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 = ty::TraitRef {
 551                 def_id: tcx.require_lang_item(LangItem::Copy, Some(self.last_span)),
 552                 substs: tcx.mk_substs_trait(place_ty.ty, &[]),
 553             };
 554
 555             // To have a `Copy` operand, the type `T` of the
 556             // value must be `Copy`. Note that we prove that `T: Copy`,
 557             // rather than using the `is_copy_modulo_regions`
 558             // test. This is important because
 559             // `is_copy_modulo_regions` ignores the resulting region
 560             // obligations and assumes they pass. This can result in
 561             // bounds from `Copy` impls being unsoundly ignored (e.g.,
 562             // #29149). Note that we decide to use `Copy` before knowing
 563             // whether the bounds fully apply: in effect, the rule is
 564             // that if a value of some type could implement `Copy`, then
 565             // it must.
 566             self.cx.prove_trait_ref(
 567                 trait_ref,
 568                 location.to_locations(),
 569                 ConstraintCategory::CopyBound,
 570             );
 571         }
 572
 573         place_ty
 574     }
 575
 576     fn sanitize_promoted(&mut self, promoted_body: &'b Body<'tcx>, location: Location) {
 577         // Determine the constraints from the promoted MIR by running the type
 578         // checker on the promoted MIR, then transfer the constraints back to
 579         // the main MIR, changing the locations to the provided location.
 580
 581         let parent_body = mem::replace(&mut self.cx.body, promoted_body);
 582
 583         // Use new sets of constraints and closure bounds so that we can
 584         // modify their locations.
 585         let all_facts = &mut None;
 586         let mut constraints = Default::default();
 587         let mut liveness_constraints =
 588             LivenessValues::new(Rc::new(RegionValueElements::new(&promoted_body)));
 589         // Don't try to add borrow_region facts for the promoted MIR
 590
 591         let mut swap_constraints = |this: &mut Self| {
 592             mem::swap(this.cx.borrowck_context.all_facts, all_facts);
 593             mem::swap(
 594                 &mut this.cx.borrowck_context.constraints.outlives_constraints,
 595                 &mut constraints,
 596             );
 597             mem::swap(
 598                 &mut this.cx.borrowck_context.constraints.liveness_constraints,
 599                 &mut liveness_constraints,
 600             );
 601         };
 602
 603         swap_constraints(self);
 604
 605         self.visit_body(&promoted_body);
 606
 607         if !self.errors_reported {
 608             // if verifier failed, don't do further checks to avoid ICEs
 609             self.cx.typeck_mir(promoted_body);
 610         }
 611
 612         self.cx.body = parent_body;
 613         // Merge the outlives constraints back in, at the given location.
 614         swap_constraints(self);
 615
 616         let locations = location.to_locations();
 617         for constraint in constraints.outlives().iter() {
 618             let mut constraint = constraint.clone();
 619             constraint.locations = locations;
 620             if let ConstraintCategory::Return(_)
 621             | ConstraintCategory::UseAsConst
 622             | ConstraintCategory::UseAsStatic = constraint.category
 623             {
 624                 // "Returning" from a promoted is an assignment to a
 625                 // temporary from the user's point of view.
 626                 constraint.category = ConstraintCategory::Boring;
 627             }
 628             self.cx.borrowck_context.constraints.outlives_constraints.push(constraint)
 629         }
 630         for region in liveness_constraints.rows() {
 631             // If the region is live at at least one location in the promoted MIR,
 632             // then add a liveness constraint to the main MIR for this region
 633             // at the location provided as an argument to this method
 634             if liveness_constraints.get_elements(region).next().is_some() {
 635                 self.cx
 636                     .borrowck_context
 637                     .constraints
 638                     .liveness_constraints
 639                     .add_element(region, location);
 640             }
 641         }
 642     }
 643
 644     fn sanitize_projection(
 645         &mut self,
 646         base: PlaceTy<'tcx>,
 647         pi: PlaceElem<'tcx>,
 648         place: &Place<'tcx>,
 649         location: Location,
 650     ) -> PlaceTy<'tcx> {
 651         debug!("sanitize_projection: {:?} {:?} {:?}", base, pi, place);
 652         let tcx = self.tcx();
 653         let base_ty = base.ty;
 654         match pi {
 655             ProjectionElem::Deref => {
 656                 let deref_ty = base_ty.builtin_deref(true);
 657                 PlaceTy::from_ty(deref_ty.map(|t| t.ty).unwrap_or_else(|| {
 658                     span_mirbug_and_err!(self, place, "deref of non-pointer {:?}", base_ty)
 659                 }))
 660             }
 661             ProjectionElem::Index(i) => {
 662                 let index_ty = Place::from(i).ty(self.body(), tcx).ty;
 663                 if index_ty != tcx.types.usize {
 664                     PlaceTy::from_ty(span_mirbug_and_err!(self, i, "index by non-usize {:?}", i))
 665                 } else {
 666                     PlaceTy::from_ty(base_ty.builtin_index().unwrap_or_else(|| {
 667                         span_mirbug_and_err!(self, place, "index of non-array {:?}", base_ty)
 668                     }))
 669                 }
 670             }
 671             ProjectionElem::ConstantIndex { .. } => {
 672                 // consider verifying in-bounds
 673                 PlaceTy::from_ty(base_ty.builtin_index().unwrap_or_else(|| {
 674                     span_mirbug_and_err!(self, place, "index of non-array {:?}", base_ty)
 675                 }))
 676             }
 677             ProjectionElem::Subslice { from, to, from_end } => {
 678                 PlaceTy::from_ty(match base_ty.kind() {
 679                     ty::Array(inner, _) => {
 680                         assert!(!from_end, "array subslices should not use from_end");
 681                         tcx.mk_array(*inner, to - from)
 682                     }
 683                     ty::Slice(..) => {
 684                         assert!(from_end, "slice subslices should use from_end");
 685                         base_ty
 686                     }
 687                     _ => span_mirbug_and_err!(self, place, "slice of non-array {:?}", base_ty),
 688                 })
 689             }
 690             ProjectionElem::Downcast(maybe_name, index) => match base_ty.kind() {
 691                 ty::Adt(adt_def, _substs) if adt_def.is_enum() => {
 692                     if index.as_usize() >= adt_def.variants().len() {
 693                         PlaceTy::from_ty(span_mirbug_and_err!(
 694                             self,
 695                             place,
 696                             "cast to variant #{:?} but enum only has {:?}",
 697                             index,
 698                             adt_def.variants().len()
 699                         ))
 700                     } else {
 701                         PlaceTy { ty: base_ty, variant_index: Some(index) }
 702                     }
 703                 }
 704                 // We do not need to handle generators here, because this runs
 705                 // before the generator transform stage.
 706                 _ => {
 707                     let ty = if let Some(name) = maybe_name {
 708                         span_mirbug_and_err!(
 709                             self,
 710                             place,
 711                             "can't downcast {:?} as {:?}",
 712                             base_ty,
 713                             name
 714                         )
 715                     } else {
 716                         span_mirbug_and_err!(self, place, "can't downcast {:?}", base_ty)
 717                     };
 718                     PlaceTy::from_ty(ty)
 719                 }
 720             },
 721             ProjectionElem::Field(field, fty) => {
 722                 let fty = self.sanitize_type(place, fty);
 723                 let fty = self.cx.normalize(fty, location);
 724                 match self.field_ty(place, base, field, location) {
 725                     Ok(ty) => {
 726                         let ty = self.cx.normalize(ty, location);
 727                         if let Err(terr) = self.cx.eq_types(
 728                             ty,
 729                             fty,
 730                             location.to_locations(),
 731                             ConstraintCategory::Boring,
 732                         ) {
 733                             span_mirbug!(
 734                                 self,
 735                                 place,
 736                                 "bad field access ({:?}: {:?}): {:?}",
 737                                 ty,
 738                                 fty,
 739                                 terr
 740                             );
 741                         }
 742                     }
 743                     Err(FieldAccessError::OutOfRange { field_count }) => span_mirbug!(
 744                         self,
 745                         place,
 746                         "accessed field #{} but variant only has {}",
 747                         field.index(),
 748                         field_count
 749                     ),
 750                 }
 751                 PlaceTy::from_ty(fty)
 752             }
 753             ProjectionElem::OpaqueCast(ty) => {
 754                 let ty = self.sanitize_type(place, ty);
 755                 let ty = self.cx.normalize(ty, location);
 756                 self.cx
 757                     .eq_types(
 758                         base.ty,
 759                         ty,
 760                         location.to_locations(),
 761                         ConstraintCategory::TypeAnnotation,
 762                     )
 763                     .unwrap();
 764                 PlaceTy::from_ty(ty)
 765             }
 766         }
 767     }
 768
 769     fn error(&mut self) -> Ty<'tcx> {
 770         self.errors_reported = true;
 771         self.tcx().ty_error()
 772     }
 773
 774     fn field_ty(
 775         &mut self,
 776         parent: &dyn fmt::Debug,
 777         base_ty: PlaceTy<'tcx>,
 778         field: Field,
 779         location: Location,
 780     ) -> Result<Ty<'tcx>, FieldAccessError> {
 781         let tcx = self.tcx();
 782
 783         let (variant, substs) = match base_ty {
 784             PlaceTy { ty, variant_index: Some(variant_index) } => match *ty.kind() {
 785                 ty::Adt(adt_def, substs) => (adt_def.variant(variant_index), substs),
 786                 ty::Generator(def_id, substs, _) => {
 787                     let mut variants = substs.as_generator().state_tys(def_id, tcx);
 788                     let Some(mut variant) = variants.nth(variant_index.into()) else {
 789                         bug!(
 790                             "variant_index of generator out of range: {:?}/{:?}",
 791                             variant_index,
 792                             substs.as_generator().state_tys(def_id, tcx).count()
 793                         );
 794                     };
 795                     return match variant.nth(field.index()) {
 796                         Some(ty) => Ok(ty),
 797                         None => Err(FieldAccessError::OutOfRange { field_count: variant.count() }),
 798                     };
 799                 }
 800                 _ => bug!("can't have downcast of non-adt non-generator type"),
 801             },
 802             PlaceTy { ty, variant_index: None } => match *ty.kind() {
 803                 ty::Adt(adt_def, substs) if !adt_def.is_enum() => {
 804                     (adt_def.variant(VariantIdx::new(0)), substs)
 805                 }
 806                 ty::Closure(_, substs) => {
 807                     return match substs
 808                         .as_closure()
 809                         .tupled_upvars_ty()
 810                         .tuple_fields()
 811                         .get(field.index())
 812                     {
 813                         Some(&ty) => Ok(ty),
 814                         None => Err(FieldAccessError::OutOfRange {
 815                             field_count: substs.as_closure().upvar_tys().count(),
 816                         }),
 817                     };
 818                 }
 819                 ty::Generator(_, substs, _) => {
 820                     // Only prefix fields (upvars and current state) are
 821                     // accessible without a variant index.
 822                     return match substs.as_generator().prefix_tys().nth(field.index()) {
 823                         Some(ty) => Ok(ty),
 824                         None => Err(FieldAccessError::OutOfRange {
 825                             field_count: substs.as_generator().prefix_tys().count(),
 826                         }),
 827                     };
 828                 }
 829                 ty::Tuple(tys) => {
 830                     return match tys.get(field.index()) {
 831                         Some(&ty) => Ok(ty),
 832                         None => Err(FieldAccessError::OutOfRange { field_count: tys.len() }),
 833                     };
 834                 }
 835                 _ => {
 836                     return Ok(span_mirbug_and_err!(
 837                         self,
 838                         parent,
 839                         "can't project out of {:?}",
 840                         base_ty
 841                     ));
 842                 }
 843             },
 844         };
 845
 846         if let Some(field) = variant.fields.get(field.index()) {
 847             Ok(self.cx.normalize(field.ty(tcx, substs), location))
 848         } else {
 849             Err(FieldAccessError::OutOfRange { field_count: variant.fields.len() })
 850         }
 851     }
 852 }
 853
 854 /// The MIR type checker. Visits the MIR and enforces all the
 855 /// constraints needed for it to be valid and well-typed. Along the
 856 /// way, it accrues region constraints -- these can later be used by
 857 /// NLL region checking.
 858 struct TypeChecker<'a, 'tcx> {
 859     infcx: &'a InferCtxt<'tcx>,
 860     param_env: ty::ParamEnv<'tcx>,
 861     last_span: Span,
 862     body: &'a Body<'tcx>,
 863     /// User type annotations are shared between the main MIR and the MIR of
 864     /// all of the promoted items.
 865     user_type_annotations: &'a CanonicalUserTypeAnnotations<'tcx>,
 866     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
 867     implicit_region_bound: ty::Region<'tcx>,
 868     reported_errors: FxHashSet<(Ty<'tcx>, Span)>,
 869     borrowck_context: &'a mut BorrowCheckContext<'a, 'tcx>,
 870 }
 871
 872 struct BorrowCheckContext<'a, 'tcx> {
 873     pub(crate) universal_regions: &'a UniversalRegions<'tcx>,
 874     location_table: &'a LocationTable,
 875     all_facts: &'a mut Option<AllFacts>,
 876     borrow_set: &'a BorrowSet<'tcx>,
 877     pub(crate) constraints: &'a mut MirTypeckRegionConstraints<'tcx>,
 878     upvars: &'a [Upvar<'tcx>],
 879 }
 880
 881 pub(crate) struct MirTypeckResults<'tcx> {
 882     pub(crate) constraints: MirTypeckRegionConstraints<'tcx>,
 883     pub(crate) universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
 884     pub(crate) opaque_type_values:
 885         VecMap<OpaqueTypeKey<'tcx>, (OpaqueHiddenType<'tcx>, OpaqueTyOrigin)>,
 886 }
 887
 888 /// A collection of region constraints that must be satisfied for the
 889 /// program to be considered well-typed.
 890 pub(crate) struct MirTypeckRegionConstraints<'tcx> {
 891     /// Maps from a `ty::Placeholder` to the corresponding
 892     /// `PlaceholderIndex` bit that we will use for it.
 893     ///
 894     /// To keep everything in sync, do not insert this set
 895     /// directly. Instead, use the `placeholder_region` helper.
 896     pub(crate) placeholder_indices: PlaceholderIndices,
 897
 898     /// Each time we add a placeholder to `placeholder_indices`, we
 899     /// also create a corresponding "representative" region vid for
 900     /// that wraps it. This vector tracks those. This way, when we
 901     /// convert the same `ty::RePlaceholder(p)` twice, we can map to
 902     /// the same underlying `RegionVid`.
 903     pub(crate) placeholder_index_to_region: IndexVec<PlaceholderIndex, ty::Region<'tcx>>,
 904
 905     /// In general, the type-checker is not responsible for enforcing
 906     /// liveness constraints; this job falls to the region inferencer,
 907     /// which performs a liveness analysis. However, in some limited
 908     /// cases, the MIR type-checker creates temporary regions that do
 909     /// not otherwise appear in the MIR -- in particular, the
 910     /// late-bound regions that it instantiates at call-sites -- and
 911     /// hence it must report on their liveness constraints.
 912     pub(crate) liveness_constraints: LivenessValues<RegionVid>,
 913
 914     pub(crate) outlives_constraints: OutlivesConstraintSet<'tcx>,
 915
 916     pub(crate) member_constraints: MemberConstraintSet<'tcx, RegionVid>,
 917
 918     pub(crate) universe_causes: FxHashMap<ty::UniverseIndex, UniverseInfo<'tcx>>,
 919
 920     pub(crate) type_tests: Vec<TypeTest<'tcx>>,
 921 }
 922
 923 impl<'tcx> MirTypeckRegionConstraints<'tcx> {
 924     fn placeholder_region(
 925         &mut self,
 926         infcx: &InferCtxt<'tcx>,
 927         placeholder: ty::PlaceholderRegion,
 928     ) -> ty::Region<'tcx> {
 929         let placeholder_index = self.placeholder_indices.insert(placeholder);
 930         match self.placeholder_index_to_region.get(placeholder_index) {
 931             Some(&v) => v,
 932             None => {
 933                 let origin = NllRegionVariableOrigin::Placeholder(placeholder);
 934                 let region = infcx.next_nll_region_var_in_universe(origin, placeholder.universe);
 935                 self.placeholder_index_to_region.push(region);
 936                 region
 937             }
 938         }
 939     }
 940 }
 941
 942 /// The `Locations` type summarizes *where* region constraints are
 943 /// required to hold. Normally, this is at a particular point which
 944 /// created the obligation, but for constraints that the user gave, we
 945 /// want the constraint to hold at all points.
 946 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
 947 pub enum Locations {
 948     /// Indicates that a type constraint should always be true. This
 949     /// is particularly important in the new borrowck analysis for
 950     /// things like the type of the return slot. Consider this
 951     /// example:
 952     ///
 953     /// ```compile_fail,E0515
 954     /// fn foo<'a>(x: &'a u32) -> &'a u32 {
 955     ///     let y = 22;
 956     ///     return &y; // error
 957     /// }
 958     /// ```
 959     ///
 960     /// Here, we wind up with the signature from the return type being
 961     /// something like `&'1 u32` where `'1` is a universal region. But
 962     /// the type of the return slot `_0` is something like `&'2 u32`
 963     /// where `'2` is an existential region variable. The type checker
 964     /// requires that `&'2 u32 = &'1 u32` -- but at what point? In the
 965     /// older NLL analysis, we required this only at the entry point
 966     /// to the function. By the nature of the constraints, this wound
 967     /// up propagating to all points reachable from start (because
 968     /// `'1` -- as a universal region -- is live everywhere). In the
 969     /// newer analysis, though, this doesn't work: `_0` is considered
 970     /// dead at the start (it has no usable value) and hence this type
 971     /// equality is basically a no-op. Then, later on, when we do `_0
 972     /// = &'3 y`, that region `'3` never winds up related to the
 973     /// universal region `'1` and hence no error occurs. Therefore, we
 974     /// use Locations::All instead, which ensures that the `'1` and
 975     /// `'2` are equal everything. We also use this for other
 976     /// user-given type annotations; e.g., if the user wrote `let mut
 977     /// x: &'static u32 = ...`, we would ensure that all values
 978     /// assigned to `x` are of `'static` lifetime.
 979     ///
 980     /// The span points to the place the constraint arose. For example,
 981     /// it points to the type in a user-given type annotation. If
 982     /// there's no sensible span then it's DUMMY_SP.
 983     All(Span),
 984
 985     /// An outlives constraint that only has to hold at a single location,
 986     /// usually it represents a point where references flow from one spot to
 987     /// another (e.g., `x = y`)
 988     Single(Location),
 989 }
 990
 991 impl Locations {
 992     pub fn from_location(&self) -> Option<Location> {
 993         match self {
 994             Locations::All(_) => None,
 995             Locations::Single(from_location) => Some(*from_location),
 996         }
 997     }
 998
 999     /// Gets a span representing the location.
1000     pub fn span(&self, body: &Body<'_>) -> Span {
1001         match self {
1002             Locations::All(span) => *span,
1003             Locations::Single(l) => body.source_info(*l).span,
1004         }
1005     }
1006 }
1007
1008 impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
1009     fn new(
1010         infcx: &'a InferCtxt<'tcx>,
1011         body: &'a Body<'tcx>,
1012         param_env: ty::ParamEnv<'tcx>,
1013         region_bound_pairs: &'a RegionBoundPairs<'tcx>,
1014         implicit_region_bound: ty::Region<'tcx>,
1015         borrowck_context: &'a mut BorrowCheckContext<'a, 'tcx>,
1016     ) -> Self {
1017         let mut checker = Self {
1018             infcx,
1019             last_span: DUMMY_SP,
1020             body,
1021             user_type_annotations: &body.user_type_annotations,
1022             param_env,
1023             region_bound_pairs,
1024             implicit_region_bound,
1025             borrowck_context,
1026             reported_errors: Default::default(),
1027         };
1028         checker.check_user_type_annotations();
1029         checker
1030     }
1031
1032     fn body(&self) -> &Body<'tcx> {
1033         self.body
1034     }
1035
1036     fn unsized_feature_enabled(&self) -> bool {
1037         let features = self.tcx().features();
1038         features.unsized_locals || features.unsized_fn_params
1039     }
1040
1041     /// Equate the inferred type and the annotated type for user type annotations
1042     #[instrument(skip(self), level = "debug")]
1043     fn check_user_type_annotations(&mut self) {
1044         debug!(?self.user_type_annotations);
1045         for user_annotation in self.user_type_annotations {
1046             let CanonicalUserTypeAnnotation { span, ref user_ty, inferred_ty } = *user_annotation;
1047             let inferred_ty = self.normalize(inferred_ty, Locations::All(span));
1048             let annotation = self.instantiate_canonical_with_fresh_inference_vars(span, user_ty);
1049             debug!(?annotation);
1050             match annotation {
1051                 UserType::Ty(mut ty) => {
1052                     ty = self.normalize(ty, Locations::All(span));
1053
1054                     if let Err(terr) = self.eq_types(
1055                         ty,
1056                         inferred_ty,
1057                         Locations::All(span),
1058                         ConstraintCategory::BoringNoLocation,
1059                     ) {
1060                         span_mirbug!(
1061                             self,
1062                             user_annotation,
1063                             "bad user type ({:?} = {:?}): {:?}",
1064                             ty,
1065                             inferred_ty,
1066                             terr
1067                         );
1068                     }
1069
1070                     self.prove_predicate(
1071                         ty::Binder::dummy(ty::PredicateKind::WellFormed(inferred_ty.into())),
1072                         Locations::All(span),
1073                         ConstraintCategory::TypeAnnotation,
1074                     );
1075                 }
1076                 UserType::TypeOf(def_id, user_substs) => {
1077                     if let Err(terr) = self.fully_perform_op(
1078                         Locations::All(span),
1079                         ConstraintCategory::BoringNoLocation,
1080                         self.param_env.and(type_op::ascribe_user_type::AscribeUserType::new(
1081                             inferred_ty,
1082                             def_id,
1083                             user_substs,
1084                         )),
1085                     ) {
1086                         span_mirbug!(
1087                             self,
1088                             user_annotation,
1089                             "bad user type AscribeUserType({:?}, {:?} {:?}, type_of={:?}): {:?}",
1090                             inferred_ty,
1091                             def_id,
1092                             user_substs,
1093                             self.tcx().type_of(def_id),
1094                             terr,
1095                         );
1096                     }
1097                 }
1098             }
1099         }
1100     }
1101
1102     #[instrument(skip(self, data), level = "debug")]
1103     fn push_region_constraints(
1104         &mut self,
1105         locations: Locations,
1106         category: ConstraintCategory<'tcx>,
1107         data: &QueryRegionConstraints<'tcx>,
1108     ) {
1109         debug!("constraints generated: {:#?}", data);
1110
1111         constraint_conversion::ConstraintConversion::new(
1112             self.infcx,
1113             self.borrowck_context.universal_regions,
1114             self.region_bound_pairs,
1115             self.implicit_region_bound,
1116             self.param_env,
1117             locations,
1118             locations.span(self.body),
1119             category,
1120             &mut self.borrowck_context.constraints,
1121         )
1122         .convert_all(data);
1123     }
1124
1125     /// Try to relate `sub <: sup`
1126     fn sub_types(
1127         &mut self,
1128         sub: Ty<'tcx>,
1129         sup: Ty<'tcx>,
1130         locations: Locations,
1131         category: ConstraintCategory<'tcx>,
1132     ) -> Fallible<()> {
1133         // Use this order of parameters because the sup type is usually the
1134         // "expected" type in diagnostics.
1135         self.relate_types(sup, ty::Variance::Contravariant, sub, locations, category)
1136     }
1137
1138     #[instrument(skip(self, category), level = "debug")]
1139     fn eq_types(
1140         &mut self,
1141         expected: Ty<'tcx>,
1142         found: Ty<'tcx>,
1143         locations: Locations,
1144         category: ConstraintCategory<'tcx>,
1145     ) -> Fallible<()> {
1146         self.relate_types(expected, ty::Variance::Invariant, found, locations, category)
1147     }
1148
1149     #[instrument(skip(self), level = "debug")]
1150     fn relate_type_and_user_type(
1151         &mut self,
1152         a: Ty<'tcx>,
1153         v: ty::Variance,
1154         user_ty: &UserTypeProjection,
1155         locations: Locations,
1156         category: ConstraintCategory<'tcx>,
1157     ) -> Fallible<()> {
1158         let annotated_type = self.user_type_annotations[user_ty.base].inferred_ty;
1159         let mut curr_projected_ty = PlaceTy::from_ty(annotated_type);
1160
1161         let tcx = self.infcx.tcx;
1162
1163         for proj in &user_ty.projs {
1164             let projected_ty = curr_projected_ty.projection_ty_core(
1165                 tcx,
1166                 self.param_env,
1167                 proj,
1168                 |this, field, _| {
1169                     let ty = this.field_ty(tcx, field);
1170                     self.normalize(ty, locations)
1171                 },
1172                 |_, _| unreachable!(),
1173             );
1174             curr_projected_ty = projected_ty;
1175         }
1176         debug!(
1177             "user_ty base: {:?} freshened: {:?} projs: {:?} yields: {:?}",
1178             user_ty.base, annotated_type, user_ty.projs, curr_projected_ty
1179         );
1180
1181         let ty = curr_projected_ty.ty;
1182         self.relate_types(ty, v.xform(ty::Variance::Contravariant), a, locations, category)?;
1183
1184         Ok(())
1185     }
1186
1187     fn tcx(&self) -> TyCtxt<'tcx> {
1188         self.infcx.tcx
1189     }
1190
1191     #[instrument(skip(self, body, location), level = "debug")]
1192     fn check_stmt(&mut self, body: &Body<'tcx>, stmt: &Statement<'tcx>, location: Location) {
1193         let tcx = self.tcx();
1194         debug!("stmt kind: {:?}", stmt.kind);
1195         match stmt.kind {
1196             StatementKind::Assign(box (ref place, ref rv)) => {
1197                 // Assignments to temporaries are not "interesting";
1198                 // they are not caused by the user, but rather artifacts
1199                 // of lowering. Assignments to other sorts of places *are* interesting
1200                 // though.
1201                 let category = match place.as_local() {
1202                     Some(RETURN_PLACE) => {
1203                         let defining_ty = &self.borrowck_context.universal_regions.defining_ty;
1204                         if defining_ty.is_const() {
1205                             if tcx.is_static(defining_ty.def_id()) {
1206                                 ConstraintCategory::UseAsStatic
1207                             } else {
1208                                 ConstraintCategory::UseAsConst
1209                             }
1210                         } else {
1211                             ConstraintCategory::Return(ReturnConstraint::Normal)
1212                         }
1213                     }
1214                     Some(l)
1215                         if matches!(
1216                             body.local_decls[l].local_info,
1217                             Some(box LocalInfo::AggregateTemp)
1218                         ) =>
1219                     {
1220                         ConstraintCategory::Usage
1221                     }
1222                     Some(l) if !body.local_decls[l].is_user_variable() => {
1223                         ConstraintCategory::Boring
1224                     }
1225                     _ => ConstraintCategory::Assignment,
1226                 };
1227                 debug!(
1228                     "assignment category: {:?} {:?}",
1229                     category,
1230                     place.as_local().map(|l| &body.local_decls[l])
1231                 );
1232
1233                 let place_ty = place.ty(body, tcx).ty;
1234                 debug!(?place_ty);
1235                 let place_ty = self.normalize(place_ty, location);
1236                 debug!("place_ty normalized: {:?}", place_ty);
1237                 let rv_ty = rv.ty(body, tcx);
1238                 debug!(?rv_ty);
1239                 let rv_ty = self.normalize(rv_ty, location);
1240                 debug!("normalized rv_ty: {:?}", rv_ty);
1241                 if let Err(terr) =
1242                     self.sub_types(rv_ty, place_ty, location.to_locations(), category)
1243                 {
1244                     span_mirbug!(
1245                         self,
1246                         stmt,
1247                         "bad assignment ({:?} = {:?}): {:?}",
1248                         place_ty,
1249                         rv_ty,
1250                         terr
1251                     );
1252                 }
1253
1254                 if let Some(annotation_index) = self.rvalue_user_ty(rv) {
1255                     if let Err(terr) = self.relate_type_and_user_type(
1256                         rv_ty,
1257                         ty::Variance::Invariant,
1258                         &UserTypeProjection { base: annotation_index, projs: vec![] },
1259                         location.to_locations(),
1260                         ConstraintCategory::Boring,
1261                     ) {
1262                         let annotation = &self.user_type_annotations[annotation_index];
1263                         span_mirbug!(
1264                             self,
1265                             stmt,
1266                             "bad user type on rvalue ({:?} = {:?}): {:?}",
1267                             annotation,
1268                             rv_ty,
1269                             terr
1270                         );
1271                     }
1272                 }
1273
1274                 self.check_rvalue(body, rv, location);
1275                 if !self.unsized_feature_enabled() {
1276                     let trait_ref = ty::TraitRef {
1277                         def_id: tcx.require_lang_item(LangItem::Sized, Some(self.last_span)),
1278                         substs: tcx.mk_substs_trait(place_ty, &[]),
1279                     };
1280                     self.prove_trait_ref(
1281                         trait_ref,
1282                         location.to_locations(),
1283                         ConstraintCategory::SizedBound,
1284                     );
1285                 }
1286             }
1287             StatementKind::AscribeUserType(box (ref place, ref projection), variance) => {
1288                 let place_ty = place.ty(body, tcx).ty;
1289                 if let Err(terr) = self.relate_type_and_user_type(
1290                     place_ty,
1291                     variance,
1292                     projection,
1293                     Locations::All(stmt.source_info.span),
1294                     ConstraintCategory::TypeAnnotation,
1295                 ) {
1296                     let annotation = &self.user_type_annotations[projection.base];
1297                     span_mirbug!(
1298                         self,
1299                         stmt,
1300                         "bad type assert ({:?} <: {:?} with projections {:?}): {:?}",
1301                         place_ty,
1302                         annotation,
1303                         projection.projs,
1304                         terr
1305                     );
1306                 }
1307             }
1308             StatementKind::Intrinsic(box ref kind) => match kind {
1309                 NonDivergingIntrinsic::Assume(op) => self.check_operand(op, location),
1310                 NonDivergingIntrinsic::CopyNonOverlapping(..) => span_bug!(
1311                     stmt.source_info.span,
1312                     "Unexpected NonDivergingIntrinsic::CopyNonOverlapping, should only appear after lowering_intrinsics",
1313                 ),
1314             },
1315             StatementKind::FakeRead(..)
1316             | StatementKind::StorageLive(..)
1317             | StatementKind::StorageDead(..)
1318             | StatementKind::Retag { .. }
1319             | StatementKind::Coverage(..)
1320             | StatementKind::Nop => {}
1321             StatementKind::Deinit(..) | StatementKind::SetDiscriminant { .. } => {
1322                 bug!("Statement not allowed in this MIR phase")
1323             }
1324         }
1325     }
1326
1327     #[instrument(skip(self, body, term_location), level = "debug")]
1328     fn check_terminator(
1329         &mut self,
1330         body: &Body<'tcx>,
1331         term: &Terminator<'tcx>,
1332         term_location: Location,
1333     ) {
1334         let tcx = self.tcx();
1335         debug!("terminator kind: {:?}", term.kind);
1336         match term.kind {
1337             TerminatorKind::Goto { .. }
1338             | TerminatorKind::Resume
1339             | TerminatorKind::Abort
1340             | TerminatorKind::Return
1341             | TerminatorKind::GeneratorDrop
1342             | TerminatorKind::Unreachable
1343             | TerminatorKind::Drop { .. }
1344             | TerminatorKind::FalseEdge { .. }
1345             | TerminatorKind::FalseUnwind { .. }
1346             | TerminatorKind::InlineAsm { .. } => {
1347                 // no checks needed for these
1348             }
1349
1350             TerminatorKind::DropAndReplace { ref place, ref value, target: _, unwind: _ } => {
1351                 let place_ty = place.ty(body, tcx).ty;
1352                 let rv_ty = value.ty(body, tcx);
1353
1354                 let locations = term_location.to_locations();
1355                 if let Err(terr) =
1356                     self.sub_types(rv_ty, place_ty, locations, ConstraintCategory::Assignment)
1357                 {
1358                     span_mirbug!(
1359                         self,
1360                         term,
1361                         "bad DropAndReplace ({:?} = {:?}): {:?}",
1362                         place_ty,
1363                         rv_ty,
1364                         terr
1365                     );
1366                 }
1367             }
1368             TerminatorKind::SwitchInt { ref discr, switch_ty, .. } => {
1369                 self.check_operand(discr, term_location);
1370
1371                 let discr_ty = discr.ty(body, tcx);
1372                 if let Err(terr) = self.sub_types(
1373                     discr_ty,
1374                     switch_ty,
1375                     term_location.to_locations(),
1376                     ConstraintCategory::Assignment,
1377                 ) {
1378                     span_mirbug!(
1379                         self,
1380                         term,
1381                         "bad SwitchInt ({:?} on {:?}): {:?}",
1382                         switch_ty,
1383                         discr_ty,
1384                         terr
1385                     );
1386                 }
1387                 if !switch_ty.is_integral() && !switch_ty.is_char() && !switch_ty.is_bool() {
1388                     span_mirbug!(self, term, "bad SwitchInt discr ty {:?}", switch_ty);
1389                 }
1390                 // FIXME: check the values
1391             }
1392             TerminatorKind::Call {
1393                 ref func,
1394                 ref args,
1395                 ref destination,
1396                 from_hir_call,
1397                 target,
1398                 ..
1399             } => {
1400                 self.check_operand(func, term_location);
1401                 for arg in args {
1402                     self.check_operand(arg, term_location);
1403                 }
1404
1405                 let func_ty = func.ty(body, tcx);
1406                 debug!("func_ty.kind: {:?}", func_ty.kind());
1407
1408                 let sig = match func_ty.kind() {
1409                     ty::FnDef(..) | ty::FnPtr(_) => func_ty.fn_sig(tcx),
1410                     _ => {
1411                         span_mirbug!(self, term, "call to non-function {:?}", func_ty);
1412                         return;
1413                     }
1414                 };
1415                 let (sig, map) = tcx.replace_late_bound_regions(sig, |br| {
1416                     self.infcx.next_region_var(LateBoundRegion(
1417                         term.source_info.span,
1418                         br.kind,
1419                         LateBoundRegionConversionTime::FnCall,
1420                     ))
1421                 });
1422                 debug!(?sig);
1423                 // IMPORTANT: We have to prove well formed for the function signature before
1424                 // we normalize it, as otherwise types like `<&'a &'b () as Trait>::Assoc`
1425                 // get normalized away, causing us to ignore the `'b: 'a` bound used by the function.
1426                 //
1427                 // Normalization results in a well formed type if the input is well formed, so we
1428                 // don't have to check it twice.
1429                 //
1430                 // See #91068 for an example.
1431                 self.prove_predicates(
1432                     sig.inputs_and_output
1433                         .iter()
1434                         .map(|ty| ty::Binder::dummy(ty::PredicateKind::WellFormed(ty.into()))),
1435                     term_location.to_locations(),
1436                     ConstraintCategory::Boring,
1437                 );
1438                 let sig = self.normalize(sig, term_location);
1439                 self.check_call_dest(body, term, &sig, *destination, target, term_location);
1440
1441                 // The ordinary liveness rules will ensure that all
1442                 // regions in the type of the callee are live here. We
1443                 // then further constrain the late-bound regions that
1444                 // were instantiated at the call site to be live as
1445                 // well. The resulting is that all the input (and
1446                 // output) types in the signature must be live, since
1447                 // all the inputs that fed into it were live.
1448                 for &late_bound_region in map.values() {
1449                     let region_vid =
1450                         self.borrowck_context.universal_regions.to_region_vid(late_bound_region);
1451                     self.borrowck_context
1452                         .constraints
1453                         .liveness_constraints
1454                         .add_element(region_vid, term_location);
1455                 }
1456
1457                 self.check_call_inputs(body, term, &sig, args, term_location, from_hir_call);
1458             }
1459             TerminatorKind::Assert { ref cond, ref msg, .. } => {
1460                 self.check_operand(cond, term_location);
1461
1462                 let cond_ty = cond.ty(body, tcx);
1463                 if cond_ty != tcx.types.bool {
1464                     span_mirbug!(self, term, "bad Assert ({:?}, not bool", cond_ty);
1465                 }
1466
1467                 if let AssertKind::BoundsCheck { ref len, ref index } = *msg {
1468                     if len.ty(body, tcx) != tcx.types.usize {
1469                         span_mirbug!(self, len, "bounds-check length non-usize {:?}", len)
1470                     }
1471                     if index.ty(body, tcx) != tcx.types.usize {
1472                         span_mirbug!(self, index, "bounds-check index non-usize {:?}", index)
1473                     }
1474                 }
1475             }
1476             TerminatorKind::Yield { ref value, .. } => {
1477                 self.check_operand(value, term_location);
1478
1479                 let value_ty = value.ty(body, tcx);
1480                 match body.yield_ty() {
1481                     None => span_mirbug!(self, term, "yield in non-generator"),
1482                     Some(ty) => {
1483                         if let Err(terr) = self.sub_types(
1484                             value_ty,
1485                             ty,
1486                             term_location.to_locations(),
1487                             ConstraintCategory::Yield,
1488                         ) {
1489                             span_mirbug!(
1490                                 self,
1491                                 term,
1492                                 "type of yield value is {:?}, but the yield type is {:?}: {:?}",
1493                                 value_ty,
1494                                 ty,
1495                                 terr
1496                             );
1497                         }
1498                     }
1499                 }
1500             }
1501         }
1502     }
1503
1504     fn check_call_dest(
1505         &mut self,
1506         body: &Body<'tcx>,
1507         term: &Terminator<'tcx>,
1508         sig: &ty::FnSig<'tcx>,
1509         destination: Place<'tcx>,
1510         target: Option<BasicBlock>,
1511         term_location: Location,
1512     ) {
1513         let tcx = self.tcx();
1514         match target {
1515             Some(_) => {
1516                 let dest_ty = destination.ty(body, tcx).ty;
1517                 let dest_ty = self.normalize(dest_ty, term_location);
1518                 let category = match destination.as_local() {
1519                     Some(RETURN_PLACE) => {
1520                         if let BorrowCheckContext {
1521                             universal_regions:
1522                                 UniversalRegions {
1523                                     defining_ty:
1524                                         DefiningTy::Const(def_id, _)
1525                                         | DefiningTy::InlineConst(def_id, _),
1526                                     ..
1527                                 },
1528                             ..
1529                         } = self.borrowck_context
1530                         {
1531                             if tcx.is_static(*def_id) {
1532                                 ConstraintCategory::UseAsStatic
1533                             } else {
1534                                 ConstraintCategory::UseAsConst
1535                             }
1536                         } else {
1537                             ConstraintCategory::Return(ReturnConstraint::Normal)
1538                         }
1539                     }
1540                     Some(l) if !body.local_decls[l].is_user_variable() => {
1541                         ConstraintCategory::Boring
1542                     }
1543                     _ => ConstraintCategory::Assignment,
1544                 };
1545
1546                 let locations = term_location.to_locations();
1547
1548                 if let Err(terr) = self.sub_types(sig.output(), dest_ty, locations, category) {
1549                     span_mirbug!(
1550                         self,
1551                         term,
1552                         "call dest mismatch ({:?} <- {:?}): {:?}",
1553                         dest_ty,
1554                         sig.output(),
1555                         terr
1556                     );
1557                 }
1558
1559                 // When `unsized_fn_params` and `unsized_locals` are both not enabled,
1560                 // this check is done at `check_local`.
1561                 if self.unsized_feature_enabled() {
1562                     let span = term.source_info.span;
1563                     self.ensure_place_sized(dest_ty, span);
1564                 }
1565             }
1566             None => {
1567                 if !sig.output().is_privately_uninhabited(self.tcx(), self.param_env) {
1568                     span_mirbug!(self, term, "call to converging function {:?} w/o dest", sig);
1569                 }
1570             }
1571         }
1572     }
1573
1574     fn check_call_inputs(
1575         &mut self,
1576         body: &Body<'tcx>,
1577         term: &Terminator<'tcx>,
1578         sig: &ty::FnSig<'tcx>,
1579         args: &[Operand<'tcx>],
1580         term_location: Location,
1581         from_hir_call: bool,
1582     ) {
1583         debug!("check_call_inputs({:?}, {:?})", sig, args);
1584         if args.len() < sig.inputs().len() || (args.len() > sig.inputs().len() && !sig.c_variadic) {
1585             span_mirbug!(self, term, "call to {:?} with wrong # of args", sig);
1586         }
1587
1588         let func_ty = if let TerminatorKind::Call { func, .. } = &term.kind {
1589             Some(func.ty(body, self.infcx.tcx))
1590         } else {
1591             None
1592         };
1593         debug!(?func_ty);
1594
1595         for (n, (fn_arg, op_arg)) in iter::zip(sig.inputs(), args).enumerate() {
1596             let op_arg_ty = op_arg.ty(body, self.tcx());
1597
1598             let op_arg_ty = self.normalize(op_arg_ty, term_location);
1599             let category = if from_hir_call {
1600                 ConstraintCategory::CallArgument(self.infcx.tcx.erase_regions(func_ty))
1601             } else {
1602                 ConstraintCategory::Boring
1603             };
1604             if let Err(terr) =
1605                 self.sub_types(op_arg_ty, *fn_arg, term_location.to_locations(), category)
1606             {
1607                 span_mirbug!(
1608                     self,
1609                     term,
1610                     "bad arg #{:?} ({:?} <- {:?}): {:?}",
1611                     n,
1612                     fn_arg,
1613                     op_arg_ty,
1614                     terr
1615                 );
1616             }
1617         }
1618     }
1619
1620     fn check_iscleanup(&mut self, body: &Body<'tcx>, block_data: &BasicBlockData<'tcx>) {
1621         let is_cleanup = block_data.is_cleanup;
1622         self.last_span = block_data.terminator().source_info.span;
1623         match block_data.terminator().kind {
1624             TerminatorKind::Goto { target } => {
1625                 self.assert_iscleanup(body, block_data, target, is_cleanup)
1626             }
1627             TerminatorKind::SwitchInt { ref targets, .. } => {
1628                 for target in targets.all_targets() {
1629                     self.assert_iscleanup(body, block_data, *target, is_cleanup);
1630                 }
1631             }
1632             TerminatorKind::Resume => {
1633                 if !is_cleanup {
1634                     span_mirbug!(self, block_data, "resume on non-cleanup block!")
1635                 }
1636             }
1637             TerminatorKind::Abort => {
1638                 if !is_cleanup {
1639                     span_mirbug!(self, block_data, "abort on non-cleanup block!")
1640                 }
1641             }
1642             TerminatorKind::Return => {
1643                 if is_cleanup {
1644                     span_mirbug!(self, block_data, "return on cleanup block")
1645                 }
1646             }
1647             TerminatorKind::GeneratorDrop { .. } => {
1648                 if is_cleanup {
1649                     span_mirbug!(self, block_data, "generator_drop in cleanup block")
1650                 }
1651             }
1652             TerminatorKind::Yield { resume, drop, .. } => {
1653                 if is_cleanup {
1654                     span_mirbug!(self, block_data, "yield in cleanup block")
1655                 }
1656                 self.assert_iscleanup(body, block_data, resume, is_cleanup);
1657                 if let Some(drop) = drop {
1658                     self.assert_iscleanup(body, block_data, drop, is_cleanup);
1659                 }
1660             }
1661             TerminatorKind::Unreachable => {}
1662             TerminatorKind::Drop { target, unwind, .. }
1663             | TerminatorKind::DropAndReplace { target, unwind, .. }
1664             | TerminatorKind::Assert { target, cleanup: unwind, .. } => {
1665                 self.assert_iscleanup(body, block_data, target, is_cleanup);
1666                 if let Some(unwind) = unwind {
1667                     if is_cleanup {
1668                         span_mirbug!(self, block_data, "unwind on cleanup block")
1669                     }
1670                     self.assert_iscleanup(body, block_data, unwind, true);
1671                 }
1672             }
1673             TerminatorKind::Call { ref target, cleanup, .. } => {
1674                 if let &Some(target) = target {
1675                     self.assert_iscleanup(body, block_data, target, is_cleanup);
1676                 }
1677                 if let Some(cleanup) = cleanup {
1678                     if is_cleanup {
1679                         span_mirbug!(self, block_data, "cleanup on cleanup block")
1680                     }
1681                     self.assert_iscleanup(body, block_data, cleanup, true);
1682                 }
1683             }
1684             TerminatorKind::FalseEdge { real_target, imaginary_target } => {
1685                 self.assert_iscleanup(body, block_data, real_target, is_cleanup);
1686                 self.assert_iscleanup(body, block_data, imaginary_target, is_cleanup);
1687             }
1688             TerminatorKind::FalseUnwind { real_target, unwind } => {
1689                 self.assert_iscleanup(body, block_data, real_target, is_cleanup);
1690                 if let Some(unwind) = unwind {
1691                     if is_cleanup {
1692                         span_mirbug!(self, block_data, "cleanup in cleanup block via false unwind");
1693                     }
1694                     self.assert_iscleanup(body, block_data, unwind, true);
1695                 }
1696             }
1697             TerminatorKind::InlineAsm { destination, cleanup, .. } => {
1698                 if let Some(target) = destination {
1699                     self.assert_iscleanup(body, block_data, target, is_cleanup);
1700                 }
1701                 if let Some(cleanup) = cleanup {
1702                     if is_cleanup {
1703                         span_mirbug!(self, block_data, "cleanup on cleanup block")
1704                     }
1705                     self.assert_iscleanup(body, block_data, cleanup, true);
1706                 }
1707             }
1708         }
1709     }
1710
1711     fn assert_iscleanup(
1712         &mut self,
1713         body: &Body<'tcx>,
1714         ctxt: &dyn fmt::Debug,
1715         bb: BasicBlock,
1716         iscleanuppad: bool,
1717     ) {
1718         if body[bb].is_cleanup != iscleanuppad {
1719             span_mirbug!(self, ctxt, "cleanuppad mismatch: {:?} should be {:?}", bb, iscleanuppad);
1720         }
1721     }
1722
1723     fn check_local(&mut self, body: &Body<'tcx>, local: Local, local_decl: &LocalDecl<'tcx>) {
1724         match body.local_kind(local) {
1725             LocalKind::ReturnPointer | LocalKind::Arg => {
1726                 // return values of normal functions are required to be
1727                 // sized by typeck, but return values of ADT constructors are
1728                 // not because we don't include a `Self: Sized` bounds on them.
1729                 //
1730                 // Unbound parts of arguments were never required to be Sized
1731                 // - maybe we should make that a warning.
1732                 return;
1733             }
1734             LocalKind::Var | LocalKind::Temp => {}
1735         }
1736
1737         // When `unsized_fn_params` or `unsized_locals` is enabled, only function calls
1738         // and nullary ops are checked in `check_call_dest`.
1739         if !self.unsized_feature_enabled() {
1740             let span = local_decl.source_info.span;
1741             let ty = local_decl.ty;
1742             self.ensure_place_sized(ty, span);
1743         }
1744     }
1745
1746     fn ensure_place_sized(&mut self, ty: Ty<'tcx>, span: Span) {
1747         let tcx = self.tcx();
1748
1749         // Erase the regions from `ty` to get a global type.  The
1750         // `Sized` bound in no way depends on precise regions, so this
1751         // shouldn't affect `is_sized`.
1752         let erased_ty = tcx.erase_regions(ty);
1753         if !erased_ty.is_sized(tcx, self.param_env) {
1754             // in current MIR construction, all non-control-flow rvalue
1755             // expressions evaluate through `as_temp` or `into` a return
1756             // slot or local, so to find all unsized rvalues it is enough
1757             // to check all temps, return slots and locals.
1758             if self.reported_errors.replace((ty, span)).is_none() {
1759                 // While this is located in `nll::typeck` this error is not
1760                 // an NLL error, it's a required check to prevent creation
1761                 // of unsized rvalues in a call expression.
1762                 self.tcx().sess.emit_err(MoveUnsized { ty, span });
1763             }
1764         }
1765     }
1766
1767     fn aggregate_field_ty(
1768         &mut self,
1769         ak: &AggregateKind<'tcx>,
1770         field_index: usize,
1771         location: Location,
1772     ) -> Result<Ty<'tcx>, FieldAccessError> {
1773         let tcx = self.tcx();
1774
1775         match *ak {
1776             AggregateKind::Adt(adt_did, variant_index, substs, _, active_field_index) => {
1777                 let def = tcx.adt_def(adt_did);
1778                 let variant = &def.variant(variant_index);
1779                 let adj_field_index = active_field_index.unwrap_or(field_index);
1780                 if let Some(field) = variant.fields.get(adj_field_index) {
1781                     Ok(self.normalize(field.ty(tcx, substs), location))
1782                 } else {
1783                     Err(FieldAccessError::OutOfRange { field_count: variant.fields.len() })
1784                 }
1785             }
1786             AggregateKind::Closure(_, substs) => {
1787                 match substs.as_closure().upvar_tys().nth(field_index) {
1788                     Some(ty) => Ok(ty),
1789                     None => Err(FieldAccessError::OutOfRange {
1790                         field_count: substs.as_closure().upvar_tys().count(),
1791                     }),
1792                 }
1793             }
1794             AggregateKind::Generator(_, substs, _) => {
1795                 // It doesn't make sense to look at a field beyond the prefix;
1796                 // these require a variant index, and are not initialized in
1797                 // aggregate rvalues.
1798                 match substs.as_generator().prefix_tys().nth(field_index) {
1799                     Some(ty) => Ok(ty),
1800                     None => Err(FieldAccessError::OutOfRange {
1801                         field_count: substs.as_generator().prefix_tys().count(),
1802                     }),
1803                 }
1804             }
1805             AggregateKind::Array(ty) => Ok(ty),
1806             AggregateKind::Tuple => {
1807                 unreachable!("This should have been covered in check_rvalues");
1808             }
1809         }
1810     }
1811
1812     fn check_operand(&mut self, op: &Operand<'tcx>, location: Location) {
1813         debug!(?op, ?location, "check_operand");
1814
1815         if let Operand::Constant(constant) = op {
1816             let maybe_uneval = match constant.literal {
1817                 ConstantKind::Val(..) | ConstantKind::Ty(_) => None,
1818                 ConstantKind::Unevaluated(uv, _) => Some(uv),
1819             };
1820
1821             if let Some(uv) = maybe_uneval {
1822                 if uv.promoted.is_none() {
1823                     let tcx = self.tcx();
1824                     let def_id = uv.def.def_id_for_type_of();
1825                     if tcx.def_kind(def_id) == DefKind::InlineConst {
1826                         let def_id = def_id.expect_local();
1827                         let predicates =
1828                             self.prove_closure_bounds(tcx, def_id, uv.substs, location);
1829                         self.normalize_and_prove_instantiated_predicates(
1830                             def_id.to_def_id(),
1831                             predicates,
1832                             location.to_locations(),
1833                         );
1834                     }
1835                 }
1836             }
1837         }
1838     }
1839
1840     #[instrument(skip(self, body), level = "debug")]
1841     fn check_rvalue(&mut self, body: &Body<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
1842         let tcx = self.tcx();
1843
1844         match rvalue {
1845             Rvalue::Aggregate(ak, ops) => {
1846                 for op in ops {
1847                     self.check_operand(op, location);
1848                 }
1849                 self.check_aggregate_rvalue(&body, rvalue, ak, ops, location)
1850             }
1851
1852             Rvalue::Repeat(operand, len) => {
1853                 self.check_operand(operand, location);
1854
1855                 // If the length cannot be evaluated we must assume that the length can be larger
1856                 // than 1.
1857                 // If the length is larger than 1, the repeat expression will need to copy the
1858                 // element, so we require the `Copy` trait.
1859                 if len.try_eval_usize(tcx, self.param_env).map_or(true, |len| len > 1) {
1860                     match operand {
1861                         Operand::Copy(..) | Operand::Constant(..) => {
1862                             // These are always okay: direct use of a const, or a value that can evidently be copied.
1863                         }
1864                         Operand::Move(place) => {
1865                             // Make sure that repeated elements implement `Copy`.
1866                             let span = body.source_info(location).span;
1867                             let ty = place.ty(body, tcx).ty;
1868                             let trait_ref = ty::TraitRef::new(
1869                                 tcx.require_lang_item(LangItem::Copy, Some(span)),
1870                                 tcx.mk_substs_trait(ty, &[]),
1871                             );
1872
1873                             self.prove_trait_ref(
1874                                 trait_ref,
1875                                 Locations::Single(location),
1876                                 ConstraintCategory::CopyBound,
1877                             );
1878                         }
1879                     }
1880                 }
1881             }
1882
1883             &Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, ty) => {
1884                 let trait_ref = ty::TraitRef {
1885                     def_id: tcx.require_lang_item(LangItem::Sized, Some(self.last_span)),
1886                     substs: tcx.mk_substs_trait(ty, &[]),
1887                 };
1888
1889                 self.prove_trait_ref(
1890                     trait_ref,
1891                     location.to_locations(),
1892                     ConstraintCategory::SizedBound,
1893                 );
1894             }
1895
1896             Rvalue::ShallowInitBox(operand, ty) => {
1897                 self.check_operand(operand, location);
1898
1899                 let trait_ref = ty::TraitRef {
1900                     def_id: tcx.require_lang_item(LangItem::Sized, Some(self.last_span)),
1901                     substs: tcx.mk_substs_trait(*ty, &[]),
1902                 };
1903
1904                 self.prove_trait_ref(
1905                     trait_ref,
1906                     location.to_locations(),
1907                     ConstraintCategory::SizedBound,
1908                 );
1909             }
1910
1911             Rvalue::Cast(cast_kind, op, ty) => {
1912                 self.check_operand(op, location);
1913
1914                 match cast_kind {
1915                     CastKind::Pointer(PointerCast::ReifyFnPointer) => {
1916                         let fn_sig = op.ty(body, tcx).fn_sig(tcx);
1917
1918                         // The type that we see in the fcx is like
1919                         // `foo::<'a, 'b>`, where `foo` is the path to a
1920                         // function definition. When we extract the
1921                         // signature, it comes from the `fn_sig` query,
1922                         // and hence may contain unnormalized results.
1923                         let fn_sig = self.normalize(fn_sig, location);
1924
1925                         let ty_fn_ptr_from = tcx.mk_fn_ptr(fn_sig);
1926
1927                         if let Err(terr) = self.eq_types(
1928                             *ty,
1929                             ty_fn_ptr_from,
1930                             location.to_locations(),
1931                             ConstraintCategory::Cast,
1932                         ) {
1933                             span_mirbug!(
1934                                 self,
1935                                 rvalue,
1936                                 "equating {:?} with {:?} yields {:?}",
1937                                 ty_fn_ptr_from,
1938                                 ty,
1939                                 terr
1940                             );
1941                         }
1942                     }
1943
1944                     CastKind::Pointer(PointerCast::ClosureFnPointer(unsafety)) => {
1945                         let sig = match op.ty(body, tcx).kind() {
1946                             ty::Closure(_, substs) => substs.as_closure().sig(),
1947                             _ => bug!(),
1948                         };
1949                         let ty_fn_ptr_from = tcx.mk_fn_ptr(tcx.signature_unclosure(sig, *unsafety));
1950
1951                         if let Err(terr) = self.eq_types(
1952                             *ty,
1953                             ty_fn_ptr_from,
1954                             location.to_locations(),
1955                             ConstraintCategory::Cast,
1956                         ) {
1957                             span_mirbug!(
1958                                 self,
1959                                 rvalue,
1960                                 "equating {:?} with {:?} yields {:?}",
1961                                 ty_fn_ptr_from,
1962                                 ty,
1963                                 terr
1964                             );
1965                         }
1966                     }
1967
1968                     CastKind::Pointer(PointerCast::UnsafeFnPointer) => {
1969                         let fn_sig = op.ty(body, tcx).fn_sig(tcx);
1970
1971                         // The type that we see in the fcx is like
1972                         // `foo::<'a, 'b>`, where `foo` is the path to a
1973                         // function definition. When we extract the
1974                         // signature, it comes from the `fn_sig` query,
1975                         // and hence may contain unnormalized results.
1976                         let fn_sig = self.normalize(fn_sig, location);
1977
1978                         let ty_fn_ptr_from = tcx.safe_to_unsafe_fn_ty(fn_sig);
1979
1980                         if let Err(terr) = self.eq_types(
1981                             *ty,
1982                             ty_fn_ptr_from,
1983                             location.to_locations(),
1984                             ConstraintCategory::Cast,
1985                         ) {
1986                             span_mirbug!(
1987                                 self,
1988                                 rvalue,
1989                                 "equating {:?} with {:?} yields {:?}",
1990                                 ty_fn_ptr_from,
1991                                 ty,
1992                                 terr
1993                             );
1994                         }
1995                     }
1996
1997                     CastKind::Pointer(PointerCast::Unsize) => {
1998                         let &ty = ty;
1999                         let trait_ref = ty::TraitRef {
2000                             def_id: tcx
2001                                 .require_lang_item(LangItem::CoerceUnsized, Some(self.last_span)),
2002                             substs: tcx.mk_substs_trait(op.ty(body, tcx), &[ty.into()]),
2003                         };
2004
2005                         self.prove_trait_ref(
2006                             trait_ref,
2007                             location.to_locations(),
2008                             ConstraintCategory::Cast,
2009                         );
2010                     }
2011
2012                     CastKind::DynStar => {
2013                         // get the constraints from the target type (`dyn* Clone`)
2014                         //
2015                         // apply them to prove that the source type `Foo` implements `Clone` etc
2016                         let (existential_predicates, region) = match ty.kind() {
2017                             Dynamic(predicates, region, ty::DynStar) => (predicates, region),
2018                             _ => panic!("Invalid dyn* cast_ty"),
2019                         };
2020
2021                         let self_ty = op.ty(body, tcx);
2022
2023                         self.prove_predicates(
2024                             existential_predicates
2025                                 .iter()
2026                                 .map(|predicate| predicate.with_self_ty(tcx, self_ty)),
2027                             location.to_locations(),
2028                             ConstraintCategory::Cast,
2029                         );
2030
2031                         let outlives_predicate =
2032                             tcx.mk_predicate(Binder::dummy(ty::PredicateKind::TypeOutlives(
2033                                 ty::OutlivesPredicate(self_ty, *region),
2034                             )));
2035                         self.prove_predicate(
2036                             outlives_predicate,
2037                             location.to_locations(),
2038                             ConstraintCategory::Cast,
2039                         );
2040                     }
2041
2042                     CastKind::Pointer(PointerCast::MutToConstPointer) => {
2043                         let ty::RawPtr(ty::TypeAndMut {
2044                             ty: ty_from,
2045                             mutbl: hir::Mutability::Mut,
2046                         }) = op.ty(body, tcx).kind() else {
2047                             span_mirbug!(
2048                                 self,
2049                                 rvalue,
2050                                 "unexpected base type for cast {:?}",
2051                                 ty,
2052                             );
2053                             return;
2054                         };
2055                         let ty::RawPtr(ty::TypeAndMut {
2056                             ty: ty_to,
2057                             mutbl: hir::Mutability::Not,
2058                         }) = ty.kind() else {
2059                             span_mirbug!(
2060                                 self,
2061                                 rvalue,
2062                                 "unexpected target type for cast {:?}",
2063                                 ty,
2064                             );
2065                             return;
2066                         };
2067                         if let Err(terr) = self.sub_types(
2068                             *ty_from,
2069                             *ty_to,
2070                             location.to_locations(),
2071                             ConstraintCategory::Cast,
2072                         ) {
2073                             span_mirbug!(
2074                                 self,
2075                                 rvalue,
2076                                 "relating {:?} with {:?} yields {:?}",
2077                                 ty_from,
2078                                 ty_to,
2079                                 terr
2080                             );
2081                         }
2082                     }
2083
2084                     CastKind::Pointer(PointerCast::ArrayToPointer) => {
2085                         let ty_from = op.ty(body, tcx);
2086
2087                         let opt_ty_elem_mut = match ty_from.kind() {
2088                             ty::RawPtr(ty::TypeAndMut { mutbl: array_mut, ty: array_ty }) => {
2089                                 match array_ty.kind() {
2090                                     ty::Array(ty_elem, _) => Some((ty_elem, *array_mut)),
2091                                     _ => None,
2092                                 }
2093                             }
2094                             _ => None,
2095                         };
2096
2097                         let Some((ty_elem, ty_mut)) = opt_ty_elem_mut else {
2098                             span_mirbug!(
2099                                 self,
2100                                 rvalue,
2101                                 "ArrayToPointer cast from unexpected type {:?}",
2102                                 ty_from,
2103                             );
2104                             return;
2105                         };
2106
2107                         let (ty_to, ty_to_mut) = match ty.kind() {
2108                             ty::RawPtr(ty::TypeAndMut { mutbl: ty_to_mut, ty: ty_to }) => {
2109                                 (ty_to, *ty_to_mut)
2110                             }
2111                             _ => {
2112                                 span_mirbug!(
2113                                     self,
2114                                     rvalue,
2115                                     "ArrayToPointer cast to unexpected type {:?}",
2116                                     ty,
2117                                 );
2118                                 return;
2119                             }
2120                         };
2121
2122                         if ty_to_mut == Mutability::Mut && ty_mut == Mutability::Not {
2123                             span_mirbug!(
2124                                 self,
2125                                 rvalue,
2126                                 "ArrayToPointer cast from const {:?} to mut {:?}",
2127                                 ty,
2128                                 ty_to
2129                             );
2130                             return;
2131                         }
2132
2133                         if let Err(terr) = self.sub_types(
2134                             *ty_elem,
2135                             *ty_to,
2136                             location.to_locations(),
2137                             ConstraintCategory::Cast,
2138                         ) {
2139                             span_mirbug!(
2140                                 self,
2141                                 rvalue,
2142                                 "relating {:?} with {:?} yields {:?}",
2143                                 ty_elem,
2144                                 ty_to,
2145                                 terr
2146                             )
2147                         }
2148                     }
2149
2150                     CastKind::PointerExposeAddress => {
2151                         let ty_from = op.ty(body, tcx);
2152                         let cast_ty_from = CastTy::from_ty(ty_from);
2153                         let cast_ty_to = CastTy::from_ty(*ty);
2154                         match (cast_ty_from, cast_ty_to) {
2155                             (Some(CastTy::Ptr(_) | CastTy::FnPtr), Some(CastTy::Int(_))) => (),
2156                             _ => {
2157                                 span_mirbug!(
2158                                     self,
2159                                     rvalue,
2160                                     "Invalid PointerExposeAddress cast {:?} -> {:?}",
2161                                     ty_from,
2162                                     ty
2163                                 )
2164                             }
2165                         }
2166                     }
2167
2168                     CastKind::PointerFromExposedAddress => {
2169                         let ty_from = op.ty(body, tcx);
2170                         let cast_ty_from = CastTy::from_ty(ty_from);
2171                         let cast_ty_to = CastTy::from_ty(*ty);
2172                         match (cast_ty_from, cast_ty_to) {
2173                             (Some(CastTy::Int(_)), Some(CastTy::Ptr(_))) => (),
2174                             _ => {
2175                                 span_mirbug!(
2176                                     self,
2177                                     rvalue,
2178                                     "Invalid PointerFromExposedAddress cast {:?} -> {:?}",
2179                                     ty_from,
2180                                     ty
2181                                 )
2182                             }
2183                         }
2184                     }
2185                     CastKind::IntToInt => {
2186                         let ty_from = op.ty(body, tcx);
2187                         let cast_ty_from = CastTy::from_ty(ty_from);
2188                         let cast_ty_to = CastTy::from_ty(*ty);
2189                         match (cast_ty_from, cast_ty_to) {
2190                             (Some(CastTy::Int(_)), Some(CastTy::Int(_))) => (),
2191                             _ => {
2192                                 span_mirbug!(
2193                                     self,
2194                                     rvalue,
2195                                     "Invalid IntToInt cast {:?} -> {:?}",
2196                                     ty_from,
2197                                     ty
2198                                 )
2199                             }
2200                         }
2201                     }
2202                     CastKind::IntToFloat => {
2203                         let ty_from = op.ty(body, tcx);
2204                         let cast_ty_from = CastTy::from_ty(ty_from);
2205                         let cast_ty_to = CastTy::from_ty(*ty);
2206                         match (cast_ty_from, cast_ty_to) {
2207                             (Some(CastTy::Int(_)), Some(CastTy::Float)) => (),
2208                             _ => {
2209                                 span_mirbug!(
2210                                     self,
2211                                     rvalue,
2212                                     "Invalid IntToFloat cast {:?} -> {:?}",
2213                                     ty_from,
2214                                     ty
2215                                 )
2216                             }
2217                         }
2218                     }
2219                     CastKind::FloatToInt => {
2220                         let ty_from = op.ty(body, tcx);
2221                         let cast_ty_from = CastTy::from_ty(ty_from);
2222                         let cast_ty_to = CastTy::from_ty(*ty);
2223                         match (cast_ty_from, cast_ty_to) {
2224                             (Some(CastTy::Float), Some(CastTy::Int(_))) => (),
2225                             _ => {
2226                                 span_mirbug!(
2227                                     self,
2228                                     rvalue,
2229                                     "Invalid FloatToInt cast {:?} -> {:?}",
2230                                     ty_from,
2231                                     ty
2232                                 )
2233                             }
2234                         }
2235                     }
2236                     CastKind::FloatToFloat => {
2237                         let ty_from = op.ty(body, tcx);
2238                         let cast_ty_from = CastTy::from_ty(ty_from);
2239                         let cast_ty_to = CastTy::from_ty(*ty);
2240                         match (cast_ty_from, cast_ty_to) {
2241                             (Some(CastTy::Float), Some(CastTy::Float)) => (),
2242                             _ => {
2243                                 span_mirbug!(
2244                                     self,
2245                                     rvalue,
2246                                     "Invalid FloatToFloat cast {:?} -> {:?}",
2247                                     ty_from,
2248                                     ty
2249                                 )
2250                             }
2251                         }
2252                     }
2253                     CastKind::FnPtrToPtr => {
2254                         let ty_from = op.ty(body, tcx);
2255                         let cast_ty_from = CastTy::from_ty(ty_from);
2256                         let cast_ty_to = CastTy::from_ty(*ty);
2257                         match (cast_ty_from, cast_ty_to) {
2258                             (Some(CastTy::FnPtr), Some(CastTy::Ptr(_))) => (),
2259                             _ => {
2260                                 span_mirbug!(
2261                                     self,
2262                                     rvalue,
2263                                     "Invalid FnPtrToPtr cast {:?} -> {:?}",
2264                                     ty_from,
2265                                     ty
2266                                 )
2267                             }
2268                         }
2269                     }
2270                     CastKind::PtrToPtr => {
2271                         let ty_from = op.ty(body, tcx);
2272                         let cast_ty_from = CastTy::from_ty(ty_from);
2273                         let cast_ty_to = CastTy::from_ty(*ty);
2274                         match (cast_ty_from, cast_ty_to) {
2275                             (Some(CastTy::Ptr(_)), Some(CastTy::Ptr(_))) => (),
2276                             _ => {
2277                                 span_mirbug!(
2278                                     self,
2279                                     rvalue,
2280                                     "Invalid PtrToPtr cast {:?} -> {:?}",
2281                                     ty_from,
2282                                     ty
2283                                 )
2284                             }
2285                         }
2286                     }
2287                 }
2288             }
2289
2290             Rvalue::Ref(region, _borrow_kind, borrowed_place) => {
2291                 self.add_reborrow_constraint(&body, location, *region, borrowed_place);
2292             }
2293
2294             Rvalue::BinaryOp(
2295                 BinOp::Eq | BinOp::Ne | BinOp::Lt | BinOp::Le | BinOp::Gt | BinOp::Ge,
2296                 box (left, right),
2297             ) => {
2298                 self.check_operand(left, location);
2299                 self.check_operand(right, location);
2300
2301                 let ty_left = left.ty(body, tcx);
2302                 match ty_left.kind() {
2303                     // Types with regions are comparable if they have a common super-type.
2304                     ty::RawPtr(_) | ty::FnPtr(_) => {
2305                         let ty_right = right.ty(body, tcx);
2306                         let common_ty = self.infcx.next_ty_var(TypeVariableOrigin {
2307                             kind: TypeVariableOriginKind::MiscVariable,
2308                             span: body.source_info(location).span,
2309                         });
2310                         self.sub_types(
2311                             ty_left,
2312                             common_ty,
2313                             location.to_locations(),
2314                             ConstraintCategory::Boring,
2315                         )
2316                         .unwrap_or_else(|err| {
2317                             bug!("Could not equate type variable with {:?}: {:?}", ty_left, err)
2318                         });
2319                         if let Err(terr) = self.sub_types(
2320                             ty_right,
2321                             common_ty,
2322                             location.to_locations(),
2323                             ConstraintCategory::Boring,
2324                         ) {
2325                             span_mirbug!(
2326                                 self,
2327                                 rvalue,
2328                                 "unexpected comparison types {:?} and {:?} yields {:?}",
2329                                 ty_left,
2330                                 ty_right,
2331                                 terr
2332                             )
2333                         }
2334                     }
2335                     // For types with no regions we can just check that the
2336                     // both operands have the same type.
2337                     ty::Int(_) | ty::Uint(_) | ty::Bool | ty::Char | ty::Float(_)
2338                         if ty_left == right.ty(body, tcx) => {}
2339                     // Other types are compared by trait methods, not by
2340                     // `Rvalue::BinaryOp`.
2341                     _ => span_mirbug!(
2342                         self,
2343                         rvalue,
2344                         "unexpected comparison types {:?} and {:?}",
2345                         ty_left,
2346                         right.ty(body, tcx)
2347                     ),
2348                 }
2349             }
2350
2351             Rvalue::Use(operand) | Rvalue::UnaryOp(_, operand) => {
2352                 self.check_operand(operand, location);
2353             }
2354             Rvalue::CopyForDeref(place) => {
2355                 let op = &Operand::Copy(*place);
2356                 self.check_operand(op, location);
2357             }
2358
2359             Rvalue::BinaryOp(_, box (left, right))
2360             | Rvalue::CheckedBinaryOp(_, box (left, right)) => {
2361                 self.check_operand(left, location);
2362                 self.check_operand(right, location);
2363             }
2364
2365             Rvalue::AddressOf(..)
2366             | Rvalue::ThreadLocalRef(..)
2367             | Rvalue::Len(..)
2368             | Rvalue::Discriminant(..) => {}
2369         }
2370     }
2371
2372     /// If this rvalue supports a user-given type annotation, then
2373     /// extract and return it. This represents the final type of the
2374     /// rvalue and will be unified with the inferred type.
2375     fn rvalue_user_ty(&self, rvalue: &Rvalue<'tcx>) -> Option<UserTypeAnnotationIndex> {
2376         match rvalue {
2377             Rvalue::Use(_)
2378             | Rvalue::ThreadLocalRef(_)
2379             | Rvalue::Repeat(..)
2380             | Rvalue::Ref(..)
2381             | Rvalue::AddressOf(..)
2382             | Rvalue::Len(..)
2383             | Rvalue::Cast(..)
2384             | Rvalue::ShallowInitBox(..)
2385             | Rvalue::BinaryOp(..)
2386             | Rvalue::CheckedBinaryOp(..)
2387             | Rvalue::NullaryOp(..)
2388             | Rvalue::CopyForDeref(..)
2389             | Rvalue::UnaryOp(..)
2390             | Rvalue::Discriminant(..) => None,
2391
2392             Rvalue::Aggregate(aggregate, _) => match **aggregate {
2393                 AggregateKind::Adt(_, _, _, user_ty, _) => user_ty,
2394                 AggregateKind::Array(_) => None,
2395                 AggregateKind::Tuple => None,
2396                 AggregateKind::Closure(_, _) => None,
2397                 AggregateKind::Generator(_, _, _) => None,
2398             },
2399         }
2400     }
2401
2402     fn check_aggregate_rvalue(
2403         &mut self,
2404         body: &Body<'tcx>,
2405         rvalue: &Rvalue<'tcx>,
2406         aggregate_kind: &AggregateKind<'tcx>,
2407         operands: &[Operand<'tcx>],
2408         location: Location,
2409     ) {
2410         let tcx = self.tcx();
2411
2412         self.prove_aggregate_predicates(aggregate_kind, location);
2413
2414         if *aggregate_kind == AggregateKind::Tuple {
2415             // tuple rvalue field type is always the type of the op. Nothing to check here.
2416             return;
2417         }
2418
2419         for (i, operand) in operands.iter().enumerate() {
2420             let field_ty = match self.aggregate_field_ty(aggregate_kind, i, location) {
2421                 Ok(field_ty) => field_ty,
2422                 Err(FieldAccessError::OutOfRange { field_count }) => {
2423                     span_mirbug!(
2424                         self,
2425                         rvalue,
2426                         "accessed field #{} but variant only has {}",
2427                         i,
2428                         field_count
2429                     );
2430                     continue;
2431                 }
2432             };
2433             let operand_ty = operand.ty(body, tcx);
2434             let operand_ty = self.normalize(operand_ty, location);
2435
2436             if let Err(terr) = self.sub_types(
2437                 operand_ty,
2438                 field_ty,
2439                 location.to_locations(),
2440                 ConstraintCategory::Boring,
2441             ) {
2442                 span_mirbug!(
2443                     self,
2444                     rvalue,
2445                     "{:?} is not a subtype of {:?}: {:?}",
2446                     operand_ty,
2447                     field_ty,
2448                     terr
2449                 );
2450             }
2451         }
2452     }
2453
2454     /// Adds the constraints that arise from a borrow expression `&'a P` at the location `L`.
2455     ///
2456     /// # Parameters
2457     ///
2458     /// - `location`: the location `L` where the borrow expression occurs
2459     /// - `borrow_region`: the region `'a` associated with the borrow
2460     /// - `borrowed_place`: the place `P` being borrowed
2461     fn add_reborrow_constraint(
2462         &mut self,
2463         body: &Body<'tcx>,
2464         location: Location,
2465         borrow_region: ty::Region<'tcx>,
2466         borrowed_place: &Place<'tcx>,
2467     ) {
2468         // These constraints are only meaningful during borrowck:
2469         let BorrowCheckContext { borrow_set, location_table, all_facts, constraints, .. } =
2470             self.borrowck_context;
2471
2472         // In Polonius mode, we also push a `loan_issued_at` fact
2473         // linking the loan to the region (in some cases, though,
2474         // there is no loan associated with this borrow expression --
2475         // that occurs when we are borrowing an unsafe place, for
2476         // example).
2477         if let Some(all_facts) = all_facts {
2478             let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
2479             if let Some(borrow_index) = borrow_set.get_index_of(&location) {
2480                 let region_vid = borrow_region.to_region_vid();
2481                 all_facts.loan_issued_at.push((
2482                     region_vid,
2483                     borrow_index,
2484                     location_table.mid_index(location),
2485                 ));
2486             }
2487         }
2488
2489         // If we are reborrowing the referent of another reference, we
2490         // need to add outlives relationships. In a case like `&mut
2491         // *p`, where the `p` has type `&'b mut Foo`, for example, we
2492         // need to ensure that `'b: 'a`.
2493
2494         debug!(
2495             "add_reborrow_constraint({:?}, {:?}, {:?})",
2496             location, borrow_region, borrowed_place
2497         );
2498
2499         let mut cursor = borrowed_place.projection.as_ref();
2500         let tcx = self.infcx.tcx;
2501         let field = path_utils::is_upvar_field_projection(
2502             tcx,
2503             &self.borrowck_context.upvars,
2504             borrowed_place.as_ref(),
2505             body,
2506         );
2507         let category = if let Some(field) = field {
2508             ConstraintCategory::ClosureUpvar(field)
2509         } else {
2510             ConstraintCategory::Boring
2511         };
2512
2513         while let [proj_base @ .., elem] = cursor {
2514             cursor = proj_base;
2515
2516             debug!("add_reborrow_constraint - iteration {:?}", elem);
2517
2518             match elem {
2519                 ProjectionElem::Deref => {
2520                     let base_ty = Place::ty_from(borrowed_place.local, proj_base, body, tcx).ty;
2521
2522                     debug!("add_reborrow_constraint - base_ty = {:?}", base_ty);
2523                     match base_ty.kind() {
2524                         ty::Ref(ref_region, _, mutbl) => {
2525                             constraints.outlives_constraints.push(OutlivesConstraint {
2526                                 sup: ref_region.to_region_vid(),
2527                                 sub: borrow_region.to_region_vid(),
2528                                 locations: location.to_locations(),
2529                                 span: location.to_locations().span(body),
2530                                 category,
2531                                 variance_info: ty::VarianceDiagInfo::default(),
2532                                 from_closure: false,
2533                             });
2534
2535                             match mutbl {
2536                                 hir::Mutability::Not => {
2537                                     // Immutable reference. We don't need the base
2538                                     // to be valid for the entire lifetime of
2539                                     // the borrow.
2540                                     break;
2541                                 }
2542                                 hir::Mutability::Mut => {
2543                                     // Mutable reference. We *do* need the base
2544                                     // to be valid, because after the base becomes
2545                                     // invalid, someone else can use our mutable deref.
2546
2547                                     // This is in order to make the following function
2548                                     // illegal:
2549                                     // ```
2550                                     // fn unsafe_deref<'a, 'b>(x: &'a &'b mut T) -> &'b mut T {
2551                                     //     &mut *x
2552                                     // }
2553                                     // ```
2554                                     //
2555                                     // As otherwise you could clone `&mut T` using the
2556                                     // following function:
2557                                     // ```
2558                                     // fn bad(x: &mut T) -> (&mut T, &mut T) {
2559                                     //     let my_clone = unsafe_deref(&'a x);
2560                                     //     ENDREGION 'a;
2561                                     //     (my_clone, x)
2562                                     // }
2563                                     // ```
2564                                 }
2565                             }
2566                         }
2567                         ty::RawPtr(..) => {
2568                             // deref of raw pointer, guaranteed to be valid
2569                             break;
2570                         }
2571                         ty::Adt(def, _) if def.is_box() => {
2572                             // deref of `Box`, need the base to be valid - propagate
2573                         }
2574                         _ => bug!("unexpected deref ty {:?} in {:?}", base_ty, borrowed_place),
2575                     }
2576                 }
2577                 ProjectionElem::Field(..)
2578                 | ProjectionElem::Downcast(..)
2579                 | ProjectionElem::OpaqueCast(..)
2580                 | ProjectionElem::Index(..)
2581                 | ProjectionElem::ConstantIndex { .. }
2582                 | ProjectionElem::Subslice { .. } => {
2583                     // other field access
2584                 }
2585             }
2586         }
2587     }
2588
2589     fn prove_aggregate_predicates(
2590         &mut self,
2591         aggregate_kind: &AggregateKind<'tcx>,
2592         location: Location,
2593     ) {
2594         let tcx = self.tcx();
2595
2596         debug!(
2597             "prove_aggregate_predicates(aggregate_kind={:?}, location={:?})",
2598             aggregate_kind, location
2599         );
2600
2601         let (def_id, instantiated_predicates) = match *aggregate_kind {
2602             AggregateKind::Adt(adt_did, _, substs, _, _) => {
2603                 (adt_did, tcx.predicates_of(adt_did).instantiate(tcx, substs))
2604             }
2605
2606             // For closures, we have some **extra requirements** we
2607             //
2608             // have to check. In particular, in their upvars and
2609             // signatures, closures often reference various regions
2610             // from the surrounding function -- we call those the
2611             // closure's free regions. When we borrow-check (and hence
2612             // region-check) closures, we may find that the closure
2613             // requires certain relationships between those free
2614             // regions. However, because those free regions refer to
2615             // portions of the CFG of their caller, the closure is not
2616             // in a position to verify those relationships. In that
2617             // case, the requirements get "propagated" to us, and so
2618             // we have to solve them here where we instantiate the
2619             // closure.
2620             //
2621             // Despite the opacity of the previous paragraph, this is
2622             // actually relatively easy to understand in terms of the
2623             // desugaring. A closure gets desugared to a struct, and
2624             // these extra requirements are basically like where
2625             // clauses on the struct.
2626             AggregateKind::Closure(def_id, substs)
2627             | AggregateKind::Generator(def_id, substs, _) => {
2628                 (def_id.to_def_id(), self.prove_closure_bounds(tcx, def_id, substs, location))
2629             }
2630
2631             AggregateKind::Array(_) | AggregateKind::Tuple => {
2632                 (CRATE_DEF_ID.to_def_id(), ty::InstantiatedPredicates::empty())
2633             }
2634         };
2635
2636         self.normalize_and_prove_instantiated_predicates(
2637             def_id,
2638             instantiated_predicates,
2639             location.to_locations(),
2640         );
2641     }
2642
2643     fn prove_closure_bounds(
2644         &mut self,
2645         tcx: TyCtxt<'tcx>,
2646         def_id: LocalDefId,
2647         substs: SubstsRef<'tcx>,
2648         location: Location,
2649     ) -> ty::InstantiatedPredicates<'tcx> {
2650         if let Some(ref closure_requirements) = tcx.mir_borrowck(def_id).closure_requirements {
2651             constraint_conversion::ConstraintConversion::new(
2652                 self.infcx,
2653                 self.borrowck_context.universal_regions,
2654                 self.region_bound_pairs,
2655                 self.implicit_region_bound,
2656                 self.param_env,
2657                 location.to_locations(),
2658                 DUMMY_SP,                   // irrelevant; will be overrided.
2659                 ConstraintCategory::Boring, // same as above.
2660                 &mut self.borrowck_context.constraints,
2661             )
2662             .apply_closure_requirements(
2663                 &closure_requirements,
2664                 def_id.to_def_id(),
2665                 substs,
2666             );
2667         }
2668
2669         // Now equate closure substs to regions inherited from `typeck_root_def_id`. Fixes #98589.
2670         let typeck_root_def_id = tcx.typeck_root_def_id(self.body.source.def_id());
2671         let typeck_root_substs = ty::InternalSubsts::identity_for_item(tcx, typeck_root_def_id);
2672
2673         let parent_substs = match tcx.def_kind(def_id) {
2674             DefKind::Closure => substs.as_closure().parent_substs(),
2675             DefKind::Generator => substs.as_generator().parent_substs(),
2676             DefKind::InlineConst => substs.as_inline_const().parent_substs(),
2677             other => bug!("unexpected item {:?}", other),
2678         };
2679         let parent_substs = tcx.mk_substs(parent_substs.iter());
2680
2681         assert_eq!(typeck_root_substs.len(), parent_substs.len());
2682         if let Err(_) = self.eq_substs(
2683             typeck_root_substs,
2684             parent_substs,
2685             location.to_locations(),
2686             ConstraintCategory::BoringNoLocation,
2687         ) {
2688             span_mirbug!(
2689                 self,
2690                 def_id,
2691                 "could not relate closure to parent {:?} != {:?}",
2692                 typeck_root_substs,
2693                 parent_substs
2694             );
2695         }
2696
2697         tcx.predicates_of(def_id).instantiate(tcx, substs)
2698     }
2699
2700     #[instrument(skip(self, body), level = "debug")]
2701     fn typeck_mir(&mut self, body: &Body<'tcx>) {
2702         self.last_span = body.span;
2703         debug!(?body.span);
2704
2705         for (local, local_decl) in body.local_decls.iter_enumerated() {
2706             self.check_local(&body, local, local_decl);
2707         }
2708
2709         for (block, block_data) in body.basic_blocks.iter_enumerated() {
2710             let mut location = Location { block, statement_index: 0 };
2711             for stmt in &block_data.statements {
2712                 if !stmt.source_info.span.is_dummy() {
2713                     self.last_span = stmt.source_info.span;
2714                 }
2715                 self.check_stmt(body, stmt, location);
2716                 location.statement_index += 1;
2717             }
2718
2719             self.check_terminator(&body, block_data.terminator(), location);
2720             self.check_iscleanup(&body, block_data);
2721         }
2722     }
2723 }
2724
2725 trait NormalizeLocation: fmt::Debug + Copy {
2726     fn to_locations(self) -> Locations;
2727 }
2728
2729 impl NormalizeLocation for Locations {
2730     fn to_locations(self) -> Locations {
2731         self
2732     }
2733 }
2734
2735 impl NormalizeLocation for Location {
2736     fn to_locations(self) -> Locations {
2737         Locations::Single(self)
2738     }
2739 }
2740
2741 /// Runs `infcx.instantiate_opaque_types`. Unlike other `TypeOp`s,
2742 /// this is not canonicalized - it directly affects the main `InferCtxt`
2743 /// that we use during MIR borrowchecking.
2744 #[derive(Debug)]
2745 pub(super) struct InstantiateOpaqueType<'tcx> {
2746     pub base_universe: Option<ty::UniverseIndex>,
2747     pub region_constraints: Option<RegionConstraintData<'tcx>>,
2748     pub obligations: Vec<PredicateObligation<'tcx>>,
2749 }
2750
2751 impl<'tcx> TypeOp<'tcx> for InstantiateOpaqueType<'tcx> {
2752     type Output = ();
2753     /// We use this type itself to store the information used
2754     /// when reporting errors. Since this is not a query, we don't
2755     /// re-run anything during error reporting - we just use the information
2756     /// we saved to help extract an error from the already-existing region
2757     /// constraints in our `InferCtxt`
2758     type ErrorInfo = InstantiateOpaqueType<'tcx>;
2759
2760     fn fully_perform(mut self, infcx: &InferCtxt<'tcx>) -> Fallible<TypeOpOutput<'tcx, Self>> {
2761         let (mut output, region_constraints) = scrape_region_constraints(infcx, || {
2762             Ok(InferOk { value: (), obligations: self.obligations.clone() })
2763         })?;
2764         self.region_constraints = Some(region_constraints);
2765         output.error_info = Some(self);
2766         Ok(output)
2767     }
2768 }