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