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