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::{NodeMap, FxHashSet};
  29
  30 use std::cell::RefCell;
  31 use std::iter;
  32 use syntax::{abi, ast};
  33 use syntax::feature_gate::{GateIssue, emit_feature_err};
  34 use syntax::symbol::Symbol;
  35 use syntax_pos::Span;
  36
  37 pub trait AstConv<'gcx, 'tcx> {
  38     fn tcx<'a>(&'a self) -> TyCtxt<'a, 'gcx, 'tcx>;
  39
  40     /// A cache used for the result of `ast_ty_to_ty_cache`
  41     fn ast_ty_to_ty_cache(&self) -> &RefCell<NodeMap<Ty<'tcx>>>;
  42
  43     /// Returns the set of bounds in scope for the type parameter with
  44     /// the given id.
  45     fn get_type_parameter_bounds(&self, span: Span, def_id: DefId)
  46                                  -> ty::GenericPredicates<'tcx>;
  47
  48     /// Return an (optional) substitution to convert bound type parameters that
  49     /// are in scope into free ones. This function should only return Some
  50     /// within a fn body.
  51     /// See ParameterEnvironment::free_substs for more information.
  52     fn get_free_substs(&self) -> Option<&Substs<'tcx>>;
  53
  54     /// What lifetime should we use when a lifetime is omitted (and not elided)?
  55     fn re_infer(&self, span: Span, _def: Option<&ty::RegionParameterDef>)
  56                 -> Option<&'tcx ty::Region>;
  57
  58     /// What type should we use when a type is omitted?
  59     fn ty_infer(&self, span: Span) -> Ty<'tcx>;
  60
  61     /// Same as ty_infer, but with a known type parameter definition.
  62     fn ty_infer_for_def(&self,
  63                         _def: &ty::TypeParameterDef,
  64                         _substs: &[Kind<'tcx>],
  65                         span: Span) -> Ty<'tcx> {
  66         self.ty_infer(span)
  67     }
  68
  69     /// Projecting an associated type from a (potentially)
  70     /// higher-ranked trait reference is more complicated, because of
  71     /// the possibility of late-bound regions appearing in the
  72     /// associated type binding. This is not legal in function
  73     /// signatures for that reason. In a function body, we can always
  74     /// handle it because we can use inference variables to remove the
  75     /// late-bound regions.
  76     fn projected_ty_from_poly_trait_ref(&self,
  77                                         span: Span,
  78                                         poly_trait_ref: ty::PolyTraitRef<'tcx>,
  79                                         item_name: ast::Name)
  80                                         -> Ty<'tcx>;
  81
  82     /// Normalize an associated type coming from the user.
  83     fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
  84
  85     /// Invoked when we encounter an error from some prior pass
  86     /// (e.g. resolve) that is translated into a ty-error. This is
  87     /// used to help suppress derived errors typeck might otherwise
  88     /// report.
  89     fn set_tainted_by_errors(&self);
  90 }
  91
  92 struct ConvertedBinding<'tcx> {
  93     item_name: ast::Name,
  94     ty: Ty<'tcx>,
  95     span: Span,
  96 }
  97
  98 /// Dummy type used for the `Self` of a `TraitRef` created for converting
  99 /// a trait object, and which gets removed in `ExistentialTraitRef`.
 100 /// This type must not appear anywhere in other converted types.
 101 const TRAIT_OBJECT_DUMMY_SELF: ty::TypeVariants<'static> = ty::TyInfer(ty::FreshTy(0));
 102
 103 impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
 104     pub fn ast_region_to_region(&self,
 105         lifetime: &hir::Lifetime,
 106         def: Option<&ty::RegionParameterDef>)
 107         -> &'tcx ty::Region
 108     {
 109         let tcx = self.tcx();
 110         let r = match tcx.named_region_map.defs.get(&lifetime.id) {
 111             Some(&rl::Region::Static) => {
 112                 tcx.types.re_static
 113             }
 114
 115             Some(&rl::Region::LateBound(debruijn, id)) => {
 116                 let name = tcx.hir.name(id);
 117                 tcx.mk_region(ty::ReLateBound(debruijn,
 118                     ty::BrNamed(tcx.hir.local_def_id(id), name)))
 119             }
 120
 121             Some(&rl::Region::LateBoundAnon(debruijn, index)) => {
 122                 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
 123             }
 124
 125             Some(&rl::Region::EarlyBound(index, id)) => {
 126                 let name = tcx.hir.name(id);
 127                 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
 128                     index: index,
 129                     name: name
 130                 }))
 131             }
 132
 133             Some(&rl::Region::Free(scope, id)) => {
 134                 let name = tcx.hir.name(id);
 135                 tcx.mk_region(ty::ReFree(ty::FreeRegion {
 136                     scope: scope.to_code_extent(&tcx.region_maps),
 137                     bound_region: ty::BrNamed(tcx.hir.local_def_id(id), name)
 138                 }))
 139
 140                     // (*) -- not late-bound, won't change
 141             }
 142
 143             None => {
 144                 self.re_infer(lifetime.span, def).expect("unelided lifetime in signature")
 145             }
 146         };
 147
 148         debug!("ast_region_to_region(lifetime={:?}) yields {:?}",
 149                 lifetime,
 150                 r);
 151
 152         r
 153     }
 154
 155     /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
 156     /// returns an appropriate set of substitutions for this particular reference to `I`.
 157     pub fn ast_path_substs_for_ty(&self,
 158         span: Span,
 159         def_id: DefId,
 160         item_segment: &hir::PathSegment)
 161         -> &'tcx Substs<'tcx>
 162     {
 163         let tcx = self.tcx();
 164
 165         match item_segment.parameters {
 166             hir::AngleBracketedParameters(_) => {}
 167             hir::ParenthesizedParameters(..) => {
 168                 struct_span_err!(tcx.sess, span, E0214,
 169                           "parenthesized parameters may only be used with a trait")
 170                     .span_label(span, &format!("only traits may use parentheses"))
 171                     .emit();
 172
 173                 return Substs::for_item(tcx, def_id, |_, _| {
 174                     tcx.types.re_static
 175                 }, |_, _| {
 176                     tcx.types.err
 177                 });
 178             }
 179         }
 180
 181         let (substs, assoc_bindings) =
 182             self.create_substs_for_ast_path(span,
 183                                             def_id,
 184                                             &item_segment.parameters,
 185                                             None);
 186
 187         assoc_bindings.first().map(|b| self.prohibit_projection(b.span));
 188
 189         substs
 190     }
 191
 192     /// Given the type/region arguments provided to some path (along with
 193     /// an implicit Self, if this is a trait reference) returns the complete
 194     /// set of substitutions. This may involve applying defaulted type parameters.
 195     ///
 196     /// Note that the type listing given here is *exactly* what the user provided.
 197     fn create_substs_for_ast_path(&self,
 198         span: Span,
 199         def_id: DefId,
 200         parameters: &hir::PathParameters,
 201         self_ty: Option<Ty<'tcx>>)
 202         -> (&'tcx Substs<'tcx>, Vec<ConvertedBinding<'tcx>>)
 203     {
 204         let tcx = self.tcx();
 205
 206         debug!("create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
 207                parameters={:?})",
 208                def_id, self_ty, parameters);
 209
 210         let (lifetimes, num_types_provided, infer_types) = match *parameters {
 211             hir::AngleBracketedParameters(ref data) => {
 212                 (&data.lifetimes[..], data.types.len(), data.infer_types)
 213             }
 214             hir::ParenthesizedParameters(_) => (&[][..], 1, false)
 215         };
 216
 217         // If the type is parameterized by this region, then replace this
 218         // region with the current anon region binding (in other words,
 219         // whatever & would get replaced with).
 220         let decl_generics = tcx.item_generics(def_id);
 221         let expected_num_region_params = decl_generics.regions.len();
 222         let supplied_num_region_params = lifetimes.len();
 223         if expected_num_region_params != supplied_num_region_params {
 224             report_lifetime_number_error(tcx, span,
 225                                          supplied_num_region_params,
 226                                          expected_num_region_params);
 227         }
 228
 229         // If a self-type was declared, one should be provided.
 230         assert_eq!(decl_generics.has_self, self_ty.is_some());
 231
 232         // Check the number of type parameters supplied by the user.
 233         let ty_param_defs = &decl_generics.types[self_ty.is_some() as usize..];
 234         if !infer_types || num_types_provided > ty_param_defs.len() {
 235             check_type_argument_count(tcx, span, num_types_provided, ty_param_defs);
 236         }
 237
 238         let is_object = self_ty.map_or(false, |ty| ty.sty == TRAIT_OBJECT_DUMMY_SELF);
 239         let default_needs_object_self = |p: &ty::TypeParameterDef| {
 240             if is_object && p.has_default {
 241                 if ty::queries::ty::get(tcx, span, p.def_id).has_self_ty() {
 242                     // There is no suitable inference default for a type parameter
 243                     // that references self, in an object type.
 244                     return true;
 245                 }
 246             }
 247
 248             false
 249         };
 250
 251         let mut output_assoc_binding = None;
 252         let substs = Substs::for_item(tcx, def_id, |def, _| {
 253             let i = def.index as usize - self_ty.is_some() as usize;
 254             if let Some(lifetime) = lifetimes.get(i) {
 255                 self.ast_region_to_region(lifetime, Some(def))
 256             } else {
 257                 tcx.types.re_static
 258             }
 259         }, |def, substs| {
 260             let i = def.index as usize;
 261
 262             // Handle Self first, so we can adjust the index to match the AST.
 263             if let (0, Some(ty)) = (i, self_ty) {
 264                 return ty;
 265             }
 266
 267             let i = i - self_ty.is_some() as usize - decl_generics.regions.len();
 268             if i < num_types_provided {
 269                 // A provided type parameter.
 270                 match *parameters {
 271                     hir::AngleBracketedParameters(ref data) => {
 272                         self.ast_ty_to_ty(&data.types[i])
 273                     }
 274                     hir::ParenthesizedParameters(ref data) => {
 275                         assert_eq!(i, 0);
 276                         let (ty, assoc) = self.convert_parenthesized_parameters(data);
 277                         output_assoc_binding = Some(assoc);
 278                         ty
 279                     }
 280                 }
 281             } else if infer_types {
 282                 // No type parameters were provided, we can infer all.
 283                 let ty_var = if !default_needs_object_self(def) {
 284                     self.ty_infer_for_def(def, substs, span)
 285                 } else {
 286                     self.ty_infer(span)
 287                 };
 288                 ty_var
 289             } else if def.has_default {
 290                 // No type parameter provided, but a default exists.
 291
 292                 // If we are converting an object type, then the
 293                 // `Self` parameter is unknown. However, some of the
 294                 // other type parameters may reference `Self` in their
 295                 // defaults. This will lead to an ICE if we are not
 296                 // careful!
 297                 if default_needs_object_self(def) {
 298                     struct_span_err!(tcx.sess, span, E0393,
 299                                      "the type parameter `{}` must be explicitly specified",
 300                                      def.name)
 301                         .span_label(span, &format!("missing reference to `{}`", def.name))
 302                         .note(&format!("because of the default `Self` reference, \
 303                                         type parameters must be specified on object types"))
 304                         .emit();
 305                     tcx.types.err
 306                 } else {
 307                     // This is a default type parameter.
 308                     self.normalize_ty(
 309                         span,
 310                         ty::queries::ty::get(tcx, span, def.def_id)
 311                             .subst_spanned(tcx, substs, Some(span))
 312                     )
 313                 }
 314             } else {
 315                 // We've already errored above about the mismatch.
 316                 tcx.types.err
 317             }
 318         });
 319
 320         let assoc_bindings = match *parameters {
 321             hir::AngleBracketedParameters(ref data) => {
 322                 data.bindings.iter().map(|b| {
 323                     ConvertedBinding {
 324                         item_name: b.name,
 325                         ty: self.ast_ty_to_ty(&b.ty),
 326                         span: b.span
 327                     }
 328                 }).collect()
 329             }
 330             hir::ParenthesizedParameters(ref data) => {
 331                 vec![output_assoc_binding.unwrap_or_else(|| {
 332                     // This is an error condition, but we should
 333                     // get the associated type binding anyway.
 334                     self.convert_parenthesized_parameters(data).1
 335                 })]
 336             }
 337         };
 338
 339         debug!("create_substs_for_ast_path(decl_generics={:?}, self_ty={:?}) -> {:?}",
 340                decl_generics, self_ty, substs);
 341
 342         (substs, assoc_bindings)
 343     }
 344
 345     fn convert_parenthesized_parameters(&self,
 346                                         data: &hir::ParenthesizedParameterData)
 347                                         -> (Ty<'tcx>, ConvertedBinding<'tcx>)
 348     {
 349         let inputs = self.tcx().mk_type_list(data.inputs.iter().map(|a_t| {
 350             self.ast_ty_to_ty(a_t)
 351         }));
 352
 353         let (output, output_span) = match data.output {
 354             Some(ref output_ty) => {
 355                 (self.ast_ty_to_ty(output_ty), output_ty.span)
 356             }
 357             None => {
 358                 (self.tcx().mk_nil(), data.span)
 359             }
 360         };
 361
 362         let output_binding = ConvertedBinding {
 363             item_name: Symbol::intern(FN_OUTPUT_NAME),
 364             ty: output,
 365             span: output_span
 366         };
 367
 368         (self.tcx().mk_ty(ty::TyTuple(inputs, false)), output_binding)
 369     }
 370
 371     /// Instantiates the path for the given trait reference, assuming that it's
 372     /// bound to a valid trait type. Returns the def_id for the defining trait.
 373     /// Fails if the type is a type other than a trait type.
 374     ///
 375     /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T=X>`
 376     /// are disallowed. Otherwise, they are pushed onto the vector given.
 377     pub fn instantiate_mono_trait_ref(&self,
 378         trait_ref: &hir::TraitRef,
 379         self_ty: Ty<'tcx>)
 380         -> ty::TraitRef<'tcx>
 381     {
 382         let trait_def_id = self.trait_def_id(trait_ref);
 383         self.ast_path_to_mono_trait_ref(trait_ref.path.span,
 384                                         trait_def_id,
 385                                         self_ty,
 386                                         trait_ref.path.segments.last().unwrap())
 387     }
 388
 389     fn trait_def_id(&self, trait_ref: &hir::TraitRef) -> DefId {
 390         let path = &trait_ref.path;
 391         match path.def {
 392             Def::Trait(trait_def_id) => trait_def_id,
 393             Def::Err => {
 394                 self.tcx().sess.fatal("cannot continue compilation due to previous error");
 395             }
 396             _ => {
 397                 span_fatal!(self.tcx().sess, path.span, E0245, "`{}` is not a trait",
 398                             self.tcx().hir.node_to_pretty_string(trait_ref.ref_id));
 399             }
 400         }
 401     }
 402
 403     pub fn instantiate_poly_trait_ref(&self,
 404         ast_trait_ref: &hir::PolyTraitRef,
 405         self_ty: Ty<'tcx>,
 406         poly_projections: &mut Vec<ty::PolyProjectionPredicate<'tcx>>)
 407         -> ty::PolyTraitRef<'tcx>
 408     {
 409         let trait_ref = &ast_trait_ref.trait_ref;
 410         let trait_def_id = self.trait_def_id(trait_ref);
 411
 412         debug!("ast_path_to_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
 413
 414         let (substs, assoc_bindings) =
 415             self.create_substs_for_ast_trait_ref(trait_ref.path.span,
 416                                                  trait_def_id,
 417                                                  self_ty,
 418                                                  trait_ref.path.segments.last().unwrap());
 419         let poly_trait_ref = ty::Binder(ty::TraitRef::new(trait_def_id, substs));
 420
 421         poly_projections.extend(assoc_bindings.iter().filter_map(|binding| {
 422             // specify type to assert that error was already reported in Err case:
 423             let predicate: Result<_, ErrorReported> =
 424                 self.ast_type_binding_to_poly_projection_predicate(trait_ref.ref_id,
 425                                                                    poly_trait_ref,
 426                                                                    binding);
 427             predicate.ok() // ok to ignore Err() because ErrorReported (see above)
 428         }));
 429
 430         debug!("ast_path_to_poly_trait_ref({:?}, projections={:?}) -> {:?}",
 431                trait_ref, poly_projections, poly_trait_ref);
 432         poly_trait_ref
 433     }
 434
 435     fn ast_path_to_mono_trait_ref(&self,
 436                                   span: Span,
 437                                   trait_def_id: DefId,
 438                                   self_ty: Ty<'tcx>,
 439                                   trait_segment: &hir::PathSegment)
 440                                   -> ty::TraitRef<'tcx>
 441     {
 442         let (substs, assoc_bindings) =
 443             self.create_substs_for_ast_trait_ref(span,
 444                                                  trait_def_id,
 445                                                  self_ty,
 446                                                  trait_segment);
 447         assoc_bindings.first().map(|b| self.prohibit_projection(b.span));
 448         ty::TraitRef::new(trait_def_id, substs)
 449     }
 450
 451     fn create_substs_for_ast_trait_ref(&self,
 452                                        span: Span,
 453                                        trait_def_id: DefId,
 454                                        self_ty: Ty<'tcx>,
 455                                        trait_segment: &hir::PathSegment)
 456                                        -> (&'tcx Substs<'tcx>, Vec<ConvertedBinding<'tcx>>)
 457     {
 458         debug!("create_substs_for_ast_trait_ref(trait_segment={:?})",
 459                trait_segment);
 460
 461         let trait_def = self.tcx().lookup_trait_def(trait_def_id);
 462
 463         match trait_segment.parameters {
 464             hir::AngleBracketedParameters(_) => {
 465                 // For now, require that parenthetical notation be used
 466                 // only with `Fn()` etc.
 467                 if !self.tcx().sess.features.borrow().unboxed_closures && trait_def.paren_sugar {
 468                     emit_feature_err(&self.tcx().sess.parse_sess,
 469                                      "unboxed_closures", span, GateIssue::Language,
 470                                      "\
 471                         the precise format of `Fn`-family traits' \
 472                         type parameters is subject to change. \
 473                         Use parenthetical notation (Fn(Foo, Bar) -> Baz) instead");
 474                 }
 475             }
 476             hir::ParenthesizedParameters(_) => {
 477                 // For now, require that parenthetical notation be used
 478                 // only with `Fn()` etc.
 479                 if !self.tcx().sess.features.borrow().unboxed_closures && !trait_def.paren_sugar {
 480                     emit_feature_err(&self.tcx().sess.parse_sess,
 481                                      "unboxed_closures", span, GateIssue::Language,
 482                                      "\
 483                         parenthetical notation is only stable when used with `Fn`-family traits");
 484                 }
 485             }
 486         }
 487
 488         self.create_substs_for_ast_path(span,
 489                                         trait_def_id,
 490                                         &trait_segment.parameters,
 491                                         Some(self_ty))
 492     }
 493
 494     fn trait_defines_associated_type_named(&self,
 495                                            trait_def_id: DefId,
 496                                            assoc_name: ast::Name)
 497                                            -> bool
 498     {
 499         self.tcx().associated_items(trait_def_id).any(|item| {
 500             item.kind == ty::AssociatedKind::Type && item.name == assoc_name
 501         })
 502     }
 503
 504     fn ast_type_binding_to_poly_projection_predicate(
 505         &self,
 506         _path_id: ast::NodeId,
 507         trait_ref: ty::PolyTraitRef<'tcx>,
 508         binding: &ConvertedBinding<'tcx>)
 509         -> Result<ty::PolyProjectionPredicate<'tcx>, ErrorReported>
 510     {
 511         let tcx = self.tcx();
 512
 513         // Given something like `U : SomeTrait<T=X>`, we want to produce a
 514         // predicate like `<U as SomeTrait>::T = X`. This is somewhat
 515         // subtle in the event that `T` is defined in a supertrait of
 516         // `SomeTrait`, because in that case we need to upcast.
 517         //
 518         // That is, consider this case:
 519         //
 520         // ```
 521         // trait SubTrait : SuperTrait<int> { }
 522         // trait SuperTrait<A> { type T; }
 523         //
 524         // ... B : SubTrait<T=foo> ...
 525         // ```
 526         //
 527         // We want to produce `<B as SuperTrait<int>>::T == foo`.
 528
 529         // Find any late-bound regions declared in `ty` that are not
 530         // declared in the trait-ref. These are not wellformed.
 531         //
 532         // Example:
 533         //
 534         //     for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
 535         //     for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
 536         let late_bound_in_trait_ref = tcx.collect_constrained_late_bound_regions(&trait_ref);
 537         let late_bound_in_ty = tcx.collect_referenced_late_bound_regions(&ty::Binder(binding.ty));
 538         debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
 539         debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
 540         for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
 541             let br_name = match *br {
 542                 ty::BrNamed(_, name) => name,
 543                 _ => {
 544                     span_bug!(
 545                         binding.span,
 546                         "anonymous bound region {:?} in binding but not trait ref",
 547                         br);
 548                 }
 549             };
 550             struct_span_err!(tcx.sess,
 551                              binding.span,
 552                              E0582,
 553                              "binding for associated type `{}` references lifetime `{}`, \
 554                               which does not appear in the trait input types",
 555                              binding.item_name, br_name)
 556                 .emit();
 557         }
 558
 559         // Simple case: X is defined in the current trait.
 560         if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
 561             return Ok(trait_ref.map_bound(|trait_ref| {
 562                 ty::ProjectionPredicate {
 563                     projection_ty: ty::ProjectionTy {
 564                         trait_ref: trait_ref,
 565                         item_name: binding.item_name,
 566                     },
 567                     ty: binding.ty,
 568                 }
 569             }));
 570         }
 571
 572         // Otherwise, we have to walk through the supertraits to find
 573         // those that do.
 574         let candidates =
 575             traits::supertraits(tcx, trait_ref.clone())
 576             .filter(|r| self.trait_defines_associated_type_named(r.def_id(), binding.item_name));
 577
 578         let candidate = self.one_bound_for_assoc_type(candidates,
 579                                                       &trait_ref.to_string(),
 580                                                       &binding.item_name.as_str(),
 581                                                       binding.span)?;
 582
 583         Ok(candidate.map_bound(|trait_ref| {
 584             ty::ProjectionPredicate {
 585                 projection_ty: ty::ProjectionTy {
 586                     trait_ref: trait_ref,
 587                     item_name: binding.item_name,
 588                 },
 589                 ty: binding.ty,
 590             }
 591         }))
 592     }
 593
 594     fn ast_path_to_ty(&self,
 595         span: Span,
 596         did: DefId,
 597         item_segment: &hir::PathSegment)
 598         -> Ty<'tcx>
 599     {
 600         let substs = self.ast_path_substs_for_ty(span, did, item_segment);
 601         self.normalize_ty(
 602             span,
 603             ty::queries::ty::get(self.tcx(), span, did).subst(self.tcx(), substs)
 604         )
 605     }
 606
 607     /// Transform a PolyTraitRef into a PolyExistentialTraitRef by
 608     /// removing the dummy Self type (TRAIT_OBJECT_DUMMY_SELF).
 609     fn trait_ref_to_existential(&self, trait_ref: ty::TraitRef<'tcx>)
 610                                 -> ty::ExistentialTraitRef<'tcx> {
 611         assert_eq!(trait_ref.self_ty().sty, TRAIT_OBJECT_DUMMY_SELF);
 612         ty::ExistentialTraitRef::erase_self_ty(self.tcx(), trait_ref)
 613     }
 614
 615     fn conv_object_ty_poly_trait_ref(&self,
 616         span: Span,
 617         trait_bounds: &[hir::PolyTraitRef],
 618         lifetime: &hir::Lifetime)
 619         -> Ty<'tcx>
 620     {
 621         let tcx = self.tcx();
 622
 623         if trait_bounds.is_empty() {
 624             span_err!(tcx.sess, span, E0224,
 625                       "at least one non-builtin trait is required for an object type");
 626             return tcx.types.err;
 627         }
 628
 629         let mut projection_bounds = vec![];
 630         let dummy_self = tcx.mk_ty(TRAIT_OBJECT_DUMMY_SELF);
 631         let principal = self.instantiate_poly_trait_ref(&trait_bounds[0],
 632                                                         dummy_self,
 633                                                         &mut projection_bounds);
 634
 635         let (auto_traits, trait_bounds) = split_auto_traits(tcx, &trait_bounds[1..]);
 636
 637         if !trait_bounds.is_empty() {
 638             let b = &trait_bounds[0];
 639             let span = b.trait_ref.path.span;
 640             struct_span_err!(self.tcx().sess, span, E0225,
 641                 "only Send/Sync traits can be used as additional traits in a trait object")
 642                 .span_label(span, &format!("non-Send/Sync additional trait"))
 643                 .emit();
 644         }
 645
 646         // Erase the dummy_self (TRAIT_OBJECT_DUMMY_SELF) used above.
 647         let existential_principal = principal.map_bound(|trait_ref| {
 648             self.trait_ref_to_existential(trait_ref)
 649         });
 650         let existential_projections = projection_bounds.iter().map(|bound| {
 651             bound.map_bound(|b| {
 652                 let p = b.projection_ty;
 653                 ty::ExistentialProjection {
 654                     trait_ref: self.trait_ref_to_existential(p.trait_ref),
 655                     item_name: p.item_name,
 656                     ty: b.ty
 657                 }
 658             })
 659         });
 660
 661         // check that there are no gross object safety violations,
 662         // most importantly, that the supertraits don't contain Self,
 663         // to avoid ICE-s.
 664         let object_safety_violations =
 665             tcx.astconv_object_safety_violations(principal.def_id());
 666         if !object_safety_violations.is_empty() {
 667             tcx.report_object_safety_error(
 668                 span, principal.def_id(), object_safety_violations)
 669                 .emit();
 670             return tcx.types.err;
 671         }
 672
 673         let mut associated_types = FxHashSet::default();
 674         for tr in traits::supertraits(tcx, principal) {
 675             associated_types.extend(tcx.associated_items(tr.def_id())
 676                 .filter(|item| item.kind == ty::AssociatedKind::Type)
 677                 .map(|item| (tr.def_id(), item.name)));
 678         }
 679
 680         for projection_bound in &projection_bounds {
 681             let pair = (projection_bound.0.projection_ty.trait_ref.def_id,
 682                         projection_bound.0.projection_ty.item_name);
 683             associated_types.remove(&pair);
 684         }
 685
 686         for (trait_def_id, name) in associated_types {
 687             struct_span_err!(tcx.sess, span, E0191,
 688                 "the value of the associated type `{}` (from the trait `{}`) must be specified",
 689                         name,
 690                         tcx.item_path_str(trait_def_id))
 691                         .span_label(span, &format!(
 692                             "missing associated type `{}` value", name))
 693                         .emit();
 694         }
 695
 696         let mut v =
 697             iter::once(ty::ExistentialPredicate::Trait(*existential_principal.skip_binder()))
 698             .chain(auto_traits.into_iter().map(ty::ExistentialPredicate::AutoTrait))
 699             .chain(existential_projections
 700                    .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())))
 701             .collect::<AccumulateVec<[_; 8]>>();
 702         v.sort_by(|a, b| a.cmp(tcx, b));
 703         let existential_predicates = ty::Binder(tcx.mk_existential_predicates(v.into_iter()));
 704
 705
 706         // Explicitly specified region bound. Use that.
 707         let region_bound = if !lifetime.is_elided() {
 708             self.ast_region_to_region(lifetime, None)
 709         } else {
 710             self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
 711                 if tcx.named_region_map.defs.contains_key(&lifetime.id) {
 712                     self.ast_region_to_region(lifetime, None)
 713                 } else {
 714                     self.re_infer(span, None).unwrap_or_else(|| {
 715                         span_err!(tcx.sess, span, E0228,
 716                                   "the lifetime bound for this object type cannot be deduced \
 717                                    from context; please supply an explicit bound");
 718                         tcx.types.re_static
 719                     })
 720                 }
 721             })
 722         };
 723
 724         debug!("region_bound: {:?}", region_bound);
 725
 726         let ty = tcx.mk_dynamic(existential_predicates, region_bound);
 727         debug!("trait_object_type: {:?}", ty);
 728         ty
 729     }
 730
 731     fn report_ambiguous_associated_type(&self,
 732                                         span: Span,
 733                                         type_str: &str,
 734                                         trait_str: &str,
 735                                         name: &str) {
 736         struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type")
 737             .span_label(span, &format!("ambiguous associated type"))
 738             .note(&format!("specify the type using the syntax `<{} as {}>::{}`",
 739                   type_str, trait_str, name))
 740             .emit();
 741
 742     }
 743
 744     // Search for a bound on a type parameter which includes the associated item
 745     // given by `assoc_name`. `ty_param_def_id` is the `DefId` for the type parameter
 746     // This function will fail if there are no suitable bounds or there is
 747     // any ambiguity.
 748     fn find_bound_for_assoc_item(&self,
 749                                  ty_param_def_id: DefId,
 750                                  assoc_name: ast::Name,
 751                                  span: Span)
 752                                  -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
 753     {
 754         let tcx = self.tcx();
 755
 756         let bounds: Vec<_> = self.get_type_parameter_bounds(span, ty_param_def_id)
 757             .predicates.into_iter().filter_map(|p| p.to_opt_poly_trait_ref()).collect();
 758
 759         // Check that there is exactly one way to find an associated type with the
 760         // correct name.
 761         let suitable_bounds =
 762             traits::transitive_bounds(tcx, &bounds)
 763             .filter(|b| self.trait_defines_associated_type_named(b.def_id(), assoc_name));
 764
 765         let param_node_id = tcx.hir.as_local_node_id(ty_param_def_id).unwrap();
 766         let param_name = tcx.hir.ty_param_name(param_node_id);
 767         self.one_bound_for_assoc_type(suitable_bounds,
 768                                       &param_name.as_str(),
 769                                       &assoc_name.as_str(),
 770                                       span)
 771     }
 772
 773
 774     // Checks that bounds contains exactly one element and reports appropriate
 775     // errors otherwise.
 776     fn one_bound_for_assoc_type<I>(&self,
 777                                 mut bounds: I,
 778                                 ty_param_name: &str,
 779                                 assoc_name: &str,
 780                                 span: Span)
 781         -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
 782         where I: Iterator<Item=ty::PolyTraitRef<'tcx>>
 783     {
 784         let bound = match bounds.next() {
 785             Some(bound) => bound,
 786             None => {
 787                 struct_span_err!(self.tcx().sess, span, E0220,
 788                           "associated type `{}` not found for `{}`",
 789                           assoc_name,
 790                           ty_param_name)
 791                   .span_label(span, &format!("associated type `{}` not found", assoc_name))
 792                   .emit();
 793                 return Err(ErrorReported);
 794             }
 795         };
 796
 797         if let Some(bound2) = bounds.next() {
 798             let bounds = iter::once(bound).chain(iter::once(bound2)).chain(bounds);
 799             let mut err = struct_span_err!(
 800                 self.tcx().sess, span, E0221,
 801                 "ambiguous associated type `{}` in bounds of `{}`",
 802                 assoc_name,
 803                 ty_param_name);
 804             err.span_label(span, &format!("ambiguous associated type `{}`", assoc_name));
 805
 806             for bound in bounds {
 807                 let bound_span = self.tcx().associated_items(bound.def_id()).find(|item| {
 808                     item.kind == ty::AssociatedKind::Type && item.name == assoc_name
 809                 })
 810                 .and_then(|item| self.tcx().hir.span_if_local(item.def_id));
 811
 812                 if let Some(span) = bound_span {
 813                     err.span_label(span, &format!("ambiguous `{}` from `{}`",
 814                                                   assoc_name,
 815                                                   bound));
 816                 } else {
 817                     span_note!(&mut err, span,
 818                                "associated type `{}` could derive from `{}`",
 819                                ty_param_name,
 820                                bound);
 821                 }
 822             }
 823             err.emit();
 824         }
 825
 826         return Ok(bound);
 827     }
 828
 829     // Create a type from a path to an associated type.
 830     // For a path A::B::C::D, ty and ty_path_def are the type and def for A::B::C
 831     // and item_segment is the path segment for D. We return a type and a def for
 832     // the whole path.
 833     // Will fail except for T::A and Self::A; i.e., if ty/ty_path_def are not a type
 834     // parameter or Self.
 835     pub fn associated_path_def_to_ty(&self,
 836                                      ref_id: ast::NodeId,
 837                                      span: Span,
 838                                      ty: Ty<'tcx>,
 839                                      ty_path_def: Def,
 840                                      item_segment: &hir::PathSegment)
 841                                      -> (Ty<'tcx>, Def)
 842     {
 843         let tcx = self.tcx();
 844         let assoc_name = item_segment.name;
 845
 846         debug!("associated_path_def_to_ty: {:?}::{}", ty, assoc_name);
 847
 848         self.prohibit_type_params(slice::ref_slice(item_segment));
 849
 850         // Find the type of the associated item, and the trait where the associated
 851         // item is declared.
 852         let bound = match (&ty.sty, ty_path_def) {
 853             (_, Def::SelfTy(Some(_), Some(impl_def_id))) => {
 854                 // `Self` in an impl of a trait - we have a concrete self type and a
 855                 // trait reference.
 856                 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
 857                     Some(trait_ref) => trait_ref,
 858                     None => {
 859                         // A cycle error occurred, most likely.
 860                         return (tcx.types.err, Def::Err);
 861                     }
 862                 };
 863
 864                 let trait_ref = if let Some(free_substs) = self.get_free_substs() {
 865                     trait_ref.subst(tcx, free_substs)
 866                 } else {
 867                     trait_ref
 868                 };
 869
 870                 let candidates =
 871                     traits::supertraits(tcx, ty::Binder(trait_ref))
 872                     .filter(|r| self.trait_defines_associated_type_named(r.def_id(),
 873                                                                          assoc_name));
 874
 875                 match self.one_bound_for_assoc_type(candidates,
 876                                                     "Self",
 877                                                     &assoc_name.as_str(),
 878                                                     span) {
 879                     Ok(bound) => bound,
 880                     Err(ErrorReported) => return (tcx.types.err, Def::Err),
 881                 }
 882             }
 883             (&ty::TyParam(_), Def::SelfTy(Some(param_did), None)) |
 884             (&ty::TyParam(_), Def::TyParam(param_did)) => {
 885                 match self.find_bound_for_assoc_item(param_did, assoc_name, span) {
 886                     Ok(bound) => bound,
 887                     Err(ErrorReported) => return (tcx.types.err, Def::Err),
 888                 }
 889             }
 890             _ => {
 891                 // Don't print TyErr to the user.
 892                 if !ty.references_error() {
 893                     self.report_ambiguous_associated_type(span,
 894                                                           &ty.to_string(),
 895                                                           "Trait",
 896                                                           &assoc_name.as_str());
 897                 }
 898                 return (tcx.types.err, Def::Err);
 899             }
 900         };
 901
 902         let trait_did = bound.0.def_id;
 903         let ty = self.projected_ty_from_poly_trait_ref(span, bound, assoc_name);
 904         let ty = self.normalize_ty(span, ty);
 905
 906         let item = tcx.associated_items(trait_did).find(|i| i.name == assoc_name);
 907         let def_id = item.expect("missing associated type").def_id;
 908         tcx.check_stability(def_id, ref_id, span);
 909         (ty, Def::AssociatedTy(def_id))
 910     }
 911
 912     fn qpath_to_ty(&self,
 913                    span: Span,
 914                    opt_self_ty: Option<Ty<'tcx>>,
 915                    trait_def_id: DefId,
 916                    trait_segment: &hir::PathSegment,
 917                    item_segment: &hir::PathSegment)
 918                    -> Ty<'tcx>
 919     {
 920         let tcx = self.tcx();
 921
 922         self.prohibit_type_params(slice::ref_slice(item_segment));
 923
 924         let self_ty = if let Some(ty) = opt_self_ty {
 925             ty
 926         } else {
 927             let path_str = tcx.item_path_str(trait_def_id);
 928             self.report_ambiguous_associated_type(span,
 929                                                   "Type",
 930                                                   &path_str,
 931                                                   &item_segment.name.as_str());
 932             return tcx.types.err;
 933         };
 934
 935         debug!("qpath_to_ty: self_type={:?}", self_ty);
 936
 937         let trait_ref = self.ast_path_to_mono_trait_ref(span,
 938                                                         trait_def_id,
 939                                                         self_ty,
 940                                                         trait_segment);
 941
 942         debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
 943
 944         self.normalize_ty(span, tcx.mk_projection(trait_ref, item_segment.name))
 945     }
 946
 947     pub fn prohibit_type_params(&self, segments: &[hir::PathSegment]) {
 948         for segment in segments {
 949             for typ in segment.parameters.types() {
 950                 struct_span_err!(self.tcx().sess, typ.span, E0109,
 951                                  "type parameters are not allowed on this type")
 952                     .span_label(typ.span, &format!("type parameter not allowed"))
 953                     .emit();
 954                 break;
 955             }
 956             for lifetime in segment.parameters.lifetimes() {
 957                 struct_span_err!(self.tcx().sess, lifetime.span, E0110,
 958                                  "lifetime parameters are not allowed on this type")
 959                     .span_label(lifetime.span,
 960                                 &format!("lifetime parameter not allowed on this type"))
 961                     .emit();
 962                 break;
 963             }
 964             for binding in segment.parameters.bindings() {
 965                 self.prohibit_projection(binding.span);
 966                 break;
 967             }
 968         }
 969     }
 970
 971     pub fn prohibit_projection(&self, span: Span) {
 972         let mut err = struct_span_err!(self.tcx().sess, span, E0229,
 973                                        "associated type bindings are not allowed here");
 974         err.span_label(span, &format!("associate type not allowed here")).emit();
 975     }
 976
 977     // Check a type Path and convert it to a Ty.
 978     pub fn def_to_ty(&self,
 979                      opt_self_ty: Option<Ty<'tcx>>,
 980                      path: &hir::Path,
 981                      permit_variants: bool)
 982                      -> Ty<'tcx> {
 983         let tcx = self.tcx();
 984
 985         debug!("base_def_to_ty(def={:?}, opt_self_ty={:?}, path_segments={:?})",
 986                path.def, opt_self_ty, path.segments);
 987
 988         let span = path.span;
 989         match path.def {
 990             Def::Enum(did) | Def::TyAlias(did) | Def::Struct(did) | Def::Union(did) => {
 991                 assert_eq!(opt_self_ty, None);
 992                 self.prohibit_type_params(path.segments.split_last().unwrap().1);
 993                 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
 994             }
 995             Def::Variant(did) if permit_variants => {
 996                 // Convert "variant type" as if it were a real type.
 997                 // The resulting `Ty` is type of the variant's enum for now.
 998                 assert_eq!(opt_self_ty, None);
 999                 self.prohibit_type_params(path.segments.split_last().unwrap().1);
1000                 self.ast_path_to_ty(span,
1001                                     tcx.parent_def_id(did).unwrap(),
1002                                     path.segments.last().unwrap())
1003             }
1004             Def::TyParam(did) => {
1005                 assert_eq!(opt_self_ty, None);
1006                 self.prohibit_type_params(&path.segments);
1007
1008                 let node_id = tcx.hir.as_local_node_id(did).unwrap();
1009                 let item_id = tcx.hir.get_parent_node(node_id);
1010                 let item_def_id = tcx.hir.local_def_id(item_id);
1011                 let generics = tcx.item_generics(item_def_id);
1012                 let index = generics.type_param_to_index[&tcx.hir.local_def_id(node_id).index];
1013                 tcx.mk_param(index, tcx.hir.name(node_id))
1014             }
1015             Def::SelfTy(_, Some(def_id)) => {
1016                 // Self in impl (we know the concrete type).
1017
1018                 assert_eq!(opt_self_ty, None);
1019                 self.prohibit_type_params(&path.segments);
1020
1021                 let ty = ty::queries::ty::get(tcx, span, def_id);
1022                 if let Some(free_substs) = self.get_free_substs() {
1023                     ty.subst(tcx, free_substs)
1024                 } else {
1025                     ty
1026                 }
1027             }
1028             Def::SelfTy(Some(_), None) => {
1029                 // Self in trait.
1030                 assert_eq!(opt_self_ty, None);
1031                 self.prohibit_type_params(&path.segments);
1032                 tcx.mk_self_type()
1033             }
1034             Def::AssociatedTy(def_id) => {
1035                 self.prohibit_type_params(&path.segments[..path.segments.len()-2]);
1036                 let trait_did = tcx.parent_def_id(def_id).unwrap();
1037                 self.qpath_to_ty(span,
1038                                  opt_self_ty,
1039                                  trait_did,
1040                                  &path.segments[path.segments.len()-2],
1041                                  path.segments.last().unwrap())
1042             }
1043             Def::PrimTy(prim_ty) => {
1044                 assert_eq!(opt_self_ty, None);
1045                 self.prohibit_type_params(&path.segments);
1046                 match prim_ty {
1047                     hir::TyBool => tcx.types.bool,
1048                     hir::TyChar => tcx.types.char,
1049                     hir::TyInt(it) => tcx.mk_mach_int(it),
1050                     hir::TyUint(uit) => tcx.mk_mach_uint(uit),
1051                     hir::TyFloat(ft) => tcx.mk_mach_float(ft),
1052                     hir::TyStr => tcx.mk_str()
1053                 }
1054             }
1055             Def::Err => {
1056                 self.set_tainted_by_errors();
1057                 return self.tcx().types.err;
1058             }
1059             _ => span_bug!(span, "unexpected definition: {:?}", path.def)
1060         }
1061     }
1062
1063     /// Parses the programmer's textual representation of a type into our
1064     /// internal notion of a type.
1065     pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty) -> Ty<'tcx> {
1066         debug!("ast_ty_to_ty(id={:?}, ast_ty={:?})",
1067                ast_ty.id, ast_ty);
1068
1069         let tcx = self.tcx();
1070
1071         let cache = self.ast_ty_to_ty_cache();
1072         if let Some(ty) = cache.borrow().get(&ast_ty.id) {
1073             return ty;
1074         }
1075
1076         let result_ty = match ast_ty.node {
1077             hir::TySlice(ref ty) => {
1078                 tcx.mk_slice(self.ast_ty_to_ty(&ty))
1079             }
1080             hir::TyPtr(ref mt) => {
1081                 tcx.mk_ptr(ty::TypeAndMut {
1082                     ty: self.ast_ty_to_ty(&mt.ty),
1083                     mutbl: mt.mutbl
1084                 })
1085             }
1086             hir::TyRptr(ref region, ref mt) => {
1087                 let r = self.ast_region_to_region(region, None);
1088                 debug!("TyRef r={:?}", r);
1089                 let t = self.ast_ty_to_ty(&mt.ty);
1090                 tcx.mk_ref(r, ty::TypeAndMut {ty: t, mutbl: mt.mutbl})
1091             }
1092             hir::TyNever => {
1093                 tcx.types.never
1094             },
1095             hir::TyTup(ref fields) => {
1096                 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)), false)
1097             }
1098             hir::TyBareFn(ref bf) => {
1099                 require_c_abi_if_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
1100                 let bare_fn_ty = self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl);
1101
1102                 // Find any late-bound regions declared in return type that do
1103                 // not appear in the arguments. These are not wellformed.
1104                 //
1105                 // Example:
1106                 //
1107                 //     for<'a> fn() -> &'a str <-- 'a is bad
1108                 //     for<'a> fn(&'a String) -> &'a str <-- 'a is ok
1109                 //
1110                 // Note that we do this check **here** and not in
1111                 // `ty_of_bare_fn` because the latter is also used to make
1112                 // the types for fn items, and we do not want to issue a
1113                 // warning then. (Once we fix #32330, the regions we are
1114                 // checking for here would be considered early bound
1115                 // anyway.)
1116                 let inputs = bare_fn_ty.inputs();
1117                 let late_bound_in_args = tcx.collect_constrained_late_bound_regions(
1118                     &inputs.map_bound(|i| i.to_owned()));
1119                 let output = bare_fn_ty.output();
1120                 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
1121                 for br in late_bound_in_ret.difference(&late_bound_in_args) {
1122                     let br_name = match *br {
1123                         ty::BrNamed(_, name) => name,
1124                         _ => {
1125                             span_bug!(
1126                                 bf.decl.output.span(),
1127                                 "anonymous bound region {:?} in return but not args",
1128                                 br);
1129                         }
1130                     };
1131                     struct_span_err!(tcx.sess,
1132                                      ast_ty.span,
1133                                      E0581,
1134                                      "return type references lifetime `{}`, \
1135                                       which does not appear in the fn input types",
1136                                      br_name)
1137                         .emit();
1138                 }
1139                 tcx.mk_fn_ptr(bare_fn_ty)
1140             }
1141             hir::TyTraitObject(ref bounds, ref lifetime) => {
1142                 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
1143             }
1144             hir::TyImplTrait(_) => {
1145                 // Figure out if we can allow an `impl Trait` here, by walking up
1146                 // to a `fn` or inherent `impl` method, going only through `Ty`
1147                 // or `TraitRef` nodes (as nothing else should be in types) and
1148                 // ensuring that we reach the `fn`/method signature's return type.
1149                 let mut node_id = ast_ty.id;
1150                 let fn_decl = loop {
1151                     let parent = tcx.hir.get_parent_node(node_id);
1152                     match tcx.hir.get(parent) {
1153                         hir::map::NodeItem(&hir::Item {
1154                             node: hir::ItemFn(ref fn_decl, ..), ..
1155                         }) => break Some(fn_decl),
1156
1157                         hir::map::NodeImplItem(&hir::ImplItem {
1158                             node: hir::ImplItemKind::Method(ref sig, _), ..
1159                         }) => {
1160                             match tcx.hir.expect_item(tcx.hir.get_parent(parent)).node {
1161                                 hir::ItemImpl(.., None, _, _) => {
1162                                     break Some(&sig.decl)
1163                                 }
1164                                 _ => break None
1165                             }
1166                         }
1167
1168                         hir::map::NodeTy(_) | hir::map::NodeTraitRef(_) => {}
1169
1170                         _ => break None
1171                     }
1172                     node_id = parent;
1173                 };
1174                 let allow = fn_decl.map_or(false, |fd| {
1175                     match fd.output {
1176                         hir::DefaultReturn(_) => false,
1177                         hir::Return(ref ty) => ty.id == node_id
1178                     }
1179                 });
1180
1181                 // Create the anonymized type.
1182                 if allow {
1183                     let def_id = tcx.hir.local_def_id(ast_ty.id);
1184                     tcx.mk_anon(def_id, Substs::identity_for_item(tcx, def_id))
1185                 } else {
1186                     span_err!(tcx.sess, ast_ty.span, E0562,
1187                               "`impl Trait` not allowed outside of function \
1188                                and inherent method return types");
1189                     tcx.types.err
1190                 }
1191             }
1192             hir::TyPath(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
1193                 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
1194                 let opt_self_ty = maybe_qself.as_ref().map(|qself| {
1195                     self.ast_ty_to_ty(qself)
1196                 });
1197                 self.def_to_ty(opt_self_ty, path, false)
1198             }
1199             hir::TyPath(hir::QPath::TypeRelative(ref qself, ref segment)) => {
1200                 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
1201                 let ty = self.ast_ty_to_ty(qself);
1202
1203                 let def = if let hir::TyPath(hir::QPath::Resolved(_, ref path)) = qself.node {
1204                     path.def
1205                 } else {
1206                     Def::Err
1207                 };
1208                 self.associated_path_def_to_ty(ast_ty.id, ast_ty.span, ty, def, segment).0
1209             }
1210             hir::TyArray(ref ty, length) => {
1211                 if let Ok(length) = eval_length(tcx, length, "array length") {
1212                     tcx.mk_array(self.ast_ty_to_ty(&ty), length)
1213                 } else {
1214                     self.tcx().types.err
1215                 }
1216             }
1217             hir::TyTypeof(ref _e) => {
1218                 struct_span_err!(tcx.sess, ast_ty.span, E0516,
1219                                  "`typeof` is a reserved keyword but unimplemented")
1220                     .span_label(ast_ty.span, &format!("reserved keyword"))
1221                     .emit();
1222
1223                 tcx.types.err
1224             }
1225             hir::TyInfer => {
1226                 // TyInfer also appears as the type of arguments or return
1227                 // values in a ExprClosure, or as
1228                 // the type of local variables. Both of these cases are
1229                 // handled specially and will not descend into this routine.
1230                 self.ty_infer(ast_ty.span)
1231             }
1232             hir::TyErr => {
1233                 tcx.types.err
1234             }
1235         };
1236
1237         cache.borrow_mut().insert(ast_ty.id, result_ty);
1238
1239         result_ty
1240     }
1241
1242     pub fn ty_of_arg(&self,
1243                      ty: &hir::Ty,
1244                      expected_ty: Option<Ty<'tcx>>)
1245                      -> Ty<'tcx>
1246     {
1247         match ty.node {
1248             hir::TyInfer if expected_ty.is_some() => expected_ty.unwrap(),
1249             hir::TyInfer => self.ty_infer(ty.span),
1250             _ => self.ast_ty_to_ty(ty),
1251         }
1252     }
1253
1254     pub fn ty_of_fn(&self,
1255                     unsafety: hir::Unsafety,
1256                     abi: abi::Abi,
1257                     decl: &hir::FnDecl)
1258                     -> ty::PolyFnSig<'tcx> {
1259         debug!("ty_of_fn");
1260
1261         let input_tys: Vec<Ty> =
1262             decl.inputs.iter().map(|a| self.ty_of_arg(a, None)).collect();
1263
1264         let output_ty = match decl.output {
1265             hir::Return(ref output) => self.ast_ty_to_ty(output),
1266             hir::DefaultReturn(..) => self.tcx().mk_nil(),
1267         };
1268
1269         debug!("ty_of_fn: output_ty={:?}", output_ty);
1270
1271         ty::Binder(self.tcx().mk_fn_sig(
1272             input_tys.into_iter(),
1273             output_ty,
1274             decl.variadic,
1275             unsafety,
1276             abi
1277         ))
1278     }
1279
1280     pub fn ty_of_closure(&self,
1281         unsafety: hir::Unsafety,
1282         decl: &hir::FnDecl,
1283         abi: abi::Abi,
1284         expected_sig: Option<ty::FnSig<'tcx>>)
1285         -> ty::PolyFnSig<'tcx>
1286     {
1287         debug!("ty_of_closure(expected_sig={:?})",
1288                expected_sig);
1289
1290         let input_tys = decl.inputs.iter().enumerate().map(|(i, a)| {
1291             let expected_arg_ty = expected_sig.as_ref().and_then(|e| {
1292                 // no guarantee that the correct number of expected args
1293                 // were supplied
1294                 if i < e.inputs().len() {
1295                     Some(e.inputs()[i])
1296                 } else {
1297                     None
1298                 }
1299             });
1300             self.ty_of_arg(a, expected_arg_ty)
1301         });
1302
1303         let expected_ret_ty = expected_sig.as_ref().map(|e| e.output());
1304
1305         let is_infer = match decl.output {
1306             hir::Return(ref output) if output.node == hir::TyInfer => true,
1307             hir::DefaultReturn(..) => true,
1308             _ => false
1309         };
1310
1311         let output_ty = match decl.output {
1312             _ if is_infer && expected_ret_ty.is_some() =>
1313                 expected_ret_ty.unwrap(),
1314             _ if is_infer => self.ty_infer(decl.output.span()),
1315             hir::Return(ref output) =>
1316                 self.ast_ty_to_ty(&output),
1317             hir::DefaultReturn(..) => bug!(),
1318         };
1319
1320         debug!("ty_of_closure: output_ty={:?}", output_ty);
1321
1322         ty::Binder(self.tcx().mk_fn_sig(
1323             input_tys,
1324             output_ty,
1325             decl.variadic,
1326             unsafety,
1327             abi
1328         ))
1329     }
1330
1331     /// Given the bounds on an object, determines what single region bound (if any) we can
1332     /// use to summarize this type. The basic idea is that we will use the bound the user
1333     /// provided, if they provided one, and otherwise search the supertypes of trait bounds
1334     /// for region bounds. It may be that we can derive no bound at all, in which case
1335     /// we return `None`.
1336     fn compute_object_lifetime_bound(&self,
1337         span: Span,
1338         existential_predicates: ty::Binder<&'tcx ty::Slice<ty::ExistentialPredicate<'tcx>>>)
1339         -> Option<&'tcx ty::Region> // if None, use the default
1340     {
1341         let tcx = self.tcx();
1342
1343         debug!("compute_opt_region_bound(existential_predicates={:?})",
1344                existential_predicates);
1345
1346         // No explicit region bound specified. Therefore, examine trait
1347         // bounds and see if we can derive region bounds from those.
1348         let derived_region_bounds =
1349             object_region_bounds(tcx, existential_predicates);
1350
1351         // If there are no derived region bounds, then report back that we
1352         // can find no region bound. The caller will use the default.
1353         if derived_region_bounds.is_empty() {
1354             return None;
1355         }
1356
1357         // If any of the derived region bounds are 'static, that is always
1358         // the best choice.
1359         if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
1360             return Some(tcx.types.re_static);
1361         }
1362
1363         // Determine whether there is exactly one unique region in the set
1364         // of derived region bounds. If so, use that. Otherwise, report an
1365         // error.
1366         let r = derived_region_bounds[0];
1367         if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
1368             span_err!(tcx.sess, span, E0227,
1369                       "ambiguous lifetime bound, explicit lifetime bound required");
1370         }
1371         return Some(r);
1372     }
1373 }
1374
1375 /// Divides a list of general trait bounds into two groups: builtin bounds (Sync/Send) and the
1376 /// remaining general trait bounds.
1377 fn split_auto_traits<'a, 'b, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
1378                                          trait_bounds: &'b [hir::PolyTraitRef])
1379     -> (Vec<DefId>, Vec<&'b hir::PolyTraitRef>)
1380 {
1381     let (auto_traits, trait_bounds): (Vec<_>, _) = trait_bounds.iter().partition(|bound| {
1382         match bound.trait_ref.path.def {
1383             Def::Trait(trait_did) => {
1384                 // Checks whether `trait_did` refers to one of the builtin
1385                 // traits, like `Send`, and adds it to `auto_traits` if so.
1386                 if Some(trait_did) == tcx.lang_items.send_trait() ||
1387                     Some(trait_did) == tcx.lang_items.sync_trait() {
1388                     let segments = &bound.trait_ref.path.segments;
1389                     let parameters = &segments[segments.len() - 1].parameters;
1390                     if !parameters.types().is_empty() {
1391                         check_type_argument_count(tcx, bound.trait_ref.path.span,
1392                                                   parameters.types().len(), &[]);
1393                     }
1394                     if !parameters.lifetimes().is_empty() {
1395                         report_lifetime_number_error(tcx, bound.trait_ref.path.span,
1396                                                      parameters.lifetimes().len(), 0);
1397                     }
1398                     true
1399                 } else {
1400                     false
1401                 }
1402             }
1403             _ => false
1404         }
1405     });
1406
1407     let auto_traits = auto_traits.into_iter().map(|tr| {
1408         if let Def::Trait(trait_did) = tr.trait_ref.path.def {
1409             trait_did
1410         } else {
1411             unreachable!()
1412         }
1413     }).collect::<Vec<_>>();
1414
1415     (auto_traits, trait_bounds)
1416 }
1417
1418 fn check_type_argument_count(tcx: TyCtxt, span: Span, supplied: usize,
1419                              ty_param_defs: &[ty::TypeParameterDef]) {
1420     let accepted = ty_param_defs.len();
1421     let required = ty_param_defs.iter().take_while(|x| !x.has_default).count();
1422     if supplied < required {
1423         let expected = if required < accepted {
1424             "expected at least"
1425         } else {
1426             "expected"
1427         };
1428         let arguments_plural = if required == 1 { "" } else { "s" };
1429
1430         struct_span_err!(tcx.sess, span, E0243,
1431                 "wrong number of type arguments: {} {}, found {}",
1432                 expected, required, supplied)
1433             .span_label(span,
1434                 &format!("{} {} type argument{}",
1435                     expected,
1436                     required,
1437                     arguments_plural))
1438             .emit();
1439     } else if supplied > accepted {
1440         let expected = if required < accepted {
1441             format!("expected at most {}", accepted)
1442         } else {
1443             format!("expected {}", accepted)
1444         };
1445         let arguments_plural = if accepted == 1 { "" } else { "s" };
1446
1447         struct_span_err!(tcx.sess, span, E0244,
1448                 "wrong number of type arguments: {}, found {}",
1449                 expected, supplied)
1450             .span_label(
1451                 span,
1452                 &format!("{} type argument{}",
1453                     if accepted == 0 { "expected no" } else { &expected },
1454                     arguments_plural)
1455             )
1456             .emit();
1457     }
1458 }
1459
1460 fn report_lifetime_number_error(tcx: TyCtxt, span: Span, number: usize, expected: usize) {
1461     let label = if number < expected {
1462         if expected == 1 {
1463             format!("expected {} lifetime parameter", expected)
1464         } else {
1465             format!("expected {} lifetime parameters", expected)
1466         }
1467     } else {
1468         let additional = number - expected;
1469         if additional == 1 {
1470             "unexpected lifetime parameter".to_string()
1471         } else {
1472             format!("{} unexpected lifetime parameters", additional)
1473         }
1474     };
1475     struct_span_err!(tcx.sess, span, E0107,
1476                      "wrong number of lifetime parameters: expected {}, found {}",
1477                      expected, number)
1478         .span_label(span, &label)
1479         .emit();
1480 }
1481
1482 // A helper struct for conveniently grouping a set of bounds which we pass to
1483 // and return from functions in multiple places.
1484 #[derive(PartialEq, Eq, Clone, Debug)]
1485 pub struct Bounds<'tcx> {
1486     pub region_bounds: Vec<&'tcx ty::Region>,
1487     pub implicitly_sized: bool,
1488     pub trait_bounds: Vec<ty::PolyTraitRef<'tcx>>,
1489     pub projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>,
1490 }
1491
1492 impl<'a, 'gcx, 'tcx> Bounds<'tcx> {
1493     pub fn predicates(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, param_ty: Ty<'tcx>)
1494                       -> Vec<ty::Predicate<'tcx>>
1495     {
1496         let mut vec = Vec::new();
1497
1498         // If it could be sized, and is, add the sized predicate
1499         if self.implicitly_sized {
1500             if let Some(sized) = tcx.lang_items.sized_trait() {
1501                 let trait_ref = ty::TraitRef {
1502                     def_id: sized,
1503                     substs: tcx.mk_substs_trait(param_ty, &[])
1504                 };
1505                 vec.push(trait_ref.to_predicate());
1506             }
1507         }
1508
1509         for &region_bound in &self.region_bounds {
1510             // account for the binder being introduced below; no need to shift `param_ty`
1511             // because, at present at least, it can only refer to early-bound regions
1512             let region_bound = tcx.mk_region(ty::fold::shift_region(*region_bound, 1));
1513             vec.push(ty::Binder(ty::OutlivesPredicate(param_ty, region_bound)).to_predicate());
1514         }
1515
1516         for bound_trait_ref in &self.trait_bounds {
1517             vec.push(bound_trait_ref.to_predicate());
1518         }
1519
1520         for projection in &self.projection_bounds {
1521             vec.push(projection.to_predicate());
1522         }
1523
1524         vec
1525     }
1526 }
1527
1528 pub enum ExplicitSelf<'tcx> {
1529     ByValue,
1530     ByReference(&'tcx ty::Region, hir::Mutability),
1531     ByBox
1532 }
1533
1534 impl<'tcx> ExplicitSelf<'tcx> {
1535     /// We wish to (for now) categorize an explicit self
1536     /// declaration like `self: SomeType` into either `self`,
1537     /// `&self`, `&mut self`, or `Box<self>`. We do this here
1538     /// by some simple pattern matching. A more precise check
1539     /// is done later in `check_method_self_type()`.
1540     ///
1541     /// Examples:
1542     ///
1543     /// ```
1544     /// impl Foo for &T {
1545     ///     // Legal declarations:
1546     ///     fn method1(self: &&T); // ExplicitSelf::ByReference
1547     ///     fn method2(self: &T); // ExplicitSelf::ByValue
1548     ///     fn method3(self: Box<&T>); // ExplicitSelf::ByBox
1549     ///
1550     ///     // Invalid cases will be caught later by `check_method_self_type`:
1551     ///     fn method_err1(self: &mut T); // ExplicitSelf::ByReference
1552     /// }
1553     /// ```
1554     ///
1555     /// To do the check we just count the number of "modifiers"
1556     /// on each type and compare them. If they are the same or
1557     /// the impl has more, we call it "by value". Otherwise, we
1558     /// look at the outermost modifier on the method decl and
1559     /// call it by-ref, by-box as appropriate. For method1, for
1560     /// example, the impl type has one modifier, but the method
1561     /// type has two, so we end up with
1562     /// ExplicitSelf::ByReference.
1563     pub fn determine(untransformed_self_ty: Ty<'tcx>,
1564                      self_arg_ty: Ty<'tcx>)
1565                      -> ExplicitSelf<'tcx> {
1566         fn count_modifiers(ty: Ty) -> usize {
1567             match ty.sty {
1568                 ty::TyRef(_, mt) => count_modifiers(mt.ty) + 1,
1569                 ty::TyAdt(def, _) if def.is_box() => count_modifiers(ty.boxed_ty()) + 1,
1570                 _ => 0,
1571             }
1572         }
1573
1574         let impl_modifiers = count_modifiers(untransformed_self_ty);
1575         let method_modifiers = count_modifiers(self_arg_ty);
1576
1577         if impl_modifiers >= method_modifiers {
1578             ExplicitSelf::ByValue
1579         } else {
1580             match self_arg_ty.sty {
1581                 ty::TyRef(r, mt) => ExplicitSelf::ByReference(r, mt.mutbl),
1582                 ty::TyAdt(def, _) if def.is_box() => ExplicitSelf::ByBox,
1583                 _ => ExplicitSelf::ByValue,
1584             }
1585         }
1586     }
1587 }