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::check::intrinsic::intrinsic_operation_unsafety;
  19 use crate::constrained_generic_params as cgp;
  20 use crate::lint;
  21 use crate::middle::resolve_lifetime as rl;
  22 use crate::middle::weak_lang_items;
  23 use rustc::hir::map::blocks::FnLikeNode;
  24 use rustc::hir::map::Map;
  25 use rustc::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
  26 use rustc::mir::mono::Linkage;
  27 use rustc::session::parse::feature_err;
  28 use rustc::traits;
  29 use rustc::ty::query::Providers;
  30 use rustc::ty::subst::GenericArgKind;
  31 use rustc::ty::subst::{InternalSubsts, Subst};
  32 use rustc::ty::util::Discr;
  33 use rustc::ty::util::IntTypeExt;
  34 use rustc::ty::{self, AdtKind, Const, DefIdTree, ToPolyTraitRef, Ty, TyCtxt, WithConstness};
  35 use rustc::ty::{ReprOptions, ToPredicate};
  36 use rustc_attr::{list_contains_name, mark_used, InlineAttr, OptimizeAttr};
  37 use rustc_data_structures::captures::Captures;
  38 use rustc_data_structures::fx::FxHashMap;
  39 use rustc_errors::{struct_span_err, Applicability, StashKey};
  40 use rustc_hir as hir;
  41 use rustc_hir::def::{CtorKind, DefKind, Res};
  42 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
  43 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  44 use rustc_hir::{GenericParamKind, Node, Unsafety};
  45 use rustc_span::symbol::{kw, sym, Symbol};
  46 use rustc_span::{Span, DUMMY_SP};
  47 use rustc_target::spec::abi;
  48 use syntax::ast;
  49 use syntax::ast::{Ident, MetaItemKind};
  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 #[derive(Default)]
 104 crate struct PlaceholderHirTyCollector(crate Vec<Span>);
 105
 106 impl<'v> Visitor<'v> for PlaceholderHirTyCollector {
 107     type Map = Map<'v>;
 108
 109     fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
 110         NestedVisitorMap::None
 111     }
 112     fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
 113         if let hir::TyKind::Infer = t.kind {
 114             self.0.push(t.span);
 115         }
 116         intravisit::walk_ty(self, t)
 117     }
 118 }
 119
 120 struct CollectItemTypesVisitor<'tcx> {
 121     tcx: TyCtxt<'tcx>,
 122 }
 123
 124 /// If there are any placeholder types (`_`), emit an error explaining that this is not allowed
 125 /// and suggest adding type parameters in the appropriate place, taking into consideration any and
 126 /// all already existing generic type parameters to avoid suggesting a name that is already in use.
 127 crate fn placeholder_type_error(
 128     tcx: TyCtxt<'tcx>,
 129     span: Span,
 130     generics: &[hir::GenericParam<'_>],
 131     placeholder_types: Vec<Span>,
 132     suggest: bool,
 133 ) {
 134     if placeholder_types.is_empty() {
 135         return;
 136     }
 137     // This is the whitelist of possible parameter names that we might suggest.
 138     let possible_names = ["T", "K", "L", "A", "B", "C"];
 139     let used_names = generics
 140         .iter()
 141         .filter_map(|p| match p.name {
 142             hir::ParamName::Plain(ident) => Some(ident.name),
 143             _ => None,
 144         })
 145         .collect::<Vec<_>>();
 146
 147     let type_name = possible_names
 148         .iter()
 149         .find(|n| !used_names.contains(&Symbol::intern(n)))
 150         .unwrap_or(&"ParamName");
 151
 152     let mut sugg: Vec<_> =
 153         placeholder_types.iter().map(|sp| (*sp, type_name.to_string())).collect();
 154     if generics.is_empty() {
 155         sugg.push((span, format!("<{}>", type_name)));
 156     } else if let Some(arg) = generics.iter().find(|arg| match arg.name {
 157         hir::ParamName::Plain(Ident { name: kw::Underscore, .. }) => true,
 158         _ => false,
 159     }) {
 160         // Account for `_` already present in cases like `struct S<_>(_);` and suggest
 161         // `struct S<T>(T);` instead of `struct S<_, T>(T);`.
 162         sugg.push((arg.span, format!("{}", type_name)));
 163     } else {
 164         sugg.push((
 165             generics.iter().last().unwrap().span.shrink_to_hi(),
 166             format!(", {}", type_name),
 167         ));
 168     }
 169     let mut err = bad_placeholder_type(tcx, placeholder_types);
 170     if suggest {
 171         err.multipart_suggestion(
 172             "use type parameters instead",
 173             sugg,
 174             Applicability::HasPlaceholders,
 175         );
 176     }
 177     err.emit();
 178 }
 179
 180 fn reject_placeholder_type_signatures_in_item(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
 181     let (generics, suggest) = match &item.kind {
 182         hir::ItemKind::Union(_, generics)
 183         | hir::ItemKind::Enum(_, generics)
 184         | hir::ItemKind::TraitAlias(generics, _)
 185         | hir::ItemKind::Trait(_, _, generics, ..)
 186         | hir::ItemKind::Impl { generics, .. }
 187         | hir::ItemKind::Struct(_, generics) => (generics, true),
 188         hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. })
 189         | hir::ItemKind::TyAlias(_, generics) => (generics, false),
 190         // `static`, `fn` and `const` are handled elsewhere to suggest appropriate type.
 191         _ => return,
 192     };
 193
 194     let mut visitor = PlaceholderHirTyCollector::default();
 195     visitor.visit_item(item);
 196
 197     placeholder_type_error(tcx, generics.span, &generics.params[..], visitor.0, suggest);
 198 }
 199
 200 impl Visitor<'tcx> for CollectItemTypesVisitor<'tcx> {
 201     type Map = Map<'tcx>;
 202
 203     fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
 204         NestedVisitorMap::OnlyBodies(&self.tcx.hir())
 205     }
 206
 207     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 208         convert_item(self.tcx, item.hir_id);
 209         reject_placeholder_type_signatures_in_item(self.tcx, item);
 210         intravisit::walk_item(self, item);
 211     }
 212
 213     fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
 214         for param in generics.params {
 215             match param.kind {
 216                 hir::GenericParamKind::Lifetime { .. } => {}
 217                 hir::GenericParamKind::Type { default: Some(_), .. } => {
 218                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 219                     self.tcx.type_of(def_id);
 220                 }
 221                 hir::GenericParamKind::Type { .. } => {}
 222                 hir::GenericParamKind::Const { .. } => {
 223                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 224                     self.tcx.type_of(def_id);
 225                 }
 226             }
 227         }
 228         intravisit::walk_generics(self, generics);
 229     }
 230
 231     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 232         if let hir::ExprKind::Closure(..) = expr.kind {
 233             let def_id = self.tcx.hir().local_def_id(expr.hir_id);
 234             self.tcx.generics_of(def_id);
 235             self.tcx.type_of(def_id);
 236         }
 237         intravisit::walk_expr(self, expr);
 238     }
 239
 240     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
 241         convert_trait_item(self.tcx, trait_item.hir_id);
 242         intravisit::walk_trait_item(self, trait_item);
 243     }
 244
 245     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 246         convert_impl_item(self.tcx, impl_item.hir_id);
 247         intravisit::walk_impl_item(self, impl_item);
 248     }
 249 }
 250
 251 ///////////////////////////////////////////////////////////////////////////
 252 // Utility types and common code for the above passes.
 253
 254 fn bad_placeholder_type(
 255     tcx: TyCtxt<'tcx>,
 256     mut spans: Vec<Span>,
 257 ) -> rustc_errors::DiagnosticBuilder<'tcx> {
 258     spans.sort();
 259     let mut err = struct_span_err!(
 260         tcx.sess,
 261         spans.clone(),
 262         E0121,
 263         "the type placeholder `_` is not allowed within types on item signatures",
 264     );
 265     for span in spans {
 266         err.span_label(span, "not allowed in type signatures");
 267     }
 268     err
 269 }
 270
 271 impl ItemCtxt<'tcx> {
 272     pub fn new(tcx: TyCtxt<'tcx>, item_def_id: DefId) -> ItemCtxt<'tcx> {
 273         ItemCtxt { tcx, item_def_id }
 274     }
 275
 276     pub fn to_ty(&self, ast_ty: &'tcx hir::Ty<'tcx>) -> Ty<'tcx> {
 277         AstConv::ast_ty_to_ty(self, ast_ty)
 278     }
 279 }
 280
 281 impl AstConv<'tcx> for ItemCtxt<'tcx> {
 282     fn tcx(&self) -> TyCtxt<'tcx> {
 283         self.tcx
 284     }
 285
 286     fn item_def_id(&self) -> Option<DefId> {
 287         Some(self.item_def_id)
 288     }
 289
 290     fn default_constness_for_trait_bounds(&self) -> ast::Constness {
 291         // FIXME: refactor this into a method
 292         let hir_id = self
 293             .tcx
 294             .hir()
 295             .as_local_hir_id(self.item_def_id)
 296             .expect("Non-local call to local provider is_const_fn");
 297
 298         let node = self.tcx.hir().get(hir_id);
 299         if let Some(fn_like) = FnLikeNode::from_node(node) {
 300             fn_like.constness()
 301         } else {
 302             ast::Constness::NotConst
 303         }
 304     }
 305
 306     fn get_type_parameter_bounds(&self, span: Span, def_id: DefId) -> ty::GenericPredicates<'tcx> {
 307         self.tcx.at(span).type_param_predicates((self.item_def_id, def_id))
 308     }
 309
 310     fn re_infer(&self, _: Option<&ty::GenericParamDef>, _: Span) -> Option<ty::Region<'tcx>> {
 311         None
 312     }
 313
 314     fn allow_ty_infer(&self) -> bool {
 315         false
 316     }
 317
 318     fn ty_infer(&self, _: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
 319         self.tcx().sess.delay_span_bug(span, "bad placeholder type");
 320         self.tcx().types.err
 321     }
 322
 323     fn ct_infer(
 324         &self,
 325         _: Ty<'tcx>,
 326         _: Option<&ty::GenericParamDef>,
 327         span: Span,
 328     ) -> &'tcx Const<'tcx> {
 329         bad_placeholder_type(self.tcx(), vec![span]).emit();
 330
 331         self.tcx().consts.err
 332     }
 333
 334     fn projected_ty_from_poly_trait_ref(
 335         &self,
 336         span: Span,
 337         item_def_id: DefId,
 338         item_segment: &hir::PathSegment<'_>,
 339         poly_trait_ref: ty::PolyTraitRef<'tcx>,
 340     ) -> Ty<'tcx> {
 341         if let Some(trait_ref) = poly_trait_ref.no_bound_vars() {
 342             let item_substs = <dyn AstConv<'tcx>>::create_substs_for_associated_item(
 343                 self,
 344                 self.tcx,
 345                 span,
 346                 item_def_id,
 347                 item_segment,
 348                 trait_ref.substs,
 349             );
 350             self.tcx().mk_projection(item_def_id, item_substs)
 351         } else {
 352             // There are no late-bound regions; we can just ignore the binder.
 353             struct_span_err!(
 354                 self.tcx().sess,
 355                 span,
 356                 E0212,
 357                 "cannot extract an associated type from a higher-ranked trait bound \
 358                  in this context"
 359             )
 360             .emit();
 361             self.tcx().types.err
 362         }
 363     }
 364
 365     fn normalize_ty(&self, _span: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
 366         // Types in item signatures are not normalized to avoid undue dependencies.
 367         ty
 368     }
 369
 370     fn set_tainted_by_errors(&self) {
 371         // There's no obvious place to track this, so just let it go.
 372     }
 373
 374     fn record_ty(&self, _hir_id: hir::HirId, _ty: Ty<'tcx>, _span: Span) {
 375         // There's no place to record types from signatures?
 376     }
 377 }
 378
 379 /// Returns the predicates defined on `item_def_id` of the form
 380 /// `X: Foo` where `X` is the type parameter `def_id`.
 381 fn type_param_predicates(
 382     tcx: TyCtxt<'_>,
 383     (item_def_id, def_id): (DefId, DefId),
 384 ) -> ty::GenericPredicates<'_> {
 385     use rustc_hir::*;
 386
 387     // In the AST, bounds can derive from two places. Either
 388     // written inline like `<T: Foo>` or in a where-clause like
 389     // `where T: Foo`.
 390
 391     let param_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 392     let param_owner = tcx.hir().ty_param_owner(param_id);
 393     let param_owner_def_id = tcx.hir().local_def_id(param_owner);
 394     let generics = tcx.generics_of(param_owner_def_id);
 395     let index = generics.param_def_id_to_index[&def_id];
 396     let ty = tcx.mk_ty_param(index, tcx.hir().ty_param_name(param_id));
 397
 398     // Don't look for bounds where the type parameter isn't in scope.
 399     let parent =
 400         if item_def_id == param_owner_def_id { None } else { tcx.generics_of(item_def_id).parent };
 401
 402     let mut result = parent
 403         .map(|parent| {
 404             let icx = ItemCtxt::new(tcx, parent);
 405             icx.get_type_parameter_bounds(DUMMY_SP, def_id)
 406         })
 407         .unwrap_or_default();
 408     let mut extend = None;
 409
 410     let item_hir_id = tcx.hir().as_local_hir_id(item_def_id).unwrap();
 411     let ast_generics = match tcx.hir().get(item_hir_id) {
 412         Node::TraitItem(item) => &item.generics,
 413
 414         Node::ImplItem(item) => &item.generics,
 415
 416         Node::Item(item) => {
 417             match item.kind {
 418                 ItemKind::Fn(.., ref generics, _)
 419                 | ItemKind::Impl { ref generics, .. }
 420                 | ItemKind::TyAlias(_, ref generics)
 421                 | ItemKind::OpaqueTy(OpaqueTy { ref generics, impl_trait_fn: None, .. })
 422                 | ItemKind::Enum(_, ref generics)
 423                 | ItemKind::Struct(_, ref generics)
 424                 | ItemKind::Union(_, ref generics) => generics,
 425                 ItemKind::Trait(_, _, ref generics, ..) => {
 426                     // Implied `Self: Trait` and supertrait bounds.
 427                     if param_id == item_hir_id {
 428                         let identity_trait_ref = ty::TraitRef::identity(tcx, item_def_id);
 429                         extend =
 430                             Some((identity_trait_ref.without_const().to_predicate(), item.span));
 431                     }
 432                     generics
 433                 }
 434                 _ => return result,
 435             }
 436         }
 437
 438         Node::ForeignItem(item) => match item.kind {
 439             ForeignItemKind::Fn(_, _, ref generics) => generics,
 440             _ => return result,
 441         },
 442
 443         _ => return result,
 444     };
 445
 446     let icx = ItemCtxt::new(tcx, item_def_id);
 447     let extra_predicates = extend.into_iter().chain(
 448         icx.type_parameter_bounds_in_generics(ast_generics, param_id, ty, OnlySelfBounds(true))
 449             .into_iter()
 450             .filter(|(predicate, _)| match predicate {
 451                 ty::Predicate::Trait(ref data, _) => data.skip_binder().self_ty().is_param(index),
 452                 _ => false,
 453             }),
 454     );
 455     result.predicates =
 456         tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(extra_predicates));
 457     result
 458 }
 459
 460 impl ItemCtxt<'tcx> {
 461     /// Finds bounds from `hir::Generics`. This requires scanning through the
 462     /// AST. We do this to avoid having to convert *all* the bounds, which
 463     /// would create artificial cycles. Instead, we can only convert the
 464     /// bounds for a type parameter `X` if `X::Foo` is used.
 465     fn type_parameter_bounds_in_generics(
 466         &self,
 467         ast_generics: &'tcx hir::Generics<'tcx>,
 468         param_id: hir::HirId,
 469         ty: Ty<'tcx>,
 470         only_self_bounds: OnlySelfBounds,
 471     ) -> Vec<(ty::Predicate<'tcx>, Span)> {
 472         let constness = self.default_constness_for_trait_bounds();
 473         let from_ty_params = ast_generics
 474             .params
 475             .iter()
 476             .filter_map(|param| match param.kind {
 477                 GenericParamKind::Type { .. } if param.hir_id == param_id => Some(&param.bounds),
 478                 _ => None,
 479             })
 480             .flat_map(|bounds| bounds.iter())
 481             .flat_map(|b| predicates_from_bound(self, ty, b, constness));
 482
 483         let from_where_clauses = ast_generics
 484             .where_clause
 485             .predicates
 486             .iter()
 487             .filter_map(|wp| match *wp {
 488                 hir::WherePredicate::BoundPredicate(ref bp) => Some(bp),
 489                 _ => None,
 490             })
 491             .flat_map(|bp| {
 492                 let bt = if is_param(self.tcx, &bp.bounded_ty, param_id) {
 493                     Some(ty)
 494                 } else if !only_self_bounds.0 {
 495                     Some(self.to_ty(&bp.bounded_ty))
 496                 } else {
 497                     None
 498                 };
 499                 bp.bounds.iter().filter_map(move |b| bt.map(|bt| (bt, b)))
 500             })
 501             .flat_map(|(bt, b)| predicates_from_bound(self, bt, b, constness));
 502
 503         from_ty_params.chain(from_where_clauses).collect()
 504     }
 505 }
 506
 507 /// Tests whether this is the AST for a reference to the type
 508 /// parameter with ID `param_id`. We use this so as to avoid running
 509 /// `ast_ty_to_ty`, because we want to avoid triggering an all-out
 510 /// conversion of the type to avoid inducing unnecessary cycles.
 511 fn is_param(tcx: TyCtxt<'_>, ast_ty: &hir::Ty<'_>, param_id: hir::HirId) -> bool {
 512     if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = ast_ty.kind {
 513         match path.res {
 514             Res::SelfTy(Some(def_id), None) | Res::Def(DefKind::TyParam, def_id) => {
 515                 def_id == tcx.hir().local_def_id(param_id)
 516             }
 517             _ => false,
 518         }
 519     } else {
 520         false
 521     }
 522 }
 523
 524 fn convert_item(tcx: TyCtxt<'_>, item_id: hir::HirId) {
 525     let it = tcx.hir().expect_item(item_id);
 526     debug!("convert: item {} with id {}", it.ident, it.hir_id);
 527     let def_id = tcx.hir().local_def_id(item_id);
 528     match it.kind {
 529         // These don't define types.
 530         hir::ItemKind::ExternCrate(_)
 531         | hir::ItemKind::Use(..)
 532         | hir::ItemKind::Mod(_)
 533         | hir::ItemKind::GlobalAsm(_) => {}
 534         hir::ItemKind::ForeignMod(ref foreign_mod) => {
 535             for item in foreign_mod.items {
 536                 let def_id = tcx.hir().local_def_id(item.hir_id);
 537                 tcx.generics_of(def_id);
 538                 tcx.type_of(def_id);
 539                 tcx.predicates_of(def_id);
 540                 if let hir::ForeignItemKind::Fn(..) = item.kind {
 541                     tcx.fn_sig(def_id);
 542                 }
 543             }
 544         }
 545         hir::ItemKind::Enum(ref enum_definition, _) => {
 546             tcx.generics_of(def_id);
 547             tcx.type_of(def_id);
 548             tcx.predicates_of(def_id);
 549             convert_enum_variant_types(tcx, def_id, &enum_definition.variants);
 550         }
 551         hir::ItemKind::Impl { .. } => {
 552             tcx.generics_of(def_id);
 553             tcx.type_of(def_id);
 554             tcx.impl_trait_ref(def_id);
 555             tcx.predicates_of(def_id);
 556         }
 557         hir::ItemKind::Trait(..) => {
 558             tcx.generics_of(def_id);
 559             tcx.trait_def(def_id);
 560             tcx.at(it.span).super_predicates_of(def_id);
 561             tcx.predicates_of(def_id);
 562         }
 563         hir::ItemKind::TraitAlias(..) => {
 564             tcx.generics_of(def_id);
 565             tcx.at(it.span).super_predicates_of(def_id);
 566             tcx.predicates_of(def_id);
 567         }
 568         hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 569             tcx.generics_of(def_id);
 570             tcx.type_of(def_id);
 571             tcx.predicates_of(def_id);
 572
 573             for f in struct_def.fields() {
 574                 let def_id = tcx.hir().local_def_id(f.hir_id);
 575                 tcx.generics_of(def_id);
 576                 tcx.type_of(def_id);
 577                 tcx.predicates_of(def_id);
 578             }
 579
 580             if let Some(ctor_hir_id) = struct_def.ctor_hir_id() {
 581                 convert_variant_ctor(tcx, ctor_hir_id);
 582             }
 583         }
 584
 585         // Desugared from `impl Trait`, so visited by the function's return type.
 586         hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(_), .. }) => {}
 587
 588         hir::ItemKind::OpaqueTy(..)
 589         | hir::ItemKind::TyAlias(..)
 590         | hir::ItemKind::Static(..)
 591         | hir::ItemKind::Const(..)
 592         | hir::ItemKind::Fn(..) => {
 593             tcx.generics_of(def_id);
 594             tcx.type_of(def_id);
 595             tcx.predicates_of(def_id);
 596             if let hir::ItemKind::Fn(..) = it.kind {
 597                 tcx.fn_sig(def_id);
 598             }
 599         }
 600     }
 601 }
 602
 603 fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::HirId) {
 604     let trait_item = tcx.hir().expect_trait_item(trait_item_id);
 605     let def_id = tcx.hir().local_def_id(trait_item.hir_id);
 606     tcx.generics_of(def_id);
 607
 608     match trait_item.kind {
 609         hir::TraitItemKind::Const(..)
 610         | hir::TraitItemKind::Type(_, Some(_))
 611         | hir::TraitItemKind::Method(..) => {
 612             tcx.type_of(def_id);
 613             if let hir::TraitItemKind::Method(..) = trait_item.kind {
 614                 tcx.fn_sig(def_id);
 615             }
 616         }
 617
 618         hir::TraitItemKind::Type(_, None) => {}
 619     };
 620
 621     tcx.predicates_of(def_id);
 622 }
 623
 624 fn convert_impl_item(tcx: TyCtxt<'_>, impl_item_id: hir::HirId) {
 625     let def_id = tcx.hir().local_def_id(impl_item_id);
 626     tcx.generics_of(def_id);
 627     tcx.type_of(def_id);
 628     tcx.predicates_of(def_id);
 629     if let hir::ImplItemKind::Method(..) = tcx.hir().expect_impl_item(impl_item_id).kind {
 630         tcx.fn_sig(def_id);
 631     }
 632 }
 633
 634 fn convert_variant_ctor(tcx: TyCtxt<'_>, ctor_id: hir::HirId) {
 635     let def_id = tcx.hir().local_def_id(ctor_id);
 636     tcx.generics_of(def_id);
 637     tcx.type_of(def_id);
 638     tcx.predicates_of(def_id);
 639 }
 640
 641 fn convert_enum_variant_types(tcx: TyCtxt<'_>, def_id: DefId, variants: &[hir::Variant<'_>]) {
 642     let def = tcx.adt_def(def_id);
 643     let repr_type = def.repr.discr_type();
 644     let initial = repr_type.initial_discriminant(tcx);
 645     let mut prev_discr = None::<Discr<'_>>;
 646
 647     // fill the discriminant values and field types
 648     for variant in variants {
 649         let wrapped_discr = prev_discr.map_or(initial, |d| d.wrap_incr(tcx));
 650         prev_discr = Some(
 651             if let Some(ref e) = variant.disr_expr {
 652                 let expr_did = tcx.hir().local_def_id(e.hir_id);
 653                 def.eval_explicit_discr(tcx, expr_did)
 654             } else if let Some(discr) = repr_type.disr_incr(tcx, prev_discr) {
 655                 Some(discr)
 656             } else {
 657                 struct_span_err!(tcx.sess, variant.span, E0370, "enum discriminant overflowed")
 658                     .span_label(
 659                         variant.span,
 660                         format!("overflowed on value after {}", prev_discr.unwrap()),
 661                     )
 662                     .note(&format!(
 663                         "explicitly set `{} = {}` if that is desired outcome",
 664                         variant.ident, wrapped_discr
 665                     ))
 666                     .emit();
 667                 None
 668             }
 669             .unwrap_or(wrapped_discr),
 670         );
 671
 672         for f in variant.data.fields() {
 673             let def_id = tcx.hir().local_def_id(f.hir_id);
 674             tcx.generics_of(def_id);
 675             tcx.type_of(def_id);
 676             tcx.predicates_of(def_id);
 677         }
 678
 679         // Convert the ctor, if any. This also registers the variant as
 680         // an item.
 681         if let Some(ctor_hir_id) = variant.data.ctor_hir_id() {
 682             convert_variant_ctor(tcx, ctor_hir_id);
 683         }
 684     }
 685 }
 686
 687 fn convert_variant(
 688     tcx: TyCtxt<'_>,
 689     variant_did: Option<DefId>,
 690     ctor_did: Option<DefId>,
 691     ident: Ident,
 692     discr: ty::VariantDiscr,
 693     def: &hir::VariantData<'_>,
 694     adt_kind: ty::AdtKind,
 695     parent_did: DefId,
 696 ) -> ty::VariantDef {
 697     let mut seen_fields: FxHashMap<ast::Ident, Span> = Default::default();
 698     let hir_id = tcx.hir().as_local_hir_id(variant_did.unwrap_or(parent_did)).unwrap();
 699     let fields = def
 700         .fields()
 701         .iter()
 702         .map(|f| {
 703             let fid = tcx.hir().local_def_id(f.hir_id);
 704             let dup_span = seen_fields.get(&f.ident.modern()).cloned();
 705             if let Some(prev_span) = dup_span {
 706                 struct_span_err!(
 707                     tcx.sess,
 708                     f.span,
 709                     E0124,
 710                     "field `{}` is already declared",
 711                     f.ident
 712                 )
 713                 .span_label(f.span, "field already declared")
 714                 .span_label(prev_span, format!("`{}` first declared here", f.ident))
 715                 .emit();
 716             } else {
 717                 seen_fields.insert(f.ident.modern(), f.span);
 718             }
 719
 720             ty::FieldDef {
 721                 did: fid,
 722                 ident: f.ident,
 723                 vis: ty::Visibility::from_hir(&f.vis, hir_id, tcx),
 724             }
 725         })
 726         .collect();
 727     let recovered = match def {
 728         hir::VariantData::Struct(_, r) => *r,
 729         _ => false,
 730     };
 731     ty::VariantDef::new(
 732         tcx,
 733         ident,
 734         variant_did,
 735         ctor_did,
 736         discr,
 737         fields,
 738         CtorKind::from_hir(def),
 739         adt_kind,
 740         parent_did,
 741         recovered,
 742     )
 743 }
 744
 745 fn adt_def(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::AdtDef {
 746     use rustc_hir::*;
 747
 748     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 749     let item = match tcx.hir().get(hir_id) {
 750         Node::Item(item) => item,
 751         _ => bug!(),
 752     };
 753
 754     let repr = ReprOptions::new(tcx, def_id);
 755     let (kind, variants) = match item.kind {
 756         ItemKind::Enum(ref def, _) => {
 757             let mut distance_from_explicit = 0;
 758             let variants = def
 759                 .variants
 760                 .iter()
 761                 .map(|v| {
 762                     let variant_did = Some(tcx.hir().local_def_id(v.id));
 763                     let ctor_did =
 764                         v.data.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
 765
 766                     let discr = if let Some(ref e) = v.disr_expr {
 767                         distance_from_explicit = 0;
 768                         ty::VariantDiscr::Explicit(tcx.hir().local_def_id(e.hir_id))
 769                     } else {
 770                         ty::VariantDiscr::Relative(distance_from_explicit)
 771                     };
 772                     distance_from_explicit += 1;
 773
 774                     convert_variant(
 775                         tcx,
 776                         variant_did,
 777                         ctor_did,
 778                         v.ident,
 779                         discr,
 780                         &v.data,
 781                         AdtKind::Enum,
 782                         def_id,
 783                     )
 784                 })
 785                 .collect();
 786
 787             (AdtKind::Enum, variants)
 788         }
 789         ItemKind::Struct(ref def, _) => {
 790             let variant_did = None;
 791             let ctor_did = def.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
 792
 793             let variants = std::iter::once(convert_variant(
 794                 tcx,
 795                 variant_did,
 796                 ctor_did,
 797                 item.ident,
 798                 ty::VariantDiscr::Relative(0),
 799                 def,
 800                 AdtKind::Struct,
 801                 def_id,
 802             ))
 803             .collect();
 804
 805             (AdtKind::Struct, variants)
 806         }
 807         ItemKind::Union(ref def, _) => {
 808             let variant_did = None;
 809             let ctor_did = def.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
 810
 811             let variants = std::iter::once(convert_variant(
 812                 tcx,
 813                 variant_did,
 814                 ctor_did,
 815                 item.ident,
 816                 ty::VariantDiscr::Relative(0),
 817                 def,
 818                 AdtKind::Union,
 819                 def_id,
 820             ))
 821             .collect();
 822
 823             (AdtKind::Union, variants)
 824         }
 825         _ => bug!(),
 826     };
 827     tcx.alloc_adt_def(def_id, kind, variants, repr)
 828 }
 829
 830 /// Ensures that the super-predicates of the trait with a `DefId`
 831 /// of `trait_def_id` are converted and stored. This also ensures that
 832 /// the transitive super-predicates are converted.
 833 fn super_predicates_of(tcx: TyCtxt<'_>, trait_def_id: DefId) -> ty::GenericPredicates<'_> {
 834     debug!("super_predicates(trait_def_id={:?})", trait_def_id);
 835     let trait_hir_id = tcx.hir().as_local_hir_id(trait_def_id).unwrap();
 836
 837     let item = match tcx.hir().get(trait_hir_id) {
 838         Node::Item(item) => item,
 839         _ => bug!("trait_node_id {} is not an item", trait_hir_id),
 840     };
 841
 842     let (generics, bounds) = match item.kind {
 843         hir::ItemKind::Trait(.., ref generics, ref supertraits, _) => (generics, supertraits),
 844         hir::ItemKind::TraitAlias(ref generics, ref supertraits) => (generics, supertraits),
 845         _ => span_bug!(item.span, "super_predicates invoked on non-trait"),
 846     };
 847
 848     let icx = ItemCtxt::new(tcx, trait_def_id);
 849
 850     // Convert the bounds that follow the colon, e.g., `Bar + Zed` in `trait Foo: Bar + Zed`.
 851     let self_param_ty = tcx.types.self_param;
 852     let superbounds1 =
 853         AstConv::compute_bounds(&icx, self_param_ty, bounds, SizedByDefault::No, item.span);
 854
 855     let superbounds1 = superbounds1.predicates(tcx, self_param_ty);
 856
 857     // Convert any explicit superbounds in the where-clause,
 858     // e.g., `trait Foo where Self: Bar`.
 859     // In the case of trait aliases, however, we include all bounds in the where-clause,
 860     // so e.g., `trait Foo = where u32: PartialEq<Self>` would include `u32: PartialEq<Self>`
 861     // as one of its "superpredicates".
 862     let is_trait_alias = tcx.is_trait_alias(trait_def_id);
 863     let superbounds2 = icx.type_parameter_bounds_in_generics(
 864         generics,
 865         item.hir_id,
 866         self_param_ty,
 867         OnlySelfBounds(!is_trait_alias),
 868     );
 869
 870     // Combine the two lists to form the complete set of superbounds:
 871     let superbounds = &*tcx.arena.alloc_from_iter(superbounds1.into_iter().chain(superbounds2));
 872
 873     // Now require that immediate supertraits are converted,
 874     // which will, in turn, reach indirect supertraits.
 875     for &(pred, span) in superbounds {
 876         debug!("superbound: {:?}", pred);
 877         if let ty::Predicate::Trait(bound, _) = pred {
 878             tcx.at(span).super_predicates_of(bound.def_id());
 879         }
 880     }
 881
 882     ty::GenericPredicates { parent: None, predicates: superbounds }
 883 }
 884
 885 fn trait_def(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::TraitDef {
 886     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 887     let item = tcx.hir().expect_item(hir_id);
 888
 889     let (is_auto, unsafety) = match item.kind {
 890         hir::ItemKind::Trait(is_auto, unsafety, ..) => (is_auto == hir::IsAuto::Yes, unsafety),
 891         hir::ItemKind::TraitAlias(..) => (false, hir::Unsafety::Normal),
 892         _ => span_bug!(item.span, "trait_def_of_item invoked on non-trait"),
 893     };
 894
 895     let paren_sugar = tcx.has_attr(def_id, sym::rustc_paren_sugar);
 896     if paren_sugar && !tcx.features().unboxed_closures {
 897         tcx.sess
 898             .struct_span_err(
 899                 item.span,
 900                 "the `#[rustc_paren_sugar]` attribute is a temporary means of controlling \
 901              which traits can use parenthetical notation",
 902             )
 903             .help("add `#![feature(unboxed_closures)]` to the crate attributes to use it")
 904             .emit();
 905     }
 906
 907     let is_marker = tcx.has_attr(def_id, sym::marker);
 908     let def_path_hash = tcx.def_path_hash(def_id);
 909     let def = ty::TraitDef::new(def_id, unsafety, paren_sugar, is_auto, is_marker, def_path_hash);
 910     tcx.arena.alloc(def)
 911 }
 912
 913 fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<Span> {
 914     struct LateBoundRegionsDetector<'tcx> {
 915         tcx: TyCtxt<'tcx>,
 916         outer_index: ty::DebruijnIndex,
 917         has_late_bound_regions: Option<Span>,
 918     }
 919
 920     impl Visitor<'tcx> for LateBoundRegionsDetector<'tcx> {
 921         type Map = Map<'tcx>;
 922
 923         fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
 924             NestedVisitorMap::None
 925         }
 926
 927         fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
 928             if self.has_late_bound_regions.is_some() {
 929                 return;
 930             }
 931             match ty.kind {
 932                 hir::TyKind::BareFn(..) => {
 933                     self.outer_index.shift_in(1);
 934                     intravisit::walk_ty(self, ty);
 935                     self.outer_index.shift_out(1);
 936                 }
 937                 _ => intravisit::walk_ty(self, ty),
 938             }
 939         }
 940
 941         fn visit_poly_trait_ref(
 942             &mut self,
 943             tr: &'tcx hir::PolyTraitRef<'tcx>,
 944             m: hir::TraitBoundModifier,
 945         ) {
 946             if self.has_late_bound_regions.is_some() {
 947                 return;
 948             }
 949             self.outer_index.shift_in(1);
 950             intravisit::walk_poly_trait_ref(self, tr, m);
 951             self.outer_index.shift_out(1);
 952         }
 953
 954         fn visit_lifetime(&mut self, lt: &'tcx hir::Lifetime) {
 955             if self.has_late_bound_regions.is_some() {
 956                 return;
 957             }
 958
 959             match self.tcx.named_region(lt.hir_id) {
 960                 Some(rl::Region::Static) | Some(rl::Region::EarlyBound(..)) => {}
 961                 Some(rl::Region::LateBound(debruijn, _, _))
 962                 | Some(rl::Region::LateBoundAnon(debruijn, _))
 963                     if debruijn < self.outer_index => {}
 964                 Some(rl::Region::LateBound(..))
 965                 | Some(rl::Region::LateBoundAnon(..))
 966                 | Some(rl::Region::Free(..))
 967                 | None => {
 968                     self.has_late_bound_regions = Some(lt.span);
 969                 }
 970             }
 971         }
 972     }
 973
 974     fn has_late_bound_regions<'tcx>(
 975         tcx: TyCtxt<'tcx>,
 976         generics: &'tcx hir::Generics<'tcx>,
 977         decl: &'tcx hir::FnDecl<'tcx>,
 978     ) -> Option<Span> {
 979         let mut visitor = LateBoundRegionsDetector {
 980             tcx,
 981             outer_index: ty::INNERMOST,
 982             has_late_bound_regions: None,
 983         };
 984         for param in generics.params {
 985             if let GenericParamKind::Lifetime { .. } = param.kind {
 986                 if tcx.is_late_bound(param.hir_id) {
 987                     return Some(param.span);
 988                 }
 989             }
 990         }
 991         visitor.visit_fn_decl(decl);
 992         visitor.has_late_bound_regions
 993     }
 994
 995     match node {
 996         Node::TraitItem(item) => match item.kind {
 997             hir::TraitItemKind::Method(ref sig, _) => {
 998                 has_late_bound_regions(tcx, &item.generics, &sig.decl)
 999             }
1000             _ => None,
1001         },
1002         Node::ImplItem(item) => match item.kind {
1003             hir::ImplItemKind::Method(ref sig, _) => {
1004                 has_late_bound_regions(tcx, &item.generics, &sig.decl)
1005             }
1006             _ => None,
1007         },
1008         Node::ForeignItem(item) => match item.kind {
1009             hir::ForeignItemKind::Fn(ref fn_decl, _, ref generics) => {
1010                 has_late_bound_regions(tcx, generics, fn_decl)
1011             }
1012             _ => None,
1013         },
1014         Node::Item(item) => match item.kind {
1015             hir::ItemKind::Fn(ref sig, .., ref generics, _) => {
1016                 has_late_bound_regions(tcx, generics, &sig.decl)
1017             }
1018             _ => None,
1019         },
1020         _ => None,
1021     }
1022 }
1023
1024 fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::Generics {
1025     use rustc_hir::*;
1026
1027     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1028
1029     let node = tcx.hir().get(hir_id);
1030     let parent_def_id = match node {
1031         Node::ImplItem(_)
1032         | Node::TraitItem(_)
1033         | Node::Variant(_)
1034         | Node::Ctor(..)
1035         | Node::Field(_) => {
1036             let parent_id = tcx.hir().get_parent_item(hir_id);
1037             Some(tcx.hir().local_def_id(parent_id))
1038         }
1039         // FIXME(#43408) enable this always when we get lazy normalization.
1040         Node::AnonConst(_) => {
1041             // HACK(eddyb) this provides the correct generics when
1042             // `feature(const_generics)` is enabled, so that const expressions
1043             // used with const generics, e.g. `Foo<{N+1}>`, can work at all.
1044             if tcx.features().const_generics {
1045                 let parent_id = tcx.hir().get_parent_item(hir_id);
1046                 Some(tcx.hir().local_def_id(parent_id))
1047             } else {
1048                 None
1049             }
1050         }
1051         Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => {
1052             Some(tcx.closure_base_def_id(def_id))
1053         }
1054         Node::Item(item) => match item.kind {
1055             ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn, .. }) => impl_trait_fn,
1056             _ => None,
1057         },
1058         _ => None,
1059     };
1060
1061     let mut opt_self = None;
1062     let mut allow_defaults = false;
1063
1064     let no_generics = hir::Generics::empty();
1065     let ast_generics = match node {
1066         Node::TraitItem(item) => &item.generics,
1067
1068         Node::ImplItem(item) => &item.generics,
1069
1070         Node::Item(item) => {
1071             match item.kind {
1072                 ItemKind::Fn(.., ref generics, _) | ItemKind::Impl { ref generics, .. } => generics,
1073
1074                 ItemKind::TyAlias(_, ref generics)
1075                 | ItemKind::Enum(_, ref generics)
1076                 | ItemKind::Struct(_, ref generics)
1077                 | ItemKind::OpaqueTy(hir::OpaqueTy { ref generics, .. })
1078                 | ItemKind::Union(_, ref generics) => {
1079                     allow_defaults = true;
1080                     generics
1081                 }
1082
1083                 ItemKind::Trait(_, _, ref generics, ..)
1084                 | ItemKind::TraitAlias(ref generics, ..) => {
1085                     // Add in the self type parameter.
1086                     //
1087                     // Something of a hack: use the node id for the trait, also as
1088                     // the node id for the Self type parameter.
1089                     let param_id = item.hir_id;
1090
1091                     opt_self = Some(ty::GenericParamDef {
1092                         index: 0,
1093                         name: kw::SelfUpper,
1094                         def_id: tcx.hir().local_def_id(param_id),
1095                         pure_wrt_drop: false,
1096                         kind: ty::GenericParamDefKind::Type {
1097                             has_default: false,
1098                             object_lifetime_default: rl::Set1::Empty,
1099                             synthetic: None,
1100                         },
1101                     });
1102
1103                     allow_defaults = true;
1104                     generics
1105                 }
1106
1107                 _ => &no_generics,
1108             }
1109         }
1110
1111         Node::ForeignItem(item) => match item.kind {
1112             ForeignItemKind::Static(..) => &no_generics,
1113             ForeignItemKind::Fn(_, _, ref generics) => generics,
1114             ForeignItemKind::Type => &no_generics,
1115         },
1116
1117         _ => &no_generics,
1118     };
1119
1120     let has_self = opt_self.is_some();
1121     let mut parent_has_self = false;
1122     let mut own_start = has_self as u32;
1123     let parent_count = parent_def_id.map_or(0, |def_id| {
1124         let generics = tcx.generics_of(def_id);
1125         assert_eq!(has_self, false);
1126         parent_has_self = generics.has_self;
1127         own_start = generics.count() as u32;
1128         generics.parent_count + generics.params.len()
1129     });
1130
1131     let mut params: Vec<_> = opt_self.into_iter().collect();
1132
1133     let early_lifetimes = early_bound_lifetimes_from_generics(tcx, ast_generics);
1134     params.extend(early_lifetimes.enumerate().map(|(i, param)| ty::GenericParamDef {
1135         name: param.name.ident().name,
1136         index: own_start + i as u32,
1137         def_id: tcx.hir().local_def_id(param.hir_id),
1138         pure_wrt_drop: param.pure_wrt_drop,
1139         kind: ty::GenericParamDefKind::Lifetime,
1140     }));
1141
1142     let object_lifetime_defaults = tcx.object_lifetime_defaults(hir_id);
1143
1144     // Now create the real type parameters.
1145     let type_start = own_start - has_self as u32 + params.len() as u32;
1146     let mut i = 0;
1147     params.extend(ast_generics.params.iter().filter_map(|param| {
1148         let kind = match param.kind {
1149             GenericParamKind::Type { ref default, synthetic, .. } => {
1150                 if !allow_defaults && default.is_some() {
1151                     if !tcx.features().default_type_parameter_fallback {
1152                         tcx.lint_hir(
1153                             lint::builtin::INVALID_TYPE_PARAM_DEFAULT,
1154                             param.hir_id,
1155                             param.span,
1156                             &format!(
1157                                 "defaults for type parameters are only allowed in \
1158                                         `struct`, `enum`, `type`, or `trait` definitions."
1159                             ),
1160                         );
1161                     }
1162                 }
1163
1164                 ty::GenericParamDefKind::Type {
1165                     has_default: default.is_some(),
1166                     object_lifetime_default: object_lifetime_defaults
1167                         .as_ref()
1168                         .map_or(rl::Set1::Empty, |o| o[i]),
1169                     synthetic,
1170                 }
1171             }
1172             GenericParamKind::Const { .. } => ty::GenericParamDefKind::Const,
1173             _ => return None,
1174         };
1175
1176         let param_def = ty::GenericParamDef {
1177             index: type_start + i as u32,
1178             name: param.name.ident().name,
1179             def_id: tcx.hir().local_def_id(param.hir_id),
1180             pure_wrt_drop: param.pure_wrt_drop,
1181             kind,
1182         };
1183         i += 1;
1184         Some(param_def)
1185     }));
1186
1187     // provide junk type parameter defs - the only place that
1188     // cares about anything but the length is instantiation,
1189     // and we don't do that for closures.
1190     if let Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(.., gen), .. }) = node {
1191         let dummy_args = if gen.is_some() {
1192             &["<yield_ty>", "<return_ty>", "<witness>"][..]
1193         } else {
1194             &["<closure_kind>", "<closure_signature>"][..]
1195         };
1196
1197         params.extend(dummy_args.iter().enumerate().map(|(i, &arg)| ty::GenericParamDef {
1198             index: type_start + i as u32,
1199             name: Symbol::intern(arg),
1200             def_id,
1201             pure_wrt_drop: false,
1202             kind: ty::GenericParamDefKind::Type {
1203                 has_default: false,
1204                 object_lifetime_default: rl::Set1::Empty,
1205                 synthetic: None,
1206             },
1207         }));
1208
1209         if let Some(upvars) = tcx.upvars(def_id) {
1210             params.extend(upvars.iter().zip((dummy_args.len() as u32)..).map(|(_, i)| {
1211                 ty::GenericParamDef {
1212                     index: type_start + i,
1213                     name: Symbol::intern("<upvar>"),
1214                     def_id,
1215                     pure_wrt_drop: false,
1216                     kind: ty::GenericParamDefKind::Type {
1217                         has_default: false,
1218                         object_lifetime_default: rl::Set1::Empty,
1219                         synthetic: None,
1220                     },
1221                 }
1222             }));
1223         }
1224     }
1225
1226     let param_def_id_to_index = params.iter().map(|param| (param.def_id, param.index)).collect();
1227
1228     tcx.arena.alloc(ty::Generics {
1229         parent: parent_def_id,
1230         parent_count,
1231         params,
1232         param_def_id_to_index,
1233         has_self: has_self || parent_has_self,
1234         has_late_bound_regions: has_late_bound_regions(tcx, node),
1235     })
1236 }
1237
1238 fn report_assoc_ty_on_inherent_impl(tcx: TyCtxt<'_>, span: Span) {
1239     struct_span_err!(
1240         tcx.sess,
1241         span,
1242         E0202,
1243         "associated types are not yet supported in inherent impls (see #8995)"
1244     )
1245     .emit();
1246 }
1247
1248 fn infer_placeholder_type(
1249     tcx: TyCtxt<'_>,
1250     def_id: DefId,
1251     body_id: hir::BodyId,
1252     span: Span,
1253     item_ident: Ident,
1254 ) -> Ty<'_> {
1255     let ty = tcx.diagnostic_only_typeck_tables_of(def_id).node_type(body_id.hir_id);
1256
1257     // If this came from a free `const` or `static mut?` item,
1258     // then the user may have written e.g. `const A = 42;`.
1259     // In this case, the parser has stashed a diagnostic for
1260     // us to improve in typeck so we do that now.
1261     match tcx.sess.diagnostic().steal_diagnostic(span, StashKey::ItemNoType) {
1262         Some(mut err) => {
1263             // The parser provided a sub-optimal `HasPlaceholders` suggestion for the type.
1264             // We are typeck and have the real type, so remove that and suggest the actual type.
1265             err.suggestions.clear();
1266             err.span_suggestion(
1267                 span,
1268                 "provide a type for the item",
1269                 format!("{}: {}", item_ident, ty),
1270                 Applicability::MachineApplicable,
1271             )
1272             .emit();
1273         }
1274         None => {
1275             let mut diag = bad_placeholder_type(tcx, vec![span]);
1276             if ty != tcx.types.err {
1277                 diag.span_suggestion(
1278                     span,
1279                     "replace `_` with the correct type",
1280                     ty.to_string(),
1281                     Applicability::MaybeIncorrect,
1282                 );
1283             }
1284             diag.emit();
1285         }
1286     }
1287
1288     ty
1289 }
1290
1291 fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
1292     use rustc_hir::*;
1293
1294     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1295
1296     let icx = ItemCtxt::new(tcx, def_id);
1297
1298     match tcx.hir().get(hir_id) {
1299         Node::TraitItem(item) => match item.kind {
1300             TraitItemKind::Method(..) => {
1301                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1302                 tcx.mk_fn_def(def_id, substs)
1303             }
1304             TraitItemKind::Const(ref ty, body_id) => body_id
1305                 .and_then(|body_id| {
1306                     if is_suggestable_infer_ty(ty) {
1307                         Some(infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident))
1308                     } else {
1309                         None
1310                     }
1311                 })
1312                 .unwrap_or_else(|| icx.to_ty(ty)),
1313             TraitItemKind::Type(_, Some(ref ty)) => icx.to_ty(ty),
1314             TraitItemKind::Type(_, None) => {
1315                 span_bug!(item.span, "associated type missing default");
1316             }
1317         },
1318
1319         Node::ImplItem(item) => match item.kind {
1320             ImplItemKind::Method(..) => {
1321                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1322                 tcx.mk_fn_def(def_id, substs)
1323             }
1324             ImplItemKind::Const(ref ty, body_id) => {
1325                 if is_suggestable_infer_ty(ty) {
1326                     infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident)
1327                 } else {
1328                     icx.to_ty(ty)
1329                 }
1330             }
1331             ImplItemKind::OpaqueTy(_) => {
1332                 if tcx.impl_trait_ref(tcx.hir().get_parent_did(hir_id)).is_none() {
1333                     report_assoc_ty_on_inherent_impl(tcx, item.span);
1334                 }
1335
1336                 find_opaque_ty_constraints(tcx, def_id)
1337             }
1338             ImplItemKind::TyAlias(ref ty) => {
1339                 if tcx.impl_trait_ref(tcx.hir().get_parent_did(hir_id)).is_none() {
1340                     report_assoc_ty_on_inherent_impl(tcx, item.span);
1341                 }
1342
1343                 icx.to_ty(ty)
1344             }
1345         },
1346
1347         Node::Item(item) => {
1348             match item.kind {
1349                 ItemKind::Static(ref ty, .., body_id) | ItemKind::Const(ref ty, body_id) => {
1350                     if is_suggestable_infer_ty(ty) {
1351                         infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident)
1352                     } else {
1353                         icx.to_ty(ty)
1354                     }
1355                 }
1356                 ItemKind::TyAlias(ref self_ty, _) | ItemKind::Impl { ref self_ty, .. } => {
1357                     icx.to_ty(self_ty)
1358                 }
1359                 ItemKind::Fn(..) => {
1360                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
1361                     tcx.mk_fn_def(def_id, substs)
1362                 }
1363                 ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
1364                     let def = tcx.adt_def(def_id);
1365                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
1366                     tcx.mk_adt(def, substs)
1367                 }
1368                 ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: None, .. }) => {
1369                     find_opaque_ty_constraints(tcx, def_id)
1370                 }
1371                 // Opaque types desugared from `impl Trait`.
1372                 ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(owner), .. }) => {
1373                     tcx.typeck_tables_of(owner)
1374                         .concrete_opaque_types
1375                         .get(&def_id)
1376                         .map(|opaque| opaque.concrete_type)
1377                         .unwrap_or_else(|| {
1378                             // This can occur if some error in the
1379                             // owner fn prevented us from populating
1380                             // the `concrete_opaque_types` table.
1381                             tcx.sess.delay_span_bug(
1382                                 DUMMY_SP,
1383                                 &format!(
1384                                     "owner {:?} has no opaque type for {:?} in its tables",
1385                                     owner, def_id,
1386                                 ),
1387                             );
1388                             tcx.types.err
1389                         })
1390                 }
1391                 ItemKind::Trait(..)
1392                 | ItemKind::TraitAlias(..)
1393                 | ItemKind::Mod(..)
1394                 | ItemKind::ForeignMod(..)
1395                 | ItemKind::GlobalAsm(..)
1396                 | ItemKind::ExternCrate(..)
1397                 | ItemKind::Use(..) => {
1398                     span_bug!(
1399                         item.span,
1400                         "compute_type_of_item: unexpected item type: {:?}",
1401                         item.kind
1402                     );
1403                 }
1404             }
1405         }
1406
1407         Node::ForeignItem(foreign_item) => match foreign_item.kind {
1408             ForeignItemKind::Fn(..) => {
1409                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1410                 tcx.mk_fn_def(def_id, substs)
1411             }
1412             ForeignItemKind::Static(ref t, _) => icx.to_ty(t),
1413             ForeignItemKind::Type => tcx.mk_foreign(def_id),
1414         },
1415
1416         Node::Ctor(&ref def) | Node::Variant(hir::Variant { data: ref def, .. }) => match *def {
1417             VariantData::Unit(..) | VariantData::Struct(..) => {
1418                 tcx.type_of(tcx.hir().get_parent_did(hir_id))
1419             }
1420             VariantData::Tuple(..) => {
1421                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1422                 tcx.mk_fn_def(def_id, substs)
1423             }
1424         },
1425
1426         Node::Field(field) => icx.to_ty(&field.ty),
1427
1428         Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(.., gen), .. }) => {
1429             if gen.is_some() {
1430                 return tcx.typeck_tables_of(def_id).node_type(hir_id);
1431             }
1432
1433             let substs = InternalSubsts::identity_for_item(tcx, def_id);
1434             tcx.mk_closure(def_id, substs)
1435         }
1436
1437         Node::AnonConst(_) => {
1438             let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
1439             match parent_node {
1440                 Node::Ty(&hir::Ty { kind: hir::TyKind::Array(_, ref constant), .. })
1441                 | Node::Ty(&hir::Ty { kind: hir::TyKind::Typeof(ref constant), .. })
1442                 | Node::Expr(&hir::Expr { kind: ExprKind::Repeat(_, ref constant), .. })
1443                     if constant.hir_id == hir_id =>
1444                 {
1445                     tcx.types.usize
1446                 }
1447
1448                 Node::Variant(Variant { disr_expr: Some(ref e), .. }) if e.hir_id == hir_id => {
1449                     tcx.adt_def(tcx.hir().get_parent_did(hir_id)).repr.discr_type().to_ty(tcx)
1450                 }
1451
1452                 Node::Ty(&hir::Ty { kind: hir::TyKind::Path(_), .. })
1453                 | Node::Expr(&hir::Expr { kind: ExprKind::Struct(..), .. })
1454                 | Node::Expr(&hir::Expr { kind: ExprKind::Path(_), .. })
1455                 | Node::TraitRef(..) => {
1456                     let path = match parent_node {
1457                         Node::Ty(&hir::Ty {
1458                             kind: hir::TyKind::Path(QPath::Resolved(_, ref path)),
1459                             ..
1460                         })
1461                         | Node::Expr(&hir::Expr {
1462                             kind: ExprKind::Path(QPath::Resolved(_, ref path)),
1463                             ..
1464                         }) => Some(&**path),
1465                         Node::Expr(&hir::Expr { kind: ExprKind::Struct(ref path, ..), .. }) => {
1466                             if let QPath::Resolved(_, ref path) = **path {
1467                                 Some(&**path)
1468                             } else {
1469                                 None
1470                             }
1471                         }
1472                         Node::TraitRef(&hir::TraitRef { ref path, .. }) => Some(&**path),
1473                         _ => None,
1474                     };
1475
1476                     if let Some(path) = path {
1477                         let arg_index = path
1478                             .segments
1479                             .iter()
1480                             .filter_map(|seg| seg.args.as_ref())
1481                             .map(|generic_args| generic_args.args.as_ref())
1482                             .find_map(|args| {
1483                                 args.iter()
1484                                     .filter(|arg| arg.is_const())
1485                                     .enumerate()
1486                                     .filter(|(_, arg)| arg.id() == hir_id)
1487                                     .map(|(index, _)| index)
1488                                     .next()
1489                             })
1490                             .unwrap_or_else(|| {
1491                                 bug!("no arg matching AnonConst in path");
1492                             });
1493
1494                         // We've encountered an `AnonConst` in some path, so we need to
1495                         // figure out which generic parameter it corresponds to and return
1496                         // the relevant type.
1497                         let generics = match path.res {
1498                             Res::Def(DefKind::Ctor(..), def_id) => {
1499                                 tcx.generics_of(tcx.parent(def_id).unwrap())
1500                             }
1501                             Res::Def(_, def_id) => tcx.generics_of(def_id),
1502                             Res::Err => return tcx.types.err,
1503                             res => {
1504                                 tcx.sess.delay_span_bug(
1505                                     DUMMY_SP,
1506                                     &format!("unexpected const parent path def {:?}", res,),
1507                                 );
1508                                 return tcx.types.err;
1509                             }
1510                         };
1511
1512                         generics
1513                             .params
1514                             .iter()
1515                             .filter(|param| {
1516                                 if let ty::GenericParamDefKind::Const = param.kind {
1517                                     true
1518                                 } else {
1519                                     false
1520                                 }
1521                             })
1522                             .nth(arg_index)
1523                             .map(|param| tcx.type_of(param.def_id))
1524                             // This is no generic parameter associated with the arg. This is
1525                             // probably from an extra arg where one is not needed.
1526                             .unwrap_or(tcx.types.err)
1527                     } else {
1528                         tcx.sess.delay_span_bug(
1529                             DUMMY_SP,
1530                             &format!("unexpected const parent path {:?}", parent_node,),
1531                         );
1532                         return tcx.types.err;
1533                     }
1534                 }
1535
1536                 x => {
1537                     tcx.sess.delay_span_bug(
1538                         DUMMY_SP,
1539                         &format!("unexpected const parent in type_of_def_id(): {:?}", x),
1540                     );
1541                     tcx.types.err
1542                 }
1543             }
1544         }
1545
1546         Node::GenericParam(param) => match &param.kind {
1547             hir::GenericParamKind::Type { default: Some(ref ty), .. } => icx.to_ty(ty),
1548             hir::GenericParamKind::Const { ty: ref hir_ty, .. } => {
1549                 let ty = icx.to_ty(hir_ty);
1550                 if !tcx.features().const_compare_raw_pointers {
1551                     let err = match ty.peel_refs().kind {
1552                         ty::FnPtr(_) => Some("function pointers"),
1553                         ty::RawPtr(_) => Some("raw pointers"),
1554                         _ => None,
1555                     };
1556                     if let Some(unsupported_type) = err {
1557                         feature_err(
1558                             &tcx.sess.parse_sess,
1559                             sym::const_compare_raw_pointers,
1560                             hir_ty.span,
1561                             &format!(
1562                                 "using {} as const generic parameters is unstable",
1563                                 unsupported_type
1564                             ),
1565                         )
1566                         .emit();
1567                     };
1568                 }
1569                 if traits::search_for_structural_match_violation(param.hir_id, param.span, tcx, ty)
1570                     .is_some()
1571                 {
1572                     struct_span_err!(
1573                         tcx.sess,
1574                         hir_ty.span,
1575                         E0741,
1576                         "the types of const generic parameters must derive `PartialEq` and `Eq`",
1577                     )
1578                     .span_label(
1579                         hir_ty.span,
1580                         format!("`{}` doesn't derive both `PartialEq` and `Eq`", ty),
1581                     )
1582                     .emit();
1583                 }
1584                 ty
1585             }
1586             x => bug!("unexpected non-type Node::GenericParam: {:?}", x),
1587         },
1588
1589         x => {
1590             bug!("unexpected sort of node in type_of_def_id(): {:?}", x);
1591         }
1592     }
1593 }
1594
1595 fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
1596     use rustc_hir::{ImplItem, Item, TraitItem};
1597
1598     debug!("find_opaque_ty_constraints({:?})", def_id);
1599
1600     struct ConstraintLocator<'tcx> {
1601         tcx: TyCtxt<'tcx>,
1602         def_id: DefId,
1603         // (first found type span, actual type, mapping from the opaque type's generic
1604         // parameters to the concrete type's generic parameters)
1605         //
1606         // The mapping is an index for each use site of a generic parameter in the concrete type
1607         //
1608         // The indices index into the generic parameters on the opaque type.
1609         found: Option<(Span, Ty<'tcx>, Vec<usize>)>,
1610     }
1611
1612     impl ConstraintLocator<'tcx> {
1613         fn check(&mut self, def_id: DefId) {
1614             // Don't try to check items that cannot possibly constrain the type.
1615             if !self.tcx.has_typeck_tables(def_id) {
1616                 debug!(
1617                     "find_opaque_ty_constraints: no constraint for `{:?}` at `{:?}`: no tables",
1618                     self.def_id, def_id,
1619                 );
1620                 return;
1621             }
1622             let ty = self.tcx.typeck_tables_of(def_id).concrete_opaque_types.get(&self.def_id);
1623             if let Some(ty::ResolvedOpaqueTy { concrete_type, substs }) = ty {
1624                 debug!(
1625                     "find_opaque_ty_constraints: found constraint for `{:?}` at `{:?}`: {:?}",
1626                     self.def_id, def_id, ty,
1627                 );
1628
1629                 // FIXME(oli-obk): trace the actual span from inference to improve errors.
1630                 let span = self.tcx.def_span(def_id);
1631                 // used to quickly look up the position of a generic parameter
1632                 let mut index_map: FxHashMap<ty::ParamTy, usize> = FxHashMap::default();
1633                 // Skipping binder is ok, since we only use this to find generic parameters and
1634                 // their positions.
1635                 for (idx, subst) in substs.iter().enumerate() {
1636                     if let GenericArgKind::Type(ty) = subst.unpack() {
1637                         if let ty::Param(p) = ty.kind {
1638                             if index_map.insert(p, idx).is_some() {
1639                                 // There was already an entry for `p`, meaning a generic parameter
1640                                 // was used twice.
1641                                 self.tcx.sess.span_err(
1642                                     span,
1643                                     &format!(
1644                                         "defining opaque type use restricts opaque \
1645                                          type by using the generic parameter `{}` twice",
1646                                         p,
1647                                     ),
1648                                 );
1649                                 return;
1650                             }
1651                         } else {
1652                             self.tcx.sess.delay_span_bug(
1653                                 span,
1654                                 &format!(
1655                                     "non-defining opaque ty use in defining scope: {:?}, {:?}",
1656                                     concrete_type, substs,
1657                                 ),
1658                             );
1659                         }
1660                     }
1661                 }
1662                 // Compute the index within the opaque type for each generic parameter used in
1663                 // the concrete type.
1664                 let indices = concrete_type
1665                     .subst(self.tcx, substs)
1666                     .walk()
1667                     .filter_map(|t| match &t.kind {
1668                         ty::Param(p) => Some(*index_map.get(p).unwrap()),
1669                         _ => None,
1670                     })
1671                     .collect();
1672                 let is_param = |ty: Ty<'_>| match ty.kind {
1673                     ty::Param(_) => true,
1674                     _ => false,
1675                 };
1676                 let bad_substs: Vec<_> = substs
1677                     .iter()
1678                     .enumerate()
1679                     .filter_map(|(i, k)| {
1680                         if let GenericArgKind::Type(ty) = k.unpack() { Some((i, ty)) } else { None }
1681                     })
1682                     .filter(|(_, ty)| !is_param(ty))
1683                     .collect();
1684
1685                 if !bad_substs.is_empty() {
1686                     let identity_substs = InternalSubsts::identity_for_item(self.tcx, self.def_id);
1687                     for (i, bad_subst) in bad_substs {
1688                         self.tcx.sess.span_err(
1689                             span,
1690                             &format!(
1691                                 "defining opaque type use does not fully define opaque type: \
1692                             generic parameter `{}` is specified as concrete type `{}`",
1693                                 identity_substs.type_at(i),
1694                                 bad_subst
1695                             ),
1696                         );
1697                     }
1698                 } else if let Some((prev_span, prev_ty, ref prev_indices)) = self.found {
1699                     let mut ty = concrete_type.walk().fuse();
1700                     let mut p_ty = prev_ty.walk().fuse();
1701                     let iter_eq = (&mut ty).zip(&mut p_ty).all(|(t, p)| match (&t.kind, &p.kind) {
1702                         // Type parameters are equal to any other type parameter for the purpose of
1703                         // concrete type equality, as it is possible to obtain the same type just
1704                         // by passing matching parameters to a function.
1705                         (ty::Param(_), ty::Param(_)) => true,
1706                         _ => t == p,
1707                     });
1708                     if !iter_eq || ty.next().is_some() || p_ty.next().is_some() {
1709                         debug!("find_opaque_ty_constraints: span={:?}", span);
1710                         // Found different concrete types for the opaque type.
1711                         let mut err = self.tcx.sess.struct_span_err(
1712                             span,
1713                             "concrete type differs from previous defining opaque type use",
1714                         );
1715                         err.span_label(
1716                             span,
1717                             format!("expected `{}`, got `{}`", prev_ty, concrete_type),
1718                         );
1719                         err.span_note(prev_span, "previous use here");
1720                         err.emit();
1721                     } else if indices != *prev_indices {
1722                         // Found "same" concrete types, but the generic parameter order differs.
1723                         let mut err = self.tcx.sess.struct_span_err(
1724                             span,
1725                             "concrete type's generic parameters differ from previous defining use",
1726                         );
1727                         use std::fmt::Write;
1728                         let mut s = String::new();
1729                         write!(s, "expected [").unwrap();
1730                         let list = |s: &mut String, indices: &Vec<usize>| {
1731                             let mut indices = indices.iter().cloned();
1732                             if let Some(first) = indices.next() {
1733                                 write!(s, "`{}`", substs[first]).unwrap();
1734                                 for i in indices {
1735                                     write!(s, ", `{}`", substs[i]).unwrap();
1736                                 }
1737                             }
1738                         };
1739                         list(&mut s, prev_indices);
1740                         write!(s, "], got [").unwrap();
1741                         list(&mut s, &indices);
1742                         write!(s, "]").unwrap();
1743                         err.span_label(span, s);
1744                         err.span_note(prev_span, "previous use here");
1745                         err.emit();
1746                     }
1747                 } else {
1748                     self.found = Some((span, concrete_type, indices));
1749                 }
1750             } else {
1751                 debug!(
1752                     "find_opaque_ty_constraints: no constraint for `{:?}` at `{:?}`",
1753                     self.def_id, def_id,
1754                 );
1755             }
1756         }
1757     }
1758
1759     impl<'tcx> intravisit::Visitor<'tcx> for ConstraintLocator<'tcx> {
1760         type Map = Map<'tcx>;
1761
1762         fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<'_, Self::Map> {
1763             intravisit::NestedVisitorMap::All(&self.tcx.hir())
1764         }
1765         fn visit_item(&mut self, it: &'tcx Item<'tcx>) {
1766             debug!("find_existential_constraints: visiting {:?}", it);
1767             let def_id = self.tcx.hir().local_def_id(it.hir_id);
1768             // The opaque type itself or its children are not within its reveal scope.
1769             if def_id != self.def_id {
1770                 self.check(def_id);
1771                 intravisit::walk_item(self, it);
1772             }
1773         }
1774         fn visit_impl_item(&mut self, it: &'tcx ImplItem<'tcx>) {
1775             debug!("find_existential_constraints: visiting {:?}", it);
1776             let def_id = self.tcx.hir().local_def_id(it.hir_id);
1777             // The opaque type itself or its children are not within its reveal scope.
1778             if def_id != self.def_id {
1779                 self.check(def_id);
1780                 intravisit::walk_impl_item(self, it);
1781             }
1782         }
1783         fn visit_trait_item(&mut self, it: &'tcx TraitItem<'tcx>) {
1784             debug!("find_existential_constraints: visiting {:?}", it);
1785             let def_id = self.tcx.hir().local_def_id(it.hir_id);
1786             self.check(def_id);
1787             intravisit::walk_trait_item(self, it);
1788         }
1789     }
1790
1791     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1792     let scope = tcx.hir().get_defining_scope(hir_id);
1793     let mut locator = ConstraintLocator { def_id, tcx, found: None };
1794
1795     debug!("find_opaque_ty_constraints: scope={:?}", scope);
1796
1797     if scope == hir::CRATE_HIR_ID {
1798         intravisit::walk_crate(&mut locator, tcx.hir().krate());
1799     } else {
1800         debug!("find_opaque_ty_constraints: scope={:?}", tcx.hir().get(scope));
1801         match tcx.hir().get(scope) {
1802             // We explicitly call `visit_*` methods, instead of using `intravisit::walk_*` methods
1803             // This allows our visitor to process the defining item itself, causing
1804             // it to pick up any 'sibling' defining uses.
1805             //
1806             // For example, this code:
1807             // ```
1808             // fn foo() {
1809             //     type Blah = impl Debug;
1810             //     let my_closure = || -> Blah { true };
1811             // }
1812             // ```
1813             //
1814             // requires us to explicitly process `foo()` in order
1815             // to notice the defining usage of `Blah`.
1816             Node::Item(ref it) => locator.visit_item(it),
1817             Node::ImplItem(ref it) => locator.visit_impl_item(it),
1818             Node::TraitItem(ref it) => locator.visit_trait_item(it),
1819             other => bug!("{:?} is not a valid scope for an opaque type item", other),
1820         }
1821     }
1822
1823     match locator.found {
1824         Some((_, ty, _)) => ty,
1825         None => {
1826             let span = tcx.def_span(def_id);
1827             tcx.sess.span_err(span, "could not find defining uses");
1828             tcx.types.err
1829         }
1830     }
1831 }
1832
1833 fn are_suggestable_generic_args(generic_args: &[hir::GenericArg<'_>]) -> bool {
1834     generic_args
1835         .iter()
1836         .filter_map(|arg| match arg {
1837             hir::GenericArg::Type(ty) => Some(ty),
1838             _ => None,
1839         })
1840         .any(is_suggestable_infer_ty)
1841 }
1842
1843 /// Whether `ty` is a type with `_` placeholders that can be infered. Used in diagnostics only to
1844 /// use inference to provide suggestions for the appropriate type if possible.
1845 fn is_suggestable_infer_ty(ty: &hir::Ty<'_>) -> bool {
1846     use hir::TyKind::*;
1847     match &ty.kind {
1848         Infer => true,
1849         Slice(ty) | Array(ty, _) => is_suggestable_infer_ty(ty),
1850         Tup(tys) => tys.iter().any(is_suggestable_infer_ty),
1851         Ptr(mut_ty) | Rptr(_, mut_ty) => is_suggestable_infer_ty(mut_ty.ty),
1852         Def(_, generic_args) => are_suggestable_generic_args(generic_args),
1853         Path(hir::QPath::TypeRelative(ty, segment)) => {
1854             is_suggestable_infer_ty(ty) || are_suggestable_generic_args(segment.generic_args().args)
1855         }
1856         Path(hir::QPath::Resolved(ty_opt, hir::Path { segments, .. })) => {
1857             ty_opt.map_or(false, is_suggestable_infer_ty)
1858                 || segments
1859                     .iter()
1860                     .any(|segment| are_suggestable_generic_args(segment.generic_args().args))
1861         }
1862         _ => false,
1863     }
1864 }
1865
1866 pub fn get_infer_ret_ty(output: &'hir hir::FunctionRetTy<'hir>) -> Option<&'hir hir::Ty<'hir>> {
1867     if let hir::FunctionRetTy::Return(ref ty) = output {
1868         if is_suggestable_infer_ty(ty) {
1869             return Some(&**ty);
1870         }
1871     }
1872     None
1873 }
1874
1875 fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
1876     use rustc_hir::Node::*;
1877     use rustc_hir::*;
1878
1879     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1880
1881     let icx = ItemCtxt::new(tcx, def_id);
1882
1883     match tcx.hir().get(hir_id) {
1884         TraitItem(hir::TraitItem {
1885             kind: TraitItemKind::Method(sig, TraitMethod::Provided(_)),
1886             ident,
1887             generics,
1888             ..
1889         })
1890         | ImplItem(hir::ImplItem { kind: ImplItemKind::Method(sig, _), ident, generics, .. })
1891         | Item(hir::Item { kind: ItemKind::Fn(sig, generics, _), ident, .. }) => {
1892             match get_infer_ret_ty(&sig.decl.output) {
1893                 Some(ty) => {
1894                     let fn_sig = tcx.typeck_tables_of(def_id).liberated_fn_sigs()[hir_id];
1895                     let mut visitor = PlaceholderHirTyCollector::default();
1896                     visitor.visit_ty(ty);
1897                     let mut diag = bad_placeholder_type(tcx, visitor.0);
1898                     let ret_ty = fn_sig.output();
1899                     if ret_ty != tcx.types.err {
1900                         diag.span_suggestion(
1901                             ty.span,
1902                             "replace with the correct return type",
1903                             ret_ty.to_string(),
1904                             Applicability::MaybeIncorrect,
1905                         );
1906                     }
1907                     diag.emit();
1908                     ty::Binder::bind(fn_sig)
1909                 }
1910                 None => AstConv::ty_of_fn(
1911                     &icx,
1912                     sig.header.unsafety,
1913                     sig.header.abi,
1914                     &sig.decl,
1915                     &generics.params[..],
1916                     Some(ident.span),
1917                 ),
1918             }
1919         }
1920
1921         TraitItem(hir::TraitItem {
1922             kind: TraitItemKind::Method(FnSig { header, decl }, _),
1923             ident,
1924             generics,
1925             ..
1926         }) => AstConv::ty_of_fn(
1927             &icx,
1928             header.unsafety,
1929             header.abi,
1930             decl,
1931             &generics.params[..],
1932             Some(ident.span),
1933         ),
1934
1935         ForeignItem(&hir::ForeignItem { kind: ForeignItemKind::Fn(ref fn_decl, _, _), .. }) => {
1936             let abi = tcx.hir().get_foreign_abi(hir_id);
1937             compute_sig_of_foreign_fn_decl(tcx, def_id, fn_decl, abi)
1938         }
1939
1940         Ctor(data) | Variant(hir::Variant { data, .. }) if data.ctor_hir_id().is_some() => {
1941             let ty = tcx.type_of(tcx.hir().get_parent_did(hir_id));
1942             let inputs =
1943                 data.fields().iter().map(|f| tcx.type_of(tcx.hir().local_def_id(f.hir_id)));
1944             ty::Binder::bind(tcx.mk_fn_sig(
1945                 inputs,
1946                 ty,
1947                 false,
1948                 hir::Unsafety::Normal,
1949                 abi::Abi::Rust,
1950             ))
1951         }
1952
1953         Expr(&hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => {
1954             // Closure signatures are not like other function
1955             // signatures and cannot be accessed through `fn_sig`. For
1956             // example, a closure signature excludes the `self`
1957             // argument. In any case they are embedded within the
1958             // closure type as part of the `ClosureSubsts`.
1959             //
1960             // To get
1961             // the signature of a closure, you should use the
1962             // `closure_sig` method on the `ClosureSubsts`:
1963             //
1964             //    closure_substs.sig(def_id, tcx)
1965             //
1966             // or, inside of an inference context, you can use
1967             //
1968             //    infcx.closure_sig(def_id, closure_substs)
1969             bug!("to get the signature of a closure, use `closure_sig()` not `fn_sig()`");
1970         }
1971
1972         x => {
1973             bug!("unexpected sort of node in fn_sig(): {:?}", x);
1974         }
1975     }
1976 }
1977
1978 fn impl_trait_ref(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ty::TraitRef<'_>> {
1979     let icx = ItemCtxt::new(tcx, def_id);
1980
1981     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1982     match tcx.hir().expect_item(hir_id).kind {
1983         hir::ItemKind::Impl { ref of_trait, .. } => of_trait.as_ref().map(|ast_trait_ref| {
1984             let selfty = tcx.type_of(def_id);
1985             AstConv::instantiate_mono_trait_ref(&icx, ast_trait_ref, selfty)
1986         }),
1987         _ => bug!(),
1988     }
1989 }
1990
1991 fn impl_polarity(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ImplPolarity {
1992     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1993     let is_rustc_reservation = tcx.has_attr(def_id, sym::rustc_reservation_impl);
1994     let item = tcx.hir().expect_item(hir_id);
1995     match &item.kind {
1996         hir::ItemKind::Impl { polarity: hir::ImplPolarity::Negative, .. } => {
1997             if is_rustc_reservation {
1998                 tcx.sess.span_err(item.span, "reservation impls can't be negative");
1999             }
2000             ty::ImplPolarity::Negative
2001         }
2002         hir::ItemKind::Impl { polarity: hir::ImplPolarity::Positive, of_trait: None, .. } => {
2003             if is_rustc_reservation {
2004                 tcx.sess.span_err(item.span, "reservation impls can't be inherent");
2005             }
2006             ty::ImplPolarity::Positive
2007         }
2008         hir::ItemKind::Impl {
2009             polarity: hir::ImplPolarity::Positive, of_trait: Some(_), ..
2010         } => {
2011             if is_rustc_reservation {
2012                 ty::ImplPolarity::Reservation
2013             } else {
2014                 ty::ImplPolarity::Positive
2015             }
2016         }
2017         ref item => bug!("impl_polarity: {:?} not an impl", item),
2018     }
2019 }
2020
2021 /// Returns the early-bound lifetimes declared in this generics
2022 /// listing. For anything other than fns/methods, this is just all
2023 /// the lifetimes that are declared. For fns or methods, we have to
2024 /// screen out those that do not appear in any where-clauses etc using
2025 /// `resolve_lifetime::early_bound_lifetimes`.
2026 fn early_bound_lifetimes_from_generics<'a, 'tcx: 'a>(
2027     tcx: TyCtxt<'tcx>,
2028     generics: &'a hir::Generics<'a>,
2029 ) -> impl Iterator<Item = &'a hir::GenericParam<'a>> + Captures<'tcx> {
2030     generics.params.iter().filter(move |param| match param.kind {
2031         GenericParamKind::Lifetime { .. } => !tcx.is_late_bound(param.hir_id),
2032         _ => false,
2033     })
2034 }
2035
2036 /// Returns a list of type predicates for the definition with ID `def_id`, including inferred
2037 /// lifetime constraints. This includes all predicates returned by `explicit_predicates_of`, plus
2038 /// inferred constraints concerning which regions outlive other regions.
2039 fn predicates_defined_on(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2040     debug!("predicates_defined_on({:?})", def_id);
2041     let mut result = tcx.explicit_predicates_of(def_id);
2042     debug!("predicates_defined_on: explicit_predicates_of({:?}) = {:?}", def_id, result,);
2043     let inferred_outlives = tcx.inferred_outlives_of(def_id);
2044     if !inferred_outlives.is_empty() {
2045         debug!(
2046             "predicates_defined_on: inferred_outlives_of({:?}) = {:?}",
2047             def_id, inferred_outlives,
2048         );
2049         if result.predicates.is_empty() {
2050             result.predicates = inferred_outlives;
2051         } else {
2052             result.predicates = tcx
2053                 .arena
2054                 .alloc_from_iter(result.predicates.iter().chain(inferred_outlives).copied());
2055         }
2056     }
2057     debug!("predicates_defined_on({:?}) = {:?}", def_id, result);
2058     result
2059 }
2060
2061 /// Returns a list of all type predicates (explicit and implicit) for the definition with
2062 /// ID `def_id`. This includes all predicates returned by `predicates_defined_on`, plus
2063 /// `Self: Trait` predicates for traits.
2064 fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2065     let mut result = tcx.predicates_defined_on(def_id);
2066
2067     if tcx.is_trait(def_id) {
2068         // For traits, add `Self: Trait` predicate. This is
2069         // not part of the predicates that a user writes, but it
2070         // is something that one must prove in order to invoke a
2071         // method or project an associated type.
2072         //
2073         // In the chalk setup, this predicate is not part of the
2074         // "predicates" for a trait item. But it is useful in
2075         // rustc because if you directly (e.g.) invoke a trait
2076         // method like `Trait::method(...)`, you must naturally
2077         // prove that the trait applies to the types that were
2078         // used, and adding the predicate into this list ensures
2079         // that this is done.
2080         let span = tcx.def_span(def_id);
2081         result.predicates =
2082             tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(std::iter::once((
2083                 ty::TraitRef::identity(tcx, def_id).without_const().to_predicate(),
2084                 span,
2085             ))));
2086     }
2087     debug!("predicates_of(def_id={:?}) = {:?}", def_id, result);
2088     result
2089 }
2090
2091 /// Returns a list of user-specified type predicates for the definition with ID `def_id`.
2092 /// N.B., this does not include any implied/inferred constraints.
2093 fn explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2094     use rustc_data_structures::fx::FxHashSet;
2095     use rustc_hir::*;
2096
2097     debug!("explicit_predicates_of(def_id={:?})", def_id);
2098
2099     /// A data structure with unique elements, which preserves order of insertion.
2100     /// Preserving the order of insertion is important here so as not to break
2101     /// compile-fail UI tests.
2102     // FIXME(eddyb) just use `IndexSet` from `indexmap`.
2103     struct UniquePredicates<'tcx> {
2104         predicates: Vec<(ty::Predicate<'tcx>, Span)>,
2105         uniques: FxHashSet<(ty::Predicate<'tcx>, Span)>,
2106     }
2107
2108     impl<'tcx> UniquePredicates<'tcx> {
2109         fn new() -> Self {
2110             UniquePredicates { predicates: vec![], uniques: FxHashSet::default() }
2111         }
2112
2113         fn push(&mut self, value: (ty::Predicate<'tcx>, Span)) {
2114             if self.uniques.insert(value) {
2115                 self.predicates.push(value);
2116             }
2117         }
2118
2119         fn extend<I: IntoIterator<Item = (ty::Predicate<'tcx>, Span)>>(&mut self, iter: I) {
2120             for value in iter {
2121                 self.push(value);
2122             }
2123         }
2124     }
2125
2126     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2127     let node = tcx.hir().get(hir_id);
2128
2129     let mut is_trait = None;
2130     let mut is_default_impl_trait = None;
2131
2132     let icx = ItemCtxt::new(tcx, def_id);
2133     let constness = icx.default_constness_for_trait_bounds();
2134
2135     const NO_GENERICS: &hir::Generics<'_> = &hir::Generics::empty();
2136
2137     let mut predicates = UniquePredicates::new();
2138
2139     let ast_generics = match node {
2140         Node::TraitItem(item) => &item.generics,
2141
2142         Node::ImplItem(item) => match item.kind {
2143             ImplItemKind::OpaqueTy(ref bounds) => {
2144                 ty::print::with_no_queries(|| {
2145                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
2146                     let opaque_ty = tcx.mk_opaque(def_id, substs);
2147                     debug!(
2148                         "explicit_predicates_of({:?}): created opaque type {:?}",
2149                         def_id, opaque_ty
2150                     );
2151
2152                     // Collect the bounds, i.e., the `A + B + 'c` in `impl A + B + 'c`.
2153                     let bounds = AstConv::compute_bounds(
2154                         &icx,
2155                         opaque_ty,
2156                         bounds,
2157                         SizedByDefault::Yes,
2158                         tcx.def_span(def_id),
2159                     );
2160
2161                     predicates.extend(bounds.predicates(tcx, opaque_ty));
2162                     &item.generics
2163                 })
2164             }
2165             _ => &item.generics,
2166         },
2167
2168         Node::Item(item) => {
2169             match item.kind {
2170                 ItemKind::Impl { defaultness, ref generics, .. } => {
2171                     if defaultness.is_default() {
2172                         is_default_impl_trait = tcx.impl_trait_ref(def_id);
2173                     }
2174                     generics
2175                 }
2176                 ItemKind::Fn(.., ref generics, _)
2177                 | ItemKind::TyAlias(_, ref generics)
2178                 | ItemKind::Enum(_, ref generics)
2179                 | ItemKind::Struct(_, ref generics)
2180                 | ItemKind::Union(_, ref generics) => generics,
2181
2182                 ItemKind::Trait(_, _, ref generics, .., items) => {
2183                     is_trait = Some((ty::TraitRef::identity(tcx, def_id), items));
2184                     generics
2185                 }
2186                 ItemKind::TraitAlias(ref generics, _) => {
2187                     is_trait = Some((ty::TraitRef::identity(tcx, def_id), &[]));
2188                     generics
2189                 }
2190                 ItemKind::OpaqueTy(OpaqueTy {
2191                     ref bounds,
2192                     impl_trait_fn,
2193                     ref generics,
2194                     origin: _,
2195                 }) => {
2196                     let bounds_predicates = ty::print::with_no_queries(|| {
2197                         let substs = InternalSubsts::identity_for_item(tcx, def_id);
2198                         let opaque_ty = tcx.mk_opaque(def_id, substs);
2199
2200                         // Collect the bounds, i.e., the `A + B + 'c` in `impl A + B + 'c`.
2201                         let bounds = AstConv::compute_bounds(
2202                             &icx,
2203                             opaque_ty,
2204                             bounds,
2205                             SizedByDefault::Yes,
2206                             tcx.def_span(def_id),
2207                         );
2208
2209                         bounds.predicates(tcx, opaque_ty)
2210                     });
2211                     if impl_trait_fn.is_some() {
2212                         // opaque types
2213                         return ty::GenericPredicates {
2214                             parent: None,
2215                             predicates: tcx.arena.alloc_from_iter(bounds_predicates),
2216                         };
2217                     } else {
2218                         // named opaque types
2219                         predicates.extend(bounds_predicates);
2220                         generics
2221                     }
2222                 }
2223
2224                 _ => NO_GENERICS,
2225             }
2226         }
2227
2228         Node::ForeignItem(item) => match item.kind {
2229             ForeignItemKind::Static(..) => NO_GENERICS,
2230             ForeignItemKind::Fn(_, _, ref generics) => generics,
2231             ForeignItemKind::Type => NO_GENERICS,
2232         },
2233
2234         _ => NO_GENERICS,
2235     };
2236
2237     let generics = tcx.generics_of(def_id);
2238     let parent_count = generics.parent_count as u32;
2239     let has_own_self = generics.has_self && parent_count == 0;
2240
2241     // Below we'll consider the bounds on the type parameters (including `Self`)
2242     // and the explicit where-clauses, but to get the full set of predicates
2243     // on a trait we need to add in the supertrait bounds and bounds found on
2244     // associated types.
2245     if let Some((_trait_ref, _)) = is_trait {
2246         predicates.extend(tcx.super_predicates_of(def_id).predicates.iter().cloned());
2247     }
2248
2249     // In default impls, we can assume that the self type implements
2250     // the trait. So in:
2251     //
2252     //     default impl Foo for Bar { .. }
2253     //
2254     // we add a default where clause `Foo: Bar`. We do a similar thing for traits
2255     // (see below). Recall that a default impl is not itself an impl, but rather a
2256     // set of defaults that can be incorporated into another impl.
2257     if let Some(trait_ref) = is_default_impl_trait {
2258         predicates.push((
2259             trait_ref.to_poly_trait_ref().without_const().to_predicate(),
2260             tcx.def_span(def_id),
2261         ));
2262     }
2263
2264     // Collect the region predicates that were declared inline as
2265     // well. In the case of parameters declared on a fn or method, we
2266     // have to be careful to only iterate over early-bound regions.
2267     let mut index = parent_count + has_own_self as u32;
2268     for param in early_bound_lifetimes_from_generics(tcx, ast_generics) {
2269         let region = tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
2270             def_id: tcx.hir().local_def_id(param.hir_id),
2271             index,
2272             name: param.name.ident().name,
2273         }));
2274         index += 1;
2275
2276         match param.kind {
2277             GenericParamKind::Lifetime { .. } => {
2278                 param.bounds.iter().for_each(|bound| match bound {
2279                     hir::GenericBound::Outlives(lt) => {
2280                         let bound = AstConv::ast_region_to_region(&icx, &lt, None);
2281                         let outlives = ty::Binder::bind(ty::OutlivesPredicate(region, bound));
2282                         predicates.push((outlives.to_predicate(), lt.span));
2283                     }
2284                     _ => bug!(),
2285                 });
2286             }
2287             _ => bug!(),
2288         }
2289     }
2290
2291     // Collect the predicates that were written inline by the user on each
2292     // type parameter (e.g., `<T: Foo>`).
2293     for param in ast_generics.params {
2294         if let GenericParamKind::Type { .. } = param.kind {
2295             let name = param.name.ident().name;
2296             let param_ty = ty::ParamTy::new(index, name).to_ty(tcx);
2297             index += 1;
2298
2299             let sized = SizedByDefault::Yes;
2300             let bounds = AstConv::compute_bounds(&icx, param_ty, &param.bounds, sized, param.span);
2301             predicates.extend(bounds.predicates(tcx, param_ty));
2302         }
2303     }
2304
2305     // Add in the bounds that appear in the where-clause.
2306     let where_clause = &ast_generics.where_clause;
2307     for predicate in where_clause.predicates {
2308         match predicate {
2309             &hir::WherePredicate::BoundPredicate(ref bound_pred) => {
2310                 let ty = icx.to_ty(&bound_pred.bounded_ty);
2311
2312                 // Keep the type around in a dummy predicate, in case of no bounds.
2313                 // That way, `where Ty:` is not a complete noop (see #53696) and `Ty`
2314                 // is still checked for WF.
2315                 if bound_pred.bounds.is_empty() {
2316                     if let ty::Param(_) = ty.kind {
2317                         // This is a `where T:`, which can be in the HIR from the
2318                         // transformation that moves `?Sized` to `T`'s declaration.
2319                         // We can skip the predicate because type parameters are
2320                         // trivially WF, but also we *should*, to avoid exposing
2321                         // users who never wrote `where Type:,` themselves, to
2322                         // compiler/tooling bugs from not handling WF predicates.
2323                     } else {
2324                         let span = bound_pred.bounded_ty.span;
2325                         let predicate = ty::OutlivesPredicate(ty, tcx.mk_region(ty::ReEmpty));
2326                         predicates.push((
2327                             ty::Predicate::TypeOutlives(ty::Binder::dummy(predicate)),
2328                             span,
2329                         ));
2330                     }
2331                 }
2332
2333                 for bound in bound_pred.bounds.iter() {
2334                     match bound {
2335                         &hir::GenericBound::Trait(ref poly_trait_ref, modifier) => {
2336                             let constness = match modifier {
2337                                 hir::TraitBoundModifier::MaybeConst => ast::Constness::NotConst,
2338                                 hir::TraitBoundModifier::None => constness,
2339                                 hir::TraitBoundModifier::Maybe => bug!("this wasn't handled"),
2340                             };
2341
2342                             let mut bounds = Bounds::default();
2343                             let _ = AstConv::instantiate_poly_trait_ref(
2344                                 &icx,
2345                                 poly_trait_ref,
2346                                 constness,
2347                                 ty,
2348                                 &mut bounds,
2349                             );
2350                             predicates.extend(bounds.predicates(tcx, ty));
2351                         }
2352
2353                         &hir::GenericBound::Outlives(ref lifetime) => {
2354                             let region = AstConv::ast_region_to_region(&icx, lifetime, None);
2355                             let pred = ty::Binder::bind(ty::OutlivesPredicate(ty, region));
2356                             predicates.push((ty::Predicate::TypeOutlives(pred), lifetime.span))
2357                         }
2358                     }
2359                 }
2360             }
2361
2362             &hir::WherePredicate::RegionPredicate(ref region_pred) => {
2363                 let r1 = AstConv::ast_region_to_region(&icx, &region_pred.lifetime, None);
2364                 predicates.extend(region_pred.bounds.iter().map(|bound| {
2365                     let (r2, span) = match bound {
2366                         hir::GenericBound::Outlives(lt) => {
2367                             (AstConv::ast_region_to_region(&icx, lt, None), lt.span)
2368                         }
2369                         _ => bug!(),
2370                     };
2371                     let pred = ty::Binder::bind(ty::OutlivesPredicate(r1, r2));
2372
2373                     (ty::Predicate::RegionOutlives(pred), span)
2374                 }))
2375             }
2376
2377             &hir::WherePredicate::EqPredicate(..) => {
2378                 // FIXME(#20041)
2379             }
2380         }
2381     }
2382
2383     // Add predicates from associated type bounds.
2384     if let Some((self_trait_ref, trait_items)) = is_trait {
2385         predicates.extend(trait_items.iter().flat_map(|trait_item_ref| {
2386             associated_item_predicates(tcx, def_id, self_trait_ref, trait_item_ref)
2387         }))
2388     }
2389
2390     let mut predicates = predicates.predicates;
2391
2392     // Subtle: before we store the predicates into the tcx, we
2393     // sort them so that predicates like `T: Foo<Item=U>` come
2394     // before uses of `U`.  This avoids false ambiguity errors
2395     // in trait checking. See `setup_constraining_predicates`
2396     // for details.
2397     if let Node::Item(&Item { kind: ItemKind::Impl { .. }, .. }) = node {
2398         let self_ty = tcx.type_of(def_id);
2399         let trait_ref = tcx.impl_trait_ref(def_id);
2400         cgp::setup_constraining_predicates(
2401             tcx,
2402             &mut predicates,
2403             trait_ref,
2404             &mut cgp::parameters_for_impl(self_ty, trait_ref),
2405         );
2406     }
2407
2408     let result = ty::GenericPredicates {
2409         parent: generics.parent,
2410         predicates: tcx.arena.alloc_from_iter(predicates),
2411     };
2412     debug!("explicit_predicates_of(def_id={:?}) = {:?}", def_id, result);
2413     result
2414 }
2415
2416 fn associated_item_predicates(
2417     tcx: TyCtxt<'tcx>,
2418     def_id: DefId,
2419     self_trait_ref: ty::TraitRef<'tcx>,
2420     trait_item_ref: &hir::TraitItemRef,
2421 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2422     let trait_item = tcx.hir().trait_item(trait_item_ref.id);
2423     let item_def_id = tcx.hir().local_def_id(trait_item_ref.id.hir_id);
2424     let bounds = match trait_item.kind {
2425         hir::TraitItemKind::Type(ref bounds, _) => bounds,
2426         _ => return Vec::new(),
2427     };
2428
2429     let is_gat = !tcx.generics_of(item_def_id).params.is_empty();
2430
2431     let mut had_error = false;
2432
2433     let mut unimplemented_error = |arg_kind: &str| {
2434         if !had_error {
2435             tcx.sess
2436                 .struct_span_err(
2437                     trait_item.span,
2438                     &format!("{}-generic associated types are not yet implemented", arg_kind),
2439                 )
2440                 .note("for more information, see https://github.com/rust-lang/rust/issues/44265")
2441                 .emit();
2442             had_error = true;
2443         }
2444     };
2445
2446     let mk_bound_param = |param: &ty::GenericParamDef, _: &_| {
2447         match param.kind {
2448             ty::GenericParamDefKind::Lifetime => tcx
2449                 .mk_region(ty::RegionKind::ReLateBound(
2450                     ty::INNERMOST,
2451                     ty::BoundRegion::BrNamed(param.def_id, param.name),
2452                 ))
2453                 .into(),
2454             // FIXME(generic_associated_types): Use bound types and constants
2455             // once they are handled by the trait system.
2456             ty::GenericParamDefKind::Type { .. } => {
2457                 unimplemented_error("type");
2458                 tcx.types.err.into()
2459             }
2460             ty::GenericParamDefKind::Const => {
2461                 unimplemented_error("const");
2462                 tcx.consts.err.into()
2463             }
2464         }
2465     };
2466
2467     let bound_substs = if is_gat {
2468         // Given:
2469         //
2470         // trait X<'a, B, const C: usize> {
2471         //     type T<'d, E, const F: usize>: Default;
2472         // }
2473         //
2474         // We need to create predicates on the trait:
2475         //
2476         // for<'d, E, const F: usize>
2477         // <Self as X<'a, B, const C: usize>>::T<'d, E, const F: usize>: Sized + Default
2478         //
2479         // We substitute escaping bound parameters for the generic
2480         // arguments to the associated type which are then bound by
2481         // the `Binder` around the the predicate.
2482         //
2483         // FIXME(generic_associated_types): Currently only lifetimes are handled.
2484         self_trait_ref.substs.extend_to(tcx, item_def_id, mk_bound_param)
2485     } else {
2486         self_trait_ref.substs
2487     };
2488
2489     let assoc_ty = tcx.mk_projection(tcx.hir().local_def_id(trait_item.hir_id), bound_substs);
2490
2491     let bounds = AstConv::compute_bounds(
2492         &ItemCtxt::new(tcx, def_id),
2493         assoc_ty,
2494         bounds,
2495         SizedByDefault::Yes,
2496         trait_item.span,
2497     );
2498
2499     let predicates = bounds.predicates(tcx, assoc_ty);
2500
2501     if is_gat {
2502         // We use shifts to get the regions that we're substituting to
2503         // be bound by the binders in the `Predicate`s rather that
2504         // escaping.
2505         let shifted_in = ty::fold::shift_vars(tcx, &predicates, 1);
2506         let substituted = shifted_in.subst(tcx, bound_substs);
2507         ty::fold::shift_out_vars(tcx, &substituted, 1)
2508     } else {
2509         predicates
2510     }
2511 }
2512
2513 /// Converts a specific `GenericBound` from the AST into a set of
2514 /// predicates that apply to the self type. A vector is returned
2515 /// because this can be anywhere from zero predicates (`T: ?Sized` adds no
2516 /// predicates) to one (`T: Foo`) to many (`T: Bar<X = i32>` adds `T: Bar`
2517 /// and `<T as Bar>::X == i32`).
2518 fn predicates_from_bound<'tcx>(
2519     astconv: &dyn AstConv<'tcx>,
2520     param_ty: Ty<'tcx>,
2521     bound: &'tcx hir::GenericBound<'tcx>,
2522     constness: ast::Constness,
2523 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2524     match *bound {
2525         hir::GenericBound::Trait(ref tr, modifier) => {
2526             let constness = match modifier {
2527                 hir::TraitBoundModifier::Maybe => return vec![],
2528                 hir::TraitBoundModifier::MaybeConst => ast::Constness::NotConst,
2529                 hir::TraitBoundModifier::None => constness,
2530             };
2531
2532             let mut bounds = Bounds::default();
2533             let _ = astconv.instantiate_poly_trait_ref(tr, constness, param_ty, &mut bounds);
2534             bounds.predicates(astconv.tcx(), param_ty)
2535         }
2536         hir::GenericBound::Outlives(ref lifetime) => {
2537             let region = astconv.ast_region_to_region(lifetime, None);
2538             let pred = ty::Binder::bind(ty::OutlivesPredicate(param_ty, region));
2539             vec![(ty::Predicate::TypeOutlives(pred), lifetime.span)]
2540         }
2541     }
2542 }
2543
2544 fn compute_sig_of_foreign_fn_decl<'tcx>(
2545     tcx: TyCtxt<'tcx>,
2546     def_id: DefId,
2547     decl: &'tcx hir::FnDecl<'tcx>,
2548     abi: abi::Abi,
2549 ) -> ty::PolyFnSig<'tcx> {
2550     let unsafety = if abi == abi::Abi::RustIntrinsic {
2551         intrinsic_operation_unsafety(&tcx.item_name(def_id).as_str())
2552     } else {
2553         hir::Unsafety::Unsafe
2554     };
2555     let fty = AstConv::ty_of_fn(&ItemCtxt::new(tcx, def_id), unsafety, abi, decl, &[], None);
2556
2557     // Feature gate SIMD types in FFI, since I am not sure that the
2558     // ABIs are handled at all correctly. -huonw
2559     if abi != abi::Abi::RustIntrinsic
2560         && abi != abi::Abi::PlatformIntrinsic
2561         && !tcx.features().simd_ffi
2562     {
2563         let check = |ast_ty: &hir::Ty<'_>, ty: Ty<'_>| {
2564             if ty.is_simd() {
2565                 tcx.sess
2566                     .struct_span_err(
2567                         ast_ty.span,
2568                         &format!(
2569                             "use of SIMD type `{}` in FFI is highly experimental and \
2570                             may result in invalid code",
2571                             tcx.hir().hir_to_pretty_string(ast_ty.hir_id)
2572                         ),
2573                     )
2574                     .help("add `#![feature(simd_ffi)]` to the crate attributes to enable")
2575                     .emit();
2576             }
2577         };
2578         for (input, ty) in decl.inputs.iter().zip(*fty.inputs().skip_binder()) {
2579             check(&input, ty)
2580         }
2581         if let hir::FunctionRetTy::Return(ref ty) = decl.output {
2582             check(&ty, *fty.output().skip_binder())
2583         }
2584     }
2585
2586     fty
2587 }
2588
2589 fn is_foreign_item(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
2590     match tcx.hir().get_if_local(def_id) {
2591         Some(Node::ForeignItem(..)) => true,
2592         Some(_) => false,
2593         _ => bug!("is_foreign_item applied to non-local def-id {:?}", def_id),
2594     }
2595 }
2596
2597 fn static_mutability(tcx: TyCtxt<'_>, def_id: DefId) -> Option<hir::Mutability> {
2598     match tcx.hir().get_if_local(def_id) {
2599         Some(Node::Item(&hir::Item { kind: hir::ItemKind::Static(_, mutbl, _), .. }))
2600         | Some(Node::ForeignItem(&hir::ForeignItem {
2601             kind: hir::ForeignItemKind::Static(_, mutbl),
2602             ..
2603         })) => Some(mutbl),
2604         Some(_) => None,
2605         _ => bug!("static_mutability applied to non-local def-id {:?}", def_id),
2606     }
2607 }
2608
2609 fn from_target_feature(
2610     tcx: TyCtxt<'_>,
2611     id: DefId,
2612     attr: &ast::Attribute,
2613     whitelist: &FxHashMap<String, Option<Symbol>>,
2614     target_features: &mut Vec<Symbol>,
2615 ) {
2616     let list = match attr.meta_item_list() {
2617         Some(list) => list,
2618         None => return,
2619     };
2620     let bad_item = |span| {
2621         let msg = "malformed `target_feature` attribute input";
2622         let code = "enable = \"..\"".to_owned();
2623         tcx.sess
2624             .struct_span_err(span, &msg)
2625             .span_suggestion(span, "must be of the form", code, Applicability::HasPlaceholders)
2626             .emit();
2627     };
2628     let rust_features = tcx.features();
2629     for item in list {
2630         // Only `enable = ...` is accepted in the meta-item list.
2631         if !item.check_name(sym::enable) {
2632             bad_item(item.span());
2633             continue;
2634         }
2635
2636         // Must be of the form `enable = "..."` (a string).
2637         let value = match item.value_str() {
2638             Some(value) => value,
2639             None => {
2640                 bad_item(item.span());
2641                 continue;
2642             }
2643         };
2644
2645         // We allow comma separation to enable multiple features.
2646         target_features.extend(value.as_str().split(',').filter_map(|feature| {
2647             // Only allow whitelisted features per platform.
2648             let feature_gate = match whitelist.get(feature) {
2649                 Some(g) => g,
2650                 None => {
2651                     let msg =
2652                         format!("the feature named `{}` is not valid for this target", feature);
2653                     let mut err = tcx.sess.struct_span_err(item.span(), &msg);
2654                     err.span_label(
2655                         item.span(),
2656                         format!("`{}` is not valid for this target", feature),
2657                     );
2658                     if feature.starts_with("+") {
2659                         let valid = whitelist.contains_key(&feature[1..]);
2660                         if valid {
2661                             err.help("consider removing the leading `+` in the feature name");
2662                         }
2663                     }
2664                     err.emit();
2665                     return None;
2666                 }
2667             };
2668
2669             // Only allow features whose feature gates have been enabled.
2670             let allowed = match feature_gate.as_ref().map(|s| *s) {
2671                 Some(sym::arm_target_feature) => rust_features.arm_target_feature,
2672                 Some(sym::aarch64_target_feature) => rust_features.aarch64_target_feature,
2673                 Some(sym::hexagon_target_feature) => rust_features.hexagon_target_feature,
2674                 Some(sym::powerpc_target_feature) => rust_features.powerpc_target_feature,
2675                 Some(sym::mips_target_feature) => rust_features.mips_target_feature,
2676                 Some(sym::avx512_target_feature) => rust_features.avx512_target_feature,
2677                 Some(sym::mmx_target_feature) => rust_features.mmx_target_feature,
2678                 Some(sym::sse4a_target_feature) => rust_features.sse4a_target_feature,
2679                 Some(sym::tbm_target_feature) => rust_features.tbm_target_feature,
2680                 Some(sym::wasm_target_feature) => rust_features.wasm_target_feature,
2681                 Some(sym::cmpxchg16b_target_feature) => rust_features.cmpxchg16b_target_feature,
2682                 Some(sym::adx_target_feature) => rust_features.adx_target_feature,
2683                 Some(sym::movbe_target_feature) => rust_features.movbe_target_feature,
2684                 Some(sym::rtm_target_feature) => rust_features.rtm_target_feature,
2685                 Some(sym::f16c_target_feature) => rust_features.f16c_target_feature,
2686                 Some(name) => bug!("unknown target feature gate {}", name),
2687                 None => true,
2688             };
2689             if !allowed && id.is_local() {
2690                 feature_err(
2691                     &tcx.sess.parse_sess,
2692                     feature_gate.unwrap(),
2693                     item.span(),
2694                     &format!("the target feature `{}` is currently unstable", feature),
2695                 )
2696                 .emit();
2697             }
2698             Some(Symbol::intern(feature))
2699         }));
2700     }
2701 }
2702
2703 fn linkage_by_name(tcx: TyCtxt<'_>, def_id: DefId, name: &str) -> Linkage {
2704     use rustc::mir::mono::Linkage::*;
2705
2706     // Use the names from src/llvm/docs/LangRef.rst here. Most types are only
2707     // applicable to variable declarations and may not really make sense for
2708     // Rust code in the first place but whitelist them anyway and trust that
2709     // the user knows what s/he's doing. Who knows, unanticipated use cases
2710     // may pop up in the future.
2711     //
2712     // ghost, dllimport, dllexport and linkonce_odr_autohide are not supported
2713     // and don't have to be, LLVM treats them as no-ops.
2714     match name {
2715         "appending" => Appending,
2716         "available_externally" => AvailableExternally,
2717         "common" => Common,
2718         "extern_weak" => ExternalWeak,
2719         "external" => External,
2720         "internal" => Internal,
2721         "linkonce" => LinkOnceAny,
2722         "linkonce_odr" => LinkOnceODR,
2723         "private" => Private,
2724         "weak" => WeakAny,
2725         "weak_odr" => WeakODR,
2726         _ => {
2727             let span = tcx.hir().span_if_local(def_id);
2728             if let Some(span) = span {
2729                 tcx.sess.span_fatal(span, "invalid linkage specified")
2730             } else {
2731                 tcx.sess.fatal(&format!("invalid linkage specified: {}", name))
2732             }
2733         }
2734     }
2735 }
2736
2737 fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
2738     let attrs = tcx.get_attrs(id);
2739
2740     let mut codegen_fn_attrs = CodegenFnAttrs::new();
2741
2742     let whitelist = tcx.target_features_whitelist(LOCAL_CRATE);
2743
2744     let mut inline_span = None;
2745     let mut link_ordinal_span = None;
2746     for attr in attrs.iter() {
2747         if attr.check_name(sym::cold) {
2748             codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
2749         } else if attr.check_name(sym::rustc_allocator) {
2750             codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR;
2751         } else if attr.check_name(sym::unwind) {
2752             codegen_fn_attrs.flags |= CodegenFnAttrFlags::UNWIND;
2753         } else if attr.check_name(sym::ffi_returns_twice) {
2754             if tcx.is_foreign_item(id) {
2755                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_RETURNS_TWICE;
2756             } else {
2757                 // `#[ffi_returns_twice]` is only allowed `extern fn`s.
2758                 struct_span_err!(
2759                     tcx.sess,
2760                     attr.span,
2761                     E0724,
2762                     "`#[ffi_returns_twice]` may only be used on foreign functions"
2763                 )
2764                 .emit();
2765             }
2766         } else if attr.check_name(sym::rustc_allocator_nounwind) {
2767             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_ALLOCATOR_NOUNWIND;
2768         } else if attr.check_name(sym::naked) {
2769             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED;
2770         } else if attr.check_name(sym::no_mangle) {
2771             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
2772         } else if attr.check_name(sym::rustc_std_internal_symbol) {
2773             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
2774         } else if attr.check_name(sym::no_debug) {
2775             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_DEBUG;
2776         } else if attr.check_name(sym::used) {
2777             codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED;
2778         } else if attr.check_name(sym::thread_local) {
2779             codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL;
2780         } else if attr.check_name(sym::track_caller) {
2781             if tcx.fn_sig(id).abi() != abi::Abi::Rust {
2782                 struct_span_err!(tcx.sess, attr.span, E0737, "`#[track_caller]` requires Rust ABI")
2783                     .emit();
2784             }
2785             codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
2786         } else if attr.check_name(sym::export_name) {
2787             if let Some(s) = attr.value_str() {
2788                 if s.as_str().contains("\0") {
2789                     // `#[export_name = ...]` will be converted to a null-terminated string,
2790                     // so it may not contain any null characters.
2791                     struct_span_err!(
2792                         tcx.sess,
2793                         attr.span,
2794                         E0648,
2795                         "`export_name` may not contain null characters"
2796                     )
2797                     .emit();
2798                 }
2799                 codegen_fn_attrs.export_name = Some(s);
2800             }
2801         } else if attr.check_name(sym::target_feature) {
2802             if tcx.fn_sig(id).unsafety() == Unsafety::Normal {
2803                 let msg = "`#[target_feature(..)]` can only be applied to `unsafe` functions";
2804                 tcx.sess
2805                     .struct_span_err(attr.span, msg)
2806                     .span_label(attr.span, "can only be applied to `unsafe` functions")
2807                     .span_label(tcx.def_span(id), "not an `unsafe` function")
2808                     .emit();
2809             }
2810             from_target_feature(tcx, id, attr, &whitelist, &mut codegen_fn_attrs.target_features);
2811         } else if attr.check_name(sym::linkage) {
2812             if let Some(val) = attr.value_str() {
2813                 codegen_fn_attrs.linkage = Some(linkage_by_name(tcx, id, &val.as_str()));
2814             }
2815         } else if attr.check_name(sym::link_section) {
2816             if let Some(val) = attr.value_str() {
2817                 if val.as_str().bytes().any(|b| b == 0) {
2818                     let msg = format!(
2819                         "illegal null byte in link_section \
2820                          value: `{}`",
2821                         &val
2822                     );
2823                     tcx.sess.span_err(attr.span, &msg);
2824                 } else {
2825                     codegen_fn_attrs.link_section = Some(val);
2826                 }
2827             }
2828         } else if attr.check_name(sym::link_name) {
2829             codegen_fn_attrs.link_name = attr.value_str();
2830         } else if attr.check_name(sym::link_ordinal) {
2831             link_ordinal_span = Some(attr.span);
2832             if let ordinal @ Some(_) = check_link_ordinal(tcx, attr) {
2833                 codegen_fn_attrs.link_ordinal = ordinal;
2834             }
2835         }
2836     }
2837
2838     codegen_fn_attrs.inline = attrs.iter().fold(InlineAttr::None, |ia, attr| {
2839         if !attr.has_name(sym::inline) {
2840             return ia;
2841         }
2842         match attr.meta().map(|i| i.kind) {
2843             Some(MetaItemKind::Word) => {
2844                 mark_used(attr);
2845                 InlineAttr::Hint
2846             }
2847             Some(MetaItemKind::List(ref items)) => {
2848                 mark_used(attr);
2849                 inline_span = Some(attr.span);
2850                 if items.len() != 1 {
2851                     struct_span_err!(
2852                         tcx.sess.diagnostic(),
2853                         attr.span,
2854                         E0534,
2855                         "expected one argument"
2856                     )
2857                     .emit();
2858                     InlineAttr::None
2859                 } else if list_contains_name(&items[..], sym::always) {
2860                     InlineAttr::Always
2861                 } else if list_contains_name(&items[..], sym::never) {
2862                     InlineAttr::Never
2863                 } else {
2864                     struct_span_err!(
2865                         tcx.sess.diagnostic(),
2866                         items[0].span(),
2867                         E0535,
2868                         "invalid argument"
2869                     )
2870                     .emit();
2871
2872                     InlineAttr::None
2873                 }
2874             }
2875             Some(MetaItemKind::NameValue(_)) => ia,
2876             None => ia,
2877         }
2878     });
2879
2880     codegen_fn_attrs.optimize = attrs.iter().fold(OptimizeAttr::None, |ia, attr| {
2881         if !attr.has_name(sym::optimize) {
2882             return ia;
2883         }
2884         let err = |sp, s| struct_span_err!(tcx.sess.diagnostic(), sp, E0722, "{}", s).emit();
2885         match attr.meta().map(|i| i.kind) {
2886             Some(MetaItemKind::Word) => {
2887                 err(attr.span, "expected one argument");
2888                 ia
2889             }
2890             Some(MetaItemKind::List(ref items)) => {
2891                 mark_used(attr);
2892                 inline_span = Some(attr.span);
2893                 if items.len() != 1 {
2894                     err(attr.span, "expected one argument");
2895                     OptimizeAttr::None
2896                 } else if list_contains_name(&items[..], sym::size) {
2897                     OptimizeAttr::Size
2898                 } else if list_contains_name(&items[..], sym::speed) {
2899                     OptimizeAttr::Speed
2900                 } else {
2901                     err(items[0].span(), "invalid argument");
2902                     OptimizeAttr::None
2903                 }
2904             }
2905             Some(MetaItemKind::NameValue(_)) => ia,
2906             None => ia,
2907         }
2908     });
2909
2910     // If a function uses #[target_feature] it can't be inlined into general
2911     // purpose functions as they wouldn't have the right target features
2912     // enabled. For that reason we also forbid #[inline(always)] as it can't be
2913     // respected.
2914
2915     if codegen_fn_attrs.target_features.len() > 0 {
2916         if codegen_fn_attrs.inline == InlineAttr::Always {
2917             if let Some(span) = inline_span {
2918                 tcx.sess.span_err(
2919                     span,
2920                     "cannot use `#[inline(always)]` with \
2921                      `#[target_feature]`",
2922                 );
2923             }
2924         }
2925     }
2926
2927     // Weak lang items have the same semantics as "std internal" symbols in the
2928     // sense that they're preserved through all our LTO passes and only
2929     // strippable by the linker.
2930     //
2931     // Additionally weak lang items have predetermined symbol names.
2932     if tcx.is_weak_lang_item(id) {
2933         codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
2934     }
2935     if let Some(name) = weak_lang_items::link_name(&attrs) {
2936         codegen_fn_attrs.export_name = Some(name);
2937         codegen_fn_attrs.link_name = Some(name);
2938     }
2939     check_link_name_xor_ordinal(tcx, &codegen_fn_attrs, link_ordinal_span);
2940
2941     // Internal symbols to the standard library all have no_mangle semantics in
2942     // that they have defined symbol names present in the function name. This
2943     // also applies to weak symbols where they all have known symbol names.
2944     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
2945         codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
2946     }
2947
2948     codegen_fn_attrs
2949 }
2950
2951 fn check_link_ordinal(tcx: TyCtxt<'_>, attr: &ast::Attribute) -> Option<usize> {
2952     use syntax::ast::{Lit, LitIntType, LitKind};
2953     let meta_item_list = attr.meta_item_list();
2954     let meta_item_list: Option<&[ast::NestedMetaItem]> = meta_item_list.as_ref().map(Vec::as_ref);
2955     let sole_meta_list = match meta_item_list {
2956         Some([item]) => item.literal(),
2957         _ => None,
2958     };
2959     if let Some(Lit { kind: LitKind::Int(ordinal, LitIntType::Unsuffixed), .. }) = sole_meta_list {
2960         if *ordinal <= std::usize::MAX as u128 {
2961             Some(*ordinal as usize)
2962         } else {
2963             let msg = format!("ordinal value in `link_ordinal` is too large: `{}`", &ordinal);
2964             tcx.sess
2965                 .struct_span_err(attr.span, &msg)
2966                 .note("the value may not exceed `std::usize::MAX`")
2967                 .emit();
2968             None
2969         }
2970     } else {
2971         tcx.sess
2972             .struct_span_err(attr.span, "illegal ordinal format in `link_ordinal`")
2973             .note("an unsuffixed integer value, e.g., `1`, is expected")
2974             .emit();
2975         None
2976     }
2977 }
2978
2979 fn check_link_name_xor_ordinal(
2980     tcx: TyCtxt<'_>,
2981     codegen_fn_attrs: &CodegenFnAttrs,
2982     inline_span: Option<Span>,
2983 ) {
2984     if codegen_fn_attrs.link_name.is_none() || codegen_fn_attrs.link_ordinal.is_none() {
2985         return;
2986     }
2987     let msg = "cannot use `#[link_name]` with `#[link_ordinal]`";
2988     if let Some(span) = inline_span {
2989         tcx.sess.span_err(span, msg);
2990     } else {
2991         tcx.sess.err(msg);
2992     }
2993 }