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, UserSelfTy, UserSubsts};
  46 use rustc::ty::{self, RegionVid, ToPolyTraitRef, Ty, TyCtxt, TyKind};
  47 use std::rc::Rc;
  48 use std::{fmt, iter};
  49 use syntax_pos::{Span, DUMMY_SP};
  50 use transform::{MirPass, MirSource};
  51
  52 use either::Either;
  53 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  54
  55 macro_rules! span_mirbug {
  56     ($context:expr, $elem:expr, $($message:tt)*) => ({
  57         $crate::borrow_check::nll::type_check::mirbug(
  58             $context.tcx(),
  59             $context.last_span,
  60             &format!(
  61                 "broken MIR in {:?} ({:?}): {}",
  62                 $context.mir_def_id,
  63                 $elem,
  64                 format_args!($($message)*),
  65             ),
  66         )
  67     })
  68 }
  69
  70 macro_rules! span_mirbug_and_err {
  71     ($context:expr, $elem:expr, $($message:tt)*) => ({
  72         {
  73             span_mirbug!($context, $elem, $($message)*);
  74             $context.error()
  75         }
  76     })
  77 }
  78
  79 mod constraint_conversion;
  80 pub mod free_region_relations;
  81 mod input_output;
  82 crate mod liveness;
  83 mod relate_tys;
  84
  85 /// Type checks the given `mir` in the context of the inference
  86 /// context `infcx`. Returns any region constraints that have yet to
  87 /// be proven. This result is includes liveness constraints that
  88 /// ensure that regions appearing in the types of all local variables
  89 /// are live at all points where that local variable may later be
  90 /// used.
  91 ///
  92 /// This phase of type-check ought to be infallible -- this is because
  93 /// the original, HIR-based type-check succeeded. So if any errors
  94 /// occur here, we will get a `bug!` reported.
  95 ///
  96 /// # Parameters
  97 ///
  98 /// - `infcx` -- inference context to use
  99 /// - `param_env` -- parameter environment to use for trait solving
 100 /// - `mir` -- MIR to type-check
 101 /// - `mir_def_id` -- DefId from which the MIR is derived (must be local)
 102 /// - `region_bound_pairs` -- the implied outlives obligations between type parameters
 103 ///   and lifetimes (e.g., `&'a T` implies `T: 'a`)
 104 /// - `implicit_region_bound` -- a region which all generic parameters are assumed
 105 ///   to outlive; should represent the fn body
 106 /// - `input_tys` -- fully liberated, but **not** normalized, expected types of the arguments;
 107 ///   the types of the input parameters found in the MIR itself will be equated with these
 108 /// - `output_ty` -- fully liberated, but **not** normalized, expected return type;
 109 ///   the type for the RETURN_PLACE will be equated with this
 110 /// - `liveness` -- results of a liveness computation on the MIR; used to create liveness
 111 ///   constraints for the regions in the types of variables
 112 /// - `flow_inits` -- results of a maybe-init dataflow analysis
 113 /// - `move_data` -- move-data constructed when performing the maybe-init dataflow analysiss
 114 pub(crate) fn type_check<'gcx, 'tcx>(
 115     infcx: &InferCtxt<'_, 'gcx, 'tcx>,
 116     param_env: ty::ParamEnv<'gcx>,
 117     mir: &Mir<'tcx>,
 118     mir_def_id: DefId,
 119     universal_regions: &Rc<UniversalRegions<'tcx>>,
 120     location_table: &LocationTable,
 121     borrow_set: &BorrowSet<'tcx>,
 122     all_facts: &mut Option<AllFacts>,
 123     flow_inits: &mut FlowAtLocation<MaybeInitializedPlaces<'_, 'gcx, 'tcx>>,
 124     move_data: &MoveData<'tcx>,
 125     elements: &Rc<RegionValueElements>,
 126 ) -> MirTypeckResults<'tcx> {
 127     let implicit_region_bound = infcx.tcx.mk_region(ty::ReVar(universal_regions.fr_fn_body));
 128     let mut constraints = MirTypeckRegionConstraints {
 129         liveness_constraints: LivenessValues::new(elements),
 130         outlives_constraints: ConstraintSet::default(),
 131         closure_bounds_mapping: 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                     let impl_self_ty = self.normalize(impl_self_ty, locations);
1023
1024                     // There may be type variables in `substs` and hence
1025                     // in `impl_self_ty`, but they should all have been
1026                     // resolved to some fixed value during the first call
1027                     // to `relate`, above. Therefore, if we use
1028                     // `resolve_type_vars_if_possible` we should get to
1029                     // something without type variables. This is important
1030                     // because the `b` type in `relate_with_variance`
1031                     // below is not permitted to have inference variables.
1032                     let impl_self_ty = self.infcx.resolve_type_vars_if_possible(&impl_self_ty);
1033                     assert!(!impl_self_ty.has_infer_types());
1034
1035                     self.eq_types(self_ty, impl_self_ty, locations, category)?;
1036                 }
1037
1038                 // Prove the predicates coming along with `def_id`.
1039                 //
1040                 // Also, normalize the `instantiated_predicates`
1041                 // because otherwise we wind up with duplicate "type
1042                 // outlives" error messages.
1043                 let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);
1044                 let instantiated_predicates = self.fold_to_region_vid(instantiated_predicates);
1045                 self.normalize_and_prove_instantiated_predicates(
1046                     instantiated_predicates,
1047                     locations,
1048                 );
1049
1050                 // In addition to proving the predicates, we have to
1051                 // prove that `ty` is well-formed -- this is because
1052                 // the WF of `ty` is predicated on the substs being
1053                 // well-formed, and we haven't proven *that*. We don't
1054                 // want to prove the WF of types from  `substs` directly because they
1055                 // haven't been normalized.
1056                 //
1057                 // FIXME(nmatsakis): Well, perhaps we should normalize
1058                 // them?  This would only be relevant if some input
1059                 // type were ill-formed but did not appear in `ty`,
1060                 // which...could happen with normalization...
1061                 self.prove_predicate(ty::Predicate::WellFormed(ty), locations, category);
1062             }
1063         }
1064
1065         Ok(())
1066     }
1067
1068     /// Replace all free regions in `value` with their NLL `RegionVid`
1069     /// equivalents; if not in NLL, does nothing. This is never
1070     /// particularly necessary -- we'll do it lazilly as we process
1071     /// the value anyway -- but in some specific cases it is useful to
1072     /// normalize so we can suppress duplicate error messages.
1073     fn fold_to_region_vid<T>(
1074         &self,
1075         value: T
1076     ) -> T
1077     where T: TypeFoldable<'tcx>
1078     {
1079         if let Some(borrowck_context) = &self.borrowck_context {
1080             self.tcx().fold_regions(&value, &mut false, |r, _debruijn| {
1081                 if r.has_free_regions() {
1082                     self.tcx().mk_region(ty::RegionKind::ReVar(
1083                         borrowck_context.universal_regions.to_region_vid(r),
1084                     ))
1085                 } else {
1086                     r
1087                 }
1088             })
1089         } else {
1090             value
1091         }
1092     }
1093
1094     fn eq_opaque_type_and_type(
1095         &mut self,
1096         revealed_ty: Ty<'tcx>,
1097         anon_ty: Ty<'tcx>,
1098         anon_owner_def_id: DefId,
1099         locations: Locations,
1100         category: ConstraintCategory,
1101     ) -> Fallible<()> {
1102         debug!(
1103             "eq_opaque_type_and_type( \
1104              revealed_ty={:?}, \
1105              anon_ty={:?})",
1106             revealed_ty, anon_ty
1107         );
1108         let infcx = self.infcx;
1109         let tcx = infcx.tcx;
1110         let param_env = self.param_env;
1111         debug!("eq_opaque_type_and_type: mir_def_id={:?}", self.mir_def_id);
1112         let opaque_type_map = self.fully_perform_op(
1113             locations,
1114             category,
1115             CustomTypeOp::new(
1116                 |infcx| {
1117                     let mut obligations = ObligationAccumulator::default();
1118
1119                     let dummy_body_id = ObligationCause::dummy().body_id;
1120                     let (output_ty, opaque_type_map) =
1121                         obligations.add(infcx.instantiate_opaque_types(
1122                             anon_owner_def_id,
1123                             dummy_body_id,
1124                             param_env,
1125                             &anon_ty,
1126                         ));
1127                     debug!(
1128                         "eq_opaque_type_and_type: \
1129                          instantiated output_ty={:?} \
1130                          opaque_type_map={:#?} \
1131                          revealed_ty={:?}",
1132                         output_ty, opaque_type_map, revealed_ty
1133                     );
1134                     obligations.add(infcx
1135                         .at(&ObligationCause::dummy(), param_env)
1136                         .eq(output_ty, revealed_ty)?);
1137
1138                     for (&opaque_def_id, opaque_decl) in &opaque_type_map {
1139                         let opaque_defn_ty = tcx.type_of(opaque_def_id);
1140                         let opaque_defn_ty = opaque_defn_ty.subst(tcx, opaque_decl.substs);
1141                         let opaque_defn_ty = renumber::renumber_regions(infcx, &opaque_defn_ty);
1142                         debug!(
1143                             "eq_opaque_type_and_type: concrete_ty={:?}={:?} opaque_defn_ty={:?}",
1144                             opaque_decl.concrete_ty,
1145                             infcx.resolve_type_vars_if_possible(&opaque_decl.concrete_ty),
1146                             opaque_defn_ty
1147                         );
1148                         obligations.add(infcx
1149                             .at(&ObligationCause::dummy(), param_env)
1150                             .eq(opaque_decl.concrete_ty, opaque_defn_ty)?);
1151                     }
1152
1153                     debug!("eq_opaque_type_and_type: equated");
1154
1155                     Ok(InferOk {
1156                         value: Some(opaque_type_map),
1157                         obligations: obligations.into_vec(),
1158                     })
1159                 },
1160                 || "input_output".to_string(),
1161             ),
1162         )?;
1163
1164         let universal_region_relations = match self.universal_region_relations {
1165             Some(rel) => rel,
1166             None => return Ok(()),
1167         };
1168
1169         // Finally, if we instantiated the anon types successfully, we
1170         // have to solve any bounds (e.g., `-> impl Iterator` needs to
1171         // prove that `T: Iterator` where `T` is the type we
1172         // instantiated it with).
1173         if let Some(opaque_type_map) = opaque_type_map {
1174             for (opaque_def_id, opaque_decl) in opaque_type_map {
1175                 self.fully_perform_op(
1176                     locations,
1177                     ConstraintCategory::OpaqueType,
1178                     CustomTypeOp::new(
1179                         |_cx| {
1180                             infcx.constrain_opaque_type(
1181                                 opaque_def_id,
1182                                 &opaque_decl,
1183                                 universal_region_relations,
1184                             );
1185                             Ok(InferOk {
1186                                 value: (),
1187                                 obligations: vec![],
1188                             })
1189                         },
1190                         || "opaque_type_map".to_string(),
1191                     ),
1192                 )?;
1193             }
1194         }
1195         Ok(())
1196     }
1197
1198     fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
1199         self.infcx.tcx
1200     }
1201
1202     fn check_stmt(&mut self, mir: &Mir<'tcx>, stmt: &Statement<'tcx>, location: Location) {
1203         debug!("check_stmt: {:?}", stmt);
1204         let tcx = self.tcx();
1205         match stmt.kind {
1206             StatementKind::Assign(ref place, ref rv) => {
1207                 // Assignments to temporaries are not "interesting";
1208                 // they are not caused by the user, but rather artifacts
1209                 // of lowering. Assignments to other sorts of places *are* interesting
1210                 // though.
1211                 let category = match *place {
1212                     Place::Local(RETURN_PLACE) => ConstraintCategory::Return,
1213                     Place::Local(l) if !mir.local_decls[l].is_user_variable.is_some() => {
1214                         ConstraintCategory::Boring
1215                     }
1216                     _ => ConstraintCategory::Assignment,
1217                 };
1218
1219                 let place_ty = place.ty(mir, tcx).to_ty(tcx);
1220                 let rv_ty = rv.ty(mir, tcx);
1221                 if let Err(terr) =
1222                     self.sub_types_or_anon(rv_ty, place_ty, location.to_locations(), category)
1223                 {
1224                     span_mirbug!(
1225                         self,
1226                         stmt,
1227                         "bad assignment ({:?} = {:?}): {:?}",
1228                         place_ty,
1229                         rv_ty,
1230                         terr
1231                     );
1232                 }
1233
1234                 if let Some(user_ty) = self.rvalue_user_ty(rv) {
1235                     if let Err(terr) = self.relate_type_and_user_type(
1236                         rv_ty,
1237                         ty::Variance::Invariant,
1238                         user_ty,
1239                         location.to_locations(),
1240                         ConstraintCategory::Boring,
1241                     ) {
1242                         span_mirbug!(
1243                             self,
1244                             stmt,
1245                             "bad user type on rvalue ({:?} = {:?}): {:?}",
1246                             user_ty,
1247                             rv_ty,
1248                             terr
1249                         );
1250                     }
1251                 }
1252
1253                 self.check_rvalue(mir, rv, location);
1254                 if !self.tcx().features().unsized_locals {
1255                     let trait_ref = ty::TraitRef {
1256                         def_id: tcx.lang_items().sized_trait().unwrap(),
1257                         substs: tcx.mk_substs_trait(place_ty, &[]),
1258                     };
1259                     self.prove_trait_ref(
1260                         trait_ref,
1261                         location.to_locations(),
1262                         ConstraintCategory::SizedBound,
1263                     );
1264                 }
1265             }
1266             StatementKind::SetDiscriminant {
1267                 ref place,
1268                 variant_index,
1269             } => {
1270                 let place_type = place.ty(mir, tcx).to_ty(tcx);
1271                 let adt = match place_type.sty {
1272                     TyKind::Adt(adt, _) if adt.is_enum() => adt,
1273                     _ => {
1274                         span_bug!(
1275                             stmt.source_info.span,
1276                             "bad set discriminant ({:?} = {:?}): lhs is not an enum",
1277                             place,
1278                             variant_index
1279                         );
1280                     }
1281                 };
1282                 if variant_index >= adt.variants.len() {
1283                     span_bug!(
1284                         stmt.source_info.span,
1285                         "bad set discriminant ({:?} = {:?}): value of of range",
1286                         place,
1287                         variant_index
1288                     );
1289                 };
1290             }
1291             StatementKind::AscribeUserType(ref place, variance, c_ty) => {
1292                 let place_ty = place.ty(mir, tcx).to_ty(tcx);
1293                 if let Err(terr) = self.relate_type_and_user_type(
1294                     place_ty,
1295                     variance,
1296                     c_ty,
1297                     Locations::All(stmt.source_info.span),
1298                     ConstraintCategory::TypeAnnotation,
1299                 ) {
1300                     span_mirbug!(
1301                         self,
1302                         stmt,
1303                         "bad type assert ({:?} <: {:?}): {:?}",
1304                         place_ty,
1305                         c_ty,
1306                         terr
1307                     );
1308                 }
1309             }
1310             StatementKind::FakeRead(..)
1311             | StatementKind::StorageLive(_)
1312             | StatementKind::StorageDead(_)
1313             | StatementKind::InlineAsm { .. }
1314             | StatementKind::EndRegion(_)
1315             | StatementKind::Validate(..)
1316             | StatementKind::Nop => {}
1317         }
1318     }
1319
1320     fn check_terminator(
1321         &mut self,
1322         mir: &Mir<'tcx>,
1323         term: &Terminator<'tcx>,
1324         term_location: Location,
1325     ) {
1326         debug!("check_terminator: {:?}", term);
1327         let tcx = self.tcx();
1328         match term.kind {
1329             TerminatorKind::Goto { .. }
1330             | TerminatorKind::Resume
1331             | TerminatorKind::Abort
1332             | TerminatorKind::Return
1333             | TerminatorKind::GeneratorDrop
1334             | TerminatorKind::Unreachable
1335             | TerminatorKind::Drop { .. }
1336             | TerminatorKind::FalseEdges { .. }
1337             | TerminatorKind::FalseUnwind { .. } => {
1338                 // no checks needed for these
1339             }
1340
1341             TerminatorKind::DropAndReplace {
1342                 ref location,
1343                 ref value,
1344                 target: _,
1345                 unwind: _,
1346             } => {
1347                 let place_ty = location.ty(mir, tcx).to_ty(tcx);
1348                 let rv_ty = value.ty(mir, tcx);
1349
1350                 let locations = term_location.to_locations();
1351                 if let Err(terr) =
1352                     self.sub_types(rv_ty, place_ty, locations, ConstraintCategory::Assignment)
1353                 {
1354                     span_mirbug!(
1355                         self,
1356                         term,
1357                         "bad DropAndReplace ({:?} = {:?}): {:?}",
1358                         place_ty,
1359                         rv_ty,
1360                         terr
1361                     );
1362                 }
1363             }
1364             TerminatorKind::SwitchInt {
1365                 ref discr,
1366                 switch_ty,
1367                 ..
1368             } => {
1369                 let discr_ty = discr.ty(mir, tcx);
1370                 if let Err(terr) = self.sub_types(
1371                     discr_ty,
1372                     switch_ty,
1373                     term_location.to_locations(),
1374                     ConstraintCategory::Assignment,
1375                 ) {
1376                     span_mirbug!(
1377                         self,
1378                         term,
1379                         "bad SwitchInt ({:?} on {:?}): {:?}",
1380                         switch_ty,
1381                         discr_ty,
1382                         terr
1383                     );
1384                 }
1385                 if !switch_ty.is_integral() && !switch_ty.is_char() && !switch_ty.is_bool() {
1386                     span_mirbug!(self, term, "bad SwitchInt discr ty {:?}", switch_ty);
1387                 }
1388                 // FIXME: check the values
1389             }
1390             TerminatorKind::Call {
1391                 ref func,
1392                 ref args,
1393                 ref destination,
1394                 ..
1395             } => {
1396                 let func_ty = func.ty(mir, tcx);
1397                 debug!("check_terminator: call, func_ty={:?}", func_ty);
1398                 let sig = match func_ty.sty {
1399                     ty::FnDef(..) | ty::FnPtr(_) => func_ty.fn_sig(tcx),
1400                     _ => {
1401                         span_mirbug!(self, term, "call to non-function {:?}", func_ty);
1402                         return;
1403                     }
1404                 };
1405                 let (sig, map) = self.infcx.replace_late_bound_regions_with_fresh_var(
1406                     term.source_info.span,
1407                     LateBoundRegionConversionTime::FnCall,
1408                     &sig,
1409                 );
1410                 let sig = self.normalize(sig, term_location);
1411                 self.check_call_dest(mir, term, &sig, destination, term_location);
1412
1413                 self.prove_predicates(
1414                     sig.inputs().iter().map(|ty| ty::Predicate::WellFormed(ty)),
1415                     term_location.to_locations(),
1416                     ConstraintCategory::Boring,
1417                 );
1418
1419                 // The ordinary liveness rules will ensure that all
1420                 // regions in the type of the callee are live here. We
1421                 // then further constrain the late-bound regions that
1422                 // were instantiated at the call site to be live as
1423                 // well. The resulting is that all the input (and
1424                 // output) types in the signature must be live, since
1425                 // all the inputs that fed into it were live.
1426                 for &late_bound_region in map.values() {
1427                     if let Some(ref mut borrowck_context) = self.borrowck_context {
1428                         let region_vid = borrowck_context
1429                             .universal_regions
1430                             .to_region_vid(late_bound_region);
1431                         borrowck_context
1432                             .constraints
1433                             .liveness_constraints
1434                             .add_element(region_vid, term_location);
1435                     }
1436                 }
1437
1438                 self.check_call_inputs(mir, term, &sig, args, term_location);
1439             }
1440             TerminatorKind::Assert {
1441                 ref cond, ref msg, ..
1442             } => {
1443                 let cond_ty = cond.ty(mir, tcx);
1444                 if cond_ty != tcx.types.bool {
1445                     span_mirbug!(self, term, "bad Assert ({:?}, not bool", cond_ty);
1446                 }
1447
1448                 if let BoundsCheck { ref len, ref index } = *msg {
1449                     if len.ty(mir, tcx) != tcx.types.usize {
1450                         span_mirbug!(self, len, "bounds-check length non-usize {:?}", len)
1451                     }
1452                     if index.ty(mir, tcx) != tcx.types.usize {
1453                         span_mirbug!(self, index, "bounds-check index non-usize {:?}", index)
1454                     }
1455                 }
1456             }
1457             TerminatorKind::Yield { ref value, .. } => {
1458                 let value_ty = value.ty(mir, tcx);
1459                 match mir.yield_ty {
1460                     None => span_mirbug!(self, term, "yield in non-generator"),
1461                     Some(ty) => {
1462                         if let Err(terr) = self.sub_types(
1463                             value_ty,
1464                             ty,
1465                             term_location.to_locations(),
1466                             ConstraintCategory::Return,
1467                         ) {
1468                             span_mirbug!(
1469                                 self,
1470                                 term,
1471                                 "type of yield value is {:?}, but the yield type is {:?}: {:?}",
1472                                 value_ty,
1473                                 ty,
1474                                 terr
1475                             );
1476                         }
1477                     }
1478                 }
1479             }
1480         }
1481     }
1482
1483     fn check_call_dest(
1484         &mut self,
1485         mir: &Mir<'tcx>,
1486         term: &Terminator<'tcx>,
1487         sig: &ty::FnSig<'tcx>,
1488         destination: &Option<(Place<'tcx>, BasicBlock)>,
1489         term_location: Location,
1490     ) {
1491         let tcx = self.tcx();
1492         match *destination {
1493             Some((ref dest, _target_block)) => {
1494                 let dest_ty = dest.ty(mir, tcx).to_ty(tcx);
1495                 let category = match *dest {
1496                     Place::Local(RETURN_PLACE) => ConstraintCategory::Return,
1497                     Place::Local(l) if !mir.local_decls[l].is_user_variable.is_some() => {
1498                         ConstraintCategory::Boring
1499                     }
1500                     _ => ConstraintCategory::Assignment,
1501                 };
1502
1503                 let locations = term_location.to_locations();
1504
1505                 if let Err(terr) =
1506                     self.sub_types_or_anon(sig.output(), dest_ty, locations, category)
1507                 {
1508                     span_mirbug!(
1509                         self,
1510                         term,
1511                         "call dest mismatch ({:?} <- {:?}): {:?}",
1512                         dest_ty,
1513                         sig.output(),
1514                         terr
1515                     );
1516                 }
1517
1518                 // When `#![feature(unsized_locals)]` is not enabled,
1519                 // this check is done at `check_local`.
1520                 if self.tcx().features().unsized_locals {
1521                     let span = term.source_info.span;
1522                     self.ensure_place_sized(dest_ty, span);
1523                 }
1524             }
1525             None => {
1526                 // FIXME(canndrew): This is_never should probably be an is_uninhabited
1527                 if !sig.output().is_never() {
1528                     span_mirbug!(self, term, "call to converging function {:?} w/o dest", sig);
1529                 }
1530             }
1531         }
1532     }
1533
1534     fn check_call_inputs(
1535         &mut self,
1536         mir: &Mir<'tcx>,
1537         term: &Terminator<'tcx>,
1538         sig: &ty::FnSig<'tcx>,
1539         args: &[Operand<'tcx>],
1540         term_location: Location,
1541     ) {
1542         debug!("check_call_inputs({:?}, {:?})", sig, args);
1543         if args.len() < sig.inputs().len() || (args.len() > sig.inputs().len() && !sig.variadic) {
1544             span_mirbug!(self, term, "call to {:?} with wrong # of args", sig);
1545         }
1546         for (n, (fn_arg, op_arg)) in sig.inputs().iter().zip(args).enumerate() {
1547             let op_arg_ty = op_arg.ty(mir, self.tcx());
1548             if let Err(terr) = self.sub_types(
1549                 op_arg_ty,
1550                 fn_arg,
1551                 term_location.to_locations(),
1552                 ConstraintCategory::CallArgument,
1553             ) {
1554                 span_mirbug!(
1555                     self,
1556                     term,
1557                     "bad arg #{:?} ({:?} <- {:?}): {:?}",
1558                     n,
1559                     fn_arg,
1560                     op_arg_ty,
1561                     terr
1562                 );
1563             }
1564         }
1565     }
1566
1567     fn check_iscleanup(&mut self, mir: &Mir<'tcx>, block_data: &BasicBlockData<'tcx>) {
1568         let is_cleanup = block_data.is_cleanup;
1569         self.last_span = block_data.terminator().source_info.span;
1570         match block_data.terminator().kind {
1571             TerminatorKind::Goto { target } => {
1572                 self.assert_iscleanup(mir, block_data, target, is_cleanup)
1573             }
1574             TerminatorKind::SwitchInt { ref targets, .. } => for target in targets {
1575                 self.assert_iscleanup(mir, block_data, *target, is_cleanup);
1576             },
1577             TerminatorKind::Resume => if !is_cleanup {
1578                 span_mirbug!(self, block_data, "resume on non-cleanup block!")
1579             },
1580             TerminatorKind::Abort => if !is_cleanup {
1581                 span_mirbug!(self, block_data, "abort on non-cleanup block!")
1582             },
1583             TerminatorKind::Return => if is_cleanup {
1584                 span_mirbug!(self, block_data, "return on cleanup block")
1585             },
1586             TerminatorKind::GeneratorDrop { .. } => if is_cleanup {
1587                 span_mirbug!(self, block_data, "generator_drop in cleanup block")
1588             },
1589             TerminatorKind::Yield { resume, drop, .. } => {
1590                 if is_cleanup {
1591                     span_mirbug!(self, block_data, "yield in cleanup block")
1592                 }
1593                 self.assert_iscleanup(mir, block_data, resume, is_cleanup);
1594                 if let Some(drop) = drop {
1595                     self.assert_iscleanup(mir, block_data, drop, is_cleanup);
1596                 }
1597             }
1598             TerminatorKind::Unreachable => {}
1599             TerminatorKind::Drop { target, unwind, .. }
1600             | TerminatorKind::DropAndReplace { target, unwind, .. }
1601             | TerminatorKind::Assert {
1602                 target,
1603                 cleanup: unwind,
1604                 ..
1605             } => {
1606                 self.assert_iscleanup(mir, block_data, target, is_cleanup);
1607                 if let Some(unwind) = unwind {
1608                     if is_cleanup {
1609                         span_mirbug!(self, block_data, "unwind on cleanup block")
1610                     }
1611                     self.assert_iscleanup(mir, block_data, unwind, true);
1612                 }
1613             }
1614             TerminatorKind::Call {
1615                 ref destination,
1616                 cleanup,
1617                 ..
1618             } => {
1619                 if let &Some((_, target)) = destination {
1620                     self.assert_iscleanup(mir, block_data, target, is_cleanup);
1621                 }
1622                 if let Some(cleanup) = cleanup {
1623                     if is_cleanup {
1624                         span_mirbug!(self, block_data, "cleanup on cleanup block")
1625                     }
1626                     self.assert_iscleanup(mir, block_data, cleanup, true);
1627                 }
1628             }
1629             TerminatorKind::FalseEdges {
1630                 real_target,
1631                 ref imaginary_targets,
1632             } => {
1633                 self.assert_iscleanup(mir, block_data, real_target, is_cleanup);
1634                 for target in imaginary_targets {
1635                     self.assert_iscleanup(mir, block_data, *target, is_cleanup);
1636                 }
1637             }
1638             TerminatorKind::FalseUnwind {
1639                 real_target,
1640                 unwind,
1641             } => {
1642                 self.assert_iscleanup(mir, block_data, real_target, is_cleanup);
1643                 if let Some(unwind) = unwind {
1644                     if is_cleanup {
1645                         span_mirbug!(
1646                             self,
1647                             block_data,
1648                             "cleanup in cleanup block via false unwind"
1649                         );
1650                     }
1651                     self.assert_iscleanup(mir, block_data, unwind, true);
1652                 }
1653             }
1654         }
1655     }
1656
1657     fn assert_iscleanup(
1658         &mut self,
1659         mir: &Mir<'tcx>,
1660         ctxt: &dyn fmt::Debug,
1661         bb: BasicBlock,
1662         iscleanuppad: bool,
1663     ) {
1664         if mir[bb].is_cleanup != iscleanuppad {
1665             span_mirbug!(
1666                 self,
1667                 ctxt,
1668                 "cleanuppad mismatch: {:?} should be {:?}",
1669                 bb,
1670                 iscleanuppad
1671             );
1672         }
1673     }
1674
1675     fn check_local(&mut self, mir: &Mir<'tcx>, local: Local, local_decl: &LocalDecl<'tcx>) {
1676         match mir.local_kind(local) {
1677             LocalKind::ReturnPointer | LocalKind::Arg => {
1678                 // return values of normal functions are required to be
1679                 // sized by typeck, but return values of ADT constructors are
1680                 // not because we don't include a `Self: Sized` bounds on them.
1681                 //
1682                 // Unbound parts of arguments were never required to be Sized
1683                 // - maybe we should make that a warning.
1684                 return;
1685             }
1686             LocalKind::Var | LocalKind::Temp => {}
1687         }
1688
1689         // When `#![feature(unsized_locals)]` is enabled, only function calls
1690         // and nullary ops are checked in `check_call_dest`.
1691         if !self.tcx().features().unsized_locals {
1692             let span = local_decl.source_info.span;
1693             let ty = local_decl.ty;
1694             self.ensure_place_sized(ty, span);
1695         }
1696     }
1697
1698     fn ensure_place_sized(&mut self, ty: Ty<'tcx>, span: Span) {
1699         let tcx = self.tcx();
1700
1701         // Erase the regions from `ty` to get a global type.  The
1702         // `Sized` bound in no way depends on precise regions, so this
1703         // shouldn't affect `is_sized`.
1704         let gcx = tcx.global_tcx();
1705         let erased_ty = gcx.lift(&tcx.erase_regions(&ty)).unwrap();
1706         if !erased_ty.is_sized(gcx.at(span), self.param_env) {
1707             // in current MIR construction, all non-control-flow rvalue
1708             // expressions evaluate through `as_temp` or `into` a return
1709             // slot or local, so to find all unsized rvalues it is enough
1710             // to check all temps, return slots and locals.
1711             if let None = self.reported_errors.replace((ty, span)) {
1712                 let mut diag = struct_span_err!(
1713                     self.tcx().sess,
1714                     span,
1715                     E0161,
1716                     "cannot move a value of type {0}: the size of {0} \
1717                      cannot be statically determined",
1718                     ty
1719                 );
1720
1721                 // While this is located in `nll::typeck` this error is not
1722                 // an NLL error, it's a required check to prevent creation
1723                 // of unsized rvalues in certain cases:
1724                 // * operand of a box expression
1725                 // * callee in a call expression
1726                 diag.emit();
1727             }
1728         }
1729     }
1730
1731     fn aggregate_field_ty(
1732         &mut self,
1733         ak: &AggregateKind<'tcx>,
1734         field_index: usize,
1735         location: Location,
1736     ) -> Result<Ty<'tcx>, FieldAccessError> {
1737         let tcx = self.tcx();
1738
1739         match *ak {
1740             AggregateKind::Adt(def, variant_index, substs, _, active_field_index) => {
1741                 let variant = &def.variants[variant_index];
1742                 let adj_field_index = active_field_index.unwrap_or(field_index);
1743                 if let Some(field) = variant.fields.get(adj_field_index) {
1744                     Ok(self.normalize(field.ty(tcx, substs), location))
1745                 } else {
1746                     Err(FieldAccessError::OutOfRange {
1747                         field_count: variant.fields.len(),
1748                     })
1749                 }
1750             }
1751             AggregateKind::Closure(def_id, substs) => {
1752                 match substs.upvar_tys(def_id, tcx).nth(field_index) {
1753                     Some(ty) => Ok(ty),
1754                     None => Err(FieldAccessError::OutOfRange {
1755                         field_count: substs.upvar_tys(def_id, tcx).count(),
1756                     }),
1757                 }
1758             }
1759             AggregateKind::Generator(def_id, substs, _) => {
1760                 // Try pre-transform fields first (upvars and current state)
1761                 if let Some(ty) = substs.pre_transforms_tys(def_id, tcx).nth(field_index) {
1762                     Ok(ty)
1763                 } else {
1764                     // Then try `field_tys` which contains all the fields, but it
1765                     // requires the final optimized MIR.
1766                     match substs.field_tys(def_id, tcx).nth(field_index) {
1767                         Some(ty) => Ok(ty),
1768                         None => Err(FieldAccessError::OutOfRange {
1769                             field_count: substs.field_tys(def_id, tcx).count(),
1770                         }),
1771                     }
1772                 }
1773             }
1774             AggregateKind::Array(ty) => Ok(ty),
1775             AggregateKind::Tuple => {
1776                 unreachable!("This should have been covered in check_rvalues");
1777             }
1778         }
1779     }
1780
1781     fn check_rvalue(&mut self, mir: &Mir<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
1782         let tcx = self.tcx();
1783
1784         match rvalue {
1785             Rvalue::Aggregate(ak, ops) => {
1786                 self.check_aggregate_rvalue(mir, rvalue, ak, ops, location)
1787             }
1788
1789             Rvalue::Repeat(operand, len) => if *len > 1 {
1790                 let operand_ty = operand.ty(mir, tcx);
1791
1792                 let trait_ref = ty::TraitRef {
1793                     def_id: tcx.lang_items().copy_trait().unwrap(),
1794                     substs: tcx.mk_substs_trait(operand_ty, &[]),
1795                 };
1796
1797                 self.prove_trait_ref(
1798                     trait_ref,
1799                     location.to_locations(),
1800                     ConstraintCategory::CopyBound,
1801                 );
1802             },
1803
1804             Rvalue::NullaryOp(_, ty) => {
1805                 // Even with unsized locals cannot box an unsized value.
1806                 if self.tcx().features().unsized_locals {
1807                     let span = mir.source_info(location).span;
1808                     self.ensure_place_sized(ty, span);
1809                 }
1810
1811                 let trait_ref = ty::TraitRef {
1812                     def_id: tcx.lang_items().sized_trait().unwrap(),
1813                     substs: tcx.mk_substs_trait(ty, &[]),
1814                 };
1815
1816                 self.prove_trait_ref(
1817                     trait_ref,
1818                     location.to_locations(),
1819                     ConstraintCategory::SizedBound,
1820                 );
1821             }
1822
1823             Rvalue::Cast(cast_kind, op, ty) => {
1824                 match cast_kind {
1825                     CastKind::ReifyFnPointer => {
1826                         let fn_sig = op.ty(mir, tcx).fn_sig(tcx);
1827
1828                         // The type that we see in the fcx is like
1829                         // `foo::<'a, 'b>`, where `foo` is the path to a
1830                         // function definition. When we extract the
1831                         // signature, it comes from the `fn_sig` query,
1832                         // and hence may contain unnormalized results.
1833                         let fn_sig = self.normalize(fn_sig, location);
1834
1835                         let ty_fn_ptr_from = tcx.mk_fn_ptr(fn_sig);
1836
1837                         if let Err(terr) = self.eq_types(
1838                             ty_fn_ptr_from,
1839                             ty,
1840                             location.to_locations(),
1841                             ConstraintCategory::Cast,
1842                         ) {
1843                             span_mirbug!(
1844                                 self,
1845                                 rvalue,
1846                                 "equating {:?} with {:?} yields {:?}",
1847                                 ty_fn_ptr_from,
1848                                 ty,
1849                                 terr
1850                             );
1851                         }
1852                     }
1853
1854                     CastKind::ClosureFnPointer => {
1855                         let sig = match op.ty(mir, tcx).sty {
1856                             ty::Closure(def_id, substs) => {
1857                                 substs.closure_sig_ty(def_id, tcx).fn_sig(tcx)
1858                             }
1859                             _ => bug!(),
1860                         };
1861                         let ty_fn_ptr_from = tcx.coerce_closure_fn_ty(sig);
1862
1863                         if let Err(terr) = self.eq_types(
1864                             ty_fn_ptr_from,
1865                             ty,
1866                             location.to_locations(),
1867                             ConstraintCategory::Cast,
1868                         ) {
1869                             span_mirbug!(
1870                                 self,
1871                                 rvalue,
1872                                 "equating {:?} with {:?} yields {:?}",
1873                                 ty_fn_ptr_from,
1874                                 ty,
1875                                 terr
1876                             );
1877                         }
1878                     }
1879
1880                     CastKind::UnsafeFnPointer => {
1881                         let fn_sig = op.ty(mir, tcx).fn_sig(tcx);
1882
1883                         // The type that we see in the fcx is like
1884                         // `foo::<'a, 'b>`, where `foo` is the path to a
1885                         // function definition. When we extract the
1886                         // signature, it comes from the `fn_sig` query,
1887                         // and hence may contain unnormalized results.
1888                         let fn_sig = self.normalize(fn_sig, location);
1889
1890                         let ty_fn_ptr_from = tcx.safe_to_unsafe_fn_ty(fn_sig);
1891
1892                         if let Err(terr) = self.eq_types(
1893                             ty_fn_ptr_from,
1894                             ty,
1895                             location.to_locations(),
1896                             ConstraintCategory::Cast,
1897                         ) {
1898                             span_mirbug!(
1899                                 self,
1900                                 rvalue,
1901                                 "equating {:?} with {:?} yields {:?}",
1902                                 ty_fn_ptr_from,
1903                                 ty,
1904                                 terr
1905                             );
1906                         }
1907                     }
1908
1909                     CastKind::Unsize => {
1910                         let &ty = ty;
1911                         let trait_ref = ty::TraitRef {
1912                             def_id: tcx.lang_items().coerce_unsized_trait().unwrap(),
1913                             substs: tcx.mk_substs_trait(op.ty(mir, tcx), &[ty.into()]),
1914                         };
1915
1916                         self.prove_trait_ref(
1917                             trait_ref,
1918                             location.to_locations(),
1919                             ConstraintCategory::Cast,
1920                         );
1921                     }
1922
1923                     CastKind::Misc => {}
1924                 }
1925             }
1926
1927             Rvalue::Ref(region, _borrow_kind, borrowed_place) => {
1928                 self.add_reborrow_constraint(location, region, borrowed_place);
1929             }
1930
1931             // FIXME: These other cases have to be implemented in future PRs
1932             Rvalue::Use(..)
1933             | Rvalue::Len(..)
1934             | Rvalue::BinaryOp(..)
1935             | Rvalue::CheckedBinaryOp(..)
1936             | Rvalue::UnaryOp(..)
1937             | Rvalue::Discriminant(..) => {}
1938         }
1939     }
1940
1941     /// If this rvalue supports a user-given type annotation, then
1942     /// extract and return it. This represents the final type of the
1943     /// rvalue and will be unified with the inferred type.
1944     fn rvalue_user_ty(&self, rvalue: &Rvalue<'tcx>) -> Option<UserTypeAnnotation<'tcx>> {
1945         match rvalue {
1946             Rvalue::Use(_)
1947             | Rvalue::Repeat(..)
1948             | Rvalue::Ref(..)
1949             | Rvalue::Len(..)
1950             | Rvalue::Cast(..)
1951             | Rvalue::BinaryOp(..)
1952             | Rvalue::CheckedBinaryOp(..)
1953             | Rvalue::NullaryOp(..)
1954             | Rvalue::UnaryOp(..)
1955             | Rvalue::Discriminant(..) => None,
1956
1957             Rvalue::Aggregate(aggregate, _) => match **aggregate {
1958                 AggregateKind::Adt(_, _, _, user_ty, _) => user_ty,
1959                 AggregateKind::Array(_) => None,
1960                 AggregateKind::Tuple => None,
1961                 AggregateKind::Closure(_, _) => None,
1962                 AggregateKind::Generator(_, _, _) => None,
1963             },
1964         }
1965     }
1966
1967     fn check_aggregate_rvalue(
1968         &mut self,
1969         mir: &Mir<'tcx>,
1970         rvalue: &Rvalue<'tcx>,
1971         aggregate_kind: &AggregateKind<'tcx>,
1972         operands: &[Operand<'tcx>],
1973         location: Location,
1974     ) {
1975         let tcx = self.tcx();
1976
1977         self.prove_aggregate_predicates(aggregate_kind, location);
1978
1979         if *aggregate_kind == AggregateKind::Tuple {
1980             // tuple rvalue field type is always the type of the op. Nothing to check here.
1981             return;
1982         }
1983
1984         for (i, operand) in operands.iter().enumerate() {
1985             let field_ty = match self.aggregate_field_ty(aggregate_kind, i, location) {
1986                 Ok(field_ty) => field_ty,
1987                 Err(FieldAccessError::OutOfRange { field_count }) => {
1988                     span_mirbug!(
1989                         self,
1990                         rvalue,
1991                         "accessed field #{} but variant only has {}",
1992                         i,
1993                         field_count
1994                     );
1995                     continue;
1996                 }
1997             };
1998             let operand_ty = operand.ty(mir, tcx);
1999
2000             if let Err(terr) = self.sub_types(
2001                 operand_ty,
2002                 field_ty,
2003                 location.to_locations(),
2004                 ConstraintCategory::Boring,
2005             ) {
2006                 span_mirbug!(
2007                     self,
2008                     rvalue,
2009                     "{:?} is not a subtype of {:?}: {:?}",
2010                     operand_ty,
2011                     field_ty,
2012                     terr
2013                 );
2014             }
2015         }
2016     }
2017
2018     /// Add the constraints that arise from a borrow expression `&'a P` at the location `L`.
2019     ///
2020     /// # Parameters
2021     ///
2022     /// - `location`: the location `L` where the borrow expression occurs
2023     /// - `borrow_region`: the region `'a` associated with the borrow
2024     /// - `borrowed_place`: the place `P` being borrowed
2025     fn add_reborrow_constraint(
2026         &mut self,
2027         location: Location,
2028         borrow_region: ty::Region<'tcx>,
2029         borrowed_place: &Place<'tcx>,
2030     ) {
2031         // These constraints are only meaningful during borrowck:
2032         let BorrowCheckContext {
2033             borrow_set,
2034             location_table,
2035             all_facts,
2036             constraints,
2037             ..
2038         } = match self.borrowck_context {
2039             Some(ref mut borrowck_context) => borrowck_context,
2040             None => return,
2041         };
2042
2043         // In Polonius mode, we also push a `borrow_region` fact
2044         // linking the loan to the region (in some cases, though,
2045         // there is no loan associated with this borrow expression --
2046         // that occurs when we are borrowing an unsafe place, for
2047         // example).
2048         if let Some(all_facts) = all_facts {
2049             if let Some(borrow_index) = borrow_set.location_map.get(&location) {
2050                 let region_vid = borrow_region.to_region_vid();
2051                 all_facts.borrow_region.push((
2052                     region_vid,
2053                     *borrow_index,
2054                     location_table.mid_index(location),
2055                 ));
2056             }
2057         }
2058
2059         // If we are reborrowing the referent of another reference, we
2060         // need to add outlives relationships. In a case like `&mut
2061         // *p`, where the `p` has type `&'b mut Foo`, for example, we
2062         // need to ensure that `'b: 'a`.
2063
2064         let mut borrowed_place = borrowed_place;
2065
2066         debug!(
2067             "add_reborrow_constraint({:?}, {:?}, {:?})",
2068             location, borrow_region, borrowed_place
2069         );
2070         while let Place::Projection(box PlaceProjection { base, elem }) = borrowed_place {
2071             debug!("add_reborrow_constraint - iteration {:?}", borrowed_place);
2072
2073             match *elem {
2074                 ProjectionElem::Deref => {
2075                     let tcx = self.infcx.tcx;
2076                     let base_ty = base.ty(self.mir, tcx).to_ty(tcx);
2077
2078                     debug!("add_reborrow_constraint - base_ty = {:?}", base_ty);
2079                     match base_ty.sty {
2080                         ty::Ref(ref_region, _, mutbl) => {
2081                             constraints.outlives_constraints.push(OutlivesConstraint {
2082                                 sup: ref_region.to_region_vid(),
2083                                 sub: borrow_region.to_region_vid(),
2084                                 locations: location.to_locations(),
2085                                 category: ConstraintCategory::Boring,
2086                             });
2087
2088                             match mutbl {
2089                                 hir::Mutability::MutImmutable => {
2090                                     // Immutable reference. We don't need the base
2091                                     // to be valid for the entire lifetime of
2092                                     // the borrow.
2093                                     break;
2094                                 }
2095                                 hir::Mutability::MutMutable => {
2096                                     // Mutable reference. We *do* need the base
2097                                     // to be valid, because after the base becomes
2098                                     // invalid, someone else can use our mutable deref.
2099
2100                                     // This is in order to make the following function
2101                                     // illegal:
2102                                     // ```
2103                                     // fn unsafe_deref<'a, 'b>(x: &'a &'b mut T) -> &'b mut T {
2104                                     //     &mut *x
2105                                     // }
2106                                     // ```
2107                                     //
2108                                     // As otherwise you could clone `&mut T` using the
2109                                     // following function:
2110                                     // ```
2111                                     // fn bad(x: &mut T) -> (&mut T, &mut T) {
2112                                     //     let my_clone = unsafe_deref(&'a x);
2113                                     //     ENDREGION 'a;
2114                                     //     (my_clone, x)
2115                                     // }
2116                                     // ```
2117                                 }
2118                             }
2119                         }
2120                         ty::RawPtr(..) => {
2121                             // deref of raw pointer, guaranteed to be valid
2122                             break;
2123                         }
2124                         ty::Adt(def, _) if def.is_box() => {
2125                             // deref of `Box`, need the base to be valid - propagate
2126                         }
2127                         _ => bug!("unexpected deref ty {:?} in {:?}", base_ty, borrowed_place),
2128                     }
2129                 }
2130                 ProjectionElem::Field(..)
2131                 | ProjectionElem::Downcast(..)
2132                 | ProjectionElem::Index(..)
2133                 | ProjectionElem::ConstantIndex { .. }
2134                 | ProjectionElem::Subslice { .. } => {
2135                     // other field access
2136                 }
2137             }
2138
2139             // The "propagate" case. We need to check that our base is valid
2140             // for the borrow's lifetime.
2141             borrowed_place = base;
2142         }
2143     }
2144
2145     fn prove_aggregate_predicates(
2146         &mut self,
2147         aggregate_kind: &AggregateKind<'tcx>,
2148         location: Location,
2149     ) {
2150         let tcx = self.tcx();
2151
2152         debug!(
2153             "prove_aggregate_predicates(aggregate_kind={:?}, location={:?})",
2154             aggregate_kind, location
2155         );
2156
2157         let instantiated_predicates = match aggregate_kind {
2158             AggregateKind::Adt(def, _, substs, _, _) => {
2159                 tcx.predicates_of(def.did).instantiate(tcx, substs)
2160             }
2161
2162             // For closures, we have some **extra requirements** we
2163             //
2164             // have to check. In particular, in their upvars and
2165             // signatures, closures often reference various regions
2166             // from the surrounding function -- we call those the
2167             // closure's free regions. When we borrow-check (and hence
2168             // region-check) closures, we may find that the closure
2169             // requires certain relationships between those free
2170             // regions. However, because those free regions refer to
2171             // portions of the CFG of their caller, the closure is not
2172             // in a position to verify those relationships. In that
2173             // case, the requirements get "propagated" to us, and so
2174             // we have to solve them here where we instantiate the
2175             // closure.
2176             //
2177             // Despite the opacity of the previous parapgrah, this is
2178             // actually relatively easy to understand in terms of the
2179             // desugaring. A closure gets desugared to a struct, and
2180             // these extra requirements are basically like where
2181             // clauses on the struct.
2182             AggregateKind::Closure(def_id, ty::ClosureSubsts { substs })
2183             | AggregateKind::Generator(def_id, ty::GeneratorSubsts { substs }, _) => {
2184                 self.prove_closure_bounds(tcx, *def_id, substs, location)
2185             }
2186
2187             AggregateKind::Array(_) | AggregateKind::Tuple => ty::InstantiatedPredicates::empty(),
2188         };
2189
2190         self.normalize_and_prove_instantiated_predicates(
2191             instantiated_predicates,
2192             location.to_locations(),
2193         );
2194     }
2195
2196     fn prove_closure_bounds(
2197         &mut self,
2198         tcx: TyCtxt<'a, 'gcx, 'tcx>,
2199         def_id: DefId,
2200         substs: &'tcx Substs<'tcx>,
2201         location: Location,
2202     ) -> ty::InstantiatedPredicates<'tcx> {
2203         if let Some(closure_region_requirements) = tcx.mir_borrowck(def_id).closure_requirements {
2204             let closure_constraints =
2205                 closure_region_requirements.apply_requirements(tcx, location, def_id, substs);
2206
2207             if let Some(ref mut borrowck_context) = self.borrowck_context {
2208                 let bounds_mapping = closure_constraints
2209                     .iter()
2210                     .enumerate()
2211                     .filter_map(|(idx, constraint)| {
2212                         let ty::OutlivesPredicate(k1, r2) =
2213                             constraint.no_late_bound_regions().unwrap_or_else(|| {
2214                                 bug!("query_constraint {:?} contained bound regions", constraint,);
2215                             });
2216
2217                         match k1.unpack() {
2218                             UnpackedKind::Lifetime(r1) => {
2219                                 // constraint is r1: r2
2220                                 let r1_vid = borrowck_context.universal_regions.to_region_vid(r1);
2221                                 let r2_vid = borrowck_context.universal_regions.to_region_vid(r2);
2222                                 let outlives_requirements =
2223                                     &closure_region_requirements.outlives_requirements[idx];
2224                                 Some((
2225                                     (r1_vid, r2_vid),
2226                                     (
2227                                         outlives_requirements.category,
2228                                         outlives_requirements.blame_span,
2229                                     ),
2230                                 ))
2231                             }
2232                             UnpackedKind::Type(_) => None,
2233                         }
2234                     })
2235                     .collect();
2236
2237                 let existing = borrowck_context
2238                     .constraints
2239                     .closure_bounds_mapping
2240                     .insert(location, bounds_mapping);
2241                 assert!(
2242                     existing.is_none(),
2243                     "Multiple closures at the same location."
2244                 );
2245             }
2246
2247             self.push_region_constraints(
2248                 location.to_locations(),
2249                 ConstraintCategory::ClosureBounds,
2250                 &closure_constraints,
2251             );
2252         }
2253
2254         tcx.predicates_of(def_id).instantiate(tcx, substs)
2255     }
2256
2257     fn prove_trait_ref(
2258         &mut self,
2259         trait_ref: ty::TraitRef<'tcx>,
2260         locations: Locations,
2261         category: ConstraintCategory,
2262     ) {
2263         self.prove_predicates(
2264             Some(ty::Predicate::Trait(
2265                 trait_ref.to_poly_trait_ref().to_poly_trait_predicate(),
2266             )),
2267             locations,
2268             category,
2269         );
2270     }
2271
2272     fn normalize_and_prove_instantiated_predicates(
2273         &mut self,
2274         instantiated_predicates: ty::InstantiatedPredicates<'tcx>,
2275         locations: Locations,
2276     ) {
2277         for predicate in instantiated_predicates.predicates {
2278             let predicate = self.normalize(predicate, locations);
2279             self.prove_predicate(predicate, locations, ConstraintCategory::Boring);
2280         }
2281     }
2282
2283     fn prove_predicates(
2284         &mut self,
2285         predicates: impl IntoIterator<Item = ty::Predicate<'tcx>>,
2286         locations: Locations,
2287         category: ConstraintCategory,
2288     ) {
2289         for predicate in predicates {
2290             debug!(
2291                 "prove_predicates(predicate={:?}, locations={:?})",
2292                 predicate, locations,
2293             );
2294
2295             self.prove_predicate(predicate, locations, category);
2296         }
2297     }
2298
2299     fn prove_predicate(
2300         &mut self,
2301         predicate: ty::Predicate<'tcx>,
2302         locations: Locations,
2303         category: ConstraintCategory,
2304     ) {
2305         debug!(
2306             "prove_predicate(predicate={:?}, location={:?})",
2307             predicate, locations,
2308         );
2309
2310         let param_env = self.param_env;
2311         self.fully_perform_op(
2312             locations,
2313             category,
2314             param_env.and(type_op::prove_predicate::ProvePredicate::new(predicate)),
2315         ).unwrap_or_else(|NoSolution| {
2316             span_mirbug!(self, NoSolution, "could not prove {:?}", predicate);
2317         })
2318     }
2319
2320     fn typeck_mir(&mut self, mir: &Mir<'tcx>) {
2321         self.last_span = mir.span;
2322         debug!("run_on_mir: {:?}", mir.span);
2323
2324         for (local, local_decl) in mir.local_decls.iter_enumerated() {
2325             self.check_local(mir, local, local_decl);
2326         }
2327
2328         for (block, block_data) in mir.basic_blocks().iter_enumerated() {
2329             let mut location = Location {
2330                 block,
2331                 statement_index: 0,
2332             };
2333             for stmt in &block_data.statements {
2334                 if !stmt.source_info.span.is_dummy() {
2335                     self.last_span = stmt.source_info.span;
2336                 }
2337                 self.check_stmt(mir, stmt, location);
2338                 location.statement_index += 1;
2339             }
2340
2341             self.check_terminator(mir, block_data.terminator(), location);
2342             self.check_iscleanup(mir, block_data);
2343         }
2344     }
2345
2346     fn normalize<T>(&mut self, value: T, location: impl NormalizeLocation) -> T
2347     where
2348         T: type_op::normalize::Normalizable<'gcx, 'tcx> + Copy,
2349     {
2350         debug!("normalize(value={:?}, location={:?})", value, location);
2351         let param_env = self.param_env;
2352         self.fully_perform_op(
2353             location.to_locations(),
2354             ConstraintCategory::Boring,
2355             param_env.and(type_op::normalize::Normalize::new(value)),
2356         ).unwrap_or_else(|NoSolution| {
2357             span_mirbug!(self, NoSolution, "failed to normalize `{:?}`", value);
2358             value
2359         })
2360     }
2361 }
2362
2363 pub struct TypeckMir;
2364
2365 impl MirPass for TypeckMir {
2366     fn run_pass<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, src: MirSource, mir: &mut Mir<'tcx>) {
2367         let def_id = src.def_id;
2368         debug!("run_pass: {:?}", def_id);
2369
2370         // When NLL is enabled, the borrow checker runs the typeck
2371         // itself, so we don't need this MIR pass anymore.
2372         if tcx.use_mir_borrowck() {
2373             return;
2374         }
2375
2376         if tcx.sess.err_count() > 0 {
2377             // compiling a broken program can obviously result in a
2378             // broken MIR, so try not to report duplicate errors.
2379             return;
2380         }
2381
2382         if tcx.is_struct_constructor(def_id) {
2383             // We just assume that the automatically generated struct constructors are
2384             // correct. See the comment in the `mir_borrowck` implementation for an
2385             // explanation why we need this.
2386             return;
2387         }
2388
2389         let param_env = tcx.param_env(def_id);
2390         tcx.infer_ctxt().enter(|infcx| {
2391             type_check_internal(
2392                 &infcx,
2393                 def_id,
2394                 param_env,
2395                 mir,
2396                 &vec![],
2397                 None,
2398                 None,
2399                 None,
2400                 |_| (),
2401             );
2402
2403             // For verification purposes, we just ignore the resulting
2404             // region constraint sets. Not our problem. =)
2405         });
2406     }
2407 }
2408
2409 trait NormalizeLocation: fmt::Debug + Copy {
2410     fn to_locations(self) -> Locations;
2411 }
2412
2413 impl NormalizeLocation for Locations {
2414     fn to_locations(self) -> Locations {
2415         self
2416     }
2417 }
2418
2419 impl NormalizeLocation for Location {
2420     fn to_locations(self) -> Locations {
2421         Locations::Single(self)
2422     }
2423 }
2424
2425 #[derive(Debug, Default)]
2426 struct ObligationAccumulator<'tcx> {
2427     obligations: PredicateObligations<'tcx>,
2428 }
2429
2430 impl<'tcx> ObligationAccumulator<'tcx> {
2431     fn add<T>(&mut self, value: InferOk<'tcx, T>) -> T {
2432         let InferOk { value, obligations } = value;
2433         self.obligations.extend(obligations);
2434         value
2435     }
2436
2437     fn into_vec(self) -> PredicateObligations<'tcx> {
2438         self.obligations
2439     }
2440 }