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 super::suggest_call_constructor;
  25 use crate::errors::{AddressOfTemporaryTaken, ReturnStmtOutsideOfFnBody, StructExprNonExhaustive};
  26 use rustc_ast as ast;
  27 use rustc_data_structures::fx::FxHashMap;
  28 use rustc_data_structures::stack::ensure_sufficient_stack;
  29 use rustc_errors::Diagnostic;
  30 use rustc_errors::EmissionGuarantee;
  31 use rustc_errors::ErrorGuaranteed;
  32 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, DiagnosticId};
  33 use rustc_hir as hir;
  34 use rustc_hir::def::{CtorKind, DefKind, Res};
  35 use rustc_hir::def_id::DefId;
  36 use rustc_hir::intravisit::Visitor;
  37 use rustc_hir::lang_items::LangItem;
  38 use rustc_hir::{ExprKind, HirId, QPath};
  39 use rustc_infer::infer;
  40 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  41 use rustc_infer::infer::InferOk;
  42 use rustc_middle::middle::stability;
  43 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AllowTwoPhase};
  44 use rustc_middle::ty::error::ExpectedFound;
  45 use rustc_middle::ty::error::TypeError::{FieldMisMatch, Sorts};
  46 use rustc_middle::ty::subst::SubstsRef;
  47 use rustc_middle::ty::{self, AdtKind, DefIdTree, Ty, TypeFoldable};
  48 use rustc_session::parse::feature_err;
  49 use rustc_span::hygiene::DesugaringKind;
  50 use rustc_span::lev_distance::find_best_match_for_name;
  51 use rustc_span::source_map::Span;
  52 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  53 use rustc_span::{BytePos, Pos};
  54 use rustc_trait_selection::infer::InferCtxtExt;
  55 use rustc_trait_selection::traits::{self, ObligationCauseCode};
  56
  57 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  58     fn check_expr_eq_type(&self, expr: &'tcx hir::Expr<'tcx>, expected: Ty<'tcx>) {
  59         let ty = self.check_expr_with_hint(expr, expected);
  60         self.demand_eqtype(expr.span, expected, ty);
  61     }
  62
  63     pub fn check_expr_has_type_or_error(
  64         &self,
  65         expr: &'tcx hir::Expr<'tcx>,
  66         expected: Ty<'tcx>,
  67         extend_err: impl Fn(&mut Diagnostic),
  68     ) -> Ty<'tcx> {
  69         self.check_expr_meets_expectation_or_error(expr, ExpectHasType(expected), extend_err)
  70     }
  71
  72     fn check_expr_meets_expectation_or_error(
  73         &self,
  74         expr: &'tcx hir::Expr<'tcx>,
  75         expected: Expectation<'tcx>,
  76         extend_err: impl Fn(&mut Diagnostic),
  77     ) -> Ty<'tcx> {
  78         let expected_ty = expected.to_option(&self).unwrap_or(self.tcx.types.bool);
  79         let mut ty = self.check_expr_with_expectation(expr, expected);
  80
  81         // While we don't allow *arbitrary* coercions here, we *do* allow
  82         // coercions from ! to `expected`.
  83         if ty.is_never() {
  84             if let Some(adjustments) = self.typeck_results.borrow().adjustments().get(expr.hir_id) {
  85                 self.tcx().sess.delay_span_bug(
  86                     expr.span,
  87                     "expression with never type wound up being adjusted",
  88                 );
  89                 return if let [Adjustment { kind: Adjust::NeverToAny, target }] = &adjustments[..] {
  90                     target.to_owned()
  91                 } else {
  92                     self.tcx().ty_error()
  93                 };
  94             }
  95
  96             let adj_ty = self.next_ty_var(TypeVariableOrigin {
  97                 kind: TypeVariableOriginKind::AdjustmentType,
  98                 span: expr.span,
  99             });
 100             self.apply_adjustments(
 101                 expr,
 102                 vec![Adjustment { kind: Adjust::NeverToAny, target: adj_ty }],
 103             );
 104             ty = adj_ty;
 105         }
 106
 107         if let Some(mut err) = self.demand_suptype_diag(expr.span, expected_ty, ty) {
 108             let expr = expr.peel_drop_temps();
 109             self.suggest_deref_ref_or_into(&mut err, expr, expected_ty, ty, None);
 110             extend_err(&mut err);
 111             err.emit();
 112         }
 113         ty
 114     }
 115
 116     pub(super) fn check_expr_coercable_to_type(
 117         &self,
 118         expr: &'tcx hir::Expr<'tcx>,
 119         expected: Ty<'tcx>,
 120         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 121     ) -> Ty<'tcx> {
 122         let ty = self.check_expr_with_hint(expr, expected);
 123         // checks don't need two phase
 124         self.demand_coerce(expr, ty, expected, expected_ty_expr, AllowTwoPhase::No)
 125     }
 126
 127     pub(super) fn check_expr_with_hint(
 128         &self,
 129         expr: &'tcx hir::Expr<'tcx>,
 130         expected: Ty<'tcx>,
 131     ) -> Ty<'tcx> {
 132         self.check_expr_with_expectation(expr, ExpectHasType(expected))
 133     }
 134
 135     fn check_expr_with_expectation_and_needs(
 136         &self,
 137         expr: &'tcx hir::Expr<'tcx>,
 138         expected: Expectation<'tcx>,
 139         needs: Needs,
 140     ) -> Ty<'tcx> {
 141         let ty = self.check_expr_with_expectation(expr, expected);
 142
 143         // If the expression is used in a place whether mutable place is required
 144         // e.g. LHS of assignment, perform the conversion.
 145         if let Needs::MutPlace = needs {
 146             self.convert_place_derefs_to_mutable(expr);
 147         }
 148
 149         ty
 150     }
 151
 152     pub(super) fn check_expr(&self, expr: &'tcx hir::Expr<'tcx>) -> Ty<'tcx> {
 153         self.check_expr_with_expectation(expr, NoExpectation)
 154     }
 155
 156     pub(super) fn check_expr_with_needs(
 157         &self,
 158         expr: &'tcx hir::Expr<'tcx>,
 159         needs: Needs,
 160     ) -> Ty<'tcx> {
 161         self.check_expr_with_expectation_and_needs(expr, NoExpectation, needs)
 162     }
 163
 164     /// Invariant:
 165     /// If an expression has any sub-expressions that result in a type error,
 166     /// inspecting that expression's type with `ty.references_error()` will return
 167     /// true. Likewise, if an expression is known to diverge, inspecting its
 168     /// type with `ty::type_is_bot` will return true (n.b.: since Rust is
 169     /// strict, _|_ can appear in the type of an expression that does not,
 170     /// itself, diverge: for example, fn() -> _|_.)
 171     /// Note that inspecting a type's structure *directly* may expose the fact
 172     /// that there are actually multiple representations for `Error`, so avoid
 173     /// that when err needs to be handled differently.
 174     #[instrument(skip(self, expr), level = "debug")]
 175     pub(super) fn check_expr_with_expectation(
 176         &self,
 177         expr: &'tcx hir::Expr<'tcx>,
 178         expected: Expectation<'tcx>,
 179     ) -> Ty<'tcx> {
 180         self.check_expr_with_expectation_and_args(expr, expected, &[])
 181     }
 182
 183     /// Same as `check_expr_with_expectation`, but allows us to pass in the arguments of a
 184     /// `ExprKind::Call` when evaluating its callee when it is an `ExprKind::Path`.
 185     pub(super) fn check_expr_with_expectation_and_args(
 186         &self,
 187         expr: &'tcx hir::Expr<'tcx>,
 188         expected: Expectation<'tcx>,
 189         args: &'tcx [hir::Expr<'tcx>],
 190     ) -> Ty<'tcx> {
 191         if self.tcx().sess.verbose() {
 192             // make this code only run with -Zverbose because it is probably slow
 193             if let Ok(lint_str) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 194                 if !lint_str.contains('\n') {
 195                     debug!("expr text: {lint_str}");
 196                 } else {
 197                     let mut lines = lint_str.lines();
 198                     if let Some(line0) = lines.next() {
 199                         let remaining_lines = lines.count();
 200                         debug!("expr text: {line0}");
 201                         debug!("expr text: ...(and {remaining_lines} more lines)");
 202                     }
 203                 }
 204             }
 205         }
 206
 207         // True if `expr` is a `Try::from_ok(())` that is a result of desugaring a try block
 208         // without the final expr (e.g. `try { return; }`). We don't want to generate an
 209         // unreachable_code lint for it since warnings for autogenerated code are confusing.
 210         let is_try_block_generated_unit_expr = match expr.kind {
 211             ExprKind::Call(_, args) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {
 212                 args.len() == 1 && args[0].span.is_desugaring(DesugaringKind::TryBlock)
 213             }
 214
 215             _ => false,
 216         };
 217
 218         // Warn for expressions after diverging siblings.
 219         if !is_try_block_generated_unit_expr {
 220             self.warn_if_unreachable(expr.hir_id, expr.span, "expression");
 221         }
 222
 223         // Hide the outer diverging and has_errors flags.
 224         let old_diverges = self.diverges.replace(Diverges::Maybe);
 225         let old_has_errors = self.has_errors.replace(false);
 226
 227         let ty = ensure_sufficient_stack(|| match &expr.kind {
 228             hir::ExprKind::Path(
 229                 qpath @ hir::QPath::Resolved(..) | qpath @ hir::QPath::TypeRelative(..),
 230             ) => self.check_expr_path(qpath, expr, args),
 231             _ => self.check_expr_kind(expr, expected),
 232         });
 233
 234         // Warn for non-block expressions with diverging children.
 235         match expr.kind {
 236             ExprKind::Block(..)
 237             | ExprKind::If(..)
 238             | ExprKind::Let(..)
 239             | ExprKind::Loop(..)
 240             | ExprKind::Match(..) => {}
 241             // If `expr` is a result of desugaring the try block and is an ok-wrapped
 242             // diverging expression (e.g. it arose from desugaring of `try { return }`),
 243             // we skip issuing a warning because it is autogenerated code.
 244             ExprKind::Call(..) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {}
 245             ExprKind::Call(callee, _) => self.warn_if_unreachable(expr.hir_id, callee.span, "call"),
 246             ExprKind::MethodCall(segment, ..) => {
 247                 self.warn_if_unreachable(expr.hir_id, segment.ident.span, "call")
 248             }
 249             _ => self.warn_if_unreachable(expr.hir_id, expr.span, "expression"),
 250         }
 251
 252         // Any expression that produces a value of type `!` must have diverged
 253         if ty.is_never() {
 254             self.diverges.set(self.diverges.get() | Diverges::always(expr.span));
 255         }
 256
 257         // Record the type, which applies it effects.
 258         // We need to do this after the warning above, so that
 259         // we don't warn for the diverging expression itself.
 260         self.write_ty(expr.hir_id, ty);
 261
 262         // Combine the diverging and has_error flags.
 263         self.diverges.set(self.diverges.get() | old_diverges);
 264         self.has_errors.set(self.has_errors.get() | old_has_errors);
 265
 266         debug!("type of {} is...", self.tcx.hir().node_to_string(expr.hir_id));
 267         debug!("... {:?}, expected is {:?}", ty, expected);
 268
 269         ty
 270     }
 271
 272     #[instrument(skip(self, expr), level = "debug")]
 273     pub(super) fn check_expr_kind(
 274         &self,
 275         expr: &'tcx hir::Expr<'tcx>,
 276         expected: Expectation<'tcx>,
 277     ) -> Ty<'tcx> {
 278         trace!("expr={:#?}", expr);
 279
 280         let tcx = self.tcx;
 281         match expr.kind {
 282             ExprKind::Box(subexpr) => self.check_expr_box(subexpr, expected),
 283             ExprKind::Lit(ref lit) => self.check_lit(&lit, expected),
 284             ExprKind::Binary(op, lhs, rhs) => self.check_binop(expr, op, lhs, rhs),
 285             ExprKind::Assign(lhs, rhs, span) => {
 286                 self.check_expr_assign(expr, expected, lhs, rhs, span)
 287             }
 288             ExprKind::AssignOp(op, lhs, rhs) => self.check_binop_assign(expr, op, lhs, rhs),
 289             ExprKind::Unary(unop, oprnd) => self.check_expr_unary(unop, oprnd, expected, expr),
 290             ExprKind::AddrOf(kind, mutbl, oprnd) => {
 291                 self.check_expr_addr_of(kind, mutbl, oprnd, expected, expr)
 292             }
 293             ExprKind::Path(QPath::LangItem(lang_item, _, hir_id)) => {
 294                 self.check_lang_item_path(lang_item, expr, hir_id)
 295             }
 296             ExprKind::Path(ref qpath) => self.check_expr_path(qpath, expr, &[]),
 297             ExprKind::InlineAsm(asm) => self.check_expr_asm(asm),
 298             ExprKind::Break(destination, ref expr_opt) => {
 299                 self.check_expr_break(destination, expr_opt.as_deref(), expr)
 300             }
 301             ExprKind::Continue(destination) => {
 302                 if destination.target_id.is_ok() {
 303                     tcx.types.never
 304                 } else {
 305                     // There was an error; make type-check fail.
 306                     tcx.ty_error()
 307                 }
 308             }
 309             ExprKind::Ret(ref expr_opt) => self.check_expr_return(expr_opt.as_deref(), expr),
 310             ExprKind::Let(let_expr) => self.check_expr_let(let_expr),
 311             ExprKind::Loop(body, _, source, _) => {
 312                 self.check_expr_loop(body, source, expected, expr)
 313             }
 314             ExprKind::Match(discrim, arms, match_src) => {
 315                 self.check_match(expr, &discrim, arms, expected, match_src)
 316             }
 317             ExprKind::Closure(capture, decl, body_id, _, gen) => {
 318                 self.check_expr_closure(expr, capture, &decl, body_id, gen, expected)
 319             }
 320             ExprKind::Block(body, _) => self.check_block_with_expected(&body, expected),
 321             ExprKind::Call(callee, args) => self.check_call(expr, &callee, args, expected),
 322             ExprKind::MethodCall(segment, args, _) => {
 323                 self.check_method_call(expr, segment, args, expected)
 324             }
 325             ExprKind::Cast(e, t) => self.check_expr_cast(e, t, expr),
 326             ExprKind::Type(e, t) => {
 327                 let ty = self.to_ty_saving_user_provided_ty(&t);
 328                 self.check_expr_eq_type(&e, ty);
 329                 ty
 330             }
 331             ExprKind::If(cond, then_expr, opt_else_expr) => {
 332                 self.check_then_else(cond, then_expr, opt_else_expr, expr.span, expected)
 333             }
 334             ExprKind::DropTemps(e) => self.check_expr_with_expectation(e, expected),
 335             ExprKind::Array(args) => self.check_expr_array(args, expected, expr),
 336             ExprKind::ConstBlock(ref anon_const) => {
 337                 self.check_expr_const_block(anon_const, expected, expr)
 338             }
 339             ExprKind::Repeat(element, ref count) => {
 340                 self.check_expr_repeat(element, count, expected, expr)
 341             }
 342             ExprKind::Tup(elts) => self.check_expr_tuple(elts, expected, expr),
 343             ExprKind::Struct(qpath, fields, ref base_expr) => {
 344                 self.check_expr_struct(expr, expected, qpath, fields, base_expr)
 345             }
 346             ExprKind::Field(base, field) => self.check_field(expr, &base, field),
 347             ExprKind::Index(base, idx) => self.check_expr_index(base, idx, expr),
 348             ExprKind::Yield(value, ref src) => self.check_expr_yield(value, expr, src),
 349             hir::ExprKind::Err => tcx.ty_error(),
 350         }
 351     }
 352
 353     fn check_expr_box(&self, expr: &'tcx hir::Expr<'tcx>, expected: Expectation<'tcx>) -> Ty<'tcx> {
 354         let expected_inner = expected.to_option(self).map_or(NoExpectation, |ty| match ty.kind() {
 355             ty::Adt(def, _) if def.is_box() => Expectation::rvalue_hint(self, ty.boxed_ty()),
 356             _ => NoExpectation,
 357         });
 358         let referent_ty = self.check_expr_with_expectation(expr, expected_inner);
 359         self.require_type_is_sized(referent_ty, expr.span, traits::SizedBoxType);
 360         self.tcx.mk_box(referent_ty)
 361     }
 362
 363     fn check_expr_unary(
 364         &self,
 365         unop: hir::UnOp,
 366         oprnd: &'tcx hir::Expr<'tcx>,
 367         expected: Expectation<'tcx>,
 368         expr: &'tcx hir::Expr<'tcx>,
 369     ) -> Ty<'tcx> {
 370         let tcx = self.tcx;
 371         let expected_inner = match unop {
 372             hir::UnOp::Not | hir::UnOp::Neg => expected,
 373             hir::UnOp::Deref => NoExpectation,
 374         };
 375         let mut oprnd_t = self.check_expr_with_expectation(&oprnd, expected_inner);
 376
 377         if !oprnd_t.references_error() {
 378             oprnd_t = self.structurally_resolved_type(expr.span, oprnd_t);
 379             match unop {
 380                 hir::UnOp::Deref => {
 381                     if let Some(ty) = self.lookup_derefing(expr, oprnd, oprnd_t) {
 382                         oprnd_t = ty;
 383                     } else {
 384                         let mut err = type_error_struct!(
 385                             tcx.sess,
 386                             expr.span,
 387                             oprnd_t,
 388                             E0614,
 389                             "type `{oprnd_t}` cannot be dereferenced",
 390                         );
 391                         let sp = tcx.sess.source_map().start_point(expr.span);
 392                         if let Some(sp) =
 393                             tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
 394                         {
 395                             tcx.sess.parse_sess.expr_parentheses_needed(&mut err, *sp);
 396                         }
 397                         err.emit();
 398                         oprnd_t = tcx.ty_error();
 399                     }
 400                 }
 401                 hir::UnOp::Not => {
 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_integral() || *oprnd_t.kind() == ty::Bool) {
 405                         oprnd_t = result;
 406                     }
 407                 }
 408                 hir::UnOp::Neg => {
 409                     let result = self.check_user_unop(expr, oprnd_t, unop);
 410                     // If it's builtin, we can reuse the type, this helps inference.
 411                     if !oprnd_t.is_numeric() {
 412                         oprnd_t = result;
 413                     }
 414                 }
 415             }
 416         }
 417         oprnd_t
 418     }
 419
 420     fn check_expr_addr_of(
 421         &self,
 422         kind: hir::BorrowKind,
 423         mutbl: hir::Mutability,
 424         oprnd: &'tcx hir::Expr<'tcx>,
 425         expected: Expectation<'tcx>,
 426         expr: &'tcx hir::Expr<'tcx>,
 427     ) -> Ty<'tcx> {
 428         let hint = expected.only_has_type(self).map_or(NoExpectation, |ty| {
 429             match ty.kind() {
 430                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 431                     if oprnd.is_syntactic_place_expr() {
 432                         // Places may legitimately have unsized types.
 433                         // For example, dereferences of a fat pointer and
 434                         // the last field of a struct can be unsized.
 435                         ExpectHasType(*ty)
 436                     } else {
 437                         Expectation::rvalue_hint(self, *ty)
 438                     }
 439                 }
 440                 _ => NoExpectation,
 441             }
 442         });
 443         let ty =
 444             self.check_expr_with_expectation_and_needs(&oprnd, hint, Needs::maybe_mut_place(mutbl));
 445
 446         let tm = ty::TypeAndMut { ty, mutbl };
 447         match kind {
 448             _ if tm.ty.references_error() => self.tcx.ty_error(),
 449             hir::BorrowKind::Raw => {
 450                 self.check_named_place_expr(oprnd);
 451                 self.tcx.mk_ptr(tm)
 452             }
 453             hir::BorrowKind::Ref => {
 454                 // Note: at this point, we cannot say what the best lifetime
 455                 // is to use for resulting pointer.  We want to use the
 456                 // shortest lifetime possible so as to avoid spurious borrowck
 457                 // errors.  Moreover, the longest lifetime will depend on the
 458                 // precise details of the value whose address is being taken
 459                 // (and how long it is valid), which we don't know yet until
 460                 // type inference is complete.
 461                 //
 462                 // Therefore, here we simply generate a region variable. The
 463                 // region inferencer will then select a suitable value.
 464                 // Finally, borrowck will infer the value of the region again,
 465                 // this time with enough precision to check that the value
 466                 // whose address was taken can actually be made to live as long
 467                 // as it needs to live.
 468                 let region = self.next_region_var(infer::AddrOfRegion(expr.span));
 469                 self.tcx.mk_ref(region, tm)
 470             }
 471         }
 472     }
 473
 474     /// Does this expression refer to a place that either:
 475     /// * Is based on a local or static.
 476     /// * Contains a dereference
 477     /// Note that the adjustments for the children of `expr` should already
 478     /// have been resolved.
 479     fn check_named_place_expr(&self, oprnd: &'tcx hir::Expr<'tcx>) {
 480         let is_named = oprnd.is_place_expr(|base| {
 481             // Allow raw borrows if there are any deref adjustments.
 482             //
 483             // const VAL: (i32,) = (0,);
 484             // const REF: &(i32,) = &(0,);
 485             //
 486             // &raw const VAL.0;            // ERROR
 487             // &raw const REF.0;            // OK, same as &raw const (*REF).0;
 488             //
 489             // This is maybe too permissive, since it allows
 490             // `let u = &raw const Box::new((1,)).0`, which creates an
 491             // immediately dangling raw pointer.
 492             self.typeck_results
 493                 .borrow()
 494                 .adjustments()
 495                 .get(base.hir_id)
 496                 .map_or(false, |x| x.iter().any(|adj| matches!(adj.kind, Adjust::Deref(_))))
 497         });
 498         if !is_named {
 499             self.tcx.sess.emit_err(AddressOfTemporaryTaken { span: oprnd.span });
 500         }
 501     }
 502
 503     fn check_lang_item_path(
 504         &self,
 505         lang_item: hir::LangItem,
 506         expr: &'tcx hir::Expr<'tcx>,
 507         hir_id: Option<hir::HirId>,
 508     ) -> Ty<'tcx> {
 509         self.resolve_lang_item_path(lang_item, expr.span, expr.hir_id, hir_id).1
 510     }
 511
 512     pub(crate) fn check_expr_path(
 513         &self,
 514         qpath: &'tcx hir::QPath<'tcx>,
 515         expr: &'tcx hir::Expr<'tcx>,
 516         args: &'tcx [hir::Expr<'tcx>],
 517     ) -> Ty<'tcx> {
 518         let tcx = self.tcx;
 519         let (res, opt_ty, segs) =
 520             self.resolve_ty_and_res_fully_qualified_call(qpath, expr.hir_id, expr.span);
 521         let ty = match res {
 522             Res::Err => {
 523                 self.set_tainted_by_errors();
 524                 tcx.ty_error()
 525             }
 526             Res::Def(DefKind::Ctor(_, CtorKind::Fictive), _) => {
 527                 report_unexpected_variant_res(tcx, res, expr.span);
 528                 tcx.ty_error()
 529             }
 530             _ => self.instantiate_value_path(segs, opt_ty, res, expr.span, expr.hir_id).0,
 531         };
 532
 533         if let ty::FnDef(..) = ty.kind() {
 534             let fn_sig = ty.fn_sig(tcx);
 535             if !tcx.features().unsized_fn_params {
 536                 // We want to remove some Sized bounds from std functions,
 537                 // but don't want to expose the removal to stable Rust.
 538                 // i.e., we don't want to allow
 539                 //
 540                 // ```rust
 541                 // drop as fn(str);
 542                 // ```
 543                 //
 544                 // to work in stable even if the Sized bound on `drop` is relaxed.
 545                 for i in 0..fn_sig.inputs().skip_binder().len() {
 546                     // We just want to check sizedness, so instead of introducing
 547                     // placeholder lifetimes with probing, we just replace higher lifetimes
 548                     // with fresh vars.
 549                     let span = args.get(i).map(|a| a.span).unwrap_or(expr.span);
 550                     let input = self
 551                         .replace_bound_vars_with_fresh_vars(
 552                             span,
 553                             infer::LateBoundRegionConversionTime::FnCall,
 554                             fn_sig.input(i),
 555                         )
 556                         .0;
 557                     self.require_type_is_sized_deferred(
 558                         input,
 559                         span,
 560                         traits::SizedArgumentType(None),
 561                     );
 562                 }
 563             }
 564             // Here we want to prevent struct constructors from returning unsized types.
 565             // There were two cases this happened: fn pointer coercion in stable
 566             // and usual function call in presence of unsized_locals.
 567             // Also, as we just want to check sizedness, instead of introducing
 568             // placeholder lifetimes with probing, we just replace higher lifetimes
 569             // with fresh vars.
 570             let output = self
 571                 .replace_bound_vars_with_fresh_vars(
 572                     expr.span,
 573                     infer::LateBoundRegionConversionTime::FnCall,
 574                     fn_sig.output(),
 575                 )
 576                 .0;
 577             self.require_type_is_sized_deferred(output, expr.span, traits::SizedReturnType);
 578         }
 579
 580         // We always require that the type provided as the value for
 581         // a type parameter outlives the moment of instantiation.
 582         let substs = self.typeck_results.borrow().node_substs(expr.hir_id);
 583         self.add_wf_bounds(substs, expr);
 584
 585         ty
 586     }
 587
 588     fn check_expr_break(
 589         &self,
 590         destination: hir::Destination,
 591         expr_opt: Option<&'tcx hir::Expr<'tcx>>,
 592         expr: &'tcx hir::Expr<'tcx>,
 593     ) -> Ty<'tcx> {
 594         let tcx = self.tcx;
 595         if let Ok(target_id) = destination.target_id {
 596             let (e_ty, cause);
 597             if let Some(e) = expr_opt {
 598                 // If this is a break with a value, we need to type-check
 599                 // the expression. Get an expected type from the loop context.
 600                 let opt_coerce_to = {
 601                     // We should release `enclosing_breakables` before the `check_expr_with_hint`
 602                     // below, so can't move this block of code to the enclosing scope and share
 603                     // `ctxt` with the second `enclosing_breakables` borrow below.
 604                     let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 605                     match enclosing_breakables.opt_find_breakable(target_id) {
 606                         Some(ctxt) => ctxt.coerce.as_ref().map(|coerce| coerce.expected_ty()),
 607                         None => {
 608                             // Avoid ICE when `break` is inside a closure (#65383).
 609                             return tcx.ty_error_with_message(
 610                                 expr.span,
 611                                 "break was outside loop, but no error was emitted",
 612                             );
 613                         }
 614                     }
 615                 };
 616
 617                 // If the loop context is not a `loop { }`, then break with
 618                 // a value is illegal, and `opt_coerce_to` will be `None`.
 619                 // Just set expectation to error in that case.
 620                 let coerce_to = opt_coerce_to.unwrap_or_else(|| tcx.ty_error());
 621
 622                 // Recurse without `enclosing_breakables` borrowed.
 623                 e_ty = self.check_expr_with_hint(e, coerce_to);
 624                 cause = self.misc(e.span);
 625             } else {
 626                 // Otherwise, this is a break *without* a value. That's
 627                 // always legal, and is equivalent to `break ()`.
 628                 e_ty = tcx.mk_unit();
 629                 cause = self.misc(expr.span);
 630             }
 631
 632             // Now that we have type-checked `expr_opt`, borrow
 633             // the `enclosing_loops` field and let's coerce the
 634             // type of `expr_opt` into what is expected.
 635             let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 636             let Some(ctxt) = enclosing_breakables.opt_find_breakable(target_id) else {
 637                 // Avoid ICE when `break` is inside a closure (#65383).
 638                 return tcx.ty_error_with_message(
 639                     expr.span,
 640                     "break was outside loop, but no error was emitted",
 641                 );
 642             };
 643
 644             if let Some(ref mut coerce) = ctxt.coerce {
 645                 if let Some(ref e) = expr_opt {
 646                     coerce.coerce(self, &cause, e, e_ty);
 647                 } else {
 648                     assert!(e_ty.is_unit());
 649                     let ty = coerce.expected_ty();
 650                     coerce.coerce_forced_unit(
 651                         self,
 652                         &cause,
 653                         &mut |mut err| {
 654                             self.suggest_mismatched_types_on_tail(
 655                                 &mut err, expr, ty, e_ty, target_id,
 656                             );
 657                             if let Some(val) = ty_kind_suggestion(ty) {
 658                                 let label = destination
 659                                     .label
 660                                     .map(|l| format!(" {}", l.ident))
 661                                     .unwrap_or_else(String::new);
 662                                 err.span_suggestion(
 663                                     expr.span,
 664                                     "give it a value of the expected type",
 665                                     format!("break{label} {val}"),
 666                                     Applicability::HasPlaceholders,
 667                                 );
 668                             }
 669                         },
 670                         false,
 671                     );
 672                 }
 673             } else {
 674                 // If `ctxt.coerce` is `None`, we can just ignore
 675                 // the type of the expression.  This is because
 676                 // either this was a break *without* a value, in
 677                 // which case it is always a legal type (`()`), or
 678                 // else an error would have been flagged by the
 679                 // `loops` pass for using break with an expression
 680                 // where you are not supposed to.
 681                 assert!(expr_opt.is_none() || self.tcx.sess.has_errors().is_some());
 682             }
 683
 684             // If we encountered a `break`, then (no surprise) it may be possible to break from the
 685             // loop... unless the value being returned from the loop diverges itself, e.g.
 686             // `break return 5` or `break loop {}`.
 687             ctxt.may_break |= !self.diverges.get().is_always();
 688
 689             // the type of a `break` is always `!`, since it diverges
 690             tcx.types.never
 691         } else {
 692             // Otherwise, we failed to find the enclosing loop;
 693             // this can only happen if the `break` was not
 694             // inside a loop at all, which is caught by the
 695             // loop-checking pass.
 696             let err = self.tcx.ty_error_with_message(
 697                 expr.span,
 698                 "break was outside loop, but no error was emitted",
 699             );
 700
 701             // We still need to assign a type to the inner expression to
 702             // prevent the ICE in #43162.
 703             if let Some(e) = expr_opt {
 704                 self.check_expr_with_hint(e, err);
 705
 706                 // ... except when we try to 'break rust;'.
 707                 // ICE this expression in particular (see #43162).
 708                 if let ExprKind::Path(QPath::Resolved(_, path)) = e.kind {
 709                     if path.segments.len() == 1 && path.segments[0].ident.name == sym::rust {
 710                         fatally_break_rust(self.tcx.sess);
 711                     }
 712                 }
 713             }
 714
 715             // There was an error; make type-check fail.
 716             err
 717         }
 718     }
 719
 720     fn check_expr_return(
 721         &self,
 722         expr_opt: Option<&'tcx hir::Expr<'tcx>>,
 723         expr: &'tcx hir::Expr<'tcx>,
 724     ) -> Ty<'tcx> {
 725         if self.ret_coercion.is_none() {
 726             let mut err = ReturnStmtOutsideOfFnBody {
 727                 span: expr.span,
 728                 encl_body_span: None,
 729                 encl_fn_span: None,
 730             };
 731
 732             let encl_item_id = self.tcx.hir().get_parent_item(expr.hir_id);
 733
 734             if let Some(hir::Node::Item(hir::Item {
 735                 kind: hir::ItemKind::Fn(..),
 736                 span: encl_fn_span,
 737                 ..
 738             }))
 739             | Some(hir::Node::TraitItem(hir::TraitItem {
 740                 kind: hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)),
 741                 span: encl_fn_span,
 742                 ..
 743             }))
 744             | Some(hir::Node::ImplItem(hir::ImplItem {
 745                 kind: hir::ImplItemKind::Fn(..),
 746                 span: encl_fn_span,
 747                 ..
 748             })) = self.tcx.hir().find_by_def_id(encl_item_id)
 749             {
 750                 // We are inside a function body, so reporting "return statement
 751                 // outside of function body" needs an explanation.
 752
 753                 let encl_body_owner_id = self.tcx.hir().enclosing_body_owner(expr.hir_id);
 754
 755                 // If this didn't hold, we would not have to report an error in
 756                 // the first place.
 757                 assert_ne!(hir::HirId::make_owner(encl_item_id), encl_body_owner_id);
 758
 759                 let encl_body_id = self.tcx.hir().body_owned_by(encl_body_owner_id);
 760                 let encl_body = self.tcx.hir().body(encl_body_id);
 761
 762                 err.encl_body_span = Some(encl_body.value.span);
 763                 err.encl_fn_span = Some(*encl_fn_span);
 764             }
 765
 766             self.tcx.sess.emit_err(err);
 767
 768             if let Some(e) = expr_opt {
 769                 // We still have to type-check `e` (issue #86188), but calling
 770                 // `check_return_expr` only works inside fn bodies.
 771                 self.check_expr(e);
 772             }
 773         } else if let Some(e) = expr_opt {
 774             if self.ret_coercion_span.get().is_none() {
 775                 self.ret_coercion_span.set(Some(e.span));
 776             }
 777             self.check_return_expr(e, true);
 778         } else {
 779             let mut coercion = self.ret_coercion.as_ref().unwrap().borrow_mut();
 780             if self.ret_coercion_span.get().is_none() {
 781                 self.ret_coercion_span.set(Some(expr.span));
 782             }
 783             let cause = self.cause(expr.span, ObligationCauseCode::ReturnNoExpression);
 784             if let Some((fn_decl, _)) = self.get_fn_decl(expr.hir_id) {
 785                 coercion.coerce_forced_unit(
 786                     self,
 787                     &cause,
 788                     &mut |db| {
 789                         let span = fn_decl.output.span();
 790                         if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
 791                             db.span_label(
 792                                 span,
 793                                 format!("expected `{snippet}` because of this return type"),
 794                             );
 795                         }
 796                     },
 797                     true,
 798                 );
 799             } else {
 800                 coercion.coerce_forced_unit(self, &cause, &mut |_| (), true);
 801             }
 802         }
 803         self.tcx.types.never
 804     }
 805
 806     /// `explicit_return` is `true` if we're checking an explicit `return expr`,
 807     /// and `false` if we're checking a trailing expression.
 808     pub(super) fn check_return_expr(
 809         &self,
 810         return_expr: &'tcx hir::Expr<'tcx>,
 811         explicit_return: bool,
 812     ) {
 813         let ret_coercion = self.ret_coercion.as_ref().unwrap_or_else(|| {
 814             span_bug!(return_expr.span, "check_return_expr called outside fn body")
 815         });
 816
 817         let ret_ty = ret_coercion.borrow().expected_ty();
 818         let return_expr_ty = self.check_expr_with_hint(return_expr, ret_ty);
 819         let mut span = return_expr.span;
 820         // Use the span of the trailing expression for our cause,
 821         // not the span of the entire function
 822         if !explicit_return {
 823             if let ExprKind::Block(body, _) = return_expr.kind && let Some(last_expr) = body.expr {
 824                 span = last_expr.span;
 825             }
 826         }
 827         ret_coercion.borrow_mut().coerce(
 828             self,
 829             &self.cause(span, ObligationCauseCode::ReturnValue(return_expr.hir_id)),
 830             return_expr,
 831             return_expr_ty,
 832         );
 833     }
 834
 835     pub(crate) fn check_lhs_assignable(
 836         &self,
 837         lhs: &'tcx hir::Expr<'tcx>,
 838         err_code: &'static str,
 839         op_span: Span,
 840         adjust_err: impl FnOnce(&mut DiagnosticBuilder<'tcx, ErrorGuaranteed>),
 841     ) {
 842         if lhs.is_syntactic_place_expr() {
 843             return;
 844         }
 845
 846         // FIXME: Make this use SessionDiagnostic once error codes can be dynamically set.
 847         let mut err = self.tcx.sess.struct_span_err_with_code(
 848             op_span,
 849             "invalid left-hand side of assignment",
 850             DiagnosticId::Error(err_code.into()),
 851         );
 852         err.span_label(lhs.span, "cannot assign to this expression");
 853
 854         self.comes_from_while_condition(lhs.hir_id, |expr| {
 855             err.span_suggestion_verbose(
 856                 expr.span.shrink_to_lo(),
 857                 "you might have meant to use pattern destructuring",
 858                 "let ".to_string(),
 859                 Applicability::MachineApplicable,
 860             );
 861         });
 862
 863         adjust_err(&mut err);
 864
 865         err.emit();
 866     }
 867
 868     // Check if an expression `original_expr_id` comes from the condition of a while loop,
 869     // as opposed from the body of a while loop, which we can naively check by iterating
 870     // parents until we find a loop...
 871     pub(super) fn comes_from_while_condition(
 872         &self,
 873         original_expr_id: HirId,
 874         then: impl FnOnce(&hir::Expr<'_>),
 875     ) {
 876         let mut parent = self.tcx.hir().get_parent_node(original_expr_id);
 877         while let Some(node) = self.tcx.hir().find(parent) {
 878             match node {
 879                 hir::Node::Expr(hir::Expr {
 880                     kind:
 881                         hir::ExprKind::Loop(
 882                             hir::Block {
 883                                 expr:
 884                                     Some(hir::Expr {
 885                                         kind:
 886                                             hir::ExprKind::Match(expr, ..) | hir::ExprKind::If(expr, ..),
 887                                         ..
 888                                     }),
 889                                 ..
 890                             },
 891                             _,
 892                             hir::LoopSource::While,
 893                             _,
 894                         ),
 895                     ..
 896                 }) => {
 897                     // Check if our original expression is a child of the condition of a while loop
 898                     let expr_is_ancestor = std::iter::successors(Some(original_expr_id), |id| {
 899                         self.tcx.hir().find_parent_node(*id)
 900                     })
 901                     .take_while(|id| *id != parent)
 902                     .any(|id| id == expr.hir_id);
 903                     // if it is, then we have a situation like `while Some(0) = value.get(0) {`,
 904                     // where `while let` was more likely intended.
 905                     if expr_is_ancestor {
 906                         then(expr);
 907                     }
 908                     break;
 909                 }
 910                 hir::Node::Item(_)
 911                 | hir::Node::ImplItem(_)
 912                 | hir::Node::TraitItem(_)
 913                 | hir::Node::Crate(_) => break,
 914                 _ => {
 915                     parent = self.tcx.hir().get_parent_node(parent);
 916                 }
 917             }
 918         }
 919     }
 920
 921     // A generic function for checking the 'then' and 'else' clauses in an 'if'
 922     // or 'if-else' expression.
 923     fn check_then_else(
 924         &self,
 925         cond_expr: &'tcx hir::Expr<'tcx>,
 926         then_expr: &'tcx hir::Expr<'tcx>,
 927         opt_else_expr: Option<&'tcx hir::Expr<'tcx>>,
 928         sp: Span,
 929         orig_expected: Expectation<'tcx>,
 930     ) -> Ty<'tcx> {
 931         let cond_ty = self.check_expr_has_type_or_error(cond_expr, self.tcx.types.bool, |_| {});
 932
 933         self.warn_if_unreachable(
 934             cond_expr.hir_id,
 935             then_expr.span,
 936             "block in `if` or `while` expression",
 937         );
 938
 939         let cond_diverges = self.diverges.get();
 940         self.diverges.set(Diverges::Maybe);
 941
 942         let expected = orig_expected.adjust_for_branches(self);
 943         let then_ty = self.check_expr_with_expectation(then_expr, expected);
 944         let then_diverges = self.diverges.get();
 945         self.diverges.set(Diverges::Maybe);
 946
 947         // We've already taken the expected type's preferences
 948         // into account when typing the `then` branch. To figure
 949         // out the initial shot at a LUB, we thus only consider
 950         // `expected` if it represents a *hard* constraint
 951         // (`only_has_type`); otherwise, we just go with a
 952         // fresh type variable.
 953         let coerce_to_ty = expected.coercion_target_type(self, sp);
 954         let mut coerce: DynamicCoerceMany<'_> = CoerceMany::new(coerce_to_ty);
 955
 956         coerce.coerce(self, &self.misc(sp), then_expr, then_ty);
 957
 958         if let Some(else_expr) = opt_else_expr {
 959             let else_ty = if sp.desugaring_kind() == Some(DesugaringKind::LetElse) {
 960                 // todo introduce `check_expr_with_expectation(.., Expectation::LetElse)`
 961                 //   for errors that point to the offending expression rather than the entire block.
 962                 //   We could use `check_expr_eq_type(.., tcx.types.never)`, but then there is no
 963                 //   way to detect that the expected type originated from let-else and provide
 964                 //   a customized error.
 965                 let else_ty = self.check_expr(else_expr);
 966                 let cause = self.cause(else_expr.span, ObligationCauseCode::LetElse);
 967
 968                 if let Some(mut err) =
 969                     self.demand_eqtype_with_origin(&cause, self.tcx.types.never, else_ty)
 970                 {
 971                     err.emit();
 972                     self.tcx.ty_error()
 973                 } else {
 974                     else_ty
 975                 }
 976             } else {
 977                 self.check_expr_with_expectation(else_expr, expected)
 978             };
 979             let else_diverges = self.diverges.get();
 980
 981             let opt_suggest_box_span = self.opt_suggest_box_span(else_ty, orig_expected);
 982             let if_cause =
 983                 self.if_cause(sp, then_expr, else_expr, then_ty, else_ty, opt_suggest_box_span);
 984
 985             coerce.coerce(self, &if_cause, else_expr, else_ty);
 986
 987             // We won't diverge unless both branches do (or the condition does).
 988             self.diverges.set(cond_diverges | then_diverges & else_diverges);
 989         } else {
 990             self.if_fallback_coercion(sp, then_expr, &mut coerce);
 991
 992             // If the condition is false we can't diverge.
 993             self.diverges.set(cond_diverges);
 994         }
 995
 996         let result_ty = coerce.complete(self);
 997         if cond_ty.references_error() { self.tcx.ty_error() } else { result_ty }
 998     }
 999
1000     /// Type check assignment expression `expr` of form `lhs = rhs`.
1001     /// The expected type is `()` and is passed to the function for the purposes of diagnostics.
1002     fn check_expr_assign(
1003         &self,
1004         expr: &'tcx hir::Expr<'tcx>,
1005         expected: Expectation<'tcx>,
1006         lhs: &'tcx hir::Expr<'tcx>,
1007         rhs: &'tcx hir::Expr<'tcx>,
1008         span: Span,
1009     ) -> Ty<'tcx> {
1010         let expected_ty = expected.coercion_target_type(self, expr.span);
1011         if expected_ty == self.tcx.types.bool {
1012             // The expected type is `bool` but this will result in `()` so we can reasonably
1013             // say that the user intended to write `lhs == rhs` instead of `lhs = rhs`.
1014             // The likely cause of this is `if foo = bar { .. }`.
1015             let actual_ty = self.tcx.mk_unit();
1016             let mut err = self.demand_suptype_diag(expr.span, expected_ty, actual_ty).unwrap();
1017             let lhs_ty = self.check_expr(&lhs);
1018             let rhs_ty = self.check_expr(&rhs);
1019             let (applicability, eq) = if self.can_coerce(rhs_ty, lhs_ty) {
1020                 (Applicability::MachineApplicable, true)
1021             } else {
1022                 (Applicability::MaybeIncorrect, false)
1023             };
1024             if !lhs.is_syntactic_place_expr() && !matches!(lhs.kind, hir::ExprKind::Lit(_)) {
1025                 // Do not suggest `if let x = y` as `==` is way more likely to be the intention.
1026                 let hir = self.tcx.hir();
1027                 if let hir::Node::Expr(hir::Expr { kind: ExprKind::If { .. }, .. }) =
1028                     hir.get(hir.get_parent_node(hir.get_parent_node(expr.hir_id)))
1029                 {
1030                     err.span_suggestion_verbose(
1031                         expr.span.shrink_to_lo(),
1032                         "you might have meant to use pattern matching",
1033                         "let ".to_string(),
1034                         applicability,
1035                     );
1036                 };
1037             }
1038             if eq {
1039                 err.span_suggestion_verbose(
1040                     span,
1041                     "you might have meant to compare for equality",
1042                     "==".to_string(),
1043                     applicability,
1044                 );
1045             }
1046
1047             // If the assignment expression itself is ill-formed, don't
1048             // bother emitting another error
1049             if lhs_ty.references_error() || rhs_ty.references_error() {
1050                 err.delay_as_bug()
1051             } else {
1052                 err.emit();
1053             }
1054             return self.tcx.ty_error();
1055         }
1056
1057         let lhs_ty = self.check_expr_with_needs(&lhs, Needs::MutPlace);
1058
1059         let suggest_deref_binop = |err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
1060                                    rhs_ty: Ty<'tcx>| {
1061             if let Some(lhs_deref_ty) = self.deref_once_mutably_for_diagnostic(lhs_ty) {
1062                 // Can only assign if the type is sized, so if `DerefMut` yields a type that is
1063                 // unsized, do not suggest dereferencing it.
1064                 let lhs_deref_ty_is_sized = self
1065                     .infcx
1066                     .type_implements_trait(
1067                         self.tcx.lang_items().sized_trait().unwrap(),
1068                         lhs_deref_ty,
1069                         ty::List::empty(),
1070                         self.param_env,
1071                     )
1072                     .may_apply();
1073                 if lhs_deref_ty_is_sized && self.can_coerce(rhs_ty, lhs_deref_ty) {
1074                     err.span_suggestion_verbose(
1075                         lhs.span.shrink_to_lo(),
1076                         "consider dereferencing here to assign to the mutably borrowed value",
1077                         "*".to_string(),
1078                         Applicability::MachineApplicable,
1079                     );
1080                 }
1081             }
1082         };
1083
1084         self.check_lhs_assignable(lhs, "E0070", span, |err| {
1085             let rhs_ty = self.check_expr(&rhs);
1086             suggest_deref_binop(err, rhs_ty);
1087         });
1088
1089         // This is (basically) inlined `check_expr_coercable_to_type`, but we want
1090         // to suggest an additional fixup here in `suggest_deref_binop`.
1091         let rhs_ty = self.check_expr_with_hint(&rhs, lhs_ty);
1092         if let (_, Some(mut diag)) =
1093             self.demand_coerce_diag(rhs, rhs_ty, lhs_ty, Some(lhs), AllowTwoPhase::No)
1094         {
1095             suggest_deref_binop(&mut diag, rhs_ty);
1096             diag.emit();
1097         }
1098
1099         self.require_type_is_sized(lhs_ty, lhs.span, traits::AssignmentLhsSized);
1100
1101         if lhs_ty.references_error() || rhs_ty.references_error() {
1102             self.tcx.ty_error()
1103         } else {
1104             self.tcx.mk_unit()
1105         }
1106     }
1107
1108     pub(super) fn check_expr_let(&self, let_expr: &'tcx hir::Let<'tcx>) -> Ty<'tcx> {
1109         // for let statements, this is done in check_stmt
1110         let init = let_expr.init;
1111         self.warn_if_unreachable(init.hir_id, init.span, "block in `let` expression");
1112         // otherwise check exactly as a let statement
1113         self.check_decl(let_expr.into());
1114         // but return a bool, for this is a boolean expression
1115         self.tcx.types.bool
1116     }
1117
1118     fn check_expr_loop(
1119         &self,
1120         body: &'tcx hir::Block<'tcx>,
1121         source: hir::LoopSource,
1122         expected: Expectation<'tcx>,
1123         expr: &'tcx hir::Expr<'tcx>,
1124     ) -> Ty<'tcx> {
1125         let coerce = match source {
1126             // you can only use break with a value from a normal `loop { }`
1127             hir::LoopSource::Loop => {
1128                 let coerce_to = expected.coercion_target_type(self, body.span);
1129                 Some(CoerceMany::new(coerce_to))
1130             }
1131
1132             hir::LoopSource::While | hir::LoopSource::ForLoop => None,
1133         };
1134
1135         let ctxt = BreakableCtxt {
1136             coerce,
1137             may_break: false, // Will get updated if/when we find a `break`.
1138         };
1139
1140         let (ctxt, ()) = self.with_breakable_ctxt(expr.hir_id, ctxt, || {
1141             self.check_block_no_value(&body);
1142         });
1143
1144         if ctxt.may_break {
1145             // No way to know whether it's diverging because
1146             // of a `break` or an outer `break` or `return`.
1147             self.diverges.set(Diverges::Maybe);
1148         }
1149
1150         // If we permit break with a value, then result type is
1151         // the LUB of the breaks (possibly ! if none); else, it
1152         // is nil. This makes sense because infinite loops
1153         // (which would have type !) are only possible iff we
1154         // permit break with a value [1].
1155         if ctxt.coerce.is_none() && !ctxt.may_break {
1156             // [1]
1157             self.tcx.sess.delay_span_bug(body.span, "no coercion, but loop may not break");
1158         }
1159         ctxt.coerce.map(|c| c.complete(self)).unwrap_or_else(|| self.tcx.mk_unit())
1160     }
1161
1162     /// Checks a method call.
1163     fn check_method_call(
1164         &self,
1165         expr: &'tcx hir::Expr<'tcx>,
1166         segment: &hir::PathSegment<'_>,
1167         args: &'tcx [hir::Expr<'tcx>],
1168         expected: Expectation<'tcx>,
1169     ) -> Ty<'tcx> {
1170         let rcvr = &args[0];
1171         let rcvr_t = self.check_expr(&rcvr);
1172         // no need to check for bot/err -- callee does that
1173         let rcvr_t = self.structurally_resolved_type(args[0].span, rcvr_t);
1174         let span = segment.ident.span;
1175
1176         let method = match self.lookup_method(rcvr_t, segment, span, expr, rcvr, args) {
1177             Ok(method) => {
1178                 // We could add a "consider `foo::<params>`" suggestion here, but I wasn't able to
1179                 // trigger this codepath causing `structurally_resolved_type` to emit an error.
1180
1181                 self.write_method_call(expr.hir_id, method);
1182                 Ok(method)
1183             }
1184             Err(error) => {
1185                 if segment.ident.name != kw::Empty {
1186                     if let Some(mut err) = self.report_method_error(
1187                         span,
1188                         rcvr_t,
1189                         segment.ident,
1190                         SelfSource::MethodCall(&args[0]),
1191                         error,
1192                         Some(args),
1193                     ) {
1194                         err.emit();
1195                     }
1196                 }
1197                 Err(())
1198             }
1199         };
1200
1201         // Call the generic checker.
1202         self.check_method_argument_types(
1203             span,
1204             expr,
1205             method,
1206             &args[1..],
1207             DontTupleArguments,
1208             expected,
1209         )
1210     }
1211
1212     fn check_expr_cast(
1213         &self,
1214         e: &'tcx hir::Expr<'tcx>,
1215         t: &'tcx hir::Ty<'tcx>,
1216         expr: &'tcx hir::Expr<'tcx>,
1217     ) -> Ty<'tcx> {
1218         // Find the type of `e`. Supply hints based on the type we are casting to,
1219         // if appropriate.
1220         let t_cast = self.to_ty_saving_user_provided_ty(t);
1221         let t_cast = self.resolve_vars_if_possible(t_cast);
1222         let t_expr = self.check_expr_with_expectation(e, ExpectCastableToType(t_cast));
1223         let t_expr = self.resolve_vars_if_possible(t_expr);
1224
1225         // Eagerly check for some obvious errors.
1226         if t_expr.references_error() || t_cast.references_error() {
1227             self.tcx.ty_error()
1228         } else {
1229             // Defer other checks until we're done type checking.
1230             let mut deferred_cast_checks = self.deferred_cast_checks.borrow_mut();
1231             match cast::CastCheck::new(self, e, t_expr, t_cast, t.span, expr.span) {
1232                 Ok(cast_check) => {
1233                     debug!(
1234                         "check_expr_cast: deferring cast from {:?} to {:?}: {:?}",
1235                         t_cast, t_expr, cast_check,
1236                     );
1237                     deferred_cast_checks.push(cast_check);
1238                     t_cast
1239                 }
1240                 Err(_) => self.tcx.ty_error(),
1241             }
1242         }
1243     }
1244
1245     fn check_expr_array(
1246         &self,
1247         args: &'tcx [hir::Expr<'tcx>],
1248         expected: Expectation<'tcx>,
1249         expr: &'tcx hir::Expr<'tcx>,
1250     ) -> Ty<'tcx> {
1251         let element_ty = if !args.is_empty() {
1252             let coerce_to = expected
1253                 .to_option(self)
1254                 .and_then(|uty| match *uty.kind() {
1255                     ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
1256                     _ => None,
1257                 })
1258                 .unwrap_or_else(|| {
1259                     self.next_ty_var(TypeVariableOrigin {
1260                         kind: TypeVariableOriginKind::TypeInference,
1261                         span: expr.span,
1262                     })
1263                 });
1264             let mut coerce = CoerceMany::with_coercion_sites(coerce_to, args);
1265             assert_eq!(self.diverges.get(), Diverges::Maybe);
1266             for e in args {
1267                 let e_ty = self.check_expr_with_hint(e, coerce_to);
1268                 let cause = self.misc(e.span);
1269                 coerce.coerce(self, &cause, e, e_ty);
1270             }
1271             coerce.complete(self)
1272         } else {
1273             self.next_ty_var(TypeVariableOrigin {
1274                 kind: TypeVariableOriginKind::TypeInference,
1275                 span: expr.span,
1276             })
1277         };
1278         self.tcx.mk_array(element_ty, args.len() as u64)
1279     }
1280
1281     fn check_expr_const_block(
1282         &self,
1283         anon_const: &'tcx hir::AnonConst,
1284         expected: Expectation<'tcx>,
1285         _expr: &'tcx hir::Expr<'tcx>,
1286     ) -> Ty<'tcx> {
1287         let body = self.tcx.hir().body(anon_const.body);
1288
1289         // Create a new function context.
1290         let fcx = FnCtxt::new(self, self.param_env.with_const(), body.value.hir_id);
1291         crate::check::GatherLocalsVisitor::new(&fcx).visit_body(body);
1292
1293         let ty = fcx.check_expr_with_expectation(&body.value, expected);
1294         fcx.require_type_is_sized(ty, body.value.span, traits::ConstSized);
1295         fcx.write_ty(anon_const.hir_id, ty);
1296         ty
1297     }
1298
1299     fn check_expr_repeat(
1300         &self,
1301         element: &'tcx hir::Expr<'tcx>,
1302         count: &'tcx hir::ArrayLen,
1303         expected: Expectation<'tcx>,
1304         _expr: &'tcx hir::Expr<'tcx>,
1305     ) -> Ty<'tcx> {
1306         let tcx = self.tcx;
1307         let count = self.array_length_to_const(count);
1308
1309         let uty = match expected {
1310             ExpectHasType(uty) => match *uty.kind() {
1311                 ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
1312                 _ => None,
1313             },
1314             _ => None,
1315         };
1316
1317         let (element_ty, t) = match uty {
1318             Some(uty) => {
1319                 self.check_expr_coercable_to_type(&element, uty, None);
1320                 (uty, uty)
1321             }
1322             None => {
1323                 let ty = self.next_ty_var(TypeVariableOrigin {
1324                     kind: TypeVariableOriginKind::MiscVariable,
1325                     span: element.span,
1326                 });
1327                 let element_ty = self.check_expr_has_type_or_error(&element, ty, |_| {});
1328                 (element_ty, ty)
1329             }
1330         };
1331
1332         if element_ty.references_error() {
1333             return tcx.ty_error();
1334         }
1335
1336         self.check_repeat_element_needs_copy_bound(element, count, element_ty);
1337
1338         tcx.mk_ty(ty::Array(t, count))
1339     }
1340
1341     fn check_repeat_element_needs_copy_bound(
1342         &self,
1343         element: &hir::Expr<'_>,
1344         count: ty::Const<'tcx>,
1345         element_ty: Ty<'tcx>,
1346     ) {
1347         let tcx = self.tcx;
1348         // Actual constants as the repeat element get inserted repeatedly instead of getting copied via Copy.
1349         match &element.kind {
1350             hir::ExprKind::ConstBlock(..) => return,
1351             hir::ExprKind::Path(qpath) => {
1352                 let res = self.typeck_results.borrow().qpath_res(qpath, element.hir_id);
1353                 if let Res::Def(DefKind::Const | DefKind::AssocConst | DefKind::AnonConst, _) = res
1354                 {
1355                     return;
1356                 }
1357             }
1358             _ => {}
1359         }
1360         // If someone calls a const fn, they can extract that call out into a separate constant (or a const
1361         // block in the future), so we check that to tell them that in the diagnostic. Does not affect typeck.
1362         let is_const_fn = match element.kind {
1363             hir::ExprKind::Call(func, _args) => match *self.node_ty(func.hir_id).kind() {
1364                 ty::FnDef(def_id, _) => tcx.is_const_fn(def_id),
1365                 _ => false,
1366             },
1367             _ => false,
1368         };
1369
1370         // If the length is 0, we don't create any elements, so we don't copy any. If the length is 1, we
1371         // don't copy that one element, we move it. Only check for Copy if the length is larger.
1372         if count.try_eval_usize(tcx, self.param_env).map_or(true, |len| len > 1) {
1373             let lang_item = self.tcx.require_lang_item(LangItem::Copy, None);
1374             let code = traits::ObligationCauseCode::RepeatElementCopy { is_const_fn };
1375             self.require_type_meets(element_ty, element.span, code, lang_item);
1376         }
1377     }
1378
1379     fn check_expr_tuple(
1380         &self,
1381         elts: &'tcx [hir::Expr<'tcx>],
1382         expected: Expectation<'tcx>,
1383         expr: &'tcx hir::Expr<'tcx>,
1384     ) -> Ty<'tcx> {
1385         let flds = expected.only_has_type(self).and_then(|ty| {
1386             let ty = self.resolve_vars_with_obligations(ty);
1387             match ty.kind() {
1388                 ty::Tuple(flds) => Some(&flds[..]),
1389                 _ => None,
1390             }
1391         });
1392
1393         let elt_ts_iter = elts.iter().enumerate().map(|(i, e)| match flds {
1394             Some(fs) if i < fs.len() => {
1395                 let ety = fs[i];
1396                 self.check_expr_coercable_to_type(&e, ety, None);
1397                 ety
1398             }
1399             _ => self.check_expr_with_expectation(&e, NoExpectation),
1400         });
1401         let tuple = self.tcx.mk_tup(elt_ts_iter);
1402         if tuple.references_error() {
1403             self.tcx.ty_error()
1404         } else {
1405             self.require_type_is_sized(tuple, expr.span, traits::TupleInitializerSized);
1406             tuple
1407         }
1408     }
1409
1410     fn check_expr_struct(
1411         &self,
1412         expr: &hir::Expr<'_>,
1413         expected: Expectation<'tcx>,
1414         qpath: &QPath<'_>,
1415         fields: &'tcx [hir::ExprField<'tcx>],
1416         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1417     ) -> Ty<'tcx> {
1418         // Find the relevant variant
1419         let Some((variant, adt_ty)) = self.check_struct_path(qpath, expr.hir_id) else {
1420             self.check_struct_fields_on_error(fields, base_expr);
1421             return self.tcx.ty_error();
1422         };
1423
1424         // Prohibit struct expressions when non-exhaustive flag is set.
1425         let adt = adt_ty.ty_adt_def().expect("`check_struct_path` returned non-ADT type");
1426         if !adt.did().is_local() && variant.is_field_list_non_exhaustive() {
1427             self.tcx
1428                 .sess
1429                 .emit_err(StructExprNonExhaustive { span: expr.span, what: adt.variant_descr() });
1430         }
1431
1432         self.check_expr_struct_fields(
1433             adt_ty,
1434             expected,
1435             expr.hir_id,
1436             qpath.span(),
1437             variant,
1438             fields,
1439             base_expr,
1440             expr.span,
1441         );
1442
1443         self.require_type_is_sized(adt_ty, expr.span, traits::StructInitializerSized);
1444         adt_ty
1445     }
1446
1447     fn check_expr_struct_fields(
1448         &self,
1449         adt_ty: Ty<'tcx>,
1450         expected: Expectation<'tcx>,
1451         expr_id: hir::HirId,
1452         span: Span,
1453         variant: &'tcx ty::VariantDef,
1454         ast_fields: &'tcx [hir::ExprField<'tcx>],
1455         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1456         expr_span: Span,
1457     ) {
1458         let tcx = self.tcx;
1459
1460         let expected_inputs =
1461             self.expected_inputs_for_expected_output(span, expected, adt_ty, &[adt_ty]);
1462         let adt_ty_hint = if let Some(expected_inputs) = expected_inputs {
1463             expected_inputs.get(0).cloned().unwrap_or(adt_ty)
1464         } else {
1465             adt_ty
1466         };
1467         // re-link the regions that EIfEO can erase.
1468         self.demand_eqtype(span, adt_ty_hint, adt_ty);
1469
1470         let (substs, adt_kind, kind_name) = match adt_ty.kind() {
1471             ty::Adt(adt, substs) => (substs, adt.adt_kind(), adt.variant_descr()),
1472             _ => span_bug!(span, "non-ADT passed to check_expr_struct_fields"),
1473         };
1474
1475         let mut remaining_fields = variant
1476             .fields
1477             .iter()
1478             .enumerate()
1479             .map(|(i, field)| (field.ident(tcx).normalize_to_macros_2_0(), (i, field)))
1480             .collect::<FxHashMap<_, _>>();
1481
1482         let mut seen_fields = FxHashMap::default();
1483
1484         let mut error_happened = false;
1485
1486         // Type-check each field.
1487         for field in ast_fields {
1488             let ident = tcx.adjust_ident(field.ident, variant.def_id);
1489             let field_type = if let Some((i, v_field)) = remaining_fields.remove(&ident) {
1490                 seen_fields.insert(ident, field.span);
1491                 self.write_field_index(field.hir_id, i);
1492
1493                 // We don't look at stability attributes on
1494                 // struct-like enums (yet...), but it's definitely not
1495                 // a bug to have constructed one.
1496                 if adt_kind != AdtKind::Enum {
1497                     tcx.check_stability(v_field.did, Some(expr_id), field.span, None);
1498                 }
1499
1500                 self.field_ty(field.span, v_field, substs)
1501             } else {
1502                 error_happened = true;
1503                 if let Some(prev_span) = seen_fields.get(&ident) {
1504                     tcx.sess.emit_err(FieldMultiplySpecifiedInInitializer {
1505                         span: field.ident.span,
1506                         prev_span: *prev_span,
1507                         ident,
1508                     });
1509                 } else {
1510                     self.report_unknown_field(
1511                         adt_ty, variant, field, ast_fields, kind_name, expr_span,
1512                     );
1513                 }
1514
1515                 tcx.ty_error()
1516             };
1517
1518             // Make sure to give a type to the field even if there's
1519             // an error, so we can continue type-checking.
1520             self.check_expr_coercable_to_type(&field.expr, field_type, None);
1521         }
1522
1523         // Make sure the programmer specified correct number of fields.
1524         if kind_name == "union" {
1525             if ast_fields.len() != 1 {
1526                 struct_span_err!(
1527                     tcx.sess,
1528                     span,
1529                     E0784,
1530                     "union expressions should have exactly one field",
1531                 )
1532                 .emit();
1533             }
1534         }
1535
1536         // If check_expr_struct_fields hit an error, do not attempt to populate
1537         // the fields with the base_expr. This could cause us to hit errors later
1538         // when certain fields are assumed to exist that in fact do not.
1539         if error_happened {
1540             return;
1541         }
1542
1543         if let Some(base_expr) = base_expr {
1544             // FIXME: We are currently creating two branches here in order to maintain
1545             // consistency. But they should be merged as much as possible.
1546             let fru_tys = if self.tcx.features().type_changing_struct_update {
1547                 let base_ty = self.check_expr(base_expr);
1548                 match adt_ty.kind() {
1549                     ty::Adt(adt, substs) if adt.is_struct() => {
1550                         match base_ty.kind() {
1551                             ty::Adt(base_adt, base_subs) if adt == base_adt => {
1552                                 variant
1553                                     .fields
1554                                     .iter()
1555                                     .map(|f| {
1556                                         let fru_ty = self.normalize_associated_types_in(
1557                                             expr_span,
1558                                             self.field_ty(base_expr.span, f, base_subs),
1559                                         );
1560                                         let ident = self
1561                                             .tcx
1562                                             .adjust_ident(f.ident(self.tcx), variant.def_id);
1563                                         if let Some(_) = remaining_fields.remove(&ident) {
1564                                             let target_ty =
1565                                                 self.field_ty(base_expr.span, f, substs);
1566                                             let cause = self.misc(base_expr.span);
1567                                             match self
1568                                                 .at(&cause, self.param_env)
1569                                                 .sup(target_ty, fru_ty)
1570                                             {
1571                                                 Ok(InferOk { obligations, value: () }) => {
1572                                                     self.register_predicates(obligations)
1573                                                 }
1574                                                 // FIXME: Need better diagnostics for `FieldMisMatch` error
1575                                                 Err(_) => {
1576                                                     self.report_mismatched_types(
1577                                                         &cause,
1578                                                         target_ty,
1579                                                         fru_ty,
1580                                                         FieldMisMatch(variant.name, ident.name),
1581                                                     )
1582                                                     .emit();
1583                                                 }
1584                                             }
1585                                         }
1586                                         fru_ty
1587                                     })
1588                                     .collect()
1589                             }
1590                             _ => {
1591                                 self.report_mismatched_types(
1592                                     &self.misc(base_expr.span),
1593                                     adt_ty,
1594                                     base_ty,
1595                                     Sorts(ExpectedFound::new(true, adt_ty, base_ty)),
1596                                 )
1597                                 .emit();
1598                                 return;
1599                             }
1600                         }
1601                     }
1602                     _ => {
1603                         self.tcx
1604                             .sess
1605                             .emit_err(FunctionalRecordUpdateOnNonStruct { span: base_expr.span });
1606                         return;
1607                     }
1608                 }
1609             } else {
1610                 self.check_expr_has_type_or_error(base_expr, adt_ty, |_| {
1611                     let base_ty = self.typeck_results.borrow().expr_ty(*base_expr);
1612                     let same_adt = match (adt_ty.kind(), base_ty.kind()) {
1613                         (ty::Adt(adt, _), ty::Adt(base_adt, _)) if adt == base_adt => true,
1614                         _ => false,
1615                     };
1616                     if self.tcx.sess.is_nightly_build() && same_adt {
1617                         feature_err(
1618                             &self.tcx.sess.parse_sess,
1619                             sym::type_changing_struct_update,
1620                             base_expr.span,
1621                             "type changing struct updating is experimental",
1622                         )
1623                         .emit();
1624                     }
1625                 });
1626                 match adt_ty.kind() {
1627                     ty::Adt(adt, substs) if adt.is_struct() => variant
1628                         .fields
1629                         .iter()
1630                         .map(|f| {
1631                             self.normalize_associated_types_in(expr_span, f.ty(self.tcx, substs))
1632                         })
1633                         .collect(),
1634                     _ => {
1635                         self.tcx
1636                             .sess
1637                             .emit_err(FunctionalRecordUpdateOnNonStruct { span: base_expr.span });
1638                         return;
1639                     }
1640                 }
1641             };
1642             self.typeck_results.borrow_mut().fru_field_types_mut().insert(expr_id, fru_tys);
1643         } else if kind_name != "union" && !remaining_fields.is_empty() {
1644             let inaccessible_remaining_fields = remaining_fields.iter().any(|(_, (_, field))| {
1645                 !field.vis.is_accessible_from(tcx.parent_module(expr_id).to_def_id(), tcx)
1646             });
1647
1648             if inaccessible_remaining_fields {
1649                 self.report_inaccessible_fields(adt_ty, span);
1650             } else {
1651                 self.report_missing_fields(
1652                     adt_ty,
1653                     span,
1654                     remaining_fields,
1655                     variant,
1656                     ast_fields,
1657                     substs,
1658                 );
1659             }
1660         }
1661     }
1662
1663     fn check_struct_fields_on_error(
1664         &self,
1665         fields: &'tcx [hir::ExprField<'tcx>],
1666         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1667     ) {
1668         for field in fields {
1669             self.check_expr(&field.expr);
1670         }
1671         if let Some(base) = *base_expr {
1672             self.check_expr(&base);
1673         }
1674     }
1675
1676     /// Report an error for a struct field expression when there are fields which aren't provided.
1677     ///
1678     /// ```text
1679     /// error: missing field `you_can_use_this_field` in initializer of `foo::Foo`
1680     ///  --> src/main.rs:8:5
1681     ///   |
1682     /// 8 |     foo::Foo {};
1683     ///   |     ^^^^^^^^ missing `you_can_use_this_field`
1684     ///
1685     /// error: aborting due to previous error
1686     /// ```
1687     fn report_missing_fields(
1688         &self,
1689         adt_ty: Ty<'tcx>,
1690         span: Span,
1691         remaining_fields: FxHashMap<Ident, (usize, &ty::FieldDef)>,
1692         variant: &'tcx ty::VariantDef,
1693         ast_fields: &'tcx [hir::ExprField<'tcx>],
1694         substs: SubstsRef<'tcx>,
1695     ) {
1696         let len = remaining_fields.len();
1697
1698         let mut displayable_field_names: Vec<&str> =
1699             remaining_fields.keys().map(|ident| ident.as_str()).collect();
1700         // sorting &str primitives here, sort_unstable is ok
1701         displayable_field_names.sort_unstable();
1702
1703         let mut truncated_fields_error = String::new();
1704         let remaining_fields_names = match &displayable_field_names[..] {
1705             [field1] => format!("`{}`", field1),
1706             [field1, field2] => format!("`{field1}` and `{field2}`"),
1707             [field1, field2, field3] => format!("`{field1}`, `{field2}` and `{field3}`"),
1708             _ => {
1709                 truncated_fields_error =
1710                     format!(" and {} other field{}", len - 3, pluralize!(len - 3));
1711                 displayable_field_names
1712                     .iter()
1713                     .take(3)
1714                     .map(|n| format!("`{n}`"))
1715                     .collect::<Vec<_>>()
1716                     .join(", ")
1717             }
1718         };
1719
1720         let mut err = struct_span_err!(
1721             self.tcx.sess,
1722             span,
1723             E0063,
1724             "missing field{} {}{} in initializer of `{}`",
1725             pluralize!(len),
1726             remaining_fields_names,
1727             truncated_fields_error,
1728             adt_ty
1729         );
1730         err.span_label(span, format!("missing {remaining_fields_names}{truncated_fields_error}"));
1731
1732         // If the last field is a range literal, but it isn't supposed to be, then they probably
1733         // meant to use functional update syntax.
1734         //
1735         // I don't use 'is_range_literal' because only double-sided, half-open ranges count.
1736         if let Some((
1737             last,
1738             ExprKind::Struct(
1739                 QPath::LangItem(LangItem::Range, ..),
1740                 &[ref range_start, ref range_end],
1741                 _,
1742             ),
1743         )) = ast_fields.last().map(|last| (last, &last.expr.kind)) &&
1744         let variant_field =
1745             variant.fields.iter().find(|field| field.ident(self.tcx) == last.ident) &&
1746         let range_def_id = self.tcx.lang_items().range_struct() &&
1747         variant_field
1748             .and_then(|field| field.ty(self.tcx, substs).ty_adt_def())
1749             .map(|adt| adt.did())
1750             != range_def_id
1751         {
1752             let instead = self
1753                 .tcx
1754                 .sess
1755                 .source_map()
1756                 .span_to_snippet(range_end.expr.span)
1757                 .map(|s| format!(" from `{s}`"))
1758                 .unwrap_or(String::new());
1759             err.span_suggestion(
1760                 range_start.span.shrink_to_hi(),
1761                 &format!("to set the remaining fields{instead}, separate the last named field with a comma"),
1762                 ",".to_string(),
1763                 Applicability::MaybeIncorrect,
1764             );
1765         }
1766
1767         err.emit();
1768     }
1769
1770     /// Report an error for a struct field expression when there are invisible fields.
1771     ///
1772     /// ```text
1773     /// error: cannot construct `Foo` with struct literal syntax due to inaccessible fields
1774     ///  --> src/main.rs:8:5
1775     ///   |
1776     /// 8 |     foo::Foo {};
1777     ///   |     ^^^^^^^^
1778     ///
1779     /// error: aborting due to previous error
1780     /// ```
1781     fn report_inaccessible_fields(&self, adt_ty: Ty<'tcx>, span: Span) {
1782         self.tcx.sess.span_err(
1783             span,
1784             &format!(
1785                 "cannot construct `{adt_ty}` with struct literal syntax due to inaccessible fields",
1786             ),
1787         );
1788     }
1789
1790     fn report_unknown_field(
1791         &self,
1792         ty: Ty<'tcx>,
1793         variant: &'tcx ty::VariantDef,
1794         field: &hir::ExprField<'_>,
1795         skip_fields: &[hir::ExprField<'_>],
1796         kind_name: &str,
1797         expr_span: Span,
1798     ) {
1799         if variant.is_recovered() {
1800             self.set_tainted_by_errors();
1801             return;
1802         }
1803         let mut err = self.type_error_struct_with_diag(
1804             field.ident.span,
1805             |actual| match ty.kind() {
1806                 ty::Adt(adt, ..) if adt.is_enum() => struct_span_err!(
1807                     self.tcx.sess,
1808                     field.ident.span,
1809                     E0559,
1810                     "{} `{}::{}` has no field named `{}`",
1811                     kind_name,
1812                     actual,
1813                     variant.name,
1814                     field.ident
1815                 ),
1816                 _ => struct_span_err!(
1817                     self.tcx.sess,
1818                     field.ident.span,
1819                     E0560,
1820                     "{} `{}` has no field named `{}`",
1821                     kind_name,
1822                     actual,
1823                     field.ident
1824                 ),
1825             },
1826             ty,
1827         );
1828
1829         let variant_ident_span = self.tcx.def_ident_span(variant.def_id).unwrap();
1830         match variant.ctor_kind {
1831             CtorKind::Fn => match ty.kind() {
1832                 ty::Adt(adt, ..) if adt.is_enum() => {
1833                     err.span_label(
1834                         variant_ident_span,
1835                         format!(
1836                             "`{adt}::{variant}` defined here",
1837                             adt = ty,
1838                             variant = variant.name,
1839                         ),
1840                     );
1841                     err.span_label(field.ident.span, "field does not exist");
1842                     err.span_suggestion_verbose(
1843                         expr_span,
1844                         &format!(
1845                             "`{adt}::{variant}` is a tuple {kind_name}, use the appropriate syntax",
1846                             adt = ty,
1847                             variant = variant.name,
1848                         ),
1849                         format!(
1850                             "{adt}::{variant}(/* fields */)",
1851                             adt = ty,
1852                             variant = variant.name,
1853                         ),
1854                         Applicability::HasPlaceholders,
1855                     );
1856                 }
1857                 _ => {
1858                     err.span_label(variant_ident_span, format!("`{adt}` defined here", adt = ty));
1859                     err.span_label(field.ident.span, "field does not exist");
1860                     err.span_suggestion_verbose(
1861                         expr_span,
1862                         &format!(
1863                             "`{adt}` is a tuple {kind_name}, use the appropriate syntax",
1864                             adt = ty,
1865                             kind_name = kind_name,
1866                         ),
1867                         format!("{adt}(/* fields */)", adt = ty),
1868                         Applicability::HasPlaceholders,
1869                     );
1870                 }
1871             },
1872             _ => {
1873                 // prevent all specified fields from being suggested
1874                 let skip_fields = skip_fields.iter().map(|x| x.ident.name);
1875                 if let Some(field_name) = self.suggest_field_name(
1876                     variant,
1877                     field.ident.name,
1878                     skip_fields.collect(),
1879                     expr_span,
1880                 ) {
1881                     err.span_suggestion(
1882                         field.ident.span,
1883                         "a field with a similar name exists",
1884                         field_name.to_string(),
1885                         Applicability::MaybeIncorrect,
1886                     );
1887                 } else {
1888                     match ty.kind() {
1889                         ty::Adt(adt, ..) => {
1890                             if adt.is_enum() {
1891                                 err.span_label(
1892                                     field.ident.span,
1893                                     format!("`{}::{}` does not have this field", ty, variant.name),
1894                                 );
1895                             } else {
1896                                 err.span_label(
1897                                     field.ident.span,
1898                                     format!("`{ty}` does not have this field"),
1899                                 );
1900                             }
1901                             let available_field_names =
1902                                 self.available_field_names(variant, expr_span);
1903                             if !available_field_names.is_empty() {
1904                                 err.note(&format!(
1905                                     "available fields are: {}",
1906                                     self.name_series_display(available_field_names)
1907                                 ));
1908                             }
1909                         }
1910                         _ => bug!("non-ADT passed to report_unknown_field"),
1911                     }
1912                 };
1913             }
1914         }
1915         err.emit();
1916     }
1917
1918     // Return a hint about the closest match in field names
1919     fn suggest_field_name(
1920         &self,
1921         variant: &'tcx ty::VariantDef,
1922         field: Symbol,
1923         skip: Vec<Symbol>,
1924         // The span where stability will be checked
1925         span: Span,
1926     ) -> Option<Symbol> {
1927         let names = variant
1928             .fields
1929             .iter()
1930             .filter_map(|field| {
1931                 // ignore already set fields and private fields from non-local crates
1932                 // and unstable fields.
1933                 if skip.iter().any(|&x| x == field.name)
1934                     || (!variant.def_id.is_local() && !field.vis.is_public())
1935                     || matches!(
1936                         self.tcx.eval_stability(field.did, None, span, None),
1937                         stability::EvalResult::Deny { .. }
1938                     )
1939                 {
1940                     None
1941                 } else {
1942                     Some(field.name)
1943                 }
1944             })
1945             .collect::<Vec<Symbol>>();
1946
1947         find_best_match_for_name(&names, field, None)
1948     }
1949
1950     fn available_field_names(
1951         &self,
1952         variant: &'tcx ty::VariantDef,
1953         access_span: Span,
1954     ) -> Vec<Symbol> {
1955         variant
1956             .fields
1957             .iter()
1958             .filter(|field| {
1959                 let def_scope = self
1960                     .tcx
1961                     .adjust_ident_and_get_scope(field.ident(self.tcx), variant.def_id, self.body_id)
1962                     .1;
1963                 field.vis.is_accessible_from(def_scope, self.tcx)
1964                     && !matches!(
1965                         self.tcx.eval_stability(field.did, None, access_span, None),
1966                         stability::EvalResult::Deny { .. }
1967                     )
1968             })
1969             .filter(|field| !self.tcx.is_doc_hidden(field.did))
1970             .map(|field| field.name)
1971             .collect()
1972     }
1973
1974     fn name_series_display(&self, names: Vec<Symbol>) -> String {
1975         // dynamic limit, to never omit just one field
1976         let limit = if names.len() == 6 { 6 } else { 5 };
1977         let mut display =
1978             names.iter().take(limit).map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
1979         if names.len() > limit {
1980             display = format!("{} ... and {} others", display, names.len() - limit);
1981         }
1982         display
1983     }
1984
1985     // Check field access expressions
1986     fn check_field(
1987         &self,
1988         expr: &'tcx hir::Expr<'tcx>,
1989         base: &'tcx hir::Expr<'tcx>,
1990         field: Ident,
1991     ) -> Ty<'tcx> {
1992         debug!("check_field(expr: {:?}, base: {:?}, field: {:?})", expr, base, field);
1993         let expr_t = self.check_expr(base);
1994         let expr_t = self.structurally_resolved_type(base.span, expr_t);
1995         let mut private_candidate = None;
1996         let mut autoderef = self.autoderef(expr.span, expr_t);
1997         while let Some((base_t, _)) = autoderef.next() {
1998             debug!("base_t: {:?}", base_t);
1999             match base_t.kind() {
2000                 ty::Adt(base_def, substs) if !base_def.is_enum() => {
2001                     debug!("struct named {:?}", base_t);
2002                     let (ident, def_scope) =
2003                         self.tcx.adjust_ident_and_get_scope(field, base_def.did(), self.body_id);
2004                     let fields = &base_def.non_enum_variant().fields;
2005                     if let Some(index) = fields
2006                         .iter()
2007                         .position(|f| f.ident(self.tcx).normalize_to_macros_2_0() == ident)
2008                     {
2009                         let field = &fields[index];
2010                         let field_ty = self.field_ty(expr.span, field, substs);
2011                         // Save the index of all fields regardless of their visibility in case
2012                         // of error recovery.
2013                         self.write_field_index(expr.hir_id, index);
2014                         let adjustments = self.adjust_steps(&autoderef);
2015                         if field.vis.is_accessible_from(def_scope, self.tcx) {
2016                             self.apply_adjustments(base, adjustments);
2017                             self.register_predicates(autoderef.into_obligations());
2018
2019                             self.tcx.check_stability(field.did, Some(expr.hir_id), expr.span, None);
2020                             return field_ty;
2021                         }
2022                         private_candidate = Some((adjustments, base_def.did(), field_ty));
2023                     }
2024                 }
2025                 ty::Tuple(tys) => {
2026                     let fstr = field.as_str();
2027                     if let Ok(index) = fstr.parse::<usize>() {
2028                         if fstr == index.to_string() {
2029                             if let Some(&field_ty) = tys.get(index) {
2030                                 let adjustments = self.adjust_steps(&autoderef);
2031                                 self.apply_adjustments(base, adjustments);
2032                                 self.register_predicates(autoderef.into_obligations());
2033
2034                                 self.write_field_index(expr.hir_id, index);
2035                                 return field_ty;
2036                             }
2037                         }
2038                     }
2039                 }
2040                 _ => {}
2041             }
2042         }
2043         self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
2044
2045         if let Some((adjustments, did, field_ty)) = private_candidate {
2046             // (#90483) apply adjustments to avoid ExprUseVisitor from
2047             // creating erroneous projection.
2048             self.apply_adjustments(base, adjustments);
2049             self.ban_private_field_access(expr, expr_t, field, did);
2050             return field_ty;
2051         }
2052
2053         if field.name == kw::Empty {
2054         } else if self.method_exists(field, expr_t, expr.hir_id, true) {
2055             self.ban_take_value_of_method(expr, expr_t, field);
2056         } else if !expr_t.is_primitive_ty() {
2057             self.ban_nonexisting_field(field, base, expr, expr_t);
2058         } else {
2059             type_error_struct!(
2060                 self.tcx().sess,
2061                 field.span,
2062                 expr_t,
2063                 E0610,
2064                 "`{expr_t}` is a primitive type and therefore doesn't have fields",
2065             )
2066             .emit();
2067         }
2068
2069         self.tcx().ty_error()
2070     }
2071
2072     fn check_call_constructor<G: EmissionGuarantee>(
2073         &self,
2074         err: &mut DiagnosticBuilder<'_, G>,
2075         base: &'tcx hir::Expr<'tcx>,
2076         def_id: DefId,
2077     ) {
2078         if let Some(local_id) = def_id.as_local() {
2079             let hir_id = self.tcx.hir().local_def_id_to_hir_id(local_id);
2080             let node = self.tcx.hir().get(hir_id);
2081
2082             if let Some(fields) = node.tuple_fields() {
2083                 let kind = match self.tcx.opt_def_kind(local_id) {
2084                     Some(DefKind::Ctor(of, _)) => of,
2085                     _ => return,
2086                 };
2087
2088                 suggest_call_constructor(base.span, kind, fields.len(), err);
2089             }
2090         } else {
2091             // The logic here isn't smart but `associated_item_def_ids`
2092             // doesn't work nicely on local.
2093             if let DefKind::Ctor(of, _) = self.tcx.def_kind(def_id) {
2094                 let parent_def_id = self.tcx.parent(def_id);
2095                 let fields = self.tcx.associated_item_def_ids(parent_def_id);
2096                 suggest_call_constructor(base.span, of, fields.len(), err);
2097             }
2098         }
2099     }
2100
2101     fn suggest_await_on_field_access(
2102         &self,
2103         err: &mut Diagnostic,
2104         field_ident: Ident,
2105         base: &'tcx hir::Expr<'tcx>,
2106         ty: Ty<'tcx>,
2107     ) {
2108         let output_ty = match self.infcx.get_impl_future_output_ty(ty) {
2109             Some(output_ty) => self.resolve_vars_if_possible(output_ty),
2110             _ => return,
2111         };
2112         let mut add_label = true;
2113         if let ty::Adt(def, _) = output_ty.skip_binder().kind() {
2114             // no field access on enum type
2115             if !def.is_enum() {
2116                 if def
2117                     .non_enum_variant()
2118                     .fields
2119                     .iter()
2120                     .any(|field| field.ident(self.tcx) == field_ident)
2121                 {
2122                     add_label = false;
2123                     err.span_label(
2124                         field_ident.span,
2125                         "field not available in `impl Future`, but it is available in its `Output`",
2126                     );
2127                     err.span_suggestion_verbose(
2128                         base.span.shrink_to_hi(),
2129                         "consider `await`ing on the `Future` and access the field of its `Output`",
2130                         ".await".to_string(),
2131                         Applicability::MaybeIncorrect,
2132                     );
2133                 }
2134             }
2135         }
2136         if add_label {
2137             err.span_label(field_ident.span, &format!("field not found in `{ty}`"));
2138         }
2139     }
2140
2141     fn ban_nonexisting_field(
2142         &self,
2143         field: Ident,
2144         base: &'tcx hir::Expr<'tcx>,
2145         expr: &'tcx hir::Expr<'tcx>,
2146         expr_t: Ty<'tcx>,
2147     ) {
2148         debug!(
2149             "ban_nonexisting_field: field={:?}, base={:?}, expr={:?}, expr_ty={:?}",
2150             field, base, expr, expr_t
2151         );
2152         let mut err = self.no_such_field_err(field, expr_t, base.hir_id);
2153
2154         match *expr_t.peel_refs().kind() {
2155             ty::Array(_, len) => {
2156                 self.maybe_suggest_array_indexing(&mut err, expr, base, field, len);
2157             }
2158             ty::RawPtr(..) => {
2159                 self.suggest_first_deref_field(&mut err, expr, base, field);
2160             }
2161             ty::Adt(def, _) if !def.is_enum() => {
2162                 self.suggest_fields_on_recordish(&mut err, def, field, expr.span);
2163             }
2164             ty::Param(param_ty) => {
2165                 self.point_at_param_definition(&mut err, param_ty);
2166             }
2167             ty::Opaque(_, _) => {
2168                 self.suggest_await_on_field_access(&mut err, field, base, expr_t.peel_refs());
2169             }
2170             ty::FnDef(def_id, _) => {
2171                 self.check_call_constructor(&mut err, base, def_id);
2172             }
2173             _ => {}
2174         }
2175
2176         if field.name == kw::Await {
2177             // We know by construction that `<expr>.await` is either on Rust 2015
2178             // or results in `ExprKind::Await`. Suggest switching the edition to 2018.
2179             err.note("to `.await` a `Future`, switch to Rust 2018 or later");
2180             err.help_use_latest_edition();
2181         }
2182
2183         err.emit();
2184     }
2185
2186     fn ban_private_field_access(
2187         &self,
2188         expr: &hir::Expr<'_>,
2189         expr_t: Ty<'tcx>,
2190         field: Ident,
2191         base_did: DefId,
2192     ) {
2193         let struct_path = self.tcx().def_path_str(base_did);
2194         let kind_name = self.tcx().def_kind(base_did).descr(base_did);
2195         let mut err = struct_span_err!(
2196             self.tcx().sess,
2197             field.span,
2198             E0616,
2199             "field `{field}` of {kind_name} `{struct_path}` is private",
2200         );
2201         err.span_label(field.span, "private field");
2202         // Also check if an accessible method exists, which is often what is meant.
2203         if self.method_exists(field, expr_t, expr.hir_id, false) && !self.expr_in_place(expr.hir_id)
2204         {
2205             self.suggest_method_call(
2206                 &mut err,
2207                 &format!("a method `{field}` also exists, call it with parentheses"),
2208                 field,
2209                 expr_t,
2210                 expr,
2211                 None,
2212             );
2213         }
2214         err.emit();
2215     }
2216
2217     fn ban_take_value_of_method(&self, expr: &hir::Expr<'_>, expr_t: Ty<'tcx>, field: Ident) {
2218         let mut err = type_error_struct!(
2219             self.tcx().sess,
2220             field.span,
2221             expr_t,
2222             E0615,
2223             "attempted to take value of method `{field}` on type `{expr_t}`",
2224         );
2225         err.span_label(field.span, "method, not a field");
2226         let expr_is_call =
2227             if let hir::Node::Expr(hir::Expr { kind: ExprKind::Call(callee, _args), .. }) =
2228                 self.tcx.hir().get(self.tcx.hir().get_parent_node(expr.hir_id))
2229             {
2230                 expr.hir_id == callee.hir_id
2231             } else {
2232                 false
2233             };
2234         let expr_snippet =
2235             self.tcx.sess.source_map().span_to_snippet(expr.span).unwrap_or(String::new());
2236         let is_wrapped = expr_snippet.starts_with('(') && expr_snippet.ends_with(')');
2237         let after_open = expr.span.lo() + rustc_span::BytePos(1);
2238         let before_close = expr.span.hi() - rustc_span::BytePos(1);
2239
2240         if expr_is_call && is_wrapped {
2241             err.multipart_suggestion(
2242                 "remove wrapping parentheses to call the method",
2243                 vec![
2244                     (expr.span.with_hi(after_open), String::new()),
2245                     (expr.span.with_lo(before_close), String::new()),
2246                 ],
2247                 Applicability::MachineApplicable,
2248             );
2249         } else if !self.expr_in_place(expr.hir_id) {
2250             // Suggest call parentheses inside the wrapping parentheses
2251             let span = if is_wrapped {
2252                 expr.span.with_lo(after_open).with_hi(before_close)
2253             } else {
2254                 expr.span
2255             };
2256             self.suggest_method_call(
2257                 &mut err,
2258                 "use parentheses to call the method",
2259                 field,
2260                 expr_t,
2261                 expr,
2262                 Some(span),
2263             );
2264         } else {
2265             let mut found = false;
2266
2267             if let ty::RawPtr(ty_and_mut) = expr_t.kind()
2268                 && let ty::Adt(adt_def, _) = ty_and_mut.ty.kind()
2269             {
2270                 if adt_def.variants().len() == 1
2271                     && adt_def
2272                         .variants()
2273                         .iter()
2274                         .next()
2275                         .unwrap()
2276                         .fields
2277                         .iter()
2278                         .any(|f| f.ident(self.tcx) == field)
2279                 {
2280                     if let Some(dot_loc) = expr_snippet.rfind('.') {
2281                         found = true;
2282                         err.span_suggestion(
2283                             expr.span.with_hi(expr.span.lo() + BytePos::from_usize(dot_loc)),
2284                             "to access the field, dereference first",
2285                             format!("(*{})", &expr_snippet[0..dot_loc]),
2286                             Applicability::MaybeIncorrect,
2287                         );
2288                     }
2289                 }
2290             }
2291
2292             if !found {
2293                 err.help("methods are immutable and cannot be assigned to");
2294             }
2295         }
2296
2297         err.emit();
2298     }
2299
2300     fn point_at_param_definition(&self, err: &mut Diagnostic, param: ty::ParamTy) {
2301         let generics = self.tcx.generics_of(self.body_id.owner.to_def_id());
2302         let generic_param = generics.type_param(&param, self.tcx);
2303         if let ty::GenericParamDefKind::Type { synthetic: true, .. } = generic_param.kind {
2304             return;
2305         }
2306         let param_def_id = generic_param.def_id;
2307         let param_hir_id = match param_def_id.as_local() {
2308             Some(x) => self.tcx.hir().local_def_id_to_hir_id(x),
2309             None => return,
2310         };
2311         let param_span = self.tcx.hir().span(param_hir_id);
2312         let param_name = self.tcx.hir().ty_param_name(param_def_id.expect_local());
2313
2314         err.span_label(param_span, &format!("type parameter '{param_name}' declared here"));
2315     }
2316
2317     fn suggest_fields_on_recordish(
2318         &self,
2319         err: &mut Diagnostic,
2320         def: ty::AdtDef<'tcx>,
2321         field: Ident,
2322         access_span: Span,
2323     ) {
2324         if let Some(suggested_field_name) =
2325             self.suggest_field_name(def.non_enum_variant(), field.name, vec![], access_span)
2326         {
2327             err.span_suggestion(
2328                 field.span,
2329                 "a field with a similar name exists",
2330                 suggested_field_name.to_string(),
2331                 Applicability::MaybeIncorrect,
2332             );
2333         } else {
2334             err.span_label(field.span, "unknown field");
2335             let struct_variant_def = def.non_enum_variant();
2336             let field_names = self.available_field_names(struct_variant_def, access_span);
2337             if !field_names.is_empty() {
2338                 err.note(&format!(
2339                     "available fields are: {}",
2340                     self.name_series_display(field_names),
2341                 ));
2342             }
2343         }
2344     }
2345
2346     fn maybe_suggest_array_indexing(
2347         &self,
2348         err: &mut Diagnostic,
2349         expr: &hir::Expr<'_>,
2350         base: &hir::Expr<'_>,
2351         field: Ident,
2352         len: ty::Const<'tcx>,
2353     ) {
2354         if let (Some(len), Ok(user_index)) =
2355             (len.try_eval_usize(self.tcx, self.param_env), field.as_str().parse::<u64>())
2356             && let Ok(base) = self.tcx.sess.source_map().span_to_snippet(base.span)
2357         {
2358             let help = "instead of using tuple indexing, use array indexing";
2359             let suggestion = format!("{base}[{field}]");
2360             let applicability = if len < user_index {
2361                 Applicability::MachineApplicable
2362             } else {
2363                 Applicability::MaybeIncorrect
2364             };
2365             err.span_suggestion(expr.span, help, suggestion, applicability);
2366         }
2367     }
2368
2369     fn suggest_first_deref_field(
2370         &self,
2371         err: &mut Diagnostic,
2372         expr: &hir::Expr<'_>,
2373         base: &hir::Expr<'_>,
2374         field: Ident,
2375     ) {
2376         if let Ok(base) = self.tcx.sess.source_map().span_to_snippet(base.span) {
2377             let msg = format!("`{base}` is a raw pointer; try dereferencing it");
2378             let suggestion = format!("(*{base}).{field}");
2379             err.span_suggestion(expr.span, &msg, suggestion, Applicability::MaybeIncorrect);
2380         }
2381     }
2382
2383     fn no_such_field_err(
2384         &self,
2385         field: Ident,
2386         expr_t: Ty<'tcx>,
2387         id: HirId,
2388     ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
2389         let span = field.span;
2390         debug!("no_such_field_err(span: {:?}, field: {:?}, expr_t: {:?})", span, field, expr_t);
2391
2392         let mut err = type_error_struct!(
2393             self.tcx().sess,
2394             field.span,
2395             expr_t,
2396             E0609,
2397             "no field `{field}` on type `{expr_t}`",
2398         );
2399
2400         // try to add a suggestion in case the field is a nested field of a field of the Adt
2401         if let Some((fields, substs)) = self.get_field_candidates(span, expr_t) {
2402             for candidate_field in fields.iter() {
2403                 if let Some(mut field_path) = self.check_for_nested_field_satisfying(
2404                     span,
2405                     &|candidate_field, _| candidate_field.ident(self.tcx()) == field,
2406                     candidate_field,
2407                     substs,
2408                     vec![],
2409                     self.tcx.parent_module(id).to_def_id(),
2410                 ) {
2411                     // field_path includes `field` that we're looking for, so pop it.
2412                     field_path.pop();
2413
2414                     let field_path_str = field_path
2415                         .iter()
2416                         .map(|id| id.name.to_ident_string())
2417                         .collect::<Vec<String>>()
2418                         .join(".");
2419                     debug!("field_path_str: {:?}", field_path_str);
2420
2421                     err.span_suggestion_verbose(
2422                         field.span.shrink_to_lo(),
2423                         "one of the expressions' fields has a field of the same name",
2424                         format!("{field_path_str}."),
2425                         Applicability::MaybeIncorrect,
2426                     );
2427                 }
2428             }
2429         }
2430         err
2431     }
2432
2433     crate fn get_field_candidates(
2434         &self,
2435         span: Span,
2436         base_t: Ty<'tcx>,
2437     ) -> Option<(&Vec<ty::FieldDef>, SubstsRef<'tcx>)> {
2438         debug!("get_field_candidates(span: {:?}, base_t: {:?}", span, base_t);
2439
2440         for (base_t, _) in self.autoderef(span, base_t) {
2441             match base_t.kind() {
2442                 ty::Adt(base_def, substs) if !base_def.is_enum() => {
2443                     let fields = &base_def.non_enum_variant().fields;
2444                     // For compile-time reasons put a limit on number of fields we search
2445                     if fields.len() > 100 {
2446                         return None;
2447                     }
2448                     return Some((fields, substs));
2449                 }
2450                 _ => {}
2451             }
2452         }
2453         None
2454     }
2455
2456     /// This method is called after we have encountered a missing field error to recursively
2457     /// search for the field
2458     crate fn check_for_nested_field_satisfying(
2459         &self,
2460         span: Span,
2461         matches: &impl Fn(&ty::FieldDef, Ty<'tcx>) -> bool,
2462         candidate_field: &ty::FieldDef,
2463         subst: SubstsRef<'tcx>,
2464         mut field_path: Vec<Ident>,
2465         id: DefId,
2466     ) -> Option<Vec<Ident>> {
2467         debug!(
2468             "check_for_nested_field_satisfying(span: {:?}, candidate_field: {:?}, field_path: {:?}",
2469             span, candidate_field, field_path
2470         );
2471
2472         if field_path.len() > 3 {
2473             // For compile-time reasons and to avoid infinite recursion we only check for fields
2474             // up to a depth of three
2475             None
2476         } else {
2477             // recursively search fields of `candidate_field` if it's a ty::Adt
2478             field_path.push(candidate_field.ident(self.tcx).normalize_to_macros_2_0());
2479             let field_ty = candidate_field.ty(self.tcx, subst);
2480             if let Some((nested_fields, subst)) = self.get_field_candidates(span, field_ty) {
2481                 for field in nested_fields.iter() {
2482                     if field.vis.is_accessible_from(id, self.tcx) {
2483                         if matches(candidate_field, field_ty) {
2484                             return Some(field_path);
2485                         } else if let Some(field_path) = self.check_for_nested_field_satisfying(
2486                             span,
2487                             matches,
2488                             field,
2489                             subst,
2490                             field_path.clone(),
2491                             id,
2492                         ) {
2493                             return Some(field_path);
2494                         }
2495                     }
2496                 }
2497             }
2498             None
2499         }
2500     }
2501
2502     fn check_expr_index(
2503         &self,
2504         base: &'tcx hir::Expr<'tcx>,
2505         idx: &'tcx hir::Expr<'tcx>,
2506         expr: &'tcx hir::Expr<'tcx>,
2507     ) -> Ty<'tcx> {
2508         let base_t = self.check_expr(&base);
2509         let idx_t = self.check_expr(&idx);
2510
2511         if base_t.references_error() {
2512             base_t
2513         } else if idx_t.references_error() {
2514             idx_t
2515         } else {
2516             let base_t = self.structurally_resolved_type(base.span, base_t);
2517             match self.lookup_indexing(expr, base, base_t, idx, idx_t) {
2518                 Some((index_ty, element_ty)) => {
2519                     // two-phase not needed because index_ty is never mutable
2520                     self.demand_coerce(idx, idx_t, index_ty, None, AllowTwoPhase::No);
2521                     element_ty
2522                 }
2523                 None => {
2524                     let mut err = type_error_struct!(
2525                         self.tcx.sess,
2526                         expr.span,
2527                         base_t,
2528                         E0608,
2529                         "cannot index into a value of type `{base_t}`",
2530                     );
2531                     // Try to give some advice about indexing tuples.
2532                     if let ty::Tuple(..) = base_t.kind() {
2533                         let mut needs_note = true;
2534                         // If the index is an integer, we can show the actual
2535                         // fixed expression:
2536                         if let ExprKind::Lit(ref lit) = idx.kind {
2537                             if let ast::LitKind::Int(i, ast::LitIntType::Unsuffixed) = lit.node {
2538                                 let snip = self.tcx.sess.source_map().span_to_snippet(base.span);
2539                                 if let Ok(snip) = snip {
2540                                     err.span_suggestion(
2541                                         expr.span,
2542                                         "to access tuple elements, use",
2543                                         format!("{snip}.{i}"),
2544                                         Applicability::MachineApplicable,
2545                                     );
2546                                     needs_note = false;
2547                                 }
2548                             }
2549                         }
2550                         if needs_note {
2551                             err.help(
2552                                 "to access tuple elements, use tuple indexing \
2553                                         syntax (e.g., `tuple.0`)",
2554                             );
2555                         }
2556                     }
2557                     err.emit();
2558                     self.tcx.ty_error()
2559                 }
2560             }
2561         }
2562     }
2563
2564     fn check_expr_yield(
2565         &self,
2566         value: &'tcx hir::Expr<'tcx>,
2567         expr: &'tcx hir::Expr<'tcx>,
2568         src: &'tcx hir::YieldSource,
2569     ) -> Ty<'tcx> {
2570         match self.resume_yield_tys {
2571             Some((resume_ty, yield_ty)) => {
2572                 self.check_expr_coercable_to_type(&value, yield_ty, None);
2573
2574                 resume_ty
2575             }
2576             // Given that this `yield` expression was generated as a result of lowering a `.await`,
2577             // we know that the yield type must be `()`; however, the context won't contain this
2578             // information. Hence, we check the source of the yield expression here and check its
2579             // value's type against `()` (this check should always hold).
2580             None if src.is_await() => {
2581                 self.check_expr_coercable_to_type(&value, self.tcx.mk_unit(), None);
2582                 self.tcx.mk_unit()
2583             }
2584             _ => {
2585                 self.tcx.sess.emit_err(YieldExprOutsideOfGenerator { span: expr.span });
2586                 // Avoid expressions without types during writeback (#78653).
2587                 self.check_expr(value);
2588                 self.tcx.mk_unit()
2589             }
2590         }
2591     }
2592
2593     fn check_expr_asm_operand(&self, expr: &'tcx hir::Expr<'tcx>, is_input: bool) {
2594         let needs = if is_input { Needs::None } else { Needs::MutPlace };
2595         let ty = self.check_expr_with_needs(expr, needs);
2596         self.require_type_is_sized(ty, expr.span, traits::InlineAsmSized);
2597
2598         if !is_input && !expr.is_syntactic_place_expr() {
2599             let mut err = self.tcx.sess.struct_span_err(expr.span, "invalid asm output");
2600             err.span_label(expr.span, "cannot assign to this expression");
2601             err.emit();
2602         }
2603
2604         // If this is an input value, we require its type to be fully resolved
2605         // at this point. This allows us to provide helpful coercions which help
2606         // pass the type candidate list in a later pass.
2607         //
2608         // We don't require output types to be resolved at this point, which
2609         // allows them to be inferred based on how they are used later in the
2610         // function.
2611         if is_input {
2612             let ty = self.structurally_resolved_type(expr.span, ty);
2613             match *ty.kind() {
2614                 ty::FnDef(..) => {
2615                     let fnptr_ty = self.tcx.mk_fn_ptr(ty.fn_sig(self.tcx));
2616                     self.demand_coerce(expr, ty, fnptr_ty, None, AllowTwoPhase::No);
2617                 }
2618                 ty::Ref(_, base_ty, mutbl) => {
2619                     let ptr_ty = self.tcx.mk_ptr(ty::TypeAndMut { ty: base_ty, mutbl });
2620                     self.demand_coerce(expr, ty, ptr_ty, None, AllowTwoPhase::No);
2621                 }
2622                 _ => {}
2623             }
2624         }
2625     }
2626
2627     fn check_expr_asm(&self, asm: &'tcx hir::InlineAsm<'tcx>) -> Ty<'tcx> {
2628         for (op, _op_sp) in asm.operands {
2629             match op {
2630                 hir::InlineAsmOperand::In { expr, .. } => {
2631                     self.check_expr_asm_operand(expr, true);
2632                 }
2633                 hir::InlineAsmOperand::Out { expr: Some(expr), .. }
2634                 | hir::InlineAsmOperand::InOut { expr, .. } => {
2635                     self.check_expr_asm_operand(expr, false);
2636                 }
2637                 hir::InlineAsmOperand::Out { expr: None, .. } => {}
2638                 hir::InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
2639                     self.check_expr_asm_operand(in_expr, true);
2640                     if let Some(out_expr) = out_expr {
2641                         self.check_expr_asm_operand(out_expr, false);
2642                     }
2643                 }
2644                 // `AnonConst`s have their own body and is type-checked separately.
2645                 // As they don't flow into the type system we don't need them to
2646                 // be well-formed.
2647                 hir::InlineAsmOperand::Const { .. } | hir::InlineAsmOperand::SymFn { .. } => {}
2648                 hir::InlineAsmOperand::SymStatic { .. } => {}
2649             }
2650         }
2651         if asm.options.contains(ast::InlineAsmOptions::NORETURN) {
2652             self.tcx.types.never
2653         } else {
2654             self.tcx.mk_unit()
2655         }
2656     }
2657 }
2658
2659 pub(super) fn ty_kind_suggestion(ty: Ty<'_>) -> Option<&'static str> {
2660     Some(match ty.kind() {
2661         ty::Bool => "true",
2662         ty::Char => "'a'",
2663         ty::Int(_) | ty::Uint(_) => "42",
2664         ty::Float(_) => "3.14159",
2665         ty::Error(_) | ty::Never => return None,
2666         _ => "value",
2667     })
2668 }