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` and a `RegionScope`.
  14 //!
  15 //! The parameterization of `ast_ty_to_ty()` is because it behaves
  16 //! somewhat differently during the collect and check phases,
  17 //! particularly with respect to looking up the types of top-level
  18 //! items.  In the collect phase, the crate context is used as the
  19 //! `AstConv` instance; in this phase, the `get_item_type_scheme()`
  20 //! function triggers a recursive call to `type_scheme_of_item()`
  21 //! (note that `ast_ty_to_ty()` will detect recursive types and report
  22 //! an error).  In the check phase, when the FnCtxt is used as the
  23 //! `AstConv`, `get_item_type_scheme()` just looks up the item type in
  24 //! `tcx.tcache` (using `ty::lookup_item_type`).
  25 //!
  26 //! The `RegionScope` trait controls what happens when the user does
  27 //! not specify a region in some location where a region is required
  28 //! (e.g., if the user writes `&Foo` as a type rather than `&'a Foo`).
  29 //! See the `rscope` module for more details.
  30 //!
  31 //! Unlike the `AstConv` trait, the region scope can change as we descend
  32 //! the type.  This is to accommodate the fact that (a) fn types are binding
  33 //! scopes and (b) the default region may change.  To understand case (a),
  34 //! consider something like:
  35 //!
  36 //!   type foo = { x: &a.int, y: |&a.int| }
  37 //!
  38 //! The type of `x` is an error because there is no region `a` in scope.
  39 //! In the type of `y`, however, region `a` is considered a bound region
  40 //! as it does not already appear in scope.
  41 //!
  42 //! Case (b) says that if you have a type:
  43 //!   type foo<'a> = ...;
  44 //!   type bar = fn(&foo, &a.foo)
  45 //! The fully expanded version of type bar is:
  46 //!   type bar = fn(&'foo &, &a.foo<'a>)
  47 //! Note that the self region for the `foo` defaulted to `&` in the first
  48 //! case but `&a` in the second.  Basically, defaults that appear inside
  49 //! an rptr (`&r.T`) use the region `r` that appears in the rptr.
  50
  51 use middle::astconv_util::{prim_ty_to_ty, check_path_args, NO_TPS, NO_REGIONS};
  52 use middle::const_eval::{self, ConstVal};
  53 use middle::const_eval::EvalHint::UncheckedExprHint;
  54 use middle::def;
  55 use middle::implicator::object_region_bounds;
  56 use middle::resolve_lifetime as rl;
  57 use middle::privacy::{AllPublic, LastMod};
  58 use middle::subst::{FnSpace, TypeSpace, SelfSpace, Subst, Substs, ParamSpace};
  59 use middle::traits;
  60 use middle::ty::{self, RegionEscape, Ty, ToPredicate, HasTypeFlags};
  61 use middle::ty_fold;
  62 use require_c_abi_if_variadic;
  63 use rscope::{self, UnelidableRscope, RegionScope, ElidableRscope,
  64              ObjectLifetimeDefaultRscope, ShiftedRscope, BindingRscope,
  65              ElisionFailureInfo, ElidedLifetime};
  66 use util::common::{ErrorReported, FN_OUTPUT_NAME};
  67 use util::nodemap::FnvHashSet;
  68
  69 use std::slice;
  70 use syntax::{abi, ast, ast_util};
  71 use syntax::codemap::{Span, Pos};
  72 use syntax::feature_gate::emit_feature_err;
  73 use syntax::parse::token;
  74 use syntax::print::pprust;
  75
  76 pub trait AstConv<'tcx> {
  77     fn tcx<'a>(&'a self) -> &'a ty::ctxt<'tcx>;
  78
  79     /// Identify the type scheme for an item with a type, like a type
  80     /// alias, fn, or struct. This allows you to figure out the set of
  81     /// type parameters defined on the item.
  82     fn get_item_type_scheme(&self, span: Span, id: ast::DefId)
  83                             -> Result<ty::TypeScheme<'tcx>, ErrorReported>;
  84
  85     /// Returns the `TraitDef` for a given trait. This allows you to
  86     /// figure out the set of type parameters defined on the trait.
  87     fn get_trait_def(&self, span: Span, id: ast::DefId)
  88                      -> Result<&'tcx ty::TraitDef<'tcx>, ErrorReported>;
  89
  90     /// Ensure that the super-predicates for the trait with the given
  91     /// id are available and also for the transitive set of
  92     /// super-predicates.
  93     fn ensure_super_predicates(&self, span: Span, id: ast::DefId)
  94                                -> Result<(), ErrorReported>;
  95
  96     /// Returns the set of bounds in scope for the type parameter with
  97     /// the given id.
  98     fn get_type_parameter_bounds(&self, span: Span, def_id: ast::NodeId)
  99                                  -> Result<Vec<ty::PolyTraitRef<'tcx>>, ErrorReported>;
 100
 101     /// Returns true if the trait with id `trait_def_id` defines an
 102     /// associated type with the name `name`.
 103     fn trait_defines_associated_type_named(&self, trait_def_id: ast::DefId, name: ast::Name)
 104                                            -> bool;
 105
 106     /// Return an (optional) substitution to convert bound type parameters that
 107     /// are in scope into free ones. This function should only return Some
 108     /// within a fn body.
 109     /// See ParameterEnvironment::free_substs for more information.
 110     fn get_free_substs(&self) -> Option<&Substs<'tcx>> {
 111         None
 112     }
 113
 114     /// What type should we use when a type is omitted?
 115         fn ty_infer(&self,
 116                     param_and_substs: Option<ty::TypeParameterDef<'tcx>>,
 117                     substs: Option<&mut Substs<'tcx>>,
 118                     space: Option<ParamSpace>,
 119                     span: Span) -> Ty<'tcx>;
 120
 121     /// Projecting an associated type from a (potentially)
 122     /// higher-ranked trait reference is more complicated, because of
 123     /// the possibility of late-bound regions appearing in the
 124     /// associated type binding. This is not legal in function
 125     /// signatures for that reason. In a function body, we can always
 126     /// handle it because we can use inference variables to remove the
 127     /// late-bound regions.
 128     fn projected_ty_from_poly_trait_ref(&self,
 129                                         span: Span,
 130                                         poly_trait_ref: ty::PolyTraitRef<'tcx>,
 131                                         item_name: ast::Name)
 132                                         -> Ty<'tcx>
 133     {
 134         if let Some(trait_ref) = self.tcx().no_late_bound_regions(&poly_trait_ref) {
 135             self.projected_ty(span, trait_ref, item_name)
 136         } else {
 137             // no late-bound regions, we can just ignore the binder
 138             span_err!(self.tcx().sess, span, E0212,
 139                 "cannot extract an associated type from a higher-ranked trait bound \
 140                  in this context");
 141             self.tcx().types.err
 142         }
 143     }
 144
 145     /// Project an associated type from a non-higher-ranked trait reference.
 146     /// This is fairly straightforward and can be accommodated in any context.
 147     fn projected_ty(&self,
 148                     span: Span,
 149                     _trait_ref: ty::TraitRef<'tcx>,
 150                     _item_name: ast::Name)
 151                     -> Ty<'tcx>;
 152 }
 153
 154 pub fn ast_region_to_region(tcx: &ty::ctxt, lifetime: &ast::Lifetime)
 155                             -> ty::Region {
 156     let r = match tcx.named_region_map.get(&lifetime.id) {
 157         None => {
 158             // should have been recorded by the `resolve_lifetime` pass
 159             tcx.sess.span_bug(lifetime.span, "unresolved lifetime");
 160         }
 161
 162         Some(&rl::DefStaticRegion) => {
 163             ty::ReStatic
 164         }
 165
 166         Some(&rl::DefLateBoundRegion(debruijn, id)) => {
 167             ty::ReLateBound(debruijn, ty::BrNamed(ast_util::local_def(id), lifetime.name))
 168         }
 169
 170         Some(&rl::DefEarlyBoundRegion(space, index, id)) => {
 171             ty::ReEarlyBound(ty::EarlyBoundRegion {
 172                 param_id: id,
 173                 space: space,
 174                 index: index,
 175                 name: lifetime.name
 176             })
 177         }
 178
 179         Some(&rl::DefFreeRegion(scope, id)) => {
 180             ty::ReFree(ty::FreeRegion {
 181                     scope: scope,
 182                     bound_region: ty::BrNamed(ast_util::local_def(id),
 183                                               lifetime.name)
 184                 })
 185         }
 186     };
 187
 188     debug!("ast_region_to_region(lifetime={:?} id={}) yields {:?}",
 189            lifetime,
 190            lifetime.id,
 191            r);
 192
 193     r
 194 }
 195
 196 fn report_elision_failure(
 197     tcx: &ty::ctxt,
 198     default_span: Span,
 199     params: Vec<ElisionFailureInfo>)
 200 {
 201     let mut m = String::new();
 202     let len = params.len();
 203     for (i, info) in params.into_iter().enumerate() {
 204         let ElisionFailureInfo {
 205             name, lifetime_count: n, have_bound_regions
 206         } = info;
 207
 208         let help_name = if name.is_empty() {
 209             format!("argument {}", i + 1)
 210         } else {
 211             format!("`{}`", name)
 212         };
 213
 214         m.push_str(&(if n == 1 {
 215             help_name
 216         } else {
 217             format!("one of {}'s {} elided {}lifetimes", help_name, n,
 218                     if have_bound_regions { "free " } else { "" } )
 219         })[..]);
 220
 221         if len == 2 && i == 0 {
 222             m.push_str(" or ");
 223         } else if i + 2 == len {
 224             m.push_str(", or ");
 225         } else if i + 1 != len {
 226             m.push_str(", ");
 227         }
 228     }
 229     if len == 1 {
 230         fileline_help!(tcx.sess, default_span,
 231                        "this function's return type contains a borrowed value, but \
 232                         the signature does not say which {} it is borrowed from",
 233                        m);
 234     } else if len == 0 {
 235         fileline_help!(tcx.sess, default_span,
 236                        "this function's return type contains a borrowed value, but \
 237                         there is no value for it to be borrowed from");
 238         fileline_help!(tcx.sess, default_span,
 239                        "consider giving it a 'static lifetime");
 240     } else {
 241         fileline_help!(tcx.sess, default_span,
 242                        "this function's return type contains a borrowed value, but \
 243                         the signature does not say whether it is borrowed from {}",
 244                        m);
 245     }
 246 }
 247
 248 pub fn opt_ast_region_to_region<'tcx>(
 249     this: &AstConv<'tcx>,
 250     rscope: &RegionScope,
 251     default_span: Span,
 252     opt_lifetime: &Option<ast::Lifetime>) -> ty::Region
 253 {
 254     let r = match *opt_lifetime {
 255         Some(ref lifetime) => {
 256             ast_region_to_region(this.tcx(), lifetime)
 257         }
 258
 259         None => match rscope.anon_regions(default_span, 1) {
 260             Ok(rs) => rs[0],
 261             Err(params) => {
 262                 span_err!(this.tcx().sess, default_span, E0106,
 263                           "missing lifetime specifier");
 264                 if let Some(params) = params {
 265                     report_elision_failure(this.tcx(), default_span, params);
 266                 }
 267                 ty::ReStatic
 268             }
 269         }
 270     };
 271
 272     debug!("opt_ast_region_to_region(opt_lifetime={:?}) yields {:?}",
 273             opt_lifetime,
 274             r);
 275
 276     r
 277 }
 278
 279 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
 280 /// returns an appropriate set of substitutions for this particular reference to `I`.
 281 pub fn ast_path_substs_for_ty<'tcx>(
 282     this: &AstConv<'tcx>,
 283     rscope: &RegionScope,
 284     span: Span,
 285     param_mode: PathParamMode,
 286     decl_generics: &ty::Generics<'tcx>,
 287     item_segment: &ast::PathSegment)
 288     -> Substs<'tcx>
 289 {
 290     let tcx = this.tcx();
 291
 292     // ast_path_substs() is only called to convert paths that are
 293     // known to refer to traits, types, or structs. In these cases,
 294     // all type parameters defined for the item being referenced will
 295     // be in the TypeSpace or SelfSpace.
 296     //
 297     // Note: in the case of traits, the self parameter is also
 298     // defined, but we don't currently create a `type_param_def` for
 299     // `Self` because it is implicit.
 300     assert!(decl_generics.regions.all(|d| d.space == TypeSpace));
 301     assert!(decl_generics.types.all(|d| d.space != FnSpace));
 302
 303     let (regions, types, assoc_bindings) = match item_segment.parameters {
 304         ast::AngleBracketedParameters(ref data) => {
 305             convert_angle_bracketed_parameters(this, rscope, span, decl_generics, data)
 306         }
 307         ast::ParenthesizedParameters(..) => {
 308             span_err!(tcx.sess, span, E0214,
 309                       "parenthesized parameters may only be used with a trait");
 310             let ty_param_defs = decl_generics.types.get_slice(TypeSpace);
 311             (Substs::empty(),
 312              ty_param_defs.iter().map(|_| tcx.types.err).collect(),
 313              vec![])
 314         }
 315     };
 316
 317     prohibit_projections(this.tcx(), &assoc_bindings);
 318
 319     create_substs_for_ast_path(this,
 320                                span,
 321                                param_mode,
 322                                decl_generics,
 323                                None,
 324                                types,
 325                                regions)
 326 }
 327
 328 #[derive(PartialEq, Eq)]
 329 pub enum PathParamMode {
 330     // Any path in a type context.
 331     Explicit,
 332     // The `module::Type` in `module::Type::method` in an expression.
 333     Optional
 334 }
 335
 336 fn create_region_substs<'tcx>(
 337     this: &AstConv<'tcx>,
 338     rscope: &RegionScope,
 339     span: Span,
 340     decl_generics: &ty::Generics<'tcx>,
 341     regions_provided: Vec<ty::Region>)
 342     -> Substs<'tcx>
 343 {
 344     let tcx = this.tcx();
 345
 346     // If the type is parameterized by the this region, then replace this
 347     // region with the current anon region binding (in other words,
 348     // whatever & would get replaced with).
 349     let expected_num_region_params = decl_generics.regions.len(TypeSpace);
 350     let supplied_num_region_params = regions_provided.len();
 351     let regions = if expected_num_region_params == supplied_num_region_params {
 352         regions_provided
 353     } else {
 354         let anon_regions =
 355             rscope.anon_regions(span, expected_num_region_params);
 356
 357         if supplied_num_region_params != 0 || anon_regions.is_err() {
 358             report_lifetime_number_error(tcx, span,
 359                                          supplied_num_region_params,
 360                                          expected_num_region_params);
 361         }
 362
 363         match anon_regions {
 364             Ok(anon_regions) => anon_regions,
 365             Err(_) => (0..expected_num_region_params).map(|_| ty::ReStatic).collect()
 366         }
 367     };
 368     Substs::new_type(vec![], regions)
 369 }
 370
 371 /// Given the type/region arguments provided to some path (along with
 372 /// an implicit Self, if this is a trait reference) returns the complete
 373 /// set of substitutions. This may involve applying defaulted type parameters.
 374 ///
 375 /// Note that the type listing given here is *exactly* what the user provided.
 376 ///
 377 /// The `region_substs` should be the result of `create_region_substs`
 378 /// -- that is, a substitution with no types but the correct number of
 379 /// regions.
 380 fn create_substs_for_ast_path<'tcx>(
 381     this: &AstConv<'tcx>,
 382     span: Span,
 383     param_mode: PathParamMode,
 384     decl_generics: &ty::Generics<'tcx>,
 385     self_ty: Option<Ty<'tcx>>,
 386     types_provided: Vec<Ty<'tcx>>,
 387     region_substs: Substs<'tcx>)
 388     -> Substs<'tcx>
 389 {
 390     let tcx = this.tcx();
 391
 392     debug!("create_substs_for_ast_path(decl_generics={:?}, self_ty={:?}, \
 393            types_provided={:?}, region_substs={:?}",
 394            decl_generics, self_ty, types_provided,
 395            region_substs);
 396
 397     assert_eq!(region_substs.regions().len(TypeSpace), decl_generics.regions.len(TypeSpace));
 398     assert!(region_substs.types.is_empty());
 399
 400     // Convert the type parameters supplied by the user.
 401     let ty_param_defs = decl_generics.types.get_slice(TypeSpace);
 402     let formal_ty_param_count = ty_param_defs.len();
 403     let required_ty_param_count = ty_param_defs.iter()
 404                                                .take_while(|x| x.default.is_none())
 405                                                .count();
 406
 407     // Fill with `ty_infer` if no params were specified, as long as
 408     // they were optional (e.g. paths inside expressions).
 409     let mut type_substs = if param_mode == PathParamMode::Optional &&
 410                              types_provided.is_empty() {
 411         let mut substs = region_substs.clone();
 412         ty_param_defs
 413             .iter()
 414             .map(|p| this.ty_infer(Some(p.clone()), Some(&mut substs), Some(TypeSpace), span))
 415             .collect()
 416     } else {
 417         types_provided
 418     };
 419
 420     let supplied_ty_param_count = type_substs.len();
 421     check_type_argument_count(this.tcx(), span, supplied_ty_param_count,
 422                               required_ty_param_count, formal_ty_param_count);
 423
 424     if supplied_ty_param_count < required_ty_param_count {
 425         while type_substs.len() < required_ty_param_count {
 426             type_substs.push(tcx.types.err);
 427         }
 428     } else if supplied_ty_param_count > formal_ty_param_count {
 429         type_substs.truncate(formal_ty_param_count);
 430     }
 431     assert!(type_substs.len() >= required_ty_param_count &&
 432             type_substs.len() <= formal_ty_param_count);
 433
 434     let mut substs = region_substs;
 435     substs.types.extend(TypeSpace, type_substs.into_iter());
 436
 437     match self_ty {
 438         None => {
 439             // If no self-type is provided, it's still possible that
 440             // one was declared, because this could be an object type.
 441         }
 442         Some(ty) => {
 443             // If a self-type is provided, one should have been
 444             // "declared" (in other words, this should be a
 445             // trait-ref).
 446             assert!(decl_generics.types.get_self().is_some());
 447             substs.types.push(SelfSpace, ty);
 448         }
 449     }
 450
 451     let actual_supplied_ty_param_count = substs.types.len(TypeSpace);
 452     for param in &ty_param_defs[actual_supplied_ty_param_count..] {
 453         if let Some(default) = param.default {
 454             // If we are converting an object type, then the
 455             // `Self` parameter is unknown. However, some of the
 456             // other type parameters may reference `Self` in their
 457             // defaults. This will lead to an ICE if we are not
 458             // careful!
 459             if self_ty.is_none() && default.has_self_ty() {
 460                 span_err!(tcx.sess, span, E0393,
 461                           "the type parameter `{}` must be explicitly specified \
 462                            in an object type because its default value `{}` references \
 463                            the type `Self`",
 464                           param.name,
 465                           default);
 466                 substs.types.push(TypeSpace, tcx.types.err);
 467             } else {
 468                 // This is a default type parameter.
 469                 let default = default.subst_spanned(tcx,
 470                                                     &substs,
 471                                                     Some(span));
 472                 substs.types.push(TypeSpace, default);
 473             }
 474         } else {
 475             tcx.sess.span_bug(span, "extra parameter without default");
 476         }
 477     }
 478
 479     substs
 480 }
 481
 482 struct ConvertedBinding<'tcx> {
 483     item_name: ast::Name,
 484     ty: Ty<'tcx>,
 485     span: Span,
 486 }
 487
 488 fn convert_angle_bracketed_parameters<'tcx>(this: &AstConv<'tcx>,
 489                                             rscope: &RegionScope,
 490                                             span: Span,
 491                                             decl_generics: &ty::Generics<'tcx>,
 492                                             data: &ast::AngleBracketedParameterData)
 493                                             -> (Substs<'tcx>,
 494                                                 Vec<Ty<'tcx>>,
 495                                                 Vec<ConvertedBinding<'tcx>>)
 496 {
 497     let regions: Vec<_> =
 498         data.lifetimes.iter()
 499                       .map(|l| ast_region_to_region(this.tcx(), l))
 500                       .collect();
 501
 502     let region_substs =
 503         create_region_substs(this, rscope, span, decl_generics, regions);
 504
 505     let types: Vec<_> =
 506         data.types.iter()
 507                   .enumerate()
 508                   .map(|(i,t)| ast_ty_arg_to_ty(this, rscope, decl_generics,
 509                                                 i, &region_substs, t))
 510                   .collect();
 511
 512     let assoc_bindings: Vec<_> =
 513         data.bindings.iter()
 514                      .map(|b| ConvertedBinding { item_name: b.ident.name,
 515                                                  ty: ast_ty_to_ty(this, rscope, &*b.ty),
 516                                                  span: b.span })
 517                      .collect();
 518
 519     (region_substs, types, assoc_bindings)
 520 }
 521
 522 /// Returns the appropriate lifetime to use for any output lifetimes
 523 /// (if one exists) and a vector of the (pattern, number of lifetimes)
 524 /// corresponding to each input type/pattern.
 525 fn find_implied_output_region<'tcx>(tcx: &ty::ctxt<'tcx>,
 526                                     input_tys: &[Ty<'tcx>],
 527                                     input_pats: Vec<String>) -> ElidedLifetime
 528 {
 529     let mut lifetimes_for_params = Vec::new();
 530     let mut possible_implied_output_region = None;
 531
 532     for (input_type, input_pat) in input_tys.iter().zip(input_pats) {
 533         let mut regions = FnvHashSet();
 534         let have_bound_regions = ty_fold::collect_regions(tcx,
 535                                                           input_type,
 536                                                           &mut regions);
 537
 538         debug!("find_implied_output_regions: collected {:?} from {:?} \
 539                 have_bound_regions={:?}", &regions, input_type, have_bound_regions);
 540
 541         if regions.len() == 1 {
 542             // there's a chance that the unique lifetime of this
 543             // iteration will be the appropriate lifetime for output
 544             // parameters, so lets store it.
 545             possible_implied_output_region = regions.iter().cloned().next();
 546         }
 547
 548         lifetimes_for_params.push(ElisionFailureInfo {
 549             name: input_pat,
 550             lifetime_count: regions.len(),
 551             have_bound_regions: have_bound_regions
 552         });
 553     }
 554
 555     if lifetimes_for_params.iter().map(|e| e.lifetime_count).sum::<usize>() == 1 {
 556         Ok(possible_implied_output_region.unwrap())
 557     } else {
 558         Err(Some(lifetimes_for_params))
 559     }
 560 }
 561
 562 fn convert_ty_with_lifetime_elision<'tcx>(this: &AstConv<'tcx>,
 563                                           elided_lifetime: ElidedLifetime,
 564                                           ty: &ast::Ty)
 565                                           -> Ty<'tcx>
 566 {
 567     match elided_lifetime {
 568         Ok(implied_output_region) => {
 569             let rb = ElidableRscope::new(implied_output_region);
 570             ast_ty_to_ty(this, &rb, ty)
 571         }
 572         Err(param_lifetimes) => {
 573             // All regions must be explicitly specified in the output
 574             // if the lifetime elision rules do not apply. This saves
 575             // the user from potentially-confusing errors.
 576             let rb = UnelidableRscope::new(param_lifetimes);
 577             ast_ty_to_ty(this, &rb, ty)
 578         }
 579     }
 580 }
 581
 582 fn convert_parenthesized_parameters<'tcx>(this: &AstConv<'tcx>,
 583                                           rscope: &RegionScope,
 584                                           span: Span,
 585                                           decl_generics: &ty::Generics<'tcx>,
 586                                           data: &ast::ParenthesizedParameterData)
 587                                           -> (Substs<'tcx>,
 588                                               Vec<Ty<'tcx>>,
 589                                               Vec<ConvertedBinding<'tcx>>)
 590 {
 591     let region_substs =
 592         create_region_substs(this, rscope, span, decl_generics, Vec::new());
 593
 594     let binding_rscope = BindingRscope::new();
 595     let inputs =
 596         data.inputs.iter()
 597                    .map(|a_t| ast_ty_arg_to_ty(this, &binding_rscope, decl_generics,
 598                                                0, &region_substs, a_t))
 599                    .collect::<Vec<Ty<'tcx>>>();
 600
 601     let input_params = vec![String::new(); inputs.len()];
 602     let implied_output_region = find_implied_output_region(this.tcx(), &inputs, input_params);
 603
 604     let input_ty = this.tcx().mk_tup(inputs);
 605
 606     let (output, output_span) = match data.output {
 607         Some(ref output_ty) => {
 608             (convert_ty_with_lifetime_elision(this,
 609                                               implied_output_region,
 610                                               &output_ty),
 611              output_ty.span)
 612         }
 613         None => {
 614             (this.tcx().mk_nil(), data.span)
 615         }
 616     };
 617
 618     let output_binding = ConvertedBinding {
 619         item_name: token::intern(FN_OUTPUT_NAME),
 620         ty: output,
 621         span: output_span
 622     };
 623
 624     (region_substs, vec![input_ty], vec![output_binding])
 625 }
 626
 627 pub fn instantiate_poly_trait_ref<'tcx>(
 628     this: &AstConv<'tcx>,
 629     rscope: &RegionScope,
 630     ast_trait_ref: &ast::PolyTraitRef,
 631     self_ty: Option<Ty<'tcx>>,
 632     poly_projections: &mut Vec<ty::PolyProjectionPredicate<'tcx>>)
 633     -> ty::PolyTraitRef<'tcx>
 634 {
 635     let trait_ref = &ast_trait_ref.trait_ref;
 636     let trait_def_id = trait_def_id(this, trait_ref);
 637     ast_path_to_poly_trait_ref(this,
 638                                rscope,
 639                                trait_ref.path.span,
 640                                PathParamMode::Explicit,
 641                                trait_def_id,
 642                                self_ty,
 643                                trait_ref.path.segments.last().unwrap(),
 644                                poly_projections)
 645 }
 646
 647 /// Instantiates the path for the given trait reference, assuming that it's
 648 /// bound to a valid trait type. Returns the def_id for the defining trait.
 649 /// Fails if the type is a type other than a trait type.
 650 ///
 651 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T=X>`
 652 /// are disallowed. Otherwise, they are pushed onto the vector given.
 653 pub fn instantiate_mono_trait_ref<'tcx>(
 654     this: &AstConv<'tcx>,
 655     rscope: &RegionScope,
 656     trait_ref: &ast::TraitRef,
 657     self_ty: Option<Ty<'tcx>>)
 658     -> ty::TraitRef<'tcx>
 659 {
 660     let trait_def_id = trait_def_id(this, trait_ref);
 661     ast_path_to_mono_trait_ref(this,
 662                                rscope,
 663                                trait_ref.path.span,
 664                                PathParamMode::Explicit,
 665                                trait_def_id,
 666                                self_ty,
 667                                trait_ref.path.segments.last().unwrap())
 668 }
 669
 670 fn trait_def_id<'tcx>(this: &AstConv<'tcx>, trait_ref: &ast::TraitRef) -> ast::DefId {
 671     let path = &trait_ref.path;
 672     match ::lookup_full_def(this.tcx(), path.span, trait_ref.ref_id) {
 673         def::DefTrait(trait_def_id) => trait_def_id,
 674         _ => {
 675             span_fatal!(this.tcx().sess, path.span, E0245, "`{}` is not a trait",
 676                         path);
 677         }
 678     }
 679 }
 680
 681 fn object_path_to_poly_trait_ref<'a,'tcx>(
 682     this: &AstConv<'tcx>,
 683     rscope: &RegionScope,
 684     span: Span,
 685     param_mode: PathParamMode,
 686     trait_def_id: ast::DefId,
 687     trait_segment: &ast::PathSegment,
 688     mut projections: &mut Vec<ty::PolyProjectionPredicate<'tcx>>)
 689     -> ty::PolyTraitRef<'tcx>
 690 {
 691     ast_path_to_poly_trait_ref(this,
 692                                rscope,
 693                                span,
 694                                param_mode,
 695                                trait_def_id,
 696                                None,
 697                                trait_segment,
 698                                projections)
 699 }
 700
 701 fn ast_path_to_poly_trait_ref<'a,'tcx>(
 702     this: &AstConv<'tcx>,
 703     rscope: &RegionScope,
 704     span: Span,
 705     param_mode: PathParamMode,
 706     trait_def_id: ast::DefId,
 707     self_ty: Option<Ty<'tcx>>,
 708     trait_segment: &ast::PathSegment,
 709     poly_projections: &mut Vec<ty::PolyProjectionPredicate<'tcx>>)
 710     -> ty::PolyTraitRef<'tcx>
 711 {
 712     // The trait reference introduces a binding level here, so
 713     // we need to shift the `rscope`. It'd be nice if we could
 714     // do away with this rscope stuff and work this knowledge
 715     // into resolve_lifetimes, as we do with non-omitted
 716     // lifetimes. Oh well, not there yet.
 717     let shifted_rscope = &ShiftedRscope::new(rscope);
 718
 719     let (substs, assoc_bindings) =
 720         create_substs_for_ast_trait_ref(this,
 721                                         shifted_rscope,
 722                                         span,
 723                                         param_mode,
 724                                         trait_def_id,
 725                                         self_ty,
 726                                         trait_segment);
 727     let poly_trait_ref = ty::Binder(ty::TraitRef::new(trait_def_id, substs));
 728
 729     {
 730         let converted_bindings =
 731             assoc_bindings
 732             .iter()
 733             .filter_map(|binding| {
 734                 // specify type to assert that error was already reported in Err case:
 735                 let predicate: Result<_, ErrorReported> =
 736                     ast_type_binding_to_poly_projection_predicate(this,
 737                                                                   poly_trait_ref.clone(),
 738                                                                   self_ty,
 739                                                                   binding);
 740                 predicate.ok() // ok to ignore Err() because ErrorReported (see above)
 741             });
 742         poly_projections.extend(converted_bindings);
 743     }
 744
 745     poly_trait_ref
 746 }
 747
 748 fn ast_path_to_mono_trait_ref<'a,'tcx>(this: &AstConv<'tcx>,
 749                                        rscope: &RegionScope,
 750                                        span: Span,
 751                                        param_mode: PathParamMode,
 752                                        trait_def_id: ast::DefId,
 753                                        self_ty: Option<Ty<'tcx>>,
 754                                        trait_segment: &ast::PathSegment)
 755                                        -> ty::TraitRef<'tcx>
 756 {
 757     let (substs, assoc_bindings) =
 758         create_substs_for_ast_trait_ref(this,
 759                                         rscope,
 760                                         span,
 761                                         param_mode,
 762                                         trait_def_id,
 763                                         self_ty,
 764                                         trait_segment);
 765     prohibit_projections(this.tcx(), &assoc_bindings);
 766     ty::TraitRef::new(trait_def_id, substs)
 767 }
 768
 769 fn create_substs_for_ast_trait_ref<'a,'tcx>(this: &AstConv<'tcx>,
 770                                             rscope: &RegionScope,
 771                                             span: Span,
 772                                             param_mode: PathParamMode,
 773                                             trait_def_id: ast::DefId,
 774                                             self_ty: Option<Ty<'tcx>>,
 775                                             trait_segment: &ast::PathSegment)
 776                                             -> (&'tcx Substs<'tcx>, Vec<ConvertedBinding<'tcx>>)
 777 {
 778     debug!("create_substs_for_ast_trait_ref(trait_segment={:?})",
 779            trait_segment);
 780
 781     let trait_def = match this.get_trait_def(span, trait_def_id) {
 782         Ok(trait_def) => trait_def,
 783         Err(ErrorReported) => {
 784             // No convenient way to recover from a cycle here. Just bail. Sorry!
 785             this.tcx().sess.abort_if_errors();
 786             this.tcx().sess.bug("ErrorReported returned, but no errors reports?")
 787         }
 788     };
 789
 790     let (regions, types, assoc_bindings) = match trait_segment.parameters {
 791         ast::AngleBracketedParameters(ref data) => {
 792             // For now, require that parenthetical notation be used
 793             // only with `Fn()` etc.
 794             if !this.tcx().sess.features.borrow().unboxed_closures && trait_def.paren_sugar {
 795                 emit_feature_err(&this.tcx().sess.parse_sess.span_diagnostic,
 796                                  "unboxed_closures", span,
 797                                  "\
 798                     the precise format of `Fn`-family traits' type parameters is \
 799                     subject to change. Use parenthetical notation (Fn(Foo, Bar) -> Baz) instead");
 800             }
 801
 802             convert_angle_bracketed_parameters(this, rscope, span, &trait_def.generics, data)
 803         }
 804         ast::ParenthesizedParameters(ref data) => {
 805             // For now, require that parenthetical notation be used
 806             // only with `Fn()` etc.
 807             if !this.tcx().sess.features.borrow().unboxed_closures && !trait_def.paren_sugar {
 808                 emit_feature_err(&this.tcx().sess.parse_sess.span_diagnostic,
 809                                  "unboxed_closures", span,
 810                                  "\
 811                     parenthetical notation is only stable when used with `Fn`-family traits");
 812             }
 813
 814             convert_parenthesized_parameters(this, rscope, span, &trait_def.generics, data)
 815         }
 816     };
 817
 818     let substs = create_substs_for_ast_path(this,
 819                                             span,
 820                                             param_mode,
 821                                             &trait_def.generics,
 822                                             self_ty,
 823                                             types,
 824                                             regions);
 825
 826     (this.tcx().mk_substs(substs), assoc_bindings)
 827 }
 828
 829 fn ast_type_binding_to_poly_projection_predicate<'tcx>(
 830     this: &AstConv<'tcx>,
 831     mut trait_ref: ty::PolyTraitRef<'tcx>,
 832     self_ty: Option<Ty<'tcx>>,
 833     binding: &ConvertedBinding<'tcx>)
 834     -> Result<ty::PolyProjectionPredicate<'tcx>, ErrorReported>
 835 {
 836     let tcx = this.tcx();
 837
 838     // Given something like `U : SomeTrait<T=X>`, we want to produce a
 839     // predicate like `<U as SomeTrait>::T = X`. This is somewhat
 840     // subtle in the event that `T` is defined in a supertrait of
 841     // `SomeTrait`, because in that case we need to upcast.
 842     //
 843     // That is, consider this case:
 844     //
 845     // ```
 846     // trait SubTrait : SuperTrait<int> { }
 847     // trait SuperTrait<A> { type T; }
 848     //
 849     // ... B : SubTrait<T=foo> ...
 850     // ```
 851     //
 852     // We want to produce `<B as SuperTrait<int>>::T == foo`.
 853
 854     // Simple case: X is defined in the current trait.
 855     if this.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
 856         return Ok(ty::Binder(ty::ProjectionPredicate {      // <-------------------+
 857             projection_ty: ty::ProjectionTy {               //                     |
 858                 trait_ref: trait_ref.skip_binder().clone(), // Binder moved here --+
 859                 item_name: binding.item_name,
 860             },
 861             ty: binding.ty,
 862         }));
 863     }
 864
 865     // Otherwise, we have to walk through the supertraits to find
 866     // those that do.  This is complicated by the fact that, for an
 867     // object type, the `Self` type is not present in the
 868     // substitutions (after all, it's being constructed right now),
 869     // but the `supertraits` iterator really wants one. To handle
 870     // this, we currently insert a dummy type and then remove it
 871     // later. Yuck.
 872
 873     let dummy_self_ty = tcx.mk_infer(ty::FreshTy(0));
 874     if self_ty.is_none() { // if converting for an object type
 875         let mut dummy_substs = trait_ref.skip_binder().substs.clone(); // binder moved here -+
 876         assert!(dummy_substs.self_ty().is_none());                     //                    |
 877         dummy_substs.types.push(SelfSpace, dummy_self_ty);             //                    |
 878         trait_ref = ty::Binder(ty::TraitRef::new(trait_ref.def_id(),   // <------------+
 879                                                  tcx.mk_substs(dummy_substs)));
 880     }
 881
 882     try!(this.ensure_super_predicates(binding.span, trait_ref.def_id()));
 883
 884     let mut candidates: Vec<ty::PolyTraitRef> =
 885         traits::supertraits(tcx, trait_ref.clone())
 886         .filter(|r| this.trait_defines_associated_type_named(r.def_id(), binding.item_name))
 887         .collect();
 888
 889     // If converting for an object type, then remove the dummy-ty from `Self` now.
 890     // Yuckety yuck.
 891     if self_ty.is_none() {
 892         for candidate in &mut candidates {
 893             let mut dummy_substs = candidate.0.substs.clone();
 894             assert!(dummy_substs.self_ty() == Some(dummy_self_ty));
 895             dummy_substs.types.pop(SelfSpace);
 896             *candidate = ty::Binder(ty::TraitRef::new(candidate.def_id(),
 897                                                       tcx.mk_substs(dummy_substs)));
 898         }
 899     }
 900
 901     let candidate = try!(one_bound_for_assoc_type(tcx,
 902                                                   candidates,
 903                                                   &trait_ref.to_string(),
 904                                                   &binding.item_name.as_str(),
 905                                                   binding.span));
 906
 907     Ok(ty::Binder(ty::ProjectionPredicate {             // <-------------------------+
 908         projection_ty: ty::ProjectionTy {               //                           |
 909             trait_ref: candidate.skip_binder().clone(), // binder is moved up here --+
 910             item_name: binding.item_name,
 911         },
 912         ty: binding.ty,
 913     }))
 914 }
 915
 916 fn ast_path_to_ty<'tcx>(
 917     this: &AstConv<'tcx>,
 918     rscope: &RegionScope,
 919     span: Span,
 920     param_mode: PathParamMode,
 921     did: ast::DefId,
 922     item_segment: &ast::PathSegment)
 923     -> Ty<'tcx>
 924 {
 925     let tcx = this.tcx();
 926     let (generics, decl_ty) = match this.get_item_type_scheme(span, did) {
 927         Ok(ty::TypeScheme { generics,  ty: decl_ty }) => {
 928             (generics, decl_ty)
 929         }
 930         Err(ErrorReported) => {
 931             return tcx.types.err;
 932         }
 933     };
 934
 935     let substs = ast_path_substs_for_ty(this,
 936                                         rscope,
 937                                         span,
 938                                         param_mode,
 939                                         &generics,
 940                                         item_segment);
 941
 942     // FIXME(#12938): This is a hack until we have full support for DST.
 943     if Some(did) == this.tcx().lang_items.owned_box() {
 944         assert_eq!(substs.types.len(TypeSpace), 1);
 945         return this.tcx().mk_box(*substs.types.get(TypeSpace, 0));
 946     }
 947
 948     decl_ty.subst(this.tcx(), &substs)
 949 }
 950
 951 type TraitAndProjections<'tcx> = (ty::PolyTraitRef<'tcx>, Vec<ty::PolyProjectionPredicate<'tcx>>);
 952
 953 fn ast_ty_to_trait_ref<'tcx>(this: &AstConv<'tcx>,
 954                              rscope: &RegionScope,
 955                              ty: &ast::Ty,
 956                              bounds: &[ast::TyParamBound])
 957                              -> Result<TraitAndProjections<'tcx>, ErrorReported>
 958 {
 959     /*!
 960      * In a type like `Foo + Send`, we want to wait to collect the
 961      * full set of bounds before we make the object type, because we
 962      * need them to infer a region bound.  (For example, if we tried
 963      * made a type from just `Foo`, then it wouldn't be enough to
 964      * infer a 'static bound, and hence the user would get an error.)
 965      * So this function is used when we're dealing with a sum type to
 966      * convert the LHS. It only accepts a type that refers to a trait
 967      * name, and reports an error otherwise.
 968      */
 969
 970     match ty.node {
 971         ast::TyPath(None, ref path) => {
 972             let def = match this.tcx().def_map.borrow().get(&ty.id) {
 973                 Some(&def::PathResolution { base_def, depth: 0, .. }) => Some(base_def),
 974                 _ => None
 975             };
 976             match def {
 977                 Some(def::DefTrait(trait_def_id)) => {
 978                     let mut projection_bounds = Vec::new();
 979                     let trait_ref = object_path_to_poly_trait_ref(this,
 980                                                                   rscope,
 981                                                                   path.span,
 982                                                                   PathParamMode::Explicit,
 983                                                                   trait_def_id,
 984                                                                   path.segments.last().unwrap(),
 985                                                                   &mut projection_bounds);
 986                     Ok((trait_ref, projection_bounds))
 987                 }
 988                 _ => {
 989                     span_err!(this.tcx().sess, ty.span, E0172, "expected a reference to a trait");
 990                     Err(ErrorReported)
 991                 }
 992             }
 993         }
 994         _ => {
 995             span_err!(this.tcx().sess, ty.span, E0178,
 996                       "expected a path on the left-hand side of `+`, not `{}`",
 997                       pprust::ty_to_string(ty));
 998             let hi = bounds.iter().map(|x| match *x {
 999                 ast::TraitTyParamBound(ref tr, _) => tr.span.hi,
1000                 ast::RegionTyParamBound(ref r) => r.span.hi,
1001             }).max_by(|x| x.to_usize());
1002             let full_span = hi.map(|hi| Span {
1003                 lo: ty.span.lo,
1004                 hi: hi,
1005                 expn_id: ty.span.expn_id,
1006             });
1007             match (&ty.node, full_span) {
1008                 (&ast::TyRptr(None, ref mut_ty), Some(full_span)) => {
1009                     let mutbl_str = if mut_ty.mutbl == ast::MutMutable { "mut " } else { "" };
1010                     this.tcx().sess
1011                         .span_suggestion(full_span, "try adding parentheses (per RFC 438):",
1012                                          format!("&{}({} +{})",
1013                                                  mutbl_str,
1014                                                  pprust::ty_to_string(&*mut_ty.ty),
1015                                                  pprust::bounds_to_string(bounds)));
1016                 }
1017                 (&ast::TyRptr(Some(ref lt), ref mut_ty), Some(full_span)) => {
1018                     let mutbl_str = if mut_ty.mutbl == ast::MutMutable { "mut " } else { "" };
1019                     this.tcx().sess
1020                         .span_suggestion(full_span, "try adding parentheses (per RFC 438):",
1021                                          format!("&{} {}({} +{})",
1022                                                  pprust::lifetime_to_string(lt),
1023                                                  mutbl_str,
1024                                                  pprust::ty_to_string(&*mut_ty.ty),
1025                                                  pprust::bounds_to_string(bounds)));
1026                 }
1027
1028                 _ => {
1029                     fileline_help!(this.tcx().sess, ty.span,
1030                                "perhaps you forgot parentheses? (per RFC 438)");
1031                 }
1032             }
1033             Err(ErrorReported)
1034         }
1035     }
1036 }
1037
1038 fn trait_ref_to_object_type<'tcx>(this: &AstConv<'tcx>,
1039                                   rscope: &RegionScope,
1040                                   span: Span,
1041                                   trait_ref: ty::PolyTraitRef<'tcx>,
1042                                   projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>,
1043                                   bounds: &[ast::TyParamBound])
1044                                   -> Ty<'tcx>
1045 {
1046     let existential_bounds = conv_existential_bounds(this,
1047                                                      rscope,
1048                                                      span,
1049                                                      trait_ref.clone(),
1050                                                      projection_bounds,
1051                                                      bounds);
1052
1053     let result = make_object_type(this, span, trait_ref, existential_bounds);
1054     debug!("trait_ref_to_object_type: result={:?}",
1055            result);
1056
1057     result
1058 }
1059
1060 fn make_object_type<'tcx>(this: &AstConv<'tcx>,
1061                           span: Span,
1062                           principal: ty::PolyTraitRef<'tcx>,
1063                           bounds: ty::ExistentialBounds<'tcx>)
1064                           -> Ty<'tcx> {
1065     let tcx = this.tcx();
1066     let object = ty::TraitTy {
1067         principal: principal,
1068         bounds: bounds
1069     };
1070     let object_trait_ref =
1071         object.principal_trait_ref_with_self_ty(tcx, tcx.types.err);
1072
1073     // ensure the super predicates and stop if we encountered an error
1074     if this.ensure_super_predicates(span, object.principal_def_id()).is_err() {
1075         return tcx.types.err;
1076     }
1077
1078     let mut associated_types: FnvHashSet<(ast::DefId, ast::Name)> =
1079         traits::supertraits(tcx, object_trait_ref)
1080         .flat_map(|tr| {
1081             let trait_def = tcx.lookup_trait_def(tr.def_id());
1082             trait_def.associated_type_names
1083                 .clone()
1084                 .into_iter()
1085                 .map(move |associated_type_name| (tr.def_id(), associated_type_name))
1086         })
1087         .collect();
1088
1089     for projection_bound in &object.bounds.projection_bounds {
1090         let pair = (projection_bound.0.projection_ty.trait_ref.def_id,
1091                     projection_bound.0.projection_ty.item_name);
1092         associated_types.remove(&pair);
1093     }
1094
1095     for (trait_def_id, name) in associated_types {
1096         span_err!(tcx.sess, span, E0191,
1097             "the value of the associated type `{}` (from the trait `{}`) must be specified",
1098                     name,
1099                     tcx.item_path_str(trait_def_id));
1100     }
1101
1102     tcx.mk_trait(object.principal, object.bounds)
1103 }
1104
1105 fn report_ambiguous_associated_type(tcx: &ty::ctxt,
1106                                     span: Span,
1107                                     type_str: &str,
1108                                     trait_str: &str,
1109                                     name: &str) {
1110     span_err!(tcx.sess, span, E0223,
1111               "ambiguous associated type; specify the type using the syntax \
1112                `<{} as {}>::{}`",
1113               type_str, trait_str, name);
1114 }
1115
1116 // Search for a bound on a type parameter which includes the associated item
1117 // given by assoc_name. ty_param_node_id is the node id for the type parameter
1118 // (which might be `Self`, but only if it is the `Self` of a trait, not an
1119 // impl). This function will fail if there are no suitable bounds or there is
1120 // any ambiguity.
1121 fn find_bound_for_assoc_item<'tcx>(this: &AstConv<'tcx>,
1122                                    ty_param_node_id: ast::NodeId,
1123                                    ty_param_name: ast::Name,
1124                                    assoc_name: ast::Name,
1125                                    span: Span)
1126                                    -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1127 {
1128     let tcx = this.tcx();
1129
1130     let bounds = match this.get_type_parameter_bounds(span, ty_param_node_id) {
1131         Ok(v) => v,
1132         Err(ErrorReported) => {
1133             return Err(ErrorReported);
1134         }
1135     };
1136
1137     // Ensure the super predicates and stop if we encountered an error.
1138     if bounds.iter().any(|b| this.ensure_super_predicates(span, b.def_id()).is_err()) {
1139         return Err(ErrorReported);
1140     }
1141
1142     // Check that there is exactly one way to find an associated type with the
1143     // correct name.
1144     let suitable_bounds: Vec<_> =
1145         traits::transitive_bounds(tcx, &bounds)
1146         .filter(|b| this.trait_defines_associated_type_named(b.def_id(), assoc_name))
1147         .collect();
1148
1149     one_bound_for_assoc_type(tcx,
1150                              suitable_bounds,
1151                              &ty_param_name.as_str(),
1152                              &assoc_name.as_str(),
1153                              span)
1154 }
1155
1156
1157 // Checks that bounds contains exactly one element and reports appropriate
1158 // errors otherwise.
1159 fn one_bound_for_assoc_type<'tcx>(tcx: &ty::ctxt<'tcx>,
1160                                   bounds: Vec<ty::PolyTraitRef<'tcx>>,
1161                                   ty_param_name: &str,
1162                                   assoc_name: &str,
1163                                   span: Span)
1164     -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1165 {
1166     if bounds.is_empty() {
1167         span_err!(tcx.sess, span, E0220,
1168                   "associated type `{}` not found for `{}`",
1169                   assoc_name,
1170                   ty_param_name);
1171         return Err(ErrorReported);
1172     }
1173
1174     if bounds.len() > 1 {
1175         span_err!(tcx.sess, span, E0221,
1176                   "ambiguous associated type `{}` in bounds of `{}`",
1177                   assoc_name,
1178                   ty_param_name);
1179
1180         for bound in &bounds {
1181             span_note!(tcx.sess, span,
1182                        "associated type `{}` could derive from `{}`",
1183                        ty_param_name,
1184                        bound);
1185         }
1186     }
1187
1188     Ok(bounds[0].clone())
1189 }
1190
1191 // Create a type from a a path to an associated type.
1192 // For a path A::B::C::D, ty and ty_path_def are the type and def for A::B::C
1193 // and item_segment is the path segment for D. We return a type and a def for
1194 // the whole path.
1195 // Will fail except for T::A and Self::A; i.e., if ty/ty_path_def are not a type
1196 // parameter or Self.
1197 fn associated_path_def_to_ty<'tcx>(this: &AstConv<'tcx>,
1198                                    span: Span,
1199                                    ty: Ty<'tcx>,
1200                                    ty_path_def: def::Def,
1201                                    item_segment: &ast::PathSegment)
1202                                    -> (Ty<'tcx>, def::Def)
1203 {
1204     let tcx = this.tcx();
1205     let assoc_name = item_segment.identifier.name;
1206
1207     debug!("associated_path_def_to_ty: {:?}::{}", ty, assoc_name);
1208
1209     check_path_args(tcx, slice::ref_slice(item_segment), NO_TPS | NO_REGIONS);
1210
1211     // Find the type of the associated item, and the trait where the associated
1212     // item is declared.
1213     let bound = match (&ty.sty, ty_path_def) {
1214         (_, def::DefSelfTy(Some(trait_did), Some((impl_id, _)))) => {
1215             // `Self` in an impl of a trait - we have a concrete self type and a
1216             // trait reference.
1217             let trait_ref = tcx.impl_trait_ref(ast_util::local_def(impl_id)).unwrap();
1218             let trait_ref = if let Some(free_substs) = this.get_free_substs() {
1219                 trait_ref.subst(tcx, free_substs)
1220             } else {
1221                 trait_ref
1222             };
1223
1224             if this.ensure_super_predicates(span, trait_did).is_err() {
1225                 return (tcx.types.err, ty_path_def);
1226             }
1227
1228             let candidates: Vec<ty::PolyTraitRef> =
1229                 traits::supertraits(tcx, ty::Binder(trait_ref))
1230                 .filter(|r| this.trait_defines_associated_type_named(r.def_id(),
1231                                                                      assoc_name))
1232                 .collect();
1233
1234             match one_bound_for_assoc_type(tcx,
1235                                            candidates,
1236                                            "Self",
1237                                            &assoc_name.as_str(),
1238                                            span) {
1239                 Ok(bound) => bound,
1240                 Err(ErrorReported) => return (tcx.types.err, ty_path_def),
1241             }
1242         }
1243         (&ty::TyParam(_), def::DefSelfTy(Some(trait_did), None)) => {
1244             assert_eq!(trait_did.krate, ast::LOCAL_CRATE);
1245             match find_bound_for_assoc_item(this,
1246                                             trait_did.node,
1247                                             token::special_idents::type_self.name,
1248                                             assoc_name,
1249                                             span) {
1250                 Ok(bound) => bound,
1251                 Err(ErrorReported) => return (tcx.types.err, ty_path_def),
1252             }
1253         }
1254         (&ty::TyParam(_), def::DefTyParam(_, _, param_did, param_name)) => {
1255             assert_eq!(param_did.krate, ast::LOCAL_CRATE);
1256             match find_bound_for_assoc_item(this,
1257                                             param_did.node,
1258                                             param_name,
1259                                             assoc_name,
1260                                             span) {
1261                 Ok(bound) => bound,
1262                 Err(ErrorReported) => return (tcx.types.err, ty_path_def),
1263             }
1264         }
1265         _ => {
1266             report_ambiguous_associated_type(tcx,
1267                                              span,
1268                                              &ty.to_string(),
1269                                              "Trait",
1270                                              &assoc_name.as_str());
1271             return (tcx.types.err, ty_path_def);
1272         }
1273     };
1274
1275     let trait_did = bound.0.def_id;
1276     let ty = this.projected_ty_from_poly_trait_ref(span, bound, assoc_name);
1277
1278     let item_did = if trait_did.krate == ast::LOCAL_CRATE {
1279         // `ty::trait_items` used below requires information generated
1280         // by type collection, which may be in progress at this point.
1281         match tcx.map.expect_item(trait_did.node).node {
1282             ast::ItemTrait(_, _, _, ref trait_items) => {
1283                 let item = trait_items.iter()
1284                                       .find(|i| i.ident.name == assoc_name)
1285                                       .expect("missing associated type");
1286                 ast_util::local_def(item.id)
1287             }
1288             _ => unreachable!()
1289         }
1290     } else {
1291         let trait_items = tcx.trait_items(trait_did);
1292         let item = trait_items.iter().find(|i| i.name() == assoc_name);
1293         item.expect("missing associated type").def_id()
1294     };
1295
1296     (ty, def::DefAssociatedTy(trait_did, item_did))
1297 }
1298
1299 fn qpath_to_ty<'tcx>(this: &AstConv<'tcx>,
1300                      rscope: &RegionScope,
1301                      span: Span,
1302                      param_mode: PathParamMode,
1303                      opt_self_ty: Option<Ty<'tcx>>,
1304                      trait_def_id: ast::DefId,
1305                      trait_segment: &ast::PathSegment,
1306                      item_segment: &ast::PathSegment)
1307                      -> Ty<'tcx>
1308 {
1309     let tcx = this.tcx();
1310
1311     check_path_args(tcx, slice::ref_slice(item_segment), NO_TPS | NO_REGIONS);
1312
1313     let self_ty = if let Some(ty) = opt_self_ty {
1314         ty
1315     } else {
1316         let path_str = tcx.item_path_str(trait_def_id);
1317         report_ambiguous_associated_type(tcx,
1318                                          span,
1319                                          "Type",
1320                                          &path_str,
1321                                          &item_segment.identifier.name.as_str());
1322         return tcx.types.err;
1323     };
1324
1325     debug!("qpath_to_ty: self_type={:?}", self_ty);
1326
1327     let trait_ref = ast_path_to_mono_trait_ref(this,
1328                                                rscope,
1329                                                span,
1330                                                param_mode,
1331                                                trait_def_id,
1332                                                Some(self_ty),
1333                                                trait_segment);
1334
1335     debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
1336
1337     this.projected_ty(span, trait_ref, item_segment.identifier.name)
1338 }
1339
1340 /// Convert a type supplied as value for a type argument from AST into our
1341 /// our internal representation. This is the same as `ast_ty_to_ty` but that
1342 /// it applies the object lifetime default.
1343 ///
1344 /// # Parameters
1345 ///
1346 /// * `this`, `rscope`: the surrounding context
1347 /// * `decl_generics`: the generics of the struct/enum/trait declaration being
1348 ///   referenced
1349 /// * `index`: the index of the type parameter being instantiated from the list
1350 ///   (we assume it is in the `TypeSpace`)
1351 /// * `region_substs`: a partial substitution consisting of
1352 ///   only the region type parameters being supplied to this type.
1353 /// * `ast_ty`: the ast representation of the type being supplied
1354 pub fn ast_ty_arg_to_ty<'tcx>(this: &AstConv<'tcx>,
1355                               rscope: &RegionScope,
1356                               decl_generics: &ty::Generics<'tcx>,
1357                               index: usize,
1358                               region_substs: &Substs<'tcx>,
1359                               ast_ty: &ast::Ty)
1360                               -> Ty<'tcx>
1361 {
1362     let tcx = this.tcx();
1363
1364     if let Some(def) = decl_generics.types.opt_get(TypeSpace, index) {
1365         let object_lifetime_default = def.object_lifetime_default.subst(tcx, region_substs);
1366         let rscope1 = &ObjectLifetimeDefaultRscope::new(rscope, object_lifetime_default);
1367         ast_ty_to_ty(this, rscope1, ast_ty)
1368     } else {
1369         ast_ty_to_ty(this, rscope, ast_ty)
1370     }
1371 }
1372
1373 // Check the base def in a PathResolution and convert it to a Ty. If there are
1374 // associated types in the PathResolution, these will need to be separately
1375 // resolved.
1376 fn base_def_to_ty<'tcx>(this: &AstConv<'tcx>,
1377                         rscope: &RegionScope,
1378                         span: Span,
1379                         param_mode: PathParamMode,
1380                         def: &def::Def,
1381                         opt_self_ty: Option<Ty<'tcx>>,
1382                         base_segments: &[ast::PathSegment])
1383                         -> Ty<'tcx> {
1384     let tcx = this.tcx();
1385
1386     match *def {
1387         def::DefTrait(trait_def_id) => {
1388             // N.B. this case overlaps somewhat with
1389             // TyObjectSum, see that fn for details
1390             let mut projection_bounds = Vec::new();
1391
1392             let trait_ref = object_path_to_poly_trait_ref(this,
1393                                                           rscope,
1394                                                           span,
1395                                                           param_mode,
1396                                                           trait_def_id,
1397                                                           base_segments.last().unwrap(),
1398                                                           &mut projection_bounds);
1399
1400             check_path_args(tcx, base_segments.split_last().unwrap().1, NO_TPS | NO_REGIONS);
1401             trait_ref_to_object_type(this,
1402                                      rscope,
1403                                      span,
1404                                      trait_ref,
1405                                      projection_bounds,
1406                                      &[])
1407         }
1408         def::DefTy(did, _) | def::DefStruct(did) => {
1409             check_path_args(tcx, base_segments.split_last().unwrap().1, NO_TPS | NO_REGIONS);
1410             ast_path_to_ty(this,
1411                            rscope,
1412                            span,
1413                            param_mode,
1414                            did,
1415                            base_segments.last().unwrap())
1416         }
1417         def::DefTyParam(space, index, _, name) => {
1418             check_path_args(tcx, base_segments, NO_TPS | NO_REGIONS);
1419             tcx.mk_param(space, index, name)
1420         }
1421         def::DefSelfTy(_, Some((_, self_ty_id))) => {
1422             // Self in impl (we know the concrete type).
1423             check_path_args(tcx, base_segments, NO_TPS | NO_REGIONS);
1424             if let Some(&ty) = tcx.ast_ty_to_ty_cache.borrow().get(&self_ty_id) {
1425                 if let Some(free_substs) = this.get_free_substs() {
1426                     ty.subst(tcx, free_substs)
1427                 } else {
1428                     ty
1429                 }
1430             } else {
1431                 tcx.sess.span_bug(span, "self type has not been fully resolved")
1432             }
1433         }
1434         def::DefSelfTy(Some(_), None) => {
1435             // Self in trait.
1436             check_path_args(tcx, base_segments, NO_TPS | NO_REGIONS);
1437             tcx.mk_self_type()
1438         }
1439         def::DefAssociatedTy(trait_did, _) => {
1440             check_path_args(tcx, &base_segments[..base_segments.len()-2], NO_TPS | NO_REGIONS);
1441             qpath_to_ty(this,
1442                         rscope,
1443                         span,
1444                         param_mode,
1445                         opt_self_ty,
1446                         trait_did,
1447                         &base_segments[base_segments.len()-2],
1448                         base_segments.last().unwrap())
1449         }
1450         def::DefMod(id) => {
1451             // Used as sentinel by callers to indicate the `<T>::A::B::C` form.
1452             // FIXME(#22519) This part of the resolution logic should be
1453             // avoided entirely for that form, once we stop needed a Def
1454             // for `associated_path_def_to_ty`.
1455             // Fixing this will also let use resolve <Self>::Foo the same way we
1456             // resolve Self::Foo, at the moment we can't resolve the former because
1457             // we don't have the trait information around, which is just sad.
1458
1459             if !base_segments.is_empty() {
1460                 span_err!(tcx.sess,
1461                           span,
1462                           E0247,
1463                           "found module name used as a type: {}",
1464                           tcx.map.node_to_string(id.node));
1465                 return this.tcx().types.err;
1466             }
1467
1468             opt_self_ty.expect("missing T in <T>::a::b::c")
1469         }
1470         def::DefPrimTy(prim_ty) => {
1471             prim_ty_to_ty(tcx, base_segments, prim_ty)
1472         }
1473         _ => {
1474             let node = def.def_id().node;
1475             span_err!(tcx.sess, span, E0248,
1476                       "found value `{}` used as a type",
1477                       tcx.map.path_to_string(node));
1478             return this.tcx().types.err;
1479         }
1480     }
1481 }
1482
1483 // Note that both base_segments and assoc_segments may be empty, although not at
1484 // the same time.
1485 pub fn finish_resolving_def_to_ty<'tcx>(this: &AstConv<'tcx>,
1486                                         rscope: &RegionScope,
1487                                         span: Span,
1488                                         param_mode: PathParamMode,
1489                                         def: &def::Def,
1490                                         opt_self_ty: Option<Ty<'tcx>>,
1491                                         base_segments: &[ast::PathSegment],
1492                                         assoc_segments: &[ast::PathSegment])
1493                                         -> Ty<'tcx> {
1494     let mut ty = base_def_to_ty(this,
1495                                 rscope,
1496                                 span,
1497                                 param_mode,
1498                                 def,
1499                                 opt_self_ty,
1500                                 base_segments);
1501     let mut def = *def;
1502     // If any associated type segments remain, attempt to resolve them.
1503     for segment in assoc_segments {
1504         if ty.sty == ty::TyError {
1505             break;
1506         }
1507         // This is pretty bad (it will fail except for T::A and Self::A).
1508         let (a_ty, a_def) = associated_path_def_to_ty(this,
1509                                                       span,
1510                                                       ty,
1511                                                       def,
1512                                                       segment);
1513         ty = a_ty;
1514         def = a_def;
1515     }
1516     ty
1517 }
1518
1519 /// Parses the programmer's textual representation of a type into our
1520 /// internal notion of a type.
1521 pub fn ast_ty_to_ty<'tcx>(this: &AstConv<'tcx>,
1522                           rscope: &RegionScope,
1523                           ast_ty: &ast::Ty)
1524                           -> Ty<'tcx>
1525 {
1526     debug!("ast_ty_to_ty(ast_ty={:?})",
1527            ast_ty);
1528
1529     let tcx = this.tcx();
1530
1531     if let Some(&ty) = tcx.ast_ty_to_ty_cache.borrow().get(&ast_ty.id) {
1532         return ty;
1533     }
1534
1535     let typ = match ast_ty.node {
1536         ast::TyVec(ref ty) => {
1537             tcx.mk_slice(ast_ty_to_ty(this, rscope, &**ty))
1538         }
1539         ast::TyObjectSum(ref ty, ref bounds) => {
1540             match ast_ty_to_trait_ref(this, rscope, &**ty, bounds) {
1541                 Ok((trait_ref, projection_bounds)) => {
1542                     trait_ref_to_object_type(this,
1543                                              rscope,
1544                                              ast_ty.span,
1545                                              trait_ref,
1546                                              projection_bounds,
1547                                              bounds)
1548                 }
1549                 Err(ErrorReported) => {
1550                     this.tcx().types.err
1551                 }
1552             }
1553         }
1554         ast::TyPtr(ref mt) => {
1555             tcx.mk_ptr(ty::TypeAndMut {
1556                 ty: ast_ty_to_ty(this, rscope, &*mt.ty),
1557                 mutbl: mt.mutbl
1558             })
1559         }
1560         ast::TyRptr(ref region, ref mt) => {
1561             let r = opt_ast_region_to_region(this, rscope, ast_ty.span, region);
1562             debug!("TyRef r={:?}", r);
1563             let rscope1 =
1564                 &ObjectLifetimeDefaultRscope::new(
1565                     rscope,
1566                     ty::ObjectLifetimeDefault::Specific(r));
1567             let t = ast_ty_to_ty(this, rscope1, &*mt.ty);
1568             tcx.mk_ref(tcx.mk_region(r), ty::TypeAndMut {ty: t, mutbl: mt.mutbl})
1569         }
1570         ast::TyTup(ref fields) => {
1571             let flds = fields.iter()
1572                              .map(|t| ast_ty_to_ty(this, rscope, &**t))
1573                              .collect();
1574             tcx.mk_tup(flds)
1575         }
1576         ast::TyParen(ref typ) => ast_ty_to_ty(this, rscope, &**typ),
1577         ast::TyBareFn(ref bf) => {
1578             require_c_abi_if_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
1579             let bare_fn = ty_of_bare_fn(this, bf.unsafety, bf.abi, &*bf.decl);
1580             tcx.mk_fn(None, tcx.mk_bare_fn(bare_fn))
1581         }
1582         ast::TyPolyTraitRef(ref bounds) => {
1583             conv_ty_poly_trait_ref(this, rscope, ast_ty.span, bounds)
1584         }
1585         ast::TyPath(ref maybe_qself, ref path) => {
1586             let path_res = if let Some(&d) = tcx.def_map.borrow().get(&ast_ty.id) {
1587                 d
1588             } else if let Some(ast::QSelf { position: 0, .. }) = *maybe_qself {
1589                 // Create some fake resolution that can't possibly be a type.
1590                 def::PathResolution {
1591                     base_def: def::DefMod(ast_util::local_def(ast::CRATE_NODE_ID)),
1592                     last_private: LastMod(AllPublic),
1593                     depth: path.segments.len()
1594                 }
1595             } else {
1596                 tcx.sess.span_bug(ast_ty.span, &format!("unbound path {:?}", ast_ty))
1597             };
1598             let def = path_res.base_def;
1599             let base_ty_end = path.segments.len() - path_res.depth;
1600             let opt_self_ty = maybe_qself.as_ref().map(|qself| {
1601                 ast_ty_to_ty(this, rscope, &qself.ty)
1602             });
1603             let ty = finish_resolving_def_to_ty(this,
1604                                                 rscope,
1605                                                 ast_ty.span,
1606                                                 PathParamMode::Explicit,
1607                                                 &def,
1608                                                 opt_self_ty,
1609                                                 &path.segments[..base_ty_end],
1610                                                 &path.segments[base_ty_end..]);
1611
1612             if path_res.depth != 0 && ty.sty != ty::TyError {
1613                 // Write back the new resolution.
1614                 tcx.def_map.borrow_mut().insert(ast_ty.id, def::PathResolution {
1615                     base_def: def,
1616                     last_private: path_res.last_private,
1617                     depth: 0
1618                 });
1619             }
1620
1621             ty
1622         }
1623         ast::TyFixedLengthVec(ref ty, ref e) => {
1624             let hint = UncheckedExprHint(tcx.types.usize);
1625             match const_eval::eval_const_expr_partial(tcx, &e, hint) {
1626                 Ok(r) => {
1627                     match r {
1628                         ConstVal::Int(i) =>
1629                             tcx.mk_array(ast_ty_to_ty(this, rscope, &**ty),
1630                                          i as usize),
1631                         ConstVal::Uint(i) =>
1632                             tcx.mk_array(ast_ty_to_ty(this, rscope, &**ty),
1633                                          i as usize),
1634                         _ => {
1635                             span_err!(tcx.sess, ast_ty.span, E0249,
1636                                       "expected constant integer expression \
1637                                        for array length");
1638                             this.tcx().types.err
1639                         }
1640                     }
1641                 }
1642                 Err(ref r) => {
1643                     let subspan  =
1644                         ast_ty.span.lo <= r.span.lo && r.span.hi <= ast_ty.span.hi;
1645                     span_err!(tcx.sess, r.span, E0250,
1646                               "array length constant evaluation error: {}",
1647                               r.description());
1648                     if !subspan {
1649                         span_note!(tcx.sess, ast_ty.span, "for array length here")
1650                     }
1651                     this.tcx().types.err
1652                 }
1653             }
1654         }
1655         ast::TyTypeof(ref _e) => {
1656             tcx.sess.span_bug(ast_ty.span, "typeof is reserved but unimplemented");
1657         }
1658         ast::TyInfer => {
1659             // TyInfer also appears as the type of arguments or return
1660             // values in a ExprClosure, or as
1661             // the type of local variables. Both of these cases are
1662             // handled specially and will not descend into this routine.
1663             this.ty_infer(None, None, None, ast_ty.span)
1664         }
1665     };
1666
1667     tcx.ast_ty_to_ty_cache.borrow_mut().insert(ast_ty.id, typ);
1668     return typ;
1669 }
1670
1671 pub fn ty_of_arg<'tcx>(this: &AstConv<'tcx>,
1672                        rscope: &RegionScope,
1673                        a: &ast::Arg,
1674                        expected_ty: Option<Ty<'tcx>>)
1675                        -> Ty<'tcx>
1676 {
1677     match a.ty.node {
1678         ast::TyInfer if expected_ty.is_some() => expected_ty.unwrap(),
1679         ast::TyInfer => this.ty_infer(None, None, None, a.ty.span),
1680         _ => ast_ty_to_ty(this, rscope, &*a.ty),
1681     }
1682 }
1683
1684 struct SelfInfo<'a, 'tcx> {
1685     untransformed_self_ty: Ty<'tcx>,
1686     explicit_self: &'a ast::ExplicitSelf,
1687 }
1688
1689 pub fn ty_of_method<'tcx>(this: &AstConv<'tcx>,
1690                           sig: &ast::MethodSig,
1691                           untransformed_self_ty: Ty<'tcx>)
1692                           -> (ty::BareFnTy<'tcx>, ty::ExplicitSelfCategory) {
1693     let self_info = Some(SelfInfo {
1694         untransformed_self_ty: untransformed_self_ty,
1695         explicit_self: &sig.explicit_self,
1696     });
1697     let (bare_fn_ty, optional_explicit_self_category) =
1698         ty_of_method_or_bare_fn(this,
1699                                 sig.unsafety,
1700                                 sig.abi,
1701                                 self_info,
1702                                 &sig.decl);
1703     (bare_fn_ty, optional_explicit_self_category.unwrap())
1704 }
1705
1706 pub fn ty_of_bare_fn<'tcx>(this: &AstConv<'tcx>, unsafety: ast::Unsafety, abi: abi::Abi,
1707                                               decl: &ast::FnDecl) -> ty::BareFnTy<'tcx> {
1708     let (bare_fn_ty, _) = ty_of_method_or_bare_fn(this, unsafety, abi, None, decl);
1709     bare_fn_ty
1710 }
1711
1712 fn ty_of_method_or_bare_fn<'a, 'tcx>(this: &AstConv<'tcx>,
1713                                      unsafety: ast::Unsafety,
1714                                      abi: abi::Abi,
1715                                      opt_self_info: Option<SelfInfo<'a, 'tcx>>,
1716                                      decl: &ast::FnDecl)
1717                                      -> (ty::BareFnTy<'tcx>, Option<ty::ExplicitSelfCategory>)
1718 {
1719     debug!("ty_of_method_or_bare_fn");
1720
1721     // New region names that appear inside of the arguments of the function
1722     // declaration are bound to that function type.
1723     let rb = rscope::BindingRscope::new();
1724
1725     // `implied_output_region` is the region that will be assumed for any
1726     // region parameters in the return type. In accordance with the rules for
1727     // lifetime elision, we can determine it in two ways. First (determined
1728     // here), if self is by-reference, then the implied output region is the
1729     // region of the self parameter.
1730     let mut explicit_self_category_result = None;
1731     let (self_ty, implied_output_region) = match opt_self_info {
1732         None => (None, None),
1733         Some(self_info) => {
1734             // This type comes from an impl or trait; no late-bound
1735             // regions should be present.
1736             assert!(!self_info.untransformed_self_ty.has_escaping_regions());
1737
1738             // Figure out and record the explicit self category.
1739             let explicit_self_category =
1740                 determine_explicit_self_category(this, &rb, &self_info);
1741             explicit_self_category_result = Some(explicit_self_category);
1742             match explicit_self_category {
1743                 ty::StaticExplicitSelfCategory => {
1744                     (None, None)
1745                 }
1746                 ty::ByValueExplicitSelfCategory => {
1747                     (Some(self_info.untransformed_self_ty), None)
1748                 }
1749                 ty::ByReferenceExplicitSelfCategory(region, mutability) => {
1750                     (Some(this.tcx().mk_ref(
1751                                       this.tcx().mk_region(region),
1752                                       ty::TypeAndMut {
1753                                         ty: self_info.untransformed_self_ty,
1754                                         mutbl: mutability
1755                                       })),
1756                      Some(region))
1757                 }
1758                 ty::ByBoxExplicitSelfCategory => {
1759                     (Some(this.tcx().mk_box(self_info.untransformed_self_ty)), None)
1760                 }
1761             }
1762         }
1763     };
1764
1765     // HACK(eddyb) replace the fake self type in the AST with the actual type.
1766     let input_params = if self_ty.is_some() {
1767         &decl.inputs[1..]
1768     } else {
1769         &decl.inputs[..]
1770     };
1771     let input_tys = input_params.iter().map(|a| ty_of_arg(this, &rb, a, None));
1772     let input_pats: Vec<String> = input_params.iter()
1773                                               .map(|a| pprust::pat_to_string(&*a.pat))
1774                                               .collect();
1775     let self_and_input_tys: Vec<Ty> =
1776         self_ty.into_iter().chain(input_tys).collect();
1777
1778
1779     // Second, if there was exactly one lifetime (either a substitution or a
1780     // reference) in the arguments, then any anonymous regions in the output
1781     // have that lifetime.
1782     let implied_output_region = match implied_output_region {
1783         Some(r) => Ok(r),
1784         None => {
1785             let input_tys = if self_ty.is_some() {
1786                 // Skip the first argument if `self` is present.
1787                 &self_and_input_tys[1..]
1788             } else {
1789                 &self_and_input_tys[..]
1790             };
1791
1792             find_implied_output_region(this.tcx(), input_tys, input_pats)
1793         }
1794     };
1795
1796     let output_ty = match decl.output {
1797         ast::Return(ref output) if output.node == ast::TyInfer =>
1798             ty::FnConverging(this.ty_infer(None, None, None, output.span)),
1799         ast::Return(ref output) =>
1800             ty::FnConverging(convert_ty_with_lifetime_elision(this,
1801                                                               implied_output_region,
1802                                                               &output)),
1803         ast::DefaultReturn(..) => ty::FnConverging(this.tcx().mk_nil()),
1804         ast::NoReturn(..) => ty::FnDiverging
1805     };
1806
1807     (ty::BareFnTy {
1808         unsafety: unsafety,
1809         abi: abi,
1810         sig: ty::Binder(ty::FnSig {
1811             inputs: self_and_input_tys,
1812             output: output_ty,
1813             variadic: decl.variadic
1814         }),
1815     }, explicit_self_category_result)
1816 }
1817
1818 fn determine_explicit_self_category<'a, 'tcx>(this: &AstConv<'tcx>,
1819                                               rscope: &RegionScope,
1820                                               self_info: &SelfInfo<'a, 'tcx>)
1821                                               -> ty::ExplicitSelfCategory
1822 {
1823     return match self_info.explicit_self.node {
1824         ast::SelfStatic => ty::StaticExplicitSelfCategory,
1825         ast::SelfValue(_) => ty::ByValueExplicitSelfCategory,
1826         ast::SelfRegion(ref lifetime, mutability, _) => {
1827             let region =
1828                 opt_ast_region_to_region(this,
1829                                          rscope,
1830                                          self_info.explicit_self.span,
1831                                          lifetime);
1832             ty::ByReferenceExplicitSelfCategory(region, mutability)
1833         }
1834         ast::SelfExplicit(ref ast_type, _) => {
1835             let explicit_type = ast_ty_to_ty(this, rscope, &**ast_type);
1836
1837             // We wish to (for now) categorize an explicit self
1838             // declaration like `self: SomeType` into either `self`,
1839             // `&self`, `&mut self`, or `Box<self>`. We do this here
1840             // by some simple pattern matching. A more precise check
1841             // is done later in `check_method_self_type()`.
1842             //
1843             // Examples:
1844             //
1845             // ```
1846             // impl Foo for &T {
1847             //     // Legal declarations:
1848             //     fn method1(self: &&T); // ByReferenceExplicitSelfCategory
1849             //     fn method2(self: &T); // ByValueExplicitSelfCategory
1850             //     fn method3(self: Box<&T>); // ByBoxExplicitSelfCategory
1851             //
1852             //     // Invalid cases will be caught later by `check_method_self_type`:
1853             //     fn method_err1(self: &mut T); // ByReferenceExplicitSelfCategory
1854             // }
1855             // ```
1856             //
1857             // To do the check we just count the number of "modifiers"
1858             // on each type and compare them. If they are the same or
1859             // the impl has more, we call it "by value". Otherwise, we
1860             // look at the outermost modifier on the method decl and
1861             // call it by-ref, by-box as appropriate. For method1, for
1862             // example, the impl type has one modifier, but the method
1863             // type has two, so we end up with
1864             // ByReferenceExplicitSelfCategory.
1865
1866             let impl_modifiers = count_modifiers(self_info.untransformed_self_ty);
1867             let method_modifiers = count_modifiers(explicit_type);
1868
1869             debug!("determine_explicit_self_category(self_info.untransformed_self_ty={:?} \
1870                    explicit_type={:?} \
1871                    modifiers=({},{})",
1872                    self_info.untransformed_self_ty,
1873                    explicit_type,
1874                    impl_modifiers,
1875                    method_modifiers);
1876
1877             if impl_modifiers >= method_modifiers {
1878                 ty::ByValueExplicitSelfCategory
1879             } else {
1880                 match explicit_type.sty {
1881                     ty::TyRef(r, mt) => ty::ByReferenceExplicitSelfCategory(*r, mt.mutbl),
1882                     ty::TyBox(_) => ty::ByBoxExplicitSelfCategory,
1883                     _ => ty::ByValueExplicitSelfCategory,
1884                 }
1885             }
1886         }
1887     };
1888
1889     fn count_modifiers(ty: Ty) -> usize {
1890         match ty.sty {
1891             ty::TyRef(_, mt) => count_modifiers(mt.ty) + 1,
1892             ty::TyBox(t) => count_modifiers(t) + 1,
1893             _ => 0,
1894         }
1895     }
1896 }
1897
1898 pub fn ty_of_closure<'tcx>(
1899     this: &AstConv<'tcx>,
1900     unsafety: ast::Unsafety,
1901     decl: &ast::FnDecl,
1902     abi: abi::Abi,
1903     expected_sig: Option<ty::FnSig<'tcx>>)
1904     -> ty::ClosureTy<'tcx>
1905 {
1906     debug!("ty_of_closure(expected_sig={:?})",
1907            expected_sig);
1908
1909     // new region names that appear inside of the fn decl are bound to
1910     // that function type
1911     let rb = rscope::BindingRscope::new();
1912
1913     let input_tys: Vec<_> = decl.inputs.iter().enumerate().map(|(i, a)| {
1914         let expected_arg_ty = expected_sig.as_ref().and_then(|e| {
1915             // no guarantee that the correct number of expected args
1916             // were supplied
1917             if i < e.inputs.len() {
1918                 Some(e.inputs[i])
1919             } else {
1920                 None
1921             }
1922         });
1923         ty_of_arg(this, &rb, a, expected_arg_ty)
1924     }).collect();
1925
1926     let expected_ret_ty = expected_sig.map(|e| e.output);
1927
1928     let is_infer = match decl.output {
1929         ast::Return(ref output) if output.node == ast::TyInfer => true,
1930         ast::DefaultReturn(..) => true,
1931         _ => false
1932     };
1933
1934     let output_ty = match decl.output {
1935         _ if is_infer && expected_ret_ty.is_some() =>
1936             expected_ret_ty.unwrap(),
1937         _ if is_infer =>
1938             ty::FnConverging(this.ty_infer(None, None, None, decl.output.span())),
1939         ast::Return(ref output) =>
1940             ty::FnConverging(ast_ty_to_ty(this, &rb, &**output)),
1941         ast::DefaultReturn(..) => unreachable!(),
1942         ast::NoReturn(..) => ty::FnDiverging
1943     };
1944
1945     debug!("ty_of_closure: input_tys={:?}", input_tys);
1946     debug!("ty_of_closure: output_ty={:?}", output_ty);
1947
1948     ty::ClosureTy {
1949         unsafety: unsafety,
1950         abi: abi,
1951         sig: ty::Binder(ty::FnSig {inputs: input_tys,
1952                                    output: output_ty,
1953                                    variadic: decl.variadic}),
1954     }
1955 }
1956
1957 /// Given an existential type like `Foo+'a+Bar`, this routine converts the `'a` and `Bar` intos an
1958 /// `ExistentialBounds` struct. The `main_trait_refs` argument specifies the `Foo` -- it is absent
1959 /// for closures. Eventually this should all be normalized, I think, so that there is no "main
1960 /// trait ref" and instead we just have a flat list of bounds as the existential type.
1961 fn conv_existential_bounds<'tcx>(
1962     this: &AstConv<'tcx>,
1963     rscope: &RegionScope,
1964     span: Span,
1965     principal_trait_ref: ty::PolyTraitRef<'tcx>,
1966     projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>,
1967     ast_bounds: &[ast::TyParamBound])
1968     -> ty::ExistentialBounds<'tcx>
1969 {
1970     let partitioned_bounds =
1971         partition_bounds(this.tcx(), span, ast_bounds);
1972
1973     conv_existential_bounds_from_partitioned_bounds(
1974         this, rscope, span, principal_trait_ref, projection_bounds, partitioned_bounds)
1975 }
1976
1977 fn conv_ty_poly_trait_ref<'tcx>(
1978     this: &AstConv<'tcx>,
1979     rscope: &RegionScope,
1980     span: Span,
1981     ast_bounds: &[ast::TyParamBound])
1982     -> Ty<'tcx>
1983 {
1984     let mut partitioned_bounds = partition_bounds(this.tcx(), span, &ast_bounds[..]);
1985
1986     let mut projection_bounds = Vec::new();
1987     let main_trait_bound = if !partitioned_bounds.trait_bounds.is_empty() {
1988         let trait_bound = partitioned_bounds.trait_bounds.remove(0);
1989         instantiate_poly_trait_ref(this,
1990                                    rscope,
1991                                    trait_bound,
1992                                    None,
1993                                    &mut projection_bounds)
1994     } else {
1995         span_err!(this.tcx().sess, span, E0224,
1996                   "at least one non-builtin trait is required for an object type");
1997         return this.tcx().types.err;
1998     };
1999
2000     let bounds =
2001         conv_existential_bounds_from_partitioned_bounds(this,
2002                                                         rscope,
2003                                                         span,
2004                                                         main_trait_bound.clone(),
2005                                                         projection_bounds,
2006                                                         partitioned_bounds);
2007
2008     make_object_type(this, span, main_trait_bound, bounds)
2009 }
2010
2011 pub fn conv_existential_bounds_from_partitioned_bounds<'tcx>(
2012     this: &AstConv<'tcx>,
2013     rscope: &RegionScope,
2014     span: Span,
2015     principal_trait_ref: ty::PolyTraitRef<'tcx>,
2016     mut projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>, // Empty for boxed closures
2017     partitioned_bounds: PartitionedBounds)
2018     -> ty::ExistentialBounds<'tcx>
2019 {
2020     let PartitionedBounds { builtin_bounds,
2021                             trait_bounds,
2022                             region_bounds } =
2023         partitioned_bounds;
2024
2025     if !trait_bounds.is_empty() {
2026         let b = &trait_bounds[0];
2027         span_err!(this.tcx().sess, b.trait_ref.path.span, E0225,
2028                   "only the builtin traits can be used as closure or object bounds");
2029     }
2030
2031     let region_bound =
2032         compute_object_lifetime_bound(this,
2033                                       span,
2034                                       &region_bounds,
2035                                       principal_trait_ref,
2036                                       builtin_bounds);
2037
2038     let region_bound = match region_bound {
2039         Some(r) => r,
2040         None => {
2041             match rscope.object_lifetime_default(span) {
2042                 Some(r) => r,
2043                 None => {
2044                     span_err!(this.tcx().sess, span, E0228,
2045                               "the lifetime bound for this object type cannot be deduced \
2046                                from context; please supply an explicit bound");
2047                     ty::ReStatic
2048                 }
2049             }
2050         }
2051     };
2052
2053     debug!("region_bound: {:?}", region_bound);
2054
2055     ty::sort_bounds_list(&mut projection_bounds);
2056
2057     ty::ExistentialBounds {
2058         region_bound: region_bound,
2059         builtin_bounds: builtin_bounds,
2060         projection_bounds: projection_bounds,
2061     }
2062 }
2063
2064 /// Given the bounds on an object, determines what single region bound
2065 /// (if any) we can use to summarize this type. The basic idea is that we will use the bound the
2066 /// user provided, if they provided one, and otherwise search the supertypes of trait bounds for
2067 /// region bounds. It may be that we can derive no bound at all, in which case we return `None`.
2068 fn compute_object_lifetime_bound<'tcx>(
2069     this: &AstConv<'tcx>,
2070     span: Span,
2071     explicit_region_bounds: &[&ast::Lifetime],
2072     principal_trait_ref: ty::PolyTraitRef<'tcx>,
2073     builtin_bounds: ty::BuiltinBounds)
2074     -> Option<ty::Region> // if None, use the default
2075 {
2076     let tcx = this.tcx();
2077
2078     debug!("compute_opt_region_bound(explicit_region_bounds={:?}, \
2079            principal_trait_ref={:?}, builtin_bounds={:?})",
2080            explicit_region_bounds,
2081            principal_trait_ref,
2082            builtin_bounds);
2083
2084     if explicit_region_bounds.len() > 1 {
2085         span_err!(tcx.sess, explicit_region_bounds[1].span, E0226,
2086             "only a single explicit lifetime bound is permitted");
2087     }
2088
2089     if !explicit_region_bounds.is_empty() {
2090         // Explicitly specified region bound. Use that.
2091         let r = explicit_region_bounds[0];
2092         return Some(ast_region_to_region(tcx, r));
2093     }
2094
2095     if let Err(ErrorReported) = this.ensure_super_predicates(span,principal_trait_ref.def_id()) {
2096         return Some(ty::ReStatic);
2097     }
2098
2099     // No explicit region bound specified. Therefore, examine trait
2100     // bounds and see if we can derive region bounds from those.
2101     let derived_region_bounds =
2102         object_region_bounds(tcx, &principal_trait_ref, builtin_bounds);
2103
2104     // If there are no derived region bounds, then report back that we
2105     // can find no region bound. The caller will use the default.
2106     if derived_region_bounds.is_empty() {
2107         return None;
2108     }
2109
2110     // If any of the derived region bounds are 'static, that is always
2111     // the best choice.
2112     if derived_region_bounds.iter().any(|r| ty::ReStatic == *r) {
2113         return Some(ty::ReStatic);
2114     }
2115
2116     // Determine whether there is exactly one unique region in the set
2117     // of derived region bounds. If so, use that. Otherwise, report an
2118     // error.
2119     let r = derived_region_bounds[0];
2120     if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2121         span_err!(tcx.sess, span, E0227,
2122                   "ambiguous lifetime bound, explicit lifetime bound required");
2123     }
2124     return Some(r);
2125 }
2126
2127 pub struct PartitionedBounds<'a> {
2128     pub builtin_bounds: ty::BuiltinBounds,
2129     pub trait_bounds: Vec<&'a ast::PolyTraitRef>,
2130     pub region_bounds: Vec<&'a ast::Lifetime>,
2131 }
2132
2133 /// Divides a list of bounds from the AST into three groups: builtin bounds (Copy, Sized etc),
2134 /// general trait bounds, and region bounds.
2135 pub fn partition_bounds<'a>(tcx: &ty::ctxt,
2136                             _span: Span,
2137                             ast_bounds: &'a [ast::TyParamBound])
2138                             -> PartitionedBounds<'a>
2139 {
2140     let mut builtin_bounds = ty::BuiltinBounds::empty();
2141     let mut region_bounds = Vec::new();
2142     let mut trait_bounds = Vec::new();
2143     for ast_bound in ast_bounds {
2144         match *ast_bound {
2145             ast::TraitTyParamBound(ref b, ast::TraitBoundModifier::None) => {
2146                 match ::lookup_full_def(tcx, b.trait_ref.path.span, b.trait_ref.ref_id) {
2147                     def::DefTrait(trait_did) => {
2148                         if tcx.try_add_builtin_trait(trait_did,
2149                                                      &mut builtin_bounds) {
2150                             let segments = &b.trait_ref.path.segments;
2151                             let parameters = &segments[segments.len() - 1].parameters;
2152                             if !parameters.types().is_empty() {
2153                                 check_type_argument_count(tcx, b.trait_ref.path.span,
2154                                                           parameters.types().len(), 0, 0);
2155                             }
2156                             if !parameters.lifetimes().is_empty() {
2157                                 report_lifetime_number_error(tcx, b.trait_ref.path.span,
2158                                                              parameters.lifetimes().len(), 0);
2159                             }
2160                             continue; // success
2161                         }
2162                     }
2163                     _ => {
2164                         // Not a trait? that's an error, but it'll get
2165                         // reported later.
2166                     }
2167                 }
2168                 trait_bounds.push(b);
2169             }
2170             ast::TraitTyParamBound(_, ast::TraitBoundModifier::Maybe) => {}
2171             ast::RegionTyParamBound(ref l) => {
2172                 region_bounds.push(l);
2173             }
2174         }
2175     }
2176
2177     PartitionedBounds {
2178         builtin_bounds: builtin_bounds,
2179         trait_bounds: trait_bounds,
2180         region_bounds: region_bounds,
2181     }
2182 }
2183
2184 fn prohibit_projections<'tcx>(tcx: &ty::ctxt<'tcx>,
2185                               bindings: &[ConvertedBinding<'tcx>])
2186 {
2187     for binding in bindings.iter().take(1) {
2188         span_err!(tcx.sess, binding.span, E0229,
2189             "associated type bindings are not allowed here");
2190     }
2191 }
2192
2193 fn check_type_argument_count(tcx: &ty::ctxt, span: Span, supplied: usize,
2194                              required: usize, accepted: usize) {
2195     if supplied < required {
2196         let expected = if required < accepted {
2197             "expected at least"
2198         } else {
2199             "expected"
2200         };
2201         span_err!(tcx.sess, span, E0243,
2202                   "wrong number of type arguments: {} {}, found {}",
2203                   expected, required, supplied);
2204     } else if supplied > accepted {
2205         let expected = if required < accepted {
2206             "expected at most"
2207         } else {
2208             "expected"
2209         };
2210         span_err!(tcx.sess, span, E0244,
2211                   "wrong number of type arguments: {} {}, found {}",
2212                   expected,
2213                   accepted,
2214                   supplied);
2215     }
2216 }
2217
2218 fn report_lifetime_number_error(tcx: &ty::ctxt, span: Span, number: usize, expected: usize) {
2219     span_err!(tcx.sess, span, E0107,
2220               "wrong number of lifetime parameters: expected {}, found {}",
2221               expected, number);
2222 }
2223
2224 // A helper struct for conveniently grouping a set of bounds which we pass to
2225 // and return from functions in multiple places.
2226 #[derive(PartialEq, Eq, Clone, Debug)]
2227 pub struct Bounds<'tcx> {
2228     pub region_bounds: Vec<ty::Region>,
2229     pub builtin_bounds: ty::BuiltinBounds,
2230     pub trait_bounds: Vec<ty::PolyTraitRef<'tcx>>,
2231     pub projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>,
2232 }
2233
2234 impl<'tcx> Bounds<'tcx> {
2235     pub fn predicates(&self,
2236         tcx: &ty::ctxt<'tcx>,
2237         param_ty: Ty<'tcx>)
2238         -> Vec<ty::Predicate<'tcx>>
2239     {
2240         let mut vec = Vec::new();
2241
2242         for builtin_bound in &self.builtin_bounds {
2243             match traits::trait_ref_for_builtin_bound(tcx, builtin_bound, param_ty) {
2244                 Ok(trait_ref) => { vec.push(trait_ref.to_predicate()); }
2245                 Err(ErrorReported) => { }
2246             }
2247         }
2248
2249         for &region_bound in &self.region_bounds {
2250             // account for the binder being introduced below; no need to shift `param_ty`
2251             // because, at present at least, it can only refer to early-bound regions
2252             let region_bound = ty_fold::shift_region(region_bound, 1);
2253             vec.push(ty::Binder(ty::OutlivesPredicate(param_ty, region_bound)).to_predicate());
2254         }
2255
2256         for bound_trait_ref in &self.trait_bounds {
2257             vec.push(bound_trait_ref.to_predicate());
2258         }
2259
2260         for projection in &self.projection_bounds {
2261             vec.push(projection.to_predicate());
2262         }
2263
2264         vec
2265     }
2266 }