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, 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 `x: &mut FnMut()`, if there is a call `x()`, we would
 183             // normally translate to `FnMut::call_mut(&mut x, ())`, but
 184             // that winds up requiring `mut x: &mut FnMut()`. A little
 185             // over the top. The simplest fix by far is to just ignore
 186             // this case and deref again, so we wind up with
 187             // `FnMut::call_mut(&mut *x, ())`.
 188             ty::Ref(..) if autoderef.step_count() == 0 => {
 189                 return None;
 190             }
 191
 192             ty::Error(_) => {
 193                 return None;
 194             }
 195
 196             _ => {}
 197         }
 198
 199         // Now, we look for the implementation of a Fn trait on the object's type.
 200         // We first do it with the explicit instruction to look for an impl of
 201         // `Fn<Tuple>`, with the tuple `Tuple` having an arity corresponding
 202         // to the number of call parameters.
 203         // If that fails (or_else branch), we try again without specifying the
 204         // shape of the tuple (hence the None). This allows to detect an Fn trait
 205         // is implemented, and use this information for diagnostic.
 206         self.try_overloaded_call_traits(call_expr, adjusted_ty, Some(arg_exprs))
 207             .or_else(|| self.try_overloaded_call_traits(call_expr, adjusted_ty, None))
 208             .map(|(autoref, method)| {
 209                 let mut adjustments = self.adjust_steps(autoderef);
 210                 adjustments.extend(autoref);
 211                 self.apply_adjustments(callee_expr, adjustments);
 212                 CallStep::Overloaded(method)
 213             })
 214     }
 215
 216     fn try_overloaded_call_traits(
 217         &self,
 218         call_expr: &hir::Expr<'_>,
 219         adjusted_ty: Ty<'tcx>,
 220         opt_arg_exprs: Option<&'tcx [hir::Expr<'tcx>]>,
 221     ) -> Option<(Option<Adjustment<'tcx>>, MethodCallee<'tcx>)> {
 222         // Try the options that are least restrictive on the caller first.
 223         for (opt_trait_def_id, method_name, borrow) in [
 224             (self.tcx.lang_items().fn_trait(), Ident::with_dummy_span(sym::call), true),
 225             (self.tcx.lang_items().fn_mut_trait(), Ident::with_dummy_span(sym::call_mut), true),
 226             (self.tcx.lang_items().fn_once_trait(), Ident::with_dummy_span(sym::call_once), false),
 227         ] {
 228             let Some(trait_def_id) = opt_trait_def_id else { continue };
 229
 230             let opt_input_type = opt_arg_exprs.map(|arg_exprs| {
 231                 self.tcx.mk_tup(arg_exprs.iter().map(|e| {
 232                     self.next_ty_var(TypeVariableOrigin {
 233                         kind: TypeVariableOriginKind::TypeInference,
 234                         span: e.span,
 235                     })
 236                 }))
 237             });
 238
 239             if let Some(ok) = self.lookup_method_in_trait(
 240                 call_expr.span,
 241                 method_name,
 242                 trait_def_id,
 243                 adjusted_ty,
 244                 opt_input_type.as_ref().map(slice::from_ref),
 245             ) {
 246                 let method = self.register_infer_ok_obligations(ok);
 247                 let mut autoref = None;
 248                 if borrow {
 249                     // Check for &self vs &mut self in the method signature. Since this is either
 250                     // the Fn or FnMut trait, it should be one of those.
 251                     let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind() else {
 252                         // The `fn`/`fn_mut` lang item is ill-formed, which should have
 253                         // caused an error elsewhere.
 254                         self.tcx
 255                             .sess
 256                             .delay_span_bug(call_expr.span, "input to call/call_mut is not a ref?");
 257                         return None;
 258                     };
 259
 260                     // For initial two-phase borrow
 261                     // deployment, conservatively omit
 262                     // overloaded function call ops.
 263                     let mutbl = AutoBorrowMutability::new(*mutbl, AllowTwoPhase::No);
 264
 265                     autoref = Some(Adjustment {
 266                         kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
 267                         target: method.sig.inputs()[0],
 268                     });
 269                 }
 270                 return Some((autoref, method));
 271             }
 272         }
 273
 274         None
 275     }
 276
 277     /// Give appropriate suggestion when encountering `||{/* not callable */}()`, where the
 278     /// likely intention is to call the closure, suggest `(||{})()`. (#55851)
 279     fn identify_bad_closure_def_and_call(
 280         &self,
 281         err: &mut Diagnostic,
 282         hir_id: hir::HirId,
 283         callee_node: &hir::ExprKind<'_>,
 284         callee_span: Span,
 285     ) {
 286         let hir = self.tcx.hir();
 287         let parent_hir_id = hir.get_parent_node(hir_id);
 288         let parent_node = hir.get(parent_hir_id);
 289         if let (
 290             hir::Node::Expr(hir::Expr {
 291                 kind: hir::ExprKind::Closure(&hir::Closure { fn_decl_span, body, .. }),
 292                 ..
 293             }),
 294             hir::ExprKind::Block(..),
 295         ) = (parent_node, callee_node)
 296         {
 297             let fn_decl_span = if hir.body(body).generator_kind
 298                 == Some(hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure))
 299             {
 300                 // Actually need to unwrap a few more layers of HIR to get to
 301                 // the _real_ closure...
 302                 let async_closure = hir.get_parent_node(hir.get_parent_node(parent_hir_id));
 303                 if let hir::Node::Expr(hir::Expr {
 304                     kind: hir::ExprKind::Closure(&hir::Closure { fn_decl_span, .. }),
 305                     ..
 306                 }) = hir.get(async_closure)
 307                 {
 308                     fn_decl_span
 309                 } else {
 310                     return;
 311                 }
 312             } else {
 313                 fn_decl_span
 314             };
 315
 316             let start = fn_decl_span.shrink_to_lo();
 317             let end = callee_span.shrink_to_hi();
 318             err.multipart_suggestion(
 319                 "if you meant to create this closure and immediately call it, surround the \
 320                 closure with parentheses",
 321                 vec![(start, "(".to_string()), (end, ")".to_string())],
 322                 Applicability::MaybeIncorrect,
 323             );
 324         }
 325     }
 326
 327     /// Give appropriate suggestion when encountering `[("a", 0) ("b", 1)]`, where the
 328     /// likely intention is to create an array containing tuples.
 329     fn maybe_suggest_bad_array_definition(
 330         &self,
 331         err: &mut Diagnostic,
 332         call_expr: &'tcx hir::Expr<'tcx>,
 333         callee_expr: &'tcx hir::Expr<'tcx>,
 334     ) -> bool {
 335         let hir_id = self.tcx.hir().get_parent_node(call_expr.hir_id);
 336         let parent_node = self.tcx.hir().get(hir_id);
 337         if let (
 338             hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Array(_), .. }),
 339             hir::ExprKind::Tup(exp),
 340             hir::ExprKind::Call(_, args),
 341         ) = (parent_node, &callee_expr.kind, &call_expr.kind)
 342             && args.len() == exp.len()
 343         {
 344             let start = callee_expr.span.shrink_to_hi();
 345             err.span_suggestion(
 346                 start,
 347                 "consider separating array elements with a comma",
 348                 ",",
 349                 Applicability::MaybeIncorrect,
 350             );
 351             return true;
 352         }
 353         false
 354     }
 355
 356     fn confirm_builtin_call(
 357         &self,
 358         call_expr: &'tcx hir::Expr<'tcx>,
 359         callee_expr: &'tcx hir::Expr<'tcx>,
 360         callee_ty: Ty<'tcx>,
 361         arg_exprs: &'tcx [hir::Expr<'tcx>],
 362         expected: Expectation<'tcx>,
 363     ) -> Ty<'tcx> {
 364         let (fn_sig, def_id) = match *callee_ty.kind() {
 365             ty::FnDef(def_id, subst) => {
 366                 let fn_sig = self.tcx.bound_fn_sig(def_id).subst(self.tcx, subst);
 367
 368                 // Unit testing: function items annotated with
 369                 // `#[rustc_evaluate_where_clauses]` trigger special output
 370                 // to let us test the trait evaluation system.
 371                 if self.tcx.has_attr(def_id, sym::rustc_evaluate_where_clauses) {
 372                     let predicates = self.tcx.predicates_of(def_id);
 373                     let predicates = predicates.instantiate(self.tcx, subst);
 374                     for (predicate, predicate_span) in
 375                         predicates.predicates.iter().zip(&predicates.spans)
 376                     {
 377                         let obligation = Obligation::new(
 378                             self.tcx,
 379                             ObligationCause::dummy_with_span(callee_expr.span),
 380                             self.param_env,
 381                             *predicate,
 382                         );
 383                         let result = self.evaluate_obligation(&obligation);
 384                         self.tcx
 385                             .sess
 386                             .struct_span_err(
 387                                 callee_expr.span,
 388                                 &format!("evaluate({:?}) = {:?}", predicate, result),
 389                             )
 390                             .span_label(*predicate_span, "predicate")
 391                             .emit();
 392                     }
 393                 }
 394                 (fn_sig, Some(def_id))
 395             }
 396             ty::FnPtr(sig) => (sig, None),
 397             _ => {
 398                 if let hir::ExprKind::Path(hir::QPath::Resolved(_, path)) = &callee_expr.kind
 399                     && let [segment] = path.segments
 400                     && let Some(mut diag) = self
 401                         .tcx
 402                         .sess
 403                         .diagnostic()
 404                         .steal_diagnostic(segment.ident.span, StashKey::CallIntoMethod)
 405                 {
 406                     // Try suggesting `foo(a)` -> `a.foo()` if possible.
 407                     if let Some(ty) =
 408                         self.suggest_call_as_method(
 409                             &mut diag,
 410                             segment,
 411                             arg_exprs,
 412                             call_expr,
 413                             expected
 414                         )
 415                     {
 416                         diag.emit();
 417                         return ty;
 418                     } else {
 419                         diag.emit();
 420                     }
 421                 }
 422
 423                 self.report_invalid_callee(call_expr, callee_expr, callee_ty, arg_exprs);
 424
 425                 // This is the "default" function signature, used in case of error.
 426                 // In that case, we check each argument against "error" in order to
 427                 // set up all the node type bindings.
 428                 (
 429                     ty::Binder::dummy(self.tcx.mk_fn_sig(
 430                         self.err_args(arg_exprs.len()).into_iter(),
 431                         self.tcx.ty_error(),
 432                         false,
 433                         hir::Unsafety::Normal,
 434                         abi::Abi::Rust,
 435                     )),
 436                     None,
 437                 )
 438             }
 439         };
 440
 441         // Replace any late-bound regions that appear in the function
 442         // signature with region variables. We also have to
 443         // renormalize the associated types at this point, since they
 444         // previously appeared within a `Binder<>` and hence would not
 445         // have been normalized before.
 446         let fn_sig = self.replace_bound_vars_with_fresh_vars(call_expr.span, infer::FnCall, fn_sig);
 447         let fn_sig = self.normalize_associated_types_in(call_expr.span, fn_sig);
 448
 449         // Call the generic checker.
 450         let expected_arg_tys = self.expected_inputs_for_expected_output(
 451             call_expr.span,
 452             expected,
 453             fn_sig.output(),
 454             fn_sig.inputs(),
 455         );
 456         self.check_argument_types(
 457             call_expr.span,
 458             call_expr,
 459             fn_sig.inputs(),
 460             expected_arg_tys,
 461             arg_exprs,
 462             fn_sig.c_variadic,
 463             TupleArgumentsFlag::DontTupleArguments,
 464             def_id,
 465         );
 466
 467         if fn_sig.abi == abi::Abi::RustCall {
 468             let sp = arg_exprs.last().map_or(call_expr.span, |expr| expr.span);
 469             if let Some(ty) = fn_sig.inputs().last().copied() {
 470                 self.register_bound(
 471                     ty,
 472                     self.tcx.require_lang_item(hir::LangItem::Tuple, Some(sp)),
 473                     traits::ObligationCause::new(sp, self.body_id, traits::RustCall),
 474                 );
 475             } else {
 476                 self.tcx.sess.span_err(
 477                         sp,
 478                         "functions with the \"rust-call\" ABI must take a single non-self tuple argument",
 479                     );
 480             }
 481         }
 482
 483         fn_sig.output()
 484     }
 485
 486     /// Attempts to reinterpret `method(rcvr, args...)` as `rcvr.method(args...)`
 487     /// and suggesting the fix if the method probe is successful.
 488     fn suggest_call_as_method(
 489         &self,
 490         diag: &mut Diagnostic,
 491         segment: &'tcx hir::PathSegment<'tcx>,
 492         arg_exprs: &'tcx [hir::Expr<'tcx>],
 493         call_expr: &'tcx hir::Expr<'tcx>,
 494         expected: Expectation<'tcx>,
 495     ) -> Option<Ty<'tcx>> {
 496         if let [callee_expr, rest @ ..] = arg_exprs {
 497             let callee_ty = self.check_expr(callee_expr);
 498             // First, do a probe with `IsSuggestion(true)` to avoid emitting
 499             // any strange errors. If it's successful, then we'll do a true
 500             // method lookup.
 501             let Ok(pick) = self
 502             .probe_for_name(
 503                 Mode::MethodCall,
 504                 segment.ident,
 505                 IsSuggestion(true),
 506                 callee_ty,
 507                 call_expr.hir_id,
 508                 // We didn't record the in scope traits during late resolution
 509                 // so we need to probe AllTraits unfortunately
 510                 ProbeScope::AllTraits,
 511             ) else {
 512                 return None;
 513             };
 514
 515             let pick = self.confirm_method(
 516                 call_expr.span,
 517                 callee_expr,
 518                 call_expr,
 519                 callee_ty,
 520                 pick,
 521                 segment,
 522             );
 523             if pick.illegal_sized_bound.is_some() {
 524                 return None;
 525             }
 526
 527             let up_to_rcvr_span = segment.ident.span.until(callee_expr.span);
 528             let rest_span = callee_expr.span.shrink_to_hi().to(call_expr.span.shrink_to_hi());
 529             let rest_snippet = if let Some(first) = rest.first() {
 530                 self.tcx
 531                     .sess
 532                     .source_map()
 533                     .span_to_snippet(first.span.to(call_expr.span.shrink_to_hi()))
 534             } else {
 535                 Ok(")".to_string())
 536             };
 537
 538             if let Ok(rest_snippet) = rest_snippet {
 539                 let sugg = if callee_expr.precedence().order() >= PREC_POSTFIX {
 540                     vec![
 541                         (up_to_rcvr_span, "".to_string()),
 542                         (rest_span, format!(".{}({rest_snippet}", segment.ident)),
 543                     ]
 544                 } else {
 545                     vec![
 546                         (up_to_rcvr_span, "(".to_string()),
 547                         (rest_span, format!(").{}({rest_snippet}", segment.ident)),
 548                     ]
 549                 };
 550                 let self_ty = self.resolve_vars_if_possible(pick.callee.sig.inputs()[0]);
 551                 diag.multipart_suggestion(
 552                     format!(
 553                         "use the `.` operator to call the method `{}{}` on `{self_ty}`",
 554                         self.tcx
 555                             .associated_item(pick.callee.def_id)
 556                             .trait_container(self.tcx)
 557                             .map_or_else(
 558                                 || String::new(),
 559                                 |trait_def_id| self.tcx.def_path_str(trait_def_id) + "::"
 560                             ),
 561                         segment.ident
 562                     ),
 563                     sugg,
 564                     Applicability::MaybeIncorrect,
 565                 );
 566
 567                 // Let's check the method fully now
 568                 let return_ty = self.check_method_argument_types(
 569                     segment.ident.span,
 570                     call_expr,
 571                     Ok(pick.callee),
 572                     rest,
 573                     TupleArgumentsFlag::DontTupleArguments,
 574                     expected,
 575                 );
 576
 577                 return Some(return_ty);
 578             }
 579         }
 580
 581         None
 582     }
 583
 584     fn report_invalid_callee(
 585         &self,
 586         call_expr: &'tcx hir::Expr<'tcx>,
 587         callee_expr: &'tcx hir::Expr<'tcx>,
 588         callee_ty: Ty<'tcx>,
 589         arg_exprs: &'tcx [hir::Expr<'tcx>],
 590     ) {
 591         let mut unit_variant = None;
 592         if let hir::ExprKind::Path(qpath) = &callee_expr.kind
 593             && let Res::Def(def::DefKind::Ctor(kind, CtorKind::Const), _)
 594                 = self.typeck_results.borrow().qpath_res(qpath, callee_expr.hir_id)
 595             // Only suggest removing parens if there are no arguments
 596             && arg_exprs.is_empty()
 597         {
 598             let descr = match kind {
 599                 def::CtorOf::Struct => "struct",
 600                 def::CtorOf::Variant => "enum variant",
 601             };
 602             let removal_span = callee_expr.span.shrink_to_hi().to(call_expr.span.shrink_to_hi());
 603             unit_variant = Some((removal_span, descr, rustc_hir_pretty::qpath_to_string(qpath)));
 604         }
 605
 606         let callee_ty = self.resolve_vars_if_possible(callee_ty);
 607         let mut err = type_error_struct!(
 608             self.tcx.sess,
 609             callee_expr.span,
 610             callee_ty,
 611             E0618,
 612             "expected function, found {}",
 613             match &unit_variant {
 614                 Some((_, kind, path)) => format!("{kind} `{path}`"),
 615                 None => format!("`{callee_ty}`"),
 616             }
 617         );
 618
 619         self.identify_bad_closure_def_and_call(
 620             &mut err,
 621             call_expr.hir_id,
 622             &callee_expr.kind,
 623             callee_expr.span,
 624         );
 625
 626         if let Some((removal_span, kind, path)) = &unit_variant {
 627             err.span_suggestion_verbose(
 628                 *removal_span,
 629                 &format!(
 630                     "`{path}` is a unit {kind}, and does not take parentheses to be constructed",
 631                 ),
 632                 "",
 633                 Applicability::MachineApplicable,
 634             );
 635         }
 636
 637         let mut inner_callee_path = None;
 638         let def = match callee_expr.kind {
 639             hir::ExprKind::Path(ref qpath) => {
 640                 self.typeck_results.borrow().qpath_res(qpath, callee_expr.hir_id)
 641             }
 642             hir::ExprKind::Call(ref inner_callee, _) => {
 643                 // If the call spans more than one line and the callee kind is
 644                 // itself another `ExprCall`, that's a clue that we might just be
 645                 // missing a semicolon (Issue #51055)
 646                 let call_is_multiline = self.tcx.sess.source_map().is_multiline(call_expr.span);
 647                 if call_is_multiline {
 648                     err.span_suggestion(
 649                         callee_expr.span.shrink_to_hi(),
 650                         "consider using a semicolon here",
 651                         ";",
 652                         Applicability::MaybeIncorrect,
 653                     );
 654                 }
 655                 if let hir::ExprKind::Path(ref inner_qpath) = inner_callee.kind {
 656                     inner_callee_path = Some(inner_qpath);
 657                     self.typeck_results.borrow().qpath_res(inner_qpath, inner_callee.hir_id)
 658                 } else {
 659                     Res::Err
 660                 }
 661             }
 662             _ => Res::Err,
 663         };
 664
 665         if !self.maybe_suggest_bad_array_definition(&mut err, call_expr, callee_expr) {
 666             if let Some((maybe_def, output_ty, _)) =
 667                 self.extract_callable_info(callee_expr, callee_ty)
 668                 && !self.type_is_sized_modulo_regions(self.param_env, output_ty, callee_expr.span)
 669             {
 670                 let descr = match maybe_def {
 671                     DefIdOrName::DefId(def_id) => self.tcx.def_kind(def_id).descr(def_id),
 672                     DefIdOrName::Name(name) => name,
 673                 };
 674                 err.span_label(
 675                     callee_expr.span,
 676                     format!("this {descr} returns an unsized value `{output_ty}`, so it cannot be called")
 677                 );
 678                 if let DefIdOrName::DefId(def_id) = maybe_def
 679                     && let Some(def_span) = self.tcx.hir().span_if_local(def_id)
 680                 {
 681                     err.span_label(def_span, "the callable type is defined here");
 682                 }
 683             } else {
 684                 err.span_label(call_expr.span, "call expression requires function");
 685             }
 686         }
 687
 688         if let Some(span) = self.tcx.hir().res_span(def) {
 689             let callee_ty = callee_ty.to_string();
 690             let label = match (unit_variant, inner_callee_path) {
 691                 (Some((_, kind, path)), _) => Some(format!("{kind} `{path}` defined here")),
 692                 (_, Some(hir::QPath::Resolved(_, path))) => self
 693                     .tcx
 694                     .sess
 695                     .source_map()
 696                     .span_to_snippet(path.span)
 697                     .ok()
 698                     .map(|p| format!("`{p}` defined here returns `{callee_ty}`")),
 699                 _ => {
 700                     match def {
 701                         // Emit a different diagnostic for local variables, as they are not
 702                         // type definitions themselves, but rather variables *of* that type.
 703                         Res::Local(hir_id) => Some(format!(
 704                             "`{}` has type `{}`",
 705                             self.tcx.hir().name(hir_id),
 706                             callee_ty
 707                         )),
 708                         Res::Def(kind, def_id) if kind.ns() == Some(Namespace::ValueNS) => {
 709                             Some(format!("`{}` defined here", self.tcx.def_path_str(def_id),))
 710                         }
 711                         _ => Some(format!("`{callee_ty}` defined here")),
 712                     }
 713                 }
 714             };
 715             if let Some(label) = label {
 716                 err.span_label(span, label);
 717             }
 718         }
 719         err.emit();
 720     }
 721
 722     fn confirm_deferred_closure_call(
 723         &self,
 724         call_expr: &'tcx hir::Expr<'tcx>,
 725         arg_exprs: &'tcx [hir::Expr<'tcx>],
 726         expected: Expectation<'tcx>,
 727         closure_def_id: LocalDefId,
 728         fn_sig: ty::FnSig<'tcx>,
 729     ) -> Ty<'tcx> {
 730         // `fn_sig` is the *signature* of the closure being called. We
 731         // don't know the full details yet (`Fn` vs `FnMut` etc), but we
 732         // do know the types expected for each argument and the return
 733         // type.
 734
 735         let expected_arg_tys = self.expected_inputs_for_expected_output(
 736             call_expr.span,
 737             expected,
 738             fn_sig.output(),
 739             fn_sig.inputs(),
 740         );
 741
 742         self.check_argument_types(
 743             call_expr.span,
 744             call_expr,
 745             fn_sig.inputs(),
 746             expected_arg_tys,
 747             arg_exprs,
 748             fn_sig.c_variadic,
 749             TupleArgumentsFlag::TupleArguments,
 750             Some(closure_def_id.to_def_id()),
 751         );
 752
 753         fn_sig.output()
 754     }
 755
 756     fn confirm_overloaded_call(
 757         &self,
 758         call_expr: &'tcx hir::Expr<'tcx>,
 759         arg_exprs: &'tcx [hir::Expr<'tcx>],
 760         expected: Expectation<'tcx>,
 761         method_callee: MethodCallee<'tcx>,
 762     ) -> Ty<'tcx> {
 763         let output_type = self.check_method_argument_types(
 764             call_expr.span,
 765             call_expr,
 766             Ok(method_callee),
 767             arg_exprs,
 768             TupleArgumentsFlag::TupleArguments,
 769             expected,
 770         );
 771
 772         self.write_method_call(call_expr.hir_id, method_callee);
 773         output_type
 774     }
 775 }
 776
 777 #[derive(Debug)]
 778 pub struct DeferredCallResolution<'tcx> {
 779     call_expr: &'tcx hir::Expr<'tcx>,
 780     callee_expr: &'tcx hir::Expr<'tcx>,
 781     adjusted_ty: Ty<'tcx>,
 782     adjustments: Vec<Adjustment<'tcx>>,
 783     fn_sig: ty::FnSig<'tcx>,
 784     closure_substs: SubstsRef<'tcx>,
 785 }
 786
 787 impl<'a, 'tcx> DeferredCallResolution<'tcx> {
 788     pub fn resolve(self, fcx: &FnCtxt<'a, 'tcx>) {
 789         debug!("DeferredCallResolution::resolve() {:?}", self);
 790
 791         // we should not be invoked until the closure kind has been
 792         // determined by upvar inference
 793         assert!(fcx.closure_kind(self.closure_substs).is_some());
 794
 795         // We may now know enough to figure out fn vs fnmut etc.
 796         match fcx.try_overloaded_call_traits(self.call_expr, self.adjusted_ty, None) {
 797             Some((autoref, method_callee)) => {
 798                 // One problem is that when we get here, we are going
 799                 // to have a newly instantiated function signature
 800                 // from the call trait. This has to be reconciled with
 801                 // the older function signature we had before. In
 802                 // principle we *should* be able to fn_sigs(), but we
 803                 // can't because of the annoying need for a TypeTrace.
 804                 // (This always bites me, should find a way to
 805                 // refactor it.)
 806                 let method_sig = method_callee.sig;
 807
 808                 debug!("attempt_resolution: method_callee={:?}", method_callee);
 809
 810                 for (method_arg_ty, self_arg_ty) in
 811                     iter::zip(method_sig.inputs().iter().skip(1), self.fn_sig.inputs())
 812                 {
 813                     fcx.demand_eqtype(self.call_expr.span, *self_arg_ty, *method_arg_ty);
 814                 }
 815
 816                 fcx.demand_eqtype(self.call_expr.span, method_sig.output(), self.fn_sig.output());
 817
 818                 let mut adjustments = self.adjustments;
 819                 adjustments.extend(autoref);
 820                 fcx.apply_adjustments(self.callee_expr, adjustments);
 821
 822                 fcx.write_method_call(self.call_expr.hir_id, method_callee);
 823             }
 824             None => {
 825                 // This can happen if `#![no_core]` is used and the `fn/fn_mut/fn_once`
 826                 // lang items are not defined (issue #86238).
 827                 let mut err = fcx.inh.tcx.sess.struct_span_err(
 828                     self.call_expr.span,
 829                     "failed to find an overloaded call trait for closure call",
 830                 );
 831                 err.help(
 832                     "make sure the `fn`/`fn_mut`/`fn_once` lang items are defined \
 833                      and have associated `call`/`call_mut`/`call_once` functions",
 834                 );
 835                 err.emit();
 836             }
 837         }
 838     }
 839 }