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, StashKey};
  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     item_ident: Ident,
1153 ) -> Ty<'_> {
1154     let ty = tcx.typeck_tables_of(def_id).node_type(body_id.hir_id);
1155
1156     // If this came from a free `const` or `static mut?` item,
1157     // then the user may have written e.g. `const A = 42;`.
1158     // In this case, the parser has stashed a diagnostic for
1159     // us to improve in typeck so we do that now.
1160     match tcx.sess.diagnostic().steal_diagnostic(span, StashKey::ItemNoType) {
1161         Some(mut err) => {
1162             // The parser provided a sub-optimal `HasPlaceholders` suggestion for the type.
1163             // We are typeck and have the real type, so remove that and suggest the actual type.
1164             err.suggestions.clear();
1165             err.span_suggestion(
1166                 span,
1167                 "provide a type for the item",
1168                 format!("{}: {}", item_ident, ty),
1169                 Applicability::MachineApplicable,
1170             )
1171             .emit();
1172         }
1173         None => {
1174             let mut diag = bad_placeholder_type(tcx, span);
1175             if ty != tcx.types.err {
1176                 diag.span_suggestion(
1177                     span,
1178                     "replace `_` with the correct type",
1179                     ty.to_string(),
1180                     Applicability::MaybeIncorrect,
1181                 );
1182             }
1183             diag.emit();
1184         }
1185     }
1186
1187     ty
1188 }
1189
1190 /// Same as [`type_of`] but returns [`Option`] instead of failing.
1191 ///
1192 /// If you want to fail anyway, you can set the `fail` parameter to true, but in this case,
1193 /// you'd better just call [`type_of`] directly.
1194 pub fn checked_type_of(tcx: TyCtxt<'_>, def_id: DefId, fail: bool) -> Option<Ty<'_>> {
1195     use rustc::hir::*;
1196
1197     let hir_id = match tcx.hir().as_local_hir_id(def_id) {
1198         Some(hir_id) => hir_id,
1199         None => {
1200             if !fail {
1201                 return None;
1202             }
1203             bug!("invalid node");
1204         }
1205     };
1206
1207     let icx = ItemCtxt::new(tcx, def_id);
1208
1209     Some(match tcx.hir().get(hir_id) {
1210         Node::TraitItem(item) => match item.node {
1211             TraitItemKind::Method(..) => {
1212                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1213                 tcx.mk_fn_def(def_id, substs)
1214             }
1215             TraitItemKind::Const(ref ty, body_id)  => {
1216                 body_id.and_then(|body_id| {
1217                     if let hir::TyKind::Infer = ty.node {
1218                         Some(infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident))
1219                     } else {
1220                         None
1221                     }
1222                 }).unwrap_or_else(|| icx.to_ty(ty))
1223             },
1224             TraitItemKind::Type(_, Some(ref ty)) => icx.to_ty(ty),
1225             TraitItemKind::Type(_, None) => {
1226                 if !fail {
1227                     return None;
1228                 }
1229                 span_bug!(item.span, "associated type missing default");
1230             }
1231         },
1232
1233         Node::ImplItem(item) => match item.node {
1234             ImplItemKind::Method(..) => {
1235                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1236                 tcx.mk_fn_def(def_id, substs)
1237             }
1238             ImplItemKind::Const(ref ty, body_id) => {
1239                 if let hir::TyKind::Infer = ty.node {
1240                     infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident)
1241                 } else {
1242                     icx.to_ty(ty)
1243                 }
1244             },
1245             ImplItemKind::OpaqueTy(_) => {
1246                 if tcx
1247                     .impl_trait_ref(tcx.hir().get_parent_did(hir_id))
1248                     .is_none()
1249                 {
1250                     report_assoc_ty_on_inherent_impl(tcx, item.span);
1251                 }
1252
1253                 find_opaque_ty_constraints(tcx, def_id)
1254             }
1255             ImplItemKind::TyAlias(ref ty) => {
1256                 if tcx
1257                     .impl_trait_ref(tcx.hir().get_parent_did(hir_id))
1258                     .is_none()
1259                 {
1260                     report_assoc_ty_on_inherent_impl(tcx, item.span);
1261                 }
1262
1263                 icx.to_ty(ty)
1264             }
1265         },
1266
1267         Node::Item(item) => {
1268             match item.node {
1269                 ItemKind::Static(ref ty, .., body_id)
1270                 | ItemKind::Const(ref ty, body_id) => {
1271                     if let hir::TyKind::Infer = ty.node {
1272                         infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident)
1273                     } else {
1274                         icx.to_ty(ty)
1275                     }
1276                 },
1277                 ItemKind::TyAlias(ref ty, _)
1278                 | ItemKind::Impl(.., ref ty, _) => icx.to_ty(ty),
1279                 ItemKind::Fn(..) => {
1280                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
1281                     tcx.mk_fn_def(def_id, substs)
1282                 }
1283                 ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
1284                     let def = tcx.adt_def(def_id);
1285                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
1286                     tcx.mk_adt(def, substs)
1287                 }
1288                 ItemKind::OpaqueTy(hir::OpaqueTy {
1289                     impl_trait_fn: None,
1290                     ..
1291                 }) => find_opaque_ty_constraints(tcx, def_id),
1292                 // Opaque types desugared from `impl Trait`.
1293                 ItemKind::OpaqueTy(hir::OpaqueTy {
1294                     impl_trait_fn: Some(owner),
1295                     ..
1296                 }) => {
1297                     tcx.typeck_tables_of(owner)
1298                         .concrete_opaque_types
1299                         .get(&def_id)
1300                         .map(|opaque| opaque.concrete_type)
1301                         .unwrap_or_else(|| {
1302                             // This can occur if some error in the
1303                             // owner fn prevented us from populating
1304                             // the `concrete_opaque_types` table.
1305                             tcx.sess.delay_span_bug(
1306                                 DUMMY_SP,
1307                                 &format!(
1308                                     "owner {:?} has no opaque type for {:?} in its tables",
1309                                     owner, def_id,
1310                                 ),
1311                             );
1312                             tcx.types.err
1313                         })
1314                 }
1315                 ItemKind::Trait(..)
1316                 | ItemKind::TraitAlias(..)
1317                 | ItemKind::Mod(..)
1318                 | ItemKind::ForeignMod(..)
1319                 | ItemKind::GlobalAsm(..)
1320                 | ItemKind::ExternCrate(..)
1321                 | ItemKind::Use(..) => {
1322                     if !fail {
1323                         return None;
1324                     }
1325                     span_bug!(
1326                         item.span,
1327                         "compute_type_of_item: unexpected item type: {:?}",
1328                         item.node
1329                     );
1330                 }
1331             }
1332         }
1333
1334         Node::ForeignItem(foreign_item) => match foreign_item.node {
1335             ForeignItemKind::Fn(..) => {
1336                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1337                 tcx.mk_fn_def(def_id, substs)
1338             }
1339             ForeignItemKind::Static(ref t, _) => icx.to_ty(t),
1340             ForeignItemKind::Type => tcx.mk_foreign(def_id),
1341         },
1342
1343         Node::Ctor(&ref def) | Node::Variant(
1344             hir::Variant { data: ref def, .. }
1345         ) => match *def {
1346             VariantData::Unit(..) | VariantData::Struct(..) => {
1347                 tcx.type_of(tcx.hir().get_parent_did(hir_id))
1348             }
1349             VariantData::Tuple(..) => {
1350                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1351                 tcx.mk_fn_def(def_id, substs)
1352             }
1353         },
1354
1355         Node::Field(field) => icx.to_ty(&field.ty),
1356
1357         Node::Expr(&hir::Expr {
1358             node: hir::ExprKind::Closure(.., gen),
1359             ..
1360         }) => {
1361             if gen.is_some() {
1362                 return Some(tcx.typeck_tables_of(def_id).node_type(hir_id));
1363             }
1364
1365             let substs = ty::ClosureSubsts {
1366                 substs: InternalSubsts::identity_for_item(tcx, def_id),
1367             };
1368
1369             tcx.mk_closure(def_id, substs)
1370         }
1371
1372         Node::AnonConst(_) => {
1373             let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
1374             match parent_node {
1375                 Node::Ty(&hir::Ty {
1376                     node: hir::TyKind::Array(_, ref constant),
1377                     ..
1378                 })
1379                 | Node::Ty(&hir::Ty {
1380                     node: hir::TyKind::Typeof(ref constant),
1381                     ..
1382                 })
1383                 | Node::Expr(&hir::Expr {
1384                     node: ExprKind::Repeat(_, ref constant),
1385                     ..
1386                 }) if constant.hir_id == hir_id =>
1387                 {
1388                     tcx.types.usize
1389                 }
1390
1391                 Node::Variant(Variant {
1392                     disr_expr: Some(ref e),
1393                     ..
1394                 }) if e.hir_id == hir_id =>
1395                 {
1396                     tcx.adt_def(tcx.hir().get_parent_did(hir_id))
1397                         .repr
1398                         .discr_type()
1399                         .to_ty(tcx)
1400                 }
1401
1402                 Node::Ty(&hir::Ty { node: hir::TyKind::Path(_), .. }) |
1403                 Node::Expr(&hir::Expr { node: ExprKind::Struct(..), .. }) |
1404                 Node::Expr(&hir::Expr { node: ExprKind::Path(_), .. }) |
1405                 Node::TraitRef(..) => {
1406                     let path = match parent_node {
1407                         Node::Ty(&hir::Ty {
1408                             node: hir::TyKind::Path(QPath::Resolved(_, ref path)),
1409                             ..
1410                         })
1411                         | Node::Expr(&hir::Expr {
1412                             node: ExprKind::Path(QPath::Resolved(_, ref path)),
1413                             ..
1414                         }) => {
1415                             Some(&**path)
1416                         }
1417                         Node::Expr(&hir::Expr { node: ExprKind::Struct(ref path, ..), .. }) => {
1418                             if let QPath::Resolved(_, ref path) = **path {
1419                                 Some(&**path)
1420                             } else {
1421                                 None
1422                             }
1423                         }
1424                         Node::TraitRef(&hir::TraitRef { ref path, .. }) => Some(&**path),
1425                         _ => None,
1426                     };
1427
1428                     if let Some(path) = path {
1429                         let arg_index = path.segments.iter()
1430                             .filter_map(|seg| seg.args.as_ref())
1431                             .map(|generic_args| generic_args.args.as_ref())
1432                             .find_map(|args| {
1433                                 args.iter()
1434                                     .filter(|arg| arg.is_const())
1435                                     .enumerate()
1436                                     .filter(|(_, arg)| arg.id() == hir_id)
1437                                     .map(|(index, _)| index)
1438                                     .next()
1439                             })
1440                             .or_else(|| {
1441                                 if !fail {
1442                                     None
1443                                 } else {
1444                                     bug!("no arg matching AnonConst in path")
1445                                 }
1446                             })?;
1447
1448                         // We've encountered an `AnonConst` in some path, so we need to
1449                         // figure out which generic parameter it corresponds to and return
1450                         // the relevant type.
1451                         let generics = match path.res {
1452                             Res::Def(DefKind::Ctor(..), def_id) => {
1453                                 tcx.generics_of(tcx.parent(def_id).unwrap())
1454                             }
1455                             Res::Def(_, def_id) => tcx.generics_of(def_id),
1456                             Res::Err => return Some(tcx.types.err),
1457                             _ if !fail => return None,
1458                             res => {
1459                                 tcx.sess.delay_span_bug(
1460                                     DUMMY_SP,
1461                                     &format!(
1462                                         "unexpected const parent path def {:?}",
1463                                         res,
1464                                     ),
1465                                 );
1466                                 return Some(tcx.types.err);
1467                             }
1468                         };
1469
1470                         generics.params.iter()
1471                             .filter(|param| {
1472                                 if let ty::GenericParamDefKind::Const = param.kind {
1473                                     true
1474                                 } else {
1475                                     false
1476                                 }
1477                             })
1478                             .nth(arg_index)
1479                             .map(|param| tcx.type_of(param.def_id))
1480                             // This is no generic parameter associated with the arg. This is
1481                             // probably from an extra arg where one is not needed.
1482                             .unwrap_or(tcx.types.err)
1483                     } else {
1484                         if !fail {
1485                             return None;
1486                         }
1487                         tcx.sess.delay_span_bug(
1488                             DUMMY_SP,
1489                             &format!(
1490                                 "unexpected const parent path {:?}",
1491                                 parent_node,
1492                             ),
1493                         );
1494                         return Some(tcx.types.err);
1495                     }
1496                 }
1497
1498                 x => {
1499                     if !fail {
1500                         return None;
1501                     }
1502                     tcx.sess.delay_span_bug(
1503                         DUMMY_SP,
1504                         &format!(
1505                             "unexpected const parent in type_of_def_id(): {:?}", x
1506                         ),
1507                     );
1508                     tcx.types.err
1509                 }
1510             }
1511         }
1512
1513         Node::GenericParam(param) => match &param.kind {
1514             hir::GenericParamKind::Type { default: Some(ref ty), .. } |
1515             hir::GenericParamKind::Const { ref ty, .. } => {
1516                 icx.to_ty(ty)
1517             }
1518             x => {
1519                 if !fail {
1520                     return None;
1521                 }
1522                 bug!("unexpected non-type Node::GenericParam: {:?}", x)
1523             },
1524         },
1525
1526         x => {
1527             if !fail {
1528                 return None;
1529             }
1530             bug!("unexpected sort of node in type_of_def_id(): {:?}", x);
1531         }
1532     })
1533 }
1534
1535 fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
1536     use rustc::hir::{ImplItem, Item, TraitItem};
1537
1538     debug!("find_opaque_ty_constraints({:?})", def_id);
1539
1540     struct ConstraintLocator<'tcx> {
1541         tcx: TyCtxt<'tcx>,
1542         def_id: DefId,
1543         // (first found type span, actual type, mapping from the opaque type's generic
1544         // parameters to the concrete type's generic parameters)
1545         //
1546         // The mapping is an index for each use site of a generic parameter in the concrete type
1547         //
1548         // The indices index into the generic parameters on the opaque type.
1549         found: Option<(Span, Ty<'tcx>, Vec<usize>)>,
1550     }
1551
1552     impl ConstraintLocator<'tcx> {
1553         fn check(&mut self, def_id: DefId) {
1554             // Don't try to check items that cannot possibly constrain the type.
1555             if !self.tcx.has_typeck_tables(def_id) {
1556                 debug!(
1557                     "find_opaque_ty_constraints: no constraint for `{:?}` at `{:?}`: no tables",
1558                     self.def_id,
1559                     def_id,
1560                 );
1561                 return;
1562             }
1563             let ty = self
1564                 .tcx
1565                 .typeck_tables_of(def_id)
1566                 .concrete_opaque_types
1567                 .get(&self.def_id);
1568             if let Some(ty::ResolvedOpaqueTy { concrete_type, substs }) = ty {
1569                 debug!(
1570                     "find_opaque_ty_constraints: found constraint for `{:?}` at `{:?}`: {:?}",
1571                     self.def_id,
1572                     def_id,
1573                     ty,
1574                 );
1575
1576                 // FIXME(oli-obk): trace the actual span from inference to improve errors.
1577                 let span = self.tcx.def_span(def_id);
1578                 // used to quickly look up the position of a generic parameter
1579                 let mut index_map: FxHashMap<ty::ParamTy, usize> = FxHashMap::default();
1580                 // Skipping binder is ok, since we only use this to find generic parameters and
1581                 // their positions.
1582                 for (idx, subst) in substs.iter().enumerate() {
1583                     if let UnpackedKind::Type(ty) = subst.unpack() {
1584                         if let ty::Param(p) = ty.sty {
1585                             if index_map.insert(p, idx).is_some() {
1586                                 // There was already an entry for `p`, meaning a generic parameter
1587                                 // was used twice.
1588                                 self.tcx.sess.span_err(
1589                                     span,
1590                                     &format!(
1591                                         "defining opaque type use restricts opaque \
1592                                          type by using the generic parameter `{}` twice",
1593                                         p,
1594                                     ),
1595                                 );
1596                                 return;
1597                             }
1598                         } else {
1599                             self.tcx.sess.delay_span_bug(
1600                                 span,
1601                                 &format!(
1602                                     "non-defining opaque ty use in defining scope: {:?}, {:?}",
1603                                     concrete_type, substs,
1604                                 ),
1605                             );
1606                         }
1607                     }
1608                 }
1609                 // Compute the index within the opaque type for each generic parameter used in
1610                 // the concrete type.
1611                 let indices = concrete_type
1612                     .subst(self.tcx, substs)
1613                     .walk()
1614                     .filter_map(|t| match &t.sty {
1615                         ty::Param(p) => Some(*index_map.get(p).unwrap()),
1616                         _ => None,
1617                     }).collect();
1618                 let is_param = |ty: Ty<'_>| match ty.sty {
1619                     ty::Param(_) => true,
1620                     _ => false,
1621                 };
1622                 if !substs.types().all(is_param) {
1623                     self.tcx.sess.span_err(
1624                         span,
1625                         "defining opaque type use does not fully define opaque type",
1626                     );
1627                 } else if let Some((prev_span, prev_ty, ref prev_indices)) = self.found {
1628                     let mut ty = concrete_type.walk().fuse();
1629                     let mut p_ty = prev_ty.walk().fuse();
1630                     let iter_eq = (&mut ty).zip(&mut p_ty).all(|(t, p)| match (&t.sty, &p.sty) {
1631                         // Type parameters are equal to any other type parameter for the purpose of
1632                         // concrete type equality, as it is possible to obtain the same type just
1633                         // by passing matching parameters to a function.
1634                         (ty::Param(_), ty::Param(_)) => true,
1635                         _ => t == p,
1636                     });
1637                     if !iter_eq || ty.next().is_some() || p_ty.next().is_some() {
1638                         debug!("find_opaque_ty_constraints: span={:?}", span);
1639                         // Found different concrete types for the opaque type.
1640                         let mut err = self.tcx.sess.struct_span_err(
1641                             span,
1642                             "concrete type differs from previous defining opaque type use",
1643                         );
1644                         err.span_label(
1645                             span,
1646                             format!("expected `{}`, got `{}`", prev_ty, concrete_type),
1647                         );
1648                         err.span_note(prev_span, "previous use here");
1649                         err.emit();
1650                     } else if indices != *prev_indices {
1651                         // Found "same" concrete types, but the generic parameter order differs.
1652                         let mut err = self.tcx.sess.struct_span_err(
1653                             span,
1654                             "concrete type's generic parameters differ from previous defining use",
1655                         );
1656                         use std::fmt::Write;
1657                         let mut s = String::new();
1658                         write!(s, "expected [").unwrap();
1659                         let list = |s: &mut String, indices: &Vec<usize>| {
1660                             let mut indices = indices.iter().cloned();
1661                             if let Some(first) = indices.next() {
1662                                 write!(s, "`{}`", substs[first]).unwrap();
1663                                 for i in indices {
1664                                     write!(s, ", `{}`", substs[i]).unwrap();
1665                                 }
1666                             }
1667                         };
1668                         list(&mut s, prev_indices);
1669                         write!(s, "], got [").unwrap();
1670                         list(&mut s, &indices);
1671                         write!(s, "]").unwrap();
1672                         err.span_label(span, s);
1673                         err.span_note(prev_span, "previous use here");
1674                         err.emit();
1675                     }
1676                 } else {
1677                     self.found = Some((span, concrete_type, indices));
1678                 }
1679             } else {
1680                 debug!(
1681                     "find_opaque_ty_constraints: no constraint for `{:?}` at `{:?}`",
1682                     self.def_id,
1683                     def_id,
1684                 );
1685             }
1686         }
1687     }
1688
1689     impl<'tcx> intravisit::Visitor<'tcx> for ConstraintLocator<'tcx> {
1690         fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
1691             intravisit::NestedVisitorMap::All(&self.tcx.hir())
1692         }
1693         fn visit_item(&mut self, it: &'tcx Item) {
1694             debug!("find_existential_constraints: visiting {:?}", it);
1695             let def_id = self.tcx.hir().local_def_id(it.hir_id);
1696             // The opaque type itself or its children are not within its reveal scope.
1697             if def_id != self.def_id {
1698                 self.check(def_id);
1699                 intravisit::walk_item(self, it);
1700             }
1701         }
1702         fn visit_impl_item(&mut self, it: &'tcx ImplItem) {
1703             debug!("find_existential_constraints: visiting {:?}", it);
1704             let def_id = self.tcx.hir().local_def_id(it.hir_id);
1705             // The opaque type itself or its children are not within its reveal scope.
1706             if def_id != self.def_id {
1707                 self.check(def_id);
1708                 intravisit::walk_impl_item(self, it);
1709             }
1710         }
1711         fn visit_trait_item(&mut self, it: &'tcx TraitItem) {
1712             debug!("find_existential_constraints: visiting {:?}", it);
1713             let def_id = self.tcx.hir().local_def_id(it.hir_id);
1714             self.check(def_id);
1715             intravisit::walk_trait_item(self, it);
1716         }
1717     }
1718
1719     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1720     let scope = tcx.hir()
1721         .get_defining_scope(hir_id)
1722         .expect("could not get defining scope");
1723     let mut locator = ConstraintLocator {
1724         def_id,
1725         tcx,
1726         found: None,
1727     };
1728
1729     debug!("find_opaque_ty_constraints: scope={:?}", scope);
1730
1731     if scope == hir::CRATE_HIR_ID {
1732         intravisit::walk_crate(&mut locator, tcx.hir().krate());
1733     } else {
1734         debug!("find_opaque_ty_constraints: scope={:?}", tcx.hir().get(scope));
1735         match tcx.hir().get(scope) {
1736             // We explicitly call `visit_*` methods, instead of using `intravisit::walk_*` methods
1737             // This allows our visitor to process the defining item itself, causing
1738             // it to pick up any 'sibling' defining uses.
1739             //
1740             // For example, this code:
1741             // ```
1742             // fn foo() {
1743             //     type Blah = impl Debug;
1744             //     let my_closure = || -> Blah { true };
1745             // }
1746             // ```
1747             //
1748             // requires us to explicitly process `foo()` in order
1749             // to notice the defining usage of `Blah`.
1750             Node::Item(ref it) => locator.visit_item(it),
1751             Node::ImplItem(ref it) => locator.visit_impl_item(it),
1752             Node::TraitItem(ref it) => locator.visit_trait_item(it),
1753             other => bug!(
1754                 "{:?} is not a valid scope for an opaque type item",
1755                 other
1756             ),
1757         }
1758     }
1759
1760     match locator.found {
1761         Some((_, ty, _)) => ty,
1762         None => {
1763             let span = tcx.def_span(def_id);
1764             tcx.sess.span_err(span, "could not find defining uses");
1765             tcx.types.err
1766         }
1767     }
1768 }
1769
1770 pub fn get_infer_ret_ty(output: &'_ hir::FunctionRetTy) -> Option<&hir::Ty> {
1771     if let hir::FunctionRetTy::Return(ref ty) = output {
1772         if let hir::TyKind::Infer = ty.node {
1773             return Some(&**ty)
1774         }
1775     }
1776     None
1777 }
1778
1779 fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
1780     use rustc::hir::*;
1781     use rustc::hir::Node::*;
1782
1783     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1784
1785     let icx = ItemCtxt::new(tcx, def_id);
1786
1787     match tcx.hir().get(hir_id) {
1788         TraitItem(hir::TraitItem {
1789             node: TraitItemKind::Method(MethodSig { header, decl }, TraitMethod::Provided(_)),
1790             ..
1791         })
1792         | ImplItem(hir::ImplItem {
1793             node: ImplItemKind::Method(MethodSig { header, decl }, _),
1794             ..
1795         })
1796         | Item(hir::Item {
1797             node: ItemKind::Fn(decl, header, _, _),
1798             ..
1799         }) => match get_infer_ret_ty(&decl.output) {
1800             Some(ty) => {
1801                 let fn_sig = tcx.typeck_tables_of(def_id).liberated_fn_sigs()[hir_id];
1802                 let mut diag = bad_placeholder_type(tcx, ty.span);
1803                 let ret_ty = fn_sig.output();
1804                 if ret_ty != tcx.types.err  {
1805                     diag.span_suggestion(
1806                         ty.span,
1807                         "replace `_` with the correct return type",
1808                         ret_ty.to_string(),
1809                         Applicability::MaybeIncorrect,
1810                     );
1811                 }
1812                 diag.emit();
1813                 ty::Binder::bind(fn_sig)
1814             },
1815             None => AstConv::ty_of_fn(&icx, header.unsafety, header.abi, decl)
1816         },
1817
1818         TraitItem(hir::TraitItem {
1819             node: TraitItemKind::Method(MethodSig { header, decl }, _),
1820             ..
1821         }) => {
1822             AstConv::ty_of_fn(&icx, header.unsafety, header.abi, decl)
1823         },
1824
1825         ForeignItem(&hir::ForeignItem {
1826             node: ForeignItemKind::Fn(ref fn_decl, _, _),
1827             ..
1828         }) => {
1829             let abi = tcx.hir().get_foreign_abi(hir_id);
1830             compute_sig_of_foreign_fn_decl(tcx, def_id, fn_decl, abi)
1831         }
1832
1833         Ctor(data) | Variant(
1834             hir::Variant { data, ..  }
1835         ) if data.ctor_hir_id().is_some() => {
1836             let ty = tcx.type_of(tcx.hir().get_parent_did(hir_id));
1837             let inputs = data.fields()
1838                 .iter()
1839                 .map(|f| tcx.type_of(tcx.hir().local_def_id(f.hir_id)));
1840             ty::Binder::bind(tcx.mk_fn_sig(
1841                 inputs,
1842                 ty,
1843                 false,
1844                 hir::Unsafety::Normal,
1845                 abi::Abi::Rust,
1846             ))
1847         }
1848
1849         Expr(&hir::Expr {
1850             node: hir::ExprKind::Closure(..),
1851             ..
1852         }) => {
1853             // Closure signatures are not like other function
1854             // signatures and cannot be accessed through `fn_sig`. For
1855             // example, a closure signature excludes the `self`
1856             // argument. In any case they are embedded within the
1857             // closure type as part of the `ClosureSubsts`.
1858             //
1859             // To get
1860             // the signature of a closure, you should use the
1861             // `closure_sig` method on the `ClosureSubsts`:
1862             //
1863             //    closure_substs.closure_sig(def_id, tcx)
1864             //
1865             // or, inside of an inference context, you can use
1866             //
1867             //    infcx.closure_sig(def_id, closure_substs)
1868             bug!("to get the signature of a closure, use `closure_sig()` not `fn_sig()`");
1869         }
1870
1871         x => {
1872             bug!("unexpected sort of node in fn_sig(): {:?}", x);
1873         }
1874     }
1875 }
1876
1877 fn impl_trait_ref(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ty::TraitRef<'_>> {
1878     let icx = ItemCtxt::new(tcx, def_id);
1879
1880     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1881     match tcx.hir().expect_item(hir_id).node {
1882         hir::ItemKind::Impl(.., ref opt_trait_ref, _, _) => {
1883             opt_trait_ref.as_ref().map(|ast_trait_ref| {
1884                 let selfty = tcx.type_of(def_id);
1885                 AstConv::instantiate_mono_trait_ref(&icx, ast_trait_ref, selfty)
1886             })
1887         }
1888         _ => bug!(),
1889     }
1890 }
1891
1892 fn impl_polarity(tcx: TyCtxt<'_>, def_id: DefId) -> hir::ImplPolarity {
1893     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1894     match tcx.hir().expect_item(hir_id).node {
1895         hir::ItemKind::Impl(_, polarity, ..) => polarity,
1896         ref item => bug!("impl_polarity: {:?} not an impl", item),
1897     }
1898 }
1899
1900 /// Returns the early-bound lifetimes declared in this generics
1901 /// listing. For anything other than fns/methods, this is just all
1902 /// the lifetimes that are declared. For fns or methods, we have to
1903 /// screen out those that do not appear in any where-clauses etc using
1904 /// `resolve_lifetime::early_bound_lifetimes`.
1905 fn early_bound_lifetimes_from_generics<'a, 'tcx: 'a>(
1906     tcx: TyCtxt<'tcx>,
1907     generics: &'a hir::Generics,
1908 ) -> impl Iterator<Item = &'a hir::GenericParam> + Captures<'tcx> {
1909     generics
1910         .params
1911         .iter()
1912         .filter(move |param| match param.kind {
1913             GenericParamKind::Lifetime { .. } => {
1914                 !tcx.is_late_bound(param.hir_id)
1915             }
1916             _ => false,
1917         })
1918 }
1919
1920 /// Returns a list of type predicates for the definition with ID `def_id`, including inferred
1921 /// lifetime constraints. This includes all predicates returned by `explicit_predicates_of`, plus
1922 /// inferred constraints concerning which regions outlive other regions.
1923 fn predicates_defined_on(
1924     tcx: TyCtxt<'_>,
1925     def_id: DefId,
1926 ) -> &ty::GenericPredicates<'_> {
1927     debug!("predicates_defined_on({:?})", def_id);
1928     let mut result = tcx.explicit_predicates_of(def_id);
1929     debug!(
1930         "predicates_defined_on: explicit_predicates_of({:?}) = {:?}",
1931         def_id,
1932         result,
1933     );
1934     let inferred_outlives = tcx.inferred_outlives_of(def_id);
1935     if !inferred_outlives.is_empty() {
1936         let span = tcx.def_span(def_id);
1937         debug!(
1938             "predicates_defined_on: inferred_outlives_of({:?}) = {:?}",
1939             def_id,
1940             inferred_outlives,
1941         );
1942         let mut predicates = (*result).clone();
1943         predicates.predicates.extend(inferred_outlives.iter().map(|&p| (p, span)));
1944         result = tcx.arena.alloc(predicates);
1945     }
1946     debug!("predicates_defined_on({:?}) = {:?}", def_id, result);
1947     result
1948 }
1949
1950 /// Returns a list of all type predicates (explicit and implicit) for the definition with
1951 /// ID `def_id`. This includes all predicates returned by `predicates_defined_on`, plus
1952 /// `Self: Trait` predicates for traits.
1953 fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::GenericPredicates<'_> {
1954     let mut result = tcx.predicates_defined_on(def_id);
1955
1956     if tcx.is_trait(def_id) {
1957         // For traits, add `Self: Trait` predicate. This is
1958         // not part of the predicates that a user writes, but it
1959         // is something that one must prove in order to invoke a
1960         // method or project an associated type.
1961         //
1962         // In the chalk setup, this predicate is not part of the
1963         // "predicates" for a trait item. But it is useful in
1964         // rustc because if you directly (e.g.) invoke a trait
1965         // method like `Trait::method(...)`, you must naturally
1966         // prove that the trait applies to the types that were
1967         // used, and adding the predicate into this list ensures
1968         // that this is done.
1969         let span = tcx.def_span(def_id);
1970         let mut predicates = (*result).clone();
1971         predicates.predicates.push((ty::TraitRef::identity(tcx, def_id).to_predicate(), span));
1972         result = tcx.arena.alloc(predicates);
1973     }
1974     debug!("predicates_of(def_id={:?}) = {:?}", def_id, result);
1975     result
1976 }
1977
1978 /// Returns a list of user-specified type predicates for the definition with ID `def_id`.
1979 /// N.B., this does not include any implied/inferred constraints.
1980 fn explicit_predicates_of(
1981     tcx: TyCtxt<'_>,
1982     def_id: DefId,
1983 ) -> &ty::GenericPredicates<'_> {
1984     use rustc::hir::*;
1985     use rustc_data_structures::fx::FxHashSet;
1986
1987     debug!("explicit_predicates_of(def_id={:?})", def_id);
1988
1989     /// A data structure with unique elements, which preserves order of insertion.
1990     /// Preserving the order of insertion is important here so as not to break
1991     /// compile-fail UI tests.
1992     struct UniquePredicates<'tcx> {
1993         predicates: Vec<(ty::Predicate<'tcx>, Span)>,
1994         uniques: FxHashSet<(ty::Predicate<'tcx>, Span)>,
1995     }
1996
1997     impl<'tcx> UniquePredicates<'tcx> {
1998         fn new() -> Self {
1999             UniquePredicates {
2000                 predicates: vec![],
2001                 uniques: FxHashSet::default(),
2002             }
2003         }
2004
2005         fn push(&mut self, value: (ty::Predicate<'tcx>, Span)) {
2006             if self.uniques.insert(value) {
2007                 self.predicates.push(value);
2008             }
2009         }
2010
2011         fn extend<I: IntoIterator<Item = (ty::Predicate<'tcx>, Span)>>(&mut self, iter: I) {
2012             for value in iter {
2013                 self.push(value);
2014             }
2015         }
2016     }
2017
2018     let hir_id = match tcx.hir().as_local_hir_id(def_id) {
2019         Some(hir_id) => hir_id,
2020         None => return tcx.predicates_of(def_id),
2021     };
2022     let node = tcx.hir().get(hir_id);
2023
2024     let mut is_trait = None;
2025     let mut is_default_impl_trait = None;
2026
2027     let icx = ItemCtxt::new(tcx, def_id);
2028
2029     const NO_GENERICS: &hir::Generics = &hir::Generics::empty();
2030
2031     let empty_trait_items = HirVec::new();
2032
2033     let mut predicates = UniquePredicates::new();
2034
2035     let ast_generics = match node {
2036         Node::TraitItem(item) => &item.generics,
2037
2038         Node::ImplItem(item) => match item.node {
2039             ImplItemKind::OpaqueTy(ref bounds) => {
2040                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
2041                 let opaque_ty = tcx.mk_opaque(def_id, substs);
2042
2043                 // Collect the bounds, i.e., the `A + B + 'c` in `impl A + B + 'c`.
2044                 let bounds = AstConv::compute_bounds(
2045                     &icx,
2046                     opaque_ty,
2047                     bounds,
2048                     SizedByDefault::Yes,
2049                     tcx.def_span(def_id),
2050                 );
2051
2052                 predicates.extend(bounds.predicates(tcx, opaque_ty));
2053                 &item.generics
2054             }
2055             _ => &item.generics,
2056         },
2057
2058         Node::Item(item) => {
2059             match item.node {
2060                 ItemKind::Impl(_, _, defaultness, ref generics, ..) => {
2061                     if defaultness.is_default() {
2062                         is_default_impl_trait = tcx.impl_trait_ref(def_id);
2063                     }
2064                     generics
2065                 }
2066                 ItemKind::Fn(.., ref generics, _)
2067                 | ItemKind::TyAlias(_, ref generics)
2068                 | ItemKind::Enum(_, ref generics)
2069                 | ItemKind::Struct(_, ref generics)
2070                 | ItemKind::Union(_, ref generics) => generics,
2071
2072                 ItemKind::Trait(_, _, ref generics, .., ref items) => {
2073                     is_trait = Some((ty::TraitRef::identity(tcx, def_id), items));
2074                     generics
2075                 }
2076                 ItemKind::TraitAlias(ref generics, _) => {
2077                     is_trait = Some((ty::TraitRef::identity(tcx, def_id), &empty_trait_items));
2078                     generics
2079                 }
2080                 ItemKind::OpaqueTy(OpaqueTy {
2081                     ref bounds,
2082                     impl_trait_fn,
2083                     ref generics,
2084                     origin: _,
2085                 }) => {
2086                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
2087                     let opaque_ty = tcx.mk_opaque(def_id, substs);
2088
2089                     // Collect the bounds, i.e., the `A + B + 'c` in `impl A + B + 'c`.
2090                     let bounds = AstConv::compute_bounds(
2091                         &icx,
2092                         opaque_ty,
2093                         bounds,
2094                         SizedByDefault::Yes,
2095                         tcx.def_span(def_id),
2096                     );
2097
2098                     let bounds_predicates = bounds.predicates(tcx, opaque_ty);
2099                     if impl_trait_fn.is_some() {
2100                         // opaque types
2101                         return tcx.arena.alloc(ty::GenericPredicates {
2102                             parent: None,
2103                             predicates: bounds_predicates,
2104                         });
2105                     } else {
2106                         // named opaque types
2107                         predicates.extend(bounds_predicates);
2108                         generics
2109                     }
2110                 }
2111
2112                 _ => NO_GENERICS,
2113             }
2114         }
2115
2116         Node::ForeignItem(item) => match item.node {
2117             ForeignItemKind::Static(..) => NO_GENERICS,
2118             ForeignItemKind::Fn(_, _, ref generics) => generics,
2119             ForeignItemKind::Type => NO_GENERICS,
2120         },
2121
2122         _ => NO_GENERICS,
2123     };
2124
2125     let generics = tcx.generics_of(def_id);
2126     let parent_count = generics.parent_count as u32;
2127     let has_own_self = generics.has_self && parent_count == 0;
2128
2129     // Below we'll consider the bounds on the type parameters (including `Self`)
2130     // and the explicit where-clauses, but to get the full set of predicates
2131     // on a trait we need to add in the supertrait bounds and bounds found on
2132     // associated types.
2133     if let Some((_trait_ref, _)) = is_trait {
2134         predicates.extend(tcx.super_predicates_of(def_id).predicates.iter().cloned());
2135     }
2136
2137     // In default impls, we can assume that the self type implements
2138     // the trait. So in:
2139     //
2140     //     default impl Foo for Bar { .. }
2141     //
2142     // we add a default where clause `Foo: Bar`. We do a similar thing for traits
2143     // (see below). Recall that a default impl is not itself an impl, but rather a
2144     // set of defaults that can be incorporated into another impl.
2145     if let Some(trait_ref) = is_default_impl_trait {
2146         predicates.push((trait_ref.to_poly_trait_ref().to_predicate(), tcx.def_span(def_id)));
2147     }
2148
2149     // Collect the region predicates that were declared inline as
2150     // well. In the case of parameters declared on a fn or method, we
2151     // have to be careful to only iterate over early-bound regions.
2152     let mut index = parent_count + has_own_self as u32;
2153     for param in early_bound_lifetimes_from_generics(tcx, ast_generics) {
2154         let region = tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
2155             def_id: tcx.hir().local_def_id(param.hir_id),
2156             index,
2157             name: param.name.ident().as_interned_str(),
2158         }));
2159         index += 1;
2160
2161         match param.kind {
2162             GenericParamKind::Lifetime { .. } => {
2163                 param.bounds.iter().for_each(|bound| match bound {
2164                     hir::GenericBound::Outlives(lt) => {
2165                         let bound = AstConv::ast_region_to_region(&icx, &lt, None);
2166                         let outlives = ty::Binder::bind(ty::OutlivesPredicate(region, bound));
2167                         predicates.push((outlives.to_predicate(), lt.span));
2168                     }
2169                     _ => bug!(),
2170                 });
2171             }
2172             _ => bug!(),
2173         }
2174     }
2175
2176     // Collect the predicates that were written inline by the user on each
2177     // type parameter (e.g., `<T: Foo>`).
2178     for param in &ast_generics.params {
2179         if let GenericParamKind::Type { .. } = param.kind {
2180             let name = param.name.ident().as_interned_str();
2181             let param_ty = ty::ParamTy::new(index, name).to_ty(tcx);
2182             index += 1;
2183
2184             let sized = SizedByDefault::Yes;
2185             let bounds = AstConv::compute_bounds(&icx, param_ty, &param.bounds, sized, param.span);
2186             predicates.extend(bounds.predicates(tcx, param_ty));
2187         }
2188     }
2189
2190     // Add in the bounds that appear in the where-clause.
2191     let where_clause = &ast_generics.where_clause;
2192     for predicate in &where_clause.predicates {
2193         match predicate {
2194             &hir::WherePredicate::BoundPredicate(ref bound_pred) => {
2195                 let ty = icx.to_ty(&bound_pred.bounded_ty);
2196
2197                 // Keep the type around in a dummy predicate, in case of no bounds.
2198                 // That way, `where Ty:` is not a complete noop (see #53696) and `Ty`
2199                 // is still checked for WF.
2200                 if bound_pred.bounds.is_empty() {
2201                     if let ty::Param(_) = ty.sty {
2202                         // This is a `where T:`, which can be in the HIR from the
2203                         // transformation that moves `?Sized` to `T`'s declaration.
2204                         // We can skip the predicate because type parameters are
2205                         // trivially WF, but also we *should*, to avoid exposing
2206                         // users who never wrote `where Type:,` themselves, to
2207                         // compiler/tooling bugs from not handling WF predicates.
2208                     } else {
2209                         let span = bound_pred.bounded_ty.span;
2210                         let predicate = ty::OutlivesPredicate(ty, tcx.mk_region(ty::ReEmpty));
2211                         predicates.push(
2212                             (ty::Predicate::TypeOutlives(ty::Binder::dummy(predicate)), span)
2213                         );
2214                     }
2215                 }
2216
2217                 for bound in bound_pred.bounds.iter() {
2218                     match bound {
2219                         &hir::GenericBound::Trait(ref poly_trait_ref, _) => {
2220                             let mut bounds = Bounds::default();
2221                             let _ = AstConv::instantiate_poly_trait_ref(
2222                                 &icx,
2223                                 poly_trait_ref,
2224                                 ty,
2225                                 &mut bounds,
2226                             );
2227                             predicates.extend(bounds.predicates(tcx, ty));
2228                         }
2229
2230                         &hir::GenericBound::Outlives(ref lifetime) => {
2231                             let region = AstConv::ast_region_to_region(&icx, lifetime, None);
2232                             let pred = ty::Binder::bind(ty::OutlivesPredicate(ty, region));
2233                             predicates.push((ty::Predicate::TypeOutlives(pred), lifetime.span))
2234                         }
2235                     }
2236                 }
2237             }
2238
2239             &hir::WherePredicate::RegionPredicate(ref region_pred) => {
2240                 let r1 = AstConv::ast_region_to_region(&icx, &region_pred.lifetime, None);
2241                 predicates.extend(region_pred.bounds.iter().map(|bound| {
2242                     let (r2, span) = match bound {
2243                         hir::GenericBound::Outlives(lt) => {
2244                             (AstConv::ast_region_to_region(&icx, lt, None), lt.span)
2245                         }
2246                         _ => bug!(),
2247                     };
2248                     let pred = ty::Binder::bind(ty::OutlivesPredicate(r1, r2));
2249
2250                     (ty::Predicate::RegionOutlives(pred), span)
2251                 }))
2252             }
2253
2254             &hir::WherePredicate::EqPredicate(..) => {
2255                 // FIXME(#20041)
2256             }
2257         }
2258     }
2259
2260     // Add predicates from associated type bounds.
2261     if let Some((self_trait_ref, trait_items)) = is_trait {
2262         predicates.extend(trait_items.iter().flat_map(|trait_item_ref| {
2263             let trait_item = tcx.hir().trait_item(trait_item_ref.id);
2264             let bounds = match trait_item.node {
2265                 hir::TraitItemKind::Type(ref bounds, _) => bounds,
2266                 _ => return Vec::new().into_iter()
2267             };
2268
2269             let assoc_ty =
2270                 tcx.mk_projection(tcx.hir().local_def_id(trait_item.hir_id),
2271                     self_trait_ref.substs);
2272
2273             let bounds = AstConv::compute_bounds(
2274                 &ItemCtxt::new(tcx, def_id),
2275                 assoc_ty,
2276                 bounds,
2277                 SizedByDefault::Yes,
2278                 trait_item.span,
2279             );
2280
2281             bounds.predicates(tcx, assoc_ty).into_iter()
2282         }))
2283     }
2284
2285     let mut predicates = predicates.predicates;
2286
2287     // Subtle: before we store the predicates into the tcx, we
2288     // sort them so that predicates like `T: Foo<Item=U>` come
2289     // before uses of `U`.  This avoids false ambiguity errors
2290     // in trait checking. See `setup_constraining_predicates`
2291     // for details.
2292     if let Node::Item(&Item {
2293         node: ItemKind::Impl(..),
2294         ..
2295     }) = node
2296     {
2297         let self_ty = tcx.type_of(def_id);
2298         let trait_ref = tcx.impl_trait_ref(def_id);
2299         cgp::setup_constraining_predicates(
2300             tcx,
2301             &mut predicates,
2302             trait_ref,
2303             &mut cgp::parameters_for_impl(self_ty, trait_ref),
2304         );
2305     }
2306
2307     let result = tcx.arena.alloc(ty::GenericPredicates {
2308         parent: generics.parent,
2309         predicates,
2310     });
2311     debug!("explicit_predicates_of(def_id={:?}) = {:?}", def_id, result);
2312     result
2313 }
2314
2315 /// Converts a specific `GenericBound` from the AST into a set of
2316 /// predicates that apply to the self type. A vector is returned
2317 /// because this can be anywhere from zero predicates (`T: ?Sized` adds no
2318 /// predicates) to one (`T: Foo`) to many (`T: Bar<X = i32>` adds `T: Bar`
2319 /// and `<T as Bar>::X == i32`).
2320 fn predicates_from_bound<'tcx>(
2321     astconv: &dyn AstConv<'tcx>,
2322     param_ty: Ty<'tcx>,
2323     bound: &'tcx hir::GenericBound,
2324 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2325     match *bound {
2326         hir::GenericBound::Trait(ref tr, hir::TraitBoundModifier::None) => {
2327             let mut bounds = Bounds::default();
2328             let _ = astconv.instantiate_poly_trait_ref(
2329                 tr,
2330                 param_ty,
2331                 &mut bounds,
2332             );
2333             bounds.predicates(astconv.tcx(), param_ty)
2334         }
2335         hir::GenericBound::Outlives(ref lifetime) => {
2336             let region = astconv.ast_region_to_region(lifetime, None);
2337             let pred = ty::Binder::bind(ty::OutlivesPredicate(param_ty, region));
2338             vec![(ty::Predicate::TypeOutlives(pred), lifetime.span)]
2339         }
2340         hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => vec![],
2341     }
2342 }
2343
2344 fn compute_sig_of_foreign_fn_decl<'tcx>(
2345     tcx: TyCtxt<'tcx>,
2346     def_id: DefId,
2347     decl: &'tcx hir::FnDecl,
2348     abi: abi::Abi,
2349 ) -> ty::PolyFnSig<'tcx> {
2350     let unsafety = if abi == abi::Abi::RustIntrinsic {
2351         intrisic_operation_unsafety(&*tcx.item_name(def_id).as_str())
2352     } else {
2353         hir::Unsafety::Unsafe
2354     };
2355     let fty = AstConv::ty_of_fn(&ItemCtxt::new(tcx, def_id), unsafety, abi, decl);
2356
2357     // Feature gate SIMD types in FFI, since I am not sure that the
2358     // ABIs are handled at all correctly. -huonw
2359     if abi != abi::Abi::RustIntrinsic
2360         && abi != abi::Abi::PlatformIntrinsic
2361         && !tcx.features().simd_ffi
2362     {
2363         let check = |ast_ty: &hir::Ty, ty: Ty<'_>| {
2364             if ty.is_simd() {
2365                 tcx.sess
2366                    .struct_span_err(
2367                        ast_ty.span,
2368                        &format!(
2369                            "use of SIMD type `{}` in FFI is highly experimental and \
2370                             may result in invalid code",
2371                            tcx.hir().hir_to_pretty_string(ast_ty.hir_id)
2372                        ),
2373                    )
2374                    .help("add `#![feature(simd_ffi)]` to the crate attributes to enable")
2375                    .emit();
2376             }
2377         };
2378         for (input, ty) in decl.inputs.iter().zip(*fty.inputs().skip_binder()) {
2379             check(&input, ty)
2380         }
2381         if let hir::Return(ref ty) = decl.output {
2382             check(&ty, *fty.output().skip_binder())
2383         }
2384     }
2385
2386     fty
2387 }
2388
2389 fn is_foreign_item(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
2390     match tcx.hir().get_if_local(def_id) {
2391         Some(Node::ForeignItem(..)) => true,
2392         Some(_) => false,
2393         _ => bug!("is_foreign_item applied to non-local def-id {:?}", def_id),
2394     }
2395 }
2396
2397 fn static_mutability(tcx: TyCtxt<'_>, def_id: DefId) -> Option<hir::Mutability> {
2398     match tcx.hir().get_if_local(def_id) {
2399         Some(Node::Item(&hir::Item {
2400             node: hir::ItemKind::Static(_, mutbl, _), ..
2401         })) |
2402         Some(Node::ForeignItem( &hir::ForeignItem {
2403             node: hir::ForeignItemKind::Static(_, mutbl), ..
2404         })) => Some(mutbl),
2405         Some(_) => None,
2406         _ => bug!("static_mutability applied to non-local def-id {:?}", def_id),
2407     }
2408 }
2409
2410 fn from_target_feature(
2411     tcx: TyCtxt<'_>,
2412     id: DefId,
2413     attr: &ast::Attribute,
2414     whitelist: &FxHashMap<String, Option<Symbol>>,
2415     target_features: &mut Vec<Symbol>,
2416 ) {
2417     let list = match attr.meta_item_list() {
2418         Some(list) => list,
2419         None => return,
2420     };
2421     let bad_item = |span| {
2422         let msg = "malformed `target_feature` attribute input";
2423         let code = "enable = \"..\"".to_owned();
2424         tcx.sess.struct_span_err(span, &msg)
2425             .span_suggestion(span, "must be of the form", code, Applicability::HasPlaceholders)
2426             .emit();
2427     };
2428     let rust_features = tcx.features();
2429     for item in list {
2430         // Only `enable = ...` is accepted in the meta-item list.
2431         if !item.check_name(sym::enable) {
2432             bad_item(item.span());
2433             continue;
2434         }
2435
2436         // Must be of the form `enable = "..."` (a string).
2437         let value = match item.value_str() {
2438             Some(value) => value,
2439             None => {
2440                 bad_item(item.span());
2441                 continue;
2442             }
2443         };
2444
2445         // We allow comma separation to enable multiple features.
2446         target_features.extend(value.as_str().split(',').filter_map(|feature| {
2447             // Only allow whitelisted features per platform.
2448             let feature_gate = match whitelist.get(feature) {
2449                 Some(g) => g,
2450                 None => {
2451                     let msg = format!(
2452                         "the feature named `{}` is not valid for this target",
2453                         feature
2454                     );
2455                     let mut err = tcx.sess.struct_span_err(item.span(), &msg);
2456                     err.span_label(
2457                         item.span(),
2458                         format!("`{}` is not valid for this target", feature),
2459                     );
2460                     if feature.starts_with("+") {
2461                         let valid = whitelist.contains_key(&feature[1..]);
2462                         if valid {
2463                             err.help("consider removing the leading `+` in the feature name");
2464                         }
2465                     }
2466                     err.emit();
2467                     return None;
2468                 }
2469             };
2470
2471             // Only allow features whose feature gates have been enabled.
2472             let allowed = match feature_gate.as_ref().map(|s| *s) {
2473                 Some(sym::arm_target_feature) => rust_features.arm_target_feature,
2474                 Some(sym::aarch64_target_feature) => rust_features.aarch64_target_feature,
2475                 Some(sym::hexagon_target_feature) => rust_features.hexagon_target_feature,
2476                 Some(sym::powerpc_target_feature) => rust_features.powerpc_target_feature,
2477                 Some(sym::mips_target_feature) => rust_features.mips_target_feature,
2478                 Some(sym::avx512_target_feature) => rust_features.avx512_target_feature,
2479                 Some(sym::mmx_target_feature) => rust_features.mmx_target_feature,
2480                 Some(sym::sse4a_target_feature) => rust_features.sse4a_target_feature,
2481                 Some(sym::tbm_target_feature) => rust_features.tbm_target_feature,
2482                 Some(sym::wasm_target_feature) => rust_features.wasm_target_feature,
2483                 Some(sym::cmpxchg16b_target_feature) => rust_features.cmpxchg16b_target_feature,
2484                 Some(sym::adx_target_feature) => rust_features.adx_target_feature,
2485                 Some(sym::movbe_target_feature) => rust_features.movbe_target_feature,
2486                 Some(sym::rtm_target_feature) => rust_features.rtm_target_feature,
2487                 Some(sym::f16c_target_feature) => rust_features.f16c_target_feature,
2488                 Some(name) => bug!("unknown target feature gate {}", name),
2489                 None => true,
2490             };
2491             if !allowed && id.is_local() {
2492                 feature_gate::emit_feature_err(
2493                     &tcx.sess.parse_sess,
2494                     feature_gate.unwrap(),
2495                     item.span(),
2496                     feature_gate::GateIssue::Language,
2497                     &format!("the target feature `{}` is currently unstable", feature),
2498                 );
2499             }
2500             Some(Symbol::intern(feature))
2501         }));
2502     }
2503 }
2504
2505 fn linkage_by_name(tcx: TyCtxt<'_>, def_id: DefId, name: &str) -> Linkage {
2506     use rustc::mir::mono::Linkage::*;
2507
2508     // Use the names from src/llvm/docs/LangRef.rst here. Most types are only
2509     // applicable to variable declarations and may not really make sense for
2510     // Rust code in the first place but whitelist them anyway and trust that
2511     // the user knows what s/he's doing. Who knows, unanticipated use cases
2512     // may pop up in the future.
2513     //
2514     // ghost, dllimport, dllexport and linkonce_odr_autohide are not supported
2515     // and don't have to be, LLVM treats them as no-ops.
2516     match name {
2517         "appending" => Appending,
2518         "available_externally" => AvailableExternally,
2519         "common" => Common,
2520         "extern_weak" => ExternalWeak,
2521         "external" => External,
2522         "internal" => Internal,
2523         "linkonce" => LinkOnceAny,
2524         "linkonce_odr" => LinkOnceODR,
2525         "private" => Private,
2526         "weak" => WeakAny,
2527         "weak_odr" => WeakODR,
2528         _ => {
2529             let span = tcx.hir().span_if_local(def_id);
2530             if let Some(span) = span {
2531                 tcx.sess.span_fatal(span, "invalid linkage specified")
2532             } else {
2533                 tcx.sess
2534                    .fatal(&format!("invalid linkage specified: {}", name))
2535             }
2536         }
2537     }
2538 }
2539
2540 fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
2541     let attrs = tcx.get_attrs(id);
2542
2543     let mut codegen_fn_attrs = CodegenFnAttrs::new();
2544
2545     let whitelist = tcx.target_features_whitelist(LOCAL_CRATE);
2546
2547     let mut inline_span = None;
2548     for attr in attrs.iter() {
2549         if attr.check_name(sym::cold) {
2550             codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
2551         } else if attr.check_name(sym::rustc_allocator) {
2552             codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR;
2553         } else if attr.check_name(sym::unwind) {
2554             codegen_fn_attrs.flags |= CodegenFnAttrFlags::UNWIND;
2555         } else if attr.check_name(sym::ffi_returns_twice) {
2556             if tcx.is_foreign_item(id) {
2557                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_RETURNS_TWICE;
2558             } else {
2559                 // `#[ffi_returns_twice]` is only allowed `extern fn`s.
2560                 struct_span_err!(
2561                     tcx.sess,
2562                     attr.span,
2563                     E0724,
2564                     "`#[ffi_returns_twice]` may only be used on foreign functions"
2565                 ).emit();
2566             }
2567         } else if attr.check_name(sym::rustc_allocator_nounwind) {
2568             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_ALLOCATOR_NOUNWIND;
2569         } else if attr.check_name(sym::naked) {
2570             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED;
2571         } else if attr.check_name(sym::no_mangle) {
2572             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
2573         } else if attr.check_name(sym::rustc_std_internal_symbol) {
2574             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
2575         } else if attr.check_name(sym::no_debug) {
2576             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_DEBUG;
2577         } else if attr.check_name(sym::used) {
2578             codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED;
2579         } else if attr.check_name(sym::thread_local) {
2580             codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL;
2581         } else if attr.check_name(sym::export_name) {
2582             if let Some(s) = attr.value_str() {
2583                 if s.as_str().contains("\0") {
2584                     // `#[export_name = ...]` will be converted to a null-terminated string,
2585                     // so it may not contain any null characters.
2586                     struct_span_err!(
2587                         tcx.sess,
2588                         attr.span,
2589                         E0648,
2590                         "`export_name` may not contain null characters"
2591                     ).emit();
2592                 }
2593                 codegen_fn_attrs.export_name = Some(s);
2594             }
2595         } else if attr.check_name(sym::target_feature) {
2596             if tcx.fn_sig(id).unsafety() == Unsafety::Normal {
2597                 let msg = "`#[target_feature(..)]` can only be applied to `unsafe` functions";
2598                 tcx.sess.struct_span_err(attr.span, msg)
2599                     .span_label(attr.span, "can only be applied to `unsafe` functions")
2600                     .span_label(tcx.def_span(id), "not an `unsafe` function")
2601                     .emit();
2602             }
2603             from_target_feature(
2604                 tcx,
2605                 id,
2606                 attr,
2607                 &whitelist,
2608                 &mut codegen_fn_attrs.target_features,
2609             );
2610         } else if attr.check_name(sym::linkage) {
2611             if let Some(val) = attr.value_str() {
2612                 codegen_fn_attrs.linkage = Some(linkage_by_name(tcx, id, &val.as_str()));
2613             }
2614         } else if attr.check_name(sym::link_section) {
2615             if let Some(val) = attr.value_str() {
2616                 if val.as_str().bytes().any(|b| b == 0) {
2617                     let msg = format!(
2618                         "illegal null byte in link_section \
2619                          value: `{}`",
2620                         &val
2621                     );
2622                     tcx.sess.span_err(attr.span, &msg);
2623                 } else {
2624                     codegen_fn_attrs.link_section = Some(val);
2625                 }
2626             }
2627         } else if attr.check_name(sym::link_name) {
2628             codegen_fn_attrs.link_name = attr.value_str();
2629         }
2630     }
2631
2632     codegen_fn_attrs.inline = attrs.iter().fold(InlineAttr::None, |ia, attr| {
2633         if attr.path != sym::inline {
2634             return ia;
2635         }
2636         match attr.meta().map(|i| i.node) {
2637             Some(MetaItemKind::Word) => {
2638                 mark_used(attr);
2639                 InlineAttr::Hint
2640             }
2641             Some(MetaItemKind::List(ref items)) => {
2642                 mark_used(attr);
2643                 inline_span = Some(attr.span);
2644                 if items.len() != 1 {
2645                     span_err!(
2646                         tcx.sess.diagnostic(),
2647                         attr.span,
2648                         E0534,
2649                         "expected one argument"
2650                     );
2651                     InlineAttr::None
2652                 } else if list_contains_name(&items[..], sym::always) {
2653                     InlineAttr::Always
2654                 } else if list_contains_name(&items[..], sym::never) {
2655                     InlineAttr::Never
2656                 } else {
2657                     span_err!(
2658                         tcx.sess.diagnostic(),
2659                         items[0].span(),
2660                         E0535,
2661                         "invalid argument"
2662                     );
2663
2664                     InlineAttr::None
2665                 }
2666             }
2667             Some(MetaItemKind::NameValue(_)) => ia,
2668             None => ia,
2669         }
2670     });
2671
2672     codegen_fn_attrs.optimize = attrs.iter().fold(OptimizeAttr::None, |ia, attr| {
2673         if attr.path != sym::optimize {
2674             return ia;
2675         }
2676         let err = |sp, s| span_err!(tcx.sess.diagnostic(), sp, E0722, "{}", s);
2677         match attr.meta().map(|i| i.node) {
2678             Some(MetaItemKind::Word) => {
2679                 err(attr.span, "expected one argument");
2680                 ia
2681             }
2682             Some(MetaItemKind::List(ref items)) => {
2683                 mark_used(attr);
2684                 inline_span = Some(attr.span);
2685                 if items.len() != 1 {
2686                     err(attr.span, "expected one argument");
2687                     OptimizeAttr::None
2688                 } else if list_contains_name(&items[..], sym::size) {
2689                     OptimizeAttr::Size
2690                 } else if list_contains_name(&items[..], sym::speed) {
2691                     OptimizeAttr::Speed
2692                 } else {
2693                     err(items[0].span(), "invalid argument");
2694                     OptimizeAttr::None
2695                 }
2696             }
2697             Some(MetaItemKind::NameValue(_)) => ia,
2698             None => ia,
2699         }
2700     });
2701
2702     // If a function uses #[target_feature] it can't be inlined into general
2703     // purpose functions as they wouldn't have the right target features
2704     // enabled. For that reason we also forbid #[inline(always)] as it can't be
2705     // respected.
2706     if codegen_fn_attrs.target_features.len() > 0 {
2707         if codegen_fn_attrs.inline == InlineAttr::Always {
2708             if let Some(span) = inline_span {
2709                 tcx.sess.span_err(
2710                     span,
2711                     "cannot use `#[inline(always)]` with \
2712                      `#[target_feature]`",
2713                 );
2714             }
2715         }
2716     }
2717
2718     // Weak lang items have the same semantics as "std internal" symbols in the
2719     // sense that they're preserved through all our LTO passes and only
2720     // strippable by the linker.
2721     //
2722     // Additionally weak lang items have predetermined symbol names.
2723     if tcx.is_weak_lang_item(id) {
2724         codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
2725     }
2726     if let Some(name) = weak_lang_items::link_name(&attrs) {
2727         codegen_fn_attrs.export_name = Some(name);
2728         codegen_fn_attrs.link_name = Some(name);
2729     }
2730
2731     // Internal symbols to the standard library all have no_mangle semantics in
2732     // that they have defined symbol names present in the function name. This
2733     // also applies to weak symbols where they all have known symbol names.
2734     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
2735         codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
2736     }
2737
2738     codegen_fn_attrs
2739 }