1 pub use self::freshen::TypeFreshener;
2 pub use self::lexical_region_resolve::RegionResolutionError;
3 pub use self::LateBoundRegionConversionTime::*;
4 pub use self::RegionVariableOrigin::*;
5 pub use self::SubregionOrigin::*;
6 pub use self::ValuePairs::*;
8 use self::opaque_types::OpaqueTypeStorage;
9 pub(crate) use self::undo_log::{InferCtxtUndoLogs, Snapshot, UndoLog};
11 use crate::traits::{self, ObligationCause, PredicateObligations, TraitEngine, TraitEngineExt};
13 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
14 use rustc_data_structures::sync::Lrc;
15 use rustc_data_structures::undo_log::Rollback;
16 use rustc_data_structures::unify as ut;
17 use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed};
18 use rustc_hir::def_id::{DefId, LocalDefId};
19 use rustc_middle::infer::canonical::{Canonical, CanonicalVarValues};
20 use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue};
21 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind, ToType};
22 use rustc_middle::mir::interpret::{ErrorHandled, EvalToValTreeResult};
23 use rustc_middle::traits::select;
24 use rustc_middle::ty::abstract_const::{AbstractConst, FailureKind};
25 use rustc_middle::ty::error::{ExpectedFound, TypeError};
26 use rustc_middle::ty::fold::BoundVarReplacerDelegate;
27 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
28 use rustc_middle::ty::relate::RelateResult;
29 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, SubstsRef};
30 use rustc_middle::ty::visit::TypeVisitable;
31 pub use rustc_middle::ty::IntVarValue;
32 use rustc_middle::ty::{self, GenericParamDefKind, InferConst, Ty, TyCtxt};
33 use rustc_middle::ty::{ConstVid, FloatVid, IntVid, TyVid};
34 use rustc_span::symbol::Symbol;
37 use std::cell::{Cell, Ref, RefCell};
40 use self::combine::CombineFields;
41 use self::free_regions::RegionRelations;
42 use self::lexical_region_resolve::LexicalRegionResolutions;
43 use self::outlives::env::OutlivesEnvironment;
44 use self::region_constraints::{GenericKind, RegionConstraintData, VarInfos, VerifyBound};
45 use self::region_constraints::{
46 RegionConstraintCollector, RegionConstraintStorage, RegionSnapshot,
48 use self::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
54 pub mod error_reporting;
61 mod lexical_region_resolve;
67 pub mod region_constraints;
70 pub mod type_variable;
75 pub struct InferOk<'tcx, T> {
77 pub obligations: PredicateObligations<'tcx>,
79 pub type InferResult<'tcx, T> = Result<InferOk<'tcx, T>, TypeError<'tcx>>;
81 pub type Bound<T> = Option<T>;
82 pub type UnitResult<'tcx> = RelateResult<'tcx, ()>; // "unify result"
83 pub type FixupResult<'tcx, T> = Result<T, FixupError<'tcx>>; // "fixup result"
85 pub(crate) type UnificationTable<'a, 'tcx, T> = ut::UnificationTable<
86 ut::InPlace<T, &'a mut ut::UnificationStorage<T>, &'a mut InferCtxtUndoLogs<'tcx>>,
89 /// This type contains all the things within `InferCtxt` that sit within a
90 /// `RefCell` and are involved with taking/rolling back snapshots. Snapshot
91 /// operations are hot enough that we want only one call to `borrow_mut` per
92 /// call to `start_snapshot` and `rollback_to`.
94 pub struct InferCtxtInner<'tcx> {
95 /// Cache for projections. This cache is snapshotted along with the infcx.
97 /// Public so that `traits::project` can use it.
98 pub projection_cache: traits::ProjectionCacheStorage<'tcx>,
100 /// We instantiate `UnificationTable` with `bounds<Ty>` because the types
101 /// that might instantiate a general type variable have an order,
102 /// represented by its upper and lower bounds.
103 type_variable_storage: type_variable::TypeVariableStorage<'tcx>,
105 /// Map from const parameter variable to the kind of const it represents.
106 const_unification_storage: ut::UnificationTableStorage<ty::ConstVid<'tcx>>,
108 /// Map from integral variable to the kind of integer it represents.
109 int_unification_storage: ut::UnificationTableStorage<ty::IntVid>,
111 /// Map from floating variable to the kind of float it represents.
112 float_unification_storage: ut::UnificationTableStorage<ty::FloatVid>,
114 /// Tracks the set of region variables and the constraints between them.
115 /// This is initially `Some(_)` but when
116 /// `resolve_regions_and_report_errors` is invoked, this gets set to `None`
117 /// -- further attempts to perform unification, etc., may fail if new
118 /// region constraints would've been added.
119 region_constraint_storage: Option<RegionConstraintStorage<'tcx>>,
121 /// A set of constraints that regionck must validate. Each
122 /// constraint has the form `T:'a`, meaning "some type `T` must
123 /// outlive the lifetime 'a". These constraints derive from
124 /// instantiated type parameters. So if you had a struct defined
126 /// ```ignore (illustrative)
127 /// struct Foo<T:'static> { ... }
129 /// then in some expression `let x = Foo { ... }` it will
130 /// instantiate the type parameter `T` with a fresh type `$0`. At
131 /// the same time, it will record a region obligation of
132 /// `$0:'static`. This will get checked later by regionck. (We
133 /// can't generally check these things right away because we have
134 /// to wait until types are resolved.)
136 /// These are stored in a map keyed to the id of the innermost
137 /// enclosing fn body / static initializer expression. This is
138 /// because the location where the obligation was incurred can be
139 /// relevant with respect to which sublifetime assumptions are in
140 /// place. The reason that we store under the fn-id, and not
141 /// something more fine-grained, is so that it is easier for
142 /// regionck to be sure that it has found *all* the region
143 /// obligations (otherwise, it's easy to fail to walk to a
144 /// particular node-id).
146 /// Before running `resolve_regions_and_report_errors`, the creator
147 /// of the inference context is expected to invoke
148 /// [`InferCtxt::process_registered_region_obligations`]
149 /// for each body-id in this map, which will process the
150 /// obligations within. This is expected to be done 'late enough'
151 /// that all type inference variables have been bound and so forth.
152 region_obligations: Vec<RegionObligation<'tcx>>,
154 undo_log: InferCtxtUndoLogs<'tcx>,
156 /// Caches for opaque type inference.
157 pub opaque_type_storage: OpaqueTypeStorage<'tcx>,
160 impl<'tcx> InferCtxtInner<'tcx> {
161 fn new() -> InferCtxtInner<'tcx> {
163 projection_cache: Default::default(),
164 type_variable_storage: type_variable::TypeVariableStorage::new(),
165 undo_log: InferCtxtUndoLogs::default(),
166 const_unification_storage: ut::UnificationTableStorage::new(),
167 int_unification_storage: ut::UnificationTableStorage::new(),
168 float_unification_storage: ut::UnificationTableStorage::new(),
169 region_constraint_storage: Some(RegionConstraintStorage::new()),
170 region_obligations: vec![],
171 opaque_type_storage: Default::default(),
176 pub fn region_obligations(&self) -> &[RegionObligation<'tcx>] {
177 &self.region_obligations
181 pub fn projection_cache(&mut self) -> traits::ProjectionCache<'_, 'tcx> {
182 self.projection_cache.with_log(&mut self.undo_log)
186 fn type_variables(&mut self) -> type_variable::TypeVariableTable<'_, 'tcx> {
187 self.type_variable_storage.with_log(&mut self.undo_log)
191 pub fn opaque_types(&mut self) -> opaque_types::OpaqueTypeTable<'_, 'tcx> {
192 self.opaque_type_storage.with_log(&mut self.undo_log)
196 fn int_unification_table(
198 ) -> ut::UnificationTable<
201 &mut ut::UnificationStorage<ty::IntVid>,
202 &mut InferCtxtUndoLogs<'tcx>,
205 self.int_unification_storage.with_log(&mut self.undo_log)
209 fn float_unification_table(
211 ) -> ut::UnificationTable<
214 &mut ut::UnificationStorage<ty::FloatVid>,
215 &mut InferCtxtUndoLogs<'tcx>,
218 self.float_unification_storage.with_log(&mut self.undo_log)
222 fn const_unification_table(
224 ) -> ut::UnificationTable<
227 &mut ut::UnificationStorage<ty::ConstVid<'tcx>>,
228 &mut InferCtxtUndoLogs<'tcx>,
231 self.const_unification_storage.with_log(&mut self.undo_log)
235 pub fn unwrap_region_constraints(&mut self) -> RegionConstraintCollector<'_, 'tcx> {
236 self.region_constraint_storage
238 .expect("region constraints already solved")
239 .with_log(&mut self.undo_log)
243 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
244 pub enum DefiningAnchor {
245 /// `DefId` of the item.
247 /// When opaque types are not resolved, we `Bubble` up, meaning
248 /// return the opaque/hidden type pair from query, for caller of query to handle it.
250 /// Used to catch type mismatch errors when handling opaque types.
254 pub struct InferCtxt<'a, 'tcx> {
255 pub tcx: TyCtxt<'tcx>,
257 /// The `DefId` of the item in whose context we are performing inference or typeck.
258 /// It is used to check whether an opaque type use is a defining use.
260 /// If it is `DefiningAnchor::Bubble`, we can't resolve opaque types here and need to bubble up
261 /// the obligation. This frequently happens for
262 /// short lived InferCtxt within queries. The opaque type obligations are forwarded
263 /// to the outside until the end up in an `InferCtxt` for typeck or borrowck.
265 /// It is default value is `DefiningAnchor::Error`, this way it is easier to catch errors that
266 /// might come up during inference or typeck.
267 pub defining_use_anchor: DefiningAnchor,
269 /// Whether this inference context should care about region obligations in
270 /// the root universe. Most notably, this is used during hir typeck as region
271 /// solving is left to borrowck instead.
272 pub considering_regions: bool,
274 /// During type-checking/inference of a body, `in_progress_typeck_results`
275 /// contains a reference to the typeck results being built up, which are
276 /// used for reading closure kinds/signatures as they are inferred,
277 /// and for error reporting logic to read arbitrary node types.
278 pub in_progress_typeck_results: Option<&'a RefCell<ty::TypeckResults<'tcx>>>,
280 pub inner: RefCell<InferCtxtInner<'tcx>>,
282 /// If set, this flag causes us to skip the 'leak check' during
283 /// higher-ranked subtyping operations. This flag is a temporary one used
284 /// to manage the removal of the leak-check: for the time being, we still run the
285 /// leak-check, but we issue warnings. This flag can only be set to true
286 /// when entering a snapshot.
287 skip_leak_check: Cell<bool>,
289 /// Once region inference is done, the values for each variable.
290 lexical_region_resolutions: RefCell<Option<LexicalRegionResolutions<'tcx>>>,
292 /// Caches the results of trait selection. This cache is used
293 /// for things that have to do with the parameters in scope.
294 pub selection_cache: select::SelectionCache<'tcx>,
296 /// Caches the results of trait evaluation.
297 pub evaluation_cache: select::EvaluationCache<'tcx>,
299 /// the set of predicates on which errors have been reported, to
300 /// avoid reporting the same error twice.
301 pub reported_trait_errors: RefCell<FxHashMap<Span, Vec<ty::Predicate<'tcx>>>>,
303 pub reported_closure_mismatch: RefCell<FxHashSet<(Span, Option<Span>)>>,
305 /// When an error occurs, we want to avoid reporting "derived"
306 /// errors that are due to this original failure. Normally, we
307 /// handle this with the `err_count_on_creation` count, which
308 /// basically just tracks how many errors were reported when we
309 /// started type-checking a fn and checks to see if any new errors
310 /// have been reported since then. Not great, but it works.
312 /// However, when errors originated in other passes -- notably
313 /// resolve -- this heuristic breaks down. Therefore, we have this
314 /// auxiliary flag that one can set whenever one creates a
315 /// type-error that is due to an error in a prior pass.
317 /// Don't read this flag directly, call `is_tainted_by_errors()`
318 /// and `set_tainted_by_errors()`.
319 tainted_by_errors_flag: Cell<bool>,
321 /// Track how many errors were reported when this infcx is created.
322 /// If the number of errors increases, that's also a sign (line
323 /// `tainted_by_errors`) to avoid reporting certain kinds of errors.
324 // FIXME(matthewjasper) Merge into `tainted_by_errors_flag`
325 err_count_on_creation: usize,
327 /// This flag is true while there is an active snapshot.
328 in_snapshot: Cell<bool>,
330 /// What is the innermost universe we have created? Starts out as
331 /// `UniverseIndex::root()` but grows from there as we enter
332 /// universal quantifiers.
334 /// N.B., at present, we exclude the universal quantifiers on the
335 /// item we are type-checking, and just consider those names as
336 /// part of the root universe. So this would only get incremented
337 /// when we enter into a higher-ranked (`for<..>`) type or trait
339 universe: Cell<ty::UniverseIndex>,
342 /// See the `error_reporting` module for more details.
343 #[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable, TypeVisitable)]
344 pub enum ValuePairs<'tcx> {
345 Regions(ExpectedFound<ty::Region<'tcx>>),
346 Terms(ExpectedFound<ty::Term<'tcx>>),
347 TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>),
348 PolyTraitRefs(ExpectedFound<ty::PolyTraitRef<'tcx>>),
351 impl<'tcx> ValuePairs<'tcx> {
352 pub fn ty(&self) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
353 if let ValuePairs::Terms(ExpectedFound {
354 expected: ty::Term::Ty(expected),
355 found: ty::Term::Ty(found),
358 Some((*expected, *found))
365 /// The trace designates the path through inference that we took to
366 /// encounter an error or subtyping constraint.
368 /// See the `error_reporting` module for more details.
369 #[derive(Clone, Debug)]
370 pub struct TypeTrace<'tcx> {
371 pub cause: ObligationCause<'tcx>,
372 pub values: ValuePairs<'tcx>,
375 /// The origin of a `r1 <= r2` constraint.
377 /// See `error_reporting` module for more details
378 #[derive(Clone, Debug)]
379 pub enum SubregionOrigin<'tcx> {
380 /// Arose from a subtyping relation
381 Subtype(Box<TypeTrace<'tcx>>),
383 /// When casting `&'a T` to an `&'b Trait` object,
384 /// relating `'a` to `'b`
385 RelateObjectBound(Span),
387 /// Some type parameter was instantiated with the given type,
388 /// and that type must outlive some region.
389 RelateParamBound(Span, Ty<'tcx>, Option<Span>),
391 /// The given region parameter was instantiated with a region
392 /// that must outlive some other region.
393 RelateRegionParamBound(Span),
395 /// Creating a pointer `b` to contents of another reference
398 /// Creating a pointer `b` to contents of an upvar
399 ReborrowUpvar(Span, ty::UpvarId),
401 /// Data with type `Ty<'tcx>` was borrowed
402 DataBorrowed(Ty<'tcx>, Span),
404 /// (&'a &'b T) where a >= b
405 ReferenceOutlivesReferent(Ty<'tcx>, Span),
407 /// Comparing the signature and requirements of an impl method against
408 /// the containing trait.
409 CompareImplItemObligation { span: Span, impl_item_def_id: LocalDefId, trait_item_def_id: DefId },
411 /// Checking that the bounds of a trait's associated type hold for a given impl
412 CheckAssociatedTypeBounds {
413 parent: Box<SubregionOrigin<'tcx>>,
414 impl_item_def_id: LocalDefId,
415 trait_item_def_id: DefId,
419 // `SubregionOrigin` is used a lot. Make sure it doesn't unintentionally get bigger.
420 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
421 static_assert_size!(SubregionOrigin<'_>, 32);
423 /// Times when we replace late-bound regions with variables:
424 #[derive(Clone, Copy, Debug)]
425 pub enum LateBoundRegionConversionTime {
426 /// when a fn is called
429 /// when two higher-ranked types are compared
432 /// when projecting an associated type
433 AssocTypeProjection(DefId),
436 /// Reasons to create a region inference variable
438 /// See `error_reporting` module for more details
439 #[derive(Copy, Clone, Debug)]
440 pub enum RegionVariableOrigin {
441 /// Region variables created for ill-categorized reasons,
442 /// mostly indicates places in need of refactoring
445 /// Regions created by a `&P` or `[...]` pattern
448 /// Regions created by `&` operator
451 /// Regions created as part of an autoref of a method receiver
454 /// Regions created as part of an automatic coercion
457 /// Region variables created as the values for early-bound regions
458 EarlyBoundRegion(Span, Symbol),
460 /// Region variables created for bound regions
461 /// in a function or method that is called
462 LateBoundRegion(Span, ty::BoundRegionKind, LateBoundRegionConversionTime),
464 UpvarRegion(ty::UpvarId, Span),
466 /// This origin is used for the inference variables that we create
467 /// during NLL region processing.
468 Nll(NllRegionVariableOrigin),
471 #[derive(Copy, Clone, Debug)]
472 pub enum NllRegionVariableOrigin {
473 /// During NLL region processing, we create variables for free
474 /// regions that we encounter in the function signature and
475 /// elsewhere. This origin indices we've got one of those.
478 /// "Universal" instantiation of a higher-ranked region (e.g.,
479 /// from a `for<'a> T` binder). Meant to represent "any region".
480 Placeholder(ty::PlaceholderRegion),
483 /// If this is true, then this variable was created to represent a lifetime
484 /// bound in a `for` binder. For example, it might have been created to
485 /// represent the lifetime `'a` in a type like `for<'a> fn(&'a u32)`.
486 /// Such variables are created when we are trying to figure out if there
487 /// is any valid instantiation of `'a` that could fit into some scenario.
489 /// This is used to inform error reporting: in the case that we are trying to
490 /// determine whether there is any valid instantiation of a `'a` variable that meets
491 /// some constraint C, we want to blame the "source" of that `for` type,
492 /// rather than blaming the source of the constraint C.
497 // FIXME(eddyb) investigate overlap between this and `TyOrConstInferVar`.
498 #[derive(Copy, Clone, Debug)]
499 pub enum FixupError<'tcx> {
500 UnresolvedIntTy(IntVid),
501 UnresolvedFloatTy(FloatVid),
503 UnresolvedConst(ConstVid<'tcx>),
506 /// See the `region_obligations` field for more information.
508 pub struct RegionObligation<'tcx> {
509 pub sub_region: ty::Region<'tcx>,
510 pub sup_type: Ty<'tcx>,
511 pub origin: SubregionOrigin<'tcx>,
514 impl<'tcx> fmt::Display for FixupError<'tcx> {
515 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
516 use self::FixupError::*;
519 UnresolvedIntTy(_) => write!(
521 "cannot determine the type of this integer; \
522 add a suffix to specify the type explicitly"
524 UnresolvedFloatTy(_) => write!(
526 "cannot determine the type of this number; \
527 add a suffix to specify the type explicitly"
529 UnresolvedTy(_) => write!(f, "unconstrained type"),
530 UnresolvedConst(_) => write!(f, "unconstrained const value"),
535 /// A temporary returned by `tcx.infer_ctxt()`. This is necessary
536 /// for multiple `InferCtxt` to share the same `in_progress_typeck_results`
537 /// without using `Rc` or something similar.
538 pub struct InferCtxtBuilder<'tcx> {
540 defining_use_anchor: DefiningAnchor,
541 considering_regions: bool,
542 fresh_typeck_results: Option<RefCell<ty::TypeckResults<'tcx>>>,
545 pub trait TyCtxtInferExt<'tcx> {
546 fn infer_ctxt(self) -> InferCtxtBuilder<'tcx>;
549 impl<'tcx> TyCtxtInferExt<'tcx> for TyCtxt<'tcx> {
550 fn infer_ctxt(self) -> InferCtxtBuilder<'tcx> {
553 defining_use_anchor: DefiningAnchor::Error,
554 considering_regions: true,
555 fresh_typeck_results: None,
560 impl<'tcx> InferCtxtBuilder<'tcx> {
561 /// Used only by `rustc_typeck` during body type-checking/inference,
562 /// will initialize `in_progress_typeck_results` with fresh `TypeckResults`.
563 /// Will also change the scope for opaque type defining use checks to the given owner.
564 pub fn with_fresh_in_progress_typeck_results(mut self, table_owner: LocalDefId) -> Self {
565 self.fresh_typeck_results = Some(RefCell::new(ty::TypeckResults::new(table_owner)));
566 self.with_opaque_type_inference(DefiningAnchor::Bind(table_owner))
569 /// Whenever the `InferCtxt` should be able to handle defining uses of opaque types,
570 /// you need to call this function. Otherwise the opaque type will be treated opaquely.
572 /// It is only meant to be called in two places, for typeck
573 /// (via `with_fresh_in_progress_typeck_results`) and for the inference context used
575 pub fn with_opaque_type_inference(mut self, defining_use_anchor: DefiningAnchor) -> Self {
576 self.defining_use_anchor = defining_use_anchor;
580 pub fn ignoring_regions(mut self) -> Self {
581 self.considering_regions = false;
585 /// Given a canonical value `C` as a starting point, create an
586 /// inference context that contains each of the bound values
587 /// within instantiated as a fresh variable. The `f` closure is
588 /// invoked with the new infcx, along with the instantiated value
589 /// `V` and a substitution `S`. This substitution `S` maps from
590 /// the bound values in `C` to their instantiated values in `V`
591 /// (in other words, `S(C) = V`).
592 pub fn enter_with_canonical<T, R>(
595 canonical: &Canonical<'tcx, T>,
596 f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>, T, CanonicalVarValues<'tcx>) -> R,
599 T: TypeFoldable<'tcx>,
603 infcx.instantiate_canonical_with_fresh_inference_vars(span, canonical);
604 f(infcx, value, subst)
608 pub fn enter<R>(&mut self, f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>) -> R) -> R {
609 let InferCtxtBuilder {
613 ref fresh_typeck_results,
615 let in_progress_typeck_results = fresh_typeck_results.as_ref();
620 in_progress_typeck_results,
621 inner: RefCell::new(InferCtxtInner::new()),
622 lexical_region_resolutions: RefCell::new(None),
623 selection_cache: Default::default(),
624 evaluation_cache: Default::default(),
625 reported_trait_errors: Default::default(),
626 reported_closure_mismatch: Default::default(),
627 tainted_by_errors_flag: Cell::new(false),
628 err_count_on_creation: tcx.sess.err_count(),
629 in_snapshot: Cell::new(false),
630 skip_leak_check: Cell::new(false),
631 universe: Cell::new(ty::UniverseIndex::ROOT),
636 impl<'tcx, T> InferOk<'tcx, T> {
637 pub fn unit(self) -> InferOk<'tcx, ()> {
638 InferOk { value: (), obligations: self.obligations }
641 /// Extracts `value`, registering any obligations into `fulfill_cx`.
642 pub fn into_value_registering_obligations(
644 infcx: &InferCtxt<'_, 'tcx>,
645 fulfill_cx: &mut dyn TraitEngine<'tcx>,
647 let InferOk { value, obligations } = self;
648 fulfill_cx.register_predicate_obligations(infcx, obligations);
653 impl<'tcx> InferOk<'tcx, ()> {
654 pub fn into_obligations(self) -> PredicateObligations<'tcx> {
659 #[must_use = "once you start a snapshot, you should always consume it"]
660 pub struct CombinedSnapshot<'a, 'tcx> {
661 undo_snapshot: Snapshot<'tcx>,
662 region_constraints_snapshot: RegionSnapshot,
663 universe: ty::UniverseIndex,
664 was_in_snapshot: bool,
665 _in_progress_typeck_results: Option<Ref<'a, ty::TypeckResults<'tcx>>>,
668 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
669 /// calls `tcx.try_unify_abstract_consts` after
670 /// canonicalizing the consts.
671 #[instrument(skip(self), level = "debug")]
672 pub fn try_unify_abstract_consts(
674 a: ty::Unevaluated<'tcx, ()>,
675 b: ty::Unevaluated<'tcx, ()>,
676 param_env: ty::ParamEnv<'tcx>,
678 // Reject any attempt to unify two unevaluated constants that contain inference
679 // variables, since inference variables in queries lead to ICEs.
680 if a.substs.has_infer_types_or_consts()
681 || b.substs.has_infer_types_or_consts()
682 || param_env.has_infer_types_or_consts()
684 debug!("a or b or param_env contain infer vars in its substs -> cannot unify");
688 let param_env_and = param_env.and((a, b));
689 let erased = self.tcx.erase_regions(param_env_and);
690 debug!("after erase_regions: {:?}", erased);
692 self.tcx.try_unify_abstract_consts(erased)
695 pub fn is_in_snapshot(&self) -> bool {
696 self.in_snapshot.get()
699 pub fn freshen<T: TypeFoldable<'tcx>>(&self, t: T) -> T {
700 t.fold_with(&mut self.freshener())
703 /// Returns the origin of the type variable identified by `vid`, or `None`
704 /// if this is not a type variable.
706 /// No attempt is made to resolve `ty`.
707 pub fn type_var_origin(&'a self, ty: Ty<'tcx>) -> Option<TypeVariableOrigin> {
709 ty::Infer(ty::TyVar(vid)) => {
710 Some(*self.inner.borrow_mut().type_variables().var_origin(vid))
716 pub fn freshener<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
717 freshen::TypeFreshener::new(self, false)
720 /// Like `freshener`, but does not replace `'static` regions.
721 pub fn freshener_keep_static<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
722 freshen::TypeFreshener::new(self, true)
725 pub fn unsolved_variables(&self) -> Vec<Ty<'tcx>> {
726 let mut inner = self.inner.borrow_mut();
727 let mut vars: Vec<Ty<'_>> = inner
729 .unsolved_variables()
731 .map(|t| self.tcx.mk_ty_var(t))
734 (0..inner.int_unification_table().len())
735 .map(|i| ty::IntVid { index: i as u32 })
736 .filter(|&vid| inner.int_unification_table().probe_value(vid).is_none())
737 .map(|v| self.tcx.mk_int_var(v)),
740 (0..inner.float_unification_table().len())
741 .map(|i| ty::FloatVid { index: i as u32 })
742 .filter(|&vid| inner.float_unification_table().probe_value(vid).is_none())
743 .map(|v| self.tcx.mk_float_var(v)),
750 trace: TypeTrace<'tcx>,
751 param_env: ty::ParamEnv<'tcx>,
752 define_opaque_types: bool,
753 ) -> CombineFields<'a, 'tcx> {
759 obligations: PredicateObligations::new(),
764 /// Clear the "currently in a snapshot" flag, invoke the closure,
765 /// then restore the flag to its original value. This flag is a
766 /// debugging measure designed to detect cases where we start a
767 /// snapshot, create type variables, and register obligations
768 /// which may involve those type variables in the fulfillment cx,
769 /// potentially leaving "dangling type variables" behind.
770 /// In such cases, an assertion will fail when attempting to
771 /// register obligations, within a snapshot. Very useful, much
772 /// better than grovelling through megabytes of `RUSTC_LOG` output.
774 /// HOWEVER, in some cases the flag is unhelpful. In particular, we
775 /// sometimes create a "mini-fulfilment-cx" in which we enroll
776 /// obligations. As long as this fulfillment cx is fully drained
777 /// before we return, this is not a problem, as there won't be any
778 /// escaping obligations in the main cx. In those cases, you can
779 /// use this function.
780 pub fn save_and_restore_in_snapshot_flag<F, R>(&self, func: F) -> R
782 F: FnOnce(&Self) -> R,
784 let flag = self.in_snapshot.replace(false);
785 let result = func(self);
786 self.in_snapshot.set(flag);
790 fn start_snapshot(&self) -> CombinedSnapshot<'a, 'tcx> {
791 debug!("start_snapshot()");
793 let in_snapshot = self.in_snapshot.replace(true);
795 let mut inner = self.inner.borrow_mut();
798 undo_snapshot: inner.undo_log.start_snapshot(),
799 region_constraints_snapshot: inner.unwrap_region_constraints().start_snapshot(),
800 universe: self.universe(),
801 was_in_snapshot: in_snapshot,
802 // Borrow typeck results "in progress" (i.e., during typeck)
803 // to ban writes from within a snapshot to them.
804 _in_progress_typeck_results: self
805 .in_progress_typeck_results
806 .map(|typeck_results| typeck_results.borrow()),
810 #[instrument(skip(self, snapshot), level = "debug")]
811 fn rollback_to(&self, cause: &str, snapshot: CombinedSnapshot<'a, 'tcx>) {
812 let CombinedSnapshot {
814 region_constraints_snapshot,
817 _in_progress_typeck_results,
820 self.in_snapshot.set(was_in_snapshot);
821 self.universe.set(universe);
823 let mut inner = self.inner.borrow_mut();
824 inner.rollback_to(undo_snapshot);
825 inner.unwrap_region_constraints().rollback_to(region_constraints_snapshot);
828 #[instrument(skip(self, snapshot), level = "debug")]
829 fn commit_from(&self, snapshot: CombinedSnapshot<'a, 'tcx>) {
830 let CombinedSnapshot {
832 region_constraints_snapshot: _,
835 _in_progress_typeck_results,
838 self.in_snapshot.set(was_in_snapshot);
840 self.inner.borrow_mut().commit(undo_snapshot);
843 /// Execute `f` and commit the bindings if closure `f` returns `Ok(_)`.
844 #[instrument(skip(self, f), level = "debug")]
845 pub fn commit_if_ok<T, E, F>(&self, f: F) -> Result<T, E>
847 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> Result<T, E>,
849 let snapshot = self.start_snapshot();
850 let r = f(&snapshot);
851 debug!("commit_if_ok() -- r.is_ok() = {}", r.is_ok());
854 self.commit_from(snapshot);
857 self.rollback_to("commit_if_ok -- error", snapshot);
863 /// Execute `f` then unroll any bindings it creates.
864 #[instrument(skip(self, f), level = "debug")]
865 pub fn probe<R, F>(&self, f: F) -> R
867 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
869 let snapshot = self.start_snapshot();
870 let r = f(&snapshot);
871 self.rollback_to("probe", snapshot);
875 /// If `should_skip` is true, then execute `f` then unroll any bindings it creates.
876 #[instrument(skip(self, f), level = "debug")]
877 pub fn probe_maybe_skip_leak_check<R, F>(&self, should_skip: bool, f: F) -> R
879 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
881 let snapshot = self.start_snapshot();
882 let was_skip_leak_check = self.skip_leak_check.get();
884 self.skip_leak_check.set(true);
886 let r = f(&snapshot);
887 self.rollback_to("probe", snapshot);
888 self.skip_leak_check.set(was_skip_leak_check);
892 /// Scan the constraints produced since `snapshot` began and returns:
894 /// - `None` -- if none of them involve "region outlives" constraints
895 /// - `Some(true)` -- if there are `'a: 'b` constraints where `'a` or `'b` is a placeholder
896 /// - `Some(false)` -- if there are `'a: 'b` constraints but none involve placeholders
897 pub fn region_constraints_added_in_snapshot(
899 snapshot: &CombinedSnapshot<'a, 'tcx>,
903 .unwrap_region_constraints()
904 .region_constraints_added_in_snapshot(&snapshot.undo_snapshot)
907 pub fn opaque_types_added_in_snapshot(&self, snapshot: &CombinedSnapshot<'a, 'tcx>) -> bool {
908 self.inner.borrow().undo_log.opaque_types_in_snapshot(&snapshot.undo_snapshot)
911 pub fn add_given(&self, sub: ty::Region<'tcx>, sup: ty::RegionVid) {
912 self.inner.borrow_mut().unwrap_region_constraints().add_given(sub, sup);
915 pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
917 T: at::ToTrace<'tcx>,
919 let origin = &ObligationCause::dummy();
921 self.at(origin, param_env).sub(a, b).map(|InferOk { obligations: _, .. }| {
922 // Ignore obligations, since we are unrolling
923 // everything anyway.
928 pub fn can_eq<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
930 T: at::ToTrace<'tcx>,
932 let origin = &ObligationCause::dummy();
934 self.at(origin, param_env).eq(a, b).map(|InferOk { obligations: _, .. }| {
935 // Ignore obligations, since we are unrolling
936 // everything anyway.
941 #[instrument(skip(self), level = "debug")]
944 origin: SubregionOrigin<'tcx>,
948 self.inner.borrow_mut().unwrap_region_constraints().make_subregion(origin, a, b);
951 /// Require that the region `r` be equal to one of the regions in
952 /// the set `regions`.
953 #[instrument(skip(self), level = "debug")]
954 pub fn member_constraint(
956 key: ty::OpaqueTypeKey<'tcx>,
957 definition_span: Span,
959 region: ty::Region<'tcx>,
960 in_regions: &Lrc<Vec<ty::Region<'tcx>>>,
962 self.inner.borrow_mut().unwrap_region_constraints().member_constraint(
971 /// Processes a `Coerce` predicate from the fulfillment context.
972 /// This is NOT the preferred way to handle coercion, which is to
973 /// invoke `FnCtxt::coerce` or a similar method (see `coercion.rs`).
975 /// This method here is actually a fallback that winds up being
976 /// invoked when `FnCtxt::coerce` encounters unresolved type variables
977 /// and records a coercion predicate. Presently, this method is equivalent
978 /// to `subtype_predicate` -- that is, "coercing" `a` to `b` winds up
979 /// actually requiring `a <: b`. This is of course a valid coercion,
980 /// but it's not as flexible as `FnCtxt::coerce` would be.
982 /// (We may refactor this in the future, but there are a number of
983 /// practical obstacles. Among other things, `FnCtxt::coerce` presently
984 /// records adjustments that are required on the HIR in order to perform
985 /// the coercion, and we don't currently have a way to manage that.)
986 pub fn coerce_predicate(
988 cause: &ObligationCause<'tcx>,
989 param_env: ty::ParamEnv<'tcx>,
990 predicate: ty::PolyCoercePredicate<'tcx>,
991 ) -> Option<InferResult<'tcx, ()>> {
992 let subtype_predicate = predicate.map_bound(|p| ty::SubtypePredicate {
993 a_is_expected: false, // when coercing from `a` to `b`, `b` is expected
997 self.subtype_predicate(cause, param_env, subtype_predicate)
1000 pub fn subtype_predicate(
1002 cause: &ObligationCause<'tcx>,
1003 param_env: ty::ParamEnv<'tcx>,
1004 predicate: ty::PolySubtypePredicate<'tcx>,
1005 ) -> Option<InferResult<'tcx, ()>> {
1006 // Check for two unresolved inference variables, in which case we can
1007 // make no progress. This is partly a micro-optimization, but it's
1008 // also an opportunity to "sub-unify" the variables. This isn't
1009 // *necessary* to prevent cycles, because they would eventually be sub-unified
1010 // anyhow during generalization, but it helps with diagnostics (we can detect
1011 // earlier that they are sub-unified).
1013 // Note that we can just skip the binders here because
1014 // type variables can't (at present, at
1015 // least) capture any of the things bound by this binder.
1017 // Note that this sub here is not just for diagnostics - it has semantic
1019 let r_a = self.shallow_resolve(predicate.skip_binder().a);
1020 let r_b = self.shallow_resolve(predicate.skip_binder().b);
1021 match (r_a.kind(), r_b.kind()) {
1022 (&ty::Infer(ty::TyVar(a_vid)), &ty::Infer(ty::TyVar(b_vid))) => {
1023 self.inner.borrow_mut().type_variables().sub(a_vid, b_vid);
1029 Some(self.commit_if_ok(|_snapshot| {
1030 let ty::SubtypePredicate { a_is_expected, a, b } =
1031 self.replace_bound_vars_with_placeholders(predicate);
1033 let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?;
1039 pub fn region_outlives_predicate(
1041 cause: &traits::ObligationCause<'tcx>,
1042 predicate: ty::PolyRegionOutlivesPredicate<'tcx>,
1044 let ty::OutlivesPredicate(r_a, r_b) = self.replace_bound_vars_with_placeholders(predicate);
1046 SubregionOrigin::from_obligation_cause(cause, || RelateRegionParamBound(cause.span));
1047 self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
1050 /// Number of type variables created so far.
1051 pub fn num_ty_vars(&self) -> usize {
1052 self.inner.borrow_mut().type_variables().num_vars()
1055 pub fn next_ty_var_id(&self, origin: TypeVariableOrigin) -> TyVid {
1056 self.inner.borrow_mut().type_variables().new_var(self.universe(), origin)
1059 pub fn next_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
1060 self.tcx.mk_ty_var(self.next_ty_var_id(origin))
1063 pub fn next_ty_var_id_in_universe(
1065 origin: TypeVariableOrigin,
1066 universe: ty::UniverseIndex,
1068 self.inner.borrow_mut().type_variables().new_var(universe, origin)
1071 pub fn next_ty_var_in_universe(
1073 origin: TypeVariableOrigin,
1074 universe: ty::UniverseIndex,
1076 let vid = self.next_ty_var_id_in_universe(origin, universe);
1077 self.tcx.mk_ty_var(vid)
1080 pub fn next_const_var(&self, ty: Ty<'tcx>, origin: ConstVariableOrigin) -> ty::Const<'tcx> {
1081 self.tcx.mk_const_var(self.next_const_var_id(origin), ty)
1084 pub fn next_const_var_in_universe(
1087 origin: ConstVariableOrigin,
1088 universe: ty::UniverseIndex,
1089 ) -> ty::Const<'tcx> {
1093 .const_unification_table()
1094 .new_key(ConstVarValue { origin, val: ConstVariableValue::Unknown { universe } });
1095 self.tcx.mk_const_var(vid, ty)
1098 pub fn next_const_var_id(&self, origin: ConstVariableOrigin) -> ConstVid<'tcx> {
1099 self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue {
1101 val: ConstVariableValue::Unknown { universe: self.universe() },
1105 fn next_int_var_id(&self) -> IntVid {
1106 self.inner.borrow_mut().int_unification_table().new_key(None)
1109 pub fn next_int_var(&self) -> Ty<'tcx> {
1110 self.tcx.mk_int_var(self.next_int_var_id())
1113 fn next_float_var_id(&self) -> FloatVid {
1114 self.inner.borrow_mut().float_unification_table().new_key(None)
1117 pub fn next_float_var(&self) -> Ty<'tcx> {
1118 self.tcx.mk_float_var(self.next_float_var_id())
1121 /// Creates a fresh region variable with the next available index.
1122 /// The variable will be created in the maximum universe created
1123 /// thus far, allowing it to name any region created thus far.
1124 pub fn next_region_var(&self, origin: RegionVariableOrigin) -> ty::Region<'tcx> {
1125 self.next_region_var_in_universe(origin, self.universe())
1128 /// Creates a fresh region variable with the next available index
1129 /// in the given universe; typically, you can use
1130 /// `next_region_var` and just use the maximal universe.
1131 pub fn next_region_var_in_universe(
1133 origin: RegionVariableOrigin,
1134 universe: ty::UniverseIndex,
1135 ) -> ty::Region<'tcx> {
1137 self.inner.borrow_mut().unwrap_region_constraints().new_region_var(universe, origin);
1138 self.tcx.mk_region(ty::ReVar(region_var))
1141 /// Return the universe that the region `r` was created in. For
1142 /// most regions (e.g., `'static`, named regions from the user,
1143 /// etc) this is the root universe U0. For inference variables or
1144 /// placeholders, however, it will return the universe which which
1145 /// they are associated.
1146 pub fn universe_of_region(&self, r: ty::Region<'tcx>) -> ty::UniverseIndex {
1147 self.inner.borrow_mut().unwrap_region_constraints().universe(r)
1150 /// Number of region variables created so far.
1151 pub fn num_region_vars(&self) -> usize {
1152 self.inner.borrow_mut().unwrap_region_constraints().num_region_vars()
1155 /// Just a convenient wrapper of `next_region_var` for using during NLL.
1156 pub fn next_nll_region_var(&self, origin: NllRegionVariableOrigin) -> ty::Region<'tcx> {
1157 self.next_region_var(RegionVariableOrigin::Nll(origin))
1160 /// Just a convenient wrapper of `next_region_var` for using during NLL.
1161 pub fn next_nll_region_var_in_universe(
1163 origin: NllRegionVariableOrigin,
1164 universe: ty::UniverseIndex,
1165 ) -> ty::Region<'tcx> {
1166 self.next_region_var_in_universe(RegionVariableOrigin::Nll(origin), universe)
1169 pub fn var_for_def(&self, span: Span, param: &ty::GenericParamDef) -> GenericArg<'tcx> {
1171 GenericParamDefKind::Lifetime => {
1172 // Create a region inference variable for the given
1173 // region parameter definition.
1174 self.next_region_var(EarlyBoundRegion(span, param.name)).into()
1176 GenericParamDefKind::Type { .. } => {
1177 // Create a type inference variable for the given
1178 // type parameter definition. The substitutions are
1179 // for actual parameters that may be referred to by
1180 // the default of this type parameter, if it exists.
1181 // e.g., `struct Foo<A, B, C = (A, B)>(...);` when
1182 // used in a path such as `Foo::<T, U>::new()` will
1183 // use an inference variable for `C` with `[T, U]`
1184 // as the substitutions for the default, `(T, U)`.
1185 let ty_var_id = self.inner.borrow_mut().type_variables().new_var(
1187 TypeVariableOrigin {
1188 kind: TypeVariableOriginKind::TypeParameterDefinition(
1196 self.tcx.mk_ty_var(ty_var_id).into()
1198 GenericParamDefKind::Const { .. } => {
1199 let origin = ConstVariableOrigin {
1200 kind: ConstVariableOriginKind::ConstParameterDefinition(
1207 self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue {
1209 val: ConstVariableValue::Unknown { universe: self.universe() },
1211 self.tcx.mk_const_var(const_var_id, self.tcx.type_of(param.def_id)).into()
1216 /// Given a set of generics defined on a type or impl, returns a substitution mapping each
1217 /// type/region parameter to a fresh inference variable.
1218 pub fn fresh_substs_for_item(&self, span: Span, def_id: DefId) -> SubstsRef<'tcx> {
1219 InternalSubsts::for_item(self.tcx, def_id, |param, _| self.var_for_def(span, param))
1222 /// Returns `true` if errors have been reported since this infcx was
1223 /// created. This is sometimes used as a heuristic to skip
1224 /// reporting errors that often occur as a result of earlier
1225 /// errors, but where it's hard to be 100% sure (e.g., unresolved
1226 /// inference variables, regionck errors).
1227 pub fn is_tainted_by_errors(&self) -> bool {
1229 "is_tainted_by_errors(err_count={}, err_count_on_creation={}, \
1230 tainted_by_errors_flag={})",
1231 self.tcx.sess.err_count(),
1232 self.err_count_on_creation,
1233 self.tainted_by_errors_flag.get()
1236 if self.tcx.sess.err_count() > self.err_count_on_creation {
1237 return true; // errors reported since this infcx was made
1239 self.tainted_by_errors_flag.get()
1242 /// Set the "tainted by errors" flag to true. We call this when we
1243 /// observe an error from a prior pass.
1244 pub fn set_tainted_by_errors(&self) {
1245 debug!("set_tainted_by_errors()");
1246 self.tainted_by_errors_flag.set(true)
1249 pub fn skip_region_resolution(&self) {
1250 let (var_infos, _) = {
1251 let mut inner = self.inner.borrow_mut();
1252 let inner = &mut *inner;
1253 // Note: `inner.region_obligations` may not be empty, because we
1254 // didn't necessarily call `process_registered_region_obligations`.
1255 // This is okay, because that doesn't introduce new vars.
1257 .region_constraint_storage
1259 .expect("regions already resolved")
1260 .with_log(&mut inner.undo_log)
1261 .into_infos_and_data()
1264 let lexical_region_resolutions = LexicalRegionResolutions {
1265 values: rustc_index::vec::IndexVec::from_elem_n(
1266 crate::infer::lexical_region_resolve::VarValue::Value(self.tcx.lifetimes.re_erased),
1271 let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions));
1272 assert!(old_value.is_none());
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 outlives_env: &OutlivesEnvironment<'tcx>,
1282 ) -> Vec<RegionResolutionError<'tcx>> {
1283 let (var_infos, data) = {
1284 let mut inner = self.inner.borrow_mut();
1285 let inner = &mut *inner;
1287 self.is_tainted_by_errors() || inner.region_obligations.is_empty(),
1288 "region_obligations not empty: {:#?}",
1289 inner.region_obligations
1292 .region_constraint_storage
1294 .expect("regions already resolved")
1295 .with_log(&mut inner.undo_log)
1296 .into_infos_and_data()
1299 let region_rels = &RegionRelations::new(self.tcx, outlives_env.free_region_map());
1301 let (lexical_region_resolutions, errors) =
1302 lexical_region_resolve::resolve(outlives_env.param_env, region_rels, var_infos, data);
1304 let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions));
1305 assert!(old_value.is_none());
1310 /// Process the region constraints and report any errors that
1311 /// result. After this, no more unification operations should be
1312 /// done -- or the compiler will panic -- but it is legal to use
1313 /// `resolve_vars_if_possible` as well as `fully_resolve`.
1315 /// Make sure to call [`InferCtxt::process_registered_region_obligations`]
1316 /// first, or preferrably use [`InferCtxt::check_region_obligations_and_report_errors`]
1317 /// to do both of these operations together.
1318 pub fn resolve_regions_and_report_errors(
1320 generic_param_scope: LocalDefId,
1321 outlives_env: &OutlivesEnvironment<'tcx>,
1323 let errors = self.resolve_regions(outlives_env);
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(generic_param_scope, &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: TypeVisitable<'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>,
1552 T: TypeFoldable<'tcx> + Copy,
1554 if let Some(inner) = value.no_bound_vars() {
1558 struct ToFreshVars<'a, 'tcx> {
1559 infcx: &'a InferCtxt<'a, 'tcx>,
1561 lbrct: LateBoundRegionConversionTime,
1562 map: FxHashMap<ty::BoundVar, ty::GenericArg<'tcx>>,
1565 impl<'tcx> BoundVarReplacerDelegate<'tcx> for ToFreshVars<'_, 'tcx> {
1566 fn replace_region(&mut self, br: ty::BoundRegion) -> ty::Region<'tcx> {
1569 .or_insert_with(|| {
1571 .next_region_var(LateBoundRegion(self.span, br.kind, self.lbrct))
1576 fn replace_ty(&mut self, bt: ty::BoundTy) -> Ty<'tcx> {
1579 .or_insert_with(|| {
1581 .next_ty_var(TypeVariableOrigin {
1582 kind: TypeVariableOriginKind::MiscVariable,
1589 fn replace_const(&mut self, bv: ty::BoundVar, ty: Ty<'tcx>) -> ty::Const<'tcx> {
1592 .or_insert_with(|| {
1596 ConstVariableOrigin {
1597 kind: ConstVariableOriginKind::MiscVariable,
1606 let delegate = ToFreshVars { infcx: self, span, lbrct, map: Default::default() };
1607 self.tcx.replace_bound_vars_uncached(value, delegate)
1610 /// See the [`region_constraints::RegionConstraintCollector::verify_generic_bound`] method.
1611 pub fn verify_generic_bound(
1613 origin: SubregionOrigin<'tcx>,
1614 kind: GenericKind<'tcx>,
1615 a: ty::Region<'tcx>,
1616 bound: VerifyBound<'tcx>,
1618 debug!("verify_generic_bound({:?}, {:?} <: {:?})", kind, a, bound);
1622 .unwrap_region_constraints()
1623 .verify_generic_bound(origin, kind, a, bound);
1626 /// Obtains the latest type of the given closure; this may be a
1627 /// closure in the current function, in which case its
1628 /// `ClosureKind` may not yet be known.
1629 pub fn closure_kind(&self, closure_substs: SubstsRef<'tcx>) -> Option<ty::ClosureKind> {
1630 let closure_kind_ty = closure_substs.as_closure().kind_ty();
1631 let closure_kind_ty = self.shallow_resolve(closure_kind_ty);
1632 closure_kind_ty.to_opt_closure_kind()
1635 /// Clears the selection, evaluation, and projection caches. This is useful when
1636 /// repeatedly attempting to select an `Obligation` while changing only
1637 /// its `ParamEnv`, since `FulfillmentContext` doesn't use probing.
1638 pub fn clear_caches(&self) {
1639 self.selection_cache.clear();
1640 self.evaluation_cache.clear();
1641 self.inner.borrow_mut().projection_cache().clear();
1644 pub fn universe(&self) -> ty::UniverseIndex {
1648 /// Creates and return a fresh universe that extends all previous
1649 /// universes. Updates `self.universe` to that new universe.
1650 pub fn create_next_universe(&self) -> ty::UniverseIndex {
1651 let u = self.universe.get().next_universe();
1652 self.universe.set(u);
1656 pub fn try_const_eval_resolve(
1658 param_env: ty::ParamEnv<'tcx>,
1659 unevaluated: ty::Unevaluated<'tcx>,
1662 ) -> Result<ty::Const<'tcx>, ErrorHandled> {
1663 match self.const_eval_resolve(param_env, unevaluated, span) {
1664 Ok(Some(val)) => Ok(ty::Const::from_value(self.tcx, val, ty)),
1667 let def_id = unevaluated.def.did;
1669 tcx.def_span(def_id),
1670 "unable to construct a constant value for the unevaluated constant {:?}",
1674 Err(err) => Err(err),
1678 /// Resolves and evaluates a constant.
1680 /// The constant can be located on a trait like `<A as B>::C`, in which case the given
1681 /// substitutions and environment are used to resolve the constant. Alternatively if the
1682 /// constant has generic parameters in scope the substitutions are used to evaluate the value of
1683 /// the constant. For example in `fn foo<T>() { let _ = [0; bar::<T>()]; }` the repeat count
1684 /// constant `bar::<T>()` requires a substitution for `T`, if the substitution for `T` is still
1685 /// too generic for the constant to be evaluated then `Err(ErrorHandled::TooGeneric)` is
1688 /// This handles inferences variables within both `param_env` and `substs` by
1689 /// performing the operation on their respective canonical forms.
1690 #[instrument(skip(self), level = "debug")]
1691 pub fn const_eval_resolve(
1693 mut param_env: ty::ParamEnv<'tcx>,
1694 unevaluated: ty::Unevaluated<'tcx>,
1696 ) -> EvalToValTreeResult<'tcx> {
1697 let mut substs = self.resolve_vars_if_possible(unevaluated.substs);
1700 // Postpone the evaluation of constants whose substs depend on inference
1702 if substs.has_infer_types_or_consts() {
1703 let ac = AbstractConst::new(self.tcx, unevaluated.shrink());
1706 substs = InternalSubsts::identity_for_item(self.tcx, unevaluated.def.did);
1707 param_env = self.tcx.param_env(unevaluated.def.did);
1710 if ct.unify_failure_kind(self.tcx) == FailureKind::Concrete {
1711 substs = replace_param_and_infer_substs_with_placeholder(self.tcx, substs);
1713 return Err(ErrorHandled::TooGeneric);
1716 Err(guar) => return Err(ErrorHandled::Reported(guar)),
1720 let param_env_erased = self.tcx.erase_regions(param_env);
1721 let substs_erased = self.tcx.erase_regions(substs);
1722 debug!(?param_env_erased);
1723 debug!(?substs_erased);
1725 let unevaluated = ty::Unevaluated {
1726 def: unevaluated.def,
1727 substs: substs_erased,
1728 promoted: unevaluated.promoted,
1731 // The return value is the evaluated value which doesn't contain any reference to inference
1732 // variables, thus we don't need to substitute back the original values.
1733 self.tcx.const_eval_resolve_for_typeck(param_env_erased, unevaluated, span)
1736 /// `ty_or_const_infer_var_changed` is equivalent to one of these two:
1737 /// * `shallow_resolve(ty) != ty` (where `ty.kind = ty::Infer(_)`)
1738 /// * `shallow_resolve(ct) != ct` (where `ct.kind = ty::ConstKind::Infer(_)`)
1740 /// However, `ty_or_const_infer_var_changed` is more efficient. It's always
1741 /// inlined, despite being large, because it has only two call sites that
1742 /// are extremely hot (both in `traits::fulfill`'s checking of `stalled_on`
1743 /// inference variables), and it handles both `Ty` and `ty::Const` without
1744 /// having to resort to storing full `GenericArg`s in `stalled_on`.
1746 pub fn ty_or_const_infer_var_changed(&self, infer_var: TyOrConstInferVar<'tcx>) -> bool {
1748 TyOrConstInferVar::Ty(v) => {
1749 use self::type_variable::TypeVariableValue;
1751 // If `inlined_probe` returns a `Known` value, it never equals
1752 // `ty::Infer(ty::TyVar(v))`.
1753 match self.inner.borrow_mut().type_variables().inlined_probe(v) {
1754 TypeVariableValue::Unknown { .. } => false,
1755 TypeVariableValue::Known { .. } => true,
1759 TyOrConstInferVar::TyInt(v) => {
1760 // If `inlined_probe_value` returns a value it's always a
1761 // `ty::Int(_)` or `ty::UInt(_)`, which never matches a
1763 self.inner.borrow_mut().int_unification_table().inlined_probe_value(v).is_some()
1766 TyOrConstInferVar::TyFloat(v) => {
1767 // If `probe_value` returns a value it's always a
1768 // `ty::Float(_)`, which never matches a `ty::Infer(_)`.
1770 // Not `inlined_probe_value(v)` because this call site is colder.
1771 self.inner.borrow_mut().float_unification_table().probe_value(v).is_some()
1774 TyOrConstInferVar::Const(v) => {
1775 // If `probe_value` returns a `Known` value, it never equals
1776 // `ty::ConstKind::Infer(ty::InferConst::Var(v))`.
1778 // Not `inlined_probe_value(v)` because this call site is colder.
1779 match self.inner.borrow_mut().const_unification_table().probe_value(v).val {
1780 ConstVariableValue::Unknown { .. } => false,
1781 ConstVariableValue::Known { .. } => true,
1788 /// Helper for `ty_or_const_infer_var_changed` (see comment on that), currently
1789 /// used only for `traits::fulfill`'s list of `stalled_on` inference variables.
1790 #[derive(Copy, Clone, Debug)]
1791 pub enum TyOrConstInferVar<'tcx> {
1792 /// Equivalent to `ty::Infer(ty::TyVar(_))`.
1794 /// Equivalent to `ty::Infer(ty::IntVar(_))`.
1796 /// Equivalent to `ty::Infer(ty::FloatVar(_))`.
1799 /// Equivalent to `ty::ConstKind::Infer(ty::InferConst::Var(_))`.
1800 Const(ConstVid<'tcx>),
1803 impl<'tcx> TyOrConstInferVar<'tcx> {
1804 /// Tries to extract an inference variable from a type or a constant, returns `None`
1805 /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`) and
1806 /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1807 pub fn maybe_from_generic_arg(arg: GenericArg<'tcx>) -> Option<Self> {
1808 match arg.unpack() {
1809 GenericArgKind::Type(ty) => Self::maybe_from_ty(ty),
1810 GenericArgKind::Const(ct) => Self::maybe_from_const(ct),
1811 GenericArgKind::Lifetime(_) => None,
1815 /// Tries to extract an inference variable from a type, returns `None`
1816 /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`).
1817 pub fn maybe_from_ty(ty: Ty<'tcx>) -> Option<Self> {
1819 ty::Infer(ty::TyVar(v)) => Some(TyOrConstInferVar::Ty(v)),
1820 ty::Infer(ty::IntVar(v)) => Some(TyOrConstInferVar::TyInt(v)),
1821 ty::Infer(ty::FloatVar(v)) => Some(TyOrConstInferVar::TyFloat(v)),
1826 /// Tries to extract an inference variable from a constant, returns `None`
1827 /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1828 pub fn maybe_from_const(ct: ty::Const<'tcx>) -> Option<Self> {
1830 ty::ConstKind::Infer(InferConst::Var(v)) => Some(TyOrConstInferVar::Const(v)),
1836 /// Replace `{integer}` with `i32` and `{float}` with `f64`.
1837 /// Used only for diagnostics.
1838 struct InferenceLiteralEraser<'tcx> {
1842 impl<'tcx> TypeFolder<'tcx> for InferenceLiteralEraser<'tcx> {
1843 fn tcx(&self) -> TyCtxt<'tcx> {
1847 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1849 ty::Infer(ty::IntVar(_) | ty::FreshIntTy(_)) => self.tcx.types.i32,
1850 ty::Infer(ty::FloatVar(_) | ty::FreshFloatTy(_)) => self.tcx.types.f64,
1851 _ => ty.super_fold_with(self),
1856 struct ShallowResolver<'a, 'tcx> {
1857 infcx: &'a InferCtxt<'a, 'tcx>,
1860 impl<'a, 'tcx> TypeFolder<'tcx> for ShallowResolver<'a, 'tcx> {
1861 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1865 /// If `ty` is a type variable of some kind, resolve it one level
1866 /// (but do not resolve types found in the result). If `typ` is
1867 /// not a type variable, just return it unmodified.
1868 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1870 ty::Infer(ty::TyVar(v)) => {
1871 // Not entirely obvious: if `typ` is a type variable,
1872 // it can be resolved to an int/float variable, which
1873 // can then be recursively resolved, hence the
1874 // recursion. Note though that we prevent type
1875 // variables from unifying to other type variables
1876 // directly (though they may be embedded
1877 // structurally), and we prevent cycles in any case,
1878 // so this recursion should always be of very limited
1881 // Note: if these two lines are combined into one we get
1882 // dynamic borrow errors on `self.inner`.
1883 let known = self.infcx.inner.borrow_mut().type_variables().probe(v).known();
1884 known.map_or(ty, |t| self.fold_ty(t))
1887 ty::Infer(ty::IntVar(v)) => self
1891 .int_unification_table()
1893 .map_or(ty, |v| v.to_type(self.infcx.tcx)),
1895 ty::Infer(ty::FloatVar(v)) => self
1899 .float_unification_table()
1901 .map_or(ty, |v| v.to_type(self.infcx.tcx)),
1907 fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
1908 if let ty::ConstKind::Infer(InferConst::Var(vid)) = ct.kind() {
1912 .const_unification_table()
1923 impl<'tcx> TypeTrace<'tcx> {
1924 pub fn span(&self) -> Span {
1929 cause: &ObligationCause<'tcx>,
1930 a_is_expected: bool,
1933 ) -> TypeTrace<'tcx> {
1935 cause: cause.clone(),
1936 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
1941 cause: &ObligationCause<'tcx>,
1942 a_is_expected: bool,
1945 ) -> TypeTrace<'tcx> {
1947 cause: cause.clone(),
1948 values: Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
1953 impl<'tcx> SubregionOrigin<'tcx> {
1954 pub fn span(&self) -> Span {
1956 Subtype(ref a) => a.span(),
1957 RelateObjectBound(a) => a,
1958 RelateParamBound(a, ..) => a,
1959 RelateRegionParamBound(a) => a,
1961 ReborrowUpvar(a, _) => a,
1962 DataBorrowed(_, a) => a,
1963 ReferenceOutlivesReferent(_, a) => a,
1964 CompareImplItemObligation { span, .. } => span,
1965 CheckAssociatedTypeBounds { ref parent, .. } => parent.span(),
1969 pub fn from_obligation_cause<F>(cause: &traits::ObligationCause<'tcx>, default: F) -> Self
1971 F: FnOnce() -> Self,
1973 match *cause.code() {
1974 traits::ObligationCauseCode::ReferenceOutlivesReferent(ref_type) => {
1975 SubregionOrigin::ReferenceOutlivesReferent(ref_type, cause.span)
1978 traits::ObligationCauseCode::CompareImplItemObligation {
1982 } => SubregionOrigin::CompareImplItemObligation {
1988 traits::ObligationCauseCode::CheckAssociatedTypeBounds {
1991 } => SubregionOrigin::CheckAssociatedTypeBounds {
1994 parent: Box::new(default()),
2002 impl RegionVariableOrigin {
2003 pub fn span(&self) -> Span {
2010 | EarlyBoundRegion(a, ..)
2011 | LateBoundRegion(a, ..)
2012 | UpvarRegion(_, a) => a,
2013 Nll(..) => bug!("NLL variable used with `span`"),
2018 impl<'tcx> fmt::Debug for RegionObligation<'tcx> {
2019 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2022 "RegionObligation(sub_region={:?}, sup_type={:?})",
2023 self.sub_region, self.sup_type
2028 /// Replaces substs that reference param or infer variables with suitable
2029 /// placeholders. This function is meant to remove these param and infer
2030 /// substs when they're not actually needed to evaluate a constant.
2031 fn replace_param_and_infer_substs_with_placeholder<'tcx>(
2033 substs: SubstsRef<'tcx>,
2034 ) -> SubstsRef<'tcx> {
2035 tcx.mk_substs(substs.iter().enumerate().map(|(idx, arg)| {
2036 match arg.unpack() {
2037 GenericArgKind::Type(_)
2038 if arg.has_param_types_or_consts() || arg.has_infer_types_or_consts() =>
2040 tcx.mk_ty(ty::Placeholder(ty::PlaceholderType {
2041 universe: ty::UniverseIndex::ROOT,
2042 name: ty::BoundVar::from_usize(idx),
2046 GenericArgKind::Const(ct)
2047 if ct.has_infer_types_or_consts() || ct.has_param_types_or_consts() =>
2050 // If the type references param or infer, replace that too...
2051 if ty.has_param_types_or_consts() || ty.has_infer_types_or_consts() {
2052 bug!("const `{ct}`'s type should not reference params or types");
2054 tcx.mk_const(ty::ConstS {
2056 kind: ty::ConstKind::Placeholder(ty::PlaceholderConst {
2057 universe: ty::UniverseIndex::ROOT,
2058 name: ty::BoundVar::from_usize(idx),