1 //! See the Book for more information.
3 pub use self::freshen::TypeFreshener;
4 pub use self::LateBoundRegionConversionTime::*;
5 pub use self::RegionVariableOrigin::*;
6 pub use self::SubregionOrigin::*;
7 pub use self::ValuePairs::*;
9 use crate::traits::{self, ObligationCause, PredicateObligations, TraitEngine};
11 use rustc::infer::canonical::{Canonical, CanonicalVarValues};
12 use rustc::infer::unify_key::{ConstVarValue, ConstVariableValue};
13 use rustc::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind, ToType};
14 use rustc::middle::free_region::RegionRelations;
15 use rustc::middle::region;
17 use rustc::mir::interpret::ConstEvalResult;
18 use rustc::traits::select;
19 use rustc::ty::error::{ExpectedFound, TypeError, UnconstrainedNumeric};
20 use rustc::ty::fold::{TypeFoldable, TypeFolder};
21 use rustc::ty::relate::RelateResult;
22 use rustc::ty::subst::{GenericArg, InternalSubsts, SubstsRef};
23 pub use rustc::ty::IntVarValue;
24 use rustc::ty::{self, GenericParamDefKind, InferConst, Ty, TyCtxt};
25 use rustc::ty::{ConstVid, FloatVid, IntVid, TyVid};
27 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
28 use rustc_data_structures::sync::Lrc;
29 use rustc_data_structures::unify as ut;
30 use rustc_errors::DiagnosticBuilder;
32 use rustc_hir::def_id::DefId;
33 use rustc_session::config::BorrowckMode;
34 use rustc_span::symbol::Symbol;
37 use std::cell::{Cell, Ref, RefCell};
38 use std::collections::BTreeMap;
41 use self::combine::CombineFields;
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::{RegionConstraintCollector, RegionSnapshot};
46 use self::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
52 pub mod error_reporting;
58 mod lexical_region_resolve;
62 pub mod region_constraints;
65 pub mod type_variable;
67 use crate::infer::canonical::OriginalQueryValues;
68 pub use rustc::infer::unify_key;
72 pub struct InferOk<'tcx, T> {
74 pub obligations: PredicateObligations<'tcx>,
76 pub type InferResult<'tcx, T> = Result<InferOk<'tcx, T>, TypeError<'tcx>>;
78 pub type Bound<T> = Option<T>;
79 pub type UnitResult<'tcx> = RelateResult<'tcx, ()>; // "unify result"
80 pub type FixupResult<'tcx, T> = Result<T, FixupError<'tcx>>; // "fixup result"
82 /// How we should handle region solving.
84 /// This is used so that the region values inferred by HIR region solving are
85 /// not exposed, and so that we can avoid doing work in HIR typeck that MIR
86 /// typeck will also do.
87 #[derive(Copy, Clone, Debug)]
88 pub enum RegionckMode {
89 /// The default mode: report region errors, don't erase regions.
91 /// Erase the results of region after solving.
93 /// A flag that is used to suppress region errors, when we are doing
94 /// region checks that the NLL borrow checker will also do -- it might
96 suppress_errors: bool,
100 impl Default for RegionckMode {
101 fn default() -> Self {
107 pub fn suppressed(self) -> bool {
109 Self::Solve => false,
110 Self::Erase { suppress_errors } => suppress_errors,
114 /// Indicates that the MIR borrowck will repeat these region
115 /// checks, so we should ignore errors if NLL is (unconditionally)
117 pub fn for_item_body(tcx: TyCtxt<'_>) -> Self {
118 // FIXME(Centril): Once we actually remove `::Migrate` also make
119 // this always `true` and then proceed to eliminate the dead code.
120 match tcx.borrowck_mode() {
121 // If we're on Migrate mode, report AST region errors
122 BorrowckMode::Migrate => RegionckMode::Erase { suppress_errors: false },
124 // If we're on MIR, don't report AST region errors as they should be reported by NLL
125 BorrowckMode::Mir => RegionckMode::Erase { suppress_errors: true },
130 /// This type contains all the things within `InferCtxt` that sit within a
131 /// `RefCell` and are involved with taking/rolling back snapshots. Snapshot
132 /// operations are hot enough that we want only one call to `borrow_mut` per
133 /// call to `start_snapshot` and `rollback_to`.
134 pub struct InferCtxtInner<'tcx> {
135 /// Cache for projections. This cache is snapshotted along with the infcx.
137 /// Public so that `traits::project` can use it.
138 pub projection_cache: traits::ProjectionCache<'tcx>,
140 /// We instantiate `UnificationTable` with `bounds<Ty>` because the types
141 /// that might instantiate a general type variable have an order,
142 /// represented by its upper and lower bounds.
143 type_variables: type_variable::TypeVariableTable<'tcx>,
145 /// Map from const parameter variable to the kind of const it represents.
146 const_unification_table: ut::UnificationTable<ut::InPlace<ty::ConstVid<'tcx>>>,
148 /// Map from integral variable to the kind of integer it represents.
149 int_unification_table: ut::UnificationTable<ut::InPlace<ty::IntVid>>,
151 /// Map from floating variable to the kind of float it represents.
152 float_unification_table: ut::UnificationTable<ut::InPlace<ty::FloatVid>>,
154 /// Tracks the set of region variables and the constraints between them.
155 /// This is initially `Some(_)` but when
156 /// `resolve_regions_and_report_errors` is invoked, this gets set to `None`
157 /// -- further attempts to perform unification, etc., may fail if new
158 /// region constraints would've been added.
159 region_constraints: Option<RegionConstraintCollector<'tcx>>,
161 /// A set of constraints that regionck must validate. Each
162 /// constraint has the form `T:'a`, meaning "some type `T` must
163 /// outlive the lifetime 'a". These constraints derive from
164 /// instantiated type parameters. So if you had a struct defined
167 /// struct Foo<T:'static> { ... }
169 /// then in some expression `let x = Foo { ... }` it will
170 /// instantiate the type parameter `T` with a fresh type `$0`. At
171 /// the same time, it will record a region obligation of
172 /// `$0:'static`. This will get checked later by regionck. (We
173 /// can't generally check these things right away because we have
174 /// to wait until types are resolved.)
176 /// These are stored in a map keyed to the id of the innermost
177 /// enclosing fn body / static initializer expression. This is
178 /// because the location where the obligation was incurred can be
179 /// relevant with respect to which sublifetime assumptions are in
180 /// place. The reason that we store under the fn-id, and not
181 /// something more fine-grained, is so that it is easier for
182 /// regionck to be sure that it has found *all* the region
183 /// obligations (otherwise, it's easy to fail to walk to a
184 /// particular node-id).
186 /// Before running `resolve_regions_and_report_errors`, the creator
187 /// of the inference context is expected to invoke
188 /// `process_region_obligations` (defined in `self::region_obligations`)
189 /// for each body-id in this map, which will process the
190 /// obligations within. This is expected to be done 'late enough'
191 /// that all type inference variables have been bound and so forth.
192 pub region_obligations: Vec<(hir::HirId, RegionObligation<'tcx>)>,
195 impl<'tcx> InferCtxtInner<'tcx> {
196 fn new() -> InferCtxtInner<'tcx> {
198 projection_cache: Default::default(),
199 type_variables: type_variable::TypeVariableTable::new(),
200 const_unification_table: ut::UnificationTable::new(),
201 int_unification_table: ut::UnificationTable::new(),
202 float_unification_table: ut::UnificationTable::new(),
203 region_constraints: Some(RegionConstraintCollector::new()),
204 region_obligations: vec![],
208 pub fn unwrap_region_constraints(&mut self) -> &mut RegionConstraintCollector<'tcx> {
209 self.region_constraints.as_mut().expect("region constraints already solved")
213 pub struct InferCtxt<'a, 'tcx> {
214 pub tcx: TyCtxt<'tcx>,
216 /// During type-checking/inference of a body, `in_progress_tables`
217 /// contains a reference to the tables being built up, which are
218 /// used for reading closure kinds/signatures as they are inferred,
219 /// and for error reporting logic to read arbitrary node types.
220 pub in_progress_tables: Option<&'a RefCell<ty::TypeckTables<'tcx>>>,
222 pub inner: RefCell<InferCtxtInner<'tcx>>,
224 /// If set, this flag causes us to skip the 'leak check' during
225 /// higher-ranked subtyping operations. This flag is a temporary one used
226 /// to manage the removal of the leak-check: for the time being, we still run the
227 /// leak-check, but we issue warnings. This flag can only be set to true
228 /// when entering a snapshot.
229 skip_leak_check: Cell<bool>,
231 /// Once region inference is done, the values for each variable.
232 lexical_region_resolutions: RefCell<Option<LexicalRegionResolutions<'tcx>>>,
234 /// Caches the results of trait selection. This cache is used
235 /// for things that have to do with the parameters in scope.
236 pub selection_cache: select::SelectionCache<'tcx>,
238 /// Caches the results of trait evaluation.
239 pub evaluation_cache: select::EvaluationCache<'tcx>,
241 /// the set of predicates on which errors have been reported, to
242 /// avoid reporting the same error twice.
243 pub reported_trait_errors: RefCell<FxHashMap<Span, Vec<ty::Predicate<'tcx>>>>,
245 pub reported_closure_mismatch: RefCell<FxHashSet<(Span, Option<Span>)>>,
247 /// When an error occurs, we want to avoid reporting "derived"
248 /// errors that are due to this original failure. Normally, we
249 /// handle this with the `err_count_on_creation` count, which
250 /// basically just tracks how many errors were reported when we
251 /// started type-checking a fn and checks to see if any new errors
252 /// have been reported since then. Not great, but it works.
254 /// However, when errors originated in other passes -- notably
255 /// resolve -- this heuristic breaks down. Therefore, we have this
256 /// auxiliary flag that one can set whenever one creates a
257 /// type-error that is due to an error in a prior pass.
259 /// Don't read this flag directly, call `is_tainted_by_errors()`
260 /// and `set_tainted_by_errors()`.
261 tainted_by_errors_flag: Cell<bool>,
263 /// Track how many errors were reported when this infcx is created.
264 /// If the number of errors increases, that's also a sign (line
265 /// `tained_by_errors`) to avoid reporting certain kinds of errors.
266 // FIXME(matthewjasper) Merge into `tainted_by_errors_flag`
267 err_count_on_creation: usize,
269 /// This flag is true while there is an active snapshot.
270 in_snapshot: Cell<bool>,
272 /// What is the innermost universe we have created? Starts out as
273 /// `UniverseIndex::root()` but grows from there as we enter
274 /// universal quantifiers.
276 /// N.B., at present, we exclude the universal quantifiers on the
277 /// item we are type-checking, and just consider those names as
278 /// part of the root universe. So this would only get incremented
279 /// when we enter into a higher-ranked (`for<..>`) type or trait
281 universe: Cell<ty::UniverseIndex>,
284 /// A map returned by `replace_bound_vars_with_placeholders()`
285 /// indicating the placeholder region that each late-bound region was
287 pub type PlaceholderMap<'tcx> = BTreeMap<ty::BoundRegion, ty::Region<'tcx>>;
289 /// See the `error_reporting` module for more details.
290 #[derive(Clone, Debug, PartialEq, Eq, TypeFoldable)]
291 pub enum ValuePairs<'tcx> {
292 Types(ExpectedFound<Ty<'tcx>>),
293 Regions(ExpectedFound<ty::Region<'tcx>>),
294 Consts(ExpectedFound<&'tcx ty::Const<'tcx>>),
295 TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>),
296 PolyTraitRefs(ExpectedFound<ty::PolyTraitRef<'tcx>>),
299 /// The trace designates the path through inference that we took to
300 /// encounter an error or subtyping constraint.
302 /// See the `error_reporting` module for more details.
303 #[derive(Clone, Debug)]
304 pub struct TypeTrace<'tcx> {
305 cause: ObligationCause<'tcx>,
306 values: ValuePairs<'tcx>,
309 /// The origin of a `r1 <= r2` constraint.
311 /// See `error_reporting` module for more details
312 #[derive(Clone, Debug)]
313 pub enum SubregionOrigin<'tcx> {
314 /// Arose from a subtyping relation
315 Subtype(Box<TypeTrace<'tcx>>),
317 /// Stack-allocated closures cannot outlive innermost loop
318 /// or function so as to ensure we only require finite stack
319 InfStackClosure(Span),
321 /// Invocation of closure must be within its lifetime
324 /// Dereference of reference must be within its lifetime
327 /// Closure bound must not outlive captured variables
328 ClosureCapture(Span, hir::HirId),
330 /// Index into slice must be within its lifetime
333 /// When casting `&'a T` to an `&'b Trait` object,
334 /// relating `'a` to `'b`
335 RelateObjectBound(Span),
337 /// Some type parameter was instantiated with the given type,
338 /// and that type must outlive some region.
339 RelateParamBound(Span, Ty<'tcx>),
341 /// The given region parameter was instantiated with a region
342 /// that must outlive some other region.
343 RelateRegionParamBound(Span),
345 /// A bound placed on type parameters that states that must outlive
346 /// the moment of their instantiation.
347 RelateDefaultParamBound(Span, Ty<'tcx>),
349 /// Creating a pointer `b` to contents of another reference
352 /// Creating a pointer `b` to contents of an upvar
353 ReborrowUpvar(Span, ty::UpvarId),
355 /// Data with type `Ty<'tcx>` was borrowed
356 DataBorrowed(Ty<'tcx>, Span),
358 /// (&'a &'b T) where a >= b
359 ReferenceOutlivesReferent(Ty<'tcx>, Span),
361 /// Type or region parameters must be in scope.
362 ParameterInScope(ParameterOrigin, Span),
364 /// The type T of an expression E must outlive the lifetime for E.
365 ExprTypeIsNotInScope(Ty<'tcx>, Span),
367 /// A `ref b` whose region does not enclose the decl site
368 BindingTypeIsNotValidAtDecl(Span),
370 /// Regions appearing in a method receiver must outlive method call
373 /// Regions appearing in a function argument must outlive func call
376 /// Region in return type of invoked fn must enclose call
379 /// Operands must be in scope
382 /// Region resulting from a `&` expr must enclose the `&` expr
385 /// An auto-borrow that does not enclose the expr where it occurs
388 /// Region constraint arriving from destructor safety
389 SafeDestructor(Span),
391 /// Comparing the signature and requirements of an impl method against
392 /// the containing trait.
393 CompareImplMethodObligation {
395 item_name: ast::Name,
396 impl_item_def_id: DefId,
397 trait_item_def_id: DefId,
401 // `SubregionOrigin` is used a lot. Make sure it doesn't unintentionally get bigger.
402 #[cfg(target_arch = "x86_64")]
403 static_assert_size!(SubregionOrigin<'_>, 32);
405 /// Places that type/region parameters can appear.
406 #[derive(Clone, Copy, Debug)]
407 pub enum ParameterOrigin {
409 MethodCall, // foo.bar() <-- parameters on impl providing bar()
410 OverloadedOperator, // a + b when overloaded
411 OverloadedDeref, // *a when overloaded
414 /// Times when we replace late-bound regions with variables:
415 #[derive(Clone, Copy, Debug)]
416 pub enum LateBoundRegionConversionTime {
417 /// when a fn is called
420 /// when two higher-ranked types are compared
423 /// when projecting an associated type
424 AssocTypeProjection(DefId),
427 /// Reasons to create a region inference variable
429 /// See `error_reporting` module for more details
430 #[derive(Copy, Clone, Debug)]
431 pub enum RegionVariableOrigin {
432 /// Region variables created for ill-categorized reasons,
433 /// mostly indicates places in need of refactoring
436 /// Regions created by a `&P` or `[...]` pattern
439 /// Regions created by `&` operator
442 /// Regions created as part of an autoref of a method receiver
445 /// Regions created as part of an automatic coercion
448 /// Region variables created as the values for early-bound regions
449 EarlyBoundRegion(Span, Symbol),
451 /// Region variables created for bound regions
452 /// in a function or method that is called
453 LateBoundRegion(Span, ty::BoundRegion, LateBoundRegionConversionTime),
455 UpvarRegion(ty::UpvarId, Span),
457 BoundRegionInCoherence(ast::Name),
459 /// This origin is used for the inference variables that we create
460 /// during NLL region processing.
461 NLL(NLLRegionVariableOrigin),
464 #[derive(Copy, Clone, Debug)]
465 pub enum NLLRegionVariableOrigin {
466 /// During NLL region processing, we create variables for free
467 /// regions that we encounter in the function signature and
468 /// elsewhere. This origin indices we've got one of those.
471 /// "Universal" instantiation of a higher-ranked region (e.g.,
472 /// from a `for<'a> T` binder). Meant to represent "any region".
473 Placeholder(ty::PlaceholderRegion),
476 /// If this is true, then this variable was created to represent a lifetime
477 /// bound in a `for` binder. For example, it might have been created to
478 /// represent the lifetime `'a` in a type like `for<'a> fn(&'a u32)`.
479 /// Such variables are created when we are trying to figure out if there
480 /// is any valid instantiation of `'a` that could fit into some scenario.
482 /// This is used to inform error reporting: in the case that we are trying to
483 /// determine whether there is any valid instantiation of a `'a` variable that meets
484 /// some constraint C, we want to blame the "source" of that `for` type,
485 /// rather than blaming the source of the constraint C.
490 impl NLLRegionVariableOrigin {
491 pub fn is_universal(self) -> bool {
493 NLLRegionVariableOrigin::FreeRegion => true,
494 NLLRegionVariableOrigin::Placeholder(..) => true,
495 NLLRegionVariableOrigin::Existential { .. } => false,
499 pub fn is_existential(self) -> bool {
504 #[derive(Copy, Clone, Debug)]
505 pub enum FixupError<'tcx> {
506 UnresolvedIntTy(IntVid),
507 UnresolvedFloatTy(FloatVid),
509 UnresolvedConst(ConstVid<'tcx>),
512 /// See the `region_obligations` field for more information.
514 pub struct RegionObligation<'tcx> {
515 pub sub_region: ty::Region<'tcx>,
516 pub sup_type: Ty<'tcx>,
517 pub origin: SubregionOrigin<'tcx>,
520 impl<'tcx> fmt::Display for FixupError<'tcx> {
521 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
522 use self::FixupError::*;
525 UnresolvedIntTy(_) => write!(
527 "cannot determine the type of this integer; \
528 add a suffix to specify the type explicitly"
530 UnresolvedFloatTy(_) => write!(
532 "cannot determine the type of this number; \
533 add a suffix to specify the type explicitly"
535 UnresolvedTy(_) => write!(f, "unconstrained type"),
536 UnresolvedConst(_) => write!(f, "unconstrained const value"),
541 /// Helper type of a temporary returned by `tcx.infer_ctxt()`.
542 /// Necessary because we can't write the following bound:
543 /// `F: for<'b, 'tcx> where 'tcx FnOnce(InferCtxt<'b, 'tcx>)`.
544 pub struct InferCtxtBuilder<'tcx> {
545 global_tcx: TyCtxt<'tcx>,
546 fresh_tables: Option<RefCell<ty::TypeckTables<'tcx>>>,
549 pub trait TyCtxtInferExt<'tcx> {
550 fn infer_ctxt(self) -> InferCtxtBuilder<'tcx>;
553 impl TyCtxtInferExt<'tcx> for TyCtxt<'tcx> {
554 fn infer_ctxt(self) -> InferCtxtBuilder<'tcx> {
555 InferCtxtBuilder { global_tcx: self, fresh_tables: None }
559 impl<'tcx> InferCtxtBuilder<'tcx> {
560 /// Used only by `rustc_typeck` during body type-checking/inference,
561 /// will initialize `in_progress_tables` with fresh `TypeckTables`.
562 pub fn with_fresh_in_progress_tables(mut self, table_owner: DefId) -> Self {
563 self.fresh_tables = Some(RefCell::new(ty::TypeckTables::empty(Some(table_owner))));
567 /// Given a canonical value `C` as a starting point, create an
568 /// inference context that contains each of the bound values
569 /// within instantiated as a fresh variable. The `f` closure is
570 /// invoked with the new infcx, along with the instantiated value
571 /// `V` and a substitution `S`. This substitution `S` maps from
572 /// the bound values in `C` to their instantiated values in `V`
573 /// (in other words, `S(C) = V`).
574 pub fn enter_with_canonical<T, R>(
577 canonical: &Canonical<'tcx, T>,
578 f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>, T, CanonicalVarValues<'tcx>) -> R,
581 T: TypeFoldable<'tcx>,
585 infcx.instantiate_canonical_with_fresh_inference_vars(span, canonical);
586 f(infcx, value, subst)
590 pub fn enter<R>(&mut self, f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>) -> R) -> R {
591 let InferCtxtBuilder { global_tcx, ref fresh_tables } = *self;
592 let in_progress_tables = fresh_tables.as_ref();
593 global_tcx.enter_local(|tcx| {
597 inner: RefCell::new(InferCtxtInner::new()),
598 lexical_region_resolutions: RefCell::new(None),
599 selection_cache: Default::default(),
600 evaluation_cache: Default::default(),
601 reported_trait_errors: Default::default(),
602 reported_closure_mismatch: Default::default(),
603 tainted_by_errors_flag: Cell::new(false),
604 err_count_on_creation: tcx.sess.err_count(),
605 in_snapshot: Cell::new(false),
606 skip_leak_check: Cell::new(false),
607 universe: Cell::new(ty::UniverseIndex::ROOT),
613 impl<'tcx, T> InferOk<'tcx, T> {
614 pub fn unit(self) -> InferOk<'tcx, ()> {
615 InferOk { value: (), obligations: self.obligations }
618 /// Extracts `value`, registering any obligations into `fulfill_cx`.
619 pub fn into_value_registering_obligations(
621 infcx: &InferCtxt<'_, 'tcx>,
622 fulfill_cx: &mut dyn TraitEngine<'tcx>,
624 let InferOk { value, obligations } = self;
625 for obligation in obligations {
626 fulfill_cx.register_predicate_obligation(infcx, obligation);
632 impl<'tcx> InferOk<'tcx, ()> {
633 pub fn into_obligations(self) -> PredicateObligations<'tcx> {
638 #[must_use = "once you start a snapshot, you should always consume it"]
639 pub struct CombinedSnapshot<'a, 'tcx> {
640 projection_cache_snapshot: traits::ProjectionCacheSnapshot,
641 type_snapshot: type_variable::Snapshot<'tcx>,
642 const_snapshot: ut::Snapshot<ut::InPlace<ty::ConstVid<'tcx>>>,
643 int_snapshot: ut::Snapshot<ut::InPlace<ty::IntVid>>,
644 float_snapshot: ut::Snapshot<ut::InPlace<ty::FloatVid>>,
645 region_constraints_snapshot: RegionSnapshot,
646 region_obligations_snapshot: usize,
647 universe: ty::UniverseIndex,
648 was_in_snapshot: bool,
649 was_skip_leak_check: bool,
650 _in_progress_tables: Option<Ref<'a, ty::TypeckTables<'tcx>>>,
653 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
654 pub fn is_in_snapshot(&self) -> bool {
655 self.in_snapshot.get()
658 pub fn freshen<T: TypeFoldable<'tcx>>(&self, t: T) -> T {
659 t.fold_with(&mut self.freshener())
662 pub fn type_var_diverges(&'a self, ty: Ty<'_>) -> bool {
664 ty::Infer(ty::TyVar(vid)) => self.inner.borrow().type_variables.var_diverges(vid),
669 pub fn freshener<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
670 freshen::TypeFreshener::new(self)
673 pub fn type_is_unconstrained_numeric(&'a self, ty: Ty<'_>) -> UnconstrainedNumeric {
674 use rustc::ty::error::UnconstrainedNumeric::Neither;
675 use rustc::ty::error::UnconstrainedNumeric::{UnconstrainedFloat, UnconstrainedInt};
677 ty::Infer(ty::IntVar(vid)) => {
678 if self.inner.borrow_mut().int_unification_table.probe_value(vid).is_some() {
684 ty::Infer(ty::FloatVar(vid)) => {
685 if self.inner.borrow_mut().float_unification_table.probe_value(vid).is_some() {
695 pub fn unsolved_variables(&self) -> Vec<Ty<'tcx>> {
696 let mut inner = self.inner.borrow_mut();
697 // FIXME(const_generics): should there be an equivalent function for const variables?
699 let mut vars: Vec<Ty<'_>> = inner
701 .unsolved_variables()
703 .map(|t| self.tcx.mk_ty_var(t))
706 (0..inner.int_unification_table.len())
707 .map(|i| ty::IntVid { index: i as u32 })
708 .filter(|&vid| inner.int_unification_table.probe_value(vid).is_none())
709 .map(|v| self.tcx.mk_int_var(v)),
712 (0..inner.float_unification_table.len())
713 .map(|i| ty::FloatVid { index: i as u32 })
714 .filter(|&vid| inner.float_unification_table.probe_value(vid).is_none())
715 .map(|v| self.tcx.mk_float_var(v)),
722 trace: TypeTrace<'tcx>,
723 param_env: ty::ParamEnv<'tcx>,
724 ) -> CombineFields<'a, 'tcx> {
730 obligations: PredicateObligations::new(),
734 /// Clear the "currently in a snapshot" flag, invoke the closure,
735 /// then restore the flag to its original value. This flag is a
736 /// debugging measure designed to detect cases where we start a
737 /// snapshot, create type variables, and register obligations
738 /// which may involve those type variables in the fulfillment cx,
739 /// potentially leaving "dangling type variables" behind.
740 /// In such cases, an assertion will fail when attempting to
741 /// register obligations, within a snapshot. Very useful, much
742 /// better than grovelling through megabytes of `RUSTC_LOG` output.
744 /// HOWEVER, in some cases the flag is unhelpful. In particular, we
745 /// sometimes create a "mini-fulfilment-cx" in which we enroll
746 /// obligations. As long as this fulfillment cx is fully drained
747 /// before we return, this is not a problem, as there won't be any
748 /// escaping obligations in the main cx. In those cases, you can
749 /// use this function.
750 pub fn save_and_restore_in_snapshot_flag<F, R>(&self, func: F) -> R
752 F: FnOnce(&Self) -> R,
754 let flag = self.in_snapshot.replace(false);
755 let result = func(self);
756 self.in_snapshot.set(flag);
760 fn start_snapshot(&self) -> CombinedSnapshot<'a, 'tcx> {
761 debug!("start_snapshot()");
763 let in_snapshot = self.in_snapshot.replace(true);
765 let mut inner = self.inner.borrow_mut();
767 projection_cache_snapshot: inner.projection_cache.snapshot(),
768 type_snapshot: inner.type_variables.snapshot(),
769 const_snapshot: inner.const_unification_table.snapshot(),
770 int_snapshot: inner.int_unification_table.snapshot(),
771 float_snapshot: inner.float_unification_table.snapshot(),
772 region_constraints_snapshot: inner.unwrap_region_constraints().start_snapshot(),
773 region_obligations_snapshot: inner.region_obligations.len(),
774 universe: self.universe(),
775 was_in_snapshot: in_snapshot,
776 was_skip_leak_check: self.skip_leak_check.get(),
777 // Borrow tables "in progress" (i.e., during typeck)
778 // to ban writes from within a snapshot to them.
779 _in_progress_tables: self.in_progress_tables.map(|tables| tables.borrow()),
783 fn rollback_to(&self, cause: &str, snapshot: CombinedSnapshot<'a, 'tcx>) {
784 debug!("rollback_to(cause={})", cause);
785 let CombinedSnapshot {
786 projection_cache_snapshot,
791 region_constraints_snapshot,
792 region_obligations_snapshot,
799 self.in_snapshot.set(was_in_snapshot);
800 self.universe.set(universe);
801 self.skip_leak_check.set(was_skip_leak_check);
803 let mut inner = self.inner.borrow_mut();
804 inner.projection_cache.rollback_to(projection_cache_snapshot);
805 inner.type_variables.rollback_to(type_snapshot);
806 inner.const_unification_table.rollback_to(const_snapshot);
807 inner.int_unification_table.rollback_to(int_snapshot);
808 inner.float_unification_table.rollback_to(float_snapshot);
809 inner.unwrap_region_constraints().rollback_to(region_constraints_snapshot);
810 inner.region_obligations.truncate(region_obligations_snapshot);
813 fn commit_from(&self, snapshot: CombinedSnapshot<'a, 'tcx>) {
814 debug!("commit_from()");
815 let CombinedSnapshot {
816 projection_cache_snapshot,
821 region_constraints_snapshot,
822 region_obligations_snapshot: _,
829 self.in_snapshot.set(was_in_snapshot);
830 self.skip_leak_check.set(was_skip_leak_check);
832 let mut inner = self.inner.borrow_mut();
833 inner.projection_cache.commit(projection_cache_snapshot);
834 inner.type_variables.commit(type_snapshot);
835 inner.const_unification_table.commit(const_snapshot);
836 inner.int_unification_table.commit(int_snapshot);
837 inner.float_unification_table.commit(float_snapshot);
838 inner.unwrap_region_constraints().commit(region_constraints_snapshot);
841 /// Executes `f` and commit the bindings.
842 pub fn commit_unconditionally<R, F>(&self, f: F) -> R
844 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
846 debug!("commit_unconditionally()");
847 let snapshot = self.start_snapshot();
848 let r = f(&snapshot);
849 self.commit_from(snapshot);
853 /// Execute `f` and commit the bindings if closure `f` returns `Ok(_)`.
854 pub fn commit_if_ok<T, E, F>(&self, f: F) -> Result<T, E>
856 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> Result<T, E>,
858 debug!("commit_if_ok()");
859 let snapshot = self.start_snapshot();
860 let r = f(&snapshot);
861 debug!("commit_if_ok() -- r.is_ok() = {}", r.is_ok());
864 self.commit_from(snapshot);
867 self.rollback_to("commit_if_ok -- error", snapshot);
873 /// Execute `f` then unroll any bindings it creates.
874 pub fn probe<R, F>(&self, f: F) -> R
876 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
879 let snapshot = self.start_snapshot();
880 let r = f(&snapshot);
881 self.rollback_to("probe", snapshot);
885 /// If `should_skip` is true, then execute `f` then unroll any bindings it creates.
886 pub fn probe_maybe_skip_leak_check<R, F>(&self, should_skip: bool, f: F) -> R
888 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
891 let snapshot = self.start_snapshot();
892 let skip_leak_check = should_skip || self.skip_leak_check.get();
893 self.skip_leak_check.set(skip_leak_check);
894 let r = f(&snapshot);
895 self.rollback_to("probe", snapshot);
899 /// Scan the constraints produced since `snapshot` began and returns:
901 /// - `None` -- if none of them involve "region outlives" constraints
902 /// - `Some(true)` -- if there are `'a: 'b` constraints where `'a` or `'b` is a placeholder
903 /// - `Some(false)` -- if there are `'a: 'b` constraints but none involve placeholders
904 pub fn region_constraints_added_in_snapshot(
906 snapshot: &CombinedSnapshot<'a, 'tcx>,
910 .unwrap_region_constraints()
911 .region_constraints_added_in_snapshot(&snapshot.region_constraints_snapshot)
914 pub fn add_given(&self, sub: ty::Region<'tcx>, sup: ty::RegionVid) {
915 self.inner.borrow_mut().unwrap_region_constraints().add_given(sub, sup);
918 pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
920 T: at::ToTrace<'tcx>,
922 let origin = &ObligationCause::dummy();
924 self.at(origin, param_env).sub(a, b).map(|InferOk { obligations: _, .. }| {
925 // Ignore obligations, since we are unrolling
926 // everything anyway.
931 pub fn can_eq<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
933 T: at::ToTrace<'tcx>,
935 let origin = &ObligationCause::dummy();
937 self.at(origin, param_env).eq(a, b).map(|InferOk { obligations: _, .. }| {
938 // Ignore obligations, since we are unrolling
939 // everything anyway.
946 origin: SubregionOrigin<'tcx>,
950 debug!("sub_regions({:?} <: {:?})", a, b);
951 self.inner.borrow_mut().unwrap_region_constraints().make_subregion(origin, a, b);
954 /// Require that the region `r` be equal to one of the regions in
955 /// the set `regions`.
956 pub fn member_constraint(
958 opaque_type_def_id: DefId,
959 definition_span: Span,
961 region: ty::Region<'tcx>,
962 in_regions: &Lrc<Vec<ty::Region<'tcx>>>,
964 debug!("member_constraint({:?} <: {:?})", region, in_regions);
965 self.inner.borrow_mut().unwrap_region_constraints().member_constraint(
974 pub fn subtype_predicate(
976 cause: &ObligationCause<'tcx>,
977 param_env: ty::ParamEnv<'tcx>,
978 predicate: &ty::PolySubtypePredicate<'tcx>,
979 ) -> Option<InferResult<'tcx, ()>> {
980 // Subtle: it's ok to skip the binder here and resolve because
981 // `shallow_resolve` just ignores anything that is not a type
982 // variable, and because type variable's can't (at present, at
983 // least) capture any of the things bound by this binder.
985 // NOTE(nmatsakis): really, there is no *particular* reason to do this
986 // `shallow_resolve` here except as a micro-optimization.
987 // Naturally I could not resist.
988 let two_unbound_type_vars = {
989 let a = self.shallow_resolve(predicate.skip_binder().a);
990 let b = self.shallow_resolve(predicate.skip_binder().b);
991 a.is_ty_var() && b.is_ty_var()
994 if two_unbound_type_vars {
995 // Two unbound type variables? Can't make progress.
999 Some(self.commit_if_ok(|snapshot| {
1000 let (ty::SubtypePredicate { a_is_expected, a, b }, placeholder_map) =
1001 self.replace_bound_vars_with_placeholders(predicate);
1003 let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?;
1005 self.leak_check(false, &placeholder_map, snapshot)?;
1011 pub fn region_outlives_predicate(
1013 cause: &traits::ObligationCause<'tcx>,
1014 predicate: &ty::PolyRegionOutlivesPredicate<'tcx>,
1015 ) -> UnitResult<'tcx> {
1016 self.commit_if_ok(|snapshot| {
1017 let (ty::OutlivesPredicate(r_a, r_b), placeholder_map) =
1018 self.replace_bound_vars_with_placeholders(predicate);
1019 let origin = SubregionOrigin::from_obligation_cause(cause, || {
1020 RelateRegionParamBound(cause.span)
1022 self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
1023 self.leak_check(false, &placeholder_map, snapshot)?;
1028 pub fn next_ty_var_id(&self, diverging: bool, origin: TypeVariableOrigin) -> TyVid {
1029 self.inner.borrow_mut().type_variables.new_var(self.universe(), diverging, origin)
1032 pub fn next_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
1033 self.tcx.mk_ty_var(self.next_ty_var_id(false, origin))
1036 pub fn next_ty_var_in_universe(
1038 origin: TypeVariableOrigin,
1039 universe: ty::UniverseIndex,
1041 let vid = self.inner.borrow_mut().type_variables.new_var(universe, false, origin);
1042 self.tcx.mk_ty_var(vid)
1045 pub fn next_diverging_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
1046 self.tcx.mk_ty_var(self.next_ty_var_id(true, origin))
1049 pub fn next_const_var(
1052 origin: ConstVariableOrigin,
1053 ) -> &'tcx ty::Const<'tcx> {
1054 self.tcx.mk_const_var(self.next_const_var_id(origin), ty)
1057 pub fn next_const_var_in_universe(
1060 origin: ConstVariableOrigin,
1061 universe: ty::UniverseIndex,
1062 ) -> &'tcx ty::Const<'tcx> {
1066 .const_unification_table
1067 .new_key(ConstVarValue { origin, val: ConstVariableValue::Unknown { universe } });
1068 self.tcx.mk_const_var(vid, ty)
1071 pub fn next_const_var_id(&self, origin: ConstVariableOrigin) -> ConstVid<'tcx> {
1072 self.inner.borrow_mut().const_unification_table.new_key(ConstVarValue {
1074 val: ConstVariableValue::Unknown { universe: self.universe() },
1078 fn next_int_var_id(&self) -> IntVid {
1079 self.inner.borrow_mut().int_unification_table.new_key(None)
1082 pub fn next_int_var(&self) -> Ty<'tcx> {
1083 self.tcx.mk_int_var(self.next_int_var_id())
1086 fn next_float_var_id(&self) -> FloatVid {
1087 self.inner.borrow_mut().float_unification_table.new_key(None)
1090 pub fn next_float_var(&self) -> Ty<'tcx> {
1091 self.tcx.mk_float_var(self.next_float_var_id())
1094 /// Creates a fresh region variable with the next available index.
1095 /// The variable will be created in the maximum universe created
1096 /// thus far, allowing it to name any region created thus far.
1097 pub fn next_region_var(&self, origin: RegionVariableOrigin) -> ty::Region<'tcx> {
1098 self.next_region_var_in_universe(origin, self.universe())
1101 /// Creates a fresh region variable with the next available index
1102 /// in the given universe; typically, you can use
1103 /// `next_region_var` and just use the maximal universe.
1104 pub fn next_region_var_in_universe(
1106 origin: RegionVariableOrigin,
1107 universe: ty::UniverseIndex,
1108 ) -> ty::Region<'tcx> {
1110 self.inner.borrow_mut().unwrap_region_constraints().new_region_var(universe, origin);
1111 self.tcx.mk_region(ty::ReVar(region_var))
1114 /// Return the universe that the region `r` was created in. For
1115 /// most regions (e.g., `'static`, named regions from the user,
1116 /// etc) this is the root universe U0. For inference variables or
1117 /// placeholders, however, it will return the universe which which
1118 /// they are associated.
1119 fn universe_of_region(&self, r: ty::Region<'tcx>) -> ty::UniverseIndex {
1120 self.inner.borrow_mut().unwrap_region_constraints().universe(r)
1123 /// Number of region variables created so far.
1124 pub fn num_region_vars(&self) -> usize {
1125 self.inner.borrow_mut().unwrap_region_constraints().num_region_vars()
1128 /// Just a convenient wrapper of `next_region_var` for using during NLL.
1129 pub fn next_nll_region_var(&self, origin: NLLRegionVariableOrigin) -> ty::Region<'tcx> {
1130 self.next_region_var(RegionVariableOrigin::NLL(origin))
1133 /// Just a convenient wrapper of `next_region_var` for using during NLL.
1134 pub fn next_nll_region_var_in_universe(
1136 origin: NLLRegionVariableOrigin,
1137 universe: ty::UniverseIndex,
1138 ) -> ty::Region<'tcx> {
1139 self.next_region_var_in_universe(RegionVariableOrigin::NLL(origin), universe)
1142 pub fn var_for_def(&self, span: Span, param: &ty::GenericParamDef) -> GenericArg<'tcx> {
1144 GenericParamDefKind::Lifetime => {
1145 // Create a region inference variable for the given
1146 // region parameter definition.
1147 self.next_region_var(EarlyBoundRegion(span, param.name)).into()
1149 GenericParamDefKind::Type { .. } => {
1150 // Create a type inference variable for the given
1151 // type parameter definition. The substitutions are
1152 // for actual parameters that may be referred to by
1153 // the default of this type parameter, if it exists.
1154 // e.g., `struct Foo<A, B, C = (A, B)>(...);` when
1155 // used in a path such as `Foo::<T, U>::new()` will
1156 // use an inference variable for `C` with `[T, U]`
1157 // as the substitutions for the default, `(T, U)`.
1158 let ty_var_id = self.inner.borrow_mut().type_variables.new_var(
1161 TypeVariableOrigin {
1162 kind: TypeVariableOriginKind::TypeParameterDefinition(
1170 self.tcx.mk_ty_var(ty_var_id).into()
1172 GenericParamDefKind::Const { .. } => {
1173 let origin = ConstVariableOrigin {
1174 kind: ConstVariableOriginKind::ConstParameterDefinition(param.name),
1178 self.inner.borrow_mut().const_unification_table.new_key(ConstVarValue {
1180 val: ConstVariableValue::Unknown { universe: self.universe() },
1182 self.tcx.mk_const_var(const_var_id, self.tcx.type_of(param.def_id)).into()
1187 /// Given a set of generics defined on a type or impl, returns a substitution mapping each
1188 /// type/region parameter to a fresh inference variable.
1189 pub fn fresh_substs_for_item(&self, span: Span, def_id: DefId) -> SubstsRef<'tcx> {
1190 InternalSubsts::for_item(self.tcx, def_id, |param, _| self.var_for_def(span, param))
1193 /// Returns `true` if errors have been reported since this infcx was
1194 /// created. This is sometimes used as a heuristic to skip
1195 /// reporting errors that often occur as a result of earlier
1196 /// errors, but where it's hard to be 100% sure (e.g., unresolved
1197 /// inference variables, regionck errors).
1198 pub fn is_tainted_by_errors(&self) -> bool {
1200 "is_tainted_by_errors(err_count={}, err_count_on_creation={}, \
1201 tainted_by_errors_flag={})",
1202 self.tcx.sess.err_count(),
1203 self.err_count_on_creation,
1204 self.tainted_by_errors_flag.get()
1207 if self.tcx.sess.err_count() > self.err_count_on_creation {
1208 return true; // errors reported since this infcx was made
1210 self.tainted_by_errors_flag.get()
1213 /// Set the "tainted by errors" flag to true. We call this when we
1214 /// observe an error from a prior pass.
1215 pub fn set_tainted_by_errors(&self) {
1216 debug!("set_tainted_by_errors()");
1217 self.tainted_by_errors_flag.set(true)
1220 /// Process the region constraints and report any errors that
1221 /// result. After this, no more unification operations should be
1222 /// done -- or the compiler will panic -- but it is legal to use
1223 /// `resolve_vars_if_possible` as well as `fully_resolve`.
1224 pub fn resolve_regions_and_report_errors(
1226 region_context: DefId,
1227 region_map: ®ion::ScopeTree,
1228 outlives_env: &OutlivesEnvironment<'tcx>,
1232 self.is_tainted_by_errors() || self.inner.borrow().region_obligations.is_empty(),
1233 "region_obligations not empty: {:#?}",
1234 self.inner.borrow().region_obligations
1236 let (var_infos, data) = self
1241 .expect("regions already resolved")
1242 .into_infos_and_data();
1244 let region_rels = &RegionRelations::new(
1248 outlives_env.free_region_map(),
1251 let (lexical_region_resolutions, errors) =
1252 lexical_region_resolve::resolve(region_rels, var_infos, data, mode);
1254 let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions));
1255 assert!(old_value.is_none());
1257 if !self.is_tainted_by_errors() {
1258 // As a heuristic, just skip reporting region errors
1259 // altogether if other errors have been reported while
1260 // this infcx was in use. This is totally hokey but
1261 // otherwise we have a hard time separating legit region
1262 // errors from silly ones.
1263 self.report_region_errors(region_map, &errors);
1267 /// Obtains (and clears) the current set of region
1268 /// constraints. The inference context is still usable: further
1269 /// unifications will simply add new constraints.
1271 /// This method is not meant to be used with normal lexical region
1272 /// resolution. Rather, it is used in the NLL mode as a kind of
1273 /// interim hack: basically we run normal type-check and generate
1274 /// region constraints as normal, but then we take them and
1275 /// translate them into the form that the NLL solver
1276 /// understands. See the NLL module for mode details.
1277 pub fn take_and_reset_region_constraints(&self) -> RegionConstraintData<'tcx> {
1279 self.inner.borrow().region_obligations.is_empty(),
1280 "region_obligations not empty: {:#?}",
1281 self.inner.borrow().region_obligations
1284 self.inner.borrow_mut().unwrap_region_constraints().take_and_reset_data()
1287 /// Gives temporary access to the region constraint data.
1288 #[allow(non_camel_case_types)] // bug with impl trait
1289 pub fn with_region_constraints<R>(
1291 op: impl FnOnce(&RegionConstraintData<'tcx>) -> R,
1293 let mut inner = self.inner.borrow_mut();
1294 op(inner.unwrap_region_constraints().data())
1297 /// Takes ownership of the list of variable regions. This implies
1298 /// that all the region constraints have already been taken, and
1299 /// hence that `resolve_regions_and_report_errors` can never be
1300 /// called. This is used only during NLL processing to "hand off" ownership
1301 /// of the set of region variables into the NLL region context.
1302 pub fn take_region_var_origins(&self) -> VarInfos {
1303 let (var_infos, data) = self
1308 .expect("regions already resolved")
1309 .into_infos_and_data();
1310 assert!(data.is_empty());
1314 pub fn ty_to_string(&self, t: Ty<'tcx>) -> String {
1315 self.resolve_vars_if_possible(&t).to_string()
1318 pub fn tys_to_string(&self, ts: &[Ty<'tcx>]) -> String {
1319 let tstrs: Vec<String> = ts.iter().map(|t| self.ty_to_string(*t)).collect();
1320 format!("({})", tstrs.join(", "))
1323 pub fn trait_ref_to_string(&self, t: &ty::TraitRef<'tcx>) -> String {
1324 self.resolve_vars_if_possible(t).print_only_trait_path().to_string()
1327 /// If `TyVar(vid)` resolves to a type, return that type. Else, return the
1328 /// universe index of `TyVar(vid)`.
1329 pub fn probe_ty_var(&self, vid: TyVid) -> Result<Ty<'tcx>, ty::UniverseIndex> {
1330 use self::type_variable::TypeVariableValue;
1332 match self.inner.borrow_mut().type_variables.probe(vid) {
1333 TypeVariableValue::Known { value } => Ok(value),
1334 TypeVariableValue::Unknown { universe } => Err(universe),
1338 /// Resolve any type variables found in `value` -- but only one
1339 /// level. So, if the variable `?X` is bound to some type
1340 /// `Foo<?Y>`, then this would return `Foo<?Y>` (but `?Y` may
1341 /// itself be bound to a type).
1343 /// Useful when you only need to inspect the outermost level of
1344 /// the type and don't care about nested types (or perhaps you
1345 /// will be resolving them as well, e.g. in a loop).
1346 pub fn shallow_resolve<T>(&self, value: T) -> T
1348 T: TypeFoldable<'tcx>,
1350 let mut r = ShallowResolver::new(self);
1351 value.fold_with(&mut r)
1354 pub fn root_var(&self, var: ty::TyVid) -> ty::TyVid {
1355 self.inner.borrow_mut().type_variables.root_var(var)
1358 /// Where possible, replaces type/const variables in
1359 /// `value` with their final value. Note that region variables
1360 /// are unaffected. If a type/const variable has not been unified, it
1361 /// is left as is. This is an idempotent operation that does
1362 /// not affect inference state in any way and so you can do it
1364 pub fn resolve_vars_if_possible<T>(&self, value: &T) -> T
1366 T: TypeFoldable<'tcx>,
1368 if !value.needs_infer() {
1369 return value.clone(); // Avoid duplicated subst-folding.
1371 let mut r = resolve::OpportunisticVarResolver::new(self);
1372 value.fold_with(&mut r)
1375 /// Returns the first unresolved variable contained in `T`. In the
1376 /// process of visiting `T`, this will resolve (where possible)
1377 /// type variables in `T`, but it never constructs the final,
1378 /// resolved type, so it's more efficient than
1379 /// `resolve_vars_if_possible()`.
1380 pub fn unresolved_type_vars<T>(&self, value: &T) -> Option<(Ty<'tcx>, Option<Span>)>
1382 T: TypeFoldable<'tcx>,
1384 let mut r = resolve::UnresolvedTypeFinder::new(self);
1385 value.visit_with(&mut r);
1389 pub fn probe_const_var(
1391 vid: ty::ConstVid<'tcx>,
1392 ) -> Result<&'tcx ty::Const<'tcx>, ty::UniverseIndex> {
1393 match self.inner.borrow_mut().const_unification_table.probe_value(vid).val {
1394 ConstVariableValue::Known { value } => Ok(value),
1395 ConstVariableValue::Unknown { universe } => Err(universe),
1399 pub fn fully_resolve<T: TypeFoldable<'tcx>>(&self, value: &T) -> FixupResult<'tcx, T> {
1401 * Attempts to resolve all type/region/const variables in
1402 * `value`. Region inference must have been run already (e.g.,
1403 * by calling `resolve_regions_and_report_errors`). If some
1404 * variable was never unified, an `Err` results.
1406 * This method is idempotent, but it not typically not invoked
1407 * except during the writeback phase.
1410 resolve::fully_resolve(self, value)
1413 // [Note-Type-error-reporting]
1414 // An invariant is that anytime the expected or actual type is Error (the special
1415 // error type, meaning that an error occurred when typechecking this expression),
1416 // this is a derived error. The error cascaded from another error (that was already
1417 // reported), so it's not useful to display it to the user.
1418 // The following methods implement this logic.
1419 // They check if either the actual or expected type is Error, and don't print the error
1420 // in this case. The typechecker should only ever report type errors involving mismatched
1421 // types using one of these methods, and should not call span_err directly for such
1424 pub fn type_error_struct_with_diag<M>(
1428 actual_ty: Ty<'tcx>,
1429 ) -> DiagnosticBuilder<'tcx>
1431 M: FnOnce(String) -> DiagnosticBuilder<'tcx>,
1433 let actual_ty = self.resolve_vars_if_possible(&actual_ty);
1434 debug!("type_error_struct_with_diag({:?}, {:?})", sp, actual_ty);
1436 // Don't report an error if actual type is `Error`.
1437 if actual_ty.references_error() {
1438 return self.tcx.sess.diagnostic().struct_dummy();
1441 mk_diag(self.ty_to_string(actual_ty))
1444 pub fn report_mismatched_types(
1446 cause: &ObligationCause<'tcx>,
1449 err: TypeError<'tcx>,
1450 ) -> DiagnosticBuilder<'tcx> {
1451 let trace = TypeTrace::types(cause, true, expected, actual);
1452 self.report_and_explain_type_error(trace, &err)
1455 pub fn replace_bound_vars_with_fresh_vars<T>(
1458 lbrct: LateBoundRegionConversionTime,
1459 value: &ty::Binder<T>,
1460 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
1462 T: TypeFoldable<'tcx>,
1464 let fld_r = |br| self.next_region_var(LateBoundRegion(span, br, lbrct));
1466 self.next_ty_var(TypeVariableOrigin {
1467 kind: TypeVariableOriginKind::MiscVariable,
1471 let fld_c = |_, ty| {
1472 self.next_const_var(
1474 ConstVariableOrigin { kind: ConstVariableOriginKind::MiscVariable, span },
1477 self.tcx.replace_bound_vars(value, fld_r, fld_t, fld_c)
1480 /// See the [`region_constraints::verify_generic_bound`] method.
1481 pub fn verify_generic_bound(
1483 origin: SubregionOrigin<'tcx>,
1484 kind: GenericKind<'tcx>,
1485 a: ty::Region<'tcx>,
1486 bound: VerifyBound<'tcx>,
1488 debug!("verify_generic_bound({:?}, {:?} <: {:?})", kind, a, bound);
1492 .unwrap_region_constraints()
1493 .verify_generic_bound(origin, kind, a, bound);
1496 /// Obtains the latest type of the given closure; this may be a
1497 /// closure in the current function, in which case its
1498 /// `ClosureKind` may not yet be known.
1499 pub fn closure_kind(
1501 closure_def_id: DefId,
1502 closure_substs: SubstsRef<'tcx>,
1503 ) -> Option<ty::ClosureKind> {
1504 let closure_kind_ty = closure_substs.as_closure().kind_ty(closure_def_id, self.tcx);
1505 let closure_kind_ty = self.shallow_resolve(closure_kind_ty);
1506 closure_kind_ty.to_opt_closure_kind()
1509 /// Obtains the signature of a closure. For closures, unlike
1510 /// `tcx.fn_sig(def_id)`, this method will work during the
1511 /// type-checking of the enclosing function and return the closure
1512 /// signature in its partially inferred state.
1513 pub fn closure_sig(&self, def_id: DefId, substs: SubstsRef<'tcx>) -> ty::PolyFnSig<'tcx> {
1514 let closure_sig_ty = substs.as_closure().sig_ty(def_id, self.tcx);
1515 let closure_sig_ty = self.shallow_resolve(closure_sig_ty);
1516 closure_sig_ty.fn_sig(self.tcx)
1519 /// Clears the selection, evaluation, and projection caches. This is useful when
1520 /// repeatedly attempting to select an `Obligation` while changing only
1521 /// its `ParamEnv`, since `FulfillmentContext` doesn't use probing.
1522 pub fn clear_caches(&self) {
1523 self.selection_cache.clear();
1524 self.evaluation_cache.clear();
1525 self.inner.borrow_mut().projection_cache.clear();
1528 fn universe(&self) -> ty::UniverseIndex {
1532 /// Creates and return a fresh universe that extends all previous
1533 /// universes. Updates `self.universe` to that new universe.
1534 pub fn create_next_universe(&self) -> ty::UniverseIndex {
1535 let u = self.universe.get().next_universe();
1536 self.universe.set(u);
1540 /// Resolves and evaluates a constant.
1542 /// The constant can be located on a trait like `<A as B>::C`, in which case the given
1543 /// substitutions and environment are used to resolve the constant. Alternatively if the
1544 /// constant has generic parameters in scope the substitutions are used to evaluate the value of
1545 /// the constant. For example in `fn foo<T>() { let _ = [0; bar::<T>()]; }` the repeat count
1546 /// constant `bar::<T>()` requires a substitution for `T`, if the substitution for `T` is still
1547 /// too generic for the constant to be evaluated then `Err(ErrorHandled::TooGeneric)` is
1550 /// This handles inferences variables within both `param_env` and `substs` by
1551 /// performing the operation on their respective canonical forms.
1552 pub fn const_eval_resolve(
1554 param_env: ty::ParamEnv<'tcx>,
1556 substs: SubstsRef<'tcx>,
1557 promoted: Option<mir::Promoted>,
1559 ) -> ConstEvalResult<'tcx> {
1560 let mut original_values = OriginalQueryValues::default();
1561 let canonical = self.canonicalize_query(&(param_env, substs), &mut original_values);
1563 let (param_env, substs) = canonical.value;
1564 // The return value is the evaluated value which doesn't contain any reference to inference
1565 // variables, thus we don't need to substitute back the original values.
1566 self.tcx.const_eval_resolve(param_env, def_id, substs, promoted, span)
1570 pub struct ShallowResolver<'a, 'tcx> {
1571 infcx: &'a InferCtxt<'a, 'tcx>,
1574 impl<'a, 'tcx> ShallowResolver<'a, 'tcx> {
1576 pub fn new(infcx: &'a InferCtxt<'a, 'tcx>) -> Self {
1577 ShallowResolver { infcx }
1580 /// If `typ` is a type variable of some kind, resolve it one level
1581 /// (but do not resolve types found in the result). If `typ` is
1582 /// not a type variable, just return it unmodified.
1583 pub fn shallow_resolve(&mut self, typ: Ty<'tcx>) -> Ty<'tcx> {
1585 ty::Infer(ty::TyVar(v)) => {
1586 // Not entirely obvious: if `typ` is a type variable,
1587 // it can be resolved to an int/float variable, which
1588 // can then be recursively resolved, hence the
1589 // recursion. Note though that we prevent type
1590 // variables from unifying to other type variables
1591 // directly (though they may be embedded
1592 // structurally), and we prevent cycles in any case,
1593 // so this recursion should always be of very limited
1596 // Note: if these two lines are combined into one we get
1597 // dynamic borrow errors on `self.infcx.inner`.
1598 let known = self.infcx.inner.borrow_mut().type_variables.probe(v).known();
1599 known.map(|t| self.fold_ty(t)).unwrap_or(typ)
1602 ty::Infer(ty::IntVar(v)) => self
1606 .int_unification_table
1608 .map(|v| v.to_type(self.infcx.tcx))
1611 ty::Infer(ty::FloatVar(v)) => self
1615 .float_unification_table
1617 .map(|v| v.to_type(self.infcx.tcx))
1624 // `resolver.shallow_resolve_changed(ty)` is equivalent to
1625 // `resolver.shallow_resolve(ty) != ty`, but more efficient. It's always
1626 // inlined, despite being large, because it has only two call sites that
1627 // are extremely hot.
1629 pub fn shallow_resolve_changed(&self, infer: ty::InferTy) -> bool {
1632 use self::type_variable::TypeVariableValue;
1634 // If `inlined_probe` returns a `Known` value its `kind` never
1636 match self.infcx.inner.borrow_mut().type_variables.inlined_probe(v) {
1637 TypeVariableValue::Unknown { .. } => false,
1638 TypeVariableValue::Known { .. } => true,
1643 // If inlined_probe_value returns a value it's always a
1644 // `ty::Int(_)` or `ty::UInt(_)`, which never matches a
1646 self.infcx.inner.borrow_mut().int_unification_table.inlined_probe_value(v).is_some()
1649 ty::FloatVar(v) => {
1650 // If inlined_probe_value returns a value it's always a
1651 // `ty::Float(_)`, which never matches a `ty::Infer(_)`.
1653 // Not `inlined_probe_value(v)` because this call site is colder.
1654 self.infcx.inner.borrow_mut().float_unification_table.probe_value(v).is_some()
1657 _ => unreachable!(),
1662 impl<'a, 'tcx> TypeFolder<'tcx> for ShallowResolver<'a, 'tcx> {
1663 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1667 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1668 self.shallow_resolve(ty)
1671 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
1672 if let ty::Const { val: ty::ConstKind::Infer(InferConst::Var(vid)), .. } = ct {
1676 .const_unification_table
1687 impl<'tcx> TypeTrace<'tcx> {
1688 pub fn span(&self) -> Span {
1693 cause: &ObligationCause<'tcx>,
1694 a_is_expected: bool,
1697 ) -> TypeTrace<'tcx> {
1698 TypeTrace { cause: cause.clone(), values: Types(ExpectedFound::new(a_is_expected, a, b)) }
1701 pub fn dummy(tcx: TyCtxt<'tcx>) -> TypeTrace<'tcx> {
1703 cause: ObligationCause::dummy(),
1704 values: Types(ExpectedFound { expected: tcx.types.err, found: tcx.types.err }),
1709 impl<'tcx> SubregionOrigin<'tcx> {
1710 pub fn span(&self) -> Span {
1712 Subtype(ref a) => a.span(),
1713 InfStackClosure(a) => a,
1714 InvokeClosure(a) => a,
1715 DerefPointer(a) => a,
1716 ClosureCapture(a, _) => a,
1718 RelateObjectBound(a) => a,
1719 RelateParamBound(a, _) => a,
1720 RelateRegionParamBound(a) => a,
1721 RelateDefaultParamBound(a, _) => a,
1723 ReborrowUpvar(a, _) => a,
1724 DataBorrowed(_, a) => a,
1725 ReferenceOutlivesReferent(_, a) => a,
1726 ParameterInScope(_, a) => a,
1727 ExprTypeIsNotInScope(_, a) => a,
1728 BindingTypeIsNotValidAtDecl(a) => a,
1735 SafeDestructor(a) => a,
1736 CompareImplMethodObligation { span, .. } => span,
1740 pub fn from_obligation_cause<F>(cause: &traits::ObligationCause<'tcx>, default: F) -> Self
1742 F: FnOnce() -> Self,
1745 traits::ObligationCauseCode::ReferenceOutlivesReferent(ref_type) => {
1746 SubregionOrigin::ReferenceOutlivesReferent(ref_type, cause.span)
1749 traits::ObligationCauseCode::CompareImplMethodObligation {
1753 } => SubregionOrigin::CompareImplMethodObligation {
1765 impl RegionVariableOrigin {
1766 pub fn span(&self) -> Span {
1768 MiscVariable(a) => a,
1769 PatternRegion(a) => a,
1770 AddrOfRegion(a) => a,
1773 EarlyBoundRegion(a, ..) => a,
1774 LateBoundRegion(a, ..) => a,
1775 BoundRegionInCoherence(_) => rustc_span::DUMMY_SP,
1776 UpvarRegion(_, a) => a,
1777 NLL(..) => bug!("NLL variable used with `span`"),
1782 impl<'tcx> fmt::Debug for RegionObligation<'tcx> {
1783 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1786 "RegionObligation(sub_region={:?}, sup_type={:?})",
1787 self.sub_region, self.sup_type