compiler/rustc_typeck/src/check/callee.rs

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