rustc_infer/infer/
mod.rs

1use std::cell::{Cell, RefCell};
2use std::fmt;
3
4pub use BoundRegionConversionTime::*;
5pub use RegionVariableOrigin::*;
6pub use SubregionOrigin::*;
7pub use at::DefineOpaqueTypes;
8use free_regions::RegionRelations;
9pub use freshen::TypeFreshener;
10use lexical_region_resolve::LexicalRegionResolutions;
11pub use lexical_region_resolve::RegionResolutionError;
12use opaque_types::OpaqueTypeStorage;
13use region_constraints::{
14    GenericKind, RegionConstraintCollector, RegionConstraintStorage, VarInfos, VerifyBound,
15};
16pub use relate::StructurallyRelateAliases;
17pub use relate::combine::PredicateEmittingRelation;
18use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
19use rustc_data_structures::undo_log::{Rollback, UndoLogs};
20use rustc_data_structures::unify as ut;
21use rustc_errors::{DiagCtxtHandle, ErrorGuaranteed};
22use rustc_hir as hir;
23use rustc_hir::def_id::{DefId, LocalDefId};
24use rustc_macros::extension;
25pub use rustc_macros::{TypeFoldable, TypeVisitable};
26use rustc_middle::bug;
27use rustc_middle::infer::canonical::{CanonicalQueryInput, CanonicalVarValues};
28use rustc_middle::mir::ConstraintCategory;
29use rustc_middle::traits::select;
30use rustc_middle::traits::solve::Goal;
31use rustc_middle::ty::error::{ExpectedFound, TypeError};
32use rustc_middle::ty::{
33    self, BoundVarReplacerDelegate, ConstVid, FloatVid, GenericArg, GenericArgKind, GenericArgs,
34    GenericArgsRef, GenericParamDefKind, InferConst, IntVid, PseudoCanonicalInput, Ty, TyCtxt,
35    TyVid, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitable, TypeVisitableExt, TypingEnv,
36    TypingMode, fold_regions,
37};
38use rustc_span::{Span, Symbol};
39use snapshot::undo_log::InferCtxtUndoLogs;
40use tracing::{debug, instrument};
41use type_variable::TypeVariableOrigin;
42
43use crate::infer::region_constraints::UndoLog;
44use crate::infer::unify_key::{ConstVariableOrigin, ConstVariableValue, ConstVidKey};
45use crate::traits::{
46    self, ObligationCause, ObligationInspector, PredicateObligations, TraitEngine,
47};
48
49pub mod at;
50pub mod canonical;
51mod context;
52mod free_regions;
53mod freshen;
54mod lexical_region_resolve;
55mod opaque_types;
56pub mod outlives;
57mod projection;
58pub mod region_constraints;
59pub mod relate;
60pub mod resolve;
61pub(crate) mod snapshot;
62mod type_variable;
63mod unify_key;
64
65/// `InferOk<'tcx, ()>` is used a lot. It may seem like a useless wrapper
66/// around `PredicateObligations<'tcx>`, but it has one important property:
67/// because `InferOk` is marked with `#[must_use]`, if you have a method
68/// `InferCtxt::f` that returns `InferResult<'tcx, ()>` and you call it with
69/// `infcx.f()?;` you'll get a warning about the obligations being discarded
70/// without use, which is probably unintentional and has been a source of bugs
71/// in the past.
72#[must_use]
73#[derive(Debug)]
74pub struct InferOk<'tcx, T> {
75    pub value: T,
76    pub obligations: PredicateObligations<'tcx>,
77}
78pub type InferResult<'tcx, T> = Result<InferOk<'tcx, T>, TypeError<'tcx>>;
79
80pub(crate) type FixupResult<T> = Result<T, FixupError>; // "fixup result"
81
82pub(crate) type UnificationTable<'a, 'tcx, T> = ut::UnificationTable<
83    ut::InPlace<T, &'a mut ut::UnificationStorage<T>, &'a mut InferCtxtUndoLogs<'tcx>>,
84>;
85
86/// This type contains all the things within `InferCtxt` that sit within a
87/// `RefCell` and are involved with taking/rolling back snapshots. Snapshot
88/// operations are hot enough that we want only one call to `borrow_mut` per
89/// call to `start_snapshot` and `rollback_to`.
90#[derive(Clone)]
91pub struct InferCtxtInner<'tcx> {
92    undo_log: InferCtxtUndoLogs<'tcx>,
93
94    /// Cache for projections.
95    ///
96    /// This cache is snapshotted along with the infcx.
97    projection_cache: traits::ProjectionCacheStorage<'tcx>,
98
99    /// We instantiate `UnificationTable` with `bounds<Ty>` because the types
100    /// that might instantiate a general type variable have an order,
101    /// represented by its upper and lower bounds.
102    type_variable_storage: type_variable::TypeVariableStorage<'tcx>,
103
104    /// Map from const parameter variable to the kind of const it represents.
105    const_unification_storage: ut::UnificationTableStorage<ConstVidKey<'tcx>>,
106
107    /// Map from integral variable to the kind of integer it represents.
108    int_unification_storage: ut::UnificationTableStorage<ty::IntVid>,
109
110    /// Map from floating variable to the kind of float it represents.
111    float_unification_storage: ut::UnificationTableStorage<ty::FloatVid>,
112
113    /// Tracks the set of region variables and the constraints between them.
114    ///
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>>,
120
121    /// A set of constraints that regionck must validate.
122    ///
123    /// Each constraint has the form `T:'a`, meaning "some type `T` must
124    /// outlive the lifetime 'a". These constraints derive from
125    /// instantiated type parameters. So if you had a struct defined
126    /// like the following:
127    /// ```ignore (illustrative)
128    /// struct Foo<T: 'static> { ... }
129    /// ```
130    /// In some expression `let x = Foo { ... }`, it will
131    /// instantiate the type parameter `T` with a fresh type `$0`. At
132    /// the same time, it will record a region obligation of
133    /// `$0: 'static`. This will get checked later by regionck. (We
134    /// can't generally check these things right away because we have
135    /// to wait until types are resolved.)
136    ///
137    /// These are stored in a map keyed to the id of the innermost
138    /// enclosing fn body / static initializer expression. This is
139    /// because the location where the obligation was incurred can be
140    /// relevant with respect to which sublifetime assumptions are in
141    /// place. The reason that we store under the fn-id, and not
142    /// something more fine-grained, is so that it is easier for
143    /// regionck to be sure that it has found *all* the region
144    /// obligations (otherwise, it's easy to fail to walk to a
145    /// particular node-id).
146    ///
147    /// Before running `resolve_regions_and_report_errors`, the creator
148    /// of the inference context is expected to invoke
149    /// [`InferCtxt::process_registered_region_obligations`]
150    /// for each body-id in this map, which will process the
151    /// obligations within. This is expected to be done 'late enough'
152    /// that all type inference variables have been bound and so forth.
153    region_obligations: Vec<RegionObligation<'tcx>>,
154
155    /// Caches for opaque type inference.
156    opaque_type_storage: OpaqueTypeStorage<'tcx>,
157}
158
159impl<'tcx> InferCtxtInner<'tcx> {
160    fn new() -> InferCtxtInner<'tcx> {
161        InferCtxtInner {
162            undo_log: InferCtxtUndoLogs::default(),
163
164            projection_cache: Default::default(),
165            type_variable_storage: Default::default(),
166            const_unification_storage: Default::default(),
167            int_unification_storage: Default::default(),
168            float_unification_storage: Default::default(),
169            region_constraint_storage: Some(Default::default()),
170            region_obligations: vec![],
171            opaque_type_storage: Default::default(),
172        }
173    }
174
175    #[inline]
176    pub fn region_obligations(&self) -> &[RegionObligation<'tcx>] {
177        &self.region_obligations
178    }
179
180    #[inline]
181    pub fn projection_cache(&mut self) -> traits::ProjectionCache<'_, 'tcx> {
182        self.projection_cache.with_log(&mut self.undo_log)
183    }
184
185    #[inline]
186    fn try_type_variables_probe_ref(
187        &self,
188        vid: ty::TyVid,
189    ) -> Option<&type_variable::TypeVariableValue<'tcx>> {
190        // Uses a read-only view of the unification table, this way we don't
191        // need an undo log.
192        self.type_variable_storage.eq_relations_ref().try_probe_value(vid)
193    }
194
195    #[inline]
196    fn type_variables(&mut self) -> type_variable::TypeVariableTable<'_, 'tcx> {
197        self.type_variable_storage.with_log(&mut self.undo_log)
198    }
199
200    #[inline]
201    fn opaque_types(&mut self) -> opaque_types::OpaqueTypeTable<'_, 'tcx> {
202        self.opaque_type_storage.with_log(&mut self.undo_log)
203    }
204
205    #[inline]
206    fn int_unification_table(&mut self) -> UnificationTable<'_, 'tcx, ty::IntVid> {
207        self.int_unification_storage.with_log(&mut self.undo_log)
208    }
209
210    #[inline]
211    fn float_unification_table(&mut self) -> UnificationTable<'_, 'tcx, ty::FloatVid> {
212        self.float_unification_storage.with_log(&mut self.undo_log)
213    }
214
215    #[inline]
216    fn const_unification_table(&mut self) -> UnificationTable<'_, 'tcx, ConstVidKey<'tcx>> {
217        self.const_unification_storage.with_log(&mut self.undo_log)
218    }
219
220    #[inline]
221    pub fn unwrap_region_constraints(&mut self) -> RegionConstraintCollector<'_, 'tcx> {
222        self.region_constraint_storage
223            .as_mut()
224            .expect("region constraints already solved")
225            .with_log(&mut self.undo_log)
226    }
227
228    // Iterates through the opaque type definitions without taking them; this holds the
229    // `InferCtxtInner` lock, so make sure to not do anything with `InferCtxt` side-effects
230    // while looping through this.
231    pub fn iter_opaque_types(
232        &self,
233    ) -> impl Iterator<Item = (ty::OpaqueTypeKey<'tcx>, ty::OpaqueHiddenType<'tcx>)> {
234        self.opaque_type_storage.opaque_types.iter().map(|(&k, &v)| (k, v))
235    }
236}
237
238pub struct InferCtxt<'tcx> {
239    pub tcx: TyCtxt<'tcx>,
240
241    /// The mode of this inference context, see the struct documentation
242    /// for more details.
243    typing_mode: TypingMode<'tcx>,
244
245    /// Whether this inference context should care about region obligations in
246    /// the root universe. Most notably, this is used during hir typeck as region
247    /// solving is left to borrowck instead.
248    pub considering_regions: bool,
249
250    /// If set, this flag causes us to skip the 'leak check' during
251    /// higher-ranked subtyping operations. This flag is a temporary one used
252    /// to manage the removal of the leak-check: for the time being, we still run the
253    /// leak-check, but we issue warnings.
254    skip_leak_check: bool,
255
256    pub inner: RefCell<InferCtxtInner<'tcx>>,
257
258    /// Once region inference is done, the values for each variable.
259    lexical_region_resolutions: RefCell<Option<LexicalRegionResolutions<'tcx>>>,
260
261    /// Caches the results of trait selection. This cache is used
262    /// for things that depends on inference variables or placeholders.
263    pub selection_cache: select::SelectionCache<'tcx, ty::ParamEnv<'tcx>>,
264
265    /// Caches the results of trait evaluation. This cache is used
266    /// for things that depends on inference variables or placeholders.
267    pub evaluation_cache: select::EvaluationCache<'tcx, ty::ParamEnv<'tcx>>,
268
269    /// The set of predicates on which errors have been reported, to
270    /// avoid reporting the same error twice.
271    pub reported_trait_errors:
272        RefCell<FxIndexMap<Span, (Vec<Goal<'tcx, ty::Predicate<'tcx>>>, ErrorGuaranteed)>>,
273
274    pub reported_signature_mismatch: RefCell<FxHashSet<(Span, Option<Span>)>>,
275
276    /// When an error occurs, we want to avoid reporting "derived"
277    /// errors that are due to this original failure. We have this
278    /// flag that one can set whenever one creates a type-error that
279    /// is due to an error in a prior pass.
280    ///
281    /// Don't read this flag directly, call `is_tainted_by_errors()`
282    /// and `set_tainted_by_errors()`.
283    tainted_by_errors: Cell<Option<ErrorGuaranteed>>,
284
285    /// What is the innermost universe we have created? Starts out as
286    /// `UniverseIndex::root()` but grows from there as we enter
287    /// universal quantifiers.
288    ///
289    /// N.B., at present, we exclude the universal quantifiers on the
290    /// item we are type-checking, and just consider those names as
291    /// part of the root universe. So this would only get incremented
292    /// when we enter into a higher-ranked (`for<..>`) type or trait
293    /// bound.
294    universe: Cell<ty::UniverseIndex>,
295
296    next_trait_solver: bool,
297
298    pub obligation_inspector: Cell<Option<ObligationInspector<'tcx>>>,
299}
300
301/// See the `error_reporting` module for more details.
302#[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable, TypeVisitable)]
303pub enum ValuePairs<'tcx> {
304    Regions(ExpectedFound<ty::Region<'tcx>>),
305    Terms(ExpectedFound<ty::Term<'tcx>>),
306    Aliases(ExpectedFound<ty::AliasTerm<'tcx>>),
307    TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>),
308    PolySigs(ExpectedFound<ty::PolyFnSig<'tcx>>),
309    ExistentialTraitRef(ExpectedFound<ty::PolyExistentialTraitRef<'tcx>>),
310    ExistentialProjection(ExpectedFound<ty::PolyExistentialProjection<'tcx>>),
311}
312
313impl<'tcx> ValuePairs<'tcx> {
314    pub fn ty(&self) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
315        if let ValuePairs::Terms(ExpectedFound { expected, found }) = self
316            && let Some(expected) = expected.as_type()
317            && let Some(found) = found.as_type()
318        {
319            Some((expected, found))
320        } else {
321            None
322        }
323    }
324}
325
326/// The trace designates the path through inference that we took to
327/// encounter an error or subtyping constraint.
328///
329/// See the `error_reporting` module for more details.
330#[derive(Clone, Debug)]
331pub struct TypeTrace<'tcx> {
332    pub cause: ObligationCause<'tcx>,
333    pub values: ValuePairs<'tcx>,
334}
335
336/// The origin of a `r1 <= r2` constraint.
337///
338/// See `error_reporting` module for more details
339#[derive(Clone, Debug)]
340pub enum SubregionOrigin<'tcx> {
341    /// Arose from a subtyping relation
342    Subtype(Box<TypeTrace<'tcx>>),
343
344    /// When casting `&'a T` to an `&'b Trait` object,
345    /// relating `'a` to `'b`.
346    RelateObjectBound(Span),
347
348    /// Some type parameter was instantiated with the given type,
349    /// and that type must outlive some region.
350    RelateParamBound(Span, Ty<'tcx>, Option<Span>),
351
352    /// The given region parameter was instantiated with a region
353    /// that must outlive some other region.
354    RelateRegionParamBound(Span, Option<Ty<'tcx>>),
355
356    /// Creating a pointer `b` to contents of another reference.
357    Reborrow(Span),
358
359    /// (&'a &'b T) where a >= b
360    ReferenceOutlivesReferent(Ty<'tcx>, Span),
361
362    /// Comparing the signature and requirements of an impl method against
363    /// the containing trait.
364    CompareImplItemObligation {
365        span: Span,
366        impl_item_def_id: LocalDefId,
367        trait_item_def_id: DefId,
368    },
369
370    /// Checking that the bounds of a trait's associated type hold for a given impl.
371    CheckAssociatedTypeBounds {
372        parent: Box<SubregionOrigin<'tcx>>,
373        impl_item_def_id: LocalDefId,
374        trait_item_def_id: DefId,
375    },
376
377    AscribeUserTypeProvePredicate(Span),
378}
379
380// `SubregionOrigin` is used a lot. Make sure it doesn't unintentionally get bigger.
381#[cfg(target_pointer_width = "64")]
382rustc_data_structures::static_assert_size!(SubregionOrigin<'_>, 32);
383
384impl<'tcx> SubregionOrigin<'tcx> {
385    pub fn to_constraint_category(&self) -> ConstraintCategory<'tcx> {
386        match self {
387            Self::Subtype(type_trace) => type_trace.cause.to_constraint_category(),
388            Self::AscribeUserTypeProvePredicate(span) => ConstraintCategory::Predicate(*span),
389            _ => ConstraintCategory::BoringNoLocation,
390        }
391    }
392}
393
394/// Times when we replace bound regions with existentials:
395#[derive(Clone, Copy, Debug)]
396pub enum BoundRegionConversionTime {
397    /// when a fn is called
398    FnCall,
399
400    /// when two higher-ranked types are compared
401    HigherRankedType,
402
403    /// when projecting an associated type
404    AssocTypeProjection(DefId),
405}
406
407/// Reasons to create a region inference variable.
408///
409/// See `error_reporting` module for more details.
410#[derive(Copy, Clone, Debug)]
411pub enum RegionVariableOrigin {
412    /// Region variables created for ill-categorized reasons.
413    ///
414    /// They mostly indicate places in need of refactoring.
415    MiscVariable(Span),
416
417    /// Regions created by a `&P` or `[...]` pattern.
418    PatternRegion(Span),
419
420    /// Regions created by `&` operator.
421    BorrowRegion(Span),
422
423    /// Regions created as part of an autoref of a method receiver.
424    Autoref(Span),
425
426    /// Regions created as part of an automatic coercion.
427    Coercion(Span),
428
429    /// Region variables created as the values for early-bound regions.
430    ///
431    /// FIXME(@lcnr): This should also store a `DefId`, similar to
432    /// `TypeVariableOrigin`.
433    RegionParameterDefinition(Span, Symbol),
434
435    /// Region variables created when instantiating a binder with
436    /// existential variables, e.g. when calling a function or method.
437    BoundRegion(Span, ty::BoundRegionKind, BoundRegionConversionTime),
438
439    UpvarRegion(ty::UpvarId, Span),
440
441    /// This origin is used for the inference variables that we create
442    /// during NLL region processing.
443    Nll(NllRegionVariableOrigin),
444}
445
446#[derive(Copy, Clone, Debug)]
447pub enum NllRegionVariableOrigin {
448    /// During NLL region processing, we create variables for free
449    /// regions that we encounter in the function signature and
450    /// elsewhere. This origin indices we've got one of those.
451    FreeRegion,
452
453    /// "Universal" instantiation of a higher-ranked region (e.g.,
454    /// from a `for<'a> T` binder). Meant to represent "any region".
455    Placeholder(ty::PlaceholderRegion),
456
457    Existential {
458        /// If this is true, then this variable was created to represent a lifetime
459        /// bound in a `for` binder. For example, it might have been created to
460        /// represent the lifetime `'a` in a type like `for<'a> fn(&'a u32)`.
461        /// Such variables are created when we are trying to figure out if there
462        /// is any valid instantiation of `'a` that could fit into some scenario.
463        ///
464        /// This is used to inform error reporting: in the case that we are trying to
465        /// determine whether there is any valid instantiation of a `'a` variable that meets
466        /// some constraint C, we want to blame the "source" of that `for` type,
467        /// rather than blaming the source of the constraint C.
468        from_forall: bool,
469    },
470}
471
472#[derive(Copy, Clone, Debug)]
473pub struct FixupError {
474    unresolved: TyOrConstInferVar,
475}
476
477impl fmt::Display for FixupError {
478    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
479        use TyOrConstInferVar::*;
480
481        match self.unresolved {
482            TyInt(_) => write!(
483                f,
484                "cannot determine the type of this integer; \
485                 add a suffix to specify the type explicitly"
486            ),
487            TyFloat(_) => write!(
488                f,
489                "cannot determine the type of this number; \
490                 add a suffix to specify the type explicitly"
491            ),
492            Ty(_) => write!(f, "unconstrained type"),
493            Const(_) => write!(f, "unconstrained const value"),
494        }
495    }
496}
497
498/// See the `region_obligations` field for more information.
499#[derive(Clone, Debug)]
500pub struct RegionObligation<'tcx> {
501    pub sub_region: ty::Region<'tcx>,
502    pub sup_type: Ty<'tcx>,
503    pub origin: SubregionOrigin<'tcx>,
504}
505
506/// Used to configure inference contexts before their creation.
507pub struct InferCtxtBuilder<'tcx> {
508    tcx: TyCtxt<'tcx>,
509    considering_regions: bool,
510    skip_leak_check: bool,
511    /// Whether we should use the new trait solver in the local inference context,
512    /// which affects things like which solver is used in `predicate_may_hold`.
513    next_trait_solver: bool,
514}
515
516#[extension(pub trait TyCtxtInferExt<'tcx>)]
517impl<'tcx> TyCtxt<'tcx> {
518    fn infer_ctxt(self) -> InferCtxtBuilder<'tcx> {
519        InferCtxtBuilder {
520            tcx: self,
521            considering_regions: true,
522            skip_leak_check: false,
523            next_trait_solver: self.next_trait_solver_globally(),
524        }
525    }
526}
527
528impl<'tcx> InferCtxtBuilder<'tcx> {
529    pub fn with_next_trait_solver(mut self, next_trait_solver: bool) -> Self {
530        self.next_trait_solver = next_trait_solver;
531        self
532    }
533
534    pub fn ignoring_regions(mut self) -> Self {
535        self.considering_regions = false;
536        self
537    }
538
539    pub fn skip_leak_check(mut self, skip_leak_check: bool) -> Self {
540        self.skip_leak_check = skip_leak_check;
541        self
542    }
543
544    /// Given a canonical value `C` as a starting point, create an
545    /// inference context that contains each of the bound values
546    /// within instantiated as a fresh variable. The `f` closure is
547    /// invoked with the new infcx, along with the instantiated value
548    /// `V` and a instantiation `S`. This instantiation `S` maps from
549    /// the bound values in `C` to their instantiated values in `V`
550    /// (in other words, `S(C) = V`).
551    pub fn build_with_canonical<T>(
552        mut self,
553        span: Span,
554        input: &CanonicalQueryInput<'tcx, T>,
555    ) -> (InferCtxt<'tcx>, T, CanonicalVarValues<'tcx>)
556    where
557        T: TypeFoldable<TyCtxt<'tcx>>,
558    {
559        let infcx = self.build(input.typing_mode);
560        let (value, args) = infcx.instantiate_canonical(span, &input.canonical);
561        (infcx, value, args)
562    }
563
564    pub fn build_with_typing_env(
565        mut self,
566        TypingEnv { typing_mode, param_env }: TypingEnv<'tcx>,
567    ) -> (InferCtxt<'tcx>, ty::ParamEnv<'tcx>) {
568        (self.build(typing_mode), param_env)
569    }
570
571    pub fn build(&mut self, typing_mode: TypingMode<'tcx>) -> InferCtxt<'tcx> {
572        let InferCtxtBuilder { tcx, considering_regions, skip_leak_check, next_trait_solver } =
573            *self;
574        InferCtxt {
575            tcx,
576            typing_mode,
577            considering_regions,
578            skip_leak_check,
579            inner: RefCell::new(InferCtxtInner::new()),
580            lexical_region_resolutions: RefCell::new(None),
581            selection_cache: Default::default(),
582            evaluation_cache: Default::default(),
583            reported_trait_errors: Default::default(),
584            reported_signature_mismatch: Default::default(),
585            tainted_by_errors: Cell::new(None),
586            universe: Cell::new(ty::UniverseIndex::ROOT),
587            next_trait_solver,
588            obligation_inspector: Cell::new(None),
589        }
590    }
591}
592
593impl<'tcx, T> InferOk<'tcx, T> {
594    /// Extracts `value`, registering any obligations into `fulfill_cx`.
595    pub fn into_value_registering_obligations<E: 'tcx>(
596        self,
597        infcx: &InferCtxt<'tcx>,
598        fulfill_cx: &mut dyn TraitEngine<'tcx, E>,
599    ) -> T {
600        let InferOk { value, obligations } = self;
601        fulfill_cx.register_predicate_obligations(infcx, obligations);
602        value
603    }
604}
605
606impl<'tcx> InferOk<'tcx, ()> {
607    pub fn into_obligations(self) -> PredicateObligations<'tcx> {
608        self.obligations
609    }
610}
611
612impl<'tcx> InferCtxt<'tcx> {
613    pub fn dcx(&self) -> DiagCtxtHandle<'_> {
614        self.tcx.dcx().taintable_handle(&self.tainted_by_errors)
615    }
616
617    pub fn next_trait_solver(&self) -> bool {
618        self.next_trait_solver
619    }
620
621    #[inline(always)]
622    pub fn typing_mode(&self) -> TypingMode<'tcx> {
623        self.typing_mode
624    }
625
626    pub fn freshen<T: TypeFoldable<TyCtxt<'tcx>>>(&self, t: T) -> T {
627        t.fold_with(&mut self.freshener())
628    }
629
630    /// Returns the origin of the type variable identified by `vid`.
631    ///
632    /// No attempt is made to resolve `vid` to its root variable.
633    pub fn type_var_origin(&self, vid: TyVid) -> TypeVariableOrigin {
634        self.inner.borrow_mut().type_variables().var_origin(vid)
635    }
636
637    /// Returns the origin of the const variable identified by `vid`
638    // FIXME: We should store origins separately from the unification table
639    // so this doesn't need to be optional.
640    pub fn const_var_origin(&self, vid: ConstVid) -> Option<ConstVariableOrigin> {
641        match self.inner.borrow_mut().const_unification_table().probe_value(vid) {
642            ConstVariableValue::Known { .. } => None,
643            ConstVariableValue::Unknown { origin, .. } => Some(origin),
644        }
645    }
646
647    pub fn freshener<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
648        freshen::TypeFreshener::new(self)
649    }
650
651    pub fn unresolved_variables(&self) -> Vec<Ty<'tcx>> {
652        let mut inner = self.inner.borrow_mut();
653        let mut vars: Vec<Ty<'_>> = inner
654            .type_variables()
655            .unresolved_variables()
656            .into_iter()
657            .map(|t| Ty::new_var(self.tcx, t))
658            .collect();
659        vars.extend(
660            (0..inner.int_unification_table().len())
661                .map(|i| ty::IntVid::from_usize(i))
662                .filter(|&vid| inner.int_unification_table().probe_value(vid).is_unknown())
663                .map(|v| Ty::new_int_var(self.tcx, v)),
664        );
665        vars.extend(
666            (0..inner.float_unification_table().len())
667                .map(|i| ty::FloatVid::from_usize(i))
668                .filter(|&vid| inner.float_unification_table().probe_value(vid).is_unknown())
669                .map(|v| Ty::new_float_var(self.tcx, v)),
670        );
671        vars
672    }
673
674    #[instrument(skip(self), level = "debug")]
675    pub fn sub_regions(
676        &self,
677        origin: SubregionOrigin<'tcx>,
678        a: ty::Region<'tcx>,
679        b: ty::Region<'tcx>,
680    ) {
681        self.inner.borrow_mut().unwrap_region_constraints().make_subregion(origin, a, b);
682    }
683
684    /// Processes a `Coerce` predicate from the fulfillment context.
685    /// This is NOT the preferred way to handle coercion, which is to
686    /// invoke `FnCtxt::coerce` or a similar method (see `coercion.rs`).
687    ///
688    /// This method here is actually a fallback that winds up being
689    /// invoked when `FnCtxt::coerce` encounters unresolved type variables
690    /// and records a coercion predicate. Presently, this method is equivalent
691    /// to `subtype_predicate` -- that is, "coercing" `a` to `b` winds up
692    /// actually requiring `a <: b`. This is of course a valid coercion,
693    /// but it's not as flexible as `FnCtxt::coerce` would be.
694    ///
695    /// (We may refactor this in the future, but there are a number of
696    /// practical obstacles. Among other things, `FnCtxt::coerce` presently
697    /// records adjustments that are required on the HIR in order to perform
698    /// the coercion, and we don't currently have a way to manage that.)
699    pub fn coerce_predicate(
700        &self,
701        cause: &ObligationCause<'tcx>,
702        param_env: ty::ParamEnv<'tcx>,
703        predicate: ty::PolyCoercePredicate<'tcx>,
704    ) -> Result<InferResult<'tcx, ()>, (TyVid, TyVid)> {
705        let subtype_predicate = predicate.map_bound(|p| ty::SubtypePredicate {
706            a_is_expected: false, // when coercing from `a` to `b`, `b` is expected
707            a: p.a,
708            b: p.b,
709        });
710        self.subtype_predicate(cause, param_env, subtype_predicate)
711    }
712
713    pub fn subtype_predicate(
714        &self,
715        cause: &ObligationCause<'tcx>,
716        param_env: ty::ParamEnv<'tcx>,
717        predicate: ty::PolySubtypePredicate<'tcx>,
718    ) -> Result<InferResult<'tcx, ()>, (TyVid, TyVid)> {
719        // Check for two unresolved inference variables, in which case we can
720        // make no progress. This is partly a micro-optimization, but it's
721        // also an opportunity to "sub-unify" the variables. This isn't
722        // *necessary* to prevent cycles, because they would eventually be sub-unified
723        // anyhow during generalization, but it helps with diagnostics (we can detect
724        // earlier that they are sub-unified).
725        //
726        // Note that we can just skip the binders here because
727        // type variables can't (at present, at
728        // least) capture any of the things bound by this binder.
729        //
730        // Note that this sub here is not just for diagnostics - it has semantic
731        // effects as well.
732        let r_a = self.shallow_resolve(predicate.skip_binder().a);
733        let r_b = self.shallow_resolve(predicate.skip_binder().b);
734        match (r_a.kind(), r_b.kind()) {
735            (&ty::Infer(ty::TyVar(a_vid)), &ty::Infer(ty::TyVar(b_vid))) => {
736                return Err((a_vid, b_vid));
737            }
738            _ => {}
739        }
740
741        self.enter_forall(predicate, |ty::SubtypePredicate { a_is_expected, a, b }| {
742            if a_is_expected {
743                Ok(self.at(cause, param_env).sub(DefineOpaqueTypes::Yes, a, b))
744            } else {
745                Ok(self.at(cause, param_env).sup(DefineOpaqueTypes::Yes, b, a))
746            }
747        })
748    }
749
750    pub fn region_outlives_predicate(
751        &self,
752        cause: &traits::ObligationCause<'tcx>,
753        predicate: ty::PolyRegionOutlivesPredicate<'tcx>,
754    ) {
755        self.enter_forall(predicate, |ty::OutlivesPredicate(r_a, r_b)| {
756            let origin = SubregionOrigin::from_obligation_cause(cause, || {
757                RelateRegionParamBound(cause.span, None)
758            });
759            self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
760        })
761    }
762
763    /// Number of type variables created so far.
764    pub fn num_ty_vars(&self) -> usize {
765        self.inner.borrow_mut().type_variables().num_vars()
766    }
767
768    pub fn next_ty_var(&self, span: Span) -> Ty<'tcx> {
769        self.next_ty_var_with_origin(TypeVariableOrigin { span, param_def_id: None })
770    }
771
772    pub fn next_ty_var_with_origin(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
773        let vid = self.inner.borrow_mut().type_variables().new_var(self.universe(), origin);
774        Ty::new_var(self.tcx, vid)
775    }
776
777    pub fn next_ty_var_id_in_universe(&self, span: Span, universe: ty::UniverseIndex) -> TyVid {
778        let origin = TypeVariableOrigin { span, param_def_id: None };
779        self.inner.borrow_mut().type_variables().new_var(universe, origin)
780    }
781
782    pub fn next_ty_var_in_universe(&self, span: Span, universe: ty::UniverseIndex) -> Ty<'tcx> {
783        let vid = self.next_ty_var_id_in_universe(span, universe);
784        Ty::new_var(self.tcx, vid)
785    }
786
787    pub fn next_const_var(&self, span: Span) -> ty::Const<'tcx> {
788        self.next_const_var_with_origin(ConstVariableOrigin { span, param_def_id: None })
789    }
790
791    pub fn next_const_var_with_origin(&self, origin: ConstVariableOrigin) -> ty::Const<'tcx> {
792        let vid = self
793            .inner
794            .borrow_mut()
795            .const_unification_table()
796            .new_key(ConstVariableValue::Unknown { origin, universe: self.universe() })
797            .vid;
798        ty::Const::new_var(self.tcx, vid)
799    }
800
801    pub fn next_const_var_in_universe(
802        &self,
803        span: Span,
804        universe: ty::UniverseIndex,
805    ) -> ty::Const<'tcx> {
806        let origin = ConstVariableOrigin { span, param_def_id: None };
807        let vid = self
808            .inner
809            .borrow_mut()
810            .const_unification_table()
811            .new_key(ConstVariableValue::Unknown { origin, universe })
812            .vid;
813        ty::Const::new_var(self.tcx, vid)
814    }
815
816    pub fn next_int_var(&self) -> Ty<'tcx> {
817        let next_int_var_id =
818            self.inner.borrow_mut().int_unification_table().new_key(ty::IntVarValue::Unknown);
819        Ty::new_int_var(self.tcx, next_int_var_id)
820    }
821
822    pub fn next_float_var(&self) -> Ty<'tcx> {
823        let next_float_var_id =
824            self.inner.borrow_mut().float_unification_table().new_key(ty::FloatVarValue::Unknown);
825        Ty::new_float_var(self.tcx, next_float_var_id)
826    }
827
828    /// Creates a fresh region variable with the next available index.
829    /// The variable will be created in the maximum universe created
830    /// thus far, allowing it to name any region created thus far.
831    pub fn next_region_var(&self, origin: RegionVariableOrigin) -> ty::Region<'tcx> {
832        self.next_region_var_in_universe(origin, self.universe())
833    }
834
835    /// Creates a fresh region variable with the next available index
836    /// in the given universe; typically, you can use
837    /// `next_region_var` and just use the maximal universe.
838    pub fn next_region_var_in_universe(
839        &self,
840        origin: RegionVariableOrigin,
841        universe: ty::UniverseIndex,
842    ) -> ty::Region<'tcx> {
843        let region_var =
844            self.inner.borrow_mut().unwrap_region_constraints().new_region_var(universe, origin);
845        ty::Region::new_var(self.tcx, region_var)
846    }
847
848    /// Return the universe that the region `r` was created in. For
849    /// most regions (e.g., `'static`, named regions from the user,
850    /// etc) this is the root universe U0. For inference variables or
851    /// placeholders, however, it will return the universe which they
852    /// are associated.
853    pub fn universe_of_region(&self, r: ty::Region<'tcx>) -> ty::UniverseIndex {
854        self.inner.borrow_mut().unwrap_region_constraints().universe(r)
855    }
856
857    /// Number of region variables created so far.
858    pub fn num_region_vars(&self) -> usize {
859        self.inner.borrow_mut().unwrap_region_constraints().num_region_vars()
860    }
861
862    /// Just a convenient wrapper of `next_region_var` for using during NLL.
863    #[instrument(skip(self), level = "debug")]
864    pub fn next_nll_region_var(&self, origin: NllRegionVariableOrigin) -> ty::Region<'tcx> {
865        self.next_region_var(RegionVariableOrigin::Nll(origin))
866    }
867
868    /// Just a convenient wrapper of `next_region_var` for using during NLL.
869    #[instrument(skip(self), level = "debug")]
870    pub fn next_nll_region_var_in_universe(
871        &self,
872        origin: NllRegionVariableOrigin,
873        universe: ty::UniverseIndex,
874    ) -> ty::Region<'tcx> {
875        self.next_region_var_in_universe(RegionVariableOrigin::Nll(origin), universe)
876    }
877
878    pub fn var_for_def(&self, span: Span, param: &ty::GenericParamDef) -> GenericArg<'tcx> {
879        match param.kind {
880            GenericParamDefKind::Lifetime => {
881                // Create a region inference variable for the given
882                // region parameter definition.
883                self.next_region_var(RegionParameterDefinition(span, param.name)).into()
884            }
885            GenericParamDefKind::Type { .. } => {
886                // Create a type inference variable for the given
887                // type parameter definition. The generic parameters are
888                // for actual parameters that may be referred to by
889                // the default of this type parameter, if it exists.
890                // e.g., `struct Foo<A, B, C = (A, B)>(...);` when
891                // used in a path such as `Foo::<T, U>::new()` will
892                // use an inference variable for `C` with `[T, U]`
893                // as the generic parameters for the default, `(T, U)`.
894                let ty_var_id = self.inner.borrow_mut().type_variables().new_var(
895                    self.universe(),
896                    TypeVariableOrigin { param_def_id: Some(param.def_id), span },
897                );
898
899                Ty::new_var(self.tcx, ty_var_id).into()
900            }
901            GenericParamDefKind::Const { .. } => {
902                let origin = ConstVariableOrigin { param_def_id: Some(param.def_id), span };
903                let const_var_id = self
904                    .inner
905                    .borrow_mut()
906                    .const_unification_table()
907                    .new_key(ConstVariableValue::Unknown { origin, universe: self.universe() })
908                    .vid;
909                ty::Const::new_var(self.tcx, const_var_id).into()
910            }
911        }
912    }
913
914    /// Given a set of generics defined on a type or impl, returns the generic parameters mapping
915    /// each type/region parameter to a fresh inference variable.
916    pub fn fresh_args_for_item(&self, span: Span, def_id: DefId) -> GenericArgsRef<'tcx> {
917        GenericArgs::for_item(self.tcx, def_id, |param, _| self.var_for_def(span, param))
918    }
919
920    /// Returns `true` if errors have been reported since this infcx was
921    /// created. This is sometimes used as a heuristic to skip
922    /// reporting errors that often occur as a result of earlier
923    /// errors, but where it's hard to be 100% sure (e.g., unresolved
924    /// inference variables, regionck errors).
925    #[must_use = "this method does not have any side effects"]
926    pub fn tainted_by_errors(&self) -> Option<ErrorGuaranteed> {
927        self.tainted_by_errors.get()
928    }
929
930    /// Set the "tainted by errors" flag to true. We call this when we
931    /// observe an error from a prior pass.
932    pub fn set_tainted_by_errors(&self, e: ErrorGuaranteed) {
933        debug!("set_tainted_by_errors(ErrorGuaranteed)");
934        self.tainted_by_errors.set(Some(e));
935    }
936
937    pub fn region_var_origin(&self, vid: ty::RegionVid) -> RegionVariableOrigin {
938        let mut inner = self.inner.borrow_mut();
939        let inner = &mut *inner;
940        inner.unwrap_region_constraints().var_origin(vid)
941    }
942
943    /// Clone the list of variable regions. This is used only during NLL processing
944    /// to put the set of region variables into the NLL region context.
945    pub fn get_region_var_infos(&self) -> VarInfos {
946        let inner = self.inner.borrow();
947        assert!(!UndoLogs::<UndoLog<'_>>::in_snapshot(&inner.undo_log));
948        let storage = inner.region_constraint_storage.as_ref().expect("regions already resolved");
949        assert!(storage.data.is_empty(), "{:#?}", storage.data);
950        // We clone instead of taking because borrowck still wants to use the
951        // inference context after calling this for diagnostics and the new
952        // trait solver.
953        storage.var_infos.clone()
954    }
955
956    #[instrument(level = "debug", skip(self), ret)]
957    pub fn take_opaque_types(&self) -> opaque_types::OpaqueTypeMap<'tcx> {
958        std::mem::take(&mut self.inner.borrow_mut().opaque_type_storage.opaque_types)
959    }
960
961    #[instrument(level = "debug", skip(self), ret)]
962    pub fn clone_opaque_types(&self) -> opaque_types::OpaqueTypeMap<'tcx> {
963        self.inner.borrow().opaque_type_storage.opaque_types.clone()
964    }
965
966    #[inline(always)]
967    pub fn can_define_opaque_ty(&self, id: impl Into<DefId>) -> bool {
968        debug_assert!(!self.next_trait_solver());
969        match self.typing_mode() {
970            TypingMode::Analysis { defining_opaque_types }
971            | TypingMode::Borrowck { defining_opaque_types } => {
972                id.into().as_local().is_some_and(|def_id| defining_opaque_types.contains(&def_id))
973            }
974            // FIXME(#132279): This function is quite weird in post-analysis
975            // and post-borrowck analysis mode. We may need to modify its uses
976            // to support PostBorrowckAnalysis in the old solver as well.
977            TypingMode::Coherence
978            | TypingMode::PostBorrowckAnalysis { .. }
979            | TypingMode::PostAnalysis => false,
980        }
981    }
982
983    pub fn ty_to_string(&self, t: Ty<'tcx>) -> String {
984        self.resolve_vars_if_possible(t).to_string()
985    }
986
987    /// If `TyVar(vid)` resolves to a type, return that type. Else, return the
988    /// universe index of `TyVar(vid)`.
989    pub fn probe_ty_var(&self, vid: TyVid) -> Result<Ty<'tcx>, ty::UniverseIndex> {
990        use self::type_variable::TypeVariableValue;
991
992        match self.inner.borrow_mut().type_variables().probe(vid) {
993            TypeVariableValue::Known { value } => Ok(value),
994            TypeVariableValue::Unknown { universe } => Err(universe),
995        }
996    }
997
998    pub fn shallow_resolve(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
999        if let ty::Infer(v) = *ty.kind() {
1000            match v {
1001                ty::TyVar(v) => {
1002                    // Not entirely obvious: if `typ` is a type variable,
1003                    // it can be resolved to an int/float variable, which
1004                    // can then be recursively resolved, hence the
1005                    // recursion. Note though that we prevent type
1006                    // variables from unifying to other type variables
1007                    // directly (though they may be embedded
1008                    // structurally), and we prevent cycles in any case,
1009                    // so this recursion should always be of very limited
1010                    // depth.
1011                    //
1012                    // Note: if these two lines are combined into one we get
1013                    // dynamic borrow errors on `self.inner`.
1014                    let known = self.inner.borrow_mut().type_variables().probe(v).known();
1015                    known.map_or(ty, |t| self.shallow_resolve(t))
1016                }
1017
1018                ty::IntVar(v) => {
1019                    match self.inner.borrow_mut().int_unification_table().probe_value(v) {
1020                        ty::IntVarValue::IntType(ty) => Ty::new_int(self.tcx, ty),
1021                        ty::IntVarValue::UintType(ty) => Ty::new_uint(self.tcx, ty),
1022                        ty::IntVarValue::Unknown => ty,
1023                    }
1024                }
1025
1026                ty::FloatVar(v) => {
1027                    match self.inner.borrow_mut().float_unification_table().probe_value(v) {
1028                        ty::FloatVarValue::Known(ty) => Ty::new_float(self.tcx, ty),
1029                        ty::FloatVarValue::Unknown => ty,
1030                    }
1031                }
1032
1033                ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_) => ty,
1034            }
1035        } else {
1036            ty
1037        }
1038    }
1039
1040    pub fn shallow_resolve_const(&self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
1041        match ct.kind() {
1042            ty::ConstKind::Infer(infer_ct) => match infer_ct {
1043                InferConst::Var(vid) => self
1044                    .inner
1045                    .borrow_mut()
1046                    .const_unification_table()
1047                    .probe_value(vid)
1048                    .known()
1049                    .unwrap_or(ct),
1050                InferConst::Fresh(_) => ct,
1051            },
1052            ty::ConstKind::Param(_)
1053            | ty::ConstKind::Bound(_, _)
1054            | ty::ConstKind::Placeholder(_)
1055            | ty::ConstKind::Unevaluated(_)
1056            | ty::ConstKind::Value(_)
1057            | ty::ConstKind::Error(_)
1058            | ty::ConstKind::Expr(_) => ct,
1059        }
1060    }
1061
1062    pub fn root_var(&self, var: ty::TyVid) -> ty::TyVid {
1063        self.inner.borrow_mut().type_variables().root_var(var)
1064    }
1065
1066    pub fn root_const_var(&self, var: ty::ConstVid) -> ty::ConstVid {
1067        self.inner.borrow_mut().const_unification_table().find(var).vid
1068    }
1069
1070    /// Resolves an int var to a rigid int type, if it was constrained to one,
1071    /// or else the root int var in the unification table.
1072    pub fn opportunistic_resolve_int_var(&self, vid: ty::IntVid) -> Ty<'tcx> {
1073        let mut inner = self.inner.borrow_mut();
1074        let value = inner.int_unification_table().probe_value(vid);
1075        match value {
1076            ty::IntVarValue::IntType(ty) => Ty::new_int(self.tcx, ty),
1077            ty::IntVarValue::UintType(ty) => Ty::new_uint(self.tcx, ty),
1078            ty::IntVarValue::Unknown => {
1079                Ty::new_int_var(self.tcx, inner.int_unification_table().find(vid))
1080            }
1081        }
1082    }
1083
1084    /// Resolves a float var to a rigid int type, if it was constrained to one,
1085    /// or else the root float var in the unification table.
1086    pub fn opportunistic_resolve_float_var(&self, vid: ty::FloatVid) -> Ty<'tcx> {
1087        let mut inner = self.inner.borrow_mut();
1088        let value = inner.float_unification_table().probe_value(vid);
1089        match value {
1090            ty::FloatVarValue::Known(ty) => Ty::new_float(self.tcx, ty),
1091            ty::FloatVarValue::Unknown => {
1092                Ty::new_float_var(self.tcx, inner.float_unification_table().find(vid))
1093            }
1094        }
1095    }
1096
1097    /// Where possible, replaces type/const variables in
1098    /// `value` with their final value. Note that region variables
1099    /// are unaffected. If a type/const variable has not been unified, it
1100    /// is left as is. This is an idempotent operation that does
1101    /// not affect inference state in any way and so you can do it
1102    /// at will.
1103    pub fn resolve_vars_if_possible<T>(&self, value: T) -> T
1104    where
1105        T: TypeFoldable<TyCtxt<'tcx>>,
1106    {
1107        if let Err(guar) = value.error_reported() {
1108            self.set_tainted_by_errors(guar);
1109        }
1110        if !value.has_non_region_infer() {
1111            return value;
1112        }
1113        let mut r = resolve::OpportunisticVarResolver::new(self);
1114        value.fold_with(&mut r)
1115    }
1116
1117    pub fn resolve_numeric_literals_with_default<T>(&self, value: T) -> T
1118    where
1119        T: TypeFoldable<TyCtxt<'tcx>>,
1120    {
1121        if !value.has_infer() {
1122            return value; // Avoid duplicated type-folding.
1123        }
1124        let mut r = InferenceLiteralEraser { tcx: self.tcx };
1125        value.fold_with(&mut r)
1126    }
1127
1128    pub fn probe_const_var(&self, vid: ty::ConstVid) -> Result<ty::Const<'tcx>, ty::UniverseIndex> {
1129        match self.inner.borrow_mut().const_unification_table().probe_value(vid) {
1130            ConstVariableValue::Known { value } => Ok(value),
1131            ConstVariableValue::Unknown { origin: _, universe } => Err(universe),
1132        }
1133    }
1134
1135    /// Attempts to resolve all type/region/const variables in
1136    /// `value`. Region inference must have been run already (e.g.,
1137    /// by calling `resolve_regions_and_report_errors`). If some
1138    /// variable was never unified, an `Err` results.
1139    ///
1140    /// This method is idempotent, but it not typically not invoked
1141    /// except during the writeback phase.
1142    pub fn fully_resolve<T: TypeFoldable<TyCtxt<'tcx>>>(&self, value: T) -> FixupResult<T> {
1143        match resolve::fully_resolve(self, value) {
1144            Ok(value) => {
1145                if value.has_non_region_infer() {
1146                    bug!("`{value:?}` is not fully resolved");
1147                }
1148                if value.has_infer_regions() {
1149                    let guar = self.dcx().delayed_bug(format!("`{value:?}` is not fully resolved"));
1150                    Ok(fold_regions(self.tcx, value, |re, _| {
1151                        if re.is_var() { ty::Region::new_error(self.tcx, guar) } else { re }
1152                    }))
1153                } else {
1154                    Ok(value)
1155                }
1156            }
1157            Err(e) => Err(e),
1158        }
1159    }
1160
1161    // Instantiates the bound variables in a given binder with fresh inference
1162    // variables in the current universe.
1163    //
1164    // Use this method if you'd like to find some generic parameters of the binder's
1165    // variables (e.g. during a method call). If there isn't a [`BoundRegionConversionTime`]
1166    // that corresponds to your use case, consider whether or not you should
1167    // use [`InferCtxt::enter_forall`] instead.
1168    pub fn instantiate_binder_with_fresh_vars<T>(
1169        &self,
1170        span: Span,
1171        lbrct: BoundRegionConversionTime,
1172        value: ty::Binder<'tcx, T>,
1173    ) -> T
1174    where
1175        T: TypeFoldable<TyCtxt<'tcx>> + Copy,
1176    {
1177        if let Some(inner) = value.no_bound_vars() {
1178            return inner;
1179        }
1180
1181        let bound_vars = value.bound_vars();
1182        let mut args = Vec::with_capacity(bound_vars.len());
1183
1184        for bound_var_kind in bound_vars {
1185            let arg: ty::GenericArg<'_> = match bound_var_kind {
1186                ty::BoundVariableKind::Ty(_) => self.next_ty_var(span).into(),
1187                ty::BoundVariableKind::Region(br) => {
1188                    self.next_region_var(BoundRegion(span, br, lbrct)).into()
1189                }
1190                ty::BoundVariableKind::Const => self.next_const_var(span).into(),
1191            };
1192            args.push(arg);
1193        }
1194
1195        struct ToFreshVars<'tcx> {
1196            args: Vec<ty::GenericArg<'tcx>>,
1197        }
1198
1199        impl<'tcx> BoundVarReplacerDelegate<'tcx> for ToFreshVars<'tcx> {
1200            fn replace_region(&mut self, br: ty::BoundRegion) -> ty::Region<'tcx> {
1201                self.args[br.var.index()].expect_region()
1202            }
1203            fn replace_ty(&mut self, bt: ty::BoundTy) -> Ty<'tcx> {
1204                self.args[bt.var.index()].expect_ty()
1205            }
1206            fn replace_const(&mut self, bv: ty::BoundVar) -> ty::Const<'tcx> {
1207                self.args[bv.index()].expect_const()
1208            }
1209        }
1210        let delegate = ToFreshVars { args };
1211        self.tcx.replace_bound_vars_uncached(value, delegate)
1212    }
1213
1214    /// See the [`region_constraints::RegionConstraintCollector::verify_generic_bound`] method.
1215    pub(crate) fn verify_generic_bound(
1216        &self,
1217        origin: SubregionOrigin<'tcx>,
1218        kind: GenericKind<'tcx>,
1219        a: ty::Region<'tcx>,
1220        bound: VerifyBound<'tcx>,
1221    ) {
1222        debug!("verify_generic_bound({:?}, {:?} <: {:?})", kind, a, bound);
1223
1224        self.inner
1225            .borrow_mut()
1226            .unwrap_region_constraints()
1227            .verify_generic_bound(origin, kind, a, bound);
1228    }
1229
1230    /// Obtains the latest type of the given closure; this may be a
1231    /// closure in the current function, in which case its
1232    /// `ClosureKind` may not yet be known.
1233    pub fn closure_kind(&self, closure_ty: Ty<'tcx>) -> Option<ty::ClosureKind> {
1234        let unresolved_kind_ty = match *closure_ty.kind() {
1235            ty::Closure(_, args) => args.as_closure().kind_ty(),
1236            ty::CoroutineClosure(_, args) => args.as_coroutine_closure().kind_ty(),
1237            _ => bug!("unexpected type {closure_ty}"),
1238        };
1239        let closure_kind_ty = self.shallow_resolve(unresolved_kind_ty);
1240        closure_kind_ty.to_opt_closure_kind()
1241    }
1242
1243    pub fn universe(&self) -> ty::UniverseIndex {
1244        self.universe.get()
1245    }
1246
1247    /// Creates and return a fresh universe that extends all previous
1248    /// universes. Updates `self.universe` to that new universe.
1249    pub fn create_next_universe(&self) -> ty::UniverseIndex {
1250        let u = self.universe.get().next_universe();
1251        debug!("create_next_universe {u:?}");
1252        self.universe.set(u);
1253        u
1254    }
1255
1256    /// Extract [`ty::TypingMode`] of this inference context to get a `TypingEnv`
1257    /// which contains the necessary information to use the trait system without
1258    /// using canonicalization or carrying this inference context around.
1259    pub fn typing_env(&self, param_env: ty::ParamEnv<'tcx>) -> ty::TypingEnv<'tcx> {
1260        let typing_mode = match self.typing_mode() {
1261            // FIXME(#132279): This erases the `defining_opaque_types` as it isn't possible
1262            // to handle them without proper canonicalization. This means we may cause cycle
1263            // errors and fail to reveal opaques while inside of bodies. We should rename this
1264            // function and require explicit comments on all use-sites in the future.
1265            ty::TypingMode::Analysis { defining_opaque_types: _ }
1266            | ty::TypingMode::Borrowck { defining_opaque_types: _ } => {
1267                TypingMode::non_body_analysis()
1268            }
1269            mode @ (ty::TypingMode::Coherence
1270            | ty::TypingMode::PostBorrowckAnalysis { .. }
1271            | ty::TypingMode::PostAnalysis) => mode,
1272        };
1273        ty::TypingEnv { typing_mode, param_env }
1274    }
1275
1276    /// Similar to [`Self::canonicalize_query`], except that it returns
1277    /// a [`PseudoCanonicalInput`] and requires both the `value` and the
1278    /// `param_env` to not contain any inference variables or placeholders.
1279    pub fn pseudo_canonicalize_query<V>(
1280        &self,
1281        param_env: ty::ParamEnv<'tcx>,
1282        value: V,
1283    ) -> PseudoCanonicalInput<'tcx, V>
1284    where
1285        V: TypeVisitable<TyCtxt<'tcx>>,
1286    {
1287        debug_assert!(!value.has_infer());
1288        debug_assert!(!value.has_placeholders());
1289        debug_assert!(!param_env.has_infer());
1290        debug_assert!(!param_env.has_placeholders());
1291        self.typing_env(param_env).as_query_input(value)
1292    }
1293
1294    /// The returned function is used in a fast path. If it returns `true` the variable is
1295    /// unchanged, `false` indicates that the status is unknown.
1296    #[inline]
1297    pub fn is_ty_infer_var_definitely_unchanged(&self) -> impl Fn(TyOrConstInferVar) -> bool {
1298        // This hoists the borrow/release out of the loop body.
1299        let inner = self.inner.try_borrow();
1300
1301        move |infer_var: TyOrConstInferVar| match (infer_var, &inner) {
1302            (TyOrConstInferVar::Ty(ty_var), Ok(inner)) => {
1303                use self::type_variable::TypeVariableValue;
1304
1305                matches!(
1306                    inner.try_type_variables_probe_ref(ty_var),
1307                    Some(TypeVariableValue::Unknown { .. })
1308                )
1309            }
1310            _ => false,
1311        }
1312    }
1313
1314    /// `ty_or_const_infer_var_changed` is equivalent to one of these two:
1315    ///   * `shallow_resolve(ty) != ty` (where `ty.kind = ty::Infer(_)`)
1316    ///   * `shallow_resolve(ct) != ct` (where `ct.kind = ty::ConstKind::Infer(_)`)
1317    ///
1318    /// However, `ty_or_const_infer_var_changed` is more efficient. It's always
1319    /// inlined, despite being large, because it has only two call sites that
1320    /// are extremely hot (both in `traits::fulfill`'s checking of `stalled_on`
1321    /// inference variables), and it handles both `Ty` and `ty::Const` without
1322    /// having to resort to storing full `GenericArg`s in `stalled_on`.
1323    #[inline(always)]
1324    pub fn ty_or_const_infer_var_changed(&self, infer_var: TyOrConstInferVar) -> bool {
1325        match infer_var {
1326            TyOrConstInferVar::Ty(v) => {
1327                use self::type_variable::TypeVariableValue;
1328
1329                // If `inlined_probe` returns a `Known` value, it never equals
1330                // `ty::Infer(ty::TyVar(v))`.
1331                match self.inner.borrow_mut().type_variables().inlined_probe(v) {
1332                    TypeVariableValue::Unknown { .. } => false,
1333                    TypeVariableValue::Known { .. } => true,
1334                }
1335            }
1336
1337            TyOrConstInferVar::TyInt(v) => {
1338                // If `inlined_probe_value` returns a value it's always a
1339                // `ty::Int(_)` or `ty::UInt(_)`, which never matches a
1340                // `ty::Infer(_)`.
1341                self.inner.borrow_mut().int_unification_table().inlined_probe_value(v).is_known()
1342            }
1343
1344            TyOrConstInferVar::TyFloat(v) => {
1345                // If `probe_value` returns a value it's always a
1346                // `ty::Float(_)`, which never matches a `ty::Infer(_)`.
1347                //
1348                // Not `inlined_probe_value(v)` because this call site is colder.
1349                self.inner.borrow_mut().float_unification_table().probe_value(v).is_known()
1350            }
1351
1352            TyOrConstInferVar::Const(v) => {
1353                // If `probe_value` returns a `Known` value, it never equals
1354                // `ty::ConstKind::Infer(ty::InferConst::Var(v))`.
1355                //
1356                // Not `inlined_probe_value(v)` because this call site is colder.
1357                match self.inner.borrow_mut().const_unification_table().probe_value(v) {
1358                    ConstVariableValue::Unknown { .. } => false,
1359                    ConstVariableValue::Known { .. } => true,
1360                }
1361            }
1362        }
1363    }
1364
1365    /// Attach a callback to be invoked on each root obligation evaluated in the new trait solver.
1366    pub fn attach_obligation_inspector(&self, inspector: ObligationInspector<'tcx>) {
1367        debug_assert!(
1368            self.obligation_inspector.get().is_none(),
1369            "shouldn't override a set obligation inspector"
1370        );
1371        self.obligation_inspector.set(Some(inspector));
1372    }
1373}
1374
1375/// Helper for [InferCtxt::ty_or_const_infer_var_changed] (see comment on that), currently
1376/// used only for `traits::fulfill`'s list of `stalled_on` inference variables.
1377#[derive(Copy, Clone, Debug)]
1378pub enum TyOrConstInferVar {
1379    /// Equivalent to `ty::Infer(ty::TyVar(_))`.
1380    Ty(TyVid),
1381    /// Equivalent to `ty::Infer(ty::IntVar(_))`.
1382    TyInt(IntVid),
1383    /// Equivalent to `ty::Infer(ty::FloatVar(_))`.
1384    TyFloat(FloatVid),
1385
1386    /// Equivalent to `ty::ConstKind::Infer(ty::InferConst::Var(_))`.
1387    Const(ConstVid),
1388}
1389
1390impl<'tcx> TyOrConstInferVar {
1391    /// Tries to extract an inference variable from a type or a constant, returns `None`
1392    /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`) and
1393    /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1394    pub fn maybe_from_generic_arg(arg: GenericArg<'tcx>) -> Option<Self> {
1395        match arg.unpack() {
1396            GenericArgKind::Type(ty) => Self::maybe_from_ty(ty),
1397            GenericArgKind::Const(ct) => Self::maybe_from_const(ct),
1398            GenericArgKind::Lifetime(_) => None,
1399        }
1400    }
1401
1402    /// Tries to extract an inference variable from a type, returns `None`
1403    /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`).
1404    fn maybe_from_ty(ty: Ty<'tcx>) -> Option<Self> {
1405        match *ty.kind() {
1406            ty::Infer(ty::TyVar(v)) => Some(TyOrConstInferVar::Ty(v)),
1407            ty::Infer(ty::IntVar(v)) => Some(TyOrConstInferVar::TyInt(v)),
1408            ty::Infer(ty::FloatVar(v)) => Some(TyOrConstInferVar::TyFloat(v)),
1409            _ => None,
1410        }
1411    }
1412
1413    /// Tries to extract an inference variable from a constant, returns `None`
1414    /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1415    fn maybe_from_const(ct: ty::Const<'tcx>) -> Option<Self> {
1416        match ct.kind() {
1417            ty::ConstKind::Infer(InferConst::Var(v)) => Some(TyOrConstInferVar::Const(v)),
1418            _ => None,
1419        }
1420    }
1421}
1422
1423/// Replace `{integer}` with `i32` and `{float}` with `f64`.
1424/// Used only for diagnostics.
1425struct InferenceLiteralEraser<'tcx> {
1426    tcx: TyCtxt<'tcx>,
1427}
1428
1429impl<'tcx> TypeFolder<TyCtxt<'tcx>> for InferenceLiteralEraser<'tcx> {
1430    fn cx(&self) -> TyCtxt<'tcx> {
1431        self.tcx
1432    }
1433
1434    fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1435        match ty.kind() {
1436            ty::Infer(ty::IntVar(_) | ty::FreshIntTy(_)) => self.tcx.types.i32,
1437            ty::Infer(ty::FloatVar(_) | ty::FreshFloatTy(_)) => self.tcx.types.f64,
1438            _ => ty.super_fold_with(self),
1439        }
1440    }
1441}
1442
1443impl<'tcx> TypeTrace<'tcx> {
1444    pub fn span(&self) -> Span {
1445        self.cause.span
1446    }
1447
1448    pub fn types(cause: &ObligationCause<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> TypeTrace<'tcx> {
1449        TypeTrace {
1450            cause: cause.clone(),
1451            values: ValuePairs::Terms(ExpectedFound::new(a.into(), b.into())),
1452        }
1453    }
1454
1455    pub fn trait_refs(
1456        cause: &ObligationCause<'tcx>,
1457        a: ty::TraitRef<'tcx>,
1458        b: ty::TraitRef<'tcx>,
1459    ) -> TypeTrace<'tcx> {
1460        TypeTrace { cause: cause.clone(), values: ValuePairs::TraitRefs(ExpectedFound::new(a, b)) }
1461    }
1462
1463    pub fn consts(
1464        cause: &ObligationCause<'tcx>,
1465        a: ty::Const<'tcx>,
1466        b: ty::Const<'tcx>,
1467    ) -> TypeTrace<'tcx> {
1468        TypeTrace {
1469            cause: cause.clone(),
1470            values: ValuePairs::Terms(ExpectedFound::new(a.into(), b.into())),
1471        }
1472    }
1473}
1474
1475impl<'tcx> SubregionOrigin<'tcx> {
1476    pub fn span(&self) -> Span {
1477        match *self {
1478            Subtype(ref a) => a.span(),
1479            RelateObjectBound(a) => a,
1480            RelateParamBound(a, ..) => a,
1481            RelateRegionParamBound(a, _) => a,
1482            Reborrow(a) => a,
1483            ReferenceOutlivesReferent(_, a) => a,
1484            CompareImplItemObligation { span, .. } => span,
1485            AscribeUserTypeProvePredicate(span) => span,
1486            CheckAssociatedTypeBounds { ref parent, .. } => parent.span(),
1487        }
1488    }
1489
1490    pub fn from_obligation_cause<F>(cause: &traits::ObligationCause<'tcx>, default: F) -> Self
1491    where
1492        F: FnOnce() -> Self,
1493    {
1494        match *cause.code() {
1495            traits::ObligationCauseCode::ReferenceOutlivesReferent(ref_type) => {
1496                SubregionOrigin::ReferenceOutlivesReferent(ref_type, cause.span)
1497            }
1498
1499            traits::ObligationCauseCode::CompareImplItem {
1500                impl_item_def_id,
1501                trait_item_def_id,
1502                kind: _,
1503            } => SubregionOrigin::CompareImplItemObligation {
1504                span: cause.span,
1505                impl_item_def_id,
1506                trait_item_def_id,
1507            },
1508
1509            traits::ObligationCauseCode::CheckAssociatedTypeBounds {
1510                impl_item_def_id,
1511                trait_item_def_id,
1512            } => SubregionOrigin::CheckAssociatedTypeBounds {
1513                impl_item_def_id,
1514                trait_item_def_id,
1515                parent: Box::new(default()),
1516            },
1517
1518            traits::ObligationCauseCode::AscribeUserTypeProvePredicate(span) => {
1519                SubregionOrigin::AscribeUserTypeProvePredicate(span)
1520            }
1521
1522            traits::ObligationCauseCode::ObjectTypeBound(ty, _reg) => {
1523                SubregionOrigin::RelateRegionParamBound(cause.span, Some(ty))
1524            }
1525
1526            _ => default(),
1527        }
1528    }
1529}
1530
1531impl RegionVariableOrigin {
1532    pub fn span(&self) -> Span {
1533        match *self {
1534            MiscVariable(a)
1535            | PatternRegion(a)
1536            | BorrowRegion(a)
1537            | Autoref(a)
1538            | Coercion(a)
1539            | RegionParameterDefinition(a, ..)
1540            | BoundRegion(a, ..)
1541            | UpvarRegion(_, a) => a,
1542            Nll(..) => bug!("NLL variable used with `span`"),
1543        }
1544    }
1545}
1546
1547impl<'tcx> InferCtxt<'tcx> {
1548    /// Given a [`hir::Block`], get the span of its last expression or
1549    /// statement, peeling off any inner blocks.
1550    pub fn find_block_span(&self, block: &'tcx hir::Block<'tcx>) -> Span {
1551        let block = block.innermost_block();
1552        if let Some(expr) = &block.expr {
1553            expr.span
1554        } else if let Some(stmt) = block.stmts.last() {
1555            // possibly incorrect trailing `;` in the else arm
1556            stmt.span
1557        } else {
1558            // empty block; point at its entirety
1559            block.span
1560        }
1561    }
1562
1563    /// Given a [`hir::HirId`] for a block, get the span of its last expression
1564    /// or statement, peeling off any inner blocks.
1565    pub fn find_block_span_from_hir_id(&self, hir_id: hir::HirId) -> Span {
1566        match self.tcx.hir_node(hir_id) {
1567            hir::Node::Block(blk) => self.find_block_span(blk),
1568            // The parser was in a weird state if either of these happen, but
1569            // it's better not to panic.
1570            hir::Node::Expr(e) => e.span,
1571            _ => rustc_span::DUMMY_SP,
1572        }
1573    }
1574}