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::astconv::AstConv as _;
   6 use crate::check::cast;
   7 use crate::check::coercion::CoerceMany;
   8 use crate::check::fatally_break_rust;
   9 use crate::check::method::{probe, MethodError, SelfSource};
  10 use crate::check::report_unexpected_variant_res;
  11 use crate::check::BreakableCtxt;
  12 use crate::check::Diverges;
  13 use crate::check::Expectation::{self, ExpectCastableToType, ExpectHasType, NoExpectation};
  14 use crate::check::FnCtxt;
  15 use crate::check::Needs;
  16 use crate::check::TupleArgumentsFlag::DontTupleArguments;
  17 use crate::type_error_struct;
  18
  19 use rustc_ast::ast;
  20 use rustc_ast::util::lev_distance::find_best_match_for_name;
  21 use rustc_data_structures::fx::FxHashMap;
  22 use rustc_errors::ErrorReported;
  23 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, DiagnosticId};
  24 use rustc_hir as hir;
  25 use rustc_hir::def::{CtorKind, DefKind, Res};
  26 use rustc_hir::def_id::DefId;
  27 use rustc_hir::lang_items;
  28 use rustc_hir::{ExprKind, QPath};
  29 use rustc_infer::infer;
  30 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  31 use rustc_middle::ty;
  32 use rustc_middle::ty::adjustment::{
  33     Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability,
  34 };
  35 use rustc_middle::ty::Ty;
  36 use rustc_middle::ty::TypeFoldable;
  37 use rustc_middle::ty::{AdtKind, Visibility};
  38 use rustc_span::hygiene::DesugaringKind;
  39 use rustc_span::source_map::Span;
  40 use rustc_span::symbol::{kw, sym, Symbol};
  41 use rustc_trait_selection::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<'tcx>, 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<'tcx>,
  54         expected: Ty<'tcx>,
  55         extend_err: impl Fn(&mut DiagnosticBuilder<'_>),
  56     ) -> Ty<'tcx> {
  57         self.check_expr_meets_expectation_or_error(expr, ExpectHasType(expected), extend_err)
  58     }
  59
  60     fn check_expr_meets_expectation_or_error(
  61         &self,
  62         expr: &'tcx hir::Expr<'tcx>,
  63         expected: Expectation<'tcx>,
  64         extend_err: impl Fn(&mut DiagnosticBuilder<'_>),
  65     ) -> Ty<'tcx> {
  66         let expected_ty = expected.to_option(&self).unwrap_or(self.tcx.types.bool);
  67         let mut ty = self.check_expr_with_expectation(expr, expected);
  68
  69         // While we don't allow *arbitrary* coercions here, we *do* allow
  70         // coercions from ! to `expected`.
  71         if ty.is_never() {
  72             assert!(
  73                 !self.tables.borrow().adjustments().contains_key(expr.hir_id),
  74                 "expression with never type wound up being adjusted"
  75             );
  76             let adj_ty = self.next_diverging_ty_var(TypeVariableOrigin {
  77                 kind: TypeVariableOriginKind::AdjustmentType,
  78                 span: expr.span,
  79             });
  80             self.apply_adjustments(
  81                 expr,
  82                 vec![Adjustment { kind: Adjust::NeverToAny, target: adj_ty }],
  83             );
  84             ty = adj_ty;
  85         }
  86
  87         if let Some(mut err) = self.demand_suptype_diag(expr.span, expected_ty, ty) {
  88             let expr = expr.peel_drop_temps();
  89             self.suggest_ref_or_into(&mut err, expr, expected_ty, ty);
  90             extend_err(&mut err);
  91             // Error possibly reported in `check_assign` so avoid emitting error again.
  92             err.emit_unless(self.is_assign_to_bool(expr, expected_ty));
  93         }
  94         ty
  95     }
  96
  97     pub(super) fn check_expr_coercable_to_type(
  98         &self,
  99         expr: &'tcx hir::Expr<'tcx>,
 100         expected: Ty<'tcx>,
 101     ) -> Ty<'tcx> {
 102         let ty = self.check_expr_with_hint(expr, expected);
 103         // checks don't need two phase
 104         self.demand_coerce(expr, ty, expected, AllowTwoPhase::No)
 105     }
 106
 107     pub(super) fn check_expr_with_hint(
 108         &self,
 109         expr: &'tcx hir::Expr<'tcx>,
 110         expected: Ty<'tcx>,
 111     ) -> Ty<'tcx> {
 112         self.check_expr_with_expectation(expr, ExpectHasType(expected))
 113     }
 114
 115     pub(super) fn check_expr_with_expectation(
 116         &self,
 117         expr: &'tcx hir::Expr<'tcx>,
 118         expected: Expectation<'tcx>,
 119     ) -> Ty<'tcx> {
 120         self.check_expr_with_expectation_and_needs(expr, expected, Needs::None)
 121     }
 122
 123     pub(super) fn check_expr(&self, expr: &'tcx hir::Expr<'tcx>) -> Ty<'tcx> {
 124         self.check_expr_with_expectation(expr, NoExpectation)
 125     }
 126
 127     pub(super) fn check_expr_with_needs(
 128         &self,
 129         expr: &'tcx hir::Expr<'tcx>,
 130         needs: Needs,
 131     ) -> Ty<'tcx> {
 132         self.check_expr_with_expectation_and_needs(expr, NoExpectation, needs)
 133     }
 134
 135     /// Invariant:
 136     /// If an expression has any sub-expressions that result in a type error,
 137     /// inspecting that expression's type with `ty.references_error()` will return
 138     /// true. Likewise, if an expression is known to diverge, inspecting its
 139     /// type with `ty::type_is_bot` will return true (n.b.: since Rust is
 140     /// strict, _|_ can appear in the type of an expression that does not,
 141     /// itself, diverge: for example, fn() -> _|_.)
 142     /// Note that inspecting a type's structure *directly* may expose the fact
 143     /// that there are actually multiple representations for `Error`, so avoid
 144     /// that when err needs to be handled differently.
 145     fn check_expr_with_expectation_and_needs(
 146         &self,
 147         expr: &'tcx hir::Expr<'tcx>,
 148         expected: Expectation<'tcx>,
 149         needs: Needs,
 150     ) -> Ty<'tcx> {
 151         debug!(">> type-checking: expr={:?} expected={:?}", expr, expected);
 152
 153         // True if `expr` is a `Try::from_ok(())` that is a result of desugaring a try block
 154         // without the final expr (e.g. `try { return; }`). We don't want to generate an
 155         // unreachable_code lint for it since warnings for autogenerated code are confusing.
 156         let is_try_block_generated_unit_expr = match expr.kind {
 157             ExprKind::Call(_, ref args) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {
 158                 args.len() == 1 && args[0].span.is_desugaring(DesugaringKind::TryBlock)
 159             }
 160
 161             _ => false,
 162         };
 163
 164         // Warn for expressions after diverging siblings.
 165         if !is_try_block_generated_unit_expr {
 166             self.warn_if_unreachable(expr.hir_id, expr.span, "expression");
 167         }
 168
 169         // Hide the outer diverging and has_errors flags.
 170         let old_diverges = self.diverges.replace(Diverges::Maybe);
 171         let old_has_errors = self.has_errors.replace(false);
 172
 173         let ty = self.check_expr_kind(expr, expected, needs);
 174
 175         // Warn for non-block expressions with diverging children.
 176         match expr.kind {
 177             ExprKind::Block(..) | ExprKind::Loop(..) | ExprKind::Match(..) => {}
 178             // If `expr` is a result of desugaring the try block and is an ok-wrapped
 179             // diverging expression (e.g. it arose from desugaring of `try { return }`),
 180             // we skip issuing a warning because it is autogenerated code.
 181             ExprKind::Call(..) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {}
 182             ExprKind::Call(ref callee, _) => {
 183                 self.warn_if_unreachable(expr.hir_id, callee.span, "call")
 184             }
 185             ExprKind::MethodCall(_, ref span, _) => {
 186                 self.warn_if_unreachable(expr.hir_id, *span, "call")
 187             }
 188             _ => self.warn_if_unreachable(expr.hir_id, expr.span, "expression"),
 189         }
 190
 191         // Any expression that produces a value of type `!` must have diverged
 192         if ty.is_never() {
 193             self.diverges.set(self.diverges.get() | Diverges::always(expr.span));
 194         }
 195
 196         // Record the type, which applies it effects.
 197         // We need to do this after the warning above, so that
 198         // we don't warn for the diverging expression itself.
 199         self.write_ty(expr.hir_id, ty);
 200
 201         // Combine the diverging and has_error flags.
 202         self.diverges.set(self.diverges.get() | old_diverges);
 203         self.has_errors.set(self.has_errors.get() | old_has_errors);
 204
 205         debug!("type of {} is...", self.tcx.hir().node_to_string(expr.hir_id));
 206         debug!("... {:?}, expected is {:?}", ty, expected);
 207
 208         ty
 209     }
 210
 211     fn check_expr_kind(
 212         &self,
 213         expr: &'tcx hir::Expr<'tcx>,
 214         expected: Expectation<'tcx>,
 215         needs: Needs,
 216     ) -> Ty<'tcx> {
 217         debug!("check_expr_kind(expr={:?}, expected={:?}, needs={:?})", expr, expected, needs,);
 218
 219         let tcx = self.tcx;
 220         match expr.kind {
 221             ExprKind::Box(ref subexpr) => self.check_expr_box(subexpr, expected),
 222             ExprKind::Lit(ref lit) => self.check_lit(&lit, expected),
 223             ExprKind::Binary(op, ref lhs, ref rhs) => self.check_binop(expr, op, lhs, rhs),
 224             ExprKind::Assign(ref lhs, ref rhs, ref span) => {
 225                 self.check_expr_assign(expr, expected, lhs, rhs, span)
 226             }
 227             ExprKind::AssignOp(op, ref lhs, ref rhs) => self.check_binop_assign(expr, op, lhs, rhs),
 228             ExprKind::Unary(unop, ref oprnd) => {
 229                 self.check_expr_unary(unop, oprnd, expected, needs, expr)
 230             }
 231             ExprKind::AddrOf(kind, mutbl, ref oprnd) => {
 232                 self.check_expr_addr_of(kind, mutbl, oprnd, expected, expr)
 233             }
 234             ExprKind::Path(ref qpath) => self.check_expr_path(qpath, expr),
 235             ExprKind::LlvmInlineAsm(ref asm) => {
 236                 for expr in asm.outputs_exprs.iter().chain(asm.inputs_exprs.iter()) {
 237                     self.check_expr(expr);
 238                 }
 239                 tcx.mk_unit()
 240             }
 241             ExprKind::Break(destination, ref expr_opt) => {
 242                 self.check_expr_break(destination, expr_opt.as_deref(), expr)
 243             }
 244             ExprKind::Continue(destination) => {
 245                 if destination.target_id.is_ok() {
 246                     tcx.types.never
 247                 } else {
 248                     // There was an error; make type-check fail.
 249                     tcx.types.err
 250                 }
 251             }
 252             ExprKind::Ret(ref expr_opt) => self.check_expr_return(expr_opt.as_deref(), expr),
 253             ExprKind::Loop(ref body, _, source) => {
 254                 self.check_expr_loop(body, source, expected, expr)
 255             }
 256             ExprKind::Match(ref discrim, ref arms, match_src) => {
 257                 self.check_match(expr, &discrim, arms, expected, match_src)
 258             }
 259             ExprKind::Closure(capture, ref decl, body_id, _, gen) => {
 260                 self.check_expr_closure(expr, capture, &decl, body_id, gen, expected)
 261             }
 262             ExprKind::Block(ref body, _) => self.check_block_with_expected(&body, expected),
 263             ExprKind::Call(ref callee, ref args) => self.check_call(expr, &callee, args, expected),
 264             ExprKind::MethodCall(ref segment, span, ref args) => {
 265                 self.check_method_call(expr, segment, span, args, expected, needs)
 266             }
 267             ExprKind::Cast(ref e, ref t) => self.check_expr_cast(e, t, expr),
 268             ExprKind::Type(ref e, ref t) => {
 269                 let ty = self.to_ty_saving_user_provided_ty(&t);
 270                 self.check_expr_eq_type(&e, ty);
 271                 ty
 272             }
 273             ExprKind::DropTemps(ref e) => self.check_expr_with_expectation(e, expected),
 274             ExprKind::Array(ref args) => self.check_expr_array(args, expected, expr),
 275             ExprKind::Repeat(ref element, ref count) => {
 276                 self.check_expr_repeat(element, count, expected, expr)
 277             }
 278             ExprKind::Tup(ref elts) => self.check_expr_tuple(elts, expected, expr),
 279             ExprKind::Struct(ref qpath, fields, ref base_expr) => {
 280                 self.check_expr_struct(expr, expected, qpath, fields, base_expr)
 281             }
 282             ExprKind::Field(ref base, field) => self.check_field(expr, needs, &base, field),
 283             ExprKind::Index(ref base, ref idx) => self.check_expr_index(base, idx, needs, expr),
 284             ExprKind::Yield(ref value, ref src) => self.check_expr_yield(value, expr, src),
 285             hir::ExprKind::Err => tcx.types.err,
 286         }
 287     }
 288
 289     fn check_expr_box(&self, expr: &'tcx hir::Expr<'tcx>, expected: Expectation<'tcx>) -> Ty<'tcx> {
 290         let expected_inner = expected.to_option(self).map_or(NoExpectation, |ty| match ty.kind {
 291             ty::Adt(def, _) if def.is_box() => Expectation::rvalue_hint(self, ty.boxed_ty()),
 292             _ => NoExpectation,
 293         });
 294         let referent_ty = self.check_expr_with_expectation(expr, expected_inner);
 295         self.tcx.mk_box(referent_ty)
 296     }
 297
 298     fn check_expr_unary(
 299         &self,
 300         unop: hir::UnOp,
 301         oprnd: &'tcx hir::Expr<'tcx>,
 302         expected: Expectation<'tcx>,
 303         needs: Needs,
 304         expr: &'tcx hir::Expr<'tcx>,
 305     ) -> Ty<'tcx> {
 306         let tcx = self.tcx;
 307         let expected_inner = match unop {
 308             hir::UnOp::UnNot | hir::UnOp::UnNeg => expected,
 309             hir::UnOp::UnDeref => NoExpectation,
 310         };
 311         let needs = match unop {
 312             hir::UnOp::UnDeref => needs,
 313             _ => Needs::None,
 314         };
 315         let mut oprnd_t = self.check_expr_with_expectation_and_needs(&oprnd, expected_inner, needs);
 316
 317         if !oprnd_t.references_error() {
 318             oprnd_t = self.structurally_resolved_type(expr.span, oprnd_t);
 319             match unop {
 320                 hir::UnOp::UnDeref => {
 321                     if let Some(mt) = oprnd_t.builtin_deref(true) {
 322                         oprnd_t = mt.ty;
 323                     } else if let Some(ok) = self.try_overloaded_deref(expr.span, oprnd_t, needs) {
 324                         let method = self.register_infer_ok_obligations(ok);
 325                         if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind {
 326                             let mutbl = match mutbl {
 327                                 hir::Mutability::Not => AutoBorrowMutability::Not,
 328                                 hir::Mutability::Mut => AutoBorrowMutability::Mut {
 329                                     // (It shouldn't actually matter for unary ops whether
 330                                     // we enable two-phase borrows or not, since a unary
 331                                     // op has no additional operands.)
 332                                     allow_two_phase_borrow: AllowTwoPhase::No,
 333                                 },
 334                             };
 335                             self.apply_adjustments(
 336                                 oprnd,
 337                                 vec![Adjustment {
 338                                     kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 339                                     target: method.sig.inputs()[0],
 340                                 }],
 341                             );
 342                         }
 343                         oprnd_t = self.make_overloaded_place_return_type(method).ty;
 344                         self.write_method_call(expr.hir_id, method);
 345                     } else {
 346                         let mut err = type_error_struct!(
 347                             tcx.sess,
 348                             expr.span,
 349                             oprnd_t,
 350                             E0614,
 351                             "type `{}` cannot be dereferenced",
 352                             oprnd_t,
 353                         );
 354                         let sp = tcx.sess.source_map().start_point(expr.span);
 355                         if let Some(sp) =
 356                             tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
 357                         {
 358                             tcx.sess.parse_sess.expr_parentheses_needed(&mut err, *sp, None);
 359                         }
 360                         err.emit();
 361                         oprnd_t = tcx.types.err;
 362                     }
 363                 }
 364                 hir::UnOp::UnNot => {
 365                     let result = self.check_user_unop(expr, oprnd_t, unop);
 366                     // If it's builtin, we can reuse the type, this helps inference.
 367                     if !(oprnd_t.is_integral() || oprnd_t.kind == ty::Bool) {
 368                         oprnd_t = result;
 369                     }
 370                 }
 371                 hir::UnOp::UnNeg => {
 372                     let result = self.check_user_unop(expr, oprnd_t, unop);
 373                     // If it's builtin, we can reuse the type, this helps inference.
 374                     if !oprnd_t.is_numeric() {
 375                         oprnd_t = result;
 376                     }
 377                 }
 378             }
 379         }
 380         oprnd_t
 381     }
 382
 383     fn check_expr_addr_of(
 384         &self,
 385         kind: hir::BorrowKind,
 386         mutbl: hir::Mutability,
 387         oprnd: &'tcx hir::Expr<'tcx>,
 388         expected: Expectation<'tcx>,
 389         expr: &'tcx hir::Expr<'tcx>,
 390     ) -> Ty<'tcx> {
 391         let hint = expected.only_has_type(self).map_or(NoExpectation, |ty| {
 392             match ty.kind {
 393                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 394                     if oprnd.is_syntactic_place_expr() {
 395                         // Places may legitimately have unsized types.
 396                         // For example, dereferences of a fat pointer and
 397                         // the last field of a struct can be unsized.
 398                         ExpectHasType(ty)
 399                     } else {
 400                         Expectation::rvalue_hint(self, ty)
 401                     }
 402                 }
 403                 _ => NoExpectation,
 404             }
 405         });
 406         let needs = Needs::maybe_mut_place(mutbl);
 407         let ty = self.check_expr_with_expectation_and_needs(&oprnd, hint, needs);
 408
 409         let tm = ty::TypeAndMut { ty, mutbl };
 410         match kind {
 411             _ if tm.ty.references_error() => self.tcx.types.err,
 412             hir::BorrowKind::Raw => {
 413                 self.check_named_place_expr(oprnd);
 414                 self.tcx.mk_ptr(tm)
 415             }
 416             hir::BorrowKind::Ref => {
 417                 // Note: at this point, we cannot say what the best lifetime
 418                 // is to use for resulting pointer.  We want to use the
 419                 // shortest lifetime possible so as to avoid spurious borrowck
 420                 // errors.  Moreover, the longest lifetime will depend on the
 421                 // precise details of the value whose address is being taken
 422                 // (and how long it is valid), which we don't know yet until
 423                 // type inference is complete.
 424                 //
 425                 // Therefore, here we simply generate a region variable. The
 426                 // region inferencer will then select a suitable value.
 427                 // Finally, borrowck will infer the value of the region again,
 428                 // this time with enough precision to check that the value
 429                 // whose address was taken can actually be made to live as long
 430                 // as it needs to live.
 431                 let region = self.next_region_var(infer::AddrOfRegion(expr.span));
 432                 self.tcx.mk_ref(region, tm)
 433             }
 434         }
 435     }
 436
 437     /// Does this expression refer to a place that either:
 438     /// * Is based on a local or static.
 439     /// * Contains a dereference
 440     /// Note that the adjustments for the children of `expr` should already
 441     /// have been resolved.
 442     fn check_named_place_expr(&self, oprnd: &'tcx hir::Expr<'tcx>) {
 443         let is_named = oprnd.is_place_expr(|base| {
 444             // Allow raw borrows if there are any deref adjustments.
 445             //
 446             // const VAL: (i32,) = (0,);
 447             // const REF: &(i32,) = &(0,);
 448             //
 449             // &raw const VAL.0;            // ERROR
 450             // &raw const REF.0;            // OK, same as &raw const (*REF).0;
 451             //
 452             // This is maybe too permissive, since it allows
 453             // `let u = &raw const Box::new((1,)).0`, which creates an
 454             // immediately dangling raw pointer.
 455             self.tables.borrow().adjustments().get(base.hir_id).map_or(false, |x| {
 456                 x.iter().any(|adj| if let Adjust::Deref(_) = adj.kind { true } else { false })
 457             })
 458         });
 459         if !is_named {
 460             struct_span_err!(
 461                 self.tcx.sess,
 462                 oprnd.span,
 463                 E0745,
 464                 "cannot take address of a temporary"
 465             )
 466             .span_label(oprnd.span, "temporary value")
 467             .emit();
 468         }
 469     }
 470
 471     fn check_expr_path(&self, qpath: &hir::QPath<'_>, expr: &'tcx hir::Expr<'tcx>) -> Ty<'tcx> {
 472         let tcx = self.tcx;
 473         let (res, opt_ty, segs) = self.resolve_ty_and_res_ufcs(qpath, expr.hir_id, expr.span);
 474         let ty = match res {
 475             Res::Err => {
 476                 self.set_tainted_by_errors();
 477                 tcx.types.err
 478             }
 479             Res::Def(DefKind::Ctor(_, CtorKind::Fictive), _) => {
 480                 report_unexpected_variant_res(tcx, res, expr.span);
 481                 tcx.types.err
 482             }
 483             _ => self.instantiate_value_path(segs, opt_ty, res, expr.span, expr.hir_id).0,
 484         };
 485
 486         if let ty::FnDef(..) = ty.kind {
 487             let fn_sig = ty.fn_sig(tcx);
 488             if !tcx.features().unsized_locals {
 489                 // We want to remove some Sized bounds from std functions,
 490                 // but don't want to expose the removal to stable Rust.
 491                 // i.e., we don't want to allow
 492                 //
 493                 // ```rust
 494                 // drop as fn(str);
 495                 // ```
 496                 //
 497                 // to work in stable even if the Sized bound on `drop` is relaxed.
 498                 for i in 0..fn_sig.inputs().skip_binder().len() {
 499                     // We just want to check sizedness, so instead of introducing
 500                     // placeholder lifetimes with probing, we just replace higher lifetimes
 501                     // with fresh vars.
 502                     let input = self
 503                         .replace_bound_vars_with_fresh_vars(
 504                             expr.span,
 505                             infer::LateBoundRegionConversionTime::FnCall,
 506                             &fn_sig.input(i),
 507                         )
 508                         .0;
 509                     self.require_type_is_sized_deferred(
 510                         input,
 511                         expr.span,
 512                         traits::SizedArgumentType,
 513                     );
 514                 }
 515             }
 516             // Here we want to prevent struct constructors from returning unsized types.
 517             // There were two cases this happened: fn pointer coercion in stable
 518             // and usual function call in presence of unsized_locals.
 519             // Also, as we just want to check sizedness, instead of introducing
 520             // placeholder lifetimes with probing, we just replace higher lifetimes
 521             // with fresh vars.
 522             let output = self
 523                 .replace_bound_vars_with_fresh_vars(
 524                     expr.span,
 525                     infer::LateBoundRegionConversionTime::FnCall,
 526                     &fn_sig.output(),
 527                 )
 528                 .0;
 529             self.require_type_is_sized_deferred(output, expr.span, traits::SizedReturnType);
 530         }
 531
 532         // We always require that the type provided as the value for
 533         // a type parameter outlives the moment of instantiation.
 534         let substs = self.tables.borrow().node_substs(expr.hir_id);
 535         self.add_wf_bounds(substs, expr);
 536
 537         ty
 538     }
 539
 540     fn check_expr_break(
 541         &self,
 542         destination: hir::Destination,
 543         expr_opt: Option<&'tcx hir::Expr<'tcx>>,
 544         expr: &'tcx hir::Expr<'tcx>,
 545     ) -> Ty<'tcx> {
 546         let tcx = self.tcx;
 547         if let Ok(target_id) = destination.target_id {
 548             let (e_ty, cause);
 549             if let Some(ref e) = expr_opt {
 550                 // If this is a break with a value, we need to type-check
 551                 // the expression. Get an expected type from the loop context.
 552                 let opt_coerce_to = {
 553                     // We should release `enclosing_breakables` before the `check_expr_with_hint`
 554                     // below, so can't move this block of code to the enclosing scope and share
 555                     // `ctxt` with the second `encloding_breakables` borrow below.
 556                     let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 557                     match enclosing_breakables.opt_find_breakable(target_id) {
 558                         Some(ctxt) => ctxt.coerce.as_ref().map(|coerce| coerce.expected_ty()),
 559                         None => {
 560                             // Avoid ICE when `break` is inside a closure (#65383).
 561                             self.tcx.sess.delay_span_bug(
 562                                 expr.span,
 563                                 "break was outside loop, but no error was emitted",
 564                             );
 565                             return tcx.types.err;
 566                         }
 567                     }
 568                 };
 569
 570                 // If the loop context is not a `loop { }`, then break with
 571                 // a value is illegal, and `opt_coerce_to` will be `None`.
 572                 // Just set expectation to error in that case.
 573                 let coerce_to = opt_coerce_to.unwrap_or(tcx.types.err);
 574
 575                 // Recurse without `enclosing_breakables` borrowed.
 576                 e_ty = self.check_expr_with_hint(e, coerce_to);
 577                 cause = self.misc(e.span);
 578             } else {
 579                 // Otherwise, this is a break *without* a value. That's
 580                 // always legal, and is equivalent to `break ()`.
 581                 e_ty = tcx.mk_unit();
 582                 cause = self.misc(expr.span);
 583             }
 584
 585             // Now that we have type-checked `expr_opt`, borrow
 586             // the `enclosing_loops` field and let's coerce the
 587             // type of `expr_opt` into what is expected.
 588             let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 589             let ctxt = match enclosing_breakables.opt_find_breakable(target_id) {
 590                 Some(ctxt) => ctxt,
 591                 None => {
 592                     // Avoid ICE when `break` is inside a closure (#65383).
 593                     self.tcx.sess.delay_span_bug(
 594                         expr.span,
 595                         "break was outside loop, but no error was emitted",
 596                     );
 597                     return tcx.types.err;
 598                 }
 599             };
 600
 601             if let Some(ref mut coerce) = ctxt.coerce {
 602                 if let Some(ref e) = expr_opt {
 603                     coerce.coerce(self, &cause, e, e_ty);
 604                 } else {
 605                     assert!(e_ty.is_unit());
 606                     let ty = coerce.expected_ty();
 607                     coerce.coerce_forced_unit(
 608                         self,
 609                         &cause,
 610                         &mut |mut err| {
 611                             self.suggest_mismatched_types_on_tail(
 612                                 &mut err, expr, ty, e_ty, cause.span, target_id,
 613                             );
 614                             if let Some(val) = ty_kind_suggestion(ty) {
 615                                 let label = destination
 616                                     .label
 617                                     .map(|l| format!(" {}", l.ident))
 618                                     .unwrap_or_else(String::new);
 619                                 err.span_suggestion(
 620                                     expr.span,
 621                                     "give it a value of the expected type",
 622                                     format!("break{} {}", label, val),
 623                                     Applicability::HasPlaceholders,
 624                                 );
 625                             }
 626                         },
 627                         false,
 628                     );
 629                 }
 630             } else {
 631                 // If `ctxt.coerce` is `None`, we can just ignore
 632                 // the type of the expression.  This is because
 633                 // either this was a break *without* a value, in
 634                 // which case it is always a legal type (`()`), or
 635                 // else an error would have been flagged by the
 636                 // `loops` pass for using break with an expression
 637                 // where you are not supposed to.
 638                 assert!(expr_opt.is_none() || self.tcx.sess.has_errors());
 639             }
 640
 641             ctxt.may_break = true;
 642
 643             // the type of a `break` is always `!`, since it diverges
 644             tcx.types.never
 645         } else {
 646             // Otherwise, we failed to find the enclosing loop;
 647             // this can only happen if the `break` was not
 648             // inside a loop at all, which is caught by the
 649             // loop-checking pass.
 650             self.tcx
 651                 .sess
 652                 .delay_span_bug(expr.span, "break was outside loop, but no error was emitted");
 653
 654             // We still need to assign a type to the inner expression to
 655             // prevent the ICE in #43162.
 656             if let Some(ref e) = expr_opt {
 657                 self.check_expr_with_hint(e, tcx.types.err);
 658
 659                 // ... except when we try to 'break rust;'.
 660                 // ICE this expression in particular (see #43162).
 661                 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
 662                     if path.segments.len() == 1 && path.segments[0].ident.name == sym::rust {
 663                         fatally_break_rust(self.tcx.sess);
 664                     }
 665                 }
 666             }
 667             // There was an error; make type-check fail.
 668             tcx.types.err
 669         }
 670     }
 671
 672     fn check_expr_return(
 673         &self,
 674         expr_opt: Option<&'tcx hir::Expr<'tcx>>,
 675         expr: &'tcx hir::Expr<'tcx>,
 676     ) -> Ty<'tcx> {
 677         if self.ret_coercion.is_none() {
 678             struct_span_err!(
 679                 self.tcx.sess,
 680                 expr.span,
 681                 E0572,
 682                 "return statement outside of function body",
 683             )
 684             .emit();
 685         } else if let Some(ref e) = expr_opt {
 686             if self.ret_coercion_span.borrow().is_none() {
 687                 *self.ret_coercion_span.borrow_mut() = Some(e.span);
 688             }
 689             self.check_return_expr(e);
 690         } else {
 691             let mut coercion = self.ret_coercion.as_ref().unwrap().borrow_mut();
 692             if self.ret_coercion_span.borrow().is_none() {
 693                 *self.ret_coercion_span.borrow_mut() = Some(expr.span);
 694             }
 695             let cause = self.cause(expr.span, ObligationCauseCode::ReturnNoExpression);
 696             if let Some((fn_decl, _)) = self.get_fn_decl(expr.hir_id) {
 697                 coercion.coerce_forced_unit(
 698                     self,
 699                     &cause,
 700                     &mut |db| {
 701                         let span = fn_decl.output.span();
 702                         if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
 703                             db.span_label(
 704                                 span,
 705                                 format!("expected `{}` because of this return type", snippet),
 706                             );
 707                         }
 708                     },
 709                     true,
 710                 );
 711             } else {
 712                 coercion.coerce_forced_unit(self, &cause, &mut |_| (), true);
 713             }
 714         }
 715         self.tcx.types.never
 716     }
 717
 718     pub(super) fn check_return_expr(&self, return_expr: &'tcx hir::Expr<'tcx>) {
 719         let ret_coercion = self.ret_coercion.as_ref().unwrap_or_else(|| {
 720             span_bug!(return_expr.span, "check_return_expr called outside fn body")
 721         });
 722
 723         let ret_ty = ret_coercion.borrow().expected_ty();
 724         let return_expr_ty = self.check_expr_with_hint(return_expr, ret_ty.clone());
 725         ret_coercion.borrow_mut().coerce(
 726             self,
 727             &self.cause(return_expr.span, ObligationCauseCode::ReturnValue(return_expr.hir_id)),
 728             return_expr,
 729             return_expr_ty,
 730         );
 731     }
 732
 733     fn is_destructuring_place_expr(&self, expr: &'tcx hir::Expr<'tcx>) -> bool {
 734         match &expr.kind {
 735             ExprKind::Array(comps) | ExprKind::Tup(comps) => {
 736                 comps.iter().all(|e| self.is_destructuring_place_expr(e))
 737             }
 738             ExprKind::Struct(_path, fields, rest) => {
 739                 rest.as_ref().map(|e| self.is_destructuring_place_expr(e)).unwrap_or(true)
 740                     && fields.iter().all(|f| self.is_destructuring_place_expr(&f.expr))
 741             }
 742             _ => expr.is_syntactic_place_expr(),
 743         }
 744     }
 745
 746     pub(crate) fn check_lhs_assignable(
 747         &self,
 748         lhs: &'tcx hir::Expr<'tcx>,
 749         err_code: &'static str,
 750         expr_span: &Span,
 751     ) {
 752         if !lhs.is_syntactic_place_expr() {
 753             let mut err = self.tcx.sess.struct_span_err_with_code(
 754                 *expr_span,
 755                 "invalid left-hand side of assignment",
 756                 DiagnosticId::Error(err_code.into()),
 757             );
 758             err.span_label(lhs.span, "cannot assign to this expression");
 759             if self.is_destructuring_place_expr(lhs) {
 760                 err.note("destructuring assignments are not currently supported");
 761                 err.note("for more information, see https://github.com/rust-lang/rfcs/issues/372");
 762             }
 763             err.emit();
 764         }
 765     }
 766
 767     /// Type check assignment expression `expr` of form `lhs = rhs`.
 768     /// The expected type is `()` and is passsed to the function for the purposes of diagnostics.
 769     fn check_expr_assign(
 770         &self,
 771         expr: &'tcx hir::Expr<'tcx>,
 772         expected: Expectation<'tcx>,
 773         lhs: &'tcx hir::Expr<'tcx>,
 774         rhs: &'tcx hir::Expr<'tcx>,
 775         span: &Span,
 776     ) -> Ty<'tcx> {
 777         let lhs_ty = self.check_expr_with_needs(&lhs, Needs::MutPlace);
 778         let rhs_ty = self.check_expr_coercable_to_type(&rhs, lhs_ty);
 779
 780         let expected_ty = expected.coercion_target_type(self, expr.span);
 781         if expected_ty == self.tcx.types.bool {
 782             // The expected type is `bool` but this will result in `()` so we can reasonably
 783             // say that the user intended to write `lhs == rhs` instead of `lhs = rhs`.
 784             // The likely cause of this is `if foo = bar { .. }`.
 785             let actual_ty = self.tcx.mk_unit();
 786             let mut err = self.demand_suptype_diag(expr.span, expected_ty, actual_ty).unwrap();
 787             let msg = "try comparing for equality";
 788             let left = self.tcx.sess.source_map().span_to_snippet(lhs.span);
 789             let right = self.tcx.sess.source_map().span_to_snippet(rhs.span);
 790             if let (Ok(left), Ok(right)) = (left, right) {
 791                 let help = format!("{} == {}", left, right);
 792                 err.span_suggestion(expr.span, msg, help, Applicability::MaybeIncorrect);
 793             } else {
 794                 err.help(msg);
 795             }
 796             err.emit();
 797         } else {
 798             self.check_lhs_assignable(lhs, "E0070", span);
 799         }
 800
 801         self.require_type_is_sized(lhs_ty, lhs.span, traits::AssignmentLhsSized);
 802
 803         if lhs_ty.references_error() || rhs_ty.references_error() {
 804             self.tcx.types.err
 805         } else {
 806             self.tcx.mk_unit()
 807         }
 808     }
 809
 810     fn check_expr_loop(
 811         &self,
 812         body: &'tcx hir::Block<'tcx>,
 813         source: hir::LoopSource,
 814         expected: Expectation<'tcx>,
 815         expr: &'tcx hir::Expr<'tcx>,
 816     ) -> Ty<'tcx> {
 817         let coerce = match source {
 818             // you can only use break with a value from a normal `loop { }`
 819             hir::LoopSource::Loop => {
 820                 let coerce_to = expected.coercion_target_type(self, body.span);
 821                 Some(CoerceMany::new(coerce_to))
 822             }
 823
 824             hir::LoopSource::While | hir::LoopSource::WhileLet | hir::LoopSource::ForLoop => None,
 825         };
 826
 827         let ctxt = BreakableCtxt {
 828             coerce,
 829             may_break: false, // Will get updated if/when we find a `break`.
 830         };
 831
 832         let (ctxt, ()) = self.with_breakable_ctxt(expr.hir_id, ctxt, || {
 833             self.check_block_no_value(&body);
 834         });
 835
 836         if ctxt.may_break {
 837             // No way to know whether it's diverging because
 838             // of a `break` or an outer `break` or `return`.
 839             self.diverges.set(Diverges::Maybe);
 840         }
 841
 842         // If we permit break with a value, then result type is
 843         // the LUB of the breaks (possibly ! if none); else, it
 844         // is nil. This makes sense because infinite loops
 845         // (which would have type !) are only possible iff we
 846         // permit break with a value [1].
 847         if ctxt.coerce.is_none() && !ctxt.may_break {
 848             // [1]
 849             self.tcx.sess.delay_span_bug(body.span, "no coercion, but loop may not break");
 850         }
 851         ctxt.coerce.map(|c| c.complete(self)).unwrap_or_else(|| self.tcx.mk_unit())
 852     }
 853
 854     /// Checks a method call.
 855     fn check_method_call(
 856         &self,
 857         expr: &'tcx hir::Expr<'tcx>,
 858         segment: &hir::PathSegment<'_>,
 859         span: Span,
 860         args: &'tcx [hir::Expr<'tcx>],
 861         expected: Expectation<'tcx>,
 862         needs: Needs,
 863     ) -> Ty<'tcx> {
 864         let rcvr = &args[0];
 865         let rcvr_t = self.check_expr_with_needs(&rcvr, needs);
 866         // no need to check for bot/err -- callee does that
 867         let rcvr_t = self.structurally_resolved_type(args[0].span, rcvr_t);
 868
 869         let method = match self.lookup_method(rcvr_t, segment, span, expr, rcvr) {
 870             Ok(method) => {
 871                 // We could add a "consider `foo::<params>`" suggestion here, but I wasn't able to
 872                 // trigger this codepath causing `structuraly_resolved_type` to emit an error.
 873
 874                 self.write_method_call(expr.hir_id, method);
 875                 Ok(method)
 876             }
 877             Err(error) => {
 878                 if segment.ident.name != kw::Invalid {
 879                     self.report_extended_method_error(segment, span, args, rcvr_t, error);
 880                 }
 881                 Err(())
 882             }
 883         };
 884
 885         // Call the generic checker.
 886         self.check_method_argument_types(
 887             span,
 888             expr,
 889             method,
 890             &args[1..],
 891             DontTupleArguments,
 892             expected,
 893         )
 894     }
 895
 896     fn report_extended_method_error(
 897         &self,
 898         segment: &hir::PathSegment<'_>,
 899         span: Span,
 900         args: &'tcx [hir::Expr<'tcx>],
 901         rcvr_t: Ty<'tcx>,
 902         error: MethodError<'tcx>,
 903     ) {
 904         let rcvr = &args[0];
 905         let try_alt_rcvr = |err: &mut DiagnosticBuilder<'_>, new_rcvr_t| {
 906             if let Some(new_rcvr_t) = new_rcvr_t {
 907                 if let Ok(pick) = self.lookup_probe(
 908                     span,
 909                     segment.ident,
 910                     new_rcvr_t,
 911                     rcvr,
 912                     probe::ProbeScope::AllTraits,
 913                 ) {
 914                     err.span_label(
 915                         pick.item.ident.span,
 916                         &format!("the method is available for `{}` here", new_rcvr_t),
 917                     );
 918                 }
 919             }
 920         };
 921
 922         if let Some(mut err) = self.report_method_error(
 923             span,
 924             rcvr_t,
 925             segment.ident,
 926             SelfSource::MethodCall(rcvr),
 927             error,
 928             Some(args),
 929         ) {
 930             if let ty::Adt(..) = rcvr_t.kind {
 931                 // Try alternative arbitrary self types that could fulfill this call.
 932                 // FIXME: probe for all types that *could* be arbitrary self-types, not
 933                 // just this whitelist.
 934                 try_alt_rcvr(&mut err, self.tcx.mk_lang_item(rcvr_t, lang_items::OwnedBoxLangItem));
 935                 try_alt_rcvr(&mut err, self.tcx.mk_lang_item(rcvr_t, lang_items::PinTypeLangItem));
 936                 try_alt_rcvr(&mut err, self.tcx.mk_diagnostic_item(rcvr_t, sym::Arc));
 937                 try_alt_rcvr(&mut err, self.tcx.mk_diagnostic_item(rcvr_t, sym::Rc));
 938             }
 939             err.emit();
 940         }
 941     }
 942
 943     fn check_expr_cast(
 944         &self,
 945         e: &'tcx hir::Expr<'tcx>,
 946         t: &'tcx hir::Ty<'tcx>,
 947         expr: &'tcx hir::Expr<'tcx>,
 948     ) -> Ty<'tcx> {
 949         // Find the type of `e`. Supply hints based on the type we are casting to,
 950         // if appropriate.
 951         let t_cast = self.to_ty_saving_user_provided_ty(t);
 952         let t_cast = self.resolve_vars_if_possible(&t_cast);
 953         let t_expr = self.check_expr_with_expectation(e, ExpectCastableToType(t_cast));
 954         let t_cast = self.resolve_vars_if_possible(&t_cast);
 955
 956         // Eagerly check for some obvious errors.
 957         if t_expr.references_error() || t_cast.references_error() {
 958             self.tcx.types.err
 959         } else {
 960             // Defer other checks until we're done type checking.
 961             let mut deferred_cast_checks = self.deferred_cast_checks.borrow_mut();
 962             match cast::CastCheck::new(self, e, t_expr, t_cast, t.span, expr.span) {
 963                 Ok(cast_check) => {
 964                     deferred_cast_checks.push(cast_check);
 965                     t_cast
 966                 }
 967                 Err(ErrorReported) => self.tcx.types.err,
 968             }
 969         }
 970     }
 971
 972     fn check_expr_array(
 973         &self,
 974         args: &'tcx [hir::Expr<'tcx>],
 975         expected: Expectation<'tcx>,
 976         expr: &'tcx hir::Expr<'tcx>,
 977     ) -> Ty<'tcx> {
 978         let element_ty = if !args.is_empty() {
 979             let coerce_to = expected
 980                 .to_option(self)
 981                 .and_then(|uty| match uty.kind {
 982                     ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
 983                     _ => None,
 984                 })
 985                 .unwrap_or_else(|| {
 986                     self.next_ty_var(TypeVariableOrigin {
 987                         kind: TypeVariableOriginKind::TypeInference,
 988                         span: expr.span,
 989                     })
 990                 });
 991             let mut coerce = CoerceMany::with_coercion_sites(coerce_to, args);
 992             assert_eq!(self.diverges.get(), Diverges::Maybe);
 993             for e in args {
 994                 let e_ty = self.check_expr_with_hint(e, coerce_to);
 995                 let cause = self.misc(e.span);
 996                 coerce.coerce(self, &cause, e, e_ty);
 997             }
 998             coerce.complete(self)
 999         } else {
1000             self.next_ty_var(TypeVariableOrigin {
1001                 kind: TypeVariableOriginKind::TypeInference,
1002                 span: expr.span,
1003             })
1004         };
1005         self.tcx.mk_array(element_ty, args.len() as u64)
1006     }
1007
1008     fn check_expr_repeat(
1009         &self,
1010         element: &'tcx hir::Expr<'tcx>,
1011         count: &'tcx hir::AnonConst,
1012         expected: Expectation<'tcx>,
1013         _expr: &'tcx hir::Expr<'tcx>,
1014     ) -> Ty<'tcx> {
1015         let tcx = self.tcx;
1016         let count = self.to_const(count);
1017
1018         let uty = match expected {
1019             ExpectHasType(uty) => match uty.kind {
1020                 ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
1021                 _ => None,
1022             },
1023             _ => None,
1024         };
1025
1026         let (element_ty, t) = match uty {
1027             Some(uty) => {
1028                 self.check_expr_coercable_to_type(&element, uty);
1029                 (uty, uty)
1030             }
1031             None => {
1032                 let ty = self.next_ty_var(TypeVariableOrigin {
1033                     kind: TypeVariableOriginKind::MiscVariable,
1034                     span: element.span,
1035                 });
1036                 let element_ty = self.check_expr_has_type_or_error(&element, ty, |_| {});
1037                 (element_ty, ty)
1038             }
1039         };
1040
1041         if element_ty.references_error() {
1042             return tcx.types.err;
1043         }
1044
1045         tcx.mk_ty(ty::Array(t, count))
1046     }
1047
1048     fn check_expr_tuple(
1049         &self,
1050         elts: &'tcx [hir::Expr<'tcx>],
1051         expected: Expectation<'tcx>,
1052         expr: &'tcx hir::Expr<'tcx>,
1053     ) -> Ty<'tcx> {
1054         let flds = expected.only_has_type(self).and_then(|ty| {
1055             let ty = self.resolve_vars_with_obligations(ty);
1056             match ty.kind {
1057                 ty::Tuple(ref flds) => Some(&flds[..]),
1058                 _ => None,
1059             }
1060         });
1061
1062         let elt_ts_iter = elts.iter().enumerate().map(|(i, e)| match flds {
1063             Some(ref fs) if i < fs.len() => {
1064                 let ety = fs[i].expect_ty();
1065                 self.check_expr_coercable_to_type(&e, ety);
1066                 ety
1067             }
1068             _ => self.check_expr_with_expectation(&e, NoExpectation),
1069         });
1070         let tuple = self.tcx.mk_tup(elt_ts_iter);
1071         if tuple.references_error() {
1072             self.tcx.types.err
1073         } else {
1074             self.require_type_is_sized(tuple, expr.span, traits::TupleInitializerSized);
1075             tuple
1076         }
1077     }
1078
1079     fn check_expr_struct(
1080         &self,
1081         expr: &hir::Expr<'_>,
1082         expected: Expectation<'tcx>,
1083         qpath: &QPath<'_>,
1084         fields: &'tcx [hir::Field<'tcx>],
1085         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1086     ) -> Ty<'tcx> {
1087         // Find the relevant variant
1088         let (variant, adt_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, expr.hir_id)
1089         {
1090             variant_ty
1091         } else {
1092             self.check_struct_fields_on_error(fields, base_expr);
1093             return self.tcx.types.err;
1094         };
1095
1096         let path_span = match *qpath {
1097             QPath::Resolved(_, ref path) => path.span,
1098             QPath::TypeRelative(ref qself, _) => qself.span,
1099         };
1100
1101         // Prohibit struct expressions when non-exhaustive flag is set.
1102         let adt = adt_ty.ty_adt_def().expect("`check_struct_path` returned non-ADT type");
1103         if !adt.did.is_local() && variant.is_field_list_non_exhaustive() {
1104             struct_span_err!(
1105                 self.tcx.sess,
1106                 expr.span,
1107                 E0639,
1108                 "cannot create non-exhaustive {} using struct expression",
1109                 adt.variant_descr()
1110             )
1111             .emit();
1112         }
1113
1114         let error_happened = self.check_expr_struct_fields(
1115             adt_ty,
1116             expected,
1117             expr.hir_id,
1118             path_span,
1119             variant,
1120             fields,
1121             base_expr.is_none(),
1122         );
1123         if let &Some(ref base_expr) = base_expr {
1124             // If check_expr_struct_fields hit an error, do not attempt to populate
1125             // the fields with the base_expr. This could cause us to hit errors later
1126             // when certain fields are assumed to exist that in fact do not.
1127             if !error_happened {
1128                 self.check_expr_has_type_or_error(base_expr, adt_ty, |_| {});
1129                 match adt_ty.kind {
1130                     ty::Adt(adt, substs) if adt.is_struct() => {
1131                         let fru_field_types = adt
1132                             .non_enum_variant()
1133                             .fields
1134                             .iter()
1135                             .map(|f| {
1136                                 self.normalize_associated_types_in(
1137                                     expr.span,
1138                                     &f.ty(self.tcx, substs),
1139                                 )
1140                             })
1141                             .collect();
1142
1143                         self.tables
1144                             .borrow_mut()
1145                             .fru_field_types_mut()
1146                             .insert(expr.hir_id, fru_field_types);
1147                     }
1148                     _ => {
1149                         struct_span_err!(
1150                             self.tcx.sess,
1151                             base_expr.span,
1152                             E0436,
1153                             "functional record update syntax requires a struct"
1154                         )
1155                         .emit();
1156                     }
1157                 }
1158             }
1159         }
1160         self.require_type_is_sized(adt_ty, expr.span, traits::StructInitializerSized);
1161         adt_ty
1162     }
1163
1164     fn check_expr_struct_fields(
1165         &self,
1166         adt_ty: Ty<'tcx>,
1167         expected: Expectation<'tcx>,
1168         expr_id: hir::HirId,
1169         span: Span,
1170         variant: &'tcx ty::VariantDef,
1171         ast_fields: &'tcx [hir::Field<'tcx>],
1172         check_completeness: bool,
1173     ) -> bool {
1174         let tcx = self.tcx;
1175
1176         let adt_ty_hint = self
1177             .expected_inputs_for_expected_output(span, expected, adt_ty, &[adt_ty])
1178             .get(0)
1179             .cloned()
1180             .unwrap_or(adt_ty);
1181         // re-link the regions that EIfEO can erase.
1182         self.demand_eqtype(span, adt_ty_hint, adt_ty);
1183
1184         let (substs, adt_kind, kind_name) = match &adt_ty.kind {
1185             &ty::Adt(adt, substs) => (substs, adt.adt_kind(), adt.variant_descr()),
1186             _ => span_bug!(span, "non-ADT passed to check_expr_struct_fields"),
1187         };
1188
1189         let mut remaining_fields = variant
1190             .fields
1191             .iter()
1192             .enumerate()
1193             .map(|(i, field)| (field.ident.normalize_to_macros_2_0(), (i, field)))
1194             .collect::<FxHashMap<_, _>>();
1195
1196         let mut seen_fields = FxHashMap::default();
1197
1198         let mut error_happened = false;
1199
1200         // Type-check each field.
1201         for field in ast_fields {
1202             let ident = tcx.adjust_ident(field.ident, variant.def_id);
1203             let field_type = if let Some((i, v_field)) = remaining_fields.remove(&ident) {
1204                 seen_fields.insert(ident, field.span);
1205                 self.write_field_index(field.hir_id, i);
1206
1207                 // We don't look at stability attributes on
1208                 // struct-like enums (yet...), but it's definitely not
1209                 // a bug to have constructed one.
1210                 if adt_kind != AdtKind::Enum {
1211                     tcx.check_stability(v_field.did, Some(expr_id), field.span);
1212                 }
1213
1214                 self.field_ty(field.span, v_field, substs)
1215             } else {
1216                 error_happened = true;
1217                 if let Some(prev_span) = seen_fields.get(&ident) {
1218                     let mut err = struct_span_err!(
1219                         self.tcx.sess,
1220                         field.ident.span,
1221                         E0062,
1222                         "field `{}` specified more than once",
1223                         ident
1224                     );
1225
1226                     err.span_label(field.ident.span, "used more than once");
1227                     err.span_label(*prev_span, format!("first use of `{}`", ident));
1228
1229                     err.emit();
1230                 } else {
1231                     self.report_unknown_field(adt_ty, variant, field, ast_fields, kind_name, span);
1232                 }
1233
1234                 tcx.types.err
1235             };
1236
1237             // Make sure to give a type to the field even if there's
1238             // an error, so we can continue type-checking.
1239             self.check_expr_coercable_to_type(&field.expr, field_type);
1240         }
1241
1242         // Make sure the programmer specified correct number of fields.
1243         if kind_name == "union" {
1244             if ast_fields.len() != 1 {
1245                 tcx.sess.span_err(span, "union expressions should have exactly one field");
1246             }
1247         } else if check_completeness && !error_happened && !remaining_fields.is_empty() {
1248             let len = remaining_fields.len();
1249
1250             let mut displayable_field_names =
1251                 remaining_fields.keys().map(|ident| ident.as_str()).collect::<Vec<_>>();
1252
1253             displayable_field_names.sort();
1254
1255             let truncated_fields_error = if len <= 3 {
1256                 String::new()
1257             } else {
1258                 format!(" and {} other field{}", (len - 3), if len - 3 == 1 { "" } else { "s" })
1259             };
1260
1261             let remaining_fields_names = displayable_field_names
1262                 .iter()
1263                 .take(3)
1264                 .map(|n| format!("`{}`", n))
1265                 .collect::<Vec<_>>()
1266                 .join(", ");
1267
1268             struct_span_err!(
1269                 tcx.sess,
1270                 span,
1271                 E0063,
1272                 "missing field{} {}{} in initializer of `{}`",
1273                 pluralize!(remaining_fields.len()),
1274                 remaining_fields_names,
1275                 truncated_fields_error,
1276                 adt_ty
1277             )
1278             .span_label(
1279                 span,
1280                 format!("missing {}{}", remaining_fields_names, truncated_fields_error),
1281             )
1282             .emit();
1283         }
1284         error_happened
1285     }
1286
1287     fn check_struct_fields_on_error(
1288         &self,
1289         fields: &'tcx [hir::Field<'tcx>],
1290         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1291     ) {
1292         for field in fields {
1293             self.check_expr(&field.expr);
1294         }
1295         if let Some(ref base) = *base_expr {
1296             self.check_expr(&base);
1297         }
1298     }
1299
1300     fn report_unknown_field(
1301         &self,
1302         ty: Ty<'tcx>,
1303         variant: &'tcx ty::VariantDef,
1304         field: &hir::Field<'_>,
1305         skip_fields: &[hir::Field<'_>],
1306         kind_name: &str,
1307         ty_span: Span,
1308     ) {
1309         if variant.recovered {
1310             self.set_tainted_by_errors();
1311             return;
1312         }
1313         let mut err = self.type_error_struct_with_diag(
1314             field.ident.span,
1315             |actual| match ty.kind {
1316                 ty::Adt(adt, ..) if adt.is_enum() => struct_span_err!(
1317                     self.tcx.sess,
1318                     field.ident.span,
1319                     E0559,
1320                     "{} `{}::{}` has no field named `{}`",
1321                     kind_name,
1322                     actual,
1323                     variant.ident,
1324                     field.ident
1325                 ),
1326                 _ => struct_span_err!(
1327                     self.tcx.sess,
1328                     field.ident.span,
1329                     E0560,
1330                     "{} `{}` has no field named `{}`",
1331                     kind_name,
1332                     actual,
1333                     field.ident
1334                 ),
1335             },
1336             ty,
1337         );
1338         match variant.ctor_kind {
1339             CtorKind::Fn => {
1340                 err.span_label(variant.ident.span, format!("`{adt}` defined here", adt = ty));
1341                 err.span_label(field.ident.span, "field does not exist");
1342                 err.span_label(
1343                     ty_span,
1344                     format!(
1345                         "`{adt}` is a tuple {kind_name}, \
1346                          use the appropriate syntax: `{adt}(/* fields */)`",
1347                         adt = ty,
1348                         kind_name = kind_name
1349                     ),
1350                 );
1351             }
1352             _ => {
1353                 // prevent all specified fields from being suggested
1354                 let skip_fields = skip_fields.iter().map(|ref x| x.ident.name);
1355                 if let Some(field_name) =
1356                     Self::suggest_field_name(variant, &field.ident.as_str(), skip_fields.collect())
1357                 {
1358                     err.span_suggestion(
1359                         field.ident.span,
1360                         "a field with a similar name exists",
1361                         field_name.to_string(),
1362                         Applicability::MaybeIncorrect,
1363                     );
1364                 } else {
1365                     match ty.kind {
1366                         ty::Adt(adt, ..) => {
1367                             if adt.is_enum() {
1368                                 err.span_label(
1369                                     field.ident.span,
1370                                     format!("`{}::{}` does not have this field", ty, variant.ident),
1371                                 );
1372                             } else {
1373                                 err.span_label(
1374                                     field.ident.span,
1375                                     format!("`{}` does not have this field", ty),
1376                                 );
1377                             }
1378                             let available_field_names = self.available_field_names(variant);
1379                             if !available_field_names.is_empty() {
1380                                 err.note(&format!(
1381                                     "available fields are: {}",
1382                                     self.name_series_display(available_field_names)
1383                                 ));
1384                             }
1385                         }
1386                         _ => bug!("non-ADT passed to report_unknown_field"),
1387                     }
1388                 };
1389             }
1390         }
1391         err.emit();
1392     }
1393
1394     // Return an hint about the closest match in field names
1395     fn suggest_field_name(
1396         variant: &'tcx ty::VariantDef,
1397         field: &str,
1398         skip: Vec<Symbol>,
1399     ) -> Option<Symbol> {
1400         let names = variant.fields.iter().filter_map(|field| {
1401             // ignore already set fields and private fields from non-local crates
1402             if skip.iter().any(|&x| x == field.ident.name)
1403                 || (!variant.def_id.is_local() && field.vis != Visibility::Public)
1404             {
1405                 None
1406             } else {
1407                 Some(&field.ident.name)
1408             }
1409         });
1410
1411         find_best_match_for_name(names, field, None)
1412     }
1413
1414     fn available_field_names(&self, variant: &'tcx ty::VariantDef) -> Vec<ast::Name> {
1415         variant
1416             .fields
1417             .iter()
1418             .filter(|field| {
1419                 let def_scope = self
1420                     .tcx
1421                     .adjust_ident_and_get_scope(field.ident, variant.def_id, self.body_id)
1422                     .1;
1423                 field.vis.is_accessible_from(def_scope, self.tcx)
1424             })
1425             .map(|field| field.ident.name)
1426             .collect()
1427     }
1428
1429     fn name_series_display(&self, names: Vec<ast::Name>) -> String {
1430         // dynamic limit, to never omit just one field
1431         let limit = if names.len() == 6 { 6 } else { 5 };
1432         let mut display =
1433             names.iter().take(limit).map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
1434         if names.len() > limit {
1435             display = format!("{} ... and {} others", display, names.len() - limit);
1436         }
1437         display
1438     }
1439
1440     // Check field access expressions
1441     fn check_field(
1442         &self,
1443         expr: &'tcx hir::Expr<'tcx>,
1444         needs: Needs,
1445         base: &'tcx hir::Expr<'tcx>,
1446         field: ast::Ident,
1447     ) -> Ty<'tcx> {
1448         let expr_t = self.check_expr_with_needs(base, needs);
1449         let expr_t = self.structurally_resolved_type(base.span, expr_t);
1450         let mut private_candidate = None;
1451         let mut autoderef = self.autoderef(expr.span, expr_t);
1452         while let Some((base_t, _)) = autoderef.next() {
1453             match base_t.kind {
1454                 ty::Adt(base_def, substs) if !base_def.is_enum() => {
1455                     debug!("struct named {:?}", base_t);
1456                     let (ident, def_scope) =
1457                         self.tcx.adjust_ident_and_get_scope(field, base_def.did, self.body_id);
1458                     let fields = &base_def.non_enum_variant().fields;
1459                     if let Some(index) =
1460                         fields.iter().position(|f| f.ident.normalize_to_macros_2_0() == ident)
1461                     {
1462                         let field = &fields[index];
1463                         let field_ty = self.field_ty(expr.span, field, substs);
1464                         // Save the index of all fields regardless of their visibility in case
1465                         // of error recovery.
1466                         self.write_field_index(expr.hir_id, index);
1467                         if field.vis.is_accessible_from(def_scope, self.tcx) {
1468                             let adjustments = autoderef.adjust_steps(self, needs);
1469                             self.apply_adjustments(base, adjustments);
1470                             autoderef.finalize(self);
1471
1472                             self.tcx.check_stability(field.did, Some(expr.hir_id), expr.span);
1473                             return field_ty;
1474                         }
1475                         private_candidate = Some((base_def.did, field_ty));
1476                     }
1477                 }
1478                 ty::Tuple(ref tys) => {
1479                     let fstr = field.as_str();
1480                     if let Ok(index) = fstr.parse::<usize>() {
1481                         if fstr == index.to_string() {
1482                             if let Some(field_ty) = tys.get(index) {
1483                                 let adjustments = autoderef.adjust_steps(self, needs);
1484                                 self.apply_adjustments(base, adjustments);
1485                                 autoderef.finalize(self);
1486
1487                                 self.write_field_index(expr.hir_id, index);
1488                                 return field_ty.expect_ty();
1489                             }
1490                         }
1491                     }
1492                 }
1493                 _ => {}
1494             }
1495         }
1496         autoderef.unambiguous_final_ty(self);
1497
1498         if let Some((did, field_ty)) = private_candidate {
1499             self.ban_private_field_access(expr, expr_t, field, did);
1500             return field_ty;
1501         }
1502
1503         if field.name == kw::Invalid {
1504         } else if self.method_exists(field, expr_t, expr.hir_id, true) {
1505             self.ban_take_value_of_method(expr, expr_t, field);
1506         } else if !expr_t.is_primitive_ty() {
1507             self.ban_nonexisting_field(field, base, expr, expr_t);
1508         } else {
1509             type_error_struct!(
1510                 self.tcx().sess,
1511                 field.span,
1512                 expr_t,
1513                 E0610,
1514                 "`{}` is a primitive type and therefore doesn't have fields",
1515                 expr_t
1516             )
1517             .emit();
1518         }
1519
1520         self.tcx().types.err
1521     }
1522
1523     fn ban_nonexisting_field(
1524         &self,
1525         field: ast::Ident,
1526         base: &'tcx hir::Expr<'tcx>,
1527         expr: &'tcx hir::Expr<'tcx>,
1528         expr_t: Ty<'tcx>,
1529     ) {
1530         let mut err = self.no_such_field_err(field.span, field, expr_t);
1531
1532         match expr_t.peel_refs().kind {
1533             ty::Array(_, len) => {
1534                 self.maybe_suggest_array_indexing(&mut err, expr, base, field, len);
1535             }
1536             ty::RawPtr(..) => {
1537                 self.suggest_first_deref_field(&mut err, expr, base, field);
1538             }
1539             ty::Adt(def, _) if !def.is_enum() => {
1540                 self.suggest_fields_on_recordish(&mut err, def, field);
1541             }
1542             ty::Param(param_ty) => {
1543                 self.point_at_param_definition(&mut err, param_ty);
1544             }
1545             _ => {}
1546         }
1547
1548         if field.name == kw::Await {
1549             // We know by construction that `<expr>.await` is either on Rust 2015
1550             // or results in `ExprKind::Await`. Suggest switching the edition to 2018.
1551             err.note("to `.await` a `Future`, switch to Rust 2018");
1552             err.help("set `edition = \"2018\"` in `Cargo.toml`");
1553             err.note("for more on editions, read https://doc.rust-lang.org/edition-guide");
1554         }
1555
1556         err.emit();
1557     }
1558
1559     fn ban_private_field_access(
1560         &self,
1561         expr: &hir::Expr<'_>,
1562         expr_t: Ty<'tcx>,
1563         field: ast::Ident,
1564         base_did: DefId,
1565     ) {
1566         let struct_path = self.tcx().def_path_str(base_did);
1567         let kind_name = match self.tcx().def_kind(base_did) {
1568             Some(def_kind) => def_kind.descr(base_did),
1569             _ => " ",
1570         };
1571         let mut err = struct_span_err!(
1572             self.tcx().sess,
1573             field.span,
1574             E0616,
1575             "field `{}` of {} `{}` is private",
1576             field,
1577             kind_name,
1578             struct_path
1579         );
1580         err.span_label(field.span, "private field");
1581         // Also check if an accessible method exists, which is often what is meant.
1582         if self.method_exists(field, expr_t, expr.hir_id, false) && !self.expr_in_place(expr.hir_id)
1583         {
1584             self.suggest_method_call(
1585                 &mut err,
1586                 &format!("a method `{}` also exists, call it with parentheses", field),
1587                 field,
1588                 expr_t,
1589                 expr,
1590             );
1591         }
1592         err.emit();
1593     }
1594
1595     fn ban_take_value_of_method(&self, expr: &hir::Expr<'_>, expr_t: Ty<'tcx>, field: ast::Ident) {
1596         let mut err = type_error_struct!(
1597             self.tcx().sess,
1598             field.span,
1599             expr_t,
1600             E0615,
1601             "attempted to take value of method `{}` on type `{}`",
1602             field,
1603             expr_t
1604         );
1605         err.span_label(field.span, "method, not a field");
1606         if !self.expr_in_place(expr.hir_id) {
1607             self.suggest_method_call(
1608                 &mut err,
1609                 "use parentheses to call the method",
1610                 field,
1611                 expr_t,
1612                 expr,
1613             );
1614         } else {
1615             err.help("methods are immutable and cannot be assigned to");
1616         }
1617
1618         err.emit();
1619     }
1620
1621     fn point_at_param_definition(&self, err: &mut DiagnosticBuilder<'_>, param: ty::ParamTy) {
1622         let generics = self.tcx.generics_of(self.body_id.owner.to_def_id());
1623         let generic_param = generics.type_param(&param, self.tcx);
1624         if let ty::GenericParamDefKind::Type { synthetic: Some(..), .. } = generic_param.kind {
1625             return;
1626         }
1627         let param_def_id = generic_param.def_id;
1628         let param_hir_id = match self.tcx.hir().as_local_hir_id(param_def_id) {
1629             Some(x) => x,
1630             None => return,
1631         };
1632         let param_span = self.tcx.hir().span(param_hir_id);
1633         let param_name = self.tcx.hir().ty_param_name(param_hir_id);
1634
1635         err.span_label(param_span, &format!("type parameter '{}' declared here", param_name));
1636     }
1637
1638     fn suggest_fields_on_recordish(
1639         &self,
1640         err: &mut DiagnosticBuilder<'_>,
1641         def: &'tcx ty::AdtDef,
1642         field: ast::Ident,
1643     ) {
1644         if let Some(suggested_field_name) =
1645             Self::suggest_field_name(def.non_enum_variant(), &field.as_str(), vec![])
1646         {
1647             err.span_suggestion(
1648                 field.span,
1649                 "a field with a similar name exists",
1650                 suggested_field_name.to_string(),
1651                 Applicability::MaybeIncorrect,
1652             );
1653         } else {
1654             err.span_label(field.span, "unknown field");
1655             let struct_variant_def = def.non_enum_variant();
1656             let field_names = self.available_field_names(struct_variant_def);
1657             if !field_names.is_empty() {
1658                 err.note(&format!(
1659                     "available fields are: {}",
1660                     self.name_series_display(field_names),
1661                 ));
1662             }
1663         }
1664     }
1665
1666     fn maybe_suggest_array_indexing(
1667         &self,
1668         err: &mut DiagnosticBuilder<'_>,
1669         expr: &hir::Expr<'_>,
1670         base: &hir::Expr<'_>,
1671         field: ast::Ident,
1672         len: &ty::Const<'tcx>,
1673     ) {
1674         if let (Some(len), Ok(user_index)) =
1675             (len.try_eval_usize(self.tcx, self.param_env), field.as_str().parse::<u64>())
1676         {
1677             if let Ok(base) = self.tcx.sess.source_map().span_to_snippet(base.span) {
1678                 let help = "instead of using tuple indexing, use array indexing";
1679                 let suggestion = format!("{}[{}]", base, field);
1680                 let applicability = if len < user_index {
1681                     Applicability::MachineApplicable
1682                 } else {
1683                     Applicability::MaybeIncorrect
1684                 };
1685                 err.span_suggestion(expr.span, help, suggestion, applicability);
1686             }
1687         }
1688     }
1689
1690     fn suggest_first_deref_field(
1691         &self,
1692         err: &mut DiagnosticBuilder<'_>,
1693         expr: &hir::Expr<'_>,
1694         base: &hir::Expr<'_>,
1695         field: ast::Ident,
1696     ) {
1697         if let Ok(base) = self.tcx.sess.source_map().span_to_snippet(base.span) {
1698             let msg = format!("`{}` is a raw pointer; try dereferencing it", base);
1699             let suggestion = format!("(*{}).{}", base, field);
1700             err.span_suggestion(expr.span, &msg, suggestion, Applicability::MaybeIncorrect);
1701         }
1702     }
1703
1704     fn no_such_field_err<T: Display>(
1705         &self,
1706         span: Span,
1707         field: T,
1708         expr_t: &ty::TyS<'_>,
1709     ) -> DiagnosticBuilder<'_> {
1710         type_error_struct!(
1711             self.tcx().sess,
1712             span,
1713             expr_t,
1714             E0609,
1715             "no field `{}` on type `{}`",
1716             field,
1717             expr_t
1718         )
1719     }
1720
1721     fn check_expr_index(
1722         &self,
1723         base: &'tcx hir::Expr<'tcx>,
1724         idx: &'tcx hir::Expr<'tcx>,
1725         needs: Needs,
1726         expr: &'tcx hir::Expr<'tcx>,
1727     ) -> Ty<'tcx> {
1728         let base_t = self.check_expr_with_needs(&base, needs);
1729         let idx_t = self.check_expr(&idx);
1730
1731         if base_t.references_error() {
1732             base_t
1733         } else if idx_t.references_error() {
1734             idx_t
1735         } else {
1736             let base_t = self.structurally_resolved_type(base.span, base_t);
1737             match self.lookup_indexing(expr, base, base_t, idx_t, needs) {
1738                 Some((index_ty, element_ty)) => {
1739                     // two-phase not needed because index_ty is never mutable
1740                     self.demand_coerce(idx, idx_t, index_ty, AllowTwoPhase::No);
1741                     element_ty
1742                 }
1743                 None => {
1744                     let mut err = type_error_struct!(
1745                         self.tcx.sess,
1746                         expr.span,
1747                         base_t,
1748                         E0608,
1749                         "cannot index into a value of type `{}`",
1750                         base_t
1751                     );
1752                     // Try to give some advice about indexing tuples.
1753                     if let ty::Tuple(..) = base_t.kind {
1754                         let mut needs_note = true;
1755                         // If the index is an integer, we can show the actual
1756                         // fixed expression:
1757                         if let ExprKind::Lit(ref lit) = idx.kind {
1758                             if let ast::LitKind::Int(i, ast::LitIntType::Unsuffixed) = lit.node {
1759                                 let snip = self.tcx.sess.source_map().span_to_snippet(base.span);
1760                                 if let Ok(snip) = snip {
1761                                     err.span_suggestion(
1762                                         expr.span,
1763                                         "to access tuple elements, use",
1764                                         format!("{}.{}", snip, i),
1765                                         Applicability::MachineApplicable,
1766                                     );
1767                                     needs_note = false;
1768                                 }
1769                             }
1770                         }
1771                         if needs_note {
1772                             err.help(
1773                                 "to access tuple elements, use tuple indexing \
1774                                         syntax (e.g., `tuple.0`)",
1775                             );
1776                         }
1777                     }
1778                     err.emit();
1779                     self.tcx.types.err
1780                 }
1781             }
1782         }
1783     }
1784
1785     fn check_expr_yield(
1786         &self,
1787         value: &'tcx hir::Expr<'tcx>,
1788         expr: &'tcx hir::Expr<'tcx>,
1789         src: &'tcx hir::YieldSource,
1790     ) -> Ty<'tcx> {
1791         match self.resume_yield_tys {
1792             Some((resume_ty, yield_ty)) => {
1793                 self.check_expr_coercable_to_type(&value, yield_ty);
1794
1795                 resume_ty
1796             }
1797             // Given that this `yield` expression was generated as a result of lowering a `.await`,
1798             // we know that the yield type must be `()`; however, the context won't contain this
1799             // information. Hence, we check the source of the yield expression here and check its
1800             // value's type against `()` (this check should always hold).
1801             None if src.is_await() => {
1802                 self.check_expr_coercable_to_type(&value, self.tcx.mk_unit());
1803                 self.tcx.mk_unit()
1804             }
1805             _ => {
1806                 struct_span_err!(
1807                     self.tcx.sess,
1808                     expr.span,
1809                     E0627,
1810                     "yield expression outside of generator literal"
1811                 )
1812                 .emit();
1813                 self.tcx.mk_unit()
1814             }
1815         }
1816     }
1817 }
1818
1819 pub(super) fn ty_kind_suggestion(ty: Ty<'_>) -> Option<&'static str> {
1820     Some(match ty.kind {
1821         ty::Bool => "true",
1822         ty::Char => "'a'",
1823         ty::Int(_) | ty::Uint(_) => "42",
1824         ty::Float(_) => "3.14159",
1825         ty::Error | ty::Never => return None,
1826         _ => "value",
1827     })
1828 }