compiler/rustc_borrowck/src/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 hir::OpaqueTyOrigin;
   9 use rustc_data_structures::frozen::Frozen;
  10 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  11 use rustc_data_structures::vec_map::VecMap;
  12 use rustc_errors::struct_span_err;
  13 use rustc_hir as hir;
  14 use rustc_hir::def::DefKind;
  15 use rustc_hir::def_id::LocalDefId;
  16 use rustc_hir::lang_items::LangItem;
  17 use rustc_index::vec::{Idx, IndexVec};
  18 use rustc_infer::infer::canonical::QueryRegionConstraints;
  19 use rustc_infer::infer::outlives::env::RegionBoundPairs;
  20 use rustc_infer::infer::region_constraints::RegionConstraintData;
  21 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  22 use rustc_infer::infer::{
  23     InferCtxt, InferOk, LateBoundRegionConversionTime, NllRegionVariableOrigin,
  24 };
  25 use rustc_middle::mir::tcx::PlaceTy;
  26 use rustc_middle::mir::visit::{NonMutatingUseContext, PlaceContext, Visitor};
  27 use rustc_middle::mir::AssertKind;
  28 use rustc_middle::mir::*;
  29 use rustc_middle::ty::adjustment::PointerCast;
  30 use rustc_middle::ty::cast::CastTy;
  31 use rustc_middle::ty::fold::TypeFoldable;
  32 use rustc_middle::ty::subst::{GenericArgKind, SubstsRef, UserSubsts};
  33 use rustc_middle::ty::{
  34     self, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations, OpaqueHiddenType,
  35     OpaqueTypeKey, RegionVid, ToPredicate, Ty, TyCtxt, UserType, UserTypeAnnotationIndex,
  36 };
  37 use rustc_span::def_id::CRATE_DEF_ID;
  38 use rustc_span::{Span, DUMMY_SP};
  39 use rustc_target::abi::VariantIdx;
  40 use rustc_trait_selection::traits::query::type_op;
  41 use rustc_trait_selection::traits::query::type_op::custom::scrape_region_constraints;
  42 use rustc_trait_selection::traits::query::type_op::custom::CustomTypeOp;
  43 use rustc_trait_selection::traits::query::type_op::{TypeOp, TypeOpOutput};
  44 use rustc_trait_selection::traits::query::Fallible;
  45 use rustc_trait_selection::traits::PredicateObligation;
  46
  47 use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
  48 use rustc_mir_dataflow::move_paths::MoveData;
  49 use rustc_mir_dataflow::ResultsCursor;
  50
  51 use crate::{
  52     borrow_set::BorrowSet,
  53     constraints::{OutlivesConstraint, OutlivesConstraintSet},
  54     diagnostics::UniverseInfo,
  55     facts::AllFacts,
  56     location::LocationTable,
  57     member_constraints::MemberConstraintSet,
  58     nll::ToRegionVid,
  59     path_utils,
  60     region_infer::values::{
  61         LivenessValues, PlaceholderIndex, PlaceholderIndices, RegionValueElements,
  62     },
  63     region_infer::{ClosureRegionRequirementsExt, TypeTest},
  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::type_check::mirbug(
  72             $context.tcx(),
  73             $context.last_span,
  74             &format!(
  75                 "broken MIR in {:?} ({:?}): {}",
  76                 $context.body().source.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 canonical;
  94 mod constraint_conversion;
  95 pub mod free_region_relations;
  96 mod input_output;
  97 pub(crate) mod liveness;
  98 mod relate_tys;
  99
 100 /// Type checks the given `mir` in the context of the inference
 101 /// context `infcx`. Returns any region constraints that have yet to
 102 /// be proven. This result includes liveness constraints that
 103 /// ensure that regions appearing in the types of all local variables
 104 /// are live at all points where that local variable may later be
 105 /// used.
 106 ///
 107 /// This phase of type-check ought to be infallible -- this is because
 108 /// the original, HIR-based type-check succeeded. So if any errors
 109 /// occur here, we will get a `bug!` reported.
 110 ///
 111 /// # Parameters
 112 ///
 113 /// - `infcx` -- inference context to use
 114 /// - `param_env` -- parameter environment to use for trait solving
 115 /// - `body` -- MIR body to type-check
 116 /// - `promoted` -- map of promoted constants within `body`
 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     universal_regions: &Rc<UniversalRegions<'tcx>>,
 130     location_table: &LocationTable,
 131     borrow_set: &BorrowSet<'tcx>,
 132     all_facts: &mut Option<AllFacts>,
 133     flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
 134     move_data: &MoveData<'tcx>,
 135     elements: &Rc<RegionValueElements>,
 136     upvars: &[Upvar<'tcx>],
 137     use_polonius: bool,
 138 ) -> MirTypeckResults<'tcx> {
 139     let implicit_region_bound = infcx.tcx.mk_region(ty::ReVar(universal_regions.fr_fn_body));
 140     let mut universe_causes = FxHashMap::default();
 141     universe_causes.insert(ty::UniverseIndex::from_u32(0), UniverseInfo::other());
 142     let mut constraints = MirTypeckRegionConstraints {
 143         placeholder_indices: PlaceholderIndices::default(),
 144         placeholder_index_to_region: IndexVec::default(),
 145         liveness_constraints: LivenessValues::new(elements.clone()),
 146         outlives_constraints: OutlivesConstraintSet::default(),
 147         member_constraints: MemberConstraintSet::default(),
 148         closure_bounds_mapping: Default::default(),
 149         type_tests: Vec::default(),
 150         universe_causes,
 151     };
 152
 153     let CreateResult {
 154         universal_region_relations,
 155         region_bound_pairs,
 156         normalized_inputs_and_output,
 157     } = free_region_relations::create(
 158         infcx,
 159         param_env,
 160         Some(implicit_region_bound),
 161         universal_regions,
 162         &mut constraints,
 163     );
 164
 165     debug!(?normalized_inputs_and_output);
 166
 167     for u in ty::UniverseIndex::ROOT..infcx.universe() {
 168         let info = UniverseInfo::other();
 169         constraints.universe_causes.insert(u, info);
 170     }
 171
 172     let mut borrowck_context = BorrowCheckContext {
 173         universal_regions,
 174         location_table,
 175         borrow_set,
 176         all_facts,
 177         constraints: &mut constraints,
 178         upvars,
 179     };
 180
 181     let opaque_type_values = type_check_internal(
 182         infcx,
 183         param_env,
 184         body,
 185         promoted,
 186         &region_bound_pairs,
 187         implicit_region_bound,
 188         &mut borrowck_context,
 189         |mut cx| {
 190             debug!("inside extra closure of type_check_internal");
 191             cx.equate_inputs_and_outputs(&body, universal_regions, &normalized_inputs_and_output);
 192             liveness::generate(
 193                 &mut cx,
 194                 body,
 195                 elements,
 196                 flow_inits,
 197                 move_data,
 198                 location_table,
 199                 use_polonius,
 200             );
 201
 202             translate_outlives_facts(&mut cx);
 203             let opaque_type_values =
 204                 infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
 205
 206             opaque_type_values
 207                 .into_iter()
 208                 .map(|(opaque_type_key, decl)| {
 209                     cx.fully_perform_op(
 210                         Locations::All(body.span),
 211                         ConstraintCategory::OpaqueType,
 212                         CustomTypeOp::new(
 213                             |infcx| {
 214                                 infcx.register_member_constraints(
 215                                     param_env,
 216                                     opaque_type_key,
 217                                     decl.hidden_type.ty,
 218                                     decl.hidden_type.span,
 219                                 );
 220                                 Ok(InferOk { value: (), obligations: vec![] })
 221                             },
 222                             || "opaque_type_map".to_string(),
 223                         ),
 224                     )
 225                     .unwrap();
 226                     let mut hidden_type = infcx.resolve_vars_if_possible(decl.hidden_type);
 227                     trace!(
 228                         "finalized opaque type {:?} to {:#?}",
 229                         opaque_type_key,
 230                         hidden_type.ty.kind()
 231                     );
 232                     if hidden_type.has_infer_types_or_consts() {
 233                         infcx.tcx.sess.delay_span_bug(
 234                             decl.hidden_type.span,
 235                             &format!("could not resolve {:#?}", hidden_type.ty.kind()),
 236                         );
 237                         hidden_type.ty = infcx.tcx.ty_error();
 238                     }
 239
 240                     (opaque_type_key, (hidden_type, decl.origin))
 241                 })
 242                 .collect()
 243         },
 244     );
 245
 246     MirTypeckResults { constraints, universal_region_relations, opaque_type_values }
 247 }
 248
 249 #[instrument(
 250     skip(infcx, body, promoted, region_bound_pairs, borrowck_context, extra),
 251     level = "debug"
 252 )]
 253 fn type_check_internal<'a, 'tcx, R>(
 254     infcx: &'a InferCtxt<'a, 'tcx>,
 255     param_env: ty::ParamEnv<'tcx>,
 256     body: &'a Body<'tcx>,
 257     promoted: &'a IndexVec<Promoted, Body<'tcx>>,
 258     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
 259     implicit_region_bound: ty::Region<'tcx>,
 260     borrowck_context: &'a mut BorrowCheckContext<'a, 'tcx>,
 261     extra: impl FnOnce(TypeChecker<'a, 'tcx>) -> R,
 262 ) -> R {
 263     debug!("body: {:#?}", body);
 264     let mut checker = TypeChecker::new(
 265         infcx,
 266         body,
 267         param_env,
 268         region_bound_pairs,
 269         implicit_region_bound,
 270         borrowck_context,
 271     );
 272     let errors_reported = {
 273         let mut verifier = TypeVerifier::new(&mut checker, promoted);
 274         verifier.visit_body(&body);
 275         verifier.errors_reported
 276     };
 277
 278     if !errors_reported {
 279         // if verifier failed, don't do further checks to avoid ICEs
 280         checker.typeck_mir(body);
 281     }
 282
 283     extra(checker)
 284 }
 285
 286 fn translate_outlives_facts(typeck: &mut TypeChecker<'_, '_>) {
 287     let cx = &mut typeck.borrowck_context;
 288     if let Some(facts) = cx.all_facts {
 289         let _prof_timer = typeck.infcx.tcx.prof.generic_activity("polonius_fact_generation");
 290         let location_table = cx.location_table;
 291         facts.subset_base.extend(cx.constraints.outlives_constraints.outlives().iter().flat_map(
 292             |constraint: &OutlivesConstraint<'_>| {
 293                 if let Some(from_location) = constraint.locations.from_location() {
 294                     Either::Left(iter::once((
 295                         constraint.sup,
 296                         constraint.sub,
 297                         location_table.mid_index(from_location),
 298                     )))
 299                 } else {
 300                     Either::Right(
 301                         location_table
 302                             .all_points()
 303                             .map(move |location| (constraint.sup, constraint.sub, location)),
 304                     )
 305                 }
 306             },
 307         ));
 308     }
 309 }
 310
 311 #[track_caller]
 312 fn mirbug(tcx: TyCtxt<'_>, span: Span, msg: &str) {
 313     // We sometimes see MIR failures (notably predicate failures) due to
 314     // the fact that we check rvalue sized predicates here. So use `delay_span_bug`
 315     // to avoid reporting bugs in those cases.
 316     tcx.sess.diagnostic().delay_span_bug(span, msg);
 317 }
 318
 319 enum FieldAccessError {
 320     OutOfRange { field_count: usize },
 321 }
 322
 323 /// Verifies that MIR types are sane to not crash further checks.
 324 ///
 325 /// The sanitize_XYZ methods here take an MIR object and compute its
 326 /// type, calling `span_mirbug` and returning an error type if there
 327 /// is a problem.
 328 struct TypeVerifier<'a, 'b, 'tcx> {
 329     cx: &'a mut TypeChecker<'b, 'tcx>,
 330     promoted: &'b IndexVec<Promoted, Body<'tcx>>,
 331     last_span: Span,
 332     errors_reported: bool,
 333 }
 334
 335 impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
 336     fn visit_span(&mut self, span: &Span) {
 337         if !span.is_dummy() {
 338             self.last_span = *span;
 339         }
 340     }
 341
 342     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, location: Location) {
 343         self.sanitize_place(place, location, context);
 344     }
 345
 346     fn visit_constant(&mut self, constant: &Constant<'tcx>, location: Location) {
 347         self.super_constant(constant, location);
 348         let ty = self.sanitize_type(constant, constant.literal.ty());
 349
 350         self.cx.infcx.tcx.for_each_free_region(&ty, |live_region| {
 351             let live_region_vid =
 352                 self.cx.borrowck_context.universal_regions.to_region_vid(live_region);
 353             self.cx
 354                 .borrowck_context
 355                 .constraints
 356                 .liveness_constraints
 357                 .add_element(live_region_vid, location);
 358         });
 359
 360         if let Some(annotation_index) = constant.user_ty {
 361             if let Err(terr) = self.cx.relate_type_and_user_type(
 362                 constant.literal.ty(),
 363                 ty::Variance::Invariant,
 364                 &UserTypeProjection { base: annotation_index, projs: vec![] },
 365                 location.to_locations(),
 366                 ConstraintCategory::Boring,
 367             ) {
 368                 let annotation = &self.cx.user_type_annotations[annotation_index];
 369                 span_mirbug!(
 370                     self,
 371                     constant,
 372                     "bad constant user type {:?} vs {:?}: {:?}",
 373                     annotation,
 374                     constant.literal.ty(),
 375                     terr,
 376                 );
 377             }
 378         } else {
 379             let tcx = self.tcx();
 380             let maybe_uneval = match constant.literal {
 381                 ConstantKind::Ty(ct) => match ct.val() {
 382                     ty::ConstKind::Unevaluated(uv) => Some(uv),
 383                     _ => None,
 384                 },
 385                 _ => None,
 386             };
 387             if let Some(uv) = maybe_uneval {
 388                 if let Some(promoted) = uv.promoted {
 389                     let check_err = |verifier: &mut TypeVerifier<'a, 'b, 'tcx>,
 390                                      promoted: &Body<'tcx>,
 391                                      ty,
 392                                      san_ty| {
 393                         if let Err(terr) = verifier.cx.eq_types(
 394                             ty,
 395                             san_ty,
 396                             location.to_locations(),
 397                             ConstraintCategory::Boring,
 398                         ) {
 399                             span_mirbug!(
 400                                 verifier,
 401                                 promoted,
 402                                 "bad promoted type ({:?}: {:?}): {:?}",
 403                                 ty,
 404                                 san_ty,
 405                                 terr
 406                             );
 407                         };
 408                     };
 409
 410                     if !self.errors_reported {
 411                         let promoted_body = &self.promoted[promoted];
 412                         self.sanitize_promoted(promoted_body, location);
 413
 414                         let promoted_ty = promoted_body.return_ty();
 415                         check_err(self, promoted_body, ty, promoted_ty);
 416                     }
 417                 } else {
 418                     if let Err(terr) = self.cx.fully_perform_op(
 419                         location.to_locations(),
 420                         ConstraintCategory::Boring,
 421                         self.cx.param_env.and(type_op::ascribe_user_type::AscribeUserType::new(
 422                             constant.literal.ty(),
 423                             uv.def.did,
 424                             UserSubsts { substs: uv.substs, user_self_ty: None },
 425                         )),
 426                     ) {
 427                         span_mirbug!(
 428                             self,
 429                             constant,
 430                             "bad constant type {:?} ({:?})",
 431                             constant,
 432                             terr
 433                         );
 434                     }
 435                 }
 436             } else if let Some(static_def_id) = constant.check_static_ptr(tcx) {
 437                 let unnormalized_ty = tcx.type_of(static_def_id);
 438                 let locations = location.to_locations();
 439                 let normalized_ty = self.cx.normalize(unnormalized_ty, locations);
 440                 let literal_ty = constant.literal.ty().builtin_deref(true).unwrap().ty;
 441
 442                 if let Err(terr) = self.cx.eq_types(
 443                     literal_ty,
 444                     normalized_ty,
 445                     locations,
 446                     ConstraintCategory::Boring,
 447                 ) {
 448                     span_mirbug!(self, constant, "bad static type {:?} ({:?})", constant, terr);
 449                 }
 450             }
 451
 452             if let ty::FnDef(def_id, substs) = *constant.literal.ty().kind() {
 453                 let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);
 454                 self.cx.normalize_and_prove_instantiated_predicates(
 455                     def_id,
 456                     instantiated_predicates,
 457                     location.to_locations(),
 458                 );
 459             }
 460         }
 461     }
 462
 463     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 464         self.super_rvalue(rvalue, location);
 465         let rval_ty = rvalue.ty(self.body(), self.tcx());
 466         self.sanitize_type(rvalue, rval_ty);
 467     }
 468
 469     fn visit_local_decl(&mut self, local: Local, local_decl: &LocalDecl<'tcx>) {
 470         self.super_local_decl(local, local_decl);
 471         self.sanitize_type(local_decl, local_decl.ty);
 472
 473         if let Some(user_ty) = &local_decl.user_ty {
 474             for (user_ty, span) in user_ty.projections_and_spans() {
 475                 let ty = if !local_decl.is_nonref_binding() {
 476                     // If we have a binding of the form `let ref x: T = ..`
 477                     // then remove the outermost reference so we can check the
 478                     // type annotation for the remaining type.
 479                     if let ty::Ref(_, rty, _) = local_decl.ty.kind() {
 480                         *rty
 481                     } else {
 482                         bug!("{:?} with ref binding has wrong type {}", local, local_decl.ty);
 483                     }
 484                 } else {
 485                     local_decl.ty
 486                 };
 487
 488                 if let Err(terr) = self.cx.relate_type_and_user_type(
 489                     ty,
 490                     ty::Variance::Invariant,
 491                     user_ty,
 492                     Locations::All(*span),
 493                     ConstraintCategory::TypeAnnotation,
 494                 ) {
 495                     span_mirbug!(
 496                         self,
 497                         local,
 498                         "bad user type on variable {:?}: {:?} != {:?} ({:?})",
 499                         local,
 500                         local_decl.ty,
 501                         local_decl.user_ty,
 502                         terr,
 503                     );
 504                 }
 505             }
 506         }
 507     }
 508
 509     fn visit_body(&mut self, body: &Body<'tcx>) {
 510         self.sanitize_type(&"return type", body.return_ty());
 511         for local_decl in &body.local_decls {
 512             self.sanitize_type(local_decl, local_decl.ty);
 513         }
 514         if self.errors_reported {
 515             return;
 516         }
 517         self.super_body(body);
 518     }
 519 }
 520
 521 impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
 522     fn new(
 523         cx: &'a mut TypeChecker<'b, 'tcx>,
 524         promoted: &'b IndexVec<Promoted, Body<'tcx>>,
 525     ) -> Self {
 526         TypeVerifier { promoted, last_span: cx.body.span, cx, errors_reported: false }
 527     }
 528
 529     fn body(&self) -> &Body<'tcx> {
 530         self.cx.body
 531     }
 532
 533     fn tcx(&self) -> TyCtxt<'tcx> {
 534         self.cx.infcx.tcx
 535     }
 536
 537     fn sanitize_type(&mut self, parent: &dyn fmt::Debug, ty: Ty<'tcx>) -> Ty<'tcx> {
 538         if ty.has_escaping_bound_vars() || ty.references_error() {
 539             span_mirbug_and_err!(self, parent, "bad type {:?}", ty)
 540         } else {
 541             ty
 542         }
 543     }
 544
 545     /// Checks that the types internal to the `place` match up with
 546     /// what would be expected.
 547     fn sanitize_place(
 548         &mut self,
 549         place: &Place<'tcx>,
 550         location: Location,
 551         context: PlaceContext,
 552     ) -> PlaceTy<'tcx> {
 553         debug!("sanitize_place: {:?}", place);
 554
 555         let mut place_ty = PlaceTy::from_ty(self.body().local_decls[place.local].ty);
 556
 557         for elem in place.projection.iter() {
 558             if place_ty.variant_index.is_none() {
 559                 if place_ty.ty.references_error() {
 560                     assert!(self.errors_reported);
 561                     return PlaceTy::from_ty(self.tcx().ty_error());
 562                 }
 563             }
 564             place_ty = self.sanitize_projection(place_ty, elem, place, location);
 565         }
 566
 567         if let PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy) = context {
 568             let tcx = self.tcx();
 569             let trait_ref = ty::TraitRef {
 570                 def_id: tcx.require_lang_item(LangItem::Copy, Some(self.last_span)),
 571                 substs: tcx.mk_substs_trait(place_ty.ty, &[]),
 572             };
 573
 574             // To have a `Copy` operand, the type `T` of the
 575             // value must be `Copy`. Note that we prove that `T: Copy`,
 576             // rather than using the `is_copy_modulo_regions`
 577             // test. This is important because
 578             // `is_copy_modulo_regions` ignores the resulting region
 579             // obligations and assumes they pass. This can result in
 580             // bounds from `Copy` impls being unsoundly ignored (e.g.,
 581             // #29149). Note that we decide to use `Copy` before knowing
 582             // whether the bounds fully apply: in effect, the rule is
 583             // that if a value of some type could implement `Copy`, then
 584             // it must.
 585             self.cx.prove_trait_ref(
 586                 trait_ref,
 587                 location.to_locations(),
 588                 ConstraintCategory::CopyBound,
 589             );
 590         }
 591
 592         place_ty
 593     }
 594
 595     fn sanitize_promoted(&mut self, promoted_body: &'b Body<'tcx>, location: Location) {
 596         // Determine the constraints from the promoted MIR by running the type
 597         // checker on the promoted MIR, then transfer the constraints back to
 598         // the main MIR, changing the locations to the provided location.
 599
 600         let parent_body = mem::replace(&mut self.cx.body, promoted_body);
 601
 602         // Use new sets of constraints and closure bounds so that we can
 603         // modify their locations.
 604         let all_facts = &mut None;
 605         let mut constraints = Default::default();
 606         let mut closure_bounds = Default::default();
 607         let mut liveness_constraints =
 608             LivenessValues::new(Rc::new(RegionValueElements::new(&promoted_body)));
 609         // Don't try to add borrow_region facts for the promoted MIR
 610
 611         let mut swap_constraints = |this: &mut Self| {
 612             mem::swap(this.cx.borrowck_context.all_facts, all_facts);
 613             mem::swap(
 614                 &mut this.cx.borrowck_context.constraints.outlives_constraints,
 615                 &mut constraints,
 616             );
 617             mem::swap(
 618                 &mut this.cx.borrowck_context.constraints.closure_bounds_mapping,
 619                 &mut closure_bounds,
 620             );
 621             mem::swap(
 622                 &mut this.cx.borrowck_context.constraints.liveness_constraints,
 623                 &mut liveness_constraints,
 624             );
 625         };
 626
 627         swap_constraints(self);
 628
 629         self.visit_body(&promoted_body);
 630
 631         if !self.errors_reported {
 632             // if verifier failed, don't do further checks to avoid ICEs
 633             self.cx.typeck_mir(promoted_body);
 634         }
 635
 636         self.cx.body = parent_body;
 637         // Merge the outlives constraints back in, at the given location.
 638         swap_constraints(self);
 639
 640         let locations = location.to_locations();
 641         for constraint in constraints.outlives().iter() {
 642             let mut constraint = constraint.clone();
 643             constraint.locations = locations;
 644             if let ConstraintCategory::Return(_)
 645             | ConstraintCategory::UseAsConst
 646             | ConstraintCategory::UseAsStatic = constraint.category
 647             {
 648                 // "Returning" from a promoted is an assignment to a
 649                 // temporary from the user's point of view.
 650                 constraint.category = ConstraintCategory::Boring;
 651             }
 652             self.cx.borrowck_context.constraints.outlives_constraints.push(constraint)
 653         }
 654         for region in liveness_constraints.rows() {
 655             // If the region is live at at least one location in the promoted MIR,
 656             // then add a liveness constraint to the main MIR for this region
 657             // at the location provided as an argument to this method
 658             if liveness_constraints.get_elements(region).next().is_some() {
 659                 self.cx
 660                     .borrowck_context
 661                     .constraints
 662                     .liveness_constraints
 663                     .add_element(region, location);
 664             }
 665         }
 666
 667         if !closure_bounds.is_empty() {
 668             let combined_bounds_mapping =
 669                 closure_bounds.into_iter().flat_map(|(_, value)| value).collect();
 670             let existing = self
 671                 .cx
 672                 .borrowck_context
 673                 .constraints
 674                 .closure_bounds_mapping
 675                 .insert(location, combined_bounds_mapping);
 676             assert!(existing.is_none(), "Multiple promoteds/closures at the same location.");
 677         }
 678     }
 679
 680     fn sanitize_projection(
 681         &mut self,
 682         base: PlaceTy<'tcx>,
 683         pi: PlaceElem<'tcx>,
 684         place: &Place<'tcx>,
 685         location: Location,
 686     ) -> PlaceTy<'tcx> {
 687         debug!("sanitize_projection: {:?} {:?} {:?}", base, pi, place);
 688         let tcx = self.tcx();
 689         let base_ty = base.ty;
 690         match pi {
 691             ProjectionElem::Deref => {
 692                 let deref_ty = base_ty.builtin_deref(true);
 693                 PlaceTy::from_ty(deref_ty.map(|t| t.ty).unwrap_or_else(|| {
 694                     span_mirbug_and_err!(self, place, "deref of non-pointer {:?}", base_ty)
 695                 }))
 696             }
 697             ProjectionElem::Index(i) => {
 698                 let index_ty = Place::from(i).ty(self.body(), tcx).ty;
 699                 if index_ty != tcx.types.usize {
 700                     PlaceTy::from_ty(span_mirbug_and_err!(self, i, "index by non-usize {:?}", i))
 701                 } else {
 702                     PlaceTy::from_ty(base_ty.builtin_index().unwrap_or_else(|| {
 703                         span_mirbug_and_err!(self, place, "index of non-array {:?}", base_ty)
 704                     }))
 705                 }
 706             }
 707             ProjectionElem::ConstantIndex { .. } => {
 708                 // consider verifying in-bounds
 709                 PlaceTy::from_ty(base_ty.builtin_index().unwrap_or_else(|| {
 710                     span_mirbug_and_err!(self, place, "index of non-array {:?}", base_ty)
 711                 }))
 712             }
 713             ProjectionElem::Subslice { from, to, from_end } => {
 714                 PlaceTy::from_ty(match base_ty.kind() {
 715                     ty::Array(inner, _) => {
 716                         assert!(!from_end, "array subslices should not use from_end");
 717                         tcx.mk_array(*inner, to - from)
 718                     }
 719                     ty::Slice(..) => {
 720                         assert!(from_end, "slice subslices should use from_end");
 721                         base_ty
 722                     }
 723                     _ => span_mirbug_and_err!(self, place, "slice of non-array {:?}", base_ty),
 724                 })
 725             }
 726             ProjectionElem::Downcast(maybe_name, index) => match base_ty.kind() {
 727                 ty::Adt(adt_def, _substs) if adt_def.is_enum() => {
 728                     if index.as_usize() >= adt_def.variants().len() {
 729                         PlaceTy::from_ty(span_mirbug_and_err!(
 730                             self,
 731                             place,
 732                             "cast to variant #{:?} but enum only has {:?}",
 733                             index,
 734                             adt_def.variants().len()
 735                         ))
 736                     } else {
 737                         PlaceTy { ty: base_ty, variant_index: Some(index) }
 738                     }
 739                 }
 740                 // We do not need to handle generators here, because this runs
 741                 // before the generator transform stage.
 742                 _ => {
 743                     let ty = if let Some(name) = maybe_name {
 744                         span_mirbug_and_err!(
 745                             self,
 746                             place,
 747                             "can't downcast {:?} as {:?}",
 748                             base_ty,
 749                             name
 750                         )
 751                     } else {
 752                         span_mirbug_and_err!(self, place, "can't downcast {:?}", base_ty)
 753                     };
 754                     PlaceTy::from_ty(ty)
 755                 }
 756             },
 757             ProjectionElem::Field(field, fty) => {
 758                 let fty = self.sanitize_type(place, fty);
 759                 let fty = self.cx.normalize(fty, location);
 760                 match self.field_ty(place, base, field, location) {
 761                     Ok(ty) => {
 762                         let ty = self.cx.normalize(ty, location);
 763                         if let Err(terr) = self.cx.eq_types(
 764                             ty,
 765                             fty,
 766                             location.to_locations(),
 767                             ConstraintCategory::Boring,
 768                         ) {
 769                             span_mirbug!(
 770                                 self,
 771                                 place,
 772                                 "bad field access ({:?}: {:?}): {:?}",
 773                                 ty,
 774                                 fty,
 775                                 terr
 776                             );
 777                         }
 778                     }
 779                     Err(FieldAccessError::OutOfRange { field_count }) => span_mirbug!(
 780                         self,
 781                         place,
 782                         "accessed field #{} but variant only has {}",
 783                         field.index(),
 784                         field_count
 785                     ),
 786                 }
 787                 PlaceTy::from_ty(fty)
 788             }
 789         }
 790     }
 791
 792     fn error(&mut self) -> Ty<'tcx> {
 793         self.errors_reported = true;
 794         self.tcx().ty_error()
 795     }
 796
 797     fn field_ty(
 798         &mut self,
 799         parent: &dyn fmt::Debug,
 800         base_ty: PlaceTy<'tcx>,
 801         field: Field,
 802         location: Location,
 803     ) -> Result<Ty<'tcx>, FieldAccessError> {
 804         let tcx = self.tcx();
 805
 806         let (variant, substs) = match base_ty {
 807             PlaceTy { ty, variant_index: Some(variant_index) } => match *ty.kind() {
 808                 ty::Adt(adt_def, substs) => (adt_def.variant(variant_index), substs),
 809                 ty::Generator(def_id, substs, _) => {
 810                     let mut variants = substs.as_generator().state_tys(def_id, tcx);
 811                     let Some(mut variant) = variants.nth(variant_index.into()) else {
 812                         bug!(
 813                             "variant_index of generator out of range: {:?}/{:?}",
 814                             variant_index,
 815                             substs.as_generator().state_tys(def_id, tcx).count()
 816                         );
 817                     };
 818                     return match variant.nth(field.index()) {
 819                         Some(ty) => Ok(ty),
 820                         None => Err(FieldAccessError::OutOfRange { field_count: variant.count() }),
 821                     };
 822                 }
 823                 _ => bug!("can't have downcast of non-adt non-generator type"),
 824             },
 825             PlaceTy { ty, variant_index: None } => match *ty.kind() {
 826                 ty::Adt(adt_def, substs) if !adt_def.is_enum() => {
 827                     (adt_def.variant(VariantIdx::new(0)), substs)
 828                 }
 829                 ty::Closure(_, substs) => {
 830                     return match substs
 831                         .as_closure()
 832                         .tupled_upvars_ty()
 833                         .tuple_fields()
 834                         .get(field.index())
 835                     {
 836                         Some(&ty) => Ok(ty),
 837                         None => Err(FieldAccessError::OutOfRange {
 838                             field_count: substs.as_closure().upvar_tys().count(),
 839                         }),
 840                     };
 841                 }
 842                 ty::Generator(_, substs, _) => {
 843                     // Only prefix fields (upvars and current state) are
 844                     // accessible without a variant index.
 845                     return match substs.as_generator().prefix_tys().nth(field.index()) {
 846                         Some(ty) => Ok(ty),
 847                         None => Err(FieldAccessError::OutOfRange {
 848                             field_count: substs.as_generator().prefix_tys().count(),
 849                         }),
 850                     };
 851                 }
 852                 ty::Tuple(tys) => {
 853                     return match tys.get(field.index()) {
 854                         Some(&ty) => Ok(ty),
 855                         None => Err(FieldAccessError::OutOfRange { field_count: tys.len() }),
 856                     };
 857                 }
 858                 _ => {
 859                     return Ok(span_mirbug_and_err!(
 860                         self,
 861                         parent,
 862                         "can't project out of {:?}",
 863                         base_ty
 864                     ));
 865                 }
 866             },
 867         };
 868
 869         if let Some(field) = variant.fields.get(field.index()) {
 870             Ok(self.cx.normalize(field.ty(tcx, substs), location))
 871         } else {
 872             Err(FieldAccessError::OutOfRange { field_count: variant.fields.len() })
 873         }
 874     }
 875 }
 876
 877 /// The MIR type checker. Visits the MIR and enforces all the
 878 /// constraints needed for it to be valid and well-typed. Along the
 879 /// way, it accrues region constraints -- these can later be used by
 880 /// NLL region checking.
 881 struct TypeChecker<'a, 'tcx> {
 882     infcx: &'a InferCtxt<'a, 'tcx>,
 883     param_env: ty::ParamEnv<'tcx>,
 884     last_span: Span,
 885     body: &'a Body<'tcx>,
 886     /// User type annotations are shared between the main MIR and the MIR of
 887     /// all of the promoted items.
 888     user_type_annotations: &'a CanonicalUserTypeAnnotations<'tcx>,
 889     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
 890     implicit_region_bound: ty::Region<'tcx>,
 891     reported_errors: FxHashSet<(Ty<'tcx>, Span)>,
 892     borrowck_context: &'a mut BorrowCheckContext<'a, 'tcx>,
 893 }
 894
 895 struct BorrowCheckContext<'a, 'tcx> {
 896     pub(crate) universal_regions: &'a UniversalRegions<'tcx>,
 897     location_table: &'a LocationTable,
 898     all_facts: &'a mut Option<AllFacts>,
 899     borrow_set: &'a BorrowSet<'tcx>,
 900     pub(crate) constraints: &'a mut MirTypeckRegionConstraints<'tcx>,
 901     upvars: &'a [Upvar<'tcx>],
 902 }
 903
 904 pub(crate) struct MirTypeckResults<'tcx> {
 905     pub(crate) constraints: MirTypeckRegionConstraints<'tcx>,
 906     pub(crate) universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
 907     pub(crate) opaque_type_values:
 908         VecMap<OpaqueTypeKey<'tcx>, (OpaqueHiddenType<'tcx>, OpaqueTyOrigin)>,
 909 }
 910
 911 /// A collection of region constraints that must be satisfied for the
 912 /// program to be considered well-typed.
 913 pub(crate) struct MirTypeckRegionConstraints<'tcx> {
 914     /// Maps from a `ty::Placeholder` to the corresponding
 915     /// `PlaceholderIndex` bit that we will use for it.
 916     ///
 917     /// To keep everything in sync, do not insert this set
 918     /// directly. Instead, use the `placeholder_region` helper.
 919     pub(crate) placeholder_indices: PlaceholderIndices,
 920
 921     /// Each time we add a placeholder to `placeholder_indices`, we
 922     /// also create a corresponding "representative" region vid for
 923     /// that wraps it. This vector tracks those. This way, when we
 924     /// convert the same `ty::RePlaceholder(p)` twice, we can map to
 925     /// the same underlying `RegionVid`.
 926     pub(crate) placeholder_index_to_region: IndexVec<PlaceholderIndex, ty::Region<'tcx>>,
 927
 928     /// In general, the type-checker is not responsible for enforcing
 929     /// liveness constraints; this job falls to the region inferencer,
 930     /// which performs a liveness analysis. However, in some limited
 931     /// cases, the MIR type-checker creates temporary regions that do
 932     /// not otherwise appear in the MIR -- in particular, the
 933     /// late-bound regions that it instantiates at call-sites -- and
 934     /// hence it must report on their liveness constraints.
 935     pub(crate) liveness_constraints: LivenessValues<RegionVid>,
 936
 937     pub(crate) outlives_constraints: OutlivesConstraintSet<'tcx>,
 938
 939     pub(crate) member_constraints: MemberConstraintSet<'tcx, RegionVid>,
 940
 941     pub(crate) closure_bounds_mapping:
 942         FxHashMap<Location, FxHashMap<(RegionVid, RegionVid), (ConstraintCategory<'tcx>, Span)>>,
 943
 944     pub(crate) universe_causes: FxHashMap<ty::UniverseIndex, UniverseInfo<'tcx>>,
 945
 946     pub(crate) type_tests: Vec<TypeTest<'tcx>>,
 947 }
 948
 949 impl<'tcx> MirTypeckRegionConstraints<'tcx> {
 950     fn placeholder_region(
 951         &mut self,
 952         infcx: &InferCtxt<'_, 'tcx>,
 953         placeholder: ty::PlaceholderRegion,
 954     ) -> ty::Region<'tcx> {
 955         let placeholder_index = self.placeholder_indices.insert(placeholder);
 956         match self.placeholder_index_to_region.get(placeholder_index) {
 957             Some(&v) => v,
 958             None => {
 959                 let origin = NllRegionVariableOrigin::Placeholder(placeholder);
 960                 let region = infcx.next_nll_region_var_in_universe(origin, placeholder.universe);
 961                 self.placeholder_index_to_region.push(region);
 962                 region
 963             }
 964         }
 965     }
 966 }
 967
 968 /// The `Locations` type summarizes *where* region constraints are
 969 /// required to hold. Normally, this is at a particular point which
 970 /// created the obligation, but for constraints that the user gave, we
 971 /// want the constraint to hold at all points.
 972 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
 973 pub enum Locations {
 974     /// Indicates that a type constraint should always be true. This
 975     /// is particularly important in the new borrowck analysis for
 976     /// things like the type of the return slot. Consider this
 977     /// example:
 978     ///
 979     /// ```compile_fail,E0515
 980     /// fn foo<'a>(x: &'a u32) -> &'a u32 {
 981     ///     let y = 22;
 982     ///     return &y; // error
 983     /// }
 984     /// ```
 985     ///
 986     /// Here, we wind up with the signature from the return type being
 987     /// something like `&'1 u32` where `'1` is a universal region. But
 988     /// the type of the return slot `_0` is something like `&'2 u32`
 989     /// where `'2` is an existential region variable. The type checker
 990     /// requires that `&'2 u32 = &'1 u32` -- but at what point? In the
 991     /// older NLL analysis, we required this only at the entry point
 992     /// to the function. By the nature of the constraints, this wound
 993     /// up propagating to all points reachable from start (because
 994     /// `'1` -- as a universal region -- is live everywhere). In the
 995     /// newer analysis, though, this doesn't work: `_0` is considered
 996     /// dead at the start (it has no usable value) and hence this type
 997     /// equality is basically a no-op. Then, later on, when we do `_0
 998     /// = &'3 y`, that region `'3` never winds up related to the
 999     /// universal region `'1` and hence no error occurs. Therefore, we
1000     /// use Locations::All instead, which ensures that the `'1` and
1001     /// `'2` are equal everything. We also use this for other
1002     /// user-given type annotations; e.g., if the user wrote `let mut
1003     /// x: &'static u32 = ...`, we would ensure that all values
1004     /// assigned to `x` are of `'static` lifetime.
1005     ///
1006     /// The span points to the place the constraint arose. For example,
1007     /// it points to the type in a user-given type annotation. If
1008     /// there's no sensible span then it's DUMMY_SP.
1009     All(Span),
1010
1011     /// An outlives constraint that only has to hold at a single location,
1012     /// usually it represents a point where references flow from one spot to
1013     /// another (e.g., `x = y`)
1014     Single(Location),
1015 }
1016
1017 impl Locations {
1018     pub fn from_location(&self) -> Option<Location> {
1019         match self {
1020             Locations::All(_) => None,
1021             Locations::Single(from_location) => Some(*from_location),
1022         }
1023     }
1024
1025     /// Gets a span representing the location.
1026     pub fn span(&self, body: &Body<'_>) -> Span {
1027         match self {
1028             Locations::All(span) => *span,
1029             Locations::Single(l) => body.source_info(*l).span,
1030         }
1031     }
1032 }
1033
1034 impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
1035     fn new(
1036         infcx: &'a InferCtxt<'a, 'tcx>,
1037         body: &'a Body<'tcx>,
1038         param_env: ty::ParamEnv<'tcx>,
1039         region_bound_pairs: &'a RegionBoundPairs<'tcx>,
1040         implicit_region_bound: ty::Region<'tcx>,
1041         borrowck_context: &'a mut BorrowCheckContext<'a, 'tcx>,
1042     ) -> Self {
1043         let mut checker = Self {
1044             infcx,
1045             last_span: DUMMY_SP,
1046             body,
1047             user_type_annotations: &body.user_type_annotations,
1048             param_env,
1049             region_bound_pairs,
1050             implicit_region_bound,
1051             borrowck_context,
1052             reported_errors: Default::default(),
1053         };
1054         checker.check_user_type_annotations();
1055         checker
1056     }
1057
1058     fn body(&self) -> &Body<'tcx> {
1059         self.body
1060     }
1061
1062     fn unsized_feature_enabled(&self) -> bool {
1063         let features = self.tcx().features();
1064         features.unsized_locals || features.unsized_fn_params
1065     }
1066
1067     /// Equate the inferred type and the annotated type for user type annotations
1068     #[instrument(skip(self), level = "debug")]
1069     fn check_user_type_annotations(&mut self) {
1070         debug!(?self.user_type_annotations);
1071         for user_annotation in self.user_type_annotations {
1072             let CanonicalUserTypeAnnotation { span, ref user_ty, inferred_ty } = *user_annotation;
1073             let inferred_ty = self.normalize(inferred_ty, Locations::All(span));
1074             let annotation = self.instantiate_canonical_with_fresh_inference_vars(span, user_ty);
1075             match annotation {
1076                 UserType::Ty(mut ty) => {
1077                     ty = self.normalize(ty, Locations::All(span));
1078
1079                     if let Err(terr) = self.eq_types(
1080                         ty,
1081                         inferred_ty,
1082                         Locations::All(span),
1083                         ConstraintCategory::BoringNoLocation,
1084                     ) {
1085                         span_mirbug!(
1086                             self,
1087                             user_annotation,
1088                             "bad user type ({:?} = {:?}): {:?}",
1089                             ty,
1090                             inferred_ty,
1091                             terr
1092                         );
1093                     }
1094
1095                     self.prove_predicate(
1096                         ty::Binder::dummy(ty::PredicateKind::WellFormed(inferred_ty.into()))
1097                             .to_predicate(self.tcx()),
1098                         Locations::All(span),
1099                         ConstraintCategory::TypeAnnotation,
1100                     );
1101                 }
1102                 UserType::TypeOf(def_id, user_substs) => {
1103                     if let Err(terr) = self.fully_perform_op(
1104                         Locations::All(span),
1105                         ConstraintCategory::BoringNoLocation,
1106                         self.param_env.and(type_op::ascribe_user_type::AscribeUserType::new(
1107                             inferred_ty,
1108                             def_id,
1109                             user_substs,
1110                         )),
1111                     ) {
1112                         span_mirbug!(
1113                             self,
1114                             user_annotation,
1115                             "bad user type AscribeUserType({:?}, {:?} {:?}, type_of={:?}): {:?}",
1116                             inferred_ty,
1117                             def_id,
1118                             user_substs,
1119                             self.tcx().type_of(def_id),
1120                             terr,
1121                         );
1122                     }
1123                 }
1124             }
1125         }
1126     }
1127
1128     #[instrument(skip(self, data), level = "debug")]
1129     fn push_region_constraints(
1130         &mut self,
1131         locations: Locations,
1132         category: ConstraintCategory<'tcx>,
1133         data: &QueryRegionConstraints<'tcx>,
1134     ) {
1135         debug!("constraints generated: {:#?}", data);
1136
1137         constraint_conversion::ConstraintConversion::new(
1138             self.infcx,
1139             self.borrowck_context.universal_regions,
1140             self.region_bound_pairs,
1141             Some(self.implicit_region_bound),
1142             self.param_env,
1143             locations,
1144             locations.span(self.body),
1145             category,
1146             &mut self.borrowck_context.constraints,
1147         )
1148         .convert_all(data);
1149     }
1150
1151     /// Try to relate `sub <: sup`
1152     fn sub_types(
1153         &mut self,
1154         sub: Ty<'tcx>,
1155         sup: Ty<'tcx>,
1156         locations: Locations,
1157         category: ConstraintCategory<'tcx>,
1158     ) -> Fallible<()> {
1159         // Use this order of parameters because the sup type is usually the
1160         // "expected" type in diagnostics.
1161         self.relate_types(sup, ty::Variance::Contravariant, sub, locations, category)
1162     }
1163
1164     #[instrument(skip(self, category), level = "debug")]
1165     fn eq_types(
1166         &mut self,
1167         expected: Ty<'tcx>,
1168         found: Ty<'tcx>,
1169         locations: Locations,
1170         category: ConstraintCategory<'tcx>,
1171     ) -> Fallible<()> {
1172         self.relate_types(expected, ty::Variance::Invariant, found, locations, category)
1173     }
1174
1175     #[instrument(skip(self), level = "debug")]
1176     fn relate_type_and_user_type(
1177         &mut self,
1178         a: Ty<'tcx>,
1179         v: ty::Variance,
1180         user_ty: &UserTypeProjection,
1181         locations: Locations,
1182         category: ConstraintCategory<'tcx>,
1183     ) -> Fallible<()> {
1184         let annotated_type = self.user_type_annotations[user_ty.base].inferred_ty;
1185         let mut curr_projected_ty = PlaceTy::from_ty(annotated_type);
1186
1187         let tcx = self.infcx.tcx;
1188
1189         for proj in &user_ty.projs {
1190             let projected_ty = curr_projected_ty.projection_ty_core(
1191                 tcx,
1192                 self.param_env,
1193                 proj,
1194                 |this, field, ()| {
1195                     let ty = this.field_ty(tcx, field);
1196                     self.normalize(ty, locations)
1197                 },
1198             );
1199             curr_projected_ty = projected_ty;
1200         }
1201         debug!(
1202             "user_ty base: {:?} freshened: {:?} projs: {:?} yields: {:?}",
1203             user_ty.base, annotated_type, user_ty.projs, curr_projected_ty
1204         );
1205
1206         let ty = curr_projected_ty.ty;
1207         self.relate_types(ty, v.xform(ty::Variance::Contravariant), a, locations, category)?;
1208
1209         Ok(())
1210     }
1211
1212     fn tcx(&self) -> TyCtxt<'tcx> {
1213         self.infcx.tcx
1214     }
1215
1216     #[instrument(skip(self, body, location), level = "debug")]
1217     fn check_stmt(&mut self, body: &Body<'tcx>, stmt: &Statement<'tcx>, location: Location) {
1218         let tcx = self.tcx();
1219         debug!("stmt kind: {:?}", stmt.kind);
1220         match stmt.kind {
1221             StatementKind::Assign(box (ref place, ref rv)) => {
1222                 // Assignments to temporaries are not "interesting";
1223                 // they are not caused by the user, but rather artifacts
1224                 // of lowering. Assignments to other sorts of places *are* interesting
1225                 // though.
1226                 let category = match place.as_local() {
1227                     Some(RETURN_PLACE) => {
1228                         let defining_ty = &self.borrowck_context.universal_regions.defining_ty;
1229                         if defining_ty.is_const() {
1230                             if tcx.is_static(defining_ty.def_id()) {
1231                                 ConstraintCategory::UseAsStatic
1232                             } else {
1233                                 ConstraintCategory::UseAsConst
1234                             }
1235                         } else {
1236                             ConstraintCategory::Return(ReturnConstraint::Normal)
1237                         }
1238                     }
1239                     Some(l)
1240                         if matches!(
1241                             body.local_decls[l].local_info,
1242                             Some(box LocalInfo::AggregateTemp)
1243                         ) =>
1244                     {
1245                         ConstraintCategory::Usage
1246                     }
1247                     Some(l) if !body.local_decls[l].is_user_variable() => {
1248                         ConstraintCategory::Boring
1249                     }
1250                     _ => ConstraintCategory::Assignment,
1251                 };
1252                 debug!(
1253                     "assignment category: {:?} {:?}",
1254                     category,
1255                     place.as_local().map(|l| &body.local_decls[l])
1256                 );
1257
1258                 let place_ty = place.ty(body, tcx).ty;
1259                 debug!(?place_ty);
1260                 let place_ty = self.normalize(place_ty, location);
1261                 debug!("place_ty normalized: {:?}", place_ty);
1262                 let rv_ty = rv.ty(body, tcx);
1263                 debug!(?rv_ty);
1264                 let rv_ty = self.normalize(rv_ty, location);
1265                 debug!("normalized rv_ty: {:?}", rv_ty);
1266                 if let Err(terr) =
1267                     self.sub_types(rv_ty, place_ty, location.to_locations(), category)
1268                 {
1269                     span_mirbug!(
1270                         self,
1271                         stmt,
1272                         "bad assignment ({:?} = {:?}): {:?}",
1273                         place_ty,
1274                         rv_ty,
1275                         terr
1276                     );
1277                 }
1278
1279                 if let Some(annotation_index) = self.rvalue_user_ty(rv) {
1280                     if let Err(terr) = self.relate_type_and_user_type(
1281                         rv_ty,
1282                         ty::Variance::Invariant,
1283                         &UserTypeProjection { base: annotation_index, projs: vec![] },
1284                         location.to_locations(),
1285                         ConstraintCategory::Boring,
1286                     ) {
1287                         let annotation = &self.user_type_annotations[annotation_index];
1288                         span_mirbug!(
1289                             self,
1290                             stmt,
1291                             "bad user type on rvalue ({:?} = {:?}): {:?}",
1292                             annotation,
1293                             rv_ty,
1294                             terr
1295                         );
1296                     }
1297                 }
1298
1299                 self.check_rvalue(body, rv, location);
1300                 if !self.unsized_feature_enabled() {
1301                     let trait_ref = ty::TraitRef {
1302                         def_id: tcx.require_lang_item(LangItem::Sized, Some(self.last_span)),
1303                         substs: tcx.mk_substs_trait(place_ty, &[]),
1304                     };
1305                     self.prove_trait_ref(
1306                         trait_ref,
1307                         location.to_locations(),
1308                         ConstraintCategory::SizedBound,
1309                     );
1310                 }
1311             }
1312             StatementKind::AscribeUserType(box (ref place, ref projection), variance) => {
1313                 let place_ty = place.ty(body, tcx).ty;
1314                 if let Err(terr) = self.relate_type_and_user_type(
1315                     place_ty,
1316                     variance,
1317                     projection,
1318                     Locations::All(stmt.source_info.span),
1319                     ConstraintCategory::TypeAnnotation,
1320                 ) {
1321                     let annotation = &self.user_type_annotations[projection.base];
1322                     span_mirbug!(
1323                         self,
1324                         stmt,
1325                         "bad type assert ({:?} <: {:?} with projections {:?}): {:?}",
1326                         place_ty,
1327                         annotation,
1328                         projection.projs,
1329                         terr
1330                     );
1331                 }
1332             }
1333             StatementKind::CopyNonOverlapping(box rustc_middle::mir::CopyNonOverlapping {
1334                 ..
1335             }) => span_bug!(
1336                 stmt.source_info.span,
1337                 "Unexpected StatementKind::CopyNonOverlapping, should only appear after lowering_intrinsics",
1338             ),
1339             StatementKind::FakeRead(..)
1340             | StatementKind::StorageLive(..)
1341             | StatementKind::StorageDead(..)
1342             | StatementKind::Retag { .. }
1343             | StatementKind::Coverage(..)
1344             | StatementKind::Nop => {}
1345             StatementKind::Deinit(..) | StatementKind::SetDiscriminant { .. } => {
1346                 bug!("Statement not allowed in this MIR phase")
1347             }
1348         }
1349     }
1350
1351     #[instrument(skip(self, body, term_location), level = "debug")]
1352     fn check_terminator(
1353         &mut self,
1354         body: &Body<'tcx>,
1355         term: &Terminator<'tcx>,
1356         term_location: Location,
1357     ) {
1358         let tcx = self.tcx();
1359         debug!("terminator kind: {:?}", term.kind);
1360         match term.kind {
1361             TerminatorKind::Goto { .. }
1362             | TerminatorKind::Resume
1363             | TerminatorKind::Abort
1364             | TerminatorKind::Return
1365             | TerminatorKind::GeneratorDrop
1366             | TerminatorKind::Unreachable
1367             | TerminatorKind::Drop { .. }
1368             | TerminatorKind::FalseEdge { .. }
1369             | TerminatorKind::FalseUnwind { .. }
1370             | TerminatorKind::InlineAsm { .. } => {
1371                 // no checks needed for these
1372             }
1373
1374             TerminatorKind::DropAndReplace { ref place, ref value, target: _, unwind: _ } => {
1375                 let place_ty = place.ty(body, tcx).ty;
1376                 let rv_ty = value.ty(body, tcx);
1377
1378                 let locations = term_location.to_locations();
1379                 if let Err(terr) =
1380                     self.sub_types(rv_ty, place_ty, locations, ConstraintCategory::Assignment)
1381                 {
1382                     span_mirbug!(
1383                         self,
1384                         term,
1385                         "bad DropAndReplace ({:?} = {:?}): {:?}",
1386                         place_ty,
1387                         rv_ty,
1388                         terr
1389                     );
1390                 }
1391             }
1392             TerminatorKind::SwitchInt { ref discr, switch_ty, .. } => {
1393                 self.check_operand(discr, term_location);
1394
1395                 let discr_ty = discr.ty(body, tcx);
1396                 if let Err(terr) = self.sub_types(
1397                     discr_ty,
1398                     switch_ty,
1399                     term_location.to_locations(),
1400                     ConstraintCategory::Assignment,
1401                 ) {
1402                     span_mirbug!(
1403                         self,
1404                         term,
1405                         "bad SwitchInt ({:?} on {:?}): {:?}",
1406                         switch_ty,
1407                         discr_ty,
1408                         terr
1409                     );
1410                 }
1411                 if !switch_ty.is_integral() && !switch_ty.is_char() && !switch_ty.is_bool() {
1412                     span_mirbug!(self, term, "bad SwitchInt discr ty {:?}", switch_ty);
1413                 }
1414                 // FIXME: check the values
1415             }
1416             TerminatorKind::Call {
1417                 ref func,
1418                 ref args,
1419                 ref destination,
1420                 from_hir_call,
1421                 target,
1422                 ..
1423             } => {
1424                 self.check_operand(func, term_location);
1425                 for arg in args {
1426                     self.check_operand(arg, term_location);
1427                 }
1428
1429                 let func_ty = func.ty(body, tcx);
1430                 debug!("func_ty.kind: {:?}", func_ty.kind());
1431
1432                 let sig = match func_ty.kind() {
1433                     ty::FnDef(..) | ty::FnPtr(_) => func_ty.fn_sig(tcx),
1434                     _ => {
1435                         span_mirbug!(self, term, "call to non-function {:?}", func_ty);
1436                         return;
1437                     }
1438                 };
1439                 let (sig, map) = self.infcx.replace_bound_vars_with_fresh_vars(
1440                     term.source_info.span,
1441                     LateBoundRegionConversionTime::FnCall,
1442                     sig,
1443                 );
1444                 debug!(?sig);
1445                 let sig = self.normalize(sig, term_location);
1446                 self.check_call_dest(body, term, &sig, *destination, target, term_location);
1447
1448                 self.prove_predicates(
1449                     sig.inputs_and_output
1450                         .iter()
1451                         .map(|ty| ty::Binder::dummy(ty::PredicateKind::WellFormed(ty.into()))),
1452                     term_location.to_locations(),
1453                     ConstraintCategory::Boring,
1454                 );
1455
1456                 // The ordinary liveness rules will ensure that all
1457                 // regions in the type of the callee are live here. We
1458                 // then further constrain the late-bound regions that
1459                 // were instantiated at the call site to be live as
1460                 // well. The resulting is that all the input (and
1461                 // output) types in the signature must be live, since
1462                 // all the inputs that fed into it were live.
1463                 for &late_bound_region in map.values() {
1464                     let region_vid =
1465                         self.borrowck_context.universal_regions.to_region_vid(late_bound_region);
1466                     self.borrowck_context
1467                         .constraints
1468                         .liveness_constraints
1469                         .add_element(region_vid, term_location);
1470                 }
1471
1472                 self.check_call_inputs(body, term, &sig, args, term_location, from_hir_call);
1473             }
1474             TerminatorKind::Assert { ref cond, ref msg, .. } => {
1475                 self.check_operand(cond, term_location);
1476
1477                 let cond_ty = cond.ty(body, tcx);
1478                 if cond_ty != tcx.types.bool {
1479                     span_mirbug!(self, term, "bad Assert ({:?}, not bool", cond_ty);
1480                 }
1481
1482                 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
1483                     if len.ty(body, tcx) != tcx.types.usize {
1484                         span_mirbug!(self, len, "bounds-check length non-usize {:?}", len)
1485                     }
1486                     if index.ty(body, tcx) != tcx.types.usize {
1487                         span_mirbug!(self, index, "bounds-check index non-usize {:?}", index)
1488                     }
1489                 }
1490             }
1491             TerminatorKind::Yield { ref value, .. } => {
1492                 self.check_operand(value, term_location);
1493
1494                 let value_ty = value.ty(body, tcx);
1495                 match body.yield_ty() {
1496                     None => span_mirbug!(self, term, "yield in non-generator"),
1497                     Some(ty) => {
1498                         if let Err(terr) = self.sub_types(
1499                             value_ty,
1500                             ty,
1501                             term_location.to_locations(),
1502                             ConstraintCategory::Yield,
1503                         ) {
1504                             span_mirbug!(
1505                                 self,
1506                                 term,
1507                                 "type of yield value is {:?}, but the yield type is {:?}: {:?}",
1508                                 value_ty,
1509                                 ty,
1510                                 terr
1511                             );
1512                         }
1513                     }
1514                 }
1515             }
1516         }
1517     }
1518
1519     fn check_call_dest(
1520         &mut self,
1521         body: &Body<'tcx>,
1522         term: &Terminator<'tcx>,
1523         sig: &ty::FnSig<'tcx>,
1524         destination: Place<'tcx>,
1525         target: Option<BasicBlock>,
1526         term_location: Location,
1527     ) {
1528         let tcx = self.tcx();
1529         match target {
1530             Some(_) => {
1531                 let dest_ty = destination.ty(body, tcx).ty;
1532                 let dest_ty = self.normalize(dest_ty, term_location);
1533                 let category = match destination.as_local() {
1534                     Some(RETURN_PLACE) => {
1535                         if let BorrowCheckContext {
1536                             universal_regions:
1537                                 UniversalRegions {
1538                                     defining_ty:
1539                                         DefiningTy::Const(def_id, _)
1540                                         | DefiningTy::InlineConst(def_id, _),
1541                                     ..
1542                                 },
1543                             ..
1544                         } = self.borrowck_context
1545                         {
1546                             if tcx.is_static(*def_id) {
1547                                 ConstraintCategory::UseAsStatic
1548                             } else {
1549                                 ConstraintCategory::UseAsConst
1550                             }
1551                         } else {
1552                             ConstraintCategory::Return(ReturnConstraint::Normal)
1553                         }
1554                     }
1555                     Some(l) if !body.local_decls[l].is_user_variable() => {
1556                         ConstraintCategory::Boring
1557                     }
1558                     _ => ConstraintCategory::Assignment,
1559                 };
1560
1561                 let locations = term_location.to_locations();
1562
1563                 if let Err(terr) = self.sub_types(sig.output(), dest_ty, locations, category) {
1564                     span_mirbug!(
1565                         self,
1566                         term,
1567                         "call dest mismatch ({:?} <- {:?}): {:?}",
1568                         dest_ty,
1569                         sig.output(),
1570                         terr
1571                     );
1572                 }
1573
1574                 // When `unsized_fn_params` and `unsized_locals` are both not enabled,
1575                 // this check is done at `check_local`.
1576                 if self.unsized_feature_enabled() {
1577                     let span = term.source_info.span;
1578                     self.ensure_place_sized(dest_ty, span);
1579                 }
1580             }
1581             None => {
1582                 if !self
1583                     .tcx()
1584                     .conservative_is_privately_uninhabited(self.param_env.and(sig.output()))
1585                 {
1586                     span_mirbug!(self, term, "call to converging function {:?} w/o dest", sig);
1587                 }
1588             }
1589         }
1590     }
1591
1592     fn check_call_inputs(
1593         &mut self,
1594         body: &Body<'tcx>,
1595         term: &Terminator<'tcx>,
1596         sig: &ty::FnSig<'tcx>,
1597         args: &[Operand<'tcx>],
1598         term_location: Location,
1599         from_hir_call: bool,
1600     ) {
1601         debug!("check_call_inputs({:?}, {:?})", sig, args);
1602         if args.len() < sig.inputs().len() || (args.len() > sig.inputs().len() && !sig.c_variadic) {
1603             span_mirbug!(self, term, "call to {:?} with wrong # of args", sig);
1604         }
1605
1606         let func_ty = if let TerminatorKind::Call { func, .. } = &term.kind {
1607             Some(func.ty(body, self.infcx.tcx))
1608         } else {
1609             None
1610         };
1611         debug!(?func_ty);
1612
1613         for (n, (fn_arg, op_arg)) in iter::zip(sig.inputs(), args).enumerate() {
1614             let op_arg_ty = op_arg.ty(body, self.tcx());
1615
1616             let op_arg_ty = self.normalize(op_arg_ty, term_location);
1617             let category = if from_hir_call {
1618                 ConstraintCategory::CallArgument(func_ty)
1619             } else {
1620                 ConstraintCategory::Boring
1621             };
1622             if let Err(terr) =
1623                 self.sub_types(op_arg_ty, *fn_arg, term_location.to_locations(), category)
1624             {
1625                 span_mirbug!(
1626                     self,
1627                     term,
1628                     "bad arg #{:?} ({:?} <- {:?}): {:?}",
1629                     n,
1630                     fn_arg,
1631                     op_arg_ty,
1632                     terr
1633                 );
1634             }
1635         }
1636     }
1637
1638     fn check_iscleanup(&mut self, body: &Body<'tcx>, block_data: &BasicBlockData<'tcx>) {
1639         let is_cleanup = block_data.is_cleanup;
1640         self.last_span = block_data.terminator().source_info.span;
1641         match block_data.terminator().kind {
1642             TerminatorKind::Goto { target } => {
1643                 self.assert_iscleanup(body, block_data, target, is_cleanup)
1644             }
1645             TerminatorKind::SwitchInt { ref targets, .. } => {
1646                 for target in targets.all_targets() {
1647                     self.assert_iscleanup(body, block_data, *target, is_cleanup);
1648                 }
1649             }
1650             TerminatorKind::Resume => {
1651                 if !is_cleanup {
1652                     span_mirbug!(self, block_data, "resume on non-cleanup block!")
1653                 }
1654             }
1655             TerminatorKind::Abort => {
1656                 if !is_cleanup {
1657                     span_mirbug!(self, block_data, "abort on non-cleanup block!")
1658                 }
1659             }
1660             TerminatorKind::Return => {
1661                 if is_cleanup {
1662                     span_mirbug!(self, block_data, "return on cleanup block")
1663                 }
1664             }
1665             TerminatorKind::GeneratorDrop { .. } => {
1666                 if is_cleanup {
1667                     span_mirbug!(self, block_data, "generator_drop in cleanup block")
1668                 }
1669             }
1670             TerminatorKind::Yield { resume, drop, .. } => {
1671                 if is_cleanup {
1672                     span_mirbug!(self, block_data, "yield in cleanup block")
1673                 }
1674                 self.assert_iscleanup(body, block_data, resume, is_cleanup);
1675                 if let Some(drop) = drop {
1676                     self.assert_iscleanup(body, block_data, drop, is_cleanup);
1677                 }
1678             }
1679             TerminatorKind::Unreachable => {}
1680             TerminatorKind::Drop { target, unwind, .. }
1681             | TerminatorKind::DropAndReplace { target, unwind, .. }
1682             | TerminatorKind::Assert { target, cleanup: unwind, .. } => {
1683                 self.assert_iscleanup(body, block_data, target, is_cleanup);
1684                 if let Some(unwind) = unwind {
1685                     if is_cleanup {
1686                         span_mirbug!(self, block_data, "unwind on cleanup block")
1687                     }
1688                     self.assert_iscleanup(body, block_data, unwind, true);
1689                 }
1690             }
1691             TerminatorKind::Call { ref target, cleanup, .. } => {
1692                 if let &Some(target) = target {
1693                     self.assert_iscleanup(body, block_data, target, is_cleanup);
1694                 }
1695                 if let Some(cleanup) = cleanup {
1696                     if is_cleanup {
1697                         span_mirbug!(self, block_data, "cleanup on cleanup block")
1698                     }
1699                     self.assert_iscleanup(body, block_data, cleanup, true);
1700                 }
1701             }
1702             TerminatorKind::FalseEdge { real_target, imaginary_target } => {
1703                 self.assert_iscleanup(body, block_data, real_target, is_cleanup);
1704                 self.assert_iscleanup(body, block_data, imaginary_target, is_cleanup);
1705             }
1706             TerminatorKind::FalseUnwind { real_target, unwind } => {
1707                 self.assert_iscleanup(body, block_data, real_target, is_cleanup);
1708                 if let Some(unwind) = unwind {
1709                     if is_cleanup {
1710                         span_mirbug!(self, block_data, "cleanup in cleanup block via false unwind");
1711                     }
1712                     self.assert_iscleanup(body, block_data, unwind, true);
1713                 }
1714             }
1715             TerminatorKind::InlineAsm { destination, cleanup, .. } => {
1716                 if let Some(target) = destination {
1717                     self.assert_iscleanup(body, block_data, target, is_cleanup);
1718                 }
1719                 if let Some(cleanup) = cleanup {
1720                     if is_cleanup {
1721                         span_mirbug!(self, block_data, "cleanup on cleanup block")
1722                     }
1723                     self.assert_iscleanup(body, block_data, cleanup, true);
1724                 }
1725             }
1726         }
1727     }
1728
1729     fn assert_iscleanup(
1730         &mut self,
1731         body: &Body<'tcx>,
1732         ctxt: &dyn fmt::Debug,
1733         bb: BasicBlock,
1734         iscleanuppad: bool,
1735     ) {
1736         if body[bb].is_cleanup != iscleanuppad {
1737             span_mirbug!(self, ctxt, "cleanuppad mismatch: {:?} should be {:?}", bb, iscleanuppad);
1738         }
1739     }
1740
1741     fn check_local(&mut self, body: &Body<'tcx>, local: Local, local_decl: &LocalDecl<'tcx>) {
1742         match body.local_kind(local) {
1743             LocalKind::ReturnPointer | LocalKind::Arg => {
1744                 // return values of normal functions are required to be
1745                 // sized by typeck, but return values of ADT constructors are
1746                 // not because we don't include a `Self: Sized` bounds on them.
1747                 //
1748                 // Unbound parts of arguments were never required to be Sized
1749                 // - maybe we should make that a warning.
1750                 return;
1751             }
1752             LocalKind::Var | LocalKind::Temp => {}
1753         }
1754
1755         // When `unsized_fn_params` or `unsized_locals` is enabled, only function calls
1756         // and nullary ops are checked in `check_call_dest`.
1757         if !self.unsized_feature_enabled() {
1758             let span = local_decl.source_info.span;
1759             let ty = local_decl.ty;
1760             self.ensure_place_sized(ty, span);
1761         }
1762     }
1763
1764     fn ensure_place_sized(&mut self, ty: Ty<'tcx>, span: Span) {
1765         let tcx = self.tcx();
1766
1767         // Erase the regions from `ty` to get a global type.  The
1768         // `Sized` bound in no way depends on precise regions, so this
1769         // shouldn't affect `is_sized`.
1770         let erased_ty = tcx.erase_regions(ty);
1771         if !erased_ty.is_sized(tcx.at(span), self.param_env) {
1772             // in current MIR construction, all non-control-flow rvalue
1773             // expressions evaluate through `as_temp` or `into` a return
1774             // slot or local, so to find all unsized rvalues it is enough
1775             // to check all temps, return slots and locals.
1776             if self.reported_errors.replace((ty, span)).is_none() {
1777                 let mut diag = struct_span_err!(
1778                     self.tcx().sess,
1779                     span,
1780                     E0161,
1781                     "cannot move a value of type {0}: the size of {0} \
1782                      cannot be statically determined",
1783                     ty
1784                 );
1785
1786                 // While this is located in `nll::typeck` this error is not
1787                 // an NLL error, it's a required check to prevent creation
1788                 // of unsized rvalues in a call expression.
1789                 diag.emit();
1790             }
1791         }
1792     }
1793
1794     fn aggregate_field_ty(
1795         &mut self,
1796         ak: &AggregateKind<'tcx>,
1797         field_index: usize,
1798         location: Location,
1799     ) -> Result<Ty<'tcx>, FieldAccessError> {
1800         let tcx = self.tcx();
1801
1802         match *ak {
1803             AggregateKind::Adt(adt_did, variant_index, substs, _, active_field_index) => {
1804                 let def = tcx.adt_def(adt_did);
1805                 let variant = &def.variant(variant_index);
1806                 let adj_field_index = active_field_index.unwrap_or(field_index);
1807                 if let Some(field) = variant.fields.get(adj_field_index) {
1808                     Ok(self.normalize(field.ty(tcx, substs), location))
1809                 } else {
1810                     Err(FieldAccessError::OutOfRange { field_count: variant.fields.len() })
1811                 }
1812             }
1813             AggregateKind::Closure(_, substs) => {
1814                 match substs.as_closure().upvar_tys().nth(field_index) {
1815                     Some(ty) => Ok(ty),
1816                     None => Err(FieldAccessError::OutOfRange {
1817                         field_count: substs.as_closure().upvar_tys().count(),
1818                     }),
1819                 }
1820             }
1821             AggregateKind::Generator(_, substs, _) => {
1822                 // It doesn't make sense to look at a field beyond the prefix;
1823                 // these require a variant index, and are not initialized in
1824                 // aggregate rvalues.
1825                 match substs.as_generator().prefix_tys().nth(field_index) {
1826                     Some(ty) => Ok(ty),
1827                     None => Err(FieldAccessError::OutOfRange {
1828                         field_count: substs.as_generator().prefix_tys().count(),
1829                     }),
1830                 }
1831             }
1832             AggregateKind::Array(ty) => Ok(ty),
1833             AggregateKind::Tuple => {
1834                 unreachable!("This should have been covered in check_rvalues");
1835             }
1836         }
1837     }
1838
1839     fn check_operand(&mut self, op: &Operand<'tcx>, location: Location) {
1840         if let Operand::Constant(constant) = op {
1841             let maybe_uneval = match constant.literal {
1842                 ConstantKind::Ty(ct) => match ct.val() {
1843                     ty::ConstKind::Unevaluated(uv) => Some(uv),
1844                     _ => None,
1845                 },
1846                 _ => None,
1847             };
1848             if let Some(uv) = maybe_uneval {
1849                 if uv.promoted.is_none() {
1850                     let tcx = self.tcx();
1851                     let def_id = uv.def.def_id_for_type_of();
1852                     if tcx.def_kind(def_id) == DefKind::InlineConst {
1853                         let predicates = self.prove_closure_bounds(
1854                             tcx,
1855                             def_id.expect_local(),
1856                             uv.substs,
1857                             location,
1858                         );
1859                         self.normalize_and_prove_instantiated_predicates(
1860                             def_id,
1861                             predicates,
1862                             location.to_locations(),
1863                         );
1864                     }
1865                 }
1866             }
1867         }
1868     }
1869
1870     #[instrument(skip(self, body), level = "debug")]
1871     fn check_rvalue(&mut self, body: &Body<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
1872         let tcx = self.tcx();
1873
1874         match rvalue {
1875             Rvalue::Aggregate(ak, ops) => {
1876                 for op in ops {
1877                     self.check_operand(op, location);
1878                 }
1879                 self.check_aggregate_rvalue(&body, rvalue, ak, ops, location)
1880             }
1881
1882             Rvalue::Repeat(operand, len) => {
1883                 self.check_operand(operand, location);
1884
1885                 // If the length cannot be evaluated we must assume that the length can be larger
1886                 // than 1.
1887                 // If the length is larger than 1, the repeat expression will need to copy the
1888                 // element, so we require the `Copy` trait.
1889                 if len.try_eval_usize(tcx, self.param_env).map_or(true, |len| len > 1) {
1890                     match operand {
1891                         Operand::Copy(..) | Operand::Constant(..) => {
1892                             // These are always okay: direct use of a const, or a value that can evidently be copied.
1893                         }
1894                         Operand::Move(place) => {
1895                             // Make sure that repeated elements implement `Copy`.
1896                             let span = body.source_info(location).span;
1897                             let ty = place.ty(body, tcx).ty;
1898                             let trait_ref = ty::TraitRef::new(
1899                                 tcx.require_lang_item(LangItem::Copy, Some(span)),
1900                                 tcx.mk_substs_trait(ty, &[]),
1901                             );
1902
1903                             self.prove_trait_ref(
1904                                 trait_ref,
1905                                 Locations::Single(location),
1906                                 ConstraintCategory::CopyBound,
1907                             );
1908                         }
1909                     }
1910                 }
1911             }
1912
1913             &Rvalue::NullaryOp(_, ty) => {
1914                 let trait_ref = ty::TraitRef {
1915                     def_id: tcx.require_lang_item(LangItem::Sized, Some(self.last_span)),
1916                     substs: tcx.mk_substs_trait(ty, &[]),
1917                 };
1918
1919                 self.prove_trait_ref(
1920                     trait_ref,
1921                     location.to_locations(),
1922                     ConstraintCategory::SizedBound,
1923                 );
1924             }
1925
1926             Rvalue::ShallowInitBox(operand, ty) => {
1927                 self.check_operand(operand, location);
1928
1929                 let trait_ref = ty::TraitRef {
1930                     def_id: tcx.require_lang_item(LangItem::Sized, Some(self.last_span)),
1931                     substs: tcx.mk_substs_trait(*ty, &[]),
1932                 };
1933
1934                 self.prove_trait_ref(
1935                     trait_ref,
1936                     location.to_locations(),
1937                     ConstraintCategory::SizedBound,
1938                 );
1939             }
1940
1941             Rvalue::Cast(cast_kind, op, ty) => {
1942                 self.check_operand(op, location);
1943
1944                 match cast_kind {
1945                     CastKind::Pointer(PointerCast::ReifyFnPointer) => {
1946                         let fn_sig = op.ty(body, tcx).fn_sig(tcx);
1947
1948                         // The type that we see in the fcx is like
1949                         // `foo::<'a, 'b>`, where `foo` is the path to a
1950                         // function definition. When we extract the
1951                         // signature, it comes from the `fn_sig` query,
1952                         // and hence may contain unnormalized results.
1953                         let fn_sig = self.normalize(fn_sig, location);
1954
1955                         let ty_fn_ptr_from = tcx.mk_fn_ptr(fn_sig);
1956
1957                         if let Err(terr) = self.eq_types(
1958                             *ty,
1959                             ty_fn_ptr_from,
1960                             location.to_locations(),
1961                             ConstraintCategory::Cast,
1962                         ) {
1963                             span_mirbug!(
1964                                 self,
1965                                 rvalue,
1966                                 "equating {:?} with {:?} yields {:?}",
1967                                 ty_fn_ptr_from,
1968                                 ty,
1969                                 terr
1970                             );
1971                         }
1972                     }
1973
1974                     CastKind::Pointer(PointerCast::ClosureFnPointer(unsafety)) => {
1975                         let sig = match op.ty(body, tcx).kind() {
1976                             ty::Closure(_, substs) => substs.as_closure().sig(),
1977                             _ => bug!(),
1978                         };
1979                         let ty_fn_ptr_from = tcx.mk_fn_ptr(tcx.signature_unclosure(sig, *unsafety));
1980
1981                         if let Err(terr) = self.eq_types(
1982                             *ty,
1983                             ty_fn_ptr_from,
1984                             location.to_locations(),
1985                             ConstraintCategory::Cast,
1986                         ) {
1987                             span_mirbug!(
1988                                 self,
1989                                 rvalue,
1990                                 "equating {:?} with {:?} yields {:?}",
1991                                 ty_fn_ptr_from,
1992                                 ty,
1993                                 terr
1994                             );
1995                         }
1996                     }
1997
1998                     CastKind::Pointer(PointerCast::UnsafeFnPointer) => {
1999                         let fn_sig = op.ty(body, tcx).fn_sig(tcx);
2000
2001                         // The type that we see in the fcx is like
2002                         // `foo::<'a, 'b>`, where `foo` is the path to a
2003                         // function definition. When we extract the
2004                         // signature, it comes from the `fn_sig` query,
2005                         // and hence may contain unnormalized results.
2006                         let fn_sig = self.normalize(fn_sig, location);
2007
2008                         let ty_fn_ptr_from = tcx.safe_to_unsafe_fn_ty(fn_sig);
2009
2010                         if let Err(terr) = self.eq_types(
2011                             *ty,
2012                             ty_fn_ptr_from,
2013                             location.to_locations(),
2014                             ConstraintCategory::Cast,
2015                         ) {
2016                             span_mirbug!(
2017                                 self,
2018                                 rvalue,
2019                                 "equating {:?} with {:?} yields {:?}",
2020                                 ty_fn_ptr_from,
2021                                 ty,
2022                                 terr
2023                             );
2024                         }
2025                     }
2026
2027                     CastKind::Pointer(PointerCast::Unsize) => {
2028                         let &ty = ty;
2029                         let trait_ref = ty::TraitRef {
2030                             def_id: tcx
2031                                 .require_lang_item(LangItem::CoerceUnsized, Some(self.last_span)),
2032                             substs: tcx.mk_substs_trait(op.ty(body, tcx), &[ty.into()]),
2033                         };
2034
2035                         self.prove_trait_ref(
2036                             trait_ref,
2037                             location.to_locations(),
2038                             ConstraintCategory::Cast,
2039                         );
2040                     }
2041
2042                     CastKind::Pointer(PointerCast::MutToConstPointer) => {
2043                         let ty::RawPtr(ty::TypeAndMut {
2044                             ty: ty_from,
2045                             mutbl: hir::Mutability::Mut,
2046                         }) = op.ty(body, tcx).kind() else {
2047                             span_mirbug!(
2048                                 self,
2049                                 rvalue,
2050                                 "unexpected base type for cast {:?}",
2051                                 ty,
2052                             );
2053                             return;
2054                         };
2055                         let ty::RawPtr(ty::TypeAndMut {
2056                             ty: ty_to,
2057                             mutbl: hir::Mutability::Not,
2058                         }) = ty.kind() else {
2059                             span_mirbug!(
2060                                 self,
2061                                 rvalue,
2062                                 "unexpected target type for cast {:?}",
2063                                 ty,
2064                             );
2065                             return;
2066                         };
2067                         if let Err(terr) = self.sub_types(
2068                             *ty_from,
2069                             *ty_to,
2070                             location.to_locations(),
2071                             ConstraintCategory::Cast,
2072                         ) {
2073                             span_mirbug!(
2074                                 self,
2075                                 rvalue,
2076                                 "relating {:?} with {:?} yields {:?}",
2077                                 ty_from,
2078                                 ty_to,
2079                                 terr
2080                             );
2081                         }
2082                     }
2083
2084                     CastKind::Pointer(PointerCast::ArrayToPointer) => {
2085                         let ty_from = op.ty(body, tcx);
2086
2087                         let opt_ty_elem_mut = match ty_from.kind() {
2088                             ty::RawPtr(ty::TypeAndMut { mutbl: array_mut, ty: array_ty }) => {
2089                                 match array_ty.kind() {
2090                                     ty::Array(ty_elem, _) => Some((ty_elem, *array_mut)),
2091                                     _ => None,
2092                                 }
2093                             }
2094                             _ => None,
2095                         };
2096
2097                         let Some((ty_elem, ty_mut)) = opt_ty_elem_mut else {
2098                             span_mirbug!(
2099                                 self,
2100                                 rvalue,
2101                                 "ArrayToPointer cast from unexpected type {:?}",
2102                                 ty_from,
2103                             );
2104                             return;
2105                         };
2106
2107                         let (ty_to, ty_to_mut) = match ty.kind() {
2108                             ty::RawPtr(ty::TypeAndMut { mutbl: ty_to_mut, ty: ty_to }) => {
2109                                 (ty_to, *ty_to_mut)
2110                             }
2111                             _ => {
2112                                 span_mirbug!(
2113                                     self,
2114                                     rvalue,
2115                                     "ArrayToPointer cast to unexpected type {:?}",
2116                                     ty,
2117                                 );
2118                                 return;
2119                             }
2120                         };
2121
2122                         if ty_to_mut == Mutability::Mut && ty_mut == Mutability::Not {
2123                             span_mirbug!(
2124                                 self,
2125                                 rvalue,
2126                                 "ArrayToPointer cast from const {:?} to mut {:?}",
2127                                 ty,
2128                                 ty_to
2129                             );
2130                             return;
2131                         }
2132
2133                         if let Err(terr) = self.sub_types(
2134                             *ty_elem,
2135                             *ty_to,
2136                             location.to_locations(),
2137                             ConstraintCategory::Cast,
2138                         ) {
2139                             span_mirbug!(
2140                                 self,
2141                                 rvalue,
2142                                 "relating {:?} with {:?} yields {:?}",
2143                                 ty_elem,
2144                                 ty_to,
2145                                 terr
2146                             )
2147                         }
2148                     }
2149
2150                     CastKind::Misc => {
2151                         let ty_from = op.ty(body, tcx);
2152                         let cast_ty_from = CastTy::from_ty(ty_from);
2153                         let cast_ty_to = CastTy::from_ty(*ty);
2154                         match (cast_ty_from, cast_ty_to) {
2155                             (None, _)
2156                             | (_, None | Some(CastTy::FnPtr))
2157                             | (Some(CastTy::Float), Some(CastTy::Ptr(_)))
2158                             | (Some(CastTy::Ptr(_) | CastTy::FnPtr), Some(CastTy::Float)) => {
2159                                 span_mirbug!(self, rvalue, "Invalid cast {:?} -> {:?}", ty_from, ty,)
2160                             }
2161                             (
2162                                 Some(CastTy::Int(_)),
2163                                 Some(CastTy::Int(_) | CastTy::Float | CastTy::Ptr(_)),
2164                             )
2165                             | (Some(CastTy::Float), Some(CastTy::Int(_) | CastTy::Float))
2166                             | (Some(CastTy::Ptr(_)), Some(CastTy::Int(_) | CastTy::Ptr(_)))
2167                             | (Some(CastTy::FnPtr), Some(CastTy::Int(_) | CastTy::Ptr(_))) => (),
2168                         }
2169                     }
2170                 }
2171             }
2172
2173             Rvalue::Ref(region, _borrow_kind, borrowed_place) => {
2174                 self.add_reborrow_constraint(&body, location, *region, borrowed_place);
2175             }
2176
2177             Rvalue::BinaryOp(
2178                 BinOp::Eq | BinOp::Ne | BinOp::Lt | BinOp::Le | BinOp::Gt | BinOp::Ge,
2179                 box (left, right),
2180             ) => {
2181                 self.check_operand(left, location);
2182                 self.check_operand(right, location);
2183
2184                 let ty_left = left.ty(body, tcx);
2185                 match ty_left.kind() {
2186                     // Types with regions are comparable if they have a common super-type.
2187                     ty::RawPtr(_) | ty::FnPtr(_) => {
2188                         let ty_right = right.ty(body, tcx);
2189                         let common_ty = self.infcx.next_ty_var(TypeVariableOrigin {
2190                             kind: TypeVariableOriginKind::MiscVariable,
2191                             span: body.source_info(location).span,
2192                         });
2193                         self.sub_types(
2194                             ty_left,
2195                             common_ty,
2196                             location.to_locations(),
2197                             ConstraintCategory::Boring,
2198                         )
2199                         .unwrap_or_else(|err| {
2200                             bug!("Could not equate type variable with {:?}: {:?}", ty_left, err)
2201                         });
2202                         if let Err(terr) = self.sub_types(
2203                             ty_right,
2204                             common_ty,
2205                             location.to_locations(),
2206                             ConstraintCategory::Boring,
2207                         ) {
2208                             span_mirbug!(
2209                                 self,
2210                                 rvalue,
2211                                 "unexpected comparison types {:?} and {:?} yields {:?}",
2212                                 ty_left,
2213                                 ty_right,
2214                                 terr
2215                             )
2216                         }
2217                     }
2218                     // For types with no regions we can just check that the
2219                     // both operands have the same type.
2220                     ty::Int(_) | ty::Uint(_) | ty::Bool | ty::Char | ty::Float(_)
2221                         if ty_left == right.ty(body, tcx) => {}
2222                     // Other types are compared by trait methods, not by
2223                     // `Rvalue::BinaryOp`.
2224                     _ => span_mirbug!(
2225                         self,
2226                         rvalue,
2227                         "unexpected comparison types {:?} and {:?}",
2228                         ty_left,
2229                         right.ty(body, tcx)
2230                     ),
2231                 }
2232             }
2233
2234             Rvalue::Use(operand) | Rvalue::UnaryOp(_, operand) => {
2235                 self.check_operand(operand, location);
2236             }
2237
2238             Rvalue::BinaryOp(_, box (left, right))
2239             | Rvalue::CheckedBinaryOp(_, box (left, right)) => {
2240                 self.check_operand(left, location);
2241                 self.check_operand(right, location);
2242             }
2243
2244             Rvalue::AddressOf(..)
2245             | Rvalue::ThreadLocalRef(..)
2246             | Rvalue::Len(..)
2247             | Rvalue::Discriminant(..) => {}
2248         }
2249     }
2250
2251     /// If this rvalue supports a user-given type annotation, then
2252     /// extract and return it. This represents the final type of the
2253     /// rvalue and will be unified with the inferred type.
2254     fn rvalue_user_ty(&self, rvalue: &Rvalue<'tcx>) -> Option<UserTypeAnnotationIndex> {
2255         match rvalue {
2256             Rvalue::Use(_)
2257             | Rvalue::ThreadLocalRef(_)
2258             | Rvalue::Repeat(..)
2259             | Rvalue::Ref(..)
2260             | Rvalue::AddressOf(..)
2261             | Rvalue::Len(..)
2262             | Rvalue::Cast(..)
2263             | Rvalue::ShallowInitBox(..)
2264             | Rvalue::BinaryOp(..)
2265             | Rvalue::CheckedBinaryOp(..)
2266             | Rvalue::NullaryOp(..)
2267             | Rvalue::UnaryOp(..)
2268             | Rvalue::Discriminant(..) => None,
2269
2270             Rvalue::Aggregate(aggregate, _) => match **aggregate {
2271                 AggregateKind::Adt(_, _, _, user_ty, _) => user_ty,
2272                 AggregateKind::Array(_) => None,
2273                 AggregateKind::Tuple => None,
2274                 AggregateKind::Closure(_, _) => None,
2275                 AggregateKind::Generator(_, _, _) => None,
2276             },
2277         }
2278     }
2279
2280     fn check_aggregate_rvalue(
2281         &mut self,
2282         body: &Body<'tcx>,
2283         rvalue: &Rvalue<'tcx>,
2284         aggregate_kind: &AggregateKind<'tcx>,
2285         operands: &[Operand<'tcx>],
2286         location: Location,
2287     ) {
2288         let tcx = self.tcx();
2289
2290         self.prove_aggregate_predicates(aggregate_kind, location);
2291
2292         if *aggregate_kind == AggregateKind::Tuple {
2293             // tuple rvalue field type is always the type of the op. Nothing to check here.
2294             return;
2295         }
2296
2297         for (i, operand) in operands.iter().enumerate() {
2298             let field_ty = match self.aggregate_field_ty(aggregate_kind, i, location) {
2299                 Ok(field_ty) => field_ty,
2300                 Err(FieldAccessError::OutOfRange { field_count }) => {
2301                     span_mirbug!(
2302                         self,
2303                         rvalue,
2304                         "accessed field #{} but variant only has {}",
2305                         i,
2306                         field_count
2307                     );
2308                     continue;
2309                 }
2310             };
2311             let operand_ty = operand.ty(body, tcx);
2312             let operand_ty = self.normalize(operand_ty, location);
2313
2314             if let Err(terr) = self.sub_types(
2315                 operand_ty,
2316                 field_ty,
2317                 location.to_locations(),
2318                 ConstraintCategory::Boring,
2319             ) {
2320                 span_mirbug!(
2321                     self,
2322                     rvalue,
2323                     "{:?} is not a subtype of {:?}: {:?}",
2324                     operand_ty,
2325                     field_ty,
2326                     terr
2327                 );
2328             }
2329         }
2330     }
2331
2332     /// Adds the constraints that arise from a borrow expression `&'a P` at the location `L`.
2333     ///
2334     /// # Parameters
2335     ///
2336     /// - `location`: the location `L` where the borrow expression occurs
2337     /// - `borrow_region`: the region `'a` associated with the borrow
2338     /// - `borrowed_place`: the place `P` being borrowed
2339     fn add_reborrow_constraint(
2340         &mut self,
2341         body: &Body<'tcx>,
2342         location: Location,
2343         borrow_region: ty::Region<'tcx>,
2344         borrowed_place: &Place<'tcx>,
2345     ) {
2346         // These constraints are only meaningful during borrowck:
2347         let BorrowCheckContext { borrow_set, location_table, all_facts, constraints, .. } =
2348             self.borrowck_context;
2349
2350         // In Polonius mode, we also push a `loan_issued_at` fact
2351         // linking the loan to the region (in some cases, though,
2352         // there is no loan associated with this borrow expression --
2353         // that occurs when we are borrowing an unsafe place, for
2354         // example).
2355         if let Some(all_facts) = all_facts {
2356             let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
2357             if let Some(borrow_index) = borrow_set.get_index_of(&location) {
2358                 let region_vid = borrow_region.to_region_vid();
2359                 all_facts.loan_issued_at.push((
2360                     region_vid,
2361                     borrow_index,
2362                     location_table.mid_index(location),
2363                 ));
2364             }
2365         }
2366
2367         // If we are reborrowing the referent of another reference, we
2368         // need to add outlives relationships. In a case like `&mut
2369         // *p`, where the `p` has type `&'b mut Foo`, for example, we
2370         // need to ensure that `'b: 'a`.
2371
2372         debug!(
2373             "add_reborrow_constraint({:?}, {:?}, {:?})",
2374             location, borrow_region, borrowed_place
2375         );
2376
2377         let mut cursor = borrowed_place.projection.as_ref();
2378         let tcx = self.infcx.tcx;
2379         let field = path_utils::is_upvar_field_projection(
2380             tcx,
2381             &self.borrowck_context.upvars,
2382             borrowed_place.as_ref(),
2383             body,
2384         );
2385         let category = if let Some(field) = field {
2386             ConstraintCategory::ClosureUpvar(field)
2387         } else {
2388             ConstraintCategory::Boring
2389         };
2390
2391         while let [proj_base @ .., elem] = cursor {
2392             cursor = proj_base;
2393
2394             debug!("add_reborrow_constraint - iteration {:?}", elem);
2395
2396             match elem {
2397                 ProjectionElem::Deref => {
2398                     let base_ty = Place::ty_from(borrowed_place.local, proj_base, body, tcx).ty;
2399
2400                     debug!("add_reborrow_constraint - base_ty = {:?}", base_ty);
2401                     match base_ty.kind() {
2402                         ty::Ref(ref_region, _, mutbl) => {
2403                             constraints.outlives_constraints.push(OutlivesConstraint {
2404                                 sup: ref_region.to_region_vid(),
2405                                 sub: borrow_region.to_region_vid(),
2406                                 locations: location.to_locations(),
2407                                 span: location.to_locations().span(body),
2408                                 category,
2409                                 variance_info: ty::VarianceDiagInfo::default(),
2410                             });
2411
2412                             match mutbl {
2413                                 hir::Mutability::Not => {
2414                                     // Immutable reference. We don't need the base
2415                                     // to be valid for the entire lifetime of
2416                                     // the borrow.
2417                                     break;
2418                                 }
2419                                 hir::Mutability::Mut => {
2420                                     // Mutable reference. We *do* need the base
2421                                     // to be valid, because after the base becomes
2422                                     // invalid, someone else can use our mutable deref.
2423
2424                                     // This is in order to make the following function
2425                                     // illegal:
2426                                     // ```
2427                                     // fn unsafe_deref<'a, 'b>(x: &'a &'b mut T) -> &'b mut T {
2428                                     //     &mut *x
2429                                     // }
2430                                     // ```
2431                                     //
2432                                     // As otherwise you could clone `&mut T` using the
2433                                     // following function:
2434                                     // ```
2435                                     // fn bad(x: &mut T) -> (&mut T, &mut T) {
2436                                     //     let my_clone = unsafe_deref(&'a x);
2437                                     //     ENDREGION 'a;
2438                                     //     (my_clone, x)
2439                                     // }
2440                                     // ```
2441                                 }
2442                             }
2443                         }
2444                         ty::RawPtr(..) => {
2445                             // deref of raw pointer, guaranteed to be valid
2446                             break;
2447                         }
2448                         ty::Adt(def, _) if def.is_box() => {
2449                             // deref of `Box`, need the base to be valid - propagate
2450                         }
2451                         _ => bug!("unexpected deref ty {:?} in {:?}", base_ty, borrowed_place),
2452                     }
2453                 }
2454                 ProjectionElem::Field(..)
2455                 | ProjectionElem::Downcast(..)
2456                 | ProjectionElem::Index(..)
2457                 | ProjectionElem::ConstantIndex { .. }
2458                 | ProjectionElem::Subslice { .. } => {
2459                     // other field access
2460                 }
2461             }
2462         }
2463     }
2464
2465     fn prove_aggregate_predicates(
2466         &mut self,
2467         aggregate_kind: &AggregateKind<'tcx>,
2468         location: Location,
2469     ) {
2470         let tcx = self.tcx();
2471
2472         debug!(
2473             "prove_aggregate_predicates(aggregate_kind={:?}, location={:?})",
2474             aggregate_kind, location
2475         );
2476
2477         let (def_id, instantiated_predicates) = match aggregate_kind {
2478             AggregateKind::Adt(adt_did, _, substs, _, _) => {
2479                 (*adt_did, tcx.predicates_of(*adt_did).instantiate(tcx, substs))
2480             }
2481
2482             // For closures, we have some **extra requirements** we
2483             //
2484             // have to check. In particular, in their upvars and
2485             // signatures, closures often reference various regions
2486             // from the surrounding function -- we call those the
2487             // closure's free regions. When we borrow-check (and hence
2488             // region-check) closures, we may find that the closure
2489             // requires certain relationships between those free
2490             // regions. However, because those free regions refer to
2491             // portions of the CFG of their caller, the closure is not
2492             // in a position to verify those relationships. In that
2493             // case, the requirements get "propagated" to us, and so
2494             // we have to solve them here where we instantiate the
2495             // closure.
2496             //
2497             // Despite the opacity of the previous paragraph, this is
2498             // actually relatively easy to understand in terms of the
2499             // desugaring. A closure gets desugared to a struct, and
2500             // these extra requirements are basically like where
2501             // clauses on the struct.
2502             AggregateKind::Closure(def_id, substs)
2503             | AggregateKind::Generator(def_id, substs, _) => {
2504                 (*def_id, self.prove_closure_bounds(tcx, def_id.expect_local(), substs, location))
2505             }
2506
2507             AggregateKind::Array(_) | AggregateKind::Tuple => {
2508                 (CRATE_DEF_ID.to_def_id(), ty::InstantiatedPredicates::empty())
2509             }
2510         };
2511
2512         self.normalize_and_prove_instantiated_predicates(
2513             def_id,
2514             instantiated_predicates,
2515             location.to_locations(),
2516         );
2517     }
2518
2519     fn prove_closure_bounds(
2520         &mut self,
2521         tcx: TyCtxt<'tcx>,
2522         def_id: LocalDefId,
2523         substs: SubstsRef<'tcx>,
2524         location: Location,
2525     ) -> ty::InstantiatedPredicates<'tcx> {
2526         if let Some(ref closure_region_requirements) = tcx.mir_borrowck(def_id).closure_requirements
2527         {
2528             let closure_constraints = QueryRegionConstraints {
2529                 outlives: closure_region_requirements.apply_requirements(
2530                     tcx,
2531                     def_id.to_def_id(),
2532                     substs,
2533                 ),
2534
2535                 // Presently, closures never propagate member
2536                 // constraints to their parents -- they are enforced
2537                 // locally.  This is largely a non-issue as member
2538                 // constraints only come from `-> impl Trait` and
2539                 // friends which don't appear (thus far...) in
2540                 // closures.
2541                 member_constraints: vec![],
2542             };
2543
2544             let bounds_mapping = closure_constraints
2545                 .outlives
2546                 .iter()
2547                 .enumerate()
2548                 .filter_map(|(idx, constraint)| {
2549                     let ty::OutlivesPredicate(k1, r2) =
2550                         constraint.no_bound_vars().unwrap_or_else(|| {
2551                             bug!("query_constraint {:?} contained bound vars", constraint,);
2552                         });
2553
2554                     match k1.unpack() {
2555                         GenericArgKind::Lifetime(r1) => {
2556                             // constraint is r1: r2
2557                             let r1_vid = self.borrowck_context.universal_regions.to_region_vid(r1);
2558                             let r2_vid = self.borrowck_context.universal_regions.to_region_vid(r2);
2559                             let outlives_requirements =
2560                                 &closure_region_requirements.outlives_requirements[idx];
2561                             Some((
2562                                 (r1_vid, r2_vid),
2563                                 (outlives_requirements.category, outlives_requirements.blame_span),
2564                             ))
2565                         }
2566                         GenericArgKind::Type(_) | GenericArgKind::Const(_) => None,
2567                     }
2568                 })
2569                 .collect();
2570
2571             let existing = self
2572                 .borrowck_context
2573                 .constraints
2574                 .closure_bounds_mapping
2575                 .insert(location, bounds_mapping);
2576             assert!(existing.is_none(), "Multiple closures at the same location.");
2577
2578             self.push_region_constraints(
2579                 location.to_locations(),
2580                 ConstraintCategory::ClosureBounds,
2581                 &closure_constraints,
2582             );
2583         }
2584
2585         tcx.predicates_of(def_id).instantiate(tcx, substs)
2586     }
2587
2588     #[instrument(skip(self, body), level = "debug")]
2589     fn typeck_mir(&mut self, body: &Body<'tcx>) {
2590         self.last_span = body.span;
2591         debug!(?body.span);
2592
2593         for (local, local_decl) in body.local_decls.iter_enumerated() {
2594             self.check_local(&body, local, local_decl);
2595         }
2596
2597         for (block, block_data) in body.basic_blocks().iter_enumerated() {
2598             let mut location = Location { block, statement_index: 0 };
2599             for stmt in &block_data.statements {
2600                 if !stmt.source_info.span.is_dummy() {
2601                     self.last_span = stmt.source_info.span;
2602                 }
2603                 self.check_stmt(body, stmt, location);
2604                 location.statement_index += 1;
2605             }
2606
2607             self.check_terminator(&body, block_data.terminator(), location);
2608             self.check_iscleanup(&body, block_data);
2609         }
2610     }
2611 }
2612
2613 trait NormalizeLocation: fmt::Debug + Copy {
2614     fn to_locations(self) -> Locations;
2615 }
2616
2617 impl NormalizeLocation for Locations {
2618     fn to_locations(self) -> Locations {
2619         self
2620     }
2621 }
2622
2623 impl NormalizeLocation for Location {
2624     fn to_locations(self) -> Locations {
2625         Locations::Single(self)
2626     }
2627 }
2628
2629 /// Runs `infcx.instantiate_opaque_types`. Unlike other `TypeOp`s,
2630 /// this is not canonicalized - it directly affects the main `InferCtxt`
2631 /// that we use during MIR borrowchecking.
2632 #[derive(Debug)]
2633 pub(super) struct InstantiateOpaqueType<'tcx> {
2634     pub base_universe: Option<ty::UniverseIndex>,
2635     pub region_constraints: Option<RegionConstraintData<'tcx>>,
2636     pub obligations: Vec<PredicateObligation<'tcx>>,
2637 }
2638
2639 impl<'tcx> TypeOp<'tcx> for InstantiateOpaqueType<'tcx> {
2640     type Output = ();
2641     /// We use this type itself to store the information used
2642     /// when reporting errors. Since this is not a query, we don't
2643     /// re-run anything during error reporting - we just use the information
2644     /// we saved to help extract an error from the already-existing region
2645     /// constraints in our `InferCtxt`
2646     type ErrorInfo = InstantiateOpaqueType<'tcx>;
2647
2648     fn fully_perform(mut self, infcx: &InferCtxt<'_, 'tcx>) -> Fallible<TypeOpOutput<'tcx, Self>> {
2649         let (mut output, region_constraints) = scrape_region_constraints(infcx, || {
2650             Ok(InferOk { value: (), obligations: self.obligations.clone() })
2651         })?;
2652         self.region_constraints = Some(region_constraints);
2653         output.error_info = Some(self);
2654         Ok(output)
2655     }
2656 }