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         self.for_item(item).with_fcx(|fcx, _| {
 281             self.check_where_clauses(fcx, item.span, trait_def_id);
 282             vec![]
 283         });
 284     }
 285
 286     fn check_item_fn(&mut self, item: &hir::Item) {
 287         self.for_item(item).with_fcx(|fcx, this| {
 288             let def_id = fcx.tcx.hir.local_def_id(item.id);
 289             let sig = fcx.tcx.fn_sig(def_id);
 290             let sig = fcx.normalize_associated_types_in(item.span, &sig);
 291             let mut implied_bounds = vec![];
 292             this.check_fn_or_method(fcx, item.span, sig,
 293                                     def_id, &mut implied_bounds);
 294             implied_bounds
 295         })
 296     }
 297
 298     fn check_item_type(&mut self,
 299                        item: &hir::Item)
 300     {
 301         debug!("check_item_type: {:?}", item);
 302
 303         self.for_item(item).with_fcx(|fcx, this| {
 304             let ty = fcx.tcx.type_of(fcx.tcx.hir.local_def_id(item.id));
 305             let item_ty = fcx.normalize_associated_types_in(item.span, &ty);
 306
 307             fcx.register_wf_obligation(item_ty, item.span, this.code.clone());
 308
 309             vec![] // no implied bounds in a const etc
 310         });
 311     }
 312
 313     fn check_impl(&mut self,
 314                   item: &hir::Item,
 315                   ast_self_ty: &hir::Ty,
 316                   ast_trait_ref: &Option<hir::TraitRef>)
 317     {
 318         debug!("check_impl: {:?}", item);
 319
 320         self.for_item(item).with_fcx(|fcx, this| {
 321             let item_def_id = fcx.tcx.hir.local_def_id(item.id);
 322
 323             match *ast_trait_ref {
 324                 Some(ref ast_trait_ref) => {
 325                     let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 326                     let trait_ref =
 327                         fcx.normalize_associated_types_in(
 328                             ast_trait_ref.path.span, &trait_ref);
 329                     let obligations =
 330                         ty::wf::trait_obligations(fcx,
 331                                                   fcx.param_env,
 332                                                   fcx.body_id,
 333                                                   &trait_ref,
 334                                                   ast_trait_ref.path.span);
 335                     for obligation in obligations {
 336                         fcx.register_predicate(obligation);
 337                     }
 338                 }
 339                 None => {
 340                     let self_ty = fcx.tcx.type_of(item_def_id);
 341                     let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 342                     fcx.register_wf_obligation(self_ty, ast_self_ty.span, this.code.clone());
 343                 }
 344             }
 345
 346             this.check_where_clauses(fcx, item.span, item_def_id);
 347
 348             fcx.impl_implied_bounds(item_def_id, item.span)
 349         });
 350     }
 351
 352     /// Checks where clauses and inline bounds that are declared on def_id.
 353     fn check_where_clauses<'fcx, 'tcx>(&mut self,
 354                                        fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 355                                        span: Span,
 356                                        def_id: DefId) {
 357         use ty::subst::Subst;
 358         use rustc::ty::TypeFoldable;
 359
 360         let mut predicates = fcx.tcx.predicates_of(def_id);
 361         let mut substituted_predicates = Vec::new();
 362
 363         let generics = self.tcx.generics_of(def_id);
 364         let is_our_default = |def: &ty::TypeParameterDef|
 365                                 def.has_default && def.index >= generics.parent_count() as u32;
 366
 367         // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
 368         // For example this forbids the declaration:
 369         // struct Foo<T = Vec<[u32]>> { .. }
 370         // Here the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
 371         for d in generics.types.iter().cloned().filter(is_our_default).map(|p| p.def_id) {
 372             let ty = fcx.tcx.type_of(d);
 373             // ignore dependent defaults -- that is, where the default of one type
 374             // parameter includes another (e.g., <T, U = T>). In those cases, we can't
 375             // be sure if it will error or not as user might always specify the other.
 376             if !ty.needs_subst() {
 377                 fcx.register_wf_obligation(ty, fcx.tcx.def_span(d), self.code.clone());
 378             }
 379         }
 380
 381         // Check that trait predicates are WF when params are substituted by their defaults.
 382         // We don't want to overly constrain the predicates that may be written but we want to
 383         // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
 384         // Therefore we check if a predicate which contains a single type param
 385         // with a concrete default is WF with that default substituted.
 386         // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
 387         //
 388         // First we build the defaulted substitution.
 389         let substs = ty::subst::Substs::for_item(fcx.tcx, def_id, |def, _| {
 390                 // All regions are identity.
 391                 fcx.tcx.mk_region(ty::ReEarlyBound(def.to_early_bound_region_data()))
 392             }, |def, _| {
 393                 // If the param has a default,
 394                 if is_our_default(def) {
 395                     let default_ty = fcx.tcx.type_of(def.def_id);
 396                     // and it's not a dependent default
 397                     if !default_ty.needs_subst() {
 398                         // then substitute with the default.
 399                         return default_ty;
 400                     }
 401                 }
 402                 // Mark unwanted params as err.
 403                 fcx.tcx.types.err
 404             });
 405         // Now we build the substituted predicates.
 406         for &pred in predicates.predicates.iter() {
 407             struct CountParams { params: FxHashSet<u32> }
 408             impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
 409                 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
 410                     match t.sty {
 411                         ty::TyParam(p) => {
 412                             self.params.insert(p.idx);
 413                             t.super_visit_with(self)
 414                         }
 415                         _ => t.super_visit_with(self)
 416                     }
 417                 }
 418             }
 419             let mut param_count = CountParams { params: FxHashSet() };
 420             pred.visit_with(&mut param_count);
 421             let substituted_pred = pred.subst(fcx.tcx, substs);
 422             // Don't check non-defaulted params, dependent defaults or preds with multiple params.
 423             if substituted_pred.references_error() || param_count.params.len() > 1 {
 424                 continue;
 425             }
 426             // Avoid duplication of predicates that contain no parameters, for example.
 427             if !predicates.predicates.contains(&substituted_pred) {
 428                 substituted_predicates.push(substituted_pred);
 429             }
 430         }
 431
 432         predicates.predicates.extend(substituted_predicates);
 433         let predicates = predicates.instantiate_identity(fcx.tcx);
 434         let predicates = fcx.normalize_associated_types_in(span, &predicates);
 435
 436         let obligations =
 437             predicates.predicates
 438                       .iter()
 439                       .flat_map(|p| ty::wf::predicate_obligations(fcx,
 440                                                                   fcx.param_env,
 441                                                                   fcx.body_id,
 442                                                                   p,
 443                                                                   span));
 444
 445         for obligation in obligations {
 446             fcx.register_predicate(obligation);
 447         }
 448     }
 449
 450     fn check_fn_or_method<'fcx, 'tcx>(&mut self,
 451                                       fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 452                                       span: Span,
 453                                       sig: ty::PolyFnSig<'tcx>,
 454                                       def_id: DefId,
 455                                       implied_bounds: &mut Vec<Ty<'tcx>>)
 456     {
 457         let sig = fcx.normalize_associated_types_in(span, &sig);
 458         let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 459
 460         for input_ty in sig.inputs() {
 461             fcx.register_wf_obligation(&input_ty, span, self.code.clone());
 462         }
 463         implied_bounds.extend(sig.inputs());
 464
 465         fcx.register_wf_obligation(sig.output(), span, self.code.clone());
 466
 467         // FIXME(#25759) return types should not be implied bounds
 468         implied_bounds.push(sig.output());
 469
 470         self.check_where_clauses(fcx, span, def_id);
 471     }
 472
 473     fn check_method_receiver<'fcx, 'tcx>(&mut self,
 474                                          fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 475                                          method_sig: &hir::MethodSig,
 476                                          method: &ty::AssociatedItem,
 477                                          self_ty: Ty<'tcx>)
 478     {
 479         // check that the method has a valid receiver type, given the type `Self`
 480         debug!("check_method_receiver({:?}, self_ty={:?})",
 481                method, self_ty);
 482
 483         if !method.method_has_self_argument {
 484             return;
 485         }
 486
 487         let span = method_sig.decl.inputs[0].span;
 488
 489         let sig = fcx.tcx.fn_sig(method.def_id);
 490         let sig = fcx.normalize_associated_types_in(span, &sig);
 491         let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 492
 493         debug!("check_method_receiver: sig={:?}", sig);
 494
 495         let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 496         let self_ty = fcx.tcx.liberate_late_bound_regions(
 497             method.def_id,
 498             &ty::Binder(self_ty)
 499         );
 500
 501         let self_arg_ty = sig.inputs()[0];
 502
 503         let cause = fcx.cause(span, ObligationCauseCode::MethodReceiver);
 504         let self_arg_ty = fcx.normalize_associated_types_in(span, &self_arg_ty);
 505         let self_arg_ty = fcx.tcx.liberate_late_bound_regions(
 506             method.def_id,
 507             &ty::Binder(self_arg_ty)
 508         );
 509
 510         let mut autoderef = fcx.autoderef(span, self_arg_ty).include_raw_pointers();
 511
 512         loop {
 513             if let Some((potential_self_ty, _)) = autoderef.next() {
 514                 debug!("check_method_receiver: potential self type `{:?}` to match `{:?}`",
 515                     potential_self_ty, self_ty);
 516
 517                 if fcx.infcx.can_eq(fcx.param_env, self_ty, potential_self_ty).is_ok() {
 518                     autoderef.finalize();
 519                     if let Some(mut err) = fcx.demand_eqtype_with_origin(
 520                         &cause, self_ty, potential_self_ty) {
 521                         err.emit();
 522                     }
 523                     break
 524                 }
 525             } else {
 526                 fcx.tcx.sess.diagnostic().mut_span_err(
 527                     span, &format!("invalid `self` type: {:?}", self_arg_ty))
 528                 .note(&format!("type must be `{:?}` or a type that dereferences to it`", self_ty))
 529                 .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 530                 .code(DiagnosticId::Error("E0307".into()))
 531                 .emit();
 532                 return
 533             }
 534         }
 535
 536         let is_self_ty = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 537         let self_kind = ExplicitSelf::determine(self_arg_ty, is_self_ty);
 538
 539         if !fcx.tcx.sess.features.borrow().arbitrary_self_types {
 540             match self_kind {
 541                 ExplicitSelf::ByValue |
 542                 ExplicitSelf::ByReference(_, _) |
 543                 ExplicitSelf::ByBox => (),
 544
 545                 ExplicitSelf::ByRawPointer(_) => {
 546                     feature_gate::feature_err(
 547                         &fcx.tcx.sess.parse_sess,
 548                         "arbitrary_self_types",
 549                         span,
 550                         GateIssue::Language,
 551                         "raw pointer `self` is unstable")
 552                     .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 553                     .emit();
 554                 }
 555
 556                 ExplicitSelf::Other => {
 557                     feature_gate::feature_err(
 558                         &fcx.tcx.sess.parse_sess,
 559                         "arbitrary_self_types",
 560                         span,
 561                         GateIssue::Language,"arbitrary `self` types are unstable")
 562                     .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 563                     .emit();
 564                 }
 565             }
 566         }
 567     }
 568
 569     fn check_variances_for_type_defn(&self,
 570                                      item: &hir::Item,
 571                                      ast_generics: &hir::Generics)
 572     {
 573         let item_def_id = self.tcx.hir.local_def_id(item.id);
 574         let ty = self.tcx.type_of(item_def_id);
 575         if self.tcx.has_error_field(ty) {
 576             return;
 577         }
 578
 579         let ty_predicates = self.tcx.predicates_of(item_def_id);
 580         assert_eq!(ty_predicates.parent, None);
 581         let variances = self.tcx.variances_of(item_def_id);
 582
 583         let mut constrained_parameters: FxHashSet<_> =
 584             variances.iter().enumerate()
 585                      .filter(|&(_, &variance)| variance != ty::Bivariant)
 586                      .map(|(index, _)| Parameter(index as u32))
 587                      .collect();
 588
 589         identify_constrained_type_params(self.tcx,
 590                                          ty_predicates.predicates.as_slice(),
 591                                          None,
 592                                          &mut constrained_parameters);
 593
 594         for (index, _) in variances.iter().enumerate() {
 595             if constrained_parameters.contains(&Parameter(index as u32)) {
 596                 continue;
 597             }
 598
 599             let (span, name) = match ast_generics.params[index] {
 600                 hir::GenericParam::Lifetime(ref ld) => (ld.lifetime.span, ld.lifetime.name.name()),
 601                 hir::GenericParam::Type(ref tp) => (tp.span, tp.name),
 602             };
 603             self.report_bivariance(span, name);
 604         }
 605     }
 606
 607     fn report_bivariance(&self,
 608                          span: Span,
 609                          param_name: ast::Name)
 610     {
 611         let mut err = error_392(self.tcx, span, param_name);
 612
 613         let suggested_marker_id = self.tcx.lang_items().phantom_data();
 614         match suggested_marker_id {
 615             Some(def_id) => {
 616                 err.help(
 617                     &format!("consider removing `{}` or using a marker such as `{}`",
 618                              param_name,
 619                              self.tcx.item_path_str(def_id)));
 620             }
 621             None => {
 622                 // no lang items, no help!
 623             }
 624         }
 625         err.emit();
 626     }
 627 }
 628
 629 fn reject_shadowing_type_parameters(tcx: TyCtxt, def_id: DefId) {
 630     let generics = tcx.generics_of(def_id);
 631     let parent = tcx.generics_of(generics.parent.unwrap());
 632     let impl_params: FxHashMap<_, _> = parent.types
 633                                        .iter()
 634                                        .map(|tp| (tp.name, tp.def_id))
 635                                        .collect();
 636
 637     for method_param in &generics.types {
 638         if impl_params.contains_key(&method_param.name) {
 639             // Tighten up the span to focus on only the shadowing type
 640             let type_span = tcx.def_span(method_param.def_id);
 641
 642             // The expectation here is that the original trait declaration is
 643             // local so it should be okay to just unwrap everything.
 644             let trait_def_id = impl_params[&method_param.name];
 645             let trait_decl_span = tcx.def_span(trait_def_id);
 646             error_194(tcx, type_span, trait_decl_span, method_param.name);
 647         }
 648     }
 649 }
 650
 651 impl<'a, 'tcx, 'v> Visitor<'v> for CheckTypeWellFormedVisitor<'a, 'tcx> {
 652     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
 653         NestedVisitorMap::None
 654     }
 655
 656     fn visit_item(&mut self, i: &hir::Item) {
 657         debug!("visit_item: {:?}", i);
 658         self.check_item_well_formed(i);
 659         intravisit::walk_item(self, i);
 660     }
 661
 662     fn visit_trait_item(&mut self, trait_item: &'v hir::TraitItem) {
 663         debug!("visit_trait_item: {:?}", trait_item);
 664         let method_sig = match trait_item.node {
 665             hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 666             _ => None
 667         };
 668         self.check_associated_item(trait_item.id, trait_item.span, method_sig);
 669         intravisit::walk_trait_item(self, trait_item)
 670     }
 671
 672     fn visit_impl_item(&mut self, impl_item: &'v hir::ImplItem) {
 673         debug!("visit_impl_item: {:?}", impl_item);
 674         let method_sig = match impl_item.node {
 675             hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 676             _ => None
 677         };
 678         self.check_associated_item(impl_item.id, impl_item.span, method_sig);
 679         intravisit::walk_impl_item(self, impl_item)
 680     }
 681 }
 682
 683 ///////////////////////////////////////////////////////////////////////////
 684 // ADT
 685
 686 struct AdtVariant<'tcx> {
 687     fields: Vec<AdtField<'tcx>>,
 688 }
 689
 690 struct AdtField<'tcx> {
 691     ty: Ty<'tcx>,
 692     span: Span,
 693 }
 694
 695 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 696     fn non_enum_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
 697         let fields =
 698             struct_def.fields().iter()
 699             .map(|field| {
 700                 let field_ty = self.tcx.type_of(self.tcx.hir.local_def_id(field.id));
 701                 let field_ty = self.normalize_associated_types_in(field.span,
 702                                                                   &field_ty);
 703                 AdtField { ty: field_ty, span: field.span }
 704             })
 705             .collect();
 706         AdtVariant { fields: fields }
 707     }
 708
 709     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
 710         enum_def.variants.iter()
 711             .map(|variant| self.non_enum_variant(&variant.node.data))
 712             .collect()
 713     }
 714
 715     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
 716         match self.tcx.impl_trait_ref(impl_def_id) {
 717             Some(ref trait_ref) => {
 718                 // Trait impl: take implied bounds from all types that
 719                 // appear in the trait reference.
 720                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
 721                 trait_ref.substs.types().collect()
 722             }
 723
 724             None => {
 725                 // Inherent impl: take implied bounds from the self type.
 726                 let self_ty = self.tcx.type_of(impl_def_id);
 727                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
 728                 vec![self_ty]
 729             }
 730         }
 731     }
 732 }
 733
 734 fn error_392<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, span: Span, param_name: ast::Name)
 735                        -> DiagnosticBuilder<'tcx> {
 736     let mut err = struct_span_err!(tcx.sess, span, E0392,
 737                   "parameter `{}` is never used", param_name);
 738     err.span_label(span, "unused type parameter");
 739     err
 740 }
 741
 742 fn error_194(tcx: TyCtxt, span: Span, trait_decl_span: Span, name: ast::Name) {
 743     struct_span_err!(tcx.sess, span, E0194,
 744               "type parameter `{}` shadows another type parameter of the same name",
 745               name)
 746         .span_label(span, "shadows another type parameter")
 747         .span_label(trait_decl_span, format!("first `{}` declared here", name))
 748         .emit();
 749 }