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, TypeSuperFoldable};
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_span::symbol::Symbol;
35 use std::cell::{Cell, Ref, RefCell};
36 use std::collections::BTreeMap;
39 use self::combine::CombineFields;
40 use self::free_regions::RegionRelations;
41 use self::lexical_region_resolve::LexicalRegionResolutions;
42 use self::outlives::env::OutlivesEnvironment;
43 use self::region_constraints::{GenericKind, RegionConstraintData, VarInfos, VerifyBound};
44 use self::region_constraints::{
45 RegionConstraintCollector, RegionConstraintStorage, RegionSnapshot,
47 use self::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
53 pub mod error_reporting;
60 mod lexical_region_resolve;
66 pub mod region_constraints;
69 pub mod type_variable;
74 pub struct InferOk<'tcx, T> {
76 pub obligations: PredicateObligations<'tcx>,
78 pub type InferResult<'tcx, T> = Result<InferOk<'tcx, T>, TypeError<'tcx>>;
80 pub type Bound<T> = Option<T>;
81 pub type UnitResult<'tcx> = RelateResult<'tcx, ()>; // "unify result"
82 pub type FixupResult<'tcx, T> = Result<T, FixupError<'tcx>>; // "fixup result"
84 pub(crate) type UnificationTable<'a, 'tcx, T> = ut::UnificationTable<
85 ut::InPlace<T, &'a mut ut::UnificationStorage<T>, &'a mut InferCtxtUndoLogs<'tcx>>,
88 /// How we should handle region solving.
90 /// This is used so that the region values inferred by HIR region solving are
91 /// not exposed, and so that we can avoid doing work in HIR typeck that MIR
92 /// typeck will also do.
93 #[derive(Copy, Clone, Debug, Default)]
94 pub enum RegionckMode {
95 /// The default mode: report region errors, don't erase regions.
98 /// Erase the results of region after solving.
102 /// This type contains all the things within `InferCtxt` that sit within a
103 /// `RefCell` and are involved with taking/rolling back snapshots. Snapshot
104 /// operations are hot enough that we want only one call to `borrow_mut` per
105 /// call to `start_snapshot` and `rollback_to`.
107 pub struct InferCtxtInner<'tcx> {
108 /// Cache for projections. This cache is snapshotted along with the infcx.
110 /// Public so that `traits::project` can use it.
111 pub projection_cache: traits::ProjectionCacheStorage<'tcx>,
113 /// We instantiate `UnificationTable` with `bounds<Ty>` because the types
114 /// that might instantiate a general type variable have an order,
115 /// represented by its upper and lower bounds.
116 type_variable_storage: type_variable::TypeVariableStorage<'tcx>,
118 /// Map from const parameter variable to the kind of const it represents.
119 const_unification_storage: ut::UnificationTableStorage<ty::ConstVid<'tcx>>,
121 /// Map from integral variable to the kind of integer it represents.
122 int_unification_storage: ut::UnificationTableStorage<ty::IntVid>,
124 /// Map from floating variable to the kind of float it represents.
125 float_unification_storage: ut::UnificationTableStorage<ty::FloatVid>,
127 /// Tracks the set of region variables and the constraints between them.
128 /// This is initially `Some(_)` but when
129 /// `resolve_regions_and_report_errors` is invoked, this gets set to `None`
130 /// -- further attempts to perform unification, etc., may fail if new
131 /// region constraints would've been added.
132 region_constraint_storage: Option<RegionConstraintStorage<'tcx>>,
134 /// A set of constraints that regionck must validate. Each
135 /// constraint has the form `T:'a`, meaning "some type `T` must
136 /// outlive the lifetime 'a". These constraints derive from
137 /// instantiated type parameters. So if you had a struct defined
139 /// ```ignore (illustrative)
140 /// struct Foo<T:'static> { ... }
142 /// then in some expression `let x = Foo { ... }` it will
143 /// instantiate the type parameter `T` with a fresh type `$0`. At
144 /// the same time, it will record a region obligation of
145 /// `$0:'static`. This will get checked later by regionck. (We
146 /// can't generally check these things right away because we have
147 /// to wait until types are resolved.)
149 /// These are stored in a map keyed to the id of the innermost
150 /// enclosing fn body / static initializer expression. This is
151 /// because the location where the obligation was incurred can be
152 /// relevant with respect to which sublifetime assumptions are in
153 /// place. The reason that we store under the fn-id, and not
154 /// something more fine-grained, is so that it is easier for
155 /// regionck to be sure that it has found *all* the region
156 /// obligations (otherwise, it's easy to fail to walk to a
157 /// particular node-id).
159 /// Before running `resolve_regions_and_report_errors`, the creator
160 /// of the inference context is expected to invoke
161 /// [`InferCtxt::process_registered_region_obligations`]
162 /// for each body-id in this map, which will process the
163 /// obligations within. This is expected to be done 'late enough'
164 /// that all type inference variables have been bound and so forth.
165 region_obligations: Vec<(hir::HirId, RegionObligation<'tcx>)>,
167 undo_log: InferCtxtUndoLogs<'tcx>,
169 /// Caches for opaque type inference.
170 pub opaque_type_storage: OpaqueTypeStorage<'tcx>,
173 impl<'tcx> InferCtxtInner<'tcx> {
174 fn new() -> InferCtxtInner<'tcx> {
176 projection_cache: Default::default(),
177 type_variable_storage: type_variable::TypeVariableStorage::new(),
178 undo_log: InferCtxtUndoLogs::default(),
179 const_unification_storage: ut::UnificationTableStorage::new(),
180 int_unification_storage: ut::UnificationTableStorage::new(),
181 float_unification_storage: ut::UnificationTableStorage::new(),
182 region_constraint_storage: Some(RegionConstraintStorage::new()),
183 region_obligations: vec![],
184 opaque_type_storage: Default::default(),
189 pub fn region_obligations(&self) -> &[(hir::HirId, RegionObligation<'tcx>)] {
190 &self.region_obligations
194 pub fn projection_cache(&mut self) -> traits::ProjectionCache<'_, 'tcx> {
195 self.projection_cache.with_log(&mut self.undo_log)
199 fn type_variables(&mut self) -> type_variable::TypeVariableTable<'_, 'tcx> {
200 self.type_variable_storage.with_log(&mut self.undo_log)
204 pub fn opaque_types(&mut self) -> opaque_types::OpaqueTypeTable<'_, 'tcx> {
205 self.opaque_type_storage.with_log(&mut self.undo_log)
209 fn int_unification_table(
211 ) -> ut::UnificationTable<
214 &mut ut::UnificationStorage<ty::IntVid>,
215 &mut InferCtxtUndoLogs<'tcx>,
218 self.int_unification_storage.with_log(&mut self.undo_log)
222 fn float_unification_table(
224 ) -> ut::UnificationTable<
227 &mut ut::UnificationStorage<ty::FloatVid>,
228 &mut InferCtxtUndoLogs<'tcx>,
231 self.float_unification_storage.with_log(&mut self.undo_log)
235 fn const_unification_table(
237 ) -> ut::UnificationTable<
240 &mut ut::UnificationStorage<ty::ConstVid<'tcx>>,
241 &mut InferCtxtUndoLogs<'tcx>,
244 self.const_unification_storage.with_log(&mut self.undo_log)
248 pub fn unwrap_region_constraints(&mut self) -> RegionConstraintCollector<'_, 'tcx> {
249 self.region_constraint_storage
251 .expect("region constraints already solved")
252 .with_log(&mut self.undo_log)
256 pub struct InferCtxt<'a, 'tcx> {
257 pub tcx: TyCtxt<'tcx>,
259 /// The `DefId` of the item in whose context we are performing inference or typeck.
260 /// It is used to check whether an opaque type use is a defining use.
262 /// If it is `None`, we can't resolve opaque types here and need to bubble up
263 /// the obligation. This frequently happens for
264 /// short lived InferCtxt within queries. The opaque type obligations are forwarded
265 /// to the outside until the end up in an `InferCtxt` for typeck or borrowck.
266 pub defining_use_anchor: Option<LocalDefId>,
268 /// During type-checking/inference of a body, `in_progress_typeck_results`
269 /// contains a reference to the typeck results being built up, which are
270 /// used for reading closure kinds/signatures as they are inferred,
271 /// and for error reporting logic to read arbitrary node types.
272 pub in_progress_typeck_results: Option<&'a RefCell<ty::TypeckResults<'tcx>>>,
274 pub inner: RefCell<InferCtxtInner<'tcx>>,
276 /// If set, this flag causes us to skip the 'leak check' during
277 /// higher-ranked subtyping operations. This flag is a temporary one used
278 /// to manage the removal of the leak-check: for the time being, we still run the
279 /// leak-check, but we issue warnings. This flag can only be set to true
280 /// when entering a snapshot.
281 skip_leak_check: Cell<bool>,
283 /// Once region inference is done, the values for each variable.
284 lexical_region_resolutions: RefCell<Option<LexicalRegionResolutions<'tcx>>>,
286 /// Caches the results of trait selection. This cache is used
287 /// for things that have to do with the parameters in scope.
288 pub selection_cache: select::SelectionCache<'tcx>,
290 /// Caches the results of trait evaluation.
291 pub evaluation_cache: select::EvaluationCache<'tcx>,
293 /// the set of predicates on which errors have been reported, to
294 /// avoid reporting the same error twice.
295 pub reported_trait_errors: RefCell<FxHashMap<Span, Vec<ty::Predicate<'tcx>>>>,
297 pub reported_closure_mismatch: RefCell<FxHashSet<(Span, Option<Span>)>>,
299 /// When an error occurs, we want to avoid reporting "derived"
300 /// errors that are due to this original failure. Normally, we
301 /// handle this with the `err_count_on_creation` count, which
302 /// basically just tracks how many errors were reported when we
303 /// started type-checking a fn and checks to see if any new errors
304 /// have been reported since then. Not great, but it works.
306 /// However, when errors originated in other passes -- notably
307 /// resolve -- this heuristic breaks down. Therefore, we have this
308 /// auxiliary flag that one can set whenever one creates a
309 /// type-error that is due to an error in a prior pass.
311 /// Don't read this flag directly, call `is_tainted_by_errors()`
312 /// and `set_tainted_by_errors()`.
313 tainted_by_errors_flag: Cell<bool>,
315 /// Track how many errors were reported when this infcx is created.
316 /// If the number of errors increases, that's also a sign (line
317 /// `tainted_by_errors`) to avoid reporting certain kinds of errors.
318 // FIXME(matthewjasper) Merge into `tainted_by_errors_flag`
319 err_count_on_creation: usize,
321 /// This flag is true while there is an active snapshot.
322 in_snapshot: Cell<bool>,
324 /// What is the innermost universe we have created? Starts out as
325 /// `UniverseIndex::root()` but grows from there as we enter
326 /// universal quantifiers.
328 /// N.B., at present, we exclude the universal quantifiers on the
329 /// item we are type-checking, and just consider those names as
330 /// part of the root universe. So this would only get incremented
331 /// when we enter into a higher-ranked (`for<..>`) type or trait
333 universe: Cell<ty::UniverseIndex>,
336 /// See the `error_reporting` module for more details.
337 #[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable)]
338 pub enum ValuePairs<'tcx> {
339 Regions(ExpectedFound<ty::Region<'tcx>>),
340 Terms(ExpectedFound<ty::Term<'tcx>>),
341 TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>),
342 PolyTraitRefs(ExpectedFound<ty::PolyTraitRef<'tcx>>),
345 impl<'tcx> ValuePairs<'tcx> {
346 pub fn ty(&self) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
347 if let ValuePairs::Terms(ExpectedFound {
348 expected: ty::Term::Ty(expected),
349 found: ty::Term::Ty(found),
352 Some((*expected, *found))
359 /// The trace designates the path through inference that we took to
360 /// encounter an error or subtyping constraint.
362 /// See the `error_reporting` module for more details.
363 #[derive(Clone, Debug)]
364 pub struct TypeTrace<'tcx> {
365 pub cause: ObligationCause<'tcx>,
366 pub values: ValuePairs<'tcx>,
369 /// The origin of a `r1 <= r2` constraint.
371 /// See `error_reporting` module for more details
372 #[derive(Clone, Debug)]
373 pub enum SubregionOrigin<'tcx> {
374 /// Arose from a subtyping relation
375 Subtype(Box<TypeTrace<'tcx>>),
377 /// When casting `&'a T` to an `&'b Trait` object,
378 /// relating `'a` to `'b`
379 RelateObjectBound(Span),
381 /// Some type parameter was instantiated with the given type,
382 /// and that type must outlive some region.
383 RelateParamBound(Span, Ty<'tcx>, Option<Span>),
385 /// The given region parameter was instantiated with a region
386 /// that must outlive some other region.
387 RelateRegionParamBound(Span),
389 /// Creating a pointer `b` to contents of another reference
392 /// Creating a pointer `b` to contents of an upvar
393 ReborrowUpvar(Span, ty::UpvarId),
395 /// Data with type `Ty<'tcx>` was borrowed
396 DataBorrowed(Ty<'tcx>, Span),
398 /// (&'a &'b T) where a >= b
399 ReferenceOutlivesReferent(Ty<'tcx>, Span),
401 /// Comparing the signature and requirements of an impl method against
402 /// the containing trait.
403 CompareImplMethodObligation {
405 impl_item_def_id: LocalDefId,
406 trait_item_def_id: DefId,
409 /// Comparing the signature and requirements of an impl associated type
410 /// against the containing trait
411 CompareImplTypeObligation { span: Span, impl_item_def_id: LocalDefId, trait_item_def_id: DefId },
413 /// Checking that the bounds of a trait's associated type hold for a given impl
414 CheckAssociatedTypeBounds {
415 parent: Box<SubregionOrigin<'tcx>>,
416 impl_item_def_id: LocalDefId,
417 trait_item_def_id: DefId,
421 // `SubregionOrigin` is used a lot. Make sure it doesn't unintentionally get bigger.
422 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
423 static_assert_size!(SubregionOrigin<'_>, 32);
425 /// Times when we replace late-bound regions with variables:
426 #[derive(Clone, Copy, Debug)]
427 pub enum LateBoundRegionConversionTime {
428 /// when a fn is called
431 /// when two higher-ranked types are compared
434 /// when projecting an associated type
435 AssocTypeProjection(DefId),
438 /// Reasons to create a region inference variable
440 /// See `error_reporting` module for more details
441 #[derive(Copy, Clone, Debug)]
442 pub enum RegionVariableOrigin {
443 /// Region variables created for ill-categorized reasons,
444 /// mostly indicates places in need of refactoring
447 /// Regions created by a `&P` or `[...]` pattern
450 /// Regions created by `&` operator
453 /// Regions created as part of an autoref of a method receiver
456 /// Regions created as part of an automatic coercion
459 /// Region variables created as the values for early-bound regions
460 EarlyBoundRegion(Span, Symbol),
462 /// Region variables created for bound regions
463 /// in a function or method that is called
464 LateBoundRegion(Span, ty::BoundRegionKind, LateBoundRegionConversionTime),
466 UpvarRegion(ty::UpvarId, Span),
468 /// This origin is used for the inference variables that we create
469 /// during NLL region processing.
470 Nll(NllRegionVariableOrigin),
473 #[derive(Copy, Clone, Debug)]
474 pub enum NllRegionVariableOrigin {
475 /// During NLL region processing, we create variables for free
476 /// regions that we encounter in the function signature and
477 /// elsewhere. This origin indices we've got one of those.
480 /// "Universal" instantiation of a higher-ranked region (e.g.,
481 /// from a `for<'a> T` binder). Meant to represent "any region".
482 Placeholder(ty::PlaceholderRegion),
484 /// The variable we create to represent `'empty(U0)`.
488 /// If this is true, then this variable was created to represent a lifetime
489 /// bound in a `for` binder. For example, it might have been created to
490 /// represent the lifetime `'a` in a type like `for<'a> fn(&'a u32)`.
491 /// Such variables are created when we are trying to figure out if there
492 /// is any valid instantiation of `'a` that could fit into some scenario.
494 /// This is used to inform error reporting: in the case that we are trying to
495 /// determine whether there is any valid instantiation of a `'a` variable that meets
496 /// some constraint C, we want to blame the "source" of that `for` type,
497 /// rather than blaming the source of the constraint C.
502 // FIXME(eddyb) investigate overlap between this and `TyOrConstInferVar`.
503 #[derive(Copy, Clone, Debug)]
504 pub enum FixupError<'tcx> {
505 UnresolvedIntTy(IntVid),
506 UnresolvedFloatTy(FloatVid),
508 UnresolvedConst(ConstVid<'tcx>),
511 /// See the `region_obligations` field for more information.
513 pub struct RegionObligation<'tcx> {
514 pub sub_region: ty::Region<'tcx>,
515 pub sup_type: Ty<'tcx>,
516 pub origin: SubregionOrigin<'tcx>,
519 impl<'tcx> fmt::Display for FixupError<'tcx> {
520 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
521 use self::FixupError::*;
524 UnresolvedIntTy(_) => write!(
526 "cannot determine the type of this integer; \
527 add a suffix to specify the type explicitly"
529 UnresolvedFloatTy(_) => write!(
531 "cannot determine the type of this number; \
532 add a suffix to specify the type explicitly"
534 UnresolvedTy(_) => write!(f, "unconstrained type"),
535 UnresolvedConst(_) => write!(f, "unconstrained const value"),
540 /// A temporary returned by `tcx.infer_ctxt()`. This is necessary
541 /// for multiple `InferCtxt` to share the same `in_progress_typeck_results`
542 /// without using `Rc` or something similar.
543 pub struct InferCtxtBuilder<'tcx> {
545 fresh_typeck_results: Option<RefCell<ty::TypeckResults<'tcx>>>,
546 defining_use_anchor: Option<LocalDefId>,
549 pub trait TyCtxtInferExt<'tcx> {
550 fn infer_ctxt(self) -> InferCtxtBuilder<'tcx>;
553 impl<'tcx> TyCtxtInferExt<'tcx> for TyCtxt<'tcx> {
554 fn infer_ctxt(self) -> InferCtxtBuilder<'tcx> {
555 InferCtxtBuilder { tcx: self, defining_use_anchor: None, fresh_typeck_results: None }
559 impl<'tcx> InferCtxtBuilder<'tcx> {
560 /// Used only by `rustc_typeck` during body type-checking/inference,
561 /// will initialize `in_progress_typeck_results` with fresh `TypeckResults`.
562 /// Will also change the scope for opaque type defining use checks to the given owner.
563 pub fn with_fresh_in_progress_typeck_results(mut self, table_owner: LocalDefId) -> Self {
564 self.fresh_typeck_results = Some(RefCell::new(ty::TypeckResults::new(table_owner)));
565 self.with_opaque_type_inference(table_owner)
568 /// Whenever the `InferCtxt` should be able to handle defining uses of opaque types,
569 /// you need to call this function. Otherwise the opaque type will be treated opaquely.
571 /// It is only meant to be called in two places, for typeck
572 /// (via `with_fresh_in_progress_typeck_results`) and for the inference context used
574 pub fn with_opaque_type_inference(mut self, defining_use_anchor: LocalDefId) -> Self {
575 self.defining_use_anchor = Some(defining_use_anchor);
579 /// Given a canonical value `C` as a starting point, create an
580 /// inference context that contains each of the bound values
581 /// within instantiated as a fresh variable. The `f` closure is
582 /// invoked with the new infcx, along with the instantiated value
583 /// `V` and a substitution `S`. This substitution `S` maps from
584 /// the bound values in `C` to their instantiated values in `V`
585 /// (in other words, `S(C) = V`).
586 pub fn enter_with_canonical<T, R>(
589 canonical: &Canonical<'tcx, T>,
590 f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>, T, CanonicalVarValues<'tcx>) -> R,
593 T: TypeFoldable<'tcx>,
597 infcx.instantiate_canonical_with_fresh_inference_vars(span, canonical);
598 f(infcx, value, subst)
602 pub fn enter<R>(&mut self, f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>) -> R) -> R {
603 let InferCtxtBuilder { tcx, defining_use_anchor, ref fresh_typeck_results } = *self;
604 let in_progress_typeck_results = fresh_typeck_results.as_ref();
608 in_progress_typeck_results,
609 inner: RefCell::new(InferCtxtInner::new()),
610 lexical_region_resolutions: RefCell::new(None),
611 selection_cache: Default::default(),
612 evaluation_cache: Default::default(),
613 reported_trait_errors: Default::default(),
614 reported_closure_mismatch: Default::default(),
615 tainted_by_errors_flag: Cell::new(false),
616 err_count_on_creation: tcx.sess.err_count(),
617 in_snapshot: Cell::new(false),
618 skip_leak_check: Cell::new(false),
619 universe: Cell::new(ty::UniverseIndex::ROOT),
624 impl<'tcx, T> InferOk<'tcx, T> {
625 pub fn unit(self) -> InferOk<'tcx, ()> {
626 InferOk { value: (), obligations: self.obligations }
629 /// Extracts `value`, registering any obligations into `fulfill_cx`.
630 pub fn into_value_registering_obligations(
632 infcx: &InferCtxt<'_, 'tcx>,
633 fulfill_cx: &mut dyn TraitEngine<'tcx>,
635 let InferOk { value, obligations } = self;
636 for obligation in obligations {
637 fulfill_cx.register_predicate_obligation(infcx, obligation);
643 impl<'tcx> InferOk<'tcx, ()> {
644 pub fn into_obligations(self) -> PredicateObligations<'tcx> {
649 #[must_use = "once you start a snapshot, you should always consume it"]
650 pub struct CombinedSnapshot<'a, 'tcx> {
651 undo_snapshot: Snapshot<'tcx>,
652 region_constraints_snapshot: RegionSnapshot,
653 universe: ty::UniverseIndex,
654 was_in_snapshot: bool,
655 _in_progress_typeck_results: Option<Ref<'a, ty::TypeckResults<'tcx>>>,
658 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
659 /// calls `tcx.try_unify_abstract_consts` after
660 /// canonicalizing the consts.
661 #[instrument(skip(self), level = "debug")]
662 pub fn try_unify_abstract_consts(
664 a: ty::Unevaluated<'tcx, ()>,
665 b: ty::Unevaluated<'tcx, ()>,
666 param_env: ty::ParamEnv<'tcx>,
668 // Reject any attempt to unify two unevaluated constants that contain inference
669 // variables, since inference variables in queries lead to ICEs.
670 if a.substs.has_infer_types_or_consts()
671 || b.substs.has_infer_types_or_consts()
672 || param_env.has_infer_types_or_consts()
674 debug!("a or b or param_env contain infer vars in its substs -> cannot unify");
678 let param_env_and = param_env.and((a, b));
679 let erased = self.tcx.erase_regions(param_env_and);
680 debug!("after erase_regions: {:?}", erased);
682 self.tcx.try_unify_abstract_consts(erased)
685 pub fn is_in_snapshot(&self) -> bool {
686 self.in_snapshot.get()
689 pub fn freshen<T: TypeFoldable<'tcx>>(&self, t: T) -> T {
690 t.fold_with(&mut self.freshener())
693 /// Returns the origin of the type variable identified by `vid`, or `None`
694 /// if this is not a type variable.
696 /// No attempt is made to resolve `ty`.
697 pub fn type_var_origin(&'a self, ty: Ty<'tcx>) -> Option<TypeVariableOrigin> {
699 ty::Infer(ty::TyVar(vid)) => {
700 Some(*self.inner.borrow_mut().type_variables().var_origin(vid))
706 pub fn freshener<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
707 freshen::TypeFreshener::new(self, false)
710 /// Like `freshener`, but does not replace `'static` regions.
711 pub fn freshener_keep_static<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
712 freshen::TypeFreshener::new(self, true)
715 pub fn unsolved_variables(&self) -> Vec<Ty<'tcx>> {
716 let mut inner = self.inner.borrow_mut();
717 let mut vars: Vec<Ty<'_>> = inner
719 .unsolved_variables()
721 .map(|t| self.tcx.mk_ty_var(t))
724 (0..inner.int_unification_table().len())
725 .map(|i| ty::IntVid { index: i as u32 })
726 .filter(|&vid| inner.int_unification_table().probe_value(vid).is_none())
727 .map(|v| self.tcx.mk_int_var(v)),
730 (0..inner.float_unification_table().len())
731 .map(|i| ty::FloatVid { index: i as u32 })
732 .filter(|&vid| inner.float_unification_table().probe_value(vid).is_none())
733 .map(|v| self.tcx.mk_float_var(v)),
740 trace: TypeTrace<'tcx>,
741 param_env: ty::ParamEnv<'tcx>,
742 define_opaque_types: bool,
743 ) -> CombineFields<'a, 'tcx> {
749 obligations: PredicateObligations::new(),
754 /// Clear the "currently in a snapshot" flag, invoke the closure,
755 /// then restore the flag to its original value. This flag is a
756 /// debugging measure designed to detect cases where we start a
757 /// snapshot, create type variables, and register obligations
758 /// which may involve those type variables in the fulfillment cx,
759 /// potentially leaving "dangling type variables" behind.
760 /// In such cases, an assertion will fail when attempting to
761 /// register obligations, within a snapshot. Very useful, much
762 /// better than grovelling through megabytes of `RUSTC_LOG` output.
764 /// HOWEVER, in some cases the flag is unhelpful. In particular, we
765 /// sometimes create a "mini-fulfilment-cx" in which we enroll
766 /// obligations. As long as this fulfillment cx is fully drained
767 /// before we return, this is not a problem, as there won't be any
768 /// escaping obligations in the main cx. In those cases, you can
769 /// use this function.
770 pub fn save_and_restore_in_snapshot_flag<F, R>(&self, func: F) -> R
772 F: FnOnce(&Self) -> R,
774 let flag = self.in_snapshot.replace(false);
775 let result = func(self);
776 self.in_snapshot.set(flag);
780 fn start_snapshot(&self) -> CombinedSnapshot<'a, 'tcx> {
781 debug!("start_snapshot()");
783 let in_snapshot = self.in_snapshot.replace(true);
785 let mut inner = self.inner.borrow_mut();
788 undo_snapshot: inner.undo_log.start_snapshot(),
789 region_constraints_snapshot: inner.unwrap_region_constraints().start_snapshot(),
790 universe: self.universe(),
791 was_in_snapshot: in_snapshot,
792 // Borrow typeck results "in progress" (i.e., during typeck)
793 // to ban writes from within a snapshot to them.
794 _in_progress_typeck_results: self
795 .in_progress_typeck_results
796 .map(|typeck_results| typeck_results.borrow()),
800 #[instrument(skip(self, snapshot), level = "debug")]
801 fn rollback_to(&self, cause: &str, snapshot: CombinedSnapshot<'a, 'tcx>) {
802 let CombinedSnapshot {
804 region_constraints_snapshot,
807 _in_progress_typeck_results,
810 self.in_snapshot.set(was_in_snapshot);
811 self.universe.set(universe);
813 let mut inner = self.inner.borrow_mut();
814 inner.rollback_to(undo_snapshot);
815 inner.unwrap_region_constraints().rollback_to(region_constraints_snapshot);
818 #[instrument(skip(self, snapshot), level = "debug")]
819 fn commit_from(&self, snapshot: CombinedSnapshot<'a, 'tcx>) {
820 let CombinedSnapshot {
822 region_constraints_snapshot: _,
825 _in_progress_typeck_results,
828 self.in_snapshot.set(was_in_snapshot);
830 self.inner.borrow_mut().commit(undo_snapshot);
833 /// Executes `f` and commit the bindings.
834 #[instrument(skip(self, f), level = "debug")]
835 pub fn commit_unconditionally<R, F>(&self, f: F) -> R
837 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
839 let snapshot = self.start_snapshot();
840 let r = f(&snapshot);
841 self.commit_from(snapshot);
845 /// Execute `f` and commit the bindings if closure `f` returns `Ok(_)`.
846 #[instrument(skip(self, f), level = "debug")]
847 pub fn commit_if_ok<T, E, F>(&self, f: F) -> Result<T, E>
849 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> Result<T, E>,
851 let snapshot = self.start_snapshot();
852 let r = f(&snapshot);
853 debug!("commit_if_ok() -- r.is_ok() = {}", r.is_ok());
856 self.commit_from(snapshot);
859 self.rollback_to("commit_if_ok -- error", snapshot);
865 /// Execute `f` then unroll any bindings it creates.
866 #[instrument(skip(self, f), level = "debug")]
867 pub fn probe<R, F>(&self, f: F) -> R
869 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
871 let snapshot = self.start_snapshot();
872 let r = f(&snapshot);
873 self.rollback_to("probe", snapshot);
877 /// If `should_skip` is true, then execute `f` then unroll any bindings it creates.
878 #[instrument(skip(self, f), level = "debug")]
879 pub fn probe_maybe_skip_leak_check<R, F>(&self, should_skip: bool, f: F) -> R
881 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
883 let snapshot = self.start_snapshot();
884 let was_skip_leak_check = self.skip_leak_check.get();
886 self.skip_leak_check.set(true);
888 let r = f(&snapshot);
889 self.rollback_to("probe", snapshot);
890 self.skip_leak_check.set(was_skip_leak_check);
894 /// Scan the constraints produced since `snapshot` began and returns:
896 /// - `None` -- if none of them involve "region outlives" constraints
897 /// - `Some(true)` -- if there are `'a: 'b` constraints where `'a` or `'b` is a placeholder
898 /// - `Some(false)` -- if there are `'a: 'b` constraints but none involve placeholders
899 pub fn region_constraints_added_in_snapshot(
901 snapshot: &CombinedSnapshot<'a, 'tcx>,
905 .unwrap_region_constraints()
906 .region_constraints_added_in_snapshot(&snapshot.undo_snapshot)
909 pub fn add_given(&self, sub: ty::Region<'tcx>, sup: ty::RegionVid) {
910 self.inner.borrow_mut().unwrap_region_constraints().add_given(sub, sup);
913 pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
915 T: at::ToTrace<'tcx>,
917 let origin = &ObligationCause::dummy();
919 self.at(origin, param_env).sub(a, b).map(|InferOk { obligations: _, .. }| {
920 // Ignore obligations, since we are unrolling
921 // everything anyway.
926 pub fn can_eq<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
928 T: at::ToTrace<'tcx>,
930 let origin = &ObligationCause::dummy();
932 self.at(origin, param_env).eq(a, b).map(|InferOk { obligations: _, .. }| {
933 // Ignore obligations, since we are unrolling
934 // everything anyway.
939 #[instrument(skip(self), level = "debug")]
942 origin: SubregionOrigin<'tcx>,
946 self.inner.borrow_mut().unwrap_region_constraints().make_subregion(origin, a, b);
949 /// Require that the region `r` be equal to one of the regions in
950 /// the set `regions`.
951 #[instrument(skip(self), level = "debug")]
952 pub fn member_constraint(
954 opaque_type_def_id: DefId,
955 definition_span: Span,
957 region: ty::Region<'tcx>,
958 in_regions: &Lrc<Vec<ty::Region<'tcx>>>,
960 self.inner.borrow_mut().unwrap_region_constraints().member_constraint(
969 /// Processes a `Coerce` predicate from the fulfillment context.
970 /// This is NOT the preferred way to handle coercion, which is to
971 /// invoke `FnCtxt::coerce` or a similar method (see `coercion.rs`).
973 /// This method here is actually a fallback that winds up being
974 /// invoked when `FnCtxt::coerce` encounters unresolved type variables
975 /// and records a coercion predicate. Presently, this method is equivalent
976 /// to `subtype_predicate` -- that is, "coercing" `a` to `b` winds up
977 /// actually requiring `a <: b`. This is of course a valid coercion,
978 /// but it's not as flexible as `FnCtxt::coerce` would be.
980 /// (We may refactor this in the future, but there are a number of
981 /// practical obstacles. Among other things, `FnCtxt::coerce` presently
982 /// records adjustments that are required on the HIR in order to perform
983 /// the coercion, and we don't currently have a way to manage that.)
984 pub fn coerce_predicate(
986 cause: &ObligationCause<'tcx>,
987 param_env: ty::ParamEnv<'tcx>,
988 predicate: ty::PolyCoercePredicate<'tcx>,
989 ) -> Option<InferResult<'tcx, ()>> {
990 let subtype_predicate = predicate.map_bound(|p| ty::SubtypePredicate {
991 a_is_expected: false, // when coercing from `a` to `b`, `b` is expected
995 self.subtype_predicate(cause, param_env, subtype_predicate)
998 pub fn subtype_predicate(
1000 cause: &ObligationCause<'tcx>,
1001 param_env: ty::ParamEnv<'tcx>,
1002 predicate: ty::PolySubtypePredicate<'tcx>,
1003 ) -> Option<InferResult<'tcx, ()>> {
1004 // Check for two unresolved inference variables, in which case we can
1005 // make no progress. This is partly a micro-optimization, but it's
1006 // also an opportunity to "sub-unify" the variables. This isn't
1007 // *necessary* to prevent cycles, because they would eventually be sub-unified
1008 // anyhow during generalization, but it helps with diagnostics (we can detect
1009 // earlier that they are sub-unified).
1011 // Note that we can just skip the binders here because
1012 // type variables can't (at present, at
1013 // least) capture any of the things bound by this binder.
1015 // Note that this sub here is not just for diagnostics - it has semantic
1017 let r_a = self.shallow_resolve(predicate.skip_binder().a);
1018 let r_b = self.shallow_resolve(predicate.skip_binder().b);
1019 match (r_a.kind(), r_b.kind()) {
1020 (&ty::Infer(ty::TyVar(a_vid)), &ty::Infer(ty::TyVar(b_vid))) => {
1021 self.inner.borrow_mut().type_variables().sub(a_vid, b_vid);
1027 Some(self.commit_if_ok(|_snapshot| {
1028 let ty::SubtypePredicate { a_is_expected, a, b } =
1029 self.replace_bound_vars_with_placeholders(predicate);
1031 let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?;
1037 pub fn region_outlives_predicate(
1039 cause: &traits::ObligationCause<'tcx>,
1040 predicate: ty::PolyRegionOutlivesPredicate<'tcx>,
1041 ) -> UnitResult<'tcx> {
1042 self.commit_if_ok(|_snapshot| {
1043 let ty::OutlivesPredicate(r_a, r_b) =
1044 self.replace_bound_vars_with_placeholders(predicate);
1045 let origin = SubregionOrigin::from_obligation_cause(cause, || {
1046 RelateRegionParamBound(cause.span)
1048 self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
1053 /// Number of type variables created so far.
1054 pub fn num_ty_vars(&self) -> usize {
1055 self.inner.borrow_mut().type_variables().num_vars()
1058 pub fn next_ty_var_id(&self, origin: TypeVariableOrigin) -> TyVid {
1059 self.inner.borrow_mut().type_variables().new_var(self.universe(), origin)
1062 pub fn next_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
1063 self.tcx.mk_ty_var(self.next_ty_var_id(origin))
1066 pub fn next_ty_var_id_in_universe(
1068 origin: TypeVariableOrigin,
1069 universe: ty::UniverseIndex,
1071 self.inner.borrow_mut().type_variables().new_var(universe, origin)
1074 pub fn next_ty_var_in_universe(
1076 origin: TypeVariableOrigin,
1077 universe: ty::UniverseIndex,
1079 let vid = self.next_ty_var_id_in_universe(origin, universe);
1080 self.tcx.mk_ty_var(vid)
1083 pub fn next_const_var(&self, ty: Ty<'tcx>, origin: ConstVariableOrigin) -> ty::Const<'tcx> {
1084 self.tcx.mk_const_var(self.next_const_var_id(origin), ty)
1087 pub fn next_const_var_in_universe(
1090 origin: ConstVariableOrigin,
1091 universe: ty::UniverseIndex,
1092 ) -> ty::Const<'tcx> {
1096 .const_unification_table()
1097 .new_key(ConstVarValue { origin, val: ConstVariableValue::Unknown { universe } });
1098 self.tcx.mk_const_var(vid, ty)
1101 pub fn next_const_var_id(&self, origin: ConstVariableOrigin) -> ConstVid<'tcx> {
1102 self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue {
1104 val: ConstVariableValue::Unknown { universe: self.universe() },
1108 fn next_int_var_id(&self) -> IntVid {
1109 self.inner.borrow_mut().int_unification_table().new_key(None)
1112 pub fn next_int_var(&self) -> Ty<'tcx> {
1113 self.tcx.mk_int_var(self.next_int_var_id())
1116 fn next_float_var_id(&self) -> FloatVid {
1117 self.inner.borrow_mut().float_unification_table().new_key(None)
1120 pub fn next_float_var(&self) -> Ty<'tcx> {
1121 self.tcx.mk_float_var(self.next_float_var_id())
1124 /// Creates a fresh region variable with the next available index.
1125 /// The variable will be created in the maximum universe created
1126 /// thus far, allowing it to name any region created thus far.
1127 pub fn next_region_var(&self, origin: RegionVariableOrigin) -> ty::Region<'tcx> {
1128 self.next_region_var_in_universe(origin, self.universe())
1131 /// Creates a fresh region variable with the next available index
1132 /// in the given universe; typically, you can use
1133 /// `next_region_var` and just use the maximal universe.
1134 pub fn next_region_var_in_universe(
1136 origin: RegionVariableOrigin,
1137 universe: ty::UniverseIndex,
1138 ) -> ty::Region<'tcx> {
1140 self.inner.borrow_mut().unwrap_region_constraints().new_region_var(universe, origin);
1141 self.tcx.mk_region(ty::ReVar(region_var))
1144 /// Return the universe that the region `r` was created in. For
1145 /// most regions (e.g., `'static`, named regions from the user,
1146 /// etc) this is the root universe U0. For inference variables or
1147 /// placeholders, however, it will return the universe which which
1148 /// they are associated.
1149 pub fn universe_of_region(&self, r: ty::Region<'tcx>) -> ty::UniverseIndex {
1150 self.inner.borrow_mut().unwrap_region_constraints().universe(r)
1153 /// Number of region variables created so far.
1154 pub fn num_region_vars(&self) -> usize {
1155 self.inner.borrow_mut().unwrap_region_constraints().num_region_vars()
1158 /// Just a convenient wrapper of `next_region_var` for using during NLL.
1159 pub fn next_nll_region_var(&self, origin: NllRegionVariableOrigin) -> ty::Region<'tcx> {
1160 self.next_region_var(RegionVariableOrigin::Nll(origin))
1163 /// Just a convenient wrapper of `next_region_var` for using during NLL.
1164 pub fn next_nll_region_var_in_universe(
1166 origin: NllRegionVariableOrigin,
1167 universe: ty::UniverseIndex,
1168 ) -> ty::Region<'tcx> {
1169 self.next_region_var_in_universe(RegionVariableOrigin::Nll(origin), universe)
1172 pub fn var_for_def(&self, span: Span, param: &ty::GenericParamDef) -> GenericArg<'tcx> {
1174 GenericParamDefKind::Lifetime => {
1175 // Create a region inference variable for the given
1176 // region parameter definition.
1177 self.next_region_var(EarlyBoundRegion(span, param.name)).into()
1179 GenericParamDefKind::Type { .. } => {
1180 // Create a type inference variable for the given
1181 // type parameter definition. The substitutions are
1182 // for actual parameters that may be referred to by
1183 // the default of this type parameter, if it exists.
1184 // e.g., `struct Foo<A, B, C = (A, B)>(...);` when
1185 // used in a path such as `Foo::<T, U>::new()` will
1186 // use an inference variable for `C` with `[T, U]`
1187 // as the substitutions for the default, `(T, U)`.
1188 let ty_var_id = self.inner.borrow_mut().type_variables().new_var(
1190 TypeVariableOrigin {
1191 kind: TypeVariableOriginKind::TypeParameterDefinition(
1199 self.tcx.mk_ty_var(ty_var_id).into()
1201 GenericParamDefKind::Const { .. } => {
1202 let origin = ConstVariableOrigin {
1203 kind: ConstVariableOriginKind::ConstParameterDefinition(
1210 self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue {
1212 val: ConstVariableValue::Unknown { universe: self.universe() },
1214 self.tcx.mk_const_var(const_var_id, self.tcx.type_of(param.def_id)).into()
1219 /// Given a set of generics defined on a type or impl, returns a substitution mapping each
1220 /// type/region parameter to a fresh inference variable.
1221 pub fn fresh_substs_for_item(&self, span: Span, def_id: DefId) -> SubstsRef<'tcx> {
1222 InternalSubsts::for_item(self.tcx, def_id, |param, _| self.var_for_def(span, param))
1225 /// Returns `true` if errors have been reported since this infcx was
1226 /// created. This is sometimes used as a heuristic to skip
1227 /// reporting errors that often occur as a result of earlier
1228 /// errors, but where it's hard to be 100% sure (e.g., unresolved
1229 /// inference variables, regionck errors).
1230 pub fn is_tainted_by_errors(&self) -> bool {
1232 "is_tainted_by_errors(err_count={}, err_count_on_creation={}, \
1233 tainted_by_errors_flag={})",
1234 self.tcx.sess.err_count(),
1235 self.err_count_on_creation,
1236 self.tainted_by_errors_flag.get()
1239 if self.tcx.sess.err_count() > self.err_count_on_creation {
1240 return true; // errors reported since this infcx was made
1242 self.tainted_by_errors_flag.get()
1245 /// Set the "tainted by errors" flag to true. We call this when we
1246 /// observe an error from a prior pass.
1247 pub fn set_tainted_by_errors(&self) {
1248 debug!("set_tainted_by_errors()");
1249 self.tainted_by_errors_flag.set(true)
1252 /// Process the region constraints and return any any errors that
1253 /// result. After this, no more unification operations should be
1254 /// done -- or the compiler will panic -- but it is legal to use
1255 /// `resolve_vars_if_possible` as well as `fully_resolve`.
1256 pub fn resolve_regions(
1258 region_context: DefId,
1259 outlives_env: &OutlivesEnvironment<'tcx>,
1261 ) -> Vec<RegionResolutionError<'tcx>> {
1262 let (var_infos, data) = {
1263 let mut inner = self.inner.borrow_mut();
1264 let inner = &mut *inner;
1266 self.is_tainted_by_errors() || inner.region_obligations.is_empty(),
1267 "region_obligations not empty: {:#?}",
1268 inner.region_obligations
1271 .region_constraint_storage
1273 .expect("regions already resolved")
1274 .with_log(&mut inner.undo_log)
1275 .into_infos_and_data()
1279 &RegionRelations::new(self.tcx, region_context, outlives_env.free_region_map());
1281 let (lexical_region_resolutions, errors) =
1282 lexical_region_resolve::resolve(region_rels, var_infos, data, mode);
1284 let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions));
1285 assert!(old_value.is_none());
1290 /// Process the region constraints and report any errors that
1291 /// result. After this, no more unification operations should be
1292 /// done -- or the compiler will panic -- but it is legal to use
1293 /// `resolve_vars_if_possible` as well as `fully_resolve`.
1294 pub fn resolve_regions_and_report_errors(
1296 region_context: DefId,
1297 outlives_env: &OutlivesEnvironment<'tcx>,
1300 let errors = self.resolve_regions(region_context, outlives_env, mode);
1302 if !self.is_tainted_by_errors() {
1303 // As a heuristic, just skip reporting region errors
1304 // altogether if other errors have been reported while
1305 // this infcx was in use. This is totally hokey but
1306 // otherwise we have a hard time separating legit region
1307 // errors from silly ones.
1308 self.report_region_errors(&errors);
1312 /// Obtains (and clears) the current set of region
1313 /// constraints. The inference context is still usable: further
1314 /// unifications will simply add new constraints.
1316 /// This method is not meant to be used with normal lexical region
1317 /// resolution. Rather, it is used in the NLL mode as a kind of
1318 /// interim hack: basically we run normal type-check and generate
1319 /// region constraints as normal, but then we take them and
1320 /// translate them into the form that the NLL solver
1321 /// understands. See the NLL module for mode details.
1322 pub fn take_and_reset_region_constraints(&self) -> RegionConstraintData<'tcx> {
1324 self.inner.borrow().region_obligations.is_empty(),
1325 "region_obligations not empty: {:#?}",
1326 self.inner.borrow().region_obligations
1329 self.inner.borrow_mut().unwrap_region_constraints().take_and_reset_data()
1332 /// Gives temporary access to the region constraint data.
1333 pub fn with_region_constraints<R>(
1335 op: impl FnOnce(&RegionConstraintData<'tcx>) -> R,
1337 let mut inner = self.inner.borrow_mut();
1338 op(inner.unwrap_region_constraints().data())
1341 pub fn region_var_origin(&self, vid: ty::RegionVid) -> RegionVariableOrigin {
1342 let mut inner = self.inner.borrow_mut();
1343 let inner = &mut *inner;
1345 .region_constraint_storage
1347 .expect("regions already resolved")
1348 .with_log(&mut inner.undo_log)
1352 /// Takes ownership of the list of variable regions. This implies
1353 /// that all the region constraints have already been taken, and
1354 /// hence that `resolve_regions_and_report_errors` can never be
1355 /// called. This is used only during NLL processing to "hand off" ownership
1356 /// of the set of region variables into the NLL region context.
1357 pub fn take_region_var_origins(&self) -> VarInfos {
1358 let mut inner = self.inner.borrow_mut();
1359 let (var_infos, data) = inner
1360 .region_constraint_storage
1362 .expect("regions already resolved")
1363 .with_log(&mut inner.undo_log)
1364 .into_infos_and_data();
1365 assert!(data.is_empty());
1369 pub fn ty_to_string(&self, t: Ty<'tcx>) -> String {
1370 self.resolve_vars_if_possible(t).to_string()
1373 /// If `TyVar(vid)` resolves to a type, return that type. Else, return the
1374 /// universe index of `TyVar(vid)`.
1375 pub fn probe_ty_var(&self, vid: TyVid) -> Result<Ty<'tcx>, ty::UniverseIndex> {
1376 use self::type_variable::TypeVariableValue;
1378 match self.inner.borrow_mut().type_variables().probe(vid) {
1379 TypeVariableValue::Known { value } => Ok(value),
1380 TypeVariableValue::Unknown { universe } => Err(universe),
1384 /// Resolve any type variables found in `value` -- but only one
1385 /// level. So, if the variable `?X` is bound to some type
1386 /// `Foo<?Y>`, then this would return `Foo<?Y>` (but `?Y` may
1387 /// itself be bound to a type).
1389 /// Useful when you only need to inspect the outermost level of
1390 /// the type and don't care about nested types (or perhaps you
1391 /// will be resolving them as well, e.g. in a loop).
1392 pub fn shallow_resolve<T>(&self, value: T) -> T
1394 T: TypeFoldable<'tcx>,
1396 value.fold_with(&mut ShallowResolver { infcx: self })
1399 pub fn root_var(&self, var: ty::TyVid) -> ty::TyVid {
1400 self.inner.borrow_mut().type_variables().root_var(var)
1403 /// Where possible, replaces type/const variables in
1404 /// `value` with their final value. Note that region variables
1405 /// are unaffected. If a type/const variable has not been unified, it
1406 /// is left as is. This is an idempotent operation that does
1407 /// not affect inference state in any way and so you can do it
1409 pub fn resolve_vars_if_possible<T>(&self, value: T) -> T
1411 T: TypeFoldable<'tcx>,
1413 if !value.needs_infer() {
1414 return value; // Avoid duplicated subst-folding.
1416 let mut r = resolve::OpportunisticVarResolver::new(self);
1417 value.fold_with(&mut r)
1420 pub fn resolve_numeric_literals_with_default<T>(&self, value: T) -> T
1422 T: TypeFoldable<'tcx>,
1424 if !value.needs_infer() {
1425 return value; // Avoid duplicated subst-folding.
1427 let mut r = InferenceLiteralEraser { tcx: self.tcx };
1428 value.fold_with(&mut r)
1431 /// Returns the first unresolved variable contained in `T`. In the
1432 /// process of visiting `T`, this will resolve (where possible)
1433 /// type variables in `T`, but it never constructs the final,
1434 /// resolved type, so it's more efficient than
1435 /// `resolve_vars_if_possible()`.
1436 pub fn unresolved_type_vars<T>(&self, value: &T) -> Option<(Ty<'tcx>, Option<Span>)>
1438 T: TypeFoldable<'tcx>,
1440 value.visit_with(&mut resolve::UnresolvedTypeFinder::new(self)).break_value()
1443 pub fn probe_const_var(
1445 vid: ty::ConstVid<'tcx>,
1446 ) -> Result<ty::Const<'tcx>, ty::UniverseIndex> {
1447 match self.inner.borrow_mut().const_unification_table().probe_value(vid).val {
1448 ConstVariableValue::Known { value } => Ok(value),
1449 ConstVariableValue::Unknown { universe } => Err(universe),
1453 pub fn fully_resolve<T: TypeFoldable<'tcx>>(&self, value: T) -> FixupResult<'tcx, T> {
1455 * Attempts to resolve all type/region/const variables in
1456 * `value`. Region inference must have been run already (e.g.,
1457 * by calling `resolve_regions_and_report_errors`). If some
1458 * variable was never unified, an `Err` results.
1460 * This method is idempotent, but it not typically not invoked
1461 * except during the writeback phase.
1464 resolve::fully_resolve(self, value)
1467 // [Note-Type-error-reporting]
1468 // An invariant is that anytime the expected or actual type is Error (the special
1469 // error type, meaning that an error occurred when typechecking this expression),
1470 // this is a derived error. The error cascaded from another error (that was already
1471 // reported), so it's not useful to display it to the user.
1472 // The following methods implement this logic.
1473 // They check if either the actual or expected type is Error, and don't print the error
1474 // in this case. The typechecker should only ever report type errors involving mismatched
1475 // types using one of these methods, and should not call span_err directly for such
1478 pub fn type_error_struct_with_diag<M>(
1482 actual_ty: Ty<'tcx>,
1483 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>
1485 M: FnOnce(String) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>,
1487 let actual_ty = self.resolve_vars_if_possible(actual_ty);
1488 debug!("type_error_struct_with_diag({:?}, {:?})", sp, actual_ty);
1490 let mut err = mk_diag(self.ty_to_string(actual_ty));
1492 // Don't report an error if actual type is `Error`.
1493 if actual_ty.references_error() {
1494 err.downgrade_to_delayed_bug();
1500 pub fn report_mismatched_types(
1502 cause: &ObligationCause<'tcx>,
1505 err: TypeError<'tcx>,
1506 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1507 let trace = TypeTrace::types(cause, true, expected, actual);
1508 self.report_and_explain_type_error(trace, &err)
1511 pub fn report_mismatched_consts(
1513 cause: &ObligationCause<'tcx>,
1514 expected: ty::Const<'tcx>,
1515 actual: ty::Const<'tcx>,
1516 err: TypeError<'tcx>,
1517 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1518 let trace = TypeTrace::consts(cause, true, expected, actual);
1519 self.report_and_explain_type_error(trace, &err)
1522 pub fn replace_bound_vars_with_fresh_vars<T>(
1525 lbrct: LateBoundRegionConversionTime,
1526 value: ty::Binder<'tcx, T>,
1527 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
1529 T: TypeFoldable<'tcx>,
1532 |br: ty::BoundRegion| self.next_region_var(LateBoundRegion(span, br.kind, lbrct));
1534 self.next_ty_var(TypeVariableOrigin {
1535 kind: TypeVariableOriginKind::MiscVariable,
1539 let fld_c = |_, ty| {
1540 self.next_const_var(
1542 ConstVariableOrigin { kind: ConstVariableOriginKind::MiscVariable, span },
1545 self.tcx.replace_bound_vars(value, fld_r, fld_t, fld_c)
1548 /// See the [`region_constraints::RegionConstraintCollector::verify_generic_bound`] method.
1549 pub fn verify_generic_bound(
1551 origin: SubregionOrigin<'tcx>,
1552 kind: GenericKind<'tcx>,
1553 a: ty::Region<'tcx>,
1554 bound: VerifyBound<'tcx>,
1556 debug!("verify_generic_bound({:?}, {:?} <: {:?})", kind, a, bound);
1560 .unwrap_region_constraints()
1561 .verify_generic_bound(origin, kind, a, bound);
1564 /// Obtains the latest type of the given closure; this may be a
1565 /// closure in the current function, in which case its
1566 /// `ClosureKind` may not yet be known.
1567 pub fn closure_kind(&self, closure_substs: SubstsRef<'tcx>) -> Option<ty::ClosureKind> {
1568 let closure_kind_ty = closure_substs.as_closure().kind_ty();
1569 let closure_kind_ty = self.shallow_resolve(closure_kind_ty);
1570 closure_kind_ty.to_opt_closure_kind()
1573 /// Clears the selection, evaluation, and projection caches. This is useful when
1574 /// repeatedly attempting to select an `Obligation` while changing only
1575 /// its `ParamEnv`, since `FulfillmentContext` doesn't use probing.
1576 pub fn clear_caches(&self) {
1577 self.selection_cache.clear();
1578 self.evaluation_cache.clear();
1579 self.inner.borrow_mut().projection_cache().clear();
1582 pub fn universe(&self) -> ty::UniverseIndex {
1586 /// Creates and return a fresh universe that extends all previous
1587 /// universes. Updates `self.universe` to that new universe.
1588 pub fn create_next_universe(&self) -> ty::UniverseIndex {
1589 let u = self.universe.get().next_universe();
1590 self.universe.set(u);
1594 /// Resolves and evaluates a constant.
1596 /// The constant can be located on a trait like `<A as B>::C`, in which case the given
1597 /// substitutions and environment are used to resolve the constant. Alternatively if the
1598 /// constant has generic parameters in scope the substitutions are used to evaluate the value of
1599 /// the constant. For example in `fn foo<T>() { let _ = [0; bar::<T>()]; }` the repeat count
1600 /// constant `bar::<T>()` requires a substitution for `T`, if the substitution for `T` is still
1601 /// too generic for the constant to be evaluated then `Err(ErrorHandled::TooGeneric)` is
1604 /// This handles inferences variables within both `param_env` and `substs` by
1605 /// performing the operation on their respective canonical forms.
1606 #[instrument(skip(self), level = "debug")]
1607 pub fn const_eval_resolve(
1609 param_env: ty::ParamEnv<'tcx>,
1610 unevaluated: ty::Unevaluated<'tcx>,
1612 ) -> EvalToConstValueResult<'tcx> {
1613 let substs = self.resolve_vars_if_possible(unevaluated.substs);
1616 // Postpone the evaluation of constants whose substs depend on inference
1618 if substs.has_infer_types_or_consts() {
1619 debug!("substs have infer types or consts: {:?}", substs);
1620 return Err(ErrorHandled::TooGeneric);
1623 let param_env_erased = self.tcx.erase_regions(param_env);
1624 let substs_erased = self.tcx.erase_regions(substs);
1625 debug!(?param_env_erased);
1626 debug!(?substs_erased);
1628 let unevaluated = ty::Unevaluated {
1629 def: unevaluated.def,
1630 substs: substs_erased,
1631 promoted: unevaluated.promoted,
1634 // The return value is the evaluated value which doesn't contain any reference to inference
1635 // variables, thus we don't need to substitute back the original values.
1636 self.tcx.const_eval_resolve(param_env_erased, unevaluated, span)
1639 /// `ty_or_const_infer_var_changed` is equivalent to one of these two:
1640 /// * `shallow_resolve(ty) != ty` (where `ty.kind = ty::Infer(_)`)
1641 /// * `shallow_resolve(ct) != ct` (where `ct.kind = ty::ConstKind::Infer(_)`)
1643 /// However, `ty_or_const_infer_var_changed` is more efficient. It's always
1644 /// inlined, despite being large, because it has only two call sites that
1645 /// are extremely hot (both in `traits::fulfill`'s checking of `stalled_on`
1646 /// inference variables), and it handles both `Ty` and `ty::Const` without
1647 /// having to resort to storing full `GenericArg`s in `stalled_on`.
1649 pub fn ty_or_const_infer_var_changed(&self, infer_var: TyOrConstInferVar<'tcx>) -> bool {
1651 TyOrConstInferVar::Ty(v) => {
1652 use self::type_variable::TypeVariableValue;
1654 // If `inlined_probe` returns a `Known` value, it never equals
1655 // `ty::Infer(ty::TyVar(v))`.
1656 match self.inner.borrow_mut().type_variables().inlined_probe(v) {
1657 TypeVariableValue::Unknown { .. } => false,
1658 TypeVariableValue::Known { .. } => true,
1662 TyOrConstInferVar::TyInt(v) => {
1663 // If `inlined_probe_value` returns a value it's always a
1664 // `ty::Int(_)` or `ty::UInt(_)`, which never matches a
1666 self.inner.borrow_mut().int_unification_table().inlined_probe_value(v).is_some()
1669 TyOrConstInferVar::TyFloat(v) => {
1670 // If `probe_value` returns a value it's always a
1671 // `ty::Float(_)`, which never matches a `ty::Infer(_)`.
1673 // Not `inlined_probe_value(v)` because this call site is colder.
1674 self.inner.borrow_mut().float_unification_table().probe_value(v).is_some()
1677 TyOrConstInferVar::Const(v) => {
1678 // If `probe_value` returns a `Known` value, it never equals
1679 // `ty::ConstKind::Infer(ty::InferConst::Var(v))`.
1681 // Not `inlined_probe_value(v)` because this call site is colder.
1682 match self.inner.borrow_mut().const_unification_table().probe_value(v).val {
1683 ConstVariableValue::Unknown { .. } => false,
1684 ConstVariableValue::Known { .. } => true,
1691 /// Helper for `ty_or_const_infer_var_changed` (see comment on that), currently
1692 /// used only for `traits::fulfill`'s list of `stalled_on` inference variables.
1693 #[derive(Copy, Clone, Debug)]
1694 pub enum TyOrConstInferVar<'tcx> {
1695 /// Equivalent to `ty::Infer(ty::TyVar(_))`.
1697 /// Equivalent to `ty::Infer(ty::IntVar(_))`.
1699 /// Equivalent to `ty::Infer(ty::FloatVar(_))`.
1702 /// Equivalent to `ty::ConstKind::Infer(ty::InferConst::Var(_))`.
1703 Const(ConstVid<'tcx>),
1706 impl<'tcx> TyOrConstInferVar<'tcx> {
1707 /// Tries to extract an inference variable from a type or a constant, returns `None`
1708 /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`) and
1709 /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1710 pub fn maybe_from_generic_arg(arg: GenericArg<'tcx>) -> Option<Self> {
1711 match arg.unpack() {
1712 GenericArgKind::Type(ty) => Self::maybe_from_ty(ty),
1713 GenericArgKind::Const(ct) => Self::maybe_from_const(ct),
1714 GenericArgKind::Lifetime(_) => None,
1718 /// Tries to extract an inference variable from a type, returns `None`
1719 /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`).
1720 pub fn maybe_from_ty(ty: Ty<'tcx>) -> Option<Self> {
1722 ty::Infer(ty::TyVar(v)) => Some(TyOrConstInferVar::Ty(v)),
1723 ty::Infer(ty::IntVar(v)) => Some(TyOrConstInferVar::TyInt(v)),
1724 ty::Infer(ty::FloatVar(v)) => Some(TyOrConstInferVar::TyFloat(v)),
1729 /// Tries to extract an inference variable from a constant, returns `None`
1730 /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1731 pub fn maybe_from_const(ct: ty::Const<'tcx>) -> Option<Self> {
1733 ty::ConstKind::Infer(InferConst::Var(v)) => Some(TyOrConstInferVar::Const(v)),
1739 /// Replace `{integer}` with `i32` and `{float}` with `f64`.
1740 /// Used only for diagnostics.
1741 struct InferenceLiteralEraser<'tcx> {
1745 impl<'tcx> TypeFolder<'tcx> for InferenceLiteralEraser<'tcx> {
1746 fn tcx(&self) -> TyCtxt<'tcx> {
1750 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1752 ty::Infer(ty::IntVar(_) | ty::FreshIntTy(_)) => self.tcx.types.i32,
1753 ty::Infer(ty::FloatVar(_) | ty::FreshFloatTy(_)) => self.tcx.types.f64,
1754 _ => ty.super_fold_with(self),
1759 struct ShallowResolver<'a, 'tcx> {
1760 infcx: &'a InferCtxt<'a, 'tcx>,
1763 impl<'a, 'tcx> TypeFolder<'tcx> for ShallowResolver<'a, 'tcx> {
1764 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1768 /// If `ty` is a type variable of some kind, resolve it one level
1769 /// (but do not resolve types found in the result). If `typ` is
1770 /// not a type variable, just return it unmodified.
1771 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1773 ty::Infer(ty::TyVar(v)) => {
1774 // Not entirely obvious: if `typ` is a type variable,
1775 // it can be resolved to an int/float variable, which
1776 // can then be recursively resolved, hence the
1777 // recursion. Note though that we prevent type
1778 // variables from unifying to other type variables
1779 // directly (though they may be embedded
1780 // structurally), and we prevent cycles in any case,
1781 // so this recursion should always be of very limited
1784 // Note: if these two lines are combined into one we get
1785 // dynamic borrow errors on `self.inner`.
1786 let known = self.infcx.inner.borrow_mut().type_variables().probe(v).known();
1787 known.map_or(ty, |t| self.fold_ty(t))
1790 ty::Infer(ty::IntVar(v)) => self
1794 .int_unification_table()
1796 .map_or(ty, |v| v.to_type(self.infcx.tcx)),
1798 ty::Infer(ty::FloatVar(v)) => self
1802 .float_unification_table()
1804 .map_or(ty, |v| v.to_type(self.infcx.tcx)),
1810 fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
1811 if let ty::ConstKind::Infer(InferConst::Var(vid)) = ct.val() {
1815 .const_unification_table()
1826 impl<'tcx> TypeTrace<'tcx> {
1827 pub fn span(&self) -> Span {
1832 cause: &ObligationCause<'tcx>,
1833 a_is_expected: bool,
1836 ) -> TypeTrace<'tcx> {
1838 cause: cause.clone(),
1839 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
1844 cause: &ObligationCause<'tcx>,
1845 a_is_expected: bool,
1848 ) -> TypeTrace<'tcx> {
1850 cause: cause.clone(),
1851 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
1856 impl<'tcx> SubregionOrigin<'tcx> {
1857 pub fn span(&self) -> Span {
1859 Subtype(ref a) => a.span(),
1860 RelateObjectBound(a) => a,
1861 RelateParamBound(a, ..) => a,
1862 RelateRegionParamBound(a) => a,
1864 ReborrowUpvar(a, _) => a,
1865 DataBorrowed(_, a) => a,
1866 ReferenceOutlivesReferent(_, a) => a,
1867 CompareImplMethodObligation { span, .. } => span,
1868 CompareImplTypeObligation { span, .. } => span,
1869 CheckAssociatedTypeBounds { ref parent, .. } => parent.span(),
1873 pub fn from_obligation_cause<F>(cause: &traits::ObligationCause<'tcx>, default: F) -> Self
1875 F: FnOnce() -> Self,
1877 match *cause.code() {
1878 traits::ObligationCauseCode::ReferenceOutlivesReferent(ref_type) => {
1879 SubregionOrigin::ReferenceOutlivesReferent(ref_type, cause.span)
1882 traits::ObligationCauseCode::CompareImplMethodObligation {
1885 } => SubregionOrigin::CompareImplMethodObligation {
1891 traits::ObligationCauseCode::CompareImplTypeObligation {
1894 } => SubregionOrigin::CompareImplTypeObligation {
1900 traits::ObligationCauseCode::CheckAssociatedTypeBounds {
1903 } => SubregionOrigin::CheckAssociatedTypeBounds {
1906 parent: Box::new(default()),
1914 impl RegionVariableOrigin {
1915 pub fn span(&self) -> Span {
1922 | EarlyBoundRegion(a, ..)
1923 | LateBoundRegion(a, ..)
1924 | UpvarRegion(_, a) => a,
1925 Nll(..) => bug!("NLL variable used with `span`"),
1930 impl<'tcx> fmt::Debug for RegionObligation<'tcx> {
1931 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1934 "RegionObligation(sub_region={:?}, sup_type={:?})",
1935 self.sub_region, self.sup_type