src/librustc_typeck/check/wfcheck.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::ExplicitSelf;
  12 use check::{Inherited, FnCtxt};
  13 use constrained_type_params::{identify_constrained_type_params, Parameter};
  14
  15 use hir::def_id::DefId;
  16 use rustc::traits::{self, ObligationCauseCode};
  17 use rustc::ty::{self, Ty, TyCtxt};
  18 use rustc::util::nodemap::{FxHashSet, FxHashMap};
  19 use rustc::middle::lang_items;
  20
  21 use syntax::ast;
  22 use syntax_pos::Span;
  23 use errors::DiagnosticBuilder;
  24
  25 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
  26 use rustc::hir;
  27
  28 pub struct CheckTypeWellFormedVisitor<'a, 'tcx:'a> {
  29     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  30     code: ObligationCauseCode<'tcx>,
  31 }
  32
  33 /// Helper type of a temporary returned by .for_item(...).
  34 /// Necessary because we can't write the following bound:
  35 /// F: for<'b, 'tcx> where 'gcx: 'tcx FnOnce(FnCtxt<'b, 'gcx, 'tcx>).
  36 struct CheckWfFcxBuilder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
  37     inherited: super::InheritedBuilder<'a, 'gcx, 'tcx>,
  38     code: ObligationCauseCode<'gcx>,
  39     id: ast::NodeId,
  40     span: Span
  41 }
  42
  43 impl<'a, 'gcx, 'tcx> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
  44     fn with_fcx<F>(&'tcx mut self, f: F) where
  45         F: for<'b> FnOnce(&FnCtxt<'b, 'gcx, 'tcx>,
  46                           &mut CheckTypeWellFormedVisitor<'b, 'gcx>) -> Vec<Ty<'tcx>>
  47     {
  48         let code = self.code.clone();
  49         let id = self.id;
  50         let span = self.span;
  51         self.inherited.enter(|inh| {
  52             let fcx = FnCtxt::new(&inh, id);
  53             let wf_tys = f(&fcx, &mut CheckTypeWellFormedVisitor {
  54                 tcx: fcx.tcx.global_tcx(),
  55                 code: code
  56             });
  57             fcx.select_all_obligations_or_error();
  58             fcx.regionck_item(id, span, &wf_tys);
  59         });
  60     }
  61 }
  62
  63 impl<'a, 'gcx> CheckTypeWellFormedVisitor<'a, 'gcx> {
  64     pub fn new(tcx: TyCtxt<'a, 'gcx, 'gcx>)
  65                -> CheckTypeWellFormedVisitor<'a, 'gcx> {
  66         CheckTypeWellFormedVisitor {
  67             tcx: tcx,
  68             code: ObligationCauseCode::MiscObligation
  69         }
  70     }
  71
  72     /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  73     /// well-formed, meaning that they do not require any constraints not declared in the struct
  74     /// definition itself. For example, this definition would be illegal:
  75     ///
  76     ///     struct Ref<'a, T> { x: &'a T }
  77     ///
  78     /// because the type did not declare that `T:'a`.
  79     ///
  80     /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  81     /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  82     /// the types first.
  83     fn check_item_well_formed(&mut self, item: &hir::Item) {
  84         let tcx = self.tcx;
  85         debug!("check_item_well_formed(it.id={}, it.name={})",
  86                item.id,
  87                tcx.item_path_str(tcx.hir.local_def_id(item.id)));
  88
  89         match item.node {
  90             /// Right now we check that every default trait implementation
  91             /// has an implementation of itself. Basically, a case like:
  92             ///
  93             /// `impl Trait for T {}`
  94             ///
  95             /// has a requirement of `T: Trait` which was required for default
  96             /// method implementations. Although this could be improved now that
  97             /// there's a better infrastructure in place for this, it's being left
  98             /// for a follow-up work.
  99             ///
 100             /// Since there's such a requirement, we need to check *just* positive
 101             /// implementations, otherwise things like:
 102             ///
 103             /// impl !Send for T {}
 104             ///
 105             /// won't be allowed unless there's an *explicit* implementation of `Send`
 106             /// for `T`
 107             hir::ItemImpl(_, hir::ImplPolarity::Positive, _, _,
 108                           ref trait_ref, ref self_ty, _) => {
 109                 self.check_impl(item, self_ty, trait_ref);
 110             }
 111             hir::ItemImpl(_, hir::ImplPolarity::Negative, _, _, Some(_), ..) => {
 112                 // FIXME(#27579) what amount of WF checking do we need for neg impls?
 113
 114                 let trait_ref = tcx.impl_trait_ref(tcx.hir.local_def_id(item.id)).unwrap();
 115                 if !tcx.trait_has_default_impl(trait_ref.def_id) {
 116                     error_192(tcx, item.span);
 117                 }
 118             }
 119             hir::ItemFn(..) => {
 120                 self.check_item_fn(item);
 121             }
 122             hir::ItemStatic(..) => {
 123                 self.check_item_type(item);
 124             }
 125             hir::ItemConst(..) => {
 126                 self.check_item_type(item);
 127             }
 128             hir::ItemStruct(ref struct_def, ref ast_generics) => {
 129                 self.check_type_defn(item, false, |fcx| {
 130                     vec![fcx.struct_variant(struct_def)]
 131                 });
 132
 133                 self.check_variances_for_type_defn(item, ast_generics);
 134             }
 135             hir::ItemUnion(ref struct_def, ref ast_generics) => {
 136                 self.check_type_defn(item, true, |fcx| {
 137                     vec![fcx.struct_variant(struct_def)]
 138                 });
 139
 140                 self.check_variances_for_type_defn(item, ast_generics);
 141             }
 142             hir::ItemEnum(ref enum_def, ref ast_generics) => {
 143                 self.check_type_defn(item, true, |fcx| {
 144                     fcx.enum_variants(enum_def)
 145                 });
 146
 147                 self.check_variances_for_type_defn(item, ast_generics);
 148             }
 149             hir::ItemTrait(..) => {
 150                 self.check_trait(item);
 151             }
 152             _ => {}
 153         }
 154     }
 155
 156     fn check_associated_item(&mut self,
 157                              item_id: ast::NodeId,
 158                              span: Span,
 159                              sig_if_method: Option<&hir::MethodSig>) {
 160         let code = self.code.clone();
 161         self.for_id(item_id, span).with_fcx(|fcx, this| {
 162             let free_substs = &fcx.parameter_environment.free_substs;
 163
 164             let item = fcx.tcx.associated_item(fcx.tcx.hir.local_def_id(item_id));
 165
 166             let (mut implied_bounds, self_ty) = match item.container {
 167                 ty::TraitContainer(_) => (vec![], fcx.tcx.mk_self_type()),
 168                 ty::ImplContainer(def_id) => (fcx.impl_implied_bounds(def_id, span),
 169                                               fcx.tcx.type_of(def_id))
 170             };
 171
 172             match item.kind {
 173                 ty::AssociatedKind::Const => {
 174                     let ty = fcx.tcx.type_of(item.def_id);
 175                     let ty = fcx.instantiate_type_scheme(span, free_substs, &ty);
 176                     fcx.register_wf_obligation(ty, span, code.clone());
 177                 }
 178                 ty::AssociatedKind::Method => {
 179                     reject_shadowing_type_parameters(fcx.tcx, item.def_id);
 180                     let method_ty = fcx.tcx.type_of(item.def_id);
 181                     let method_ty = fcx.instantiate_type_scheme(span, free_substs, &method_ty);
 182                     let predicates = fcx.instantiate_bounds(span, item.def_id, free_substs);
 183                     let sig = method_ty.fn_sig();
 184                     this.check_fn_or_method(fcx, span, sig, &predicates,
 185                                             item.def_id, &mut implied_bounds);
 186                     let sig_if_method = sig_if_method.expect("bad signature for method");
 187                     this.check_method_receiver(fcx, sig_if_method, &item, self_ty);
 188                 }
 189                 ty::AssociatedKind::Type => {
 190                     if item.defaultness.has_value() {
 191                         let ty = fcx.tcx.type_of(item.def_id);
 192                         let ty = fcx.instantiate_type_scheme(span, free_substs, &ty);
 193                         fcx.register_wf_obligation(ty, span, code.clone());
 194                     }
 195                 }
 196             }
 197
 198             implied_bounds
 199         })
 200     }
 201
 202     fn for_item<'tcx>(&self, item: &hir::Item)
 203                       -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 204         self.for_id(item.id, item.span)
 205     }
 206
 207     fn for_id<'tcx>(&self, id: ast::NodeId, span: Span)
 208                     -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 209         CheckWfFcxBuilder {
 210             inherited: Inherited::build(self.tcx, self.tcx.hir.local_def_id(id)),
 211             code: self.code.clone(),
 212             id: id,
 213             span: span
 214         }
 215     }
 216
 217     /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 218     fn check_type_defn<F>(&mut self, item: &hir::Item, all_sized: bool, mut lookup_fields: F)
 219         where F: for<'fcx, 'tcx> FnMut(&FnCtxt<'fcx, 'gcx, 'tcx>) -> Vec<AdtVariant<'tcx>>
 220     {
 221         self.for_item(item).with_fcx(|fcx, this| {
 222             let variants = lookup_fields(fcx);
 223
 224             for variant in &variants {
 225                 // For DST, all intermediate types must be sized.
 226                 let unsized_len = if all_sized || variant.fields.is_empty() { 0 } else { 1 };
 227                 for field in &variant.fields[..variant.fields.len() - unsized_len] {
 228                     fcx.register_bound(
 229                         field.ty,
 230                         fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 231                         traits::ObligationCause::new(field.span,
 232                                                      fcx.body_id,
 233                                                      traits::FieldSized));
 234                 }
 235
 236                 // All field types must be well-formed.
 237                 for field in &variant.fields {
 238                     fcx.register_wf_obligation(field.ty, field.span, this.code.clone())
 239                 }
 240             }
 241
 242             let free_substs = &fcx.parameter_environment.free_substs;
 243             let def_id = fcx.tcx.hir.local_def_id(item.id);
 244             let predicates = fcx.instantiate_bounds(item.span, def_id, free_substs);
 245             this.check_where_clauses(fcx, item.span, &predicates);
 246
 247             vec![] // no implied bounds in a struct def'n
 248         });
 249     }
 250
 251     fn check_auto_trait(&mut self, trait_def_id: DefId, span: Span) {
 252         // We want to ensure:
 253         //
 254         // 1) that there are no items contained within
 255         // the trait defintion
 256         //
 257         // 2) that the definition doesn't violate the no-super trait rule
 258         // for auto traits.
 259         //
 260         // 3) that the trait definition does not have any type parameters
 261
 262         let predicates = self.tcx.predicates_of(trait_def_id);
 263
 264         // We must exclude the Self : Trait predicate contained by all
 265         // traits.
 266         let has_predicates =
 267             predicates.predicates.iter().any(|predicate| {
 268                 match predicate {
 269                     &ty::Predicate::Trait(ref poly_trait_ref) => {
 270                         let self_ty = poly_trait_ref.0.self_ty();
 271                         !(self_ty.is_self() && poly_trait_ref.def_id() == trait_def_id)
 272                     },
 273                     _ => true,
 274                 }
 275             });
 276
 277         let has_ty_params = self.tcx.generics_of(trait_def_id).types.len() > 1;
 278
 279         // We use an if-else here, since the generics will also trigger
 280         // an extraneous error message when we find predicates like
 281         // `T : Sized` for a trait like: `trait Magic<T>`.
 282         //
 283         // We also put the check on the number of items here,
 284         // as it seems confusing to report an error about
 285         // extraneous predicates created by things like
 286         // an associated type inside the trait.
 287         let mut err = None;
 288         if !self.tcx.associated_item_def_ids(trait_def_id).is_empty() {
 289             error_380(self.tcx, span);
 290         } else if has_ty_params {
 291             err = Some(struct_span_err!(self.tcx.sess, span, E0567,
 292                 "traits with auto impls (`e.g. impl \
 293                     Trait for ..`) can not have type parameters"));
 294         } else if has_predicates {
 295             err = Some(struct_span_err!(self.tcx.sess, span, E0568,
 296                 "traits with auto impls (`e.g. impl \
 297                     Trait for ..`) cannot have predicates"));
 298         }
 299
 300         // Finally if either of the above conditions apply we should add a note
 301         // indicating that this error is the result of a recent soundness fix.
 302         match err {
 303             None => {},
 304             Some(mut e) => {
 305                 e.note("the new auto trait rules are the result of a \
 306                           recent soundness fix; see #29859 for more details");
 307                 e.emit();
 308             }
 309         }
 310     }
 311
 312     fn check_trait(&mut self, item: &hir::Item) {
 313         let trait_def_id = self.tcx.hir.local_def_id(item.id);
 314
 315         if self.tcx.trait_has_default_impl(trait_def_id) {
 316             self.check_auto_trait(trait_def_id, item.span);
 317         }
 318
 319         self.for_item(item).with_fcx(|fcx, this| {
 320             let free_substs = &fcx.parameter_environment.free_substs;
 321             let predicates = fcx.instantiate_bounds(item.span, trait_def_id, free_substs);
 322             this.check_where_clauses(fcx, item.span, &predicates);
 323             vec![]
 324         });
 325     }
 326
 327     fn check_item_fn(&mut self, item: &hir::Item) {
 328         self.for_item(item).with_fcx(|fcx, this| {
 329             let free_substs = &fcx.parameter_environment.free_substs;
 330             let def_id = fcx.tcx.hir.local_def_id(item.id);
 331             let ty = fcx.tcx.type_of(def_id);
 332             let item_ty = fcx.instantiate_type_scheme(item.span, free_substs, &ty);
 333             let sig = item_ty.fn_sig();
 334
 335             let predicates = fcx.instantiate_bounds(item.span, def_id, free_substs);
 336
 337             let mut implied_bounds = vec![];
 338             this.check_fn_or_method(fcx, item.span, sig, &predicates,
 339                                     def_id, &mut implied_bounds);
 340             implied_bounds
 341         })
 342     }
 343
 344     fn check_item_type(&mut self,
 345                        item: &hir::Item)
 346     {
 347         debug!("check_item_type: {:?}", item);
 348
 349         self.for_item(item).with_fcx(|fcx, this| {
 350             let ty = fcx.tcx.type_of(fcx.tcx.hir.local_def_id(item.id));
 351             let item_ty = fcx.instantiate_type_scheme(item.span,
 352                                                       &fcx.parameter_environment
 353                                                           .free_substs,
 354                                                       &ty);
 355
 356             fcx.register_wf_obligation(item_ty, item.span, this.code.clone());
 357
 358             vec![] // no implied bounds in a const etc
 359         });
 360     }
 361
 362     fn check_impl(&mut self,
 363                   item: &hir::Item,
 364                   ast_self_ty: &hir::Ty,
 365                   ast_trait_ref: &Option<hir::TraitRef>)
 366     {
 367         debug!("check_impl: {:?}", item);
 368
 369         self.for_item(item).with_fcx(|fcx, this| {
 370             let free_substs = &fcx.parameter_environment.free_substs;
 371             let item_def_id = fcx.tcx.hir.local_def_id(item.id);
 372
 373             match *ast_trait_ref {
 374                 Some(ref ast_trait_ref) => {
 375                     let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 376                     let trait_ref =
 377                         fcx.instantiate_type_scheme(
 378                             ast_trait_ref.path.span, free_substs, &trait_ref);
 379                     let obligations =
 380                         ty::wf::trait_obligations(fcx,
 381                                                   fcx.body_id,
 382                                                   &trait_ref,
 383                                                   ast_trait_ref.path.span);
 384                     for obligation in obligations {
 385                         fcx.register_predicate(obligation);
 386                     }
 387                 }
 388                 None => {
 389                     let self_ty = fcx.tcx.type_of(item_def_id);
 390                     let self_ty = fcx.instantiate_type_scheme(item.span, free_substs, &self_ty);
 391                     fcx.register_wf_obligation(self_ty, ast_self_ty.span, this.code.clone());
 392                 }
 393             }
 394
 395             let predicates = fcx.instantiate_bounds(item.span, item_def_id, free_substs);
 396             this.check_where_clauses(fcx, item.span, &predicates);
 397
 398             fcx.impl_implied_bounds(item_def_id, item.span)
 399         });
 400     }
 401
 402     fn check_where_clauses<'fcx, 'tcx>(&mut self,
 403                                        fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 404                                        span: Span,
 405                                        predicates: &ty::InstantiatedPredicates<'tcx>)
 406     {
 407         let obligations =
 408             predicates.predicates
 409                       .iter()
 410                       .flat_map(|p| ty::wf::predicate_obligations(fcx,
 411                                                                   fcx.body_id,
 412                                                                   p,
 413                                                                   span));
 414
 415         for obligation in obligations {
 416             fcx.register_predicate(obligation);
 417         }
 418     }
 419
 420     fn check_fn_or_method<'fcx, 'tcx>(&mut self,
 421                                       fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 422                                       span: Span,
 423                                       sig: ty::PolyFnSig<'tcx>,
 424                                       predicates: &ty::InstantiatedPredicates<'tcx>,
 425                                       def_id: DefId,
 426                                       implied_bounds: &mut Vec<Ty<'tcx>>)
 427     {
 428         let free_substs = &fcx.parameter_environment.free_substs;
 429         let sig = fcx.instantiate_type_scheme(span, free_substs, &sig);
 430         let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 431
 432         for input_ty in sig.inputs() {
 433             fcx.register_wf_obligation(&input_ty, span, self.code.clone());
 434         }
 435         implied_bounds.extend(sig.inputs());
 436
 437         fcx.register_wf_obligation(sig.output(), span, self.code.clone());
 438
 439         // FIXME(#25759) return types should not be implied bounds
 440         implied_bounds.push(sig.output());
 441
 442         self.check_where_clauses(fcx, span, predicates);
 443     }
 444
 445     fn check_method_receiver<'fcx, 'tcx>(&mut self,
 446                                          fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 447                                          method_sig: &hir::MethodSig,
 448                                          method: &ty::AssociatedItem,
 449                                          self_ty: ty::Ty<'tcx>)
 450     {
 451         // check that the type of the method's receiver matches the
 452         // method's first parameter.
 453         debug!("check_method_receiver({:?}, self_ty={:?})",
 454                method, self_ty);
 455
 456         if !method.method_has_self_argument {
 457             return;
 458         }
 459
 460         let span = method_sig.decl.inputs[0].span;
 461
 462         let free_substs = &fcx.parameter_environment.free_substs;
 463         let method_ty = fcx.tcx.type_of(method.def_id);
 464         let fty = fcx.instantiate_type_scheme(span, free_substs, &method_ty);
 465         let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &fty.fn_sig());
 466
 467         debug!("check_method_receiver: sig={:?}", sig);
 468
 469         let self_arg_ty = sig.inputs()[0];
 470         let rcvr_ty = match ExplicitSelf::determine(self_ty, self_arg_ty) {
 471             ExplicitSelf::ByValue => self_ty,
 472             ExplicitSelf::ByReference(region, mutbl) => {
 473                 fcx.tcx.mk_ref(region, ty::TypeAndMut {
 474                     ty: self_ty,
 475                     mutbl: mutbl
 476                 })
 477             }
 478             ExplicitSelf::ByBox => fcx.tcx.mk_box(self_ty)
 479         };
 480         let rcvr_ty = fcx.instantiate_type_scheme(span, free_substs, &rcvr_ty);
 481         let rcvr_ty = fcx.tcx.liberate_late_bound_regions(method.def_id,
 482                                                           &ty::Binder(rcvr_ty));
 483
 484         debug!("check_method_receiver: receiver ty = {:?}", rcvr_ty);
 485
 486         let cause = fcx.cause(span, ObligationCauseCode::MethodReceiver);
 487         if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, rcvr_ty, self_arg_ty) {
 488             err.emit();
 489         }
 490     }
 491
 492     fn check_variances_for_type_defn(&self,
 493                                      item: &hir::Item,
 494                                      ast_generics: &hir::Generics)
 495     {
 496         let item_def_id = self.tcx.hir.local_def_id(item.id);
 497         let ty = self.tcx.type_of(item_def_id);
 498         if self.tcx.has_error_field(ty) {
 499             return;
 500         }
 501
 502         let ty_predicates = self.tcx.predicates_of(item_def_id);
 503         assert_eq!(ty_predicates.parent, None);
 504         let variances = self.tcx.variances_of(item_def_id);
 505
 506         let mut constrained_parameters: FxHashSet<_> =
 507             variances.iter().enumerate()
 508                      .filter(|&(_, &variance)| variance != ty::Bivariant)
 509                      .map(|(index, _)| Parameter(index as u32))
 510                      .collect();
 511
 512         identify_constrained_type_params(ty_predicates.predicates.as_slice(),
 513                                          None,
 514                                          &mut constrained_parameters);
 515
 516         for (index, _) in variances.iter().enumerate() {
 517             if constrained_parameters.contains(&Parameter(index as u32)) {
 518                 continue;
 519             }
 520
 521             let (span, name) = if index < ast_generics.lifetimes.len() {
 522                 (ast_generics.lifetimes[index].lifetime.span,
 523                  ast_generics.lifetimes[index].lifetime.name)
 524             } else {
 525                 let index = index - ast_generics.lifetimes.len();
 526                 (ast_generics.ty_params[index].span,
 527                  ast_generics.ty_params[index].name)
 528             };
 529             self.report_bivariance(span, name);
 530         }
 531     }
 532
 533     fn report_bivariance(&self,
 534                          span: Span,
 535                          param_name: ast::Name)
 536     {
 537         let mut err = error_392(self.tcx, span, param_name);
 538
 539         let suggested_marker_id = self.tcx.lang_items.phantom_data();
 540         match suggested_marker_id {
 541             Some(def_id) => {
 542                 err.help(
 543                     &format!("consider removing `{}` or using a marker such as `{}`",
 544                              param_name,
 545                              self.tcx.item_path_str(def_id)));
 546             }
 547             None => {
 548                 // no lang items, no help!
 549             }
 550         }
 551         err.emit();
 552     }
 553 }
 554
 555 fn reject_shadowing_type_parameters(tcx: TyCtxt, def_id: DefId) {
 556     let generics = tcx.generics_of(def_id);
 557     let parent = tcx.generics_of(generics.parent.unwrap());
 558     let impl_params: FxHashMap<_, _> = parent.types
 559                                        .iter()
 560                                        .map(|tp| (tp.name, tp.def_id))
 561                                        .collect();
 562
 563     for method_param in &generics.types {
 564         if impl_params.contains_key(&method_param.name) {
 565             // Tighten up the span to focus on only the shadowing type
 566             let type_span = tcx.def_span(method_param.def_id);
 567
 568             // The expectation here is that the original trait declaration is
 569             // local so it should be okay to just unwrap everything.
 570             let trait_def_id = impl_params[&method_param.name];
 571             let trait_decl_span = tcx.def_span(trait_def_id);
 572             error_194(tcx, type_span, trait_decl_span, method_param.name);
 573         }
 574     }
 575 }
 576
 577 impl<'a, 'tcx, 'v> Visitor<'v> for CheckTypeWellFormedVisitor<'a, 'tcx> {
 578     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
 579         NestedVisitorMap::None
 580     }
 581
 582     fn visit_item(&mut self, i: &hir::Item) {
 583         debug!("visit_item: {:?}", i);
 584         self.check_item_well_formed(i);
 585         intravisit::walk_item(self, i);
 586     }
 587
 588     fn visit_trait_item(&mut self, trait_item: &'v hir::TraitItem) {
 589         debug!("visit_trait_item: {:?}", trait_item);
 590         let method_sig = match trait_item.node {
 591             hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 592             _ => None
 593         };
 594         self.check_associated_item(trait_item.id, trait_item.span, method_sig);
 595         intravisit::walk_trait_item(self, trait_item)
 596     }
 597
 598     fn visit_impl_item(&mut self, impl_item: &'v hir::ImplItem) {
 599         debug!("visit_impl_item: {:?}", impl_item);
 600         let method_sig = match impl_item.node {
 601             hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 602             _ => None
 603         };
 604         self.check_associated_item(impl_item.id, impl_item.span, method_sig);
 605         intravisit::walk_impl_item(self, impl_item)
 606     }
 607 }
 608
 609 ///////////////////////////////////////////////////////////////////////////
 610 // ADT
 611
 612 struct AdtVariant<'tcx> {
 613     fields: Vec<AdtField<'tcx>>,
 614 }
 615
 616 struct AdtField<'tcx> {
 617     ty: Ty<'tcx>,
 618     span: Span,
 619 }
 620
 621 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 622     fn struct_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
 623         let fields =
 624             struct_def.fields().iter()
 625             .map(|field| {
 626                 let field_ty = self.tcx.type_of(self.tcx.hir.local_def_id(field.id));
 627                 let field_ty = self.instantiate_type_scheme(field.span,
 628                                                             &self.parameter_environment
 629                                                                  .free_substs,
 630                                                             &field_ty);
 631                 AdtField { ty: field_ty, span: field.span }
 632             })
 633             .collect();
 634         AdtVariant { fields: fields }
 635     }
 636
 637     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
 638         enum_def.variants.iter()
 639             .map(|variant| self.struct_variant(&variant.node.data))
 640             .collect()
 641     }
 642
 643     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
 644         let free_substs = &self.parameter_environment.free_substs;
 645         match self.tcx.impl_trait_ref(impl_def_id) {
 646             Some(ref trait_ref) => {
 647                 // Trait impl: take implied bounds from all types that
 648                 // appear in the trait reference.
 649                 let trait_ref = self.instantiate_type_scheme(span, free_substs, trait_ref);
 650                 trait_ref.substs.types().collect()
 651             }
 652
 653             None => {
 654                 // Inherent impl: take implied bounds from the self type.
 655                 let self_ty = self.tcx.type_of(impl_def_id);
 656                 let self_ty = self.instantiate_type_scheme(span, free_substs, &self_ty);
 657                 vec![self_ty]
 658             }
 659         }
 660     }
 661 }
 662
 663 fn error_192(tcx: TyCtxt, span: Span) {
 664     span_err!(tcx.sess, span, E0192,
 665               "negative impls are only allowed for traits with \
 666                default impls (e.g., `Send` and `Sync`)")
 667 }
 668
 669 fn error_380(tcx: TyCtxt, span: Span) {
 670     span_err!(tcx.sess, span, E0380,
 671               "traits with default impls (`e.g. impl \
 672                Trait for ..`) must have no methods or associated items")
 673 }
 674
 675 fn error_392<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, span: Span, param_name: ast::Name)
 676                        -> DiagnosticBuilder<'tcx> {
 677     let mut err = struct_span_err!(tcx.sess, span, E0392,
 678                   "parameter `{}` is never used", param_name);
 679     err.span_label(span, "unused type parameter");
 680     err
 681 }
 682
 683 fn error_194(tcx: TyCtxt, span: Span, trait_decl_span: Span, name: ast::Name) {
 684     struct_span_err!(tcx.sess, span, E0194,
 685               "type parameter `{}` shadows another type parameter of the same name",
 686               name)
 687         .span_label(span, "shadows another type parameter")
 688         .span_label(trait_decl_span, format!("first `{}` declared here", name))
 689         .emit();
 690 }