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