src/librustc_typeck/check/callee.rs

   1 use super::autoderef::Autoderef;
   2 use super::method::MethodCallee;
   3 use super::{Expectation, FnCtxt, Needs, TupleArgumentsFlag};
   4
   5 use errors::{Applicability, DiagnosticBuilder};
   6 use hir::def::Res;
   7 use hir::def_id::{DefId, LOCAL_CRATE};
   8 use rustc::ty::adjustment::{Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
   9 use rustc::ty::{self, Ty, TyCtxt, TypeFoldable};
  10 use rustc::{infer, traits};
  11 use rustc::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  12 use rustc_target::spec::abi;
  13 use syntax::ast::Ident;
  14 use syntax_pos::Span;
  15
  16 use rustc::hir;
  17
  18 /// Checks that it is legal to call methods of the trait corresponding
  19 /// to `trait_id` (this only cares about the trait, not the specific
  20 /// method that is called).
  21 pub fn check_legal_trait_for_method_call(tcx: TyCtxt<'_>, span: Span, trait_id: DefId) {
  22     if tcx.lang_items().drop_trait() == Some(trait_id) {
  23         struct_span_err!(tcx.sess, span, E0040, "explicit use of destructor method")
  24             .span_label(span, "explicit destructor calls not allowed")
  25             .emit();
  26     }
  27 }
  28
  29 enum CallStep<'tcx> {
  30     Builtin(Ty<'tcx>),
  31     DeferredClosure(ty::FnSig<'tcx>),
  32     /// E.g., enum variant constructors.
  33     Overloaded(MethodCallee<'tcx>),
  34 }
  35
  36 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  37     pub fn check_call(
  38         &self,
  39         call_expr: &'tcx hir::Expr,
  40         callee_expr: &'tcx hir::Expr,
  41         arg_exprs: &'tcx [hir::Expr],
  42         expected: Expectation<'tcx>,
  43     ) -> Ty<'tcx> {
  44         let original_callee_ty = self.check_expr(callee_expr);
  45         let expr_ty = self.structurally_resolved_type(call_expr.span, original_callee_ty);
  46
  47         let mut autoderef = self.autoderef(callee_expr.span, expr_ty);
  48         let mut result = None;
  49         while result.is_none() && autoderef.next().is_some() {
  50             result = self.try_overloaded_call_step(call_expr, callee_expr, arg_exprs, &autoderef);
  51         }
  52         autoderef.finalize(self);
  53
  54         let output = match result {
  55             None => {
  56                 // this will report an error since original_callee_ty is not a fn
  57                 self.confirm_builtin_call(call_expr, original_callee_ty, arg_exprs, expected)
  58             }
  59
  60             Some(CallStep::Builtin(callee_ty)) => {
  61                 self.confirm_builtin_call(call_expr, callee_ty, arg_exprs, expected)
  62             }
  63
  64             Some(CallStep::DeferredClosure(fn_sig)) => {
  65                 self.confirm_deferred_closure_call(call_expr, arg_exprs, expected, fn_sig)
  66             }
  67
  68             Some(CallStep::Overloaded(method_callee)) => {
  69                 self.confirm_overloaded_call(call_expr, arg_exprs, expected, method_callee)
  70             }
  71         };
  72
  73         // we must check that return type of called functions is WF:
  74         self.register_wf_obligation(output, call_expr.span, traits::MiscObligation);
  75
  76         output
  77     }
  78
  79     fn try_overloaded_call_step(
  80         &self,
  81         call_expr: &'tcx hir::Expr,
  82         callee_expr: &'tcx hir::Expr,
  83         arg_exprs: &'tcx [hir::Expr],
  84         autoderef: &Autoderef<'a, 'tcx>,
  85     ) -> Option<CallStep<'tcx>> {
  86         let adjusted_ty = autoderef.unambiguous_final_ty(self);
  87         debug!(
  88             "try_overloaded_call_step(call_expr={:?}, adjusted_ty={:?})",
  89             call_expr, adjusted_ty
  90         );
  91
  92         // If the callee is a bare function or a closure, then we're all set.
  93         match adjusted_ty.kind {
  94             ty::FnDef(..) | ty::FnPtr(_) => {
  95                 let adjustments = autoderef.adjust_steps(self, Needs::None);
  96                 self.apply_adjustments(callee_expr, adjustments);
  97                 return Some(CallStep::Builtin(adjusted_ty));
  98             }
  99
 100             ty::Closure(def_id, substs) => {
 101                 assert_eq!(def_id.krate, LOCAL_CRATE);
 102
 103                 // Check whether this is a call to a closure where we
 104                 // haven't yet decided on whether the closure is fn vs
 105                 // fnmut vs fnonce. If so, we have to defer further processing.
 106                 if self.closure_kind(def_id, substs).is_none() {
 107                     let closure_ty = self.closure_sig(def_id, substs);
 108                     let fn_sig = self
 109                         .replace_bound_vars_with_fresh_vars(
 110                             call_expr.span,
 111                             infer::FnCall,
 112                             &closure_ty,
 113                         )
 114                         .0;
 115                     let adjustments = autoderef.adjust_steps(self, Needs::None);
 116                     self.record_deferred_call_resolution(
 117                         def_id,
 118                         DeferredCallResolution {
 119                             call_expr,
 120                             callee_expr,
 121                             adjusted_ty,
 122                             adjustments,
 123                             fn_sig,
 124                             closure_def_id: def_id,
 125                             closure_substs: substs,
 126                         },
 127                     );
 128                     return Some(CallStep::DeferredClosure(fn_sig));
 129                 }
 130             }
 131
 132             // Hack: we know that there are traits implementing Fn for &F
 133             // where F:Fn and so forth. In the particular case of types
 134             // like `x: &mut FnMut()`, if there is a call `x()`, we would
 135             // normally translate to `FnMut::call_mut(&mut x, ())`, but
 136             // that winds up requiring `mut x: &mut FnMut()`. A little
 137             // over the top. The simplest fix by far is to just ignore
 138             // this case and deref again, so we wind up with
 139             // `FnMut::call_mut(&mut *x, ())`.
 140             ty::Ref(..) if autoderef.step_count() == 0 => {
 141                 return None;
 142             }
 143
 144             _ => {}
 145         }
 146
 147         // Now, we look for the implementation of a Fn trait on the object's type.
 148         // We first do it with the explicit instruction to look for an impl of
 149         // `Fn<Tuple>`, with the tuple `Tuple` having an arity corresponding
 150         // to the number of call parameters.
 151         // If that fails (or_else branch), we try again without specifying the
 152         // shape of the tuple (hence the None). This allows to detect an Fn trait
 153         // is implemented, and use this information for diagnostic.
 154         self.try_overloaded_call_traits(call_expr, adjusted_ty, Some(arg_exprs))
 155             .or_else(|| self.try_overloaded_call_traits(call_expr, adjusted_ty, None))
 156             .map(|(autoref, method)| {
 157                 let mut adjustments = autoderef.adjust_steps(self, Needs::None);
 158                 adjustments.extend(autoref);
 159                 self.apply_adjustments(callee_expr, adjustments);
 160                 CallStep::Overloaded(method)
 161             })
 162     }
 163
 164     fn try_overloaded_call_traits(
 165         &self,
 166         call_expr: &hir::Expr,
 167         adjusted_ty: Ty<'tcx>,
 168         opt_arg_exprs: Option<&'tcx [hir::Expr]>,
 169     ) -> Option<(Option<Adjustment<'tcx>>, MethodCallee<'tcx>)> {
 170         // Try the options that are least restrictive on the caller first.
 171         for &(opt_trait_def_id, method_name, borrow) in &[
 172             (
 173                 self.tcx.lang_items().fn_trait(),
 174                 Ident::from_str("call"),
 175                 true,
 176             ),
 177             (
 178                 self.tcx.lang_items().fn_mut_trait(),
 179                 Ident::from_str("call_mut"),
 180                 true,
 181             ),
 182             (
 183                 self.tcx.lang_items().fn_once_trait(),
 184                 Ident::from_str("call_once"),
 185                 false,
 186             ),
 187         ] {
 188             let trait_def_id = match opt_trait_def_id {
 189                 Some(def_id) => def_id,
 190                 None => continue,
 191             };
 192
 193             let opt_input_types = opt_arg_exprs.map(|arg_exprs| [self.tcx.mk_tup(
 194                 arg_exprs
 195                 .iter()
 196                 .map(|e| {
 197                     self.next_ty_var(TypeVariableOrigin {
 198                         kind: TypeVariableOriginKind::TypeInference,
 199                         span: e.span,
 200                     })
 201                 })
 202             )]);
 203             let opt_input_types = opt_input_types.as_ref().map(AsRef::as_ref);
 204
 205             if let Some(ok) = self.lookup_method_in_trait(
 206                 call_expr.span,
 207                 method_name,
 208                 trait_def_id,
 209                 adjusted_ty,
 210                 opt_input_types,
 211             ) {
 212                 let method = self.register_infer_ok_obligations(ok);
 213                 let mut autoref = None;
 214                 if borrow {
 215                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind {
 216                         let mutbl = match mutbl {
 217                             hir::MutImmutable => AutoBorrowMutability::Immutable,
 218                             hir::MutMutable => AutoBorrowMutability::Mutable {
 219                                 // For initial two-phase borrow
 220                                 // deployment, conservatively omit
 221                                 // overloaded function call ops.
 222                                 allow_two_phase_borrow: AllowTwoPhase::No,
 223                             },
 224                         };
 225                         autoref = Some(Adjustment {
 226                             kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 227                             target: method.sig.inputs()[0],
 228                         });
 229                     }
 230                 }
 231                 return Some((autoref, method));
 232             }
 233         }
 234
 235         None
 236     }
 237
 238     /// Give appropriate suggestion when encountering `||{/* not callable */}()`, where the
 239     /// likely intention is to call the closure, suggest `(||{})()`. (#55851)
 240     fn identify_bad_closure_def_and_call(
 241         &self,
 242         err: &mut DiagnosticBuilder<'a>,
 243         hir_id: hir::HirId,
 244         callee_node: &hir::ExprKind,
 245         callee_span: Span,
 246     ) {
 247         let hir_id = self.tcx.hir().get_parent_node(hir_id);
 248         let parent_node = self.tcx.hir().get(hir_id);
 249         if let (
 250             hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(_, _, _, sp, ..), .. }),
 251             hir::ExprKind::Block(..),
 252         ) = (parent_node, callee_node) {
 253             let start = sp.shrink_to_lo();
 254             let end = self.tcx.sess.source_map().next_point(callee_span);
 255             err.multipart_suggestion(
 256                 "if you meant to create this closure and immediately call it, surround the \
 257                 closure with parenthesis",
 258                 vec![(start, "(".to_string()), (end, ")".to_string())],
 259                 Applicability::MaybeIncorrect,
 260             );
 261         }
 262     }
 263
 264     fn confirm_builtin_call(
 265         &self,
 266         call_expr: &'tcx hir::Expr,
 267         callee_ty: Ty<'tcx>,
 268         arg_exprs: &'tcx [hir::Expr],
 269         expected: Expectation<'tcx>,
 270     ) -> Ty<'tcx> {
 271         let (fn_sig, def_span) = match callee_ty.kind {
 272             ty::FnDef(def_id, _) => (
 273                 callee_ty.fn_sig(self.tcx),
 274                 self.tcx.hir().span_if_local(def_id),
 275             ),
 276             ty::FnPtr(sig) => (sig, None),
 277             ref t => {
 278                 let mut unit_variant = None;
 279                 if let &ty::Adt(adt_def, ..) = t {
 280                     if adt_def.is_enum() {
 281                         if let hir::ExprKind::Call(ref expr, _) = call_expr.kind {
 282                             unit_variant = Some(self.tcx.hir().hir_to_pretty_string(expr.hir_id))
 283                         }
 284                     }
 285                 }
 286
 287                 if let hir::ExprKind::Call(ref callee, _) = call_expr.kind {
 288                     let mut err = type_error_struct!(
 289                         self.tcx.sess,
 290                         callee.span,
 291                         callee_ty,
 292                         E0618,
 293                         "expected function, found {}",
 294                         match unit_variant {
 295                             Some(ref path) => format!("enum variant `{}`", path),
 296                             None => format!("`{}`", callee_ty),
 297                         }
 298                     );
 299
 300                     self.identify_bad_closure_def_and_call(
 301                         &mut err,
 302                         call_expr.hir_id,
 303                         &callee.kind,
 304                         callee.span,
 305                     );
 306
 307                     if let Some(ref path) = unit_variant {
 308                         err.span_suggestion(
 309                             call_expr.span,
 310                             &format!(
 311                                 "`{}` is a unit variant, you need to write it \
 312                                  without the parenthesis",
 313                                 path
 314                             ),
 315                             path.to_string(),
 316                             Applicability::MachineApplicable,
 317                         );
 318                     }
 319
 320                     let mut inner_callee_path = None;
 321                     let def = match callee.kind {
 322                         hir::ExprKind::Path(ref qpath) => {
 323                             self.tables.borrow().qpath_res(qpath, callee.hir_id)
 324                         }
 325                         hir::ExprKind::Call(ref inner_callee, _) => {
 326                             // If the call spans more than one line and the callee kind is
 327                             // itself another `ExprCall`, that's a clue that we might just be
 328                             // missing a semicolon (Issue #51055)
 329                             let call_is_multiline =
 330                                 self.tcx.sess.source_map().is_multiline(call_expr.span);
 331                             if call_is_multiline {
 332                                 let span = self.tcx.sess.source_map().next_point(callee.span);
 333                                 err.span_suggestion(
 334                                     span,
 335                                     "try adding a semicolon",
 336                                     ";".to_owned(),
 337                                     Applicability::MaybeIncorrect,
 338                                 );
 339                             }
 340                             if let hir::ExprKind::Path(ref inner_qpath) = inner_callee.kind {
 341                                 inner_callee_path = Some(inner_qpath);
 342                                 self.tables
 343                                     .borrow()
 344                                     .qpath_res(inner_qpath, inner_callee.hir_id)
 345                             } else {
 346                                 Res::Err
 347                             }
 348                         }
 349                         _ => Res::Err,
 350                     };
 351
 352                     err.span_label(call_expr.span, "call expression requires function");
 353
 354                     if let Some(span) = self.tcx.hir().res_span(def) {
 355                         let label = match (unit_variant, inner_callee_path) {
 356                             (Some(path), _) => format!("`{}` defined here", path),
 357                             (_, Some(hir::QPath::Resolved(_, path))) => format!(
 358                                 "`{}` defined here returns `{}`",
 359                                 path,
 360                                 callee_ty.to_string()
 361                             ),
 362                             _ => format!("`{}` defined here", callee_ty.to_string()),
 363                         };
 364                         err.span_label(span, label);
 365                     }
 366                     err.emit();
 367                 } else {
 368                     bug!(
 369                         "call_expr.kind should be an ExprKind::Call, got {:?}",
 370                         call_expr.kind
 371                     );
 372                 }
 373
 374                 // This is the "default" function signature, used in case of error.
 375                 // In that case, we check each argument against "error" in order to
 376                 // set up all the node type bindings.
 377                 (
 378                     ty::Binder::bind(self.tcx.mk_fn_sig(
 379                         self.err_args(arg_exprs.len()).into_iter(),
 380                         self.tcx.types.err,
 381                         false,
 382                         hir::Unsafety::Normal,
 383                         abi::Abi::Rust,
 384                     )),
 385                     None,
 386                 )
 387             }
 388         };
 389
 390         // Replace any late-bound regions that appear in the function
 391         // signature with region variables. We also have to
 392         // renormalize the associated types at this point, since they
 393         // previously appeared within a `Binder<>` and hence would not
 394         // have been normalized before.
 395         let fn_sig = self
 396             .replace_bound_vars_with_fresh_vars(call_expr.span, infer::FnCall, &fn_sig)
 397             .0;
 398         let fn_sig = self.normalize_associated_types_in(call_expr.span, &fn_sig);
 399
 400         // Call the generic checker.
 401         let expected_arg_tys = self.expected_inputs_for_expected_output(
 402             call_expr.span,
 403             expected,
 404             fn_sig.output(),
 405             fn_sig.inputs(),
 406         );
 407         self.check_argument_types(
 408             call_expr.span,
 409             call_expr,
 410             fn_sig.inputs(),
 411             &expected_arg_tys[..],
 412             arg_exprs,
 413             fn_sig.c_variadic,
 414             TupleArgumentsFlag::DontTupleArguments,
 415             def_span,
 416         );
 417
 418         fn_sig.output()
 419     }
 420
 421     fn confirm_deferred_closure_call(
 422         &self,
 423         call_expr: &'tcx hir::Expr,
 424         arg_exprs: &'tcx [hir::Expr],
 425         expected: Expectation<'tcx>,
 426         fn_sig: ty::FnSig<'tcx>,
 427     ) -> Ty<'tcx> {
 428         // `fn_sig` is the *signature* of the cosure being called. We
 429         // don't know the full details yet (`Fn` vs `FnMut` etc), but we
 430         // do know the types expected for each argument and the return
 431         // type.
 432
 433         let expected_arg_tys = self.expected_inputs_for_expected_output(
 434             call_expr.span,
 435             expected,
 436             fn_sig.output().clone(),
 437             fn_sig.inputs(),
 438         );
 439
 440         self.check_argument_types(
 441             call_expr.span,
 442             call_expr,
 443             fn_sig.inputs(),
 444             &expected_arg_tys,
 445             arg_exprs,
 446             fn_sig.c_variadic,
 447             TupleArgumentsFlag::TupleArguments,
 448             None,
 449         );
 450
 451         fn_sig.output()
 452     }
 453
 454     fn confirm_overloaded_call(
 455         &self,
 456         call_expr: &'tcx hir::Expr,
 457         arg_exprs: &'tcx [hir::Expr],
 458         expected: Expectation<'tcx>,
 459         method_callee: MethodCallee<'tcx>,
 460     ) -> Ty<'tcx> {
 461         let output_type = self.check_method_argument_types(
 462             call_expr.span,
 463             call_expr,
 464             Ok(method_callee),
 465             arg_exprs,
 466             TupleArgumentsFlag::TupleArguments,
 467             expected,
 468         );
 469
 470         self.write_method_call(call_expr.hir_id, method_callee);
 471         output_type
 472     }
 473 }
 474
 475 #[derive(Debug)]
 476 pub struct DeferredCallResolution<'tcx> {
 477     call_expr: &'tcx hir::Expr,
 478     callee_expr: &'tcx hir::Expr,
 479     adjusted_ty: Ty<'tcx>,
 480     adjustments: Vec<Adjustment<'tcx>>,
 481     fn_sig: ty::FnSig<'tcx>,
 482     closure_def_id: DefId,
 483     closure_substs: ty::ClosureSubsts<'tcx>,
 484 }
 485
 486 impl<'a, 'tcx> DeferredCallResolution<'tcx> {
 487     pub fn resolve(self, fcx: &FnCtxt<'a, 'tcx>) {
 488         debug!("DeferredCallResolution::resolve() {:?}", self);
 489
 490         // we should not be invoked until the closure kind has been
 491         // determined by upvar inference
 492         assert!(fcx
 493             .closure_kind(self.closure_def_id, self.closure_substs)
 494             .is_some());
 495
 496         // We may now know enough to figure out fn vs fnmut etc.
 497         match fcx.try_overloaded_call_traits(self.call_expr, self.adjusted_ty, None) {
 498             Some((autoref, method_callee)) => {
 499                 // One problem is that when we get here, we are going
 500                 // to have a newly instantiated function signature
 501                 // from the call trait. This has to be reconciled with
 502                 // the older function signature we had before. In
 503                 // principle we *should* be able to fn_sigs(), but we
 504                 // can't because of the annoying need for a TypeTrace.
 505                 // (This always bites me, should find a way to
 506                 // refactor it.)
 507                 let method_sig = method_callee.sig;
 508
 509                 debug!("attempt_resolution: method_callee={:?}", method_callee);
 510
 511                 for (method_arg_ty, self_arg_ty) in
 512                     method_sig.inputs().iter().skip(1).zip(self.fn_sig.inputs())
 513                 {
 514                     fcx.demand_eqtype(self.call_expr.span, &self_arg_ty, &method_arg_ty);
 515                 }
 516
 517                 fcx.demand_eqtype(
 518                     self.call_expr.span,
 519                     method_sig.output(),
 520                     self.fn_sig.output(),
 521                 );
 522
 523                 let mut adjustments = self.adjustments;
 524                 adjustments.extend(autoref);
 525                 fcx.apply_adjustments(self.callee_expr, adjustments);
 526
 527                 fcx.write_method_call(self.call_expr.hir_id, method_callee);
 528             }
 529             None => {
 530                 span_bug!(
 531                     self.call_expr.span,
 532                     "failed to find an overloaded call trait for closure call"
 533                 );
 534             }
 535         }
 536     }
 537 }