src/librustc_typeck/check/callee.rs

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