
1681 match self.const_eval_resolve(param_env, unevaluated, span) {
1682 Ok(Some(val)) => Ok(ty::Const::from_value(self.tcx, val, ty)),
1685 let def_id = unevaluated.def.did;
1687 tcx.def_span(def_id),
1688 "unable to construct a constant value for the unevaluated constant {:?}",
1692 Err(err) => Err(err),
1696 /// Resolves and evaluates a constant.
1698 /// The constant can be located on a trait like `<A as B>::C`, in which case the given
1699 /// substitutions and environment are used to resolve the constant. Alternatively if the
1700 /// constant has generic parameters in scope the substitutions are used to evaluate the value of
1701 /// the constant. For example in `fn foo<T>() { let _ = [0; bar::<T>()]; }` the repeat count
1702 /// constant `bar::<T>()` requires a substitution for `T`, if the substitution for `T` is still
1703 /// too generic for the constant to be evaluated then `Err(ErrorHandled::TooGeneric)` is
1706 /// This handles inferences variables within both `param_env` and `substs` by
1707 /// performing the operation on their respective canonical forms.
1708 #[instrument(skip(self), level = "debug")]
1709 pub fn const_eval_resolve(
1711 mut param_env: ty::ParamEnv<'tcx>,
1712 unevaluated: ty::Unevaluated<'tcx>,
1714 ) -> EvalToValTreeResult<'tcx> {
1715 let mut substs = self.resolve_vars_if_possible(unevaluated.substs);
1718 // Postpone the evaluation of constants whose substs depend on inference
1720 if substs.has_infer_types_or_consts() {
1721 let ac = AbstractConst::new(self.tcx, unevaluated.shrink());
1724 substs = InternalSubsts::identity_for_item(self.tcx, unevaluated.def.did);
1725 param_env = self.tcx.param_env(unevaluated.def.did);
1728 if ct.unify_failure_kind(self.tcx) == FailureKind::Concrete {
1729 substs = replace_param_and_infer_substs_with_placeholder(self.tcx, substs);
1731 return Err(ErrorHandled::TooGeneric);
1734 Err(guar) => return Err(ErrorHandled::Reported(guar)),
1738 let param_env_erased = self.tcx.erase_regions(param_env);
1739 let substs_erased = self.tcx.erase_regions(substs);
1740 debug!(?param_env_erased);
1741 debug!(?substs_erased);
1743 let unevaluated = ty::Unevaluated {
1744 def: unevaluated.def,
1745 substs: substs_erased,
1746 promoted: unevaluated.promoted,
1749 // The return value is the evaluated value which doesn't contain any reference to inference
1750 // variables, thus we don't need to substitute back the original values.
1751 self.tcx.const_eval_resolve_for_typeck(param_env_erased, unevaluated, span)
1754 /// `ty_or_const_infer_var_changed` is equivalent to one of these two:
1755 /// * `shallow_resolve(ty) != ty` (where `ty.kind = ty::Infer(_)`)
1756 /// * `shallow_resolve(ct) != ct` (where `ct.kind = ty::ConstKind::Infer(_)`)
1758 /// However, `ty_or_const_infer_var_changed` is more efficient. It's always
1759 /// inlined, despite being large, because it has only two call sites that
1760 /// are extremely hot (both in `traits::fulfill`'s checking of `stalled_on`
1761 /// inference variables), and it handles both `Ty` and `ty::Const` without
1762 /// having to resort to storing full `GenericArg`s in `stalled_on`.
1764 pub fn ty_or_const_infer_var_changed(&self, infer_var: TyOrConstInferVar<'tcx>) -> bool {
1766 TyOrConstInferVar::Ty(v) => {
1767 use self::type_variable::TypeVariableValue;
1769 // If `inlined_probe` returns a `Known` value, it never equals
1770 // `ty::Infer(ty::TyVar(v))`.
1771 match self.inner.borrow_mut().type_variables().inlined_probe(v) {
1772 TypeVariableValue::Unknown { .. } => false,
1773 TypeVariableValue::Known { .. } => true,
1777 TyOrConstInferVar::TyInt(v) => {
1778 // If `inlined_probe_value` returns a value it's always a
1779 // `ty::Int(_)` or `ty::UInt(_)`, which never matches a
1781 self.inner.borrow_mut().int_unification_table().inlined_probe_value(v).is_some()
1784 TyOrConstInferVar::TyFloat(v) => {
1785 // If `probe_value` returns a value it's always a
1786 // `ty::Float(_)`, which never matches a `ty::Infer(_)`.
1788 // Not `inlined_probe_value(v)` because this call site is colder.
1789 self.inner.borrow_mut().float_unification_table().probe_value(v).is_some()
1792 TyOrConstInferVar::Const(v) => {
1793 // If `probe_value` returns a `Known` value, it never equals
1794 // `ty::ConstKind::Infer(ty::InferConst::Var(v))`.
1796 // Not `inlined_probe_value(v)` because this call site is colder.
1797 match self.inner.borrow_mut().const_unification_table().probe_value(v).val {
1798 ConstVariableValue::Unknown { .. } => false,
1799 ConstVariableValue::Known { .. } => true,
1806 /// Helper for `ty_or_const_infer_var_changed` (see comment on that), currently
1807 /// used only for `traits::fulfill`'s list of `stalled_on` inference variables.
1808 #[derive(Copy, Clone, Debug)]
1809 pub enum TyOrConstInferVar<'tcx> {
1810 /// Equivalent to `ty::Infer(ty::TyVar(_))`.
1812 /// Equivalent to `ty::Infer(ty::IntVar(_))`.
1814 /// Equivalent to `ty::Infer(ty::FloatVar(_))`.
1817 /// Equivalent to `ty::ConstKind::Infer(ty::InferConst::Var(_))`.
1818 Const(ConstVid<'tcx>),
1821 impl<'tcx> TyOrConstInferVar<'tcx> {
1822 /// Tries to extract an inference variable from a type or a constant, returns `None`
1823 /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`) and
1824 /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1825 pub fn maybe_from_generic_arg(arg: GenericArg<'tcx>) -> Option<Self> {
1826 match arg.unpack() {
1827 GenericArgKind::Type(ty) => Self::maybe_from_ty(ty),
1828 GenericArgKind::Const(ct) => Self::maybe_from_const(ct),
1829 GenericArgKind::Lifetime(_) => None,
1833 /// Tries to extract an inference variable from a type, returns `None`
1834 /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`).
1835 pub fn maybe_from_ty(ty: Ty<'tcx>) -> Option<Self> {
1837 ty::Infer(ty::TyVar(v)) => Some(TyOrConstInferVar::Ty(v)),
1838 ty::Infer(ty::IntVar(v)) => Some(TyOrConstInferVar::TyInt(v)),
1839 ty::Infer(ty::FloatVar(v)) => Some(TyOrConstInferVar::TyFloat(v)),
1844 /// Tries to extract an inference variable from a constant, returns `None`
1845 /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1846 pub fn maybe_from_const(ct: ty::Const<'tcx>) -> Option<Self> {
1848 ty::ConstKind::Infer(InferConst::Var(v)) => Some(TyOrConstInferVar::Const(v)),
1854 /// Replace `{integer}` with `i32` and `{float}` with `f64`.
1855 /// Used only for diagnostics.
1856 struct InferenceLiteralEraser<'tcx> {
1860 impl<'tcx> TypeFolder<'tcx> for InferenceLiteralEraser<'tcx> {
1861 fn tcx(&self) -> TyCtxt<'tcx> {
1865 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1867 ty::Infer(ty::IntVar(_) | ty::FreshIntTy(_)) => self.tcx.types.i32,
1868 ty::Infer(ty::FloatVar(_) | ty::FreshFloatTy(_)) => self.tcx.types.f64,
1869 _ => ty.super_fold_with(self),
1874 struct ShallowResolver<'a, 'tcx> {
1875 infcx: &'a InferCtxt<'a, 'tcx>,
1878 impl<'a, 'tcx> TypeFolder<'tcx> for ShallowResolver<'a, 'tcx> {
1879 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1883 /// If `ty` is a type variable of some kind, resolve it one level
1884 /// (but do not resolve types found in the result). If `typ` is
1885 /// not a type variable, just return it unmodified.
1886 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1888 ty::Infer(ty::TyVar(v)) => {
1889 // Not entirely obvious: if `typ` is a type variable,
1890 // it can be resolved to an int/float variable, which
1891 // can then be recursively resolved, hence the
1892 // recursion. Note though that we prevent type
1893 // variables from unifying to other type variables
1894 // directly (though they may be embedded
1895 // structurally), and we prevent cycles in any case,
1896 // so this recursion should always be of very limited
1899 // Note: if these two lines are combined into one we get
1900 // dynamic borrow errors on `self.inner`.
1901 let known = self.infcx.inner.borrow_mut().type_variables().probe(v).known();
1902 known.map_or(ty, |t| self.fold_ty(t))
1905 ty::Infer(ty::IntVar(v)) => self
1909 .int_unification_table()
1911 .map_or(ty, |v| v.to_type(self.infcx.tcx)),
1913 ty::Infer(ty::FloatVar(v)) => self
1917 .float_unification_table()
1919 .map_or(ty, |v| v.to_type(self.infcx.tcx)),
1925 fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
1926 if let ty::ConstKind::Infer(InferConst::Var(vid)) = ct.kind() {
1930 .const_unification_table()
1941 impl<'tcx> TypeTrace<'tcx> {
1942 pub fn span(&self) -> Span {
1947 cause: &ObligationCause<'tcx>,
1948 a_is_expected: bool,
1951 ) -> TypeTrace<'tcx> {
1953 cause: cause.clone(),
1954 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
1958 pub fn poly_trait_refs(
1959 cause: &ObligationCause<'tcx>,
1960 a_is_expected: bool,
1961 a: ty::PolyTraitRef<'tcx>,
1962 b: ty::PolyTraitRef<'tcx>,
1963 ) -> TypeTrace<'tcx> {
1965 cause: cause.clone(),
1966 values: PolyTraitRefs(ExpectedFound::new(a_is_expected, a.into(), b.into())),
1971 cause: &ObligationCause<'tcx>,
1972 a_is_expected: bool,
1975 ) -> TypeTrace<'tcx> {
1977 cause: cause.clone(),
1978 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
1983 impl<'tcx> SubregionOrigin<'tcx> {
1984 pub fn span(&self) -> Span {
1986 Subtype(ref a) => a.span(),
1987 RelateObjectBound(a) => a,
1988 RelateParamBound(a, ..) => a,
1989 RelateRegionParamBound(a) => a,
1991 ReborrowUpvar(a, _) => a,
1992 DataBorrowed(_, a) => a,
1993 ReferenceOutlivesReferent(_, a) => a,
1994 CompareImplItemObligation { span, .. } => span,
1995 CheckAssociatedTypeBounds { ref parent, .. } => parent.span(),
1999 pub fn from_obligation_cause<F>(cause: &traits::ObligationCause<'tcx>, default: F) -> Self
2001 F: FnOnce() -> Self,
2003 match *cause.code() {
2004 traits::ObligationCauseCode::ReferenceOutlivesReferent(ref_type) => {
2005 SubregionOrigin::ReferenceOutlivesReferent(ref_type, cause.span)
2008 traits::ObligationCauseCode::CompareImplItemObligation {
2012 } => SubregionOrigin::CompareImplItemObligation {
2018 traits::ObligationCauseCode::CheckAssociatedTypeBounds {
2021 } => SubregionOrigin::CheckAssociatedTypeBounds {
2024 parent: Box::new(default()),
2032 impl RegionVariableOrigin {
2033 pub fn span(&self) -> Span {
2040 | EarlyBoundRegion(a, ..)
2041 | LateBoundRegion(a, ..)
2042 | UpvarRegion(_, a) => a,
2043 Nll(..) => bug!("NLL variable used with `span`"),
2048 /// Replaces substs that reference param or infer variables with suitable
2049 /// placeholders. This function is meant to remove these param and infer
2050 /// substs when they're not actually needed to evaluate a constant.
2051 fn replace_param_and_infer_substs_with_placeholder<'tcx>(
2053 substs: SubstsRef<'tcx>,
2054 ) -> SubstsRef<'tcx> {
2055 tcx.mk_substs(substs.iter().enumerate().map(|(idx, arg)| {
2056 match arg.unpack() {
2057 GenericArgKind::Type(_)
2058 if arg.has_param_types_or_consts() || arg.has_infer_types_or_consts() =>
2060 tcx.mk_ty(ty::Placeholder(ty::PlaceholderType {
2061 universe: ty::UniverseIndex::ROOT,
2062 name: ty::BoundVar::from_usize(idx),
2066 GenericArgKind::Const(ct)
2067 if ct.has_infer_types_or_consts() || ct.has_param_types_or_consts() =>
2070 // If the type references param or infer, replace that too...
2071 if ty.has_param_types_or_consts() || ty.has_infer_types_or_consts() {
2072 bug!("const `{ct}`'s type should not reference params or types");
2074 tcx.mk_const(ty::ConstS {
2076 kind: ty::ConstKind::Placeholder(ty::PlaceholderConst {
2077 universe: ty::UniverseIndex::ROOT,
2078 name: ty::BoundVar::from_usize(idx),