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};
  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::parse::token;
  73 use syntax::print::pprust;
  74
  75 pub trait AstConv<'tcx> {
  76     fn tcx<'a>(&'a self) -> &'a ty::ctxt<'tcx>;
  77
  78     /// Identify the type scheme for an item with a type, like a type
  79     /// alias, fn, or struct. This allows you to figure out the set of
  80     /// type parameters defined on the item.
  81     fn get_item_type_scheme(&self, span: Span, id: ast::DefId)
  82                             -> Result<ty::TypeScheme<'tcx>, ErrorReported>;
  83
  84     /// Returns the `TraitDef` for a given trait. This allows you to
  85     /// figure out the set of type parameters defined on the trait.
  86     fn get_trait_def(&self, span: Span, id: ast::DefId)
  87                      -> Result<&'tcx ty::TraitDef<'tcx>, ErrorReported>;
  88
  89     /// Ensure that the super-predicates for the trait with the given
  90     /// id are available and also for the transitive set of
  91     /// super-predicates.
  92     fn ensure_super_predicates(&self, span: Span, id: ast::DefId)
  93                                -> Result<(), ErrorReported>;
  94
  95     /// Returns the set of bounds in scope for the type parameter with
  96     /// the given id.
  97     fn get_type_parameter_bounds(&self, span: Span, def_id: ast::NodeId)
  98                                  -> Result<Vec<ty::PolyTraitRef<'tcx>>, ErrorReported>;
  99
 100     /// Returns true if the trait with id `trait_def_id` defines an
 101     /// associated type with the name `name`.
 102     fn trait_defines_associated_type_named(&self, trait_def_id: ast::DefId, name: ast::Name)
 103                                            -> bool;
 104
 105     /// Return an (optional) substitution to convert bound type parameters that
 106     /// are in scope into free ones. This function should only return Some
 107     /// within a fn body.
 108     /// See ParameterEnvironment::free_substs for more information.
 109     fn get_free_substs(&self) -> Option<&Substs<'tcx>> {
 110         None
 111     }
 112
 113     /// What type should we use when a type is omitted?
 114     fn ty_infer(&self, span: Span) -> Ty<'tcx>;
 115
 116     /// Projecting an associated type from a (potentially)
 117     /// higher-ranked trait reference is more complicated, because of
 118     /// the possibility of late-bound regions appearing in the
 119     /// associated type binding. This is not legal in function
 120     /// signatures for that reason. In a function body, we can always
 121     /// handle it because we can use inference variables to remove the
 122     /// late-bound regions.
 123     fn projected_ty_from_poly_trait_ref(&self,
 124                                         span: Span,
 125                                         poly_trait_ref: ty::PolyTraitRef<'tcx>,
 126                                         item_name: ast::Name)
 127                                         -> Ty<'tcx>
 128     {
 129         if let Some(trait_ref) = self.tcx().no_late_bound_regions(&poly_trait_ref) {
 130             self.projected_ty(span, trait_ref, item_name)
 131         } else {
 132             // no late-bound regions, we can just ignore the binder
 133             span_err!(self.tcx().sess, span, E0212,
 134                 "cannot extract an associated type from a higher-ranked trait bound \
 135                  in this context");
 136             self.tcx().types.err
 137         }
 138     }
 139
 140     /// Project an associated type from a non-higher-ranked trait reference.
 141     /// This is fairly straightforward and can be accommodated in any context.
 142     fn projected_ty(&self,
 143                     span: Span,
 144                     _trait_ref: ty::TraitRef<'tcx>,
 145                     _item_name: ast::Name)
 146                     -> Ty<'tcx>;
 147 }
 148
 149 pub fn ast_region_to_region(tcx: &ty::ctxt, lifetime: &ast::Lifetime)
 150                             -> ty::Region {
 151     let r = match tcx.named_region_map.get(&lifetime.id) {
 152         None => {
 153             // should have been recorded by the `resolve_lifetime` pass
 154             tcx.sess.span_bug(lifetime.span, "unresolved lifetime");
 155         }
 156
 157         Some(&rl::DefStaticRegion) => {
 158             ty::ReStatic
 159         }
 160
 161         Some(&rl::DefLateBoundRegion(debruijn, id)) => {
 162             ty::ReLateBound(debruijn, ty::BrNamed(ast_util::local_def(id), lifetime.name))
 163         }
 164
 165         Some(&rl::DefEarlyBoundRegion(space, index, id)) => {
 166             ty::ReEarlyBound(ty::EarlyBoundRegion {
 167                 param_id: id,
 168                 space: space,
 169                 index: index,
 170                 name: lifetime.name
 171             })
 172         }
 173
 174         Some(&rl::DefFreeRegion(scope, id)) => {
 175             ty::ReFree(ty::FreeRegion {
 176                     scope: scope,
 177                     bound_region: ty::BrNamed(ast_util::local_def(id),
 178                                               lifetime.name)
 179                 })
 180         }
 181     };
 182
 183     debug!("ast_region_to_region(lifetime={:?} id={}) yields {:?}",
 184            lifetime,
 185            lifetime.id,
 186            r);
 187
 188     r
 189 }
 190
 191 fn report_elision_failure(
 192     tcx: &ty::ctxt,
 193     default_span: Span,
 194     params: Vec<ElisionFailureInfo>)
 195 {
 196     let mut m = String::new();
 197     let len = params.len();
 198     for (i, info) in params.into_iter().enumerate() {
 199         let ElisionFailureInfo {
 200             name, lifetime_count: n, have_bound_regions
 201         } = info;
 202
 203         let help_name = if name.is_empty() {
 204             format!("argument {}", i + 1)
 205         } else {
 206             format!("`{}`", name)
 207         };
 208
 209         m.push_str(&(if n == 1 {
 210             help_name
 211         } else {
 212             format!("one of {}'s {} elided {}lifetimes", help_name, n,
 213                     if have_bound_regions { "free " } else { "" } )
 214         })[..]);
 215
 216         if len == 2 && i == 0 {
 217             m.push_str(" or ");
 218         } else if i + 2 == len {
 219             m.push_str(", or ");
 220         } else if i + 1 != len {
 221             m.push_str(", ");
 222         }
 223     }
 224     if len == 1 {
 225         fileline_help!(tcx.sess, default_span,
 226                        "this function's return type contains a borrowed value, but \
 227                         the signature does not say which {} it is borrowed from",
 228                        m);
 229     } else if len == 0 {
 230         fileline_help!(tcx.sess, default_span,
 231                        "this function's return type contains a borrowed value, but \
 232                         there is no value for it to be borrowed from");
 233         fileline_help!(tcx.sess, default_span,
 234                        "consider giving it a 'static lifetime");
 235     } else {
 236         fileline_help!(tcx.sess, default_span,
 237                        "this function's return type contains a borrowed value, but \
 238                         the signature does not say whether it is borrowed from {}",
 239                        m);
 240     }
 241 }
 242
 243 pub fn opt_ast_region_to_region<'tcx>(
 244     this: &AstConv<'tcx>,
 245     rscope: &RegionScope,
 246     default_span: Span,
 247     opt_lifetime: &Option<ast::Lifetime>) -> ty::Region
 248 {
 249     let r = match *opt_lifetime {
 250         Some(ref lifetime) => {
 251             ast_region_to_region(this.tcx(), lifetime)
 252         }
 253
 254         None => match rscope.anon_regions(default_span, 1) {
 255             Ok(rs) => rs[0],
 256             Err(params) => {
 257                 span_err!(this.tcx().sess, default_span, E0106,
 258                           "missing lifetime specifier");
 259                 if let Some(params) = params {
 260                     report_elision_failure(this.tcx(), default_span, params);
 261                 }
 262                 ty::ReStatic
 263             }
 264         }
 265     };
 266
 267     debug!("opt_ast_region_to_region(opt_lifetime={:?}) yields {:?}",
 268             opt_lifetime,
 269             r);
 270
 271     r
 272 }
 273
 274 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
 275 /// returns an appropriate set of substitutions for this particular reference to `I`.
 276 pub fn ast_path_substs_for_ty<'tcx>(
 277     this: &AstConv<'tcx>,
 278     rscope: &RegionScope,
 279     span: Span,
 280     param_mode: PathParamMode,
 281     decl_generics: &ty::Generics<'tcx>,
 282     item_segment: &ast::PathSegment)
 283     -> Substs<'tcx>
 284 {
 285     let tcx = this.tcx();
 286
 287     // ast_path_substs() is only called to convert paths that are
 288     // known to refer to traits, types, or structs. In these cases,
 289     // all type parameters defined for the item being referenced will
 290     // be in the TypeSpace or SelfSpace.
 291     //
 292     // Note: in the case of traits, the self parameter is also
 293     // defined, but we don't currently create a `type_param_def` for
 294     // `Self` because it is implicit.
 295     assert!(decl_generics.regions.all(|d| d.space == TypeSpace));
 296     assert!(decl_generics.types.all(|d| d.space != FnSpace));
 297
 298     let (regions, types, assoc_bindings) = match item_segment.parameters {
 299         ast::AngleBracketedParameters(ref data) => {
 300             convert_angle_bracketed_parameters(this, rscope, span, decl_generics, data)
 301         }
 302         ast::ParenthesizedParameters(..) => {
 303             span_err!(tcx.sess, span, E0214,
 304                       "parenthesized parameters may only be used with a trait");
 305             let ty_param_defs = decl_generics.types.get_slice(TypeSpace);
 306             (Substs::empty(),
 307              ty_param_defs.iter().map(|_| tcx.types.err).collect(),
 308              vec![])
 309         }
 310     };
 311
 312     prohibit_projections(this.tcx(), &assoc_bindings);
 313
 314     create_substs_for_ast_path(this,
 315                                span,
 316                                param_mode,
 317                                decl_generics,
 318                                None,
 319                                types,
 320                                regions)
 321 }
 322
 323 #[derive(PartialEq, Eq)]
 324 pub enum PathParamMode {
 325     // Any path in a type context.
 326     Explicit,
 327     // The `module::Type` in `module::Type::method` in an expression.
 328     Optional
 329 }
 330
 331 fn create_region_substs<'tcx>(
 332     this: &AstConv<'tcx>,
 333     rscope: &RegionScope,
 334     span: Span,
 335     decl_generics: &ty::Generics<'tcx>,
 336     regions_provided: Vec<ty::Region>)
 337     -> Substs<'tcx>
 338 {
 339     let tcx = this.tcx();
 340
 341     // If the type is parameterized by the this region, then replace this
 342     // region with the current anon region binding (in other words,
 343     // whatever & would get replaced with).
 344     let expected_num_region_params = decl_generics.regions.len(TypeSpace);
 345     let supplied_num_region_params = regions_provided.len();
 346     let regions = if expected_num_region_params == supplied_num_region_params {
 347         regions_provided
 348     } else {
 349         let anon_regions =
 350             rscope.anon_regions(span, expected_num_region_params);
 351
 352         if supplied_num_region_params != 0 || anon_regions.is_err() {
 353             report_lifetime_number_error(tcx, span,
 354                                          supplied_num_region_params,
 355                                          expected_num_region_params);
 356         }
 357
 358         match anon_regions {
 359             Ok(anon_regions) => anon_regions,
 360             Err(_) => (0..expected_num_region_params).map(|_| ty::ReStatic).collect()
 361         }
 362     };
 363     Substs::new_type(vec![], regions)
 364 }
 365
 366 /// Given the type/region arguments provided to some path (along with
 367 /// an implicit Self, if this is a trait reference) returns the complete
 368 /// set of substitutions. This may involve applying defaulted type parameters.
 369 ///
 370 /// Note that the type listing given here is *exactly* what the user provided.
 371 ///
 372 /// The `region_substs` should be the result of `create_region_substs`
 373 /// -- that is, a substitution with no types but the correct number of
 374 /// regions.
 375 fn create_substs_for_ast_path<'tcx>(
 376     this: &AstConv<'tcx>,
 377     span: Span,
 378     param_mode: PathParamMode,
 379     decl_generics: &ty::Generics<'tcx>,
 380     self_ty: Option<Ty<'tcx>>,
 381     types_provided: Vec<Ty<'tcx>>,
 382     region_substs: Substs<'tcx>)
 383     -> Substs<'tcx>
 384 {
 385     let tcx = this.tcx();
 386
 387     debug!("create_substs_for_ast_path(decl_generics={:?}, self_ty={:?}, \
 388            types_provided={:?}, region_substs={:?}",
 389            decl_generics, self_ty, types_provided,
 390            region_substs);
 391
 392     assert_eq!(region_substs.regions().len(TypeSpace), decl_generics.regions.len(TypeSpace));
 393     assert!(region_substs.types.is_empty());
 394
 395     // Convert the type parameters supplied by the user.
 396     let ty_param_defs = decl_generics.types.get_slice(TypeSpace);
 397     let formal_ty_param_count = ty_param_defs.len();
 398     let required_ty_param_count = ty_param_defs.iter()
 399                                                .take_while(|x| x.default.is_none())
 400                                                .count();
 401
 402     // Fill with `ty_infer` if no params were specified, as long as
 403     // they were optional (e.g. paths inside expressions).
 404     let mut type_substs = if param_mode == PathParamMode::Optional &&
 405                              types_provided.is_empty() {
 406         (0..formal_ty_param_count).map(|_| this.ty_infer(span)).collect()
 407     } else {
 408         types_provided
 409     };
 410
 411     let supplied_ty_param_count = type_substs.len();
 412     check_type_argument_count(this.tcx(), span, supplied_ty_param_count,
 413                               required_ty_param_count, formal_ty_param_count);
 414
 415     if supplied_ty_param_count < required_ty_param_count {
 416         while type_substs.len() < required_ty_param_count {
 417             type_substs.push(tcx.types.err);
 418         }
 419     } else if supplied_ty_param_count > formal_ty_param_count {
 420         type_substs.truncate(formal_ty_param_count);
 421     }
 422     assert!(type_substs.len() >= required_ty_param_count &&
 423             type_substs.len() <= formal_ty_param_count);
 424
 425     let mut substs = region_substs;
 426     substs.types.extend(TypeSpace, type_substs.into_iter());
 427
 428     match self_ty {
 429         None => {
 430             // If no self-type is provided, it's still possible that
 431             // one was declared, because this could be an object type.
 432         }
 433         Some(ty) => {
 434             // If a self-type is provided, one should have been
 435             // "declared" (in other words, this should be a
 436             // trait-ref).
 437             assert!(decl_generics.types.get_self().is_some());
 438             substs.types.push(SelfSpace, ty);
 439         }
 440     }
 441
 442     let actual_supplied_ty_param_count = substs.types.len(TypeSpace);
 443     for param in &ty_param_defs[actual_supplied_ty_param_count..] {
 444         if let Some(default) = param.default {
 445             // If we are converting an object type, then the
 446             // `Self` parameter is unknown. However, some of the
 447             // other type parameters may reference `Self` in their
 448             // defaults. This will lead to an ICE if we are not
 449             // careful!
 450             if self_ty.is_none() && default.has_self_ty() {
 451                 span_err!(tcx.sess, span, E0393,
 452                           "the type parameter `{}` must be explicitly specified \
 453                            in an object type because its default value `{}` references \
 454                            the type `Self`",
 455                           param.name,
 456                           default);
 457                 substs.types.push(TypeSpace, tcx.types.err);
 458             } else {
 459                 // This is a default type parameter.
 460                 let default = default.subst_spanned(tcx,
 461                                                     &substs,
 462                                                     Some(span));
 463                 substs.types.push(TypeSpace, default);
 464             }
 465         } else {
 466             tcx.sess.span_bug(span, "extra parameter without default");
 467         }
 468     }
 469
 470     substs
 471 }
 472
 473 struct ConvertedBinding<'tcx> {
 474     item_name: ast::Name,
 475     ty: Ty<'tcx>,
 476     span: Span,
 477 }
 478
 479 fn convert_angle_bracketed_parameters<'tcx>(this: &AstConv<'tcx>,
 480                                             rscope: &RegionScope,
 481                                             span: Span,
 482                                             decl_generics: &ty::Generics<'tcx>,
 483                                             data: &ast::AngleBracketedParameterData)
 484                                             -> (Substs<'tcx>,
 485                                                 Vec<Ty<'tcx>>,
 486                                                 Vec<ConvertedBinding<'tcx>>)
 487 {
 488     let regions: Vec<_> =
 489         data.lifetimes.iter()
 490                       .map(|l| ast_region_to_region(this.tcx(), l))
 491                       .collect();
 492
 493     let region_substs =
 494         create_region_substs(this, rscope, span, decl_generics, regions);
 495
 496     let types: Vec<_> =
 497         data.types.iter()
 498                   .enumerate()
 499                   .map(|(i,t)| ast_ty_arg_to_ty(this, rscope, decl_generics,
 500                                                 i, &region_substs, t))
 501                   .collect();
 502
 503     let assoc_bindings: Vec<_> =
 504         data.bindings.iter()
 505                      .map(|b| ConvertedBinding { item_name: b.ident.name,
 506                                                  ty: ast_ty_to_ty(this, rscope, &*b.ty),
 507                                                  span: b.span })
 508                      .collect();
 509
 510     (region_substs, types, assoc_bindings)
 511 }
 512
 513 /// Returns the appropriate lifetime to use for any output lifetimes
 514 /// (if one exists) and a vector of the (pattern, number of lifetimes)
 515 /// corresponding to each input type/pattern.
 516 fn find_implied_output_region<'tcx>(tcx: &ty::ctxt<'tcx>,
 517                                     input_tys: &[Ty<'tcx>],
 518                                     input_pats: Vec<String>) -> ElidedLifetime
 519 {
 520     let mut lifetimes_for_params = Vec::new();
 521     let mut possible_implied_output_region = None;
 522
 523     for (input_type, input_pat) in input_tys.iter().zip(input_pats) {
 524         let mut regions = FnvHashSet();
 525         let have_bound_regions = ty_fold::collect_regions(tcx,
 526                                                           input_type,
 527                                                           &mut regions);
 528
 529         debug!("find_implied_output_regions: collected {:?} from {:?} \
 530                 have_bound_regions={:?}", &regions, input_type, have_bound_regions);
 531
 532         if regions.len() == 1 {
 533             // there's a chance that the unique lifetime of this
 534             // iteration will be the appropriate lifetime for output
 535             // parameters, so lets store it.
 536             possible_implied_output_region = regions.iter().cloned().next();
 537         }
 538
 539         lifetimes_for_params.push(ElisionFailureInfo {
 540             name: input_pat,
 541             lifetime_count: regions.len(),
 542             have_bound_regions: have_bound_regions
 543         });
 544     }
 545
 546     if lifetimes_for_params.iter().map(|e| e.lifetime_count).sum::<usize>() == 1 {
 547         Ok(possible_implied_output_region.unwrap())
 548     } else {
 549         Err(Some(lifetimes_for_params))
 550     }
 551 }
 552
 553 fn convert_ty_with_lifetime_elision<'tcx>(this: &AstConv<'tcx>,
 554                                           elided_lifetime: ElidedLifetime,
 555                                           ty: &ast::Ty)
 556                                           -> Ty<'tcx>
 557 {
 558     match elided_lifetime {
 559         Ok(implied_output_region) => {
 560             let rb = ElidableRscope::new(implied_output_region);
 561             ast_ty_to_ty(this, &rb, ty)
 562         }
 563         Err(param_lifetimes) => {
 564             // All regions must be explicitly specified in the output
 565             // if the lifetime elision rules do not apply. This saves
 566             // the user from potentially-confusing errors.
 567             let rb = UnelidableRscope::new(param_lifetimes);
 568             ast_ty_to_ty(this, &rb, ty)
 569         }
 570     }
 571 }
 572
 573 fn convert_parenthesized_parameters<'tcx>(this: &AstConv<'tcx>,
 574                                           rscope: &RegionScope,
 575                                           span: Span,
 576                                           decl_generics: &ty::Generics<'tcx>,
 577                                           data: &ast::ParenthesizedParameterData)
 578                                           -> (Substs<'tcx>,
 579                                               Vec<Ty<'tcx>>,
 580                                               Vec<ConvertedBinding<'tcx>>)
 581 {
 582     let region_substs =
 583         create_region_substs(this, rscope, span, decl_generics, Vec::new());
 584
 585     let binding_rscope = BindingRscope::new();
 586     let inputs =
 587         data.inputs.iter()
 588                    .map(|a_t| ast_ty_arg_to_ty(this, &binding_rscope, decl_generics,
 589                                                0, &region_substs, a_t))
 590                    .collect::<Vec<Ty<'tcx>>>();
 591
 592     let input_params = vec![String::new(); inputs.len()];
 593     let implied_output_region = find_implied_output_region(this.tcx(), &inputs, input_params);
 594
 595     let input_ty = this.tcx().mk_tup(inputs);
 596
 597     let (output, output_span) = match data.output {
 598         Some(ref output_ty) => {
 599             (convert_ty_with_lifetime_elision(this,
 600                                               implied_output_region,
 601                                               &output_ty),
 602              output_ty.span)
 603         }
 604         None => {
 605             (this.tcx().mk_nil(), data.span)
 606         }
 607     };
 608
 609     let output_binding = ConvertedBinding {
 610         item_name: token::intern(FN_OUTPUT_NAME),
 611         ty: output,
 612         span: output_span
 613     };
 614
 615     (region_substs, vec![input_ty], vec![output_binding])
 616 }
 617
 618 pub fn instantiate_poly_trait_ref<'tcx>(
 619     this: &AstConv<'tcx>,
 620     rscope: &RegionScope,
 621     ast_trait_ref: &ast::PolyTraitRef,
 622     self_ty: Option<Ty<'tcx>>,
 623     poly_projections: &mut Vec<ty::PolyProjectionPredicate<'tcx>>)
 624     -> ty::PolyTraitRef<'tcx>
 625 {
 626     let trait_ref = &ast_trait_ref.trait_ref;
 627     let trait_def_id = trait_def_id(this, trait_ref);
 628     ast_path_to_poly_trait_ref(this,
 629                                rscope,
 630                                trait_ref.path.span,
 631                                PathParamMode::Explicit,
 632                                trait_def_id,
 633                                self_ty,
 634                                trait_ref.path.segments.last().unwrap(),
 635                                poly_projections)
 636 }
 637
 638 /// Instantiates the path for the given trait reference, assuming that it's
 639 /// bound to a valid trait type. Returns the def_id for the defining trait.
 640 /// Fails if the type is a type other than a trait type.
 641 ///
 642 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T=X>`
 643 /// are disallowed. Otherwise, they are pushed onto the vector given.
 644 pub fn instantiate_mono_trait_ref<'tcx>(
 645     this: &AstConv<'tcx>,
 646     rscope: &RegionScope,
 647     trait_ref: &ast::TraitRef,
 648     self_ty: Option<Ty<'tcx>>)
 649     -> ty::TraitRef<'tcx>
 650 {
 651     let trait_def_id = trait_def_id(this, trait_ref);
 652     ast_path_to_mono_trait_ref(this,
 653                                rscope,
 654                                trait_ref.path.span,
 655                                PathParamMode::Explicit,
 656                                trait_def_id,
 657                                self_ty,
 658                                trait_ref.path.segments.last().unwrap())
 659 }
 660
 661 fn trait_def_id<'tcx>(this: &AstConv<'tcx>, trait_ref: &ast::TraitRef) -> ast::DefId {
 662     let path = &trait_ref.path;
 663     match ::lookup_full_def(this.tcx(), path.span, trait_ref.ref_id) {
 664         def::DefTrait(trait_def_id) => trait_def_id,
 665         _ => {
 666             span_fatal!(this.tcx().sess, path.span, E0245, "`{}` is not a trait",
 667                         path);
 668         }
 669     }
 670 }
 671
 672 fn object_path_to_poly_trait_ref<'a,'tcx>(
 673     this: &AstConv<'tcx>,
 674     rscope: &RegionScope,
 675     span: Span,
 676     param_mode: PathParamMode,
 677     trait_def_id: ast::DefId,
 678     trait_segment: &ast::PathSegment,
 679     mut projections: &mut Vec<ty::PolyProjectionPredicate<'tcx>>)
 680     -> ty::PolyTraitRef<'tcx>
 681 {
 682     ast_path_to_poly_trait_ref(this,
 683                                rscope,
 684                                span,
 685                                param_mode,
 686                                trait_def_id,
 687                                None,
 688                                trait_segment,
 689                                projections)
 690 }
 691
 692 fn ast_path_to_poly_trait_ref<'a,'tcx>(
 693     this: &AstConv<'tcx>,
 694     rscope: &RegionScope,
 695     span: Span,
 696     param_mode: PathParamMode,
 697     trait_def_id: ast::DefId,
 698     self_ty: Option<Ty<'tcx>>,
 699     trait_segment: &ast::PathSegment,
 700     poly_projections: &mut Vec<ty::PolyProjectionPredicate<'tcx>>)
 701     -> ty::PolyTraitRef<'tcx>
 702 {
 703     // The trait reference introduces a binding level here, so
 704     // we need to shift the `rscope`. It'd be nice if we could
 705     // do away with this rscope stuff and work this knowledge
 706     // into resolve_lifetimes, as we do with non-omitted
 707     // lifetimes. Oh well, not there yet.
 708     let shifted_rscope = &ShiftedRscope::new(rscope);
 709
 710     let (substs, assoc_bindings) =
 711         create_substs_for_ast_trait_ref(this,
 712                                         shifted_rscope,
 713                                         span,
 714                                         param_mode,
 715                                         trait_def_id,
 716                                         self_ty,
 717                                         trait_segment);
 718     let poly_trait_ref = ty::Binder(ty::TraitRef::new(trait_def_id, substs));
 719
 720     {
 721         let converted_bindings =
 722             assoc_bindings
 723             .iter()
 724             .filter_map(|binding| {
 725                 // specify type to assert that error was already reported in Err case:
 726                 let predicate: Result<_, ErrorReported> =
 727                     ast_type_binding_to_poly_projection_predicate(this,
 728                                                                   poly_trait_ref.clone(),
 729                                                                   self_ty,
 730                                                                   binding);
 731                 predicate.ok() // ok to ignore Err() because ErrorReported (see above)
 732             });
 733         poly_projections.extend(converted_bindings);
 734     }
 735
 736     poly_trait_ref
 737 }
 738
 739 fn ast_path_to_mono_trait_ref<'a,'tcx>(this: &AstConv<'tcx>,
 740                                        rscope: &RegionScope,
 741                                        span: Span,
 742                                        param_mode: PathParamMode,
 743                                        trait_def_id: ast::DefId,
 744                                        self_ty: Option<Ty<'tcx>>,
 745                                        trait_segment: &ast::PathSegment)
 746                                        -> ty::TraitRef<'tcx>
 747 {
 748     let (substs, assoc_bindings) =
 749         create_substs_for_ast_trait_ref(this,
 750                                         rscope,
 751                                         span,
 752                                         param_mode,
 753                                         trait_def_id,
 754                                         self_ty,
 755                                         trait_segment);
 756     prohibit_projections(this.tcx(), &assoc_bindings);
 757     ty::TraitRef::new(trait_def_id, substs)
 758 }
 759
 760 fn create_substs_for_ast_trait_ref<'a,'tcx>(this: &AstConv<'tcx>,
 761                                             rscope: &RegionScope,
 762                                             span: Span,
 763                                             param_mode: PathParamMode,
 764                                             trait_def_id: ast::DefId,
 765                                             self_ty: Option<Ty<'tcx>>,
 766                                             trait_segment: &ast::PathSegment)
 767                                             -> (&'tcx Substs<'tcx>, Vec<ConvertedBinding<'tcx>>)
 768 {
 769     debug!("create_substs_for_ast_trait_ref(trait_segment={:?})",
 770            trait_segment);
 771
 772     let trait_def = match this.get_trait_def(span, trait_def_id) {
 773         Ok(trait_def) => trait_def,
 774         Err(ErrorReported) => {
 775             // No convenient way to recover from a cycle here. Just bail. Sorry!
 776             this.tcx().sess.abort_if_errors();
 777             this.tcx().sess.bug("ErrorReported returned, but no errors reports?")
 778         }
 779     };
 780
 781     let (regions, types, assoc_bindings) = match trait_segment.parameters {
 782         ast::AngleBracketedParameters(ref data) => {
 783             // For now, require that parenthetical notation be used
 784             // only with `Fn()` etc.
 785             if !this.tcx().sess.features.borrow().unboxed_closures && trait_def.paren_sugar {
 786                 span_err!(this.tcx().sess, span, E0215,
 787                                          "angle-bracket notation is not stable when \
 788                                          used with the `Fn` family of traits, use parentheses");
 789                 fileline_help!(this.tcx().sess, span,
 790                            "add `#![feature(unboxed_closures)]` to \
 791                             the crate attributes to enable");
 792             }
 793
 794             convert_angle_bracketed_parameters(this, rscope, span, &trait_def.generics, data)
 795         }
 796         ast::ParenthesizedParameters(ref data) => {
 797             // For now, require that parenthetical notation be used
 798             // only with `Fn()` etc.
 799             if !this.tcx().sess.features.borrow().unboxed_closures && !trait_def.paren_sugar {
 800                 span_err!(this.tcx().sess, span, E0216,
 801                                          "parenthetical notation is only stable when \
 802                                          used with the `Fn` family of traits");
 803                 fileline_help!(this.tcx().sess, span,
 804                            "add `#![feature(unboxed_closures)]` to \
 805                             the crate attributes to enable");
 806             }
 807
 808             convert_parenthesized_parameters(this, rscope, span, &trait_def.generics, data)
 809         }
 810     };
 811
 812     let substs = create_substs_for_ast_path(this,
 813                                             span,
 814                                             param_mode,
 815                                             &trait_def.generics,
 816                                             self_ty,
 817                                             types,
 818                                             regions);
 819
 820     (this.tcx().mk_substs(substs), assoc_bindings)
 821 }
 822
 823 fn ast_type_binding_to_poly_projection_predicate<'tcx>(
 824     this: &AstConv<'tcx>,
 825     mut trait_ref: ty::PolyTraitRef<'tcx>,
 826     self_ty: Option<Ty<'tcx>>,
 827     binding: &ConvertedBinding<'tcx>)
 828     -> Result<ty::PolyProjectionPredicate<'tcx>, ErrorReported>
 829 {
 830     let tcx = this.tcx();
 831
 832     // Given something like `U : SomeTrait<T=X>`, we want to produce a
 833     // predicate like `<U as SomeTrait>::T = X`. This is somewhat
 834     // subtle in the event that `T` is defined in a supertrait of
 835     // `SomeTrait`, because in that case we need to upcast.
 836     //
 837     // That is, consider this case:
 838     //
 839     // ```
 840     // trait SubTrait : SuperTrait<int> { }
 841     // trait SuperTrait<A> { type T; }
 842     //
 843     // ... B : SubTrait<T=foo> ...
 844     // ```
 845     //
 846     // We want to produce `<B as SuperTrait<int>>::T == foo`.
 847
 848     // Simple case: X is defined in the current trait.
 849     if this.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
 850         return Ok(ty::Binder(ty::ProjectionPredicate {      // <-------------------+
 851             projection_ty: ty::ProjectionTy {               //                     |
 852                 trait_ref: trait_ref.skip_binder().clone(), // Binder moved here --+
 853                 item_name: binding.item_name,
 854             },
 855             ty: binding.ty,
 856         }));
 857     }
 858
 859     // Otherwise, we have to walk through the supertraits to find
 860     // those that do.  This is complicated by the fact that, for an
 861     // object type, the `Self` type is not present in the
 862     // substitutions (after all, it's being constructed right now),
 863     // but the `supertraits` iterator really wants one. To handle
 864     // this, we currently insert a dummy type and then remove it
 865     // later. Yuck.
 866
 867     let dummy_self_ty = tcx.mk_infer(ty::FreshTy(0));
 868     if self_ty.is_none() { // if converting for an object type
 869         let mut dummy_substs = trait_ref.skip_binder().substs.clone(); // binder moved here -+
 870         assert!(dummy_substs.self_ty().is_none());                     //                    |
 871         dummy_substs.types.push(SelfSpace, dummy_self_ty);             //                    |
 872         trait_ref = ty::Binder(ty::TraitRef::new(trait_ref.def_id(),   // <------------+
 873                                                  tcx.mk_substs(dummy_substs)));
 874     }
 875
 876     try!(this.ensure_super_predicates(binding.span, trait_ref.def_id()));
 877
 878     let mut candidates: Vec<ty::PolyTraitRef> =
 879         traits::supertraits(tcx, trait_ref.clone())
 880         .filter(|r| this.trait_defines_associated_type_named(r.def_id(), binding.item_name))
 881         .collect();
 882
 883     // If converting for an object type, then remove the dummy-ty from `Self` now.
 884     // Yuckety yuck.
 885     if self_ty.is_none() {
 886         for candidate in &mut candidates {
 887             let mut dummy_substs = candidate.0.substs.clone();
 888             assert!(dummy_substs.self_ty() == Some(dummy_self_ty));
 889             dummy_substs.types.pop(SelfSpace);
 890             *candidate = ty::Binder(ty::TraitRef::new(candidate.def_id(),
 891                                                       tcx.mk_substs(dummy_substs)));
 892         }
 893     }
 894
 895     let candidate = try!(one_bound_for_assoc_type(tcx,
 896                                                   candidates,
 897                                                   &trait_ref.to_string(),
 898                                                   &token::get_name(binding.item_name),
 899                                                   binding.span));
 900
 901     Ok(ty::Binder(ty::ProjectionPredicate {             // <-------------------------+
 902         projection_ty: ty::ProjectionTy {               //                           |
 903             trait_ref: candidate.skip_binder().clone(), // binder is moved up here --+
 904             item_name: binding.item_name,
 905         },
 906         ty: binding.ty,
 907     }))
 908 }
 909
 910 fn ast_path_to_ty<'tcx>(
 911     this: &AstConv<'tcx>,
 912     rscope: &RegionScope,
 913     span: Span,
 914     param_mode: PathParamMode,
 915     did: ast::DefId,
 916     item_segment: &ast::PathSegment)
 917     -> Ty<'tcx>
 918 {
 919     let tcx = this.tcx();
 920     let (generics, decl_ty) = match this.get_item_type_scheme(span, did) {
 921         Ok(ty::TypeScheme { generics,  ty: decl_ty }) => {
 922             (generics, decl_ty)
 923         }
 924         Err(ErrorReported) => {
 925             return tcx.types.err;
 926         }
 927     };
 928
 929     let substs = ast_path_substs_for_ty(this,
 930                                         rscope,
 931                                         span,
 932                                         param_mode,
 933                                         &generics,
 934                                         item_segment);
 935
 936     // FIXME(#12938): This is a hack until we have full support for DST.
 937     if Some(did) == this.tcx().lang_items.owned_box() {
 938         assert_eq!(substs.types.len(TypeSpace), 1);
 939         return this.tcx().mk_box(*substs.types.get(TypeSpace, 0));
 940     }
 941
 942     decl_ty.subst(this.tcx(), &substs)
 943 }
 944
 945 type TraitAndProjections<'tcx> = (ty::PolyTraitRef<'tcx>, Vec<ty::PolyProjectionPredicate<'tcx>>);
 946
 947 fn ast_ty_to_trait_ref<'tcx>(this: &AstConv<'tcx>,
 948                              rscope: &RegionScope,
 949                              ty: &ast::Ty,
 950                              bounds: &[ast::TyParamBound])
 951                              -> Result<TraitAndProjections<'tcx>, ErrorReported>
 952 {
 953     /*!
 954      * In a type like `Foo + Send`, we want to wait to collect the
 955      * full set of bounds before we make the object type, because we
 956      * need them to infer a region bound.  (For example, if we tried
 957      * made a type from just `Foo`, then it wouldn't be enough to
 958      * infer a 'static bound, and hence the user would get an error.)
 959      * So this function is used when we're dealing with a sum type to
 960      * convert the LHS. It only accepts a type that refers to a trait
 961      * name, and reports an error otherwise.
 962      */
 963
 964     match ty.node {
 965         ast::TyPath(None, ref path) => {
 966             let def = match this.tcx().def_map.borrow().get(&ty.id) {
 967                 Some(&def::PathResolution { base_def, depth: 0, .. }) => Some(base_def),
 968                 _ => None
 969             };
 970             match def {
 971                 Some(def::DefTrait(trait_def_id)) => {
 972                     let mut projection_bounds = Vec::new();
 973                     let trait_ref = object_path_to_poly_trait_ref(this,
 974                                                                   rscope,
 975                                                                   path.span,
 976                                                                   PathParamMode::Explicit,
 977                                                                   trait_def_id,
 978                                                                   path.segments.last().unwrap(),
 979                                                                   &mut projection_bounds);
 980                     Ok((trait_ref, projection_bounds))
 981                 }
 982                 _ => {
 983                     span_err!(this.tcx().sess, ty.span, E0172, "expected a reference to a trait");
 984                     Err(ErrorReported)
 985                 }
 986             }
 987         }
 988         _ => {
 989             span_err!(this.tcx().sess, ty.span, E0178,
 990                       "expected a path on the left-hand side of `+`, not `{}`",
 991                       pprust::ty_to_string(ty));
 992             let hi = bounds.iter().map(|x| match *x {
 993                 ast::TraitTyParamBound(ref tr, _) => tr.span.hi,
 994                 ast::RegionTyParamBound(ref r) => r.span.hi,
 995             }).max_by(|x| x.to_usize());
 996             let full_span = hi.map(|hi| Span {
 997                 lo: ty.span.lo,
 998                 hi: hi,
 999                 expn_id: ty.span.expn_id,
1000             });
1001             match (&ty.node, full_span) {
1002                 (&ast::TyRptr(None, ref mut_ty), Some(full_span)) => {
1003                     let mutbl_str = if mut_ty.mutbl == ast::MutMutable { "mut " } else { "" };
1004                     this.tcx().sess
1005                         .span_suggestion(full_span, "try adding parentheses (per RFC 438):",
1006                                          format!("&{}({} +{})",
1007                                                  mutbl_str,
1008                                                  pprust::ty_to_string(&*mut_ty.ty),
1009                                                  pprust::bounds_to_string(bounds)));
1010                 }
1011                 (&ast::TyRptr(Some(ref lt), ref mut_ty), Some(full_span)) => {
1012                     let mutbl_str = if mut_ty.mutbl == ast::MutMutable { "mut " } else { "" };
1013                     this.tcx().sess
1014                         .span_suggestion(full_span, "try adding parentheses (per RFC 438):",
1015                                          format!("&{} {}({} +{})",
1016                                                  pprust::lifetime_to_string(lt),
1017                                                  mutbl_str,
1018                                                  pprust::ty_to_string(&*mut_ty.ty),
1019                                                  pprust::bounds_to_string(bounds)));
1020                 }
1021
1022                 _ => {
1023                     fileline_help!(this.tcx().sess, ty.span,
1024                                "perhaps you forgot parentheses? (per RFC 438)");
1025                 }
1026             }
1027             Err(ErrorReported)
1028         }
1029     }
1030 }
1031
1032 fn trait_ref_to_object_type<'tcx>(this: &AstConv<'tcx>,
1033                                   rscope: &RegionScope,
1034                                   span: Span,
1035                                   trait_ref: ty::PolyTraitRef<'tcx>,
1036                                   projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>,
1037                                   bounds: &[ast::TyParamBound])
1038                                   -> Ty<'tcx>
1039 {
1040     let existential_bounds = conv_existential_bounds(this,
1041                                                      rscope,
1042                                                      span,
1043                                                      trait_ref.clone(),
1044                                                      projection_bounds,
1045                                                      bounds);
1046
1047     let result = make_object_type(this, span, trait_ref, existential_bounds);
1048     debug!("trait_ref_to_object_type: result={:?}",
1049            result);
1050
1051     result
1052 }
1053
1054 fn make_object_type<'tcx>(this: &AstConv<'tcx>,
1055                           span: Span,
1056                           principal: ty::PolyTraitRef<'tcx>,
1057                           bounds: ty::ExistentialBounds<'tcx>)
1058                           -> Ty<'tcx> {
1059     let tcx = this.tcx();
1060     let object = ty::TraitTy {
1061         principal: principal,
1062         bounds: bounds
1063     };
1064     let object_trait_ref =
1065         object.principal_trait_ref_with_self_ty(tcx, tcx.types.err);
1066
1067     // ensure the super predicates and stop if we encountered an error
1068     if this.ensure_super_predicates(span, object.principal_def_id()).is_err() {
1069         return tcx.types.err;
1070     }
1071
1072     let mut associated_types: FnvHashSet<(ast::DefId, ast::Name)> =
1073         traits::supertraits(tcx, object_trait_ref)
1074         .flat_map(|tr| {
1075             let trait_def = tcx.lookup_trait_def(tr.def_id());
1076             trait_def.associated_type_names
1077                 .clone()
1078                 .into_iter()
1079                 .map(move |associated_type_name| (tr.def_id(), associated_type_name))
1080         })
1081         .collect();
1082
1083     for projection_bound in &object.bounds.projection_bounds {
1084         let pair = (projection_bound.0.projection_ty.trait_ref.def_id,
1085                     projection_bound.0.projection_ty.item_name);
1086         associated_types.remove(&pair);
1087     }
1088
1089     for (trait_def_id, name) in associated_types {
1090         span_err!(tcx.sess, span, E0191,
1091             "the value of the associated type `{}` (from the trait `{}`) must be specified",
1092                     name,
1093                     tcx.item_path_str(trait_def_id));
1094     }
1095
1096     tcx.mk_trait(object.principal, object.bounds)
1097 }
1098
1099 fn report_ambiguous_associated_type(tcx: &ty::ctxt,
1100                                     span: Span,
1101                                     type_str: &str,
1102                                     trait_str: &str,
1103                                     name: &str) {
1104     span_err!(tcx.sess, span, E0223,
1105               "ambiguous associated type; specify the type using the syntax \
1106                `<{} as {}>::{}`",
1107               type_str, trait_str, name);
1108 }
1109
1110 // Search for a bound on a type parameter which includes the associated item
1111 // given by assoc_name. ty_param_node_id is the node id for the type parameter
1112 // (which might be `Self`, but only if it is the `Self` of a trait, not an
1113 // impl). This function will fail if there are no suitable bounds or there is
1114 // any ambiguity.
1115 fn find_bound_for_assoc_item<'tcx>(this: &AstConv<'tcx>,
1116                                    ty_param_node_id: ast::NodeId,
1117                                    ty_param_name: ast::Name,
1118                                    assoc_name: ast::Name,
1119                                    span: Span)
1120                                    -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1121 {
1122     let tcx = this.tcx();
1123
1124     let bounds = match this.get_type_parameter_bounds(span, ty_param_node_id) {
1125         Ok(v) => v,
1126         Err(ErrorReported) => {
1127             return Err(ErrorReported);
1128         }
1129     };
1130
1131     // Ensure the super predicates and stop if we encountered an error.
1132     if bounds.iter().any(|b| this.ensure_super_predicates(span, b.def_id()).is_err()) {
1133         return Err(ErrorReported);
1134     }
1135
1136     // Check that there is exactly one way to find an associated type with the
1137     // correct name.
1138     let suitable_bounds: Vec<_> =
1139         traits::transitive_bounds(tcx, &bounds)
1140         .filter(|b| this.trait_defines_associated_type_named(b.def_id(), assoc_name))
1141         .collect();
1142
1143     one_bound_for_assoc_type(tcx,
1144                              suitable_bounds,
1145                              &token::get_name(ty_param_name),
1146                              &token::get_name(assoc_name),
1147                              span)
1148 }
1149
1150
1151 // Checks that bounds contains exactly one element and reports appropriate
1152 // errors otherwise.
1153 fn one_bound_for_assoc_type<'tcx>(tcx: &ty::ctxt<'tcx>,
1154                                   bounds: Vec<ty::PolyTraitRef<'tcx>>,
1155                                   ty_param_name: &str,
1156                                   assoc_name: &str,
1157                                   span: Span)
1158     -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1159 {
1160     if bounds.is_empty() {
1161         span_err!(tcx.sess, span, E0220,
1162                   "associated type `{}` not found for `{}`",
1163                   assoc_name,
1164                   ty_param_name);
1165         return Err(ErrorReported);
1166     }
1167
1168     if bounds.len() > 1 {
1169         span_err!(tcx.sess, span, E0221,
1170                   "ambiguous associated type `{}` in bounds of `{}`",
1171                   assoc_name,
1172                   ty_param_name);
1173
1174         for bound in &bounds {
1175             span_note!(tcx.sess, span,
1176                        "associated type `{}` could derive from `{}`",
1177                        ty_param_name,
1178                        bound);
1179         }
1180     }
1181
1182     Ok(bounds[0].clone())
1183 }
1184
1185 // Create a type from a a path to an associated type.
1186 // For a path A::B::C::D, ty and ty_path_def are the type and def for A::B::C
1187 // and item_segment is the path segment for D. We return a type and a def for
1188 // the whole path.
1189 // Will fail except for T::A and Self::A; i.e., if ty/ty_path_def are not a type
1190 // parameter or Self.
1191 fn associated_path_def_to_ty<'tcx>(this: &AstConv<'tcx>,
1192                                    span: Span,
1193                                    ty: Ty<'tcx>,
1194                                    ty_path_def: def::Def,
1195                                    item_segment: &ast::PathSegment)
1196                                    -> (Ty<'tcx>, def::Def)
1197 {
1198     let tcx = this.tcx();
1199     let assoc_name = item_segment.identifier.name;
1200
1201     debug!("associated_path_def_to_ty: {:?}::{}", ty, assoc_name);
1202
1203     check_path_args(tcx, slice::ref_slice(item_segment), NO_TPS | NO_REGIONS);
1204
1205     // Find the type of the associated item, and the trait where the associated
1206     // item is declared.
1207     let bound = match (&ty.sty, ty_path_def) {
1208         (_, def::DefSelfTy(Some(trait_did), Some((impl_id, _)))) => {
1209             // `Self` in an impl of a trait - we have a concrete self type and a
1210             // trait reference.
1211             let trait_ref = tcx.impl_trait_ref(ast_util::local_def(impl_id)).unwrap();
1212             let trait_ref = if let Some(free_substs) = this.get_free_substs() {
1213                 trait_ref.subst(tcx, free_substs)
1214             } else {
1215                 trait_ref
1216             };
1217
1218             if this.ensure_super_predicates(span, trait_did).is_err() {
1219                 return (tcx.types.err, ty_path_def);
1220             }
1221
1222             let candidates: Vec<ty::PolyTraitRef> =
1223                 traits::supertraits(tcx, ty::Binder(trait_ref))
1224                 .filter(|r| this.trait_defines_associated_type_named(r.def_id(),
1225                                                                      assoc_name))
1226                 .collect();
1227
1228             match one_bound_for_assoc_type(tcx,
1229                                            candidates,
1230                                            "Self",
1231                                            &token::get_name(assoc_name),
1232                                            span) {
1233                 Ok(bound) => bound,
1234                 Err(ErrorReported) => return (tcx.types.err, ty_path_def),
1235             }
1236         }
1237         (&ty::TyParam(_), def::DefSelfTy(Some(trait_did), None)) => {
1238             assert_eq!(trait_did.krate, ast::LOCAL_CRATE);
1239             match find_bound_for_assoc_item(this,
1240                                             trait_did.node,
1241                                             token::special_idents::type_self.name,
1242                                             assoc_name,
1243                                             span) {
1244                 Ok(bound) => bound,
1245                 Err(ErrorReported) => return (tcx.types.err, ty_path_def),
1246             }
1247         }
1248         (&ty::TyParam(_), def::DefTyParam(_, _, param_did, param_name)) => {
1249             assert_eq!(param_did.krate, ast::LOCAL_CRATE);
1250             match find_bound_for_assoc_item(this,
1251                                             param_did.node,
1252                                             param_name,
1253                                             assoc_name,
1254                                             span) {
1255                 Ok(bound) => bound,
1256                 Err(ErrorReported) => return (tcx.types.err, ty_path_def),
1257             }
1258         }
1259         _ => {
1260             report_ambiguous_associated_type(tcx,
1261                                              span,
1262                                              &ty.to_string(),
1263                                              "Trait",
1264                                              &token::get_name(assoc_name));
1265             return (tcx.types.err, ty_path_def);
1266         }
1267     };
1268
1269     let trait_did = bound.0.def_id;
1270     let ty = this.projected_ty_from_poly_trait_ref(span, bound, assoc_name);
1271
1272     let item_did = if trait_did.krate == ast::LOCAL_CRATE {
1273         // `ty::trait_items` used below requires information generated
1274         // by type collection, which may be in progress at this point.
1275         match tcx.map.expect_item(trait_did.node).node {
1276             ast::ItemTrait(_, _, _, ref trait_items) => {
1277                 let item = trait_items.iter()
1278                                       .find(|i| i.ident.name == assoc_name)
1279                                       .expect("missing associated type");
1280                 ast_util::local_def(item.id)
1281             }
1282             _ => unreachable!()
1283         }
1284     } else {
1285         let trait_items = tcx.trait_items(trait_did);
1286         let item = trait_items.iter().find(|i| i.name() == assoc_name);
1287         item.expect("missing associated type").def_id()
1288     };
1289
1290     (ty, def::DefAssociatedTy(trait_did, item_did))
1291 }
1292
1293 fn qpath_to_ty<'tcx>(this: &AstConv<'tcx>,
1294                      rscope: &RegionScope,
1295                      span: Span,
1296                      param_mode: PathParamMode,
1297                      opt_self_ty: Option<Ty<'tcx>>,
1298                      trait_def_id: ast::DefId,
1299                      trait_segment: &ast::PathSegment,
1300                      item_segment: &ast::PathSegment)
1301                      -> Ty<'tcx>
1302 {
1303     let tcx = this.tcx();
1304
1305     check_path_args(tcx, slice::ref_slice(item_segment), NO_TPS | NO_REGIONS);
1306
1307     let self_ty = if let Some(ty) = opt_self_ty {
1308         ty
1309     } else {
1310         let path_str = tcx.item_path_str(trait_def_id);
1311         report_ambiguous_associated_type(tcx,
1312                                          span,
1313                                          "Type",
1314                                          &path_str,
1315                                          &token::get_ident(item_segment.identifier));
1316         return tcx.types.err;
1317     };
1318
1319     debug!("qpath_to_ty: self_type={:?}", self_ty);
1320
1321     let trait_ref = ast_path_to_mono_trait_ref(this,
1322                                                rscope,
1323                                                span,
1324                                                param_mode,
1325                                                trait_def_id,
1326                                                Some(self_ty),
1327                                                trait_segment);
1328
1329     debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
1330
1331     this.projected_ty(span, trait_ref, item_segment.identifier.name)
1332 }
1333
1334 /// Convert a type supplied as value for a type argument from AST into our
1335 /// our internal representation. This is the same as `ast_ty_to_ty` but that
1336 /// it applies the object lifetime default.
1337 ///
1338 /// # Parameters
1339 ///
1340 /// * `this`, `rscope`: the surrounding context
1341 /// * `decl_generics`: the generics of the struct/enum/trait declaration being
1342 ///   referenced
1343 /// * `index`: the index of the type parameter being instantiated from the list
1344 ///   (we assume it is in the `TypeSpace`)
1345 /// * `region_substs`: a partial substitution consisting of
1346 ///   only the region type parameters being supplied to this type.
1347 /// * `ast_ty`: the ast representation of the type being supplied
1348 pub fn ast_ty_arg_to_ty<'tcx>(this: &AstConv<'tcx>,
1349                               rscope: &RegionScope,
1350                               decl_generics: &ty::Generics<'tcx>,
1351                               index: usize,
1352                               region_substs: &Substs<'tcx>,
1353                               ast_ty: &ast::Ty)
1354                               -> Ty<'tcx>
1355 {
1356     let tcx = this.tcx();
1357
1358     if let Some(def) = decl_generics.types.opt_get(TypeSpace, index) {
1359         let object_lifetime_default = def.object_lifetime_default.subst(tcx, region_substs);
1360         let rscope1 = &ObjectLifetimeDefaultRscope::new(rscope, object_lifetime_default);
1361         ast_ty_to_ty(this, rscope1, ast_ty)
1362     } else {
1363         ast_ty_to_ty(this, rscope, ast_ty)
1364     }
1365 }
1366
1367 // Check the base def in a PathResolution and convert it to a Ty. If there are
1368 // associated types in the PathResolution, these will need to be separately
1369 // resolved.
1370 fn base_def_to_ty<'tcx>(this: &AstConv<'tcx>,
1371                         rscope: &RegionScope,
1372                         span: Span,
1373                         param_mode: PathParamMode,
1374                         def: &def::Def,
1375                         opt_self_ty: Option<Ty<'tcx>>,
1376                         base_segments: &[ast::PathSegment])
1377                         -> Ty<'tcx> {
1378     let tcx = this.tcx();
1379
1380     match *def {
1381         def::DefTrait(trait_def_id) => {
1382             // N.B. this case overlaps somewhat with
1383             // TyObjectSum, see that fn for details
1384             let mut projection_bounds = Vec::new();
1385
1386             let trait_ref = object_path_to_poly_trait_ref(this,
1387                                                           rscope,
1388                                                           span,
1389                                                           param_mode,
1390                                                           trait_def_id,
1391                                                           base_segments.last().unwrap(),
1392                                                           &mut projection_bounds);
1393
1394             check_path_args(tcx, base_segments.split_last().unwrap().1, NO_TPS | NO_REGIONS);
1395             trait_ref_to_object_type(this,
1396                                      rscope,
1397                                      span,
1398                                      trait_ref,
1399                                      projection_bounds,
1400                                      &[])
1401         }
1402         def::DefTy(did, _) | def::DefStruct(did) => {
1403             check_path_args(tcx, base_segments.split_last().unwrap().1, NO_TPS | NO_REGIONS);
1404             ast_path_to_ty(this,
1405                            rscope,
1406                            span,
1407                            param_mode,
1408                            did,
1409                            base_segments.last().unwrap())
1410         }
1411         def::DefTyParam(space, index, _, name) => {
1412             check_path_args(tcx, base_segments, NO_TPS | NO_REGIONS);
1413             tcx.mk_param(space, index, name)
1414         }
1415         def::DefSelfTy(_, Some((_, self_ty_id))) => {
1416             // Self in impl (we know the concrete type).
1417             check_path_args(tcx, base_segments, NO_TPS | NO_REGIONS);
1418             if let Some(&ty) = tcx.ast_ty_to_ty_cache.borrow().get(&self_ty_id) {
1419                 if let Some(free_substs) = this.get_free_substs() {
1420                     ty.subst(tcx, free_substs)
1421                 } else {
1422                     ty
1423                 }
1424             } else {
1425                 tcx.sess.span_bug(span, "self type has not been fully resolved")
1426             }
1427         }
1428         def::DefSelfTy(Some(_), None) => {
1429             // Self in trait.
1430             check_path_args(tcx, base_segments, NO_TPS | NO_REGIONS);
1431             tcx.mk_self_type()
1432         }
1433         def::DefAssociatedTy(trait_did, _) => {
1434             check_path_args(tcx, &base_segments[..base_segments.len()-2], NO_TPS | NO_REGIONS);
1435             qpath_to_ty(this,
1436                         rscope,
1437                         span,
1438                         param_mode,
1439                         opt_self_ty,
1440                         trait_did,
1441                         &base_segments[base_segments.len()-2],
1442                         base_segments.last().unwrap())
1443         }
1444         def::DefMod(id) => {
1445             // Used as sentinel by callers to indicate the `<T>::A::B::C` form.
1446             // FIXME(#22519) This part of the resolution logic should be
1447             // avoided entirely for that form, once we stop needed a Def
1448             // for `associated_path_def_to_ty`.
1449             // Fixing this will also let use resolve <Self>::Foo the same way we
1450             // resolve Self::Foo, at the moment we can't resolve the former because
1451             // we don't have the trait information around, which is just sad.
1452
1453             if !base_segments.is_empty() {
1454                 span_err!(tcx.sess,
1455                           span,
1456                           E0247,
1457                           "found module name used as a type: {}",
1458                           tcx.map.node_to_string(id.node));
1459                 return this.tcx().types.err;
1460             }
1461
1462             opt_self_ty.expect("missing T in <T>::a::b::c")
1463         }
1464         def::DefPrimTy(prim_ty) => {
1465             prim_ty_to_ty(tcx, base_segments, prim_ty)
1466         }
1467         _ => {
1468             let node = def.def_id().node;
1469             span_err!(tcx.sess, span, E0248,
1470                       "found value `{}` used as a type",
1471                       tcx.map.path_to_string(node));
1472             return this.tcx().types.err;
1473         }
1474     }
1475 }
1476
1477 // Note that both base_segments and assoc_segments may be empty, although not at
1478 // the same time.
1479 pub fn finish_resolving_def_to_ty<'tcx>(this: &AstConv<'tcx>,
1480                                         rscope: &RegionScope,
1481                                         span: Span,
1482                                         param_mode: PathParamMode,
1483                                         def: &def::Def,
1484                                         opt_self_ty: Option<Ty<'tcx>>,
1485                                         base_segments: &[ast::PathSegment],
1486                                         assoc_segments: &[ast::PathSegment])
1487                                         -> Ty<'tcx> {
1488     let mut ty = base_def_to_ty(this,
1489                                 rscope,
1490                                 span,
1491                                 param_mode,
1492                                 def,
1493                                 opt_self_ty,
1494                                 base_segments);
1495     let mut def = *def;
1496     // If any associated type segments remain, attempt to resolve them.
1497     for segment in assoc_segments {
1498         if ty.sty == ty::TyError {
1499             break;
1500         }
1501         // This is pretty bad (it will fail except for T::A and Self::A).
1502         let (a_ty, a_def) = associated_path_def_to_ty(this,
1503                                                       span,
1504                                                       ty,
1505                                                       def,
1506                                                       segment);
1507         ty = a_ty;
1508         def = a_def;
1509     }
1510     ty
1511 }
1512
1513 /// Parses the programmer's textual representation of a type into our
1514 /// internal notion of a type.
1515 pub fn ast_ty_to_ty<'tcx>(this: &AstConv<'tcx>,
1516                           rscope: &RegionScope,
1517                           ast_ty: &ast::Ty)
1518                           -> Ty<'tcx>
1519 {
1520     debug!("ast_ty_to_ty(ast_ty={:?})",
1521            ast_ty);
1522
1523     let tcx = this.tcx();
1524
1525     if let Some(&ty) = tcx.ast_ty_to_ty_cache.borrow().get(&ast_ty.id) {
1526         return ty;
1527     }
1528
1529     let typ = match ast_ty.node {
1530         ast::TyVec(ref ty) => {
1531             tcx.mk_slice(ast_ty_to_ty(this, rscope, &**ty))
1532         }
1533         ast::TyObjectSum(ref ty, ref bounds) => {
1534             match ast_ty_to_trait_ref(this, rscope, &**ty, bounds) {
1535                 Ok((trait_ref, projection_bounds)) => {
1536                     trait_ref_to_object_type(this,
1537                                              rscope,
1538                                              ast_ty.span,
1539                                              trait_ref,
1540                                              projection_bounds,
1541                                              bounds)
1542                 }
1543                 Err(ErrorReported) => {
1544                     this.tcx().types.err
1545                 }
1546             }
1547         }
1548         ast::TyPtr(ref mt) => {
1549             tcx.mk_ptr(ty::TypeAndMut {
1550                 ty: ast_ty_to_ty(this, rscope, &*mt.ty),
1551                 mutbl: mt.mutbl
1552             })
1553         }
1554         ast::TyRptr(ref region, ref mt) => {
1555             let r = opt_ast_region_to_region(this, rscope, ast_ty.span, region);
1556             debug!("TyRef r={:?}", r);
1557             let rscope1 =
1558                 &ObjectLifetimeDefaultRscope::new(
1559                     rscope,
1560                     ty::ObjectLifetimeDefault::Specific(r));
1561             let t = ast_ty_to_ty(this, rscope1, &*mt.ty);
1562             tcx.mk_ref(tcx.mk_region(r), ty::TypeAndMut {ty: t, mutbl: mt.mutbl})
1563         }
1564         ast::TyTup(ref fields) => {
1565             let flds = fields.iter()
1566                              .map(|t| ast_ty_to_ty(this, rscope, &**t))
1567                              .collect();
1568             tcx.mk_tup(flds)
1569         }
1570         ast::TyParen(ref typ) => ast_ty_to_ty(this, rscope, &**typ),
1571         ast::TyBareFn(ref bf) => {
1572             require_c_abi_if_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
1573             let bare_fn = ty_of_bare_fn(this, bf.unsafety, bf.abi, &*bf.decl);
1574             tcx.mk_fn(None, tcx.mk_bare_fn(bare_fn))
1575         }
1576         ast::TyPolyTraitRef(ref bounds) => {
1577             conv_ty_poly_trait_ref(this, rscope, ast_ty.span, bounds)
1578         }
1579         ast::TyPath(ref maybe_qself, ref path) => {
1580             let path_res = if let Some(&d) = tcx.def_map.borrow().get(&ast_ty.id) {
1581                 d
1582             } else if let Some(ast::QSelf { position: 0, .. }) = *maybe_qself {
1583                 // Create some fake resolution that can't possibly be a type.
1584                 def::PathResolution {
1585                     base_def: def::DefMod(ast_util::local_def(ast::CRATE_NODE_ID)),
1586                     last_private: LastMod(AllPublic),
1587                     depth: path.segments.len()
1588                 }
1589             } else {
1590                 tcx.sess.span_bug(ast_ty.span, &format!("unbound path {:?}", ast_ty))
1591             };
1592             let def = path_res.base_def;
1593             let base_ty_end = path.segments.len() - path_res.depth;
1594             let opt_self_ty = maybe_qself.as_ref().map(|qself| {
1595                 ast_ty_to_ty(this, rscope, &qself.ty)
1596             });
1597             let ty = finish_resolving_def_to_ty(this,
1598                                                 rscope,
1599                                                 ast_ty.span,
1600                                                 PathParamMode::Explicit,
1601                                                 &def,
1602                                                 opt_self_ty,
1603                                                 &path.segments[..base_ty_end],
1604                                                 &path.segments[base_ty_end..]);
1605
1606             if path_res.depth != 0 && ty.sty != ty::TyError {
1607                 // Write back the new resolution.
1608                 tcx.def_map.borrow_mut().insert(ast_ty.id, def::PathResolution {
1609                     base_def: def,
1610                     last_private: path_res.last_private,
1611                     depth: 0
1612                 });
1613             }
1614
1615             ty
1616         }
1617         ast::TyFixedLengthVec(ref ty, ref e) => {
1618             let hint = UncheckedExprHint(tcx.types.usize);
1619             match const_eval::eval_const_expr_partial(tcx, &e, hint) {
1620                 Ok(r) => {
1621                     match r {
1622                         ConstVal::Int(i) =>
1623                             tcx.mk_array(ast_ty_to_ty(this, rscope, &**ty),
1624                                          i as usize),
1625                         ConstVal::Uint(i) =>
1626                             tcx.mk_array(ast_ty_to_ty(this, rscope, &**ty),
1627                                          i as usize),
1628                         _ => {
1629                             span_err!(tcx.sess, ast_ty.span, E0249,
1630                                       "expected constant integer expression \
1631                                        for array length");
1632                             this.tcx().types.err
1633                         }
1634                     }
1635                 }
1636                 Err(ref r) => {
1637                     let subspan  =
1638                         ast_ty.span.lo <= r.span.lo && r.span.hi <= ast_ty.span.hi;
1639                     span_err!(tcx.sess, r.span, E0250,
1640                               "array length constant evaluation error: {}",
1641                               r.description());
1642                     if !subspan {
1643                         span_note!(tcx.sess, ast_ty.span, "for array length here")
1644                     }
1645                     this.tcx().types.err
1646                 }
1647             }
1648         }
1649         ast::TyTypeof(ref _e) => {
1650             tcx.sess.span_bug(ast_ty.span, "typeof is reserved but unimplemented");
1651         }
1652         ast::TyInfer => {
1653             // TyInfer also appears as the type of arguments or return
1654             // values in a ExprClosure, or as
1655             // the type of local variables. Both of these cases are
1656             // handled specially and will not descend into this routine.
1657             this.ty_infer(ast_ty.span)
1658         }
1659     };
1660
1661     tcx.ast_ty_to_ty_cache.borrow_mut().insert(ast_ty.id, typ);
1662     return typ;
1663 }
1664
1665 pub fn ty_of_arg<'tcx>(this: &AstConv<'tcx>,
1666                        rscope: &RegionScope,
1667                        a: &ast::Arg,
1668                        expected_ty: Option<Ty<'tcx>>)
1669                        -> Ty<'tcx>
1670 {
1671     match a.ty.node {
1672         ast::TyInfer if expected_ty.is_some() => expected_ty.unwrap(),
1673         ast::TyInfer => this.ty_infer(a.ty.span),
1674         _ => ast_ty_to_ty(this, rscope, &*a.ty),
1675     }
1676 }
1677
1678 struct SelfInfo<'a, 'tcx> {
1679     untransformed_self_ty: Ty<'tcx>,
1680     explicit_self: &'a ast::ExplicitSelf,
1681 }
1682
1683 pub fn ty_of_method<'tcx>(this: &AstConv<'tcx>,
1684                           sig: &ast::MethodSig,
1685                           untransformed_self_ty: Ty<'tcx>)
1686                           -> (ty::BareFnTy<'tcx>, ty::ExplicitSelfCategory) {
1687     let self_info = Some(SelfInfo {
1688         untransformed_self_ty: untransformed_self_ty,
1689         explicit_self: &sig.explicit_self,
1690     });
1691     let (bare_fn_ty, optional_explicit_self_category) =
1692         ty_of_method_or_bare_fn(this,
1693                                 sig.unsafety,
1694                                 sig.abi,
1695                                 self_info,
1696                                 &sig.decl);
1697     (bare_fn_ty, optional_explicit_self_category.unwrap())
1698 }
1699
1700 pub fn ty_of_bare_fn<'tcx>(this: &AstConv<'tcx>, unsafety: ast::Unsafety, abi: abi::Abi,
1701                                               decl: &ast::FnDecl) -> ty::BareFnTy<'tcx> {
1702     let (bare_fn_ty, _) = ty_of_method_or_bare_fn(this, unsafety, abi, None, decl);
1703     bare_fn_ty
1704 }
1705
1706 fn ty_of_method_or_bare_fn<'a, 'tcx>(this: &AstConv<'tcx>,
1707                                      unsafety: ast::Unsafety,
1708                                      abi: abi::Abi,
1709                                      opt_self_info: Option<SelfInfo<'a, 'tcx>>,
1710                                      decl: &ast::FnDecl)
1711                                      -> (ty::BareFnTy<'tcx>, Option<ty::ExplicitSelfCategory>)
1712 {
1713     debug!("ty_of_method_or_bare_fn");
1714
1715     // New region names that appear inside of the arguments of the function
1716     // declaration are bound to that function type.
1717     let rb = rscope::BindingRscope::new();
1718
1719     // `implied_output_region` is the region that will be assumed for any
1720     // region parameters in the return type. In accordance with the rules for
1721     // lifetime elision, we can determine it in two ways. First (determined
1722     // here), if self is by-reference, then the implied output region is the
1723     // region of the self parameter.
1724     let mut explicit_self_category_result = None;
1725     let (self_ty, implied_output_region) = match opt_self_info {
1726         None => (None, None),
1727         Some(self_info) => {
1728             // This type comes from an impl or trait; no late-bound
1729             // regions should be present.
1730             assert!(!self_info.untransformed_self_ty.has_escaping_regions());
1731
1732             // Figure out and record the explicit self category.
1733             let explicit_self_category =
1734                 determine_explicit_self_category(this, &rb, &self_info);
1735             explicit_self_category_result = Some(explicit_self_category);
1736             match explicit_self_category {
1737                 ty::StaticExplicitSelfCategory => {
1738                     (None, None)
1739                 }
1740                 ty::ByValueExplicitSelfCategory => {
1741                     (Some(self_info.untransformed_self_ty), None)
1742                 }
1743                 ty::ByReferenceExplicitSelfCategory(region, mutability) => {
1744                     (Some(this.tcx().mk_ref(
1745                                       this.tcx().mk_region(region),
1746                                       ty::TypeAndMut {
1747                                         ty: self_info.untransformed_self_ty,
1748                                         mutbl: mutability
1749                                       })),
1750                      Some(region))
1751                 }
1752                 ty::ByBoxExplicitSelfCategory => {
1753                     (Some(this.tcx().mk_box(self_info.untransformed_self_ty)), None)
1754                 }
1755             }
1756         }
1757     };
1758
1759     // HACK(eddyb) replace the fake self type in the AST with the actual type.
1760     let input_params = if self_ty.is_some() {
1761         &decl.inputs[1..]
1762     } else {
1763         &decl.inputs[..]
1764     };
1765     let input_tys = input_params.iter().map(|a| ty_of_arg(this, &rb, a, None));
1766     let input_pats: Vec<String> = input_params.iter()
1767                                               .map(|a| pprust::pat_to_string(&*a.pat))
1768                                               .collect();
1769     let self_and_input_tys: Vec<Ty> =
1770         self_ty.into_iter().chain(input_tys).collect();
1771
1772
1773     // Second, if there was exactly one lifetime (either a substitution or a
1774     // reference) in the arguments, then any anonymous regions in the output
1775     // have that lifetime.
1776     let implied_output_region = match implied_output_region {
1777         Some(r) => Ok(r),
1778         None => {
1779             let input_tys = if self_ty.is_some() {
1780                 // Skip the first argument if `self` is present.
1781                 &self_and_input_tys[1..]
1782             } else {
1783                 &self_and_input_tys[..]
1784             };
1785
1786             find_implied_output_region(this.tcx(), input_tys, input_pats)
1787         }
1788     };
1789
1790     let output_ty = match decl.output {
1791         ast::Return(ref output) if output.node == ast::TyInfer =>
1792             ty::FnConverging(this.ty_infer(output.span)),
1793         ast::Return(ref output) =>
1794             ty::FnConverging(convert_ty_with_lifetime_elision(this,
1795                                                               implied_output_region,
1796                                                               &output)),
1797         ast::DefaultReturn(..) => ty::FnConverging(this.tcx().mk_nil()),
1798         ast::NoReturn(..) => ty::FnDiverging
1799     };
1800
1801     (ty::BareFnTy {
1802         unsafety: unsafety,
1803         abi: abi,
1804         sig: ty::Binder(ty::FnSig {
1805             inputs: self_and_input_tys,
1806             output: output_ty,
1807             variadic: decl.variadic
1808         }),
1809     }, explicit_self_category_result)
1810 }
1811
1812 fn determine_explicit_self_category<'a, 'tcx>(this: &AstConv<'tcx>,
1813                                               rscope: &RegionScope,
1814                                               self_info: &SelfInfo<'a, 'tcx>)
1815                                               -> ty::ExplicitSelfCategory
1816 {
1817     return match self_info.explicit_self.node {
1818         ast::SelfStatic => ty::StaticExplicitSelfCategory,
1819         ast::SelfValue(_) => ty::ByValueExplicitSelfCategory,
1820         ast::SelfRegion(ref lifetime, mutability, _) => {
1821             let region =
1822                 opt_ast_region_to_region(this,
1823                                          rscope,
1824                                          self_info.explicit_self.span,
1825                                          lifetime);
1826             ty::ByReferenceExplicitSelfCategory(region, mutability)
1827         }
1828         ast::SelfExplicit(ref ast_type, _) => {
1829             let explicit_type = ast_ty_to_ty(this, rscope, &**ast_type);
1830
1831             // We wish to (for now) categorize an explicit self
1832             // declaration like `self: SomeType` into either `self`,
1833             // `&self`, `&mut self`, or `Box<self>`. We do this here
1834             // by some simple pattern matching. A more precise check
1835             // is done later in `check_method_self_type()`.
1836             //
1837             // Examples:
1838             //
1839             // ```
1840             // impl Foo for &T {
1841             //     // Legal declarations:
1842             //     fn method1(self: &&T); // ByReferenceExplicitSelfCategory
1843             //     fn method2(self: &T); // ByValueExplicitSelfCategory
1844             //     fn method3(self: Box<&T>); // ByBoxExplicitSelfCategory
1845             //
1846             //     // Invalid cases will be caught later by `check_method_self_type`:
1847             //     fn method_err1(self: &mut T); // ByReferenceExplicitSelfCategory
1848             // }
1849             // ```
1850             //
1851             // To do the check we just count the number of "modifiers"
1852             // on each type and compare them. If they are the same or
1853             // the impl has more, we call it "by value". Otherwise, we
1854             // look at the outermost modifier on the method decl and
1855             // call it by-ref, by-box as appropriate. For method1, for
1856             // example, the impl type has one modifier, but the method
1857             // type has two, so we end up with
1858             // ByReferenceExplicitSelfCategory.
1859
1860             let impl_modifiers = count_modifiers(self_info.untransformed_self_ty);
1861             let method_modifiers = count_modifiers(explicit_type);
1862
1863             debug!("determine_explicit_self_category(self_info.untransformed_self_ty={:?} \
1864                    explicit_type={:?} \
1865                    modifiers=({},{})",
1866                    self_info.untransformed_self_ty,
1867                    explicit_type,
1868                    impl_modifiers,
1869                    method_modifiers);
1870
1871             if impl_modifiers >= method_modifiers {
1872                 ty::ByValueExplicitSelfCategory
1873             } else {
1874                 match explicit_type.sty {
1875                     ty::TyRef(r, mt) => ty::ByReferenceExplicitSelfCategory(*r, mt.mutbl),
1876                     ty::TyBox(_) => ty::ByBoxExplicitSelfCategory,
1877                     _ => ty::ByValueExplicitSelfCategory,
1878                 }
1879             }
1880         }
1881     };
1882
1883     fn count_modifiers(ty: Ty) -> usize {
1884         match ty.sty {
1885             ty::TyRef(_, mt) => count_modifiers(mt.ty) + 1,
1886             ty::TyBox(t) => count_modifiers(t) + 1,
1887             _ => 0,
1888         }
1889     }
1890 }
1891
1892 pub fn ty_of_closure<'tcx>(
1893     this: &AstConv<'tcx>,
1894     unsafety: ast::Unsafety,
1895     decl: &ast::FnDecl,
1896     abi: abi::Abi,
1897     expected_sig: Option<ty::FnSig<'tcx>>)
1898     -> ty::ClosureTy<'tcx>
1899 {
1900     debug!("ty_of_closure(expected_sig={:?})",
1901            expected_sig);
1902
1903     // new region names that appear inside of the fn decl are bound to
1904     // that function type
1905     let rb = rscope::BindingRscope::new();
1906
1907     let input_tys: Vec<_> = decl.inputs.iter().enumerate().map(|(i, a)| {
1908         let expected_arg_ty = expected_sig.as_ref().and_then(|e| {
1909             // no guarantee that the correct number of expected args
1910             // were supplied
1911             if i < e.inputs.len() {
1912                 Some(e.inputs[i])
1913             } else {
1914                 None
1915             }
1916         });
1917         ty_of_arg(this, &rb, a, expected_arg_ty)
1918     }).collect();
1919
1920     let expected_ret_ty = expected_sig.map(|e| e.output);
1921
1922     let is_infer = match decl.output {
1923         ast::Return(ref output) if output.node == ast::TyInfer => true,
1924         ast::DefaultReturn(..) => true,
1925         _ => false
1926     };
1927
1928     let output_ty = match decl.output {
1929         _ if is_infer && expected_ret_ty.is_some() =>
1930             expected_ret_ty.unwrap(),
1931         _ if is_infer =>
1932             ty::FnConverging(this.ty_infer(decl.output.span())),
1933         ast::Return(ref output) =>
1934             ty::FnConverging(ast_ty_to_ty(this, &rb, &**output)),
1935         ast::DefaultReturn(..) => unreachable!(),
1936         ast::NoReturn(..) => ty::FnDiverging
1937     };
1938
1939     debug!("ty_of_closure: input_tys={:?}", input_tys);
1940     debug!("ty_of_closure: output_ty={:?}", output_ty);
1941
1942     ty::ClosureTy {
1943         unsafety: unsafety,
1944         abi: abi,
1945         sig: ty::Binder(ty::FnSig {inputs: input_tys,
1946                                    output: output_ty,
1947                                    variadic: decl.variadic}),
1948     }
1949 }
1950
1951 /// Given an existential type like `Foo+'a+Bar`, this routine converts the `'a` and `Bar` intos an
1952 /// `ExistentialBounds` struct. The `main_trait_refs` argument specifies the `Foo` -- it is absent
1953 /// for closures. Eventually this should all be normalized, I think, so that there is no "main
1954 /// trait ref" and instead we just have a flat list of bounds as the existential type.
1955 fn conv_existential_bounds<'tcx>(
1956     this: &AstConv<'tcx>,
1957     rscope: &RegionScope,
1958     span: Span,
1959     principal_trait_ref: ty::PolyTraitRef<'tcx>,
1960     projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>,
1961     ast_bounds: &[ast::TyParamBound])
1962     -> ty::ExistentialBounds<'tcx>
1963 {
1964     let partitioned_bounds =
1965         partition_bounds(this.tcx(), span, ast_bounds);
1966
1967     conv_existential_bounds_from_partitioned_bounds(
1968         this, rscope, span, principal_trait_ref, projection_bounds, partitioned_bounds)
1969 }
1970
1971 fn conv_ty_poly_trait_ref<'tcx>(
1972     this: &AstConv<'tcx>,
1973     rscope: &RegionScope,
1974     span: Span,
1975     ast_bounds: &[ast::TyParamBound])
1976     -> Ty<'tcx>
1977 {
1978     let mut partitioned_bounds = partition_bounds(this.tcx(), span, &ast_bounds[..]);
1979
1980     let mut projection_bounds = Vec::new();
1981     let main_trait_bound = if !partitioned_bounds.trait_bounds.is_empty() {
1982         let trait_bound = partitioned_bounds.trait_bounds.remove(0);
1983         instantiate_poly_trait_ref(this,
1984                                    rscope,
1985                                    trait_bound,
1986                                    None,
1987                                    &mut projection_bounds)
1988     } else {
1989         span_err!(this.tcx().sess, span, E0224,
1990                   "at least one non-builtin trait is required for an object type");
1991         return this.tcx().types.err;
1992     };
1993
1994     let bounds =
1995         conv_existential_bounds_from_partitioned_bounds(this,
1996                                                         rscope,
1997                                                         span,
1998                                                         main_trait_bound.clone(),
1999                                                         projection_bounds,
2000                                                         partitioned_bounds);
2001
2002     make_object_type(this, span, main_trait_bound, bounds)
2003 }
2004
2005 pub fn conv_existential_bounds_from_partitioned_bounds<'tcx>(
2006     this: &AstConv<'tcx>,
2007     rscope: &RegionScope,
2008     span: Span,
2009     principal_trait_ref: ty::PolyTraitRef<'tcx>,
2010     mut projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>, // Empty for boxed closures
2011     partitioned_bounds: PartitionedBounds)
2012     -> ty::ExistentialBounds<'tcx>
2013 {
2014     let PartitionedBounds { builtin_bounds,
2015                             trait_bounds,
2016                             region_bounds } =
2017         partitioned_bounds;
2018
2019     if !trait_bounds.is_empty() {
2020         let b = &trait_bounds[0];
2021         span_err!(this.tcx().sess, b.trait_ref.path.span, E0225,
2022                   "only the builtin traits can be used as closure or object bounds");
2023     }
2024
2025     let region_bound =
2026         compute_object_lifetime_bound(this,
2027                                       span,
2028                                       &region_bounds,
2029                                       principal_trait_ref,
2030                                       builtin_bounds);
2031
2032     let region_bound = match region_bound {
2033         Some(r) => r,
2034         None => {
2035             match rscope.object_lifetime_default(span) {
2036                 Some(r) => r,
2037                 None => {
2038                     span_err!(this.tcx().sess, span, E0228,
2039                               "the lifetime bound for this object type cannot be deduced \
2040                                from context; please supply an explicit bound");
2041                     ty::ReStatic
2042                 }
2043             }
2044         }
2045     };
2046
2047     debug!("region_bound: {:?}", region_bound);
2048
2049     ty::sort_bounds_list(&mut projection_bounds);
2050
2051     ty::ExistentialBounds {
2052         region_bound: region_bound,
2053         builtin_bounds: builtin_bounds,
2054         projection_bounds: projection_bounds,
2055     }
2056 }
2057
2058 /// Given the bounds on an object, determines what single region bound
2059 /// (if any) we can use to summarize this type. The basic idea is that we will use the bound the
2060 /// user provided, if they provided one, and otherwise search the supertypes of trait bounds for
2061 /// region bounds. It may be that we can derive no bound at all, in which case we return `None`.
2062 fn compute_object_lifetime_bound<'tcx>(
2063     this: &AstConv<'tcx>,
2064     span: Span,
2065     explicit_region_bounds: &[&ast::Lifetime],
2066     principal_trait_ref: ty::PolyTraitRef<'tcx>,
2067     builtin_bounds: ty::BuiltinBounds)
2068     -> Option<ty::Region> // if None, use the default
2069 {
2070     let tcx = this.tcx();
2071
2072     debug!("compute_opt_region_bound(explicit_region_bounds={:?}, \
2073            principal_trait_ref={:?}, builtin_bounds={:?})",
2074            explicit_region_bounds,
2075            principal_trait_ref,
2076            builtin_bounds);
2077
2078     if explicit_region_bounds.len() > 1 {
2079         span_err!(tcx.sess, explicit_region_bounds[1].span, E0226,
2080             "only a single explicit lifetime bound is permitted");
2081     }
2082
2083     if !explicit_region_bounds.is_empty() {
2084         // Explicitly specified region bound. Use that.
2085         let r = explicit_region_bounds[0];
2086         return Some(ast_region_to_region(tcx, r));
2087     }
2088
2089     if let Err(ErrorReported) = this.ensure_super_predicates(span,principal_trait_ref.def_id()) {
2090         return Some(ty::ReStatic);
2091     }
2092
2093     // No explicit region bound specified. Therefore, examine trait
2094     // bounds and see if we can derive region bounds from those.
2095     let derived_region_bounds =
2096         object_region_bounds(tcx, &principal_trait_ref, builtin_bounds);
2097
2098     // If there are no derived region bounds, then report back that we
2099     // can find no region bound. The caller will use the default.
2100     if derived_region_bounds.is_empty() {
2101         return None;
2102     }
2103
2104     // If any of the derived region bounds are 'static, that is always
2105     // the best choice.
2106     if derived_region_bounds.iter().any(|r| ty::ReStatic == *r) {
2107         return Some(ty::ReStatic);
2108     }
2109
2110     // Determine whether there is exactly one unique region in the set
2111     // of derived region bounds. If so, use that. Otherwise, report an
2112     // error.
2113     let r = derived_region_bounds[0];
2114     if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2115         span_err!(tcx.sess, span, E0227,
2116                   "ambiguous lifetime bound, explicit lifetime bound required");
2117     }
2118     return Some(r);
2119 }
2120
2121 pub struct PartitionedBounds<'a> {
2122     pub builtin_bounds: ty::BuiltinBounds,
2123     pub trait_bounds: Vec<&'a ast::PolyTraitRef>,
2124     pub region_bounds: Vec<&'a ast::Lifetime>,
2125 }
2126
2127 /// Divides a list of bounds from the AST into three groups: builtin bounds (Copy, Sized etc),
2128 /// general trait bounds, and region bounds.
2129 pub fn partition_bounds<'a>(tcx: &ty::ctxt,
2130                             _span: Span,
2131                             ast_bounds: &'a [ast::TyParamBound])
2132                             -> PartitionedBounds<'a>
2133 {
2134     let mut builtin_bounds = ty::BuiltinBounds::empty();
2135     let mut region_bounds = Vec::new();
2136     let mut trait_bounds = Vec::new();
2137     for ast_bound in ast_bounds {
2138         match *ast_bound {
2139             ast::TraitTyParamBound(ref b, ast::TraitBoundModifier::None) => {
2140                 match ::lookup_full_def(tcx, b.trait_ref.path.span, b.trait_ref.ref_id) {
2141                     def::DefTrait(trait_did) => {
2142                         if tcx.try_add_builtin_trait(trait_did,
2143                                                      &mut builtin_bounds) {
2144                             let segments = &b.trait_ref.path.segments;
2145                             let parameters = &segments[segments.len() - 1].parameters;
2146                             if !parameters.types().is_empty() {
2147                                 check_type_argument_count(tcx, b.trait_ref.path.span,
2148                                                           parameters.types().len(), 0, 0);
2149                             }
2150                             if !parameters.lifetimes().is_empty() {
2151                                 report_lifetime_number_error(tcx, b.trait_ref.path.span,
2152                                                              parameters.lifetimes().len(), 0);
2153                             }
2154                             continue; // success
2155                         }
2156                     }
2157                     _ => {
2158                         // Not a trait? that's an error, but it'll get
2159                         // reported later.
2160                     }
2161                 }
2162                 trait_bounds.push(b);
2163             }
2164             ast::TraitTyParamBound(_, ast::TraitBoundModifier::Maybe) => {}
2165             ast::RegionTyParamBound(ref l) => {
2166                 region_bounds.push(l);
2167             }
2168         }
2169     }
2170
2171     PartitionedBounds {
2172         builtin_bounds: builtin_bounds,
2173         trait_bounds: trait_bounds,
2174         region_bounds: region_bounds,
2175     }
2176 }
2177
2178 fn prohibit_projections<'tcx>(tcx: &ty::ctxt<'tcx>,
2179                               bindings: &[ConvertedBinding<'tcx>])
2180 {
2181     for binding in bindings.iter().take(1) {
2182         span_err!(tcx.sess, binding.span, E0229,
2183             "associated type bindings are not allowed here");
2184     }
2185 }
2186
2187 fn check_type_argument_count(tcx: &ty::ctxt, span: Span, supplied: usize,
2188                              required: usize, accepted: usize) {
2189     if supplied < required {
2190         let expected = if required < accepted {
2191             "expected at least"
2192         } else {
2193             "expected"
2194         };
2195         span_err!(tcx.sess, span, E0243,
2196                   "wrong number of type arguments: {} {}, found {}",
2197                   expected, required, supplied);
2198     } else if supplied > accepted {
2199         let expected = if required < accepted {
2200             "expected at most"
2201         } else {
2202             "expected"
2203         };
2204         span_err!(tcx.sess, span, E0244,
2205                   "wrong number of type arguments: {} {}, found {}",
2206                   expected,
2207                   accepted,
2208                   supplied);
2209     }
2210 }
2211
2212 fn report_lifetime_number_error(tcx: &ty::ctxt, span: Span, number: usize, expected: usize) {
2213     span_err!(tcx.sess, span, E0107,
2214               "wrong number of lifetime parameters: expected {}, found {}",
2215               expected, number);
2216 }
2217
2218 // A helper struct for conveniently grouping a set of bounds which we pass to
2219 // and return from functions in multiple places.
2220 #[derive(PartialEq, Eq, Clone, Debug)]
2221 pub struct Bounds<'tcx> {
2222     pub region_bounds: Vec<ty::Region>,
2223     pub builtin_bounds: ty::BuiltinBounds,
2224     pub trait_bounds: Vec<ty::PolyTraitRef<'tcx>>,
2225     pub projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>,
2226 }
2227
2228 impl<'tcx> Bounds<'tcx> {
2229     pub fn predicates(&self,
2230         tcx: &ty::ctxt<'tcx>,
2231         param_ty: Ty<'tcx>)
2232         -> Vec<ty::Predicate<'tcx>>
2233     {
2234         let mut vec = Vec::new();
2235
2236         for builtin_bound in &self.builtin_bounds {
2237             match traits::trait_ref_for_builtin_bound(tcx, builtin_bound, param_ty) {
2238                 Ok(trait_ref) => { vec.push(trait_ref.to_predicate()); }
2239                 Err(ErrorReported) => { }
2240             }
2241         }
2242
2243         for &region_bound in &self.region_bounds {
2244             // account for the binder being introduced below; no need to shift `param_ty`
2245             // because, at present at least, it can only refer to early-bound regions
2246             let region_bound = ty_fold::shift_region(region_bound, 1);
2247             vec.push(ty::Binder(ty::OutlivesPredicate(param_ty, region_bound)).to_predicate());
2248         }
2249
2250         for bound_trait_ref in &self.trait_bounds {
2251             vec.push(bound_trait_ref.to_predicate());
2252         }
2253
2254         for projection in &self.projection_bounds {
2255             vec.push(projection.to_predicate());
2256         }
2257
2258         vec
2259     }
2260 }