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: 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: 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 method_ty = fcx.tcx.type_of(item.def_id);
 181                     let method_ty = fcx.normalize_associated_types_in(span, &method_ty);
 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                     let sig = method_ty.fn_sig();
 186                     this.check_fn_or_method(fcx, span, sig, &predicates,
 187                                             item.def_id, &mut implied_bounds);
 188                     let sig_if_method = sig_if_method.expect("bad signature for method");
 189                     this.check_method_receiver(fcx, sig_if_method, &item, self_ty);
 190                 }
 191                 ty::AssociatedKind::Type => {
 192                     if item.defaultness.has_value() {
 193                         let ty = fcx.tcx.type_of(item.def_id);
 194                         let ty = fcx.normalize_associated_types_in(span, &ty);
 195                         fcx.register_wf_obligation(ty, span, code.clone());
 196                     }
 197                 }
 198             }
 199
 200             implied_bounds
 201         })
 202     }
 203
 204     fn for_item<'tcx>(&self, item: &hir::Item)
 205                       -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 206         self.for_id(item.id, item.span)
 207     }
 208
 209     fn for_id<'tcx>(&self, id: ast::NodeId, span: Span)
 210                     -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 211         let def_id = self.tcx.hir.local_def_id(id);
 212         CheckWfFcxBuilder {
 213             inherited: Inherited::build(self.tcx, def_id),
 214             code: self.code.clone(),
 215             id: id,
 216             span: span,
 217             param_env: self.tcx.param_env(def_id),
 218         }
 219     }
 220
 221     /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 222     fn check_type_defn<F>(&mut self, item: &hir::Item, all_sized: bool, mut lookup_fields: F)
 223         where F: for<'fcx, 'tcx> FnMut(&FnCtxt<'fcx, 'gcx, 'tcx>) -> Vec<AdtVariant<'tcx>>
 224     {
 225         self.for_item(item).with_fcx(|fcx, this| {
 226             let variants = lookup_fields(fcx);
 227
 228             for variant in &variants {
 229                 // For DST, all intermediate types must be sized.
 230                 let unsized_len = if all_sized || variant.fields.is_empty() { 0 } else { 1 };
 231                 for field in &variant.fields[..variant.fields.len() - unsized_len] {
 232                     fcx.register_bound(
 233                         field.ty,
 234                         fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 235                         traits::ObligationCause::new(field.span,
 236                                                      fcx.body_id,
 237                                                      traits::FieldSized));
 238                 }
 239
 240                 // All field types must be well-formed.
 241                 for field in &variant.fields {
 242                     fcx.register_wf_obligation(field.ty, field.span, this.code.clone())
 243                 }
 244             }
 245
 246             let def_id = fcx.tcx.hir.local_def_id(item.id);
 247             let predicates = fcx.tcx.predicates_of(def_id).instantiate_identity(fcx.tcx);
 248             let predicates = fcx.normalize_associated_types_in(item.span, &predicates);
 249             this.check_where_clauses(fcx, item.span, &predicates);
 250
 251             vec![] // no implied bounds in a struct def'n
 252         });
 253     }
 254
 255     fn check_auto_trait(&mut self, trait_def_id: DefId, span: Span) {
 256         // We want to ensure:
 257         //
 258         // 1) that there are no items contained within
 259         // the trait defintion
 260         //
 261         // 2) that the definition doesn't violate the no-super trait rule
 262         // for auto traits.
 263         //
 264         // 3) that the trait definition does not have any type parameters
 265
 266         let predicates = self.tcx.predicates_of(trait_def_id);
 267
 268         // We must exclude the Self : Trait predicate contained by all
 269         // traits.
 270         let has_predicates =
 271             predicates.predicates.iter().any(|predicate| {
 272                 match predicate {
 273                     &ty::Predicate::Trait(ref poly_trait_ref) => {
 274                         let self_ty = poly_trait_ref.0.self_ty();
 275                         !(self_ty.is_self() && poly_trait_ref.def_id() == trait_def_id)
 276                     },
 277                     _ => true,
 278                 }
 279             });
 280
 281         let has_ty_params = self.tcx.generics_of(trait_def_id).types.len() > 1;
 282
 283         // We use an if-else here, since the generics will also trigger
 284         // an extraneous error message when we find predicates like
 285         // `T : Sized` for a trait like: `trait Magic<T>`.
 286         //
 287         // We also put the check on the number of items here,
 288         // as it seems confusing to report an error about
 289         // extraneous predicates created by things like
 290         // an associated type inside the trait.
 291         let mut err = None;
 292         if !self.tcx.associated_item_def_ids(trait_def_id).is_empty() {
 293             error_380(self.tcx, span);
 294         } else if has_ty_params {
 295             err = Some(struct_span_err!(self.tcx.sess, span, E0567,
 296                 "traits with auto impls (`e.g. impl \
 297                     Trait for ..`) can not have type parameters"));
 298         } else if has_predicates {
 299             err = Some(struct_span_err!(self.tcx.sess, span, E0568,
 300                 "traits with auto impls (`e.g. impl \
 301                     Trait for ..`) cannot have predicates"));
 302         }
 303
 304         // Finally if either of the above conditions apply we should add a note
 305         // indicating that this error is the result of a recent soundness fix.
 306         match err {
 307             None => {},
 308             Some(mut e) => {
 309                 e.note("the new auto trait rules are the result of a \
 310                           recent soundness fix; see #29859 for more details");
 311                 e.emit();
 312             }
 313         }
 314     }
 315
 316     fn check_trait(&mut self, item: &hir::Item) {
 317         let trait_def_id = self.tcx.hir.local_def_id(item.id);
 318
 319         if self.tcx.trait_has_default_impl(trait_def_id) {
 320             self.check_auto_trait(trait_def_id, item.span);
 321         }
 322
 323         self.for_item(item).with_fcx(|fcx, this| {
 324             let predicates = fcx.tcx.predicates_of(trait_def_id).instantiate_identity(fcx.tcx);
 325             let predicates = fcx.normalize_associated_types_in(item.span, &predicates);
 326             this.check_where_clauses(fcx, item.span, &predicates);
 327             vec![]
 328         });
 329     }
 330
 331     fn check_item_fn(&mut self, item: &hir::Item) {
 332         self.for_item(item).with_fcx(|fcx, this| {
 333             let def_id = fcx.tcx.hir.local_def_id(item.id);
 334             let ty = fcx.tcx.type_of(def_id);
 335             let item_ty = fcx.normalize_associated_types_in(item.span, &ty);
 336             let sig = item_ty.fn_sig();
 337
 338             let predicates = fcx.tcx.predicates_of(def_id).instantiate_identity(fcx.tcx);
 339             let predicates = fcx.normalize_associated_types_in(item.span, &predicates);
 340
 341             let mut implied_bounds = vec![];
 342             this.check_fn_or_method(fcx, item.span, sig, &predicates,
 343                                     def_id, &mut implied_bounds);
 344             implied_bounds
 345         })
 346     }
 347
 348     fn check_item_type(&mut self,
 349                        item: &hir::Item)
 350     {
 351         debug!("check_item_type: {:?}", item);
 352
 353         self.for_item(item).with_fcx(|fcx, this| {
 354             let ty = fcx.tcx.type_of(fcx.tcx.hir.local_def_id(item.id));
 355             let item_ty = fcx.normalize_associated_types_in(item.span, &ty);
 356
 357             fcx.register_wf_obligation(item_ty, item.span, this.code.clone());
 358
 359             vec![] // no implied bounds in a const etc
 360         });
 361     }
 362
 363     fn check_impl(&mut self,
 364                   item: &hir::Item,
 365                   ast_self_ty: &hir::Ty,
 366                   ast_trait_ref: &Option<hir::TraitRef>)
 367     {
 368         debug!("check_impl: {:?}", item);
 369
 370         self.for_item(item).with_fcx(|fcx, this| {
 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.normalize_associated_types_in(
 378                             ast_trait_ref.path.span, &trait_ref);
 379                     let obligations =
 380                         ty::wf::trait_obligations(fcx,
 381                                                   fcx.param_env,
 382                                                   fcx.body_id,
 383                                                   &trait_ref,
 384                                                   ast_trait_ref.path.span);
 385                     for obligation in obligations {
 386                         fcx.register_predicate(obligation);
 387                     }
 388                 }
 389                 None => {
 390                     let self_ty = fcx.tcx.type_of(item_def_id);
 391                     let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 392                     fcx.register_wf_obligation(self_ty, ast_self_ty.span, this.code.clone());
 393                 }
 394             }
 395
 396             let predicates = fcx.tcx.predicates_of(item_def_id).instantiate_identity(fcx.tcx);
 397             let predicates = fcx.normalize_associated_types_in(item.span, &predicates);
 398             this.check_where_clauses(fcx, item.span, &predicates);
 399
 400             fcx.impl_implied_bounds(item_def_id, item.span)
 401         });
 402     }
 403
 404     fn check_where_clauses<'fcx, 'tcx>(&mut self,
 405                                        fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 406                                        span: Span,
 407                                        predicates: &ty::InstantiatedPredicates<'tcx>)
 408     {
 409         let obligations =
 410             predicates.predicates
 411                       .iter()
 412                       .flat_map(|p| ty::wf::predicate_obligations(fcx,
 413                                                                   fcx.param_env,
 414                                                                   fcx.body_id,
 415                                                                   p,
 416                                                                   span));
 417
 418         for obligation in obligations {
 419             fcx.register_predicate(obligation);
 420         }
 421     }
 422
 423     fn check_fn_or_method<'fcx, 'tcx>(&mut self,
 424                                       fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 425                                       span: Span,
 426                                       sig: ty::PolyFnSig<'tcx>,
 427                                       predicates: &ty::InstantiatedPredicates<'tcx>,
 428                                       def_id: DefId,
 429                                       implied_bounds: &mut Vec<Ty<'tcx>>)
 430     {
 431         let sig = fcx.normalize_associated_types_in(span, &sig);
 432         let sig = fcx.liberate_late_bound_regions(def_id, &sig);
 433
 434         for input_ty in sig.inputs() {
 435             fcx.register_wf_obligation(&input_ty, span, self.code.clone());
 436         }
 437         implied_bounds.extend(sig.inputs());
 438
 439         fcx.register_wf_obligation(sig.output(), span, self.code.clone());
 440
 441         // FIXME(#25759) return types should not be implied bounds
 442         implied_bounds.push(sig.output());
 443
 444         self.check_where_clauses(fcx, span, predicates);
 445     }
 446
 447     fn check_method_receiver<'fcx, 'tcx>(&mut self,
 448                                          fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 449                                          method_sig: &hir::MethodSig,
 450                                          method: &ty::AssociatedItem,
 451                                          self_ty: ty::Ty<'tcx>)
 452     {
 453         // check that the type of the method's receiver matches the
 454         // method's first parameter.
 455         debug!("check_method_receiver({:?}, self_ty={:?})",
 456                method, self_ty);
 457
 458         if !method.method_has_self_argument {
 459             return;
 460         }
 461
 462         let span = method_sig.decl.inputs[0].span;
 463
 464         let method_ty = fcx.tcx.type_of(method.def_id);
 465         let fty = fcx.normalize_associated_types_in(span, &method_ty);
 466         let sig = fcx.liberate_late_bound_regions(method.def_id, &fty.fn_sig());
 467
 468         debug!("check_method_receiver: sig={:?}", sig);
 469
 470         let self_arg_ty = sig.inputs()[0];
 471         let rcvr_ty = match ExplicitSelf::determine(self_ty, self_arg_ty) {
 472             ExplicitSelf::ByValue => self_ty,
 473             ExplicitSelf::ByReference(region, mutbl) => {
 474                 fcx.tcx.mk_ref(region, ty::TypeAndMut {
 475                     ty: self_ty,
 476                     mutbl: mutbl
 477                 })
 478             }
 479             ExplicitSelf::ByBox => fcx.tcx.mk_box(self_ty)
 480         };
 481         let rcvr_ty = fcx.normalize_associated_types_in(span, &rcvr_ty);
 482         let rcvr_ty = fcx.liberate_late_bound_regions(method.def_id,
 483                                                       &ty::Binder(rcvr_ty));
 484
 485         debug!("check_method_receiver: receiver ty = {:?}", rcvr_ty);
 486
 487         let cause = fcx.cause(span, ObligationCauseCode::MethodReceiver);
 488         if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, rcvr_ty, self_arg_ty) {
 489             err.emit();
 490         }
 491     }
 492
 493     fn check_variances_for_type_defn(&self,
 494                                      item: &hir::Item,
 495                                      ast_generics: &hir::Generics)
 496     {
 497         let item_def_id = self.tcx.hir.local_def_id(item.id);
 498         let ty = self.tcx.type_of(item_def_id);
 499         if self.tcx.has_error_field(ty) {
 500             return;
 501         }
 502
 503         let ty_predicates = self.tcx.predicates_of(item_def_id);
 504         assert_eq!(ty_predicates.parent, None);
 505         let variances = self.tcx.variances_of(item_def_id);
 506
 507         let mut constrained_parameters: FxHashSet<_> =
 508             variances.iter().enumerate()
 509                      .filter(|&(_, &variance)| variance != ty::Bivariant)
 510                      .map(|(index, _)| Parameter(index as u32))
 511                      .collect();
 512
 513         identify_constrained_type_params(ty_predicates.predicates.as_slice(),
 514                                          None,
 515                                          &mut constrained_parameters);
 516
 517         for (index, _) in variances.iter().enumerate() {
 518             if constrained_parameters.contains(&Parameter(index as u32)) {
 519                 continue;
 520             }
 521
 522             let (span, name) = if index < ast_generics.lifetimes.len() {
 523                 (ast_generics.lifetimes[index].lifetime.span,
 524                  ast_generics.lifetimes[index].lifetime.name)
 525             } else {
 526                 let index = index - ast_generics.lifetimes.len();
 527                 (ast_generics.ty_params[index].span,
 528                  ast_generics.ty_params[index].name)
 529             };
 530             self.report_bivariance(span, name);
 531         }
 532     }
 533
 534     fn report_bivariance(&self,
 535                          span: Span,
 536                          param_name: ast::Name)
 537     {
 538         let mut err = error_392(self.tcx, span, param_name);
 539
 540         let suggested_marker_id = self.tcx.lang_items.phantom_data();
 541         match suggested_marker_id {
 542             Some(def_id) => {
 543                 err.help(
 544                     &format!("consider removing `{}` or using a marker such as `{}`",
 545                              param_name,
 546                              self.tcx.item_path_str(def_id)));
 547             }
 548             None => {
 549                 // no lang items, no help!
 550             }
 551         }
 552         err.emit();
 553     }
 554 }
 555
 556 fn reject_shadowing_type_parameters(tcx: TyCtxt, def_id: DefId) {
 557     let generics = tcx.generics_of(def_id);
 558     let parent = tcx.generics_of(generics.parent.unwrap());
 559     let impl_params: FxHashMap<_, _> = parent.types
 560                                        .iter()
 561                                        .map(|tp| (tp.name, tp.def_id))
 562                                        .collect();
 563
 564     for method_param in &generics.types {
 565         if impl_params.contains_key(&method_param.name) {
 566             // Tighten up the span to focus on only the shadowing type
 567             let type_span = tcx.def_span(method_param.def_id);
 568
 569             // The expectation here is that the original trait declaration is
 570             // local so it should be okay to just unwrap everything.
 571             let trait_def_id = impl_params[&method_param.name];
 572             let trait_decl_span = tcx.def_span(trait_def_id);
 573             error_194(tcx, type_span, trait_decl_span, method_param.name);
 574         }
 575     }
 576 }
 577
 578 impl<'a, 'tcx, 'v> Visitor<'v> for CheckTypeWellFormedVisitor<'a, 'tcx> {
 579     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
 580         NestedVisitorMap::None
 581     }
 582
 583     fn visit_item(&mut self, i: &hir::Item) {
 584         debug!("visit_item: {:?}", i);
 585         self.check_item_well_formed(i);
 586         intravisit::walk_item(self, i);
 587     }
 588
 589     fn visit_trait_item(&mut self, trait_item: &'v hir::TraitItem) {
 590         debug!("visit_trait_item: {:?}", trait_item);
 591         let method_sig = match trait_item.node {
 592             hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 593             _ => None
 594         };
 595         self.check_associated_item(trait_item.id, trait_item.span, method_sig);
 596         intravisit::walk_trait_item(self, trait_item)
 597     }
 598
 599     fn visit_impl_item(&mut self, impl_item: &'v hir::ImplItem) {
 600         debug!("visit_impl_item: {:?}", impl_item);
 601         let method_sig = match impl_item.node {
 602             hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 603             _ => None
 604         };
 605         self.check_associated_item(impl_item.id, impl_item.span, method_sig);
 606         intravisit::walk_impl_item(self, impl_item)
 607     }
 608 }
 609
 610 ///////////////////////////////////////////////////////////////////////////
 611 // ADT
 612
 613 struct AdtVariant<'tcx> {
 614     fields: Vec<AdtField<'tcx>>,
 615 }
 616
 617 struct AdtField<'tcx> {
 618     ty: Ty<'tcx>,
 619     span: Span,
 620 }
 621
 622 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 623     fn struct_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
 624         let fields =
 625             struct_def.fields().iter()
 626             .map(|field| {
 627                 let field_ty = self.tcx.type_of(self.tcx.hir.local_def_id(field.id));
 628                 let field_ty = self.normalize_associated_types_in(field.span,
 629                                                                   &field_ty);
 630                 AdtField { ty: field_ty, span: field.span }
 631             })
 632             .collect();
 633         AdtVariant { fields: fields }
 634     }
 635
 636     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
 637         enum_def.variants.iter()
 638             .map(|variant| self.struct_variant(&variant.node.data))
 639             .collect()
 640     }
 641
 642     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
 643         match self.tcx.impl_trait_ref(impl_def_id) {
 644             Some(ref trait_ref) => {
 645                 // Trait impl: take implied bounds from all types that
 646                 // appear in the trait reference.
 647                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
 648                 trait_ref.substs.types().collect()
 649             }
 650
 651             None => {
 652                 // Inherent impl: take implied bounds from the self type.
 653                 let self_ty = self.tcx.type_of(impl_def_id);
 654                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
 655                 vec![self_ty]
 656             }
 657         }
 658     }
 659 }
 660
 661 fn error_192(tcx: TyCtxt, span: Span) {
 662     span_err!(tcx.sess, span, E0192,
 663               "negative impls are only allowed for traits with \
 664                default impls (e.g., `Send` and `Sync`)")
 665 }
 666
 667 fn error_380(tcx: TyCtxt, span: Span) {
 668     span_err!(tcx.sess, span, E0380,
 669               "traits with default impls (`e.g. impl \
 670                Trait for ..`) must have no methods or associated items")
 671 }
 672
 673 fn error_392<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, span: Span, param_name: ast::Name)
 674                        -> DiagnosticBuilder<'tcx> {
 675     let mut err = struct_span_err!(tcx.sess, span, E0392,
 676                   "parameter `{}` is never used", param_name);
 677     err.span_label(span, "unused type parameter");
 678     err
 679 }
 680
 681 fn error_194(tcx: TyCtxt, span: Span, trait_decl_span: Span, name: ast::Name) {
 682     struct_span_err!(tcx.sess, span, E0194,
 683               "type parameter `{}` shadows another type parameter of the same name",
 684               name)
 685         .span_label(span, "shadows another type parameter")
 686         .span_label(trait_decl_span, format!("first `{}` declared here", name))
 687         .emit();
 688 }