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