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 use crate::util::common::ErrorReported;
  19
  20 use rustc::middle::lang_items;
  21 use rustc::ty;
  22 use rustc::ty::adjustment::{Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
  23 use rustc::ty::Ty;
  24 use rustc::ty::TypeFoldable;
  25 use rustc::ty::{AdtKind, Visibility};
  26 use rustc_ast::ast;
  27 use rustc_ast::util::lev_distance::find_best_match_for_name;
  28 use rustc_data_structures::fx::FxHashMap;
  29 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, DiagnosticId};
  30 use rustc_hir as hir;
  31 use rustc_hir::def::{CtorKind, DefKind, Res};
  32 use rustc_hir::def_id::DefId;
  33 use rustc_hir::{ExprKind, QPath};
  34 use rustc_infer::infer;
  35 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  36 use rustc_infer::traits::{self, ObligationCauseCode};
  37 use rustc_span::hygiene::DesugaringKind;
  38 use rustc_span::source_map::Span;
  39 use rustc_span::symbol::{kw, sym, Symbol};
  40
  41 use std::fmt::Display;
  42
  43 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  44     fn check_expr_eq_type(&self, expr: &'tcx hir::Expr<'tcx>, expected: Ty<'tcx>) {
  45         let ty = self.check_expr_with_hint(expr, expected);
  46         self.demand_eqtype(expr.span, expected, ty);
  47     }
  48
  49     pub fn check_expr_has_type_or_error(
  50         &self,
  51         expr: &'tcx hir::Expr<'tcx>,
  52         expected: Ty<'tcx>,
  53         extend_err: impl Fn(&mut DiagnosticBuilder<'_>),
  54     ) -> Ty<'tcx> {
  55         self.check_expr_meets_expectation_or_error(expr, ExpectHasType(expected), extend_err)
  56     }
  57
  58     fn check_expr_meets_expectation_or_error(
  59         &self,
  60         expr: &'tcx hir::Expr<'tcx>,
  61         expected: Expectation<'tcx>,
  62         extend_err: impl Fn(&mut DiagnosticBuilder<'_>),
  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!(
  71                 !self.tables.borrow().adjustments().contains_key(expr.hir_id),
  72                 "expression with never type wound up being adjusted"
  73             );
  74             let adj_ty = self.next_diverging_ty_var(TypeVariableOrigin {
  75                 kind: TypeVariableOriginKind::AdjustmentType,
  76                 span: expr.span,
  77             });
  78             self.apply_adjustments(
  79                 expr,
  80                 vec![Adjustment { kind: Adjust::NeverToAny, 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 = expr.peel_drop_temps();
  87             self.suggest_ref_or_into(&mut err, expr, expected_ty, ty);
  88             extend_err(&mut err);
  89             // Error possibly reported in `check_assign` so avoid emitting error again.
  90             err.emit_unless(self.is_assign_to_bool(expr, expected_ty));
  91         }
  92         ty
  93     }
  94
  95     pub(super) fn check_expr_coercable_to_type(
  96         &self,
  97         expr: &'tcx hir::Expr<'tcx>,
  98         expected: Ty<'tcx>,
  99     ) -> Ty<'tcx> {
 100         let ty = self.check_expr_with_hint(expr, expected);
 101         // checks don't need two phase
 102         self.demand_coerce(expr, ty, expected, AllowTwoPhase::No)
 103     }
 104
 105     pub(super) fn check_expr_with_hint(
 106         &self,
 107         expr: &'tcx hir::Expr<'tcx>,
 108         expected: Ty<'tcx>,
 109     ) -> Ty<'tcx> {
 110         self.check_expr_with_expectation(expr, ExpectHasType(expected))
 111     }
 112
 113     pub(super) fn check_expr_with_expectation(
 114         &self,
 115         expr: &'tcx hir::Expr<'tcx>,
 116         expected: Expectation<'tcx>,
 117     ) -> Ty<'tcx> {
 118         self.check_expr_with_expectation_and_needs(expr, expected, Needs::None)
 119     }
 120
 121     pub(super) fn check_expr(&self, expr: &'tcx hir::Expr<'tcx>) -> Ty<'tcx> {
 122         self.check_expr_with_expectation(expr, NoExpectation)
 123     }
 124
 125     pub(super) fn check_expr_with_needs(
 126         &self,
 127         expr: &'tcx hir::Expr<'tcx>,
 128         needs: Needs,
 129     ) -> Ty<'tcx> {
 130         self.check_expr_with_expectation_and_needs(expr, NoExpectation, needs)
 131     }
 132
 133     /// Invariant:
 134     /// If an expression has any sub-expressions that result in a type error,
 135     /// inspecting that expression's type with `ty.references_error()` will return
 136     /// true. Likewise, if an expression is known to diverge, inspecting its
 137     /// type with `ty::type_is_bot` will return true (n.b.: since Rust is
 138     /// strict, _|_ can appear in the type of an expression that does not,
 139     /// itself, diverge: for example, fn() -> _|_.)
 140     /// Note that inspecting a type's structure *directly* may expose the fact
 141     /// that there are actually multiple representations for `Error`, so avoid
 142     /// that when err needs to be handled differently.
 143     fn check_expr_with_expectation_and_needs(
 144         &self,
 145         expr: &'tcx hir::Expr<'tcx>,
 146         expected: Expectation<'tcx>,
 147         needs: Needs,
 148     ) -> Ty<'tcx> {
 149         debug!(">> type-checking: expr={:?} expected={:?}", expr, expected);
 150
 151         // True if `expr` is a `Try::from_ok(())` that is a result of desugaring a try block
 152         // without the final expr (e.g. `try { return; }`). We don't want to generate an
 153         // unreachable_code lint for it since warnings for autogenerated code are confusing.
 154         let is_try_block_generated_unit_expr = match expr.kind {
 155             ExprKind::Call(_, ref args) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {
 156                 args.len() == 1 && args[0].span.is_desugaring(DesugaringKind::TryBlock)
 157             }
 158
 159             _ => false,
 160         };
 161
 162         // Warn for expressions after diverging siblings.
 163         if !is_try_block_generated_unit_expr {
 164             self.warn_if_unreachable(expr.hir_id, expr.span, "expression");
 165         }
 166
 167         // Hide the outer diverging and has_errors flags.
 168         let old_diverges = self.diverges.replace(Diverges::Maybe);
 169         let old_has_errors = self.has_errors.replace(false);
 170
 171         let ty = self.check_expr_kind(expr, expected, needs);
 172
 173         // Warn for non-block expressions with diverging children.
 174         match expr.kind {
 175             ExprKind::Block(..) | ExprKind::Loop(..) | ExprKind::Match(..) => {}
 176             // If `expr` is a result of desugaring the try block and is an ok-wrapped
 177             // diverging expression (e.g. it arose from desugaring of `try { return }`),
 178             // we skip issuing a warning because it is autogenerated code.
 179             ExprKind::Call(..) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {}
 180             ExprKind::Call(ref callee, _) => {
 181                 self.warn_if_unreachable(expr.hir_id, callee.span, "call")
 182             }
 183             ExprKind::MethodCall(_, ref span, _) => {
 184                 self.warn_if_unreachable(expr.hir_id, *span, "call")
 185             }
 186             _ => self.warn_if_unreachable(expr.hir_id, expr.span, "expression"),
 187         }
 188
 189         // Any expression that produces a value of type `!` must have diverged
 190         if ty.is_never() {
 191             self.diverges.set(self.diverges.get() | Diverges::always(expr.span));
 192         }
 193
 194         // Record the type, which applies it effects.
 195         // We need to do this after the warning above, so that
 196         // we don't warn for the diverging expression itself.
 197         self.write_ty(expr.hir_id, ty);
 198
 199         // Combine the diverging and has_error flags.
 200         self.diverges.set(self.diverges.get() | old_diverges);
 201         self.has_errors.set(self.has_errors.get() | old_has_errors);
 202
 203         debug!("type of {} is...", self.tcx.hir().node_to_string(expr.hir_id));
 204         debug!("... {:?}, expected is {:?}", ty, expected);
 205
 206         ty
 207     }
 208
 209     fn check_expr_kind(
 210         &self,
 211         expr: &'tcx hir::Expr<'tcx>,
 212         expected: Expectation<'tcx>,
 213         needs: Needs,
 214     ) -> Ty<'tcx> {
 215         debug!("check_expr_kind(expr={:?}, expected={:?}, needs={:?})", expr, expected, needs,);
 216
 217         let tcx = self.tcx;
 218         match expr.kind {
 219             ExprKind::Box(ref subexpr) => self.check_expr_box(subexpr, expected),
 220             ExprKind::Lit(ref lit) => self.check_lit(&lit, expected),
 221             ExprKind::Binary(op, ref lhs, ref rhs) => self.check_binop(expr, op, lhs, rhs),
 222             ExprKind::Assign(ref lhs, ref rhs, ref span) => {
 223                 self.check_expr_assign(expr, expected, lhs, rhs, span)
 224             }
 225             ExprKind::AssignOp(op, ref lhs, ref rhs) => self.check_binop_assign(expr, op, lhs, rhs),
 226             ExprKind::Unary(unop, ref oprnd) => {
 227                 self.check_expr_unary(unop, oprnd, expected, needs, expr)
 228             }
 229             ExprKind::AddrOf(kind, mutbl, ref oprnd) => {
 230                 self.check_expr_addr_of(kind, mutbl, oprnd, expected, expr)
 231             }
 232             ExprKind::Path(ref qpath) => self.check_expr_path(qpath, expr),
 233             ExprKind::InlineAsm(ref asm) => {
 234                 for expr in asm.outputs_exprs.iter().chain(asm.inputs_exprs.iter()) {
 235                     self.check_expr(expr);
 236                 }
 237                 tcx.mk_unit()
 238             }
 239             ExprKind::Break(destination, ref expr_opt) => {
 240                 self.check_expr_break(destination, expr_opt.as_deref(), expr)
 241             }
 242             ExprKind::Continue(destination) => {
 243                 if destination.target_id.is_ok() {
 244                     tcx.types.never
 245                 } else {
 246                     // There was an error; make type-check fail.
 247                     tcx.types.err
 248                 }
 249             }
 250             ExprKind::Ret(ref expr_opt) => self.check_expr_return(expr_opt.as_deref(), expr),
 251             ExprKind::Loop(ref body, _, source) => {
 252                 self.check_expr_loop(body, source, expected, expr)
 253             }
 254             ExprKind::Match(ref discrim, ref arms, match_src) => {
 255                 self.check_match(expr, &discrim, arms, expected, match_src)
 256             }
 257             ExprKind::Closure(capture, ref decl, body_id, _, gen) => {
 258                 self.check_expr_closure(expr, capture, &decl, body_id, gen, expected)
 259             }
 260             ExprKind::Block(ref body, _) => self.check_block_with_expected(&body, expected),
 261             ExprKind::Call(ref callee, ref args) => self.check_call(expr, &callee, args, expected),
 262             ExprKind::MethodCall(ref segment, span, ref args) => {
 263                 self.check_method_call(expr, segment, span, args, expected, needs)
 264             }
 265             ExprKind::Cast(ref e, ref t) => self.check_expr_cast(e, t, expr),
 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) => self.check_expr_with_expectation(e, expected),
 272             ExprKind::Array(ref args) => self.check_expr_array(args, expected, expr),
 273             ExprKind::Repeat(ref element, ref count) => {
 274                 self.check_expr_repeat(element, count, expected, expr)
 275             }
 276             ExprKind::Tup(ref elts) => self.check_expr_tuple(elts, expected, expr),
 277             ExprKind::Struct(ref qpath, fields, ref base_expr) => {
 278                 self.check_expr_struct(expr, expected, qpath, fields, base_expr)
 279             }
 280             ExprKind::Field(ref base, field) => self.check_field(expr, needs, &base, field),
 281             ExprKind::Index(ref base, ref idx) => self.check_expr_index(base, idx, needs, expr),
 282             ExprKind::Yield(ref value, ref src) => self.check_expr_yield(value, expr, src),
 283             hir::ExprKind::Err => tcx.types.err,
 284         }
 285     }
 286
 287     fn check_expr_box(&self, expr: &'tcx hir::Expr<'tcx>, expected: Expectation<'tcx>) -> Ty<'tcx> {
 288         let expected_inner = expected.to_option(self).map_or(NoExpectation, |ty| match ty.kind {
 289             ty::Adt(def, _) if def.is_box() => Expectation::rvalue_hint(self, ty.boxed_ty()),
 290             _ => NoExpectation,
 291         });
 292         let referent_ty = self.check_expr_with_expectation(expr, expected_inner);
 293         self.tcx.mk_box(referent_ty)
 294     }
 295
 296     fn check_expr_unary(
 297         &self,
 298         unop: hir::UnOp,
 299         oprnd: &'tcx hir::Expr<'tcx>,
 300         expected: Expectation<'tcx>,
 301         needs: Needs,
 302         expr: &'tcx hir::Expr<'tcx>,
 303     ) -> Ty<'tcx> {
 304         let tcx = self.tcx;
 305         let expected_inner = match unop {
 306             hir::UnOp::UnNot | hir::UnOp::UnNeg => expected,
 307             hir::UnOp::UnDeref => NoExpectation,
 308         };
 309         let needs = match unop {
 310             hir::UnOp::UnDeref => needs,
 311             _ => Needs::None,
 312         };
 313         let mut oprnd_t = self.check_expr_with_expectation_and_needs(&oprnd, expected_inner, needs);
 314
 315         if !oprnd_t.references_error() {
 316             oprnd_t = self.structurally_resolved_type(expr.span, oprnd_t);
 317             match unop {
 318                 hir::UnOp::UnDeref => {
 319                     if let Some(mt) = oprnd_t.builtin_deref(true) {
 320                         oprnd_t = mt.ty;
 321                     } else if let Some(ok) = self.try_overloaded_deref(expr.span, oprnd_t, needs) {
 322                         let method = self.register_infer_ok_obligations(ok);
 323                         if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind {
 324                             let mutbl = match mutbl {
 325                                 hir::Mutability::Not => AutoBorrowMutability::Not,
 326                                 hir::Mutability::Mut => AutoBorrowMutability::Mut {
 327                                     // (It shouldn't actually matter for unary ops whether
 328                                     // we enable two-phase borrows or not, since a unary
 329                                     // op has no additional operands.)
 330                                     allow_two_phase_borrow: AllowTwoPhase::No,
 331                                 },
 332                             };
 333                             self.apply_adjustments(
 334                                 oprnd,
 335                                 vec![Adjustment {
 336                                     kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 337                                     target: method.sig.inputs()[0],
 338                                 }],
 339                             );
 340                         }
 341                         oprnd_t = self.make_overloaded_place_return_type(method).ty;
 342                         self.write_method_call(expr.hir_id, method);
 343                     } else {
 344                         let mut err = type_error_struct!(
 345                             tcx.sess,
 346                             expr.span,
 347                             oprnd_t,
 348                             E0614,
 349                             "type `{}` cannot be dereferenced",
 350                             oprnd_t,
 351                         );
 352                         let sp = tcx.sess.source_map().start_point(expr.span);
 353                         if let Some(sp) =
 354                             tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
 355                         {
 356                             tcx.sess.parse_sess.expr_parentheses_needed(&mut err, *sp, None);
 357                         }
 358                         err.emit();
 359                         oprnd_t = tcx.types.err;
 360                     }
 361                 }
 362                 hir::UnOp::UnNot => {
 363                     let result = self.check_user_unop(expr, oprnd_t, unop);
 364                     // If it's builtin, we can reuse the type, this helps inference.
 365                     if !(oprnd_t.is_integral() || oprnd_t.kind == ty::Bool) {
 366                         oprnd_t = result;
 367                     }
 368                 }
 369                 hir::UnOp::UnNeg => {
 370                     let result = self.check_user_unop(expr, oprnd_t, unop);
 371                     // If it's builtin, we can reuse the type, this helps inference.
 372                     if !oprnd_t.is_numeric() {
 373                         oprnd_t = result;
 374                     }
 375                 }
 376             }
 377         }
 378         oprnd_t
 379     }
 380
 381     fn check_expr_addr_of(
 382         &self,
 383         kind: hir::BorrowKind,
 384         mutbl: hir::Mutability,
 385         oprnd: &'tcx hir::Expr<'tcx>,
 386         expected: Expectation<'tcx>,
 387         expr: &'tcx hir::Expr<'tcx>,
 388     ) -> Ty<'tcx> {
 389         let hint = expected.only_has_type(self).map_or(NoExpectation, |ty| {
 390             match ty.kind {
 391                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 392                     if oprnd.is_syntactic_place_expr() {
 393                         // Places may legitimately have unsized types.
 394                         // For example, dereferences of a fat pointer and
 395                         // the last field of a struct can be unsized.
 396                         ExpectHasType(ty)
 397                     } else {
 398                         Expectation::rvalue_hint(self, ty)
 399                     }
 400                 }
 401                 _ => NoExpectation,
 402             }
 403         });
 404         let needs = Needs::maybe_mut_place(mutbl);
 405         let ty = self.check_expr_with_expectation_and_needs(&oprnd, hint, needs);
 406
 407         let tm = ty::TypeAndMut { ty: ty, mutbl: mutbl };
 408         match kind {
 409             _ if tm.ty.references_error() => self.tcx.types.err,
 410             hir::BorrowKind::Raw => {
 411                 self.check_named_place_expr(oprnd);
 412                 self.tcx.mk_ptr(tm)
 413             }
 414             hir::BorrowKind::Ref => {
 415                 // Note: at this point, we cannot say what the best lifetime
 416                 // is to use for resulting pointer.  We want to use the
 417                 // shortest lifetime possible so as to avoid spurious borrowck
 418                 // errors.  Moreover, the longest lifetime will depend on the
 419                 // precise details of the value whose address is being taken
 420                 // (and how long it is valid), which we don't know yet until
 421                 // type inference is complete.
 422                 //
 423                 // Therefore, here we simply generate a region variable. The
 424                 // region inferencer will then select a suitable value.
 425                 // Finally, borrowck will infer the value of the region again,
 426                 // this time with enough precision to check that the value
 427                 // whose address was taken can actually be made to live as long
 428                 // as it needs to live.
 429                 let region = self.next_region_var(infer::AddrOfRegion(expr.span));
 430                 self.tcx.mk_ref(region, tm)
 431             }
 432         }
 433     }
 434
 435     /// Does this expression refer to a place that either:
 436     /// * Is based on a local or static.
 437     /// * Contains a dereference
 438     /// Note that the adjustments for the children of `expr` should already
 439     /// have been resolved.
 440     fn check_named_place_expr(&self, oprnd: &'tcx hir::Expr<'tcx>) {
 441         let is_named = oprnd.is_place_expr(|base| {
 442             // Allow raw borrows if there are any deref adjustments.
 443             //
 444             // const VAL: (i32,) = (0,);
 445             // const REF: &(i32,) = &(0,);
 446             //
 447             // &raw const VAL.0;            // ERROR
 448             // &raw const REF.0;            // OK, same as &raw const (*REF).0;
 449             //
 450             // This is maybe too permissive, since it allows
 451             // `let u = &raw const Box::new((1,)).0`, which creates an
 452             // immediately dangling raw pointer.
 453             self.tables.borrow().adjustments().get(base.hir_id).map_or(false, |x| {
 454                 x.iter().any(|adj| if let Adjust::Deref(_) = adj.kind { true } else { false })
 455             })
 456         });
 457         if !is_named {
 458             struct_span_err!(
 459                 self.tcx.sess,
 460                 oprnd.span,
 461                 E0745,
 462                 "cannot take address of a temporary"
 463             )
 464             .span_label(oprnd.span, "temporary value")
 465             .emit();
 466         }
 467     }
 468
 469     fn check_expr_path(&self, qpath: &hir::QPath<'_>, expr: &'tcx hir::Expr<'tcx>) -> Ty<'tcx> {
 470         let tcx = self.tcx;
 471         let (res, opt_ty, segs) = self.resolve_ty_and_res_ufcs(qpath, expr.hir_id, expr.span);
 472         let ty = match res {
 473             Res::Err => {
 474                 self.set_tainted_by_errors();
 475                 tcx.types.err
 476             }
 477             Res::Def(DefKind::Ctor(_, CtorKind::Fictive), _) => {
 478                 report_unexpected_variant_res(tcx, res, expr.span, qpath);
 479                 tcx.types.err
 480             }
 481             _ => self.instantiate_value_path(segs, opt_ty, res, expr.span, expr.hir_id).0,
 482         };
 483
 484         if let ty::FnDef(..) = ty.kind {
 485             let fn_sig = ty.fn_sig(tcx);
 486             if !tcx.features().unsized_locals {
 487                 // We want to remove some Sized bounds from std functions,
 488                 // but don't want to expose the removal to stable Rust.
 489                 // i.e., we don't want to allow
 490                 //
 491                 // ```rust
 492                 // drop as fn(str);
 493                 // ```
 494                 //
 495                 // to work in stable even if the Sized bound on `drop` is relaxed.
 496                 for i in 0..fn_sig.inputs().skip_binder().len() {
 497                     // We just want to check sizedness, so instead of introducing
 498                     // placeholder lifetimes with probing, we just replace higher lifetimes
 499                     // with fresh vars.
 500                     let input = self
 501                         .replace_bound_vars_with_fresh_vars(
 502                             expr.span,
 503                             infer::LateBoundRegionConversionTime::FnCall,
 504                             &fn_sig.input(i),
 505                         )
 506                         .0;
 507                     self.require_type_is_sized_deferred(
 508                         input,
 509                         expr.span,
 510                         traits::SizedArgumentType,
 511                     );
 512                 }
 513             }
 514             // Here we want to prevent struct constructors from returning unsized types.
 515             // There were two cases this happened: fn pointer coercion in stable
 516             // and usual function call in presence of unsized_locals.
 517             // Also, as we just want to check sizedness, instead of introducing
 518             // placeholder lifetimes with probing, we just replace higher lifetimes
 519             // with fresh vars.
 520             let output = self
 521                 .replace_bound_vars_with_fresh_vars(
 522                     expr.span,
 523                     infer::LateBoundRegionConversionTime::FnCall,
 524                     &fn_sig.output(),
 525                 )
 526                 .0;
 527             self.require_type_is_sized_deferred(output, expr.span, traits::SizedReturnType);
 528         }
 529
 530         // We always require that the type provided as the value for
 531         // a type parameter outlives the moment of instantiation.
 532         let substs = self.tables.borrow().node_substs(expr.hir_id);
 533         self.add_wf_bounds(substs, expr);
 534
 535         ty
 536     }
 537
 538     fn check_expr_break(
 539         &self,
 540         destination: hir::Destination,
 541         expr_opt: Option<&'tcx hir::Expr<'tcx>>,
 542         expr: &'tcx hir::Expr<'tcx>,
 543     ) -> Ty<'tcx> {
 544         let tcx = self.tcx;
 545         if let Ok(target_id) = destination.target_id {
 546             let (e_ty, cause);
 547             if let Some(ref e) = expr_opt {
 548                 // If this is a break with a value, we need to type-check
 549                 // the expression. Get an expected type from the loop context.
 550                 let opt_coerce_to = {
 551                     // We should release `enclosing_breakables` before the `check_expr_with_hint`
 552                     // below, so can't move this block of code to the enclosing scope and share
 553                     // `ctxt` with the second `encloding_breakables` borrow below.
 554                     let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 555                     match enclosing_breakables.opt_find_breakable(target_id) {
 556                         Some(ctxt) => ctxt.coerce.as_ref().map(|coerce| coerce.expected_ty()),
 557                         None => {
 558                             // Avoid ICE when `break` is inside a closure (#65383).
 559                             self.tcx.sess.delay_span_bug(
 560                                 expr.span,
 561                                 "break was outside loop, but no error was emitted",
 562                             );
 563                             return tcx.types.err;
 564                         }
 565                     }
 566                 };
 567
 568                 // If the loop context is not a `loop { }`, then break with
 569                 // a value is illegal, and `opt_coerce_to` will be `None`.
 570                 // Just set expectation to error in that case.
 571                 let coerce_to = opt_coerce_to.unwrap_or(tcx.types.err);
 572
 573                 // Recurse without `enclosing_breakables` borrowed.
 574                 e_ty = self.check_expr_with_hint(e, coerce_to);
 575                 cause = self.misc(e.span);
 576             } else {
 577                 // Otherwise, this is a break *without* a value. That's
 578                 // always legal, and is equivalent to `break ()`.
 579                 e_ty = tcx.mk_unit();
 580                 cause = self.misc(expr.span);
 581             }
 582
 583             // Now that we have type-checked `expr_opt`, borrow
 584             // the `enclosing_loops` field and let's coerce the
 585             // type of `expr_opt` into what is expected.
 586             let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 587             let ctxt = match enclosing_breakables.opt_find_breakable(target_id) {
 588                 Some(ctxt) => ctxt,
 589                 None => {
 590                     // Avoid ICE when `break` is inside a closure (#65383).
 591                     self.tcx.sess.delay_span_bug(
 592                         expr.span,
 593                         "break was outside loop, but no error was emitted",
 594                     );
 595                     return tcx.types.err;
 596                 }
 597             };
 598
 599             if let Some(ref mut coerce) = ctxt.coerce {
 600                 if let Some(ref e) = expr_opt {
 601                     coerce.coerce(self, &cause, e, e_ty);
 602                 } else {
 603                     assert!(e_ty.is_unit());
 604                     let ty = coerce.expected_ty();
 605                     coerce.coerce_forced_unit(
 606                         self,
 607                         &cause,
 608                         &mut |mut err| {
 609                             self.suggest_mismatched_types_on_tail(
 610                                 &mut err, expr, ty, e_ty, cause.span, target_id,
 611                             );
 612                             if let Some(val) = ty_kind_suggestion(ty) {
 613                                 let label = destination
 614                                     .label
 615                                     .map(|l| format!(" {}", l.ident))
 616                                     .unwrap_or_else(String::new);
 617                                 err.span_suggestion(
 618                                     expr.span,
 619                                     "give it a value of the expected type",
 620                                     format!("break{} {}", label, val),
 621                                     Applicability::HasPlaceholders,
 622                                 );
 623                             }
 624                         },
 625                         false,
 626                     );
 627                 }
 628             } else {
 629                 // If `ctxt.coerce` is `None`, we can just ignore
 630                 // the type of the expression.  This is because
 631                 // either this was a break *without* a value, in
 632                 // which case it is always a legal type (`()`), or
 633                 // else an error would have been flagged by the
 634                 // `loops` pass for using break with an expression
 635                 // where you are not supposed to.
 636                 assert!(expr_opt.is_none() || self.tcx.sess.has_errors());
 637             }
 638
 639             ctxt.may_break = true;
 640
 641             // the type of a `break` is always `!`, since it diverges
 642             tcx.types.never
 643         } else {
 644             // Otherwise, we failed to find the enclosing loop;
 645             // this can only happen if the `break` was not
 646             // inside a loop at all, which is caught by the
 647             // loop-checking pass.
 648             self.tcx
 649                 .sess
 650                 .delay_span_bug(expr.span, "break was outside loop, but no error was emitted");
 651
 652             // We still need to assign a type to the inner expression to
 653             // prevent the ICE in #43162.
 654             if let Some(ref e) = expr_opt {
 655                 self.check_expr_with_hint(e, tcx.types.err);
 656
 657                 // ... except when we try to 'break rust;'.
 658                 // ICE this expression in particular (see #43162).
 659                 if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
 660                     if path.segments.len() == 1 && path.segments[0].ident.name == sym::rust {
 661                         fatally_break_rust(self.tcx.sess);
 662                     }
 663                 }
 664             }
 665             // There was an error; make type-check fail.
 666             tcx.types.err
 667         }
 668     }
 669
 670     fn check_expr_return(
 671         &self,
 672         expr_opt: Option<&'tcx hir::Expr<'tcx>>,
 673         expr: &'tcx hir::Expr<'tcx>,
 674     ) -> Ty<'tcx> {
 675         if self.ret_coercion.is_none() {
 676             struct_span_err!(
 677                 self.tcx.sess,
 678                 expr.span,
 679                 E0572,
 680                 "return statement outside of function body",
 681             )
 682             .emit();
 683         } else if let Some(ref e) = expr_opt {
 684             if self.ret_coercion_span.borrow().is_none() {
 685                 *self.ret_coercion_span.borrow_mut() = Some(e.span);
 686             }
 687             self.check_return_expr(e);
 688         } else {
 689             let mut coercion = self.ret_coercion.as_ref().unwrap().borrow_mut();
 690             if self.ret_coercion_span.borrow().is_none() {
 691                 *self.ret_coercion_span.borrow_mut() = Some(expr.span);
 692             }
 693             let cause = self.cause(expr.span, ObligationCauseCode::ReturnNoExpression);
 694             if let Some((fn_decl, _)) = self.get_fn_decl(expr.hir_id) {
 695                 coercion.coerce_forced_unit(
 696                     self,
 697                     &cause,
 698                     &mut |db| {
 699                         db.span_label(
 700                             fn_decl.output.span(),
 701                             format!("expected `{}` because of this return type", fn_decl.output,),
 702                         );
 703                     },
 704                     true,
 705                 );
 706             } else {
 707                 coercion.coerce_forced_unit(self, &cause, &mut |_| (), true);
 708             }
 709         }
 710         self.tcx.types.never
 711     }
 712
 713     pub(super) fn check_return_expr(&self, return_expr: &'tcx hir::Expr<'tcx>) {
 714         let ret_coercion = self.ret_coercion.as_ref().unwrap_or_else(|| {
 715             span_bug!(return_expr.span, "check_return_expr called outside fn body")
 716         });
 717
 718         let ret_ty = ret_coercion.borrow().expected_ty();
 719         let return_expr_ty = self.check_expr_with_hint(return_expr, ret_ty.clone());
 720         ret_coercion.borrow_mut().coerce(
 721             self,
 722             &self.cause(return_expr.span, ObligationCauseCode::ReturnValue(return_expr.hir_id)),
 723             return_expr,
 724             return_expr_ty,
 725         );
 726     }
 727
 728     fn is_destructuring_place_expr(&self, expr: &'tcx hir::Expr<'tcx>) -> bool {
 729         match &expr.kind {
 730             ExprKind::Array(comps) | ExprKind::Tup(comps) => {
 731                 comps.iter().all(|e| self.is_destructuring_place_expr(e))
 732             }
 733             ExprKind::Struct(_path, fields, rest) => {
 734                 rest.as_ref().map(|e| self.is_destructuring_place_expr(e)).unwrap_or(true)
 735                     && fields.iter().all(|f| self.is_destructuring_place_expr(&f.expr))
 736             }
 737             _ => expr.is_syntactic_place_expr(),
 738         }
 739     }
 740
 741     pub(crate) fn check_lhs_assignable(
 742         &self,
 743         lhs: &'tcx hir::Expr<'tcx>,
 744         err_code: &'static str,
 745         expr_span: &Span,
 746     ) {
 747         if !lhs.is_syntactic_place_expr() {
 748             let mut err = self.tcx.sess.struct_span_err_with_code(
 749                 *expr_span,
 750                 "invalid left-hand side of assignment",
 751                 DiagnosticId::Error(err_code.into()),
 752             );
 753             err.span_label(lhs.span, "cannot assign to this expression");
 754             if self.is_destructuring_place_expr(lhs) {
 755                 err.note("destructuring assignments are not currently supported");
 756                 err.note("for more information, see https://github.com/rust-lang/rfcs/issues/372");
 757             }
 758             err.emit();
 759         }
 760     }
 761
 762     /// Type check assignment expression `expr` of form `lhs = rhs`.
 763     /// The expected type is `()` and is passsed to the function for the purposes of diagnostics.
 764     fn check_expr_assign(
 765         &self,
 766         expr: &'tcx hir::Expr<'tcx>,
 767         expected: Expectation<'tcx>,
 768         lhs: &'tcx hir::Expr<'tcx>,
 769         rhs: &'tcx hir::Expr<'tcx>,
 770         span: &Span,
 771     ) -> Ty<'tcx> {
 772         let lhs_ty = self.check_expr_with_needs(&lhs, Needs::MutPlace);
 773         let rhs_ty = self.check_expr_coercable_to_type(&rhs, lhs_ty);
 774
 775         let expected_ty = expected.coercion_target_type(self, expr.span);
 776         if expected_ty == self.tcx.types.bool {
 777             // The expected type is `bool` but this will result in `()` so we can reasonably
 778             // say that the user intended to write `lhs == rhs` instead of `lhs = rhs`.
 779             // The likely cause of this is `if foo = bar { .. }`.
 780             let actual_ty = self.tcx.mk_unit();
 781             let mut err = self.demand_suptype_diag(expr.span, expected_ty, actual_ty).unwrap();
 782             let msg = "try comparing for equality";
 783             let left = self.tcx.sess.source_map().span_to_snippet(lhs.span);
 784             let right = self.tcx.sess.source_map().span_to_snippet(rhs.span);
 785             if let (Ok(left), Ok(right)) = (left, right) {
 786                 let help = format!("{} == {}", left, right);
 787                 err.span_suggestion(expr.span, msg, help, Applicability::MaybeIncorrect);
 788             } else {
 789                 err.help(msg);
 790             }
 791             err.emit();
 792         } else {
 793             self.check_lhs_assignable(lhs, "E0070", span);
 794         }
 795
 796         self.require_type_is_sized(lhs_ty, lhs.span, traits::AssignmentLhsSized);
 797
 798         if lhs_ty.references_error() || rhs_ty.references_error() {
 799             self.tcx.types.err
 800         } else {
 801             self.tcx.mk_unit()
 802         }
 803     }
 804
 805     fn check_expr_loop(
 806         &self,
 807         body: &'tcx hir::Block<'tcx>,
 808         source: hir::LoopSource,
 809         expected: Expectation<'tcx>,
 810         expr: &'tcx hir::Expr<'tcx>,
 811     ) -> Ty<'tcx> {
 812         let coerce = match source {
 813             // you can only use break with a value from a normal `loop { }`
 814             hir::LoopSource::Loop => {
 815                 let coerce_to = expected.coercion_target_type(self, body.span);
 816                 Some(CoerceMany::new(coerce_to))
 817             }
 818
 819             hir::LoopSource::While | hir::LoopSource::WhileLet | hir::LoopSource::ForLoop => None,
 820         };
 821
 822         let ctxt = BreakableCtxt {
 823             coerce,
 824             may_break: false, // Will get updated if/when we find a `break`.
 825         };
 826
 827         let (ctxt, ()) = self.with_breakable_ctxt(expr.hir_id, ctxt, || {
 828             self.check_block_no_value(&body);
 829         });
 830
 831         if ctxt.may_break {
 832             // No way to know whether it's diverging because
 833             // of a `break` or an outer `break` or `return`.
 834             self.diverges.set(Diverges::Maybe);
 835         }
 836
 837         // If we permit break with a value, then result type is
 838         // the LUB of the breaks (possibly ! if none); else, it
 839         // is nil. This makes sense because infinite loops
 840         // (which would have type !) are only possible iff we
 841         // permit break with a value [1].
 842         if ctxt.coerce.is_none() && !ctxt.may_break {
 843             // [1]
 844             self.tcx.sess.delay_span_bug(body.span, "no coercion, but loop may not break");
 845         }
 846         ctxt.coerce.map(|c| c.complete(self)).unwrap_or_else(|| self.tcx.mk_unit())
 847     }
 848
 849     /// Checks a method call.
 850     fn check_method_call(
 851         &self,
 852         expr: &'tcx hir::Expr<'tcx>,
 853         segment: &hir::PathSegment<'_>,
 854         span: Span,
 855         args: &'tcx [hir::Expr<'tcx>],
 856         expected: Expectation<'tcx>,
 857         needs: Needs,
 858     ) -> Ty<'tcx> {
 859         let rcvr = &args[0];
 860         let rcvr_t = self.check_expr_with_needs(&rcvr, needs);
 861         // no need to check for bot/err -- callee does that
 862         let rcvr_t = self.structurally_resolved_type(args[0].span, rcvr_t);
 863
 864         let method = match self.lookup_method(rcvr_t, segment, span, expr, rcvr) {
 865             Ok(method) => {
 866                 // We could add a "consider `foo::<params>`" suggestion here, but I wasn't able to
 867                 // trigger this codepath causing `structuraly_resolved_type` to emit an error.
 868
 869                 self.write_method_call(expr.hir_id, method);
 870                 Ok(method)
 871             }
 872             Err(error) => {
 873                 if segment.ident.name != kw::Invalid {
 874                     self.report_extended_method_error(segment, span, args, rcvr_t, error);
 875                 }
 876                 Err(())
 877             }
 878         };
 879
 880         // Call the generic checker.
 881         self.check_method_argument_types(
 882             span,
 883             expr,
 884             method,
 885             &args[1..],
 886             DontTupleArguments,
 887             expected,
 888         )
 889     }
 890
 891     fn report_extended_method_error(
 892         &self,
 893         segment: &hir::PathSegment<'_>,
 894         span: Span,
 895         args: &'tcx [hir::Expr<'tcx>],
 896         rcvr_t: Ty<'tcx>,
 897         error: MethodError<'tcx>,
 898     ) {
 899         let rcvr = &args[0];
 900         let try_alt_rcvr = |err: &mut DiagnosticBuilder<'_>, rcvr_t, lang_item| {
 901             if let Some(new_rcvr_t) = self.tcx.mk_lang_item(rcvr_t, lang_item) {
 902                 if let Ok(pick) = self.lookup_probe(
 903                     span,
 904                     segment.ident,
 905                     new_rcvr_t,
 906                     rcvr,
 907                     probe::ProbeScope::AllTraits,
 908                 ) {
 909                     err.span_label(
 910                         pick.item.ident.span,
 911                         &format!("the method is available for `{}` here", new_rcvr_t),
 912                     );
 913                 }
 914             }
 915         };
 916
 917         if let Some(mut err) = self.report_method_error(
 918             span,
 919             rcvr_t,
 920             segment.ident,
 921             SelfSource::MethodCall(rcvr),
 922             error,
 923             Some(args),
 924         ) {
 925             if let ty::Adt(..) = rcvr_t.kind {
 926                 // Try alternative arbitrary self types that could fulfill this call.
 927                 // FIXME: probe for all types that *could* be arbitrary self-types, not
 928                 // just this whitelist.
 929                 try_alt_rcvr(&mut err, rcvr_t, lang_items::OwnedBoxLangItem);
 930                 try_alt_rcvr(&mut err, rcvr_t, lang_items::PinTypeLangItem);
 931                 try_alt_rcvr(&mut err, rcvr_t, lang_items::Arc);
 932                 try_alt_rcvr(&mut err, rcvr_t, lang_items::Rc);
 933             }
 934             err.emit();
 935         }
 936     }
 937
 938     fn check_expr_cast(
 939         &self,
 940         e: &'tcx hir::Expr<'tcx>,
 941         t: &'tcx hir::Ty<'tcx>,
 942         expr: &'tcx hir::Expr<'tcx>,
 943     ) -> Ty<'tcx> {
 944         // Find the type of `e`. Supply hints based on the type we are casting to,
 945         // if appropriate.
 946         let t_cast = self.to_ty_saving_user_provided_ty(t);
 947         let t_cast = self.resolve_vars_if_possible(&t_cast);
 948         let t_expr = self.check_expr_with_expectation(e, ExpectCastableToType(t_cast));
 949         let t_cast = self.resolve_vars_if_possible(&t_cast);
 950
 951         // Eagerly check for some obvious errors.
 952         if t_expr.references_error() || t_cast.references_error() {
 953             self.tcx.types.err
 954         } else {
 955             // Defer other checks until we're done type checking.
 956             let mut deferred_cast_checks = self.deferred_cast_checks.borrow_mut();
 957             match cast::CastCheck::new(self, e, t_expr, t_cast, t.span, expr.span) {
 958                 Ok(cast_check) => {
 959                     deferred_cast_checks.push(cast_check);
 960                     t_cast
 961                 }
 962                 Err(ErrorReported) => self.tcx.types.err,
 963             }
 964         }
 965     }
 966
 967     fn check_expr_array(
 968         &self,
 969         args: &'tcx [hir::Expr<'tcx>],
 970         expected: Expectation<'tcx>,
 971         expr: &'tcx hir::Expr<'tcx>,
 972     ) -> Ty<'tcx> {
 973         let uty = expected.to_option(self).and_then(|uty| match uty.kind {
 974             ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
 975             _ => None,
 976         });
 977
 978         let element_ty = if !args.is_empty() {
 979             let coerce_to = uty.unwrap_or_else(|| {
 980                 self.next_ty_var(TypeVariableOrigin {
 981                     kind: TypeVariableOriginKind::TypeInference,
 982                     span: expr.span,
 983                 })
 984             });
 985             let mut coerce = CoerceMany::with_coercion_sites(coerce_to, args);
 986             assert_eq!(self.diverges.get(), Diverges::Maybe);
 987             for e in args {
 988                 let e_ty = self.check_expr_with_hint(e, coerce_to);
 989                 let cause = self.misc(e.span);
 990                 coerce.coerce(self, &cause, e, e_ty);
 991             }
 992             coerce.complete(self)
 993         } else {
 994             self.next_ty_var(TypeVariableOrigin {
 995                 kind: TypeVariableOriginKind::TypeInference,
 996                 span: expr.span,
 997             })
 998         };
 999         self.tcx.mk_array(element_ty, args.len() as u64)
1000     }
1001
1002     fn check_expr_repeat(
1003         &self,
1004         element: &'tcx hir::Expr<'tcx>,
1005         count: &'tcx hir::AnonConst,
1006         expected: Expectation<'tcx>,
1007         _expr: &'tcx hir::Expr<'tcx>,
1008     ) -> Ty<'tcx> {
1009         let tcx = self.tcx;
1010         let count_def_id = tcx.hir().local_def_id(count.hir_id);
1011         let count = if self.const_param_def_id(count).is_some() {
1012             Ok(self.to_const(count, tcx.type_of(count_def_id)))
1013         } else {
1014             tcx.const_eval_poly(count_def_id)
1015                 .map(|val| ty::Const::from_value(tcx, val, tcx.type_of(count_def_id)))
1016         };
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             tcx.types.err
1043         } else if let Ok(count) = count {
1044             tcx.mk_ty(ty::Array(t, count))
1045         } else {
1046             tcx.types.err
1047         }
1048     }
1049
1050     fn check_expr_tuple(
1051         &self,
1052         elts: &'tcx [hir::Expr<'tcx>],
1053         expected: Expectation<'tcx>,
1054         expr: &'tcx hir::Expr<'tcx>,
1055     ) -> Ty<'tcx> {
1056         let flds = expected.only_has_type(self).and_then(|ty| {
1057             let ty = self.resolve_vars_with_obligations(ty);
1058             match ty.kind {
1059                 ty::Tuple(ref flds) => Some(&flds[..]),
1060                 _ => None,
1061             }
1062         });
1063
1064         let elt_ts_iter = elts.iter().enumerate().map(|(i, e)| {
1065             let t = match flds {
1066                 Some(ref fs) if i < fs.len() => {
1067                     let ety = fs[i].expect_ty();
1068                     self.check_expr_coercable_to_type(&e, ety);
1069                     ety
1070                 }
1071                 _ => self.check_expr_with_expectation(&e, NoExpectation),
1072             };
1073             t
1074         });
1075         let tuple = self.tcx.mk_tup(elt_ts_iter);
1076         if tuple.references_error() {
1077             self.tcx.types.err
1078         } else {
1079             self.require_type_is_sized(tuple, expr.span, traits::TupleInitializerSized);
1080             tuple
1081         }
1082     }
1083
1084     fn check_expr_struct(
1085         &self,
1086         expr: &hir::Expr<'_>,
1087         expected: Expectation<'tcx>,
1088         qpath: &QPath<'_>,
1089         fields: &'tcx [hir::Field<'tcx>],
1090         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1091     ) -> Ty<'tcx> {
1092         // Find the relevant variant
1093         let (variant, adt_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, expr.hir_id)
1094         {
1095             variant_ty
1096         } else {
1097             self.check_struct_fields_on_error(fields, base_expr);
1098             return self.tcx.types.err;
1099         };
1100
1101         let path_span = match *qpath {
1102             QPath::Resolved(_, ref path) => path.span,
1103             QPath::TypeRelative(ref qself, _) => qself.span,
1104         };
1105
1106         // Prohibit struct expressions when non-exhaustive flag is set.
1107         let adt = adt_ty.ty_adt_def().expect("`check_struct_path` returned non-ADT type");
1108         if !adt.did.is_local() && variant.is_field_list_non_exhaustive() {
1109             struct_span_err!(
1110                 self.tcx.sess,
1111                 expr.span,
1112                 E0639,
1113                 "cannot create non-exhaustive {} using struct expression",
1114                 adt.variant_descr()
1115             )
1116             .emit();
1117         }
1118
1119         let error_happened = self.check_expr_struct_fields(
1120             adt_ty,
1121             expected,
1122             expr.hir_id,
1123             path_span,
1124             variant,
1125             fields,
1126             base_expr.is_none(),
1127         );
1128         if let &Some(ref base_expr) = base_expr {
1129             // If check_expr_struct_fields hit an error, do not attempt to populate
1130             // the fields with the base_expr. This could cause us to hit errors later
1131             // when certain fields are assumed to exist that in fact do not.
1132             if !error_happened {
1133                 self.check_expr_has_type_or_error(base_expr, adt_ty, |_| {});
1134                 match adt_ty.kind {
1135                     ty::Adt(adt, substs) if adt.is_struct() => {
1136                         let fru_field_types = adt
1137                             .non_enum_variant()
1138                             .fields
1139                             .iter()
1140                             .map(|f| {
1141                                 self.normalize_associated_types_in(
1142                                     expr.span,
1143                                     &f.ty(self.tcx, substs),
1144                                 )
1145                             })
1146                             .collect();
1147
1148                         self.tables
1149                             .borrow_mut()
1150                             .fru_field_types_mut()
1151                             .insert(expr.hir_id, fru_field_types);
1152                     }
1153                     _ => {
1154                         struct_span_err!(
1155                             self.tcx.sess,
1156                             base_expr.span,
1157                             E0436,
1158                             "functional record update syntax requires a struct"
1159                         )
1160                         .emit();
1161                     }
1162                 }
1163             }
1164         }
1165         self.require_type_is_sized(adt_ty, expr.span, traits::StructInitializerSized);
1166         adt_ty
1167     }
1168
1169     fn check_expr_struct_fields(
1170         &self,
1171         adt_ty: Ty<'tcx>,
1172         expected: Expectation<'tcx>,
1173         expr_id: hir::HirId,
1174         span: Span,
1175         variant: &'tcx ty::VariantDef,
1176         ast_fields: &'tcx [hir::Field<'tcx>],
1177         check_completeness: bool,
1178     ) -> bool {
1179         let tcx = self.tcx;
1180
1181         let adt_ty_hint = self
1182             .expected_inputs_for_expected_output(span, expected, adt_ty, &[adt_ty])
1183             .get(0)
1184             .cloned()
1185             .unwrap_or(adt_ty);
1186         // re-link the regions that EIfEO can erase.
1187         self.demand_eqtype(span, adt_ty_hint, adt_ty);
1188
1189         let (substs, adt_kind, kind_name) = match &adt_ty.kind {
1190             &ty::Adt(adt, substs) => (substs, adt.adt_kind(), adt.variant_descr()),
1191             _ => span_bug!(span, "non-ADT passed to check_expr_struct_fields"),
1192         };
1193
1194         let mut remaining_fields = variant
1195             .fields
1196             .iter()
1197             .enumerate()
1198             .map(|(i, field)| (field.ident.modern(), (i, field)))
1199             .collect::<FxHashMap<_, _>>();
1200
1201         let mut seen_fields = FxHashMap::default();
1202
1203         let mut error_happened = false;
1204
1205         // Type-check each field.
1206         for field in ast_fields {
1207             let ident = tcx.adjust_ident(field.ident, variant.def_id);
1208             let field_type = if let Some((i, v_field)) = remaining_fields.remove(&ident) {
1209                 seen_fields.insert(ident, field.span);
1210                 self.write_field_index(field.hir_id, i);
1211
1212                 // We don't look at stability attributes on
1213                 // struct-like enums (yet...), but it's definitely not
1214                 // a bug to have constructed one.
1215                 if adt_kind != AdtKind::Enum {
1216                     tcx.check_stability(v_field.did, Some(expr_id), field.span);
1217                 }
1218
1219                 self.field_ty(field.span, v_field, substs)
1220             } else {
1221                 error_happened = true;
1222                 if let Some(prev_span) = seen_fields.get(&ident) {
1223                     let mut err = struct_span_err!(
1224                         self.tcx.sess,
1225                         field.ident.span,
1226                         E0062,
1227                         "field `{}` specified more than once",
1228                         ident
1229                     );
1230
1231                     err.span_label(field.ident.span, "used more than once");
1232                     err.span_label(*prev_span, format!("first use of `{}`", ident));
1233
1234                     err.emit();
1235                 } else {
1236                     self.report_unknown_field(adt_ty, variant, field, ast_fields, kind_name, span);
1237                 }
1238
1239                 tcx.types.err
1240             };
1241
1242             // Make sure to give a type to the field even if there's
1243             // an error, so we can continue type-checking.
1244             self.check_expr_coercable_to_type(&field.expr, field_type);
1245         }
1246
1247         // Make sure the programmer specified correct number of fields.
1248         if kind_name == "union" {
1249             if ast_fields.len() != 1 {
1250                 tcx.sess.span_err(span, "union expressions should have exactly one field");
1251             }
1252         } else if check_completeness && !error_happened && !remaining_fields.is_empty() {
1253             let len = remaining_fields.len();
1254
1255             let mut displayable_field_names =
1256                 remaining_fields.keys().map(|ident| ident.as_str()).collect::<Vec<_>>();
1257
1258             displayable_field_names.sort();
1259
1260             let truncated_fields_error = if len <= 3 {
1261                 String::new()
1262             } else {
1263                 format!(" and {} other field{}", (len - 3), if len - 3 == 1 { "" } else { "s" })
1264             };
1265
1266             let remaining_fields_names = displayable_field_names
1267                 .iter()
1268                 .take(3)
1269                 .map(|n| format!("`{}`", n))
1270                 .collect::<Vec<_>>()
1271                 .join(", ");
1272
1273             struct_span_err!(
1274                 tcx.sess,
1275                 span,
1276                 E0063,
1277                 "missing field{} {}{} in initializer of `{}`",
1278                 pluralize!(remaining_fields.len()),
1279                 remaining_fields_names,
1280                 truncated_fields_error,
1281                 adt_ty
1282             )
1283             .span_label(
1284                 span,
1285                 format!("missing {}{}", remaining_fields_names, truncated_fields_error),
1286             )
1287             .emit();
1288         }
1289         error_happened
1290     }
1291
1292     fn check_struct_fields_on_error(
1293         &self,
1294         fields: &'tcx [hir::Field<'tcx>],
1295         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1296     ) {
1297         for field in fields {
1298             self.check_expr(&field.expr);
1299         }
1300         if let Some(ref base) = *base_expr {
1301             self.check_expr(&base);
1302         }
1303     }
1304
1305     fn report_unknown_field(
1306         &self,
1307         ty: Ty<'tcx>,
1308         variant: &'tcx ty::VariantDef,
1309         field: &hir::Field<'_>,
1310         skip_fields: &[hir::Field<'_>],
1311         kind_name: &str,
1312         ty_span: Span,
1313     ) {
1314         if variant.recovered {
1315             self.set_tainted_by_errors();
1316             return;
1317         }
1318         let mut err = self.type_error_struct_with_diag(
1319             field.ident.span,
1320             |actual| match ty.kind {
1321                 ty::Adt(adt, ..) if adt.is_enum() => struct_span_err!(
1322                     self.tcx.sess,
1323                     field.ident.span,
1324                     E0559,
1325                     "{} `{}::{}` has no field named `{}`",
1326                     kind_name,
1327                     actual,
1328                     variant.ident,
1329                     field.ident
1330                 ),
1331                 _ => struct_span_err!(
1332                     self.tcx.sess,
1333                     field.ident.span,
1334                     E0560,
1335                     "{} `{}` has no field named `{}`",
1336                     kind_name,
1337                     actual,
1338                     field.ident
1339                 ),
1340             },
1341             ty,
1342         );
1343         match variant.ctor_kind {
1344             CtorKind::Fn => {
1345                 err.span_label(variant.ident.span, format!("`{adt}` defined here", adt = ty));
1346                 err.span_label(field.ident.span, "field does not exist");
1347                 err.span_label(
1348                     ty_span,
1349                     format!(
1350                         "`{adt}` is a tuple {kind_name}, \
1351                          use the appropriate syntax: `{adt}(/* fields */)`",
1352                         adt = ty,
1353                         kind_name = kind_name
1354                     ),
1355                 );
1356             }
1357             _ => {
1358                 // prevent all specified fields from being suggested
1359                 let skip_fields = skip_fields.iter().map(|ref x| x.ident.name);
1360                 if let Some(field_name) =
1361                     Self::suggest_field_name(variant, &field.ident.as_str(), skip_fields.collect())
1362                 {
1363                     err.span_suggestion(
1364                         field.ident.span,
1365                         "a field with a similar name exists",
1366                         field_name.to_string(),
1367                         Applicability::MaybeIncorrect,
1368                     );
1369                 } else {
1370                     match ty.kind {
1371                         ty::Adt(adt, ..) => {
1372                             if adt.is_enum() {
1373                                 err.span_label(
1374                                     field.ident.span,
1375                                     format!("`{}::{}` does not have this field", ty, variant.ident),
1376                                 );
1377                             } else {
1378                                 err.span_label(
1379                                     field.ident.span,
1380                                     format!("`{}` does not have this field", ty),
1381                                 );
1382                             }
1383                             let available_field_names = self.available_field_names(variant);
1384                             if !available_field_names.is_empty() {
1385                                 err.note(&format!(
1386                                     "available fields are: {}",
1387                                     self.name_series_display(available_field_names)
1388                                 ));
1389                             }
1390                         }
1391                         _ => bug!("non-ADT passed to report_unknown_field"),
1392                     }
1393                 };
1394             }
1395         }
1396         err.emit();
1397     }
1398
1399     // Return an hint about the closest match in field names
1400     fn suggest_field_name(
1401         variant: &'tcx ty::VariantDef,
1402         field: &str,
1403         skip: Vec<Symbol>,
1404     ) -> Option<Symbol> {
1405         let names = variant.fields.iter().filter_map(|field| {
1406             // ignore already set fields and private fields from non-local crates
1407             if skip.iter().any(|&x| x == field.ident.name)
1408                 || (!variant.def_id.is_local() && field.vis != Visibility::Public)
1409             {
1410                 None
1411             } else {
1412                 Some(&field.ident.name)
1413             }
1414         });
1415
1416         find_best_match_for_name(names, field, None)
1417     }
1418
1419     fn available_field_names(&self, variant: &'tcx ty::VariantDef) -> Vec<ast::Name> {
1420         variant
1421             .fields
1422             .iter()
1423             .filter(|field| {
1424                 let def_scope = self
1425                     .tcx
1426                     .adjust_ident_and_get_scope(field.ident, variant.def_id, self.body_id)
1427                     .1;
1428                 field.vis.is_accessible_from(def_scope, self.tcx)
1429             })
1430             .map(|field| field.ident.name)
1431             .collect()
1432     }
1433
1434     fn name_series_display(&self, names: Vec<ast::Name>) -> String {
1435         // dynamic limit, to never omit just one field
1436         let limit = if names.len() == 6 { 6 } else { 5 };
1437         let mut display =
1438             names.iter().take(limit).map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
1439         if names.len() > limit {
1440             display = format!("{} ... and {} others", display, names.len() - limit);
1441         }
1442         display
1443     }
1444
1445     // Check field access expressions
1446     fn check_field(
1447         &self,
1448         expr: &'tcx hir::Expr<'tcx>,
1449         needs: Needs,
1450         base: &'tcx hir::Expr<'tcx>,
1451         field: ast::Ident,
1452     ) -> Ty<'tcx> {
1453         let expr_t = self.check_expr_with_needs(base, needs);
1454         let expr_t = self.structurally_resolved_type(base.span, expr_t);
1455         let mut private_candidate = None;
1456         let mut autoderef = self.autoderef(expr.span, expr_t);
1457         while let Some((base_t, _)) = autoderef.next() {
1458             match base_t.kind {
1459                 ty::Adt(base_def, substs) if !base_def.is_enum() => {
1460                     debug!("struct named {:?}", base_t);
1461                     let (ident, def_scope) =
1462                         self.tcx.adjust_ident_and_get_scope(field, base_def.did, self.body_id);
1463                     let fields = &base_def.non_enum_variant().fields;
1464                     if let Some(index) = fields.iter().position(|f| f.ident.modern() == ident) {
1465                         let field = &fields[index];
1466                         let field_ty = self.field_ty(expr.span, field, substs);
1467                         // Save the index of all fields regardless of their visibility in case
1468                         // of error recovery.
1469                         self.write_field_index(expr.hir_id, index);
1470                         if field.vis.is_accessible_from(def_scope, self.tcx) {
1471                             let adjustments = autoderef.adjust_steps(self, needs);
1472                             self.apply_adjustments(base, adjustments);
1473                             autoderef.finalize(self);
1474
1475                             self.tcx.check_stability(field.did, Some(expr.hir_id), expr.span);
1476                             return field_ty;
1477                         }
1478                         private_candidate = Some((base_def.did, field_ty));
1479                     }
1480                 }
1481                 ty::Tuple(ref tys) => {
1482                     let fstr = field.as_str();
1483                     if let Ok(index) = fstr.parse::<usize>() {
1484                         if fstr == index.to_string() {
1485                             if let Some(field_ty) = tys.get(index) {
1486                                 let adjustments = autoderef.adjust_steps(self, needs);
1487                                 self.apply_adjustments(base, adjustments);
1488                                 autoderef.finalize(self);
1489
1490                                 self.write_field_index(expr.hir_id, index);
1491                                 return field_ty.expect_ty();
1492                             }
1493                         }
1494                     }
1495                 }
1496                 _ => {}
1497             }
1498         }
1499         autoderef.unambiguous_final_ty(self);
1500
1501         if let Some((did, field_ty)) = private_candidate {
1502             self.ban_private_field_access(expr, expr_t, field, did);
1503             return field_ty;
1504         }
1505
1506         if field.name == kw::Invalid {
1507         } else if self.method_exists(field, expr_t, expr.hir_id, true) {
1508             self.ban_take_value_of_method(expr, expr_t, field);
1509         } else if !expr_t.is_primitive_ty() {
1510             self.ban_nonexisting_field(field, base, expr, expr_t);
1511         } else {
1512             type_error_struct!(
1513                 self.tcx().sess,
1514                 field.span,
1515                 expr_t,
1516                 E0610,
1517                 "`{}` is a primitive type and therefore doesn't have fields",
1518                 expr_t
1519             )
1520             .emit();
1521         }
1522
1523         self.tcx().types.err
1524     }
1525
1526     fn ban_nonexisting_field(
1527         &self,
1528         field: ast::Ident,
1529         base: &'tcx hir::Expr<'tcx>,
1530         expr: &'tcx hir::Expr<'tcx>,
1531         expr_t: Ty<'tcx>,
1532     ) {
1533         let mut err = self.no_such_field_err(field.span, field, expr_t);
1534
1535         match expr_t.peel_refs().kind {
1536             ty::Array(_, len) => {
1537                 self.maybe_suggest_array_indexing(&mut err, expr, base, field, len);
1538             }
1539             ty::RawPtr(..) => {
1540                 self.suggest_first_deref_field(&mut err, expr, base, field);
1541             }
1542             ty::Adt(def, _) if !def.is_enum() => {
1543                 self.suggest_fields_on_recordish(&mut err, def, field);
1544             }
1545             ty::Param(param_ty) => {
1546                 self.point_at_param_definition(&mut err, param_ty);
1547             }
1548             _ => {}
1549         }
1550
1551         if field.name == kw::Await {
1552             // We know by construction that `<expr>.await` is either on Rust 2015
1553             // or results in `ExprKind::Await`. Suggest switching the edition to 2018.
1554             err.note("to `.await` a `Future`, switch to Rust 2018");
1555             err.help("set `edition = \"2018\"` in `Cargo.toml`");
1556             err.note("for more on editions, read https://doc.rust-lang.org/edition-guide");
1557         }
1558
1559         err.emit();
1560     }
1561
1562     fn ban_private_field_access(
1563         &self,
1564         expr: &hir::Expr<'_>,
1565         expr_t: Ty<'tcx>,
1566         field: ast::Ident,
1567         base_did: DefId,
1568     ) {
1569         let struct_path = self.tcx().def_path_str(base_did);
1570         let kind_name = match self.tcx().def_kind(base_did) {
1571             Some(def_kind) => def_kind.descr(base_did),
1572             _ => " ",
1573         };
1574         let mut err = struct_span_err!(
1575             self.tcx().sess,
1576             expr.span,
1577             E0616,
1578             "field `{}` of {} `{}` is private",
1579             field,
1580             kind_name,
1581             struct_path
1582         );
1583         // Also check if an accessible method exists, which is often what is meant.
1584         if self.method_exists(field, expr_t, expr.hir_id, false) && !self.expr_in_place(expr.hir_id)
1585         {
1586             self.suggest_method_call(
1587                 &mut err,
1588                 &format!("a method `{}` also exists, call it with parentheses", field),
1589                 field,
1590                 expr_t,
1591                 expr,
1592             );
1593         }
1594         err.emit();
1595     }
1596
1597     fn ban_take_value_of_method(&self, expr: &hir::Expr<'_>, expr_t: Ty<'tcx>, field: ast::Ident) {
1598         let mut err = type_error_struct!(
1599             self.tcx().sess,
1600             field.span,
1601             expr_t,
1602             E0615,
1603             "attempted to take value of method `{}` on type `{}`",
1604             field,
1605             expr_t
1606         );
1607
1608         if !self.expr_in_place(expr.hir_id) {
1609             self.suggest_method_call(
1610                 &mut err,
1611                 "use parentheses to call the method",
1612                 field,
1613                 expr_t,
1614                 expr,
1615             );
1616         } else {
1617             err.help("methods are immutable and cannot be assigned to");
1618         }
1619
1620         err.emit();
1621     }
1622
1623     fn point_at_param_definition(&self, err: &mut DiagnosticBuilder<'_>, param: ty::ParamTy) {
1624         let generics = self.tcx.generics_of(self.body_id.owner_def_id());
1625         let generic_param = generics.type_param(&param, self.tcx);
1626         if let ty::GenericParamDefKind::Type { synthetic: Some(..), .. } = generic_param.kind {
1627             return;
1628         }
1629         let param_def_id = generic_param.def_id;
1630         let param_hir_id = match self.tcx.hir().as_local_hir_id(param_def_id) {
1631             Some(x) => x,
1632             None => return,
1633         };
1634         let param_span = self.tcx.hir().span(param_hir_id);
1635         let param_name = self.tcx.hir().ty_param_name(param_hir_id);
1636
1637         err.span_label(param_span, &format!("type parameter '{}' declared here", param_name));
1638     }
1639
1640     fn suggest_fields_on_recordish(
1641         &self,
1642         err: &mut DiagnosticBuilder<'_>,
1643         def: &'tcx ty::AdtDef,
1644         field: ast::Ident,
1645     ) {
1646         if let Some(suggested_field_name) =
1647             Self::suggest_field_name(def.non_enum_variant(), &field.as_str(), vec![])
1648         {
1649             err.span_suggestion(
1650                 field.span,
1651                 "a field with a similar name exists",
1652                 suggested_field_name.to_string(),
1653                 Applicability::MaybeIncorrect,
1654             );
1655         } else {
1656             err.span_label(field.span, "unknown field");
1657             let struct_variant_def = def.non_enum_variant();
1658             let field_names = self.available_field_names(struct_variant_def);
1659             if !field_names.is_empty() {
1660                 err.note(&format!(
1661                     "available fields are: {}",
1662                     self.name_series_display(field_names),
1663                 ));
1664             }
1665         }
1666     }
1667
1668     fn maybe_suggest_array_indexing(
1669         &self,
1670         err: &mut DiagnosticBuilder<'_>,
1671         expr: &hir::Expr<'_>,
1672         base: &hir::Expr<'_>,
1673         field: ast::Ident,
1674         len: &ty::Const<'tcx>,
1675     ) {
1676         if let (Some(len), Ok(user_index)) =
1677             (len.try_eval_usize(self.tcx, self.param_env), field.as_str().parse::<u64>())
1678         {
1679             let base = self
1680                 .tcx
1681                 .sess
1682                 .source_map()
1683                 .span_to_snippet(base.span)
1684                 .unwrap_or_else(|_| self.tcx.hir().hir_to_pretty_string(base.hir_id));
1685             let help = "instead of using tuple indexing, use array indexing";
1686             let suggestion = format!("{}[{}]", base, field);
1687             let applicability = if len < user_index {
1688                 Applicability::MachineApplicable
1689             } else {
1690                 Applicability::MaybeIncorrect
1691             };
1692             err.span_suggestion(expr.span, help, suggestion, applicability);
1693         }
1694     }
1695
1696     fn suggest_first_deref_field(
1697         &self,
1698         err: &mut DiagnosticBuilder<'_>,
1699         expr: &hir::Expr<'_>,
1700         base: &hir::Expr<'_>,
1701         field: ast::Ident,
1702     ) {
1703         let base = self
1704             .tcx
1705             .sess
1706             .source_map()
1707             .span_to_snippet(base.span)
1708             .unwrap_or_else(|_| self.tcx.hir().hir_to_pretty_string(base.hir_id));
1709         let msg = format!("`{}` is a raw pointer; try dereferencing it", base);
1710         let suggestion = format!("(*{}).{}", base, field);
1711         err.span_suggestion(expr.span, &msg, suggestion, Applicability::MaybeIncorrect);
1712     }
1713
1714     fn no_such_field_err<T: Display>(
1715         &self,
1716         span: Span,
1717         field: T,
1718         expr_t: &ty::TyS<'_>,
1719     ) -> DiagnosticBuilder<'_> {
1720         type_error_struct!(
1721             self.tcx().sess,
1722             span,
1723             expr_t,
1724             E0609,
1725             "no field `{}` on type `{}`",
1726             field,
1727             expr_t
1728         )
1729     }
1730
1731     fn check_expr_index(
1732         &self,
1733         base: &'tcx hir::Expr<'tcx>,
1734         idx: &'tcx hir::Expr<'tcx>,
1735         needs: Needs,
1736         expr: &'tcx hir::Expr<'tcx>,
1737     ) -> Ty<'tcx> {
1738         let base_t = self.check_expr_with_needs(&base, needs);
1739         let idx_t = self.check_expr(&idx);
1740
1741         if base_t.references_error() {
1742             base_t
1743         } else if idx_t.references_error() {
1744             idx_t
1745         } else {
1746             let base_t = self.structurally_resolved_type(base.span, base_t);
1747             match self.lookup_indexing(expr, base, base_t, idx_t, needs) {
1748                 Some((index_ty, element_ty)) => {
1749                     // two-phase not needed because index_ty is never mutable
1750                     self.demand_coerce(idx, idx_t, index_ty, AllowTwoPhase::No);
1751                     element_ty
1752                 }
1753                 None => {
1754                     let mut err = type_error_struct!(
1755                         self.tcx.sess,
1756                         expr.span,
1757                         base_t,
1758                         E0608,
1759                         "cannot index into a value of type `{}`",
1760                         base_t
1761                     );
1762                     // Try to give some advice about indexing tuples.
1763                     if let ty::Tuple(..) = base_t.kind {
1764                         let mut needs_note = true;
1765                         // If the index is an integer, we can show the actual
1766                         // fixed expression:
1767                         if let ExprKind::Lit(ref lit) = idx.kind {
1768                             if let ast::LitKind::Int(i, ast::LitIntType::Unsuffixed) = lit.node {
1769                                 let snip = self.tcx.sess.source_map().span_to_snippet(base.span);
1770                                 if let Ok(snip) = snip {
1771                                     err.span_suggestion(
1772                                         expr.span,
1773                                         "to access tuple elements, use",
1774                                         format!("{}.{}", snip, i),
1775                                         Applicability::MachineApplicable,
1776                                     );
1777                                     needs_note = false;
1778                                 }
1779                             }
1780                         }
1781                         if needs_note {
1782                             err.help(
1783                                 "to access tuple elements, use tuple indexing \
1784                                         syntax (e.g., `tuple.0`)",
1785                             );
1786                         }
1787                     }
1788                     err.emit();
1789                     self.tcx.types.err
1790                 }
1791             }
1792         }
1793     }
1794
1795     fn check_expr_yield(
1796         &self,
1797         value: &'tcx hir::Expr<'tcx>,
1798         expr: &'tcx hir::Expr<'tcx>,
1799         src: &'tcx hir::YieldSource,
1800     ) -> Ty<'tcx> {
1801         match self.resume_yield_tys {
1802             Some((resume_ty, yield_ty)) => {
1803                 self.check_expr_coercable_to_type(&value, yield_ty);
1804
1805                 resume_ty
1806             }
1807             // Given that this `yield` expression was generated as a result of lowering a `.await`,
1808             // we know that the yield type must be `()`; however, the context won't contain this
1809             // information. Hence, we check the source of the yield expression here and check its
1810             // value's type against `()` (this check should always hold).
1811             None if src == &hir::YieldSource::Await => {
1812                 self.check_expr_coercable_to_type(&value, self.tcx.mk_unit());
1813                 self.tcx.mk_unit()
1814             }
1815             _ => {
1816                 struct_span_err!(
1817                     self.tcx.sess,
1818                     expr.span,
1819                     E0627,
1820                     "yield expression outside of generator literal"
1821                 )
1822                 .emit();
1823                 self.tcx.mk_unit()
1824             }
1825         }
1826     }
1827 }
1828
1829 pub(super) fn ty_kind_suggestion(ty: Ty<'_>) -> Option<&'static str> {
1830     Some(match ty.kind {
1831         ty::Bool => "true",
1832         ty::Char => "'a'",
1833         ty::Int(_) | ty::Uint(_) => "42",
1834         ty::Float(_) => "3.14159",
1835         ty::Error | ty::Never => return None,
1836         _ => "value",
1837     })
1838 }