compiler/rustc_typeck/src/collect.rs

   1 // ignore-tidy-filelength
   2 //! "Collection" is the process of determining the type and other external
   3 //! details of each item in Rust. Collection is specifically concerned
   4 //! with *inter-procedural* things -- for example, for a function
   5 //! definition, collection will figure out the type and signature of the
   6 //! function, but it will not visit the *body* of the function in any way,
   7 //! nor examine type annotations on local variables (that's the job of
   8 //! type *checking*).
   9 //!
  10 //! Collecting is ultimately defined by a bundle of queries that
  11 //! inquire after various facts about the items in the crate (e.g.,
  12 //! `type_of`, `generics_of`, `predicates_of`, etc). See the `provide` function
  13 //! for the full set.
  14 //!
  15 //! At present, however, we do run collection across all items in the
  16 //! crate as a kind of pass. This should eventually be factored away.
  17
  18 use crate::astconv::AstConv;
  19 use crate::bounds::Bounds;
  20 use crate::check::intrinsic::intrinsic_operation_unsafety;
  21 use crate::constrained_generic_params as cgp;
  22 use crate::errors;
  23 use crate::middle::resolve_lifetime as rl;
  24 use rustc_ast as ast;
  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, DiagnosticBuilder, ErrorGuaranteed};
  30 use rustc_hir as hir;
  31 use rustc_hir::def::{CtorKind, DefKind};
  32 use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID, LOCAL_CRATE};
  33 use rustc_hir::intravisit::{self, Visitor};
  34 use rustc_hir::weak_lang_items;
  35 use rustc_hir::{GenericParamKind, HirId, Node};
  36 use rustc_middle::hir::nested_filter;
  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         type_of: type_of::type_of,
  72         item_bounds: item_bounds::item_bounds,
  73         explicit_item_bounds: item_bounds::explicit_item_bounds,
  74         generics_of,
  75         predicates_of,
  76         predicates_defined_on,
  77         explicit_predicates_of,
  78         super_predicates_of,
  79         super_predicates_that_define_assoc_type,
  80         trait_explicit_predicates_and_bounds,
  81         type_param_predicates,
  82         trait_def,
  83         adt_def,
  84         fn_sig,
  85         impl_trait_ref,
  86         impl_polarity,
  87         is_foreign_item,
  88         generator_kind,
  89         codegen_fn_attrs,
  90         asm_target_features,
  91         collect_mod_item_types,
  92         should_inherit_track_caller,
  93         ..*providers
  94     };
  95 }
  96
  97 ///////////////////////////////////////////////////////////////////////////
  98
  99 /// Context specific to some particular item. This is what implements
 100 /// `AstConv`. It has information about the predicates that are defined
 101 /// on the trait. Unfortunately, this predicate information is
 102 /// available in various different forms at various points in the
 103 /// process. So we can't just store a pointer to e.g., the AST or the
 104 /// parsed ty form, we have to be more flexible. To this end, the
 105 /// `ItemCtxt` is parameterized by a `DefId` that it uses to satisfy
 106 /// `get_type_parameter_bounds` requests, drawing the information from
 107 /// the AST (`hir::Generics`), recursively.
 108 pub struct ItemCtxt<'tcx> {
 109     tcx: TyCtxt<'tcx>,
 110     item_def_id: DefId,
 111 }
 112
 113 ///////////////////////////////////////////////////////////////////////////
 114
 115 #[derive(Default)]
 116 crate struct HirPlaceholderCollector(crate Vec<Span>);
 117
 118 impl<'v> Visitor<'v> for HirPlaceholderCollector {
 119     fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
 120         if let hir::TyKind::Infer = t.kind {
 121             self.0.push(t.span);
 122         }
 123         intravisit::walk_ty(self, t)
 124     }
 125     fn visit_generic_arg(&mut self, generic_arg: &'v hir::GenericArg<'v>) {
 126         match generic_arg {
 127             hir::GenericArg::Infer(inf) => {
 128                 self.0.push(inf.span);
 129                 intravisit::walk_inf(self, inf);
 130             }
 131             hir::GenericArg::Type(t) => self.visit_ty(t),
 132             _ => {}
 133         }
 134     }
 135     fn visit_array_length(&mut self, length: &'v hir::ArrayLen) {
 136         if let &hir::ArrayLen::Infer(_, span) = length {
 137             self.0.push(span);
 138         }
 139         intravisit::walk_array_len(self, length)
 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, 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 && let hir::TyKind::BareFn(_) = hir_ty.kind {
 193             is_fn = true;
 194
 195             // Check if parent is const or static
 196             let parent_id = tcx.hir().get_parent_node(hir_ty.hir_id);
 197             let parent_node = tcx.hir().get(parent_id);
 198
 199             is_const_or_static = matches!(
 200                 parent_node,
 201                 Node::Item(&hir::Item {
 202                     kind: hir::ItemKind::Const(..) | hir::ItemKind::Static(..),
 203                     ..
 204                 }) | Node::TraitItem(&hir::TraitItem {
 205                     kind: hir::TraitItemKind::Const(..),
 206                     ..
 207                 }) | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Const(..), .. })
 208             );
 209         }
 210
 211         // if function is wrapped around a const or static,
 212         // then don't show the suggestion
 213         if !(is_fn && is_const_or_static) {
 214             err.multipart_suggestion(
 215                 "use type parameters instead",
 216                 sugg,
 217                 Applicability::HasPlaceholders,
 218             );
 219         }
 220     }
 221     err.emit();
 222 }
 223
 224 fn reject_placeholder_type_signatures_in_item<'tcx>(
 225     tcx: TyCtxt<'tcx>,
 226     item: &'tcx hir::Item<'tcx>,
 227 ) {
 228     let (generics, suggest) = match &item.kind {
 229         hir::ItemKind::Union(_, generics)
 230         | hir::ItemKind::Enum(_, generics)
 231         | hir::ItemKind::TraitAlias(generics, _)
 232         | hir::ItemKind::Trait(_, _, generics, ..)
 233         | hir::ItemKind::Impl(hir::Impl { generics, .. })
 234         | hir::ItemKind::Struct(_, generics) => (generics, true),
 235         hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. })
 236         | hir::ItemKind::TyAlias(_, generics) => (generics, false),
 237         // `static`, `fn` and `const` are handled elsewhere to suggest appropriate type.
 238         _ => return,
 239     };
 240
 241     let mut visitor = HirPlaceholderCollector::default();
 242     visitor.visit_item(item);
 243
 244     placeholder_type_error(
 245         tcx,
 246         Some(generics.span),
 247         generics.params,
 248         visitor.0,
 249         suggest,
 250         None,
 251         item.kind.descr(),
 252     );
 253 }
 254
 255 impl<'tcx> Visitor<'tcx> for CollectItemTypesVisitor<'tcx> {
 256     type NestedFilter = nested_filter::OnlyBodies;
 257
 258     fn nested_visit_map(&mut self) -> Self::Map {
 259         self.tcx.hir()
 260     }
 261
 262     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 263         convert_item(self.tcx, item.item_id());
 264         reject_placeholder_type_signatures_in_item(self.tcx, item);
 265         intravisit::walk_item(self, item);
 266     }
 267
 268     fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
 269         for param in generics.params {
 270             match param.kind {
 271                 hir::GenericParamKind::Lifetime { .. } => {}
 272                 hir::GenericParamKind::Type { default: Some(_), .. } => {
 273                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 274                     self.tcx.ensure().type_of(def_id);
 275                 }
 276                 hir::GenericParamKind::Type { .. } => {}
 277                 hir::GenericParamKind::Const { default, .. } => {
 278                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 279                     self.tcx.ensure().type_of(def_id);
 280                     if let Some(default) = default {
 281                         let default_def_id = self.tcx.hir().local_def_id(default.hir_id);
 282                         // need to store default and type of default
 283                         self.tcx.ensure().type_of(default_def_id);
 284                         self.tcx.ensure().const_param_default(def_id);
 285                     }
 286                 }
 287             }
 288         }
 289         intravisit::walk_generics(self, generics);
 290     }
 291
 292     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 293         if let hir::ExprKind::Closure(..) = expr.kind {
 294             let def_id = self.tcx.hir().local_def_id(expr.hir_id);
 295             self.tcx.ensure().generics_of(def_id);
 296             // We do not call `type_of` for closures here as that
 297             // depends on typecheck and would therefore hide
 298             // any further errors in case one typeck fails.
 299         }
 300         intravisit::walk_expr(self, expr);
 301     }
 302
 303     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
 304         convert_trait_item(self.tcx, trait_item.trait_item_id());
 305         intravisit::walk_trait_item(self, trait_item);
 306     }
 307
 308     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 309         convert_impl_item(self.tcx, impl_item.impl_item_id());
 310         intravisit::walk_impl_item(self, impl_item);
 311     }
 312 }
 313
 314 ///////////////////////////////////////////////////////////////////////////
 315 // Utility types and common code for the above passes.
 316
 317 fn bad_placeholder<'tcx>(
 318     tcx: TyCtxt<'tcx>,
 319     mut spans: Vec<Span>,
 320     kind: &'static str,
 321 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
 322     let kind = if kind.ends_with('s') { format!("{}es", kind) } else { format!("{}s", kind) };
 323
 324     spans.sort();
 325     let mut err = struct_span_err!(
 326         tcx.sess,
 327         spans.clone(),
 328         E0121,
 329         "the placeholder `_` is not allowed within types on item signatures for {}",
 330         kind
 331     );
 332     for span in spans {
 333         err.span_label(span, "not allowed in type signatures");
 334     }
 335     err
 336 }
 337
 338 impl<'tcx> ItemCtxt<'tcx> {
 339     pub fn new(tcx: TyCtxt<'tcx>, item_def_id: DefId) -> ItemCtxt<'tcx> {
 340         ItemCtxt { tcx, item_def_id }
 341     }
 342
 343     pub fn to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
 344         <dyn AstConv<'_>>::ast_ty_to_ty(self, ast_ty)
 345     }
 346
 347     pub fn hir_id(&self) -> hir::HirId {
 348         self.tcx.hir().local_def_id_to_hir_id(self.item_def_id.expect_local())
 349     }
 350
 351     pub fn node(&self) -> hir::Node<'tcx> {
 352         self.tcx.hir().get(self.hir_id())
 353     }
 354 }
 355
 356 impl<'tcx> AstConv<'tcx> for ItemCtxt<'tcx> {
 357     fn tcx(&self) -> TyCtxt<'tcx> {
 358         self.tcx
 359     }
 360
 361     fn item_def_id(&self) -> Option<DefId> {
 362         Some(self.item_def_id)
 363     }
 364
 365     fn get_type_parameter_bounds(
 366         &self,
 367         span: Span,
 368         def_id: DefId,
 369         assoc_name: Ident,
 370     ) -> ty::GenericPredicates<'tcx> {
 371         self.tcx.at(span).type_param_predicates((
 372             self.item_def_id,
 373             def_id.expect_local(),
 374             assoc_name,
 375         ))
 376     }
 377
 378     fn re_infer(&self, _: Option<&ty::GenericParamDef>, _: Span) -> Option<ty::Region<'tcx>> {
 379         None
 380     }
 381
 382     fn allow_ty_infer(&self) -> bool {
 383         false
 384     }
 385
 386     fn ty_infer(&self, _: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
 387         self.tcx().ty_error_with_message(span, "bad placeholder type")
 388     }
 389
 390     fn ct_infer(&self, ty: Ty<'tcx>, _: Option<&ty::GenericParamDef>, span: Span) -> Const<'tcx> {
 391         let ty = self.tcx.fold_regions(ty, &mut false, |r, _| match *r {
 392             ty::ReErased => self.tcx.lifetimes.re_static,
 393             _ => r,
 394         });
 395         self.tcx().const_error_with_message(ty, span, "bad placeholder constant")
 396     }
 397
 398     fn projected_ty_from_poly_trait_ref(
 399         &self,
 400         span: Span,
 401         item_def_id: DefId,
 402         item_segment: &hir::PathSegment<'_>,
 403         poly_trait_ref: ty::PolyTraitRef<'tcx>,
 404     ) -> Ty<'tcx> {
 405         if let Some(trait_ref) = poly_trait_ref.no_bound_vars() {
 406             let item_substs = <dyn AstConv<'tcx>>::create_substs_for_associated_item(
 407                 self,
 408                 self.tcx,
 409                 span,
 410                 item_def_id,
 411                 item_segment,
 412                 trait_ref.substs,
 413             );
 414             self.tcx().mk_projection(item_def_id, item_substs)
 415         } else {
 416             // There are no late-bound regions; we can just ignore the binder.
 417             let mut err = struct_span_err!(
 418                 self.tcx().sess,
 419                 span,
 420                 E0212,
 421                 "cannot use the associated type of a trait \
 422                  with uninferred generic parameters"
 423             );
 424
 425             match self.node() {
 426                 hir::Node::Field(_) | hir::Node::Ctor(_) | hir::Node::Variant(_) => {
 427                     let item =
 428                         self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(self.hir_id()));
 429                     match &item.kind {
 430                         hir::ItemKind::Enum(_, generics)
 431                         | hir::ItemKind::Struct(_, generics)
 432                         | hir::ItemKind::Union(_, generics) => {
 433                             let lt_name = get_new_lifetime_name(self.tcx, poly_trait_ref, generics);
 434                             let (lt_sp, sugg) = match generics.params {
 435                                 [] => (generics.span, format!("<{}>", lt_name)),
 436                                 [bound, ..] => {
 437                                     (bound.span.shrink_to_lo(), format!("{}, ", lt_name))
 438                                 }
 439                             };
 440                             let suggestions = vec![
 441                                 (lt_sp, sugg),
 442                                 (
 443                                     span.with_hi(item_segment.ident.span.lo()),
 444                                     format!(
 445                                         "{}::",
 446                                         // Replace the existing lifetimes with a new named lifetime.
 447                                         self.tcx
 448                                             .replace_late_bound_regions(poly_trait_ref, |_| {
 449                                                 self.tcx.mk_region(ty::ReEarlyBound(
 450                                                     ty::EarlyBoundRegion {
 451                                                         def_id: item_def_id,
 452                                                         index: 0,
 453                                                         name: Symbol::intern(&lt_name),
 454                                                     },
 455                                                 ))
 456                                             })
 457                                             .0,
 458                                     ),
 459                                 ),
 460                             ];
 461                             err.multipart_suggestion(
 462                                 "use a fully qualified path with explicit lifetimes",
 463                                 suggestions,
 464                                 Applicability::MaybeIncorrect,
 465                             );
 466                         }
 467                         _ => {}
 468                     }
 469                 }
 470                 hir::Node::Item(hir::Item {
 471                     kind:
 472                         hir::ItemKind::Struct(..) | hir::ItemKind::Enum(..) | hir::ItemKind::Union(..),
 473                     ..
 474                 }) => {}
 475                 hir::Node::Item(_)
 476                 | hir::Node::ForeignItem(_)
 477                 | hir::Node::TraitItem(_)
 478                 | hir::Node::ImplItem(_) => {
 479                     err.span_suggestion_verbose(
 480                         span.with_hi(item_segment.ident.span.lo()),
 481                         "use a fully qualified path with inferred lifetimes",
 482                         format!(
 483                             "{}::",
 484                             // Erase named lt, we want `<A as B<'_>::C`, not `<A as B<'a>::C`.
 485                             self.tcx.anonymize_late_bound_regions(poly_trait_ref).skip_binder(),
 486                         ),
 487                         Applicability::MaybeIncorrect,
 488                     );
 489                 }
 490                 _ => {}
 491             }
 492             err.emit();
 493             self.tcx().ty_error()
 494         }
 495     }
 496
 497     fn normalize_ty(&self, _span: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
 498         // Types in item signatures are not normalized to avoid undue dependencies.
 499         ty
 500     }
 501
 502     fn set_tainted_by_errors(&self) {
 503         // There's no obvious place to track this, so just let it go.
 504     }
 505
 506     fn record_ty(&self, _hir_id: hir::HirId, _ty: Ty<'tcx>, _span: Span) {
 507         // There's no place to record types from signatures?
 508     }
 509 }
 510
 511 /// Synthesize a new lifetime name that doesn't clash with any of the lifetimes already present.
 512 fn get_new_lifetime_name<'tcx>(
 513     tcx: TyCtxt<'tcx>,
 514     poly_trait_ref: ty::PolyTraitRef<'tcx>,
 515     generics: &hir::Generics<'tcx>,
 516 ) -> String {
 517     let existing_lifetimes = tcx
 518         .collect_referenced_late_bound_regions(&poly_trait_ref)
 519         .into_iter()
 520         .filter_map(|lt| {
 521             if let ty::BoundRegionKind::BrNamed(_, name) = lt {
 522                 Some(name.as_str().to_string())
 523             } else {
 524                 None
 525             }
 526         })
 527         .chain(generics.params.iter().filter_map(|param| {
 528             if let hir::GenericParamKind::Lifetime { .. } = &param.kind {
 529                 Some(param.name.ident().as_str().to_string())
 530             } else {
 531                 None
 532             }
 533         }))
 534         .collect::<FxHashSet<String>>();
 535
 536     let a_to_z_repeat_n = |n| {
 537         (b'a'..=b'z').map(move |c| {
 538             let mut s = '\''.to_string();
 539             s.extend(std::iter::repeat(char::from(c)).take(n));
 540             s
 541         })
 542     };
 543
 544     // If all single char lifetime names are present, we wrap around and double the chars.
 545     (1..).flat_map(a_to_z_repeat_n).find(|lt| !existing_lifetimes.contains(lt.as_str())).unwrap()
 546 }
 547
 548 /// Returns the predicates defined on `item_def_id` of the form
 549 /// `X: Foo` where `X` is the type parameter `def_id`.
 550 fn type_param_predicates(
 551     tcx: TyCtxt<'_>,
 552     (item_def_id, def_id, assoc_name): (DefId, LocalDefId, Ident),
 553 ) -> ty::GenericPredicates<'_> {
 554     use rustc_hir::*;
 555
 556     // In the AST, bounds can derive from two places. Either
 557     // written inline like `<T: Foo>` or in a where-clause like
 558     // `where T: Foo`.
 559
 560     let param_id = tcx.hir().local_def_id_to_hir_id(def_id);
 561     let param_owner = tcx.hir().ty_param_owner(param_id);
 562     let generics = tcx.generics_of(param_owner);
 563     let index = generics.param_def_id_to_index[&def_id.to_def_id()];
 564     let ty = tcx.mk_ty_param(index, tcx.hir().ty_param_name(param_id));
 565
 566     // Don't look for bounds where the type parameter isn't in scope.
 567     let parent = if item_def_id == param_owner.to_def_id() {
 568         None
 569     } else {
 570         tcx.generics_of(item_def_id).parent
 571     };
 572
 573     let mut result = parent
 574         .map(|parent| {
 575             let icx = ItemCtxt::new(tcx, parent);
 576             icx.get_type_parameter_bounds(DUMMY_SP, def_id.to_def_id(), assoc_name)
 577         })
 578         .unwrap_or_default();
 579     let mut extend = None;
 580
 581     let item_hir_id = tcx.hir().local_def_id_to_hir_id(item_def_id.expect_local());
 582     let ast_generics = match tcx.hir().get(item_hir_id) {
 583         Node::TraitItem(item) => &item.generics,
 584
 585         Node::ImplItem(item) => &item.generics,
 586
 587         Node::Item(item) => {
 588             match item.kind {
 589                 ItemKind::Fn(.., ref generics, _)
 590                 | ItemKind::Impl(hir::Impl { ref generics, .. })
 591                 | ItemKind::TyAlias(_, ref generics)
 592                 | ItemKind::OpaqueTy(OpaqueTy {
 593                     ref generics,
 594                     origin: hir::OpaqueTyOrigin::TyAlias,
 595                     ..
 596                 })
 597                 | ItemKind::Enum(_, ref generics)
 598                 | ItemKind::Struct(_, ref generics)
 599                 | ItemKind::Union(_, ref generics) => generics,
 600                 ItemKind::Trait(_, _, ref generics, ..) => {
 601                     // Implied `Self: Trait` and supertrait bounds.
 602                     if param_id == item_hir_id {
 603                         let identity_trait_ref = ty::TraitRef::identity(tcx, item_def_id);
 604                         extend =
 605                             Some((identity_trait_ref.without_const().to_predicate(tcx), item.span));
 606                     }
 607                     generics
 608                 }
 609                 _ => return result,
 610             }
 611         }
 612
 613         Node::ForeignItem(item) => match item.kind {
 614             ForeignItemKind::Fn(_, _, ref generics) => generics,
 615             _ => return result,
 616         },
 617
 618         _ => return result,
 619     };
 620
 621     let icx = ItemCtxt::new(tcx, item_def_id);
 622     let extra_predicates = extend.into_iter().chain(
 623         icx.type_parameter_bounds_in_generics(
 624             ast_generics,
 625             param_id,
 626             ty,
 627             OnlySelfBounds(true),
 628             Some(assoc_name),
 629         )
 630         .into_iter()
 631         .filter(|(predicate, _)| match predicate.kind().skip_binder() {
 632             ty::PredicateKind::Trait(data) => data.self_ty().is_param(index),
 633             _ => false,
 634         }),
 635     );
 636     result.predicates =
 637         tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(extra_predicates));
 638     result
 639 }
 640
 641 impl<'tcx> ItemCtxt<'tcx> {
 642     /// Finds bounds from `hir::Generics`. This requires scanning through the
 643     /// AST. We do this to avoid having to convert *all* the bounds, which
 644     /// would create artificial cycles. Instead, we can only convert the
 645     /// bounds for a type parameter `X` if `X::Foo` is used.
 646     fn type_parameter_bounds_in_generics(
 647         &self,
 648         ast_generics: &'tcx hir::Generics<'tcx>,
 649         param_id: hir::HirId,
 650         ty: Ty<'tcx>,
 651         only_self_bounds: OnlySelfBounds,
 652         assoc_name: Option<Ident>,
 653     ) -> Vec<(ty::Predicate<'tcx>, Span)> {
 654         let from_ty_params = ast_generics
 655             .params
 656             .iter()
 657             .filter_map(|param| match param.kind {
 658                 GenericParamKind::Type { .. } | GenericParamKind::Const { .. }
 659                     if param.hir_id == param_id =>
 660                 {
 661                     Some(&param.bounds)
 662                 }
 663                 _ => None,
 664             })
 665             .flat_map(|bounds| bounds.iter())
 666             .filter(|b| match assoc_name {
 667                 Some(assoc_name) => self.bound_defines_assoc_item(b, assoc_name),
 668                 None => true,
 669             })
 670             .flat_map(|b| predicates_from_bound(self, ty, b, ty::List::empty()));
 671
 672         let param_def_id = self.tcx.hir().local_def_id(param_id).to_def_id();
 673         let from_where_clauses = ast_generics
 674             .where_clause
 675             .predicates
 676             .iter()
 677             .filter_map(|wp| match *wp {
 678                 hir::WherePredicate::BoundPredicate(ref bp) => Some(bp),
 679                 _ => None,
 680             })
 681             .flat_map(|bp| {
 682                 let bt = if bp.is_param_bound(param_def_id) {
 683                     Some(ty)
 684                 } else if !only_self_bounds.0 {
 685                     Some(self.to_ty(bp.bounded_ty))
 686                 } else {
 687                     None
 688                 };
 689                 let bvars = self.tcx.late_bound_vars(bp.bounded_ty.hir_id);
 690
 691                 bp.bounds
 692                     .iter()
 693                     .filter(|b| match assoc_name {
 694                         Some(assoc_name) => self.bound_defines_assoc_item(b, assoc_name),
 695                         None => true,
 696                     })
 697                     .filter_map(move |b| bt.map(|bt| (bt, b, bvars)))
 698             })
 699             .flat_map(|(bt, b, bvars)| predicates_from_bound(self, bt, b, bvars));
 700
 701         from_ty_params.chain(from_where_clauses).collect()
 702     }
 703
 704     fn bound_defines_assoc_item(&self, b: &hir::GenericBound<'_>, assoc_name: Ident) -> bool {
 705         debug!("bound_defines_assoc_item(b={:?}, assoc_name={:?})", b, assoc_name);
 706
 707         match b {
 708             hir::GenericBound::Trait(poly_trait_ref, _) => {
 709                 let trait_ref = &poly_trait_ref.trait_ref;
 710                 if let Some(trait_did) = trait_ref.trait_def_id() {
 711                     self.tcx.trait_may_define_assoc_type(trait_did, assoc_name)
 712                 } else {
 713                     false
 714                 }
 715             }
 716             _ => false,
 717         }
 718     }
 719 }
 720
 721 fn convert_item(tcx: TyCtxt<'_>, item_id: hir::ItemId) {
 722     let it = tcx.hir().item(item_id);
 723     debug!("convert: item {} with id {}", it.ident, it.hir_id());
 724     let def_id = item_id.def_id;
 725
 726     match it.kind {
 727         // These don't define types.
 728         hir::ItemKind::ExternCrate(_)
 729         | hir::ItemKind::Use(..)
 730         | hir::ItemKind::Macro(..)
 731         | hir::ItemKind::Mod(_)
 732         | hir::ItemKind::GlobalAsm(_) => {}
 733         hir::ItemKind::ForeignMod { items, .. } => {
 734             for item in items {
 735                 let item = tcx.hir().foreign_item(item.id);
 736                 tcx.ensure().generics_of(item.def_id);
 737                 tcx.ensure().type_of(item.def_id);
 738                 tcx.ensure().predicates_of(item.def_id);
 739                 match item.kind {
 740                     hir::ForeignItemKind::Fn(..) => tcx.ensure().fn_sig(item.def_id),
 741                     hir::ForeignItemKind::Static(..) => {
 742                         let mut visitor = HirPlaceholderCollector::default();
 743                         visitor.visit_foreign_item(item);
 744                         placeholder_type_error(
 745                             tcx,
 746                             None,
 747                             &[],
 748                             visitor.0,
 749                             false,
 750                             None,
 751                             "static variable",
 752                         );
 753                     }
 754                     _ => (),
 755                 }
 756             }
 757         }
 758         hir::ItemKind::Enum(ref enum_definition, _) => {
 759             tcx.ensure().generics_of(def_id);
 760             tcx.ensure().type_of(def_id);
 761             tcx.ensure().predicates_of(def_id);
 762             convert_enum_variant_types(tcx, def_id.to_def_id(), enum_definition.variants);
 763         }
 764         hir::ItemKind::Impl { .. } => {
 765             tcx.ensure().generics_of(def_id);
 766             tcx.ensure().type_of(def_id);
 767             tcx.ensure().impl_trait_ref(def_id);
 768             tcx.ensure().predicates_of(def_id);
 769         }
 770         hir::ItemKind::Trait(..) => {
 771             tcx.ensure().generics_of(def_id);
 772             tcx.ensure().trait_def(def_id);
 773             tcx.at(it.span).super_predicates_of(def_id);
 774             tcx.ensure().predicates_of(def_id);
 775         }
 776         hir::ItemKind::TraitAlias(..) => {
 777             tcx.ensure().generics_of(def_id);
 778             tcx.at(it.span).super_predicates_of(def_id);
 779             tcx.ensure().predicates_of(def_id);
 780         }
 781         hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 782             tcx.ensure().generics_of(def_id);
 783             tcx.ensure().type_of(def_id);
 784             tcx.ensure().predicates_of(def_id);
 785
 786             for f in struct_def.fields() {
 787                 let def_id = tcx.hir().local_def_id(f.hir_id);
 788                 tcx.ensure().generics_of(def_id);
 789                 tcx.ensure().type_of(def_id);
 790                 tcx.ensure().predicates_of(def_id);
 791             }
 792
 793             if let Some(ctor_hir_id) = struct_def.ctor_hir_id() {
 794                 convert_variant_ctor(tcx, ctor_hir_id);
 795             }
 796         }
 797
 798         // Desugared from `impl Trait`, so visited by the function's return type.
 799         hir::ItemKind::OpaqueTy(hir::OpaqueTy {
 800             origin: hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..),
 801             ..
 802         }) => {}
 803
 804         // Don't call `type_of` on opaque types, since that depends on type
 805         // checking function bodies. `check_item_type` ensures that it's called
 806         // instead.
 807         hir::ItemKind::OpaqueTy(..) => {
 808             tcx.ensure().generics_of(def_id);
 809             tcx.ensure().predicates_of(def_id);
 810             tcx.ensure().explicit_item_bounds(def_id);
 811         }
 812         hir::ItemKind::TyAlias(..)
 813         | hir::ItemKind::Static(..)
 814         | hir::ItemKind::Const(..)
 815         | hir::ItemKind::Fn(..) => {
 816             tcx.ensure().generics_of(def_id);
 817             tcx.ensure().type_of(def_id);
 818             tcx.ensure().predicates_of(def_id);
 819             match it.kind {
 820                 hir::ItemKind::Fn(..) => tcx.ensure().fn_sig(def_id),
 821                 hir::ItemKind::OpaqueTy(..) => tcx.ensure().item_bounds(def_id),
 822                 hir::ItemKind::Const(ty, ..) | hir::ItemKind::Static(ty, ..) => {
 823                     // (#75889): Account for `const C: dyn Fn() -> _ = "";`
 824                     if let hir::TyKind::TraitObject(..) = ty.kind {
 825                         let mut visitor = HirPlaceholderCollector::default();
 826                         visitor.visit_item(it);
 827                         placeholder_type_error(
 828                             tcx,
 829                             None,
 830                             &[],
 831                             visitor.0,
 832                             false,
 833                             None,
 834                             it.kind.descr(),
 835                         );
 836                     }
 837                 }
 838                 _ => (),
 839             }
 840         }
 841     }
 842 }
 843
 844 fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::TraitItemId) {
 845     let trait_item = tcx.hir().trait_item(trait_item_id);
 846     tcx.ensure().generics_of(trait_item_id.def_id);
 847
 848     match trait_item.kind {
 849         hir::TraitItemKind::Fn(..) => {
 850             tcx.ensure().type_of(trait_item_id.def_id);
 851             tcx.ensure().fn_sig(trait_item_id.def_id);
 852         }
 853
 854         hir::TraitItemKind::Const(.., Some(_)) => {
 855             tcx.ensure().type_of(trait_item_id.def_id);
 856         }
 857
 858         hir::TraitItemKind::Const(..) => {
 859             tcx.ensure().type_of(trait_item_id.def_id);
 860             // Account for `const C: _;`.
 861             let mut visitor = HirPlaceholderCollector::default();
 862             visitor.visit_trait_item(trait_item);
 863             placeholder_type_error(tcx, None, &[], visitor.0, false, None, "constant");
 864         }
 865
 866         hir::TraitItemKind::Type(_, Some(_)) => {
 867             tcx.ensure().item_bounds(trait_item_id.def_id);
 868             tcx.ensure().type_of(trait_item_id.def_id);
 869             // Account for `type T = _;`.
 870             let mut visitor = HirPlaceholderCollector::default();
 871             visitor.visit_trait_item(trait_item);
 872             placeholder_type_error(tcx, None, &[], visitor.0, false, None, "associated type");
 873         }
 874
 875         hir::TraitItemKind::Type(_, None) => {
 876             tcx.ensure().item_bounds(trait_item_id.def_id);
 877             // #74612: Visit and try to find bad placeholders
 878             // even if there is no concrete type.
 879             let mut visitor = HirPlaceholderCollector::default();
 880             visitor.visit_trait_item(trait_item);
 881
 882             placeholder_type_error(tcx, None, &[], visitor.0, false, None, "associated type");
 883         }
 884     };
 885
 886     tcx.ensure().predicates_of(trait_item_id.def_id);
 887 }
 888
 889 fn convert_impl_item(tcx: TyCtxt<'_>, impl_item_id: hir::ImplItemId) {
 890     let def_id = impl_item_id.def_id;
 891     tcx.ensure().generics_of(def_id);
 892     tcx.ensure().type_of(def_id);
 893     tcx.ensure().predicates_of(def_id);
 894     let impl_item = tcx.hir().impl_item(impl_item_id);
 895     match impl_item.kind {
 896         hir::ImplItemKind::Fn(..) => {
 897             tcx.ensure().fn_sig(def_id);
 898         }
 899         hir::ImplItemKind::TyAlias(_) => {
 900             // Account for `type T = _;`
 901             let mut visitor = HirPlaceholderCollector::default();
 902             visitor.visit_impl_item(impl_item);
 903
 904             placeholder_type_error(tcx, None, &[], visitor.0, false, None, "associated type");
 905         }
 906         hir::ImplItemKind::Const(..) => {}
 907     }
 908 }
 909
 910 fn convert_variant_ctor(tcx: TyCtxt<'_>, ctor_id: hir::HirId) {
 911     let def_id = tcx.hir().local_def_id(ctor_id);
 912     tcx.ensure().generics_of(def_id);
 913     tcx.ensure().type_of(def_id);
 914     tcx.ensure().predicates_of(def_id);
 915 }
 916
 917 fn convert_enum_variant_types(tcx: TyCtxt<'_>, def_id: DefId, variants: &[hir::Variant<'_>]) {
 918     let def = tcx.adt_def(def_id);
 919     let repr_type = def.repr().discr_type();
 920     let initial = repr_type.initial_discriminant(tcx);
 921     let mut prev_discr = None::<Discr<'_>>;
 922
 923     // fill the discriminant values and field types
 924     for variant in variants {
 925         let wrapped_discr = prev_discr.map_or(initial, |d| d.wrap_incr(tcx));
 926         prev_discr = Some(
 927             if let Some(ref e) = variant.disr_expr {
 928                 let expr_did = tcx.hir().local_def_id(e.hir_id);
 929                 def.eval_explicit_discr(tcx, expr_did.to_def_id())
 930             } else if let Some(discr) = repr_type.disr_incr(tcx, prev_discr) {
 931                 Some(discr)
 932             } else {
 933                 struct_span_err!(tcx.sess, variant.span, E0370, "enum discriminant overflowed")
 934                     .span_label(
 935                         variant.span,
 936                         format!("overflowed on value after {}", prev_discr.unwrap()),
 937                     )
 938                     .note(&format!(
 939                         "explicitly set `{} = {}` if that is desired outcome",
 940                         variant.ident, wrapped_discr
 941                     ))
 942                     .emit();
 943                 None
 944             }
 945             .unwrap_or(wrapped_discr),
 946         );
 947
 948         for f in variant.data.fields() {
 949             let def_id = tcx.hir().local_def_id(f.hir_id);
 950             tcx.ensure().generics_of(def_id);
 951             tcx.ensure().type_of(def_id);
 952             tcx.ensure().predicates_of(def_id);
 953         }
 954
 955         // Convert the ctor, if any. This also registers the variant as
 956         // an item.
 957         if let Some(ctor_hir_id) = variant.data.ctor_hir_id() {
 958             convert_variant_ctor(tcx, ctor_hir_id);
 959         }
 960     }
 961 }
 962
 963 fn convert_variant(
 964     tcx: TyCtxt<'_>,
 965     variant_did: Option<LocalDefId>,
 966     ctor_did: Option<LocalDefId>,
 967     ident: Ident,
 968     discr: ty::VariantDiscr,
 969     def: &hir::VariantData<'_>,
 970     adt_kind: ty::AdtKind,
 971     parent_did: LocalDefId,
 972 ) -> ty::VariantDef {
 973     let mut seen_fields: FxHashMap<Ident, Span> = Default::default();
 974     let fields = def
 975         .fields()
 976         .iter()
 977         .map(|f| {
 978             let fid = tcx.hir().local_def_id(f.hir_id);
 979             let dup_span = seen_fields.get(&f.ident.normalize_to_macros_2_0()).cloned();
 980             if let Some(prev_span) = dup_span {
 981                 tcx.sess.emit_err(errors::FieldAlreadyDeclared {
 982                     field_name: f.ident,
 983                     span: f.span,
 984                     prev_span,
 985                 });
 986             } else {
 987                 seen_fields.insert(f.ident.normalize_to_macros_2_0(), f.span);
 988             }
 989
 990             ty::FieldDef { did: fid.to_def_id(), name: f.ident.name, vis: tcx.visibility(fid) }
 991         })
 992         .collect();
 993     let recovered = match def {
 994         hir::VariantData::Struct(_, r) => *r,
 995         _ => false,
 996     };
 997     ty::VariantDef::new(
 998         ident.name,
 999         variant_did.map(LocalDefId::to_def_id),
1000         ctor_did.map(LocalDefId::to_def_id),
1001         discr,
1002         fields,
1003         CtorKind::from_hir(def),
1004         adt_kind,
1005         parent_did.to_def_id(),
1006         recovered,
1007         adt_kind == AdtKind::Struct && tcx.has_attr(parent_did.to_def_id(), sym::non_exhaustive)
1008             || variant_did.map_or(false, |variant_did| {
1009                 tcx.has_attr(variant_did.to_def_id(), sym::non_exhaustive)
1010             }),
1011     )
1012 }
1013
1014 fn adt_def<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> ty::AdtDef<'tcx> {
1015     use rustc_hir::*;
1016
1017     let def_id = def_id.expect_local();
1018     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
1019     let Node::Item(item) = tcx.hir().get(hir_id) else {
1020         bug!();
1021     };
1022
1023     let repr = ReprOptions::new(tcx, def_id.to_def_id());
1024     let (kind, variants) = match item.kind {
1025         ItemKind::Enum(ref def, _) => {
1026             let mut distance_from_explicit = 0;
1027             let variants = def
1028                 .variants
1029                 .iter()
1030                 .map(|v| {
1031                     let variant_did = Some(tcx.hir().local_def_id(v.id));
1032                     let ctor_did =
1033                         v.data.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
1034
1035                     let discr = if let Some(ref e) = v.disr_expr {
1036                         distance_from_explicit = 0;
1037                         ty::VariantDiscr::Explicit(tcx.hir().local_def_id(e.hir_id).to_def_id())
1038                     } else {
1039                         ty::VariantDiscr::Relative(distance_from_explicit)
1040                     };
1041                     distance_from_explicit += 1;
1042
1043                     convert_variant(
1044                         tcx,
1045                         variant_did,
1046                         ctor_did,
1047                         v.ident,
1048                         discr,
1049                         &v.data,
1050                         AdtKind::Enum,
1051                         def_id,
1052                     )
1053                 })
1054                 .collect();
1055
1056             (AdtKind::Enum, variants)
1057         }
1058         ItemKind::Struct(ref def, _) => {
1059             let variant_did = None::<LocalDefId>;
1060             let ctor_did = def.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
1061
1062             let variants = std::iter::once(convert_variant(
1063                 tcx,
1064                 variant_did,
1065                 ctor_did,
1066                 item.ident,
1067                 ty::VariantDiscr::Relative(0),
1068                 def,
1069                 AdtKind::Struct,
1070                 def_id,
1071             ))
1072             .collect();
1073
1074             (AdtKind::Struct, variants)
1075         }
1076         ItemKind::Union(ref def, _) => {
1077             let variant_did = None;
1078             let ctor_did = def.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
1079
1080             let variants = std::iter::once(convert_variant(
1081                 tcx,
1082                 variant_did,
1083                 ctor_did,
1084                 item.ident,
1085                 ty::VariantDiscr::Relative(0),
1086                 def,
1087                 AdtKind::Union,
1088                 def_id,
1089             ))
1090             .collect();
1091
1092             (AdtKind::Union, variants)
1093         }
1094         _ => bug!(),
1095     };
1096     tcx.alloc_adt_def(def_id.to_def_id(), kind, variants, repr)
1097 }
1098
1099 /// Ensures that the super-predicates of the trait with a `DefId`
1100 /// of `trait_def_id` are converted and stored. This also ensures that
1101 /// the transitive super-predicates are converted.
1102 fn super_predicates_of(tcx: TyCtxt<'_>, trait_def_id: DefId) -> ty::GenericPredicates<'_> {
1103     debug!("super_predicates(trait_def_id={:?})", trait_def_id);
1104     tcx.super_predicates_that_define_assoc_type((trait_def_id, None))
1105 }
1106
1107 /// Ensures that the super-predicates of the trait with a `DefId`
1108 /// of `trait_def_id` are converted and stored. This also ensures that
1109 /// the transitive super-predicates are converted.
1110 fn super_predicates_that_define_assoc_type(
1111     tcx: TyCtxt<'_>,
1112     (trait_def_id, assoc_name): (DefId, Option<Ident>),
1113 ) -> ty::GenericPredicates<'_> {
1114     debug!(
1115         "super_predicates_that_define_assoc_type(trait_def_id={:?}, assoc_name={:?})",
1116         trait_def_id, assoc_name
1117     );
1118     if trait_def_id.is_local() {
1119         debug!("super_predicates_that_define_assoc_type: local trait_def_id={:?}", trait_def_id);
1120         let trait_hir_id = tcx.hir().local_def_id_to_hir_id(trait_def_id.expect_local());
1121
1122         let Node::Item(item) = tcx.hir().get(trait_hir_id) else {
1123             bug!("trait_node_id {} is not an item", trait_hir_id);
1124         };
1125
1126         let (generics, bounds) = match item.kind {
1127             hir::ItemKind::Trait(.., ref generics, ref supertraits, _) => (generics, supertraits),
1128             hir::ItemKind::TraitAlias(ref generics, ref supertraits) => (generics, supertraits),
1129             _ => span_bug!(item.span, "super_predicates invoked on non-trait"),
1130         };
1131
1132         let icx = ItemCtxt::new(tcx, trait_def_id);
1133
1134         // Convert the bounds that follow the colon, e.g., `Bar + Zed` in `trait Foo: Bar + Zed`.
1135         let self_param_ty = tcx.types.self_param;
1136         let superbounds1 = if let Some(assoc_name) = assoc_name {
1137             <dyn AstConv<'_>>::compute_bounds_that_match_assoc_type(
1138                 &icx,
1139                 self_param_ty,
1140                 bounds,
1141                 assoc_name,
1142             )
1143         } else {
1144             <dyn AstConv<'_>>::compute_bounds(&icx, self_param_ty, bounds)
1145         };
1146
1147         let superbounds1 = superbounds1.predicates(tcx, self_param_ty);
1148
1149         // Convert any explicit superbounds in the where-clause,
1150         // e.g., `trait Foo where Self: Bar`.
1151         // In the case of trait aliases, however, we include all bounds in the where-clause,
1152         // so e.g., `trait Foo = where u32: PartialEq<Self>` would include `u32: PartialEq<Self>`
1153         // as one of its "superpredicates".
1154         let is_trait_alias = tcx.is_trait_alias(trait_def_id);
1155         let superbounds2 = icx.type_parameter_bounds_in_generics(
1156             generics,
1157             item.hir_id(),
1158             self_param_ty,
1159             OnlySelfBounds(!is_trait_alias),
1160             assoc_name,
1161         );
1162
1163         // Combine the two lists to form the complete set of superbounds:
1164         let superbounds = &*tcx.arena.alloc_from_iter(superbounds1.into_iter().chain(superbounds2));
1165
1166         // Now require that immediate supertraits are converted,
1167         // which will, in turn, reach indirect supertraits.
1168         if assoc_name.is_none() {
1169             // Now require that immediate supertraits are converted,
1170             // which will, in turn, reach indirect supertraits.
1171             for &(pred, span) in superbounds {
1172                 debug!("superbound: {:?}", pred);
1173                 if let ty::PredicateKind::Trait(bound) = pred.kind().skip_binder() {
1174                     tcx.at(span).super_predicates_of(bound.def_id());
1175                 }
1176             }
1177         }
1178
1179         ty::GenericPredicates { parent: None, predicates: superbounds }
1180     } else {
1181         // if `assoc_name` is None, then the query should've been redirected to an
1182         // external provider
1183         assert!(assoc_name.is_some());
1184         tcx.super_predicates_of(trait_def_id)
1185     }
1186 }
1187
1188 fn trait_def(tcx: TyCtxt<'_>, def_id: DefId) -> ty::TraitDef {
1189     let item = tcx.hir().expect_item(def_id.expect_local());
1190
1191     let (is_auto, unsafety, items) = match item.kind {
1192         hir::ItemKind::Trait(is_auto, unsafety, .., items) => {
1193             (is_auto == hir::IsAuto::Yes, unsafety, items)
1194         }
1195         hir::ItemKind::TraitAlias(..) => (false, hir::Unsafety::Normal, &[][..]),
1196         _ => span_bug!(item.span, "trait_def_of_item invoked on non-trait"),
1197     };
1198
1199     let paren_sugar = tcx.has_attr(def_id, sym::rustc_paren_sugar);
1200     if paren_sugar && !tcx.features().unboxed_closures {
1201         tcx.sess
1202             .struct_span_err(
1203                 item.span,
1204                 "the `#[rustc_paren_sugar]` attribute is a temporary means of controlling \
1205                  which traits can use parenthetical notation",
1206             )
1207             .help("add `#![feature(unboxed_closures)]` to the crate attributes to use it")
1208             .emit();
1209     }
1210
1211     let is_marker = tcx.has_attr(def_id, sym::marker);
1212     let skip_array_during_method_dispatch =
1213         tcx.has_attr(def_id, sym::rustc_skip_array_during_method_dispatch);
1214     let spec_kind = if tcx.has_attr(def_id, sym::rustc_unsafe_specialization_marker) {
1215         ty::trait_def::TraitSpecializationKind::Marker
1216     } else if tcx.has_attr(def_id, sym::rustc_specialization_trait) {
1217         ty::trait_def::TraitSpecializationKind::AlwaysApplicable
1218     } else {
1219         ty::trait_def::TraitSpecializationKind::None
1220     };
1221     let def_path_hash = tcx.def_path_hash(def_id);
1222
1223     let must_implement_one_of = tcx
1224         .get_attrs(def_id)
1225         .iter()
1226         .find(|attr| attr.has_name(sym::rustc_must_implement_one_of))
1227         // Check that there are at least 2 arguments of `#[rustc_must_implement_one_of]`
1228         // and that they are all identifiers
1229         .and_then(|attr| match attr.meta_item_list() {
1230             Some(items) if items.len() < 2 => {
1231                 tcx.sess
1232                     .struct_span_err(
1233                         attr.span,
1234                         "the `#[rustc_must_implement_one_of]` attribute must be \
1235                         used with at least 2 args",
1236                     )
1237                     .emit();
1238
1239                 None
1240             }
1241             Some(items) => items
1242                 .into_iter()
1243                 .map(|item| item.ident().ok_or(item.span()))
1244                 .collect::<Result<Box<[_]>, _>>()
1245                 .map_err(|span| {
1246                     tcx.sess
1247                         .struct_span_err(span, "must be a name of an associated function")
1248                         .emit();
1249                 })
1250                 .ok()
1251                 .zip(Some(attr.span)),
1252             // Error is reported by `rustc_attr!`
1253             None => None,
1254         })
1255         // Check that all arguments of `#[rustc_must_implement_one_of]` reference
1256         // functions in the trait with default implementations
1257         .and_then(|(list, attr_span)| {
1258             let errors = list.iter().filter_map(|ident| {
1259                 let item = items.iter().find(|item| item.ident == *ident);
1260
1261                 match item {
1262                     Some(item) if matches!(item.kind, hir::AssocItemKind::Fn { .. }) => {
1263                         if !item.defaultness.has_value() {
1264                             tcx.sess
1265                                 .struct_span_err(
1266                                     item.span,
1267                                     "This function doesn't have a default implementation",
1268                                 )
1269                                 .span_note(attr_span, "required by this annotation")
1270                                 .emit();
1271
1272                             return Some(());
1273                         }
1274
1275                         return None;
1276                     }
1277                     Some(item) => {
1278                         tcx.sess
1279                             .struct_span_err(item.span, "Not a function")
1280                             .span_note(attr_span, "required by this annotation")
1281                             .note(
1282                                 "All `#[rustc_must_implement_one_of]` arguments \
1283                             must be associated function names",
1284                             )
1285                             .emit();
1286                     }
1287                     None => {
1288                         tcx.sess
1289                             .struct_span_err(ident.span, "Function not found in this trait")
1290                             .emit();
1291                     }
1292                 }
1293
1294                 Some(())
1295             });
1296
1297             (errors.count() == 0).then_some(list)
1298         })
1299         // Check for duplicates
1300         .and_then(|list| {
1301             let mut set: FxHashMap<Symbol, Span> = FxHashMap::default();
1302             let mut no_dups = true;
1303
1304             for ident in &*list {
1305                 if let Some(dup) = set.insert(ident.name, ident.span) {
1306                     tcx.sess
1307                         .struct_span_err(vec![dup, ident.span], "Functions names are duplicated")
1308                         .note(
1309                             "All `#[rustc_must_implement_one_of]` arguments \
1310                             must be unique",
1311                         )
1312                         .emit();
1313
1314                     no_dups = false;
1315                 }
1316             }
1317
1318             no_dups.then_some(list)
1319         });
1320
1321     ty::TraitDef::new(
1322         def_id,
1323         unsafety,
1324         paren_sugar,
1325         is_auto,
1326         is_marker,
1327         skip_array_during_method_dispatch,
1328         spec_kind,
1329         def_path_hash,
1330         must_implement_one_of,
1331     )
1332 }
1333
1334 fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<Span> {
1335     struct LateBoundRegionsDetector<'tcx> {
1336         tcx: TyCtxt<'tcx>,
1337         outer_index: ty::DebruijnIndex,
1338         has_late_bound_regions: Option<Span>,
1339     }
1340
1341     impl<'tcx> Visitor<'tcx> for LateBoundRegionsDetector<'tcx> {
1342         fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
1343             if self.has_late_bound_regions.is_some() {
1344                 return;
1345             }
1346             match ty.kind {
1347                 hir::TyKind::BareFn(..) => {
1348                     self.outer_index.shift_in(1);
1349                     intravisit::walk_ty(self, ty);
1350                     self.outer_index.shift_out(1);
1351                 }
1352                 _ => intravisit::walk_ty(self, ty),
1353             }
1354         }
1355
1356         fn visit_poly_trait_ref(
1357             &mut self,
1358             tr: &'tcx hir::PolyTraitRef<'tcx>,
1359             m: hir::TraitBoundModifier,
1360         ) {
1361             if self.has_late_bound_regions.is_some() {
1362                 return;
1363             }
1364             self.outer_index.shift_in(1);
1365             intravisit::walk_poly_trait_ref(self, tr, m);
1366             self.outer_index.shift_out(1);
1367         }
1368
1369         fn visit_lifetime(&mut self, lt: &'tcx hir::Lifetime) {
1370             if self.has_late_bound_regions.is_some() {
1371                 return;
1372             }
1373
1374             match self.tcx.named_region(lt.hir_id) {
1375                 Some(rl::Region::Static | rl::Region::EarlyBound(..)) => {}
1376                 Some(
1377                     rl::Region::LateBound(debruijn, _, _)
1378                     | rl::Region::LateBoundAnon(debruijn, _, _),
1379                 ) if debruijn < self.outer_index => {}
1380                 Some(
1381                     rl::Region::LateBound(..)
1382                     | rl::Region::LateBoundAnon(..)
1383                     | rl::Region::Free(..),
1384                 )
1385                 | None => {
1386                     self.has_late_bound_regions = Some(lt.span);
1387                 }
1388             }
1389         }
1390     }
1391
1392     fn has_late_bound_regions<'tcx>(
1393         tcx: TyCtxt<'tcx>,
1394         generics: &'tcx hir::Generics<'tcx>,
1395         decl: &'tcx hir::FnDecl<'tcx>,
1396     ) -> Option<Span> {
1397         let mut visitor = LateBoundRegionsDetector {
1398             tcx,
1399             outer_index: ty::INNERMOST,
1400             has_late_bound_regions: None,
1401         };
1402         for param in generics.params {
1403             if let GenericParamKind::Lifetime { .. } = param.kind {
1404                 if tcx.is_late_bound(param.hir_id) {
1405                     return Some(param.span);
1406                 }
1407             }
1408         }
1409         visitor.visit_fn_decl(decl);
1410         visitor.has_late_bound_regions
1411     }
1412
1413     match node {
1414         Node::TraitItem(item) => match item.kind {
1415             hir::TraitItemKind::Fn(ref sig, _) => {
1416                 has_late_bound_regions(tcx, &item.generics, sig.decl)
1417             }
1418             _ => None,
1419         },
1420         Node::ImplItem(item) => match item.kind {
1421             hir::ImplItemKind::Fn(ref sig, _) => {
1422                 has_late_bound_regions(tcx, &item.generics, sig.decl)
1423             }
1424             _ => None,
1425         },
1426         Node::ForeignItem(item) => match item.kind {
1427             hir::ForeignItemKind::Fn(fn_decl, _, ref generics) => {
1428                 has_late_bound_regions(tcx, generics, fn_decl)
1429             }
1430             _ => None,
1431         },
1432         Node::Item(item) => match item.kind {
1433             hir::ItemKind::Fn(ref sig, .., ref generics, _) => {
1434                 has_late_bound_regions(tcx, generics, sig.decl)
1435             }
1436             _ => None,
1437         },
1438         _ => None,
1439     }
1440 }
1441
1442 struct AnonConstInParamTyDetector {
1443     in_param_ty: bool,
1444     found_anon_const_in_param_ty: bool,
1445     ct: HirId,
1446 }
1447
1448 impl<'v> Visitor<'v> for AnonConstInParamTyDetector {
1449     fn visit_generic_param(&mut self, p: &'v hir::GenericParam<'v>) {
1450         if let GenericParamKind::Const { ty, default: _ } = p.kind {
1451             let prev = self.in_param_ty;
1452             self.in_param_ty = true;
1453             self.visit_ty(ty);
1454             self.in_param_ty = prev;
1455         }
1456     }
1457
1458     fn visit_anon_const(&mut self, c: &'v hir::AnonConst) {
1459         if self.in_param_ty && self.ct == c.hir_id {
1460             self.found_anon_const_in_param_ty = true;
1461         } else {
1462             intravisit::walk_anon_const(self, c)
1463         }
1464     }
1465 }
1466
1467 fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
1468     use rustc_hir::*;
1469
1470     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
1471
1472     let node = tcx.hir().get(hir_id);
1473     let parent_def_id = match node {
1474         Node::ImplItem(_)
1475         | Node::TraitItem(_)
1476         | Node::Variant(_)
1477         | Node::Ctor(..)
1478         | Node::Field(_) => {
1479             let parent_id = tcx.hir().get_parent_item(hir_id);
1480             Some(parent_id.to_def_id())
1481         }
1482         // FIXME(#43408) always enable this once `lazy_normalization` is
1483         // stable enough and does not need a feature gate anymore.
1484         Node::AnonConst(_) => {
1485             let parent_def_id = tcx.hir().get_parent_item(hir_id);
1486
1487             let mut in_param_ty = false;
1488             for (_parent, node) in tcx.hir().parent_iter(hir_id) {
1489                 if let Some(generics) = node.generics() {
1490                     let mut visitor = AnonConstInParamTyDetector {
1491                         in_param_ty: false,
1492                         found_anon_const_in_param_ty: false,
1493                         ct: hir_id,
1494                     };
1495
1496                     visitor.visit_generics(generics);
1497                     in_param_ty = visitor.found_anon_const_in_param_ty;
1498                     break;
1499                 }
1500             }
1501
1502             if in_param_ty {
1503                 // We do not allow generic parameters in anon consts if we are inside
1504                 // of a const parameter type, e.g. `struct Foo<const N: usize, const M: [u8; N]>` is not allowed.
1505                 None
1506             } else if tcx.lazy_normalization() {
1507                 if let Some(param_id) = tcx.hir().opt_const_param_default_param_hir_id(hir_id) {
1508                     // If the def_id we are calling generics_of on is an anon ct default i.e:
1509                     //
1510                     // struct Foo<const N: usize = { .. }>;
1511                     //        ^^^       ^          ^^^^^^ def id of this anon const
1512                     //        ^         ^ param_id
1513                     //        ^ parent_def_id
1514                     //
1515                     // then we only want to return generics for params to the left of `N`. If we don't do that we
1516                     // end up with that const looking like: `ty::ConstKind::Unevaluated(def_id, substs: [N#0])`.
1517                     //
1518                     // This causes ICEs (#86580) when building the substs for Foo in `fn foo() -> Foo { .. }` as
1519                     // we substitute the defaults with the partially built substs when we build the substs. Subst'ing
1520                     // the `N#0` on the unevaluated const indexes into the empty substs we're in the process of building.
1521                     //
1522                     // We fix this by having this function return the parent's generics ourselves and truncating the
1523                     // generics to only include non-forward declared params (with the exception of the `Self` ty)
1524                     //
1525                     // For the above code example that means we want `substs: []`
1526                     // For the following struct def we want `substs: [N#0]` when generics_of is called on
1527                     // the def id of the `{ N + 1 }` anon const
1528                     // struct Foo<const N: usize, const M: usize = { N + 1 }>;
1529                     //
1530                     // This has some implications for how we get the predicates available to the anon const
1531                     // see `explicit_predicates_of` for more information on this
1532                     let generics = tcx.generics_of(parent_def_id.to_def_id());
1533                     let param_def = tcx.hir().local_def_id(param_id).to_def_id();
1534                     let param_def_idx = generics.param_def_id_to_index[&param_def];
1535                     // In the above example this would be .params[..N#0]
1536                     let params = generics.params[..param_def_idx as usize].to_owned();
1537                     let param_def_id_to_index =
1538                         params.iter().map(|param| (param.def_id, param.index)).collect();
1539
1540                     return ty::Generics {
1541                         // we set the parent of these generics to be our parent's parent so that we
1542                         // dont end up with substs: [N, M, N] for the const default on a struct like this:
1543                         // struct Foo<const N: usize, const M: usize = { ... }>;
1544                         parent: generics.parent,
1545                         parent_count: generics.parent_count,
1546                         params,
1547                         param_def_id_to_index,
1548                         has_self: generics.has_self,
1549                         has_late_bound_regions: generics.has_late_bound_regions,
1550                     };
1551                 }
1552
1553                 // HACK(eddyb) this provides the correct generics when
1554                 // `feature(generic_const_expressions)` is enabled, so that const expressions
1555                 // used with const generics, e.g. `Foo<{N+1}>`, can work at all.
1556                 //
1557                 // Note that we do not supply the parent generics when using
1558                 // `min_const_generics`.
1559                 Some(parent_def_id.to_def_id())
1560             } else {
1561                 let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
1562                 match parent_node {
1563                     // HACK(eddyb) this provides the correct generics for repeat
1564                     // expressions' count (i.e. `N` in `[x; N]`), and explicit
1565                     // `enum` discriminants (i.e. `D` in `enum Foo { Bar = D }`),
1566                     // as they shouldn't be able to cause query cycle errors.
1567                     Node::Expr(&Expr { kind: ExprKind::Repeat(_, ref constant), .. })
1568                         if constant.hir_id() == hir_id =>
1569                     {
1570                         Some(parent_def_id.to_def_id())
1571                     }
1572                     Node::Variant(Variant { disr_expr: Some(ref constant), .. })
1573                         if constant.hir_id == hir_id =>
1574                     {
1575                         Some(parent_def_id.to_def_id())
1576                     }
1577                     Node::Expr(&Expr { kind: ExprKind::ConstBlock(_), .. }) => {
1578                         Some(tcx.typeck_root_def_id(def_id))
1579                     }
1580                     _ => None,
1581                 }
1582             }
1583         }
1584         Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => {
1585             Some(tcx.typeck_root_def_id(def_id))
1586         }
1587         Node::Item(item) => match item.kind {
1588             ItemKind::OpaqueTy(hir::OpaqueTy {
1589                 origin:
1590                     hir::OpaqueTyOrigin::FnReturn(fn_def_id) | hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
1591                 ..
1592             }) => Some(fn_def_id.to_def_id()),
1593             ItemKind::OpaqueTy(hir::OpaqueTy { origin: hir::OpaqueTyOrigin::TyAlias, .. }) => {
1594                 let parent_id = tcx.hir().get_parent_item(hir_id);
1595                 assert_ne!(parent_id, CRATE_DEF_ID);
1596                 debug!("generics_of: parent of opaque ty {:?} is {:?}", def_id, parent_id);
1597                 // Opaque types are always nested within another item, and
1598                 // inherit the generics of the item.
1599                 Some(parent_id.to_def_id())
1600             }
1601             _ => None,
1602         },
1603         _ => None,
1604     };
1605
1606     let mut opt_self = None;
1607     let mut allow_defaults = false;
1608
1609     let no_generics = hir::Generics::empty();
1610     let ast_generics = match node {
1611         Node::TraitItem(item) => &item.generics,
1612
1613         Node::ImplItem(item) => &item.generics,
1614
1615         Node::Item(item) => {
1616             match item.kind {
1617                 ItemKind::Fn(.., ref generics, _)
1618                 | ItemKind::Impl(hir::Impl { ref generics, .. }) => generics,
1619
1620                 ItemKind::TyAlias(_, ref generics)
1621                 | ItemKind::Enum(_, ref generics)
1622                 | ItemKind::Struct(_, ref generics)
1623                 | ItemKind::OpaqueTy(hir::OpaqueTy { ref generics, .. })
1624                 | ItemKind::Union(_, ref generics) => {
1625                     allow_defaults = true;
1626                     generics
1627                 }
1628
1629                 ItemKind::Trait(_, _, ref generics, ..)
1630                 | ItemKind::TraitAlias(ref generics, ..) => {
1631                     // Add in the self type parameter.
1632                     //
1633                     // Something of a hack: use the node id for the trait, also as
1634                     // the node id for the Self type parameter.
1635                     let param_id = item.def_id;
1636
1637                     opt_self = Some(ty::GenericParamDef {
1638                         index: 0,
1639                         name: kw::SelfUpper,
1640                         def_id: param_id.to_def_id(),
1641                         pure_wrt_drop: false,
1642                         kind: ty::GenericParamDefKind::Type {
1643                             has_default: false,
1644                             object_lifetime_default: rl::Set1::Empty,
1645                             synthetic: false,
1646                         },
1647                     });
1648
1649                     allow_defaults = true;
1650                     generics
1651                 }
1652
1653                 _ => &no_generics,
1654             }
1655         }
1656
1657         Node::ForeignItem(item) => match item.kind {
1658             ForeignItemKind::Static(..) => &no_generics,
1659             ForeignItemKind::Fn(_, _, ref generics) => generics,
1660             ForeignItemKind::Type => &no_generics,
1661         },
1662
1663         _ => &no_generics,
1664     };
1665
1666     let has_self = opt_self.is_some();
1667     let mut parent_has_self = false;
1668     let mut own_start = has_self as u32;
1669     let parent_count = parent_def_id.map_or(0, |def_id| {
1670         let generics = tcx.generics_of(def_id);
1671         assert!(!has_self);
1672         parent_has_self = generics.has_self;
1673         own_start = generics.count() as u32;
1674         generics.parent_count + generics.params.len()
1675     });
1676
1677     let mut params: Vec<_> = Vec::with_capacity(ast_generics.params.len() + has_self as usize);
1678
1679     if let Some(opt_self) = opt_self {
1680         params.push(opt_self);
1681     }
1682
1683     let early_lifetimes = early_bound_lifetimes_from_generics(tcx, ast_generics);
1684     params.extend(early_lifetimes.enumerate().map(|(i, param)| ty::GenericParamDef {
1685         name: param.name.ident().name,
1686         index: own_start + i as u32,
1687         def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
1688         pure_wrt_drop: param.pure_wrt_drop,
1689         kind: ty::GenericParamDefKind::Lifetime,
1690     }));
1691
1692     let object_lifetime_defaults = tcx.object_lifetime_defaults(hir_id.owner);
1693
1694     // Now create the real type and const parameters.
1695     let type_start = own_start - has_self as u32 + params.len() as u32;
1696     let mut i = 0;
1697
1698     params.extend(ast_generics.params.iter().filter_map(|param| match param.kind {
1699         GenericParamKind::Lifetime { .. } => None,
1700         GenericParamKind::Type { ref default, synthetic, .. } => {
1701             if !allow_defaults && default.is_some() {
1702                 if !tcx.features().default_type_parameter_fallback {
1703                     tcx.struct_span_lint_hir(
1704                         lint::builtin::INVALID_TYPE_PARAM_DEFAULT,
1705                         param.hir_id,
1706                         param.span,
1707                         |lint| {
1708                             lint.build(
1709                                 "defaults for type parameters are only allowed in \
1710                                  `struct`, `enum`, `type`, or `trait` definitions",
1711                             )
1712                             .emit();
1713                         },
1714                     );
1715                 }
1716             }
1717
1718             let kind = ty::GenericParamDefKind::Type {
1719                 has_default: default.is_some(),
1720                 object_lifetime_default: object_lifetime_defaults
1721                     .as_ref()
1722                     .map_or(rl::Set1::Empty, |o| o[i]),
1723                 synthetic,
1724             };
1725
1726             let param_def = ty::GenericParamDef {
1727                 index: type_start + i as u32,
1728                 name: param.name.ident().name,
1729                 def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
1730                 pure_wrt_drop: param.pure_wrt_drop,
1731                 kind,
1732             };
1733             i += 1;
1734             Some(param_def)
1735         }
1736         GenericParamKind::Const { default, .. } => {
1737             if !allow_defaults && default.is_some() {
1738                 tcx.sess.span_err(
1739                     param.span,
1740                     "defaults for const parameters are only allowed in \
1741                     `struct`, `enum`, `type`, or `trait` definitions",
1742                 );
1743             }
1744
1745             let param_def = ty::GenericParamDef {
1746                 index: type_start + i as u32,
1747                 name: param.name.ident().name,
1748                 def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
1749                 pure_wrt_drop: param.pure_wrt_drop,
1750                 kind: ty::GenericParamDefKind::Const { has_default: default.is_some() },
1751             };
1752             i += 1;
1753             Some(param_def)
1754         }
1755     }));
1756
1757     // provide junk type parameter defs - the only place that
1758     // cares about anything but the length is instantiation,
1759     // and we don't do that for closures.
1760     if let Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure(.., gen), .. }) = node {
1761         let dummy_args = if gen.is_some() {
1762             &["<resume_ty>", "<yield_ty>", "<return_ty>", "<witness>", "<upvars>"][..]
1763         } else {
1764             &["<closure_kind>", "<closure_signature>", "<upvars>"][..]
1765         };
1766
1767         params.extend(dummy_args.iter().enumerate().map(|(i, &arg)| ty::GenericParamDef {
1768             index: type_start + i as u32,
1769             name: Symbol::intern(arg),
1770             def_id,
1771             pure_wrt_drop: false,
1772             kind: ty::GenericParamDefKind::Type {
1773                 has_default: false,
1774                 object_lifetime_default: rl::Set1::Empty,
1775                 synthetic: false,
1776             },
1777         }));
1778     }
1779
1780     // provide junk type parameter defs for const blocks.
1781     if let Node::AnonConst(_) = node {
1782         let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
1783         if let Node::Expr(&Expr { kind: ExprKind::ConstBlock(_), .. }) = parent_node {
1784             params.push(ty::GenericParamDef {
1785                 index: type_start,
1786                 name: Symbol::intern("<const_ty>"),
1787                 def_id,
1788                 pure_wrt_drop: false,
1789                 kind: ty::GenericParamDefKind::Type {
1790                     has_default: false,
1791                     object_lifetime_default: rl::Set1::Empty,
1792                     synthetic: false,
1793                 },
1794             });
1795         }
1796     }
1797
1798     let param_def_id_to_index = params.iter().map(|param| (param.def_id, param.index)).collect();
1799
1800     ty::Generics {
1801         parent: parent_def_id,
1802         parent_count,
1803         params,
1804         param_def_id_to_index,
1805         has_self: has_self || parent_has_self,
1806         has_late_bound_regions: has_late_bound_regions(tcx, node),
1807     }
1808 }
1809
1810 fn are_suggestable_generic_args(generic_args: &[hir::GenericArg<'_>]) -> bool {
1811     generic_args.iter().any(|arg| match arg {
1812         hir::GenericArg::Type(ty) => is_suggestable_infer_ty(ty),
1813         hir::GenericArg::Infer(_) => true,
1814         _ => false,
1815     })
1816 }
1817
1818 /// Whether `ty` is a type with `_` placeholders that can be inferred. Used in diagnostics only to
1819 /// use inference to provide suggestions for the appropriate type if possible.
1820 fn is_suggestable_infer_ty(ty: &hir::Ty<'_>) -> bool {
1821     debug!(?ty);
1822     use hir::TyKind::*;
1823     match &ty.kind {
1824         Infer => true,
1825         Slice(ty) => is_suggestable_infer_ty(ty),
1826         Array(ty, length) => {
1827             is_suggestable_infer_ty(ty) || matches!(length, hir::ArrayLen::Infer(_, _))
1828         }
1829         Tup(tys) => tys.iter().any(is_suggestable_infer_ty),
1830         Ptr(mut_ty) | Rptr(_, mut_ty) => is_suggestable_infer_ty(mut_ty.ty),
1831         OpaqueDef(_, generic_args) => are_suggestable_generic_args(generic_args),
1832         Path(hir::QPath::TypeRelative(ty, segment)) => {
1833             is_suggestable_infer_ty(ty) || are_suggestable_generic_args(segment.args().args)
1834         }
1835         Path(hir::QPath::Resolved(ty_opt, hir::Path { segments, .. })) => {
1836             ty_opt.map_or(false, is_suggestable_infer_ty)
1837                 || segments.iter().any(|segment| are_suggestable_generic_args(segment.args().args))
1838         }
1839         _ => false,
1840     }
1841 }
1842
1843 pub fn get_infer_ret_ty<'hir>(output: &'hir hir::FnRetTy<'hir>) -> Option<&'hir hir::Ty<'hir>> {
1844     if let hir::FnRetTy::Return(ty) = output {
1845         if is_suggestable_infer_ty(ty) {
1846             return Some(&*ty);
1847         }
1848     }
1849     None
1850 }
1851
1852 fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
1853     use rustc_hir::Node::*;
1854     use rustc_hir::*;
1855
1856     let def_id = def_id.expect_local();
1857     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
1858
1859     let icx = ItemCtxt::new(tcx, def_id.to_def_id());
1860
1861     match tcx.hir().get(hir_id) {
1862         TraitItem(hir::TraitItem {
1863             kind: TraitItemKind::Fn(sig, TraitFn::Provided(_)),
1864             ident,
1865             generics,
1866             ..
1867         })
1868         | ImplItem(hir::ImplItem { kind: ImplItemKind::Fn(sig, _), ident, generics, .. })
1869         | Item(hir::Item { kind: ItemKind::Fn(sig, generics, _), ident, .. }) => {
1870             match get_infer_ret_ty(&sig.decl.output) {
1871                 Some(ty) => {
1872                     let fn_sig = tcx.typeck(def_id).liberated_fn_sigs()[hir_id];
1873                     // Typeck doesn't expect erased regions to be returned from `type_of`.
1874                     let fn_sig = tcx.fold_regions(fn_sig, &mut false, |r, _| match *r {
1875                         ty::ReErased => tcx.lifetimes.re_static,
1876                         _ => r,
1877                     });
1878                     let fn_sig = ty::Binder::dummy(fn_sig);
1879
1880                     let mut visitor = HirPlaceholderCollector::default();
1881                     visitor.visit_ty(ty);
1882                     let mut diag = bad_placeholder(tcx, visitor.0, "return type");
1883                     let ret_ty = fn_sig.skip_binder().output();
1884                     if !ret_ty.references_error() {
1885                         if !ret_ty.is_closure() {
1886                             let ret_ty_str = match ret_ty.kind() {
1887                                 // Suggest a function pointer return type instead of a unique function definition
1888                                 // (e.g. `fn() -> i32` instead of `fn() -> i32 { f }`, the latter of which is invalid
1889                                 // syntax)
1890                                 ty::FnDef(..) => ret_ty.fn_sig(tcx).to_string(),
1891                                 _ => ret_ty.to_string(),
1892                             };
1893                             diag.span_suggestion(
1894                                 ty.span,
1895                                 "replace with the correct return type",
1896                                 ret_ty_str,
1897                                 Applicability::MaybeIncorrect,
1898                             );
1899                         } else {
1900                             // We're dealing with a closure, so we should suggest using `impl Fn` or trait bounds
1901                             // to prevent the user from getting a papercut while trying to use the unique closure
1902                             // syntax (e.g. `[closure@src/lib.rs:2:5: 2:9]`).
1903                             diag.help("consider using an `Fn`, `FnMut`, or `FnOnce` trait bound");
1904                             diag.note("for more information on `Fn` traits and closure types, see https://doc.rust-lang.org/book/ch13-01-closures.html");
1905                         }
1906                     }
1907                     diag.emit();
1908
1909                     fn_sig
1910                 }
1911                 None => <dyn AstConv<'_>>::ty_of_fn(
1912                     &icx,
1913                     hir_id,
1914                     sig.header.unsafety,
1915                     sig.header.abi,
1916                     sig.decl,
1917                     generics,
1918                     Some(ident.span),
1919                     None,
1920                 ),
1921             }
1922         }
1923
1924         TraitItem(hir::TraitItem {
1925             kind: TraitItemKind::Fn(FnSig { header, decl, span: _ }, _),
1926             ident,
1927             generics,
1928             ..
1929         }) => <dyn AstConv<'_>>::ty_of_fn(
1930             &icx,
1931             hir_id,
1932             header.unsafety,
1933             header.abi,
1934             decl,
1935             generics,
1936             Some(ident.span),
1937             None,
1938         ),
1939
1940         ForeignItem(&hir::ForeignItem {
1941             kind: ForeignItemKind::Fn(fn_decl, _, _), ident, ..
1942         }) => {
1943             let abi = tcx.hir().get_foreign_abi(hir_id);
1944             compute_sig_of_foreign_fn_decl(tcx, def_id.to_def_id(), fn_decl, abi, ident)
1945         }
1946
1947         Ctor(data) | Variant(hir::Variant { data, .. }) if data.ctor_hir_id().is_some() => {
1948             let ty = tcx.type_of(tcx.hir().get_parent_item(hir_id));
1949             let inputs =
1950                 data.fields().iter().map(|f| tcx.type_of(tcx.hir().local_def_id(f.hir_id)));
1951             ty::Binder::dummy(tcx.mk_fn_sig(
1952                 inputs,
1953                 ty,
1954                 false,
1955                 hir::Unsafety::Normal,
1956                 abi::Abi::Rust,
1957             ))
1958         }
1959
1960         Expr(&hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => {
1961             // Closure signatures are not like other function
1962             // signatures and cannot be accessed through `fn_sig`. For
1963             // example, a closure signature excludes the `self`
1964             // argument. In any case they are embedded within the
1965             // closure type as part of the `ClosureSubsts`.
1966             //
1967             // To get the signature of a closure, you should use the
1968             // `sig` method on the `ClosureSubsts`:
1969             //
1970             //    substs.as_closure().sig(def_id, tcx)
1971             bug!(
1972                 "to get the signature of a closure, use `substs.as_closure().sig()` not `fn_sig()`",
1973             );
1974         }
1975
1976         x => {
1977             bug!("unexpected sort of node in fn_sig(): {:?}", x);
1978         }
1979     }
1980 }
1981
1982 fn impl_trait_ref(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ty::TraitRef<'_>> {
1983     let icx = ItemCtxt::new(tcx, def_id);
1984     match tcx.hir().expect_item(def_id.expect_local()).kind {
1985         hir::ItemKind::Impl(ref impl_) => impl_.of_trait.as_ref().map(|ast_trait_ref| {
1986             let selfty = tcx.type_of(def_id);
1987             <dyn AstConv<'_>>::instantiate_mono_trait_ref(&icx, ast_trait_ref, selfty)
1988         }),
1989         _ => bug!(),
1990     }
1991 }
1992
1993 fn impl_polarity(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ImplPolarity {
1994     let is_rustc_reservation = tcx.has_attr(def_id, sym::rustc_reservation_impl);
1995     let item = tcx.hir().expect_item(def_id.expect_local());
1996     match &item.kind {
1997         hir::ItemKind::Impl(hir::Impl {
1998             polarity: hir::ImplPolarity::Negative(span),
1999             of_trait,
2000             ..
2001         }) => {
2002             if is_rustc_reservation {
2003                 let span = span.to(of_trait.as_ref().map_or(*span, |t| t.path.span));
2004                 tcx.sess.span_err(span, "reservation impls can't be negative");
2005             }
2006             ty::ImplPolarity::Negative
2007         }
2008         hir::ItemKind::Impl(hir::Impl {
2009             polarity: hir::ImplPolarity::Positive,
2010             of_trait: None,
2011             ..
2012         }) => {
2013             if is_rustc_reservation {
2014                 tcx.sess.span_err(item.span, "reservation impls can't be inherent");
2015             }
2016             ty::ImplPolarity::Positive
2017         }
2018         hir::ItemKind::Impl(hir::Impl {
2019             polarity: hir::ImplPolarity::Positive,
2020             of_trait: Some(_),
2021             ..
2022         }) => {
2023             if is_rustc_reservation {
2024                 ty::ImplPolarity::Reservation
2025             } else {
2026                 ty::ImplPolarity::Positive
2027             }
2028         }
2029         item => bug!("impl_polarity: {:?} not an impl", item),
2030     }
2031 }
2032
2033 /// Returns the early-bound lifetimes declared in this generics
2034 /// listing. For anything other than fns/methods, this is just all
2035 /// the lifetimes that are declared. For fns or methods, we have to
2036 /// screen out those that do not appear in any where-clauses etc using
2037 /// `resolve_lifetime::early_bound_lifetimes`.
2038 fn early_bound_lifetimes_from_generics<'a, 'tcx: 'a>(
2039     tcx: TyCtxt<'tcx>,
2040     generics: &'a hir::Generics<'a>,
2041 ) -> impl Iterator<Item = &'a hir::GenericParam<'a>> + Captures<'tcx> {
2042     generics.params.iter().filter(move |param| match param.kind {
2043         GenericParamKind::Lifetime { .. } => !tcx.is_late_bound(param.hir_id),
2044         _ => false,
2045     })
2046 }
2047
2048 /// Returns a list of type predicates for the definition with ID `def_id`, including inferred
2049 /// lifetime constraints. This includes all predicates returned by `explicit_predicates_of`, plus
2050 /// inferred constraints concerning which regions outlive other regions.
2051 fn predicates_defined_on(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2052     debug!("predicates_defined_on({:?})", def_id);
2053     let mut result = tcx.explicit_predicates_of(def_id);
2054     debug!("predicates_defined_on: explicit_predicates_of({:?}) = {:?}", def_id, result,);
2055     let inferred_outlives = tcx.inferred_outlives_of(def_id);
2056     if !inferred_outlives.is_empty() {
2057         debug!(
2058             "predicates_defined_on: inferred_outlives_of({:?}) = {:?}",
2059             def_id, inferred_outlives,
2060         );
2061         if result.predicates.is_empty() {
2062             result.predicates = inferred_outlives;
2063         } else {
2064             result.predicates = tcx
2065                 .arena
2066                 .alloc_from_iter(result.predicates.iter().chain(inferred_outlives).copied());
2067         }
2068     }
2069
2070     debug!("predicates_defined_on({:?}) = {:?}", def_id, result);
2071     result
2072 }
2073
2074 /// Returns a list of all type predicates (explicit and implicit) for the definition with
2075 /// ID `def_id`. This includes all predicates returned by `predicates_defined_on`, plus
2076 /// `Self: Trait` predicates for traits.
2077 fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2078     let mut result = tcx.predicates_defined_on(def_id);
2079
2080     if tcx.is_trait(def_id) {
2081         // For traits, add `Self: Trait` predicate. This is
2082         // not part of the predicates that a user writes, but it
2083         // is something that one must prove in order to invoke a
2084         // method or project an associated type.
2085         //
2086         // In the chalk setup, this predicate is not part of the
2087         // "predicates" for a trait item. But it is useful in
2088         // rustc because if you directly (e.g.) invoke a trait
2089         // method like `Trait::method(...)`, you must naturally
2090         // prove that the trait applies to the types that were
2091         // used, and adding the predicate into this list ensures
2092         // that this is done.
2093         //
2094         // We use a DUMMY_SP here as a way to signal trait bounds that come
2095         // from the trait itself that *shouldn't* be shown as the source of
2096         // an obligation and instead be skipped. Otherwise we'd use
2097         // `tcx.def_span(def_id);`
2098         let span = rustc_span::DUMMY_SP;
2099         result.predicates =
2100             tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(std::iter::once((
2101                 ty::TraitRef::identity(tcx, def_id).without_const().to_predicate(tcx),
2102                 span,
2103             ))));
2104     }
2105     debug!("predicates_of(def_id={:?}) = {:?}", def_id, result);
2106     result
2107 }
2108
2109 /// Returns a list of user-specified type predicates for the definition with ID `def_id`.
2110 /// N.B., this does not include any implied/inferred constraints.
2111 fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2112     use rustc_hir::*;
2113
2114     debug!("explicit_predicates_of(def_id={:?})", def_id);
2115
2116     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2117     let node = tcx.hir().get(hir_id);
2118
2119     let mut is_trait = None;
2120     let mut is_default_impl_trait = None;
2121
2122     let icx = ItemCtxt::new(tcx, def_id);
2123
2124     const NO_GENERICS: &hir::Generics<'_> = &hir::Generics::empty();
2125
2126     // We use an `IndexSet` to preserves order of insertion.
2127     // Preserving the order of insertion is important here so as not to break UI tests.
2128     let mut predicates: FxIndexSet<(ty::Predicate<'_>, Span)> = FxIndexSet::default();
2129
2130     let ast_generics = match node {
2131         Node::TraitItem(item) => &item.generics,
2132
2133         Node::ImplItem(item) => &item.generics,
2134
2135         Node::Item(item) => {
2136             match item.kind {
2137                 ItemKind::Impl(ref impl_) => {
2138                     if impl_.defaultness.is_default() {
2139                         is_default_impl_trait = tcx.impl_trait_ref(def_id).map(ty::Binder::dummy);
2140                     }
2141                     &impl_.generics
2142                 }
2143                 ItemKind::Fn(.., ref generics, _)
2144                 | ItemKind::TyAlias(_, ref generics)
2145                 | ItemKind::Enum(_, ref generics)
2146                 | ItemKind::Struct(_, ref generics)
2147                 | ItemKind::Union(_, ref generics) => generics,
2148
2149                 ItemKind::Trait(_, _, ref generics, ..) => {
2150                     is_trait = Some(ty::TraitRef::identity(tcx, def_id));
2151                     generics
2152                 }
2153                 ItemKind::TraitAlias(ref generics, _) => {
2154                     is_trait = Some(ty::TraitRef::identity(tcx, def_id));
2155                     generics
2156                 }
2157                 ItemKind::OpaqueTy(OpaqueTy {
2158                     origin: hir::OpaqueTyOrigin::AsyncFn(..) | hir::OpaqueTyOrigin::FnReturn(..),
2159                     ..
2160                 }) => {
2161                     // return-position impl trait
2162                     //
2163                     // We don't inherit predicates from the parent here:
2164                     // If we have, say `fn f<'a, T: 'a>() -> impl Sized {}`
2165                     // then the return type is `f::<'static, T>::{{opaque}}`.
2166                     //
2167                     // If we inherited the predicates of `f` then we would
2168                     // require that `T: 'static` to show that the return
2169                     // type is well-formed.
2170                     //
2171                     // The only way to have something with this opaque type
2172                     // is from the return type of the containing function,
2173                     // which will ensure that the function's predicates
2174                     // hold.
2175                     return ty::GenericPredicates { parent: None, predicates: &[] };
2176                 }
2177                 ItemKind::OpaqueTy(OpaqueTy {
2178                     ref generics,
2179                     origin: hir::OpaqueTyOrigin::TyAlias,
2180                     ..
2181                 }) => {
2182                     // type-alias impl trait
2183                     generics
2184                 }
2185
2186                 _ => NO_GENERICS,
2187             }
2188         }
2189
2190         Node::ForeignItem(item) => match item.kind {
2191             ForeignItemKind::Static(..) => NO_GENERICS,
2192             ForeignItemKind::Fn(_, _, ref generics) => generics,
2193             ForeignItemKind::Type => NO_GENERICS,
2194         },
2195
2196         _ => NO_GENERICS,
2197     };
2198
2199     let generics = tcx.generics_of(def_id);
2200     let parent_count = generics.parent_count as u32;
2201     let has_own_self = generics.has_self && parent_count == 0;
2202
2203     // Below we'll consider the bounds on the type parameters (including `Self`)
2204     // and the explicit where-clauses, but to get the full set of predicates
2205     // on a trait we need to add in the supertrait bounds and bounds found on
2206     // associated types.
2207     if let Some(_trait_ref) = is_trait {
2208         predicates.extend(tcx.super_predicates_of(def_id).predicates.iter().cloned());
2209     }
2210
2211     // In default impls, we can assume that the self type implements
2212     // the trait. So in:
2213     //
2214     //     default impl Foo for Bar { .. }
2215     //
2216     // we add a default where clause `Foo: Bar`. We do a similar thing for traits
2217     // (see below). Recall that a default impl is not itself an impl, but rather a
2218     // set of defaults that can be incorporated into another impl.
2219     if let Some(trait_ref) = is_default_impl_trait {
2220         predicates.insert((trait_ref.without_const().to_predicate(tcx), tcx.def_span(def_id)));
2221     }
2222
2223     // Collect the region predicates that were declared inline as
2224     // well. In the case of parameters declared on a fn or method, we
2225     // have to be careful to only iterate over early-bound regions.
2226     let mut index = parent_count + has_own_self as u32;
2227     for param in early_bound_lifetimes_from_generics(tcx, ast_generics) {
2228         let region = tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
2229             def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
2230             index,
2231             name: param.name.ident().name,
2232         }));
2233         index += 1;
2234
2235         match param.kind {
2236             GenericParamKind::Lifetime { .. } => {
2237                 param.bounds.iter().for_each(|bound| match bound {
2238                     hir::GenericBound::Outlives(lt) => {
2239                         let bound = <dyn AstConv<'_>>::ast_region_to_region(&icx, lt, None);
2240                         let outlives = ty::Binder::dummy(ty::OutlivesPredicate(region, bound));
2241                         predicates.insert((outlives.to_predicate(tcx), lt.span));
2242                     }
2243                     _ => bug!(),
2244                 });
2245             }
2246             _ => bug!(),
2247         }
2248     }
2249
2250     // Collect the predicates that were written inline by the user on each
2251     // type parameter (e.g., `<T: Foo>`).
2252     for param in ast_generics.params {
2253         match param.kind {
2254             // We already dealt with early bound lifetimes above.
2255             GenericParamKind::Lifetime { .. } => (),
2256             GenericParamKind::Type { .. } => {
2257                 let name = param.name.ident().name;
2258                 let param_ty = ty::ParamTy::new(index, name).to_ty(tcx);
2259                 index += 1;
2260
2261                 let mut bounds = <dyn AstConv<'_>>::compute_bounds(&icx, param_ty, param.bounds);
2262                 // Params are implicitly sized unless a `?Sized` bound is found
2263                 <dyn AstConv<'_>>::add_implicitly_sized(
2264                     &icx,
2265                     &mut bounds,
2266                     param.bounds,
2267                     Some((param.hir_id, ast_generics.where_clause.predicates)),
2268                     param.span,
2269                 );
2270                 predicates.extend(bounds.predicates(tcx, param_ty));
2271             }
2272             GenericParamKind::Const { .. } => {
2273                 // Bounds on const parameters are currently not possible.
2274                 debug_assert!(param.bounds.is_empty());
2275                 index += 1;
2276             }
2277         }
2278     }
2279
2280     // Add in the bounds that appear in the where-clause.
2281     let where_clause = &ast_generics.where_clause;
2282     for predicate in where_clause.predicates {
2283         match predicate {
2284             hir::WherePredicate::BoundPredicate(bound_pred) => {
2285                 let ty = icx.to_ty(bound_pred.bounded_ty);
2286                 let bound_vars = icx.tcx.late_bound_vars(bound_pred.bounded_ty.hir_id);
2287
2288                 // Keep the type around in a dummy predicate, in case of no bounds.
2289                 // That way, `where Ty:` is not a complete noop (see #53696) and `Ty`
2290                 // is still checked for WF.
2291                 if bound_pred.bounds.is_empty() {
2292                     if let ty::Param(_) = ty.kind() {
2293                         // This is a `where T:`, which can be in the HIR from the
2294                         // transformation that moves `?Sized` to `T`'s declaration.
2295                         // We can skip the predicate because type parameters are
2296                         // trivially WF, but also we *should*, to avoid exposing
2297                         // users who never wrote `where Type:,` themselves, to
2298                         // compiler/tooling bugs from not handling WF predicates.
2299                     } else {
2300                         let span = bound_pred.bounded_ty.span;
2301                         let re_root_empty = tcx.lifetimes.re_root_empty;
2302                         let predicate = ty::Binder::bind_with_vars(
2303                             ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(
2304                                 ty,
2305                                 re_root_empty,
2306                             )),
2307                             bound_vars,
2308                         );
2309                         predicates.insert((predicate.to_predicate(tcx), span));
2310                     }
2311                 }
2312
2313                 let mut bounds = Bounds::default();
2314                 <dyn AstConv<'_>>::add_bounds(
2315                     &icx,
2316                     ty,
2317                     bound_pred.bounds.iter(),
2318                     &mut bounds,
2319                     bound_vars,
2320                 );
2321                 predicates.extend(bounds.predicates(tcx, ty));
2322             }
2323
2324             hir::WherePredicate::RegionPredicate(region_pred) => {
2325                 let r1 = <dyn AstConv<'_>>::ast_region_to_region(&icx, &region_pred.lifetime, None);
2326                 predicates.extend(region_pred.bounds.iter().map(|bound| {
2327                     let (r2, span) = match bound {
2328                         hir::GenericBound::Outlives(lt) => {
2329                             (<dyn AstConv<'_>>::ast_region_to_region(&icx, lt, None), lt.span)
2330                         }
2331                         _ => bug!(),
2332                     };
2333                     let pred = ty::Binder::dummy(ty::PredicateKind::RegionOutlives(
2334                         ty::OutlivesPredicate(r1, r2),
2335                     ))
2336                     .to_predicate(icx.tcx);
2337
2338                     (pred, span)
2339                 }))
2340             }
2341
2342             hir::WherePredicate::EqPredicate(..) => {
2343                 // FIXME(#20041)
2344             }
2345         }
2346     }
2347
2348     if tcx.features().generic_const_exprs {
2349         predicates.extend(const_evaluatable_predicates_of(tcx, def_id.expect_local()));
2350     }
2351
2352     let mut predicates: Vec<_> = predicates.into_iter().collect();
2353
2354     // Subtle: before we store the predicates into the tcx, we
2355     // sort them so that predicates like `T: Foo<Item=U>` come
2356     // before uses of `U`.  This avoids false ambiguity errors
2357     // in trait checking. See `setup_constraining_predicates`
2358     // for details.
2359     if let Node::Item(&Item { kind: ItemKind::Impl { .. }, .. }) = node {
2360         let self_ty = tcx.type_of(def_id);
2361         let trait_ref = tcx.impl_trait_ref(def_id);
2362         cgp::setup_constraining_predicates(
2363             tcx,
2364             &mut predicates,
2365             trait_ref,
2366             &mut cgp::parameters_for_impl(self_ty, trait_ref),
2367         );
2368     }
2369
2370     let result = ty::GenericPredicates {
2371         parent: generics.parent,
2372         predicates: tcx.arena.alloc_from_iter(predicates),
2373     };
2374     debug!("explicit_predicates_of(def_id={:?}) = {:?}", def_id, result);
2375     result
2376 }
2377
2378 fn const_evaluatable_predicates_of<'tcx>(
2379     tcx: TyCtxt<'tcx>,
2380     def_id: LocalDefId,
2381 ) -> FxIndexSet<(ty::Predicate<'tcx>, Span)> {
2382     struct ConstCollector<'tcx> {
2383         tcx: TyCtxt<'tcx>,
2384         preds: FxIndexSet<(ty::Predicate<'tcx>, Span)>,
2385     }
2386
2387     impl<'tcx> intravisit::Visitor<'tcx> for ConstCollector<'tcx> {
2388         fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) {
2389             let def_id = self.tcx.hir().local_def_id(c.hir_id);
2390             let ct = ty::Const::from_anon_const(self.tcx, def_id);
2391             if let ty::ConstKind::Unevaluated(uv) = ct.val() {
2392                 assert_eq!(uv.promoted, None);
2393                 let span = self.tcx.hir().span(c.hir_id);
2394                 self.preds.insert((
2395                     ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(uv.shrink()))
2396                         .to_predicate(self.tcx),
2397                     span,
2398                 ));
2399             }
2400         }
2401
2402         fn visit_const_param_default(&mut self, _param: HirId, _ct: &'tcx hir::AnonConst) {
2403             // Do not look into const param defaults,
2404             // these get checked when they are actually instantiated.
2405             //
2406             // We do not want the following to error:
2407             //
2408             //     struct Foo<const N: usize, const M: usize = { N + 1 }>;
2409             //     struct Bar<const N: usize>(Foo<N, 3>);
2410         }
2411     }
2412
2413     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
2414     let node = tcx.hir().get(hir_id);
2415
2416     let mut collector = ConstCollector { tcx, preds: FxIndexSet::default() };
2417     if let hir::Node::Item(item) = node && let hir::ItemKind::Impl(ref impl_) = item.kind {
2418         if let Some(of_trait) = &impl_.of_trait {
2419             debug!("const_evaluatable_predicates_of({:?}): visit impl trait_ref", def_id);
2420             collector.visit_trait_ref(of_trait);
2421         }
2422
2423         debug!("const_evaluatable_predicates_of({:?}): visit_self_ty", def_id);
2424         collector.visit_ty(impl_.self_ty);
2425     }
2426
2427     if let Some(generics) = node.generics() {
2428         debug!("const_evaluatable_predicates_of({:?}): visit_generics", def_id);
2429         collector.visit_generics(generics);
2430     }
2431
2432     if let Some(fn_sig) = tcx.hir().fn_sig_by_hir_id(hir_id) {
2433         debug!("const_evaluatable_predicates_of({:?}): visit_fn_decl", def_id);
2434         collector.visit_fn_decl(fn_sig.decl);
2435     }
2436     debug!("const_evaluatable_predicates_of({:?}) = {:?}", def_id, collector.preds);
2437
2438     collector.preds
2439 }
2440
2441 fn trait_explicit_predicates_and_bounds(
2442     tcx: TyCtxt<'_>,
2443     def_id: LocalDefId,
2444 ) -> ty::GenericPredicates<'_> {
2445     assert_eq!(tcx.def_kind(def_id), DefKind::Trait);
2446     gather_explicit_predicates_of(tcx, def_id.to_def_id())
2447 }
2448
2449 fn explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2450     let def_kind = tcx.def_kind(def_id);
2451     if let DefKind::Trait = def_kind {
2452         // Remove bounds on associated types from the predicates, they will be
2453         // returned by `explicit_item_bounds`.
2454         let predicates_and_bounds = tcx.trait_explicit_predicates_and_bounds(def_id.expect_local());
2455         let trait_identity_substs = InternalSubsts::identity_for_item(tcx, def_id);
2456
2457         let is_assoc_item_ty = |ty: Ty<'_>| {
2458             // For a predicate from a where clause to become a bound on an
2459             // associated type:
2460             // * It must use the identity substs of the item.
2461             //     * Since any generic parameters on the item are not in scope,
2462             //       this means that the item is not a GAT, and its identity
2463             //       substs are the same as the trait's.
2464             // * It must be an associated type for this trait (*not* a
2465             //   supertrait).
2466             if let ty::Projection(projection) = ty.kind() {
2467                 projection.substs == trait_identity_substs
2468                     && tcx.associated_item(projection.item_def_id).container.id() == def_id
2469             } else {
2470                 false
2471             }
2472         };
2473
2474         let predicates: Vec<_> = predicates_and_bounds
2475             .predicates
2476             .iter()
2477             .copied()
2478             .filter(|(pred, _)| match pred.kind().skip_binder() {
2479                 ty::PredicateKind::Trait(tr) => !is_assoc_item_ty(tr.self_ty()),
2480                 ty::PredicateKind::Projection(proj) => {
2481                     !is_assoc_item_ty(proj.projection_ty.self_ty())
2482                 }
2483                 ty::PredicateKind::TypeOutlives(outlives) => !is_assoc_item_ty(outlives.0),
2484                 _ => true,
2485             })
2486             .collect();
2487         if predicates.len() == predicates_and_bounds.predicates.len() {
2488             predicates_and_bounds
2489         } else {
2490             ty::GenericPredicates {
2491                 parent: predicates_and_bounds.parent,
2492                 predicates: tcx.arena.alloc_slice(&predicates),
2493             }
2494         }
2495     } else {
2496         if matches!(def_kind, DefKind::AnonConst) && tcx.lazy_normalization() {
2497             let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2498             if tcx.hir().opt_const_param_default_param_hir_id(hir_id).is_some() {
2499                 // In `generics_of` we set the generics' parent to be our parent's parent which means that
2500                 // we lose out on the predicates of our actual parent if we dont return those predicates here.
2501                 // (See comment in `generics_of` for more information on why the parent shenanigans is necessary)
2502                 //
2503                 // struct Foo<T, const N: usize = { <T as Trait>::ASSOC }>(T) where T: Trait;
2504                 //        ^^^                     ^^^^^^^^^^^^^^^^^^^^^^^ the def id we are calling
2505                 //        ^^^                                             explicit_predicates_of on
2506                 //        parent item we dont have set as the
2507                 //        parent of generics returned by `generics_of`
2508                 //
2509                 // In the above code we want the anon const to have predicates in its param env for `T: Trait`
2510                 let item_def_id = tcx.hir().get_parent_item(hir_id);
2511                 // In the above code example we would be calling `explicit_predicates_of(Foo)` here
2512                 return tcx.explicit_predicates_of(item_def_id);
2513             }
2514         }
2515         gather_explicit_predicates_of(tcx, def_id)
2516     }
2517 }
2518
2519 /// Converts a specific `GenericBound` from the AST into a set of
2520 /// predicates that apply to the self type. A vector is returned
2521 /// because this can be anywhere from zero predicates (`T: ?Sized` adds no
2522 /// predicates) to one (`T: Foo`) to many (`T: Bar<X = i32>` adds `T: Bar`
2523 /// and `<T as Bar>::X == i32`).
2524 fn predicates_from_bound<'tcx>(
2525     astconv: &dyn AstConv<'tcx>,
2526     param_ty: Ty<'tcx>,
2527     bound: &'tcx hir::GenericBound<'tcx>,
2528     bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
2529 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2530     let mut bounds = Bounds::default();
2531     astconv.add_bounds(param_ty, [bound].into_iter(), &mut bounds, bound_vars);
2532     bounds.predicates(astconv.tcx(), param_ty).collect()
2533 }
2534
2535 fn compute_sig_of_foreign_fn_decl<'tcx>(
2536     tcx: TyCtxt<'tcx>,
2537     def_id: DefId,
2538     decl: &'tcx hir::FnDecl<'tcx>,
2539     abi: abi::Abi,
2540     ident: Ident,
2541 ) -> ty::PolyFnSig<'tcx> {
2542     let unsafety = if abi == abi::Abi::RustIntrinsic {
2543         intrinsic_operation_unsafety(tcx.item_name(def_id))
2544     } else {
2545         hir::Unsafety::Unsafe
2546     };
2547     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2548     let fty = <dyn AstConv<'_>>::ty_of_fn(
2549         &ItemCtxt::new(tcx, def_id),
2550         hir_id,
2551         unsafety,
2552         abi,
2553         decl,
2554         &hir::Generics::empty(),
2555         Some(ident.span),
2556         None,
2557     );
2558
2559     // Feature gate SIMD types in FFI, since I am not sure that the
2560     // ABIs are handled at all correctly. -huonw
2561     if abi != abi::Abi::RustIntrinsic
2562         && abi != abi::Abi::PlatformIntrinsic
2563         && !tcx.features().simd_ffi
2564     {
2565         let check = |ast_ty: &hir::Ty<'_>, ty: Ty<'_>| {
2566             if ty.is_simd() {
2567                 let snip = tcx
2568                     .sess
2569                     .source_map()
2570                     .span_to_snippet(ast_ty.span)
2571                     .map_or_else(|_| String::new(), |s| format!(" `{}`", s));
2572                 tcx.sess
2573                     .struct_span_err(
2574                         ast_ty.span,
2575                         &format!(
2576                             "use of SIMD type{} in FFI is highly experimental and \
2577                              may result in invalid code",
2578                             snip
2579                         ),
2580                     )
2581                     .help("add `#![feature(simd_ffi)]` to the crate attributes to enable")
2582                     .emit();
2583             }
2584         };
2585         for (input, ty) in iter::zip(decl.inputs, fty.inputs().skip_binder()) {
2586             check(input, *ty)
2587         }
2588         if let hir::FnRetTy::Return(ref ty) = decl.output {
2589             check(ty, fty.output().skip_binder())
2590         }
2591     }
2592
2593     fty
2594 }
2595
2596 fn is_foreign_item(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
2597     match tcx.hir().get_if_local(def_id) {
2598         Some(Node::ForeignItem(..)) => true,
2599         Some(_) => false,
2600         _ => bug!("is_foreign_item applied to non-local def-id {:?}", def_id),
2601     }
2602 }
2603
2604 fn generator_kind(tcx: TyCtxt<'_>, def_id: DefId) -> Option<hir::GeneratorKind> {
2605     match tcx.hir().get_if_local(def_id) {
2606         Some(Node::Expr(&rustc_hir::Expr {
2607             kind: rustc_hir::ExprKind::Closure(_, _, body_id, _, _),
2608             ..
2609         })) => tcx.hir().body(body_id).generator_kind(),
2610         Some(_) => None,
2611         _ => bug!("generator_kind applied to non-local def-id {:?}", def_id),
2612     }
2613 }
2614
2615 fn from_target_feature(
2616     tcx: TyCtxt<'_>,
2617     id: DefId,
2618     attr: &ast::Attribute,
2619     supported_target_features: &FxHashMap<String, Option<Symbol>>,
2620     target_features: &mut Vec<Symbol>,
2621 ) {
2622     let Some(list) = attr.meta_item_list() else { return };
2623     let bad_item = |span| {
2624         let msg = "malformed `target_feature` attribute input";
2625         let code = "enable = \"..\"".to_owned();
2626         tcx.sess
2627             .struct_span_err(span, msg)
2628             .span_suggestion(span, "must be of the form", code, Applicability::HasPlaceholders)
2629             .emit();
2630     };
2631     let rust_features = tcx.features();
2632     for item in list {
2633         // Only `enable = ...` is accepted in the meta-item list.
2634         if !item.has_name(sym::enable) {
2635             bad_item(item.span());
2636             continue;
2637         }
2638
2639         // Must be of the form `enable = "..."` (a string).
2640         let Some(value) = item.value_str() else {
2641             bad_item(item.span());
2642             continue;
2643         };
2644
2645         // We allow comma separation to enable multiple features.
2646         target_features.extend(value.as_str().split(',').filter_map(|feature| {
2647             let Some(feature_gate) = supported_target_features.get(feature) else {
2648                 let msg =
2649                     format!("the feature named `{}` is not valid for this target", feature);
2650                 let mut err = tcx.sess.struct_span_err(item.span(), &msg);
2651                 err.span_label(
2652                     item.span(),
2653                     format!("`{}` is not valid for this target", feature),
2654                 );
2655                 if let Some(stripped) = feature.strip_prefix('+') {
2656                     let valid = supported_target_features.contains_key(stripped);
2657                     if valid {
2658                         err.help("consider removing the leading `+` in the feature name");
2659                     }
2660                 }
2661                 err.emit();
2662                 return None;
2663             };
2664
2665             // Only allow features whose feature gates have been enabled.
2666             let allowed = match feature_gate.as_ref().copied() {
2667                 Some(sym::arm_target_feature) => rust_features.arm_target_feature,
2668                 Some(sym::hexagon_target_feature) => rust_features.hexagon_target_feature,
2669                 Some(sym::powerpc_target_feature) => rust_features.powerpc_target_feature,
2670                 Some(sym::mips_target_feature) => rust_features.mips_target_feature,
2671                 Some(sym::riscv_target_feature) => rust_features.riscv_target_feature,
2672                 Some(sym::avx512_target_feature) => rust_features.avx512_target_feature,
2673                 Some(sym::sse4a_target_feature) => rust_features.sse4a_target_feature,
2674                 Some(sym::tbm_target_feature) => rust_features.tbm_target_feature,
2675                 Some(sym::wasm_target_feature) => rust_features.wasm_target_feature,
2676                 Some(sym::cmpxchg16b_target_feature) => rust_features.cmpxchg16b_target_feature,
2677                 Some(sym::movbe_target_feature) => rust_features.movbe_target_feature,
2678                 Some(sym::rtm_target_feature) => rust_features.rtm_target_feature,
2679                 Some(sym::f16c_target_feature) => rust_features.f16c_target_feature,
2680                 Some(sym::ermsb_target_feature) => rust_features.ermsb_target_feature,
2681                 Some(sym::bpf_target_feature) => rust_features.bpf_target_feature,
2682                 Some(sym::aarch64_ver_target_feature) => rust_features.aarch64_ver_target_feature,
2683                 Some(name) => bug!("unknown target feature gate {}", name),
2684                 None => true,
2685             };
2686             if !allowed && id.is_local() {
2687                 feature_err(
2688                     &tcx.sess.parse_sess,
2689                     feature_gate.unwrap(),
2690                     item.span(),
2691                     &format!("the target feature `{}` is currently unstable", feature),
2692                 )
2693                 .emit();
2694             }
2695             Some(Symbol::intern(feature))
2696         }));
2697     }
2698 }
2699
2700 fn linkage_by_name(tcx: TyCtxt<'_>, def_id: DefId, name: &str) -> Linkage {
2701     use rustc_middle::mir::mono::Linkage::*;
2702
2703     // Use the names from src/llvm/docs/LangRef.rst here. Most types are only
2704     // applicable to variable declarations and may not really make sense for
2705     // Rust code in the first place but allow them anyway and trust that the
2706     // user knows what s/he's doing. Who knows, unanticipated use cases may pop
2707     // up in the future.
2708     //
2709     // ghost, dllimport, dllexport and linkonce_odr_autohide are not supported
2710     // and don't have to be, LLVM treats them as no-ops.
2711     match name {
2712         "appending" => Appending,
2713         "available_externally" => AvailableExternally,
2714         "common" => Common,
2715         "extern_weak" => ExternalWeak,
2716         "external" => External,
2717         "internal" => Internal,
2718         "linkonce" => LinkOnceAny,
2719         "linkonce_odr" => LinkOnceODR,
2720         "private" => Private,
2721         "weak" => WeakAny,
2722         "weak_odr" => WeakODR,
2723         _ => {
2724             let span = tcx.hir().span_if_local(def_id);
2725             if let Some(span) = span {
2726                 tcx.sess.span_fatal(span, "invalid linkage specified")
2727             } else {
2728                 tcx.sess.fatal(&format!("invalid linkage specified: {}", name))
2729             }
2730         }
2731     }
2732 }
2733
2734 fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
2735     let attrs = tcx.get_attrs(id);
2736
2737     let mut codegen_fn_attrs = CodegenFnAttrs::new();
2738     if tcx.should_inherit_track_caller(id) {
2739         codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
2740     }
2741
2742     // With -Z panic-in-drop=abort, drop_in_place never unwinds.
2743     if tcx.sess.opts.debugging_opts.panic_in_drop == PanicStrategy::Abort {
2744         if Some(id) == tcx.lang_items().drop_in_place_fn() {
2745             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
2746         }
2747     }
2748
2749     // The panic_no_unwind function called by TerminatorKind::Abort will never
2750     // unwind. If the panic handler that it invokes unwind then it will simply
2751     // call the panic handler again.
2752     if Some(id) == tcx.lang_items().panic_no_unwind() {
2753         codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
2754     }
2755
2756     let supported_target_features = tcx.supported_target_features(LOCAL_CRATE);
2757
2758     let mut inline_span = None;
2759     let mut link_ordinal_span = None;
2760     let mut no_sanitize_span = None;
2761     for attr in attrs.iter() {
2762         if attr.has_name(sym::cold) {
2763             codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
2764         } else if attr.has_name(sym::rustc_allocator) {
2765             codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR;
2766         } else if attr.has_name(sym::ffi_returns_twice) {
2767             if tcx.is_foreign_item(id) {
2768                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_RETURNS_TWICE;
2769             } else {
2770                 // `#[ffi_returns_twice]` is only allowed `extern fn`s.
2771                 struct_span_err!(
2772                     tcx.sess,
2773                     attr.span,
2774                     E0724,
2775                     "`#[ffi_returns_twice]` may only be used on foreign functions"
2776                 )
2777                 .emit();
2778             }
2779         } else if attr.has_name(sym::ffi_pure) {
2780             if tcx.is_foreign_item(id) {
2781                 if attrs.iter().any(|a| a.has_name(sym::ffi_const)) {
2782                     // `#[ffi_const]` functions cannot be `#[ffi_pure]`
2783                     struct_span_err!(
2784                         tcx.sess,
2785                         attr.span,
2786                         E0757,
2787                         "`#[ffi_const]` function cannot be `#[ffi_pure]`"
2788                     )
2789                     .emit();
2790                 } else {
2791                     codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_PURE;
2792                 }
2793             } else {
2794                 // `#[ffi_pure]` is only allowed on foreign functions
2795                 struct_span_err!(
2796                     tcx.sess,
2797                     attr.span,
2798                     E0755,
2799                     "`#[ffi_pure]` may only be used on foreign functions"
2800                 )
2801                 .emit();
2802             }
2803         } else if attr.has_name(sym::ffi_const) {
2804             if tcx.is_foreign_item(id) {
2805                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_CONST;
2806             } else {
2807                 // `#[ffi_const]` is only allowed on foreign functions
2808                 struct_span_err!(
2809                     tcx.sess,
2810                     attr.span,
2811                     E0756,
2812                     "`#[ffi_const]` may only be used on foreign functions"
2813                 )
2814                 .emit();
2815             }
2816         } else if attr.has_name(sym::rustc_allocator_nounwind) {
2817             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
2818         } else if attr.has_name(sym::naked) {
2819             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED;
2820         } else if attr.has_name(sym::no_mangle) {
2821             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
2822         } else if attr.has_name(sym::no_coverage) {
2823             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_COVERAGE;
2824         } else if attr.has_name(sym::rustc_std_internal_symbol) {
2825             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
2826         } else if attr.has_name(sym::used) {
2827             let inner = attr.meta_item_list();
2828             match inner.as_deref() {
2829                 Some([item]) if item.has_name(sym::linker) => {
2830                     if !tcx.features().used_with_arg {
2831                         feature_err(
2832                             &tcx.sess.parse_sess,
2833                             sym::used_with_arg,
2834                             attr.span,
2835                             "`#[used(linker)]` is currently unstable",
2836                         )
2837                         .emit();
2838                     }
2839                     codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED_LINKER;
2840                 }
2841                 Some([item]) if item.has_name(sym::compiler) => {
2842                     if !tcx.features().used_with_arg {
2843                         feature_err(
2844                             &tcx.sess.parse_sess,
2845                             sym::used_with_arg,
2846                             attr.span,
2847                             "`#[used(compiler)]` is currently unstable",
2848                         )
2849                         .emit();
2850                     }
2851                     codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED;
2852                 }
2853                 Some(_) => {
2854                     tcx.sess
2855                         .struct_span_err(
2856                             attr.span,
2857                             "expected `used`, `used(compiler)` or `used(linker)`",
2858                         )
2859                         .emit();
2860                 }
2861                 None => codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED,
2862             }
2863         } else if attr.has_name(sym::cmse_nonsecure_entry) {
2864             if !matches!(tcx.fn_sig(id).abi(), abi::Abi::C { .. }) {
2865                 struct_span_err!(
2866                     tcx.sess,
2867                     attr.span,
2868                     E0776,
2869                     "`#[cmse_nonsecure_entry]` requires C ABI"
2870                 )
2871                 .emit();
2872             }
2873             if !tcx.sess.target.llvm_target.contains("thumbv8m") {
2874                 struct_span_err!(tcx.sess, attr.span, E0775, "`#[cmse_nonsecure_entry]` is only valid for targets with the TrustZone-M extension")
2875                     .emit();
2876             }
2877             codegen_fn_attrs.flags |= CodegenFnAttrFlags::CMSE_NONSECURE_ENTRY;
2878         } else if attr.has_name(sym::thread_local) {
2879             codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL;
2880         } else if attr.has_name(sym::track_caller) {
2881             if !tcx.is_closure(id) && tcx.fn_sig(id).abi() != abi::Abi::Rust {
2882                 struct_span_err!(tcx.sess, attr.span, E0737, "`#[track_caller]` requires Rust ABI")
2883                     .emit();
2884             }
2885             if tcx.is_closure(id) && !tcx.features().closure_track_caller {
2886                 feature_err(
2887                     &tcx.sess.parse_sess,
2888                     sym::closure_track_caller,
2889                     attr.span,
2890                     "`#[track_caller]` on closures is currently unstable",
2891                 )
2892                 .emit();
2893             }
2894             codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
2895         } else if attr.has_name(sym::export_name) {
2896             if let Some(s) = attr.value_str() {
2897                 if s.as_str().contains('\0') {
2898                     // `#[export_name = ...]` will be converted to a null-terminated string,
2899                     // so it may not contain any null characters.
2900                     struct_span_err!(
2901                         tcx.sess,
2902                         attr.span,
2903                         E0648,
2904                         "`export_name` may not contain null characters"
2905                     )
2906                     .emit();
2907                 }
2908                 codegen_fn_attrs.export_name = Some(s);
2909             }
2910         } else if attr.has_name(sym::target_feature) {
2911             if !tcx.is_closure(id) && tcx.fn_sig(id).unsafety() == hir::Unsafety::Normal {
2912                 if tcx.sess.target.is_like_wasm || tcx.sess.opts.actually_rustdoc {
2913                     // The `#[target_feature]` attribute is allowed on
2914                     // WebAssembly targets on all functions, including safe
2915                     // ones. Other targets require that `#[target_feature]` is
2916                     // only applied to unsafe functions (pending the
2917                     // `target_feature_11` feature) because on most targets
2918                     // execution of instructions that are not supported is
2919                     // considered undefined behavior. For WebAssembly which is a
2920                     // 100% safe target at execution time it's not possible to
2921                     // execute undefined instructions, and even if a future
2922                     // feature was added in some form for this it would be a
2923                     // deterministic trap. There is no undefined behavior when
2924                     // executing WebAssembly so `#[target_feature]` is allowed
2925                     // on safe functions (but again, only for WebAssembly)
2926                     //
2927                     // Note that this is also allowed if `actually_rustdoc` so
2928                     // if a target is documenting some wasm-specific code then
2929                     // it's not spuriously denied.
2930                 } else if !tcx.features().target_feature_11 {
2931                     let mut err = feature_err(
2932                         &tcx.sess.parse_sess,
2933                         sym::target_feature_11,
2934                         attr.span,
2935                         "`#[target_feature(..)]` can only be applied to `unsafe` functions",
2936                     );
2937                     err.span_label(tcx.def_span(id), "not an `unsafe` function");
2938                     err.emit();
2939                 } else if let Some(local_id) = id.as_local() {
2940                     check_target_feature_trait_unsafe(tcx, local_id, attr.span);
2941                 }
2942             }
2943             from_target_feature(
2944                 tcx,
2945                 id,
2946                 attr,
2947                 supported_target_features,
2948                 &mut codegen_fn_attrs.target_features,
2949             );
2950         } else if attr.has_name(sym::linkage) {
2951             if let Some(val) = attr.value_str() {
2952                 codegen_fn_attrs.linkage = Some(linkage_by_name(tcx, id, val.as_str()));
2953             }
2954         } else if attr.has_name(sym::link_section) {
2955             if let Some(val) = attr.value_str() {
2956                 if val.as_str().bytes().any(|b| b == 0) {
2957                     let msg = format!(
2958                         "illegal null byte in link_section \
2959                          value: `{}`",
2960                         &val
2961                     );
2962                     tcx.sess.span_err(attr.span, &msg);
2963                 } else {
2964                     codegen_fn_attrs.link_section = Some(val);
2965                 }
2966             }
2967         } else if attr.has_name(sym::link_name) {
2968             codegen_fn_attrs.link_name = attr.value_str();
2969         } else if attr.has_name(sym::link_ordinal) {
2970             link_ordinal_span = Some(attr.span);
2971             if let ordinal @ Some(_) = check_link_ordinal(tcx, attr) {
2972                 codegen_fn_attrs.link_ordinal = ordinal;
2973             }
2974         } else if attr.has_name(sym::no_sanitize) {
2975             no_sanitize_span = Some(attr.span);
2976             if let Some(list) = attr.meta_item_list() {
2977                 for item in list.iter() {
2978                     if item.has_name(sym::address) {
2979                         codegen_fn_attrs.no_sanitize |= SanitizerSet::ADDRESS;
2980                     } else if item.has_name(sym::cfi) {
2981                         codegen_fn_attrs.no_sanitize |= SanitizerSet::CFI;
2982                     } else if item.has_name(sym::memory) {
2983                         codegen_fn_attrs.no_sanitize |= SanitizerSet::MEMORY;
2984                     } else if item.has_name(sym::memtag) {
2985                         codegen_fn_attrs.no_sanitize |= SanitizerSet::MEMTAG;
2986                     } else if item.has_name(sym::thread) {
2987                         codegen_fn_attrs.no_sanitize |= SanitizerSet::THREAD;
2988                     } else if item.has_name(sym::hwaddress) {
2989                         codegen_fn_attrs.no_sanitize |= SanitizerSet::HWADDRESS;
2990                     } else {
2991                         tcx.sess
2992                             .struct_span_err(item.span(), "invalid argument for `no_sanitize`")
2993                             .note("expected one of: `address`, `cfi`, `hwaddress`, `memory`, `memtag`, or `thread`")
2994                             .emit();
2995                     }
2996                 }
2997             }
2998         } else if attr.has_name(sym::instruction_set) {
2999             codegen_fn_attrs.instruction_set = match attr.meta_kind() {
3000                 Some(MetaItemKind::List(ref items)) => match items.as_slice() {
3001                     [NestedMetaItem::MetaItem(set)] => {
3002                         let segments =
3003                             set.path.segments.iter().map(|x| x.ident.name).collect::<Vec<_>>();
3004                         match segments.as_slice() {
3005                             [sym::arm, sym::a32] | [sym::arm, sym::t32] => {
3006                                 if !tcx.sess.target.has_thumb_interworking {
3007                                     struct_span_err!(
3008                                         tcx.sess.diagnostic(),
3009                                         attr.span,
3010                                         E0779,
3011                                         "target does not support `#[instruction_set]`"
3012                                     )
3013                                     .emit();
3014                                     None
3015                                 } else if segments[1] == sym::a32 {
3016                                     Some(InstructionSetAttr::ArmA32)
3017                                 } else if segments[1] == sym::t32 {
3018                                     Some(InstructionSetAttr::ArmT32)
3019                                 } else {
3020                                     unreachable!()
3021                                 }
3022                             }
3023                             _ => {
3024                                 struct_span_err!(
3025                                     tcx.sess.diagnostic(),
3026                                     attr.span,
3027                                     E0779,
3028                                     "invalid instruction set specified",
3029                                 )
3030                                 .emit();
3031                                 None
3032                             }
3033                         }
3034                     }
3035                     [] => {
3036                         struct_span_err!(
3037                             tcx.sess.diagnostic(),
3038                             attr.span,
3039                             E0778,
3040                             "`#[instruction_set]` requires an argument"
3041                         )
3042                         .emit();
3043                         None
3044                     }
3045                     _ => {
3046                         struct_span_err!(
3047                             tcx.sess.diagnostic(),
3048                             attr.span,
3049                             E0779,
3050                             "cannot specify more than one instruction set"
3051                         )
3052                         .emit();
3053                         None
3054                     }
3055                 },
3056                 _ => {
3057                     struct_span_err!(
3058                         tcx.sess.diagnostic(),
3059                         attr.span,
3060                         E0778,
3061                         "must specify an instruction set"
3062                     )
3063                     .emit();
3064                     None
3065                 }
3066             };
3067         } else if attr.has_name(sym::repr) {
3068             codegen_fn_attrs.alignment = match attr.meta_item_list() {
3069                 Some(items) => match items.as_slice() {
3070                     [item] => match item.name_value_literal() {
3071                         Some((sym::align, literal)) => {
3072                             let alignment = rustc_attr::parse_alignment(&literal.kind);
3073
3074                             match alignment {
3075                                 Ok(align) => Some(align),
3076                                 Err(msg) => {
3077                                     struct_span_err!(
3078                                         tcx.sess.diagnostic(),
3079                                         attr.span,
3080                                         E0589,
3081                                         "invalid `repr(align)` attribute: {}",
3082                                         msg
3083                                     )
3084                                     .emit();
3085
3086                                     None
3087                                 }
3088                             }
3089                         }
3090                         _ => None,
3091                     },
3092                     [] => None,
3093                     _ => None,
3094                 },
3095                 None => None,
3096             };
3097         }
3098     }
3099
3100     codegen_fn_attrs.inline = attrs.iter().fold(InlineAttr::None, |ia, attr| {
3101         if !attr.has_name(sym::inline) {
3102             return ia;
3103         }
3104         match attr.meta_kind() {
3105             Some(MetaItemKind::Word) => InlineAttr::Hint,
3106             Some(MetaItemKind::List(ref items)) => {
3107                 inline_span = Some(attr.span);
3108                 if items.len() != 1 {
3109                     struct_span_err!(
3110                         tcx.sess.diagnostic(),
3111                         attr.span,
3112                         E0534,
3113                         "expected one argument"
3114                     )
3115                     .emit();
3116                     InlineAttr::None
3117                 } else if list_contains_name(&items, sym::always) {
3118                     InlineAttr::Always
3119                 } else if list_contains_name(&items, sym::never) {
3120                     InlineAttr::Never
3121                 } else {
3122                     struct_span_err!(
3123                         tcx.sess.diagnostic(),
3124                         items[0].span(),
3125                         E0535,
3126                         "invalid argument"
3127                     )
3128                     .emit();
3129
3130                     InlineAttr::None
3131                 }
3132             }
3133             Some(MetaItemKind::NameValue(_)) => ia,
3134             None => ia,
3135         }
3136     });
3137
3138     codegen_fn_attrs.optimize = attrs.iter().fold(OptimizeAttr::None, |ia, attr| {
3139         if !attr.has_name(sym::optimize) {
3140             return ia;
3141         }
3142         let err = |sp, s| struct_span_err!(tcx.sess.diagnostic(), sp, E0722, "{}", s).emit();
3143         match attr.meta_kind() {
3144             Some(MetaItemKind::Word) => {
3145                 err(attr.span, "expected one argument");
3146                 ia
3147             }
3148             Some(MetaItemKind::List(ref items)) => {
3149                 inline_span = Some(attr.span);
3150                 if items.len() != 1 {
3151                     err(attr.span, "expected one argument");
3152                     OptimizeAttr::None
3153                 } else if list_contains_name(&items, sym::size) {
3154                     OptimizeAttr::Size
3155                 } else if list_contains_name(&items, sym::speed) {
3156                     OptimizeAttr::Speed
3157                 } else {
3158                     err(items[0].span(), "invalid argument");
3159                     OptimizeAttr::None
3160                 }
3161             }
3162             Some(MetaItemKind::NameValue(_)) => ia,
3163             None => ia,
3164         }
3165     });
3166
3167     // #73631: closures inherit `#[target_feature]` annotations
3168     if tcx.features().target_feature_11 && tcx.is_closure(id) {
3169         let owner_id = tcx.parent(id).expect("closure should have a parent");
3170         codegen_fn_attrs
3171             .target_features
3172             .extend(tcx.codegen_fn_attrs(owner_id).target_features.iter().copied())
3173     }
3174
3175     // If a function uses #[target_feature] it can't be inlined into general
3176     // purpose functions as they wouldn't have the right target features
3177     // enabled. For that reason we also forbid #[inline(always)] as it can't be
3178     // respected.
3179     if !codegen_fn_attrs.target_features.is_empty() {
3180         if codegen_fn_attrs.inline == InlineAttr::Always {
3181             if let Some(span) = inline_span {
3182                 tcx.sess.span_err(
3183                     span,
3184                     "cannot use `#[inline(always)]` with \
3185                      `#[target_feature]`",
3186                 );
3187             }
3188         }
3189     }
3190
3191     if !codegen_fn_attrs.no_sanitize.is_empty() {
3192         if codegen_fn_attrs.inline == InlineAttr::Always {
3193             if let (Some(no_sanitize_span), Some(inline_span)) = (no_sanitize_span, inline_span) {
3194                 let hir_id = tcx.hir().local_def_id_to_hir_id(id.expect_local());
3195                 tcx.struct_span_lint_hir(
3196                     lint::builtin::INLINE_NO_SANITIZE,
3197                     hir_id,
3198                     no_sanitize_span,
3199                     |lint| {
3200                         lint.build("`no_sanitize` will have no effect after inlining")
3201                             .span_note(inline_span, "inlining requested here")
3202                             .emit();
3203                     },
3204                 )
3205             }
3206         }
3207     }
3208
3209     // Weak lang items have the same semantics as "std internal" symbols in the
3210     // sense that they're preserved through all our LTO passes and only
3211     // strippable by the linker.
3212     //
3213     // Additionally weak lang items have predetermined symbol names.
3214     if tcx.is_weak_lang_item(id) {
3215         codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
3216     }
3217     if let Some(name) = weak_lang_items::link_name(attrs) {
3218         codegen_fn_attrs.export_name = Some(name);
3219         codegen_fn_attrs.link_name = Some(name);
3220     }
3221     check_link_name_xor_ordinal(tcx, &codegen_fn_attrs, link_ordinal_span);
3222
3223     // Internal symbols to the standard library all have no_mangle semantics in
3224     // that they have defined symbol names present in the function name. This
3225     // also applies to weak symbols where they all have known symbol names.
3226     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
3227         codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
3228     }
3229
3230     // Any linkage to LLVM intrinsics for now forcibly marks them all as never
3231     // unwinds since LLVM sometimes can't handle codegen which `invoke`s
3232     // intrinsic functions.
3233     if let Some(name) = &codegen_fn_attrs.link_name {
3234         if name.as_str().starts_with("llvm.") {
3235             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
3236         }
3237     }
3238
3239     codegen_fn_attrs
3240 }
3241
3242 /// Computes the set of target features used in a function for the purposes of
3243 /// inline assembly.
3244 fn asm_target_features<'tcx>(tcx: TyCtxt<'tcx>, id: DefId) -> &'tcx FxHashSet<Symbol> {
3245     let mut target_features = tcx.sess.target_features.clone();
3246     let attrs = tcx.codegen_fn_attrs(id);
3247     target_features.extend(&attrs.target_features);
3248     match attrs.instruction_set {
3249         None => {}
3250         Some(InstructionSetAttr::ArmA32) => {
3251             target_features.remove(&sym::thumb_mode);
3252         }
3253         Some(InstructionSetAttr::ArmT32) => {
3254             target_features.insert(sym::thumb_mode);
3255         }
3256     }
3257     tcx.arena.alloc(target_features)
3258 }
3259
3260 /// Checks if the provided DefId is a method in a trait impl for a trait which has track_caller
3261 /// applied to the method prototype.
3262 fn should_inherit_track_caller(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
3263     if let Some(impl_item) = tcx.opt_associated_item(def_id)
3264         && let ty::AssocItemContainer::ImplContainer(_) = impl_item.container
3265         && let Some(trait_item) = impl_item.trait_item_def_id
3266     {
3267         return tcx
3268             .codegen_fn_attrs(trait_item)
3269             .flags
3270             .intersects(CodegenFnAttrFlags::TRACK_CALLER);
3271     }
3272
3273     false
3274 }
3275
3276 fn check_link_ordinal(tcx: TyCtxt<'_>, attr: &ast::Attribute) -> Option<u16> {
3277     use rustc_ast::{Lit, LitIntType, LitKind};
3278     let meta_item_list = attr.meta_item_list();
3279     let meta_item_list: Option<&[ast::NestedMetaItem]> = meta_item_list.as_ref().map(Vec::as_ref);
3280     let sole_meta_list = match meta_item_list {
3281         Some([item]) => item.literal(),
3282         Some(_) => {
3283             tcx.sess
3284                 .struct_span_err(attr.span, "incorrect number of arguments to `#[link_ordinal]`")
3285                 .note("the attribute requires exactly one argument")
3286                 .emit();
3287             return None;
3288         }
3289         _ => None,
3290     };
3291     if let Some(Lit { kind: LitKind::Int(ordinal, LitIntType::Unsuffixed), .. }) = sole_meta_list {
3292         // According to the table at https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#import-header,
3293         // the ordinal must fit into 16 bits.  Similarly, the Ordinal field in COFFShortExport (defined
3294         // in llvm/include/llvm/Object/COFFImportFile.h), which we use to communicate import information
3295         // to LLVM for `#[link(kind = "raw-dylib"_])`, is also defined to be uint16_t.
3296         //
3297         // FIXME: should we allow an ordinal of 0?  The MSVC toolchain has inconsistent support for this:
3298         // both LINK.EXE and LIB.EXE signal errors and abort when given a .DEF file that specifies
3299         // a zero ordinal.  However, llvm-dlltool is perfectly happy to generate an import library
3300         // for such a .DEF file, and MSVC's LINK.EXE is also perfectly happy to consume an import
3301         // library produced by LLVM with an ordinal of 0, and it generates an .EXE.  (I don't know yet
3302         // if the resulting EXE runs, as I haven't yet built the necessary DLL -- see earlier comment
3303         // about LINK.EXE failing.)
3304         if *ordinal <= u16::MAX as u128 {
3305             Some(*ordinal as u16)
3306         } else {
3307             let msg = format!("ordinal value in `link_ordinal` is too large: `{}`", &ordinal);
3308             tcx.sess
3309                 .struct_span_err(attr.span, &msg)
3310                 .note("the value may not exceed `u16::MAX`")
3311                 .emit();
3312             None
3313         }
3314     } else {
3315         tcx.sess
3316             .struct_span_err(attr.span, "illegal ordinal format in `link_ordinal`")
3317             .note("an unsuffixed integer value, e.g., `1`, is expected")
3318             .emit();
3319         None
3320     }
3321 }
3322
3323 fn check_link_name_xor_ordinal(
3324     tcx: TyCtxt<'_>,
3325     codegen_fn_attrs: &CodegenFnAttrs,
3326     inline_span: Option<Span>,
3327 ) {
3328     if codegen_fn_attrs.link_name.is_none() || codegen_fn_attrs.link_ordinal.is_none() {
3329         return;
3330     }
3331     let msg = "cannot use `#[link_name]` with `#[link_ordinal]`";
3332     if let Some(span) = inline_span {
3333         tcx.sess.span_err(span, msg);
3334     } else {
3335         tcx.sess.err(msg);
3336     }
3337 }
3338
3339 /// Checks the function annotated with `#[target_feature]` is not a safe
3340 /// trait method implementation, reporting an error if it is.
3341 fn check_target_feature_trait_unsafe(tcx: TyCtxt<'_>, id: LocalDefId, attr_span: Span) {
3342     let hir_id = tcx.hir().local_def_id_to_hir_id(id);
3343     let node = tcx.hir().get(hir_id);
3344     if let Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }) = node {
3345         let parent_id = tcx.hir().get_parent_item(hir_id);
3346         let parent_item = tcx.hir().expect_item(parent_id);
3347         if let hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) = parent_item.kind {
3348             tcx.sess
3349                 .struct_span_err(
3350                     attr_span,
3351                     "`#[target_feature(..)]` cannot be applied to safe trait method",
3352                 )
3353                 .span_label(attr_span, "cannot be applied to safe trait method")
3354                 .span_label(tcx.def_span(id), "not an `unsafe` function")
3355                 .emit();
3356         }
3357     }
3358 }