src/librustc_typeck/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::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::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     trait_id: DefId,
  29 ) {
  30     if tcx.lang_items().drop_trait() == Some(trait_id) {
  31         let mut err = struct_span_err!(tcx.sess, span, E0040, "explicit use of destructor method");
  32         err.span_label(span, "explicit destructor calls not allowed");
  33
  34         let snippet = receiver
  35             .and_then(|s| tcx.sess.source_map().span_to_snippet(s).ok())
  36             .unwrap_or_default();
  37
  38         let suggestion =
  39             if snippet.is_empty() { "drop".to_string() } else { format!("drop({})", snippet) };
  40
  41         err.span_suggestion(
  42             span,
  43             &format!("consider using `drop` function: `{}`", suggestion),
  44             String::new(),
  45             Applicability::Unspecified,
  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(call_expr, original_callee_ty, arg_exprs, expected)
  81             }
  82
  83             Some(CallStep::Builtin(callee_ty)) => {
  84                 self.confirm_builtin_call(call_expr, callee_ty, arg_exprs, expected)
  85             }
  86
  87             Some(CallStep::DeferredClosure(fn_sig)) => {
  88                 self.confirm_deferred_closure_call(call_expr, arg_exprs, expected, fn_sig)
  89             }
  90
  91             Some(CallStep::Overloaded(method_callee)) => {
  92                 self.confirm_overloaded_call(call_expr, arg_exprs, expected, method_callee)
  93             }
  94         };
  95
  96         // we must check that return type of called functions is WF:
  97         self.register_wf_obligation(output.into(), call_expr.span, traits::MiscObligation);
  98
  99         output
 100     }
 101
 102     fn try_overloaded_call_step(
 103         &self,
 104         call_expr: &'tcx hir::Expr<'tcx>,
 105         callee_expr: &'tcx hir::Expr<'tcx>,
 106         arg_exprs: &'tcx [hir::Expr<'tcx>],
 107         autoderef: &Autoderef<'a, 'tcx>,
 108     ) -> Option<CallStep<'tcx>> {
 109         let adjusted_ty =
 110             self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
 111         debug!(
 112             "try_overloaded_call_step(call_expr={:?}, adjusted_ty={:?})",
 113             call_expr, adjusted_ty
 114         );
 115
 116         // If the callee is a bare function or a closure, then we're all set.
 117         match adjusted_ty.kind {
 118             ty::FnDef(..) | ty::FnPtr(_) => {
 119                 let adjustments = self.adjust_steps(autoderef);
 120                 self.apply_adjustments(callee_expr, adjustments);
 121                 return Some(CallStep::Builtin(adjusted_ty));
 122             }
 123
 124             ty::Closure(def_id, substs) => {
 125                 assert_eq!(def_id.krate, LOCAL_CRATE);
 126
 127                 // Check whether this is a call to a closure where we
 128                 // haven't yet decided on whether the closure is fn vs
 129                 // fnmut vs fnonce. If so, we have to defer further processing.
 130                 if self.closure_kind(substs).is_none() {
 131                     let closure_sig = substs.as_closure().sig();
 132                     let closure_sig = self
 133                         .replace_bound_vars_with_fresh_vars(
 134                             call_expr.span,
 135                             infer::FnCall,
 136                             &closure_sig,
 137                         )
 138                         .0;
 139                     let adjustments = self.adjust_steps(autoderef);
 140                     self.record_deferred_call_resolution(
 141                         def_id,
 142                         DeferredCallResolution {
 143                             call_expr,
 144                             callee_expr,
 145                             adjusted_ty,
 146                             adjustments,
 147                             fn_sig: closure_sig,
 148                             closure_substs: substs,
 149                         },
 150                     );
 151                     return Some(CallStep::DeferredClosure(closure_sig));
 152                 }
 153             }
 154
 155             // Hack: we know that there are traits implementing Fn for &F
 156             // where F:Fn and so forth. In the particular case of types
 157             // like `x: &mut FnMut()`, if there is a call `x()`, we would
 158             // normally translate to `FnMut::call_mut(&mut x, ())`, but
 159             // that winds up requiring `mut x: &mut FnMut()`. A little
 160             // over the top. The simplest fix by far is to just ignore
 161             // this case and deref again, so we wind up with
 162             // `FnMut::call_mut(&mut *x, ())`.
 163             ty::Ref(..) if autoderef.step_count() == 0 => {
 164                 return None;
 165             }
 166
 167             _ => {}
 168         }
 169
 170         // Now, we look for the implementation of a Fn trait on the object's type.
 171         // We first do it with the explicit instruction to look for an impl of
 172         // `Fn<Tuple>`, with the tuple `Tuple` having an arity corresponding
 173         // to the number of call parameters.
 174         // If that fails (or_else branch), we try again without specifying the
 175         // shape of the tuple (hence the None). This allows to detect an Fn trait
 176         // is implemented, and use this information for diagnostic.
 177         self.try_overloaded_call_traits(call_expr, adjusted_ty, Some(arg_exprs))
 178             .or_else(|| self.try_overloaded_call_traits(call_expr, adjusted_ty, None))
 179             .map(|(autoref, method)| {
 180                 let mut adjustments = self.adjust_steps(autoderef);
 181                 adjustments.extend(autoref);
 182                 self.apply_adjustments(callee_expr, adjustments);
 183                 CallStep::Overloaded(method)
 184             })
 185     }
 186
 187     fn try_overloaded_call_traits(
 188         &self,
 189         call_expr: &hir::Expr<'_>,
 190         adjusted_ty: Ty<'tcx>,
 191         opt_arg_exprs: Option<&'tcx [hir::Expr<'tcx>]>,
 192     ) -> Option<(Option<Adjustment<'tcx>>, MethodCallee<'tcx>)> {
 193         // Try the options that are least restrictive on the caller first.
 194         for &(opt_trait_def_id, method_name, borrow) in &[
 195             (self.tcx.lang_items().fn_trait(), Ident::from_str("call"), true),
 196             (self.tcx.lang_items().fn_mut_trait(), Ident::from_str("call_mut"), true),
 197             (self.tcx.lang_items().fn_once_trait(), Ident::from_str("call_once"), false),
 198         ] {
 199             let trait_def_id = match opt_trait_def_id {
 200                 Some(def_id) => def_id,
 201                 None => continue,
 202             };
 203
 204             let opt_input_types = opt_arg_exprs.map(|arg_exprs| {
 205                 [self.tcx.mk_tup(arg_exprs.iter().map(|e| {
 206                     self.next_ty_var(TypeVariableOrigin {
 207                         kind: TypeVariableOriginKind::TypeInference,
 208                         span: e.span,
 209                     })
 210                 }))]
 211             });
 212             let opt_input_types = opt_input_types.as_ref().map(AsRef::as_ref);
 213
 214             if let Some(ok) = self.lookup_method_in_trait(
 215                 call_expr.span,
 216                 method_name,
 217                 trait_def_id,
 218                 adjusted_ty,
 219                 opt_input_types,
 220             ) {
 221                 let method = self.register_infer_ok_obligations(ok);
 222                 let mut autoref = None;
 223                 if borrow {
 224                     // Check for &self vs &mut self in the method signature. Since this is either
 225                     // the Fn or FnMut trait, it should be one of those.
 226                     let (region, mutbl) = if let ty::Ref(r, _, mutbl) = method.sig.inputs()[0].kind
 227                     {
 228                         (r, mutbl)
 229                     } else {
 230                         span_bug!(call_expr.span, "input to call/call_mut is not a ref?");
 231                     };
 232
 233                     let mutbl = match mutbl {
 234                         hir::Mutability::Not => AutoBorrowMutability::Not,
 235                         hir::Mutability::Mut => AutoBorrowMutability::Mut {
 236                             // For initial two-phase borrow
 237                             // deployment, conservatively omit
 238                             // overloaded function call ops.
 239                             allow_two_phase_borrow: AllowTwoPhase::No,
 240                         },
 241                     };
 242                     autoref = Some(Adjustment {
 243                         kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 244                         target: method.sig.inputs()[0],
 245                     });
 246                 }
 247                 return Some((autoref, method));
 248             }
 249         }
 250
 251         None
 252     }
 253
 254     /// Give appropriate suggestion when encountering `||{/* not callable */}()`, where the
 255     /// likely intention is to call the closure, suggest `(||{})()`. (#55851)
 256     fn identify_bad_closure_def_and_call(
 257         &self,
 258         err: &mut DiagnosticBuilder<'a>,
 259         hir_id: hir::HirId,
 260         callee_node: &hir::ExprKind<'_>,
 261         callee_span: Span,
 262     ) {
 263         let hir_id = self.tcx.hir().get_parent_node(hir_id);
 264         let parent_node = self.tcx.hir().get(hir_id);
 265         if let (
 266             hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(_, _, _, sp, ..), .. }),
 267             hir::ExprKind::Block(..),
 268         ) = (parent_node, callee_node)
 269         {
 270             let start = sp.shrink_to_lo();
 271             let end = callee_span.shrink_to_hi();
 272             err.multipart_suggestion(
 273                 "if you meant to create this closure and immediately call it, surround the \
 274                 closure with parenthesis",
 275                 vec![(start, "(".to_string()), (end, ")".to_string())],
 276                 Applicability::MaybeIncorrect,
 277             );
 278         }
 279     }
 280
 281     fn confirm_builtin_call(
 282         &self,
 283         call_expr: &'tcx hir::Expr<'tcx>,
 284         callee_ty: Ty<'tcx>,
 285         arg_exprs: &'tcx [hir::Expr<'tcx>],
 286         expected: Expectation<'tcx>,
 287     ) -> Ty<'tcx> {
 288         let (fn_sig, def_span) = match callee_ty.kind {
 289             ty::FnDef(def_id, _) => {
 290                 (callee_ty.fn_sig(self.tcx), self.tcx.hir().span_if_local(def_id))
 291             }
 292             ty::FnPtr(sig) => (sig, None),
 293             ref t => {
 294                 let mut unit_variant = None;
 295                 if let &ty::Adt(adt_def, ..) = t {
 296                     if adt_def.is_enum() {
 297                         if let hir::ExprKind::Call(ref expr, _) = call_expr.kind {
 298                             unit_variant =
 299                                 self.tcx.sess.source_map().span_to_snippet(expr.span).ok();
 300                         }
 301                     }
 302                 }
 303
 304                 if let hir::ExprKind::Call(ref callee, _) = call_expr.kind {
 305                     let mut err = type_error_struct!(
 306                         self.tcx.sess,
 307                         callee.span,
 308                         callee_ty,
 309                         E0618,
 310                         "expected function, found {}",
 311                         match unit_variant {
 312                             Some(ref path) => format!("enum variant `{}`", path),
 313                             None => format!("`{}`", callee_ty),
 314                         }
 315                     );
 316
 317                     self.identify_bad_closure_def_and_call(
 318                         &mut err,
 319                         call_expr.hir_id,
 320                         &callee.kind,
 321                         callee.span,
 322                     );
 323
 324                     if let Some(ref path) = unit_variant {
 325                         err.span_suggestion(
 326                             call_expr.span,
 327                             &format!(
 328                                 "`{}` is a unit variant, you need to write it \
 329                                  without the parenthesis",
 330                                 path
 331                             ),
 332                             path.to_string(),
 333                             Applicability::MachineApplicable,
 334                         );
 335                     }
 336
 337                     let mut inner_callee_path = None;
 338                     let def = match callee.kind {
 339                         hir::ExprKind::Path(ref qpath) => {
 340                             self.tables.borrow().qpath_res(qpath, callee.hir_id)
 341                         }
 342                         hir::ExprKind::Call(ref inner_callee, _) => {
 343                             // If the call spans more than one line and the callee kind is
 344                             // itself another `ExprCall`, that's a clue that we might just be
 345                             // missing a semicolon (Issue #51055)
 346                             let call_is_multiline =
 347                                 self.tcx.sess.source_map().is_multiline(call_expr.span);
 348                             if call_is_multiline {
 349                                 err.span_suggestion(
 350                                     callee.span.shrink_to_hi(),
 351                                     "try adding a semicolon",
 352                                     ";".to_owned(),
 353                                     Applicability::MaybeIncorrect,
 354                                 );
 355                             }
 356                             if let hir::ExprKind::Path(ref inner_qpath) = inner_callee.kind {
 357                                 inner_callee_path = Some(inner_qpath);
 358                                 self.tables.borrow().qpath_res(inner_qpath, inner_callee.hir_id)
 359                             } else {
 360                                 Res::Err
 361                             }
 362                         }
 363                         _ => Res::Err,
 364                     };
 365
 366                     err.span_label(call_expr.span, "call expression requires function");
 367
 368                     if let Some(span) = self.tcx.hir().res_span(def) {
 369                         let callee_ty = callee_ty.to_string();
 370                         let label = match (unit_variant, inner_callee_path) {
 371                             (Some(path), _) => Some(format!("`{}` defined here", path)),
 372                             (_, Some(hir::QPath::Resolved(_, path))) => {
 373                                 self.tcx.sess.source_map().span_to_snippet(path.span).ok().map(
 374                                     |p| format!("`{}` defined here returns `{}`", p, callee_ty),
 375                                 )
 376                             }
 377                             _ => Some(format!("`{}` defined here", callee_ty)),
 378                         };
 379                         if let Some(label) = label {
 380                             err.span_label(span, label);
 381                         }
 382                     }
 383                     err.emit();
 384                 } else {
 385                     bug!("call_expr.kind should be an ExprKind::Call, got {:?}", call_expr.kind);
 386                 }
 387
 388                 // This is the "default" function signature, used in case of error.
 389                 // In that case, we check each argument against "error" in order to
 390                 // set up all the node type bindings.
 391                 (
 392                     ty::Binder::bind(self.tcx.mk_fn_sig(
 393                         self.err_args(arg_exprs.len()).into_iter(),
 394                         self.tcx.ty_error(),
 395                         false,
 396                         hir::Unsafety::Normal,
 397                         abi::Abi::Rust,
 398                     )),
 399                     None,
 400                 )
 401             }
 402         };
 403
 404         // Replace any late-bound regions that appear in the function
 405         // signature with region variables. We also have to
 406         // renormalize the associated types at this point, since they
 407         // previously appeared within a `Binder<>` and hence would not
 408         // have been normalized before.
 409         let fn_sig =
 410             self.replace_bound_vars_with_fresh_vars(call_expr.span, infer::FnCall, &fn_sig).0;
 411         let fn_sig = self.normalize_associated_types_in(call_expr.span, &fn_sig);
 412
 413         // Call the generic checker.
 414         let expected_arg_tys = self.expected_inputs_for_expected_output(
 415             call_expr.span,
 416             expected,
 417             fn_sig.output(),
 418             fn_sig.inputs(),
 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::DontTupleArguments,
 428             def_span,
 429         );
 430
 431         fn_sig.output()
 432     }
 433
 434     fn confirm_deferred_closure_call(
 435         &self,
 436         call_expr: &'tcx hir::Expr<'tcx>,
 437         arg_exprs: &'tcx [hir::Expr<'tcx>],
 438         expected: Expectation<'tcx>,
 439         fn_sig: ty::FnSig<'tcx>,
 440     ) -> Ty<'tcx> {
 441         // `fn_sig` is the *signature* of the cosure being called. We
 442         // don't know the full details yet (`Fn` vs `FnMut` etc), but we
 443         // do know the types expected for each argument and the return
 444         // type.
 445
 446         let expected_arg_tys = self.expected_inputs_for_expected_output(
 447             call_expr.span,
 448             expected,
 449             fn_sig.output().clone(),
 450             fn_sig.inputs(),
 451         );
 452
 453         self.check_argument_types(
 454             call_expr.span,
 455             call_expr,
 456             fn_sig.inputs(),
 457             &expected_arg_tys,
 458             arg_exprs,
 459             fn_sig.c_variadic,
 460             TupleArgumentsFlag::TupleArguments,
 461             None,
 462         );
 463
 464         fn_sig.output()
 465     }
 466
 467     fn confirm_overloaded_call(
 468         &self,
 469         call_expr: &'tcx hir::Expr<'tcx>,
 470         arg_exprs: &'tcx [hir::Expr<'tcx>],
 471         expected: Expectation<'tcx>,
 472         method_callee: MethodCallee<'tcx>,
 473     ) -> Ty<'tcx> {
 474         let output_type = self.check_method_argument_types(
 475             call_expr.span,
 476             call_expr,
 477             Ok(method_callee),
 478             arg_exprs,
 479             TupleArgumentsFlag::TupleArguments,
 480             expected,
 481         );
 482
 483         self.write_method_call(call_expr.hir_id, method_callee);
 484         output_type
 485     }
 486 }
 487
 488 #[derive(Debug)]
 489 pub struct DeferredCallResolution<'tcx> {
 490     call_expr: &'tcx hir::Expr<'tcx>,
 491     callee_expr: &'tcx hir::Expr<'tcx>,
 492     adjusted_ty: Ty<'tcx>,
 493     adjustments: Vec<Adjustment<'tcx>>,
 494     fn_sig: ty::FnSig<'tcx>,
 495     closure_substs: SubstsRef<'tcx>,
 496 }
 497
 498 impl<'a, 'tcx> DeferredCallResolution<'tcx> {
 499     pub fn resolve(self, fcx: &FnCtxt<'a, 'tcx>) {
 500         debug!("DeferredCallResolution::resolve() {:?}", self);
 501
 502         // we should not be invoked until the closure kind has been
 503         // determined by upvar inference
 504         assert!(fcx.closure_kind(self.closure_substs).is_some());
 505
 506         // We may now know enough to figure out fn vs fnmut etc.
 507         match fcx.try_overloaded_call_traits(self.call_expr, self.adjusted_ty, None) {
 508             Some((autoref, method_callee)) => {
 509                 // One problem is that when we get here, we are going
 510                 // to have a newly instantiated function signature
 511                 // from the call trait. This has to be reconciled with
 512                 // the older function signature we had before. In
 513                 // principle we *should* be able to fn_sigs(), but we
 514                 // can't because of the annoying need for a TypeTrace.
 515                 // (This always bites me, should find a way to
 516                 // refactor it.)
 517                 let method_sig = method_callee.sig;
 518
 519                 debug!("attempt_resolution: method_callee={:?}", method_callee);
 520
 521                 for (method_arg_ty, self_arg_ty) in
 522                     method_sig.inputs().iter().skip(1).zip(self.fn_sig.inputs())
 523                 {
 524                     fcx.demand_eqtype(self.call_expr.span, &self_arg_ty, &method_arg_ty);
 525                 }
 526
 527                 fcx.demand_eqtype(self.call_expr.span, method_sig.output(), self.fn_sig.output());
 528
 529                 let mut adjustments = self.adjustments;
 530                 adjustments.extend(autoref);
 531                 fcx.apply_adjustments(self.callee_expr, adjustments);
 532
 533                 fcx.write_method_call(self.call_expr.hir_id, method_callee);
 534             }
 535             None => {
 536                 span_bug!(
 537                     self.call_expr.span,
 538                     "failed to find an overloaded call trait for closure call"
 539                 );
 540             }
 541         }
 542     }
 543 }