src/librustc_typeck/check/method/confirm.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use super::probe;
  12
  13 use check::{self, FnCtxt, callee, demand};
  14 use check::UnresolvedTypeAction;
  15 use middle::def_id::DefId;
  16 use middle::subst::{self};
  17 use middle::traits;
  18 use middle::ty::{self, NoPreference, PreferMutLvalue, Ty};
  19 use middle::ty::adjustment::{AdjustDerefRef, AutoDerefRef, AutoPtr};
  20 use middle::ty::fold::TypeFoldable;
  21 use middle::infer;
  22 use middle::infer::InferCtxt;
  23 use syntax::codemap::Span;
  24 use rustc_front::hir;
  25
  26 struct ConfirmContext<'a, 'tcx:'a> {
  27     fcx: &'a FnCtxt<'a, 'tcx>,
  28     span: Span,
  29     self_expr: &'tcx hir::Expr,
  30     call_expr: &'tcx hir::Expr,
  31 }
  32
  33 struct InstantiatedMethodSig<'tcx> {
  34     /// Function signature of the method being invoked. The 0th
  35     /// argument is the receiver.
  36     method_sig: ty::FnSig<'tcx>,
  37
  38     /// Substitutions for all types/early-bound-regions declared on
  39     /// the method.
  40     all_substs: subst::Substs<'tcx>,
  41
  42     /// Generic bounds on the method's parameters which must be added
  43     /// as pending obligations.
  44     method_predicates: ty::InstantiatedPredicates<'tcx>,
  45 }
  46
  47 pub fn confirm<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
  48                          span: Span,
  49                          self_expr: &'tcx hir::Expr,
  50                          call_expr: &'tcx hir::Expr,
  51                          unadjusted_self_ty: Ty<'tcx>,
  52                          pick: probe::Pick<'tcx>,
  53                          supplied_method_types: Vec<Ty<'tcx>>)
  54                          -> ty::MethodCallee<'tcx>
  55 {
  56     debug!("confirm(unadjusted_self_ty={:?}, pick={:?}, supplied_method_types={:?})",
  57            unadjusted_self_ty,
  58            pick,
  59            supplied_method_types);
  60
  61     let mut confirm_cx = ConfirmContext::new(fcx, span, self_expr, call_expr);
  62     confirm_cx.confirm(unadjusted_self_ty, pick, supplied_method_types)
  63 }
  64
  65 impl<'a,'tcx> ConfirmContext<'a,'tcx> {
  66     fn new(fcx: &'a FnCtxt<'a, 'tcx>,
  67            span: Span,
  68            self_expr: &'tcx hir::Expr,
  69            call_expr: &'tcx hir::Expr)
  70            -> ConfirmContext<'a, 'tcx>
  71     {
  72         ConfirmContext { fcx: fcx, span: span, self_expr: self_expr, call_expr: call_expr }
  73     }
  74
  75     fn confirm(&mut self,
  76                unadjusted_self_ty: Ty<'tcx>,
  77                pick: probe::Pick<'tcx>,
  78                supplied_method_types: Vec<Ty<'tcx>>)
  79                -> ty::MethodCallee<'tcx>
  80     {
  81         // Adjust the self expression the user provided and obtain the adjusted type.
  82         let self_ty = self.adjust_self_ty(unadjusted_self_ty, &pick);
  83
  84         // Make sure nobody calls `drop()` explicitly.
  85         self.enforce_illegal_method_limitations(&pick);
  86
  87         // Create substitutions for the method's type parameters.
  88         let rcvr_substs = self.fresh_receiver_substs(self_ty, &pick);
  89         let all_substs =
  90             self.instantiate_method_substs(
  91                 &pick,
  92                 supplied_method_types,
  93                 rcvr_substs);
  94
  95         debug!("all_substs={:?}", all_substs);
  96
  97         // Create the final signature for the method, replacing late-bound regions.
  98         let InstantiatedMethodSig {
  99             method_sig, all_substs, method_predicates
 100         } = self.instantiate_method_sig(&pick, all_substs);
 101         let method_self_ty = method_sig.inputs[0];
 102
 103         // Unify the (adjusted) self type with what the method expects.
 104         self.unify_receivers(self_ty, method_self_ty);
 105
 106         // Add any trait/regions obligations specified on the method's type parameters.
 107         self.add_obligations(&pick, &all_substs, &method_predicates);
 108
 109         // Create the final `MethodCallee`.
 110         let method_ty = pick.item.as_opt_method().unwrap();
 111         let fty = self.tcx().mk_fn(None, self.tcx().mk_bare_fn(ty::BareFnTy {
 112             sig: ty::Binder(method_sig),
 113             unsafety: method_ty.fty.unsafety,
 114             abi: method_ty.fty.abi.clone(),
 115         }));
 116         let callee = ty::MethodCallee {
 117             def_id: pick.item.def_id(),
 118             ty: fty,
 119             substs: self.tcx().mk_substs(all_substs)
 120         };
 121
 122         // If this is an `&mut self` method, bias the receiver
 123         // expression towards mutability (this will switch
 124         // e.g. `Deref` to `DerefMut` in overloaded derefs and so on).
 125         self.fixup_derefs_on_method_receiver_if_necessary(&callee);
 126
 127         callee
 128     }
 129
 130     ///////////////////////////////////////////////////////////////////////////
 131     // ADJUSTMENTS
 132
 133     fn adjust_self_ty(&mut self,
 134                       unadjusted_self_ty: Ty<'tcx>,
 135                       pick: &probe::Pick<'tcx>)
 136                       -> Ty<'tcx>
 137     {
 138         let (autoref, unsize) = if let Some(mutbl) = pick.autoref {
 139             let region = self.infcx().next_region_var(infer::Autoref(self.span));
 140             let autoref = AutoPtr(self.tcx().mk_region(region), mutbl);
 141             (Some(autoref), pick.unsize.map(|target| {
 142                 target.adjust_for_autoref(self.tcx(), Some(autoref))
 143             }))
 144         } else {
 145             // No unsizing should be performed without autoref (at
 146             // least during method dispach). This is because we
 147             // currently only unsize `[T;N]` to `[T]`, and naturally
 148             // that must occur being a reference.
 149             assert!(pick.unsize.is_none());
 150             (None, None)
 151         };
 152
 153         // Commit the autoderefs by calling `autoderef again, but this
 154         // time writing the results into the various tables.
 155         let (autoderefd_ty, n, result) = check::autoderef(self.fcx,
 156                                                           self.span,
 157                                                           unadjusted_self_ty,
 158                                                           Some(self.self_expr),
 159                                                           UnresolvedTypeAction::Error,
 160                                                           NoPreference,
 161                                                           |_, n| {
 162             if n == pick.autoderefs {
 163                 Some(())
 164             } else {
 165                 None
 166             }
 167         });
 168         assert_eq!(n, pick.autoderefs);
 169         assert_eq!(result, Some(()));
 170
 171         // Write out the final adjustment.
 172         self.fcx.write_adjustment(self.self_expr.id,
 173                                   AdjustDerefRef(AutoDerefRef {
 174             autoderefs: pick.autoderefs,
 175             autoref: autoref,
 176             unsize: unsize
 177         }));
 178
 179         if let Some(target) = unsize {
 180             target
 181         } else {
 182             autoderefd_ty.adjust_for_autoref(self.tcx(), autoref)
 183         }
 184     }
 185
 186     ///////////////////////////////////////////////////////////////////////////
 187     //
 188
 189     /// Returns a set of substitutions for the method *receiver* where all type and region
 190     /// parameters are instantiated with fresh variables. This substitution does not include any
 191     /// parameters declared on the method itself.
 192     ///
 193     /// Note that this substitution may include late-bound regions from the impl level. If so,
 194     /// these are instantiated later in the `instantiate_method_sig` routine.
 195     fn fresh_receiver_substs(&mut self,
 196                              self_ty: Ty<'tcx>,
 197                              pick: &probe::Pick<'tcx>)
 198                              -> subst::Substs<'tcx>
 199     {
 200         match pick.kind {
 201             probe::InherentImplPick => {
 202                 let impl_def_id = pick.item.container().id();
 203                 assert!(self.tcx().impl_trait_ref(impl_def_id).is_none(),
 204                         "impl {:?} is not an inherent impl", impl_def_id);
 205                 check::impl_self_ty(self.fcx, self.span, impl_def_id).substs
 206             }
 207
 208             probe::ObjectPick => {
 209                 let trait_def_id = pick.item.container().id();
 210                 self.extract_trait_ref(self_ty, |this, object_ty, data| {
 211                     // The object data has no entry for the Self
 212                     // Type. For the purposes of this method call, we
 213                     // substitute the object type itself. This
 214                     // wouldn't be a sound substitution in all cases,
 215                     // since each instance of the object type is a
 216                     // different existential and hence could match
 217                     // distinct types (e.g., if `Self` appeared as an
 218                     // argument type), but those cases have already
 219                     // been ruled out when we deemed the trait to be
 220                     // "object safe".
 221                     let original_poly_trait_ref =
 222                         data.principal_trait_ref_with_self_ty(this.tcx(), object_ty);
 223                     let upcast_poly_trait_ref =
 224                         this.upcast(original_poly_trait_ref.clone(), trait_def_id);
 225                     let upcast_trait_ref =
 226                         this.replace_late_bound_regions_with_fresh_var(&upcast_poly_trait_ref);
 227                     debug!("original_poly_trait_ref={:?} upcast_trait_ref={:?} target_trait={:?}",
 228                            original_poly_trait_ref,
 229                            upcast_trait_ref,
 230                            trait_def_id);
 231                     upcast_trait_ref.substs.clone()
 232                 })
 233             }
 234
 235             probe::ExtensionImplPick(impl_def_id) => {
 236                 // The method being invoked is the method as defined on the trait,
 237                 // so return the substitutions from the trait. Consider:
 238                 //
 239                 //     impl<A,B,C> Trait<A,B> for Foo<C> { ... }
 240                 //
 241                 // If we instantiate A, B, and C with $A, $B, and $C
 242                 // respectively, then we want to return the type
 243                 // parameters from the trait ([$A,$B]), not those from
 244                 // the impl ([$A,$B,$C]) not the receiver type ([$C]).
 245                 let impl_polytype = check::impl_self_ty(self.fcx, self.span, impl_def_id);
 246                 let impl_trait_ref =
 247                     self.fcx.instantiate_type_scheme(
 248                         self.span,
 249                         &impl_polytype.substs,
 250                         &self.tcx().impl_trait_ref(impl_def_id).unwrap());
 251                 impl_trait_ref.substs.clone()
 252             }
 253
 254             probe::TraitPick => {
 255                 let trait_def_id = pick.item.container().id();
 256                 let trait_def = self.tcx().lookup_trait_def(trait_def_id);
 257
 258                 // Make a trait reference `$0 : Trait<$1...$n>`
 259                 // consisting entirely of type variables. Later on in
 260                 // the process we will unify the transformed-self-type
 261                 // of the method with the actual type in order to
 262                 // unify some of these variables.
 263                 self.infcx().fresh_substs_for_trait(self.span,
 264                                                     &trait_def.generics,
 265                                                     self.infcx().next_ty_var())
 266             }
 267
 268             probe::WhereClausePick(ref poly_trait_ref) => {
 269                 // Where clauses can have bound regions in them. We need to instantiate
 270                 // those to convert from a poly-trait-ref to a trait-ref.
 271                 self.replace_late_bound_regions_with_fresh_var(&*poly_trait_ref).substs.clone()
 272             }
 273         }
 274     }
 275
 276     fn extract_trait_ref<R, F>(&mut self, self_ty: Ty<'tcx>, mut closure: F) -> R where
 277         F: FnMut(&mut ConfirmContext<'a, 'tcx>, Ty<'tcx>, &ty::TraitTy<'tcx>) -> R,
 278     {
 279         // If we specified that this is an object method, then the
 280         // self-type ought to be something that can be dereferenced to
 281         // yield an object-type (e.g., `&Object` or `Box<Object>`
 282         // etc).
 283
 284         let (_, _, result) = check::autoderef(self.fcx,
 285                                               self.span,
 286                                               self_ty,
 287                                               None,
 288                                               UnresolvedTypeAction::Error,
 289                                               NoPreference,
 290                                               |ty, _| {
 291             match ty.sty {
 292                 ty::TyTrait(ref data) => Some(closure(self, ty, &**data)),
 293                 _ => None,
 294             }
 295         });
 296
 297         match result {
 298             Some(r) => r,
 299             None => {
 300                 self.tcx().sess.span_bug(
 301                     self.span,
 302                     &format!("self-type `{}` for ObjectPick never dereferenced to an object",
 303                             self_ty))
 304             }
 305         }
 306     }
 307
 308     fn instantiate_method_substs(&mut self,
 309                                  pick: &probe::Pick<'tcx>,
 310                                  supplied_method_types: Vec<Ty<'tcx>>,
 311                                  substs: subst::Substs<'tcx>)
 312                                  -> subst::Substs<'tcx>
 313     {
 314         // Determine the values for the generic parameters of the method.
 315         // If they were not explicitly supplied, just construct fresh
 316         // variables.
 317         let num_supplied_types = supplied_method_types.len();
 318         let method = pick.item.as_opt_method().unwrap();
 319         let method_types = method.generics.types.get_slice(subst::FnSpace);
 320         let num_method_types = method_types.len();
 321
 322
 323         // Create subst for early-bound lifetime parameters, combining
 324         // parameters from the type and those from the method.
 325         //
 326         // FIXME -- permit users to manually specify lifetimes
 327         let method_regions =
 328             self.fcx.infcx().region_vars_for_defs(
 329                 self.span,
 330                 pick.item.as_opt_method().unwrap()
 331                     .generics.regions.get_slice(subst::FnSpace));
 332
 333         let subst::Substs { types, regions } = substs;
 334         let regions = regions.map(|r| r.with_vec(subst::FnSpace, method_regions));
 335         let mut final_substs = subst::Substs { types: types, regions: regions };
 336
 337         if num_supplied_types == 0 {
 338             self.fcx.infcx().type_vars_for_defs(
 339                 self.span,
 340                 subst::FnSpace,
 341                 &mut final_substs,
 342                 method_types);
 343         } else if num_method_types == 0 {
 344             span_err!(self.tcx().sess, self.span, E0035,
 345                 "does not take type parameters");
 346             self.fcx.infcx().type_vars_for_defs(
 347                 self.span,
 348                 subst::FnSpace,
 349                 &mut final_substs,
 350                 method_types);
 351         } else if num_supplied_types != num_method_types {
 352             span_err!(self.tcx().sess, self.span, E0036,
 353                 "incorrect number of type parameters given for this method");
 354             final_substs.types.replace(
 355                 subst::FnSpace,
 356                 vec![self.tcx().types.err; num_method_types]);
 357         } else {
 358             final_substs.types.replace(subst::FnSpace, supplied_method_types);
 359         }
 360
 361         return final_substs;
 362     }
 363
 364     fn unify_receivers(&mut self,
 365                        self_ty: Ty<'tcx>,
 366                        method_self_ty: Ty<'tcx>)
 367     {
 368         match self.fcx.mk_subty(false, infer::Misc(self.span), self_ty, method_self_ty) {
 369             Ok(_) => {}
 370             Err(_) => {
 371                 self.tcx().sess.span_bug(
 372                     self.span,
 373                     &format!("{} was a subtype of {} but now is not?",
 374                              self_ty, method_self_ty));
 375             }
 376         }
 377     }
 378
 379     ///////////////////////////////////////////////////////////////////////////
 380     //
 381
 382     fn instantiate_method_sig(&mut self,
 383                               pick: &probe::Pick<'tcx>,
 384                               all_substs: subst::Substs<'tcx>)
 385                               -> InstantiatedMethodSig<'tcx>
 386     {
 387         debug!("instantiate_method_sig(pick={:?}, all_substs={:?})",
 388                pick,
 389                all_substs);
 390
 391         // Instantiate the bounds on the method with the
 392         // type/early-bound-regions substitutions performed. There can
 393         // be no late-bound regions appearing here.
 394         let method_predicates = pick.item.as_opt_method().unwrap()
 395                                     .predicates.instantiate(self.tcx(), &all_substs);
 396         let method_predicates = self.fcx.normalize_associated_types_in(self.span,
 397                                                                        &method_predicates);
 398
 399         debug!("method_predicates after subst = {:?}",
 400                method_predicates);
 401
 402         // Instantiate late-bound regions and substitute the trait
 403         // parameters into the method type to get the actual method type.
 404         //
 405         // NB: Instantiate late-bound regions first so that
 406         // `instantiate_type_scheme` can normalize associated types that
 407         // may reference those regions.
 408         let method_sig = self.replace_late_bound_regions_with_fresh_var(
 409             &pick.item.as_opt_method().unwrap().fty.sig);
 410         debug!("late-bound lifetimes from method instantiated, method_sig={:?}",
 411                method_sig);
 412
 413         let method_sig = self.fcx.instantiate_type_scheme(self.span, &all_substs, &method_sig);
 414         debug!("type scheme substituted, method_sig={:?}",
 415                method_sig);
 416
 417         InstantiatedMethodSig {
 418             method_sig: method_sig,
 419             all_substs: all_substs,
 420             method_predicates: method_predicates,
 421         }
 422     }
 423
 424     fn add_obligations(&mut self,
 425                        pick: &probe::Pick<'tcx>,
 426                        all_substs: &subst::Substs<'tcx>,
 427                        method_predicates: &ty::InstantiatedPredicates<'tcx>) {
 428         debug!("add_obligations: pick={:?} all_substs={:?} method_predicates={:?}",
 429                pick,
 430                all_substs,
 431                method_predicates);
 432
 433         self.fcx.add_obligations_for_parameters(
 434             traits::ObligationCause::misc(self.span, self.fcx.body_id),
 435             method_predicates);
 436
 437         // this is a projection from a trait reference, so we have to
 438         // make sure that the trait reference inputs are well-formed.
 439         self.fcx.add_wf_bounds(
 440             all_substs,
 441             self.call_expr);
 442     }
 443
 444     ///////////////////////////////////////////////////////////////////////////
 445     // RECONCILIATION
 446
 447     /// When we select a method with an `&mut self` receiver, we have to go convert any
 448     /// auto-derefs, indices, etc from `Deref` and `Index` into `DerefMut` and `IndexMut`
 449     /// respectively.
 450     fn fixup_derefs_on_method_receiver_if_necessary(&self,
 451                                                     method_callee: &ty::MethodCallee) {
 452         let sig = match method_callee.ty.sty {
 453             ty::TyBareFn(_, ref f) => f.sig.clone(),
 454             _ => return,
 455         };
 456
 457         match sig.0.inputs[0].sty {
 458             ty::TyRef(_, ty::TypeAndMut {
 459                 ty: _,
 460                 mutbl: hir::MutMutable,
 461             }) => {}
 462             _ => return,
 463         }
 464
 465         // Gather up expressions we want to munge.
 466         let mut exprs = Vec::new();
 467         exprs.push(self.self_expr);
 468         loop {
 469             let last = exprs[exprs.len() - 1];
 470             match last.node {
 471                 hir::ExprParen(ref expr) |
 472                 hir::ExprField(ref expr, _) |
 473                 hir::ExprTupField(ref expr, _) |
 474                 hir::ExprIndex(ref expr, _) |
 475                 hir::ExprUnary(hir::UnDeref, ref expr) => exprs.push(&**expr),
 476                 _ => break,
 477             }
 478         }
 479
 480         debug!("fixup_derefs_on_method_receiver_if_necessary: exprs={:?}",
 481                exprs);
 482
 483         // Fix up autoderefs and derefs.
 484         for (i, &expr) in exprs.iter().rev().enumerate() {
 485             // Count autoderefs.
 486             let autoderef_count = match self.fcx
 487                                             .inh
 488                                             .tables
 489                                             .borrow()
 490                                             .adjustments
 491                                             .get(&expr.id) {
 492                 Some(&AdjustDerefRef(ref adj)) => adj.autoderefs,
 493                 Some(_) | None => 0,
 494             };
 495
 496             debug!("fixup_derefs_on_method_receiver_if_necessary: i={} expr={:?} \
 497                                                                   autoderef_count={}",
 498                    i, expr, autoderef_count);
 499
 500             if autoderef_count > 0 {
 501                 check::autoderef(self.fcx,
 502                                  expr.span,
 503                                  self.fcx.expr_ty(expr),
 504                                  Some(expr),
 505                                  UnresolvedTypeAction::Error,
 506                                  PreferMutLvalue,
 507                                  |_, autoderefs| {
 508                                      if autoderefs == autoderef_count + 1 {
 509                                          Some(())
 510                                      } else {
 511                                          None
 512                                      }
 513                                  });
 514             }
 515
 516             // Don't retry the first one or we might infinite loop!
 517             if i != 0 {
 518                 match expr.node {
 519                     hir::ExprIndex(ref base_expr, ref index_expr) => {
 520                         // If this is an overloaded index, the
 521                         // adjustment will include an extra layer of
 522                         // autoref because the method is an &self/&mut
 523                         // self method. We have to peel it off to get
 524                         // the raw adjustment that `try_index_step`
 525                         // expects. This is annoying and horrible. We
 526                         // ought to recode this routine so it doesn't
 527                         // (ab)use the normal type checking paths.
 528                         let adj = self.fcx.inh.tables.borrow().adjustments.get(&base_expr.id)
 529                                                                           .cloned();
 530                         let (autoderefs, unsize) = match adj {
 531                             Some(AdjustDerefRef(adr)) => match adr.autoref {
 532                                 None => {
 533                                     assert!(adr.unsize.is_none());
 534                                     (adr.autoderefs, None)
 535                                 }
 536                                 Some(AutoPtr(_, _)) => {
 537                                     (adr.autoderefs, adr.unsize.map(|target| {
 538                                         target.builtin_deref(false, NoPreference)
 539                                               .expect("fixup: AutoPtr is not &T").ty
 540                                     }))
 541                                 }
 542                                 Some(_) => {
 543                                     self.tcx().sess.span_bug(
 544                                         base_expr.span,
 545                                         &format!("unexpected adjustment autoref {:?}",
 546                                                 adr));
 547                                 }
 548                             },
 549                             None => (0, None),
 550                             Some(_) => {
 551                                 self.tcx().sess.span_bug(
 552                                     base_expr.span,
 553                                     "unexpected adjustment type");
 554                             }
 555                         };
 556
 557                         let (adjusted_base_ty, unsize) = if let Some(target) = unsize {
 558                             (target, true)
 559                         } else {
 560                             (self.fcx.adjust_expr_ty(base_expr,
 561                                 Some(&AdjustDerefRef(AutoDerefRef {
 562                                     autoderefs: autoderefs,
 563                                     autoref: None,
 564                                     unsize: None
 565                                 }))), false)
 566                         };
 567                         let index_expr_ty = self.fcx.expr_ty(&**index_expr);
 568
 569                         let result = check::try_index_step(
 570                             self.fcx,
 571                             ty::MethodCall::expr(expr.id),
 572                             expr,
 573                             &**base_expr,
 574                             adjusted_base_ty,
 575                             autoderefs,
 576                             unsize,
 577                             PreferMutLvalue,
 578                             index_expr_ty);
 579
 580                         if let Some((input_ty, return_ty)) = result {
 581                             demand::suptype(self.fcx, index_expr.span, input_ty, index_expr_ty);
 582
 583                             let expr_ty = self.fcx.expr_ty(&*expr);
 584                             demand::suptype(self.fcx, expr.span, expr_ty, return_ty);
 585                         }
 586                     }
 587                     hir::ExprUnary(hir::UnDeref, ref base_expr) => {
 588                         // if this is an overloaded deref, then re-evaluate with
 589                         // a preference for mut
 590                         let method_call = ty::MethodCall::expr(expr.id);
 591                         if self.fcx.inh.tables.borrow().method_map.contains_key(&method_call) {
 592                             check::try_overloaded_deref(
 593                                 self.fcx,
 594                                 expr.span,
 595                                 Some(method_call),
 596                                 Some(&**base_expr),
 597                                 self.fcx.expr_ty(&**base_expr),
 598                                 PreferMutLvalue);
 599                         }
 600                     }
 601                     _ => {}
 602                 }
 603             }
 604         }
 605     }
 606
 607     ///////////////////////////////////////////////////////////////////////////
 608     // MISCELLANY
 609
 610     fn tcx(&self) -> &'a ty::ctxt<'tcx> {
 611         self.fcx.tcx()
 612     }
 613
 614     fn infcx(&self) -> &'a InferCtxt<'a, 'tcx> {
 615         self.fcx.infcx()
 616     }
 617
 618     fn enforce_illegal_method_limitations(&self, pick: &probe::Pick) {
 619         // Disallow calls to the method `drop` defined in the `Drop` trait.
 620         match pick.item.container() {
 621             ty::TraitContainer(trait_def_id) => {
 622                 callee::check_legal_trait_for_method_call(self.fcx.ccx, self.span, trait_def_id)
 623             }
 624             ty::ImplContainer(..) => {
 625                 // Since `drop` is a trait method, we expect that any
 626                 // potential calls to it will wind up in the other
 627                 // arm. But just to be sure, check that the method id
 628                 // does not appear in the list of destructors.
 629                 assert!(!self.tcx().destructors.borrow().contains(&pick.item.def_id()));
 630             }
 631         }
 632     }
 633
 634     fn upcast(&mut self,
 635               source_trait_ref: ty::PolyTraitRef<'tcx>,
 636               target_trait_def_id: DefId)
 637               -> ty::PolyTraitRef<'tcx>
 638     {
 639         let upcast_trait_refs = traits::upcast(self.tcx(),
 640                                                source_trait_ref.clone(),
 641                                                target_trait_def_id);
 642
 643         // must be exactly one trait ref or we'd get an ambig error etc
 644         if upcast_trait_refs.len() != 1 {
 645             self.tcx().sess.span_bug(
 646                 self.span,
 647                 &format!("cannot uniquely upcast `{:?}` to `{:?}`: `{:?}`",
 648                          source_trait_ref,
 649                          target_trait_def_id,
 650                          upcast_trait_refs));
 651         }
 652
 653         upcast_trait_refs.into_iter().next().unwrap()
 654     }
 655
 656     fn replace_late_bound_regions_with_fresh_var<T>(&self, value: &ty::Binder<T>) -> T
 657         where T : TypeFoldable<'tcx>
 658     {
 659         self.infcx().replace_late_bound_regions_with_fresh_var(
 660             self.span, infer::FnCall, value).0
 661     }
 662 }