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