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::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, UserSubsts, UserSelfTy};
  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: FxHashMap(),
 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: FxHashSet(),
 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
1023                     // There may be type variables in `substs` and hence
1024                     // in `impl_self_ty`, but they should all have been
1025                     // resolved to some fixed value during the first call
1026                     // to `relate`, above. Therefore, if we use
1027                     // `resolve_type_vars_if_possible` we should get to
1028                     // something without type variables. This is important
1029                     // because the `b` type in `relate_with_variance`
1030                     // below is not permitted to have inference variables.
1031                     let impl_self_ty = self.infcx.resolve_type_vars_if_possible(&impl_self_ty);
1032                     assert!(!impl_self_ty.has_infer_types());
1033
1034                     self.eq_types(self_ty, impl_self_ty, locations, category)?;
1035                 }
1036
1037                 self.prove_predicate(ty::Predicate::WellFormed(ty), locations, category);
1038             }
1039         }
1040
1041         Ok(())
1042     }
1043
1044     fn eq_opaque_type_and_type(
1045         &mut self,
1046         revealed_ty: Ty<'tcx>,
1047         anon_ty: Ty<'tcx>,
1048         anon_owner_def_id: DefId,
1049         locations: Locations,
1050         category: ConstraintCategory,
1051     ) -> Fallible<()> {
1052         debug!(
1053             "eq_opaque_type_and_type( \
1054              revealed_ty={:?}, \
1055              anon_ty={:?})",
1056             revealed_ty, anon_ty
1057         );
1058         let infcx = self.infcx;
1059         let tcx = infcx.tcx;
1060         let param_env = self.param_env;
1061         debug!("eq_opaque_type_and_type: mir_def_id={:?}", self.mir_def_id);
1062         let opaque_type_map = self.fully_perform_op(
1063             locations,
1064             category,
1065             CustomTypeOp::new(
1066                 |infcx| {
1067                     let mut obligations = ObligationAccumulator::default();
1068
1069                     let dummy_body_id = ObligationCause::dummy().body_id;
1070                     let (output_ty, opaque_type_map) =
1071                         obligations.add(infcx.instantiate_opaque_types(
1072                             anon_owner_def_id,
1073                             dummy_body_id,
1074                             param_env,
1075                             &anon_ty,
1076                         ));
1077                     debug!(
1078                         "eq_opaque_type_and_type: \
1079                          instantiated output_ty={:?} \
1080                          opaque_type_map={:#?} \
1081                          revealed_ty={:?}",
1082                         output_ty, opaque_type_map, revealed_ty
1083                     );
1084                     obligations.add(infcx
1085                         .at(&ObligationCause::dummy(), param_env)
1086                         .eq(output_ty, revealed_ty)?);
1087
1088                     for (&opaque_def_id, opaque_decl) in &opaque_type_map {
1089                         let opaque_defn_ty = tcx.type_of(opaque_def_id);
1090                         let opaque_defn_ty = opaque_defn_ty.subst(tcx, opaque_decl.substs);
1091                         let opaque_defn_ty = renumber::renumber_regions(infcx, &opaque_defn_ty);
1092                         debug!(
1093                             "eq_opaque_type_and_type: concrete_ty={:?}={:?} opaque_defn_ty={:?}",
1094                             opaque_decl.concrete_ty,
1095                             infcx.resolve_type_vars_if_possible(&opaque_decl.concrete_ty),
1096                             opaque_defn_ty
1097                         );
1098                         obligations.add(infcx
1099                             .at(&ObligationCause::dummy(), param_env)
1100                             .eq(opaque_decl.concrete_ty, opaque_defn_ty)?);
1101                     }
1102
1103                     debug!("eq_opaque_type_and_type: equated");
1104
1105                     Ok(InferOk {
1106                         value: Some(opaque_type_map),
1107                         obligations: obligations.into_vec(),
1108                     })
1109                 },
1110                 || "input_output".to_string(),
1111             ),
1112         )?;
1113
1114         let universal_region_relations = match self.universal_region_relations {
1115             Some(rel) => rel,
1116             None => return Ok(()),
1117         };
1118
1119         // Finally, if we instantiated the anon types successfully, we
1120         // have to solve any bounds (e.g., `-> impl Iterator` needs to
1121         // prove that `T: Iterator` where `T` is the type we
1122         // instantiated it with).
1123         if let Some(opaque_type_map) = opaque_type_map {
1124             for (opaque_def_id, opaque_decl) in opaque_type_map {
1125                 self.fully_perform_op(
1126                     locations,
1127                     ConstraintCategory::OpaqueType,
1128                     CustomTypeOp::new(
1129                         |_cx| {
1130                             infcx.constrain_opaque_type(
1131                                 opaque_def_id,
1132                                 &opaque_decl,
1133                                 universal_region_relations,
1134                             );
1135                             Ok(InferOk {
1136                                 value: (),
1137                                 obligations: vec![],
1138                             })
1139                         },
1140                         || "opaque_type_map".to_string(),
1141                     ),
1142                 )?;
1143             }
1144         }
1145         Ok(())
1146     }
1147
1148     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
1149         self.infcx.tcx
1150     }
1151
1152     fn check_stmt(&mut self, mir: &Mir<'tcx>, stmt: &Statement<'tcx>, location: Location) {
1153         debug!("check_stmt: {:?}", stmt);
1154         let tcx = self.tcx();
1155         match stmt.kind {
1156             StatementKind::Assign(ref place, ref rv) => {
1157                 // Assignments to temporaries are not "interesting";
1158                 // they are not caused by the user, but rather artifacts
1159                 // of lowering. Assignments to other sorts of places *are* interesting
1160                 // though.
1161                 let category = match *place {
1162                     Place::Local(RETURN_PLACE) => ConstraintCategory::Return,
1163                     Place::Local(l) if !mir.local_decls[l].is_user_variable.is_some() => {
1164                         ConstraintCategory::Boring
1165                     }
1166                     _ => ConstraintCategory::Assignment,
1167                 };
1168
1169                 let place_ty = place.ty(mir, tcx).to_ty(tcx);
1170                 let rv_ty = rv.ty(mir, tcx);
1171                 if let Err(terr) =
1172                     self.sub_types_or_anon(rv_ty, place_ty, location.to_locations(), category)
1173                 {
1174                     span_mirbug!(
1175                         self,
1176                         stmt,
1177                         "bad assignment ({:?} = {:?}): {:?}",
1178                         place_ty,
1179                         rv_ty,
1180                         terr
1181                     );
1182                 }
1183
1184                 if let Some(user_ty) = self.rvalue_user_ty(rv) {
1185                     if let Err(terr) = self.relate_type_and_user_type(
1186                         rv_ty,
1187                         ty::Variance::Invariant,
1188                         user_ty,
1189                         location.to_locations(),
1190                         ConstraintCategory::Boring,
1191                     ) {
1192                         span_mirbug!(
1193                             self,
1194                             stmt,
1195                             "bad user type on rvalue ({:?} = {:?}): {:?}",
1196                             user_ty,
1197                             rv_ty,
1198                             terr
1199                         );
1200                     }
1201                 }
1202
1203                 self.check_rvalue(mir, rv, location);
1204                 if !self.tcx().features().unsized_locals {
1205                     let trait_ref = ty::TraitRef {
1206                         def_id: tcx.lang_items().sized_trait().unwrap(),
1207                         substs: tcx.mk_substs_trait(place_ty, &[]),
1208                     };
1209                     self.prove_trait_ref(
1210                         trait_ref,
1211                         location.to_locations(),
1212                         ConstraintCategory::SizedBound,
1213                     );
1214                 }
1215             }
1216             StatementKind::SetDiscriminant {
1217                 ref place,
1218                 variant_index,
1219             } => {
1220                 let place_type = place.ty(mir, tcx).to_ty(tcx);
1221                 let adt = match place_type.sty {
1222                     TyKind::Adt(adt, _) if adt.is_enum() => adt,
1223                     _ => {
1224                         span_bug!(
1225                             stmt.source_info.span,
1226                             "bad set discriminant ({:?} = {:?}): lhs is not an enum",
1227                             place,
1228                             variant_index
1229                         );
1230                     }
1231                 };
1232                 if variant_index >= adt.variants.len() {
1233                     span_bug!(
1234                         stmt.source_info.span,
1235                         "bad set discriminant ({:?} = {:?}): value of of range",
1236                         place,
1237                         variant_index
1238                     );
1239                 };
1240             }
1241             StatementKind::AscribeUserType(ref place, variance, c_ty) => {
1242                 let place_ty = place.ty(mir, tcx).to_ty(tcx);
1243                 if let Err(terr) = self.relate_type_and_user_type(
1244                     place_ty,
1245                     variance,
1246                     c_ty,
1247                     Locations::All(stmt.source_info.span),
1248                     ConstraintCategory::TypeAnnotation,
1249                 ) {
1250                     span_mirbug!(
1251                         self,
1252                         stmt,
1253                         "bad type assert ({:?} <: {:?}): {:?}",
1254                         place_ty,
1255                         c_ty,
1256                         terr
1257                     );
1258                 }
1259             }
1260             StatementKind::FakeRead(..)
1261             | StatementKind::StorageLive(_)
1262             | StatementKind::StorageDead(_)
1263             | StatementKind::InlineAsm { .. }
1264             | StatementKind::EndRegion(_)
1265             | StatementKind::Validate(..)
1266             | StatementKind::Nop => {}
1267         }
1268     }
1269
1270     fn check_terminator(
1271         &mut self,
1272         mir: &Mir<'tcx>,
1273         term: &Terminator<'tcx>,
1274         term_location: Location,
1275     ) {
1276         debug!("check_terminator: {:?}", term);
1277         let tcx = self.tcx();
1278         match term.kind {
1279             TerminatorKind::Goto { .. }
1280             | TerminatorKind::Resume
1281             | TerminatorKind::Abort
1282             | TerminatorKind::Return
1283             | TerminatorKind::GeneratorDrop
1284             | TerminatorKind::Unreachable
1285             | TerminatorKind::Drop { .. }
1286             | TerminatorKind::FalseEdges { .. }
1287             | TerminatorKind::FalseUnwind { .. } => {
1288                 // no checks needed for these
1289             }
1290
1291             TerminatorKind::DropAndReplace {
1292                 ref location,
1293                 ref value,
1294                 target: _,
1295                 unwind: _,
1296             } => {
1297                 let place_ty = location.ty(mir, tcx).to_ty(tcx);
1298                 let rv_ty = value.ty(mir, tcx);
1299
1300                 let locations = term_location.to_locations();
1301                 if let Err(terr) =
1302                     self.sub_types(rv_ty, place_ty, locations, ConstraintCategory::Assignment)
1303                 {
1304                     span_mirbug!(
1305                         self,
1306                         term,
1307                         "bad DropAndReplace ({:?} = {:?}): {:?}",
1308                         place_ty,
1309                         rv_ty,
1310                         terr
1311                     );
1312                 }
1313             }
1314             TerminatorKind::SwitchInt {
1315                 ref discr,
1316                 switch_ty,
1317                 ..
1318             } => {
1319                 let discr_ty = discr.ty(mir, tcx);
1320                 if let Err(terr) = self.sub_types(
1321                     discr_ty,
1322                     switch_ty,
1323                     term_location.to_locations(),
1324                     ConstraintCategory::Assignment,
1325                 ) {
1326                     span_mirbug!(
1327                         self,
1328                         term,
1329                         "bad SwitchInt ({:?} on {:?}): {:?}",
1330                         switch_ty,
1331                         discr_ty,
1332                         terr
1333                     );
1334                 }
1335                 if !switch_ty.is_integral() && !switch_ty.is_char() && !switch_ty.is_bool() {
1336                     span_mirbug!(self, term, "bad SwitchInt discr ty {:?}", switch_ty);
1337                 }
1338                 // FIXME: check the values
1339             }
1340             TerminatorKind::Call {
1341                 ref func,
1342                 ref args,
1343                 ref destination,
1344                 ..
1345             } => {
1346                 let func_ty = func.ty(mir, tcx);
1347                 debug!("check_terminator: call, func_ty={:?}", func_ty);
1348                 let sig = match func_ty.sty {
1349                     ty::FnDef(..) | ty::FnPtr(_) => func_ty.fn_sig(tcx),
1350                     _ => {
1351                         span_mirbug!(self, term, "call to non-function {:?}", func_ty);
1352                         return;
1353                     }
1354                 };
1355                 let (sig, map) = self.infcx.replace_late_bound_regions_with_fresh_var(
1356                     term.source_info.span,
1357                     LateBoundRegionConversionTime::FnCall,
1358                     &sig,
1359                 );
1360                 let sig = self.normalize(sig, term_location);
1361                 self.check_call_dest(mir, term, &sig, destination, term_location);
1362
1363                 self.prove_predicates(
1364                     sig.inputs().iter().map(|ty| ty::Predicate::WellFormed(ty)),
1365                     term_location.to_locations(),
1366                     ConstraintCategory::Boring,
1367                 );
1368
1369                 // The ordinary liveness rules will ensure that all
1370                 // regions in the type of the callee are live here. We
1371                 // then further constrain the late-bound regions that
1372                 // were instantiated at the call site to be live as
1373                 // well. The resulting is that all the input (and
1374                 // output) types in the signature must be live, since
1375                 // all the inputs that fed into it were live.
1376                 for &late_bound_region in map.values() {
1377                     if let Some(ref mut borrowck_context) = self.borrowck_context {
1378                         let region_vid = borrowck_context
1379                             .universal_regions
1380                             .to_region_vid(late_bound_region);
1381                         borrowck_context
1382                             .constraints
1383                             .liveness_constraints
1384                             .add_element(region_vid, term_location);
1385                     }
1386                 }
1387
1388                 self.check_call_inputs(mir, term, &sig, args, term_location);
1389             }
1390             TerminatorKind::Assert {
1391                 ref cond, ref msg, ..
1392             } => {
1393                 let cond_ty = cond.ty(mir, tcx);
1394                 if cond_ty != tcx.types.bool {
1395                     span_mirbug!(self, term, "bad Assert ({:?}, not bool", cond_ty);
1396                 }
1397
1398                 if let BoundsCheck { ref len, ref index } = *msg {
1399                     if len.ty(mir, tcx) != tcx.types.usize {
1400                         span_mirbug!(self, len, "bounds-check length non-usize {:?}", len)
1401                     }
1402                     if index.ty(mir, tcx) != tcx.types.usize {
1403                         span_mirbug!(self, index, "bounds-check index non-usize {:?}", index)
1404                     }
1405                 }
1406             }
1407             TerminatorKind::Yield { ref value, .. } => {
1408                 let value_ty = value.ty(mir, tcx);
1409                 match mir.yield_ty {
1410                     None => span_mirbug!(self, term, "yield in non-generator"),
1411                     Some(ty) => {
1412                         if let Err(terr) = self.sub_types(
1413                             value_ty,
1414                             ty,
1415                             term_location.to_locations(),
1416                             ConstraintCategory::Return,
1417                         ) {
1418                             span_mirbug!(
1419                                 self,
1420                                 term,
1421                                 "type of yield value is {:?}, but the yield type is {:?}: {:?}",
1422                                 value_ty,
1423                                 ty,
1424                                 terr
1425                             );
1426                         }
1427                     }
1428                 }
1429             }
1430         }
1431     }
1432
1433     fn check_call_dest(
1434         &mut self,
1435         mir: &Mir<'tcx>,
1436         term: &Terminator<'tcx>,
1437         sig: &ty::FnSig<'tcx>,
1438         destination: &Option<(Place<'tcx>, BasicBlock)>,
1439         term_location: Location,
1440     ) {
1441         let tcx = self.tcx();
1442         match *destination {
1443             Some((ref dest, _target_block)) => {
1444                 let dest_ty = dest.ty(mir, tcx).to_ty(tcx);
1445                 let category = match *dest {
1446                     Place::Local(RETURN_PLACE) => ConstraintCategory::Return,
1447                     Place::Local(l) if !mir.local_decls[l].is_user_variable.is_some() => {
1448                         ConstraintCategory::Boring
1449                     }
1450                     _ => ConstraintCategory::Assignment,
1451                 };
1452
1453                 let locations = term_location.to_locations();
1454
1455                 if let Err(terr) =
1456                     self.sub_types_or_anon(sig.output(), dest_ty, locations, category)
1457                 {
1458                     span_mirbug!(
1459                         self,
1460                         term,
1461                         "call dest mismatch ({:?} <- {:?}): {:?}",
1462                         dest_ty,
1463                         sig.output(),
1464                         terr
1465                     );
1466                 }
1467
1468                 // When `#![feature(unsized_locals)]` is not enabled,
1469                 // this check is done at `check_local`.
1470                 if self.tcx().features().unsized_locals {
1471                     let span = term.source_info.span;
1472                     self.ensure_place_sized(dest_ty, span);
1473                 }
1474             }
1475             None => {
1476                 // FIXME(canndrew): This is_never should probably be an is_uninhabited
1477                 if !sig.output().is_never() {
1478                     span_mirbug!(self, term, "call to converging function {:?} w/o dest", sig);
1479                 }
1480             }
1481         }
1482     }
1483
1484     fn check_call_inputs(
1485         &mut self,
1486         mir: &Mir<'tcx>,
1487         term: &Terminator<'tcx>,
1488         sig: &ty::FnSig<'tcx>,
1489         args: &[Operand<'tcx>],
1490         term_location: Location,
1491     ) {
1492         debug!("check_call_inputs({:?}, {:?})", sig, args);
1493         if args.len() < sig.inputs().len() || (args.len() > sig.inputs().len() && !sig.variadic) {
1494             span_mirbug!(self, term, "call to {:?} with wrong # of args", sig);
1495         }
1496         for (n, (fn_arg, op_arg)) in sig.inputs().iter().zip(args).enumerate() {
1497             let op_arg_ty = op_arg.ty(mir, self.tcx());
1498             if let Err(terr) = self.sub_types(
1499                 op_arg_ty,
1500                 fn_arg,
1501                 term_location.to_locations(),
1502                 ConstraintCategory::CallArgument,
1503             ) {
1504                 span_mirbug!(
1505                     self,
1506                     term,
1507                     "bad arg #{:?} ({:?} <- {:?}): {:?}",
1508                     n,
1509                     fn_arg,
1510                     op_arg_ty,
1511                     terr
1512                 );
1513             }
1514         }
1515     }
1516
1517     fn check_iscleanup(&mut self, mir: &Mir<'tcx>, block_data: &BasicBlockData<'tcx>) {
1518         let is_cleanup = block_data.is_cleanup;
1519         self.last_span = block_data.terminator().source_info.span;
1520         match block_data.terminator().kind {
1521             TerminatorKind::Goto { target } => {
1522                 self.assert_iscleanup(mir, block_data, target, is_cleanup)
1523             }
1524             TerminatorKind::SwitchInt { ref targets, .. } => for target in targets {
1525                 self.assert_iscleanup(mir, block_data, *target, is_cleanup);
1526             },
1527             TerminatorKind::Resume => if !is_cleanup {
1528                 span_mirbug!(self, block_data, "resume on non-cleanup block!")
1529             },
1530             TerminatorKind::Abort => if !is_cleanup {
1531                 span_mirbug!(self, block_data, "abort on non-cleanup block!")
1532             },
1533             TerminatorKind::Return => if is_cleanup {
1534                 span_mirbug!(self, block_data, "return on cleanup block")
1535             },
1536             TerminatorKind::GeneratorDrop { .. } => if is_cleanup {
1537                 span_mirbug!(self, block_data, "generator_drop in cleanup block")
1538             },
1539             TerminatorKind::Yield { resume, drop, .. } => {
1540                 if is_cleanup {
1541                     span_mirbug!(self, block_data, "yield in cleanup block")
1542                 }
1543                 self.assert_iscleanup(mir, block_data, resume, is_cleanup);
1544                 if let Some(drop) = drop {
1545                     self.assert_iscleanup(mir, block_data, drop, is_cleanup);
1546                 }
1547             }
1548             TerminatorKind::Unreachable => {}
1549             TerminatorKind::Drop { target, unwind, .. }
1550             | TerminatorKind::DropAndReplace { target, unwind, .. }
1551             | TerminatorKind::Assert {
1552                 target,
1553                 cleanup: unwind,
1554                 ..
1555             } => {
1556                 self.assert_iscleanup(mir, block_data, target, is_cleanup);
1557                 if let Some(unwind) = unwind {
1558                     if is_cleanup {
1559                         span_mirbug!(self, block_data, "unwind on cleanup block")
1560                     }
1561                     self.assert_iscleanup(mir, block_data, unwind, true);
1562                 }
1563             }
1564             TerminatorKind::Call {
1565                 ref destination,
1566                 cleanup,
1567                 ..
1568             } => {
1569                 if let &Some((_, target)) = destination {
1570                     self.assert_iscleanup(mir, block_data, target, is_cleanup);
1571                 }
1572                 if let Some(cleanup) = cleanup {
1573                     if is_cleanup {
1574                         span_mirbug!(self, block_data, "cleanup on cleanup block")
1575                     }
1576                     self.assert_iscleanup(mir, block_data, cleanup, true);
1577                 }
1578             }
1579             TerminatorKind::FalseEdges {
1580                 real_target,
1581                 ref imaginary_targets,
1582             } => {
1583                 self.assert_iscleanup(mir, block_data, real_target, is_cleanup);
1584                 for target in imaginary_targets {
1585                     self.assert_iscleanup(mir, block_data, *target, is_cleanup);
1586                 }
1587             }
1588             TerminatorKind::FalseUnwind {
1589                 real_target,
1590                 unwind,
1591             } => {
1592                 self.assert_iscleanup(mir, block_data, real_target, is_cleanup);
1593                 if let Some(unwind) = unwind {
1594                     if is_cleanup {
1595                         span_mirbug!(
1596                             self,
1597                             block_data,
1598                             "cleanup in cleanup block via false unwind"
1599                         );
1600                     }
1601                     self.assert_iscleanup(mir, block_data, unwind, true);
1602                 }
1603             }
1604         }
1605     }
1606
1607     fn assert_iscleanup(
1608         &mut self,
1609         mir: &Mir<'tcx>,
1610         ctxt: &dyn fmt::Debug,
1611         bb: BasicBlock,
1612         iscleanuppad: bool,
1613     ) {
1614         if mir[bb].is_cleanup != iscleanuppad {
1615             span_mirbug!(
1616                 self,
1617                 ctxt,
1618                 "cleanuppad mismatch: {:?} should be {:?}",
1619                 bb,
1620                 iscleanuppad
1621             );
1622         }
1623     }
1624
1625     fn check_local(&mut self, mir: &Mir<'tcx>, local: Local, local_decl: &LocalDecl<'tcx>) {
1626         match mir.local_kind(local) {
1627             LocalKind::ReturnPointer | LocalKind::Arg => {
1628                 // return values of normal functions are required to be
1629                 // sized by typeck, but return values of ADT constructors are
1630                 // not because we don't include a `Self: Sized` bounds on them.
1631                 //
1632                 // Unbound parts of arguments were never required to be Sized
1633                 // - maybe we should make that a warning.
1634                 return;
1635             }
1636             LocalKind::Var | LocalKind::Temp => {}
1637         }
1638
1639         // When `#![feature(unsized_locals)]` is enabled, only function calls
1640         // and nullary ops are checked in `check_call_dest`.
1641         if !self.tcx().features().unsized_locals {
1642             let span = local_decl.source_info.span;
1643             let ty = local_decl.ty;
1644             self.ensure_place_sized(ty, span);
1645         }
1646     }
1647
1648     fn ensure_place_sized(&mut self, ty: Ty<'tcx>, span: Span) {
1649         let tcx = self.tcx();
1650
1651         // Erase the regions from `ty` to get a global type.  The
1652         // `Sized` bound in no way depends on precise regions, so this
1653         // shouldn't affect `is_sized`.
1654         let gcx = tcx.global_tcx();
1655         let erased_ty = gcx.lift(&tcx.erase_regions(&ty)).unwrap();
1656         if !erased_ty.is_sized(gcx.at(span), self.param_env) {
1657             // in current MIR construction, all non-control-flow rvalue
1658             // expressions evaluate through `as_temp` or `into` a return
1659             // slot or local, so to find all unsized rvalues it is enough
1660             // to check all temps, return slots and locals.
1661             if let None = self.reported_errors.replace((ty, span)) {
1662                 let mut diag = struct_span_err!(
1663                     self.tcx().sess,
1664                     span,
1665                     E0161,
1666                     "cannot move a value of type {0}: the size of {0} \
1667                      cannot be statically determined",
1668                     ty
1669                 );
1670
1671                 // While this is located in `nll::typeck` this error is not
1672                 // an NLL error, it's a required check to prevent creation
1673                 // of unsized rvalues in certain cases:
1674                 // * operand of a box expression
1675                 // * callee in a call expression
1676                 diag.emit();
1677             }
1678         }
1679     }
1680
1681     fn aggregate_field_ty(
1682         &mut self,
1683         ak: &AggregateKind<'tcx>,
1684         field_index: usize,
1685         location: Location,
1686     ) -> Result<Ty<'tcx>, FieldAccessError> {
1687         let tcx = self.tcx();
1688
1689         match *ak {
1690             AggregateKind::Adt(def, variant_index, substs, _, active_field_index) => {
1691                 let variant = &def.variants[variant_index];
1692                 let adj_field_index = active_field_index.unwrap_or(field_index);
1693                 if let Some(field) = variant.fields.get(adj_field_index) {
1694                     Ok(self.normalize(field.ty(tcx, substs), location))
1695                 } else {
1696                     Err(FieldAccessError::OutOfRange {
1697                         field_count: variant.fields.len(),
1698                     })
1699                 }
1700             }
1701             AggregateKind::Closure(def_id, substs) => {
1702                 match substs.upvar_tys(def_id, tcx).nth(field_index) {
1703                     Some(ty) => Ok(ty),
1704                     None => Err(FieldAccessError::OutOfRange {
1705                         field_count: substs.upvar_tys(def_id, tcx).count(),
1706                     }),
1707                 }
1708             }
1709             AggregateKind::Generator(def_id, substs, _) => {
1710                 // Try pre-transform fields first (upvars and current state)
1711                 if let Some(ty) = substs.pre_transforms_tys(def_id, tcx).nth(field_index) {
1712                     Ok(ty)
1713                 } else {
1714                     // Then try `field_tys` which contains all the fields, but it
1715                     // requires the final optimized MIR.
1716                     match substs.field_tys(def_id, tcx).nth(field_index) {
1717                         Some(ty) => Ok(ty),
1718                         None => Err(FieldAccessError::OutOfRange {
1719                             field_count: substs.field_tys(def_id, tcx).count(),
1720                         }),
1721                     }
1722                 }
1723             }
1724             AggregateKind::Array(ty) => Ok(ty),
1725             AggregateKind::Tuple => {
1726                 unreachable!("This should have been covered in check_rvalues");
1727             }
1728         }
1729     }
1730
1731     fn check_rvalue(&mut self, mir: &Mir<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
1732         let tcx = self.tcx();
1733
1734         match rvalue {
1735             Rvalue::Aggregate(ak, ops) => {
1736                 self.check_aggregate_rvalue(mir, rvalue, ak, ops, location)
1737             }
1738
1739             Rvalue::Repeat(operand, len) => if *len > 1 {
1740                 let operand_ty = operand.ty(mir, tcx);
1741
1742                 let trait_ref = ty::TraitRef {
1743                     def_id: tcx.lang_items().copy_trait().unwrap(),
1744                     substs: tcx.mk_substs_trait(operand_ty, &[]),
1745                 };
1746
1747                 self.prove_trait_ref(
1748                     trait_ref,
1749                     location.to_locations(),
1750                     ConstraintCategory::CopyBound,
1751                 );
1752             },
1753
1754             Rvalue::NullaryOp(_, ty) => {
1755                 // Even with unsized locals cannot box an unsized value.
1756                 if self.tcx().features().unsized_locals {
1757                     let span = mir.source_info(location).span;
1758                     self.ensure_place_sized(ty, span);
1759                 }
1760
1761                 let trait_ref = ty::TraitRef {
1762                     def_id: tcx.lang_items().sized_trait().unwrap(),
1763                     substs: tcx.mk_substs_trait(ty, &[]),
1764                 };
1765
1766                 self.prove_trait_ref(
1767                     trait_ref,
1768                     location.to_locations(),
1769                     ConstraintCategory::SizedBound,
1770                 );
1771             }
1772
1773             Rvalue::Cast(cast_kind, op, ty) => {
1774                 match cast_kind {
1775                     CastKind::ReifyFnPointer => {
1776                         let fn_sig = op.ty(mir, tcx).fn_sig(tcx);
1777
1778                         // The type that we see in the fcx is like
1779                         // `foo::<'a, 'b>`, where `foo` is the path to a
1780                         // function definition. When we extract the
1781                         // signature, it comes from the `fn_sig` query,
1782                         // and hence may contain unnormalized results.
1783                         let fn_sig = self.normalize(fn_sig, location);
1784
1785                         let ty_fn_ptr_from = tcx.mk_fn_ptr(fn_sig);
1786
1787                         if let Err(terr) = self.eq_types(
1788                             ty_fn_ptr_from,
1789                             ty,
1790                             location.to_locations(),
1791                             ConstraintCategory::Cast,
1792                         ) {
1793                             span_mirbug!(
1794                                 self,
1795                                 rvalue,
1796                                 "equating {:?} with {:?} yields {:?}",
1797                                 ty_fn_ptr_from,
1798                                 ty,
1799                                 terr
1800                             );
1801                         }
1802                     }
1803
1804                     CastKind::ClosureFnPointer => {
1805                         let sig = match op.ty(mir, tcx).sty {
1806                             ty::Closure(def_id, substs) => {
1807                                 substs.closure_sig_ty(def_id, tcx).fn_sig(tcx)
1808                             }
1809                             _ => bug!(),
1810                         };
1811                         let ty_fn_ptr_from = tcx.coerce_closure_fn_ty(sig);
1812
1813                         if let Err(terr) = self.eq_types(
1814                             ty_fn_ptr_from,
1815                             ty,
1816                             location.to_locations(),
1817                             ConstraintCategory::Cast,
1818                         ) {
1819                             span_mirbug!(
1820                                 self,
1821                                 rvalue,
1822                                 "equating {:?} with {:?} yields {:?}",
1823                                 ty_fn_ptr_from,
1824                                 ty,
1825                                 terr
1826                             );
1827                         }
1828                     }
1829
1830                     CastKind::UnsafeFnPointer => {
1831                         let fn_sig = op.ty(mir, tcx).fn_sig(tcx);
1832
1833                         // The type that we see in the fcx is like
1834                         // `foo::<'a, 'b>`, where `foo` is the path to a
1835                         // function definition. When we extract the
1836                         // signature, it comes from the `fn_sig` query,
1837                         // and hence may contain unnormalized results.
1838                         let fn_sig = self.normalize(fn_sig, location);
1839
1840                         let ty_fn_ptr_from = tcx.safe_to_unsafe_fn_ty(fn_sig);
1841
1842                         if let Err(terr) = self.eq_types(
1843                             ty_fn_ptr_from,
1844                             ty,
1845                             location.to_locations(),
1846                             ConstraintCategory::Cast,
1847                         ) {
1848                             span_mirbug!(
1849                                 self,
1850                                 rvalue,
1851                                 "equating {:?} with {:?} yields {:?}",
1852                                 ty_fn_ptr_from,
1853                                 ty,
1854                                 terr
1855                             );
1856                         }
1857                     }
1858
1859                     CastKind::Unsize => {
1860                         let &ty = ty;
1861                         let trait_ref = ty::TraitRef {
1862                             def_id: tcx.lang_items().coerce_unsized_trait().unwrap(),
1863                             substs: tcx.mk_substs_trait(op.ty(mir, tcx), &[ty.into()]),
1864                         };
1865
1866                         self.prove_trait_ref(
1867                             trait_ref,
1868                             location.to_locations(),
1869                             ConstraintCategory::Cast,
1870                         );
1871                     }
1872
1873                     CastKind::Misc => {}
1874                 }
1875             }
1876
1877             Rvalue::Ref(region, _borrow_kind, borrowed_place) => {
1878                 self.add_reborrow_constraint(location, region, borrowed_place);
1879             }
1880
1881             // FIXME: These other cases have to be implemented in future PRs
1882             Rvalue::Use(..)
1883             | Rvalue::Len(..)
1884             | Rvalue::BinaryOp(..)
1885             | Rvalue::CheckedBinaryOp(..)
1886             | Rvalue::UnaryOp(..)
1887             | Rvalue::Discriminant(..) => {}
1888         }
1889     }
1890
1891     /// If this rvalue supports a user-given type annotation, then
1892     /// extract and return it. This represents the final type of the
1893     /// rvalue and will be unified with the inferred type.
1894     fn rvalue_user_ty(&self, rvalue: &Rvalue<'tcx>) -> Option<UserTypeAnnotation<'tcx>> {
1895         match rvalue {
1896             Rvalue::Use(_)
1897             | Rvalue::Repeat(..)
1898             | Rvalue::Ref(..)
1899             | Rvalue::Len(..)
1900             | Rvalue::Cast(..)
1901             | Rvalue::BinaryOp(..)
1902             | Rvalue::CheckedBinaryOp(..)
1903             | Rvalue::NullaryOp(..)
1904             | Rvalue::UnaryOp(..)
1905             | Rvalue::Discriminant(..) => None,
1906
1907             Rvalue::Aggregate(aggregate, _) => match **aggregate {
1908                 AggregateKind::Adt(_, _, _, user_ty, _) => user_ty,
1909                 AggregateKind::Array(_) => None,
1910                 AggregateKind::Tuple => None,
1911                 AggregateKind::Closure(_, _) => None,
1912                 AggregateKind::Generator(_, _, _) => None,
1913             },
1914         }
1915     }
1916
1917     fn check_aggregate_rvalue(
1918         &mut self,
1919         mir: &Mir<'tcx>,
1920         rvalue: &Rvalue<'tcx>,
1921         aggregate_kind: &AggregateKind<'tcx>,
1922         operands: &[Operand<'tcx>],
1923         location: Location,
1924     ) {
1925         let tcx = self.tcx();
1926
1927         self.prove_aggregate_predicates(aggregate_kind, location);
1928
1929         if *aggregate_kind == AggregateKind::Tuple {
1930             // tuple rvalue field type is always the type of the op. Nothing to check here.
1931             return;
1932         }
1933
1934         for (i, operand) in operands.iter().enumerate() {
1935             let field_ty = match self.aggregate_field_ty(aggregate_kind, i, location) {
1936                 Ok(field_ty) => field_ty,
1937                 Err(FieldAccessError::OutOfRange { field_count }) => {
1938                     span_mirbug!(
1939                         self,
1940                         rvalue,
1941                         "accessed field #{} but variant only has {}",
1942                         i,
1943                         field_count
1944                     );
1945                     continue;
1946                 }
1947             };
1948             let operand_ty = operand.ty(mir, tcx);
1949
1950             if let Err(terr) = self.sub_types(
1951                 operand_ty,
1952                 field_ty,
1953                 location.to_locations(),
1954                 ConstraintCategory::Boring,
1955             ) {
1956                 span_mirbug!(
1957                     self,
1958                     rvalue,
1959                     "{:?} is not a subtype of {:?}: {:?}",
1960                     operand_ty,
1961                     field_ty,
1962                     terr
1963                 );
1964             }
1965         }
1966     }
1967
1968     /// Add the constraints that arise from a borrow expression `&'a P` at the location `L`.
1969     ///
1970     /// # Parameters
1971     ///
1972     /// - `location`: the location `L` where the borrow expression occurs
1973     /// - `borrow_region`: the region `'a` associated with the borrow
1974     /// - `borrowed_place`: the place `P` being borrowed
1975     fn add_reborrow_constraint(
1976         &mut self,
1977         location: Location,
1978         borrow_region: ty::Region<'tcx>,
1979         borrowed_place: &Place<'tcx>,
1980     ) {
1981         // These constraints are only meaningful during borrowck:
1982         let BorrowCheckContext {
1983             borrow_set,
1984             location_table,
1985             all_facts,
1986             constraints,
1987             ..
1988         } = match self.borrowck_context {
1989             Some(ref mut borrowck_context) => borrowck_context,
1990             None => return,
1991         };
1992
1993         // In Polonius mode, we also push a `borrow_region` fact
1994         // linking the loan to the region (in some cases, though,
1995         // there is no loan associated with this borrow expression --
1996         // that occurs when we are borrowing an unsafe place, for
1997         // example).
1998         if let Some(all_facts) = all_facts {
1999             if let Some(borrow_index) = borrow_set.location_map.get(&location) {
2000                 let region_vid = borrow_region.to_region_vid();
2001                 all_facts.borrow_region.push((
2002                     region_vid,
2003                     *borrow_index,
2004                     location_table.mid_index(location),
2005                 ));
2006             }
2007         }
2008
2009         // If we are reborrowing the referent of another reference, we
2010         // need to add outlives relationships. In a case like `&mut
2011         // *p`, where the `p` has type `&'b mut Foo`, for example, we
2012         // need to ensure that `'b: 'a`.
2013
2014         let mut borrowed_place = borrowed_place;
2015
2016         debug!(
2017             "add_reborrow_constraint({:?}, {:?}, {:?})",
2018             location, borrow_region, borrowed_place
2019         );
2020         while let Place::Projection(box PlaceProjection { base, elem }) = borrowed_place {
2021             debug!("add_reborrow_constraint - iteration {:?}", borrowed_place);
2022
2023             match *elem {
2024                 ProjectionElem::Deref => {
2025                     let tcx = self.infcx.tcx;
2026                     let base_ty = base.ty(self.mir, tcx).to_ty(tcx);
2027
2028                     debug!("add_reborrow_constraint - base_ty = {:?}", base_ty);
2029                     match base_ty.sty {
2030                         ty::Ref(ref_region, _, mutbl) => {
2031                             constraints.outlives_constraints.push(OutlivesConstraint {
2032                                 sup: ref_region.to_region_vid(),
2033                                 sub: borrow_region.to_region_vid(),
2034                                 locations: location.to_locations(),
2035                                 category: ConstraintCategory::Boring,
2036                             });
2037
2038                             match mutbl {
2039                                 hir::Mutability::MutImmutable => {
2040                                     // Immutable reference. We don't need the base
2041                                     // to be valid for the entire lifetime of
2042                                     // the borrow.
2043                                     break;
2044                                 }
2045                                 hir::Mutability::MutMutable => {
2046                                     // Mutable reference. We *do* need the base
2047                                     // to be valid, because after the base becomes
2048                                     // invalid, someone else can use our mutable deref.
2049
2050                                     // This is in order to make the following function
2051                                     // illegal:
2052                                     // ```
2053                                     // fn unsafe_deref<'a, 'b>(x: &'a &'b mut T) -> &'b mut T {
2054                                     //     &mut *x
2055                                     // }
2056                                     // ```
2057                                     //
2058                                     // As otherwise you could clone `&mut T` using the
2059                                     // following function:
2060                                     // ```
2061                                     // fn bad(x: &mut T) -> (&mut T, &mut T) {
2062                                     //     let my_clone = unsafe_deref(&'a x);
2063                                     //     ENDREGION 'a;
2064                                     //     (my_clone, x)
2065                                     // }
2066                                     // ```
2067                                 }
2068                             }
2069                         }
2070                         ty::RawPtr(..) => {
2071                             // deref of raw pointer, guaranteed to be valid
2072                             break;
2073                         }
2074                         ty::Adt(def, _) if def.is_box() => {
2075                             // deref of `Box`, need the base to be valid - propagate
2076                         }
2077                         _ => bug!("unexpected deref ty {:?} in {:?}", base_ty, borrowed_place),
2078                     }
2079                 }
2080                 ProjectionElem::Field(..)
2081                 | ProjectionElem::Downcast(..)
2082                 | ProjectionElem::Index(..)
2083                 | ProjectionElem::ConstantIndex { .. }
2084                 | ProjectionElem::Subslice { .. } => {
2085                     // other field access
2086                 }
2087             }
2088
2089             // The "propagate" case. We need to check that our base is valid
2090             // for the borrow's lifetime.
2091             borrowed_place = base;
2092         }
2093     }
2094
2095     fn prove_aggregate_predicates(
2096         &mut self,
2097         aggregate_kind: &AggregateKind<'tcx>,
2098         location: Location,
2099     ) {
2100         let tcx = self.tcx();
2101
2102         debug!(
2103             "prove_aggregate_predicates(aggregate_kind={:?}, location={:?})",
2104             aggregate_kind, location
2105         );
2106
2107         let instantiated_predicates = match aggregate_kind {
2108             AggregateKind::Adt(def, _, substs, _, _) => {
2109                 tcx.predicates_of(def.did).instantiate(tcx, substs)
2110             }
2111
2112             // For closures, we have some **extra requirements** we
2113             //
2114             // have to check. In particular, in their upvars and
2115             // signatures, closures often reference various regions
2116             // from the surrounding function -- we call those the
2117             // closure's free regions. When we borrow-check (and hence
2118             // region-check) closures, we may find that the closure
2119             // requires certain relationships between those free
2120             // regions. However, because those free regions refer to
2121             // portions of the CFG of their caller, the closure is not
2122             // in a position to verify those relationships. In that
2123             // case, the requirements get "propagated" to us, and so
2124             // we have to solve them here where we instantiate the
2125             // closure.
2126             //
2127             // Despite the opacity of the previous parapgrah, this is
2128             // actually relatively easy to understand in terms of the
2129             // desugaring. A closure gets desugared to a struct, and
2130             // these extra requirements are basically like where
2131             // clauses on the struct.
2132             AggregateKind::Closure(def_id, ty::ClosureSubsts { substs })
2133             | AggregateKind::Generator(def_id, ty::GeneratorSubsts { substs }, _) => {
2134                 self.prove_closure_bounds(tcx, *def_id, substs, location)
2135             }
2136
2137             AggregateKind::Array(_) | AggregateKind::Tuple => ty::InstantiatedPredicates::empty(),
2138         };
2139
2140         self.normalize_and_prove_instantiated_predicates(
2141             instantiated_predicates,
2142             location.to_locations(),
2143         );
2144     }
2145
2146     fn prove_closure_bounds(
2147         &mut self,
2148         tcx: TyCtxt<'a, 'gcx, 'tcx>,
2149         def_id: DefId,
2150         substs: &'tcx Substs<'tcx>,
2151         location: Location,
2152     ) -> ty::InstantiatedPredicates<'tcx> {
2153         if let Some(closure_region_requirements) = tcx.mir_borrowck(def_id).closure_requirements {
2154             let closure_constraints =
2155                 closure_region_requirements.apply_requirements(tcx, location, def_id, substs);
2156
2157             if let Some(ref mut borrowck_context) = self.borrowck_context {
2158                 let bounds_mapping = closure_constraints
2159                     .iter()
2160                     .enumerate()
2161                     .filter_map(|(idx, constraint)| {
2162                         let ty::OutlivesPredicate(k1, r2) =
2163                             constraint.no_late_bound_regions().unwrap_or_else(|| {
2164                                 bug!("query_constraint {:?} contained bound regions", constraint,);
2165                             });
2166
2167                         match k1.unpack() {
2168                             UnpackedKind::Lifetime(r1) => {
2169                                 // constraint is r1: r2
2170                                 let r1_vid = borrowck_context.universal_regions.to_region_vid(r1);
2171                                 let r2_vid = borrowck_context.universal_regions.to_region_vid(r2);
2172                                 let outlives_requirements =
2173                                     &closure_region_requirements.outlives_requirements[idx];
2174                                 Some((
2175                                     (r1_vid, r2_vid),
2176                                     (
2177                                         outlives_requirements.category,
2178                                         outlives_requirements.blame_span,
2179                                     ),
2180                                 ))
2181                             }
2182                             UnpackedKind::Type(_) => None,
2183                         }
2184                     })
2185                     .collect();
2186
2187                 let existing = borrowck_context
2188                     .constraints
2189                     .closure_bounds_mapping
2190                     .insert(location, bounds_mapping);
2191                 assert!(
2192                     existing.is_none(),
2193                     "Multiple closures at the same location."
2194                 );
2195             }
2196
2197             self.push_region_constraints(
2198                 location.to_locations(),
2199                 ConstraintCategory::ClosureBounds,
2200                 &closure_constraints,
2201             );
2202         }
2203
2204         tcx.predicates_of(def_id).instantiate(tcx, substs)
2205     }
2206
2207     fn prove_trait_ref(
2208         &mut self,
2209         trait_ref: ty::TraitRef<'tcx>,
2210         locations: Locations,
2211         category: ConstraintCategory,
2212     ) {
2213         self.prove_predicates(
2214             Some(ty::Predicate::Trait(
2215                 trait_ref.to_poly_trait_ref().to_poly_trait_predicate(),
2216             )),
2217             locations,
2218             category,
2219         );
2220     }
2221
2222     fn normalize_and_prove_instantiated_predicates(
2223         &mut self,
2224         instantiated_predicates: ty::InstantiatedPredicates<'tcx>,
2225         locations: Locations,
2226     ) {
2227         for predicate in instantiated_predicates.predicates {
2228             let predicate = self.normalize(predicate, locations);
2229             self.prove_predicate(predicate, locations, ConstraintCategory::Boring);
2230         }
2231     }
2232
2233     fn prove_predicates(
2234         &mut self,
2235         predicates: impl IntoIterator<Item = ty::Predicate<'tcx>>,
2236         locations: Locations,
2237         category: ConstraintCategory,
2238     ) {
2239         for predicate in predicates {
2240             debug!(
2241                 "prove_predicates(predicate={:?}, locations={:?})",
2242                 predicate, locations,
2243             );
2244
2245             self.prove_predicate(predicate, locations, category);
2246         }
2247     }
2248
2249     fn prove_predicate(
2250         &mut self,
2251         predicate: ty::Predicate<'tcx>,
2252         locations: Locations,
2253         category: ConstraintCategory,
2254     ) {
2255         debug!(
2256             "prove_predicate(predicate={:?}, location={:?})",
2257             predicate, locations,
2258         );
2259
2260         let param_env = self.param_env;
2261         self.fully_perform_op(
2262             locations,
2263             category,
2264             param_env.and(type_op::prove_predicate::ProvePredicate::new(predicate)),
2265         ).unwrap_or_else(|NoSolution| {
2266             span_mirbug!(self, NoSolution, "could not prove {:?}", predicate);
2267         })
2268     }
2269
2270     fn typeck_mir(&mut self, mir: &Mir<'tcx>) {
2271         self.last_span = mir.span;
2272         debug!("run_on_mir: {:?}", mir.span);
2273
2274         for (local, local_decl) in mir.local_decls.iter_enumerated() {
2275             self.check_local(mir, local, local_decl);
2276         }
2277
2278         for (block, block_data) in mir.basic_blocks().iter_enumerated() {
2279             let mut location = Location {
2280                 block,
2281                 statement_index: 0,
2282             };
2283             for stmt in &block_data.statements {
2284                 if !stmt.source_info.span.is_dummy() {
2285                     self.last_span = stmt.source_info.span;
2286                 }
2287                 self.check_stmt(mir, stmt, location);
2288                 location.statement_index += 1;
2289             }
2290
2291             self.check_terminator(mir, block_data.terminator(), location);
2292             self.check_iscleanup(mir, block_data);
2293         }
2294     }
2295
2296     fn normalize<T>(&mut self, value: T, location: impl NormalizeLocation) -> T
2297     where
2298         T: type_op::normalize::Normalizable<'gcx, 'tcx> + Copy,
2299     {
2300         debug!("normalize(value={:?}, location={:?})", value, location);
2301         let param_env = self.param_env;
2302         self.fully_perform_op(
2303             location.to_locations(),
2304             ConstraintCategory::Boring,
2305             param_env.and(type_op::normalize::Normalize::new(value)),
2306         ).unwrap_or_else(|NoSolution| {
2307             span_mirbug!(self, NoSolution, "failed to normalize `{:?}`", value);
2308             value
2309         })
2310     }
2311 }
2312
2313 pub struct TypeckMir;
2314
2315 impl MirPass for TypeckMir {
2316     fn run_pass<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, src: MirSource, mir: &mut Mir<'tcx>) {
2317         let def_id = src.def_id;
2318         debug!("run_pass: {:?}", def_id);
2319
2320         // When NLL is enabled, the borrow checker runs the typeck
2321         // itself, so we don't need this MIR pass anymore.
2322         if tcx.use_mir_borrowck() {
2323             return;
2324         }
2325
2326         if tcx.sess.err_count() > 0 {
2327             // compiling a broken program can obviously result in a
2328             // broken MIR, so try not to report duplicate errors.
2329             return;
2330         }
2331
2332         if tcx.is_struct_constructor(def_id) {
2333             // We just assume that the automatically generated struct constructors are
2334             // correct. See the comment in the `mir_borrowck` implementation for an
2335             // explanation why we need this.
2336             return;
2337         }
2338
2339         let param_env = tcx.param_env(def_id);
2340         tcx.infer_ctxt().enter(|infcx| {
2341             type_check_internal(
2342                 &infcx,
2343                 def_id,
2344                 param_env,
2345                 mir,
2346                 &vec![],
2347                 None,
2348                 None,
2349                 None,
2350                 |_| (),
2351             );
2352
2353             // For verification purposes, we just ignore the resulting
2354             // region constraint sets. Not our problem. =)
2355         });
2356     }
2357 }
2358
2359 trait NormalizeLocation: fmt::Debug + Copy {
2360     fn to_locations(self) -> Locations;
2361 }
2362
2363 impl NormalizeLocation for Locations {
2364     fn to_locations(self) -> Locations {
2365         self
2366     }
2367 }
2368
2369 impl NormalizeLocation for Location {
2370     fn to_locations(self) -> Locations {
2371         Locations::Single(self)
2372     }
2373 }
2374
2375 #[derive(Debug, Default)]
2376 struct ObligationAccumulator<'tcx> {
2377     obligations: PredicateObligations<'tcx>,
2378 }
2379
2380 impl<'tcx> ObligationAccumulator<'tcx> {
2381     fn add<T>(&mut self, value: InferOk<'tcx, T>) -> T {
2382         let InferOk { value, obligations } = value;
2383         self.obligations.extend(obligations);
2384         value
2385     }
2386
2387     fn into_vec(self) -> PredicateObligations<'tcx> {
2388         self.obligations
2389     }
2390 }