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;
  53 use middle::def;
  54 use middle::resolve_lifetime as rl;
  55 use middle::privacy::{AllPublic, LastMod};
  56 use middle::subst::{FnSpace, TypeSpace, SelfSpace, Subst, Substs};
  57 use middle::traits;
  58 use middle::ty::{self, RegionEscape, Ty};
  59 use rscope::{self, UnelidableRscope, RegionScope, ElidableRscope, ExplicitRscope,
  60              ObjectLifetimeDefaultRscope, ShiftedRscope, BindingRscope};
  61 use util::common::{ErrorReported, FN_OUTPUT_NAME};
  62 use util::nodemap::FnvHashSet;
  63 use util::ppaux::{self, Repr, UserString};
  64
  65 use std::iter::repeat;
  66 use std::rc::Rc;
  67 use std::slice;
  68 use syntax::{abi, ast, ast_util};
  69 use syntax::codemap::{Span, Pos};
  70 use syntax::parse::token;
  71 use syntax::print::pprust;
  72
  73 pub trait AstConv<'tcx> {
  74     fn tcx<'a>(&'a self) -> &'a ty::ctxt<'tcx>;
  75
  76     /// Identify the type scheme for an item with a type, like a type
  77     /// alias, fn, or struct. This allows you to figure out the set of
  78     /// type parameters defined on the item.
  79     fn get_item_type_scheme(&self, span: Span, id: ast::DefId)
  80                             -> Result<ty::TypeScheme<'tcx>, ErrorReported>;
  81
  82     /// Returns the `TraitDef` for a given trait. This allows you to
  83     /// figure out the set of type parameters defined on the trait.
  84     fn get_trait_def(&self, span: Span, id: ast::DefId)
  85                      -> Result<Rc<ty::TraitDef<'tcx>>, ErrorReported>;
  86
  87     /// Ensure that the super-predicates for the trait with the given
  88     /// id are available and also for the transitive set of
  89     /// super-predicates.
  90     fn ensure_super_predicates(&self, span: Span, id: ast::DefId)
  91                                -> Result<(), ErrorReported>;
  92
  93     /// Returns the set of bounds in scope for the type parameter with
  94     /// the given id.
  95     fn get_type_parameter_bounds(&self, span: Span, def_id: ast::NodeId)
  96                                  -> Result<Vec<ty::PolyTraitRef<'tcx>>, ErrorReported>;
  97
  98     /// Returns true if the trait with id `trait_def_id` defines an
  99     /// associated type with the name `name`.
 100     fn trait_defines_associated_type_named(&self, trait_def_id: ast::DefId, name: ast::Name)
 101                                            -> bool;
 102
 103     /// Return an (optional) substitution to convert bound type parameters that
 104     /// are in scope into free ones. This function should only return Some
 105     /// within a fn body.
 106     /// See ParameterEnvironment::free_substs for more information.
 107     fn get_free_substs(&self) -> Option<&Substs<'tcx>> {
 108         None
 109     }
 110
 111     /// What type should we use when a type is omitted?
 112     fn ty_infer(&self, span: Span) -> Ty<'tcx>;
 113
 114     /// Projecting an associated type from a (potentially)
 115     /// higher-ranked trait reference is more complicated, because of
 116     /// the possibility of late-bound regions appearing in the
 117     /// associated type binding. This is not legal in function
 118     /// signatures for that reason. In a function body, we can always
 119     /// handle it because we can use inference variables to remove the
 120     /// late-bound regions.
 121     fn projected_ty_from_poly_trait_ref(&self,
 122                                         span: Span,
 123                                         poly_trait_ref: ty::PolyTraitRef<'tcx>,
 124                                         item_name: ast::Name)
 125                                         -> Ty<'tcx>
 126     {
 127         if ty::binds_late_bound_regions(self.tcx(), &poly_trait_ref) {
 128             span_err!(self.tcx().sess, span, E0212,
 129                 "cannot extract an associated type from a higher-ranked trait bound \
 130                  in this context");
 131             self.tcx().types.err
 132         } else {
 133             // no late-bound regions, we can just ignore the binder
 134             self.projected_ty(span, poly_trait_ref.0.clone(), item_name)
 135         }
 136     }
 137
 138     /// Project an associated type from a non-higher-ranked trait reference.
 139     /// This is fairly straightforward and can be accommodated in any context.
 140     fn projected_ty(&self,
 141                     span: Span,
 142                     _trait_ref: Rc<ty::TraitRef<'tcx>>,
 143                     _item_name: ast::Name)
 144                     -> Ty<'tcx>;
 145 }
 146
 147 pub fn ast_region_to_region(tcx: &ty::ctxt, lifetime: &ast::Lifetime)
 148                             -> ty::Region {
 149     let r = match tcx.named_region_map.get(&lifetime.id) {
 150         None => {
 151             // should have been recorded by the `resolve_lifetime` pass
 152             tcx.sess.span_bug(lifetime.span, "unresolved lifetime");
 153         }
 154
 155         Some(&rl::DefStaticRegion) => {
 156             ty::ReStatic
 157         }
 158
 159         Some(&rl::DefLateBoundRegion(debruijn, id)) => {
 160             ty::ReLateBound(debruijn, ty::BrNamed(ast_util::local_def(id), lifetime.name))
 161         }
 162
 163         Some(&rl::DefEarlyBoundRegion(space, index, id)) => {
 164             ty::ReEarlyBound(ty::EarlyBoundRegion {
 165                 param_id: id,
 166                 space: space,
 167                 index: index,
 168                 name: lifetime.name
 169             })
 170         }
 171
 172         Some(&rl::DefFreeRegion(scope, id)) => {
 173             ty::ReFree(ty::FreeRegion {
 174                     scope: scope,
 175                     bound_region: ty::BrNamed(ast_util::local_def(id),
 176                                               lifetime.name)
 177                 })
 178         }
 179     };
 180
 181     debug!("ast_region_to_region(lifetime={} id={}) yields {}",
 182            lifetime.repr(tcx),
 183            lifetime.id,
 184            r.repr(tcx));
 185
 186     r
 187 }
 188
 189 pub fn opt_ast_region_to_region<'tcx>(
 190     this: &AstConv<'tcx>,
 191     rscope: &RegionScope,
 192     default_span: Span,
 193     opt_lifetime: &Option<ast::Lifetime>) -> ty::Region
 194 {
 195     let r = match *opt_lifetime {
 196         Some(ref lifetime) => {
 197             ast_region_to_region(this.tcx(), lifetime)
 198         }
 199
 200         None => {
 201             match rscope.anon_regions(default_span, 1) {
 202                 Err(v) => {
 203                     debug!("optional region in illegal location");
 204                     span_err!(this.tcx().sess, default_span, E0106,
 205                         "missing lifetime specifier");
 206                     match v {
 207                         Some(v) => {
 208                             let mut m = String::new();
 209                             let len = v.len();
 210                             for (i, (name, n)) in v.into_iter().enumerate() {
 211                                 let help_name = if name.is_empty() {
 212                                     format!("argument {}", i + 1)
 213                                 } else {
 214                                     format!("`{}`", name)
 215                                 };
 216
 217                                 m.push_str(&(if n == 1 {
 218                                     help_name
 219                                 } else {
 220                                     format!("one of {}'s {} elided lifetimes", help_name, n)
 221                                 })[..]);
 222
 223                                 if len == 2 && i == 0 {
 224                                     m.push_str(" or ");
 225                                 } else if i + 2 == len {
 226                                     m.push_str(", or ");
 227                                 } else if i + 1 != len {
 228                                     m.push_str(", ");
 229                                 }
 230                             }
 231                             if len == 1 {
 232                                 fileline_help!(this.tcx().sess, default_span,
 233                                     "this function's return type contains a borrowed value, but \
 234                                      the signature does not say which {} it is borrowed from",
 235                                     m);
 236                             } else if len == 0 {
 237                                 fileline_help!(this.tcx().sess, default_span,
 238                                     "this function's return type contains a borrowed value, but \
 239                                      there is no value for it to be borrowed from");
 240                                 fileline_help!(this.tcx().sess, default_span,
 241                                     "consider giving it a 'static lifetime");
 242                             } else {
 243                                 fileline_help!(this.tcx().sess, default_span,
 244                                     "this function's return type contains a borrowed value, but \
 245                                      the signature does not say whether it is borrowed from {}",
 246                                     m);
 247                             }
 248                         }
 249                         None => {},
 250                     }
 251                     ty::ReStatic
 252                 }
 253
 254                 Ok(rs) => rs[0],
 255             }
 256         }
 257     };
 258
 259     debug!("opt_ast_region_to_region(opt_lifetime={}) yields {}",
 260             opt_lifetime.repr(this.tcx()),
 261             r.repr(this.tcx()));
 262
 263     r
 264 }
 265
 266 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
 267 /// returns an appropriate set of substitutions for this particular reference to `I`.
 268 pub fn ast_path_substs_for_ty<'tcx>(
 269     this: &AstConv<'tcx>,
 270     rscope: &RegionScope,
 271     span: Span,
 272     param_mode: PathParamMode,
 273     decl_generics: &ty::Generics<'tcx>,
 274     item_segment: &ast::PathSegment)
 275     -> Substs<'tcx>
 276 {
 277     let tcx = this.tcx();
 278
 279     // ast_path_substs() is only called to convert paths that are
 280     // known to refer to traits, types, or structs. In these cases,
 281     // all type parameters defined for the item being referenced will
 282     // be in the TypeSpace or SelfSpace.
 283     //
 284     // Note: in the case of traits, the self parameter is also
 285     // defined, but we don't currently create a `type_param_def` for
 286     // `Self` because it is implicit.
 287     assert!(decl_generics.regions.all(|d| d.space == TypeSpace));
 288     assert!(decl_generics.types.all(|d| d.space != FnSpace));
 289
 290     let (regions, types, assoc_bindings) = match item_segment.parameters {
 291         ast::AngleBracketedParameters(ref data) => {
 292             convert_angle_bracketed_parameters(this, rscope, span, decl_generics, data)
 293         }
 294         ast::ParenthesizedParameters(ref data) => {
 295             span_err!(tcx.sess, span, E0214,
 296                 "parenthesized parameters may only be used with a trait");
 297             convert_parenthesized_parameters(this, rscope, span, decl_generics, data)
 298         }
 299     };
 300
 301     prohibit_projections(this.tcx(), &assoc_bindings);
 302
 303     create_substs_for_ast_path(this,
 304                                span,
 305                                param_mode,
 306                                decl_generics,
 307                                None,
 308                                types,
 309                                regions)
 310 }
 311
 312 #[derive(PartialEq, Eq)]
 313 pub enum PathParamMode {
 314     // Any path in a type context.
 315     Explicit,
 316     // The `module::Type` in `module::Type::method` in an expression.
 317     Optional
 318 }
 319
 320 fn create_region_substs<'tcx>(
 321     this: &AstConv<'tcx>,
 322     rscope: &RegionScope,
 323     span: Span,
 324     decl_generics: &ty::Generics<'tcx>,
 325     regions_provided: Vec<ty::Region>)
 326     -> Substs<'tcx>
 327 {
 328     let tcx = this.tcx();
 329
 330     // If the type is parameterized by the this region, then replace this
 331     // region with the current anon region binding (in other words,
 332     // whatever & would get replaced with).
 333     let expected_num_region_params = decl_generics.regions.len(TypeSpace);
 334     let supplied_num_region_params = regions_provided.len();
 335     let regions = if expected_num_region_params == supplied_num_region_params {
 336         regions_provided
 337     } else {
 338         let anon_regions =
 339             rscope.anon_regions(span, expected_num_region_params);
 340
 341         if supplied_num_region_params != 0 || anon_regions.is_err() {
 342             report_lifetime_number_error(tcx, span,
 343                                          supplied_num_region_params,
 344                                          expected_num_region_params);
 345         }
 346
 347         match anon_regions {
 348             Ok(anon_regions) => anon_regions,
 349             Err(_) => (0..expected_num_region_params).map(|_| ty::ReStatic).collect()
 350         }
 351     };
 352     Substs::new_type(vec![], regions)
 353 }
 354
 355 /// Given the type/region arguments provided to some path (along with
 356 /// an implicit Self, if this is a trait reference) returns the complete
 357 /// set of substitutions. This may involve applying defaulted type parameters.
 358 ///
 359 /// Note that the type listing given here is *exactly* what the user provided.
 360 ///
 361 /// The `region_substs` should be the result of `create_region_substs`
 362 /// -- that is, a substitution with no types but the correct number of
 363 /// regions.
 364 fn create_substs_for_ast_path<'tcx>(
 365     this: &AstConv<'tcx>,
 366     span: Span,
 367     param_mode: PathParamMode,
 368     decl_generics: &ty::Generics<'tcx>,
 369     self_ty: Option<Ty<'tcx>>,
 370     types_provided: Vec<Ty<'tcx>>,
 371     region_substs: Substs<'tcx>)
 372     -> Substs<'tcx>
 373 {
 374     let tcx = this.tcx();
 375
 376     debug!("create_substs_for_ast_path(decl_generics={}, self_ty={}, \
 377            types_provided={}, region_substs={}",
 378            decl_generics.repr(tcx), self_ty.repr(tcx), types_provided.repr(tcx),
 379            region_substs.repr(tcx));
 380
 381     assert_eq!(region_substs.regions().len(TypeSpace), decl_generics.regions.len(TypeSpace));
 382     assert!(region_substs.types.is_empty());
 383
 384     // Convert the type parameters supplied by the user.
 385     let ty_param_defs = decl_generics.types.get_slice(TypeSpace);
 386     let formal_ty_param_count = ty_param_defs.len();
 387     let required_ty_param_count = ty_param_defs.iter()
 388                                                .take_while(|x| x.default.is_none())
 389                                                .count();
 390
 391     // Fill with `ty_infer` if no params were specified, as long as
 392     // they were optional (e.g. paths inside expressions).
 393     let mut type_substs = if param_mode == PathParamMode::Optional &&
 394                              types_provided.is_empty() {
 395         (0..formal_ty_param_count).map(|_| this.ty_infer(span)).collect()
 396     } else {
 397         types_provided
 398     };
 399
 400     let supplied_ty_param_count = type_substs.len();
 401     check_type_argument_count(this.tcx(), span, supplied_ty_param_count,
 402                               required_ty_param_count, formal_ty_param_count);
 403
 404     if supplied_ty_param_count < required_ty_param_count {
 405         while type_substs.len() < required_ty_param_count {
 406             type_substs.push(tcx.types.err);
 407         }
 408     } else if supplied_ty_param_count > formal_ty_param_count {
 409         type_substs.truncate(formal_ty_param_count);
 410     }
 411     assert!(type_substs.len() >= required_ty_param_count &&
 412             type_substs.len() <= formal_ty_param_count);
 413
 414     let mut substs = region_substs;
 415     substs.types.extend(TypeSpace, type_substs.into_iter());
 416
 417     match self_ty {
 418         None => {
 419             // If no self-type is provided, it's still possible that
 420             // one was declared, because this could be an object type.
 421         }
 422         Some(ty) => {
 423             // If a self-type is provided, one should have been
 424             // "declared" (in other words, this should be a
 425             // trait-ref).
 426             assert!(decl_generics.types.get_self().is_some());
 427             substs.types.push(SelfSpace, ty);
 428         }
 429     }
 430
 431     let actual_supplied_ty_param_count = substs.types.len(TypeSpace);
 432     for param in &ty_param_defs[actual_supplied_ty_param_count..] {
 433         if let Some(default) = param.default {
 434             // If we are converting an object type, then the
 435             // `Self` parameter is unknown. However, some of the
 436             // other type parameters may reference `Self` in their
 437             // defaults. This will lead to an ICE if we are not
 438             // careful!
 439             if self_ty.is_none() && ty::type_has_self(default) {
 440                 tcx.sess.span_err(
 441                     span,
 442                     &format!("the type parameter `{}` must be explicitly specified \
 443                               in an object type because its default value `{}` references \
 444                               the type `Self`",
 445                              param.name.user_string(tcx),
 446                              default.user_string(tcx)));
 447                 substs.types.push(TypeSpace, tcx.types.err);
 448             } else {
 449                 // This is a default type parameter.
 450                 let default = default.subst_spanned(tcx,
 451                                                     &substs,
 452                                                     Some(span));
 453                 substs.types.push(TypeSpace, default);
 454             }
 455         } else {
 456             tcx.sess.span_bug(span, "extra parameter without default");
 457         }
 458     }
 459
 460     substs
 461 }
 462
 463 struct ConvertedBinding<'tcx> {
 464     item_name: ast::Name,
 465     ty: Ty<'tcx>,
 466     span: Span,
 467 }
 468
 469 fn convert_angle_bracketed_parameters<'tcx>(this: &AstConv<'tcx>,
 470                                             rscope: &RegionScope,
 471                                             span: Span,
 472                                             decl_generics: &ty::Generics<'tcx>,
 473                                             data: &ast::AngleBracketedParameterData)
 474                                             -> (Substs<'tcx>,
 475                                                 Vec<Ty<'tcx>>,
 476                                                 Vec<ConvertedBinding<'tcx>>)
 477 {
 478     let regions: Vec<_> =
 479         data.lifetimes.iter()
 480                       .map(|l| ast_region_to_region(this.tcx(), l))
 481                       .collect();
 482
 483     let region_substs =
 484         create_region_substs(this, rscope, span, decl_generics, regions);
 485
 486     let types: Vec<_> =
 487         data.types.iter()
 488                   .enumerate()
 489                   .map(|(i,t)| ast_ty_arg_to_ty(this, rscope, decl_generics,
 490                                                 i, &region_substs, t))
 491                   .collect();
 492
 493     let assoc_bindings: Vec<_> =
 494         data.bindings.iter()
 495                      .map(|b| ConvertedBinding { item_name: b.ident.name,
 496                                                  ty: ast_ty_to_ty(this, rscope, &*b.ty),
 497                                                  span: b.span })
 498                      .collect();
 499
 500     (region_substs, types, assoc_bindings)
 501 }
 502
 503 /// Returns the appropriate lifetime to use for any output lifetimes
 504 /// (if one exists) and a vector of the (pattern, number of lifetimes)
 505 /// corresponding to each input type/pattern.
 506 fn find_implied_output_region(input_tys: &[Ty], input_pats: Vec<String>)
 507                               -> (Option<ty::Region>, Vec<(String, usize)>)
 508 {
 509     let mut lifetimes_for_params: Vec<(String, usize)> = Vec::new();
 510     let mut possible_implied_output_region = None;
 511
 512     for (input_type, input_pat) in input_tys.iter().zip(input_pats.into_iter()) {
 513         let mut accumulator = Vec::new();
 514         ty::accumulate_lifetimes_in_type(&mut accumulator, *input_type);
 515
 516         if accumulator.len() == 1 {
 517             // there's a chance that the unique lifetime of this
 518             // iteration will be the appropriate lifetime for output
 519             // parameters, so lets store it.
 520             possible_implied_output_region = Some(accumulator[0])
 521         }
 522
 523         lifetimes_for_params.push((input_pat, accumulator.len()));
 524     }
 525
 526     let implied_output_region =
 527         if lifetimes_for_params.iter().map(|&(_, n)| n).sum::<usize>() == 1 {
 528             assert!(possible_implied_output_region.is_some());
 529             possible_implied_output_region
 530         } else {
 531             None
 532         };
 533     (implied_output_region, lifetimes_for_params)
 534 }
 535
 536 fn convert_ty_with_lifetime_elision<'tcx>(this: &AstConv<'tcx>,
 537                                           implied_output_region: Option<ty::Region>,
 538                                           param_lifetimes: Vec<(String, usize)>,
 539                                           ty: &ast::Ty)
 540                                           -> Ty<'tcx>
 541 {
 542     match implied_output_region {
 543         Some(implied_output_region) => {
 544             let rb = ElidableRscope::new(implied_output_region);
 545             ast_ty_to_ty(this, &rb, ty)
 546         }
 547         None => {
 548             // All regions must be explicitly specified in the output
 549             // if the lifetime elision rules do not apply. This saves
 550             // the user from potentially-confusing errors.
 551             let rb = UnelidableRscope::new(param_lifetimes);
 552             ast_ty_to_ty(this, &rb, ty)
 553         }
 554     }
 555 }
 556
 557 fn convert_parenthesized_parameters<'tcx>(this: &AstConv<'tcx>,
 558                                           rscope: &RegionScope,
 559                                           span: Span,
 560                                           decl_generics: &ty::Generics<'tcx>,
 561                                           data: &ast::ParenthesizedParameterData)
 562                                           -> (Substs<'tcx>,
 563                                               Vec<Ty<'tcx>>,
 564                                               Vec<ConvertedBinding<'tcx>>)
 565 {
 566     let region_substs =
 567         create_region_substs(this, rscope, span, decl_generics, Vec::new());
 568
 569     let binding_rscope = BindingRscope::new();
 570     let inputs =
 571         data.inputs.iter()
 572                    .map(|a_t| ast_ty_arg_to_ty(this, &binding_rscope, decl_generics,
 573                                                0, &region_substs, a_t))
 574                    .collect::<Vec<Ty<'tcx>>>();
 575
 576     let input_params: Vec<_> = repeat(String::new()).take(inputs.len()).collect();
 577     let (implied_output_region,
 578          params_lifetimes) = find_implied_output_region(&*inputs, input_params);
 579
 580     let input_ty = ty::mk_tup(this.tcx(), inputs);
 581
 582     let (output, output_span) = match data.output {
 583         Some(ref output_ty) => {
 584             (convert_ty_with_lifetime_elision(this,
 585                                               implied_output_region,
 586                                               params_lifetimes,
 587                                               &**output_ty),
 588              output_ty.span)
 589         }
 590         None => {
 591             (ty::mk_nil(this.tcx()), data.span)
 592         }
 593     };
 594
 595     let output_binding = ConvertedBinding {
 596         item_name: token::intern(FN_OUTPUT_NAME),
 597         ty: output,
 598         span: output_span
 599     };
 600
 601     (region_substs, vec![input_ty], vec![output_binding])
 602 }
 603
 604 pub fn instantiate_poly_trait_ref<'tcx>(
 605     this: &AstConv<'tcx>,
 606     rscope: &RegionScope,
 607     ast_trait_ref: &ast::PolyTraitRef,
 608     self_ty: Option<Ty<'tcx>>,
 609     poly_projections: &mut Vec<ty::PolyProjectionPredicate<'tcx>>)
 610     -> ty::PolyTraitRef<'tcx>
 611 {
 612     let trait_ref = &ast_trait_ref.trait_ref;
 613     let trait_def_id = trait_def_id(this, trait_ref);
 614     ast_path_to_poly_trait_ref(this,
 615                                rscope,
 616                                trait_ref.path.span,
 617                                PathParamMode::Explicit,
 618                                trait_def_id,
 619                                self_ty,
 620                                trait_ref.path.segments.last().unwrap(),
 621                                poly_projections)
 622 }
 623
 624 /// Instantiates the path for the given trait reference, assuming that it's
 625 /// bound to a valid trait type. Returns the def_id for the defining trait.
 626 /// Fails if the type is a type other than a trait type.
 627 ///
 628 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T=X>`
 629 /// are disallowed. Otherwise, they are pushed onto the vector given.
 630 pub fn instantiate_mono_trait_ref<'tcx>(
 631     this: &AstConv<'tcx>,
 632     rscope: &RegionScope,
 633     trait_ref: &ast::TraitRef,
 634     self_ty: Option<Ty<'tcx>>)
 635     -> Rc<ty::TraitRef<'tcx>>
 636 {
 637     let trait_def_id = trait_def_id(this, trait_ref);
 638     ast_path_to_mono_trait_ref(this,
 639                                rscope,
 640                                trait_ref.path.span,
 641                                PathParamMode::Explicit,
 642                                trait_def_id,
 643                                self_ty,
 644                                trait_ref.path.segments.last().unwrap())
 645 }
 646
 647 fn trait_def_id<'tcx>(this: &AstConv<'tcx>, trait_ref: &ast::TraitRef) -> ast::DefId {
 648     let path = &trait_ref.path;
 649     match ::lookup_full_def(this.tcx(), path.span, trait_ref.ref_id) {
 650         def::DefTrait(trait_def_id) => trait_def_id,
 651         _ => {
 652             span_fatal!(this.tcx().sess, path.span, E0245, "`{}` is not a trait",
 653                         path.user_string(this.tcx()));
 654         }
 655     }
 656 }
 657
 658 fn object_path_to_poly_trait_ref<'a,'tcx>(
 659     this: &AstConv<'tcx>,
 660     rscope: &RegionScope,
 661     span: Span,
 662     param_mode: PathParamMode,
 663     trait_def_id: ast::DefId,
 664     trait_segment: &ast::PathSegment,
 665     mut projections: &mut Vec<ty::PolyProjectionPredicate<'tcx>>)
 666     -> ty::PolyTraitRef<'tcx>
 667 {
 668     ast_path_to_poly_trait_ref(this,
 669                                rscope,
 670                                span,
 671                                param_mode,
 672                                trait_def_id,
 673                                None,
 674                                trait_segment,
 675                                projections)
 676 }
 677
 678 fn ast_path_to_poly_trait_ref<'a,'tcx>(
 679     this: &AstConv<'tcx>,
 680     rscope: &RegionScope,
 681     span: Span,
 682     param_mode: PathParamMode,
 683     trait_def_id: ast::DefId,
 684     self_ty: Option<Ty<'tcx>>,
 685     trait_segment: &ast::PathSegment,
 686     poly_projections: &mut Vec<ty::PolyProjectionPredicate<'tcx>>)
 687     -> ty::PolyTraitRef<'tcx>
 688 {
 689     // The trait reference introduces a binding level here, so
 690     // we need to shift the `rscope`. It'd be nice if we could
 691     // do away with this rscope stuff and work this knowledge
 692     // into resolve_lifetimes, as we do with non-omitted
 693     // lifetimes. Oh well, not there yet.
 694     let shifted_rscope = &ShiftedRscope::new(rscope);
 695
 696     let (substs, assoc_bindings) =
 697         create_substs_for_ast_trait_ref(this,
 698                                         shifted_rscope,
 699                                         span,
 700                                         param_mode,
 701                                         trait_def_id,
 702                                         self_ty,
 703                                         trait_segment);
 704     let poly_trait_ref = ty::Binder(Rc::new(ty::TraitRef::new(trait_def_id, substs)));
 705
 706     {
 707         let converted_bindings =
 708             assoc_bindings
 709             .iter()
 710             .filter_map(|binding| {
 711                 // specify type to assert that error was already reported in Err case:
 712                 let predicate: Result<_, ErrorReported> =
 713                     ast_type_binding_to_poly_projection_predicate(this,
 714                                                                   poly_trait_ref.clone(),
 715                                                                   self_ty,
 716                                                                   binding);
 717                 predicate.ok() // ok to ignore Err() because ErrorReported (see above)
 718             });
 719         poly_projections.extend(converted_bindings);
 720     }
 721
 722     poly_trait_ref
 723 }
 724
 725 fn ast_path_to_mono_trait_ref<'a,'tcx>(this: &AstConv<'tcx>,
 726                                        rscope: &RegionScope,
 727                                        span: Span,
 728                                        param_mode: PathParamMode,
 729                                        trait_def_id: ast::DefId,
 730                                        self_ty: Option<Ty<'tcx>>,
 731                                        trait_segment: &ast::PathSegment)
 732                                        -> Rc<ty::TraitRef<'tcx>>
 733 {
 734     let (substs, assoc_bindings) =
 735         create_substs_for_ast_trait_ref(this,
 736                                         rscope,
 737                                         span,
 738                                         param_mode,
 739                                         trait_def_id,
 740                                         self_ty,
 741                                         trait_segment);
 742     prohibit_projections(this.tcx(), &assoc_bindings);
 743     Rc::new(ty::TraitRef::new(trait_def_id, substs))
 744 }
 745
 746 fn create_substs_for_ast_trait_ref<'a,'tcx>(this: &AstConv<'tcx>,
 747                                             rscope: &RegionScope,
 748                                             span: Span,
 749                                             param_mode: PathParamMode,
 750                                             trait_def_id: ast::DefId,
 751                                             self_ty: Option<Ty<'tcx>>,
 752                                             trait_segment: &ast::PathSegment)
 753                                             -> (&'tcx Substs<'tcx>, Vec<ConvertedBinding<'tcx>>)
 754 {
 755     debug!("create_substs_for_ast_trait_ref(trait_segment={:?})",
 756            trait_segment);
 757
 758     let trait_def = match this.get_trait_def(span, trait_def_id) {
 759         Ok(trait_def) => trait_def,
 760         Err(ErrorReported) => {
 761             // No convenient way to recover from a cycle here. Just bail. Sorry!
 762             this.tcx().sess.abort_if_errors();
 763             this.tcx().sess.bug("ErrorReported returned, but no errors reports?")
 764         }
 765     };
 766
 767     let (regions, types, assoc_bindings) = match trait_segment.parameters {
 768         ast::AngleBracketedParameters(ref data) => {
 769             // For now, require that parenthetical notation be used
 770             // only with `Fn()` etc.
 771             if !this.tcx().sess.features.borrow().unboxed_closures && trait_def.paren_sugar {
 772                 span_err!(this.tcx().sess, span, E0215,
 773                                          "angle-bracket notation is not stable when \
 774                                          used with the `Fn` family of traits, use parentheses");
 775                 fileline_help!(this.tcx().sess, span,
 776                            "add `#![feature(unboxed_closures)]` to \
 777                             the crate attributes to enable");
 778             }
 779
 780             convert_angle_bracketed_parameters(this, rscope, span, &trait_def.generics, data)
 781         }
 782         ast::ParenthesizedParameters(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, E0216,
 787                                          "parenthetical notation is only stable when \
 788                                          used with the `Fn` family of traits");
 789                 fileline_help!(this.tcx().sess, span,
 790                            "add `#![feature(unboxed_closures)]` to \
 791                             the crate attributes to enable");
 792             }
 793
 794             convert_parenthesized_parameters(this, rscope, span, &trait_def.generics, data)
 795         }
 796     };
 797
 798     let substs = create_substs_for_ast_path(this,
 799                                             span,
 800                                             param_mode,
 801                                             &trait_def.generics,
 802                                             self_ty,
 803                                             types,
 804                                             regions);
 805
 806     (this.tcx().mk_substs(substs), assoc_bindings)
 807 }
 808
 809 fn ast_type_binding_to_poly_projection_predicate<'tcx>(
 810     this: &AstConv<'tcx>,
 811     mut trait_ref: ty::PolyTraitRef<'tcx>,
 812     self_ty: Option<Ty<'tcx>>,
 813     binding: &ConvertedBinding<'tcx>)
 814     -> Result<ty::PolyProjectionPredicate<'tcx>, ErrorReported>
 815 {
 816     let tcx = this.tcx();
 817
 818     // Given something like `U : SomeTrait<T=X>`, we want to produce a
 819     // predicate like `<U as SomeTrait>::T = X`. This is somewhat
 820     // subtle in the event that `T` is defined in a supertrait of
 821     // `SomeTrait`, because in that case we need to upcast.
 822     //
 823     // That is, consider this case:
 824     //
 825     // ```
 826     // trait SubTrait : SuperTrait<int> { }
 827     // trait SuperTrait<A> { type T; }
 828     //
 829     // ... B : SubTrait<T=foo> ...
 830     // ```
 831     //
 832     // We want to produce `<B as SuperTrait<int>>::T == foo`.
 833
 834     // Simple case: X is defined in the current trait.
 835     if this.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
 836         return Ok(ty::Binder(ty::ProjectionPredicate {      // <-------------------+
 837             projection_ty: ty::ProjectionTy {               //                     |
 838                 trait_ref: trait_ref.skip_binder().clone(), // Binder moved here --+
 839                 item_name: binding.item_name,
 840             },
 841             ty: binding.ty,
 842         }));
 843     }
 844
 845     // Otherwise, we have to walk through the supertraits to find
 846     // those that do.  This is complicated by the fact that, for an
 847     // object type, the `Self` type is not present in the
 848     // substitutions (after all, it's being constructed right now),
 849     // but the `supertraits` iterator really wants one. To handle
 850     // this, we currently insert a dummy type and then remove it
 851     // later. Yuck.
 852
 853     let dummy_self_ty = ty::mk_infer(tcx, ty::FreshTy(0));
 854     if self_ty.is_none() { // if converting for an object type
 855         let mut dummy_substs = trait_ref.skip_binder().substs.clone(); // binder moved here -+
 856         assert!(dummy_substs.self_ty().is_none());                     //                    |
 857         dummy_substs.types.push(SelfSpace, dummy_self_ty);             //                    |
 858         trait_ref = ty::Binder(Rc::new(ty::TraitRef::new(trait_ref.def_id(), // <------------+
 859                                                          tcx.mk_substs(dummy_substs))));
 860     }
 861
 862     try!(this.ensure_super_predicates(binding.span, trait_ref.def_id()));
 863
 864     let mut candidates: Vec<ty::PolyTraitRef> =
 865         traits::supertraits(tcx, trait_ref.clone())
 866         .filter(|r| this.trait_defines_associated_type_named(r.def_id(), binding.item_name))
 867         .collect();
 868
 869     // If converting for an object type, then remove the dummy-ty from `Self` now.
 870     // Yuckety yuck.
 871     if self_ty.is_none() {
 872         for candidate in &mut candidates {
 873             let mut dummy_substs = candidate.0.substs.clone();
 874             assert!(dummy_substs.self_ty() == Some(dummy_self_ty));
 875             dummy_substs.types.pop(SelfSpace);
 876             *candidate = ty::Binder(Rc::new(ty::TraitRef::new(candidate.def_id(),
 877                                                               tcx.mk_substs(dummy_substs))));
 878         }
 879     }
 880
 881     let candidate = try!(one_bound_for_assoc_type(tcx,
 882                                                   candidates,
 883                                                   &trait_ref.user_string(tcx),
 884                                                   &token::get_name(binding.item_name),
 885                                                   binding.span));
 886
 887     Ok(ty::Binder(ty::ProjectionPredicate {             // <-------------------------+
 888         projection_ty: ty::ProjectionTy {               //                           |
 889             trait_ref: candidate.skip_binder().clone(), // binder is moved up here --+
 890             item_name: binding.item_name,
 891         },
 892         ty: binding.ty,
 893     }))
 894 }
 895
 896 fn ast_path_to_ty<'tcx>(
 897     this: &AstConv<'tcx>,
 898     rscope: &RegionScope,
 899     span: Span,
 900     param_mode: PathParamMode,
 901     did: ast::DefId,
 902     item_segment: &ast::PathSegment)
 903     -> Ty<'tcx>
 904 {
 905     let tcx = this.tcx();
 906     let (generics, decl_ty) = match this.get_item_type_scheme(span, did) {
 907         Ok(ty::TypeScheme { generics,  ty: decl_ty }) => {
 908             (generics, decl_ty)
 909         }
 910         Err(ErrorReported) => {
 911             return tcx.types.err;
 912         }
 913     };
 914
 915     let substs = ast_path_substs_for_ty(this,
 916                                         rscope,
 917                                         span,
 918                                         param_mode,
 919                                         &generics,
 920                                         item_segment);
 921
 922     // FIXME(#12938): This is a hack until we have full support for DST.
 923     if Some(did) == this.tcx().lang_items.owned_box() {
 924         assert_eq!(substs.types.len(TypeSpace), 1);
 925         return ty::mk_uniq(this.tcx(), *substs.types.get(TypeSpace, 0));
 926     }
 927
 928     decl_ty.subst(this.tcx(), &substs)
 929 }
 930
 931 type TraitAndProjections<'tcx> = (ty::PolyTraitRef<'tcx>, Vec<ty::PolyProjectionPredicate<'tcx>>);
 932
 933 fn ast_ty_to_trait_ref<'tcx>(this: &AstConv<'tcx>,
 934                              rscope: &RegionScope,
 935                              ty: &ast::Ty,
 936                              bounds: &[ast::TyParamBound])
 937                              -> Result<TraitAndProjections<'tcx>, ErrorReported>
 938 {
 939     /*!
 940      * In a type like `Foo + Send`, we want to wait to collect the
 941      * full set of bounds before we make the object type, because we
 942      * need them to infer a region bound.  (For example, if we tried
 943      * made a type from just `Foo`, then it wouldn't be enough to
 944      * infer a 'static bound, and hence the user would get an error.)
 945      * So this function is used when we're dealing with a sum type to
 946      * convert the LHS. It only accepts a type that refers to a trait
 947      * name, and reports an error otherwise.
 948      */
 949
 950     match ty.node {
 951         ast::TyPath(None, ref path) => {
 952             let def = match this.tcx().def_map.borrow().get(&ty.id) {
 953                 Some(&def::PathResolution { base_def, depth: 0, .. }) => Some(base_def),
 954                 _ => None
 955             };
 956             match def {
 957                 Some(def::DefTrait(trait_def_id)) => {
 958                     let mut projection_bounds = Vec::new();
 959                     let trait_ref = object_path_to_poly_trait_ref(this,
 960                                                                   rscope,
 961                                                                   path.span,
 962                                                                   PathParamMode::Explicit,
 963                                                                   trait_def_id,
 964                                                                   path.segments.last().unwrap(),
 965                                                                   &mut projection_bounds);
 966                     Ok((trait_ref, projection_bounds))
 967                 }
 968                 _ => {
 969                     span_err!(this.tcx().sess, ty.span, E0172, "expected a reference to a trait");
 970                     Err(ErrorReported)
 971                 }
 972             }
 973         }
 974         _ => {
 975             span_err!(this.tcx().sess, ty.span, E0178,
 976                       "expected a path on the left-hand side of `+`, not `{}`",
 977                       pprust::ty_to_string(ty));
 978             let hi = bounds.iter().map(|x| match *x {
 979                 ast::TraitTyParamBound(ref tr, _) => tr.span.hi,
 980                 ast::RegionTyParamBound(ref r) => r.span.hi,
 981             }).max_by(|x| x.to_usize());
 982             let full_span = hi.map(|hi| Span {
 983                 lo: ty.span.lo,
 984                 hi: hi,
 985                 expn_id: ty.span.expn_id,
 986             });
 987             match (&ty.node, full_span) {
 988                 (&ast::TyRptr(None, ref mut_ty), Some(full_span)) => {
 989                     this.tcx().sess
 990                         .span_suggestion(full_span, "try adding parentheses (per RFC 438):",
 991                                          format!("&{}({} +{})",
 992                                                  ppaux::mutability_to_string(mut_ty.mutbl),
 993                                                  pprust::ty_to_string(&*mut_ty.ty),
 994                                                  pprust::bounds_to_string(bounds)));
 995                 }
 996                 (&ast::TyRptr(Some(ref lt), ref mut_ty), Some(full_span)) => {
 997                     this.tcx().sess
 998                         .span_suggestion(full_span, "try adding parentheses (per RFC 438):",
 999                                          format!("&{} {}({} +{})",
1000                                                  pprust::lifetime_to_string(lt),
1001                                                  ppaux::mutability_to_string(mut_ty.mutbl),
1002                                                  pprust::ty_to_string(&*mut_ty.ty),
1003                                                  pprust::bounds_to_string(bounds)));
1004                 }
1005
1006                 _ => {
1007                     fileline_help!(this.tcx().sess, ty.span,
1008                                "perhaps you forgot parentheses? (per RFC 438)");
1009                 }
1010             }
1011             Err(ErrorReported)
1012         }
1013     }
1014 }
1015
1016 fn trait_ref_to_object_type<'tcx>(this: &AstConv<'tcx>,
1017                                   rscope: &RegionScope,
1018                                   span: Span,
1019                                   trait_ref: ty::PolyTraitRef<'tcx>,
1020                                   projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>,
1021                                   bounds: &[ast::TyParamBound])
1022                                   -> Ty<'tcx>
1023 {
1024     let existential_bounds = conv_existential_bounds(this,
1025                                                      rscope,
1026                                                      span,
1027                                                      trait_ref.clone(),
1028                                                      projection_bounds,
1029                                                      bounds);
1030
1031     let result = make_object_type(this, span, trait_ref, existential_bounds);
1032     debug!("trait_ref_to_object_type: result={}",
1033            result.repr(this.tcx()));
1034
1035     result
1036 }
1037
1038 fn make_object_type<'tcx>(this: &AstConv<'tcx>,
1039                           span: Span,
1040                           principal: ty::PolyTraitRef<'tcx>,
1041                           bounds: ty::ExistentialBounds<'tcx>)
1042                           -> Ty<'tcx> {
1043     let tcx = this.tcx();
1044     let object = ty::TyTrait {
1045         principal: principal,
1046         bounds: bounds
1047     };
1048     let object_trait_ref =
1049         object.principal_trait_ref_with_self_ty(tcx, tcx.types.err);
1050
1051     // ensure the super predicates and stop if we encountered an error
1052     if this.ensure_super_predicates(span, object.principal_def_id()).is_err() {
1053         return tcx.types.err;
1054     }
1055
1056     let mut associated_types: FnvHashSet<(ast::DefId, ast::Name)> =
1057         traits::supertraits(tcx, object_trait_ref)
1058         .flat_map(|tr| {
1059             let trait_def = ty::lookup_trait_def(tcx, tr.def_id());
1060             trait_def.associated_type_names
1061                 .clone()
1062                 .into_iter()
1063                 .map(move |associated_type_name| (tr.def_id(), associated_type_name))
1064         })
1065         .collect();
1066
1067     for projection_bound in &object.bounds.projection_bounds {
1068         let pair = (projection_bound.0.projection_ty.trait_ref.def_id,
1069                     projection_bound.0.projection_ty.item_name);
1070         associated_types.remove(&pair);
1071     }
1072
1073     for (trait_def_id, name) in associated_types {
1074         span_err!(tcx.sess, span, E0191,
1075             "the value of the associated type `{}` (from the trait `{}`) must be specified",
1076                     name.user_string(tcx),
1077                     ty::item_path_str(tcx, trait_def_id));
1078     }
1079
1080     ty::mk_trait(tcx, object.principal, object.bounds)
1081 }
1082
1083 fn report_ambiguous_associated_type(tcx: &ty::ctxt,
1084                                     span: Span,
1085                                     type_str: &str,
1086                                     trait_str: &str,
1087                                     name: &str) {
1088     span_err!(tcx.sess, span, E0223,
1089               "ambiguous associated type; specify the type using the syntax \
1090                `<{} as {}>::{}`",
1091               type_str, trait_str, name);
1092 }
1093
1094 // Search for a bound on a type parameter which includes the associated item
1095 // given by assoc_name. ty_param_node_id is the node id for the type parameter
1096 // (which might be `Self`, but only if it is the `Self` of a trait, not an
1097 // impl). This function will fail if there are no suitable bounds or there is
1098 // any ambiguity.
1099 fn find_bound_for_assoc_item<'tcx>(this: &AstConv<'tcx>,
1100                                    ty_param_node_id: ast::NodeId,
1101                                    assoc_name: ast::Name,
1102                                    span: Span)
1103                                    -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1104 {
1105     let tcx = this.tcx();
1106
1107     let bounds = match this.get_type_parameter_bounds(span, ty_param_node_id) {
1108         Ok(v) => v,
1109         Err(ErrorReported) => {
1110             return Err(ErrorReported);
1111         }
1112     };
1113
1114     // Ensure the super predicates and stop if we encountered an error.
1115     if bounds.iter().any(|b| this.ensure_super_predicates(span, b.def_id()).is_err()) {
1116         return Err(ErrorReported);
1117     }
1118
1119     // Check that there is exactly one way to find an associated type with the
1120     // correct name.
1121     let suitable_bounds: Vec<_> =
1122         traits::transitive_bounds(tcx, &bounds)
1123         .filter(|b| this.trait_defines_associated_type_named(b.def_id(), assoc_name))
1124         .collect();
1125
1126     let ty_param_name = tcx.type_parameter_def(ty_param_node_id).name;
1127     one_bound_for_assoc_type(tcx,
1128                              suitable_bounds,
1129                              &token::get_name(ty_param_name),
1130                              &token::get_name(assoc_name),
1131                              span)
1132 }
1133
1134
1135 // Checks that bounds contains exactly one element and reports appropriate
1136 // errors otherwise.
1137 fn one_bound_for_assoc_type<'tcx>(tcx: &ty::ctxt<'tcx>,
1138                                   bounds: Vec<ty::PolyTraitRef<'tcx>>,
1139                                   ty_param_name: &str,
1140                                   assoc_name: &str,
1141                                   span: Span)
1142     -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1143 {
1144     if bounds.is_empty() {
1145         span_err!(tcx.sess, span, E0220,
1146                   "associated type `{}` not found for `{}`",
1147                   assoc_name,
1148                   ty_param_name);
1149         return Err(ErrorReported);
1150     }
1151
1152     if bounds.len() > 1 {
1153         span_err!(tcx.sess, span, E0221,
1154                   "ambiguous associated type `{}` in bounds of `{}`",
1155                   assoc_name,
1156                   ty_param_name);
1157
1158         for bound in &bounds {
1159             span_note!(tcx.sess, span,
1160                        "associated type `{}` could derive from `{}`",
1161                        ty_param_name,
1162                        bound.user_string(tcx));
1163         }
1164     }
1165
1166     Ok(bounds[0].clone())
1167 }
1168
1169 // Create a type from a a path to an associated type.
1170 // For a path A::B::C::D, ty and ty_path_def are the type and def for A::B::C
1171 // and item_segment is the path segment for D. We return a type and a def for
1172 // the whole path.
1173 // Will fail except for T::A and Self::A; i.e., if ty/ty_path_def are not a type
1174 // parameter or Self.
1175 fn associated_path_def_to_ty<'tcx>(this: &AstConv<'tcx>,
1176                                    span: Span,
1177                                    ty: Ty<'tcx>,
1178                                    ty_path_def: def::Def,
1179                                    item_segment: &ast::PathSegment)
1180                                    -> (Ty<'tcx>, def::Def)
1181 {
1182     let tcx = this.tcx();
1183     let assoc_name = item_segment.identifier.name;
1184
1185     debug!("associated_path_def_to_ty: {}::{}", ty.repr(tcx), token::get_name(assoc_name));
1186
1187     check_path_args(tcx, slice::ref_slice(item_segment), NO_TPS | NO_REGIONS);
1188
1189     // Find the type of the associated item, and the trait where the associated
1190     // item is declared.
1191     let bound = match (&ty.sty, ty_path_def) {
1192         (_, def::DefSelfTy(Some(trait_did), Some((impl_id, _)))) => {
1193             // `Self` in an impl of a trait - we have a concrete self type and a
1194             // trait reference.
1195             match tcx.map.expect_item(impl_id).node {
1196                 ast::ItemImpl(_, _, _, Some(ref trait_ref), _, _) => {
1197                     if this.ensure_super_predicates(span, trait_did).is_err() {
1198                         return (tcx.types.err, ty_path_def);
1199                     }
1200
1201                     let trait_segment = &trait_ref.path.segments.last().unwrap();
1202                     let trait_ref = ast_path_to_mono_trait_ref(this,
1203                                                                &ExplicitRscope,
1204                                                                span,
1205                                                                PathParamMode::Explicit,
1206                                                                trait_did,
1207                                                                Some(ty),
1208                                                                trait_segment);
1209
1210                     let candidates: Vec<ty::PolyTraitRef> =
1211                         traits::supertraits(tcx, ty::Binder(trait_ref.clone()))
1212                         .filter(|r| this.trait_defines_associated_type_named(r.def_id(),
1213                                                                              assoc_name))
1214                         .collect();
1215
1216                     match one_bound_for_assoc_type(tcx,
1217                                                    candidates,
1218                                                    "Self",
1219                                                    &token::get_name(assoc_name),
1220                                                    span) {
1221                         Ok(bound) => bound,
1222                         Err(ErrorReported) => return (tcx.types.err, ty_path_def),
1223                     }
1224                 }
1225                 _ => unreachable!()
1226             }
1227         }
1228         (&ty::ty_param(_), def::DefTyParam(..)) |
1229         (&ty::ty_param(_), def::DefSelfTy(Some(_), None)) => {
1230             // A type parameter or Self, we need to find the associated item from
1231             // a bound.
1232             let ty_param_node_id = ty_path_def.local_node_id();
1233             match find_bound_for_assoc_item(this, ty_param_node_id, assoc_name, span) {
1234                 Ok(bound) => bound,
1235                 Err(ErrorReported) => return (tcx.types.err, ty_path_def),
1236             }
1237         }
1238         _ => {
1239             report_ambiguous_associated_type(tcx,
1240                                              span,
1241                                              &ty.user_string(tcx),
1242                                              "Trait",
1243                                              &token::get_name(assoc_name));
1244             return (tcx.types.err, ty_path_def);
1245         }
1246     };
1247
1248     let trait_did = bound.0.def_id;
1249     let ty = this.projected_ty_from_poly_trait_ref(span, bound, assoc_name);
1250
1251     let item_did = if trait_did.krate == ast::LOCAL_CRATE {
1252         // `ty::trait_items` used below requires information generated
1253         // by type collection, which may be in progress at this point.
1254         match tcx.map.expect_item(trait_did.node).node {
1255             ast::ItemTrait(_, _, _, ref trait_items) => {
1256                 let item = trait_items.iter()
1257                                       .find(|i| i.ident.name == assoc_name)
1258                                       .expect("missing associated type");
1259                 ast_util::local_def(item.id)
1260             }
1261             _ => unreachable!()
1262         }
1263     } else {
1264         let trait_items = ty::trait_items(tcx, trait_did);
1265         let item = trait_items.iter().find(|i| i.name() == assoc_name);
1266         item.expect("missing associated type").def_id()
1267     };
1268
1269     (ty, def::DefAssociatedTy(trait_did, item_did))
1270 }
1271
1272 fn qpath_to_ty<'tcx>(this: &AstConv<'tcx>,
1273                      rscope: &RegionScope,
1274                      span: Span,
1275                      param_mode: PathParamMode,
1276                      opt_self_ty: Option<Ty<'tcx>>,
1277                      trait_def_id: ast::DefId,
1278                      trait_segment: &ast::PathSegment,
1279                      item_segment: &ast::PathSegment)
1280                      -> Ty<'tcx>
1281 {
1282     let tcx = this.tcx();
1283
1284     check_path_args(tcx, slice::ref_slice(item_segment), NO_TPS | NO_REGIONS);
1285
1286     let self_ty = if let Some(ty) = opt_self_ty {
1287         ty
1288     } else {
1289         let path_str = ty::item_path_str(tcx, trait_def_id);
1290         report_ambiguous_associated_type(tcx,
1291                                          span,
1292                                          "Type",
1293                                          &path_str,
1294                                          &token::get_ident(item_segment.identifier));
1295         return tcx.types.err;
1296     };
1297
1298     debug!("qpath_to_ty: self_type={}", self_ty.repr(tcx));
1299
1300     let trait_ref = ast_path_to_mono_trait_ref(this,
1301                                                rscope,
1302                                                span,
1303                                                param_mode,
1304                                                trait_def_id,
1305                                                Some(self_ty),
1306                                                trait_segment);
1307
1308     debug!("qpath_to_ty: trait_ref={}", trait_ref.repr(tcx));
1309
1310     this.projected_ty(span, trait_ref, item_segment.identifier.name)
1311 }
1312
1313 /// Convert a type supplied as value for a type argument from AST into our
1314 /// our internal representation. This is the same as `ast_ty_to_ty` but that
1315 /// it applies the object lifetime default.
1316 ///
1317 /// # Parameters
1318 ///
1319 /// * `this`, `rscope`: the surrounding context
1320 /// * `decl_generics`: the generics of the struct/enum/trait declaration being
1321 ///   referenced
1322 /// * `index`: the index of the type parameter being instantiated from the list
1323 ///   (we assume it is in the `TypeSpace`)
1324 /// * `region_substs`: a partial substitution consisting of
1325 ///   only the region type parameters being supplied to this type.
1326 /// * `ast_ty`: the ast representation of the type being supplied
1327 pub fn ast_ty_arg_to_ty<'tcx>(this: &AstConv<'tcx>,
1328                               rscope: &RegionScope,
1329                               decl_generics: &ty::Generics<'tcx>,
1330                               index: usize,
1331                               region_substs: &Substs<'tcx>,
1332                               ast_ty: &ast::Ty)
1333                               -> Ty<'tcx>
1334 {
1335     let tcx = this.tcx();
1336
1337     if let Some(def) = decl_generics.types.opt_get(TypeSpace, index) {
1338         let object_lifetime_default = def.object_lifetime_default.subst(tcx, region_substs);
1339         let rscope1 = &ObjectLifetimeDefaultRscope::new(rscope, object_lifetime_default);
1340         ast_ty_to_ty(this, rscope1, ast_ty)
1341     } else {
1342         ast_ty_to_ty(this, rscope, ast_ty)
1343     }
1344 }
1345
1346 // Check the base def in a PathResolution and convert it to a Ty. If there are
1347 // associated types in the PathResolution, these will need to be seperately
1348 // resolved.
1349 fn base_def_to_ty<'tcx>(this: &AstConv<'tcx>,
1350                         rscope: &RegionScope,
1351                         span: Span,
1352                         param_mode: PathParamMode,
1353                         def: &def::Def,
1354                         opt_self_ty: Option<Ty<'tcx>>,
1355                         base_segments: &[ast::PathSegment])
1356                         -> Ty<'tcx> {
1357     let tcx = this.tcx();
1358
1359     match *def {
1360         def::DefTrait(trait_def_id) => {
1361             // N.B. this case overlaps somewhat with
1362             // TyObjectSum, see that fn for details
1363             let mut projection_bounds = Vec::new();
1364
1365             let trait_ref = object_path_to_poly_trait_ref(this,
1366                                                           rscope,
1367                                                           span,
1368                                                           param_mode,
1369                                                           trait_def_id,
1370                                                           base_segments.last().unwrap(),
1371                                                           &mut projection_bounds);
1372
1373             check_path_args(tcx, base_segments.init(), NO_TPS | NO_REGIONS);
1374             trait_ref_to_object_type(this,
1375                                      rscope,
1376                                      span,
1377                                      trait_ref,
1378                                      projection_bounds,
1379                                      &[])
1380         }
1381         def::DefTy(did, _) | def::DefStruct(did) => {
1382             check_path_args(tcx, base_segments.init(), NO_TPS | NO_REGIONS);
1383             ast_path_to_ty(this,
1384                            rscope,
1385                            span,
1386                            param_mode,
1387                            did,
1388                            base_segments.last().unwrap())
1389         }
1390         def::DefTyParam(space, index, _, name) => {
1391             check_path_args(tcx, base_segments, NO_TPS | NO_REGIONS);
1392             ty::mk_param(tcx, space, index, name)
1393         }
1394         def::DefSelfTy(_, Some((_, self_ty_id))) => {
1395             // Self in impl (we know the concrete type).
1396             check_path_args(tcx, base_segments, NO_TPS | NO_REGIONS);
1397             if let Some(&ty) = tcx.ast_ty_to_ty_cache.borrow().get(&self_ty_id) {
1398                 ty
1399             } else {
1400                 tcx.sess.span_bug(span, "self type has not been fully resolved")
1401             }
1402         }
1403         def::DefSelfTy(Some(_), None) => {
1404             // Self in trait.
1405             check_path_args(tcx, base_segments, NO_TPS | NO_REGIONS);
1406             ty::mk_self_type(tcx)
1407         }
1408         def::DefAssociatedTy(trait_did, _) => {
1409             check_path_args(tcx, &base_segments[..base_segments.len()-2], NO_TPS | NO_REGIONS);
1410             qpath_to_ty(this,
1411                         rscope,
1412                         span,
1413                         param_mode,
1414                         opt_self_ty,
1415                         trait_did,
1416                         &base_segments[base_segments.len()-2],
1417                         base_segments.last().unwrap())
1418         }
1419         def::DefMod(id) => {
1420             // Used as sentinel by callers to indicate the `<T>::A::B::C` form.
1421             // FIXME(#22519) This part of the resolution logic should be
1422             // avoided entirely for that form, once we stop needed a Def
1423             // for `associated_path_def_to_ty`.
1424             // Fixing this will also let use resolve <Self>::Foo the same way we
1425             // resolve Self::Foo, at the moment we can't resolve the former because
1426             // we don't have the trait information around, which is just sad.
1427
1428             if !base_segments.is_empty() {
1429                 span_err!(tcx.sess,
1430                           span,
1431                           E0247,
1432                           "found module name used as a type: {}",
1433                           tcx.map.node_to_string(id.node));
1434                 return this.tcx().types.err;
1435             }
1436
1437             opt_self_ty.expect("missing T in <T>::a::b::c")
1438         }
1439         def::DefPrimTy(prim_ty) => {
1440             prim_ty_to_ty(tcx, base_segments, prim_ty)
1441         }
1442         _ => {
1443             span_err!(tcx.sess, span, E0248,
1444                       "found value name used as a type: {:?}", *def);
1445             return this.tcx().types.err;
1446         }
1447     }
1448 }
1449
1450 // Note that both base_segments and assoc_segments may be empty, although not at
1451 // the same time.
1452 pub fn finish_resolving_def_to_ty<'tcx>(this: &AstConv<'tcx>,
1453                                         rscope: &RegionScope,
1454                                         span: Span,
1455                                         param_mode: PathParamMode,
1456                                         def: &def::Def,
1457                                         opt_self_ty: Option<Ty<'tcx>>,
1458                                         base_segments: &[ast::PathSegment],
1459                                         assoc_segments: &[ast::PathSegment])
1460                                         -> Ty<'tcx> {
1461     let mut ty = base_def_to_ty(this,
1462                                 rscope,
1463                                 span,
1464                                 param_mode,
1465                                 def,
1466                                 opt_self_ty,
1467                                 base_segments);
1468     let mut def = *def;
1469     // If any associated type segments remain, attempt to resolve them.
1470     for segment in assoc_segments {
1471         if ty.sty == ty::ty_err {
1472             break;
1473         }
1474         // This is pretty bad (it will fail except for T::A and Self::A).
1475         let (a_ty, a_def) = associated_path_def_to_ty(this,
1476                                                       span,
1477                                                       ty,
1478                                                       def,
1479                                                       segment);
1480         ty = a_ty;
1481         def = a_def;
1482     }
1483     ty
1484 }
1485
1486 /// Parses the programmer's textual representation of a type into our
1487 /// internal notion of a type.
1488 pub fn ast_ty_to_ty<'tcx>(this: &AstConv<'tcx>,
1489                           rscope: &RegionScope,
1490                           ast_ty: &ast::Ty)
1491                           -> Ty<'tcx>
1492 {
1493     debug!("ast_ty_to_ty(ast_ty={})",
1494            ast_ty.repr(this.tcx()));
1495
1496     let tcx = this.tcx();
1497
1498     if let Some(&ty) = tcx.ast_ty_to_ty_cache.borrow().get(&ast_ty.id) {
1499         return ty;
1500     }
1501
1502     let typ = match ast_ty.node {
1503         ast::TyVec(ref ty) => {
1504             ty::mk_vec(tcx, ast_ty_to_ty(this, rscope, &**ty), None)
1505         }
1506         ast::TyObjectSum(ref ty, ref bounds) => {
1507             match ast_ty_to_trait_ref(this, rscope, &**ty, bounds) {
1508                 Ok((trait_ref, projection_bounds)) => {
1509                     trait_ref_to_object_type(this,
1510                                              rscope,
1511                                              ast_ty.span,
1512                                              trait_ref,
1513                                              projection_bounds,
1514                                              bounds)
1515                 }
1516                 Err(ErrorReported) => {
1517                     this.tcx().types.err
1518                 }
1519             }
1520         }
1521         ast::TyPtr(ref mt) => {
1522             ty::mk_ptr(tcx, ty::mt {
1523                 ty: ast_ty_to_ty(this, rscope, &*mt.ty),
1524                 mutbl: mt.mutbl
1525             })
1526         }
1527         ast::TyRptr(ref region, ref mt) => {
1528             let r = opt_ast_region_to_region(this, rscope, ast_ty.span, region);
1529             debug!("ty_rptr r={}", r.repr(this.tcx()));
1530             let rscope1 =
1531                 &ObjectLifetimeDefaultRscope::new(
1532                     rscope,
1533                     Some(ty::ObjectLifetimeDefault::Specific(r)));
1534             let t = ast_ty_to_ty(this, rscope1, &*mt.ty);
1535             ty::mk_rptr(tcx, tcx.mk_region(r), ty::mt {ty: t, mutbl: mt.mutbl})
1536         }
1537         ast::TyTup(ref fields) => {
1538             let flds = fields.iter()
1539                              .map(|t| ast_ty_to_ty(this, rscope, &**t))
1540                              .collect();
1541             ty::mk_tup(tcx, flds)
1542         }
1543         ast::TyParen(ref typ) => ast_ty_to_ty(this, rscope, &**typ),
1544         ast::TyBareFn(ref bf) => {
1545             if bf.decl.variadic && bf.abi != abi::C {
1546                 span_err!(tcx.sess, ast_ty.span, E0222,
1547                           "variadic function must have C calling convention");
1548             }
1549             let bare_fn = ty_of_bare_fn(this, bf.unsafety, bf.abi, &*bf.decl);
1550             ty::mk_bare_fn(tcx, None, tcx.mk_bare_fn(bare_fn))
1551         }
1552         ast::TyPolyTraitRef(ref bounds) => {
1553             conv_ty_poly_trait_ref(this, rscope, ast_ty.span, bounds)
1554         }
1555         ast::TyPath(ref maybe_qself, ref path) => {
1556             let path_res = if let Some(&d) = tcx.def_map.borrow().get(&ast_ty.id) {
1557                 d
1558             } else if let Some(ast::QSelf { position: 0, .. }) = *maybe_qself {
1559                 // Create some fake resolution that can't possibly be a type.
1560                 def::PathResolution {
1561                     base_def: def::DefMod(ast_util::local_def(ast::CRATE_NODE_ID)),
1562                     last_private: LastMod(AllPublic),
1563                     depth: path.segments.len()
1564                 }
1565             } else {
1566                 tcx.sess.span_bug(ast_ty.span,
1567                                   &format!("unbound path {}", ast_ty.repr(tcx)))
1568             };
1569             let def = path_res.base_def;
1570             let base_ty_end = path.segments.len() - path_res.depth;
1571             let opt_self_ty = maybe_qself.as_ref().map(|qself| {
1572                 ast_ty_to_ty(this, rscope, &qself.ty)
1573             });
1574             let ty = finish_resolving_def_to_ty(this,
1575                                                 rscope,
1576                                                 ast_ty.span,
1577                                                 PathParamMode::Explicit,
1578                                                 &def,
1579                                                 opt_self_ty,
1580                                                 &path.segments[..base_ty_end],
1581                                                 &path.segments[base_ty_end..]);
1582
1583             if path_res.depth != 0 && ty.sty != ty::ty_err {
1584                 // Write back the new resolution.
1585                 tcx.def_map.borrow_mut().insert(ast_ty.id, def::PathResolution {
1586                     base_def: def,
1587                     last_private: path_res.last_private,
1588                     depth: 0
1589                 });
1590             }
1591
1592             ty
1593         }
1594         ast::TyFixedLengthVec(ref ty, ref e) => {
1595             match const_eval::eval_const_expr_partial(tcx, &**e, Some(tcx.types.usize)) {
1596                 Ok(r) => {
1597                     match r {
1598                         const_eval::const_int(i) =>
1599                             ty::mk_vec(tcx, ast_ty_to_ty(this, rscope, &**ty),
1600                                         Some(i as usize)),
1601                         const_eval::const_uint(i) =>
1602                             ty::mk_vec(tcx, ast_ty_to_ty(this, rscope, &**ty),
1603                                         Some(i as usize)),
1604                         _ => {
1605                             span_err!(tcx.sess, ast_ty.span, E0249,
1606                                       "expected constant expr for array length");
1607                             this.tcx().types.err
1608                         }
1609                     }
1610                 }
1611                 Err(ref r) => {
1612                     let subspan  =
1613                         ast_ty.span.lo <= r.span.lo && r.span.hi <= ast_ty.span.hi;
1614                     span_err!(tcx.sess, r.span, E0250,
1615                               "array length constant evaluation error: {}",
1616                               r.description());
1617                     if !subspan {
1618                         span_note!(tcx.sess, ast_ty.span, "for array length here")
1619                     }
1620                     this.tcx().types.err
1621                 }
1622             }
1623         }
1624         ast::TyTypeof(ref _e) => {
1625             tcx.sess.span_bug(ast_ty.span, "typeof is reserved but unimplemented");
1626         }
1627         ast::TyInfer => {
1628             // TyInfer also appears as the type of arguments or return
1629             // values in a ExprClosure, or as
1630             // the type of local variables. Both of these cases are
1631             // handled specially and will not descend into this routine.
1632             this.ty_infer(ast_ty.span)
1633         }
1634     };
1635
1636     tcx.ast_ty_to_ty_cache.borrow_mut().insert(ast_ty.id, typ);
1637     return typ;
1638 }
1639
1640 pub fn ty_of_arg<'tcx>(this: &AstConv<'tcx>,
1641                        rscope: &RegionScope,
1642                        a: &ast::Arg,
1643                        expected_ty: Option<Ty<'tcx>>)
1644                        -> Ty<'tcx>
1645 {
1646     match a.ty.node {
1647         ast::TyInfer if expected_ty.is_some() => expected_ty.unwrap(),
1648         ast::TyInfer => this.ty_infer(a.ty.span),
1649         _ => ast_ty_to_ty(this, rscope, &*a.ty),
1650     }
1651 }
1652
1653 struct SelfInfo<'a, 'tcx> {
1654     untransformed_self_ty: Ty<'tcx>,
1655     explicit_self: &'a ast::ExplicitSelf,
1656 }
1657
1658 pub fn ty_of_method<'tcx>(this: &AstConv<'tcx>,
1659                           sig: &ast::MethodSig,
1660                           untransformed_self_ty: Ty<'tcx>)
1661                           -> (ty::BareFnTy<'tcx>, ty::ExplicitSelfCategory) {
1662     let self_info = Some(SelfInfo {
1663         untransformed_self_ty: untransformed_self_ty,
1664         explicit_self: &sig.explicit_self,
1665     });
1666     let (bare_fn_ty, optional_explicit_self_category) =
1667         ty_of_method_or_bare_fn(this,
1668                                 sig.unsafety,
1669                                 sig.abi,
1670                                 self_info,
1671                                 &sig.decl);
1672     (bare_fn_ty, optional_explicit_self_category.unwrap())
1673 }
1674
1675 pub fn ty_of_bare_fn<'tcx>(this: &AstConv<'tcx>, unsafety: ast::Unsafety, abi: abi::Abi,
1676                                               decl: &ast::FnDecl) -> ty::BareFnTy<'tcx> {
1677     let (bare_fn_ty, _) = ty_of_method_or_bare_fn(this, unsafety, abi, None, decl);
1678     bare_fn_ty
1679 }
1680
1681 fn ty_of_method_or_bare_fn<'a, 'tcx>(this: &AstConv<'tcx>,
1682                                      unsafety: ast::Unsafety,
1683                                      abi: abi::Abi,
1684                                      opt_self_info: Option<SelfInfo<'a, 'tcx>>,
1685                                      decl: &ast::FnDecl)
1686                                      -> (ty::BareFnTy<'tcx>, Option<ty::ExplicitSelfCategory>)
1687 {
1688     debug!("ty_of_method_or_bare_fn");
1689
1690     // New region names that appear inside of the arguments of the function
1691     // declaration are bound to that function type.
1692     let rb = rscope::BindingRscope::new();
1693
1694     // `implied_output_region` is the region that will be assumed for any
1695     // region parameters in the return type. In accordance with the rules for
1696     // lifetime elision, we can determine it in two ways. First (determined
1697     // here), if self is by-reference, then the implied output region is the
1698     // region of the self parameter.
1699     let mut explicit_self_category_result = None;
1700     let (self_ty, mut implied_output_region) = match opt_self_info {
1701         None => (None, None),
1702         Some(self_info) => {
1703             // This type comes from an impl or trait; no late-bound
1704             // regions should be present.
1705             assert!(!self_info.untransformed_self_ty.has_escaping_regions());
1706
1707             // Figure out and record the explicit self category.
1708             let explicit_self_category =
1709                 determine_explicit_self_category(this, &rb, &self_info);
1710             explicit_self_category_result = Some(explicit_self_category);
1711             match explicit_self_category {
1712                 ty::StaticExplicitSelfCategory => {
1713                     (None, None)
1714                 }
1715                 ty::ByValueExplicitSelfCategory => {
1716                     (Some(self_info.untransformed_self_ty), None)
1717                 }
1718                 ty::ByReferenceExplicitSelfCategory(region, mutability) => {
1719                     (Some(ty::mk_rptr(this.tcx(),
1720                                       this.tcx().mk_region(region),
1721                                       ty::mt {
1722                                         ty: self_info.untransformed_self_ty,
1723                                         mutbl: mutability
1724                                       })),
1725                      Some(region))
1726                 }
1727                 ty::ByBoxExplicitSelfCategory => {
1728                     (Some(ty::mk_uniq(this.tcx(), self_info.untransformed_self_ty)), None)
1729                 }
1730             }
1731         }
1732     };
1733
1734     // HACK(eddyb) replace the fake self type in the AST with the actual type.
1735     let input_params = if self_ty.is_some() {
1736         &decl.inputs[1..]
1737     } else {
1738         &decl.inputs[..]
1739     };
1740     let input_tys = input_params.iter().map(|a| ty_of_arg(this, &rb, a, None));
1741     let input_pats: Vec<String> = input_params.iter()
1742                                               .map(|a| pprust::pat_to_string(&*a.pat))
1743                                               .collect();
1744     let self_and_input_tys: Vec<Ty> =
1745         self_ty.into_iter().chain(input_tys).collect();
1746
1747
1748     // Second, if there was exactly one lifetime (either a substitution or a
1749     // reference) in the arguments, then any anonymous regions in the output
1750     // have that lifetime.
1751     let lifetimes_for_params = if implied_output_region.is_none() {
1752         let input_tys = if self_ty.is_some() {
1753             // Skip the first argument if `self` is present.
1754             &self_and_input_tys[1..]
1755         } else {
1756             &self_and_input_tys[..]
1757         };
1758
1759         let (ior, lfp) = find_implied_output_region(input_tys, input_pats);
1760         implied_output_region = ior;
1761         lfp
1762     } else {
1763         vec![]
1764     };
1765
1766     let output_ty = match decl.output {
1767         ast::Return(ref output) if output.node == ast::TyInfer =>
1768             ty::FnConverging(this.ty_infer(output.span)),
1769         ast::Return(ref output) =>
1770             ty::FnConverging(convert_ty_with_lifetime_elision(this,
1771                                                               implied_output_region,
1772                                                               lifetimes_for_params,
1773                                                               &**output)),
1774         ast::DefaultReturn(..) => ty::FnConverging(ty::mk_nil(this.tcx())),
1775         ast::NoReturn(..) => ty::FnDiverging
1776     };
1777
1778     (ty::BareFnTy {
1779         unsafety: unsafety,
1780         abi: abi,
1781         sig: ty::Binder(ty::FnSig {
1782             inputs: self_and_input_tys,
1783             output: output_ty,
1784             variadic: decl.variadic
1785         }),
1786     }, explicit_self_category_result)
1787 }
1788
1789 fn determine_explicit_self_category<'a, 'tcx>(this: &AstConv<'tcx>,
1790                                               rscope: &RegionScope,
1791                                               self_info: &SelfInfo<'a, 'tcx>)
1792                                               -> ty::ExplicitSelfCategory
1793 {
1794     return match self_info.explicit_self.node {
1795         ast::SelfStatic => ty::StaticExplicitSelfCategory,
1796         ast::SelfValue(_) => ty::ByValueExplicitSelfCategory,
1797         ast::SelfRegion(ref lifetime, mutability, _) => {
1798             let region =
1799                 opt_ast_region_to_region(this,
1800                                          rscope,
1801                                          self_info.explicit_self.span,
1802                                          lifetime);
1803             ty::ByReferenceExplicitSelfCategory(region, mutability)
1804         }
1805         ast::SelfExplicit(ref ast_type, _) => {
1806             let explicit_type = ast_ty_to_ty(this, rscope, &**ast_type);
1807
1808             // We wish to (for now) categorize an explicit self
1809             // declaration like `self: SomeType` into either `self`,
1810             // `&self`, `&mut self`, or `Box<self>`. We do this here
1811             // by some simple pattern matching. A more precise check
1812             // is done later in `check_method_self_type()`.
1813             //
1814             // Examples:
1815             //
1816             // ```
1817             // impl Foo for &T {
1818             //     // Legal declarations:
1819             //     fn method1(self: &&T); // ByReferenceExplicitSelfCategory
1820             //     fn method2(self: &T); // ByValueExplicitSelfCategory
1821             //     fn method3(self: Box<&T>); // ByBoxExplicitSelfCategory
1822             //
1823             //     // Invalid cases will be caught later by `check_method_self_type`:
1824             //     fn method_err1(self: &mut T); // ByReferenceExplicitSelfCategory
1825             // }
1826             // ```
1827             //
1828             // To do the check we just count the number of "modifiers"
1829             // on each type and compare them. If they are the same or
1830             // the impl has more, we call it "by value". Otherwise, we
1831             // look at the outermost modifier on the method decl and
1832             // call it by-ref, by-box as appropriate. For method1, for
1833             // example, the impl type has one modifier, but the method
1834             // type has two, so we end up with
1835             // ByReferenceExplicitSelfCategory.
1836
1837             let impl_modifiers = count_modifiers(self_info.untransformed_self_ty);
1838             let method_modifiers = count_modifiers(explicit_type);
1839
1840             debug!("determine_explicit_self_category(self_info.untransformed_self_ty={} \
1841                    explicit_type={} \
1842                    modifiers=({},{})",
1843                    self_info.untransformed_self_ty.repr(this.tcx()),
1844                    explicit_type.repr(this.tcx()),
1845                    impl_modifiers,
1846                    method_modifiers);
1847
1848             if impl_modifiers >= method_modifiers {
1849                 ty::ByValueExplicitSelfCategory
1850             } else {
1851                 match explicit_type.sty {
1852                     ty::ty_rptr(r, mt) => ty::ByReferenceExplicitSelfCategory(*r, mt.mutbl),
1853                     ty::ty_uniq(_) => ty::ByBoxExplicitSelfCategory,
1854                     _ => ty::ByValueExplicitSelfCategory,
1855                 }
1856             }
1857         }
1858     };
1859
1860     fn count_modifiers(ty: Ty) -> usize {
1861         match ty.sty {
1862             ty::ty_rptr(_, mt) => count_modifiers(mt.ty) + 1,
1863             ty::ty_uniq(t) => count_modifiers(t) + 1,
1864             _ => 0,
1865         }
1866     }
1867 }
1868
1869 pub fn ty_of_closure<'tcx>(
1870     this: &AstConv<'tcx>,
1871     unsafety: ast::Unsafety,
1872     decl: &ast::FnDecl,
1873     abi: abi::Abi,
1874     expected_sig: Option<ty::FnSig<'tcx>>)
1875     -> ty::ClosureTy<'tcx>
1876 {
1877     debug!("ty_of_closure(expected_sig={})",
1878            expected_sig.repr(this.tcx()));
1879
1880     // new region names that appear inside of the fn decl are bound to
1881     // that function type
1882     let rb = rscope::BindingRscope::new();
1883
1884     let input_tys: Vec<_> = decl.inputs.iter().enumerate().map(|(i, a)| {
1885         let expected_arg_ty = expected_sig.as_ref().and_then(|e| {
1886             // no guarantee that the correct number of expected args
1887             // were supplied
1888             if i < e.inputs.len() {
1889                 Some(e.inputs[i])
1890             } else {
1891                 None
1892             }
1893         });
1894         ty_of_arg(this, &rb, a, expected_arg_ty)
1895     }).collect();
1896
1897     let expected_ret_ty = expected_sig.map(|e| e.output);
1898
1899     let is_infer = match decl.output {
1900         ast::Return(ref output) if output.node == ast::TyInfer => true,
1901         ast::DefaultReturn(..) => true,
1902         _ => false
1903     };
1904
1905     let output_ty = match decl.output {
1906         _ if is_infer && expected_ret_ty.is_some() =>
1907             expected_ret_ty.unwrap(),
1908         _ if is_infer =>
1909             ty::FnConverging(this.ty_infer(decl.output.span())),
1910         ast::Return(ref output) =>
1911             ty::FnConverging(ast_ty_to_ty(this, &rb, &**output)),
1912         ast::DefaultReturn(..) => unreachable!(),
1913         ast::NoReturn(..) => ty::FnDiverging
1914     };
1915
1916     debug!("ty_of_closure: input_tys={}", input_tys.repr(this.tcx()));
1917     debug!("ty_of_closure: output_ty={}", output_ty.repr(this.tcx()));
1918
1919     ty::ClosureTy {
1920         unsafety: unsafety,
1921         abi: abi,
1922         sig: ty::Binder(ty::FnSig {inputs: input_tys,
1923                                    output: output_ty,
1924                                    variadic: decl.variadic}),
1925     }
1926 }
1927
1928 /// Given an existential type like `Foo+'a+Bar`, this routine converts the `'a` and `Bar` intos an
1929 /// `ExistentialBounds` struct. The `main_trait_refs` argument specifies the `Foo` -- it is absent
1930 /// for closures. Eventually this should all be normalized, I think, so that there is no "main
1931 /// trait ref" and instead we just have a flat list of bounds as the existential type.
1932 fn conv_existential_bounds<'tcx>(
1933     this: &AstConv<'tcx>,
1934     rscope: &RegionScope,
1935     span: Span,
1936     principal_trait_ref: ty::PolyTraitRef<'tcx>,
1937     projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>,
1938     ast_bounds: &[ast::TyParamBound])
1939     -> ty::ExistentialBounds<'tcx>
1940 {
1941     let partitioned_bounds =
1942         partition_bounds(this.tcx(), span, ast_bounds);
1943
1944     conv_existential_bounds_from_partitioned_bounds(
1945         this, rscope, span, principal_trait_ref, projection_bounds, partitioned_bounds)
1946 }
1947
1948 fn conv_ty_poly_trait_ref<'tcx>(
1949     this: &AstConv<'tcx>,
1950     rscope: &RegionScope,
1951     span: Span,
1952     ast_bounds: &[ast::TyParamBound])
1953     -> Ty<'tcx>
1954 {
1955     let mut partitioned_bounds = partition_bounds(this.tcx(), span, &ast_bounds[..]);
1956
1957     let mut projection_bounds = Vec::new();
1958     let main_trait_bound = if !partitioned_bounds.trait_bounds.is_empty() {
1959         let trait_bound = partitioned_bounds.trait_bounds.remove(0);
1960         instantiate_poly_trait_ref(this,
1961                                    rscope,
1962                                    trait_bound,
1963                                    None,
1964                                    &mut projection_bounds)
1965     } else {
1966         span_err!(this.tcx().sess, span, E0224,
1967                   "at least one non-builtin trait is required for an object type");
1968         return this.tcx().types.err;
1969     };
1970
1971     let bounds =
1972         conv_existential_bounds_from_partitioned_bounds(this,
1973                                                         rscope,
1974                                                         span,
1975                                                         main_trait_bound.clone(),
1976                                                         projection_bounds,
1977                                                         partitioned_bounds);
1978
1979     make_object_type(this, span, main_trait_bound, bounds)
1980 }
1981
1982 pub fn conv_existential_bounds_from_partitioned_bounds<'tcx>(
1983     this: &AstConv<'tcx>,
1984     rscope: &RegionScope,
1985     span: Span,
1986     principal_trait_ref: ty::PolyTraitRef<'tcx>,
1987     mut projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>, // Empty for boxed closures
1988     partitioned_bounds: PartitionedBounds)
1989     -> ty::ExistentialBounds<'tcx>
1990 {
1991     let PartitionedBounds { builtin_bounds,
1992                             trait_bounds,
1993                             region_bounds } =
1994         partitioned_bounds;
1995
1996     if !trait_bounds.is_empty() {
1997         let b = &trait_bounds[0];
1998         span_err!(this.tcx().sess, b.trait_ref.path.span, E0225,
1999                   "only the builtin traits can be used as closure or object bounds");
2000     }
2001
2002     let region_bound = compute_object_lifetime_bound(this,
2003                                                      rscope,
2004                                                      span,
2005                                                      &region_bounds,
2006                                                      principal_trait_ref,
2007                                                      builtin_bounds);
2008
2009     ty::sort_bounds_list(&mut projection_bounds);
2010
2011     ty::ExistentialBounds {
2012         region_bound: region_bound,
2013         builtin_bounds: builtin_bounds,
2014         projection_bounds: projection_bounds,
2015     }
2016 }
2017
2018 /// Given the bounds on an object, determines what single region bound
2019 /// (if any) we can use to summarize this type. The basic idea is that we will use the bound the
2020 /// user provided, if they provided one, and otherwise search the supertypes of trait bounds for
2021 /// region bounds. It may be that we can derive no bound at all, in which case we return `None`.
2022 fn compute_object_lifetime_bound<'tcx>(
2023     this: &AstConv<'tcx>,
2024     rscope: &RegionScope,
2025     span: Span,
2026     explicit_region_bounds: &[&ast::Lifetime],
2027     principal_trait_ref: ty::PolyTraitRef<'tcx>,
2028     builtin_bounds: ty::BuiltinBounds)
2029     -> ty::Region
2030 {
2031     let tcx = this.tcx();
2032
2033     debug!("compute_opt_region_bound(explicit_region_bounds={:?}, \
2034            principal_trait_ref={}, builtin_bounds={})",
2035            explicit_region_bounds,
2036            principal_trait_ref.repr(tcx),
2037            builtin_bounds.repr(tcx));
2038
2039     if explicit_region_bounds.len() > 1 {
2040         span_err!(tcx.sess, explicit_region_bounds[1].span, E0226,
2041             "only a single explicit lifetime bound is permitted");
2042     }
2043
2044     if !explicit_region_bounds.is_empty() {
2045         // Explicitly specified region bound. Use that.
2046         let r = explicit_region_bounds[0];
2047         return ast_region_to_region(tcx, r);
2048     }
2049
2050     if let Err(ErrorReported) = this.ensure_super_predicates(span,principal_trait_ref.def_id()) {
2051         return ty::ReStatic;
2052     }
2053
2054     // No explicit region bound specified. Therefore, examine trait
2055     // bounds and see if we can derive region bounds from those.
2056     let derived_region_bounds =
2057         object_region_bounds(tcx, &principal_trait_ref, builtin_bounds);
2058
2059     // If there are no derived region bounds, then report back that we
2060     // can find no region bound.
2061     if derived_region_bounds.is_empty() {
2062         match rscope.object_lifetime_default(span) {
2063             Some(r) => { return r; }
2064             None => {
2065                 span_err!(this.tcx().sess, span, E0228,
2066                           "the lifetime bound for this object type cannot be deduced \
2067                            from context; please supply an explicit bound");
2068                 return ty::ReStatic;
2069             }
2070         }
2071     }
2072
2073     // If any of the derived region bounds are 'static, that is always
2074     // the best choice.
2075     if derived_region_bounds.iter().any(|r| ty::ReStatic == *r) {
2076         return ty::ReStatic;
2077     }
2078
2079     // Determine whether there is exactly one unique region in the set
2080     // of derived region bounds. If so, use that. Otherwise, report an
2081     // error.
2082     let r = derived_region_bounds[0];
2083     if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2084         span_err!(tcx.sess, span, E0227,
2085                   "ambiguous lifetime bound, explicit lifetime bound required");
2086     }
2087     return r;
2088 }
2089
2090 /// Given an object type like `SomeTrait+Send`, computes the lifetime
2091 /// bounds that must hold on the elided self type. These are derived
2092 /// from the declarations of `SomeTrait`, `Send`, and friends -- if
2093 /// they declare `trait SomeTrait : 'static`, for example, then
2094 /// `'static` would appear in the list. The hard work is done by
2095 /// `ty::required_region_bounds`, see that for more information.
2096 pub fn object_region_bounds<'tcx>(
2097     tcx: &ty::ctxt<'tcx>,
2098     principal: &ty::PolyTraitRef<'tcx>,
2099     others: ty::BuiltinBounds)
2100     -> Vec<ty::Region>
2101 {
2102     // Since we don't actually *know* the self type for an object,
2103     // this "open(err)" serves as a kind of dummy standin -- basically
2104     // a skolemized type.
2105     let open_ty = ty::mk_infer(tcx, ty::FreshTy(0));
2106
2107     // Note that we preserve the overall binding levels here.
2108     assert!(!open_ty.has_escaping_regions());
2109     let substs = tcx.mk_substs(principal.0.substs.with_self_ty(open_ty));
2110     let trait_refs = vec!(ty::Binder(Rc::new(ty::TraitRef::new(principal.0.def_id, substs))));
2111
2112     let param_bounds = ty::ParamBounds {
2113         region_bounds: Vec::new(),
2114         builtin_bounds: others,
2115         trait_bounds: trait_refs,
2116         projection_bounds: Vec::new(), // not relevant to computing region bounds
2117     };
2118
2119     let predicates = ty::predicates(tcx, open_ty, &param_bounds);
2120     ty::required_region_bounds(tcx, open_ty, predicates)
2121 }
2122
2123 pub struct PartitionedBounds<'a> {
2124     pub builtin_bounds: ty::BuiltinBounds,
2125     pub trait_bounds: Vec<&'a ast::PolyTraitRef>,
2126     pub region_bounds: Vec<&'a ast::Lifetime>,
2127 }
2128
2129 /// Divides a list of bounds from the AST into three groups: builtin bounds (Copy, Sized etc),
2130 /// general trait bounds, and region bounds.
2131 pub fn partition_bounds<'a>(tcx: &ty::ctxt,
2132                             _span: Span,
2133                             ast_bounds: &'a [ast::TyParamBound])
2134                             -> PartitionedBounds<'a>
2135 {
2136     let mut builtin_bounds = ty::empty_builtin_bounds();
2137     let mut region_bounds = Vec::new();
2138     let mut trait_bounds = Vec::new();
2139     for ast_bound in ast_bounds {
2140         match *ast_bound {
2141             ast::TraitTyParamBound(ref b, ast::TraitBoundModifier::None) => {
2142                 match ::lookup_full_def(tcx, b.trait_ref.path.span, b.trait_ref.ref_id) {
2143                     def::DefTrait(trait_did) => {
2144                         if ty::try_add_builtin_trait(tcx,
2145                                                      trait_did,
2146                                                      &mut builtin_bounds) {
2147                             let segments = &b.trait_ref.path.segments;
2148                             let parameters = &segments[segments.len() - 1].parameters;
2149                             if !parameters.types().is_empty() {
2150                                 check_type_argument_count(tcx, b.trait_ref.path.span,
2151                                                           parameters.types().len(), 0, 0);
2152                             }
2153                             if !parameters.lifetimes().is_empty() {
2154                                 report_lifetime_number_error(tcx, b.trait_ref.path.span,
2155                                                              parameters.lifetimes().len(), 0);
2156                             }
2157                             continue; // success
2158                         }
2159                     }
2160                     _ => {
2161                         // Not a trait? that's an error, but it'll get
2162                         // reported later.
2163                     }
2164                 }
2165                 trait_bounds.push(b);
2166             }
2167             ast::TraitTyParamBound(_, ast::TraitBoundModifier::Maybe) => {}
2168             ast::RegionTyParamBound(ref l) => {
2169                 region_bounds.push(l);
2170             }
2171         }
2172     }
2173
2174     PartitionedBounds {
2175         builtin_bounds: builtin_bounds,
2176         trait_bounds: trait_bounds,
2177         region_bounds: region_bounds,
2178     }
2179 }
2180
2181 fn prohibit_projections<'tcx>(tcx: &ty::ctxt<'tcx>,
2182                               bindings: &[ConvertedBinding<'tcx>])
2183 {
2184     for binding in bindings.iter().take(1) {
2185         span_err!(tcx.sess, binding.span, E0229,
2186             "associated type bindings are not allowed here");
2187     }
2188 }
2189
2190 fn check_type_argument_count(tcx: &ty::ctxt, span: Span, supplied: usize,
2191                              required: usize, accepted: usize) {
2192     if supplied < required {
2193         let expected = if required < accepted {
2194             "expected at least"
2195         } else {
2196             "expected"
2197         };
2198         span_err!(tcx.sess, span, E0243,
2199                   "wrong number of type arguments: {} {}, found {}",
2200                   expected, required, supplied);
2201     } else if supplied > accepted {
2202         let expected = if required < accepted {
2203             "expected at most"
2204         } else {
2205             "expected"
2206         };
2207         span_err!(tcx.sess, span, E0244,
2208                   "wrong number of type arguments: {} {}, found {}",
2209                   expected,
2210                   accepted,
2211                   supplied);
2212     }
2213 }
2214
2215 fn report_lifetime_number_error(tcx: &ty::ctxt, span: Span, number: usize, expected: usize) {
2216     span_err!(tcx.sess, span, E0107,
2217               "wrong number of lifetime parameters: expected {}, found {}",
2218               expected, number);
2219 }