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                     for obligation in obligations {
 347                         fcx.register_predicate(obligation);
 348                     }
 349                 }
 350                 None => {
 351                     let self_ty = fcx.tcx.type_of(item_def_id);
 352                     let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 353                     fcx.register_wf_obligation(self_ty, ast_self_ty.span, this.code.clone());
 354                 }
 355             }
 356
 357             let predicates = fcx.tcx.predicates_of(item_def_id).instantiate_identity(fcx.tcx);
 358             let predicates = fcx.normalize_associated_types_in(item.span, &predicates);
 359             this.check_where_clauses(fcx, item.span, &predicates);
 360
 361             fcx.impl_implied_bounds(item_def_id, item.span)
 362         });
 363     }
 364
 365     fn check_where_clauses<'fcx, 'tcx>(&mut self,
 366                                        fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 367                                        span: Span,
 368                                        predicates: &ty::InstantiatedPredicates<'tcx>)
 369     {
 370         let obligations =
 371             predicates.predicates
 372                       .iter()
 373                       .flat_map(|p| ty::wf::predicate_obligations(fcx,
 374                                                                   fcx.param_env,
 375                                                                   fcx.body_id,
 376                                                                   p,
 377                                                                   span));
 378
 379         for obligation in obligations {
 380             fcx.register_predicate(obligation);
 381         }
 382     }
 383
 384     fn check_fn_or_method<'fcx, 'tcx>(&mut self,
 385                                       fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 386                                       span: Span,
 387                                       sig: ty::PolyFnSig<'tcx>,
 388                                       predicates: &ty::InstantiatedPredicates<'tcx>,
 389                                       def_id: DefId,
 390                                       implied_bounds: &mut Vec<Ty<'tcx>>)
 391     {
 392         let sig = fcx.normalize_associated_types_in(span, &sig);
 393         let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 394
 395         for input_ty in sig.inputs() {
 396             fcx.register_wf_obligation(&input_ty, span, self.code.clone());
 397         }
 398         implied_bounds.extend(sig.inputs());
 399
 400         fcx.register_wf_obligation(sig.output(), span, self.code.clone());
 401
 402         // FIXME(#25759) return types should not be implied bounds
 403         implied_bounds.push(sig.output());
 404
 405         self.check_where_clauses(fcx, span, predicates);
 406     }
 407
 408     fn check_method_receiver<'fcx, 'tcx>(&mut self,
 409                                          fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 410                                          method_sig: &hir::MethodSig,
 411                                          method: &ty::AssociatedItem,
 412                                          self_ty: Ty<'tcx>)
 413     {
 414         // check that the method has a valid receiver type, given the type `Self`
 415         debug!("check_method_receiver({:?}, self_ty={:?})",
 416                method, self_ty);
 417
 418         if !method.method_has_self_argument {
 419             return;
 420         }
 421
 422         let span = method_sig.decl.inputs[0].span;
 423
 424         let sig = fcx.tcx.fn_sig(method.def_id);
 425         let sig = fcx.normalize_associated_types_in(span, &sig);
 426         let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 427
 428         debug!("check_method_receiver: sig={:?}", sig);
 429
 430         let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 431         let self_ty = fcx.tcx.liberate_late_bound_regions(
 432             method.def_id,
 433             &ty::Binder(self_ty)
 434         );
 435
 436         let self_arg_ty = sig.inputs()[0];
 437
 438         let cause = fcx.cause(span, ObligationCauseCode::MethodReceiver);
 439         let self_arg_ty = fcx.normalize_associated_types_in(span, &self_arg_ty);
 440         let self_arg_ty = fcx.tcx.liberate_late_bound_regions(
 441             method.def_id,
 442             &ty::Binder(self_arg_ty)
 443         );
 444
 445         let mut autoderef = fcx.autoderef(span, self_arg_ty).include_raw_pointers();
 446
 447         loop {
 448             if let Some((potential_self_ty, _)) = autoderef.next() {
 449                 debug!("check_method_receiver: potential self type `{:?}` to match `{:?}`",
 450                     potential_self_ty, self_ty);
 451
 452                 if fcx.infcx.can_eq(fcx.param_env, self_ty, potential_self_ty).is_ok() {
 453                     autoderef.finalize();
 454                     if let Some(mut err) = fcx.demand_eqtype_with_origin(
 455                         &cause, self_ty, potential_self_ty) {
 456                         err.emit();
 457                     }
 458                     break
 459                 }
 460             } else {
 461                 fcx.tcx.sess.diagnostic().mut_span_err(
 462                     span, &format!("invalid `self` type: {:?}", self_arg_ty))
 463                 .note(&format!("type must be `{:?}` or a type that dereferences to it`", self_ty))
 464                 .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 465                 .code(DiagnosticId::Error("E0307".into()))
 466                 .emit();
 467                 return
 468             }
 469         }
 470
 471         let is_self_ty = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 472         let self_kind = ExplicitSelf::determine(self_arg_ty, is_self_ty);
 473
 474         if !fcx.tcx.sess.features.borrow().arbitrary_self_types {
 475             match self_kind {
 476                 ExplicitSelf::ByValue |
 477                 ExplicitSelf::ByReference(_, _) |
 478                 ExplicitSelf::ByBox => (),
 479
 480                 ExplicitSelf::ByRawPointer(_) => {
 481                     feature_gate::feature_err(
 482                         &fcx.tcx.sess.parse_sess,
 483                         "arbitrary_self_types",
 484                         span,
 485                         GateIssue::Language,
 486                         "raw pointer `self` is unstable")
 487                     .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 488                     .emit();
 489                 }
 490
 491                 ExplicitSelf::Other => {
 492                     feature_gate::feature_err(
 493                         &fcx.tcx.sess.parse_sess,
 494                         "arbitrary_self_types",
 495                         span,
 496                         GateIssue::Language,"arbitrary `self` types are unstable")
 497                     .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 498                     .emit();
 499                 }
 500             }
 501         }
 502     }
 503
 504     fn check_variances_for_type_defn(&self,
 505                                      item: &hir::Item,
 506                                      ast_generics: &hir::Generics)
 507     {
 508         let item_def_id = self.tcx.hir.local_def_id(item.id);
 509         let ty = self.tcx.type_of(item_def_id);
 510         if self.tcx.has_error_field(ty) {
 511             return;
 512         }
 513
 514         let ty_predicates = self.tcx.predicates_of(item_def_id);
 515         assert_eq!(ty_predicates.parent, None);
 516         let variances = self.tcx.variances_of(item_def_id);
 517
 518         let mut constrained_parameters: FxHashSet<_> =
 519             variances.iter().enumerate()
 520                      .filter(|&(_, &variance)| variance != ty::Bivariant)
 521                      .map(|(index, _)| Parameter(index as u32))
 522                      .collect();
 523
 524         identify_constrained_type_params(self.tcx,
 525                                          ty_predicates.predicates.as_slice(),
 526                                          None,
 527                                          &mut constrained_parameters);
 528
 529         for (index, _) in variances.iter().enumerate() {
 530             if constrained_parameters.contains(&Parameter(index as u32)) {
 531                 continue;
 532             }
 533
 534             let (span, name) = match ast_generics.params[index] {
 535                 hir::GenericParam::Lifetime(ref ld) => (ld.lifetime.span, ld.lifetime.name.name()),
 536                 hir::GenericParam::Type(ref tp) => (tp.span, tp.name),
 537             };
 538             self.report_bivariance(span, name);
 539         }
 540     }
 541
 542     fn report_bivariance(&self,
 543                          span: Span,
 544                          param_name: ast::Name)
 545     {
 546         let mut err = error_392(self.tcx, span, param_name);
 547
 548         let suggested_marker_id = self.tcx.lang_items().phantom_data();
 549         match suggested_marker_id {
 550             Some(def_id) => {
 551                 err.help(
 552                     &format!("consider removing `{}` or using a marker such as `{}`",
 553                              param_name,
 554                              self.tcx.item_path_str(def_id)));
 555             }
 556             None => {
 557                 // no lang items, no help!
 558             }
 559         }
 560         err.emit();
 561     }
 562 }
 563
 564 fn reject_shadowing_type_parameters(tcx: TyCtxt, def_id: DefId) {
 565     let generics = tcx.generics_of(def_id);
 566     let parent = tcx.generics_of(generics.parent.unwrap());
 567     let impl_params: FxHashMap<_, _> = parent.types
 568                                        .iter()
 569                                        .map(|tp| (tp.name, tp.def_id))
 570                                        .collect();
 571
 572     for method_param in &generics.types {
 573         if impl_params.contains_key(&method_param.name) {
 574             // Tighten up the span to focus on only the shadowing type
 575             let type_span = tcx.def_span(method_param.def_id);
 576
 577             // The expectation here is that the original trait declaration is
 578             // local so it should be okay to just unwrap everything.
 579             let trait_def_id = impl_params[&method_param.name];
 580             let trait_decl_span = tcx.def_span(trait_def_id);
 581             error_194(tcx, type_span, trait_decl_span, method_param.name);
 582         }
 583     }
 584 }
 585
 586 impl<'a, 'tcx, 'v> Visitor<'v> for CheckTypeWellFormedVisitor<'a, 'tcx> {
 587     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
 588         NestedVisitorMap::None
 589     }
 590
 591     fn visit_item(&mut self, i: &hir::Item) {
 592         debug!("visit_item: {:?}", i);
 593         self.check_item_well_formed(i);
 594         intravisit::walk_item(self, i);
 595     }
 596
 597     fn visit_trait_item(&mut self, trait_item: &'v hir::TraitItem) {
 598         debug!("visit_trait_item: {:?}", trait_item);
 599         let method_sig = match trait_item.node {
 600             hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 601             _ => None
 602         };
 603         self.check_associated_item(trait_item.id, trait_item.span, method_sig);
 604         intravisit::walk_trait_item(self, trait_item)
 605     }
 606
 607     fn visit_impl_item(&mut self, impl_item: &'v hir::ImplItem) {
 608         debug!("visit_impl_item: {:?}", impl_item);
 609         let method_sig = match impl_item.node {
 610             hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 611             _ => None
 612         };
 613         self.check_associated_item(impl_item.id, impl_item.span, method_sig);
 614         intravisit::walk_impl_item(self, impl_item)
 615     }
 616 }
 617
 618 ///////////////////////////////////////////////////////////////////////////
 619 // ADT
 620
 621 struct AdtVariant<'tcx> {
 622     fields: Vec<AdtField<'tcx>>,
 623 }
 624
 625 struct AdtField<'tcx> {
 626     ty: Ty<'tcx>,
 627     span: Span,
 628 }
 629
 630 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 631     fn non_enum_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
 632         let fields =
 633             struct_def.fields().iter()
 634             .map(|field| {
 635                 let field_ty = self.tcx.type_of(self.tcx.hir.local_def_id(field.id));
 636                 let field_ty = self.normalize_associated_types_in(field.span,
 637                                                                   &field_ty);
 638                 AdtField { ty: field_ty, span: field.span }
 639             })
 640             .collect();
 641         AdtVariant { fields: fields }
 642     }
 643
 644     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
 645         enum_def.variants.iter()
 646             .map(|variant| self.non_enum_variant(&variant.node.data))
 647             .collect()
 648     }
 649
 650     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
 651         match self.tcx.impl_trait_ref(impl_def_id) {
 652             Some(ref trait_ref) => {
 653                 // Trait impl: take implied bounds from all types that
 654                 // appear in the trait reference.
 655                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
 656                 trait_ref.substs.types().collect()
 657             }
 658
 659             None => {
 660                 // Inherent impl: take implied bounds from the self type.
 661                 let self_ty = self.tcx.type_of(impl_def_id);
 662                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
 663                 vec![self_ty]
 664             }
 665         }
 666     }
 667 }
 668
 669 fn error_392<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, span: Span, param_name: ast::Name)
 670                        -> DiagnosticBuilder<'tcx> {
 671     let mut err = struct_span_err!(tcx.sess, span, E0392,
 672                   "parameter `{}` is never used", param_name);
 673     err.span_label(span, "unused type parameter");
 674     err
 675 }
 676
 677 fn error_194(tcx: TyCtxt, span: Span, trait_decl_span: Span, name: ast::Name) {
 678     struct_span_err!(tcx.sess, span, E0194,
 679               "type parameter `{}` shadows another type parameter of the same name",
 680               name)
 681         .span_label(span, "shadows another type parameter")
 682         .span_label(trait_decl_span, format!("first `{}` declared here", name))
 683         .emit();
 684 }