compiler/rustc_typeck/src/check/expr.rs

   1 //! Type checking expressions.
   2 //!
   3 //! See `mod.rs` for more context on type checking in general.
   4
   5 use crate::astconv::AstConv as _;
   6 use crate::check::cast;
   7 use crate::check::coercion::CoerceMany;
   8 use crate::check::fatally_break_rust;
   9 use crate::check::method::SelfSource;
  10 use crate::check::report_unexpected_variant_res;
  11 use crate::check::BreakableCtxt;
  12 use crate::check::Diverges;
  13 use crate::check::DynamicCoerceMany;
  14 use crate::check::Expectation::{self, ExpectCastableToType, ExpectHasType, NoExpectation};
  15 use crate::check::FnCtxt;
  16 use crate::check::Needs;
  17 use crate::check::TupleArgumentsFlag::DontTupleArguments;
  18 use crate::errors::{
  19     FieldMultiplySpecifiedInInitializer, FunctionalRecordUpdateOnNonStruct,
  20     YieldExprOutsideOfGenerator,
  21 };
  22 use crate::type_error_struct;
  23
  24 use crate::errors::{AddressOfTemporaryTaken, ReturnStmtOutsideOfFnBody, StructExprNonExhaustive};
  25 use rustc_ast as ast;
  26 use rustc_data_structures::fx::FxHashMap;
  27 use rustc_data_structures::stack::ensure_sufficient_stack;
  28 use rustc_errors::Diagnostic;
  29 use rustc_errors::ErrorGuaranteed;
  30 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, DiagnosticId};
  31 use rustc_hir as hir;
  32 use rustc_hir::def::{CtorKind, DefKind, Res};
  33 use rustc_hir::def_id::DefId;
  34 use rustc_hir::intravisit::Visitor;
  35 use rustc_hir::lang_items::LangItem;
  36 use rustc_hir::{ExprKind, HirId, QPath};
  37 use rustc_infer::infer;
  38 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  39 use rustc_infer::infer::InferOk;
  40 use rustc_middle::middle::stability;
  41 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AllowTwoPhase};
  42 use rustc_middle::ty::error::ExpectedFound;
  43 use rustc_middle::ty::error::TypeError::{FieldMisMatch, Sorts};
  44 use rustc_middle::ty::subst::SubstsRef;
  45 use rustc_middle::ty::{self, AdtKind, Ty, TypeFoldable};
  46 use rustc_session::parse::feature_err;
  47 use rustc_span::hygiene::DesugaringKind;
  48 use rustc_span::lev_distance::find_best_match_for_name;
  49 use rustc_span::source_map::Span;
  50 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  51 use rustc_span::{BytePos, Pos};
  52 use rustc_trait_selection::traits::{self, ObligationCauseCode};
  53
  54 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  55     fn check_expr_eq_type(&self, expr: &'tcx hir::Expr<'tcx>, expected: Ty<'tcx>) {
  56         let ty = self.check_expr_with_hint(expr, expected);
  57         self.demand_eqtype(expr.span, expected, ty);
  58     }
  59
  60     pub fn check_expr_has_type_or_error(
  61         &self,
  62         expr: &'tcx hir::Expr<'tcx>,
  63         expected: Ty<'tcx>,
  64         extend_err: impl Fn(&mut Diagnostic),
  65     ) -> Ty<'tcx> {
  66         self.check_expr_meets_expectation_or_error(expr, ExpectHasType(expected), extend_err)
  67     }
  68
  69     fn check_expr_meets_expectation_or_error(
  70         &self,
  71         expr: &'tcx hir::Expr<'tcx>,
  72         expected: Expectation<'tcx>,
  73         extend_err: impl Fn(&mut Diagnostic),
  74     ) -> Ty<'tcx> {
  75         let expected_ty = expected.to_option(&self).unwrap_or(self.tcx.types.bool);
  76         let mut ty = self.check_expr_with_expectation(expr, expected);
  77
  78         // While we don't allow *arbitrary* coercions here, we *do* allow
  79         // coercions from ! to `expected`.
  80         if ty.is_never() {
  81             assert!(
  82                 !self.typeck_results.borrow().adjustments().contains_key(expr.hir_id),
  83                 "expression with never type wound up being adjusted"
  84             );
  85             let adj_ty = self.next_ty_var(TypeVariableOrigin {
  86                 kind: TypeVariableOriginKind::AdjustmentType,
  87                 span: expr.span,
  88             });
  89             self.apply_adjustments(
  90                 expr,
  91                 vec![Adjustment { kind: Adjust::NeverToAny, target: adj_ty }],
  92             );
  93             ty = adj_ty;
  94         }
  95
  96         if let Some(mut err) = self.demand_suptype_diag(expr.span, expected_ty, ty) {
  97             let expr = expr.peel_drop_temps();
  98             self.suggest_deref_ref_or_into(&mut err, expr, expected_ty, ty, None);
  99             extend_err(&mut err);
 100             err.emit();
 101         }
 102         ty
 103     }
 104
 105     pub(super) fn check_expr_coercable_to_type(
 106         &self,
 107         expr: &'tcx hir::Expr<'tcx>,
 108         expected: Ty<'tcx>,
 109         expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 110     ) -> Ty<'tcx> {
 111         let ty = self.check_expr_with_hint(expr, expected);
 112         // checks don't need two phase
 113         self.demand_coerce(expr, ty, expected, expected_ty_expr, AllowTwoPhase::No)
 114     }
 115
 116     pub(super) fn check_expr_with_hint(
 117         &self,
 118         expr: &'tcx hir::Expr<'tcx>,
 119         expected: Ty<'tcx>,
 120     ) -> Ty<'tcx> {
 121         self.check_expr_with_expectation(expr, ExpectHasType(expected))
 122     }
 123
 124     fn check_expr_with_expectation_and_needs(
 125         &self,
 126         expr: &'tcx hir::Expr<'tcx>,
 127         expected: Expectation<'tcx>,
 128         needs: Needs,
 129     ) -> Ty<'tcx> {
 130         let ty = self.check_expr_with_expectation(expr, expected);
 131
 132         // If the expression is used in a place whether mutable place is required
 133         // e.g. LHS of assignment, perform the conversion.
 134         if let Needs::MutPlace = needs {
 135             self.convert_place_derefs_to_mutable(expr);
 136         }
 137
 138         ty
 139     }
 140
 141     pub(super) fn check_expr(&self, expr: &'tcx hir::Expr<'tcx>) -> Ty<'tcx> {
 142         self.check_expr_with_expectation(expr, NoExpectation)
 143     }
 144
 145     pub(super) fn check_expr_with_needs(
 146         &self,
 147         expr: &'tcx hir::Expr<'tcx>,
 148         needs: Needs,
 149     ) -> Ty<'tcx> {
 150         self.check_expr_with_expectation_and_needs(expr, NoExpectation, needs)
 151     }
 152
 153     /// Invariant:
 154     /// If an expression has any sub-expressions that result in a type error,
 155     /// inspecting that expression's type with `ty.references_error()` will return
 156     /// true. Likewise, if an expression is known to diverge, inspecting its
 157     /// type with `ty::type_is_bot` will return true (n.b.: since Rust is
 158     /// strict, _|_ can appear in the type of an expression that does not,
 159     /// itself, diverge: for example, fn() -> _|_.)
 160     /// Note that inspecting a type's structure *directly* may expose the fact
 161     /// that there are actually multiple representations for `Error`, so avoid
 162     /// that when err needs to be handled differently.
 163     #[instrument(skip(self, expr), level = "debug")]
 164     pub(super) fn check_expr_with_expectation(
 165         &self,
 166         expr: &'tcx hir::Expr<'tcx>,
 167         expected: Expectation<'tcx>,
 168     ) -> Ty<'tcx> {
 169         self.check_expr_with_expectation_and_args(expr, expected, &[])
 170     }
 171
 172     /// Same as `check_expr_with_expectation`, but allows us to pass in the arguments of a
 173     /// `ExprKind::Call` when evaluating its callee when it is an `ExprKind::Path`.
 174     pub(super) fn check_expr_with_expectation_and_args(
 175         &self,
 176         expr: &'tcx hir::Expr<'tcx>,
 177         expected: Expectation<'tcx>,
 178         args: &'tcx [hir::Expr<'tcx>],
 179     ) -> Ty<'tcx> {
 180         if self.tcx().sess.verbose() {
 181             // make this code only run with -Zverbose because it is probably slow
 182             if let Ok(lint_str) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
 183                 if !lint_str.contains('\n') {
 184                     debug!("expr text: {lint_str}");
 185                 } else {
 186                     let mut lines = lint_str.lines();
 187                     if let Some(line0) = lines.next() {
 188                         let remaining_lines = lines.count();
 189                         debug!("expr text: {line0}");
 190                         debug!("expr text: ...(and {remaining_lines} more lines)");
 191                     }
 192                 }
 193             }
 194         }
 195
 196         // True if `expr` is a `Try::from_ok(())` that is a result of desugaring a try block
 197         // without the final expr (e.g. `try { return; }`). We don't want to generate an
 198         // unreachable_code lint for it since warnings for autogenerated code are confusing.
 199         let is_try_block_generated_unit_expr = match expr.kind {
 200             ExprKind::Call(_, args) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {
 201                 args.len() == 1 && args[0].span.is_desugaring(DesugaringKind::TryBlock)
 202             }
 203
 204             _ => false,
 205         };
 206
 207         // Warn for expressions after diverging siblings.
 208         if !is_try_block_generated_unit_expr {
 209             self.warn_if_unreachable(expr.hir_id, expr.span, "expression");
 210         }
 211
 212         // Hide the outer diverging and has_errors flags.
 213         let old_diverges = self.diverges.replace(Diverges::Maybe);
 214         let old_has_errors = self.has_errors.replace(false);
 215
 216         let ty = ensure_sufficient_stack(|| match &expr.kind {
 217             hir::ExprKind::Path(
 218                 qpath @ hir::QPath::Resolved(..) | qpath @ hir::QPath::TypeRelative(..),
 219             ) => self.check_expr_path(qpath, expr, args),
 220             _ => self.check_expr_kind(expr, expected),
 221         });
 222
 223         // Warn for non-block expressions with diverging children.
 224         match expr.kind {
 225             ExprKind::Block(..)
 226             | ExprKind::If(..)
 227             | ExprKind::Let(..)
 228             | ExprKind::Loop(..)
 229             | ExprKind::Match(..) => {}
 230             // If `expr` is a result of desugaring the try block and is an ok-wrapped
 231             // diverging expression (e.g. it arose from desugaring of `try { return }`),
 232             // we skip issuing a warning because it is autogenerated code.
 233             ExprKind::Call(..) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {}
 234             ExprKind::Call(callee, _) => self.warn_if_unreachable(expr.hir_id, callee.span, "call"),
 235             ExprKind::MethodCall(segment, ..) => {
 236                 self.warn_if_unreachable(expr.hir_id, segment.ident.span, "call")
 237             }
 238             _ => self.warn_if_unreachable(expr.hir_id, expr.span, "expression"),
 239         }
 240
 241         // Any expression that produces a value of type `!` must have diverged
 242         if ty.is_never() {
 243             self.diverges.set(self.diverges.get() | Diverges::always(expr.span));
 244         }
 245
 246         // Record the type, which applies it effects.
 247         // We need to do this after the warning above, so that
 248         // we don't warn for the diverging expression itself.
 249         self.write_ty(expr.hir_id, ty);
 250
 251         // Combine the diverging and has_error flags.
 252         self.diverges.set(self.diverges.get() | old_diverges);
 253         self.has_errors.set(self.has_errors.get() | old_has_errors);
 254
 255         debug!("type of {} is...", self.tcx.hir().node_to_string(expr.hir_id));
 256         debug!("... {:?}, expected is {:?}", ty, expected);
 257
 258         ty
 259     }
 260
 261     #[instrument(skip(self, expr), level = "debug")]
 262     pub(super) fn check_expr_kind(
 263         &self,
 264         expr: &'tcx hir::Expr<'tcx>,
 265         expected: Expectation<'tcx>,
 266     ) -> Ty<'tcx> {
 267         trace!("expr={:#?}", expr);
 268
 269         let tcx = self.tcx;
 270         match expr.kind {
 271             ExprKind::Box(subexpr) => self.check_expr_box(subexpr, expected),
 272             ExprKind::Lit(ref lit) => self.check_lit(&lit, expected),
 273             ExprKind::Binary(op, lhs, rhs) => self.check_binop(expr, op, lhs, rhs),
 274             ExprKind::Assign(lhs, rhs, span) => {
 275                 self.check_expr_assign(expr, expected, lhs, rhs, span)
 276             }
 277             ExprKind::AssignOp(op, lhs, rhs) => self.check_binop_assign(expr, op, lhs, rhs),
 278             ExprKind::Unary(unop, oprnd) => self.check_expr_unary(unop, oprnd, expected, expr),
 279             ExprKind::AddrOf(kind, mutbl, oprnd) => {
 280                 self.check_expr_addr_of(kind, mutbl, oprnd, expected, expr)
 281             }
 282             ExprKind::Path(QPath::LangItem(lang_item, _, hir_id)) => {
 283                 self.check_lang_item_path(lang_item, expr, hir_id)
 284             }
 285             ExprKind::Path(ref qpath) => self.check_expr_path(qpath, expr, &[]),
 286             ExprKind::InlineAsm(asm) => self.check_expr_asm(asm),
 287             ExprKind::Break(destination, ref expr_opt) => {
 288                 self.check_expr_break(destination, expr_opt.as_deref(), expr)
 289             }
 290             ExprKind::Continue(destination) => {
 291                 if destination.target_id.is_ok() {
 292                     tcx.types.never
 293                 } else {
 294                     // There was an error; make type-check fail.
 295                     tcx.ty_error()
 296                 }
 297             }
 298             ExprKind::Ret(ref expr_opt) => self.check_expr_return(expr_opt.as_deref(), expr),
 299             ExprKind::Let(let_expr) => self.check_expr_let(let_expr),
 300             ExprKind::Loop(body, _, source, _) => {
 301                 self.check_expr_loop(body, source, expected, expr)
 302             }
 303             ExprKind::Match(discrim, arms, match_src) => {
 304                 self.check_match(expr, &discrim, arms, expected, match_src)
 305             }
 306             ExprKind::Closure(capture, decl, body_id, _, gen) => {
 307                 self.check_expr_closure(expr, capture, &decl, body_id, gen, expected)
 308             }
 309             ExprKind::Block(body, _) => self.check_block_with_expected(&body, expected),
 310             ExprKind::Call(callee, args) => self.check_call(expr, &callee, args, expected),
 311             ExprKind::MethodCall(segment, args, _) => {
 312                 self.check_method_call(expr, segment, args, expected)
 313             }
 314             ExprKind::Cast(e, t) => self.check_expr_cast(e, t, expr),
 315             ExprKind::Type(e, t) => {
 316                 let ty = self.to_ty_saving_user_provided_ty(&t);
 317                 self.check_expr_eq_type(&e, ty);
 318                 ty
 319             }
 320             ExprKind::If(cond, then_expr, opt_else_expr) => {
 321                 self.check_then_else(cond, then_expr, opt_else_expr, expr.span, expected)
 322             }
 323             ExprKind::DropTemps(e) => self.check_expr_with_expectation(e, expected),
 324             ExprKind::Array(args) => self.check_expr_array(args, expected, expr),
 325             ExprKind::ConstBlock(ref anon_const) => {
 326                 self.check_expr_const_block(anon_const, expected, expr)
 327             }
 328             ExprKind::Repeat(element, ref count) => {
 329                 self.check_expr_repeat(element, count, expected, expr)
 330             }
 331             ExprKind::Tup(elts) => self.check_expr_tuple(elts, expected, expr),
 332             ExprKind::Struct(qpath, fields, ref base_expr) => {
 333                 self.check_expr_struct(expr, expected, qpath, fields, base_expr)
 334             }
 335             ExprKind::Field(base, field) => self.check_field(expr, &base, field),
 336             ExprKind::Index(base, idx) => self.check_expr_index(base, idx, expr),
 337             ExprKind::Yield(value, ref src) => self.check_expr_yield(value, expr, src),
 338             hir::ExprKind::Err => tcx.ty_error(),
 339         }
 340     }
 341
 342     fn check_expr_box(&self, expr: &'tcx hir::Expr<'tcx>, expected: Expectation<'tcx>) -> Ty<'tcx> {
 343         let expected_inner = expected.to_option(self).map_or(NoExpectation, |ty| match ty.kind() {
 344             ty::Adt(def, _) if def.is_box() => Expectation::rvalue_hint(self, ty.boxed_ty()),
 345             _ => NoExpectation,
 346         });
 347         let referent_ty = self.check_expr_with_expectation(expr, expected_inner);
 348         self.require_type_is_sized(referent_ty, expr.span, traits::SizedBoxType);
 349         self.tcx.mk_box(referent_ty)
 350     }
 351
 352     fn check_expr_unary(
 353         &self,
 354         unop: hir::UnOp,
 355         oprnd: &'tcx hir::Expr<'tcx>,
 356         expected: Expectation<'tcx>,
 357         expr: &'tcx hir::Expr<'tcx>,
 358     ) -> Ty<'tcx> {
 359         let tcx = self.tcx;
 360         let expected_inner = match unop {
 361             hir::UnOp::Not | hir::UnOp::Neg => expected,
 362             hir::UnOp::Deref => NoExpectation,
 363         };
 364         let mut oprnd_t = self.check_expr_with_expectation(&oprnd, expected_inner);
 365
 366         if !oprnd_t.references_error() {
 367             oprnd_t = self.structurally_resolved_type(expr.span, oprnd_t);
 368             match unop {
 369                 hir::UnOp::Deref => {
 370                     if let Some(ty) = self.lookup_derefing(expr, oprnd, oprnd_t) {
 371                         oprnd_t = ty;
 372                     } else {
 373                         let mut err = type_error_struct!(
 374                             tcx.sess,
 375                             expr.span,
 376                             oprnd_t,
 377                             E0614,
 378                             "type `{oprnd_t}` cannot be dereferenced",
 379                         );
 380                         let sp = tcx.sess.source_map().start_point(expr.span);
 381                         if let Some(sp) =
 382                             tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
 383                         {
 384                             tcx.sess.parse_sess.expr_parentheses_needed(&mut err, *sp);
 385                         }
 386                         err.emit();
 387                         oprnd_t = tcx.ty_error();
 388                     }
 389                 }
 390                 hir::UnOp::Not => {
 391                     let result = self.check_user_unop(expr, oprnd_t, unop);
 392                     // If it's builtin, we can reuse the type, this helps inference.
 393                     if !(oprnd_t.is_integral() || *oprnd_t.kind() == ty::Bool) {
 394                         oprnd_t = result;
 395                     }
 396                 }
 397                 hir::UnOp::Neg => {
 398                     let result = self.check_user_unop(expr, oprnd_t, unop);
 399                     // If it's builtin, we can reuse the type, this helps inference.
 400                     if !oprnd_t.is_numeric() {
 401                         oprnd_t = result;
 402                     }
 403                 }
 404             }
 405         }
 406         oprnd_t
 407     }
 408
 409     fn check_expr_addr_of(
 410         &self,
 411         kind: hir::BorrowKind,
 412         mutbl: hir::Mutability,
 413         oprnd: &'tcx hir::Expr<'tcx>,
 414         expected: Expectation<'tcx>,
 415         expr: &'tcx hir::Expr<'tcx>,
 416     ) -> Ty<'tcx> {
 417         let hint = expected.only_has_type(self).map_or(NoExpectation, |ty| {
 418             match ty.kind() {
 419                 ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
 420                     if oprnd.is_syntactic_place_expr() {
 421                         // Places may legitimately have unsized types.
 422                         // For example, dereferences of a fat pointer and
 423                         // the last field of a struct can be unsized.
 424                         ExpectHasType(*ty)
 425                     } else {
 426                         Expectation::rvalue_hint(self, *ty)
 427                     }
 428                 }
 429                 _ => NoExpectation,
 430             }
 431         });
 432         let ty =
 433             self.check_expr_with_expectation_and_needs(&oprnd, hint, Needs::maybe_mut_place(mutbl));
 434
 435         let tm = ty::TypeAndMut { ty, mutbl };
 436         match kind {
 437             _ if tm.ty.references_error() => self.tcx.ty_error(),
 438             hir::BorrowKind::Raw => {
 439                 self.check_named_place_expr(oprnd);
 440                 self.tcx.mk_ptr(tm)
 441             }
 442             hir::BorrowKind::Ref => {
 443                 // Note: at this point, we cannot say what the best lifetime
 444                 // is to use for resulting pointer.  We want to use the
 445                 // shortest lifetime possible so as to avoid spurious borrowck
 446                 // errors.  Moreover, the longest lifetime will depend on the
 447                 // precise details of the value whose address is being taken
 448                 // (and how long it is valid), which we don't know yet until
 449                 // type inference is complete.
 450                 //
 451                 // Therefore, here we simply generate a region variable. The
 452                 // region inferencer will then select a suitable value.
 453                 // Finally, borrowck will infer the value of the region again,
 454                 // this time with enough precision to check that the value
 455                 // whose address was taken can actually be made to live as long
 456                 // as it needs to live.
 457                 let region = self.next_region_var(infer::AddrOfRegion(expr.span));
 458                 self.tcx.mk_ref(region, tm)
 459             }
 460         }
 461     }
 462
 463     /// Does this expression refer to a place that either:
 464     /// * Is based on a local or static.
 465     /// * Contains a dereference
 466     /// Note that the adjustments for the children of `expr` should already
 467     /// have been resolved.
 468     fn check_named_place_expr(&self, oprnd: &'tcx hir::Expr<'tcx>) {
 469         let is_named = oprnd.is_place_expr(|base| {
 470             // Allow raw borrows if there are any deref adjustments.
 471             //
 472             // const VAL: (i32,) = (0,);
 473             // const REF: &(i32,) = &(0,);
 474             //
 475             // &raw const VAL.0;            // ERROR
 476             // &raw const REF.0;            // OK, same as &raw const (*REF).0;
 477             //
 478             // This is maybe too permissive, since it allows
 479             // `let u = &raw const Box::new((1,)).0`, which creates an
 480             // immediately dangling raw pointer.
 481             self.typeck_results
 482                 .borrow()
 483                 .adjustments()
 484                 .get(base.hir_id)
 485                 .map_or(false, |x| x.iter().any(|adj| matches!(adj.kind, Adjust::Deref(_))))
 486         });
 487         if !is_named {
 488             self.tcx.sess.emit_err(AddressOfTemporaryTaken { span: oprnd.span });
 489         }
 490     }
 491
 492     fn check_lang_item_path(
 493         &self,
 494         lang_item: hir::LangItem,
 495         expr: &'tcx hir::Expr<'tcx>,
 496         hir_id: Option<hir::HirId>,
 497     ) -> Ty<'tcx> {
 498         self.resolve_lang_item_path(lang_item, expr.span, expr.hir_id, hir_id).1
 499     }
 500
 501     pub(crate) fn check_expr_path(
 502         &self,
 503         qpath: &'tcx hir::QPath<'tcx>,
 504         expr: &'tcx hir::Expr<'tcx>,
 505         args: &'tcx [hir::Expr<'tcx>],
 506     ) -> Ty<'tcx> {
 507         let tcx = self.tcx;
 508         let (res, opt_ty, segs) =
 509             self.resolve_ty_and_res_fully_qualified_call(qpath, expr.hir_id, expr.span);
 510         let ty = match res {
 511             Res::Err => {
 512                 self.set_tainted_by_errors();
 513                 tcx.ty_error()
 514             }
 515             Res::Def(DefKind::Ctor(_, CtorKind::Fictive), _) => {
 516                 report_unexpected_variant_res(tcx, res, expr.span);
 517                 tcx.ty_error()
 518             }
 519             _ => self.instantiate_value_path(segs, opt_ty, res, expr.span, expr.hir_id).0,
 520         };
 521
 522         if let ty::FnDef(..) = ty.kind() {
 523             let fn_sig = ty.fn_sig(tcx);
 524             if !tcx.features().unsized_fn_params {
 525                 // We want to remove some Sized bounds from std functions,
 526                 // but don't want to expose the removal to stable Rust.
 527                 // i.e., we don't want to allow
 528                 //
 529                 // ```rust
 530                 // drop as fn(str);
 531                 // ```
 532                 //
 533                 // to work in stable even if the Sized bound on `drop` is relaxed.
 534                 for i in 0..fn_sig.inputs().skip_binder().len() {
 535                     // We just want to check sizedness, so instead of introducing
 536                     // placeholder lifetimes with probing, we just replace higher lifetimes
 537                     // with fresh vars.
 538                     let span = args.get(i).map(|a| a.span).unwrap_or(expr.span);
 539                     let input = self
 540                         .replace_bound_vars_with_fresh_vars(
 541                             span,
 542                             infer::LateBoundRegionConversionTime::FnCall,
 543                             fn_sig.input(i),
 544                         )
 545                         .0;
 546                     self.require_type_is_sized_deferred(
 547                         input,
 548                         span,
 549                         traits::SizedArgumentType(None),
 550                     );
 551                 }
 552             }
 553             // Here we want to prevent struct constructors from returning unsized types.
 554             // There were two cases this happened: fn pointer coercion in stable
 555             // and usual function call in presence of unsized_locals.
 556             // Also, as we just want to check sizedness, instead of introducing
 557             // placeholder lifetimes with probing, we just replace higher lifetimes
 558             // with fresh vars.
 559             let output = self
 560                 .replace_bound_vars_with_fresh_vars(
 561                     expr.span,
 562                     infer::LateBoundRegionConversionTime::FnCall,
 563                     fn_sig.output(),
 564                 )
 565                 .0;
 566             self.require_type_is_sized_deferred(output, expr.span, traits::SizedReturnType);
 567         }
 568
 569         // We always require that the type provided as the value for
 570         // a type parameter outlives the moment of instantiation.
 571         let substs = self.typeck_results.borrow().node_substs(expr.hir_id);
 572         self.add_wf_bounds(substs, expr);
 573
 574         ty
 575     }
 576
 577     fn check_expr_break(
 578         &self,
 579         destination: hir::Destination,
 580         expr_opt: Option<&'tcx hir::Expr<'tcx>>,
 581         expr: &'tcx hir::Expr<'tcx>,
 582     ) -> Ty<'tcx> {
 583         let tcx = self.tcx;
 584         if let Ok(target_id) = destination.target_id {
 585             let (e_ty, cause);
 586             if let Some(e) = expr_opt {
 587                 // If this is a break with a value, we need to type-check
 588                 // the expression. Get an expected type from the loop context.
 589                 let opt_coerce_to = {
 590                     // We should release `enclosing_breakables` before the `check_expr_with_hint`
 591                     // below, so can't move this block of code to the enclosing scope and share
 592                     // `ctxt` with the second `enclosing_breakables` borrow below.
 593                     let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 594                     match enclosing_breakables.opt_find_breakable(target_id) {
 595                         Some(ctxt) => ctxt.coerce.as_ref().map(|coerce| coerce.expected_ty()),
 596                         None => {
 597                             // Avoid ICE when `break` is inside a closure (#65383).
 598                             return tcx.ty_error_with_message(
 599                                 expr.span,
 600                                 "break was outside loop, but no error was emitted",
 601                             );
 602                         }
 603                     }
 604                 };
 605
 606                 // If the loop context is not a `loop { }`, then break with
 607                 // a value is illegal, and `opt_coerce_to` will be `None`.
 608                 // Just set expectation to error in that case.
 609                 let coerce_to = opt_coerce_to.unwrap_or_else(|| tcx.ty_error());
 610
 611                 // Recurse without `enclosing_breakables` borrowed.
 612                 e_ty = self.check_expr_with_hint(e, coerce_to);
 613                 cause = self.misc(e.span);
 614             } else {
 615                 // Otherwise, this is a break *without* a value. That's
 616                 // always legal, and is equivalent to `break ()`.
 617                 e_ty = tcx.mk_unit();
 618                 cause = self.misc(expr.span);
 619             }
 620
 621             // Now that we have type-checked `expr_opt`, borrow
 622             // the `enclosing_loops` field and let's coerce the
 623             // type of `expr_opt` into what is expected.
 624             let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
 625             let Some(ctxt) = enclosing_breakables.opt_find_breakable(target_id) else {
 626                 // Avoid ICE when `break` is inside a closure (#65383).
 627                 return tcx.ty_error_with_message(
 628                     expr.span,
 629                     "break was outside loop, but no error was emitted",
 630                 );
 631             };
 632
 633             if let Some(ref mut coerce) = ctxt.coerce {
 634                 if let Some(ref e) = expr_opt {
 635                     coerce.coerce(self, &cause, e, e_ty);
 636                 } else {
 637                     assert!(e_ty.is_unit());
 638                     let ty = coerce.expected_ty();
 639                     coerce.coerce_forced_unit(
 640                         self,
 641                         &cause,
 642                         &mut |mut err| {
 643                             self.suggest_mismatched_types_on_tail(
 644                                 &mut err, expr, ty, e_ty, target_id,
 645                             );
 646                             if let Some(val) = ty_kind_suggestion(ty) {
 647                                 let label = destination
 648                                     .label
 649                                     .map(|l| format!(" {}", l.ident))
 650                                     .unwrap_or_else(String::new);
 651                                 err.span_suggestion(
 652                                     expr.span,
 653                                     "give it a value of the expected type",
 654                                     format!("break{label} {val}"),
 655                                     Applicability::HasPlaceholders,
 656                                 );
 657                             }
 658                         },
 659                         false,
 660                     );
 661                 }
 662             } else {
 663                 // If `ctxt.coerce` is `None`, we can just ignore
 664                 // the type of the expression.  This is because
 665                 // either this was a break *without* a value, in
 666                 // which case it is always a legal type (`()`), or
 667                 // else an error would have been flagged by the
 668                 // `loops` pass for using break with an expression
 669                 // where you are not supposed to.
 670                 assert!(expr_opt.is_none() || self.tcx.sess.has_errors().is_some());
 671             }
 672
 673             // If we encountered a `break`, then (no surprise) it may be possible to break from the
 674             // loop... unless the value being returned from the loop diverges itself, e.g.
 675             // `break return 5` or `break loop {}`.
 676             ctxt.may_break |= !self.diverges.get().is_always();
 677
 678             // the type of a `break` is always `!`, since it diverges
 679             tcx.types.never
 680         } else {
 681             // Otherwise, we failed to find the enclosing loop;
 682             // this can only happen if the `break` was not
 683             // inside a loop at all, which is caught by the
 684             // loop-checking pass.
 685             let err = self.tcx.ty_error_with_message(
 686                 expr.span,
 687                 "break was outside loop, but no error was emitted",
 688             );
 689
 690             // We still need to assign a type to the inner expression to
 691             // prevent the ICE in #43162.
 692             if let Some(e) = expr_opt {
 693                 self.check_expr_with_hint(e, err);
 694
 695                 // ... except when we try to 'break rust;'.
 696                 // ICE this expression in particular (see #43162).
 697                 if let ExprKind::Path(QPath::Resolved(_, path)) = e.kind {
 698                     if path.segments.len() == 1 && path.segments[0].ident.name == sym::rust {
 699                         fatally_break_rust(self.tcx.sess);
 700                     }
 701                 }
 702             }
 703
 704             // There was an error; make type-check fail.
 705             err
 706         }
 707     }
 708
 709     fn check_expr_return(
 710         &self,
 711         expr_opt: Option<&'tcx hir::Expr<'tcx>>,
 712         expr: &'tcx hir::Expr<'tcx>,
 713     ) -> Ty<'tcx> {
 714         if self.ret_coercion.is_none() {
 715             let mut err = ReturnStmtOutsideOfFnBody {
 716                 span: expr.span,
 717                 encl_body_span: None,
 718                 encl_fn_span: None,
 719             };
 720
 721             let encl_item_id = self.tcx.hir().get_parent_item(expr.hir_id);
 722
 723             if let Some(hir::Node::Item(hir::Item {
 724                 kind: hir::ItemKind::Fn(..),
 725                 span: encl_fn_span,
 726                 ..
 727             }))
 728             | Some(hir::Node::TraitItem(hir::TraitItem {
 729                 kind: hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)),
 730                 span: encl_fn_span,
 731                 ..
 732             }))
 733             | Some(hir::Node::ImplItem(hir::ImplItem {
 734                 kind: hir::ImplItemKind::Fn(..),
 735                 span: encl_fn_span,
 736                 ..
 737             })) = self.tcx.hir().find_by_def_id(encl_item_id)
 738             {
 739                 // We are inside a function body, so reporting "return statement
 740                 // outside of function body" needs an explanation.
 741
 742                 let encl_body_owner_id = self.tcx.hir().enclosing_body_owner(expr.hir_id);
 743
 744                 // If this didn't hold, we would not have to report an error in
 745                 // the first place.
 746                 assert_ne!(hir::HirId::make_owner(encl_item_id), encl_body_owner_id);
 747
 748                 let encl_body_id = self.tcx.hir().body_owned_by(encl_body_owner_id);
 749                 let encl_body = self.tcx.hir().body(encl_body_id);
 750
 751                 err.encl_body_span = Some(encl_body.value.span);
 752                 err.encl_fn_span = Some(*encl_fn_span);
 753             }
 754
 755             self.tcx.sess.emit_err(err);
 756
 757             if let Some(e) = expr_opt {
 758                 // We still have to type-check `e` (issue #86188), but calling
 759                 // `check_return_expr` only works inside fn bodies.
 760                 self.check_expr(e);
 761             }
 762         } else if let Some(e) = expr_opt {
 763             if self.ret_coercion_span.get().is_none() {
 764                 self.ret_coercion_span.set(Some(e.span));
 765             }
 766             self.check_return_expr(e, true);
 767         } else {
 768             let mut coercion = self.ret_coercion.as_ref().unwrap().borrow_mut();
 769             if self.ret_coercion_span.get().is_none() {
 770                 self.ret_coercion_span.set(Some(expr.span));
 771             }
 772             let cause = self.cause(expr.span, ObligationCauseCode::ReturnNoExpression);
 773             if let Some((fn_decl, _)) = self.get_fn_decl(expr.hir_id) {
 774                 coercion.coerce_forced_unit(
 775                     self,
 776                     &cause,
 777                     &mut |db| {
 778                         let span = fn_decl.output.span();
 779                         if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
 780                             db.span_label(
 781                                 span,
 782                                 format!("expected `{snippet}` because of this return type"),
 783                             );
 784                         }
 785                     },
 786                     true,
 787                 );
 788             } else {
 789                 coercion.coerce_forced_unit(self, &cause, &mut |_| (), true);
 790             }
 791         }
 792         self.tcx.types.never
 793     }
 794
 795     /// `explicit_return` is `true` if we're checking an explicit `return expr`,
 796     /// and `false` if we're checking a trailing expression.
 797     pub(super) fn check_return_expr(
 798         &self,
 799         return_expr: &'tcx hir::Expr<'tcx>,
 800         explicit_return: bool,
 801     ) {
 802         let ret_coercion = self.ret_coercion.as_ref().unwrap_or_else(|| {
 803             span_bug!(return_expr.span, "check_return_expr called outside fn body")
 804         });
 805
 806         let ret_ty = ret_coercion.borrow().expected_ty();
 807         let return_expr_ty = self.check_expr_with_hint(return_expr, ret_ty);
 808         let mut span = return_expr.span;
 809         // Use the span of the trailing expression for our cause,
 810         // not the span of the entire function
 811         if !explicit_return {
 812             if let ExprKind::Block(body, _) = return_expr.kind && let Some(last_expr) = body.expr {
 813                 span = last_expr.span;
 814             }
 815         }
 816         ret_coercion.borrow_mut().coerce(
 817             self,
 818             &self.cause(span, ObligationCauseCode::ReturnValue(return_expr.hir_id)),
 819             return_expr,
 820             return_expr_ty,
 821         );
 822     }
 823
 824     pub(crate) fn check_lhs_assignable(
 825         &self,
 826         lhs: &'tcx hir::Expr<'tcx>,
 827         err_code: &'static str,
 828         op_span: Span,
 829     ) {
 830         if lhs.is_syntactic_place_expr() {
 831             return;
 832         }
 833
 834         // FIXME: Make this use SessionDiagnostic once error codes can be dynamically set.
 835         let mut err = self.tcx.sess.struct_span_err_with_code(
 836             op_span,
 837             "invalid left-hand side of assignment",
 838             DiagnosticId::Error(err_code.into()),
 839         );
 840         err.span_label(lhs.span, "cannot assign to this expression");
 841
 842         self.comes_from_while_condition(lhs.hir_id, |expr| {
 843             err.span_suggestion_verbose(
 844                 expr.span.shrink_to_lo(),
 845                 "you might have meant to use pattern destructuring",
 846                 "let ".to_string(),
 847                 Applicability::MachineApplicable,
 848             );
 849         });
 850
 851         err.emit();
 852     }
 853
 854     // Check if an expression `original_expr_id` comes from the condition of a while loop,
 855     // as opposed from the body of a while loop, which we can naively check by iterating
 856     // parents until we find a loop...
 857     pub(super) fn comes_from_while_condition(
 858         &self,
 859         original_expr_id: HirId,
 860         then: impl FnOnce(&hir::Expr<'_>),
 861     ) {
 862         let mut parent = self.tcx.hir().get_parent_node(original_expr_id);
 863         while let Some(node) = self.tcx.hir().find(parent) {
 864             match node {
 865                 hir::Node::Expr(hir::Expr {
 866                     kind:
 867                         hir::ExprKind::Loop(
 868                             hir::Block {
 869                                 expr:
 870                                     Some(hir::Expr {
 871                                         kind:
 872                                             hir::ExprKind::Match(expr, ..) | hir::ExprKind::If(expr, ..),
 873                                         ..
 874                                     }),
 875                                 ..
 876                             },
 877                             _,
 878                             hir::LoopSource::While,
 879                             _,
 880                         ),
 881                     ..
 882                 }) => {
 883                     // Check if our original expression is a child of the condition of a while loop
 884                     let expr_is_ancestor = std::iter::successors(Some(original_expr_id), |id| {
 885                         self.tcx.hir().find_parent_node(*id)
 886                     })
 887                     .take_while(|id| *id != parent)
 888                     .any(|id| id == expr.hir_id);
 889                     // if it is, then we have a situation like `while Some(0) = value.get(0) {`,
 890                     // where `while let` was more likely intended.
 891                     if expr_is_ancestor {
 892                         then(expr);
 893                     }
 894                     break;
 895                 }
 896                 hir::Node::Item(_)
 897                 | hir::Node::ImplItem(_)
 898                 | hir::Node::TraitItem(_)
 899                 | hir::Node::Crate(_) => break,
 900                 _ => {
 901                     parent = self.tcx.hir().get_parent_node(parent);
 902                 }
 903             }
 904         }
 905     }
 906
 907     // A generic function for checking the 'then' and 'else' clauses in an 'if'
 908     // or 'if-else' expression.
 909     fn check_then_else(
 910         &self,
 911         cond_expr: &'tcx hir::Expr<'tcx>,
 912         then_expr: &'tcx hir::Expr<'tcx>,
 913         opt_else_expr: Option<&'tcx hir::Expr<'tcx>>,
 914         sp: Span,
 915         orig_expected: Expectation<'tcx>,
 916     ) -> Ty<'tcx> {
 917         let cond_ty = self.check_expr_has_type_or_error(cond_expr, self.tcx.types.bool, |_| {});
 918
 919         self.warn_if_unreachable(
 920             cond_expr.hir_id,
 921             then_expr.span,
 922             "block in `if` or `while` expression",
 923         );
 924
 925         let cond_diverges = self.diverges.get();
 926         self.diverges.set(Diverges::Maybe);
 927
 928         let expected = orig_expected.adjust_for_branches(self);
 929         let then_ty = self.check_expr_with_expectation(then_expr, expected);
 930         let then_diverges = self.diverges.get();
 931         self.diverges.set(Diverges::Maybe);
 932
 933         // We've already taken the expected type's preferences
 934         // into account when typing the `then` branch. To figure
 935         // out the initial shot at a LUB, we thus only consider
 936         // `expected` if it represents a *hard* constraint
 937         // (`only_has_type`); otherwise, we just go with a
 938         // fresh type variable.
 939         let coerce_to_ty = expected.coercion_target_type(self, sp);
 940         let mut coerce: DynamicCoerceMany<'_> = CoerceMany::new(coerce_to_ty);
 941
 942         coerce.coerce(self, &self.misc(sp), then_expr, then_ty);
 943
 944         if let Some(else_expr) = opt_else_expr {
 945             let else_ty = if sp.desugaring_kind() == Some(DesugaringKind::LetElse) {
 946                 // todo introduce `check_expr_with_expectation(.., Expectation::LetElse)`
 947                 //   for errors that point to the offending expression rather than the entire block.
 948                 //   We could use `check_expr_eq_type(.., tcx.types.never)`, but then there is no
 949                 //   way to detect that the expected type originated from let-else and provide
 950                 //   a customized error.
 951                 let else_ty = self.check_expr(else_expr);
 952                 let cause = self.cause(else_expr.span, ObligationCauseCode::LetElse);
 953
 954                 if let Some(mut err) =
 955                     self.demand_eqtype_with_origin(&cause, self.tcx.types.never, else_ty)
 956                 {
 957                     err.emit();
 958                     self.tcx.ty_error()
 959                 } else {
 960                     else_ty
 961                 }
 962             } else {
 963                 self.check_expr_with_expectation(else_expr, expected)
 964             };
 965             let else_diverges = self.diverges.get();
 966
 967             let opt_suggest_box_span = self.opt_suggest_box_span(else_ty, orig_expected);
 968             let if_cause =
 969                 self.if_cause(sp, then_expr, else_expr, then_ty, else_ty, opt_suggest_box_span);
 970
 971             coerce.coerce(self, &if_cause, else_expr, else_ty);
 972
 973             // We won't diverge unless both branches do (or the condition does).
 974             self.diverges.set(cond_diverges | then_diverges & else_diverges);
 975         } else {
 976             self.if_fallback_coercion(sp, then_expr, &mut coerce);
 977
 978             // If the condition is false we can't diverge.
 979             self.diverges.set(cond_diverges);
 980         }
 981
 982         let result_ty = coerce.complete(self);
 983         if cond_ty.references_error() { self.tcx.ty_error() } else { result_ty }
 984     }
 985
 986     /// Type check assignment expression `expr` of form `lhs = rhs`.
 987     /// The expected type is `()` and is passed to the function for the purposes of diagnostics.
 988     fn check_expr_assign(
 989         &self,
 990         expr: &'tcx hir::Expr<'tcx>,
 991         expected: Expectation<'tcx>,
 992         lhs: &'tcx hir::Expr<'tcx>,
 993         rhs: &'tcx hir::Expr<'tcx>,
 994         span: Span,
 995     ) -> Ty<'tcx> {
 996         let expected_ty = expected.coercion_target_type(self, expr.span);
 997         if expected_ty == self.tcx.types.bool {
 998             // The expected type is `bool` but this will result in `()` so we can reasonably
 999             // say that the user intended to write `lhs == rhs` instead of `lhs = rhs`.
1000             // The likely cause of this is `if foo = bar { .. }`.
1001             let actual_ty = self.tcx.mk_unit();
1002             let mut err = self.demand_suptype_diag(expr.span, expected_ty, actual_ty).unwrap();
1003             let lhs_ty = self.check_expr(&lhs);
1004             let rhs_ty = self.check_expr(&rhs);
1005             let (applicability, eq) = if self.can_coerce(rhs_ty, lhs_ty) {
1006                 (Applicability::MachineApplicable, true)
1007             } else {
1008                 (Applicability::MaybeIncorrect, false)
1009             };
1010             if !lhs.is_syntactic_place_expr() && !matches!(lhs.kind, hir::ExprKind::Lit(_)) {
1011                 // Do not suggest `if let x = y` as `==` is way more likely to be the intention.
1012                 let hir = self.tcx.hir();
1013                 if let hir::Node::Expr(hir::Expr { kind: ExprKind::If { .. }, .. }) =
1014                     hir.get(hir.get_parent_node(hir.get_parent_node(expr.hir_id)))
1015                 {
1016                     err.span_suggestion_verbose(
1017                         expr.span.shrink_to_lo(),
1018                         "you might have meant to use pattern matching",
1019                         "let ".to_string(),
1020                         applicability,
1021                     );
1022                 };
1023             }
1024             if eq {
1025                 err.span_suggestion_verbose(
1026                     span,
1027                     "you might have meant to compare for equality",
1028                     "==".to_string(),
1029                     applicability,
1030                 );
1031             }
1032
1033             // If the assignment expression itself is ill-formed, don't
1034             // bother emitting another error
1035             if lhs_ty.references_error() || rhs_ty.references_error() {
1036                 err.delay_as_bug()
1037             } else {
1038                 err.emit();
1039             }
1040             return self.tcx.ty_error();
1041         }
1042
1043         self.check_lhs_assignable(lhs, "E0070", span);
1044
1045         let lhs_ty = self.check_expr_with_needs(&lhs, Needs::MutPlace);
1046         let rhs_ty = self.check_expr_coercable_to_type(&rhs, lhs_ty, Some(lhs));
1047
1048         self.require_type_is_sized(lhs_ty, lhs.span, traits::AssignmentLhsSized);
1049
1050         if lhs_ty.references_error() || rhs_ty.references_error() {
1051             self.tcx.ty_error()
1052         } else {
1053             self.tcx.mk_unit()
1054         }
1055     }
1056
1057     fn check_expr_let(&self, let_expr: &'tcx hir::Let<'tcx>) -> Ty<'tcx> {
1058         // for let statements, this is done in check_stmt
1059         let init = let_expr.init;
1060         self.warn_if_unreachable(init.hir_id, init.span, "block in `let` expression");
1061         // otherwise check exactly as a let statement
1062         self.check_decl(let_expr.into());
1063         // but return a bool, for this is a boolean expression
1064         self.tcx.types.bool
1065     }
1066
1067     fn check_expr_loop(
1068         &self,
1069         body: &'tcx hir::Block<'tcx>,
1070         source: hir::LoopSource,
1071         expected: Expectation<'tcx>,
1072         expr: &'tcx hir::Expr<'tcx>,
1073     ) -> Ty<'tcx> {
1074         let coerce = match source {
1075             // you can only use break with a value from a normal `loop { }`
1076             hir::LoopSource::Loop => {
1077                 let coerce_to = expected.coercion_target_type(self, body.span);
1078                 Some(CoerceMany::new(coerce_to))
1079             }
1080
1081             hir::LoopSource::While | hir::LoopSource::ForLoop => None,
1082         };
1083
1084         let ctxt = BreakableCtxt {
1085             coerce,
1086             may_break: false, // Will get updated if/when we find a `break`.
1087         };
1088
1089         let (ctxt, ()) = self.with_breakable_ctxt(expr.hir_id, ctxt, || {
1090             self.check_block_no_value(&body);
1091         });
1092
1093         if ctxt.may_break {
1094             // No way to know whether it's diverging because
1095             // of a `break` or an outer `break` or `return`.
1096             self.diverges.set(Diverges::Maybe);
1097         }
1098
1099         // If we permit break with a value, then result type is
1100         // the LUB of the breaks (possibly ! if none); else, it
1101         // is nil. This makes sense because infinite loops
1102         // (which would have type !) are only possible iff we
1103         // permit break with a value [1].
1104         if ctxt.coerce.is_none() && !ctxt.may_break {
1105             // [1]
1106             self.tcx.sess.delay_span_bug(body.span, "no coercion, but loop may not break");
1107         }
1108         ctxt.coerce.map(|c| c.complete(self)).unwrap_or_else(|| self.tcx.mk_unit())
1109     }
1110
1111     /// Checks a method call.
1112     fn check_method_call(
1113         &self,
1114         expr: &'tcx hir::Expr<'tcx>,
1115         segment: &hir::PathSegment<'_>,
1116         args: &'tcx [hir::Expr<'tcx>],
1117         expected: Expectation<'tcx>,
1118     ) -> Ty<'tcx> {
1119         let rcvr = &args[0];
1120         let rcvr_t = self.check_expr(&rcvr);
1121         // no need to check for bot/err -- callee does that
1122         let rcvr_t = self.structurally_resolved_type(args[0].span, rcvr_t);
1123         let span = segment.ident.span;
1124
1125         let method = match self.lookup_method(rcvr_t, segment, span, expr, rcvr, args) {
1126             Ok(method) => {
1127                 // We could add a "consider `foo::<params>`" suggestion here, but I wasn't able to
1128                 // trigger this codepath causing `structurally_resolved_type` to emit an error.
1129
1130                 self.write_method_call(expr.hir_id, method);
1131                 Ok(method)
1132             }
1133             Err(error) => {
1134                 if segment.ident.name != kw::Empty {
1135                     if let Some(mut err) = self.report_method_error(
1136                         span,
1137                         rcvr_t,
1138                         segment.ident,
1139                         SelfSource::MethodCall(&args[0]),
1140                         error,
1141                         Some(args),
1142                     ) {
1143                         err.emit();
1144                     }
1145                 }
1146                 Err(())
1147             }
1148         };
1149
1150         // Call the generic checker.
1151         self.check_method_argument_types(
1152             span,
1153             expr,
1154             method,
1155             &args[1..],
1156             DontTupleArguments,
1157             expected,
1158         )
1159     }
1160
1161     fn check_expr_cast(
1162         &self,
1163         e: &'tcx hir::Expr<'tcx>,
1164         t: &'tcx hir::Ty<'tcx>,
1165         expr: &'tcx hir::Expr<'tcx>,
1166     ) -> Ty<'tcx> {
1167         // Find the type of `e`. Supply hints based on the type we are casting to,
1168         // if appropriate.
1169         let t_cast = self.to_ty_saving_user_provided_ty(t);
1170         let t_cast = self.resolve_vars_if_possible(t_cast);
1171         let t_expr = self.check_expr_with_expectation(e, ExpectCastableToType(t_cast));
1172         let t_expr = self.resolve_vars_if_possible(t_expr);
1173
1174         // Eagerly check for some obvious errors.
1175         if t_expr.references_error() || t_cast.references_error() {
1176             self.tcx.ty_error()
1177         } else {
1178             // Defer other checks until we're done type checking.
1179             let mut deferred_cast_checks = self.deferred_cast_checks.borrow_mut();
1180             match cast::CastCheck::new(self, e, t_expr, t_cast, t.span, expr.span) {
1181                 Ok(cast_check) => {
1182                     debug!(
1183                         "check_expr_cast: deferring cast from {:?} to {:?}: {:?}",
1184                         t_cast, t_expr, cast_check,
1185                     );
1186                     deferred_cast_checks.push(cast_check);
1187                     t_cast
1188                 }
1189                 Err(_) => self.tcx.ty_error(),
1190             }
1191         }
1192     }
1193
1194     fn check_expr_array(
1195         &self,
1196         args: &'tcx [hir::Expr<'tcx>],
1197         expected: Expectation<'tcx>,
1198         expr: &'tcx hir::Expr<'tcx>,
1199     ) -> Ty<'tcx> {
1200         let element_ty = if !args.is_empty() {
1201             let coerce_to = expected
1202                 .to_option(self)
1203                 .and_then(|uty| match *uty.kind() {
1204                     ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
1205                     _ => None,
1206                 })
1207                 .unwrap_or_else(|| {
1208                     self.next_ty_var(TypeVariableOrigin {
1209                         kind: TypeVariableOriginKind::TypeInference,
1210                         span: expr.span,
1211                     })
1212                 });
1213             let mut coerce = CoerceMany::with_coercion_sites(coerce_to, args);
1214             assert_eq!(self.diverges.get(), Diverges::Maybe);
1215             for e in args {
1216                 let e_ty = self.check_expr_with_hint(e, coerce_to);
1217                 let cause = self.misc(e.span);
1218                 coerce.coerce(self, &cause, e, e_ty);
1219             }
1220             coerce.complete(self)
1221         } else {
1222             self.next_ty_var(TypeVariableOrigin {
1223                 kind: TypeVariableOriginKind::TypeInference,
1224                 span: expr.span,
1225             })
1226         };
1227         self.tcx.mk_array(element_ty, args.len() as u64)
1228     }
1229
1230     fn check_expr_const_block(
1231         &self,
1232         anon_const: &'tcx hir::AnonConst,
1233         expected: Expectation<'tcx>,
1234         _expr: &'tcx hir::Expr<'tcx>,
1235     ) -> Ty<'tcx> {
1236         let body = self.tcx.hir().body(anon_const.body);
1237
1238         // Create a new function context.
1239         let fcx = FnCtxt::new(self, self.param_env.with_const(), body.value.hir_id);
1240         crate::check::GatherLocalsVisitor::new(&fcx).visit_body(body);
1241
1242         let ty = fcx.check_expr_with_expectation(&body.value, expected);
1243         fcx.require_type_is_sized(ty, body.value.span, traits::ConstSized);
1244         fcx.write_ty(anon_const.hir_id, ty);
1245         ty
1246     }
1247
1248     fn check_expr_repeat(
1249         &self,
1250         element: &'tcx hir::Expr<'tcx>,
1251         count: &'tcx hir::ArrayLen,
1252         expected: Expectation<'tcx>,
1253         _expr: &'tcx hir::Expr<'tcx>,
1254     ) -> Ty<'tcx> {
1255         let tcx = self.tcx;
1256         let count = self.array_length_to_const(count);
1257
1258         let uty = match expected {
1259             ExpectHasType(uty) => match *uty.kind() {
1260                 ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
1261                 _ => None,
1262             },
1263             _ => None,
1264         };
1265
1266         let (element_ty, t) = match uty {
1267             Some(uty) => {
1268                 self.check_expr_coercable_to_type(&element, uty, None);
1269                 (uty, uty)
1270             }
1271             None => {
1272                 let ty = self.next_ty_var(TypeVariableOrigin {
1273                     kind: TypeVariableOriginKind::MiscVariable,
1274                     span: element.span,
1275                 });
1276                 let element_ty = self.check_expr_has_type_or_error(&element, ty, |_| {});
1277                 (element_ty, ty)
1278             }
1279         };
1280
1281         if element_ty.references_error() {
1282             return tcx.ty_error();
1283         }
1284
1285         tcx.mk_ty(ty::Array(t, count))
1286     }
1287
1288     fn check_expr_tuple(
1289         &self,
1290         elts: &'tcx [hir::Expr<'tcx>],
1291         expected: Expectation<'tcx>,
1292         expr: &'tcx hir::Expr<'tcx>,
1293     ) -> Ty<'tcx> {
1294         let flds = expected.only_has_type(self).and_then(|ty| {
1295             let ty = self.resolve_vars_with_obligations(ty);
1296             match ty.kind() {
1297                 ty::Tuple(flds) => Some(&flds[..]),
1298                 _ => None,
1299             }
1300         });
1301
1302         let elt_ts_iter = elts.iter().enumerate().map(|(i, e)| match flds {
1303             Some(fs) if i < fs.len() => {
1304                 let ety = fs[i];
1305                 self.check_expr_coercable_to_type(&e, ety, None);
1306                 ety
1307             }
1308             _ => self.check_expr_with_expectation(&e, NoExpectation),
1309         });
1310         let tuple = self.tcx.mk_tup(elt_ts_iter);
1311         if tuple.references_error() {
1312             self.tcx.ty_error()
1313         } else {
1314             self.require_type_is_sized(tuple, expr.span, traits::TupleInitializerSized);
1315             tuple
1316         }
1317     }
1318
1319     fn check_expr_struct(
1320         &self,
1321         expr: &hir::Expr<'_>,
1322         expected: Expectation<'tcx>,
1323         qpath: &QPath<'_>,
1324         fields: &'tcx [hir::ExprField<'tcx>],
1325         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1326     ) -> Ty<'tcx> {
1327         // Find the relevant variant
1328         let Some((variant, adt_ty)) = self.check_struct_path(qpath, expr.hir_id) else {
1329             self.check_struct_fields_on_error(fields, base_expr);
1330             return self.tcx.ty_error();
1331         };
1332
1333         // Prohibit struct expressions when non-exhaustive flag is set.
1334         let adt = adt_ty.ty_adt_def().expect("`check_struct_path` returned non-ADT type");
1335         if !adt.did().is_local() && variant.is_field_list_non_exhaustive() {
1336             self.tcx
1337                 .sess
1338                 .emit_err(StructExprNonExhaustive { span: expr.span, what: adt.variant_descr() });
1339         }
1340
1341         self.check_expr_struct_fields(
1342             adt_ty,
1343             expected,
1344             expr.hir_id,
1345             qpath.span(),
1346             variant,
1347             fields,
1348             base_expr,
1349             expr.span,
1350         );
1351
1352         self.require_type_is_sized(adt_ty, expr.span, traits::StructInitializerSized);
1353         adt_ty
1354     }
1355
1356     fn check_expr_struct_fields(
1357         &self,
1358         adt_ty: Ty<'tcx>,
1359         expected: Expectation<'tcx>,
1360         expr_id: hir::HirId,
1361         span: Span,
1362         variant: &'tcx ty::VariantDef,
1363         ast_fields: &'tcx [hir::ExprField<'tcx>],
1364         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1365         expr_span: Span,
1366     ) {
1367         let tcx = self.tcx;
1368
1369         let expected_inputs =
1370             self.expected_inputs_for_expected_output(span, expected, adt_ty, &[adt_ty]);
1371         let adt_ty_hint = if let Some(expected_inputs) = expected_inputs {
1372             expected_inputs.get(0).cloned().unwrap_or(adt_ty)
1373         } else {
1374             adt_ty
1375         };
1376         // re-link the regions that EIfEO can erase.
1377         self.demand_eqtype(span, adt_ty_hint, adt_ty);
1378
1379         let (substs, adt_kind, kind_name) = match adt_ty.kind() {
1380             ty::Adt(adt, substs) => (substs, adt.adt_kind(), adt.variant_descr()),
1381             _ => span_bug!(span, "non-ADT passed to check_expr_struct_fields"),
1382         };
1383
1384         let mut remaining_fields = variant
1385             .fields
1386             .iter()
1387             .enumerate()
1388             .map(|(i, field)| (field.ident(tcx).normalize_to_macros_2_0(), (i, field)))
1389             .collect::<FxHashMap<_, _>>();
1390
1391         let mut seen_fields = FxHashMap::default();
1392
1393         let mut error_happened = false;
1394
1395         // Type-check each field.
1396         for field in ast_fields {
1397             let ident = tcx.adjust_ident(field.ident, variant.def_id);
1398             let field_type = if let Some((i, v_field)) = remaining_fields.remove(&ident) {
1399                 seen_fields.insert(ident, field.span);
1400                 self.write_field_index(field.hir_id, i);
1401
1402                 // We don't look at stability attributes on
1403                 // struct-like enums (yet...), but it's definitely not
1404                 // a bug to have constructed one.
1405                 if adt_kind != AdtKind::Enum {
1406                     tcx.check_stability(v_field.did, Some(expr_id), field.span, None);
1407                 }
1408
1409                 self.field_ty(field.span, v_field, substs)
1410             } else {
1411                 error_happened = true;
1412                 if let Some(prev_span) = seen_fields.get(&ident) {
1413                     tcx.sess.emit_err(FieldMultiplySpecifiedInInitializer {
1414                         span: field.ident.span,
1415                         prev_span: *prev_span,
1416                         ident,
1417                     });
1418                 } else {
1419                     self.report_unknown_field(
1420                         adt_ty, variant, field, ast_fields, kind_name, expr_span,
1421                     );
1422                 }
1423
1424                 tcx.ty_error()
1425             };
1426
1427             // Make sure to give a type to the field even if there's
1428             // an error, so we can continue type-checking.
1429             self.check_expr_coercable_to_type(&field.expr, field_type, None);
1430         }
1431
1432         // Make sure the programmer specified correct number of fields.
1433         if kind_name == "union" {
1434             if ast_fields.len() != 1 {
1435                 struct_span_err!(
1436                     tcx.sess,
1437                     span,
1438                     E0784,
1439                     "union expressions should have exactly one field",
1440                 )
1441                 .emit();
1442             }
1443         }
1444
1445         // If check_expr_struct_fields hit an error, do not attempt to populate
1446         // the fields with the base_expr. This could cause us to hit errors later
1447         // when certain fields are assumed to exist that in fact do not.
1448         if error_happened {
1449             return;
1450         }
1451
1452         if let Some(base_expr) = base_expr {
1453             // FIXME: We are currently creating two branches here in order to maintain
1454             // consistency. But they should be merged as much as possible.
1455             let fru_tys = if self.tcx.features().type_changing_struct_update {
1456                 let base_ty = self.check_expr(base_expr);
1457                 match adt_ty.kind() {
1458                     ty::Adt(adt, substs) if adt.is_struct() => {
1459                         match base_ty.kind() {
1460                             ty::Adt(base_adt, base_subs) if adt == base_adt => {
1461                                 variant
1462                                     .fields
1463                                     .iter()
1464                                     .map(|f| {
1465                                         let fru_ty = self.normalize_associated_types_in(
1466                                             expr_span,
1467                                             self.field_ty(base_expr.span, f, base_subs),
1468                                         );
1469                                         let ident = self
1470                                             .tcx
1471                                             .adjust_ident(f.ident(self.tcx), variant.def_id);
1472                                         if let Some(_) = remaining_fields.remove(&ident) {
1473                                             let target_ty =
1474                                                 self.field_ty(base_expr.span, f, substs);
1475                                             let cause = self.misc(base_expr.span);
1476                                             match self
1477                                                 .at(&cause, self.param_env)
1478                                                 .sup(target_ty, fru_ty)
1479                                             {
1480                                                 Ok(InferOk { obligations, value: () }) => {
1481                                                     self.register_predicates(obligations)
1482                                                 }
1483                                                 // FIXME: Need better diagnostics for `FieldMisMatch` error
1484                                                 Err(_) => {
1485                                                     self.report_mismatched_types(
1486                                                         &cause,
1487                                                         target_ty,
1488                                                         fru_ty,
1489                                                         FieldMisMatch(variant.name, ident.name),
1490                                                     )
1491                                                     .emit();
1492                                                 }
1493                                             }
1494                                         }
1495                                         fru_ty
1496                                     })
1497                                     .collect()
1498                             }
1499                             _ => {
1500                                 self.report_mismatched_types(
1501                                     &self.misc(base_expr.span),
1502                                     adt_ty,
1503                                     base_ty,
1504                                     Sorts(ExpectedFound::new(true, adt_ty, base_ty)),
1505                                 )
1506                                 .emit();
1507                                 return;
1508                             }
1509                         }
1510                     }
1511                     _ => {
1512                         self.tcx
1513                             .sess
1514                             .emit_err(FunctionalRecordUpdateOnNonStruct { span: base_expr.span });
1515                         return;
1516                     }
1517                 }
1518             } else {
1519                 self.check_expr_has_type_or_error(base_expr, adt_ty, |_| {
1520                     let base_ty = self.typeck_results.borrow().expr_ty(*base_expr);
1521                     let same_adt = match (adt_ty.kind(), base_ty.kind()) {
1522                         (ty::Adt(adt, _), ty::Adt(base_adt, _)) if adt == base_adt => true,
1523                         _ => false,
1524                     };
1525                     if self.tcx.sess.is_nightly_build() && same_adt {
1526                         feature_err(
1527                             &self.tcx.sess.parse_sess,
1528                             sym::type_changing_struct_update,
1529                             base_expr.span,
1530                             "type changing struct updating is experimental",
1531                         )
1532                         .emit();
1533                     }
1534                 });
1535                 match adt_ty.kind() {
1536                     ty::Adt(adt, substs) if adt.is_struct() => variant
1537                         .fields
1538                         .iter()
1539                         .map(|f| {
1540                             self.normalize_associated_types_in(expr_span, f.ty(self.tcx, substs))
1541                         })
1542                         .collect(),
1543                     _ => {
1544                         self.tcx
1545                             .sess
1546                             .emit_err(FunctionalRecordUpdateOnNonStruct { span: base_expr.span });
1547                         return;
1548                     }
1549                 }
1550             };
1551             self.typeck_results.borrow_mut().fru_field_types_mut().insert(expr_id, fru_tys);
1552         } else if kind_name != "union" && !remaining_fields.is_empty() {
1553             let inaccessible_remaining_fields = remaining_fields.iter().any(|(_, (_, field))| {
1554                 !field.vis.is_accessible_from(tcx.parent_module(expr_id).to_def_id(), tcx)
1555             });
1556
1557             if inaccessible_remaining_fields {
1558                 self.report_inaccessible_fields(adt_ty, span);
1559             } else {
1560                 self.report_missing_fields(
1561                     adt_ty,
1562                     span,
1563                     remaining_fields,
1564                     variant,
1565                     ast_fields,
1566                     substs,
1567                 );
1568             }
1569         }
1570     }
1571
1572     fn check_struct_fields_on_error(
1573         &self,
1574         fields: &'tcx [hir::ExprField<'tcx>],
1575         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
1576     ) {
1577         for field in fields {
1578             self.check_expr(&field.expr);
1579         }
1580         if let Some(base) = *base_expr {
1581             self.check_expr(&base);
1582         }
1583     }
1584
1585     /// Report an error for a struct field expression when there are fields which aren't provided.
1586     ///
1587     /// ```text
1588     /// error: missing field `you_can_use_this_field` in initializer of `foo::Foo`
1589     ///  --> src/main.rs:8:5
1590     ///   |
1591     /// 8 |     foo::Foo {};
1592     ///   |     ^^^^^^^^ missing `you_can_use_this_field`
1593     ///
1594     /// error: aborting due to previous error
1595     /// ```
1596     fn report_missing_fields(
1597         &self,
1598         adt_ty: Ty<'tcx>,
1599         span: Span,
1600         remaining_fields: FxHashMap<Ident, (usize, &ty::FieldDef)>,
1601         variant: &'tcx ty::VariantDef,
1602         ast_fields: &'tcx [hir::ExprField<'tcx>],
1603         substs: SubstsRef<'tcx>,
1604     ) {
1605         let len = remaining_fields.len();
1606
1607         let mut displayable_field_names: Vec<&str> =
1608             remaining_fields.keys().map(|ident| ident.as_str()).collect();
1609         // sorting &str primitives here, sort_unstable is ok
1610         displayable_field_names.sort_unstable();
1611
1612         let mut truncated_fields_error = String::new();
1613         let remaining_fields_names = match &displayable_field_names[..] {
1614             [field1] => format!("`{}`", field1),
1615             [field1, field2] => format!("`{field1}` and `{field2}`"),
1616             [field1, field2, field3] => format!("`{field1}`, `{field2}` and `{field3}`"),
1617             _ => {
1618                 truncated_fields_error =
1619                     format!(" and {} other field{}", len - 3, pluralize!(len - 3));
1620                 displayable_field_names
1621                     .iter()
1622                     .take(3)
1623                     .map(|n| format!("`{n}`"))
1624                     .collect::<Vec<_>>()
1625                     .join(", ")
1626             }
1627         };
1628
1629         let mut err = struct_span_err!(
1630             self.tcx.sess,
1631             span,
1632             E0063,
1633             "missing field{} {}{} in initializer of `{}`",
1634             pluralize!(len),
1635             remaining_fields_names,
1636             truncated_fields_error,
1637             adt_ty
1638         );
1639         err.span_label(span, format!("missing {remaining_fields_names}{truncated_fields_error}"));
1640
1641         // If the last field is a range literal, but it isn't supposed to be, then they probably
1642         // meant to use functional update syntax.
1643         //
1644         // I don't use 'is_range_literal' because only double-sided, half-open ranges count.
1645         if let Some((
1646             last,
1647             ExprKind::Struct(
1648                 QPath::LangItem(LangItem::Range, ..),
1649                 &[ref range_start, ref range_end],
1650                 _,
1651             ),
1652         )) = ast_fields.last().map(|last| (last, &last.expr.kind)) &&
1653         let variant_field =
1654             variant.fields.iter().find(|field| field.ident(self.tcx) == last.ident) &&
1655         let range_def_id = self.tcx.lang_items().range_struct() &&
1656         variant_field
1657             .and_then(|field| field.ty(self.tcx, substs).ty_adt_def())
1658             .map(|adt| adt.did())
1659             != range_def_id
1660         {
1661             let instead = self
1662                 .tcx
1663                 .sess
1664                 .source_map()
1665                 .span_to_snippet(range_end.expr.span)
1666                 .map(|s| format!(" from `{s}`"))
1667                 .unwrap_or(String::new());
1668             err.span_suggestion(
1669                 range_start.span.shrink_to_hi(),
1670                 &format!("to set the remaining fields{instead}, separate the last named field with a comma"),
1671                 ",".to_string(),
1672                 Applicability::MaybeIncorrect,
1673             );
1674         }
1675
1676         err.emit();
1677     }
1678
1679     /// Report an error for a struct field expression when there are invisible fields.
1680     ///
1681     /// ```text
1682     /// error: cannot construct `Foo` with struct literal syntax due to inaccessible fields
1683     ///  --> src/main.rs:8:5
1684     ///   |
1685     /// 8 |     foo::Foo {};
1686     ///   |     ^^^^^^^^
1687     ///
1688     /// error: aborting due to previous error
1689     /// ```
1690     fn report_inaccessible_fields(&self, adt_ty: Ty<'tcx>, span: Span) {
1691         self.tcx.sess.span_err(
1692             span,
1693             &format!(
1694                 "cannot construct `{adt_ty}` with struct literal syntax due to inaccessible fields",
1695             ),
1696         );
1697     }
1698
1699     fn report_unknown_field(
1700         &self,
1701         ty: Ty<'tcx>,
1702         variant: &'tcx ty::VariantDef,
1703         field: &hir::ExprField<'_>,
1704         skip_fields: &[hir::ExprField<'_>],
1705         kind_name: &str,
1706         expr_span: Span,
1707     ) {
1708         if variant.is_recovered() {
1709             self.set_tainted_by_errors();
1710             return;
1711         }
1712         let mut err = self.type_error_struct_with_diag(
1713             field.ident.span,
1714             |actual| match ty.kind() {
1715                 ty::Adt(adt, ..) if adt.is_enum() => struct_span_err!(
1716                     self.tcx.sess,
1717                     field.ident.span,
1718                     E0559,
1719                     "{} `{}::{}` has no field named `{}`",
1720                     kind_name,
1721                     actual,
1722                     variant.name,
1723                     field.ident
1724                 ),
1725                 _ => struct_span_err!(
1726                     self.tcx.sess,
1727                     field.ident.span,
1728                     E0560,
1729                     "{} `{}` has no field named `{}`",
1730                     kind_name,
1731                     actual,
1732                     field.ident
1733                 ),
1734             },
1735             ty,
1736         );
1737
1738         let variant_ident_span = self.tcx.def_ident_span(variant.def_id).unwrap();
1739         match variant.ctor_kind {
1740             CtorKind::Fn => match ty.kind() {
1741                 ty::Adt(adt, ..) if adt.is_enum() => {
1742                     err.span_label(
1743                         variant_ident_span,
1744                         format!(
1745                             "`{adt}::{variant}` defined here",
1746                             adt = ty,
1747                             variant = variant.name,
1748                         ),
1749                     );
1750                     err.span_label(field.ident.span, "field does not exist");
1751                     err.span_suggestion_verbose(
1752                         expr_span,
1753                         &format!(
1754                             "`{adt}::{variant}` is a tuple {kind_name}, use the appropriate syntax",
1755                             adt = ty,
1756                             variant = variant.name,
1757                         ),
1758                         format!(
1759                             "{adt}::{variant}(/* fields */)",
1760                             adt = ty,
1761                             variant = variant.name,
1762                         ),
1763                         Applicability::HasPlaceholders,
1764                     );
1765                 }
1766                 _ => {
1767                     err.span_label(variant_ident_span, format!("`{adt}` defined here", adt = ty));
1768                     err.span_label(field.ident.span, "field does not exist");
1769                     err.span_suggestion_verbose(
1770                         expr_span,
1771                         &format!(
1772                             "`{adt}` is a tuple {kind_name}, use the appropriate syntax",
1773                             adt = ty,
1774                             kind_name = kind_name,
1775                         ),
1776                         format!("{adt}(/* fields */)", adt = ty),
1777                         Applicability::HasPlaceholders,
1778                     );
1779                 }
1780             },
1781             _ => {
1782                 // prevent all specified fields from being suggested
1783                 let skip_fields = skip_fields.iter().map(|x| x.ident.name);
1784                 if let Some(field_name) = self.suggest_field_name(
1785                     variant,
1786                     field.ident.name,
1787                     skip_fields.collect(),
1788                     expr_span,
1789                 ) {
1790                     err.span_suggestion(
1791                         field.ident.span,
1792                         "a field with a similar name exists",
1793                         field_name.to_string(),
1794                         Applicability::MaybeIncorrect,
1795                     );
1796                 } else {
1797                     match ty.kind() {
1798                         ty::Adt(adt, ..) => {
1799                             if adt.is_enum() {
1800                                 err.span_label(
1801                                     field.ident.span,
1802                                     format!("`{}::{}` does not have this field", ty, variant.name),
1803                                 );
1804                             } else {
1805                                 err.span_label(
1806                                     field.ident.span,
1807                                     format!("`{ty}` does not have this field"),
1808                                 );
1809                             }
1810                             let available_field_names =
1811                                 self.available_field_names(variant, expr_span);
1812                             if !available_field_names.is_empty() {
1813                                 err.note(&format!(
1814                                     "available fields are: {}",
1815                                     self.name_series_display(available_field_names)
1816                                 ));
1817                             }
1818                         }
1819                         _ => bug!("non-ADT passed to report_unknown_field"),
1820                     }
1821                 };
1822             }
1823         }
1824         err.emit();
1825     }
1826
1827     // Return a hint about the closest match in field names
1828     fn suggest_field_name(
1829         &self,
1830         variant: &'tcx ty::VariantDef,
1831         field: Symbol,
1832         skip: Vec<Symbol>,
1833         // The span where stability will be checked
1834         span: Span,
1835     ) -> Option<Symbol> {
1836         let names = variant
1837             .fields
1838             .iter()
1839             .filter_map(|field| {
1840                 // ignore already set fields and private fields from non-local crates
1841                 // and unstable fields.
1842                 if skip.iter().any(|&x| x == field.name)
1843                     || (!variant.def_id.is_local() && !field.vis.is_public())
1844                     || matches!(
1845                         self.tcx.eval_stability(field.did, None, span, None),
1846                         stability::EvalResult::Deny { .. }
1847                     )
1848                 {
1849                     None
1850                 } else {
1851                     Some(field.name)
1852                 }
1853             })
1854             .collect::<Vec<Symbol>>();
1855
1856         find_best_match_for_name(&names, field, None)
1857     }
1858
1859     fn available_field_names(
1860         &self,
1861         variant: &'tcx ty::VariantDef,
1862         access_span: Span,
1863     ) -> Vec<Symbol> {
1864         variant
1865             .fields
1866             .iter()
1867             .filter(|field| {
1868                 let def_scope = self
1869                     .tcx
1870                     .adjust_ident_and_get_scope(field.ident(self.tcx), variant.def_id, self.body_id)
1871                     .1;
1872                 field.vis.is_accessible_from(def_scope, self.tcx)
1873                     && !matches!(
1874                         self.tcx.eval_stability(field.did, None, access_span, None),
1875                         stability::EvalResult::Deny { .. }
1876                     )
1877             })
1878             .filter(|field| !self.tcx.is_doc_hidden(field.did))
1879             .map(|field| field.name)
1880             .collect()
1881     }
1882
1883     fn name_series_display(&self, names: Vec<Symbol>) -> String {
1884         // dynamic limit, to never omit just one field
1885         let limit = if names.len() == 6 { 6 } else { 5 };
1886         let mut display =
1887             names.iter().take(limit).map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
1888         if names.len() > limit {
1889             display = format!("{} ... and {} others", display, names.len() - limit);
1890         }
1891         display
1892     }
1893
1894     // Check field access expressions
1895     fn check_field(
1896         &self,
1897         expr: &'tcx hir::Expr<'tcx>,
1898         base: &'tcx hir::Expr<'tcx>,
1899         field: Ident,
1900     ) -> Ty<'tcx> {
1901         debug!("check_field(expr: {:?}, base: {:?}, field: {:?})", expr, base, field);
1902         let expr_t = self.check_expr(base);
1903         let expr_t = self.structurally_resolved_type(base.span, expr_t);
1904         let mut private_candidate = None;
1905         let mut autoderef = self.autoderef(expr.span, expr_t);
1906         while let Some((base_t, _)) = autoderef.next() {
1907             debug!("base_t: {:?}", base_t);
1908             match base_t.kind() {
1909                 ty::Adt(base_def, substs) if !base_def.is_enum() => {
1910                     debug!("struct named {:?}", base_t);
1911                     let (ident, def_scope) =
1912                         self.tcx.adjust_ident_and_get_scope(field, base_def.did(), self.body_id);
1913                     let fields = &base_def.non_enum_variant().fields;
1914                     if let Some(index) = fields
1915                         .iter()
1916                         .position(|f| f.ident(self.tcx).normalize_to_macros_2_0() == ident)
1917                     {
1918                         let field = &fields[index];
1919                         let field_ty = self.field_ty(expr.span, field, substs);
1920                         // Save the index of all fields regardless of their visibility in case
1921                         // of error recovery.
1922                         self.write_field_index(expr.hir_id, index);
1923                         let adjustments = self.adjust_steps(&autoderef);
1924                         if field.vis.is_accessible_from(def_scope, self.tcx) {
1925                             self.apply_adjustments(base, adjustments);
1926                             self.register_predicates(autoderef.into_obligations());
1927
1928                             self.tcx.check_stability(field.did, Some(expr.hir_id), expr.span, None);
1929                             return field_ty;
1930                         }
1931                         private_candidate = Some((adjustments, base_def.did(), field_ty));
1932                     }
1933                 }
1934                 ty::Tuple(tys) => {
1935                     let fstr = field.as_str();
1936                     if let Ok(index) = fstr.parse::<usize>() {
1937                         if fstr == index.to_string() {
1938                             if let Some(&field_ty) = tys.get(index) {
1939                                 let adjustments = self.adjust_steps(&autoderef);
1940                                 self.apply_adjustments(base, adjustments);
1941                                 self.register_predicates(autoderef.into_obligations());
1942
1943                                 self.write_field_index(expr.hir_id, index);
1944                                 return field_ty;
1945                             }
1946                         }
1947                     }
1948                 }
1949                 _ => {}
1950             }
1951         }
1952         self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
1953
1954         if let Some((adjustments, did, field_ty)) = private_candidate {
1955             // (#90483) apply adjustments to avoid ExprUseVisitor from
1956             // creating erroneous projection.
1957             self.apply_adjustments(base, adjustments);
1958             self.ban_private_field_access(expr, expr_t, field, did);
1959             return field_ty;
1960         }
1961
1962         if field.name == kw::Empty {
1963         } else if self.method_exists(field, expr_t, expr.hir_id, true) {
1964             self.ban_take_value_of_method(expr, expr_t, field);
1965         } else if !expr_t.is_primitive_ty() {
1966             self.ban_nonexisting_field(field, base, expr, expr_t);
1967         } else {
1968             type_error_struct!(
1969                 self.tcx().sess,
1970                 field.span,
1971                 expr_t,
1972                 E0610,
1973                 "`{expr_t}` is a primitive type and therefore doesn't have fields",
1974             )
1975             .emit();
1976         }
1977
1978         self.tcx().ty_error()
1979     }
1980
1981     fn suggest_await_on_field_access(
1982         &self,
1983         err: &mut Diagnostic,
1984         field_ident: Ident,
1985         base: &'tcx hir::Expr<'tcx>,
1986         ty: Ty<'tcx>,
1987     ) {
1988         let output_ty = match self.infcx.get_impl_future_output_ty(ty) {
1989             Some(output_ty) => self.resolve_vars_if_possible(output_ty),
1990             _ => return,
1991         };
1992         let mut add_label = true;
1993         if let ty::Adt(def, _) = output_ty.skip_binder().kind() {
1994             // no field access on enum type
1995             if !def.is_enum() {
1996                 if def
1997                     .non_enum_variant()
1998                     .fields
1999                     .iter()
2000                     .any(|field| field.ident(self.tcx) == field_ident)
2001                 {
2002                     add_label = false;
2003                     err.span_label(
2004                         field_ident.span,
2005                         "field not available in `impl Future`, but it is available in its `Output`",
2006                     );
2007                     err.span_suggestion_verbose(
2008                         base.span.shrink_to_hi(),
2009                         "consider `await`ing on the `Future` and access the field of its `Output`",
2010                         ".await".to_string(),
2011                         Applicability::MaybeIncorrect,
2012                     );
2013                 }
2014             }
2015         }
2016         if add_label {
2017             err.span_label(field_ident.span, &format!("field not found in `{ty}`"));
2018         }
2019     }
2020
2021     fn ban_nonexisting_field(
2022         &self,
2023         field: Ident,
2024         base: &'tcx hir::Expr<'tcx>,
2025         expr: &'tcx hir::Expr<'tcx>,
2026         expr_t: Ty<'tcx>,
2027     ) {
2028         debug!(
2029             "ban_nonexisting_field: field={:?}, base={:?}, expr={:?}, expr_ty={:?}",
2030             field, base, expr, expr_t
2031         );
2032         let mut err = self.no_such_field_err(field, expr_t, base.hir_id);
2033
2034         match *expr_t.peel_refs().kind() {
2035             ty::Array(_, len) => {
2036                 self.maybe_suggest_array_indexing(&mut err, expr, base, field, len);
2037             }
2038             ty::RawPtr(..) => {
2039                 self.suggest_first_deref_field(&mut err, expr, base, field);
2040             }
2041             ty::Adt(def, _) if !def.is_enum() => {
2042                 self.suggest_fields_on_recordish(&mut err, def, field, expr.span);
2043             }
2044             ty::Param(param_ty) => {
2045                 self.point_at_param_definition(&mut err, param_ty);
2046             }
2047             ty::Opaque(_, _) => {
2048                 self.suggest_await_on_field_access(&mut err, field, base, expr_t.peel_refs());
2049             }
2050             _ => {}
2051         }
2052
2053         if field.name == kw::Await {
2054             // We know by construction that `<expr>.await` is either on Rust 2015
2055             // or results in `ExprKind::Await`. Suggest switching the edition to 2018.
2056             err.note("to `.await` a `Future`, switch to Rust 2018 or later");
2057             err.help_use_latest_edition();
2058         }
2059
2060         err.emit();
2061     }
2062
2063     fn ban_private_field_access(
2064         &self,
2065         expr: &hir::Expr<'_>,
2066         expr_t: Ty<'tcx>,
2067         field: Ident,
2068         base_did: DefId,
2069     ) {
2070         let struct_path = self.tcx().def_path_str(base_did);
2071         let kind_name = self.tcx().def_kind(base_did).descr(base_did);
2072         let mut err = struct_span_err!(
2073             self.tcx().sess,
2074             field.span,
2075             E0616,
2076             "field `{field}` of {kind_name} `{struct_path}` is private",
2077         );
2078         err.span_label(field.span, "private field");
2079         // Also check if an accessible method exists, which is often what is meant.
2080         if self.method_exists(field, expr_t, expr.hir_id, false) && !self.expr_in_place(expr.hir_id)
2081         {
2082             self.suggest_method_call(
2083                 &mut err,
2084                 &format!("a method `{field}` also exists, call it with parentheses"),
2085                 field,
2086                 expr_t,
2087                 expr,
2088                 None,
2089             );
2090         }
2091         err.emit();
2092     }
2093
2094     fn ban_take_value_of_method(&self, expr: &hir::Expr<'_>, expr_t: Ty<'tcx>, field: Ident) {
2095         let mut err = type_error_struct!(
2096             self.tcx().sess,
2097             field.span,
2098             expr_t,
2099             E0615,
2100             "attempted to take value of method `{field}` on type `{expr_t}`",
2101         );
2102         err.span_label(field.span, "method, not a field");
2103         let expr_is_call =
2104             if let hir::Node::Expr(hir::Expr { kind: ExprKind::Call(callee, _args), .. }) =
2105                 self.tcx.hir().get(self.tcx.hir().get_parent_node(expr.hir_id))
2106             {
2107                 expr.hir_id == callee.hir_id
2108             } else {
2109                 false
2110             };
2111         let expr_snippet =
2112             self.tcx.sess.source_map().span_to_snippet(expr.span).unwrap_or(String::new());
2113         let is_wrapped = expr_snippet.starts_with('(') && expr_snippet.ends_with(')');
2114         let after_open = expr.span.lo() + rustc_span::BytePos(1);
2115         let before_close = expr.span.hi() - rustc_span::BytePos(1);
2116
2117         if expr_is_call && is_wrapped {
2118             err.multipart_suggestion(
2119                 "remove wrapping parentheses to call the method",
2120                 vec![
2121                     (expr.span.with_hi(after_open), String::new()),
2122                     (expr.span.with_lo(before_close), String::new()),
2123                 ],
2124                 Applicability::MachineApplicable,
2125             );
2126         } else if !self.expr_in_place(expr.hir_id) {
2127             // Suggest call parentheses inside the wrapping parentheses
2128             let span = if is_wrapped {
2129                 expr.span.with_lo(after_open).with_hi(before_close)
2130             } else {
2131                 expr.span
2132             };
2133             self.suggest_method_call(
2134                 &mut err,
2135                 "use parentheses to call the method",
2136                 field,
2137                 expr_t,
2138                 expr,
2139                 Some(span),
2140             );
2141         } else {
2142             let mut found = false;
2143
2144             if let ty::RawPtr(ty_and_mut) = expr_t.kind()
2145                 && let ty::Adt(adt_def, _) = ty_and_mut.ty.kind()
2146             {
2147                 if adt_def.variants().len() == 1
2148                     && adt_def
2149                         .variants()
2150                         .iter()
2151                         .next()
2152                         .unwrap()
2153                         .fields
2154                         .iter()
2155                         .any(|f| f.ident(self.tcx) == field)
2156                 {
2157                     if let Some(dot_loc) = expr_snippet.rfind('.') {
2158                         found = true;
2159                         err.span_suggestion(
2160                             expr.span.with_hi(expr.span.lo() + BytePos::from_usize(dot_loc)),
2161                             "to access the field, dereference first",
2162                             format!("(*{})", &expr_snippet[0..dot_loc]),
2163                             Applicability::MaybeIncorrect,
2164                         );
2165                     }
2166                 }
2167             }
2168
2169             if !found {
2170                 err.help("methods are immutable and cannot be assigned to");
2171             }
2172         }
2173
2174         err.emit();
2175     }
2176
2177     fn point_at_param_definition(&self, err: &mut Diagnostic, param: ty::ParamTy) {
2178         let generics = self.tcx.generics_of(self.body_id.owner.to_def_id());
2179         let generic_param = generics.type_param(&param, self.tcx);
2180         if let ty::GenericParamDefKind::Type { synthetic: true, .. } = generic_param.kind {
2181             return;
2182         }
2183         let param_def_id = generic_param.def_id;
2184         let param_hir_id = match param_def_id.as_local() {
2185             Some(x) => self.tcx.hir().local_def_id_to_hir_id(x),
2186             None => return,
2187         };
2188         let param_span = self.tcx.hir().span(param_hir_id);
2189         let param_name = self.tcx.hir().ty_param_name(param_def_id.expect_local());
2190
2191         err.span_label(param_span, &format!("type parameter '{param_name}' declared here"));
2192     }
2193
2194     fn suggest_fields_on_recordish(
2195         &self,
2196         err: &mut Diagnostic,
2197         def: ty::AdtDef<'tcx>,
2198         field: Ident,
2199         access_span: Span,
2200     ) {
2201         if let Some(suggested_field_name) =
2202             self.suggest_field_name(def.non_enum_variant(), field.name, vec![], access_span)
2203         {
2204             err.span_suggestion(
2205                 field.span,
2206                 "a field with a similar name exists",
2207                 suggested_field_name.to_string(),
2208                 Applicability::MaybeIncorrect,
2209             );
2210         } else {
2211             err.span_label(field.span, "unknown field");
2212             let struct_variant_def = def.non_enum_variant();
2213             let field_names = self.available_field_names(struct_variant_def, access_span);
2214             if !field_names.is_empty() {
2215                 err.note(&format!(
2216                     "available fields are: {}",
2217                     self.name_series_display(field_names),
2218                 ));
2219             }
2220         }
2221     }
2222
2223     fn maybe_suggest_array_indexing(
2224         &self,
2225         err: &mut Diagnostic,
2226         expr: &hir::Expr<'_>,
2227         base: &hir::Expr<'_>,
2228         field: Ident,
2229         len: ty::Const<'tcx>,
2230     ) {
2231         if let (Some(len), Ok(user_index)) =
2232             (len.try_eval_usize(self.tcx, self.param_env), field.as_str().parse::<u64>())
2233             && let Ok(base) = self.tcx.sess.source_map().span_to_snippet(base.span)
2234         {
2235             let help = "instead of using tuple indexing, use array indexing";
2236             let suggestion = format!("{base}[{field}]");
2237             let applicability = if len < user_index {
2238                 Applicability::MachineApplicable
2239             } else {
2240                 Applicability::MaybeIncorrect
2241             };
2242             err.span_suggestion(expr.span, help, suggestion, applicability);
2243         }
2244     }
2245
2246     fn suggest_first_deref_field(
2247         &self,
2248         err: &mut Diagnostic,
2249         expr: &hir::Expr<'_>,
2250         base: &hir::Expr<'_>,
2251         field: Ident,
2252     ) {
2253         if let Ok(base) = self.tcx.sess.source_map().span_to_snippet(base.span) {
2254             let msg = format!("`{base}` is a raw pointer; try dereferencing it");
2255             let suggestion = format!("(*{base}).{field}");
2256             err.span_suggestion(expr.span, &msg, suggestion, Applicability::MaybeIncorrect);
2257         }
2258     }
2259
2260     fn no_such_field_err(
2261         &self,
2262         field: Ident,
2263         expr_t: Ty<'tcx>,
2264         id: HirId,
2265     ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
2266         let span = field.span;
2267         debug!("no_such_field_err(span: {:?}, field: {:?}, expr_t: {:?})", span, field, expr_t);
2268
2269         let mut err = type_error_struct!(
2270             self.tcx().sess,
2271             field.span,
2272             expr_t,
2273             E0609,
2274             "no field `{field}` on type `{expr_t}`",
2275         );
2276
2277         // try to add a suggestion in case the field is a nested field of a field of the Adt
2278         if let Some((fields, substs)) = self.get_field_candidates(span, expr_t) {
2279             for candidate_field in fields.iter() {
2280                 if let Some(field_path) = self.check_for_nested_field(
2281                     span,
2282                     field,
2283                     candidate_field,
2284                     substs,
2285                     vec![],
2286                     self.tcx.parent_module(id).to_def_id(),
2287                 ) {
2288                     let field_path_str = field_path
2289                         .iter()
2290                         .map(|id| id.name.to_ident_string())
2291                         .collect::<Vec<String>>()
2292                         .join(".");
2293                     debug!("field_path_str: {:?}", field_path_str);
2294
2295                     err.span_suggestion_verbose(
2296                         field.span.shrink_to_lo(),
2297                         "one of the expressions' fields has a field of the same name",
2298                         format!("{field_path_str}."),
2299                         Applicability::MaybeIncorrect,
2300                     );
2301                 }
2302             }
2303         }
2304         err
2305     }
2306
2307     fn get_field_candidates(
2308         &self,
2309         span: Span,
2310         base_t: Ty<'tcx>,
2311     ) -> Option<(&Vec<ty::FieldDef>, SubstsRef<'tcx>)> {
2312         debug!("get_field_candidates(span: {:?}, base_t: {:?}", span, base_t);
2313
2314         for (base_t, _) in self.autoderef(span, base_t) {
2315             match base_t.kind() {
2316                 ty::Adt(base_def, substs) if !base_def.is_enum() => {
2317                     let fields = &base_def.non_enum_variant().fields;
2318                     // For compile-time reasons put a limit on number of fields we search
2319                     if fields.len() > 100 {
2320                         return None;
2321                     }
2322                     return Some((fields, substs));
2323                 }
2324                 _ => {}
2325             }
2326         }
2327         None
2328     }
2329
2330     /// This method is called after we have encountered a missing field error to recursively
2331     /// search for the field
2332     fn check_for_nested_field(
2333         &self,
2334         span: Span,
2335         target_field: Ident,
2336         candidate_field: &ty::FieldDef,
2337         subst: SubstsRef<'tcx>,
2338         mut field_path: Vec<Ident>,
2339         id: DefId,
2340     ) -> Option<Vec<Ident>> {
2341         debug!(
2342             "check_for_nested_field(span: {:?}, candidate_field: {:?}, field_path: {:?}",
2343             span, candidate_field, field_path
2344         );
2345
2346         if candidate_field.ident(self.tcx) == target_field {
2347             Some(field_path)
2348         } else if field_path.len() > 3 {
2349             // For compile-time reasons and to avoid infinite recursion we only check for fields
2350             // up to a depth of three
2351             None
2352         } else {
2353             // recursively search fields of `candidate_field` if it's a ty::Adt
2354
2355             field_path.push(candidate_field.ident(self.tcx).normalize_to_macros_2_0());
2356             let field_ty = candidate_field.ty(self.tcx, subst);
2357             if let Some((nested_fields, subst)) = self.get_field_candidates(span, field_ty) {
2358                 for field in nested_fields.iter() {
2359                     let accessible = field.vis.is_accessible_from(id, self.tcx);
2360                     if accessible {
2361                         let ident = field.ident(self.tcx).normalize_to_macros_2_0();
2362                         if ident == target_field {
2363                             return Some(field_path);
2364                         }
2365                         let field_path = field_path.clone();
2366                         if let Some(path) = self.check_for_nested_field(
2367                             span,
2368                             target_field,
2369                             field,
2370                             subst,
2371                             field_path,
2372                             id,
2373                         ) {
2374                             return Some(path);
2375                         }
2376                     }
2377                 }
2378             }
2379             None
2380         }
2381     }
2382
2383     fn check_expr_index(
2384         &self,
2385         base: &'tcx hir::Expr<'tcx>,
2386         idx: &'tcx hir::Expr<'tcx>,
2387         expr: &'tcx hir::Expr<'tcx>,
2388     ) -> Ty<'tcx> {
2389         let base_t = self.check_expr(&base);
2390         let idx_t = self.check_expr(&idx);
2391
2392         if base_t.references_error() {
2393             base_t
2394         } else if idx_t.references_error() {
2395             idx_t
2396         } else {
2397             let base_t = self.structurally_resolved_type(base.span, base_t);
2398             match self.lookup_indexing(expr, base, base_t, idx, idx_t) {
2399                 Some((index_ty, element_ty)) => {
2400                     // two-phase not needed because index_ty is never mutable
2401                     self.demand_coerce(idx, idx_t, index_ty, None, AllowTwoPhase::No);
2402                     element_ty
2403                 }
2404                 None => {
2405                     let mut err = type_error_struct!(
2406                         self.tcx.sess,
2407                         expr.span,
2408                         base_t,
2409                         E0608,
2410                         "cannot index into a value of type `{base_t}`",
2411                     );
2412                     // Try to give some advice about indexing tuples.
2413                     if let ty::Tuple(..) = base_t.kind() {
2414                         let mut needs_note = true;
2415                         // If the index is an integer, we can show the actual
2416                         // fixed expression:
2417                         if let ExprKind::Lit(ref lit) = idx.kind {
2418                             if let ast::LitKind::Int(i, ast::LitIntType::Unsuffixed) = lit.node {
2419                                 let snip = self.tcx.sess.source_map().span_to_snippet(base.span);
2420                                 if let Ok(snip) = snip {
2421                                     err.span_suggestion(
2422                                         expr.span,
2423                                         "to access tuple elements, use",
2424                                         format!("{snip}.{i}"),
2425                                         Applicability::MachineApplicable,
2426                                     );
2427                                     needs_note = false;
2428                                 }
2429                             }
2430                         }
2431                         if needs_note {
2432                             err.help(
2433                                 "to access tuple elements, use tuple indexing \
2434                                         syntax (e.g., `tuple.0`)",
2435                             );
2436                         }
2437                     }
2438                     err.emit();
2439                     self.tcx.ty_error()
2440                 }
2441             }
2442         }
2443     }
2444
2445     fn check_expr_yield(
2446         &self,
2447         value: &'tcx hir::Expr<'tcx>,
2448         expr: &'tcx hir::Expr<'tcx>,
2449         src: &'tcx hir::YieldSource,
2450     ) -> Ty<'tcx> {
2451         match self.resume_yield_tys {
2452             Some((resume_ty, yield_ty)) => {
2453                 self.check_expr_coercable_to_type(&value, yield_ty, None);
2454
2455                 resume_ty
2456             }
2457             // Given that this `yield` expression was generated as a result of lowering a `.await`,
2458             // we know that the yield type must be `()`; however, the context won't contain this
2459             // information. Hence, we check the source of the yield expression here and check its
2460             // value's type against `()` (this check should always hold).
2461             None if src.is_await() => {
2462                 self.check_expr_coercable_to_type(&value, self.tcx.mk_unit(), None);
2463                 self.tcx.mk_unit()
2464             }
2465             _ => {
2466                 self.tcx.sess.emit_err(YieldExprOutsideOfGenerator { span: expr.span });
2467                 // Avoid expressions without types during writeback (#78653).
2468                 self.check_expr(value);
2469                 self.tcx.mk_unit()
2470             }
2471         }
2472     }
2473
2474     fn check_expr_asm_operand(&self, expr: &'tcx hir::Expr<'tcx>, is_input: bool) {
2475         let needs = if is_input { Needs::None } else { Needs::MutPlace };
2476         let ty = self.check_expr_with_needs(expr, needs);
2477         self.require_type_is_sized(ty, expr.span, traits::InlineAsmSized);
2478
2479         if !is_input && !expr.is_syntactic_place_expr() {
2480             let mut err = self.tcx.sess.struct_span_err(expr.span, "invalid asm output");
2481             err.span_label(expr.span, "cannot assign to this expression");
2482             err.emit();
2483         }
2484
2485         // If this is an input value, we require its type to be fully resolved
2486         // at this point. This allows us to provide helpful coercions which help
2487         // pass the type candidate list in a later pass.
2488         //
2489         // We don't require output types to be resolved at this point, which
2490         // allows them to be inferred based on how they are used later in the
2491         // function.
2492         if is_input {
2493             let ty = self.structurally_resolved_type(expr.span, ty);
2494             match *ty.kind() {
2495                 ty::FnDef(..) => {
2496                     let fnptr_ty = self.tcx.mk_fn_ptr(ty.fn_sig(self.tcx));
2497                     self.demand_coerce(expr, ty, fnptr_ty, None, AllowTwoPhase::No);
2498                 }
2499                 ty::Ref(_, base_ty, mutbl) => {
2500                     let ptr_ty = self.tcx.mk_ptr(ty::TypeAndMut { ty: base_ty, mutbl });
2501                     self.demand_coerce(expr, ty, ptr_ty, None, AllowTwoPhase::No);
2502                 }
2503                 _ => {}
2504             }
2505         }
2506     }
2507
2508     fn check_expr_asm(&self, asm: &'tcx hir::InlineAsm<'tcx>) -> Ty<'tcx> {
2509         for (op, _op_sp) in asm.operands {
2510             match op {
2511                 hir::InlineAsmOperand::In { expr, .. } => {
2512                     self.check_expr_asm_operand(expr, true);
2513                 }
2514                 hir::InlineAsmOperand::Out { expr: Some(expr), .. }
2515                 | hir::InlineAsmOperand::InOut { expr, .. } => {
2516                     self.check_expr_asm_operand(expr, false);
2517                 }
2518                 hir::InlineAsmOperand::Out { expr: None, .. } => {}
2519                 hir::InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
2520                     self.check_expr_asm_operand(in_expr, true);
2521                     if let Some(out_expr) = out_expr {
2522                         self.check_expr_asm_operand(out_expr, false);
2523                     }
2524                 }
2525                 hir::InlineAsmOperand::Const { anon_const }
2526                 | hir::InlineAsmOperand::SymFn { anon_const } => {
2527                     self.to_const(anon_const);
2528                 }
2529                 hir::InlineAsmOperand::SymStatic { .. } => {}
2530             }
2531         }
2532         if asm.options.contains(ast::InlineAsmOptions::NORETURN) {
2533             self.tcx.types.never
2534         } else {
2535             self.tcx.mk_unit()
2536         }
2537     }
2538 }
2539
2540 pub(super) fn ty_kind_suggestion(ty: Ty<'_>) -> Option<&'static str> {
2541     Some(match ty.kind() {
2542         ty::Bool => "true",
2543         ty::Char => "'a'",
2544         ty::Int(_) | ty::Uint(_) => "42",
2545         ty::Float(_) => "3.14159",
2546         ty::Error(_) | ty::Never => return None,
2547         _ => "value",
2548     })
2549 }