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::infer;
  21 use rustc::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  22 use rustc::middle::lang_items;
  23 use rustc::traits::{self, ObligationCauseCode};
  24 use rustc::ty;
  25 use rustc::ty::adjustment::{Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
  26 use rustc::ty::Ty;
  27 use rustc::ty::TypeFoldable;
  28 use rustc::ty::{AdtKind, Visibility};
  29 use rustc_data_structures::fx::FxHashMap;
  30 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, DiagnosticId};
  31 use rustc_hir as hir;
  32 use rustc_hir::def::{CtorKind, DefKind, Res};
  33 use rustc_hir::def_id::DefId;
  34 use rustc_hir::{ExprKind, QPath};
  35 use rustc_span::hygiene::DesugaringKind;
  36 use rustc_span::source_map::Span;
  37 use rustc_span::symbol::{kw, sym, Symbol};
  38 use syntax::ast;
  39 use syntax::util::lev_distance::find_best_match_for_name;
  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         };
1016
1017         let uty = match expected {
1018             ExpectHasType(uty) => match uty.kind {
1019                 ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
1020                 _ => None,
1021             },
1022             _ => None,
1023         };
1024
1025         let (element_ty, t) = match uty {
1026             Some(uty) => {
1027                 self.check_expr_coercable_to_type(&element, uty);
1028                 (uty, uty)
1029             }
1030             None => {
1031                 let ty = self.next_ty_var(TypeVariableOrigin {
1032                     kind: TypeVariableOriginKind::MiscVariable,
1033                     span: element.span,
1034                 });
1035                 let element_ty = self.check_expr_has_type_or_error(&element, ty, |_| {});
1036                 (element_ty, ty)
1037             }
1038         };
1039
1040         if element_ty.references_error() {
1041             tcx.types.err
1042         } else if let Ok(count) = count {
1043             tcx.mk_ty(ty::Array(t, count))
1044         } else {
1045             tcx.types.err
1046         }
1047     }
1048
1049     fn check_expr_tuple(
1050         &self,
1051         elts: &'tcx [hir::Expr<'tcx>],
1052         expected: Expectation<'tcx>,
1053         expr: &'tcx hir::Expr<'tcx>,
1054     ) -> Ty<'tcx> {
1055         let flds = expected.only_has_type(self).and_then(|ty| {
1056             let ty = self.resolve_vars_with_obligations(ty);
1057             match ty.kind {
1058                 ty::Tuple(ref flds) => Some(&flds[..]),
1059                 _ => None,
1060             }
1061         });
1062
1063         let elt_ts_iter = elts.iter().enumerate().map(|(i, e)| {
1064             let t = match flds {
1065                 Some(ref fs) if i < fs.len() => {
1066                     let ety = fs[i].expect_ty();
1067                     self.check_expr_coercable_to_type(&e, ety);
1068                     ety
1069                 }
1070                 _ => self.check_expr_with_expectation(&e, NoExpectation),
1071             };
1072             t
1073         });
1074         let tuple = self.tcx.mk_tup(elt_ts_iter);
1075         if tuple.references_error() {
1076             self.tcx.types.err
1077         } else {
1078             self.require_type_is_sized(tuple, expr.span, traits::TupleInitializerSized);
1079             tuple
1080         }
1081     }
1082
1083     fn check_expr_struct(
1084         &self,
1085         expr: &hir::Expr<'_>,
1086         expected: Expectation<'tcx>,
1087         qpath: &QPath<'_>,
1088         fields: &'tcx [hir::Field<'tcx>],
1089         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1090     ) -> Ty<'tcx> {
1091         // Find the relevant variant
1092         let (variant, adt_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, expr.hir_id)
1093         {
1094             variant_ty
1095         } else {
1096             self.check_struct_fields_on_error(fields, base_expr);
1097             return self.tcx.types.err;
1098         };
1099
1100         let path_span = match *qpath {
1101             QPath::Resolved(_, ref path) => path.span,
1102             QPath::TypeRelative(ref qself, _) => qself.span,
1103         };
1104
1105         // Prohibit struct expressions when non-exhaustive flag is set.
1106         let adt = adt_ty.ty_adt_def().expect("`check_struct_path` returned non-ADT type");
1107         if !adt.did.is_local() && variant.is_field_list_non_exhaustive() {
1108             struct_span_err!(
1109                 self.tcx.sess,
1110                 expr.span,
1111                 E0639,
1112                 "cannot create non-exhaustive {} using struct expression",
1113                 adt.variant_descr()
1114             )
1115             .emit();
1116         }
1117
1118         let error_happened = self.check_expr_struct_fields(
1119             adt_ty,
1120             expected,
1121             expr.hir_id,
1122             path_span,
1123             variant,
1124             fields,
1125             base_expr.is_none(),
1126         );
1127         if let &Some(ref base_expr) = base_expr {
1128             // If check_expr_struct_fields hit an error, do not attempt to populate
1129             // the fields with the base_expr. This could cause us to hit errors later
1130             // when certain fields are assumed to exist that in fact do not.
1131             if !error_happened {
1132                 self.check_expr_has_type_or_error(base_expr, adt_ty, |_| {});
1133                 match adt_ty.kind {
1134                     ty::Adt(adt, substs) if adt.is_struct() => {
1135                         let fru_field_types = adt
1136                             .non_enum_variant()
1137                             .fields
1138                             .iter()
1139                             .map(|f| {
1140                                 self.normalize_associated_types_in(
1141                                     expr.span,
1142                                     &f.ty(self.tcx, substs),
1143                                 )
1144                             })
1145                             .collect();
1146
1147                         self.tables
1148                             .borrow_mut()
1149                             .fru_field_types_mut()
1150                             .insert(expr.hir_id, fru_field_types);
1151                     }
1152                     _ => {
1153                         struct_span_err!(
1154                             self.tcx.sess,
1155                             base_expr.span,
1156                             E0436,
1157                             "functional record update syntax requires a struct"
1158                         )
1159                         .emit();
1160                     }
1161                 }
1162             }
1163         }
1164         self.require_type_is_sized(adt_ty, expr.span, traits::StructInitializerSized);
1165         adt_ty
1166     }
1167
1168     fn check_expr_struct_fields(
1169         &self,
1170         adt_ty: Ty<'tcx>,
1171         expected: Expectation<'tcx>,
1172         expr_id: hir::HirId,
1173         span: Span,
1174         variant: &'tcx ty::VariantDef,
1175         ast_fields: &'tcx [hir::Field<'tcx>],
1176         check_completeness: bool,
1177     ) -> bool {
1178         let tcx = self.tcx;
1179
1180         let adt_ty_hint = self
1181             .expected_inputs_for_expected_output(span, expected, adt_ty, &[adt_ty])
1182             .get(0)
1183             .cloned()
1184             .unwrap_or(adt_ty);
1185         // re-link the regions that EIfEO can erase.
1186         self.demand_eqtype(span, adt_ty_hint, adt_ty);
1187
1188         let (substs, adt_kind, kind_name) = match &adt_ty.kind {
1189             &ty::Adt(adt, substs) => (substs, adt.adt_kind(), adt.variant_descr()),
1190             _ => span_bug!(span, "non-ADT passed to check_expr_struct_fields"),
1191         };
1192
1193         let mut remaining_fields = variant
1194             .fields
1195             .iter()
1196             .enumerate()
1197             .map(|(i, field)| (field.ident.modern(), (i, field)))
1198             .collect::<FxHashMap<_, _>>();
1199
1200         let mut seen_fields = FxHashMap::default();
1201
1202         let mut error_happened = false;
1203
1204         // Type-check each field.
1205         for field in ast_fields {
1206             let ident = tcx.adjust_ident(field.ident, variant.def_id);
1207             let field_type = if let Some((i, v_field)) = remaining_fields.remove(&ident) {
1208                 seen_fields.insert(ident, field.span);
1209                 self.write_field_index(field.hir_id, i);
1210
1211                 // We don't look at stability attributes on
1212                 // struct-like enums (yet...), but it's definitely not
1213                 // a bug to have constructed one.
1214                 if adt_kind != AdtKind::Enum {
1215                     tcx.check_stability(v_field.did, Some(expr_id), field.span);
1216                 }
1217
1218                 self.field_ty(field.span, v_field, substs)
1219             } else {
1220                 error_happened = true;
1221                 if let Some(prev_span) = seen_fields.get(&ident) {
1222                     let mut err = struct_span_err!(
1223                         self.tcx.sess,
1224                         field.ident.span,
1225                         E0062,
1226                         "field `{}` specified more than once",
1227                         ident
1228                     );
1229
1230                     err.span_label(field.ident.span, "used more than once");
1231                     err.span_label(*prev_span, format!("first use of `{}`", ident));
1232
1233                     err.emit();
1234                 } else {
1235                     self.report_unknown_field(adt_ty, variant, field, ast_fields, kind_name, span);
1236                 }
1237
1238                 tcx.types.err
1239             };
1240
1241             // Make sure to give a type to the field even if there's
1242             // an error, so we can continue type-checking.
1243             self.check_expr_coercable_to_type(&field.expr, field_type);
1244         }
1245
1246         // Make sure the programmer specified correct number of fields.
1247         if kind_name == "union" {
1248             if ast_fields.len() != 1 {
1249                 tcx.sess.span_err(span, "union expressions should have exactly one field");
1250             }
1251         } else if check_completeness && !error_happened && !remaining_fields.is_empty() {
1252             let len = remaining_fields.len();
1253
1254             let mut displayable_field_names =
1255                 remaining_fields.keys().map(|ident| ident.as_str()).collect::<Vec<_>>();
1256
1257             displayable_field_names.sort();
1258
1259             let truncated_fields_error = if len <= 3 {
1260                 String::new()
1261             } else {
1262                 format!(" and {} other field{}", (len - 3), if len - 3 == 1 { "" } else { "s" })
1263             };
1264
1265             let remaining_fields_names = displayable_field_names
1266                 .iter()
1267                 .take(3)
1268                 .map(|n| format!("`{}`", n))
1269                 .collect::<Vec<_>>()
1270                 .join(", ");
1271
1272             struct_span_err!(
1273                 tcx.sess,
1274                 span,
1275                 E0063,
1276                 "missing field{} {}{} in initializer of `{}`",
1277                 pluralize!(remaining_fields.len()),
1278                 remaining_fields_names,
1279                 truncated_fields_error,
1280                 adt_ty
1281             )
1282             .span_label(
1283                 span,
1284                 format!("missing {}{}", remaining_fields_names, truncated_fields_error),
1285             )
1286             .emit();
1287         }
1288         error_happened
1289     }
1290
1291     fn check_struct_fields_on_error(
1292         &self,
1293         fields: &'tcx [hir::Field<'tcx>],
1294         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1295     ) {
1296         for field in fields {
1297             self.check_expr(&field.expr);
1298         }
1299         if let Some(ref base) = *base_expr {
1300             self.check_expr(&base);
1301         }
1302     }
1303
1304     fn report_unknown_field(
1305         &self,
1306         ty: Ty<'tcx>,
1307         variant: &'tcx ty::VariantDef,
1308         field: &hir::Field<'_>,
1309         skip_fields: &[hir::Field<'_>],
1310         kind_name: &str,
1311         ty_span: Span,
1312     ) {
1313         if variant.recovered {
1314             return;
1315         }
1316         let mut err = self.type_error_struct_with_diag(
1317             field.ident.span,
1318             |actual| match ty.kind {
1319                 ty::Adt(adt, ..) if adt.is_enum() => struct_span_err!(
1320                     self.tcx.sess,
1321                     field.ident.span,
1322                     E0559,
1323                     "{} `{}::{}` has no field named `{}`",
1324                     kind_name,
1325                     actual,
1326                     variant.ident,
1327                     field.ident
1328                 ),
1329                 _ => struct_span_err!(
1330                     self.tcx.sess,
1331                     field.ident.span,
1332                     E0560,
1333                     "{} `{}` has no field named `{}`",
1334                     kind_name,
1335                     actual,
1336                     field.ident
1337                 ),
1338             },
1339             ty,
1340         );
1341         match variant.ctor_kind {
1342             CtorKind::Fn => {
1343                 err.span_label(variant.ident.span, format!("`{adt}` defined here", adt = ty));
1344                 err.span_label(field.ident.span, "field does not exist");
1345                 err.span_label(
1346                     ty_span,
1347                     format!(
1348                         "`{adt}` is a tuple {kind_name}, \
1349                          use the appropriate syntax: `{adt}(/* fields */)`",
1350                         adt = ty,
1351                         kind_name = kind_name
1352                     ),
1353                 );
1354             }
1355             _ => {
1356                 // prevent all specified fields from being suggested
1357                 let skip_fields = skip_fields.iter().map(|ref x| x.ident.name);
1358                 if let Some(field_name) =
1359                     Self::suggest_field_name(variant, &field.ident.as_str(), skip_fields.collect())
1360                 {
1361                     err.span_suggestion(
1362                         field.ident.span,
1363                         "a field with a similar name exists",
1364                         field_name.to_string(),
1365                         Applicability::MaybeIncorrect,
1366                     );
1367                 } else {
1368                     match ty.kind {
1369                         ty::Adt(adt, ..) => {
1370                             if adt.is_enum() {
1371                                 err.span_label(
1372                                     field.ident.span,
1373                                     format!("`{}::{}` does not have this field", ty, variant.ident),
1374                                 );
1375                             } else {
1376                                 err.span_label(
1377                                     field.ident.span,
1378                                     format!("`{}` does not have this field", ty),
1379                                 );
1380                             }
1381                             let available_field_names = self.available_field_names(variant);
1382                             if !available_field_names.is_empty() {
1383                                 err.note(&format!(
1384                                     "available fields are: {}",
1385                                     self.name_series_display(available_field_names)
1386                                 ));
1387                             }
1388                         }
1389                         _ => bug!("non-ADT passed to report_unknown_field"),
1390                     }
1391                 };
1392             }
1393         }
1394         err.emit();
1395     }
1396
1397     // Return an hint about the closest match in field names
1398     fn suggest_field_name(
1399         variant: &'tcx ty::VariantDef,
1400         field: &str,
1401         skip: Vec<Symbol>,
1402     ) -> Option<Symbol> {
1403         let names = variant.fields.iter().filter_map(|field| {
1404             // ignore already set fields and private fields from non-local crates
1405             if skip.iter().any(|&x| x == field.ident.name)
1406                 || (!variant.def_id.is_local() && field.vis != Visibility::Public)
1407             {
1408                 None
1409             } else {
1410                 Some(&field.ident.name)
1411             }
1412         });
1413
1414         find_best_match_for_name(names, field, None)
1415     }
1416
1417     fn available_field_names(&self, variant: &'tcx ty::VariantDef) -> Vec<ast::Name> {
1418         variant
1419             .fields
1420             .iter()
1421             .filter(|field| {
1422                 let def_scope = self
1423                     .tcx
1424                     .adjust_ident_and_get_scope(field.ident, variant.def_id, self.body_id)
1425                     .1;
1426                 field.vis.is_accessible_from(def_scope, self.tcx)
1427             })
1428             .map(|field| field.ident.name)
1429             .collect()
1430     }
1431
1432     fn name_series_display(&self, names: Vec<ast::Name>) -> String {
1433         // dynamic limit, to never omit just one field
1434         let limit = if names.len() == 6 { 6 } else { 5 };
1435         let mut display =
1436             names.iter().take(limit).map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
1437         if names.len() > limit {
1438             display = format!("{} ... and {} others", display, names.len() - limit);
1439         }
1440         display
1441     }
1442
1443     // Check field access expressions
1444     fn check_field(
1445         &self,
1446         expr: &'tcx hir::Expr<'tcx>,
1447         needs: Needs,
1448         base: &'tcx hir::Expr<'tcx>,
1449         field: ast::Ident,
1450     ) -> Ty<'tcx> {
1451         let expr_t = self.check_expr_with_needs(base, needs);
1452         let expr_t = self.structurally_resolved_type(base.span, expr_t);
1453         let mut private_candidate = None;
1454         let mut autoderef = self.autoderef(expr.span, expr_t);
1455         while let Some((base_t, _)) = autoderef.next() {
1456             match base_t.kind {
1457                 ty::Adt(base_def, substs) if !base_def.is_enum() => {
1458                     debug!("struct named {:?}", base_t);
1459                     let (ident, def_scope) =
1460                         self.tcx.adjust_ident_and_get_scope(field, base_def.did, self.body_id);
1461                     let fields = &base_def.non_enum_variant().fields;
1462                     if let Some(index) = fields.iter().position(|f| f.ident.modern() == ident) {
1463                         let field = &fields[index];
1464                         let field_ty = self.field_ty(expr.span, field, substs);
1465                         // Save the index of all fields regardless of their visibility in case
1466                         // of error recovery.
1467                         self.write_field_index(expr.hir_id, index);
1468                         if field.vis.is_accessible_from(def_scope, self.tcx) {
1469                             let adjustments = autoderef.adjust_steps(self, needs);
1470                             self.apply_adjustments(base, adjustments);
1471                             autoderef.finalize(self);
1472
1473                             self.tcx.check_stability(field.did, Some(expr.hir_id), expr.span);
1474                             return field_ty;
1475                         }
1476                         private_candidate = Some((base_def.did, field_ty));
1477                     }
1478                 }
1479                 ty::Tuple(ref tys) => {
1480                     let fstr = field.as_str();
1481                     if let Ok(index) = fstr.parse::<usize>() {
1482                         if fstr == index.to_string() {
1483                             if let Some(field_ty) = tys.get(index) {
1484                                 let adjustments = autoderef.adjust_steps(self, needs);
1485                                 self.apply_adjustments(base, adjustments);
1486                                 autoderef.finalize(self);
1487
1488                                 self.write_field_index(expr.hir_id, index);
1489                                 return field_ty.expect_ty();
1490                             }
1491                         }
1492                     }
1493                 }
1494                 _ => {}
1495             }
1496         }
1497         autoderef.unambiguous_final_ty(self);
1498
1499         if let Some((did, field_ty)) = private_candidate {
1500             self.ban_private_field_access(expr, expr_t, field, did);
1501             return field_ty;
1502         }
1503
1504         if field.name == kw::Invalid {
1505         } else if self.method_exists(field, expr_t, expr.hir_id, true) {
1506             self.ban_take_value_of_method(expr, expr_t, field);
1507         } else if !expr_t.is_primitive_ty() {
1508             self.ban_nonexisting_field(field, base, expr, expr_t);
1509         } else {
1510             type_error_struct!(
1511                 self.tcx().sess,
1512                 field.span,
1513                 expr_t,
1514                 E0610,
1515                 "`{}` is a primitive type and therefore doesn't have fields",
1516                 expr_t
1517             )
1518             .emit();
1519         }
1520
1521         self.tcx().types.err
1522     }
1523
1524     fn ban_nonexisting_field(
1525         &self,
1526         field: ast::Ident,
1527         base: &'tcx hir::Expr<'tcx>,
1528         expr: &'tcx hir::Expr<'tcx>,
1529         expr_t: Ty<'tcx>,
1530     ) {
1531         let mut err = self.no_such_field_err(field.span, field, expr_t);
1532
1533         match expr_t.peel_refs().kind {
1534             ty::Array(_, len) => {
1535                 self.maybe_suggest_array_indexing(&mut err, expr, base, field, len);
1536             }
1537             ty::RawPtr(..) => {
1538                 self.suggest_first_deref_field(&mut err, expr, base, field);
1539             }
1540             ty::Adt(def, _) if !def.is_enum() => {
1541                 self.suggest_fields_on_recordish(&mut err, def, field);
1542             }
1543             ty::Param(param_ty) => {
1544                 self.point_at_param_definition(&mut err, param_ty);
1545             }
1546             _ => {}
1547         }
1548
1549         if field.name == kw::Await {
1550             // We know by construction that `<expr>.await` is either on Rust 2015
1551             // or results in `ExprKind::Await`. Suggest switching the edition to 2018.
1552             err.note("to `.await` a `Future`, switch to Rust 2018");
1553             err.help("set `edition = \"2018\"` in `Cargo.toml`");
1554             err.note("for more on editions, read https://doc.rust-lang.org/edition-guide");
1555         }
1556
1557         err.emit();
1558     }
1559
1560     fn ban_private_field_access(
1561         &self,
1562         expr: &hir::Expr<'_>,
1563         expr_t: Ty<'tcx>,
1564         field: ast::Ident,
1565         base_did: DefId,
1566     ) {
1567         let struct_path = self.tcx().def_path_str(base_did);
1568         let kind_name = match self.tcx().def_kind(base_did) {
1569             Some(def_kind) => def_kind.descr(base_did),
1570             _ => " ",
1571         };
1572         let mut err = struct_span_err!(
1573             self.tcx().sess,
1574             expr.span,
1575             E0616,
1576             "field `{}` of {} `{}` is private",
1577             field,
1578             kind_name,
1579             struct_path
1580         );
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.hir_id,
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
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.hir_id,
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_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             let base = self
1678                 .tcx
1679                 .sess
1680                 .source_map()
1681                 .span_to_snippet(base.span)
1682                 .unwrap_or_else(|_| self.tcx.hir().hir_to_pretty_string(base.hir_id));
1683             let help = "instead of using tuple indexing, use array indexing";
1684             let suggestion = format!("{}[{}]", base, field);
1685             let applicability = if len < user_index {
1686                 Applicability::MachineApplicable
1687             } else {
1688                 Applicability::MaybeIncorrect
1689             };
1690             err.span_suggestion(expr.span, help, suggestion, applicability);
1691         }
1692     }
1693
1694     fn suggest_first_deref_field(
1695         &self,
1696         err: &mut DiagnosticBuilder<'_>,
1697         expr: &hir::Expr<'_>,
1698         base: &hir::Expr<'_>,
1699         field: ast::Ident,
1700     ) {
1701         let base = self
1702             .tcx
1703             .sess
1704             .source_map()
1705             .span_to_snippet(base.span)
1706             .unwrap_or_else(|_| self.tcx.hir().hir_to_pretty_string(base.hir_id));
1707         let msg = format!("`{}` is a raw pointer; try dereferencing it", base);
1708         let suggestion = format!("(*{}).{}", base, field);
1709         err.span_suggestion(expr.span, &msg, suggestion, Applicability::MaybeIncorrect);
1710     }
1711
1712     fn no_such_field_err<T: Display>(
1713         &self,
1714         span: Span,
1715         field: T,
1716         expr_t: &ty::TyS<'_>,
1717     ) -> DiagnosticBuilder<'_> {
1718         type_error_struct!(
1719             self.tcx().sess,
1720             span,
1721             expr_t,
1722             E0609,
1723             "no field `{}` on type `{}`",
1724             field,
1725             expr_t
1726         )
1727     }
1728
1729     fn check_expr_index(
1730         &self,
1731         base: &'tcx hir::Expr<'tcx>,
1732         idx: &'tcx hir::Expr<'tcx>,
1733         needs: Needs,
1734         expr: &'tcx hir::Expr<'tcx>,
1735     ) -> Ty<'tcx> {
1736         let base_t = self.check_expr_with_needs(&base, needs);
1737         let idx_t = self.check_expr(&idx);
1738
1739         if base_t.references_error() {
1740             base_t
1741         } else if idx_t.references_error() {
1742             idx_t
1743         } else {
1744             let base_t = self.structurally_resolved_type(base.span, base_t);
1745             match self.lookup_indexing(expr, base, base_t, idx_t, needs) {
1746                 Some((index_ty, element_ty)) => {
1747                     // two-phase not needed because index_ty is never mutable
1748                     self.demand_coerce(idx, idx_t, index_ty, AllowTwoPhase::No);
1749                     element_ty
1750                 }
1751                 None => {
1752                     let mut err = type_error_struct!(
1753                         self.tcx.sess,
1754                         expr.span,
1755                         base_t,
1756                         E0608,
1757                         "cannot index into a value of type `{}`",
1758                         base_t
1759                     );
1760                     // Try to give some advice about indexing tuples.
1761                     if let ty::Tuple(..) = base_t.kind {
1762                         let mut needs_note = true;
1763                         // If the index is an integer, we can show the actual
1764                         // fixed expression:
1765                         if let ExprKind::Lit(ref lit) = idx.kind {
1766                             if let ast::LitKind::Int(i, ast::LitIntType::Unsuffixed) = lit.node {
1767                                 let snip = self.tcx.sess.source_map().span_to_snippet(base.span);
1768                                 if let Ok(snip) = snip {
1769                                     err.span_suggestion(
1770                                         expr.span,
1771                                         "to access tuple elements, use",
1772                                         format!("{}.{}", snip, i),
1773                                         Applicability::MachineApplicable,
1774                                     );
1775                                     needs_note = false;
1776                                 }
1777                             }
1778                         }
1779                         if needs_note {
1780                             err.help(
1781                                 "to access tuple elements, use tuple indexing \
1782                                         syntax (e.g., `tuple.0`)",
1783                             );
1784                         }
1785                     }
1786                     err.emit();
1787                     self.tcx.types.err
1788                 }
1789             }
1790         }
1791     }
1792
1793     fn check_expr_yield(
1794         &self,
1795         value: &'tcx hir::Expr<'tcx>,
1796         expr: &'tcx hir::Expr<'tcx>,
1797         src: &'tcx hir::YieldSource,
1798     ) -> Ty<'tcx> {
1799         match self.yield_ty {
1800             Some(ty) => {
1801                 self.check_expr_coercable_to_type(&value, ty);
1802             }
1803             // Given that this `yield` expression was generated as a result of lowering a `.await`,
1804             // we know that the yield type must be `()`; however, the context won't contain this
1805             // information. Hence, we check the source of the yield expression here and check its
1806             // value's type against `()` (this check should always hold).
1807             None if src == &hir::YieldSource::Await => {
1808                 self.check_expr_coercable_to_type(&value, self.tcx.mk_unit());
1809             }
1810             _ => {
1811                 struct_span_err!(
1812                     self.tcx.sess,
1813                     expr.span,
1814                     E0627,
1815                     "yield expression outside of generator literal"
1816                 )
1817                 .emit();
1818             }
1819         }
1820         self.tcx.mk_unit()
1821     }
1822 }
1823
1824 pub(super) fn ty_kind_suggestion(ty: Ty<'_>) -> Option<&'static str> {
1825     Some(match ty.kind {
1826         ty::Bool => "true",
1827         ty::Char => "'a'",
1828         ty::Int(_) | ty::Uint(_) => "42",
1829         ty::Float(_) => "3.14159",
1830         ty::Error | ty::Never => return None,
1831         _ => "value",
1832     })
1833 }