compiler/rustc_typeck/src/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, SizedByDefault};
  18 use crate::bounds::Bounds;
  19 use crate::check::intrinsic::intrinsic_operation_unsafety;
  20 use crate::constrained_generic_params as cgp;
  21 use crate::errors;
  22 use crate::middle::resolve_lifetime as rl;
  23 use rustc_ast as ast;
  24 use rustc_ast::{MetaItemKind, NestedMetaItem};
  25 use rustc_attr::{list_contains_name, InlineAttr, InstructionSetAttr, OptimizeAttr};
  26 use rustc_data_structures::captures::Captures;
  27 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
  28 use rustc_errors::{struct_span_err, Applicability};
  29 use rustc_hir as hir;
  30 use rustc_hir::def::{CtorKind, DefKind, Res};
  31 use rustc_hir::def_id::{DefId, LocalDefId, LOCAL_CRATE};
  32 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  33 use rustc_hir::weak_lang_items;
  34 use rustc_hir::{GenericParamKind, HirId, Node};
  35 use rustc_middle::hir::map::blocks::FnLikeNode;
  36 use rustc_middle::hir::map::Map;
  37 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
  38 use rustc_middle::mir::mono::Linkage;
  39 use rustc_middle::ty::query::Providers;
  40 use rustc_middle::ty::subst::InternalSubsts;
  41 use rustc_middle::ty::util::Discr;
  42 use rustc_middle::ty::util::IntTypeExt;
  43 use rustc_middle::ty::{self, AdtKind, Const, DefIdTree, ToPolyTraitRef, Ty, TyCtxt};
  44 use rustc_middle::ty::{ReprOptions, ToPredicate, WithConstness};
  45 use rustc_session::config::SanitizerSet;
  46 use rustc_session::lint;
  47 use rustc_session::parse::feature_err;
  48 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  49 use rustc_span::{Span, DUMMY_SP};
  50 use rustc_target::spec::abi;
  51 use rustc_trait_selection::traits::error_reporting::suggestions::NextTypeParamName;
  52
  53 use std::ops::ControlFlow;
  54
  55 mod item_bounds;
  56 mod type_of;
  57
  58 struct OnlySelfBounds(bool);
  59
  60 ///////////////////////////////////////////////////////////////////////////
  61 // Main entry point
  62
  63 fn collect_mod_item_types(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
  64     tcx.hir().visit_item_likes_in_module(
  65         module_def_id,
  66         &mut CollectItemTypesVisitor { tcx }.as_deep_visitor(),
  67     );
  68 }
  69
  70 pub fn provide(providers: &mut Providers) {
  71     *providers = Providers {
  72         opt_const_param_of: type_of::opt_const_param_of,
  73         type_of: type_of::type_of,
  74         item_bounds: item_bounds::item_bounds,
  75         explicit_item_bounds: item_bounds::explicit_item_bounds,
  76         generics_of,
  77         predicates_of,
  78         predicates_defined_on,
  79         projection_ty_from_predicates,
  80         explicit_predicates_of,
  81         super_predicates_of,
  82         trait_explicit_predicates_and_bounds,
  83         type_param_predicates,
  84         trait_def,
  85         adt_def,
  86         fn_sig,
  87         impl_trait_ref,
  88         impl_polarity,
  89         is_foreign_item,
  90         static_mutability,
  91         generator_kind,
  92         codegen_fn_attrs,
  93         collect_mod_item_types,
  94         ..*providers
  95     };
  96 }
  97
  98 ///////////////////////////////////////////////////////////////////////////
  99
 100 /// Context specific to some particular item. This is what implements
 101 /// `AstConv`. It has information about the predicates that are defined
 102 /// on the trait. Unfortunately, this predicate information is
 103 /// available in various different forms at various points in the
 104 /// process. So we can't just store a pointer to e.g., the AST or the
 105 /// parsed ty form, we have to be more flexible. To this end, the
 106 /// `ItemCtxt` is parameterized by a `DefId` that it uses to satisfy
 107 /// `get_type_parameter_bounds` requests, drawing the information from
 108 /// the AST (`hir::Generics`), recursively.
 109 pub struct ItemCtxt<'tcx> {
 110     tcx: TyCtxt<'tcx>,
 111     item_def_id: DefId,
 112 }
 113
 114 ///////////////////////////////////////////////////////////////////////////
 115
 116 #[derive(Default)]
 117 crate struct PlaceholderHirTyCollector(crate Vec<Span>);
 118
 119 impl<'v> Visitor<'v> for PlaceholderHirTyCollector {
 120     type Map = intravisit::ErasedMap<'v>;
 121
 122     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 123         NestedVisitorMap::None
 124     }
 125     fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
 126         if let hir::TyKind::Infer = t.kind {
 127             self.0.push(t.span);
 128         }
 129         intravisit::walk_ty(self, t)
 130     }
 131 }
 132
 133 struct CollectItemTypesVisitor<'tcx> {
 134     tcx: TyCtxt<'tcx>,
 135 }
 136
 137 /// If there are any placeholder types (`_`), emit an error explaining that this is not allowed
 138 /// and suggest adding type parameters in the appropriate place, taking into consideration any and
 139 /// all already existing generic type parameters to avoid suggesting a name that is already in use.
 140 crate fn placeholder_type_error(
 141     tcx: TyCtxt<'tcx>,
 142     span: Option<Span>,
 143     generics: &[hir::GenericParam<'_>],
 144     placeholder_types: Vec<Span>,
 145     suggest: bool,
 146 ) {
 147     if placeholder_types.is_empty() {
 148         return;
 149     }
 150
 151     let type_name = generics.next_type_param_name(None);
 152     let mut sugg: Vec<_> =
 153         placeholder_types.iter().map(|sp| (*sp, (*type_name).to_string())).collect();
 154
 155     if generics.is_empty() {
 156         if let Some(span) = span {
 157             sugg.push((span, format!("<{}>", type_name)));
 158         }
 159     } else if let Some(arg) = generics
 160         .iter()
 161         .find(|arg| matches!(arg.name, hir::ParamName::Plain(Ident { name: kw::Underscore, .. })))
 162     {
 163         // Account for `_` already present in cases like `struct S<_>(_);` and suggest
 164         // `struct S<T>(T);` instead of `struct S<_, T>(T);`.
 165         sugg.push((arg.span, (*type_name).to_string()));
 166     } else {
 167         let last = generics.iter().last().unwrap();
 168         sugg.push((
 169             // Account for bounds, we want `fn foo<T: E, K>(_: K)` not `fn foo<T, K: E>(_: K)`.
 170             last.bounds_span().unwrap_or(last.span).shrink_to_hi(),
 171             format!(", {}", type_name),
 172         ));
 173     }
 174
 175     let mut err = bad_placeholder_type(tcx, placeholder_types);
 176     if suggest {
 177         err.multipart_suggestion(
 178             "use type parameters instead",
 179             sugg,
 180             Applicability::HasPlaceholders,
 181         );
 182     }
 183     err.emit();
 184 }
 185
 186 fn reject_placeholder_type_signatures_in_item(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
 187     let (generics, suggest) = match &item.kind {
 188         hir::ItemKind::Union(_, generics)
 189         | hir::ItemKind::Enum(_, generics)
 190         | hir::ItemKind::TraitAlias(generics, _)
 191         | hir::ItemKind::Trait(_, _, generics, ..)
 192         | hir::ItemKind::Impl(hir::Impl { generics, .. })
 193         | hir::ItemKind::Struct(_, generics) => (generics, true),
 194         hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. })
 195         | hir::ItemKind::TyAlias(_, generics) => (generics, false),
 196         // `static`, `fn` and `const` are handled elsewhere to suggest appropriate type.
 197         _ => return,
 198     };
 199
 200     let mut visitor = PlaceholderHirTyCollector::default();
 201     visitor.visit_item(item);
 202
 203     placeholder_type_error(tcx, Some(generics.span), &generics.params[..], visitor.0, suggest);
 204 }
 205
 206 impl Visitor<'tcx> for CollectItemTypesVisitor<'tcx> {
 207     type Map = Map<'tcx>;
 208
 209     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 210         NestedVisitorMap::OnlyBodies(self.tcx.hir())
 211     }
 212
 213     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 214         convert_item(self.tcx, item.hir_id);
 215         reject_placeholder_type_signatures_in_item(self.tcx, item);
 216         intravisit::walk_item(self, item);
 217     }
 218
 219     fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
 220         for param in generics.params {
 221             match param.kind {
 222                 hir::GenericParamKind::Lifetime { .. } => {}
 223                 hir::GenericParamKind::Type { default: Some(_), .. } => {
 224                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 225                     self.tcx.ensure().type_of(def_id);
 226                 }
 227                 hir::GenericParamKind::Type { .. } => {}
 228                 hir::GenericParamKind::Const { .. } => {
 229                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 230                     self.tcx.ensure().type_of(def_id);
 231                     // FIXME(const_generics_defaults)
 232                 }
 233             }
 234         }
 235         intravisit::walk_generics(self, generics);
 236     }
 237
 238     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 239         if let hir::ExprKind::Closure(..) = expr.kind {
 240             let def_id = self.tcx.hir().local_def_id(expr.hir_id);
 241             self.tcx.ensure().generics_of(def_id);
 242             self.tcx.ensure().type_of(def_id);
 243         }
 244         intravisit::walk_expr(self, expr);
 245     }
 246
 247     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
 248         convert_trait_item(self.tcx, trait_item.hir_id);
 249         intravisit::walk_trait_item(self, trait_item);
 250     }
 251
 252     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 253         convert_impl_item(self.tcx, impl_item.hir_id);
 254         intravisit::walk_impl_item(self, impl_item);
 255     }
 256 }
 257
 258 ///////////////////////////////////////////////////////////////////////////
 259 // Utility types and common code for the above passes.
 260
 261 fn bad_placeholder_type(
 262     tcx: TyCtxt<'tcx>,
 263     mut spans: Vec<Span>,
 264 ) -> rustc_errors::DiagnosticBuilder<'tcx> {
 265     spans.sort();
 266     let mut err = struct_span_err!(
 267         tcx.sess,
 268         spans.clone(),
 269         E0121,
 270         "the type placeholder `_` is not allowed within types on item signatures",
 271     );
 272     for span in spans {
 273         err.span_label(span, "not allowed in type signatures");
 274     }
 275     err
 276 }
 277
 278 impl ItemCtxt<'tcx> {
 279     pub fn new(tcx: TyCtxt<'tcx>, item_def_id: DefId) -> ItemCtxt<'tcx> {
 280         ItemCtxt { tcx, item_def_id }
 281     }
 282
 283     pub fn to_ty(&self, ast_ty: &'tcx hir::Ty<'tcx>) -> Ty<'tcx> {
 284         AstConv::ast_ty_to_ty(self, ast_ty)
 285     }
 286
 287     pub fn hir_id(&self) -> hir::HirId {
 288         self.tcx.hir().local_def_id_to_hir_id(self.item_def_id.expect_local())
 289     }
 290
 291     pub fn node(&self) -> hir::Node<'tcx> {
 292         self.tcx.hir().get(self.hir_id())
 293     }
 294 }
 295
 296 impl AstConv<'tcx> for ItemCtxt<'tcx> {
 297     fn tcx(&self) -> TyCtxt<'tcx> {
 298         self.tcx
 299     }
 300
 301     fn item_def_id(&self) -> Option<DefId> {
 302         Some(self.item_def_id)
 303     }
 304
 305     fn default_constness_for_trait_bounds(&self) -> hir::Constness {
 306         if let Some(fn_like) = FnLikeNode::from_node(self.node()) {
 307             fn_like.constness()
 308         } else {
 309             hir::Constness::NotConst
 310         }
 311     }
 312
 313     fn get_type_parameter_bounds(&self, span: Span, def_id: DefId) -> ty::GenericPredicates<'tcx> {
 314         self.tcx.at(span).type_param_predicates((self.item_def_id, def_id.expect_local()))
 315     }
 316
 317     fn re_infer(&self, _: Option<&ty::GenericParamDef>, _: Span) -> Option<ty::Region<'tcx>> {
 318         None
 319     }
 320
 321     fn allow_ty_infer(&self) -> bool {
 322         false
 323     }
 324
 325     fn ty_infer(&self, _: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
 326         self.tcx().ty_error_with_message(span, "bad_placeholder_type")
 327     }
 328
 329     fn ct_infer(
 330         &self,
 331         ty: Ty<'tcx>,
 332         _: Option<&ty::GenericParamDef>,
 333         span: Span,
 334     ) -> &'tcx Const<'tcx> {
 335         bad_placeholder_type(self.tcx(), vec![span]).emit();
 336         self.tcx().const_error(ty)
 337     }
 338
 339     fn projected_ty_from_poly_trait_ref(
 340         &self,
 341         span: Span,
 342         item_def_id: DefId,
 343         item_segment: &hir::PathSegment<'_>,
 344         poly_trait_ref: ty::PolyTraitRef<'tcx>,
 345     ) -> Ty<'tcx> {
 346         if let Some(trait_ref) = poly_trait_ref.no_bound_vars() {
 347             let item_substs = <dyn AstConv<'tcx>>::create_substs_for_associated_item(
 348                 self,
 349                 self.tcx,
 350                 span,
 351                 item_def_id,
 352                 item_segment,
 353                 trait_ref.substs,
 354             );
 355             self.tcx().mk_projection(item_def_id, item_substs)
 356         } else {
 357             // There are no late-bound regions; we can just ignore the binder.
 358             let mut err = struct_span_err!(
 359                 self.tcx().sess,
 360                 span,
 361                 E0212,
 362                 "cannot use the associated type of a trait \
 363                  with uninferred generic parameters"
 364             );
 365
 366             match self.node() {
 367                 hir::Node::Field(_) | hir::Node::Ctor(_) | hir::Node::Variant(_) => {
 368                     let item =
 369                         self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(self.hir_id()));
 370                     match &item.kind {
 371                         hir::ItemKind::Enum(_, generics)
 372                         | hir::ItemKind::Struct(_, generics)
 373                         | hir::ItemKind::Union(_, generics) => {
 374                             let lt_name = get_new_lifetime_name(self.tcx, poly_trait_ref, generics);
 375                             let (lt_sp, sugg) = match &generics.params[..] {
 376                                 [] => (generics.span, format!("<{}>", lt_name)),
 377                                 [bound, ..] => {
 378                                     (bound.span.shrink_to_lo(), format!("{}, ", lt_name))
 379                                 }
 380                             };
 381                             let suggestions = vec![
 382                                 (lt_sp, sugg),
 383                                 (
 384                                     span,
 385                                     format!(
 386                                         "{}::{}",
 387                                         // Replace the existing lifetimes with a new named lifetime.
 388                                         self.tcx
 389                                             .replace_late_bound_regions(poly_trait_ref, |_| {
 390                                                 self.tcx.mk_region(ty::ReEarlyBound(
 391                                                     ty::EarlyBoundRegion {
 392                                                         def_id: item_def_id,
 393                                                         index: 0,
 394                                                         name: Symbol::intern(&lt_name),
 395                                                     },
 396                                                 ))
 397                                             })
 398                                             .0,
 399                                         item_segment.ident
 400                                     ),
 401                                 ),
 402                             ];
 403                             err.multipart_suggestion(
 404                                 "use a fully qualified path with explicit lifetimes",
 405                                 suggestions,
 406                                 Applicability::MaybeIncorrect,
 407                             );
 408                         }
 409                         _ => {}
 410                     }
 411                 }
 412                 hir::Node::Item(hir::Item {
 413                     kind:
 414                         hir::ItemKind::Struct(..) | hir::ItemKind::Enum(..) | hir::ItemKind::Union(..),
 415                     ..
 416                 }) => {}
 417                 hir::Node::Item(_)
 418                 | hir::Node::ForeignItem(_)
 419                 | hir::Node::TraitItem(_)
 420                 | hir::Node::ImplItem(_) => {
 421                     err.span_suggestion(
 422                         span,
 423                         "use a fully qualified path with inferred lifetimes",
 424                         format!(
 425                             "{}::{}",
 426                             // Erase named lt, we want `<A as B<'_>::C`, not `<A as B<'a>::C`.
 427                             self.tcx.anonymize_late_bound_regions(poly_trait_ref).skip_binder(),
 428                             item_segment.ident
 429                         ),
 430                         Applicability::MaybeIncorrect,
 431                     );
 432                 }
 433                 _ => {}
 434             }
 435             err.emit();
 436             self.tcx().ty_error()
 437         }
 438     }
 439
 440     fn normalize_ty(&self, _span: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
 441         // Types in item signatures are not normalized to avoid undue dependencies.
 442         ty
 443     }
 444
 445     fn set_tainted_by_errors(&self) {
 446         // There's no obvious place to track this, so just let it go.
 447     }
 448
 449     fn record_ty(&self, _hir_id: hir::HirId, _ty: Ty<'tcx>, _span: Span) {
 450         // There's no place to record types from signatures?
 451     }
 452 }
 453
 454 /// Synthesize a new lifetime name that doesn't clash with any of the lifetimes already present.
 455 fn get_new_lifetime_name<'tcx>(
 456     tcx: TyCtxt<'tcx>,
 457     poly_trait_ref: ty::PolyTraitRef<'tcx>,
 458     generics: &hir::Generics<'tcx>,
 459 ) -> String {
 460     let existing_lifetimes = tcx
 461         .collect_referenced_late_bound_regions(&poly_trait_ref)
 462         .into_iter()
 463         .filter_map(|lt| {
 464             if let ty::BoundRegionKind::BrNamed(_, name) = lt {
 465                 Some(name.as_str().to_string())
 466             } else {
 467                 None
 468             }
 469         })
 470         .chain(generics.params.iter().filter_map(|param| {
 471             if let hir::GenericParamKind::Lifetime { .. } = &param.kind {
 472                 Some(param.name.ident().as_str().to_string())
 473             } else {
 474                 None
 475             }
 476         }))
 477         .collect::<FxHashSet<String>>();
 478
 479     let a_to_z_repeat_n = |n| {
 480         (b'a'..=b'z').map(move |c| {
 481             let mut s = '\''.to_string();
 482             s.extend(std::iter::repeat(char::from(c)).take(n));
 483             s
 484         })
 485     };
 486
 487     // If all single char lifetime names are present, we wrap around and double the chars.
 488     (1..).flat_map(a_to_z_repeat_n).find(|lt| !existing_lifetimes.contains(lt.as_str())).unwrap()
 489 }
 490
 491 /// Returns the predicates defined on `item_def_id` of the form
 492 /// `X: Foo` where `X` is the type parameter `def_id`.
 493 fn type_param_predicates(
 494     tcx: TyCtxt<'_>,
 495     (item_def_id, def_id): (DefId, LocalDefId),
 496 ) -> ty::GenericPredicates<'_> {
 497     use rustc_hir::*;
 498
 499     // In the AST, bounds can derive from two places. Either
 500     // written inline like `<T: Foo>` or in a where-clause like
 501     // `where T: Foo`.
 502
 503     let param_id = tcx.hir().local_def_id_to_hir_id(def_id);
 504     let param_owner = tcx.hir().ty_param_owner(param_id);
 505     let param_owner_def_id = tcx.hir().local_def_id(param_owner);
 506     let generics = tcx.generics_of(param_owner_def_id);
 507     let index = generics.param_def_id_to_index[&def_id.to_def_id()];
 508     let ty = tcx.mk_ty_param(index, tcx.hir().ty_param_name(param_id));
 509
 510     // Don't look for bounds where the type parameter isn't in scope.
 511     let parent = if item_def_id == param_owner_def_id.to_def_id() {
 512         None
 513     } else {
 514         tcx.generics_of(item_def_id).parent
 515     };
 516
 517     let mut result = parent
 518         .map(|parent| {
 519             let icx = ItemCtxt::new(tcx, parent);
 520             icx.get_type_parameter_bounds(DUMMY_SP, def_id.to_def_id())
 521         })
 522         .unwrap_or_default();
 523     let mut extend = None;
 524
 525     let item_hir_id = tcx.hir().local_def_id_to_hir_id(item_def_id.expect_local());
 526     let ast_generics = match tcx.hir().get(item_hir_id) {
 527         Node::TraitItem(item) => &item.generics,
 528
 529         Node::ImplItem(item) => &item.generics,
 530
 531         Node::Item(item) => {
 532             match item.kind {
 533                 ItemKind::Fn(.., ref generics, _)
 534                 | ItemKind::Impl(hir::Impl { ref generics, .. })
 535                 | ItemKind::TyAlias(_, ref generics)
 536                 | ItemKind::OpaqueTy(OpaqueTy { ref generics, impl_trait_fn: None, .. })
 537                 | ItemKind::Enum(_, ref generics)
 538                 | ItemKind::Struct(_, ref generics)
 539                 | ItemKind::Union(_, ref generics) => generics,
 540                 ItemKind::Trait(_, _, ref generics, ..) => {
 541                     // Implied `Self: Trait` and supertrait bounds.
 542                     if param_id == item_hir_id {
 543                         let identity_trait_ref = ty::TraitRef::identity(tcx, item_def_id);
 544                         extend =
 545                             Some((identity_trait_ref.without_const().to_predicate(tcx), item.span));
 546                     }
 547                     generics
 548                 }
 549                 _ => return result,
 550             }
 551         }
 552
 553         Node::ForeignItem(item) => match item.kind {
 554             ForeignItemKind::Fn(_, _, ref generics) => generics,
 555             _ => return result,
 556         },
 557
 558         _ => return result,
 559     };
 560
 561     let icx = ItemCtxt::new(tcx, item_def_id);
 562     let extra_predicates = extend.into_iter().chain(
 563         icx.type_parameter_bounds_in_generics(ast_generics, param_id, ty, OnlySelfBounds(true))
 564             .into_iter()
 565             .filter(|(predicate, _)| match predicate.kind().skip_binder() {
 566                 ty::PredicateKind::Trait(data, _) => data.self_ty().is_param(index),
 567                 _ => false,
 568             }),
 569     );
 570     result.predicates =
 571         tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(extra_predicates));
 572     result
 573 }
 574
 575 impl ItemCtxt<'tcx> {
 576     /// Finds bounds from `hir::Generics`. This requires scanning through the
 577     /// AST. We do this to avoid having to convert *all* the bounds, which
 578     /// would create artificial cycles. Instead, we can only convert the
 579     /// bounds for a type parameter `X` if `X::Foo` is used.
 580     fn type_parameter_bounds_in_generics(
 581         &self,
 582         ast_generics: &'tcx hir::Generics<'tcx>,
 583         param_id: hir::HirId,
 584         ty: Ty<'tcx>,
 585         only_self_bounds: OnlySelfBounds,
 586     ) -> Vec<(ty::Predicate<'tcx>, Span)> {
 587         let constness = self.default_constness_for_trait_bounds();
 588         let from_ty_params = ast_generics
 589             .params
 590             .iter()
 591             .filter_map(|param| match param.kind {
 592                 GenericParamKind::Type { .. } if param.hir_id == param_id => Some(&param.bounds),
 593                 _ => None,
 594             })
 595             .flat_map(|bounds| bounds.iter())
 596             .flat_map(|b| predicates_from_bound(self, ty, b, constness));
 597
 598         let from_where_clauses = ast_generics
 599             .where_clause
 600             .predicates
 601             .iter()
 602             .filter_map(|wp| match *wp {
 603                 hir::WherePredicate::BoundPredicate(ref bp) => Some(bp),
 604                 _ => None,
 605             })
 606             .flat_map(|bp| {
 607                 let bt = if is_param(self.tcx, &bp.bounded_ty, param_id) {
 608                     Some(ty)
 609                 } else if !only_self_bounds.0 {
 610                     Some(self.to_ty(&bp.bounded_ty))
 611                 } else {
 612                     None
 613                 };
 614                 bp.bounds.iter().filter_map(move |b| bt.map(|bt| (bt, b)))
 615             })
 616             .flat_map(|(bt, b)| predicates_from_bound(self, bt, b, constness));
 617
 618         from_ty_params.chain(from_where_clauses).collect()
 619     }
 620 }
 621
 622 /// Tests whether this is the AST for a reference to the type
 623 /// parameter with ID `param_id`. We use this so as to avoid running
 624 /// `ast_ty_to_ty`, because we want to avoid triggering an all-out
 625 /// conversion of the type to avoid inducing unnecessary cycles.
 626 fn is_param(tcx: TyCtxt<'_>, ast_ty: &hir::Ty<'_>, param_id: hir::HirId) -> bool {
 627     if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = ast_ty.kind {
 628         match path.res {
 629             Res::SelfTy(Some(def_id), None) | Res::Def(DefKind::TyParam, def_id) => {
 630                 def_id == tcx.hir().local_def_id(param_id).to_def_id()
 631             }
 632             _ => false,
 633         }
 634     } else {
 635         false
 636     }
 637 }
 638
 639 fn convert_item(tcx: TyCtxt<'_>, item_id: hir::HirId) {
 640     let it = tcx.hir().expect_item(item_id);
 641     debug!("convert: item {} with id {}", it.ident, it.hir_id);
 642     let def_id = tcx.hir().local_def_id(item_id);
 643     match it.kind {
 644         // These don't define types.
 645         hir::ItemKind::ExternCrate(_)
 646         | hir::ItemKind::Use(..)
 647         | hir::ItemKind::Mod(_)
 648         | hir::ItemKind::GlobalAsm(_) => {}
 649         hir::ItemKind::ForeignMod { items, .. } => {
 650             for item in items {
 651                 let item = tcx.hir().foreign_item(item.id);
 652                 let def_id = tcx.hir().local_def_id(item.hir_id);
 653                 tcx.ensure().generics_of(def_id);
 654                 tcx.ensure().type_of(def_id);
 655                 tcx.ensure().predicates_of(def_id);
 656                 if let hir::ForeignItemKind::Fn(..) = item.kind {
 657                     tcx.ensure().fn_sig(def_id);
 658                 }
 659             }
 660         }
 661         hir::ItemKind::Enum(ref enum_definition, _) => {
 662             tcx.ensure().generics_of(def_id);
 663             tcx.ensure().type_of(def_id);
 664             tcx.ensure().predicates_of(def_id);
 665             convert_enum_variant_types(tcx, def_id.to_def_id(), &enum_definition.variants);
 666         }
 667         hir::ItemKind::Impl { .. } => {
 668             tcx.ensure().generics_of(def_id);
 669             tcx.ensure().type_of(def_id);
 670             tcx.ensure().impl_trait_ref(def_id);
 671             tcx.ensure().predicates_of(def_id);
 672         }
 673         hir::ItemKind::Trait(..) => {
 674             tcx.ensure().generics_of(def_id);
 675             tcx.ensure().trait_def(def_id);
 676             tcx.at(it.span).super_predicates_of(def_id);
 677             tcx.ensure().predicates_of(def_id);
 678         }
 679         hir::ItemKind::TraitAlias(..) => {
 680             tcx.ensure().generics_of(def_id);
 681             tcx.at(it.span).super_predicates_of(def_id);
 682             tcx.ensure().predicates_of(def_id);
 683         }
 684         hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 685             tcx.ensure().generics_of(def_id);
 686             tcx.ensure().type_of(def_id);
 687             tcx.ensure().predicates_of(def_id);
 688
 689             for f in struct_def.fields() {
 690                 let def_id = tcx.hir().local_def_id(f.hir_id);
 691                 tcx.ensure().generics_of(def_id);
 692                 tcx.ensure().type_of(def_id);
 693                 tcx.ensure().predicates_of(def_id);
 694             }
 695
 696             if let Some(ctor_hir_id) = struct_def.ctor_hir_id() {
 697                 convert_variant_ctor(tcx, ctor_hir_id);
 698             }
 699         }
 700
 701         // Desugared from `impl Trait`, so visited by the function's return type.
 702         hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(_), .. }) => {}
 703
 704         // Don't call `type_of` on opaque types, since that depends on type
 705         // checking function bodies. `check_item_type` ensures that it's called
 706         // instead.
 707         hir::ItemKind::OpaqueTy(..) => {
 708             tcx.ensure().generics_of(def_id);
 709             tcx.ensure().predicates_of(def_id);
 710             tcx.ensure().explicit_item_bounds(def_id);
 711         }
 712         hir::ItemKind::TyAlias(..)
 713         | hir::ItemKind::Static(..)
 714         | hir::ItemKind::Const(..)
 715         | hir::ItemKind::Fn(..) => {
 716             tcx.ensure().generics_of(def_id);
 717             tcx.ensure().type_of(def_id);
 718             tcx.ensure().predicates_of(def_id);
 719             match it.kind {
 720                 hir::ItemKind::Fn(..) => tcx.ensure().fn_sig(def_id),
 721                 hir::ItemKind::OpaqueTy(..) => tcx.ensure().item_bounds(def_id),
 722                 _ => (),
 723             }
 724         }
 725     }
 726 }
 727
 728 fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::HirId) {
 729     let trait_item = tcx.hir().expect_trait_item(trait_item_id);
 730     let def_id = tcx.hir().local_def_id(trait_item.hir_id);
 731     tcx.ensure().generics_of(def_id);
 732
 733     match trait_item.kind {
 734         hir::TraitItemKind::Fn(..) => {
 735             tcx.ensure().type_of(def_id);
 736             tcx.ensure().fn_sig(def_id);
 737         }
 738
 739         hir::TraitItemKind::Const(.., Some(_)) => {
 740             tcx.ensure().type_of(def_id);
 741         }
 742
 743         hir::TraitItemKind::Const(..) => {
 744             tcx.ensure().type_of(def_id);
 745             // Account for `const C: _;`.
 746             let mut visitor = PlaceholderHirTyCollector::default();
 747             visitor.visit_trait_item(trait_item);
 748             placeholder_type_error(tcx, None, &[], visitor.0, false);
 749         }
 750
 751         hir::TraitItemKind::Type(_, Some(_)) => {
 752             tcx.ensure().item_bounds(def_id);
 753             tcx.ensure().type_of(def_id);
 754             // Account for `type T = _;`.
 755             let mut visitor = PlaceholderHirTyCollector::default();
 756             visitor.visit_trait_item(trait_item);
 757             placeholder_type_error(tcx, None, &[], visitor.0, false);
 758         }
 759
 760         hir::TraitItemKind::Type(_, None) => {
 761             tcx.ensure().item_bounds(def_id);
 762             // #74612: Visit and try to find bad placeholders
 763             // even if there is no concrete type.
 764             let mut visitor = PlaceholderHirTyCollector::default();
 765             visitor.visit_trait_item(trait_item);
 766             placeholder_type_error(tcx, None, &[], visitor.0, false);
 767         }
 768     };
 769
 770     tcx.ensure().predicates_of(def_id);
 771 }
 772
 773 fn convert_impl_item(tcx: TyCtxt<'_>, impl_item_id: hir::HirId) {
 774     let def_id = tcx.hir().local_def_id(impl_item_id);
 775     tcx.ensure().generics_of(def_id);
 776     tcx.ensure().type_of(def_id);
 777     tcx.ensure().predicates_of(def_id);
 778     let impl_item = tcx.hir().expect_impl_item(impl_item_id);
 779     match impl_item.kind {
 780         hir::ImplItemKind::Fn(..) => {
 781             tcx.ensure().fn_sig(def_id);
 782         }
 783         hir::ImplItemKind::TyAlias(_) => {
 784             // Account for `type T = _;`
 785             let mut visitor = PlaceholderHirTyCollector::default();
 786             visitor.visit_impl_item(impl_item);
 787             placeholder_type_error(tcx, None, &[], visitor.0, false);
 788         }
 789         hir::ImplItemKind::Const(..) => {}
 790     }
 791 }
 792
 793 fn convert_variant_ctor(tcx: TyCtxt<'_>, ctor_id: hir::HirId) {
 794     let def_id = tcx.hir().local_def_id(ctor_id);
 795     tcx.ensure().generics_of(def_id);
 796     tcx.ensure().type_of(def_id);
 797     tcx.ensure().predicates_of(def_id);
 798 }
 799
 800 fn convert_enum_variant_types(tcx: TyCtxt<'_>, def_id: DefId, variants: &[hir::Variant<'_>]) {
 801     let def = tcx.adt_def(def_id);
 802     let repr_type = def.repr.discr_type();
 803     let initial = repr_type.initial_discriminant(tcx);
 804     let mut prev_discr = None::<Discr<'_>>;
 805
 806     // fill the discriminant values and field types
 807     for variant in variants {
 808         let wrapped_discr = prev_discr.map_or(initial, |d| d.wrap_incr(tcx));
 809         prev_discr = Some(
 810             if let Some(ref e) = variant.disr_expr {
 811                 let expr_did = tcx.hir().local_def_id(e.hir_id);
 812                 def.eval_explicit_discr(tcx, expr_did.to_def_id())
 813             } else if let Some(discr) = repr_type.disr_incr(tcx, prev_discr) {
 814                 Some(discr)
 815             } else {
 816                 struct_span_err!(tcx.sess, variant.span, E0370, "enum discriminant overflowed")
 817                     .span_label(
 818                         variant.span,
 819                         format!("overflowed on value after {}", prev_discr.unwrap()),
 820                     )
 821                     .note(&format!(
 822                         "explicitly set `{} = {}` if that is desired outcome",
 823                         variant.ident, wrapped_discr
 824                     ))
 825                     .emit();
 826                 None
 827             }
 828             .unwrap_or(wrapped_discr),
 829         );
 830
 831         for f in variant.data.fields() {
 832             let def_id = tcx.hir().local_def_id(f.hir_id);
 833             tcx.ensure().generics_of(def_id);
 834             tcx.ensure().type_of(def_id);
 835             tcx.ensure().predicates_of(def_id);
 836         }
 837
 838         // Convert the ctor, if any. This also registers the variant as
 839         // an item.
 840         if let Some(ctor_hir_id) = variant.data.ctor_hir_id() {
 841             convert_variant_ctor(tcx, ctor_hir_id);
 842         }
 843     }
 844 }
 845
 846 fn convert_variant(
 847     tcx: TyCtxt<'_>,
 848     variant_did: Option<LocalDefId>,
 849     ctor_did: Option<LocalDefId>,
 850     ident: Ident,
 851     discr: ty::VariantDiscr,
 852     def: &hir::VariantData<'_>,
 853     adt_kind: ty::AdtKind,
 854     parent_did: LocalDefId,
 855 ) -> ty::VariantDef {
 856     let mut seen_fields: FxHashMap<Ident, Span> = Default::default();
 857     let fields = def
 858         .fields()
 859         .iter()
 860         .map(|f| {
 861             let fid = tcx.hir().local_def_id(f.hir_id);
 862             let dup_span = seen_fields.get(&f.ident.normalize_to_macros_2_0()).cloned();
 863             if let Some(prev_span) = dup_span {
 864                 tcx.sess.emit_err(errors::FieldAlreadyDeclared {
 865                     field_name: f.ident,
 866                     span: f.span,
 867                     prev_span,
 868                 });
 869             } else {
 870                 seen_fields.insert(f.ident.normalize_to_macros_2_0(), f.span);
 871             }
 872
 873             ty::FieldDef { did: fid.to_def_id(), ident: f.ident, vis: tcx.visibility(fid) }
 874         })
 875         .collect();
 876     let recovered = match def {
 877         hir::VariantData::Struct(_, r) => *r,
 878         _ => false,
 879     };
 880     ty::VariantDef::new(
 881         ident,
 882         variant_did.map(LocalDefId::to_def_id),
 883         ctor_did.map(LocalDefId::to_def_id),
 884         discr,
 885         fields,
 886         CtorKind::from_hir(def),
 887         adt_kind,
 888         parent_did.to_def_id(),
 889         recovered,
 890         adt_kind == AdtKind::Struct && tcx.has_attr(parent_did.to_def_id(), sym::non_exhaustive)
 891             || variant_did.map_or(false, |variant_did| {
 892                 tcx.has_attr(variant_did.to_def_id(), sym::non_exhaustive)
 893             }),
 894     )
 895 }
 896
 897 fn adt_def(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::AdtDef {
 898     use rustc_hir::*;
 899
 900     let def_id = def_id.expect_local();
 901     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 902     let item = match tcx.hir().get(hir_id) {
 903         Node::Item(item) => item,
 904         _ => bug!(),
 905     };
 906
 907     let repr = ReprOptions::new(tcx, def_id.to_def_id());
 908     let (kind, variants) = match item.kind {
 909         ItemKind::Enum(ref def, _) => {
 910             let mut distance_from_explicit = 0;
 911             let variants = def
 912                 .variants
 913                 .iter()
 914                 .map(|v| {
 915                     let variant_did = Some(tcx.hir().local_def_id(v.id));
 916                     let ctor_did =
 917                         v.data.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
 918
 919                     let discr = if let Some(ref e) = v.disr_expr {
 920                         distance_from_explicit = 0;
 921                         ty::VariantDiscr::Explicit(tcx.hir().local_def_id(e.hir_id).to_def_id())
 922                     } else {
 923                         ty::VariantDiscr::Relative(distance_from_explicit)
 924                     };
 925                     distance_from_explicit += 1;
 926
 927                     convert_variant(
 928                         tcx,
 929                         variant_did,
 930                         ctor_did,
 931                         v.ident,
 932                         discr,
 933                         &v.data,
 934                         AdtKind::Enum,
 935                         def_id,
 936                     )
 937                 })
 938                 .collect();
 939
 940             (AdtKind::Enum, variants)
 941         }
 942         ItemKind::Struct(ref def, _) => {
 943             let variant_did = None::<LocalDefId>;
 944             let ctor_did = def.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
 945
 946             let variants = std::iter::once(convert_variant(
 947                 tcx,
 948                 variant_did,
 949                 ctor_did,
 950                 item.ident,
 951                 ty::VariantDiscr::Relative(0),
 952                 def,
 953                 AdtKind::Struct,
 954                 def_id,
 955             ))
 956             .collect();
 957
 958             (AdtKind::Struct, variants)
 959         }
 960         ItemKind::Union(ref def, _) => {
 961             let variant_did = None;
 962             let ctor_did = def.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
 963
 964             let variants = std::iter::once(convert_variant(
 965                 tcx,
 966                 variant_did,
 967                 ctor_did,
 968                 item.ident,
 969                 ty::VariantDiscr::Relative(0),
 970                 def,
 971                 AdtKind::Union,
 972                 def_id,
 973             ))
 974             .collect();
 975
 976             (AdtKind::Union, variants)
 977         }
 978         _ => bug!(),
 979     };
 980     tcx.alloc_adt_def(def_id.to_def_id(), kind, variants, repr)
 981 }
 982
 983 /// Ensures that the super-predicates of the trait with a `DefId`
 984 /// of `trait_def_id` are converted and stored. This also ensures that
 985 /// the transitive super-predicates are converted.
 986 fn super_predicates_of(tcx: TyCtxt<'_>, trait_def_id: DefId) -> ty::GenericPredicates<'_> {
 987     debug!("super_predicates(trait_def_id={:?})", trait_def_id);
 988     let trait_hir_id = tcx.hir().local_def_id_to_hir_id(trait_def_id.expect_local());
 989
 990     let item = match tcx.hir().get(trait_hir_id) {
 991         Node::Item(item) => item,
 992         _ => bug!("trait_node_id {} is not an item", trait_hir_id),
 993     };
 994
 995     let (generics, bounds) = match item.kind {
 996         hir::ItemKind::Trait(.., ref generics, ref supertraits, _) => (generics, supertraits),
 997         hir::ItemKind::TraitAlias(ref generics, ref supertraits) => (generics, supertraits),
 998         _ => span_bug!(item.span, "super_predicates invoked on non-trait"),
 999     };
1000
1001     let icx = ItemCtxt::new(tcx, trait_def_id);
1002
1003     // Convert the bounds that follow the colon, e.g., `Bar + Zed` in `trait Foo: Bar + Zed`.
1004     let self_param_ty = tcx.types.self_param;
1005     let superbounds1 =
1006         AstConv::compute_bounds(&icx, self_param_ty, bounds, SizedByDefault::No, item.span);
1007
1008     let superbounds1 = superbounds1.predicates(tcx, self_param_ty);
1009
1010     // Convert any explicit superbounds in the where-clause,
1011     // e.g., `trait Foo where Self: Bar`.
1012     // In the case of trait aliases, however, we include all bounds in the where-clause,
1013     // so e.g., `trait Foo = where u32: PartialEq<Self>` would include `u32: PartialEq<Self>`
1014     // as one of its "superpredicates".
1015     let is_trait_alias = tcx.is_trait_alias(trait_def_id);
1016     let superbounds2 = icx.type_parameter_bounds_in_generics(
1017         generics,
1018         item.hir_id,
1019         self_param_ty,
1020         OnlySelfBounds(!is_trait_alias),
1021     );
1022
1023     // Combine the two lists to form the complete set of superbounds:
1024     let superbounds = &*tcx.arena.alloc_from_iter(superbounds1.into_iter().chain(superbounds2));
1025
1026     // Now require that immediate supertraits are converted,
1027     // which will, in turn, reach indirect supertraits.
1028     for &(pred, span) in superbounds {
1029         debug!("superbound: {:?}", pred);
1030         if let ty::PredicateKind::Trait(bound, _) = pred.kind().skip_binder() {
1031             tcx.at(span).super_predicates_of(bound.def_id());
1032         }
1033     }
1034
1035     ty::GenericPredicates { parent: None, predicates: superbounds }
1036 }
1037
1038 fn trait_def(tcx: TyCtxt<'_>, def_id: DefId) -> ty::TraitDef {
1039     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
1040     let item = tcx.hir().expect_item(hir_id);
1041
1042     let (is_auto, unsafety) = match item.kind {
1043         hir::ItemKind::Trait(is_auto, unsafety, ..) => (is_auto == hir::IsAuto::Yes, unsafety),
1044         hir::ItemKind::TraitAlias(..) => (false, hir::Unsafety::Normal),
1045         _ => span_bug!(item.span, "trait_def_of_item invoked on non-trait"),
1046     };
1047
1048     let paren_sugar = tcx.has_attr(def_id, sym::rustc_paren_sugar);
1049     if paren_sugar && !tcx.features().unboxed_closures {
1050         tcx.sess
1051             .struct_span_err(
1052                 item.span,
1053                 "the `#[rustc_paren_sugar]` attribute is a temporary means of controlling \
1054                  which traits can use parenthetical notation",
1055             )
1056             .help("add `#![feature(unboxed_closures)]` to the crate attributes to use it")
1057             .emit();
1058     }
1059
1060     let is_marker = tcx.has_attr(def_id, sym::marker);
1061     let spec_kind = if tcx.has_attr(def_id, sym::rustc_unsafe_specialization_marker) {
1062         ty::trait_def::TraitSpecializationKind::Marker
1063     } else if tcx.has_attr(def_id, sym::rustc_specialization_trait) {
1064         ty::trait_def::TraitSpecializationKind::AlwaysApplicable
1065     } else {
1066         ty::trait_def::TraitSpecializationKind::None
1067     };
1068     let def_path_hash = tcx.def_path_hash(def_id);
1069     ty::TraitDef::new(def_id, unsafety, paren_sugar, is_auto, is_marker, spec_kind, def_path_hash)
1070 }
1071
1072 fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<Span> {
1073     struct LateBoundRegionsDetector<'tcx> {
1074         tcx: TyCtxt<'tcx>,
1075         outer_index: ty::DebruijnIndex,
1076         has_late_bound_regions: Option<Span>,
1077     }
1078
1079     impl Visitor<'tcx> for LateBoundRegionsDetector<'tcx> {
1080         type Map = intravisit::ErasedMap<'tcx>;
1081
1082         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1083             NestedVisitorMap::None
1084         }
1085
1086         fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
1087             if self.has_late_bound_regions.is_some() {
1088                 return;
1089             }
1090             match ty.kind {
1091                 hir::TyKind::BareFn(..) => {
1092                     self.outer_index.shift_in(1);
1093                     intravisit::walk_ty(self, ty);
1094                     self.outer_index.shift_out(1);
1095                 }
1096                 _ => intravisit::walk_ty(self, ty),
1097             }
1098         }
1099
1100         fn visit_poly_trait_ref(
1101             &mut self,
1102             tr: &'tcx hir::PolyTraitRef<'tcx>,
1103             m: hir::TraitBoundModifier,
1104         ) {
1105             if self.has_late_bound_regions.is_some() {
1106                 return;
1107             }
1108             self.outer_index.shift_in(1);
1109             intravisit::walk_poly_trait_ref(self, tr, m);
1110             self.outer_index.shift_out(1);
1111         }
1112
1113         fn visit_lifetime(&mut self, lt: &'tcx hir::Lifetime) {
1114             if self.has_late_bound_regions.is_some() {
1115                 return;
1116             }
1117
1118             match self.tcx.named_region(lt.hir_id) {
1119                 Some(rl::Region::Static | rl::Region::EarlyBound(..)) => {}
1120                 Some(
1121                     rl::Region::LateBound(debruijn, _, _) | rl::Region::LateBoundAnon(debruijn, _),
1122                 ) if debruijn < self.outer_index => {}
1123                 Some(
1124                     rl::Region::LateBound(..)
1125                     | rl::Region::LateBoundAnon(..)
1126                     | rl::Region::Free(..),
1127                 )
1128                 | None => {
1129                     self.has_late_bound_regions = Some(lt.span);
1130                 }
1131             }
1132         }
1133     }
1134
1135     fn has_late_bound_regions<'tcx>(
1136         tcx: TyCtxt<'tcx>,
1137         generics: &'tcx hir::Generics<'tcx>,
1138         decl: &'tcx hir::FnDecl<'tcx>,
1139     ) -> Option<Span> {
1140         let mut visitor = LateBoundRegionsDetector {
1141             tcx,
1142             outer_index: ty::INNERMOST,
1143             has_late_bound_regions: None,
1144         };
1145         for param in generics.params {
1146             if let GenericParamKind::Lifetime { .. } = param.kind {
1147                 if tcx.is_late_bound(param.hir_id) {
1148                     return Some(param.span);
1149                 }
1150             }
1151         }
1152         visitor.visit_fn_decl(decl);
1153         visitor.has_late_bound_regions
1154     }
1155
1156     match node {
1157         Node::TraitItem(item) => match item.kind {
1158             hir::TraitItemKind::Fn(ref sig, _) => {
1159                 has_late_bound_regions(tcx, &item.generics, &sig.decl)
1160             }
1161             _ => None,
1162         },
1163         Node::ImplItem(item) => match item.kind {
1164             hir::ImplItemKind::Fn(ref sig, _) => {
1165                 has_late_bound_regions(tcx, &item.generics, &sig.decl)
1166             }
1167             _ => None,
1168         },
1169         Node::ForeignItem(item) => match item.kind {
1170             hir::ForeignItemKind::Fn(ref fn_decl, _, ref generics) => {
1171                 has_late_bound_regions(tcx, generics, fn_decl)
1172             }
1173             _ => None,
1174         },
1175         Node::Item(item) => match item.kind {
1176             hir::ItemKind::Fn(ref sig, .., ref generics, _) => {
1177                 has_late_bound_regions(tcx, generics, &sig.decl)
1178             }
1179             _ => None,
1180         },
1181         _ => None,
1182     }
1183 }
1184
1185 struct AnonConstInParamListDetector {
1186     in_param_list: bool,
1187     found_anon_const_in_list: bool,
1188     ct: HirId,
1189 }
1190
1191 impl<'v> Visitor<'v> for AnonConstInParamListDetector {
1192     type Map = intravisit::ErasedMap<'v>;
1193
1194     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1195         NestedVisitorMap::None
1196     }
1197
1198     fn visit_generic_param(&mut self, p: &'v hir::GenericParam<'v>) {
1199         let prev = self.in_param_list;
1200         self.in_param_list = true;
1201         intravisit::walk_generic_param(self, p);
1202         self.in_param_list = prev;
1203     }
1204
1205     fn visit_anon_const(&mut self, c: &'v hir::AnonConst) {
1206         if self.in_param_list && self.ct == c.hir_id {
1207             self.found_anon_const_in_list = true;
1208         } else {
1209             intravisit::walk_anon_const(self, c)
1210         }
1211     }
1212 }
1213
1214 fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
1215     use rustc_hir::*;
1216
1217     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
1218
1219     let node = tcx.hir().get(hir_id);
1220     let parent_def_id = match node {
1221         Node::ImplItem(_)
1222         | Node::TraitItem(_)
1223         | Node::Variant(_)
1224         | Node::Ctor(..)
1225         | Node::Field(_) => {
1226             let parent_id = tcx.hir().get_parent_item(hir_id);
1227             Some(tcx.hir().local_def_id(parent_id).to_def_id())
1228         }
1229         // FIXME(#43408) always enable this once `lazy_normalization` is
1230         // stable enough and does not need a feature gate anymore.
1231         Node::AnonConst(_) => {
1232             let parent_id = tcx.hir().get_parent_item(hir_id);
1233             let parent_def_id = tcx.hir().local_def_id(parent_id);
1234
1235             let mut in_param_list = false;
1236             for (_parent, node) in tcx.hir().parent_iter(hir_id) {
1237                 if let Some(generics) = node.generics() {
1238                     let mut visitor = AnonConstInParamListDetector {
1239                         in_param_list: false,
1240                         found_anon_const_in_list: false,
1241                         ct: hir_id,
1242                     };
1243
1244                     visitor.visit_generics(generics);
1245                     in_param_list = visitor.found_anon_const_in_list;
1246                     break;
1247                 }
1248             }
1249
1250             if in_param_list {
1251                 // We do not allow generic parameters in anon consts if we are inside
1252                 // of a param list.
1253                 //
1254                 // This affects both default type bindings, e.g. `struct<T, U = [u8; std::mem::size_of::<T>()]>(T, U)`,
1255                 // and the types of const parameters, e.g. `struct V<const N: usize, const M: [u8; N]>();`.
1256                 None
1257             } else if tcx.lazy_normalization() {
1258                 // HACK(eddyb) this provides the correct generics when
1259                 // `feature(const_generics)` is enabled, so that const expressions
1260                 // used with const generics, e.g. `Foo<{N+1}>`, can work at all.
1261                 //
1262                 // Note that we do not supply the parent generics when using
1263                 // `min_const_generics`.
1264                 Some(parent_def_id.to_def_id())
1265             } else {
1266                 let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
1267                 match parent_node {
1268                     // HACK(eddyb) this provides the correct generics for repeat
1269                     // expressions' count (i.e. `N` in `[x; N]`), and explicit
1270                     // `enum` discriminants (i.e. `D` in `enum Foo { Bar = D }`),
1271                     // as they shouldn't be able to cause query cycle errors.
1272                     Node::Expr(&Expr { kind: ExprKind::Repeat(_, ref constant), .. })
1273                     | Node::Variant(Variant { disr_expr: Some(ref constant), .. })
1274                         if constant.hir_id == hir_id =>
1275                     {
1276                         Some(parent_def_id.to_def_id())
1277                     }
1278
1279                     _ => None,
1280                 }
1281             }
1282         }
1283         Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => {
1284             Some(tcx.closure_base_def_id(def_id))
1285         }
1286         Node::Item(item) => match item.kind {
1287             ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn, .. }) => {
1288                 impl_trait_fn.or_else(|| {
1289                     let parent_id = tcx.hir().get_parent_item(hir_id);
1290                     assert!(parent_id != hir_id && parent_id != CRATE_HIR_ID);
1291                     debug!("generics_of: parent of opaque ty {:?} is {:?}", def_id, parent_id);
1292                     // Opaque types are always nested within another item, and
1293                     // inherit the generics of the item.
1294                     Some(tcx.hir().local_def_id(parent_id).to_def_id())
1295                 })
1296             }
1297             _ => None,
1298         },
1299         _ => None,
1300     };
1301
1302     let mut opt_self = None;
1303     let mut allow_defaults = false;
1304
1305     let no_generics = hir::Generics::empty();
1306     let ast_generics = match node {
1307         Node::TraitItem(item) => &item.generics,
1308
1309         Node::ImplItem(item) => &item.generics,
1310
1311         Node::Item(item) => {
1312             match item.kind {
1313                 ItemKind::Fn(.., ref generics, _)
1314                 | ItemKind::Impl(hir::Impl { ref generics, .. }) => generics,
1315
1316                 ItemKind::TyAlias(_, ref generics)
1317                 | ItemKind::Enum(_, ref generics)
1318                 | ItemKind::Struct(_, ref generics)
1319                 | ItemKind::OpaqueTy(hir::OpaqueTy { ref generics, .. })
1320                 | ItemKind::Union(_, ref generics) => {
1321                     allow_defaults = true;
1322                     generics
1323                 }
1324
1325                 ItemKind::Trait(_, _, ref generics, ..)
1326                 | ItemKind::TraitAlias(ref generics, ..) => {
1327                     // Add in the self type parameter.
1328                     //
1329                     // Something of a hack: use the node id for the trait, also as
1330                     // the node id for the Self type parameter.
1331                     let param_id = item.hir_id;
1332
1333                     opt_self = Some(ty::GenericParamDef {
1334                         index: 0,
1335                         name: kw::SelfUpper,
1336                         def_id: tcx.hir().local_def_id(param_id).to_def_id(),
1337                         pure_wrt_drop: false,
1338                         kind: ty::GenericParamDefKind::Type {
1339                             has_default: false,
1340                             object_lifetime_default: rl::Set1::Empty,
1341                             synthetic: None,
1342                         },
1343                     });
1344
1345                     allow_defaults = true;
1346                     generics
1347                 }
1348
1349                 _ => &no_generics,
1350             }
1351         }
1352
1353         Node::ForeignItem(item) => match item.kind {
1354             ForeignItemKind::Static(..) => &no_generics,
1355             ForeignItemKind::Fn(_, _, ref generics) => generics,
1356             ForeignItemKind::Type => &no_generics,
1357         },
1358
1359         _ => &no_generics,
1360     };
1361
1362     let has_self = opt_self.is_some();
1363     let mut parent_has_self = false;
1364     let mut own_start = has_self as u32;
1365     let parent_count = parent_def_id.map_or(0, |def_id| {
1366         let generics = tcx.generics_of(def_id);
1367         assert_eq!(has_self, false);
1368         parent_has_self = generics.has_self;
1369         own_start = generics.count() as u32;
1370         generics.parent_count + generics.params.len()
1371     });
1372
1373     let mut params: Vec<_> = Vec::with_capacity(ast_generics.params.len() + has_self as usize);
1374
1375     if let Some(opt_self) = opt_self {
1376         params.push(opt_self);
1377     }
1378
1379     let early_lifetimes = early_bound_lifetimes_from_generics(tcx, ast_generics);
1380     params.extend(early_lifetimes.enumerate().map(|(i, param)| ty::GenericParamDef {
1381         name: param.name.ident().name,
1382         index: own_start + i as u32,
1383         def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
1384         pure_wrt_drop: param.pure_wrt_drop,
1385         kind: ty::GenericParamDefKind::Lifetime,
1386     }));
1387
1388     let object_lifetime_defaults = tcx.object_lifetime_defaults(hir_id);
1389
1390     // Now create the real type and const parameters.
1391     let type_start = own_start - has_self as u32 + params.len() as u32;
1392     let mut i = 0;
1393
1394     params.extend(ast_generics.params.iter().filter_map(|param| match param.kind {
1395         GenericParamKind::Lifetime { .. } => None,
1396         GenericParamKind::Type { ref default, synthetic, .. } => {
1397             if !allow_defaults && default.is_some() {
1398                 if !tcx.features().default_type_parameter_fallback {
1399                     tcx.struct_span_lint_hir(
1400                         lint::builtin::INVALID_TYPE_PARAM_DEFAULT,
1401                         param.hir_id,
1402                         param.span,
1403                         |lint| {
1404                             lint.build(
1405                                 "defaults for type parameters are only allowed in \
1406                                  `struct`, `enum`, `type`, or `trait` definitions.",
1407                             )
1408                             .emit();
1409                         },
1410                     );
1411                 }
1412             }
1413
1414             let kind = ty::GenericParamDefKind::Type {
1415                 has_default: default.is_some(),
1416                 object_lifetime_default: object_lifetime_defaults
1417                     .as_ref()
1418                     .map_or(rl::Set1::Empty, |o| o[i]),
1419                 synthetic,
1420             };
1421
1422             let param_def = ty::GenericParamDef {
1423                 index: type_start + i as u32,
1424                 name: param.name.ident().name,
1425                 def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
1426                 pure_wrt_drop: param.pure_wrt_drop,
1427                 kind,
1428             };
1429             i += 1;
1430             Some(param_def)
1431         }
1432         GenericParamKind::Const { .. } => {
1433             let param_def = ty::GenericParamDef {
1434                 index: type_start + i as u32,
1435                 name: param.name.ident().name,
1436                 def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
1437                 pure_wrt_drop: param.pure_wrt_drop,
1438                 kind: ty::GenericParamDefKind::Const,
1439             };
1440             i += 1;
1441             Some(param_def)
1442         }
1443     }));
1444
1445     // provide junk type parameter defs - the only place that
1446     // cares about anything but the length is instantiation,
1447     // and we don't do that for closures.
1448     if let Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(.., gen), .. }) = node {
1449         let dummy_args = if gen.is_some() {
1450             &["<resume_ty>", "<yield_ty>", "<return_ty>", "<witness>", "<upvars>"][..]
1451         } else {
1452             &["<closure_kind>", "<closure_signature>", "<upvars>"][..]
1453         };
1454
1455         params.extend(dummy_args.iter().enumerate().map(|(i, &arg)| ty::GenericParamDef {
1456             index: type_start + i as u32,
1457             name: Symbol::intern(arg),
1458             def_id,
1459             pure_wrt_drop: false,
1460             kind: ty::GenericParamDefKind::Type {
1461                 has_default: false,
1462                 object_lifetime_default: rl::Set1::Empty,
1463                 synthetic: None,
1464             },
1465         }));
1466     }
1467
1468     let param_def_id_to_index = params.iter().map(|param| (param.def_id, param.index)).collect();
1469
1470     ty::Generics {
1471         parent: parent_def_id,
1472         parent_count,
1473         params,
1474         param_def_id_to_index,
1475         has_self: has_self || parent_has_self,
1476         has_late_bound_regions: has_late_bound_regions(tcx, node),
1477     }
1478 }
1479
1480 fn are_suggestable_generic_args(generic_args: &[hir::GenericArg<'_>]) -> bool {
1481     generic_args
1482         .iter()
1483         .filter_map(|arg| match arg {
1484             hir::GenericArg::Type(ty) => Some(ty),
1485             _ => None,
1486         })
1487         .any(is_suggestable_infer_ty)
1488 }
1489
1490 /// Whether `ty` is a type with `_` placeholders that can be inferred. Used in diagnostics only to
1491 /// use inference to provide suggestions for the appropriate type if possible.
1492 fn is_suggestable_infer_ty(ty: &hir::Ty<'_>) -> bool {
1493     use hir::TyKind::*;
1494     match &ty.kind {
1495         Infer => true,
1496         Slice(ty) | Array(ty, _) => is_suggestable_infer_ty(ty),
1497         Tup(tys) => tys.iter().any(is_suggestable_infer_ty),
1498         Ptr(mut_ty) | Rptr(_, mut_ty) => is_suggestable_infer_ty(mut_ty.ty),
1499         OpaqueDef(_, generic_args) => are_suggestable_generic_args(generic_args),
1500         Path(hir::QPath::TypeRelative(ty, segment)) => {
1501             is_suggestable_infer_ty(ty) || are_suggestable_generic_args(segment.args().args)
1502         }
1503         Path(hir::QPath::Resolved(ty_opt, hir::Path { segments, .. })) => {
1504             ty_opt.map_or(false, is_suggestable_infer_ty)
1505                 || segments.iter().any(|segment| are_suggestable_generic_args(segment.args().args))
1506         }
1507         _ => false,
1508     }
1509 }
1510
1511 pub fn get_infer_ret_ty(output: &'hir hir::FnRetTy<'hir>) -> Option<&'hir hir::Ty<'hir>> {
1512     if let hir::FnRetTy::Return(ref ty) = output {
1513         if is_suggestable_infer_ty(ty) {
1514             return Some(&**ty);
1515         }
1516     }
1517     None
1518 }
1519
1520 fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
1521     use rustc_hir::Node::*;
1522     use rustc_hir::*;
1523
1524     let def_id = def_id.expect_local();
1525     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
1526
1527     let icx = ItemCtxt::new(tcx, def_id.to_def_id());
1528
1529     match tcx.hir().get(hir_id) {
1530         TraitItem(hir::TraitItem {
1531             kind: TraitItemKind::Fn(sig, TraitFn::Provided(_)),
1532             ident,
1533             generics,
1534             ..
1535         })
1536         | ImplItem(hir::ImplItem { kind: ImplItemKind::Fn(sig, _), ident, generics, .. })
1537         | Item(hir::Item { kind: ItemKind::Fn(sig, generics, _), ident, .. }) => {
1538             match get_infer_ret_ty(&sig.decl.output) {
1539                 Some(ty) => {
1540                     let fn_sig = tcx.typeck(def_id).liberated_fn_sigs()[hir_id];
1541                     let mut visitor = PlaceholderHirTyCollector::default();
1542                     visitor.visit_ty(ty);
1543                     let mut diag = bad_placeholder_type(tcx, visitor.0);
1544                     let ret_ty = fn_sig.output();
1545                     if ret_ty != tcx.ty_error() {
1546                         if !ret_ty.is_closure() {
1547                             let ret_ty_str = match ret_ty.kind() {
1548                                 // Suggest a function pointer return type instead of a unique function definition
1549                                 // (e.g. `fn() -> i32` instead of `fn() -> i32 { f }`, the latter of which is invalid
1550                                 // syntax)
1551                                 ty::FnDef(..) => ret_ty.fn_sig(tcx).to_string(),
1552                                 _ => ret_ty.to_string(),
1553                             };
1554                             diag.span_suggestion(
1555                                 ty.span,
1556                                 "replace with the correct return type",
1557                                 ret_ty_str,
1558                                 Applicability::MaybeIncorrect,
1559                             );
1560                         } else {
1561                             // We're dealing with a closure, so we should suggest using `impl Fn` or trait bounds
1562                             // to prevent the user from getting a papercut while trying to use the unique closure
1563                             // syntax (e.g. `[closure@src/lib.rs:2:5: 2:9]`).
1564                             diag.help("consider using an `Fn`, `FnMut`, or `FnOnce` trait bound");
1565                             diag.note("for more information on `Fn` traits and closure types, see https://doc.rust-lang.org/book/ch13-01-closures.html");
1566                         }
1567                     }
1568                     diag.emit();
1569                     ty::Binder::bind(fn_sig)
1570                 }
1571                 None => AstConv::ty_of_fn(
1572                     &icx,
1573                     sig.header.unsafety,
1574                     sig.header.abi,
1575                     &sig.decl,
1576                     &generics,
1577                     Some(ident.span),
1578                 ),
1579             }
1580         }
1581
1582         TraitItem(hir::TraitItem {
1583             kind: TraitItemKind::Fn(FnSig { header, decl, span: _ }, _),
1584             ident,
1585             generics,
1586             ..
1587         }) => {
1588             AstConv::ty_of_fn(&icx, header.unsafety, header.abi, decl, &generics, Some(ident.span))
1589         }
1590
1591         ForeignItem(&hir::ForeignItem {
1592             kind: ForeignItemKind::Fn(ref fn_decl, _, _),
1593             ident,
1594             ..
1595         }) => {
1596             let abi = tcx.hir().get_foreign_abi(hir_id);
1597             compute_sig_of_foreign_fn_decl(tcx, def_id.to_def_id(), fn_decl, abi, ident)
1598         }
1599
1600         Ctor(data) | Variant(hir::Variant { data, .. }) if data.ctor_hir_id().is_some() => {
1601             let ty = tcx.type_of(tcx.hir().get_parent_did(hir_id).to_def_id());
1602             let inputs =
1603                 data.fields().iter().map(|f| tcx.type_of(tcx.hir().local_def_id(f.hir_id)));
1604             ty::Binder::bind(tcx.mk_fn_sig(
1605                 inputs,
1606                 ty,
1607                 false,
1608                 hir::Unsafety::Normal,
1609                 abi::Abi::Rust,
1610             ))
1611         }
1612
1613         Expr(&hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => {
1614             // Closure signatures are not like other function
1615             // signatures and cannot be accessed through `fn_sig`. For
1616             // example, a closure signature excludes the `self`
1617             // argument. In any case they are embedded within the
1618             // closure type as part of the `ClosureSubsts`.
1619             //
1620             // To get the signature of a closure, you should use the
1621             // `sig` method on the `ClosureSubsts`:
1622             //
1623             //    substs.as_closure().sig(def_id, tcx)
1624             bug!(
1625                 "to get the signature of a closure, use `substs.as_closure().sig()` not `fn_sig()`",
1626             );
1627         }
1628
1629         x => {
1630             bug!("unexpected sort of node in fn_sig(): {:?}", x);
1631         }
1632     }
1633 }
1634
1635 fn impl_trait_ref(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ty::TraitRef<'_>> {
1636     let icx = ItemCtxt::new(tcx, def_id);
1637
1638     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
1639     match tcx.hir().expect_item(hir_id).kind {
1640         hir::ItemKind::Impl(ref impl_) => impl_.of_trait.as_ref().map(|ast_trait_ref| {
1641             let selfty = tcx.type_of(def_id);
1642             AstConv::instantiate_mono_trait_ref(&icx, ast_trait_ref, selfty)
1643         }),
1644         _ => bug!(),
1645     }
1646 }
1647
1648 fn impl_polarity(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ImplPolarity {
1649     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
1650     let is_rustc_reservation = tcx.has_attr(def_id, sym::rustc_reservation_impl);
1651     let item = tcx.hir().expect_item(hir_id);
1652     match &item.kind {
1653         hir::ItemKind::Impl(hir::Impl {
1654             polarity: hir::ImplPolarity::Negative(span),
1655             of_trait,
1656             ..
1657         }) => {
1658             if is_rustc_reservation {
1659                 let span = span.to(of_trait.as_ref().map_or(*span, |t| t.path.span));
1660                 tcx.sess.span_err(span, "reservation impls can't be negative");
1661             }
1662             ty::ImplPolarity::Negative
1663         }
1664         hir::ItemKind::Impl(hir::Impl {
1665             polarity: hir::ImplPolarity::Positive,
1666             of_trait: None,
1667             ..
1668         }) => {
1669             if is_rustc_reservation {
1670                 tcx.sess.span_err(item.span, "reservation impls can't be inherent");
1671             }
1672             ty::ImplPolarity::Positive
1673         }
1674         hir::ItemKind::Impl(hir::Impl {
1675             polarity: hir::ImplPolarity::Positive,
1676             of_trait: Some(_),
1677             ..
1678         }) => {
1679             if is_rustc_reservation {
1680                 ty::ImplPolarity::Reservation
1681             } else {
1682                 ty::ImplPolarity::Positive
1683             }
1684         }
1685         item => bug!("impl_polarity: {:?} not an impl", item),
1686     }
1687 }
1688
1689 /// Returns the early-bound lifetimes declared in this generics
1690 /// listing. For anything other than fns/methods, this is just all
1691 /// the lifetimes that are declared. For fns or methods, we have to
1692 /// screen out those that do not appear in any where-clauses etc using
1693 /// `resolve_lifetime::early_bound_lifetimes`.
1694 fn early_bound_lifetimes_from_generics<'a, 'tcx: 'a>(
1695     tcx: TyCtxt<'tcx>,
1696     generics: &'a hir::Generics<'a>,
1697 ) -> impl Iterator<Item = &'a hir::GenericParam<'a>> + Captures<'tcx> {
1698     generics.params.iter().filter(move |param| match param.kind {
1699         GenericParamKind::Lifetime { .. } => !tcx.is_late_bound(param.hir_id),
1700         _ => false,
1701     })
1702 }
1703
1704 /// Returns a list of type predicates for the definition with ID `def_id`, including inferred
1705 /// lifetime constraints. This includes all predicates returned by `explicit_predicates_of`, plus
1706 /// inferred constraints concerning which regions outlive other regions.
1707 fn predicates_defined_on(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
1708     debug!("predicates_defined_on({:?})", def_id);
1709     let mut result = tcx.explicit_predicates_of(def_id);
1710     debug!("predicates_defined_on: explicit_predicates_of({:?}) = {:?}", def_id, result,);
1711     let inferred_outlives = tcx.inferred_outlives_of(def_id);
1712     if !inferred_outlives.is_empty() {
1713         debug!(
1714             "predicates_defined_on: inferred_outlives_of({:?}) = {:?}",
1715             def_id, inferred_outlives,
1716         );
1717         if result.predicates.is_empty() {
1718             result.predicates = inferred_outlives;
1719         } else {
1720             result.predicates = tcx
1721                 .arena
1722                 .alloc_from_iter(result.predicates.iter().chain(inferred_outlives).copied());
1723         }
1724     }
1725
1726     debug!("predicates_defined_on({:?}) = {:?}", def_id, result);
1727     result
1728 }
1729
1730 /// Returns a list of all type predicates (explicit and implicit) for the definition with
1731 /// ID `def_id`. This includes all predicates returned by `predicates_defined_on`, plus
1732 /// `Self: Trait` predicates for traits.
1733 fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
1734     let mut result = tcx.predicates_defined_on(def_id);
1735
1736     if tcx.is_trait(def_id) {
1737         // For traits, add `Self: Trait` predicate. This is
1738         // not part of the predicates that a user writes, but it
1739         // is something that one must prove in order to invoke a
1740         // method or project an associated type.
1741         //
1742         // In the chalk setup, this predicate is not part of the
1743         // "predicates" for a trait item. But it is useful in
1744         // rustc because if you directly (e.g.) invoke a trait
1745         // method like `Trait::method(...)`, you must naturally
1746         // prove that the trait applies to the types that were
1747         // used, and adding the predicate into this list ensures
1748         // that this is done.
1749         let span = tcx.sess.source_map().guess_head_span(tcx.def_span(def_id));
1750         result.predicates =
1751             tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(std::iter::once((
1752                 ty::TraitRef::identity(tcx, def_id).without_const().to_predicate(tcx),
1753                 span,
1754             ))));
1755     }
1756     debug!("predicates_of(def_id={:?}) = {:?}", def_id, result);
1757     result
1758 }
1759
1760 /// Returns a list of user-specified type predicates for the definition with ID `def_id`.
1761 /// N.B., this does not include any implied/inferred constraints.
1762 fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
1763     use rustc_hir::*;
1764
1765     debug!("explicit_predicates_of(def_id={:?})", def_id);
1766
1767     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
1768     let node = tcx.hir().get(hir_id);
1769
1770     let mut is_trait = None;
1771     let mut is_default_impl_trait = None;
1772
1773     let icx = ItemCtxt::new(tcx, def_id);
1774     let constness = icx.default_constness_for_trait_bounds();
1775
1776     const NO_GENERICS: &hir::Generics<'_> = &hir::Generics::empty();
1777
1778     // We use an `IndexSet` to preserves order of insertion.
1779     // Preserving the order of insertion is important here so as not to break UI tests.
1780     let mut predicates: FxIndexSet<(ty::Predicate<'_>, Span)> = FxIndexSet::default();
1781
1782     let ast_generics = match node {
1783         Node::TraitItem(item) => &item.generics,
1784
1785         Node::ImplItem(item) => &item.generics,
1786
1787         Node::Item(item) => {
1788             match item.kind {
1789                 ItemKind::Impl(ref impl_) => {
1790                     if impl_.defaultness.is_default() {
1791                         is_default_impl_trait = tcx.impl_trait_ref(def_id);
1792                     }
1793                     &impl_.generics
1794                 }
1795                 ItemKind::Fn(.., ref generics, _)
1796                 | ItemKind::TyAlias(_, ref generics)
1797                 | ItemKind::Enum(_, ref generics)
1798                 | ItemKind::Struct(_, ref generics)
1799                 | ItemKind::Union(_, ref generics) => generics,
1800
1801                 ItemKind::Trait(_, _, ref generics, ..) => {
1802                     is_trait = Some(ty::TraitRef::identity(tcx, def_id));
1803                     generics
1804                 }
1805                 ItemKind::TraitAlias(ref generics, _) => {
1806                     is_trait = Some(ty::TraitRef::identity(tcx, def_id));
1807                     generics
1808                 }
1809                 ItemKind::OpaqueTy(OpaqueTy {
1810                     bounds: _,
1811                     impl_trait_fn,
1812                     ref generics,
1813                     origin: _,
1814                 }) => {
1815                     if impl_trait_fn.is_some() {
1816                         // return-position impl trait
1817                         //
1818                         // We don't inherit predicates from the parent here:
1819                         // If we have, say `fn f<'a, T: 'a>() -> impl Sized {}`
1820                         // then the return type is `f::<'static, T>::{{opaque}}`.
1821                         //
1822                         // If we inherited the predicates of `f` then we would
1823                         // require that `T: 'static` to show that the return
1824                         // type is well-formed.
1825                         //
1826                         // The only way to have something with this opaque type
1827                         // is from the return type of the containing function,
1828                         // which will ensure that the function's predicates
1829                         // hold.
1830                         return ty::GenericPredicates { parent: None, predicates: &[] };
1831                     } else {
1832                         // type-alias impl trait
1833                         generics
1834                     }
1835                 }
1836
1837                 _ => NO_GENERICS,
1838             }
1839         }
1840
1841         Node::ForeignItem(item) => match item.kind {
1842             ForeignItemKind::Static(..) => NO_GENERICS,
1843             ForeignItemKind::Fn(_, _, ref generics) => generics,
1844             ForeignItemKind::Type => NO_GENERICS,
1845         },
1846
1847         _ => NO_GENERICS,
1848     };
1849
1850     let generics = tcx.generics_of(def_id);
1851     let parent_count = generics.parent_count as u32;
1852     let has_own_self = generics.has_self && parent_count == 0;
1853
1854     // Below we'll consider the bounds on the type parameters (including `Self`)
1855     // and the explicit where-clauses, but to get the full set of predicates
1856     // on a trait we need to add in the supertrait bounds and bounds found on
1857     // associated types.
1858     if let Some(_trait_ref) = is_trait {
1859         predicates.extend(tcx.super_predicates_of(def_id).predicates.iter().cloned());
1860     }
1861
1862     // In default impls, we can assume that the self type implements
1863     // the trait. So in:
1864     //
1865     //     default impl Foo for Bar { .. }
1866     //
1867     // we add a default where clause `Foo: Bar`. We do a similar thing for traits
1868     // (see below). Recall that a default impl is not itself an impl, but rather a
1869     // set of defaults that can be incorporated into another impl.
1870     if let Some(trait_ref) = is_default_impl_trait {
1871         predicates.insert((
1872             trait_ref.to_poly_trait_ref().without_const().to_predicate(tcx),
1873             tcx.def_span(def_id),
1874         ));
1875     }
1876
1877     // Collect the region predicates that were declared inline as
1878     // well. In the case of parameters declared on a fn or method, we
1879     // have to be careful to only iterate over early-bound regions.
1880     let mut index = parent_count + has_own_self as u32;
1881     for param in early_bound_lifetimes_from_generics(tcx, ast_generics) {
1882         let region = tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
1883             def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
1884             index,
1885             name: param.name.ident().name,
1886         }));
1887         index += 1;
1888
1889         match param.kind {
1890             GenericParamKind::Lifetime { .. } => {
1891                 param.bounds.iter().for_each(|bound| match bound {
1892                     hir::GenericBound::Outlives(lt) => {
1893                         let bound = AstConv::ast_region_to_region(&icx, &lt, None);
1894                         let outlives = ty::Binder::bind(ty::OutlivesPredicate(region, bound));
1895                         predicates.insert((outlives.to_predicate(tcx), lt.span));
1896                     }
1897                     _ => bug!(),
1898                 });
1899             }
1900             _ => bug!(),
1901         }
1902     }
1903
1904     // Collect the predicates that were written inline by the user on each
1905     // type parameter (e.g., `<T: Foo>`).
1906     for param in ast_generics.params {
1907         match param.kind {
1908             // We already dealt with early bound lifetimes above.
1909             GenericParamKind::Lifetime { .. } => (),
1910             GenericParamKind::Type { .. } => {
1911                 let name = param.name.ident().name;
1912                 let param_ty = ty::ParamTy::new(index, name).to_ty(tcx);
1913                 index += 1;
1914
1915                 let sized = SizedByDefault::Yes;
1916                 let bounds =
1917                     AstConv::compute_bounds(&icx, param_ty, &param.bounds, sized, param.span);
1918                 predicates.extend(bounds.predicates(tcx, param_ty));
1919             }
1920             GenericParamKind::Const { .. } => {
1921                 // Bounds on const parameters are currently not possible.
1922                 debug_assert!(param.bounds.is_empty());
1923                 index += 1;
1924             }
1925         }
1926     }
1927
1928     // Add in the bounds that appear in the where-clause.
1929     let where_clause = &ast_generics.where_clause;
1930     for predicate in where_clause.predicates {
1931         match predicate {
1932             hir::WherePredicate::BoundPredicate(bound_pred) => {
1933                 let ty = icx.to_ty(&bound_pred.bounded_ty);
1934
1935                 // Keep the type around in a dummy predicate, in case of no bounds.
1936                 // That way, `where Ty:` is not a complete noop (see #53696) and `Ty`
1937                 // is still checked for WF.
1938                 if bound_pred.bounds.is_empty() {
1939                     if let ty::Param(_) = ty.kind() {
1940                         // This is a `where T:`, which can be in the HIR from the
1941                         // transformation that moves `?Sized` to `T`'s declaration.
1942                         // We can skip the predicate because type parameters are
1943                         // trivially WF, but also we *should*, to avoid exposing
1944                         // users who never wrote `where Type:,` themselves, to
1945                         // compiler/tooling bugs from not handling WF predicates.
1946                     } else {
1947                         let span = bound_pred.bounded_ty.span;
1948                         let re_root_empty = tcx.lifetimes.re_root_empty;
1949                         let predicate = ty::Binder::bind(ty::PredicateKind::TypeOutlives(
1950                             ty::OutlivesPredicate(ty, re_root_empty),
1951                         ));
1952                         predicates.insert((predicate.to_predicate(tcx), span));
1953                     }
1954                 }
1955
1956                 for bound in bound_pred.bounds.iter() {
1957                     match bound {
1958                         hir::GenericBound::Trait(poly_trait_ref, modifier) => {
1959                             let constness = match modifier {
1960                                 hir::TraitBoundModifier::MaybeConst => hir::Constness::NotConst,
1961                                 hir::TraitBoundModifier::None => constness,
1962                                 hir::TraitBoundModifier::Maybe => bug!("this wasn't handled"),
1963                             };
1964
1965                             let mut bounds = Bounds::default();
1966                             let _ = AstConv::instantiate_poly_trait_ref(
1967                                 &icx,
1968                                 &poly_trait_ref,
1969                                 constness,
1970                                 ty,
1971                                 &mut bounds,
1972                             );
1973                             predicates.extend(bounds.predicates(tcx, ty));
1974                         }
1975
1976                         &hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => {
1977                             let mut bounds = Bounds::default();
1978                             AstConv::instantiate_lang_item_trait_ref(
1979                                 &icx,
1980                                 lang_item,
1981                                 span,
1982                                 hir_id,
1983                                 args,
1984                                 ty,
1985                                 &mut bounds,
1986                             );
1987                             predicates.extend(bounds.predicates(tcx, ty));
1988                         }
1989
1990                         hir::GenericBound::Outlives(lifetime) => {
1991                             let region = AstConv::ast_region_to_region(&icx, lifetime, None);
1992                             predicates.insert((
1993                                 ty::Binder::bind(ty::PredicateKind::TypeOutlives(
1994                                     ty::OutlivesPredicate(ty, region),
1995                                 ))
1996                                 .to_predicate(tcx),
1997                                 lifetime.span,
1998                             ));
1999                         }
2000                     }
2001                 }
2002             }
2003
2004             hir::WherePredicate::RegionPredicate(region_pred) => {
2005                 let r1 = AstConv::ast_region_to_region(&icx, &region_pred.lifetime, None);
2006                 predicates.extend(region_pred.bounds.iter().map(|bound| {
2007                     let (r2, span) = match bound {
2008                         hir::GenericBound::Outlives(lt) => {
2009                             (AstConv::ast_region_to_region(&icx, lt, None), lt.span)
2010                         }
2011                         _ => bug!(),
2012                     };
2013                     let pred = ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(r1, r2))
2014                         .to_predicate(icx.tcx);
2015
2016                     (pred, span)
2017                 }))
2018             }
2019
2020             hir::WherePredicate::EqPredicate(..) => {
2021                 // FIXME(#20041)
2022             }
2023         }
2024     }
2025
2026     if tcx.features().const_evaluatable_checked {
2027         predicates.extend(const_evaluatable_predicates_of(tcx, def_id.expect_local()));
2028     }
2029
2030     let mut predicates: Vec<_> = predicates.into_iter().collect();
2031
2032     // Subtle: before we store the predicates into the tcx, we
2033     // sort them so that predicates like `T: Foo<Item=U>` come
2034     // before uses of `U`.  This avoids false ambiguity errors
2035     // in trait checking. See `setup_constraining_predicates`
2036     // for details.
2037     if let Node::Item(&Item { kind: ItemKind::Impl { .. }, .. }) = node {
2038         let self_ty = tcx.type_of(def_id);
2039         let trait_ref = tcx.impl_trait_ref(def_id);
2040         cgp::setup_constraining_predicates(
2041             tcx,
2042             &mut predicates,
2043             trait_ref,
2044             &mut cgp::parameters_for_impl(self_ty, trait_ref),
2045         );
2046     }
2047
2048     let result = ty::GenericPredicates {
2049         parent: generics.parent,
2050         predicates: tcx.arena.alloc_from_iter(predicates),
2051     };
2052     debug!("explicit_predicates_of(def_id={:?}) = {:?}", def_id, result);
2053     result
2054 }
2055
2056 fn const_evaluatable_predicates_of<'tcx>(
2057     tcx: TyCtxt<'tcx>,
2058     def_id: LocalDefId,
2059 ) -> FxIndexSet<(ty::Predicate<'tcx>, Span)> {
2060     struct ConstCollector<'tcx> {
2061         tcx: TyCtxt<'tcx>,
2062         preds: FxIndexSet<(ty::Predicate<'tcx>, Span)>,
2063     }
2064
2065     impl<'tcx> intravisit::Visitor<'tcx> for ConstCollector<'tcx> {
2066         type Map = Map<'tcx>;
2067
2068         fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
2069             intravisit::NestedVisitorMap::None
2070         }
2071
2072         fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) {
2073             let def_id = self.tcx.hir().local_def_id(c.hir_id);
2074             let ct = ty::Const::from_anon_const(self.tcx, def_id);
2075             if let ty::ConstKind::Unevaluated(def, substs, None) = ct.val {
2076                 let span = self.tcx.hir().span(c.hir_id);
2077                 self.preds.insert((
2078                     ty::PredicateKind::ConstEvaluatable(def, substs).to_predicate(self.tcx),
2079                     span,
2080                 ));
2081             }
2082         }
2083
2084         // Look into `TyAlias`.
2085         fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
2086             use ty::fold::{TypeFoldable, TypeVisitor};
2087             struct TyAliasVisitor<'a, 'tcx> {
2088                 tcx: TyCtxt<'tcx>,
2089                 preds: &'a mut FxIndexSet<(ty::Predicate<'tcx>, Span)>,
2090                 span: Span,
2091             }
2092
2093             impl<'a, 'tcx> TypeVisitor<'tcx> for TyAliasVisitor<'a, 'tcx> {
2094                 fn visit_const(&mut self, ct: &'tcx Const<'tcx>) -> ControlFlow<Self::BreakTy> {
2095                     if let ty::ConstKind::Unevaluated(def, substs, None) = ct.val {
2096                         self.preds.insert((
2097                             ty::PredicateKind::ConstEvaluatable(def, substs).to_predicate(self.tcx),
2098                             self.span,
2099                         ));
2100                     }
2101                     ControlFlow::CONTINUE
2102                 }
2103             }
2104
2105             if let hir::TyKind::Path(hir::QPath::Resolved(None, path)) = ty.kind {
2106                 if let Res::Def(DefKind::TyAlias, def_id) = path.res {
2107                     let mut visitor =
2108                         TyAliasVisitor { tcx: self.tcx, preds: &mut self.preds, span: path.span };
2109                     self.tcx.type_of(def_id).visit_with(&mut visitor);
2110                 }
2111             }
2112
2113             intravisit::walk_ty(self, ty)
2114         }
2115     }
2116
2117     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
2118     let node = tcx.hir().get(hir_id);
2119
2120     let mut collector = ConstCollector { tcx, preds: FxIndexSet::default() };
2121     if let hir::Node::Item(item) = node {
2122         if let hir::ItemKind::Impl(ref impl_) = item.kind {
2123             if let Some(of_trait) = &impl_.of_trait {
2124                 debug!("const_evaluatable_predicates_of({:?}): visit impl trait_ref", def_id);
2125                 collector.visit_trait_ref(of_trait);
2126             }
2127
2128             debug!("const_evaluatable_predicates_of({:?}): visit_self_ty", def_id);
2129             collector.visit_ty(impl_.self_ty);
2130         }
2131     }
2132
2133     if let Some(generics) = node.generics() {
2134         debug!("const_evaluatable_predicates_of({:?}): visit_generics", def_id);
2135         collector.visit_generics(generics);
2136     }
2137
2138     if let Some(fn_sig) = tcx.hir().fn_sig_by_hir_id(hir_id) {
2139         debug!("const_evaluatable_predicates_of({:?}): visit_fn_decl", def_id);
2140         collector.visit_fn_decl(fn_sig.decl);
2141     }
2142     debug!("const_evaluatable_predicates_of({:?}) = {:?}", def_id, collector.preds);
2143
2144     collector.preds
2145 }
2146
2147 fn trait_explicit_predicates_and_bounds(
2148     tcx: TyCtxt<'_>,
2149     def_id: LocalDefId,
2150 ) -> ty::GenericPredicates<'_> {
2151     assert_eq!(tcx.def_kind(def_id), DefKind::Trait);
2152     gather_explicit_predicates_of(tcx, def_id.to_def_id())
2153 }
2154
2155 fn explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2156     if let DefKind::Trait = tcx.def_kind(def_id) {
2157         // Remove bounds on associated types from the predicates, they will be
2158         // returned by `explicit_item_bounds`.
2159         let predicates_and_bounds = tcx.trait_explicit_predicates_and_bounds(def_id.expect_local());
2160         let trait_identity_substs = InternalSubsts::identity_for_item(tcx, def_id);
2161
2162         let is_assoc_item_ty = |ty: Ty<'_>| {
2163             // For a predicate from a where clause to become a bound on an
2164             // associated type:
2165             // * It must use the identity substs of the item.
2166             //     * Since any generic parameters on the item are not in scope,
2167             //       this means that the item is not a GAT, and its identity
2168             //       substs are the same as the trait's.
2169             // * It must be an associated type for this trait (*not* a
2170             //   supertrait).
2171             if let ty::Projection(projection) = ty.kind() {
2172                 projection.substs == trait_identity_substs
2173                     && tcx.associated_item(projection.item_def_id).container.id() == def_id
2174             } else {
2175                 false
2176             }
2177         };
2178
2179         let predicates: Vec<_> = predicates_and_bounds
2180             .predicates
2181             .iter()
2182             .copied()
2183             .filter(|(pred, _)| match pred.kind().skip_binder() {
2184                 ty::PredicateKind::Trait(tr, _) => !is_assoc_item_ty(tr.self_ty()),
2185                 ty::PredicateKind::Projection(proj) => {
2186                     !is_assoc_item_ty(proj.projection_ty.self_ty())
2187                 }
2188                 ty::PredicateKind::TypeOutlives(outlives) => !is_assoc_item_ty(outlives.0),
2189                 _ => true,
2190             })
2191             .collect();
2192         if predicates.len() == predicates_and_bounds.predicates.len() {
2193             predicates_and_bounds
2194         } else {
2195             ty::GenericPredicates {
2196                 parent: predicates_and_bounds.parent,
2197                 predicates: tcx.arena.alloc_slice(&predicates),
2198             }
2199         }
2200     } else {
2201         gather_explicit_predicates_of(tcx, def_id)
2202     }
2203 }
2204
2205 fn projection_ty_from_predicates(
2206     tcx: TyCtxt<'tcx>,
2207     key: (
2208         // ty_def_id
2209         DefId,
2210         // def_id of `N` in `<T as Trait>::N`
2211         DefId,
2212     ),
2213 ) -> Option<ty::ProjectionTy<'tcx>> {
2214     let (ty_def_id, item_def_id) = key;
2215     let mut projection_ty = None;
2216     for (predicate, _) in tcx.predicates_of(ty_def_id).predicates {
2217         if let ty::PredicateKind::Projection(projection_predicate) = predicate.kind().skip_binder()
2218         {
2219             if item_def_id == projection_predicate.projection_ty.item_def_id {
2220                 projection_ty = Some(projection_predicate.projection_ty);
2221                 break;
2222             }
2223         }
2224     }
2225     projection_ty
2226 }
2227
2228 /// Converts a specific `GenericBound` from the AST into a set of
2229 /// predicates that apply to the self type. A vector is returned
2230 /// because this can be anywhere from zero predicates (`T: ?Sized` adds no
2231 /// predicates) to one (`T: Foo`) to many (`T: Bar<X = i32>` adds `T: Bar`
2232 /// and `<T as Bar>::X == i32`).
2233 fn predicates_from_bound<'tcx>(
2234     astconv: &dyn AstConv<'tcx>,
2235     param_ty: Ty<'tcx>,
2236     bound: &'tcx hir::GenericBound<'tcx>,
2237     constness: hir::Constness,
2238 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2239     match *bound {
2240         hir::GenericBound::Trait(ref tr, modifier) => {
2241             let constness = match modifier {
2242                 hir::TraitBoundModifier::Maybe => return vec![],
2243                 hir::TraitBoundModifier::MaybeConst => hir::Constness::NotConst,
2244                 hir::TraitBoundModifier::None => constness,
2245             };
2246
2247             let mut bounds = Bounds::default();
2248             let _ = astconv.instantiate_poly_trait_ref(tr, constness, param_ty, &mut bounds);
2249             bounds.predicates(astconv.tcx(), param_ty)
2250         }
2251         hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => {
2252             let mut bounds = Bounds::default();
2253             astconv.instantiate_lang_item_trait_ref(
2254                 lang_item,
2255                 span,
2256                 hir_id,
2257                 args,
2258                 param_ty,
2259                 &mut bounds,
2260             );
2261             bounds.predicates(astconv.tcx(), param_ty)
2262         }
2263         hir::GenericBound::Outlives(ref lifetime) => {
2264             let region = astconv.ast_region_to_region(lifetime, None);
2265             let pred = ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(param_ty, region))
2266                 .to_predicate(astconv.tcx());
2267             vec![(pred, lifetime.span)]
2268         }
2269     }
2270 }
2271
2272 fn compute_sig_of_foreign_fn_decl<'tcx>(
2273     tcx: TyCtxt<'tcx>,
2274     def_id: DefId,
2275     decl: &'tcx hir::FnDecl<'tcx>,
2276     abi: abi::Abi,
2277     ident: Ident,
2278 ) -> ty::PolyFnSig<'tcx> {
2279     let unsafety = if abi == abi::Abi::RustIntrinsic {
2280         intrinsic_operation_unsafety(tcx.item_name(def_id))
2281     } else {
2282         hir::Unsafety::Unsafe
2283     };
2284     let fty = AstConv::ty_of_fn(
2285         &ItemCtxt::new(tcx, def_id),
2286         unsafety,
2287         abi,
2288         decl,
2289         &hir::Generics::empty(),
2290         Some(ident.span),
2291     );
2292
2293     // Feature gate SIMD types in FFI, since I am not sure that the
2294     // ABIs are handled at all correctly. -huonw
2295     if abi != abi::Abi::RustIntrinsic
2296         && abi != abi::Abi::PlatformIntrinsic
2297         && !tcx.features().simd_ffi
2298     {
2299         let check = |ast_ty: &hir::Ty<'_>, ty: Ty<'_>| {
2300             if ty.is_simd() {
2301                 let snip = tcx
2302                     .sess
2303                     .source_map()
2304                     .span_to_snippet(ast_ty.span)
2305                     .map_or(String::new(), |s| format!(" `{}`", s));
2306                 tcx.sess
2307                     .struct_span_err(
2308                         ast_ty.span,
2309                         &format!(
2310                             "use of SIMD type{} in FFI is highly experimental and \
2311                              may result in invalid code",
2312                             snip
2313                         ),
2314                     )
2315                     .help("add `#![feature(simd_ffi)]` to the crate attributes to enable")
2316                     .emit();
2317             }
2318         };
2319         for (input, ty) in decl.inputs.iter().zip(fty.inputs().skip_binder()) {
2320             check(&input, ty)
2321         }
2322         if let hir::FnRetTy::Return(ref ty) = decl.output {
2323             check(&ty, fty.output().skip_binder())
2324         }
2325     }
2326
2327     fty
2328 }
2329
2330 fn is_foreign_item(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
2331     match tcx.hir().get_if_local(def_id) {
2332         Some(Node::ForeignItem(..)) => true,
2333         Some(_) => false,
2334         _ => bug!("is_foreign_item applied to non-local def-id {:?}", def_id),
2335     }
2336 }
2337
2338 fn static_mutability(tcx: TyCtxt<'_>, def_id: DefId) -> Option<hir::Mutability> {
2339     match tcx.hir().get_if_local(def_id) {
2340         Some(
2341             Node::Item(&hir::Item { kind: hir::ItemKind::Static(_, mutbl, _), .. })
2342             | Node::ForeignItem(&hir::ForeignItem {
2343                 kind: hir::ForeignItemKind::Static(_, mutbl),
2344                 ..
2345             }),
2346         ) => Some(mutbl),
2347         Some(_) => None,
2348         _ => bug!("static_mutability applied to non-local def-id {:?}", def_id),
2349     }
2350 }
2351
2352 fn generator_kind(tcx: TyCtxt<'_>, def_id: DefId) -> Option<hir::GeneratorKind> {
2353     match tcx.hir().get_if_local(def_id) {
2354         Some(Node::Expr(&rustc_hir::Expr {
2355             kind: rustc_hir::ExprKind::Closure(_, _, body_id, _, _),
2356             ..
2357         })) => tcx.hir().body(body_id).generator_kind(),
2358         Some(_) => None,
2359         _ => bug!("generator_kind applied to non-local def-id {:?}", def_id),
2360     }
2361 }
2362
2363 fn from_target_feature(
2364     tcx: TyCtxt<'_>,
2365     id: DefId,
2366     attr: &ast::Attribute,
2367     supported_target_features: &FxHashMap<String, Option<Symbol>>,
2368     target_features: &mut Vec<Symbol>,
2369 ) {
2370     let list = match attr.meta_item_list() {
2371         Some(list) => list,
2372         None => return,
2373     };
2374     let bad_item = |span| {
2375         let msg = "malformed `target_feature` attribute input";
2376         let code = "enable = \"..\"".to_owned();
2377         tcx.sess
2378             .struct_span_err(span, &msg)
2379             .span_suggestion(span, "must be of the form", code, Applicability::HasPlaceholders)
2380             .emit();
2381     };
2382     let rust_features = tcx.features();
2383     for item in list {
2384         // Only `enable = ...` is accepted in the meta-item list.
2385         if !item.has_name(sym::enable) {
2386             bad_item(item.span());
2387             continue;
2388         }
2389
2390         // Must be of the form `enable = "..."` (a string).
2391         let value = match item.value_str() {
2392             Some(value) => value,
2393             None => {
2394                 bad_item(item.span());
2395                 continue;
2396             }
2397         };
2398
2399         // We allow comma separation to enable multiple features.
2400         target_features.extend(value.as_str().split(',').filter_map(|feature| {
2401             let feature_gate = match supported_target_features.get(feature) {
2402                 Some(g) => g,
2403                 None => {
2404                     let msg =
2405                         format!("the feature named `{}` is not valid for this target", feature);
2406                     let mut err = tcx.sess.struct_span_err(item.span(), &msg);
2407                     err.span_label(
2408                         item.span(),
2409                         format!("`{}` is not valid for this target", feature),
2410                     );
2411                     if let Some(stripped) = feature.strip_prefix('+') {
2412                         let valid = supported_target_features.contains_key(stripped);
2413                         if valid {
2414                             err.help("consider removing the leading `+` in the feature name");
2415                         }
2416                     }
2417                     err.emit();
2418                     return None;
2419                 }
2420             };
2421
2422             // Only allow features whose feature gates have been enabled.
2423             let allowed = match feature_gate.as_ref().copied() {
2424                 Some(sym::arm_target_feature) => rust_features.arm_target_feature,
2425                 Some(sym::aarch64_target_feature) => rust_features.aarch64_target_feature,
2426                 Some(sym::hexagon_target_feature) => rust_features.hexagon_target_feature,
2427                 Some(sym::powerpc_target_feature) => rust_features.powerpc_target_feature,
2428                 Some(sym::mips_target_feature) => rust_features.mips_target_feature,
2429                 Some(sym::riscv_target_feature) => rust_features.riscv_target_feature,
2430                 Some(sym::avx512_target_feature) => rust_features.avx512_target_feature,
2431                 Some(sym::sse4a_target_feature) => rust_features.sse4a_target_feature,
2432                 Some(sym::tbm_target_feature) => rust_features.tbm_target_feature,
2433                 Some(sym::wasm_target_feature) => rust_features.wasm_target_feature,
2434                 Some(sym::cmpxchg16b_target_feature) => rust_features.cmpxchg16b_target_feature,
2435                 Some(sym::adx_target_feature) => rust_features.adx_target_feature,
2436                 Some(sym::movbe_target_feature) => rust_features.movbe_target_feature,
2437                 Some(sym::rtm_target_feature) => rust_features.rtm_target_feature,
2438                 Some(sym::f16c_target_feature) => rust_features.f16c_target_feature,
2439                 Some(sym::ermsb_target_feature) => rust_features.ermsb_target_feature,
2440                 Some(name) => bug!("unknown target feature gate {}", name),
2441                 None => true,
2442             };
2443             if !allowed && id.is_local() {
2444                 feature_err(
2445                     &tcx.sess.parse_sess,
2446                     feature_gate.unwrap(),
2447                     item.span(),
2448                     &format!("the target feature `{}` is currently unstable", feature),
2449                 )
2450                 .emit();
2451             }
2452             Some(Symbol::intern(feature))
2453         }));
2454     }
2455 }
2456
2457 fn linkage_by_name(tcx: TyCtxt<'_>, def_id: DefId, name: &str) -> Linkage {
2458     use rustc_middle::mir::mono::Linkage::*;
2459
2460     // Use the names from src/llvm/docs/LangRef.rst here. Most types are only
2461     // applicable to variable declarations and may not really make sense for
2462     // Rust code in the first place but allow them anyway and trust that the
2463     // user knows what s/he's doing. Who knows, unanticipated use cases may pop
2464     // up in the future.
2465     //
2466     // ghost, dllimport, dllexport and linkonce_odr_autohide are not supported
2467     // and don't have to be, LLVM treats them as no-ops.
2468     match name {
2469         "appending" => Appending,
2470         "available_externally" => AvailableExternally,
2471         "common" => Common,
2472         "extern_weak" => ExternalWeak,
2473         "external" => External,
2474         "internal" => Internal,
2475         "linkonce" => LinkOnceAny,
2476         "linkonce_odr" => LinkOnceODR,
2477         "private" => Private,
2478         "weak" => WeakAny,
2479         "weak_odr" => WeakODR,
2480         _ => {
2481             let span = tcx.hir().span_if_local(def_id);
2482             if let Some(span) = span {
2483                 tcx.sess.span_fatal(span, "invalid linkage specified")
2484             } else {
2485                 tcx.sess.fatal(&format!("invalid linkage specified: {}", name))
2486             }
2487         }
2488     }
2489 }
2490
2491 fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
2492     let attrs = tcx.get_attrs(id);
2493
2494     let mut codegen_fn_attrs = CodegenFnAttrs::new();
2495     if should_inherit_track_caller(tcx, id) {
2496         codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
2497     }
2498
2499     let supported_target_features = tcx.supported_target_features(LOCAL_CRATE);
2500
2501     let mut inline_span = None;
2502     let mut link_ordinal_span = None;
2503     let mut no_sanitize_span = None;
2504     for attr in attrs.iter() {
2505         if tcx.sess.check_name(attr, sym::cold) {
2506             codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
2507         } else if tcx.sess.check_name(attr, sym::rustc_allocator) {
2508             codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR;
2509         } else if tcx.sess.check_name(attr, sym::unwind) {
2510             codegen_fn_attrs.flags |= CodegenFnAttrFlags::UNWIND;
2511         } else if tcx.sess.check_name(attr, sym::ffi_returns_twice) {
2512             if tcx.is_foreign_item(id) {
2513                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_RETURNS_TWICE;
2514             } else {
2515                 // `#[ffi_returns_twice]` is only allowed `extern fn`s.
2516                 struct_span_err!(
2517                     tcx.sess,
2518                     attr.span,
2519                     E0724,
2520                     "`#[ffi_returns_twice]` may only be used on foreign functions"
2521                 )
2522                 .emit();
2523             }
2524         } else if tcx.sess.check_name(attr, sym::ffi_pure) {
2525             if tcx.is_foreign_item(id) {
2526                 if attrs.iter().any(|a| tcx.sess.check_name(a, sym::ffi_const)) {
2527                     // `#[ffi_const]` functions cannot be `#[ffi_pure]`
2528                     struct_span_err!(
2529                         tcx.sess,
2530                         attr.span,
2531                         E0757,
2532                         "`#[ffi_const]` function cannot be `#[ffi_pure]`"
2533                     )
2534                     .emit();
2535                 } else {
2536                     codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_PURE;
2537                 }
2538             } else {
2539                 // `#[ffi_pure]` is only allowed on foreign functions
2540                 struct_span_err!(
2541                     tcx.sess,
2542                     attr.span,
2543                     E0755,
2544                     "`#[ffi_pure]` may only be used on foreign functions"
2545                 )
2546                 .emit();
2547             }
2548         } else if tcx.sess.check_name(attr, sym::ffi_const) {
2549             if tcx.is_foreign_item(id) {
2550                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_CONST;
2551             } else {
2552                 // `#[ffi_const]` is only allowed on foreign functions
2553                 struct_span_err!(
2554                     tcx.sess,
2555                     attr.span,
2556                     E0756,
2557                     "`#[ffi_const]` may only be used on foreign functions"
2558                 )
2559                 .emit();
2560             }
2561         } else if tcx.sess.check_name(attr, sym::rustc_allocator_nounwind) {
2562             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_ALLOCATOR_NOUNWIND;
2563         } else if tcx.sess.check_name(attr, sym::naked) {
2564             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED;
2565         } else if tcx.sess.check_name(attr, sym::no_mangle) {
2566             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
2567         } else if tcx.sess.check_name(attr, sym::rustc_std_internal_symbol) {
2568             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
2569         } else if tcx.sess.check_name(attr, sym::used) {
2570             codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED;
2571         } else if tcx.sess.check_name(attr, sym::cmse_nonsecure_entry) {
2572             if tcx.fn_sig(id).abi() != abi::Abi::C {
2573                 struct_span_err!(
2574                     tcx.sess,
2575                     attr.span,
2576                     E0776,
2577                     "`#[cmse_nonsecure_entry]` requires C ABI"
2578                 )
2579                 .emit();
2580             }
2581             if !tcx.sess.target.llvm_target.contains("thumbv8m") {
2582                 struct_span_err!(tcx.sess, attr.span, E0775, "`#[cmse_nonsecure_entry]` is only valid for targets with the TrustZone-M extension")
2583                     .emit();
2584             }
2585             codegen_fn_attrs.flags |= CodegenFnAttrFlags::CMSE_NONSECURE_ENTRY;
2586         } else if tcx.sess.check_name(attr, sym::thread_local) {
2587             codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL;
2588         } else if tcx.sess.check_name(attr, sym::track_caller) {
2589             if tcx.is_closure(id) || tcx.fn_sig(id).abi() != abi::Abi::Rust {
2590                 struct_span_err!(tcx.sess, attr.span, E0737, "`#[track_caller]` requires Rust ABI")
2591                     .emit();
2592             }
2593             codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
2594         } else if tcx.sess.check_name(attr, sym::export_name) {
2595             if let Some(s) = attr.value_str() {
2596                 if s.as_str().contains('\0') {
2597                     // `#[export_name = ...]` will be converted to a null-terminated string,
2598                     // so it may not contain any null characters.
2599                     struct_span_err!(
2600                         tcx.sess,
2601                         attr.span,
2602                         E0648,
2603                         "`export_name` may not contain null characters"
2604                     )
2605                     .emit();
2606                 }
2607                 codegen_fn_attrs.export_name = Some(s);
2608             }
2609         } else if tcx.sess.check_name(attr, sym::target_feature) {
2610             if !tcx.is_closure(id) && tcx.fn_sig(id).unsafety() == hir::Unsafety::Normal {
2611                 if !tcx.features().target_feature_11 {
2612                     let mut err = feature_err(
2613                         &tcx.sess.parse_sess,
2614                         sym::target_feature_11,
2615                         attr.span,
2616                         "`#[target_feature(..)]` can only be applied to `unsafe` functions",
2617                     );
2618                     err.span_label(tcx.def_span(id), "not an `unsafe` function");
2619                     err.emit();
2620                 } else if let Some(local_id) = id.as_local() {
2621                     check_target_feature_trait_unsafe(tcx, local_id, attr.span);
2622                 }
2623             }
2624             from_target_feature(
2625                 tcx,
2626                 id,
2627                 attr,
2628                 &supported_target_features,
2629                 &mut codegen_fn_attrs.target_features,
2630             );
2631         } else if tcx.sess.check_name(attr, sym::linkage) {
2632             if let Some(val) = attr.value_str() {
2633                 codegen_fn_attrs.linkage = Some(linkage_by_name(tcx, id, &val.as_str()));
2634             }
2635         } else if tcx.sess.check_name(attr, sym::link_section) {
2636             if let Some(val) = attr.value_str() {
2637                 if val.as_str().bytes().any(|b| b == 0) {
2638                     let msg = format!(
2639                         "illegal null byte in link_section \
2640                          value: `{}`",
2641                         &val
2642                     );
2643                     tcx.sess.span_err(attr.span, &msg);
2644                 } else {
2645                     codegen_fn_attrs.link_section = Some(val);
2646                 }
2647             }
2648         } else if tcx.sess.check_name(attr, sym::link_name) {
2649             codegen_fn_attrs.link_name = attr.value_str();
2650         } else if tcx.sess.check_name(attr, sym::link_ordinal) {
2651             link_ordinal_span = Some(attr.span);
2652             if let ordinal @ Some(_) = check_link_ordinal(tcx, attr) {
2653                 codegen_fn_attrs.link_ordinal = ordinal;
2654             }
2655         } else if tcx.sess.check_name(attr, sym::no_sanitize) {
2656             no_sanitize_span = Some(attr.span);
2657             if let Some(list) = attr.meta_item_list() {
2658                 for item in list.iter() {
2659                     if item.has_name(sym::address) {
2660                         codegen_fn_attrs.no_sanitize |= SanitizerSet::ADDRESS;
2661                     } else if item.has_name(sym::memory) {
2662                         codegen_fn_attrs.no_sanitize |= SanitizerSet::MEMORY;
2663                     } else if item.has_name(sym::thread) {
2664                         codegen_fn_attrs.no_sanitize |= SanitizerSet::THREAD;
2665                     } else {
2666                         tcx.sess
2667                             .struct_span_err(item.span(), "invalid argument for `no_sanitize`")
2668                             .note("expected one of: `address`, `memory` or `thread`")
2669                             .emit();
2670                     }
2671                 }
2672             }
2673         } else if tcx.sess.check_name(attr, sym::instruction_set) {
2674             codegen_fn_attrs.instruction_set = match attr.meta().map(|i| i.kind) {
2675                 Some(MetaItemKind::List(ref items)) => match items.as_slice() {
2676                     [NestedMetaItem::MetaItem(set)] => {
2677                         let segments =
2678                             set.path.segments.iter().map(|x| x.ident.name).collect::<Vec<_>>();
2679                         match segments.as_slice() {
2680                             [sym::arm, sym::a32] | [sym::arm, sym::t32] => {
2681                                 if !tcx.sess.target.has_thumb_interworking {
2682                                     struct_span_err!(
2683                                         tcx.sess.diagnostic(),
2684                                         attr.span,
2685                                         E0779,
2686                                         "target does not support `#[instruction_set]`"
2687                                     )
2688                                     .emit();
2689                                     None
2690                                 } else if segments[1] == sym::a32 {
2691                                     Some(InstructionSetAttr::ArmA32)
2692                                 } else if segments[1] == sym::t32 {
2693                                     Some(InstructionSetAttr::ArmT32)
2694                                 } else {
2695                                     unreachable!()
2696                                 }
2697                             }
2698                             _ => {
2699                                 struct_span_err!(
2700                                     tcx.sess.diagnostic(),
2701                                     attr.span,
2702                                     E0779,
2703                                     "invalid instruction set specified",
2704                                 )
2705                                 .emit();
2706                                 None
2707                             }
2708                         }
2709                     }
2710                     [] => {
2711                         struct_span_err!(
2712                             tcx.sess.diagnostic(),
2713                             attr.span,
2714                             E0778,
2715                             "`#[instruction_set]` requires an argument"
2716                         )
2717                         .emit();
2718                         None
2719                     }
2720                     _ => {
2721                         struct_span_err!(
2722                             tcx.sess.diagnostic(),
2723                             attr.span,
2724                             E0779,
2725                             "cannot specify more than one instruction set"
2726                         )
2727                         .emit();
2728                         None
2729                     }
2730                 },
2731                 _ => {
2732                     struct_span_err!(
2733                         tcx.sess.diagnostic(),
2734                         attr.span,
2735                         E0778,
2736                         "must specify an instruction set"
2737                     )
2738                     .emit();
2739                     None
2740                 }
2741             };
2742         }
2743     }
2744
2745     codegen_fn_attrs.inline = attrs.iter().fold(InlineAttr::None, |ia, attr| {
2746         if !attr.has_name(sym::inline) {
2747             return ia;
2748         }
2749         match attr.meta().map(|i| i.kind) {
2750             Some(MetaItemKind::Word) => {
2751                 tcx.sess.mark_attr_used(attr);
2752                 InlineAttr::Hint
2753             }
2754             Some(MetaItemKind::List(ref items)) => {
2755                 tcx.sess.mark_attr_used(attr);
2756                 inline_span = Some(attr.span);
2757                 if items.len() != 1 {
2758                     struct_span_err!(
2759                         tcx.sess.diagnostic(),
2760                         attr.span,
2761                         E0534,
2762                         "expected one argument"
2763                     )
2764                     .emit();
2765                     InlineAttr::None
2766                 } else if list_contains_name(&items[..], sym::always) {
2767                     InlineAttr::Always
2768                 } else if list_contains_name(&items[..], sym::never) {
2769                     InlineAttr::Never
2770                 } else {
2771                     struct_span_err!(
2772                         tcx.sess.diagnostic(),
2773                         items[0].span(),
2774                         E0535,
2775                         "invalid argument"
2776                     )
2777                     .emit();
2778
2779                     InlineAttr::None
2780                 }
2781             }
2782             Some(MetaItemKind::NameValue(_)) => ia,
2783             None => ia,
2784         }
2785     });
2786
2787     codegen_fn_attrs.optimize = attrs.iter().fold(OptimizeAttr::None, |ia, attr| {
2788         if !attr.has_name(sym::optimize) {
2789             return ia;
2790         }
2791         let err = |sp, s| struct_span_err!(tcx.sess.diagnostic(), sp, E0722, "{}", s).emit();
2792         match attr.meta().map(|i| i.kind) {
2793             Some(MetaItemKind::Word) => {
2794                 err(attr.span, "expected one argument");
2795                 ia
2796             }
2797             Some(MetaItemKind::List(ref items)) => {
2798                 tcx.sess.mark_attr_used(attr);
2799                 inline_span = Some(attr.span);
2800                 if items.len() != 1 {
2801                     err(attr.span, "expected one argument");
2802                     OptimizeAttr::None
2803                 } else if list_contains_name(&items[..], sym::size) {
2804                     OptimizeAttr::Size
2805                 } else if list_contains_name(&items[..], sym::speed) {
2806                     OptimizeAttr::Speed
2807                 } else {
2808                     err(items[0].span(), "invalid argument");
2809                     OptimizeAttr::None
2810                 }
2811             }
2812             Some(MetaItemKind::NameValue(_)) => ia,
2813             None => ia,
2814         }
2815     });
2816
2817     // #73631: closures inherit `#[target_feature]` annotations
2818     if tcx.features().target_feature_11 && tcx.is_closure(id) {
2819         let owner_id = tcx.parent(id).expect("closure should have a parent");
2820         codegen_fn_attrs
2821             .target_features
2822             .extend(tcx.codegen_fn_attrs(owner_id).target_features.iter().copied())
2823     }
2824
2825     // If a function uses #[target_feature] it can't be inlined into general
2826     // purpose functions as they wouldn't have the right target features
2827     // enabled. For that reason we also forbid #[inline(always)] as it can't be
2828     // respected.
2829     if !codegen_fn_attrs.target_features.is_empty() {
2830         if codegen_fn_attrs.inline == InlineAttr::Always {
2831             if let Some(span) = inline_span {
2832                 tcx.sess.span_err(
2833                     span,
2834                     "cannot use `#[inline(always)]` with \
2835                      `#[target_feature]`",
2836                 );
2837             }
2838         }
2839     }
2840
2841     if !codegen_fn_attrs.no_sanitize.is_empty() {
2842         if codegen_fn_attrs.inline == InlineAttr::Always {
2843             if let (Some(no_sanitize_span), Some(inline_span)) = (no_sanitize_span, inline_span) {
2844                 let hir_id = tcx.hir().local_def_id_to_hir_id(id.expect_local());
2845                 tcx.struct_span_lint_hir(
2846                     lint::builtin::INLINE_NO_SANITIZE,
2847                     hir_id,
2848                     no_sanitize_span,
2849                     |lint| {
2850                         lint.build("`no_sanitize` will have no effect after inlining")
2851                             .span_note(inline_span, "inlining requested here")
2852                             .emit();
2853                     },
2854                 )
2855             }
2856         }
2857     }
2858
2859     // Weak lang items have the same semantics as "std internal" symbols in the
2860     // sense that they're preserved through all our LTO passes and only
2861     // strippable by the linker.
2862     //
2863     // Additionally weak lang items have predetermined symbol names.
2864     if tcx.is_weak_lang_item(id) {
2865         codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
2866     }
2867     let check_name = |attr, sym| tcx.sess.check_name(attr, sym);
2868     if let Some(name) = weak_lang_items::link_name(check_name, &attrs) {
2869         codegen_fn_attrs.export_name = Some(name);
2870         codegen_fn_attrs.link_name = Some(name);
2871     }
2872     check_link_name_xor_ordinal(tcx, &codegen_fn_attrs, link_ordinal_span);
2873
2874     // Internal symbols to the standard library all have no_mangle semantics in
2875     // that they have defined symbol names present in the function name. This
2876     // also applies to weak symbols where they all have known symbol names.
2877     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
2878         codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
2879     }
2880
2881     codegen_fn_attrs
2882 }
2883
2884 /// Checks if the provided DefId is a method in a trait impl for a trait which has track_caller
2885 /// applied to the method prototype.
2886 fn should_inherit_track_caller(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
2887     if let Some(impl_item) = tcx.opt_associated_item(def_id) {
2888         if let ty::AssocItemContainer::ImplContainer(impl_def_id) = impl_item.container {
2889             if let Some(trait_def_id) = tcx.trait_id_of_impl(impl_def_id) {
2890                 if let Some(trait_item) = tcx
2891                     .associated_items(trait_def_id)
2892                     .filter_by_name_unhygienic(impl_item.ident.name)
2893                     .find(move |trait_item| {
2894                         trait_item.kind == ty::AssocKind::Fn
2895                             && tcx.hygienic_eq(impl_item.ident, trait_item.ident, trait_def_id)
2896                     })
2897                 {
2898                     return tcx
2899                         .codegen_fn_attrs(trait_item.def_id)
2900                         .flags
2901                         .intersects(CodegenFnAttrFlags::TRACK_CALLER);
2902                 }
2903             }
2904         }
2905     }
2906
2907     false
2908 }
2909
2910 fn check_link_ordinal(tcx: TyCtxt<'_>, attr: &ast::Attribute) -> Option<usize> {
2911     use rustc_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 <= 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 `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 }
2953
2954 /// Checks the function annotated with `#[target_feature]` is not a safe
2955 /// trait method implementation, reporting an error if it is.
2956 fn check_target_feature_trait_unsafe(tcx: TyCtxt<'_>, id: LocalDefId, attr_span: Span) {
2957     let hir_id = tcx.hir().local_def_id_to_hir_id(id);
2958     let node = tcx.hir().get(hir_id);
2959     if let Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }) = node {
2960         let parent_id = tcx.hir().get_parent_item(hir_id);
2961         let parent_item = tcx.hir().expect_item(parent_id);
2962         if let hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) = parent_item.kind {
2963             tcx.sess
2964                 .struct_span_err(
2965                     attr_span,
2966                     "`#[target_feature(..)]` cannot be applied to safe trait method",
2967                 )
2968                 .span_label(attr_span, "cannot be applied to safe trait method")
2969                 .span_label(tcx.def_span(id), "not an `unsafe` function")
2970                 .emit();
2971         }
2972     }
2973 }