src/librustc_typeck/collect.rs

   1 //! "Collection" is the process of determining the type and other external
   2 //! details of each item in Rust. Collection is specifically concerned
   3 //! with *inter-procedural* things -- for example, for a function
   4 //! definition, collection will figure out the type and signature of the
   5 //! function, but it will not visit the *body* of the function in any way,
   6 //! nor examine type annotations on local variables (that's the job of
   7 //! type *checking*).
   8 //!
   9 //! Collecting is ultimately defined by a bundle of queries that
  10 //! inquire after various facts about the items in the crate (e.g.,
  11 //! `type_of`, `generics_of`, `predicates_of`, etc). See the `provide` function
  12 //! for the full set.
  13 //!
  14 //! At present, however, we do run collection across all items in the
  15 //! crate as a kind of pass. This should eventually be factored away.
  16
  17 use crate::astconv::{AstConv, Bounds, SizedByDefault};
  18 use crate::constrained_generic_params as cgp;
  19 use crate::check::intrinsic::intrisic_operation_unsafety;
  20 use crate::lint;
  21 use crate::middle::resolve_lifetime as rl;
  22 use crate::middle::weak_lang_items;
  23 use rustc::mir::mono::Linkage;
  24 use rustc::ty::query::Providers;
  25 use rustc::ty::subst::{Subst, InternalSubsts};
  26 use rustc::ty::util::Discr;
  27 use rustc::ty::util::IntTypeExt;
  28 use rustc::ty::subst::UnpackedKind;
  29 use rustc::ty::{self, AdtKind, DefIdTree, ToPolyTraitRef, Ty, TyCtxt, Const};
  30 use rustc::ty::{ReprOptions, ToPredicate};
  31 use rustc::util::captures::Captures;
  32 use rustc::util::nodemap::FxHashMap;
  33 use rustc_target::spec::abi;
  34
  35 use syntax::ast;
  36 use syntax::ast::{Ident, MetaItemKind};
  37 use syntax::attr::{InlineAttr, OptimizeAttr, list_contains_name, mark_used};
  38 use syntax::feature_gate;
  39 use syntax::symbol::{InternedString, kw, Symbol, sym};
  40 use syntax_pos::{Span, DUMMY_SP};
  41
  42 use rustc::hir::def::{CtorKind, Res, DefKind};
  43 use rustc::hir::Node;
  44 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
  45 use rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
  46 use rustc::hir::GenericParamKind;
  47 use rustc::hir::{self, CodegenFnAttrFlags, CodegenFnAttrs, Unsafety};
  48
  49 use errors::{Applicability, DiagnosticId};
  50
  51 struct OnlySelfBounds(bool);
  52
  53 ///////////////////////////////////////////////////////////////////////////
  54 // Main entry point
  55
  56 fn collect_mod_item_types(tcx: TyCtxt<'_>, module_def_id: DefId) {
  57     tcx.hir().visit_item_likes_in_module(
  58         module_def_id,
  59         &mut CollectItemTypesVisitor { tcx }.as_deep_visitor()
  60     );
  61 }
  62
  63 pub fn provide(providers: &mut Providers<'_>) {
  64     *providers = Providers {
  65         type_of,
  66         generics_of,
  67         predicates_of,
  68         predicates_defined_on,
  69         explicit_predicates_of,
  70         super_predicates_of,
  71         type_param_predicates,
  72         trait_def,
  73         adt_def,
  74         fn_sig,
  75         impl_trait_ref,
  76         impl_polarity,
  77         is_foreign_item,
  78         static_mutability,
  79         codegen_fn_attrs,
  80         collect_mod_item_types,
  81         ..*providers
  82     };
  83 }
  84
  85 ///////////////////////////////////////////////////////////////////////////
  86
  87 /// Context specific to some particular item. This is what implements
  88 /// `AstConv`. It has information about the predicates that are defined
  89 /// on the trait. Unfortunately, this predicate information is
  90 /// available in various different forms at various points in the
  91 /// process. So we can't just store a pointer to e.g., the AST or the
  92 /// parsed ty form, we have to be more flexible. To this end, the
  93 /// `ItemCtxt` is parameterized by a `DefId` that it uses to satisfy
  94 /// `get_type_parameter_bounds` requests, drawing the information from
  95 /// the AST (`hir::Generics`), recursively.
  96 pub struct ItemCtxt<'tcx> {
  97     tcx: TyCtxt<'tcx>,
  98     item_def_id: DefId,
  99 }
 100
 101 ///////////////////////////////////////////////////////////////////////////
 102
 103 struct CollectItemTypesVisitor<'tcx> {
 104     tcx: TyCtxt<'tcx>,
 105 }
 106
 107 impl Visitor<'tcx> for CollectItemTypesVisitor<'tcx> {
 108     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 109         NestedVisitorMap::OnlyBodies(&self.tcx.hir())
 110     }
 111
 112     fn visit_item(&mut self, item: &'tcx hir::Item) {
 113         convert_item(self.tcx, item.hir_id);
 114         intravisit::walk_item(self, item);
 115     }
 116
 117     fn visit_generics(&mut self, generics: &'tcx hir::Generics) {
 118         for param in &generics.params {
 119             match param.kind {
 120                 hir::GenericParamKind::Lifetime { .. } => {}
 121                 hir::GenericParamKind::Type {
 122                     default: Some(_), ..
 123                 } => {
 124                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 125                     self.tcx.type_of(def_id);
 126                 }
 127                 hir::GenericParamKind::Type { .. } => {}
 128                 hir::GenericParamKind::Const { .. } => {
 129                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 130                     self.tcx.type_of(def_id);
 131                 }
 132             }
 133         }
 134         intravisit::walk_generics(self, generics);
 135     }
 136
 137     fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
 138         if let hir::ExprKind::Closure(..) = expr.node {
 139             let def_id = self.tcx.hir().local_def_id(expr.hir_id);
 140             self.tcx.generics_of(def_id);
 141             self.tcx.type_of(def_id);
 142         }
 143         intravisit::walk_expr(self, expr);
 144     }
 145
 146     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
 147         convert_trait_item(self.tcx, trait_item.hir_id);
 148         intravisit::walk_trait_item(self, trait_item);
 149     }
 150
 151     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
 152         convert_impl_item(self.tcx, impl_item.hir_id);
 153         intravisit::walk_impl_item(self, impl_item);
 154     }
 155 }
 156
 157 ///////////////////////////////////////////////////////////////////////////
 158 // Utility types and common code for the above passes.
 159
 160 fn bad_placeholder_type(tcx: TyCtxt<'tcx>, span: Span) -> errors::DiagnosticBuilder<'tcx> {
 161     let mut diag = tcx.sess.struct_span_err_with_code(
 162         span,
 163         "the type placeholder `_` is not allowed within types on item signatures",
 164         DiagnosticId::Error("E0121".into()),
 165     );
 166     diag.span_label(span, "not allowed in type signatures");
 167     diag
 168 }
 169
 170 impl ItemCtxt<'tcx> {
 171     pub fn new(tcx: TyCtxt<'tcx>, item_def_id: DefId) -> ItemCtxt<'tcx> {
 172         ItemCtxt { tcx, item_def_id }
 173     }
 174
 175     pub fn to_ty(&self, ast_ty: &'tcx hir::Ty) -> Ty<'tcx> {
 176         AstConv::ast_ty_to_ty(self, ast_ty)
 177     }
 178 }
 179
 180 impl AstConv<'tcx> for ItemCtxt<'tcx> {
 181     fn tcx(&self) -> TyCtxt<'tcx> {
 182         self.tcx
 183     }
 184
 185     fn get_type_parameter_bounds(&self, span: Span, def_id: DefId)
 186                                  -> &'tcx ty::GenericPredicates<'tcx> {
 187         self.tcx
 188             .at(span)
 189             .type_param_predicates((self.item_def_id, def_id))
 190     }
 191
 192     fn re_infer(
 193         &self,
 194         _: Option<&ty::GenericParamDef>,
 195         _: Span,
 196     ) -> Option<ty::Region<'tcx>> {
 197         None
 198     }
 199
 200     fn ty_infer(&self, _: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
 201         bad_placeholder_type(self.tcx(), span).emit();
 202
 203         self.tcx().types.err
 204     }
 205
 206     fn ct_infer(
 207         &self,
 208         _: Ty<'tcx>,
 209         _: Option<&ty::GenericParamDef>,
 210         span: Span,
 211     ) -> &'tcx Const<'tcx> {
 212         bad_placeholder_type(self.tcx(), span).emit();
 213
 214         self.tcx().consts.err
 215     }
 216
 217     fn projected_ty_from_poly_trait_ref(
 218         &self,
 219         span: Span,
 220         item_def_id: DefId,
 221         poly_trait_ref: ty::PolyTraitRef<'tcx>,
 222     ) -> Ty<'tcx> {
 223         if let Some(trait_ref) = poly_trait_ref.no_bound_vars() {
 224             self.tcx().mk_projection(item_def_id, trait_ref.substs)
 225         } else {
 226             // There are no late-bound regions; we can just ignore the binder.
 227             span_err!(
 228                 self.tcx().sess,
 229                 span,
 230                 E0212,
 231                 "cannot extract an associated type from a higher-ranked trait bound \
 232                  in this context"
 233             );
 234             self.tcx().types.err
 235         }
 236     }
 237
 238     fn normalize_ty(&self, _span: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
 239         // Types in item signatures are not normalized to avoid undue dependencies.
 240         ty
 241     }
 242
 243     fn set_tainted_by_errors(&self) {
 244         // There's no obvious place to track this, so just let it go.
 245     }
 246
 247     fn record_ty(&self, _hir_id: hir::HirId, _ty: Ty<'tcx>, _span: Span) {
 248         // There's no place to record types from signatures?
 249     }
 250 }
 251
 252 /// Returns the predicates defined on `item_def_id` of the form
 253 /// `X: Foo` where `X` is the type parameter `def_id`.
 254 fn type_param_predicates(
 255     tcx: TyCtxt<'_>,
 256     (item_def_id, def_id): (DefId, DefId),
 257 ) -> &ty::GenericPredicates<'_> {
 258     use rustc::hir::*;
 259
 260     // In the AST, bounds can derive from two places. Either
 261     // written inline like `<T: Foo>` or in a where-clause like
 262     // `where T: Foo`.
 263
 264     let param_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 265     let param_owner = tcx.hir().ty_param_owner(param_id);
 266     let param_owner_def_id = tcx.hir().local_def_id(param_owner);
 267     let generics = tcx.generics_of(param_owner_def_id);
 268     let index = generics.param_def_id_to_index[&def_id];
 269     let ty = tcx.mk_ty_param(index, tcx.hir().ty_param_name(param_id).as_interned_str());
 270
 271     // Don't look for bounds where the type parameter isn't in scope.
 272     let parent = if item_def_id == param_owner_def_id {
 273         None
 274     } else {
 275         tcx.generics_of(item_def_id).parent
 276     };
 277
 278     let result = parent.map_or(&tcx.common.empty_predicates, |parent| {
 279         let icx = ItemCtxt::new(tcx, parent);
 280         icx.get_type_parameter_bounds(DUMMY_SP, def_id)
 281     });
 282     let mut extend = None;
 283
 284     let item_hir_id = tcx.hir().as_local_hir_id(item_def_id).unwrap();
 285     let ast_generics = match tcx.hir().get(item_hir_id) {
 286         Node::TraitItem(item) => &item.generics,
 287
 288         Node::ImplItem(item) => &item.generics,
 289
 290         Node::Item(item) => {
 291             match item.node {
 292                 ItemKind::Fn(.., ref generics, _)
 293                 | ItemKind::Impl(_, _, _, ref generics, ..)
 294                 | ItemKind::TyAlias(_, ref generics)
 295                 | ItemKind::OpaqueTy(OpaqueTy {
 296                     ref generics,
 297                     impl_trait_fn: None,
 298                     ..
 299                 })
 300                 | ItemKind::Enum(_, ref generics)
 301                 | ItemKind::Struct(_, ref generics)
 302                 | ItemKind::Union(_, ref generics) => generics,
 303                 ItemKind::Trait(_, _, ref generics, ..) => {
 304                     // Implied `Self: Trait` and supertrait bounds.
 305                     if param_id == item_hir_id {
 306                         let identity_trait_ref = ty::TraitRef::identity(tcx, item_def_id);
 307                         extend = Some((identity_trait_ref.to_predicate(), item.span));
 308                     }
 309                     generics
 310                 }
 311                 _ => return result,
 312             }
 313         }
 314
 315         Node::ForeignItem(item) => match item.node {
 316             ForeignItemKind::Fn(_, _, ref generics) => generics,
 317             _ => return result,
 318         },
 319
 320         _ => return result,
 321     };
 322
 323     let icx = ItemCtxt::new(tcx, item_def_id);
 324     let mut result = (*result).clone();
 325     result.predicates.extend(extend.into_iter());
 326     result.predicates.extend(
 327         icx.type_parameter_bounds_in_generics(ast_generics, param_id, ty, OnlySelfBounds(true))
 328             .into_iter()
 329             .filter(|(predicate, _)| {
 330                 match predicate {
 331                     ty::Predicate::Trait(ref data) => data.skip_binder().self_ty().is_param(index),
 332                     _ => false,
 333                 }
 334             })
 335     );
 336     tcx.arena.alloc(result)
 337 }
 338
 339 impl ItemCtxt<'tcx> {
 340     /// Finds bounds from `hir::Generics`. This requires scanning through the
 341     /// AST. We do this to avoid having to convert *all* the bounds, which
 342     /// would create artificial cycles. Instead, we can only convert the
 343     /// bounds for a type parameter `X` if `X::Foo` is used.
 344     fn type_parameter_bounds_in_generics(
 345         &self,
 346         ast_generics: &'tcx hir::Generics,
 347         param_id: hir::HirId,
 348         ty: Ty<'tcx>,
 349         only_self_bounds: OnlySelfBounds,
 350     ) -> Vec<(ty::Predicate<'tcx>, Span)> {
 351         let from_ty_params = ast_generics
 352             .params
 353             .iter()
 354             .filter_map(|param| match param.kind {
 355                 GenericParamKind::Type { .. } if param.hir_id == param_id => Some(&param.bounds),
 356                 _ => None,
 357             })
 358             .flat_map(|bounds| bounds.iter())
 359             .flat_map(|b| predicates_from_bound(self, ty, b));
 360
 361         let from_where_clauses = ast_generics
 362             .where_clause
 363             .predicates
 364             .iter()
 365             .filter_map(|wp| match *wp {
 366                 hir::WherePredicate::BoundPredicate(ref bp) => Some(bp),
 367                 _ => None,
 368             })
 369             .flat_map(|bp| {
 370                 let bt = if is_param(self.tcx, &bp.bounded_ty, param_id) {
 371                     Some(ty)
 372                 } else if !only_self_bounds.0 {
 373                     Some(self.to_ty(&bp.bounded_ty))
 374                 } else {
 375                     None
 376                 };
 377                 bp.bounds.iter().filter_map(move |b| bt.map(|bt| (bt, b)))
 378             })
 379             .flat_map(|(bt, b)| predicates_from_bound(self, bt, b));
 380
 381         from_ty_params.chain(from_where_clauses).collect()
 382     }
 383 }
 384
 385 /// Tests whether this is the AST for a reference to the type
 386 /// parameter with ID `param_id`. We use this so as to avoid running
 387 /// `ast_ty_to_ty`, because we want to avoid triggering an all-out
 388 /// conversion of the type to avoid inducing unnecessary cycles.
 389 fn is_param(tcx: TyCtxt<'_>, ast_ty: &hir::Ty, param_id: hir::HirId) -> bool {
 390     if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = ast_ty.node {
 391         match path.res {
 392             Res::SelfTy(Some(def_id), None) | Res::Def(DefKind::TyParam, def_id) => {
 393                 def_id == tcx.hir().local_def_id(param_id)
 394             }
 395             _ => false,
 396         }
 397     } else {
 398         false
 399     }
 400 }
 401
 402 fn convert_item(tcx: TyCtxt<'_>, item_id: hir::HirId) {
 403     let it = tcx.hir().expect_item(item_id);
 404     debug!("convert: item {} with id {}", it.ident, it.hir_id);
 405     let def_id = tcx.hir().local_def_id(item_id);
 406     match it.node {
 407         // These don't define types.
 408         hir::ItemKind::ExternCrate(_)
 409         | hir::ItemKind::Use(..)
 410         | hir::ItemKind::Mod(_)
 411         | hir::ItemKind::GlobalAsm(_) => {}
 412         hir::ItemKind::ForeignMod(ref foreign_mod) => {
 413             for item in &foreign_mod.items {
 414                 let def_id = tcx.hir().local_def_id(item.hir_id);
 415                 tcx.generics_of(def_id);
 416                 tcx.type_of(def_id);
 417                 tcx.predicates_of(def_id);
 418                 if let hir::ForeignItemKind::Fn(..) = item.node {
 419                     tcx.fn_sig(def_id);
 420                 }
 421             }
 422         }
 423         hir::ItemKind::Enum(ref enum_definition, _) => {
 424             tcx.generics_of(def_id);
 425             tcx.type_of(def_id);
 426             tcx.predicates_of(def_id);
 427             convert_enum_variant_types(tcx, def_id, &enum_definition.variants);
 428         }
 429         hir::ItemKind::Impl(..) => {
 430             tcx.generics_of(def_id);
 431             tcx.type_of(def_id);
 432             tcx.impl_trait_ref(def_id);
 433             tcx.predicates_of(def_id);
 434         }
 435         hir::ItemKind::Trait(..) => {
 436             tcx.generics_of(def_id);
 437             tcx.trait_def(def_id);
 438             tcx.at(it.span).super_predicates_of(def_id);
 439             tcx.predicates_of(def_id);
 440         }
 441         hir::ItemKind::TraitAlias(..) => {
 442             tcx.generics_of(def_id);
 443             tcx.at(it.span).super_predicates_of(def_id);
 444             tcx.predicates_of(def_id);
 445         }
 446         hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 447             tcx.generics_of(def_id);
 448             tcx.type_of(def_id);
 449             tcx.predicates_of(def_id);
 450
 451             for f in struct_def.fields() {
 452                 let def_id = tcx.hir().local_def_id(f.hir_id);
 453                 tcx.generics_of(def_id);
 454                 tcx.type_of(def_id);
 455                 tcx.predicates_of(def_id);
 456             }
 457
 458             if let Some(ctor_hir_id) = struct_def.ctor_hir_id() {
 459                 convert_variant_ctor(tcx, ctor_hir_id);
 460             }
 461         }
 462
 463         // Desugared from `impl Trait`, so visited by the function's return type.
 464         hir::ItemKind::OpaqueTy(hir::OpaqueTy {
 465             impl_trait_fn: Some(_),
 466             ..
 467         }) => {}
 468
 469         hir::ItemKind::OpaqueTy(..)
 470         | hir::ItemKind::TyAlias(..)
 471         | hir::ItemKind::Static(..)
 472         | hir::ItemKind::Const(..)
 473         | hir::ItemKind::Fn(..) => {
 474             tcx.generics_of(def_id);
 475             tcx.type_of(def_id);
 476             tcx.predicates_of(def_id);
 477             if let hir::ItemKind::Fn(..) = it.node {
 478                 tcx.fn_sig(def_id);
 479             }
 480         }
 481     }
 482 }
 483
 484 fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::HirId) {
 485     let trait_item = tcx.hir().expect_trait_item(trait_item_id);
 486     let def_id = tcx.hir().local_def_id(trait_item.hir_id);
 487     tcx.generics_of(def_id);
 488
 489     match trait_item.node {
 490         hir::TraitItemKind::Const(..)
 491         | hir::TraitItemKind::Type(_, Some(_))
 492         | hir::TraitItemKind::Method(..) => {
 493             tcx.type_of(def_id);
 494             if let hir::TraitItemKind::Method(..) = trait_item.node {
 495                 tcx.fn_sig(def_id);
 496             }
 497         }
 498
 499         hir::TraitItemKind::Type(_, None) => {}
 500     };
 501
 502     tcx.predicates_of(def_id);
 503 }
 504
 505 fn convert_impl_item(tcx: TyCtxt<'_>, impl_item_id: hir::HirId) {
 506     let def_id = tcx.hir().local_def_id(impl_item_id);
 507     tcx.generics_of(def_id);
 508     tcx.type_of(def_id);
 509     tcx.predicates_of(def_id);
 510     if let hir::ImplItemKind::Method(..) = tcx.hir().expect_impl_item(impl_item_id).node {
 511         tcx.fn_sig(def_id);
 512     }
 513 }
 514
 515 fn convert_variant_ctor(tcx: TyCtxt<'_>, ctor_id: hir::HirId) {
 516     let def_id = tcx.hir().local_def_id(ctor_id);
 517     tcx.generics_of(def_id);
 518     tcx.type_of(def_id);
 519     tcx.predicates_of(def_id);
 520 }
 521
 522 fn convert_enum_variant_types(
 523     tcx: TyCtxt<'_>,
 524     def_id: DefId,
 525     variants: &[hir::Variant]
 526 ) {
 527     let def = tcx.adt_def(def_id);
 528     let repr_type = def.repr.discr_type();
 529     let initial = repr_type.initial_discriminant(tcx);
 530     let mut prev_discr = None::<Discr<'_>>;
 531
 532     // fill the discriminant values and field types
 533     for variant in variants {
 534         let wrapped_discr = prev_discr.map_or(initial, |d| d.wrap_incr(tcx));
 535         prev_discr = Some(
 536             if let Some(ref e) = variant.disr_expr {
 537                 let expr_did = tcx.hir().local_def_id(e.hir_id);
 538                 def.eval_explicit_discr(tcx, expr_did)
 539             } else if let Some(discr) = repr_type.disr_incr(tcx, prev_discr) {
 540                 Some(discr)
 541             } else {
 542                 struct_span_err!(
 543                     tcx.sess,
 544                     variant.span,
 545                     E0370,
 546                     "enum discriminant overflowed"
 547                 ).span_label(
 548                     variant.span,
 549                     format!("overflowed on value after {}", prev_discr.unwrap()),
 550                 ).note(&format!(
 551                     "explicitly set `{} = {}` if that is desired outcome",
 552                     variant.ident, wrapped_discr
 553                 ))
 554                 .emit();
 555                 None
 556             }.unwrap_or(wrapped_discr),
 557         );
 558
 559         for f in variant.data.fields() {
 560             let def_id = tcx.hir().local_def_id(f.hir_id);
 561             tcx.generics_of(def_id);
 562             tcx.type_of(def_id);
 563             tcx.predicates_of(def_id);
 564         }
 565
 566         // Convert the ctor, if any. This also registers the variant as
 567         // an item.
 568         if let Some(ctor_hir_id) = variant.data.ctor_hir_id() {
 569             convert_variant_ctor(tcx, ctor_hir_id);
 570         }
 571     }
 572 }
 573
 574 fn convert_variant(
 575     tcx: TyCtxt<'_>,
 576     variant_did: Option<DefId>,
 577     ctor_did: Option<DefId>,
 578     ident: Ident,
 579     discr: ty::VariantDiscr,
 580     def: &hir::VariantData,
 581     adt_kind: ty::AdtKind,
 582     parent_did: DefId,
 583 ) -> ty::VariantDef {
 584     let mut seen_fields: FxHashMap<ast::Ident, Span> = Default::default();
 585     let hir_id = tcx.hir().as_local_hir_id(variant_did.unwrap_or(parent_did)).unwrap();
 586     let fields = def
 587         .fields()
 588         .iter()
 589         .map(|f| {
 590             let fid = tcx.hir().local_def_id(f.hir_id);
 591             let dup_span = seen_fields.get(&f.ident.modern()).cloned();
 592             if let Some(prev_span) = dup_span {
 593                 struct_span_err!(
 594                     tcx.sess,
 595                     f.span,
 596                     E0124,
 597                     "field `{}` is already declared",
 598                     f.ident
 599                 ).span_label(f.span, "field already declared")
 600                  .span_label(prev_span, format!("`{}` first declared here", f.ident))
 601                  .emit();
 602             } else {
 603                 seen_fields.insert(f.ident.modern(), f.span);
 604             }
 605
 606             ty::FieldDef {
 607                 did: fid,
 608                 ident: f.ident,
 609                 vis: ty::Visibility::from_hir(&f.vis, hir_id, tcx),
 610             }
 611         })
 612         .collect();
 613     let recovered = match def {
 614         hir::VariantData::Struct(_, r) => *r,
 615         _ => false,
 616     };
 617     ty::VariantDef::new(
 618         tcx,
 619         ident,
 620         variant_did,
 621         ctor_did,
 622         discr,
 623         fields,
 624         CtorKind::from_hir(def),
 625         adt_kind,
 626         parent_did,
 627         recovered,
 628     )
 629 }
 630
 631 fn adt_def(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::AdtDef {
 632     use rustc::hir::*;
 633
 634     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 635     let item = match tcx.hir().get(hir_id) {
 636         Node::Item(item) => item,
 637         _ => bug!(),
 638     };
 639
 640     let repr = ReprOptions::new(tcx, def_id);
 641     let (kind, variants) = match item.node {
 642         ItemKind::Enum(ref def, _) => {
 643             let mut distance_from_explicit = 0;
 644             let variants = def.variants
 645                 .iter()
 646                 .map(|v| {
 647                     let variant_did = Some(tcx.hir().local_def_id(v.id));
 648                     let ctor_did = v.data.ctor_hir_id()
 649                         .map(|hir_id| tcx.hir().local_def_id(hir_id));
 650
 651                     let discr = if let Some(ref e) = v.disr_expr {
 652                         distance_from_explicit = 0;
 653                         ty::VariantDiscr::Explicit(tcx.hir().local_def_id(e.hir_id))
 654                     } else {
 655                         ty::VariantDiscr::Relative(distance_from_explicit)
 656                     };
 657                     distance_from_explicit += 1;
 658
 659                     convert_variant(tcx, variant_did, ctor_did, v.ident, discr,
 660                                     &v.data, AdtKind::Enum, def_id)
 661                 })
 662                 .collect();
 663
 664             (AdtKind::Enum, variants)
 665         }
 666         ItemKind::Struct(ref def, _) => {
 667             let variant_did = None;
 668             let ctor_did = def.ctor_hir_id()
 669                 .map(|hir_id| tcx.hir().local_def_id(hir_id));
 670
 671             let variants = std::iter::once(convert_variant(
 672                 tcx, variant_did, ctor_did, item.ident, ty::VariantDiscr::Relative(0), def,
 673                 AdtKind::Struct, def_id,
 674             )).collect();
 675
 676             (AdtKind::Struct, variants)
 677         }
 678         ItemKind::Union(ref def, _) => {
 679             let variant_did = None;
 680             let ctor_did = def.ctor_hir_id()
 681                 .map(|hir_id| tcx.hir().local_def_id(hir_id));
 682
 683             let variants = std::iter::once(convert_variant(
 684                 tcx, variant_did, ctor_did, item.ident, ty::VariantDiscr::Relative(0), def,
 685                 AdtKind::Union, def_id,
 686             )).collect();
 687
 688             (AdtKind::Union, variants)
 689         },
 690         _ => bug!(),
 691     };
 692     tcx.alloc_adt_def(def_id, kind, variants, repr)
 693 }
 694
 695 /// Ensures that the super-predicates of the trait with a `DefId`
 696 /// of `trait_def_id` are converted and stored. This also ensures that
 697 /// the transitive super-predicates are converted.
 698 fn super_predicates_of(
 699     tcx: TyCtxt<'_>,
 700     trait_def_id: DefId,
 701 ) -> &ty::GenericPredicates<'_> {
 702     debug!("super_predicates(trait_def_id={:?})", trait_def_id);
 703     let trait_hir_id = tcx.hir().as_local_hir_id(trait_def_id).unwrap();
 704
 705     let item = match tcx.hir().get(trait_hir_id) {
 706         Node::Item(item) => item,
 707         _ => bug!("trait_node_id {} is not an item", trait_hir_id),
 708     };
 709
 710     let (generics, bounds) = match item.node {
 711         hir::ItemKind::Trait(.., ref generics, ref supertraits, _) => (generics, supertraits),
 712         hir::ItemKind::TraitAlias(ref generics, ref supertraits) => (generics, supertraits),
 713         _ => span_bug!(item.span, "super_predicates invoked on non-trait"),
 714     };
 715
 716     let icx = ItemCtxt::new(tcx, trait_def_id);
 717
 718     // Convert the bounds that follow the colon, e.g., `Bar + Zed` in `trait Foo: Bar + Zed`.
 719     let self_param_ty = tcx.types.self_param;
 720     let superbounds1 = AstConv::compute_bounds(&icx, self_param_ty, bounds, SizedByDefault::No,
 721         item.span);
 722
 723     let superbounds1 = superbounds1.predicates(tcx, self_param_ty);
 724
 725     // Convert any explicit superbounds in the where-clause,
 726     // e.g., `trait Foo where Self: Bar`.
 727     // In the case of trait aliases, however, we include all bounds in the where-clause,
 728     // so e.g., `trait Foo = where u32: PartialEq<Self>` would include `u32: PartialEq<Self>`
 729     // as one of its "superpredicates".
 730     let is_trait_alias = tcx.is_trait_alias(trait_def_id);
 731     let superbounds2 = icx.type_parameter_bounds_in_generics(
 732         generics, item.hir_id, self_param_ty, OnlySelfBounds(!is_trait_alias));
 733
 734     // Combine the two lists to form the complete set of superbounds:
 735     let superbounds: Vec<_> = superbounds1.into_iter().chain(superbounds2).collect();
 736
 737     // Now require that immediate supertraits are converted,
 738     // which will, in turn, reach indirect supertraits.
 739     for &(pred, span) in &superbounds {
 740         debug!("superbound: {:?}", pred);
 741         if let ty::Predicate::Trait(bound) = pred {
 742             tcx.at(span).super_predicates_of(bound.def_id());
 743         }
 744     }
 745
 746     tcx.arena.alloc(ty::GenericPredicates {
 747         parent: None,
 748         predicates: superbounds,
 749     })
 750 }
 751
 752 fn trait_def(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::TraitDef {
 753     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 754     let item = tcx.hir().expect_item(hir_id);
 755
 756     let (is_auto, unsafety) = match item.node {
 757         hir::ItemKind::Trait(is_auto, unsafety, ..) => (is_auto == hir::IsAuto::Yes, unsafety),
 758         hir::ItemKind::TraitAlias(..) => (false, hir::Unsafety::Normal),
 759         _ => span_bug!(item.span, "trait_def_of_item invoked on non-trait"),
 760     };
 761
 762     let paren_sugar = tcx.has_attr(def_id, sym::rustc_paren_sugar);
 763     if paren_sugar && !tcx.features().unboxed_closures {
 764         let mut err = tcx.sess.struct_span_err(
 765             item.span,
 766             "the `#[rustc_paren_sugar]` attribute is a temporary means of controlling \
 767              which traits can use parenthetical notation",
 768         );
 769         help!(
 770             &mut err,
 771             "add `#![feature(unboxed_closures)]` to \
 772              the crate attributes to use it"
 773         );
 774         err.emit();
 775     }
 776
 777     let is_marker = tcx.has_attr(def_id, sym::marker);
 778     let def_path_hash = tcx.def_path_hash(def_id);
 779     let def = ty::TraitDef::new(def_id, unsafety, paren_sugar, is_auto, is_marker, def_path_hash);
 780     tcx.arena.alloc(def)
 781 }
 782
 783 fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<Span> {
 784     struct LateBoundRegionsDetector<'tcx> {
 785         tcx: TyCtxt<'tcx>,
 786         outer_index: ty::DebruijnIndex,
 787         has_late_bound_regions: Option<Span>,
 788     }
 789
 790     impl Visitor<'tcx> for LateBoundRegionsDetector<'tcx> {
 791         fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 792             NestedVisitorMap::None
 793         }
 794
 795         fn visit_ty(&mut self, ty: &'tcx hir::Ty) {
 796             if self.has_late_bound_regions.is_some() {
 797                 return;
 798             }
 799             match ty.node {
 800                 hir::TyKind::BareFn(..) => {
 801                     self.outer_index.shift_in(1);
 802                     intravisit::walk_ty(self, ty);
 803                     self.outer_index.shift_out(1);
 804                 }
 805                 _ => intravisit::walk_ty(self, ty),
 806             }
 807         }
 808
 809         fn visit_poly_trait_ref(
 810             &mut self,
 811             tr: &'tcx hir::PolyTraitRef,
 812             m: hir::TraitBoundModifier,
 813         ) {
 814             if self.has_late_bound_regions.is_some() {
 815                 return;
 816             }
 817             self.outer_index.shift_in(1);
 818             intravisit::walk_poly_trait_ref(self, tr, m);
 819             self.outer_index.shift_out(1);
 820         }
 821
 822         fn visit_lifetime(&mut self, lt: &'tcx hir::Lifetime) {
 823             if self.has_late_bound_regions.is_some() {
 824                 return;
 825             }
 826
 827             match self.tcx.named_region(lt.hir_id) {
 828                 Some(rl::Region::Static) | Some(rl::Region::EarlyBound(..)) => {}
 829                 Some(rl::Region::LateBound(debruijn, _, _))
 830                 | Some(rl::Region::LateBoundAnon(debruijn, _)) if debruijn < self.outer_index => {}
 831                 Some(rl::Region::LateBound(..))
 832                 | Some(rl::Region::LateBoundAnon(..))
 833                 | Some(rl::Region::Free(..))
 834                 | None => {
 835                     self.has_late_bound_regions = Some(lt.span);
 836                 }
 837             }
 838         }
 839     }
 840
 841     fn has_late_bound_regions<'tcx>(
 842         tcx: TyCtxt<'tcx>,
 843         generics: &'tcx hir::Generics,
 844         decl: &'tcx hir::FnDecl,
 845     ) -> Option<Span> {
 846         let mut visitor = LateBoundRegionsDetector {
 847             tcx,
 848             outer_index: ty::INNERMOST,
 849             has_late_bound_regions: None,
 850         };
 851         for param in &generics.params {
 852             if let GenericParamKind::Lifetime { .. } = param.kind {
 853                 if tcx.is_late_bound(param.hir_id) {
 854                     return Some(param.span);
 855                 }
 856             }
 857         }
 858         visitor.visit_fn_decl(decl);
 859         visitor.has_late_bound_regions
 860     }
 861
 862     match node {
 863         Node::TraitItem(item) => match item.node {
 864             hir::TraitItemKind::Method(ref sig, _) => {
 865                 has_late_bound_regions(tcx, &item.generics, &sig.decl)
 866             }
 867             _ => None,
 868         },
 869         Node::ImplItem(item) => match item.node {
 870             hir::ImplItemKind::Method(ref sig, _) => {
 871                 has_late_bound_regions(tcx, &item.generics, &sig.decl)
 872             }
 873             _ => None,
 874         },
 875         Node::ForeignItem(item) => match item.node {
 876             hir::ForeignItemKind::Fn(ref fn_decl, _, ref generics) => {
 877                 has_late_bound_regions(tcx, generics, fn_decl)
 878             }
 879             _ => None,
 880         },
 881         Node::Item(item) => match item.node {
 882             hir::ItemKind::Fn(ref fn_decl, .., ref generics, _) => {
 883                 has_late_bound_regions(tcx, generics, fn_decl)
 884             }
 885             _ => None,
 886         },
 887         _ => None,
 888     }
 889 }
 890
 891 fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::Generics {
 892     use rustc::hir::*;
 893
 894     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 895
 896     let node = tcx.hir().get(hir_id);
 897     let parent_def_id = match node {
 898         Node::ImplItem(_) | Node::TraitItem(_) | Node::Variant(_) |
 899         Node::Ctor(..) | Node::Field(_) => {
 900             let parent_id = tcx.hir().get_parent_item(hir_id);
 901             Some(tcx.hir().local_def_id(parent_id))
 902         }
 903         // FIXME(#43408) enable this in all cases when we get lazy normalization.
 904         Node::AnonConst(&anon_const) => {
 905             // HACK(eddyb) this provides the correct generics when the workaround
 906             // for a const parameter `AnonConst` is being used elsewhere, as then
 907             // there won't be the kind of cyclic dependency blocking #43408.
 908             let expr = &tcx.hir().body(anon_const.body).value;
 909             let icx = ItemCtxt::new(tcx, def_id);
 910             if AstConv::const_param_def_id(&icx, expr).is_some() {
 911                 let parent_id = tcx.hir().get_parent_item(hir_id);
 912                 Some(tcx.hir().local_def_id(parent_id))
 913             } else {
 914                 None
 915             }
 916         }
 917         Node::Expr(&hir::Expr {
 918             node: hir::ExprKind::Closure(..),
 919             ..
 920         }) => Some(tcx.closure_base_def_id(def_id)),
 921         Node::Item(item) => match item.node {
 922             ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn, .. }) => impl_trait_fn,
 923             _ => None,
 924         },
 925         _ => None,
 926     };
 927
 928     let mut opt_self = None;
 929     let mut allow_defaults = false;
 930
 931     let no_generics = hir::Generics::empty();
 932     let ast_generics = match node {
 933         Node::TraitItem(item) => &item.generics,
 934
 935         Node::ImplItem(item) => &item.generics,
 936
 937         Node::Item(item) => {
 938             match item.node {
 939                 ItemKind::Fn(.., ref generics, _) | ItemKind::Impl(_, _, _, ref generics, ..) => {
 940                     generics
 941                 }
 942
 943                 ItemKind::TyAlias(_, ref generics)
 944                 | ItemKind::Enum(_, ref generics)
 945                 | ItemKind::Struct(_, ref generics)
 946                 | ItemKind::OpaqueTy(hir::OpaqueTy { ref generics, .. })
 947                 | ItemKind::Union(_, ref generics) => {
 948                     allow_defaults = true;
 949                     generics
 950                 }
 951
 952                 ItemKind::Trait(_, _, ref generics, ..)
 953                 | ItemKind::TraitAlias(ref generics, ..) => {
 954                     // Add in the self type parameter.
 955                     //
 956                     // Something of a hack: use the node id for the trait, also as
 957                     // the node id for the Self type parameter.
 958                     let param_id = item.hir_id;
 959
 960                     opt_self = Some(ty::GenericParamDef {
 961                         index: 0,
 962                         name: kw::SelfUpper.as_interned_str(),
 963                         def_id: tcx.hir().local_def_id(param_id),
 964                         pure_wrt_drop: false,
 965                         kind: ty::GenericParamDefKind::Type {
 966                             has_default: false,
 967                             object_lifetime_default: rl::Set1::Empty,
 968                             synthetic: None,
 969                         },
 970                     });
 971
 972                     allow_defaults = true;
 973                     generics
 974                 }
 975
 976                 _ => &no_generics,
 977             }
 978         }
 979
 980         Node::ForeignItem(item) => match item.node {
 981             ForeignItemKind::Static(..) => &no_generics,
 982             ForeignItemKind::Fn(_, _, ref generics) => generics,
 983             ForeignItemKind::Type => &no_generics,
 984         },
 985
 986         _ => &no_generics,
 987     };
 988
 989     let has_self = opt_self.is_some();
 990     let mut parent_has_self = false;
 991     let mut own_start = has_self as u32;
 992     let parent_count = parent_def_id.map_or(0, |def_id| {
 993         let generics = tcx.generics_of(def_id);
 994         assert_eq!(has_self, false);
 995         parent_has_self = generics.has_self;
 996         own_start = generics.count() as u32;
 997         generics.parent_count + generics.params.len()
 998     });
 999
1000     let mut params: Vec<_> = opt_self.into_iter().collect();
1001
1002     let early_lifetimes = early_bound_lifetimes_from_generics(tcx, ast_generics);
1003     params.extend(
1004         early_lifetimes
1005             .enumerate()
1006             .map(|(i, param)| ty::GenericParamDef {
1007                 name: param.name.ident().as_interned_str(),
1008                 index: own_start + i as u32,
1009                 def_id: tcx.hir().local_def_id(param.hir_id),
1010                 pure_wrt_drop: param.pure_wrt_drop,
1011                 kind: ty::GenericParamDefKind::Lifetime,
1012             }),
1013     );
1014
1015     let object_lifetime_defaults = tcx.object_lifetime_defaults(hir_id);
1016
1017     // Now create the real type parameters.
1018     let type_start = own_start - has_self as u32 + params.len() as u32;
1019     let mut i = 0;
1020     params.extend(
1021         ast_generics
1022             .params
1023             .iter()
1024             .filter_map(|param| {
1025                 let kind = match param.kind {
1026                     GenericParamKind::Type {
1027                         ref default,
1028                         synthetic,
1029                         ..
1030                     } => {
1031                         if !allow_defaults && default.is_some() {
1032                             if !tcx.features().default_type_parameter_fallback {
1033                                 tcx.lint_hir(
1034                                     lint::builtin::INVALID_TYPE_PARAM_DEFAULT,
1035                                     param.hir_id,
1036                                     param.span,
1037                                     &format!(
1038                                         "defaults for type parameters are only allowed in \
1039                                         `struct`, `enum`, `type`, or `trait` definitions."
1040                                     ),
1041                                 );
1042                             }
1043                         }
1044
1045                         ty::GenericParamDefKind::Type {
1046                             has_default: default.is_some(),
1047                             object_lifetime_default: object_lifetime_defaults
1048                                 .as_ref()
1049                                 .map_or(rl::Set1::Empty, |o| o[i]),
1050                             synthetic,
1051                         }
1052                     }
1053                     GenericParamKind::Const { .. } => {
1054                         ty::GenericParamDefKind::Const
1055                     }
1056                     _ => return None,
1057                 };
1058
1059                 let param_def = ty::GenericParamDef {
1060                     index: type_start + i as u32,
1061                     name: param.name.ident().as_interned_str(),
1062                     def_id: tcx.hir().local_def_id(param.hir_id),
1063                     pure_wrt_drop: param.pure_wrt_drop,
1064                     kind,
1065                 };
1066                 i += 1;
1067                 Some(param_def)
1068             })
1069     );
1070
1071     // provide junk type parameter defs - the only place that
1072     // cares about anything but the length is instantiation,
1073     // and we don't do that for closures.
1074     if let Node::Expr(&hir::Expr {
1075         node: hir::ExprKind::Closure(.., gen),
1076         ..
1077     }) = node
1078     {
1079         let dummy_args = if gen.is_some() {
1080             &["<yield_ty>", "<return_ty>", "<witness>"][..]
1081         } else {
1082             &["<closure_kind>", "<closure_signature>"][..]
1083         };
1084
1085         params.extend(
1086             dummy_args
1087                 .iter()
1088                 .enumerate()
1089                 .map(|(i, &arg)| ty::GenericParamDef {
1090                     index: type_start + i as u32,
1091                     name: InternedString::intern(arg),
1092                     def_id,
1093                     pure_wrt_drop: false,
1094                     kind: ty::GenericParamDefKind::Type {
1095                         has_default: false,
1096                         object_lifetime_default: rl::Set1::Empty,
1097                         synthetic: None,
1098                     },
1099                 }),
1100         );
1101
1102         if let Some(upvars) = tcx.upvars(def_id) {
1103             params.extend(upvars.iter().zip((dummy_args.len() as u32)..).map(|(_, i)| {
1104                 ty::GenericParamDef {
1105                     index: type_start + i,
1106                     name: InternedString::intern("<upvar>"),
1107                     def_id,
1108                     pure_wrt_drop: false,
1109                     kind: ty::GenericParamDefKind::Type {
1110                         has_default: false,
1111                         object_lifetime_default: rl::Set1::Empty,
1112                         synthetic: None,
1113                     },
1114                 }
1115             }));
1116         }
1117     }
1118
1119     let param_def_id_to_index = params
1120         .iter()
1121         .map(|param| (param.def_id, param.index))
1122         .collect();
1123
1124     tcx.arena.alloc(ty::Generics {
1125         parent: parent_def_id,
1126         parent_count,
1127         params,
1128         param_def_id_to_index,
1129         has_self: has_self || parent_has_self,
1130         has_late_bound_regions: has_late_bound_regions(tcx, node),
1131     })
1132 }
1133
1134 fn report_assoc_ty_on_inherent_impl(tcx: TyCtxt<'_>, span: Span) {
1135     span_err!(
1136         tcx.sess,
1137         span,
1138         E0202,
1139         "associated types are not yet supported in inherent impls (see #8995)"
1140     );
1141 }
1142
1143 fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
1144     checked_type_of(tcx, def_id, true).unwrap()
1145 }
1146
1147 fn infer_placeholder_type(
1148     tcx: TyCtxt<'_>,
1149     def_id: DefId,
1150     body_id: hir::BodyId,
1151     span: Span,
1152 ) -> Ty<'_> {
1153     let ty = tcx.typeck_tables_of(def_id).node_type(body_id.hir_id);
1154     let mut diag = bad_placeholder_type(tcx, span);
1155     if ty != tcx.types.err {
1156         diag.span_suggestion(
1157             span,
1158             "replace `_` with the correct type",
1159             ty.to_string(),
1160             Applicability::MaybeIncorrect,
1161         );
1162     }
1163     diag.emit();
1164     ty
1165 }
1166
1167 /// Same as [`type_of`] but returns [`Option`] instead of failing.
1168 ///
1169 /// If you want to fail anyway, you can set the `fail` parameter to true, but in this case,
1170 /// you'd better just call [`type_of`] directly.
1171 pub fn checked_type_of(tcx: TyCtxt<'_>, def_id: DefId, fail: bool) -> Option<Ty<'_>> {
1172     use rustc::hir::*;
1173
1174     let hir_id = match tcx.hir().as_local_hir_id(def_id) {
1175         Some(hir_id) => hir_id,
1176         None => {
1177             if !fail {
1178                 return None;
1179             }
1180             bug!("invalid node");
1181         }
1182     };
1183
1184     let icx = ItemCtxt::new(tcx, def_id);
1185
1186     Some(match tcx.hir().get(hir_id) {
1187         Node::TraitItem(item) => match item.node {
1188             TraitItemKind::Method(..) => {
1189                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1190                 tcx.mk_fn_def(def_id, substs)
1191             }
1192             TraitItemKind::Const(ref ty, body_id)  => {
1193                 body_id.and_then(|body_id| {
1194                     if let hir::TyKind::Infer = ty.node {
1195                         Some(infer_placeholder_type(tcx, def_id, body_id, ty.span))
1196                     } else {
1197                         None
1198                     }
1199                 }).unwrap_or_else(|| icx.to_ty(ty))
1200             },
1201             TraitItemKind::Type(_, Some(ref ty)) => icx.to_ty(ty),
1202             TraitItemKind::Type(_, None) => {
1203                 if !fail {
1204                     return None;
1205                 }
1206                 span_bug!(item.span, "associated type missing default");
1207             }
1208         },
1209
1210         Node::ImplItem(item) => match item.node {
1211             ImplItemKind::Method(..) => {
1212                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1213                 tcx.mk_fn_def(def_id, substs)
1214             }
1215             ImplItemKind::Const(ref ty, body_id) => {
1216                 if let hir::TyKind::Infer = ty.node {
1217                     infer_placeholder_type(tcx, def_id, body_id, ty.span)
1218                 } else {
1219                     icx.to_ty(ty)
1220                 }
1221             },
1222             ImplItemKind::OpaqueTy(_) => {
1223                 if tcx
1224                     .impl_trait_ref(tcx.hir().get_parent_did(hir_id))
1225                     .is_none()
1226                 {
1227                     report_assoc_ty_on_inherent_impl(tcx, item.span);
1228                 }
1229
1230                 find_opaque_ty_constraints(tcx, def_id)
1231             }
1232             ImplItemKind::TyAlias(ref ty) => {
1233                 if tcx
1234                     .impl_trait_ref(tcx.hir().get_parent_did(hir_id))
1235                     .is_none()
1236                 {
1237                     report_assoc_ty_on_inherent_impl(tcx, item.span);
1238                 }
1239
1240                 icx.to_ty(ty)
1241             }
1242         },
1243
1244         Node::Item(item) => {
1245             match item.node {
1246                 ItemKind::Static(ref ty, .., body_id)
1247                 | ItemKind::Const(ref ty, body_id) => {
1248                     if let hir::TyKind::Infer = ty.node {
1249                         infer_placeholder_type(tcx, def_id, body_id, ty.span)
1250                     } else {
1251                         icx.to_ty(ty)
1252                     }
1253                 },
1254                 ItemKind::TyAlias(ref ty, _)
1255                 | ItemKind::Impl(.., ref ty, _) => icx.to_ty(ty),
1256                 ItemKind::Fn(..) => {
1257                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
1258                     tcx.mk_fn_def(def_id, substs)
1259                 }
1260                 ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
1261                     let def = tcx.adt_def(def_id);
1262                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
1263                     tcx.mk_adt(def, substs)
1264                 }
1265                 ItemKind::OpaqueTy(hir::OpaqueTy {
1266                     impl_trait_fn: None,
1267                     ..
1268                 }) => find_opaque_ty_constraints(tcx, def_id),
1269                 // Opaque types desugared from `impl Trait`.
1270                 ItemKind::OpaqueTy(hir::OpaqueTy {
1271                     impl_trait_fn: Some(owner),
1272                     ..
1273                 }) => {
1274                     tcx.typeck_tables_of(owner)
1275                         .concrete_opaque_types
1276                         .get(&def_id)
1277                         .map(|opaque| opaque.concrete_type)
1278                         .unwrap_or_else(|| {
1279                             // This can occur if some error in the
1280                             // owner fn prevented us from populating
1281                             // the `concrete_opaque_types` table.
1282                             tcx.sess.delay_span_bug(
1283                                 DUMMY_SP,
1284                                 &format!(
1285                                     "owner {:?} has no opaque type for {:?} in its tables",
1286                                     owner, def_id,
1287                                 ),
1288                             );
1289                             tcx.types.err
1290                         })
1291                 }
1292                 ItemKind::Trait(..)
1293                 | ItemKind::TraitAlias(..)
1294                 | ItemKind::Mod(..)
1295                 | ItemKind::ForeignMod(..)
1296                 | ItemKind::GlobalAsm(..)
1297                 | ItemKind::ExternCrate(..)
1298                 | ItemKind::Use(..) => {
1299                     if !fail {
1300                         return None;
1301                     }
1302                     span_bug!(
1303                         item.span,
1304                         "compute_type_of_item: unexpected item type: {:?}",
1305                         item.node
1306                     );
1307                 }
1308             }
1309         }
1310
1311         Node::ForeignItem(foreign_item) => match foreign_item.node {
1312             ForeignItemKind::Fn(..) => {
1313                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1314                 tcx.mk_fn_def(def_id, substs)
1315             }
1316             ForeignItemKind::Static(ref t, _) => icx.to_ty(t),
1317             ForeignItemKind::Type => tcx.mk_foreign(def_id),
1318         },
1319
1320         Node::Ctor(&ref def) | Node::Variant(
1321             hir::Variant { data: ref def, .. }
1322         ) => match *def {
1323             VariantData::Unit(..) | VariantData::Struct(..) => {
1324                 tcx.type_of(tcx.hir().get_parent_did(hir_id))
1325             }
1326             VariantData::Tuple(..) => {
1327                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1328                 tcx.mk_fn_def(def_id, substs)
1329             }
1330         },
1331
1332         Node::Field(field) => icx.to_ty(&field.ty),
1333
1334         Node::Expr(&hir::Expr {
1335             node: hir::ExprKind::Closure(.., gen),
1336             ..
1337         }) => {
1338             if gen.is_some() {
1339                 return Some(tcx.typeck_tables_of(def_id).node_type(hir_id));
1340             }
1341
1342             let substs = ty::ClosureSubsts {
1343                 substs: InternalSubsts::identity_for_item(tcx, def_id),
1344             };
1345
1346             tcx.mk_closure(def_id, substs)
1347         }
1348
1349         Node::AnonConst(_) => {
1350             let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
1351             match parent_node {
1352                 Node::Ty(&hir::Ty {
1353                     node: hir::TyKind::Array(_, ref constant),
1354                     ..
1355                 })
1356                 | Node::Ty(&hir::Ty {
1357                     node: hir::TyKind::Typeof(ref constant),
1358                     ..
1359                 })
1360                 | Node::Expr(&hir::Expr {
1361                     node: ExprKind::Repeat(_, ref constant),
1362                     ..
1363                 }) if constant.hir_id == hir_id =>
1364                 {
1365                     tcx.types.usize
1366                 }
1367
1368                 Node::Variant(Variant {
1369                     disr_expr: Some(ref e),
1370                     ..
1371                 }) if e.hir_id == hir_id =>
1372                 {
1373                     tcx.adt_def(tcx.hir().get_parent_did(hir_id))
1374                         .repr
1375                         .discr_type()
1376                         .to_ty(tcx)
1377                 }
1378
1379                 Node::Ty(&hir::Ty { node: hir::TyKind::Path(_), .. }) |
1380                 Node::Expr(&hir::Expr { node: ExprKind::Struct(..), .. }) |
1381                 Node::Expr(&hir::Expr { node: ExprKind::Path(_), .. }) |
1382                 Node::TraitRef(..) => {
1383                     let path = match parent_node {
1384                         Node::Ty(&hir::Ty {
1385                             node: hir::TyKind::Path(QPath::Resolved(_, ref path)),
1386                             ..
1387                         })
1388                         | Node::Expr(&hir::Expr {
1389                             node: ExprKind::Path(QPath::Resolved(_, ref path)),
1390                             ..
1391                         }) => {
1392                             Some(&**path)
1393                         }
1394                         Node::Expr(&hir::Expr { node: ExprKind::Struct(ref path, ..), .. }) => {
1395                             if let QPath::Resolved(_, ref path) = **path {
1396                                 Some(&**path)
1397                             } else {
1398                                 None
1399                             }
1400                         }
1401                         Node::TraitRef(&hir::TraitRef { ref path, .. }) => Some(&**path),
1402                         _ => None,
1403                     };
1404
1405                     if let Some(path) = path {
1406                         let arg_index = path.segments.iter()
1407                             .filter_map(|seg| seg.args.as_ref())
1408                             .map(|generic_args| generic_args.args.as_ref())
1409                             .find_map(|args| {
1410                                 args.iter()
1411                                     .filter(|arg| arg.is_const())
1412                                     .enumerate()
1413                                     .filter(|(_, arg)| arg.id() == hir_id)
1414                                     .map(|(index, _)| index)
1415                                     .next()
1416                             })
1417                             .or_else(|| {
1418                                 if !fail {
1419                                     None
1420                                 } else {
1421                                     bug!("no arg matching AnonConst in path")
1422                                 }
1423                             })?;
1424
1425                         // We've encountered an `AnonConst` in some path, so we need to
1426                         // figure out which generic parameter it corresponds to and return
1427                         // the relevant type.
1428                         let generics = match path.res {
1429                             Res::Def(DefKind::Ctor(..), def_id) => {
1430                                 tcx.generics_of(tcx.parent(def_id).unwrap())
1431                             }
1432                             Res::Def(_, def_id) => tcx.generics_of(def_id),
1433                             Res::Err => return Some(tcx.types.err),
1434                             _ if !fail => return None,
1435                             res => {
1436                                 tcx.sess.delay_span_bug(
1437                                     DUMMY_SP,
1438                                     &format!(
1439                                         "unexpected const parent path def {:?}",
1440                                         res,
1441                                     ),
1442                                 );
1443                                 return Some(tcx.types.err);
1444                             }
1445                         };
1446
1447                         generics.params.iter()
1448                             .filter(|param| {
1449                                 if let ty::GenericParamDefKind::Const = param.kind {
1450                                     true
1451                                 } else {
1452                                     false
1453                                 }
1454                             })
1455                             .nth(arg_index)
1456                             .map(|param| tcx.type_of(param.def_id))
1457                             // This is no generic parameter associated with the arg. This is
1458                             // probably from an extra arg where one is not needed.
1459                             .unwrap_or(tcx.types.err)
1460                     } else {
1461                         if !fail {
1462                             return None;
1463                         }
1464                         tcx.sess.delay_span_bug(
1465                             DUMMY_SP,
1466                             &format!(
1467                                 "unexpected const parent path {:?}",
1468                                 parent_node,
1469                             ),
1470                         );
1471                         return Some(tcx.types.err);
1472                     }
1473                 }
1474
1475                 x => {
1476                     if !fail {
1477                         return None;
1478                     }
1479                     tcx.sess.delay_span_bug(
1480                         DUMMY_SP,
1481                         &format!(
1482                             "unexpected const parent in type_of_def_id(): {:?}", x
1483                         ),
1484                     );
1485                     tcx.types.err
1486                 }
1487             }
1488         }
1489
1490         Node::GenericParam(param) => match &param.kind {
1491             hir::GenericParamKind::Type { default: Some(ref ty), .. } |
1492             hir::GenericParamKind::Const { ref ty, .. } => {
1493                 icx.to_ty(ty)
1494             }
1495             x => {
1496                 if !fail {
1497                     return None;
1498                 }
1499                 bug!("unexpected non-type Node::GenericParam: {:?}", x)
1500             },
1501         },
1502
1503         x => {
1504             if !fail {
1505                 return None;
1506             }
1507             bug!("unexpected sort of node in type_of_def_id(): {:?}", x);
1508         }
1509     })
1510 }
1511
1512 fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
1513     use rustc::hir::{ImplItem, Item, TraitItem};
1514
1515     debug!("find_opaque_ty_constraints({:?})", def_id);
1516
1517     struct ConstraintLocator<'tcx> {
1518         tcx: TyCtxt<'tcx>,
1519         def_id: DefId,
1520         // (first found type span, actual type, mapping from the opaque type's generic
1521         // parameters to the concrete type's generic parameters)
1522         //
1523         // The mapping is an index for each use site of a generic parameter in the concrete type
1524         //
1525         // The indices index into the generic parameters on the opaque type.
1526         found: Option<(Span, Ty<'tcx>, Vec<usize>)>,
1527     }
1528
1529     impl ConstraintLocator<'tcx> {
1530         fn check(&mut self, def_id: DefId) {
1531             // Don't try to check items that cannot possibly constrain the type.
1532             if !self.tcx.has_typeck_tables(def_id) {
1533                 debug!(
1534                     "find_opaque_ty_constraints: no constraint for `{:?}` at `{:?}`: no tables",
1535                     self.def_id,
1536                     def_id,
1537                 );
1538                 return;
1539             }
1540             let ty = self
1541                 .tcx
1542                 .typeck_tables_of(def_id)
1543                 .concrete_opaque_types
1544                 .get(&self.def_id);
1545             if let Some(ty::ResolvedOpaqueTy { concrete_type, substs }) = ty {
1546                 debug!(
1547                     "find_opaque_ty_constraints: found constraint for `{:?}` at `{:?}`: {:?}",
1548                     self.def_id,
1549                     def_id,
1550                     ty,
1551                 );
1552
1553                 // FIXME(oli-obk): trace the actual span from inference to improve errors.
1554                 let span = self.tcx.def_span(def_id);
1555                 // used to quickly look up the position of a generic parameter
1556                 let mut index_map: FxHashMap<ty::ParamTy, usize> = FxHashMap::default();
1557                 // Skipping binder is ok, since we only use this to find generic parameters and
1558                 // their positions.
1559                 for (idx, subst) in substs.iter().enumerate() {
1560                     if let UnpackedKind::Type(ty) = subst.unpack() {
1561                         if let ty::Param(p) = ty.sty {
1562                             if index_map.insert(p, idx).is_some() {
1563                                 // There was already an entry for `p`, meaning a generic parameter
1564                                 // was used twice.
1565                                 self.tcx.sess.span_err(
1566                                     span,
1567                                     &format!(
1568                                         "defining opaque type use restricts opaque \
1569                                          type by using the generic parameter `{}` twice",
1570                                         p,
1571                                     ),
1572                                 );
1573                                 return;
1574                             }
1575                         } else {
1576                             self.tcx.sess.delay_span_bug(
1577                                 span,
1578                                 &format!(
1579                                     "non-defining opaque ty use in defining scope: {:?}, {:?}",
1580                                     concrete_type, substs,
1581                                 ),
1582                             );
1583                         }
1584                     }
1585                 }
1586                 // Compute the index within the opaque type for each generic parameter used in
1587                 // the concrete type.
1588                 let indices = concrete_type
1589                     .subst(self.tcx, substs)
1590                     .walk()
1591                     .filter_map(|t| match &t.sty {
1592                         ty::Param(p) => Some(*index_map.get(p).unwrap()),
1593                         _ => None,
1594                     }).collect();
1595                 let is_param = |ty: Ty<'_>| match ty.sty {
1596                     ty::Param(_) => true,
1597                     _ => false,
1598                 };
1599                 if !substs.types().all(is_param) {
1600                     self.tcx.sess.span_err(
1601                         span,
1602                         "defining opaque type use does not fully define opaque type",
1603                     );
1604                 } else if let Some((prev_span, prev_ty, ref prev_indices)) = self.found {
1605                     let mut ty = concrete_type.walk().fuse();
1606                     let mut p_ty = prev_ty.walk().fuse();
1607                     let iter_eq = (&mut ty).zip(&mut p_ty).all(|(t, p)| match (&t.sty, &p.sty) {
1608                         // Type parameters are equal to any other type parameter for the purpose of
1609                         // concrete type equality, as it is possible to obtain the same type just
1610                         // by passing matching parameters to a function.
1611                         (ty::Param(_), ty::Param(_)) => true,
1612                         _ => t == p,
1613                     });
1614                     if !iter_eq || ty.next().is_some() || p_ty.next().is_some() {
1615                         debug!("find_opaque_ty_constraints: span={:?}", span);
1616                         // Found different concrete types for the opaque type.
1617                         let mut err = self.tcx.sess.struct_span_err(
1618                             span,
1619                             "concrete type differs from previous defining opaque type use",
1620                         );
1621                         err.span_label(
1622                             span,
1623                             format!("expected `{}`, got `{}`", prev_ty, concrete_type),
1624                         );
1625                         err.span_note(prev_span, "previous use here");
1626                         err.emit();
1627                     } else if indices != *prev_indices {
1628                         // Found "same" concrete types, but the generic parameter order differs.
1629                         let mut err = self.tcx.sess.struct_span_err(
1630                             span,
1631                             "concrete type's generic parameters differ from previous defining use",
1632                         );
1633                         use std::fmt::Write;
1634                         let mut s = String::new();
1635                         write!(s, "expected [").unwrap();
1636                         let list = |s: &mut String, indices: &Vec<usize>| {
1637                             let mut indices = indices.iter().cloned();
1638                             if let Some(first) = indices.next() {
1639                                 write!(s, "`{}`", substs[first]).unwrap();
1640                                 for i in indices {
1641                                     write!(s, ", `{}`", substs[i]).unwrap();
1642                                 }
1643                             }
1644                         };
1645                         list(&mut s, prev_indices);
1646                         write!(s, "], got [").unwrap();
1647                         list(&mut s, &indices);
1648                         write!(s, "]").unwrap();
1649                         err.span_label(span, s);
1650                         err.span_note(prev_span, "previous use here");
1651                         err.emit();
1652                     }
1653                 } else {
1654                     self.found = Some((span, concrete_type, indices));
1655                 }
1656             } else {
1657                 debug!(
1658                     "find_opaque_ty_constraints: no constraint for `{:?}` at `{:?}`",
1659                     self.def_id,
1660                     def_id,
1661                 );
1662             }
1663         }
1664     }
1665
1666     impl<'tcx> intravisit::Visitor<'tcx> for ConstraintLocator<'tcx> {
1667         fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
1668             intravisit::NestedVisitorMap::All(&self.tcx.hir())
1669         }
1670         fn visit_item(&mut self, it: &'tcx Item) {
1671             debug!("find_existential_constraints: visiting {:?}", it);
1672             let def_id = self.tcx.hir().local_def_id(it.hir_id);
1673             // The opaque type itself or its children are not within its reveal scope.
1674             if def_id != self.def_id {
1675                 self.check(def_id);
1676                 intravisit::walk_item(self, it);
1677             }
1678         }
1679         fn visit_impl_item(&mut self, it: &'tcx ImplItem) {
1680             debug!("find_existential_constraints: visiting {:?}", it);
1681             let def_id = self.tcx.hir().local_def_id(it.hir_id);
1682             // The opaque type itself or its children are not within its reveal scope.
1683             if def_id != self.def_id {
1684                 self.check(def_id);
1685                 intravisit::walk_impl_item(self, it);
1686             }
1687         }
1688         fn visit_trait_item(&mut self, it: &'tcx TraitItem) {
1689             debug!("find_existential_constraints: visiting {:?}", it);
1690             let def_id = self.tcx.hir().local_def_id(it.hir_id);
1691             self.check(def_id);
1692             intravisit::walk_trait_item(self, it);
1693         }
1694     }
1695
1696     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1697     let scope = tcx.hir()
1698         .get_defining_scope(hir_id)
1699         .expect("could not get defining scope");
1700     let mut locator = ConstraintLocator {
1701         def_id,
1702         tcx,
1703         found: None,
1704     };
1705
1706     debug!("find_opaque_ty_constraints: scope={:?}", scope);
1707
1708     if scope == hir::CRATE_HIR_ID {
1709         intravisit::walk_crate(&mut locator, tcx.hir().krate());
1710     } else {
1711         debug!("find_opaque_ty_constraints: scope={:?}", tcx.hir().get(scope));
1712         match tcx.hir().get(scope) {
1713             // We explicitly call `visit_*` methods, instead of using `intravisit::walk_*` methods
1714             // This allows our visitor to process the defining item itself, causing
1715             // it to pick up any 'sibling' defining uses.
1716             //
1717             // For example, this code:
1718             // ```
1719             // fn foo() {
1720             //     type Blah = impl Debug;
1721             //     let my_closure = || -> Blah { true };
1722             // }
1723             // ```
1724             //
1725             // requires us to explicitly process `foo()` in order
1726             // to notice the defining usage of `Blah`.
1727             Node::Item(ref it) => locator.visit_item(it),
1728             Node::ImplItem(ref it) => locator.visit_impl_item(it),
1729             Node::TraitItem(ref it) => locator.visit_trait_item(it),
1730             other => bug!(
1731                 "{:?} is not a valid scope for an opaque type item",
1732                 other
1733             ),
1734         }
1735     }
1736
1737     match locator.found {
1738         Some((_, ty, _)) => ty,
1739         None => {
1740             let span = tcx.def_span(def_id);
1741             tcx.sess.span_err(span, "could not find defining uses");
1742             tcx.types.err
1743         }
1744     }
1745 }
1746
1747 pub fn get_infer_ret_ty(output: &'_ hir::FunctionRetTy) -> Option<&hir::Ty> {
1748     if let hir::FunctionRetTy::Return(ref ty) = output {
1749         if let hir::TyKind::Infer = ty.node {
1750             return Some(&**ty)
1751         }
1752     }
1753     None
1754 }
1755
1756 fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
1757     use rustc::hir::*;
1758     use rustc::hir::Node::*;
1759
1760     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1761
1762     let icx = ItemCtxt::new(tcx, def_id);
1763
1764     match tcx.hir().get(hir_id) {
1765         TraitItem(hir::TraitItem {
1766             node: TraitItemKind::Method(MethodSig { header, decl }, TraitMethod::Provided(_)),
1767             ..
1768         })
1769         | ImplItem(hir::ImplItem {
1770             node: ImplItemKind::Method(MethodSig { header, decl }, _),
1771             ..
1772         })
1773         | Item(hir::Item {
1774             node: ItemKind::Fn(decl, header, _, _),
1775             ..
1776         }) => match get_infer_ret_ty(&decl.output) {
1777             Some(ty) => {
1778                 let fn_sig = tcx.typeck_tables_of(def_id).liberated_fn_sigs()[hir_id];
1779                 let mut diag = bad_placeholder_type(tcx, ty.span);
1780                 let ret_ty = fn_sig.output();
1781                 if ret_ty != tcx.types.err  {
1782                     diag.span_suggestion(
1783                         ty.span,
1784                         "replace `_` with the correct return type",
1785                         ret_ty.to_string(),
1786                         Applicability::MaybeIncorrect,
1787                     );
1788                 }
1789                 diag.emit();
1790                 ty::Binder::bind(fn_sig)
1791             },
1792             None => AstConv::ty_of_fn(&icx, header.unsafety, header.abi, decl)
1793         },
1794
1795         TraitItem(hir::TraitItem {
1796             node: TraitItemKind::Method(MethodSig { header, decl }, _),
1797             ..
1798         }) => {
1799             AstConv::ty_of_fn(&icx, header.unsafety, header.abi, decl)
1800         },
1801
1802         ForeignItem(&hir::ForeignItem {
1803             node: ForeignItemKind::Fn(ref fn_decl, _, _),
1804             ..
1805         }) => {
1806             let abi = tcx.hir().get_foreign_abi(hir_id);
1807             compute_sig_of_foreign_fn_decl(tcx, def_id, fn_decl, abi)
1808         }
1809
1810         Ctor(data) | Variant(
1811             hir::Variant { data, ..  }
1812         ) if data.ctor_hir_id().is_some() => {
1813             let ty = tcx.type_of(tcx.hir().get_parent_did(hir_id));
1814             let inputs = data.fields()
1815                 .iter()
1816                 .map(|f| tcx.type_of(tcx.hir().local_def_id(f.hir_id)));
1817             ty::Binder::bind(tcx.mk_fn_sig(
1818                 inputs,
1819                 ty,
1820                 false,
1821                 hir::Unsafety::Normal,
1822                 abi::Abi::Rust,
1823             ))
1824         }
1825
1826         Expr(&hir::Expr {
1827             node: hir::ExprKind::Closure(..),
1828             ..
1829         }) => {
1830             // Closure signatures are not like other function
1831             // signatures and cannot be accessed through `fn_sig`. For
1832             // example, a closure signature excludes the `self`
1833             // argument. In any case they are embedded within the
1834             // closure type as part of the `ClosureSubsts`.
1835             //
1836             // To get
1837             // the signature of a closure, you should use the
1838             // `closure_sig` method on the `ClosureSubsts`:
1839             //
1840             //    closure_substs.closure_sig(def_id, tcx)
1841             //
1842             // or, inside of an inference context, you can use
1843             //
1844             //    infcx.closure_sig(def_id, closure_substs)
1845             bug!("to get the signature of a closure, use `closure_sig()` not `fn_sig()`");
1846         }
1847
1848         x => {
1849             bug!("unexpected sort of node in fn_sig(): {:?}", x);
1850         }
1851     }
1852 }
1853
1854 fn impl_trait_ref(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ty::TraitRef<'_>> {
1855     let icx = ItemCtxt::new(tcx, def_id);
1856
1857     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1858     match tcx.hir().expect_item(hir_id).node {
1859         hir::ItemKind::Impl(.., ref opt_trait_ref, _, _) => {
1860             opt_trait_ref.as_ref().map(|ast_trait_ref| {
1861                 let selfty = tcx.type_of(def_id);
1862                 AstConv::instantiate_mono_trait_ref(&icx, ast_trait_ref, selfty)
1863             })
1864         }
1865         _ => bug!(),
1866     }
1867 }
1868
1869 fn impl_polarity(tcx: TyCtxt<'_>, def_id: DefId) -> hir::ImplPolarity {
1870     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1871     match tcx.hir().expect_item(hir_id).node {
1872         hir::ItemKind::Impl(_, polarity, ..) => polarity,
1873         ref item => bug!("impl_polarity: {:?} not an impl", item),
1874     }
1875 }
1876
1877 /// Returns the early-bound lifetimes declared in this generics
1878 /// listing. For anything other than fns/methods, this is just all
1879 /// the lifetimes that are declared. For fns or methods, we have to
1880 /// screen out those that do not appear in any where-clauses etc using
1881 /// `resolve_lifetime::early_bound_lifetimes`.
1882 fn early_bound_lifetimes_from_generics<'a, 'tcx: 'a>(
1883     tcx: TyCtxt<'tcx>,
1884     generics: &'a hir::Generics,
1885 ) -> impl Iterator<Item = &'a hir::GenericParam> + Captures<'tcx> {
1886     generics
1887         .params
1888         .iter()
1889         .filter(move |param| match param.kind {
1890             GenericParamKind::Lifetime { .. } => {
1891                 !tcx.is_late_bound(param.hir_id)
1892             }
1893             _ => false,
1894         })
1895 }
1896
1897 /// Returns a list of type predicates for the definition with ID `def_id`, including inferred
1898 /// lifetime constraints. This includes all predicates returned by `explicit_predicates_of`, plus
1899 /// inferred constraints concerning which regions outlive other regions.
1900 fn predicates_defined_on(
1901     tcx: TyCtxt<'_>,
1902     def_id: DefId,
1903 ) -> &ty::GenericPredicates<'_> {
1904     debug!("predicates_defined_on({:?})", def_id);
1905     let mut result = tcx.explicit_predicates_of(def_id);
1906     debug!(
1907         "predicates_defined_on: explicit_predicates_of({:?}) = {:?}",
1908         def_id,
1909         result,
1910     );
1911     let inferred_outlives = tcx.inferred_outlives_of(def_id);
1912     if !inferred_outlives.is_empty() {
1913         let span = tcx.def_span(def_id);
1914         debug!(
1915             "predicates_defined_on: inferred_outlives_of({:?}) = {:?}",
1916             def_id,
1917             inferred_outlives,
1918         );
1919         let mut predicates = (*result).clone();
1920         predicates.predicates.extend(inferred_outlives.iter().map(|&p| (p, span)));
1921         result = tcx.arena.alloc(predicates);
1922     }
1923     debug!("predicates_defined_on({:?}) = {:?}", def_id, result);
1924     result
1925 }
1926
1927 /// Returns a list of all type predicates (explicit and implicit) for the definition with
1928 /// ID `def_id`. This includes all predicates returned by `predicates_defined_on`, plus
1929 /// `Self: Trait` predicates for traits.
1930 fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::GenericPredicates<'_> {
1931     let mut result = tcx.predicates_defined_on(def_id);
1932
1933     if tcx.is_trait(def_id) {
1934         // For traits, add `Self: Trait` predicate. This is
1935         // not part of the predicates that a user writes, but it
1936         // is something that one must prove in order to invoke a
1937         // method or project an associated type.
1938         //
1939         // In the chalk setup, this predicate is not part of the
1940         // "predicates" for a trait item. But it is useful in
1941         // rustc because if you directly (e.g.) invoke a trait
1942         // method like `Trait::method(...)`, you must naturally
1943         // prove that the trait applies to the types that were
1944         // used, and adding the predicate into this list ensures
1945         // that this is done.
1946         let span = tcx.def_span(def_id);
1947         let mut predicates = (*result).clone();
1948         predicates.predicates.push((ty::TraitRef::identity(tcx, def_id).to_predicate(), span));
1949         result = tcx.arena.alloc(predicates);
1950     }
1951     debug!("predicates_of(def_id={:?}) = {:?}", def_id, result);
1952     result
1953 }
1954
1955 /// Returns a list of user-specified type predicates for the definition with ID `def_id`.
1956 /// N.B., this does not include any implied/inferred constraints.
1957 fn explicit_predicates_of(
1958     tcx: TyCtxt<'_>,
1959     def_id: DefId,
1960 ) -> &ty::GenericPredicates<'_> {
1961     use rustc::hir::*;
1962     use rustc_data_structures::fx::FxHashSet;
1963
1964     debug!("explicit_predicates_of(def_id={:?})", def_id);
1965
1966     /// A data structure with unique elements, which preserves order of insertion.
1967     /// Preserving the order of insertion is important here so as not to break
1968     /// compile-fail UI tests.
1969     struct UniquePredicates<'tcx> {
1970         predicates: Vec<(ty::Predicate<'tcx>, Span)>,
1971         uniques: FxHashSet<(ty::Predicate<'tcx>, Span)>,
1972     }
1973
1974     impl<'tcx> UniquePredicates<'tcx> {
1975         fn new() -> Self {
1976             UniquePredicates {
1977                 predicates: vec![],
1978                 uniques: FxHashSet::default(),
1979             }
1980         }
1981
1982         fn push(&mut self, value: (ty::Predicate<'tcx>, Span)) {
1983             if self.uniques.insert(value) {
1984                 self.predicates.push(value);
1985             }
1986         }
1987
1988         fn extend<I: IntoIterator<Item = (ty::Predicate<'tcx>, Span)>>(&mut self, iter: I) {
1989             for value in iter {
1990                 self.push(value);
1991             }
1992         }
1993     }
1994
1995     let hir_id = match tcx.hir().as_local_hir_id(def_id) {
1996         Some(hir_id) => hir_id,
1997         None => return tcx.predicates_of(def_id),
1998     };
1999     let node = tcx.hir().get(hir_id);
2000
2001     let mut is_trait = None;
2002     let mut is_default_impl_trait = None;
2003
2004     let icx = ItemCtxt::new(tcx, def_id);
2005
2006     const NO_GENERICS: &hir::Generics = &hir::Generics::empty();
2007
2008     let empty_trait_items = HirVec::new();
2009
2010     let mut predicates = UniquePredicates::new();
2011
2012     let ast_generics = match node {
2013         Node::TraitItem(item) => &item.generics,
2014
2015         Node::ImplItem(item) => match item.node {
2016             ImplItemKind::OpaqueTy(ref bounds) => {
2017                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
2018                 let opaque_ty = tcx.mk_opaque(def_id, substs);
2019
2020                 // Collect the bounds, i.e., the `A + B + 'c` in `impl A + B + 'c`.
2021                 let bounds = AstConv::compute_bounds(
2022                     &icx,
2023                     opaque_ty,
2024                     bounds,
2025                     SizedByDefault::Yes,
2026                     tcx.def_span(def_id),
2027                 );
2028
2029                 predicates.extend(bounds.predicates(tcx, opaque_ty));
2030                 &item.generics
2031             }
2032             _ => &item.generics,
2033         },
2034
2035         Node::Item(item) => {
2036             match item.node {
2037                 ItemKind::Impl(_, _, defaultness, ref generics, ..) => {
2038                     if defaultness.is_default() {
2039                         is_default_impl_trait = tcx.impl_trait_ref(def_id);
2040                     }
2041                     generics
2042                 }
2043                 ItemKind::Fn(.., ref generics, _)
2044                 | ItemKind::TyAlias(_, ref generics)
2045                 | ItemKind::Enum(_, ref generics)
2046                 | ItemKind::Struct(_, ref generics)
2047                 | ItemKind::Union(_, ref generics) => generics,
2048
2049                 ItemKind::Trait(_, _, ref generics, .., ref items) => {
2050                     is_trait = Some((ty::TraitRef::identity(tcx, def_id), items));
2051                     generics
2052                 }
2053                 ItemKind::TraitAlias(ref generics, _) => {
2054                     is_trait = Some((ty::TraitRef::identity(tcx, def_id), &empty_trait_items));
2055                     generics
2056                 }
2057                 ItemKind::OpaqueTy(OpaqueTy {
2058                     ref bounds,
2059                     impl_trait_fn,
2060                     ref generics,
2061                     origin: _,
2062                 }) => {
2063                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
2064                     let opaque_ty = tcx.mk_opaque(def_id, substs);
2065
2066                     // Collect the bounds, i.e., the `A + B + 'c` in `impl A + B + 'c`.
2067                     let bounds = AstConv::compute_bounds(
2068                         &icx,
2069                         opaque_ty,
2070                         bounds,
2071                         SizedByDefault::Yes,
2072                         tcx.def_span(def_id),
2073                     );
2074
2075                     let bounds_predicates = bounds.predicates(tcx, opaque_ty);
2076                     if impl_trait_fn.is_some() {
2077                         // opaque types
2078                         return tcx.arena.alloc(ty::GenericPredicates {
2079                             parent: None,
2080                             predicates: bounds_predicates,
2081                         });
2082                     } else {
2083                         // named opaque types
2084                         predicates.extend(bounds_predicates);
2085                         generics
2086                     }
2087                 }
2088
2089                 _ => NO_GENERICS,
2090             }
2091         }
2092
2093         Node::ForeignItem(item) => match item.node {
2094             ForeignItemKind::Static(..) => NO_GENERICS,
2095             ForeignItemKind::Fn(_, _, ref generics) => generics,
2096             ForeignItemKind::Type => NO_GENERICS,
2097         },
2098
2099         _ => NO_GENERICS,
2100     };
2101
2102     let generics = tcx.generics_of(def_id);
2103     let parent_count = generics.parent_count as u32;
2104     let has_own_self = generics.has_self && parent_count == 0;
2105
2106     // Below we'll consider the bounds on the type parameters (including `Self`)
2107     // and the explicit where-clauses, but to get the full set of predicates
2108     // on a trait we need to add in the supertrait bounds and bounds found on
2109     // associated types.
2110     if let Some((_trait_ref, _)) = is_trait {
2111         predicates.extend(tcx.super_predicates_of(def_id).predicates.iter().cloned());
2112     }
2113
2114     // In default impls, we can assume that the self type implements
2115     // the trait. So in:
2116     //
2117     //     default impl Foo for Bar { .. }
2118     //
2119     // we add a default where clause `Foo: Bar`. We do a similar thing for traits
2120     // (see below). Recall that a default impl is not itself an impl, but rather a
2121     // set of defaults that can be incorporated into another impl.
2122     if let Some(trait_ref) = is_default_impl_trait {
2123         predicates.push((trait_ref.to_poly_trait_ref().to_predicate(), tcx.def_span(def_id)));
2124     }
2125
2126     // Collect the region predicates that were declared inline as
2127     // well. In the case of parameters declared on a fn or method, we
2128     // have to be careful to only iterate over early-bound regions.
2129     let mut index = parent_count + has_own_self as u32;
2130     for param in early_bound_lifetimes_from_generics(tcx, ast_generics) {
2131         let region = tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
2132             def_id: tcx.hir().local_def_id(param.hir_id),
2133             index,
2134             name: param.name.ident().as_interned_str(),
2135         }));
2136         index += 1;
2137
2138         match param.kind {
2139             GenericParamKind::Lifetime { .. } => {
2140                 param.bounds.iter().for_each(|bound| match bound {
2141                     hir::GenericBound::Outlives(lt) => {
2142                         let bound = AstConv::ast_region_to_region(&icx, &lt, None);
2143                         let outlives = ty::Binder::bind(ty::OutlivesPredicate(region, bound));
2144                         predicates.push((outlives.to_predicate(), lt.span));
2145                     }
2146                     _ => bug!(),
2147                 });
2148             }
2149             _ => bug!(),
2150         }
2151     }
2152
2153     // Collect the predicates that were written inline by the user on each
2154     // type parameter (e.g., `<T: Foo>`).
2155     for param in &ast_generics.params {
2156         if let GenericParamKind::Type { .. } = param.kind {
2157             let name = param.name.ident().as_interned_str();
2158             let param_ty = ty::ParamTy::new(index, name).to_ty(tcx);
2159             index += 1;
2160
2161             let sized = SizedByDefault::Yes;
2162             let bounds = AstConv::compute_bounds(&icx, param_ty, &param.bounds, sized, param.span);
2163             predicates.extend(bounds.predicates(tcx, param_ty));
2164         }
2165     }
2166
2167     // Add in the bounds that appear in the where-clause.
2168     let where_clause = &ast_generics.where_clause;
2169     for predicate in &where_clause.predicates {
2170         match predicate {
2171             &hir::WherePredicate::BoundPredicate(ref bound_pred) => {
2172                 let ty = icx.to_ty(&bound_pred.bounded_ty);
2173
2174                 // Keep the type around in a dummy predicate, in case of no bounds.
2175                 // That way, `where Ty:` is not a complete noop (see #53696) and `Ty`
2176                 // is still checked for WF.
2177                 if bound_pred.bounds.is_empty() {
2178                     if let ty::Param(_) = ty.sty {
2179                         // This is a `where T:`, which can be in the HIR from the
2180                         // transformation that moves `?Sized` to `T`'s declaration.
2181                         // We can skip the predicate because type parameters are
2182                         // trivially WF, but also we *should*, to avoid exposing
2183                         // users who never wrote `where Type:,` themselves, to
2184                         // compiler/tooling bugs from not handling WF predicates.
2185                     } else {
2186                         let span = bound_pred.bounded_ty.span;
2187                         let predicate = ty::OutlivesPredicate(ty, tcx.mk_region(ty::ReEmpty));
2188                         predicates.push(
2189                             (ty::Predicate::TypeOutlives(ty::Binder::dummy(predicate)), span)
2190                         );
2191                     }
2192                 }
2193
2194                 for bound in bound_pred.bounds.iter() {
2195                     match bound {
2196                         &hir::GenericBound::Trait(ref poly_trait_ref, _) => {
2197                             let mut bounds = Bounds::default();
2198                             let _ = AstConv::instantiate_poly_trait_ref(
2199                                 &icx,
2200                                 poly_trait_ref,
2201                                 ty,
2202                                 &mut bounds,
2203                             );
2204                             predicates.extend(bounds.predicates(tcx, ty));
2205                         }
2206
2207                         &hir::GenericBound::Outlives(ref lifetime) => {
2208                             let region = AstConv::ast_region_to_region(&icx, lifetime, None);
2209                             let pred = ty::Binder::bind(ty::OutlivesPredicate(ty, region));
2210                             predicates.push((ty::Predicate::TypeOutlives(pred), lifetime.span))
2211                         }
2212                     }
2213                 }
2214             }
2215
2216             &hir::WherePredicate::RegionPredicate(ref region_pred) => {
2217                 let r1 = AstConv::ast_region_to_region(&icx, &region_pred.lifetime, None);
2218                 predicates.extend(region_pred.bounds.iter().map(|bound| {
2219                     let (r2, span) = match bound {
2220                         hir::GenericBound::Outlives(lt) => {
2221                             (AstConv::ast_region_to_region(&icx, lt, None), lt.span)
2222                         }
2223                         _ => bug!(),
2224                     };
2225                     let pred = ty::Binder::bind(ty::OutlivesPredicate(r1, r2));
2226
2227                     (ty::Predicate::RegionOutlives(pred), span)
2228                 }))
2229             }
2230
2231             &hir::WherePredicate::EqPredicate(..) => {
2232                 // FIXME(#20041)
2233             }
2234         }
2235     }
2236
2237     // Add predicates from associated type bounds.
2238     if let Some((self_trait_ref, trait_items)) = is_trait {
2239         predicates.extend(trait_items.iter().flat_map(|trait_item_ref| {
2240             let trait_item = tcx.hir().trait_item(trait_item_ref.id);
2241             let bounds = match trait_item.node {
2242                 hir::TraitItemKind::Type(ref bounds, _) => bounds,
2243                 _ => return Vec::new().into_iter()
2244             };
2245
2246             let assoc_ty =
2247                 tcx.mk_projection(tcx.hir().local_def_id(trait_item.hir_id),
2248                     self_trait_ref.substs);
2249
2250             let bounds = AstConv::compute_bounds(
2251                 &ItemCtxt::new(tcx, def_id),
2252                 assoc_ty,
2253                 bounds,
2254                 SizedByDefault::Yes,
2255                 trait_item.span,
2256             );
2257
2258             bounds.predicates(tcx, assoc_ty).into_iter()
2259         }))
2260     }
2261
2262     let mut predicates = predicates.predicates;
2263
2264     // Subtle: before we store the predicates into the tcx, we
2265     // sort them so that predicates like `T: Foo<Item=U>` come
2266     // before uses of `U`.  This avoids false ambiguity errors
2267     // in trait checking. See `setup_constraining_predicates`
2268     // for details.
2269     if let Node::Item(&Item {
2270         node: ItemKind::Impl(..),
2271         ..
2272     }) = node
2273     {
2274         let self_ty = tcx.type_of(def_id);
2275         let trait_ref = tcx.impl_trait_ref(def_id);
2276         cgp::setup_constraining_predicates(
2277             tcx,
2278             &mut predicates,
2279             trait_ref,
2280             &mut cgp::parameters_for_impl(self_ty, trait_ref),
2281         );
2282     }
2283
2284     let result = tcx.arena.alloc(ty::GenericPredicates {
2285         parent: generics.parent,
2286         predicates,
2287     });
2288     debug!("explicit_predicates_of(def_id={:?}) = {:?}", def_id, result);
2289     result
2290 }
2291
2292 /// Converts a specific `GenericBound` from the AST into a set of
2293 /// predicates that apply to the self type. A vector is returned
2294 /// because this can be anywhere from zero predicates (`T: ?Sized` adds no
2295 /// predicates) to one (`T: Foo`) to many (`T: Bar<X = i32>` adds `T: Bar`
2296 /// and `<T as Bar>::X == i32`).
2297 fn predicates_from_bound<'tcx>(
2298     astconv: &dyn AstConv<'tcx>,
2299     param_ty: Ty<'tcx>,
2300     bound: &'tcx hir::GenericBound,
2301 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2302     match *bound {
2303         hir::GenericBound::Trait(ref tr, hir::TraitBoundModifier::None) => {
2304             let mut bounds = Bounds::default();
2305             let _ = astconv.instantiate_poly_trait_ref(
2306                 tr,
2307                 param_ty,
2308                 &mut bounds,
2309             );
2310             bounds.predicates(astconv.tcx(), param_ty)
2311         }
2312         hir::GenericBound::Outlives(ref lifetime) => {
2313             let region = astconv.ast_region_to_region(lifetime, None);
2314             let pred = ty::Binder::bind(ty::OutlivesPredicate(param_ty, region));
2315             vec![(ty::Predicate::TypeOutlives(pred), lifetime.span)]
2316         }
2317         hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => vec![],
2318     }
2319 }
2320
2321 fn compute_sig_of_foreign_fn_decl<'tcx>(
2322     tcx: TyCtxt<'tcx>,
2323     def_id: DefId,
2324     decl: &'tcx hir::FnDecl,
2325     abi: abi::Abi,
2326 ) -> ty::PolyFnSig<'tcx> {
2327     let unsafety = if abi == abi::Abi::RustIntrinsic {
2328         intrisic_operation_unsafety(&*tcx.item_name(def_id).as_str())
2329     } else {
2330         hir::Unsafety::Unsafe
2331     };
2332     let fty = AstConv::ty_of_fn(&ItemCtxt::new(tcx, def_id), unsafety, abi, decl);
2333
2334     // Feature gate SIMD types in FFI, since I am not sure that the
2335     // ABIs are handled at all correctly. -huonw
2336     if abi != abi::Abi::RustIntrinsic
2337         && abi != abi::Abi::PlatformIntrinsic
2338         && !tcx.features().simd_ffi
2339     {
2340         let check = |ast_ty: &hir::Ty, ty: Ty<'_>| {
2341             if ty.is_simd() {
2342                 tcx.sess
2343                    .struct_span_err(
2344                        ast_ty.span,
2345                        &format!(
2346                            "use of SIMD type `{}` in FFI is highly experimental and \
2347                             may result in invalid code",
2348                            tcx.hir().hir_to_pretty_string(ast_ty.hir_id)
2349                        ),
2350                    )
2351                    .help("add `#![feature(simd_ffi)]` to the crate attributes to enable")
2352                    .emit();
2353             }
2354         };
2355         for (input, ty) in decl.inputs.iter().zip(*fty.inputs().skip_binder()) {
2356             check(&input, ty)
2357         }
2358         if let hir::Return(ref ty) = decl.output {
2359             check(&ty, *fty.output().skip_binder())
2360         }
2361     }
2362
2363     fty
2364 }
2365
2366 fn is_foreign_item(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
2367     match tcx.hir().get_if_local(def_id) {
2368         Some(Node::ForeignItem(..)) => true,
2369         Some(_) => false,
2370         _ => bug!("is_foreign_item applied to non-local def-id {:?}", def_id),
2371     }
2372 }
2373
2374 fn static_mutability(tcx: TyCtxt<'_>, def_id: DefId) -> Option<hir::Mutability> {
2375     match tcx.hir().get_if_local(def_id) {
2376         Some(Node::Item(&hir::Item {
2377             node: hir::ItemKind::Static(_, mutbl, _), ..
2378         })) |
2379         Some(Node::ForeignItem( &hir::ForeignItem {
2380             node: hir::ForeignItemKind::Static(_, mutbl), ..
2381         })) => Some(mutbl),
2382         Some(_) => None,
2383         _ => bug!("static_mutability applied to non-local def-id {:?}", def_id),
2384     }
2385 }
2386
2387 fn from_target_feature(
2388     tcx: TyCtxt<'_>,
2389     id: DefId,
2390     attr: &ast::Attribute,
2391     whitelist: &FxHashMap<String, Option<Symbol>>,
2392     target_features: &mut Vec<Symbol>,
2393 ) {
2394     let list = match attr.meta_item_list() {
2395         Some(list) => list,
2396         None => return,
2397     };
2398     let bad_item = |span| {
2399         let msg = "malformed `target_feature` attribute input";
2400         let code = "enable = \"..\"".to_owned();
2401         tcx.sess.struct_span_err(span, &msg)
2402             .span_suggestion(span, "must be of the form", code, Applicability::HasPlaceholders)
2403             .emit();
2404     };
2405     let rust_features = tcx.features();
2406     for item in list {
2407         // Only `enable = ...` is accepted in the meta-item list.
2408         if !item.check_name(sym::enable) {
2409             bad_item(item.span());
2410             continue;
2411         }
2412
2413         // Must be of the form `enable = "..."` (a string).
2414         let value = match item.value_str() {
2415             Some(value) => value,
2416             None => {
2417                 bad_item(item.span());
2418                 continue;
2419             }
2420         };
2421
2422         // We allow comma separation to enable multiple features.
2423         target_features.extend(value.as_str().split(',').filter_map(|feature| {
2424             // Only allow whitelisted features per platform.
2425             let feature_gate = match whitelist.get(feature) {
2426                 Some(g) => g,
2427                 None => {
2428                     let msg = format!(
2429                         "the feature named `{}` is not valid for this target",
2430                         feature
2431                     );
2432                     let mut err = tcx.sess.struct_span_err(item.span(), &msg);
2433                     err.span_label(
2434                         item.span(),
2435                         format!("`{}` is not valid for this target", feature),
2436                     );
2437                     if feature.starts_with("+") {
2438                         let valid = whitelist.contains_key(&feature[1..]);
2439                         if valid {
2440                             err.help("consider removing the leading `+` in the feature name");
2441                         }
2442                     }
2443                     err.emit();
2444                     return None;
2445                 }
2446             };
2447
2448             // Only allow features whose feature gates have been enabled.
2449             let allowed = match feature_gate.as_ref().map(|s| *s) {
2450                 Some(sym::arm_target_feature) => rust_features.arm_target_feature,
2451                 Some(sym::aarch64_target_feature) => rust_features.aarch64_target_feature,
2452                 Some(sym::hexagon_target_feature) => rust_features.hexagon_target_feature,
2453                 Some(sym::powerpc_target_feature) => rust_features.powerpc_target_feature,
2454                 Some(sym::mips_target_feature) => rust_features.mips_target_feature,
2455                 Some(sym::avx512_target_feature) => rust_features.avx512_target_feature,
2456                 Some(sym::mmx_target_feature) => rust_features.mmx_target_feature,
2457                 Some(sym::sse4a_target_feature) => rust_features.sse4a_target_feature,
2458                 Some(sym::tbm_target_feature) => rust_features.tbm_target_feature,
2459                 Some(sym::wasm_target_feature) => rust_features.wasm_target_feature,
2460                 Some(sym::cmpxchg16b_target_feature) => rust_features.cmpxchg16b_target_feature,
2461                 Some(sym::adx_target_feature) => rust_features.adx_target_feature,
2462                 Some(sym::movbe_target_feature) => rust_features.movbe_target_feature,
2463                 Some(sym::rtm_target_feature) => rust_features.rtm_target_feature,
2464                 Some(sym::f16c_target_feature) => rust_features.f16c_target_feature,
2465                 Some(name) => bug!("unknown target feature gate {}", name),
2466                 None => true,
2467             };
2468             if !allowed && id.is_local() {
2469                 feature_gate::emit_feature_err(
2470                     &tcx.sess.parse_sess,
2471                     feature_gate.unwrap(),
2472                     item.span(),
2473                     feature_gate::GateIssue::Language,
2474                     &format!("the target feature `{}` is currently unstable", feature),
2475                 );
2476             }
2477             Some(Symbol::intern(feature))
2478         }));
2479     }
2480 }
2481
2482 fn linkage_by_name(tcx: TyCtxt<'_>, def_id: DefId, name: &str) -> Linkage {
2483     use rustc::mir::mono::Linkage::*;
2484
2485     // Use the names from src/llvm/docs/LangRef.rst here. Most types are only
2486     // applicable to variable declarations and may not really make sense for
2487     // Rust code in the first place but whitelist them anyway and trust that
2488     // the user knows what s/he's doing. Who knows, unanticipated use cases
2489     // may pop up in the future.
2490     //
2491     // ghost, dllimport, dllexport and linkonce_odr_autohide are not supported
2492     // and don't have to be, LLVM treats them as no-ops.
2493     match name {
2494         "appending" => Appending,
2495         "available_externally" => AvailableExternally,
2496         "common" => Common,
2497         "extern_weak" => ExternalWeak,
2498         "external" => External,
2499         "internal" => Internal,
2500         "linkonce" => LinkOnceAny,
2501         "linkonce_odr" => LinkOnceODR,
2502         "private" => Private,
2503         "weak" => WeakAny,
2504         "weak_odr" => WeakODR,
2505         _ => {
2506             let span = tcx.hir().span_if_local(def_id);
2507             if let Some(span) = span {
2508                 tcx.sess.span_fatal(span, "invalid linkage specified")
2509             } else {
2510                 tcx.sess
2511                    .fatal(&format!("invalid linkage specified: {}", name))
2512             }
2513         }
2514     }
2515 }
2516
2517 fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
2518     let attrs = tcx.get_attrs(id);
2519
2520     let mut codegen_fn_attrs = CodegenFnAttrs::new();
2521
2522     let whitelist = tcx.target_features_whitelist(LOCAL_CRATE);
2523
2524     let mut inline_span = None;
2525     for attr in attrs.iter() {
2526         if attr.check_name(sym::cold) {
2527             codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
2528         } else if attr.check_name(sym::rustc_allocator) {
2529             codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR;
2530         } else if attr.check_name(sym::unwind) {
2531             codegen_fn_attrs.flags |= CodegenFnAttrFlags::UNWIND;
2532         } else if attr.check_name(sym::ffi_returns_twice) {
2533             if tcx.is_foreign_item(id) {
2534                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_RETURNS_TWICE;
2535             } else {
2536                 // `#[ffi_returns_twice]` is only allowed `extern fn`s.
2537                 struct_span_err!(
2538                     tcx.sess,
2539                     attr.span,
2540                     E0724,
2541                     "`#[ffi_returns_twice]` may only be used on foreign functions"
2542                 ).emit();
2543             }
2544         } else if attr.check_name(sym::rustc_allocator_nounwind) {
2545             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_ALLOCATOR_NOUNWIND;
2546         } else if attr.check_name(sym::naked) {
2547             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED;
2548         } else if attr.check_name(sym::no_mangle) {
2549             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
2550         } else if attr.check_name(sym::rustc_std_internal_symbol) {
2551             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
2552         } else if attr.check_name(sym::no_debug) {
2553             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_DEBUG;
2554         } else if attr.check_name(sym::used) {
2555             codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED;
2556         } else if attr.check_name(sym::thread_local) {
2557             codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL;
2558         } else if attr.check_name(sym::export_name) {
2559             if let Some(s) = attr.value_str() {
2560                 if s.as_str().contains("\0") {
2561                     // `#[export_name = ...]` will be converted to a null-terminated string,
2562                     // so it may not contain any null characters.
2563                     struct_span_err!(
2564                         tcx.sess,
2565                         attr.span,
2566                         E0648,
2567                         "`export_name` may not contain null characters"
2568                     ).emit();
2569                 }
2570                 codegen_fn_attrs.export_name = Some(s);
2571             }
2572         } else if attr.check_name(sym::target_feature) {
2573             if tcx.fn_sig(id).unsafety() == Unsafety::Normal {
2574                 let msg = "`#[target_feature(..)]` can only be applied to `unsafe` functions";
2575                 tcx.sess.struct_span_err(attr.span, msg)
2576                     .span_label(attr.span, "can only be applied to `unsafe` functions")
2577                     .span_label(tcx.def_span(id), "not an `unsafe` function")
2578                     .emit();
2579             }
2580             from_target_feature(
2581                 tcx,
2582                 id,
2583                 attr,
2584                 &whitelist,
2585                 &mut codegen_fn_attrs.target_features,
2586             );
2587         } else if attr.check_name(sym::linkage) {
2588             if let Some(val) = attr.value_str() {
2589                 codegen_fn_attrs.linkage = Some(linkage_by_name(tcx, id, &val.as_str()));
2590             }
2591         } else if attr.check_name(sym::link_section) {
2592             if let Some(val) = attr.value_str() {
2593                 if val.as_str().bytes().any(|b| b == 0) {
2594                     let msg = format!(
2595                         "illegal null byte in link_section \
2596                          value: `{}`",
2597                         &val
2598                     );
2599                     tcx.sess.span_err(attr.span, &msg);
2600                 } else {
2601                     codegen_fn_attrs.link_section = Some(val);
2602                 }
2603             }
2604         } else if attr.check_name(sym::link_name) {
2605             codegen_fn_attrs.link_name = attr.value_str();
2606         }
2607     }
2608
2609     codegen_fn_attrs.inline = attrs.iter().fold(InlineAttr::None, |ia, attr| {
2610         if attr.path != sym::inline {
2611             return ia;
2612         }
2613         match attr.meta().map(|i| i.node) {
2614             Some(MetaItemKind::Word) => {
2615                 mark_used(attr);
2616                 InlineAttr::Hint
2617             }
2618             Some(MetaItemKind::List(ref items)) => {
2619                 mark_used(attr);
2620                 inline_span = Some(attr.span);
2621                 if items.len() != 1 {
2622                     span_err!(
2623                         tcx.sess.diagnostic(),
2624                         attr.span,
2625                         E0534,
2626                         "expected one argument"
2627                     );
2628                     InlineAttr::None
2629                 } else if list_contains_name(&items[..], sym::always) {
2630                     InlineAttr::Always
2631                 } else if list_contains_name(&items[..], sym::never) {
2632                     InlineAttr::Never
2633                 } else {
2634                     span_err!(
2635                         tcx.sess.diagnostic(),
2636                         items[0].span(),
2637                         E0535,
2638                         "invalid argument"
2639                     );
2640
2641                     InlineAttr::None
2642                 }
2643             }
2644             Some(MetaItemKind::NameValue(_)) => ia,
2645             None => ia,
2646         }
2647     });
2648
2649     codegen_fn_attrs.optimize = attrs.iter().fold(OptimizeAttr::None, |ia, attr| {
2650         if attr.path != sym::optimize {
2651             return ia;
2652         }
2653         let err = |sp, s| span_err!(tcx.sess.diagnostic(), sp, E0722, "{}", s);
2654         match attr.meta().map(|i| i.node) {
2655             Some(MetaItemKind::Word) => {
2656                 err(attr.span, "expected one argument");
2657                 ia
2658             }
2659             Some(MetaItemKind::List(ref items)) => {
2660                 mark_used(attr);
2661                 inline_span = Some(attr.span);
2662                 if items.len() != 1 {
2663                     err(attr.span, "expected one argument");
2664                     OptimizeAttr::None
2665                 } else if list_contains_name(&items[..], sym::size) {
2666                     OptimizeAttr::Size
2667                 } else if list_contains_name(&items[..], sym::speed) {
2668                     OptimizeAttr::Speed
2669                 } else {
2670                     err(items[0].span(), "invalid argument");
2671                     OptimizeAttr::None
2672                 }
2673             }
2674             Some(MetaItemKind::NameValue(_)) => ia,
2675             None => ia,
2676         }
2677     });
2678
2679     // If a function uses #[target_feature] it can't be inlined into general
2680     // purpose functions as they wouldn't have the right target features
2681     // enabled. For that reason we also forbid #[inline(always)] as it can't be
2682     // respected.
2683     if codegen_fn_attrs.target_features.len() > 0 {
2684         if codegen_fn_attrs.inline == InlineAttr::Always {
2685             if let Some(span) = inline_span {
2686                 tcx.sess.span_err(
2687                     span,
2688                     "cannot use `#[inline(always)]` with \
2689                      `#[target_feature]`",
2690                 );
2691             }
2692         }
2693     }
2694
2695     // Weak lang items have the same semantics as "std internal" symbols in the
2696     // sense that they're preserved through all our LTO passes and only
2697     // strippable by the linker.
2698     //
2699     // Additionally weak lang items have predetermined symbol names.
2700     if tcx.is_weak_lang_item(id) {
2701         codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
2702     }
2703     if let Some(name) = weak_lang_items::link_name(&attrs) {
2704         codegen_fn_attrs.export_name = Some(name);
2705         codegen_fn_attrs.link_name = Some(name);
2706     }
2707
2708     // Internal symbols to the standard library all have no_mangle semantics in
2709     // that they have defined symbol names present in the function name. This
2710     // also applies to weak symbols where they all have known symbol names.
2711     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
2712         codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
2713     }
2714
2715     codegen_fn_attrs
2716 }