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 middle::region::{CodeExtent};
  17 use rustc::traits::{self, ObligationCauseCode};
  18 use rustc::ty::{self, Ty, TyCtxt};
  19 use rustc::util::nodemap::{FxHashSet, FxHashMap};
  20 use rustc::middle::lang_items;
  21
  22 use syntax::ast;
  23 use syntax_pos::Span;
  24 use errors::DiagnosticBuilder;
  25
  26 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
  27 use rustc::hir;
  28
  29 pub struct CheckTypeWellFormedVisitor<'a, 'tcx:'a> {
  30     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  31     code: ObligationCauseCode<'tcx>,
  32 }
  33
  34 /// Helper type of a temporary returned by .for_item(...).
  35 /// Necessary because we can't write the following bound:
  36 /// F: for<'b, 'tcx> where 'gcx: 'tcx FnOnce(FnCtxt<'b, 'gcx, 'tcx>).
  37 struct CheckWfFcxBuilder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
  38     inherited: super::InheritedBuilder<'a, 'gcx, 'tcx>,
  39     code: ObligationCauseCode<'gcx>,
  40     id: ast::NodeId,
  41     span: Span
  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         self.inherited.enter(|inh| {
  53             let fcx = FnCtxt::new(&inh, id);
  54             let wf_tys = f(&fcx, &mut CheckTypeWellFormedVisitor {
  55                 tcx: fcx.tcx.global_tcx(),
  56                 code: code
  57             });
  58             fcx.select_all_obligations_or_error();
  59             fcx.regionck_item(id, span, &wf_tys);
  60         });
  61     }
  62 }
  63
  64 impl<'a, 'gcx> CheckTypeWellFormedVisitor<'a, 'gcx> {
  65     pub fn new(tcx: TyCtxt<'a, 'gcx, 'gcx>)
  66                -> CheckTypeWellFormedVisitor<'a, 'gcx> {
  67         CheckTypeWellFormedVisitor {
  68             tcx: tcx,
  69             code: ObligationCauseCode::MiscObligation
  70         }
  71     }
  72
  73     /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  74     /// well-formed, meaning that they do not require any constraints not declared in the struct
  75     /// definition itself. For example, this definition would be illegal:
  76     ///
  77     ///     struct Ref<'a, T> { x: &'a T }
  78     ///
  79     /// because the type did not declare that `T:'a`.
  80     ///
  81     /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  82     /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  83     /// the types first.
  84     fn check_item_well_formed(&mut self, item: &hir::Item) {
  85         let tcx = self.tcx;
  86         debug!("check_item_well_formed(it.id={}, it.name={})",
  87                item.id,
  88                tcx.item_path_str(tcx.hir.local_def_id(item.id)));
  89
  90         match item.node {
  91             /// Right now we check that every default trait implementation
  92             /// has an implementation of itself. Basically, a case like:
  93             ///
  94             /// `impl Trait for T {}`
  95             ///
  96             /// has a requirement of `T: Trait` which was required for default
  97             /// method implementations. Although this could be improved now that
  98             /// there's a better infrastructure in place for this, it's being left
  99             /// for a follow-up work.
 100             ///
 101             /// Since there's such a requirement, we need to check *just* positive
 102             /// implementations, otherwise things like:
 103             ///
 104             /// impl !Send for T {}
 105             ///
 106             /// won't be allowed unless there's an *explicit* implementation of `Send`
 107             /// for `T`
 108             hir::ItemImpl(_, hir::ImplPolarity::Positive, _, _,
 109                           ref trait_ref, ref self_ty, _) => {
 110                 self.check_impl(item, self_ty, trait_ref);
 111             }
 112             hir::ItemImpl(_, hir::ImplPolarity::Negative, _, _, Some(_), ..) => {
 113                 // FIXME(#27579) what amount of WF checking do we need for neg impls?
 114
 115                 let trait_ref = tcx.impl_trait_ref(tcx.hir.local_def_id(item.id)).unwrap();
 116                 if !tcx.trait_has_default_impl(trait_ref.def_id) {
 117                     error_192(tcx, item.span);
 118                 }
 119             }
 120             hir::ItemFn(.., body_id) => {
 121                 self.check_item_fn(item, body_id);
 122             }
 123             hir::ItemStatic(..) => {
 124                 self.check_item_type(item);
 125             }
 126             hir::ItemConst(..) => {
 127                 self.check_item_type(item);
 128             }
 129             hir::ItemStruct(ref struct_def, ref ast_generics) => {
 130                 self.check_type_defn(item, false, |fcx| {
 131                     vec![fcx.struct_variant(struct_def)]
 132                 });
 133
 134                 self.check_variances_for_type_defn(item, ast_generics);
 135             }
 136             hir::ItemUnion(ref struct_def, ref ast_generics) => {
 137                 self.check_type_defn(item, true, |fcx| {
 138                     vec![fcx.struct_variant(struct_def)]
 139                 });
 140
 141                 self.check_variances_for_type_defn(item, ast_generics);
 142             }
 143             hir::ItemEnum(ref enum_def, ref ast_generics) => {
 144                 self.check_type_defn(item, true, |fcx| {
 145                     fcx.enum_variants(enum_def)
 146                 });
 147
 148                 self.check_variances_for_type_defn(item, ast_generics);
 149             }
 150             hir::ItemTrait(..) => {
 151                 self.check_trait(item);
 152             }
 153             _ => {}
 154         }
 155     }
 156
 157     fn check_associated_item(&mut self,
 158                              item_id: ast::NodeId,
 159                              span: Span,
 160                              sig_if_method: Option<&hir::MethodSig>) {
 161         let code = self.code.clone();
 162         self.for_id(item_id, span).with_fcx(|fcx, this| {
 163             let free_substs = &fcx.parameter_environment.free_substs;
 164             let free_id_outlive = fcx.parameter_environment.free_id_outlive;
 165
 166             let item = fcx.tcx.associated_item(fcx.tcx.hir.local_def_id(item_id));
 167
 168             let (mut implied_bounds, self_ty) = match item.container {
 169                 ty::TraitContainer(_) => (vec![], fcx.tcx.mk_self_type()),
 170                 ty::ImplContainer(def_id) => (fcx.impl_implied_bounds(def_id, span),
 171                                               fcx.tcx.type_of(def_id))
 172             };
 173
 174             match item.kind {
 175                 ty::AssociatedKind::Const => {
 176                     let ty = fcx.tcx.type_of(item.def_id);
 177                     let ty = fcx.instantiate_type_scheme(span, free_substs, &ty);
 178                     fcx.register_wf_obligation(ty, span, code.clone());
 179                 }
 180                 ty::AssociatedKind::Method => {
 181                     reject_shadowing_type_parameters(fcx.tcx, item.def_id);
 182                     let method_ty = fcx.tcx.type_of(item.def_id);
 183                     let method_ty = fcx.instantiate_type_scheme(span, free_substs, &method_ty);
 184                     let predicates = fcx.instantiate_bounds(span, item.def_id, free_substs);
 185                     let sig = method_ty.fn_sig();
 186                     this.check_fn_or_method(fcx, span, sig, &predicates,
 187                                             free_id_outlive, &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,
 190                                                free_id_outlive, self_ty);
 191                 }
 192                 ty::AssociatedKind::Type => {
 193                     if item.defaultness.has_value() {
 194                         let ty = fcx.tcx.type_of(item.def_id);
 195                         let ty = fcx.instantiate_type_scheme(span, free_substs, &ty);
 196                         fcx.register_wf_obligation(ty, span, code.clone());
 197                     }
 198                 }
 199             }
 200
 201             implied_bounds
 202         })
 203     }
 204
 205     fn for_item<'tcx>(&self, item: &hir::Item)
 206                       -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 207         self.for_id(item.id, item.span)
 208     }
 209
 210     fn for_id<'tcx>(&self, id: ast::NodeId, span: Span)
 211                     -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 212         CheckWfFcxBuilder {
 213             inherited: Inherited::build(self.tcx, id),
 214             code: self.code.clone(),
 215             id: id,
 216             span: span
 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));
 237                 }
 238
 239                 // All field types must be well-formed.
 240                 for field in &variant.fields {
 241                     fcx.register_wf_obligation(field.ty, field.span, this.code.clone())
 242                 }
 243             }
 244
 245             let free_substs = &fcx.parameter_environment.free_substs;
 246             let def_id = fcx.tcx.hir.local_def_id(item.id);
 247             let predicates = fcx.instantiate_bounds(item.span, def_id, free_substs);
 248             this.check_where_clauses(fcx, item.span, &predicates);
 249
 250             vec![] // no implied bounds in a struct def'n
 251         });
 252     }
 253
 254     fn check_auto_trait(&mut self, trait_def_id: DefId, span: Span) {
 255         // We want to ensure:
 256         //
 257         // 1) that there are no items contained within
 258         // the trait defintion
 259         //
 260         // 2) that the definition doesn't violate the no-super trait rule
 261         // for auto traits.
 262         //
 263         // 3) that the trait definition does not have any type parameters
 264
 265         let predicates = self.tcx.predicates_of(trait_def_id);
 266
 267         // We must exclude the Self : Trait predicate contained by all
 268         // traits.
 269         let has_predicates =
 270             predicates.predicates.iter().any(|predicate| {
 271                 match predicate {
 272                     &ty::Predicate::Trait(ref poly_trait_ref) => {
 273                         let self_ty = poly_trait_ref.0.self_ty();
 274                         !(self_ty.is_self() && poly_trait_ref.def_id() == trait_def_id)
 275                     },
 276                     _ => true,
 277                 }
 278             });
 279
 280         let has_ty_params = self.tcx.generics_of(trait_def_id).types.len() > 1;
 281
 282         // We use an if-else here, since the generics will also trigger
 283         // an extraneous error message when we find predicates like
 284         // `T : Sized` for a trait like: `trait Magic<T>`.
 285         //
 286         // We also put the check on the number of items here,
 287         // as it seems confusing to report an error about
 288         // extraneous predicates created by things like
 289         // an associated type inside the trait.
 290         let mut err = None;
 291         if !self.tcx.associated_item_def_ids(trait_def_id).is_empty() {
 292             error_380(self.tcx, span);
 293         } else if has_ty_params {
 294             err = Some(struct_span_err!(self.tcx.sess, span, E0567,
 295                 "traits with auto impls (`e.g. impl \
 296                     Trait for ..`) can not have type parameters"));
 297         } else if has_predicates {
 298             err = Some(struct_span_err!(self.tcx.sess, span, E0568,
 299                 "traits with auto impls (`e.g. impl \
 300                     Trait for ..`) cannot have predicates"));
 301         }
 302
 303         // Finally if either of the above conditions apply we should add a note
 304         // indicating that this error is the result of a recent soundness fix.
 305         match err {
 306             None => {},
 307             Some(mut e) => {
 308                 e.note("the new auto trait rules are the result of a \
 309                           recent soundness fix; see #29859 for more details");
 310                 e.emit();
 311             }
 312         }
 313     }
 314
 315     fn check_trait(&mut self, item: &hir::Item) {
 316         let trait_def_id = self.tcx.hir.local_def_id(item.id);
 317
 318         if self.tcx.trait_has_default_impl(trait_def_id) {
 319             self.check_auto_trait(trait_def_id, item.span);
 320         }
 321
 322         self.for_item(item).with_fcx(|fcx, this| {
 323             let free_substs = &fcx.parameter_environment.free_substs;
 324             let predicates = fcx.instantiate_bounds(item.span, trait_def_id, free_substs);
 325             this.check_where_clauses(fcx, item.span, &predicates);
 326             vec![]
 327         });
 328     }
 329
 330     fn check_item_fn(&mut self,
 331                      item: &hir::Item,
 332                      body_id: hir::BodyId)
 333     {
 334         self.for_item(item).with_fcx(|fcx, this| {
 335             let free_substs = &fcx.parameter_environment.free_substs;
 336             let def_id = fcx.tcx.hir.local_def_id(item.id);
 337             let ty = fcx.tcx.type_of(def_id);
 338             let item_ty = fcx.instantiate_type_scheme(item.span, free_substs, &ty);
 339             let sig = item_ty.fn_sig();
 340
 341             let predicates = fcx.instantiate_bounds(item.span, def_id, free_substs);
 342
 343             let mut implied_bounds = vec![];
 344             let free_id_outlive = fcx.tcx.call_site_extent(item.id, body_id.node_id);
 345             this.check_fn_or_method(fcx, item.span, sig, &predicates,
 346                                     Some(free_id_outlive), &mut implied_bounds);
 347             implied_bounds
 348         })
 349     }
 350
 351     fn check_item_type(&mut self,
 352                        item: &hir::Item)
 353     {
 354         debug!("check_item_type: {:?}", item);
 355
 356         self.for_item(item).with_fcx(|fcx, this| {
 357             let ty = fcx.tcx.type_of(fcx.tcx.hir.local_def_id(item.id));
 358             let item_ty = fcx.instantiate_type_scheme(item.span,
 359                                                       &fcx.parameter_environment
 360                                                           .free_substs,
 361                                                       &ty);
 362
 363             fcx.register_wf_obligation(item_ty, item.span, this.code.clone());
 364
 365             vec![] // no implied bounds in a const etc
 366         });
 367     }
 368
 369     fn check_impl(&mut self,
 370                   item: &hir::Item,
 371                   ast_self_ty: &hir::Ty,
 372                   ast_trait_ref: &Option<hir::TraitRef>)
 373     {
 374         debug!("check_impl: {:?}", item);
 375
 376         self.for_item(item).with_fcx(|fcx, this| {
 377             let free_substs = &fcx.parameter_environment.free_substs;
 378             let item_def_id = fcx.tcx.hir.local_def_id(item.id);
 379
 380             match *ast_trait_ref {
 381                 Some(ref ast_trait_ref) => {
 382                     let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 383                     let trait_ref =
 384                         fcx.instantiate_type_scheme(
 385                             ast_trait_ref.path.span, free_substs, &trait_ref);
 386                     let obligations =
 387                         ty::wf::trait_obligations(fcx,
 388                                                   fcx.body_id,
 389                                                   &trait_ref,
 390                                                   ast_trait_ref.path.span);
 391                     for obligation in obligations {
 392                         fcx.register_predicate(obligation);
 393                     }
 394                 }
 395                 None => {
 396                     let self_ty = fcx.tcx.type_of(item_def_id);
 397                     let self_ty = fcx.instantiate_type_scheme(item.span, free_substs, &self_ty);
 398                     fcx.register_wf_obligation(self_ty, ast_self_ty.span, this.code.clone());
 399                 }
 400             }
 401
 402             let predicates = fcx.instantiate_bounds(item.span, item_def_id, free_substs);
 403             this.check_where_clauses(fcx, item.span, &predicates);
 404
 405             fcx.impl_implied_bounds(item_def_id, item.span)
 406         });
 407     }
 408
 409     fn check_where_clauses<'fcx, 'tcx>(&mut self,
 410                                        fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 411                                        span: Span,
 412                                        predicates: &ty::InstantiatedPredicates<'tcx>)
 413     {
 414         let obligations =
 415             predicates.predicates
 416                       .iter()
 417                       .flat_map(|p| ty::wf::predicate_obligations(fcx,
 418                                                                   fcx.body_id,
 419                                                                   p,
 420                                                                   span));
 421
 422         for obligation in obligations {
 423             fcx.register_predicate(obligation);
 424         }
 425     }
 426
 427     fn check_fn_or_method<'fcx, 'tcx>(&mut self,
 428                                       fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 429                                       span: Span,
 430                                       sig: ty::PolyFnSig<'tcx>,
 431                                       predicates: &ty::InstantiatedPredicates<'tcx>,
 432                                       free_id_outlive: Option<CodeExtent<'tcx>>,
 433                                       implied_bounds: &mut Vec<Ty<'tcx>>)
 434     {
 435         let free_substs = &fcx.parameter_environment.free_substs;
 436         let sig = fcx.instantiate_type_scheme(span, free_substs, &sig);
 437         let sig = fcx.tcx.liberate_late_bound_regions(free_id_outlive, &sig);
 438
 439         for input_ty in sig.inputs() {
 440             fcx.register_wf_obligation(&input_ty, span, self.code.clone());
 441         }
 442         implied_bounds.extend(sig.inputs());
 443
 444         fcx.register_wf_obligation(sig.output(), span, self.code.clone());
 445
 446         // FIXME(#25759) return types should not be implied bounds
 447         implied_bounds.push(sig.output());
 448
 449         self.check_where_clauses(fcx, span, predicates);
 450     }
 451
 452     fn check_method_receiver<'fcx, 'tcx>(&mut self,
 453                                          fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 454                                          method_sig: &hir::MethodSig,
 455                                          method: &ty::AssociatedItem,
 456                                          free_id_outlive: Option<CodeExtent<'tcx>>,
 457                                          self_ty: ty::Ty<'tcx>)
 458     {
 459         // check that the type of the method's receiver matches the
 460         // method's first parameter.
 461         debug!("check_method_receiver({:?}, self_ty={:?})",
 462                method, self_ty);
 463
 464         if !method.method_has_self_argument {
 465             return;
 466         }
 467
 468         let span = method_sig.decl.inputs[0].span;
 469
 470         let free_substs = &fcx.parameter_environment.free_substs;
 471         let method_ty = fcx.tcx.type_of(method.def_id);
 472         let fty = fcx.instantiate_type_scheme(span, free_substs, &method_ty);
 473         let sig = fcx.tcx.liberate_late_bound_regions(free_id_outlive, &fty.fn_sig());
 474
 475         debug!("check_method_receiver: sig={:?}", sig);
 476
 477         let self_arg_ty = sig.inputs()[0];
 478         let rcvr_ty = match ExplicitSelf::determine(self_ty, self_arg_ty) {
 479             ExplicitSelf::ByValue => self_ty,
 480             ExplicitSelf::ByReference(region, mutbl) => {
 481                 fcx.tcx.mk_ref(region, ty::TypeAndMut {
 482                     ty: self_ty,
 483                     mutbl: mutbl
 484                 })
 485             }
 486             ExplicitSelf::ByBox => fcx.tcx.mk_box(self_ty)
 487         };
 488         let rcvr_ty = fcx.instantiate_type_scheme(span, free_substs, &rcvr_ty);
 489         let rcvr_ty = fcx.tcx.liberate_late_bound_regions(free_id_outlive,
 490                                                           &ty::Binder(rcvr_ty));
 491
 492         debug!("check_method_receiver: receiver ty = {:?}", rcvr_ty);
 493
 494         let cause = fcx.cause(span, ObligationCauseCode::MethodReceiver);
 495         if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, rcvr_ty, self_arg_ty) {
 496             err.emit();
 497         }
 498     }
 499
 500     fn check_variances_for_type_defn(&self,
 501                                      item: &hir::Item,
 502                                      ast_generics: &hir::Generics)
 503     {
 504         let item_def_id = self.tcx.hir.local_def_id(item.id);
 505         let ty = self.tcx.type_of(item_def_id);
 506         if self.tcx.has_error_field(ty) {
 507             return;
 508         }
 509
 510         let ty_predicates = self.tcx.predicates_of(item_def_id);
 511         assert_eq!(ty_predicates.parent, None);
 512         let variances = self.tcx.variances_of(item_def_id);
 513
 514         let mut constrained_parameters: FxHashSet<_> =
 515             variances.iter().enumerate()
 516                      .filter(|&(_, &variance)| variance != ty::Bivariant)
 517                      .map(|(index, _)| Parameter(index as u32))
 518                      .collect();
 519
 520         identify_constrained_type_params(ty_predicates.predicates.as_slice(),
 521                                          None,
 522                                          &mut constrained_parameters);
 523
 524         for (index, _) in variances.iter().enumerate() {
 525             if constrained_parameters.contains(&Parameter(index as u32)) {
 526                 continue;
 527             }
 528
 529             let (span, name) = if index < ast_generics.lifetimes.len() {
 530                 (ast_generics.lifetimes[index].lifetime.span,
 531                  ast_generics.lifetimes[index].lifetime.name)
 532             } else {
 533                 let index = index - ast_generics.lifetimes.len();
 534                 (ast_generics.ty_params[index].span,
 535                  ast_generics.ty_params[index].name)
 536             };
 537             self.report_bivariance(span, name);
 538         }
 539     }
 540
 541     fn report_bivariance(&self,
 542                          span: Span,
 543                          param_name: ast::Name)
 544     {
 545         let mut err = error_392(self.tcx, span, param_name);
 546
 547         let suggested_marker_id = self.tcx.lang_items.phantom_data();
 548         match suggested_marker_id {
 549             Some(def_id) => {
 550                 err.help(
 551                     &format!("consider removing `{}` or using a marker such as `{}`",
 552                              param_name,
 553                              self.tcx.item_path_str(def_id)));
 554             }
 555             None => {
 556                 // no lang items, no help!
 557             }
 558         }
 559         err.emit();
 560     }
 561 }
 562
 563 fn reject_shadowing_type_parameters(tcx: TyCtxt, def_id: DefId) {
 564     let generics = tcx.generics_of(def_id);
 565     let parent = tcx.generics_of(generics.parent.unwrap());
 566     let impl_params: FxHashMap<_, _> = parent.types
 567                                        .iter()
 568                                        .map(|tp| (tp.name, tp.def_id))
 569                                        .collect();
 570
 571     for method_param in &generics.types {
 572         if impl_params.contains_key(&method_param.name) {
 573             // Tighten up the span to focus on only the shadowing type
 574             let type_span = tcx.def_span(method_param.def_id);
 575
 576             // The expectation here is that the original trait declaration is
 577             // local so it should be okay to just unwrap everything.
 578             let trait_def_id = impl_params[&method_param.name];
 579             let trait_decl_span = tcx.def_span(trait_def_id);
 580             error_194(tcx, type_span, trait_decl_span, method_param.name);
 581         }
 582     }
 583 }
 584
 585 impl<'a, 'tcx, 'v> Visitor<'v> for CheckTypeWellFormedVisitor<'a, 'tcx> {
 586     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
 587         NestedVisitorMap::None
 588     }
 589
 590     fn visit_item(&mut self, i: &hir::Item) {
 591         debug!("visit_item: {:?}", i);
 592         self.check_item_well_formed(i);
 593         intravisit::walk_item(self, i);
 594     }
 595
 596     fn visit_trait_item(&mut self, trait_item: &'v hir::TraitItem) {
 597         debug!("visit_trait_item: {:?}", trait_item);
 598         let method_sig = match trait_item.node {
 599             hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 600             _ => None
 601         };
 602         self.check_associated_item(trait_item.id, trait_item.span, method_sig);
 603         intravisit::walk_trait_item(self, trait_item)
 604     }
 605
 606     fn visit_impl_item(&mut self, impl_item: &'v hir::ImplItem) {
 607         debug!("visit_impl_item: {:?}", impl_item);
 608         let method_sig = match impl_item.node {
 609             hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 610             _ => None
 611         };
 612         self.check_associated_item(impl_item.id, impl_item.span, method_sig);
 613         intravisit::walk_impl_item(self, impl_item)
 614     }
 615 }
 616
 617 ///////////////////////////////////////////////////////////////////////////
 618 // ADT
 619
 620 struct AdtVariant<'tcx> {
 621     fields: Vec<AdtField<'tcx>>,
 622 }
 623
 624 struct AdtField<'tcx> {
 625     ty: Ty<'tcx>,
 626     span: Span,
 627 }
 628
 629 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 630     fn struct_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
 631         let fields =
 632             struct_def.fields().iter()
 633             .map(|field| {
 634                 let field_ty = self.tcx.type_of(self.tcx.hir.local_def_id(field.id));
 635                 let field_ty = self.instantiate_type_scheme(field.span,
 636                                                             &self.parameter_environment
 637                                                                  .free_substs,
 638                                                             &field_ty);
 639                 AdtField { ty: field_ty, span: field.span }
 640             })
 641             .collect();
 642         AdtVariant { fields: fields }
 643     }
 644
 645     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
 646         enum_def.variants.iter()
 647             .map(|variant| self.struct_variant(&variant.node.data))
 648             .collect()
 649     }
 650
 651     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
 652         let free_substs = &self.parameter_environment.free_substs;
 653         match self.tcx.impl_trait_ref(impl_def_id) {
 654             Some(ref trait_ref) => {
 655                 // Trait impl: take implied bounds from all types that
 656                 // appear in the trait reference.
 657                 let trait_ref = self.instantiate_type_scheme(span, free_substs, trait_ref);
 658                 trait_ref.substs.types().collect()
 659             }
 660
 661             None => {
 662                 // Inherent impl: take implied bounds from the self type.
 663                 let self_ty = self.tcx.type_of(impl_def_id);
 664                 let self_ty = self.instantiate_type_scheme(span, free_substs, &self_ty);
 665                 vec![self_ty]
 666             }
 667         }
 668     }
 669 }
 670
 671 fn error_192(tcx: TyCtxt, span: Span) {
 672     span_err!(tcx.sess, span, E0192,
 673               "negative impls are only allowed for traits with \
 674                default impls (e.g., `Send` and `Sync`)")
 675 }
 676
 677 fn error_380(tcx: TyCtxt, span: Span) {
 678     span_err!(tcx.sess, span, E0380,
 679               "traits with default impls (`e.g. impl \
 680                Trait for ..`) must have no methods or associated items")
 681 }
 682
 683 fn error_392<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, span: Span, param_name: ast::Name)
 684                        -> DiagnosticBuilder<'tcx> {
 685     let mut err = struct_span_err!(tcx.sess, span, E0392,
 686                   "parameter `{}` is never used", param_name);
 687     err.span_label(span, &format!("unused type parameter"));
 688     err
 689 }
 690
 691 fn error_194(tcx: TyCtxt, span: Span, trait_decl_span: Span, name: ast::Name) {
 692     struct_span_err!(tcx.sess, span, E0194,
 693               "type parameter `{}` shadows another type parameter of the same name",
 694               name)
 695         .span_label(span, &format!("shadows another type parameter"))
 696         .span_label(trait_decl_span, &format!("first `{}` declared here", name))
 697         .emit();
 698 }