compiler/rustc_typeck/src/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::SelfSource;
  10 use crate::check::report_unexpected_variant_res;
  11 use crate::check::BreakableCtxt;
  12 use crate::check::Diverges;
  13 use crate::check::DynamicCoerceMany;
  14 use crate::check::Expectation::{self, ExpectCastableToType, ExpectHasType, NoExpectation};
  15 use crate::check::FnCtxt;
  16 use crate::check::Needs;
  17 use crate::check::TupleArgumentsFlag::DontTupleArguments;
  18 use crate::errors::{
  19     FieldMultiplySpecifiedInInitializer, FunctionalRecordUpdateOnNonStruct,
  20     YieldExprOutsideOfGenerator,
  21 };
  22 use crate::type_error_struct;
  23
  24 use crate::errors::{AddressOfTemporaryTaken, ReturnStmtOutsideOfFnBody, StructExprNonExhaustive};
  25 use rustc_ast as ast;
  26 use rustc_data_structures::fx::FxHashMap;
  27 use rustc_data_structures::stack::ensure_sufficient_stack;
  28 use rustc_errors::ErrorReported;
  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::intravisit::Visitor;
  34 use rustc_hir::{ExprKind, QPath};
  35 use rustc_infer::infer;
  36 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  37 use rustc_infer::infer::InferOk;
  38 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AllowTwoPhase};
  39 use rustc_middle::ty::error::TypeError::{FieldMisMatch, Sorts};
  40 use rustc_middle::ty::relate::expected_found_bool;
  41 use rustc_middle::ty::subst::SubstsRef;
  42 use rustc_middle::ty::{self, AdtKind, Ty, TypeFoldable};
  43 use rustc_session::parse::feature_err;
  44 use rustc_span::edition::LATEST_STABLE_EDITION;
  45 use rustc_span::hygiene::DesugaringKind;
  46 use rustc_span::lev_distance::find_best_match_for_name;
  47 use rustc_span::source_map::Span;
  48 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  49 use rustc_trait_selection::traits::{self, ObligationCauseCode};
  50
  51 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  52     fn check_expr_eq_type(&self, expr: &'tcx hir::Expr<'tcx>, expected: Ty<'tcx>) {
  53         let ty = self.check_expr_with_hint(expr, expected);
  54         self.demand_eqtype(expr.span, expected, ty);
  55     }
  56
  57     pub fn check_expr_has_type_or_error(
  58         &self,
  59         expr: &'tcx hir::Expr<'tcx>,
  60         expected: Ty<'tcx>,
  61         extend_err: impl Fn(&mut DiagnosticBuilder<'_>),
  62     ) -> Ty<'tcx> {
  63         self.check_expr_meets_expectation_or_error(expr, ExpectHasType(expected), extend_err)
  64     }
  65
  66     fn check_expr_meets_expectation_or_error(
  67         &self,
  68         expr: &'tcx hir::Expr<'tcx>,
  69         expected: Expectation<'tcx>,
  70         extend_err: impl Fn(&mut DiagnosticBuilder<'_>),
  71     ) -> Ty<'tcx> {
  72         let expected_ty = expected.to_option(&self).unwrap_or(self.tcx.types.bool);
  73         let mut ty = self.check_expr_with_expectation(expr, expected);
  74
  75         // While we don't allow *arbitrary* coercions here, we *do* allow
  76         // coercions from ! to `expected`.
  77         if ty.is_never() {
  78             assert!(
  79                 !self.typeck_results.borrow().adjustments().contains_key(expr.hir_id),
  80                 "expression with never type wound up being adjusted"
  81             );
  82             let adj_ty = self.next_ty_var(TypeVariableOrigin {
  83                 kind: TypeVariableOriginKind::AdjustmentType,
  84                 span: expr.span,
  85             });
  86             self.apply_adjustments(
  87                 expr,
  88                 vec![Adjustment { kind: Adjust::NeverToAny, target: adj_ty }],
  89             );
  90             ty = adj_ty;
  91         }
  92
  93         if let Some(mut err) = self.demand_suptype_diag(expr.span, expected_ty, ty) {
  94             let expr = expr.peel_drop_temps();
  95             self.suggest_deref_ref_or_into(&mut err, expr, expected_ty, ty, None);
  96             extend_err(&mut err);
  97             err.emit();
  98         }
  99         ty
 100     }
 101
 102     pub(super) fn check_expr_coercable_to_type(
 103         &self,
 104         expr: &'tcx hir::Expr<'tcx>,
 105         expected: Ty<'tcx>,
 106         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 107     ) -> Ty<'tcx> {
 108         let ty = self.check_expr_with_hint(expr, expected);
 109         // checks don't need two phase
 110         self.demand_coerce(expr, ty, expected, expected_ty_expr, AllowTwoPhase::No)
 111     }
 112
 113     pub(super) fn check_expr_with_hint(
 114         &self,
 115         expr: &'tcx hir::Expr<'tcx>,
 116         expected: Ty<'tcx>,
 117     ) -> Ty<'tcx> {
 118         self.check_expr_with_expectation(expr, ExpectHasType(expected))
 119     }
 120
 121     fn check_expr_with_expectation_and_needs(
 122         &self,
 123         expr: &'tcx hir::Expr<'tcx>,
 124         expected: Expectation<'tcx>,
 125         needs: Needs,
 126     ) -> Ty<'tcx> {
 127         let ty = self.check_expr_with_expectation(expr, expected);
 128
 129         // If the expression is used in a place whether mutable place is required
 130         // e.g. LHS of assignment, perform the conversion.
 131         if let Needs::MutPlace = needs {
 132             self.convert_place_derefs_to_mutable(expr);
 133         }
 134
 135         ty
 136     }
 137
 138     pub(super) fn check_expr(&self, expr: &'tcx hir::Expr<'tcx>) -> Ty<'tcx> {
 139         self.check_expr_with_expectation(expr, NoExpectation)
 140     }
 141
 142     pub(super) fn check_expr_with_needs(
 143         &self,
 144         expr: &'tcx hir::Expr<'tcx>,
 145         needs: Needs,
 146     ) -> Ty<'tcx> {
 147         self.check_expr_with_expectation_and_needs(expr, NoExpectation, needs)
 148     }
 149
 150     /// Invariant:
 151     /// If an expression has any sub-expressions that result in a type error,
 152     /// inspecting that expression's type with `ty.references_error()` will return
 153     /// true. Likewise, if an expression is known to diverge, inspecting its
 154     /// type with `ty::type_is_bot` will return true (n.b.: since Rust is
 155     /// strict, _|_ can appear in the type of an expression that does not,
 156     /// itself, diverge: for example, fn() -> _|_.)
 157     /// Note that inspecting a type's structure *directly* may expose the fact
 158     /// that there are actually multiple representations for `Error`, so avoid
 159     /// that when err needs to be handled differently.
 160     #[instrument(skip(self, expr), level = "debug")]
 161     pub(super) fn check_expr_with_expectation(
 162         &self,
 163         expr: &'tcx hir::Expr<'tcx>,
 164         expected: Expectation<'tcx>,
 165     ) -> Ty<'tcx> {
 166         self.check_expr_with_expectation_and_args(expr, expected, &[])
 167     }
 168
 169     /// Same as `check_expr_with_expectation`, but allows us to pass in the arguments of a
 170     /// `ExprKind::Call` when evaluating its callee when it is an `ExprKind::Path`.
 171     pub(super) fn check_expr_with_expectation_and_args(
 172         &self,
 173         expr: &'tcx hir::Expr<'tcx>,
 174         expected: Expectation<'tcx>,
 175         args: &'tcx [hir::Expr<'tcx>],
 176     ) -> Ty<'tcx> {
 177         if self.tcx().sess.verbose() {
 178             // make this code only run with -Zverbose because it is probably slow
 179             if let Ok(lint_str) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 180                 if !lint_str.contains('\n') {
 181                     debug!("expr text: {}", lint_str);
 182                 } else {
 183                     let mut lines = lint_str.lines();
 184                     if let Some(line0) = lines.next() {
 185                         let remaining_lines = lines.count();
 186                         debug!("expr text: {}", line0);
 187                         debug!("expr text: ...(and {} more lines)", remaining_lines);
 188                     }
 189                 }
 190             }
 191         }
 192
 193         // True if `expr` is a `Try::from_ok(())` that is a result of desugaring a try block
 194         // without the final expr (e.g. `try { return; }`). We don't want to generate an
 195         // unreachable_code lint for it since warnings for autogenerated code are confusing.
 196         let is_try_block_generated_unit_expr = match expr.kind {
 197             ExprKind::Call(_, args) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {
 198                 args.len() == 1 && args[0].span.is_desugaring(DesugaringKind::TryBlock)
 199             }
 200
 201             _ => false,
 202         };
 203
 204         // Warn for expressions after diverging siblings.
 205         if !is_try_block_generated_unit_expr {
 206             self.warn_if_unreachable(expr.hir_id, expr.span, "expression");
 207         }
 208
 209         // Hide the outer diverging and has_errors flags.
 210         let old_diverges = self.diverges.replace(Diverges::Maybe);
 211         let old_has_errors = self.has_errors.replace(false);
 212
 213         let ty = ensure_sufficient_stack(|| match &expr.kind {
 214             hir::ExprKind::Path(
 215                 qpath @ hir::QPath::Resolved(..) | qpath @ hir::QPath::TypeRelative(..),
 216             ) => self.check_expr_path(qpath, expr, args),
 217             _ => self.check_expr_kind(expr, expected),
 218         });
 219
 220         // Warn for non-block expressions with diverging children.
 221         match expr.kind {
 222             ExprKind::Block(..)
 223             | ExprKind::If(..)
 224             | ExprKind::Let(..)
 225             | ExprKind::Loop(..)
 226             | ExprKind::Match(..) => {}
 227             // If `expr` is a result of desugaring the try block and is an ok-wrapped
 228             // diverging expression (e.g. it arose from desugaring of `try { return }`),
 229             // we skip issuing a warning because it is autogenerated code.
 230             ExprKind::Call(..) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {}
 231             ExprKind::Call(callee, _) => self.warn_if_unreachable(expr.hir_id, callee.span, "call"),
 232             ExprKind::MethodCall(_, ref span, _, _) => {
 233                 self.warn_if_unreachable(expr.hir_id, *span, "call")
 234             }
 235             _ => self.warn_if_unreachable(expr.hir_id, expr.span, "expression"),
 236         }
 237
 238         // Any expression that produces a value of type `!` must have diverged
 239         if ty.is_never() {
 240             self.diverges.set(self.diverges.get() | Diverges::always(expr.span));
 241         }
 242
 243         // Record the type, which applies it effects.
 244         // We need to do this after the warning above, so that
 245         // we don't warn for the diverging expression itself.
 246         self.write_ty(expr.hir_id, ty);
 247
 248         // Combine the diverging and has_error flags.
 249         self.diverges.set(self.diverges.get() | old_diverges);
 250         self.has_errors.set(self.has_errors.get() | old_has_errors);
 251
 252         debug!("type of {} is...", self.tcx.hir().node_to_string(expr.hir_id));
 253         debug!("... {:?}, expected is {:?}", ty, expected);
 254
 255         ty
 256     }
 257
 258     #[instrument(skip(self, expr), level = "debug")]
 259     fn check_expr_kind(
 260         &self,
 261         expr: &'tcx hir::Expr<'tcx>,
 262         expected: Expectation<'tcx>,
 263     ) -> Ty<'tcx> {
 264         trace!("expr={:#?}", expr);
 265
 266         let tcx = self.tcx;
 267         match expr.kind {
 268             ExprKind::Box(subexpr) => self.check_expr_box(subexpr, expected),
 269             ExprKind::Lit(ref lit) => self.check_lit(&lit, expected),
 270             ExprKind::Binary(op, lhs, rhs) => self.check_binop(expr, op, lhs, rhs),
 271             ExprKind::Assign(lhs, rhs, ref span) => {
 272                 self.check_expr_assign(expr, expected, lhs, rhs, span)
 273             }
 274             ExprKind::AssignOp(op, lhs, rhs) => self.check_binop_assign(expr, op, lhs, rhs),
 275             ExprKind::Unary(unop, oprnd) => self.check_expr_unary(unop, oprnd, expected, expr),
 276             ExprKind::AddrOf(kind, mutbl, oprnd) => {
 277                 self.check_expr_addr_of(kind, mutbl, oprnd, expected, expr)
 278             }
 279             ExprKind::Path(QPath::LangItem(lang_item, _)) => {
 280                 self.check_lang_item_path(lang_item, expr)
 281             }
 282             ExprKind::Path(ref qpath) => self.check_expr_path(qpath, expr, &[]),
 283             ExprKind::InlineAsm(asm) => self.check_expr_asm(asm),
 284             ExprKind::LlvmInlineAsm(asm) => {
 285                 for expr in asm.outputs_exprs.iter().chain(asm.inputs_exprs.iter()) {
 286                     self.check_expr(expr);
 287                 }
 288                 tcx.mk_unit()
 289             }
 290             ExprKind::Break(destination, ref expr_opt) => {
 291                 self.check_expr_break(destination, expr_opt.as_deref(), expr)
 292             }
 293             ExprKind::Continue(destination) => {
 294                 if destination.target_id.is_ok() {
 295                     tcx.types.never
 296                 } else {
 297                     // There was an error; make type-check fail.
 298                     tcx.ty_error()
 299                 }
 300             }
 301             ExprKind::Ret(ref expr_opt) => self.check_expr_return(expr_opt.as_deref(), expr),
 302             ExprKind::Let(pat, let_expr, _) => self.check_expr_let(let_expr, pat),
 303             ExprKind::Loop(body, _, source, _) => {
 304                 self.check_expr_loop(body, source, expected, expr)
 305             }
 306             ExprKind::Match(discrim, arms, match_src) => {
 307                 self.check_match(expr, &discrim, arms, expected, match_src)
 308             }
 309             ExprKind::Closure(capture, decl, body_id, _, gen) => {
 310                 self.check_expr_closure(expr, capture, &decl, body_id, gen, expected)
 311             }
 312             ExprKind::Block(body, _) => self.check_block_with_expected(&body, expected),
 313             ExprKind::Call(callee, args) => self.check_call(expr, &callee, args, expected),
 314             ExprKind::MethodCall(segment, span, args, _) => {
 315                 self.check_method_call(expr, segment, span, args, expected)
 316             }
 317             ExprKind::Cast(e, t) => self.check_expr_cast(e, t, expr),
 318             ExprKind::Type(e, t) => {
 319                 let ty = self.to_ty_saving_user_provided_ty(&t);
 320                 self.check_expr_eq_type(&e, ty);
 321                 ty
 322             }
 323             ExprKind::If(cond, then_expr, opt_else_expr) => {
 324                 self.check_then_else(cond, then_expr, opt_else_expr, expr.span, expected)
 325             }
 326             ExprKind::DropTemps(e) => self.check_expr_with_expectation(e, expected),
 327             ExprKind::Array(args) => self.check_expr_array(args, expected, expr),
 328             ExprKind::ConstBlock(ref anon_const) => {
 329                 self.check_expr_const_block(anon_const, expected, expr)
 330             }
 331             ExprKind::Repeat(element, ref count) => {
 332                 self.check_expr_repeat(element, count, expected, expr)
 333             }
 334             ExprKind::Tup(elts) => self.check_expr_tuple(elts, expected, expr),
 335             ExprKind::Struct(qpath, fields, ref base_expr) => {
 336                 self.check_expr_struct(expr, expected, qpath, fields, base_expr)
 337             }
 338             ExprKind::Field(base, field) => self.check_field(expr, &base, field),
 339             ExprKind::Index(base, idx) => self.check_expr_index(base, idx, expr),
 340             ExprKind::Yield(value, ref src) => self.check_expr_yield(value, expr, src),
 341             hir::ExprKind::Err => tcx.ty_error(),
 342         }
 343     }
 344
 345     fn check_expr_box(&self, expr: &'tcx hir::Expr<'tcx>, expected: Expectation<'tcx>) -> Ty<'tcx> {
 346         let expected_inner = expected.to_option(self).map_or(NoExpectation, |ty| match ty.kind() {
 347             ty::Adt(def, _) if def.is_box() => Expectation::rvalue_hint(self, ty.boxed_ty()),
 348             _ => NoExpectation,
 349         });
 350         let referent_ty = self.check_expr_with_expectation(expr, expected_inner);
 351         self.require_type_is_sized(referent_ty, expr.span, traits::SizedBoxType);
 352         self.tcx.mk_box(referent_ty)
 353     }
 354
 355     fn check_expr_unary(
 356         &self,
 357         unop: hir::UnOp,
 358         oprnd: &'tcx hir::Expr<'tcx>,
 359         expected: Expectation<'tcx>,
 360         expr: &'tcx hir::Expr<'tcx>,
 361     ) -> Ty<'tcx> {
 362         let tcx = self.tcx;
 363         let expected_inner = match unop {
 364             hir::UnOp::Not | hir::UnOp::Neg => expected,
 365             hir::UnOp::Deref => NoExpectation,
 366         };
 367         let mut oprnd_t = self.check_expr_with_expectation(&oprnd, expected_inner);
 368
 369         if !oprnd_t.references_error() {
 370             oprnd_t = self.structurally_resolved_type(expr.span, oprnd_t);
 371             match unop {
 372                 hir::UnOp::Deref => {
 373                     if let Some(ty) = self.lookup_derefing(expr, oprnd, oprnd_t) {
 374                         oprnd_t = ty;
 375                     } else {
 376                         let mut err = type_error_struct!(
 377                             tcx.sess,
 378                             expr.span,
 379                             oprnd_t,
 380                             E0614,
 381                             "type `{}` cannot be dereferenced",
 382                             oprnd_t,
 383                         );
 384                         let sp = tcx.sess.source_map().start_point(expr.span);
 385                         if let Some(sp) =
 386                             tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
 387                         {
 388                             tcx.sess.parse_sess.expr_parentheses_needed(&mut err, *sp);
 389                         }
 390                         err.emit();
 391                         oprnd_t = tcx.ty_error();
 392                     }
 393                 }
 394                 hir::UnOp::Not => {
 395                     let result = self.check_user_unop(expr, oprnd_t, unop);
 396                     // If it's builtin, we can reuse the type, this helps inference.
 397                     if !(oprnd_t.is_integral() || *oprnd_t.kind() == ty::Bool) {
 398                         oprnd_t = result;
 399                     }
 400                 }
 401                 hir::UnOp::Neg => {
 402                     let result = self.check_user_unop(expr, oprnd_t, unop);
 403                     // If it's builtin, we can reuse the type, this helps inference.
 404                     if !oprnd_t.is_numeric() {
 405                         oprnd_t = result;
 406                     }
 407                 }
 408             }
 409         }
 410         oprnd_t
 411     }
 412
 413     fn check_expr_addr_of(
 414         &self,
 415         kind: hir::BorrowKind,
 416         mutbl: hir::Mutability,
 417         oprnd: &'tcx hir::Expr<'tcx>,
 418         expected: Expectation<'tcx>,
 419         expr: &'tcx hir::Expr<'tcx>,
 420     ) -> Ty<'tcx> {
 421         let hint = expected.only_has_type(self).map_or(NoExpectation, |ty| {
 422             match ty.kind() {
 423                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 424                     if oprnd.is_syntactic_place_expr() {
 425                         // Places may legitimately have unsized types.
 426                         // For example, dereferences of a fat pointer and
 427                         // the last field of a struct can be unsized.
 428                         ExpectHasType(ty)
 429                     } else {
 430                         Expectation::rvalue_hint(self, ty)
 431                     }
 432                 }
 433                 _ => NoExpectation,
 434             }
 435         });
 436         let ty =
 437             self.check_expr_with_expectation_and_needs(&oprnd, hint, Needs::maybe_mut_place(mutbl));
 438
 439         let tm = ty::TypeAndMut { ty, mutbl };
 440         match kind {
 441             _ if tm.ty.references_error() => self.tcx.ty_error(),
 442             hir::BorrowKind::Raw => {
 443                 self.check_named_place_expr(oprnd);
 444                 self.tcx.mk_ptr(tm)
 445             }
 446             hir::BorrowKind::Ref => {
 447                 // Note: at this point, we cannot say what the best lifetime
 448                 // is to use for resulting pointer.  We want to use the
 449                 // shortest lifetime possible so as to avoid spurious borrowck
 450                 // errors.  Moreover, the longest lifetime will depend on the
 451                 // precise details of the value whose address is being taken
 452                 // (and how long it is valid), which we don't know yet until
 453                 // type inference is complete.
 454                 //
 455                 // Therefore, here we simply generate a region variable. The
 456                 // region inferencer will then select a suitable value.
 457                 // Finally, borrowck will infer the value of the region again,
 458                 // this time with enough precision to check that the value
 459                 // whose address was taken can actually be made to live as long
 460                 // as it needs to live.
 461                 let region = self.next_region_var(infer::AddrOfRegion(expr.span));
 462                 self.tcx.mk_ref(region, tm)
 463             }
 464         }
 465     }
 466
 467     /// Does this expression refer to a place that either:
 468     /// * Is based on a local or static.
 469     /// * Contains a dereference
 470     /// Note that the adjustments for the children of `expr` should already
 471     /// have been resolved.
 472     fn check_named_place_expr(&self, oprnd: &'tcx hir::Expr<'tcx>) {
 473         let is_named = oprnd.is_place_expr(|base| {
 474             // Allow raw borrows if there are any deref adjustments.
 475             //
 476             // const VAL: (i32,) = (0,);
 477             // const REF: &(i32,) = &(0,);
 478             //
 479             // &raw const VAL.0;            // ERROR
 480             // &raw const REF.0;            // OK, same as &raw const (*REF).0;
 481             //
 482             // This is maybe too permissive, since it allows
 483             // `let u = &raw const Box::new((1,)).0`, which creates an
 484             // immediately dangling raw pointer.
 485             self.typeck_results
 486                 .borrow()
 487                 .adjustments()
 488                 .get(base.hir_id)
 489                 .map_or(false, |x| x.iter().any(|adj| matches!(adj.kind, Adjust::Deref(_))))
 490         });
 491         if !is_named {
 492             self.tcx.sess.emit_err(AddressOfTemporaryTaken { span: oprnd.span })
 493         }
 494     }
 495
 496     fn check_lang_item_path(
 497         &self,
 498         lang_item: hir::LangItem,
 499         expr: &'tcx hir::Expr<'tcx>,
 500     ) -> Ty<'tcx> {
 501         self.resolve_lang_item_path(lang_item, expr.span, expr.hir_id).1
 502     }
 503
 504     pub(crate) fn check_expr_path(
 505         &self,
 506         qpath: &'tcx hir::QPath<'tcx>,
 507         expr: &'tcx hir::Expr<'tcx>,
 508         args: &'tcx [hir::Expr<'tcx>],
 509     ) -> Ty<'tcx> {
 510         let tcx = self.tcx;
 511         let (res, opt_ty, segs) =
 512             self.resolve_ty_and_res_fully_qualified_call(qpath, expr.hir_id, expr.span);
 513         let ty = match res {
 514             Res::Err => {
 515                 self.set_tainted_by_errors();
 516                 tcx.ty_error()
 517             }
 518             Res::Def(DefKind::Ctor(_, CtorKind::Fictive), _) => {
 519                 report_unexpected_variant_res(tcx, res, expr.span);
 520                 tcx.ty_error()
 521             }
 522             _ => self.instantiate_value_path(segs, opt_ty, res, expr.span, expr.hir_id).0,
 523         };
 524
 525         if let ty::FnDef(..) = ty.kind() {
 526             let fn_sig = ty.fn_sig(tcx);
 527             if !tcx.features().unsized_fn_params {
 528                 // We want to remove some Sized bounds from std functions,
 529                 // but don't want to expose the removal to stable Rust.
 530                 // i.e., we don't want to allow
 531                 //
 532                 // ```rust
 533                 // drop as fn(str);
 534                 // ```
 535                 //
 536                 // to work in stable even if the Sized bound on `drop` is relaxed.
 537                 for i in 0..fn_sig.inputs().skip_binder().len() {
 538                     // We just want to check sizedness, so instead of introducing
 539                     // placeholder lifetimes with probing, we just replace higher lifetimes
 540                     // with fresh vars.
 541                     let span = args.get(i).map(|a| a.span).unwrap_or(expr.span);
 542                     let input = self
 543                         .replace_bound_vars_with_fresh_vars(
 544                             span,
 545                             infer::LateBoundRegionConversionTime::FnCall,
 546                             fn_sig.input(i),
 547                         )
 548                         .0;
 549                     self.require_type_is_sized_deferred(
 550                         input,
 551                         span,
 552                         traits::SizedArgumentType(None),
 553                     );
 554                 }
 555             }
 556             // Here we want to prevent struct constructors from returning unsized types.
 557             // There were two cases this happened: fn pointer coercion in stable
 558             // and usual function call in presence of unsized_locals.
 559             // Also, as we just want to check sizedness, instead of introducing
 560             // placeholder lifetimes with probing, we just replace higher lifetimes
 561             // with fresh vars.
 562             let output = self
 563                 .replace_bound_vars_with_fresh_vars(
 564                     expr.span,
 565                     infer::LateBoundRegionConversionTime::FnCall,
 566                     fn_sig.output(),
 567                 )
 568                 .0;
 569             self.require_type_is_sized_deferred(output, expr.span, traits::SizedReturnType);
 570         }
 571
 572         // We always require that the type provided as the value for
 573         // a type parameter outlives the moment of instantiation.
 574         let substs = self.typeck_results.borrow().node_substs(expr.hir_id);
 575         self.add_wf_bounds(substs, expr);
 576
 577         ty
 578     }
 579
 580     fn check_expr_break(
 581         &self,
 582         destination: hir::Destination,
 583         expr_opt: Option<&'tcx hir::Expr<'tcx>>,
 584         expr: &'tcx hir::Expr<'tcx>,
 585     ) -> Ty<'tcx> {
 586         let tcx = self.tcx;
 587         if let Ok(target_id) = destination.target_id {
 588             let (e_ty, cause);
 589             if let Some(e) = expr_opt {
 590                 // If this is a break with a value, we need to type-check
 591                 // the expression. Get an expected type from the loop context.
 592                 let opt_coerce_to = {
 593                     // We should release `enclosing_breakables` before the `check_expr_with_hint`
 594                     // below, so can't move this block of code to the enclosing scope and share
 595                     // `ctxt` with the second `encloding_breakables` borrow below.
 596                     let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 597                     match enclosing_breakables.opt_find_breakable(target_id) {
 598                         Some(ctxt) => ctxt.coerce.as_ref().map(|coerce| coerce.expected_ty()),
 599                         None => {
 600                             // Avoid ICE when `break` is inside a closure (#65383).
 601                             return tcx.ty_error_with_message(
 602                                 expr.span,
 603                                 "break was outside loop, but no error was emitted",
 604                             );
 605                         }
 606                     }
 607                 };
 608
 609                 // If the loop context is not a `loop { }`, then break with
 610                 // a value is illegal, and `opt_coerce_to` will be `None`.
 611                 // Just set expectation to error in that case.
 612                 let coerce_to = opt_coerce_to.unwrap_or_else(|| tcx.ty_error());
 613
 614                 // Recurse without `enclosing_breakables` borrowed.
 615                 e_ty = self.check_expr_with_hint(e, coerce_to);
 616                 cause = self.misc(e.span);
 617             } else {
 618                 // Otherwise, this is a break *without* a value. That's
 619                 // always legal, and is equivalent to `break ()`.
 620                 e_ty = tcx.mk_unit();
 621                 cause = self.misc(expr.span);
 622             }
 623
 624             // Now that we have type-checked `expr_opt`, borrow
 625             // the `enclosing_loops` field and let's coerce the
 626             // type of `expr_opt` into what is expected.
 627             let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 628             let ctxt = match enclosing_breakables.opt_find_breakable(target_id) {
 629                 Some(ctxt) => ctxt,
 630                 None => {
 631                     // Avoid ICE when `break` is inside a closure (#65383).
 632                     return tcx.ty_error_with_message(
 633                         expr.span,
 634                         "break was outside loop, but no error was emitted",
 635                     );
 636                 }
 637             };
 638
 639             if let Some(ref mut coerce) = ctxt.coerce {
 640                 if let Some(ref e) = expr_opt {
 641                     coerce.coerce(self, &cause, e, e_ty);
 642                 } else {
 643                     assert!(e_ty.is_unit());
 644                     let ty = coerce.expected_ty();
 645                     coerce.coerce_forced_unit(
 646                         self,
 647                         &cause,
 648                         &mut |mut err| {
 649                             self.suggest_mismatched_types_on_tail(
 650                                 &mut err, expr, ty, e_ty, target_id,
 651                             );
 652                             if let Some(val) = ty_kind_suggestion(ty) {
 653                                 let label = destination
 654                                     .label
 655                                     .map(|l| format!(" {}", l.ident))
 656                                     .unwrap_or_else(String::new);
 657                                 err.span_suggestion(
 658                                     expr.span,
 659                                     "give it a value of the expected type",
 660                                     format!("break{} {}", label, val),
 661                                     Applicability::HasPlaceholders,
 662                                 );
 663                             }
 664                         },
 665                         false,
 666                     );
 667                 }
 668             } else {
 669                 // If `ctxt.coerce` is `None`, we can just ignore
 670                 // the type of the expression.  This is because
 671                 // either this was a break *without* a value, in
 672                 // which case it is always a legal type (`()`), or
 673                 // else an error would have been flagged by the
 674                 // `loops` pass for using break with an expression
 675                 // where you are not supposed to.
 676                 assert!(expr_opt.is_none() || self.tcx.sess.has_errors());
 677             }
 678
 679             // If we encountered a `break`, then (no surprise) it may be possible to break from the
 680             // loop... unless the value being returned from the loop diverges itself, e.g.
 681             // `break return 5` or `break loop {}`.
 682             ctxt.may_break |= !self.diverges.get().is_always();
 683
 684             // the type of a `break` is always `!`, since it diverges
 685             tcx.types.never
 686         } else {
 687             // Otherwise, we failed to find the enclosing loop;
 688             // this can only happen if the `break` was not
 689             // inside a loop at all, which is caught by the
 690             // loop-checking pass.
 691             let err = self.tcx.ty_error_with_message(
 692                 expr.span,
 693                 "break was outside loop, but no error was emitted",
 694             );
 695
 696             // We still need to assign a type to the inner expression to
 697             // prevent the ICE in #43162.
 698             if let Some(e) = expr_opt {
 699                 self.check_expr_with_hint(e, err);
 700
 701                 // ... except when we try to 'break rust;'.
 702                 // ICE this expression in particular (see #43162).
 703                 if let ExprKind::Path(QPath::Resolved(_, path)) = e.kind {
 704                     if path.segments.len() == 1 && path.segments[0].ident.name == sym::rust {
 705                         fatally_break_rust(self.tcx.sess);
 706                     }
 707                 }
 708             }
 709
 710             // There was an error; make type-check fail.
 711             err
 712         }
 713     }
 714
 715     fn check_expr_return(
 716         &self,
 717         expr_opt: Option<&'tcx hir::Expr<'tcx>>,
 718         expr: &'tcx hir::Expr<'tcx>,
 719     ) -> Ty<'tcx> {
 720         if self.ret_coercion.is_none() {
 721             let mut err = ReturnStmtOutsideOfFnBody {
 722                 span: expr.span,
 723                 encl_body_span: None,
 724                 encl_fn_span: None,
 725             };
 726
 727             let encl_item_id = self.tcx.hir().get_parent_item(expr.hir_id);
 728
 729             if let Some(hir::Node::Item(hir::Item {
 730                 kind: hir::ItemKind::Fn(..),
 731                 span: encl_fn_span,
 732                 ..
 733             }))
 734             | Some(hir::Node::TraitItem(hir::TraitItem {
 735                 kind: hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)),
 736                 span: encl_fn_span,
 737                 ..
 738             }))
 739             | Some(hir::Node::ImplItem(hir::ImplItem {
 740                 kind: hir::ImplItemKind::Fn(..),
 741                 span: encl_fn_span,
 742                 ..
 743             })) = self.tcx.hir().find(encl_item_id)
 744             {
 745                 // We are inside a function body, so reporting "return statement
 746                 // outside of function body" needs an explanation.
 747
 748                 let encl_body_owner_id = self.tcx.hir().enclosing_body_owner(expr.hir_id);
 749
 750                 // If this didn't hold, we would not have to report an error in
 751                 // the first place.
 752                 assert_ne!(encl_item_id, encl_body_owner_id);
 753
 754                 let encl_body_id = self.tcx.hir().body_owned_by(encl_body_owner_id);
 755                 let encl_body = self.tcx.hir().body(encl_body_id);
 756
 757                 err.encl_body_span = Some(encl_body.value.span);
 758                 err.encl_fn_span = Some(*encl_fn_span);
 759             }
 760
 761             self.tcx.sess.emit_err(err);
 762
 763             if let Some(e) = expr_opt {
 764                 // We still have to type-check `e` (issue #86188), but calling
 765                 // `check_return_expr` only works inside fn bodies.
 766                 self.check_expr(e);
 767             }
 768         } else if let Some(e) = expr_opt {
 769             if self.ret_coercion_span.get().is_none() {
 770                 self.ret_coercion_span.set(Some(e.span));
 771             }
 772             self.check_return_expr(e, true);
 773         } else {
 774             let mut coercion = self.ret_coercion.as_ref().unwrap().borrow_mut();
 775             if self.ret_coercion_span.get().is_none() {
 776                 self.ret_coercion_span.set(Some(expr.span));
 777             }
 778             let cause = self.cause(expr.span, ObligationCauseCode::ReturnNoExpression);
 779             if let Some((fn_decl, _)) = self.get_fn_decl(expr.hir_id) {
 780                 coercion.coerce_forced_unit(
 781                     self,
 782                     &cause,
 783                     &mut |db| {
 784                         let span = fn_decl.output.span();
 785                         if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
 786                             db.span_label(
 787                                 span,
 788                                 format!("expected `{}` because of this return type", snippet),
 789                             );
 790                         }
 791                     },
 792                     true,
 793                 );
 794             } else {
 795                 coercion.coerce_forced_unit(self, &cause, &mut |_| (), true);
 796             }
 797         }
 798         self.tcx.types.never
 799     }
 800
 801     /// `explicit_return` is `true` if we're checkng an explicit `return expr`,
 802     /// and `false` if we're checking a trailing expression.
 803     pub(super) fn check_return_expr(
 804         &self,
 805         return_expr: &'tcx hir::Expr<'tcx>,
 806         explicit_return: bool,
 807     ) {
 808         let ret_coercion = self.ret_coercion.as_ref().unwrap_or_else(|| {
 809             span_bug!(return_expr.span, "check_return_expr called outside fn body")
 810         });
 811
 812         let ret_ty = ret_coercion.borrow().expected_ty();
 813         let return_expr_ty = self.check_expr_with_hint(return_expr, ret_ty);
 814         let mut span = return_expr.span;
 815         // Use the span of the trailing expression for our cause,
 816         // not the span of the entire function
 817         if !explicit_return {
 818             if let ExprKind::Block(body, _) = return_expr.kind {
 819                 if let Some(last_expr) = body.expr {
 820                     span = last_expr.span;
 821                 }
 822             }
 823         }
 824         ret_coercion.borrow_mut().coerce(
 825             self,
 826             &self.cause(span, ObligationCauseCode::ReturnValue(return_expr.hir_id)),
 827             return_expr,
 828             return_expr_ty,
 829         );
 830     }
 831
 832     pub(crate) fn check_lhs_assignable(
 833         &self,
 834         lhs: &'tcx hir::Expr<'tcx>,
 835         err_code: &'static str,
 836         expr_span: &Span,
 837     ) {
 838         if lhs.is_syntactic_place_expr() {
 839             return;
 840         }
 841
 842         // FIXME: Make this use SessionDiagnostic once error codes can be dynamically set.
 843         let mut err = self.tcx.sess.struct_span_err_with_code(
 844             *expr_span,
 845             "invalid left-hand side of assignment",
 846             DiagnosticId::Error(err_code.into()),
 847         );
 848         err.span_label(lhs.span, "cannot assign to this expression");
 849         err.emit();
 850     }
 851
 852     // A generic function for checking the 'then' and 'else' clauses in an 'if'
 853     // or 'if-else' expression.
 854     fn check_then_else(
 855         &self,
 856         cond_expr: &'tcx hir::Expr<'tcx>,
 857         then_expr: &'tcx hir::Expr<'tcx>,
 858         opt_else_expr: Option<&'tcx hir::Expr<'tcx>>,
 859         sp: Span,
 860         orig_expected: Expectation<'tcx>,
 861     ) -> Ty<'tcx> {
 862         let cond_ty = self.check_expr_has_type_or_error(cond_expr, self.tcx.types.bool, |_| {});
 863
 864         self.warn_if_unreachable(
 865             cond_expr.hir_id,
 866             then_expr.span,
 867             "block in `if` or `while` expression",
 868         );
 869
 870         let cond_diverges = self.diverges.get();
 871         self.diverges.set(Diverges::Maybe);
 872
 873         let expected = orig_expected.adjust_for_branches(self);
 874         let then_ty = self.check_expr_with_expectation(then_expr, expected);
 875         let then_diverges = self.diverges.get();
 876         self.diverges.set(Diverges::Maybe);
 877
 878         // We've already taken the expected type's preferences
 879         // into account when typing the `then` branch. To figure
 880         // out the initial shot at a LUB, we thus only consider
 881         // `expected` if it represents a *hard* constraint
 882         // (`only_has_type`); otherwise, we just go with a
 883         // fresh type variable.
 884         let coerce_to_ty = expected.coercion_target_type(self, sp);
 885         let mut coerce: DynamicCoerceMany<'_> = CoerceMany::new(coerce_to_ty);
 886
 887         coerce.coerce(self, &self.misc(sp), then_expr, then_ty);
 888
 889         if let Some(else_expr) = opt_else_expr {
 890             let else_ty = if sp.desugaring_kind() == Some(DesugaringKind::LetElse) {
 891                 // todo introduce `check_expr_with_expectation(.., Expectation::LetElse)`
 892                 //   for errors that point to the offending expression rather than the entire block.
 893                 //   We could use `check_expr_eq_type(.., tcx.types.never)`, but then there is no
 894                 //   way to detect that the expected type originated from let-else and provide
 895                 //   a customized error.
 896                 let else_ty = self.check_expr(else_expr);
 897                 let cause = self.cause(else_expr.span, ObligationCauseCode::LetElse);
 898
 899                 if let Some(mut err) =
 900                     self.demand_eqtype_with_origin(&cause, self.tcx.types.never, else_ty)
 901                 {
 902                     err.emit();
 903                     self.tcx.ty_error()
 904                 } else {
 905                     else_ty
 906                 }
 907             } else {
 908                 self.check_expr_with_expectation(else_expr, expected)
 909             };
 910             let else_diverges = self.diverges.get();
 911
 912             let opt_suggest_box_span =
 913                 self.opt_suggest_box_span(else_expr.span, else_ty, orig_expected);
 914             let if_cause =
 915                 self.if_cause(sp, then_expr, else_expr, then_ty, else_ty, opt_suggest_box_span);
 916
 917             coerce.coerce(self, &if_cause, else_expr, else_ty);
 918
 919             // We won't diverge unless both branches do (or the condition does).
 920             self.diverges.set(cond_diverges | then_diverges & else_diverges);
 921         } else {
 922             self.if_fallback_coercion(sp, then_expr, &mut coerce);
 923
 924             // If the condition is false we can't diverge.
 925             self.diverges.set(cond_diverges);
 926         }
 927
 928         let result_ty = coerce.complete(self);
 929         if cond_ty.references_error() { self.tcx.ty_error() } else { result_ty }
 930     }
 931
 932     /// Type check assignment expression `expr` of form `lhs = rhs`.
 933     /// The expected type is `()` and is passed to the function for the purposes of diagnostics.
 934     fn check_expr_assign(
 935         &self,
 936         expr: &'tcx hir::Expr<'tcx>,
 937         expected: Expectation<'tcx>,
 938         lhs: &'tcx hir::Expr<'tcx>,
 939         rhs: &'tcx hir::Expr<'tcx>,
 940         span: &Span,
 941     ) -> Ty<'tcx> {
 942         let expected_ty = expected.coercion_target_type(self, expr.span);
 943         if expected_ty == self.tcx.types.bool {
 944             // The expected type is `bool` but this will result in `()` so we can reasonably
 945             // say that the user intended to write `lhs == rhs` instead of `lhs = rhs`.
 946             // The likely cause of this is `if foo = bar { .. }`.
 947             let actual_ty = self.tcx.mk_unit();
 948             let mut err = self.demand_suptype_diag(expr.span, expected_ty, actual_ty).unwrap();
 949             let lhs_ty = self.check_expr(&lhs);
 950             let rhs_ty = self.check_expr(&rhs);
 951             let (applicability, eq) = if self.can_coerce(rhs_ty, lhs_ty) {
 952                 (Applicability::MachineApplicable, true)
 953             } else {
 954                 (Applicability::MaybeIncorrect, false)
 955             };
 956             if !lhs.is_syntactic_place_expr() {
 957                 // Do not suggest `if let x = y` as `==` is way more likely to be the intention.
 958                 let hir = self.tcx.hir();
 959                 if let hir::Node::Expr(hir::Expr { kind: ExprKind::If { .. }, .. }) =
 960                     hir.get(hir.get_parent_node(hir.get_parent_node(expr.hir_id)))
 961                 {
 962                     err.span_suggestion_verbose(
 963                         expr.span.shrink_to_lo(),
 964                         "you might have meant to use pattern matching",
 965                         "let ".to_string(),
 966                         applicability,
 967                     );
 968                 }
 969             }
 970             if eq {
 971                 err.span_suggestion_verbose(
 972                     *span,
 973                     "you might have meant to compare for equality",
 974                     "==".to_string(),
 975                     applicability,
 976                 );
 977             }
 978
 979             // If the assignment expression itself is ill-formed, don't
 980             // bother emitting another error
 981             if lhs_ty.references_error() || rhs_ty.references_error() {
 982                 err.delay_as_bug()
 983             } else {
 984                 err.emit();
 985             }
 986             return self.tcx.ty_error();
 987         }
 988
 989         self.check_lhs_assignable(lhs, "E0070", span);
 990
 991         let lhs_ty = self.check_expr_with_needs(&lhs, Needs::MutPlace);
 992         let rhs_ty = self.check_expr_coercable_to_type(&rhs, lhs_ty, Some(lhs));
 993
 994         self.require_type_is_sized(lhs_ty, lhs.span, traits::AssignmentLhsSized);
 995
 996         if lhs_ty.references_error() || rhs_ty.references_error() {
 997             self.tcx.ty_error()
 998         } else {
 999             self.tcx.mk_unit()
1000         }
1001     }
1002
1003     fn check_expr_let(&self, expr: &'tcx hir::Expr<'tcx>, pat: &'tcx hir::Pat<'tcx>) -> Ty<'tcx> {
1004         self.warn_if_unreachable(expr.hir_id, expr.span, "block in `let` expression");
1005         let expr_ty = self.demand_scrutinee_type(expr, pat.contains_explicit_ref_binding(), false);
1006         self.check_pat_top(pat, expr_ty, Some(expr.span), true);
1007         self.tcx.types.bool
1008     }
1009
1010     fn check_expr_loop(
1011         &self,
1012         body: &'tcx hir::Block<'tcx>,
1013         source: hir::LoopSource,
1014         expected: Expectation<'tcx>,
1015         expr: &'tcx hir::Expr<'tcx>,
1016     ) -> Ty<'tcx> {
1017         let coerce = match source {
1018             // you can only use break with a value from a normal `loop { }`
1019             hir::LoopSource::Loop => {
1020                 let coerce_to = expected.coercion_target_type(self, body.span);
1021                 Some(CoerceMany::new(coerce_to))
1022             }
1023
1024             hir::LoopSource::While | hir::LoopSource::ForLoop => None,
1025         };
1026
1027         let ctxt = BreakableCtxt {
1028             coerce,
1029             may_break: false, // Will get updated if/when we find a `break`.
1030         };
1031
1032         let (ctxt, ()) = self.with_breakable_ctxt(expr.hir_id, ctxt, || {
1033             self.check_block_no_value(&body);
1034         });
1035
1036         if ctxt.may_break {
1037             // No way to know whether it's diverging because
1038             // of a `break` or an outer `break` or `return`.
1039             self.diverges.set(Diverges::Maybe);
1040         }
1041
1042         // If we permit break with a value, then result type is
1043         // the LUB of the breaks (possibly ! if none); else, it
1044         // is nil. This makes sense because infinite loops
1045         // (which would have type !) are only possible iff we
1046         // permit break with a value [1].
1047         if ctxt.coerce.is_none() && !ctxt.may_break {
1048             // [1]
1049             self.tcx.sess.delay_span_bug(body.span, "no coercion, but loop may not break");
1050         }
1051         ctxt.coerce.map(|c| c.complete(self)).unwrap_or_else(|| self.tcx.mk_unit())
1052     }
1053
1054     /// Checks a method call.
1055     fn check_method_call(
1056         &self,
1057         expr: &'tcx hir::Expr<'tcx>,
1058         segment: &hir::PathSegment<'_>,
1059         span: Span,
1060         args: &'tcx [hir::Expr<'tcx>],
1061         expected: Expectation<'tcx>,
1062     ) -> Ty<'tcx> {
1063         let rcvr = &args[0];
1064         let rcvr_t = self.check_expr(&rcvr);
1065         // no need to check for bot/err -- callee does that
1066         let rcvr_t = self.structurally_resolved_type(args[0].span, rcvr_t);
1067
1068         let method = match self.lookup_method(rcvr_t, segment, span, expr, rcvr, args) {
1069             Ok(method) => {
1070                 // We could add a "consider `foo::<params>`" suggestion here, but I wasn't able to
1071                 // trigger this codepath causing `structuraly_resolved_type` to emit an error.
1072
1073                 self.write_method_call(expr.hir_id, method);
1074                 Ok(method)
1075             }
1076             Err(error) => {
1077                 if segment.ident.name != kw::Empty {
1078                     if let Some(mut err) = self.report_method_error(
1079                         span,
1080                         rcvr_t,
1081                         segment.ident,
1082                         SelfSource::MethodCall(&args[0]),
1083                         error,
1084                         Some(args),
1085                     ) {
1086                         err.emit();
1087                     }
1088                 }
1089                 Err(())
1090             }
1091         };
1092
1093         // Call the generic checker.
1094         self.check_method_argument_types(
1095             span,
1096             expr,
1097             method,
1098             &args[1..],
1099             DontTupleArguments,
1100             expected,
1101         )
1102     }
1103
1104     fn check_expr_cast(
1105         &self,
1106         e: &'tcx hir::Expr<'tcx>,
1107         t: &'tcx hir::Ty<'tcx>,
1108         expr: &'tcx hir::Expr<'tcx>,
1109     ) -> Ty<'tcx> {
1110         // Find the type of `e`. Supply hints based on the type we are casting to,
1111         // if appropriate.
1112         let t_cast = self.to_ty_saving_user_provided_ty(t);
1113         let t_cast = self.resolve_vars_if_possible(t_cast);
1114         let t_expr = self.check_expr_with_expectation(e, ExpectCastableToType(t_cast));
1115         let t_expr = self.resolve_vars_if_possible(t_expr);
1116
1117         // Eagerly check for some obvious errors.
1118         if t_expr.references_error() || t_cast.references_error() {
1119             self.tcx.ty_error()
1120         } else {
1121             // Defer other checks until we're done type checking.
1122             let mut deferred_cast_checks = self.deferred_cast_checks.borrow_mut();
1123             match cast::CastCheck::new(self, e, t_expr, t_cast, t.span, expr.span) {
1124                 Ok(cast_check) => {
1125                     debug!(
1126                         "check_expr_cast: deferring cast from {:?} to {:?}: {:?}",
1127                         t_cast, t_expr, cast_check,
1128                     );
1129                     deferred_cast_checks.push(cast_check);
1130                     t_cast
1131                 }
1132                 Err(ErrorReported) => self.tcx.ty_error(),
1133             }
1134         }
1135     }
1136
1137     fn check_expr_array(
1138         &self,
1139         args: &'tcx [hir::Expr<'tcx>],
1140         expected: Expectation<'tcx>,
1141         expr: &'tcx hir::Expr<'tcx>,
1142     ) -> Ty<'tcx> {
1143         let element_ty = if !args.is_empty() {
1144             let coerce_to = expected
1145                 .to_option(self)
1146                 .and_then(|uty| match *uty.kind() {
1147                     ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
1148                     _ => None,
1149                 })
1150                 .unwrap_or_else(|| {
1151                     self.next_ty_var(TypeVariableOrigin {
1152                         kind: TypeVariableOriginKind::TypeInference,
1153                         span: expr.span,
1154                     })
1155                 });
1156             let mut coerce = CoerceMany::with_coercion_sites(coerce_to, args);
1157             assert_eq!(self.diverges.get(), Diverges::Maybe);
1158             for e in args {
1159                 let e_ty = self.check_expr_with_hint(e, coerce_to);
1160                 let cause = self.misc(e.span);
1161                 coerce.coerce(self, &cause, e, e_ty);
1162             }
1163             coerce.complete(self)
1164         } else {
1165             self.next_ty_var(TypeVariableOrigin {
1166                 kind: TypeVariableOriginKind::TypeInference,
1167                 span: expr.span,
1168             })
1169         };
1170         self.tcx.mk_array(element_ty, args.len() as u64)
1171     }
1172
1173     fn check_expr_const_block(
1174         &self,
1175         anon_const: &'tcx hir::AnonConst,
1176         expected: Expectation<'tcx>,
1177         _expr: &'tcx hir::Expr<'tcx>,
1178     ) -> Ty<'tcx> {
1179         let body = self.tcx.hir().body(anon_const.body);
1180
1181         // Create a new function context.
1182         let fcx = FnCtxt::new(self, self.param_env, body.value.hir_id);
1183         crate::check::GatherLocalsVisitor::new(&fcx).visit_body(body);
1184
1185         let ty = fcx.check_expr_with_expectation(&body.value, expected);
1186         fcx.require_type_is_sized(ty, body.value.span, traits::ConstSized);
1187         fcx.write_ty(anon_const.hir_id, ty);
1188         ty
1189     }
1190
1191     fn check_expr_repeat(
1192         &self,
1193         element: &'tcx hir::Expr<'tcx>,
1194         count: &'tcx hir::AnonConst,
1195         expected: Expectation<'tcx>,
1196         _expr: &'tcx hir::Expr<'tcx>,
1197     ) -> Ty<'tcx> {
1198         let tcx = self.tcx;
1199         let count = self.to_const(count);
1200
1201         let uty = match expected {
1202             ExpectHasType(uty) => match *uty.kind() {
1203                 ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
1204                 _ => None,
1205             },
1206             _ => None,
1207         };
1208
1209         let (element_ty, t) = match uty {
1210             Some(uty) => {
1211                 self.check_expr_coercable_to_type(&element, uty, None);
1212                 (uty, uty)
1213             }
1214             None => {
1215                 let ty = self.next_ty_var(TypeVariableOrigin {
1216                     kind: TypeVariableOriginKind::MiscVariable,
1217                     span: element.span,
1218                 });
1219                 let element_ty = self.check_expr_has_type_or_error(&element, ty, |_| {});
1220                 (element_ty, ty)
1221             }
1222         };
1223
1224         if element_ty.references_error() {
1225             return tcx.ty_error();
1226         }
1227
1228         tcx.mk_ty(ty::Array(t, count))
1229     }
1230
1231     fn check_expr_tuple(
1232         &self,
1233         elts: &'tcx [hir::Expr<'tcx>],
1234         expected: Expectation<'tcx>,
1235         expr: &'tcx hir::Expr<'tcx>,
1236     ) -> Ty<'tcx> {
1237         let flds = expected.only_has_type(self).and_then(|ty| {
1238             let ty = self.resolve_vars_with_obligations(ty);
1239             match ty.kind() {
1240                 ty::Tuple(flds) => Some(&flds[..]),
1241                 _ => None,
1242             }
1243         });
1244
1245         let elt_ts_iter = elts.iter().enumerate().map(|(i, e)| match flds {
1246             Some(fs) if i < fs.len() => {
1247                 let ety = fs[i].expect_ty();
1248                 self.check_expr_coercable_to_type(&e, ety, None);
1249                 ety
1250             }
1251             _ => self.check_expr_with_expectation(&e, NoExpectation),
1252         });
1253         let tuple = self.tcx.mk_tup(elt_ts_iter);
1254         if tuple.references_error() {
1255             self.tcx.ty_error()
1256         } else {
1257             self.require_type_is_sized(tuple, expr.span, traits::TupleInitializerSized);
1258             tuple
1259         }
1260     }
1261
1262     fn check_expr_struct(
1263         &self,
1264         expr: &hir::Expr<'_>,
1265         expected: Expectation<'tcx>,
1266         qpath: &QPath<'_>,
1267         fields: &'tcx [hir::ExprField<'tcx>],
1268         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1269     ) -> Ty<'tcx> {
1270         // Find the relevant variant
1271         let (variant, adt_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, expr.hir_id)
1272         {
1273             variant_ty
1274         } else {
1275             self.check_struct_fields_on_error(fields, base_expr);
1276             return self.tcx.ty_error();
1277         };
1278
1279         // Prohibit struct expressions when non-exhaustive flag is set.
1280         let adt = adt_ty.ty_adt_def().expect("`check_struct_path` returned non-ADT type");
1281         if !adt.did.is_local() && variant.is_field_list_non_exhaustive() {
1282             self.tcx
1283                 .sess
1284                 .emit_err(StructExprNonExhaustive { span: expr.span, what: adt.variant_descr() });
1285         }
1286
1287         self.check_expr_struct_fields(
1288             adt_ty,
1289             expected,
1290             expr.hir_id,
1291             qpath.span(),
1292             variant,
1293             fields,
1294             base_expr,
1295             expr.span,
1296         );
1297
1298         self.require_type_is_sized(adt_ty, expr.span, traits::StructInitializerSized);
1299         adt_ty
1300     }
1301
1302     fn check_expr_struct_fields(
1303         &self,
1304         adt_ty: Ty<'tcx>,
1305         expected: Expectation<'tcx>,
1306         expr_id: hir::HirId,
1307         span: Span,
1308         variant: &'tcx ty::VariantDef,
1309         ast_fields: &'tcx [hir::ExprField<'tcx>],
1310         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1311         expr_span: Span,
1312     ) {
1313         let tcx = self.tcx;
1314
1315         let adt_ty_hint = self
1316             .expected_inputs_for_expected_output(span, expected, adt_ty, &[adt_ty])
1317             .get(0)
1318             .cloned()
1319             .unwrap_or(adt_ty);
1320         // re-link the regions that EIfEO can erase.
1321         self.demand_eqtype(span, adt_ty_hint, adt_ty);
1322
1323         let (substs, adt_kind, kind_name) = match adt_ty.kind() {
1324             ty::Adt(adt, substs) => (substs, adt.adt_kind(), adt.variant_descr()),
1325             _ => span_bug!(span, "non-ADT passed to check_expr_struct_fields"),
1326         };
1327
1328         let mut remaining_fields = variant
1329             .fields
1330             .iter()
1331             .enumerate()
1332             .map(|(i, field)| (field.ident.normalize_to_macros_2_0(), (i, field)))
1333             .collect::<FxHashMap<_, _>>();
1334
1335         let mut seen_fields = FxHashMap::default();
1336
1337         let mut error_happened = false;
1338
1339         // Type-check each field.
1340         for field in ast_fields {
1341             let ident = tcx.adjust_ident(field.ident, variant.def_id);
1342             let field_type = if let Some((i, v_field)) = remaining_fields.remove(&ident) {
1343                 seen_fields.insert(ident, field.span);
1344                 self.write_field_index(field.hir_id, i);
1345
1346                 // We don't look at stability attributes on
1347                 // struct-like enums (yet...), but it's definitely not
1348                 // a bug to have constructed one.
1349                 if adt_kind != AdtKind::Enum {
1350                     tcx.check_stability(v_field.did, Some(expr_id), field.span, None);
1351                 }
1352
1353                 self.field_ty(field.span, v_field, substs)
1354             } else {
1355                 error_happened = true;
1356                 if let Some(prev_span) = seen_fields.get(&ident) {
1357                     tcx.sess.emit_err(FieldMultiplySpecifiedInInitializer {
1358                         span: field.ident.span,
1359                         prev_span: *prev_span,
1360                         ident,
1361                     });
1362                 } else {
1363                     self.report_unknown_field(
1364                         adt_ty, variant, field, ast_fields, kind_name, expr_span,
1365                     );
1366                 }
1367
1368                 tcx.ty_error()
1369             };
1370
1371             // Make sure to give a type to the field even if there's
1372             // an error, so we can continue type-checking.
1373             self.check_expr_coercable_to_type(&field.expr, field_type, None);
1374         }
1375
1376         // Make sure the programmer specified correct number of fields.
1377         if kind_name == "union" {
1378             if ast_fields.len() != 1 {
1379                 struct_span_err!(
1380                     tcx.sess,
1381                     span,
1382                     E0784,
1383                     "union expressions should have exactly one field",
1384                 )
1385                 .emit();
1386             }
1387         }
1388
1389         // If check_expr_struct_fields hit an error, do not attempt to populate
1390         // the fields with the base_expr. This could cause us to hit errors later
1391         // when certain fields are assumed to exist that in fact do not.
1392         if error_happened {
1393             return;
1394         }
1395
1396         if let Some(base_expr) = base_expr {
1397             // FIXME: We are currently creating two branches here in order to maintain
1398             // consistency. But they should be merged as much as possible.
1399             let fru_tys = if self.tcx.features().type_changing_struct_update {
1400                 let base_ty = self.check_expr(base_expr);
1401                 match adt_ty.kind() {
1402                     ty::Adt(adt, substs) if adt.is_struct() => {
1403                         match base_ty.kind() {
1404                             ty::Adt(base_adt, base_subs) if adt == base_adt => {
1405                                 variant
1406                                     .fields
1407                                     .iter()
1408                                     .map(|f| {
1409                                         let fru_ty = self.normalize_associated_types_in(
1410                                             expr_span,
1411                                             self.field_ty(base_expr.span, f, base_subs),
1412                                         );
1413                                         let ident = self.tcx.adjust_ident(f.ident, variant.def_id);
1414                                         if let Some(_) = remaining_fields.remove(&ident) {
1415                                             let target_ty =
1416                                                 self.field_ty(base_expr.span, f, substs);
1417                                             let cause = self.misc(base_expr.span);
1418                                             match self
1419                                                 .at(&cause, self.param_env)
1420                                                 .sup(target_ty, fru_ty)
1421                                             {
1422                                                 Ok(InferOk { obligations, value: () }) => {
1423                                                     self.register_predicates(obligations)
1424                                                 }
1425                                                 // FIXME: Need better diagnostics for `FieldMisMatch` error
1426                                                 Err(_) => self
1427                                                     .report_mismatched_types(
1428                                                         &cause,
1429                                                         target_ty,
1430                                                         fru_ty,
1431                                                         FieldMisMatch(
1432                                                             variant.ident.name,
1433                                                             ident.name,
1434                                                         ),
1435                                                     )
1436                                                     .emit(),
1437                                             }
1438                                         }
1439                                         fru_ty
1440                                     })
1441                                     .collect()
1442                             }
1443                             _ => {
1444                                 return self
1445                                     .report_mismatched_types(
1446                                         &self.misc(base_expr.span),
1447                                         adt_ty,
1448                                         base_ty,
1449                                         Sorts(expected_found_bool(true, adt_ty, base_ty)),
1450                                     )
1451                                     .emit();
1452                             }
1453                         }
1454                     }
1455                     _ => {
1456                         return self
1457                             .tcx
1458                             .sess
1459                             .emit_err(FunctionalRecordUpdateOnNonStruct { span: base_expr.span });
1460                     }
1461                 }
1462             } else {
1463                 self.check_expr_has_type_or_error(base_expr, adt_ty, |_| {
1464                     let base_ty = self.check_expr(base_expr);
1465                     let same_adt = match (adt_ty.kind(), base_ty.kind()) {
1466                         (ty::Adt(adt, _), ty::Adt(base_adt, _)) if adt == base_adt => true,
1467                         _ => false,
1468                     };
1469                     if self.tcx.sess.is_nightly_build() && same_adt {
1470                         feature_err(
1471                             &self.tcx.sess.parse_sess,
1472                             sym::type_changing_struct_update,
1473                             base_expr.span,
1474                             "type changing struct updating is experimental",
1475                         )
1476                         .emit();
1477                     }
1478                 });
1479                 match adt_ty.kind() {
1480                     ty::Adt(adt, substs) if adt.is_struct() => variant
1481                         .fields
1482                         .iter()
1483                         .map(|f| {
1484                             self.normalize_associated_types_in(expr_span, f.ty(self.tcx, substs))
1485                         })
1486                         .collect(),
1487                     _ => {
1488                         return self
1489                             .tcx
1490                             .sess
1491                             .emit_err(FunctionalRecordUpdateOnNonStruct { span: base_expr.span });
1492                     }
1493                 }
1494             };
1495             self.typeck_results.borrow_mut().fru_field_types_mut().insert(expr_id, fru_tys);
1496         } else if kind_name != "union" && !remaining_fields.is_empty() {
1497             let inaccessible_remaining_fields = remaining_fields.iter().any(|(_, (_, field))| {
1498                 !field.vis.is_accessible_from(tcx.parent_module(expr_id).to_def_id(), tcx)
1499             });
1500
1501             if inaccessible_remaining_fields {
1502                 self.report_inaccessible_fields(adt_ty, span);
1503             } else {
1504                 self.report_missing_fields(adt_ty, span, remaining_fields);
1505             }
1506         }
1507     }
1508
1509     fn check_struct_fields_on_error(
1510         &self,
1511         fields: &'tcx [hir::ExprField<'tcx>],
1512         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1513     ) {
1514         for field in fields {
1515             self.check_expr(&field.expr);
1516         }
1517         if let Some(base) = *base_expr {
1518             self.check_expr(&base);
1519         }
1520     }
1521
1522     /// Report an error for a struct field expression when there are fields which aren't provided.
1523     ///
1524     /// ```text
1525     /// error: missing field `you_can_use_this_field` in initializer of `foo::Foo`
1526     ///  --> src/main.rs:8:5
1527     ///   |
1528     /// 8 |     foo::Foo {};
1529     ///   |     ^^^^^^^^ missing `you_can_use_this_field`
1530     ///
1531     /// error: aborting due to previous error
1532     /// ```
1533     fn report_missing_fields(
1534         &self,
1535         adt_ty: Ty<'tcx>,
1536         span: Span,
1537         remaining_fields: FxHashMap<Ident, (usize, &ty::FieldDef)>,
1538     ) {
1539         let len = remaining_fields.len();
1540
1541         let mut displayable_field_names =
1542             remaining_fields.keys().map(|ident| ident.as_str()).collect::<Vec<_>>();
1543
1544         displayable_field_names.sort();
1545
1546         let mut truncated_fields_error = String::new();
1547         let remaining_fields_names = match &displayable_field_names[..] {
1548             [field1] => format!("`{}`", field1),
1549             [field1, field2] => format!("`{}` and `{}`", field1, field2),
1550             [field1, field2, field3] => format!("`{}`, `{}` and `{}`", field1, field2, field3),
1551             _ => {
1552                 truncated_fields_error =
1553                     format!(" and {} other field{}", len - 3, pluralize!(len - 3));
1554                 displayable_field_names
1555                     .iter()
1556                     .take(3)
1557                     .map(|n| format!("`{}`", n))
1558                     .collect::<Vec<_>>()
1559                     .join(", ")
1560             }
1561         };
1562
1563         struct_span_err!(
1564             self.tcx.sess,
1565             span,
1566             E0063,
1567             "missing field{} {}{} in initializer of `{}`",
1568             pluralize!(len),
1569             remaining_fields_names,
1570             truncated_fields_error,
1571             adt_ty
1572         )
1573         .span_label(span, format!("missing {}{}", remaining_fields_names, truncated_fields_error))
1574         .emit();
1575     }
1576
1577     /// Report an error for a struct field expression when there are invisible fields.
1578     ///
1579     /// ```text
1580     /// error: cannot construct `Foo` with struct literal syntax due to inaccessible fields
1581     ///  --> src/main.rs:8:5
1582     ///   |
1583     /// 8 |     foo::Foo {};
1584     ///   |     ^^^^^^^^
1585     ///
1586     /// error: aborting due to previous error
1587     /// ```
1588     fn report_inaccessible_fields(&self, adt_ty: Ty<'tcx>, span: Span) {
1589         self.tcx.sess.span_err(
1590             span,
1591             &format!(
1592                 "cannot construct `{}` with struct literal syntax due to inaccessible fields",
1593                 adt_ty,
1594             ),
1595         );
1596     }
1597
1598     fn report_unknown_field(
1599         &self,
1600         ty: Ty<'tcx>,
1601         variant: &'tcx ty::VariantDef,
1602         field: &hir::ExprField<'_>,
1603         skip_fields: &[hir::ExprField<'_>],
1604         kind_name: &str,
1605         expr_span: Span,
1606     ) {
1607         if variant.is_recovered() {
1608             self.set_tainted_by_errors();
1609             return;
1610         }
1611         let mut err = self.type_error_struct_with_diag(
1612             field.ident.span,
1613             |actual| match ty.kind() {
1614                 ty::Adt(adt, ..) if adt.is_enum() => struct_span_err!(
1615                     self.tcx.sess,
1616                     field.ident.span,
1617                     E0559,
1618                     "{} `{}::{}` has no field named `{}`",
1619                     kind_name,
1620                     actual,
1621                     variant.ident,
1622                     field.ident
1623                 ),
1624                 _ => struct_span_err!(
1625                     self.tcx.sess,
1626                     field.ident.span,
1627                     E0560,
1628                     "{} `{}` has no field named `{}`",
1629                     kind_name,
1630                     actual,
1631                     field.ident
1632                 ),
1633             },
1634             ty,
1635         );
1636         match variant.ctor_kind {
1637             CtorKind::Fn => match ty.kind() {
1638                 ty::Adt(adt, ..) if adt.is_enum() => {
1639                     err.span_label(
1640                         variant.ident.span,
1641                         format!(
1642                             "`{adt}::{variant}` defined here",
1643                             adt = ty,
1644                             variant = variant.ident,
1645                         ),
1646                     );
1647                     err.span_label(field.ident.span, "field does not exist");
1648                     err.span_suggestion_verbose(
1649                         expr_span,
1650                         &format!(
1651                             "`{adt}::{variant}` is a tuple {kind_name}, use the appropriate syntax",
1652                             adt = ty,
1653                             variant = variant.ident,
1654                         ),
1655                         format!(
1656                             "{adt}::{variant}(/* fields */)",
1657                             adt = ty,
1658                             variant = variant.ident,
1659                         ),
1660                         Applicability::HasPlaceholders,
1661                     );
1662                 }
1663                 _ => {
1664                     err.span_label(variant.ident.span, format!("`{adt}` defined here", adt = ty));
1665                     err.span_label(field.ident.span, "field does not exist");
1666                     err.span_suggestion_verbose(
1667                         expr_span,
1668                         &format!(
1669                             "`{adt}` is a tuple {kind_name}, use the appropriate syntax",
1670                             adt = ty,
1671                             kind_name = kind_name,
1672                         ),
1673                         format!("{adt}(/* fields */)", adt = ty),
1674                         Applicability::HasPlaceholders,
1675                     );
1676                 }
1677             },
1678             _ => {
1679                 // prevent all specified fields from being suggested
1680                 let skip_fields = skip_fields.iter().map(|x| x.ident.name);
1681                 if let Some(field_name) =
1682                     Self::suggest_field_name(variant, field.ident.name, skip_fields.collect())
1683                 {
1684                     err.span_suggestion(
1685                         field.ident.span,
1686                         "a field with a similar name exists",
1687                         field_name.to_string(),
1688                         Applicability::MaybeIncorrect,
1689                     );
1690                 } else {
1691                     match ty.kind() {
1692                         ty::Adt(adt, ..) => {
1693                             if adt.is_enum() {
1694                                 err.span_label(
1695                                     field.ident.span,
1696                                     format!("`{}::{}` does not have this field", ty, variant.ident),
1697                                 );
1698                             } else {
1699                                 err.span_label(
1700                                     field.ident.span,
1701                                     format!("`{}` does not have this field", ty),
1702                                 );
1703                             }
1704                             let available_field_names = self.available_field_names(variant);
1705                             if !available_field_names.is_empty() {
1706                                 err.note(&format!(
1707                                     "available fields are: {}",
1708                                     self.name_series_display(available_field_names)
1709                                 ));
1710                             }
1711                         }
1712                         _ => bug!("non-ADT passed to report_unknown_field"),
1713                     }
1714                 };
1715             }
1716         }
1717         err.emit();
1718     }
1719
1720     // Return an hint about the closest match in field names
1721     fn suggest_field_name(
1722         variant: &'tcx ty::VariantDef,
1723         field: Symbol,
1724         skip: Vec<Symbol>,
1725     ) -> Option<Symbol> {
1726         let names = variant
1727             .fields
1728             .iter()
1729             .filter_map(|field| {
1730                 // ignore already set fields and private fields from non-local crates
1731                 if skip.iter().any(|&x| x == field.ident.name)
1732                     || (!variant.def_id.is_local() && !field.vis.is_public())
1733                 {
1734                     None
1735                 } else {
1736                     Some(field.ident.name)
1737                 }
1738             })
1739             .collect::<Vec<Symbol>>();
1740
1741         find_best_match_for_name(&names, field, None)
1742     }
1743
1744     fn available_field_names(&self, variant: &'tcx ty::VariantDef) -> Vec<Symbol> {
1745         variant
1746             .fields
1747             .iter()
1748             .filter(|field| {
1749                 let def_scope = self
1750                     .tcx
1751                     .adjust_ident_and_get_scope(field.ident, variant.def_id, self.body_id)
1752                     .1;
1753                 field.vis.is_accessible_from(def_scope, self.tcx)
1754             })
1755             .map(|field| field.ident.name)
1756             .collect()
1757     }
1758
1759     fn name_series_display(&self, names: Vec<Symbol>) -> String {
1760         // dynamic limit, to never omit just one field
1761         let limit = if names.len() == 6 { 6 } else { 5 };
1762         let mut display =
1763             names.iter().take(limit).map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
1764         if names.len() > limit {
1765             display = format!("{} ... and {} others", display, names.len() - limit);
1766         }
1767         display
1768     }
1769
1770     // Check field access expressions
1771     fn check_field(
1772         &self,
1773         expr: &'tcx hir::Expr<'tcx>,
1774         base: &'tcx hir::Expr<'tcx>,
1775         field: Ident,
1776     ) -> Ty<'tcx> {
1777         debug!("check_field(expr: {:?}, base: {:?}, field: {:?})", expr, base, field);
1778         let expr_t = self.check_expr(base);
1779         let expr_t = self.structurally_resolved_type(base.span, expr_t);
1780         let mut private_candidate = None;
1781         let mut autoderef = self.autoderef(expr.span, expr_t);
1782         while let Some((base_t, _)) = autoderef.next() {
1783             debug!("base_t: {:?}", base_t);
1784             match base_t.kind() {
1785                 ty::Adt(base_def, substs) if !base_def.is_enum() => {
1786                     debug!("struct named {:?}", base_t);
1787                     let (ident, def_scope) =
1788                         self.tcx.adjust_ident_and_get_scope(field, base_def.did, self.body_id);
1789                     let fields = &base_def.non_enum_variant().fields;
1790                     if let Some(index) =
1791                         fields.iter().position(|f| f.ident.normalize_to_macros_2_0() == ident)
1792                     {
1793                         let field = &fields[index];
1794                         let field_ty = self.field_ty(expr.span, field, substs);
1795                         // Save the index of all fields regardless of their visibility in case
1796                         // of error recovery.
1797                         self.write_field_index(expr.hir_id, index);
1798                         let adjustments = self.adjust_steps(&autoderef);
1799                         if field.vis.is_accessible_from(def_scope, self.tcx) {
1800                             self.apply_adjustments(base, adjustments);
1801                             self.register_predicates(autoderef.into_obligations());
1802
1803                             self.tcx.check_stability(field.did, Some(expr.hir_id), expr.span, None);
1804                             return field_ty;
1805                         }
1806                         private_candidate = Some((adjustments, base_def.did, field_ty));
1807                     }
1808                 }
1809                 ty::Tuple(tys) => {
1810                     let fstr = field.as_str();
1811                     if let Ok(index) = fstr.parse::<usize>() {
1812                         if fstr == index.to_string() {
1813                             if let Some(field_ty) = tys.get(index) {
1814                                 let adjustments = self.adjust_steps(&autoderef);
1815                                 self.apply_adjustments(base, adjustments);
1816                                 self.register_predicates(autoderef.into_obligations());
1817
1818                                 self.write_field_index(expr.hir_id, index);
1819                                 return field_ty.expect_ty();
1820                             }
1821                         }
1822                     }
1823                 }
1824                 _ => {}
1825             }
1826         }
1827         self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
1828
1829         if let Some((adjustments, did, field_ty)) = private_candidate {
1830             // (#90483) apply adjustments to avoid ExprUseVisitor from
1831             // creating erroneous projection.
1832             self.apply_adjustments(base, adjustments);
1833             self.ban_private_field_access(expr, expr_t, field, did);
1834             return field_ty;
1835         }
1836
1837         if field.name == kw::Empty {
1838         } else if self.method_exists(field, expr_t, expr.hir_id, true) {
1839             self.ban_take_value_of_method(expr, expr_t, field);
1840         } else if !expr_t.is_primitive_ty() {
1841             self.ban_nonexisting_field(field, base, expr, expr_t);
1842         } else {
1843             type_error_struct!(
1844                 self.tcx().sess,
1845                 field.span,
1846                 expr_t,
1847                 E0610,
1848                 "`{}` is a primitive type and therefore doesn't have fields",
1849                 expr_t
1850             )
1851             .emit();
1852         }
1853
1854         self.tcx().ty_error()
1855     }
1856
1857     fn suggest_await_on_field_access(
1858         &self,
1859         err: &mut DiagnosticBuilder<'_>,
1860         field_ident: Ident,
1861         base: &'tcx hir::Expr<'tcx>,
1862         ty: Ty<'tcx>,
1863     ) {
1864         let output_ty = match self.infcx.get_impl_future_output_ty(ty) {
1865             Some(output_ty) => self.resolve_vars_if_possible(output_ty),
1866             _ => return,
1867         };
1868         let mut add_label = true;
1869         if let ty::Adt(def, _) = output_ty.kind() {
1870             // no field access on enum type
1871             if !def.is_enum() {
1872                 if def.non_enum_variant().fields.iter().any(|field| field.ident == field_ident) {
1873                     add_label = false;
1874                     err.span_label(
1875                         field_ident.span,
1876                         "field not available in `impl Future`, but it is available in its `Output`",
1877                     );
1878                     err.span_suggestion_verbose(
1879                         base.span.shrink_to_hi(),
1880                         "consider `await`ing on the `Future` and access the field of its `Output`",
1881                         ".await".to_string(),
1882                         Applicability::MaybeIncorrect,
1883                     );
1884                 }
1885             }
1886         }
1887         if add_label {
1888             err.span_label(field_ident.span, &format!("field not found in `{}`", ty));
1889         }
1890     }
1891
1892     fn ban_nonexisting_field(
1893         &self,
1894         field: Ident,
1895         base: &'tcx hir::Expr<'tcx>,
1896         expr: &'tcx hir::Expr<'tcx>,
1897         expr_t: Ty<'tcx>,
1898     ) {
1899         debug!(
1900             "ban_nonexisting_field: field={:?}, base={:?}, expr={:?}, expr_ty={:?}",
1901             field, base, expr, expr_t
1902         );
1903         let mut err = self.no_such_field_err(field, expr_t);
1904
1905         match *expr_t.peel_refs().kind() {
1906             ty::Array(_, len) => {
1907                 self.maybe_suggest_array_indexing(&mut err, expr, base, field, len);
1908             }
1909             ty::RawPtr(..) => {
1910                 self.suggest_first_deref_field(&mut err, expr, base, field);
1911             }
1912             ty::Adt(def, _) if !def.is_enum() => {
1913                 self.suggest_fields_on_recordish(&mut err, def, field);
1914             }
1915             ty::Param(param_ty) => {
1916                 self.point_at_param_definition(&mut err, param_ty);
1917             }
1918             ty::Opaque(_, _) => {
1919                 self.suggest_await_on_field_access(&mut err, field, base, expr_t.peel_refs());
1920             }
1921             _ => {}
1922         }
1923
1924         if field.name == kw::Await {
1925             // We know by construction that `<expr>.await` is either on Rust 2015
1926             // or results in `ExprKind::Await`. Suggest switching the edition to 2018.
1927             err.note("to `.await` a `Future`, switch to Rust 2018 or later");
1928             err.help(&format!("set `edition = \"{}\"` in `Cargo.toml`", LATEST_STABLE_EDITION));
1929             err.note("for more on editions, read https://doc.rust-lang.org/edition-guide");
1930         }
1931
1932         err.emit();
1933     }
1934
1935     fn ban_private_field_access(
1936         &self,
1937         expr: &hir::Expr<'_>,
1938         expr_t: Ty<'tcx>,
1939         field: Ident,
1940         base_did: DefId,
1941     ) {
1942         let struct_path = self.tcx().def_path_str(base_did);
1943         let kind_name = self.tcx().def_kind(base_did).descr(base_did);
1944         let mut err = struct_span_err!(
1945             self.tcx().sess,
1946             field.span,
1947             E0616,
1948             "field `{}` of {} `{}` is private",
1949             field,
1950             kind_name,
1951             struct_path
1952         );
1953         err.span_label(field.span, "private field");
1954         // Also check if an accessible method exists, which is often what is meant.
1955         if self.method_exists(field, expr_t, expr.hir_id, false) && !self.expr_in_place(expr.hir_id)
1956         {
1957             self.suggest_method_call(
1958                 &mut err,
1959                 &format!("a method `{}` also exists, call it with parentheses", field),
1960                 field,
1961                 expr_t,
1962                 expr,
1963                 None,
1964             );
1965         }
1966         err.emit();
1967     }
1968
1969     fn ban_take_value_of_method(&self, expr: &hir::Expr<'_>, expr_t: Ty<'tcx>, field: Ident) {
1970         let mut err = type_error_struct!(
1971             self.tcx().sess,
1972             field.span,
1973             expr_t,
1974             E0615,
1975             "attempted to take value of method `{}` on type `{}`",
1976             field,
1977             expr_t
1978         );
1979         err.span_label(field.span, "method, not a field");
1980         let expr_is_call =
1981             if let hir::Node::Expr(hir::Expr { kind: ExprKind::Call(callee, _args), .. }) =
1982                 self.tcx.hir().get(self.tcx.hir().get_parent_node(expr.hir_id))
1983             {
1984                 expr.hir_id == callee.hir_id
1985             } else {
1986                 false
1987             };
1988         let expr_snippet =
1989             self.tcx.sess.source_map().span_to_snippet(expr.span).unwrap_or(String::new());
1990         let is_wrapped = expr_snippet.starts_with('(') && expr_snippet.ends_with(')');
1991         let after_open = expr.span.lo() + rustc_span::BytePos(1);
1992         let before_close = expr.span.hi() - rustc_span::BytePos(1);
1993
1994         if expr_is_call && is_wrapped {
1995             err.multipart_suggestion(
1996                 "remove wrapping parentheses to call the method",
1997                 vec![
1998                     (expr.span.with_hi(after_open), String::new()),
1999                     (expr.span.with_lo(before_close), String::new()),
2000                 ],
2001                 Applicability::MachineApplicable,
2002             );
2003         } else if !self.expr_in_place(expr.hir_id) {
2004             // Suggest call parentheses inside the wrapping parentheses
2005             let span = if is_wrapped {
2006                 expr.span.with_lo(after_open).with_hi(before_close)
2007             } else {
2008                 expr.span
2009             };
2010             self.suggest_method_call(
2011                 &mut err,
2012                 "use parentheses to call the method",
2013                 field,
2014                 expr_t,
2015                 expr,
2016                 Some(span),
2017             );
2018         } else {
2019             err.help("methods are immutable and cannot be assigned to");
2020         }
2021
2022         err.emit();
2023     }
2024
2025     fn point_at_param_definition(&self, err: &mut DiagnosticBuilder<'_>, param: ty::ParamTy) {
2026         let generics = self.tcx.generics_of(self.body_id.owner.to_def_id());
2027         let generic_param = generics.type_param(&param, self.tcx);
2028         if let ty::GenericParamDefKind::Type { synthetic: Some(..), .. } = generic_param.kind {
2029             return;
2030         }
2031         let param_def_id = generic_param.def_id;
2032         let param_hir_id = match param_def_id.as_local() {
2033             Some(x) => self.tcx.hir().local_def_id_to_hir_id(x),
2034             None => return,
2035         };
2036         let param_span = self.tcx.hir().span(param_hir_id);
2037         let param_name = self.tcx.hir().ty_param_name(param_hir_id);
2038
2039         err.span_label(param_span, &format!("type parameter '{}' declared here", param_name));
2040     }
2041
2042     fn suggest_fields_on_recordish(
2043         &self,
2044         err: &mut DiagnosticBuilder<'_>,
2045         def: &'tcx ty::AdtDef,
2046         field: Ident,
2047     ) {
2048         if let Some(suggested_field_name) =
2049             Self::suggest_field_name(def.non_enum_variant(), field.name, vec![])
2050         {
2051             err.span_suggestion(
2052                 field.span,
2053                 "a field with a similar name exists",
2054                 suggested_field_name.to_string(),
2055                 Applicability::MaybeIncorrect,
2056             );
2057         } else {
2058             err.span_label(field.span, "unknown field");
2059             let struct_variant_def = def.non_enum_variant();
2060             let field_names = self.available_field_names(struct_variant_def);
2061             if !field_names.is_empty() {
2062                 err.note(&format!(
2063                     "available fields are: {}",
2064                     self.name_series_display(field_names),
2065                 ));
2066             }
2067         }
2068     }
2069
2070     fn maybe_suggest_array_indexing(
2071         &self,
2072         err: &mut DiagnosticBuilder<'_>,
2073         expr: &hir::Expr<'_>,
2074         base: &hir::Expr<'_>,
2075         field: Ident,
2076         len: &ty::Const<'tcx>,
2077     ) {
2078         if let (Some(len), Ok(user_index)) =
2079             (len.try_eval_usize(self.tcx, self.param_env), field.as_str().parse::<u64>())
2080         {
2081             if let Ok(base) = self.tcx.sess.source_map().span_to_snippet(base.span) {
2082                 let help = "instead of using tuple indexing, use array indexing";
2083                 let suggestion = format!("{}[{}]", base, field);
2084                 let applicability = if len < user_index {
2085                     Applicability::MachineApplicable
2086                 } else {
2087                     Applicability::MaybeIncorrect
2088                 };
2089                 err.span_suggestion(expr.span, help, suggestion, applicability);
2090             }
2091         }
2092     }
2093
2094     fn suggest_first_deref_field(
2095         &self,
2096         err: &mut DiagnosticBuilder<'_>,
2097         expr: &hir::Expr<'_>,
2098         base: &hir::Expr<'_>,
2099         field: Ident,
2100     ) {
2101         if let Ok(base) = self.tcx.sess.source_map().span_to_snippet(base.span) {
2102             let msg = format!("`{}` is a raw pointer; try dereferencing it", base);
2103             let suggestion = format!("(*{}).{}", base, field);
2104             err.span_suggestion(expr.span, &msg, suggestion, Applicability::MaybeIncorrect);
2105         }
2106     }
2107
2108     fn no_such_field_err(
2109         &self,
2110         field: Ident,
2111         expr_t: &'tcx ty::TyS<'tcx>,
2112     ) -> DiagnosticBuilder<'_> {
2113         let span = field.span;
2114         debug!("no_such_field_err(span: {:?}, field: {:?}, expr_t: {:?})", span, field, expr_t);
2115
2116         let mut err = type_error_struct!(
2117             self.tcx().sess,
2118             field.span,
2119             expr_t,
2120             E0609,
2121             "no field `{}` on type `{}`",
2122             field,
2123             expr_t
2124         );
2125
2126         // try to add a suggestion in case the field is a nested field of a field of the Adt
2127         if let Some((fields, substs)) = self.get_field_candidates(span, &expr_t) {
2128             for candidate_field in fields.iter() {
2129                 if let Some(field_path) =
2130                     self.check_for_nested_field(span, field, candidate_field, substs, vec![])
2131                 {
2132                     let field_path_str = field_path
2133                         .iter()
2134                         .map(|id| id.name.to_ident_string())
2135                         .collect::<Vec<String>>()
2136                         .join(".");
2137                     debug!("field_path_str: {:?}", field_path_str);
2138
2139                     err.span_suggestion_verbose(
2140                         field.span.shrink_to_lo(),
2141                         "one of the expressions' fields has a field of the same name",
2142                         format!("{}.", field_path_str),
2143                         Applicability::MaybeIncorrect,
2144                     );
2145                 }
2146             }
2147         }
2148         err
2149     }
2150
2151     fn get_field_candidates(
2152         &self,
2153         span: Span,
2154         base_t: Ty<'tcx>,
2155     ) -> Option<(&Vec<ty::FieldDef>, SubstsRef<'tcx>)> {
2156         debug!("get_field_candidates(span: {:?}, base_t: {:?}", span, base_t);
2157
2158         for (base_t, _) in self.autoderef(span, base_t) {
2159             match base_t.kind() {
2160                 ty::Adt(base_def, substs) if !base_def.is_enum() => {
2161                     let fields = &base_def.non_enum_variant().fields;
2162                     // For compile-time reasons put a limit on number of fields we search
2163                     if fields.len() > 100 {
2164                         return None;
2165                     }
2166                     return Some((fields, substs));
2167                 }
2168                 _ => {}
2169             }
2170         }
2171         None
2172     }
2173
2174     /// This method is called after we have encountered a missing field error to recursively
2175     /// search for the field
2176     fn check_for_nested_field(
2177         &self,
2178         span: Span,
2179         target_field: Ident,
2180         candidate_field: &ty::FieldDef,
2181         subst: SubstsRef<'tcx>,
2182         mut field_path: Vec<Ident>,
2183     ) -> Option<Vec<Ident>> {
2184         debug!(
2185             "check_for_nested_field(span: {:?}, candidate_field: {:?}, field_path: {:?}",
2186             span, candidate_field, field_path
2187         );
2188
2189         if candidate_field.ident == target_field {
2190             Some(field_path)
2191         } else if field_path.len() > 3 {
2192             // For compile-time reasons and to avoid infinite recursion we only check for fields
2193             // up to a depth of three
2194             None
2195         } else {
2196             // recursively search fields of `candidate_field` if it's a ty::Adt
2197
2198             field_path.push(candidate_field.ident.normalize_to_macros_2_0());
2199             let field_ty = candidate_field.ty(self.tcx, subst);
2200             if let Some((nested_fields, subst)) = self.get_field_candidates(span, &field_ty) {
2201                 for field in nested_fields.iter() {
2202                     let ident = field.ident.normalize_to_macros_2_0();
2203                     if ident == target_field {
2204                         return Some(field_path);
2205                     } else {
2206                         let field_path = field_path.clone();
2207                         if let Some(path) = self.check_for_nested_field(
2208                             span,
2209                             target_field,
2210                             field,
2211                             subst,
2212                             field_path,
2213                         ) {
2214                             return Some(path);
2215                         }
2216                     }
2217                 }
2218             }
2219             None
2220         }
2221     }
2222
2223     fn check_expr_index(
2224         &self,
2225         base: &'tcx hir::Expr<'tcx>,
2226         idx: &'tcx hir::Expr<'tcx>,
2227         expr: &'tcx hir::Expr<'tcx>,
2228     ) -> Ty<'tcx> {
2229         let base_t = self.check_expr(&base);
2230         let idx_t = self.check_expr(&idx);
2231
2232         if base_t.references_error() {
2233             base_t
2234         } else if idx_t.references_error() {
2235             idx_t
2236         } else {
2237             let base_t = self.structurally_resolved_type(base.span, base_t);
2238             match self.lookup_indexing(expr, base, base_t, idx, idx_t) {
2239                 Some((index_ty, element_ty)) => {
2240                     // two-phase not needed because index_ty is never mutable
2241                     self.demand_coerce(idx, idx_t, index_ty, None, AllowTwoPhase::No);
2242                     element_ty
2243                 }
2244                 None => {
2245                     let mut err = type_error_struct!(
2246                         self.tcx.sess,
2247                         expr.span,
2248                         base_t,
2249                         E0608,
2250                         "cannot index into a value of type `{}`",
2251                         base_t
2252                     );
2253                     // Try to give some advice about indexing tuples.
2254                     if let ty::Tuple(..) = base_t.kind() {
2255                         let mut needs_note = true;
2256                         // If the index is an integer, we can show the actual
2257                         // fixed expression:
2258                         if let ExprKind::Lit(ref lit) = idx.kind {
2259                             if let ast::LitKind::Int(i, ast::LitIntType::Unsuffixed) = lit.node {
2260                                 let snip = self.tcx.sess.source_map().span_to_snippet(base.span);
2261                                 if let Ok(snip) = snip {
2262                                     err.span_suggestion(
2263                                         expr.span,
2264                                         "to access tuple elements, use",
2265                                         format!("{}.{}", snip, i),
2266                                         Applicability::MachineApplicable,
2267                                     );
2268                                     needs_note = false;
2269                                 }
2270                             }
2271                         }
2272                         if needs_note {
2273                             err.help(
2274                                 "to access tuple elements, use tuple indexing \
2275                                         syntax (e.g., `tuple.0`)",
2276                             );
2277                         }
2278                     }
2279                     err.emit();
2280                     self.tcx.ty_error()
2281                 }
2282             }
2283         }
2284     }
2285
2286     fn check_expr_yield(
2287         &self,
2288         value: &'tcx hir::Expr<'tcx>,
2289         expr: &'tcx hir::Expr<'tcx>,
2290         src: &'tcx hir::YieldSource,
2291     ) -> Ty<'tcx> {
2292         match self.resume_yield_tys {
2293             Some((resume_ty, yield_ty)) => {
2294                 self.check_expr_coercable_to_type(&value, yield_ty, None);
2295
2296                 resume_ty
2297             }
2298             // Given that this `yield` expression was generated as a result of lowering a `.await`,
2299             // we know that the yield type must be `()`; however, the context won't contain this
2300             // information. Hence, we check the source of the yield expression here and check its
2301             // value's type against `()` (this check should always hold).
2302             None if src.is_await() => {
2303                 self.check_expr_coercable_to_type(&value, self.tcx.mk_unit(), None);
2304                 self.tcx.mk_unit()
2305             }
2306             _ => {
2307                 self.tcx.sess.emit_err(YieldExprOutsideOfGenerator { span: expr.span });
2308                 // Avoid expressions without types during writeback (#78653).
2309                 self.check_expr(value);
2310                 self.tcx.mk_unit()
2311             }
2312         }
2313     }
2314
2315     fn check_expr_asm_operand(&self, expr: &'tcx hir::Expr<'tcx>, is_input: bool) {
2316         let needs = if is_input { Needs::None } else { Needs::MutPlace };
2317         let ty = self.check_expr_with_needs(expr, needs);
2318         self.require_type_is_sized(ty, expr.span, traits::InlineAsmSized);
2319
2320         if !is_input && !expr.is_syntactic_place_expr() {
2321             let mut err = self.tcx.sess.struct_span_err(expr.span, "invalid asm output");
2322             err.span_label(expr.span, "cannot assign to this expression");
2323             err.emit();
2324         }
2325
2326         // If this is an input value, we require its type to be fully resolved
2327         // at this point. This allows us to provide helpful coercions which help
2328         // pass the type candidate list in a later pass.
2329         //
2330         // We don't require output types to be resolved at this point, which
2331         // allows them to be inferred based on how they are used later in the
2332         // function.
2333         if is_input {
2334             let ty = self.structurally_resolved_type(expr.span, &ty);
2335             match *ty.kind() {
2336                 ty::FnDef(..) => {
2337                     let fnptr_ty = self.tcx.mk_fn_ptr(ty.fn_sig(self.tcx));
2338                     self.demand_coerce(expr, ty, fnptr_ty, None, AllowTwoPhase::No);
2339                 }
2340                 ty::Ref(_, base_ty, mutbl) => {
2341                     let ptr_ty = self.tcx.mk_ptr(ty::TypeAndMut { ty: base_ty, mutbl });
2342                     self.demand_coerce(expr, ty, ptr_ty, None, AllowTwoPhase::No);
2343                 }
2344                 _ => {}
2345             }
2346         }
2347     }
2348
2349     fn check_expr_asm(&self, asm: &'tcx hir::InlineAsm<'tcx>) -> Ty<'tcx> {
2350         for (op, _op_sp) in asm.operands {
2351             match op {
2352                 hir::InlineAsmOperand::In { expr, .. } => {
2353                     self.check_expr_asm_operand(expr, true);
2354                 }
2355                 hir::InlineAsmOperand::Out { expr: Some(expr), .. }
2356                 | hir::InlineAsmOperand::InOut { expr, .. } => {
2357                     self.check_expr_asm_operand(expr, false);
2358                 }
2359                 hir::InlineAsmOperand::Out { expr: None, .. } => {}
2360                 hir::InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
2361                     self.check_expr_asm_operand(in_expr, true);
2362                     if let Some(out_expr) = out_expr {
2363                         self.check_expr_asm_operand(out_expr, false);
2364                     }
2365                 }
2366                 hir::InlineAsmOperand::Const { anon_const } => {
2367                     self.to_const(anon_const);
2368                 }
2369                 hir::InlineAsmOperand::Sym { expr } => {
2370                     self.check_expr(expr);
2371                 }
2372             }
2373         }
2374         if asm.options.contains(ast::InlineAsmOptions::NORETURN) {
2375             self.tcx.types.never
2376         } else {
2377             self.tcx.mk_unit()
2378         }
2379     }
2380 }
2381
2382 pub(super) fn ty_kind_suggestion(ty: Ty<'_>) -> Option<&'static str> {
2383     Some(match ty.kind() {
2384         ty::Bool => "true",
2385         ty::Char => "'a'",
2386         ty::Int(_) | ty::Uint(_) => "42",
2387         ty::Float(_) => "3.14159",
2388         ty::Error(_) | ty::Never => return None,
2389         _ => "value",
2390     })
2391 }