compiler/rustc_hir_typeck/src/callee.rs

   1 use super::method::probe::{IsSuggestion, Mode, ProbeScope};
   2 use super::method::MethodCallee;
   3 use super::{Expectation, FnCtxt, TupleArgumentsFlag};
   4
   5 use crate::type_error_struct;
   6 use rustc_ast::util::parser::PREC_POSTFIX;
   7 use rustc_errors::{struct_span_err, Applicability, Diagnostic, ErrorGuaranteed, StashKey};
   8 use rustc_hir as hir;
   9 use rustc_hir::def::{self, CtorKind, Namespace, Res};
  10 use rustc_hir::def_id::DefId;
  11 use rustc_infer::{
  12     infer,
  13     traits::{self, Obligation},
  14 };
  15 use rustc_infer::{
  16     infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind},
  17     traits::ObligationCause,
  18 };
  19 use rustc_middle::ty::adjustment::{
  20     Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability,
  21 };
  22 use rustc_middle::ty::SubstsRef;
  23 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitable};
  24 use rustc_span::def_id::LocalDefId;
  25 use rustc_span::symbol::{sym, Ident};
  26 use rustc_span::Span;
  27 use rustc_target::spec::abi;
  28 use rustc_trait_selection::autoderef::Autoderef;
  29 use rustc_trait_selection::infer::InferCtxtExt as _;
  30 use rustc_trait_selection::traits::error_reporting::DefIdOrName;
  31 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
  32
  33 use std::{iter, slice};
  34
  35 /// Checks that it is legal to call methods of the trait corresponding
  36 /// to `trait_id` (this only cares about the trait, not the specific
  37 /// method that is called).
  38 pub fn check_legal_trait_for_method_call(
  39     tcx: TyCtxt<'_>,
  40     span: Span,
  41     receiver: Option<Span>,
  42     expr_span: Span,
  43     trait_id: DefId,
  44 ) {
  45     if tcx.lang_items().drop_trait() == Some(trait_id) {
  46         let mut err = struct_span_err!(tcx.sess, span, E0040, "explicit use of destructor method");
  47         err.span_label(span, "explicit destructor calls not allowed");
  48
  49         let (sp, suggestion) = receiver
  50             .and_then(|s| tcx.sess.source_map().span_to_snippet(s).ok())
  51             .filter(|snippet| !snippet.is_empty())
  52             .map(|snippet| (expr_span, format!("drop({snippet})")))
  53             .unwrap_or_else(|| (span, "drop".to_string()));
  54
  55         err.span_suggestion(
  56             sp,
  57             "consider using `drop` function",
  58             suggestion,
  59             Applicability::MaybeIncorrect,
  60         );
  61
  62         err.emit();
  63     }
  64 }
  65
  66 #[derive(Debug)]
  67 enum CallStep<'tcx> {
  68     Builtin(Ty<'tcx>),
  69     DeferredClosure(LocalDefId, ty::FnSig<'tcx>),
  70     /// E.g., enum variant constructors.
  71     Overloaded(MethodCallee<'tcx>),
  72 }
  73
  74 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  75     pub fn check_call(
  76         &self,
  77         call_expr: &'tcx hir::Expr<'tcx>,
  78         callee_expr: &'tcx hir::Expr<'tcx>,
  79         arg_exprs: &'tcx [hir::Expr<'tcx>],
  80         expected: Expectation<'tcx>,
  81     ) -> Ty<'tcx> {
  82         let original_callee_ty = match &callee_expr.kind {
  83             hir::ExprKind::Path(hir::QPath::Resolved(..) | hir::QPath::TypeRelative(..)) => self
  84                 .check_expr_with_expectation_and_args(
  85                     callee_expr,
  86                     Expectation::NoExpectation,
  87                     arg_exprs,
  88                 ),
  89             _ => self.check_expr(callee_expr),
  90         };
  91
  92         let expr_ty = self.structurally_resolved_type(call_expr.span, original_callee_ty);
  93
  94         let mut autoderef = self.autoderef(callee_expr.span, expr_ty);
  95         let mut result = None;
  96         while result.is_none() && autoderef.next().is_some() {
  97             result = self.try_overloaded_call_step(call_expr, callee_expr, arg_exprs, &autoderef);
  98         }
  99         self.register_predicates(autoderef.into_obligations());
 100
 101         let output = match result {
 102             None => {
 103                 // this will report an error since original_callee_ty is not a fn
 104                 self.confirm_builtin_call(
 105                     call_expr,
 106                     callee_expr,
 107                     original_callee_ty,
 108                     arg_exprs,
 109                     expected,
 110                 )
 111             }
 112
 113             Some(CallStep::Builtin(callee_ty)) => {
 114                 self.confirm_builtin_call(call_expr, callee_expr, callee_ty, arg_exprs, expected)
 115             }
 116
 117             Some(CallStep::DeferredClosure(def_id, fn_sig)) => {
 118                 self.confirm_deferred_closure_call(call_expr, arg_exprs, expected, def_id, fn_sig)
 119             }
 120
 121             Some(CallStep::Overloaded(method_callee)) => {
 122                 self.confirm_overloaded_call(call_expr, arg_exprs, expected, method_callee)
 123             }
 124         };
 125
 126         // we must check that return type of called functions is WF:
 127         self.register_wf_obligation(output.into(), call_expr.span, traits::WellFormed(None));
 128
 129         output
 130     }
 131
 132     #[instrument(level = "debug", skip(self, call_expr, callee_expr, arg_exprs, autoderef), ret)]
 133     fn try_overloaded_call_step(
 134         &self,
 135         call_expr: &'tcx hir::Expr<'tcx>,
 136         callee_expr: &'tcx hir::Expr<'tcx>,
 137         arg_exprs: &'tcx [hir::Expr<'tcx>],
 138         autoderef: &Autoderef<'a, 'tcx>,
 139     ) -> Option<CallStep<'tcx>> {
 140         let adjusted_ty =
 141             self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
 142
 143         // If the callee is a bare function or a closure, then we're all set.
 144         match *adjusted_ty.kind() {
 145             ty::FnDef(..) | ty::FnPtr(_) => {
 146                 let adjustments = self.adjust_steps(autoderef);
 147                 self.apply_adjustments(callee_expr, adjustments);
 148                 return Some(CallStep::Builtin(adjusted_ty));
 149             }
 150
 151             ty::Closure(def_id, substs) => {
 152                 let def_id = def_id.expect_local();
 153
 154                 // Check whether this is a call to a closure where we
 155                 // haven't yet decided on whether the closure is fn vs
 156                 // fnmut vs fnonce. If so, we have to defer further processing.
 157                 if self.closure_kind(substs).is_none() {
 158                     let closure_sig = substs.as_closure().sig();
 159                     let closure_sig = self.replace_bound_vars_with_fresh_vars(
 160                         call_expr.span,
 161                         infer::FnCall,
 162                         closure_sig,
 163                     );
 164                     let adjustments = self.adjust_steps(autoderef);
 165                     self.record_deferred_call_resolution(
 166                         def_id,
 167                         DeferredCallResolution {
 168                             call_expr,
 169                             callee_expr,
 170                             adjusted_ty,
 171                             adjustments,
 172                             fn_sig: closure_sig,
 173                             closure_substs: substs,
 174                         },
 175                     );
 176                     return Some(CallStep::DeferredClosure(def_id, closure_sig));
 177                 }
 178             }
 179
 180             // Hack: we know that there are traits implementing Fn for &F
 181             // where F:Fn and so forth. In the particular case of types
 182             // like `f: &mut FnMut()`, if there is a call `f()`, we would
 183             // normally translate to `FnMut::call_mut(&mut f, ())`, but
 184             // that winds up potentially requiring the user to mark their
 185             // variable as `mut` which feels unnecessary and unexpected.
 186             //
 187             //     fn foo(f: &mut impl FnMut()) { f() }
 188             //            ^ without this hack `f` would have to be declared as mutable
 189             //
 190             // The simplest fix by far is to just ignore this case and deref again,
 191             // so we wind up with `FnMut::call_mut(&mut *f, ())`.
 192             ty::Ref(..) if autoderef.step_count() == 0 => {
 193                 return None;
 194             }
 195
 196             ty::Error(_) => {
 197                 return None;
 198             }
 199
 200             _ => {}
 201         }
 202
 203         // Now, we look for the implementation of a Fn trait on the object's type.
 204         // We first do it with the explicit instruction to look for an impl of
 205         // `Fn<Tuple>`, with the tuple `Tuple` having an arity corresponding
 206         // to the number of call parameters.
 207         // If that fails (or_else branch), we try again without specifying the
 208         // shape of the tuple (hence the None). This allows to detect an Fn trait
 209         // is implemented, and use this information for diagnostic.
 210         self.try_overloaded_call_traits(call_expr, adjusted_ty, Some(arg_exprs))
 211             .or_else(|| self.try_overloaded_call_traits(call_expr, adjusted_ty, None))
 212             .map(|(autoref, method)| {
 213                 let mut adjustments = self.adjust_steps(autoderef);
 214                 adjustments.extend(autoref);
 215                 self.apply_adjustments(callee_expr, adjustments);
 216                 CallStep::Overloaded(method)
 217             })
 218     }
 219
 220     fn try_overloaded_call_traits(
 221         &self,
 222         call_expr: &hir::Expr<'_>,
 223         adjusted_ty: Ty<'tcx>,
 224         opt_arg_exprs: Option<&'tcx [hir::Expr<'tcx>]>,
 225     ) -> Option<(Option<Adjustment<'tcx>>, MethodCallee<'tcx>)> {
 226         // Try the options that are least restrictive on the caller first.
 227         for (opt_trait_def_id, method_name, borrow) in [
 228             (self.tcx.lang_items().fn_trait(), Ident::with_dummy_span(sym::call), true),
 229             (self.tcx.lang_items().fn_mut_trait(), Ident::with_dummy_span(sym::call_mut), true),
 230             (self.tcx.lang_items().fn_once_trait(), Ident::with_dummy_span(sym::call_once), false),
 231         ] {
 232             let Some(trait_def_id) = opt_trait_def_id else { continue };
 233
 234             let opt_input_type = opt_arg_exprs.map(|arg_exprs| {
 235                 self.tcx.mk_tup(arg_exprs.iter().map(|e| {
 236                     self.next_ty_var(TypeVariableOrigin {
 237                         kind: TypeVariableOriginKind::TypeInference,
 238                         span: e.span,
 239                     })
 240                 }))
 241             });
 242
 243             if let Some(ok) = self.lookup_method_in_trait(
 244                 self.misc(call_expr.span),
 245                 method_name,
 246                 trait_def_id,
 247                 adjusted_ty,
 248                 opt_input_type.as_ref().map(slice::from_ref),
 249             ) {
 250                 let method = self.register_infer_ok_obligations(ok);
 251                 let mut autoref = None;
 252                 if borrow {
 253                     // Check for &self vs &mut self in the method signature. Since this is either
 254                     // the Fn or FnMut trait, it should be one of those.
 255                     let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind() else {
 256                         // The `fn`/`fn_mut` lang item is ill-formed, which should have
 257                         // caused an error elsewhere.
 258                         self.tcx
 259                             .sess
 260                             .delay_span_bug(call_expr.span, "input to call/call_mut is not a ref?");
 261                         return None;
 262                     };
 263
 264                     // For initial two-phase borrow
 265                     // deployment, conservatively omit
 266                     // overloaded function call ops.
 267                     let mutbl = AutoBorrowMutability::new(*mutbl, AllowTwoPhase::No);
 268
 269                     autoref = Some(Adjustment {
 270                         kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
 271                         target: method.sig.inputs()[0],
 272                     });
 273                 }
 274                 return Some((autoref, method));
 275             }
 276         }
 277
 278         None
 279     }
 280
 281     /// Give appropriate suggestion when encountering `||{/* not callable */}()`, where the
 282     /// likely intention is to call the closure, suggest `(||{})()`. (#55851)
 283     fn identify_bad_closure_def_and_call(
 284         &self,
 285         err: &mut Diagnostic,
 286         hir_id: hir::HirId,
 287         callee_node: &hir::ExprKind<'_>,
 288         callee_span: Span,
 289     ) {
 290         let hir = self.tcx.hir();
 291         let parent_hir_id = hir.parent_id(hir_id);
 292         let parent_node = hir.get(parent_hir_id);
 293         if let (
 294             hir::Node::Expr(hir::Expr {
 295                 kind: hir::ExprKind::Closure(&hir::Closure { fn_decl_span, body, .. }),
 296                 ..
 297             }),
 298             hir::ExprKind::Block(..),
 299         ) = (parent_node, callee_node)
 300         {
 301             let fn_decl_span = if hir.body(body).generator_kind
 302                 == Some(hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure))
 303             {
 304                 // Actually need to unwrap a few more layers of HIR to get to
 305                 // the _real_ closure...
 306                 let async_closure = hir.parent_id(hir.parent_id(parent_hir_id));
 307                 if let hir::Node::Expr(hir::Expr {
 308                     kind: hir::ExprKind::Closure(&hir::Closure { fn_decl_span, .. }),
 309                     ..
 310                 }) = hir.get(async_closure)
 311                 {
 312                     fn_decl_span
 313                 } else {
 314                     return;
 315                 }
 316             } else {
 317                 fn_decl_span
 318             };
 319
 320             let start = fn_decl_span.shrink_to_lo();
 321             let end = callee_span.shrink_to_hi();
 322             err.multipart_suggestion(
 323                 "if you meant to create this closure and immediately call it, surround the \
 324                 closure with parentheses",
 325                 vec![(start, "(".to_string()), (end, ")".to_string())],
 326                 Applicability::MaybeIncorrect,
 327             );
 328         }
 329     }
 330
 331     /// Give appropriate suggestion when encountering `[("a", 0) ("b", 1)]`, where the
 332     /// likely intention is to create an array containing tuples.
 333     fn maybe_suggest_bad_array_definition(
 334         &self,
 335         err: &mut Diagnostic,
 336         call_expr: &'tcx hir::Expr<'tcx>,
 337         callee_expr: &'tcx hir::Expr<'tcx>,
 338     ) -> bool {
 339         let hir_id = self.tcx.hir().parent_id(call_expr.hir_id);
 340         let parent_node = self.tcx.hir().get(hir_id);
 341         if let (
 342             hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Array(_), .. }),
 343             hir::ExprKind::Tup(exp),
 344             hir::ExprKind::Call(_, args),
 345         ) = (parent_node, &callee_expr.kind, &call_expr.kind)
 346             && args.len() == exp.len()
 347         {
 348             let start = callee_expr.span.shrink_to_hi();
 349             err.span_suggestion(
 350                 start,
 351                 "consider separating array elements with a comma",
 352                 ",",
 353                 Applicability::MaybeIncorrect,
 354             );
 355             return true;
 356         }
 357         false
 358     }
 359
 360     fn confirm_builtin_call(
 361         &self,
 362         call_expr: &'tcx hir::Expr<'tcx>,
 363         callee_expr: &'tcx hir::Expr<'tcx>,
 364         callee_ty: Ty<'tcx>,
 365         arg_exprs: &'tcx [hir::Expr<'tcx>],
 366         expected: Expectation<'tcx>,
 367     ) -> Ty<'tcx> {
 368         let (fn_sig, def_id) = match *callee_ty.kind() {
 369             ty::FnDef(def_id, subst) => {
 370                 let fn_sig = self.tcx.bound_fn_sig(def_id).subst(self.tcx, subst);
 371
 372                 // Unit testing: function items annotated with
 373                 // `#[rustc_evaluate_where_clauses]` trigger special output
 374                 // to let us test the trait evaluation system.
 375                 if self.tcx.has_attr(def_id, sym::rustc_evaluate_where_clauses) {
 376                     let predicates = self.tcx.predicates_of(def_id);
 377                     let predicates = predicates.instantiate(self.tcx, subst);
 378                     for (predicate, predicate_span) in
 379                         predicates.predicates.iter().zip(&predicates.spans)
 380                     {
 381                         let obligation = Obligation::new(
 382                             self.tcx,
 383                             ObligationCause::dummy_with_span(callee_expr.span),
 384                             self.param_env,
 385                             *predicate,
 386                         );
 387                         let result = self.evaluate_obligation(&obligation);
 388                         self.tcx
 389                             .sess
 390                             .struct_span_err(
 391                                 callee_expr.span,
 392                                 &format!("evaluate({:?}) = {:?}", predicate, result),
 393                             )
 394                             .span_label(*predicate_span, "predicate")
 395                             .emit();
 396                     }
 397                 }
 398                 (fn_sig, Some(def_id))
 399             }
 400             ty::FnPtr(sig) => (sig, None),
 401             _ => {
 402                 for arg in arg_exprs {
 403                     self.check_expr(arg);
 404                 }
 405
 406                 if let hir::ExprKind::Path(hir::QPath::Resolved(_, path)) = &callee_expr.kind
 407                     && let [segment] = path.segments
 408                     && let Some(mut diag) = self
 409                         .tcx
 410                         .sess
 411                         .diagnostic()
 412                         .steal_diagnostic(segment.ident.span, StashKey::CallIntoMethod)
 413                 {
 414                     // Try suggesting `foo(a)` -> `a.foo()` if possible.
 415                     if let Some(ty) =
 416                         self.suggest_call_as_method(
 417                             &mut diag,
 418                             segment,
 419                             arg_exprs,
 420                             call_expr,
 421                             expected
 422                         )
 423                     {
 424                         diag.emit();
 425                         return ty;
 426                     } else {
 427                         diag.emit();
 428                     }
 429                 }
 430
 431                 let err = self.report_invalid_callee(call_expr, callee_expr, callee_ty, arg_exprs);
 432
 433                 return self.tcx.ty_error_with_guaranteed(err);
 434             }
 435         };
 436
 437         // Replace any late-bound regions that appear in the function
 438         // signature with region variables. We also have to
 439         // renormalize the associated types at this point, since they
 440         // previously appeared within a `Binder<>` and hence would not
 441         // have been normalized before.
 442         let fn_sig = self.replace_bound_vars_with_fresh_vars(call_expr.span, infer::FnCall, fn_sig);
 443         let fn_sig = self.normalize(call_expr.span, fn_sig);
 444
 445         // Call the generic checker.
 446         let expected_arg_tys = self.expected_inputs_for_expected_output(
 447             call_expr.span,
 448             expected,
 449             fn_sig.output(),
 450             fn_sig.inputs(),
 451         );
 452         self.check_argument_types(
 453             call_expr.span,
 454             call_expr,
 455             fn_sig.inputs(),
 456             expected_arg_tys,
 457             arg_exprs,
 458             fn_sig.c_variadic,
 459             TupleArgumentsFlag::DontTupleArguments,
 460             def_id,
 461         );
 462
 463         if fn_sig.abi == abi::Abi::RustCall {
 464             let sp = arg_exprs.last().map_or(call_expr.span, |expr| expr.span);
 465             if let Some(ty) = fn_sig.inputs().last().copied() {
 466                 self.register_bound(
 467                     ty,
 468                     self.tcx.require_lang_item(hir::LangItem::Tuple, Some(sp)),
 469                     traits::ObligationCause::new(sp, self.body_id, traits::RustCall),
 470                 );
 471             } else {
 472                 self.tcx.sess.span_err(
 473                         sp,
 474                         "functions with the \"rust-call\" ABI must take a single non-self tuple argument",
 475                     );
 476             }
 477         }
 478
 479         fn_sig.output()
 480     }
 481
 482     /// Attempts to reinterpret `method(rcvr, args...)` as `rcvr.method(args...)`
 483     /// and suggesting the fix if the method probe is successful.
 484     fn suggest_call_as_method(
 485         &self,
 486         diag: &mut Diagnostic,
 487         segment: &'tcx hir::PathSegment<'tcx>,
 488         arg_exprs: &'tcx [hir::Expr<'tcx>],
 489         call_expr: &'tcx hir::Expr<'tcx>,
 490         expected: Expectation<'tcx>,
 491     ) -> Option<Ty<'tcx>> {
 492         if let [callee_expr, rest @ ..] = arg_exprs {
 493             let callee_ty = self.typeck_results.borrow().expr_ty_adjusted_opt(callee_expr)?;
 494
 495             // First, do a probe with `IsSuggestion(true)` to avoid emitting
 496             // any strange errors. If it's successful, then we'll do a true
 497             // method lookup.
 498             let Ok(pick) = self
 499             .probe_for_name(
 500                 Mode::MethodCall,
 501                 segment.ident,
 502                 IsSuggestion(true),
 503                 callee_ty,
 504                 call_expr.hir_id,
 505                 // We didn't record the in scope traits during late resolution
 506                 // so we need to probe AllTraits unfortunately
 507                 ProbeScope::AllTraits,
 508             ) else {
 509                 return None;
 510             };
 511
 512             let pick = self.confirm_method(
 513                 call_expr.span,
 514                 callee_expr,
 515                 call_expr,
 516                 callee_ty,
 517                 &pick,
 518                 segment,
 519             );
 520             if pick.illegal_sized_bound.is_some() {
 521                 return None;
 522             }
 523
 524             let up_to_rcvr_span = segment.ident.span.until(callee_expr.span);
 525             let rest_span = callee_expr.span.shrink_to_hi().to(call_expr.span.shrink_to_hi());
 526             let rest_snippet = if let Some(first) = rest.first() {
 527                 self.tcx
 528                     .sess
 529                     .source_map()
 530                     .span_to_snippet(first.span.to(call_expr.span.shrink_to_hi()))
 531             } else {
 532                 Ok(")".to_string())
 533             };
 534
 535             if let Ok(rest_snippet) = rest_snippet {
 536                 let sugg = if callee_expr.precedence().order() >= PREC_POSTFIX {
 537                     vec![
 538                         (up_to_rcvr_span, "".to_string()),
 539                         (rest_span, format!(".{}({rest_snippet}", segment.ident)),
 540                     ]
 541                 } else {
 542                     vec![
 543                         (up_to_rcvr_span, "(".to_string()),
 544                         (rest_span, format!(").{}({rest_snippet}", segment.ident)),
 545                     ]
 546                 };
 547                 let self_ty = self.resolve_vars_if_possible(pick.callee.sig.inputs()[0]);
 548                 diag.multipart_suggestion(
 549                     format!(
 550                         "use the `.` operator to call the method `{}{}` on `{self_ty}`",
 551                         self.tcx
 552                             .associated_item(pick.callee.def_id)
 553                             .trait_container(self.tcx)
 554                             .map_or_else(
 555                                 || String::new(),
 556                                 |trait_def_id| self.tcx.def_path_str(trait_def_id) + "::"
 557                             ),
 558                         segment.ident
 559                     ),
 560                     sugg,
 561                     Applicability::MaybeIncorrect,
 562                 );
 563
 564                 // Let's check the method fully now
 565                 let return_ty = self.check_method_argument_types(
 566                     segment.ident.span,
 567                     call_expr,
 568                     Ok(pick.callee),
 569                     rest,
 570                     TupleArgumentsFlag::DontTupleArguments,
 571                     expected,
 572                 );
 573
 574                 return Some(return_ty);
 575             }
 576         }
 577
 578         None
 579     }
 580
 581     fn report_invalid_callee(
 582         &self,
 583         call_expr: &'tcx hir::Expr<'tcx>,
 584         callee_expr: &'tcx hir::Expr<'tcx>,
 585         callee_ty: Ty<'tcx>,
 586         arg_exprs: &'tcx [hir::Expr<'tcx>],
 587     ) -> ErrorGuaranteed {
 588         let mut unit_variant = None;
 589         if let hir::ExprKind::Path(qpath) = &callee_expr.kind
 590             && let Res::Def(def::DefKind::Ctor(kind, CtorKind::Const), _)
 591                 = self.typeck_results.borrow().qpath_res(qpath, callee_expr.hir_id)
 592             // Only suggest removing parens if there are no arguments
 593             && arg_exprs.is_empty()
 594         {
 595             let descr = match kind {
 596                 def::CtorOf::Struct => "struct",
 597                 def::CtorOf::Variant => "enum variant",
 598             };
 599             let removal_span = callee_expr.span.shrink_to_hi().to(call_expr.span.shrink_to_hi());
 600             unit_variant = Some((removal_span, descr, rustc_hir_pretty::qpath_to_string(qpath)));
 601         }
 602
 603         let callee_ty = self.resolve_vars_if_possible(callee_ty);
 604         let mut err = type_error_struct!(
 605             self.tcx.sess,
 606             callee_expr.span,
 607             callee_ty,
 608             E0618,
 609             "expected function, found {}",
 610             match &unit_variant {
 611                 Some((_, kind, path)) => format!("{kind} `{path}`"),
 612                 None => format!("`{callee_ty}`"),
 613             }
 614         );
 615
 616         self.identify_bad_closure_def_and_call(
 617             &mut err,
 618             call_expr.hir_id,
 619             &callee_expr.kind,
 620             callee_expr.span,
 621         );
 622
 623         if let Some((removal_span, kind, path)) = &unit_variant {
 624             err.span_suggestion_verbose(
 625                 *removal_span,
 626                 &format!(
 627                     "`{path}` is a unit {kind}, and does not take parentheses to be constructed",
 628                 ),
 629                 "",
 630                 Applicability::MachineApplicable,
 631             );
 632         }
 633
 634         let mut inner_callee_path = None;
 635         let def = match callee_expr.kind {
 636             hir::ExprKind::Path(ref qpath) => {
 637                 self.typeck_results.borrow().qpath_res(qpath, callee_expr.hir_id)
 638             }
 639             hir::ExprKind::Call(ref inner_callee, _) => {
 640                 // If the call spans more than one line and the callee kind is
 641                 // itself another `ExprCall`, that's a clue that we might just be
 642                 // missing a semicolon (Issue #51055)
 643                 let call_is_multiline = self.tcx.sess.source_map().is_multiline(call_expr.span);
 644                 if call_is_multiline {
 645                     err.span_suggestion(
 646                         callee_expr.span.shrink_to_hi(),
 647                         "consider using a semicolon here",
 648                         ";",
 649                         Applicability::MaybeIncorrect,
 650                     );
 651                 }
 652                 if let hir::ExprKind::Path(ref inner_qpath) = inner_callee.kind {
 653                     inner_callee_path = Some(inner_qpath);
 654                     self.typeck_results.borrow().qpath_res(inner_qpath, inner_callee.hir_id)
 655                 } else {
 656                     Res::Err
 657                 }
 658             }
 659             _ => Res::Err,
 660         };
 661
 662         if !self.maybe_suggest_bad_array_definition(&mut err, call_expr, callee_expr) {
 663             if let Some((maybe_def, output_ty, _)) =
 664                 self.extract_callable_info(callee_expr, callee_ty)
 665                 && !self.type_is_sized_modulo_regions(self.param_env, output_ty, callee_expr.span)
 666             {
 667                 let descr = match maybe_def {
 668                     DefIdOrName::DefId(def_id) => self.tcx.def_kind(def_id).descr(def_id),
 669                     DefIdOrName::Name(name) => name,
 670                 };
 671                 err.span_label(
 672                     callee_expr.span,
 673                     format!("this {descr} returns an unsized value `{output_ty}`, so it cannot be called")
 674                 );
 675                 if let DefIdOrName::DefId(def_id) = maybe_def
 676                     && let Some(def_span) = self.tcx.hir().span_if_local(def_id)
 677                 {
 678                     err.span_label(def_span, "the callable type is defined here");
 679                 }
 680             } else {
 681                 err.span_label(call_expr.span, "call expression requires function");
 682             }
 683         }
 684
 685         if let Some(span) = self.tcx.hir().res_span(def) {
 686             let callee_ty = callee_ty.to_string();
 687             let label = match (unit_variant, inner_callee_path) {
 688                 (Some((_, kind, path)), _) => Some(format!("{kind} `{path}` defined here")),
 689                 (_, Some(hir::QPath::Resolved(_, path))) => self
 690                     .tcx
 691                     .sess
 692                     .source_map()
 693                     .span_to_snippet(path.span)
 694                     .ok()
 695                     .map(|p| format!("`{p}` defined here returns `{callee_ty}`")),
 696                 _ => {
 697                     match def {
 698                         // Emit a different diagnostic for local variables, as they are not
 699                         // type definitions themselves, but rather variables *of* that type.
 700                         Res::Local(hir_id) => Some(format!(
 701                             "`{}` has type `{}`",
 702                             self.tcx.hir().name(hir_id),
 703                             callee_ty
 704                         )),
 705                         Res::Def(kind, def_id) if kind.ns() == Some(Namespace::ValueNS) => {
 706                             Some(format!("`{}` defined here", self.tcx.def_path_str(def_id),))
 707                         }
 708                         _ => Some(format!("`{callee_ty}` defined here")),
 709                     }
 710                 }
 711             };
 712             if let Some(label) = label {
 713                 err.span_label(span, label);
 714             }
 715         }
 716         err.emit()
 717     }
 718
 719     fn confirm_deferred_closure_call(
 720         &self,
 721         call_expr: &'tcx hir::Expr<'tcx>,
 722         arg_exprs: &'tcx [hir::Expr<'tcx>],
 723         expected: Expectation<'tcx>,
 724         closure_def_id: LocalDefId,
 725         fn_sig: ty::FnSig<'tcx>,
 726     ) -> Ty<'tcx> {
 727         // `fn_sig` is the *signature* of the closure being called. We
 728         // don't know the full details yet (`Fn` vs `FnMut` etc), but we
 729         // do know the types expected for each argument and the return
 730         // type.
 731
 732         let expected_arg_tys = self.expected_inputs_for_expected_output(
 733             call_expr.span,
 734             expected,
 735             fn_sig.output(),
 736             fn_sig.inputs(),
 737         );
 738
 739         self.check_argument_types(
 740             call_expr.span,
 741             call_expr,
 742             fn_sig.inputs(),
 743             expected_arg_tys,
 744             arg_exprs,
 745             fn_sig.c_variadic,
 746             TupleArgumentsFlag::TupleArguments,
 747             Some(closure_def_id.to_def_id()),
 748         );
 749
 750         fn_sig.output()
 751     }
 752
 753     fn confirm_overloaded_call(
 754         &self,
 755         call_expr: &'tcx hir::Expr<'tcx>,
 756         arg_exprs: &'tcx [hir::Expr<'tcx>],
 757         expected: Expectation<'tcx>,
 758         method_callee: MethodCallee<'tcx>,
 759     ) -> Ty<'tcx> {
 760         let output_type = self.check_method_argument_types(
 761             call_expr.span,
 762             call_expr,
 763             Ok(method_callee),
 764             arg_exprs,
 765             TupleArgumentsFlag::TupleArguments,
 766             expected,
 767         );
 768
 769         self.write_method_call(call_expr.hir_id, method_callee);
 770         output_type
 771     }
 772 }
 773
 774 #[derive(Debug)]
 775 pub struct DeferredCallResolution<'tcx> {
 776     call_expr: &'tcx hir::Expr<'tcx>,
 777     callee_expr: &'tcx hir::Expr<'tcx>,
 778     adjusted_ty: Ty<'tcx>,
 779     adjustments: Vec<Adjustment<'tcx>>,
 780     fn_sig: ty::FnSig<'tcx>,
 781     closure_substs: SubstsRef<'tcx>,
 782 }
 783
 784 impl<'a, 'tcx> DeferredCallResolution<'tcx> {
 785     pub fn resolve(self, fcx: &FnCtxt<'a, 'tcx>) {
 786         debug!("DeferredCallResolution::resolve() {:?}", self);
 787
 788         // we should not be invoked until the closure kind has been
 789         // determined by upvar inference
 790         assert!(fcx.closure_kind(self.closure_substs).is_some());
 791
 792         // We may now know enough to figure out fn vs fnmut etc.
 793         match fcx.try_overloaded_call_traits(self.call_expr, self.adjusted_ty, None) {
 794             Some((autoref, method_callee)) => {
 795                 // One problem is that when we get here, we are going
 796                 // to have a newly instantiated function signature
 797                 // from the call trait. This has to be reconciled with
 798                 // the older function signature we had before. In
 799                 // principle we *should* be able to fn_sigs(), but we
 800                 // can't because of the annoying need for a TypeTrace.
 801                 // (This always bites me, should find a way to
 802                 // refactor it.)
 803                 let method_sig = method_callee.sig;
 804
 805                 debug!("attempt_resolution: method_callee={:?}", method_callee);
 806
 807                 for (method_arg_ty, self_arg_ty) in
 808                     iter::zip(method_sig.inputs().iter().skip(1), self.fn_sig.inputs())
 809                 {
 810                     fcx.demand_eqtype(self.call_expr.span, *self_arg_ty, *method_arg_ty);
 811                 }
 812
 813                 fcx.demand_eqtype(self.call_expr.span, method_sig.output(), self.fn_sig.output());
 814
 815                 let mut adjustments = self.adjustments;
 816                 adjustments.extend(autoref);
 817                 fcx.apply_adjustments(self.callee_expr, adjustments);
 818
 819                 fcx.write_method_call(self.call_expr.hir_id, method_callee);
 820             }
 821             None => {
 822                 // This can happen if `#![no_core]` is used and the `fn/fn_mut/fn_once`
 823                 // lang items are not defined (issue #86238).
 824                 let mut err = fcx.inh.tcx.sess.struct_span_err(
 825                     self.call_expr.span,
 826                     "failed to find an overloaded call trait for closure call",
 827                 );
 828                 err.help(
 829                     "make sure the `fn`/`fn_mut`/`fn_once` lang items are defined \
 830                      and have associated `call`/`call_mut`/`call_once` functions",
 831                 );
 832                 err.emit();
 833             }
 834         }
 835     }
 836 }