src/librustc_typeck/check/expr.rs

   1 //! Type checking expressions.
   2 //!
   3 //! See `mod.rs` for more context on type checking in general.
   4
   5 use crate::check::BreakableCtxt;
   6 use crate::check::cast;
   7 use crate::check::coercion::CoerceMany;
   8 use crate::check::Diverges;
   9 use crate::check::FnCtxt;
  10 use crate::check::Expectation::{self, NoExpectation, ExpectHasType, ExpectCastableToType};
  11 use crate::check::fatally_break_rust;
  12 use crate::check::report_unexpected_variant_res;
  13 use crate::check::Needs;
  14 use crate::check::TupleArgumentsFlag::DontTupleArguments;
  15 use crate::check::method::SelfSource;
  16 use crate::middle::lang_items;
  17 use crate::util::common::ErrorReported;
  18 use crate::util::nodemap::FxHashMap;
  19 use crate::astconv::AstConv as _;
  20
  21 use errors::{Applicability, DiagnosticBuilder};
  22 use syntax::ast;
  23 use syntax::ptr::P;
  24 use syntax::symbol::{Symbol, LocalInternedString, kw, sym};
  25 use syntax::source_map::Span;
  26 use syntax::util::lev_distance::find_best_match_for_name;
  27 use rustc::hir;
  28 use rustc::hir::{ExprKind, QPath};
  29 use rustc::hir::def::{CtorKind, Res, DefKind};
  30 use rustc::infer;
  31 use rustc::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  32 use rustc::mir::interpret::GlobalId;
  33 use rustc::ty;
  34 use rustc::ty::adjustment::{
  35     Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability,
  36 };
  37 use rustc::ty::{AdtKind, Visibility};
  38 use rustc::ty::Ty;
  39 use rustc::ty::TypeFoldable;
  40 use rustc::ty::subst::InternalSubsts;
  41 use rustc::traits::{self, ObligationCauseCode};
  42
  43 use std::fmt::Display;
  44
  45 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  46     fn check_expr_eq_type(&self, expr: &'tcx hir::Expr, expected: Ty<'tcx>) {
  47         let ty = self.check_expr_with_hint(expr, expected);
  48         self.demand_eqtype(expr.span, expected, ty);
  49     }
  50
  51     pub fn check_expr_has_type_or_error(
  52         &self,
  53         expr: &'tcx hir::Expr,
  54         expected: Ty<'tcx>,
  55     ) -> Ty<'tcx> {
  56         self.check_expr_meets_expectation_or_error(expr, ExpectHasType(expected))
  57     }
  58
  59     fn check_expr_meets_expectation_or_error(
  60         &self,
  61         expr: &'tcx hir::Expr,
  62         expected: Expectation<'tcx>,
  63     ) -> Ty<'tcx> {
  64         let expected_ty = expected.to_option(&self).unwrap_or(self.tcx.types.bool);
  65         let mut ty = self.check_expr_with_expectation(expr, expected);
  66
  67         // While we don't allow *arbitrary* coercions here, we *do* allow
  68         // coercions from ! to `expected`.
  69         if ty.is_never() {
  70             assert!(!self.tables.borrow().adjustments().contains_key(expr.hir_id),
  71                     "expression with never type wound up being adjusted");
  72             let adj_ty = self.next_diverging_ty_var(
  73                 TypeVariableOrigin {
  74                     kind: TypeVariableOriginKind::AdjustmentType,
  75                     span: expr.span,
  76                 },
  77             );
  78             self.apply_adjustments(expr, vec![Adjustment {
  79                 kind: Adjust::NeverToAny,
  80                 target: adj_ty
  81             }]);
  82             ty = adj_ty;
  83         }
  84
  85         if let Some(mut err) = self.demand_suptype_diag(expr.span, expected_ty, ty) {
  86             let expr = match &expr.node {
  87                 ExprKind::DropTemps(expr) => expr,
  88                 _ => expr,
  89             };
  90             // Error possibly reported in `check_assign` so avoid emitting error again.
  91             err.emit_unless(self.is_assign_to_bool(expr, expected_ty));
  92         }
  93         ty
  94     }
  95
  96     pub(super) fn check_expr_coercable_to_type(
  97         &self,
  98         expr: &'tcx hir::Expr,
  99         expected: Ty<'tcx>
 100     ) -> Ty<'tcx> {
 101         let ty = self.check_expr_with_hint(expr, expected);
 102         // checks don't need two phase
 103         self.demand_coerce(expr, ty, expected, AllowTwoPhase::No)
 104     }
 105
 106     pub(super) fn check_expr_with_hint(
 107         &self,
 108         expr: &'tcx hir::Expr,
 109         expected: Ty<'tcx>
 110     ) -> Ty<'tcx> {
 111         self.check_expr_with_expectation(expr, ExpectHasType(expected))
 112     }
 113
 114     pub(super) fn check_expr_with_expectation(
 115         &self,
 116         expr: &'tcx hir::Expr,
 117         expected: Expectation<'tcx>,
 118     ) -> Ty<'tcx> {
 119         self.check_expr_with_expectation_and_needs(expr, expected, Needs::None)
 120     }
 121
 122     pub(super) fn check_expr(&self, expr: &'tcx hir::Expr) -> Ty<'tcx> {
 123         self.check_expr_with_expectation(expr, NoExpectation)
 124     }
 125
 126     pub(super) fn check_expr_with_needs(&self, expr: &'tcx hir::Expr, needs: Needs) -> Ty<'tcx> {
 127         self.check_expr_with_expectation_and_needs(expr, NoExpectation, needs)
 128     }
 129
 130     /// Invariant:
 131     /// If an expression has any sub-expressions that result in a type error,
 132     /// inspecting that expression's type with `ty.references_error()` will return
 133     /// true. Likewise, if an expression is known to diverge, inspecting its
 134     /// type with `ty::type_is_bot` will return true (n.b.: since Rust is
 135     /// strict, _|_ can appear in the type of an expression that does not,
 136     /// itself, diverge: for example, fn() -> _|_.)
 137     /// Note that inspecting a type's structure *directly* may expose the fact
 138     /// that there are actually multiple representations for `Error`, so avoid
 139     /// that when err needs to be handled differently.
 140     fn check_expr_with_expectation_and_needs(
 141         &self,
 142         expr: &'tcx hir::Expr,
 143         expected: Expectation<'tcx>,
 144         needs: Needs,
 145     ) -> Ty<'tcx> {
 146         debug!(">> type-checking: expr={:?} expected={:?}",
 147                expr, expected);
 148
 149         // Warn for expressions after diverging siblings.
 150         self.warn_if_unreachable(expr.hir_id, expr.span, "expression");
 151
 152         // Hide the outer diverging and has_errors flags.
 153         let old_diverges = self.diverges.get();
 154         let old_has_errors = self.has_errors.get();
 155         self.diverges.set(Diverges::Maybe);
 156         self.has_errors.set(false);
 157
 158         let ty = self.check_expr_kind(expr, expected, needs);
 159
 160         // Warn for non-block expressions with diverging children.
 161         match expr.node {
 162             ExprKind::Block(..) |
 163             ExprKind::Loop(..) | ExprKind::While(..) |
 164             ExprKind::Match(..) => {}
 165
 166             _ => self.warn_if_unreachable(expr.hir_id, expr.span, "expression")
 167         }
 168
 169         // Any expression that produces a value of type `!` must have diverged
 170         if ty.is_never() {
 171             self.diverges.set(self.diverges.get() | Diverges::Always);
 172         }
 173
 174         // Record the type, which applies it effects.
 175         // We need to do this after the warning above, so that
 176         // we don't warn for the diverging expression itself.
 177         self.write_ty(expr.hir_id, ty);
 178
 179         // Combine the diverging and has_error flags.
 180         self.diverges.set(self.diverges.get() | old_diverges);
 181         self.has_errors.set(self.has_errors.get() | old_has_errors);
 182
 183         debug!("type of {} is...", self.tcx.hir().node_to_string(expr.hir_id));
 184         debug!("... {:?}, expected is {:?}", ty, expected);
 185
 186         ty
 187     }
 188
 189     fn check_expr_kind(
 190         &self,
 191         expr: &'tcx hir::Expr,
 192         expected: Expectation<'tcx>,
 193         needs: Needs,
 194     ) -> Ty<'tcx> {
 195         debug!(
 196             "check_expr_kind(expr={:?}, expected={:?}, needs={:?})",
 197             expr,
 198             expected,
 199             needs,
 200         );
 201
 202         let tcx = self.tcx;
 203         match expr.node {
 204             ExprKind::Box(ref subexpr) => {
 205                 self.check_expr_box(subexpr, expected)
 206             }
 207             ExprKind::Lit(ref lit) => {
 208                 self.check_lit(&lit, expected)
 209             }
 210             ExprKind::Binary(op, ref lhs, ref rhs) => {
 211                 self.check_binop(expr, op, lhs, rhs)
 212             }
 213             ExprKind::AssignOp(op, ref lhs, ref rhs) => {
 214                 self.check_binop_assign(expr, op, lhs, rhs)
 215             }
 216             ExprKind::Unary(unop, ref oprnd) => {
 217                 self.check_expr_unary(unop, oprnd, expected, needs, expr)
 218             }
 219             ExprKind::AddrOf(mutbl, ref oprnd) => {
 220                 self.check_expr_addr_of(mutbl, oprnd, expected, expr)
 221             }
 222             ExprKind::Path(ref qpath) => {
 223                 self.check_expr_path(qpath, expr)
 224             }
 225             ExprKind::InlineAsm(_, ref outputs, ref inputs) => {
 226                 for expr in outputs.iter().chain(inputs.iter()) {
 227                     self.check_expr(expr);
 228                 }
 229                 tcx.mk_unit()
 230             }
 231             ExprKind::Break(destination, ref expr_opt) => {
 232                 self.check_expr_break(destination, expr_opt.deref(), expr)
 233             }
 234             ExprKind::Continue(destination) => {
 235                 if destination.target_id.is_ok() {
 236                     tcx.types.never
 237                 } else {
 238                     // There was an error; make type-check fail.
 239                     tcx.types.err
 240                 }
 241             }
 242             ExprKind::Ret(ref expr_opt) => {
 243                 self.check_expr_return(expr_opt.deref(), expr)
 244             }
 245             ExprKind::Assign(ref lhs, ref rhs) => {
 246                 self.check_expr_assign(expr, expected, lhs, rhs)
 247             }
 248             ExprKind::While(ref cond, ref body, _) => {
 249                 self.check_expr_while(cond, body, expr)
 250             }
 251             ExprKind::Loop(ref body, _, source) => {
 252                 self.check_expr_loop(body, source, expected, expr)
 253             }
 254             ExprKind::Match(ref discrim, ref arms, match_src) => {
 255                 self.check_match(expr, &discrim, arms, expected, match_src)
 256             }
 257             ExprKind::Closure(capture, ref decl, body_id, _, gen) => {
 258                 self.check_expr_closure(expr, capture, &decl, body_id, gen, expected)
 259             }
 260             ExprKind::Block(ref body, _) => {
 261                 self.check_block_with_expected(&body, expected)
 262             }
 263             ExprKind::Call(ref callee, ref args) => {
 264                 self.check_call(expr, &callee, args, expected)
 265             }
 266             ExprKind::MethodCall(ref segment, span, ref args) => {
 267                 self.check_method_call(expr, segment, span, args, expected, needs)
 268             }
 269             ExprKind::Cast(ref e, ref t) => {
 270                 self.check_expr_cast(e, t, expr)
 271             }
 272             ExprKind::Type(ref e, ref t) => {
 273                 let ty = self.to_ty_saving_user_provided_ty(&t);
 274                 self.check_expr_eq_type(&e, ty);
 275                 ty
 276             }
 277             ExprKind::DropTemps(ref e) => {
 278                 self.check_expr_with_expectation(e, expected)
 279             }
 280             ExprKind::Array(ref args) => {
 281                 self.check_expr_array(args, expected, expr)
 282             }
 283             ExprKind::Repeat(ref element, ref count) => {
 284                 self.check_expr_repeat(element, count, expected, expr)
 285             }
 286             ExprKind::Tup(ref elts) => {
 287                 self.check_expr_tuple(elts, expected, expr)
 288             }
 289             ExprKind::Struct(ref qpath, ref fields, ref base_expr) => {
 290                 self.check_expr_struct(expr, expected, qpath, fields, base_expr)
 291             }
 292             ExprKind::Field(ref base, field) => {
 293                 self.check_field(expr, needs, &base, field)
 294             }
 295             ExprKind::Index(ref base, ref idx) => {
 296                 self.check_expr_index(base, idx, needs, expr)
 297             }
 298             ExprKind::Yield(ref value, _) => {
 299                 self.check_expr_yield(value, expr)
 300             }
 301             hir::ExprKind::Err => {
 302                 tcx.types.err
 303             }
 304         }
 305     }
 306
 307     fn check_expr_box(&self, expr: &'tcx hir::Expr, expected: Expectation<'tcx>) -> Ty<'tcx> {
 308         let expected_inner = expected.to_option(self).map_or(NoExpectation, |ty| {
 309             match ty.sty {
 310                 ty::Adt(def, _) if def.is_box()
 311                     => Expectation::rvalue_hint(self, ty.boxed_ty()),
 312                 _ => NoExpectation
 313             }
 314         });
 315         let referent_ty = self.check_expr_with_expectation(expr, expected_inner);
 316         self.tcx.mk_box(referent_ty)
 317     }
 318
 319     fn check_expr_unary(
 320         &self,
 321         unop: hir::UnOp,
 322         oprnd: &'tcx hir::Expr,
 323         expected: Expectation<'tcx>,
 324         needs: Needs,
 325         expr: &'tcx hir::Expr,
 326     ) -> Ty<'tcx> {
 327         let tcx = self.tcx;
 328         let expected_inner = match unop {
 329             hir::UnNot | hir::UnNeg => expected,
 330             hir::UnDeref => NoExpectation,
 331         };
 332         let needs = match unop {
 333             hir::UnDeref => needs,
 334             _ => Needs::None
 335         };
 336         let mut oprnd_t = self.check_expr_with_expectation_and_needs(&oprnd, expected_inner, needs);
 337
 338         if !oprnd_t.references_error() {
 339             oprnd_t = self.structurally_resolved_type(expr.span, oprnd_t);
 340             match unop {
 341                 hir::UnDeref => {
 342                     if let Some(mt) = oprnd_t.builtin_deref(true) {
 343                         oprnd_t = mt.ty;
 344                     } else if let Some(ok) = self.try_overloaded_deref(
 345                             expr.span, oprnd_t, needs) {
 346                         let method = self.register_infer_ok_obligations(ok);
 347                         if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].sty {
 348                             let mutbl = match mutbl {
 349                                 hir::MutImmutable => AutoBorrowMutability::Immutable,
 350                                 hir::MutMutable => AutoBorrowMutability::Mutable {
 351                                     // (It shouldn't actually matter for unary ops whether
 352                                     // we enable two-phase borrows or not, since a unary
 353                                     // op has no additional operands.)
 354                                     allow_two_phase_borrow: AllowTwoPhase::No,
 355                                 }
 356                             };
 357                             self.apply_adjustments(oprnd, vec![Adjustment {
 358                                 kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 359                                 target: method.sig.inputs()[0]
 360                             }]);
 361                         }
 362                         oprnd_t = self.make_overloaded_place_return_type(method).ty;
 363                         self.write_method_call(expr.hir_id, method);
 364                     } else {
 365                         let mut err = type_error_struct!(
 366                             tcx.sess,
 367                             expr.span,
 368                             oprnd_t,
 369                             E0614,
 370                             "type `{}` cannot be dereferenced",
 371                             oprnd_t,
 372                         );
 373                         let sp = tcx.sess.source_map().start_point(expr.span);
 374                         if let Some(sp) = tcx.sess.parse_sess.ambiguous_block_expr_parse
 375                             .borrow().get(&sp)
 376                         {
 377                             tcx.sess.parse_sess.expr_parentheses_needed(
 378                                 &mut err,
 379                                 *sp,
 380                                 None,
 381                             );
 382                         }
 383                         err.emit();
 384                         oprnd_t = tcx.types.err;
 385                     }
 386                 }
 387                 hir::UnNot => {
 388                     let result = self.check_user_unop(expr, oprnd_t, unop);
 389                     // If it's builtin, we can reuse the type, this helps inference.
 390                     if !(oprnd_t.is_integral() || oprnd_t.sty == ty::Bool) {
 391                         oprnd_t = result;
 392                     }
 393                 }
 394                 hir::UnNeg => {
 395                     let result = self.check_user_unop(expr, oprnd_t, unop);
 396                     // If it's builtin, we can reuse the type, this helps inference.
 397                     if !oprnd_t.is_numeric() {
 398                         oprnd_t = result;
 399                     }
 400                 }
 401             }
 402         }
 403         oprnd_t
 404     }
 405
 406     fn check_expr_addr_of(
 407         &self,
 408         mutbl: hir::Mutability,
 409         oprnd: &'tcx hir::Expr,
 410         expected: Expectation<'tcx>,
 411         expr: &'tcx hir::Expr,
 412     ) -> Ty<'tcx> {
 413         let hint = expected.only_has_type(self).map_or(NoExpectation, |ty| {
 414             match ty.sty {
 415                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 416                     if oprnd.is_place_expr() {
 417                         // Places may legitimately have unsized types.
 418                         // For example, dereferences of a fat pointer and
 419                         // the last field of a struct can be unsized.
 420                         ExpectHasType(ty)
 421                     } else {
 422                         Expectation::rvalue_hint(self, ty)
 423                     }
 424                 }
 425                 _ => NoExpectation
 426             }
 427         });
 428         let needs = Needs::maybe_mut_place(mutbl);
 429         let ty = self.check_expr_with_expectation_and_needs(&oprnd, hint, needs);
 430
 431         let tm = ty::TypeAndMut { ty: ty, mutbl: mutbl };
 432         if tm.ty.references_error() {
 433             self.tcx.types.err
 434         } else {
 435             // Note: at this point, we cannot say what the best lifetime
 436             // is to use for resulting pointer.  We want to use the
 437             // shortest lifetime possible so as to avoid spurious borrowck
 438             // errors.  Moreover, the longest lifetime will depend on the
 439             // precise details of the value whose address is being taken
 440             // (and how long it is valid), which we don't know yet until type
 441             // inference is complete.
 442             //
 443             // Therefore, here we simply generate a region variable.  The
 444             // region inferencer will then select the ultimate value.
 445             // Finally, borrowck is charged with guaranteeing that the
 446             // value whose address was taken can actually be made to live
 447             // as long as it needs to live.
 448             let region = self.next_region_var(infer::AddrOfRegion(expr.span));
 449             self.tcx.mk_ref(region, tm)
 450         }
 451     }
 452
 453     fn check_expr_path(&self, qpath: &hir::QPath, expr: &'tcx hir::Expr) -> Ty<'tcx> {
 454         let tcx = self.tcx;
 455         let (res, opt_ty, segs) = self.resolve_ty_and_res_ufcs(qpath, expr.hir_id, expr.span);
 456         let ty = match res {
 457             Res::Err => {
 458                 self.set_tainted_by_errors();
 459                 tcx.types.err
 460             }
 461             Res::Def(DefKind::Ctor(_, CtorKind::Fictive), _) => {
 462                 report_unexpected_variant_res(tcx, res, expr.span, qpath);
 463                 tcx.types.err
 464             }
 465             _ => self.instantiate_value_path(segs, opt_ty, res, expr.span, expr.hir_id).0,
 466         };
 467
 468         if let ty::FnDef(..) = ty.sty {
 469             let fn_sig = ty.fn_sig(tcx);
 470             if !tcx.features().unsized_locals {
 471                 // We want to remove some Sized bounds from std functions,
 472                 // but don't want to expose the removal to stable Rust.
 473                 // i.e., we don't want to allow
 474                 //
 475                 // ```rust
 476                 // drop as fn(str);
 477                 // ```
 478                 //
 479                 // to work in stable even if the Sized bound on `drop` is relaxed.
 480                 for i in 0..fn_sig.inputs().skip_binder().len() {
 481                     // We just want to check sizedness, so instead of introducing
 482                     // placeholder lifetimes with probing, we just replace higher lifetimes
 483                     // with fresh vars.
 484                     let input = self.replace_bound_vars_with_fresh_vars(
 485                         expr.span,
 486                         infer::LateBoundRegionConversionTime::FnCall,
 487                         &fn_sig.input(i)).0;
 488                     self.require_type_is_sized_deferred(input, expr.span,
 489                                                         traits::SizedArgumentType);
 490                 }
 491             }
 492             // Here we want to prevent struct constructors from returning unsized types.
 493             // There were two cases this happened: fn pointer coercion in stable
 494             // and usual function call in presense of unsized_locals.
 495             // Also, as we just want to check sizedness, instead of introducing
 496             // placeholder lifetimes with probing, we just replace higher lifetimes
 497             // with fresh vars.
 498             let output = self.replace_bound_vars_with_fresh_vars(
 499                 expr.span,
 500                 infer::LateBoundRegionConversionTime::FnCall,
 501                 &fn_sig.output()).0;
 502             self.require_type_is_sized_deferred(output, expr.span, traits::SizedReturnType);
 503         }
 504
 505         // We always require that the type provided as the value for
 506         // a type parameter outlives the moment of instantiation.
 507         let substs = self.tables.borrow().node_substs(expr.hir_id);
 508         self.add_wf_bounds(substs, expr);
 509
 510         ty
 511     }
 512
 513     fn check_expr_break(
 514         &self,
 515         destination: hir::Destination,
 516         expr_opt: Option<&'tcx hir::Expr>,
 517         expr: &'tcx hir::Expr,
 518     ) -> Ty<'tcx> {
 519         let tcx = self.tcx;
 520         if let Ok(target_id) = destination.target_id {
 521             let (e_ty, cause);
 522             if let Some(ref e) = expr_opt {
 523                 // If this is a break with a value, we need to type-check
 524                 // the expression. Get an expected type from the loop context.
 525                 let opt_coerce_to = {
 526                     let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 527                     enclosing_breakables.find_breakable(target_id)
 528                                         .coerce
 529                                         .as_ref()
 530                                         .map(|coerce| coerce.expected_ty())
 531                 };
 532
 533                 // If the loop context is not a `loop { }`, then break with
 534                 // a value is illegal, and `opt_coerce_to` will be `None`.
 535                 // Just set expectation to error in that case.
 536                 let coerce_to = opt_coerce_to.unwrap_or(tcx.types.err);
 537
 538                 // Recurse without `enclosing_breakables` borrowed.
 539                 e_ty = self.check_expr_with_hint(e, coerce_to);
 540                 cause = self.misc(e.span);
 541             } else {
 542                 // Otherwise, this is a break *without* a value. That's
 543                 // always legal, and is equivalent to `break ()`.
 544                 e_ty = tcx.mk_unit();
 545                 cause = self.misc(expr.span);
 546             }
 547
 548             // Now that we have type-checked `expr_opt`, borrow
 549             // the `enclosing_loops` field and let's coerce the
 550             // type of `expr_opt` into what is expected.
 551             let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 552             let ctxt = enclosing_breakables.find_breakable(target_id);
 553             if let Some(ref mut coerce) = ctxt.coerce {
 554                 if let Some(ref e) = expr_opt {
 555                     coerce.coerce(self, &cause, e, e_ty);
 556                 } else {
 557                     assert!(e_ty.is_unit());
 558                     coerce.coerce_forced_unit(self, &cause, &mut |_| (), true);
 559                 }
 560             } else {
 561                 // If `ctxt.coerce` is `None`, we can just ignore
 562                 // the type of the expresison.  This is because
 563                 // either this was a break *without* a value, in
 564                 // which case it is always a legal type (`()`), or
 565                 // else an error would have been flagged by the
 566                 // `loops` pass for using break with an expression
 567                 // where you are not supposed to.
 568                 assert!(expr_opt.is_none() || self.tcx.sess.has_errors());
 569             }
 570
 571             ctxt.may_break = true;
 572
 573             // the type of a `break` is always `!`, since it diverges
 574             tcx.types.never
 575         } else {
 576             // Otherwise, we failed to find the enclosing loop;
 577             // this can only happen if the `break` was not
 578             // inside a loop at all, which is caught by the
 579             // loop-checking pass.
 580             self.tcx.sess.delay_span_bug(expr.span,
 581                 "break was outside loop, but no error was emitted");
 582
 583             // We still need to assign a type to the inner expression to
 584             // prevent the ICE in #43162.
 585             if let Some(ref e) = expr_opt {
 586                 self.check_expr_with_hint(e, tcx.types.err);
 587
 588                 // ... except when we try to 'break rust;'.
 589                 // ICE this expression in particular (see #43162).
 590                 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.node {
 591                     if path.segments.len() == 1 &&
 592                         path.segments[0].ident.name == sym::rust {
 593                         fatally_break_rust(self.tcx.sess);
 594                     }
 595                 }
 596             }
 597             // There was an error; make type-check fail.
 598             tcx.types.err
 599         }
 600     }
 601
 602     fn check_expr_return(
 603         &self,
 604         expr_opt: Option<&'tcx hir::Expr>,
 605         expr: &'tcx hir::Expr
 606     ) -> Ty<'tcx> {
 607         if self.ret_coercion.is_none() {
 608             struct_span_err!(self.tcx.sess, expr.span, E0572,
 609                                 "return statement outside of function body").emit();
 610         } else if let Some(ref e) = expr_opt {
 611             if self.ret_coercion_span.borrow().is_none() {
 612                 *self.ret_coercion_span.borrow_mut() = Some(e.span);
 613             }
 614             self.check_return_expr(e);
 615         } else {
 616             let mut coercion = self.ret_coercion.as_ref().unwrap().borrow_mut();
 617             if self.ret_coercion_span.borrow().is_none() {
 618                 *self.ret_coercion_span.borrow_mut() = Some(expr.span);
 619             }
 620             let cause = self.cause(expr.span, ObligationCauseCode::ReturnNoExpression);
 621             if let Some((fn_decl, _)) = self.get_fn_decl(expr.hir_id) {
 622                 coercion.coerce_forced_unit(
 623                     self,
 624                     &cause,
 625                     &mut |db| {
 626                         db.span_label(
 627                             fn_decl.output.span(),
 628                             format!(
 629                                 "expected `{}` because of this return type",
 630                                 fn_decl.output,
 631                             ),
 632                         );
 633                     },
 634                     true,
 635                 );
 636             } else {
 637                 coercion.coerce_forced_unit(self, &cause, &mut |_| (), true);
 638             }
 639         }
 640         self.tcx.types.never
 641     }
 642
 643     pub(super) fn check_return_expr(&self, return_expr: &'tcx hir::Expr) {
 644         let ret_coercion =
 645             self.ret_coercion
 646                 .as_ref()
 647                 .unwrap_or_else(|| span_bug!(return_expr.span,
 648                                              "check_return_expr called outside fn body"));
 649
 650         let ret_ty = ret_coercion.borrow().expected_ty();
 651         let return_expr_ty = self.check_expr_with_hint(return_expr, ret_ty.clone());
 652         ret_coercion.borrow_mut()
 653                     .coerce(self,
 654                             &self.cause(return_expr.span,
 655                                         ObligationCauseCode::ReturnType(return_expr.hir_id)),
 656                             return_expr,
 657                             return_expr_ty);
 658     }
 659
 660     /// Type check assignment expression `expr` of form `lhs = rhs`.
 661     /// The expected type is `()` and is passsed to the function for the purposes of diagnostics.
 662     fn check_expr_assign(
 663         &self,
 664         expr: &'tcx hir::Expr,
 665         expected: Expectation<'tcx>,
 666         lhs: &'tcx hir::Expr,
 667         rhs: &'tcx hir::Expr,
 668     ) -> Ty<'tcx> {
 669         let lhs_ty = self.check_expr_with_needs(&lhs, Needs::MutPlace);
 670         let rhs_ty = self.check_expr_coercable_to_type(&rhs, lhs_ty);
 671
 672         let expected_ty = expected.coercion_target_type(self, expr.span);
 673         if expected_ty == self.tcx.types.bool {
 674             // The expected type is `bool` but this will result in `()` so we can reasonably
 675             // say that the user intended to write `lhs == rhs` instead of `lhs = rhs`.
 676             // The likely cause of this is `if foo = bar { .. }`.
 677             let actual_ty = self.tcx.mk_unit();
 678             let mut err = self.demand_suptype_diag(expr.span, expected_ty, actual_ty).unwrap();
 679             let msg = "try comparing for equality";
 680             let left = self.tcx.sess.source_map().span_to_snippet(lhs.span);
 681             let right = self.tcx.sess.source_map().span_to_snippet(rhs.span);
 682             if let (Ok(left), Ok(right)) = (left, right) {
 683                 let help = format!("{} == {}", left, right);
 684                 err.span_suggestion(expr.span, msg, help, Applicability::MaybeIncorrect);
 685             } else {
 686                 err.help(msg);
 687             }
 688             err.emit();
 689         } else if !lhs.is_place_expr() {
 690             struct_span_err!(self.tcx.sess, expr.span, E0070,
 691                                 "invalid left-hand side expression")
 692                 .span_label(expr.span, "left-hand of expression not valid")
 693                 .emit();
 694         }
 695
 696         self.require_type_is_sized(lhs_ty, lhs.span, traits::AssignmentLhsSized);
 697
 698         if lhs_ty.references_error() || rhs_ty.references_error() {
 699             self.tcx.types.err
 700         } else {
 701             self.tcx.mk_unit()
 702         }
 703     }
 704
 705     fn check_expr_while(
 706         &self,
 707         cond: &'tcx hir::Expr,
 708         body: &'tcx hir::Block,
 709         expr: &'tcx hir::Expr
 710     ) -> Ty<'tcx> {
 711         let ctxt = BreakableCtxt {
 712             // Cannot use break with a value from a while loop.
 713             coerce: None,
 714             may_break: false, // Will get updated if/when we find a `break`.
 715         };
 716
 717         let (ctxt, ()) = self.with_breakable_ctxt(expr.hir_id, ctxt, || {
 718             self.check_expr_has_type_or_error(&cond, self.tcx.types.bool);
 719             let cond_diverging = self.diverges.get();
 720             self.check_block_no_value(&body);
 721
 722             // We may never reach the body so it diverging means nothing.
 723             self.diverges.set(cond_diverging);
 724         });
 725
 726         if ctxt.may_break {
 727             // No way to know whether it's diverging because
 728             // of a `break` or an outer `break` or `return`.
 729             self.diverges.set(Diverges::Maybe);
 730         }
 731
 732         self.tcx.mk_unit()
 733     }
 734
 735     fn check_expr_loop(
 736         &self,
 737         body: &'tcx hir::Block,
 738         source: hir::LoopSource,
 739         expected: Expectation<'tcx>,
 740         expr: &'tcx hir::Expr,
 741     ) -> Ty<'tcx> {
 742         let coerce = match source {
 743             // you can only use break with a value from a normal `loop { }`
 744             hir::LoopSource::Loop => {
 745                 let coerce_to = expected.coercion_target_type(self, body.span);
 746                 Some(CoerceMany::new(coerce_to))
 747             }
 748
 749             hir::LoopSource::WhileLet |
 750             hir::LoopSource::ForLoop => {
 751                 None
 752             }
 753         };
 754
 755         let ctxt = BreakableCtxt {
 756             coerce,
 757             may_break: false, // Will get updated if/when we find a `break`.
 758         };
 759
 760         let (ctxt, ()) = self.with_breakable_ctxt(expr.hir_id, ctxt, || {
 761             self.check_block_no_value(&body);
 762         });
 763
 764         if ctxt.may_break {
 765             // No way to know whether it's diverging because
 766             // of a `break` or an outer `break` or `return`.
 767             self.diverges.set(Diverges::Maybe);
 768         }
 769
 770         // If we permit break with a value, then result type is
 771         // the LUB of the breaks (possibly ! if none); else, it
 772         // is nil. This makes sense because infinite loops
 773         // (which would have type !) are only possible iff we
 774         // permit break with a value [1].
 775         if ctxt.coerce.is_none() && !ctxt.may_break {
 776             // [1]
 777             self.tcx.sess.delay_span_bug(body.span, "no coercion, but loop may not break");
 778         }
 779         ctxt.coerce.map(|c| c.complete(self)).unwrap_or_else(|| self.tcx.mk_unit())
 780     }
 781
 782     /// Checks a method call.
 783     fn check_method_call(
 784         &self,
 785         expr: &'tcx hir::Expr,
 786         segment: &hir::PathSegment,
 787         span: Span,
 788         args: &'tcx [hir::Expr],
 789         expected: Expectation<'tcx>,
 790         needs: Needs,
 791     ) -> Ty<'tcx> {
 792         let rcvr = &args[0];
 793         let rcvr_t = self.check_expr_with_needs(&rcvr, needs);
 794         // no need to check for bot/err -- callee does that
 795         let rcvr_t = self.structurally_resolved_type(args[0].span, rcvr_t);
 796
 797         let method = match self.lookup_method(rcvr_t,
 798                                               segment,
 799                                               span,
 800                                               expr,
 801                                               rcvr) {
 802             Ok(method) => {
 803                 self.write_method_call(expr.hir_id, method);
 804                 Ok(method)
 805             }
 806             Err(error) => {
 807                 if segment.ident.name != kw::Invalid {
 808                     self.report_method_error(span,
 809                                              rcvr_t,
 810                                              segment.ident,
 811                                              SelfSource::MethodCall(rcvr),
 812                                              error,
 813                                              Some(args));
 814                 }
 815                 Err(())
 816             }
 817         };
 818
 819         // Call the generic checker.
 820         self.check_method_argument_types(span,
 821                                          expr.span,
 822                                          method,
 823                                          &args[1..],
 824                                          DontTupleArguments,
 825                                          expected)
 826     }
 827
 828     fn check_expr_cast(
 829         &self,
 830         e: &'tcx hir::Expr,
 831         t: &'tcx hir::Ty,
 832         expr: &'tcx hir::Expr,
 833     ) -> Ty<'tcx> {
 834         // Find the type of `e`. Supply hints based on the type we are casting to,
 835         // if appropriate.
 836         let t_cast = self.to_ty_saving_user_provided_ty(t);
 837         let t_cast = self.resolve_vars_if_possible(&t_cast);
 838         let t_expr = self.check_expr_with_expectation(e, ExpectCastableToType(t_cast));
 839         let t_cast = self.resolve_vars_if_possible(&t_cast);
 840
 841         // Eagerly check for some obvious errors.
 842         if t_expr.references_error() || t_cast.references_error() {
 843             self.tcx.types.err
 844         } else {
 845             // Defer other checks until we're done type checking.
 846             let mut deferred_cast_checks = self.deferred_cast_checks.borrow_mut();
 847             match cast::CastCheck::new(self, e, t_expr, t_cast, t.span, expr.span) {
 848                 Ok(cast_check) => {
 849                     deferred_cast_checks.push(cast_check);
 850                     t_cast
 851                 }
 852                 Err(ErrorReported) => {
 853                     self.tcx.types.err
 854                 }
 855             }
 856         }
 857     }
 858
 859     fn check_expr_array(
 860         &self,
 861         args: &'tcx [hir::Expr],
 862         expected: Expectation<'tcx>,
 863         expr: &'tcx hir::Expr
 864     ) -> Ty<'tcx> {
 865         let uty = expected.to_option(self).and_then(|uty| {
 866             match uty.sty {
 867                 ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
 868                 _ => None
 869             }
 870         });
 871
 872         let element_ty = if !args.is_empty() {
 873             let coerce_to = uty.unwrap_or_else(|| {
 874                 self.next_ty_var(TypeVariableOrigin {
 875                     kind: TypeVariableOriginKind::TypeInference,
 876                     span: expr.span,
 877                 })
 878             });
 879             let mut coerce = CoerceMany::with_coercion_sites(coerce_to, args);
 880             assert_eq!(self.diverges.get(), Diverges::Maybe);
 881             for e in args {
 882                 let e_ty = self.check_expr_with_hint(e, coerce_to);
 883                 let cause = self.misc(e.span);
 884                 coerce.coerce(self, &cause, e, e_ty);
 885             }
 886             coerce.complete(self)
 887         } else {
 888             self.next_ty_var(TypeVariableOrigin {
 889                 kind: TypeVariableOriginKind::TypeInference,
 890                 span: expr.span,
 891             })
 892         };
 893         self.tcx.mk_array(element_ty, args.len() as u64)
 894     }
 895
 896     fn check_expr_repeat(
 897         &self,
 898         element: &'tcx hir::Expr,
 899         count: &'tcx hir::AnonConst,
 900         expected: Expectation<'tcx>,
 901         expr: &'tcx hir::Expr,
 902     ) -> Ty<'tcx> {
 903         let tcx = self.tcx;
 904         let count_def_id = tcx.hir().local_def_id_from_hir_id(count.hir_id);
 905         let count = if self.const_param_def_id(count).is_some() {
 906             Ok(self.to_const(count, tcx.type_of(count_def_id)))
 907         } else {
 908             let param_env = ty::ParamEnv::empty();
 909             let substs = InternalSubsts::identity_for_item(tcx.global_tcx(), count_def_id);
 910             let instance = ty::Instance::resolve(
 911                 tcx.global_tcx(),
 912                 param_env,
 913                 count_def_id,
 914                 substs,
 915             ).unwrap();
 916             let global_id = GlobalId {
 917                 instance,
 918                 promoted: None
 919             };
 920
 921             tcx.const_eval(param_env.and(global_id))
 922         };
 923
 924         let uty = match expected {
 925             ExpectHasType(uty) => {
 926                 match uty.sty {
 927                     ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
 928                     _ => None
 929                 }
 930             }
 931             _ => None
 932         };
 933
 934         let (element_ty, t) = match uty {
 935             Some(uty) => {
 936                 self.check_expr_coercable_to_type(&element, uty);
 937                 (uty, uty)
 938             }
 939             None => {
 940                 let ty = self.next_ty_var(TypeVariableOrigin {
 941                     kind: TypeVariableOriginKind::MiscVariable,
 942                     span: element.span,
 943                 });
 944                 let element_ty = self.check_expr_has_type_or_error(&element, ty);
 945                 (element_ty, ty)
 946             }
 947         };
 948
 949         if let Ok(count) = count {
 950             let zero_or_one = count.assert_usize(tcx).map_or(false, |count| count <= 1);
 951             if !zero_or_one {
 952                 // For [foo, ..n] where n > 1, `foo` must have
 953                 // Copy type:
 954                 let lang_item = tcx.require_lang_item(lang_items::CopyTraitLangItem);
 955                 self.require_type_meets(t, expr.span, traits::RepeatVec, lang_item);
 956             }
 957         }
 958
 959         if element_ty.references_error() {
 960             tcx.types.err
 961         } else if let Ok(count) = count {
 962             tcx.mk_ty(ty::Array(t, count))
 963         } else {
 964             tcx.types.err
 965         }
 966     }
 967
 968     fn check_expr_tuple(
 969         &self,
 970         elts: &'tcx [hir::Expr],
 971         expected: Expectation<'tcx>,
 972         expr: &'tcx hir::Expr,
 973     ) -> Ty<'tcx> {
 974         let flds = expected.only_has_type(self).and_then(|ty| {
 975             let ty = self.resolve_type_vars_with_obligations(ty);
 976             match ty.sty {
 977                 ty::Tuple(ref flds) => Some(&flds[..]),
 978                 _ => None
 979             }
 980         });
 981
 982         let elt_ts_iter = elts.iter().enumerate().map(|(i, e)| {
 983             let t = match flds {
 984                 Some(ref fs) if i < fs.len() => {
 985                     let ety = fs[i].expect_ty();
 986                     self.check_expr_coercable_to_type(&e, ety);
 987                     ety
 988                 }
 989                 _ => {
 990                     self.check_expr_with_expectation(&e, NoExpectation)
 991                 }
 992             };
 993             t
 994         });
 995         let tuple = self.tcx.mk_tup(elt_ts_iter);
 996         if tuple.references_error() {
 997             self.tcx.types.err
 998         } else {
 999             self.require_type_is_sized(tuple, expr.span, traits::TupleInitializerSized);
1000             tuple
1001         }
1002     }
1003
1004     fn check_expr_struct(
1005         &self,
1006         expr: &hir::Expr,
1007         expected: Expectation<'tcx>,
1008         qpath: &QPath,
1009         fields: &'tcx [hir::Field],
1010         base_expr: &'tcx Option<P<hir::Expr>>,
1011     ) -> Ty<'tcx> {
1012         // Find the relevant variant
1013         let (variant, adt_ty) =
1014             if let Some(variant_ty) = self.check_struct_path(qpath, expr.hir_id) {
1015                 variant_ty
1016             } else {
1017                 self.check_struct_fields_on_error(fields, base_expr);
1018                 return self.tcx.types.err;
1019             };
1020
1021         let path_span = match *qpath {
1022             QPath::Resolved(_, ref path) => path.span,
1023             QPath::TypeRelative(ref qself, _) => qself.span
1024         };
1025
1026         // Prohibit struct expressions when non-exhaustive flag is set.
1027         let adt = adt_ty.ty_adt_def().expect("`check_struct_path` returned non-ADT type");
1028         if !adt.did.is_local() && variant.is_field_list_non_exhaustive() {
1029             span_err!(self.tcx.sess, expr.span, E0639,
1030                       "cannot create non-exhaustive {} using struct expression",
1031                       adt.variant_descr());
1032         }
1033
1034         let error_happened = self.check_expr_struct_fields(adt_ty, expected, expr.hir_id, path_span,
1035                                                            variant, fields, base_expr.is_none());
1036         if let &Some(ref base_expr) = base_expr {
1037             // If check_expr_struct_fields hit an error, do not attempt to populate
1038             // the fields with the base_expr. This could cause us to hit errors later
1039             // when certain fields are assumed to exist that in fact do not.
1040             if !error_happened {
1041                 self.check_expr_has_type_or_error(base_expr, adt_ty);
1042                 match adt_ty.sty {
1043                     ty::Adt(adt, substs) if adt.is_struct() => {
1044                         let fru_field_types = adt.non_enum_variant().fields.iter().map(|f| {
1045                             self.normalize_associated_types_in(expr.span, &f.ty(self.tcx, substs))
1046                         }).collect();
1047
1048                         self.tables
1049                             .borrow_mut()
1050                             .fru_field_types_mut()
1051                             .insert(expr.hir_id, fru_field_types);
1052                     }
1053                     _ => {
1054                         span_err!(self.tcx.sess, base_expr.span, E0436,
1055                                   "functional record update syntax requires a struct");
1056                     }
1057                 }
1058             }
1059         }
1060         self.require_type_is_sized(adt_ty, expr.span, traits::StructInitializerSized);
1061         adt_ty
1062     }
1063
1064     fn check_expr_struct_fields(
1065         &self,
1066         adt_ty: Ty<'tcx>,
1067         expected: Expectation<'tcx>,
1068         expr_id: hir::HirId,
1069         span: Span,
1070         variant: &'tcx ty::VariantDef,
1071         ast_fields: &'tcx [hir::Field],
1072         check_completeness: bool,
1073     ) -> bool {
1074         let tcx = self.tcx;
1075
1076         let adt_ty_hint =
1077             self.expected_inputs_for_expected_output(span, expected, adt_ty, &[adt_ty])
1078                 .get(0).cloned().unwrap_or(adt_ty);
1079         // re-link the regions that EIfEO can erase.
1080         self.demand_eqtype(span, adt_ty_hint, adt_ty);
1081
1082         let (substs, adt_kind, kind_name) = match &adt_ty.sty {
1083             &ty::Adt(adt, substs) => {
1084                 (substs, adt.adt_kind(), adt.variant_descr())
1085             }
1086             _ => span_bug!(span, "non-ADT passed to check_expr_struct_fields")
1087         };
1088
1089         let mut remaining_fields = variant.fields.iter().enumerate().map(|(i, field)|
1090             (field.ident.modern(), (i, field))
1091         ).collect::<FxHashMap<_, _>>();
1092
1093         let mut seen_fields = FxHashMap::default();
1094
1095         let mut error_happened = false;
1096
1097         // Type-check each field.
1098         for field in ast_fields {
1099             let ident = tcx.adjust_ident(field.ident, variant.def_id);
1100             let field_type = if let Some((i, v_field)) = remaining_fields.remove(&ident) {
1101                 seen_fields.insert(ident, field.span);
1102                 self.write_field_index(field.hir_id, i);
1103
1104                 // We don't look at stability attributes on
1105                 // struct-like enums (yet...), but it's definitely not
1106                 // a bug to have constructed one.
1107                 if adt_kind != AdtKind::Enum {
1108                     tcx.check_stability(v_field.did, Some(expr_id), field.span);
1109                 }
1110
1111                 self.field_ty(field.span, v_field, substs)
1112             } else {
1113                 error_happened = true;
1114                 if let Some(prev_span) = seen_fields.get(&ident) {
1115                     let mut err = struct_span_err!(self.tcx.sess,
1116                                                    field.ident.span,
1117                                                    E0062,
1118                                                    "field `{}` specified more than once",
1119                                                    ident);
1120
1121                     err.span_label(field.ident.span, "used more than once");
1122                     err.span_label(*prev_span, format!("first use of `{}`", ident));
1123
1124                     err.emit();
1125                 } else {
1126                     self.report_unknown_field(adt_ty, variant, field, ast_fields, kind_name, span);
1127                 }
1128
1129                 tcx.types.err
1130             };
1131
1132             // Make sure to give a type to the field even if there's
1133             // an error, so we can continue type-checking.
1134             self.check_expr_coercable_to_type(&field.expr, field_type);
1135         }
1136
1137         // Make sure the programmer specified correct number of fields.
1138         if kind_name == "union" {
1139             if ast_fields.len() != 1 {
1140                 tcx.sess.span_err(span, "union expressions should have exactly one field");
1141             }
1142         } else if check_completeness && !error_happened && !remaining_fields.is_empty() {
1143             let len = remaining_fields.len();
1144
1145             let mut displayable_field_names = remaining_fields
1146                                               .keys()
1147                                               .map(|ident| ident.as_str())
1148                                               .collect::<Vec<_>>();
1149
1150             displayable_field_names.sort();
1151
1152             let truncated_fields_error = if len <= 3 {
1153                 String::new()
1154             } else {
1155                 format!(" and {} other field{}", (len - 3), if len - 3 == 1 {""} else {"s"})
1156             };
1157
1158             let remaining_fields_names = displayable_field_names.iter().take(3)
1159                                         .map(|n| format!("`{}`", n))
1160                                         .collect::<Vec<_>>()
1161                                         .join(", ");
1162
1163             struct_span_err!(tcx.sess, span, E0063,
1164                              "missing field{} {}{} in initializer of `{}`",
1165                              if remaining_fields.len() == 1 { "" } else { "s" },
1166                              remaining_fields_names,
1167                              truncated_fields_error,
1168                              adt_ty)
1169                 .span_label(span, format!("missing {}{}",
1170                                           remaining_fields_names,
1171                                           truncated_fields_error))
1172                 .emit();
1173         }
1174         error_happened
1175     }
1176
1177     fn check_struct_fields_on_error(
1178         &self,
1179         fields: &'tcx [hir::Field],
1180         base_expr: &'tcx Option<P<hir::Expr>>,
1181     ) {
1182         for field in fields {
1183             self.check_expr(&field.expr);
1184         }
1185         if let Some(ref base) = *base_expr {
1186             self.check_expr(&base);
1187         }
1188     }
1189
1190     fn report_unknown_field(
1191         &self,
1192         ty: Ty<'tcx>,
1193         variant: &'tcx ty::VariantDef,
1194         field: &hir::Field,
1195         skip_fields: &[hir::Field],
1196         kind_name: &str,
1197         ty_span: Span
1198     ) {
1199         if variant.recovered {
1200             return;
1201         }
1202         let mut err = self.type_error_struct_with_diag(
1203             field.ident.span,
1204             |actual| match ty.sty {
1205                 ty::Adt(adt, ..) if adt.is_enum() => {
1206                     struct_span_err!(self.tcx.sess, field.ident.span, E0559,
1207                                      "{} `{}::{}` has no field named `{}`",
1208                                      kind_name, actual, variant.ident, field.ident)
1209                 }
1210                 _ => {
1211                     struct_span_err!(self.tcx.sess, field.ident.span, E0560,
1212                                      "{} `{}` has no field named `{}`",
1213                                      kind_name, actual, field.ident)
1214                 }
1215             },
1216             ty);
1217         match variant.ctor_kind {
1218             CtorKind::Fn => {
1219                 err.span_label(variant.ident.span, format!("`{adt}` defined here", adt=ty));
1220                 err.span_label(field.ident.span, "field does not exist");
1221                 err.span_label(ty_span, format!(
1222                         "`{adt}` is a tuple {kind_name}, \
1223                          use the appropriate syntax: `{adt}(/* fields */)`",
1224                     adt=ty,
1225                     kind_name=kind_name
1226                 ));
1227             }
1228             _ => {
1229                 // prevent all specified fields from being suggested
1230                 let skip_fields = skip_fields.iter().map(|ref x| x.ident.as_str());
1231                 if let Some(field_name) = Self::suggest_field_name(
1232                     variant,
1233                     &field.ident.as_str(),
1234                     skip_fields.collect()
1235                 ) {
1236                     err.span_suggestion(
1237                         field.ident.span,
1238                         "a field with a similar name exists",
1239                         field_name.to_string(),
1240                         Applicability::MaybeIncorrect,
1241                     );
1242                 } else {
1243                     match ty.sty {
1244                         ty::Adt(adt, ..) => {
1245                             if adt.is_enum() {
1246                                 err.span_label(field.ident.span, format!(
1247                                     "`{}::{}` does not have this field",
1248                                     ty,
1249                                     variant.ident
1250                                 ));
1251                             } else {
1252                                 err.span_label(field.ident.span, format!(
1253                                     "`{}` does not have this field",
1254                                     ty
1255                                 ));
1256                             }
1257                             let available_field_names = self.available_field_names(variant);
1258                             if !available_field_names.is_empty() {
1259                                 err.note(&format!("available fields are: {}",
1260                                                   self.name_series_display(available_field_names)));
1261                             }
1262                         }
1263                         _ => bug!("non-ADT passed to report_unknown_field")
1264                     }
1265                 };
1266             }
1267         }
1268         err.emit();
1269     }
1270
1271     // Return an hint about the closest match in field names
1272     fn suggest_field_name(variant: &'tcx ty::VariantDef,
1273                           field: &str,
1274                           skip: Vec<LocalInternedString>)
1275                           -> Option<Symbol> {
1276         let names = variant.fields.iter().filter_map(|field| {
1277             // ignore already set fields and private fields from non-local crates
1278             if skip.iter().any(|x| *x == field.ident.as_str()) ||
1279                (!variant.def_id.is_local() && field.vis != Visibility::Public)
1280             {
1281                 None
1282             } else {
1283                 Some(&field.ident.name)
1284             }
1285         });
1286
1287         find_best_match_for_name(names, field, None)
1288     }
1289
1290     fn available_field_names(&self, variant: &'tcx ty::VariantDef) -> Vec<ast::Name> {
1291         variant.fields.iter().filter(|field| {
1292             let def_scope =
1293                 self.tcx.adjust_ident_and_get_scope(field.ident, variant.def_id, self.body_id).1;
1294             field.vis.is_accessible_from(def_scope, self.tcx)
1295         })
1296         .map(|field| field.ident.name)
1297         .collect()
1298     }
1299
1300     fn name_series_display(&self, names: Vec<ast::Name>) -> String {
1301         // dynamic limit, to never omit just one field
1302         let limit = if names.len() == 6 { 6 } else { 5 };
1303         let mut display = names.iter().take(limit)
1304             .map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
1305         if names.len() > limit {
1306             display = format!("{} ... and {} others", display, names.len() - limit);
1307         }
1308         display
1309     }
1310
1311     // Check field access expressions
1312     fn check_field(
1313         &self,
1314         expr: &'tcx hir::Expr,
1315         needs: Needs,
1316         base: &'tcx hir::Expr,
1317         field: ast::Ident,
1318     ) -> Ty<'tcx> {
1319         let expr_t = self.check_expr_with_needs(base, needs);
1320         let expr_t = self.structurally_resolved_type(base.span,
1321                                                      expr_t);
1322         let mut private_candidate = None;
1323         let mut autoderef = self.autoderef(expr.span, expr_t);
1324         while let Some((base_t, _)) = autoderef.next() {
1325             match base_t.sty {
1326                 ty::Adt(base_def, substs) if !base_def.is_enum() => {
1327                     debug!("struct named {:?}",  base_t);
1328                     let (ident, def_scope) =
1329                         self.tcx.adjust_ident_and_get_scope(field, base_def.did, self.body_id);
1330                     let fields = &base_def.non_enum_variant().fields;
1331                     if let Some(index) = fields.iter().position(|f| f.ident.modern() == ident) {
1332                         let field = &fields[index];
1333                         let field_ty = self.field_ty(expr.span, field, substs);
1334                         // Save the index of all fields regardless of their visibility in case
1335                         // of error recovery.
1336                         self.write_field_index(expr.hir_id, index);
1337                         if field.vis.is_accessible_from(def_scope, self.tcx) {
1338                             let adjustments = autoderef.adjust_steps(self, needs);
1339                             self.apply_adjustments(base, adjustments);
1340                             autoderef.finalize(self);
1341
1342                             self.tcx.check_stability(field.did, Some(expr.hir_id), expr.span);
1343                             return field_ty;
1344                         }
1345                         private_candidate = Some((base_def.did, field_ty));
1346                     }
1347                 }
1348                 ty::Tuple(ref tys) => {
1349                     let fstr = field.as_str();
1350                     if let Ok(index) = fstr.parse::<usize>() {
1351                         if fstr == index.to_string() {
1352                             if let Some(field_ty) = tys.get(index) {
1353                                 let adjustments = autoderef.adjust_steps(self, needs);
1354                                 self.apply_adjustments(base, adjustments);
1355                                 autoderef.finalize(self);
1356
1357                                 self.write_field_index(expr.hir_id, index);
1358                                 return field_ty.expect_ty();
1359                             }
1360                         }
1361                     }
1362                 }
1363                 _ => {}
1364             }
1365         }
1366         autoderef.unambiguous_final_ty(self);
1367
1368         if let Some((did, field_ty)) = private_candidate {
1369             let struct_path = self.tcx().def_path_str(did);
1370             let mut err = struct_span_err!(self.tcx().sess, expr.span, E0616,
1371                                            "field `{}` of struct `{}` is private",
1372                                            field, struct_path);
1373             // Also check if an accessible method exists, which is often what is meant.
1374             if self.method_exists(field, expr_t, expr.hir_id, false)
1375                 && !self.expr_in_place(expr.hir_id)
1376             {
1377                 self.suggest_method_call(
1378                     &mut err,
1379                     &format!("a method `{}` also exists, call it with parentheses", field),
1380                     field,
1381                     expr_t,
1382                     expr.hir_id,
1383                 );
1384             }
1385             err.emit();
1386             field_ty
1387         } else if field.name == kw::Invalid {
1388             self.tcx().types.err
1389         } else if self.method_exists(field, expr_t, expr.hir_id, true) {
1390             let mut err = type_error_struct!(self.tcx().sess, field.span, expr_t, E0615,
1391                                "attempted to take value of method `{}` on type `{}`",
1392                                field, expr_t);
1393
1394             if !self.expr_in_place(expr.hir_id) {
1395                 self.suggest_method_call(
1396                     &mut err,
1397                     "use parentheses to call the method",
1398                     field,
1399                     expr_t,
1400                     expr.hir_id
1401                 );
1402             } else {
1403                 err.help("methods are immutable and cannot be assigned to");
1404             }
1405
1406             err.emit();
1407             self.tcx().types.err
1408         } else {
1409             if !expr_t.is_primitive_ty() {
1410                 let mut err = self.no_such_field_err(field.span, field, expr_t);
1411
1412                 match expr_t.sty {
1413                     ty::Adt(def, _) if !def.is_enum() => {
1414                         if let Some(suggested_field_name) =
1415                             Self::suggest_field_name(def.non_enum_variant(),
1416                                                      &field.as_str(), vec![]) {
1417                                 err.span_suggestion(
1418                                     field.span,
1419                                     "a field with a similar name exists",
1420                                     suggested_field_name.to_string(),
1421                                     Applicability::MaybeIncorrect,
1422                                 );
1423                             } else {
1424                                 err.span_label(field.span, "unknown field");
1425                                 let struct_variant_def = def.non_enum_variant();
1426                                 let field_names = self.available_field_names(struct_variant_def);
1427                                 if !field_names.is_empty() {
1428                                     err.note(&format!("available fields are: {}",
1429                                                       self.name_series_display(field_names)));
1430                                 }
1431                             };
1432                     }
1433                     ty::Array(_, len) => {
1434                         if let (Some(len), Ok(user_index)) = (
1435                             len.assert_usize(self.tcx),
1436                             field.as_str().parse::<u64>()
1437                         ) {
1438                             let base = self.tcx.sess.source_map()
1439                                 .span_to_snippet(base.span)
1440                                 .unwrap_or_else(|_|
1441                                     self.tcx.hir().hir_to_pretty_string(base.hir_id));
1442                             let help = "instead of using tuple indexing, use array indexing";
1443                             let suggestion = format!("{}[{}]", base, field);
1444                             let applicability = if len < user_index {
1445                                 Applicability::MachineApplicable
1446                             } else {
1447                                 Applicability::MaybeIncorrect
1448                             };
1449                             err.span_suggestion(
1450                                 expr.span, help, suggestion, applicability
1451                             );
1452                         }
1453                     }
1454                     ty::RawPtr(..) => {
1455                         let base = self.tcx.sess.source_map()
1456                             .span_to_snippet(base.span)
1457                             .unwrap_or_else(|_| self.tcx.hir().hir_to_pretty_string(base.hir_id));
1458                         let msg = format!("`{}` is a raw pointer; try dereferencing it", base);
1459                         let suggestion = format!("(*{}).{}", base, field);
1460                         err.span_suggestion(
1461                             expr.span,
1462                             &msg,
1463                             suggestion,
1464                             Applicability::MaybeIncorrect,
1465                         );
1466                     }
1467                     _ => {}
1468                 }
1469                 err
1470             } else {
1471                 type_error_struct!(self.tcx().sess, field.span, expr_t, E0610,
1472                                    "`{}` is a primitive type and therefore doesn't have fields",
1473                                    expr_t)
1474             }.emit();
1475             self.tcx().types.err
1476         }
1477     }
1478
1479     fn no_such_field_err<T: Display>(&self, span: Span, field: T, expr_t: &ty::TyS<'_>)
1480         -> DiagnosticBuilder<'_> {
1481         type_error_struct!(self.tcx().sess, span, expr_t, E0609,
1482                            "no field `{}` on type `{}`",
1483                            field, expr_t)
1484     }
1485
1486     fn check_expr_index(
1487         &self,
1488         base: &'tcx hir::Expr,
1489         idx: &'tcx hir::Expr,
1490         needs: Needs,
1491         expr: &'tcx hir::Expr,
1492     ) -> Ty<'tcx> {
1493         let base_t = self.check_expr_with_needs(&base, needs);
1494         let idx_t = self.check_expr(&idx);
1495
1496         if base_t.references_error() {
1497             base_t
1498         } else if idx_t.references_error() {
1499             idx_t
1500         } else {
1501             let base_t = self.structurally_resolved_type(base.span, base_t);
1502             match self.lookup_indexing(expr, base, base_t, idx_t, needs) {
1503                 Some((index_ty, element_ty)) => {
1504                     // two-phase not needed because index_ty is never mutable
1505                     self.demand_coerce(idx, idx_t, index_ty, AllowTwoPhase::No);
1506                     element_ty
1507                 }
1508                 None => {
1509                     let mut err =
1510                         type_error_struct!(self.tcx.sess, expr.span, base_t, E0608,
1511                                             "cannot index into a value of type `{}`",
1512                                             base_t);
1513                     // Try to give some advice about indexing tuples.
1514                     if let ty::Tuple(..) = base_t.sty {
1515                         let mut needs_note = true;
1516                         // If the index is an integer, we can show the actual
1517                         // fixed expression:
1518                         if let ExprKind::Lit(ref lit) = idx.node {
1519                             if let ast::LitKind::Int(i, ast::LitIntType::Unsuffixed) = lit.node {
1520                                 let snip = self.tcx.sess.source_map().span_to_snippet(base.span);
1521                                 if let Ok(snip) = snip {
1522                                     err.span_suggestion(
1523                                         expr.span,
1524                                         "to access tuple elements, use",
1525                                         format!("{}.{}", snip, i),
1526                                         Applicability::MachineApplicable,
1527                                     );
1528                                     needs_note = false;
1529                                 }
1530                             }
1531                         }
1532                         if needs_note {
1533                             err.help("to access tuple elements, use tuple indexing \
1534                                         syntax (e.g., `tuple.0`)");
1535                         }
1536                     }
1537                     err.emit();
1538                     self.tcx.types.err
1539                 }
1540             }
1541         }
1542     }
1543
1544     fn check_expr_yield(&self, value: &'tcx hir::Expr, expr: &'tcx hir::Expr) -> Ty<'tcx> {
1545         match self.yield_ty {
1546             Some(ty) => {
1547                 self.check_expr_coercable_to_type(&value, ty);
1548             }
1549             None => {
1550                 struct_span_err!(self.tcx.sess, expr.span, E0627,
1551                                     "yield statement outside of generator literal").emit();
1552             }
1553         }
1554         self.tcx.mk_unit()
1555     }
1556 }