src/librustc_typeck/check/wf.rs

   1 // Copyright 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 use astconv::AstConv;
  12 use check::{FnCtxt, Inherited, blank_fn_ctxt, regionck, wfcheck};
  13 use constrained_type_params::{identify_constrained_type_params, Parameter};
  14 use CrateCtxt;
  15 use middle::region;
  16 use middle::subst::{self, TypeSpace, FnSpace, ParamSpace, SelfSpace};
  17 use middle::traits;
  18 use middle::ty::{self, Ty};
  19 use middle::ty_fold::{TypeFolder, TypeFoldable, super_fold_ty};
  20
  21 use std::cell::RefCell;
  22 use std::collections::HashSet;
  23 use syntax::ast;
  24 use syntax::ast_util::local_def;
  25 use syntax::codemap::{DUMMY_SP, Span};
  26 use syntax::parse::token::{special_idents};
  27 use syntax::visit;
  28 use syntax::visit::Visitor;
  29
  30 pub struct CheckTypeWellFormedVisitor<'ccx, 'tcx:'ccx> {
  31     ccx: &'ccx CrateCtxt<'ccx, 'tcx>,
  32     cache: HashSet<Ty<'tcx>>
  33 }
  34
  35 impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
  36     pub fn new(ccx: &'ccx CrateCtxt<'ccx, 'tcx>) -> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
  37         CheckTypeWellFormedVisitor { ccx: ccx, cache: HashSet::new() }
  38     }
  39
  40     fn tcx(&self) -> &ty::ctxt<'tcx> {
  41         self.ccx.tcx
  42     }
  43
  44     /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  45     /// well-formed, meaning that they do not require any constraints not declared in the struct
  46     /// definition itself. For example, this definition would be illegal:
  47     ///
  48     ///     struct Ref<'a, T> { x: &'a T }
  49     ///
  50     /// because the type did not declare that `T:'a`.
  51     ///
  52     /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  53     /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  54     /// the types first.
  55     fn check_item_well_formed(&mut self, item: &ast::Item) {
  56         let ccx = self.ccx;
  57         debug!("check_item_well_formed(it.id={}, it.ident={})",
  58                item.id,
  59                ccx.tcx.item_path_str(local_def(item.id)));
  60
  61         match item.node {
  62             /// Right now we check that every default trait implementation
  63             /// has an implementation of itself. Basically, a case like:
  64             ///
  65             /// `impl Trait for T {}`
  66             ///
  67             /// has a requirement of `T: Trait` which was required for default
  68             /// method implementations. Although this could be improved now that
  69             /// there's a better infrastructure in place for this, it's being left
  70             /// for a follow-up work.
  71             ///
  72             /// Since there's such a requirement, we need to check *just* positive
  73             /// implementations, otherwise things like:
  74             ///
  75             /// impl !Send for T {}
  76             ///
  77             /// won't be allowed unless there's an *explicit* implementation of `Send`
  78             /// for `T`
  79             ast::ItemImpl(_, ast::ImplPolarity::Positive, _, _, _, _) => {
  80                 self.check_impl(item);
  81             }
  82             ast::ItemImpl(_, ast::ImplPolarity::Negative, _, Some(_), _, _) => {
  83                 let trait_ref = ccx.tcx.impl_trait_ref(local_def(item.id)).unwrap();
  84                 ccx.tcx.populate_implementations_for_trait_if_necessary(trait_ref.def_id);
  85                 match ccx.tcx.lang_items.to_builtin_kind(trait_ref.def_id) {
  86                     Some(ty::BoundSend) | Some(ty::BoundSync) => {}
  87                     Some(_) | None => {
  88                         if !ccx.tcx.trait_has_default_impl(trait_ref.def_id) {
  89                             wfcheck::error_192(ccx, item.span);
  90                         }
  91                     }
  92                 }
  93             }
  94             ast::ItemFn(..) => {
  95                 self.check_item_type(item);
  96             }
  97             ast::ItemStatic(..) => {
  98                 self.check_item_type(item);
  99             }
 100             ast::ItemConst(..) => {
 101                 self.check_item_type(item);
 102             }
 103             ast::ItemStruct(ref struct_def, ref ast_generics) => {
 104                 self.check_type_defn(item, |fcx| {
 105                     vec![struct_variant(fcx, &**struct_def)]
 106                 });
 107
 108                 self.check_variances_for_type_defn(item, ast_generics);
 109             }
 110             ast::ItemEnum(ref enum_def, ref ast_generics) => {
 111                 self.check_type_defn(item, |fcx| {
 112                     enum_variants(fcx, enum_def)
 113                 });
 114
 115                 self.check_variances_for_type_defn(item, ast_generics);
 116             }
 117             ast::ItemTrait(_, _, _, ref items) => {
 118                 let trait_predicates =
 119                     ccx.tcx.lookup_predicates(local_def(item.id));
 120                 reject_non_type_param_bounds(ccx.tcx, item.span, &trait_predicates);
 121                 if ccx.tcx.trait_has_default_impl(local_def(item.id)) {
 122                     if !items.is_empty() {
 123                         wfcheck::error_380(ccx, item.span);
 124                     }
 125                 }
 126             }
 127             _ => {}
 128         }
 129     }
 130
 131     fn with_fcx<F>(&mut self, item: &ast::Item, mut f: F) where
 132         F: for<'fcx> FnMut(&mut CheckTypeWellFormedVisitor<'ccx, 'tcx>, &FnCtxt<'fcx, 'tcx>),
 133     {
 134         let ccx = self.ccx;
 135         let item_def_id = local_def(item.id);
 136         let type_scheme = ccx.tcx.lookup_item_type(item_def_id);
 137         let type_predicates = ccx.tcx.lookup_predicates(item_def_id);
 138         reject_non_type_param_bounds(ccx.tcx, item.span, &type_predicates);
 139         let param_env = ccx.tcx.construct_parameter_environment(item.span,
 140                                                                 &type_scheme.generics,
 141                                                                 &type_predicates,
 142                                                                 item.id);
 143         let tables = RefCell::new(ty::Tables::empty());
 144         let inh = Inherited::new(ccx.tcx, &tables, param_env);
 145         let fcx = blank_fn_ctxt(ccx, &inh, ty::FnConverging(type_scheme.ty), item.id);
 146         f(self, &fcx);
 147         fcx.select_all_obligations_or_error();
 148         regionck::regionck_item(&fcx, item.id, item.span, &[]);
 149     }
 150
 151     /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 152     fn check_type_defn<F>(&mut self, item: &ast::Item, mut lookup_fields: F) where
 153         F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
 154     {
 155         self.with_fcx(item, |this, fcx| {
 156             let variants = lookup_fields(fcx);
 157             let mut bounds_checker = BoundsChecker::new(fcx,
 158                                                         item.id,
 159                                                         Some(&mut this.cache));
 160             debug!("check_type_defn at bounds_checker.scope: {:?}", bounds_checker.scope);
 161
 162             for variant in &variants {
 163                 for field in &variant.fields {
 164                     // Regions are checked below.
 165                     bounds_checker.check_traits_in_ty(field.ty, field.span);
 166                 }
 167
 168                 // For DST, all intermediate types must be sized.
 169                 if let Some((_, fields)) = variant.fields.split_last() {
 170                     for field in fields {
 171                         fcx.register_builtin_bound(
 172                             field.ty,
 173                             ty::BoundSized,
 174                             traits::ObligationCause::new(field.span,
 175                                                          fcx.body_id,
 176                                                          traits::FieldSized));
 177                     }
 178                 }
 179             }
 180
 181             let field_tys: Vec<Ty> =
 182                 variants.iter().flat_map(|v| v.fields.iter().map(|f| f.ty)).collect();
 183
 184             for &field_ty in &field_tys {
 185                 fcx.register_wf_obligation(field_ty, item.span, traits::MiscObligation);
 186             }
 187         });
 188     }
 189
 190     fn check_item_type(&mut self,
 191                        item: &ast::Item)
 192     {
 193         self.with_fcx(item, |this, fcx| {
 194             let mut bounds_checker = BoundsChecker::new(fcx,
 195                                                         item.id,
 196                                                         Some(&mut this.cache));
 197             debug!("check_item_type at bounds_checker.scope: {:?}", bounds_checker.scope);
 198
 199             let type_scheme = fcx.tcx().lookup_item_type(local_def(item.id));
 200             let item_ty = fcx.instantiate_type_scheme(item.span,
 201                                                       &fcx.inh
 202                                                           .infcx
 203                                                           .parameter_environment
 204                                                           .free_substs,
 205                                                       &type_scheme.ty);
 206
 207             bounds_checker.check_traits_in_ty(item_ty, item.span);
 208         });
 209     }
 210
 211     fn check_impl(&mut self,
 212                   item: &ast::Item)
 213     {
 214         self.with_fcx(item, |this, fcx| {
 215             let mut bounds_checker = BoundsChecker::new(fcx,
 216                                                         item.id,
 217                                                         Some(&mut this.cache));
 218             debug!("check_impl at bounds_checker.scope: {:?}", bounds_checker.scope);
 219
 220             // Find the impl self type as seen from the "inside" --
 221             // that is, with all type parameters converted from bound
 222             // to free.
 223             let self_ty = fcx.tcx().node_id_to_type(item.id);
 224             let self_ty = fcx.instantiate_type_scheme(item.span,
 225                                                       &fcx.inh
 226                                                           .infcx
 227                                                           .parameter_environment
 228                                                           .free_substs,
 229                                                       &self_ty);
 230
 231             bounds_checker.check_traits_in_ty(self_ty, item.span);
 232
 233             // Similarly, obtain an "inside" reference to the trait
 234             // that the impl implements.
 235             let trait_ref = match fcx.tcx().impl_trait_ref(local_def(item.id)) {
 236                 None => { return; }
 237                 Some(t) => { t }
 238             };
 239
 240             let trait_ref = fcx.instantiate_type_scheme(item.span,
 241                                                         &fcx.inh
 242                                                             .infcx
 243                                                             .parameter_environment
 244                                                             .free_substs,
 245                                                         &trait_ref);
 246
 247             // We are stricter on the trait-ref in an impl than the
 248             // self-type.  In particular, we enforce region
 249             // relationships. The reason for this is that (at least
 250             // presently) "applying" an impl does not require that the
 251             // application site check the well-formedness constraints on the
 252             // trait reference. Instead, this is done at the impl site.
 253             // Arguably this is wrong and we should treat the trait-reference
 254             // the same way as we treat the self-type.
 255             bounds_checker.check_trait_ref(&trait_ref, item.span);
 256
 257             let cause =
 258                 traits::ObligationCause::new(
 259                     item.span,
 260                     fcx.body_id,
 261                     traits::ItemObligation(trait_ref.def_id));
 262
 263             // Find the supertrait bounds. This will add `int:Bar`.
 264             let poly_trait_ref = ty::Binder(trait_ref);
 265             let predicates = fcx.tcx().lookup_super_predicates(poly_trait_ref.def_id());
 266             let predicates = predicates.instantiate_supertrait(fcx.tcx(), &poly_trait_ref);
 267             let predicates = {
 268                 let selcx = &mut traits::SelectionContext::new(fcx.infcx());
 269                 traits::normalize(selcx, cause.clone(), &predicates)
 270             };
 271             for predicate in predicates.value.predicates {
 272                 fcx.register_predicate(traits::Obligation::new(cause.clone(), predicate));
 273             }
 274             for obligation in predicates.obligations {
 275                 fcx.register_predicate(obligation);
 276             }
 277         });
 278     }
 279
 280     fn check_variances_for_type_defn(&self,
 281                                      item: &ast::Item,
 282                                      ast_generics: &ast::Generics)
 283     {
 284         let item_def_id = local_def(item.id);
 285         let ty_predicates = self.tcx().lookup_predicates(item_def_id);
 286         let variances = self.tcx().item_variances(item_def_id);
 287
 288         let mut constrained_parameters: HashSet<_> =
 289             variances.types
 290                      .iter_enumerated()
 291                      .filter(|&(_, _, &variance)| variance != ty::Bivariant)
 292                      .map(|(space, index, _)| self.param_ty(ast_generics, space, index))
 293                      .map(|p| Parameter::Type(p))
 294                      .collect();
 295
 296         identify_constrained_type_params(self.tcx(),
 297                                          ty_predicates.predicates.as_slice(),
 298                                          None,
 299                                          &mut constrained_parameters);
 300
 301         for (space, index, _) in variances.types.iter_enumerated() {
 302             let param_ty = self.param_ty(ast_generics, space, index);
 303             if constrained_parameters.contains(&Parameter::Type(param_ty)) {
 304                 continue;
 305             }
 306             let span = self.ty_param_span(ast_generics, item, space, index);
 307             self.report_bivariance(span, param_ty.name);
 308         }
 309
 310         for (space, index, &variance) in variances.regions.iter_enumerated() {
 311             if variance != ty::Bivariant {
 312                 continue;
 313             }
 314
 315             assert_eq!(space, TypeSpace);
 316             let span = ast_generics.lifetimes[index].lifetime.span;
 317             let name = ast_generics.lifetimes[index].lifetime.name;
 318             self.report_bivariance(span, name);
 319         }
 320     }
 321
 322     fn param_ty(&self,
 323                 ast_generics: &ast::Generics,
 324                 space: ParamSpace,
 325                 index: usize)
 326                 -> ty::ParamTy
 327     {
 328         let name = match space {
 329             TypeSpace => ast_generics.ty_params[index].ident.name,
 330             SelfSpace => special_idents::type_self.name,
 331             FnSpace => self.tcx().sess.bug("Fn space occupied?"),
 332         };
 333
 334         ty::ParamTy { space: space, idx: index as u32, name: name }
 335     }
 336
 337     fn ty_param_span(&self,
 338                      ast_generics: &ast::Generics,
 339                      item: &ast::Item,
 340                      space: ParamSpace,
 341                      index: usize)
 342                      -> Span
 343     {
 344         match space {
 345             TypeSpace => ast_generics.ty_params[index].span,
 346             SelfSpace => item.span,
 347             FnSpace => self.tcx().sess.span_bug(item.span, "Fn space occupied?"),
 348         }
 349     }
 350
 351     fn report_bivariance(&self,
 352                          span: Span,
 353                          param_name: ast::Name)
 354     {
 355         wfcheck::error_392(self.tcx(), span, param_name);
 356
 357         let suggested_marker_id = self.tcx().lang_items.phantom_data();
 358         match suggested_marker_id {
 359             Some(def_id) => {
 360                 self.tcx().sess.fileline_help(
 361                     span,
 362                     &format!("consider removing `{}` or using a marker such as `{}`",
 363                              param_name,
 364                              self.tcx().item_path_str(def_id)));
 365             }
 366             None => {
 367                 // no lang items, no help!
 368             }
 369         }
 370     }
 371 }
 372
 373 // Reject any predicates that do not involve a type parameter.
 374 fn reject_non_type_param_bounds<'tcx>(tcx: &ty::ctxt<'tcx>,
 375                                       span: Span,
 376                                       predicates: &ty::GenericPredicates<'tcx>) {
 377     for predicate in &predicates.predicates {
 378         match predicate {
 379             &ty::Predicate::Trait(ty::Binder(ref tr)) => {
 380                 let found_param = tr.input_types().iter()
 381                                     .flat_map(|ty| ty.walk())
 382                                     .any(is_ty_param);
 383                 if !found_param { report_bound_error(tcx, span, tr.self_ty() )}
 384             }
 385             &ty::Predicate::TypeOutlives(ty::Binder(ty::OutlivesPredicate(ty, _))) => {
 386                 let found_param = ty.walk().any(|t| is_ty_param(t));
 387                 if !found_param { report_bound_error(tcx, span, ty) }
 388             }
 389             _ => {}
 390         };
 391     }
 392
 393     fn report_bound_error<'t>(tcx: &ty::ctxt<'t>,
 394                           span: Span,
 395                           bounded_ty: ty::Ty<'t>) {
 396         span_err!(tcx.sess, span, E0193,
 397             "cannot bound type `{}`, where clause \
 398                 bounds may only be attached to types involving \
 399                 type parameters",
 400                 bounded_ty)
 401     }
 402
 403     fn is_ty_param(ty: ty::Ty) -> bool {
 404         match &ty.sty {
 405             &ty::TyParam(_) => true,
 406             _ => false
 407         }
 408     }
 409 }
 410
 411 fn reject_shadowing_type_parameters<'tcx>(tcx: &ty::ctxt<'tcx>,
 412                                           span: Span,
 413                                           generics: &ty::Generics<'tcx>) {
 414     let impl_params = generics.types.get_slice(subst::TypeSpace).iter()
 415         .map(|tp| tp.name).collect::<HashSet<_>>();
 416
 417     for method_param in generics.types.get_slice(subst::FnSpace) {
 418         if impl_params.contains(&method_param.name) {
 419             wfcheck::error_194(tcx, span, method_param.name);
 420         }
 421     }
 422 }
 423
 424 impl<'ccx, 'tcx, 'v> Visitor<'v> for CheckTypeWellFormedVisitor<'ccx, 'tcx> {
 425     fn visit_item(&mut self, i: &ast::Item) {
 426         self.check_item_well_formed(i);
 427         visit::walk_item(self, i);
 428     }
 429
 430     fn visit_fn(&mut self,
 431                 fk: visit::FnKind<'v>, fd: &'v ast::FnDecl,
 432                 b: &'v ast::Block, span: Span, id: ast::NodeId) {
 433         match fk {
 434             visit::FkFnBlock | visit::FkItemFn(..) => {}
 435             visit::FkMethod(..) => {
 436                 match self.tcx().impl_or_trait_item(local_def(id)) {
 437                     ty::ImplOrTraitItem::MethodTraitItem(ty_method) => {
 438                         reject_shadowing_type_parameters(self.tcx(), span, &ty_method.generics)
 439                     }
 440                     _ => {}
 441                 }
 442             }
 443         }
 444         visit::walk_fn(self, fk, fd, b, span)
 445     }
 446
 447     fn visit_trait_item(&mut self, trait_item: &'v ast::TraitItem) {
 448         if let ast::MethodTraitItem(_, None) = trait_item.node {
 449             match self.tcx().impl_or_trait_item(local_def(trait_item.id)) {
 450                 ty::ImplOrTraitItem::MethodTraitItem(ty_method) => {
 451                     reject_non_type_param_bounds(
 452                         self.tcx(),
 453                         trait_item.span,
 454                         &ty_method.predicates);
 455                     reject_shadowing_type_parameters(
 456                         self.tcx(),
 457                         trait_item.span,
 458                         &ty_method.generics);
 459                 }
 460                 _ => {}
 461             }
 462         }
 463
 464         visit::walk_trait_item(self, trait_item)
 465     }
 466 }
 467
 468 pub struct BoundsChecker<'cx,'tcx:'cx> {
 469     fcx: &'cx FnCtxt<'cx,'tcx>,
 470     span: Span,
 471
 472     // This field is often attached to item impls; it is not clear
 473     // that `CodeExtent` is well-defined for such nodes, so pnkfelix
 474     // has left it as a NodeId rather than porting to CodeExtent.
 475     scope: ast::NodeId,
 476
 477     binding_count: usize,
 478     cache: Option<&'cx mut HashSet<Ty<'tcx>>>,
 479 }
 480
 481 impl<'cx,'tcx> BoundsChecker<'cx,'tcx> {
 482     pub fn new(fcx: &'cx FnCtxt<'cx,'tcx>,
 483                scope: ast::NodeId,
 484                cache: Option<&'cx mut HashSet<Ty<'tcx>>>)
 485                -> BoundsChecker<'cx,'tcx> {
 486         BoundsChecker { fcx: fcx, span: DUMMY_SP, scope: scope,
 487                         cache: cache, binding_count: 0 }
 488     }
 489
 490     /// Given a trait ref like `A : Trait<B>`, where `Trait` is defined as (say):
 491     ///
 492     ///     trait Trait<B:OtherTrait> : Copy { ... }
 493     ///
 494     /// This routine will check that `B : OtherTrait` and `A : Trait<B>`. It will also recursively
 495     /// check that the types `A` and `B` are well-formed.
 496     ///
 497     /// Note that it does not (currently, at least) check that `A : Copy` (that check is delegated
 498     /// to the point where impl `A : Trait<B>` is implemented).
 499     pub fn check_trait_ref(&mut self, trait_ref: &ty::TraitRef<'tcx>, span: Span) {
 500         let trait_predicates = self.fcx.tcx().lookup_predicates(trait_ref.def_id);
 501
 502         let bounds = self.fcx.instantiate_bounds(span,
 503                                                  trait_ref.substs,
 504                                                  &trait_predicates);
 505
 506         self.fcx.add_obligations_for_parameters(
 507             traits::ObligationCause::new(
 508                 span,
 509                 self.fcx.body_id,
 510                 traits::ItemObligation(trait_ref.def_id)),
 511             &bounds);
 512
 513         for &ty in &trait_ref.substs.types {
 514             self.check_traits_in_ty(ty, span);
 515         }
 516     }
 517
 518     fn check_traits_in_ty(&mut self, ty: Ty<'tcx>, span: Span) {
 519         self.span = span;
 520         // When checking types outside of a type def'n, we ignore
 521         // region obligations. See discussion below in fold_ty().
 522         self.binding_count += 1;
 523         ty.fold_with(self);
 524         self.binding_count -= 1;
 525     }
 526 }
 527
 528 impl<'cx,'tcx> TypeFolder<'tcx> for BoundsChecker<'cx,'tcx> {
 529     fn tcx(&self) -> &ty::ctxt<'tcx> {
 530         self.fcx.tcx()
 531     }
 532
 533     fn fold_binder<T>(&mut self, binder: &ty::Binder<T>) -> ty::Binder<T>
 534         where T : TypeFoldable<'tcx>
 535     {
 536         self.binding_count += 1;
 537         let value = self.fcx.tcx().liberate_late_bound_regions(
 538             region::DestructionScopeData::new(self.scope),
 539             binder);
 540         debug!("BoundsChecker::fold_binder: late-bound regions replaced: {:?} at scope: {:?}",
 541                value, self.scope);
 542         let value = value.fold_with(self);
 543         self.binding_count -= 1;
 544         ty::Binder(value)
 545     }
 546
 547     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
 548         debug!("BoundsChecker t={:?}",
 549                t);
 550
 551         match self.cache {
 552             Some(ref mut cache) => {
 553                 if !cache.insert(t) {
 554                     // Already checked this type! Don't check again.
 555                     debug!("cached");
 556                     return t;
 557                 }
 558             }
 559             None => { }
 560         }
 561
 562         match t.sty{
 563             ty::TyStruct(def, substs) |
 564             ty::TyEnum(def, substs) => {
 565                 let type_predicates = def.predicates(self.fcx.tcx());
 566                 let bounds = self.fcx.instantiate_bounds(self.span, substs,
 567                                                          &type_predicates);
 568
 569                 if self.binding_count == 0 {
 570                     self.fcx.add_obligations_for_parameters(
 571                         traits::ObligationCause::new(self.span,
 572                                                      self.fcx.body_id,
 573                                                      traits::ItemObligation(def.did)),
 574                         &bounds);
 575                 } else {
 576                     // There are two circumstances in which we ignore
 577                     // region obligations.
 578                     //
 579                     // The first is when we are inside of a closure
 580                     // type. This is because in that case the region
 581                     // obligations for the parameter types are things
 582                     // that the closure body gets to assume and the
 583                     // caller must prove at the time of call. In other
 584                     // words, if there is a type like `<'a, 'b> | &'a
 585                     // &'b int |`, it is well-formed, and caller will
 586                     // have to show that `'b : 'a` at the time of
 587                     // call.
 588                     //
 589                     // The second is when we are checking for
 590                     // well-formedness outside of a type def'n or fn
 591                     // body. This is for a similar reason: in general,
 592                     // we only do WF checking for regions in the
 593                     // result of expressions and type definitions, so
 594                     // to as allow for implicit where clauses.
 595                     //
 596                     // (I believe we should do the same for traits, but
 597                     // that will require an RFC. -nmatsakis)
 598                     let bounds = filter_to_trait_obligations(bounds);
 599                     self.fcx.add_obligations_for_parameters(
 600                         traits::ObligationCause::new(self.span,
 601                                                      self.fcx.body_id,
 602                                                      traits::ItemObligation(def.did)),
 603                         &bounds);
 604                 }
 605
 606                 self.fold_substs(substs);
 607             }
 608             _ => {
 609                 super_fold_ty(self, t);
 610             }
 611         }
 612
 613         t // we're not folding to produce a new type, so just return `t` here
 614     }
 615 }
 616
 617 ///////////////////////////////////////////////////////////////////////////
 618 // ADT
 619
 620 struct AdtVariant<'tcx> {
 621     fields: Vec<AdtField<'tcx>>,
 622 }
 623
 624 struct AdtField<'tcx> {
 625     ty: Ty<'tcx>,
 626     span: Span,
 627 }
 628
 629 fn struct_variant<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 630                             struct_def: &ast::StructDef)
 631                             -> AdtVariant<'tcx> {
 632     let fields =
 633         struct_def.fields
 634         .iter()
 635         .map(|field| {
 636             let field_ty = fcx.tcx().node_id_to_type(field.node.id);
 637             let field_ty = fcx.instantiate_type_scheme(field.span,
 638                                                        &fcx.inh
 639                                                            .infcx
 640                                                            .parameter_environment
 641                                                            .free_substs,
 642                                                        &field_ty);
 643             AdtField { ty: field_ty, span: field.span }
 644         })
 645         .collect();
 646     AdtVariant { fields: fields }
 647 }
 648
 649 fn enum_variants<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 650                            enum_def: &ast::EnumDef)
 651                            -> Vec<AdtVariant<'tcx>> {
 652     enum_def.variants.iter()
 653         .map(|variant| {
 654             match variant.node.kind {
 655                 ast::TupleVariantKind(ref args) if !args.is_empty() => {
 656                     let ctor_ty = fcx.tcx().node_id_to_type(variant.node.id);
 657
 658                     // the regions in the argument types come from the
 659                     // enum def'n, and hence will all be early bound
 660                     let arg_tys = fcx.tcx().no_late_bound_regions(&ctor_ty.fn_args()).unwrap();
 661                     AdtVariant {
 662                         fields: args.iter().enumerate().map(|(index, arg)| {
 663                             let arg_ty = arg_tys[index];
 664                             let arg_ty =
 665                                 fcx.instantiate_type_scheme(variant.span,
 666                                                             &fcx.inh
 667                                                                 .infcx
 668                                                                 .parameter_environment
 669                                                                 .free_substs,
 670                                                             &arg_ty);
 671                             AdtField {
 672                                 ty: arg_ty,
 673                                 span: arg.ty.span
 674                             }
 675                         }).collect()
 676                     }
 677                 }
 678                 ast::TupleVariantKind(_) => {
 679                     AdtVariant {
 680                         fields: Vec::new()
 681                     }
 682                 }
 683                 ast::StructVariantKind(ref struct_def) => {
 684                     struct_variant(fcx, &**struct_def)
 685                 }
 686             }
 687         })
 688         .collect()
 689 }
 690
 691 fn filter_to_trait_obligations<'tcx>(bounds: ty::InstantiatedPredicates<'tcx>)
 692                                      -> ty::InstantiatedPredicates<'tcx>
 693 {
 694     let mut result = ty::InstantiatedPredicates::empty();
 695     for (space, _, predicate) in bounds.predicates.iter_enumerated() {
 696         match *predicate {
 697             ty::Predicate::Trait(..) |
 698             ty::Predicate::Projection(..) => {
 699                 result.predicates.push(space, predicate.clone())
 700             }
 701             ty::Predicate::WellFormed(..) |
 702             ty::Predicate::ObjectSafe(..) |
 703             ty::Predicate::Equate(..) |
 704             ty::Predicate::TypeOutlives(..) |
 705             ty::Predicate::RegionOutlives(..) => {
 706             }
 707         }
 708     }
 709     result
 710 }