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

   1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! This pass type-checks the MIR to ensure it is not broken.
  12 #![allow(unreachable_code)]
  13
  14 use borrow_check::borrow_set::BorrowSet;
  15 use borrow_check::location::LocationTable;
  16 use borrow_check::nll::constraints::{ConstraintSet, OutlivesConstraint};
  17 use borrow_check::nll::facts::AllFacts;
  18 use borrow_check::nll::region_infer::values::LivenessValues;
  19 use borrow_check::nll::region_infer::values::PlaceholderIndices;
  20 use borrow_check::nll::region_infer::values::RegionValueElements;
  21 use borrow_check::nll::region_infer::{ClosureRegionRequirementsExt, TypeTest};
  22 use borrow_check::nll::renumber;
  23 use borrow_check::nll::type_check::free_region_relations::{
  24     CreateResult, UniversalRegionRelations,
  25 };
  26 use borrow_check::nll::universal_regions::{DefiningTy, UniversalRegions};
  27 use borrow_check::nll::ToRegionVid;
  28 use dataflow::move_paths::MoveData;
  29 use dataflow::FlowAtLocation;
  30 use dataflow::MaybeInitializedPlaces;
  31 use rustc::hir;
  32 use rustc::hir::def_id::DefId;
  33 use rustc::infer::canonical::QueryRegionConstraint;
  34 use rustc::infer::outlives::env::RegionBoundPairs;
  35 use rustc::infer::{InferCtxt, InferOk, LateBoundRegionConversionTime};
  36 use rustc::mir::interpret::EvalErrorKind::BoundsCheck;
  37 use rustc::mir::tcx::PlaceTy;
  38 use rustc::mir::visit::{PlaceContext, Visitor};
  39 use rustc::mir::*;
  40 use rustc::traits::query::type_op;
  41 use rustc::traits::query::type_op::custom::CustomTypeOp;
  42 use rustc::traits::query::{Fallible, NoSolution};
  43 use rustc::traits::{ObligationCause, PredicateObligations};
  44 use rustc::ty::fold::TypeFoldable;
  45 use rustc::ty::subst::{Subst, Substs, UnpackedKind, UserSelfTy, UserSubsts};
  46 use rustc::ty::{self, RegionVid, ToPolyTraitRef, Ty, TyCtxt, TyKind};
  47 use std::rc::Rc;
  48 use std::{fmt, iter};
  49 use syntax_pos::{Span, DUMMY_SP};
  50 use transform::{MirPass, MirSource};
  51
  52 use either::Either;
  53 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  54
  55 macro_rules! span_mirbug {
  56     ($context:expr, $elem:expr, $($message:tt)*) => ({
  57         $crate::borrow_check::nll::type_check::mirbug(
  58             $context.tcx(),
  59             $context.last_span,
  60             &format!(
  61                 "broken MIR in {:?} ({:?}): {}",
  62                 $context.mir_def_id,
  63                 $elem,
  64                 format_args!($($message)*),
  65             ),
  66         )
  67     })
  68 }
  69
  70 macro_rules! span_mirbug_and_err {
  71     ($context:expr, $elem:expr, $($message:tt)*) => ({
  72         {
  73             span_mirbug!($context, $elem, $($message)*);
  74             $context.error()
  75         }
  76     })
  77 }
  78
  79 mod constraint_conversion;
  80 pub mod free_region_relations;
  81 mod input_output;
  82 crate mod liveness;
  83 mod relate_tys;
  84
  85 /// Type checks the given `mir` in the context of the inference
  86 /// context `infcx`. Returns any region constraints that have yet to
  87 /// be proven. This result is includes liveness constraints that
  88 /// ensure that regions appearing in the types of all local variables
  89 /// are live at all points where that local variable may later be
  90 /// used.
  91 ///
  92 /// This phase of type-check ought to be infallible -- this is because
  93 /// the original, HIR-based type-check succeeded. So if any errors
  94 /// occur here, we will get a `bug!` reported.
  95 ///
  96 /// # Parameters
  97 ///
  98 /// - `infcx` -- inference context to use
  99 /// - `param_env` -- parameter environment to use for trait solving
 100 /// - `mir` -- MIR to type-check
 101 /// - `mir_def_id` -- DefId from which the MIR is derived (must be local)
 102 /// - `region_bound_pairs` -- the implied outlives obligations between type parameters
 103 ///   and lifetimes (e.g., `&'a T` implies `T: 'a`)
 104 /// - `implicit_region_bound` -- a region which all generic parameters are assumed
 105 ///   to outlive; should represent the fn body
 106 /// - `input_tys` -- fully liberated, but **not** normalized, expected types of the arguments;
 107 ///   the types of the input parameters found in the MIR itself will be equated with these
 108 /// - `output_ty` -- fully liberated, but **not** normalized, expected return type;
 109 ///   the type for the RETURN_PLACE will be equated with this
 110 /// - `liveness` -- results of a liveness computation on the MIR; used to create liveness
 111 ///   constraints for the regions in the types of variables
 112 /// - `flow_inits` -- results of a maybe-init dataflow analysis
 113 /// - `move_data` -- move-data constructed when performing the maybe-init dataflow analysiss
 114 pub(crate) fn type_check<'gcx, 'tcx>(
 115     infcx: &InferCtxt<'_, 'gcx, 'tcx>,
 116     param_env: ty::ParamEnv<'gcx>,
 117     mir: &Mir<'tcx>,
 118     mir_def_id: DefId,
 119     universal_regions: &Rc<UniversalRegions<'tcx>>,
 120     location_table: &LocationTable,
 121     borrow_set: &BorrowSet<'tcx>,
 122     all_facts: &mut Option<AllFacts>,
 123     flow_inits: &mut FlowAtLocation<MaybeInitializedPlaces<'_, 'gcx, 'tcx>>,
 124     move_data: &MoveData<'tcx>,
 125     elements: &Rc<RegionValueElements>,
 126 ) -> MirTypeckResults<'tcx> {
 127     let implicit_region_bound = infcx.tcx.mk_region(ty::ReVar(universal_regions.fr_fn_body));
 128     let mut constraints = MirTypeckRegionConstraints {
 129         liveness_constraints: LivenessValues::new(elements),
 130         outlives_constraints: ConstraintSet::default(),
 131         closure_bounds_mapping: Default::default(),
 132         type_tests: Vec::default(),
 133     };
 134     let mut placeholder_indices = PlaceholderIndices::default();
 135
 136     let CreateResult {
 137         universal_region_relations,
 138         region_bound_pairs,
 139         normalized_inputs_and_output,
 140     } = free_region_relations::create(
 141         infcx,
 142         param_env,
 143         Some(implicit_region_bound),
 144         universal_regions,
 145         &mut constraints,
 146     );
 147
 148     let mut borrowck_context = BorrowCheckContext {
 149         universal_regions,
 150         location_table,
 151         borrow_set,
 152         all_facts,
 153         constraints: &mut constraints,
 154         placeholder_indices: &mut placeholder_indices,
 155     };
 156
 157     type_check_internal(
 158         infcx,
 159         mir_def_id,
 160         param_env,
 161         mir,
 162         &region_bound_pairs,
 163         Some(implicit_region_bound),
 164         Some(&mut borrowck_context),
 165         Some(&universal_region_relations),
 166         |cx| {
 167             cx.equate_inputs_and_outputs(mir, universal_regions, &normalized_inputs_and_output);
 168             liveness::generate(cx, mir, elements, flow_inits, move_data, location_table);
 169
 170             cx.borrowck_context
 171                 .as_mut()
 172                 .map(|bcx| translate_outlives_facts(bcx));
 173         },
 174     );
 175
 176     MirTypeckResults {
 177         constraints,
 178         placeholder_indices,
 179         universal_region_relations,
 180     }
 181 }
 182
 183 fn type_check_internal<'a, 'gcx, 'tcx, R>(
 184     infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 185     mir_def_id: DefId,
 186     param_env: ty::ParamEnv<'gcx>,
 187     mir: &'a Mir<'tcx>,
 188     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
 189     implicit_region_bound: Option<ty::Region<'tcx>>,
 190     borrowck_context: Option<&'a mut BorrowCheckContext<'a, 'tcx>>,
 191     universal_region_relations: Option<&'a UniversalRegionRelations<'tcx>>,
 192     mut extra: impl FnMut(&mut TypeChecker<'a, 'gcx, 'tcx>) -> R,
 193 ) -> R where {
 194     let mut checker = TypeChecker::new(
 195         infcx,
 196         mir,
 197         mir_def_id,
 198         param_env,
 199         region_bound_pairs,
 200         implicit_region_bound,
 201         borrowck_context,
 202         universal_region_relations,
 203     );
 204     let errors_reported = {
 205         let mut verifier = TypeVerifier::new(&mut checker, mir);
 206         verifier.visit_mir(mir);
 207         verifier.errors_reported
 208     };
 209
 210     if !errors_reported {
 211         // if verifier failed, don't do further checks to avoid ICEs
 212         checker.typeck_mir(mir);
 213     }
 214
 215     extra(&mut checker)
 216 }
 217
 218 fn translate_outlives_facts(cx: &mut BorrowCheckContext) {
 219     if let Some(facts) = cx.all_facts {
 220         let location_table = cx.location_table;
 221         facts
 222             .outlives
 223             .extend(cx.constraints.outlives_constraints.iter().flat_map(
 224                 |constraint: &OutlivesConstraint| {
 225                     if let Some(from_location) = constraint.locations.from_location() {
 226                         Either::Left(iter::once((
 227                             constraint.sup,
 228                             constraint.sub,
 229                             location_table.mid_index(from_location),
 230                         )))
 231                     } else {
 232                         Either::Right(
 233                             location_table
 234                                 .all_points()
 235                                 .map(move |location| (constraint.sup, constraint.sub, location)),
 236                         )
 237                     }
 238                 },
 239             ));
 240     }
 241 }
 242
 243 fn mirbug(tcx: TyCtxt, span: Span, msg: &str) {
 244     // We sometimes see MIR failures (notably predicate failures) due to
 245     // the fact that we check rvalue sized predicates here. So use `delay_span_bug`
 246     // to avoid reporting bugs in those cases.
 247     tcx.sess.diagnostic().delay_span_bug(span, msg);
 248 }
 249
 250 enum FieldAccessError {
 251     OutOfRange { field_count: usize },
 252 }
 253
 254 /// Verifies that MIR types are sane to not crash further checks.
 255 ///
 256 /// The sanitize_XYZ methods here take an MIR object and compute its
 257 /// type, calling `span_mirbug` and returning an error type if there
 258 /// is a problem.
 259 struct TypeVerifier<'a, 'b: 'a, 'gcx: 'tcx, 'tcx: 'b> {
 260     cx: &'a mut TypeChecker<'b, 'gcx, 'tcx>,
 261     mir: &'a Mir<'tcx>,
 262     last_span: Span,
 263     mir_def_id: DefId,
 264     errors_reported: bool,
 265 }
 266
 267 impl<'a, 'b, 'gcx, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'gcx, 'tcx> {
 268     fn visit_span(&mut self, span: &Span) {
 269         if !span.is_dummy() {
 270             self.last_span = *span;
 271         }
 272     }
 273
 274     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, location: Location) {
 275         self.sanitize_place(place, location, context);
 276     }
 277
 278     fn visit_constant(&mut self, constant: &Constant<'tcx>, location: Location) {
 279         self.super_constant(constant, location);
 280         self.sanitize_constant(constant, location);
 281         self.sanitize_type(constant, constant.ty);
 282
 283         if let Some(user_ty) = constant.user_ty {
 284             if let Err(terr) = self.cx.relate_type_and_user_type(
 285                 constant.ty,
 286                 ty::Variance::Invariant,
 287                 user_ty,
 288                 location.to_locations(),
 289                 ConstraintCategory::Boring,
 290             ) {
 291                 span_mirbug!(
 292                     self,
 293                     constant,
 294                     "bad constant user type {:?} vs {:?}: {:?}",
 295                     user_ty,
 296                     constant.ty,
 297                     terr,
 298                 );
 299             }
 300         }
 301     }
 302
 303     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 304         self.super_rvalue(rvalue, location);
 305         let rval_ty = rvalue.ty(self.mir, self.tcx());
 306         self.sanitize_type(rvalue, rval_ty);
 307     }
 308
 309     fn visit_local_decl(&mut self, local: Local, local_decl: &LocalDecl<'tcx>) {
 310         self.super_local_decl(local, local_decl);
 311         self.sanitize_type(local_decl, local_decl.ty);
 312
 313         if let Some((user_ty, span)) = local_decl.user_ty {
 314             if let Err(terr) = self.cx.relate_type_and_user_type(
 315                 local_decl.ty,
 316                 ty::Variance::Invariant,
 317                 user_ty,
 318                 Locations::All(span),
 319                 ConstraintCategory::TypeAnnotation,
 320             ) {
 321                 span_mirbug!(
 322                     self,
 323                     local,
 324                     "bad user type on variable {:?}: {:?} != {:?} ({:?})",
 325                     local,
 326                     local_decl.ty,
 327                     local_decl.user_ty,
 328                     terr,
 329                 );
 330             }
 331         }
 332     }
 333
 334     fn visit_mir(&mut self, mir: &Mir<'tcx>) {
 335         self.sanitize_type(&"return type", mir.return_ty());
 336         for local_decl in &mir.local_decls {
 337             self.sanitize_type(local_decl, local_decl.ty);
 338         }
 339         if self.errors_reported {
 340             return;
 341         }
 342         self.super_mir(mir);
 343     }
 344 }
 345
 346 impl<'a, 'b, 'gcx, 'tcx> TypeVerifier<'a, 'b, 'gcx, 'tcx> {
 347     fn new(cx: &'a mut TypeChecker<'b, 'gcx, 'tcx>, mir: &'a Mir<'tcx>) -> Self {
 348         TypeVerifier {
 349             mir,
 350             mir_def_id: cx.mir_def_id,
 351             cx,
 352             last_span: mir.span,
 353             errors_reported: false,
 354         }
 355     }
 356
 357     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
 358         self.cx.infcx.tcx
 359     }
 360
 361     fn sanitize_type(&mut self, parent: &dyn fmt::Debug, ty: Ty<'tcx>) -> Ty<'tcx> {
 362         if ty.has_escaping_regions() || ty.references_error() {
 363             span_mirbug_and_err!(self, parent, "bad type {:?}", ty)
 364         } else {
 365             ty
 366         }
 367     }
 368
 369     /// Checks that the constant's `ty` field matches up with what
 370     /// would be expected from its literal.
 371     fn sanitize_constant(&mut self, constant: &Constant<'tcx>, location: Location) {
 372         debug!(
 373             "sanitize_constant(constant={:?}, location={:?})",
 374             constant, location
 375         );
 376
 377         // FIXME(#46702) -- We need some way to get the predicates
 378         // associated with the "pre-evaluated" form of the
 379         // constant. For example, consider that the constant
 380         // may have associated constant projections (`<Foo as
 381         // Trait<'a, 'b>>::SOME_CONST`) that impose
 382         // constraints on `'a` and `'b`. These constraints
 383         // would be lost if we just look at the normalized
 384         // value.
 385         if let ty::FnDef(def_id, substs) = constant.literal.ty.sty {
 386             let tcx = self.tcx();
 387             let type_checker = &mut self.cx;
 388
 389             // FIXME -- For now, use the substitutions from
 390             // `value.ty` rather than `value.val`. The
 391             // renumberer will rewrite them to independent
 392             // sets of regions; in principle, we ought to
 393             // derive the type of the `value.val` from "first
 394             // principles" and equate with value.ty, but as we
 395             // are transitioning to the miri-based system, we
 396             // don't have a handy function for that, so for
 397             // now we just ignore `value.val` regions.
 398
 399             let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);
 400             type_checker.normalize_and_prove_instantiated_predicates(
 401                 instantiated_predicates,
 402                 location.to_locations(),
 403             );
 404         }
 405
 406         debug!("sanitize_constant: expected_ty={:?}", constant.literal.ty);
 407
 408         if let Err(terr) = self.cx.eq_types(
 409             constant.literal.ty,
 410             constant.ty,
 411             location.to_locations(),
 412             ConstraintCategory::Boring,
 413         ) {
 414             span_mirbug!(
 415                 self,
 416                 constant,
 417                 "constant {:?} should have type {:?} but has {:?} ({:?})",
 418                 constant,
 419                 constant.literal.ty,
 420                 constant.ty,
 421                 terr,
 422             );
 423         }
 424     }
 425
 426     /// Checks that the types internal to the `place` match up with
 427     /// what would be expected.
 428     fn sanitize_place(
 429         &mut self,
 430         place: &Place<'tcx>,
 431         location: Location,
 432         context: PlaceContext,
 433     ) -> PlaceTy<'tcx> {
 434         debug!("sanitize_place: {:?}", place);
 435         let place_ty = match *place {
 436             Place::Local(index) => PlaceTy::Ty {
 437                 ty: self.mir.local_decls[index].ty,
 438             },
 439             Place::Promoted(box (_index, sty)) => {
 440                 let sty = self.sanitize_type(place, sty);
 441                 // FIXME -- promoted MIR return types reference
 442                 // various "free regions" (e.g., scopes and things)
 443                 // that they ought not to do. We have to figure out
 444                 // how best to handle that -- probably we want treat
 445                 // promoted MIR much like closures, renumbering all
 446                 // their free regions and propagating constraints
 447                 // upwards. We have the same acyclic guarantees, so
 448                 // that should be possible. But for now, ignore them.
 449                 //
 450                 // let promoted_mir = &self.mir.promoted[index];
 451                 // promoted_mir.return_ty()
 452                 PlaceTy::Ty { ty: sty }
 453             }
 454             Place::Static(box Static { def_id, ty: sty }) => {
 455                 let sty = self.sanitize_type(place, sty);
 456                 let ty = self.tcx().type_of(def_id);
 457                 let ty = self.cx.normalize(ty, location);
 458                 if let Err(terr) =
 459                     self.cx
 460                         .eq_types(ty, sty, location.to_locations(), ConstraintCategory::Boring)
 461                 {
 462                     span_mirbug!(
 463                         self,
 464                         place,
 465                         "bad static type ({:?}: {:?}): {:?}",
 466                         ty,
 467                         sty,
 468                         terr
 469                     );
 470                 }
 471                 PlaceTy::Ty { ty: sty }
 472             }
 473             Place::Projection(ref proj) => {
 474                 let base_context = if context.is_mutating_use() {
 475                     PlaceContext::Projection(Mutability::Mut)
 476                 } else {
 477                     PlaceContext::Projection(Mutability::Not)
 478                 };
 479                 let base_ty = self.sanitize_place(&proj.base, location, base_context);
 480                 if let PlaceTy::Ty { ty } = base_ty {
 481                     if ty.references_error() {
 482                         assert!(self.errors_reported);
 483                         return PlaceTy::Ty {
 484                             ty: self.tcx().types.err,
 485                         };
 486                     }
 487                 }
 488                 self.sanitize_projection(base_ty, &proj.elem, place, location)
 489             }
 490         };
 491         if let PlaceContext::Copy = context {
 492             let tcx = self.tcx();
 493             let trait_ref = ty::TraitRef {
 494                 def_id: tcx.lang_items().copy_trait().unwrap(),
 495                 substs: tcx.mk_substs_trait(place_ty.to_ty(tcx), &[]),
 496             };
 497
 498             // In order to have a Copy operand, the type T of the value must be Copy. Note that we
 499             // prove that T: Copy, rather than using the type_moves_by_default test. This is
 500             // important because type_moves_by_default ignores the resulting region obligations and
 501             // assumes they pass. This can result in bounds from Copy impls being unsoundly ignored
 502             // (e.g., #29149). Note that we decide to use Copy before knowing whether the bounds
 503             // fully apply: in effect, the rule is that if a value of some type could implement
 504             // Copy, then it must.
 505             self.cx.prove_trait_ref(
 506                 trait_ref,
 507                 location.to_locations(),
 508                 ConstraintCategory::CopyBound,
 509             );
 510         }
 511         place_ty
 512     }
 513
 514     fn sanitize_projection(
 515         &mut self,
 516         base: PlaceTy<'tcx>,
 517         pi: &PlaceElem<'tcx>,
 518         place: &Place<'tcx>,
 519         location: Location,
 520     ) -> PlaceTy<'tcx> {
 521         debug!("sanitize_projection: {:?} {:?} {:?}", base, pi, place);
 522         let tcx = self.tcx();
 523         let base_ty = base.to_ty(tcx);
 524         match *pi {
 525             ProjectionElem::Deref => {
 526                 let deref_ty = base_ty.builtin_deref(true);
 527                 PlaceTy::Ty {
 528                     ty: deref_ty.map(|t| t.ty).unwrap_or_else(|| {
 529                         span_mirbug_and_err!(self, place, "deref of non-pointer {:?}", base_ty)
 530                     }),
 531                 }
 532             }
 533             ProjectionElem::Index(i) => {
 534                 let index_ty = Place::Local(i).ty(self.mir, tcx).to_ty(tcx);
 535                 if index_ty != tcx.types.usize {
 536                     PlaceTy::Ty {
 537                         ty: span_mirbug_and_err!(self, i, "index by non-usize {:?}", i),
 538                     }
 539                 } else {
 540                     PlaceTy::Ty {
 541                         ty: base_ty.builtin_index().unwrap_or_else(|| {
 542                             span_mirbug_and_err!(self, place, "index of non-array {:?}", base_ty)
 543                         }),
 544                     }
 545                 }
 546             }
 547             ProjectionElem::ConstantIndex { .. } => {
 548                 // consider verifying in-bounds
 549                 PlaceTy::Ty {
 550                     ty: base_ty.builtin_index().unwrap_or_else(|| {
 551                         span_mirbug_and_err!(self, place, "index of non-array {:?}", base_ty)
 552                     }),
 553                 }
 554             }
 555             ProjectionElem::Subslice { from, to } => PlaceTy::Ty {
 556                 ty: match base_ty.sty {
 557                     ty::Array(inner, size) => {
 558                         let size = size.unwrap_usize(tcx);
 559                         let min_size = (from as u64) + (to as u64);
 560                         if let Some(rest_size) = size.checked_sub(min_size) {
 561                             tcx.mk_array(inner, rest_size)
 562                         } else {
 563                             span_mirbug_and_err!(
 564                                 self,
 565                                 place,
 566                                 "taking too-small slice of {:?}",
 567                                 base_ty
 568                             )
 569                         }
 570                     }
 571                     ty::Slice(..) => base_ty,
 572                     _ => span_mirbug_and_err!(self, place, "slice of non-array {:?}", base_ty),
 573                 },
 574             },
 575             ProjectionElem::Downcast(adt_def1, index) => match base_ty.sty {
 576                 ty::Adt(adt_def, substs) if adt_def.is_enum() && adt_def == adt_def1 => {
 577                     if index >= adt_def.variants.len() {
 578                         PlaceTy::Ty {
 579                             ty: span_mirbug_and_err!(
 580                                 self,
 581                                 place,
 582                                 "cast to variant #{:?} but enum only has {:?}",
 583                                 index,
 584                                 adt_def.variants.len()
 585                             ),
 586                         }
 587                     } else {
 588                         PlaceTy::Downcast {
 589                             adt_def,
 590                             substs,
 591                             variant_index: index,
 592                         }
 593                     }
 594                 }
 595                 _ => PlaceTy::Ty {
 596                     ty: span_mirbug_and_err!(
 597                         self,
 598                         place,
 599                         "can't downcast {:?} as {:?}",
 600                         base_ty,
 601                         adt_def1
 602                     ),
 603                 },
 604             },
 605             ProjectionElem::Field(field, fty) => {
 606                 let fty = self.sanitize_type(place, fty);
 607                 match self.field_ty(place, base, field, location) {
 608                     Ok(ty) => if let Err(terr) = self.cx.eq_types(
 609                         ty,
 610                         fty,
 611                         location.to_locations(),
 612                         ConstraintCategory::Boring,
 613                     ) {
 614                         span_mirbug!(
 615                             self,
 616                             place,
 617                             "bad field access ({:?}: {:?}): {:?}",
 618                             ty,
 619                             fty,
 620                             terr
 621                         );
 622                     },
 623                     Err(FieldAccessError::OutOfRange { field_count }) => span_mirbug!(
 624                         self,
 625                         place,
 626                         "accessed field #{} but variant only has {}",
 627                         field.index(),
 628                         field_count
 629                     ),
 630                 }
 631                 PlaceTy::Ty { ty: fty }
 632             }
 633         }
 634     }
 635
 636     fn error(&mut self) -> Ty<'tcx> {
 637         self.errors_reported = true;
 638         self.tcx().types.err
 639     }
 640
 641     fn field_ty(
 642         &mut self,
 643         parent: &dyn fmt::Debug,
 644         base_ty: PlaceTy<'tcx>,
 645         field: Field,
 646         location: Location,
 647     ) -> Result<Ty<'tcx>, FieldAccessError> {
 648         let tcx = self.tcx();
 649
 650         let (variant, substs) = match base_ty {
 651             PlaceTy::Downcast {
 652                 adt_def,
 653                 substs,
 654                 variant_index,
 655             } => (&adt_def.variants[variant_index], substs),
 656             PlaceTy::Ty { ty } => match ty.sty {
 657                 ty::Adt(adt_def, substs) if !adt_def.is_enum() => (&adt_def.variants[0], substs),
 658                 ty::Closure(def_id, substs) => {
 659                     return match substs.upvar_tys(def_id, tcx).nth(field.index()) {
 660                         Some(ty) => Ok(ty),
 661                         None => Err(FieldAccessError::OutOfRange {
 662                             field_count: substs.upvar_tys(def_id, tcx).count(),
 663                         }),
 664                     }
 665                 }
 666                 ty::Generator(def_id, substs, _) => {
 667                     // Try pre-transform fields first (upvars and current state)
 668                     if let Some(ty) = substs.pre_transforms_tys(def_id, tcx).nth(field.index()) {
 669                         return Ok(ty);
 670                     }
 671
 672                     // Then try `field_tys` which contains all the fields, but it
 673                     // requires the final optimized MIR.
 674                     return match substs.field_tys(def_id, tcx).nth(field.index()) {
 675                         Some(ty) => Ok(ty),
 676                         None => Err(FieldAccessError::OutOfRange {
 677                             field_count: substs.field_tys(def_id, tcx).count(),
 678                         }),
 679                     };
 680                 }
 681                 ty::Tuple(tys) => {
 682                     return match tys.get(field.index()) {
 683                         Some(&ty) => Ok(ty),
 684                         None => Err(FieldAccessError::OutOfRange {
 685                             field_count: tys.len(),
 686                         }),
 687                     }
 688                 }
 689                 _ => {
 690                     return Ok(span_mirbug_and_err!(
 691                         self,
 692                         parent,
 693                         "can't project out of {:?}",
 694                         base_ty
 695                     ))
 696                 }
 697             },
 698         };
 699
 700         if let Some(field) = variant.fields.get(field.index()) {
 701             Ok(self.cx.normalize(&field.ty(tcx, substs), location))
 702         } else {
 703             Err(FieldAccessError::OutOfRange {
 704                 field_count: variant.fields.len(),
 705             })
 706         }
 707     }
 708 }
 709
 710 /// The MIR type checker. Visits the MIR and enforces all the
 711 /// constraints needed for it to be valid and well-typed. Along the
 712 /// way, it accrues region constraints -- these can later be used by
 713 /// NLL region checking.
 714 struct TypeChecker<'a, 'gcx: 'tcx, 'tcx: 'a> {
 715     infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 716     param_env: ty::ParamEnv<'gcx>,
 717     last_span: Span,
 718     mir: &'a Mir<'tcx>,
 719     mir_def_id: DefId,
 720     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
 721     implicit_region_bound: Option<ty::Region<'tcx>>,
 722     reported_errors: FxHashSet<(Ty<'tcx>, Span)>,
 723     borrowck_context: Option<&'a mut BorrowCheckContext<'a, 'tcx>>,
 724     universal_region_relations: Option<&'a UniversalRegionRelations<'tcx>>,
 725 }
 726
 727 struct BorrowCheckContext<'a, 'tcx: 'a> {
 728     universal_regions: &'a UniversalRegions<'tcx>,
 729     location_table: &'a LocationTable,
 730     all_facts: &'a mut Option<AllFacts>,
 731     borrow_set: &'a BorrowSet<'tcx>,
 732     constraints: &'a mut MirTypeckRegionConstraints<'tcx>,
 733     placeholder_indices: &'a mut PlaceholderIndices,
 734 }
 735
 736 crate struct MirTypeckResults<'tcx> {
 737     crate constraints: MirTypeckRegionConstraints<'tcx>,
 738     crate placeholder_indices: PlaceholderIndices,
 739     crate universal_region_relations: Rc<UniversalRegionRelations<'tcx>>,
 740 }
 741
 742 /// A collection of region constraints that must be satisfied for the
 743 /// program to be considered well-typed.
 744 crate struct MirTypeckRegionConstraints<'tcx> {
 745     /// In general, the type-checker is not responsible for enforcing
 746     /// liveness constraints; this job falls to the region inferencer,
 747     /// which performs a liveness analysis. However, in some limited
 748     /// cases, the MIR type-checker creates temporary regions that do
 749     /// not otherwise appear in the MIR -- in particular, the
 750     /// late-bound regions that it instantiates at call-sites -- and
 751     /// hence it must report on their liveness constraints.
 752     crate liveness_constraints: LivenessValues<RegionVid>,
 753
 754     crate outlives_constraints: ConstraintSet,
 755
 756     crate closure_bounds_mapping:
 757         FxHashMap<Location, FxHashMap<(RegionVid, RegionVid), (ConstraintCategory, Span)>>,
 758
 759     crate type_tests: Vec<TypeTest<'tcx>>,
 760 }
 761
 762 /// The `Locations` type summarizes *where* region constraints are
 763 /// required to hold. Normally, this is at a particular point which
 764 /// created the obligation, but for constraints that the user gave, we
 765 /// want the constraint to hold at all points.
 766 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
 767 pub enum Locations {
 768     /// Indicates that a type constraint should always be true. This
 769     /// is particularly important in the new borrowck analysis for
 770     /// things like the type of the return slot. Consider this
 771     /// example:
 772     ///
 773     /// ```
 774     /// fn foo<'a>(x: &'a u32) -> &'a u32 {
 775     ///     let y = 22;
 776     ///     return &y; // error
 777     /// }
 778     /// ```
 779     ///
 780     /// Here, we wind up with the signature from the return type being
 781     /// something like `&'1 u32` where `'1` is a universal region. But
 782     /// the type of the return slot `_0` is something like `&'2 u32`
 783     /// where `'2` is an existential region variable. The type checker
 784     /// requires that `&'2 u32 = &'1 u32` -- but at what point? In the
 785     /// older NLL analysis, we required this only at the entry point
 786     /// to the function. By the nature of the constraints, this wound
 787     /// up propagating to all points reachable from start (because
 788     /// `'1` -- as a universal region -- is live everywhere).  In the
 789     /// newer analysis, though, this doesn't work: `_0` is considered
 790     /// dead at the start (it has no usable value) and hence this type
 791     /// equality is basically a no-op. Then, later on, when we do `_0
 792     /// = &'3 y`, that region `'3` never winds up related to the
 793     /// universal region `'1` and hence no error occurs. Therefore, we
 794     /// use Locations::All instead, which ensures that the `'1` and
 795     /// `'2` are equal everything. We also use this for other
 796     /// user-given type annotations; e.g., if the user wrote `let mut
 797     /// x: &'static u32 = ...`, we would ensure that all values
 798     /// assigned to `x` are of `'static` lifetime.
 799     ///
 800     /// The span points to the place the constraint arose. For example,
 801     /// it points to the type in a user-given type annotation. If
 802     /// there's no sensible span then it's DUMMY_SP.
 803     All(Span),
 804
 805     /// An outlives constraint that only has to hold at a single location,
 806     /// usually it represents a point where references flow from one spot to
 807     /// another (e.g., `x = y`)
 808     Single(Location),
 809 }
 810
 811 impl Locations {
 812     pub fn from_location(&self) -> Option<Location> {
 813         match self {
 814             Locations::All(_) => None,
 815             Locations::Single(from_location) => Some(*from_location),
 816         }
 817     }
 818
 819     /// Gets a span representing the location.
 820     pub fn span(&self, mir: &Mir<'_>) -> Span {
 821         match self {
 822             Locations::All(span) => *span,
 823             Locations::Single(l) => mir.source_info(*l).span,
 824         }
 825     }
 826 }
 827
 828 impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
 829     fn new(
 830         infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 831         mir: &'a Mir<'tcx>,
 832         mir_def_id: DefId,
 833         param_env: ty::ParamEnv<'gcx>,
 834         region_bound_pairs: &'a RegionBoundPairs<'tcx>,
 835         implicit_region_bound: Option<ty::Region<'tcx>>,
 836         borrowck_context: Option<&'a mut BorrowCheckContext<'a, 'tcx>>,
 837         universal_region_relations: Option<&'a UniversalRegionRelations<'tcx>>,
 838     ) -> Self {
 839         TypeChecker {
 840             infcx,
 841             last_span: DUMMY_SP,
 842             mir,
 843             mir_def_id,
 844             param_env,
 845             region_bound_pairs,
 846             implicit_region_bound,
 847             borrowck_context,
 848             reported_errors: Default::default(),
 849             universal_region_relations,
 850         }
 851     }
 852
 853     /// Given some operation `op` that manipulates types, proves
 854     /// predicates, or otherwise uses the inference context, executes
 855     /// `op` and then executes all the further obligations that `op`
 856     /// returns. This will yield a set of outlives constraints amongst
 857     /// regions which are extracted and stored as having occurred at
 858     /// `locations`.
 859     ///
 860     /// **Any `rustc::infer` operations that might generate region
 861     /// constraints should occur within this method so that those
 862     /// constraints can be properly localized!**
 863     fn fully_perform_op<R>(
 864         &mut self,
 865         locations: Locations,
 866         category: ConstraintCategory,
 867         op: impl type_op::TypeOp<'gcx, 'tcx, Output = R>,
 868     ) -> Fallible<R> {
 869         let (r, opt_data) = op.fully_perform(self.infcx)?;
 870
 871         if let Some(data) = &opt_data {
 872             self.push_region_constraints(locations, category, data);
 873         }
 874
 875         Ok(r)
 876     }
 877
 878     fn push_region_constraints(
 879         &mut self,
 880         locations: Locations,
 881         category: ConstraintCategory,
 882         data: &[QueryRegionConstraint<'tcx>],
 883     ) {
 884         debug!(
 885             "push_region_constraints: constraints generated at {:?} are {:#?}",
 886             locations, data
 887         );
 888
 889         if let Some(ref mut borrowck_context) = self.borrowck_context {
 890             constraint_conversion::ConstraintConversion::new(
 891                 self.infcx.tcx,
 892                 borrowck_context.universal_regions,
 893                 self.region_bound_pairs,
 894                 self.implicit_region_bound,
 895                 self.param_env,
 896                 locations,
 897                 category,
 898                 &mut borrowck_context.constraints.outlives_constraints,
 899                 &mut borrowck_context.constraints.type_tests,
 900             ).convert_all(&data);
 901         }
 902     }
 903
 904     /// Convenient wrapper around `relate_tys::relate_types` -- see
 905     /// that fn for docs.
 906     fn relate_types(
 907         &mut self,
 908         a: Ty<'tcx>,
 909         v: ty::Variance,
 910         b: Ty<'tcx>,
 911         locations: Locations,
 912         category: ConstraintCategory,
 913     ) -> Fallible<()> {
 914         relate_tys::relate_types(
 915             self.infcx,
 916             a,
 917             v,
 918             b,
 919             locations,
 920             category,
 921             self.borrowck_context.as_mut().map(|x| &mut **x),
 922         )
 923     }
 924
 925     fn sub_types(
 926         &mut self,
 927         sub: Ty<'tcx>,
 928         sup: Ty<'tcx>,
 929         locations: Locations,
 930         category: ConstraintCategory,
 931     ) -> Fallible<()> {
 932         self.relate_types(sub, ty::Variance::Covariant, sup, locations, category)
 933     }
 934
 935     /// Try to relate `sub <: sup`; if this fails, instantiate opaque
 936     /// variables in `sub` with their inferred definitions and try
 937     /// again. This is used for opaque types in places (e.g., `let x:
 938     /// impl Foo = ..`).
 939     fn sub_types_or_anon(
 940         &mut self,
 941         sub: Ty<'tcx>,
 942         sup: Ty<'tcx>,
 943         locations: Locations,
 944         category: ConstraintCategory,
 945     ) -> Fallible<()> {
 946         if let Err(terr) = self.sub_types(sub, sup, locations, category) {
 947             if let TyKind::Opaque(..) = sup.sty {
 948                 // When you have `let x: impl Foo = ...` in a closure,
 949                 // the resulting inferend values are stored with the
 950                 // def-id of the base function.
 951                 let parent_def_id = self.tcx().closure_base_def_id(self.mir_def_id);
 952                 return self.eq_opaque_type_and_type(sub, sup, parent_def_id, locations, category);
 953             } else {
 954                 return Err(terr);
 955             }
 956         }
 957         Ok(())
 958     }
 959
 960     fn eq_types(
 961         &mut self,
 962         a: Ty<'tcx>,
 963         b: Ty<'tcx>,
 964         locations: Locations,
 965         category: ConstraintCategory,
 966     ) -> Fallible<()> {
 967         self.relate_types(a, ty::Variance::Invariant, b, locations, category)
 968     }
 969
 970     fn relate_type_and_user_type(
 971         &mut self,
 972         a: Ty<'tcx>,
 973         v: ty::Variance,
 974         user_ty: UserTypeAnnotation<'tcx>,
 975         locations: Locations,
 976         category: ConstraintCategory,
 977     ) -> Fallible<()> {
 978         let tcx = self.tcx();
 979
 980         debug!(
 981             "relate_type_and_user_type(a={:?}, v={:?}, b={:?}, locations={:?})",
 982             a, v, user_ty, locations
 983         );
 984
 985         // The `TypeRelating` code assumes that "unresolved inference
 986         // variables" appear in the "a" side, so flip `Contravariant`
 987         // ambient variance to get the right relationship.
 988         let v1 = ty::Contravariant.xform(v);
 989
 990         match user_ty {
 991             UserTypeAnnotation::Ty(canonical_ty) => {
 992                 let (ty, _) = self.infcx
 993                     .instantiate_canonical_with_fresh_inference_vars(DUMMY_SP, &canonical_ty);
 994
 995                 self.relate_types(ty, v1, a, locations, category)?;
 996
 997                 self.prove_predicate(ty::Predicate::WellFormed(ty), locations, category);
 998             }
 999             UserTypeAnnotation::TypeOf(def_id, canonical_substs) => {
1000                 let (
1001                     UserSubsts {
1002                         substs,
1003                         user_self_ty,
1004                     },
1005                     _,
1006                 ) = self.infcx
1007                     .instantiate_canonical_with_fresh_inference_vars(DUMMY_SP, &canonical_substs);
1008
1009                 let ty = self.tcx().type_of(def_id);
1010                 let ty = ty.subst(tcx, substs);
1011                 let ty = self.normalize(ty, locations);
1012
1013                 self.relate_types(ty, v1, a, locations, category)?;
1014
1015                 if let Some(UserSelfTy {
1016                     impl_def_id,
1017                     self_ty,
1018                 }) = user_self_ty
1019                 {
1020                     let impl_self_ty = tcx.type_of(impl_def_id);
1021                     let impl_self_ty = impl_self_ty.subst(tcx, &substs);
1022                     let impl_self_ty = self.normalize(impl_self_ty, locations);
1023
1024                     // There may be type variables in `substs` and hence
1025                     // in `impl_self_ty`, but they should all have been
1026                     // resolved to some fixed value during the first call
1027                     // to `relate`, above. Therefore, if we use
1028                     // `resolve_type_vars_if_possible` we should get to
1029                     // something without type variables. This is important
1030                     // because the `b` type in `relate_with_variance`
1031                     // below is not permitted to have inference variables.
1032                     let impl_self_ty = self.infcx.resolve_type_vars_if_possible(&impl_self_ty);
1033                     assert!(!impl_self_ty.has_infer_types());
1034
1035                     self.eq_types(self_ty, impl_self_ty, locations, category)?;
1036
1037                     self.prove_predicate(
1038                         ty::Predicate::WellFormed(impl_self_ty),
1039                         locations,
1040                         category,
1041                     );
1042                 }
1043
1044                 // Prove the predicates coming along with `def_id`.
1045                 //
1046                 // Also, normalize the `instantiated_predicates`
1047                 // because otherwise we wind up with duplicate "type
1048                 // outlives" error messages.
1049                 let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);
1050                 let instantiated_predicates = self.fold_to_region_vid(instantiated_predicates);
1051                 self.normalize_and_prove_instantiated_predicates(
1052                     instantiated_predicates,
1053                     locations,
1054                 );
1055
1056                 // In addition to proving the predicates, we have to
1057                 // prove that `ty` is well-formed -- this is because
1058                 // the WF of `ty` is predicated on the substs being
1059                 // well-formed, and we haven't proven *that*. We don't
1060                 // want to prove the WF of types from  `substs` directly because they
1061                 // haven't been normalized.
1062                 //
1063                 // FIXME(nmatsakis): Well, perhaps we should normalize
1064                 // them?  This would only be relevant if some input
1065                 // type were ill-formed but did not appear in `ty`,
1066                 // which...could happen with normalization...
1067                 self.prove_predicate(ty::Predicate::WellFormed(ty), locations, category);
1068             }
1069         }
1070
1071         Ok(())
1072     }
1073
1074     /// Replace all free regions in `value` with their NLL `RegionVid`
1075     /// equivalents; if not in NLL, does nothing. This is never
1076     /// particularly necessary -- we'll do it lazilly as we process
1077     /// the value anyway -- but in some specific cases it is useful to
1078     /// normalize so we can suppress duplicate error messages.
1079     fn fold_to_region_vid<T>(&self, value: T) -> T
1080     where
1081         T: TypeFoldable<'tcx>,
1082     {
1083         if let Some(borrowck_context) = &self.borrowck_context {
1084             self.tcx().fold_regions(&value, &mut false, |r, _debruijn| {
1085                 if r.has_free_regions() {
1086                     self.tcx().mk_region(ty::RegionKind::ReVar(
1087                         borrowck_context.universal_regions.to_region_vid(r),
1088                     ))
1089                 } else {
1090                     r
1091                 }
1092             })
1093         } else {
1094             value
1095         }
1096     }
1097
1098     fn eq_opaque_type_and_type(
1099         &mut self,
1100         revealed_ty: Ty<'tcx>,
1101         anon_ty: Ty<'tcx>,
1102         anon_owner_def_id: DefId,
1103         locations: Locations,
1104         category: ConstraintCategory,
1105     ) -> Fallible<()> {
1106         debug!(
1107             "eq_opaque_type_and_type( \
1108              revealed_ty={:?}, \
1109              anon_ty={:?})",
1110             revealed_ty, anon_ty
1111         );
1112         let infcx = self.infcx;
1113         let tcx = infcx.tcx;
1114         let param_env = self.param_env;
1115         debug!("eq_opaque_type_and_type: mir_def_id={:?}", self.mir_def_id);
1116         let opaque_type_map = self.fully_perform_op(
1117             locations,
1118             category,
1119             CustomTypeOp::new(
1120                 |infcx| {
1121                     let mut obligations = ObligationAccumulator::default();
1122
1123                     let dummy_body_id = ObligationCause::dummy().body_id;
1124                     let (output_ty, opaque_type_map) =
1125                         obligations.add(infcx.instantiate_opaque_types(
1126                             anon_owner_def_id,
1127                             dummy_body_id,
1128                             param_env,
1129                             &anon_ty,
1130                         ));
1131                     debug!(
1132                         "eq_opaque_type_and_type: \
1133                          instantiated output_ty={:?} \
1134                          opaque_type_map={:#?} \
1135                          revealed_ty={:?}",
1136                         output_ty, opaque_type_map, revealed_ty
1137                     );
1138                     obligations.add(infcx
1139                         .at(&ObligationCause::dummy(), param_env)
1140                         .eq(output_ty, revealed_ty)?);
1141
1142                     for (&opaque_def_id, opaque_decl) in &opaque_type_map {
1143                         let opaque_defn_ty = tcx.type_of(opaque_def_id);
1144                         let opaque_defn_ty = opaque_defn_ty.subst(tcx, opaque_decl.substs);
1145                         let opaque_defn_ty = renumber::renumber_regions(infcx, &opaque_defn_ty);
1146                         debug!(
1147                             "eq_opaque_type_and_type: concrete_ty={:?}={:?} opaque_defn_ty={:?}",
1148                             opaque_decl.concrete_ty,
1149                             infcx.resolve_type_vars_if_possible(&opaque_decl.concrete_ty),
1150                             opaque_defn_ty
1151                         );
1152                         obligations.add(infcx
1153                             .at(&ObligationCause::dummy(), param_env)
1154                             .eq(opaque_decl.concrete_ty, opaque_defn_ty)?);
1155                     }
1156
1157                     debug!("eq_opaque_type_and_type: equated");
1158
1159                     Ok(InferOk {
1160                         value: Some(opaque_type_map),
1161                         obligations: obligations.into_vec(),
1162                     })
1163                 },
1164                 || "input_output".to_string(),
1165             ),
1166         )?;
1167
1168         let universal_region_relations = match self.universal_region_relations {
1169             Some(rel) => rel,
1170             None => return Ok(()),
1171         };
1172
1173         // Finally, if we instantiated the anon types successfully, we
1174         // have to solve any bounds (e.g., `-> impl Iterator` needs to
1175         // prove that `T: Iterator` where `T` is the type we
1176         // instantiated it with).
1177         if let Some(opaque_type_map) = opaque_type_map {
1178             for (opaque_def_id, opaque_decl) in opaque_type_map {
1179                 self.fully_perform_op(
1180                     locations,
1181                     ConstraintCategory::OpaqueType,
1182                     CustomTypeOp::new(
1183                         |_cx| {
1184                             infcx.constrain_opaque_type(
1185                                 opaque_def_id,
1186                                 &opaque_decl,
1187                                 universal_region_relations,
1188                             );
1189                             Ok(InferOk {
1190                                 value: (),
1191                                 obligations: vec![],
1192                             })
1193                         },
1194                         || "opaque_type_map".to_string(),
1195                     ),
1196                 )?;
1197             }
1198         }
1199         Ok(())
1200     }
1201
1202     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
1203         self.infcx.tcx
1204     }
1205
1206     fn check_stmt(&mut self, mir: &Mir<'tcx>, stmt: &Statement<'tcx>, location: Location) {
1207         debug!("check_stmt: {:?}", stmt);
1208         let tcx = self.tcx();
1209         match stmt.kind {
1210             StatementKind::Assign(ref place, ref rv) => {
1211                 // Assignments to temporaries are not "interesting";
1212                 // they are not caused by the user, but rather artifacts
1213                 // of lowering. Assignments to other sorts of places *are* interesting
1214                 // though.
1215                 let category = match *place {
1216                     Place::Local(RETURN_PLACE) => if let Some(BorrowCheckContext {
1217                         universal_regions:
1218                             UniversalRegions {
1219                                 defining_ty: DefiningTy::Const(def_id, _),
1220                                 ..
1221                             },
1222                         ..
1223                     }) = self.borrowck_context
1224                     {
1225                         if tcx.is_static(*def_id).is_some() {
1226                             ConstraintCategory::UseAsStatic
1227                         } else {
1228                             ConstraintCategory::UseAsConst
1229                         }
1230                     } else {
1231                         ConstraintCategory::Return
1232                     },
1233                     Place::Local(l) if !mir.local_decls[l].is_user_variable.is_some() => {
1234                         ConstraintCategory::Boring
1235                     }
1236                     _ => ConstraintCategory::Assignment,
1237                 };
1238
1239                 let place_ty = place.ty(mir, tcx).to_ty(tcx);
1240                 let rv_ty = rv.ty(mir, tcx);
1241                 if let Err(terr) =
1242                     self.sub_types_or_anon(rv_ty, place_ty, location.to_locations(), category)
1243                 {
1244                     span_mirbug!(
1245                         self,
1246                         stmt,
1247                         "bad assignment ({:?} = {:?}): {:?}",
1248                         place_ty,
1249                         rv_ty,
1250                         terr
1251                     );
1252                 }
1253
1254                 if let Some(user_ty) = self.rvalue_user_ty(rv) {
1255                     if let Err(terr) = self.relate_type_and_user_type(
1256                         rv_ty,
1257                         ty::Variance::Invariant,
1258                         user_ty,
1259                         location.to_locations(),
1260                         ConstraintCategory::Boring,
1261                     ) {
1262                         span_mirbug!(
1263                             self,
1264                             stmt,
1265                             "bad user type on rvalue ({:?} = {:?}): {:?}",
1266                             user_ty,
1267                             rv_ty,
1268                             terr
1269                         );
1270                     }
1271                 }
1272
1273                 self.check_rvalue(mir, rv, location);
1274                 if !self.tcx().features().unsized_locals {
1275                     let trait_ref = ty::TraitRef {
1276                         def_id: tcx.lang_items().sized_trait().unwrap(),
1277                         substs: tcx.mk_substs_trait(place_ty, &[]),
1278                     };
1279                     self.prove_trait_ref(
1280                         trait_ref,
1281                         location.to_locations(),
1282                         ConstraintCategory::SizedBound,
1283                     );
1284                 }
1285             }
1286             StatementKind::SetDiscriminant {
1287                 ref place,
1288                 variant_index,
1289             } => {
1290                 let place_type = place.ty(mir, tcx).to_ty(tcx);
1291                 let adt = match place_type.sty {
1292                     TyKind::Adt(adt, _) if adt.is_enum() => adt,
1293                     _ => {
1294                         span_bug!(
1295                             stmt.source_info.span,
1296                             "bad set discriminant ({:?} = {:?}): lhs is not an enum",
1297                             place,
1298                             variant_index
1299                         );
1300                     }
1301                 };
1302                 if variant_index >= adt.variants.len() {
1303                     span_bug!(
1304                         stmt.source_info.span,
1305                         "bad set discriminant ({:?} = {:?}): value of of range",
1306                         place,
1307                         variant_index
1308                     );
1309                 };
1310             }
1311             StatementKind::AscribeUserType(ref place, variance, c_ty) => {
1312                 let place_ty = place.ty(mir, tcx).to_ty(tcx);
1313                 if let Err(terr) = self.relate_type_and_user_type(
1314                     place_ty,
1315                     variance,
1316                     c_ty,
1317                     Locations::All(stmt.source_info.span),
1318                     ConstraintCategory::TypeAnnotation,
1319                 ) {
1320                     span_mirbug!(
1321                         self,
1322                         stmt,
1323                         "bad type assert ({:?} <: {:?}): {:?}",
1324                         place_ty,
1325                         c_ty,
1326                         terr
1327                     );
1328                 }
1329             }
1330             StatementKind::FakeRead(..)
1331             | StatementKind::StorageLive(_)
1332             | StatementKind::StorageDead(_)
1333             | StatementKind::InlineAsm { .. }
1334             | StatementKind::EndRegion(_)
1335             | StatementKind::Validate(..)
1336             | StatementKind::Nop => {}
1337         }
1338     }
1339
1340     fn check_terminator(
1341         &mut self,
1342         mir: &Mir<'tcx>,
1343         term: &Terminator<'tcx>,
1344         term_location: Location,
1345     ) {
1346         debug!("check_terminator: {:?}", term);
1347         let tcx = self.tcx();
1348         match term.kind {
1349             TerminatorKind::Goto { .. }
1350             | TerminatorKind::Resume
1351             | TerminatorKind::Abort
1352             | TerminatorKind::Return
1353             | TerminatorKind::GeneratorDrop
1354             | TerminatorKind::Unreachable
1355             | TerminatorKind::Drop { .. }
1356             | TerminatorKind::FalseEdges { .. }
1357             | TerminatorKind::FalseUnwind { .. } => {
1358                 // no checks needed for these
1359             }
1360
1361             TerminatorKind::DropAndReplace {
1362                 ref location,
1363                 ref value,
1364                 target: _,
1365                 unwind: _,
1366             } => {
1367                 let place_ty = location.ty(mir, tcx).to_ty(tcx);
1368                 let rv_ty = value.ty(mir, tcx);
1369
1370                 let locations = term_location.to_locations();
1371                 if let Err(terr) =
1372                     self.sub_types(rv_ty, place_ty, locations, ConstraintCategory::Assignment)
1373                 {
1374                     span_mirbug!(
1375                         self,
1376                         term,
1377                         "bad DropAndReplace ({:?} = {:?}): {:?}",
1378                         place_ty,
1379                         rv_ty,
1380                         terr
1381                     );
1382                 }
1383             }
1384             TerminatorKind::SwitchInt {
1385                 ref discr,
1386                 switch_ty,
1387                 ..
1388             } => {
1389                 let discr_ty = discr.ty(mir, tcx);
1390                 if let Err(terr) = self.sub_types(
1391                     discr_ty,
1392                     switch_ty,
1393                     term_location.to_locations(),
1394                     ConstraintCategory::Assignment,
1395                 ) {
1396                     span_mirbug!(
1397                         self,
1398                         term,
1399                         "bad SwitchInt ({:?} on {:?}): {:?}",
1400                         switch_ty,
1401                         discr_ty,
1402                         terr
1403                     );
1404                 }
1405                 if !switch_ty.is_integral() && !switch_ty.is_char() && !switch_ty.is_bool() {
1406                     span_mirbug!(self, term, "bad SwitchInt discr ty {:?}", switch_ty);
1407                 }
1408                 // FIXME: check the values
1409             }
1410             TerminatorKind::Call {
1411                 ref func,
1412                 ref args,
1413                 ref destination,
1414                 from_hir_call,
1415                 ..
1416             } => {
1417                 let func_ty = func.ty(mir, tcx);
1418                 debug!("check_terminator: call, func_ty={:?}", func_ty);
1419                 let sig = match func_ty.sty {
1420                     ty::FnDef(..) | ty::FnPtr(_) => func_ty.fn_sig(tcx),
1421                     _ => {
1422                         span_mirbug!(self, term, "call to non-function {:?}", func_ty);
1423                         return;
1424                     }
1425                 };
1426                 let (sig, map) = self.infcx.replace_late_bound_regions_with_fresh_var(
1427                     term.source_info.span,
1428                     LateBoundRegionConversionTime::FnCall,
1429                     &sig,
1430                 );
1431                 let sig = self.normalize(sig, term_location);
1432                 self.check_call_dest(mir, term, &sig, destination, term_location);
1433
1434                 self.prove_predicates(
1435                     sig.inputs().iter().map(|ty| ty::Predicate::WellFormed(ty)),
1436                     term_location.to_locations(),
1437                     ConstraintCategory::Boring,
1438                 );
1439
1440                 // The ordinary liveness rules will ensure that all
1441                 // regions in the type of the callee are live here. We
1442                 // then further constrain the late-bound regions that
1443                 // were instantiated at the call site to be live as
1444                 // well. The resulting is that all the input (and
1445                 // output) types in the signature must be live, since
1446                 // all the inputs that fed into it were live.
1447                 for &late_bound_region in map.values() {
1448                     if let Some(ref mut borrowck_context) = self.borrowck_context {
1449                         let region_vid = borrowck_context
1450                             .universal_regions
1451                             .to_region_vid(late_bound_region);
1452                         borrowck_context
1453                             .constraints
1454                             .liveness_constraints
1455                             .add_element(region_vid, term_location);
1456                     }
1457                 }
1458
1459                 self.check_call_inputs(mir, term, &sig, args, term_location, from_hir_call);
1460             }
1461             TerminatorKind::Assert {
1462                 ref cond, ref msg, ..
1463             } => {
1464                 let cond_ty = cond.ty(mir, tcx);
1465                 if cond_ty != tcx.types.bool {
1466                     span_mirbug!(self, term, "bad Assert ({:?}, not bool", cond_ty);
1467                 }
1468
1469                 if let BoundsCheck { ref len, ref index } = *msg {
1470                     if len.ty(mir, tcx) != tcx.types.usize {
1471                         span_mirbug!(self, len, "bounds-check length non-usize {:?}", len)
1472                     }
1473                     if index.ty(mir, tcx) != tcx.types.usize {
1474                         span_mirbug!(self, index, "bounds-check index non-usize {:?}", index)
1475                     }
1476                 }
1477             }
1478             TerminatorKind::Yield { ref value, .. } => {
1479                 let value_ty = value.ty(mir, tcx);
1480                 match mir.yield_ty {
1481                     None => span_mirbug!(self, term, "yield in non-generator"),
1482                     Some(ty) => {
1483                         if let Err(terr) = self.sub_types(
1484                             value_ty,
1485                             ty,
1486                             term_location.to_locations(),
1487                             ConstraintCategory::Return,
1488                         ) {
1489                             span_mirbug!(
1490                                 self,
1491                                 term,
1492                                 "type of yield value is {:?}, but the yield type is {:?}: {:?}",
1493                                 value_ty,
1494                                 ty,
1495                                 terr
1496                             );
1497                         }
1498                     }
1499                 }
1500             }
1501         }
1502     }
1503
1504     fn check_call_dest(
1505         &mut self,
1506         mir: &Mir<'tcx>,
1507         term: &Terminator<'tcx>,
1508         sig: &ty::FnSig<'tcx>,
1509         destination: &Option<(Place<'tcx>, BasicBlock)>,
1510         term_location: Location,
1511     ) {
1512         let tcx = self.tcx();
1513         match *destination {
1514             Some((ref dest, _target_block)) => {
1515                 let dest_ty = dest.ty(mir, tcx).to_ty(tcx);
1516                 let category = match *dest {
1517                     Place::Local(RETURN_PLACE) => {
1518                         if let Some(BorrowCheckContext {
1519                             universal_regions:
1520                                 UniversalRegions {
1521                                     defining_ty: DefiningTy::Const(def_id, _),
1522                                     ..
1523                                 },
1524                             ..
1525                         }) = self.borrowck_context
1526                         {
1527                             if tcx.is_static(*def_id).is_some() {
1528                                 ConstraintCategory::UseAsStatic
1529                             } else {
1530                                 ConstraintCategory::UseAsConst
1531                             }
1532                         } else {
1533                             ConstraintCategory::Return
1534                         }
1535                     }
1536                     Place::Local(l) if !mir.local_decls[l].is_user_variable.is_some() => {
1537                         ConstraintCategory::Boring
1538                     }
1539                     _ => ConstraintCategory::Assignment,
1540                 };
1541
1542                 let locations = term_location.to_locations();
1543
1544                 if let Err(terr) =
1545                     self.sub_types_or_anon(sig.output(), dest_ty, locations, category)
1546                 {
1547                     span_mirbug!(
1548                         self,
1549                         term,
1550                         "call dest mismatch ({:?} <- {:?}): {:?}",
1551                         dest_ty,
1552                         sig.output(),
1553                         terr
1554                     );
1555                 }
1556
1557                 // When `#![feature(unsized_locals)]` is not enabled,
1558                 // this check is done at `check_local`.
1559                 if self.tcx().features().unsized_locals {
1560                     let span = term.source_info.span;
1561                     self.ensure_place_sized(dest_ty, span);
1562                 }
1563             }
1564             None => {
1565                 // FIXME(canndrew): This is_never should probably be an is_uninhabited
1566                 if !sig.output().is_never() {
1567                     span_mirbug!(self, term, "call to converging function {:?} w/o dest", sig);
1568                 }
1569             }
1570         }
1571     }
1572
1573     fn check_call_inputs(
1574         &mut self,
1575         mir: &Mir<'tcx>,
1576         term: &Terminator<'tcx>,
1577         sig: &ty::FnSig<'tcx>,
1578         args: &[Operand<'tcx>],
1579         term_location: Location,
1580         from_hir_call: bool,
1581     ) {
1582         debug!("check_call_inputs({:?}, {:?})", sig, args);
1583         if args.len() < sig.inputs().len() || (args.len() > sig.inputs().len() && !sig.variadic) {
1584             span_mirbug!(self, term, "call to {:?} with wrong # of args", sig);
1585         }
1586         for (n, (fn_arg, op_arg)) in sig.inputs().iter().zip(args).enumerate() {
1587             let op_arg_ty = op_arg.ty(mir, self.tcx());
1588             let category = if from_hir_call {
1589                 ConstraintCategory::CallArgument
1590             } else {
1591                 ConstraintCategory::Boring
1592             };
1593             if let Err(terr) =
1594                 self.sub_types(op_arg_ty, fn_arg, term_location.to_locations(), category)
1595             {
1596                 span_mirbug!(
1597                     self,
1598                     term,
1599                     "bad arg #{:?} ({:?} <- {:?}): {:?}",
1600                     n,
1601                     fn_arg,
1602                     op_arg_ty,
1603                     terr
1604                 );
1605             }
1606         }
1607     }
1608
1609     fn check_iscleanup(&mut self, mir: &Mir<'tcx>, block_data: &BasicBlockData<'tcx>) {
1610         let is_cleanup = block_data.is_cleanup;
1611         self.last_span = block_data.terminator().source_info.span;
1612         match block_data.terminator().kind {
1613             TerminatorKind::Goto { target } => {
1614                 self.assert_iscleanup(mir, block_data, target, is_cleanup)
1615             }
1616             TerminatorKind::SwitchInt { ref targets, .. } => for target in targets {
1617                 self.assert_iscleanup(mir, block_data, *target, is_cleanup);
1618             },
1619             TerminatorKind::Resume => if !is_cleanup {
1620                 span_mirbug!(self, block_data, "resume on non-cleanup block!")
1621             },
1622             TerminatorKind::Abort => if !is_cleanup {
1623                 span_mirbug!(self, block_data, "abort on non-cleanup block!")
1624             },
1625             TerminatorKind::Return => if is_cleanup {
1626                 span_mirbug!(self, block_data, "return on cleanup block")
1627             },
1628             TerminatorKind::GeneratorDrop { .. } => if is_cleanup {
1629                 span_mirbug!(self, block_data, "generator_drop in cleanup block")
1630             },
1631             TerminatorKind::Yield { resume, drop, .. } => {
1632                 if is_cleanup {
1633                     span_mirbug!(self, block_data, "yield in cleanup block")
1634                 }
1635                 self.assert_iscleanup(mir, block_data, resume, is_cleanup);
1636                 if let Some(drop) = drop {
1637                     self.assert_iscleanup(mir, block_data, drop, is_cleanup);
1638                 }
1639             }
1640             TerminatorKind::Unreachable => {}
1641             TerminatorKind::Drop { target, unwind, .. }
1642             | TerminatorKind::DropAndReplace { target, unwind, .. }
1643             | TerminatorKind::Assert {
1644                 target,
1645                 cleanup: unwind,
1646                 ..
1647             } => {
1648                 self.assert_iscleanup(mir, block_data, target, is_cleanup);
1649                 if let Some(unwind) = unwind {
1650                     if is_cleanup {
1651                         span_mirbug!(self, block_data, "unwind on cleanup block")
1652                     }
1653                     self.assert_iscleanup(mir, block_data, unwind, true);
1654                 }
1655             }
1656             TerminatorKind::Call {
1657                 ref destination,
1658                 cleanup,
1659                 ..
1660             } => {
1661                 if let &Some((_, target)) = destination {
1662                     self.assert_iscleanup(mir, block_data, target, is_cleanup);
1663                 }
1664                 if let Some(cleanup) = cleanup {
1665                     if is_cleanup {
1666                         span_mirbug!(self, block_data, "cleanup on cleanup block")
1667                     }
1668                     self.assert_iscleanup(mir, block_data, cleanup, true);
1669                 }
1670             }
1671             TerminatorKind::FalseEdges {
1672                 real_target,
1673                 ref imaginary_targets,
1674             } => {
1675                 self.assert_iscleanup(mir, block_data, real_target, is_cleanup);
1676                 for target in imaginary_targets {
1677                     self.assert_iscleanup(mir, block_data, *target, is_cleanup);
1678                 }
1679             }
1680             TerminatorKind::FalseUnwind {
1681                 real_target,
1682                 unwind,
1683             } => {
1684                 self.assert_iscleanup(mir, block_data, real_target, is_cleanup);
1685                 if let Some(unwind) = unwind {
1686                     if is_cleanup {
1687                         span_mirbug!(
1688                             self,
1689                             block_data,
1690                             "cleanup in cleanup block via false unwind"
1691                         );
1692                     }
1693                     self.assert_iscleanup(mir, block_data, unwind, true);
1694                 }
1695             }
1696         }
1697     }
1698
1699     fn assert_iscleanup(
1700         &mut self,
1701         mir: &Mir<'tcx>,
1702         ctxt: &dyn fmt::Debug,
1703         bb: BasicBlock,
1704         iscleanuppad: bool,
1705     ) {
1706         if mir[bb].is_cleanup != iscleanuppad {
1707             span_mirbug!(
1708                 self,
1709                 ctxt,
1710                 "cleanuppad mismatch: {:?} should be {:?}",
1711                 bb,
1712                 iscleanuppad
1713             );
1714         }
1715     }
1716
1717     fn check_local(&mut self, mir: &Mir<'tcx>, local: Local, local_decl: &LocalDecl<'tcx>) {
1718         match mir.local_kind(local) {
1719             LocalKind::ReturnPointer | LocalKind::Arg => {
1720                 // return values of normal functions are required to be
1721                 // sized by typeck, but return values of ADT constructors are
1722                 // not because we don't include a `Self: Sized` bounds on them.
1723                 //
1724                 // Unbound parts of arguments were never required to be Sized
1725                 // - maybe we should make that a warning.
1726                 return;
1727             }
1728             LocalKind::Var | LocalKind::Temp => {}
1729         }
1730
1731         // When `#![feature(unsized_locals)]` is enabled, only function calls
1732         // and nullary ops are checked in `check_call_dest`.
1733         if !self.tcx().features().unsized_locals {
1734             let span = local_decl.source_info.span;
1735             let ty = local_decl.ty;
1736             self.ensure_place_sized(ty, span);
1737         }
1738     }
1739
1740     fn ensure_place_sized(&mut self, ty: Ty<'tcx>, span: Span) {
1741         let tcx = self.tcx();
1742
1743         // Erase the regions from `ty` to get a global type.  The
1744         // `Sized` bound in no way depends on precise regions, so this
1745         // shouldn't affect `is_sized`.
1746         let gcx = tcx.global_tcx();
1747         let erased_ty = gcx.lift(&tcx.erase_regions(&ty)).unwrap();
1748         if !erased_ty.is_sized(gcx.at(span), self.param_env) {
1749             // in current MIR construction, all non-control-flow rvalue
1750             // expressions evaluate through `as_temp` or `into` a return
1751             // slot or local, so to find all unsized rvalues it is enough
1752             // to check all temps, return slots and locals.
1753             if let None = self.reported_errors.replace((ty, span)) {
1754                 let mut diag = struct_span_err!(
1755                     self.tcx().sess,
1756                     span,
1757                     E0161,
1758                     "cannot move a value of type {0}: the size of {0} \
1759                      cannot be statically determined",
1760                     ty
1761                 );
1762
1763                 // While this is located in `nll::typeck` this error is not
1764                 // an NLL error, it's a required check to prevent creation
1765                 // of unsized rvalues in certain cases:
1766                 // * operand of a box expression
1767                 // * callee in a call expression
1768                 diag.emit();
1769             }
1770         }
1771     }
1772
1773     fn aggregate_field_ty(
1774         &mut self,
1775         ak: &AggregateKind<'tcx>,
1776         field_index: usize,
1777         location: Location,
1778     ) -> Result<Ty<'tcx>, FieldAccessError> {
1779         let tcx = self.tcx();
1780
1781         match *ak {
1782             AggregateKind::Adt(def, variant_index, substs, _, active_field_index) => {
1783                 let variant = &def.variants[variant_index];
1784                 let adj_field_index = active_field_index.unwrap_or(field_index);
1785                 if let Some(field) = variant.fields.get(adj_field_index) {
1786                     Ok(self.normalize(field.ty(tcx, substs), location))
1787                 } else {
1788                     Err(FieldAccessError::OutOfRange {
1789                         field_count: variant.fields.len(),
1790                     })
1791                 }
1792             }
1793             AggregateKind::Closure(def_id, substs) => {
1794                 match substs.upvar_tys(def_id, tcx).nth(field_index) {
1795                     Some(ty) => Ok(ty),
1796                     None => Err(FieldAccessError::OutOfRange {
1797                         field_count: substs.upvar_tys(def_id, tcx).count(),
1798                     }),
1799                 }
1800             }
1801             AggregateKind::Generator(def_id, substs, _) => {
1802                 // Try pre-transform fields first (upvars and current state)
1803                 if let Some(ty) = substs.pre_transforms_tys(def_id, tcx).nth(field_index) {
1804                     Ok(ty)
1805                 } else {
1806                     // Then try `field_tys` which contains all the fields, but it
1807                     // requires the final optimized MIR.
1808                     match substs.field_tys(def_id, tcx).nth(field_index) {
1809                         Some(ty) => Ok(ty),
1810                         None => Err(FieldAccessError::OutOfRange {
1811                             field_count: substs.field_tys(def_id, tcx).count(),
1812                         }),
1813                     }
1814                 }
1815             }
1816             AggregateKind::Array(ty) => Ok(ty),
1817             AggregateKind::Tuple => {
1818                 unreachable!("This should have been covered in check_rvalues");
1819             }
1820         }
1821     }
1822
1823     fn check_rvalue(&mut self, mir: &Mir<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
1824         let tcx = self.tcx();
1825
1826         match rvalue {
1827             Rvalue::Aggregate(ak, ops) => {
1828                 self.check_aggregate_rvalue(mir, rvalue, ak, ops, location)
1829             }
1830
1831             Rvalue::Repeat(operand, len) => if *len > 1 {
1832                 let operand_ty = operand.ty(mir, tcx);
1833
1834                 let trait_ref = ty::TraitRef {
1835                     def_id: tcx.lang_items().copy_trait().unwrap(),
1836                     substs: tcx.mk_substs_trait(operand_ty, &[]),
1837                 };
1838
1839                 self.prove_trait_ref(
1840                     trait_ref,
1841                     location.to_locations(),
1842                     ConstraintCategory::CopyBound,
1843                 );
1844             },
1845
1846             Rvalue::NullaryOp(_, ty) => {
1847                 // Even with unsized locals cannot box an unsized value.
1848                 if self.tcx().features().unsized_locals {
1849                     let span = mir.source_info(location).span;
1850                     self.ensure_place_sized(ty, span);
1851                 }
1852
1853                 let trait_ref = ty::TraitRef {
1854                     def_id: tcx.lang_items().sized_trait().unwrap(),
1855                     substs: tcx.mk_substs_trait(ty, &[]),
1856                 };
1857
1858                 self.prove_trait_ref(
1859                     trait_ref,
1860                     location.to_locations(),
1861                     ConstraintCategory::SizedBound,
1862                 );
1863             }
1864
1865             Rvalue::Cast(cast_kind, op, ty) => {
1866                 match cast_kind {
1867                     CastKind::ReifyFnPointer => {
1868                         let fn_sig = op.ty(mir, tcx).fn_sig(tcx);
1869
1870                         // The type that we see in the fcx is like
1871                         // `foo::<'a, 'b>`, where `foo` is the path to a
1872                         // function definition. When we extract the
1873                         // signature, it comes from the `fn_sig` query,
1874                         // and hence may contain unnormalized results.
1875                         let fn_sig = self.normalize(fn_sig, location);
1876
1877                         let ty_fn_ptr_from = tcx.mk_fn_ptr(fn_sig);
1878
1879                         if let Err(terr) = self.eq_types(
1880                             ty_fn_ptr_from,
1881                             ty,
1882                             location.to_locations(),
1883                             ConstraintCategory::Cast,
1884                         ) {
1885                             span_mirbug!(
1886                                 self,
1887                                 rvalue,
1888                                 "equating {:?} with {:?} yields {:?}",
1889                                 ty_fn_ptr_from,
1890                                 ty,
1891                                 terr
1892                             );
1893                         }
1894                     }
1895
1896                     CastKind::ClosureFnPointer => {
1897                         let sig = match op.ty(mir, tcx).sty {
1898                             ty::Closure(def_id, substs) => {
1899                                 substs.closure_sig_ty(def_id, tcx).fn_sig(tcx)
1900                             }
1901                             _ => bug!(),
1902                         };
1903                         let ty_fn_ptr_from = tcx.coerce_closure_fn_ty(sig);
1904
1905                         if let Err(terr) = self.eq_types(
1906                             ty_fn_ptr_from,
1907                             ty,
1908                             location.to_locations(),
1909                             ConstraintCategory::Cast,
1910                         ) {
1911                             span_mirbug!(
1912                                 self,
1913                                 rvalue,
1914                                 "equating {:?} with {:?} yields {:?}",
1915                                 ty_fn_ptr_from,
1916                                 ty,
1917                                 terr
1918                             );
1919                         }
1920                     }
1921
1922                     CastKind::UnsafeFnPointer => {
1923                         let fn_sig = op.ty(mir, tcx).fn_sig(tcx);
1924
1925                         // The type that we see in the fcx is like
1926                         // `foo::<'a, 'b>`, where `foo` is the path to a
1927                         // function definition. When we extract the
1928                         // signature, it comes from the `fn_sig` query,
1929                         // and hence may contain unnormalized results.
1930                         let fn_sig = self.normalize(fn_sig, location);
1931
1932                         let ty_fn_ptr_from = tcx.safe_to_unsafe_fn_ty(fn_sig);
1933
1934                         if let Err(terr) = self.eq_types(
1935                             ty_fn_ptr_from,
1936                             ty,
1937                             location.to_locations(),
1938                             ConstraintCategory::Cast,
1939                         ) {
1940                             span_mirbug!(
1941                                 self,
1942                                 rvalue,
1943                                 "equating {:?} with {:?} yields {:?}",
1944                                 ty_fn_ptr_from,
1945                                 ty,
1946                                 terr
1947                             );
1948                         }
1949                     }
1950
1951                     CastKind::Unsize => {
1952                         let &ty = ty;
1953                         let trait_ref = ty::TraitRef {
1954                             def_id: tcx.lang_items().coerce_unsized_trait().unwrap(),
1955                             substs: tcx.mk_substs_trait(op.ty(mir, tcx), &[ty.into()]),
1956                         };
1957
1958                         self.prove_trait_ref(
1959                             trait_ref,
1960                             location.to_locations(),
1961                             ConstraintCategory::Cast,
1962                         );
1963                     }
1964
1965                     CastKind::Misc => {}
1966                 }
1967             }
1968
1969             Rvalue::Ref(region, _borrow_kind, borrowed_place) => {
1970                 self.add_reborrow_constraint(location, region, borrowed_place);
1971             }
1972
1973             // FIXME: These other cases have to be implemented in future PRs
1974             Rvalue::Use(..)
1975             | Rvalue::Len(..)
1976             | Rvalue::BinaryOp(..)
1977             | Rvalue::CheckedBinaryOp(..)
1978             | Rvalue::UnaryOp(..)
1979             | Rvalue::Discriminant(..) => {}
1980         }
1981     }
1982
1983     /// If this rvalue supports a user-given type annotation, then
1984     /// extract and return it. This represents the final type of the
1985     /// rvalue and will be unified with the inferred type.
1986     fn rvalue_user_ty(&self, rvalue: &Rvalue<'tcx>) -> Option<UserTypeAnnotation<'tcx>> {
1987         match rvalue {
1988             Rvalue::Use(_)
1989             | Rvalue::Repeat(..)
1990             | Rvalue::Ref(..)
1991             | Rvalue::Len(..)
1992             | Rvalue::Cast(..)
1993             | Rvalue::BinaryOp(..)
1994             | Rvalue::CheckedBinaryOp(..)
1995             | Rvalue::NullaryOp(..)
1996             | Rvalue::UnaryOp(..)
1997             | Rvalue::Discriminant(..) => None,
1998
1999             Rvalue::Aggregate(aggregate, _) => match **aggregate {
2000                 AggregateKind::Adt(_, _, _, user_ty, _) => user_ty,
2001                 AggregateKind::Array(_) => None,
2002                 AggregateKind::Tuple => None,
2003                 AggregateKind::Closure(_, _) => None,
2004                 AggregateKind::Generator(_, _, _) => None,
2005             },
2006         }
2007     }
2008
2009     fn check_aggregate_rvalue(
2010         &mut self,
2011         mir: &Mir<'tcx>,
2012         rvalue: &Rvalue<'tcx>,
2013         aggregate_kind: &AggregateKind<'tcx>,
2014         operands: &[Operand<'tcx>],
2015         location: Location,
2016     ) {
2017         let tcx = self.tcx();
2018
2019         self.prove_aggregate_predicates(aggregate_kind, location);
2020
2021         if *aggregate_kind == AggregateKind::Tuple {
2022             // tuple rvalue field type is always the type of the op. Nothing to check here.
2023             return;
2024         }
2025
2026         for (i, operand) in operands.iter().enumerate() {
2027             let field_ty = match self.aggregate_field_ty(aggregate_kind, i, location) {
2028                 Ok(field_ty) => field_ty,
2029                 Err(FieldAccessError::OutOfRange { field_count }) => {
2030                     span_mirbug!(
2031                         self,
2032                         rvalue,
2033                         "accessed field #{} but variant only has {}",
2034                         i,
2035                         field_count
2036                     );
2037                     continue;
2038                 }
2039             };
2040             let operand_ty = operand.ty(mir, tcx);
2041
2042             if let Err(terr) = self.sub_types(
2043                 operand_ty,
2044                 field_ty,
2045                 location.to_locations(),
2046                 ConstraintCategory::Boring,
2047             ) {
2048                 span_mirbug!(
2049                     self,
2050                     rvalue,
2051                     "{:?} is not a subtype of {:?}: {:?}",
2052                     operand_ty,
2053                     field_ty,
2054                     terr
2055                 );
2056             }
2057         }
2058     }
2059
2060     /// Add the constraints that arise from a borrow expression `&'a P` at the location `L`.
2061     ///
2062     /// # Parameters
2063     ///
2064     /// - `location`: the location `L` where the borrow expression occurs
2065     /// - `borrow_region`: the region `'a` associated with the borrow
2066     /// - `borrowed_place`: the place `P` being borrowed
2067     fn add_reborrow_constraint(
2068         &mut self,
2069         location: Location,
2070         borrow_region: ty::Region<'tcx>,
2071         borrowed_place: &Place<'tcx>,
2072     ) {
2073         // These constraints are only meaningful during borrowck:
2074         let BorrowCheckContext {
2075             borrow_set,
2076             location_table,
2077             all_facts,
2078             constraints,
2079             ..
2080         } = match self.borrowck_context {
2081             Some(ref mut borrowck_context) => borrowck_context,
2082             None => return,
2083         };
2084
2085         // In Polonius mode, we also push a `borrow_region` fact
2086         // linking the loan to the region (in some cases, though,
2087         // there is no loan associated with this borrow expression --
2088         // that occurs when we are borrowing an unsafe place, for
2089         // example).
2090         if let Some(all_facts) = all_facts {
2091             if let Some(borrow_index) = borrow_set.location_map.get(&location) {
2092                 let region_vid = borrow_region.to_region_vid();
2093                 all_facts.borrow_region.push((
2094                     region_vid,
2095                     *borrow_index,
2096                     location_table.mid_index(location),
2097                 ));
2098             }
2099         }
2100
2101         // If we are reborrowing the referent of another reference, we
2102         // need to add outlives relationships. In a case like `&mut
2103         // *p`, where the `p` has type `&'b mut Foo`, for example, we
2104         // need to ensure that `'b: 'a`.
2105
2106         let mut borrowed_place = borrowed_place;
2107
2108         debug!(
2109             "add_reborrow_constraint({:?}, {:?}, {:?})",
2110             location, borrow_region, borrowed_place
2111         );
2112         while let Place::Projection(box PlaceProjection { base, elem }) = borrowed_place {
2113             debug!("add_reborrow_constraint - iteration {:?}", borrowed_place);
2114
2115             match *elem {
2116                 ProjectionElem::Deref => {
2117                     let tcx = self.infcx.tcx;
2118                     let base_ty = base.ty(self.mir, tcx).to_ty(tcx);
2119
2120                     debug!("add_reborrow_constraint - base_ty = {:?}", base_ty);
2121                     match base_ty.sty {
2122                         ty::Ref(ref_region, _, mutbl) => {
2123                             constraints.outlives_constraints.push(OutlivesConstraint {
2124                                 sup: ref_region.to_region_vid(),
2125                                 sub: borrow_region.to_region_vid(),
2126                                 locations: location.to_locations(),
2127                                 category: ConstraintCategory::Boring,
2128                             });
2129
2130                             match mutbl {
2131                                 hir::Mutability::MutImmutable => {
2132                                     // Immutable reference. We don't need the base
2133                                     // to be valid for the entire lifetime of
2134                                     // the borrow.
2135                                     break;
2136                                 }
2137                                 hir::Mutability::MutMutable => {
2138                                     // Mutable reference. We *do* need the base
2139                                     // to be valid, because after the base becomes
2140                                     // invalid, someone else can use our mutable deref.
2141
2142                                     // This is in order to make the following function
2143                                     // illegal:
2144                                     // ```
2145                                     // fn unsafe_deref<'a, 'b>(x: &'a &'b mut T) -> &'b mut T {
2146                                     //     &mut *x
2147                                     // }
2148                                     // ```
2149                                     //
2150                                     // As otherwise you could clone `&mut T` using the
2151                                     // following function:
2152                                     // ```
2153                                     // fn bad(x: &mut T) -> (&mut T, &mut T) {
2154                                     //     let my_clone = unsafe_deref(&'a x);
2155                                     //     ENDREGION 'a;
2156                                     //     (my_clone, x)
2157                                     // }
2158                                     // ```
2159                                 }
2160                             }
2161                         }
2162                         ty::RawPtr(..) => {
2163                             // deref of raw pointer, guaranteed to be valid
2164                             break;
2165                         }
2166                         ty::Adt(def, _) if def.is_box() => {
2167                             // deref of `Box`, need the base to be valid - propagate
2168                         }
2169                         _ => bug!("unexpected deref ty {:?} in {:?}", base_ty, borrowed_place),
2170                     }
2171                 }
2172                 ProjectionElem::Field(..)
2173                 | ProjectionElem::Downcast(..)
2174                 | ProjectionElem::Index(..)
2175                 | ProjectionElem::ConstantIndex { .. }
2176                 | ProjectionElem::Subslice { .. } => {
2177                     // other field access
2178                 }
2179             }
2180
2181             // The "propagate" case. We need to check that our base is valid
2182             // for the borrow's lifetime.
2183             borrowed_place = base;
2184         }
2185     }
2186
2187     fn prove_aggregate_predicates(
2188         &mut self,
2189         aggregate_kind: &AggregateKind<'tcx>,
2190         location: Location,
2191     ) {
2192         let tcx = self.tcx();
2193
2194         debug!(
2195             "prove_aggregate_predicates(aggregate_kind={:?}, location={:?})",
2196             aggregate_kind, location
2197         );
2198
2199         let instantiated_predicates = match aggregate_kind {
2200             AggregateKind::Adt(def, _, substs, _, _) => {
2201                 tcx.predicates_of(def.did).instantiate(tcx, substs)
2202             }
2203
2204             // For closures, we have some **extra requirements** we
2205             //
2206             // have to check. In particular, in their upvars and
2207             // signatures, closures often reference various regions
2208             // from the surrounding function -- we call those the
2209             // closure's free regions. When we borrow-check (and hence
2210             // region-check) closures, we may find that the closure
2211             // requires certain relationships between those free
2212             // regions. However, because those free regions refer to
2213             // portions of the CFG of their caller, the closure is not
2214             // in a position to verify those relationships. In that
2215             // case, the requirements get "propagated" to us, and so
2216             // we have to solve them here where we instantiate the
2217             // closure.
2218             //
2219             // Despite the opacity of the previous parapgrah, this is
2220             // actually relatively easy to understand in terms of the
2221             // desugaring. A closure gets desugared to a struct, and
2222             // these extra requirements are basically like where
2223             // clauses on the struct.
2224             AggregateKind::Closure(def_id, ty::ClosureSubsts { substs })
2225             | AggregateKind::Generator(def_id, ty::GeneratorSubsts { substs }, _) => {
2226                 self.prove_closure_bounds(tcx, *def_id, substs, location)
2227             }
2228
2229             AggregateKind::Array(_) | AggregateKind::Tuple => ty::InstantiatedPredicates::empty(),
2230         };
2231
2232         self.normalize_and_prove_instantiated_predicates(
2233             instantiated_predicates,
2234             location.to_locations(),
2235         );
2236     }
2237
2238     fn prove_closure_bounds(
2239         &mut self,
2240         tcx: TyCtxt<'a, 'gcx, 'tcx>,
2241         def_id: DefId,
2242         substs: &'tcx Substs<'tcx>,
2243         location: Location,
2244     ) -> ty::InstantiatedPredicates<'tcx> {
2245         if let Some(closure_region_requirements) = tcx.mir_borrowck(def_id).closure_requirements {
2246             let closure_constraints =
2247                 closure_region_requirements.apply_requirements(tcx, location, def_id, substs);
2248
2249             if let Some(ref mut borrowck_context) = self.borrowck_context {
2250                 let bounds_mapping = closure_constraints
2251                     .iter()
2252                     .enumerate()
2253                     .filter_map(|(idx, constraint)| {
2254                         let ty::OutlivesPredicate(k1, r2) =
2255                             constraint.no_late_bound_regions().unwrap_or_else(|| {
2256                                 bug!("query_constraint {:?} contained bound regions", constraint,);
2257                             });
2258
2259                         match k1.unpack() {
2260                             UnpackedKind::Lifetime(r1) => {
2261                                 // constraint is r1: r2
2262                                 let r1_vid = borrowck_context.universal_regions.to_region_vid(r1);
2263                                 let r2_vid = borrowck_context.universal_regions.to_region_vid(r2);
2264                                 let outlives_requirements =
2265                                     &closure_region_requirements.outlives_requirements[idx];
2266                                 Some((
2267                                     (r1_vid, r2_vid),
2268                                     (
2269                                         outlives_requirements.category,
2270                                         outlives_requirements.blame_span,
2271                                     ),
2272                                 ))
2273                             }
2274                             UnpackedKind::Type(_) => None,
2275                         }
2276                     })
2277                     .collect();
2278
2279                 let existing = borrowck_context
2280                     .constraints
2281                     .closure_bounds_mapping
2282                     .insert(location, bounds_mapping);
2283                 assert!(
2284                     existing.is_none(),
2285                     "Multiple closures at the same location."
2286                 );
2287             }
2288
2289             self.push_region_constraints(
2290                 location.to_locations(),
2291                 ConstraintCategory::ClosureBounds,
2292                 &closure_constraints,
2293             );
2294         }
2295
2296         tcx.predicates_of(def_id).instantiate(tcx, substs)
2297     }
2298
2299     fn prove_trait_ref(
2300         &mut self,
2301         trait_ref: ty::TraitRef<'tcx>,
2302         locations: Locations,
2303         category: ConstraintCategory,
2304     ) {
2305         self.prove_predicates(
2306             Some(ty::Predicate::Trait(
2307                 trait_ref.to_poly_trait_ref().to_poly_trait_predicate(),
2308             )),
2309             locations,
2310             category,
2311         );
2312     }
2313
2314     fn normalize_and_prove_instantiated_predicates(
2315         &mut self,
2316         instantiated_predicates: ty::InstantiatedPredicates<'tcx>,
2317         locations: Locations,
2318     ) {
2319         for predicate in instantiated_predicates.predicates {
2320             let predicate = self.normalize(predicate, locations);
2321             self.prove_predicate(predicate, locations, ConstraintCategory::Boring);
2322         }
2323     }
2324
2325     fn prove_predicates(
2326         &mut self,
2327         predicates: impl IntoIterator<Item = ty::Predicate<'tcx>>,
2328         locations: Locations,
2329         category: ConstraintCategory,
2330     ) {
2331         for predicate in predicates {
2332             debug!(
2333                 "prove_predicates(predicate={:?}, locations={:?})",
2334                 predicate, locations,
2335             );
2336
2337             self.prove_predicate(predicate, locations, category);
2338         }
2339     }
2340
2341     fn prove_predicate(
2342         &mut self,
2343         predicate: ty::Predicate<'tcx>,
2344         locations: Locations,
2345         category: ConstraintCategory,
2346     ) {
2347         debug!(
2348             "prove_predicate(predicate={:?}, location={:?})",
2349             predicate, locations,
2350         );
2351
2352         let param_env = self.param_env;
2353         self.fully_perform_op(
2354             locations,
2355             category,
2356             param_env.and(type_op::prove_predicate::ProvePredicate::new(predicate)),
2357         ).unwrap_or_else(|NoSolution| {
2358             span_mirbug!(self, NoSolution, "could not prove {:?}", predicate);
2359         })
2360     }
2361
2362     fn typeck_mir(&mut self, mir: &Mir<'tcx>) {
2363         self.last_span = mir.span;
2364         debug!("run_on_mir: {:?}", mir.span);
2365
2366         for (local, local_decl) in mir.local_decls.iter_enumerated() {
2367             self.check_local(mir, local, local_decl);
2368         }
2369
2370         for (block, block_data) in mir.basic_blocks().iter_enumerated() {
2371             let mut location = Location {
2372                 block,
2373                 statement_index: 0,
2374             };
2375             for stmt in &block_data.statements {
2376                 if !stmt.source_info.span.is_dummy() {
2377                     self.last_span = stmt.source_info.span;
2378                 }
2379                 self.check_stmt(mir, stmt, location);
2380                 location.statement_index += 1;
2381             }
2382
2383             self.check_terminator(mir, block_data.terminator(), location);
2384             self.check_iscleanup(mir, block_data);
2385         }
2386     }
2387
2388     fn normalize<T>(&mut self, value: T, location: impl NormalizeLocation) -> T
2389     where
2390         T: type_op::normalize::Normalizable<'gcx, 'tcx> + Copy,
2391     {
2392         debug!("normalize(value={:?}, location={:?})", value, location);
2393         let param_env = self.param_env;
2394         self.fully_perform_op(
2395             location.to_locations(),
2396             ConstraintCategory::Boring,
2397             param_env.and(type_op::normalize::Normalize::new(value)),
2398         ).unwrap_or_else(|NoSolution| {
2399             span_mirbug!(self, NoSolution, "failed to normalize `{:?}`", value);
2400             value
2401         })
2402     }
2403 }
2404
2405 pub struct TypeckMir;
2406
2407 impl MirPass for TypeckMir {
2408     fn run_pass<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, src: MirSource, mir: &mut Mir<'tcx>) {
2409         let def_id = src.def_id;
2410         debug!("run_pass: {:?}", def_id);
2411
2412         // When NLL is enabled, the borrow checker runs the typeck
2413         // itself, so we don't need this MIR pass anymore.
2414         if tcx.use_mir_borrowck() {
2415             return;
2416         }
2417
2418         if tcx.sess.err_count() > 0 {
2419             // compiling a broken program can obviously result in a
2420             // broken MIR, so try not to report duplicate errors.
2421             return;
2422         }
2423
2424         if tcx.is_struct_constructor(def_id) {
2425             // We just assume that the automatically generated struct constructors are
2426             // correct. See the comment in the `mir_borrowck` implementation for an
2427             // explanation why we need this.
2428             return;
2429         }
2430
2431         let param_env = tcx.param_env(def_id);
2432         tcx.infer_ctxt().enter(|infcx| {
2433             type_check_internal(
2434                 &infcx,
2435                 def_id,
2436                 param_env,
2437                 mir,
2438                 &vec![],
2439                 None,
2440                 None,
2441                 None,
2442                 |_| (),
2443             );
2444
2445             // For verification purposes, we just ignore the resulting
2446             // region constraint sets. Not our problem. =)
2447         });
2448     }
2449 }
2450
2451 trait NormalizeLocation: fmt::Debug + Copy {
2452     fn to_locations(self) -> Locations;
2453 }
2454
2455 impl NormalizeLocation for Locations {
2456     fn to_locations(self) -> Locations {
2457         self
2458     }
2459 }
2460
2461 impl NormalizeLocation for Location {
2462     fn to_locations(self) -> Locations {
2463         Locations::Single(self)
2464     }
2465 }
2466
2467 #[derive(Debug, Default)]
2468 struct ObligationAccumulator<'tcx> {
2469     obligations: PredicateObligations<'tcx>,
2470 }
2471
2472 impl<'tcx> ObligationAccumulator<'tcx> {
2473     fn add<T>(&mut self, value: InferOk<'tcx, T>) -> T {
2474         let InferOk { value, obligations } = value;
2475         self.obligations.extend(obligations);
2476         value
2477     }
2478
2479     fn into_vec(self) -> PredicateObligations<'tcx> {
2480         self.obligations
2481     }
2482 }