compiler/rustc_infer/src/infer/mod.rs

   1 pub use self::freshen::TypeFreshener;
   2 pub use self::lexical_region_resolve::RegionResolutionError;
   3 pub use self::LateBoundRegionConversionTime::*;
   4 pub use self::RegionVariableOrigin::*;
   5 pub use self::SubregionOrigin::*;
   6 pub use self::ValuePairs::*;
   7
   8 use self::opaque_types::OpaqueTypeMap;
   9 pub(crate) use self::undo_log::{InferCtxtUndoLogs, Snapshot, UndoLog};
  10
  11 use crate::traits::{self, ObligationCause, PredicateObligations, TraitEngine};
  12
  13 use hir::def_id::CRATE_DEF_ID;
  14 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  15 use rustc_data_structures::sync::Lrc;
  16 use rustc_data_structures::undo_log::Rollback;
  17 use rustc_data_structures::unify as ut;
  18 use rustc_errors::DiagnosticBuilder;
  19 use rustc_hir as hir;
  20 use rustc_hir::def_id::{DefId, LocalDefId};
  21 use rustc_middle::infer::canonical::{Canonical, CanonicalVarValues};
  22 use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue};
  23 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind, ToType};
  24 use rustc_middle::mir::interpret::EvalToConstValueResult;
  25 use rustc_middle::traits::select;
  26 use rustc_middle::ty::error::{ExpectedFound, TypeError};
  27 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
  28 use rustc_middle::ty::relate::RelateResult;
  29 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, SubstsRef};
  30 pub use rustc_middle::ty::IntVarValue;
  31 use rustc_middle::ty::{self, GenericParamDefKind, InferConst, Ty, TyCtxt};
  32 use rustc_middle::ty::{ConstVid, FloatVid, IntVid, TyVid};
  33 use rustc_session::config::BorrowckMode;
  34 use rustc_span::symbol::Symbol;
  35 use rustc_span::Span;
  36
  37 use std::cell::{Cell, Ref, RefCell};
  38 use std::collections::BTreeMap;
  39 use std::fmt;
  40
  41 use self::combine::CombineFields;
  42 use self::free_regions::RegionRelations;
  43 use self::lexical_region_resolve::LexicalRegionResolutions;
  44 use self::outlives::env::OutlivesEnvironment;
  45 use self::region_constraints::{GenericKind, RegionConstraintData, VarInfos, VerifyBound};
  46 use self::region_constraints::{
  47     RegionConstraintCollector, RegionConstraintStorage, RegionSnapshot,
  48 };
  49 use self::type_variable::{Diverging, TypeVariableOrigin, TypeVariableOriginKind};
  50
  51 pub mod at;
  52 pub mod canonical;
  53 mod combine;
  54 mod equate;
  55 pub mod error_reporting;
  56 pub mod free_regions;
  57 mod freshen;
  58 mod fudge;
  59 mod glb;
  60 mod higher_ranked;
  61 pub mod lattice;
  62 mod lexical_region_resolve;
  63 mod lub;
  64 pub mod nll_relate;
  65 pub mod opaque_types;
  66 pub mod outlives;
  67 pub mod region_constraints;
  68 pub mod resolve;
  69 mod sub;
  70 pub mod type_variable;
  71 mod undo_log;
  72
  73 use crate::infer::canonical::OriginalQueryValues;
  74 pub use rustc_middle::infer::unify_key;
  75
  76 #[must_use]
  77 #[derive(Debug)]
  78 pub struct InferOk<'tcx, T> {
  79     pub value: T,
  80     pub obligations: PredicateObligations<'tcx>,
  81 }
  82 pub type InferResult<'tcx, T> = Result<InferOk<'tcx, T>, TypeError<'tcx>>;
  83
  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"
  87
  88 pub(crate) type UnificationTable<'a, 'tcx, T> = ut::UnificationTable<
  89     ut::InPlace<T, &'a mut ut::UnificationStorage<T>, &'a mut InferCtxtUndoLogs<'tcx>>,
  90 >;
  91
  92 /// How we should handle region solving.
  93 ///
  94 /// This is used so that the region values inferred by HIR region solving are
  95 /// not exposed, and so that we can avoid doing work in HIR typeck that MIR
  96 /// typeck will also do.
  97 #[derive(Copy, Clone, Debug)]
  98 pub enum RegionckMode {
  99     /// The default mode: report region errors, don't erase regions.
 100     Solve,
 101     /// Erase the results of region after solving.
 102     Erase {
 103         /// A flag that is used to suppress region errors, when we are doing
 104         /// region checks that the NLL borrow checker will also do -- it might
 105         /// be set to true.
 106         suppress_errors: bool,
 107     },
 108 }
 109
 110 impl Default for RegionckMode {
 111     fn default() -> Self {
 112         RegionckMode::Solve
 113     }
 114 }
 115
 116 impl RegionckMode {
 117     /// Indicates that the MIR borrowck will repeat these region
 118     /// checks, so we should ignore errors if NLL is (unconditionally)
 119     /// enabled.
 120     pub fn for_item_body(tcx: TyCtxt<'_>) -> Self {
 121         // FIXME(Centril): Once we actually remove `::Migrate` also make
 122         // this always `true` and then proceed to eliminate the dead code.
 123         match tcx.borrowck_mode() {
 124             // If we're on Migrate mode, report AST region errors
 125             BorrowckMode::Migrate => RegionckMode::Erase { suppress_errors: false },
 126
 127             // If we're on MIR, don't report AST region errors as they should be reported by NLL
 128             BorrowckMode::Mir => RegionckMode::Erase { suppress_errors: true },
 129         }
 130     }
 131 }
 132
 133 /// This type contains all the things within `InferCtxt` that sit within a
 134 /// `RefCell` and are involved with taking/rolling back snapshots. Snapshot
 135 /// operations are hot enough that we want only one call to `borrow_mut` per
 136 /// call to `start_snapshot` and `rollback_to`.
 137 pub struct InferCtxtInner<'tcx> {
 138     /// Cache for projections. This cache is snapshotted along with the infcx.
 139     ///
 140     /// Public so that `traits::project` can use it.
 141     pub projection_cache: traits::ProjectionCacheStorage<'tcx>,
 142
 143     /// We instantiate `UnificationTable` with `bounds<Ty>` because the types
 144     /// that might instantiate a general type variable have an order,
 145     /// represented by its upper and lower bounds.
 146     type_variable_storage: type_variable::TypeVariableStorage<'tcx>,
 147
 148     /// Map from const parameter variable to the kind of const it represents.
 149     const_unification_storage: ut::UnificationTableStorage<ty::ConstVid<'tcx>>,
 150
 151     /// Map from integral variable to the kind of integer it represents.
 152     int_unification_storage: ut::UnificationTableStorage<ty::IntVid>,
 153
 154     /// Map from floating variable to the kind of float it represents.
 155     float_unification_storage: ut::UnificationTableStorage<ty::FloatVid>,
 156
 157     /// Tracks the set of region variables and the constraints between them.
 158     /// This is initially `Some(_)` but when
 159     /// `resolve_regions_and_report_errors` is invoked, this gets set to `None`
 160     /// -- further attempts to perform unification, etc., may fail if new
 161     /// region constraints would've been added.
 162     region_constraint_storage: Option<RegionConstraintStorage<'tcx>>,
 163
 164     /// A set of constraints that regionck must validate. Each
 165     /// constraint has the form `T:'a`, meaning "some type `T` must
 166     /// outlive the lifetime 'a". These constraints derive from
 167     /// instantiated type parameters. So if you had a struct defined
 168     /// like
 169     ///
 170     ///     struct Foo<T:'static> { ... }
 171     ///
 172     /// then in some expression `let x = Foo { ... }` it will
 173     /// instantiate the type parameter `T` with a fresh type `$0`. At
 174     /// the same time, it will record a region obligation of
 175     /// `$0:'static`. This will get checked later by regionck. (We
 176     /// can't generally check these things right away because we have
 177     /// to wait until types are resolved.)
 178     ///
 179     /// These are stored in a map keyed to the id of the innermost
 180     /// enclosing fn body / static initializer expression. This is
 181     /// because the location where the obligation was incurred can be
 182     /// relevant with respect to which sublifetime assumptions are in
 183     /// place. The reason that we store under the fn-id, and not
 184     /// something more fine-grained, is so that it is easier for
 185     /// regionck to be sure that it has found *all* the region
 186     /// obligations (otherwise, it's easy to fail to walk to a
 187     /// particular node-id).
 188     ///
 189     /// Before running `resolve_regions_and_report_errors`, the creator
 190     /// of the inference context is expected to invoke
 191     /// `process_region_obligations` (defined in `self::region_obligations`)
 192     /// for each body-id in this map, which will process the
 193     /// obligations within. This is expected to be done 'late enough'
 194     /// that all type inference variables have been bound and so forth.
 195     region_obligations: Vec<(hir::HirId, RegionObligation<'tcx>)>,
 196
 197     undo_log: InferCtxtUndoLogs<'tcx>,
 198
 199     // Opaque types found in explicit return types and their
 200     // associated fresh inference variable. Writeback resolves these
 201     // variables to get the concrete type, which can be used to
 202     // 'de-opaque' OpaqueTypeDecl, after typeck is done with all functions.
 203     pub opaque_types: OpaqueTypeMap<'tcx>,
 204
 205     /// A map from inference variables created from opaque
 206     /// type instantiations (`ty::Infer`) to the actual opaque
 207     /// type (`ty::Opaque`). Used during fallback to map unconstrained
 208     /// opaque type inference variables to their corresponding
 209     /// opaque type.
 210     pub opaque_types_vars: FxHashMap<Ty<'tcx>, Ty<'tcx>>,
 211 }
 212
 213 impl<'tcx> InferCtxtInner<'tcx> {
 214     fn new() -> InferCtxtInner<'tcx> {
 215         InferCtxtInner {
 216             projection_cache: Default::default(),
 217             type_variable_storage: type_variable::TypeVariableStorage::new(),
 218             undo_log: InferCtxtUndoLogs::default(),
 219             const_unification_storage: ut::UnificationTableStorage::new(),
 220             int_unification_storage: ut::UnificationTableStorage::new(),
 221             float_unification_storage: ut::UnificationTableStorage::new(),
 222             region_constraint_storage: Some(RegionConstraintStorage::new()),
 223             region_obligations: vec![],
 224             opaque_types: Default::default(),
 225             opaque_types_vars: Default::default(),
 226         }
 227     }
 228
 229     #[inline]
 230     pub fn region_obligations(&self) -> &[(hir::HirId, RegionObligation<'tcx>)] {
 231         &self.region_obligations
 232     }
 233
 234     #[inline]
 235     pub fn projection_cache(&mut self) -> traits::ProjectionCache<'_, 'tcx> {
 236         self.projection_cache.with_log(&mut self.undo_log)
 237     }
 238
 239     #[inline]
 240     fn type_variables(&mut self) -> type_variable::TypeVariableTable<'_, 'tcx> {
 241         self.type_variable_storage.with_log(&mut self.undo_log)
 242     }
 243
 244     #[inline]
 245     fn int_unification_table(
 246         &mut self,
 247     ) -> ut::UnificationTable<
 248         ut::InPlace<
 249             ty::IntVid,
 250             &mut ut::UnificationStorage<ty::IntVid>,
 251             &mut InferCtxtUndoLogs<'tcx>,
 252         >,
 253     > {
 254         self.int_unification_storage.with_log(&mut self.undo_log)
 255     }
 256
 257     #[inline]
 258     fn float_unification_table(
 259         &mut self,
 260     ) -> ut::UnificationTable<
 261         ut::InPlace<
 262             ty::FloatVid,
 263             &mut ut::UnificationStorage<ty::FloatVid>,
 264             &mut InferCtxtUndoLogs<'tcx>,
 265         >,
 266     > {
 267         self.float_unification_storage.with_log(&mut self.undo_log)
 268     }
 269
 270     #[inline]
 271     fn const_unification_table(
 272         &mut self,
 273     ) -> ut::UnificationTable<
 274         ut::InPlace<
 275             ty::ConstVid<'tcx>,
 276             &mut ut::UnificationStorage<ty::ConstVid<'tcx>>,
 277             &mut InferCtxtUndoLogs<'tcx>,
 278         >,
 279     > {
 280         self.const_unification_storage.with_log(&mut self.undo_log)
 281     }
 282
 283     #[inline]
 284     pub fn unwrap_region_constraints(&mut self) -> RegionConstraintCollector<'_, 'tcx> {
 285         self.region_constraint_storage
 286             .as_mut()
 287             .expect("region constraints already solved")
 288             .with_log(&mut self.undo_log)
 289     }
 290 }
 291
 292 pub struct InferCtxt<'a, 'tcx> {
 293     pub tcx: TyCtxt<'tcx>,
 294
 295     /// The `DefId` of the item in whose context we are performing inference or typeck.
 296     /// It is used to check whether an opaque type use is a defining use.
 297     pub defining_use_anchor: LocalDefId,
 298
 299     /// During type-checking/inference of a body, `in_progress_typeck_results`
 300     /// contains a reference to the typeck results being built up, which are
 301     /// used for reading closure kinds/signatures as they are inferred,
 302     /// and for error reporting logic to read arbitrary node types.
 303     pub in_progress_typeck_results: Option<&'a RefCell<ty::TypeckResults<'tcx>>>,
 304
 305     pub inner: RefCell<InferCtxtInner<'tcx>>,
 306
 307     /// If set, this flag causes us to skip the 'leak check' during
 308     /// higher-ranked subtyping operations. This flag is a temporary one used
 309     /// to manage the removal of the leak-check: for the time being, we still run the
 310     /// leak-check, but we issue warnings. This flag can only be set to true
 311     /// when entering a snapshot.
 312     skip_leak_check: Cell<bool>,
 313
 314     /// Once region inference is done, the values for each variable.
 315     lexical_region_resolutions: RefCell<Option<LexicalRegionResolutions<'tcx>>>,
 316
 317     /// Caches the results of trait selection. This cache is used
 318     /// for things that have to do with the parameters in scope.
 319     pub selection_cache: select::SelectionCache<'tcx>,
 320
 321     /// Caches the results of trait evaluation.
 322     pub evaluation_cache: select::EvaluationCache<'tcx>,
 323
 324     /// the set of predicates on which errors have been reported, to
 325     /// avoid reporting the same error twice.
 326     pub reported_trait_errors: RefCell<FxHashMap<Span, Vec<ty::Predicate<'tcx>>>>,
 327
 328     pub reported_closure_mismatch: RefCell<FxHashSet<(Span, Option<Span>)>>,
 329
 330     /// When an error occurs, we want to avoid reporting "derived"
 331     /// errors that are due to this original failure. Normally, we
 332     /// handle this with the `err_count_on_creation` count, which
 333     /// basically just tracks how many errors were reported when we
 334     /// started type-checking a fn and checks to see if any new errors
 335     /// have been reported since then. Not great, but it works.
 336     ///
 337     /// However, when errors originated in other passes -- notably
 338     /// resolve -- this heuristic breaks down. Therefore, we have this
 339     /// auxiliary flag that one can set whenever one creates a
 340     /// type-error that is due to an error in a prior pass.
 341     ///
 342     /// Don't read this flag directly, call `is_tainted_by_errors()`
 343     /// and `set_tainted_by_errors()`.
 344     tainted_by_errors_flag: Cell<bool>,
 345
 346     /// Track how many errors were reported when this infcx is created.
 347     /// If the number of errors increases, that's also a sign (line
 348     /// `tained_by_errors`) to avoid reporting certain kinds of errors.
 349     // FIXME(matthewjasper) Merge into `tainted_by_errors_flag`
 350     err_count_on_creation: usize,
 351
 352     /// This flag is true while there is an active snapshot.
 353     in_snapshot: Cell<bool>,
 354
 355     /// What is the innermost universe we have created? Starts out as
 356     /// `UniverseIndex::root()` but grows from there as we enter
 357     /// universal quantifiers.
 358     ///
 359     /// N.B., at present, we exclude the universal quantifiers on the
 360     /// item we are type-checking, and just consider those names as
 361     /// part of the root universe. So this would only get incremented
 362     /// when we enter into a higher-ranked (`for<..>`) type or trait
 363     /// bound.
 364     universe: Cell<ty::UniverseIndex>,
 365 }
 366
 367 /// See the `error_reporting` module for more details.
 368 #[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable)]
 369 pub enum ValuePairs<'tcx> {
 370     Types(ExpectedFound<Ty<'tcx>>),
 371     Regions(ExpectedFound<ty::Region<'tcx>>),
 372     Consts(ExpectedFound<&'tcx ty::Const<'tcx>>),
 373     TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>),
 374     PolyTraitRefs(ExpectedFound<ty::PolyTraitRef<'tcx>>),
 375 }
 376
 377 /// The trace designates the path through inference that we took to
 378 /// encounter an error or subtyping constraint.
 379 ///
 380 /// See the `error_reporting` module for more details.
 381 #[derive(Clone, Debug)]
 382 pub struct TypeTrace<'tcx> {
 383     cause: ObligationCause<'tcx>,
 384     values: ValuePairs<'tcx>,
 385 }
 386
 387 /// The origin of a `r1 <= r2` constraint.
 388 ///
 389 /// See `error_reporting` module for more details
 390 #[derive(Clone, Debug)]
 391 pub enum SubregionOrigin<'tcx> {
 392     /// Arose from a subtyping relation
 393     Subtype(Box<TypeTrace<'tcx>>),
 394
 395     /// When casting `&'a T` to an `&'b Trait` object,
 396     /// relating `'a` to `'b`
 397     RelateObjectBound(Span),
 398
 399     /// Some type parameter was instantiated with the given type,
 400     /// and that type must outlive some region.
 401     RelateParamBound(Span, Ty<'tcx>, Option<Span>),
 402
 403     /// The given region parameter was instantiated with a region
 404     /// that must outlive some other region.
 405     RelateRegionParamBound(Span),
 406
 407     /// Creating a pointer `b` to contents of another reference
 408     Reborrow(Span),
 409
 410     /// Creating a pointer `b` to contents of an upvar
 411     ReborrowUpvar(Span, ty::UpvarId),
 412
 413     /// Data with type `Ty<'tcx>` was borrowed
 414     DataBorrowed(Ty<'tcx>, Span),
 415
 416     /// (&'a &'b T) where a >= b
 417     ReferenceOutlivesReferent(Ty<'tcx>, Span),
 418
 419     /// Region in return type of invoked fn must enclose call
 420     CallReturn(Span),
 421
 422     /// Comparing the signature and requirements of an impl method against
 423     /// the containing trait.
 424     CompareImplMethodObligation {
 425         span: Span,
 426         item_name: Symbol,
 427         impl_item_def_id: DefId,
 428         trait_item_def_id: DefId,
 429     },
 430 }
 431
 432 // `SubregionOrigin` is used a lot. Make sure it doesn't unintentionally get bigger.
 433 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
 434 static_assert_size!(SubregionOrigin<'_>, 32);
 435
 436 /// Times when we replace late-bound regions with variables:
 437 #[derive(Clone, Copy, Debug)]
 438 pub enum LateBoundRegionConversionTime {
 439     /// when a fn is called
 440     FnCall,
 441
 442     /// when two higher-ranked types are compared
 443     HigherRankedType,
 444
 445     /// when projecting an associated type
 446     AssocTypeProjection(DefId),
 447 }
 448
 449 /// Reasons to create a region inference variable
 450 ///
 451 /// See `error_reporting` module for more details
 452 #[derive(Copy, Clone, Debug)]
 453 pub enum RegionVariableOrigin {
 454     /// Region variables created for ill-categorized reasons,
 455     /// mostly indicates places in need of refactoring
 456     MiscVariable(Span),
 457
 458     /// Regions created by a `&P` or `[...]` pattern
 459     PatternRegion(Span),
 460
 461     /// Regions created by `&` operator
 462     AddrOfRegion(Span),
 463
 464     /// Regions created as part of an autoref of a method receiver
 465     Autoref(Span, ty::AssocItem),
 466
 467     /// Regions created as part of an automatic coercion
 468     Coercion(Span),
 469
 470     /// Region variables created as the values for early-bound regions
 471     EarlyBoundRegion(Span, Symbol),
 472
 473     /// Region variables created for bound regions
 474     /// in a function or method that is called
 475     LateBoundRegion(Span, ty::BoundRegionKind, LateBoundRegionConversionTime),
 476
 477     UpvarRegion(ty::UpvarId, Span),
 478
 479     /// This origin is used for the inference variables that we create
 480     /// during NLL region processing.
 481     Nll(NllRegionVariableOrigin),
 482 }
 483
 484 #[derive(Copy, Clone, Debug)]
 485 pub enum NllRegionVariableOrigin {
 486     /// During NLL region processing, we create variables for free
 487     /// regions that we encounter in the function signature and
 488     /// elsewhere. This origin indices we've got one of those.
 489     FreeRegion,
 490
 491     /// "Universal" instantiation of a higher-ranked region (e.g.,
 492     /// from a `for<'a> T` binder). Meant to represent "any region".
 493     Placeholder(ty::PlaceholderRegion),
 494
 495     /// The variable we create to represent `'empty(U0)`.
 496     RootEmptyRegion,
 497
 498     Existential {
 499         /// If this is true, then this variable was created to represent a lifetime
 500         /// bound in a `for` binder. For example, it might have been created to
 501         /// represent the lifetime `'a` in a type like `for<'a> fn(&'a u32)`.
 502         /// Such variables are created when we are trying to figure out if there
 503         /// is any valid instantiation of `'a` that could fit into some scenario.
 504         ///
 505         /// This is used to inform error reporting: in the case that we are trying to
 506         /// determine whether there is any valid instantiation of a `'a` variable that meets
 507         /// some constraint C, we want to blame the "source" of that `for` type,
 508         /// rather than blaming the source of the constraint C.
 509         from_forall: bool,
 510     },
 511 }
 512
 513 // FIXME(eddyb) investigate overlap between this and `TyOrConstInferVar`.
 514 #[derive(Copy, Clone, Debug)]
 515 pub enum FixupError<'tcx> {
 516     UnresolvedIntTy(IntVid),
 517     UnresolvedFloatTy(FloatVid),
 518     UnresolvedTy(TyVid),
 519     UnresolvedConst(ConstVid<'tcx>),
 520 }
 521
 522 /// See the `region_obligations` field for more information.
 523 #[derive(Clone)]
 524 pub struct RegionObligation<'tcx> {
 525     pub sub_region: ty::Region<'tcx>,
 526     pub sup_type: Ty<'tcx>,
 527     pub origin: SubregionOrigin<'tcx>,
 528 }
 529
 530 impl<'tcx> fmt::Display for FixupError<'tcx> {
 531     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 532         use self::FixupError::*;
 533
 534         match *self {
 535             UnresolvedIntTy(_) => write!(
 536                 f,
 537                 "cannot determine the type of this integer; \
 538                  add a suffix to specify the type explicitly"
 539             ),
 540             UnresolvedFloatTy(_) => write!(
 541                 f,
 542                 "cannot determine the type of this number; \
 543                  add a suffix to specify the type explicitly"
 544             ),
 545             UnresolvedTy(_) => write!(f, "unconstrained type"),
 546             UnresolvedConst(_) => write!(f, "unconstrained const value"),
 547         }
 548     }
 549 }
 550
 551 /// Helper type of a temporary returned by `tcx.infer_ctxt()`.
 552 /// Necessary because we can't write the following bound:
 553 /// `F: for<'b, 'tcx> where 'tcx FnOnce(InferCtxt<'b, 'tcx>)`.
 554 pub struct InferCtxtBuilder<'tcx> {
 555     tcx: TyCtxt<'tcx>,
 556     fresh_typeck_results: Option<RefCell<ty::TypeckResults<'tcx>>>,
 557     defining_use_anchor: LocalDefId,
 558 }
 559
 560 pub trait TyCtxtInferExt<'tcx> {
 561     fn infer_ctxt(self) -> InferCtxtBuilder<'tcx>;
 562 }
 563
 564 impl TyCtxtInferExt<'tcx> for TyCtxt<'tcx> {
 565     fn infer_ctxt(self) -> InferCtxtBuilder<'tcx> {
 566         InferCtxtBuilder {
 567             tcx: self,
 568             defining_use_anchor: CRATE_DEF_ID,
 569             fresh_typeck_results: None,
 570         }
 571     }
 572 }
 573
 574 impl<'tcx> InferCtxtBuilder<'tcx> {
 575     /// Used only by `rustc_typeck` during body type-checking/inference,
 576     /// will initialize `in_progress_typeck_results` with fresh `TypeckResults`.
 577     /// Will also change the scope for opaque type defining use checks to the given owner.
 578     pub fn with_fresh_in_progress_typeck_results(mut self, table_owner: LocalDefId) -> Self {
 579         self.fresh_typeck_results = Some(RefCell::new(ty::TypeckResults::new(table_owner)));
 580         self.with_opaque_type_inference(table_owner)
 581     }
 582
 583     /// Whenever the `InferCtxt` should be able to handle defining uses of opaque types,
 584     /// you need to call this function. Otherwise the opaque type will be treated opaquely.
 585     ///
 586     /// It is only meant to be called in two places, for typeck
 587     /// (via `with_fresh_in_progress_typeck_results`) and for the inference context used
 588     /// in mir borrowck.
 589     pub fn with_opaque_type_inference(mut self, defining_use_anchor: LocalDefId) -> Self {
 590         self.defining_use_anchor = defining_use_anchor;
 591         self
 592     }
 593
 594     /// Given a canonical value `C` as a starting point, create an
 595     /// inference context that contains each of the bound values
 596     /// within instantiated as a fresh variable. The `f` closure is
 597     /// invoked with the new infcx, along with the instantiated value
 598     /// `V` and a substitution `S`. This substitution `S` maps from
 599     /// the bound values in `C` to their instantiated values in `V`
 600     /// (in other words, `S(C) = V`).
 601     pub fn enter_with_canonical<T, R>(
 602         &mut self,
 603         span: Span,
 604         canonical: &Canonical<'tcx, T>,
 605         f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>, T, CanonicalVarValues<'tcx>) -> R,
 606     ) -> R
 607     where
 608         T: TypeFoldable<'tcx>,
 609     {
 610         self.enter(|infcx| {
 611             let (value, subst) =
 612                 infcx.instantiate_canonical_with_fresh_inference_vars(span, canonical);
 613             f(infcx, value, subst)
 614         })
 615     }
 616
 617     pub fn enter<R>(&mut self, f: impl for<'a> FnOnce(InferCtxt<'a, 'tcx>) -> R) -> R {
 618         let InferCtxtBuilder { tcx, defining_use_anchor, ref fresh_typeck_results } = *self;
 619         let in_progress_typeck_results = fresh_typeck_results.as_ref();
 620         f(InferCtxt {
 621             tcx,
 622             defining_use_anchor,
 623             in_progress_typeck_results,
 624             inner: RefCell::new(InferCtxtInner::new()),
 625             lexical_region_resolutions: RefCell::new(None),
 626             selection_cache: Default::default(),
 627             evaluation_cache: Default::default(),
 628             reported_trait_errors: Default::default(),
 629             reported_closure_mismatch: Default::default(),
 630             tainted_by_errors_flag: Cell::new(false),
 631             err_count_on_creation: tcx.sess.err_count(),
 632             in_snapshot: Cell::new(false),
 633             skip_leak_check: Cell::new(false),
 634             universe: Cell::new(ty::UniverseIndex::ROOT),
 635         })
 636     }
 637 }
 638
 639 impl<'tcx, T> InferOk<'tcx, T> {
 640     pub fn unit(self) -> InferOk<'tcx, ()> {
 641         InferOk { value: (), obligations: self.obligations }
 642     }
 643
 644     /// Extracts `value`, registering any obligations into `fulfill_cx`.
 645     pub fn into_value_registering_obligations(
 646         self,
 647         infcx: &InferCtxt<'_, 'tcx>,
 648         fulfill_cx: &mut dyn TraitEngine<'tcx>,
 649     ) -> T {
 650         let InferOk { value, obligations } = self;
 651         for obligation in obligations {
 652             fulfill_cx.register_predicate_obligation(infcx, obligation);
 653         }
 654         value
 655     }
 656 }
 657
 658 impl<'tcx> InferOk<'tcx, ()> {
 659     pub fn into_obligations(self) -> PredicateObligations<'tcx> {
 660         self.obligations
 661     }
 662 }
 663
 664 #[must_use = "once you start a snapshot, you should always consume it"]
 665 pub struct CombinedSnapshot<'a, 'tcx> {
 666     undo_snapshot: Snapshot<'tcx>,
 667     region_constraints_snapshot: RegionSnapshot,
 668     universe: ty::UniverseIndex,
 669     was_in_snapshot: bool,
 670     _in_progress_typeck_results: Option<Ref<'a, ty::TypeckResults<'tcx>>>,
 671 }
 672
 673 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
 674     /// calls `tcx.try_unify_abstract_consts` after
 675     /// canonicalizing the consts.
 676     pub fn try_unify_abstract_consts(
 677         &self,
 678         a: ty::Unevaluated<'tcx, ()>,
 679         b: ty::Unevaluated<'tcx, ()>,
 680     ) -> bool {
 681         let canonical = self.canonicalize_query((a, b), &mut OriginalQueryValues::default());
 682         debug!("canonical consts: {:?}", &canonical.value);
 683
 684         self.tcx.try_unify_abstract_consts(canonical.value)
 685     }
 686
 687     pub fn is_in_snapshot(&self) -> bool {
 688         self.in_snapshot.get()
 689     }
 690
 691     pub fn freshen<T: TypeFoldable<'tcx>>(&self, t: T) -> T {
 692         t.fold_with(&mut self.freshener())
 693     }
 694
 695     /// Returns whether `ty` is a diverging type variable or not.
 696     /// (If `ty` is not a type variable at all, returns not diverging.)
 697     ///
 698     /// No attempt is made to resolve `ty`.
 699     pub fn type_var_diverges(&'a self, ty: Ty<'_>) -> Diverging {
 700         match *ty.kind() {
 701             ty::Infer(ty::TyVar(vid)) => self.inner.borrow_mut().type_variables().var_diverges(vid),
 702             _ => Diverging::NotDiverging,
 703         }
 704     }
 705
 706     /// Returns the origin of the type variable identified by `vid`, or `None`
 707     /// if this is not a type variable.
 708     ///
 709     /// No attempt is made to resolve `ty`.
 710     pub fn type_var_origin(&'a self, ty: Ty<'tcx>) -> Option<TypeVariableOrigin> {
 711         match *ty.kind() {
 712             ty::Infer(ty::TyVar(vid)) => {
 713                 Some(*self.inner.borrow_mut().type_variables().var_origin(vid))
 714             }
 715             _ => None,
 716         }
 717     }
 718
 719     pub fn freshener<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
 720         freshen::TypeFreshener::new(self, false)
 721     }
 722
 723     /// Like `freshener`, but does not replace `'static` regions.
 724     pub fn freshener_keep_static<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
 725         freshen::TypeFreshener::new(self, true)
 726     }
 727
 728     pub fn unsolved_variables(&self) -> Vec<Ty<'tcx>> {
 729         let mut inner = self.inner.borrow_mut();
 730         let mut vars: Vec<Ty<'_>> = inner
 731             .type_variables()
 732             .unsolved_variables()
 733             .into_iter()
 734             .map(|t| self.tcx.mk_ty_var(t))
 735             .collect();
 736         vars.extend(
 737             (0..inner.int_unification_table().len())
 738                 .map(|i| ty::IntVid { index: i as u32 })
 739                 .filter(|&vid| inner.int_unification_table().probe_value(vid).is_none())
 740                 .map(|v| self.tcx.mk_int_var(v)),
 741         );
 742         vars.extend(
 743             (0..inner.float_unification_table().len())
 744                 .map(|i| ty::FloatVid { index: i as u32 })
 745                 .filter(|&vid| inner.float_unification_table().probe_value(vid).is_none())
 746                 .map(|v| self.tcx.mk_float_var(v)),
 747         );
 748         vars
 749     }
 750
 751     fn combine_fields(
 752         &'a self,
 753         trace: TypeTrace<'tcx>,
 754         param_env: ty::ParamEnv<'tcx>,
 755     ) -> CombineFields<'a, 'tcx> {
 756         CombineFields {
 757             infcx: self,
 758             trace,
 759             cause: None,
 760             param_env,
 761             obligations: PredicateObligations::new(),
 762         }
 763     }
 764
 765     /// Clear the "currently in a snapshot" flag, invoke the closure,
 766     /// then restore the flag to its original value. This flag is a
 767     /// debugging measure designed to detect cases where we start a
 768     /// snapshot, create type variables, and register obligations
 769     /// which may involve those type variables in the fulfillment cx,
 770     /// potentially leaving "dangling type variables" behind.
 771     /// In such cases, an assertion will fail when attempting to
 772     /// register obligations, within a snapshot. Very useful, much
 773     /// better than grovelling through megabytes of `RUSTC_LOG` output.
 774     ///
 775     /// HOWEVER, in some cases the flag is unhelpful. In particular, we
 776     /// sometimes create a "mini-fulfilment-cx" in which we enroll
 777     /// obligations. As long as this fulfillment cx is fully drained
 778     /// before we return, this is not a problem, as there won't be any
 779     /// escaping obligations in the main cx. In those cases, you can
 780     /// use this function.
 781     pub fn save_and_restore_in_snapshot_flag<F, R>(&self, func: F) -> R
 782     where
 783         F: FnOnce(&Self) -> R,
 784     {
 785         let flag = self.in_snapshot.replace(false);
 786         let result = func(self);
 787         self.in_snapshot.set(flag);
 788         result
 789     }
 790
 791     fn start_snapshot(&self) -> CombinedSnapshot<'a, 'tcx> {
 792         debug!("start_snapshot()");
 793
 794         let in_snapshot = self.in_snapshot.replace(true);
 795
 796         let mut inner = self.inner.borrow_mut();
 797
 798         CombinedSnapshot {
 799             undo_snapshot: inner.undo_log.start_snapshot(),
 800             region_constraints_snapshot: inner.unwrap_region_constraints().start_snapshot(),
 801             universe: self.universe(),
 802             was_in_snapshot: in_snapshot,
 803             // Borrow typeck results "in progress" (i.e., during typeck)
 804             // to ban writes from within a snapshot to them.
 805             _in_progress_typeck_results: self
 806                 .in_progress_typeck_results
 807                 .map(|typeck_results| typeck_results.borrow()),
 808         }
 809     }
 810
 811     fn rollback_to(&self, cause: &str, snapshot: CombinedSnapshot<'a, 'tcx>) {
 812         debug!("rollback_to(cause={})", cause);
 813         let CombinedSnapshot {
 814             undo_snapshot,
 815             region_constraints_snapshot,
 816             universe,
 817             was_in_snapshot,
 818             _in_progress_typeck_results,
 819         } = snapshot;
 820
 821         self.in_snapshot.set(was_in_snapshot);
 822         self.universe.set(universe);
 823
 824         let mut inner = self.inner.borrow_mut();
 825         inner.rollback_to(undo_snapshot);
 826         inner.unwrap_region_constraints().rollback_to(region_constraints_snapshot);
 827     }
 828
 829     fn commit_from(&self, snapshot: CombinedSnapshot<'a, 'tcx>) {
 830         debug!("commit_from()");
 831         let CombinedSnapshot {
 832             undo_snapshot,
 833             region_constraints_snapshot: _,
 834             universe: _,
 835             was_in_snapshot,
 836             _in_progress_typeck_results,
 837         } = snapshot;
 838
 839         self.in_snapshot.set(was_in_snapshot);
 840
 841         self.inner.borrow_mut().commit(undo_snapshot);
 842     }
 843
 844     /// Executes `f` and commit the bindings.
 845     pub fn commit_unconditionally<R, F>(&self, f: F) -> R
 846     where
 847         F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
 848     {
 849         debug!("commit_unconditionally()");
 850         let snapshot = self.start_snapshot();
 851         let r = f(&snapshot);
 852         self.commit_from(snapshot);
 853         r
 854     }
 855
 856     /// Execute `f` and commit the bindings if closure `f` returns `Ok(_)`.
 857     pub fn commit_if_ok<T, E, F>(&self, f: F) -> Result<T, E>
 858     where
 859         F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> Result<T, E>,
 860     {
 861         debug!("commit_if_ok()");
 862         let snapshot = self.start_snapshot();
 863         let r = f(&snapshot);
 864         debug!("commit_if_ok() -- r.is_ok() = {}", r.is_ok());
 865         match r {
 866             Ok(_) => {
 867                 self.commit_from(snapshot);
 868             }
 869             Err(_) => {
 870                 self.rollback_to("commit_if_ok -- error", snapshot);
 871             }
 872         }
 873         r
 874     }
 875
 876     /// Execute `f` then unroll any bindings it creates.
 877     pub fn probe<R, F>(&self, f: F) -> R
 878     where
 879         F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
 880     {
 881         debug!("probe()");
 882         let snapshot = self.start_snapshot();
 883         let r = f(&snapshot);
 884         self.rollback_to("probe", snapshot);
 885         r
 886     }
 887
 888     /// If `should_skip` is true, then execute `f` then unroll any bindings it creates.
 889     pub fn probe_maybe_skip_leak_check<R, F>(&self, should_skip: bool, f: F) -> R
 890     where
 891         F: FnOnce(&CombinedSnapshot<'a, 'tcx>) -> R,
 892     {
 893         debug!("probe()");
 894         let snapshot = self.start_snapshot();
 895         let was_skip_leak_check = self.skip_leak_check.get();
 896         if should_skip {
 897             self.skip_leak_check.set(true);
 898         }
 899         let r = f(&snapshot);
 900         self.rollback_to("probe", snapshot);
 901         self.skip_leak_check.set(was_skip_leak_check);
 902         r
 903     }
 904
 905     /// Scan the constraints produced since `snapshot` began and returns:
 906     ///
 907     /// - `None` -- if none of them involve "region outlives" constraints
 908     /// - `Some(true)` -- if there are `'a: 'b` constraints where `'a` or `'b` is a placeholder
 909     /// - `Some(false)` -- if there are `'a: 'b` constraints but none involve placeholders
 910     pub fn region_constraints_added_in_snapshot(
 911         &self,
 912         snapshot: &CombinedSnapshot<'a, 'tcx>,
 913     ) -> Option<bool> {
 914         self.inner
 915             .borrow_mut()
 916             .unwrap_region_constraints()
 917             .region_constraints_added_in_snapshot(&snapshot.undo_snapshot)
 918     }
 919
 920     pub fn add_given(&self, sub: ty::Region<'tcx>, sup: ty::RegionVid) {
 921         self.inner.borrow_mut().unwrap_region_constraints().add_given(sub, sup);
 922     }
 923
 924     pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
 925     where
 926         T: at::ToTrace<'tcx>,
 927     {
 928         let origin = &ObligationCause::dummy();
 929         self.probe(|_| {
 930             self.at(origin, param_env).sub(a, b).map(|InferOk { obligations: _, .. }| {
 931                 // Ignore obligations, since we are unrolling
 932                 // everything anyway.
 933             })
 934         })
 935     }
 936
 937     pub fn can_eq<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> UnitResult<'tcx>
 938     where
 939         T: at::ToTrace<'tcx>,
 940     {
 941         let origin = &ObligationCause::dummy();
 942         self.probe(|_| {
 943             self.at(origin, param_env).eq(a, b).map(|InferOk { obligations: _, .. }| {
 944                 // Ignore obligations, since we are unrolling
 945                 // everything anyway.
 946             })
 947         })
 948     }
 949
 950     pub fn sub_regions(
 951         &self,
 952         origin: SubregionOrigin<'tcx>,
 953         a: ty::Region<'tcx>,
 954         b: ty::Region<'tcx>,
 955     ) {
 956         debug!("sub_regions({:?} <: {:?})", a, b);
 957         self.inner.borrow_mut().unwrap_region_constraints().make_subregion(origin, a, b);
 958     }
 959
 960     /// Require that the region `r` be equal to one of the regions in
 961     /// the set `regions`.
 962     pub fn member_constraint(
 963         &self,
 964         opaque_type_def_id: DefId,
 965         definition_span: Span,
 966         hidden_ty: Ty<'tcx>,
 967         region: ty::Region<'tcx>,
 968         in_regions: &Lrc<Vec<ty::Region<'tcx>>>,
 969     ) {
 970         debug!("member_constraint({:?} <: {:?})", region, in_regions);
 971         self.inner.borrow_mut().unwrap_region_constraints().member_constraint(
 972             opaque_type_def_id,
 973             definition_span,
 974             hidden_ty,
 975             region,
 976             in_regions,
 977         );
 978     }
 979
 980     /// Processes a `Coerce` predicate from the fulfillment context.
 981     /// This is NOT the preferred way to handle coercion, which is to
 982     /// invoke `FnCtxt::coerce` or a similar method (see `coercion.rs`).
 983     ///
 984     /// This method here is actually a fallback that winds up being
 985     /// invoked when `FnCtxt::coerce` encounters unresolved type variables
 986     /// and records a coercion predicate. Presently, this method is equivalent
 987     /// to `subtype_predicate` -- that is, "coercing" `a` to `b` winds up
 988     /// actually requiring `a <: b`. This is of course a valid coercion,
 989     /// but it's not as flexible as `FnCtxt::coerce` would be.
 990     ///
 991     /// (We may refactor this in the future, but there are a number of
 992     /// practical obstacles. Among other things, `FnCtxt::coerce` presently
 993     /// records adjustments that are required on the HIR in order to perform
 994     /// the coercion, and we don't currently have a way to manage that.)
 995     pub fn coerce_predicate(
 996         &self,
 997         cause: &ObligationCause<'tcx>,
 998         param_env: ty::ParamEnv<'tcx>,
 999         predicate: ty::PolyCoercePredicate<'tcx>,
1000     ) -> Option<InferResult<'tcx, ()>> {
1001         let subtype_predicate = predicate.map_bound(|p| ty::SubtypePredicate {
1002             a_is_expected: false, // when coercing from `a` to `b`, `b` is expected
1003             a: p.a,
1004             b: p.b,
1005         });
1006         self.subtype_predicate(cause, param_env, subtype_predicate)
1007     }
1008
1009     pub fn subtype_predicate(
1010         &self,
1011         cause: &ObligationCause<'tcx>,
1012         param_env: ty::ParamEnv<'tcx>,
1013         predicate: ty::PolySubtypePredicate<'tcx>,
1014     ) -> Option<InferResult<'tcx, ()>> {
1015         // Check for two unresolved inference variables, in which case we can
1016         // make no progress. This is partly a micro-optimization, but it's
1017         // also an opportunity to "sub-unify" the variables. This isn't
1018         // *necessary* to prevent cycles, because they would eventually be sub-unified
1019         // anyhow during generalization, but it helps with diagnostics (we can detect
1020         // earlier that they are sub-unified).
1021         //
1022         // Note that we can just skip the binders here because
1023         // type variables can't (at present, at
1024         // least) capture any of the things bound by this binder.
1025         //
1026         // Note that this sub here is not just for diagnostics - it has semantic
1027         // effects as well.
1028         let r_a = self.shallow_resolve(predicate.skip_binder().a);
1029         let r_b = self.shallow_resolve(predicate.skip_binder().b);
1030         match (r_a.kind(), r_b.kind()) {
1031             (&ty::Infer(ty::TyVar(a_vid)), &ty::Infer(ty::TyVar(b_vid))) => {
1032                 self.inner.borrow_mut().type_variables().sub(a_vid, b_vid);
1033                 return None;
1034             }
1035             _ => {}
1036         }
1037
1038         Some(self.commit_if_ok(|_snapshot| {
1039             let ty::SubtypePredicate { a_is_expected, a, b } =
1040                 self.replace_bound_vars_with_placeholders(predicate);
1041
1042             let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?;
1043
1044             Ok(ok.unit())
1045         }))
1046     }
1047
1048     pub fn region_outlives_predicate(
1049         &self,
1050         cause: &traits::ObligationCause<'tcx>,
1051         predicate: ty::PolyRegionOutlivesPredicate<'tcx>,
1052     ) -> UnitResult<'tcx> {
1053         self.commit_if_ok(|_snapshot| {
1054             let ty::OutlivesPredicate(r_a, r_b) =
1055                 self.replace_bound_vars_with_placeholders(predicate);
1056             let origin = SubregionOrigin::from_obligation_cause(cause, || {
1057                 RelateRegionParamBound(cause.span)
1058             });
1059             self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
1060             Ok(())
1061         })
1062     }
1063
1064     pub fn next_ty_var_id(&self, diverging: Diverging, origin: TypeVariableOrigin) -> TyVid {
1065         self.inner.borrow_mut().type_variables().new_var(self.universe(), diverging, origin)
1066     }
1067
1068     pub fn next_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
1069         self.tcx.mk_ty_var(self.next_ty_var_id(Diverging::NotDiverging, origin))
1070     }
1071
1072     pub fn next_ty_var_in_universe(
1073         &self,
1074         origin: TypeVariableOrigin,
1075         universe: ty::UniverseIndex,
1076     ) -> Ty<'tcx> {
1077         let vid = self.inner.borrow_mut().type_variables().new_var(
1078             universe,
1079             Diverging::NotDiverging,
1080             origin,
1081         );
1082         self.tcx.mk_ty_var(vid)
1083     }
1084
1085     pub fn next_diverging_ty_var(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
1086         self.tcx.mk_ty_var(self.next_ty_var_id(Diverging::Diverges, origin))
1087     }
1088
1089     pub fn next_const_var(
1090         &self,
1091         ty: Ty<'tcx>,
1092         origin: ConstVariableOrigin,
1093     ) -> &'tcx ty::Const<'tcx> {
1094         self.tcx.mk_const_var(self.next_const_var_id(origin), ty)
1095     }
1096
1097     pub fn next_const_var_in_universe(
1098         &self,
1099         ty: Ty<'tcx>,
1100         origin: ConstVariableOrigin,
1101         universe: ty::UniverseIndex,
1102     ) -> &'tcx ty::Const<'tcx> {
1103         let vid = self
1104             .inner
1105             .borrow_mut()
1106             .const_unification_table()
1107             .new_key(ConstVarValue { origin, val: ConstVariableValue::Unknown { universe } });
1108         self.tcx.mk_const_var(vid, ty)
1109     }
1110
1111     pub fn next_const_var_id(&self, origin: ConstVariableOrigin) -> ConstVid<'tcx> {
1112         self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue {
1113             origin,
1114             val: ConstVariableValue::Unknown { universe: self.universe() },
1115         })
1116     }
1117
1118     fn next_int_var_id(&self) -> IntVid {
1119         self.inner.borrow_mut().int_unification_table().new_key(None)
1120     }
1121
1122     pub fn next_int_var(&self) -> Ty<'tcx> {
1123         self.tcx.mk_int_var(self.next_int_var_id())
1124     }
1125
1126     fn next_float_var_id(&self) -> FloatVid {
1127         self.inner.borrow_mut().float_unification_table().new_key(None)
1128     }
1129
1130     pub fn next_float_var(&self) -> Ty<'tcx> {
1131         self.tcx.mk_float_var(self.next_float_var_id())
1132     }
1133
1134     /// Creates a fresh region variable with the next available index.
1135     /// The variable will be created in the maximum universe created
1136     /// thus far, allowing it to name any region created thus far.
1137     pub fn next_region_var(&self, origin: RegionVariableOrigin) -> ty::Region<'tcx> {
1138         self.next_region_var_in_universe(origin, self.universe())
1139     }
1140
1141     /// Creates a fresh region variable with the next available index
1142     /// in the given universe; typically, you can use
1143     /// `next_region_var` and just use the maximal universe.
1144     pub fn next_region_var_in_universe(
1145         &self,
1146         origin: RegionVariableOrigin,
1147         universe: ty::UniverseIndex,
1148     ) -> ty::Region<'tcx> {
1149         let region_var =
1150             self.inner.borrow_mut().unwrap_region_constraints().new_region_var(universe, origin);
1151         self.tcx.mk_region(ty::ReVar(region_var))
1152     }
1153
1154     /// Return the universe that the region `r` was created in.  For
1155     /// most regions (e.g., `'static`, named regions from the user,
1156     /// etc) this is the root universe U0. For inference variables or
1157     /// placeholders, however, it will return the universe which which
1158     /// they are associated.
1159     pub fn universe_of_region(&self, r: ty::Region<'tcx>) -> ty::UniverseIndex {
1160         self.inner.borrow_mut().unwrap_region_constraints().universe(r)
1161     }
1162
1163     /// Number of region variables created so far.
1164     pub fn num_region_vars(&self) -> usize {
1165         self.inner.borrow_mut().unwrap_region_constraints().num_region_vars()
1166     }
1167
1168     /// Just a convenient wrapper of `next_region_var` for using during NLL.
1169     pub fn next_nll_region_var(&self, origin: NllRegionVariableOrigin) -> ty::Region<'tcx> {
1170         self.next_region_var(RegionVariableOrigin::Nll(origin))
1171     }
1172
1173     /// Just a convenient wrapper of `next_region_var` for using during NLL.
1174     pub fn next_nll_region_var_in_universe(
1175         &self,
1176         origin: NllRegionVariableOrigin,
1177         universe: ty::UniverseIndex,
1178     ) -> ty::Region<'tcx> {
1179         self.next_region_var_in_universe(RegionVariableOrigin::Nll(origin), universe)
1180     }
1181
1182     pub fn var_for_def(&self, span: Span, param: &ty::GenericParamDef) -> GenericArg<'tcx> {
1183         match param.kind {
1184             GenericParamDefKind::Lifetime => {
1185                 // Create a region inference variable for the given
1186                 // region parameter definition.
1187                 self.next_region_var(EarlyBoundRegion(span, param.name)).into()
1188             }
1189             GenericParamDefKind::Type { .. } => {
1190                 // Create a type inference variable for the given
1191                 // type parameter definition. The substitutions are
1192                 // for actual parameters that may be referred to by
1193                 // the default of this type parameter, if it exists.
1194                 // e.g., `struct Foo<A, B, C = (A, B)>(...);` when
1195                 // used in a path such as `Foo::<T, U>::new()` will
1196                 // use an inference variable for `C` with `[T, U]`
1197                 // as the substitutions for the default, `(T, U)`.
1198                 let ty_var_id = self.inner.borrow_mut().type_variables().new_var(
1199                     self.universe(),
1200                     Diverging::NotDiverging,
1201                     TypeVariableOrigin {
1202                         kind: TypeVariableOriginKind::TypeParameterDefinition(
1203                             param.name,
1204                             Some(param.def_id),
1205                         ),
1206                         span,
1207                     },
1208                 );
1209
1210                 self.tcx.mk_ty_var(ty_var_id).into()
1211             }
1212             GenericParamDefKind::Const { .. } => {
1213                 let origin = ConstVariableOrigin {
1214                     kind: ConstVariableOriginKind::ConstParameterDefinition(
1215                         param.name,
1216                         param.def_id,
1217                     ),
1218                     span,
1219                 };
1220                 let const_var_id =
1221                     self.inner.borrow_mut().const_unification_table().new_key(ConstVarValue {
1222                         origin,
1223                         val: ConstVariableValue::Unknown { universe: self.universe() },
1224                     });
1225                 self.tcx.mk_const_var(const_var_id, self.tcx.type_of(param.def_id)).into()
1226             }
1227         }
1228     }
1229
1230     /// Given a set of generics defined on a type or impl, returns a substitution mapping each
1231     /// type/region parameter to a fresh inference variable.
1232     pub fn fresh_substs_for_item(&self, span: Span, def_id: DefId) -> SubstsRef<'tcx> {
1233         InternalSubsts::for_item(self.tcx, def_id, |param, _| self.var_for_def(span, param))
1234     }
1235
1236     /// Returns `true` if errors have been reported since this infcx was
1237     /// created. This is sometimes used as a heuristic to skip
1238     /// reporting errors that often occur as a result of earlier
1239     /// errors, but where it's hard to be 100% sure (e.g., unresolved
1240     /// inference variables, regionck errors).
1241     pub fn is_tainted_by_errors(&self) -> bool {
1242         debug!(
1243             "is_tainted_by_errors(err_count={}, err_count_on_creation={}, \
1244              tainted_by_errors_flag={})",
1245             self.tcx.sess.err_count(),
1246             self.err_count_on_creation,
1247             self.tainted_by_errors_flag.get()
1248         );
1249
1250         if self.tcx.sess.err_count() > self.err_count_on_creation {
1251             return true; // errors reported since this infcx was made
1252         }
1253         self.tainted_by_errors_flag.get()
1254     }
1255
1256     /// Set the "tainted by errors" flag to true. We call this when we
1257     /// observe an error from a prior pass.
1258     pub fn set_tainted_by_errors(&self) {
1259         debug!("set_tainted_by_errors()");
1260         self.tainted_by_errors_flag.set(true)
1261     }
1262
1263     /// Process the region constraints and report any errors that
1264     /// result. After this, no more unification operations should be
1265     /// done -- or the compiler will panic -- but it is legal to use
1266     /// `resolve_vars_if_possible` as well as `fully_resolve`.
1267     pub fn resolve_regions_and_report_errors(
1268         &self,
1269         region_context: DefId,
1270         outlives_env: &OutlivesEnvironment<'tcx>,
1271         mode: RegionckMode,
1272     ) {
1273         let (var_infos, data) = {
1274             let mut inner = self.inner.borrow_mut();
1275             let inner = &mut *inner;
1276             assert!(
1277                 self.is_tainted_by_errors() || inner.region_obligations.is_empty(),
1278                 "region_obligations not empty: {:#?}",
1279                 inner.region_obligations
1280             );
1281             inner
1282                 .region_constraint_storage
1283                 .take()
1284                 .expect("regions already resolved")
1285                 .with_log(&mut inner.undo_log)
1286                 .into_infos_and_data()
1287         };
1288
1289         let region_rels =
1290             &RegionRelations::new(self.tcx, region_context, outlives_env.free_region_map());
1291
1292         let (lexical_region_resolutions, errors) =
1293             lexical_region_resolve::resolve(region_rels, var_infos, data, mode);
1294
1295         let old_value = self.lexical_region_resolutions.replace(Some(lexical_region_resolutions));
1296         assert!(old_value.is_none());
1297
1298         if !self.is_tainted_by_errors() {
1299             // As a heuristic, just skip reporting region errors
1300             // altogether if other errors have been reported while
1301             // this infcx was in use.  This is totally hokey but
1302             // otherwise we have a hard time separating legit region
1303             // errors from silly ones.
1304             self.report_region_errors(&errors);
1305         }
1306     }
1307
1308     /// Obtains (and clears) the current set of region
1309     /// constraints. The inference context is still usable: further
1310     /// unifications will simply add new constraints.
1311     ///
1312     /// This method is not meant to be used with normal lexical region
1313     /// resolution. Rather, it is used in the NLL mode as a kind of
1314     /// interim hack: basically we run normal type-check and generate
1315     /// region constraints as normal, but then we take them and
1316     /// translate them into the form that the NLL solver
1317     /// understands. See the NLL module for mode details.
1318     pub fn take_and_reset_region_constraints(&self) -> RegionConstraintData<'tcx> {
1319         assert!(
1320             self.inner.borrow().region_obligations.is_empty(),
1321             "region_obligations not empty: {:#?}",
1322             self.inner.borrow().region_obligations
1323         );
1324
1325         self.inner.borrow_mut().unwrap_region_constraints().take_and_reset_data()
1326     }
1327
1328     /// Gives temporary access to the region constraint data.
1329     pub fn with_region_constraints<R>(
1330         &self,
1331         op: impl FnOnce(&RegionConstraintData<'tcx>) -> R,
1332     ) -> R {
1333         let mut inner = self.inner.borrow_mut();
1334         op(inner.unwrap_region_constraints().data())
1335     }
1336
1337     pub fn region_var_origin(&self, vid: ty::RegionVid) -> RegionVariableOrigin {
1338         let mut inner = self.inner.borrow_mut();
1339         let inner = &mut *inner;
1340         inner
1341             .region_constraint_storage
1342             .as_mut()
1343             .expect("regions already resolved")
1344             .with_log(&mut inner.undo_log)
1345             .var_origin(vid)
1346     }
1347
1348     /// Takes ownership of the list of variable regions. This implies
1349     /// that all the region constraints have already been taken, and
1350     /// hence that `resolve_regions_and_report_errors` can never be
1351     /// called. This is used only during NLL processing to "hand off" ownership
1352     /// of the set of region variables into the NLL region context.
1353     pub fn take_region_var_origins(&self) -> VarInfos {
1354         let mut inner = self.inner.borrow_mut();
1355         let (var_infos, data) = inner
1356             .region_constraint_storage
1357             .take()
1358             .expect("regions already resolved")
1359             .with_log(&mut inner.undo_log)
1360             .into_infos_and_data();
1361         assert!(data.is_empty());
1362         var_infos
1363     }
1364
1365     pub fn ty_to_string(&self, t: Ty<'tcx>) -> String {
1366         self.resolve_vars_if_possible(t).to_string()
1367     }
1368
1369     /// If `TyVar(vid)` resolves to a type, return that type. Else, return the
1370     /// universe index of `TyVar(vid)`.
1371     pub fn probe_ty_var(&self, vid: TyVid) -> Result<Ty<'tcx>, ty::UniverseIndex> {
1372         use self::type_variable::TypeVariableValue;
1373
1374         match self.inner.borrow_mut().type_variables().probe(vid) {
1375             TypeVariableValue::Known { value } => Ok(value),
1376             TypeVariableValue::Unknown { universe } => Err(universe),
1377         }
1378     }
1379
1380     /// Resolve any type variables found in `value` -- but only one
1381     /// level.  So, if the variable `?X` is bound to some type
1382     /// `Foo<?Y>`, then this would return `Foo<?Y>` (but `?Y` may
1383     /// itself be bound to a type).
1384     ///
1385     /// Useful when you only need to inspect the outermost level of
1386     /// the type and don't care about nested types (or perhaps you
1387     /// will be resolving them as well, e.g. in a loop).
1388     pub fn shallow_resolve<T>(&self, value: T) -> T
1389     where
1390         T: TypeFoldable<'tcx>,
1391     {
1392         value.fold_with(&mut ShallowResolver { infcx: self })
1393     }
1394
1395     pub fn root_var(&self, var: ty::TyVid) -> ty::TyVid {
1396         self.inner.borrow_mut().type_variables().root_var(var)
1397     }
1398
1399     /// Where possible, replaces type/const variables in
1400     /// `value` with their final value. Note that region variables
1401     /// are unaffected. If a type/const variable has not been unified, it
1402     /// is left as is. This is an idempotent operation that does
1403     /// not affect inference state in any way and so you can do it
1404     /// at will.
1405     pub fn resolve_vars_if_possible<T>(&self, value: T) -> T
1406     where
1407         T: TypeFoldable<'tcx>,
1408     {
1409         if !value.needs_infer() {
1410             return value; // Avoid duplicated subst-folding.
1411         }
1412         let mut r = resolve::OpportunisticVarResolver::new(self);
1413         value.fold_with(&mut r)
1414     }
1415
1416     /// Returns the first unresolved variable contained in `T`. In the
1417     /// process of visiting `T`, this will resolve (where possible)
1418     /// type variables in `T`, but it never constructs the final,
1419     /// resolved type, so it's more efficient than
1420     /// `resolve_vars_if_possible()`.
1421     pub fn unresolved_type_vars<T>(&self, value: &T) -> Option<(Ty<'tcx>, Option<Span>)>
1422     where
1423         T: TypeFoldable<'tcx>,
1424     {
1425         value.visit_with(&mut resolve::UnresolvedTypeFinder::new(self)).break_value()
1426     }
1427
1428     pub fn probe_const_var(
1429         &self,
1430         vid: ty::ConstVid<'tcx>,
1431     ) -> Result<&'tcx ty::Const<'tcx>, ty::UniverseIndex> {
1432         match self.inner.borrow_mut().const_unification_table().probe_value(vid).val {
1433             ConstVariableValue::Known { value } => Ok(value),
1434             ConstVariableValue::Unknown { universe } => Err(universe),
1435         }
1436     }
1437
1438     pub fn fully_resolve<T: TypeFoldable<'tcx>>(&self, value: T) -> FixupResult<'tcx, T> {
1439         /*!
1440          * Attempts to resolve all type/region/const variables in
1441          * `value`. Region inference must have been run already (e.g.,
1442          * by calling `resolve_regions_and_report_errors`). If some
1443          * variable was never unified, an `Err` results.
1444          *
1445          * This method is idempotent, but it not typically not invoked
1446          * except during the writeback phase.
1447          */
1448
1449         resolve::fully_resolve(self, value)
1450     }
1451
1452     // [Note-Type-error-reporting]
1453     // An invariant is that anytime the expected or actual type is Error (the special
1454     // error type, meaning that an error occurred when typechecking this expression),
1455     // this is a derived error. The error cascaded from another error (that was already
1456     // reported), so it's not useful to display it to the user.
1457     // The following methods implement this logic.
1458     // They check if either the actual or expected type is Error, and don't print the error
1459     // in this case. The typechecker should only ever report type errors involving mismatched
1460     // types using one of these methods, and should not call span_err directly for such
1461     // errors.
1462
1463     pub fn type_error_struct_with_diag<M>(
1464         &self,
1465         sp: Span,
1466         mk_diag: M,
1467         actual_ty: Ty<'tcx>,
1468     ) -> DiagnosticBuilder<'tcx>
1469     where
1470         M: FnOnce(String) -> DiagnosticBuilder<'tcx>,
1471     {
1472         let actual_ty = self.resolve_vars_if_possible(actual_ty);
1473         debug!("type_error_struct_with_diag({:?}, {:?})", sp, actual_ty);
1474
1475         // Don't report an error if actual type is `Error`.
1476         if actual_ty.references_error() {
1477             return self.tcx.sess.diagnostic().struct_dummy();
1478         }
1479
1480         mk_diag(self.ty_to_string(actual_ty))
1481     }
1482
1483     pub fn report_mismatched_types(
1484         &self,
1485         cause: &ObligationCause<'tcx>,
1486         expected: Ty<'tcx>,
1487         actual: Ty<'tcx>,
1488         err: TypeError<'tcx>,
1489     ) -> DiagnosticBuilder<'tcx> {
1490         let trace = TypeTrace::types(cause, true, expected, actual);
1491         self.report_and_explain_type_error(trace, &err)
1492     }
1493
1494     pub fn report_mismatched_consts(
1495         &self,
1496         cause: &ObligationCause<'tcx>,
1497         expected: &'tcx ty::Const<'tcx>,
1498         actual: &'tcx ty::Const<'tcx>,
1499         err: TypeError<'tcx>,
1500     ) -> DiagnosticBuilder<'tcx> {
1501         let trace = TypeTrace::consts(cause, true, expected, actual);
1502         self.report_and_explain_type_error(trace, &err)
1503     }
1504
1505     pub fn replace_bound_vars_with_fresh_vars<T>(
1506         &self,
1507         span: Span,
1508         lbrct: LateBoundRegionConversionTime,
1509         value: ty::Binder<'tcx, T>,
1510     ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
1511     where
1512         T: TypeFoldable<'tcx>,
1513     {
1514         let fld_r =
1515             |br: ty::BoundRegion| self.next_region_var(LateBoundRegion(span, br.kind, lbrct));
1516         let fld_t = |_| {
1517             self.next_ty_var(TypeVariableOrigin {
1518                 kind: TypeVariableOriginKind::MiscVariable,
1519                 span,
1520             })
1521         };
1522         let fld_c = |_, ty| {
1523             self.next_const_var(
1524                 ty,
1525                 ConstVariableOrigin { kind: ConstVariableOriginKind::MiscVariable, span },
1526             )
1527         };
1528         self.tcx.replace_bound_vars(value, fld_r, fld_t, fld_c)
1529     }
1530
1531     /// See the [`region_constraints::RegionConstraintCollector::verify_generic_bound`] method.
1532     pub fn verify_generic_bound(
1533         &self,
1534         origin: SubregionOrigin<'tcx>,
1535         kind: GenericKind<'tcx>,
1536         a: ty::Region<'tcx>,
1537         bound: VerifyBound<'tcx>,
1538     ) {
1539         debug!("verify_generic_bound({:?}, {:?} <: {:?})", kind, a, bound);
1540
1541         self.inner
1542             .borrow_mut()
1543             .unwrap_region_constraints()
1544             .verify_generic_bound(origin, kind, a, bound);
1545     }
1546
1547     /// Obtains the latest type of the given closure; this may be a
1548     /// closure in the current function, in which case its
1549     /// `ClosureKind` may not yet be known.
1550     pub fn closure_kind(&self, closure_substs: SubstsRef<'tcx>) -> Option<ty::ClosureKind> {
1551         let closure_kind_ty = closure_substs.as_closure().kind_ty();
1552         let closure_kind_ty = self.shallow_resolve(closure_kind_ty);
1553         closure_kind_ty.to_opt_closure_kind()
1554     }
1555
1556     /// Clears the selection, evaluation, and projection caches. This is useful when
1557     /// repeatedly attempting to select an `Obligation` while changing only
1558     /// its `ParamEnv`, since `FulfillmentContext` doesn't use probing.
1559     pub fn clear_caches(&self) {
1560         self.selection_cache.clear();
1561         self.evaluation_cache.clear();
1562         self.inner.borrow_mut().projection_cache().clear();
1563     }
1564
1565     pub fn universe(&self) -> ty::UniverseIndex {
1566         self.universe.get()
1567     }
1568
1569     /// Creates and return a fresh universe that extends all previous
1570     /// universes. Updates `self.universe` to that new universe.
1571     pub fn create_next_universe(&self) -> ty::UniverseIndex {
1572         let u = self.universe.get().next_universe();
1573         self.universe.set(u);
1574         u
1575     }
1576
1577     /// Resolves and evaluates a constant.
1578     ///
1579     /// The constant can be located on a trait like `<A as B>::C`, in which case the given
1580     /// substitutions and environment are used to resolve the constant. Alternatively if the
1581     /// constant has generic parameters in scope the substitutions are used to evaluate the value of
1582     /// the constant. For example in `fn foo<T>() { let _ = [0; bar::<T>()]; }` the repeat count
1583     /// constant `bar::<T>()` requires a substitution for `T`, if the substitution for `T` is still
1584     /// too generic for the constant to be evaluated then `Err(ErrorHandled::TooGeneric)` is
1585     /// returned.
1586     ///
1587     /// This handles inferences variables within both `param_env` and `substs` by
1588     /// performing the operation on their respective canonical forms.
1589     pub fn const_eval_resolve(
1590         &self,
1591         param_env: ty::ParamEnv<'tcx>,
1592         unevaluated: ty::Unevaluated<'tcx>,
1593         span: Option<Span>,
1594     ) -> EvalToConstValueResult<'tcx> {
1595         let mut original_values = OriginalQueryValues::default();
1596         let canonical = self.canonicalize_query((param_env, unevaluated), &mut original_values);
1597
1598         let (param_env, unevaluated) = canonical.value;
1599         // The return value is the evaluated value which doesn't contain any reference to inference
1600         // variables, thus we don't need to substitute back the original values.
1601         self.tcx.const_eval_resolve(param_env, unevaluated, span)
1602     }
1603
1604     /// If `typ` is a type variable of some kind, resolve it one level
1605     /// (but do not resolve types found in the result). If `typ` is
1606     /// not a type variable, just return it unmodified.
1607     // FIXME(eddyb) inline into `ShallowResolver::visit_ty`.
1608     fn shallow_resolve_ty(&self, typ: Ty<'tcx>) -> Ty<'tcx> {
1609         match *typ.kind() {
1610             ty::Infer(ty::TyVar(v)) => {
1611                 // Not entirely obvious: if `typ` is a type variable,
1612                 // it can be resolved to an int/float variable, which
1613                 // can then be recursively resolved, hence the
1614                 // recursion. Note though that we prevent type
1615                 // variables from unifying to other type variables
1616                 // directly (though they may be embedded
1617                 // structurally), and we prevent cycles in any case,
1618                 // so this recursion should always be of very limited
1619                 // depth.
1620                 //
1621                 // Note: if these two lines are combined into one we get
1622                 // dynamic borrow errors on `self.inner`.
1623                 let known = self.inner.borrow_mut().type_variables().probe(v).known();
1624                 known.map_or(typ, |t| self.shallow_resolve_ty(t))
1625             }
1626
1627             ty::Infer(ty::IntVar(v)) => self
1628                 .inner
1629                 .borrow_mut()
1630                 .int_unification_table()
1631                 .probe_value(v)
1632                 .map(|v| v.to_type(self.tcx))
1633                 .unwrap_or(typ),
1634
1635             ty::Infer(ty::FloatVar(v)) => self
1636                 .inner
1637                 .borrow_mut()
1638                 .float_unification_table()
1639                 .probe_value(v)
1640                 .map(|v| v.to_type(self.tcx))
1641                 .unwrap_or(typ),
1642
1643             _ => typ,
1644         }
1645     }
1646
1647     /// `ty_or_const_infer_var_changed` is equivalent to one of these two:
1648     ///   * `shallow_resolve(ty) != ty` (where `ty.kind = ty::Infer(_)`)
1649     ///   * `shallow_resolve(ct) != ct` (where `ct.kind = ty::ConstKind::Infer(_)`)
1650     ///
1651     /// However, `ty_or_const_infer_var_changed` is more efficient. It's always
1652     /// inlined, despite being large, because it has only two call sites that
1653     /// are extremely hot (both in `traits::fulfill`'s checking of `stalled_on`
1654     /// inference variables), and it handles both `Ty` and `ty::Const` without
1655     /// having to resort to storing full `GenericArg`s in `stalled_on`.
1656     #[inline(always)]
1657     pub fn ty_or_const_infer_var_changed(&self, infer_var: TyOrConstInferVar<'tcx>) -> bool {
1658         match infer_var {
1659             TyOrConstInferVar::Ty(v) => {
1660                 use self::type_variable::TypeVariableValue;
1661
1662                 // If `inlined_probe` returns a `Known` value, it never equals
1663                 // `ty::Infer(ty::TyVar(v))`.
1664                 match self.inner.borrow_mut().type_variables().inlined_probe(v) {
1665                     TypeVariableValue::Unknown { .. } => false,
1666                     TypeVariableValue::Known { .. } => true,
1667                 }
1668             }
1669
1670             TyOrConstInferVar::TyInt(v) => {
1671                 // If `inlined_probe_value` returns a value it's always a
1672                 // `ty::Int(_)` or `ty::UInt(_)`, which never matches a
1673                 // `ty::Infer(_)`.
1674                 self.inner.borrow_mut().int_unification_table().inlined_probe_value(v).is_some()
1675             }
1676
1677             TyOrConstInferVar::TyFloat(v) => {
1678                 // If `probe_value` returns a value it's always a
1679                 // `ty::Float(_)`, which never matches a `ty::Infer(_)`.
1680                 //
1681                 // Not `inlined_probe_value(v)` because this call site is colder.
1682                 self.inner.borrow_mut().float_unification_table().probe_value(v).is_some()
1683             }
1684
1685             TyOrConstInferVar::Const(v) => {
1686                 // If `probe_value` returns a `Known` value, it never equals
1687                 // `ty::ConstKind::Infer(ty::InferConst::Var(v))`.
1688                 //
1689                 // Not `inlined_probe_value(v)` because this call site is colder.
1690                 match self.inner.borrow_mut().const_unification_table().probe_value(v).val {
1691                     ConstVariableValue::Unknown { .. } => false,
1692                     ConstVariableValue::Known { .. } => true,
1693                 }
1694             }
1695         }
1696     }
1697 }
1698
1699 /// Helper for `ty_or_const_infer_var_changed` (see comment on that), currently
1700 /// used only for `traits::fulfill`'s list of `stalled_on` inference variables.
1701 #[derive(Copy, Clone, Debug)]
1702 pub enum TyOrConstInferVar<'tcx> {
1703     /// Equivalent to `ty::Infer(ty::TyVar(_))`.
1704     Ty(TyVid),
1705     /// Equivalent to `ty::Infer(ty::IntVar(_))`.
1706     TyInt(IntVid),
1707     /// Equivalent to `ty::Infer(ty::FloatVar(_))`.
1708     TyFloat(FloatVid),
1709
1710     /// Equivalent to `ty::ConstKind::Infer(ty::InferConst::Var(_))`.
1711     Const(ConstVid<'tcx>),
1712 }
1713
1714 impl TyOrConstInferVar<'tcx> {
1715     /// Tries to extract an inference variable from a type or a constant, returns `None`
1716     /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`) and
1717     /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1718     pub fn maybe_from_generic_arg(arg: GenericArg<'tcx>) -> Option<Self> {
1719         match arg.unpack() {
1720             GenericArgKind::Type(ty) => Self::maybe_from_ty(ty),
1721             GenericArgKind::Const(ct) => Self::maybe_from_const(ct),
1722             GenericArgKind::Lifetime(_) => None,
1723         }
1724     }
1725
1726     /// Tries to extract an inference variable from a type, returns `None`
1727     /// for types other than `ty::Infer(_)` (or `InferTy::Fresh*`).
1728     pub fn maybe_from_ty(ty: Ty<'tcx>) -> Option<Self> {
1729         match *ty.kind() {
1730             ty::Infer(ty::TyVar(v)) => Some(TyOrConstInferVar::Ty(v)),
1731             ty::Infer(ty::IntVar(v)) => Some(TyOrConstInferVar::TyInt(v)),
1732             ty::Infer(ty::FloatVar(v)) => Some(TyOrConstInferVar::TyFloat(v)),
1733             _ => None,
1734         }
1735     }
1736
1737     /// Tries to extract an inference variable from a constant, returns `None`
1738     /// for constants other than `ty::ConstKind::Infer(_)` (or `InferConst::Fresh`).
1739     pub fn maybe_from_const(ct: &'tcx ty::Const<'tcx>) -> Option<Self> {
1740         match ct.val {
1741             ty::ConstKind::Infer(InferConst::Var(v)) => Some(TyOrConstInferVar::Const(v)),
1742             _ => None,
1743         }
1744     }
1745 }
1746
1747 struct ShallowResolver<'a, 'tcx> {
1748     infcx: &'a InferCtxt<'a, 'tcx>,
1749 }
1750
1751 impl<'a, 'tcx> TypeFolder<'tcx> for ShallowResolver<'a, 'tcx> {
1752     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
1753         self.infcx.tcx
1754     }
1755
1756     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1757         self.infcx.shallow_resolve_ty(ty)
1758     }
1759
1760     fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
1761         if let ty::Const { val: ty::ConstKind::Infer(InferConst::Var(vid)), .. } = ct {
1762             self.infcx
1763                 .inner
1764                 .borrow_mut()
1765                 .const_unification_table()
1766                 .probe_value(*vid)
1767                 .val
1768                 .known()
1769                 .unwrap_or(ct)
1770         } else {
1771             ct
1772         }
1773     }
1774 }
1775
1776 impl<'tcx> TypeTrace<'tcx> {
1777     pub fn span(&self) -> Span {
1778         self.cause.span
1779     }
1780
1781     pub fn types(
1782         cause: &ObligationCause<'tcx>,
1783         a_is_expected: bool,
1784         a: Ty<'tcx>,
1785         b: Ty<'tcx>,
1786     ) -> TypeTrace<'tcx> {
1787         TypeTrace { cause: cause.clone(), values: Types(ExpectedFound::new(a_is_expected, a, b)) }
1788     }
1789
1790     pub fn consts(
1791         cause: &ObligationCause<'tcx>,
1792         a_is_expected: bool,
1793         a: &'tcx ty::Const<'tcx>,
1794         b: &'tcx ty::Const<'tcx>,
1795     ) -> TypeTrace<'tcx> {
1796         TypeTrace { cause: cause.clone(), values: Consts(ExpectedFound::new(a_is_expected, a, b)) }
1797     }
1798 }
1799
1800 impl<'tcx> SubregionOrigin<'tcx> {
1801     pub fn span(&self) -> Span {
1802         match *self {
1803             Subtype(ref a) => a.span(),
1804             RelateObjectBound(a) => a,
1805             RelateParamBound(a, ..) => a,
1806             RelateRegionParamBound(a) => a,
1807             Reborrow(a) => a,
1808             ReborrowUpvar(a, _) => a,
1809             DataBorrowed(_, a) => a,
1810             ReferenceOutlivesReferent(_, a) => a,
1811             CallReturn(a) => a,
1812             CompareImplMethodObligation { span, .. } => span,
1813         }
1814     }
1815
1816     pub fn from_obligation_cause<F>(cause: &traits::ObligationCause<'tcx>, default: F) -> Self
1817     where
1818         F: FnOnce() -> Self,
1819     {
1820         match cause.code {
1821             traits::ObligationCauseCode::ReferenceOutlivesReferent(ref_type) => {
1822                 SubregionOrigin::ReferenceOutlivesReferent(ref_type, cause.span)
1823             }
1824
1825             traits::ObligationCauseCode::CompareImplMethodObligation {
1826                 item_name,
1827                 impl_item_def_id,
1828                 trait_item_def_id,
1829             } => SubregionOrigin::CompareImplMethodObligation {
1830                 span: cause.span,
1831                 item_name,
1832                 impl_item_def_id,
1833                 trait_item_def_id,
1834             },
1835
1836             _ => default(),
1837         }
1838     }
1839 }
1840
1841 impl RegionVariableOrigin {
1842     pub fn span(&self) -> Span {
1843         match *self {
1844             MiscVariable(a)
1845             | PatternRegion(a)
1846             | AddrOfRegion(a)
1847             | Autoref(a, _)
1848             | Coercion(a)
1849             | EarlyBoundRegion(a, ..)
1850             | LateBoundRegion(a, ..)
1851             | UpvarRegion(_, a) => a,
1852             Nll(..) => bug!("NLL variable used with `span`"),
1853         }
1854     }
1855 }
1856
1857 impl<'tcx> fmt::Debug for RegionObligation<'tcx> {
1858     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1859         write!(
1860             f,
1861             "RegionObligation(sub_region={:?}, sup_type={:?})",
1862             self.sub_region, self.sup_type
1863         )
1864     }
1865 }