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;
  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::Attribute;
  25 use rustc_ast::{MetaItemKind, NestedMetaItem};
  26 use rustc_attr::{list_contains_name, InlineAttr, InstructionSetAttr, OptimizeAttr};
  27 use rustc_data_structures::captures::Captures;
  28 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
  29 use rustc_errors::{struct_span_err, Applicability};
  30 use rustc_hir as hir;
  31 use rustc_hir::def::{CtorKind, DefKind};
  32 use rustc_hir::def_id::{DefId, LocalDefId, LOCAL_CRATE};
  33 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  34 use rustc_hir::weak_lang_items;
  35 use rustc_hir::{GenericParamKind, HirId, Node};
  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, Ty, TyCtxt};
  44 use rustc_middle::ty::{ReprOptions, ToPredicate, TypeFoldable};
  45 use rustc_session::lint;
  46 use rustc_session::parse::feature_err;
  47 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  48 use rustc_span::{Span, DUMMY_SP};
  49 use rustc_target::spec::{abi, PanicStrategy, SanitizerSet};
  50 use rustc_trait_selection::traits::error_reporting::suggestions::NextTypeParamName;
  51 use std::iter;
  52
  53 mod item_bounds;
  54 mod type_of;
  55
  56 struct OnlySelfBounds(bool);
  57
  58 ///////////////////////////////////////////////////////////////////////////
  59 // Main entry point
  60
  61 fn collect_mod_item_types(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
  62     tcx.hir().visit_item_likes_in_module(
  63         module_def_id,
  64         &mut CollectItemTypesVisitor { tcx }.as_deep_visitor(),
  65     );
  66 }
  67
  68 pub fn provide(providers: &mut Providers) {
  69     *providers = Providers {
  70         opt_const_param_of: type_of::opt_const_param_of,
  71         default_anon_const_substs: type_of::default_anon_const_substs,
  72         type_of: type_of::type_of,
  73         item_bounds: item_bounds::item_bounds,
  74         explicit_item_bounds: item_bounds::explicit_item_bounds,
  75         generics_of,
  76         predicates_of,
  77         predicates_defined_on,
  78         explicit_predicates_of,
  79         super_predicates_of,
  80         super_predicates_that_define_assoc_type,
  81         trait_explicit_predicates_and_bounds,
  82         type_param_predicates,
  83         trait_def,
  84         adt_def,
  85         fn_sig,
  86         impl_trait_ref,
  87         impl_polarity,
  88         is_foreign_item,
  89         static_mutability,
  90         generator_kind,
  91         codegen_fn_attrs,
  92         collect_mod_item_types,
  93         should_inherit_track_caller,
  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     fn visit_generic_arg(&mut self, generic_arg: &'v hir::GenericArg<'v>) {
 132         match generic_arg {
 133             hir::GenericArg::Infer(inf) => {
 134                 self.0.push(inf.span);
 135                 intravisit::walk_inf(self, inf);
 136             }
 137             hir::GenericArg::Type(t) => self.visit_ty(t),
 138             _ => {}
 139         }
 140     }
 141 }
 142
 143 struct CollectItemTypesVisitor<'tcx> {
 144     tcx: TyCtxt<'tcx>,
 145 }
 146
 147 /// If there are any placeholder types (`_`), emit an error explaining that this is not allowed
 148 /// and suggest adding type parameters in the appropriate place, taking into consideration any and
 149 /// all already existing generic type parameters to avoid suggesting a name that is already in use.
 150 crate fn placeholder_type_error<'tcx>(
 151     tcx: TyCtxt<'tcx>,
 152     span: Option<Span>,
 153     generics: &[hir::GenericParam<'_>],
 154     placeholder_types: Vec<Span>,
 155     suggest: bool,
 156     hir_ty: Option<&hir::Ty<'_>>,
 157     kind: &'static str,
 158 ) {
 159     if placeholder_types.is_empty() {
 160         return;
 161     }
 162
 163     let type_name = generics.next_type_param_name(None);
 164     let mut sugg: Vec<_> =
 165         placeholder_types.iter().map(|sp| (*sp, (*type_name).to_string())).collect();
 166
 167     if generics.is_empty() {
 168         if let Some(span) = span {
 169             sugg.push((span, format!("<{}>", type_name)));
 170         }
 171     } else if let Some(arg) = generics
 172         .iter()
 173         .find(|arg| matches!(arg.name, hir::ParamName::Plain(Ident { name: kw::Underscore, .. })))
 174     {
 175         // Account for `_` already present in cases like `struct S<_>(_);` and suggest
 176         // `struct S<T>(T);` instead of `struct S<_, T>(T);`.
 177         sugg.push((arg.span, (*type_name).to_string()));
 178     } else {
 179         let last = generics.iter().last().unwrap();
 180         // Account for bounds, we want `fn foo<T: E, K>(_: K)` not `fn foo<T, K: E>(_: K)`.
 181         let span = last.bounds_span_for_suggestions().unwrap_or(last.span.shrink_to_hi());
 182         sugg.push((span, format!(", {}", type_name)));
 183     }
 184
 185     let mut err = bad_placeholder(tcx, "type", placeholder_types, kind);
 186
 187     // Suggest, but only if it is not a function in const or static
 188     if suggest {
 189         let mut is_fn = false;
 190         let mut is_const_or_static = false;
 191
 192         if let Some(hir_ty) = hir_ty {
 193             if let hir::TyKind::BareFn(_) = hir_ty.kind {
 194                 is_fn = true;
 195
 196                 // Check if parent is const or static
 197                 let parent_id = tcx.hir().get_parent_node(hir_ty.hir_id);
 198                 let parent_node = tcx.hir().get(parent_id);
 199
 200                 is_const_or_static = matches!(
 201                     parent_node,
 202                     Node::Item(&hir::Item {
 203                         kind: hir::ItemKind::Const(..) | hir::ItemKind::Static(..),
 204                         ..
 205                     }) | Node::TraitItem(&hir::TraitItem {
 206                         kind: hir::TraitItemKind::Const(..),
 207                         ..
 208                     }) | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Const(..), .. })
 209                 );
 210             }
 211         }
 212
 213         // if function is wrapped around a const or static,
 214         // then don't show the suggestion
 215         if !(is_fn && is_const_or_static) {
 216             err.multipart_suggestion(
 217                 "use type parameters instead",
 218                 sugg,
 219                 Applicability::HasPlaceholders,
 220             );
 221         }
 222     }
 223     err.emit();
 224 }
 225
 226 fn reject_placeholder_type_signatures_in_item<'tcx>(
 227     tcx: TyCtxt<'tcx>,
 228     item: &'tcx hir::Item<'tcx>,
 229 ) {
 230     let (generics, suggest) = match &item.kind {
 231         hir::ItemKind::Union(_, generics)
 232         | hir::ItemKind::Enum(_, generics)
 233         | hir::ItemKind::TraitAlias(generics, _)
 234         | hir::ItemKind::Trait(_, _, generics, ..)
 235         | hir::ItemKind::Impl(hir::Impl { generics, .. })
 236         | hir::ItemKind::Struct(_, generics) => (generics, true),
 237         hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. })
 238         | hir::ItemKind::TyAlias(_, generics) => (generics, false),
 239         // `static`, `fn` and `const` are handled elsewhere to suggest appropriate type.
 240         _ => return,
 241     };
 242
 243     let mut visitor = PlaceholderHirTyCollector::default();
 244     visitor.visit_item(item);
 245
 246     placeholder_type_error(
 247         tcx,
 248         Some(generics.span),
 249         generics.params,
 250         visitor.0,
 251         suggest,
 252         None,
 253         item.kind.descr(),
 254     );
 255 }
 256
 257 impl<'tcx> Visitor<'tcx> for CollectItemTypesVisitor<'tcx> {
 258     type Map = Map<'tcx>;
 259
 260     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 261         NestedVisitorMap::OnlyBodies(self.tcx.hir())
 262     }
 263
 264     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 265         convert_item(self.tcx, item.item_id());
 266         reject_placeholder_type_signatures_in_item(self.tcx, item);
 267         intravisit::walk_item(self, item);
 268     }
 269
 270     fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
 271         for param in generics.params {
 272             match param.kind {
 273                 hir::GenericParamKind::Lifetime { .. } => {}
 274                 hir::GenericParamKind::Type { default: Some(_), .. } => {
 275                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 276                     self.tcx.ensure().type_of(def_id);
 277                 }
 278                 hir::GenericParamKind::Type { .. } => {}
 279                 hir::GenericParamKind::Const { default, .. } => {
 280                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 281                     self.tcx.ensure().type_of(def_id);
 282                     if let Some(default) = default {
 283                         let default_def_id = self.tcx.hir().local_def_id(default.hir_id);
 284                         // need to store default and type of default
 285                         self.tcx.ensure().type_of(default_def_id);
 286                         self.tcx.ensure().const_param_default(def_id);
 287                     }
 288                 }
 289             }
 290         }
 291         intravisit::walk_generics(self, generics);
 292     }
 293
 294     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 295         if let hir::ExprKind::Closure(..) = expr.kind {
 296             let def_id = self.tcx.hir().local_def_id(expr.hir_id);
 297             self.tcx.ensure().generics_of(def_id);
 298             // We do not call `type_of` for closures here as that
 299             // depends on typecheck and would therefore hide
 300             // any further errors in case one typeck fails.
 301         }
 302         intravisit::walk_expr(self, expr);
 303     }
 304
 305     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
 306         convert_trait_item(self.tcx, trait_item.trait_item_id());
 307         intravisit::walk_trait_item(self, trait_item);
 308     }
 309
 310     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 311         convert_impl_item(self.tcx, impl_item.impl_item_id());
 312         intravisit::walk_impl_item(self, impl_item);
 313     }
 314 }
 315
 316 ///////////////////////////////////////////////////////////////////////////
 317 // Utility types and common code for the above passes.
 318
 319 fn bad_placeholder<'tcx>(
 320     tcx: TyCtxt<'tcx>,
 321     placeholder_kind: &'static str,
 322     mut spans: Vec<Span>,
 323     kind: &'static str,
 324 ) -> rustc_errors::DiagnosticBuilder<'tcx> {
 325     let kind = if kind.ends_with('s') { format!("{}es", kind) } else { format!("{}s", kind) };
 326
 327     spans.sort();
 328     let mut err = struct_span_err!(
 329         tcx.sess,
 330         spans.clone(),
 331         E0121,
 332         "the {} placeholder `_` is not allowed within types on item signatures for {}",
 333         placeholder_kind,
 334         kind
 335     );
 336     for span in spans {
 337         err.span_label(span, "not allowed in type signatures");
 338     }
 339     err
 340 }
 341
 342 impl<'tcx> ItemCtxt<'tcx> {
 343     pub fn new(tcx: TyCtxt<'tcx>, item_def_id: DefId) -> ItemCtxt<'tcx> {
 344         ItemCtxt { tcx, item_def_id }
 345     }
 346
 347     pub fn to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
 348         <dyn AstConv<'_>>::ast_ty_to_ty(self, ast_ty)
 349     }
 350
 351     pub fn hir_id(&self) -> hir::HirId {
 352         self.tcx.hir().local_def_id_to_hir_id(self.item_def_id.expect_local())
 353     }
 354
 355     pub fn node(&self) -> hir::Node<'tcx> {
 356         self.tcx.hir().get(self.hir_id())
 357     }
 358 }
 359
 360 impl<'tcx> AstConv<'tcx> for ItemCtxt<'tcx> {
 361     fn tcx(&self) -> TyCtxt<'tcx> {
 362         self.tcx
 363     }
 364
 365     fn item_def_id(&self) -> Option<DefId> {
 366         Some(self.item_def_id)
 367     }
 368
 369     fn get_type_parameter_bounds(
 370         &self,
 371         span: Span,
 372         def_id: DefId,
 373         assoc_name: Ident,
 374     ) -> ty::GenericPredicates<'tcx> {
 375         self.tcx.at(span).type_param_predicates((
 376             self.item_def_id,
 377             def_id.expect_local(),
 378             assoc_name,
 379         ))
 380     }
 381
 382     fn re_infer(&self, _: Option<&ty::GenericParamDef>, _: Span) -> Option<ty::Region<'tcx>> {
 383         None
 384     }
 385
 386     fn allow_ty_infer(&self) -> bool {
 387         false
 388     }
 389
 390     fn ty_infer(&self, _: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
 391         self.tcx().ty_error_with_message(span, "bad_placeholder_type")
 392     }
 393
 394     fn ct_infer(
 395         &self,
 396         ty: Ty<'tcx>,
 397         _: Option<&ty::GenericParamDef>,
 398         span: Span,
 399     ) -> &'tcx Const<'tcx> {
 400         bad_placeholder(self.tcx(), "const", vec![span], "generic").emit();
 401         // Typeck doesn't expect erased regions to be returned from `type_of`.
 402         let ty = self.tcx.fold_regions(ty, &mut false, |r, _| match r {
 403             ty::ReErased => self.tcx.lifetimes.re_static,
 404             _ => r,
 405         });
 406         self.tcx().const_error(ty)
 407     }
 408
 409     fn projected_ty_from_poly_trait_ref(
 410         &self,
 411         span: Span,
 412         item_def_id: DefId,
 413         item_segment: &hir::PathSegment<'_>,
 414         poly_trait_ref: ty::PolyTraitRef<'tcx>,
 415     ) -> Ty<'tcx> {
 416         if let Some(trait_ref) = poly_trait_ref.no_bound_vars() {
 417             let item_substs = <dyn AstConv<'tcx>>::create_substs_for_associated_item(
 418                 self,
 419                 self.tcx,
 420                 span,
 421                 item_def_id,
 422                 item_segment,
 423                 trait_ref.substs,
 424             );
 425             self.tcx().mk_projection(item_def_id, item_substs)
 426         } else {
 427             // There are no late-bound regions; we can just ignore the binder.
 428             let mut err = struct_span_err!(
 429                 self.tcx().sess,
 430                 span,
 431                 E0212,
 432                 "cannot use the associated type of a trait \
 433                  with uninferred generic parameters"
 434             );
 435
 436             match self.node() {
 437                 hir::Node::Field(_) | hir::Node::Ctor(_) | hir::Node::Variant(_) => {
 438                     let item =
 439                         self.tcx.hir().expect_item(self.tcx.hir().get_parent_did(self.hir_id()));
 440                     match &item.kind {
 441                         hir::ItemKind::Enum(_, generics)
 442                         | hir::ItemKind::Struct(_, generics)
 443                         | hir::ItemKind::Union(_, generics) => {
 444                             let lt_name = get_new_lifetime_name(self.tcx, poly_trait_ref, generics);
 445                             let (lt_sp, sugg) = match generics.params {
 446                                 [] => (generics.span, format!("<{}>", lt_name)),
 447                                 [bound, ..] => {
 448                                     (bound.span.shrink_to_lo(), format!("{}, ", lt_name))
 449                                 }
 450                             };
 451                             let suggestions = vec![
 452                                 (lt_sp, sugg),
 453                                 (
 454                                     span.with_hi(item_segment.ident.span.lo()),
 455                                     format!(
 456                                         "{}::",
 457                                         // Replace the existing lifetimes with a new named lifetime.
 458                                         self.tcx
 459                                             .replace_late_bound_regions(poly_trait_ref, |_| {
 460                                                 self.tcx.mk_region(ty::ReEarlyBound(
 461                                                     ty::EarlyBoundRegion {
 462                                                         def_id: item_def_id,
 463                                                         index: 0,
 464                                                         name: Symbol::intern(&lt_name),
 465                                                     },
 466                                                 ))
 467                                             })
 468                                             .0,
 469                                     ),
 470                                 ),
 471                             ];
 472                             err.multipart_suggestion(
 473                                 "use a fully qualified path with explicit lifetimes",
 474                                 suggestions,
 475                                 Applicability::MaybeIncorrect,
 476                             );
 477                         }
 478                         _ => {}
 479                     }
 480                 }
 481                 hir::Node::Item(hir::Item {
 482                     kind:
 483                         hir::ItemKind::Struct(..) | hir::ItemKind::Enum(..) | hir::ItemKind::Union(..),
 484                     ..
 485                 }) => {}
 486                 hir::Node::Item(_)
 487                 | hir::Node::ForeignItem(_)
 488                 | hir::Node::TraitItem(_)
 489                 | hir::Node::ImplItem(_) => {
 490                     err.span_suggestion_verbose(
 491                         span.with_hi(item_segment.ident.span.lo()),
 492                         "use a fully qualified path with inferred lifetimes",
 493                         format!(
 494                             "{}::",
 495                             // Erase named lt, we want `<A as B<'_>::C`, not `<A as B<'a>::C`.
 496                             self.tcx.anonymize_late_bound_regions(poly_trait_ref).skip_binder(),
 497                         ),
 498                         Applicability::MaybeIncorrect,
 499                     );
 500                 }
 501                 _ => {}
 502             }
 503             err.emit();
 504             self.tcx().ty_error()
 505         }
 506     }
 507
 508     fn normalize_ty(&self, _span: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
 509         // Types in item signatures are not normalized to avoid undue dependencies.
 510         ty
 511     }
 512
 513     fn set_tainted_by_errors(&self) {
 514         // There's no obvious place to track this, so just let it go.
 515     }
 516
 517     fn record_ty(&self, _hir_id: hir::HirId, _ty: Ty<'tcx>, _span: Span) {
 518         // There's no place to record types from signatures?
 519     }
 520 }
 521
 522 /// Synthesize a new lifetime name that doesn't clash with any of the lifetimes already present.
 523 fn get_new_lifetime_name<'tcx>(
 524     tcx: TyCtxt<'tcx>,
 525     poly_trait_ref: ty::PolyTraitRef<'tcx>,
 526     generics: &hir::Generics<'tcx>,
 527 ) -> String {
 528     let existing_lifetimes = tcx
 529         .collect_referenced_late_bound_regions(&poly_trait_ref)
 530         .into_iter()
 531         .filter_map(|lt| {
 532             if let ty::BoundRegionKind::BrNamed(_, name) = lt {
 533                 Some(name.as_str().to_string())
 534             } else {
 535                 None
 536             }
 537         })
 538         .chain(generics.params.iter().filter_map(|param| {
 539             if let hir::GenericParamKind::Lifetime { .. } = &param.kind {
 540                 Some(param.name.ident().as_str().to_string())
 541             } else {
 542                 None
 543             }
 544         }))
 545         .collect::<FxHashSet<String>>();
 546
 547     let a_to_z_repeat_n = |n| {
 548         (b'a'..=b'z').map(move |c| {
 549             let mut s = '\''.to_string();
 550             s.extend(std::iter::repeat(char::from(c)).take(n));
 551             s
 552         })
 553     };
 554
 555     // If all single char lifetime names are present, we wrap around and double the chars.
 556     (1..).flat_map(a_to_z_repeat_n).find(|lt| !existing_lifetimes.contains(lt.as_str())).unwrap()
 557 }
 558
 559 /// Returns the predicates defined on `item_def_id` of the form
 560 /// `X: Foo` where `X` is the type parameter `def_id`.
 561 fn type_param_predicates(
 562     tcx: TyCtxt<'_>,
 563     (item_def_id, def_id, assoc_name): (DefId, LocalDefId, Ident),
 564 ) -> ty::GenericPredicates<'_> {
 565     use rustc_hir::*;
 566
 567     // In the AST, bounds can derive from two places. Either
 568     // written inline like `<T: Foo>` or in a where-clause like
 569     // `where T: Foo`.
 570
 571     let param_id = tcx.hir().local_def_id_to_hir_id(def_id);
 572     let param_owner = tcx.hir().ty_param_owner(param_id);
 573     let param_owner_def_id = tcx.hir().local_def_id(param_owner);
 574     let generics = tcx.generics_of(param_owner_def_id);
 575     let index = generics.param_def_id_to_index[&def_id.to_def_id()];
 576     let ty = tcx.mk_ty_param(index, tcx.hir().ty_param_name(param_id));
 577
 578     // Don't look for bounds where the type parameter isn't in scope.
 579     let parent = if item_def_id == param_owner_def_id.to_def_id() {
 580         None
 581     } else {
 582         tcx.generics_of(item_def_id).parent
 583     };
 584
 585     let mut result = parent
 586         .map(|parent| {
 587             let icx = ItemCtxt::new(tcx, parent);
 588             icx.get_type_parameter_bounds(DUMMY_SP, def_id.to_def_id(), assoc_name)
 589         })
 590         .unwrap_or_default();
 591     let mut extend = None;
 592
 593     let item_hir_id = tcx.hir().local_def_id_to_hir_id(item_def_id.expect_local());
 594     let ast_generics = match tcx.hir().get(item_hir_id) {
 595         Node::TraitItem(item) => &item.generics,
 596
 597         Node::ImplItem(item) => &item.generics,
 598
 599         Node::Item(item) => {
 600             match item.kind {
 601                 ItemKind::Fn(.., ref generics, _)
 602                 | ItemKind::Impl(hir::Impl { ref generics, .. })
 603                 | ItemKind::TyAlias(_, ref generics)
 604                 | ItemKind::OpaqueTy(OpaqueTy {
 605                     ref generics,
 606                     origin: hir::OpaqueTyOrigin::TyAlias,
 607                     ..
 608                 })
 609                 | ItemKind::Enum(_, ref generics)
 610                 | ItemKind::Struct(_, ref generics)
 611                 | ItemKind::Union(_, ref generics) => generics,
 612                 ItemKind::Trait(_, _, ref generics, ..) => {
 613                     // Implied `Self: Trait` and supertrait bounds.
 614                     if param_id == item_hir_id {
 615                         let identity_trait_ref = ty::TraitRef::identity(tcx, item_def_id);
 616                         extend =
 617                             Some((identity_trait_ref.without_const().to_predicate(tcx), item.span));
 618                     }
 619                     generics
 620                 }
 621                 _ => return result,
 622             }
 623         }
 624
 625         Node::ForeignItem(item) => match item.kind {
 626             ForeignItemKind::Fn(_, _, ref generics) => generics,
 627             _ => return result,
 628         },
 629
 630         _ => return result,
 631     };
 632
 633     let icx = ItemCtxt::new(tcx, item_def_id);
 634     let extra_predicates = extend.into_iter().chain(
 635         icx.type_parameter_bounds_in_generics(
 636             ast_generics,
 637             param_id,
 638             ty,
 639             OnlySelfBounds(true),
 640             Some(assoc_name),
 641         )
 642         .into_iter()
 643         .filter(|(predicate, _)| match predicate.kind().skip_binder() {
 644             ty::PredicateKind::Trait(data) => data.self_ty().is_param(index),
 645             _ => false,
 646         }),
 647     );
 648     result.predicates =
 649         tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(extra_predicates));
 650     result
 651 }
 652
 653 impl<'tcx> ItemCtxt<'tcx> {
 654     /// Finds bounds from `hir::Generics`. This requires scanning through the
 655     /// AST. We do this to avoid having to convert *all* the bounds, which
 656     /// would create artificial cycles. Instead, we can only convert the
 657     /// bounds for a type parameter `X` if `X::Foo` is used.
 658     fn type_parameter_bounds_in_generics(
 659         &self,
 660         ast_generics: &'tcx hir::Generics<'tcx>,
 661         param_id: hir::HirId,
 662         ty: Ty<'tcx>,
 663         only_self_bounds: OnlySelfBounds,
 664         assoc_name: Option<Ident>,
 665     ) -> Vec<(ty::Predicate<'tcx>, Span)> {
 666         let from_ty_params = ast_generics
 667             .params
 668             .iter()
 669             .filter_map(|param| match param.kind {
 670                 GenericParamKind::Type { .. } if param.hir_id == param_id => Some(&param.bounds),
 671                 _ => None,
 672             })
 673             .flat_map(|bounds| bounds.iter())
 674             .filter(|b| match assoc_name {
 675                 Some(assoc_name) => self.bound_defines_assoc_item(b, assoc_name),
 676                 None => true,
 677             })
 678             .flat_map(|b| predicates_from_bound(self, ty, b, ty::List::empty()));
 679
 680         let param_def_id = self.tcx.hir().local_def_id(param_id).to_def_id();
 681         let from_where_clauses = ast_generics
 682             .where_clause
 683             .predicates
 684             .iter()
 685             .filter_map(|wp| match *wp {
 686                 hir::WherePredicate::BoundPredicate(ref bp) => Some(bp),
 687                 _ => None,
 688             })
 689             .flat_map(|bp| {
 690                 let bt = if bp.is_param_bound(param_def_id) {
 691                     Some(ty)
 692                 } else if !only_self_bounds.0 {
 693                     Some(self.to_ty(bp.bounded_ty))
 694                 } else {
 695                     None
 696                 };
 697                 let bvars = self.tcx.late_bound_vars(bp.bounded_ty.hir_id);
 698
 699                 bp.bounds
 700                     .iter()
 701                     .filter(|b| match assoc_name {
 702                         Some(assoc_name) => self.bound_defines_assoc_item(b, assoc_name),
 703                         None => true,
 704                     })
 705                     .filter_map(move |b| bt.map(|bt| (bt, b, bvars)))
 706             })
 707             .flat_map(|(bt, b, bvars)| predicates_from_bound(self, bt, b, bvars));
 708
 709         from_ty_params.chain(from_where_clauses).collect()
 710     }
 711
 712     fn bound_defines_assoc_item(&self, b: &hir::GenericBound<'_>, assoc_name: Ident) -> bool {
 713         debug!("bound_defines_assoc_item(b={:?}, assoc_name={:?})", b, assoc_name);
 714
 715         match b {
 716             hir::GenericBound::Trait(poly_trait_ref, _) => {
 717                 let trait_ref = &poly_trait_ref.trait_ref;
 718                 if let Some(trait_did) = trait_ref.trait_def_id() {
 719                     self.tcx.trait_may_define_assoc_type(trait_did, assoc_name)
 720                 } else {
 721                     false
 722                 }
 723             }
 724             _ => false,
 725         }
 726     }
 727 }
 728
 729 fn convert_item(tcx: TyCtxt<'_>, item_id: hir::ItemId) {
 730     let it = tcx.hir().item(item_id);
 731     debug!("convert: item {} with id {}", it.ident, it.hir_id());
 732     let def_id = item_id.def_id;
 733
 734     match it.kind {
 735         // These don't define types.
 736         hir::ItemKind::ExternCrate(_)
 737         | hir::ItemKind::Use(..)
 738         | hir::ItemKind::Macro(_)
 739         | hir::ItemKind::Mod(_)
 740         | hir::ItemKind::GlobalAsm(_) => {}
 741         hir::ItemKind::ForeignMod { items, .. } => {
 742             for item in items {
 743                 let item = tcx.hir().foreign_item(item.id);
 744                 tcx.ensure().generics_of(item.def_id);
 745                 tcx.ensure().type_of(item.def_id);
 746                 tcx.ensure().predicates_of(item.def_id);
 747                 match item.kind {
 748                     hir::ForeignItemKind::Fn(..) => tcx.ensure().fn_sig(item.def_id),
 749                     hir::ForeignItemKind::Static(..) => {
 750                         let mut visitor = PlaceholderHirTyCollector::default();
 751                         visitor.visit_foreign_item(item);
 752                         placeholder_type_error(
 753                             tcx,
 754                             None,
 755                             &[],
 756                             visitor.0,
 757                             false,
 758                             None,
 759                             "static variable",
 760                         );
 761                     }
 762                     _ => (),
 763                 }
 764             }
 765         }
 766         hir::ItemKind::Enum(ref enum_definition, _) => {
 767             tcx.ensure().generics_of(def_id);
 768             tcx.ensure().type_of(def_id);
 769             tcx.ensure().predicates_of(def_id);
 770             convert_enum_variant_types(tcx, def_id.to_def_id(), enum_definition.variants);
 771         }
 772         hir::ItemKind::Impl { .. } => {
 773             tcx.ensure().generics_of(def_id);
 774             tcx.ensure().type_of(def_id);
 775             tcx.ensure().impl_trait_ref(def_id);
 776             tcx.ensure().predicates_of(def_id);
 777         }
 778         hir::ItemKind::Trait(..) => {
 779             tcx.ensure().generics_of(def_id);
 780             tcx.ensure().trait_def(def_id);
 781             tcx.at(it.span).super_predicates_of(def_id);
 782             tcx.ensure().predicates_of(def_id);
 783         }
 784         hir::ItemKind::TraitAlias(..) => {
 785             tcx.ensure().generics_of(def_id);
 786             tcx.at(it.span).super_predicates_of(def_id);
 787             tcx.ensure().predicates_of(def_id);
 788         }
 789         hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 790             tcx.ensure().generics_of(def_id);
 791             tcx.ensure().type_of(def_id);
 792             tcx.ensure().predicates_of(def_id);
 793
 794             for f in struct_def.fields() {
 795                 let def_id = tcx.hir().local_def_id(f.hir_id);
 796                 tcx.ensure().generics_of(def_id);
 797                 tcx.ensure().type_of(def_id);
 798                 tcx.ensure().predicates_of(def_id);
 799             }
 800
 801             if let Some(ctor_hir_id) = struct_def.ctor_hir_id() {
 802                 convert_variant_ctor(tcx, ctor_hir_id);
 803             }
 804         }
 805
 806         // Desugared from `impl Trait`, so visited by the function's return type.
 807         hir::ItemKind::OpaqueTy(hir::OpaqueTy {
 808             origin: hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..),
 809             ..
 810         }) => {}
 811
 812         // Don't call `type_of` on opaque types, since that depends on type
 813         // checking function bodies. `check_item_type` ensures that it's called
 814         // instead.
 815         hir::ItemKind::OpaqueTy(..) => {
 816             tcx.ensure().generics_of(def_id);
 817             tcx.ensure().predicates_of(def_id);
 818             tcx.ensure().explicit_item_bounds(def_id);
 819         }
 820         hir::ItemKind::TyAlias(..)
 821         | hir::ItemKind::Static(..)
 822         | hir::ItemKind::Const(..)
 823         | hir::ItemKind::Fn(..) => {
 824             tcx.ensure().generics_of(def_id);
 825             tcx.ensure().type_of(def_id);
 826             tcx.ensure().predicates_of(def_id);
 827             match it.kind {
 828                 hir::ItemKind::Fn(..) => tcx.ensure().fn_sig(def_id),
 829                 hir::ItemKind::OpaqueTy(..) => tcx.ensure().item_bounds(def_id),
 830                 hir::ItemKind::Const(ty, ..) | hir::ItemKind::Static(ty, ..) => {
 831                     // (#75889): Account for `const C: dyn Fn() -> _ = "";`
 832                     if let hir::TyKind::TraitObject(..) = ty.kind {
 833                         let mut visitor = PlaceholderHirTyCollector::default();
 834                         visitor.visit_item(it);
 835                         placeholder_type_error(
 836                             tcx,
 837                             None,
 838                             &[],
 839                             visitor.0,
 840                             false,
 841                             None,
 842                             it.kind.descr(),
 843                         );
 844                     }
 845                 }
 846                 _ => (),
 847             }
 848         }
 849     }
 850 }
 851
 852 fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::TraitItemId) {
 853     let trait_item = tcx.hir().trait_item(trait_item_id);
 854     tcx.ensure().generics_of(trait_item_id.def_id);
 855
 856     match trait_item.kind {
 857         hir::TraitItemKind::Fn(..) => {
 858             tcx.ensure().type_of(trait_item_id.def_id);
 859             tcx.ensure().fn_sig(trait_item_id.def_id);
 860         }
 861
 862         hir::TraitItemKind::Const(.., Some(_)) => {
 863             tcx.ensure().type_of(trait_item_id.def_id);
 864         }
 865
 866         hir::TraitItemKind::Const(..) => {
 867             tcx.ensure().type_of(trait_item_id.def_id);
 868             // Account for `const C: _;`.
 869             let mut visitor = PlaceholderHirTyCollector::default();
 870             visitor.visit_trait_item(trait_item);
 871             placeholder_type_error(tcx, None, &[], visitor.0, false, None, "constant");
 872         }
 873
 874         hir::TraitItemKind::Type(_, Some(_)) => {
 875             tcx.ensure().item_bounds(trait_item_id.def_id);
 876             tcx.ensure().type_of(trait_item_id.def_id);
 877             // Account for `type T = _;`.
 878             let mut visitor = PlaceholderHirTyCollector::default();
 879             visitor.visit_trait_item(trait_item);
 880             placeholder_type_error(tcx, None, &[], visitor.0, false, None, "associated type");
 881         }
 882
 883         hir::TraitItemKind::Type(_, None) => {
 884             tcx.ensure().item_bounds(trait_item_id.def_id);
 885             // #74612: Visit and try to find bad placeholders
 886             // even if there is no concrete type.
 887             let mut visitor = PlaceholderHirTyCollector::default();
 888             visitor.visit_trait_item(trait_item);
 889
 890             placeholder_type_error(tcx, None, &[], visitor.0, false, None, "associated type");
 891         }
 892     };
 893
 894     tcx.ensure().predicates_of(trait_item_id.def_id);
 895 }
 896
 897 fn convert_impl_item(tcx: TyCtxt<'_>, impl_item_id: hir::ImplItemId) {
 898     let def_id = impl_item_id.def_id;
 899     tcx.ensure().generics_of(def_id);
 900     tcx.ensure().type_of(def_id);
 901     tcx.ensure().predicates_of(def_id);
 902     let impl_item = tcx.hir().impl_item(impl_item_id);
 903     match impl_item.kind {
 904         hir::ImplItemKind::Fn(..) => {
 905             tcx.ensure().fn_sig(def_id);
 906         }
 907         hir::ImplItemKind::TyAlias(_) => {
 908             // Account for `type T = _;`
 909             let mut visitor = PlaceholderHirTyCollector::default();
 910             visitor.visit_impl_item(impl_item);
 911
 912             placeholder_type_error(tcx, None, &[], visitor.0, false, None, "associated type");
 913         }
 914         hir::ImplItemKind::Const(..) => {}
 915     }
 916 }
 917
 918 fn convert_variant_ctor(tcx: TyCtxt<'_>, ctor_id: hir::HirId) {
 919     let def_id = tcx.hir().local_def_id(ctor_id);
 920     tcx.ensure().generics_of(def_id);
 921     tcx.ensure().type_of(def_id);
 922     tcx.ensure().predicates_of(def_id);
 923 }
 924
 925 fn convert_enum_variant_types(tcx: TyCtxt<'_>, def_id: DefId, variants: &[hir::Variant<'_>]) {
 926     let def = tcx.adt_def(def_id);
 927     let repr_type = def.repr.discr_type();
 928     let initial = repr_type.initial_discriminant(tcx);
 929     let mut prev_discr = None::<Discr<'_>>;
 930
 931     // fill the discriminant values and field types
 932     for variant in variants {
 933         let wrapped_discr = prev_discr.map_or(initial, |d| d.wrap_incr(tcx));
 934         prev_discr = Some(
 935             if let Some(ref e) = variant.disr_expr {
 936                 let expr_did = tcx.hir().local_def_id(e.hir_id);
 937                 def.eval_explicit_discr(tcx, expr_did.to_def_id())
 938             } else if let Some(discr) = repr_type.disr_incr(tcx, prev_discr) {
 939                 Some(discr)
 940             } else {
 941                 struct_span_err!(tcx.sess, variant.span, E0370, "enum discriminant overflowed")
 942                     .span_label(
 943                         variant.span,
 944                         format!("overflowed on value after {}", prev_discr.unwrap()),
 945                     )
 946                     .note(&format!(
 947                         "explicitly set `{} = {}` if that is desired outcome",
 948                         variant.ident, wrapped_discr
 949                     ))
 950                     .emit();
 951                 None
 952             }
 953             .unwrap_or(wrapped_discr),
 954         );
 955
 956         for f in variant.data.fields() {
 957             let def_id = tcx.hir().local_def_id(f.hir_id);
 958             tcx.ensure().generics_of(def_id);
 959             tcx.ensure().type_of(def_id);
 960             tcx.ensure().predicates_of(def_id);
 961         }
 962
 963         // Convert the ctor, if any. This also registers the variant as
 964         // an item.
 965         if let Some(ctor_hir_id) = variant.data.ctor_hir_id() {
 966             convert_variant_ctor(tcx, ctor_hir_id);
 967         }
 968     }
 969 }
 970
 971 fn convert_variant(
 972     tcx: TyCtxt<'_>,
 973     variant_did: Option<LocalDefId>,
 974     ctor_did: Option<LocalDefId>,
 975     ident: Ident,
 976     discr: ty::VariantDiscr,
 977     def: &hir::VariantData<'_>,
 978     adt_kind: ty::AdtKind,
 979     parent_did: LocalDefId,
 980 ) -> ty::VariantDef {
 981     let mut seen_fields: FxHashMap<Ident, Span> = Default::default();
 982     let fields = def
 983         .fields()
 984         .iter()
 985         .map(|f| {
 986             let fid = tcx.hir().local_def_id(f.hir_id);
 987             let dup_span = seen_fields.get(&f.ident.normalize_to_macros_2_0()).cloned();
 988             if let Some(prev_span) = dup_span {
 989                 tcx.sess.emit_err(errors::FieldAlreadyDeclared {
 990                     field_name: f.ident,
 991                     span: f.span,
 992                     prev_span,
 993                 });
 994             } else {
 995                 seen_fields.insert(f.ident.normalize_to_macros_2_0(), f.span);
 996             }
 997
 998             ty::FieldDef { did: fid.to_def_id(), ident: f.ident, vis: tcx.visibility(fid) }
 999         })
1000         .collect();
1001     let recovered = match def {
1002         hir::VariantData::Struct(_, r) => *r,
1003         _ => false,
1004     };
1005     ty::VariantDef::new(
1006         ident,
1007         variant_did.map(LocalDefId::to_def_id),
1008         ctor_did.map(LocalDefId::to_def_id),
1009         discr,
1010         fields,
1011         CtorKind::from_hir(def),
1012         adt_kind,
1013         parent_did.to_def_id(),
1014         recovered,
1015         adt_kind == AdtKind::Struct && tcx.has_attr(parent_did.to_def_id(), sym::non_exhaustive)
1016             || variant_did.map_or(false, |variant_did| {
1017                 tcx.has_attr(variant_did.to_def_id(), sym::non_exhaustive)
1018             }),
1019     )
1020 }
1021
1022 fn adt_def(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::AdtDef {
1023     use rustc_hir::*;
1024
1025     let def_id = def_id.expect_local();
1026     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
1027     let item = match tcx.hir().get(hir_id) {
1028         Node::Item(item) => item,
1029         _ => bug!(),
1030     };
1031
1032     let repr = ReprOptions::new(tcx, def_id.to_def_id());
1033     let (kind, variants) = match item.kind {
1034         ItemKind::Enum(ref def, _) => {
1035             let mut distance_from_explicit = 0;
1036             let variants = def
1037                 .variants
1038                 .iter()
1039                 .map(|v| {
1040                     let variant_did = Some(tcx.hir().local_def_id(v.id));
1041                     let ctor_did =
1042                         v.data.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
1043
1044                     let discr = if let Some(ref e) = v.disr_expr {
1045                         distance_from_explicit = 0;
1046                         ty::VariantDiscr::Explicit(tcx.hir().local_def_id(e.hir_id).to_def_id())
1047                     } else {
1048                         ty::VariantDiscr::Relative(distance_from_explicit)
1049                     };
1050                     distance_from_explicit += 1;
1051
1052                     convert_variant(
1053                         tcx,
1054                         variant_did,
1055                         ctor_did,
1056                         v.ident,
1057                         discr,
1058                         &v.data,
1059                         AdtKind::Enum,
1060                         def_id,
1061                     )
1062                 })
1063                 .collect();
1064
1065             (AdtKind::Enum, variants)
1066         }
1067         ItemKind::Struct(ref def, _) => {
1068             let variant_did = None::<LocalDefId>;
1069             let ctor_did = def.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
1070
1071             let variants = std::iter::once(convert_variant(
1072                 tcx,
1073                 variant_did,
1074                 ctor_did,
1075                 item.ident,
1076                 ty::VariantDiscr::Relative(0),
1077                 def,
1078                 AdtKind::Struct,
1079                 def_id,
1080             ))
1081             .collect();
1082
1083             (AdtKind::Struct, variants)
1084         }
1085         ItemKind::Union(ref def, _) => {
1086             let variant_did = None;
1087             let ctor_did = def.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
1088
1089             let variants = std::iter::once(convert_variant(
1090                 tcx,
1091                 variant_did,
1092                 ctor_did,
1093                 item.ident,
1094                 ty::VariantDiscr::Relative(0),
1095                 def,
1096                 AdtKind::Union,
1097                 def_id,
1098             ))
1099             .collect();
1100
1101             (AdtKind::Union, variants)
1102         }
1103         _ => bug!(),
1104     };
1105     tcx.alloc_adt_def(def_id.to_def_id(), kind, variants, repr)
1106 }
1107
1108 /// Ensures that the super-predicates of the trait with a `DefId`
1109 /// of `trait_def_id` are converted and stored. This also ensures that
1110 /// the transitive super-predicates are converted.
1111 fn super_predicates_of(tcx: TyCtxt<'_>, trait_def_id: DefId) -> ty::GenericPredicates<'_> {
1112     debug!("super_predicates(trait_def_id={:?})", trait_def_id);
1113     tcx.super_predicates_that_define_assoc_type((trait_def_id, None))
1114 }
1115
1116 /// Ensures that the super-predicates of the trait with a `DefId`
1117 /// of `trait_def_id` are converted and stored. This also ensures that
1118 /// the transitive super-predicates are converted.
1119 fn super_predicates_that_define_assoc_type(
1120     tcx: TyCtxt<'_>,
1121     (trait_def_id, assoc_name): (DefId, Option<Ident>),
1122 ) -> ty::GenericPredicates<'_> {
1123     debug!(
1124         "super_predicates_that_define_assoc_type(trait_def_id={:?}, assoc_name={:?})",
1125         trait_def_id, assoc_name
1126     );
1127     if trait_def_id.is_local() {
1128         debug!("super_predicates_that_define_assoc_type: local trait_def_id={:?}", trait_def_id);
1129         let trait_hir_id = tcx.hir().local_def_id_to_hir_id(trait_def_id.expect_local());
1130
1131         let item = match tcx.hir().get(trait_hir_id) {
1132             Node::Item(item) => item,
1133             _ => bug!("trait_node_id {} is not an item", trait_hir_id),
1134         };
1135
1136         let (generics, bounds) = match item.kind {
1137             hir::ItemKind::Trait(.., ref generics, ref supertraits, _) => (generics, supertraits),
1138             hir::ItemKind::TraitAlias(ref generics, ref supertraits) => (generics, supertraits),
1139             _ => span_bug!(item.span, "super_predicates invoked on non-trait"),
1140         };
1141
1142         let icx = ItemCtxt::new(tcx, trait_def_id);
1143
1144         // Convert the bounds that follow the colon, e.g., `Bar + Zed` in `trait Foo: Bar + Zed`.
1145         let self_param_ty = tcx.types.self_param;
1146         let superbounds1 = if let Some(assoc_name) = assoc_name {
1147             <dyn AstConv<'_>>::compute_bounds_that_match_assoc_type(
1148                 &icx,
1149                 self_param_ty,
1150                 bounds,
1151                 assoc_name,
1152             )
1153         } else {
1154             <dyn AstConv<'_>>::compute_bounds(&icx, self_param_ty, bounds)
1155         };
1156
1157         let superbounds1 = superbounds1.predicates(tcx, self_param_ty);
1158
1159         // Convert any explicit superbounds in the where-clause,
1160         // e.g., `trait Foo where Self: Bar`.
1161         // In the case of trait aliases, however, we include all bounds in the where-clause,
1162         // so e.g., `trait Foo = where u32: PartialEq<Self>` would include `u32: PartialEq<Self>`
1163         // as one of its "superpredicates".
1164         let is_trait_alias = tcx.is_trait_alias(trait_def_id);
1165         let superbounds2 = icx.type_parameter_bounds_in_generics(
1166             generics,
1167             item.hir_id(),
1168             self_param_ty,
1169             OnlySelfBounds(!is_trait_alias),
1170             assoc_name,
1171         );
1172
1173         // Combine the two lists to form the complete set of superbounds:
1174         let superbounds = &*tcx.arena.alloc_from_iter(superbounds1.into_iter().chain(superbounds2));
1175
1176         // Now require that immediate supertraits are converted,
1177         // which will, in turn, reach indirect supertraits.
1178         if assoc_name.is_none() {
1179             // Now require that immediate supertraits are converted,
1180             // which will, in turn, reach indirect supertraits.
1181             for &(pred, span) in superbounds {
1182                 debug!("superbound: {:?}", pred);
1183                 if let ty::PredicateKind::Trait(bound) = pred.kind().skip_binder() {
1184                     tcx.at(span).super_predicates_of(bound.def_id());
1185                 }
1186             }
1187         }
1188
1189         ty::GenericPredicates { parent: None, predicates: superbounds }
1190     } else {
1191         // if `assoc_name` is None, then the query should've been redirected to an
1192         // external provider
1193         assert!(assoc_name.is_some());
1194         tcx.super_predicates_of(trait_def_id)
1195     }
1196 }
1197
1198 fn trait_def(tcx: TyCtxt<'_>, def_id: DefId) -> ty::TraitDef {
1199     let item = tcx.hir().expect_item(def_id.expect_local());
1200
1201     let (is_auto, unsafety) = match item.kind {
1202         hir::ItemKind::Trait(is_auto, unsafety, ..) => (is_auto == hir::IsAuto::Yes, unsafety),
1203         hir::ItemKind::TraitAlias(..) => (false, hir::Unsafety::Normal),
1204         _ => span_bug!(item.span, "trait_def_of_item invoked on non-trait"),
1205     };
1206
1207     let paren_sugar = tcx.has_attr(def_id, sym::rustc_paren_sugar);
1208     if paren_sugar && !tcx.features().unboxed_closures {
1209         tcx.sess
1210             .struct_span_err(
1211                 item.span,
1212                 "the `#[rustc_paren_sugar]` attribute is a temporary means of controlling \
1213                  which traits can use parenthetical notation",
1214             )
1215             .help("add `#![feature(unboxed_closures)]` to the crate attributes to use it")
1216             .emit();
1217     }
1218
1219     let is_marker = tcx.has_attr(def_id, sym::marker);
1220     let skip_array_during_method_dispatch =
1221         tcx.has_attr(def_id, sym::rustc_skip_array_during_method_dispatch);
1222     let spec_kind = if tcx.has_attr(def_id, sym::rustc_unsafe_specialization_marker) {
1223         ty::trait_def::TraitSpecializationKind::Marker
1224     } else if tcx.has_attr(def_id, sym::rustc_specialization_trait) {
1225         ty::trait_def::TraitSpecializationKind::AlwaysApplicable
1226     } else {
1227         ty::trait_def::TraitSpecializationKind::None
1228     };
1229     let def_path_hash = tcx.def_path_hash(def_id);
1230     ty::TraitDef::new(
1231         def_id,
1232         unsafety,
1233         paren_sugar,
1234         is_auto,
1235         is_marker,
1236         skip_array_during_method_dispatch,
1237         spec_kind,
1238         def_path_hash,
1239     )
1240 }
1241
1242 fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<Span> {
1243     struct LateBoundRegionsDetector<'tcx> {
1244         tcx: TyCtxt<'tcx>,
1245         outer_index: ty::DebruijnIndex,
1246         has_late_bound_regions: Option<Span>,
1247     }
1248
1249     impl<'tcx> Visitor<'tcx> for LateBoundRegionsDetector<'tcx> {
1250         type Map = intravisit::ErasedMap<'tcx>;
1251
1252         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1253             NestedVisitorMap::None
1254         }
1255
1256         fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
1257             if self.has_late_bound_regions.is_some() {
1258                 return;
1259             }
1260             match ty.kind {
1261                 hir::TyKind::BareFn(..) => {
1262                     self.outer_index.shift_in(1);
1263                     intravisit::walk_ty(self, ty);
1264                     self.outer_index.shift_out(1);
1265                 }
1266                 _ => intravisit::walk_ty(self, ty),
1267             }
1268         }
1269
1270         fn visit_poly_trait_ref(
1271             &mut self,
1272             tr: &'tcx hir::PolyTraitRef<'tcx>,
1273             m: hir::TraitBoundModifier,
1274         ) {
1275             if self.has_late_bound_regions.is_some() {
1276                 return;
1277             }
1278             self.outer_index.shift_in(1);
1279             intravisit::walk_poly_trait_ref(self, tr, m);
1280             self.outer_index.shift_out(1);
1281         }
1282
1283         fn visit_lifetime(&mut self, lt: &'tcx hir::Lifetime) {
1284             if self.has_late_bound_regions.is_some() {
1285                 return;
1286             }
1287
1288             match self.tcx.named_region(lt.hir_id) {
1289                 Some(rl::Region::Static | rl::Region::EarlyBound(..)) => {}
1290                 Some(
1291                     rl::Region::LateBound(debruijn, _, _, _)
1292                     | rl::Region::LateBoundAnon(debruijn, _, _),
1293                 ) if debruijn < self.outer_index => {}
1294                 Some(
1295                     rl::Region::LateBound(..)
1296                     | rl::Region::LateBoundAnon(..)
1297                     | rl::Region::Free(..),
1298                 )
1299                 | None => {
1300                     self.has_late_bound_regions = Some(lt.span);
1301                 }
1302             }
1303         }
1304     }
1305
1306     fn has_late_bound_regions<'tcx>(
1307         tcx: TyCtxt<'tcx>,
1308         generics: &'tcx hir::Generics<'tcx>,
1309         decl: &'tcx hir::FnDecl<'tcx>,
1310     ) -> Option<Span> {
1311         let mut visitor = LateBoundRegionsDetector {
1312             tcx,
1313             outer_index: ty::INNERMOST,
1314             has_late_bound_regions: None,
1315         };
1316         for param in generics.params {
1317             if let GenericParamKind::Lifetime { .. } = param.kind {
1318                 if tcx.is_late_bound(param.hir_id) {
1319                     return Some(param.span);
1320                 }
1321             }
1322         }
1323         visitor.visit_fn_decl(decl);
1324         visitor.has_late_bound_regions
1325     }
1326
1327     match node {
1328         Node::TraitItem(item) => match item.kind {
1329             hir::TraitItemKind::Fn(ref sig, _) => {
1330                 has_late_bound_regions(tcx, &item.generics, sig.decl)
1331             }
1332             _ => None,
1333         },
1334         Node::ImplItem(item) => match item.kind {
1335             hir::ImplItemKind::Fn(ref sig, _) => {
1336                 has_late_bound_regions(tcx, &item.generics, sig.decl)
1337             }
1338             _ => None,
1339         },
1340         Node::ForeignItem(item) => match item.kind {
1341             hir::ForeignItemKind::Fn(fn_decl, _, ref generics) => {
1342                 has_late_bound_regions(tcx, generics, fn_decl)
1343             }
1344             _ => None,
1345         },
1346         Node::Item(item) => match item.kind {
1347             hir::ItemKind::Fn(ref sig, .., ref generics, _) => {
1348                 has_late_bound_regions(tcx, generics, sig.decl)
1349             }
1350             _ => None,
1351         },
1352         _ => None,
1353     }
1354 }
1355
1356 struct AnonConstInParamTyDetector {
1357     in_param_ty: bool,
1358     found_anon_const_in_param_ty: bool,
1359     ct: HirId,
1360 }
1361
1362 impl<'v> Visitor<'v> for AnonConstInParamTyDetector {
1363     type Map = intravisit::ErasedMap<'v>;
1364
1365     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1366         NestedVisitorMap::None
1367     }
1368
1369     fn visit_generic_param(&mut self, p: &'v hir::GenericParam<'v>) {
1370         if let GenericParamKind::Const { ty, default: _ } = p.kind {
1371             let prev = self.in_param_ty;
1372             self.in_param_ty = true;
1373             self.visit_ty(ty);
1374             self.in_param_ty = prev;
1375         }
1376     }
1377
1378     fn visit_anon_const(&mut self, c: &'v hir::AnonConst) {
1379         if self.in_param_ty && self.ct == c.hir_id {
1380             self.found_anon_const_in_param_ty = true;
1381         } else {
1382             intravisit::walk_anon_const(self, c)
1383         }
1384     }
1385 }
1386
1387 fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
1388     use rustc_hir::*;
1389
1390     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
1391
1392     let node = tcx.hir().get(hir_id);
1393     let parent_def_id = match node {
1394         Node::ImplItem(_)
1395         | Node::TraitItem(_)
1396         | Node::Variant(_)
1397         | Node::Ctor(..)
1398         | Node::Field(_) => {
1399             let parent_id = tcx.hir().get_parent_item(hir_id);
1400             Some(tcx.hir().local_def_id(parent_id).to_def_id())
1401         }
1402         // FIXME(#43408) always enable this once `lazy_normalization` is
1403         // stable enough and does not need a feature gate anymore.
1404         Node::AnonConst(_) => {
1405             let parent_id = tcx.hir().get_parent_item(hir_id);
1406             let parent_def_id = tcx.hir().local_def_id(parent_id);
1407
1408             let mut in_param_ty = false;
1409             for (_parent, node) in tcx.hir().parent_iter(hir_id) {
1410                 if let Some(generics) = node.generics() {
1411                     let mut visitor = AnonConstInParamTyDetector {
1412                         in_param_ty: false,
1413                         found_anon_const_in_param_ty: false,
1414                         ct: hir_id,
1415                     };
1416
1417                     visitor.visit_generics(generics);
1418                     in_param_ty = visitor.found_anon_const_in_param_ty;
1419                     break;
1420                 }
1421             }
1422
1423             if in_param_ty {
1424                 // We do not allow generic parameters in anon consts if we are inside
1425                 // of a const parameter type, e.g. `struct Foo<const N: usize, const M: [u8; N]>` is not allowed.
1426                 None
1427             } else if tcx.lazy_normalization() {
1428                 if let Some(param_id) = tcx.hir().opt_const_param_default_param_hir_id(hir_id) {
1429                     // If the def_id we are calling generics_of on is an anon ct default i.e:
1430                     //
1431                     // struct Foo<const N: usize = { .. }>;
1432                     //        ^^^       ^          ^^^^^^ def id of this anon const
1433                     //        ^         ^ param_id
1434                     //        ^ parent_def_id
1435                     //
1436                     // then we only want to return generics for params to the left of `N`. If we don't do that we
1437                     // end up with that const looking like: `ty::ConstKind::Unevaluated(def_id, substs: [N#0])`.
1438                     //
1439                     // This causes ICEs (#86580) when building the substs for Foo in `fn foo() -> Foo { .. }` as
1440                     // we substitute the defaults with the partially built substs when we build the substs. Subst'ing
1441                     // the `N#0` on the unevaluated const indexes into the empty substs we're in the process of building.
1442                     //
1443                     // We fix this by having this function return the parent's generics ourselves and truncating the
1444                     // generics to only include non-forward declared params (with the exception of the `Self` ty)
1445                     //
1446                     // For the above code example that means we want `substs: []`
1447                     // For the following struct def we want `substs: [N#0]` when generics_of is called on
1448                     // the def id of the `{ N + 1 }` anon const
1449                     // struct Foo<const N: usize, const M: usize = { N + 1 }>;
1450                     //
1451                     // This has some implications for how we get the predicates available to the anon const
1452                     // see `explicit_predicates_of` for more information on this
1453                     let generics = tcx.generics_of(parent_def_id.to_def_id());
1454                     let param_def = tcx.hir().local_def_id(param_id).to_def_id();
1455                     let param_def_idx = generics.param_def_id_to_index[&param_def];
1456                     // In the above example this would be .params[..N#0]
1457                     let params = generics.params[..param_def_idx as usize].to_owned();
1458                     let param_def_id_to_index =
1459                         params.iter().map(|param| (param.def_id, param.index)).collect();
1460
1461                     return ty::Generics {
1462                         // we set the parent of these generics to be our parent's parent so that we
1463                         // dont end up with substs: [N, M, N] for the const default on a struct like this:
1464                         // struct Foo<const N: usize, const M: usize = { ... }>;
1465                         parent: generics.parent,
1466                         parent_count: generics.parent_count,
1467                         params,
1468                         param_def_id_to_index,
1469                         has_self: generics.has_self,
1470                         has_late_bound_regions: generics.has_late_bound_regions,
1471                     };
1472                 }
1473
1474                 // HACK(eddyb) this provides the correct generics when
1475                 // `feature(generic_const_expressions)` is enabled, so that const expressions
1476                 // used with const generics, e.g. `Foo<{N+1}>`, can work at all.
1477                 //
1478                 // Note that we do not supply the parent generics when using
1479                 // `min_const_generics`.
1480                 Some(parent_def_id.to_def_id())
1481             } else {
1482                 let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
1483                 match parent_node {
1484                     // HACK(eddyb) this provides the correct generics for repeat
1485                     // expressions' count (i.e. `N` in `[x; N]`), and explicit
1486                     // `enum` discriminants (i.e. `D` in `enum Foo { Bar = D }`),
1487                     // as they shouldn't be able to cause query cycle errors.
1488                     Node::Expr(&Expr { kind: ExprKind::Repeat(_, ref constant), .. })
1489                         if constant.hir_id() == hir_id =>
1490                     {
1491                         Some(parent_def_id.to_def_id())
1492                     }
1493                     Node::Variant(Variant { disr_expr: Some(ref constant), .. })
1494                         if constant.hir_id == hir_id =>
1495                     {
1496                         Some(parent_def_id.to_def_id())
1497                     }
1498                     Node::Expr(&Expr { kind: ExprKind::ConstBlock(_), .. }) => {
1499                         Some(tcx.typeck_root_def_id(def_id))
1500                     }
1501                     _ => None,
1502                 }
1503             }
1504         }
1505         Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => {
1506             Some(tcx.typeck_root_def_id(def_id))
1507         }
1508         Node::Item(item) => match item.kind {
1509             ItemKind::OpaqueTy(hir::OpaqueTy {
1510                 origin:
1511                     hir::OpaqueTyOrigin::FnReturn(fn_def_id) | hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
1512                 ..
1513             }) => Some(fn_def_id.to_def_id()),
1514             ItemKind::OpaqueTy(hir::OpaqueTy { origin: hir::OpaqueTyOrigin::TyAlias, .. }) => {
1515                 let parent_id = tcx.hir().get_parent_item(hir_id);
1516                 assert!(parent_id != hir_id && parent_id != CRATE_HIR_ID);
1517                 debug!("generics_of: parent of opaque ty {:?} is {:?}", def_id, parent_id);
1518                 // Opaque types are always nested within another item, and
1519                 // inherit the generics of the item.
1520                 Some(tcx.hir().local_def_id(parent_id).to_def_id())
1521             }
1522             _ => None,
1523         },
1524         _ => None,
1525     };
1526
1527     let mut opt_self = None;
1528     let mut allow_defaults = false;
1529
1530     let no_generics = hir::Generics::empty();
1531     let ast_generics = match node {
1532         Node::TraitItem(item) => &item.generics,
1533
1534         Node::ImplItem(item) => &item.generics,
1535
1536         Node::Item(item) => {
1537             match item.kind {
1538                 ItemKind::Fn(.., ref generics, _)
1539                 | ItemKind::Impl(hir::Impl { ref generics, .. }) => generics,
1540
1541                 ItemKind::TyAlias(_, ref generics)
1542                 | ItemKind::Enum(_, ref generics)
1543                 | ItemKind::Struct(_, ref generics)
1544                 | ItemKind::OpaqueTy(hir::OpaqueTy { ref generics, .. })
1545                 | ItemKind::Union(_, ref generics) => {
1546                     allow_defaults = true;
1547                     generics
1548                 }
1549
1550                 ItemKind::Trait(_, _, ref generics, ..)
1551                 | ItemKind::TraitAlias(ref generics, ..) => {
1552                     // Add in the self type parameter.
1553                     //
1554                     // Something of a hack: use the node id for the trait, also as
1555                     // the node id for the Self type parameter.
1556                     let param_id = item.def_id;
1557
1558                     opt_self = Some(ty::GenericParamDef {
1559                         index: 0,
1560                         name: kw::SelfUpper,
1561                         def_id: param_id.to_def_id(),
1562                         pure_wrt_drop: false,
1563                         kind: ty::GenericParamDefKind::Type {
1564                             has_default: false,
1565                             object_lifetime_default: rl::Set1::Empty,
1566                             synthetic: false,
1567                         },
1568                     });
1569
1570                     allow_defaults = true;
1571                     generics
1572                 }
1573
1574                 _ => &no_generics,
1575             }
1576         }
1577
1578         Node::ForeignItem(item) => match item.kind {
1579             ForeignItemKind::Static(..) => &no_generics,
1580             ForeignItemKind::Fn(_, _, ref generics) => generics,
1581             ForeignItemKind::Type => &no_generics,
1582         },
1583
1584         _ => &no_generics,
1585     };
1586
1587     let has_self = opt_self.is_some();
1588     let mut parent_has_self = false;
1589     let mut own_start = has_self as u32;
1590     let parent_count = parent_def_id.map_or(0, |def_id| {
1591         let generics = tcx.generics_of(def_id);
1592         assert!(!has_self);
1593         parent_has_self = generics.has_self;
1594         own_start = generics.count() as u32;
1595         generics.parent_count + generics.params.len()
1596     });
1597
1598     let mut params: Vec<_> = Vec::with_capacity(ast_generics.params.len() + has_self as usize);
1599
1600     if let Some(opt_self) = opt_self {
1601         params.push(opt_self);
1602     }
1603
1604     let early_lifetimes = early_bound_lifetimes_from_generics(tcx, ast_generics);
1605     params.extend(early_lifetimes.enumerate().map(|(i, param)| ty::GenericParamDef {
1606         name: param.name.ident().name,
1607         index: own_start + i as u32,
1608         def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
1609         pure_wrt_drop: param.pure_wrt_drop,
1610         kind: ty::GenericParamDefKind::Lifetime,
1611     }));
1612
1613     let object_lifetime_defaults = tcx.object_lifetime_defaults(hir_id);
1614
1615     // Now create the real type and const parameters.
1616     let type_start = own_start - has_self as u32 + params.len() as u32;
1617     let mut i = 0;
1618
1619     params.extend(ast_generics.params.iter().filter_map(|param| match param.kind {
1620         GenericParamKind::Lifetime { .. } => None,
1621         GenericParamKind::Type { ref default, synthetic, .. } => {
1622             if !allow_defaults && default.is_some() {
1623                 if !tcx.features().default_type_parameter_fallback {
1624                     tcx.struct_span_lint_hir(
1625                         lint::builtin::INVALID_TYPE_PARAM_DEFAULT,
1626                         param.hir_id,
1627                         param.span,
1628                         |lint| {
1629                             lint.build(
1630                                 "defaults for type parameters are only allowed in \
1631                                  `struct`, `enum`, `type`, or `trait` definitions",
1632                             )
1633                             .emit();
1634                         },
1635                     );
1636                 }
1637             }
1638
1639             let kind = ty::GenericParamDefKind::Type {
1640                 has_default: default.is_some(),
1641                 object_lifetime_default: object_lifetime_defaults
1642                     .as_ref()
1643                     .map_or(rl::Set1::Empty, |o| o[i]),
1644                 synthetic,
1645             };
1646
1647             let param_def = ty::GenericParamDef {
1648                 index: type_start + i as u32,
1649                 name: param.name.ident().name,
1650                 def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
1651                 pure_wrt_drop: param.pure_wrt_drop,
1652                 kind,
1653             };
1654             i += 1;
1655             Some(param_def)
1656         }
1657         GenericParamKind::Const { default, .. } => {
1658             if !allow_defaults && default.is_some() {
1659                 tcx.sess.span_err(
1660                     param.span,
1661                     "defaults for const parameters are only allowed in \
1662                     `struct`, `enum`, `type`, or `trait` definitions",
1663                 );
1664             }
1665
1666             let param_def = ty::GenericParamDef {
1667                 index: type_start + i as u32,
1668                 name: param.name.ident().name,
1669                 def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
1670                 pure_wrt_drop: param.pure_wrt_drop,
1671                 kind: ty::GenericParamDefKind::Const { has_default: default.is_some() },
1672             };
1673             i += 1;
1674             Some(param_def)
1675         }
1676     }));
1677
1678     // provide junk type parameter defs - the only place that
1679     // cares about anything but the length is instantiation,
1680     // and we don't do that for closures.
1681     if let Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(.., gen), .. }) = node {
1682         let dummy_args = if gen.is_some() {
1683             &["<resume_ty>", "<yield_ty>", "<return_ty>", "<witness>", "<upvars>"][..]
1684         } else {
1685             &["<closure_kind>", "<closure_signature>", "<upvars>"][..]
1686         };
1687
1688         params.extend(dummy_args.iter().enumerate().map(|(i, &arg)| ty::GenericParamDef {
1689             index: type_start + i as u32,
1690             name: Symbol::intern(arg),
1691             def_id,
1692             pure_wrt_drop: false,
1693             kind: ty::GenericParamDefKind::Type {
1694                 has_default: false,
1695                 object_lifetime_default: rl::Set1::Empty,
1696                 synthetic: false,
1697             },
1698         }));
1699     }
1700
1701     // provide junk type parameter defs for const blocks.
1702     if let Node::AnonConst(_) = node {
1703         let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
1704         if let Node::Expr(&Expr { kind: ExprKind::ConstBlock(_), .. }) = parent_node {
1705             params.push(ty::GenericParamDef {
1706                 index: type_start,
1707                 name: Symbol::intern("<const_ty>"),
1708                 def_id,
1709                 pure_wrt_drop: false,
1710                 kind: ty::GenericParamDefKind::Type {
1711                     has_default: false,
1712                     object_lifetime_default: rl::Set1::Empty,
1713                     synthetic: false,
1714                 },
1715             });
1716         }
1717     }
1718
1719     let param_def_id_to_index = params.iter().map(|param| (param.def_id, param.index)).collect();
1720
1721     ty::Generics {
1722         parent: parent_def_id,
1723         parent_count,
1724         params,
1725         param_def_id_to_index,
1726         has_self: has_self || parent_has_self,
1727         has_late_bound_regions: has_late_bound_regions(tcx, node),
1728     }
1729 }
1730
1731 fn are_suggestable_generic_args(generic_args: &[hir::GenericArg<'_>]) -> bool {
1732     generic_args.iter().any(|arg| match arg {
1733         hir::GenericArg::Type(ty) => is_suggestable_infer_ty(ty),
1734         hir::GenericArg::Infer(_) => true,
1735         _ => false,
1736     })
1737 }
1738
1739 /// Whether `ty` is a type with `_` placeholders that can be inferred. Used in diagnostics only to
1740 /// use inference to provide suggestions for the appropriate type if possible.
1741 fn is_suggestable_infer_ty(ty: &hir::Ty<'_>) -> bool {
1742     use hir::TyKind::*;
1743     match &ty.kind {
1744         Infer => true,
1745         Slice(ty) | Array(ty, _) => is_suggestable_infer_ty(ty),
1746         Tup(tys) => tys.iter().any(is_suggestable_infer_ty),
1747         Ptr(mut_ty) | Rptr(_, mut_ty) => is_suggestable_infer_ty(mut_ty.ty),
1748         OpaqueDef(_, generic_args) => are_suggestable_generic_args(generic_args),
1749         Path(hir::QPath::TypeRelative(ty, segment)) => {
1750             is_suggestable_infer_ty(ty) || are_suggestable_generic_args(segment.args().args)
1751         }
1752         Path(hir::QPath::Resolved(ty_opt, hir::Path { segments, .. })) => {
1753             ty_opt.map_or(false, is_suggestable_infer_ty)
1754                 || segments.iter().any(|segment| are_suggestable_generic_args(segment.args().args))
1755         }
1756         _ => false,
1757     }
1758 }
1759
1760 pub fn get_infer_ret_ty<'hir>(output: &'hir hir::FnRetTy<'hir>) -> Option<&'hir hir::Ty<'hir>> {
1761     if let hir::FnRetTy::Return(ty) = output {
1762         if is_suggestable_infer_ty(ty) {
1763             return Some(&*ty);
1764         }
1765     }
1766     None
1767 }
1768
1769 fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
1770     use rustc_hir::Node::*;
1771     use rustc_hir::*;
1772
1773     let def_id = def_id.expect_local();
1774     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
1775
1776     let icx = ItemCtxt::new(tcx, def_id.to_def_id());
1777
1778     match tcx.hir().get(hir_id) {
1779         TraitItem(hir::TraitItem {
1780             kind: TraitItemKind::Fn(sig, TraitFn::Provided(_)),
1781             ident,
1782             generics,
1783             ..
1784         })
1785         | ImplItem(hir::ImplItem { kind: ImplItemKind::Fn(sig, _), ident, generics, .. })
1786         | Item(hir::Item { kind: ItemKind::Fn(sig, generics, _), ident, .. }) => {
1787             match get_infer_ret_ty(&sig.decl.output) {
1788                 Some(ty) => {
1789                     let fn_sig = tcx.typeck(def_id).liberated_fn_sigs()[hir_id];
1790                     // Typeck doesn't expect erased regions to be returned from `type_of`.
1791                     let fn_sig = tcx.fold_regions(fn_sig, &mut false, |r, _| match r {
1792                         ty::ReErased => tcx.lifetimes.re_static,
1793                         _ => r,
1794                     });
1795                     let fn_sig = ty::Binder::dummy(fn_sig);
1796
1797                     let mut visitor = PlaceholderHirTyCollector::default();
1798                     visitor.visit_ty(ty);
1799                     let mut diag = bad_placeholder(tcx, "type", visitor.0, "return type");
1800                     let ret_ty = fn_sig.skip_binder().output();
1801                     if !ret_ty.references_error() {
1802                         if !ret_ty.is_closure() {
1803                             let ret_ty_str = match ret_ty.kind() {
1804                                 // Suggest a function pointer return type instead of a unique function definition
1805                                 // (e.g. `fn() -> i32` instead of `fn() -> i32 { f }`, the latter of which is invalid
1806                                 // syntax)
1807                                 ty::FnDef(..) => ret_ty.fn_sig(tcx).to_string(),
1808                                 _ => ret_ty.to_string(),
1809                             };
1810                             diag.span_suggestion(
1811                                 ty.span,
1812                                 "replace with the correct return type",
1813                                 ret_ty_str,
1814                                 Applicability::MaybeIncorrect,
1815                             );
1816                         } else {
1817                             // We're dealing with a closure, so we should suggest using `impl Fn` or trait bounds
1818                             // to prevent the user from getting a papercut while trying to use the unique closure
1819                             // syntax (e.g. `[closure@src/lib.rs:2:5: 2:9]`).
1820                             diag.help("consider using an `Fn`, `FnMut`, or `FnOnce` trait bound");
1821                             diag.note("for more information on `Fn` traits and closure types, see https://doc.rust-lang.org/book/ch13-01-closures.html");
1822                         }
1823                     }
1824                     diag.emit();
1825
1826                     fn_sig
1827                 }
1828                 None => <dyn AstConv<'_>>::ty_of_fn(
1829                     &icx,
1830                     hir_id,
1831                     sig.header.unsafety,
1832                     sig.header.abi,
1833                     sig.decl,
1834                     generics,
1835                     Some(ident.span),
1836                     None,
1837                 ),
1838             }
1839         }
1840
1841         TraitItem(hir::TraitItem {
1842             kind: TraitItemKind::Fn(FnSig { header, decl, span: _ }, _),
1843             ident,
1844             generics,
1845             ..
1846         }) => <dyn AstConv<'_>>::ty_of_fn(
1847             &icx,
1848             hir_id,
1849             header.unsafety,
1850             header.abi,
1851             decl,
1852             generics,
1853             Some(ident.span),
1854             None,
1855         ),
1856
1857         ForeignItem(&hir::ForeignItem {
1858             kind: ForeignItemKind::Fn(fn_decl, _, _), ident, ..
1859         }) => {
1860             let abi = tcx.hir().get_foreign_abi(hir_id);
1861             compute_sig_of_foreign_fn_decl(tcx, def_id.to_def_id(), fn_decl, abi, ident)
1862         }
1863
1864         Ctor(data) | Variant(hir::Variant { data, .. }) if data.ctor_hir_id().is_some() => {
1865             let ty = tcx.type_of(tcx.hir().get_parent_did(hir_id).to_def_id());
1866             let inputs =
1867                 data.fields().iter().map(|f| tcx.type_of(tcx.hir().local_def_id(f.hir_id)));
1868             ty::Binder::dummy(tcx.mk_fn_sig(
1869                 inputs,
1870                 ty,
1871                 false,
1872                 hir::Unsafety::Normal,
1873                 abi::Abi::Rust,
1874             ))
1875         }
1876
1877         Expr(&hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => {
1878             // Closure signatures are not like other function
1879             // signatures and cannot be accessed through `fn_sig`. For
1880             // example, a closure signature excludes the `self`
1881             // argument. In any case they are embedded within the
1882             // closure type as part of the `ClosureSubsts`.
1883             //
1884             // To get the signature of a closure, you should use the
1885             // `sig` method on the `ClosureSubsts`:
1886             //
1887             //    substs.as_closure().sig(def_id, tcx)
1888             bug!(
1889                 "to get the signature of a closure, use `substs.as_closure().sig()` not `fn_sig()`",
1890             );
1891         }
1892
1893         x => {
1894             bug!("unexpected sort of node in fn_sig(): {:?}", x);
1895         }
1896     }
1897 }
1898
1899 fn impl_trait_ref(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ty::TraitRef<'_>> {
1900     let icx = ItemCtxt::new(tcx, def_id);
1901     match tcx.hir().expect_item(def_id.expect_local()).kind {
1902         hir::ItemKind::Impl(ref impl_) => impl_.of_trait.as_ref().map(|ast_trait_ref| {
1903             let selfty = tcx.type_of(def_id);
1904             <dyn AstConv<'_>>::instantiate_mono_trait_ref(&icx, ast_trait_ref, selfty)
1905         }),
1906         _ => bug!(),
1907     }
1908 }
1909
1910 fn impl_polarity(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ImplPolarity {
1911     let is_rustc_reservation = tcx.has_attr(def_id, sym::rustc_reservation_impl);
1912     let item = tcx.hir().expect_item(def_id.expect_local());
1913     match &item.kind {
1914         hir::ItemKind::Impl(hir::Impl {
1915             polarity: hir::ImplPolarity::Negative(span),
1916             of_trait,
1917             ..
1918         }) => {
1919             if is_rustc_reservation {
1920                 let span = span.to(of_trait.as_ref().map_or(*span, |t| t.path.span));
1921                 tcx.sess.span_err(span, "reservation impls can't be negative");
1922             }
1923             ty::ImplPolarity::Negative
1924         }
1925         hir::ItemKind::Impl(hir::Impl {
1926             polarity: hir::ImplPolarity::Positive,
1927             of_trait: None,
1928             ..
1929         }) => {
1930             if is_rustc_reservation {
1931                 tcx.sess.span_err(item.span, "reservation impls can't be inherent");
1932             }
1933             ty::ImplPolarity::Positive
1934         }
1935         hir::ItemKind::Impl(hir::Impl {
1936             polarity: hir::ImplPolarity::Positive,
1937             of_trait: Some(_),
1938             ..
1939         }) => {
1940             if is_rustc_reservation {
1941                 ty::ImplPolarity::Reservation
1942             } else {
1943                 ty::ImplPolarity::Positive
1944             }
1945         }
1946         item => bug!("impl_polarity: {:?} not an impl", item),
1947     }
1948 }
1949
1950 /// Returns the early-bound lifetimes declared in this generics
1951 /// listing. For anything other than fns/methods, this is just all
1952 /// the lifetimes that are declared. For fns or methods, we have to
1953 /// screen out those that do not appear in any where-clauses etc using
1954 /// `resolve_lifetime::early_bound_lifetimes`.
1955 fn early_bound_lifetimes_from_generics<'a, 'tcx: 'a>(
1956     tcx: TyCtxt<'tcx>,
1957     generics: &'a hir::Generics<'a>,
1958 ) -> impl Iterator<Item = &'a hir::GenericParam<'a>> + Captures<'tcx> {
1959     generics.params.iter().filter(move |param| match param.kind {
1960         GenericParamKind::Lifetime { .. } => !tcx.is_late_bound(param.hir_id),
1961         _ => false,
1962     })
1963 }
1964
1965 /// Returns a list of type predicates for the definition with ID `def_id`, including inferred
1966 /// lifetime constraints. This includes all predicates returned by `explicit_predicates_of`, plus
1967 /// inferred constraints concerning which regions outlive other regions.
1968 fn predicates_defined_on(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
1969     debug!("predicates_defined_on({:?})", def_id);
1970     let mut result = tcx.explicit_predicates_of(def_id);
1971     debug!("predicates_defined_on: explicit_predicates_of({:?}) = {:?}", def_id, result,);
1972     let inferred_outlives = tcx.inferred_outlives_of(def_id);
1973     if !inferred_outlives.is_empty() {
1974         debug!(
1975             "predicates_defined_on: inferred_outlives_of({:?}) = {:?}",
1976             def_id, inferred_outlives,
1977         );
1978         if result.predicates.is_empty() {
1979             result.predicates = inferred_outlives;
1980         } else {
1981             result.predicates = tcx
1982                 .arena
1983                 .alloc_from_iter(result.predicates.iter().chain(inferred_outlives).copied());
1984         }
1985     }
1986
1987     debug!("predicates_defined_on({:?}) = {:?}", def_id, result);
1988     result
1989 }
1990
1991 /// Returns a list of all type predicates (explicit and implicit) for the definition with
1992 /// ID `def_id`. This includes all predicates returned by `predicates_defined_on`, plus
1993 /// `Self: Trait` predicates for traits.
1994 fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
1995     let mut result = tcx.predicates_defined_on(def_id);
1996
1997     if tcx.is_trait(def_id) {
1998         // For traits, add `Self: Trait` predicate. This is
1999         // not part of the predicates that a user writes, but it
2000         // is something that one must prove in order to invoke a
2001         // method or project an associated type.
2002         //
2003         // In the chalk setup, this predicate is not part of the
2004         // "predicates" for a trait item. But it is useful in
2005         // rustc because if you directly (e.g.) invoke a trait
2006         // method like `Trait::method(...)`, you must naturally
2007         // prove that the trait applies to the types that were
2008         // used, and adding the predicate into this list ensures
2009         // that this is done.
2010         //
2011         // We use a DUMMY_SP here as a way to signal trait bounds that come
2012         // from the trait itself that *shouldn't* be shown as the source of
2013         // an obligation and instead be skipped. Otherwise we'd use
2014         // `tcx.def_span(def_id);`
2015         let span = rustc_span::DUMMY_SP;
2016         result.predicates =
2017             tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(std::iter::once((
2018                 ty::TraitRef::identity(tcx, def_id).without_const().to_predicate(tcx),
2019                 span,
2020             ))));
2021     }
2022     debug!("predicates_of(def_id={:?}) = {:?}", def_id, result);
2023     result
2024 }
2025
2026 /// Returns a list of user-specified type predicates for the definition with ID `def_id`.
2027 /// N.B., this does not include any implied/inferred constraints.
2028 fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2029     use rustc_hir::*;
2030
2031     debug!("explicit_predicates_of(def_id={:?})", def_id);
2032
2033     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2034     let node = tcx.hir().get(hir_id);
2035
2036     let mut is_trait = None;
2037     let mut is_default_impl_trait = None;
2038
2039     let icx = ItemCtxt::new(tcx, def_id);
2040
2041     const NO_GENERICS: &hir::Generics<'_> = &hir::Generics::empty();
2042
2043     // We use an `IndexSet` to preserves order of insertion.
2044     // Preserving the order of insertion is important here so as not to break UI tests.
2045     let mut predicates: FxIndexSet<(ty::Predicate<'_>, Span)> = FxIndexSet::default();
2046
2047     let ast_generics = match node {
2048         Node::TraitItem(item) => &item.generics,
2049
2050         Node::ImplItem(item) => &item.generics,
2051
2052         Node::Item(item) => {
2053             match item.kind {
2054                 ItemKind::Impl(ref impl_) => {
2055                     if impl_.defaultness.is_default() {
2056                         is_default_impl_trait = tcx.impl_trait_ref(def_id).map(ty::Binder::dummy);
2057                     }
2058                     &impl_.generics
2059                 }
2060                 ItemKind::Fn(.., ref generics, _)
2061                 | ItemKind::TyAlias(_, ref generics)
2062                 | ItemKind::Enum(_, ref generics)
2063                 | ItemKind::Struct(_, ref generics)
2064                 | ItemKind::Union(_, ref generics) => generics,
2065
2066                 ItemKind::Trait(_, _, ref generics, ..) => {
2067                     is_trait = Some(ty::TraitRef::identity(tcx, def_id));
2068                     generics
2069                 }
2070                 ItemKind::TraitAlias(ref generics, _) => {
2071                     is_trait = Some(ty::TraitRef::identity(tcx, def_id));
2072                     generics
2073                 }
2074                 ItemKind::OpaqueTy(OpaqueTy {
2075                     origin: hir::OpaqueTyOrigin::AsyncFn(..) | hir::OpaqueTyOrigin::FnReturn(..),
2076                     ..
2077                 }) => {
2078                     // return-position impl trait
2079                     //
2080                     // We don't inherit predicates from the parent here:
2081                     // If we have, say `fn f<'a, T: 'a>() -> impl Sized {}`
2082                     // then the return type is `f::<'static, T>::{{opaque}}`.
2083                     //
2084                     // If we inherited the predicates of `f` then we would
2085                     // require that `T: 'static` to show that the return
2086                     // type is well-formed.
2087                     //
2088                     // The only way to have something with this opaque type
2089                     // is from the return type of the containing function,
2090                     // which will ensure that the function's predicates
2091                     // hold.
2092                     return ty::GenericPredicates { parent: None, predicates: &[] };
2093                 }
2094                 ItemKind::OpaqueTy(OpaqueTy {
2095                     ref generics,
2096                     origin: hir::OpaqueTyOrigin::TyAlias,
2097                     ..
2098                 }) => {
2099                     // type-alias impl trait
2100                     generics
2101                 }
2102
2103                 _ => NO_GENERICS,
2104             }
2105         }
2106
2107         Node::ForeignItem(item) => match item.kind {
2108             ForeignItemKind::Static(..) => NO_GENERICS,
2109             ForeignItemKind::Fn(_, _, ref generics) => generics,
2110             ForeignItemKind::Type => NO_GENERICS,
2111         },
2112
2113         _ => NO_GENERICS,
2114     };
2115
2116     let generics = tcx.generics_of(def_id);
2117     let parent_count = generics.parent_count as u32;
2118     let has_own_self = generics.has_self && parent_count == 0;
2119
2120     // Below we'll consider the bounds on the type parameters (including `Self`)
2121     // and the explicit where-clauses, but to get the full set of predicates
2122     // on a trait we need to add in the supertrait bounds and bounds found on
2123     // associated types.
2124     if let Some(_trait_ref) = is_trait {
2125         predicates.extend(tcx.super_predicates_of(def_id).predicates.iter().cloned());
2126     }
2127
2128     // In default impls, we can assume that the self type implements
2129     // the trait. So in:
2130     //
2131     //     default impl Foo for Bar { .. }
2132     //
2133     // we add a default where clause `Foo: Bar`. We do a similar thing for traits
2134     // (see below). Recall that a default impl is not itself an impl, but rather a
2135     // set of defaults that can be incorporated into another impl.
2136     if let Some(trait_ref) = is_default_impl_trait {
2137         predicates.insert((trait_ref.without_const().to_predicate(tcx), tcx.def_span(def_id)));
2138     }
2139
2140     // Collect the region predicates that were declared inline as
2141     // well. In the case of parameters declared on a fn or method, we
2142     // have to be careful to only iterate over early-bound regions.
2143     let mut index = parent_count + has_own_self as u32;
2144     for param in early_bound_lifetimes_from_generics(tcx, ast_generics) {
2145         let region = tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
2146             def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
2147             index,
2148             name: param.name.ident().name,
2149         }));
2150         index += 1;
2151
2152         match param.kind {
2153             GenericParamKind::Lifetime { .. } => {
2154                 param.bounds.iter().for_each(|bound| match bound {
2155                     hir::GenericBound::Outlives(lt) => {
2156                         let bound = <dyn AstConv<'_>>::ast_region_to_region(&icx, lt, None);
2157                         let outlives = ty::Binder::dummy(ty::OutlivesPredicate(region, bound));
2158                         predicates.insert((outlives.to_predicate(tcx), lt.span));
2159                     }
2160                     _ => bug!(),
2161                 });
2162             }
2163             _ => bug!(),
2164         }
2165     }
2166
2167     // Collect the predicates that were written inline by the user on each
2168     // type parameter (e.g., `<T: Foo>`).
2169     for param in ast_generics.params {
2170         match param.kind {
2171             // We already dealt with early bound lifetimes above.
2172             GenericParamKind::Lifetime { .. } => (),
2173             GenericParamKind::Type { .. } => {
2174                 let name = param.name.ident().name;
2175                 let param_ty = ty::ParamTy::new(index, name).to_ty(tcx);
2176                 index += 1;
2177
2178                 let mut bounds = <dyn AstConv<'_>>::compute_bounds(&icx, param_ty, param.bounds);
2179                 // Params are implicitly sized unless a `?Sized` bound is found
2180                 <dyn AstConv<'_>>::add_implicitly_sized(
2181                     &icx,
2182                     &mut bounds,
2183                     param.bounds,
2184                     Some((param.hir_id, ast_generics.where_clause.predicates)),
2185                     param.span,
2186                 );
2187                 predicates.extend(bounds.predicates(tcx, param_ty));
2188             }
2189             GenericParamKind::Const { .. } => {
2190                 // Bounds on const parameters are currently not possible.
2191                 debug_assert!(param.bounds.is_empty());
2192                 index += 1;
2193             }
2194         }
2195     }
2196
2197     // Add in the bounds that appear in the where-clause.
2198     let where_clause = &ast_generics.where_clause;
2199     for predicate in where_clause.predicates {
2200         match predicate {
2201             hir::WherePredicate::BoundPredicate(bound_pred) => {
2202                 let ty = icx.to_ty(bound_pred.bounded_ty);
2203                 let bound_vars = icx.tcx.late_bound_vars(bound_pred.bounded_ty.hir_id);
2204
2205                 // Keep the type around in a dummy predicate, in case of no bounds.
2206                 // That way, `where Ty:` is not a complete noop (see #53696) and `Ty`
2207                 // is still checked for WF.
2208                 if bound_pred.bounds.is_empty() {
2209                     if let ty::Param(_) = ty.kind() {
2210                         // This is a `where T:`, which can be in the HIR from the
2211                         // transformation that moves `?Sized` to `T`'s declaration.
2212                         // We can skip the predicate because type parameters are
2213                         // trivially WF, but also we *should*, to avoid exposing
2214                         // users who never wrote `where Type:,` themselves, to
2215                         // compiler/tooling bugs from not handling WF predicates.
2216                     } else {
2217                         let span = bound_pred.bounded_ty.span;
2218                         let re_root_empty = tcx.lifetimes.re_root_empty;
2219                         let predicate = ty::Binder::bind_with_vars(
2220                             ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(
2221                                 ty,
2222                                 re_root_empty,
2223                             )),
2224                             bound_vars,
2225                         );
2226                         predicates.insert((predicate.to_predicate(tcx), span));
2227                     }
2228                 }
2229
2230                 let mut bounds = Bounds::default();
2231                 <dyn AstConv<'_>>::add_bounds(
2232                     &icx,
2233                     ty,
2234                     bound_pred.bounds.iter(),
2235                     &mut bounds,
2236                     bound_vars,
2237                 );
2238                 predicates.extend(bounds.predicates(tcx, ty));
2239             }
2240
2241             hir::WherePredicate::RegionPredicate(region_pred) => {
2242                 let r1 = <dyn AstConv<'_>>::ast_region_to_region(&icx, &region_pred.lifetime, None);
2243                 predicates.extend(region_pred.bounds.iter().map(|bound| {
2244                     let (r2, span) = match bound {
2245                         hir::GenericBound::Outlives(lt) => {
2246                             (<dyn AstConv<'_>>::ast_region_to_region(&icx, lt, None), lt.span)
2247                         }
2248                         _ => bug!(),
2249                     };
2250                     let pred = ty::Binder::dummy(ty::PredicateKind::RegionOutlives(
2251                         ty::OutlivesPredicate(r1, r2),
2252                     ))
2253                     .to_predicate(icx.tcx);
2254
2255                     (pred, span)
2256                 }))
2257             }
2258
2259             hir::WherePredicate::EqPredicate(..) => {
2260                 // FIXME(#20041)
2261             }
2262         }
2263     }
2264
2265     if tcx.features().generic_const_exprs {
2266         predicates.extend(const_evaluatable_predicates_of(tcx, def_id.expect_local()));
2267     }
2268
2269     let mut predicates: Vec<_> = predicates.into_iter().collect();
2270
2271     // Subtle: before we store the predicates into the tcx, we
2272     // sort them so that predicates like `T: Foo<Item=U>` come
2273     // before uses of `U`.  This avoids false ambiguity errors
2274     // in trait checking. See `setup_constraining_predicates`
2275     // for details.
2276     if let Node::Item(&Item { kind: ItemKind::Impl { .. }, .. }) = node {
2277         let self_ty = tcx.type_of(def_id);
2278         let trait_ref = tcx.impl_trait_ref(def_id);
2279         cgp::setup_constraining_predicates(
2280             tcx,
2281             &mut predicates,
2282             trait_ref,
2283             &mut cgp::parameters_for_impl(tcx, self_ty, trait_ref),
2284         );
2285     }
2286
2287     let result = ty::GenericPredicates {
2288         parent: generics.parent,
2289         predicates: tcx.arena.alloc_from_iter(predicates),
2290     };
2291     debug!("explicit_predicates_of(def_id={:?}) = {:?}", def_id, result);
2292     result
2293 }
2294
2295 fn const_evaluatable_predicates_of<'tcx>(
2296     tcx: TyCtxt<'tcx>,
2297     def_id: LocalDefId,
2298 ) -> FxIndexSet<(ty::Predicate<'tcx>, Span)> {
2299     struct ConstCollector<'tcx> {
2300         tcx: TyCtxt<'tcx>,
2301         preds: FxIndexSet<(ty::Predicate<'tcx>, Span)>,
2302     }
2303
2304     impl<'tcx> intravisit::Visitor<'tcx> for ConstCollector<'tcx> {
2305         type Map = Map<'tcx>;
2306
2307         fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
2308             intravisit::NestedVisitorMap::None
2309         }
2310
2311         fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) {
2312             let def_id = self.tcx.hir().local_def_id(c.hir_id);
2313             let ct = ty::Const::from_anon_const(self.tcx, def_id);
2314             if let ty::ConstKind::Unevaluated(uv) = ct.val {
2315                 assert_eq!(uv.promoted, None);
2316                 let span = self.tcx.hir().span(c.hir_id);
2317                 self.preds.insert((
2318                     ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(uv.shrink()))
2319                         .to_predicate(self.tcx),
2320                     span,
2321                 ));
2322             }
2323         }
2324
2325         fn visit_const_param_default(&mut self, _param: HirId, _ct: &'tcx hir::AnonConst) {
2326             // Do not look into const param defaults,
2327             // these get checked when they are actually instantiated.
2328             //
2329             // We do not want the following to error:
2330             //
2331             //     struct Foo<const N: usize, const M: usize = { N + 1 }>;
2332             //     struct Bar<const N: usize>(Foo<N, 3>);
2333         }
2334     }
2335
2336     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
2337     let node = tcx.hir().get(hir_id);
2338
2339     let mut collector = ConstCollector { tcx, preds: FxIndexSet::default() };
2340     if let hir::Node::Item(item) = node {
2341         if let hir::ItemKind::Impl(ref impl_) = item.kind {
2342             if let Some(of_trait) = &impl_.of_trait {
2343                 debug!("const_evaluatable_predicates_of({:?}): visit impl trait_ref", def_id);
2344                 collector.visit_trait_ref(of_trait);
2345             }
2346
2347             debug!("const_evaluatable_predicates_of({:?}): visit_self_ty", def_id);
2348             collector.visit_ty(impl_.self_ty);
2349         }
2350     }
2351
2352     if let Some(generics) = node.generics() {
2353         debug!("const_evaluatable_predicates_of({:?}): visit_generics", def_id);
2354         collector.visit_generics(generics);
2355     }
2356
2357     if let Some(fn_sig) = tcx.hir().fn_sig_by_hir_id(hir_id) {
2358         debug!("const_evaluatable_predicates_of({:?}): visit_fn_decl", def_id);
2359         collector.visit_fn_decl(fn_sig.decl);
2360     }
2361     debug!("const_evaluatable_predicates_of({:?}) = {:?}", def_id, collector.preds);
2362
2363     collector.preds
2364 }
2365
2366 fn trait_explicit_predicates_and_bounds(
2367     tcx: TyCtxt<'_>,
2368     def_id: LocalDefId,
2369 ) -> ty::GenericPredicates<'_> {
2370     assert_eq!(tcx.def_kind(def_id), DefKind::Trait);
2371     gather_explicit_predicates_of(tcx, def_id.to_def_id())
2372 }
2373
2374 fn explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2375     let def_kind = tcx.def_kind(def_id);
2376     if let DefKind::Trait = def_kind {
2377         // Remove bounds on associated types from the predicates, they will be
2378         // returned by `explicit_item_bounds`.
2379         let predicates_and_bounds = tcx.trait_explicit_predicates_and_bounds(def_id.expect_local());
2380         let trait_identity_substs = InternalSubsts::identity_for_item(tcx, def_id);
2381
2382         let is_assoc_item_ty = |ty: Ty<'_>| {
2383             // For a predicate from a where clause to become a bound on an
2384             // associated type:
2385             // * It must use the identity substs of the item.
2386             //     * Since any generic parameters on the item are not in scope,
2387             //       this means that the item is not a GAT, and its identity
2388             //       substs are the same as the trait's.
2389             // * It must be an associated type for this trait (*not* a
2390             //   supertrait).
2391             if let ty::Projection(projection) = ty.kind() {
2392                 projection.substs == trait_identity_substs
2393                     && tcx.associated_item(projection.item_def_id).container.id() == def_id
2394             } else {
2395                 false
2396             }
2397         };
2398
2399         let predicates: Vec<_> = predicates_and_bounds
2400             .predicates
2401             .iter()
2402             .copied()
2403             .filter(|(pred, _)| match pred.kind().skip_binder() {
2404                 ty::PredicateKind::Trait(tr) => !is_assoc_item_ty(tr.self_ty()),
2405                 ty::PredicateKind::Projection(proj) => {
2406                     !is_assoc_item_ty(proj.projection_ty.self_ty())
2407                 }
2408                 ty::PredicateKind::TypeOutlives(outlives) => !is_assoc_item_ty(outlives.0),
2409                 _ => true,
2410             })
2411             .collect();
2412         if predicates.len() == predicates_and_bounds.predicates.len() {
2413             predicates_and_bounds
2414         } else {
2415             ty::GenericPredicates {
2416                 parent: predicates_and_bounds.parent,
2417                 predicates: tcx.arena.alloc_slice(&predicates),
2418             }
2419         }
2420     } else {
2421         if matches!(def_kind, DefKind::AnonConst) && tcx.lazy_normalization() {
2422             let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2423             if tcx.hir().opt_const_param_default_param_hir_id(hir_id).is_some() {
2424                 // In `generics_of` we set the generics' parent to be our parent's parent which means that
2425                 // we lose out on the predicates of our actual parent if we dont return those predicates here.
2426                 // (See comment in `generics_of` for more information on why the parent shenanigans is necessary)
2427                 //
2428                 // struct Foo<T, const N: usize = { <T as Trait>::ASSOC }>(T) where T: Trait;
2429                 //        ^^^                     ^^^^^^^^^^^^^^^^^^^^^^^ the def id we are calling
2430                 //        ^^^                                             explicit_predicates_of on
2431                 //        parent item we dont have set as the
2432                 //        parent of generics returned by `generics_of`
2433                 //
2434                 // In the above code we want the anon const to have predicates in its param env for `T: Trait`
2435                 let item_id = tcx.hir().get_parent_item(hir_id);
2436                 let item_def_id = tcx.hir().local_def_id(item_id).to_def_id();
2437                 // In the above code example we would be calling `explicit_predicates_of(Foo)` here
2438                 return tcx.explicit_predicates_of(item_def_id);
2439             }
2440         }
2441         gather_explicit_predicates_of(tcx, def_id)
2442     }
2443 }
2444
2445 /// Converts a specific `GenericBound` from the AST into a set of
2446 /// predicates that apply to the self type. A vector is returned
2447 /// because this can be anywhere from zero predicates (`T: ?Sized` adds no
2448 /// predicates) to one (`T: Foo`) to many (`T: Bar<X = i32>` adds `T: Bar`
2449 /// and `<T as Bar>::X == i32`).
2450 fn predicates_from_bound<'tcx>(
2451     astconv: &dyn AstConv<'tcx>,
2452     param_ty: Ty<'tcx>,
2453     bound: &'tcx hir::GenericBound<'tcx>,
2454     bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
2455 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2456     let mut bounds = Bounds::default();
2457     astconv.add_bounds(param_ty, [bound].into_iter(), &mut bounds, bound_vars);
2458     bounds.predicates(astconv.tcx(), param_ty)
2459 }
2460
2461 fn compute_sig_of_foreign_fn_decl<'tcx>(
2462     tcx: TyCtxt<'tcx>,
2463     def_id: DefId,
2464     decl: &'tcx hir::FnDecl<'tcx>,
2465     abi: abi::Abi,
2466     ident: Ident,
2467 ) -> ty::PolyFnSig<'tcx> {
2468     let unsafety = if abi == abi::Abi::RustIntrinsic {
2469         intrinsic_operation_unsafety(tcx.item_name(def_id))
2470     } else {
2471         hir::Unsafety::Unsafe
2472     };
2473     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2474     let fty = <dyn AstConv<'_>>::ty_of_fn(
2475         &ItemCtxt::new(tcx, def_id),
2476         hir_id,
2477         unsafety,
2478         abi,
2479         decl,
2480         &hir::Generics::empty(),
2481         Some(ident.span),
2482         None,
2483     );
2484
2485     // Feature gate SIMD types in FFI, since I am not sure that the
2486     // ABIs are handled at all correctly. -huonw
2487     if abi != abi::Abi::RustIntrinsic
2488         && abi != abi::Abi::PlatformIntrinsic
2489         && !tcx.features().simd_ffi
2490     {
2491         let check = |ast_ty: &hir::Ty<'_>, ty: Ty<'_>| {
2492             if ty.is_simd() {
2493                 let snip = tcx
2494                     .sess
2495                     .source_map()
2496                     .span_to_snippet(ast_ty.span)
2497                     .map_or_else(|_| String::new(), |s| format!(" `{}`", s));
2498                 tcx.sess
2499                     .struct_span_err(
2500                         ast_ty.span,
2501                         &format!(
2502                             "use of SIMD type{} in FFI is highly experimental and \
2503                              may result in invalid code",
2504                             snip
2505                         ),
2506                     )
2507                     .help("add `#![feature(simd_ffi)]` to the crate attributes to enable")
2508                     .emit();
2509             }
2510         };
2511         for (input, ty) in iter::zip(decl.inputs, fty.inputs().skip_binder()) {
2512             check(input, ty)
2513         }
2514         if let hir::FnRetTy::Return(ref ty) = decl.output {
2515             check(ty, fty.output().skip_binder())
2516         }
2517     }
2518
2519     fty
2520 }
2521
2522 fn is_foreign_item(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
2523     match tcx.hir().get_if_local(def_id) {
2524         Some(Node::ForeignItem(..)) => true,
2525         Some(_) => false,
2526         _ => bug!("is_foreign_item applied to non-local def-id {:?}", def_id),
2527     }
2528 }
2529
2530 fn static_mutability(tcx: TyCtxt<'_>, def_id: DefId) -> Option<hir::Mutability> {
2531     match tcx.hir().get_if_local(def_id) {
2532         Some(
2533             Node::Item(&hir::Item { kind: hir::ItemKind::Static(_, mutbl, _), .. })
2534             | Node::ForeignItem(&hir::ForeignItem {
2535                 kind: hir::ForeignItemKind::Static(_, mutbl),
2536                 ..
2537             }),
2538         ) => Some(mutbl),
2539         Some(_) => None,
2540         _ => bug!("static_mutability applied to non-local def-id {:?}", def_id),
2541     }
2542 }
2543
2544 fn generator_kind(tcx: TyCtxt<'_>, def_id: DefId) -> Option<hir::GeneratorKind> {
2545     match tcx.hir().get_if_local(def_id) {
2546         Some(Node::Expr(&rustc_hir::Expr {
2547             kind: rustc_hir::ExprKind::Closure(_, _, body_id, _, _),
2548             ..
2549         })) => tcx.hir().body(body_id).generator_kind(),
2550         Some(_) => None,
2551         _ => bug!("generator_kind applied to non-local def-id {:?}", def_id),
2552     }
2553 }
2554
2555 fn from_target_feature(
2556     tcx: TyCtxt<'_>,
2557     id: DefId,
2558     attr: &ast::Attribute,
2559     supported_target_features: &FxHashMap<String, Option<Symbol>>,
2560     target_features: &mut Vec<Symbol>,
2561 ) {
2562     let list = match attr.meta_item_list() {
2563         Some(list) => list,
2564         None => return,
2565     };
2566     let bad_item = |span| {
2567         let msg = "malformed `target_feature` attribute input";
2568         let code = "enable = \"..\"".to_owned();
2569         tcx.sess
2570             .struct_span_err(span, msg)
2571             .span_suggestion(span, "must be of the form", code, Applicability::HasPlaceholders)
2572             .emit();
2573     };
2574     let rust_features = tcx.features();
2575     for item in list {
2576         // Only `enable = ...` is accepted in the meta-item list.
2577         if !item.has_name(sym::enable) {
2578             bad_item(item.span());
2579             continue;
2580         }
2581
2582         // Must be of the form `enable = "..."` (a string).
2583         let value = match item.value_str() {
2584             Some(value) => value,
2585             None => {
2586                 bad_item(item.span());
2587                 continue;
2588             }
2589         };
2590
2591         // We allow comma separation to enable multiple features.
2592         target_features.extend(value.as_str().split(',').filter_map(|feature| {
2593             let feature_gate = match supported_target_features.get(feature) {
2594                 Some(g) => g,
2595                 None => {
2596                     let msg =
2597                         format!("the feature named `{}` is not valid for this target", feature);
2598                     let mut err = tcx.sess.struct_span_err(item.span(), &msg);
2599                     err.span_label(
2600                         item.span(),
2601                         format!("`{}` is not valid for this target", feature),
2602                     );
2603                     if let Some(stripped) = feature.strip_prefix('+') {
2604                         let valid = supported_target_features.contains_key(stripped);
2605                         if valid {
2606                             err.help("consider removing the leading `+` in the feature name");
2607                         }
2608                     }
2609                     err.emit();
2610                     return None;
2611                 }
2612             };
2613
2614             // Only allow features whose feature gates have been enabled.
2615             let allowed = match feature_gate.as_ref().copied() {
2616                 Some(sym::arm_target_feature) => rust_features.arm_target_feature,
2617                 Some(sym::aarch64_target_feature) => rust_features.aarch64_target_feature,
2618                 Some(sym::hexagon_target_feature) => rust_features.hexagon_target_feature,
2619                 Some(sym::powerpc_target_feature) => rust_features.powerpc_target_feature,
2620                 Some(sym::mips_target_feature) => rust_features.mips_target_feature,
2621                 Some(sym::riscv_target_feature) => rust_features.riscv_target_feature,
2622                 Some(sym::avx512_target_feature) => rust_features.avx512_target_feature,
2623                 Some(sym::sse4a_target_feature) => rust_features.sse4a_target_feature,
2624                 Some(sym::tbm_target_feature) => rust_features.tbm_target_feature,
2625                 Some(sym::wasm_target_feature) => rust_features.wasm_target_feature,
2626                 Some(sym::cmpxchg16b_target_feature) => rust_features.cmpxchg16b_target_feature,
2627                 Some(sym::adx_target_feature) => rust_features.adx_target_feature,
2628                 Some(sym::movbe_target_feature) => rust_features.movbe_target_feature,
2629                 Some(sym::rtm_target_feature) => rust_features.rtm_target_feature,
2630                 Some(sym::f16c_target_feature) => rust_features.f16c_target_feature,
2631                 Some(sym::ermsb_target_feature) => rust_features.ermsb_target_feature,
2632                 Some(sym::bpf_target_feature) => rust_features.bpf_target_feature,
2633                 Some(name) => bug!("unknown target feature gate {}", name),
2634                 None => true,
2635             };
2636             if !allowed && id.is_local() {
2637                 feature_err(
2638                     &tcx.sess.parse_sess,
2639                     feature_gate.unwrap(),
2640                     item.span(),
2641                     &format!("the target feature `{}` is currently unstable", feature),
2642                 )
2643                 .emit();
2644             }
2645             Some(Symbol::intern(feature))
2646         }));
2647     }
2648 }
2649
2650 fn linkage_by_name(tcx: TyCtxt<'_>, def_id: DefId, name: &str) -> Linkage {
2651     use rustc_middle::mir::mono::Linkage::*;
2652
2653     // Use the names from src/llvm/docs/LangRef.rst here. Most types are only
2654     // applicable to variable declarations and may not really make sense for
2655     // Rust code in the first place but allow them anyway and trust that the
2656     // user knows what s/he's doing. Who knows, unanticipated use cases may pop
2657     // up in the future.
2658     //
2659     // ghost, dllimport, dllexport and linkonce_odr_autohide are not supported
2660     // and don't have to be, LLVM treats them as no-ops.
2661     match name {
2662         "appending" => Appending,
2663         "available_externally" => AvailableExternally,
2664         "common" => Common,
2665         "extern_weak" => ExternalWeak,
2666         "external" => External,
2667         "internal" => Internal,
2668         "linkonce" => LinkOnceAny,
2669         "linkonce_odr" => LinkOnceODR,
2670         "private" => Private,
2671         "weak" => WeakAny,
2672         "weak_odr" => WeakODR,
2673         _ => {
2674             let span = tcx.hir().span_if_local(def_id);
2675             if let Some(span) = span {
2676                 tcx.sess.span_fatal(span, "invalid linkage specified")
2677             } else {
2678                 tcx.sess.fatal(&format!("invalid linkage specified: {}", name))
2679             }
2680         }
2681     }
2682 }
2683
2684 fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
2685     let attrs = tcx.get_attrs(id);
2686
2687     let mut codegen_fn_attrs = CodegenFnAttrs::new();
2688     if tcx.should_inherit_track_caller(id) {
2689         codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
2690     }
2691
2692     // With -Z panic-in-drop=abort, drop_in_place never unwinds.
2693     if tcx.sess.opts.debugging_opts.panic_in_drop == PanicStrategy::Abort {
2694         if Some(id) == tcx.lang_items().drop_in_place_fn() {
2695             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
2696         }
2697     }
2698
2699     let supported_target_features = tcx.supported_target_features(LOCAL_CRATE);
2700
2701     let mut inline_span = None;
2702     let mut link_ordinal_span = None;
2703     let mut no_sanitize_span = None;
2704     for attr in attrs.iter() {
2705         if attr.has_name(sym::cold) {
2706             codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
2707         } else if attr.has_name(sym::rustc_allocator) {
2708             codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR;
2709         } else if attr.has_name(sym::ffi_returns_twice) {
2710             if tcx.is_foreign_item(id) {
2711                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_RETURNS_TWICE;
2712             } else {
2713                 // `#[ffi_returns_twice]` is only allowed `extern fn`s.
2714                 struct_span_err!(
2715                     tcx.sess,
2716                     attr.span,
2717                     E0724,
2718                     "`#[ffi_returns_twice]` may only be used on foreign functions"
2719                 )
2720                 .emit();
2721             }
2722         } else if attr.has_name(sym::ffi_pure) {
2723             if tcx.is_foreign_item(id) {
2724                 if attrs.iter().any(|a| a.has_name(sym::ffi_const)) {
2725                     // `#[ffi_const]` functions cannot be `#[ffi_pure]`
2726                     struct_span_err!(
2727                         tcx.sess,
2728                         attr.span,
2729                         E0757,
2730                         "`#[ffi_const]` function cannot be `#[ffi_pure]`"
2731                     )
2732                     .emit();
2733                 } else {
2734                     codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_PURE;
2735                 }
2736             } else {
2737                 // `#[ffi_pure]` is only allowed on foreign functions
2738                 struct_span_err!(
2739                     tcx.sess,
2740                     attr.span,
2741                     E0755,
2742                     "`#[ffi_pure]` may only be used on foreign functions"
2743                 )
2744                 .emit();
2745             }
2746         } else if attr.has_name(sym::ffi_const) {
2747             if tcx.is_foreign_item(id) {
2748                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_CONST;
2749             } else {
2750                 // `#[ffi_const]` is only allowed on foreign functions
2751                 struct_span_err!(
2752                     tcx.sess,
2753                     attr.span,
2754                     E0756,
2755                     "`#[ffi_const]` may only be used on foreign functions"
2756                 )
2757                 .emit();
2758             }
2759         } else if attr.has_name(sym::rustc_allocator_nounwind) {
2760             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
2761         } else if attr.has_name(sym::naked) {
2762             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED;
2763         } else if attr.has_name(sym::no_mangle) {
2764             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
2765         } else if attr.has_name(sym::no_coverage) {
2766             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_COVERAGE;
2767         } else if attr.has_name(sym::rustc_std_internal_symbol) {
2768             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
2769         } else if attr.has_name(sym::used) {
2770             codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED;
2771         } else if attr.has_name(sym::cmse_nonsecure_entry) {
2772             if !matches!(tcx.fn_sig(id).abi(), abi::Abi::C { .. }) {
2773                 struct_span_err!(
2774                     tcx.sess,
2775                     attr.span,
2776                     E0776,
2777                     "`#[cmse_nonsecure_entry]` requires C ABI"
2778                 )
2779                 .emit();
2780             }
2781             if !tcx.sess.target.llvm_target.contains("thumbv8m") {
2782                 struct_span_err!(tcx.sess, attr.span, E0775, "`#[cmse_nonsecure_entry]` is only valid for targets with the TrustZone-M extension")
2783                     .emit();
2784             }
2785             codegen_fn_attrs.flags |= CodegenFnAttrFlags::CMSE_NONSECURE_ENTRY;
2786         } else if attr.has_name(sym::thread_local) {
2787             codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL;
2788         } else if attr.has_name(sym::track_caller) {
2789             if !tcx.is_closure(id) && tcx.fn_sig(id).abi() != abi::Abi::Rust {
2790                 struct_span_err!(tcx.sess, attr.span, E0737, "`#[track_caller]` requires Rust ABI")
2791                     .emit();
2792             }
2793             if tcx.is_closure(id) && !tcx.features().closure_track_caller {
2794                 feature_err(
2795                     &tcx.sess.parse_sess,
2796                     sym::closure_track_caller,
2797                     attr.span,
2798                     "`#[track_caller]` on closures is currently unstable",
2799                 )
2800                 .emit();
2801             }
2802             codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
2803         } else if attr.has_name(sym::export_name) {
2804             if let Some(s) = attr.value_str() {
2805                 if s.as_str().contains('\0') {
2806                     // `#[export_name = ...]` will be converted to a null-terminated string,
2807                     // so it may not contain any null characters.
2808                     struct_span_err!(
2809                         tcx.sess,
2810                         attr.span,
2811                         E0648,
2812                         "`export_name` may not contain null characters"
2813                     )
2814                     .emit();
2815                 }
2816                 codegen_fn_attrs.export_name = Some(s);
2817             }
2818         } else if attr.has_name(sym::target_feature) {
2819             if !tcx.is_closure(id) && tcx.fn_sig(id).unsafety() == hir::Unsafety::Normal {
2820                 if tcx.sess.target.is_like_wasm || tcx.sess.opts.actually_rustdoc {
2821                     // The `#[target_feature]` attribute is allowed on
2822                     // WebAssembly targets on all functions, including safe
2823                     // ones. Other targets require that `#[target_feature]` is
2824                     // only applied to unsafe funtions (pending the
2825                     // `target_feature_11` feature) because on most targets
2826                     // execution of instructions that are not supported is
2827                     // considered undefined behavior. For WebAssembly which is a
2828                     // 100% safe target at execution time it's not possible to
2829                     // execute undefined instructions, and even if a future
2830                     // feature was added in some form for this it would be a
2831                     // deterministic trap. There is no undefined behavior when
2832                     // executing WebAssembly so `#[target_feature]` is allowed
2833                     // on safe functions (but again, only for WebAssembly)
2834                     //
2835                     // Note that this is also allowed if `actually_rustdoc` so
2836                     // if a target is documenting some wasm-specific code then
2837                     // it's not spuriously denied.
2838                 } else if !tcx.features().target_feature_11 {
2839                     let mut err = feature_err(
2840                         &tcx.sess.parse_sess,
2841                         sym::target_feature_11,
2842                         attr.span,
2843                         "`#[target_feature(..)]` can only be applied to `unsafe` functions",
2844                     );
2845                     err.span_label(tcx.def_span(id), "not an `unsafe` function");
2846                     err.emit();
2847                 } else if let Some(local_id) = id.as_local() {
2848                     check_target_feature_trait_unsafe(tcx, local_id, attr.span);
2849                 }
2850             }
2851             from_target_feature(
2852                 tcx,
2853                 id,
2854                 attr,
2855                 supported_target_features,
2856                 &mut codegen_fn_attrs.target_features,
2857             );
2858         } else if attr.has_name(sym::linkage) {
2859             if let Some(val) = attr.value_str() {
2860                 codegen_fn_attrs.linkage = Some(linkage_by_name(tcx, id, val.as_str()));
2861             }
2862         } else if attr.has_name(sym::link_section) {
2863             if let Some(val) = attr.value_str() {
2864                 if val.as_str().bytes().any(|b| b == 0) {
2865                     let msg = format!(
2866                         "illegal null byte in link_section \
2867                          value: `{}`",
2868                         &val
2869                     );
2870                     tcx.sess.span_err(attr.span, &msg);
2871                 } else {
2872                     codegen_fn_attrs.link_section = Some(val);
2873                 }
2874             }
2875         } else if attr.has_name(sym::link_name) {
2876             codegen_fn_attrs.link_name = attr.value_str();
2877         } else if attr.has_name(sym::link_ordinal) {
2878             link_ordinal_span = Some(attr.span);
2879             if let ordinal @ Some(_) = check_link_ordinal(tcx, attr) {
2880                 codegen_fn_attrs.link_ordinal = ordinal;
2881             }
2882         } else if attr.has_name(sym::no_sanitize) {
2883             no_sanitize_span = Some(attr.span);
2884             if let Some(list) = attr.meta_item_list() {
2885                 for item in list.iter() {
2886                     if item.has_name(sym::address) {
2887                         codegen_fn_attrs.no_sanitize |= SanitizerSet::ADDRESS;
2888                     } else if item.has_name(sym::cfi) {
2889                         codegen_fn_attrs.no_sanitize |= SanitizerSet::CFI;
2890                     } else if item.has_name(sym::memory) {
2891                         codegen_fn_attrs.no_sanitize |= SanitizerSet::MEMORY;
2892                     } else if item.has_name(sym::thread) {
2893                         codegen_fn_attrs.no_sanitize |= SanitizerSet::THREAD;
2894                     } else if item.has_name(sym::hwaddress) {
2895                         codegen_fn_attrs.no_sanitize |= SanitizerSet::HWADDRESS;
2896                     } else {
2897                         tcx.sess
2898                             .struct_span_err(item.span(), "invalid argument for `no_sanitize`")
2899                             .note("expected one of: `address`, `hwaddress`, `memory` or `thread`")
2900                             .emit();
2901                     }
2902                 }
2903             }
2904         } else if attr.has_name(sym::instruction_set) {
2905             codegen_fn_attrs.instruction_set = match attr.meta_kind() {
2906                 Some(MetaItemKind::List(ref items)) => match items.as_slice() {
2907                     [NestedMetaItem::MetaItem(set)] => {
2908                         let segments =
2909                             set.path.segments.iter().map(|x| x.ident.name).collect::<Vec<_>>();
2910                         match segments.as_slice() {
2911                             [sym::arm, sym::a32] | [sym::arm, sym::t32] => {
2912                                 if !tcx.sess.target.has_thumb_interworking {
2913                                     struct_span_err!(
2914                                         tcx.sess.diagnostic(),
2915                                         attr.span,
2916                                         E0779,
2917                                         "target does not support `#[instruction_set]`"
2918                                     )
2919                                     .emit();
2920                                     None
2921                                 } else if segments[1] == sym::a32 {
2922                                     Some(InstructionSetAttr::ArmA32)
2923                                 } else if segments[1] == sym::t32 {
2924                                     Some(InstructionSetAttr::ArmT32)
2925                                 } else {
2926                                     unreachable!()
2927                                 }
2928                             }
2929                             _ => {
2930                                 struct_span_err!(
2931                                     tcx.sess.diagnostic(),
2932                                     attr.span,
2933                                     E0779,
2934                                     "invalid instruction set specified",
2935                                 )
2936                                 .emit();
2937                                 None
2938                             }
2939                         }
2940                     }
2941                     [] => {
2942                         struct_span_err!(
2943                             tcx.sess.diagnostic(),
2944                             attr.span,
2945                             E0778,
2946                             "`#[instruction_set]` requires an argument"
2947                         )
2948                         .emit();
2949                         None
2950                     }
2951                     _ => {
2952                         struct_span_err!(
2953                             tcx.sess.diagnostic(),
2954                             attr.span,
2955                             E0779,
2956                             "cannot specify more than one instruction set"
2957                         )
2958                         .emit();
2959                         None
2960                     }
2961                 },
2962                 _ => {
2963                     struct_span_err!(
2964                         tcx.sess.diagnostic(),
2965                         attr.span,
2966                         E0778,
2967                         "must specify an instruction set"
2968                     )
2969                     .emit();
2970                     None
2971                 }
2972             };
2973         } else if attr.has_name(sym::repr) {
2974             codegen_fn_attrs.alignment = match attr.meta_item_list() {
2975                 Some(items) => match items.as_slice() {
2976                     [item] => match item.name_value_literal() {
2977                         Some((sym::align, literal)) => {
2978                             let alignment = rustc_attr::parse_alignment(&literal.kind);
2979
2980                             match alignment {
2981                                 Ok(align) => Some(align),
2982                                 Err(msg) => {
2983                                     struct_span_err!(
2984                                         tcx.sess.diagnostic(),
2985                                         attr.span,
2986                                         E0589,
2987                                         "invalid `repr(align)` attribute: {}",
2988                                         msg
2989                                     )
2990                                     .emit();
2991
2992                                     None
2993                                 }
2994                             }
2995                         }
2996                         _ => None,
2997                     },
2998                     [] => None,
2999                     _ => None,
3000                 },
3001                 None => None,
3002             };
3003         }
3004     }
3005
3006     codegen_fn_attrs.inline = attrs.iter().fold(InlineAttr::None, |ia, attr| {
3007         if !attr.has_name(sym::inline) {
3008             return ia;
3009         }
3010         match attr.meta_kind() {
3011             Some(MetaItemKind::Word) => InlineAttr::Hint,
3012             Some(MetaItemKind::List(ref items)) => {
3013                 inline_span = Some(attr.span);
3014                 if items.len() != 1 {
3015                     struct_span_err!(
3016                         tcx.sess.diagnostic(),
3017                         attr.span,
3018                         E0534,
3019                         "expected one argument"
3020                     )
3021                     .emit();
3022                     InlineAttr::None
3023                 } else if list_contains_name(&items, sym::always) {
3024                     InlineAttr::Always
3025                 } else if list_contains_name(&items, sym::never) {
3026                     InlineAttr::Never
3027                 } else {
3028                     struct_span_err!(
3029                         tcx.sess.diagnostic(),
3030                         items[0].span(),
3031                         E0535,
3032                         "invalid argument"
3033                     )
3034                     .emit();
3035
3036                     InlineAttr::None
3037                 }
3038             }
3039             Some(MetaItemKind::NameValue(_)) => ia,
3040             None => ia,
3041         }
3042     });
3043
3044     codegen_fn_attrs.optimize = attrs.iter().fold(OptimizeAttr::None, |ia, attr| {
3045         if !attr.has_name(sym::optimize) {
3046             return ia;
3047         }
3048         let err = |sp, s| struct_span_err!(tcx.sess.diagnostic(), sp, E0722, "{}", s).emit();
3049         match attr.meta_kind() {
3050             Some(MetaItemKind::Word) => {
3051                 err(attr.span, "expected one argument");
3052                 ia
3053             }
3054             Some(MetaItemKind::List(ref items)) => {
3055                 inline_span = Some(attr.span);
3056                 if items.len() != 1 {
3057                     err(attr.span, "expected one argument");
3058                     OptimizeAttr::None
3059                 } else if list_contains_name(&items, sym::size) {
3060                     OptimizeAttr::Size
3061                 } else if list_contains_name(&items, sym::speed) {
3062                     OptimizeAttr::Speed
3063                 } else {
3064                     err(items[0].span(), "invalid argument");
3065                     OptimizeAttr::None
3066                 }
3067             }
3068             Some(MetaItemKind::NameValue(_)) => ia,
3069             None => ia,
3070         }
3071     });
3072
3073     // #73631: closures inherit `#[target_feature]` annotations
3074     if tcx.features().target_feature_11 && tcx.is_closure(id) {
3075         let owner_id = tcx.parent(id).expect("closure should have a parent");
3076         codegen_fn_attrs
3077             .target_features
3078             .extend(tcx.codegen_fn_attrs(owner_id).target_features.iter().copied())
3079     }
3080
3081     // If a function uses #[target_feature] it can't be inlined into general
3082     // purpose functions as they wouldn't have the right target features
3083     // enabled. For that reason we also forbid #[inline(always)] as it can't be
3084     // respected.
3085     if !codegen_fn_attrs.target_features.is_empty() {
3086         if codegen_fn_attrs.inline == InlineAttr::Always {
3087             if let Some(span) = inline_span {
3088                 tcx.sess.span_err(
3089                     span,
3090                     "cannot use `#[inline(always)]` with \
3091                      `#[target_feature]`",
3092                 );
3093             }
3094         }
3095     }
3096
3097     if !codegen_fn_attrs.no_sanitize.is_empty() {
3098         if codegen_fn_attrs.inline == InlineAttr::Always {
3099             if let (Some(no_sanitize_span), Some(inline_span)) = (no_sanitize_span, inline_span) {
3100                 let hir_id = tcx.hir().local_def_id_to_hir_id(id.expect_local());
3101                 tcx.struct_span_lint_hir(
3102                     lint::builtin::INLINE_NO_SANITIZE,
3103                     hir_id,
3104                     no_sanitize_span,
3105                     |lint| {
3106                         lint.build("`no_sanitize` will have no effect after inlining")
3107                             .span_note(inline_span, "inlining requested here")
3108                             .emit();
3109                     },
3110                 )
3111             }
3112         }
3113     }
3114
3115     // Weak lang items have the same semantics as "std internal" symbols in the
3116     // sense that they're preserved through all our LTO passes and only
3117     // strippable by the linker.
3118     //
3119     // Additionally weak lang items have predetermined symbol names.
3120     if tcx.is_weak_lang_item(id) {
3121         codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
3122     }
3123     let check_name = |attr: &Attribute, sym| attr.has_name(sym);
3124     if let Some(name) = weak_lang_items::link_name(check_name, attrs) {
3125         codegen_fn_attrs.export_name = Some(name);
3126         codegen_fn_attrs.link_name = Some(name);
3127     }
3128     check_link_name_xor_ordinal(tcx, &codegen_fn_attrs, link_ordinal_span);
3129
3130     // Internal symbols to the standard library all have no_mangle semantics in
3131     // that they have defined symbol names present in the function name. This
3132     // also applies to weak symbols where they all have known symbol names.
3133     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
3134         codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
3135     }
3136
3137     // Any linkage to LLVM intrinsics for now forcibly marks them all as never
3138     // unwinds since LLVM sometimes can't handle codegen which `invoke`s
3139     // intrinsic functions.
3140     if let Some(name) = &codegen_fn_attrs.link_name {
3141         if name.as_str().starts_with("llvm.") {
3142             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
3143         }
3144     }
3145
3146     codegen_fn_attrs
3147 }
3148
3149 /// Checks if the provided DefId is a method in a trait impl for a trait which has track_caller
3150 /// applied to the method prototype.
3151 fn should_inherit_track_caller(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
3152     if let Some(impl_item) = tcx.opt_associated_item(def_id) {
3153         if let ty::AssocItemContainer::ImplContainer(impl_def_id) = impl_item.container {
3154             if let Some(trait_def_id) = tcx.trait_id_of_impl(impl_def_id) {
3155                 if let Some(trait_item) = tcx
3156                     .associated_items(trait_def_id)
3157                     .filter_by_name_unhygienic(impl_item.ident.name)
3158                     .find(move |trait_item| {
3159                         trait_item.kind == ty::AssocKind::Fn
3160                             && tcx.hygienic_eq(impl_item.ident, trait_item.ident, trait_def_id)
3161                     })
3162                 {
3163                     return tcx
3164                         .codegen_fn_attrs(trait_item.def_id)
3165                         .flags
3166                         .intersects(CodegenFnAttrFlags::TRACK_CALLER);
3167                 }
3168             }
3169         }
3170     }
3171
3172     false
3173 }
3174
3175 fn check_link_ordinal(tcx: TyCtxt<'_>, attr: &ast::Attribute) -> Option<u16> {
3176     use rustc_ast::{Lit, LitIntType, LitKind};
3177     let meta_item_list = attr.meta_item_list();
3178     let meta_item_list: Option<&[ast::NestedMetaItem]> = meta_item_list.as_ref().map(Vec::as_ref);
3179     let sole_meta_list = match meta_item_list {
3180         Some([item]) => item.literal(),
3181         Some(_) => {
3182             tcx.sess
3183                 .struct_span_err(attr.span, "incorrect number of arguments to `#[link_ordinal]`")
3184                 .note("the attribute requires exactly one argument")
3185                 .emit();
3186             return None;
3187         }
3188         _ => None,
3189     };
3190     if let Some(Lit { kind: LitKind::Int(ordinal, LitIntType::Unsuffixed), .. }) = sole_meta_list {
3191         // According to the table at https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#import-header,
3192         // the ordinal must fit into 16 bits.  Similarly, the Ordinal field in COFFShortExport (defined
3193         // in llvm/include/llvm/Object/COFFImportFile.h), which we use to communicate import information
3194         // to LLVM for `#[link(kind = "raw-dylib"_])`, is also defined to be uint16_t.
3195         //
3196         // FIXME: should we allow an ordinal of 0?  The MSVC toolchain has inconsistent support for this:
3197         // both LINK.EXE and LIB.EXE signal errors and abort when given a .DEF file that specifies
3198         // a zero ordinal.  However, llvm-dlltool is perfectly happy to generate an import library
3199         // for such a .DEF file, and MSVC's LINK.EXE is also perfectly happy to consume an import
3200         // library produced by LLVM with an ordinal of 0, and it generates an .EXE.  (I don't know yet
3201         // if the resulting EXE runs, as I haven't yet built the necessary DLL -- see earlier comment
3202         // about LINK.EXE failing.)
3203         if *ordinal <= u16::MAX as u128 {
3204             Some(*ordinal as u16)
3205         } else {
3206             let msg = format!("ordinal value in `link_ordinal` is too large: `{}`", &ordinal);
3207             tcx.sess
3208                 .struct_span_err(attr.span, &msg)
3209                 .note("the value may not exceed `u16::MAX`")
3210                 .emit();
3211             None
3212         }
3213     } else {
3214         tcx.sess
3215             .struct_span_err(attr.span, "illegal ordinal format in `link_ordinal`")
3216             .note("an unsuffixed integer value, e.g., `1`, is expected")
3217             .emit();
3218         None
3219     }
3220 }
3221
3222 fn check_link_name_xor_ordinal(
3223     tcx: TyCtxt<'_>,
3224     codegen_fn_attrs: &CodegenFnAttrs,
3225     inline_span: Option<Span>,
3226 ) {
3227     if codegen_fn_attrs.link_name.is_none() || codegen_fn_attrs.link_ordinal.is_none() {
3228         return;
3229     }
3230     let msg = "cannot use `#[link_name]` with `#[link_ordinal]`";
3231     if let Some(span) = inline_span {
3232         tcx.sess.span_err(span, msg);
3233     } else {
3234         tcx.sess.err(msg);
3235     }
3236 }
3237
3238 /// Checks the function annotated with `#[target_feature]` is not a safe
3239 /// trait method implementation, reporting an error if it is.
3240 fn check_target_feature_trait_unsafe(tcx: TyCtxt<'_>, id: LocalDefId, attr_span: Span) {
3241     let hir_id = tcx.hir().local_def_id_to_hir_id(id);
3242     let node = tcx.hir().get(hir_id);
3243     if let Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }) = node {
3244         let parent_id = tcx.hir().get_parent_did(hir_id);
3245         let parent_item = tcx.hir().expect_item(parent_id);
3246         if let hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) = parent_item.kind {
3247             tcx.sess
3248                 .struct_span_err(
3249                     attr_span,
3250                     "`#[target_feature(..)]` cannot be applied to safe trait method",
3251                 )
3252                 .span_label(attr_span, "cannot be applied to safe trait method")
3253                 .span_label(tcx.def_span(id), "not an `unsafe` function")
3254                 .emit();
3255         }
3256     }
3257 }