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_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.
 354     fn check_where_clauses<'fcx, 'tcx>(&mut self,
 355                                        fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 356                                        span: Span,
 357                                        def_id: DefId)
 358     {
 359         use ty::subst::Subst;
 360         use ty::Predicate;
 361
 362         // Check that each default fulfills the bounds on it's parameter.
 363         // We go over each predicate and duplicate it, substituting defaults in the self type.
 364         let mut predicates = fcx.tcx.predicates_of(def_id);
 365         let mut default_predicates = Vec::new();
 366         for pred in &predicates.predicates {
 367             let mut self_ty = match pred {
 368                 Predicate::Trait(trait_pred) => trait_pred.skip_binder().self_ty(),
 369                 Predicate::TypeOutlives(outlives_pred) => (outlives_pred.0).0,
 370                 Predicate::Projection(proj_pred) => {
 371                     fcx.tcx.mk_ty(ty::TyProjection(proj_pred.skip_binder().projection_ty))
 372                 }
 373                 // Lifetime params can't have defaults.
 374                 Predicate::RegionOutlives(..) => continue,
 375                 _ => bug!("Predicate {:?} not supported in where clauses.", pred)
 376             };
 377
 378             let mut skip = false;
 379             let mut no_default = true;
 380             let generics = self.tcx.generics_of(def_id);
 381             let substs = ty::subst::Substs::for_item(fcx.tcx, def_id, |def, _| {
 382                 // All regions are identity.
 383                 fcx.tcx.mk_region(ty::ReEarlyBound(def.to_early_bound_region_data()))
 384             }, |def, _| {
 385                 // No default or generic comes from parent, identity substitution.
 386                 if !def.has_default || (def.index as usize) < generics.parent_count() {
 387                     fcx.tcx.mk_param_from_def(def)
 388                 } else {
 389                     no_default = false;
 390                     // Has a default, use it in the substitution.
 391                     let default_ty = fcx.tcx.type_of(def.def_id);
 392                     // Skip `Self : Self` in traits, it's problematic.
 393                     // This means we probably check less than we could.
 394                     let should_skip = match self_ty.sty {
 395                         ty::TyParam(ref p) => {
 396                             // lhs is Self && rhs is Self
 397                             p.is_self() && match pred {
 398                                 Predicate::Trait(p) => p.def_id() == def_id,
 399                                 Predicate::TypeOutlives(_) => false,
 400                                 _ => bug!("Unexpected predicate {:?}", pred)
 401                             }
 402                         }
 403                         ty::TyProjection(ref proj) => {
 404                             let mut projection = proj;
 405                             let mut next_typ = &projection.substs[0].as_type().unwrap().sty;
 406                             // Dig through projections.
 407                             while let ty::TyProjection(ref proj) = next_typ {
 408                                 projection = proj;
 409                                 next_typ = &projection.substs[0].as_type().unwrap().sty;
 410                             }
 411                             let lhs_is_self = match next_typ {
 412                                 ty::TyParam(ref p) => p.is_self(),
 413                                 _ => false
 414                             };
 415                             let rhs = fcx.tcx.associated_item(projection.item_def_id)
 416                                                      .container
 417                                                      .assert_trait();
 418                             lhs_is_self && rhs == def_id
 419                         }
 420                         _ => false
 421                     };
 422                     skip = skip || should_skip;
 423
 424                    match default_ty.sty {
 425                         // Skip `Self: Sized` when `Self` is the default. Needed in traits.
 426                         ty::TyParam(ref p) if p.is_self() => {
 427                             if let Predicate::Trait(p) = pred {
 428                                 if Some(p.def_id()) == fcx.tcx.lang_items().sized_trait() {
 429                                     skip = true;
 430                                 }
 431                             }
 432                         }
 433                         _ => ()
 434                     }
 435                     default_ty
 436                 }
 437             });
 438
 439             if skip || no_default {
 440                 continue;
 441             }
 442
 443             self_ty = self_ty.subst(fcx.tcx, substs);
 444             default_predicates.push(match pred {
 445                 Predicate::Trait(trait_pred) => {
 446                     let mut substs = trait_pred.skip_binder().trait_ref.substs.to_vec();
 447                     substs[0] = self_ty.into();
 448                     let substs = fcx.tcx.intern_substs(&substs);
 449                     let trait_ref = ty::Binder(ty::TraitRef::new(trait_pred.def_id(), substs));
 450                     Predicate::Trait(trait_ref.to_poly_trait_predicate())
 451                 }
 452                 Predicate::TypeOutlives(pred) => {
 453                     Predicate::TypeOutlives(ty::Binder(ty::OutlivesPredicate(self_ty, (pred.0).1)))
 454                 }
 455                 Predicate::Projection(proj_pred) => {
 456                     let projection_ty = match self_ty.sty {
 457                         ty::TyProjection(proj_ty) => proj_ty,
 458                         _ => bug!("self_ty not projection for projection predicate.")
 459                     };
 460                     Predicate::Projection(ty::Binder(ty::ProjectionPredicate {
 461                                                         projection_ty,
 462                                                         ty: proj_pred.ty().skip_binder()
 463                                                     }))
 464                 }
 465                 _ => bug!("Predicate {:?} not supported for type params.", pred)
 466             });
 467         }
 468
 469         predicates.predicates.extend(default_predicates);
 470         let predicates = predicates.instantiate_identity(fcx.tcx);
 471         let predicates = fcx.normalize_associated_types_in(span, &predicates);
 472
 473         let obligations =
 474             predicates.predicates
 475                       .iter()
 476                       .flat_map(|p| ty::wf::predicate_obligations(fcx,
 477                                                                   fcx.param_env,
 478                                                                   fcx.body_id,
 479                                                                   p,
 480                                                                   span));
 481
 482         for obligation in obligations {
 483             fcx.register_predicate(obligation);
 484         }
 485     }
 486
 487     fn check_fn_or_method<'fcx, 'tcx>(&mut self,
 488                                       fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 489                                       span: Span,
 490                                       sig: ty::PolyFnSig<'tcx>,
 491                                       def_id: DefId,
 492                                       implied_bounds: &mut Vec<Ty<'tcx>>)
 493     {
 494         let sig = fcx.normalize_associated_types_in(span, &sig);
 495         let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 496
 497         for input_ty in sig.inputs() {
 498             fcx.register_wf_obligation(&input_ty, span, self.code.clone());
 499         }
 500         implied_bounds.extend(sig.inputs());
 501
 502         fcx.register_wf_obligation(sig.output(), span, self.code.clone());
 503
 504         // FIXME(#25759) return types should not be implied bounds
 505         implied_bounds.push(sig.output());
 506
 507         self.check_where_clauses(fcx, span, def_id);
 508     }
 509
 510     fn check_method_receiver<'fcx, 'tcx>(&mut self,
 511                                          fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 512                                          method_sig: &hir::MethodSig,
 513                                          method: &ty::AssociatedItem,
 514                                          self_ty: Ty<'tcx>)
 515     {
 516         // check that the method has a valid receiver type, given the type `Self`
 517         debug!("check_method_receiver({:?}, self_ty={:?})",
 518                method, self_ty);
 519
 520         if !method.method_has_self_argument {
 521             return;
 522         }
 523
 524         let span = method_sig.decl.inputs[0].span;
 525
 526         let sig = fcx.tcx.fn_sig(method.def_id);
 527         let sig = fcx.normalize_associated_types_in(span, &sig);
 528         let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 529
 530         debug!("check_method_receiver: sig={:?}", sig);
 531
 532         let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 533         let self_ty = fcx.tcx.liberate_late_bound_regions(
 534             method.def_id,
 535             &ty::Binder(self_ty)
 536         );
 537
 538         let self_arg_ty = sig.inputs()[0];
 539
 540         let cause = fcx.cause(span, ObligationCauseCode::MethodReceiver);
 541         let self_arg_ty = fcx.normalize_associated_types_in(span, &self_arg_ty);
 542         let self_arg_ty = fcx.tcx.liberate_late_bound_regions(
 543             method.def_id,
 544             &ty::Binder(self_arg_ty)
 545         );
 546
 547         let mut autoderef = fcx.autoderef(span, self_arg_ty).include_raw_pointers();
 548
 549         loop {
 550             if let Some((potential_self_ty, _)) = autoderef.next() {
 551                 debug!("check_method_receiver: potential self type `{:?}` to match `{:?}`",
 552                     potential_self_ty, self_ty);
 553
 554                 if fcx.infcx.can_eq(fcx.param_env, self_ty, potential_self_ty).is_ok() {
 555                     autoderef.finalize();
 556                     if let Some(mut err) = fcx.demand_eqtype_with_origin(
 557                         &cause, self_ty, potential_self_ty) {
 558                         err.emit();
 559                     }
 560                     break
 561                 }
 562             } else {
 563                 fcx.tcx.sess.diagnostic().mut_span_err(
 564                     span, &format!("invalid `self` type: {:?}", self_arg_ty))
 565                 .note(&format!("type must be `{:?}` or a type that dereferences to it`", self_ty))
 566                 .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 567                 .code(DiagnosticId::Error("E0307".into()))
 568                 .emit();
 569                 return
 570             }
 571         }
 572
 573         let is_self_ty = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 574         let self_kind = ExplicitSelf::determine(self_arg_ty, is_self_ty);
 575
 576         if !fcx.tcx.sess.features.borrow().arbitrary_self_types {
 577             match self_kind {
 578                 ExplicitSelf::ByValue |
 579                 ExplicitSelf::ByReference(_, _) |
 580                 ExplicitSelf::ByBox => (),
 581
 582                 ExplicitSelf::ByRawPointer(_) => {
 583                     feature_gate::feature_err(
 584                         &fcx.tcx.sess.parse_sess,
 585                         "arbitrary_self_types",
 586                         span,
 587                         GateIssue::Language,
 588                         "raw pointer `self` is unstable")
 589                     .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 590                     .emit();
 591                 }
 592
 593                 ExplicitSelf::Other => {
 594                     feature_gate::feature_err(
 595                         &fcx.tcx.sess.parse_sess,
 596                         "arbitrary_self_types",
 597                         span,
 598                         GateIssue::Language,"arbitrary `self` types are unstable")
 599                     .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 600                     .emit();
 601                 }
 602             }
 603         }
 604     }
 605
 606     fn check_variances_for_type_defn(&self,
 607                                      item: &hir::Item,
 608                                      ast_generics: &hir::Generics)
 609     {
 610         let item_def_id = self.tcx.hir.local_def_id(item.id);
 611         let ty = self.tcx.type_of(item_def_id);
 612         if self.tcx.has_error_field(ty) {
 613             return;
 614         }
 615
 616         let ty_predicates = self.tcx.predicates_of(item_def_id);
 617         assert_eq!(ty_predicates.parent, None);
 618         let variances = self.tcx.variances_of(item_def_id);
 619
 620         let mut constrained_parameters: FxHashSet<_> =
 621             variances.iter().enumerate()
 622                      .filter(|&(_, &variance)| variance != ty::Bivariant)
 623                      .map(|(index, _)| Parameter(index as u32))
 624                      .collect();
 625
 626         identify_constrained_type_params(self.tcx,
 627                                          ty_predicates.predicates.as_slice(),
 628                                          None,
 629                                          &mut constrained_parameters);
 630
 631         for (index, _) in variances.iter().enumerate() {
 632             if constrained_parameters.contains(&Parameter(index as u32)) {
 633                 continue;
 634             }
 635
 636             let (span, name) = match ast_generics.params[index] {
 637                 hir::GenericParam::Lifetime(ref ld) => (ld.lifetime.span, ld.lifetime.name.name()),
 638                 hir::GenericParam::Type(ref tp) => (tp.span, tp.name),
 639             };
 640             self.report_bivariance(span, name);
 641         }
 642     }
 643
 644     fn report_bivariance(&self,
 645                          span: Span,
 646                          param_name: ast::Name)
 647     {
 648         let mut err = error_392(self.tcx, span, param_name);
 649
 650         let suggested_marker_id = self.tcx.lang_items().phantom_data();
 651         match suggested_marker_id {
 652             Some(def_id) => {
 653                 err.help(
 654                     &format!("consider removing `{}` or using a marker such as `{}`",
 655                              param_name,
 656                              self.tcx.item_path_str(def_id)));
 657             }
 658             None => {
 659                 // no lang items, no help!
 660             }
 661         }
 662         err.emit();
 663     }
 664 }
 665
 666 fn reject_shadowing_type_parameters(tcx: TyCtxt, def_id: DefId) {
 667     let generics = tcx.generics_of(def_id);
 668     let parent = tcx.generics_of(generics.parent.unwrap());
 669     let impl_params: FxHashMap<_, _> = parent.types
 670                                        .iter()
 671                                        .map(|tp| (tp.name, tp.def_id))
 672                                        .collect();
 673
 674     for method_param in &generics.types {
 675         if impl_params.contains_key(&method_param.name) {
 676             // Tighten up the span to focus on only the shadowing type
 677             let type_span = tcx.def_span(method_param.def_id);
 678
 679             // The expectation here is that the original trait declaration is
 680             // local so it should be okay to just unwrap everything.
 681             let trait_def_id = impl_params[&method_param.name];
 682             let trait_decl_span = tcx.def_span(trait_def_id);
 683             error_194(tcx, type_span, trait_decl_span, method_param.name);
 684         }
 685     }
 686 }
 687
 688 impl<'a, 'tcx, 'v> Visitor<'v> for CheckTypeWellFormedVisitor<'a, 'tcx> {
 689     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
 690         NestedVisitorMap::None
 691     }
 692
 693     fn visit_item(&mut self, i: &hir::Item) {
 694         debug!("visit_item: {:?}", i);
 695         self.check_item_well_formed(i);
 696         intravisit::walk_item(self, i);
 697     }
 698
 699     fn visit_trait_item(&mut self, trait_item: &'v hir::TraitItem) {
 700         debug!("visit_trait_item: {:?}", trait_item);
 701         let method_sig = match trait_item.node {
 702             hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 703             _ => None
 704         };
 705         self.check_associated_item(trait_item.id, trait_item.span, method_sig);
 706         intravisit::walk_trait_item(self, trait_item)
 707     }
 708
 709     fn visit_impl_item(&mut self, impl_item: &'v hir::ImplItem) {
 710         debug!("visit_impl_item: {:?}", impl_item);
 711         let method_sig = match impl_item.node {
 712             hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 713             _ => None
 714         };
 715         self.check_associated_item(impl_item.id, impl_item.span, method_sig);
 716         intravisit::walk_impl_item(self, impl_item)
 717     }
 718 }
 719
 720 ///////////////////////////////////////////////////////////////////////////
 721 // ADT
 722
 723 struct AdtVariant<'tcx> {
 724     fields: Vec<AdtField<'tcx>>,
 725 }
 726
 727 struct AdtField<'tcx> {
 728     ty: Ty<'tcx>,
 729     span: Span,
 730 }
 731
 732 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 733     fn non_enum_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
 734         let fields =
 735             struct_def.fields().iter()
 736             .map(|field| {
 737                 let field_ty = self.tcx.type_of(self.tcx.hir.local_def_id(field.id));
 738                 let field_ty = self.normalize_associated_types_in(field.span,
 739                                                                   &field_ty);
 740                 AdtField { ty: field_ty, span: field.span }
 741             })
 742             .collect();
 743         AdtVariant { fields: fields }
 744     }
 745
 746     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
 747         enum_def.variants.iter()
 748             .map(|variant| self.non_enum_variant(&variant.node.data))
 749             .collect()
 750     }
 751
 752     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
 753         match self.tcx.impl_trait_ref(impl_def_id) {
 754             Some(ref trait_ref) => {
 755                 // Trait impl: take implied bounds from all types that
 756                 // appear in the trait reference.
 757                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
 758                 trait_ref.substs.types().collect()
 759             }
 760
 761             None => {
 762                 // Inherent impl: take implied bounds from the self type.
 763                 let self_ty = self.tcx.type_of(impl_def_id);
 764                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
 765                 vec![self_ty]
 766             }
 767         }
 768     }
 769 }
 770
 771 fn error_392<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, span: Span, param_name: ast::Name)
 772                        -> DiagnosticBuilder<'tcx> {
 773     let mut err = struct_span_err!(tcx.sess, span, E0392,
 774                   "parameter `{}` is never used", param_name);
 775     err.span_label(span, "unused type parameter");
 776     err
 777 }
 778
 779 fn error_194(tcx: TyCtxt, span: Span, trait_decl_span: Span, name: ast::Name) {
 780     struct_span_err!(tcx.sess, span, E0194,
 781               "type parameter `{}` shadows another type parameter of the same name",
 782               name)
 783         .span_label(span, "shadows another type parameter")
 784         .span_label(trait_decl_span, format!("first `{}` declared here", name))
 785         .emit();
 786 }