compiler/rustc_borrowck/src/type_check/mod.rs

   1 #![deny(rustc::untranslatable_diagnostic)]
   2 #![deny(rustc::diagnostic_outside_of_impl)]
   3 //! This pass type-checks the MIR to ensure it is not broken.
   4
   5 use std::rc::Rc;
   6 use std::{fmt, iter, mem};
   7
   8 use either::Either;
   9
  10 use hir::OpaqueTyOrigin;
  11 use rustc_data_structures::frozen::Frozen;
  12 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  13 use rustc_data_structures::vec_map::VecMap;
  14 use rustc_hir as hir;
  15 use rustc_hir::def::DefKind;
  16 use rustc_hir::def_id::LocalDefId;
  17 use rustc_hir::lang_items::LangItem;
  18 use rustc_index::vec::{Idx, IndexVec};
  19 use rustc_infer::infer::canonical::QueryRegionConstraints;
  20 use rustc_infer::infer::outlives::env::RegionBoundPairs;
  21 use rustc_infer::infer::region_constraints::RegionConstraintData;
  22 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  23 use rustc_infer::infer::{
  24     InferCtxt, InferOk, LateBoundRegion, LateBoundRegionConversionTime, NllRegionVariableOrigin,
  25 };
  26 use rustc_middle::mir::tcx::PlaceTy;
  27 use rustc_middle::mir::visit::{NonMutatingUseContext, PlaceContext, Visitor};
  28 use rustc_middle::mir::AssertKind;
  29 use rustc_middle::mir::*;
  30 use rustc_middle::ty::adjustment::PointerCast;
  31 use rustc_middle::ty::cast::CastTy;
  32 use rustc_middle::ty::subst::{SubstsRef, UserSubsts};
  33 use rustc_middle::ty::visit::TypeVisitable;
  34 use rustc_middle::ty::{
  35     self, Binder, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations, Dynamic,
  36     OpaqueHiddenType, OpaqueTypeKey, RegionVid, Ty, TyCtxt, UserType, UserTypeAnnotationIndex,
  37 };
  38 use rustc_span::def_id::CRATE_DEF_ID;
  39 use rustc_span::{Span, DUMMY_SP};
  40 use rustc_target::abi::VariantIdx;
  41 use rustc_trait_selection::traits::query::type_op;
  42 use rustc_trait_selection::traits::query::type_op::custom::scrape_region_constraints;
  43 use rustc_trait_selection::traits::query::type_op::custom::CustomTypeOp;
  44 use rustc_trait_selection::traits::query::type_op::{TypeOp, TypeOpOutput};
  45 use rustc_trait_selection::traits::query::Fallible;
  46 use rustc_trait_selection::traits::PredicateObligation;
  47
  48 use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
  49 use rustc_mir_dataflow::move_paths::MoveData;
  50 use rustc_mir_dataflow::ResultsCursor;
  51
  52 use crate::session_diagnostics::MoveUnsized;
  53 use crate::{
  54     borrow_set::BorrowSet,
  55     constraints::{OutlivesConstraint, OutlivesConstraintSet},
  56     diagnostics::UniverseInfo,
  57     facts::AllFacts,
  58     location::LocationTable,
  59     member_constraints::MemberConstraintSet,
  60     nll::ToRegionVid,
  61     path_utils,
  62     region_infer::values::{
  63         LivenessValues, PlaceholderIndex, PlaceholderIndices, RegionValueElements,
  64     },
  65     region_infer::TypeTest,
  66     type_check::free_region_relations::{CreateResult, UniversalRegionRelations},
  67     universal_regions::{DefiningTy, UniversalRegions},
  68     Upvar,
  69 };
  70
  71 macro_rules! span_mirbug {
  72     ($context:expr, $elem:expr, $($message:tt)*) => ({
  73         $crate::type_check::mirbug(
  74             $context.tcx(),
  75             $context.last_span,
  76             &format!(
  77                 "broken MIR in {:?} ({:?}): {}",
  78                 $context.body().source.def_id(),
  79                 $elem,
  80                 format_args!($($message)*),
  81             ),
  82         )
  83     })
  84 }
  85
  86 macro_rules! span_mirbug_and_err {
  87     ($context:expr, $elem:expr, $($message:tt)*) => ({
  88         {
  89             span_mirbug!($context, $elem, $($message)*);
  90             $context.error()
  91         }
  92     })
  93 }
  94
  95 mod canonical;
  96 mod constraint_conversion;
  97 pub mod free_region_relations;
  98 mod input_output;
  99 pub(crate) mod liveness;
 100 mod relate_tys;
 101
 102 /// Type checks the given `mir` in the context of the inference
 103 /// context `infcx`. Returns any region constraints that have yet to
 104 /// be proven. This result includes liveness constraints that
 105 /// ensure that regions appearing in the types of all local variables
 106 /// are live at all points where that local variable may later be
 107 /// used.
 108 ///
 109 /// This phase of type-check ought to be infallible -- this is because
 110 /// the original, HIR-based type-check succeeded. So if any errors
 111 /// occur here, we will get a `bug!` reported.
 112 ///
 113 /// # Parameters
 114 ///
 115 /// - `infcx` -- inference context to use
 116 /// - `param_env` -- parameter environment to use for trait solving
 117 /// - `body` -- MIR body to type-check
 118 /// - `promoted` -- map of promoted constants within `body`
 119 /// - `universal_regions` -- the universal regions from `body`s function signature
 120 /// - `location_table` -- MIR location map of `body`
 121 /// - `borrow_set` -- information about borrows occurring in `body`
 122 /// - `all_facts` -- when using Polonius, this is the generated set of Polonius facts
 123 /// - `flow_inits` -- results of a maybe-init dataflow analysis
 124 /// - `move_data` -- move-data constructed when performing the maybe-init dataflow analysis
 125 /// - `elements` -- MIR region map
 126 pub(crate) fn type_check<'mir, 'tcx>(
 127     infcx: &InferCtxt<'tcx>,
 128     param_env: ty::ParamEnv<'tcx>,
 129     body: &Body<'tcx>,
 130     promoted: &IndexVec<Promoted, Body<'tcx>>,
 131     universal_regions: &Rc<UniversalRegions<'tcx>>,
 132     location_table: &LocationTable,
 133     borrow_set: &BorrowSet<'tcx>,
 134     all_facts: &mut Option<AllFacts>,
 135     flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
 136     move_data: &MoveData<'tcx>,
 137     elements: &Rc<RegionValueElements>,
 138     upvars: &[Upvar<'tcx>],
 139     use_polonius: bool,
 140 ) -> MirTypeckResults<'tcx> {
 141     let implicit_region_bound = infcx.tcx.mk_region(ty::ReVar(universal_regions.fr_fn_body));
 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         type_tests: Vec::default(),
 149         universe_causes: FxHashMap::default(),
 150     };
 151
 152     let CreateResult {
 153         universal_region_relations,
 154         region_bound_pairs,
 155         normalized_inputs_and_output,
 156     } = free_region_relations::create(
 157         infcx,
 158         param_env,
 159         implicit_region_bound,
 160         universal_regions,
 161         &mut constraints,
 162     );
 163
 164     debug!(?normalized_inputs_and_output);
 165
 166     for u in ty::UniverseIndex::ROOT..=infcx.universe() {
 167         constraints.universe_causes.insert(u, UniverseInfo::other());
 168     }
 169
 170     let mut borrowck_context = BorrowCheckContext {
 171         universal_regions,
 172         location_table,
 173         borrow_set,
 174         all_facts,
 175         constraints: &mut constraints,
 176         upvars,
 177     };
 178
 179     let mut checker = TypeChecker::new(
 180         infcx,
 181         body,
 182         param_env,
 183         &region_bound_pairs,
 184         implicit_region_bound,
 185         &mut borrowck_context,
 186     );
 187
 188     let errors_reported = {
 189         let mut verifier = TypeVerifier::new(&mut checker, promoted);
 190         verifier.visit_body(&body);
 191         verifier.errors_reported
 192     };
 193
 194     if !errors_reported {
 195         // if verifier failed, don't do further checks to avoid ICEs
 196         checker.typeck_mir(body);
 197     }
 198
 199     checker.equate_inputs_and_outputs(&body, universal_regions, &normalized_inputs_and_output);
 200     liveness::generate(
 201         &mut checker,
 202         body,
 203         elements,
 204         flow_inits,
 205         move_data,
 206         location_table,
 207         use_polonius,
 208     );
 209
 210     translate_outlives_facts(&mut checker);
 211     let opaque_type_values = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
 212
 213     let opaque_type_values = opaque_type_values
 214         .into_iter()
 215         .map(|(opaque_type_key, decl)| {
 216             checker
 217                 .fully_perform_op(
 218                     Locations::All(body.span),
 219                     ConstraintCategory::OpaqueType,
 220                     CustomTypeOp::new(
 221                         |infcx| {
 222                             infcx.register_member_constraints(
 223                                 param_env,
 224                                 opaque_type_key,
 225                                 decl.hidden_type.ty,
 226                                 decl.hidden_type.span,
 227                             );
 228                             Ok(InferOk { value: (), obligations: vec![] })
 229                         },
 230                         || "opaque_type_map".to_string(),
 231                     ),
 232                 )
 233                 .unwrap();
 234             let mut hidden_type = infcx.resolve_vars_if_possible(decl.hidden_type);
 235             trace!("finalized opaque type {:?} to {:#?}", opaque_type_key, hidden_type.ty.kind());
 236             if hidden_type.has_non_region_infer() {
 237                 let reported = infcx.tcx.sess.delay_span_bug(
 238                     decl.hidden_type.span,
 239                     &format!("could not resolve {:#?}", hidden_type.ty.kind()),
 240                 );
 241                 hidden_type.ty = infcx.tcx.ty_error_with_guaranteed(reported);
 242             }
 243
 244             (opaque_type_key, (hidden_type, decl.origin))
 245         })
 246         .collect();
 247
 248     MirTypeckResults { constraints, universal_region_relations, opaque_type_values }
 249 }
 250
 251 fn translate_outlives_facts(typeck: &mut TypeChecker<'_, '_>) {
 252     let cx = &mut typeck.borrowck_context;
 253     if let Some(facts) = cx.all_facts {
 254         let _prof_timer = typeck.infcx.tcx.prof.generic_activity("polonius_fact_generation");
 255         let location_table = cx.location_table;
 256         facts.subset_base.extend(cx.constraints.outlives_constraints.outlives().iter().flat_map(
 257             |constraint: &OutlivesConstraint<'_>| {
 258                 if let Some(from_location) = constraint.locations.from_location() {
 259                     Either::Left(iter::once((
 260                         constraint.sup,
 261                         constraint.sub,
 262                         location_table.mid_index(from_location),
 263                     )))
 264                 } else {
 265                     Either::Right(
 266                         location_table
 267                             .all_points()
 268                             .map(move |location| (constraint.sup, constraint.sub, location)),
 269                     )
 270                 }
 271             },
 272         ));
 273     }
 274 }
 275
 276 #[track_caller]
 277 fn mirbug(tcx: TyCtxt<'_>, span: Span, msg: &str) {
 278     // We sometimes see MIR failures (notably predicate failures) due to
 279     // the fact that we check rvalue sized predicates here. So use `delay_span_bug`
 280     // to avoid reporting bugs in those cases.
 281     tcx.sess.diagnostic().delay_span_bug(span, msg);
 282 }
 283
 284 enum FieldAccessError {
 285     OutOfRange { field_count: usize },
 286 }
 287
 288 /// Verifies that MIR types are sane to not crash further checks.
 289 ///
 290 /// The sanitize_XYZ methods here take an MIR object and compute its
 291 /// type, calling `span_mirbug` and returning an error type if there
 292 /// is a problem.
 293 struct TypeVerifier<'a, 'b, 'tcx> {
 294     cx: &'a mut TypeChecker<'b, 'tcx>,
 295     promoted: &'b IndexVec<Promoted, Body<'tcx>>,
 296     last_span: Span,
 297     errors_reported: bool,
 298 }
 299
 300 impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
 301     fn visit_span(&mut self, span: Span) {
 302         if !span.is_dummy() {
 303             self.last_span = span;
 304         }
 305     }
 306
 307     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, location: Location) {
 308         self.sanitize_place(place, location, context);
 309     }
 310
 311     fn visit_constant(&mut self, constant: &Constant<'tcx>, location: Location) {
 312         debug!(?constant, ?location, "visit_constant");
 313
 314         self.super_constant(constant, location);
 315         let ty = self.sanitize_type(constant, constant.literal.ty());
 316
 317         self.cx.infcx.tcx.for_each_free_region(&ty, |live_region| {
 318             let live_region_vid =
 319                 self.cx.borrowck_context.universal_regions.to_region_vid(live_region);
 320             self.cx
 321                 .borrowck_context
 322                 .constraints
 323                 .liveness_constraints
 324                 .add_element(live_region_vid, location);
 325         });
 326
 327         // HACK(compiler-errors): Constants that are gathered into Body.required_consts
 328         // have their locations erased...
 329         let locations = if location != Location::START {
 330             location.to_locations()
 331         } else {
 332             Locations::All(constant.span)
 333         };
 334
 335         if let Some(annotation_index) = constant.user_ty {
 336             if let Err(terr) = self.cx.relate_type_and_user_type(
 337                 constant.literal.ty(),
 338                 ty::Variance::Invariant,
 339                 &UserTypeProjection { base: annotation_index, projs: vec![] },
 340                 locations,
 341                 ConstraintCategory::Boring,
 342             ) {
 343                 let annotation = &self.cx.user_type_annotations[annotation_index];
 344                 span_mirbug!(
 345                     self,
 346                     constant,
 347                     "bad constant user type {:?} vs {:?}: {:?}",
 348                     annotation,
 349                     constant.literal.ty(),
 350                     terr,
 351                 );
 352             }
 353         } else {
 354             let tcx = self.tcx();
 355             let maybe_uneval = match constant.literal {
 356                 ConstantKind::Ty(ct) => match ct.kind() {
 357                     ty::ConstKind::Unevaluated(_) => {
 358                         bug!("should not encounter unevaluated ConstantKind::Ty here, got {:?}", ct)
 359                     }
 360                     _ => None,
 361                 },
 362                 ConstantKind::Unevaluated(uv, _) => Some(uv),
 363                 _ => None,
 364             };
 365
 366             if let Some(uv) = maybe_uneval {
 367                 if let Some(promoted) = uv.promoted {
 368                     let check_err = |verifier: &mut TypeVerifier<'a, 'b, 'tcx>,
 369                                      promoted: &Body<'tcx>,
 370                                      ty,
 371                                      san_ty| {
 372                         if let Err(terr) =
 373                             verifier.cx.eq_types(ty, san_ty, locations, ConstraintCategory::Boring)
 374                         {
 375                             span_mirbug!(
 376                                 verifier,
 377                                 promoted,
 378                                 "bad promoted type ({:?}: {:?}): {:?}",
 379                                 ty,
 380                                 san_ty,
 381                                 terr
 382                             );
 383                         };
 384                     };
 385
 386                     if !self.errors_reported {
 387                         let promoted_body = &self.promoted[promoted];
 388                         self.sanitize_promoted(promoted_body, location);
 389
 390                         let promoted_ty = promoted_body.return_ty();
 391                         check_err(self, promoted_body, ty, promoted_ty);
 392                     }
 393                 } else {
 394                     if let Err(terr) = self.cx.fully_perform_op(
 395                         locations,
 396                         ConstraintCategory::Boring,
 397                         self.cx.param_env.and(type_op::ascribe_user_type::AscribeUserType::new(
 398                             constant.literal.ty(),
 399                             uv.def.did,
 400                             UserSubsts { substs: uv.substs, user_self_ty: None },
 401                         )),
 402                     ) {
 403                         span_mirbug!(
 404                             self,
 405                             constant,
 406                             "bad constant type {:?} ({:?})",
 407                             constant,
 408                             terr
 409                         );
 410                     }
 411                 }
 412             } else if let Some(static_def_id) = constant.check_static_ptr(tcx) {
 413                 let unnormalized_ty = tcx.type_of(static_def_id);
 414                 let normalized_ty = self.cx.normalize(unnormalized_ty, locations);
 415                 let literal_ty = constant.literal.ty().builtin_deref(true).unwrap().ty;
 416
 417                 if let Err(terr) = self.cx.eq_types(
 418                     literal_ty,
 419                     normalized_ty,
 420                     locations,
 421                     ConstraintCategory::Boring,
 422                 ) {
 423                     span_mirbug!(self, constant, "bad static type {:?} ({:?})", constant, terr);
 424                 }
 425             }
 426
 427             if let ty::FnDef(def_id, substs) = *constant.literal.ty().kind() {
 428                 // const_trait_impl: use a non-const param env when checking that a FnDef type is well formed.
 429                 // this is because the well-formedness of the function does not need to be proved to have `const`
 430                 // impls for trait bounds.
 431                 let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);
 432                 let prev = self.cx.param_env;
 433                 self.cx.param_env = prev.without_const();
 434                 self.cx.normalize_and_prove_instantiated_predicates(
 435                     def_id,
 436                     instantiated_predicates,
 437                     locations,
 438                 );
 439                 self.cx.param_env = prev;
 440             }
 441         }
 442     }
 443
 444     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 445         self.super_rvalue(rvalue, location);
 446         let rval_ty = rvalue.ty(self.body(), self.tcx());
 447         self.sanitize_type(rvalue, rval_ty);
 448     }
 449
 450     fn visit_local_decl(&mut self, local: Local, local_decl: &LocalDecl<'tcx>) {
 451         self.super_local_decl(local, local_decl);
 452         self.sanitize_type(local_decl, local_decl.ty);
 453
 454         if let Some(user_ty) = &local_decl.user_ty {
 455             for (user_ty, span) in user_ty.projections_and_spans() {
 456                 let ty = if !local_decl.is_nonref_binding() {
 457                     // If we have a binding of the form `let ref x: T = ..`
 458                     // then remove the outermost reference so we can check the
 459                     // type annotation for the remaining type.
 460                     if let ty::Ref(_, rty, _) = local_decl.ty.kind() {
 461                         *rty
 462                     } else {
 463                         bug!("{:?} with ref binding has wrong type {}", local, local_decl.ty);
 464                     }
 465                 } else {
 466                     local_decl.ty
 467                 };
 468
 469                 if let Err(terr) = self.cx.relate_type_and_user_type(
 470                     ty,
 471                     ty::Variance::Invariant,
 472                     user_ty,
 473                     Locations::All(*span),
 474                     ConstraintCategory::TypeAnnotation,
 475                 ) {
 476                     span_mirbug!(
 477                         self,
 478                         local,
 479                         "bad user type on variable {:?}: {:?} != {:?} ({:?})",
 480                         local,
 481                         local_decl.ty,
 482                         local_decl.user_ty,
 483                         terr,
 484                     );
 485                 }
 486             }
 487         }
 488     }
 489
 490     fn visit_body(&mut self, body: &Body<'tcx>) {
 491         self.sanitize_type(&"return type", body.return_ty());
 492         for local_decl in &body.local_decls {
 493             self.sanitize_type(local_decl, local_decl.ty);
 494         }
 495         if self.errors_reported {
 496             return;
 497         }
 498         self.super_body(body);
 499     }
 500 }
 501
 502 impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
 503     fn new(
 504         cx: &'a mut TypeChecker<'b, 'tcx>,
 505         promoted: &'b IndexVec<Promoted, Body<'tcx>>,
 506     ) -> Self {
 507         TypeVerifier { promoted, last_span: cx.body.span, cx, errors_reported: false }
 508     }
 509
 510     fn body(&self) -> &Body<'tcx> {
 511         self.cx.body
 512     }
 513
 514     fn tcx(&self) -> TyCtxt<'tcx> {
 515         self.cx.infcx.tcx
 516     }
 517
 518     fn sanitize_type(&mut self, parent: &dyn fmt::Debug, ty: Ty<'tcx>) -> Ty<'tcx> {
 519         if ty.has_escaping_bound_vars() || ty.references_error() {
 520             span_mirbug_and_err!(self, parent, "bad type {:?}", ty)
 521         } else {
 522             ty
 523         }
 524     }
 525
 526     /// Checks that the types internal to the `place` match up with
 527     /// what would be expected.
 528     fn sanitize_place(
 529         &mut self,
 530         place: &Place<'tcx>,
 531         location: Location,
 532         context: PlaceContext,
 533     ) -> PlaceTy<'tcx> {
 534         debug!("sanitize_place: {:?}", place);
 535
 536         let mut place_ty = PlaceTy::from_ty(self.body().local_decls[place.local].ty);
 537
 538         for elem in place.projection.iter() {
 539             if place_ty.variant_index.is_none() {
 540                 if place_ty.ty.references_error() {
 541                     assert!(self.errors_reported);
 542                     return PlaceTy::from_ty(self.tcx().ty_error());
 543                 }
 544             }
 545             place_ty = self.sanitize_projection(place_ty, elem, place, location);
 546         }
 547
 548         if let PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy) = context {
 549             let tcx = self.tcx();
 550             let trait_ref = tcx.at(self.last_span).mk_trait_ref(LangItem::Copy, [place_ty.ty]);
 551
 552             // To have a `Copy` operand, the type `T` of the
 553             // value must be `Copy`. Note that we prove that `T: Copy`,
 554             // rather than using the `is_copy_modulo_regions`
 555             // test. This is important because
 556             // `is_copy_modulo_regions` ignores the resulting region
 557             // obligations and assumes they pass. This can result in
 558             // bounds from `Copy` impls being unsoundly ignored (e.g.,
 559             // #29149). Note that we decide to use `Copy` before knowing
 560             // whether the bounds fully apply: in effect, the rule is
 561             // that if a value of some type could implement `Copy`, then
 562             // it must.
 563             self.cx.prove_trait_ref(
 564                 trait_ref,
 565                 location.to_locations(),
 566                 ConstraintCategory::CopyBound,
 567             );
 568         }
 569
 570         place_ty
 571     }
 572
 573     fn sanitize_promoted(&mut self, promoted_body: &'b Body<'tcx>, location: Location) {
 574         // Determine the constraints from the promoted MIR by running the type
 575         // checker on the promoted MIR, then transfer the constraints back to
 576         // the main MIR, changing the locations to the provided location.
 577
 578         let parent_body = mem::replace(&mut self.cx.body, promoted_body);
 579
 580         // Use new sets of constraints and closure bounds so that we can
 581         // modify their locations.
 582         let all_facts = &mut None;
 583         let mut constraints = Default::default();
 584         let mut liveness_constraints =
 585             LivenessValues::new(Rc::new(RegionValueElements::new(&promoted_body)));
 586         // Don't try to add borrow_region facts for the promoted MIR
 587
 588         let mut swap_constraints = |this: &mut Self| {
 589             mem::swap(this.cx.borrowck_context.all_facts, all_facts);
 590             mem::swap(
 591                 &mut this.cx.borrowck_context.constraints.outlives_constraints,
 592                 &mut constraints,
 593             );
 594             mem::swap(
 595                 &mut this.cx.borrowck_context.constraints.liveness_constraints,
 596                 &mut liveness_constraints,
 597             );
 598         };
 599
 600         swap_constraints(self);
 601
 602         self.visit_body(&promoted_body);
 603
 604         if !self.errors_reported {
 605             // if verifier failed, don't do further checks to avoid ICEs
 606             self.cx.typeck_mir(promoted_body);
 607         }
 608
 609         self.cx.body = parent_body;
 610         // Merge the outlives constraints back in, at the given location.
 611         swap_constraints(self);
 612
 613         let locations = location.to_locations();
 614         for constraint in constraints.outlives().iter() {
 615             let mut constraint = *constraint;
 616             constraint.locations = locations;
 617             if let ConstraintCategory::Return(_)
 618             | ConstraintCategory::UseAsConst
 619             | ConstraintCategory::UseAsStatic = constraint.category
 620             {
 621                 // "Returning" from a promoted is an assignment to a
 622                 // temporary from the user's point of view.
 623                 constraint.category = ConstraintCategory::Boring;
 624             }
 625             self.cx.borrowck_context.constraints.outlives_constraints.push(constraint)
 626         }
 627         for region in liveness_constraints.rows() {
 628             // If the region is live at at least one location in the promoted MIR,
 629             // then add a liveness constraint to the main MIR for this region
 630             // at the location provided as an argument to this method
 631             if liveness_constraints.get_elements(region).next().is_some() {
 632                 self.cx
 633                     .borrowck_context
 634                     .constraints
 635                     .liveness_constraints
 636                     .add_element(region, location);
 637             }
 638         }
 639     }
 640
 641     fn sanitize_projection(
 642         &mut self,
 643         base: PlaceTy<'tcx>,
 644         pi: PlaceElem<'tcx>,
 645         place: &Place<'tcx>,
 646         location: Location,
 647     ) -> PlaceTy<'tcx> {
 648         debug!("sanitize_projection: {:?} {:?} {:?}", base, pi, place);
 649         let tcx = self.tcx();
 650         let base_ty = base.ty;
 651         match pi {
 652             ProjectionElem::Deref => {
 653                 let deref_ty = base_ty.builtin_deref(true);
 654                 PlaceTy::from_ty(deref_ty.map(|t| t.ty).unwrap_or_else(|| {
 655                     span_mirbug_and_err!(self, place, "deref of non-pointer {:?}", base_ty)
 656                 }))
 657             }
 658             ProjectionElem::Index(i) => {
 659                 let index_ty = Place::from(i).ty(self.body(), tcx).ty;
 660                 if index_ty != tcx.types.usize {
 661                     PlaceTy::from_ty(span_mirbug_and_err!(self, i, "index by non-usize {:?}", i))
 662                 } else {
 663                     PlaceTy::from_ty(base_ty.builtin_index().unwrap_or_else(|| {
 664                         span_mirbug_and_err!(self, place, "index of non-array {:?}", base_ty)
 665                     }))
 666                 }
 667             }
 668             ProjectionElem::ConstantIndex { .. } => {
 669                 // consider verifying in-bounds
 670                 PlaceTy::from_ty(base_ty.builtin_index().unwrap_or_else(|| {
 671                     span_mirbug_and_err!(self, place, "index of non-array {:?}", base_ty)
 672                 }))
 673             }
 674             ProjectionElem::Subslice { from, to, from_end } => {
 675                 PlaceTy::from_ty(match base_ty.kind() {
 676                     ty::Array(inner, _) => {
 677                         assert!(!from_end, "array subslices should not use from_end");
 678                         tcx.mk_array(*inner, to - from)
 679                     }
 680                     ty::Slice(..) => {
 681                         assert!(from_end, "slice subslices should use from_end");
 682                         base_ty
 683                     }
 684                     _ => span_mirbug_and_err!(self, place, "slice of non-array {:?}", base_ty),
 685                 })
 686             }
 687             ProjectionElem::Downcast(maybe_name, index) => match base_ty.kind() {
 688                 ty::Adt(adt_def, _substs) if adt_def.is_enum() => {
 689                     if index.as_usize() >= adt_def.variants().len() {
 690                         PlaceTy::from_ty(span_mirbug_and_err!(
 691                             self,
 692                             place,
 693                             "cast to variant #{:?} but enum only has {:?}",
 694                             index,
 695                             adt_def.variants().len()
 696                         ))
 697                     } else {
 698                         PlaceTy { ty: base_ty, variant_index: Some(index) }
 699                     }
 700                 }
 701                 // We do not need to handle generators here, because this runs
 702                 // before the generator transform stage.
 703                 _ => {
 704                     let ty = if let Some(name) = maybe_name {
 705                         span_mirbug_and_err!(
 706                             self,
 707                             place,
 708                             "can't downcast {:?} as {:?}",
 709                             base_ty,
 710                             name
 711                         )
 712                     } else {
 713                         span_mirbug_and_err!(self, place, "can't downcast {:?}", base_ty)
 714                     };
 715                     PlaceTy::from_ty(ty)
 716                 }
 717             },
 718             ProjectionElem::Field(field, fty) => {
 719                 let fty = self.sanitize_type(place, fty);
 720                 let fty = self.cx.normalize(fty, location);
 721                 match self.field_ty(place, base, field, location) {
 722                     Ok(ty) => {
 723                         let ty = self.cx.normalize(ty, location);
 724                         if let Err(terr) = self.cx.eq_types(
 725                             ty,
 726                             fty,
 727                             location.to_locations(),
 728                             ConstraintCategory::Boring,
 729                         ) {
 730                             span_mirbug!(
 731                                 self,
 732                                 place,
 733                                 "bad field access ({:?}: {:?}): {:?}",
 734                                 ty,
 735                                 fty,
 736                                 terr
 737                             );
 738                         }
 739                     }
 740                     Err(FieldAccessError::OutOfRange { field_count }) => span_mirbug!(
 741                         self,
 742                         place,
 743                         "accessed field #{} but variant only has {}",
 744                         field.index(),
 745                         field_count
 746                     ),
 747                 }
 748                 PlaceTy::from_ty(fty)
 749             }
 750             ProjectionElem::OpaqueCast(ty) => {
 751                 let ty = self.sanitize_type(place, ty);
 752                 let ty = self.cx.normalize(ty, location);
 753                 self.cx
 754                     .eq_types(
 755                         base.ty,
 756                         ty,
 757                         location.to_locations(),
 758                         ConstraintCategory::TypeAnnotation,
 759                     )
 760                     .unwrap();
 761                 PlaceTy::from_ty(ty)
 762             }
 763         }
 764     }
 765
 766     fn error(&mut self) -> Ty<'tcx> {
 767         self.errors_reported = true;
 768         self.tcx().ty_error()
 769     }
 770
 771     fn field_ty(
 772         &mut self,
 773         parent: &dyn fmt::Debug,
 774         base_ty: PlaceTy<'tcx>,
 775         field: Field,
 776         location: Location,
 777     ) -> Result<Ty<'tcx>, FieldAccessError> {
 778         let tcx = self.tcx();
 779
 780         let (variant, substs) = match base_ty {
 781             PlaceTy { ty, variant_index: Some(variant_index) } => match *ty.kind() {
 782                 ty::Adt(adt_def, substs) => (adt_def.variant(variant_index), substs),
 783                 ty::Generator(def_id, substs, _) => {
 784                     let mut variants = substs.as_generator().state_tys(def_id, tcx);
 785                     let Some(mut variant) = variants.nth(variant_index.into()) else {
 786                         bug!(
 787                             "variant_index of generator out of range: {:?}/{:?}",
 788                             variant_index,
 789                             substs.as_generator().state_tys(def_id, tcx).count()
 790                         );
 791                     };
 792                     return match variant.nth(field.index()) {
 793                         Some(ty) => Ok(ty),
 794                         None => Err(FieldAccessError::OutOfRange { field_count: variant.count() }),
 795                     };
 796                 }
 797                 _ => bug!("can't have downcast of non-adt non-generator type"),
 798             },
 799             PlaceTy { ty, variant_index: None } => match *ty.kind() {
 800                 ty::Adt(adt_def, substs) if !adt_def.is_enum() => {
 801                     (adt_def.variant(VariantIdx::new(0)), substs)
 802                 }
 803                 ty::Closure(_, substs) => {
 804                     return match substs
 805                         .as_closure()
 806                         .tupled_upvars_ty()
 807                         .tuple_fields()
 808                         .get(field.index())
 809                     {
 810                         Some(&ty) => Ok(ty),
 811                         None => Err(FieldAccessError::OutOfRange {
 812                             field_count: substs.as_closure().upvar_tys().count(),
 813                         }),
 814                     };
 815                 }
 816                 ty::Generator(_, substs, _) => {
 817                     // Only prefix fields (upvars and current state) are
 818                     // accessible without a variant index.
 819                     return match substs.as_generator().prefix_tys().nth(field.index()) {
 820                         Some(ty) => Ok(ty),
 821                         None => Err(FieldAccessError::OutOfRange {
 822                             field_count: substs.as_generator().prefix_tys().count(),
 823                         }),
 824                     };
 825                 }
 826                 ty::Tuple(tys) => {
 827                     return match tys.get(field.index()) {
 828                         Some(&ty) => Ok(ty),
 829                         None => Err(FieldAccessError::OutOfRange { field_count: tys.len() }),
 830                     };
 831                 }
 832                 _ => {
 833                     return Ok(span_mirbug_and_err!(
 834                         self,
 835                         parent,
 836                         "can't project out of {:?}",
 837                         base_ty
 838                     ));
 839                 }
 840             },
 841         };
 842
 843         if let Some(field) = variant.fields.get(field.index()) {
 844             Ok(self.cx.normalize(field.ty(tcx, substs), location))
 845         } else {
 846             Err(FieldAccessError::OutOfRange { field_count: variant.fields.len() })
 847         }
 848     }
 849 }
 850
 851 /// The MIR type checker. Visits the MIR and enforces all the
 852 /// constraints needed for it to be valid and well-typed. Along the
 853 /// way, it accrues region constraints -- these can later be used by
 854 /// NLL region checking.
 855 struct TypeChecker<'a, 'tcx> {
 856     infcx: &'a InferCtxt<'tcx>,
 857     param_env: ty::ParamEnv<'tcx>,
 858     last_span: Span,
 859     body: &'a Body<'tcx>,
 860     /// User type annotations are shared between the main MIR and the MIR of
 861     /// all of the promoted items.
 862     user_type_annotations: &'a CanonicalUserTypeAnnotations<'tcx>,
 863     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
 864     implicit_region_bound: ty::Region<'tcx>,
 865     reported_errors: FxHashSet<(Ty<'tcx>, Span)>,
 866     borrowck_context: &'a mut BorrowCheckContext<'a, 'tcx>,
 867 }
 868
 869 struct BorrowCheckContext<'a, 'tcx> {
 870     pub(crate) universal_regions: &'a UniversalRegions<'tcx>,
 871     location_table: &'a LocationTable,
 872     all_facts: &'a mut Option<AllFacts>,
 873     borrow_set: &'a BorrowSet<'tcx>,
 874     pub(crate) constraints: &'a mut MirTypeckRegionConstraints<'tcx>,
 875     upvars: &'a [Upvar<'tcx>],
 876 }
 877
 878 pub(crate) struct MirTypeckResults<'tcx> {
 879     pub(crate) constraints: MirTypeckRegionConstraints<'tcx>,
 880     pub(crate) universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
 881     pub(crate) opaque_type_values:
 882         VecMap<OpaqueTypeKey<'tcx>, (OpaqueHiddenType<'tcx>, OpaqueTyOrigin)>,
 883 }
 884
 885 /// A collection of region constraints that must be satisfied for the
 886 /// program to be considered well-typed.
 887 pub(crate) struct MirTypeckRegionConstraints<'tcx> {
 888     /// Maps from a `ty::Placeholder` to the corresponding
 889     /// `PlaceholderIndex` bit that we will use for it.
 890     ///
 891     /// To keep everything in sync, do not insert this set
 892     /// directly. Instead, use the `placeholder_region` helper.
 893     pub(crate) placeholder_indices: PlaceholderIndices,
 894
 895     /// Each time we add a placeholder to `placeholder_indices`, we
 896     /// also create a corresponding "representative" region vid for
 897     /// that wraps it. This vector tracks those. This way, when we
 898     /// convert the same `ty::RePlaceholder(p)` twice, we can map to
 899     /// the same underlying `RegionVid`.
 900     pub(crate) placeholder_index_to_region: IndexVec<PlaceholderIndex, ty::Region<'tcx>>,
 901
 902     /// In general, the type-checker is not responsible for enforcing
 903     /// liveness constraints; this job falls to the region inferencer,
 904     /// which performs a liveness analysis. However, in some limited
 905     /// cases, the MIR type-checker creates temporary regions that do
 906     /// not otherwise appear in the MIR -- in particular, the
 907     /// late-bound regions that it instantiates at call-sites -- and
 908     /// hence it must report on their liveness constraints.
 909     pub(crate) liveness_constraints: LivenessValues<RegionVid>,
 910
 911     pub(crate) outlives_constraints: OutlivesConstraintSet<'tcx>,
 912
 913     pub(crate) member_constraints: MemberConstraintSet<'tcx, RegionVid>,
 914
 915     pub(crate) universe_causes: FxHashMap<ty::UniverseIndex, UniverseInfo<'tcx>>,
 916
 917     pub(crate) type_tests: Vec<TypeTest<'tcx>>,
 918 }
 919
 920 impl<'tcx> MirTypeckRegionConstraints<'tcx> {
 921     fn placeholder_region(
 922         &mut self,
 923         infcx: &InferCtxt<'tcx>,
 924         placeholder: ty::PlaceholderRegion,
 925     ) -> ty::Region<'tcx> {
 926         let placeholder_index = self.placeholder_indices.insert(placeholder);
 927         match self.placeholder_index_to_region.get(placeholder_index) {
 928             Some(&v) => v,
 929             None => {
 930                 let origin = NllRegionVariableOrigin::Placeholder(placeholder);
 931                 let region = infcx.next_nll_region_var_in_universe(origin, placeholder.universe);
 932                 self.placeholder_index_to_region.push(region);
 933                 region
 934             }
 935         }
 936     }
 937 }
 938
 939 /// The `Locations` type summarizes *where* region constraints are
 940 /// required to hold. Normally, this is at a particular point which
 941 /// created the obligation, but for constraints that the user gave, we
 942 /// want the constraint to hold at all points.
 943 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
 944 pub enum Locations {
 945     /// Indicates that a type constraint should always be true. This
 946     /// is particularly important in the new borrowck analysis for
 947     /// things like the type of the return slot. Consider this
 948     /// example:
 949     ///
 950     /// ```compile_fail,E0515
 951     /// fn foo<'a>(x: &'a u32) -> &'a u32 {
 952     ///     let y = 22;
 953     ///     return &y; // error
 954     /// }
 955     /// ```
 956     ///
 957     /// Here, we wind up with the signature from the return type being
 958     /// something like `&'1 u32` where `'1` is a universal region. But
 959     /// the type of the return slot `_0` is something like `&'2 u32`
 960     /// where `'2` is an existential region variable. The type checker
 961     /// requires that `&'2 u32 = &'1 u32` -- but at what point? In the
 962     /// older NLL analysis, we required this only at the entry point
 963     /// to the function. By the nature of the constraints, this wound
 964     /// up propagating to all points reachable from start (because
 965     /// `'1` -- as a universal region -- is live everywhere). In the
 966     /// newer analysis, though, this doesn't work: `_0` is considered
 967     /// dead at the start (it has no usable value) and hence this type
 968     /// equality is basically a no-op. Then, later on, when we do `_0
 969     /// = &'3 y`, that region `'3` never winds up related to the
 970     /// universal region `'1` and hence no error occurs. Therefore, we
 971     /// use Locations::All instead, which ensures that the `'1` and
 972     /// `'2` are equal everything. We also use this for other
 973     /// user-given type annotations; e.g., if the user wrote `let mut
 974     /// x: &'static u32 = ...`, we would ensure that all values
 975     /// assigned to `x` are of `'static` lifetime.
 976     ///
 977     /// The span points to the place the constraint arose. For example,
 978     /// it points to the type in a user-given type annotation. If
 979     /// there's no sensible span then it's DUMMY_SP.
 980     All(Span),
 981
 982     /// An outlives constraint that only has to hold at a single location,
 983     /// usually it represents a point where references flow from one spot to
 984     /// another (e.g., `x = y`)
 985     Single(Location),
 986 }
 987
 988 impl Locations {
 989     pub fn from_location(&self) -> Option<Location> {
 990         match self {
 991             Locations::All(_) => None,
 992             Locations::Single(from_location) => Some(*from_location),
 993         }
 994     }
 995
 996     /// Gets a span representing the location.
 997     pub fn span(&self, body: &Body<'_>) -> Span {
 998         match self {
 999             Locations::All(span) => *span,
1000             Locations::Single(l) => body.source_info(*l).span,
1001         }
1002     }
1003 }
1004
1005 impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
1006     fn new(
1007         infcx: &'a InferCtxt<'tcx>,
1008         body: &'a Body<'tcx>,
1009         param_env: ty::ParamEnv<'tcx>,
1010         region_bound_pairs: &'a RegionBoundPairs<'tcx>,
1011         implicit_region_bound: ty::Region<'tcx>,
1012         borrowck_context: &'a mut BorrowCheckContext<'a, 'tcx>,
1013     ) -> Self {
1014         let mut checker = Self {
1015             infcx,
1016             last_span: DUMMY_SP,
1017             body,
1018             user_type_annotations: &body.user_type_annotations,
1019             param_env,
1020             region_bound_pairs,
1021             implicit_region_bound,
1022             borrowck_context,
1023             reported_errors: Default::default(),
1024         };
1025         checker.check_user_type_annotations();
1026         checker
1027     }
1028
1029     fn body(&self) -> &Body<'tcx> {
1030         self.body
1031     }
1032
1033     fn unsized_feature_enabled(&self) -> bool {
1034         let features = self.tcx().features();
1035         features.unsized_locals || features.unsized_fn_params
1036     }
1037
1038     /// Equate the inferred type and the annotated type for user type annotations
1039     #[instrument(skip(self), level = "debug")]
1040     fn check_user_type_annotations(&mut self) {
1041         debug!(?self.user_type_annotations);
1042         for user_annotation in self.user_type_annotations {
1043             let CanonicalUserTypeAnnotation { span, ref user_ty, inferred_ty } = *user_annotation;
1044             let inferred_ty = self.normalize(inferred_ty, Locations::All(span));
1045             let annotation = self.instantiate_canonical_with_fresh_inference_vars(span, user_ty);
1046             debug!(?annotation);
1047             match annotation {
1048                 UserType::Ty(mut ty) => {
1049                     ty = self.normalize(ty, Locations::All(span));
1050
1051                     if let Err(terr) = self.eq_types(
1052                         ty,
1053                         inferred_ty,
1054                         Locations::All(span),
1055                         ConstraintCategory::BoringNoLocation,
1056                     ) {
1057                         span_mirbug!(
1058                             self,
1059                             user_annotation,
1060                             "bad user type ({:?} = {:?}): {:?}",
1061                             ty,
1062                             inferred_ty,
1063                             terr
1064                         );
1065                     }
1066
1067                     self.prove_predicate(
1068                         ty::Binder::dummy(ty::PredicateKind::WellFormed(inferred_ty.into())),
1069                         Locations::All(span),
1070                         ConstraintCategory::TypeAnnotation,
1071                     );
1072                 }
1073                 UserType::TypeOf(def_id, user_substs) => {
1074                     if let Err(terr) = self.fully_perform_op(
1075                         Locations::All(span),
1076                         ConstraintCategory::BoringNoLocation,
1077                         self.param_env.and(type_op::ascribe_user_type::AscribeUserType::new(
1078                             inferred_ty,
1079                             def_id,
1080                             user_substs,
1081                         )),
1082                     ) {
1083                         span_mirbug!(
1084                             self,
1085                             user_annotation,
1086                             "bad user type AscribeUserType({:?}, {:?} {:?}, type_of={:?}): {:?}",
1087                             inferred_ty,
1088                             def_id,
1089                             user_substs,
1090                             self.tcx().type_of(def_id),
1091                             terr,
1092                         );
1093                     }
1094                 }
1095             }
1096         }
1097     }
1098
1099     #[instrument(skip(self, data), level = "debug")]
1100     fn push_region_constraints(
1101         &mut self,
1102         locations: Locations,
1103         category: ConstraintCategory<'tcx>,
1104         data: &QueryRegionConstraints<'tcx>,
1105     ) {
1106         debug!("constraints generated: {:#?}", data);
1107
1108         constraint_conversion::ConstraintConversion::new(
1109             self.infcx,
1110             self.borrowck_context.universal_regions,
1111             self.region_bound_pairs,
1112             self.implicit_region_bound,
1113             self.param_env,
1114             locations,
1115             locations.span(self.body),
1116             category,
1117             &mut self.borrowck_context.constraints,
1118         )
1119         .convert_all(data);
1120     }
1121
1122     /// Try to relate `sub <: sup`
1123     fn sub_types(
1124         &mut self,
1125         sub: Ty<'tcx>,
1126         sup: Ty<'tcx>,
1127         locations: Locations,
1128         category: ConstraintCategory<'tcx>,
1129     ) -> Fallible<()> {
1130         // Use this order of parameters because the sup type is usually the
1131         // "expected" type in diagnostics.
1132         self.relate_types(sup, ty::Variance::Contravariant, sub, locations, category)
1133     }
1134
1135     #[instrument(skip(self, category), level = "debug")]
1136     fn eq_types(
1137         &mut self,
1138         expected: Ty<'tcx>,
1139         found: Ty<'tcx>,
1140         locations: Locations,
1141         category: ConstraintCategory<'tcx>,
1142     ) -> Fallible<()> {
1143         self.relate_types(expected, ty::Variance::Invariant, found, locations, category)
1144     }
1145
1146     #[instrument(skip(self), level = "debug")]
1147     fn relate_type_and_user_type(
1148         &mut self,
1149         a: Ty<'tcx>,
1150         v: ty::Variance,
1151         user_ty: &UserTypeProjection,
1152         locations: Locations,
1153         category: ConstraintCategory<'tcx>,
1154     ) -> Fallible<()> {
1155         let annotated_type = self.user_type_annotations[user_ty.base].inferred_ty;
1156         trace!(?annotated_type);
1157         let mut curr_projected_ty = PlaceTy::from_ty(annotated_type);
1158
1159         let tcx = self.infcx.tcx;
1160
1161         for proj in &user_ty.projs {
1162             let projected_ty = curr_projected_ty.projection_ty_core(
1163                 tcx,
1164                 self.param_env,
1165                 proj,
1166                 |this, field, _| {
1167                     let ty = this.field_ty(tcx, field);
1168                     self.normalize(ty, locations)
1169                 },
1170                 |_, _| unreachable!(),
1171             );
1172             curr_projected_ty = projected_ty;
1173         }
1174         trace!(?curr_projected_ty);
1175
1176         let ty = curr_projected_ty.ty;
1177         self.relate_types(ty, v.xform(ty::Variance::Contravariant), a, locations, category)?;
1178
1179         Ok(())
1180     }
1181
1182     fn tcx(&self) -> TyCtxt<'tcx> {
1183         self.infcx.tcx
1184     }
1185
1186     #[instrument(skip(self, body, location), level = "debug")]
1187     fn check_stmt(&mut self, body: &Body<'tcx>, stmt: &Statement<'tcx>, location: Location) {
1188         let tcx = self.tcx();
1189         debug!("stmt kind: {:?}", stmt.kind);
1190         match &stmt.kind {
1191             StatementKind::Assign(box (place, rv)) => {
1192                 // Assignments to temporaries are not "interesting";
1193                 // they are not caused by the user, but rather artifacts
1194                 // of lowering. Assignments to other sorts of places *are* interesting
1195                 // though.
1196                 let category = match place.as_local() {
1197                     Some(RETURN_PLACE) => {
1198                         let defining_ty = &self.borrowck_context.universal_regions.defining_ty;
1199                         if defining_ty.is_const() {
1200                             if tcx.is_static(defining_ty.def_id()) {
1201                                 ConstraintCategory::UseAsStatic
1202                             } else {
1203                                 ConstraintCategory::UseAsConst
1204                             }
1205                         } else {
1206                             ConstraintCategory::Return(ReturnConstraint::Normal)
1207                         }
1208                     }
1209                     Some(l)
1210                         if matches!(
1211                             body.local_decls[l].local_info,
1212                             Some(box LocalInfo::AggregateTemp)
1213                         ) =>
1214                     {
1215                         ConstraintCategory::Usage
1216                     }
1217                     Some(l) if !body.local_decls[l].is_user_variable() => {
1218                         ConstraintCategory::Boring
1219                     }
1220                     _ => ConstraintCategory::Assignment,
1221                 };
1222                 debug!(
1223                     "assignment category: {:?} {:?}",
1224                     category,
1225                     place.as_local().map(|l| &body.local_decls[l])
1226                 );
1227
1228                 let place_ty = place.ty(body, tcx).ty;
1229                 debug!(?place_ty);
1230                 let place_ty = self.normalize(place_ty, location);
1231                 debug!("place_ty normalized: {:?}", place_ty);
1232                 let rv_ty = rv.ty(body, tcx);
1233                 debug!(?rv_ty);
1234                 let rv_ty = self.normalize(rv_ty, location);
1235                 debug!("normalized rv_ty: {:?}", rv_ty);
1236                 if let Err(terr) =
1237                     self.sub_types(rv_ty, place_ty, location.to_locations(), category)
1238                 {
1239                     span_mirbug!(
1240                         self,
1241                         stmt,
1242                         "bad assignment ({:?} = {:?}): {:?}",
1243                         place_ty,
1244                         rv_ty,
1245                         terr
1246                     );
1247                 }
1248
1249                 if let Some(annotation_index) = self.rvalue_user_ty(rv) {
1250                     if let Err(terr) = self.relate_type_and_user_type(
1251                         rv_ty,
1252                         ty::Variance::Invariant,
1253                         &UserTypeProjection { base: annotation_index, projs: vec![] },
1254                         location.to_locations(),
1255                         ConstraintCategory::Boring,
1256                     ) {
1257                         let annotation = &self.user_type_annotations[annotation_index];
1258                         span_mirbug!(
1259                             self,
1260                             stmt,
1261                             "bad user type on rvalue ({:?} = {:?}): {:?}",
1262                             annotation,
1263                             rv_ty,
1264                             terr
1265                         );
1266                     }
1267                 }
1268
1269                 self.check_rvalue(body, rv, location);
1270                 if !self.unsized_feature_enabled() {
1271                     let trait_ref =
1272                         tcx.at(self.last_span).mk_trait_ref(LangItem::Sized, [place_ty]);
1273                     self.prove_trait_ref(
1274                         trait_ref,
1275                         location.to_locations(),
1276                         ConstraintCategory::SizedBound,
1277                     );
1278                 }
1279             }
1280             StatementKind::AscribeUserType(box (place, projection), variance) => {
1281                 let place_ty = place.ty(body, tcx).ty;
1282                 if let Err(terr) = self.relate_type_and_user_type(
1283                     place_ty,
1284                     *variance,
1285                     projection,
1286                     Locations::All(stmt.source_info.span),
1287                     ConstraintCategory::TypeAnnotation,
1288                 ) {
1289                     let annotation = &self.user_type_annotations[projection.base];
1290                     span_mirbug!(
1291                         self,
1292                         stmt,
1293                         "bad type assert ({:?} <: {:?} with projections {:?}): {:?}",
1294                         place_ty,
1295                         annotation,
1296                         projection.projs,
1297                         terr
1298                     );
1299                 }
1300             }
1301             StatementKind::Intrinsic(box kind) => match kind {
1302                 NonDivergingIntrinsic::Assume(op) => self.check_operand(op, location),
1303                 NonDivergingIntrinsic::CopyNonOverlapping(..) => span_bug!(
1304                     stmt.source_info.span,
1305                     "Unexpected NonDivergingIntrinsic::CopyNonOverlapping, should only appear after lowering_intrinsics",
1306                 ),
1307             },
1308             StatementKind::FakeRead(..)
1309             | StatementKind::StorageLive(..)
1310             | StatementKind::StorageDead(..)
1311             | StatementKind::Retag { .. }
1312             | StatementKind::Coverage(..)
1313             | StatementKind::Nop => {}
1314             StatementKind::Deinit(..) | StatementKind::SetDiscriminant { .. } => {
1315                 bug!("Statement not allowed in this MIR phase")
1316             }
1317         }
1318     }
1319
1320     #[instrument(skip(self, body, term_location), level = "debug")]
1321     fn check_terminator(
1322         &mut self,
1323         body: &Body<'tcx>,
1324         term: &Terminator<'tcx>,
1325         term_location: Location,
1326     ) {
1327         let tcx = self.tcx();
1328         debug!("terminator kind: {:?}", term.kind);
1329         match &term.kind {
1330             TerminatorKind::Goto { .. }
1331             | TerminatorKind::Resume
1332             | TerminatorKind::Abort
1333             | TerminatorKind::Return
1334             | TerminatorKind::GeneratorDrop
1335             | TerminatorKind::Unreachable
1336             | TerminatorKind::Drop { .. }
1337             | TerminatorKind::FalseEdge { .. }
1338             | TerminatorKind::FalseUnwind { .. }
1339             | TerminatorKind::InlineAsm { .. } => {
1340                 // no checks needed for these
1341             }
1342
1343             TerminatorKind::DropAndReplace { place, value, target: _, unwind: _ } => {
1344                 let place_ty = place.ty(body, tcx).ty;
1345                 let rv_ty = value.ty(body, tcx);
1346
1347                 let locations = term_location.to_locations();
1348                 if let Err(terr) =
1349                     self.sub_types(rv_ty, place_ty, locations, ConstraintCategory::Assignment)
1350                 {
1351                     span_mirbug!(
1352                         self,
1353                         term,
1354                         "bad DropAndReplace ({:?} = {:?}): {:?}",
1355                         place_ty,
1356                         rv_ty,
1357                         terr
1358                     );
1359                 }
1360             }
1361             TerminatorKind::SwitchInt { discr, .. } => {
1362                 self.check_operand(discr, term_location);
1363
1364                 let switch_ty = discr.ty(body, tcx);
1365                 if !switch_ty.is_integral() && !switch_ty.is_char() && !switch_ty.is_bool() {
1366                     span_mirbug!(self, term, "bad SwitchInt discr ty {:?}", switch_ty);
1367                 }
1368                 // FIXME: check the values
1369             }
1370             TerminatorKind::Call { func, args, destination, from_hir_call, target, .. } => {
1371                 self.check_operand(func, term_location);
1372                 for arg in args {
1373                     self.check_operand(arg, term_location);
1374                 }
1375
1376                 let func_ty = func.ty(body, tcx);
1377                 debug!("func_ty.kind: {:?}", func_ty.kind());
1378
1379                 let sig = match func_ty.kind() {
1380                     ty::FnDef(..) | ty::FnPtr(_) => func_ty.fn_sig(tcx),
1381                     _ => {
1382                         span_mirbug!(self, term, "call to non-function {:?}", func_ty);
1383                         return;
1384                     }
1385                 };
1386                 let (sig, map) = tcx.replace_late_bound_regions(sig, |br| {
1387                     self.infcx.next_region_var(LateBoundRegion(
1388                         term.source_info.span,
1389                         br.kind,
1390                         LateBoundRegionConversionTime::FnCall,
1391                     ))
1392                 });
1393                 debug!(?sig);
1394                 // IMPORTANT: We have to prove well formed for the function signature before
1395                 // we normalize it, as otherwise types like `<&'a &'b () as Trait>::Assoc`
1396                 // get normalized away, causing us to ignore the `'b: 'a` bound used by the function.
1397                 //
1398                 // Normalization results in a well formed type if the input is well formed, so we
1399                 // don't have to check it twice.
1400                 //
1401                 // See #91068 for an example.
1402                 self.prove_predicates(
1403                     sig.inputs_and_output
1404                         .iter()
1405                         .map(|ty| ty::Binder::dummy(ty::PredicateKind::WellFormed(ty.into()))),
1406                     term_location.to_locations(),
1407                     ConstraintCategory::Boring,
1408                 );
1409                 let sig = self.normalize(sig, term_location);
1410                 self.check_call_dest(body, term, &sig, *destination, *target, term_location);
1411
1412                 // The ordinary liveness rules will ensure that all
1413                 // regions in the type of the callee are live here. We
1414                 // then further constrain the late-bound regions that
1415                 // were instantiated at the call site to be live as
1416                 // well. The resulting is that all the input (and
1417                 // output) types in the signature must be live, since
1418                 // all the inputs that fed into it were live.
1419                 for &late_bound_region in map.values() {
1420                     let region_vid =
1421                         self.borrowck_context.universal_regions.to_region_vid(late_bound_region);
1422                     self.borrowck_context
1423                         .constraints
1424                         .liveness_constraints
1425                         .add_element(region_vid, term_location);
1426                 }
1427
1428                 self.check_call_inputs(body, term, &sig, args, term_location, *from_hir_call);
1429             }
1430             TerminatorKind::Assert { cond, msg, .. } => {
1431                 self.check_operand(cond, term_location);
1432
1433                 let cond_ty = cond.ty(body, tcx);
1434                 if cond_ty != tcx.types.bool {
1435                     span_mirbug!(self, term, "bad Assert ({:?}, not bool", cond_ty);
1436                 }
1437
1438                 if let AssertKind::BoundsCheck { len, index } = msg {
1439                     if len.ty(body, tcx) != tcx.types.usize {
1440                         span_mirbug!(self, len, "bounds-check length non-usize {:?}", len)
1441                     }
1442                     if index.ty(body, tcx) != tcx.types.usize {
1443                         span_mirbug!(self, index, "bounds-check index non-usize {:?}", index)
1444                     }
1445                 }
1446             }
1447             TerminatorKind::Yield { value, .. } => {
1448                 self.check_operand(value, term_location);
1449
1450                 let value_ty = value.ty(body, tcx);
1451                 match body.yield_ty() {
1452                     None => span_mirbug!(self, term, "yield in non-generator"),
1453                     Some(ty) => {
1454                         if let Err(terr) = self.sub_types(
1455                             value_ty,
1456                             ty,
1457                             term_location.to_locations(),
1458                             ConstraintCategory::Yield,
1459                         ) {
1460                             span_mirbug!(
1461                                 self,
1462                                 term,
1463                                 "type of yield value is {:?}, but the yield type is {:?}: {:?}",
1464                                 value_ty,
1465                                 ty,
1466                                 terr
1467                             );
1468                         }
1469                     }
1470                 }
1471             }
1472         }
1473     }
1474
1475     fn check_call_dest(
1476         &mut self,
1477         body: &Body<'tcx>,
1478         term: &Terminator<'tcx>,
1479         sig: &ty::FnSig<'tcx>,
1480         destination: Place<'tcx>,
1481         target: Option<BasicBlock>,
1482         term_location: Location,
1483     ) {
1484         let tcx = self.tcx();
1485         match target {
1486             Some(_) => {
1487                 let dest_ty = destination.ty(body, tcx).ty;
1488                 let dest_ty = self.normalize(dest_ty, term_location);
1489                 let category = match destination.as_local() {
1490                     Some(RETURN_PLACE) => {
1491                         if let BorrowCheckContext {
1492                             universal_regions:
1493                                 UniversalRegions {
1494                                     defining_ty:
1495                                         DefiningTy::Const(def_id, _)
1496                                         | DefiningTy::InlineConst(def_id, _),
1497                                     ..
1498                                 },
1499                             ..
1500                         } = self.borrowck_context
1501                         {
1502                             if tcx.is_static(*def_id) {
1503                                 ConstraintCategory::UseAsStatic
1504                             } else {
1505                                 ConstraintCategory::UseAsConst
1506                             }
1507                         } else {
1508                             ConstraintCategory::Return(ReturnConstraint::Normal)
1509                         }
1510                     }
1511                     Some(l) if !body.local_decls[l].is_user_variable() => {
1512                         ConstraintCategory::Boring
1513                     }
1514                     _ => ConstraintCategory::Assignment,
1515                 };
1516
1517                 let locations = term_location.to_locations();
1518
1519                 if let Err(terr) = self.sub_types(sig.output(), dest_ty, locations, category) {
1520                     span_mirbug!(
1521                         self,
1522                         term,
1523                         "call dest mismatch ({:?} <- {:?}): {:?}",
1524                         dest_ty,
1525                         sig.output(),
1526                         terr
1527                     );
1528                 }
1529
1530                 // When `unsized_fn_params` and `unsized_locals` are both not enabled,
1531                 // this check is done at `check_local`.
1532                 if self.unsized_feature_enabled() {
1533                     let span = term.source_info.span;
1534                     self.ensure_place_sized(dest_ty, span);
1535                 }
1536             }
1537             None => {
1538                 if !sig.output().is_privately_uninhabited(self.tcx(), self.param_env) {
1539                     span_mirbug!(self, term, "call to converging function {:?} w/o dest", sig);
1540                 }
1541             }
1542         }
1543     }
1544
1545     fn check_call_inputs(
1546         &mut self,
1547         body: &Body<'tcx>,
1548         term: &Terminator<'tcx>,
1549         sig: &ty::FnSig<'tcx>,
1550         args: &[Operand<'tcx>],
1551         term_location: Location,
1552         from_hir_call: bool,
1553     ) {
1554         debug!("check_call_inputs({:?}, {:?})", sig, args);
1555         if args.len() < sig.inputs().len() || (args.len() > sig.inputs().len() && !sig.c_variadic) {
1556             span_mirbug!(self, term, "call to {:?} with wrong # of args", sig);
1557         }
1558
1559         let func_ty = if let TerminatorKind::Call { func, .. } = &term.kind {
1560             Some(func.ty(body, self.infcx.tcx))
1561         } else {
1562             None
1563         };
1564         debug!(?func_ty);
1565
1566         for (n, (fn_arg, op_arg)) in iter::zip(sig.inputs(), args).enumerate() {
1567             let op_arg_ty = op_arg.ty(body, self.tcx());
1568
1569             let op_arg_ty = self.normalize(op_arg_ty, term_location);
1570             let category = if from_hir_call {
1571                 ConstraintCategory::CallArgument(self.infcx.tcx.erase_regions(func_ty))
1572             } else {
1573                 ConstraintCategory::Boring
1574             };
1575             if let Err(terr) =
1576                 self.sub_types(op_arg_ty, *fn_arg, term_location.to_locations(), category)
1577             {
1578                 span_mirbug!(
1579                     self,
1580                     term,
1581                     "bad arg #{:?} ({:?} <- {:?}): {:?}",
1582                     n,
1583                     fn_arg,
1584                     op_arg_ty,
1585                     terr
1586                 );
1587             }
1588         }
1589     }
1590
1591     fn check_iscleanup(&mut self, body: &Body<'tcx>, block_data: &BasicBlockData<'tcx>) {
1592         let is_cleanup = block_data.is_cleanup;
1593         self.last_span = block_data.terminator().source_info.span;
1594         match block_data.terminator().kind {
1595             TerminatorKind::Goto { target } => {
1596                 self.assert_iscleanup(body, block_data, target, is_cleanup)
1597             }
1598             TerminatorKind::SwitchInt { ref targets, .. } => {
1599                 for target in targets.all_targets() {
1600                     self.assert_iscleanup(body, block_data, *target, is_cleanup);
1601                 }
1602             }
1603             TerminatorKind::Resume => {
1604                 if !is_cleanup {
1605                     span_mirbug!(self, block_data, "resume on non-cleanup block!")
1606                 }
1607             }
1608             TerminatorKind::Abort => {
1609                 if !is_cleanup {
1610                     span_mirbug!(self, block_data, "abort on non-cleanup block!")
1611                 }
1612             }
1613             TerminatorKind::Return => {
1614                 if is_cleanup {
1615                     span_mirbug!(self, block_data, "return on cleanup block")
1616                 }
1617             }
1618             TerminatorKind::GeneratorDrop { .. } => {
1619                 if is_cleanup {
1620                     span_mirbug!(self, block_data, "generator_drop in cleanup block")
1621                 }
1622             }
1623             TerminatorKind::Yield { resume, drop, .. } => {
1624                 if is_cleanup {
1625                     span_mirbug!(self, block_data, "yield in cleanup block")
1626                 }
1627                 self.assert_iscleanup(body, block_data, resume, is_cleanup);
1628                 if let Some(drop) = drop {
1629                     self.assert_iscleanup(body, block_data, drop, is_cleanup);
1630                 }
1631             }
1632             TerminatorKind::Unreachable => {}
1633             TerminatorKind::Drop { target, unwind, .. }
1634             | TerminatorKind::DropAndReplace { target, unwind, .. }
1635             | TerminatorKind::Assert { target, cleanup: unwind, .. } => {
1636                 self.assert_iscleanup(body, block_data, target, is_cleanup);
1637                 if let Some(unwind) = unwind {
1638                     if is_cleanup {
1639                         span_mirbug!(self, block_data, "unwind on cleanup block")
1640                     }
1641                     self.assert_iscleanup(body, block_data, unwind, true);
1642                 }
1643             }
1644             TerminatorKind::Call { ref target, cleanup, .. } => {
1645                 if let &Some(target) = target {
1646                     self.assert_iscleanup(body, block_data, target, is_cleanup);
1647                 }
1648                 if let Some(cleanup) = cleanup {
1649                     if is_cleanup {
1650                         span_mirbug!(self, block_data, "cleanup on cleanup block")
1651                     }
1652                     self.assert_iscleanup(body, block_data, cleanup, true);
1653                 }
1654             }
1655             TerminatorKind::FalseEdge { real_target, imaginary_target } => {
1656                 self.assert_iscleanup(body, block_data, real_target, is_cleanup);
1657                 self.assert_iscleanup(body, block_data, imaginary_target, is_cleanup);
1658             }
1659             TerminatorKind::FalseUnwind { real_target, unwind } => {
1660                 self.assert_iscleanup(body, block_data, real_target, is_cleanup);
1661                 if let Some(unwind) = unwind {
1662                     if is_cleanup {
1663                         span_mirbug!(self, block_data, "cleanup in cleanup block via false unwind");
1664                     }
1665                     self.assert_iscleanup(body, block_data, unwind, true);
1666                 }
1667             }
1668             TerminatorKind::InlineAsm { destination, cleanup, .. } => {
1669                 if let Some(target) = destination {
1670                     self.assert_iscleanup(body, block_data, target, is_cleanup);
1671                 }
1672                 if let Some(cleanup) = cleanup {
1673                     if is_cleanup {
1674                         span_mirbug!(self, block_data, "cleanup on cleanup block")
1675                     }
1676                     self.assert_iscleanup(body, block_data, cleanup, true);
1677                 }
1678             }
1679         }
1680     }
1681
1682     fn assert_iscleanup(
1683         &mut self,
1684         body: &Body<'tcx>,
1685         ctxt: &dyn fmt::Debug,
1686         bb: BasicBlock,
1687         iscleanuppad: bool,
1688     ) {
1689         if body[bb].is_cleanup != iscleanuppad {
1690             span_mirbug!(self, ctxt, "cleanuppad mismatch: {:?} should be {:?}", bb, iscleanuppad);
1691         }
1692     }
1693
1694     fn check_local(&mut self, body: &Body<'tcx>, local: Local, local_decl: &LocalDecl<'tcx>) {
1695         match body.local_kind(local) {
1696             LocalKind::ReturnPointer | LocalKind::Arg => {
1697                 // return values of normal functions are required to be
1698                 // sized by typeck, but return values of ADT constructors are
1699                 // not because we don't include a `Self: Sized` bounds on them.
1700                 //
1701                 // Unbound parts of arguments were never required to be Sized
1702                 // - maybe we should make that a warning.
1703                 return;
1704             }
1705             LocalKind::Var | LocalKind::Temp => {}
1706         }
1707
1708         // When `unsized_fn_params` or `unsized_locals` is enabled, only function calls
1709         // and nullary ops are checked in `check_call_dest`.
1710         if !self.unsized_feature_enabled() {
1711             let span = local_decl.source_info.span;
1712             let ty = local_decl.ty;
1713             self.ensure_place_sized(ty, span);
1714         }
1715     }
1716
1717     fn ensure_place_sized(&mut self, ty: Ty<'tcx>, span: Span) {
1718         let tcx = self.tcx();
1719
1720         // Erase the regions from `ty` to get a global type.  The
1721         // `Sized` bound in no way depends on precise regions, so this
1722         // shouldn't affect `is_sized`.
1723         let erased_ty = tcx.erase_regions(ty);
1724         if !erased_ty.is_sized(tcx, self.param_env) {
1725             // in current MIR construction, all non-control-flow rvalue
1726             // expressions evaluate through `as_temp` or `into` a return
1727             // slot or local, so to find all unsized rvalues it is enough
1728             // to check all temps, return slots and locals.
1729             if self.reported_errors.replace((ty, span)).is_none() {
1730                 // While this is located in `nll::typeck` this error is not
1731                 // an NLL error, it's a required check to prevent creation
1732                 // of unsized rvalues in a call expression.
1733                 self.tcx().sess.emit_err(MoveUnsized { ty, span });
1734             }
1735         }
1736     }
1737
1738     fn aggregate_field_ty(
1739         &mut self,
1740         ak: &AggregateKind<'tcx>,
1741         field_index: usize,
1742         location: Location,
1743     ) -> Result<Ty<'tcx>, FieldAccessError> {
1744         let tcx = self.tcx();
1745
1746         match *ak {
1747             AggregateKind::Adt(adt_did, variant_index, substs, _, active_field_index) => {
1748                 let def = tcx.adt_def(adt_did);
1749                 let variant = &def.variant(variant_index);
1750                 let adj_field_index = active_field_index.unwrap_or(field_index);
1751                 if let Some(field) = variant.fields.get(adj_field_index) {
1752                     Ok(self.normalize(field.ty(tcx, substs), location))
1753                 } else {
1754                     Err(FieldAccessError::OutOfRange { field_count: variant.fields.len() })
1755                 }
1756             }
1757             AggregateKind::Closure(_, substs) => {
1758                 match substs.as_closure().upvar_tys().nth(field_index) {
1759                     Some(ty) => Ok(ty),
1760                     None => Err(FieldAccessError::OutOfRange {
1761                         field_count: substs.as_closure().upvar_tys().count(),
1762                     }),
1763                 }
1764             }
1765             AggregateKind::Generator(_, substs, _) => {
1766                 // It doesn't make sense to look at a field beyond the prefix;
1767                 // these require a variant index, and are not initialized in
1768                 // aggregate rvalues.
1769                 match substs.as_generator().prefix_tys().nth(field_index) {
1770                     Some(ty) => Ok(ty),
1771                     None => Err(FieldAccessError::OutOfRange {
1772                         field_count: substs.as_generator().prefix_tys().count(),
1773                     }),
1774                 }
1775             }
1776             AggregateKind::Array(ty) => Ok(ty),
1777             AggregateKind::Tuple => {
1778                 unreachable!("This should have been covered in check_rvalues");
1779             }
1780         }
1781     }
1782
1783     fn check_operand(&mut self, op: &Operand<'tcx>, location: Location) {
1784         debug!(?op, ?location, "check_operand");
1785
1786         if let Operand::Constant(constant) = op {
1787             let maybe_uneval = match constant.literal {
1788                 ConstantKind::Val(..) | ConstantKind::Ty(_) => None,
1789                 ConstantKind::Unevaluated(uv, _) => Some(uv),
1790             };
1791
1792             if let Some(uv) = maybe_uneval {
1793                 if uv.promoted.is_none() {
1794                     let tcx = self.tcx();
1795                     let def_id = uv.def.def_id_for_type_of();
1796                     if tcx.def_kind(def_id) == DefKind::InlineConst {
1797                         let def_id = def_id.expect_local();
1798                         let predicates =
1799                             self.prove_closure_bounds(tcx, def_id, uv.substs, location);
1800                         self.normalize_and_prove_instantiated_predicates(
1801                             def_id.to_def_id(),
1802                             predicates,
1803                             location.to_locations(),
1804                         );
1805                     }
1806                 }
1807             }
1808         }
1809     }
1810
1811     #[instrument(skip(self, body), level = "debug")]
1812     fn check_rvalue(&mut self, body: &Body<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
1813         let tcx = self.tcx();
1814         let span = body.source_info(location).span;
1815
1816         match rvalue {
1817             Rvalue::Aggregate(ak, ops) => {
1818                 for op in ops {
1819                     self.check_operand(op, location);
1820                 }
1821                 self.check_aggregate_rvalue(&body, rvalue, ak, ops, location)
1822             }
1823
1824             Rvalue::Repeat(operand, len) => {
1825                 self.check_operand(operand, location);
1826
1827                 // If the length cannot be evaluated we must assume that the length can be larger
1828                 // than 1.
1829                 // If the length is larger than 1, the repeat expression will need to copy the
1830                 // element, so we require the `Copy` trait.
1831                 if len.try_eval_usize(tcx, self.param_env).map_or(true, |len| len > 1) {
1832                     match operand {
1833                         Operand::Copy(..) | Operand::Constant(..) => {
1834                             // These are always okay: direct use of a const, or a value that can evidently be copied.
1835                         }
1836                         Operand::Move(place) => {
1837                             // Make sure that repeated elements implement `Copy`.
1838                             let ty = place.ty(body, tcx).ty;
1839                             let trait_ref = tcx.at(span).mk_trait_ref(LangItem::Copy, [ty]);
1840
1841                             self.prove_trait_ref(
1842                                 trait_ref,
1843                                 Locations::Single(location),
1844                                 ConstraintCategory::CopyBound,
1845                             );
1846                         }
1847                     }
1848                 }
1849             }
1850
1851             &Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, ty) => {
1852                 let trait_ref = tcx.at(span).mk_trait_ref(LangItem::Sized, [ty]);
1853
1854                 self.prove_trait_ref(
1855                     trait_ref,
1856                     location.to_locations(),
1857                     ConstraintCategory::SizedBound,
1858                 );
1859             }
1860
1861             Rvalue::ShallowInitBox(operand, ty) => {
1862                 self.check_operand(operand, location);
1863
1864                 let trait_ref = tcx.at(span).mk_trait_ref(LangItem::Sized, [*ty]);
1865
1866                 self.prove_trait_ref(
1867                     trait_ref,
1868                     location.to_locations(),
1869                     ConstraintCategory::SizedBound,
1870                 );
1871             }
1872
1873             Rvalue::Cast(cast_kind, op, ty) => {
1874                 self.check_operand(op, location);
1875
1876                 match cast_kind {
1877                     CastKind::Pointer(PointerCast::ReifyFnPointer) => {
1878                         let fn_sig = op.ty(body, tcx).fn_sig(tcx);
1879
1880                         // The type that we see in the fcx is like
1881                         // `foo::<'a, 'b>`, where `foo` is the path to a
1882                         // function definition. When we extract the
1883                         // signature, it comes from the `fn_sig` query,
1884                         // and hence may contain unnormalized results.
1885                         let fn_sig = self.normalize(fn_sig, location);
1886
1887                         let ty_fn_ptr_from = tcx.mk_fn_ptr(fn_sig);
1888
1889                         if let Err(terr) = self.eq_types(
1890                             *ty,
1891                             ty_fn_ptr_from,
1892                             location.to_locations(),
1893                             ConstraintCategory::Cast,
1894                         ) {
1895                             span_mirbug!(
1896                                 self,
1897                                 rvalue,
1898                                 "equating {:?} with {:?} yields {:?}",
1899                                 ty_fn_ptr_from,
1900                                 ty,
1901                                 terr
1902                             );
1903                         }
1904                     }
1905
1906                     CastKind::Pointer(PointerCast::ClosureFnPointer(unsafety)) => {
1907                         let sig = match op.ty(body, tcx).kind() {
1908                             ty::Closure(_, substs) => substs.as_closure().sig(),
1909                             _ => bug!(),
1910                         };
1911                         let ty_fn_ptr_from = tcx.mk_fn_ptr(tcx.signature_unclosure(sig, *unsafety));
1912
1913                         if let Err(terr) = self.eq_types(
1914                             *ty,
1915                             ty_fn_ptr_from,
1916                             location.to_locations(),
1917                             ConstraintCategory::Cast,
1918                         ) {
1919                             span_mirbug!(
1920                                 self,
1921                                 rvalue,
1922                                 "equating {:?} with {:?} yields {:?}",
1923                                 ty_fn_ptr_from,
1924                                 ty,
1925                                 terr
1926                             );
1927                         }
1928                     }
1929
1930                     CastKind::Pointer(PointerCast::UnsafeFnPointer) => {
1931                         let fn_sig = op.ty(body, tcx).fn_sig(tcx);
1932
1933                         // The type that we see in the fcx is like
1934                         // `foo::<'a, 'b>`, where `foo` is the path to a
1935                         // function definition. When we extract the
1936                         // signature, it comes from the `fn_sig` query,
1937                         // and hence may contain unnormalized results.
1938                         let fn_sig = self.normalize(fn_sig, location);
1939
1940                         let ty_fn_ptr_from = tcx.safe_to_unsafe_fn_ty(fn_sig);
1941
1942                         if let Err(terr) = self.eq_types(
1943                             *ty,
1944                             ty_fn_ptr_from,
1945                             location.to_locations(),
1946                             ConstraintCategory::Cast,
1947                         ) {
1948                             span_mirbug!(
1949                                 self,
1950                                 rvalue,
1951                                 "equating {:?} with {:?} yields {:?}",
1952                                 ty_fn_ptr_from,
1953                                 ty,
1954                                 terr
1955                             );
1956                         }
1957                     }
1958
1959                     CastKind::Pointer(PointerCast::Unsize) => {
1960                         let &ty = ty;
1961                         let trait_ref = tcx
1962                             .at(span)
1963                             .mk_trait_ref(LangItem::CoerceUnsized, [op.ty(body, tcx), ty]);
1964
1965                         self.prove_trait_ref(
1966                             trait_ref,
1967                             location.to_locations(),
1968                             ConstraintCategory::Cast,
1969                         );
1970                     }
1971
1972                     CastKind::DynStar => {
1973                         // get the constraints from the target type (`dyn* Clone`)
1974                         //
1975                         // apply them to prove that the source type `Foo` implements `Clone` etc
1976                         let (existential_predicates, region) = match ty.kind() {
1977                             Dynamic(predicates, region, ty::DynStar) => (predicates, region),
1978                             _ => panic!("Invalid dyn* cast_ty"),
1979                         };
1980
1981                         let self_ty = op.ty(body, tcx);
1982
1983                         self.prove_predicates(
1984                             existential_predicates
1985                                 .iter()
1986                                 .map(|predicate| predicate.with_self_ty(tcx, self_ty)),
1987                             location.to_locations(),
1988                             ConstraintCategory::Cast,
1989                         );
1990
1991                         let outlives_predicate =
1992                             tcx.mk_predicate(Binder::dummy(ty::PredicateKind::Clause(
1993                                 ty::Clause::TypeOutlives(ty::OutlivesPredicate(self_ty, *region)),
1994                             )));
1995                         self.prove_predicate(
1996                             outlives_predicate,
1997                             location.to_locations(),
1998                             ConstraintCategory::Cast,
1999                         );
2000                     }
2001
2002                     CastKind::Pointer(PointerCast::MutToConstPointer) => {
2003                         let ty::RawPtr(ty::TypeAndMut {
2004                             ty: ty_from,
2005                             mutbl: hir::Mutability::Mut,
2006                         }) = op.ty(body, tcx).kind() else {
2007                             span_mirbug!(
2008                                 self,
2009                                 rvalue,
2010                                 "unexpected base type for cast {:?}",
2011                                 ty,
2012                             );
2013                             return;
2014                         };
2015                         let ty::RawPtr(ty::TypeAndMut {
2016                             ty: ty_to,
2017                             mutbl: hir::Mutability::Not,
2018                         }) = ty.kind() else {
2019                             span_mirbug!(
2020                                 self,
2021                                 rvalue,
2022                                 "unexpected target type for cast {:?}",
2023                                 ty,
2024                             );
2025                             return;
2026                         };
2027                         if let Err(terr) = self.sub_types(
2028                             *ty_from,
2029                             *ty_to,
2030                             location.to_locations(),
2031                             ConstraintCategory::Cast,
2032                         ) {
2033                             span_mirbug!(
2034                                 self,
2035                                 rvalue,
2036                                 "relating {:?} with {:?} yields {:?}",
2037                                 ty_from,
2038                                 ty_to,
2039                                 terr
2040                             );
2041                         }
2042                     }
2043
2044                     CastKind::Pointer(PointerCast::ArrayToPointer) => {
2045                         let ty_from = op.ty(body, tcx);
2046
2047                         let opt_ty_elem_mut = match ty_from.kind() {
2048                             ty::RawPtr(ty::TypeAndMut { mutbl: array_mut, ty: array_ty }) => {
2049                                 match array_ty.kind() {
2050                                     ty::Array(ty_elem, _) => Some((ty_elem, *array_mut)),
2051                                     _ => None,
2052                                 }
2053                             }
2054                             _ => None,
2055                         };
2056
2057                         let Some((ty_elem, ty_mut)) = opt_ty_elem_mut else {
2058                             span_mirbug!(
2059                                 self,
2060                                 rvalue,
2061                                 "ArrayToPointer cast from unexpected type {:?}",
2062                                 ty_from,
2063                             );
2064                             return;
2065                         };
2066
2067                         let (ty_to, ty_to_mut) = match ty.kind() {
2068                             ty::RawPtr(ty::TypeAndMut { mutbl: ty_to_mut, ty: ty_to }) => {
2069                                 (ty_to, *ty_to_mut)
2070                             }
2071                             _ => {
2072                                 span_mirbug!(
2073                                     self,
2074                                     rvalue,
2075                                     "ArrayToPointer cast to unexpected type {:?}",
2076                                     ty,
2077                                 );
2078                                 return;
2079                             }
2080                         };
2081
2082                         if ty_to_mut == Mutability::Mut && ty_mut == Mutability::Not {
2083                             span_mirbug!(
2084                                 self,
2085                                 rvalue,
2086                                 "ArrayToPointer cast from const {:?} to mut {:?}",
2087                                 ty,
2088                                 ty_to
2089                             );
2090                             return;
2091                         }
2092
2093                         if let Err(terr) = self.sub_types(
2094                             *ty_elem,
2095                             *ty_to,
2096                             location.to_locations(),
2097                             ConstraintCategory::Cast,
2098                         ) {
2099                             span_mirbug!(
2100                                 self,
2101                                 rvalue,
2102                                 "relating {:?} with {:?} yields {:?}",
2103                                 ty_elem,
2104                                 ty_to,
2105                                 terr
2106                             )
2107                         }
2108                     }
2109
2110                     CastKind::PointerExposeAddress => {
2111                         let ty_from = op.ty(body, tcx);
2112                         let cast_ty_from = CastTy::from_ty(ty_from);
2113                         let cast_ty_to = CastTy::from_ty(*ty);
2114                         match (cast_ty_from, cast_ty_to) {
2115                             (Some(CastTy::Ptr(_) | CastTy::FnPtr), Some(CastTy::Int(_))) => (),
2116                             _ => {
2117                                 span_mirbug!(
2118                                     self,
2119                                     rvalue,
2120                                     "Invalid PointerExposeAddress cast {:?} -> {:?}",
2121                                     ty_from,
2122                                     ty
2123                                 )
2124                             }
2125                         }
2126                     }
2127
2128                     CastKind::PointerFromExposedAddress => {
2129                         let ty_from = op.ty(body, tcx);
2130                         let cast_ty_from = CastTy::from_ty(ty_from);
2131                         let cast_ty_to = CastTy::from_ty(*ty);
2132                         match (cast_ty_from, cast_ty_to) {
2133                             (Some(CastTy::Int(_)), Some(CastTy::Ptr(_))) => (),
2134                             _ => {
2135                                 span_mirbug!(
2136                                     self,
2137                                     rvalue,
2138                                     "Invalid PointerFromExposedAddress cast {:?} -> {:?}",
2139                                     ty_from,
2140                                     ty
2141                                 )
2142                             }
2143                         }
2144                     }
2145                     CastKind::IntToInt => {
2146                         let ty_from = op.ty(body, tcx);
2147                         let cast_ty_from = CastTy::from_ty(ty_from);
2148                         let cast_ty_to = CastTy::from_ty(*ty);
2149                         match (cast_ty_from, cast_ty_to) {
2150                             (Some(CastTy::Int(_)), Some(CastTy::Int(_))) => (),
2151                             _ => {
2152                                 span_mirbug!(
2153                                     self,
2154                                     rvalue,
2155                                     "Invalid IntToInt cast {:?} -> {:?}",
2156                                     ty_from,
2157                                     ty
2158                                 )
2159                             }
2160                         }
2161                     }
2162                     CastKind::IntToFloat => {
2163                         let ty_from = op.ty(body, tcx);
2164                         let cast_ty_from = CastTy::from_ty(ty_from);
2165                         let cast_ty_to = CastTy::from_ty(*ty);
2166                         match (cast_ty_from, cast_ty_to) {
2167                             (Some(CastTy::Int(_)), Some(CastTy::Float)) => (),
2168                             _ => {
2169                                 span_mirbug!(
2170                                     self,
2171                                     rvalue,
2172                                     "Invalid IntToFloat cast {:?} -> {:?}",
2173                                     ty_from,
2174                                     ty
2175                                 )
2176                             }
2177                         }
2178                     }
2179                     CastKind::FloatToInt => {
2180                         let ty_from = op.ty(body, tcx);
2181                         let cast_ty_from = CastTy::from_ty(ty_from);
2182                         let cast_ty_to = CastTy::from_ty(*ty);
2183                         match (cast_ty_from, cast_ty_to) {
2184                             (Some(CastTy::Float), Some(CastTy::Int(_))) => (),
2185                             _ => {
2186                                 span_mirbug!(
2187                                     self,
2188                                     rvalue,
2189                                     "Invalid FloatToInt cast {:?} -> {:?}",
2190                                     ty_from,
2191                                     ty
2192                                 )
2193                             }
2194                         }
2195                     }
2196                     CastKind::FloatToFloat => {
2197                         let ty_from = op.ty(body, tcx);
2198                         let cast_ty_from = CastTy::from_ty(ty_from);
2199                         let cast_ty_to = CastTy::from_ty(*ty);
2200                         match (cast_ty_from, cast_ty_to) {
2201                             (Some(CastTy::Float), Some(CastTy::Float)) => (),
2202                             _ => {
2203                                 span_mirbug!(
2204                                     self,
2205                                     rvalue,
2206                                     "Invalid FloatToFloat cast {:?} -> {:?}",
2207                                     ty_from,
2208                                     ty
2209                                 )
2210                             }
2211                         }
2212                     }
2213                     CastKind::FnPtrToPtr => {
2214                         let ty_from = op.ty(body, tcx);
2215                         let cast_ty_from = CastTy::from_ty(ty_from);
2216                         let cast_ty_to = CastTy::from_ty(*ty);
2217                         match (cast_ty_from, cast_ty_to) {
2218                             (Some(CastTy::FnPtr), Some(CastTy::Ptr(_))) => (),
2219                             _ => {
2220                                 span_mirbug!(
2221                                     self,
2222                                     rvalue,
2223                                     "Invalid FnPtrToPtr cast {:?} -> {:?}",
2224                                     ty_from,
2225                                     ty
2226                                 )
2227                             }
2228                         }
2229                     }
2230                     CastKind::PtrToPtr => {
2231                         let ty_from = op.ty(body, tcx);
2232                         let cast_ty_from = CastTy::from_ty(ty_from);
2233                         let cast_ty_to = CastTy::from_ty(*ty);
2234                         match (cast_ty_from, cast_ty_to) {
2235                             (Some(CastTy::Ptr(_)), Some(CastTy::Ptr(_))) => (),
2236                             _ => {
2237                                 span_mirbug!(
2238                                     self,
2239                                     rvalue,
2240                                     "Invalid PtrToPtr cast {:?} -> {:?}",
2241                                     ty_from,
2242                                     ty
2243                                 )
2244                             }
2245                         }
2246                     }
2247                 }
2248             }
2249
2250             Rvalue::Ref(region, _borrow_kind, borrowed_place) => {
2251                 self.add_reborrow_constraint(&body, location, *region, borrowed_place);
2252             }
2253
2254             Rvalue::BinaryOp(
2255                 BinOp::Eq | BinOp::Ne | BinOp::Lt | BinOp::Le | BinOp::Gt | BinOp::Ge,
2256                 box (left, right),
2257             ) => {
2258                 self.check_operand(left, location);
2259                 self.check_operand(right, location);
2260
2261                 let ty_left = left.ty(body, tcx);
2262                 match ty_left.kind() {
2263                     // Types with regions are comparable if they have a common super-type.
2264                     ty::RawPtr(_) | ty::FnPtr(_) => {
2265                         let ty_right = right.ty(body, tcx);
2266                         let common_ty = self.infcx.next_ty_var(TypeVariableOrigin {
2267                             kind: TypeVariableOriginKind::MiscVariable,
2268                             span: body.source_info(location).span,
2269                         });
2270                         self.sub_types(
2271                             ty_left,
2272                             common_ty,
2273                             location.to_locations(),
2274                             ConstraintCategory::Boring,
2275                         )
2276                         .unwrap_or_else(|err| {
2277                             bug!("Could not equate type variable with {:?}: {:?}", ty_left, err)
2278                         });
2279                         if let Err(terr) = self.sub_types(
2280                             ty_right,
2281                             common_ty,
2282                             location.to_locations(),
2283                             ConstraintCategory::Boring,
2284                         ) {
2285                             span_mirbug!(
2286                                 self,
2287                                 rvalue,
2288                                 "unexpected comparison types {:?} and {:?} yields {:?}",
2289                                 ty_left,
2290                                 ty_right,
2291                                 terr
2292                             )
2293                         }
2294                     }
2295                     // For types with no regions we can just check that the
2296                     // both operands have the same type.
2297                     ty::Int(_) | ty::Uint(_) | ty::Bool | ty::Char | ty::Float(_)
2298                         if ty_left == right.ty(body, tcx) => {}
2299                     // Other types are compared by trait methods, not by
2300                     // `Rvalue::BinaryOp`.
2301                     _ => span_mirbug!(
2302                         self,
2303                         rvalue,
2304                         "unexpected comparison types {:?} and {:?}",
2305                         ty_left,
2306                         right.ty(body, tcx)
2307                     ),
2308                 }
2309             }
2310
2311             Rvalue::Use(operand) | Rvalue::UnaryOp(_, operand) => {
2312                 self.check_operand(operand, location);
2313             }
2314             Rvalue::CopyForDeref(place) => {
2315                 let op = &Operand::Copy(*place);
2316                 self.check_operand(op, location);
2317             }
2318
2319             Rvalue::BinaryOp(_, box (left, right))
2320             | Rvalue::CheckedBinaryOp(_, box (left, right)) => {
2321                 self.check_operand(left, location);
2322                 self.check_operand(right, location);
2323             }
2324
2325             Rvalue::AddressOf(..)
2326             | Rvalue::ThreadLocalRef(..)
2327             | Rvalue::Len(..)
2328             | Rvalue::Discriminant(..) => {}
2329         }
2330     }
2331
2332     /// If this rvalue supports a user-given type annotation, then
2333     /// extract and return it. This represents the final type of the
2334     /// rvalue and will be unified with the inferred type.
2335     fn rvalue_user_ty(&self, rvalue: &Rvalue<'tcx>) -> Option<UserTypeAnnotationIndex> {
2336         match rvalue {
2337             Rvalue::Use(_)
2338             | Rvalue::ThreadLocalRef(_)
2339             | Rvalue::Repeat(..)
2340             | Rvalue::Ref(..)
2341             | Rvalue::AddressOf(..)
2342             | Rvalue::Len(..)
2343             | Rvalue::Cast(..)
2344             | Rvalue::ShallowInitBox(..)
2345             | Rvalue::BinaryOp(..)
2346             | Rvalue::CheckedBinaryOp(..)
2347             | Rvalue::NullaryOp(..)
2348             | Rvalue::CopyForDeref(..)
2349             | Rvalue::UnaryOp(..)
2350             | Rvalue::Discriminant(..) => None,
2351
2352             Rvalue::Aggregate(aggregate, _) => match **aggregate {
2353                 AggregateKind::Adt(_, _, _, user_ty, _) => user_ty,
2354                 AggregateKind::Array(_) => None,
2355                 AggregateKind::Tuple => None,
2356                 AggregateKind::Closure(_, _) => None,
2357                 AggregateKind::Generator(_, _, _) => None,
2358             },
2359         }
2360     }
2361
2362     fn check_aggregate_rvalue(
2363         &mut self,
2364         body: &Body<'tcx>,
2365         rvalue: &Rvalue<'tcx>,
2366         aggregate_kind: &AggregateKind<'tcx>,
2367         operands: &[Operand<'tcx>],
2368         location: Location,
2369     ) {
2370         let tcx = self.tcx();
2371
2372         self.prove_aggregate_predicates(aggregate_kind, location);
2373
2374         if *aggregate_kind == AggregateKind::Tuple {
2375             // tuple rvalue field type is always the type of the op. Nothing to check here.
2376             return;
2377         }
2378
2379         for (i, operand) in operands.iter().enumerate() {
2380             let field_ty = match self.aggregate_field_ty(aggregate_kind, i, location) {
2381                 Ok(field_ty) => field_ty,
2382                 Err(FieldAccessError::OutOfRange { field_count }) => {
2383                     span_mirbug!(
2384                         self,
2385                         rvalue,
2386                         "accessed field #{} but variant only has {}",
2387                         i,
2388                         field_count
2389                     );
2390                     continue;
2391                 }
2392             };
2393             let operand_ty = operand.ty(body, tcx);
2394             let operand_ty = self.normalize(operand_ty, location);
2395
2396             if let Err(terr) = self.sub_types(
2397                 operand_ty,
2398                 field_ty,
2399                 location.to_locations(),
2400                 ConstraintCategory::Boring,
2401             ) {
2402                 span_mirbug!(
2403                     self,
2404                     rvalue,
2405                     "{:?} is not a subtype of {:?}: {:?}",
2406                     operand_ty,
2407                     field_ty,
2408                     terr
2409                 );
2410             }
2411         }
2412     }
2413
2414     /// Adds the constraints that arise from a borrow expression `&'a P` at the location `L`.
2415     ///
2416     /// # Parameters
2417     ///
2418     /// - `location`: the location `L` where the borrow expression occurs
2419     /// - `borrow_region`: the region `'a` associated with the borrow
2420     /// - `borrowed_place`: the place `P` being borrowed
2421     fn add_reborrow_constraint(
2422         &mut self,
2423         body: &Body<'tcx>,
2424         location: Location,
2425         borrow_region: ty::Region<'tcx>,
2426         borrowed_place: &Place<'tcx>,
2427     ) {
2428         // These constraints are only meaningful during borrowck:
2429         let BorrowCheckContext { borrow_set, location_table, all_facts, constraints, .. } =
2430             self.borrowck_context;
2431
2432         // In Polonius mode, we also push a `loan_issued_at` fact
2433         // linking the loan to the region (in some cases, though,
2434         // there is no loan associated with this borrow expression --
2435         // that occurs when we are borrowing an unsafe place, for
2436         // example).
2437         if let Some(all_facts) = all_facts {
2438             let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
2439             if let Some(borrow_index) = borrow_set.get_index_of(&location) {
2440                 let region_vid = borrow_region.to_region_vid();
2441                 all_facts.loan_issued_at.push((
2442                     region_vid,
2443                     borrow_index,
2444                     location_table.mid_index(location),
2445                 ));
2446             }
2447         }
2448
2449         // If we are reborrowing the referent of another reference, we
2450         // need to add outlives relationships. In a case like `&mut
2451         // *p`, where the `p` has type `&'b mut Foo`, for example, we
2452         // need to ensure that `'b: 'a`.
2453
2454         debug!(
2455             "add_reborrow_constraint({:?}, {:?}, {:?})",
2456             location, borrow_region, borrowed_place
2457         );
2458
2459         let mut cursor = borrowed_place.projection.as_ref();
2460         let tcx = self.infcx.tcx;
2461         let field = path_utils::is_upvar_field_projection(
2462             tcx,
2463             &self.borrowck_context.upvars,
2464             borrowed_place.as_ref(),
2465             body,
2466         );
2467         let category = if let Some(field) = field {
2468             ConstraintCategory::ClosureUpvar(field)
2469         } else {
2470             ConstraintCategory::Boring
2471         };
2472
2473         while let [proj_base @ .., elem] = cursor {
2474             cursor = proj_base;
2475
2476             debug!("add_reborrow_constraint - iteration {:?}", elem);
2477
2478             match elem {
2479                 ProjectionElem::Deref => {
2480                     let base_ty = Place::ty_from(borrowed_place.local, proj_base, body, tcx).ty;
2481
2482                     debug!("add_reborrow_constraint - base_ty = {:?}", base_ty);
2483                     match base_ty.kind() {
2484                         ty::Ref(ref_region, _, mutbl) => {
2485                             constraints.outlives_constraints.push(OutlivesConstraint {
2486                                 sup: ref_region.to_region_vid(),
2487                                 sub: borrow_region.to_region_vid(),
2488                                 locations: location.to_locations(),
2489                                 span: location.to_locations().span(body),
2490                                 category,
2491                                 variance_info: ty::VarianceDiagInfo::default(),
2492                                 from_closure: false,
2493                             });
2494
2495                             match mutbl {
2496                                 hir::Mutability::Not => {
2497                                     // Immutable reference. We don't need the base
2498                                     // to be valid for the entire lifetime of
2499                                     // the borrow.
2500                                     break;
2501                                 }
2502                                 hir::Mutability::Mut => {
2503                                     // Mutable reference. We *do* need the base
2504                                     // to be valid, because after the base becomes
2505                                     // invalid, someone else can use our mutable deref.
2506
2507                                     // This is in order to make the following function
2508                                     // illegal:
2509                                     // ```
2510                                     // fn unsafe_deref<'a, 'b>(x: &'a &'b mut T) -> &'b mut T {
2511                                     //     &mut *x
2512                                     // }
2513                                     // ```
2514                                     //
2515                                     // As otherwise you could clone `&mut T` using the
2516                                     // following function:
2517                                     // ```
2518                                     // fn bad(x: &mut T) -> (&mut T, &mut T) {
2519                                     //     let my_clone = unsafe_deref(&'a x);
2520                                     //     ENDREGION 'a;
2521                                     //     (my_clone, x)
2522                                     // }
2523                                     // ```
2524                                 }
2525                             }
2526                         }
2527                         ty::RawPtr(..) => {
2528                             // deref of raw pointer, guaranteed to be valid
2529                             break;
2530                         }
2531                         ty::Adt(def, _) if def.is_box() => {
2532                             // deref of `Box`, need the base to be valid - propagate
2533                         }
2534                         _ => bug!("unexpected deref ty {:?} in {:?}", base_ty, borrowed_place),
2535                     }
2536                 }
2537                 ProjectionElem::Field(..)
2538                 | ProjectionElem::Downcast(..)
2539                 | ProjectionElem::OpaqueCast(..)
2540                 | ProjectionElem::Index(..)
2541                 | ProjectionElem::ConstantIndex { .. }
2542                 | ProjectionElem::Subslice { .. } => {
2543                     // other field access
2544                 }
2545             }
2546         }
2547     }
2548
2549     fn prove_aggregate_predicates(
2550         &mut self,
2551         aggregate_kind: &AggregateKind<'tcx>,
2552         location: Location,
2553     ) {
2554         let tcx = self.tcx();
2555
2556         debug!(
2557             "prove_aggregate_predicates(aggregate_kind={:?}, location={:?})",
2558             aggregate_kind, location
2559         );
2560
2561         let (def_id, instantiated_predicates) = match *aggregate_kind {
2562             AggregateKind::Adt(adt_did, _, substs, _, _) => {
2563                 (adt_did, tcx.predicates_of(adt_did).instantiate(tcx, substs))
2564             }
2565
2566             // For closures, we have some **extra requirements** we
2567             // have to check. In particular, in their upvars and
2568             // signatures, closures often reference various regions
2569             // from the surrounding function -- we call those the
2570             // closure's free regions. When we borrow-check (and hence
2571             // region-check) closures, we may find that the closure
2572             // requires certain relationships between those free
2573             // regions. However, because those free regions refer to
2574             // portions of the CFG of their caller, the closure is not
2575             // in a position to verify those relationships. In that
2576             // case, the requirements get "propagated" to us, and so
2577             // we have to solve them here where we instantiate the
2578             // closure.
2579             //
2580             // Despite the opacity of the previous paragraph, this is
2581             // actually relatively easy to understand in terms of the
2582             // desugaring. A closure gets desugared to a struct, and
2583             // these extra requirements are basically like where
2584             // clauses on the struct.
2585             AggregateKind::Closure(def_id, substs)
2586             | AggregateKind::Generator(def_id, substs, _) => {
2587                 (def_id.to_def_id(), self.prove_closure_bounds(tcx, def_id, substs, location))
2588             }
2589
2590             AggregateKind::Array(_) | AggregateKind::Tuple => {
2591                 (CRATE_DEF_ID.to_def_id(), ty::InstantiatedPredicates::empty())
2592             }
2593         };
2594
2595         self.normalize_and_prove_instantiated_predicates(
2596             def_id,
2597             instantiated_predicates,
2598             location.to_locations(),
2599         );
2600     }
2601
2602     fn prove_closure_bounds(
2603         &mut self,
2604         tcx: TyCtxt<'tcx>,
2605         def_id: LocalDefId,
2606         substs: SubstsRef<'tcx>,
2607         location: Location,
2608     ) -> ty::InstantiatedPredicates<'tcx> {
2609         if let Some(closure_requirements) = &tcx.mir_borrowck(def_id).closure_requirements {
2610             constraint_conversion::ConstraintConversion::new(
2611                 self.infcx,
2612                 self.borrowck_context.universal_regions,
2613                 self.region_bound_pairs,
2614                 self.implicit_region_bound,
2615                 self.param_env,
2616                 location.to_locations(),
2617                 DUMMY_SP,                   // irrelevant; will be overrided.
2618                 ConstraintCategory::Boring, // same as above.
2619                 &mut self.borrowck_context.constraints,
2620             )
2621             .apply_closure_requirements(
2622                 &closure_requirements,
2623                 def_id.to_def_id(),
2624                 substs,
2625             );
2626         }
2627
2628         // Now equate closure substs to regions inherited from `typeck_root_def_id`. Fixes #98589.
2629         let typeck_root_def_id = tcx.typeck_root_def_id(self.body.source.def_id());
2630         let typeck_root_substs = ty::InternalSubsts::identity_for_item(tcx, typeck_root_def_id);
2631
2632         let parent_substs = match tcx.def_kind(def_id) {
2633             DefKind::Closure => substs.as_closure().parent_substs(),
2634             DefKind::Generator => substs.as_generator().parent_substs(),
2635             DefKind::InlineConst => substs.as_inline_const().parent_substs(),
2636             other => bug!("unexpected item {:?}", other),
2637         };
2638         let parent_substs = tcx.mk_substs(parent_substs.iter());
2639
2640         assert_eq!(typeck_root_substs.len(), parent_substs.len());
2641         if let Err(_) = self.eq_substs(
2642             typeck_root_substs,
2643             parent_substs,
2644             location.to_locations(),
2645             ConstraintCategory::BoringNoLocation,
2646         ) {
2647             span_mirbug!(
2648                 self,
2649                 def_id,
2650                 "could not relate closure to parent {:?} != {:?}",
2651                 typeck_root_substs,
2652                 parent_substs
2653             );
2654         }
2655
2656         tcx.predicates_of(def_id).instantiate(tcx, substs)
2657     }
2658
2659     #[instrument(skip(self, body), level = "debug")]
2660     fn typeck_mir(&mut self, body: &Body<'tcx>) {
2661         self.last_span = body.span;
2662         debug!(?body.span);
2663
2664         for (local, local_decl) in body.local_decls.iter_enumerated() {
2665             self.check_local(&body, local, local_decl);
2666         }
2667
2668         for (block, block_data) in body.basic_blocks.iter_enumerated() {
2669             let mut location = Location { block, statement_index: 0 };
2670             for stmt in &block_data.statements {
2671                 if !stmt.source_info.span.is_dummy() {
2672                     self.last_span = stmt.source_info.span;
2673                 }
2674                 self.check_stmt(body, stmt, location);
2675                 location.statement_index += 1;
2676             }
2677
2678             self.check_terminator(&body, block_data.terminator(), location);
2679             self.check_iscleanup(&body, block_data);
2680         }
2681     }
2682 }
2683
2684 trait NormalizeLocation: fmt::Debug + Copy {
2685     fn to_locations(self) -> Locations;
2686 }
2687
2688 impl NormalizeLocation for Locations {
2689     fn to_locations(self) -> Locations {
2690         self
2691     }
2692 }
2693
2694 impl NormalizeLocation for Location {
2695     fn to_locations(self) -> Locations {
2696         Locations::Single(self)
2697     }
2698 }
2699
2700 /// Runs `infcx.instantiate_opaque_types`. Unlike other `TypeOp`s,
2701 /// this is not canonicalized - it directly affects the main `InferCtxt`
2702 /// that we use during MIR borrowchecking.
2703 #[derive(Debug)]
2704 pub(super) struct InstantiateOpaqueType<'tcx> {
2705     pub base_universe: Option<ty::UniverseIndex>,
2706     pub region_constraints: Option<RegionConstraintData<'tcx>>,
2707     pub obligations: Vec<PredicateObligation<'tcx>>,
2708 }
2709
2710 impl<'tcx> TypeOp<'tcx> for InstantiateOpaqueType<'tcx> {
2711     type Output = ();
2712     /// We use this type itself to store the information used
2713     /// when reporting errors. Since this is not a query, we don't
2714     /// re-run anything during error reporting - we just use the information
2715     /// we saved to help extract an error from the already-existing region
2716     /// constraints in our `InferCtxt`
2717     type ErrorInfo = InstantiateOpaqueType<'tcx>;
2718
2719     fn fully_perform(mut self, infcx: &InferCtxt<'tcx>) -> Fallible<TypeOpOutput<'tcx, Self>> {
2720         let (mut output, region_constraints) = scrape_region_constraints(infcx, || {
2721             Ok(InferOk { value: (), obligations: self.obligations.clone() })
2722         })?;
2723         self.region_constraints = Some(region_constraints);
2724         output.error_info = Some(self);
2725         Ok(output)
2726     }
2727 }