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::Map;
  24 use rustc::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
  25 use rustc::mir::mono::Linkage;
  26 use rustc::session::parse::feature_err;
  27 use rustc::traits;
  28 use rustc::ty::query::Providers;
  29 use rustc::ty::subst::GenericArgKind;
  30 use rustc::ty::subst::{InternalSubsts, Subst};
  31 use rustc::ty::util::Discr;
  32 use rustc::ty::util::IntTypeExt;
  33 use rustc::ty::{self, AdtKind, Const, DefIdTree, ToPolyTraitRef, Ty, TyCtxt};
  34 use rustc::ty::{ReprOptions, ToPredicate};
  35 use rustc_data_structures::captures::Captures;
  36 use rustc_data_structures::fx::FxHashMap;
  37 use rustc_errors::{struct_span_err, Applicability, StashKey};
  38 use rustc_hir as hir;
  39 use rustc_hir::def::{CtorKind, DefKind, Res};
  40 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
  41 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  42 use rustc_hir::{GenericParamKind, Node, Unsafety};
  43 use rustc_span::symbol::{kw, sym, Symbol};
  44 use rustc_span::{Span, DUMMY_SP};
  45 use rustc_target::spec::abi;
  46 use syntax::ast;
  47 use syntax::ast::{Ident, MetaItemKind};
  48 use syntax::attr::{list_contains_name, mark_used, InlineAttr, OptimizeAttr};
  49
  50 use rustc_error_codes::*;
  51
  52 struct OnlySelfBounds(bool);
  53
  54 ///////////////////////////////////////////////////////////////////////////
  55 // Main entry point
  56
  57 fn collect_mod_item_types(tcx: TyCtxt<'_>, module_def_id: DefId) {
  58     tcx.hir().visit_item_likes_in_module(
  59         module_def_id,
  60         &mut CollectItemTypesVisitor { tcx }.as_deep_visitor(),
  61     );
  62 }
  63
  64 pub fn provide(providers: &mut Providers<'_>) {
  65     *providers = Providers {
  66         type_of,
  67         generics_of,
  68         predicates_of,
  69         predicates_defined_on,
  70         explicit_predicates_of,
  71         super_predicates_of,
  72         type_param_predicates,
  73         trait_def,
  74         adt_def,
  75         fn_sig,
  76         impl_trait_ref,
  77         impl_polarity,
  78         is_foreign_item,
  79         static_mutability,
  80         codegen_fn_attrs,
  81         collect_mod_item_types,
  82         ..*providers
  83     };
  84 }
  85
  86 ///////////////////////////////////////////////////////////////////////////
  87
  88 /// Context specific to some particular item. This is what implements
  89 /// `AstConv`. It has information about the predicates that are defined
  90 /// on the trait. Unfortunately, this predicate information is
  91 /// available in various different forms at various points in the
  92 /// process. So we can't just store a pointer to e.g., the AST or the
  93 /// parsed ty form, we have to be more flexible. To this end, the
  94 /// `ItemCtxt` is parameterized by a `DefId` that it uses to satisfy
  95 /// `get_type_parameter_bounds` requests, drawing the information from
  96 /// the AST (`hir::Generics`), recursively.
  97 pub struct ItemCtxt<'tcx> {
  98     tcx: TyCtxt<'tcx>,
  99     item_def_id: DefId,
 100 }
 101
 102 ///////////////////////////////////////////////////////////////////////////
 103
 104 #[derive(Default)]
 105 crate struct PlaceholderHirTyCollector(crate Vec<Span>);
 106
 107 impl<'v> Visitor<'v> for PlaceholderHirTyCollector {
 108     type Map = Map<'v>;
 109
 110     fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
 111         NestedVisitorMap::None
 112     }
 113     fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
 114         if let hir::TyKind::Infer = t.kind {
 115             self.0.push(t.span);
 116         }
 117         intravisit::walk_ty(self, t)
 118     }
 119 }
 120
 121 struct CollectItemTypesVisitor<'tcx> {
 122     tcx: TyCtxt<'tcx>,
 123 }
 124
 125 /// If there are any placeholder types (`_`), emit an error explaining that this is not allowed
 126 /// and suggest adding type parameters in the appropriate place, taking into consideration any and
 127 /// all already existing generic type parameters to avoid suggesting a name that is already in use.
 128 crate fn placeholder_type_error(
 129     tcx: TyCtxt<'tcx>,
 130     span: Span,
 131     generics: &[hir::GenericParam<'_>],
 132     placeholder_types: Vec<Span>,
 133     suggest: bool,
 134 ) {
 135     if placeholder_types.is_empty() {
 136         return;
 137     }
 138     // This is the whitelist of possible parameter names that we might suggest.
 139     let possible_names = ["T", "K", "L", "A", "B", "C"];
 140     let used_names = generics
 141         .iter()
 142         .filter_map(|p| match p.name {
 143             hir::ParamName::Plain(ident) => Some(ident.name),
 144             _ => None,
 145         })
 146         .collect::<Vec<_>>();
 147
 148     let type_name = possible_names
 149         .iter()
 150         .find(|n| !used_names.contains(&Symbol::intern(n)))
 151         .unwrap_or(&"ParamName");
 152
 153     let mut sugg: Vec<_> =
 154         placeholder_types.iter().map(|sp| (*sp, type_name.to_string())).collect();
 155     if generics.is_empty() {
 156         sugg.push((span, format!("<{}>", type_name)));
 157     } else if let Some(arg) = generics.iter().find(|arg| match arg.name {
 158         hir::ParamName::Plain(Ident { name: kw::Underscore, .. }) => true,
 159         _ => false,
 160     }) {
 161         // Account for `_` already present in cases like `struct S<_>(_);` and suggest
 162         // `struct S<T>(T);` instead of `struct S<_, T>(T);`.
 163         sugg.push((arg.span, format!("{}", type_name)));
 164     } else {
 165         sugg.push((
 166             generics.iter().last().unwrap().span.shrink_to_hi(),
 167             format!(", {}", type_name),
 168         ));
 169     }
 170     let mut err = bad_placeholder_type(tcx, placeholder_types);
 171     if suggest {
 172         err.multipart_suggestion(
 173             "use type parameters instead",
 174             sugg,
 175             Applicability::HasPlaceholders,
 176         );
 177     }
 178     err.emit();
 179 }
 180
 181 fn reject_placeholder_type_signatures_in_item(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
 182     let (generics, suggest) = match &item.kind {
 183         hir::ItemKind::Union(_, generics)
 184         | hir::ItemKind::Enum(_, generics)
 185         | hir::ItemKind::TraitAlias(generics, _)
 186         | hir::ItemKind::Trait(_, _, generics, ..)
 187         | hir::ItemKind::Impl { generics, .. }
 188         | hir::ItemKind::Struct(_, generics) => (generics, true),
 189         hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. })
 190         | hir::ItemKind::TyAlias(_, generics) => (generics, false),
 191         // `static`, `fn` and `const` are handled elsewhere to suggest appropriate type.
 192         _ => return,
 193     };
 194
 195     let mut visitor = PlaceholderHirTyCollector::default();
 196     visitor.visit_item(item);
 197
 198     placeholder_type_error(tcx, generics.span, &generics.params[..], visitor.0, suggest);
 199 }
 200
 201 impl Visitor<'tcx> for CollectItemTypesVisitor<'tcx> {
 202     type Map = Map<'tcx>;
 203
 204     fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
 205         NestedVisitorMap::OnlyBodies(&self.tcx.hir())
 206     }
 207
 208     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 209         convert_item(self.tcx, item.hir_id);
 210         reject_placeholder_type_signatures_in_item(self.tcx, item);
 211         intravisit::walk_item(self, item);
 212     }
 213
 214     fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
 215         for param in generics.params {
 216             match param.kind {
 217                 hir::GenericParamKind::Lifetime { .. } => {}
 218                 hir::GenericParamKind::Type { default: Some(_), .. } => {
 219                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 220                     self.tcx.type_of(def_id);
 221                 }
 222                 hir::GenericParamKind::Type { .. } => {}
 223                 hir::GenericParamKind::Const { .. } => {
 224                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 225                     self.tcx.type_of(def_id);
 226                 }
 227             }
 228         }
 229         intravisit::walk_generics(self, generics);
 230     }
 231
 232     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 233         if let hir::ExprKind::Closure(..) = expr.kind {
 234             let def_id = self.tcx.hir().local_def_id(expr.hir_id);
 235             self.tcx.generics_of(def_id);
 236             self.tcx.type_of(def_id);
 237         }
 238         intravisit::walk_expr(self, expr);
 239     }
 240
 241     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
 242         convert_trait_item(self.tcx, trait_item.hir_id);
 243         intravisit::walk_trait_item(self, trait_item);
 244     }
 245
 246     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 247         convert_impl_item(self.tcx, impl_item.hir_id);
 248         intravisit::walk_impl_item(self, impl_item);
 249     }
 250 }
 251
 252 ///////////////////////////////////////////////////////////////////////////
 253 // Utility types and common code for the above passes.
 254
 255 fn bad_placeholder_type(
 256     tcx: TyCtxt<'tcx>,
 257     mut spans: Vec<Span>,
 258 ) -> rustc_errors::DiagnosticBuilder<'tcx> {
 259     spans.sort();
 260     let mut err = struct_span_err!(
 261         tcx.sess,
 262         spans.clone(),
 263         E0121,
 264         "the type placeholder `_` is not allowed within types on item signatures",
 265     );
 266     for span in spans {
 267         err.span_label(span, "not allowed in type signatures");
 268     }
 269     err
 270 }
 271
 272 impl ItemCtxt<'tcx> {
 273     pub fn new(tcx: TyCtxt<'tcx>, item_def_id: DefId) -> ItemCtxt<'tcx> {
 274         ItemCtxt { tcx, item_def_id }
 275     }
 276
 277     pub fn to_ty(&self, ast_ty: &'tcx hir::Ty<'tcx>) -> Ty<'tcx> {
 278         AstConv::ast_ty_to_ty(self, ast_ty)
 279     }
 280 }
 281
 282 impl AstConv<'tcx> for ItemCtxt<'tcx> {
 283     fn tcx(&self) -> TyCtxt<'tcx> {
 284         self.tcx
 285     }
 286
 287     fn item_def_id(&self) -> Option<DefId> {
 288         Some(self.item_def_id)
 289     }
 290
 291     fn get_type_parameter_bounds(&self, span: Span, def_id: DefId) -> ty::GenericPredicates<'tcx> {
 292         self.tcx.at(span).type_param_predicates((self.item_def_id, def_id))
 293     }
 294
 295     fn re_infer(&self, _: Option<&ty::GenericParamDef>, _: Span) -> Option<ty::Region<'tcx>> {
 296         None
 297     }
 298
 299     fn allow_ty_infer(&self) -> bool {
 300         false
 301     }
 302
 303     fn ty_infer(&self, _: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
 304         self.tcx().sess.delay_span_bug(span, "bad placeholder type");
 305         self.tcx().types.err
 306     }
 307
 308     fn ct_infer(
 309         &self,
 310         _: Ty<'tcx>,
 311         _: Option<&ty::GenericParamDef>,
 312         span: Span,
 313     ) -> &'tcx Const<'tcx> {
 314         bad_placeholder_type(self.tcx(), vec![span]).emit();
 315
 316         self.tcx().consts.err
 317     }
 318
 319     fn projected_ty_from_poly_trait_ref(
 320         &self,
 321         span: Span,
 322         item_def_id: DefId,
 323         item_segment: &hir::PathSegment<'_>,
 324         poly_trait_ref: ty::PolyTraitRef<'tcx>,
 325     ) -> Ty<'tcx> {
 326         if let Some(trait_ref) = poly_trait_ref.no_bound_vars() {
 327             let item_substs = <dyn AstConv<'tcx>>::create_substs_for_associated_item(
 328                 self,
 329                 self.tcx,
 330                 span,
 331                 item_def_id,
 332                 item_segment,
 333                 trait_ref.substs,
 334             );
 335             self.tcx().mk_projection(item_def_id, item_substs)
 336         } else {
 337             // There are no late-bound regions; we can just ignore the binder.
 338             struct_span_err!(
 339                 self.tcx().sess,
 340                 span,
 341                 E0212,
 342                 "cannot extract an associated type from a higher-ranked trait bound \
 343                  in this context"
 344             )
 345             .emit();
 346             self.tcx().types.err
 347         }
 348     }
 349
 350     fn normalize_ty(&self, _span: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
 351         // Types in item signatures are not normalized to avoid undue dependencies.
 352         ty
 353     }
 354
 355     fn set_tainted_by_errors(&self) {
 356         // There's no obvious place to track this, so just let it go.
 357     }
 358
 359     fn record_ty(&self, _hir_id: hir::HirId, _ty: Ty<'tcx>, _span: Span) {
 360         // There's no place to record types from signatures?
 361     }
 362 }
 363
 364 /// Returns the predicates defined on `item_def_id` of the form
 365 /// `X: Foo` where `X` is the type parameter `def_id`.
 366 fn type_param_predicates(
 367     tcx: TyCtxt<'_>,
 368     (item_def_id, def_id): (DefId, DefId),
 369 ) -> ty::GenericPredicates<'_> {
 370     use rustc_hir::*;
 371
 372     // In the AST, bounds can derive from two places. Either
 373     // written inline like `<T: Foo>` or in a where-clause like
 374     // `where T: Foo`.
 375
 376     let param_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 377     let param_owner = tcx.hir().ty_param_owner(param_id);
 378     let param_owner_def_id = tcx.hir().local_def_id(param_owner);
 379     let generics = tcx.generics_of(param_owner_def_id);
 380     let index = generics.param_def_id_to_index[&def_id];
 381     let ty = tcx.mk_ty_param(index, tcx.hir().ty_param_name(param_id));
 382
 383     // Don't look for bounds where the type parameter isn't in scope.
 384     let parent =
 385         if item_def_id == param_owner_def_id { None } else { tcx.generics_of(item_def_id).parent };
 386
 387     let mut result = parent
 388         .map(|parent| {
 389             let icx = ItemCtxt::new(tcx, parent);
 390             icx.get_type_parameter_bounds(DUMMY_SP, def_id)
 391         })
 392         .unwrap_or_default();
 393     let mut extend = None;
 394
 395     let item_hir_id = tcx.hir().as_local_hir_id(item_def_id).unwrap();
 396     let ast_generics = match tcx.hir().get(item_hir_id) {
 397         Node::TraitItem(item) => &item.generics,
 398
 399         Node::ImplItem(item) => &item.generics,
 400
 401         Node::Item(item) => {
 402             match item.kind {
 403                 ItemKind::Fn(.., ref generics, _)
 404                 | ItemKind::Impl { ref generics, .. }
 405                 | ItemKind::TyAlias(_, ref generics)
 406                 | ItemKind::OpaqueTy(OpaqueTy { ref generics, impl_trait_fn: None, .. })
 407                 | ItemKind::Enum(_, ref generics)
 408                 | ItemKind::Struct(_, ref generics)
 409                 | ItemKind::Union(_, ref generics) => generics,
 410                 ItemKind::Trait(_, _, ref generics, ..) => {
 411                     // Implied `Self: Trait` and supertrait bounds.
 412                     if param_id == item_hir_id {
 413                         let identity_trait_ref = ty::TraitRef::identity(tcx, item_def_id);
 414                         extend = Some((identity_trait_ref.to_predicate(), item.span));
 415                     }
 416                     generics
 417                 }
 418                 _ => return result,
 419             }
 420         }
 421
 422         Node::ForeignItem(item) => match item.kind {
 423             ForeignItemKind::Fn(_, _, ref generics) => generics,
 424             _ => return result,
 425         },
 426
 427         _ => return result,
 428     };
 429
 430     let icx = ItemCtxt::new(tcx, item_def_id);
 431     let extra_predicates = extend.into_iter().chain(
 432         icx.type_parameter_bounds_in_generics(ast_generics, param_id, ty, OnlySelfBounds(true))
 433             .into_iter()
 434             .filter(|(predicate, _)| match predicate {
 435                 ty::Predicate::Trait(ref data) => data.skip_binder().self_ty().is_param(index),
 436                 _ => false,
 437             }),
 438     );
 439     result.predicates =
 440         tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(extra_predicates));
 441     result
 442 }
 443
 444 impl ItemCtxt<'tcx> {
 445     /// Finds bounds from `hir::Generics`. This requires scanning through the
 446     /// AST. We do this to avoid having to convert *all* the bounds, which
 447     /// would create artificial cycles. Instead, we can only convert the
 448     /// bounds for a type parameter `X` if `X::Foo` is used.
 449     fn type_parameter_bounds_in_generics(
 450         &self,
 451         ast_generics: &'tcx hir::Generics<'tcx>,
 452         param_id: hir::HirId,
 453         ty: Ty<'tcx>,
 454         only_self_bounds: OnlySelfBounds,
 455     ) -> Vec<(ty::Predicate<'tcx>, Span)> {
 456         let from_ty_params = ast_generics
 457             .params
 458             .iter()
 459             .filter_map(|param| match param.kind {
 460                 GenericParamKind::Type { .. } if param.hir_id == param_id => Some(&param.bounds),
 461                 _ => None,
 462             })
 463             .flat_map(|bounds| bounds.iter())
 464             .flat_map(|b| predicates_from_bound(self, ty, b));
 465
 466         let from_where_clauses = ast_generics
 467             .where_clause
 468             .predicates
 469             .iter()
 470             .filter_map(|wp| match *wp {
 471                 hir::WherePredicate::BoundPredicate(ref bp) => Some(bp),
 472                 _ => None,
 473             })
 474             .flat_map(|bp| {
 475                 let bt = if is_param(self.tcx, &bp.bounded_ty, param_id) {
 476                     Some(ty)
 477                 } else if !only_self_bounds.0 {
 478                     Some(self.to_ty(&bp.bounded_ty))
 479                 } else {
 480                     None
 481                 };
 482                 bp.bounds.iter().filter_map(move |b| bt.map(|bt| (bt, b)))
 483             })
 484             .flat_map(|(bt, b)| predicates_from_bound(self, bt, b));
 485
 486         from_ty_params.chain(from_where_clauses).collect()
 487     }
 488 }
 489
 490 /// Tests whether this is the AST for a reference to the type
 491 /// parameter with ID `param_id`. We use this so as to avoid running
 492 /// `ast_ty_to_ty`, because we want to avoid triggering an all-out
 493 /// conversion of the type to avoid inducing unnecessary cycles.
 494 fn is_param(tcx: TyCtxt<'_>, ast_ty: &hir::Ty<'_>, param_id: hir::HirId) -> bool {
 495     if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = ast_ty.kind {
 496         match path.res {
 497             Res::SelfTy(Some(def_id), None) | Res::Def(DefKind::TyParam, def_id) => {
 498                 def_id == tcx.hir().local_def_id(param_id)
 499             }
 500             _ => false,
 501         }
 502     } else {
 503         false
 504     }
 505 }
 506
 507 fn convert_item(tcx: TyCtxt<'_>, item_id: hir::HirId) {
 508     let it = tcx.hir().expect_item(item_id);
 509     debug!("convert: item {} with id {}", it.ident, it.hir_id);
 510     let def_id = tcx.hir().local_def_id(item_id);
 511     match it.kind {
 512         // These don't define types.
 513         hir::ItemKind::ExternCrate(_)
 514         | hir::ItemKind::Use(..)
 515         | hir::ItemKind::Mod(_)
 516         | hir::ItemKind::GlobalAsm(_) => {}
 517         hir::ItemKind::ForeignMod(ref foreign_mod) => {
 518             for item in foreign_mod.items {
 519                 let def_id = tcx.hir().local_def_id(item.hir_id);
 520                 tcx.generics_of(def_id);
 521                 tcx.type_of(def_id);
 522                 tcx.predicates_of(def_id);
 523                 if let hir::ForeignItemKind::Fn(..) = item.kind {
 524                     tcx.fn_sig(def_id);
 525                 }
 526             }
 527         }
 528         hir::ItemKind::Enum(ref enum_definition, _) => {
 529             tcx.generics_of(def_id);
 530             tcx.type_of(def_id);
 531             tcx.predicates_of(def_id);
 532             convert_enum_variant_types(tcx, def_id, &enum_definition.variants);
 533         }
 534         hir::ItemKind::Impl { .. } => {
 535             tcx.generics_of(def_id);
 536             tcx.type_of(def_id);
 537             tcx.impl_trait_ref(def_id);
 538             tcx.predicates_of(def_id);
 539         }
 540         hir::ItemKind::Trait(..) => {
 541             tcx.generics_of(def_id);
 542             tcx.trait_def(def_id);
 543             tcx.at(it.span).super_predicates_of(def_id);
 544             tcx.predicates_of(def_id);
 545         }
 546         hir::ItemKind::TraitAlias(..) => {
 547             tcx.generics_of(def_id);
 548             tcx.at(it.span).super_predicates_of(def_id);
 549             tcx.predicates_of(def_id);
 550         }
 551         hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 552             tcx.generics_of(def_id);
 553             tcx.type_of(def_id);
 554             tcx.predicates_of(def_id);
 555
 556             for f in struct_def.fields() {
 557                 let def_id = tcx.hir().local_def_id(f.hir_id);
 558                 tcx.generics_of(def_id);
 559                 tcx.type_of(def_id);
 560                 tcx.predicates_of(def_id);
 561             }
 562
 563             if let Some(ctor_hir_id) = struct_def.ctor_hir_id() {
 564                 convert_variant_ctor(tcx, ctor_hir_id);
 565             }
 566         }
 567
 568         // Desugared from `impl Trait`, so visited by the function's return type.
 569         hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(_), .. }) => {}
 570
 571         hir::ItemKind::OpaqueTy(..)
 572         | hir::ItemKind::TyAlias(..)
 573         | hir::ItemKind::Static(..)
 574         | hir::ItemKind::Const(..)
 575         | hir::ItemKind::Fn(..) => {
 576             tcx.generics_of(def_id);
 577             tcx.type_of(def_id);
 578             tcx.predicates_of(def_id);
 579             if let hir::ItemKind::Fn(..) = it.kind {
 580                 tcx.fn_sig(def_id);
 581             }
 582         }
 583     }
 584 }
 585
 586 fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::HirId) {
 587     let trait_item = tcx.hir().expect_trait_item(trait_item_id);
 588     let def_id = tcx.hir().local_def_id(trait_item.hir_id);
 589     tcx.generics_of(def_id);
 590
 591     match trait_item.kind {
 592         hir::TraitItemKind::Const(..)
 593         | hir::TraitItemKind::Type(_, Some(_))
 594         | hir::TraitItemKind::Method(..) => {
 595             tcx.type_of(def_id);
 596             if let hir::TraitItemKind::Method(..) = trait_item.kind {
 597                 tcx.fn_sig(def_id);
 598             }
 599         }
 600
 601         hir::TraitItemKind::Type(_, None) => {}
 602     };
 603
 604     tcx.predicates_of(def_id);
 605 }
 606
 607 fn convert_impl_item(tcx: TyCtxt<'_>, impl_item_id: hir::HirId) {
 608     let def_id = tcx.hir().local_def_id(impl_item_id);
 609     tcx.generics_of(def_id);
 610     tcx.type_of(def_id);
 611     tcx.predicates_of(def_id);
 612     if let hir::ImplItemKind::Method(..) = tcx.hir().expect_impl_item(impl_item_id).kind {
 613         tcx.fn_sig(def_id);
 614     }
 615 }
 616
 617 fn convert_variant_ctor(tcx: TyCtxt<'_>, ctor_id: hir::HirId) {
 618     let def_id = tcx.hir().local_def_id(ctor_id);
 619     tcx.generics_of(def_id);
 620     tcx.type_of(def_id);
 621     tcx.predicates_of(def_id);
 622 }
 623
 624 fn convert_enum_variant_types(tcx: TyCtxt<'_>, def_id: DefId, variants: &[hir::Variant<'_>]) {
 625     let def = tcx.adt_def(def_id);
 626     let repr_type = def.repr.discr_type();
 627     let initial = repr_type.initial_discriminant(tcx);
 628     let mut prev_discr = None::<Discr<'_>>;
 629
 630     // fill the discriminant values and field types
 631     for variant in variants {
 632         let wrapped_discr = prev_discr.map_or(initial, |d| d.wrap_incr(tcx));
 633         prev_discr = Some(
 634             if let Some(ref e) = variant.disr_expr {
 635                 let expr_did = tcx.hir().local_def_id(e.hir_id);
 636                 def.eval_explicit_discr(tcx, expr_did)
 637             } else if let Some(discr) = repr_type.disr_incr(tcx, prev_discr) {
 638                 Some(discr)
 639             } else {
 640                 struct_span_err!(tcx.sess, variant.span, E0370, "enum discriminant overflowed")
 641                     .span_label(
 642                         variant.span,
 643                         format!("overflowed on value after {}", prev_discr.unwrap()),
 644                     )
 645                     .note(&format!(
 646                         "explicitly set `{} = {}` if that is desired outcome",
 647                         variant.ident, wrapped_discr
 648                     ))
 649                     .emit();
 650                 None
 651             }
 652             .unwrap_or(wrapped_discr),
 653         );
 654
 655         for f in variant.data.fields() {
 656             let def_id = tcx.hir().local_def_id(f.hir_id);
 657             tcx.generics_of(def_id);
 658             tcx.type_of(def_id);
 659             tcx.predicates_of(def_id);
 660         }
 661
 662         // Convert the ctor, if any. This also registers the variant as
 663         // an item.
 664         if let Some(ctor_hir_id) = variant.data.ctor_hir_id() {
 665             convert_variant_ctor(tcx, ctor_hir_id);
 666         }
 667     }
 668 }
 669
 670 fn convert_variant(
 671     tcx: TyCtxt<'_>,
 672     variant_did: Option<DefId>,
 673     ctor_did: Option<DefId>,
 674     ident: Ident,
 675     discr: ty::VariantDiscr,
 676     def: &hir::VariantData<'_>,
 677     adt_kind: ty::AdtKind,
 678     parent_did: DefId,
 679 ) -> ty::VariantDef {
 680     let mut seen_fields: FxHashMap<ast::Ident, Span> = Default::default();
 681     let hir_id = tcx.hir().as_local_hir_id(variant_did.unwrap_or(parent_did)).unwrap();
 682     let fields = def
 683         .fields()
 684         .iter()
 685         .map(|f| {
 686             let fid = tcx.hir().local_def_id(f.hir_id);
 687             let dup_span = seen_fields.get(&f.ident.modern()).cloned();
 688             if let Some(prev_span) = dup_span {
 689                 struct_span_err!(
 690                     tcx.sess,
 691                     f.span,
 692                     E0124,
 693                     "field `{}` is already declared",
 694                     f.ident
 695                 )
 696                 .span_label(f.span, "field already declared")
 697                 .span_label(prev_span, format!("`{}` first declared here", f.ident))
 698                 .emit();
 699             } else {
 700                 seen_fields.insert(f.ident.modern(), f.span);
 701             }
 702
 703             ty::FieldDef {
 704                 did: fid,
 705                 ident: f.ident,
 706                 vis: ty::Visibility::from_hir(&f.vis, hir_id, tcx),
 707             }
 708         })
 709         .collect();
 710     let recovered = match def {
 711         hir::VariantData::Struct(_, r) => *r,
 712         _ => false,
 713     };
 714     ty::VariantDef::new(
 715         tcx,
 716         ident,
 717         variant_did,
 718         ctor_did,
 719         discr,
 720         fields,
 721         CtorKind::from_hir(def),
 722         adt_kind,
 723         parent_did,
 724         recovered,
 725     )
 726 }
 727
 728 fn adt_def(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::AdtDef {
 729     use rustc_hir::*;
 730
 731     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 732     let item = match tcx.hir().get(hir_id) {
 733         Node::Item(item) => item,
 734         _ => bug!(),
 735     };
 736
 737     let repr = ReprOptions::new(tcx, def_id);
 738     let (kind, variants) = match item.kind {
 739         ItemKind::Enum(ref def, _) => {
 740             let mut distance_from_explicit = 0;
 741             let variants = def
 742                 .variants
 743                 .iter()
 744                 .map(|v| {
 745                     let variant_did = Some(tcx.hir().local_def_id(v.id));
 746                     let ctor_did =
 747                         v.data.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
 748
 749                     let discr = if let Some(ref e) = v.disr_expr {
 750                         distance_from_explicit = 0;
 751                         ty::VariantDiscr::Explicit(tcx.hir().local_def_id(e.hir_id))
 752                     } else {
 753                         ty::VariantDiscr::Relative(distance_from_explicit)
 754                     };
 755                     distance_from_explicit += 1;
 756
 757                     convert_variant(
 758                         tcx,
 759                         variant_did,
 760                         ctor_did,
 761                         v.ident,
 762                         discr,
 763                         &v.data,
 764                         AdtKind::Enum,
 765                         def_id,
 766                     )
 767                 })
 768                 .collect();
 769
 770             (AdtKind::Enum, variants)
 771         }
 772         ItemKind::Struct(ref def, _) => {
 773             let variant_did = None;
 774             let ctor_did = def.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
 775
 776             let variants = std::iter::once(convert_variant(
 777                 tcx,
 778                 variant_did,
 779                 ctor_did,
 780                 item.ident,
 781                 ty::VariantDiscr::Relative(0),
 782                 def,
 783                 AdtKind::Struct,
 784                 def_id,
 785             ))
 786             .collect();
 787
 788             (AdtKind::Struct, variants)
 789         }
 790         ItemKind::Union(ref def, _) => {
 791             let variant_did = None;
 792             let ctor_did = def.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
 793
 794             let variants = std::iter::once(convert_variant(
 795                 tcx,
 796                 variant_did,
 797                 ctor_did,
 798                 item.ident,
 799                 ty::VariantDiscr::Relative(0),
 800                 def,
 801                 AdtKind::Union,
 802                 def_id,
 803             ))
 804             .collect();
 805
 806             (AdtKind::Union, variants)
 807         }
 808         _ => bug!(),
 809     };
 810     tcx.alloc_adt_def(def_id, kind, variants, repr)
 811 }
 812
 813 /// Ensures that the super-predicates of the trait with a `DefId`
 814 /// of `trait_def_id` are converted and stored. This also ensures that
 815 /// the transitive super-predicates are converted.
 816 fn super_predicates_of(tcx: TyCtxt<'_>, trait_def_id: DefId) -> ty::GenericPredicates<'_> {
 817     debug!("super_predicates(trait_def_id={:?})", trait_def_id);
 818     let trait_hir_id = tcx.hir().as_local_hir_id(trait_def_id).unwrap();
 819
 820     let item = match tcx.hir().get(trait_hir_id) {
 821         Node::Item(item) => item,
 822         _ => bug!("trait_node_id {} is not an item", trait_hir_id),
 823     };
 824
 825     let (generics, bounds) = match item.kind {
 826         hir::ItemKind::Trait(.., ref generics, ref supertraits, _) => (generics, supertraits),
 827         hir::ItemKind::TraitAlias(ref generics, ref supertraits) => (generics, supertraits),
 828         _ => span_bug!(item.span, "super_predicates invoked on non-trait"),
 829     };
 830
 831     let icx = ItemCtxt::new(tcx, trait_def_id);
 832
 833     // Convert the bounds that follow the colon, e.g., `Bar + Zed` in `trait Foo: Bar + Zed`.
 834     let self_param_ty = tcx.types.self_param;
 835     let superbounds1 =
 836         AstConv::compute_bounds(&icx, self_param_ty, bounds, SizedByDefault::No, item.span);
 837
 838     let superbounds1 = superbounds1.predicates(tcx, self_param_ty);
 839
 840     // Convert any explicit superbounds in the where-clause,
 841     // e.g., `trait Foo where Self: Bar`.
 842     // In the case of trait aliases, however, we include all bounds in the where-clause,
 843     // so e.g., `trait Foo = where u32: PartialEq<Self>` would include `u32: PartialEq<Self>`
 844     // as one of its "superpredicates".
 845     let is_trait_alias = tcx.is_trait_alias(trait_def_id);
 846     let superbounds2 = icx.type_parameter_bounds_in_generics(
 847         generics,
 848         item.hir_id,
 849         self_param_ty,
 850         OnlySelfBounds(!is_trait_alias),
 851     );
 852
 853     // Combine the two lists to form the complete set of superbounds:
 854     let superbounds = &*tcx.arena.alloc_from_iter(superbounds1.into_iter().chain(superbounds2));
 855
 856     // Now require that immediate supertraits are converted,
 857     // which will, in turn, reach indirect supertraits.
 858     for &(pred, span) in superbounds {
 859         debug!("superbound: {:?}", pred);
 860         if let ty::Predicate::Trait(bound) = pred {
 861             tcx.at(span).super_predicates_of(bound.def_id());
 862         }
 863     }
 864
 865     ty::GenericPredicates { parent: None, predicates: superbounds }
 866 }
 867
 868 fn trait_def(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::TraitDef {
 869     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 870     let item = tcx.hir().expect_item(hir_id);
 871
 872     let (is_auto, unsafety) = match item.kind {
 873         hir::ItemKind::Trait(is_auto, unsafety, ..) => (is_auto == hir::IsAuto::Yes, unsafety),
 874         hir::ItemKind::TraitAlias(..) => (false, hir::Unsafety::Normal),
 875         _ => span_bug!(item.span, "trait_def_of_item invoked on non-trait"),
 876     };
 877
 878     let paren_sugar = tcx.has_attr(def_id, sym::rustc_paren_sugar);
 879     if paren_sugar && !tcx.features().unboxed_closures {
 880         tcx.sess
 881             .struct_span_err(
 882                 item.span,
 883                 "the `#[rustc_paren_sugar]` attribute is a temporary means of controlling \
 884              which traits can use parenthetical notation",
 885             )
 886             .help("add `#![feature(unboxed_closures)]` to the crate attributes to use it")
 887             .emit();
 888     }
 889
 890     let is_marker = tcx.has_attr(def_id, sym::marker);
 891     let def_path_hash = tcx.def_path_hash(def_id);
 892     let def = ty::TraitDef::new(def_id, unsafety, paren_sugar, is_auto, is_marker, def_path_hash);
 893     tcx.arena.alloc(def)
 894 }
 895
 896 fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<Span> {
 897     struct LateBoundRegionsDetector<'tcx> {
 898         tcx: TyCtxt<'tcx>,
 899         outer_index: ty::DebruijnIndex,
 900         has_late_bound_regions: Option<Span>,
 901     }
 902
 903     impl Visitor<'tcx> for LateBoundRegionsDetector<'tcx> {
 904         type Map = Map<'tcx>;
 905
 906         fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
 907             NestedVisitorMap::None
 908         }
 909
 910         fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
 911             if self.has_late_bound_regions.is_some() {
 912                 return;
 913             }
 914             match ty.kind {
 915                 hir::TyKind::BareFn(..) => {
 916                     self.outer_index.shift_in(1);
 917                     intravisit::walk_ty(self, ty);
 918                     self.outer_index.shift_out(1);
 919                 }
 920                 _ => intravisit::walk_ty(self, ty),
 921             }
 922         }
 923
 924         fn visit_poly_trait_ref(
 925             &mut self,
 926             tr: &'tcx hir::PolyTraitRef<'tcx>,
 927             m: hir::TraitBoundModifier,
 928         ) {
 929             if self.has_late_bound_regions.is_some() {
 930                 return;
 931             }
 932             self.outer_index.shift_in(1);
 933             intravisit::walk_poly_trait_ref(self, tr, m);
 934             self.outer_index.shift_out(1);
 935         }
 936
 937         fn visit_lifetime(&mut self, lt: &'tcx hir::Lifetime) {
 938             if self.has_late_bound_regions.is_some() {
 939                 return;
 940             }
 941
 942             match self.tcx.named_region(lt.hir_id) {
 943                 Some(rl::Region::Static) | Some(rl::Region::EarlyBound(..)) => {}
 944                 Some(rl::Region::LateBound(debruijn, _, _))
 945                 | Some(rl::Region::LateBoundAnon(debruijn, _))
 946                     if debruijn < self.outer_index => {}
 947                 Some(rl::Region::LateBound(..))
 948                 | Some(rl::Region::LateBoundAnon(..))
 949                 | Some(rl::Region::Free(..))
 950                 | None => {
 951                     self.has_late_bound_regions = Some(lt.span);
 952                 }
 953             }
 954         }
 955     }
 956
 957     fn has_late_bound_regions<'tcx>(
 958         tcx: TyCtxt<'tcx>,
 959         generics: &'tcx hir::Generics<'tcx>,
 960         decl: &'tcx hir::FnDecl<'tcx>,
 961     ) -> Option<Span> {
 962         let mut visitor = LateBoundRegionsDetector {
 963             tcx,
 964             outer_index: ty::INNERMOST,
 965             has_late_bound_regions: None,
 966         };
 967         for param in generics.params {
 968             if let GenericParamKind::Lifetime { .. } = param.kind {
 969                 if tcx.is_late_bound(param.hir_id) {
 970                     return Some(param.span);
 971                 }
 972             }
 973         }
 974         visitor.visit_fn_decl(decl);
 975         visitor.has_late_bound_regions
 976     }
 977
 978     match node {
 979         Node::TraitItem(item) => match item.kind {
 980             hir::TraitItemKind::Method(ref sig, _) => {
 981                 has_late_bound_regions(tcx, &item.generics, &sig.decl)
 982             }
 983             _ => None,
 984         },
 985         Node::ImplItem(item) => match item.kind {
 986             hir::ImplItemKind::Method(ref sig, _) => {
 987                 has_late_bound_regions(tcx, &item.generics, &sig.decl)
 988             }
 989             _ => None,
 990         },
 991         Node::ForeignItem(item) => match item.kind {
 992             hir::ForeignItemKind::Fn(ref fn_decl, _, ref generics) => {
 993                 has_late_bound_regions(tcx, generics, fn_decl)
 994             }
 995             _ => None,
 996         },
 997         Node::Item(item) => match item.kind {
 998             hir::ItemKind::Fn(ref sig, .., ref generics, _) => {
 999                 has_late_bound_regions(tcx, generics, &sig.decl)
1000             }
1001             _ => None,
1002         },
1003         _ => None,
1004     }
1005 }
1006
1007 fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::Generics {
1008     use rustc_hir::*;
1009
1010     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1011
1012     let node = tcx.hir().get(hir_id);
1013     let parent_def_id = match node {
1014         Node::ImplItem(_)
1015         | Node::TraitItem(_)
1016         | Node::Variant(_)
1017         | Node::Ctor(..)
1018         | Node::Field(_) => {
1019             let parent_id = tcx.hir().get_parent_item(hir_id);
1020             Some(tcx.hir().local_def_id(parent_id))
1021         }
1022         // FIXME(#43408) enable this always when we get lazy normalization.
1023         Node::AnonConst(_) => {
1024             // HACK(eddyb) this provides the correct generics when
1025             // `feature(const_generics)` is enabled, so that const expressions
1026             // used with const generics, e.g. `Foo<{N+1}>`, can work at all.
1027             if tcx.features().const_generics {
1028                 let parent_id = tcx.hir().get_parent_item(hir_id);
1029                 Some(tcx.hir().local_def_id(parent_id))
1030             } else {
1031                 None
1032             }
1033         }
1034         Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => {
1035             Some(tcx.closure_base_def_id(def_id))
1036         }
1037         Node::Item(item) => match item.kind {
1038             ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn, .. }) => impl_trait_fn,
1039             _ => None,
1040         },
1041         _ => None,
1042     };
1043
1044     let mut opt_self = None;
1045     let mut allow_defaults = false;
1046
1047     let no_generics = hir::Generics::empty();
1048     let ast_generics = match node {
1049         Node::TraitItem(item) => &item.generics,
1050
1051         Node::ImplItem(item) => &item.generics,
1052
1053         Node::Item(item) => {
1054             match item.kind {
1055                 ItemKind::Fn(.., ref generics, _) | ItemKind::Impl { ref generics, .. } => generics,
1056
1057                 ItemKind::TyAlias(_, ref generics)
1058                 | ItemKind::Enum(_, ref generics)
1059                 | ItemKind::Struct(_, ref generics)
1060                 | ItemKind::OpaqueTy(hir::OpaqueTy { ref generics, .. })
1061                 | ItemKind::Union(_, ref generics) => {
1062                     allow_defaults = true;
1063                     generics
1064                 }
1065
1066                 ItemKind::Trait(_, _, ref generics, ..)
1067                 | ItemKind::TraitAlias(ref generics, ..) => {
1068                     // Add in the self type parameter.
1069                     //
1070                     // Something of a hack: use the node id for the trait, also as
1071                     // the node id for the Self type parameter.
1072                     let param_id = item.hir_id;
1073
1074                     opt_self = Some(ty::GenericParamDef {
1075                         index: 0,
1076                         name: kw::SelfUpper,
1077                         def_id: tcx.hir().local_def_id(param_id),
1078                         pure_wrt_drop: false,
1079                         kind: ty::GenericParamDefKind::Type {
1080                             has_default: false,
1081                             object_lifetime_default: rl::Set1::Empty,
1082                             synthetic: None,
1083                         },
1084                     });
1085
1086                     allow_defaults = true;
1087                     generics
1088                 }
1089
1090                 _ => &no_generics,
1091             }
1092         }
1093
1094         Node::ForeignItem(item) => match item.kind {
1095             ForeignItemKind::Static(..) => &no_generics,
1096             ForeignItemKind::Fn(_, _, ref generics) => generics,
1097             ForeignItemKind::Type => &no_generics,
1098         },
1099
1100         _ => &no_generics,
1101     };
1102
1103     let has_self = opt_self.is_some();
1104     let mut parent_has_self = false;
1105     let mut own_start = has_self as u32;
1106     let parent_count = parent_def_id.map_or(0, |def_id| {
1107         let generics = tcx.generics_of(def_id);
1108         assert_eq!(has_self, false);
1109         parent_has_self = generics.has_self;
1110         own_start = generics.count() as u32;
1111         generics.parent_count + generics.params.len()
1112     });
1113
1114     let mut params: Vec<_> = opt_self.into_iter().collect();
1115
1116     let early_lifetimes = early_bound_lifetimes_from_generics(tcx, ast_generics);
1117     params.extend(early_lifetimes.enumerate().map(|(i, param)| ty::GenericParamDef {
1118         name: param.name.ident().name,
1119         index: own_start + i as u32,
1120         def_id: tcx.hir().local_def_id(param.hir_id),
1121         pure_wrt_drop: param.pure_wrt_drop,
1122         kind: ty::GenericParamDefKind::Lifetime,
1123     }));
1124
1125     let object_lifetime_defaults = tcx.object_lifetime_defaults(hir_id);
1126
1127     // Now create the real type parameters.
1128     let type_start = own_start - has_self as u32 + params.len() as u32;
1129     let mut i = 0;
1130     params.extend(ast_generics.params.iter().filter_map(|param| {
1131         let kind = match param.kind {
1132             GenericParamKind::Type { ref default, synthetic, .. } => {
1133                 if !allow_defaults && default.is_some() {
1134                     if !tcx.features().default_type_parameter_fallback {
1135                         tcx.lint_hir(
1136                             lint::builtin::INVALID_TYPE_PARAM_DEFAULT,
1137                             param.hir_id,
1138                             param.span,
1139                             &format!(
1140                                 "defaults for type parameters are only allowed in \
1141                                         `struct`, `enum`, `type`, or `trait` definitions."
1142                             ),
1143                         );
1144                     }
1145                 }
1146
1147                 ty::GenericParamDefKind::Type {
1148                     has_default: default.is_some(),
1149                     object_lifetime_default: object_lifetime_defaults
1150                         .as_ref()
1151                         .map_or(rl::Set1::Empty, |o| o[i]),
1152                     synthetic,
1153                 }
1154             }
1155             GenericParamKind::Const { .. } => ty::GenericParamDefKind::Const,
1156             _ => return None,
1157         };
1158
1159         let param_def = ty::GenericParamDef {
1160             index: type_start + i as u32,
1161             name: param.name.ident().name,
1162             def_id: tcx.hir().local_def_id(param.hir_id),
1163             pure_wrt_drop: param.pure_wrt_drop,
1164             kind,
1165         };
1166         i += 1;
1167         Some(param_def)
1168     }));
1169
1170     // provide junk type parameter defs - the only place that
1171     // cares about anything but the length is instantiation,
1172     // and we don't do that for closures.
1173     if let Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(.., gen), .. }) = node {
1174         let dummy_args = if gen.is_some() {
1175             &["<yield_ty>", "<return_ty>", "<witness>"][..]
1176         } else {
1177             &["<closure_kind>", "<closure_signature>"][..]
1178         };
1179
1180         params.extend(dummy_args.iter().enumerate().map(|(i, &arg)| ty::GenericParamDef {
1181             index: type_start + i as u32,
1182             name: Symbol::intern(arg),
1183             def_id,
1184             pure_wrt_drop: false,
1185             kind: ty::GenericParamDefKind::Type {
1186                 has_default: false,
1187                 object_lifetime_default: rl::Set1::Empty,
1188                 synthetic: None,
1189             },
1190         }));
1191
1192         if let Some(upvars) = tcx.upvars(def_id) {
1193             params.extend(upvars.iter().zip((dummy_args.len() as u32)..).map(|(_, i)| {
1194                 ty::GenericParamDef {
1195                     index: type_start + i,
1196                     name: Symbol::intern("<upvar>"),
1197                     def_id,
1198                     pure_wrt_drop: false,
1199                     kind: ty::GenericParamDefKind::Type {
1200                         has_default: false,
1201                         object_lifetime_default: rl::Set1::Empty,
1202                         synthetic: None,
1203                     },
1204                 }
1205             }));
1206         }
1207     }
1208
1209     let param_def_id_to_index = params.iter().map(|param| (param.def_id, param.index)).collect();
1210
1211     tcx.arena.alloc(ty::Generics {
1212         parent: parent_def_id,
1213         parent_count,
1214         params,
1215         param_def_id_to_index,
1216         has_self: has_self || parent_has_self,
1217         has_late_bound_regions: has_late_bound_regions(tcx, node),
1218     })
1219 }
1220
1221 fn report_assoc_ty_on_inherent_impl(tcx: TyCtxt<'_>, span: Span) {
1222     struct_span_err!(
1223         tcx.sess,
1224         span,
1225         E0202,
1226         "associated types are not yet supported in inherent impls (see #8995)"
1227     )
1228     .emit();
1229 }
1230
1231 fn infer_placeholder_type(
1232     tcx: TyCtxt<'_>,
1233     def_id: DefId,
1234     body_id: hir::BodyId,
1235     span: Span,
1236     item_ident: Ident,
1237 ) -> Ty<'_> {
1238     let ty = tcx.diagnostic_only_typeck_tables_of(def_id).node_type(body_id.hir_id);
1239
1240     // If this came from a free `const` or `static mut?` item,
1241     // then the user may have written e.g. `const A = 42;`.
1242     // In this case, the parser has stashed a diagnostic for
1243     // us to improve in typeck so we do that now.
1244     match tcx.sess.diagnostic().steal_diagnostic(span, StashKey::ItemNoType) {
1245         Some(mut err) => {
1246             // The parser provided a sub-optimal `HasPlaceholders` suggestion for the type.
1247             // We are typeck and have the real type, so remove that and suggest the actual type.
1248             err.suggestions.clear();
1249             err.span_suggestion(
1250                 span,
1251                 "provide a type for the item",
1252                 format!("{}: {}", item_ident, ty),
1253                 Applicability::MachineApplicable,
1254             )
1255             .emit();
1256         }
1257         None => {
1258             let mut diag = bad_placeholder_type(tcx, vec![span]);
1259             if ty != tcx.types.err {
1260                 diag.span_suggestion(
1261                     span,
1262                     "replace `_` with the correct type",
1263                     ty.to_string(),
1264                     Applicability::MaybeIncorrect,
1265                 );
1266             }
1267             diag.emit();
1268         }
1269     }
1270
1271     ty
1272 }
1273
1274 fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
1275     use rustc_hir::*;
1276
1277     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1278
1279     let icx = ItemCtxt::new(tcx, def_id);
1280
1281     match tcx.hir().get(hir_id) {
1282         Node::TraitItem(item) => match item.kind {
1283             TraitItemKind::Method(..) => {
1284                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1285                 tcx.mk_fn_def(def_id, substs)
1286             }
1287             TraitItemKind::Const(ref ty, body_id) => body_id
1288                 .and_then(|body_id| {
1289                     if is_suggestable_infer_ty(ty) {
1290                         Some(infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident))
1291                     } else {
1292                         None
1293                     }
1294                 })
1295                 .unwrap_or_else(|| icx.to_ty(ty)),
1296             TraitItemKind::Type(_, Some(ref ty)) => icx.to_ty(ty),
1297             TraitItemKind::Type(_, None) => {
1298                 span_bug!(item.span, "associated type missing default");
1299             }
1300         },
1301
1302         Node::ImplItem(item) => match item.kind {
1303             ImplItemKind::Method(..) => {
1304                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1305                 tcx.mk_fn_def(def_id, substs)
1306             }
1307             ImplItemKind::Const(ref ty, body_id) => {
1308                 if is_suggestable_infer_ty(ty) {
1309                     infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident)
1310                 } else {
1311                     icx.to_ty(ty)
1312                 }
1313             }
1314             ImplItemKind::OpaqueTy(_) => {
1315                 if tcx.impl_trait_ref(tcx.hir().get_parent_did(hir_id)).is_none() {
1316                     report_assoc_ty_on_inherent_impl(tcx, item.span);
1317                 }
1318
1319                 find_opaque_ty_constraints(tcx, def_id)
1320             }
1321             ImplItemKind::TyAlias(ref ty) => {
1322                 if tcx.impl_trait_ref(tcx.hir().get_parent_did(hir_id)).is_none() {
1323                     report_assoc_ty_on_inherent_impl(tcx, item.span);
1324                 }
1325
1326                 icx.to_ty(ty)
1327             }
1328         },
1329
1330         Node::Item(item) => {
1331             match item.kind {
1332                 ItemKind::Static(ref ty, .., body_id) | ItemKind::Const(ref ty, body_id) => {
1333                     if is_suggestable_infer_ty(ty) {
1334                         infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident)
1335                     } else {
1336                         icx.to_ty(ty)
1337                     }
1338                 }
1339                 ItemKind::TyAlias(ref self_ty, _) | ItemKind::Impl { ref self_ty, .. } => {
1340                     icx.to_ty(self_ty)
1341                 }
1342                 ItemKind::Fn(..) => {
1343                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
1344                     tcx.mk_fn_def(def_id, substs)
1345                 }
1346                 ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
1347                     let def = tcx.adt_def(def_id);
1348                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
1349                     tcx.mk_adt(def, substs)
1350                 }
1351                 ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: None, .. }) => {
1352                     find_opaque_ty_constraints(tcx, def_id)
1353                 }
1354                 // Opaque types desugared from `impl Trait`.
1355                 ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(owner), .. }) => {
1356                     tcx.typeck_tables_of(owner)
1357                         .concrete_opaque_types
1358                         .get(&def_id)
1359                         .map(|opaque| opaque.concrete_type)
1360                         .unwrap_or_else(|| {
1361                             // This can occur if some error in the
1362                             // owner fn prevented us from populating
1363                             // the `concrete_opaque_types` table.
1364                             tcx.sess.delay_span_bug(
1365                                 DUMMY_SP,
1366                                 &format!(
1367                                     "owner {:?} has no opaque type for {:?} in its tables",
1368                                     owner, def_id,
1369                                 ),
1370                             );
1371                             tcx.types.err
1372                         })
1373                 }
1374                 ItemKind::Trait(..)
1375                 | ItemKind::TraitAlias(..)
1376                 | ItemKind::Mod(..)
1377                 | ItemKind::ForeignMod(..)
1378                 | ItemKind::GlobalAsm(..)
1379                 | ItemKind::ExternCrate(..)
1380                 | ItemKind::Use(..) => {
1381                     span_bug!(
1382                         item.span,
1383                         "compute_type_of_item: unexpected item type: {:?}",
1384                         item.kind
1385                     );
1386                 }
1387             }
1388         }
1389
1390         Node::ForeignItem(foreign_item) => match foreign_item.kind {
1391             ForeignItemKind::Fn(..) => {
1392                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1393                 tcx.mk_fn_def(def_id, substs)
1394             }
1395             ForeignItemKind::Static(ref t, _) => icx.to_ty(t),
1396             ForeignItemKind::Type => tcx.mk_foreign(def_id),
1397         },
1398
1399         Node::Ctor(&ref def) | Node::Variant(hir::Variant { data: ref def, .. }) => match *def {
1400             VariantData::Unit(..) | VariantData::Struct(..) => {
1401                 tcx.type_of(tcx.hir().get_parent_did(hir_id))
1402             }
1403             VariantData::Tuple(..) => {
1404                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
1405                 tcx.mk_fn_def(def_id, substs)
1406             }
1407         },
1408
1409         Node::Field(field) => icx.to_ty(&field.ty),
1410
1411         Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(.., gen), .. }) => {
1412             if gen.is_some() {
1413                 return tcx.typeck_tables_of(def_id).node_type(hir_id);
1414             }
1415
1416             let substs = InternalSubsts::identity_for_item(tcx, def_id);
1417             tcx.mk_closure(def_id, substs)
1418         }
1419
1420         Node::AnonConst(_) => {
1421             let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
1422             match parent_node {
1423                 Node::Ty(&hir::Ty { kind: hir::TyKind::Array(_, ref constant), .. })
1424                 | Node::Ty(&hir::Ty { kind: hir::TyKind::Typeof(ref constant), .. })
1425                 | Node::Expr(&hir::Expr { kind: ExprKind::Repeat(_, ref constant), .. })
1426                     if constant.hir_id == hir_id =>
1427                 {
1428                     tcx.types.usize
1429                 }
1430
1431                 Node::Variant(Variant { disr_expr: Some(ref e), .. }) if e.hir_id == hir_id => {
1432                     tcx.adt_def(tcx.hir().get_parent_did(hir_id)).repr.discr_type().to_ty(tcx)
1433                 }
1434
1435                 Node::Ty(&hir::Ty { kind: hir::TyKind::Path(_), .. })
1436                 | Node::Expr(&hir::Expr { kind: ExprKind::Struct(..), .. })
1437                 | Node::Expr(&hir::Expr { kind: ExprKind::Path(_), .. })
1438                 | Node::TraitRef(..) => {
1439                     let path = match parent_node {
1440                         Node::Ty(&hir::Ty {
1441                             kind: hir::TyKind::Path(QPath::Resolved(_, ref path)),
1442                             ..
1443                         })
1444                         | Node::Expr(&hir::Expr {
1445                             kind: ExprKind::Path(QPath::Resolved(_, ref path)),
1446                             ..
1447                         }) => Some(&**path),
1448                         Node::Expr(&hir::Expr { kind: ExprKind::Struct(ref path, ..), .. }) => {
1449                             if let QPath::Resolved(_, ref path) = **path {
1450                                 Some(&**path)
1451                             } else {
1452                                 None
1453                             }
1454                         }
1455                         Node::TraitRef(&hir::TraitRef { ref path, .. }) => Some(&**path),
1456                         _ => None,
1457                     };
1458
1459                     if let Some(path) = path {
1460                         let arg_index = path
1461                             .segments
1462                             .iter()
1463                             .filter_map(|seg| seg.args.as_ref())
1464                             .map(|generic_args| generic_args.args.as_ref())
1465                             .find_map(|args| {
1466                                 args.iter()
1467                                     .filter(|arg| arg.is_const())
1468                                     .enumerate()
1469                                     .filter(|(_, arg)| arg.id() == hir_id)
1470                                     .map(|(index, _)| index)
1471                                     .next()
1472                             })
1473                             .unwrap_or_else(|| {
1474                                 bug!("no arg matching AnonConst in path");
1475                             });
1476
1477                         // We've encountered an `AnonConst` in some path, so we need to
1478                         // figure out which generic parameter it corresponds to and return
1479                         // the relevant type.
1480                         let generics = match path.res {
1481                             Res::Def(DefKind::Ctor(..), def_id) => {
1482                                 tcx.generics_of(tcx.parent(def_id).unwrap())
1483                             }
1484                             Res::Def(_, def_id) => tcx.generics_of(def_id),
1485                             Res::Err => return tcx.types.err,
1486                             res => {
1487                                 tcx.sess.delay_span_bug(
1488                                     DUMMY_SP,
1489                                     &format!("unexpected const parent path def {:?}", res,),
1490                                 );
1491                                 return tcx.types.err;
1492                             }
1493                         };
1494
1495                         generics
1496                             .params
1497                             .iter()
1498                             .filter(|param| {
1499                                 if let ty::GenericParamDefKind::Const = param.kind {
1500                                     true
1501                                 } else {
1502                                     false
1503                                 }
1504                             })
1505                             .nth(arg_index)
1506                             .map(|param| tcx.type_of(param.def_id))
1507                             // This is no generic parameter associated with the arg. This is
1508                             // probably from an extra arg where one is not needed.
1509                             .unwrap_or(tcx.types.err)
1510                     } else {
1511                         tcx.sess.delay_span_bug(
1512                             DUMMY_SP,
1513                             &format!("unexpected const parent path {:?}", parent_node,),
1514                         );
1515                         return tcx.types.err;
1516                     }
1517                 }
1518
1519                 x => {
1520                     tcx.sess.delay_span_bug(
1521                         DUMMY_SP,
1522                         &format!("unexpected const parent in type_of_def_id(): {:?}", x),
1523                     );
1524                     tcx.types.err
1525                 }
1526             }
1527         }
1528
1529         Node::GenericParam(param) => match &param.kind {
1530             hir::GenericParamKind::Type { default: Some(ref ty), .. } => icx.to_ty(ty),
1531             hir::GenericParamKind::Const { ty: ref hir_ty, .. } => {
1532                 let ty = icx.to_ty(hir_ty);
1533                 if !tcx.features().const_compare_raw_pointers {
1534                     let err = match ty.peel_refs().kind {
1535                         ty::FnPtr(_) => Some("function pointers"),
1536                         ty::RawPtr(_) => Some("raw pointers"),
1537                         _ => None,
1538                     };
1539                     if let Some(unsupported_type) = err {
1540                         feature_err(
1541                             &tcx.sess.parse_sess,
1542                             sym::const_compare_raw_pointers,
1543                             hir_ty.span,
1544                             &format!(
1545                                 "using {} as const generic parameters is unstable",
1546                                 unsupported_type
1547                             ),
1548                         )
1549                         .emit();
1550                     };
1551                 }
1552                 if traits::search_for_structural_match_violation(param.hir_id, param.span, tcx, ty)
1553                     .is_some()
1554                 {
1555                     struct_span_err!(
1556                         tcx.sess,
1557                         hir_ty.span,
1558                         E0741,
1559                         "the types of const generic parameters must derive `PartialEq` and `Eq`",
1560                     )
1561                     .span_label(
1562                         hir_ty.span,
1563                         format!("`{}` doesn't derive both `PartialEq` and `Eq`", ty),
1564                     )
1565                     .emit();
1566                 }
1567                 ty
1568             }
1569             x => bug!("unexpected non-type Node::GenericParam: {:?}", x),
1570         },
1571
1572         x => {
1573             bug!("unexpected sort of node in type_of_def_id(): {:?}", x);
1574         }
1575     }
1576 }
1577
1578 fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
1579     use rustc_hir::{ImplItem, Item, TraitItem};
1580
1581     debug!("find_opaque_ty_constraints({:?})", def_id);
1582
1583     struct ConstraintLocator<'tcx> {
1584         tcx: TyCtxt<'tcx>,
1585         def_id: DefId,
1586         // (first found type span, actual type, mapping from the opaque type's generic
1587         // parameters to the concrete type's generic parameters)
1588         //
1589         // The mapping is an index for each use site of a generic parameter in the concrete type
1590         //
1591         // The indices index into the generic parameters on the opaque type.
1592         found: Option<(Span, Ty<'tcx>, Vec<usize>)>,
1593     }
1594
1595     impl ConstraintLocator<'tcx> {
1596         fn check(&mut self, def_id: DefId) {
1597             // Don't try to check items that cannot possibly constrain the type.
1598             if !self.tcx.has_typeck_tables(def_id) {
1599                 debug!(
1600                     "find_opaque_ty_constraints: no constraint for `{:?}` at `{:?}`: no tables",
1601                     self.def_id, def_id,
1602                 );
1603                 return;
1604             }
1605             let ty = self.tcx.typeck_tables_of(def_id).concrete_opaque_types.get(&self.def_id);
1606             if let Some(ty::ResolvedOpaqueTy { concrete_type, substs }) = ty {
1607                 debug!(
1608                     "find_opaque_ty_constraints: found constraint for `{:?}` at `{:?}`: {:?}",
1609                     self.def_id, def_id, ty,
1610                 );
1611
1612                 // FIXME(oli-obk): trace the actual span from inference to improve errors.
1613                 let span = self.tcx.def_span(def_id);
1614                 // used to quickly look up the position of a generic parameter
1615                 let mut index_map: FxHashMap<ty::ParamTy, usize> = FxHashMap::default();
1616                 // Skipping binder is ok, since we only use this to find generic parameters and
1617                 // their positions.
1618                 for (idx, subst) in substs.iter().enumerate() {
1619                     if let GenericArgKind::Type(ty) = subst.unpack() {
1620                         if let ty::Param(p) = ty.kind {
1621                             if index_map.insert(p, idx).is_some() {
1622                                 // There was already an entry for `p`, meaning a generic parameter
1623                                 // was used twice.
1624                                 self.tcx.sess.span_err(
1625                                     span,
1626                                     &format!(
1627                                         "defining opaque type use restricts opaque \
1628                                          type by using the generic parameter `{}` twice",
1629                                         p,
1630                                     ),
1631                                 );
1632                                 return;
1633                             }
1634                         } else {
1635                             self.tcx.sess.delay_span_bug(
1636                                 span,
1637                                 &format!(
1638                                     "non-defining opaque ty use in defining scope: {:?}, {:?}",
1639                                     concrete_type, substs,
1640                                 ),
1641                             );
1642                         }
1643                     }
1644                 }
1645                 // Compute the index within the opaque type for each generic parameter used in
1646                 // the concrete type.
1647                 let indices = concrete_type
1648                     .subst(self.tcx, substs)
1649                     .walk()
1650                     .filter_map(|t| match &t.kind {
1651                         ty::Param(p) => Some(*index_map.get(p).unwrap()),
1652                         _ => None,
1653                     })
1654                     .collect();
1655                 let is_param = |ty: Ty<'_>| match ty.kind {
1656                     ty::Param(_) => true,
1657                     _ => false,
1658                 };
1659                 let bad_substs: Vec<_> =
1660                     substs.types().enumerate().filter(|(_, ty)| !is_param(ty)).collect();
1661                 if !bad_substs.is_empty() {
1662                     let identity_substs = InternalSubsts::identity_for_item(self.tcx, self.def_id);
1663                     for (i, bad_subst) in bad_substs {
1664                         self.tcx.sess.span_err(
1665                             span,
1666                             &format!(
1667                                 "defining opaque type use does not fully define opaque type: \
1668                             generic parameter `{}` is specified as concrete type `{}`",
1669                                 identity_substs.type_at(i),
1670                                 bad_subst
1671                             ),
1672                         );
1673                     }
1674                 } else if let Some((prev_span, prev_ty, ref prev_indices)) = self.found {
1675                     let mut ty = concrete_type.walk().fuse();
1676                     let mut p_ty = prev_ty.walk().fuse();
1677                     let iter_eq = (&mut ty).zip(&mut p_ty).all(|(t, p)| match (&t.kind, &p.kind) {
1678                         // Type parameters are equal to any other type parameter for the purpose of
1679                         // concrete type equality, as it is possible to obtain the same type just
1680                         // by passing matching parameters to a function.
1681                         (ty::Param(_), ty::Param(_)) => true,
1682                         _ => t == p,
1683                     });
1684                     if !iter_eq || ty.next().is_some() || p_ty.next().is_some() {
1685                         debug!("find_opaque_ty_constraints: span={:?}", span);
1686                         // Found different concrete types for the opaque type.
1687                         let mut err = self.tcx.sess.struct_span_err(
1688                             span,
1689                             "concrete type differs from previous defining opaque type use",
1690                         );
1691                         err.span_label(
1692                             span,
1693                             format!("expected `{}`, got `{}`", prev_ty, concrete_type),
1694                         );
1695                         err.span_note(prev_span, "previous use here");
1696                         err.emit();
1697                     } else if indices != *prev_indices {
1698                         // Found "same" concrete types, but the generic parameter order differs.
1699                         let mut err = self.tcx.sess.struct_span_err(
1700                             span,
1701                             "concrete type's generic parameters differ from previous defining use",
1702                         );
1703                         use std::fmt::Write;
1704                         let mut s = String::new();
1705                         write!(s, "expected [").unwrap();
1706                         let list = |s: &mut String, indices: &Vec<usize>| {
1707                             let mut indices = indices.iter().cloned();
1708                             if let Some(first) = indices.next() {
1709                                 write!(s, "`{}`", substs[first]).unwrap();
1710                                 for i in indices {
1711                                     write!(s, ", `{}`", substs[i]).unwrap();
1712                                 }
1713                             }
1714                         };
1715                         list(&mut s, prev_indices);
1716                         write!(s, "], got [").unwrap();
1717                         list(&mut s, &indices);
1718                         write!(s, "]").unwrap();
1719                         err.span_label(span, s);
1720                         err.span_note(prev_span, "previous use here");
1721                         err.emit();
1722                     }
1723                 } else {
1724                     self.found = Some((span, concrete_type, indices));
1725                 }
1726             } else {
1727                 debug!(
1728                     "find_opaque_ty_constraints: no constraint for `{:?}` at `{:?}`",
1729                     self.def_id, def_id,
1730                 );
1731             }
1732         }
1733     }
1734
1735     impl<'tcx> intravisit::Visitor<'tcx> for ConstraintLocator<'tcx> {
1736         type Map = Map<'tcx>;
1737
1738         fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<'_, Self::Map> {
1739             intravisit::NestedVisitorMap::All(&self.tcx.hir())
1740         }
1741         fn visit_item(&mut self, it: &'tcx Item<'tcx>) {
1742             debug!("find_existential_constraints: visiting {:?}", it);
1743             let def_id = self.tcx.hir().local_def_id(it.hir_id);
1744             // The opaque type itself or its children are not within its reveal scope.
1745             if def_id != self.def_id {
1746                 self.check(def_id);
1747                 intravisit::walk_item(self, it);
1748             }
1749         }
1750         fn visit_impl_item(&mut self, it: &'tcx ImplItem<'tcx>) {
1751             debug!("find_existential_constraints: visiting {:?}", it);
1752             let def_id = self.tcx.hir().local_def_id(it.hir_id);
1753             // The opaque type itself or its children are not within its reveal scope.
1754             if def_id != self.def_id {
1755                 self.check(def_id);
1756                 intravisit::walk_impl_item(self, it);
1757             }
1758         }
1759         fn visit_trait_item(&mut self, it: &'tcx TraitItem<'tcx>) {
1760             debug!("find_existential_constraints: visiting {:?}", it);
1761             let def_id = self.tcx.hir().local_def_id(it.hir_id);
1762             self.check(def_id);
1763             intravisit::walk_trait_item(self, it);
1764         }
1765     }
1766
1767     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1768     let scope = tcx.hir().get_defining_scope(hir_id);
1769     let mut locator = ConstraintLocator { def_id, tcx, found: None };
1770
1771     debug!("find_opaque_ty_constraints: scope={:?}", scope);
1772
1773     if scope == hir::CRATE_HIR_ID {
1774         intravisit::walk_crate(&mut locator, tcx.hir().krate());
1775     } else {
1776         debug!("find_opaque_ty_constraints: scope={:?}", tcx.hir().get(scope));
1777         match tcx.hir().get(scope) {
1778             // We explicitly call `visit_*` methods, instead of using `intravisit::walk_*` methods
1779             // This allows our visitor to process the defining item itself, causing
1780             // it to pick up any 'sibling' defining uses.
1781             //
1782             // For example, this code:
1783             // ```
1784             // fn foo() {
1785             //     type Blah = impl Debug;
1786             //     let my_closure = || -> Blah { true };
1787             // }
1788             // ```
1789             //
1790             // requires us to explicitly process `foo()` in order
1791             // to notice the defining usage of `Blah`.
1792             Node::Item(ref it) => locator.visit_item(it),
1793             Node::ImplItem(ref it) => locator.visit_impl_item(it),
1794             Node::TraitItem(ref it) => locator.visit_trait_item(it),
1795             other => bug!("{:?} is not a valid scope for an opaque type item", other),
1796         }
1797     }
1798
1799     match locator.found {
1800         Some((_, ty, _)) => ty,
1801         None => {
1802             let span = tcx.def_span(def_id);
1803             tcx.sess.span_err(span, "could not find defining uses");
1804             tcx.types.err
1805         }
1806     }
1807 }
1808
1809 fn are_suggestable_generic_args(generic_args: &[hir::GenericArg<'_>]) -> bool {
1810     generic_args
1811         .iter()
1812         .filter_map(|arg| match arg {
1813             hir::GenericArg::Type(ty) => Some(ty),
1814             _ => None,
1815         })
1816         .any(is_suggestable_infer_ty)
1817 }
1818
1819 /// Whether `ty` is a type with `_` placeholders that can be infered. Used in diagnostics only to
1820 /// use inference to provide suggestions for the appropriate type if possible.
1821 fn is_suggestable_infer_ty(ty: &hir::Ty<'_>) -> bool {
1822     use hir::TyKind::*;
1823     match &ty.kind {
1824         Infer => true,
1825         Slice(ty) | Array(ty, _) => is_suggestable_infer_ty(ty),
1826         Tup(tys) => tys.iter().any(is_suggestable_infer_ty),
1827         Ptr(mut_ty) | Rptr(_, mut_ty) => is_suggestable_infer_ty(mut_ty.ty),
1828         Def(_, generic_args) => are_suggestable_generic_args(generic_args),
1829         Path(hir::QPath::TypeRelative(ty, segment)) => {
1830             is_suggestable_infer_ty(ty) || are_suggestable_generic_args(segment.generic_args().args)
1831         }
1832         Path(hir::QPath::Resolved(ty_opt, hir::Path { segments, .. })) => {
1833             ty_opt.map_or(false, is_suggestable_infer_ty)
1834                 || segments
1835                     .iter()
1836                     .any(|segment| are_suggestable_generic_args(segment.generic_args().args))
1837         }
1838         _ => false,
1839     }
1840 }
1841
1842 pub fn get_infer_ret_ty(output: &'hir hir::FunctionRetTy<'hir>) -> Option<&'hir hir::Ty<'hir>> {
1843     if let hir::FunctionRetTy::Return(ref ty) = output {
1844         if is_suggestable_infer_ty(ty) {
1845             return Some(&**ty);
1846         }
1847     }
1848     None
1849 }
1850
1851 fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
1852     use rustc_hir::Node::*;
1853     use rustc_hir::*;
1854
1855     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1856
1857     let icx = ItemCtxt::new(tcx, def_id);
1858
1859     match tcx.hir().get(hir_id) {
1860         TraitItem(hir::TraitItem {
1861             kind: TraitItemKind::Method(sig, TraitMethod::Provided(_)),
1862             ident,
1863             generics,
1864             ..
1865         })
1866         | ImplItem(hir::ImplItem { kind: ImplItemKind::Method(sig, _), ident, generics, .. })
1867         | Item(hir::Item { kind: ItemKind::Fn(sig, generics, _), ident, .. }) => {
1868             match get_infer_ret_ty(&sig.decl.output) {
1869                 Some(ty) => {
1870                     let fn_sig = tcx.typeck_tables_of(def_id).liberated_fn_sigs()[hir_id];
1871                     let mut visitor = PlaceholderHirTyCollector::default();
1872                     visitor.visit_ty(ty);
1873                     let mut diag = bad_placeholder_type(tcx, visitor.0);
1874                     let ret_ty = fn_sig.output();
1875                     if ret_ty != tcx.types.err {
1876                         diag.span_suggestion(
1877                             ty.span,
1878                             "replace with the correct return type",
1879                             ret_ty.to_string(),
1880                             Applicability::MaybeIncorrect,
1881                         );
1882                     }
1883                     diag.emit();
1884                     ty::Binder::bind(fn_sig)
1885                 }
1886                 None => AstConv::ty_of_fn(
1887                     &icx,
1888                     sig.header.unsafety,
1889                     sig.header.abi,
1890                     &sig.decl,
1891                     &generics.params[..],
1892                     Some(ident.span),
1893                 ),
1894             }
1895         }
1896
1897         TraitItem(hir::TraitItem {
1898             kind: TraitItemKind::Method(FnSig { header, decl }, _),
1899             ident,
1900             generics,
1901             ..
1902         }) => AstConv::ty_of_fn(
1903             &icx,
1904             header.unsafety,
1905             header.abi,
1906             decl,
1907             &generics.params[..],
1908             Some(ident.span),
1909         ),
1910
1911         ForeignItem(&hir::ForeignItem { kind: ForeignItemKind::Fn(ref fn_decl, _, _), .. }) => {
1912             let abi = tcx.hir().get_foreign_abi(hir_id);
1913             compute_sig_of_foreign_fn_decl(tcx, def_id, fn_decl, abi)
1914         }
1915
1916         Ctor(data) | Variant(hir::Variant { data, .. }) if data.ctor_hir_id().is_some() => {
1917             let ty = tcx.type_of(tcx.hir().get_parent_did(hir_id));
1918             let inputs =
1919                 data.fields().iter().map(|f| tcx.type_of(tcx.hir().local_def_id(f.hir_id)));
1920             ty::Binder::bind(tcx.mk_fn_sig(
1921                 inputs,
1922                 ty,
1923                 false,
1924                 hir::Unsafety::Normal,
1925                 abi::Abi::Rust,
1926             ))
1927         }
1928
1929         Expr(&hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => {
1930             // Closure signatures are not like other function
1931             // signatures and cannot be accessed through `fn_sig`. For
1932             // example, a closure signature excludes the `self`
1933             // argument. In any case they are embedded within the
1934             // closure type as part of the `ClosureSubsts`.
1935             //
1936             // To get
1937             // the signature of a closure, you should use the
1938             // `closure_sig` method on the `ClosureSubsts`:
1939             //
1940             //    closure_substs.sig(def_id, tcx)
1941             //
1942             // or, inside of an inference context, you can use
1943             //
1944             //    infcx.closure_sig(def_id, closure_substs)
1945             bug!("to get the signature of a closure, use `closure_sig()` not `fn_sig()`");
1946         }
1947
1948         x => {
1949             bug!("unexpected sort of node in fn_sig(): {:?}", x);
1950         }
1951     }
1952 }
1953
1954 fn impl_trait_ref(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ty::TraitRef<'_>> {
1955     let icx = ItemCtxt::new(tcx, def_id);
1956
1957     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1958     match tcx.hir().expect_item(hir_id).kind {
1959         hir::ItemKind::Impl { ref of_trait, .. } => of_trait.as_ref().map(|ast_trait_ref| {
1960             let selfty = tcx.type_of(def_id);
1961             AstConv::instantiate_mono_trait_ref(&icx, ast_trait_ref, selfty)
1962         }),
1963         _ => bug!(),
1964     }
1965 }
1966
1967 fn impl_polarity(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ImplPolarity {
1968     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
1969     let is_rustc_reservation = tcx.has_attr(def_id, sym::rustc_reservation_impl);
1970     let item = tcx.hir().expect_item(hir_id);
1971     match &item.kind {
1972         hir::ItemKind::Impl { polarity: hir::ImplPolarity::Negative, .. } => {
1973             if is_rustc_reservation {
1974                 tcx.sess.span_err(item.span, "reservation impls can't be negative");
1975             }
1976             ty::ImplPolarity::Negative
1977         }
1978         hir::ItemKind::Impl { polarity: hir::ImplPolarity::Positive, of_trait: None, .. } => {
1979             if is_rustc_reservation {
1980                 tcx.sess.span_err(item.span, "reservation impls can't be inherent");
1981             }
1982             ty::ImplPolarity::Positive
1983         }
1984         hir::ItemKind::Impl {
1985             polarity: hir::ImplPolarity::Positive, of_trait: Some(_), ..
1986         } => {
1987             if is_rustc_reservation {
1988                 ty::ImplPolarity::Reservation
1989             } else {
1990                 ty::ImplPolarity::Positive
1991             }
1992         }
1993         ref item => bug!("impl_polarity: {:?} not an impl", item),
1994     }
1995 }
1996
1997 /// Returns the early-bound lifetimes declared in this generics
1998 /// listing. For anything other than fns/methods, this is just all
1999 /// the lifetimes that are declared. For fns or methods, we have to
2000 /// screen out those that do not appear in any where-clauses etc using
2001 /// `resolve_lifetime::early_bound_lifetimes`.
2002 fn early_bound_lifetimes_from_generics<'a, 'tcx: 'a>(
2003     tcx: TyCtxt<'tcx>,
2004     generics: &'a hir::Generics<'a>,
2005 ) -> impl Iterator<Item = &'a hir::GenericParam<'a>> + Captures<'tcx> {
2006     generics.params.iter().filter(move |param| match param.kind {
2007         GenericParamKind::Lifetime { .. } => !tcx.is_late_bound(param.hir_id),
2008         _ => false,
2009     })
2010 }
2011
2012 /// Returns a list of type predicates for the definition with ID `def_id`, including inferred
2013 /// lifetime constraints. This includes all predicates returned by `explicit_predicates_of`, plus
2014 /// inferred constraints concerning which regions outlive other regions.
2015 fn predicates_defined_on(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2016     debug!("predicates_defined_on({:?})", def_id);
2017     let mut result = tcx.explicit_predicates_of(def_id);
2018     debug!("predicates_defined_on: explicit_predicates_of({:?}) = {:?}", def_id, result,);
2019     let inferred_outlives = tcx.inferred_outlives_of(def_id);
2020     if !inferred_outlives.is_empty() {
2021         debug!(
2022             "predicates_defined_on: inferred_outlives_of({:?}) = {:?}",
2023             def_id, inferred_outlives,
2024         );
2025         if result.predicates.is_empty() {
2026             result.predicates = inferred_outlives;
2027         } else {
2028             result.predicates = tcx
2029                 .arena
2030                 .alloc_from_iter(result.predicates.iter().chain(inferred_outlives).copied());
2031         }
2032     }
2033     debug!("predicates_defined_on({:?}) = {:?}", def_id, result);
2034     result
2035 }
2036
2037 /// Returns a list of all type predicates (explicit and implicit) for the definition with
2038 /// ID `def_id`. This includes all predicates returned by `predicates_defined_on`, plus
2039 /// `Self: Trait` predicates for traits.
2040 fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2041     let mut result = tcx.predicates_defined_on(def_id);
2042
2043     if tcx.is_trait(def_id) {
2044         // For traits, add `Self: Trait` predicate. This is
2045         // not part of the predicates that a user writes, but it
2046         // is something that one must prove in order to invoke a
2047         // method or project an associated type.
2048         //
2049         // In the chalk setup, this predicate is not part of the
2050         // "predicates" for a trait item. But it is useful in
2051         // rustc because if you directly (e.g.) invoke a trait
2052         // method like `Trait::method(...)`, you must naturally
2053         // prove that the trait applies to the types that were
2054         // used, and adding the predicate into this list ensures
2055         // that this is done.
2056         let span = tcx.def_span(def_id);
2057         result.predicates =
2058             tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(std::iter::once((
2059                 ty::TraitRef::identity(tcx, def_id).to_predicate(),
2060                 span,
2061             ))));
2062     }
2063     debug!("predicates_of(def_id={:?}) = {:?}", def_id, result);
2064     result
2065 }
2066
2067 /// Returns a list of user-specified type predicates for the definition with ID `def_id`.
2068 /// N.B., this does not include any implied/inferred constraints.
2069 fn explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2070     use rustc_data_structures::fx::FxHashSet;
2071     use rustc_hir::*;
2072
2073     debug!("explicit_predicates_of(def_id={:?})", def_id);
2074
2075     /// A data structure with unique elements, which preserves order of insertion.
2076     /// Preserving the order of insertion is important here so as not to break
2077     /// compile-fail UI tests.
2078     // FIXME(eddyb) just use `IndexSet` from `indexmap`.
2079     struct UniquePredicates<'tcx> {
2080         predicates: Vec<(ty::Predicate<'tcx>, Span)>,
2081         uniques: FxHashSet<(ty::Predicate<'tcx>, Span)>,
2082     }
2083
2084     impl<'tcx> UniquePredicates<'tcx> {
2085         fn new() -> Self {
2086             UniquePredicates { predicates: vec![], uniques: FxHashSet::default() }
2087         }
2088
2089         fn push(&mut self, value: (ty::Predicate<'tcx>, Span)) {
2090             if self.uniques.insert(value) {
2091                 self.predicates.push(value);
2092             }
2093         }
2094
2095         fn extend<I: IntoIterator<Item = (ty::Predicate<'tcx>, Span)>>(&mut self, iter: I) {
2096             for value in iter {
2097                 self.push(value);
2098             }
2099         }
2100     }
2101
2102     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2103     let node = tcx.hir().get(hir_id);
2104
2105     let mut is_trait = None;
2106     let mut is_default_impl_trait = None;
2107
2108     let icx = ItemCtxt::new(tcx, def_id);
2109
2110     const NO_GENERICS: &hir::Generics<'_> = &hir::Generics::empty();
2111
2112     let mut predicates = UniquePredicates::new();
2113
2114     let ast_generics = match node {
2115         Node::TraitItem(item) => &item.generics,
2116
2117         Node::ImplItem(item) => match item.kind {
2118             ImplItemKind::OpaqueTy(ref bounds) => {
2119                 ty::print::with_no_queries(|| {
2120                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
2121                     let opaque_ty = tcx.mk_opaque(def_id, substs);
2122                     debug!(
2123                         "explicit_predicates_of({:?}): created opaque type {:?}",
2124                         def_id, opaque_ty
2125                     );
2126
2127                     // Collect the bounds, i.e., the `A + B + 'c` in `impl A + B + 'c`.
2128                     let bounds = AstConv::compute_bounds(
2129                         &icx,
2130                         opaque_ty,
2131                         bounds,
2132                         SizedByDefault::Yes,
2133                         tcx.def_span(def_id),
2134                     );
2135
2136                     predicates.extend(bounds.predicates(tcx, opaque_ty));
2137                     &item.generics
2138                 })
2139             }
2140             _ => &item.generics,
2141         },
2142
2143         Node::Item(item) => {
2144             match item.kind {
2145                 ItemKind::Impl { defaultness, ref generics, .. } => {
2146                     if defaultness.is_default() {
2147                         is_default_impl_trait = tcx.impl_trait_ref(def_id);
2148                     }
2149                     generics
2150                 }
2151                 ItemKind::Fn(.., ref generics, _)
2152                 | ItemKind::TyAlias(_, ref generics)
2153                 | ItemKind::Enum(_, ref generics)
2154                 | ItemKind::Struct(_, ref generics)
2155                 | ItemKind::Union(_, ref generics) => generics,
2156
2157                 ItemKind::Trait(_, _, ref generics, .., items) => {
2158                     is_trait = Some((ty::TraitRef::identity(tcx, def_id), items));
2159                     generics
2160                 }
2161                 ItemKind::TraitAlias(ref generics, _) => {
2162                     is_trait = Some((ty::TraitRef::identity(tcx, def_id), &[]));
2163                     generics
2164                 }
2165                 ItemKind::OpaqueTy(OpaqueTy {
2166                     ref bounds,
2167                     impl_trait_fn,
2168                     ref generics,
2169                     origin: _,
2170                 }) => {
2171                     let bounds_predicates = ty::print::with_no_queries(|| {
2172                         let substs = InternalSubsts::identity_for_item(tcx, def_id);
2173                         let opaque_ty = tcx.mk_opaque(def_id, substs);
2174
2175                         // Collect the bounds, i.e., the `A + B + 'c` in `impl A + B + 'c`.
2176                         let bounds = AstConv::compute_bounds(
2177                             &icx,
2178                             opaque_ty,
2179                             bounds,
2180                             SizedByDefault::Yes,
2181                             tcx.def_span(def_id),
2182                         );
2183
2184                         bounds.predicates(tcx, opaque_ty)
2185                     });
2186                     if impl_trait_fn.is_some() {
2187                         // opaque types
2188                         return ty::GenericPredicates {
2189                             parent: None,
2190                             predicates: tcx.arena.alloc_from_iter(bounds_predicates),
2191                         };
2192                     } else {
2193                         // named opaque types
2194                         predicates.extend(bounds_predicates);
2195                         generics
2196                     }
2197                 }
2198
2199                 _ => NO_GENERICS,
2200             }
2201         }
2202
2203         Node::ForeignItem(item) => match item.kind {
2204             ForeignItemKind::Static(..) => NO_GENERICS,
2205             ForeignItemKind::Fn(_, _, ref generics) => generics,
2206             ForeignItemKind::Type => NO_GENERICS,
2207         },
2208
2209         _ => NO_GENERICS,
2210     };
2211
2212     let generics = tcx.generics_of(def_id);
2213     let parent_count = generics.parent_count as u32;
2214     let has_own_self = generics.has_self && parent_count == 0;
2215
2216     // Below we'll consider the bounds on the type parameters (including `Self`)
2217     // and the explicit where-clauses, but to get the full set of predicates
2218     // on a trait we need to add in the supertrait bounds and bounds found on
2219     // associated types.
2220     if let Some((_trait_ref, _)) = is_trait {
2221         predicates.extend(tcx.super_predicates_of(def_id).predicates.iter().cloned());
2222     }
2223
2224     // In default impls, we can assume that the self type implements
2225     // the trait. So in:
2226     //
2227     //     default impl Foo for Bar { .. }
2228     //
2229     // we add a default where clause `Foo: Bar`. We do a similar thing for traits
2230     // (see below). Recall that a default impl is not itself an impl, but rather a
2231     // set of defaults that can be incorporated into another impl.
2232     if let Some(trait_ref) = is_default_impl_trait {
2233         predicates.push((trait_ref.to_poly_trait_ref().to_predicate(), tcx.def_span(def_id)));
2234     }
2235
2236     // Collect the region predicates that were declared inline as
2237     // well. In the case of parameters declared on a fn or method, we
2238     // have to be careful to only iterate over early-bound regions.
2239     let mut index = parent_count + has_own_self as u32;
2240     for param in early_bound_lifetimes_from_generics(tcx, ast_generics) {
2241         let region = tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
2242             def_id: tcx.hir().local_def_id(param.hir_id),
2243             index,
2244             name: param.name.ident().name,
2245         }));
2246         index += 1;
2247
2248         match param.kind {
2249             GenericParamKind::Lifetime { .. } => {
2250                 param.bounds.iter().for_each(|bound| match bound {
2251                     hir::GenericBound::Outlives(lt) => {
2252                         let bound = AstConv::ast_region_to_region(&icx, &lt, None);
2253                         let outlives = ty::Binder::bind(ty::OutlivesPredicate(region, bound));
2254                         predicates.push((outlives.to_predicate(), lt.span));
2255                     }
2256                     _ => bug!(),
2257                 });
2258             }
2259             _ => bug!(),
2260         }
2261     }
2262
2263     // Collect the predicates that were written inline by the user on each
2264     // type parameter (e.g., `<T: Foo>`).
2265     for param in ast_generics.params {
2266         if let GenericParamKind::Type { .. } = param.kind {
2267             let name = param.name.ident().name;
2268             let param_ty = ty::ParamTy::new(index, name).to_ty(tcx);
2269             index += 1;
2270
2271             let sized = SizedByDefault::Yes;
2272             let bounds = AstConv::compute_bounds(&icx, param_ty, &param.bounds, sized, param.span);
2273             predicates.extend(bounds.predicates(tcx, param_ty));
2274         }
2275     }
2276
2277     // Add in the bounds that appear in the where-clause.
2278     let where_clause = &ast_generics.where_clause;
2279     for predicate in where_clause.predicates {
2280         match predicate {
2281             &hir::WherePredicate::BoundPredicate(ref bound_pred) => {
2282                 let ty = icx.to_ty(&bound_pred.bounded_ty);
2283
2284                 // Keep the type around in a dummy predicate, in case of no bounds.
2285                 // That way, `where Ty:` is not a complete noop (see #53696) and `Ty`
2286                 // is still checked for WF.
2287                 if bound_pred.bounds.is_empty() {
2288                     if let ty::Param(_) = ty.kind {
2289                         // This is a `where T:`, which can be in the HIR from the
2290                         // transformation that moves `?Sized` to `T`'s declaration.
2291                         // We can skip the predicate because type parameters are
2292                         // trivially WF, but also we *should*, to avoid exposing
2293                         // users who never wrote `where Type:,` themselves, to
2294                         // compiler/tooling bugs from not handling WF predicates.
2295                     } else {
2296                         let span = bound_pred.bounded_ty.span;
2297                         let predicate = ty::OutlivesPredicate(ty, tcx.mk_region(ty::ReEmpty));
2298                         predicates.push((
2299                             ty::Predicate::TypeOutlives(ty::Binder::dummy(predicate)),
2300                             span,
2301                         ));
2302                     }
2303                 }
2304
2305                 for bound in bound_pred.bounds.iter() {
2306                     match bound {
2307                         &hir::GenericBound::Trait(ref poly_trait_ref, _) => {
2308                             let mut bounds = Bounds::default();
2309                             let _ = AstConv::instantiate_poly_trait_ref(
2310                                 &icx,
2311                                 poly_trait_ref,
2312                                 ty,
2313                                 &mut bounds,
2314                             );
2315                             predicates.extend(bounds.predicates(tcx, ty));
2316                         }
2317
2318                         &hir::GenericBound::Outlives(ref lifetime) => {
2319                             let region = AstConv::ast_region_to_region(&icx, lifetime, None);
2320                             let pred = ty::Binder::bind(ty::OutlivesPredicate(ty, region));
2321                             predicates.push((ty::Predicate::TypeOutlives(pred), lifetime.span))
2322                         }
2323                     }
2324                 }
2325             }
2326
2327             &hir::WherePredicate::RegionPredicate(ref region_pred) => {
2328                 let r1 = AstConv::ast_region_to_region(&icx, &region_pred.lifetime, None);
2329                 predicates.extend(region_pred.bounds.iter().map(|bound| {
2330                     let (r2, span) = match bound {
2331                         hir::GenericBound::Outlives(lt) => {
2332                             (AstConv::ast_region_to_region(&icx, lt, None), lt.span)
2333                         }
2334                         _ => bug!(),
2335                     };
2336                     let pred = ty::Binder::bind(ty::OutlivesPredicate(r1, r2));
2337
2338                     (ty::Predicate::RegionOutlives(pred), span)
2339                 }))
2340             }
2341
2342             &hir::WherePredicate::EqPredicate(..) => {
2343                 // FIXME(#20041)
2344             }
2345         }
2346     }
2347
2348     // Add predicates from associated type bounds.
2349     if let Some((self_trait_ref, trait_items)) = is_trait {
2350         predicates.extend(trait_items.iter().flat_map(|trait_item_ref| {
2351             associated_item_predicates(tcx, def_id, self_trait_ref, trait_item_ref)
2352         }))
2353     }
2354
2355     let mut predicates = predicates.predicates;
2356
2357     // Subtle: before we store the predicates into the tcx, we
2358     // sort them so that predicates like `T: Foo<Item=U>` come
2359     // before uses of `U`.  This avoids false ambiguity errors
2360     // in trait checking. See `setup_constraining_predicates`
2361     // for details.
2362     if let Node::Item(&Item { kind: ItemKind::Impl { .. }, .. }) = node {
2363         let self_ty = tcx.type_of(def_id);
2364         let trait_ref = tcx.impl_trait_ref(def_id);
2365         cgp::setup_constraining_predicates(
2366             tcx,
2367             &mut predicates,
2368             trait_ref,
2369             &mut cgp::parameters_for_impl(self_ty, trait_ref),
2370         );
2371     }
2372
2373     let result = ty::GenericPredicates {
2374         parent: generics.parent,
2375         predicates: tcx.arena.alloc_from_iter(predicates),
2376     };
2377     debug!("explicit_predicates_of(def_id={:?}) = {:?}", def_id, result);
2378     result
2379 }
2380
2381 fn associated_item_predicates(
2382     tcx: TyCtxt<'tcx>,
2383     def_id: DefId,
2384     self_trait_ref: ty::TraitRef<'tcx>,
2385     trait_item_ref: &hir::TraitItemRef,
2386 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2387     let trait_item = tcx.hir().trait_item(trait_item_ref.id);
2388     let item_def_id = tcx.hir().local_def_id(trait_item_ref.id.hir_id);
2389     let bounds = match trait_item.kind {
2390         hir::TraitItemKind::Type(ref bounds, _) => bounds,
2391         _ => return Vec::new(),
2392     };
2393
2394     let is_gat = !tcx.generics_of(item_def_id).params.is_empty();
2395
2396     let mut had_error = false;
2397
2398     let mut unimplemented_error = |arg_kind: &str| {
2399         if !had_error {
2400             tcx.sess
2401                 .struct_span_err(
2402                     trait_item.span,
2403                     &format!("{}-generic associated types are not yet implemented", arg_kind),
2404                 )
2405                 .note("for more information, see https://github.com/rust-lang/rust/issues/44265")
2406                 .emit();
2407             had_error = true;
2408         }
2409     };
2410
2411     let mk_bound_param = |param: &ty::GenericParamDef, _: &_| {
2412         match param.kind {
2413             ty::GenericParamDefKind::Lifetime => tcx
2414                 .mk_region(ty::RegionKind::ReLateBound(
2415                     ty::INNERMOST,
2416                     ty::BoundRegion::BrNamed(param.def_id, param.name),
2417                 ))
2418                 .into(),
2419             // FIXME(generic_associated_types): Use bound types and constants
2420             // once they are handled by the trait system.
2421             ty::GenericParamDefKind::Type { .. } => {
2422                 unimplemented_error("type");
2423                 tcx.types.err.into()
2424             }
2425             ty::GenericParamDefKind::Const => {
2426                 unimplemented_error("const");
2427                 tcx.consts.err.into()
2428             }
2429         }
2430     };
2431
2432     let bound_substs = if is_gat {
2433         // Given:
2434         //
2435         // trait X<'a, B, const C: usize> {
2436         //     type T<'d, E, const F: usize>: Default;
2437         // }
2438         //
2439         // We need to create predicates on the trait:
2440         //
2441         // for<'d, E, const F: usize>
2442         // <Self as X<'a, B, const C: usize>>::T<'d, E, const F: usize>: Sized + Default
2443         //
2444         // We substitute escaping bound parameters for the generic
2445         // arguments to the associated type which are then bound by
2446         // the `Binder` around the the predicate.
2447         //
2448         // FIXME(generic_associated_types): Currently only lifetimes are handled.
2449         self_trait_ref.substs.extend_to(tcx, item_def_id, mk_bound_param)
2450     } else {
2451         self_trait_ref.substs
2452     };
2453
2454     let assoc_ty = tcx.mk_projection(tcx.hir().local_def_id(trait_item.hir_id), bound_substs);
2455
2456     let bounds = AstConv::compute_bounds(
2457         &ItemCtxt::new(tcx, def_id),
2458         assoc_ty,
2459         bounds,
2460         SizedByDefault::Yes,
2461         trait_item.span,
2462     );
2463
2464     let predicates = bounds.predicates(tcx, assoc_ty);
2465
2466     if is_gat {
2467         // We use shifts to get the regions that we're substituting to
2468         // be bound by the binders in the `Predicate`s rather that
2469         // escaping.
2470         let shifted_in = ty::fold::shift_vars(tcx, &predicates, 1);
2471         let substituted = shifted_in.subst(tcx, bound_substs);
2472         ty::fold::shift_out_vars(tcx, &substituted, 1)
2473     } else {
2474         predicates
2475     }
2476 }
2477
2478 /// Converts a specific `GenericBound` from the AST into a set of
2479 /// predicates that apply to the self type. A vector is returned
2480 /// because this can be anywhere from zero predicates (`T: ?Sized` adds no
2481 /// predicates) to one (`T: Foo`) to many (`T: Bar<X = i32>` adds `T: Bar`
2482 /// and `<T as Bar>::X == i32`).
2483 fn predicates_from_bound<'tcx>(
2484     astconv: &dyn AstConv<'tcx>,
2485     param_ty: Ty<'tcx>,
2486     bound: &'tcx hir::GenericBound<'tcx>,
2487 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2488     match *bound {
2489         hir::GenericBound::Trait(ref tr, hir::TraitBoundModifier::None) => {
2490             let mut bounds = Bounds::default();
2491             let _ = astconv.instantiate_poly_trait_ref(tr, param_ty, &mut bounds);
2492             bounds.predicates(astconv.tcx(), param_ty)
2493         }
2494         hir::GenericBound::Outlives(ref lifetime) => {
2495             let region = astconv.ast_region_to_region(lifetime, None);
2496             let pred = ty::Binder::bind(ty::OutlivesPredicate(param_ty, region));
2497             vec![(ty::Predicate::TypeOutlives(pred), lifetime.span)]
2498         }
2499         hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => vec![],
2500     }
2501 }
2502
2503 fn compute_sig_of_foreign_fn_decl<'tcx>(
2504     tcx: TyCtxt<'tcx>,
2505     def_id: DefId,
2506     decl: &'tcx hir::FnDecl<'tcx>,
2507     abi: abi::Abi,
2508 ) -> ty::PolyFnSig<'tcx> {
2509     let unsafety = if abi == abi::Abi::RustIntrinsic {
2510         intrinsic_operation_unsafety(&tcx.item_name(def_id).as_str())
2511     } else {
2512         hir::Unsafety::Unsafe
2513     };
2514     let fty = AstConv::ty_of_fn(&ItemCtxt::new(tcx, def_id), unsafety, abi, decl, &[], None);
2515
2516     // Feature gate SIMD types in FFI, since I am not sure that the
2517     // ABIs are handled at all correctly. -huonw
2518     if abi != abi::Abi::RustIntrinsic
2519         && abi != abi::Abi::PlatformIntrinsic
2520         && !tcx.features().simd_ffi
2521     {
2522         let check = |ast_ty: &hir::Ty<'_>, ty: Ty<'_>| {
2523             if ty.is_simd() {
2524                 tcx.sess
2525                     .struct_span_err(
2526                         ast_ty.span,
2527                         &format!(
2528                             "use of SIMD type `{}` in FFI is highly experimental and \
2529                             may result in invalid code",
2530                             tcx.hir().hir_to_pretty_string(ast_ty.hir_id)
2531                         ),
2532                     )
2533                     .help("add `#![feature(simd_ffi)]` to the crate attributes to enable")
2534                     .emit();
2535             }
2536         };
2537         for (input, ty) in decl.inputs.iter().zip(*fty.inputs().skip_binder()) {
2538             check(&input, ty)
2539         }
2540         if let hir::FunctionRetTy::Return(ref ty) = decl.output {
2541             check(&ty, *fty.output().skip_binder())
2542         }
2543     }
2544
2545     fty
2546 }
2547
2548 fn is_foreign_item(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
2549     match tcx.hir().get_if_local(def_id) {
2550         Some(Node::ForeignItem(..)) => true,
2551         Some(_) => false,
2552         _ => bug!("is_foreign_item applied to non-local def-id {:?}", def_id),
2553     }
2554 }
2555
2556 fn static_mutability(tcx: TyCtxt<'_>, def_id: DefId) -> Option<hir::Mutability> {
2557     match tcx.hir().get_if_local(def_id) {
2558         Some(Node::Item(&hir::Item { kind: hir::ItemKind::Static(_, mutbl, _), .. }))
2559         | Some(Node::ForeignItem(&hir::ForeignItem {
2560             kind: hir::ForeignItemKind::Static(_, mutbl),
2561             ..
2562         })) => Some(mutbl),
2563         Some(_) => None,
2564         _ => bug!("static_mutability applied to non-local def-id {:?}", def_id),
2565     }
2566 }
2567
2568 fn from_target_feature(
2569     tcx: TyCtxt<'_>,
2570     id: DefId,
2571     attr: &ast::Attribute,
2572     whitelist: &FxHashMap<String, Option<Symbol>>,
2573     target_features: &mut Vec<Symbol>,
2574 ) {
2575     let list = match attr.meta_item_list() {
2576         Some(list) => list,
2577         None => return,
2578     };
2579     let bad_item = |span| {
2580         let msg = "malformed `target_feature` attribute input";
2581         let code = "enable = \"..\"".to_owned();
2582         tcx.sess
2583             .struct_span_err(span, &msg)
2584             .span_suggestion(span, "must be of the form", code, Applicability::HasPlaceholders)
2585             .emit();
2586     };
2587     let rust_features = tcx.features();
2588     for item in list {
2589         // Only `enable = ...` is accepted in the meta-item list.
2590         if !item.check_name(sym::enable) {
2591             bad_item(item.span());
2592             continue;
2593         }
2594
2595         // Must be of the form `enable = "..."` (a string).
2596         let value = match item.value_str() {
2597             Some(value) => value,
2598             None => {
2599                 bad_item(item.span());
2600                 continue;
2601             }
2602         };
2603
2604         // We allow comma separation to enable multiple features.
2605         target_features.extend(value.as_str().split(',').filter_map(|feature| {
2606             // Only allow whitelisted features per platform.
2607             let feature_gate = match whitelist.get(feature) {
2608                 Some(g) => g,
2609                 None => {
2610                     let msg =
2611                         format!("the feature named `{}` is not valid for this target", feature);
2612                     let mut err = tcx.sess.struct_span_err(item.span(), &msg);
2613                     err.span_label(
2614                         item.span(),
2615                         format!("`{}` is not valid for this target", feature),
2616                     );
2617                     if feature.starts_with("+") {
2618                         let valid = whitelist.contains_key(&feature[1..]);
2619                         if valid {
2620                             err.help("consider removing the leading `+` in the feature name");
2621                         }
2622                     }
2623                     err.emit();
2624                     return None;
2625                 }
2626             };
2627
2628             // Only allow features whose feature gates have been enabled.
2629             let allowed = match feature_gate.as_ref().map(|s| *s) {
2630                 Some(sym::arm_target_feature) => rust_features.arm_target_feature,
2631                 Some(sym::aarch64_target_feature) => rust_features.aarch64_target_feature,
2632                 Some(sym::hexagon_target_feature) => rust_features.hexagon_target_feature,
2633                 Some(sym::powerpc_target_feature) => rust_features.powerpc_target_feature,
2634                 Some(sym::mips_target_feature) => rust_features.mips_target_feature,
2635                 Some(sym::avx512_target_feature) => rust_features.avx512_target_feature,
2636                 Some(sym::mmx_target_feature) => rust_features.mmx_target_feature,
2637                 Some(sym::sse4a_target_feature) => rust_features.sse4a_target_feature,
2638                 Some(sym::tbm_target_feature) => rust_features.tbm_target_feature,
2639                 Some(sym::wasm_target_feature) => rust_features.wasm_target_feature,
2640                 Some(sym::cmpxchg16b_target_feature) => rust_features.cmpxchg16b_target_feature,
2641                 Some(sym::adx_target_feature) => rust_features.adx_target_feature,
2642                 Some(sym::movbe_target_feature) => rust_features.movbe_target_feature,
2643                 Some(sym::rtm_target_feature) => rust_features.rtm_target_feature,
2644                 Some(sym::f16c_target_feature) => rust_features.f16c_target_feature,
2645                 Some(name) => bug!("unknown target feature gate {}", name),
2646                 None => true,
2647             };
2648             if !allowed && id.is_local() {
2649                 feature_err(
2650                     &tcx.sess.parse_sess,
2651                     feature_gate.unwrap(),
2652                     item.span(),
2653                     &format!("the target feature `{}` is currently unstable", feature),
2654                 )
2655                 .emit();
2656             }
2657             Some(Symbol::intern(feature))
2658         }));
2659     }
2660 }
2661
2662 fn linkage_by_name(tcx: TyCtxt<'_>, def_id: DefId, name: &str) -> Linkage {
2663     use rustc::mir::mono::Linkage::*;
2664
2665     // Use the names from src/llvm/docs/LangRef.rst here. Most types are only
2666     // applicable to variable declarations and may not really make sense for
2667     // Rust code in the first place but whitelist them anyway and trust that
2668     // the user knows what s/he's doing. Who knows, unanticipated use cases
2669     // may pop up in the future.
2670     //
2671     // ghost, dllimport, dllexport and linkonce_odr_autohide are not supported
2672     // and don't have to be, LLVM treats them as no-ops.
2673     match name {
2674         "appending" => Appending,
2675         "available_externally" => AvailableExternally,
2676         "common" => Common,
2677         "extern_weak" => ExternalWeak,
2678         "external" => External,
2679         "internal" => Internal,
2680         "linkonce" => LinkOnceAny,
2681         "linkonce_odr" => LinkOnceODR,
2682         "private" => Private,
2683         "weak" => WeakAny,
2684         "weak_odr" => WeakODR,
2685         _ => {
2686             let span = tcx.hir().span_if_local(def_id);
2687             if let Some(span) = span {
2688                 tcx.sess.span_fatal(span, "invalid linkage specified")
2689             } else {
2690                 tcx.sess.fatal(&format!("invalid linkage specified: {}", name))
2691             }
2692         }
2693     }
2694 }
2695
2696 fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
2697     let attrs = tcx.get_attrs(id);
2698
2699     let mut codegen_fn_attrs = CodegenFnAttrs::new();
2700
2701     let whitelist = tcx.target_features_whitelist(LOCAL_CRATE);
2702
2703     let mut inline_span = None;
2704     let mut link_ordinal_span = None;
2705     for attr in attrs.iter() {
2706         if attr.check_name(sym::cold) {
2707             codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
2708         } else if attr.check_name(sym::rustc_allocator) {
2709             codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR;
2710         } else if attr.check_name(sym::unwind) {
2711             codegen_fn_attrs.flags |= CodegenFnAttrFlags::UNWIND;
2712         } else if attr.check_name(sym::ffi_returns_twice) {
2713             if tcx.is_foreign_item(id) {
2714                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_RETURNS_TWICE;
2715             } else {
2716                 // `#[ffi_returns_twice]` is only allowed `extern fn`s.
2717                 struct_span_err!(
2718                     tcx.sess,
2719                     attr.span,
2720                     E0724,
2721                     "`#[ffi_returns_twice]` may only be used on foreign functions"
2722                 )
2723                 .emit();
2724             }
2725         } else if attr.check_name(sym::rustc_allocator_nounwind) {
2726             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_ALLOCATOR_NOUNWIND;
2727         } else if attr.check_name(sym::naked) {
2728             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED;
2729         } else if attr.check_name(sym::no_mangle) {
2730             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
2731         } else if attr.check_name(sym::rustc_std_internal_symbol) {
2732             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
2733         } else if attr.check_name(sym::no_debug) {
2734             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_DEBUG;
2735         } else if attr.check_name(sym::used) {
2736             codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED;
2737         } else if attr.check_name(sym::thread_local) {
2738             codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL;
2739         } else if attr.check_name(sym::track_caller) {
2740             if tcx.fn_sig(id).abi() != abi::Abi::Rust {
2741                 struct_span_err!(tcx.sess, attr.span, E0737, "`#[track_caller]` requires Rust ABI")
2742                     .emit();
2743             }
2744             codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
2745         } else if attr.check_name(sym::export_name) {
2746             if let Some(s) = attr.value_str() {
2747                 if s.as_str().contains("\0") {
2748                     // `#[export_name = ...]` will be converted to a null-terminated string,
2749                     // so it may not contain any null characters.
2750                     struct_span_err!(
2751                         tcx.sess,
2752                         attr.span,
2753                         E0648,
2754                         "`export_name` may not contain null characters"
2755                     )
2756                     .emit();
2757                 }
2758                 codegen_fn_attrs.export_name = Some(s);
2759             }
2760         } else if attr.check_name(sym::target_feature) {
2761             if tcx.fn_sig(id).unsafety() == Unsafety::Normal {
2762                 let msg = "`#[target_feature(..)]` can only be applied to `unsafe` functions";
2763                 tcx.sess
2764                     .struct_span_err(attr.span, msg)
2765                     .span_label(attr.span, "can only be applied to `unsafe` functions")
2766                     .span_label(tcx.def_span(id), "not an `unsafe` function")
2767                     .emit();
2768             }
2769             from_target_feature(tcx, id, attr, &whitelist, &mut codegen_fn_attrs.target_features);
2770         } else if attr.check_name(sym::linkage) {
2771             if let Some(val) = attr.value_str() {
2772                 codegen_fn_attrs.linkage = Some(linkage_by_name(tcx, id, &val.as_str()));
2773             }
2774         } else if attr.check_name(sym::link_section) {
2775             if let Some(val) = attr.value_str() {
2776                 if val.as_str().bytes().any(|b| b == 0) {
2777                     let msg = format!(
2778                         "illegal null byte in link_section \
2779                          value: `{}`",
2780                         &val
2781                     );
2782                     tcx.sess.span_err(attr.span, &msg);
2783                 } else {
2784                     codegen_fn_attrs.link_section = Some(val);
2785                 }
2786             }
2787         } else if attr.check_name(sym::link_name) {
2788             codegen_fn_attrs.link_name = attr.value_str();
2789         } else if attr.check_name(sym::link_ordinal) {
2790             link_ordinal_span = Some(attr.span);
2791             if let ordinal @ Some(_) = check_link_ordinal(tcx, attr) {
2792                 codegen_fn_attrs.link_ordinal = ordinal;
2793             }
2794         }
2795     }
2796
2797     codegen_fn_attrs.inline = attrs.iter().fold(InlineAttr::None, |ia, attr| {
2798         if !attr.has_name(sym::inline) {
2799             return ia;
2800         }
2801         match attr.meta().map(|i| i.kind) {
2802             Some(MetaItemKind::Word) => {
2803                 mark_used(attr);
2804                 InlineAttr::Hint
2805             }
2806             Some(MetaItemKind::List(ref items)) => {
2807                 mark_used(attr);
2808                 inline_span = Some(attr.span);
2809                 if items.len() != 1 {
2810                     struct_span_err!(
2811                         tcx.sess.diagnostic(),
2812                         attr.span,
2813                         E0534,
2814                         "expected one argument"
2815                     )
2816                     .emit();
2817                     InlineAttr::None
2818                 } else if list_contains_name(&items[..], sym::always) {
2819                     InlineAttr::Always
2820                 } else if list_contains_name(&items[..], sym::never) {
2821                     InlineAttr::Never
2822                 } else {
2823                     struct_span_err!(
2824                         tcx.sess.diagnostic(),
2825                         items[0].span(),
2826                         E0535,
2827                         "invalid argument"
2828                     )
2829                     .emit();
2830
2831                     InlineAttr::None
2832                 }
2833             }
2834             Some(MetaItemKind::NameValue(_)) => ia,
2835             None => ia,
2836         }
2837     });
2838
2839     codegen_fn_attrs.optimize = attrs.iter().fold(OptimizeAttr::None, |ia, attr| {
2840         if !attr.has_name(sym::optimize) {
2841             return ia;
2842         }
2843         let err = |sp, s| struct_span_err!(tcx.sess.diagnostic(), sp, E0722, "{}", s).emit();
2844         match attr.meta().map(|i| i.kind) {
2845             Some(MetaItemKind::Word) => {
2846                 err(attr.span, "expected one argument");
2847                 ia
2848             }
2849             Some(MetaItemKind::List(ref items)) => {
2850                 mark_used(attr);
2851                 inline_span = Some(attr.span);
2852                 if items.len() != 1 {
2853                     err(attr.span, "expected one argument");
2854                     OptimizeAttr::None
2855                 } else if list_contains_name(&items[..], sym::size) {
2856                     OptimizeAttr::Size
2857                 } else if list_contains_name(&items[..], sym::speed) {
2858                     OptimizeAttr::Speed
2859                 } else {
2860                     err(items[0].span(), "invalid argument");
2861                     OptimizeAttr::None
2862                 }
2863             }
2864             Some(MetaItemKind::NameValue(_)) => ia,
2865             None => ia,
2866         }
2867     });
2868
2869     // If a function uses #[target_feature] it can't be inlined into general
2870     // purpose functions as they wouldn't have the right target features
2871     // enabled. For that reason we also forbid #[inline(always)] as it can't be
2872     // respected.
2873
2874     if codegen_fn_attrs.target_features.len() > 0 {
2875         if codegen_fn_attrs.inline == InlineAttr::Always {
2876             if let Some(span) = inline_span {
2877                 tcx.sess.span_err(
2878                     span,
2879                     "cannot use `#[inline(always)]` with \
2880                      `#[target_feature]`",
2881                 );
2882             }
2883         }
2884     }
2885
2886     // Weak lang items have the same semantics as "std internal" symbols in the
2887     // sense that they're preserved through all our LTO passes and only
2888     // strippable by the linker.
2889     //
2890     // Additionally weak lang items have predetermined symbol names.
2891     if tcx.is_weak_lang_item(id) {
2892         codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
2893     }
2894     if let Some(name) = weak_lang_items::link_name(&attrs) {
2895         codegen_fn_attrs.export_name = Some(name);
2896         codegen_fn_attrs.link_name = Some(name);
2897     }
2898     check_link_name_xor_ordinal(tcx, &codegen_fn_attrs, link_ordinal_span);
2899
2900     // Internal symbols to the standard library all have no_mangle semantics in
2901     // that they have defined symbol names present in the function name. This
2902     // also applies to weak symbols where they all have known symbol names.
2903     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
2904         codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
2905     }
2906
2907     codegen_fn_attrs
2908 }
2909
2910 fn check_link_ordinal(tcx: TyCtxt<'_>, attr: &ast::Attribute) -> Option<usize> {
2911     use syntax::ast::{Lit, LitIntType, LitKind};
2912     let meta_item_list = attr.meta_item_list();
2913     let meta_item_list: Option<&[ast::NestedMetaItem]> = meta_item_list.as_ref().map(Vec::as_ref);
2914     let sole_meta_list = match meta_item_list {
2915         Some([item]) => item.literal(),
2916         _ => None,
2917     };
2918     if let Some(Lit { kind: LitKind::Int(ordinal, LitIntType::Unsuffixed), .. }) = sole_meta_list {
2919         if *ordinal <= std::usize::MAX as u128 {
2920             Some(*ordinal as usize)
2921         } else {
2922             let msg = format!("ordinal value in `link_ordinal` is too large: `{}`", &ordinal);
2923             tcx.sess
2924                 .struct_span_err(attr.span, &msg)
2925                 .note("the value may not exceed `std::usize::MAX`")
2926                 .emit();
2927             None
2928         }
2929     } else {
2930         tcx.sess
2931             .struct_span_err(attr.span, "illegal ordinal format in `link_ordinal`")
2932             .note("an unsuffixed integer value, e.g., `1`, is expected")
2933             .emit();
2934         None
2935     }
2936 }
2937
2938 fn check_link_name_xor_ordinal(
2939     tcx: TyCtxt<'_>,
2940     codegen_fn_attrs: &CodegenFnAttrs,
2941     inline_span: Option<Span>,
2942 ) {
2943     if codegen_fn_attrs.link_name.is_none() || codegen_fn_attrs.link_ordinal.is_none() {
2944         return;
2945     }
2946     let msg = "cannot use `#[link_name]` with `#[link_ordinal]`";
2947     if let Some(span) = inline_span {
2948         tcx.sess.span_err(span, msg);
2949     } else {
2950         tcx.sess.err(msg);
2951     }
2952 }