src/librustc_mir/borrow_check/type_check/mod.rs

   1 //! This pass type-checks the MIR to ensure it is not broken.
   2
   3 use std::rc::Rc;
   4 use std::{fmt, iter, mem};
   5
   6 use either::Either;
   7
   8 use rustc_data_structures::frozen::Frozen;
   9 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  10 use rustc_errors::struct_span_err;
  11 use rustc_hir as hir;
  12 use rustc_hir::def_id::{DefId, LocalDefId};
  13 use rustc_hir::lang_items::LangItem;
  14 use rustc_index::vec::{Idx, IndexVec};
  15 use rustc_infer::infer::canonical::QueryRegionConstraints;
  16 use rustc_infer::infer::outlives::env::RegionBoundPairs;
  17 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  18 use rustc_infer::infer::{
  19     InferCtxt, InferOk, LateBoundRegionConversionTime, NLLRegionVariableOrigin,
  20 };
  21 use rustc_middle::mir::tcx::PlaceTy;
  22 use rustc_middle::mir::visit::{NonMutatingUseContext, PlaceContext, Visitor};
  23 use rustc_middle::mir::AssertKind;
  24 use rustc_middle::mir::*;
  25 use rustc_middle::ty::adjustment::PointerCast;
  26 use rustc_middle::ty::cast::CastTy;
  27 use rustc_middle::ty::fold::TypeFoldable;
  28 use rustc_middle::ty::subst::{GenericArgKind, Subst, SubstsRef, UserSubsts};
  29 use rustc_middle::ty::{
  30     self, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations, RegionVid, ToPredicate, Ty,
  31     TyCtxt, UserType, UserTypeAnnotationIndex, WithConstness,
  32 };
  33 use rustc_span::{Span, DUMMY_SP};
  34 use rustc_target::abi::VariantIdx;
  35 use rustc_trait_selection::infer::InferCtxtExt as _;
  36 use rustc_trait_selection::opaque_types::{GenerateMemberConstraints, InferCtxtExt};
  37 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
  38 use rustc_trait_selection::traits::query::type_op;
  39 use rustc_trait_selection::traits::query::type_op::custom::CustomTypeOp;
  40 use rustc_trait_selection::traits::query::{Fallible, NoSolution};
  41 use rustc_trait_selection::traits::{self, ObligationCause, PredicateObligations};
  42
  43 use crate::dataflow::impls::MaybeInitializedPlaces;
  44 use crate::dataflow::move_paths::MoveData;
  45 use crate::dataflow::ResultsCursor;
  46 use crate::transform::{
  47     check_consts::ConstCx,
  48     promote_consts::should_suggest_const_in_array_repeat_expressions_attribute,
  49 };
  50
  51 use crate::borrow_check::{
  52     borrow_set::BorrowSet,
  53     constraints::{OutlivesConstraint, OutlivesConstraintSet},
  54     facts::AllFacts,
  55     location::LocationTable,
  56     member_constraints::MemberConstraintSet,
  57     nll::ToRegionVid,
  58     path_utils,
  59     region_infer::values::{
  60         LivenessValues, PlaceholderIndex, PlaceholderIndices, RegionValueElements,
  61     },
  62     region_infer::{ClosureRegionRequirementsExt, TypeTest},
  63     renumber,
  64     type_check::free_region_relations::{CreateResult, UniversalRegionRelations},
  65     universal_regions::{DefiningTy, UniversalRegions},
  66     Upvar,
  67 };
  68
  69 macro_rules! span_mirbug {
  70     ($context:expr, $elem:expr, $($message:tt)*) => ({
  71         $crate::borrow_check::type_check::mirbug(
  72             $context.tcx(),
  73             $context.last_span,
  74             &format!(
  75                 "broken MIR in {:?} ({:?}): {}",
  76                 $context.mir_def_id,
  77                 $elem,
  78                 format_args!($($message)*),
  79             ),
  80         )
  81     })
  82 }
  83
  84 macro_rules! span_mirbug_and_err {
  85     ($context:expr, $elem:expr, $($message:tt)*) => ({
  86         {
  87             span_mirbug!($context, $elem, $($message)*);
  88             $context.error()
  89         }
  90     })
  91 }
  92
  93 mod constraint_conversion;
  94 pub mod free_region_relations;
  95 mod input_output;
  96 crate mod liveness;
  97 mod relate_tys;
  98
  99 /// Type checks the given `mir` in the context of the inference
 100 /// context `infcx`. Returns any region constraints that have yet to
 101 /// be proven. This result is includes liveness constraints that
 102 /// ensure that regions appearing in the types of all local variables
 103 /// are live at all points where that local variable may later be
 104 /// used.
 105 ///
 106 /// This phase of type-check ought to be infallible -- this is because
 107 /// the original, HIR-based type-check succeeded. So if any errors
 108 /// occur here, we will get a `bug!` reported.
 109 ///
 110 /// # Parameters
 111 ///
 112 /// - `infcx` -- inference context to use
 113 /// - `param_env` -- parameter environment to use for trait solving
 114 /// - `body` -- MIR body to type-check
 115 /// - `promoted` -- map of promoted constants within `body`
 116 /// - `mir_def_id` -- `LocalDefId` from which the MIR is derived
 117 /// - `universal_regions` -- the universal regions from `body`s function signature
 118 /// - `location_table` -- MIR location map of `body`
 119 /// - `borrow_set` -- information about borrows occurring in `body`
 120 /// - `all_facts` -- when using Polonius, this is the generated set of Polonius facts
 121 /// - `flow_inits` -- results of a maybe-init dataflow analysis
 122 /// - `move_data` -- move-data constructed when performing the maybe-init dataflow analysis
 123 /// - `elements` -- MIR region map
 124 pub(crate) fn type_check<'mir, 'tcx>(
 125     infcx: &InferCtxt<'_, 'tcx>,
 126     param_env: ty::ParamEnv<'tcx>,
 127     body: &Body<'tcx>,
 128     promoted: &IndexVec<Promoted, Body<'tcx>>,
 129     mir_def_id: LocalDefId,
 130     universal_regions: &Rc<UniversalRegions<'tcx>>,
 131     location_table: &LocationTable,
 132     borrow_set: &BorrowSet<'tcx>,
 133     all_facts: &mut Option<AllFacts>,
 134     flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
 135     move_data: &MoveData<'tcx>,
 136     elements: &Rc<RegionValueElements>,
 137     upvars: &[Upvar],
 138 ) -> MirTypeckResults<'tcx> {
 139     let implicit_region_bound = infcx.tcx.mk_region(ty::ReVar(universal_regions.fr_fn_body));
 140     let mut constraints = MirTypeckRegionConstraints {
 141         placeholder_indices: PlaceholderIndices::default(),
 142         placeholder_index_to_region: IndexVec::default(),
 143         liveness_constraints: LivenessValues::new(elements.clone()),
 144         outlives_constraints: OutlivesConstraintSet::default(),
 145         member_constraints: MemberConstraintSet::default(),
 146         closure_bounds_mapping: Default::default(),
 147         type_tests: Vec::default(),
 148     };
 149
 150     let CreateResult {
 151         universal_region_relations,
 152         region_bound_pairs,
 153         normalized_inputs_and_output,
 154     } = free_region_relations::create(
 155         infcx,
 156         param_env,
 157         Some(implicit_region_bound),
 158         universal_regions,
 159         &mut constraints,
 160     );
 161
 162     let mut borrowck_context = BorrowCheckContext {
 163         universal_regions,
 164         location_table,
 165         borrow_set,
 166         all_facts,
 167         constraints: &mut constraints,
 168         upvars,
 169     };
 170
 171     let opaque_type_values = type_check_internal(
 172         infcx,
 173         mir_def_id,
 174         param_env,
 175         body,
 176         promoted,
 177         &region_bound_pairs,
 178         implicit_region_bound,
 179         &mut borrowck_context,
 180         &universal_region_relations,
 181         |mut cx| {
 182             cx.equate_inputs_and_outputs(&body, universal_regions, &normalized_inputs_and_output);
 183             liveness::generate(&mut cx, body, elements, flow_inits, move_data, location_table);
 184
 185             translate_outlives_facts(&mut cx);
 186             cx.opaque_type_values
 187         },
 188     );
 189
 190     MirTypeckResults { constraints, universal_region_relations, opaque_type_values }
 191 }
 192
 193 fn type_check_internal<'a, 'tcx, R>(
 194     infcx: &'a InferCtxt<'a, 'tcx>,
 195     mir_def_id: LocalDefId,
 196     param_env: ty::ParamEnv<'tcx>,
 197     body: &'a Body<'tcx>,
 198     promoted: &'a IndexVec<Promoted, Body<'tcx>>,
 199     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
 200     implicit_region_bound: ty::Region<'tcx>,
 201     borrowck_context: &'a mut BorrowCheckContext<'a, 'tcx>,
 202     universal_region_relations: &'a UniversalRegionRelations<'tcx>,
 203     extra: impl FnOnce(TypeChecker<'a, 'tcx>) -> R,
 204 ) -> R {
 205     let mut checker = TypeChecker::new(
 206         infcx,
 207         body,
 208         mir_def_id,
 209         param_env,
 210         region_bound_pairs,
 211         implicit_region_bound,
 212         borrowck_context,
 213         universal_region_relations,
 214     );
 215     let errors_reported = {
 216         let mut verifier = TypeVerifier::new(&mut checker, body, promoted);
 217         verifier.visit_body(&body);
 218         verifier.errors_reported
 219     };
 220
 221     if !errors_reported {
 222         // if verifier failed, don't do further checks to avoid ICEs
 223         checker.typeck_mir(body);
 224     }
 225
 226     extra(checker)
 227 }
 228
 229 fn translate_outlives_facts(typeck: &mut TypeChecker<'_, '_>) {
 230     let cx = &mut typeck.borrowck_context;
 231     if let Some(facts) = cx.all_facts {
 232         let _prof_timer = typeck.infcx.tcx.prof.generic_activity("polonius_fact_generation");
 233         let location_table = cx.location_table;
 234         facts.outlives.extend(cx.constraints.outlives_constraints.outlives().iter().flat_map(
 235             |constraint: &OutlivesConstraint| {
 236                 if let Some(from_location) = constraint.locations.from_location() {
 237                     Either::Left(iter::once((
 238                         constraint.sup,
 239                         constraint.sub,
 240                         location_table.mid_index(from_location),
 241                     )))
 242                 } else {
 243                     Either::Right(
 244                         location_table
 245                             .all_points()
 246                             .map(move |location| (constraint.sup, constraint.sub, location)),
 247                     )
 248                 }
 249             },
 250         ));
 251     }
 252 }
 253
 254 fn mirbug(tcx: TyCtxt<'_>, span: Span, msg: &str) {
 255     // We sometimes see MIR failures (notably predicate failures) due to
 256     // the fact that we check rvalue sized predicates here. So use `delay_span_bug`
 257     // to avoid reporting bugs in those cases.
 258     tcx.sess.diagnostic().delay_span_bug(span, msg);
 259 }
 260
 261 enum FieldAccessError {
 262     OutOfRange { field_count: usize },
 263 }
 264
 265 /// Verifies that MIR types are sane to not crash further checks.
 266 ///
 267 /// The sanitize_XYZ methods here take an MIR object and compute its
 268 /// type, calling `span_mirbug` and returning an error type if there
 269 /// is a problem.
 270 struct TypeVerifier<'a, 'b, 'tcx> {
 271     cx: &'a mut TypeChecker<'b, 'tcx>,
 272     body: &'b Body<'tcx>,
 273     promoted: &'b IndexVec<Promoted, Body<'tcx>>,
 274     last_span: Span,
 275     mir_def_id: LocalDefId,
 276     errors_reported: bool,
 277 }
 278
 279 impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
 280     fn visit_span(&mut self, span: &Span) {
 281         if !span.is_dummy() {
 282             self.last_span = *span;
 283         }
 284     }
 285
 286     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, location: Location) {
 287         self.sanitize_place(place, location, context);
 288     }
 289
 290     fn visit_constant(&mut self, constant: &Constant<'tcx>, location: Location) {
 291         self.super_constant(constant, location);
 292         let ty = self.sanitize_type(constant, constant.literal.ty);
 293
 294         self.cx.infcx.tcx.for_each_free_region(&ty, |live_region| {
 295             let live_region_vid =
 296                 self.cx.borrowck_context.universal_regions.to_region_vid(live_region);
 297             self.cx
 298                 .borrowck_context
 299                 .constraints
 300                 .liveness_constraints
 301                 .add_element(live_region_vid, location);
 302         });
 303
 304         if let Some(annotation_index) = constant.user_ty {
 305             if let Err(terr) = self.cx.relate_type_and_user_type(
 306                 constant.literal.ty,
 307                 ty::Variance::Invariant,
 308                 &UserTypeProjection { base: annotation_index, projs: vec![] },
 309                 location.to_locations(),
 310                 ConstraintCategory::Boring,
 311             ) {
 312                 let annotation = &self.cx.user_type_annotations[annotation_index];
 313                 span_mirbug!(
 314                     self,
 315                     constant,
 316                     "bad constant user type {:?} vs {:?}: {:?}",
 317                     annotation,
 318                     constant.literal.ty,
 319                     terr,
 320                 );
 321             }
 322         } else {
 323             let tcx = self.tcx();
 324             if let ty::ConstKind::Unevaluated(def, substs, promoted) = constant.literal.val {
 325                 if let Some(promoted) = promoted {
 326                     let check_err = |verifier: &mut TypeVerifier<'a, 'b, 'tcx>,
 327                                      promoted: &Body<'tcx>,
 328                                      ty,
 329                                      san_ty| {
 330                         if let Err(terr) = verifier.cx.eq_types(
 331                             san_ty,
 332                             ty,
 333                             location.to_locations(),
 334                             ConstraintCategory::Boring,
 335                         ) {
 336                             span_mirbug!(
 337                                 verifier,
 338                                 promoted,
 339                                 "bad promoted type ({:?}: {:?}): {:?}",
 340                                 ty,
 341                                 san_ty,
 342                                 terr
 343                             );
 344                         };
 345                     };
 346
 347                     if !self.errors_reported {
 348                         let promoted_body = &self.promoted[promoted];
 349                         self.sanitize_promoted(promoted_body, location);
 350
 351                         let promoted_ty = promoted_body.return_ty();
 352                         check_err(self, promoted_body, ty, promoted_ty);
 353                     }
 354                 } else {
 355                     if let Err(terr) = self.cx.fully_perform_op(
 356                         location.to_locations(),
 357                         ConstraintCategory::Boring,
 358                         self.cx.param_env.and(type_op::ascribe_user_type::AscribeUserType::new(
 359                             constant.literal.ty,
 360                             def.did,
 361                             UserSubsts { substs, user_self_ty: None },
 362                         )),
 363                     ) {
 364                         span_mirbug!(
 365                             self,
 366                             constant,
 367                             "bad constant type {:?} ({:?})",
 368                             constant,
 369                             terr
 370                         );
 371                     }
 372                 }
 373             } else if let Some(static_def_id) = constant.check_static_ptr(tcx) {
 374                 let unnormalized_ty = tcx.type_of(static_def_id);
 375                 let locations = location.to_locations();
 376                 let normalized_ty = self.cx.normalize(unnormalized_ty, locations);
 377                 let literal_ty = constant.literal.ty.builtin_deref(true).unwrap().ty;
 378
 379                 if let Err(terr) = self.cx.eq_types(
 380                     normalized_ty,
 381                     literal_ty,
 382                     locations,
 383                     ConstraintCategory::Boring,
 384                 ) {
 385                     span_mirbug!(self, constant, "bad static type {:?} ({:?})", constant, terr);
 386                 }
 387             }
 388
 389             if let ty::FnDef(def_id, substs) = constant.literal.ty.kind {
 390                 let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);
 391                 self.cx.normalize_and_prove_instantiated_predicates(
 392                     instantiated_predicates,
 393                     location.to_locations(),
 394                 );
 395             }
 396         }
 397     }
 398
 399     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 400         self.super_rvalue(rvalue, location);
 401         let rval_ty = rvalue.ty(self.body, self.tcx());
 402         self.sanitize_type(rvalue, rval_ty);
 403     }
 404
 405     fn visit_local_decl(&mut self, local: Local, local_decl: &LocalDecl<'tcx>) {
 406         self.super_local_decl(local, local_decl);
 407         self.sanitize_type(local_decl, local_decl.ty);
 408
 409         if let Some(user_ty) = &local_decl.user_ty {
 410             for (user_ty, span) in user_ty.projections_and_spans() {
 411                 let ty = if !local_decl.is_nonref_binding() {
 412                     // If we have a binding of the form `let ref x: T = ..`
 413                     // then remove the outermost reference so we can check the
 414                     // type annotation for the remaining type.
 415                     if let ty::Ref(_, rty, _) = local_decl.ty.kind {
 416                         rty
 417                     } else {
 418                         bug!("{:?} with ref binding has wrong type {}", local, local_decl.ty);
 419                     }
 420                 } else {
 421                     local_decl.ty
 422                 };
 423
 424                 if let Err(terr) = self.cx.relate_type_and_user_type(
 425                     ty,
 426                     ty::Variance::Invariant,
 427                     user_ty,
 428                     Locations::All(*span),
 429                     ConstraintCategory::TypeAnnotation,
 430                 ) {
 431                     span_mirbug!(
 432                         self,
 433                         local,
 434                         "bad user type on variable {:?}: {:?} != {:?} ({:?})",
 435                         local,
 436                         local_decl.ty,
 437                         local_decl.user_ty,
 438                         terr,
 439                     );
 440                 }
 441             }
 442         }
 443     }
 444
 445     fn visit_body(&mut self, body: &Body<'tcx>) {
 446         self.sanitize_type(&"return type", body.return_ty());
 447         for local_decl in &body.local_decls {
 448             self.sanitize_type(local_decl, local_decl.ty);
 449         }
 450         if self.errors_reported {
 451             return;
 452         }
 453         self.super_body(body);
 454     }
 455 }
 456
 457 impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
 458     fn new(
 459         cx: &'a mut TypeChecker<'b, 'tcx>,
 460         body: &'b Body<'tcx>,
 461         promoted: &'b IndexVec<Promoted, Body<'tcx>>,
 462     ) -> Self {
 463         TypeVerifier {
 464             body,
 465             promoted,
 466             mir_def_id: cx.mir_def_id,
 467             cx,
 468             last_span: body.span,
 469             errors_reported: false,
 470         }
 471     }
 472
 473     fn tcx(&self) -> TyCtxt<'tcx> {
 474         self.cx.infcx.tcx
 475     }
 476
 477     fn sanitize_type(&mut self, parent: &dyn fmt::Debug, ty: Ty<'tcx>) -> Ty<'tcx> {
 478         if ty.has_escaping_bound_vars() || ty.references_error() {
 479             span_mirbug_and_err!(self, parent, "bad type {:?}", ty)
 480         } else {
 481             ty
 482         }
 483     }
 484
 485     /// Checks that the types internal to the `place` match up with
 486     /// what would be expected.
 487     fn sanitize_place(
 488         &mut self,
 489         place: &Place<'tcx>,
 490         location: Location,
 491         context: PlaceContext,
 492     ) -> PlaceTy<'tcx> {
 493         debug!("sanitize_place: {:?}", place);
 494
 495         let mut place_ty = PlaceTy::from_ty(self.body.local_decls[place.local].ty);
 496
 497         for elem in place.projection.iter() {
 498             if place_ty.variant_index.is_none() {
 499                 if place_ty.ty.references_error() {
 500                     assert!(self.errors_reported);
 501                     return PlaceTy::from_ty(self.tcx().ty_error());
 502                 }
 503             }
 504             place_ty = self.sanitize_projection(place_ty, elem, place, location)
 505         }
 506
 507         if let PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy) = context {
 508             let tcx = self.tcx();
 509             let trait_ref = ty::TraitRef {
 510                 def_id: tcx.require_lang_item(LangItem::Copy, Some(self.last_span)),
 511                 substs: tcx.mk_substs_trait(place_ty.ty, &[]),
 512             };
 513
 514             // To have a `Copy` operand, the type `T` of the
 515             // value must be `Copy`. Note that we prove that `T: Copy`,
 516             // rather than using the `is_copy_modulo_regions`
 517             // test. This is important because
 518             // `is_copy_modulo_regions` ignores the resulting region
 519             // obligations and assumes they pass. This can result in
 520             // bounds from `Copy` impls being unsoundly ignored (e.g.,
 521             // #29149). Note that we decide to use `Copy` before knowing
 522             // whether the bounds fully apply: in effect, the rule is
 523             // that if a value of some type could implement `Copy`, then
 524             // it must.
 525             self.cx.prove_trait_ref(
 526                 trait_ref,
 527                 location.to_locations(),
 528                 ConstraintCategory::CopyBound,
 529             );
 530         }
 531
 532         place_ty
 533     }
 534
 535     fn sanitize_promoted(&mut self, promoted_body: &'b Body<'tcx>, location: Location) {
 536         // Determine the constraints from the promoted MIR by running the type
 537         // checker on the promoted MIR, then transfer the constraints back to
 538         // the main MIR, changing the locations to the provided location.
 539
 540         let parent_body = mem::replace(&mut self.body, promoted_body);
 541
 542         // Use new sets of constraints and closure bounds so that we can
 543         // modify their locations.
 544         let all_facts = &mut None;
 545         let mut constraints = Default::default();
 546         let mut closure_bounds = Default::default();
 547         let mut liveness_constraints =
 548             LivenessValues::new(Rc::new(RegionValueElements::new(&promoted_body)));
 549         // Don't try to add borrow_region facts for the promoted MIR
 550
 551         let mut swap_constraints = |this: &mut Self| {
 552             mem::swap(this.cx.borrowck_context.all_facts, all_facts);
 553             mem::swap(
 554                 &mut this.cx.borrowck_context.constraints.outlives_constraints,
 555                 &mut constraints,
 556             );
 557             mem::swap(
 558                 &mut this.cx.borrowck_context.constraints.closure_bounds_mapping,
 559                 &mut closure_bounds,
 560             );
 561             mem::swap(
 562                 &mut this.cx.borrowck_context.constraints.liveness_constraints,
 563                 &mut liveness_constraints,
 564             );
 565         };
 566
 567         swap_constraints(self);
 568
 569         self.visit_body(&promoted_body);
 570
 571         if !self.errors_reported {
 572             // if verifier failed, don't do further checks to avoid ICEs
 573             self.cx.typeck_mir(promoted_body);
 574         }
 575
 576         self.body = parent_body;
 577         // Merge the outlives constraints back in, at the given location.
 578         swap_constraints(self);
 579
 580         let locations = location.to_locations();
 581         for constraint in constraints.outlives().iter() {
 582             let mut constraint = *constraint;
 583             constraint.locations = locations;
 584             if let ConstraintCategory::Return(_)
 585             | ConstraintCategory::UseAsConst
 586             | ConstraintCategory::UseAsStatic = constraint.category
 587             {
 588                 // "Returning" from a promoted is an assignment to a
 589                 // temporary from the user's point of view.
 590                 constraint.category = ConstraintCategory::Boring;
 591             }
 592             self.cx.borrowck_context.constraints.outlives_constraints.push(constraint)
 593         }
 594         for live_region in liveness_constraints.rows() {
 595             self.cx
 596                 .borrowck_context
 597                 .constraints
 598                 .liveness_constraints
 599                 .add_element(live_region, location);
 600         }
 601
 602         if !closure_bounds.is_empty() {
 603             let combined_bounds_mapping =
 604                 closure_bounds.into_iter().flat_map(|(_, value)| value).collect();
 605             let existing = self
 606                 .cx
 607                 .borrowck_context
 608                 .constraints
 609                 .closure_bounds_mapping
 610                 .insert(location, combined_bounds_mapping);
 611             assert!(existing.is_none(), "Multiple promoteds/closures at the same location.");
 612         }
 613     }
 614
 615     fn sanitize_projection(
 616         &mut self,
 617         base: PlaceTy<'tcx>,
 618         pi: PlaceElem<'tcx>,
 619         place: &Place<'tcx>,
 620         location: Location,
 621     ) -> PlaceTy<'tcx> {
 622         debug!("sanitize_projection: {:?} {:?} {:?}", base, pi, place);
 623         let tcx = self.tcx();
 624         let base_ty = base.ty;
 625         match pi {
 626             ProjectionElem::Deref => {
 627                 let deref_ty = base_ty.builtin_deref(true);
 628                 PlaceTy::from_ty(deref_ty.map(|t| t.ty).unwrap_or_else(|| {
 629                     span_mirbug_and_err!(self, place, "deref of non-pointer {:?}", base_ty)
 630                 }))
 631             }
 632             ProjectionElem::Index(i) => {
 633                 let index_ty = Place::from(i).ty(self.body, tcx).ty;
 634                 if index_ty != tcx.types.usize {
 635                     PlaceTy::from_ty(span_mirbug_and_err!(self, i, "index by non-usize {:?}", i))
 636                 } else {
 637                     PlaceTy::from_ty(base_ty.builtin_index().unwrap_or_else(|| {
 638                         span_mirbug_and_err!(self, place, "index of non-array {:?}", base_ty)
 639                     }))
 640                 }
 641             }
 642             ProjectionElem::ConstantIndex { .. } => {
 643                 // consider verifying in-bounds
 644                 PlaceTy::from_ty(base_ty.builtin_index().unwrap_or_else(|| {
 645                     span_mirbug_and_err!(self, place, "index of non-array {:?}", base_ty)
 646                 }))
 647             }
 648             ProjectionElem::Subslice { from, to, from_end } => {
 649                 PlaceTy::from_ty(match base_ty.kind {
 650                     ty::Array(inner, _) => {
 651                         assert!(!from_end, "array subslices should not use from_end");
 652                         tcx.mk_array(inner, (to - from) as u64)
 653                     }
 654                     ty::Slice(..) => {
 655                         assert!(from_end, "slice subslices should use from_end");
 656                         base_ty
 657                     }
 658                     _ => span_mirbug_and_err!(self, place, "slice of non-array {:?}", base_ty),
 659                 })
 660             }
 661             ProjectionElem::Downcast(maybe_name, index) => match base_ty.kind {
 662                 ty::Adt(adt_def, _substs) if adt_def.is_enum() => {
 663                     if index.as_usize() >= adt_def.variants.len() {
 664                         PlaceTy::from_ty(span_mirbug_and_err!(
 665                             self,
 666                             place,
 667                             "cast to variant #{:?} but enum only has {:?}",
 668                             index,
 669                             adt_def.variants.len()
 670                         ))
 671                     } else {
 672                         PlaceTy { ty: base_ty, variant_index: Some(index) }
 673                     }
 674                 }
 675                 // We do not need to handle generators here, because this runs
 676                 // before the generator transform stage.
 677                 _ => {
 678                     let ty = if let Some(name) = maybe_name {
 679                         span_mirbug_and_err!(
 680                             self,
 681                             place,
 682                             "can't downcast {:?} as {:?}",
 683                             base_ty,
 684                             name
 685                         )
 686                     } else {
 687                         span_mirbug_and_err!(self, place, "can't downcast {:?}", base_ty)
 688                     };
 689                     PlaceTy::from_ty(ty)
 690                 }
 691             },
 692             ProjectionElem::Field(field, fty) => {
 693                 let fty = self.sanitize_type(place, fty);
 694                 match self.field_ty(place, base, field, location) {
 695                     Ok(ty) => {
 696                         let ty = self.cx.normalize(ty, location);
 697                         if let Err(terr) = self.cx.eq_types(
 698                             ty,
 699                             fty,
 700                             location.to_locations(),
 701                             ConstraintCategory::Boring,
 702                         ) {
 703                             span_mirbug!(
 704                                 self,
 705                                 place,
 706                                 "bad field access ({:?}: {:?}): {:?}",
 707                                 ty,
 708                                 fty,
 709                                 terr
 710                             );
 711                         }
 712                     }
 713                     Err(FieldAccessError::OutOfRange { field_count }) => span_mirbug!(
 714                         self,
 715                         place,
 716                         "accessed field #{} but variant only has {}",
 717                         field.index(),
 718                         field_count
 719                     ),
 720                 }
 721                 PlaceTy::from_ty(fty)
 722             }
 723         }
 724     }
 725
 726     fn error(&mut self) -> Ty<'tcx> {
 727         self.errors_reported = true;
 728         self.tcx().ty_error()
 729     }
 730
 731     fn field_ty(
 732         &mut self,
 733         parent: &dyn fmt::Debug,
 734         base_ty: PlaceTy<'tcx>,
 735         field: Field,
 736         location: Location,
 737     ) -> Result<Ty<'tcx>, FieldAccessError> {
 738         let tcx = self.tcx();
 739
 740         let (variant, substs) = match base_ty {
 741             PlaceTy { ty, variant_index: Some(variant_index) } => match ty.kind {
 742                 ty::Adt(adt_def, substs) => (&adt_def.variants[variant_index], substs),
 743                 ty::Generator(def_id, substs, _) => {
 744                     let mut variants = substs.as_generator().state_tys(def_id, tcx);
 745                     let mut variant = match variants.nth(variant_index.into()) {
 746                         Some(v) => v,
 747                         None => bug!(
 748                             "variant_index of generator out of range: {:?}/{:?}",
 749                             variant_index,
 750                             substs.as_generator().state_tys(def_id, tcx).count()
 751                         ),
 752                     };
 753                     return match variant.nth(field.index()) {
 754                         Some(ty) => Ok(ty),
 755                         None => Err(FieldAccessError::OutOfRange { field_count: variant.count() }),
 756                     };
 757                 }
 758                 _ => bug!("can't have downcast of non-adt non-generator type"),
 759             },
 760             PlaceTy { ty, variant_index: None } => match ty.kind {
 761                 ty::Adt(adt_def, substs) if !adt_def.is_enum() => {
 762                     (&adt_def.variants[VariantIdx::new(0)], substs)
 763                 }
 764                 ty::Closure(_, substs) => {
 765                     return match substs.as_closure().upvar_tys().nth(field.index()) {
 766                         Some(ty) => Ok(ty),
 767                         None => Err(FieldAccessError::OutOfRange {
 768                             field_count: substs.as_closure().upvar_tys().count(),
 769                         }),
 770                     };
 771                 }
 772                 ty::Generator(_, substs, _) => {
 773                     // Only prefix fields (upvars and current state) are
 774                     // accessible without a variant index.
 775                     return match substs.as_generator().prefix_tys().nth(field.index()) {
 776                         Some(ty) => Ok(ty),
 777                         None => Err(FieldAccessError::OutOfRange {
 778                             field_count: substs.as_generator().prefix_tys().count(),
 779                         }),
 780                     };
 781                 }
 782                 ty::Tuple(tys) => {
 783                     return match tys.get(field.index()) {
 784                         Some(&ty) => Ok(ty.expect_ty()),
 785                         None => Err(FieldAccessError::OutOfRange { field_count: tys.len() }),
 786                     };
 787                 }
 788                 _ => {
 789                     return Ok(span_mirbug_and_err!(
 790                         self,
 791                         parent,
 792                         "can't project out of {:?}",
 793                         base_ty
 794                     ));
 795                 }
 796             },
 797         };
 798
 799         if let Some(field) = variant.fields.get(field.index()) {
 800             Ok(self.cx.normalize(&field.ty(tcx, substs), location))
 801         } else {
 802             Err(FieldAccessError::OutOfRange { field_count: variant.fields.len() })
 803         }
 804     }
 805 }
 806
 807 /// The MIR type checker. Visits the MIR and enforces all the
 808 /// constraints needed for it to be valid and well-typed. Along the
 809 /// way, it accrues region constraints -- these can later be used by
 810 /// NLL region checking.
 811 struct TypeChecker<'a, 'tcx> {
 812     infcx: &'a InferCtxt<'a, 'tcx>,
 813     param_env: ty::ParamEnv<'tcx>,
 814     last_span: Span,
 815     body: &'a Body<'tcx>,
 816     /// User type annotations are shared between the main MIR and the MIR of
 817     /// all of the promoted items.
 818     user_type_annotations: &'a CanonicalUserTypeAnnotations<'tcx>,
 819     mir_def_id: LocalDefId,
 820     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
 821     implicit_region_bound: ty::Region<'tcx>,
 822     reported_errors: FxHashSet<(Ty<'tcx>, Span)>,
 823     borrowck_context: &'a mut BorrowCheckContext<'a, 'tcx>,
 824     universal_region_relations: &'a UniversalRegionRelations<'tcx>,
 825     opaque_type_values: FxHashMap<DefId, ty::ResolvedOpaqueTy<'tcx>>,
 826 }
 827
 828 struct BorrowCheckContext<'a, 'tcx> {
 829     universal_regions: &'a UniversalRegions<'tcx>,
 830     location_table: &'a LocationTable,
 831     all_facts: &'a mut Option<AllFacts>,
 832     borrow_set: &'a BorrowSet<'tcx>,
 833     constraints: &'a mut MirTypeckRegionConstraints<'tcx>,
 834     upvars: &'a [Upvar],
 835 }
 836
 837 crate struct MirTypeckResults<'tcx> {
 838     crate constraints: MirTypeckRegionConstraints<'tcx>,
 839     pub(in crate::borrow_check) universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
 840     crate opaque_type_values: FxHashMap<DefId, ty::ResolvedOpaqueTy<'tcx>>,
 841 }
 842
 843 /// A collection of region constraints that must be satisfied for the
 844 /// program to be considered well-typed.
 845 crate struct MirTypeckRegionConstraints<'tcx> {
 846     /// Maps from a `ty::Placeholder` to the corresponding
 847     /// `PlaceholderIndex` bit that we will use for it.
 848     ///
 849     /// To keep everything in sync, do not insert this set
 850     /// directly. Instead, use the `placeholder_region` helper.
 851     crate placeholder_indices: PlaceholderIndices,
 852
 853     /// Each time we add a placeholder to `placeholder_indices`, we
 854     /// also create a corresponding "representative" region vid for
 855     /// that wraps it. This vector tracks those. This way, when we
 856     /// convert the same `ty::RePlaceholder(p)` twice, we can map to
 857     /// the same underlying `RegionVid`.
 858     crate placeholder_index_to_region: IndexVec<PlaceholderIndex, ty::Region<'tcx>>,
 859
 860     /// In general, the type-checker is not responsible for enforcing
 861     /// liveness constraints; this job falls to the region inferencer,
 862     /// which performs a liveness analysis. However, in some limited
 863     /// cases, the MIR type-checker creates temporary regions that do
 864     /// not otherwise appear in the MIR -- in particular, the
 865     /// late-bound regions that it instantiates at call-sites -- and
 866     /// hence it must report on their liveness constraints.
 867     crate liveness_constraints: LivenessValues<RegionVid>,
 868
 869     crate outlives_constraints: OutlivesConstraintSet,
 870
 871     crate member_constraints: MemberConstraintSet<'tcx, RegionVid>,
 872
 873     crate closure_bounds_mapping:
 874         FxHashMap<Location, FxHashMap<(RegionVid, RegionVid), (ConstraintCategory, Span)>>,
 875
 876     crate type_tests: Vec<TypeTest<'tcx>>,
 877 }
 878
 879 impl MirTypeckRegionConstraints<'tcx> {
 880     fn placeholder_region(
 881         &mut self,
 882         infcx: &InferCtxt<'_, 'tcx>,
 883         placeholder: ty::PlaceholderRegion,
 884     ) -> ty::Region<'tcx> {
 885         let placeholder_index = self.placeholder_indices.insert(placeholder);
 886         match self.placeholder_index_to_region.get(placeholder_index) {
 887             Some(&v) => v,
 888             None => {
 889                 let origin = NLLRegionVariableOrigin::Placeholder(placeholder);
 890                 let region = infcx.next_nll_region_var_in_universe(origin, placeholder.universe);
 891                 self.placeholder_index_to_region.push(region);
 892                 region
 893             }
 894         }
 895     }
 896 }
 897
 898 /// The `Locations` type summarizes *where* region constraints are
 899 /// required to hold. Normally, this is at a particular point which
 900 /// created the obligation, but for constraints that the user gave, we
 901 /// want the constraint to hold at all points.
 902 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
 903 pub enum Locations {
 904     /// Indicates that a type constraint should always be true. This
 905     /// is particularly important in the new borrowck analysis for
 906     /// things like the type of the return slot. Consider this
 907     /// example:
 908     ///
 909     /// ```
 910     /// fn foo<'a>(x: &'a u32) -> &'a u32 {
 911     ///     let y = 22;
 912     ///     return &y; // error
 913     /// }
 914     /// ```
 915     ///
 916     /// Here, we wind up with the signature from the return type being
 917     /// something like `&'1 u32` where `'1` is a universal region. But
 918     /// the type of the return slot `_0` is something like `&'2 u32`
 919     /// where `'2` is an existential region variable. The type checker
 920     /// requires that `&'2 u32 = &'1 u32` -- but at what point? In the
 921     /// older NLL analysis, we required this only at the entry point
 922     /// to the function. By the nature of the constraints, this wound
 923     /// up propagating to all points reachable from start (because
 924     /// `'1` -- as a universal region -- is live everywhere). In the
 925     /// newer analysis, though, this doesn't work: `_0` is considered
 926     /// dead at the start (it has no usable value) and hence this type
 927     /// equality is basically a no-op. Then, later on, when we do `_0
 928     /// = &'3 y`, that region `'3` never winds up related to the
 929     /// universal region `'1` and hence no error occurs. Therefore, we
 930     /// use Locations::All instead, which ensures that the `'1` and
 931     /// `'2` are equal everything. We also use this for other
 932     /// user-given type annotations; e.g., if the user wrote `let mut
 933     /// x: &'static u32 = ...`, we would ensure that all values
 934     /// assigned to `x` are of `'static` lifetime.
 935     ///
 936     /// The span points to the place the constraint arose. For example,
 937     /// it points to the type in a user-given type annotation. If
 938     /// there's no sensible span then it's DUMMY_SP.
 939     All(Span),
 940
 941     /// An outlives constraint that only has to hold at a single location,
 942     /// usually it represents a point where references flow from one spot to
 943     /// another (e.g., `x = y`)
 944     Single(Location),
 945 }
 946
 947 impl Locations {
 948     pub fn from_location(&self) -> Option<Location> {
 949         match self {
 950             Locations::All(_) => None,
 951             Locations::Single(from_location) => Some(*from_location),
 952         }
 953     }
 954
 955     /// Gets a span representing the location.
 956     pub fn span(&self, body: &Body<'_>) -> Span {
 957         match self {
 958             Locations::All(span) => *span,
 959             Locations::Single(l) => body.source_info(*l).span,
 960         }
 961     }
 962 }
 963
 964 impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
 965     fn new(
 966         infcx: &'a InferCtxt<'a, 'tcx>,
 967         body: &'a Body<'tcx>,
 968         mir_def_id: LocalDefId,
 969         param_env: ty::ParamEnv<'tcx>,
 970         region_bound_pairs: &'a RegionBoundPairs<'tcx>,
 971         implicit_region_bound: ty::Region<'tcx>,
 972         borrowck_context: &'a mut BorrowCheckContext<'a, 'tcx>,
 973         universal_region_relations: &'a UniversalRegionRelations<'tcx>,
 974     ) -> Self {
 975         let mut checker = Self {
 976             infcx,
 977             last_span: DUMMY_SP,
 978             mir_def_id,
 979             body,
 980             user_type_annotations: &body.user_type_annotations,
 981             param_env,
 982             region_bound_pairs,
 983             implicit_region_bound,
 984             borrowck_context,
 985             reported_errors: Default::default(),
 986             universal_region_relations,
 987             opaque_type_values: FxHashMap::default(),
 988         };
 989         checker.check_user_type_annotations();
 990         checker
 991     }
 992
 993     /// Equate the inferred type and the annotated type for user type annotations
 994     fn check_user_type_annotations(&mut self) {
 995         debug!(
 996             "check_user_type_annotations: user_type_annotations={:?}",
 997             self.user_type_annotations
 998         );
 999         for user_annotation in self.user_type_annotations {
1000             let CanonicalUserTypeAnnotation { span, ref user_ty, inferred_ty } = *user_annotation;
1001             let (annotation, _) =
1002                 self.infcx.instantiate_canonical_with_fresh_inference_vars(span, user_ty);
1003             match annotation {
1004                 UserType::Ty(mut ty) => {
1005                     ty = self.normalize(ty, Locations::All(span));
1006
1007                     if let Err(terr) = self.eq_types(
1008                         ty,
1009                         inferred_ty,
1010                         Locations::All(span),
1011                         ConstraintCategory::BoringNoLocation,
1012                     ) {
1013                         span_mirbug!(
1014                             self,
1015                             user_annotation,
1016                             "bad user type ({:?} = {:?}): {:?}",
1017                             ty,
1018                             inferred_ty,
1019                             terr
1020                         );
1021                     }
1022
1023                     self.prove_predicate(
1024                         ty::PredicateAtom::WellFormed(inferred_ty.into()).to_predicate(self.tcx()),
1025                         Locations::All(span),
1026                         ConstraintCategory::TypeAnnotation,
1027                     );
1028                 }
1029                 UserType::TypeOf(def_id, user_substs) => {
1030                     if let Err(terr) = self.fully_perform_op(
1031                         Locations::All(span),
1032                         ConstraintCategory::BoringNoLocation,
1033                         self.param_env.and(type_op::ascribe_user_type::AscribeUserType::new(
1034                             inferred_ty,
1035                             def_id,
1036                             user_substs,
1037                         )),
1038                     ) {
1039                         span_mirbug!(
1040                             self,
1041                             user_annotation,
1042                             "bad user type AscribeUserType({:?}, {:?} {:?}): {:?}",
1043                             inferred_ty,
1044                             def_id,
1045                             user_substs,
1046                             terr
1047                         );
1048                     }
1049                 }
1050             }
1051         }
1052     }
1053
1054     /// Given some operation `op` that manipulates types, proves
1055     /// predicates, or otherwise uses the inference context, executes
1056     /// `op` and then executes all the further obligations that `op`
1057     /// returns. This will yield a set of outlives constraints amongst
1058     /// regions which are extracted and stored as having occurred at
1059     /// `locations`.
1060     ///
1061     /// **Any `rustc_infer::infer` operations that might generate region
1062     /// constraints should occur within this method so that those
1063     /// constraints can be properly localized!**
1064     fn fully_perform_op<R>(
1065         &mut self,
1066         locations: Locations,
1067         category: ConstraintCategory,
1068         op: impl type_op::TypeOp<'tcx, Output = R>,
1069     ) -> Fallible<R> {
1070         let (r, opt_data) = op.fully_perform(self.infcx)?;
1071
1072         if let Some(data) = &opt_data {
1073             self.push_region_constraints(locations, category, data);
1074         }
1075
1076         Ok(r)
1077     }
1078
1079     fn push_region_constraints(
1080         &mut self,
1081         locations: Locations,
1082         category: ConstraintCategory,
1083         data: &QueryRegionConstraints<'tcx>,
1084     ) {
1085         debug!("push_region_constraints: constraints generated at {:?} are {:#?}", locations, data);
1086
1087         constraint_conversion::ConstraintConversion::new(
1088             self.infcx,
1089             self.borrowck_context.universal_regions,
1090             self.region_bound_pairs,
1091             Some(self.implicit_region_bound),
1092             self.param_env,
1093             locations,
1094             category,
1095             &mut self.borrowck_context.constraints,
1096         )
1097         .convert_all(data);
1098     }
1099
1100     /// Convenient wrapper around `relate_tys::relate_types` -- see
1101     /// that fn for docs.
1102     fn relate_types(
1103         &mut self,
1104         a: Ty<'tcx>,
1105         v: ty::Variance,
1106         b: Ty<'tcx>,
1107         locations: Locations,
1108         category: ConstraintCategory,
1109     ) -> Fallible<()> {
1110         relate_tys::relate_types(
1111             self.infcx,
1112             a,
1113             v,
1114             b,
1115             locations,
1116             category,
1117             Some(self.borrowck_context),
1118         )
1119     }
1120
1121     fn sub_types(
1122         &mut self,
1123         sub: Ty<'tcx>,
1124         sup: Ty<'tcx>,
1125         locations: Locations,
1126         category: ConstraintCategory,
1127     ) -> Fallible<()> {
1128         self.relate_types(sub, ty::Variance::Covariant, sup, locations, category)
1129     }
1130
1131     /// Try to relate `sub <: sup`; if this fails, instantiate opaque
1132     /// variables in `sub` with their inferred definitions and try
1133     /// again. This is used for opaque types in places (e.g., `let x:
1134     /// impl Foo = ..`).
1135     fn sub_types_or_anon(
1136         &mut self,
1137         sub: Ty<'tcx>,
1138         sup: Ty<'tcx>,
1139         locations: Locations,
1140         category: ConstraintCategory,
1141     ) -> Fallible<()> {
1142         if let Err(terr) = self.sub_types(sub, sup, locations, category) {
1143             if let ty::Opaque(..) = sup.kind {
1144                 // When you have `let x: impl Foo = ...` in a closure,
1145                 // the resulting inferend values are stored with the
1146                 // def-id of the base function.
1147                 let parent_def_id =
1148                     self.tcx().closure_base_def_id(self.mir_def_id.to_def_id()).expect_local();
1149                 return self.eq_opaque_type_and_type(sub, sup, parent_def_id, locations, category);
1150             } else {
1151                 return Err(terr);
1152             }
1153         }
1154         Ok(())
1155     }
1156
1157     fn eq_types(
1158         &mut self,
1159         a: Ty<'tcx>,
1160         b: Ty<'tcx>,
1161         locations: Locations,
1162         category: ConstraintCategory,
1163     ) -> Fallible<()> {
1164         self.relate_types(a, ty::Variance::Invariant, b, locations, category)
1165     }
1166
1167     fn relate_type_and_user_type(
1168         &mut self,
1169         a: Ty<'tcx>,
1170         v: ty::Variance,
1171         user_ty: &UserTypeProjection,
1172         locations: Locations,
1173         category: ConstraintCategory,
1174     ) -> Fallible<()> {
1175         debug!(
1176             "relate_type_and_user_type(a={:?}, v={:?}, user_ty={:?}, locations={:?})",
1177             a, v, user_ty, locations,
1178         );
1179
1180         let annotated_type = self.user_type_annotations[user_ty.base].inferred_ty;
1181         let mut curr_projected_ty = PlaceTy::from_ty(annotated_type);
1182
1183         let tcx = self.infcx.tcx;
1184
1185         for proj in &user_ty.projs {
1186             let projected_ty = curr_projected_ty.projection_ty_core(
1187                 tcx,
1188                 self.param_env,
1189                 proj,
1190                 |this, field, &()| {
1191                     let ty = this.field_ty(tcx, field);
1192                     self.normalize(ty, locations)
1193                 },
1194             );
1195             curr_projected_ty = projected_ty;
1196         }
1197         debug!(
1198             "user_ty base: {:?} freshened: {:?} projs: {:?} yields: {:?}",
1199             user_ty.base, annotated_type, user_ty.projs, curr_projected_ty
1200         );
1201
1202         let ty = curr_projected_ty.ty;
1203         self.relate_types(a, v, ty, locations, category)?;
1204
1205         Ok(())
1206     }
1207
1208     fn eq_opaque_type_and_type(
1209         &mut self,
1210         revealed_ty: Ty<'tcx>,
1211         anon_ty: Ty<'tcx>,
1212         anon_owner_def_id: LocalDefId,
1213         locations: Locations,
1214         category: ConstraintCategory,
1215     ) -> Fallible<()> {
1216         debug!(
1217             "eq_opaque_type_and_type( \
1218              revealed_ty={:?}, \
1219              anon_ty={:?})",
1220             revealed_ty, anon_ty
1221         );
1222
1223         // Fast path for the common case.
1224         if !anon_ty.has_opaque_types() {
1225             if let Err(terr) = self.eq_types(anon_ty, revealed_ty, locations, category) {
1226                 span_mirbug!(
1227                     self,
1228                     locations,
1229                     "eq_opaque_type_and_type: `{:?}=={:?}` failed with `{:?}`",
1230                     revealed_ty,
1231                     anon_ty,
1232                     terr
1233                 );
1234             }
1235             return Ok(());
1236         }
1237
1238         let infcx = self.infcx;
1239         let tcx = infcx.tcx;
1240         let param_env = self.param_env;
1241         let body = self.body;
1242         let concrete_opaque_types = &tcx.typeck(anon_owner_def_id).concrete_opaque_types;
1243         let mut opaque_type_values = Vec::new();
1244
1245         debug!("eq_opaque_type_and_type: mir_def_id={:?}", self.mir_def_id);
1246         let opaque_type_map = self.fully_perform_op(
1247             locations,
1248             category,
1249             CustomTypeOp::new(
1250                 |infcx| {
1251                     let mut obligations = ObligationAccumulator::default();
1252
1253                     let dummy_body_id = hir::CRATE_HIR_ID;
1254                     let (output_ty, opaque_type_map) =
1255                         obligations.add(infcx.instantiate_opaque_types(
1256                             anon_owner_def_id,
1257                             dummy_body_id,
1258                             param_env,
1259                             &anon_ty,
1260                             locations.span(body),
1261                         ));
1262                     debug!(
1263                         "eq_opaque_type_and_type: \
1264                          instantiated output_ty={:?} \
1265                          opaque_type_map={:#?} \
1266                          revealed_ty={:?}",
1267                         output_ty, opaque_type_map, revealed_ty
1268                     );
1269                     // Make sure that the inferred types are well-formed. I'm
1270                     // not entirely sure this is needed (the HIR type check
1271                     // didn't do this) but it seems sensible to prevent opaque
1272                     // types hiding ill-formed types.
1273                     obligations.obligations.push(traits::Obligation::new(
1274                         ObligationCause::dummy(),
1275                         param_env,
1276                         ty::PredicateAtom::WellFormed(revealed_ty.into()).to_predicate(infcx.tcx),
1277                     ));
1278                     obligations.add(
1279                         infcx
1280                             .at(&ObligationCause::dummy(), param_env)
1281                             .eq(output_ty, revealed_ty)?,
1282                     );
1283
1284                     for (&opaque_def_id, opaque_decl) in &opaque_type_map {
1285                         let resolved_ty = infcx.resolve_vars_if_possible(&opaque_decl.concrete_ty);
1286                         let concrete_is_opaque = if let ty::Opaque(def_id, _) = resolved_ty.kind {
1287                             def_id == opaque_def_id
1288                         } else {
1289                             false
1290                         };
1291                         let opaque_defn_ty = match concrete_opaque_types.get(&opaque_def_id) {
1292                             None => {
1293                                 if !concrete_is_opaque {
1294                                     tcx.sess.delay_span_bug(
1295                                         body.span,
1296                                         &format!(
1297                                             "Non-defining use of {:?} with revealed type",
1298                                             opaque_def_id,
1299                                         ),
1300                                     );
1301                                 }
1302                                 continue;
1303                             }
1304                             Some(opaque_defn_ty) => opaque_defn_ty,
1305                         };
1306                         debug!("opaque_defn_ty = {:?}", opaque_defn_ty);
1307                         let subst_opaque_defn_ty =
1308                             opaque_defn_ty.concrete_type.subst(tcx, opaque_decl.substs);
1309                         let renumbered_opaque_defn_ty =
1310                             renumber::renumber_regions(infcx, &subst_opaque_defn_ty);
1311
1312                         debug!(
1313                             "eq_opaque_type_and_type: concrete_ty={:?}={:?} opaque_defn_ty={:?}",
1314                             opaque_decl.concrete_ty, resolved_ty, renumbered_opaque_defn_ty,
1315                         );
1316
1317                         if !concrete_is_opaque {
1318                             // Equate concrete_ty (an inference variable) with
1319                             // the renumbered type from typeck.
1320                             obligations.add(
1321                                 infcx
1322                                     .at(&ObligationCause::dummy(), param_env)
1323                                     .eq(opaque_decl.concrete_ty, renumbered_opaque_defn_ty)?,
1324                             );
1325                             opaque_type_values.push((
1326                                 opaque_def_id,
1327                                 ty::ResolvedOpaqueTy {
1328                                     concrete_type: renumbered_opaque_defn_ty,
1329                                     substs: opaque_decl.substs,
1330                                 },
1331                             ));
1332                         } else {
1333                             // We're using an opaque `impl Trait` type without
1334                             // 'revealing' it. For example, code like this:
1335                             //
1336                             // type Foo = impl Debug;
1337                             // fn foo1() -> Foo { ... }
1338                             // fn foo2() -> Foo { foo1() }
1339                             //
1340                             // In `foo2`, we're not revealing the type of `Foo` - we're
1341                             // just treating it as the opaque type.
1342                             //
1343                             // When this occurs, we do *not* want to try to equate
1344                             // the concrete type with the underlying defining type
1345                             // of the opaque type - this will always fail, since
1346                             // the defining type of an opaque type is always
1347                             // some other type (e.g. not itself)
1348                             // Essentially, none of the normal obligations apply here -
1349                             // we're just passing around some unknown opaque type,
1350                             // without actually looking at the underlying type it
1351                             // gets 'revealed' into
1352                             debug!(
1353                                 "eq_opaque_type_and_type: non-defining use of {:?}",
1354                                 opaque_def_id,
1355                             );
1356                         }
1357                     }
1358
1359                     debug!("eq_opaque_type_and_type: equated");
1360
1361                     Ok(InferOk {
1362                         value: Some(opaque_type_map),
1363                         obligations: obligations.into_vec(),
1364                     })
1365                 },
1366                 || "input_output".to_string(),
1367             ),
1368         )?;
1369
1370         self.opaque_type_values.extend(opaque_type_values);
1371
1372         let universal_region_relations = self.universal_region_relations;
1373
1374         // Finally, if we instantiated the anon types successfully, we
1375         // have to solve any bounds (e.g., `-> impl Iterator` needs to
1376         // prove that `T: Iterator` where `T` is the type we
1377         // instantiated it with).
1378         if let Some(opaque_type_map) = opaque_type_map {
1379             for (opaque_def_id, opaque_decl) in opaque_type_map {
1380                 self.fully_perform_op(
1381                     locations,
1382                     ConstraintCategory::OpaqueType,
1383                     CustomTypeOp::new(
1384                         |_cx| {
1385                             infcx.constrain_opaque_type(
1386                                 opaque_def_id,
1387                                 &opaque_decl,
1388                                 GenerateMemberConstraints::IfNoStaticBound,
1389                                 universal_region_relations,
1390                             );
1391                             Ok(InferOk { value: (), obligations: vec![] })
1392                         },
1393                         || "opaque_type_map".to_string(),
1394                     ),
1395                 )?;
1396             }
1397         }
1398         Ok(())
1399     }
1400
1401     fn tcx(&self) -> TyCtxt<'tcx> {
1402         self.infcx.tcx
1403     }
1404
1405     fn check_stmt(&mut self, body: &Body<'tcx>, stmt: &Statement<'tcx>, location: Location) {
1406         debug!("check_stmt: {:?}", stmt);
1407         let tcx = self.tcx();
1408         match stmt.kind {
1409             StatementKind::Assign(box (ref place, ref rv)) => {
1410                 // Assignments to temporaries are not "interesting";
1411                 // they are not caused by the user, but rather artifacts
1412                 // of lowering. Assignments to other sorts of places *are* interesting
1413                 // though.
1414                 let category = match place.as_local() {
1415                     Some(RETURN_PLACE) => {
1416                         if let BorrowCheckContext {
1417                             universal_regions:
1418                                 UniversalRegions { defining_ty: DefiningTy::Const(def_id, _), .. },
1419                             ..
1420                         } = self.borrowck_context
1421                         {
1422                             if tcx.is_static(*def_id) {
1423                                 ConstraintCategory::UseAsStatic
1424                             } else {
1425                                 ConstraintCategory::UseAsConst
1426                             }
1427                         } else {
1428                             ConstraintCategory::Return(ReturnConstraint::Normal)
1429                         }
1430                     }
1431                     Some(l) if !body.local_decls[l].is_user_variable() => {
1432                         ConstraintCategory::Boring
1433                     }
1434                     _ => ConstraintCategory::Assignment,
1435                 };
1436
1437                 let place_ty = place.ty(body, tcx).ty;
1438                 let place_ty = self.normalize(place_ty, location);
1439                 let rv_ty = rv.ty(body, tcx);
1440                 let rv_ty = self.normalize(rv_ty, location);
1441                 if let Err(terr) =
1442                     self.sub_types_or_anon(rv_ty, place_ty, location.to_locations(), category)
1443                 {
1444                     span_mirbug!(
1445                         self,
1446                         stmt,
1447                         "bad assignment ({:?} = {:?}): {:?}",
1448                         place_ty,
1449                         rv_ty,
1450                         terr
1451                     );
1452                 }
1453
1454                 if let Some(annotation_index) = self.rvalue_user_ty(rv) {
1455                     if let Err(terr) = self.relate_type_and_user_type(
1456                         rv_ty,
1457                         ty::Variance::Invariant,
1458                         &UserTypeProjection { base: annotation_index, projs: vec![] },
1459                         location.to_locations(),
1460                         ConstraintCategory::Boring,
1461                     ) {
1462                         let annotation = &self.user_type_annotations[annotation_index];
1463                         span_mirbug!(
1464                             self,
1465                             stmt,
1466                             "bad user type on rvalue ({:?} = {:?}): {:?}",
1467                             annotation,
1468                             rv_ty,
1469                             terr
1470                         );
1471                     }
1472                 }
1473
1474                 self.check_rvalue(body, rv, location);
1475                 if !self.tcx().features().unsized_locals {
1476                     let trait_ref = ty::TraitRef {
1477                         def_id: tcx.require_lang_item(LangItem::Sized, Some(self.last_span)),
1478                         substs: tcx.mk_substs_trait(place_ty, &[]),
1479                     };
1480                     self.prove_trait_ref(
1481                         trait_ref,
1482                         location.to_locations(),
1483                         ConstraintCategory::SizedBound,
1484                     );
1485                 }
1486             }
1487             StatementKind::SetDiscriminant { ref place, variant_index } => {
1488                 let place_type = place.ty(body, tcx).ty;
1489                 let adt = match place_type.kind {
1490                     ty::Adt(adt, _) if adt.is_enum() => adt,
1491                     _ => {
1492                         span_bug!(
1493                             stmt.source_info.span,
1494                             "bad set discriminant ({:?} = {:?}): lhs is not an enum",
1495                             place,
1496                             variant_index
1497                         );
1498                     }
1499                 };
1500                 if variant_index.as_usize() >= adt.variants.len() {
1501                     span_bug!(
1502                         stmt.source_info.span,
1503                         "bad set discriminant ({:?} = {:?}): value of of range",
1504                         place,
1505                         variant_index
1506                     );
1507                 };
1508             }
1509             StatementKind::AscribeUserType(box (ref place, ref projection), variance) => {
1510                 let place_ty = place.ty(body, tcx).ty;
1511                 if let Err(terr) = self.relate_type_and_user_type(
1512                     place_ty,
1513                     variance,
1514                     projection,
1515                     Locations::All(stmt.source_info.span),
1516                     ConstraintCategory::TypeAnnotation,
1517                 ) {
1518                     let annotation = &self.user_type_annotations[projection.base];
1519                     span_mirbug!(
1520                         self,
1521                         stmt,
1522                         "bad type assert ({:?} <: {:?} with projections {:?}): {:?}",
1523                         place_ty,
1524                         annotation,
1525                         projection.projs,
1526                         terr
1527                     );
1528                 }
1529             }
1530             StatementKind::FakeRead(..)
1531             | StatementKind::StorageLive(..)
1532             | StatementKind::StorageDead(..)
1533             | StatementKind::LlvmInlineAsm { .. }
1534             | StatementKind::Retag { .. }
1535             | StatementKind::Coverage(..)
1536             | StatementKind::Nop => {}
1537         }
1538     }
1539
1540     fn check_terminator(
1541         &mut self,
1542         body: &Body<'tcx>,
1543         term: &Terminator<'tcx>,
1544         term_location: Location,
1545     ) {
1546         debug!("check_terminator: {:?}", term);
1547         let tcx = self.tcx();
1548         match term.kind {
1549             TerminatorKind::Goto { .. }
1550             | TerminatorKind::Resume
1551             | TerminatorKind::Abort
1552             | TerminatorKind::Return
1553             | TerminatorKind::GeneratorDrop
1554             | TerminatorKind::Unreachable
1555             | TerminatorKind::Drop { .. }
1556             | TerminatorKind::FalseEdge { .. }
1557             | TerminatorKind::FalseUnwind { .. }
1558             | TerminatorKind::InlineAsm { .. } => {
1559                 // no checks needed for these
1560             }
1561
1562             TerminatorKind::DropAndReplace { ref place, ref value, target: _, unwind: _ } => {
1563                 let place_ty = place.ty(body, tcx).ty;
1564                 let rv_ty = value.ty(body, tcx);
1565
1566                 let locations = term_location.to_locations();
1567                 if let Err(terr) =
1568                     self.sub_types(rv_ty, place_ty, locations, ConstraintCategory::Assignment)
1569                 {
1570                     span_mirbug!(
1571                         self,
1572                         term,
1573                         "bad DropAndReplace ({:?} = {:?}): {:?}",
1574                         place_ty,
1575                         rv_ty,
1576                         terr
1577                     );
1578                 }
1579             }
1580             TerminatorKind::SwitchInt { ref discr, switch_ty, .. } => {
1581                 let discr_ty = discr.ty(body, tcx);
1582                 if let Err(terr) = self.sub_types(
1583                     discr_ty,
1584                     switch_ty,
1585                     term_location.to_locations(),
1586                     ConstraintCategory::Assignment,
1587                 ) {
1588                     span_mirbug!(
1589                         self,
1590                         term,
1591                         "bad SwitchInt ({:?} on {:?}): {:?}",
1592                         switch_ty,
1593                         discr_ty,
1594                         terr
1595                     );
1596                 }
1597                 if !switch_ty.is_integral() && !switch_ty.is_char() && !switch_ty.is_bool() {
1598                     span_mirbug!(self, term, "bad SwitchInt discr ty {:?}", switch_ty);
1599                 }
1600                 // FIXME: check the values
1601             }
1602             TerminatorKind::Call { ref func, ref args, ref destination, from_hir_call, .. } => {
1603                 let func_ty = func.ty(body, tcx);
1604                 debug!("check_terminator: call, func_ty={:?}", func_ty);
1605                 let sig = match func_ty.kind {
1606                     ty::FnDef(..) | ty::FnPtr(_) => func_ty.fn_sig(tcx),
1607                     _ => {
1608                         span_mirbug!(self, term, "call to non-function {:?}", func_ty);
1609                         return;
1610                     }
1611                 };
1612                 let (sig, map) = self.infcx.replace_bound_vars_with_fresh_vars(
1613                     term.source_info.span,
1614                     LateBoundRegionConversionTime::FnCall,
1615                     &sig,
1616                 );
1617                 let sig = self.normalize(sig, term_location);
1618                 self.check_call_dest(body, term, &sig, destination, term_location);
1619
1620                 self.prove_predicates(
1621                     sig.inputs_and_output.iter().map(|ty| ty::PredicateAtom::WellFormed(ty.into())),
1622                     term_location.to_locations(),
1623                     ConstraintCategory::Boring,
1624                 );
1625
1626                 // The ordinary liveness rules will ensure that all
1627                 // regions in the type of the callee are live here. We
1628                 // then further constrain the late-bound regions that
1629                 // were instantiated at the call site to be live as
1630                 // well. The resulting is that all the input (and
1631                 // output) types in the signature must be live, since
1632                 // all the inputs that fed into it were live.
1633                 for &late_bound_region in map.values() {
1634                     let region_vid =
1635                         self.borrowck_context.universal_regions.to_region_vid(late_bound_region);
1636                     self.borrowck_context
1637                         .constraints
1638                         .liveness_constraints
1639                         .add_element(region_vid, term_location);
1640                 }
1641
1642                 self.check_call_inputs(body, term, &sig, args, term_location, from_hir_call);
1643             }
1644             TerminatorKind::Assert { ref cond, ref msg, .. } => {
1645                 let cond_ty = cond.ty(body, tcx);
1646                 if cond_ty != tcx.types.bool {
1647                     span_mirbug!(self, term, "bad Assert ({:?}, not bool", cond_ty);
1648                 }
1649
1650                 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
1651                     if len.ty(body, tcx) != tcx.types.usize {
1652                         span_mirbug!(self, len, "bounds-check length non-usize {:?}", len)
1653                     }
1654                     if index.ty(body, tcx) != tcx.types.usize {
1655                         span_mirbug!(self, index, "bounds-check index non-usize {:?}", index)
1656                     }
1657                 }
1658             }
1659             TerminatorKind::Yield { ref value, .. } => {
1660                 let value_ty = value.ty(body, tcx);
1661                 match body.yield_ty {
1662                     None => span_mirbug!(self, term, "yield in non-generator"),
1663                     Some(ty) => {
1664                         if let Err(terr) = self.sub_types(
1665                             value_ty,
1666                             ty,
1667                             term_location.to_locations(),
1668                             ConstraintCategory::Yield,
1669                         ) {
1670                             span_mirbug!(
1671                                 self,
1672                                 term,
1673                                 "type of yield value is {:?}, but the yield type is {:?}: {:?}",
1674                                 value_ty,
1675                                 ty,
1676                                 terr
1677                             );
1678                         }
1679                     }
1680                 }
1681             }
1682         }
1683     }
1684
1685     fn check_call_dest(
1686         &mut self,
1687         body: &Body<'tcx>,
1688         term: &Terminator<'tcx>,
1689         sig: &ty::FnSig<'tcx>,
1690         destination: &Option<(Place<'tcx>, BasicBlock)>,
1691         term_location: Location,
1692     ) {
1693         let tcx = self.tcx();
1694         match *destination {
1695             Some((ref dest, _target_block)) => {
1696                 let dest_ty = dest.ty(body, tcx).ty;
1697                 let dest_ty = self.normalize(dest_ty, term_location);
1698                 let category = match dest.as_local() {
1699                     Some(RETURN_PLACE) => {
1700                         if let BorrowCheckContext {
1701                             universal_regions:
1702                                 UniversalRegions { defining_ty: DefiningTy::Const(def_id, _), .. },
1703                             ..
1704                         } = self.borrowck_context
1705                         {
1706                             if tcx.is_static(*def_id) {
1707                                 ConstraintCategory::UseAsStatic
1708                             } else {
1709                                 ConstraintCategory::UseAsConst
1710                             }
1711                         } else {
1712                             ConstraintCategory::Return(ReturnConstraint::Normal)
1713                         }
1714                     }
1715                     Some(l) if !body.local_decls[l].is_user_variable() => {
1716                         ConstraintCategory::Boring
1717                     }
1718                     _ => ConstraintCategory::Assignment,
1719                 };
1720
1721                 let locations = term_location.to_locations();
1722
1723                 if let Err(terr) =
1724                     self.sub_types_or_anon(sig.output(), dest_ty, locations, category)
1725                 {
1726                     span_mirbug!(
1727                         self,
1728                         term,
1729                         "call dest mismatch ({:?} <- {:?}): {:?}",
1730                         dest_ty,
1731                         sig.output(),
1732                         terr
1733                     );
1734                 }
1735
1736                 // When `#![feature(unsized_locals)]` is not enabled,
1737                 // this check is done at `check_local`.
1738                 if self.tcx().features().unsized_locals {
1739                     let span = term.source_info.span;
1740                     self.ensure_place_sized(dest_ty, span);
1741                 }
1742             }
1743             None => {
1744                 if !sig.output().conservative_is_privately_uninhabited(self.tcx()) {
1745                     span_mirbug!(self, term, "call to converging function {:?} w/o dest", sig);
1746                 }
1747             }
1748         }
1749     }
1750
1751     fn check_call_inputs(
1752         &mut self,
1753         body: &Body<'tcx>,
1754         term: &Terminator<'tcx>,
1755         sig: &ty::FnSig<'tcx>,
1756         args: &[Operand<'tcx>],
1757         term_location: Location,
1758         from_hir_call: bool,
1759     ) {
1760         debug!("check_call_inputs({:?}, {:?})", sig, args);
1761         if args.len() < sig.inputs().len() || (args.len() > sig.inputs().len() && !sig.c_variadic) {
1762             span_mirbug!(self, term, "call to {:?} with wrong # of args", sig);
1763         }
1764         for (n, (fn_arg, op_arg)) in sig.inputs().iter().zip(args).enumerate() {
1765             let op_arg_ty = op_arg.ty(body, self.tcx());
1766             let op_arg_ty = self.normalize(op_arg_ty, term_location);
1767             let category = if from_hir_call {
1768                 ConstraintCategory::CallArgument
1769             } else {
1770                 ConstraintCategory::Boring
1771             };
1772             if let Err(terr) =
1773                 self.sub_types(op_arg_ty, fn_arg, term_location.to_locations(), category)
1774             {
1775                 span_mirbug!(
1776                     self,
1777                     term,
1778                     "bad arg #{:?} ({:?} <- {:?}): {:?}",
1779                     n,
1780                     fn_arg,
1781                     op_arg_ty,
1782                     terr
1783                 );
1784             }
1785         }
1786     }
1787
1788     fn check_iscleanup(&mut self, body: &Body<'tcx>, block_data: &BasicBlockData<'tcx>) {
1789         let is_cleanup = block_data.is_cleanup;
1790         self.last_span = block_data.terminator().source_info.span;
1791         match block_data.terminator().kind {
1792             TerminatorKind::Goto { target } => {
1793                 self.assert_iscleanup(body, block_data, target, is_cleanup)
1794             }
1795             TerminatorKind::SwitchInt { ref targets, .. } => {
1796                 for target in targets {
1797                     self.assert_iscleanup(body, block_data, *target, is_cleanup);
1798                 }
1799             }
1800             TerminatorKind::Resume => {
1801                 if !is_cleanup {
1802                     span_mirbug!(self, block_data, "resume on non-cleanup block!")
1803                 }
1804             }
1805             TerminatorKind::Abort => {
1806                 if !is_cleanup {
1807                     span_mirbug!(self, block_data, "abort on non-cleanup block!")
1808                 }
1809             }
1810             TerminatorKind::Return => {
1811                 if is_cleanup {
1812                     span_mirbug!(self, block_data, "return on cleanup block")
1813                 }
1814             }
1815             TerminatorKind::GeneratorDrop { .. } => {
1816                 if is_cleanup {
1817                     span_mirbug!(self, block_data, "generator_drop in cleanup block")
1818                 }
1819             }
1820             TerminatorKind::Yield { resume, drop, .. } => {
1821                 if is_cleanup {
1822                     span_mirbug!(self, block_data, "yield in cleanup block")
1823                 }
1824                 self.assert_iscleanup(body, block_data, resume, is_cleanup);
1825                 if let Some(drop) = drop {
1826                     self.assert_iscleanup(body, block_data, drop, is_cleanup);
1827                 }
1828             }
1829             TerminatorKind::Unreachable => {}
1830             TerminatorKind::Drop { target, unwind, .. }
1831             | TerminatorKind::DropAndReplace { target, unwind, .. }
1832             | TerminatorKind::Assert { target, cleanup: unwind, .. } => {
1833                 self.assert_iscleanup(body, block_data, target, is_cleanup);
1834                 if let Some(unwind) = unwind {
1835                     if is_cleanup {
1836                         span_mirbug!(self, block_data, "unwind on cleanup block")
1837                     }
1838                     self.assert_iscleanup(body, block_data, unwind, true);
1839                 }
1840             }
1841             TerminatorKind::Call { ref destination, cleanup, .. } => {
1842                 if let &Some((_, target)) = destination {
1843                     self.assert_iscleanup(body, block_data, target, is_cleanup);
1844                 }
1845                 if let Some(cleanup) = cleanup {
1846                     if is_cleanup {
1847                         span_mirbug!(self, block_data, "cleanup on cleanup block")
1848                     }
1849                     self.assert_iscleanup(body, block_data, cleanup, true);
1850                 }
1851             }
1852             TerminatorKind::FalseEdge { real_target, imaginary_target } => {
1853                 self.assert_iscleanup(body, block_data, real_target, is_cleanup);
1854                 self.assert_iscleanup(body, block_data, imaginary_target, is_cleanup);
1855             }
1856             TerminatorKind::FalseUnwind { real_target, unwind } => {
1857                 self.assert_iscleanup(body, block_data, real_target, is_cleanup);
1858                 if let Some(unwind) = unwind {
1859                     if is_cleanup {
1860                         span_mirbug!(self, block_data, "cleanup in cleanup block via false unwind");
1861                     }
1862                     self.assert_iscleanup(body, block_data, unwind, true);
1863                 }
1864             }
1865             TerminatorKind::InlineAsm { ref destination, .. } => {
1866                 if let &Some(target) = destination {
1867                     self.assert_iscleanup(body, block_data, target, is_cleanup);
1868                 }
1869             }
1870         }
1871     }
1872
1873     fn assert_iscleanup(
1874         &mut self,
1875         body: &Body<'tcx>,
1876         ctxt: &dyn fmt::Debug,
1877         bb: BasicBlock,
1878         iscleanuppad: bool,
1879     ) {
1880         if body[bb].is_cleanup != iscleanuppad {
1881             span_mirbug!(self, ctxt, "cleanuppad mismatch: {:?} should be {:?}", bb, iscleanuppad);
1882         }
1883     }
1884
1885     fn check_local(&mut self, body: &Body<'tcx>, local: Local, local_decl: &LocalDecl<'tcx>) {
1886         match body.local_kind(local) {
1887             LocalKind::ReturnPointer | LocalKind::Arg => {
1888                 // return values of normal functions are required to be
1889                 // sized by typeck, but return values of ADT constructors are
1890                 // not because we don't include a `Self: Sized` bounds on them.
1891                 //
1892                 // Unbound parts of arguments were never required to be Sized
1893                 // - maybe we should make that a warning.
1894                 return;
1895             }
1896             LocalKind::Var | LocalKind::Temp => {}
1897         }
1898
1899         // When `#![feature(unsized_locals)]` is enabled, only function calls
1900         // and nullary ops are checked in `check_call_dest`.
1901         if !self.tcx().features().unsized_locals {
1902             let span = local_decl.source_info.span;
1903             let ty = local_decl.ty;
1904             self.ensure_place_sized(ty, span);
1905         }
1906     }
1907
1908     fn ensure_place_sized(&mut self, ty: Ty<'tcx>, span: Span) {
1909         let tcx = self.tcx();
1910
1911         // Erase the regions from `ty` to get a global type.  The
1912         // `Sized` bound in no way depends on precise regions, so this
1913         // shouldn't affect `is_sized`.
1914         let erased_ty = tcx.erase_regions(&ty);
1915         if !erased_ty.is_sized(tcx.at(span), self.param_env) {
1916             // in current MIR construction, all non-control-flow rvalue
1917             // expressions evaluate through `as_temp` or `into` a return
1918             // slot or local, so to find all unsized rvalues it is enough
1919             // to check all temps, return slots and locals.
1920             if self.reported_errors.replace((ty, span)).is_none() {
1921                 let mut diag = struct_span_err!(
1922                     self.tcx().sess,
1923                     span,
1924                     E0161,
1925                     "cannot move a value of type {0}: the size of {0} \
1926                      cannot be statically determined",
1927                     ty
1928                 );
1929
1930                 // While this is located in `nll::typeck` this error is not
1931                 // an NLL error, it's a required check to prevent creation
1932                 // of unsized rvalues in certain cases:
1933                 // * operand of a box expression
1934                 // * callee in a call expression
1935                 diag.emit();
1936             }
1937         }
1938     }
1939
1940     fn aggregate_field_ty(
1941         &mut self,
1942         ak: &AggregateKind<'tcx>,
1943         field_index: usize,
1944         location: Location,
1945     ) -> Result<Ty<'tcx>, FieldAccessError> {
1946         let tcx = self.tcx();
1947
1948         match *ak {
1949             AggregateKind::Adt(def, variant_index, substs, _, active_field_index) => {
1950                 let variant = &def.variants[variant_index];
1951                 let adj_field_index = active_field_index.unwrap_or(field_index);
1952                 if let Some(field) = variant.fields.get(adj_field_index) {
1953                     Ok(self.normalize(field.ty(tcx, substs), location))
1954                 } else {
1955                     Err(FieldAccessError::OutOfRange { field_count: variant.fields.len() })
1956                 }
1957             }
1958             AggregateKind::Closure(_, substs) => {
1959                 match substs.as_closure().upvar_tys().nth(field_index) {
1960                     Some(ty) => Ok(ty),
1961                     None => Err(FieldAccessError::OutOfRange {
1962                         field_count: substs.as_closure().upvar_tys().count(),
1963                     }),
1964                 }
1965             }
1966             AggregateKind::Generator(_, substs, _) => {
1967                 // It doesn't make sense to look at a field beyond the prefix;
1968                 // these require a variant index, and are not initialized in
1969                 // aggregate rvalues.
1970                 match substs.as_generator().prefix_tys().nth(field_index) {
1971                     Some(ty) => Ok(ty),
1972                     None => Err(FieldAccessError::OutOfRange {
1973                         field_count: substs.as_generator().prefix_tys().count(),
1974                     }),
1975                 }
1976             }
1977             AggregateKind::Array(ty) => Ok(ty),
1978             AggregateKind::Tuple => {
1979                 unreachable!("This should have been covered in check_rvalues");
1980             }
1981         }
1982     }
1983
1984     fn check_rvalue(&mut self, body: &Body<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
1985         let tcx = self.tcx();
1986
1987         match rvalue {
1988             Rvalue::Aggregate(ak, ops) => {
1989                 self.check_aggregate_rvalue(&body, rvalue, ak, ops, location)
1990             }
1991
1992             Rvalue::Repeat(operand, len) => {
1993                 // If the length cannot be evaluated we must assume that the length can be larger
1994                 // than 1.
1995                 // If the length is larger than 1, the repeat expression will need to copy the
1996                 // element, so we require the `Copy` trait.
1997                 if len.try_eval_usize(tcx, self.param_env).map_or(true, |len| len > 1) {
1998                     if let Operand::Move(_) = operand {
1999                         // While this is located in `nll::typeck` this error is not an NLL error, it's
2000                         // a required check to make sure that repeated elements implement `Copy`.
2001                         let span = body.source_info(location).span;
2002                         let ty = operand.ty(body, tcx);
2003                         if !self.infcx.type_is_copy_modulo_regions(self.param_env, ty, span) {
2004                             let ccx = ConstCx::new_with_param_env(
2005                                 tcx,
2006                                 self.mir_def_id,
2007                                 body,
2008                                 self.param_env,
2009                             );
2010                             // To determine if `const_in_array_repeat_expressions` feature gate should
2011                             // be mentioned, need to check if the rvalue is promotable.
2012                             let should_suggest =
2013                                 should_suggest_const_in_array_repeat_expressions_attribute(
2014                                     &ccx, operand,
2015                                 );
2016                             debug!("check_rvalue: should_suggest={:?}", should_suggest);
2017
2018                             self.infcx.report_selection_error(
2019                                 &traits::Obligation::new(
2020                                     ObligationCause::new(
2021                                         span,
2022                                         self.tcx().hir().local_def_id_to_hir_id(self.mir_def_id),
2023                                         traits::ObligationCauseCode::RepeatVec(should_suggest),
2024                                     ),
2025                                     self.param_env,
2026                                     ty::Binder::bind(ty::TraitRef::new(
2027                                         self.tcx().require_lang_item(
2028                                             LangItem::Copy,
2029                                             Some(self.last_span),
2030                                         ),
2031                                         tcx.mk_substs_trait(ty, &[]),
2032                                     ))
2033                                     .without_const()
2034                                     .to_predicate(self.tcx()),
2035                                 ),
2036                                 &traits::SelectionError::Unimplemented,
2037                                 false,
2038                                 false,
2039                             );
2040                         }
2041                     }
2042                 }
2043             }
2044
2045             Rvalue::NullaryOp(_, ty) => {
2046                 // Even with unsized locals cannot box an unsized value.
2047                 if self.tcx().features().unsized_locals {
2048                     let span = body.source_info(location).span;
2049                     self.ensure_place_sized(ty, span);
2050                 }
2051
2052                 let trait_ref = ty::TraitRef {
2053                     def_id: tcx.require_lang_item(LangItem::Sized, Some(self.last_span)),
2054                     substs: tcx.mk_substs_trait(ty, &[]),
2055                 };
2056
2057                 self.prove_trait_ref(
2058                     trait_ref,
2059                     location.to_locations(),
2060                     ConstraintCategory::SizedBound,
2061                 );
2062             }
2063
2064             Rvalue::Cast(cast_kind, op, ty) => {
2065                 match cast_kind {
2066                     CastKind::Pointer(PointerCast::ReifyFnPointer) => {
2067                         let fn_sig = op.ty(body, tcx).fn_sig(tcx);
2068
2069                         // The type that we see in the fcx is like
2070                         // `foo::<'a, 'b>`, where `foo` is the path to a
2071                         // function definition. When we extract the
2072                         // signature, it comes from the `fn_sig` query,
2073                         // and hence may contain unnormalized results.
2074                         let fn_sig = self.normalize(fn_sig, location);
2075
2076                         let ty_fn_ptr_from = tcx.mk_fn_ptr(fn_sig);
2077
2078                         if let Err(terr) = self.eq_types(
2079                             ty_fn_ptr_from,
2080                             ty,
2081                             location.to_locations(),
2082                             ConstraintCategory::Cast,
2083                         ) {
2084                             span_mirbug!(
2085                                 self,
2086                                 rvalue,
2087                                 "equating {:?} with {:?} yields {:?}",
2088                                 ty_fn_ptr_from,
2089                                 ty,
2090                                 terr
2091                             );
2092                         }
2093                     }
2094
2095                     CastKind::Pointer(PointerCast::ClosureFnPointer(unsafety)) => {
2096                         let sig = match op.ty(body, tcx).kind {
2097                             ty::Closure(_, substs) => substs.as_closure().sig(),
2098                             _ => bug!(),
2099                         };
2100                         let ty_fn_ptr_from = tcx.mk_fn_ptr(tcx.signature_unclosure(sig, *unsafety));
2101
2102                         if let Err(terr) = self.eq_types(
2103                             ty_fn_ptr_from,
2104                             ty,
2105                             location.to_locations(),
2106                             ConstraintCategory::Cast,
2107                         ) {
2108                             span_mirbug!(
2109                                 self,
2110                                 rvalue,
2111                                 "equating {:?} with {:?} yields {:?}",
2112                                 ty_fn_ptr_from,
2113                                 ty,
2114                                 terr
2115                             );
2116                         }
2117                     }
2118
2119                     CastKind::Pointer(PointerCast::UnsafeFnPointer) => {
2120                         let fn_sig = op.ty(body, tcx).fn_sig(tcx);
2121
2122                         // The type that we see in the fcx is like
2123                         // `foo::<'a, 'b>`, where `foo` is the path to a
2124                         // function definition. When we extract the
2125                         // signature, it comes from the `fn_sig` query,
2126                         // and hence may contain unnormalized results.
2127                         let fn_sig = self.normalize(fn_sig, location);
2128
2129                         let ty_fn_ptr_from = tcx.safe_to_unsafe_fn_ty(fn_sig);
2130
2131                         if let Err(terr) = self.eq_types(
2132                             ty_fn_ptr_from,
2133                             ty,
2134                             location.to_locations(),
2135                             ConstraintCategory::Cast,
2136                         ) {
2137                             span_mirbug!(
2138                                 self,
2139                                 rvalue,
2140                                 "equating {:?} with {:?} yields {:?}",
2141                                 ty_fn_ptr_from,
2142                                 ty,
2143                                 terr
2144                             );
2145                         }
2146                     }
2147
2148                     CastKind::Pointer(PointerCast::Unsize) => {
2149                         let &ty = ty;
2150                         let trait_ref = ty::TraitRef {
2151                             def_id: tcx
2152                                 .require_lang_item(LangItem::CoerceUnsized, Some(self.last_span)),
2153                             substs: tcx.mk_substs_trait(op.ty(body, tcx), &[ty.into()]),
2154                         };
2155
2156                         self.prove_trait_ref(
2157                             trait_ref,
2158                             location.to_locations(),
2159                             ConstraintCategory::Cast,
2160                         );
2161                     }
2162
2163                     CastKind::Pointer(PointerCast::MutToConstPointer) => {
2164                         let ty_from = match op.ty(body, tcx).kind {
2165                             ty::RawPtr(ty::TypeAndMut {
2166                                 ty: ty_from,
2167                                 mutbl: hir::Mutability::Mut,
2168                             }) => ty_from,
2169                             _ => {
2170                                 span_mirbug!(
2171                                     self,
2172                                     rvalue,
2173                                     "unexpected base type for cast {:?}",
2174                                     ty,
2175                                 );
2176                                 return;
2177                             }
2178                         };
2179                         let ty_to = match ty.kind {
2180                             ty::RawPtr(ty::TypeAndMut {
2181                                 ty: ty_to,
2182                                 mutbl: hir::Mutability::Not,
2183                             }) => ty_to,
2184                             _ => {
2185                                 span_mirbug!(
2186                                     self,
2187                                     rvalue,
2188                                     "unexpected target type for cast {:?}",
2189                                     ty,
2190                                 );
2191                                 return;
2192                             }
2193                         };
2194                         if let Err(terr) = self.sub_types(
2195                             ty_from,
2196                             ty_to,
2197                             location.to_locations(),
2198                             ConstraintCategory::Cast,
2199                         ) {
2200                             span_mirbug!(
2201                                 self,
2202                                 rvalue,
2203                                 "relating {:?} with {:?} yields {:?}",
2204                                 ty_from,
2205                                 ty_to,
2206                                 terr
2207                             );
2208                         }
2209                     }
2210
2211                     CastKind::Pointer(PointerCast::ArrayToPointer) => {
2212                         let ty_from = op.ty(body, tcx);
2213
2214                         let opt_ty_elem = match ty_from.kind {
2215                             ty::RawPtr(ty::TypeAndMut {
2216                                 mutbl: hir::Mutability::Not,
2217                                 ty: array_ty,
2218                             }) => match array_ty.kind {
2219                                 ty::Array(ty_elem, _) => Some(ty_elem),
2220                                 _ => None,
2221                             },
2222                             _ => None,
2223                         };
2224
2225                         let ty_elem = match opt_ty_elem {
2226                             Some(ty_elem) => ty_elem,
2227                             None => {
2228                                 span_mirbug!(
2229                                     self,
2230                                     rvalue,
2231                                     "ArrayToPointer cast from unexpected type {:?}",
2232                                     ty_from,
2233                                 );
2234                                 return;
2235                             }
2236                         };
2237
2238                         let ty_to = match ty.kind {
2239                             ty::RawPtr(ty::TypeAndMut {
2240                                 mutbl: hir::Mutability::Not,
2241                                 ty: ty_to,
2242                             }) => ty_to,
2243                             _ => {
2244                                 span_mirbug!(
2245                                     self,
2246                                     rvalue,
2247                                     "ArrayToPointer cast to unexpected type {:?}",
2248                                     ty,
2249                                 );
2250                                 return;
2251                             }
2252                         };
2253
2254                         if let Err(terr) = self.sub_types(
2255                             ty_elem,
2256                             ty_to,
2257                             location.to_locations(),
2258                             ConstraintCategory::Cast,
2259                         ) {
2260                             span_mirbug!(
2261                                 self,
2262                                 rvalue,
2263                                 "relating {:?} with {:?} yields {:?}",
2264                                 ty_elem,
2265                                 ty_to,
2266                                 terr
2267                             )
2268                         }
2269                     }
2270
2271                     CastKind::Misc => {
2272                         let ty_from = op.ty(body, tcx);
2273                         let cast_ty_from = CastTy::from_ty(ty_from);
2274                         let cast_ty_to = CastTy::from_ty(ty);
2275                         match (cast_ty_from, cast_ty_to) {
2276                             (None, _)
2277                             | (_, None | Some(CastTy::FnPtr))
2278                             | (Some(CastTy::Float), Some(CastTy::Ptr(_)))
2279                             | (Some(CastTy::Ptr(_) | CastTy::FnPtr), Some(CastTy::Float)) => {
2280                                 span_mirbug!(self, rvalue, "Invalid cast {:?} -> {:?}", ty_from, ty,)
2281                             }
2282                             (
2283                                 Some(CastTy::Int(_)),
2284                                 Some(CastTy::Int(_) | CastTy::Float | CastTy::Ptr(_)),
2285                             )
2286                             | (Some(CastTy::Float), Some(CastTy::Int(_) | CastTy::Float))
2287                             | (Some(CastTy::Ptr(_)), Some(CastTy::Int(_) | CastTy::Ptr(_)))
2288                             | (Some(CastTy::FnPtr), Some(CastTy::Int(_) | CastTy::Ptr(_))) => (),
2289                         }
2290                     }
2291                 }
2292             }
2293
2294             Rvalue::Ref(region, _borrow_kind, borrowed_place) => {
2295                 self.add_reborrow_constraint(&body, location, region, borrowed_place);
2296             }
2297
2298             Rvalue::BinaryOp(
2299                 BinOp::Eq | BinOp::Ne | BinOp::Lt | BinOp::Le | BinOp::Gt | BinOp::Ge,
2300                 left,
2301                 right,
2302             ) => {
2303                 let ty_left = left.ty(body, tcx);
2304                 match ty_left.kind {
2305                     // Types with regions are comparable if they have a common super-type.
2306                     ty::RawPtr(_) | ty::FnPtr(_) => {
2307                         let ty_right = right.ty(body, tcx);
2308                         let common_ty = self.infcx.next_ty_var(TypeVariableOrigin {
2309                             kind: TypeVariableOriginKind::MiscVariable,
2310                             span: body.source_info(location).span,
2311                         });
2312                         self.relate_types(
2313                             common_ty,
2314                             ty::Variance::Contravariant,
2315                             ty_left,
2316                             location.to_locations(),
2317                             ConstraintCategory::Boring,
2318                         )
2319                         .unwrap_or_else(|err| {
2320                             bug!("Could not equate type variable with {:?}: {:?}", ty_left, err)
2321                         });
2322                         if let Err(terr) = self.relate_types(
2323                             common_ty,
2324                             ty::Variance::Contravariant,
2325                             ty_right,
2326                             location.to_locations(),
2327                             ConstraintCategory::Boring,
2328                         ) {
2329                             span_mirbug!(
2330                                 self,
2331                                 rvalue,
2332                                 "unexpected comparison types {:?} and {:?} yields {:?}",
2333                                 ty_left,
2334                                 ty_right,
2335                                 terr
2336                             )
2337                         }
2338                     }
2339                     // For types with no regions we can just check that the
2340                     // both operands have the same type.
2341                     ty::Int(_) | ty::Uint(_) | ty::Bool | ty::Char | ty::Float(_)
2342                         if ty_left == right.ty(body, tcx) => {}
2343                     // Other types are compared by trait methods, not by
2344                     // `Rvalue::BinaryOp`.
2345                     _ => span_mirbug!(
2346                         self,
2347                         rvalue,
2348                         "unexpected comparison types {:?} and {:?}",
2349                         ty_left,
2350                         right.ty(body, tcx)
2351                     ),
2352                 }
2353             }
2354
2355             Rvalue::AddressOf(..)
2356             | Rvalue::ThreadLocalRef(..)
2357             | Rvalue::Use(..)
2358             | Rvalue::Len(..)
2359             | Rvalue::BinaryOp(..)
2360             | Rvalue::CheckedBinaryOp(..)
2361             | Rvalue::UnaryOp(..)
2362             | Rvalue::Discriminant(..) => {}
2363         }
2364     }
2365
2366     /// If this rvalue supports a user-given type annotation, then
2367     /// extract and return it. This represents the final type of the
2368     /// rvalue and will be unified with the inferred type.
2369     fn rvalue_user_ty(&self, rvalue: &Rvalue<'tcx>) -> Option<UserTypeAnnotationIndex> {
2370         match rvalue {
2371             Rvalue::Use(_)
2372             | Rvalue::ThreadLocalRef(_)
2373             | Rvalue::Repeat(..)
2374             | Rvalue::Ref(..)
2375             | Rvalue::AddressOf(..)
2376             | Rvalue::Len(..)
2377             | Rvalue::Cast(..)
2378             | Rvalue::BinaryOp(..)
2379             | Rvalue::CheckedBinaryOp(..)
2380             | Rvalue::NullaryOp(..)
2381             | Rvalue::UnaryOp(..)
2382             | Rvalue::Discriminant(..) => None,
2383
2384             Rvalue::Aggregate(aggregate, _) => match **aggregate {
2385                 AggregateKind::Adt(_, _, _, user_ty, _) => user_ty,
2386                 AggregateKind::Array(_) => None,
2387                 AggregateKind::Tuple => None,
2388                 AggregateKind::Closure(_, _) => None,
2389                 AggregateKind::Generator(_, _, _) => None,
2390             },
2391         }
2392     }
2393
2394     fn check_aggregate_rvalue(
2395         &mut self,
2396         body: &Body<'tcx>,
2397         rvalue: &Rvalue<'tcx>,
2398         aggregate_kind: &AggregateKind<'tcx>,
2399         operands: &[Operand<'tcx>],
2400         location: Location,
2401     ) {
2402         let tcx = self.tcx();
2403
2404         self.prove_aggregate_predicates(aggregate_kind, location);
2405
2406         if *aggregate_kind == AggregateKind::Tuple {
2407             // tuple rvalue field type is always the type of the op. Nothing to check here.
2408             return;
2409         }
2410
2411         for (i, operand) in operands.iter().enumerate() {
2412             let field_ty = match self.aggregate_field_ty(aggregate_kind, i, location) {
2413                 Ok(field_ty) => field_ty,
2414                 Err(FieldAccessError::OutOfRange { field_count }) => {
2415                     span_mirbug!(
2416                         self,
2417                         rvalue,
2418                         "accessed field #{} but variant only has {}",
2419                         i,
2420                         field_count
2421                     );
2422                     continue;
2423                 }
2424             };
2425             let operand_ty = operand.ty(body, tcx);
2426             let operand_ty = self.normalize(operand_ty, location);
2427
2428             if let Err(terr) = self.sub_types(
2429                 operand_ty,
2430                 field_ty,
2431                 location.to_locations(),
2432                 ConstraintCategory::Boring,
2433             ) {
2434                 span_mirbug!(
2435                     self,
2436                     rvalue,
2437                     "{:?} is not a subtype of {:?}: {:?}",
2438                     operand_ty,
2439                     field_ty,
2440                     terr
2441                 );
2442             }
2443         }
2444     }
2445
2446     /// Adds the constraints that arise from a borrow expression `&'a P` at the location `L`.
2447     ///
2448     /// # Parameters
2449     ///
2450     /// - `location`: the location `L` where the borrow expression occurs
2451     /// - `borrow_region`: the region `'a` associated with the borrow
2452     /// - `borrowed_place`: the place `P` being borrowed
2453     fn add_reborrow_constraint(
2454         &mut self,
2455         body: &Body<'tcx>,
2456         location: Location,
2457         borrow_region: ty::Region<'tcx>,
2458         borrowed_place: &Place<'tcx>,
2459     ) {
2460         // These constraints are only meaningful during borrowck:
2461         let BorrowCheckContext { borrow_set, location_table, all_facts, constraints, .. } =
2462             self.borrowck_context;
2463
2464         // In Polonius mode, we also push a `borrow_region` fact
2465         // linking the loan to the region (in some cases, though,
2466         // there is no loan associated with this borrow expression --
2467         // that occurs when we are borrowing an unsafe place, for
2468         // example).
2469         if let Some(all_facts) = all_facts {
2470             let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
2471             if let Some(borrow_index) = borrow_set.get_index_of(&location) {
2472                 let region_vid = borrow_region.to_region_vid();
2473                 all_facts.borrow_region.push((
2474                     region_vid,
2475                     borrow_index,
2476                     location_table.mid_index(location),
2477                 ));
2478             }
2479         }
2480
2481         // If we are reborrowing the referent of another reference, we
2482         // need to add outlives relationships. In a case like `&mut
2483         // *p`, where the `p` has type `&'b mut Foo`, for example, we
2484         // need to ensure that `'b: 'a`.
2485
2486         debug!(
2487             "add_reborrow_constraint({:?}, {:?}, {:?})",
2488             location, borrow_region, borrowed_place
2489         );
2490
2491         let mut cursor = borrowed_place.projection.as_ref();
2492         let tcx = self.infcx.tcx;
2493         let field = path_utils::is_upvar_field_projection(
2494             tcx,
2495             &self.borrowck_context.upvars,
2496             borrowed_place.as_ref(),
2497             body,
2498         );
2499         let category = if let Some(field) = field {
2500             ConstraintCategory::ClosureUpvar(self.borrowck_context.upvars[field.index()].var_hir_id)
2501         } else {
2502             ConstraintCategory::Boring
2503         };
2504
2505         while let [proj_base @ .., elem] = cursor {
2506             cursor = proj_base;
2507
2508             debug!("add_reborrow_constraint - iteration {:?}", elem);
2509
2510             match elem {
2511                 ProjectionElem::Deref => {
2512                     let base_ty = Place::ty_from(borrowed_place.local, proj_base, body, tcx).ty;
2513
2514                     debug!("add_reborrow_constraint - base_ty = {:?}", base_ty);
2515                     match base_ty.kind {
2516                         ty::Ref(ref_region, _, mutbl) => {
2517                             constraints.outlives_constraints.push(OutlivesConstraint {
2518                                 sup: ref_region.to_region_vid(),
2519                                 sub: borrow_region.to_region_vid(),
2520                                 locations: location.to_locations(),
2521                                 category,
2522                             });
2523
2524                             match mutbl {
2525                                 hir::Mutability::Not => {
2526                                     // Immutable reference. We don't need the base
2527                                     // to be valid for the entire lifetime of
2528                                     // the borrow.
2529                                     break;
2530                                 }
2531                                 hir::Mutability::Mut => {
2532                                     // Mutable reference. We *do* need the base
2533                                     // to be valid, because after the base becomes
2534                                     // invalid, someone else can use our mutable deref.
2535
2536                                     // This is in order to make the following function
2537                                     // illegal:
2538                                     // ```
2539                                     // fn unsafe_deref<'a, 'b>(x: &'a &'b mut T) -> &'b mut T {
2540                                     //     &mut *x
2541                                     // }
2542                                     // ```
2543                                     //
2544                                     // As otherwise you could clone `&mut T` using the
2545                                     // following function:
2546                                     // ```
2547                                     // fn bad(x: &mut T) -> (&mut T, &mut T) {
2548                                     //     let my_clone = unsafe_deref(&'a x);
2549                                     //     ENDREGION 'a;
2550                                     //     (my_clone, x)
2551                                     // }
2552                                     // ```
2553                                 }
2554                             }
2555                         }
2556                         ty::RawPtr(..) => {
2557                             // deref of raw pointer, guaranteed to be valid
2558                             break;
2559                         }
2560                         ty::Adt(def, _) if def.is_box() => {
2561                             // deref of `Box`, need the base to be valid - propagate
2562                         }
2563                         _ => bug!("unexpected deref ty {:?} in {:?}", base_ty, borrowed_place),
2564                     }
2565                 }
2566                 ProjectionElem::Field(..)
2567                 | ProjectionElem::Downcast(..)
2568                 | ProjectionElem::Index(..)
2569                 | ProjectionElem::ConstantIndex { .. }
2570                 | ProjectionElem::Subslice { .. } => {
2571                     // other field access
2572                 }
2573             }
2574         }
2575     }
2576
2577     fn prove_aggregate_predicates(
2578         &mut self,
2579         aggregate_kind: &AggregateKind<'tcx>,
2580         location: Location,
2581     ) {
2582         let tcx = self.tcx();
2583
2584         debug!(
2585             "prove_aggregate_predicates(aggregate_kind={:?}, location={:?})",
2586             aggregate_kind, location
2587         );
2588
2589         let instantiated_predicates = match aggregate_kind {
2590             AggregateKind::Adt(def, _, substs, _, _) => {
2591                 tcx.predicates_of(def.did).instantiate(tcx, substs)
2592             }
2593
2594             // For closures, we have some **extra requirements** we
2595             //
2596             // have to check. In particular, in their upvars and
2597             // signatures, closures often reference various regions
2598             // from the surrounding function -- we call those the
2599             // closure's free regions. When we borrow-check (and hence
2600             // region-check) closures, we may find that the closure
2601             // requires certain relationships between those free
2602             // regions. However, because those free regions refer to
2603             // portions of the CFG of their caller, the closure is not
2604             // in a position to verify those relationships. In that
2605             // case, the requirements get "propagated" to us, and so
2606             // we have to solve them here where we instantiate the
2607             // closure.
2608             //
2609             // Despite the opacity of the previous parapgrah, this is
2610             // actually relatively easy to understand in terms of the
2611             // desugaring. A closure gets desugared to a struct, and
2612             // these extra requirements are basically like where
2613             // clauses on the struct.
2614             AggregateKind::Closure(def_id, substs)
2615             | AggregateKind::Generator(def_id, substs, _) => {
2616                 self.prove_closure_bounds(tcx, def_id.expect_local(), substs, location)
2617             }
2618
2619             AggregateKind::Array(_) | AggregateKind::Tuple => ty::InstantiatedPredicates::empty(),
2620         };
2621
2622         self.normalize_and_prove_instantiated_predicates(
2623             instantiated_predicates,
2624             location.to_locations(),
2625         );
2626     }
2627
2628     fn prove_closure_bounds(
2629         &mut self,
2630         tcx: TyCtxt<'tcx>,
2631         def_id: LocalDefId,
2632         substs: SubstsRef<'tcx>,
2633         location: Location,
2634     ) -> ty::InstantiatedPredicates<'tcx> {
2635         if let Some(ref closure_region_requirements) = tcx.mir_borrowck(def_id).closure_requirements
2636         {
2637             let closure_constraints = QueryRegionConstraints {
2638                 outlives: closure_region_requirements.apply_requirements(
2639                     tcx,
2640                     def_id.to_def_id(),
2641                     substs,
2642                 ),
2643
2644                 // Presently, closures never propagate member
2645                 // constraints to their parents -- they are enforced
2646                 // locally.  This is largely a non-issue as member
2647                 // constraints only come from `-> impl Trait` and
2648                 // friends which don't appear (thus far...) in
2649                 // closures.
2650                 member_constraints: vec![],
2651             };
2652
2653             let bounds_mapping = closure_constraints
2654                 .outlives
2655                 .iter()
2656                 .enumerate()
2657                 .filter_map(|(idx, constraint)| {
2658                     let ty::OutlivesPredicate(k1, r2) =
2659                         constraint.no_bound_vars().unwrap_or_else(|| {
2660                             bug!("query_constraint {:?} contained bound vars", constraint,);
2661                         });
2662
2663                     match k1.unpack() {
2664                         GenericArgKind::Lifetime(r1) => {
2665                             // constraint is r1: r2
2666                             let r1_vid = self.borrowck_context.universal_regions.to_region_vid(r1);
2667                             let r2_vid = self.borrowck_context.universal_regions.to_region_vid(r2);
2668                             let outlives_requirements =
2669                                 &closure_region_requirements.outlives_requirements[idx];
2670                             Some((
2671                                 (r1_vid, r2_vid),
2672                                 (outlives_requirements.category, outlives_requirements.blame_span),
2673                             ))
2674                         }
2675                         GenericArgKind::Type(_) | GenericArgKind::Const(_) => None,
2676                     }
2677                 })
2678                 .collect();
2679
2680             let existing = self
2681                 .borrowck_context
2682                 .constraints
2683                 .closure_bounds_mapping
2684                 .insert(location, bounds_mapping);
2685             assert!(existing.is_none(), "Multiple closures at the same location.");
2686
2687             self.push_region_constraints(
2688                 location.to_locations(),
2689                 ConstraintCategory::ClosureBounds,
2690                 &closure_constraints,
2691             );
2692         }
2693
2694         tcx.predicates_of(def_id).instantiate(tcx, substs)
2695     }
2696
2697     fn prove_trait_ref(
2698         &mut self,
2699         trait_ref: ty::TraitRef<'tcx>,
2700         locations: Locations,
2701         category: ConstraintCategory,
2702     ) {
2703         self.prove_predicates(
2704             Some(ty::PredicateAtom::Trait(
2705                 ty::TraitPredicate { trait_ref },
2706                 hir::Constness::NotConst,
2707             )),
2708             locations,
2709             category,
2710         );
2711     }
2712
2713     fn normalize_and_prove_instantiated_predicates(
2714         &mut self,
2715         instantiated_predicates: ty::InstantiatedPredicates<'tcx>,
2716         locations: Locations,
2717     ) {
2718         for predicate in instantiated_predicates.predicates {
2719             let predicate = self.normalize(predicate, locations);
2720             self.prove_predicate(predicate, locations, ConstraintCategory::Boring);
2721         }
2722     }
2723
2724     fn prove_predicates(
2725         &mut self,
2726         predicates: impl IntoIterator<Item = impl ToPredicate<'tcx>>,
2727         locations: Locations,
2728         category: ConstraintCategory,
2729     ) {
2730         for predicate in predicates {
2731             let predicate = predicate.to_predicate(self.tcx());
2732             debug!("prove_predicates(predicate={:?}, locations={:?})", predicate, locations,);
2733
2734             self.prove_predicate(predicate, locations, category);
2735         }
2736     }
2737
2738     fn prove_predicate(
2739         &mut self,
2740         predicate: ty::Predicate<'tcx>,
2741         locations: Locations,
2742         category: ConstraintCategory,
2743     ) {
2744         debug!("prove_predicate(predicate={:?}, location={:?})", predicate, locations,);
2745
2746         let param_env = self.param_env;
2747         self.fully_perform_op(
2748             locations,
2749             category,
2750             param_env.and(type_op::prove_predicate::ProvePredicate::new(predicate)),
2751         )
2752         .unwrap_or_else(|NoSolution| {
2753             span_mirbug!(self, NoSolution, "could not prove {:?}", predicate);
2754         })
2755     }
2756
2757     fn typeck_mir(&mut self, body: &Body<'tcx>) {
2758         self.last_span = body.span;
2759         debug!("run_on_mir: {:?}", body.span);
2760
2761         for (local, local_decl) in body.local_decls.iter_enumerated() {
2762             self.check_local(&body, local, local_decl);
2763         }
2764
2765         for (block, block_data) in body.basic_blocks().iter_enumerated() {
2766             let mut location = Location { block, statement_index: 0 };
2767             for stmt in &block_data.statements {
2768                 if !stmt.source_info.span.is_dummy() {
2769                     self.last_span = stmt.source_info.span;
2770                 }
2771                 self.check_stmt(body, stmt, location);
2772                 location.statement_index += 1;
2773             }
2774
2775             self.check_terminator(&body, block_data.terminator(), location);
2776             self.check_iscleanup(&body, block_data);
2777         }
2778     }
2779
2780     fn normalize<T>(&mut self, value: T, location: impl NormalizeLocation) -> T
2781     where
2782         T: type_op::normalize::Normalizable<'tcx> + Copy + 'tcx,
2783     {
2784         debug!("normalize(value={:?}, location={:?})", value, location);
2785         let param_env = self.param_env;
2786         self.fully_perform_op(
2787             location.to_locations(),
2788             ConstraintCategory::Boring,
2789             param_env.and(type_op::normalize::Normalize::new(value)),
2790         )
2791         .unwrap_or_else(|NoSolution| {
2792             span_mirbug!(self, NoSolution, "failed to normalize `{:?}`", value);
2793             value
2794         })
2795     }
2796 }
2797
2798 trait NormalizeLocation: fmt::Debug + Copy {
2799     fn to_locations(self) -> Locations;
2800 }
2801
2802 impl NormalizeLocation for Locations {
2803     fn to_locations(self) -> Locations {
2804         self
2805     }
2806 }
2807
2808 impl NormalizeLocation for Location {
2809     fn to_locations(self) -> Locations {
2810         Locations::Single(self)
2811     }
2812 }
2813
2814 #[derive(Debug, Default)]
2815 struct ObligationAccumulator<'tcx> {
2816     obligations: PredicateObligations<'tcx>,
2817 }
2818
2819 impl<'tcx> ObligationAccumulator<'tcx> {
2820     fn add<T>(&mut self, value: InferOk<'tcx, T>) -> T {
2821         let InferOk { value, obligations } = value;
2822         self.obligations.extend(obligations);
2823         value
2824     }
2825
2826     fn into_vec(self) -> PredicateObligations<'tcx> {
2827         self.obligations
2828     }
2829 }