src/librustc_mir/borrow_check/nll/type_check/mod.rs

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