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};
12 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
13 use rustc_data_structures::snapshot_vec as sv;
14 use rustc_data_structures::sync::Lrc;
15 use rustc_data_structures::undo_log::{Rollback, Snapshots, UndoLogs};
16 use rustc_data_structures::unify as ut;
17 use rustc_errors::DiagnosticBuilder;
19 use rustc_hir::def_id::{DefId, LocalDefId};
20 use rustc_middle::infer::canonical::{Canonical, CanonicalVarValues};
21 use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue};
22 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind, ToType};
23 use rustc_middle::middle::region;
24 use rustc_middle::mir;
25 use rustc_middle::mir::interpret::ConstEvalResult;
26 use rustc_middle::traits::select;
27 use rustc_middle::ty::error::{ExpectedFound, TypeError, UnconstrainedNumeric};
28 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
29 use rustc_middle::ty::relate::RelateResult;
30 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, SubstsRef};
31 pub use rustc_middle::ty::IntVarValue;
32 use rustc_middle::ty::{self, GenericParamDefKind, InferConst, Ty, TyCtxt};
33 use rustc_middle::ty::{ConstVid, FloatVid, IntVid, TyVid};
34 use rustc_session::config::BorrowckMode;
35 use rustc_span::symbol::Symbol;
38 use std::cell::{Cell, Ref, RefCell};
39 use std::collections::BTreeMap;
41 use std::marker::PhantomData;
43 use self::combine::CombineFields;
44 use self::free_regions::RegionRelations;
45 use self::lexical_region_resolve::LexicalRegionResolutions;
46 use self::outlives::env::OutlivesEnvironment;
47 use self::region_constraints::{GenericKind, RegionConstraintData, VarInfos, VerifyBound};
48 use self::region_constraints::{
49 RegionConstraintCollector, RegionConstraintStorage, RegionSnapshot,
51 use self::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
57 pub mod error_reporting;
64 mod lexical_region_resolve;
68 pub mod region_constraints;
71 pub mod type_variable;
73 use crate::infer::canonical::OriginalQueryValues;
74 pub use rustc_middle::infer::unify_key;
78 pub struct InferOk<'tcx, T> {
80 pub obligations: PredicateObligations<'tcx>,
82 pub type InferResult<'tcx, T> = Result<InferOk<'tcx, T>, TypeError<'tcx>>;
84 pub type Bound<T> = Option<T>;
85 pub type UnitResult<'tcx> = RelateResult<'tcx, ()>; // "unify result"
86 pub type FixupResult<'tcx, T> = Result<T, FixupError<'tcx>>; // "fixup result"
88 /// How we should handle region solving.
90 /// This is used so that the region values inferred by HIR region solving are
91 /// not exposed, and so that we can avoid doing work in HIR typeck that MIR
92 /// typeck will also do.
93 #[derive(Copy, Clone, Debug)]
94 pub enum RegionckMode {
95 /// The default mode: report region errors, don't erase regions.
97 /// Erase the results of region after solving.
99 /// A flag that is used to suppress region errors, when we are doing
100 /// region checks that the NLL borrow checker will also do -- it might
102 suppress_errors: bool,
106 impl Default for RegionckMode {
107 fn default() -> Self {
113 pub fn suppressed(self) -> bool {
115 Self::Solve => false,
116 Self::Erase { suppress_errors } => suppress_errors,
120 /// Indicates that the MIR borrowck will repeat these region
121 /// checks, so we should ignore errors if NLL is (unconditionally)
123 pub fn for_item_body(tcx: TyCtxt<'_>) -> Self {
124 // FIXME(Centril): Once we actually remove `::Migrate` also make
125 // this always `true` and then proceed to eliminate the dead code.
126 match tcx.borrowck_mode() {
127 // If we're on Migrate mode, report AST region errors
128 BorrowckMode::Migrate => RegionckMode::Erase { suppress_errors: false },
130 // If we're on MIR, don't report AST region errors as they should be reported by NLL
131 BorrowckMode::Mir => RegionckMode::Erase { suppress_errors: true },
136 /// This type contains all the things within `InferCtxt` that sit within a
137 /// `RefCell` and are involved with taking/rolling back snapshots. Snapshot
138 /// operations are hot enough that we want only one call to `borrow_mut` per
139 /// call to `start_snapshot` and `rollback_to`.
140 pub struct InferCtxtInner<'tcx> {
141 /// Cache for projections. This cache is snapshotted along with the infcx.
143 /// Public so that `traits::project` can use it.
144 pub projection_cache: traits::ProjectionCache<'tcx>,
146 /// We instantiate `UnificationTable` with `bounds<Ty>` because the types
147 /// that might instantiate a general type variable have an order,
148 /// represented by its upper and lower bounds.
149 type_variables: type_variable::TypeVariableStorage<'tcx>,
150 undo_log: Logs<'tcx>,
152 /// Map from const parameter variable to the kind of const it represents.
153 const_unification_table: ut::UnificationStorage<ty::ConstVid<'tcx>>,
155 /// Map from integral variable to the kind of integer it represents.
156 int_unification_table: ut::UnificationStorage<ty::IntVid>,
158 /// Map from floating variable to the kind of float it represents.
159 float_unification_table: ut::UnificationStorage<ty::FloatVid>,
161 /// Tracks the set of region variables and the constraints between them.
162 /// This is initially `Some(_)` but when
163 /// `resolve_regions_and_report_errors` is invoked, this gets set to `None`
164 /// -- further attempts to perform unification, etc., may fail if new
165 /// region constraints would've been added.
166 region_constraints: Option<RegionConstraintStorage<'tcx>>,
168 /// A set of constraints that regionck must validate. Each
169 /// constraint has the form `T:'a`, meaning "some type `T` must
170 /// outlive the lifetime 'a". These constraints derive from
171 /// instantiated type parameters. So if you had a struct defined
174 /// struct Foo<T:'static> { ... }
176 /// then in some expression `let x = Foo { ... }` it will
177 /// instantiate the type parameter `T` with a fresh type `$0`. At
178 /// the same time, it will record a region obligation of
179 /// `$0:'static`. This will get checked later by regionck. (We
180 /// can't generally check these things right away because we have
181 /// to wait until types are resolved.)
183 /// These are stored in a map keyed to the id of the innermost
184 /// enclosing fn body / static initializer expression. This is
185 /// because the location where the obligation was incurred can be
186 /// relevant with respect to which sublifetime assumptions are in
187 /// place. The reason that we store under the fn-id, and not
188 /// something more fine-grained, is so that it is easier for
189 /// regionck to be sure that it has found *all* the region
190 /// obligations (otherwise, it's easy to fail to walk to a
191 /// particular node-id).
193 /// Before running `resolve_regions_and_report_errors`, the creator
194 /// of the inference context is expected to invoke
195 /// `process_region_obligations` (defined in `self::region_obligations`)
196 /// for each body-id in this map, which will process the
197 /// obligations within. This is expected to be done 'late enough'
198 /// that all type inference variables have been bound and so forth.
199 pub region_obligations: Vec<(hir::HirId, RegionObligation<'tcx>)>,
202 impl<'tcx> InferCtxtInner<'tcx> {
203 fn new() -> InferCtxtInner<'tcx> {
205 projection_cache: Default::default(),
206 type_variables: type_variable::TypeVariableStorage::new(),
207 undo_log: Logs::default(),
208 const_unification_table: ut::UnificationStorage::new(),
209 int_unification_table: ut::UnificationStorage::new(),
210 float_unification_table: ut::UnificationStorage::new(),
211 region_constraints: Some(RegionConstraintStorage::new()),
212 region_obligations: vec![],
216 fn type_variables(&mut self) -> type_variable::TypeVariableTable<'tcx, '_> {
217 self.type_variables.with_log(&mut self.undo_log)
220 fn int_unification_table(
222 ) -> ut::UnificationTable<
223 ut::InPlace<ty::IntVid, &mut ut::UnificationStorage<ty::IntVid>, &mut Logs<'tcx>>,
225 ut::UnificationTable::with_log(&mut self.int_unification_table, &mut self.undo_log)
228 fn float_unification_table(
230 ) -> ut::UnificationTable<
231 ut::InPlace<ty::FloatVid, &mut ut::UnificationStorage<ty::FloatVid>, &mut Logs<'tcx>>,
233 ut::UnificationTable::with_log(&mut self.float_unification_table, &mut self.undo_log)
236 fn const_unification_table(
238 ) -> ut::UnificationTable<
241 &mut ut::UnificationStorage<ty::ConstVid<'tcx>>,
245 ut::UnificationTable::with_log(&mut self.const_unification_table, &mut self.undo_log)
248 pub fn unwrap_region_constraints(&mut self) -> RegionConstraintCollector<'tcx, '_> {
249 self.region_constraints
251 .expect("region constraints already solved")
252 .with_log(&mut self.undo_log)
256 pub struct Snapshot<'tcx> {
258 _marker: PhantomData<&'tcx ()>,
261 pub(crate) enum UndoLog<'tcx> {
262 TypeVariables(type_variable::UndoLog<'tcx>),
263 ConstUnificationTable(sv::UndoLog<ut::Delegate<ty::ConstVid<'tcx>>>),
264 IntUnificationTable(sv::UndoLog<ut::Delegate<ty::IntVid>>),
265 FloatUnificationTable(sv::UndoLog<ut::Delegate<ty::FloatVid>>),
266 RegionConstraintCollector(region_constraints::UndoLog<'tcx>),
267 RegionUnificationTable(sv::UndoLog<ut::Delegate<ty::RegionVid>>),
270 impl<'tcx> From<region_constraints::UndoLog<'tcx>> for UndoLog<'tcx> {
271 fn from(l: region_constraints::UndoLog<'tcx>) -> Self {
272 UndoLog::RegionConstraintCollector(l)
276 impl<'tcx> From<sv::UndoLog<ut::Delegate<type_variable::TyVidEqKey<'tcx>>>> for UndoLog<'tcx> {
277 fn from(l: sv::UndoLog<ut::Delegate<type_variable::TyVidEqKey<'tcx>>>) -> Self {
278 UndoLog::TypeVariables(type_variable::UndoLog::EqRelation(l))
282 impl<'tcx> From<sv::UndoLog<ut::Delegate<ty::TyVid>>> for UndoLog<'tcx> {
283 fn from(l: sv::UndoLog<ut::Delegate<ty::TyVid>>) -> Self {
284 UndoLog::TypeVariables(type_variable::UndoLog::SubRelation(l))
288 impl<'tcx> From<sv::UndoLog<type_variable::Delegate>> for UndoLog<'tcx> {
289 fn from(l: sv::UndoLog<type_variable::Delegate>) -> Self {
290 UndoLog::TypeVariables(type_variable::UndoLog::Values(l))
294 impl<'tcx> From<type_variable::Instantiate> for UndoLog<'tcx> {
295 fn from(l: type_variable::Instantiate) -> Self {
296 UndoLog::TypeVariables(type_variable::UndoLog::from(l))
300 impl From<type_variable::UndoLog<'tcx>> for UndoLog<'tcx> {
301 fn from(t: type_variable::UndoLog<'tcx>) -> Self {
302 Self::TypeVariables(t)
306 impl<'tcx> From<sv::UndoLog<ut::Delegate<ty::ConstVid<'tcx>>>> for UndoLog<'tcx> {
307 fn from(l: sv::UndoLog<ut::Delegate<ty::ConstVid<'tcx>>>) -> Self {
308 Self::ConstUnificationTable(l)
312 impl<'tcx> From<sv::UndoLog<ut::Delegate<ty::IntVid>>> for UndoLog<'tcx> {
313 fn from(l: sv::UndoLog<ut::Delegate<ty::IntVid>>) -> Self {
314 Self::IntUnificationTable(l)
318 impl<'tcx> From<sv::UndoLog<ut::Delegate<ty::FloatVid>>> for UndoLog<'tcx> {
319 fn from(l: sv::UndoLog<ut::Delegate<ty::FloatVid>>) -> Self {
320 Self::FloatUnificationTable(l)
324 impl<'tcx> From<sv::UndoLog<ut::Delegate<ty::RegionVid>>> for UndoLog<'tcx> {
325 fn from(l: sv::UndoLog<ut::Delegate<ty::RegionVid>>) -> Self {
326 Self::RegionUnificationTable(l)
330 pub(crate) type UnificationTable<'a, 'tcx, T> =
331 ut::UnificationTable<ut::InPlace<T, &'a mut ut::UnificationStorage<T>, &'a mut Logs<'tcx>>>;
333 struct RollbackView<'tcx, 'a> {
334 type_variables: type_variable::RollbackView<'tcx, 'a>,
335 const_unification_table: &'a mut ut::UnificationStorage<ty::ConstVid<'tcx>>,
336 int_unification_table: &'a mut ut::UnificationStorage<ty::IntVid>,
337 float_unification_table: &'a mut ut::UnificationStorage<ty::FloatVid>,
338 region_constraints: &'a mut RegionConstraintStorage<'tcx>,
341 impl<'tcx> Rollback<UndoLog<'tcx>> for RollbackView<'tcx, '_> {
342 fn reverse(&mut self, undo: UndoLog<'tcx>) {
344 UndoLog::TypeVariables(undo) => self.type_variables.reverse(undo),
345 UndoLog::ConstUnificationTable(undo) => self.const_unification_table.reverse(undo),
346 UndoLog::IntUnificationTable(undo) => self.int_unification_table.reverse(undo),
347 UndoLog::FloatUnificationTable(undo) => self.float_unification_table.reverse(undo),
348 UndoLog::RegionConstraintCollector(undo) => self.region_constraints.reverse(undo),
349 UndoLog::RegionUnificationTable(undo) => {
350 self.region_constraints.unification_table.reverse(undo)
356 pub(crate) struct Logs<'tcx> {
357 logs: Vec<UndoLog<'tcx>>,
358 num_open_snapshots: usize,
361 impl Default for Logs<'_> {
362 fn default() -> Self {
363 Self { logs: Default::default(), num_open_snapshots: Default::default() }
367 impl<'tcx, T> UndoLogs<T> for Logs<'tcx>
369 UndoLog<'tcx>: From<T>,
371 fn num_open_snapshots(&self) -> usize {
372 self.num_open_snapshots
374 fn push(&mut self, undo: T) {
375 if self.in_snapshot() {
376 self.logs.push(undo.into())
379 fn clear(&mut self) {
381 self.num_open_snapshots = 0;
383 fn extend<J>(&mut self, undos: J)
386 J: IntoIterator<Item = T>,
388 if self.in_snapshot() {
389 self.logs.extend(undos.into_iter().map(UndoLog::from))
394 impl<'tcx> Snapshots<UndoLog<'tcx>> for Logs<'tcx> {
395 type Snapshot = Snapshot<'tcx>;
396 fn actions_since_snapshot(&self, snapshot: &Self::Snapshot) -> &[UndoLog<'tcx>] {
397 &self.logs[snapshot.undo_len..]
400 fn start_snapshot(&mut self) -> Self::Snapshot {
404 fn rollback_to(&mut self, values: &mut impl Rollback<UndoLog<'tcx>>, snapshot: Self::Snapshot) {
405 debug!("rollback_to({})", snapshot.undo_len);
406 self.assert_open_snapshot(&snapshot);
408 while self.logs.len() > snapshot.undo_len {
409 values.reverse(self.logs.pop().unwrap());
412 if self.num_open_snapshots == 1 {
413 // The root snapshot. It's safe to clear the undo log because
414 // there's no snapshot further out that we might need to roll back
416 assert!(snapshot.undo_len == 0);
420 self.num_open_snapshots -= 1;
423 fn commit(&mut self, snapshot: Self::Snapshot) {
424 debug!("commit({})", snapshot.undo_len);
426 if self.num_open_snapshots == 1 {
427 // The root snapshot. It's safe to clear the undo log because
428 // there's no snapshot further out that we might need to roll back
430 assert!(snapshot.undo_len == 0);
434 self.num_open_snapshots -= 1;
438 impl<'tcx> Logs<'tcx> {
439 pub(crate) fn region_constraints(
442 ) -> impl Iterator<Item = &'_ region_constraints::UndoLog<'tcx>> + Clone {
443 self.logs[after..].iter().filter_map(|log| match log {
444 UndoLog::RegionConstraintCollector(log) => Some(log),
449 fn assert_open_snapshot(&self, snapshot: &Snapshot<'tcx>) {
450 // Failures here may indicate a failure to follow a stack discipline.
451 assert!(self.logs.len() >= snapshot.undo_len);
452 assert!(self.num_open_snapshots > 0);
456 pub struct InferCtxt<'a, 'tcx> {
457 pub tcx: TyCtxt<'tcx>,
459 /// During type-checking/inference of a body, `in_progress_tables`
460 /// contains a reference to the tables being built up, which are
461 /// used for reading closure kinds/signatures as they are inferred,
462 /// and for error reporting logic to read arbitrary node types.
463 pub in_progress_tables: Option<&'a RefCell<ty::TypeckTables<'tcx>>>,
465 pub inner: RefCell<InferCtxtInner<'tcx>>,
467 /// If set, this flag causes us to skip the 'leak check' during
468 /// higher-ranked subtyping operations. This flag is a temporary one used
469 /// to manage the removal of the leak-check: for the time being, we still run the
470 /// leak-check, but we issue warnings. This flag can only be set to true
471 /// when entering a snapshot.
472 skip_leak_check: Cell<bool>,
474 /// Once region inference is done, the values for each variable.
475 lexical_region_resolutions: RefCell<Option<LexicalRegionResolutions<'tcx>>>,
477 /// Caches the results of trait selection. This cache is used
478 /// for things that have to do with the parameters in scope.
479 pub selection_cache: select::SelectionCache<'tcx>,
481 /// Caches the results of trait evaluation.
482 pub evaluation_cache: select::EvaluationCache<'tcx>,
484 /// the set of predicates on which errors have been reported, to
485 /// avoid reporting the same error twice.
486 pub reported_trait_errors: RefCell<FxHashMap<Span, Vec<ty::Predicate<'tcx>>>>,
488 pub reported_closure_mismatch: RefCell<FxHashSet<(Span, Option<Span>)>>,
490 /// When an error occurs, we want to avoid reporting "derived"
491 /// errors that are due to this original failure. Normally, we
492 /// handle this with the `err_count_on_creation` count, which
493 /// basically just tracks how many errors were reported when we
494 /// started type-checking a fn and checks to see if any new errors
495 /// have been reported since then. Not great, but it works.
497 /// However, when errors originated in other passes -- notably
498 /// resolve -- this heuristic breaks down. Therefore, we have this
499 /// auxiliary flag that one can set whenever one creates a
500 /// type-error that is due to an error in a prior pass.
502 /// Don't read this flag directly, call `is_tainted_by_errors()`
503 /// and `set_tainted_by_errors()`.
504 tainted_by_errors_flag: Cell<bool>,
506 /// Track how many errors were reported when this infcx is created.
507 /// If the number of errors increases, that's also a sign (line
508 /// `tained_by_errors`) to avoid reporting certain kinds of errors.
509 // FIXME(matthewjasper) Merge into `tainted_by_errors_flag`
510 err_count_on_creation: usize,
512 /// This flag is true while there is an active snapshot.
513 in_snapshot: Cell<bool>,
515 /// What is the innermost universe we have created? Starts out as
516 /// `UniverseIndex::root()` but grows from there as we enter
517 /// universal quantifiers.
519 /// N.B., at present, we exclude the universal quantifiers on the
520 /// item we are type-checking, and just consider those names as
521 /// part of the root universe. So this would only get incremented
522 /// when we enter into a higher-ranked (`for<..>`) type or trait
524 universe: Cell<ty::UniverseIndex>,
527 /// A map returned by `replace_bound_vars_with_placeholders()`
528 /// indicating the placeholder region that each late-bound region was
530 pub type PlaceholderMap<'tcx> = BTreeMap<ty::BoundRegion, ty::Region<'tcx>>;
532 /// See the `error_reporting` module for more details.
533 #[derive(Clone, Debug, PartialEq, Eq, TypeFoldable)]
534 pub enum ValuePairs<'tcx> {
535 Types(ExpectedFound<Ty<'tcx>>),
536 Regions(ExpectedFound<ty::Region<'tcx>>),
537 Consts(ExpectedFound<&'tcx ty::Const<'tcx>>),
538 TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>),
539 PolyTraitRefs(ExpectedFound<ty::PolyTraitRef<'tcx>>),
542 /// The trace designates the path through inference that we took to
543 /// encounter an error or subtyping constraint.
545 /// See the `error_reporting` module for more details.
546 #[derive(Clone, Debug)]
547 pub struct TypeTrace<'tcx> {
548 cause: ObligationCause<'tcx>,
549 values: ValuePairs<'tcx>,
552 /// The origin of a `r1 <= r2` constraint.
554 /// See `error_reporting` module for more details
555 #[derive(Clone, Debug)]
556 pub enum SubregionOrigin<'tcx> {
557 /// Arose from a subtyping relation
558 Subtype(Box<TypeTrace<'tcx>>),
560 /// Stack-allocated closures cannot outlive innermost loop
561 /// or function so as to ensure we only require finite stack
562 InfStackClosure(Span),
564 /// Invocation of closure must be within its lifetime
567 /// Dereference of reference must be within its lifetime
570 /// Closure bound must not outlive captured variables
571 ClosureCapture(Span, hir::HirId),
573 /// Index into slice must be within its lifetime
576 /// When casting `&'a T` to an `&'b Trait` object,
577 /// relating `'a` to `'b`
578 RelateObjectBound(Span),
580 /// Some type parameter was instantiated with the given type,
581 /// and that type must outlive some region.
582 RelateParamBound(Span, Ty<'tcx>),
584 /// The given region parameter was instantiated with a region
585 /// that must outlive some other region.
586 RelateRegionParamBound(Span),
588 /// A bound placed on type parameters that states that must outlive
589 /// the moment of their instantiation.
590 RelateDefaultParamBound(Span, Ty<'tcx>),
592 /// Creating a pointer `b` to contents of another reference
595 /// Creating a pointer `b` to contents of an upvar
596 ReborrowUpvar(Span, ty::UpvarId),
598 /// Data with type `Ty<'tcx>` was borrowed
599 DataBorrowed(Ty<'tcx>, Span),
601 /// (&'a &'b T) where a >= b
602 ReferenceOutlivesReferent(Ty<'tcx>, Span),
604 /// Type or region parameters must be in scope.
605 ParameterInScope(ParameterOrigin, Span),
607 /// The type T of an expression E must outlive the lifetime for E.
608 ExprTypeIsNotInScope(Ty<'tcx>, Span),
610 /// A `ref b` whose region does not enclose the decl site
611 BindingTypeIsNotValidAtDecl(Span),
613 /// Regions appearing in a method receiver must outlive method call
616 /// Regions appearing in a function argument must outlive func call
619 /// Region in return type of invoked fn must enclose call
622 /// Operands must be in scope
625 /// Region resulting from a `&` expr must enclose the `&` expr
628 /// An auto-borrow that does not enclose the expr where it occurs
631 /// Region constraint arriving from destructor safety
632 SafeDestructor(Span),
634 /// Comparing the signature and requirements of an impl method against
635 /// the containing trait.
636 CompareImplMethodObligation {
638 item_name: ast::Name,
639 impl_item_def_id: DefId,
640 trait_item_def_id: DefId,
644 // `SubregionOrigin` is used a lot. Make sure it doesn't unintentionally get bigger.
645 #[cfg(target_arch = "x86_64")]
646 static_assert_size!(SubregionOrigin<'_>, 32);
648 /// Places that type/region parameters can appear.
649 #[derive(Clone, Copy, Debug)]
650 pub enum ParameterOrigin {
652 MethodCall, // foo.bar() <-- parameters on impl providing bar()
653 OverloadedOperator, // a + b when overloaded
654 OverloadedDeref, // *a when overloaded
657 /// Times when we replace late-bound regions with variables:
658 #[derive(Clone, Copy, Debug)]
659 pub enum LateBoundRegionConversionTime {
660 /// when a fn is called
663 /// when two higher-ranked types are compared
666 /// when projecting an associated type
667 AssocTypeProjection(DefId),
670 /// Reasons to create a region inference variable
672 /// See `error_reporting` module for more details
673 #[derive(Copy, Clone, Debug)]
674 pub enum RegionVariableOrigin {
675 /// Region variables created for ill-categorized reasons,
676 /// mostly indicates places in need of refactoring
679 /// Regions created by a `&P` or `[...]` pattern
682 /// Regions created by `&` operator
685 /// Regions created as part of an autoref of a method receiver
688 /// Regions created as part of an automatic coercion
691 /// Region variables created as the values for early-bound regions
692 EarlyBoundRegion(Span, Symbol),
694 /// Region variables created for bound regions
695 /// in a function or method that is called
696 LateBoundRegion(Span, ty::BoundRegion, LateBoundRegionConversionTime),
698 UpvarRegion(ty::UpvarId, Span),
700 BoundRegionInCoherence(ast::Name),
702 /// This origin is used for the inference variables that we create
703 /// during NLL region processing.
704 NLL(NLLRegionVariableOrigin),
707 #[derive(Copy, Clone, Debug)]
708 pub enum NLLRegionVariableOrigin {
709 /// During NLL region processing, we create variables for free
710 /// regions that we encounter in the function signature and
711 /// elsewhere. This origin indices we've got one of those.
714 /// "Universal" instantiation of a higher-ranked region (e.g.,
715 /// from a `for<'a> T` binder). Meant to represent "any region".
716 Placeholder(ty::PlaceholderRegion),
718 /// The variable we create to represent `'empty(U0)`.
722 /// If this is true, then this variable was created to represent a lifetime
723 /// bound in a `for` binder. For example, it might have been created to
724 /// represent the lifetime `'a` in a type like `for<'a> fn(&'a u32)`.
725 /// Such variables are created when we are trying to figure out if there
726 /// is any valid instantiation of `'a` that could fit into some scenario.
728 /// This is used to inform error reporting: in the case that we are trying to
729 /// determine whether there is any valid instantiation of a `'a` variable that meets
730 /// some constraint C, we want to blame the "source" of that `for` type,
731 /// rather than blaming the source of the constraint C.
736 impl NLLRegionVariableOrigin {
737 pub fn is_universal(self) -> bool {
739 NLLRegionVariableOrigin::FreeRegion => true,
740 NLLRegionVariableOrigin::Placeholder(..) => true,
741 NLLRegionVariableOrigin::Existential { .. } => false,
742 NLLRegionVariableOrigin::RootEmptyRegion => false,
746 pub fn is_existential(self) -> bool {
751 // FIXME(eddyb) investigate overlap between this and `TyOrConstInferVar`.
752 #[derive(Copy, Clone, Debug)]
753 pub enum FixupError<'tcx> {
754 UnresolvedIntTy(IntVid),
755 UnresolvedFloatTy(FloatVid),
757 UnresolvedConst(ConstVid<'tcx>),
760 /// See the `region_obligations` field for more information.
762 pub struct RegionObligation<'tcx> {
763 pub sub_region: ty::Region<'tcx>,
764 pub sup_type: Ty<'tcx>,
765 pub origin: SubregionOrigin<'tcx>,
768 impl<'tcx> fmt::Display for FixupError<'tcx> {
769 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
770 use self::FixupError::*;
773 UnresolvedIntTy(_) => write!(
775 "cannot determine the type of this integer; \
776 add a suffix to specify the type explicitly"
778 UnresolvedFloatTy(_) => write!(
780 "cannot determine the type of this number; \
781 add a suffix to specify the type explicitly"
783 UnresolvedTy(_) => write!(f, "unconstrained type"),
784 UnresolvedConst(_) => write!(f, "unconstrained const value"),
789 /// Helper type of a temporary returned by `tcx.infer_ctxt()`.
790 /// Necessary because we can't write the following bound:
791 /// `F: for<'b, 'tcx> where 'tcx FnOnce(InferCtxt<'b, 'tcx>)`.
792 pub struct InferCtxtBuilder<'tcx> {
793 global_tcx: TyCtxt<'tcx>,
794 fresh_tables: Option<RefCell<ty::TypeckTables<'tcx>>>,
797 pub trait TyCtxtInferExt<'tcx> {
798 fn infer_ctxt(self) -> InferCtxtBuilder<'tcx>;
801 impl TyCtxtInferExt<'tcx> for TyCtxt<'tcx> {
802 fn infer_ctxt(self) -> InferCtxtBuilder<'tcx> {
803 InferCtxtBuilder { global_tcx: self, fresh_tables: None }
807 impl<'tcx> InferCtxtBuilder<'tcx> {
808 /// Used only by `rustc_typeck` during body type-checking/inference,
809 /// will initialize `in_progress_tables` with fresh `TypeckTables`.
810 pub fn with_fresh_in_progress_tables(mut self, table_owner: LocalDefId) -> Self {
811 self.fresh_tables = Some(RefCell::new(ty::TypeckTables::empty(Some(table_owner))));
815 /// Given a canonical value `C` as a starting point, create an
816 /// inference context that contains each of the bound values
817 /// within instantiated as a fresh variable. The `f` closure is
818 /// invoked with the new infcx, along with the instantiated value
819 /// `V` and a substitution `S`. This substitution `S` maps from
820 /// the bound values in `C` to their instantiated values in `V`
821 /// (in other words, `S(C) = V`).
822 pub fn enter_with_canonical<T, R>(
825 canonical: &Canonical<'tcx, T>,
826 f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>, T, CanonicalVarValues<'tcx>) -> R,
829 T: TypeFoldable<'tcx>,
833 infcx.instantiate_canonical_with_fresh_inference_vars(span, canonical);
834 f(infcx, value, subst)
838 pub fn enter<R>(&mut self, f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>) -> R) -> R {
839 let InferCtxtBuilder { global_tcx, ref fresh_tables } = *self;
840 let in_progress_tables = fresh_tables.as_ref();
841 global_tcx.enter_local(|tcx| {
845 inner: RefCell::new(InferCtxtInner::new()),
846 lexical_region_resolutions: RefCell::new(None),
847 selection_cache: Default::default(),
848 evaluation_cache: Default::default(),
849 reported_trait_errors: Default::default(),
850 reported_closure_mismatch: Default::default(),
851 tainted_by_errors_flag: Cell::new(false),
852 err_count_on_creation: tcx.sess.err_count(),
853 in_snapshot: Cell::new(false),
854 skip_leak_check: Cell::new(false),
855 universe: Cell::new(ty::UniverseIndex::ROOT),
861 impl<'tcx, T> InferOk<'tcx, T> {
862 pub fn unit(self) -> InferOk<'tcx, ()> {
863 InferOk { value: (), obligations: self.obligations }
866 /// Extracts `value`, registering any obligations into `fulfill_cx`.
867 pub fn into_value_registering_obligations(
869 infcx: &InferCtxt<'_, 'tcx>,
870 fulfill_cx: &mut dyn TraitEngine<'tcx>,
872 let InferOk { value, obligations } = self;
873 for obligation in obligations {
874 fulfill_cx.register_predicate_obligation(infcx, obligation);
880 impl<'tcx> InferOk<'tcx, ()> {
881 pub fn into_obligations(self) -> PredicateObligations<'tcx> {
886 #[must_use = "once you start a snapshot, you should always consume it"]
887 pub struct CombinedSnapshot<'a, 'tcx> {
888 projection_cache_snapshot: traits::ProjectionCacheSnapshot,
889 undo_snapshot: Snapshot<'tcx>,
890 type_snapshot: type_variable::Snapshot<'tcx>,
891 const_snapshot: usize,
893 float_snapshot: usize,
894 region_constraints_snapshot: RegionSnapshot,
895 region_obligations_snapshot: usize,
896 universe: ty::UniverseIndex,
897 was_in_snapshot: bool,
898 was_skip_leak_check: bool,
899 _in_progress_tables: Option<Ref<'a, ty::TypeckTables<'tcx>>>,
902 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
903 pub fn is_in_snapshot(&self) -> bool {
904 self.in_snapshot.get()
907 pub fn freshen<T: TypeFoldable<'tcx>>(&self, t: T) -> T {
908 t.fold_with(&mut self.freshener())
911 pub fn type_var_diverges(&'a self, ty: Ty<'_>) -> bool {
913 ty::Infer(ty::TyVar(vid)) => self.inner.borrow_mut().type_variables().var_diverges(vid),
918 pub fn freshener<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
919 freshen::TypeFreshener::new(self)
922 pub fn type_is_unconstrained_numeric(&'a self, ty: Ty<'_>) -> UnconstrainedNumeric {
923 use rustc_middle::ty::error::UnconstrainedNumeric::Neither;
924 use rustc_middle::ty::error::UnconstrainedNumeric::{UnconstrainedFloat, UnconstrainedInt};
926 ty::Infer(ty::IntVar(vid)) => {
927 if self.inner.borrow_mut().int_unification_table().probe_value(vid).is_some() {
933 ty::Infer(ty::FloatVar(vid)) => {
934 if self.inner.borrow_mut().float_unification_table().probe_value(vid).is_some() {
944 pub fn unsolved_variables(&self) -> Vec<Ty<'tcx>> {
945 let mut inner = self.inner.borrow_mut();
946 // FIXME(const_generics): should there be an equivalent function for const variables?
948 let mut vars: Vec<Ty<'_>> = inner
950 .unsolved_variables()
952 .map(|t| self.tcx.mk_ty_var(t))
955 (0..inner.int_unification_table().len())
956 .map(|i| ty::IntVid { index: i as u32 })
957 .filter(|&vid| inner.int_unification_table().probe_value(vid).is_none())
958 .map(|v| self.tcx.mk_int_var(v)),
961 (0..inner.float_unification_table().len())
962 .map(|i| ty::FloatVid { index: i as u32 })
963 .filter(|&vid| inner.float_unification_table().probe_value(vid).is_none())
964 .map(|v| self.tcx.mk_float_var(v)),
971 trace: TypeTrace<'tcx>,
972 param_env: ty::ParamEnv<'tcx>,
973 ) -> CombineFields<'a, 'tcx> {
979 obligations: PredicateObligations::new(),
983 /// Clear the "currently in a snapshot" flag, invoke the closure,
984 /// then restore the flag to its original value. This flag is a
985 /// debugging measure designed to detect cases where we start a
986 /// snapshot, create type variables, and register obligations
987 /// which may involve those type variables in the fulfillment cx,
988 /// potentially leaving "dangling type variables" behind.
989 /// In such cases, an assertion will fail when attempting to
990 /// register obligations, within a snapshot. Very useful, much
991 /// better than grovelling through megabytes of `RUSTC_LOG` output.
993 /// HOWEVER, in some cases the flag is unhelpful. In particular, we
994 /// sometimes create a "mini-fulfilment-cx" in which we enroll
995 /// obligations. As long as this fulfillment cx is fully drained
996 /// before we return, this is not a problem, as there won't be any
997 /// escaping obligations in the main cx. In those cases, you can
998 /// use this function.
999 pub fn save_and_restore_in_snapshot_flag<F, R>(&self, func: F) -> R
1001 F: FnOnce(&Self) -> R,
1003 let flag = self.in_snapshot.replace(false);
1004 let result = func(self);
1005 self.in_snapshot.set(flag);
1009 fn start_snapshot(&self) -> CombinedSnapshot<'a, 'tcx> {
1010 debug!("start_snapshot()");
1012 let in_snapshot = self.in_snapshot.replace(true);
1014 let mut inner = self.inner.borrow_mut();
1016 inner.undo_log.num_open_snapshots += 1;
1017 let undo_snapshot = Snapshot { undo_len: inner.undo_log.logs.len(), _marker: PhantomData };
1019 projection_cache_snapshot: inner.projection_cache.snapshot(),
1021 type_snapshot: inner.type_variables().snapshot(),
1022 const_snapshot: inner.const_unification_table().len(),
1023 int_snapshot: inner.int_unification_table().len(),
1024 float_snapshot: inner.float_unification_table().len(),
1025 region_constraints_snapshot: inner.unwrap_region_constraints().start_snapshot(),
1026 region_obligations_snapshot: inner.region_obligations.len(),
1027 universe: self.universe(),
1028 was_in_snapshot: in_snapshot,
1029 was_skip_leak_check: self.skip_leak_check.get(),
1030 // Borrow tables "in progress" (i.e., during typeck)
1031 // to ban writes from within a snapshot to them.
1032 _in_progress_tables: self.in_progress_tables.map(|tables| tables.borrow()),
1036 fn rollback_to(&self, cause: &str, snapshot: CombinedSnapshot<'a, 'tcx>) {
1037 debug!("rollback_to(cause={})", cause);
1038 let CombinedSnapshot {
1039 projection_cache_snapshot,
1045 region_constraints_snapshot: _,
1046 region_obligations_snapshot,
1049 was_skip_leak_check,
1050 _in_progress_tables,
1053 self.in_snapshot.set(was_in_snapshot);
1054 self.universe.set(universe);
1055 self.skip_leak_check.set(was_skip_leak_check);
1057 let mut inner = self.inner.borrow_mut();
1058 let inner = &mut *inner;
1059 let InferCtxtInner {
1061 const_unification_table,
1062 int_unification_table,
1063 float_unification_table,
1067 inner.undo_log.rollback_to(
1069 type_variables: type_variable::RollbackView::from(type_variables),
1070 const_unification_table,
1071 int_unification_table,
1072 float_unification_table,
1073 region_constraints: region_constraints.as_mut().unwrap(),
1077 inner.projection_cache.rollback_to(projection_cache_snapshot);
1078 inner.region_obligations.truncate(region_obligations_snapshot);
1081 fn commit_from(&self, snapshot: CombinedSnapshot<'a, 'tcx>) {
1082 debug!("commit_from()");
1083 let CombinedSnapshot {
1084 projection_cache_snapshot,
1090 region_constraints_snapshot: _,
1091 region_obligations_snapshot: _,
1094 was_skip_leak_check,
1095 _in_progress_tables,
1098 self.in_snapshot.set(was_in_snapshot);
1099 self.skip_leak_check.set(was_skip_leak_check);
1101 let mut inner = self.inner.borrow_mut();
1102 inner.undo_log.commit(undo_snapshot);
1103 inner.projection_cache.commit(projection_cache_snapshot);
1106 /// Executes `f` and commit the bindings.
1107 pub fn commit_unconditionally<R, F>(&self, f: F) -> R
1109 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
1111 debug!("commit_unconditionally()");
1112 let snapshot = self.start_snapshot();
1113 let r = f(&snapshot);
1114 self.commit_from(snapshot);
1118 /// Execute `f` and commit the bindings if closure `f` returns `Ok(_)`.
1119 pub fn commit_if_ok<T, E, F>(&self, f: F) -> Result<T, E>
1121 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> Result<T, E>,
1123 debug!("commit_if_ok()");
1124 let snapshot = self.start_snapshot();
1125 let r = f(&snapshot);
1126 debug!("commit_if_ok() -- r.is_ok() = {}", r.is_ok());
1129 self.commit_from(snapshot);
1132 self.rollback_to("commit_if_ok -- error", snapshot);
1138 /// Execute `f` then unroll any bindings it creates.
1139 pub fn probe<R, F>(&self, f: F) -> R
1141 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
1144 let snapshot = self.start_snapshot();
1145 let r = f(&snapshot);
1146 self.rollback_to("probe", snapshot);
1150 /// If `should_skip` is true, then execute `f` then unroll any bindings it creates.
1151 pub fn probe_maybe_skip_leak_check<R, F>(&self, should_skip: bool, f: F) -> R
1153 F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
1156 let snapshot = self.start_snapshot();
1157 let skip_leak_check = should_skip || self.skip_leak_check.get();
1158 self.skip_leak_check.set(skip_leak_check);
1159 let r = f(&snapshot);
1160 self.rollback_to("probe", snapshot);
1164 /// Scan the constraints produced since `snapshot` began and returns:
1166 /// - `None` -- if none of them involve "region outlives" constraints
1167 /// - `Some(true)` -- if there are `'a: 'b` constraints where `'a` or `'b` is a placeholder
1168 /// - `Some(false)` -- if there are `'a: 'b` constraints but none involve placeholders
1169 pub fn region_constraints_added_in_snapshot(
1171 snapshot: &CombinedSnapshot<'a, 'tcx>,
1175 .unwrap_region_constraints()
1176 .region_constraints_added_in_snapshot(&snapshot.undo_snapshot)
1179 pub fn add_given(&self, sub: ty::Region<'tcx>, sup: ty::RegionVid) {
1180 self.inner.borrow_mut().unwrap_region_constraints().add_given(sub, sup);
1183 pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
1185 T: at::ToTrace<'tcx>,
1187 let origin = &ObligationCause::dummy();
1189 self.at(origin, param_env).sub(a, b).map(|InferOk { obligations: _, .. }| {
1190 // Ignore obligations, since we are unrolling
1191 // everything anyway.
1196 pub fn can_eq<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
1198 T: at::ToTrace<'tcx>,
1200 let origin = &ObligationCause::dummy();
1202 self.at(origin, param_env).eq(a, b).map(|InferOk { obligations: _, .. }| {
1203 // Ignore obligations, since we are unrolling
1204 // everything anyway.
1211 origin: SubregionOrigin<'tcx>,
1212 a: ty::Region<'tcx>,
1213 b: ty::Region<'tcx>,
1215 debug!("sub_regions({:?} <: {:?})", a, b);
1216 self.inner.borrow_mut().unwrap_region_constraints().make_subregion(origin, a, b);
1219 /// Require that the region `r` be equal to one of the regions in
1220 /// the set `regions`.
1221 pub fn member_constraint(
1223 opaque_type_def_id: DefId,
1224 definition_span: Span,
1225 hidden_ty: Ty<'tcx>,
1226 region: ty::Region<'tcx>,
1227 in_regions: &Lrc<Vec<ty::Region<'tcx>>>,
1229 debug!("member_constraint({:?} <: {:?})", region, in_regions);
1230 self.inner.borrow_mut().unwrap_region_constraints().member_constraint(
1239 pub fn subtype_predicate(
1241 cause: &ObligationCause<'tcx>,
1242 param_env: ty::ParamEnv<'tcx>,
1243 predicate: &ty::PolySubtypePredicate<'tcx>,
1244 ) -> Option<InferResult<'tcx, ()>> {
1245 // Subtle: it's ok to skip the binder here and resolve because
1246 // `shallow_resolve` just ignores anything that is not a type
1247 // variable, and because type variable's can't (at present, at
1248 // least) capture any of the things bound by this binder.
1250 // NOTE(nmatsakis): really, there is no *particular* reason to do this
1251 // `shallow_resolve` here except as a micro-optimization.
1252 // Naturally I could not resist.
1253 let two_unbound_type_vars = {
1254 let a = self.shallow_resolve(predicate.skip_binder().a);
1255 let b = self.shallow_resolve(predicate.skip_binder().b);
1256 a.is_ty_var() && b.is_ty_var()
1259 if two_unbound_type_vars {
1260 // Two unbound type variables? Can't make progress.
1264 Some(self.commit_if_ok(|snapshot| {
1265 let (ty::SubtypePredicate { a_is_expected, a, b }, placeholder_map) =
1266 self.replace_bound_vars_with_placeholders(predicate);
1268 let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?;
1270 self.leak_check(false, &placeholder_map, snapshot)?;
1276 pub fn region_outlives_predicate(
1278 cause: &traits::ObligationCause<'tcx>,
1279 predicate: &ty::PolyRegionOutlivesPredicate<'tcx>,
1280 ) -> UnitResult<'tcx> {
1281 self.commit_if_ok(|snapshot| {
1282 let (ty::OutlivesPredicate(r_a, r_b), placeholder_map) =
1283 self.replace_bound_vars_with_placeholders(predicate);
1284 let origin = SubregionOrigin::from_obligation_cause(cause, || {
1285 RelateRegionParamBound(cause.span)
1287 self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
1288 self.leak_check(false, &placeholder_map, snapshot)?;
1293 pub fn next_ty_var_id(&self, diverging: bool, origin: TypeVariableOrigin) -> TyVid {
1294 self.inner.borrow_mut().type_variables().new_var(self.universe(), diverging, origin)
1297 pub fn next_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
1298 self.tcx.mk_ty_var(self.next_ty_var_id(false, origin))
1301 pub fn next_ty_var_in_universe(
1303 origin: TypeVariableOrigin,
1304 universe: ty::UniverseIndex,
1306 let vid = self.inner.borrow_mut().type_variables().new_var(universe, false, origin);
1307 self.tcx.mk_ty_var(vid)
1310 pub fn next_diverging_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
1311 self.tcx.mk_ty_var(self.next_ty_var_id(true, origin))
1314 pub fn next_const_var(
1317 origin: ConstVariableOrigin,
1318 ) -> &'tcx ty::Const<'tcx> {
1319 self.tcx.mk_const_var(self.next_const_var_id(origin), ty)
1322 pub fn next_const_var_in_universe(
1325 origin: ConstVariableOrigin,
1326 universe: ty::UniverseIndex,
1327 ) -> &'tcx ty::Const<'tcx> {
1331 .const_unification_table()
1332 .new_key(ConstVarValue { origin, val: ConstVariableValue::Unknown { universe } });
1333 self.tcx.mk_const_var(vid, ty)
1336 pub fn next_const_var_id(&self, origin: ConstVariableOrigin) -> ConstVid<'tcx> {
1337 self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue {
1339 val: ConstVariableValue::Unknown { universe: self.universe() },
1343 fn next_int_var_id(&self) -> IntVid {
1344 self.inner.borrow_mut().int_unification_table().new_key(None)
1347 pub fn next_int_var(&self) -> Ty<'tcx> {
1348 self.tcx.mk_int_var(self.next_int_var_id())
1351 fn next_float_var_id(&self) -> FloatVid {
1352 self.inner.borrow_mut().float_unification_table().new_key(None)
1355 pub fn next_float_var(&self) -> Ty<'tcx> {
1356 self.tcx.mk_float_var(self.next_float_var_id())
1359 /// Creates a fresh region variable with the next available index.
1360 /// The variable will be created in the maximum universe created
1361 /// thus far, allowing it to name any region created thus far.
1362 pub fn next_region_var(&self, origin: RegionVariableOrigin) -> ty::Region<'tcx> {
1363 self.next_region_var_in_universe(origin, self.universe())
1366 /// Creates a fresh region variable with the next available index
1367 /// in the given universe; typically, you can use
1368 /// `next_region_var` and just use the maximal universe.
1369 pub fn next_region_var_in_universe(
1371 origin: RegionVariableOrigin,
1372 universe: ty::UniverseIndex,
1373 ) -> ty::Region<'tcx> {
1375 self.inner.borrow_mut().unwrap_region_constraints().new_region_var(universe, origin);
1376 self.tcx.mk_region(ty::ReVar(region_var))
1379 /// Return the universe that the region `r` was created in. For
1380 /// most regions (e.g., `'static`, named regions from the user,
1381 /// etc) this is the root universe U0. For inference variables or
1382 /// placeholders, however, it will return the universe which which
1383 /// they are associated.
1384 fn universe_of_region(&self, r: ty::Region<'tcx>) -> ty::UniverseIndex {
1385 self.inner.borrow_mut().unwrap_region_constraints().universe(r)
1388 /// Number of region variables created so far.
1389 pub fn num_region_vars(&self) -> usize {
1390 self.inner.borrow_mut().unwrap_region_constraints().num_region_vars()
1393 /// Just a convenient wrapper of `next_region_var` for using during NLL.
1394 pub fn next_nll_region_var(&self, origin: NLLRegionVariableOrigin) -> ty::Region<'tcx> {
1395 self.next_region_var(RegionVariableOrigin::NLL(origin))
1398 /// Just a convenient wrapper of `next_region_var` for using during NLL.
1399 pub fn next_nll_region_var_in_universe(
1401 origin: NLLRegionVariableOrigin,
1402 universe: ty::UniverseIndex,
1403 ) -> ty::Region<'tcx> {
1404 self.next_region_var_in_universe(RegionVariableOrigin::NLL(origin), universe)
1407 pub fn var_for_def(&self, span: Span, param: &ty::GenericParamDef) -> GenericArg<'tcx> {
1409 GenericParamDefKind::Lifetime => {
1410 // Create a region inference variable for the given
1411 // region parameter definition.
1412 self.next_region_var(EarlyBoundRegion(span, param.name)).into()
1414 GenericParamDefKind::Type { .. } => {
1415 // Create a type inference variable for the given
1416 // type parameter definition. The substitutions are
1417 // for actual parameters that may be referred to by
1418 // the default of this type parameter, if it exists.
1419 // e.g., `struct Foo<A, B, C = (A, B)>(...);` when
1420 // used in a path such as `Foo::<T, U>::new()` will
1421 // use an inference variable for `C` with `[T, U]`
1422 // as the substitutions for the default, `(T, U)`.
1423 let ty_var_id = self.inner.borrow_mut().type_variables().new_var(
1426 TypeVariableOrigin {
1427 kind: TypeVariableOriginKind::TypeParameterDefinition(
1435 self.tcx.mk_ty_var(ty_var_id).into()
1437 GenericParamDefKind::Const { .. } => {
1438 let origin = ConstVariableOrigin {
1439 kind: ConstVariableOriginKind::ConstParameterDefinition(param.name),
1443 self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue {
1445 val: ConstVariableValue::Unknown { universe: self.universe() },
1447 self.tcx.mk_const_var(const_var_id, self.tcx.type_of(param.def_id)).into()
1452 /// Given a set of generics defined on a type or impl, returns a substitution mapping each
1453 /// type/region parameter to a fresh inference variable.
1454 pub fn fresh_substs_for_item(&self, span: Span, def_id: DefId) -> SubstsRef<'tcx> {
1455 InternalSubsts::for_item(self.tcx, def_id, |param, _| self.var_for_def(span, param))
1458 /// Returns `true` if errors have been reported since this infcx was
1459 /// created. This is sometimes used as a heuristic to skip
1460 /// reporting errors that often occur as a result of earlier
1461 /// errors, but where it's hard to be 100% sure (e.g., unresolved
1462 /// inference variables, regionck errors).
1463 pub fn is_tainted_by_errors(&self) -> bool {
1465 "is_tainted_by_errors(err_count={}, err_count_on_creation={}, \
1466 tainted_by_errors_flag={})",
1467 self.tcx.sess.err_count(),
1468 self.err_count_on_creation,
1469 self.tainted_by_errors_flag.get()
1472 if self.tcx.sess.err_count() > self.err_count_on_creation {
1473 return true; // errors reported since this infcx was made
1475 self.tainted_by_errors_flag.get()
1478 /// Set the "tainted by errors" flag to true. We call this when we
1479 /// observe an error from a prior pass.
1480 pub fn set_tainted_by_errors(&self) {
1481 debug!("set_tainted_by_errors()");
1482 self.tainted_by_errors_flag.set(true)
1485 /// Process the region constraints and report any errors that
1486 /// result. After this, no more unification operations should be
1487 /// done -- or the compiler will panic -- but it is legal to use
1488 /// `resolve_vars_if_possible` as well as `fully_resolve`.
1489 pub fn resolve_regions_and_report_errors(
1491 region_context: DefId,
1492 region_map: ®ion::ScopeTree,
1493 outlives_env: &OutlivesEnvironment<'tcx>,
1497 self.is_tainted_by_errors() || self.inner.borrow().region_obligations.is_empty(),
1498 "region_obligations not empty: {:#?}",
1499 self.inner.borrow().region_obligations
1501 let (var_infos, data) = self
1506 .expect("regions already resolved")
1507 .with_log(&mut inner.undo_log)
1508 .into_infos_and_data();
1510 let region_rels = &RegionRelations::new(
1514 outlives_env.free_region_map(),
1517 let (lexical_region_resolutions, errors) =
1518 lexical_region_resolve::resolve(region_rels, var_infos, data, mode);
1520 let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions));
1521 assert!(old_value.is_none());
1523 if !self.is_tainted_by_errors() {
1524 // As a heuristic, just skip reporting region errors
1525 // altogether if other errors have been reported while
1526 // this infcx was in use. This is totally hokey but
1527 // otherwise we have a hard time separating legit region
1528 // errors from silly ones.
1529 self.report_region_errors(region_map, &errors);
1533 /// Obtains (and clears) the current set of region
1534 /// constraints. The inference context is still usable: further
1535 /// unifications will simply add new constraints.
1537 /// This method is not meant to be used with normal lexical region
1538 /// resolution. Rather, it is used in the NLL mode as a kind of
1539 /// interim hack: basically we run normal type-check and generate
1540 /// region constraints as normal, but then we take them and
1541 /// translate them into the form that the NLL solver
1542 /// understands. See the NLL module for mode details.
1543 pub fn take_and_reset_region_constraints(&self) -> RegionConstraintData<'tcx> {
1545 self.inner.borrow().region_obligations.is_empty(),
1546 "region_obligations not empty: {:#?}",
1547 self.inner.borrow().region_obligations
1550 self.inner.borrow_mut().unwrap_region_constraints().take_and_reset_data()
1553 /// Gives temporary access to the region constraint data.
1554 #[allow(non_camel_case_types)] // bug with impl trait
1555 pub fn with_region_constraints<R>(
1557 op: impl FnOnce(&RegionConstraintData<'tcx>) -> R,
1559 let mut inner = self.inner.borrow_mut();
1560 op(inner.unwrap_region_constraints().data())
1563 /// Takes ownership of the list of variable regions. This implies
1564 /// that all the region constraints have already been taken, and
1565 /// hence that `resolve_regions_and_report_errors` can never be
1566 /// called. This is used only during NLL processing to "hand off" ownership
1567 /// of the set of region variables into the NLL region context.
1568 pub fn take_region_var_origins(&self) -> VarInfos {
1569 let mut inner = self.inner.borrow_mut();
1570 let (var_infos, data) = inner
1573 .expect("regions already resolved")
1574 .with_log(&mut inner.undo_log)
1575 .into_infos_and_data();
1576 assert!(data.is_empty());
1580 pub fn ty_to_string(&self, t: Ty<'tcx>) -> String {
1581 self.resolve_vars_if_possible(&t).to_string()
1584 pub fn tys_to_string(&self, ts: &[Ty<'tcx>]) -> String {
1585 let tstrs: Vec<String> = ts.iter().map(|t| self.ty_to_string(*t)).collect();
1586 format!("({})", tstrs.join(", "))
1589 pub fn trait_ref_to_string(&self, t: &ty::TraitRef<'tcx>) -> String {
1590 self.resolve_vars_if_possible(t).print_only_trait_path().to_string()
1593 /// If `TyVar(vid)` resolves to a type, return that type. Else, return the
1594 /// universe index of `TyVar(vid)`.
1595 pub fn probe_ty_var(&self, vid: TyVid) -> Result<Ty<'tcx>, ty::UniverseIndex> {
1596 use self::type_variable::TypeVariableValue;
1598 match self.inner.borrow_mut().type_variables().probe(vid) {
1599 TypeVariableValue::Known { value } => Ok(value),
1600 TypeVariableValue::Unknown { universe } => Err(universe),
1604 /// Resolve any type variables found in `value` -- but only one
1605 /// level. So, if the variable `?X` is bound to some type
1606 /// `Foo<?Y>`, then this would return `Foo<?Y>` (but `?Y` may
1607 /// itself be bound to a type).
1609 /// Useful when you only need to inspect the outermost level of
1610 /// the type and don't care about nested types (or perhaps you
1611 /// will be resolving them as well, e.g. in a loop).
1612 pub fn shallow_resolve<T>(&self, value: T) -> T
1614 T: TypeFoldable<'tcx>,
1616 value.fold_with(&mut ShallowResolver { infcx: self })
1619 pub fn root_var(&self, var: ty::TyVid) -> ty::TyVid {
1620 self.inner.borrow_mut().type_variables().root_var(var)
1623 /// Where possible, replaces type/const variables in
1624 /// `value` with their final value. Note that region variables
1625 /// are unaffected. If a type/const variable has not been unified, it
1626 /// is left as is. This is an idempotent operation that does
1627 /// not affect inference state in any way and so you can do it
1629 pub fn resolve_vars_if_possible<T>(&self, value: &T) -> T
1631 T: TypeFoldable<'tcx>,
1633 if !value.needs_infer() {
1634 return value.clone(); // Avoid duplicated subst-folding.
1636 let mut r = resolve::OpportunisticVarResolver::new(self);
1637 value.fold_with(&mut r)
1640 /// Returns the first unresolved variable contained in `T`. In the
1641 /// process of visiting `T`, this will resolve (where possible)
1642 /// type variables in `T`, but it never constructs the final,
1643 /// resolved type, so it's more efficient than
1644 /// `resolve_vars_if_possible()`.
1645 pub fn unresolved_type_vars<T>(&self, value: &T) -> Option<(Ty<'tcx>, Option<Span>)>
1647 T: TypeFoldable<'tcx>,
1649 let mut r = resolve::UnresolvedTypeFinder::new(self);
1650 value.visit_with(&mut r);
1654 pub fn probe_const_var(
1656 vid: ty::ConstVid<'tcx>,
1657 ) -> Result<&'tcx ty::Const<'tcx>, ty::UniverseIndex> {
1658 match self.inner.borrow_mut().const_unification_table().probe_value(vid).val {
1659 ConstVariableValue::Known { value } => Ok(value),
1660 ConstVariableValue::Unknown { universe } => Err(universe),
1664 pub fn fully_resolve<T: TypeFoldable<'tcx>>(&self, value: &T) -> FixupResult<'tcx, T> {
1666 * Attempts to resolve all type/region/const variables in
1667 * `value`. Region inference must have been run already (e.g.,
1668 * by calling `resolve_regions_and_report_errors`). If some
1669 * variable was never unified, an `Err` results.
1671 * This method is idempotent, but it not typically not invoked
1672 * except during the writeback phase.
1675 resolve::fully_resolve(self, value)
1678 // [Note-Type-error-reporting]
1679 // An invariant is that anytime the expected or actual type is Error (the special
1680 // error type, meaning that an error occurred when typechecking this expression),
1681 // this is a derived error. The error cascaded from another error (that was already
1682 // reported), so it's not useful to display it to the user.
1683 // The following methods implement this logic.
1684 // They check if either the actual or expected type is Error, and don't print the error
1685 // in this case. The typechecker should only ever report type errors involving mismatched
1686 // types using one of these methods, and should not call span_err directly for such
1689 pub fn type_error_struct_with_diag<M>(
1693 actual_ty: Ty<'tcx>,
1694 ) -> DiagnosticBuilder<'tcx>
1696 M: FnOnce(String) -> DiagnosticBuilder<'tcx>,
1698 let actual_ty = self.resolve_vars_if_possible(&actual_ty);
1699 debug!("type_error_struct_with_diag({:?}, {:?})", sp, actual_ty);
1701 // Don't report an error if actual type is `Error`.
1702 if actual_ty.references_error() {
1703 return self.tcx.sess.diagnostic().struct_dummy();
1706 mk_diag(self.ty_to_string(actual_ty))
1709 pub fn report_mismatched_types(
1711 cause: &ObligationCause<'tcx>,
1714 err: TypeError<'tcx>,
1715 ) -> DiagnosticBuilder<'tcx> {
1716 let trace = TypeTrace::types(cause, true, expected, actual);
1717 self.report_and_explain_type_error(trace, &err)
1720 pub fn replace_bound_vars_with_fresh_vars<T>(
1723 lbrct: LateBoundRegionConversionTime,
1724 value: &ty::Binder<T>,
1725 ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
1727 T: TypeFoldable<'tcx>,
1729 let fld_r = |br| self.next_region_var(LateBoundRegion(span, br, lbrct));
1731 self.next_ty_var(TypeVariableOrigin {
1732 kind: TypeVariableOriginKind::MiscVariable,
1736 let fld_c = |_, ty| {
1737 self.next_const_var(
1739 ConstVariableOrigin { kind: ConstVariableOriginKind::MiscVariable, span },
1742 self.tcx.replace_bound_vars(value, fld_r, fld_t, fld_c)
1745 /// See the [`region_constraints::RegionConstraintCollector::verify_generic_bound`] method.
1746 pub fn verify_generic_bound(
1748 origin: SubregionOrigin<'tcx>,
1749 kind: GenericKind<'tcx>,
1750 a: ty::Region<'tcx>,
1751 bound: VerifyBound<'tcx>,
1753 debug!("verify_generic_bound({:?}, {:?} <: {:?})", kind, a, bound);
1757 .unwrap_region_constraints()
1758 .verify_generic_bound(origin, kind, a, bound);
1761 /// Obtains the latest type of the given closure; this may be a
1762 /// closure in the current function, in which case its
1763 /// `ClosureKind` may not yet be known.
1764 pub fn closure_kind(&self, closure_substs: SubstsRef<'tcx>) -> Option<ty::ClosureKind> {
1765 let closure_kind_ty = closure_substs.as_closure().kind_ty();
1766 let closure_kind_ty = self.shallow_resolve(closure_kind_ty);
1767 closure_kind_ty.to_opt_closure_kind()
1770 /// Clears the selection, evaluation, and projection caches. This is useful when
1771 /// repeatedly attempting to select an `Obligation` while changing only
1772 /// its `ParamEnv`, since `FulfillmentContext` doesn't use probing.
1773 pub fn clear_caches(&self) {
1774 self.selection_cache.clear();
1775 self.evaluation_cache.clear();
1776 self.inner.borrow_mut().projection_cache.clear();
1779 fn universe(&self) -> ty::UniverseIndex {
1783 /// Creates and return a fresh universe that extends all previous
1784 /// universes. Updates `self.universe` to that new universe.
1785 pub fn create_next_universe(&self) -> ty::UniverseIndex {
1786 let u = self.universe.get().next_universe();
1787 self.universe.set(u);
1791 /// Resolves and evaluates a constant.
1793 /// The constant can be located on a trait like `<A as B>::C`, in which case the given
1794 /// substitutions and environment are used to resolve the constant. Alternatively if the
1795 /// constant has generic parameters in scope the substitutions are used to evaluate the value of
1796 /// the constant. For example in `fn foo<T>() { let _ = [0; bar::<T>()]; }` the repeat count
1797 /// constant `bar::<T>()` requires a substitution for `T`, if the substitution for `T` is still
1798 /// too generic for the constant to be evaluated then `Err(ErrorHandled::TooGeneric)` is
1801 /// This handles inferences variables within both `param_env` and `substs` by
1802 /// performing the operation on their respective canonical forms.
1803 pub fn const_eval_resolve(
1805 param_env: ty::ParamEnv<'tcx>,
1807 substs: SubstsRef<'tcx>,
1808 promoted: Option<mir::Promoted>,
1810 ) -> ConstEvalResult<'tcx> {
1811 let mut original_values = OriginalQueryValues::default();
1812 let canonical = self.canonicalize_query(&(param_env, substs), &mut original_values);
1814 let (param_env, substs) = canonical.value;
1815 // The return value is the evaluated value which doesn't contain any reference to inference
1816 // variables, thus we don't need to substitute back the original values.
1817 self.tcx.const_eval_resolve(param_env, def_id, substs, promoted, span)
1820 /// If `typ` is a type variable of some kind, resolve it one level
1821 /// (but do not resolve types found in the result). If `typ` is
1822 /// not a type variable, just return it unmodified.
1823 // FIXME(eddyb) inline into `ShallowResolver::visit_ty`.
1824 fn shallow_resolve_ty(&self, typ: Ty<'tcx>) -> Ty<'tcx> {
1826 ty::Infer(ty::TyVar(v)) => {
1827 // Not entirely obvious: if `typ` is a type variable,
1828 // it can be resolved to an int/float variable, which
1829 // can then be recursively resolved, hence the
1830 // recursion. Note though that we prevent type
1831 // variables from unifying to other type variables
1832 // directly (though they may be embedded
1833 // structurally), and we prevent cycles in any case,
1834 // so this recursion should always be of very limited
1837 // Note: if these two lines are combined into one we get
1838 // dynamic borrow errors on `self.inner`.
1839 let known = self.inner.borrow_mut().type_variables().probe(v).known();
1840 known.map(|t| self.shallow_resolve_ty(t)).unwrap_or(typ)
1843 ty::Infer(ty::IntVar(v)) => self
1846 .int_unification_table()
1848 .map(|v| v.to_type(self.tcx))
1851 ty::Infer(ty::FloatVar(v)) => self
1854 .float_unification_table()
1856 .map(|v| v.to_type(self.tcx))
1863 /// `ty_or_const_infer_var_changed` is equivalent to one of these two:
1864 /// * `shallow_resolve(ty) != ty` (where `ty.kind = ty::Infer(_)`)
1865 /// * `shallow_resolve(ct) != ct` (where `ct.kind = ty::ConstKind::Infer(_)`)
1867 /// However, `ty_or_const_infer_var_changed` is more efficient. It's always
1868 /// inlined, despite being large, because it has only two call sites that
1869 /// are extremely hot (both in `traits::fulfill`'s checking of `stalled_on`
1870 /// inference variables), and it handles both `Ty` and `ty::Const` without
1871 /// having to resort to storing full `GenericArg`s in `stalled_on`.
1873 pub fn ty_or_const_infer_var_changed(&self, infer_var: TyOrConstInferVar<'tcx>) -> bool {
1875 TyOrConstInferVar::Ty(v) => {
1876 use self::type_variable::TypeVariableValue;
1878 // If `inlined_probe` returns a `Known` value, it never equals
1879 // `ty::Infer(ty::TyVar(v))`.
1880 match self.inner.borrow_mut().type_variables().inlined_probe(v) {
1881 TypeVariableValue::Unknown { .. } => false,
1882 TypeVariableValue::Known { .. } => true,
1886 TyOrConstInferVar::TyInt(v) => {
1887 // If `inlined_probe_value` returns a value it's always a
1888 // `ty::Int(_)` or `ty::UInt(_)`, which never matches a
1890 self.inner.borrow_mut().int_unification_table().inlined_probe_value(v).is_some()
1893 TyOrConstInferVar::TyFloat(v) => {
1894 // If `probe_value` returns a value it's always a
1895 // `ty::Float(_)`, which never matches a `ty::Infer(_)`.
1897 // Not `inlined_probe_value(v)` because this call site is colder.
1898 self.inner.borrow_mut().float_unification_table().probe_value(v).is_some()
1901 TyOrConstInferVar::Const(v) => {
1902 // If `probe_value` returns a `Known` value, it never equals
1903 // `ty::ConstKind::Infer(ty::InferConst::Var(v))`.
1905 // Not `inlined_probe_value(v)` because this call site is colder.
1906 match self.inner.borrow_mut().const_unification_table.probe_value(v).val {
1907 ConstVariableValue::Unknown { .. } => false,
1908 ConstVariableValue::Known { .. } => true,
1915 /// Helper for `ty_or_const_infer_var_changed` (see comment on that), currently
1916 /// used only for `traits::fulfill`'s list of `stalled_on` inference variables.
1917 #[derive(Copy, Clone, Debug)]
1918 pub enum TyOrConstInferVar<'tcx> {
1919 /// Equivalent to `ty::Infer(ty::TyVar(_))`.
1921 /// Equivalent to `ty::Infer(ty::IntVar(_))`.
1923 /// Equivalent to `ty::Infer(ty::FloatVar(_))`.
1926 /// Equivalent to `ty::ConstKind::Infer(ty::InferConst::Var(_))`.
1927 Const(ConstVid<'tcx>),
1930 impl TyOrConstInferVar<'tcx> {
1931 /// Tries to extract an inference variable from a type or a constant, returns `None`
1932 /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`) and
1933 /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1934 pub fn maybe_from_generic_arg(arg: GenericArg<'tcx>) -> Option<Self> {
1935 match arg.unpack() {
1936 GenericArgKind::Type(ty) => Self::maybe_from_ty(ty),
1937 GenericArgKind::Const(ct) => Self::maybe_from_const(ct),
1938 GenericArgKind::Lifetime(_) => None,
1942 /// Tries to extract an inference variable from a type, returns `None`
1943 /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`).
1944 pub fn maybe_from_ty(ty: Ty<'tcx>) -> Option<Self> {
1946 ty::Infer(ty::TyVar(v)) => Some(TyOrConstInferVar::Ty(v)),
1947 ty::Infer(ty::IntVar(v)) => Some(TyOrConstInferVar::TyInt(v)),
1948 ty::Infer(ty::FloatVar(v)) => Some(TyOrConstInferVar::TyFloat(v)),
1953 /// Tries to extract an inference variable from a constant, returns `None`
1954 /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1955 pub fn maybe_from_const(ct: &'tcx ty::Const<'tcx>) -> Option<Self> {
1957 ty::ConstKind::Infer(InferConst::Var(v)) => Some(TyOrConstInferVar::Const(v)),
1963 struct ShallowResolver<'a, 'tcx> {
1964 infcx: &'a InferCtxt<'a, 'tcx>,
1967 impl<'a, 'tcx> TypeFolder<'tcx> for ShallowResolver<'a, 'tcx> {
1968 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1972 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1973 self.infcx.shallow_resolve_ty(ty)
1976 fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
1977 if let ty::Const { val: ty::ConstKind::Infer(InferConst::Var(vid)), .. } = ct {
1981 .const_unification_table()
1992 impl<'tcx> TypeTrace<'tcx> {
1993 pub fn span(&self) -> Span {
1998 cause: &ObligationCause<'tcx>,
1999 a_is_expected: bool,
2002 ) -> TypeTrace<'tcx> {
2003 TypeTrace { cause: cause.clone(), values: Types(ExpectedFound::new(a_is_expected, a, b)) }
2006 pub fn dummy(tcx: TyCtxt<'tcx>) -> TypeTrace<'tcx> {
2008 cause: ObligationCause::dummy(),
2009 values: Types(ExpectedFound { expected: tcx.types.err, found: tcx.types.err }),
2014 impl<'tcx> SubregionOrigin<'tcx> {
2015 pub fn span(&self) -> Span {
2017 Subtype(ref a) => a.span(),
2018 InfStackClosure(a) => a,
2019 InvokeClosure(a) => a,
2020 DerefPointer(a) => a,
2021 ClosureCapture(a, _) => a,
2023 RelateObjectBound(a) => a,
2024 RelateParamBound(a, _) => a,
2025 RelateRegionParamBound(a) => a,
2026 RelateDefaultParamBound(a, _) => a,
2028 ReborrowUpvar(a, _) => a,
2029 DataBorrowed(_, a) => a,
2030 ReferenceOutlivesReferent(_, a) => a,
2031 ParameterInScope(_, a) => a,
2032 ExprTypeIsNotInScope(_, a) => a,
2033 BindingTypeIsNotValidAtDecl(a) => a,
2040 SafeDestructor(a) => a,
2041 CompareImplMethodObligation { span, .. } => span,
2045 pub fn from_obligation_cause<F>(cause: &traits::ObligationCause<'tcx>, default: F) -> Self
2047 F: FnOnce() -> Self,
2050 traits::ObligationCauseCode::ReferenceOutlivesReferent(ref_type) => {
2051 SubregionOrigin::ReferenceOutlivesReferent(ref_type, cause.span)
2054 traits::ObligationCauseCode::CompareImplMethodObligation {
2058 } => SubregionOrigin::CompareImplMethodObligation {
2070 impl RegionVariableOrigin {
2071 pub fn span(&self) -> Span {
2073 MiscVariable(a) => a,
2074 PatternRegion(a) => a,
2075 AddrOfRegion(a) => a,
2078 EarlyBoundRegion(a, ..) => a,
2079 LateBoundRegion(a, ..) => a,
2080 BoundRegionInCoherence(_) => rustc_span::DUMMY_SP,
2081 UpvarRegion(_, a) => a,
2082 NLL(..) => bug!("NLL variable used with `span`"),
2087 impl<'tcx> fmt::Debug for RegionObligation<'tcx> {
2088 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2091 "RegionObligation(sub_region={:?}, sup_type={:?})",
2092 self.sub_region, self.sup_type