compiler/rustc_hir_analysis/src/check/callee.rs

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