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