src/librustc_typeck/astconv.rs

   1 // Copyright 2012-2014 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 //! Conversion from AST representation of types to the ty.rs
  12 //! representation.  The main routine here is `ast_ty_to_ty()`: each use
  13 //! is parameterized by an instance of `AstConv`.
  14
  15 use rustc::middle::const_val::eval_length;
  16 use rustc_data_structures::accumulate_vec::AccumulateVec;
  17 use hir;
  18 use hir::def::Def;
  19 use hir::def_id::DefId;
  20 use middle::resolve_lifetime as rl;
  21 use rustc::ty::subst::{Kind, Subst, Substs};
  22 use rustc::traits;
  23 use rustc::ty::{self, Ty, TyCtxt, ToPredicate, TypeFoldable};
  24 use rustc::ty::wf::object_region_bounds;
  25 use rustc_back::slice;
  26 use require_c_abi_if_variadic;
  27 use util::common::ErrorReported;
  28 use util::nodemap::FxHashSet;
  29
  30 use std::iter;
  31 use syntax::{abi, ast};
  32 use syntax::feature_gate::{GateIssue, emit_feature_err};
  33 use syntax_pos::Span;
  34
  35 pub trait AstConv<'gcx, 'tcx> {
  36     fn tcx<'a>(&'a self) -> TyCtxt<'a, 'gcx, 'tcx>;
  37
  38     /// Returns the set of bounds in scope for the type parameter with
  39     /// the given id.
  40     fn get_type_parameter_bounds(&self, span: Span, def_id: DefId)
  41                                  -> ty::GenericPredicates<'tcx>;
  42
  43     /// What lifetime should we use when a lifetime is omitted (and not elided)?
  44     fn re_infer(&self, span: Span, _def: Option<&ty::RegionParameterDef>)
  45                 -> Option<ty::Region<'tcx>>;
  46
  47     /// What type should we use when a type is omitted?
  48     fn ty_infer(&self, span: Span) -> Ty<'tcx>;
  49
  50     /// Same as ty_infer, but with a known type parameter definition.
  51     fn ty_infer_for_def(&self,
  52                         _def: &ty::TypeParameterDef,
  53                         _substs: &[Kind<'tcx>],
  54                         span: Span) -> Ty<'tcx> {
  55         self.ty_infer(span)
  56     }
  57
  58     /// Projecting an associated type from a (potentially)
  59     /// higher-ranked trait reference is more complicated, because of
  60     /// the possibility of late-bound regions appearing in the
  61     /// associated type binding. This is not legal in function
  62     /// signatures for that reason. In a function body, we can always
  63     /// handle it because we can use inference variables to remove the
  64     /// late-bound regions.
  65     fn projected_ty_from_poly_trait_ref(&self,
  66                                         span: Span,
  67                                         item_def_id: DefId,
  68                                         poly_trait_ref: ty::PolyTraitRef<'tcx>)
  69                                         -> Ty<'tcx>;
  70
  71     /// Normalize an associated type coming from the user.
  72     fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
  73
  74     /// Invoked when we encounter an error from some prior pass
  75     /// (e.g. resolve) that is translated into a ty-error. This is
  76     /// used to help suppress derived errors typeck might otherwise
  77     /// report.
  78     fn set_tainted_by_errors(&self);
  79 }
  80
  81 struct ConvertedBinding<'tcx> {
  82     item_name: ast::Name,
  83     ty: Ty<'tcx>,
  84     span: Span,
  85 }
  86
  87 /// Dummy type used for the `Self` of a `TraitRef` created for converting
  88 /// a trait object, and which gets removed in `ExistentialTraitRef`.
  89 /// This type must not appear anywhere in other converted types.
  90 const TRAIT_OBJECT_DUMMY_SELF: ty::TypeVariants<'static> = ty::TyInfer(ty::FreshTy(0));
  91
  92 impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
  93     pub fn ast_region_to_region(&self,
  94         lifetime: &hir::Lifetime,
  95         def: Option<&ty::RegionParameterDef>)
  96         -> ty::Region<'tcx>
  97     {
  98         let tcx = self.tcx();
  99         let r = match tcx.named_region_map.defs.get(&lifetime.id) {
 100             Some(&rl::Region::Static) => {
 101                 tcx.types.re_static
 102             }
 103
 104             Some(&rl::Region::LateBound(debruijn, id)) => {
 105                 let name = tcx.hir.name(id);
 106                 tcx.mk_region(ty::ReLateBound(debruijn,
 107                     ty::BrNamed(tcx.hir.local_def_id(id), name)))
 108             }
 109
 110             Some(&rl::Region::LateBoundAnon(debruijn, index)) => {
 111                 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
 112             }
 113
 114             Some(&rl::Region::EarlyBound(index, id)) => {
 115                 let name = tcx.hir.name(id);
 116                 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
 117                     def_id: tcx.hir.local_def_id(id),
 118                     index,
 119                     name,
 120                 }))
 121             }
 122
 123             Some(&rl::Region::Free(scope, id)) => {
 124                 let name = tcx.hir.name(id);
 125                 tcx.mk_region(ty::ReFree(ty::FreeRegion {
 126                     scope,
 127                     bound_region: ty::BrNamed(tcx.hir.local_def_id(id), name)
 128                 }))
 129
 130                     // (*) -- not late-bound, won't change
 131             }
 132
 133             None => {
 134                 self.re_infer(lifetime.span, def).expect("unelided lifetime in signature")
 135             }
 136         };
 137
 138         debug!("ast_region_to_region(lifetime={:?}) yields {:?}",
 139                 lifetime,
 140                 r);
 141
 142         r
 143     }
 144
 145     /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
 146     /// returns an appropriate set of substitutions for this particular reference to `I`.
 147     pub fn ast_path_substs_for_ty(&self,
 148         span: Span,
 149         def_id: DefId,
 150         item_segment: &hir::PathSegment)
 151         -> &'tcx Substs<'tcx>
 152     {
 153         let (substs, assoc_bindings) =
 154             self.create_substs_for_ast_path(span,
 155                                             def_id,
 156                                             &item_segment.parameters,
 157                                             None);
 158
 159         assoc_bindings.first().map(|b| self.prohibit_projection(b.span));
 160
 161         substs
 162     }
 163
 164     /// Given the type/region arguments provided to some path (along with
 165     /// an implicit Self, if this is a trait reference) returns the complete
 166     /// set of substitutions. This may involve applying defaulted type parameters.
 167     ///
 168     /// Note that the type listing given here is *exactly* what the user provided.
 169     fn create_substs_for_ast_path(&self,
 170         span: Span,
 171         def_id: DefId,
 172         parameters: &hir::PathParameters,
 173         self_ty: Option<Ty<'tcx>>)
 174         -> (&'tcx Substs<'tcx>, Vec<ConvertedBinding<'tcx>>)
 175     {
 176         let tcx = self.tcx();
 177
 178         debug!("create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
 179                parameters={:?})",
 180                def_id, self_ty, parameters);
 181
 182         // If the type is parameterized by this region, then replace this
 183         // region with the current anon region binding (in other words,
 184         // whatever & would get replaced with).
 185         let decl_generics = tcx.generics_of(def_id);
 186         let num_types_provided = parameters.types.len();
 187         let expected_num_region_params = decl_generics.regions.len();
 188         let supplied_num_region_params = parameters.lifetimes.len();
 189         if expected_num_region_params != supplied_num_region_params {
 190             report_lifetime_number_error(tcx, span,
 191                                          supplied_num_region_params,
 192                                          expected_num_region_params);
 193         }
 194
 195         // If a self-type was declared, one should be provided.
 196         assert_eq!(decl_generics.has_self, self_ty.is_some());
 197
 198         // Check the number of type parameters supplied by the user.
 199         let ty_param_defs = &decl_generics.types[self_ty.is_some() as usize..];
 200         if !parameters.infer_types || num_types_provided > ty_param_defs.len() {
 201             check_type_argument_count(tcx, span, num_types_provided, ty_param_defs);
 202         }
 203
 204         let is_object = self_ty.map_or(false, |ty| ty.sty == TRAIT_OBJECT_DUMMY_SELF);
 205         let default_needs_object_self = |p: &ty::TypeParameterDef| {
 206             if is_object && p.has_default {
 207                 if tcx.at(span).type_of(p.def_id).has_self_ty() {
 208                     // There is no suitable inference default for a type parameter
 209                     // that references self, in an object type.
 210                     return true;
 211                 }
 212             }
 213
 214             false
 215         };
 216
 217         let substs = Substs::for_item(tcx, def_id, |def, _| {
 218             let i = def.index as usize - self_ty.is_some() as usize;
 219             if let Some(lifetime) = parameters.lifetimes.get(i) {
 220                 self.ast_region_to_region(lifetime, Some(def))
 221             } else {
 222                 tcx.types.re_static
 223             }
 224         }, |def, substs| {
 225             let i = def.index as usize;
 226
 227             // Handle Self first, so we can adjust the index to match the AST.
 228             if let (0, Some(ty)) = (i, self_ty) {
 229                 return ty;
 230             }
 231
 232             let i = i - self_ty.is_some() as usize - decl_generics.regions.len();
 233             if i < num_types_provided {
 234                 // A provided type parameter.
 235                 self.ast_ty_to_ty(&parameters.types[i])
 236             } else if parameters.infer_types {
 237                 // No type parameters were provided, we can infer all.
 238                 let ty_var = if !default_needs_object_self(def) {
 239                     self.ty_infer_for_def(def, substs, span)
 240                 } else {
 241                     self.ty_infer(span)
 242                 };
 243                 ty_var
 244             } else if def.has_default {
 245                 // No type parameter provided, but a default exists.
 246
 247                 // If we are converting an object type, then the
 248                 // `Self` parameter is unknown. However, some of the
 249                 // other type parameters may reference `Self` in their
 250                 // defaults. This will lead to an ICE if we are not
 251                 // careful!
 252                 if default_needs_object_self(def) {
 253                     struct_span_err!(tcx.sess, span, E0393,
 254                                      "the type parameter `{}` must be explicitly specified",
 255                                      def.name)
 256                         .span_label(span, format!("missing reference to `{}`", def.name))
 257                         .note(&format!("because of the default `Self` reference, \
 258                                         type parameters must be specified on object types"))
 259                         .emit();
 260                     tcx.types.err
 261                 } else {
 262                     // This is a default type parameter.
 263                     self.normalize_ty(
 264                         span,
 265                         tcx.at(span).type_of(def.def_id)
 266                             .subst_spanned(tcx, substs, Some(span))
 267                     )
 268                 }
 269             } else {
 270                 // We've already errored above about the mismatch.
 271                 tcx.types.err
 272             }
 273         });
 274
 275         let assoc_bindings = parameters.bindings.iter().map(|binding| {
 276             ConvertedBinding {
 277                 item_name: binding.name,
 278                 ty: self.ast_ty_to_ty(&binding.ty),
 279                 span: binding.span,
 280             }
 281         }).collect();
 282
 283         debug!("create_substs_for_ast_path(decl_generics={:?}, self_ty={:?}) -> {:?}",
 284                decl_generics, self_ty, substs);
 285
 286         (substs, assoc_bindings)
 287     }
 288
 289     /// Instantiates the path for the given trait reference, assuming that it's
 290     /// bound to a valid trait type. Returns the def_id for the defining trait.
 291     /// Fails if the type is a type other than a trait type.
 292     ///
 293     /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T=X>`
 294     /// are disallowed. Otherwise, they are pushed onto the vector given.
 295     pub fn instantiate_mono_trait_ref(&self,
 296         trait_ref: &hir::TraitRef,
 297         self_ty: Ty<'tcx>)
 298         -> ty::TraitRef<'tcx>
 299     {
 300         self.prohibit_type_params(trait_ref.path.segments.split_last().unwrap().1);
 301
 302         let trait_def_id = self.trait_def_id(trait_ref);
 303         self.ast_path_to_mono_trait_ref(trait_ref.path.span,
 304                                         trait_def_id,
 305                                         self_ty,
 306                                         trait_ref.path.segments.last().unwrap())
 307     }
 308
 309     fn trait_def_id(&self, trait_ref: &hir::TraitRef) -> DefId {
 310         let path = &trait_ref.path;
 311         match path.def {
 312             Def::Trait(trait_def_id) => trait_def_id,
 313             Def::Err => {
 314                 self.tcx().sess.fatal("cannot continue compilation due to previous error");
 315             }
 316             _ => {
 317                 span_fatal!(self.tcx().sess, path.span, E0245, "`{}` is not a trait",
 318                             self.tcx().hir.node_to_pretty_string(trait_ref.ref_id));
 319             }
 320         }
 321     }
 322
 323     pub fn instantiate_poly_trait_ref(&self,
 324         ast_trait_ref: &hir::PolyTraitRef,
 325         self_ty: Ty<'tcx>,
 326         poly_projections: &mut Vec<ty::PolyProjectionPredicate<'tcx>>)
 327         -> ty::PolyTraitRef<'tcx>
 328     {
 329         let trait_ref = &ast_trait_ref.trait_ref;
 330         let trait_def_id = self.trait_def_id(trait_ref);
 331
 332         debug!("ast_path_to_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
 333
 334         self.prohibit_type_params(trait_ref.path.segments.split_last().unwrap().1);
 335
 336         let (substs, assoc_bindings) =
 337             self.create_substs_for_ast_trait_ref(trait_ref.path.span,
 338                                                  trait_def_id,
 339                                                  self_ty,
 340                                                  trait_ref.path.segments.last().unwrap());
 341         let poly_trait_ref = ty::Binder(ty::TraitRef::new(trait_def_id, substs));
 342
 343         poly_projections.extend(assoc_bindings.iter().filter_map(|binding| {
 344             // specify type to assert that error was already reported in Err case:
 345             let predicate: Result<_, ErrorReported> =
 346                 self.ast_type_binding_to_poly_projection_predicate(trait_ref.ref_id,
 347                                                                    poly_trait_ref,
 348                                                                    binding);
 349             predicate.ok() // ok to ignore Err() because ErrorReported (see above)
 350         }));
 351
 352         debug!("ast_path_to_poly_trait_ref({:?}, projections={:?}) -> {:?}",
 353                trait_ref, poly_projections, poly_trait_ref);
 354         poly_trait_ref
 355     }
 356
 357     fn ast_path_to_mono_trait_ref(&self,
 358                                   span: Span,
 359                                   trait_def_id: DefId,
 360                                   self_ty: Ty<'tcx>,
 361                                   trait_segment: &hir::PathSegment)
 362                                   -> ty::TraitRef<'tcx>
 363     {
 364         let (substs, assoc_bindings) =
 365             self.create_substs_for_ast_trait_ref(span,
 366                                                  trait_def_id,
 367                                                  self_ty,
 368                                                  trait_segment);
 369         assoc_bindings.first().map(|b| self.prohibit_projection(b.span));
 370         ty::TraitRef::new(trait_def_id, substs)
 371     }
 372
 373     fn create_substs_for_ast_trait_ref(&self,
 374                                        span: Span,
 375                                        trait_def_id: DefId,
 376                                        self_ty: Ty<'tcx>,
 377                                        trait_segment: &hir::PathSegment)
 378                                        -> (&'tcx Substs<'tcx>, Vec<ConvertedBinding<'tcx>>)
 379     {
 380         debug!("create_substs_for_ast_trait_ref(trait_segment={:?})",
 381                trait_segment);
 382
 383         let trait_def = self.tcx().trait_def(trait_def_id);
 384
 385         if !self.tcx().sess.features.borrow().unboxed_closures &&
 386            trait_segment.parameters.parenthesized != trait_def.paren_sugar {
 387             // For now, require that parenthetical notation be used only with `Fn()` etc.
 388             let msg = if trait_def.paren_sugar {
 389                 "the precise format of `Fn`-family traits' type parameters is subject to change. \
 390                  Use parenthetical notation (Fn(Foo, Bar) -> Baz) instead"
 391             } else {
 392                 "parenthetical notation is only stable when used with `Fn`-family traits"
 393             };
 394             emit_feature_err(&self.tcx().sess.parse_sess, "unboxed_closures",
 395                              span, GateIssue::Language, msg);
 396         }
 397
 398         self.create_substs_for_ast_path(span,
 399                                         trait_def_id,
 400                                         &trait_segment.parameters,
 401                                         Some(self_ty))
 402     }
 403
 404     fn trait_defines_associated_type_named(&self,
 405                                            trait_def_id: DefId,
 406                                            assoc_name: ast::Name)
 407                                            -> bool
 408     {
 409         self.tcx().associated_items(trait_def_id).any(|item| {
 410             item.kind == ty::AssociatedKind::Type && item.name == assoc_name
 411         })
 412     }
 413
 414     fn ast_type_binding_to_poly_projection_predicate(
 415         &self,
 416         _path_id: ast::NodeId,
 417         trait_ref: ty::PolyTraitRef<'tcx>,
 418         binding: &ConvertedBinding<'tcx>)
 419         -> Result<ty::PolyProjectionPredicate<'tcx>, ErrorReported>
 420     {
 421         let tcx = self.tcx();
 422
 423         // Given something like `U : SomeTrait<T=X>`, we want to produce a
 424         // predicate like `<U as SomeTrait>::T = X`. This is somewhat
 425         // subtle in the event that `T` is defined in a supertrait of
 426         // `SomeTrait`, because in that case we need to upcast.
 427         //
 428         // That is, consider this case:
 429         //
 430         // ```
 431         // trait SubTrait : SuperTrait<int> { }
 432         // trait SuperTrait<A> { type T; }
 433         //
 434         // ... B : SubTrait<T=foo> ...
 435         // ```
 436         //
 437         // We want to produce `<B as SuperTrait<int>>::T == foo`.
 438
 439         // Find any late-bound regions declared in `ty` that are not
 440         // declared in the trait-ref. These are not wellformed.
 441         //
 442         // Example:
 443         //
 444         //     for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
 445         //     for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
 446         let late_bound_in_trait_ref = tcx.collect_constrained_late_bound_regions(&trait_ref);
 447         let late_bound_in_ty = tcx.collect_referenced_late_bound_regions(&ty::Binder(binding.ty));
 448         debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
 449         debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
 450         for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
 451             let br_name = match *br {
 452                 ty::BrNamed(_, name) => name,
 453                 _ => {
 454                     span_bug!(
 455                         binding.span,
 456                         "anonymous bound region {:?} in binding but not trait ref",
 457                         br);
 458                 }
 459             };
 460             struct_span_err!(tcx.sess,
 461                              binding.span,
 462                              E0582,
 463                              "binding for associated type `{}` references lifetime `{}`, \
 464                               which does not appear in the trait input types",
 465                              binding.item_name, br_name)
 466                 .emit();
 467         }
 468
 469         // Simple case: X is defined in the current trait.
 470         if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
 471             return Ok(trait_ref.map_bound(|trait_ref| {
 472                 ty::ProjectionPredicate {
 473                     projection_ty: ty::ProjectionTy::from_ref_and_name(
 474                         tcx,
 475                         trait_ref,
 476                         binding.item_name,
 477                     ),
 478                     ty: binding.ty,
 479                 }
 480             }));
 481         }
 482
 483         // Otherwise, we have to walk through the supertraits to find
 484         // those that do.
 485         let candidates =
 486             traits::supertraits(tcx, trait_ref.clone())
 487             .filter(|r| self.trait_defines_associated_type_named(r.def_id(), binding.item_name));
 488
 489         let candidate = self.one_bound_for_assoc_type(candidates,
 490                                                       &trait_ref.to_string(),
 491                                                       &binding.item_name.as_str(),
 492                                                       binding.span)?;
 493
 494         Ok(candidate.map_bound(|trait_ref| {
 495             ty::ProjectionPredicate {
 496                 projection_ty: ty::ProjectionTy::from_ref_and_name(
 497                     tcx,
 498                     trait_ref,
 499                     binding.item_name,
 500                 ),
 501                 ty: binding.ty,
 502             }
 503         }))
 504     }
 505
 506     fn ast_path_to_ty(&self,
 507         span: Span,
 508         did: DefId,
 509         item_segment: &hir::PathSegment)
 510         -> Ty<'tcx>
 511     {
 512         let substs = self.ast_path_substs_for_ty(span, did, item_segment);
 513         self.normalize_ty(
 514             span,
 515             self.tcx().at(span).type_of(did).subst(self.tcx(), substs)
 516         )
 517     }
 518
 519     /// Transform a PolyTraitRef into a PolyExistentialTraitRef by
 520     /// removing the dummy Self type (TRAIT_OBJECT_DUMMY_SELF).
 521     fn trait_ref_to_existential(&self, trait_ref: ty::TraitRef<'tcx>)
 522                                 -> ty::ExistentialTraitRef<'tcx> {
 523         assert_eq!(trait_ref.self_ty().sty, TRAIT_OBJECT_DUMMY_SELF);
 524         ty::ExistentialTraitRef::erase_self_ty(self.tcx(), trait_ref)
 525     }
 526
 527     fn conv_object_ty_poly_trait_ref(&self,
 528         span: Span,
 529         trait_bounds: &[hir::PolyTraitRef],
 530         lifetime: &hir::Lifetime)
 531         -> Ty<'tcx>
 532     {
 533         let tcx = self.tcx();
 534
 535         if trait_bounds.is_empty() {
 536             span_err!(tcx.sess, span, E0224,
 537                       "at least one non-builtin trait is required for an object type");
 538             return tcx.types.err;
 539         }
 540
 541         let mut projection_bounds = vec![];
 542         let dummy_self = tcx.mk_ty(TRAIT_OBJECT_DUMMY_SELF);
 543         let principal = self.instantiate_poly_trait_ref(&trait_bounds[0],
 544                                                         dummy_self,
 545                                                         &mut projection_bounds);
 546
 547         for trait_bound in trait_bounds[1..].iter() {
 548             // Sanity check for non-principal trait bounds
 549             self.instantiate_poly_trait_ref(trait_bound,
 550                                             dummy_self,
 551                                             &mut vec![]);
 552         }
 553
 554         let (auto_traits, trait_bounds) = split_auto_traits(tcx, &trait_bounds[1..]);
 555
 556         if !trait_bounds.is_empty() {
 557             let b = &trait_bounds[0];
 558             let span = b.trait_ref.path.span;
 559             struct_span_err!(self.tcx().sess, span, E0225,
 560                 "only Send/Sync traits can be used as additional traits in a trait object")
 561                 .span_label(span, "non-Send/Sync additional trait")
 562                 .emit();
 563         }
 564
 565         // Erase the dummy_self (TRAIT_OBJECT_DUMMY_SELF) used above.
 566         let existential_principal = principal.map_bound(|trait_ref| {
 567             self.trait_ref_to_existential(trait_ref)
 568         });
 569         let existential_projections = projection_bounds.iter().map(|bound| {
 570             bound.map_bound(|b| {
 571                 let trait_ref = self.trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
 572                 ty::ExistentialProjection {
 573                     ty: b.ty,
 574                     item_def_id: b.projection_ty.item_def_id,
 575                     substs: trait_ref.substs,
 576                 }
 577             })
 578         });
 579
 580         // check that there are no gross object safety violations,
 581         // most importantly, that the supertraits don't contain Self,
 582         // to avoid ICE-s.
 583         let object_safety_violations =
 584             tcx.astconv_object_safety_violations(principal.def_id());
 585         if !object_safety_violations.is_empty() {
 586             tcx.report_object_safety_error(
 587                 span, principal.def_id(), object_safety_violations)
 588                 .emit();
 589             return tcx.types.err;
 590         }
 591
 592         let mut associated_types = FxHashSet::default();
 593         for tr in traits::supertraits(tcx, principal) {
 594             associated_types.extend(tcx.associated_items(tr.def_id())
 595                 .filter(|item| item.kind == ty::AssociatedKind::Type)
 596                 .map(|item| item.def_id));
 597         }
 598
 599         for projection_bound in &projection_bounds {
 600             associated_types.remove(&projection_bound.0.projection_ty.item_def_id);
 601         }
 602
 603         for item_def_id in associated_types {
 604             let assoc_item = tcx.associated_item(item_def_id);
 605             let trait_def_id = assoc_item.container.id();
 606             struct_span_err!(tcx.sess, span, E0191,
 607                 "the value of the associated type `{}` (from the trait `{}`) must be specified",
 608                         assoc_item.name,
 609                         tcx.item_path_str(trait_def_id))
 610                         .span_label(span, format!(
 611                             "missing associated type `{}` value", assoc_item.name))
 612                         .emit();
 613         }
 614
 615         let mut v =
 616             iter::once(ty::ExistentialPredicate::Trait(*existential_principal.skip_binder()))
 617             .chain(auto_traits.into_iter().map(ty::ExistentialPredicate::AutoTrait))
 618             .chain(existential_projections
 619                    .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())))
 620             .collect::<AccumulateVec<[_; 8]>>();
 621         v.sort_by(|a, b| a.cmp(tcx, b));
 622         let existential_predicates = ty::Binder(tcx.mk_existential_predicates(v.into_iter()));
 623
 624
 625         // Explicitly specified region bound. Use that.
 626         let region_bound = if !lifetime.is_elided() {
 627             self.ast_region_to_region(lifetime, None)
 628         } else {
 629             self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
 630                 if tcx.named_region_map.defs.contains_key(&lifetime.id) {
 631                     self.ast_region_to_region(lifetime, None)
 632                 } else {
 633                     self.re_infer(span, None).unwrap_or_else(|| {
 634                         span_err!(tcx.sess, span, E0228,
 635                                   "the lifetime bound for this object type cannot be deduced \
 636                                    from context; please supply an explicit bound");
 637                         tcx.types.re_static
 638                     })
 639                 }
 640             })
 641         };
 642
 643         debug!("region_bound: {:?}", region_bound);
 644
 645         let ty = tcx.mk_dynamic(existential_predicates, region_bound);
 646         debug!("trait_object_type: {:?}", ty);
 647         ty
 648     }
 649
 650     fn report_ambiguous_associated_type(&self,
 651                                         span: Span,
 652                                         type_str: &str,
 653                                         trait_str: &str,
 654                                         name: &str) {
 655         struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type")
 656             .span_label(span, "ambiguous associated type")
 657             .note(&format!("specify the type using the syntax `<{} as {}>::{}`",
 658                   type_str, trait_str, name))
 659             .emit();
 660
 661     }
 662
 663     // Search for a bound on a type parameter which includes the associated item
 664     // given by `assoc_name`. `ty_param_def_id` is the `DefId` for the type parameter
 665     // This function will fail if there are no suitable bounds or there is
 666     // any ambiguity.
 667     fn find_bound_for_assoc_item(&self,
 668                                  ty_param_def_id: DefId,
 669                                  assoc_name: ast::Name,
 670                                  span: Span)
 671                                  -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
 672     {
 673         let tcx = self.tcx();
 674
 675         let bounds: Vec<_> = self.get_type_parameter_bounds(span, ty_param_def_id)
 676             .predicates.into_iter().filter_map(|p| p.to_opt_poly_trait_ref()).collect();
 677
 678         // Check that there is exactly one way to find an associated type with the
 679         // correct name.
 680         let suitable_bounds =
 681             traits::transitive_bounds(tcx, &bounds)
 682             .filter(|b| self.trait_defines_associated_type_named(b.def_id(), assoc_name));
 683
 684         let param_node_id = tcx.hir.as_local_node_id(ty_param_def_id).unwrap();
 685         let param_name = tcx.hir.ty_param_name(param_node_id);
 686         self.one_bound_for_assoc_type(suitable_bounds,
 687                                       &param_name.as_str(),
 688                                       &assoc_name.as_str(),
 689                                       span)
 690     }
 691
 692
 693     // Checks that bounds contains exactly one element and reports appropriate
 694     // errors otherwise.
 695     fn one_bound_for_assoc_type<I>(&self,
 696                                 mut bounds: I,
 697                                 ty_param_name: &str,
 698                                 assoc_name: &str,
 699                                 span: Span)
 700         -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
 701         where I: Iterator<Item=ty::PolyTraitRef<'tcx>>
 702     {
 703         let bound = match bounds.next() {
 704             Some(bound) => bound,
 705             None => {
 706                 struct_span_err!(self.tcx().sess, span, E0220,
 707                           "associated type `{}` not found for `{}`",
 708                           assoc_name,
 709                           ty_param_name)
 710                   .span_label(span, format!("associated type `{}` not found", assoc_name))
 711                   .emit();
 712                 return Err(ErrorReported);
 713             }
 714         };
 715
 716         if let Some(bound2) = bounds.next() {
 717             let bounds = iter::once(bound).chain(iter::once(bound2)).chain(bounds);
 718             let mut err = struct_span_err!(
 719                 self.tcx().sess, span, E0221,
 720                 "ambiguous associated type `{}` in bounds of `{}`",
 721                 assoc_name,
 722                 ty_param_name);
 723             err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
 724
 725             for bound in bounds {
 726                 let bound_span = self.tcx().associated_items(bound.def_id()).find(|item| {
 727                     item.kind == ty::AssociatedKind::Type && item.name == assoc_name
 728                 })
 729                 .and_then(|item| self.tcx().hir.span_if_local(item.def_id));
 730
 731                 if let Some(span) = bound_span {
 732                     err.span_label(span, format!("ambiguous `{}` from `{}`",
 733                                                   assoc_name,
 734                                                   bound));
 735                 } else {
 736                     span_note!(&mut err, span,
 737                                "associated type `{}` could derive from `{}`",
 738                                ty_param_name,
 739                                bound);
 740                 }
 741             }
 742             err.emit();
 743         }
 744
 745         return Ok(bound);
 746     }
 747
 748     // Create a type from a path to an associated type.
 749     // For a path A::B::C::D, ty and ty_path_def are the type and def for A::B::C
 750     // and item_segment is the path segment for D. We return a type and a def for
 751     // the whole path.
 752     // Will fail except for T::A and Self::A; i.e., if ty/ty_path_def are not a type
 753     // parameter or Self.
 754     pub fn associated_path_def_to_ty(&self,
 755                                      ref_id: ast::NodeId,
 756                                      span: Span,
 757                                      ty: Ty<'tcx>,
 758                                      ty_path_def: Def,
 759                                      item_segment: &hir::PathSegment)
 760                                      -> (Ty<'tcx>, Def)
 761     {
 762         let tcx = self.tcx();
 763         let assoc_name = item_segment.name;
 764
 765         debug!("associated_path_def_to_ty: {:?}::{}", ty, assoc_name);
 766
 767         self.prohibit_type_params(slice::ref_slice(item_segment));
 768
 769         // Find the type of the associated item, and the trait where the associated
 770         // item is declared.
 771         let bound = match (&ty.sty, ty_path_def) {
 772             (_, Def::SelfTy(Some(_), Some(impl_def_id))) => {
 773                 // `Self` in an impl of a trait - we have a concrete self type and a
 774                 // trait reference.
 775                 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
 776                     Some(trait_ref) => trait_ref,
 777                     None => {
 778                         // A cycle error occurred, most likely.
 779                         return (tcx.types.err, Def::Err);
 780                     }
 781                 };
 782
 783                 let candidates =
 784                     traits::supertraits(tcx, ty::Binder(trait_ref))
 785                     .filter(|r| self.trait_defines_associated_type_named(r.def_id(),
 786                                                                          assoc_name));
 787
 788                 match self.one_bound_for_assoc_type(candidates,
 789                                                     "Self",
 790                                                     &assoc_name.as_str(),
 791                                                     span) {
 792                     Ok(bound) => bound,
 793                     Err(ErrorReported) => return (tcx.types.err, Def::Err),
 794                 }
 795             }
 796             (&ty::TyParam(_), Def::SelfTy(Some(param_did), None)) |
 797             (&ty::TyParam(_), Def::TyParam(param_did)) => {
 798                 match self.find_bound_for_assoc_item(param_did, assoc_name, span) {
 799                     Ok(bound) => bound,
 800                     Err(ErrorReported) => return (tcx.types.err, Def::Err),
 801                 }
 802             }
 803             _ => {
 804                 // Don't print TyErr to the user.
 805                 if !ty.references_error() {
 806                     self.report_ambiguous_associated_type(span,
 807                                                           &ty.to_string(),
 808                                                           "Trait",
 809                                                           &assoc_name.as_str());
 810                 }
 811                 return (tcx.types.err, Def::Err);
 812             }
 813         };
 814
 815         let trait_did = bound.0.def_id;
 816         let item = tcx.associated_items(trait_did).find(|i| i.name == assoc_name)
 817                                                   .expect("missing associated type");
 818
 819         let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, bound);
 820         let ty = self.normalize_ty(span, ty);
 821
 822         let def = Def::AssociatedTy(item.def_id);
 823         let def_scope = tcx.adjust(assoc_name, item.container.id(), ref_id).1;
 824         if !item.vis.is_accessible_from(def_scope, tcx) {
 825             let msg = format!("{} `{}` is private", def.kind_name(), assoc_name);
 826             tcx.sess.span_err(span, &msg);
 827         }
 828         tcx.check_stability(item.def_id, ref_id, span);
 829
 830         (ty, def)
 831     }
 832
 833     fn qpath_to_ty(&self,
 834                    span: Span,
 835                    opt_self_ty: Option<Ty<'tcx>>,
 836                    item_def_id: DefId,
 837                    trait_segment: &hir::PathSegment,
 838                    item_segment: &hir::PathSegment)
 839                    -> Ty<'tcx>
 840     {
 841         let tcx = self.tcx();
 842         let trait_def_id = tcx.parent_def_id(item_def_id).unwrap();
 843
 844         self.prohibit_type_params(slice::ref_slice(item_segment));
 845
 846         let self_ty = if let Some(ty) = opt_self_ty {
 847             ty
 848         } else {
 849             let path_str = tcx.item_path_str(trait_def_id);
 850             self.report_ambiguous_associated_type(span,
 851                                                   "Type",
 852                                                   &path_str,
 853                                                   &item_segment.name.as_str());
 854             return tcx.types.err;
 855         };
 856
 857         debug!("qpath_to_ty: self_type={:?}", self_ty);
 858
 859         let trait_ref = self.ast_path_to_mono_trait_ref(span,
 860                                                         trait_def_id,
 861                                                         self_ty,
 862                                                         trait_segment);
 863
 864         debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
 865
 866         self.normalize_ty(span, tcx.mk_projection(item_def_id, trait_ref.substs))
 867     }
 868
 869     pub fn prohibit_type_params(&self, segments: &[hir::PathSegment]) {
 870         for segment in segments {
 871             for typ in &segment.parameters.types {
 872                 struct_span_err!(self.tcx().sess, typ.span, E0109,
 873                                  "type parameters are not allowed on this type")
 874                     .span_label(typ.span, "type parameter not allowed")
 875                     .emit();
 876                 break;
 877             }
 878             for lifetime in &segment.parameters.lifetimes {
 879                 struct_span_err!(self.tcx().sess, lifetime.span, E0110,
 880                                  "lifetime parameters are not allowed on this type")
 881                     .span_label(lifetime.span,
 882                                 "lifetime parameter not allowed on this type")
 883                     .emit();
 884                 break;
 885             }
 886             for binding in &segment.parameters.bindings {
 887                 self.prohibit_projection(binding.span);
 888                 break;
 889             }
 890         }
 891     }
 892
 893     pub fn prohibit_projection(&self, span: Span) {
 894         let mut err = struct_span_err!(self.tcx().sess, span, E0229,
 895                                        "associated type bindings are not allowed here");
 896         err.span_label(span, "associated type not allowed here").emit();
 897     }
 898
 899     // Check a type Path and convert it to a Ty.
 900     pub fn def_to_ty(&self,
 901                      opt_self_ty: Option<Ty<'tcx>>,
 902                      path: &hir::Path,
 903                      permit_variants: bool)
 904                      -> Ty<'tcx> {
 905         let tcx = self.tcx();
 906
 907         debug!("base_def_to_ty(def={:?}, opt_self_ty={:?}, path_segments={:?})",
 908                path.def, opt_self_ty, path.segments);
 909
 910         let span = path.span;
 911         match path.def {
 912             Def::Enum(did) | Def::TyAlias(did) | Def::Struct(did) | Def::Union(did) => {
 913                 assert_eq!(opt_self_ty, None);
 914                 self.prohibit_type_params(path.segments.split_last().unwrap().1);
 915                 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
 916             }
 917             Def::Variant(did) if permit_variants => {
 918                 // Convert "variant type" as if it were a real type.
 919                 // The resulting `Ty` is type of the variant's enum for now.
 920                 assert_eq!(opt_self_ty, None);
 921                 self.prohibit_type_params(path.segments.split_last().unwrap().1);
 922                 self.ast_path_to_ty(span,
 923                                     tcx.parent_def_id(did).unwrap(),
 924                                     path.segments.last().unwrap())
 925             }
 926             Def::TyParam(did) => {
 927                 assert_eq!(opt_self_ty, None);
 928                 self.prohibit_type_params(&path.segments);
 929
 930                 let node_id = tcx.hir.as_local_node_id(did).unwrap();
 931                 let item_id = tcx.hir.get_parent_node(node_id);
 932                 let item_def_id = tcx.hir.local_def_id(item_id);
 933                 let generics = tcx.generics_of(item_def_id);
 934                 let index = generics.type_param_to_index[&tcx.hir.local_def_id(node_id).index];
 935                 tcx.mk_param(index, tcx.hir.name(node_id))
 936             }
 937             Def::SelfTy(_, Some(def_id)) => {
 938                 // Self in impl (we know the concrete type).
 939
 940                 assert_eq!(opt_self_ty, None);
 941                 self.prohibit_type_params(&path.segments);
 942
 943                 tcx.at(span).type_of(def_id)
 944             }
 945             Def::SelfTy(Some(_), None) => {
 946                 // Self in trait.
 947                 assert_eq!(opt_self_ty, None);
 948                 self.prohibit_type_params(&path.segments);
 949                 tcx.mk_self_type()
 950             }
 951             Def::AssociatedTy(def_id) => {
 952                 self.prohibit_type_params(&path.segments[..path.segments.len()-2]);
 953                 self.qpath_to_ty(span,
 954                                  opt_self_ty,
 955                                  def_id,
 956                                  &path.segments[path.segments.len()-2],
 957                                  path.segments.last().unwrap())
 958             }
 959             Def::PrimTy(prim_ty) => {
 960                 assert_eq!(opt_self_ty, None);
 961                 self.prohibit_type_params(&path.segments);
 962                 match prim_ty {
 963                     hir::TyBool => tcx.types.bool,
 964                     hir::TyChar => tcx.types.char,
 965                     hir::TyInt(it) => tcx.mk_mach_int(it),
 966                     hir::TyUint(uit) => tcx.mk_mach_uint(uit),
 967                     hir::TyFloat(ft) => tcx.mk_mach_float(ft),
 968                     hir::TyStr => tcx.mk_str()
 969                 }
 970             }
 971             Def::Err => {
 972                 self.set_tainted_by_errors();
 973                 return self.tcx().types.err;
 974             }
 975             _ => span_bug!(span, "unexpected definition: {:?}", path.def)
 976         }
 977     }
 978
 979     /// Parses the programmer's textual representation of a type into our
 980     /// internal notion of a type.
 981     pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty) -> Ty<'tcx> {
 982         debug!("ast_ty_to_ty(id={:?}, ast_ty={:?})",
 983                ast_ty.id, ast_ty);
 984
 985         let tcx = self.tcx();
 986
 987         let result_ty = match ast_ty.node {
 988             hir::TySlice(ref ty) => {
 989                 tcx.mk_slice(self.ast_ty_to_ty(&ty))
 990             }
 991             hir::TyPtr(ref mt) => {
 992                 tcx.mk_ptr(ty::TypeAndMut {
 993                     ty: self.ast_ty_to_ty(&mt.ty),
 994                     mutbl: mt.mutbl
 995                 })
 996             }
 997             hir::TyRptr(ref region, ref mt) => {
 998                 let r = self.ast_region_to_region(region, None);
 999                 debug!("TyRef r={:?}", r);
1000                 let t = self.ast_ty_to_ty(&mt.ty);
1001                 tcx.mk_ref(r, ty::TypeAndMut {ty: t, mutbl: mt.mutbl})
1002             }
1003             hir::TyNever => {
1004                 tcx.types.never
1005             },
1006             hir::TyTup(ref fields) => {
1007                 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)), false)
1008             }
1009             hir::TyBareFn(ref bf) => {
1010                 require_c_abi_if_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
1011                 tcx.mk_fn_ptr(self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl))
1012             }
1013             hir::TyTraitObject(ref bounds, ref lifetime) => {
1014                 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
1015             }
1016             hir::TyImplTrait(_) => {
1017                 // Figure out if we can allow an `impl Trait` here, by walking up
1018                 // to a `fn` or inherent `impl` method, going only through `Ty`
1019                 // or `TraitRef` nodes (as nothing else should be in types) and
1020                 // ensuring that we reach the `fn`/method signature's return type.
1021                 let mut node_id = ast_ty.id;
1022                 let fn_decl = loop {
1023                     let parent = tcx.hir.get_parent_node(node_id);
1024                     match tcx.hir.get(parent) {
1025                         hir::map::NodeItem(&hir::Item {
1026                             node: hir::ItemFn(ref fn_decl, ..), ..
1027                         }) => break Some(fn_decl),
1028
1029                         hir::map::NodeImplItem(&hir::ImplItem {
1030                             node: hir::ImplItemKind::Method(ref sig, _), ..
1031                         }) => {
1032                             match tcx.hir.expect_item(tcx.hir.get_parent(parent)).node {
1033                                 hir::ItemImpl(.., None, _, _) => {
1034                                     break Some(&sig.decl)
1035                                 }
1036                                 _ => break None
1037                             }
1038                         }
1039
1040                         hir::map::NodeTy(_) | hir::map::NodeTraitRef(_) => {}
1041
1042                         _ => break None
1043                     }
1044                     node_id = parent;
1045                 };
1046                 let allow = fn_decl.map_or(false, |fd| {
1047                     match fd.output {
1048                         hir::DefaultReturn(_) => false,
1049                         hir::Return(ref ty) => ty.id == node_id
1050                     }
1051                 });
1052
1053                 // Create the anonymized type.
1054                 if allow {
1055                     let def_id = tcx.hir.local_def_id(ast_ty.id);
1056                     tcx.mk_anon(def_id, Substs::identity_for_item(tcx, def_id))
1057                 } else {
1058                     span_err!(tcx.sess, ast_ty.span, E0562,
1059                               "`impl Trait` not allowed outside of function \
1060                                and inherent method return types");
1061                     tcx.types.err
1062                 }
1063             }
1064             hir::TyPath(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
1065                 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
1066                 let opt_self_ty = maybe_qself.as_ref().map(|qself| {
1067                     self.ast_ty_to_ty(qself)
1068                 });
1069                 self.def_to_ty(opt_self_ty, path, false)
1070             }
1071             hir::TyPath(hir::QPath::TypeRelative(ref qself, ref segment)) => {
1072                 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
1073                 let ty = self.ast_ty_to_ty(qself);
1074
1075                 let def = if let hir::TyPath(hir::QPath::Resolved(_, ref path)) = qself.node {
1076                     path.def
1077                 } else {
1078                     Def::Err
1079                 };
1080                 self.associated_path_def_to_ty(ast_ty.id, ast_ty.span, ty, def, segment).0
1081             }
1082             hir::TyArray(ref ty, length) => {
1083                 if let Ok(length) = eval_length(tcx, length, "array length") {
1084                     tcx.mk_array(self.ast_ty_to_ty(&ty), length)
1085                 } else {
1086                     self.tcx().types.err
1087                 }
1088             }
1089             hir::TyTypeof(ref _e) => {
1090                 struct_span_err!(tcx.sess, ast_ty.span, E0516,
1091                                  "`typeof` is a reserved keyword but unimplemented")
1092                     .span_label(ast_ty.span, "reserved keyword")
1093                     .emit();
1094
1095                 tcx.types.err
1096             }
1097             hir::TyInfer => {
1098                 // TyInfer also appears as the type of arguments or return
1099                 // values in a ExprClosure, or as
1100                 // the type of local variables. Both of these cases are
1101                 // handled specially and will not descend into this routine.
1102                 self.ty_infer(ast_ty.span)
1103             }
1104             hir::TyErr => {
1105                 tcx.types.err
1106             }
1107         };
1108
1109         result_ty
1110     }
1111
1112     pub fn ty_of_arg(&self,
1113                      ty: &hir::Ty,
1114                      expected_ty: Option<Ty<'tcx>>)
1115                      -> Ty<'tcx>
1116     {
1117         match ty.node {
1118             hir::TyInfer if expected_ty.is_some() => expected_ty.unwrap(),
1119             hir::TyInfer => self.ty_infer(ty.span),
1120             _ => self.ast_ty_to_ty(ty),
1121         }
1122     }
1123
1124     pub fn ty_of_fn(&self,
1125                     unsafety: hir::Unsafety,
1126                     abi: abi::Abi,
1127                     decl: &hir::FnDecl)
1128                     -> ty::PolyFnSig<'tcx> {
1129         debug!("ty_of_fn");
1130
1131         let tcx = self.tcx();
1132         let input_tys: Vec<Ty> =
1133             decl.inputs.iter().map(|a| self.ty_of_arg(a, None)).collect();
1134
1135         let output_ty = match decl.output {
1136             hir::Return(ref output) => self.ast_ty_to_ty(output),
1137             hir::DefaultReturn(..) => tcx.mk_nil(),
1138         };
1139
1140         debug!("ty_of_fn: output_ty={:?}", output_ty);
1141
1142         let bare_fn_ty = ty::Binder(tcx.mk_fn_sig(
1143             input_tys.into_iter(),
1144             output_ty,
1145             decl.variadic,
1146             unsafety,
1147             abi
1148         ));
1149
1150         // Find any late-bound regions declared in return type that do
1151         // not appear in the arguments. These are not wellformed.
1152         //
1153         // Example:
1154         //     for<'a> fn() -> &'a str <-- 'a is bad
1155         //     for<'a> fn(&'a String) -> &'a str <-- 'a is ok
1156         let inputs = bare_fn_ty.inputs();
1157         let late_bound_in_args = tcx.collect_constrained_late_bound_regions(
1158             &inputs.map_bound(|i| i.to_owned()));
1159         let output = bare_fn_ty.output();
1160         let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
1161         for br in late_bound_in_ret.difference(&late_bound_in_args) {
1162             let br_name = match *br {
1163                 ty::BrNamed(_, name) => name,
1164                 _ => {
1165                     span_bug!(
1166                         decl.output.span(),
1167                         "anonymous bound region {:?} in return but not args",
1168                         br);
1169                 }
1170             };
1171             struct_span_err!(tcx.sess,
1172                              decl.output.span(),
1173                              E0581,
1174                              "return type references lifetime `{}`, \
1175                              which does not appear in the fn input types",
1176                              br_name)
1177                 .emit();
1178         }
1179
1180         bare_fn_ty
1181     }
1182
1183     pub fn ty_of_closure(&self,
1184         unsafety: hir::Unsafety,
1185         decl: &hir::FnDecl,
1186         abi: abi::Abi,
1187         expected_sig: Option<ty::FnSig<'tcx>>)
1188         -> ty::PolyFnSig<'tcx>
1189     {
1190         debug!("ty_of_closure(expected_sig={:?})",
1191                expected_sig);
1192
1193         let input_tys = decl.inputs.iter().enumerate().map(|(i, a)| {
1194             let expected_arg_ty = expected_sig.as_ref().and_then(|e| {
1195                 // no guarantee that the correct number of expected args
1196                 // were supplied
1197                 if i < e.inputs().len() {
1198                     Some(e.inputs()[i])
1199                 } else {
1200                     None
1201                 }
1202             });
1203             self.ty_of_arg(a, expected_arg_ty)
1204         });
1205
1206         let expected_ret_ty = expected_sig.as_ref().map(|e| e.output());
1207
1208         let is_infer = match decl.output {
1209             hir::Return(ref output) if output.node == hir::TyInfer => true,
1210             hir::DefaultReturn(..) => true,
1211             _ => false
1212         };
1213
1214         let output_ty = match decl.output {
1215             _ if is_infer && expected_ret_ty.is_some() =>
1216                 expected_ret_ty.unwrap(),
1217             _ if is_infer => self.ty_infer(decl.output.span()),
1218             hir::Return(ref output) =>
1219                 self.ast_ty_to_ty(&output),
1220             hir::DefaultReturn(..) => bug!(),
1221         };
1222
1223         debug!("ty_of_closure: output_ty={:?}", output_ty);
1224
1225         ty::Binder(self.tcx().mk_fn_sig(
1226             input_tys,
1227             output_ty,
1228             decl.variadic,
1229             unsafety,
1230             abi
1231         ))
1232     }
1233
1234     /// Given the bounds on an object, determines what single region bound (if any) we can
1235     /// use to summarize this type. The basic idea is that we will use the bound the user
1236     /// provided, if they provided one, and otherwise search the supertypes of trait bounds
1237     /// for region bounds. It may be that we can derive no bound at all, in which case
1238     /// we return `None`.
1239     fn compute_object_lifetime_bound(&self,
1240         span: Span,
1241         existential_predicates: ty::Binder<&'tcx ty::Slice<ty::ExistentialPredicate<'tcx>>>)
1242         -> Option<ty::Region<'tcx>> // if None, use the default
1243     {
1244         let tcx = self.tcx();
1245
1246         debug!("compute_opt_region_bound(existential_predicates={:?})",
1247                existential_predicates);
1248
1249         // No explicit region bound specified. Therefore, examine trait
1250         // bounds and see if we can derive region bounds from those.
1251         let derived_region_bounds =
1252             object_region_bounds(tcx, existential_predicates);
1253
1254         // If there are no derived region bounds, then report back that we
1255         // can find no region bound. The caller will use the default.
1256         if derived_region_bounds.is_empty() {
1257             return None;
1258         }
1259
1260         // If any of the derived region bounds are 'static, that is always
1261         // the best choice.
1262         if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
1263             return Some(tcx.types.re_static);
1264         }
1265
1266         // Determine whether there is exactly one unique region in the set
1267         // of derived region bounds. If so, use that. Otherwise, report an
1268         // error.
1269         let r = derived_region_bounds[0];
1270         if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
1271             span_err!(tcx.sess, span, E0227,
1272                       "ambiguous lifetime bound, explicit lifetime bound required");
1273         }
1274         return Some(r);
1275     }
1276 }
1277
1278 /// Divides a list of general trait bounds into two groups: builtin bounds (Sync/Send) and the
1279 /// remaining general trait bounds.
1280 fn split_auto_traits<'a, 'b, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
1281                                          trait_bounds: &'b [hir::PolyTraitRef])
1282     -> (Vec<DefId>, Vec<&'b hir::PolyTraitRef>)
1283 {
1284     let (auto_traits, trait_bounds): (Vec<_>, _) = trait_bounds.iter().partition(|bound| {
1285         match bound.trait_ref.path.def {
1286             Def::Trait(trait_did) => {
1287                 // Checks whether `trait_did` refers to one of the builtin
1288                 // traits, like `Send`, and adds it to `auto_traits` if so.
1289                 if Some(trait_did) == tcx.lang_items.send_trait() ||
1290                     Some(trait_did) == tcx.lang_items.sync_trait() {
1291                     let segments = &bound.trait_ref.path.segments;
1292                     let parameters = &segments[segments.len() - 1].parameters;
1293                     if !parameters.types.is_empty() {
1294                         check_type_argument_count(tcx, bound.trait_ref.path.span,
1295                                                   parameters.types.len(), &[]);
1296                     }
1297                     if !parameters.lifetimes.is_empty() {
1298                         report_lifetime_number_error(tcx, bound.trait_ref.path.span,
1299                                                      parameters.lifetimes.len(), 0);
1300                     }
1301                     true
1302                 } else {
1303                     false
1304                 }
1305             }
1306             _ => false
1307         }
1308     });
1309
1310     let auto_traits = auto_traits.into_iter().map(|tr| {
1311         if let Def::Trait(trait_did) = tr.trait_ref.path.def {
1312             trait_did
1313         } else {
1314             unreachable!()
1315         }
1316     }).collect::<Vec<_>>();
1317
1318     (auto_traits, trait_bounds)
1319 }
1320
1321 fn check_type_argument_count(tcx: TyCtxt, span: Span, supplied: usize,
1322                              ty_param_defs: &[ty::TypeParameterDef]) {
1323     let accepted = ty_param_defs.len();
1324     let required = ty_param_defs.iter().take_while(|x| !x.has_default).count();
1325     if supplied < required {
1326         let expected = if required < accepted {
1327             "expected at least"
1328         } else {
1329             "expected"
1330         };
1331         let arguments_plural = if required == 1 { "" } else { "s" };
1332
1333         struct_span_err!(tcx.sess, span, E0243,
1334                 "wrong number of type arguments: {} {}, found {}",
1335                 expected, required, supplied)
1336             .span_label(span,
1337                 format!("{} {} type argument{}",
1338                     expected,
1339                     required,
1340                     arguments_plural))
1341             .emit();
1342     } else if supplied > accepted {
1343         let expected = if required < accepted {
1344             format!("expected at most {}", accepted)
1345         } else {
1346             format!("expected {}", accepted)
1347         };
1348         let arguments_plural = if accepted == 1 { "" } else { "s" };
1349
1350         struct_span_err!(tcx.sess, span, E0244,
1351                 "wrong number of type arguments: {}, found {}",
1352                 expected, supplied)
1353             .span_label(
1354                 span,
1355                 format!("{} type argument{}",
1356                     if accepted == 0 { "expected no" } else { &expected },
1357                     arguments_plural)
1358             )
1359             .emit();
1360     }
1361 }
1362
1363 fn report_lifetime_number_error(tcx: TyCtxt, span: Span, number: usize, expected: usize) {
1364     let label = if number < expected {
1365         if expected == 1 {
1366             format!("expected {} lifetime parameter", expected)
1367         } else {
1368             format!("expected {} lifetime parameters", expected)
1369         }
1370     } else {
1371         let additional = number - expected;
1372         if additional == 1 {
1373             "unexpected lifetime parameter".to_string()
1374         } else {
1375             format!("{} unexpected lifetime parameters", additional)
1376         }
1377     };
1378     struct_span_err!(tcx.sess, span, E0107,
1379                      "wrong number of lifetime parameters: expected {}, found {}",
1380                      expected, number)
1381         .span_label(span, label)
1382         .emit();
1383 }
1384
1385 // A helper struct for conveniently grouping a set of bounds which we pass to
1386 // and return from functions in multiple places.
1387 #[derive(PartialEq, Eq, Clone, Debug)]
1388 pub struct Bounds<'tcx> {
1389     pub region_bounds: Vec<ty::Region<'tcx>>,
1390     pub implicitly_sized: bool,
1391     pub trait_bounds: Vec<ty::PolyTraitRef<'tcx>>,
1392     pub projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>,
1393 }
1394
1395 impl<'a, 'gcx, 'tcx> Bounds<'tcx> {
1396     pub fn predicates(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, param_ty: Ty<'tcx>)
1397                       -> Vec<ty::Predicate<'tcx>>
1398     {
1399         let mut vec = Vec::new();
1400
1401         // If it could be sized, and is, add the sized predicate
1402         if self.implicitly_sized {
1403             if let Some(sized) = tcx.lang_items.sized_trait() {
1404                 let trait_ref = ty::TraitRef {
1405                     def_id: sized,
1406                     substs: tcx.mk_substs_trait(param_ty, &[])
1407                 };
1408                 vec.push(trait_ref.to_predicate());
1409             }
1410         }
1411
1412         for &region_bound in &self.region_bounds {
1413             // account for the binder being introduced below; no need to shift `param_ty`
1414             // because, at present at least, it can only refer to early-bound regions
1415             let region_bound = tcx.mk_region(ty::fold::shift_region(*region_bound, 1));
1416             vec.push(ty::Binder(ty::OutlivesPredicate(param_ty, region_bound)).to_predicate());
1417         }
1418
1419         for bound_trait_ref in &self.trait_bounds {
1420             vec.push(bound_trait_ref.to_predicate());
1421         }
1422
1423         for projection in &self.projection_bounds {
1424             vec.push(projection.to_predicate());
1425         }
1426
1427         vec
1428     }
1429 }
1430
1431 pub enum ExplicitSelf<'tcx> {
1432     ByValue,
1433     ByReference(ty::Region<'tcx>, hir::Mutability),
1434     ByBox
1435 }
1436
1437 impl<'tcx> ExplicitSelf<'tcx> {
1438     /// We wish to (for now) categorize an explicit self
1439     /// declaration like `self: SomeType` into either `self`,
1440     /// `&self`, `&mut self`, or `Box<self>`. We do this here
1441     /// by some simple pattern matching. A more precise check
1442     /// is done later in `check_method_self_type()`.
1443     ///
1444     /// Examples:
1445     ///
1446     /// ```
1447     /// impl Foo for &T {
1448     ///     // Legal declarations:
1449     ///     fn method1(self: &&T); // ExplicitSelf::ByReference
1450     ///     fn method2(self: &T); // ExplicitSelf::ByValue
1451     ///     fn method3(self: Box<&T>); // ExplicitSelf::ByBox
1452     ///
1453     ///     // Invalid cases will be caught later by `check_method_self_type`:
1454     ///     fn method_err1(self: &mut T); // ExplicitSelf::ByReference
1455     /// }
1456     /// ```
1457     ///
1458     /// To do the check we just count the number of "modifiers"
1459     /// on each type and compare them. If they are the same or
1460     /// the impl has more, we call it "by value". Otherwise, we
1461     /// look at the outermost modifier on the method decl and
1462     /// call it by-ref, by-box as appropriate. For method1, for
1463     /// example, the impl type has one modifier, but the method
1464     /// type has two, so we end up with
1465     /// ExplicitSelf::ByReference.
1466     pub fn determine(untransformed_self_ty: Ty<'tcx>,
1467                      self_arg_ty: Ty<'tcx>)
1468                      -> ExplicitSelf<'tcx> {
1469         fn count_modifiers(ty: Ty) -> usize {
1470             match ty.sty {
1471                 ty::TyRef(_, mt) => count_modifiers(mt.ty) + 1,
1472                 ty::TyAdt(def, _) if def.is_box() => count_modifiers(ty.boxed_ty()) + 1,
1473                 _ => 0,
1474             }
1475         }
1476
1477         let impl_modifiers = count_modifiers(untransformed_self_ty);
1478         let method_modifiers = count_modifiers(self_arg_ty);
1479
1480         if impl_modifiers >= method_modifiers {
1481             ExplicitSelf::ByValue
1482         } else {
1483             match self_arg_ty.sty {
1484                 ty::TyRef(r, mt) => ExplicitSelf::ByReference(r, mt.mutbl),
1485                 ty::TyAdt(def, _) if def.is_box() => ExplicitSelf::ByBox,
1486                 _ => ExplicitSelf::ByValue,
1487             }
1488         }
1489     }
1490 }