compiler/rustc_typeck/src/check/expr.rs

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