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 check::{Inherited, FnCtxt};
  12 use constrained_type_params::{identify_constrained_type_params, Parameter};
  13
  14 use hir::def_id::DefId;
  15 use rustc::traits::{self, ObligationCauseCode};
  16 use rustc::ty::{self, Lift, Ty, TyCtxt};
  17 use rustc::ty::util::ExplicitSelf;
  18 use rustc::util::nodemap::{FxHashSet, FxHashMap};
  19 use rustc::middle::lang_items;
  20
  21 use syntax::ast;
  22 use syntax::feature_gate::{self, GateIssue};
  23 use syntax_pos::Span;
  24 use errors::{DiagnosticBuilder, DiagnosticId};
  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     param_env: ty::ParamEnv<'tcx>,
  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         let param_env = self.param_env;
  54         self.inherited.enter(|inh| {
  55             let fcx = FnCtxt::new(&inh, param_env, id);
  56             let wf_tys = f(&fcx, &mut CheckTypeWellFormedVisitor {
  57                 tcx: fcx.tcx.global_tcx(),
  58                 code,
  59             });
  60             fcx.select_all_obligations_or_error();
  61             fcx.regionck_item(id, span, &wf_tys);
  62         });
  63     }
  64 }
  65
  66 impl<'a, 'gcx> CheckTypeWellFormedVisitor<'a, 'gcx> {
  67     pub fn new(tcx: TyCtxt<'a, 'gcx, 'gcx>)
  68                -> CheckTypeWellFormedVisitor<'a, 'gcx> {
  69         CheckTypeWellFormedVisitor {
  70             tcx,
  71             code: ObligationCauseCode::MiscObligation
  72         }
  73     }
  74
  75     /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  76     /// well-formed, meaning that they do not require any constraints not declared in the struct
  77     /// definition itself. For example, this definition would be illegal:
  78     ///
  79     ///     struct Ref<'a, T> { x: &'a T }
  80     ///
  81     /// because the type did not declare that `T:'a`.
  82     ///
  83     /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  84     /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  85     /// the types first.
  86     fn check_item_well_formed(&mut self, item: &hir::Item) {
  87         let tcx = self.tcx;
  88         debug!("check_item_well_formed(it.id={}, it.name={})",
  89                item.id,
  90                tcx.item_path_str(tcx.hir.local_def_id(item.id)));
  91
  92         match item.node {
  93             // Right now we check that every default trait implementation
  94             // has an implementation of itself. Basically, a case like:
  95             //
  96             // `impl Trait for T {}`
  97             //
  98             // has a requirement of `T: Trait` which was required for default
  99             // method implementations. Although this could be improved now that
 100             // there's a better infrastructure in place for this, it's being left
 101             // for a follow-up work.
 102             //
 103             // Since there's such a requirement, we need to check *just* positive
 104             // implementations, otherwise things like:
 105             //
 106             // impl !Send for T {}
 107             //
 108             // won't be allowed unless there's an *explicit* implementation of `Send`
 109             // for `T`
 110             hir::ItemImpl(_, polarity, defaultness, _, ref trait_ref, ref self_ty, _) => {
 111                 let is_auto = tcx.impl_trait_ref(tcx.hir.local_def_id(item.id))
 112                                  .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
 113                 if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
 114                     tcx.sess.span_err(item.span, "impls of auto traits cannot be default");
 115                 }
 116                 if polarity == hir::ImplPolarity::Positive {
 117                     self.check_impl(item, self_ty, trait_ref);
 118                 } else {
 119                     // FIXME(#27579) what amount of WF checking do we need for neg impls?
 120                     if trait_ref.is_some() && !is_auto {
 121                         span_err!(tcx.sess, item.span, E0192,
 122                                   "negative impls are only allowed for \
 123                                    auto traits (e.g., `Send` and `Sync`)")
 124                     }
 125                 }
 126             }
 127             hir::ItemFn(..) => {
 128                 self.check_item_fn(item);
 129             }
 130             hir::ItemStatic(..) => {
 131                 self.check_item_type(item);
 132             }
 133             hir::ItemConst(..) => {
 134                 self.check_item_type(item);
 135             }
 136             hir::ItemStruct(ref struct_def, ref ast_generics) => {
 137                 self.check_type_defn(item, false, |fcx| {
 138                     vec![fcx.non_enum_variant(struct_def)]
 139                 });
 140
 141                 self.check_variances_for_type_defn(item, ast_generics);
 142             }
 143             hir::ItemUnion(ref struct_def, ref ast_generics) => {
 144                 self.check_type_defn(item, true, |fcx| {
 145                     vec![fcx.non_enum_variant(struct_def)]
 146                 });
 147
 148                 self.check_variances_for_type_defn(item, ast_generics);
 149             }
 150             hir::ItemEnum(ref enum_def, ref ast_generics) => {
 151                 self.check_type_defn(item, true, |fcx| {
 152                     fcx.enum_variants(enum_def)
 153                 });
 154
 155                 self.check_variances_for_type_defn(item, ast_generics);
 156             }
 157             hir::ItemTrait(..) => {
 158                 self.check_trait(item);
 159             }
 160             _ => {}
 161         }
 162     }
 163
 164     fn check_associated_item(&mut self,
 165                              item_id: ast::NodeId,
 166                              span: Span,
 167                              sig_if_method: Option<&hir::MethodSig>) {
 168         let code = self.code.clone();
 169         self.for_id(item_id, span).with_fcx(|fcx, this| {
 170             let item = fcx.tcx.associated_item(fcx.tcx.hir.local_def_id(item_id));
 171
 172             let (mut implied_bounds, self_ty) = match item.container {
 173                 ty::TraitContainer(_) => (vec![], fcx.tcx.mk_self_type()),
 174                 ty::ImplContainer(def_id) => (fcx.impl_implied_bounds(def_id, span),
 175                                               fcx.tcx.type_of(def_id))
 176             };
 177
 178             match item.kind {
 179                 ty::AssociatedKind::Const => {
 180                     let ty = fcx.tcx.type_of(item.def_id);
 181                     let ty = fcx.normalize_associated_types_in(span, &ty);
 182                     fcx.register_wf_obligation(ty, span, code.clone());
 183                 }
 184                 ty::AssociatedKind::Method => {
 185                     reject_shadowing_type_parameters(fcx.tcx, item.def_id);
 186                     let sig = fcx.tcx.fn_sig(item.def_id);
 187                     let sig = fcx.normalize_associated_types_in(span, &sig);
 188                     let predicates = fcx.tcx.predicates_of(item.def_id)
 189                         .instantiate_identity(fcx.tcx);
 190                     let predicates = fcx.normalize_associated_types_in(span, &predicates);
 191                     this.check_fn_or_method(fcx, span, sig, &predicates,
 192                                             item.def_id, &mut implied_bounds);
 193                     let sig_if_method = sig_if_method.expect("bad signature for method");
 194                     this.check_method_receiver(fcx, sig_if_method, &item, self_ty);
 195                 }
 196                 ty::AssociatedKind::Type => {
 197                     if item.defaultness.has_value() {
 198                         let ty = fcx.tcx.type_of(item.def_id);
 199                         let ty = fcx.normalize_associated_types_in(span, &ty);
 200                         fcx.register_wf_obligation(ty, span, code.clone());
 201                     }
 202                 }
 203             }
 204
 205             implied_bounds
 206         })
 207     }
 208
 209     fn for_item<'tcx>(&self, item: &hir::Item)
 210                       -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 211         self.for_id(item.id, item.span)
 212     }
 213
 214     fn for_id<'tcx>(&self, id: ast::NodeId, span: Span)
 215                     -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 216         let def_id = self.tcx.hir.local_def_id(id);
 217         CheckWfFcxBuilder {
 218             inherited: Inherited::build(self.tcx, def_id),
 219             code: self.code.clone(),
 220             id,
 221             span,
 222             param_env: self.tcx.param_env(def_id),
 223         }
 224     }
 225
 226     /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 227     fn check_type_defn<F>(&mut self, item: &hir::Item, all_sized: bool, mut lookup_fields: F)
 228         where F: for<'fcx, 'tcx> FnMut(&FnCtxt<'fcx, 'gcx, 'tcx>) -> Vec<AdtVariant<'tcx>>
 229     {
 230         self.for_item(item).with_fcx(|fcx, this| {
 231             let variants = lookup_fields(fcx);
 232             let def_id = fcx.tcx.hir.local_def_id(item.id);
 233             let packed = fcx.tcx.adt_def(def_id).repr.packed();
 234
 235             for variant in &variants {
 236                 // For DST, or when drop needs to copy things around, all
 237                 // intermediate types must be sized.
 238                 let needs_drop_copy = || {
 239                     packed && {
 240                         let ty = variant.fields.last().unwrap().ty;
 241                         let ty = fcx.tcx.erase_regions(&ty).lift_to_tcx(this.tcx)
 242                             .unwrap_or_else(|| {
 243                                 span_bug!(item.span, "inference variables in {:?}", ty)
 244                             });
 245                         ty.needs_drop(this.tcx, this.tcx.param_env(def_id))
 246                     }
 247                 };
 248                 let unsized_len = if
 249                     all_sized ||
 250                     variant.fields.is_empty() ||
 251                     needs_drop_copy()
 252                 {
 253                     0
 254                 } else {
 255                     1
 256                 };
 257                 for field in &variant.fields[..variant.fields.len() - unsized_len] {
 258                     fcx.register_bound(
 259                         field.ty,
 260                         fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 261                         traits::ObligationCause::new(field.span,
 262                                                      fcx.body_id,
 263                                                      traits::FieldSized(match item.node.adt_kind() {
 264                                                         Some(i) => i,
 265                                                         None => bug!(),
 266                                                      })));
 267                 }
 268
 269                 // All field types must be well-formed.
 270                 for field in &variant.fields {
 271                     fcx.register_wf_obligation(field.ty, field.span, this.code.clone())
 272                 }
 273             }
 274
 275             let predicates = fcx.tcx.predicates_of(def_id).instantiate_identity(fcx.tcx);
 276             let predicates = fcx.normalize_associated_types_in(item.span, &predicates);
 277             this.check_where_clauses(fcx, item.span, &predicates);
 278
 279             vec![] // no implied bounds in a struct def'n
 280         });
 281     }
 282
 283     fn check_trait(&mut self, item: &hir::Item) {
 284         let trait_def_id = self.tcx.hir.local_def_id(item.id);
 285         self.for_item(item).with_fcx(|fcx, this| {
 286             let predicates = fcx.tcx.predicates_of(trait_def_id).instantiate_identity(fcx.tcx);
 287             let predicates = fcx.normalize_associated_types_in(item.span, &predicates);
 288             this.check_where_clauses(fcx, item.span, &predicates);
 289             vec![]
 290         });
 291     }
 292
 293     fn check_item_fn(&mut self, item: &hir::Item) {
 294         self.for_item(item).with_fcx(|fcx, this| {
 295             let def_id = fcx.tcx.hir.local_def_id(item.id);
 296             let sig = fcx.tcx.fn_sig(def_id);
 297             let sig = fcx.normalize_associated_types_in(item.span, &sig);
 298
 299             let predicates = fcx.tcx.predicates_of(def_id).instantiate_identity(fcx.tcx);
 300             let predicates = fcx.normalize_associated_types_in(item.span, &predicates);
 301
 302             let mut implied_bounds = vec![];
 303             this.check_fn_or_method(fcx, item.span, sig, &predicates,
 304                                     def_id, &mut implied_bounds);
 305             implied_bounds
 306         })
 307     }
 308
 309     fn check_item_type(&mut self,
 310                        item: &hir::Item)
 311     {
 312         debug!("check_item_type: {:?}", item);
 313
 314         self.for_item(item).with_fcx(|fcx, this| {
 315             let ty = fcx.tcx.type_of(fcx.tcx.hir.local_def_id(item.id));
 316             let item_ty = fcx.normalize_associated_types_in(item.span, &ty);
 317
 318             fcx.register_wf_obligation(item_ty, item.span, this.code.clone());
 319
 320             vec![] // no implied bounds in a const etc
 321         });
 322     }
 323
 324     fn check_impl(&mut self,
 325                   item: &hir::Item,
 326                   ast_self_ty: &hir::Ty,
 327                   ast_trait_ref: &Option<hir::TraitRef>)
 328     {
 329         debug!("check_impl: {:?}", item);
 330
 331         self.for_item(item).with_fcx(|fcx, this| {
 332             let item_def_id = fcx.tcx.hir.local_def_id(item.id);
 333
 334             match *ast_trait_ref {
 335                 Some(ref ast_trait_ref) => {
 336                     let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 337                     let trait_ref =
 338                         fcx.normalize_associated_types_in(
 339                             ast_trait_ref.path.span, &trait_ref);
 340                     let obligations =
 341                         ty::wf::trait_obligations(fcx,
 342                                                   fcx.param_env,
 343                                                   fcx.body_id,
 344                                                   &trait_ref,
 345                                                   ast_trait_ref.path.span);
 346
 347                     // not registering predicates associcated with a `default impl`
 348                     let impl_is_default = fcx.tcx.impl_is_default(item_def_id);
 349                     for obligation in obligations {
 350                         let register = match obligation.predicate {
 351                             ty::Predicate::Trait(..)  => !impl_is_default,
 352                             _ => true
 353                         };
 354
 355                         if register {
 356                             fcx.register_predicate(obligation);
 357                         }
 358                     }
 359                 }
 360                 None => {
 361                     let self_ty = fcx.tcx.type_of(item_def_id);
 362                     let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 363                     fcx.register_wf_obligation(self_ty, ast_self_ty.span, this.code.clone());
 364                 }
 365             }
 366
 367             let predicates = fcx.tcx.predicates_of(item_def_id).instantiate_identity(fcx.tcx);
 368             let predicates = fcx.normalize_associated_types_in(item.span, &predicates);
 369             this.check_where_clauses(fcx, item.span, &predicates);
 370
 371             fcx.impl_implied_bounds(item_def_id, item.span)
 372         });
 373     }
 374
 375     fn check_where_clauses<'fcx, 'tcx>(&mut self,
 376                                        fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 377                                        span: Span,
 378                                        predicates: &ty::InstantiatedPredicates<'tcx>)
 379     {
 380         let obligations =
 381             predicates.predicates
 382                       .iter()
 383                       .flat_map(|p| ty::wf::predicate_obligations(fcx,
 384                                                                   fcx.param_env,
 385                                                                   fcx.body_id,
 386                                                                   p,
 387                                                                   span));
 388
 389         for obligation in obligations {
 390             fcx.register_predicate(obligation);
 391         }
 392     }
 393
 394     fn check_fn_or_method<'fcx, 'tcx>(&mut self,
 395                                       fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 396                                       span: Span,
 397                                       sig: ty::PolyFnSig<'tcx>,
 398                                       predicates: &ty::InstantiatedPredicates<'tcx>,
 399                                       def_id: DefId,
 400                                       implied_bounds: &mut Vec<Ty<'tcx>>)
 401     {
 402         let sig = fcx.normalize_associated_types_in(span, &sig);
 403         let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 404
 405         for input_ty in sig.inputs() {
 406             fcx.register_wf_obligation(&input_ty, span, self.code.clone());
 407         }
 408         implied_bounds.extend(sig.inputs());
 409
 410         fcx.register_wf_obligation(sig.output(), span, self.code.clone());
 411
 412         // FIXME(#25759) return types should not be implied bounds
 413         implied_bounds.push(sig.output());
 414
 415         self.check_where_clauses(fcx, span, predicates);
 416     }
 417
 418     fn check_method_receiver<'fcx, 'tcx>(&mut self,
 419                                          fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 420                                          method_sig: &hir::MethodSig,
 421                                          method: &ty::AssociatedItem,
 422                                          self_ty: Ty<'tcx>)
 423     {
 424         // check that the method has a valid receiver type, given the type `Self`
 425         debug!("check_method_receiver({:?}, self_ty={:?})",
 426                method, self_ty);
 427
 428         if !method.method_has_self_argument {
 429             return;
 430         }
 431
 432         let span = method_sig.decl.inputs[0].span;
 433
 434         let sig = fcx.tcx.fn_sig(method.def_id);
 435         let sig = fcx.normalize_associated_types_in(span, &sig);
 436         let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 437
 438         debug!("check_method_receiver: sig={:?}", sig);
 439
 440         let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 441         let self_ty = fcx.tcx.liberate_late_bound_regions(
 442             method.def_id,
 443             &ty::Binder(self_ty)
 444         );
 445
 446         let self_arg_ty = sig.inputs()[0];
 447
 448         let cause = fcx.cause(span, ObligationCauseCode::MethodReceiver);
 449         let self_arg_ty = fcx.normalize_associated_types_in(span, &self_arg_ty);
 450         let self_arg_ty = fcx.tcx.liberate_late_bound_regions(
 451             method.def_id,
 452             &ty::Binder(self_arg_ty)
 453         );
 454
 455         let mut autoderef = fcx.autoderef(span, self_arg_ty).include_raw_pointers();
 456
 457         loop {
 458             if let Some((potential_self_ty, _)) = autoderef.next() {
 459                 debug!("check_method_receiver: potential self type `{:?}` to match `{:?}`",
 460                     potential_self_ty, self_ty);
 461
 462                 if fcx.infcx.can_eq(fcx.param_env, self_ty, potential_self_ty).is_ok() {
 463                     autoderef.finalize();
 464                     if let Some(mut err) = fcx.demand_eqtype_with_origin(
 465                         &cause, self_ty, potential_self_ty) {
 466                         err.emit();
 467                     }
 468                     break
 469                 }
 470             } else {
 471                 fcx.tcx.sess.diagnostic().mut_span_err(
 472                     span, &format!("invalid `self` type: {:?}", self_arg_ty))
 473                 .note(&format!("type must be `{:?}` or a type that dereferences to it`", self_ty))
 474                 .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 475                 .code(DiagnosticId::Error("E0307".into()))
 476                 .emit();
 477                 return
 478             }
 479         }
 480
 481         let is_self_ty = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 482         let self_kind = ExplicitSelf::determine(self_arg_ty, is_self_ty);
 483
 484         if !fcx.tcx.sess.features.borrow().arbitrary_self_types {
 485             match self_kind {
 486                 ExplicitSelf::ByValue |
 487                 ExplicitSelf::ByReference(_, _) |
 488                 ExplicitSelf::ByBox => (),
 489
 490                 ExplicitSelf::ByRawPointer(_) => {
 491                     feature_gate::feature_err(
 492                         &fcx.tcx.sess.parse_sess,
 493                         "arbitrary_self_types",
 494                         span,
 495                         GateIssue::Language,
 496                         "raw pointer `self` is unstable")
 497                     .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 498                     .emit();
 499                 }
 500
 501                 ExplicitSelf::Other => {
 502                     feature_gate::feature_err(
 503                         &fcx.tcx.sess.parse_sess,
 504                         "arbitrary_self_types",
 505                         span,
 506                         GateIssue::Language,"arbitrary `self` types are unstable")
 507                     .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 508                     .emit();
 509                 }
 510             }
 511         }
 512     }
 513
 514     fn check_variances_for_type_defn(&self,
 515                                      item: &hir::Item,
 516                                      ast_generics: &hir::Generics)
 517     {
 518         let item_def_id = self.tcx.hir.local_def_id(item.id);
 519         let ty = self.tcx.type_of(item_def_id);
 520         if self.tcx.has_error_field(ty) {
 521             return;
 522         }
 523
 524         let ty_predicates = self.tcx.predicates_of(item_def_id);
 525         assert_eq!(ty_predicates.parent, None);
 526         let variances = self.tcx.variances_of(item_def_id);
 527
 528         let mut constrained_parameters: FxHashSet<_> =
 529             variances.iter().enumerate()
 530                      .filter(|&(_, &variance)| variance != ty::Bivariant)
 531                      .map(|(index, _)| Parameter(index as u32))
 532                      .collect();
 533
 534         identify_constrained_type_params(self.tcx,
 535                                          ty_predicates.predicates.as_slice(),
 536                                          None,
 537                                          &mut constrained_parameters);
 538
 539         for (index, _) in variances.iter().enumerate() {
 540             if constrained_parameters.contains(&Parameter(index as u32)) {
 541                 continue;
 542             }
 543
 544             let (span, name) = match ast_generics.params[index] {
 545                 hir::GenericParam::Lifetime(ref ld) => (ld.lifetime.span, ld.lifetime.name.name()),
 546                 hir::GenericParam::Type(ref tp) => (tp.span, tp.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.tcx, 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.generics_of(def_id);
 576     let parent = tcx.generics_of(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<'a, 'tcx, 'v> Visitor<'v> for CheckTypeWellFormedVisitor<'a, '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::TraitItemKind::Method(ref sig, _) => Some(sig),
 611             _ => None
 612         };
 613         self.check_associated_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_associated_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 non_enum_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.type_of(self.tcx.hir.local_def_id(field.id));
 646                 let field_ty = self.normalize_associated_types_in(field.span,
 647                                                                   &field_ty);
 648                 AdtField { ty: field_ty, span: field.span }
 649             })
 650             .collect();
 651         AdtVariant { fields: fields }
 652     }
 653
 654     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
 655         enum_def.variants.iter()
 656             .map(|variant| self.non_enum_variant(&variant.node.data))
 657             .collect()
 658     }
 659
 660     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
 661         match self.tcx.impl_trait_ref(impl_def_id) {
 662             Some(ref trait_ref) => {
 663                 // Trait impl: take implied bounds from all types that
 664                 // appear in the trait reference.
 665                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
 666                 trait_ref.substs.types().collect()
 667             }
 668
 669             None => {
 670                 // Inherent impl: take implied bounds from the self type.
 671                 let self_ty = self.tcx.type_of(impl_def_id);
 672                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
 673                 vec![self_ty]
 674             }
 675         }
 676     }
 677 }
 678
 679 fn error_392<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, span: Span, param_name: ast::Name)
 680                        -> DiagnosticBuilder<'tcx> {
 681     let mut err = struct_span_err!(tcx.sess, span, E0392,
 682                   "parameter `{}` is never used", param_name);
 683     err.span_label(span, "unused type parameter");
 684     err
 685 }
 686
 687 fn error_194(tcx: TyCtxt, span: Span, trait_decl_span: Span, name: ast::Name) {
 688     struct_span_err!(tcx.sess, span, E0194,
 689               "type parameter `{}` shadows another type parameter of the same name",
 690               name)
 691         .span_label(span, "shadows another type parameter")
 692         .span_label(trait_decl_span, format!("first `{}` declared here", name))
 693         .emit();
 694 }