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