compiler/rustc_hir_analysis/src/check/callee.rs

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