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()` function
  20 //! triggers a recursive call to `ty_of_item()`  (note that
  21 //! `ast_ty_to_ty()` will detect recursive types and report an error).
  22 //! In the check phase, when the FnCtxt is used as the `AstConv`,
  23 //! `get_item_type_scheme()` just looks up the item type in `tcx.tcache`.
  24 //!
  25 //! The `RegionScope` trait controls what happens when the user does
  26 //! not specify a region in some location where a region is required
  27 //! (e.g., if the user writes `&Foo` as a type rather than `&'a Foo`).
  28 //! See the `rscope` module for more details.
  29 //!
  30 //! Unlike the `AstConv` trait, the region scope can change as we descend
  31 //! the type.  This is to accommodate the fact that (a) fn types are binding
  32 //! scopes and (b) the default region may change.  To understand case (a),
  33 //! consider something like:
  34 //!
  35 //!   type foo = { x: &a.int, y: |&a.int| }
  36 //!
  37 //! The type of `x` is an error because there is no region `a` in scope.
  38 //! In the type of `y`, however, region `a` is considered a bound region
  39 //! as it does not already appear in scope.
  40 //!
  41 //! Case (b) says that if you have a type:
  42 //!   type foo<'a> = ...;
  43 //!   type bar = fn(&foo, &a.foo)
  44 //! The fully expanded version of type bar is:
  45 //!   type bar = fn(&'foo &, &a.foo<'a>)
  46 //! Note that the self region for the `foo` defaulted to `&` in the first
  47 //! case but `&a` in the second.  Basically, defaults that appear inside
  48 //! an rptr (`&r.T`) use the region `r` that appears in the rptr.
  49
  50 use middle::astconv_util::{ast_ty_to_prim_ty, check_path_args, NO_TPS, NO_REGIONS};
  51 use middle::const_eval;
  52 use middle::def;
  53 use middle::resolve_lifetime as rl;
  54 use middle::subst::{FnSpace, TypeSpace, SelfSpace, Subst, Substs};
  55 use middle::traits;
  56 use middle::ty::{self, RegionEscape, ToPolyTraitRef, Ty};
  57 use rscope::{self, UnelidableRscope, RegionScope, SpecificRscope,
  58              ShiftedRscope, BindingRscope};
  59 use TypeAndSubsts;
  60 use util::common::ErrorReported;
  61 use util::nodemap::DefIdMap;
  62 use util::ppaux::{self, Repr, UserString};
  63
  64 use std::rc::Rc;
  65 use std::iter::{repeat, AdditiveIterator};
  66 use syntax::{abi, ast, ast_util};
  67 use syntax::codemap::Span;
  68 use syntax::parse::token;
  69 use syntax::print::pprust;
  70
  71 pub trait AstConv<'tcx> {
  72     fn tcx<'a>(&'a self) -> &'a ty::ctxt<'tcx>;
  73
  74     fn get_item_type_scheme(&self, id: ast::DefId) -> ty::TypeScheme<'tcx>;
  75
  76     fn get_trait_def(&self, id: ast::DefId) -> Rc<ty::TraitDef<'tcx>>;
  77
  78     /// Return an (optional) substitution to convert bound type parameters that
  79     /// are in scope into free ones. This function should only return Some
  80     /// within a fn body.
  81     /// See ParameterEnvironment::free_substs for more information.
  82     fn get_free_substs(&self) -> Option<&Substs<'tcx>> {
  83         None
  84     }
  85
  86     /// What type should we use when a type is omitted?
  87     fn ty_infer(&self, span: Span) -> Ty<'tcx>;
  88
  89     /// Projecting an associated type from a (potentially)
  90     /// higher-ranked trait reference is more complicated, because of
  91     /// the possibility of late-bound regions appearing in the
  92     /// associated type binding. This is not legal in function
  93     /// signatures for that reason. In a function body, we can always
  94     /// handle it because we can use inference variables to remove the
  95     /// late-bound regions.
  96     fn projected_ty_from_poly_trait_ref(&self,
  97                                         span: Span,
  98                                         poly_trait_ref: ty::PolyTraitRef<'tcx>,
  99                                         item_name: ast::Name)
 100                                         -> Ty<'tcx>
 101     {
 102         if ty::binds_late_bound_regions(self.tcx(), &poly_trait_ref) {
 103             self.tcx().sess.span_err(
 104                 span,
 105                 "cannot extract an associated type from a higher-ranked trait bound \
 106                  in this context");
 107             self.tcx().types.err
 108         } else {
 109             // no late-bound regions, we can just ignore the binder
 110             self.projected_ty(span, poly_trait_ref.0.clone(), item_name)
 111         }
 112     }
 113
 114     /// Project an associated type from a non-higher-ranked trait reference.
 115     /// This is fairly straightforward and can be accommodated in any context.
 116     fn projected_ty(&self,
 117                     span: Span,
 118                     _trait_ref: Rc<ty::TraitRef<'tcx>>,
 119                     _item_name: ast::Name)
 120                     -> Ty<'tcx>
 121     {
 122         self.tcx().sess.span_err(
 123             span,
 124             "associated types are not accepted in this context");
 125
 126         self.tcx().types.err
 127     }
 128 }
 129
 130 pub fn ast_region_to_region(tcx: &ty::ctxt, lifetime: &ast::Lifetime)
 131                             -> ty::Region {
 132     let r = match tcx.named_region_map.get(&lifetime.id) {
 133         None => {
 134             // should have been recorded by the `resolve_lifetime` pass
 135             tcx.sess.span_bug(lifetime.span, "unresolved lifetime");
 136         }
 137
 138         Some(&rl::DefStaticRegion) => {
 139             ty::ReStatic
 140         }
 141
 142         Some(&rl::DefLateBoundRegion(debruijn, id)) => {
 143             ty::ReLateBound(debruijn, ty::BrNamed(ast_util::local_def(id), lifetime.name))
 144         }
 145
 146         Some(&rl::DefEarlyBoundRegion(space, index, id)) => {
 147             ty::ReEarlyBound(id, space, index, lifetime.name)
 148         }
 149
 150         Some(&rl::DefFreeRegion(scope, id)) => {
 151             ty::ReFree(ty::FreeRegion {
 152                     scope: scope,
 153                     bound_region: ty::BrNamed(ast_util::local_def(id),
 154                                               lifetime.name)
 155                 })
 156         }
 157     };
 158
 159     debug!("ast_region_to_region(lifetime={} id={}) yields {}",
 160            lifetime.repr(tcx),
 161            lifetime.id,
 162            r.repr(tcx));
 163
 164     r
 165 }
 166
 167 pub fn opt_ast_region_to_region<'tcx>(
 168     this: &AstConv<'tcx>,
 169     rscope: &RegionScope,
 170     default_span: Span,
 171     opt_lifetime: &Option<ast::Lifetime>) -> ty::Region
 172 {
 173     let r = match *opt_lifetime {
 174         Some(ref lifetime) => {
 175             ast_region_to_region(this.tcx(), lifetime)
 176         }
 177
 178         None => {
 179             match rscope.anon_regions(default_span, 1) {
 180                 Err(v) => {
 181                     debug!("optional region in illegal location");
 182                     span_err!(this.tcx().sess, default_span, E0106,
 183                         "missing lifetime specifier");
 184                     match v {
 185                         Some(v) => {
 186                             let mut m = String::new();
 187                             let len = v.len();
 188                             for (i, (name, n)) in v.into_iter().enumerate() {
 189                                 let help_name = if name.is_empty() {
 190                                     format!("argument {}", i + 1)
 191                                 } else {
 192                                     format!("`{}`", name)
 193                                 };
 194
 195                                 m.push_str(&(if n == 1 {
 196                                     help_name
 197                                 } else {
 198                                     format!("one of {}'s {} elided lifetimes", help_name, n)
 199                                 })[]);
 200
 201                                 if len == 2 && i == 0 {
 202                                     m.push_str(" or ");
 203                                 } else if i == len - 2 {
 204                                     m.push_str(", or ");
 205                                 } else if i != len - 1 {
 206                                     m.push_str(", ");
 207                                 }
 208                             }
 209                             if len == 1 {
 210                                 span_help!(this.tcx().sess, default_span,
 211                                     "this function's return type contains a borrowed value, but \
 212                                      the signature does not say which {} it is borrowed from",
 213                                     m);
 214                             } else if len == 0 {
 215                                 span_help!(this.tcx().sess, default_span,
 216                                     "this function's return type contains a borrowed value, but \
 217                                      there is no value for it to be borrowed from");
 218                                 span_help!(this.tcx().sess, default_span,
 219                                     "consider giving it a 'static lifetime");
 220                             } else {
 221                                 span_help!(this.tcx().sess, default_span,
 222                                     "this function's return type contains a borrowed value, but \
 223                                      the signature does not say whether it is borrowed from {}",
 224                                     m);
 225                             }
 226                         }
 227                         None => {},
 228                     }
 229                     ty::ReStatic
 230                 }
 231
 232                 Ok(rs) => rs[0],
 233             }
 234         }
 235     };
 236
 237     debug!("opt_ast_region_to_region(opt_lifetime={}) yields {}",
 238             opt_lifetime.repr(this.tcx()),
 239             r.repr(this.tcx()));
 240
 241     r
 242 }
 243
 244 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
 245 /// returns an appropriate set of substitutions for this particular reference to `I`.
 246 pub fn ast_path_substs_for_ty<'tcx>(
 247     this: &AstConv<'tcx>,
 248     rscope: &RegionScope,
 249     decl_generics: &ty::Generics<'tcx>,
 250     path: &ast::Path)
 251     -> Substs<'tcx>
 252 {
 253     let tcx = this.tcx();
 254
 255     // ast_path_substs() is only called to convert paths that are
 256     // known to refer to traits, types, or structs. In these cases,
 257     // all type parameters defined for the item being referenced will
 258     // be in the TypeSpace or SelfSpace.
 259     //
 260     // Note: in the case of traits, the self parameter is also
 261     // defined, but we don't currently create a `type_param_def` for
 262     // `Self` because it is implicit.
 263     assert!(decl_generics.regions.all(|d| d.space == TypeSpace));
 264     assert!(decl_generics.types.all(|d| d.space != FnSpace));
 265
 266     let (regions, types, assoc_bindings) = match path.segments.last().unwrap().parameters {
 267         ast::AngleBracketedParameters(ref data) => {
 268             convert_angle_bracketed_parameters(this, rscope, data)
 269         }
 270         ast::ParenthesizedParameters(ref data) => {
 271             tcx.sess.span_err(
 272                 path.span,
 273                 "parenthesized parameters may only be used with a trait");
 274             (Vec::new(), convert_parenthesized_parameters(this, data), Vec::new())
 275         }
 276     };
 277
 278     prohibit_projections(this.tcx(), assoc_bindings.as_slice());
 279
 280     create_substs_for_ast_path(this,
 281                                rscope,
 282                                path.span,
 283                                decl_generics,
 284                                None,
 285                                types,
 286                                regions)
 287 }
 288
 289 fn create_substs_for_ast_path<'tcx>(
 290     this: &AstConv<'tcx>,
 291     rscope: &RegionScope,
 292     span: Span,
 293     decl_generics: &ty::Generics<'tcx>,
 294     self_ty: Option<Ty<'tcx>>,
 295     types: Vec<Ty<'tcx>>,
 296     regions: Vec<ty::Region>)
 297     -> Substs<'tcx>
 298 {
 299     let tcx = this.tcx();
 300
 301     // If the type is parameterized by the this region, then replace this
 302     // region with the current anon region binding (in other words,
 303     // whatever & would get replaced with).
 304     let expected_num_region_params = decl_generics.regions.len(TypeSpace);
 305     let supplied_num_region_params = regions.len();
 306     let regions = if expected_num_region_params == supplied_num_region_params {
 307         regions
 308     } else {
 309         let anon_regions =
 310             rscope.anon_regions(span, expected_num_region_params);
 311
 312         if supplied_num_region_params != 0 || anon_regions.is_err() {
 313             span_err!(tcx.sess, span, E0107,
 314                       "wrong number of lifetime parameters: expected {}, found {}",
 315                       expected_num_region_params, supplied_num_region_params);
 316         }
 317
 318         match anon_regions {
 319             Ok(v) => v.into_iter().collect(),
 320             Err(_) => range(0, expected_num_region_params)
 321                           .map(|_| ty::ReStatic).collect() // hokey
 322         }
 323     };
 324
 325     // Convert the type parameters supplied by the user.
 326     let ty_param_defs = decl_generics.types.get_slice(TypeSpace);
 327     let supplied_ty_param_count = types.len();
 328     let formal_ty_param_count =
 329         ty_param_defs.iter()
 330         .take_while(|x| !ty::is_associated_type(tcx, x.def_id))
 331         .count();
 332     let required_ty_param_count =
 333         ty_param_defs.iter()
 334         .take_while(|x| {
 335             x.default.is_none() &&
 336                 !ty::is_associated_type(tcx, x.def_id)
 337         })
 338         .count();
 339     if supplied_ty_param_count < required_ty_param_count {
 340         let expected = if required_ty_param_count < formal_ty_param_count {
 341             "expected at least"
 342         } else {
 343             "expected"
 344         };
 345         this.tcx().sess.span_fatal(span,
 346                                    &format!("wrong number of type arguments: {} {}, found {}",
 347                                            expected,
 348                                            required_ty_param_count,
 349                                            supplied_ty_param_count)[]);
 350     } else if supplied_ty_param_count > formal_ty_param_count {
 351         let expected = if required_ty_param_count < formal_ty_param_count {
 352             "expected at most"
 353         } else {
 354             "expected"
 355         };
 356         this.tcx().sess.span_fatal(span,
 357                                    &format!("wrong number of type arguments: {} {}, found {}",
 358                                            expected,
 359                                            formal_ty_param_count,
 360                                            supplied_ty_param_count)[]);
 361     }
 362
 363     let mut substs = Substs::new_type(types, regions);
 364
 365     match self_ty {
 366         None => {
 367             // If no self-type is provided, it's still possible that
 368             // one was declared, because this could be an object type.
 369         }
 370         Some(ty) => {
 371             // If a self-type is provided, one should have been
 372             // "declared" (in other words, this should be a
 373             // trait-ref).
 374             assert!(decl_generics.types.get_self().is_some());
 375             substs.types.push(SelfSpace, ty);
 376         }
 377     }
 378
 379     for param in ty_param_defs[supplied_ty_param_count..].iter() {
 380         match param.default {
 381             Some(default) => {
 382                 // This is a default type parameter.
 383                 let default = default.subst_spanned(tcx,
 384                                                     &substs,
 385                                                     Some(span));
 386                 substs.types.push(TypeSpace, default);
 387             }
 388             None => {
 389                 tcx.sess.span_bug(span, "extra parameter without default");
 390             }
 391         }
 392     }
 393
 394     return substs;
 395 }
 396
 397 struct ConvertedBinding<'tcx> {
 398     item_name: ast::Name,
 399     ty: Ty<'tcx>,
 400     span: Span,
 401 }
 402
 403 fn convert_angle_bracketed_parameters<'tcx>(this: &AstConv<'tcx>,
 404                                             rscope: &RegionScope,
 405                                             data: &ast::AngleBracketedParameterData)
 406                                             -> (Vec<ty::Region>,
 407                                                 Vec<Ty<'tcx>>,
 408                                                 Vec<ConvertedBinding<'tcx>>)
 409 {
 410     let regions: Vec<_> =
 411         data.lifetimes.iter()
 412         .map(|l| ast_region_to_region(this.tcx(), l))
 413         .collect();
 414
 415     let types: Vec<_> =
 416         data.types.iter()
 417         .map(|t| ast_ty_to_ty(this, rscope, &**t))
 418         .collect();
 419
 420     let assoc_bindings: Vec<_> =
 421         data.bindings.iter()
 422         .map(|b| ConvertedBinding { item_name: b.ident.name,
 423                                     ty: ast_ty_to_ty(this, rscope, &*b.ty),
 424                                     span: b.span })
 425         .collect();
 426
 427     (regions, types, assoc_bindings)
 428 }
 429
 430 /// Returns the appropriate lifetime to use for any output lifetimes
 431 /// (if one exists) and a vector of the (pattern, number of lifetimes)
 432 /// corresponding to each input type/pattern.
 433 fn find_implied_output_region(input_tys: &[Ty], input_pats: Vec<String>)
 434                               -> (Option<ty::Region>, Vec<(String, uint)>)
 435 {
 436     let mut lifetimes_for_params: Vec<(String, uint)> = Vec::new();
 437     let mut possible_implied_output_region = None;
 438
 439     for (input_type, input_pat) in input_tys.iter().zip(input_pats.into_iter()) {
 440         let mut accumulator = Vec::new();
 441         ty::accumulate_lifetimes_in_type(&mut accumulator, *input_type);
 442
 443         if accumulator.len() == 1 {
 444             // there's a chance that the unique lifetime of this
 445             // iteration will be the appropriate lifetime for output
 446             // parameters, so lets store it.
 447             possible_implied_output_region = Some(accumulator[0])
 448         }
 449
 450         lifetimes_for_params.push((input_pat, accumulator.len()));
 451     }
 452
 453     let implied_output_region = if lifetimes_for_params.iter().map(|&(_, n)| n).sum() == 1 {
 454         assert!(possible_implied_output_region.is_some());
 455         possible_implied_output_region
 456     } else {
 457         None
 458     };
 459     (implied_output_region, lifetimes_for_params)
 460 }
 461
 462 fn convert_ty_with_lifetime_elision<'tcx>(this: &AstConv<'tcx>,
 463                                           implied_output_region: Option<ty::Region>,
 464                                           param_lifetimes: Vec<(String, uint)>,
 465                                           ty: &ast::Ty)
 466                                           -> Ty<'tcx>
 467 {
 468     match implied_output_region {
 469         Some(implied_output_region) => {
 470             let rb = SpecificRscope::new(implied_output_region);
 471             ast_ty_to_ty(this, &rb, ty)
 472         }
 473         None => {
 474             // All regions must be explicitly specified in the output
 475             // if the lifetime elision rules do not apply. This saves
 476             // the user from potentially-confusing errors.
 477             let rb = UnelidableRscope::new(param_lifetimes);
 478             ast_ty_to_ty(this, &rb, ty)
 479         }
 480     }
 481 }
 482
 483 fn convert_parenthesized_parameters<'tcx>(this: &AstConv<'tcx>,
 484                                           data: &ast::ParenthesizedParameterData)
 485                                           -> Vec<Ty<'tcx>>
 486 {
 487     let binding_rscope = BindingRscope::new();
 488     let inputs = data.inputs.iter()
 489                             .map(|a_t| ast_ty_to_ty(this, &binding_rscope, &**a_t))
 490                             .collect::<Vec<Ty<'tcx>>>();
 491
 492     let input_params: Vec<_> = repeat(String::new()).take(inputs.len()).collect();
 493     let (implied_output_region,
 494          params_lifetimes) = find_implied_output_region(&*inputs, input_params);
 495
 496     let input_ty = ty::mk_tup(this.tcx(), inputs);
 497
 498     let output = match data.output {
 499         Some(ref output_ty) => convert_ty_with_lifetime_elision(this,
 500                                                                 implied_output_region,
 501                                                                 params_lifetimes,
 502                                                                 &**output_ty),
 503         None => ty::mk_nil(this.tcx()),
 504     };
 505
 506     vec![input_ty, output]
 507 }
 508
 509 pub fn instantiate_poly_trait_ref<'tcx>(
 510     this: &AstConv<'tcx>,
 511     rscope: &RegionScope,
 512     ast_trait_ref: &ast::PolyTraitRef,
 513     self_ty: Option<Ty<'tcx>>,
 514     poly_projections: &mut Vec<ty::PolyProjectionPredicate<'tcx>>)
 515     -> ty::PolyTraitRef<'tcx>
 516 {
 517     let mut projections = Vec::new();
 518
 519     let trait_ref =
 520         instantiate_trait_ref(this, rscope, &ast_trait_ref.trait_ref,
 521                               self_ty, Some(&mut projections));
 522
 523     for projection in projections.into_iter() {
 524         poly_projections.push(ty::Binder(projection));
 525     }
 526
 527     ty::Binder(trait_ref)
 528 }
 529
 530 /// Instantiates the path for the given trait reference, assuming that it's
 531 /// bound to a valid trait type. Returns the def_id for the defining trait.
 532 /// Fails if the type is a type other than a trait type.
 533 ///
 534 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T=X>`
 535 /// are disallowed. Otherwise, they are pushed onto the vector given.
 536 pub fn instantiate_trait_ref<'tcx>(
 537     this: &AstConv<'tcx>,
 538     rscope: &RegionScope,
 539     ast_trait_ref: &ast::TraitRef,
 540     self_ty: Option<Ty<'tcx>>,
 541     projections: Option<&mut Vec<ty::ProjectionPredicate<'tcx>>>)
 542     -> Rc<ty::TraitRef<'tcx>>
 543 {
 544     match ::lookup_def_tcx(this.tcx(), ast_trait_ref.path.span, ast_trait_ref.ref_id) {
 545         def::DefTrait(trait_def_id) => {
 546             let trait_ref = ast_path_to_trait_ref(this,
 547                                                   rscope,
 548                                                   trait_def_id,
 549                                                   self_ty,
 550                                                   &ast_trait_ref.path,
 551                                                   projections);
 552             this.tcx().trait_refs.borrow_mut().insert(ast_trait_ref.ref_id, trait_ref.clone());
 553             trait_ref
 554         }
 555         _ => {
 556             this.tcx().sess.span_fatal(
 557                 ast_trait_ref.path.span,
 558                 &format!("`{}` is not a trait",
 559                         ast_trait_ref.path.user_string(this.tcx()))[]);
 560         }
 561     }
 562 }
 563
 564 fn ast_path_to_trait_ref<'a,'tcx>(
 565     this: &AstConv<'tcx>,
 566     rscope: &RegionScope,
 567     trait_def_id: ast::DefId,
 568     self_ty: Option<Ty<'tcx>>,
 569     path: &ast::Path,
 570     mut projections: Option<&mut Vec<ty::ProjectionPredicate<'tcx>>>)
 571     -> Rc<ty::TraitRef<'tcx>>
 572 {
 573     debug!("ast_path_to_trait_ref {:?}", path);
 574     let trait_def = this.get_trait_def(trait_def_id);
 575
 576     // the trait reference introduces a binding level here, so
 577     // we need to shift the `rscope`. It'd be nice if we could
 578     // do away with this rscope stuff and work this knowledge
 579     // into resolve_lifetimes, as we do with non-omitted
 580     // lifetimes. Oh well, not there yet.
 581     let shifted_rscope = ShiftedRscope::new(rscope);
 582
 583     let (regions, types, assoc_bindings) = match path.segments.last().unwrap().parameters {
 584         ast::AngleBracketedParameters(ref data) => {
 585             // For now, require that parenthetical notation be used
 586             // only with `Fn()` etc.
 587             if !this.tcx().sess.features.borrow().unboxed_closures &&
 588                 this.tcx().lang_items.fn_trait_kind(trait_def_id).is_some()
 589             {
 590                 this.tcx().sess.span_err(path.span,
 591                                          "angle-bracket notation is not stable when \
 592                                          used with the `Fn` family of traits, use parentheses");
 593                 span_help!(this.tcx().sess, path.span,
 594                            "add `#![feature(unboxed_closures)]` to \
 595                             the crate attributes to enable");
 596             }
 597
 598             convert_angle_bracketed_parameters(this, &shifted_rscope, data)
 599         }
 600         ast::ParenthesizedParameters(ref data) => {
 601             // For now, require that parenthetical notation be used
 602             // only with `Fn()` etc.
 603             if !this.tcx().sess.features.borrow().unboxed_closures &&
 604                 this.tcx().lang_items.fn_trait_kind(trait_def_id).is_none()
 605             {
 606                 this.tcx().sess.span_err(path.span,
 607                                          "parenthetical notation is only stable when \
 608                                          used with the `Fn` family of traits");
 609                 span_help!(this.tcx().sess, path.span,
 610                            "add `#![feature(unboxed_closures)]` to \
 611                             the crate attributes to enable");
 612             }
 613
 614             (Vec::new(), convert_parenthesized_parameters(this, data), Vec::new())
 615         }
 616     };
 617
 618     let substs = create_substs_for_ast_path(this,
 619                                             &shifted_rscope,
 620                                             path.span,
 621                                             &trait_def.generics,
 622                                             self_ty,
 623                                             types,
 624                                             regions);
 625     let substs = this.tcx().mk_substs(substs);
 626
 627     let trait_ref = Rc::new(ty::TraitRef::new(trait_def_id, substs));
 628
 629     match projections {
 630         None => {
 631             prohibit_projections(this.tcx(), assoc_bindings.as_slice());
 632         }
 633         Some(ref mut v) => {
 634             for binding in assoc_bindings.iter() {
 635                 match ast_type_binding_to_projection_predicate(this, trait_ref.clone(),
 636                                                                self_ty, binding) {
 637                     Ok(pp) => { v.push(pp); }
 638                     Err(ErrorReported) => { }
 639                 }
 640             }
 641         }
 642     }
 643
 644     trait_ref
 645 }
 646
 647 fn ast_type_binding_to_projection_predicate<'tcx>(
 648     this: &AstConv<'tcx>,
 649     mut trait_ref: Rc<ty::TraitRef<'tcx>>,
 650     self_ty: Option<Ty<'tcx>>,
 651     binding: &ConvertedBinding<'tcx>)
 652     -> Result<ty::ProjectionPredicate<'tcx>, ErrorReported>
 653 {
 654     let tcx = this.tcx();
 655
 656     // Given something like `U : SomeTrait<T=X>`, we want to produce a
 657     // predicate like `<U as SomeTrait>::T = X`. This is somewhat
 658     // subtle in the event that `T` is defined in a supertrait of
 659     // `SomeTrait`, because in that case we need to upcast.
 660     //
 661     // That is, consider this case:
 662     //
 663     // ```
 664     // trait SubTrait : SuperTrait<int> { }
 665     // trait SuperTrait<A> { type T; }
 666     //
 667     // ... B : SubTrait<T=foo> ...
 668     // ```
 669     //
 670     // We want to produce `<B as SuperTrait<int>>::T == foo`.
 671
 672     // Simple case: X is defined in the current trait.
 673     if trait_defines_associated_type_named(this, trait_ref.def_id, binding.item_name) {
 674         return Ok(ty::ProjectionPredicate {
 675             projection_ty: ty::ProjectionTy {
 676                 trait_ref: trait_ref,
 677                 item_name: binding.item_name,
 678             },
 679             ty: binding.ty,
 680         });
 681     }
 682
 683     // Otherwise, we have to walk through the supertraits to find
 684     // those that do.  This is complicated by the fact that, for an
 685     // object type, the `Self` type is not present in the
 686     // substitutions (after all, it's being constructed right now),
 687     // but the `supertraits` iterator really wants one. To handle
 688     // this, we currently insert a dummy type and then remove it
 689     // later. Yuck.
 690
 691     let dummy_self_ty = ty::mk_infer(tcx, ty::FreshTy(0));
 692     if self_ty.is_none() { // if converting for an object type
 693         let mut dummy_substs = trait_ref.substs.clone();
 694         assert!(dummy_substs.self_ty().is_none());
 695         dummy_substs.types.push(SelfSpace, dummy_self_ty);
 696         trait_ref = Rc::new(ty::TraitRef::new(trait_ref.def_id,
 697                                               tcx.mk_substs(dummy_substs)));
 698     }
 699
 700     let mut candidates: Vec<ty::PolyTraitRef> =
 701         traits::supertraits(tcx, trait_ref.to_poly_trait_ref())
 702         .filter(|r| trait_defines_associated_type_named(this, r.def_id(), binding.item_name))
 703         .collect();
 704
 705     // If converting for an object type, then remove the dummy-ty from `Self` now.
 706     // Yuckety yuck.
 707     if self_ty.is_none() {
 708         for candidate in candidates.iter_mut() {
 709             let mut dummy_substs = candidate.0.substs.clone();
 710             assert!(dummy_substs.self_ty() == Some(dummy_self_ty));
 711             dummy_substs.types.pop(SelfSpace);
 712             *candidate = ty::Binder(Rc::new(ty::TraitRef::new(candidate.def_id(),
 713                                                               tcx.mk_substs(dummy_substs))));
 714         }
 715     }
 716
 717     if candidates.len() > 1 {
 718         tcx.sess.span_err(
 719             binding.span,
 720             format!("ambiguous associated type: `{}` defined in multiple supertraits `{}`",
 721                     token::get_name(binding.item_name),
 722                     candidates.user_string(tcx)).as_slice());
 723         return Err(ErrorReported);
 724     }
 725
 726     let candidate = match candidates.pop() {
 727         Some(c) => c,
 728         None => {
 729             tcx.sess.span_err(
 730                 binding.span,
 731                 format!("no associated type `{}` defined in `{}`",
 732                         token::get_name(binding.item_name),
 733                         trait_ref.user_string(tcx)).as_slice());
 734             return Err(ErrorReported);
 735         }
 736     };
 737
 738     if ty::binds_late_bound_regions(tcx, &candidate) {
 739         tcx.sess.span_err(
 740             binding.span,
 741             format!("associated type `{}` defined in higher-ranked supertrait `{}`",
 742                     token::get_name(binding.item_name),
 743                     candidate.user_string(tcx)).as_slice());
 744         return Err(ErrorReported);
 745     }
 746
 747     Ok(ty::ProjectionPredicate {
 748         projection_ty: ty::ProjectionTy {
 749             trait_ref: candidate.0,
 750             item_name: binding.item_name,
 751         },
 752         ty: binding.ty,
 753     })
 754 }
 755
 756 pub fn ast_path_to_ty<'tcx>(
 757     this: &AstConv<'tcx>,
 758     rscope: &RegionScope,
 759     did: ast::DefId,
 760     path: &ast::Path)
 761     -> TypeAndSubsts<'tcx>
 762 {
 763     let tcx = this.tcx();
 764     let ty::TypeScheme {
 765         generics,
 766         ty: decl_ty
 767     } = this.get_item_type_scheme(did);
 768
 769     let substs = ast_path_substs_for_ty(this,
 770                                         rscope,
 771                                         &generics,
 772                                         path);
 773     let ty = decl_ty.subst(tcx, &substs);
 774     TypeAndSubsts { substs: substs, ty: ty }
 775 }
 776
 777 /// Converts the given AST type to a built-in type. A "built-in type" is, at
 778 /// present, either a core numeric type, a string, or `Box`.
 779 pub fn ast_ty_to_builtin_ty<'tcx>(
 780         this: &AstConv<'tcx>,
 781         rscope: &RegionScope,
 782         ast_ty: &ast::Ty)
 783         -> Option<Ty<'tcx>> {
 784     match ast_ty_to_prim_ty(this.tcx(), ast_ty) {
 785         Some(typ) => return Some(typ),
 786         None => {}
 787     }
 788
 789     match ast_ty.node {
 790         ast::TyPath(ref path, id) => {
 791             let a_def = match this.tcx().def_map.borrow().get(&id) {
 792                 None => {
 793                     this.tcx()
 794                         .sess
 795                         .span_bug(ast_ty.span,
 796                                   &format!("unbound path {}",
 797                                           path.repr(this.tcx()))[])
 798                 }
 799                 Some(&d) => d
 800             };
 801
 802             // FIXME(#12938): This is a hack until we have full support for
 803             // DST.
 804             match a_def {
 805                 def::DefTy(did, _) |
 806                 def::DefStruct(did) if Some(did) == this.tcx().lang_items.owned_box() => {
 807                     let ty = ast_path_to_ty(this, rscope, did, path).ty;
 808                     match ty.sty {
 809                         ty::ty_struct(struct_def_id, ref substs) => {
 810                             assert_eq!(struct_def_id, did);
 811                             assert_eq!(substs.types.len(TypeSpace), 1);
 812                             let referent_ty = *substs.types.get(TypeSpace, 0);
 813                             Some(ty::mk_uniq(this.tcx(), referent_ty))
 814                         }
 815                         _ => {
 816                             this.tcx().sess.span_bug(
 817                                 path.span,
 818                                 &format!("converting `Box` to `{}`",
 819                                         ty.repr(this.tcx()))[]);
 820                         }
 821                     }
 822                 }
 823                 _ => None
 824             }
 825         }
 826         _ => None
 827     }
 828 }
 829
 830 type TraitAndProjections<'tcx> = (ty::PolyTraitRef<'tcx>, Vec<ty::PolyProjectionPredicate<'tcx>>);
 831
 832 fn ast_ty_to_trait_ref<'tcx>(this: &AstConv<'tcx>,
 833                              rscope: &RegionScope,
 834                              ty: &ast::Ty,
 835                              bounds: &[ast::TyParamBound])
 836                              -> Result<TraitAndProjections<'tcx>, ErrorReported>
 837 {
 838     /*!
 839      * In a type like `Foo + Send`, we want to wait to collect the
 840      * full set of bounds before we make the object type, because we
 841      * need them to infer a region bound.  (For example, if we tried
 842      * made a type from just `Foo`, then it wouldn't be enough to
 843      * infer a 'static bound, and hence the user would get an error.)
 844      * So this function is used when we're dealing with a sum type to
 845      * convert the LHS. It only accepts a type that refers to a trait
 846      * name, and reports an error otherwise.
 847      */
 848
 849     match ty.node {
 850         ast::TyPath(ref path, id) => {
 851             match this.tcx().def_map.borrow().get(&id) {
 852                 Some(&def::DefTrait(trait_def_id)) => {
 853                     let mut projection_bounds = Vec::new();
 854                     let trait_ref = ty::Binder(ast_path_to_trait_ref(this,
 855                                                                      rscope,
 856                                                                      trait_def_id,
 857                                                                      None,
 858                                                                      path,
 859                                                                      Some(&mut projection_bounds)));
 860                     let projection_bounds = projection_bounds.into_iter()
 861                                                              .map(ty::Binder)
 862                                                              .collect();
 863                     Ok((trait_ref, projection_bounds))
 864                 }
 865                 _ => {
 866                     span_err!(this.tcx().sess, ty.span, E0172, "expected a reference to a trait");
 867                     Err(ErrorReported)
 868                 }
 869             }
 870         }
 871         _ => {
 872             span_err!(this.tcx().sess, ty.span, E0178,
 873                       "expected a path on the left-hand side of `+`, not `{}`",
 874                       pprust::ty_to_string(ty));
 875             match ty.node {
 876                 ast::TyRptr(None, ref mut_ty) => {
 877                     span_note!(this.tcx().sess, ty.span,
 878                                "perhaps you meant `&{}({} +{})`? (per RFC 438)",
 879                                ppaux::mutability_to_string(mut_ty.mutbl),
 880                                pprust::ty_to_string(&*mut_ty.ty),
 881                                pprust::bounds_to_string(bounds));
 882                 }
 883                ast::TyRptr(Some(ref lt), ref mut_ty) => {
 884                     span_note!(this.tcx().sess, ty.span,
 885                                "perhaps you meant `&{} {}({} +{})`? (per RFC 438)",
 886                                pprust::lifetime_to_string(lt),
 887                                ppaux::mutability_to_string(mut_ty.mutbl),
 888                                pprust::ty_to_string(&*mut_ty.ty),
 889                                pprust::bounds_to_string(bounds));
 890                 }
 891
 892                 _ => {
 893                     span_note!(this.tcx().sess, ty.span,
 894                                "perhaps you forgot parentheses? (per RFC 438)");
 895                 }
 896             }
 897             Err(ErrorReported)
 898         }
 899     }
 900 }
 901
 902 fn trait_ref_to_object_type<'tcx>(this: &AstConv<'tcx>,
 903                                   rscope: &RegionScope,
 904                                   span: Span,
 905                                   trait_ref: ty::PolyTraitRef<'tcx>,
 906                                   projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>,
 907                                   bounds: &[ast::TyParamBound])
 908                                   -> Ty<'tcx>
 909 {
 910     let existential_bounds = conv_existential_bounds(this,
 911                                                      rscope,
 912                                                      span,
 913                                                      Some(trait_ref.clone()),
 914                                                      projection_bounds,
 915                                                      bounds);
 916
 917     let result = ty::mk_trait(this.tcx(), trait_ref, existential_bounds);
 918     debug!("trait_ref_to_object_type: result={}",
 919            result.repr(this.tcx()));
 920
 921     result
 922 }
 923
 924 fn associated_path_def_to_ty<'tcx>(this: &AstConv<'tcx>,
 925                                    ast_ty: &ast::Ty,
 926                                    provenance: def::TyParamProvenance,
 927                                    assoc_name: ast::Name)
 928                                    -> Ty<'tcx>
 929 {
 930     let tcx = this.tcx();
 931     let ty_param_def_id = provenance.def_id();
 932
 933     let mut suitable_bounds: Vec<_>;
 934     let ty_param_name: ast::Name;
 935     { // contain scope of refcell:
 936         let ty_param_defs = tcx.ty_param_defs.borrow();
 937         let ty_param_def = &ty_param_defs[ty_param_def_id.node];
 938         ty_param_name = ty_param_def.name;
 939
 940         // FIXME(#20300) -- search where clauses, not bounds
 941         suitable_bounds =
 942             traits::transitive_bounds(tcx, ty_param_def.bounds.trait_bounds.as_slice())
 943             .filter(|b| trait_defines_associated_type_named(this, b.def_id(), assoc_name))
 944             .collect();
 945     }
 946
 947     if suitable_bounds.len() == 0 {
 948         tcx.sess.span_err(ast_ty.span,
 949                           format!("associated type `{}` not found for type parameter `{}`",
 950                                   token::get_name(assoc_name),
 951                                   token::get_name(ty_param_name)).as_slice());
 952         return this.tcx().types.err;
 953     }
 954
 955     if suitable_bounds.len() > 1 {
 956         tcx.sess.span_err(ast_ty.span,
 957                           format!("ambiguous associated type `{}` in bounds of `{}`",
 958                                   token::get_name(assoc_name),
 959                                   token::get_name(ty_param_name)).as_slice());
 960
 961         for suitable_bound in suitable_bounds.iter() {
 962             span_note!(this.tcx().sess, ast_ty.span,
 963                        "associated type `{}` could derive from `{}`",
 964                        token::get_name(ty_param_name),
 965                        suitable_bound.user_string(this.tcx()));
 966         }
 967     }
 968
 969     let suitable_bound = suitable_bounds.pop().unwrap().clone();
 970     return this.projected_ty_from_poly_trait_ref(ast_ty.span, suitable_bound, assoc_name);
 971 }
 972
 973 fn trait_defines_associated_type_named(this: &AstConv,
 974                                        trait_def_id: ast::DefId,
 975                                        assoc_name: ast::Name)
 976                                        -> bool
 977 {
 978     let tcx = this.tcx();
 979     let trait_def = ty::lookup_trait_def(tcx, trait_def_id);
 980     trait_def.associated_type_names.contains(&assoc_name)
 981 }
 982
 983 fn qpath_to_ty<'tcx>(this: &AstConv<'tcx>,
 984                      rscope: &RegionScope,
 985                      ast_ty: &ast::Ty, // the TyQPath
 986                      qpath: &ast::QPath)
 987                      -> Ty<'tcx>
 988 {
 989     debug!("qpath_to_ty(ast_ty={})",
 990            ast_ty.repr(this.tcx()));
 991
 992     let self_type = ast_ty_to_ty(this, rscope, &*qpath.self_type);
 993
 994     debug!("qpath_to_ty: self_type={}", self_type.repr(this.tcx()));
 995
 996     let trait_ref = instantiate_trait_ref(this,
 997                                           rscope,
 998                                           &*qpath.trait_ref,
 999                                           Some(self_type),
1000                                           None);
1001
1002     debug!("qpath_to_ty: trait_ref={}", trait_ref.repr(this.tcx()));
1003
1004     // `<T as Trait>::U<V>` shouldn't parse right now.
1005     assert!(qpath.item_path.parameters.is_empty());
1006
1007     return this.projected_ty(ast_ty.span,
1008                              trait_ref,
1009                              qpath.item_path.identifier.name);
1010 }
1011
1012 // Parses the programmer's textual representation of a type into our
1013 // internal notion of a type.
1014 pub fn ast_ty_to_ty<'tcx>(
1015         this: &AstConv<'tcx>, rscope: &RegionScope, ast_ty: &ast::Ty) -> Ty<'tcx>
1016 {
1017     debug!("ast_ty_to_ty(ast_ty={})",
1018            ast_ty.repr(this.tcx()));
1019
1020     let tcx = this.tcx();
1021
1022     let mut ast_ty_to_ty_cache = tcx.ast_ty_to_ty_cache.borrow_mut();
1023     match ast_ty_to_ty_cache.get(&ast_ty.id) {
1024         Some(&ty::atttce_resolved(ty)) => return ty,
1025         Some(&ty::atttce_unresolved) => {
1026             tcx.sess.span_fatal(ast_ty.span,
1027                                 "illegal recursive type; insert an enum \
1028                                  or struct in the cycle, if this is \
1029                                  desired");
1030         }
1031         None => { /* go on */ }
1032     }
1033     ast_ty_to_ty_cache.insert(ast_ty.id, ty::atttce_unresolved);
1034     drop(ast_ty_to_ty_cache);
1035
1036     let typ = ast_ty_to_builtin_ty(this, rscope, ast_ty).unwrap_or_else(|| {
1037         match ast_ty.node {
1038             ast::TyVec(ref ty) => {
1039                 ty::mk_vec(tcx, ast_ty_to_ty(this, rscope, &**ty), None)
1040             }
1041             ast::TyObjectSum(ref ty, ref bounds) => {
1042                 match ast_ty_to_trait_ref(this, rscope, &**ty, &bounds[]) {
1043                     Ok((trait_ref, projection_bounds)) => {
1044                         trait_ref_to_object_type(this,
1045                                                  rscope,
1046                                                  ast_ty.span,
1047                                                  trait_ref,
1048                                                  projection_bounds,
1049                                                  &bounds[])
1050                     }
1051                     Err(ErrorReported) => {
1052                         this.tcx().types.err
1053                     }
1054                 }
1055             }
1056             ast::TyPtr(ref mt) => {
1057                 ty::mk_ptr(tcx, ty::mt {
1058                     ty: ast_ty_to_ty(this, rscope, &*mt.ty),
1059                     mutbl: mt.mutbl
1060                 })
1061             }
1062             ast::TyRptr(ref region, ref mt) => {
1063                 let r = opt_ast_region_to_region(this, rscope, ast_ty.span, region);
1064                 debug!("ty_rptr r={}", r.repr(this.tcx()));
1065                 let t = ast_ty_to_ty(this, rscope, &*mt.ty);
1066                 ty::mk_rptr(tcx, tcx.mk_region(r), ty::mt {ty: t, mutbl: mt.mutbl})
1067             }
1068             ast::TyTup(ref fields) => {
1069                 let flds = fields.iter()
1070                                  .map(|t| ast_ty_to_ty(this, rscope, &**t))
1071                                  .collect();
1072                 ty::mk_tup(tcx, flds)
1073             }
1074             ast::TyParen(ref typ) => ast_ty_to_ty(this, rscope, &**typ),
1075             ast::TyBareFn(ref bf) => {
1076                 if bf.decl.variadic && bf.abi != abi::C {
1077                     tcx.sess.span_err(ast_ty.span,
1078                                       "variadic function must have C calling convention");
1079                 }
1080                 let bare_fn = ty_of_bare_fn(this, bf.unsafety, bf.abi, &*bf.decl);
1081                 ty::mk_bare_fn(tcx, None, tcx.mk_bare_fn(bare_fn))
1082             }
1083             ast::TyPolyTraitRef(ref bounds) => {
1084                 conv_ty_poly_trait_ref(this, rscope, ast_ty.span, &bounds[])
1085             }
1086             ast::TyPath(ref path, id) => {
1087                 let a_def = match tcx.def_map.borrow().get(&id) {
1088                     None => {
1089                         tcx.sess
1090                            .span_bug(ast_ty.span,
1091                                      &format!("unbound path {}",
1092                                              path.repr(tcx))[])
1093                     }
1094                     Some(&d) => d
1095                 };
1096                 match a_def {
1097                     def::DefTrait(trait_def_id) => {
1098                         // N.B. this case overlaps somewhat with
1099                         // TyObjectSum, see that fn for details
1100                         let mut projection_bounds = Vec::new();
1101                         let trait_ref = ast_path_to_trait_ref(this,
1102                                                               rscope,
1103                                                               trait_def_id,
1104                                                               None,
1105                                                               path,
1106                                                               Some(&mut projection_bounds));
1107                         let trait_ref = ty::Binder(trait_ref);
1108                         let projection_bounds = projection_bounds.into_iter()
1109                                                                  .map(ty::Binder)
1110                                                                  .collect();
1111                         trait_ref_to_object_type(this, rscope, path.span,
1112                                                  trait_ref, projection_bounds, &[])
1113                     }
1114                     def::DefTy(did, _) | def::DefStruct(did) => {
1115                         ast_path_to_ty(this, rscope, did, path).ty
1116                     }
1117                     def::DefTyParam(space, index, _, name) => {
1118                         check_path_args(tcx, path, NO_TPS | NO_REGIONS);
1119                         ty::mk_param(tcx, space, index, name)
1120                     }
1121                     def::DefSelfTy(_) => {
1122                         // n.b.: resolve guarantees that the this type only appears in a
1123                         // trait, which we rely upon in various places when creating
1124                         // substs
1125                         check_path_args(tcx, path, NO_TPS | NO_REGIONS);
1126                         ty::mk_self_type(tcx)
1127                     }
1128                     def::DefMod(id) => {
1129                         tcx.sess.span_fatal(ast_ty.span,
1130                             &format!("found module name used as a type: {}",
1131                                     tcx.map.node_to_string(id.node))[]);
1132                     }
1133                     def::DefPrimTy(_) => {
1134                         panic!("DefPrimTy arm missed in previous ast_ty_to_prim_ty call");
1135                     }
1136                     def::DefAssociatedTy(trait_type_id) => {
1137                         let path_str = tcx.map.path_to_string(
1138                             tcx.map.get_parent(trait_type_id.node));
1139                         tcx.sess.span_err(ast_ty.span,
1140                                           &format!("ambiguous associated \
1141                                                    type; specify the type \
1142                                                    using the syntax `<Type \
1143                                                    as {}>::{}`",
1144                                                   path_str,
1145                                                   token::get_ident(
1146                                                       path.segments
1147                                                           .last()
1148                                                           .unwrap()
1149                                                           .identifier)
1150                                                   .get())[]);
1151                         this.tcx().types.err
1152                     }
1153                     def::DefAssociatedPath(provenance, assoc_ident) => {
1154                         associated_path_def_to_ty(this, ast_ty, provenance, assoc_ident.name)
1155                     }
1156                     _ => {
1157                         tcx.sess.span_fatal(ast_ty.span,
1158                                             &format!("found value name used \
1159                                                      as a type: {:?}",
1160                                                     a_def)[]);
1161                     }
1162                 }
1163             }
1164             ast::TyQPath(ref qpath) => {
1165                 qpath_to_ty(this, rscope, ast_ty, &**qpath)
1166             }
1167             ast::TyFixedLengthVec(ref ty, ref e) => {
1168                 match const_eval::eval_const_expr_partial(tcx, &**e) {
1169                     Ok(ref r) => {
1170                         match *r {
1171                             const_eval::const_int(i) =>
1172                                 ty::mk_vec(tcx, ast_ty_to_ty(this, rscope, &**ty),
1173                                            Some(i as uint)),
1174                             const_eval::const_uint(i) =>
1175                                 ty::mk_vec(tcx, ast_ty_to_ty(this, rscope, &**ty),
1176                                            Some(i as uint)),
1177                             _ => {
1178                                 tcx.sess.span_fatal(
1179                                     ast_ty.span, "expected constant expr for array length");
1180                             }
1181                         }
1182                     }
1183                     Err(ref r) => {
1184                         tcx.sess.span_fatal(
1185                             ast_ty.span,
1186                             &format!("expected constant expr for array \
1187                                      length: {}",
1188                                     *r)[]);
1189                     }
1190                 }
1191             }
1192             ast::TyTypeof(ref _e) => {
1193                 tcx.sess.span_bug(ast_ty.span, "typeof is reserved but unimplemented");
1194             }
1195             ast::TyInfer => {
1196                 // TyInfer also appears as the type of arguments or return
1197                 // values in a ExprClosure, or as
1198                 // the type of local variables. Both of these cases are
1199                 // handled specially and will not descend into this routine.
1200                 this.ty_infer(ast_ty.span)
1201             }
1202         }
1203     });
1204
1205     tcx.ast_ty_to_ty_cache.borrow_mut().insert(ast_ty.id, ty::atttce_resolved(typ));
1206     return typ;
1207 }
1208
1209 pub fn ty_of_arg<'tcx>(this: &AstConv<'tcx>,
1210                        rscope: &RegionScope,
1211                        a: &ast::Arg,
1212                        expected_ty: Option<Ty<'tcx>>)
1213                        -> Ty<'tcx>
1214 {
1215     match a.ty.node {
1216         ast::TyInfer if expected_ty.is_some() => expected_ty.unwrap(),
1217         ast::TyInfer => this.ty_infer(a.ty.span),
1218         _ => ast_ty_to_ty(this, rscope, &*a.ty),
1219     }
1220 }
1221
1222 struct SelfInfo<'a, 'tcx> {
1223     untransformed_self_ty: Ty<'tcx>,
1224     explicit_self: &'a ast::ExplicitSelf,
1225 }
1226
1227 pub fn ty_of_method<'tcx>(this: &AstConv<'tcx>,
1228                           unsafety: ast::Unsafety,
1229                           untransformed_self_ty: Ty<'tcx>,
1230                           explicit_self: &ast::ExplicitSelf,
1231                           decl: &ast::FnDecl,
1232                           abi: abi::Abi)
1233                           -> (ty::BareFnTy<'tcx>, ty::ExplicitSelfCategory) {
1234     let self_info = Some(SelfInfo {
1235         untransformed_self_ty: untransformed_self_ty,
1236         explicit_self: explicit_self,
1237     });
1238     let (bare_fn_ty, optional_explicit_self_category) =
1239         ty_of_method_or_bare_fn(this,
1240                                 unsafety,
1241                                 abi,
1242                                 self_info,
1243                                 decl);
1244     (bare_fn_ty, optional_explicit_self_category.unwrap())
1245 }
1246
1247 pub fn ty_of_bare_fn<'tcx>(this: &AstConv<'tcx>, unsafety: ast::Unsafety, abi: abi::Abi,
1248                                               decl: &ast::FnDecl) -> ty::BareFnTy<'tcx> {
1249     let (bare_fn_ty, _) = ty_of_method_or_bare_fn(this, unsafety, abi, None, decl);
1250     bare_fn_ty
1251 }
1252
1253 fn ty_of_method_or_bare_fn<'a, 'tcx>(this: &AstConv<'tcx>,
1254                                      unsafety: ast::Unsafety,
1255                                      abi: abi::Abi,
1256                                      opt_self_info: Option<SelfInfo<'a, 'tcx>>,
1257                                      decl: &ast::FnDecl)
1258                                      -> (ty::BareFnTy<'tcx>, Option<ty::ExplicitSelfCategory>)
1259 {
1260     debug!("ty_of_method_or_bare_fn");
1261
1262     // New region names that appear inside of the arguments of the function
1263     // declaration are bound to that function type.
1264     let rb = rscope::BindingRscope::new();
1265
1266     // `implied_output_region` is the region that will be assumed for any
1267     // region parameters in the return type. In accordance with the rules for
1268     // lifetime elision, we can determine it in two ways. First (determined
1269     // here), if self is by-reference, then the implied output region is the
1270     // region of the self parameter.
1271     let mut explicit_self_category_result = None;
1272     let (self_ty, mut implied_output_region) = match opt_self_info {
1273         None => (None, None),
1274         Some(self_info) => {
1275             // This type comes from an impl or trait; no late-bound
1276             // regions should be present.
1277             assert!(!self_info.untransformed_self_ty.has_escaping_regions());
1278
1279             // Figure out and record the explicit self category.
1280             let explicit_self_category =
1281                 determine_explicit_self_category(this, &rb, &self_info);
1282             explicit_self_category_result = Some(explicit_self_category);
1283             match explicit_self_category {
1284                 ty::StaticExplicitSelfCategory => {
1285                     (None, None)
1286                 }
1287                 ty::ByValueExplicitSelfCategory => {
1288                     (Some(self_info.untransformed_self_ty), None)
1289                 }
1290                 ty::ByReferenceExplicitSelfCategory(region, mutability) => {
1291                     (Some(ty::mk_rptr(this.tcx(),
1292                                       this.tcx().mk_region(region),
1293                                       ty::mt {
1294                                         ty: self_info.untransformed_self_ty,
1295                                         mutbl: mutability
1296                                       })),
1297                      Some(region))
1298                 }
1299                 ty::ByBoxExplicitSelfCategory => {
1300                     (Some(ty::mk_uniq(this.tcx(), self_info.untransformed_self_ty)), None)
1301                 }
1302             }
1303         }
1304     };
1305
1306     // HACK(eddyb) replace the fake self type in the AST with the actual type.
1307     let input_params = if self_ty.is_some() {
1308         decl.inputs.slice_from(1)
1309     } else {
1310         &decl.inputs[]
1311     };
1312     let input_tys = input_params.iter().map(|a| ty_of_arg(this, &rb, a, None));
1313     let input_pats: Vec<String> = input_params.iter()
1314                                               .map(|a| pprust::pat_to_string(&*a.pat))
1315                                               .collect();
1316     let self_and_input_tys: Vec<Ty> =
1317         self_ty.into_iter().chain(input_tys).collect();
1318
1319
1320     // Second, if there was exactly one lifetime (either a substitution or a
1321     // reference) in the arguments, then any anonymous regions in the output
1322     // have that lifetime.
1323     let lifetimes_for_params = if implied_output_region.is_none() {
1324         let input_tys = if self_ty.is_some() {
1325             // Skip the first argument if `self` is present.
1326             self_and_input_tys.slice_from(1)
1327         } else {
1328             self_and_input_tys.slice_from(0)
1329         };
1330
1331         let (ior, lfp) = find_implied_output_region(input_tys, input_pats);
1332         implied_output_region = ior;
1333         lfp
1334     } else {
1335         vec![]
1336     };
1337
1338     let output_ty = match decl.output {
1339         ast::Return(ref output) if output.node == ast::TyInfer =>
1340             ty::FnConverging(this.ty_infer(output.span)),
1341         ast::Return(ref output) =>
1342             ty::FnConverging(convert_ty_with_lifetime_elision(this,
1343                                                               implied_output_region,
1344                                                               lifetimes_for_params,
1345                                                               &**output)),
1346         ast::NoReturn(_) => ty::FnDiverging
1347     };
1348
1349     (ty::BareFnTy {
1350         unsafety: unsafety,
1351         abi: abi,
1352         sig: ty::Binder(ty::FnSig {
1353             inputs: self_and_input_tys,
1354             output: output_ty,
1355             variadic: decl.variadic
1356         }),
1357     }, explicit_self_category_result)
1358 }
1359
1360 fn determine_explicit_self_category<'a, 'tcx>(this: &AstConv<'tcx>,
1361                                               rscope: &RegionScope,
1362                                               self_info: &SelfInfo<'a, 'tcx>)
1363                                               -> ty::ExplicitSelfCategory
1364 {
1365     return match self_info.explicit_self.node {
1366         ast::SelfStatic => ty::StaticExplicitSelfCategory,
1367         ast::SelfValue(_) => ty::ByValueExplicitSelfCategory,
1368         ast::SelfRegion(ref lifetime, mutability, _) => {
1369             let region =
1370                 opt_ast_region_to_region(this,
1371                                          rscope,
1372                                          self_info.explicit_self.span,
1373                                          lifetime);
1374             ty::ByReferenceExplicitSelfCategory(region, mutability)
1375         }
1376         ast::SelfExplicit(ref ast_type, _) => {
1377             let explicit_type = ast_ty_to_ty(this, rscope, &**ast_type);
1378
1379             // We wish to (for now) categorize an explicit self
1380             // declaration like `self: SomeType` into either `self`,
1381             // `&self`, `&mut self`, or `Box<self>`. We do this here
1382             // by some simple pattern matching. A more precise check
1383             // is done later in `check_method_self_type()`.
1384             //
1385             // Examples:
1386             //
1387             // ```
1388             // impl Foo for &T {
1389             //     // Legal declarations:
1390             //     fn method1(self: &&T); // ByReferenceExplicitSelfCategory
1391             //     fn method2(self: &T); // ByValueExplicitSelfCategory
1392             //     fn method3(self: Box<&T>); // ByBoxExplicitSelfCategory
1393             //
1394             //     // Invalid cases will be caught later by `check_method_self_type`:
1395             //     fn method_err1(self: &mut T); // ByReferenceExplicitSelfCategory
1396             // }
1397             // ```
1398             //
1399             // To do the check we just count the number of "modifiers"
1400             // on each type and compare them. If they are the same or
1401             // the impl has more, we call it "by value". Otherwise, we
1402             // look at the outermost modifier on the method decl and
1403             // call it by-ref, by-box as appropriate. For method1, for
1404             // example, the impl type has one modifier, but the method
1405             // type has two, so we end up with
1406             // ByReferenceExplicitSelfCategory.
1407
1408             let impl_modifiers = count_modifiers(self_info.untransformed_self_ty);
1409             let method_modifiers = count_modifiers(explicit_type);
1410
1411             debug!("determine_explicit_self_category(self_info.untransformed_self_ty={} \
1412                    explicit_type={} \
1413                    modifiers=({},{})",
1414                    self_info.untransformed_self_ty.repr(this.tcx()),
1415                    explicit_type.repr(this.tcx()),
1416                    impl_modifiers,
1417                    method_modifiers);
1418
1419             if impl_modifiers >= method_modifiers {
1420                 ty::ByValueExplicitSelfCategory
1421             } else {
1422                 match explicit_type.sty {
1423                     ty::ty_rptr(r, mt) => ty::ByReferenceExplicitSelfCategory(*r, mt.mutbl),
1424                     ty::ty_uniq(_) => ty::ByBoxExplicitSelfCategory,
1425                     _ => ty::ByValueExplicitSelfCategory,
1426                 }
1427             }
1428         }
1429     };
1430
1431     fn count_modifiers(ty: Ty) -> uint {
1432         match ty.sty {
1433             ty::ty_rptr(_, mt) => count_modifiers(mt.ty) + 1,
1434             ty::ty_uniq(t) => count_modifiers(t) + 1,
1435             _ => 0,
1436         }
1437     }
1438 }
1439
1440 pub fn ty_of_closure<'tcx>(
1441     this: &AstConv<'tcx>,
1442     unsafety: ast::Unsafety,
1443     onceness: ast::Onceness,
1444     bounds: ty::ExistentialBounds<'tcx>,
1445     store: ty::TraitStore,
1446     decl: &ast::FnDecl,
1447     abi: abi::Abi,
1448     expected_sig: Option<ty::FnSig<'tcx>>)
1449     -> ty::ClosureTy<'tcx>
1450 {
1451     debug!("ty_of_closure(expected_sig={})",
1452            expected_sig.repr(this.tcx()));
1453
1454     // new region names that appear inside of the fn decl are bound to
1455     // that function type
1456     let rb = rscope::BindingRscope::new();
1457
1458     let input_tys: Vec<_> = decl.inputs.iter().enumerate().map(|(i, a)| {
1459         let expected_arg_ty = expected_sig.as_ref().and_then(|e| {
1460             // no guarantee that the correct number of expected args
1461             // were supplied
1462             if i < e.inputs.len() {
1463                 Some(e.inputs[i])
1464             } else {
1465                 None
1466             }
1467         });
1468         ty_of_arg(this, &rb, a, expected_arg_ty)
1469     }).collect();
1470
1471     let expected_ret_ty = expected_sig.map(|e| e.output);
1472
1473     let output_ty = match decl.output {
1474         ast::Return(ref output) if output.node == ast::TyInfer && expected_ret_ty.is_some() =>
1475             expected_ret_ty.unwrap(),
1476         ast::Return(ref output) if output.node == ast::TyInfer =>
1477             ty::FnConverging(this.ty_infer(output.span)),
1478         ast::Return(ref output) =>
1479             ty::FnConverging(ast_ty_to_ty(this, &rb, &**output)),
1480         ast::NoReturn(_) => ty::FnDiverging
1481     };
1482
1483     debug!("ty_of_closure: input_tys={}", input_tys.repr(this.tcx()));
1484     debug!("ty_of_closure: output_ty={}", output_ty.repr(this.tcx()));
1485
1486     ty::ClosureTy {
1487         unsafety: unsafety,
1488         onceness: onceness,
1489         store: store,
1490         bounds: bounds,
1491         abi: abi,
1492         sig: ty::Binder(ty::FnSig {inputs: input_tys,
1493                                    output: output_ty,
1494                                    variadic: decl.variadic}),
1495     }
1496 }
1497
1498 /// Given an existential type like `Foo+'a+Bar`, this routine converts the `'a` and `Bar` intos an
1499 /// `ExistentialBounds` struct. The `main_trait_refs` argument specifies the `Foo` -- it is absent
1500 /// for closures. Eventually this should all be normalized, I think, so that there is no "main
1501 /// trait ref" and instead we just have a flat list of bounds as the existential type.
1502 pub fn conv_existential_bounds<'tcx>(
1503     this: &AstConv<'tcx>,
1504     rscope: &RegionScope,
1505     span: Span,
1506     principal_trait_ref: Option<ty::PolyTraitRef<'tcx>>, // None for boxed closures
1507     projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>,
1508     ast_bounds: &[ast::TyParamBound])
1509     -> ty::ExistentialBounds<'tcx>
1510 {
1511     let partitioned_bounds =
1512         partition_bounds(this.tcx(), span, ast_bounds);
1513
1514     conv_existential_bounds_from_partitioned_bounds(
1515         this, rscope, span, principal_trait_ref, projection_bounds, partitioned_bounds)
1516 }
1517
1518 fn conv_ty_poly_trait_ref<'tcx>(
1519     this: &AstConv<'tcx>,
1520     rscope: &RegionScope,
1521     span: Span,
1522     ast_bounds: &[ast::TyParamBound])
1523     -> Ty<'tcx>
1524 {
1525     let mut partitioned_bounds = partition_bounds(this.tcx(), span, &ast_bounds[]);
1526
1527     let mut projection_bounds = Vec::new();
1528     let main_trait_bound = if !partitioned_bounds.trait_bounds.is_empty() {
1529         let trait_bound = partitioned_bounds.trait_bounds.remove(0);
1530         Some(instantiate_poly_trait_ref(this,
1531                                         rscope,
1532                                         trait_bound,
1533                                         None,
1534                                         &mut projection_bounds))
1535     } else {
1536         this.tcx().sess.span_err(
1537             span,
1538             "at least one non-builtin trait is required for an object type");
1539         None
1540     };
1541
1542     let bounds =
1543         conv_existential_bounds_from_partitioned_bounds(this,
1544                                                         rscope,
1545                                                         span,
1546                                                         main_trait_bound.clone(),
1547                                                         projection_bounds,
1548                                                         partitioned_bounds);
1549
1550     match main_trait_bound {
1551         None => this.tcx().types.err,
1552         Some(principal) => ty::mk_trait(this.tcx(), principal, bounds)
1553     }
1554 }
1555
1556 pub fn conv_existential_bounds_from_partitioned_bounds<'tcx>(
1557     this: &AstConv<'tcx>,
1558     rscope: &RegionScope,
1559     span: Span,
1560     principal_trait_ref: Option<ty::PolyTraitRef<'tcx>>, // None for boxed closures
1561     mut projection_bounds: Vec<ty::PolyProjectionPredicate<'tcx>>, // Empty for boxed closures
1562     partitioned_bounds: PartitionedBounds)
1563     -> ty::ExistentialBounds<'tcx>
1564 {
1565     let PartitionedBounds { builtin_bounds,
1566                             trait_bounds,
1567                             region_bounds } =
1568         partitioned_bounds;
1569
1570     if !trait_bounds.is_empty() {
1571         let b = &trait_bounds[0];
1572         this.tcx().sess.span_err(
1573             b.trait_ref.path.span,
1574             &format!("only the builtin traits can be used \
1575                      as closure or object bounds")[]);
1576     }
1577
1578     let region_bound = compute_region_bound(this,
1579                                             rscope,
1580                                             span,
1581                                             region_bounds.as_slice(),
1582                                             principal_trait_ref,
1583                                             builtin_bounds);
1584
1585     ty::sort_bounds_list(projection_bounds.as_mut_slice());
1586
1587     ty::ExistentialBounds {
1588         region_bound: region_bound,
1589         builtin_bounds: builtin_bounds,
1590         projection_bounds: projection_bounds,
1591     }
1592 }
1593
1594 /// Given the bounds on a type parameter / existential type, determines what single region bound
1595 /// (if any) we can use to summarize this type. The basic idea is that we will use the bound the
1596 /// user provided, if they provided one, and otherwise search the supertypes of trait bounds for
1597 /// region bounds. It may be that we can derive no bound at all, in which case we return `None`.
1598 fn compute_opt_region_bound<'tcx>(tcx: &ty::ctxt<'tcx>,
1599                                   span: Span,
1600                                   explicit_region_bounds: &[&ast::Lifetime],
1601                                   principal_trait_ref: Option<ty::PolyTraitRef<'tcx>>,
1602                                   builtin_bounds: ty::BuiltinBounds)
1603                                   -> Option<ty::Region>
1604 {
1605     debug!("compute_opt_region_bound(explicit_region_bounds={:?}, \
1606            principal_trait_ref={}, builtin_bounds={})",
1607            explicit_region_bounds,
1608            principal_trait_ref.repr(tcx),
1609            builtin_bounds.repr(tcx));
1610
1611     if explicit_region_bounds.len() > 1 {
1612         tcx.sess.span_err(
1613             explicit_region_bounds[1].span,
1614             format!("only a single explicit lifetime bound is permitted").as_slice());
1615     }
1616
1617     if explicit_region_bounds.len() != 0 {
1618         // Explicitly specified region bound. Use that.
1619         let r = explicit_region_bounds[0];
1620         return Some(ast_region_to_region(tcx, r));
1621     }
1622
1623     // No explicit region bound specified. Therefore, examine trait
1624     // bounds and see if we can derive region bounds from those.
1625     let derived_region_bounds =
1626         ty::object_region_bounds(tcx, principal_trait_ref.as_ref(), builtin_bounds);
1627
1628     // If there are no derived region bounds, then report back that we
1629     // can find no region bound.
1630     if derived_region_bounds.len() == 0 {
1631         return None;
1632     }
1633
1634     // If any of the derived region bounds are 'static, that is always
1635     // the best choice.
1636     if derived_region_bounds.iter().any(|r| ty::ReStatic == *r) {
1637         return Some(ty::ReStatic);
1638     }
1639
1640     // Determine whether there is exactly one unique region in the set
1641     // of derived region bounds. If so, use that. Otherwise, report an
1642     // error.
1643     let r = derived_region_bounds[0];
1644     if derived_region_bounds.slice_from(1).iter().any(|r1| r != *r1) {
1645         tcx.sess.span_err(
1646             span,
1647             &format!("ambiguous lifetime bound, \
1648                      explicit lifetime bound required")[]);
1649     }
1650     return Some(r);
1651 }
1652
1653 /// A version of `compute_opt_region_bound` for use where some region bound is required
1654 /// (existential types, basically). Reports an error if no region bound can be derived and we are
1655 /// in an `rscope` that does not provide a default.
1656 fn compute_region_bound<'tcx>(
1657     this: &AstConv<'tcx>,
1658     rscope: &RegionScope,
1659     span: Span,
1660     region_bounds: &[&ast::Lifetime],
1661     principal_trait_ref: Option<ty::PolyTraitRef<'tcx>>, // None for closures
1662     builtin_bounds: ty::BuiltinBounds)
1663     -> ty::Region
1664 {
1665     match compute_opt_region_bound(this.tcx(), span, region_bounds,
1666                                    principal_trait_ref, builtin_bounds) {
1667         Some(r) => r,
1668         None => {
1669             match rscope.default_region_bound(span) {
1670                 Some(r) => { r }
1671                 None => {
1672                     this.tcx().sess.span_err(
1673                         span,
1674                         &format!("explicit lifetime bound required")[]);
1675                     ty::ReStatic
1676                 }
1677             }
1678         }
1679     }
1680 }
1681
1682 pub struct PartitionedBounds<'a> {
1683     pub builtin_bounds: ty::BuiltinBounds,
1684     pub trait_bounds: Vec<&'a ast::PolyTraitRef>,
1685     pub region_bounds: Vec<&'a ast::Lifetime>,
1686 }
1687
1688 /// Divides a list of bounds from the AST into three groups: builtin bounds (Copy, Sized etc),
1689 /// general trait bounds, and region bounds.
1690 pub fn partition_bounds<'a>(tcx: &ty::ctxt,
1691                             _span: Span,
1692                             ast_bounds: &'a [ast::TyParamBound])
1693                             -> PartitionedBounds<'a>
1694 {
1695     let mut builtin_bounds = ty::empty_builtin_bounds();
1696     let mut region_bounds = Vec::new();
1697     let mut trait_bounds = Vec::new();
1698     let mut trait_def_ids = DefIdMap::new();
1699     for ast_bound in ast_bounds.iter() {
1700         match *ast_bound {
1701             ast::TraitTyParamBound(ref b, ast::TraitBoundModifier::None) => {
1702                 match ::lookup_def_tcx(tcx, b.trait_ref.path.span, b.trait_ref.ref_id) {
1703                     def::DefTrait(trait_did) => {
1704                         match trait_def_ids.get(&trait_did) {
1705                             // Already seen this trait. We forbid
1706                             // duplicates in the list (for some
1707                             // reason).
1708                             Some(span) => {
1709                                 span_err!(
1710                                     tcx.sess, b.trait_ref.path.span, E0127,
1711                                     "trait `{}` already appears in the \
1712                                      list of bounds",
1713                                     b.trait_ref.path.user_string(tcx));
1714                                 tcx.sess.span_note(
1715                                     *span,
1716                                     "previous appearance is here");
1717
1718                                 continue;
1719                             }
1720
1721                             None => { }
1722                         }
1723
1724                         trait_def_ids.insert(trait_did, b.trait_ref.path.span);
1725
1726                         if ty::try_add_builtin_trait(tcx,
1727                                                      trait_did,
1728                                                      &mut builtin_bounds) {
1729                             // FIXME(#20302) -- we should check for things like Copy<T>
1730                             continue; // success
1731                         }
1732                     }
1733                     _ => {
1734                         // Not a trait? that's an error, but it'll get
1735                         // reported later.
1736                     }
1737                 }
1738                 trait_bounds.push(b);
1739             }
1740             ast::TraitTyParamBound(_, ast::TraitBoundModifier::Maybe) => {}
1741             ast::RegionTyParamBound(ref l) => {
1742                 region_bounds.push(l);
1743             }
1744         }
1745     }
1746
1747     PartitionedBounds {
1748         builtin_bounds: builtin_bounds,
1749         trait_bounds: trait_bounds,
1750         region_bounds: region_bounds,
1751     }
1752 }
1753
1754 fn prohibit_projections<'tcx>(tcx: &ty::ctxt<'tcx>,
1755                               bindings: &[ConvertedBinding<'tcx>])
1756 {
1757     for binding in bindings.iter().take(1) {
1758         tcx.sess.span_err(
1759             binding.span,
1760             "associated type bindings are not allowed here");
1761     }
1762 }