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, FN_OUTPUT_NAME};
  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::symbol::Symbol;
  34 use syntax_pos::Span;
  35
  36 pub trait AstConv<'gcx, 'tcx> {
  37     fn tcx<'a>(&'a self) -> TyCtxt<'a, 'gcx, 'tcx>;
  38
  39     /// Returns the set of bounds in scope for the type parameter with
  40     /// the given id.
  41     fn get_type_parameter_bounds(&self, span: Span, def_id: DefId)
  42                                  -> ty::GenericPredicates<'tcx>;
  43
  44     /// Return an (optional) substitution to convert bound type parameters that
  45     /// are in scope into free ones. This function should only return Some
  46     /// within a fn body.
  47     /// See ParameterEnvironment::free_substs for more information.
  48     fn get_free_substs(&self) -> Option<&Substs<'tcx>>;
  49
  50     /// What lifetime should we use when a lifetime is omitted (and not elided)?
  51     fn re_infer(&self, span: Span, _def: Option<&ty::RegionParameterDef>)
  52                 -> Option<ty::Region<'tcx>>;
  53
  54     /// What type should we use when a type is omitted?
  55     fn ty_infer(&self, span: Span) -> Ty<'tcx>;
  56
  57     /// Same as ty_infer, but with a known type parameter definition.
  58     fn ty_infer_for_def(&self,
  59                         _def: &ty::TypeParameterDef,
  60                         _substs: &[Kind<'tcx>],
  61                         span: Span) -> Ty<'tcx> {
  62         self.ty_infer(span)
  63     }
  64
  65     /// Projecting an associated type from a (potentially)
  66     /// higher-ranked trait reference is more complicated, because of
  67     /// the possibility of late-bound regions appearing in the
  68     /// associated type binding. This is not legal in function
  69     /// signatures for that reason. In a function body, we can always
  70     /// handle it because we can use inference variables to remove the
  71     /// late-bound regions.
  72     fn projected_ty_from_poly_trait_ref(&self,
  73                                         span: Span,
  74                                         poly_trait_ref: ty::PolyTraitRef<'tcx>,
  75                                         item_name: ast::Name)
  76                                         -> Ty<'tcx>;
  77
  78     /// Normalize an associated type coming from the user.
  79     fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
  80
  81     /// Invoked when we encounter an error from some prior pass
  82     /// (e.g. resolve) that is translated into a ty-error. This is
  83     /// used to help suppress derived errors typeck might otherwise
  84     /// report.
  85     fn set_tainted_by_errors(&self);
  86 }
  87
  88 struct ConvertedBinding<'tcx> {
  89     item_name: ast::Name,
  90     ty: Ty<'tcx>,
  91     span: Span,
  92 }
  93
  94 /// Dummy type used for the `Self` of a `TraitRef` created for converting
  95 /// a trait object, and which gets removed in `ExistentialTraitRef`.
  96 /// This type must not appear anywhere in other converted types.
  97 const TRAIT_OBJECT_DUMMY_SELF: ty::TypeVariants<'static> = ty::TyInfer(ty::FreshTy(0));
  98
  99 impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
 100     pub fn ast_region_to_region(&self,
 101         lifetime: &hir::Lifetime,
 102         def: Option<&ty::RegionParameterDef>)
 103         -> ty::Region<'tcx>
 104     {
 105         let tcx = self.tcx();
 106         let r = match tcx.named_region_map.defs.get(&lifetime.id) {
 107             Some(&rl::Region::Static) => {
 108                 tcx.types.re_static
 109             }
 110
 111             Some(&rl::Region::LateBound(debruijn, id)) => {
 112                 let name = tcx.hir.name(id);
 113                 tcx.mk_region(ty::ReLateBound(debruijn,
 114                     ty::BrNamed(tcx.hir.local_def_id(id), name)))
 115             }
 116
 117             Some(&rl::Region::LateBoundAnon(debruijn, index)) => {
 118                 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
 119             }
 120
 121             Some(&rl::Region::EarlyBound(index, id)) => {
 122                 let name = tcx.hir.name(id);
 123                 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
 124                     index: index,
 125                     name: name
 126                 }))
 127             }
 128
 129             Some(&rl::Region::Free(scope, id)) => {
 130                 let name = tcx.hir.name(id);
 131                 tcx.mk_region(ty::ReFree(ty::FreeRegion {
 132                     scope: Some(scope.to_code_extent(tcx)),
 133                     bound_region: ty::BrNamed(tcx.hir.local_def_id(id), name)
 134                 }))
 135
 136                     // (*) -- not late-bound, won't change
 137             }
 138
 139             None => {
 140                 self.re_infer(lifetime.span, def).expect("unelided lifetime in signature")
 141             }
 142         };
 143
 144         debug!("ast_region_to_region(lifetime={:?}) yields {:?}",
 145                 lifetime,
 146                 r);
 147
 148         r
 149     }
 150
 151     /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
 152     /// returns an appropriate set of substitutions for this particular reference to `I`.
 153     pub fn ast_path_substs_for_ty(&self,
 154         span: Span,
 155         def_id: DefId,
 156         item_segment: &hir::PathSegment)
 157         -> &'tcx Substs<'tcx>
 158     {
 159         let tcx = self.tcx();
 160
 161         match item_segment.parameters {
 162             hir::AngleBracketedParameters(_) => {}
 163             hir::ParenthesizedParameters(..) => {
 164                 struct_span_err!(tcx.sess, span, E0214,
 165                           "parenthesized parameters may only be used with a trait")
 166                     .span_label(span, "only traits may use parentheses")
 167                     .emit();
 168
 169                 return Substs::for_item(tcx, def_id, |_, _| {
 170                     tcx.types.re_static
 171                 }, |_, _| {
 172                     tcx.types.err
 173                 });
 174             }
 175         }
 176
 177         let (substs, assoc_bindings) =
 178             self.create_substs_for_ast_path(span,
 179                                             def_id,
 180                                             &item_segment.parameters,
 181                                             None);
 182
 183         assoc_bindings.first().map(|b| self.prohibit_projection(b.span));
 184
 185         substs
 186     }
 187
 188     /// Given the type/region arguments provided to some path (along with
 189     /// an implicit Self, if this is a trait reference) returns the complete
 190     /// set of substitutions. This may involve applying defaulted type parameters.
 191     ///
 192     /// Note that the type listing given here is *exactly* what the user provided.
 193     fn create_substs_for_ast_path(&self,
 194         span: Span,
 195         def_id: DefId,
 196         parameters: &hir::PathParameters,
 197         self_ty: Option<Ty<'tcx>>)
 198         -> (&'tcx Substs<'tcx>, Vec<ConvertedBinding<'tcx>>)
 199     {
 200         let tcx = self.tcx();
 201
 202         debug!("create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
 203                parameters={:?})",
 204                def_id, self_ty, parameters);
 205
 206         let (lifetimes, num_types_provided, infer_types) = match *parameters {
 207             hir::AngleBracketedParameters(ref data) => {
 208                 (&data.lifetimes[..], data.types.len(), data.infer_types)
 209             }
 210             hir::ParenthesizedParameters(_) => (&[][..], 1, false)
 211         };
 212
 213         // If the type is parameterized by this region, then replace this
 214         // region with the current anon region binding (in other words,
 215         // whatever & would get replaced with).
 216         let decl_generics = tcx.generics_of(def_id);
 217         let expected_num_region_params = decl_generics.regions.len();
 218         let supplied_num_region_params = lifetimes.len();
 219         if expected_num_region_params != supplied_num_region_params {
 220             report_lifetime_number_error(tcx, span,
 221                                          supplied_num_region_params,
 222                                          expected_num_region_params);
 223         }
 224
 225         // If a self-type was declared, one should be provided.
 226         assert_eq!(decl_generics.has_self, self_ty.is_some());
 227
 228         // Check the number of type parameters supplied by the user.
 229         let ty_param_defs = &decl_generics.types[self_ty.is_some() as usize..];
 230         if !infer_types || num_types_provided > ty_param_defs.len() {
 231             check_type_argument_count(tcx, span, num_types_provided, ty_param_defs);
 232         }
 233
 234         let is_object = self_ty.map_or(false, |ty| ty.sty == TRAIT_OBJECT_DUMMY_SELF);
 235         let default_needs_object_self = |p: &ty::TypeParameterDef| {
 236             if is_object && p.has_default {
 237                 if tcx.at(span).type_of(p.def_id).has_self_ty() {
 238                     // There is no suitable inference default for a type parameter
 239                     // that references self, in an object type.
 240                     return true;
 241                 }
 242             }
 243
 244             false
 245         };
 246
 247         let mut output_assoc_binding = None;
 248         let substs = Substs::for_item(tcx, def_id, |def, _| {
 249             let i = def.index as usize - self_ty.is_some() as usize;
 250             if let Some(lifetime) = lifetimes.get(i) {
 251                 self.ast_region_to_region(lifetime, Some(def))
 252             } else {
 253                 tcx.types.re_static
 254             }
 255         }, |def, substs| {
 256             let i = def.index as usize;
 257
 258             // Handle Self first, so we can adjust the index to match the AST.
 259             if let (0, Some(ty)) = (i, self_ty) {
 260                 return ty;
 261             }
 262
 263             let i = i - self_ty.is_some() as usize - decl_generics.regions.len();
 264             if i < num_types_provided {
 265                 // A provided type parameter.
 266                 match *parameters {
 267                     hir::AngleBracketedParameters(ref data) => {
 268                         self.ast_ty_to_ty(&data.types[i])
 269                     }
 270                     hir::ParenthesizedParameters(ref data) => {
 271                         assert_eq!(i, 0);
 272                         let (ty, assoc) = self.convert_parenthesized_parameters(data);
 273                         output_assoc_binding = Some(assoc);
 274                         ty
 275                     }
 276                 }
 277             } else if infer_types {
 278                 // No type parameters were provided, we can infer all.
 279                 let ty_var = if !default_needs_object_self(def) {
 280                     self.ty_infer_for_def(def, substs, span)
 281                 } else {
 282                     self.ty_infer(span)
 283                 };
 284                 ty_var
 285             } else if def.has_default {
 286                 // No type parameter provided, but a default exists.
 287
 288                 // If we are converting an object type, then the
 289                 // `Self` parameter is unknown. However, some of the
 290                 // other type parameters may reference `Self` in their
 291                 // defaults. This will lead to an ICE if we are not
 292                 // careful!
 293                 if default_needs_object_self(def) {
 294                     struct_span_err!(tcx.sess, span, E0393,
 295                                      "the type parameter `{}` must be explicitly specified",
 296                                      def.name)
 297                         .span_label(span, format!("missing reference to `{}`", def.name))
 298                         .note(&format!("because of the default `Self` reference, \
 299                                         type parameters must be specified on object types"))
 300                         .emit();
 301                     tcx.types.err
 302                 } else {
 303                     // This is a default type parameter.
 304                     self.normalize_ty(
 305                         span,
 306                         tcx.at(span).type_of(def.def_id)
 307                             .subst_spanned(tcx, substs, Some(span))
 308                     )
 309                 }
 310             } else {
 311                 // We've already errored above about the mismatch.
 312                 tcx.types.err
 313             }
 314         });
 315
 316         let assoc_bindings = match *parameters {
 317             hir::AngleBracketedParameters(ref data) => {
 318                 data.bindings.iter().map(|b| {
 319                     ConvertedBinding {
 320                         item_name: b.name,
 321                         ty: self.ast_ty_to_ty(&b.ty),
 322                         span: b.span
 323                     }
 324                 }).collect()
 325             }
 326             hir::ParenthesizedParameters(ref data) => {
 327                 vec![output_assoc_binding.unwrap_or_else(|| {
 328                     // This is an error condition, but we should
 329                     // get the associated type binding anyway.
 330                     self.convert_parenthesized_parameters(data).1
 331                 })]
 332             }
 333         };
 334
 335         debug!("create_substs_for_ast_path(decl_generics={:?}, self_ty={:?}) -> {:?}",
 336                decl_generics, self_ty, substs);
 337
 338         (substs, assoc_bindings)
 339     }
 340
 341     fn convert_parenthesized_parameters(&self,
 342                                         data: &hir::ParenthesizedParameterData)
 343                                         -> (Ty<'tcx>, ConvertedBinding<'tcx>)
 344     {
 345         let inputs = self.tcx().mk_type_list(data.inputs.iter().map(|a_t| {
 346             self.ast_ty_to_ty(a_t)
 347         }));
 348
 349         let (output, output_span) = match data.output {
 350             Some(ref output_ty) => {
 351                 (self.ast_ty_to_ty(output_ty), output_ty.span)
 352             }
 353             None => {
 354                 (self.tcx().mk_nil(), data.span)
 355             }
 356         };
 357
 358         let output_binding = ConvertedBinding {
 359             item_name: Symbol::intern(FN_OUTPUT_NAME),
 360             ty: output,
 361             span: output_span
 362         };
 363
 364         (self.tcx().mk_ty(ty::TyTuple(inputs, false)), output_binding)
 365     }
 366
 367     /// Instantiates the path for the given trait reference, assuming that it's
 368     /// bound to a valid trait type. Returns the def_id for the defining trait.
 369     /// Fails if the type is a type other than a trait type.
 370     ///
 371     /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T=X>`
 372     /// are disallowed. Otherwise, they are pushed onto the vector given.
 373     pub fn instantiate_mono_trait_ref(&self,
 374         trait_ref: &hir::TraitRef,
 375         self_ty: Ty<'tcx>)
 376         -> ty::TraitRef<'tcx>
 377     {
 378         let trait_def_id = self.trait_def_id(trait_ref);
 379         self.ast_path_to_mono_trait_ref(trait_ref.path.span,
 380                                         trait_def_id,
 381                                         self_ty,
 382                                         trait_ref.path.segments.last().unwrap())
 383     }
 384
 385     fn trait_def_id(&self, trait_ref: &hir::TraitRef) -> DefId {
 386         let path = &trait_ref.path;
 387         match path.def {
 388             Def::Trait(trait_def_id) => trait_def_id,
 389             Def::Err => {
 390                 self.tcx().sess.fatal("cannot continue compilation due to previous error");
 391             }
 392             _ => {
 393                 span_fatal!(self.tcx().sess, path.span, E0245, "`{}` is not a trait",
 394                             self.tcx().hir.node_to_pretty_string(trait_ref.ref_id));
 395             }
 396         }
 397     }
 398
 399     pub fn instantiate_poly_trait_ref(&self,
 400         ast_trait_ref: &hir::PolyTraitRef,
 401         self_ty: Ty<'tcx>,
 402         poly_projections: &mut Vec<ty::PolyProjectionPredicate<'tcx>>)
 403         -> ty::PolyTraitRef<'tcx>
 404     {
 405         let trait_ref = &ast_trait_ref.trait_ref;
 406         let trait_def_id = self.trait_def_id(trait_ref);
 407
 408         debug!("ast_path_to_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
 409
 410         let (substs, assoc_bindings) =
 411             self.create_substs_for_ast_trait_ref(trait_ref.path.span,
 412                                                  trait_def_id,
 413                                                  self_ty,
 414                                                  trait_ref.path.segments.last().unwrap());
 415         let poly_trait_ref = ty::Binder(ty::TraitRef::new(trait_def_id, substs));
 416
 417         poly_projections.extend(assoc_bindings.iter().filter_map(|binding| {
 418             // specify type to assert that error was already reported in Err case:
 419             let predicate: Result<_, ErrorReported> =
 420                 self.ast_type_binding_to_poly_projection_predicate(trait_ref.ref_id,
 421                                                                    poly_trait_ref,
 422                                                                    binding);
 423             predicate.ok() // ok to ignore Err() because ErrorReported (see above)
 424         }));
 425
 426         debug!("ast_path_to_poly_trait_ref({:?}, projections={:?}) -> {:?}",
 427                trait_ref, poly_projections, poly_trait_ref);
 428         poly_trait_ref
 429     }
 430
 431     fn ast_path_to_mono_trait_ref(&self,
 432                                   span: Span,
 433                                   trait_def_id: DefId,
 434                                   self_ty: Ty<'tcx>,
 435                                   trait_segment: &hir::PathSegment)
 436                                   -> ty::TraitRef<'tcx>
 437     {
 438         let (substs, assoc_bindings) =
 439             self.create_substs_for_ast_trait_ref(span,
 440                                                  trait_def_id,
 441                                                  self_ty,
 442                                                  trait_segment);
 443         assoc_bindings.first().map(|b| self.prohibit_projection(b.span));
 444         ty::TraitRef::new(trait_def_id, substs)
 445     }
 446
 447     fn create_substs_for_ast_trait_ref(&self,
 448                                        span: Span,
 449                                        trait_def_id: DefId,
 450                                        self_ty: Ty<'tcx>,
 451                                        trait_segment: &hir::PathSegment)
 452                                        -> (&'tcx Substs<'tcx>, Vec<ConvertedBinding<'tcx>>)
 453     {
 454         debug!("create_substs_for_ast_trait_ref(trait_segment={:?})",
 455                trait_segment);
 456
 457         let trait_def = self.tcx().trait_def(trait_def_id);
 458
 459         match trait_segment.parameters {
 460             hir::AngleBracketedParameters(_) => {
 461                 // For now, require that parenthetical notation be used
 462                 // only with `Fn()` etc.
 463                 if !self.tcx().sess.features.borrow().unboxed_closures && trait_def.paren_sugar {
 464                     emit_feature_err(&self.tcx().sess.parse_sess,
 465                                      "unboxed_closures", span, GateIssue::Language,
 466                                      "\
 467                         the precise format of `Fn`-family traits' \
 468                         type parameters is subject to change. \
 469                         Use parenthetical notation (Fn(Foo, Bar) -> Baz) instead");
 470                 }
 471             }
 472             hir::ParenthesizedParameters(_) => {
 473                 // For now, require that parenthetical notation be used
 474                 // only with `Fn()` etc.
 475                 if !self.tcx().sess.features.borrow().unboxed_closures && !trait_def.paren_sugar {
 476                     emit_feature_err(&self.tcx().sess.parse_sess,
 477                                      "unboxed_closures", span, GateIssue::Language,
 478                                      "\
 479                         parenthetical notation is only stable when used with `Fn`-family traits");
 480                 }
 481             }
 482         }
 483
 484         self.create_substs_for_ast_path(span,
 485                                         trait_def_id,
 486                                         &trait_segment.parameters,
 487                                         Some(self_ty))
 488     }
 489
 490     fn trait_defines_associated_type_named(&self,
 491                                            trait_def_id: DefId,
 492                                            assoc_name: ast::Name)
 493                                            -> bool
 494     {
 495         self.tcx().associated_items(trait_def_id).any(|item| {
 496             item.kind == ty::AssociatedKind::Type && item.name == assoc_name
 497         })
 498     }
 499
 500     fn ast_type_binding_to_poly_projection_predicate(
 501         &self,
 502         _path_id: ast::NodeId,
 503         trait_ref: ty::PolyTraitRef<'tcx>,
 504         binding: &ConvertedBinding<'tcx>)
 505         -> Result<ty::PolyProjectionPredicate<'tcx>, ErrorReported>
 506     {
 507         let tcx = self.tcx();
 508
 509         // Given something like `U : SomeTrait<T=X>`, we want to produce a
 510         // predicate like `<U as SomeTrait>::T = X`. This is somewhat
 511         // subtle in the event that `T` is defined in a supertrait of
 512         // `SomeTrait`, because in that case we need to upcast.
 513         //
 514         // That is, consider this case:
 515         //
 516         // ```
 517         // trait SubTrait : SuperTrait<int> { }
 518         // trait SuperTrait<A> { type T; }
 519         //
 520         // ... B : SubTrait<T=foo> ...
 521         // ```
 522         //
 523         // We want to produce `<B as SuperTrait<int>>::T == foo`.
 524
 525         // Find any late-bound regions declared in `ty` that are not
 526         // declared in the trait-ref. These are not wellformed.
 527         //
 528         // Example:
 529         //
 530         //     for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
 531         //     for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
 532         let late_bound_in_trait_ref = tcx.collect_constrained_late_bound_regions(&trait_ref);
 533         let late_bound_in_ty = tcx.collect_referenced_late_bound_regions(&ty::Binder(binding.ty));
 534         debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
 535         debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
 536         for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
 537             let br_name = match *br {
 538                 ty::BrNamed(_, name) => name,
 539                 _ => {
 540                     span_bug!(
 541                         binding.span,
 542                         "anonymous bound region {:?} in binding but not trait ref",
 543                         br);
 544                 }
 545             };
 546             struct_span_err!(tcx.sess,
 547                              binding.span,
 548                              E0582,
 549                              "binding for associated type `{}` references lifetime `{}`, \
 550                               which does not appear in the trait input types",
 551                              binding.item_name, br_name)
 552                 .emit();
 553         }
 554
 555         // Simple case: X is defined in the current trait.
 556         if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
 557             return Ok(trait_ref.map_bound(|trait_ref| {
 558                 ty::ProjectionPredicate {
 559                     projection_ty: ty::ProjectionTy {
 560                         trait_ref: trait_ref,
 561                         item_name: binding.item_name,
 562                     },
 563                     ty: binding.ty,
 564                 }
 565             }));
 566         }
 567
 568         // Otherwise, we have to walk through the supertraits to find
 569         // those that do.
 570         let candidates =
 571             traits::supertraits(tcx, trait_ref.clone())
 572             .filter(|r| self.trait_defines_associated_type_named(r.def_id(), binding.item_name));
 573
 574         let candidate = self.one_bound_for_assoc_type(candidates,
 575                                                       &trait_ref.to_string(),
 576                                                       &binding.item_name.as_str(),
 577                                                       binding.span)?;
 578
 579         Ok(candidate.map_bound(|trait_ref| {
 580             ty::ProjectionPredicate {
 581                 projection_ty: ty::ProjectionTy {
 582                     trait_ref: trait_ref,
 583                     item_name: binding.item_name,
 584                 },
 585                 ty: binding.ty,
 586             }
 587         }))
 588     }
 589
 590     fn ast_path_to_ty(&self,
 591         span: Span,
 592         did: DefId,
 593         item_segment: &hir::PathSegment)
 594         -> Ty<'tcx>
 595     {
 596         let substs = self.ast_path_substs_for_ty(span, did, item_segment);
 597         self.normalize_ty(
 598             span,
 599             self.tcx().at(span).type_of(did).subst(self.tcx(), substs)
 600         )
 601     }
 602
 603     /// Transform a PolyTraitRef into a PolyExistentialTraitRef by
 604     /// removing the dummy Self type (TRAIT_OBJECT_DUMMY_SELF).
 605     fn trait_ref_to_existential(&self, trait_ref: ty::TraitRef<'tcx>)
 606                                 -> ty::ExistentialTraitRef<'tcx> {
 607         assert_eq!(trait_ref.self_ty().sty, TRAIT_OBJECT_DUMMY_SELF);
 608         ty::ExistentialTraitRef::erase_self_ty(self.tcx(), trait_ref)
 609     }
 610
 611     fn conv_object_ty_poly_trait_ref(&self,
 612         span: Span,
 613         trait_bounds: &[hir::PolyTraitRef],
 614         lifetime: &hir::Lifetime)
 615         -> Ty<'tcx>
 616     {
 617         let tcx = self.tcx();
 618
 619         if trait_bounds.is_empty() {
 620             span_err!(tcx.sess, span, E0224,
 621                       "at least one non-builtin trait is required for an object type");
 622             return tcx.types.err;
 623         }
 624
 625         let mut projection_bounds = vec![];
 626         let dummy_self = tcx.mk_ty(TRAIT_OBJECT_DUMMY_SELF);
 627         let principal = self.instantiate_poly_trait_ref(&trait_bounds[0],
 628                                                         dummy_self,
 629                                                         &mut projection_bounds);
 630
 631         let (auto_traits, trait_bounds) = split_auto_traits(tcx, &trait_bounds[1..]);
 632
 633         if !trait_bounds.is_empty() {
 634             let b = &trait_bounds[0];
 635             let span = b.trait_ref.path.span;
 636             struct_span_err!(self.tcx().sess, span, E0225,
 637                 "only Send/Sync traits can be used as additional traits in a trait object")
 638                 .span_label(span, "non-Send/Sync additional trait")
 639                 .emit();
 640         }
 641
 642         // Erase the dummy_self (TRAIT_OBJECT_DUMMY_SELF) used above.
 643         let existential_principal = principal.map_bound(|trait_ref| {
 644             self.trait_ref_to_existential(trait_ref)
 645         });
 646         let existential_projections = projection_bounds.iter().map(|bound| {
 647             bound.map_bound(|b| {
 648                 let p = b.projection_ty;
 649                 ty::ExistentialProjection {
 650                     trait_ref: self.trait_ref_to_existential(p.trait_ref),
 651                     item_name: p.item_name,
 652                     ty: b.ty
 653                 }
 654             })
 655         });
 656
 657         // check that there are no gross object safety violations,
 658         // most importantly, that the supertraits don't contain Self,
 659         // to avoid ICE-s.
 660         let object_safety_violations =
 661             tcx.astconv_object_safety_violations(principal.def_id());
 662         if !object_safety_violations.is_empty() {
 663             tcx.report_object_safety_error(
 664                 span, principal.def_id(), object_safety_violations)
 665                 .emit();
 666             return tcx.types.err;
 667         }
 668
 669         let mut associated_types = FxHashSet::default();
 670         for tr in traits::supertraits(tcx, principal) {
 671             associated_types.extend(tcx.associated_items(tr.def_id())
 672                 .filter(|item| item.kind == ty::AssociatedKind::Type)
 673                 .map(|item| (tr.def_id(), item.name)));
 674         }
 675
 676         for projection_bound in &projection_bounds {
 677             let pair = (projection_bound.0.projection_ty.trait_ref.def_id,
 678                         projection_bound.0.projection_ty.item_name);
 679             associated_types.remove(&pair);
 680         }
 681
 682         for (trait_def_id, name) in associated_types {
 683             struct_span_err!(tcx.sess, span, E0191,
 684                 "the value of the associated type `{}` (from the trait `{}`) must be specified",
 685                         name,
 686                         tcx.item_path_str(trait_def_id))
 687                         .span_label(span, format!(
 688                             "missing associated type `{}` value", name))
 689                         .emit();
 690         }
 691
 692         let mut v =
 693             iter::once(ty::ExistentialPredicate::Trait(*existential_principal.skip_binder()))
 694             .chain(auto_traits.into_iter().map(ty::ExistentialPredicate::AutoTrait))
 695             .chain(existential_projections
 696                    .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())))
 697             .collect::<AccumulateVec<[_; 8]>>();
 698         v.sort_by(|a, b| a.cmp(tcx, b));
 699         let existential_predicates = ty::Binder(tcx.mk_existential_predicates(v.into_iter()));
 700
 701
 702         // Explicitly specified region bound. Use that.
 703         let region_bound = if !lifetime.is_elided() {
 704             self.ast_region_to_region(lifetime, None)
 705         } else {
 706             self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
 707                 if tcx.named_region_map.defs.contains_key(&lifetime.id) {
 708                     self.ast_region_to_region(lifetime, None)
 709                 } else {
 710                     self.re_infer(span, None).unwrap_or_else(|| {
 711                         span_err!(tcx.sess, span, E0228,
 712                                   "the lifetime bound for this object type cannot be deduced \
 713                                    from context; please supply an explicit bound");
 714                         tcx.types.re_static
 715                     })
 716                 }
 717             })
 718         };
 719
 720         debug!("region_bound: {:?}", region_bound);
 721
 722         let ty = tcx.mk_dynamic(existential_predicates, region_bound);
 723         debug!("trait_object_type: {:?}", ty);
 724         ty
 725     }
 726
 727     fn report_ambiguous_associated_type(&self,
 728                                         span: Span,
 729                                         type_str: &str,
 730                                         trait_str: &str,
 731                                         name: &str) {
 732         struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type")
 733             .span_label(span, "ambiguous associated type")
 734             .note(&format!("specify the type using the syntax `<{} as {}>::{}`",
 735                   type_str, trait_str, name))
 736             .emit();
 737
 738     }
 739
 740     // Search for a bound on a type parameter which includes the associated item
 741     // given by `assoc_name`. `ty_param_def_id` is the `DefId` for the type parameter
 742     // This function will fail if there are no suitable bounds or there is
 743     // any ambiguity.
 744     fn find_bound_for_assoc_item(&self,
 745                                  ty_param_def_id: DefId,
 746                                  assoc_name: ast::Name,
 747                                  span: Span)
 748                                  -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
 749     {
 750         let tcx = self.tcx();
 751
 752         let bounds: Vec<_> = self.get_type_parameter_bounds(span, ty_param_def_id)
 753             .predicates.into_iter().filter_map(|p| p.to_opt_poly_trait_ref()).collect();
 754
 755         // Check that there is exactly one way to find an associated type with the
 756         // correct name.
 757         let suitable_bounds =
 758             traits::transitive_bounds(tcx, &bounds)
 759             .filter(|b| self.trait_defines_associated_type_named(b.def_id(), assoc_name));
 760
 761         let param_node_id = tcx.hir.as_local_node_id(ty_param_def_id).unwrap();
 762         let param_name = tcx.hir.ty_param_name(param_node_id);
 763         self.one_bound_for_assoc_type(suitable_bounds,
 764                                       &param_name.as_str(),
 765                                       &assoc_name.as_str(),
 766                                       span)
 767     }
 768
 769
 770     // Checks that bounds contains exactly one element and reports appropriate
 771     // errors otherwise.
 772     fn one_bound_for_assoc_type<I>(&self,
 773                                 mut bounds: I,
 774                                 ty_param_name: &str,
 775                                 assoc_name: &str,
 776                                 span: Span)
 777         -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
 778         where I: Iterator<Item=ty::PolyTraitRef<'tcx>>
 779     {
 780         let bound = match bounds.next() {
 781             Some(bound) => bound,
 782             None => {
 783                 struct_span_err!(self.tcx().sess, span, E0220,
 784                           "associated type `{}` not found for `{}`",
 785                           assoc_name,
 786                           ty_param_name)
 787                   .span_label(span, format!("associated type `{}` not found", assoc_name))
 788                   .emit();
 789                 return Err(ErrorReported);
 790             }
 791         };
 792
 793         if let Some(bound2) = bounds.next() {
 794             let bounds = iter::once(bound).chain(iter::once(bound2)).chain(bounds);
 795             let mut err = struct_span_err!(
 796                 self.tcx().sess, span, E0221,
 797                 "ambiguous associated type `{}` in bounds of `{}`",
 798                 assoc_name,
 799                 ty_param_name);
 800             err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
 801
 802             for bound in bounds {
 803                 let bound_span = self.tcx().associated_items(bound.def_id()).find(|item| {
 804                     item.kind == ty::AssociatedKind::Type && item.name == assoc_name
 805                 })
 806                 .and_then(|item| self.tcx().hir.span_if_local(item.def_id));
 807
 808                 if let Some(span) = bound_span {
 809                     err.span_label(span, format!("ambiguous `{}` from `{}`",
 810                                                   assoc_name,
 811                                                   bound));
 812                 } else {
 813                     span_note!(&mut err, span,
 814                                "associated type `{}` could derive from `{}`",
 815                                ty_param_name,
 816                                bound);
 817                 }
 818             }
 819             err.emit();
 820         }
 821
 822         return Ok(bound);
 823     }
 824
 825     // Create a type from a path to an associated type.
 826     // For a path A::B::C::D, ty and ty_path_def are the type and def for A::B::C
 827     // and item_segment is the path segment for D. We return a type and a def for
 828     // the whole path.
 829     // Will fail except for T::A and Self::A; i.e., if ty/ty_path_def are not a type
 830     // parameter or Self.
 831     pub fn associated_path_def_to_ty(&self,
 832                                      ref_id: ast::NodeId,
 833                                      span: Span,
 834                                      ty: Ty<'tcx>,
 835                                      ty_path_def: Def,
 836                                      item_segment: &hir::PathSegment)
 837                                      -> (Ty<'tcx>, Def)
 838     {
 839         let tcx = self.tcx();
 840         let assoc_name = item_segment.name;
 841
 842         debug!("associated_path_def_to_ty: {:?}::{}", ty, assoc_name);
 843
 844         self.prohibit_type_params(slice::ref_slice(item_segment));
 845
 846         // Find the type of the associated item, and the trait where the associated
 847         // item is declared.
 848         let bound = match (&ty.sty, ty_path_def) {
 849             (_, Def::SelfTy(Some(_), Some(impl_def_id))) => {
 850                 // `Self` in an impl of a trait - we have a concrete self type and a
 851                 // trait reference.
 852                 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
 853                     Some(trait_ref) => trait_ref,
 854                     None => {
 855                         // A cycle error occurred, most likely.
 856                         return (tcx.types.err, Def::Err);
 857                     }
 858                 };
 859
 860                 let trait_ref = if let Some(free_substs) = self.get_free_substs() {
 861                     trait_ref.subst(tcx, free_substs)
 862                 } else {
 863                     trait_ref
 864                 };
 865
 866                 let candidates =
 867                     traits::supertraits(tcx, ty::Binder(trait_ref))
 868                     .filter(|r| self.trait_defines_associated_type_named(r.def_id(),
 869                                                                          assoc_name));
 870
 871                 match self.one_bound_for_assoc_type(candidates,
 872                                                     "Self",
 873                                                     &assoc_name.as_str(),
 874                                                     span) {
 875                     Ok(bound) => bound,
 876                     Err(ErrorReported) => return (tcx.types.err, Def::Err),
 877                 }
 878             }
 879             (&ty::TyParam(_), Def::SelfTy(Some(param_did), None)) |
 880             (&ty::TyParam(_), Def::TyParam(param_did)) => {
 881                 match self.find_bound_for_assoc_item(param_did, assoc_name, span) {
 882                     Ok(bound) => bound,
 883                     Err(ErrorReported) => return (tcx.types.err, Def::Err),
 884                 }
 885             }
 886             _ => {
 887                 // Don't print TyErr to the user.
 888                 if !ty.references_error() {
 889                     self.report_ambiguous_associated_type(span,
 890                                                           &ty.to_string(),
 891                                                           "Trait",
 892                                                           &assoc_name.as_str());
 893                 }
 894                 return (tcx.types.err, Def::Err);
 895             }
 896         };
 897
 898         let trait_did = bound.0.def_id;
 899         let ty = self.projected_ty_from_poly_trait_ref(span, bound, assoc_name);
 900         let ty = self.normalize_ty(span, ty);
 901
 902         let item = tcx.associated_items(trait_did).find(|i| i.name == assoc_name)
 903                                                   .expect("missing associated type");
 904         let def = Def::AssociatedTy(item.def_id);
 905         if !tcx.vis_is_accessible_from(item.vis, ref_id) {
 906             let msg = format!("{} `{}` is private", def.kind_name(), assoc_name);
 907             tcx.sess.span_err(span, &msg);
 908         }
 909         tcx.check_stability(item.def_id, ref_id, span);
 910
 911         (ty, def)
 912     }
 913
 914     fn qpath_to_ty(&self,
 915                    span: Span,
 916                    opt_self_ty: Option<Ty<'tcx>>,
 917                    trait_def_id: DefId,
 918                    trait_segment: &hir::PathSegment,
 919                    item_segment: &hir::PathSegment)
 920                    -> Ty<'tcx>
 921     {
 922         let tcx = self.tcx();
 923
 924         self.prohibit_type_params(slice::ref_slice(item_segment));
 925
 926         let self_ty = if let Some(ty) = opt_self_ty {
 927             ty
 928         } else {
 929             let path_str = tcx.item_path_str(trait_def_id);
 930             self.report_ambiguous_associated_type(span,
 931                                                   "Type",
 932                                                   &path_str,
 933                                                   &item_segment.name.as_str());
 934             return tcx.types.err;
 935         };
 936
 937         debug!("qpath_to_ty: self_type={:?}", self_ty);
 938
 939         let trait_ref = self.ast_path_to_mono_trait_ref(span,
 940                                                         trait_def_id,
 941                                                         self_ty,
 942                                                         trait_segment);
 943
 944         debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
 945
 946         self.normalize_ty(span, tcx.mk_projection(trait_ref, item_segment.name))
 947     }
 948
 949     pub fn prohibit_type_params(&self, segments: &[hir::PathSegment]) {
 950         for segment in segments {
 951             for typ in segment.parameters.types() {
 952                 struct_span_err!(self.tcx().sess, typ.span, E0109,
 953                                  "type parameters are not allowed on this type")
 954                     .span_label(typ.span, "type parameter not allowed")
 955                     .emit();
 956                 break;
 957             }
 958             for lifetime in segment.parameters.lifetimes() {
 959                 struct_span_err!(self.tcx().sess, lifetime.span, E0110,
 960                                  "lifetime parameters are not allowed on this type")
 961                     .span_label(lifetime.span,
 962                                 "lifetime parameter not allowed on this type")
 963                     .emit();
 964                 break;
 965             }
 966             for binding in segment.parameters.bindings() {
 967                 self.prohibit_projection(binding.span);
 968                 break;
 969             }
 970         }
 971     }
 972
 973     pub fn prohibit_projection(&self, span: Span) {
 974         let mut err = struct_span_err!(self.tcx().sess, span, E0229,
 975                                        "associated type bindings are not allowed here");
 976         err.span_label(span, "associate type not allowed here").emit();
 977     }
 978
 979     // Check a type Path and convert it to a Ty.
 980     pub fn def_to_ty(&self,
 981                      opt_self_ty: Option<Ty<'tcx>>,
 982                      path: &hir::Path,
 983                      permit_variants: bool)
 984                      -> Ty<'tcx> {
 985         let tcx = self.tcx();
 986
 987         debug!("base_def_to_ty(def={:?}, opt_self_ty={:?}, path_segments={:?})",
 988                path.def, opt_self_ty, path.segments);
 989
 990         let span = path.span;
 991         match path.def {
 992             Def::Enum(did) | Def::TyAlias(did) | Def::Struct(did) | Def::Union(did) => {
 993                 assert_eq!(opt_self_ty, None);
 994                 self.prohibit_type_params(path.segments.split_last().unwrap().1);
 995                 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
 996             }
 997             Def::Variant(did) if permit_variants => {
 998                 // Convert "variant type" as if it were a real type.
 999                 // The resulting `Ty` is type of the variant's enum for now.
1000                 assert_eq!(opt_self_ty, None);
1001                 self.prohibit_type_params(path.segments.split_last().unwrap().1);
1002                 self.ast_path_to_ty(span,
1003                                     tcx.parent_def_id(did).unwrap(),
1004                                     path.segments.last().unwrap())
1005             }
1006             Def::TyParam(did) => {
1007                 assert_eq!(opt_self_ty, None);
1008                 self.prohibit_type_params(&path.segments);
1009
1010                 let node_id = tcx.hir.as_local_node_id(did).unwrap();
1011                 let item_id = tcx.hir.get_parent_node(node_id);
1012                 let item_def_id = tcx.hir.local_def_id(item_id);
1013                 let generics = tcx.generics_of(item_def_id);
1014                 let index = generics.type_param_to_index[&tcx.hir.local_def_id(node_id).index];
1015                 tcx.mk_param(index, tcx.hir.name(node_id))
1016             }
1017             Def::SelfTy(_, Some(def_id)) => {
1018                 // Self in impl (we know the concrete type).
1019
1020                 assert_eq!(opt_self_ty, None);
1021                 self.prohibit_type_params(&path.segments);
1022
1023                 let ty = tcx.at(span).type_of(def_id);
1024                 if let Some(free_substs) = self.get_free_substs() {
1025                     ty.subst(tcx, free_substs)
1026                 } else {
1027                     ty
1028                 }
1029             }
1030             Def::SelfTy(Some(_), None) => {
1031                 // Self in trait.
1032                 assert_eq!(opt_self_ty, None);
1033                 self.prohibit_type_params(&path.segments);
1034                 tcx.mk_self_type()
1035             }
1036             Def::AssociatedTy(def_id) => {
1037                 self.prohibit_type_params(&path.segments[..path.segments.len()-2]);
1038                 let trait_did = tcx.parent_def_id(def_id).unwrap();
1039                 self.qpath_to_ty(span,
1040                                  opt_self_ty,
1041                                  trait_did,
1042                                  &path.segments[path.segments.len()-2],
1043                                  path.segments.last().unwrap())
1044             }
1045             Def::PrimTy(prim_ty) => {
1046                 assert_eq!(opt_self_ty, None);
1047                 self.prohibit_type_params(&path.segments);
1048                 match prim_ty {
1049                     hir::TyBool => tcx.types.bool,
1050                     hir::TyChar => tcx.types.char,
1051                     hir::TyInt(it) => tcx.mk_mach_int(it),
1052                     hir::TyUint(uit) => tcx.mk_mach_uint(uit),
1053                     hir::TyFloat(ft) => tcx.mk_mach_float(ft),
1054                     hir::TyStr => tcx.mk_str()
1055                 }
1056             }
1057             Def::Err => {
1058                 self.set_tainted_by_errors();
1059                 return self.tcx().types.err;
1060             }
1061             _ => span_bug!(span, "unexpected definition: {:?}", path.def)
1062         }
1063     }
1064
1065     /// Parses the programmer's textual representation of a type into our
1066     /// internal notion of a type.
1067     pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty) -> Ty<'tcx> {
1068         debug!("ast_ty_to_ty(id={:?}, ast_ty={:?})",
1069                ast_ty.id, ast_ty);
1070
1071         let tcx = self.tcx();
1072
1073         let result_ty = match ast_ty.node {
1074             hir::TySlice(ref ty) => {
1075                 tcx.mk_slice(self.ast_ty_to_ty(&ty))
1076             }
1077             hir::TyPtr(ref mt) => {
1078                 tcx.mk_ptr(ty::TypeAndMut {
1079                     ty: self.ast_ty_to_ty(&mt.ty),
1080                     mutbl: mt.mutbl
1081                 })
1082             }
1083             hir::TyRptr(ref region, ref mt) => {
1084                 let r = self.ast_region_to_region(region, None);
1085                 debug!("TyRef r={:?}", r);
1086                 let t = self.ast_ty_to_ty(&mt.ty);
1087                 tcx.mk_ref(r, ty::TypeAndMut {ty: t, mutbl: mt.mutbl})
1088             }
1089             hir::TyNever => {
1090                 tcx.types.never
1091             },
1092             hir::TyTup(ref fields) => {
1093                 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)), false)
1094             }
1095             hir::TyBareFn(ref bf) => {
1096                 require_c_abi_if_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
1097                 let bare_fn_ty = self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl);
1098
1099                 // Find any late-bound regions declared in return type that do
1100                 // not appear in the arguments. These are not wellformed.
1101                 //
1102                 // Example:
1103                 //
1104                 //     for<'a> fn() -> &'a str <-- 'a is bad
1105                 //     for<'a> fn(&'a String) -> &'a str <-- 'a is ok
1106                 //
1107                 // Note that we do this check **here** and not in
1108                 // `ty_of_bare_fn` because the latter is also used to make
1109                 // the types for fn items, and we do not want to issue a
1110                 // warning then. (Once we fix #32330, the regions we are
1111                 // checking for here would be considered early bound
1112                 // anyway.)
1113                 let inputs = bare_fn_ty.inputs();
1114                 let late_bound_in_args = tcx.collect_constrained_late_bound_regions(
1115                     &inputs.map_bound(|i| i.to_owned()));
1116                 let output = bare_fn_ty.output();
1117                 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
1118                 for br in late_bound_in_ret.difference(&late_bound_in_args) {
1119                     let br_name = match *br {
1120                         ty::BrNamed(_, name) => name,
1121                         _ => {
1122                             span_bug!(
1123                                 bf.decl.output.span(),
1124                                 "anonymous bound region {:?} in return but not args",
1125                                 br);
1126                         }
1127                     };
1128                     struct_span_err!(tcx.sess,
1129                                      ast_ty.span,
1130                                      E0581,
1131                                      "return type references lifetime `{}`, \
1132                                       which does not appear in the fn input types",
1133                                      br_name)
1134                         .emit();
1135                 }
1136                 tcx.mk_fn_ptr(bare_fn_ty)
1137             }
1138             hir::TyTraitObject(ref bounds, ref lifetime) => {
1139                 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
1140             }
1141             hir::TyImplTrait(_) => {
1142                 // Figure out if we can allow an `impl Trait` here, by walking up
1143                 // to a `fn` or inherent `impl` method, going only through `Ty`
1144                 // or `TraitRef` nodes (as nothing else should be in types) and
1145                 // ensuring that we reach the `fn`/method signature's return type.
1146                 let mut node_id = ast_ty.id;
1147                 let fn_decl = loop {
1148                     let parent = tcx.hir.get_parent_node(node_id);
1149                     match tcx.hir.get(parent) {
1150                         hir::map::NodeItem(&hir::Item {
1151                             node: hir::ItemFn(ref fn_decl, ..), ..
1152                         }) => break Some(fn_decl),
1153
1154                         hir::map::NodeImplItem(&hir::ImplItem {
1155                             node: hir::ImplItemKind::Method(ref sig, _), ..
1156                         }) => {
1157                             match tcx.hir.expect_item(tcx.hir.get_parent(parent)).node {
1158                                 hir::ItemImpl(.., None, _, _) => {
1159                                     break Some(&sig.decl)
1160                                 }
1161                                 _ => break None
1162                             }
1163                         }
1164
1165                         hir::map::NodeTy(_) | hir::map::NodeTraitRef(_) => {}
1166
1167                         _ => break None
1168                     }
1169                     node_id = parent;
1170                 };
1171                 let allow = fn_decl.map_or(false, |fd| {
1172                     match fd.output {
1173                         hir::DefaultReturn(_) => false,
1174                         hir::Return(ref ty) => ty.id == node_id
1175                     }
1176                 });
1177
1178                 // Create the anonymized type.
1179                 if allow {
1180                     let def_id = tcx.hir.local_def_id(ast_ty.id);
1181                     tcx.mk_anon(def_id, Substs::identity_for_item(tcx, def_id))
1182                 } else {
1183                     span_err!(tcx.sess, ast_ty.span, E0562,
1184                               "`impl Trait` not allowed outside of function \
1185                                and inherent method return types");
1186                     tcx.types.err
1187                 }
1188             }
1189             hir::TyPath(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
1190                 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
1191                 let opt_self_ty = maybe_qself.as_ref().map(|qself| {
1192                     self.ast_ty_to_ty(qself)
1193                 });
1194                 self.def_to_ty(opt_self_ty, path, false)
1195             }
1196             hir::TyPath(hir::QPath::TypeRelative(ref qself, ref segment)) => {
1197                 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
1198                 let ty = self.ast_ty_to_ty(qself);
1199
1200                 let def = if let hir::TyPath(hir::QPath::Resolved(_, ref path)) = qself.node {
1201                     path.def
1202                 } else {
1203                     Def::Err
1204                 };
1205                 self.associated_path_def_to_ty(ast_ty.id, ast_ty.span, ty, def, segment).0
1206             }
1207             hir::TyArray(ref ty, length) => {
1208                 if let Ok(length) = eval_length(tcx, length, "array length") {
1209                     tcx.mk_array(self.ast_ty_to_ty(&ty), length)
1210                 } else {
1211                     self.tcx().types.err
1212                 }
1213             }
1214             hir::TyTypeof(ref _e) => {
1215                 struct_span_err!(tcx.sess, ast_ty.span, E0516,
1216                                  "`typeof` is a reserved keyword but unimplemented")
1217                     .span_label(ast_ty.span, "reserved keyword")
1218                     .emit();
1219
1220                 tcx.types.err
1221             }
1222             hir::TyInfer => {
1223                 // TyInfer also appears as the type of arguments or return
1224                 // values in a ExprClosure, or as
1225                 // the type of local variables. Both of these cases are
1226                 // handled specially and will not descend into this routine.
1227                 self.ty_infer(ast_ty.span)
1228             }
1229             hir::TyErr => {
1230                 tcx.types.err
1231             }
1232         };
1233
1234         result_ty
1235     }
1236
1237     pub fn ty_of_arg(&self,
1238                      ty: &hir::Ty,
1239                      expected_ty: Option<Ty<'tcx>>)
1240                      -> Ty<'tcx>
1241     {
1242         match ty.node {
1243             hir::TyInfer if expected_ty.is_some() => expected_ty.unwrap(),
1244             hir::TyInfer => self.ty_infer(ty.span),
1245             _ => self.ast_ty_to_ty(ty),
1246         }
1247     }
1248
1249     pub fn ty_of_fn(&self,
1250                     unsafety: hir::Unsafety,
1251                     abi: abi::Abi,
1252                     decl: &hir::FnDecl)
1253                     -> ty::PolyFnSig<'tcx> {
1254         debug!("ty_of_fn");
1255
1256         let input_tys: Vec<Ty> =
1257             decl.inputs.iter().map(|a| self.ty_of_arg(a, None)).collect();
1258
1259         let output_ty = match decl.output {
1260             hir::Return(ref output) => self.ast_ty_to_ty(output),
1261             hir::DefaultReturn(..) => self.tcx().mk_nil(),
1262         };
1263
1264         debug!("ty_of_fn: output_ty={:?}", output_ty);
1265
1266         ty::Binder(self.tcx().mk_fn_sig(
1267             input_tys.into_iter(),
1268             output_ty,
1269             decl.variadic,
1270             unsafety,
1271             abi
1272         ))
1273     }
1274
1275     pub fn ty_of_closure(&self,
1276         unsafety: hir::Unsafety,
1277         decl: &hir::FnDecl,
1278         abi: abi::Abi,
1279         expected_sig: Option<ty::FnSig<'tcx>>)
1280         -> ty::PolyFnSig<'tcx>
1281     {
1282         debug!("ty_of_closure(expected_sig={:?})",
1283                expected_sig);
1284
1285         let input_tys = decl.inputs.iter().enumerate().map(|(i, a)| {
1286             let expected_arg_ty = expected_sig.as_ref().and_then(|e| {
1287                 // no guarantee that the correct number of expected args
1288                 // were supplied
1289                 if i < e.inputs().len() {
1290                     Some(e.inputs()[i])
1291                 } else {
1292                     None
1293                 }
1294             });
1295             self.ty_of_arg(a, expected_arg_ty)
1296         });
1297
1298         let expected_ret_ty = expected_sig.as_ref().map(|e| e.output());
1299
1300         let is_infer = match decl.output {
1301             hir::Return(ref output) if output.node == hir::TyInfer => true,
1302             hir::DefaultReturn(..) => true,
1303             _ => false
1304         };
1305
1306         let output_ty = match decl.output {
1307             _ if is_infer && expected_ret_ty.is_some() =>
1308                 expected_ret_ty.unwrap(),
1309             _ if is_infer => self.ty_infer(decl.output.span()),
1310             hir::Return(ref output) =>
1311                 self.ast_ty_to_ty(&output),
1312             hir::DefaultReturn(..) => bug!(),
1313         };
1314
1315         debug!("ty_of_closure: output_ty={:?}", output_ty);
1316
1317         ty::Binder(self.tcx().mk_fn_sig(
1318             input_tys,
1319             output_ty,
1320             decl.variadic,
1321             unsafety,
1322             abi
1323         ))
1324     }
1325
1326     /// Given the bounds on an object, determines what single region bound (if any) we can
1327     /// use to summarize this type. The basic idea is that we will use the bound the user
1328     /// provided, if they provided one, and otherwise search the supertypes of trait bounds
1329     /// for region bounds. It may be that we can derive no bound at all, in which case
1330     /// we return `None`.
1331     fn compute_object_lifetime_bound(&self,
1332         span: Span,
1333         existential_predicates: ty::Binder<&'tcx ty::Slice<ty::ExistentialPredicate<'tcx>>>)
1334         -> Option<ty::Region<'tcx>> // if None, use the default
1335     {
1336         let tcx = self.tcx();
1337
1338         debug!("compute_opt_region_bound(existential_predicates={:?})",
1339                existential_predicates);
1340
1341         // No explicit region bound specified. Therefore, examine trait
1342         // bounds and see if we can derive region bounds from those.
1343         let derived_region_bounds =
1344             object_region_bounds(tcx, existential_predicates);
1345
1346         // If there are no derived region bounds, then report back that we
1347         // can find no region bound. The caller will use the default.
1348         if derived_region_bounds.is_empty() {
1349             return None;
1350         }
1351
1352         // If any of the derived region bounds are 'static, that is always
1353         // the best choice.
1354         if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
1355             return Some(tcx.types.re_static);
1356         }
1357
1358         // Determine whether there is exactly one unique region in the set
1359         // of derived region bounds. If so, use that. Otherwise, report an
1360         // error.
1361         let r = derived_region_bounds[0];
1362         if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
1363             span_err!(tcx.sess, span, E0227,
1364                       "ambiguous lifetime bound, explicit lifetime bound required");
1365         }
1366         return Some(r);
1367     }
1368 }
1369
1370 /// Divides a list of general trait bounds into two groups: builtin bounds (Sync/Send) and the
1371 /// remaining general trait bounds.
1372 fn split_auto_traits<'a, 'b, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
1373                                          trait_bounds: &'b [hir::PolyTraitRef])
1374     -> (Vec<DefId>, Vec<&'b hir::PolyTraitRef>)
1375 {
1376     let (auto_traits, trait_bounds): (Vec<_>, _) = trait_bounds.iter().partition(|bound| {
1377         match bound.trait_ref.path.def {
1378             Def::Trait(trait_did) => {
1379                 // Checks whether `trait_did` refers to one of the builtin
1380                 // traits, like `Send`, and adds it to `auto_traits` if so.
1381                 if Some(trait_did) == tcx.lang_items.send_trait() ||
1382                     Some(trait_did) == tcx.lang_items.sync_trait() {
1383                     let segments = &bound.trait_ref.path.segments;
1384                     let parameters = &segments[segments.len() - 1].parameters;
1385                     if !parameters.types().is_empty() {
1386                         check_type_argument_count(tcx, bound.trait_ref.path.span,
1387                                                   parameters.types().len(), &[]);
1388                     }
1389                     if !parameters.lifetimes().is_empty() {
1390                         report_lifetime_number_error(tcx, bound.trait_ref.path.span,
1391                                                      parameters.lifetimes().len(), 0);
1392                     }
1393                     true
1394                 } else {
1395                     false
1396                 }
1397             }
1398             _ => false
1399         }
1400     });
1401
1402     let auto_traits = auto_traits.into_iter().map(|tr| {
1403         if let Def::Trait(trait_did) = tr.trait_ref.path.def {
1404             trait_did
1405         } else {
1406             unreachable!()
1407         }
1408     }).collect::<Vec<_>>();
1409
1410     (auto_traits, trait_bounds)
1411 }
1412
1413 fn check_type_argument_count(tcx: TyCtxt, span: Span, supplied: usize,
1414                              ty_param_defs: &[ty::TypeParameterDef]) {
1415     let accepted = ty_param_defs.len();
1416     let required = ty_param_defs.iter().take_while(|x| !x.has_default).count();
1417     if supplied < required {
1418         let expected = if required < accepted {
1419             "expected at least"
1420         } else {
1421             "expected"
1422         };
1423         let arguments_plural = if required == 1 { "" } else { "s" };
1424
1425         struct_span_err!(tcx.sess, span, E0243,
1426                 "wrong number of type arguments: {} {}, found {}",
1427                 expected, required, supplied)
1428             .span_label(span,
1429                 format!("{} {} type argument{}",
1430                     expected,
1431                     required,
1432                     arguments_plural))
1433             .emit();
1434     } else if supplied > accepted {
1435         let expected = if required < accepted {
1436             format!("expected at most {}", accepted)
1437         } else {
1438             format!("expected {}", accepted)
1439         };
1440         let arguments_plural = if accepted == 1 { "" } else { "s" };
1441
1442         struct_span_err!(tcx.sess, span, E0244,
1443                 "wrong number of type arguments: {}, found {}",
1444                 expected, supplied)
1445             .span_label(
1446                 span,
1447                 format!("{} type argument{}",
1448                     if accepted == 0 { "expected no" } else { &expected },
1449                     arguments_plural)
1450             )
1451             .emit();
1452     }
1453 }
1454
1455 fn report_lifetime_number_error(tcx: TyCtxt, span: Span, number: usize, expected: usize) {
1456     let label = if number < expected {
1457         if expected == 1 {
1458             format!("expected {} lifetime parameter", expected)
1459         } else {
1460             format!("expected {} lifetime parameters", expected)
1461         }
1462     } else {
1463         let additional = number - expected;
1464         if additional == 1 {
1465             "unexpected lifetime parameter".to_string()
1466         } else {
1467             format!("{} unexpected lifetime parameters", additional)
1468         }
1469     };
1470     struct_span_err!(tcx.sess, span, E0107,
1471                      "wrong number of lifetime parameters: expected {}, found {}",
1472                      expected, number)
1473         .span_label(span, label)
1474         .emit();
1475 }
1476
1477 // A helper struct for conveniently grouping a set of bounds which we pass to
1478 // and return from functions in multiple places.
1479 #[derive(PartialEq, Eq, Clone, Debug)]
1480 pub struct Bounds<'tcx> {
1481     pub region_bounds: Vec<ty::Region<'tcx>>,
1482     pub implicitly_sized: bool,
1483     pub trait_bounds: Vec<ty::PolyTraitRef<'tcx>>,
1484     pub projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>,
1485 }
1486
1487 impl<'a, 'gcx, 'tcx> Bounds<'tcx> {
1488     pub fn predicates(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, param_ty: Ty<'tcx>)
1489                       -> Vec<ty::Predicate<'tcx>>
1490     {
1491         let mut vec = Vec::new();
1492
1493         // If it could be sized, and is, add the sized predicate
1494         if self.implicitly_sized {
1495             if let Some(sized) = tcx.lang_items.sized_trait() {
1496                 let trait_ref = ty::TraitRef {
1497                     def_id: sized,
1498                     substs: tcx.mk_substs_trait(param_ty, &[])
1499                 };
1500                 vec.push(trait_ref.to_predicate());
1501             }
1502         }
1503
1504         for &region_bound in &self.region_bounds {
1505             // account for the binder being introduced below; no need to shift `param_ty`
1506             // because, at present at least, it can only refer to early-bound regions
1507             let region_bound = tcx.mk_region(ty::fold::shift_region(*region_bound, 1));
1508             vec.push(ty::Binder(ty::OutlivesPredicate(param_ty, region_bound)).to_predicate());
1509         }
1510
1511         for bound_trait_ref in &self.trait_bounds {
1512             vec.push(bound_trait_ref.to_predicate());
1513         }
1514
1515         for projection in &self.projection_bounds {
1516             vec.push(projection.to_predicate());
1517         }
1518
1519         vec
1520     }
1521 }
1522
1523 pub enum ExplicitSelf<'tcx> {
1524     ByValue,
1525     ByReference(ty::Region<'tcx>, hir::Mutability),
1526     ByBox
1527 }
1528
1529 impl<'tcx> ExplicitSelf<'tcx> {
1530     /// We wish to (for now) categorize an explicit self
1531     /// declaration like `self: SomeType` into either `self`,
1532     /// `&self`, `&mut self`, or `Box<self>`. We do this here
1533     /// by some simple pattern matching. A more precise check
1534     /// is done later in `check_method_self_type()`.
1535     ///
1536     /// Examples:
1537     ///
1538     /// ```
1539     /// impl Foo for &T {
1540     ///     // Legal declarations:
1541     ///     fn method1(self: &&T); // ExplicitSelf::ByReference
1542     ///     fn method2(self: &T); // ExplicitSelf::ByValue
1543     ///     fn method3(self: Box<&T>); // ExplicitSelf::ByBox
1544     ///
1545     ///     // Invalid cases will be caught later by `check_method_self_type`:
1546     ///     fn method_err1(self: &mut T); // ExplicitSelf::ByReference
1547     /// }
1548     /// ```
1549     ///
1550     /// To do the check we just count the number of "modifiers"
1551     /// on each type and compare them. If they are the same or
1552     /// the impl has more, we call it "by value". Otherwise, we
1553     /// look at the outermost modifier on the method decl and
1554     /// call it by-ref, by-box as appropriate. For method1, for
1555     /// example, the impl type has one modifier, but the method
1556     /// type has two, so we end up with
1557     /// ExplicitSelf::ByReference.
1558     pub fn determine(untransformed_self_ty: Ty<'tcx>,
1559                      self_arg_ty: Ty<'tcx>)
1560                      -> ExplicitSelf<'tcx> {
1561         fn count_modifiers(ty: Ty) -> usize {
1562             match ty.sty {
1563                 ty::TyRef(_, mt) => count_modifiers(mt.ty) + 1,
1564                 ty::TyAdt(def, _) if def.is_box() => count_modifiers(ty.boxed_ty()) + 1,
1565                 _ => 0,
1566             }
1567         }
1568
1569         let impl_modifiers = count_modifiers(untransformed_self_ty);
1570         let method_modifiers = count_modifiers(self_arg_ty);
1571
1572         if impl_modifiers >= method_modifiers {
1573             ExplicitSelf::ByValue
1574         } else {
1575             match self_arg_ty.sty {
1576                 ty::TyRef(r, mt) => ExplicitSelf::ByReference(r, mt.mutbl),
1577                 ty::TyAdt(def, _) if def.is_box() => ExplicitSelf::ByBox,
1578                 _ => ExplicitSelf::ByValue,
1579             }
1580         }
1581     }
1582 }