compiler/rustc_hir_analysis/src/check/callee.rs

   1 use super::method::MethodCallee;
   2 use super::{DefIdOrName, 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::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::infer::InferCtxtExt as _;
  28 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
  29
  30 use std::iter;
  31
  32 /// Checks that it is legal to call methods of the trait corresponding
  33 /// to `trait_id` (this only cares about the trait, not the specific
  34 /// method that is called).
  35 pub fn check_legal_trait_for_method_call(
  36     tcx: TyCtxt<'_>,
  37     span: Span,
  38     receiver: Option<Span>,
  39     expr_span: Span,
  40     trait_id: DefId,
  41 ) {
  42     if tcx.lang_items().drop_trait() == Some(trait_id) {
  43         let mut err = struct_span_err!(tcx.sess, span, E0040, "explicit use of destructor method");
  44         err.span_label(span, "explicit destructor calls not allowed");
  45
  46         let (sp, suggestion) = receiver
  47             .and_then(|s| tcx.sess.source_map().span_to_snippet(s).ok())
  48             .filter(|snippet| !snippet.is_empty())
  49             .map(|snippet| (expr_span, format!("drop({snippet})")))
  50             .unwrap_or_else(|| (span, "drop".to_string()));
  51
  52         err.span_suggestion(
  53             sp,
  54             "consider using `drop` function",
  55             suggestion,
  56             Applicability::MaybeIncorrect,
  57         );
  58
  59         err.emit();
  60     }
  61 }
  62
  63 enum CallStep<'tcx> {
  64     Builtin(Ty<'tcx>),
  65     DeferredClosure(LocalDefId, ty::FnSig<'tcx>),
  66     /// E.g., enum variant constructors.
  67     Overloaded(MethodCallee<'tcx>),
  68 }
  69
  70 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  71     pub fn check_call(
  72         &self,
  73         call_expr: &'tcx hir::Expr<'tcx>,
  74         callee_expr: &'tcx hir::Expr<'tcx>,
  75         arg_exprs: &'tcx [hir::Expr<'tcx>],
  76         expected: Expectation<'tcx>,
  77     ) -> Ty<'tcx> {
  78         let original_callee_ty = match &callee_expr.kind {
  79             hir::ExprKind::Path(hir::QPath::Resolved(..) | hir::QPath::TypeRelative(..)) => self
  80                 .check_expr_with_expectation_and_args(
  81                     callee_expr,
  82                     Expectation::NoExpectation,
  83                     arg_exprs,
  84                 ),
  85             _ => self.check_expr(callee_expr),
  86         };
  87
  88         let expr_ty = self.structurally_resolved_type(call_expr.span, original_callee_ty);
  89
  90         let mut autoderef = self.autoderef(callee_expr.span, expr_ty);
  91         let mut result = None;
  92         while result.is_none() && autoderef.next().is_some() {
  93             result = self.try_overloaded_call_step(call_expr, callee_expr, arg_exprs, &autoderef);
  94         }
  95         self.register_predicates(autoderef.into_obligations());
  96
  97         let output = match result {
  98             None => {
  99                 // this will report an error since original_callee_ty is not a fn
 100                 self.confirm_builtin_call(
 101                     call_expr,
 102                     callee_expr,
 103                     original_callee_ty,
 104                     arg_exprs,
 105                     expected,
 106                 )
 107             }
 108
 109             Some(CallStep::Builtin(callee_ty)) => {
 110                 self.confirm_builtin_call(call_expr, callee_expr, callee_ty, arg_exprs, expected)
 111             }
 112
 113             Some(CallStep::DeferredClosure(def_id, fn_sig)) => {
 114                 self.confirm_deferred_closure_call(call_expr, arg_exprs, expected, def_id, fn_sig)
 115             }
 116
 117             Some(CallStep::Overloaded(method_callee)) => {
 118                 self.confirm_overloaded_call(call_expr, arg_exprs, expected, method_callee)
 119             }
 120         };
 121
 122         // we must check that return type of called functions is WF:
 123         self.register_wf_obligation(output.into(), call_expr.span, traits::WellFormed(None));
 124
 125         output
 126     }
 127
 128     fn try_overloaded_call_step(
 129         &self,
 130         call_expr: &'tcx hir::Expr<'tcx>,
 131         callee_expr: &'tcx hir::Expr<'tcx>,
 132         arg_exprs: &'tcx [hir::Expr<'tcx>],
 133         autoderef: &Autoderef<'a, 'tcx>,
 134     ) -> Option<CallStep<'tcx>> {
 135         let adjusted_ty =
 136             self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
 137         debug!(
 138             "try_overloaded_call_step(call_expr={:?}, adjusted_ty={:?})",
 139             call_expr, adjusted_ty
 140         );
 141
 142         // If the callee is a bare function or a closure, then we're all set.
 143         match *adjusted_ty.kind() {
 144             ty::FnDef(..) | ty::FnPtr(_) => {
 145                 let adjustments = self.adjust_steps(autoderef);
 146                 self.apply_adjustments(callee_expr, adjustments);
 147                 return Some(CallStep::Builtin(adjusted_ty));
 148             }
 149
 150             ty::Closure(def_id, substs) => {
 151                 let def_id = def_id.expect_local();
 152
 153                 // Check whether this is a call to a closure where we
 154                 // haven't yet decided on whether the closure is fn vs
 155                 // fnmut vs fnonce. If so, we have to defer further processing.
 156                 if self.closure_kind(substs).is_none() {
 157                     let closure_sig = substs.as_closure().sig();
 158                     let closure_sig = self.replace_bound_vars_with_fresh_vars(
 159                         call_expr.span,
 160                         infer::FnCall,
 161                         closure_sig,
 162                     );
 163                     let adjustments = self.adjust_steps(autoderef);
 164                     self.record_deferred_call_resolution(
 165                         def_id,
 166                         DeferredCallResolution {
 167                             call_expr,
 168                             callee_expr,
 169                             adjusted_ty,
 170                             adjustments,
 171                             fn_sig: closure_sig,
 172                             closure_substs: substs,
 173                         },
 174                     );
 175                     return Some(CallStep::DeferredClosure(def_id, closure_sig));
 176                 }
 177             }
 178
 179             // Hack: we know that there are traits implementing Fn for &F
 180             // where F:Fn and so forth. In the particular case of types
 181             // like `x: &mut FnMut()`, if there is a call `x()`, we would
 182             // normally translate to `FnMut::call_mut(&mut x, ())`, but
 183             // that winds up requiring `mut x: &mut FnMut()`. A little
 184             // over the top. The simplest fix by far is to just ignore
 185             // this case and deref again, so we wind up with
 186             // `FnMut::call_mut(&mut *x, ())`.
 187             ty::Ref(..) if autoderef.step_count() == 0 => {
 188                 return None;
 189             }
 190
 191             _ => {}
 192         }
 193
 194         // Now, we look for the implementation of a Fn trait on the object's type.
 195         // We first do it with the explicit instruction to look for an impl of
 196         // `Fn<Tuple>`, with the tuple `Tuple` having an arity corresponding
 197         // to the number of call parameters.
 198         // If that fails (or_else branch), we try again without specifying the
 199         // shape of the tuple (hence the None). This allows to detect an Fn trait
 200         // is implemented, and use this information for diagnostic.
 201         self.try_overloaded_call_traits(call_expr, adjusted_ty, Some(arg_exprs))
 202             .or_else(|| self.try_overloaded_call_traits(call_expr, adjusted_ty, None))
 203             .map(|(autoref, method)| {
 204                 let mut adjustments = self.adjust_steps(autoderef);
 205                 adjustments.extend(autoref);
 206                 self.apply_adjustments(callee_expr, adjustments);
 207                 CallStep::Overloaded(method)
 208             })
 209     }
 210
 211     fn try_overloaded_call_traits(
 212         &self,
 213         call_expr: &hir::Expr<'_>,
 214         adjusted_ty: Ty<'tcx>,
 215         opt_arg_exprs: Option<&'tcx [hir::Expr<'tcx>]>,
 216     ) -> Option<(Option<Adjustment<'tcx>>, MethodCallee<'tcx>)> {
 217         // Try the options that are least restrictive on the caller first.
 218         for (opt_trait_def_id, method_name, borrow) in [
 219             (self.tcx.lang_items().fn_trait(), Ident::with_dummy_span(sym::call), true),
 220             (self.tcx.lang_items().fn_mut_trait(), Ident::with_dummy_span(sym::call_mut), true),
 221             (self.tcx.lang_items().fn_once_trait(), Ident::with_dummy_span(sym::call_once), false),
 222         ] {
 223             let Some(trait_def_id) = opt_trait_def_id else { continue };
 224
 225             let opt_input_types = opt_arg_exprs.map(|arg_exprs| {
 226                 [self.tcx.mk_tup(arg_exprs.iter().map(|e| {
 227                     self.next_ty_var(TypeVariableOrigin {
 228                         kind: TypeVariableOriginKind::TypeInference,
 229                         span: e.span,
 230                     })
 231                 }))]
 232             });
 233             let opt_input_types = opt_input_types.as_ref().map(AsRef::as_ref);
 234
 235             if let Some(ok) = self.lookup_method_in_trait(
 236                 call_expr.span,
 237                 method_name,
 238                 trait_def_id,
 239                 adjusted_ty,
 240                 opt_input_types,
 241             ) {
 242                 let method = self.register_infer_ok_obligations(ok);
 243                 let mut autoref = None;
 244                 if borrow {
 245                     // Check for &self vs &mut self in the method signature. Since this is either
 246                     // the Fn or FnMut trait, it should be one of those.
 247                     let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind() else {
 248                         // The `fn`/`fn_mut` lang item is ill-formed, which should have
 249                         // caused an error elsewhere.
 250                         self.tcx
 251                             .sess
 252                             .delay_span_bug(call_expr.span, "input to call/call_mut is not a ref?");
 253                         return None;
 254                     };
 255
 256                     let mutbl = match mutbl {
 257                         hir::Mutability::Not => AutoBorrowMutability::Not,
 258                         hir::Mutability::Mut => AutoBorrowMutability::Mut {
 259                             // For initial two-phase borrow
 260                             // deployment, conservatively omit
 261                             // overloaded function call ops.
 262                             allow_two_phase_borrow: AllowTwoPhase::No,
 263                         },
 264                     };
 265                     autoref = Some(Adjustment {
 266                         kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
 267                         target: method.sig.inputs()[0],
 268                     });
 269                 }
 270                 return Some((autoref, method));
 271             }
 272         }
 273
 274         None
 275     }
 276
 277     /// Give appropriate suggestion when encountering `||{/* not callable */}()`, where the
 278     /// likely intention is to call the closure, suggest `(||{})()`. (#55851)
 279     fn identify_bad_closure_def_and_call(
 280         &self,
 281         err: &mut Diagnostic,
 282         hir_id: hir::HirId,
 283         callee_node: &hir::ExprKind<'_>,
 284         callee_span: Span,
 285     ) {
 286         let hir = self.tcx.hir();
 287         let parent_hir_id = hir.get_parent_node(hir_id);
 288         let parent_node = hir.get(parent_hir_id);
 289         if let (
 290             hir::Node::Expr(hir::Expr {
 291                 kind: hir::ExprKind::Closure(&hir::Closure { fn_decl_span, body, .. }),
 292                 ..
 293             }),
 294             hir::ExprKind::Block(..),
 295         ) = (parent_node, callee_node)
 296         {
 297             let fn_decl_span = if hir.body(body).generator_kind
 298                 == Some(hir::GeneratorKind::Async(hir::AsyncGeneratorKind::Closure))
 299             {
 300                 // Actually need to unwrap a few more layers of HIR to get to
 301                 // the _real_ closure...
 302                 let async_closure = hir.get_parent_node(hir.get_parent_node(parent_hir_id));
 303                 if let hir::Node::Expr(hir::Expr {
 304                     kind: hir::ExprKind::Closure(&hir::Closure { fn_decl_span, .. }),
 305                     ..
 306                 }) = hir.get(async_closure)
 307                 {
 308                     fn_decl_span
 309                 } else {
 310                     return;
 311                 }
 312             } else {
 313                 fn_decl_span
 314             };
 315
 316             let start = fn_decl_span.shrink_to_lo();
 317             let end = callee_span.shrink_to_hi();
 318             err.multipart_suggestion(
 319                 "if you meant to create this closure and immediately call it, surround the \
 320                 closure with parentheses",
 321                 vec![(start, "(".to_string()), (end, ")".to_string())],
 322                 Applicability::MaybeIncorrect,
 323             );
 324         }
 325     }
 326
 327     /// Give appropriate suggestion when encountering `[("a", 0) ("b", 1)]`, where the
 328     /// likely intention is to create an array containing tuples.
 329     fn maybe_suggest_bad_array_definition(
 330         &self,
 331         err: &mut Diagnostic,
 332         call_expr: &'tcx hir::Expr<'tcx>,
 333         callee_expr: &'tcx hir::Expr<'tcx>,
 334     ) -> bool {
 335         let hir_id = self.tcx.hir().get_parent_node(call_expr.hir_id);
 336         let parent_node = self.tcx.hir().get(hir_id);
 337         if let (
 338             hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Array(_), .. }),
 339             hir::ExprKind::Tup(exp),
 340             hir::ExprKind::Call(_, args),
 341         ) = (parent_node, &callee_expr.kind, &call_expr.kind)
 342             && args.len() == exp.len()
 343         {
 344             let start = callee_expr.span.shrink_to_hi();
 345             err.span_suggestion(
 346                 start,
 347                 "consider separating array elements with a comma",
 348                 ",",
 349                 Applicability::MaybeIncorrect,
 350             );
 351             return true;
 352         }
 353         false
 354     }
 355
 356     fn confirm_builtin_call(
 357         &self,
 358         call_expr: &'tcx hir::Expr<'tcx>,
 359         callee_expr: &'tcx hir::Expr<'tcx>,
 360         callee_ty: Ty<'tcx>,
 361         arg_exprs: &'tcx [hir::Expr<'tcx>],
 362         expected: Expectation<'tcx>,
 363     ) -> Ty<'tcx> {
 364         let (fn_sig, def_id) = match *callee_ty.kind() {
 365             ty::FnDef(def_id, subst) => {
 366                 let fn_sig = self.tcx.bound_fn_sig(def_id).subst(self.tcx, subst);
 367
 368                 // Unit testing: function items annotated with
 369                 // `#[rustc_evaluate_where_clauses]` trigger special output
 370                 // to let us test the trait evaluation system.
 371                 if self.tcx.has_attr(def_id, sym::rustc_evaluate_where_clauses) {
 372                     let predicates = self.tcx.predicates_of(def_id);
 373                     let predicates = predicates.instantiate(self.tcx, subst);
 374                     for (predicate, predicate_span) in
 375                         predicates.predicates.iter().zip(&predicates.spans)
 376                     {
 377                         let obligation = Obligation::new(
 378                             ObligationCause::dummy_with_span(callee_expr.span),
 379                             self.param_env,
 380                             *predicate,
 381                         );
 382                         let result = self.evaluate_obligation(&obligation);
 383                         self.tcx
 384                             .sess
 385                             .struct_span_err(
 386                                 callee_expr.span,
 387                                 &format!("evaluate({:?}) = {:?}", predicate, result),
 388                             )
 389                             .span_label(*predicate_span, "predicate")
 390                             .emit();
 391                     }
 392                 }
 393                 (fn_sig, Some(def_id))
 394             }
 395             ty::FnPtr(sig) => (sig, None),
 396             _ => {
 397                 self.report_invalid_callee(call_expr, callee_expr, callee_ty, arg_exprs);
 398
 399                 // This is the "default" function signature, used in case of error.
 400                 // In that case, we check each argument against "error" in order to
 401                 // set up all the node type bindings.
 402                 (
 403                     ty::Binder::dummy(self.tcx.mk_fn_sig(
 404                         self.err_args(arg_exprs.len()).into_iter(),
 405                         self.tcx.ty_error(),
 406                         false,
 407                         hir::Unsafety::Normal,
 408                         abi::Abi::Rust,
 409                     )),
 410                     None,
 411                 )
 412             }
 413         };
 414
 415         // Replace any late-bound regions that appear in the function
 416         // signature with region variables. We also have to
 417         // renormalize the associated types at this point, since they
 418         // previously appeared within a `Binder<>` and hence would not
 419         // have been normalized before.
 420         let fn_sig = self.replace_bound_vars_with_fresh_vars(call_expr.span, infer::FnCall, fn_sig);
 421         let fn_sig = self.normalize_associated_types_in(call_expr.span, fn_sig);
 422
 423         // Call the generic checker.
 424         let expected_arg_tys = self.expected_inputs_for_expected_output(
 425             call_expr.span,
 426             expected,
 427             fn_sig.output(),
 428             fn_sig.inputs(),
 429         );
 430         self.check_argument_types(
 431             call_expr.span,
 432             call_expr,
 433             fn_sig.inputs(),
 434             expected_arg_tys,
 435             arg_exprs,
 436             fn_sig.c_variadic,
 437             TupleArgumentsFlag::DontTupleArguments,
 438             def_id,
 439         );
 440
 441         fn_sig.output()
 442     }
 443
 444     fn report_invalid_callee(
 445         &self,
 446         call_expr: &'tcx hir::Expr<'tcx>,
 447         callee_expr: &'tcx hir::Expr<'tcx>,
 448         callee_ty: Ty<'tcx>,
 449         arg_exprs: &'tcx [hir::Expr<'tcx>],
 450     ) {
 451         let mut unit_variant = None;
 452         if let hir::ExprKind::Path(qpath) = &callee_expr.kind
 453             && let Res::Def(def::DefKind::Ctor(kind, def::CtorKind::Const), _)
 454                 = self.typeck_results.borrow().qpath_res(qpath, callee_expr.hir_id)
 455             // Only suggest removing parens if there are no arguments
 456             && arg_exprs.is_empty()
 457         {
 458             let descr = match kind {
 459                 def::CtorOf::Struct => "struct",
 460                 def::CtorOf::Variant => "enum variant",
 461             };
 462             let removal_span =
 463                 callee_expr.span.shrink_to_hi().to(call_expr.span.shrink_to_hi());
 464             unit_variant =
 465                 Some((removal_span, descr, rustc_hir_pretty::qpath_to_string(qpath)));
 466         }
 467
 468         let callee_ty = self.resolve_vars_if_possible(callee_ty);
 469         let mut err = type_error_struct!(
 470             self.tcx.sess,
 471             callee_expr.span,
 472             callee_ty,
 473             E0618,
 474             "expected function, found {}",
 475             match &unit_variant {
 476                 Some((_, kind, path)) => format!("{kind} `{path}`"),
 477                 None => format!("`{callee_ty}`"),
 478             }
 479         );
 480
 481         self.identify_bad_closure_def_and_call(
 482             &mut err,
 483             call_expr.hir_id,
 484             &callee_expr.kind,
 485             callee_expr.span,
 486         );
 487
 488         if let Some((removal_span, kind, path)) = &unit_variant {
 489             err.span_suggestion_verbose(
 490                 *removal_span,
 491                 &format!(
 492                     "`{path}` is a unit {kind}, and does not take parentheses to be constructed",
 493                 ),
 494                 "",
 495                 Applicability::MachineApplicable,
 496             );
 497         }
 498
 499         let mut inner_callee_path = None;
 500         let def = match callee_expr.kind {
 501             hir::ExprKind::Path(ref qpath) => {
 502                 self.typeck_results.borrow().qpath_res(qpath, callee_expr.hir_id)
 503             }
 504             hir::ExprKind::Call(ref inner_callee, _) => {
 505                 // If the call spans more than one line and the callee kind is
 506                 // itself another `ExprCall`, that's a clue that we might just be
 507                 // missing a semicolon (Issue #51055)
 508                 let call_is_multiline = self.tcx.sess.source_map().is_multiline(call_expr.span);
 509                 if call_is_multiline {
 510                     err.span_suggestion(
 511                         callee_expr.span.shrink_to_hi(),
 512                         "consider using a semicolon here",
 513                         ";",
 514                         Applicability::MaybeIncorrect,
 515                     );
 516                 }
 517                 if let hir::ExprKind::Path(ref inner_qpath) = inner_callee.kind {
 518                     inner_callee_path = Some(inner_qpath);
 519                     self.typeck_results.borrow().qpath_res(inner_qpath, inner_callee.hir_id)
 520                 } else {
 521                     Res::Err
 522                 }
 523             }
 524             _ => Res::Err,
 525         };
 526
 527         if !self.maybe_suggest_bad_array_definition(&mut err, call_expr, callee_expr) {
 528             if let Some((maybe_def, output_ty, _)) = self.extract_callable_info(callee_expr, callee_ty)
 529                 && !self.type_is_sized_modulo_regions(self.param_env, output_ty, callee_expr.span)
 530             {
 531                 let descr = match maybe_def {
 532                     DefIdOrName::DefId(def_id) => self.tcx.def_kind(def_id).descr(def_id),
 533                     DefIdOrName::Name(name) => name,
 534                 };
 535                 err.span_label(
 536                     callee_expr.span,
 537                     format!("this {descr} returns an unsized value `{output_ty}`, so it cannot be called")
 538                 );
 539                 if let DefIdOrName::DefId(def_id) = maybe_def
 540                     && let Some(def_span) = self.tcx.hir().span_if_local(def_id)
 541                 {
 542                     err.span_label(def_span, "the callable type is defined here");
 543                 }
 544             } else {
 545                 err.span_label(call_expr.span, "call expression requires function");
 546             }
 547         }
 548
 549         if let Some(span) = self.tcx.hir().res_span(def) {
 550             let callee_ty = callee_ty.to_string();
 551             let label = match (unit_variant, inner_callee_path) {
 552                 (Some((_, kind, path)), _) => Some(format!("{kind} `{path}` defined here")),
 553                 (_, Some(hir::QPath::Resolved(_, path))) => self
 554                     .tcx
 555                     .sess
 556                     .source_map()
 557                     .span_to_snippet(path.span)
 558                     .ok()
 559                     .map(|p| format!("`{p}` defined here returns `{callee_ty}`")),
 560                 _ => {
 561                     match def {
 562                         // Emit a different diagnostic for local variables, as they are not
 563                         // type definitions themselves, but rather variables *of* that type.
 564                         Res::Local(hir_id) => Some(format!(
 565                             "`{}` has type `{}`",
 566                             self.tcx.hir().name(hir_id),
 567                             callee_ty
 568                         )),
 569                         Res::Def(kind, def_id) if kind.ns() == Some(Namespace::ValueNS) => {
 570                             Some(format!("`{}` defined here", self.tcx.def_path_str(def_id),))
 571                         }
 572                         _ => Some(format!("`{callee_ty}` defined here")),
 573                     }
 574                 }
 575             };
 576             if let Some(label) = label {
 577                 err.span_label(span, label);
 578             }
 579         }
 580         err.emit();
 581     }
 582
 583     fn confirm_deferred_closure_call(
 584         &self,
 585         call_expr: &'tcx hir::Expr<'tcx>,
 586         arg_exprs: &'tcx [hir::Expr<'tcx>],
 587         expected: Expectation<'tcx>,
 588         closure_def_id: LocalDefId,
 589         fn_sig: ty::FnSig<'tcx>,
 590     ) -> Ty<'tcx> {
 591         // `fn_sig` is the *signature* of the closure being called. We
 592         // don't know the full details yet (`Fn` vs `FnMut` etc), but we
 593         // do know the types expected for each argument and the return
 594         // type.
 595
 596         let expected_arg_tys = self.expected_inputs_for_expected_output(
 597             call_expr.span,
 598             expected,
 599             fn_sig.output(),
 600             fn_sig.inputs(),
 601         );
 602
 603         self.check_argument_types(
 604             call_expr.span,
 605             call_expr,
 606             fn_sig.inputs(),
 607             expected_arg_tys,
 608             arg_exprs,
 609             fn_sig.c_variadic,
 610             TupleArgumentsFlag::TupleArguments,
 611             Some(closure_def_id.to_def_id()),
 612         );
 613
 614         fn_sig.output()
 615     }
 616
 617     fn confirm_overloaded_call(
 618         &self,
 619         call_expr: &'tcx hir::Expr<'tcx>,
 620         arg_exprs: &'tcx [hir::Expr<'tcx>],
 621         expected: Expectation<'tcx>,
 622         method_callee: MethodCallee<'tcx>,
 623     ) -> Ty<'tcx> {
 624         let output_type = self.check_method_argument_types(
 625             call_expr.span,
 626             call_expr,
 627             Ok(method_callee),
 628             arg_exprs,
 629             TupleArgumentsFlag::TupleArguments,
 630             expected,
 631         );
 632
 633         self.write_method_call(call_expr.hir_id, method_callee);
 634         output_type
 635     }
 636 }
 637
 638 #[derive(Debug)]
 639 pub struct DeferredCallResolution<'tcx> {
 640     call_expr: &'tcx hir::Expr<'tcx>,
 641     callee_expr: &'tcx hir::Expr<'tcx>,
 642     adjusted_ty: Ty<'tcx>,
 643     adjustments: Vec<Adjustment<'tcx>>,
 644     fn_sig: ty::FnSig<'tcx>,
 645     closure_substs: SubstsRef<'tcx>,
 646 }
 647
 648 impl<'a, 'tcx> DeferredCallResolution<'tcx> {
 649     pub fn resolve(self, fcx: &FnCtxt<'a, 'tcx>) {
 650         debug!("DeferredCallResolution::resolve() {:?}", self);
 651
 652         // we should not be invoked until the closure kind has been
 653         // determined by upvar inference
 654         assert!(fcx.closure_kind(self.closure_substs).is_some());
 655
 656         // We may now know enough to figure out fn vs fnmut etc.
 657         match fcx.try_overloaded_call_traits(self.call_expr, self.adjusted_ty, None) {
 658             Some((autoref, method_callee)) => {
 659                 // One problem is that when we get here, we are going
 660                 // to have a newly instantiated function signature
 661                 // from the call trait. This has to be reconciled with
 662                 // the older function signature we had before. In
 663                 // principle we *should* be able to fn_sigs(), but we
 664                 // can't because of the annoying need for a TypeTrace.
 665                 // (This always bites me, should find a way to
 666                 // refactor it.)
 667                 let method_sig = method_callee.sig;
 668
 669                 debug!("attempt_resolution: method_callee={:?}", method_callee);
 670
 671                 for (method_arg_ty, self_arg_ty) in
 672                     iter::zip(method_sig.inputs().iter().skip(1), self.fn_sig.inputs())
 673                 {
 674                     fcx.demand_eqtype(self.call_expr.span, *self_arg_ty, *method_arg_ty);
 675                 }
 676
 677                 fcx.demand_eqtype(self.call_expr.span, method_sig.output(), self.fn_sig.output());
 678
 679                 let mut adjustments = self.adjustments;
 680                 adjustments.extend(autoref);
 681                 fcx.apply_adjustments(self.callee_expr, adjustments);
 682
 683                 fcx.write_method_call(self.call_expr.hir_id, method_callee);
 684             }
 685             None => {
 686                 // This can happen if `#![no_core]` is used and the `fn/fn_mut/fn_once`
 687                 // lang items are not defined (issue #86238).
 688                 let mut err = fcx.inh.tcx.sess.struct_span_err(
 689                     self.call_expr.span,
 690                     "failed to find an overloaded call trait for closure call",
 691                 );
 692                 err.help(
 693                     "make sure the `fn`/`fn_mut`/`fn_once` lang items are defined \
 694                      and have associated `call`/`call_mut`/`call_once` functions",
 695                 );
 696                 err.emit();
 697             }
 698         }
 699     }
 700 }