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                     this.check_fn_or_method(fcx, span, sig,
 189                                             item.def_id, &mut implied_bounds);
 190                     let sig_if_method = sig_if_method.expect("bad signature for method");
 191                     this.check_method_receiver(fcx, sig_if_method, &item, self_ty);
 192                 }
 193                 ty::AssociatedKind::Type => {
 194                     if item.defaultness.has_value() {
 195                         let ty = fcx.tcx.type_of(item.def_id);
 196                         let ty = fcx.normalize_associated_types_in(span, &ty);
 197                         fcx.register_wf_obligation(ty, span, code.clone());
 198                     }
 199                 }
 200             }
 201
 202             implied_bounds
 203         })
 204     }
 205
 206     fn for_item<'tcx>(&self, item: &hir::Item)
 207                       -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 208         self.for_id(item.id, item.span)
 209     }
 210
 211     fn for_id<'tcx>(&self, id: ast::NodeId, span: Span)
 212                     -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 213         let def_id = self.tcx.hir.local_def_id(id);
 214         CheckWfFcxBuilder {
 215             inherited: Inherited::build(self.tcx, def_id),
 216             code: self.code.clone(),
 217             id,
 218             span,
 219             param_env: self.tcx.param_env(def_id),
 220         }
 221     }
 222
 223     /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 224     fn check_type_defn<F>(&mut self, item: &hir::Item, all_sized: bool, mut lookup_fields: F)
 225         where F: for<'fcx, 'tcx> FnMut(&FnCtxt<'fcx, 'gcx, 'tcx>) -> Vec<AdtVariant<'tcx>>
 226     {
 227         self.for_item(item).with_fcx(|fcx, this| {
 228             let variants = lookup_fields(fcx);
 229             let def_id = fcx.tcx.hir.local_def_id(item.id);
 230             let packed = fcx.tcx.adt_def(def_id).repr.packed();
 231
 232             for variant in &variants {
 233                 // For DST, or when drop needs to copy things around, all
 234                 // intermediate types must be sized.
 235                 let needs_drop_copy = || {
 236                     packed && {
 237                         let ty = variant.fields.last().unwrap().ty;
 238                         let ty = fcx.tcx.erase_regions(&ty).lift_to_tcx(this.tcx)
 239                             .unwrap_or_else(|| {
 240                                 span_bug!(item.span, "inference variables in {:?}", ty)
 241                             });
 242                         ty.needs_drop(this.tcx, this.tcx.param_env(def_id))
 243                     }
 244                 };
 245                 let unsized_len = if
 246                     all_sized ||
 247                     variant.fields.is_empty() ||
 248                     needs_drop_copy()
 249                 {
 250                     0
 251                 } else {
 252                     1
 253                 };
 254                 for field in &variant.fields[..variant.fields.len() - unsized_len] {
 255                     fcx.register_bound(
 256                         field.ty,
 257                         fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 258                         traits::ObligationCause::new(field.span,
 259                                                      fcx.body_id,
 260                                                      traits::FieldSized(match item.node.adt_kind() {
 261                                                         Some(i) => i,
 262                                                         None => bug!(),
 263                                                      })));
 264                 }
 265
 266                 // All field types must be well-formed.
 267                 for field in &variant.fields {
 268                     fcx.register_wf_obligation(field.ty, field.span, this.code.clone())
 269                 }
 270             }
 271
 272             self.check_where_clauses(fcx, item.span, def_id);
 273
 274             vec![] // no implied bounds in a struct def'n
 275         });
 276     }
 277
 278     fn check_trait(&mut self, item: &hir::Item) {
 279         let trait_def_id = self.tcx.hir.local_def_id(item.id);
 280
 281         self.for_item(item).with_fcx(|fcx, _| {
 282             self.check_trait_where_clauses(fcx, item.span, trait_def_id);
 283             vec![]
 284         });
 285     }
 286
 287     fn check_item_fn(&mut self, item: &hir::Item) {
 288         self.for_item(item).with_fcx(|fcx, this| {
 289             let def_id = fcx.tcx.hir.local_def_id(item.id);
 290             let sig = fcx.tcx.fn_sig(def_id);
 291             let sig = fcx.normalize_associated_types_in(item.span, &sig);
 292             let mut implied_bounds = vec![];
 293             this.check_fn_or_method(fcx, item.span, sig,
 294                                     def_id, &mut implied_bounds);
 295             implied_bounds
 296         })
 297     }
 298
 299     fn check_item_type(&mut self,
 300                        item: &hir::Item)
 301     {
 302         debug!("check_item_type: {:?}", item);
 303
 304         self.for_item(item).with_fcx(|fcx, this| {
 305             let ty = fcx.tcx.type_of(fcx.tcx.hir.local_def_id(item.id));
 306             let item_ty = fcx.normalize_associated_types_in(item.span, &ty);
 307
 308             fcx.register_wf_obligation(item_ty, item.span, this.code.clone());
 309
 310             vec![] // no implied bounds in a const etc
 311         });
 312     }
 313
 314     fn check_impl(&mut self,
 315                   item: &hir::Item,
 316                   ast_self_ty: &hir::Ty,
 317                   ast_trait_ref: &Option<hir::TraitRef>)
 318     {
 319         debug!("check_impl: {:?}", item);
 320
 321         self.for_item(item).with_fcx(|fcx, this| {
 322             let item_def_id = fcx.tcx.hir.local_def_id(item.id);
 323
 324             match *ast_trait_ref {
 325                 Some(ref ast_trait_ref) => {
 326                     let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 327                     let trait_ref =
 328                         fcx.normalize_associated_types_in(
 329                             ast_trait_ref.path.span, &trait_ref);
 330                     let obligations =
 331                         ty::wf::trait_obligations(fcx,
 332                                                   fcx.param_env,
 333                                                   fcx.body_id,
 334                                                   &trait_ref,
 335                                                   ast_trait_ref.path.span);
 336                     for obligation in obligations {
 337                         fcx.register_predicate(obligation);
 338                     }
 339                 }
 340                 None => {
 341                     let self_ty = fcx.tcx.type_of(item_def_id);
 342                     let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 343                     fcx.register_wf_obligation(self_ty, ast_self_ty.span, this.code.clone());
 344                 }
 345             }
 346
 347             this.check_where_clauses(fcx, item.span, item_def_id);
 348
 349             fcx.impl_implied_bounds(item_def_id, item.span)
 350         });
 351     }
 352
 353     /// Checks where clauses and inline bounds that are declared on def_id.
 354     fn check_where_clauses<'fcx, 'tcx>(&mut self,
 355                                        fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 356                                        span: Span,
 357                                        def_id: DefId) {
 358         self.inner_check_where_clauses(fcx, span, def_id, false)
 359     }
 360
 361     fn check_trait_where_clauses<'fcx, 'tcx>(&mut self,
 362                                        fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 363                                        span: Span,
 364                                        def_id: DefId) {
 365         self.inner_check_where_clauses(fcx, span, def_id, true)
 366     }
 367
 368     /// Checks where clauses and inline bounds that are declared on def_id.
 369     fn inner_check_where_clauses<'fcx, 'tcx>(&mut self,
 370                                        fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 371                                        span: Span,
 372                                        def_id: DefId,
 373                                        is_trait: bool)
 374     {
 375         use ty::subst::Subst;
 376         use rustc::ty::TypeFoldable;
 377
 378         let generics = self.tcx.generics_of(def_id);
 379         let defaulted_params = generics.types.iter()
 380                                              .filter(|def| def.has_default &&
 381                                                      def.index >= generics.parent_count() as u32);
 382         // Defaults must be well-formed.
 383         for d in defaulted_params.map(|p| p.def_id) {
 384             fcx.register_wf_obligation(fcx.tcx.type_of(d), fcx.tcx.def_span(d), self.code.clone());
 385         }
 386         // Check that each default fulfills the bounds on it's parameter.
 387         // We go over each predicate and duplicate it, substituting defaults in the self type.
 388         let mut predicates = fcx.tcx.predicates_of(def_id);
 389         let mut default_predicates = Vec::new();
 390         // In `trait Trait : Super` predicates as `Self: Trait` and `Self: Super` are a problem.
 391         // Therefore we skip such predicates. This means we check less than we could.
 392         for pred in predicates.predicates.iter().filter(|p| !(is_trait && p.has_self_ty())) {
 393             let mut skip = false;
 394             let mut no_default = true;
 395             let substs = ty::subst::Substs::for_item(fcx.tcx, def_id, |def, _| {
 396                 // All regions are identity.
 397                 fcx.tcx.mk_region(ty::ReEarlyBound(def.to_early_bound_region_data()))
 398             }, |def, _| {
 399                 // No default or generic comes from parent, identity substitution.
 400                 if !def.has_default || (def.index as usize) < generics.parent_count() {
 401                     fcx.tcx.mk_param_from_def(def)
 402                 } else {
 403                     no_default = false;
 404                     // Has a default, use it in the substitution.
 405                     let default_ty = fcx.tcx.type_of(def.def_id);
 406
 407                     match default_ty.sty {
 408                         // Skip `Self: Sized` when `Self` is the default. Needed in traits.
 409                         ty::TyParam(ref p) if is_trait && p.is_self() => {
 410                             if let ty::Predicate::Trait(p) = pred {
 411                                 if Some(p.def_id()) == fcx.tcx.lang_items().sized_trait() {
 412                                     skip = true;
 413                                 }
 414                             }
 415                         }
 416                         _ => ()
 417                     }
 418                     default_ty
 419                 }
 420             });
 421
 422             if skip || no_default {
 423                 continue;
 424             }
 425
 426             default_predicates.push(pred.subst(fcx.tcx, substs));
 427         }
 428
 429         predicates.predicates.extend(default_predicates);
 430         let predicates = predicates.instantiate_identity(fcx.tcx);
 431         let predicates = fcx.normalize_associated_types_in(span, &predicates);
 432
 433         let obligations =
 434             predicates.predicates
 435                       .iter()
 436                       .flat_map(|p| ty::wf::predicate_obligations(fcx,
 437                                                                   fcx.param_env,
 438                                                                   fcx.body_id,
 439                                                                   p,
 440                                                                   span));
 441
 442         for obligation in obligations {
 443             fcx.register_predicate(obligation);
 444         }
 445     }
 446
 447     fn check_fn_or_method<'fcx, 'tcx>(&mut self,
 448                                       fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 449                                       span: Span,
 450                                       sig: ty::PolyFnSig<'tcx>,
 451                                       def_id: DefId,
 452                                       implied_bounds: &mut Vec<Ty<'tcx>>)
 453     {
 454         let sig = fcx.normalize_associated_types_in(span, &sig);
 455         let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 456
 457         for input_ty in sig.inputs() {
 458             fcx.register_wf_obligation(&input_ty, span, self.code.clone());
 459         }
 460         implied_bounds.extend(sig.inputs());
 461
 462         fcx.register_wf_obligation(sig.output(), span, self.code.clone());
 463
 464         // FIXME(#25759) return types should not be implied bounds
 465         implied_bounds.push(sig.output());
 466
 467         self.check_where_clauses(fcx, span, def_id);
 468     }
 469
 470     fn check_method_receiver<'fcx, 'tcx>(&mut self,
 471                                          fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 472                                          method_sig: &hir::MethodSig,
 473                                          method: &ty::AssociatedItem,
 474                                          self_ty: Ty<'tcx>)
 475     {
 476         // check that the method has a valid receiver type, given the type `Self`
 477         debug!("check_method_receiver({:?}, self_ty={:?})",
 478                method, self_ty);
 479
 480         if !method.method_has_self_argument {
 481             return;
 482         }
 483
 484         let span = method_sig.decl.inputs[0].span;
 485
 486         let sig = fcx.tcx.fn_sig(method.def_id);
 487         let sig = fcx.normalize_associated_types_in(span, &sig);
 488         let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 489
 490         debug!("check_method_receiver: sig={:?}", sig);
 491
 492         let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 493         let self_ty = fcx.tcx.liberate_late_bound_regions(
 494             method.def_id,
 495             &ty::Binder(self_ty)
 496         );
 497
 498         let self_arg_ty = sig.inputs()[0];
 499
 500         let cause = fcx.cause(span, ObligationCauseCode::MethodReceiver);
 501         let self_arg_ty = fcx.normalize_associated_types_in(span, &self_arg_ty);
 502         let self_arg_ty = fcx.tcx.liberate_late_bound_regions(
 503             method.def_id,
 504             &ty::Binder(self_arg_ty)
 505         );
 506
 507         let mut autoderef = fcx.autoderef(span, self_arg_ty).include_raw_pointers();
 508
 509         loop {
 510             if let Some((potential_self_ty, _)) = autoderef.next() {
 511                 debug!("check_method_receiver: potential self type `{:?}` to match `{:?}`",
 512                     potential_self_ty, self_ty);
 513
 514                 if fcx.infcx.can_eq(fcx.param_env, self_ty, potential_self_ty).is_ok() {
 515                     autoderef.finalize();
 516                     if let Some(mut err) = fcx.demand_eqtype_with_origin(
 517                         &cause, self_ty, potential_self_ty) {
 518                         err.emit();
 519                     }
 520                     break
 521                 }
 522             } else {
 523                 fcx.tcx.sess.diagnostic().mut_span_err(
 524                     span, &format!("invalid `self` type: {:?}", self_arg_ty))
 525                 .note(&format!("type must be `{:?}` or a type that dereferences to it`", self_ty))
 526                 .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 527                 .code(DiagnosticId::Error("E0307".into()))
 528                 .emit();
 529                 return
 530             }
 531         }
 532
 533         let is_self_ty = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 534         let self_kind = ExplicitSelf::determine(self_arg_ty, is_self_ty);
 535
 536         if !fcx.tcx.sess.features.borrow().arbitrary_self_types {
 537             match self_kind {
 538                 ExplicitSelf::ByValue |
 539                 ExplicitSelf::ByReference(_, _) |
 540                 ExplicitSelf::ByBox => (),
 541
 542                 ExplicitSelf::ByRawPointer(_) => {
 543                     feature_gate::feature_err(
 544                         &fcx.tcx.sess.parse_sess,
 545                         "arbitrary_self_types",
 546                         span,
 547                         GateIssue::Language,
 548                         "raw pointer `self` is unstable")
 549                     .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 550                     .emit();
 551                 }
 552
 553                 ExplicitSelf::Other => {
 554                     feature_gate::feature_err(
 555                         &fcx.tcx.sess.parse_sess,
 556                         "arbitrary_self_types",
 557                         span,
 558                         GateIssue::Language,"arbitrary `self` types are unstable")
 559                     .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 560                     .emit();
 561                 }
 562             }
 563         }
 564     }
 565
 566     fn check_variances_for_type_defn(&self,
 567                                      item: &hir::Item,
 568                                      ast_generics: &hir::Generics)
 569     {
 570         let item_def_id = self.tcx.hir.local_def_id(item.id);
 571         let ty = self.tcx.type_of(item_def_id);
 572         if self.tcx.has_error_field(ty) {
 573             return;
 574         }
 575
 576         let ty_predicates = self.tcx.predicates_of(item_def_id);
 577         assert_eq!(ty_predicates.parent, None);
 578         let variances = self.tcx.variances_of(item_def_id);
 579
 580         let mut constrained_parameters: FxHashSet<_> =
 581             variances.iter().enumerate()
 582                      .filter(|&(_, &variance)| variance != ty::Bivariant)
 583                      .map(|(index, _)| Parameter(index as u32))
 584                      .collect();
 585
 586         identify_constrained_type_params(self.tcx,
 587                                          ty_predicates.predicates.as_slice(),
 588                                          None,
 589                                          &mut constrained_parameters);
 590
 591         for (index, _) in variances.iter().enumerate() {
 592             if constrained_parameters.contains(&Parameter(index as u32)) {
 593                 continue;
 594             }
 595
 596             let (span, name) = match ast_generics.params[index] {
 597                 hir::GenericParam::Lifetime(ref ld) => (ld.lifetime.span, ld.lifetime.name.name()),
 598                 hir::GenericParam::Type(ref tp) => (tp.span, tp.name),
 599             };
 600             self.report_bivariance(span, name);
 601         }
 602     }
 603
 604     fn report_bivariance(&self,
 605                          span: Span,
 606                          param_name: ast::Name)
 607     {
 608         let mut err = error_392(self.tcx, span, param_name);
 609
 610         let suggested_marker_id = self.tcx.lang_items().phantom_data();
 611         match suggested_marker_id {
 612             Some(def_id) => {
 613                 err.help(
 614                     &format!("consider removing `{}` or using a marker such as `{}`",
 615                              param_name,
 616                              self.tcx.item_path_str(def_id)));
 617             }
 618             None => {
 619                 // no lang items, no help!
 620             }
 621         }
 622         err.emit();
 623     }
 624 }
 625
 626 fn reject_shadowing_type_parameters(tcx: TyCtxt, def_id: DefId) {
 627     let generics = tcx.generics_of(def_id);
 628     let parent = tcx.generics_of(generics.parent.unwrap());
 629     let impl_params: FxHashMap<_, _> = parent.types
 630                                        .iter()
 631                                        .map(|tp| (tp.name, tp.def_id))
 632                                        .collect();
 633
 634     for method_param in &generics.types {
 635         if impl_params.contains_key(&method_param.name) {
 636             // Tighten up the span to focus on only the shadowing type
 637             let type_span = tcx.def_span(method_param.def_id);
 638
 639             // The expectation here is that the original trait declaration is
 640             // local so it should be okay to just unwrap everything.
 641             let trait_def_id = impl_params[&method_param.name];
 642             let trait_decl_span = tcx.def_span(trait_def_id);
 643             error_194(tcx, type_span, trait_decl_span, method_param.name);
 644         }
 645     }
 646 }
 647
 648 impl<'a, 'tcx, 'v> Visitor<'v> for CheckTypeWellFormedVisitor<'a, 'tcx> {
 649     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
 650         NestedVisitorMap::None
 651     }
 652
 653     fn visit_item(&mut self, i: &hir::Item) {
 654         debug!("visit_item: {:?}", i);
 655         self.check_item_well_formed(i);
 656         intravisit::walk_item(self, i);
 657     }
 658
 659     fn visit_trait_item(&mut self, trait_item: &'v hir::TraitItem) {
 660         debug!("visit_trait_item: {:?}", trait_item);
 661         let method_sig = match trait_item.node {
 662             hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 663             _ => None
 664         };
 665         self.check_associated_item(trait_item.id, trait_item.span, method_sig);
 666         intravisit::walk_trait_item(self, trait_item)
 667     }
 668
 669     fn visit_impl_item(&mut self, impl_item: &'v hir::ImplItem) {
 670         debug!("visit_impl_item: {:?}", impl_item);
 671         let method_sig = match impl_item.node {
 672             hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 673             _ => None
 674         };
 675         self.check_associated_item(impl_item.id, impl_item.span, method_sig);
 676         intravisit::walk_impl_item(self, impl_item)
 677     }
 678 }
 679
 680 ///////////////////////////////////////////////////////////////////////////
 681 // ADT
 682
 683 struct AdtVariant<'tcx> {
 684     fields: Vec<AdtField<'tcx>>,
 685 }
 686
 687 struct AdtField<'tcx> {
 688     ty: Ty<'tcx>,
 689     span: Span,
 690 }
 691
 692 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 693     fn non_enum_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
 694         let fields =
 695             struct_def.fields().iter()
 696             .map(|field| {
 697                 let field_ty = self.tcx.type_of(self.tcx.hir.local_def_id(field.id));
 698                 let field_ty = self.normalize_associated_types_in(field.span,
 699                                                                   &field_ty);
 700                 AdtField { ty: field_ty, span: field.span }
 701             })
 702             .collect();
 703         AdtVariant { fields: fields }
 704     }
 705
 706     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
 707         enum_def.variants.iter()
 708             .map(|variant| self.non_enum_variant(&variant.node.data))
 709             .collect()
 710     }
 711
 712     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
 713         match self.tcx.impl_trait_ref(impl_def_id) {
 714             Some(ref trait_ref) => {
 715                 // Trait impl: take implied bounds from all types that
 716                 // appear in the trait reference.
 717                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
 718                 trait_ref.substs.types().collect()
 719             }
 720
 721             None => {
 722                 // Inherent impl: take implied bounds from the self type.
 723                 let self_ty = self.tcx.type_of(impl_def_id);
 724                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
 725                 vec![self_ty]
 726             }
 727         }
 728     }
 729 }
 730
 731 fn error_392<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, span: Span, param_name: ast::Name)
 732                        -> DiagnosticBuilder<'tcx> {
 733     let mut err = struct_span_err!(tcx.sess, span, E0392,
 734                   "parameter `{}` is never used", param_name);
 735     err.span_label(span, "unused type parameter");
 736     err
 737 }
 738
 739 fn error_194(tcx: TyCtxt, span: Span, trait_decl_span: Span, name: ast::Name) {
 740     struct_span_err!(tcx.sess, span, E0194,
 741               "type parameter `{}` shadows another type parameter of the same name",
 742               name)
 743         .span_label(span, "shadows another type parameter")
 744         .span_label(trait_decl_span, format!("first `{}` declared here", name))
 745         .emit();
 746 }