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};
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};
19 use rustc_hir::def_id::{DefId, LocalDefId};
20 use rustc_middle::infer::canonical::{Canonical, CanonicalVarValues};
21 use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue};
22 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind, ToType};
23 use rustc_middle::mir::interpret::{ErrorHandled, EvalToConstValueResult};
24 use rustc_middle::traits::select;
25 use rustc_middle::ty::error::{ExpectedFound, TypeError};
26 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
27 use rustc_middle::ty::relate::RelateResult;
28 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, SubstsRef};
29 pub use rustc_middle::ty::IntVarValue;
30 use rustc_middle::ty::{self, GenericParamDefKind, InferConst, Ty, TyCtxt};
31 use rustc_middle::ty::{ConstVid, FloatVid, IntVid, TyVid};
32 use rustc_session::config::BorrowckMode;
33 use rustc_span::symbol::Symbol;
36 use std::cell::{Cell, Ref, RefCell};
37 use std::collections::BTreeMap;
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 /// How we should handle region solving.
91 /// This is used so that the region values inferred by HIR region solving are
92 /// not exposed, and so that we can avoid doing work in HIR typeck that MIR
93 /// typeck will also do.
94 #[derive(Copy, Clone, Debug, Default)]
95 pub enum RegionckMode {
96 /// The default mode: report region errors, don't erase regions.
99 /// Erase the results of region after solving.
101 /// A flag that is used to suppress region errors, when we are doing
102 /// region checks that the NLL borrow checker will also do -- it might
104 suppress_errors: bool,
109 /// Indicates that the MIR borrowck will repeat these region
110 /// checks, so we should ignore errors if NLL is (unconditionally)
112 pub fn for_item_body(tcx: TyCtxt<'_>) -> Self {
113 // FIXME(Centril): Once we actually remove `::Migrate` also make
114 // this always `true` and then proceed to eliminate the dead code.
115 match tcx.borrowck_mode() {
116 // If we're on Migrate mode, report AST region errors
117 BorrowckMode::Migrate => RegionckMode::Erase { suppress_errors: false },
119 // If we're on MIR, don't report AST region errors as they should be reported by NLL
120 BorrowckMode::Mir => RegionckMode::Erase { suppress_errors: true },
125 /// This type contains all the things within `InferCtxt` that sit within a
126 /// `RefCell` and are involved with taking/rolling back snapshots. Snapshot
127 /// operations are hot enough that we want only one call to `borrow_mut` per
128 /// call to `start_snapshot` and `rollback_to`.
130 pub struct InferCtxtInner<'tcx> {
131 /// Cache for projections. This cache is snapshotted along with the infcx.
133 /// Public so that `traits::project` can use it.
134 pub projection_cache: traits::ProjectionCacheStorage<'tcx>,
136 /// We instantiate `UnificationTable` with `bounds<Ty>` because the types
137 /// that might instantiate a general type variable have an order,
138 /// represented by its upper and lower bounds.
139 type_variable_storage: type_variable::TypeVariableStorage<'tcx>,
141 /// Map from const parameter variable to the kind of const it represents.
142 const_unification_storage: ut::UnificationTableStorage<ty::ConstVid<'tcx>>,
144 /// Map from integral variable to the kind of integer it represents.
145 int_unification_storage: ut::UnificationTableStorage<ty::IntVid>,
147 /// Map from floating variable to the kind of float it represents.
148 float_unification_storage: ut::UnificationTableStorage<ty::FloatVid>,
150 /// Tracks the set of region variables and the constraints between them.
151 /// This is initially `Some(_)` but when
152 /// `resolve_regions_and_report_errors` is invoked, this gets set to `None`
153 /// -- further attempts to perform unification, etc., may fail if new
154 /// region constraints would've been added.
155 region_constraint_storage: Option<RegionConstraintStorage<'tcx>>,
157 /// A set of constraints that regionck must validate. Each
158 /// constraint has the form `T:'a`, meaning "some type `T` must
159 /// outlive the lifetime 'a". These constraints derive from
160 /// instantiated type parameters. So if you had a struct defined
163 /// struct Foo<T:'static> { ... }
165 /// then in some expression `let x = Foo { ... }` it will
166 /// instantiate the type parameter `T` with a fresh type `$0`. At
167 /// the same time, it will record a region obligation of
168 /// `$0:'static`. This will get checked later by regionck. (We
169 /// can't generally check these things right away because we have
170 /// to wait until types are resolved.)
172 /// These are stored in a map keyed to the id of the innermost
173 /// enclosing fn body / static initializer expression. This is
174 /// because the location where the obligation was incurred can be
175 /// relevant with respect to which sublifetime assumptions are in
176 /// place. The reason that we store under the fn-id, and not
177 /// something more fine-grained, is so that it is easier for
178 /// regionck to be sure that it has found *all* the region
179 /// obligations (otherwise, it's easy to fail to walk to a
180 /// particular node-id).
182 /// Before running `resolve_regions_and_report_errors`, the creator
183 /// of the inference context is expected to invoke
184 /// `process_region_obligations` (defined in `self::region_obligations`)
185 /// for each body-id in this map, which will process the
186 /// obligations within. This is expected to be done 'late enough'
187 /// that all type inference variables have been bound and so forth.
188 region_obligations: Vec<(hir::HirId, RegionObligation<'tcx>)>,
190 undo_log: InferCtxtUndoLogs<'tcx>,
192 /// Caches for opaque type inference.
193 pub opaque_type_storage: OpaqueTypeStorage<'tcx>,
196 impl<'tcx> InferCtxtInner<'tcx> {
197 fn new() -> InferCtxtInner<'tcx> {
199 projection_cache: Default::default(),
200 type_variable_storage: type_variable::TypeVariableStorage::new(),
201 undo_log: InferCtxtUndoLogs::default(),
202 const_unification_storage: ut::UnificationTableStorage::new(),
203 int_unification_storage: ut::UnificationTableStorage::new(),
204 float_unification_storage: ut::UnificationTableStorage::new(),
205 region_constraint_storage: Some(RegionConstraintStorage::new()),
206 region_obligations: vec![],
207 opaque_type_storage: Default::default(),
212 pub fn region_obligations(&self) -> &[(hir::HirId, RegionObligation<'tcx>)] {
213 &self.region_obligations
217 pub fn projection_cache(&mut self) -> traits::ProjectionCache<'_, 'tcx> {
218 self.projection_cache.with_log(&mut self.undo_log)
222 fn type_variables(&mut self) -> type_variable::TypeVariableTable<'_, 'tcx> {
223 self.type_variable_storage.with_log(&mut self.undo_log)
227 pub fn opaque_types(&mut self) -> opaque_types::OpaqueTypeTable<'_, 'tcx> {
228 self.opaque_type_storage.with_log(&mut self.undo_log)
232 fn int_unification_table(
234 ) -> ut::UnificationTable<
237 &mut ut::UnificationStorage<ty::IntVid>,
238 &mut InferCtxtUndoLogs<'tcx>,
241 self.int_unification_storage.with_log(&mut self.undo_log)
245 fn float_unification_table(
247 ) -> ut::UnificationTable<
250 &mut ut::UnificationStorage<ty::FloatVid>,
251 &mut InferCtxtUndoLogs<'tcx>,
254 self.float_unification_storage.with_log(&mut self.undo_log)
258 fn const_unification_table(
260 ) -> ut::UnificationTable<
263 &mut ut::UnificationStorage<ty::ConstVid<'tcx>>,
264 &mut InferCtxtUndoLogs<'tcx>,
267 self.const_unification_storage.with_log(&mut self.undo_log)
271 pub fn unwrap_region_constraints(&mut self) -> RegionConstraintCollector<'_, 'tcx> {
272 self.region_constraint_storage
274 .expect("region constraints already solved")
275 .with_log(&mut self.undo_log)
279 pub struct InferCtxt<'a, 'tcx> {
280 pub tcx: TyCtxt<'tcx>,
282 /// The `DefId` of the item in whose context we are performing inference or typeck.
283 /// It is used to check whether an opaque type use is a defining use.
285 /// If it is `None`, we can't resolve opaque types here and need to bubble up
286 /// the obligation. This frequently happens for
287 /// short lived InferCtxt within queries. The opaque type obligations are forwarded
288 /// to the outside until the end up in an `InferCtxt` for typeck or borrowck.
289 pub defining_use_anchor: Option<LocalDefId>,
291 /// During type-checking/inference of a body, `in_progress_typeck_results`
292 /// contains a reference to the typeck results being built up, which are
293 /// used for reading closure kinds/signatures as they are inferred,
294 /// and for error reporting logic to read arbitrary node types.
295 pub in_progress_typeck_results: Option<&'a RefCell<ty::TypeckResults<'tcx>>>,
297 pub inner: RefCell<InferCtxtInner<'tcx>>,
299 /// If set, this flag causes us to skip the 'leak check' during
300 /// higher-ranked subtyping operations. This flag is a temporary one used
301 /// to manage the removal of the leak-check: for the time being, we still run the
302 /// leak-check, but we issue warnings. This flag can only be set to true
303 /// when entering a snapshot.
304 skip_leak_check: Cell<bool>,
306 /// Once region inference is done, the values for each variable.
307 lexical_region_resolutions: RefCell<Option<LexicalRegionResolutions<'tcx>>>,
309 /// Caches the results of trait selection. This cache is used
310 /// for things that have to do with the parameters in scope.
311 pub selection_cache: select::SelectionCache<'tcx>,
313 /// Caches the results of trait evaluation.
314 pub evaluation_cache: select::EvaluationCache<'tcx>,
316 /// the set of predicates on which errors have been reported, to
317 /// avoid reporting the same error twice.
318 pub reported_trait_errors: RefCell<FxHashMap<Span, Vec<ty::Predicate<'tcx>>>>,
320 pub reported_closure_mismatch: RefCell<FxHashSet<(Span, Option<Span>)>>,
322 /// When an error occurs, we want to avoid reporting "derived"
323 /// errors that are due to this original failure. Normally, we
324 /// handle this with the `err_count_on_creation` count, which
325 /// basically just tracks how many errors were reported when we
326 /// started type-checking a fn and checks to see if any new errors
327 /// have been reported since then. Not great, but it works.
329 /// However, when errors originated in other passes -- notably
330 /// resolve -- this heuristic breaks down. Therefore, we have this
331 /// auxiliary flag that one can set whenever one creates a
332 /// type-error that is due to an error in a prior pass.
334 /// Don't read this flag directly, call `is_tainted_by_errors()`
335 /// and `set_tainted_by_errors()`.
336 tainted_by_errors_flag: Cell<bool>,
338 /// Track how many errors were reported when this infcx is created.
339 /// If the number of errors increases, that's also a sign (line
340 /// `tainted_by_errors`) to avoid reporting certain kinds of errors.
341 // FIXME(matthewjasper) Merge into `tainted_by_errors_flag`
342 err_count_on_creation: usize,
344 /// This flag is true while there is an active snapshot.
345 in_snapshot: Cell<bool>,
347 /// What is the innermost universe we have created? Starts out as
348 /// `UniverseIndex::root()` but grows from there as we enter
349 /// universal quantifiers.
351 /// N.B., at present, we exclude the universal quantifiers on the
352 /// item we are type-checking, and just consider those names as
353 /// part of the root universe. So this would only get incremented
354 /// when we enter into a higher-ranked (`for<..>`) type or trait
356 universe: Cell<ty::UniverseIndex>,
359 /// See the `error_reporting` module for more details.
360 #[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable)]
361 pub enum ValuePairs<'tcx> {
362 Regions(ExpectedFound<ty::Region<'tcx>>),
363 Terms(ExpectedFound<ty::Term<'tcx>>),
364 TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>),
365 PolyTraitRefs(ExpectedFound<ty::PolyTraitRef<'tcx>>),
368 impl<'tcx> ValuePairs<'tcx> {
369 pub fn ty(&self) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
370 if let ValuePairs::Terms(ExpectedFound {
371 expected: ty::Term::Ty(expected),
372 found: ty::Term::Ty(found),
375 Some((*expected, *found))
382 /// The trace designates the path through inference that we took to
383 /// encounter an error or subtyping constraint.
385 /// See the `error_reporting` module for more details.
386 #[derive(Clone, Debug)]
387 pub struct TypeTrace<'tcx> {
388 pub cause: ObligationCause<'tcx>,
389 pub values: ValuePairs<'tcx>,
392 /// The origin of a `r1 <= r2` constraint.
394 /// See `error_reporting` module for more details
395 #[derive(Clone, Debug)]
396 pub enum SubregionOrigin<'tcx> {
397 /// Arose from a subtyping relation
398 Subtype(Box<TypeTrace<'tcx>>),
400 /// When casting `&'a T` to an `&'b Trait` object,
401 /// relating `'a` to `'b`
402 RelateObjectBound(Span),
404 /// Some type parameter was instantiated with the given type,
405 /// and that type must outlive some region.
406 RelateParamBound(Span, Ty<'tcx>, Option<Span>),
408 /// The given region parameter was instantiated with a region
409 /// that must outlive some other region.
410 RelateRegionParamBound(Span),
412 /// Creating a pointer `b` to contents of another reference
415 /// Creating a pointer `b` to contents of an upvar
416 ReborrowUpvar(Span, ty::UpvarId),
418 /// Data with type `Ty<'tcx>` was borrowed
419 DataBorrowed(Ty<'tcx>, Span),
421 /// (&'a &'b T) where a >= b
422 ReferenceOutlivesReferent(Ty<'tcx>, Span),
424 /// Comparing the signature and requirements of an impl method against
425 /// the containing trait.
426 CompareImplMethodObligation {
428 impl_item_def_id: LocalDefId,
429 trait_item_def_id: DefId,
432 /// Comparing the signature and requirements of an impl associated type
433 /// against the containing trait
434 CompareImplTypeObligation { span: Span, impl_item_def_id: LocalDefId, trait_item_def_id: DefId },
436 /// Checking that the bounds of a trait's associated type hold for a given impl
437 CheckAssociatedTypeBounds {
438 parent: Box<SubregionOrigin<'tcx>>,
439 impl_item_def_id: LocalDefId,
440 trait_item_def_id: DefId,
444 // `SubregionOrigin` is used a lot. Make sure it doesn't unintentionally get bigger.
445 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
446 static_assert_size!(SubregionOrigin<'_>, 32);
448 /// Times when we replace late-bound regions with variables:
449 #[derive(Clone, Copy, Debug)]
450 pub enum LateBoundRegionConversionTime {
451 /// when a fn is called
454 /// when two higher-ranked types are compared
457 /// when projecting an associated type
458 AssocTypeProjection(DefId),
461 /// Reasons to create a region inference variable
463 /// See `error_reporting` module for more details
464 #[derive(Copy, Clone, Debug)]
465 pub enum RegionVariableOrigin {
466 /// Region variables created for ill-categorized reasons,
467 /// mostly indicates places in need of refactoring
470 /// Regions created by a `&P` or `[...]` pattern
473 /// Regions created by `&` operator
476 /// Regions created as part of an autoref of a method receiver
479 /// Regions created as part of an automatic coercion
482 /// Region variables created as the values for early-bound regions
483 EarlyBoundRegion(Span, Symbol),
485 /// Region variables created for bound regions
486 /// in a function or method that is called
487 LateBoundRegion(Span, ty::BoundRegionKind, LateBoundRegionConversionTime),
489 UpvarRegion(ty::UpvarId, Span),
491 /// This origin is used for the inference variables that we create
492 /// during NLL region processing.
493 Nll(NllRegionVariableOrigin),
496 #[derive(Copy, Clone, Debug)]
497 pub enum NllRegionVariableOrigin {
498 /// During NLL region processing, we create variables for free
499 /// regions that we encounter in the function signature and
500 /// elsewhere. This origin indices we've got one of those.
503 /// "Universal" instantiation of a higher-ranked region (e.g.,
504 /// from a `for<'a> T` binder). Meant to represent "any region".
505 Placeholder(ty::PlaceholderRegion),
507 /// The variable we create to represent `'empty(U0)`.
511 /// If this is true, then this variable was created to represent a lifetime
512 /// bound in a `for` binder. For example, it might have been created to
513 /// represent the lifetime `'a` in a type like `for<'a> fn(&'a u32)`.
514 /// Such variables are created when we are trying to figure out if there
515 /// is any valid instantiation of `'a` that could fit into some scenario.
517 /// This is used to inform error reporting: in the case that we are trying to
518 /// determine whether there is any valid instantiation of a `'a` variable that meets
519 /// some constraint C, we want to blame the "source" of that `for` type,
520 /// rather than blaming the source of the constraint C.
525 // FIXME(eddyb) investigate overlap between this and `TyOrConstInferVar`.
526 #[derive(Copy, Clone, Debug)]
527 pub enum FixupError<'tcx> {
528 UnresolvedIntTy(IntVid),
529 UnresolvedFloatTy(FloatVid),
531 UnresolvedConst(ConstVid<'tcx>),
534 /// See the `region_obligations` field for more information.
536 pub struct RegionObligation<'tcx> {
537 pub sub_region: ty::Region<'tcx>,
538 pub sup_type: Ty<'tcx>,
539 pub origin: SubregionOrigin<'tcx>,
542 impl<'tcx> fmt::Display for FixupError<'tcx> {
543 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
544 use self::FixupError::*;
547 UnresolvedIntTy(_) => write!(
549 "cannot determine the type of this integer; \
550 add a suffix to specify the type explicitly"
552 UnresolvedFloatTy(_) => write!(
554 "cannot determine the type of this number; \
555 add a suffix to specify the type explicitly"
557 UnresolvedTy(_) => write!(f, "unconstrained type"),
558 UnresolvedConst(_) => write!(f, "unconstrained const value"),
563 /// A temporary returned by `tcx.infer_ctxt()`. This is necessary
564 /// for multiple `InferCtxt` to share the same `in_progress_typeck_results`
565 /// without using `Rc` or something similar.
566 pub struct InferCtxtBuilder<'tcx> {
568 fresh_typeck_results: Option<RefCell<ty::TypeckResults<'tcx>>>,
569 defining_use_anchor: Option<LocalDefId>,
572 pub trait TyCtxtInferExt<'tcx> {
573 fn infer_ctxt(self) -> InferCtxtBuilder<'tcx>;
576 impl<'tcx> TyCtxtInferExt<'tcx> for TyCtxt<'tcx> {
577 fn infer_ctxt(self) -> InferCtxtBuilder<'tcx> {
578 InferCtxtBuilder { tcx: self, defining_use_anchor: None, fresh_typeck_results: None }
582 impl<'tcx> InferCtxtBuilder<'tcx> {
583 /// Used only by `rustc_typeck` during body type-checking/inference,
584 /// will initialize `in_progress_typeck_results` with fresh `TypeckResults`.
585 /// Will also change the scope for opaque type defining use checks to the given owner.
586 pub fn with_fresh_in_progress_typeck_results(mut self, table_owner: LocalDefId) -> Self {
587 self.fresh_typeck_results = Some(RefCell::new(ty::TypeckResults::new(table_owner)));
588 self.with_opaque_type_inference(table_owner)
591 /// Whenever the `InferCtxt` should be able to handle defining uses of opaque types,
592 /// you need to call this function. Otherwise the opaque type will be treated opaquely.
594 /// It is only meant to be called in two places, for typeck
595 /// (via `with_fresh_in_progress_typeck_results`) and for the inference context used
597 pub fn with_opaque_type_inference(mut self, defining_use_anchor: LocalDefId) -> Self {
598 self.defining_use_anchor = Some(defining_use_anchor);
602 /// Given a canonical value `C` as a starting point, create an
603 /// inference context that contains each of the bound values
604 /// within instantiated as a fresh variable. The `f` closure is
605 /// invoked with the new infcx, along with the instantiated value
606 /// `V` and a substitution `S`. This substitution `S` maps from
607 /// the bound values in `C` to their instantiated values in `V`
608 /// (in other words, `S(C) = V`).
609 pub fn enter_with_canonical<T, R>(
612 canonical: &Canonical<'tcx, T>,
613 f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>, T, CanonicalVarValues<'tcx>) -> R,
616 T: TypeFoldable<'tcx>,
620 infcx.instantiate_canonical_with_fresh_inference_vars(span, canonical);
621 f(infcx, value, subst)
625 pub fn enter<R>(&mut self, f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>) -> R) -> R {
626 let InferCtxtBuilder { tcx, defining_use_anchor, ref fresh_typeck_results } = *self;
627 let in_progress_typeck_results = fresh_typeck_results.as_ref();
631 in_progress_typeck_results,
632 inner: RefCell::new(InferCtxtInner::new()),
633 lexical_region_resolutions: RefCell::new(None),
634 selection_cache: Default::default(),
635 evaluation_cache: Default::default(),
636 reported_trait_errors: Default::default(),
637 reported_closure_mismatch: Default::default(),
638 tainted_by_errors_flag: Cell::new(false),
639 err_count_on_creation: tcx.sess.err_count(),
640 in_snapshot: Cell::new(false),
641 skip_leak_check: Cell::new(false),
642 universe: Cell::new(ty::UniverseIndex::ROOT),
647 impl<'tcx, T> InferOk<'tcx, T> {
648 pub fn unit(self) -> InferOk<'tcx, ()> {
649 InferOk { value: (), obligations: self.obligations }
652 /// Extracts `value`, registering any obligations into `fulfill_cx`.
653 pub fn into_value_registering_obligations(
655 infcx: &InferCtxt<'_, 'tcx>,
656 fulfill_cx: &mut dyn TraitEngine<'tcx>,
658 let InferOk { value, obligations } = self;
659 for obligation in obligations {
660 fulfill_cx.register_predicate_obligation(infcx, obligation);
666 impl<'tcx> InferOk<'tcx, ()> {
667 pub fn into_obligations(self) -> PredicateObligations<'tcx> {
672 #[must_use = "once you start a snapshot, you should always consume it"]
673 pub struct CombinedSnapshot<'a, 'tcx> {
674 undo_snapshot: Snapshot<'tcx>,
675 region_constraints_snapshot: RegionSnapshot,
676 universe: ty::UniverseIndex,
677 was_in_snapshot: bool,
678 _in_progress_typeck_results: Option<Ref<'a, ty::TypeckResults<'tcx>>>,
681 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
682 /// calls `tcx.try_unify_abstract_consts` after
683 /// canonicalizing the consts.
684 #[instrument(skip(self), level = "debug")]
685 pub fn try_unify_abstract_consts(
687 a: ty::Unevaluated<'tcx, ()>,
688 b: ty::Unevaluated<'tcx, ()>,
689 param_env: ty::ParamEnv<'tcx>,
691 // Reject any attempt to unify two unevaluated constants that contain inference
692 // variables, since inference variables in queries lead to ICEs.
693 if a.substs.has_infer_types_or_consts()
694 || b.substs.has_infer_types_or_consts()
695 || param_env.has_infer_types_or_consts()
697 debug!("a or b or param_env contain infer vars in its substs -> cannot unify");
701 let param_env_and = param_env.and((a, b));
702 let erased = self.tcx.erase_regions(param_env_and);
703 debug!("after erase_regions: {:?}", erased);
705 self.tcx.try_unify_abstract_consts(erased)
708 pub fn is_in_snapshot(&self) -> bool {
709 self.in_snapshot.get()
712 pub fn freshen<T: TypeFoldable<'tcx>>(&self, t: T) -> T {
713 t.fold_with(&mut self.freshener())
716 /// Returns the origin of the type variable identified by `vid`, or `None`
717 /// if this is not a type variable.
719 /// No attempt is made to resolve `ty`.
720 pub fn type_var_origin(&'a self, ty: Ty<'tcx>) -> Option<TypeVariableOrigin> {
722 ty::Infer(ty::TyVar(vid)) => {
723 Some(*self.inner.borrow_mut().type_variables().var_origin(vid))
729 pub fn freshener<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
730 freshen::TypeFreshener::new(self, false)
733 /// Like `freshener`, but does not replace `'static` regions.
734 pub fn freshener_keep_static<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
735 freshen::TypeFreshener::new(self, true)
738 pub fn unsolved_variables(&self) -> Vec<Ty<'tcx>> {
739 let mut inner = self.inner.borrow_mut();
740 let mut vars: Vec<Ty<'_>> = inner
742 .unsolved_variables()
744 .map(|t| self.tcx.mk_ty_var(t))
747 (0..inner.int_unification_table().len())
748 .map(|i| ty::IntVid { index: i as u32 })
749 .filter(|&vid| inner.int_unification_table().probe_value(vid).is_none())
750 .map(|v| self.tcx.mk_int_var(v)),
753 (0..inner.float_unification_table().len())
754 .map(|i| ty::FloatVid { index: i as u32 })
755 .filter(|&vid| inner.float_unification_table().probe_value(vid).is_none())
756 .map(|v| self.tcx.mk_float_var(v)),
763 trace: TypeTrace<'tcx>,
764 param_env: ty::ParamEnv<'tcx>,
765 define_opaque_types: bool,
766 ) -> CombineFields<'a, 'tcx> {
772 obligations: PredicateObligations::new(),
777 /// Clear the "currently in a snapshot" flag, invoke the closure,
778 /// then restore the flag to its original value. This flag is a
779 /// debugging measure designed to detect cases where we start a
780 /// snapshot, create type variables, and register obligations
781 /// which may involve those type variables in the fulfillment cx,
782 /// potentially leaving "dangling type variables" behind.
783 /// In such cases, an assertion will fail when attempting to
784 /// register obligations, within a snapshot. Very useful, much
785 /// better than grovelling through megabytes of `RUSTC_LOG` output.
787 /// HOWEVER, in some cases the flag is unhelpful. In particular, we
788 /// sometimes create a "mini-fulfilment-cx" in which we enroll
789 /// obligations. As long as this fulfillment cx is fully drained
790 /// before we return, this is not a problem, as there won't be any
791 /// escaping obligations in the main cx. In those cases, you can
792 /// use this function.
793 pub fn save_and_restore_in_snapshot_flag<F, R>(&self, func: F) -> R
795 F: FnOnce(&Self) -> R,
797 let flag = self.in_snapshot.replace(false);
798 let result = func(self);
799 self.in_snapshot.set(flag);
803 fn start_snapshot(&self) -> CombinedSnapshot<'a, 'tcx> {
804 debug!("start_snapshot()");
806 let in_snapshot = self.in_snapshot.replace(true);
808 let mut inner = self.inner.borrow_mut();
811 undo_snapshot: inner.undo_log.start_snapshot(),
812 region_constraints_snapshot: inner.unwrap_region_constraints().start_snapshot(),
813 universe: self.universe(),
814 was_in_snapshot: in_snapshot,
815 // Borrow typeck results "in progress" (i.e., during typeck)
816 // to ban writes from within a snapshot to them.
817 _in_progress_typeck_results: self
818 .in_progress_typeck_results
819 .map(|typeck_results| typeck_results.borrow()),
823 #[instrument(skip(self, snapshot), level = "debug")]
824 fn rollback_to(&self, cause: &str, snapshot: CombinedSnapshot<'a, 'tcx>) {
825 let CombinedSnapshot {
827 region_constraints_snapshot,
830 _in_progress_typeck_results,
833 self.in_snapshot.set(was_in_snapshot);
834 self.universe.set(universe);
836 let mut inner = self.inner.borrow_mut();
837 inner.rollback_to(undo_snapshot);
838 inner.unwrap_region_constraints().rollback_to(region_constraints_snapshot);
841 #[instrument(skip(self, snapshot), level = "debug")]
842 fn commit_from(&self, snapshot: CombinedSnapshot<'a, 'tcx>) {
843 let CombinedSnapshot {
845 region_constraints_snapshot: _,
848 _in_progress_typeck_results,
851 self.in_snapshot.set(was_in_snapshot);
853 self.inner.borrow_mut().commit(undo_snapshot);
856 /// Executes `f` and commit the bindings.
857 #[instrument(skip(self, f), level = "debug")]
858 pub fn commit_unconditionally<R, F>(&self, f: F) -> R
860 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
862 let snapshot = self.start_snapshot();
863 let r = f(&snapshot);
864 self.commit_from(snapshot);
868 /// Execute `f` and commit the bindings if closure `f` returns `Ok(_)`.
869 #[instrument(skip(self, f), level = "debug")]
870 pub fn commit_if_ok<T, E, F>(&self, f: F) -> Result<T, E>
872 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> Result<T, E>,
874 let snapshot = self.start_snapshot();
875 let r = f(&snapshot);
876 debug!("commit_if_ok() -- r.is_ok() = {}", r.is_ok());
879 self.commit_from(snapshot);
882 self.rollback_to("commit_if_ok -- error", snapshot);
888 /// Execute `f` then unroll any bindings it creates.
889 #[instrument(skip(self, f), level = "debug")]
890 pub fn probe<R, F>(&self, f: F) -> R
892 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
894 let snapshot = self.start_snapshot();
895 let r = f(&snapshot);
896 self.rollback_to("probe", snapshot);
900 /// If `should_skip` is true, then execute `f` then unroll any bindings it creates.
901 #[instrument(skip(self, f), level = "debug")]
902 pub fn probe_maybe_skip_leak_check<R, F>(&self, should_skip: bool, f: F) -> R
904 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
906 let snapshot = self.start_snapshot();
907 let was_skip_leak_check = self.skip_leak_check.get();
909 self.skip_leak_check.set(true);
911 let r = f(&snapshot);
912 self.rollback_to("probe", snapshot);
913 self.skip_leak_check.set(was_skip_leak_check);
917 /// Scan the constraints produced since `snapshot` began and returns:
919 /// - `None` -- if none of them involve "region outlives" constraints
920 /// - `Some(true)` -- if there are `'a: 'b` constraints where `'a` or `'b` is a placeholder
921 /// - `Some(false)` -- if there are `'a: 'b` constraints but none involve placeholders
922 pub fn region_constraints_added_in_snapshot(
924 snapshot: &CombinedSnapshot<'a, 'tcx>,
928 .unwrap_region_constraints()
929 .region_constraints_added_in_snapshot(&snapshot.undo_snapshot)
932 pub fn add_given(&self, sub: ty::Region<'tcx>, sup: ty::RegionVid) {
933 self.inner.borrow_mut().unwrap_region_constraints().add_given(sub, sup);
936 pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
938 T: at::ToTrace<'tcx>,
940 let origin = &ObligationCause::dummy();
942 self.at(origin, param_env).sub(a, b).map(|InferOk { obligations: _, .. }| {
943 // Ignore obligations, since we are unrolling
944 // everything anyway.
949 pub fn can_eq<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
951 T: at::ToTrace<'tcx>,
953 let origin = &ObligationCause::dummy();
955 self.at(origin, param_env).eq(a, b).map(|InferOk { obligations: _, .. }| {
956 // Ignore obligations, since we are unrolling
957 // everything anyway.
962 #[instrument(skip(self), level = "debug")]
965 origin: SubregionOrigin<'tcx>,
969 self.inner.borrow_mut().unwrap_region_constraints().make_subregion(origin, a, b);
972 /// Require that the region `r` be equal to one of the regions in
973 /// the set `regions`.
974 #[instrument(skip(self), level = "debug")]
975 pub fn member_constraint(
977 opaque_type_def_id: DefId,
978 definition_span: Span,
980 region: ty::Region<'tcx>,
981 in_regions: &Lrc<Vec<ty::Region<'tcx>>>,
983 self.inner.borrow_mut().unwrap_region_constraints().member_constraint(
992 /// Processes a `Coerce` predicate from the fulfillment context.
993 /// This is NOT the preferred way to handle coercion, which is to
994 /// invoke `FnCtxt::coerce` or a similar method (see `coercion.rs`).
996 /// This method here is actually a fallback that winds up being
997 /// invoked when `FnCtxt::coerce` encounters unresolved type variables
998 /// and records a coercion predicate. Presently, this method is equivalent
999 /// to `subtype_predicate` -- that is, "coercing" `a` to `b` winds up
1000 /// actually requiring `a <: b`. This is of course a valid coercion,
1001 /// but it's not as flexible as `FnCtxt::coerce` would be.
1003 /// (We may refactor this in the future, but there are a number of
1004 /// practical obstacles. Among other things, `FnCtxt::coerce` presently
1005 /// records adjustments that are required on the HIR in order to perform
1006 /// the coercion, and we don't currently have a way to manage that.)
1007 pub fn coerce_predicate(
1009 cause: &ObligationCause<'tcx>,
1010 param_env: ty::ParamEnv<'tcx>,
1011 predicate: ty::PolyCoercePredicate<'tcx>,
1012 ) -> Option<InferResult<'tcx, ()>> {
1013 let subtype_predicate = predicate.map_bound(|p| ty::SubtypePredicate {
1014 a_is_expected: false, // when coercing from `a` to `b`, `b` is expected
1018 self.subtype_predicate(cause, param_env, subtype_predicate)
1021 pub fn subtype_predicate(
1023 cause: &ObligationCause<'tcx>,
1024 param_env: ty::ParamEnv<'tcx>,
1025 predicate: ty::PolySubtypePredicate<'tcx>,
1026 ) -> Option<InferResult<'tcx, ()>> {
1027 // Check for two unresolved inference variables, in which case we can
1028 // make no progress. This is partly a micro-optimization, but it's
1029 // also an opportunity to "sub-unify" the variables. This isn't
1030 // *necessary* to prevent cycles, because they would eventually be sub-unified
1031 // anyhow during generalization, but it helps with diagnostics (we can detect
1032 // earlier that they are sub-unified).
1034 // Note that we can just skip the binders here because
1035 // type variables can't (at present, at
1036 // least) capture any of the things bound by this binder.
1038 // Note that this sub here is not just for diagnostics - it has semantic
1040 let r_a = self.shallow_resolve(predicate.skip_binder().a);
1041 let r_b = self.shallow_resolve(predicate.skip_binder().b);
1042 match (r_a.kind(), r_b.kind()) {
1043 (&ty::Infer(ty::TyVar(a_vid)), &ty::Infer(ty::TyVar(b_vid))) => {
1044 self.inner.borrow_mut().type_variables().sub(a_vid, b_vid);
1050 Some(self.commit_if_ok(|_snapshot| {
1051 let ty::SubtypePredicate { a_is_expected, a, b } =
1052 self.replace_bound_vars_with_placeholders(predicate);
1054 let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?;
1060 pub fn region_outlives_predicate(
1062 cause: &traits::ObligationCause<'tcx>,
1063 predicate: ty::PolyRegionOutlivesPredicate<'tcx>,
1064 ) -> UnitResult<'tcx> {
1065 self.commit_if_ok(|_snapshot| {
1066 let ty::OutlivesPredicate(r_a, r_b) =
1067 self.replace_bound_vars_with_placeholders(predicate);
1068 let origin = SubregionOrigin::from_obligation_cause(cause, || {
1069 RelateRegionParamBound(cause.span)
1071 self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
1076 /// Number of type variables created so far.
1077 pub fn num_ty_vars(&self) -> usize {
1078 self.inner.borrow_mut().type_variables().num_vars()
1081 pub fn next_ty_var_id(&self, origin: TypeVariableOrigin) -> TyVid {
1082 self.inner.borrow_mut().type_variables().new_var(self.universe(), origin)
1085 pub fn next_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
1086 self.tcx.mk_ty_var(self.next_ty_var_id(origin))
1089 pub fn next_ty_var_id_in_universe(
1091 origin: TypeVariableOrigin,
1092 universe: ty::UniverseIndex,
1094 self.inner.borrow_mut().type_variables().new_var(universe, origin)
1097 pub fn next_ty_var_in_universe(
1099 origin: TypeVariableOrigin,
1100 universe: ty::UniverseIndex,
1102 let vid = self.next_ty_var_id_in_universe(origin, universe);
1103 self.tcx.mk_ty_var(vid)
1106 pub fn next_const_var(&self, ty: Ty<'tcx>, origin: ConstVariableOrigin) -> ty::Const<'tcx> {
1107 self.tcx.mk_const_var(self.next_const_var_id(origin), ty)
1110 pub fn next_const_var_in_universe(
1113 origin: ConstVariableOrigin,
1114 universe: ty::UniverseIndex,
1115 ) -> ty::Const<'tcx> {
1119 .const_unification_table()
1120 .new_key(ConstVarValue { origin, val: ConstVariableValue::Unknown { universe } });
1121 self.tcx.mk_const_var(vid, ty)
1124 pub fn next_const_var_id(&self, origin: ConstVariableOrigin) -> ConstVid<'tcx> {
1125 self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue {
1127 val: ConstVariableValue::Unknown { universe: self.universe() },
1131 fn next_int_var_id(&self) -> IntVid {
1132 self.inner.borrow_mut().int_unification_table().new_key(None)
1135 pub fn next_int_var(&self) -> Ty<'tcx> {
1136 self.tcx.mk_int_var(self.next_int_var_id())
1139 fn next_float_var_id(&self) -> FloatVid {
1140 self.inner.borrow_mut().float_unification_table().new_key(None)
1143 pub fn next_float_var(&self) -> Ty<'tcx> {
1144 self.tcx.mk_float_var(self.next_float_var_id())
1147 /// Creates a fresh region variable with the next available index.
1148 /// The variable will be created in the maximum universe created
1149 /// thus far, allowing it to name any region created thus far.
1150 pub fn next_region_var(&self, origin: RegionVariableOrigin) -> ty::Region<'tcx> {
1151 self.next_region_var_in_universe(origin, self.universe())
1154 /// Creates a fresh region variable with the next available index
1155 /// in the given universe; typically, you can use
1156 /// `next_region_var` and just use the maximal universe.
1157 pub fn next_region_var_in_universe(
1159 origin: RegionVariableOrigin,
1160 universe: ty::UniverseIndex,
1161 ) -> ty::Region<'tcx> {
1163 self.inner.borrow_mut().unwrap_region_constraints().new_region_var(universe, origin);
1164 self.tcx.mk_region(ty::ReVar(region_var))
1167 /// Return the universe that the region `r` was created in. For
1168 /// most regions (e.g., `'static`, named regions from the user,
1169 /// etc) this is the root universe U0. For inference variables or
1170 /// placeholders, however, it will return the universe which which
1171 /// they are associated.
1172 pub fn universe_of_region(&self, r: ty::Region<'tcx>) -> ty::UniverseIndex {
1173 self.inner.borrow_mut().unwrap_region_constraints().universe(r)
1176 /// Number of region variables created so far.
1177 pub fn num_region_vars(&self) -> usize {
1178 self.inner.borrow_mut().unwrap_region_constraints().num_region_vars()
1181 /// Just a convenient wrapper of `next_region_var` for using during NLL.
1182 pub fn next_nll_region_var(&self, origin: NllRegionVariableOrigin) -> ty::Region<'tcx> {
1183 self.next_region_var(RegionVariableOrigin::Nll(origin))
1186 /// Just a convenient wrapper of `next_region_var` for using during NLL.
1187 pub fn next_nll_region_var_in_universe(
1189 origin: NllRegionVariableOrigin,
1190 universe: ty::UniverseIndex,
1191 ) -> ty::Region<'tcx> {
1192 self.next_region_var_in_universe(RegionVariableOrigin::Nll(origin), universe)
1195 pub fn var_for_def(&self, span: Span, param: &ty::GenericParamDef) -> GenericArg<'tcx> {
1197 GenericParamDefKind::Lifetime => {
1198 // Create a region inference variable for the given
1199 // region parameter definition.
1200 self.next_region_var(EarlyBoundRegion(span, param.name)).into()
1202 GenericParamDefKind::Type { .. } => {
1203 // Create a type inference variable for the given
1204 // type parameter definition. The substitutions are
1205 // for actual parameters that may be referred to by
1206 // the default of this type parameter, if it exists.
1207 // e.g., `struct Foo<A, B, C = (A, B)>(...);` when
1208 // used in a path such as `Foo::<T, U>::new()` will
1209 // use an inference variable for `C` with `[T, U]`
1210 // as the substitutions for the default, `(T, U)`.
1211 let ty_var_id = self.inner.borrow_mut().type_variables().new_var(
1213 TypeVariableOrigin {
1214 kind: TypeVariableOriginKind::TypeParameterDefinition(
1222 self.tcx.mk_ty_var(ty_var_id).into()
1224 GenericParamDefKind::Const { .. } => {
1225 let origin = ConstVariableOrigin {
1226 kind: ConstVariableOriginKind::ConstParameterDefinition(
1233 self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue {
1235 val: ConstVariableValue::Unknown { universe: self.universe() },
1237 self.tcx.mk_const_var(const_var_id, self.tcx.type_of(param.def_id)).into()
1242 /// Given a set of generics defined on a type or impl, returns a substitution mapping each
1243 /// type/region parameter to a fresh inference variable.
1244 pub fn fresh_substs_for_item(&self, span: Span, def_id: DefId) -> SubstsRef<'tcx> {
1245 InternalSubsts::for_item(self.tcx, def_id, |param, _| self.var_for_def(span, param))
1248 /// Returns `true` if errors have been reported since this infcx was
1249 /// created. This is sometimes used as a heuristic to skip
1250 /// reporting errors that often occur as a result of earlier
1251 /// errors, but where it's hard to be 100% sure (e.g., unresolved
1252 /// inference variables, regionck errors).
1253 pub fn is_tainted_by_errors(&self) -> bool {
1255 "is_tainted_by_errors(err_count={}, err_count_on_creation={}, \
1256 tainted_by_errors_flag={})",
1257 self.tcx.sess.err_count(),
1258 self.err_count_on_creation,
1259 self.tainted_by_errors_flag.get()
1262 if self.tcx.sess.err_count() > self.err_count_on_creation {
1263 return true; // errors reported since this infcx was made
1265 self.tainted_by_errors_flag.get()
1268 /// Set the "tainted by errors" flag to true. We call this when we
1269 /// observe an error from a prior pass.
1270 pub fn set_tainted_by_errors(&self) {
1271 debug!("set_tainted_by_errors()");
1272 self.tainted_by_errors_flag.set(true)
1275 /// Process the region constraints and return any any errors that
1276 /// result. After this, no more unification operations should be
1277 /// done -- or the compiler will panic -- but it is legal to use
1278 /// `resolve_vars_if_possible` as well as `fully_resolve`.
1279 pub fn resolve_regions(
1281 region_context: DefId,
1282 outlives_env: &OutlivesEnvironment<'tcx>,
1284 ) -> Vec<RegionResolutionError<'tcx>> {
1285 let (var_infos, data) = {
1286 let mut inner = self.inner.borrow_mut();
1287 let inner = &mut *inner;
1289 self.is_tainted_by_errors() || inner.region_obligations.is_empty(),
1290 "region_obligations not empty: {:#?}",
1291 inner.region_obligations
1294 .region_constraint_storage
1296 .expect("regions already resolved")
1297 .with_log(&mut inner.undo_log)
1298 .into_infos_and_data()
1302 &RegionRelations::new(self.tcx, region_context, outlives_env.free_region_map());
1304 let (lexical_region_resolutions, errors) =
1305 lexical_region_resolve::resolve(region_rels, var_infos, data, mode);
1307 let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions));
1308 assert!(old_value.is_none());
1313 /// Process the region constraints and report any errors that
1314 /// result. After this, no more unification operations should be
1315 /// done -- or the compiler will panic -- but it is legal to use
1316 /// `resolve_vars_if_possible` as well as `fully_resolve`.
1317 pub fn resolve_regions_and_report_errors(
1319 region_context: DefId,
1320 outlives_env: &OutlivesEnvironment<'tcx>,
1323 let errors = self.resolve_regions(region_context, outlives_env, mode);
1325 if !self.is_tainted_by_errors() {
1326 // As a heuristic, just skip reporting region errors
1327 // altogether if other errors have been reported while
1328 // this infcx was in use. This is totally hokey but
1329 // otherwise we have a hard time separating legit region
1330 // errors from silly ones.
1331 self.report_region_errors(&errors);
1335 /// Obtains (and clears) the current set of region
1336 /// constraints. The inference context is still usable: further
1337 /// unifications will simply add new constraints.
1339 /// This method is not meant to be used with normal lexical region
1340 /// resolution. Rather, it is used in the NLL mode as a kind of
1341 /// interim hack: basically we run normal type-check and generate
1342 /// region constraints as normal, but then we take them and
1343 /// translate them into the form that the NLL solver
1344 /// understands. See the NLL module for mode details.
1345 pub fn take_and_reset_region_constraints(&self) -> RegionConstraintData<'tcx> {
1347 self.inner.borrow().region_obligations.is_empty(),
1348 "region_obligations not empty: {:#?}",
1349 self.inner.borrow().region_obligations
1352 self.inner.borrow_mut().unwrap_region_constraints().take_and_reset_data()
1355 /// Gives temporary access to the region constraint data.
1356 pub fn with_region_constraints<R>(
1358 op: impl FnOnce(&RegionConstraintData<'tcx>) -> R,
1360 let mut inner = self.inner.borrow_mut();
1361 op(inner.unwrap_region_constraints().data())
1364 pub fn region_var_origin(&self, vid: ty::RegionVid) -> RegionVariableOrigin {
1365 let mut inner = self.inner.borrow_mut();
1366 let inner = &mut *inner;
1368 .region_constraint_storage
1370 .expect("regions already resolved")
1371 .with_log(&mut inner.undo_log)
1375 /// Takes ownership of the list of variable regions. This implies
1376 /// that all the region constraints have already been taken, and
1377 /// hence that `resolve_regions_and_report_errors` can never be
1378 /// called. This is used only during NLL processing to "hand off" ownership
1379 /// of the set of region variables into the NLL region context.
1380 pub fn take_region_var_origins(&self) -> VarInfos {
1381 let mut inner = self.inner.borrow_mut();
1382 let (var_infos, data) = inner
1383 .region_constraint_storage
1385 .expect("regions already resolved")
1386 .with_log(&mut inner.undo_log)
1387 .into_infos_and_data();
1388 assert!(data.is_empty());
1392 pub fn ty_to_string(&self, t: Ty<'tcx>) -> String {
1393 self.resolve_vars_if_possible(t).to_string()
1396 /// If `TyVar(vid)` resolves to a type, return that type. Else, return the
1397 /// universe index of `TyVar(vid)`.
1398 pub fn probe_ty_var(&self, vid: TyVid) -> Result<Ty<'tcx>, ty::UniverseIndex> {
1399 use self::type_variable::TypeVariableValue;
1401 match self.inner.borrow_mut().type_variables().probe(vid) {
1402 TypeVariableValue::Known { value } => Ok(value),
1403 TypeVariableValue::Unknown { universe } => Err(universe),
1407 /// Resolve any type variables found in `value` -- but only one
1408 /// level. So, if the variable `?X` is bound to some type
1409 /// `Foo<?Y>`, then this would return `Foo<?Y>` (but `?Y` may
1410 /// itself be bound to a type).
1412 /// Useful when you only need to inspect the outermost level of
1413 /// the type and don't care about nested types (or perhaps you
1414 /// will be resolving them as well, e.g. in a loop).
1415 pub fn shallow_resolve<T>(&self, value: T) -> T
1417 T: TypeFoldable<'tcx>,
1419 value.fold_with(&mut ShallowResolver { infcx: self })
1422 pub fn root_var(&self, var: ty::TyVid) -> ty::TyVid {
1423 self.inner.borrow_mut().type_variables().root_var(var)
1426 /// Where possible, replaces type/const variables in
1427 /// `value` with their final value. Note that region variables
1428 /// are unaffected. If a type/const variable has not been unified, it
1429 /// is left as is. This is an idempotent operation that does
1430 /// not affect inference state in any way and so you can do it
1432 pub fn resolve_vars_if_possible<T>(&self, value: T) -> T
1434 T: TypeFoldable<'tcx>,
1436 if !value.needs_infer() {
1437 return value; // Avoid duplicated subst-folding.
1439 let mut r = resolve::OpportunisticVarResolver::new(self);
1440 value.fold_with(&mut r)
1443 pub fn resolve_numeric_literals_with_default<T>(&self, value: T) -> T
1445 T: TypeFoldable<'tcx>,
1447 if !value.needs_infer() {
1448 return value; // Avoid duplicated subst-folding.
1450 let mut r = InferenceLiteralEraser { tcx: self.tcx };
1451 value.fold_with(&mut r)
1454 /// Returns the first unresolved variable contained in `T`. In the
1455 /// process of visiting `T`, this will resolve (where possible)
1456 /// type variables in `T`, but it never constructs the final,
1457 /// resolved type, so it's more efficient than
1458 /// `resolve_vars_if_possible()`.
1459 pub fn unresolved_type_vars<T>(&self, value: &T) -> Option<(Ty<'tcx>, Option<Span>)>
1461 T: TypeFoldable<'tcx>,
1463 value.visit_with(&mut resolve::UnresolvedTypeFinder::new(self)).break_value()
1466 pub fn probe_const_var(
1468 vid: ty::ConstVid<'tcx>,
1469 ) -> Result<ty::Const<'tcx>, ty::UniverseIndex> {
1470 match self.inner.borrow_mut().const_unification_table().probe_value(vid).val {
1471 ConstVariableValue::Known { value } => Ok(value),
1472 ConstVariableValue::Unknown { universe } => Err(universe),
1476 pub fn fully_resolve<T: TypeFoldable<'tcx>>(&self, value: T) -> FixupResult<'tcx, T> {
1478 * Attempts to resolve all type/region/const variables in
1479 * `value`. Region inference must have been run already (e.g.,
1480 * by calling `resolve_regions_and_report_errors`). If some
1481 * variable was never unified, an `Err` results.
1483 * This method is idempotent, but it not typically not invoked
1484 * except during the writeback phase.
1487 resolve::fully_resolve(self, value)
1490 // [Note-Type-error-reporting]
1491 // An invariant is that anytime the expected or actual type is Error (the special
1492 // error type, meaning that an error occurred when typechecking this expression),
1493 // this is a derived error. The error cascaded from another error (that was already
1494 // reported), so it's not useful to display it to the user.
1495 // The following methods implement this logic.
1496 // They check if either the actual or expected type is Error, and don't print the error
1497 // in this case. The typechecker should only ever report type errors involving mismatched
1498 // types using one of these methods, and should not call span_err directly for such
1501 pub fn type_error_struct_with_diag<M>(
1505 actual_ty: Ty<'tcx>,
1506 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>
1508 M: FnOnce(String) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>,
1510 let actual_ty = self.resolve_vars_if_possible(actual_ty);
1511 debug!("type_error_struct_with_diag({:?}, {:?})", sp, actual_ty);
1513 let mut err = mk_diag(self.ty_to_string(actual_ty));
1515 // Don't report an error if actual type is `Error`.
1516 if actual_ty.references_error() {
1517 err.downgrade_to_delayed_bug();
1523 pub fn report_mismatched_types(
1525 cause: &ObligationCause<'tcx>,
1528 err: TypeError<'tcx>,
1529 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1530 let trace = TypeTrace::types(cause, true, expected, actual);
1531 self.report_and_explain_type_error(trace, &err)
1534 pub fn report_mismatched_consts(
1536 cause: &ObligationCause<'tcx>,
1537 expected: ty::Const<'tcx>,
1538 actual: ty::Const<'tcx>,
1539 err: TypeError<'tcx>,
1540 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1541 let trace = TypeTrace::consts(cause, true, expected, actual);
1542 self.report_and_explain_type_error(trace, &err)
1545 pub fn replace_bound_vars_with_fresh_vars<T>(
1548 lbrct: LateBoundRegionConversionTime,
1549 value: ty::Binder<'tcx, T>,
1550 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
1552 T: TypeFoldable<'tcx>,
1555 |br: ty::BoundRegion| self.next_region_var(LateBoundRegion(span, br.kind, lbrct));
1557 self.next_ty_var(TypeVariableOrigin {
1558 kind: TypeVariableOriginKind::MiscVariable,
1562 let fld_c = |_, ty| {
1563 self.next_const_var(
1565 ConstVariableOrigin { kind: ConstVariableOriginKind::MiscVariable, span },
1568 self.tcx.replace_bound_vars(value, fld_r, fld_t, fld_c)
1571 /// See the [`region_constraints::RegionConstraintCollector::verify_generic_bound`] method.
1572 pub fn verify_generic_bound(
1574 origin: SubregionOrigin<'tcx>,
1575 kind: GenericKind<'tcx>,
1576 a: ty::Region<'tcx>,
1577 bound: VerifyBound<'tcx>,
1579 debug!("verify_generic_bound({:?}, {:?} <: {:?})", kind, a, bound);
1583 .unwrap_region_constraints()
1584 .verify_generic_bound(origin, kind, a, bound);
1587 /// Obtains the latest type of the given closure; this may be a
1588 /// closure in the current function, in which case its
1589 /// `ClosureKind` may not yet be known.
1590 pub fn closure_kind(&self, closure_substs: SubstsRef<'tcx>) -> Option<ty::ClosureKind> {
1591 let closure_kind_ty = closure_substs.as_closure().kind_ty();
1592 let closure_kind_ty = self.shallow_resolve(closure_kind_ty);
1593 closure_kind_ty.to_opt_closure_kind()
1596 /// Clears the selection, evaluation, and projection caches. This is useful when
1597 /// repeatedly attempting to select an `Obligation` while changing only
1598 /// its `ParamEnv`, since `FulfillmentContext` doesn't use probing.
1599 pub fn clear_caches(&self) {
1600 self.selection_cache.clear();
1601 self.evaluation_cache.clear();
1602 self.inner.borrow_mut().projection_cache().clear();
1605 pub fn universe(&self) -> ty::UniverseIndex {
1609 /// Creates and return a fresh universe that extends all previous
1610 /// universes. Updates `self.universe` to that new universe.
1611 pub fn create_next_universe(&self) -> ty::UniverseIndex {
1612 let u = self.universe.get().next_universe();
1613 self.universe.set(u);
1617 /// Resolves and evaluates a constant.
1619 /// The constant can be located on a trait like `<A as B>::C`, in which case the given
1620 /// substitutions and environment are used to resolve the constant. Alternatively if the
1621 /// constant has generic parameters in scope the substitutions are used to evaluate the value of
1622 /// the constant. For example in `fn foo<T>() { let _ = [0; bar::<T>()]; }` the repeat count
1623 /// constant `bar::<T>()` requires a substitution for `T`, if the substitution for `T` is still
1624 /// too generic for the constant to be evaluated then `Err(ErrorHandled::TooGeneric)` is
1627 /// This handles inferences variables within both `param_env` and `substs` by
1628 /// performing the operation on their respective canonical forms.
1629 #[instrument(skip(self), level = "debug")]
1630 pub fn const_eval_resolve(
1632 param_env: ty::ParamEnv<'tcx>,
1633 unevaluated: ty::Unevaluated<'tcx>,
1635 ) -> EvalToConstValueResult<'tcx> {
1636 let substs = self.resolve_vars_if_possible(unevaluated.substs);
1639 // Postpone the evaluation of constants whose substs depend on inference
1641 if substs.has_infer_types_or_consts() {
1642 debug!("substs have infer types or consts: {:?}", substs);
1643 return Err(ErrorHandled::TooGeneric);
1646 let param_env_erased = self.tcx.erase_regions(param_env);
1647 let substs_erased = self.tcx.erase_regions(substs);
1648 debug!(?param_env_erased);
1649 debug!(?substs_erased);
1651 let unevaluated = ty::Unevaluated {
1652 def: unevaluated.def,
1653 substs: substs_erased,
1654 promoted: unevaluated.promoted,
1657 // The return value is the evaluated value which doesn't contain any reference to inference
1658 // variables, thus we don't need to substitute back the original values.
1659 self.tcx.const_eval_resolve(param_env_erased, unevaluated, span)
1662 /// `ty_or_const_infer_var_changed` is equivalent to one of these two:
1663 /// * `shallow_resolve(ty) != ty` (where `ty.kind = ty::Infer(_)`)
1664 /// * `shallow_resolve(ct) != ct` (where `ct.kind = ty::ConstKind::Infer(_)`)
1666 /// However, `ty_or_const_infer_var_changed` is more efficient. It's always
1667 /// inlined, despite being large, because it has only two call sites that
1668 /// are extremely hot (both in `traits::fulfill`'s checking of `stalled_on`
1669 /// inference variables), and it handles both `Ty` and `ty::Const` without
1670 /// having to resort to storing full `GenericArg`s in `stalled_on`.
1672 pub fn ty_or_const_infer_var_changed(&self, infer_var: TyOrConstInferVar<'tcx>) -> bool {
1674 TyOrConstInferVar::Ty(v) => {
1675 use self::type_variable::TypeVariableValue;
1677 // If `inlined_probe` returns a `Known` value, it never equals
1678 // `ty::Infer(ty::TyVar(v))`.
1679 match self.inner.borrow_mut().type_variables().inlined_probe(v) {
1680 TypeVariableValue::Unknown { .. } => false,
1681 TypeVariableValue::Known { .. } => true,
1685 TyOrConstInferVar::TyInt(v) => {
1686 // If `inlined_probe_value` returns a value it's always a
1687 // `ty::Int(_)` or `ty::UInt(_)`, which never matches a
1689 self.inner.borrow_mut().int_unification_table().inlined_probe_value(v).is_some()
1692 TyOrConstInferVar::TyFloat(v) => {
1693 // If `probe_value` returns a value it's always a
1694 // `ty::Float(_)`, which never matches a `ty::Infer(_)`.
1696 // Not `inlined_probe_value(v)` because this call site is colder.
1697 self.inner.borrow_mut().float_unification_table().probe_value(v).is_some()
1700 TyOrConstInferVar::Const(v) => {
1701 // If `probe_value` returns a `Known` value, it never equals
1702 // `ty::ConstKind::Infer(ty::InferConst::Var(v))`.
1704 // Not `inlined_probe_value(v)` because this call site is colder.
1705 match self.inner.borrow_mut().const_unification_table().probe_value(v).val {
1706 ConstVariableValue::Unknown { .. } => false,
1707 ConstVariableValue::Known { .. } => true,
1714 /// Helper for `ty_or_const_infer_var_changed` (see comment on that), currently
1715 /// used only for `traits::fulfill`'s list of `stalled_on` inference variables.
1716 #[derive(Copy, Clone, Debug)]
1717 pub enum TyOrConstInferVar<'tcx> {
1718 /// Equivalent to `ty::Infer(ty::TyVar(_))`.
1720 /// Equivalent to `ty::Infer(ty::IntVar(_))`.
1722 /// Equivalent to `ty::Infer(ty::FloatVar(_))`.
1725 /// Equivalent to `ty::ConstKind::Infer(ty::InferConst::Var(_))`.
1726 Const(ConstVid<'tcx>),
1729 impl<'tcx> TyOrConstInferVar<'tcx> {
1730 /// Tries to extract an inference variable from a type or a constant, returns `None`
1731 /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`) and
1732 /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1733 pub fn maybe_from_generic_arg(arg: GenericArg<'tcx>) -> Option<Self> {
1734 match arg.unpack() {
1735 GenericArgKind::Type(ty) => Self::maybe_from_ty(ty),
1736 GenericArgKind::Const(ct) => Self::maybe_from_const(ct),
1737 GenericArgKind::Lifetime(_) => None,
1741 /// Tries to extract an inference variable from a type, returns `None`
1742 /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`).
1743 pub fn maybe_from_ty(ty: Ty<'tcx>) -> Option<Self> {
1745 ty::Infer(ty::TyVar(v)) => Some(TyOrConstInferVar::Ty(v)),
1746 ty::Infer(ty::IntVar(v)) => Some(TyOrConstInferVar::TyInt(v)),
1747 ty::Infer(ty::FloatVar(v)) => Some(TyOrConstInferVar::TyFloat(v)),
1752 /// Tries to extract an inference variable from a constant, returns `None`
1753 /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1754 pub fn maybe_from_const(ct: ty::Const<'tcx>) -> Option<Self> {
1756 ty::ConstKind::Infer(InferConst::Var(v)) => Some(TyOrConstInferVar::Const(v)),
1762 /// Replace `{integer}` with `i32` and `{float}` with `f64`.
1763 /// Used only for diagnostics.
1764 struct InferenceLiteralEraser<'tcx> {
1768 impl<'tcx> TypeFolder<'tcx> for InferenceLiteralEraser<'tcx> {
1769 fn tcx(&self) -> TyCtxt<'tcx> {
1773 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1775 ty::Infer(ty::IntVar(_) | ty::FreshIntTy(_)) => self.tcx.types.i32,
1776 ty::Infer(ty::FloatVar(_) | ty::FreshFloatTy(_)) => self.tcx.types.f64,
1777 _ => ty.super_fold_with(self),
1782 struct ShallowResolver<'a, 'tcx> {
1783 infcx: &'a InferCtxt<'a, 'tcx>,
1786 impl<'a, 'tcx> TypeFolder<'tcx> for ShallowResolver<'a, 'tcx> {
1787 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1791 /// If `ty` is a type variable of some kind, resolve it one level
1792 /// (but do not resolve types found in the result). If `typ` is
1793 /// not a type variable, just return it unmodified.
1794 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1796 ty::Infer(ty::TyVar(v)) => {
1797 // Not entirely obvious: if `typ` is a type variable,
1798 // it can be resolved to an int/float variable, which
1799 // can then be recursively resolved, hence the
1800 // recursion. Note though that we prevent type
1801 // variables from unifying to other type variables
1802 // directly (though they may be embedded
1803 // structurally), and we prevent cycles in any case,
1804 // so this recursion should always be of very limited
1807 // Note: if these two lines are combined into one we get
1808 // dynamic borrow errors on `self.inner`.
1809 let known = self.infcx.inner.borrow_mut().type_variables().probe(v).known();
1810 known.map_or(ty, |t| self.fold_ty(t))
1813 ty::Infer(ty::IntVar(v)) => self
1817 .int_unification_table()
1819 .map_or(ty, |v| v.to_type(self.infcx.tcx)),
1821 ty::Infer(ty::FloatVar(v)) => self
1825 .float_unification_table()
1827 .map_or(ty, |v| v.to_type(self.infcx.tcx)),
1833 fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
1834 if let ty::ConstKind::Infer(InferConst::Var(vid)) = ct.val() {
1838 .const_unification_table()
1849 impl<'tcx> TypeTrace<'tcx> {
1850 pub fn span(&self) -> Span {
1855 cause: &ObligationCause<'tcx>,
1856 a_is_expected: bool,
1859 ) -> TypeTrace<'tcx> {
1861 cause: cause.clone(),
1862 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
1867 cause: &ObligationCause<'tcx>,
1868 a_is_expected: bool,
1871 ) -> TypeTrace<'tcx> {
1873 cause: cause.clone(),
1874 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
1879 impl<'tcx> SubregionOrigin<'tcx> {
1880 pub fn span(&self) -> Span {
1882 Subtype(ref a) => a.span(),
1883 RelateObjectBound(a) => a,
1884 RelateParamBound(a, ..) => a,
1885 RelateRegionParamBound(a) => a,
1887 ReborrowUpvar(a, _) => a,
1888 DataBorrowed(_, a) => a,
1889 ReferenceOutlivesReferent(_, a) => a,
1890 CompareImplMethodObligation { span, .. } => span,
1891 CompareImplTypeObligation { span, .. } => span,
1892 CheckAssociatedTypeBounds { ref parent, .. } => parent.span(),
1896 pub fn from_obligation_cause<F>(cause: &traits::ObligationCause<'tcx>, default: F) -> Self
1898 F: FnOnce() -> Self,
1900 match *cause.code() {
1901 traits::ObligationCauseCode::ReferenceOutlivesReferent(ref_type) => {
1902 SubregionOrigin::ReferenceOutlivesReferent(ref_type, cause.span)
1905 traits::ObligationCauseCode::CompareImplMethodObligation {
1908 } => SubregionOrigin::CompareImplMethodObligation {
1914 traits::ObligationCauseCode::CompareImplTypeObligation {
1917 } => SubregionOrigin::CompareImplTypeObligation {
1923 traits::ObligationCauseCode::CheckAssociatedTypeBounds {
1926 } => SubregionOrigin::CheckAssociatedTypeBounds {
1929 parent: Box::new(default()),
1937 impl RegionVariableOrigin {
1938 pub fn span(&self) -> Span {
1945 | EarlyBoundRegion(a, ..)
1946 | LateBoundRegion(a, ..)
1947 | UpvarRegion(_, a) => a,
1948 Nll(..) => bug!("NLL variable used with `span`"),
1953 impl<'tcx> fmt::Debug for RegionObligation<'tcx> {
1954 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1957 "RegionObligation(sub_region={:?}, sup_type={:?})",
1958 self.sub_region, self.sup_type