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::FnCtxt;
  13 use constrained_type_params::{identify_constrained_type_params, Parameter};
  14 use CrateCtxt;
  15
  16 use hir::def_id::DefId;
  17 use middle::region::{CodeExtent};
  18 use rustc::traits::{self, ObligationCauseCode};
  19 use rustc::ty::{self, Ty, TyCtxt};
  20 use rustc::util::nodemap::{FxHashSet, FxHashMap};
  21 use rustc::middle::lang_items;
  22
  23 use syntax::ast;
  24 use syntax_pos::Span;
  25 use errors::DiagnosticBuilder;
  26
  27 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
  28 use rustc::hir;
  29
  30 pub struct CheckTypeWellFormedVisitor<'ccx, 'tcx:'ccx> {
  31     ccx: &'ccx CrateCtxt<'ccx, 'tcx>,
  32     code: ObligationCauseCode<'tcx>,
  33 }
  34
  35 /// Helper type of a temporary returned by .for_item(...).
  36 /// Necessary because we can't write the following bound:
  37 /// F: for<'b, 'tcx> where 'gcx: 'tcx FnOnce(FnCtxt<'b, 'gcx, 'tcx>).
  38 struct CheckWfFcxBuilder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
  39     inherited: super::InheritedBuilder<'a, 'gcx, 'tcx>,
  40     code: ObligationCauseCode<'gcx>,
  41     id: ast::NodeId,
  42     span: Span
  43 }
  44
  45 impl<'a, 'gcx, 'tcx> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
  46     fn with_fcx<F>(&'tcx mut self, f: F) where
  47         F: for<'b> FnOnce(&FnCtxt<'b, 'gcx, 'tcx>,
  48                           &mut CheckTypeWellFormedVisitor<'b, 'gcx>) -> Vec<Ty<'tcx>>
  49     {
  50         let code = self.code.clone();
  51         let id = self.id;
  52         let span = self.span;
  53         self.inherited.enter(|inh| {
  54             let fcx = FnCtxt::new(&inh, Some(inh.ccx.tcx.types.never), id);
  55             let wf_tys = f(&fcx, &mut CheckTypeWellFormedVisitor {
  56                 ccx: fcx.ccx,
  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<'ccx, 'gcx> CheckTypeWellFormedVisitor<'ccx, 'gcx> {
  66     pub fn new(ccx: &'ccx CrateCtxt<'ccx, 'gcx>)
  67                -> CheckTypeWellFormedVisitor<'ccx, 'gcx> {
  68         CheckTypeWellFormedVisitor {
  69             ccx: ccx,
  70             code: ObligationCauseCode::MiscObligation
  71         }
  72     }
  73
  74     fn tcx(&self) -> TyCtxt<'ccx, 'gcx, 'gcx> {
  75         self.ccx.tcx
  76     }
  77
  78     /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  79     /// well-formed, meaning that they do not require any constraints not declared in the struct
  80     /// definition itself. For example, this definition would be illegal:
  81     ///
  82     ///     struct Ref<'a, T> { x: &'a T }
  83     ///
  84     /// because the type did not declare that `T:'a`.
  85     ///
  86     /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  87     /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  88     /// the types first.
  89     fn check_item_well_formed(&mut self, item: &hir::Item) {
  90         let ccx = self.ccx;
  91         debug!("check_item_well_formed(it.id={}, it.name={})",
  92                item.id,
  93                ccx.tcx.item_path_str(ccx.tcx.map.local_def_id(item.id)));
  94
  95         match item.node {
  96             /// Right now we check that every default trait implementation
  97             /// has an implementation of itself. Basically, a case like:
  98             ///
  99             /// `impl Trait for T {}`
 100             ///
 101             /// has a requirement of `T: Trait` which was required for default
 102             /// method implementations. Although this could be improved now that
 103             /// there's a better infrastructure in place for this, it's being left
 104             /// for a follow-up work.
 105             ///
 106             /// Since there's such a requirement, we need to check *just* positive
 107             /// implementations, otherwise things like:
 108             ///
 109             /// impl !Send for T {}
 110             ///
 111             /// won't be allowed unless there's an *explicit* implementation of `Send`
 112             /// for `T`
 113             hir::ItemImpl(_, hir::ImplPolarity::Positive, _,
 114                           ref trait_ref, ref self_ty, _) => {
 115                 self.check_impl(item, self_ty, trait_ref);
 116             }
 117             hir::ItemImpl(_, hir::ImplPolarity::Negative, _, Some(_), ..) => {
 118                 // FIXME(#27579) what amount of WF checking do we need for neg impls?
 119
 120                 let trait_ref = ccx.tcx.impl_trait_ref(ccx.tcx.map.local_def_id(item.id)).unwrap();
 121                 if !ccx.tcx.trait_has_default_impl(trait_ref.def_id) {
 122                     error_192(ccx, item.span);
 123                 }
 124             }
 125             hir::ItemFn(.., body_id) => {
 126                 self.check_item_fn(item, body_id);
 127             }
 128             hir::ItemStatic(..) => {
 129                 self.check_item_type(item);
 130             }
 131             hir::ItemConst(..) => {
 132                 self.check_item_type(item);
 133             }
 134             hir::ItemStruct(ref struct_def, ref ast_generics) => {
 135                 self.check_type_defn(item, false, |fcx| {
 136                     vec![fcx.struct_variant(struct_def)]
 137                 });
 138
 139                 self.check_variances_for_type_defn(item, ast_generics);
 140             }
 141             hir::ItemUnion(ref struct_def, ref ast_generics) => {
 142                 self.check_type_defn(item, true, |fcx| {
 143                     vec![fcx.struct_variant(struct_def)]
 144                 });
 145
 146                 self.check_variances_for_type_defn(item, ast_generics);
 147             }
 148             hir::ItemEnum(ref enum_def, ref ast_generics) => {
 149                 self.check_type_defn(item, true, |fcx| {
 150                     fcx.enum_variants(enum_def)
 151                 });
 152
 153                 self.check_variances_for_type_defn(item, ast_generics);
 154             }
 155             hir::ItemTrait(..) => {
 156                 self.check_trait(item);
 157             }
 158             _ => {}
 159         }
 160     }
 161
 162     fn check_trait_or_impl_item(&mut self,
 163                                 item_id: ast::NodeId,
 164                                 span: Span,
 165                                 sig_if_method: Option<&hir::MethodSig>) {
 166         let code = self.code.clone();
 167         self.for_id(item_id, span).with_fcx(|fcx, this| {
 168             let free_substs = &fcx.parameter_environment.free_substs;
 169             let free_id_outlive = fcx.parameter_environment.free_id_outlive;
 170
 171             let item = fcx.tcx.associated_item(fcx.tcx.map.local_def_id(item_id));
 172
 173             let (mut implied_bounds, self_ty) = match item.container {
 174                 ty::TraitContainer(_) => (vec![], fcx.tcx.mk_self_type()),
 175                 ty::ImplContainer(def_id) => (fcx.impl_implied_bounds(def_id, span),
 176                                               fcx.tcx.item_type(def_id))
 177             };
 178
 179             match item.kind {
 180                 ty::AssociatedKind::Const => {
 181                     let ty = fcx.tcx.item_type(item.def_id);
 182                     let ty = fcx.instantiate_type_scheme(span, free_substs, &ty);
 183                     fcx.register_wf_obligation(ty, span, code.clone());
 184                 }
 185                 ty::AssociatedKind::Method => {
 186                     reject_shadowing_type_parameters(fcx.tcx, item.def_id);
 187                     let method_ty = fcx.tcx.item_type(item.def_id);
 188                     let method_ty = fcx.instantiate_type_scheme(span, free_substs, &method_ty);
 189                     let predicates = fcx.instantiate_bounds(span, item.def_id, free_substs);
 190                     let fty = match method_ty.sty {
 191                         ty::TyFnDef(_, _, f) => f,
 192                         _ => bug!()
 193                     };
 194                     this.check_fn_or_method(fcx, span, fty, &predicates,
 195                                             free_id_outlive, &mut implied_bounds);
 196                     let sig_if_method = sig_if_method.expect("bad signature for method");
 197                     this.check_method_receiver(fcx, sig_if_method, &item,
 198                                                free_id_outlive, self_ty);
 199                 }
 200                 ty::AssociatedKind::Type => {
 201                     if item.defaultness.has_value() {
 202                         let ty = fcx.tcx.item_type(item.def_id);
 203                         let ty = fcx.instantiate_type_scheme(span, free_substs, &ty);
 204                         fcx.register_wf_obligation(ty, span, code.clone());
 205                     }
 206                 }
 207             }
 208
 209             implied_bounds
 210         })
 211     }
 212
 213     fn for_item<'tcx>(&self, item: &hir::Item)
 214                       -> CheckWfFcxBuilder<'ccx, 'gcx, 'tcx> {
 215         self.for_id(item.id, item.span)
 216     }
 217
 218     fn for_id<'tcx>(&self, id: ast::NodeId, span: Span)
 219                     -> CheckWfFcxBuilder<'ccx, 'gcx, 'tcx> {
 220         CheckWfFcxBuilder {
 221             inherited: self.ccx.inherited(id),
 222             code: self.code.clone(),
 223             id: id,
 224             span: span
 225         }
 226     }
 227
 228     /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 229     fn check_type_defn<F>(&mut self, item: &hir::Item, all_sized: bool, mut lookup_fields: F)
 230         where F: for<'fcx, 'tcx> FnMut(&FnCtxt<'fcx, 'gcx, 'tcx>) -> Vec<AdtVariant<'tcx>>
 231     {
 232         self.for_item(item).with_fcx(|fcx, this| {
 233             let variants = lookup_fields(fcx);
 234
 235             for variant in &variants {
 236                 // For DST, all intermediate types must be sized.
 237                 let unsized_len = if all_sized || variant.fields.is_empty() { 0 } else { 1 };
 238                 for field in &variant.fields[..variant.fields.len() - unsized_len] {
 239                     fcx.register_bound(
 240                         field.ty,
 241                         fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 242                         traits::ObligationCause::new(field.span,
 243                                                      fcx.body_id,
 244                                                      traits::FieldSized));
 245                 }
 246
 247                 // All field types must be well-formed.
 248                 for field in &variant.fields {
 249                     fcx.register_wf_obligation(field.ty, field.span, this.code.clone())
 250                 }
 251             }
 252
 253             let free_substs = &fcx.parameter_environment.free_substs;
 254             let def_id = fcx.tcx.map.local_def_id(item.id);
 255             let predicates = fcx.instantiate_bounds(item.span, def_id, free_substs);
 256             this.check_where_clauses(fcx, item.span, &predicates);
 257
 258             vec![] // no implied bounds in a struct def'n
 259         });
 260     }
 261
 262     fn check_auto_trait(&mut self, trait_def_id: DefId, span: Span) {
 263         // We want to ensure:
 264         //
 265         // 1) that there are no items contained within
 266         // the trait defintion
 267         //
 268         // 2) that the definition doesn't violate the no-super trait rule
 269         // for auto traits.
 270         //
 271         // 3) that the trait definition does not have any type parameters
 272
 273         let predicates = self.tcx().item_predicates(trait_def_id);
 274
 275         // We must exclude the Self : Trait predicate contained by all
 276         // traits.
 277         let has_predicates =
 278             predicates.predicates.iter().any(|predicate| {
 279                 match predicate {
 280                     &ty::Predicate::Trait(ref poly_trait_ref) => {
 281                         let self_ty = poly_trait_ref.0.self_ty();
 282                         !(self_ty.is_self() && poly_trait_ref.def_id() == trait_def_id)
 283                     },
 284                     _ => true,
 285                 }
 286             });
 287
 288         let has_ty_params = self.tcx().item_generics(trait_def_id).types.len() > 1;
 289
 290         // We use an if-else here, since the generics will also trigger
 291         // an extraneous error message when we find predicates like
 292         // `T : Sized` for a trait like: `trait Magic<T>`.
 293         //
 294         // We also put the check on the number of items here,
 295         // as it seems confusing to report an error about
 296         // extraneous predicates created by things like
 297         // an associated type inside the trait.
 298         let mut err = None;
 299         if !self.tcx().associated_item_def_ids(trait_def_id).is_empty() {
 300             error_380(self.ccx, span);
 301         } else if has_ty_params {
 302             err = Some(struct_span_err!(self.tcx().sess, span, E0567,
 303                 "traits with auto impls (`e.g. impl \
 304                     Trait for ..`) can not have type parameters"));
 305         } else if has_predicates {
 306             err = Some(struct_span_err!(self.tcx().sess, span, E0568,
 307                 "traits with auto impls (`e.g. impl \
 308                     Trait for ..`) cannot have predicates"));
 309         }
 310
 311         // Finally if either of the above conditions apply we should add a note
 312         // indicating that this error is the result of a recent soundness fix.
 313         match err {
 314             None => {},
 315             Some(mut e) => {
 316                 e.note("the new auto trait rules are the result of a \
 317                           recent soundness fix; see #29859 for more details");
 318                 e.emit();
 319             }
 320         }
 321     }
 322
 323     fn check_trait(&mut self, item: &hir::Item) {
 324         let trait_def_id = self.tcx().map.local_def_id(item.id);
 325
 326         if self.tcx().trait_has_default_impl(trait_def_id) {
 327             self.check_auto_trait(trait_def_id, item.span);
 328         }
 329
 330         self.for_item(item).with_fcx(|fcx, this| {
 331             let free_substs = &fcx.parameter_environment.free_substs;
 332             let predicates = fcx.instantiate_bounds(item.span, trait_def_id, free_substs);
 333             this.check_where_clauses(fcx, item.span, &predicates);
 334             vec![]
 335         });
 336     }
 337
 338     fn check_item_fn(&mut self,
 339                      item: &hir::Item,
 340                      body_id: hir::ExprId)
 341     {
 342         self.for_item(item).with_fcx(|fcx, this| {
 343             let free_substs = &fcx.parameter_environment.free_substs;
 344             let def_id = fcx.tcx.map.local_def_id(item.id);
 345             let ty = fcx.tcx.item_type(def_id);
 346             let item_ty = fcx.instantiate_type_scheme(item.span, free_substs, &ty);
 347             let bare_fn_ty = match item_ty.sty {
 348                 ty::TyFnDef(.., ref bare_fn_ty) => bare_fn_ty,
 349                 _ => {
 350                     span_bug!(item.span, "Fn item without fn type");
 351                 }
 352             };
 353
 354             let predicates = fcx.instantiate_bounds(item.span, def_id, free_substs);
 355
 356             let mut implied_bounds = vec![];
 357             let free_id_outlive = fcx.tcx.region_maps.call_site_extent(item.id, body_id.node_id());
 358             this.check_fn_or_method(fcx, item.span, bare_fn_ty, &predicates,
 359                                     free_id_outlive, &mut implied_bounds);
 360             implied_bounds
 361         })
 362     }
 363
 364     fn check_item_type(&mut self,
 365                        item: &hir::Item)
 366     {
 367         debug!("check_item_type: {:?}", item);
 368
 369         self.for_item(item).with_fcx(|fcx, this| {
 370             let ty = fcx.tcx.item_type(fcx.tcx.map.local_def_id(item.id));
 371             let item_ty = fcx.instantiate_type_scheme(item.span,
 372                                                       &fcx.parameter_environment
 373                                                           .free_substs,
 374                                                       &ty);
 375
 376             fcx.register_wf_obligation(item_ty, item.span, this.code.clone());
 377
 378             vec![] // no implied bounds in a const etc
 379         });
 380     }
 381
 382     fn check_impl(&mut self,
 383                   item: &hir::Item,
 384                   ast_self_ty: &hir::Ty,
 385                   ast_trait_ref: &Option<hir::TraitRef>)
 386     {
 387         debug!("check_impl: {:?}", item);
 388
 389         self.for_item(item).with_fcx(|fcx, this| {
 390             let free_substs = &fcx.parameter_environment.free_substs;
 391             let item_def_id = fcx.tcx.map.local_def_id(item.id);
 392
 393             match *ast_trait_ref {
 394                 Some(ref ast_trait_ref) => {
 395                     let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 396                     let trait_ref =
 397                         fcx.instantiate_type_scheme(
 398                             ast_trait_ref.path.span, free_substs, &trait_ref);
 399                     let obligations =
 400                         ty::wf::trait_obligations(fcx,
 401                                                   fcx.body_id,
 402                                                   &trait_ref,
 403                                                   ast_trait_ref.path.span);
 404                     for obligation in obligations {
 405                         fcx.register_predicate(obligation);
 406                     }
 407                 }
 408                 None => {
 409                     let self_ty = fcx.tcx.item_type(item_def_id);
 410                     let self_ty = fcx.instantiate_type_scheme(item.span, free_substs, &self_ty);
 411                     fcx.register_wf_obligation(self_ty, ast_self_ty.span, this.code.clone());
 412                 }
 413             }
 414
 415             let predicates = fcx.instantiate_bounds(item.span, item_def_id, free_substs);
 416             this.check_where_clauses(fcx, item.span, &predicates);
 417
 418             fcx.impl_implied_bounds(item_def_id, item.span)
 419         });
 420     }
 421
 422     fn check_where_clauses<'fcx, 'tcx>(&mut self,
 423                                        fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 424                                        span: Span,
 425                                        predicates: &ty::InstantiatedPredicates<'tcx>)
 426     {
 427         let obligations =
 428             predicates.predicates
 429                       .iter()
 430                       .flat_map(|p| ty::wf::predicate_obligations(fcx,
 431                                                                   fcx.body_id,
 432                                                                   p,
 433                                                                   span));
 434
 435         for obligation in obligations {
 436             fcx.register_predicate(obligation);
 437         }
 438     }
 439
 440     fn check_fn_or_method<'fcx, 'tcx>(&mut self,
 441                                       fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 442                                       span: Span,
 443                                       fty: &'tcx ty::BareFnTy<'tcx>,
 444                                       predicates: &ty::InstantiatedPredicates<'tcx>,
 445                                       free_id_outlive: CodeExtent,
 446                                       implied_bounds: &mut Vec<Ty<'tcx>>)
 447     {
 448         let free_substs = &fcx.parameter_environment.free_substs;
 449         let fty = fcx.instantiate_type_scheme(span, free_substs, &fty);
 450         let sig = fcx.tcx.liberate_late_bound_regions(free_id_outlive, &fty.sig);
 451
 452         for input_ty in sig.inputs() {
 453             fcx.register_wf_obligation(&input_ty, span, self.code.clone());
 454         }
 455         implied_bounds.extend(sig.inputs());
 456
 457         fcx.register_wf_obligation(sig.output(), span, self.code.clone());
 458
 459         // FIXME(#25759) return types should not be implied bounds
 460         implied_bounds.push(sig.output());
 461
 462         self.check_where_clauses(fcx, span, predicates);
 463     }
 464
 465     fn check_method_receiver<'fcx, 'tcx>(&mut self,
 466                                          fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 467                                          method_sig: &hir::MethodSig,
 468                                          method: &ty::AssociatedItem,
 469                                          free_id_outlive: CodeExtent,
 470                                          self_ty: ty::Ty<'tcx>)
 471     {
 472         // check that the type of the method's receiver matches the
 473         // method's first parameter.
 474         debug!("check_method_receiver({:?}, self_ty={:?})",
 475                method, self_ty);
 476
 477         if !method.method_has_self_argument {
 478             return;
 479         }
 480
 481         let span = method_sig.decl.inputs[0].pat.span;
 482
 483         let free_substs = &fcx.parameter_environment.free_substs;
 484         let method_ty = fcx.tcx.item_type(method.def_id);
 485         let fty = fcx.instantiate_type_scheme(span, free_substs, &method_ty);
 486         let sig = fcx.tcx.liberate_late_bound_regions(free_id_outlive, &fty.fn_sig());
 487
 488         debug!("check_method_receiver: sig={:?}", sig);
 489
 490         let self_arg_ty = sig.inputs()[0];
 491         let rcvr_ty = match ExplicitSelf::determine(self_ty, self_arg_ty) {
 492             ExplicitSelf::ByValue => self_ty,
 493             ExplicitSelf::ByReference(region, mutbl) => {
 494                 fcx.tcx.mk_ref(region, ty::TypeAndMut {
 495                     ty: self_ty,
 496                     mutbl: mutbl
 497                 })
 498             }
 499             ExplicitSelf::ByBox => fcx.tcx.mk_box(self_ty)
 500         };
 501         let rcvr_ty = fcx.instantiate_type_scheme(span, free_substs, &rcvr_ty);
 502         let rcvr_ty = fcx.tcx.liberate_late_bound_regions(free_id_outlive,
 503                                                           &ty::Binder(rcvr_ty));
 504
 505         debug!("check_method_receiver: receiver ty = {:?}", rcvr_ty);
 506
 507         let cause = fcx.cause(span, ObligationCauseCode::MethodReceiver);
 508         fcx.demand_eqtype_with_origin(&cause, rcvr_ty, self_arg_ty);
 509     }
 510
 511     fn check_variances_for_type_defn(&self,
 512                                      item: &hir::Item,
 513                                      ast_generics: &hir::Generics)
 514     {
 515         let item_def_id = self.tcx().map.local_def_id(item.id);
 516         let ty = self.tcx().item_type(item_def_id);
 517         if self.tcx().has_error_field(ty) {
 518             return;
 519         }
 520
 521         let ty_predicates = self.tcx().item_predicates(item_def_id);
 522         assert_eq!(ty_predicates.parent, None);
 523         let variances = self.tcx().item_variances(item_def_id);
 524
 525         let mut constrained_parameters: FxHashSet<_> =
 526             variances.iter().enumerate()
 527                      .filter(|&(_, &variance)| variance != ty::Bivariant)
 528                      .map(|(index, _)| Parameter(index as u32))
 529                      .collect();
 530
 531         identify_constrained_type_params(ty_predicates.predicates.as_slice(),
 532                                          None,
 533                                          &mut constrained_parameters);
 534
 535         for (index, _) in variances.iter().enumerate() {
 536             if constrained_parameters.contains(&Parameter(index as u32)) {
 537                 continue;
 538             }
 539
 540             let (span, name) = if index < ast_generics.lifetimes.len() {
 541                 (ast_generics.lifetimes[index].lifetime.span,
 542                  ast_generics.lifetimes[index].lifetime.name)
 543             } else {
 544                 let index = index - ast_generics.lifetimes.len();
 545                 (ast_generics.ty_params[index].span,
 546                  ast_generics.ty_params[index].name)
 547             };
 548             self.report_bivariance(span, name);
 549         }
 550     }
 551
 552     fn report_bivariance(&self,
 553                          span: Span,
 554                          param_name: ast::Name)
 555     {
 556         let mut err = error_392(self.ccx, span, param_name);
 557
 558         let suggested_marker_id = self.tcx().lang_items.phantom_data();
 559         match suggested_marker_id {
 560             Some(def_id) => {
 561                 err.help(
 562                     &format!("consider removing `{}` or using a marker such as `{}`",
 563                              param_name,
 564                              self.tcx().item_path_str(def_id)));
 565             }
 566             None => {
 567                 // no lang items, no help!
 568             }
 569         }
 570         err.emit();
 571     }
 572 }
 573
 574 fn reject_shadowing_type_parameters(tcx: TyCtxt, def_id: DefId) {
 575     let generics = tcx.item_generics(def_id);
 576     let parent = tcx.item_generics(generics.parent.unwrap());
 577     let impl_params: FxHashMap<_, _> = parent.types
 578                                        .iter()
 579                                        .map(|tp| (tp.name, tp.def_id))
 580                                        .collect();
 581
 582     for method_param in &generics.types {
 583         if impl_params.contains_key(&method_param.name) {
 584             // Tighten up the span to focus on only the shadowing type
 585             let type_span = tcx.def_span(method_param.def_id);
 586
 587             // The expectation here is that the original trait declaration is
 588             // local so it should be okay to just unwrap everything.
 589             let trait_def_id = impl_params[&method_param.name];
 590             let trait_decl_span = tcx.def_span(trait_def_id);
 591             error_194(tcx, type_span, trait_decl_span, method_param.name);
 592         }
 593     }
 594 }
 595
 596 impl<'ccx, 'tcx, 'v> Visitor<'v> for CheckTypeWellFormedVisitor<'ccx, 'tcx> {
 597     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
 598         NestedVisitorMap::None
 599     }
 600
 601     fn visit_item(&mut self, i: &hir::Item) {
 602         debug!("visit_item: {:?}", i);
 603         self.check_item_well_formed(i);
 604         intravisit::walk_item(self, i);
 605     }
 606
 607     fn visit_trait_item(&mut self, trait_item: &'v hir::TraitItem) {
 608         debug!("visit_trait_item: {:?}", trait_item);
 609         let method_sig = match trait_item.node {
 610             hir::TraitItem_::MethodTraitItem(ref sig, _) => Some(sig),
 611             _ => None
 612         };
 613         self.check_trait_or_impl_item(trait_item.id, trait_item.span, method_sig);
 614         intravisit::walk_trait_item(self, trait_item)
 615     }
 616
 617     fn visit_impl_item(&mut self, impl_item: &'v hir::ImplItem) {
 618         debug!("visit_impl_item: {:?}", impl_item);
 619         let method_sig = match impl_item.node {
 620             hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 621             _ => None
 622         };
 623         self.check_trait_or_impl_item(impl_item.id, impl_item.span, method_sig);
 624         intravisit::walk_impl_item(self, impl_item)
 625     }
 626 }
 627
 628 ///////////////////////////////////////////////////////////////////////////
 629 // ADT
 630
 631 struct AdtVariant<'tcx> {
 632     fields: Vec<AdtField<'tcx>>,
 633 }
 634
 635 struct AdtField<'tcx> {
 636     ty: Ty<'tcx>,
 637     span: Span,
 638 }
 639
 640 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 641     fn struct_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
 642         let fields =
 643             struct_def.fields().iter()
 644             .map(|field| {
 645                 let field_ty = self.tcx.item_type(self.tcx.map.local_def_id(field.id));
 646                 let field_ty = self.instantiate_type_scheme(field.span,
 647                                                             &self.parameter_environment
 648                                                                  .free_substs,
 649                                                             &field_ty);
 650                 AdtField { ty: field_ty, span: field.span }
 651             })
 652             .collect();
 653         AdtVariant { fields: fields }
 654     }
 655
 656     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
 657         enum_def.variants.iter()
 658             .map(|variant| self.struct_variant(&variant.node.data))
 659             .collect()
 660     }
 661
 662     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
 663         let free_substs = &self.parameter_environment.free_substs;
 664         match self.tcx.impl_trait_ref(impl_def_id) {
 665             Some(ref trait_ref) => {
 666                 // Trait impl: take implied bounds from all types that
 667                 // appear in the trait reference.
 668                 let trait_ref = self.instantiate_type_scheme(span, free_substs, trait_ref);
 669                 trait_ref.substs.types().collect()
 670             }
 671
 672             None => {
 673                 // Inherent impl: take implied bounds from the self type.
 674                 let self_ty = self.tcx.item_type(impl_def_id);
 675                 let self_ty = self.instantiate_type_scheme(span, free_substs, &self_ty);
 676                 vec![self_ty]
 677             }
 678         }
 679     }
 680 }
 681
 682 fn error_192(ccx: &CrateCtxt, span: Span) {
 683     span_err!(ccx.tcx.sess, span, E0192,
 684               "negative impls are only allowed for traits with \
 685                default impls (e.g., `Send` and `Sync`)")
 686 }
 687
 688 fn error_380(ccx: &CrateCtxt, span: Span) {
 689     span_err!(ccx.tcx.sess, span, E0380,
 690               "traits with default impls (`e.g. impl \
 691                Trait for ..`) must have no methods or associated items")
 692 }
 693
 694 fn error_392<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>, span: Span, param_name: ast::Name)
 695                        -> DiagnosticBuilder<'tcx> {
 696     let mut err = struct_span_err!(ccx.tcx.sess, span, E0392,
 697                   "parameter `{}` is never used", param_name);
 698     err.span_label(span, &format!("unused type parameter"));
 699     err
 700 }
 701
 702 fn error_194(tcx: TyCtxt, span: Span, trait_decl_span: Span, name: ast::Name) {
 703     struct_span_err!(tcx.sess, span, E0194,
 704               "type parameter `{}` shadows another type parameter of the same name",
 705               name)
 706         .span_label(span, &format!("shadows another type parameter"))
 707         .span_label(trait_decl_span, &format!("first `{}` declared here", name))
 708         .emit();
 709 }