compiler/rustc_typeck/src/collect.rs

   1 //! "Collection" is the process of determining the type and other external
   2 //! details of each item in Rust. Collection is specifically concerned
   3 //! with *inter-procedural* things -- for example, for a function
   4 //! definition, collection will figure out the type and signature of the
   5 //! function, but it will not visit the *body* of the function in any way,
   6 //! nor examine type annotations on local variables (that's the job of
   7 //! type *checking*).
   8 //!
   9 //! Collecting is ultimately defined by a bundle of queries that
  10 //! inquire after various facts about the items in the crate (e.g.,
  11 //! `type_of`, `generics_of`, `predicates_of`, etc). See the `provide` function
  12 //! for the full set.
  13 //!
  14 //! At present, however, we do run collection across all items in the
  15 //! crate as a kind of pass. This should eventually be factored away.
  16
  17 use crate::astconv::AstConv;
  18 use crate::bounds::Bounds;
  19 use crate::check::intrinsic::intrinsic_operation_unsafety;
  20 use crate::constrained_generic_params as cgp;
  21 use crate::errors;
  22 use crate::middle::resolve_lifetime as rl;
  23 use rustc_ast as ast;
  24 use rustc_ast::{MetaItemKind, NestedMetaItem};
  25 use rustc_attr::{list_contains_name, InlineAttr, InstructionSetAttr, OptimizeAttr};
  26 use rustc_data_structures::captures::Captures;
  27 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
  28 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed, StashKey};
  29 use rustc_hir as hir;
  30 use rustc_hir::def::{CtorKind, DefKind};
  31 use rustc_hir::def_id::{DefId, LocalDefId, LOCAL_CRATE};
  32 use rustc_hir::intravisit::{self, Visitor};
  33 use rustc_hir::weak_lang_items;
  34 use rustc_hir::{GenericParamKind, HirId, Node};
  35 use rustc_middle::hir::nested_filter;
  36 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
  37 use rustc_middle::mir::mono::Linkage;
  38 use rustc_middle::ty::query::Providers;
  39 use rustc_middle::ty::subst::InternalSubsts;
  40 use rustc_middle::ty::util::Discr;
  41 use rustc_middle::ty::util::IntTypeExt;
  42 use rustc_middle::ty::{self, AdtKind, Const, DefIdTree, IsSuggestable, Ty, TyCtxt};
  43 use rustc_middle::ty::{ReprOptions, ToPredicate};
  44 use rustc_session::lint;
  45 use rustc_session::parse::feature_err;
  46 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  47 use rustc_span::{Span, DUMMY_SP};
  48 use rustc_target::spec::{abi, SanitizerSet};
  49 use rustc_trait_selection::traits::error_reporting::suggestions::NextTypeParamName;
  50 use std::iter;
  51
  52 mod item_bounds;
  53 mod type_of;
  54
  55 #[derive(Debug)]
  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(module_def_id, &mut CollectItemTypesVisitor { tcx });
  63 }
  64
  65 pub fn provide(providers: &mut Providers) {
  66     *providers = Providers {
  67         opt_const_param_of: type_of::opt_const_param_of,
  68         type_of: type_of::type_of,
  69         item_bounds: item_bounds::item_bounds,
  70         explicit_item_bounds: item_bounds::explicit_item_bounds,
  71         generics_of,
  72         predicates_of,
  73         predicates_defined_on,
  74         explicit_predicates_of,
  75         super_predicates_of,
  76         super_predicates_that_define_assoc_type,
  77         trait_explicit_predicates_and_bounds,
  78         type_param_predicates,
  79         trait_def,
  80         adt_def,
  81         fn_sig,
  82         impl_trait_ref,
  83         impl_polarity,
  84         is_foreign_item,
  85         generator_kind,
  86         codegen_fn_attrs,
  87         asm_target_features,
  88         collect_mod_item_types,
  89         should_inherit_track_caller,
  90         ..*providers
  91     };
  92 }
  93
  94 ///////////////////////////////////////////////////////////////////////////
  95
  96 /// Context specific to some particular item. This is what implements
  97 /// [`AstConv`].
  98 ///
  99 /// # `ItemCtxt` vs `FnCtxt`
 100 ///
 101 /// `ItemCtxt` is primarily used to type-check item signatures and lower them
 102 /// from HIR to their [`ty::Ty`] representation, which is exposed using [`AstConv`].
 103 /// It's also used for the bodies of items like structs where the body (the fields)
 104 /// are just signatures.
 105 ///
 106 /// This is in contrast to [`FnCtxt`], which is used to type-check bodies of
 107 /// functions, closures, and `const`s -- anywhere that expressions and statements show up.
 108 ///
 109 /// An important thing to note is that `ItemCtxt` does no inference -- it has no [`InferCtxt`] --
 110 /// while `FnCtxt` does do inference.
 111 ///
 112 /// [`FnCtxt`]: crate::check::FnCtxt
 113 /// [`InferCtxt`]: rustc_infer::infer::InferCtxt
 114 ///
 115 /// # Trait predicates
 116 ///
 117 /// `ItemCtxt` has information about the predicates that are defined
 118 /// on the trait. Unfortunately, this predicate information is
 119 /// available in various different forms at various points in the
 120 /// process. So we can't just store a pointer to e.g., the AST or the
 121 /// parsed ty form, we have to be more flexible. To this end, the
 122 /// `ItemCtxt` is parameterized by a `DefId` that it uses to satisfy
 123 /// `get_type_parameter_bounds` requests, drawing the information from
 124 /// the AST (`hir::Generics`), recursively.
 125 pub struct ItemCtxt<'tcx> {
 126     tcx: TyCtxt<'tcx>,
 127     item_def_id: DefId,
 128 }
 129
 130 ///////////////////////////////////////////////////////////////////////////
 131
 132 #[derive(Default)]
 133 pub(crate) struct HirPlaceholderCollector(pub(crate) Vec<Span>);
 134
 135 impl<'v> Visitor<'v> for HirPlaceholderCollector {
 136     fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
 137         if let hir::TyKind::Infer = t.kind {
 138             self.0.push(t.span);
 139         }
 140         intravisit::walk_ty(self, t)
 141     }
 142     fn visit_generic_arg(&mut self, generic_arg: &'v hir::GenericArg<'v>) {
 143         match generic_arg {
 144             hir::GenericArg::Infer(inf) => {
 145                 self.0.push(inf.span);
 146                 intravisit::walk_inf(self, inf);
 147             }
 148             hir::GenericArg::Type(t) => self.visit_ty(t),
 149             _ => {}
 150         }
 151     }
 152     fn visit_array_length(&mut self, length: &'v hir::ArrayLen) {
 153         if let &hir::ArrayLen::Infer(_, span) = length {
 154             self.0.push(span);
 155         }
 156         intravisit::walk_array_len(self, length)
 157     }
 158 }
 159
 160 struct CollectItemTypesVisitor<'tcx> {
 161     tcx: TyCtxt<'tcx>,
 162 }
 163
 164 /// If there are any placeholder types (`_`), emit an error explaining that this is not allowed
 165 /// and suggest adding type parameters in the appropriate place, taking into consideration any and
 166 /// all already existing generic type parameters to avoid suggesting a name that is already in use.
 167 pub(crate) fn placeholder_type_error<'tcx>(
 168     tcx: TyCtxt<'tcx>,
 169     generics: Option<&hir::Generics<'_>>,
 170     placeholder_types: Vec<Span>,
 171     suggest: bool,
 172     hir_ty: Option<&hir::Ty<'_>>,
 173     kind: &'static str,
 174 ) {
 175     if placeholder_types.is_empty() {
 176         return;
 177     }
 178
 179     placeholder_type_error_diag(tcx, generics, placeholder_types, vec![], suggest, hir_ty, kind)
 180         .emit();
 181 }
 182
 183 pub(crate) fn placeholder_type_error_diag<'tcx>(
 184     tcx: TyCtxt<'tcx>,
 185     generics: Option<&hir::Generics<'_>>,
 186     placeholder_types: Vec<Span>,
 187     additional_spans: Vec<Span>,
 188     suggest: bool,
 189     hir_ty: Option<&hir::Ty<'_>>,
 190     kind: &'static str,
 191 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
 192     if placeholder_types.is_empty() {
 193         return bad_placeholder(tcx, additional_spans, kind);
 194     }
 195
 196     let params = generics.map(|g| g.params).unwrap_or_default();
 197     let type_name = params.next_type_param_name(None);
 198     let mut sugg: Vec<_> =
 199         placeholder_types.iter().map(|sp| (*sp, (*type_name).to_string())).collect();
 200
 201     if let Some(generics) = generics {
 202         if let Some(arg) = params.iter().find(|arg| {
 203             matches!(arg.name, hir::ParamName::Plain(Ident { name: kw::Underscore, .. }))
 204         }) {
 205             // Account for `_` already present in cases like `struct S<_>(_);` and suggest
 206             // `struct S<T>(T);` instead of `struct S<_, T>(T);`.
 207             sugg.push((arg.span, (*type_name).to_string()));
 208         } else if let Some(span) = generics.span_for_param_suggestion() {
 209             // Account for bounds, we want `fn foo<T: E, K>(_: K)` not `fn foo<T, K: E>(_: K)`.
 210             sugg.push((span, format!(", {}", type_name)));
 211         } else {
 212             sugg.push((generics.span, format!("<{}>", type_name)));
 213         }
 214     }
 215
 216     let mut err =
 217         bad_placeholder(tcx, placeholder_types.into_iter().chain(additional_spans).collect(), kind);
 218
 219     // Suggest, but only if it is not a function in const or static
 220     if suggest {
 221         let mut is_fn = false;
 222         let mut is_const_or_static = false;
 223
 224         if let Some(hir_ty) = hir_ty && let hir::TyKind::BareFn(_) = hir_ty.kind {
 225             is_fn = true;
 226
 227             // Check if parent is const or static
 228             let parent_id = tcx.hir().get_parent_node(hir_ty.hir_id);
 229             let parent_node = tcx.hir().get(parent_id);
 230
 231             is_const_or_static = matches!(
 232                 parent_node,
 233                 Node::Item(&hir::Item {
 234                     kind: hir::ItemKind::Const(..) | hir::ItemKind::Static(..),
 235                     ..
 236                 }) | Node::TraitItem(&hir::TraitItem {
 237                     kind: hir::TraitItemKind::Const(..),
 238                     ..
 239                 }) | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Const(..), .. })
 240             );
 241         }
 242
 243         // if function is wrapped around a const or static,
 244         // then don't show the suggestion
 245         if !(is_fn && is_const_or_static) {
 246             err.multipart_suggestion(
 247                 "use type parameters instead",
 248                 sugg,
 249                 Applicability::HasPlaceholders,
 250             );
 251         }
 252     }
 253
 254     err
 255 }
 256
 257 fn reject_placeholder_type_signatures_in_item<'tcx>(
 258     tcx: TyCtxt<'tcx>,
 259     item: &'tcx hir::Item<'tcx>,
 260 ) {
 261     let (generics, suggest) = match &item.kind {
 262         hir::ItemKind::Union(_, generics)
 263         | hir::ItemKind::Enum(_, generics)
 264         | hir::ItemKind::TraitAlias(generics, _)
 265         | hir::ItemKind::Trait(_, _, generics, ..)
 266         | hir::ItemKind::Impl(hir::Impl { generics, .. })
 267         | hir::ItemKind::Struct(_, generics) => (generics, true),
 268         hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. })
 269         | hir::ItemKind::TyAlias(_, generics) => (generics, false),
 270         // `static`, `fn` and `const` are handled elsewhere to suggest appropriate type.
 271         _ => return,
 272     };
 273
 274     let mut visitor = HirPlaceholderCollector::default();
 275     visitor.visit_item(item);
 276
 277     placeholder_type_error(tcx, Some(generics), visitor.0, suggest, None, item.kind.descr());
 278 }
 279
 280 impl<'tcx> Visitor<'tcx> for CollectItemTypesVisitor<'tcx> {
 281     type NestedFilter = nested_filter::OnlyBodies;
 282
 283     fn nested_visit_map(&mut self) -> Self::Map {
 284         self.tcx.hir()
 285     }
 286
 287     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 288         convert_item(self.tcx, item.item_id());
 289         reject_placeholder_type_signatures_in_item(self.tcx, item);
 290         intravisit::walk_item(self, item);
 291     }
 292
 293     fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
 294         for param in generics.params {
 295             match param.kind {
 296                 hir::GenericParamKind::Lifetime { .. } => {}
 297                 hir::GenericParamKind::Type { default: Some(_), .. } => {
 298                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 299                     self.tcx.ensure().type_of(def_id);
 300                 }
 301                 hir::GenericParamKind::Type { .. } => {}
 302                 hir::GenericParamKind::Const { default, .. } => {
 303                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
 304                     self.tcx.ensure().type_of(def_id);
 305                     if let Some(default) = default {
 306                         let default_def_id = self.tcx.hir().local_def_id(default.hir_id);
 307                         // need to store default and type of default
 308                         self.tcx.ensure().type_of(default_def_id);
 309                         self.tcx.ensure().const_param_default(def_id);
 310                     }
 311                 }
 312             }
 313         }
 314         intravisit::walk_generics(self, generics);
 315     }
 316
 317     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 318         if let hir::ExprKind::Closure { .. } = expr.kind {
 319             let def_id = self.tcx.hir().local_def_id(expr.hir_id);
 320             self.tcx.ensure().generics_of(def_id);
 321             // We do not call `type_of` for closures here as that
 322             // depends on typecheck and would therefore hide
 323             // any further errors in case one typeck fails.
 324         }
 325         intravisit::walk_expr(self, expr);
 326     }
 327
 328     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
 329         convert_trait_item(self.tcx, trait_item.trait_item_id());
 330         intravisit::walk_trait_item(self, trait_item);
 331     }
 332
 333     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 334         convert_impl_item(self.tcx, impl_item.impl_item_id());
 335         intravisit::walk_impl_item(self, impl_item);
 336     }
 337 }
 338
 339 ///////////////////////////////////////////////////////////////////////////
 340 // Utility types and common code for the above passes.
 341
 342 fn bad_placeholder<'tcx>(
 343     tcx: TyCtxt<'tcx>,
 344     mut spans: Vec<Span>,
 345     kind: &'static str,
 346 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
 347     let kind = if kind.ends_with('s') { format!("{}es", kind) } else { format!("{}s", kind) };
 348
 349     spans.sort();
 350     let mut err = struct_span_err!(
 351         tcx.sess,
 352         spans.clone(),
 353         E0121,
 354         "the placeholder `_` is not allowed within types on item signatures for {}",
 355         kind
 356     );
 357     for span in spans {
 358         err.span_label(span, "not allowed in type signatures");
 359     }
 360     err
 361 }
 362
 363 impl<'tcx> ItemCtxt<'tcx> {
 364     pub fn new(tcx: TyCtxt<'tcx>, item_def_id: DefId) -> ItemCtxt<'tcx> {
 365         ItemCtxt { tcx, item_def_id }
 366     }
 367
 368     pub fn to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
 369         <dyn AstConv<'_>>::ast_ty_to_ty(self, ast_ty)
 370     }
 371
 372     pub fn hir_id(&self) -> hir::HirId {
 373         self.tcx.hir().local_def_id_to_hir_id(self.item_def_id.expect_local())
 374     }
 375
 376     pub fn node(&self) -> hir::Node<'tcx> {
 377         self.tcx.hir().get(self.hir_id())
 378     }
 379 }
 380
 381 impl<'tcx> AstConv<'tcx> for ItemCtxt<'tcx> {
 382     fn tcx(&self) -> TyCtxt<'tcx> {
 383         self.tcx
 384     }
 385
 386     fn item_def_id(&self) -> Option<DefId> {
 387         Some(self.item_def_id)
 388     }
 389
 390     fn get_type_parameter_bounds(
 391         &self,
 392         span: Span,
 393         def_id: DefId,
 394         assoc_name: Ident,
 395     ) -> ty::GenericPredicates<'tcx> {
 396         self.tcx.at(span).type_param_predicates((
 397             self.item_def_id,
 398             def_id.expect_local(),
 399             assoc_name,
 400         ))
 401     }
 402
 403     fn re_infer(&self, _: Option<&ty::GenericParamDef>, _: Span) -> Option<ty::Region<'tcx>> {
 404         None
 405     }
 406
 407     fn allow_ty_infer(&self) -> bool {
 408         false
 409     }
 410
 411     fn ty_infer(&self, _: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
 412         self.tcx().ty_error_with_message(span, "bad placeholder type")
 413     }
 414
 415     fn ct_infer(&self, ty: Ty<'tcx>, _: Option<&ty::GenericParamDef>, span: Span) -> Const<'tcx> {
 416         let ty = self.tcx.fold_regions(ty, |r, _| match *r {
 417             ty::ReErased => self.tcx.lifetimes.re_static,
 418             _ => r,
 419         });
 420         self.tcx().const_error_with_message(ty, span, "bad placeholder constant")
 421     }
 422
 423     fn projected_ty_from_poly_trait_ref(
 424         &self,
 425         span: Span,
 426         item_def_id: DefId,
 427         item_segment: &hir::PathSegment<'_>,
 428         poly_trait_ref: ty::PolyTraitRef<'tcx>,
 429     ) -> Ty<'tcx> {
 430         if let Some(trait_ref) = poly_trait_ref.no_bound_vars() {
 431             let item_substs = <dyn AstConv<'tcx>>::create_substs_for_associated_item(
 432                 self,
 433                 self.tcx,
 434                 span,
 435                 item_def_id,
 436                 item_segment,
 437                 trait_ref.substs,
 438             );
 439             self.tcx().mk_projection(item_def_id, item_substs)
 440         } else {
 441             // There are no late-bound regions; we can just ignore the binder.
 442             let mut err = struct_span_err!(
 443                 self.tcx().sess,
 444                 span,
 445                 E0212,
 446                 "cannot use the associated type of a trait \
 447                  with uninferred generic parameters"
 448             );
 449
 450             match self.node() {
 451                 hir::Node::Field(_) | hir::Node::Ctor(_) | hir::Node::Variant(_) => {
 452                     let item = self
 453                         .tcx
 454                         .hir()
 455                         .expect_item(self.tcx.hir().get_parent_item(self.hir_id()).def_id);
 456                     match &item.kind {
 457                         hir::ItemKind::Enum(_, generics)
 458                         | hir::ItemKind::Struct(_, generics)
 459                         | hir::ItemKind::Union(_, generics) => {
 460                             let lt_name = get_new_lifetime_name(self.tcx, poly_trait_ref, generics);
 461                             let (lt_sp, sugg) = match generics.params {
 462                                 [] => (generics.span, format!("<{}>", lt_name)),
 463                                 [bound, ..] => {
 464                                     (bound.span.shrink_to_lo(), format!("{}, ", lt_name))
 465                                 }
 466                             };
 467                             let suggestions = vec![
 468                                 (lt_sp, sugg),
 469                                 (
 470                                     span.with_hi(item_segment.ident.span.lo()),
 471                                     format!(
 472                                         "{}::",
 473                                         // Replace the existing lifetimes with a new named lifetime.
 474                                         self.tcx.replace_late_bound_regions_uncached(
 475                                             poly_trait_ref,
 476                                             |_| {
 477                                                 self.tcx.mk_region(ty::ReEarlyBound(
 478                                                     ty::EarlyBoundRegion {
 479                                                         def_id: item_def_id,
 480                                                         index: 0,
 481                                                         name: Symbol::intern(&lt_name),
 482                                                     },
 483                                                 ))
 484                                             }
 485                                         ),
 486                                     ),
 487                                 ),
 488                             ];
 489                             err.multipart_suggestion(
 490                                 "use a fully qualified path with explicit lifetimes",
 491                                 suggestions,
 492                                 Applicability::MaybeIncorrect,
 493                             );
 494                         }
 495                         _ => {}
 496                     }
 497                 }
 498                 hir::Node::Item(hir::Item {
 499                     kind:
 500                         hir::ItemKind::Struct(..) | hir::ItemKind::Enum(..) | hir::ItemKind::Union(..),
 501                     ..
 502                 }) => {}
 503                 hir::Node::Item(_)
 504                 | hir::Node::ForeignItem(_)
 505                 | hir::Node::TraitItem(_)
 506                 | hir::Node::ImplItem(_) => {
 507                     err.span_suggestion_verbose(
 508                         span.with_hi(item_segment.ident.span.lo()),
 509                         "use a fully qualified path with inferred lifetimes",
 510                         format!(
 511                             "{}::",
 512                             // Erase named lt, we want `<A as B<'_>::C`, not `<A as B<'a>::C`.
 513                             self.tcx.anonymize_late_bound_regions(poly_trait_ref).skip_binder(),
 514                         ),
 515                         Applicability::MaybeIncorrect,
 516                     );
 517                 }
 518                 _ => {}
 519             }
 520             err.emit();
 521             self.tcx().ty_error()
 522         }
 523     }
 524
 525     fn normalize_ty(&self, _span: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
 526         // Types in item signatures are not normalized to avoid undue dependencies.
 527         ty
 528     }
 529
 530     fn set_tainted_by_errors(&self) {
 531         // There's no obvious place to track this, so just let it go.
 532     }
 533
 534     fn record_ty(&self, _hir_id: hir::HirId, _ty: Ty<'tcx>, _span: Span) {
 535         // There's no place to record types from signatures?
 536     }
 537 }
 538
 539 /// Synthesize a new lifetime name that doesn't clash with any of the lifetimes already present.
 540 fn get_new_lifetime_name<'tcx>(
 541     tcx: TyCtxt<'tcx>,
 542     poly_trait_ref: ty::PolyTraitRef<'tcx>,
 543     generics: &hir::Generics<'tcx>,
 544 ) -> String {
 545     let existing_lifetimes = tcx
 546         .collect_referenced_late_bound_regions(&poly_trait_ref)
 547         .into_iter()
 548         .filter_map(|lt| {
 549             if let ty::BoundRegionKind::BrNamed(_, name) = lt {
 550                 Some(name.as_str().to_string())
 551             } else {
 552                 None
 553             }
 554         })
 555         .chain(generics.params.iter().filter_map(|param| {
 556             if let hir::GenericParamKind::Lifetime { .. } = &param.kind {
 557                 Some(param.name.ident().as_str().to_string())
 558             } else {
 559                 None
 560             }
 561         }))
 562         .collect::<FxHashSet<String>>();
 563
 564     let a_to_z_repeat_n = |n| {
 565         (b'a'..=b'z').map(move |c| {
 566             let mut s = '\''.to_string();
 567             s.extend(std::iter::repeat(char::from(c)).take(n));
 568             s
 569         })
 570     };
 571
 572     // If all single char lifetime names are present, we wrap around and double the chars.
 573     (1..).flat_map(a_to_z_repeat_n).find(|lt| !existing_lifetimes.contains(lt.as_str())).unwrap()
 574 }
 575
 576 /// Returns the predicates defined on `item_def_id` of the form
 577 /// `X: Foo` where `X` is the type parameter `def_id`.
 578 #[instrument(level = "trace", skip(tcx))]
 579 fn type_param_predicates(
 580     tcx: TyCtxt<'_>,
 581     (item_def_id, def_id, assoc_name): (DefId, LocalDefId, Ident),
 582 ) -> ty::GenericPredicates<'_> {
 583     use rustc_hir::*;
 584
 585     // In the AST, bounds can derive from two places. Either
 586     // written inline like `<T: Foo>` or in a where-clause like
 587     // `where T: Foo`.
 588
 589     let param_id = tcx.hir().local_def_id_to_hir_id(def_id);
 590     let param_owner = tcx.hir().ty_param_owner(def_id);
 591     let generics = tcx.generics_of(param_owner);
 592     let index = generics.param_def_id_to_index[&def_id.to_def_id()];
 593     let ty = tcx.mk_ty_param(index, tcx.hir().ty_param_name(def_id));
 594
 595     // Don't look for bounds where the type parameter isn't in scope.
 596     let parent = if item_def_id == param_owner.to_def_id() {
 597         None
 598     } else {
 599         tcx.generics_of(item_def_id).parent
 600     };
 601
 602     let mut result = parent
 603         .map(|parent| {
 604             let icx = ItemCtxt::new(tcx, parent);
 605             icx.get_type_parameter_bounds(DUMMY_SP, def_id.to_def_id(), assoc_name)
 606         })
 607         .unwrap_or_default();
 608     let mut extend = None;
 609
 610     let item_hir_id = tcx.hir().local_def_id_to_hir_id(item_def_id.expect_local());
 611     let ast_generics = match tcx.hir().get(item_hir_id) {
 612         Node::TraitItem(item) => &item.generics,
 613
 614         Node::ImplItem(item) => &item.generics,
 615
 616         Node::Item(item) => {
 617             match item.kind {
 618                 ItemKind::Fn(.., ref generics, _)
 619                 | ItemKind::Impl(hir::Impl { ref generics, .. })
 620                 | ItemKind::TyAlias(_, ref generics)
 621                 | ItemKind::OpaqueTy(OpaqueTy {
 622                     ref generics,
 623                     origin: hir::OpaqueTyOrigin::TyAlias,
 624                     ..
 625                 })
 626                 | ItemKind::Enum(_, ref generics)
 627                 | ItemKind::Struct(_, ref generics)
 628                 | ItemKind::Union(_, ref generics) => generics,
 629                 ItemKind::Trait(_, _, ref generics, ..) => {
 630                     // Implied `Self: Trait` and supertrait bounds.
 631                     if param_id == item_hir_id {
 632                         let identity_trait_ref = ty::TraitRef::identity(tcx, item_def_id);
 633                         extend =
 634                             Some((identity_trait_ref.without_const().to_predicate(tcx), item.span));
 635                     }
 636                     generics
 637                 }
 638                 _ => return result,
 639             }
 640         }
 641
 642         Node::ForeignItem(item) => match item.kind {
 643             ForeignItemKind::Fn(_, _, ref generics) => generics,
 644             _ => return result,
 645         },
 646
 647         _ => return result,
 648     };
 649
 650     let icx = ItemCtxt::new(tcx, item_def_id);
 651     let extra_predicates = extend.into_iter().chain(
 652         icx.type_parameter_bounds_in_generics(
 653             ast_generics,
 654             param_id,
 655             ty,
 656             OnlySelfBounds(true),
 657             Some(assoc_name),
 658         )
 659         .into_iter()
 660         .filter(|(predicate, _)| match predicate.kind().skip_binder() {
 661             ty::PredicateKind::Trait(data) => data.self_ty().is_param(index),
 662             _ => false,
 663         }),
 664     );
 665     result.predicates =
 666         tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(extra_predicates));
 667     result
 668 }
 669
 670 impl<'tcx> ItemCtxt<'tcx> {
 671     /// Finds bounds from `hir::Generics`. This requires scanning through the
 672     /// AST. We do this to avoid having to convert *all* the bounds, which
 673     /// would create artificial cycles. Instead, we can only convert the
 674     /// bounds for a type parameter `X` if `X::Foo` is used.
 675     #[instrument(level = "trace", skip(self, ast_generics))]
 676     fn type_parameter_bounds_in_generics(
 677         &self,
 678         ast_generics: &'tcx hir::Generics<'tcx>,
 679         param_id: hir::HirId,
 680         ty: Ty<'tcx>,
 681         only_self_bounds: OnlySelfBounds,
 682         assoc_name: Option<Ident>,
 683     ) -> Vec<(ty::Predicate<'tcx>, Span)> {
 684         let param_def_id = self.tcx.hir().local_def_id(param_id).to_def_id();
 685         trace!(?param_def_id);
 686         ast_generics
 687             .predicates
 688             .iter()
 689             .filter_map(|wp| match *wp {
 690                 hir::WherePredicate::BoundPredicate(ref bp) => Some(bp),
 691                 _ => None,
 692             })
 693             .flat_map(|bp| {
 694                 let bt = if bp.is_param_bound(param_def_id) {
 695                     Some(ty)
 696                 } else if !only_self_bounds.0 {
 697                     Some(self.to_ty(bp.bounded_ty))
 698                 } else {
 699                     None
 700                 };
 701                 let bvars = self.tcx.late_bound_vars(bp.bounded_ty.hir_id);
 702
 703                 bp.bounds.iter().filter_map(move |b| bt.map(|bt| (bt, b, bvars))).filter(
 704                     |(_, b, _)| match assoc_name {
 705                         Some(assoc_name) => self.bound_defines_assoc_item(b, assoc_name),
 706                         None => true,
 707                     },
 708                 )
 709             })
 710             .flat_map(|(bt, b, bvars)| predicates_from_bound(self, bt, b, bvars))
 711             .collect()
 712     }
 713
 714     #[instrument(level = "trace", skip(self))]
 715     fn bound_defines_assoc_item(&self, b: &hir::GenericBound<'_>, assoc_name: Ident) -> bool {
 716         match b {
 717             hir::GenericBound::Trait(poly_trait_ref, _) => {
 718                 let trait_ref = &poly_trait_ref.trait_ref;
 719                 if let Some(trait_did) = trait_ref.trait_def_id() {
 720                     self.tcx.trait_may_define_assoc_type(trait_did, assoc_name)
 721                 } else {
 722                     false
 723                 }
 724             }
 725             _ => false,
 726         }
 727     }
 728 }
 729
 730 fn convert_item(tcx: TyCtxt<'_>, item_id: hir::ItemId) {
 731     let it = tcx.hir().item(item_id);
 732     debug!("convert: item {} with id {}", it.ident, it.hir_id());
 733     let def_id = item_id.def_id.def_id;
 734
 735     match it.kind {
 736         // These don't define types.
 737         hir::ItemKind::ExternCrate(_)
 738         | hir::ItemKind::Use(..)
 739         | hir::ItemKind::Macro(..)
 740         | hir::ItemKind::Mod(_)
 741         | hir::ItemKind::GlobalAsm(_) => {}
 742         hir::ItemKind::ForeignMod { items, .. } => {
 743             for item in items {
 744                 let item = tcx.hir().foreign_item(item.id);
 745                 tcx.ensure().generics_of(item.def_id);
 746                 tcx.ensure().type_of(item.def_id);
 747                 tcx.ensure().predicates_of(item.def_id);
 748                 match item.kind {
 749                     hir::ForeignItemKind::Fn(..) => tcx.ensure().fn_sig(item.def_id),
 750                     hir::ForeignItemKind::Static(..) => {
 751                         let mut visitor = HirPlaceholderCollector::default();
 752                         visitor.visit_foreign_item(item);
 753                         placeholder_type_error(
 754                             tcx,
 755                             None,
 756                             visitor.0,
 757                             false,
 758                             None,
 759                             "static variable",
 760                         );
 761                     }
 762                     _ => (),
 763                 }
 764             }
 765         }
 766         hir::ItemKind::Enum(ref enum_definition, _) => {
 767             tcx.ensure().generics_of(def_id);
 768             tcx.ensure().type_of(def_id);
 769             tcx.ensure().predicates_of(def_id);
 770             convert_enum_variant_types(tcx, def_id.to_def_id(), enum_definition.variants);
 771         }
 772         hir::ItemKind::Impl { .. } => {
 773             tcx.ensure().generics_of(def_id);
 774             tcx.ensure().type_of(def_id);
 775             tcx.ensure().impl_trait_ref(def_id);
 776             tcx.ensure().predicates_of(def_id);
 777         }
 778         hir::ItemKind::Trait(..) => {
 779             tcx.ensure().generics_of(def_id);
 780             tcx.ensure().trait_def(def_id);
 781             tcx.at(it.span).super_predicates_of(def_id);
 782             tcx.ensure().predicates_of(def_id);
 783         }
 784         hir::ItemKind::TraitAlias(..) => {
 785             tcx.ensure().generics_of(def_id);
 786             tcx.at(it.span).super_predicates_of(def_id);
 787             tcx.ensure().predicates_of(def_id);
 788         }
 789         hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 790             tcx.ensure().generics_of(def_id);
 791             tcx.ensure().type_of(def_id);
 792             tcx.ensure().predicates_of(def_id);
 793
 794             for f in struct_def.fields() {
 795                 let def_id = tcx.hir().local_def_id(f.hir_id);
 796                 tcx.ensure().generics_of(def_id);
 797                 tcx.ensure().type_of(def_id);
 798                 tcx.ensure().predicates_of(def_id);
 799             }
 800
 801             if let Some(ctor_hir_id) = struct_def.ctor_hir_id() {
 802                 convert_variant_ctor(tcx, ctor_hir_id);
 803             }
 804         }
 805
 806         // Desugared from `impl Trait`, so visited by the function's return type.
 807         hir::ItemKind::OpaqueTy(hir::OpaqueTy {
 808             origin: hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..),
 809             ..
 810         }) => {}
 811
 812         // Don't call `type_of` on opaque types, since that depends on type
 813         // checking function bodies. `check_item_type` ensures that it's called
 814         // instead.
 815         hir::ItemKind::OpaqueTy(..) => {
 816             tcx.ensure().generics_of(def_id);
 817             tcx.ensure().predicates_of(def_id);
 818             tcx.ensure().explicit_item_bounds(def_id);
 819         }
 820         hir::ItemKind::TyAlias(..)
 821         | hir::ItemKind::Static(..)
 822         | hir::ItemKind::Const(..)
 823         | hir::ItemKind::Fn(..) => {
 824             tcx.ensure().generics_of(def_id);
 825             tcx.ensure().type_of(def_id);
 826             tcx.ensure().predicates_of(def_id);
 827             match it.kind {
 828                 hir::ItemKind::Fn(..) => tcx.ensure().fn_sig(def_id),
 829                 hir::ItemKind::OpaqueTy(..) => tcx.ensure().item_bounds(def_id),
 830                 hir::ItemKind::Const(ty, ..) | hir::ItemKind::Static(ty, ..) => {
 831                     if !is_suggestable_infer_ty(ty) {
 832                         let mut visitor = HirPlaceholderCollector::default();
 833                         visitor.visit_item(it);
 834                         placeholder_type_error(tcx, None, visitor.0, false, None, it.kind.descr());
 835                     }
 836                 }
 837                 _ => (),
 838             }
 839         }
 840     }
 841 }
 842
 843 fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::TraitItemId) {
 844     let trait_item = tcx.hir().trait_item(trait_item_id);
 845     let def_id = trait_item_id.def_id;
 846     tcx.ensure().generics_of(def_id);
 847
 848     match trait_item.kind {
 849         hir::TraitItemKind::Fn(..) => {
 850             tcx.ensure().type_of(def_id);
 851             tcx.ensure().fn_sig(def_id);
 852         }
 853
 854         hir::TraitItemKind::Const(.., Some(_)) => {
 855             tcx.ensure().type_of(def_id);
 856         }
 857
 858         hir::TraitItemKind::Const(hir_ty, _) => {
 859             tcx.ensure().type_of(def_id);
 860             // Account for `const C: _;`.
 861             let mut visitor = HirPlaceholderCollector::default();
 862             visitor.visit_trait_item(trait_item);
 863             if !tcx.sess.diagnostic().has_stashed_diagnostic(hir_ty.span, StashKey::ItemNoType) {
 864                 placeholder_type_error(tcx, None, visitor.0, false, None, "constant");
 865             }
 866         }
 867
 868         hir::TraitItemKind::Type(_, Some(_)) => {
 869             tcx.ensure().item_bounds(def_id);
 870             tcx.ensure().type_of(def_id);
 871             // Account for `type T = _;`.
 872             let mut visitor = HirPlaceholderCollector::default();
 873             visitor.visit_trait_item(trait_item);
 874             placeholder_type_error(tcx, None, visitor.0, false, None, "associated type");
 875         }
 876
 877         hir::TraitItemKind::Type(_, None) => {
 878             tcx.ensure().item_bounds(def_id);
 879             // #74612: Visit and try to find bad placeholders
 880             // even if there is no concrete type.
 881             let mut visitor = HirPlaceholderCollector::default();
 882             visitor.visit_trait_item(trait_item);
 883
 884             placeholder_type_error(tcx, None, visitor.0, false, None, "associated type");
 885         }
 886     };
 887
 888     tcx.ensure().predicates_of(def_id);
 889 }
 890
 891 fn convert_impl_item(tcx: TyCtxt<'_>, impl_item_id: hir::ImplItemId) {
 892     let def_id = impl_item_id.def_id;
 893     tcx.ensure().generics_of(def_id);
 894     tcx.ensure().type_of(def_id);
 895     tcx.ensure().predicates_of(def_id);
 896     let impl_item = tcx.hir().impl_item(impl_item_id);
 897     match impl_item.kind {
 898         hir::ImplItemKind::Fn(..) => {
 899             tcx.ensure().fn_sig(def_id);
 900         }
 901         hir::ImplItemKind::TyAlias(_) => {
 902             // Account for `type T = _;`
 903             let mut visitor = HirPlaceholderCollector::default();
 904             visitor.visit_impl_item(impl_item);
 905
 906             placeholder_type_error(tcx, None, visitor.0, false, None, "associated type");
 907         }
 908         hir::ImplItemKind::Const(..) => {}
 909     }
 910 }
 911
 912 fn convert_variant_ctor(tcx: TyCtxt<'_>, ctor_id: hir::HirId) {
 913     let def_id = tcx.hir().local_def_id(ctor_id);
 914     tcx.ensure().generics_of(def_id);
 915     tcx.ensure().type_of(def_id);
 916     tcx.ensure().predicates_of(def_id);
 917 }
 918
 919 fn convert_enum_variant_types(tcx: TyCtxt<'_>, def_id: DefId, variants: &[hir::Variant<'_>]) {
 920     let def = tcx.adt_def(def_id);
 921     let repr_type = def.repr().discr_type();
 922     let initial = repr_type.initial_discriminant(tcx);
 923     let mut prev_discr = None::<Discr<'_>>;
 924
 925     // fill the discriminant values and field types
 926     for variant in variants {
 927         let wrapped_discr = prev_discr.map_or(initial, |d| d.wrap_incr(tcx));
 928         prev_discr = Some(
 929             if let Some(ref e) = variant.disr_expr {
 930                 let expr_did = tcx.hir().local_def_id(e.hir_id);
 931                 def.eval_explicit_discr(tcx, expr_did.to_def_id())
 932             } else if let Some(discr) = repr_type.disr_incr(tcx, prev_discr) {
 933                 Some(discr)
 934             } else {
 935                 struct_span_err!(tcx.sess, variant.span, E0370, "enum discriminant overflowed")
 936                     .span_label(
 937                         variant.span,
 938                         format!("overflowed on value after {}", prev_discr.unwrap()),
 939                     )
 940                     .note(&format!(
 941                         "explicitly set `{} = {}` if that is desired outcome",
 942                         variant.ident, wrapped_discr
 943                     ))
 944                     .emit();
 945                 None
 946             }
 947             .unwrap_or(wrapped_discr),
 948         );
 949
 950         for f in variant.data.fields() {
 951             let def_id = tcx.hir().local_def_id(f.hir_id);
 952             tcx.ensure().generics_of(def_id);
 953             tcx.ensure().type_of(def_id);
 954             tcx.ensure().predicates_of(def_id);
 955         }
 956
 957         // Convert the ctor, if any. This also registers the variant as
 958         // an item.
 959         if let Some(ctor_hir_id) = variant.data.ctor_hir_id() {
 960             convert_variant_ctor(tcx, ctor_hir_id);
 961         }
 962     }
 963 }
 964
 965 fn convert_variant(
 966     tcx: TyCtxt<'_>,
 967     variant_did: Option<LocalDefId>,
 968     ctor_did: Option<LocalDefId>,
 969     ident: Ident,
 970     discr: ty::VariantDiscr,
 971     def: &hir::VariantData<'_>,
 972     adt_kind: ty::AdtKind,
 973     parent_did: LocalDefId,
 974 ) -> ty::VariantDef {
 975     let mut seen_fields: FxHashMap<Ident, Span> = Default::default();
 976     let fields = def
 977         .fields()
 978         .iter()
 979         .map(|f| {
 980             let fid = tcx.hir().local_def_id(f.hir_id);
 981             let dup_span = seen_fields.get(&f.ident.normalize_to_macros_2_0()).cloned();
 982             if let Some(prev_span) = dup_span {
 983                 tcx.sess.emit_err(errors::FieldAlreadyDeclared {
 984                     field_name: f.ident,
 985                     span: f.span,
 986                     prev_span,
 987                 });
 988             } else {
 989                 seen_fields.insert(f.ident.normalize_to_macros_2_0(), f.span);
 990             }
 991
 992             ty::FieldDef { did: fid.to_def_id(), name: f.ident.name, vis: tcx.visibility(fid) }
 993         })
 994         .collect();
 995     let recovered = match def {
 996         hir::VariantData::Struct(_, r) => *r,
 997         _ => false,
 998     };
 999     ty::VariantDef::new(
1000         ident.name,
1001         variant_did.map(LocalDefId::to_def_id),
1002         ctor_did.map(LocalDefId::to_def_id),
1003         discr,
1004         fields,
1005         CtorKind::from_hir(def),
1006         adt_kind,
1007         parent_did.to_def_id(),
1008         recovered,
1009         adt_kind == AdtKind::Struct && tcx.has_attr(parent_did.to_def_id(), sym::non_exhaustive)
1010             || variant_did.map_or(false, |variant_did| {
1011                 tcx.has_attr(variant_did.to_def_id(), sym::non_exhaustive)
1012             }),
1013     )
1014 }
1015
1016 fn adt_def<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> ty::AdtDef<'tcx> {
1017     use rustc_hir::*;
1018
1019     let def_id = def_id.expect_local();
1020     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
1021     let Node::Item(item) = tcx.hir().get(hir_id) else {
1022         bug!();
1023     };
1024
1025     let repr = ReprOptions::new(tcx, def_id.to_def_id());
1026     let (kind, variants) = match item.kind {
1027         ItemKind::Enum(ref def, _) => {
1028             let mut distance_from_explicit = 0;
1029             let variants = def
1030                 .variants
1031                 .iter()
1032                 .map(|v| {
1033                     let variant_did = Some(tcx.hir().local_def_id(v.id));
1034                     let ctor_did =
1035                         v.data.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
1036
1037                     let discr = if let Some(ref e) = v.disr_expr {
1038                         distance_from_explicit = 0;
1039                         ty::VariantDiscr::Explicit(tcx.hir().local_def_id(e.hir_id).to_def_id())
1040                     } else {
1041                         ty::VariantDiscr::Relative(distance_from_explicit)
1042                     };
1043                     distance_from_explicit += 1;
1044
1045                     convert_variant(
1046                         tcx,
1047                         variant_did,
1048                         ctor_did,
1049                         v.ident,
1050                         discr,
1051                         &v.data,
1052                         AdtKind::Enum,
1053                         def_id,
1054                     )
1055                 })
1056                 .collect();
1057
1058             (AdtKind::Enum, variants)
1059         }
1060         ItemKind::Struct(ref def, _) => {
1061             let variant_did = None::<LocalDefId>;
1062             let ctor_did = def.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
1063
1064             let variants = std::iter::once(convert_variant(
1065                 tcx,
1066                 variant_did,
1067                 ctor_did,
1068                 item.ident,
1069                 ty::VariantDiscr::Relative(0),
1070                 def,
1071                 AdtKind::Struct,
1072                 def_id,
1073             ))
1074             .collect();
1075
1076             (AdtKind::Struct, variants)
1077         }
1078         ItemKind::Union(ref def, _) => {
1079             let variant_did = None;
1080             let ctor_did = def.ctor_hir_id().map(|hir_id| tcx.hir().local_def_id(hir_id));
1081
1082             let variants = std::iter::once(convert_variant(
1083                 tcx,
1084                 variant_did,
1085                 ctor_did,
1086                 item.ident,
1087                 ty::VariantDiscr::Relative(0),
1088                 def,
1089                 AdtKind::Union,
1090                 def_id,
1091             ))
1092             .collect();
1093
1094             (AdtKind::Union, variants)
1095         }
1096         _ => bug!(),
1097     };
1098     tcx.alloc_adt_def(def_id.to_def_id(), kind, variants, repr)
1099 }
1100
1101 /// Ensures that the super-predicates of the trait with a `DefId`
1102 /// of `trait_def_id` are converted and stored. This also ensures that
1103 /// the transitive super-predicates are converted.
1104 fn super_predicates_of(tcx: TyCtxt<'_>, trait_def_id: DefId) -> ty::GenericPredicates<'_> {
1105     debug!("super_predicates(trait_def_id={:?})", trait_def_id);
1106     tcx.super_predicates_that_define_assoc_type((trait_def_id, None))
1107 }
1108
1109 /// Ensures that the super-predicates of the trait with a `DefId`
1110 /// of `trait_def_id` are converted and stored. This also ensures that
1111 /// the transitive super-predicates are converted.
1112 fn super_predicates_that_define_assoc_type(
1113     tcx: TyCtxt<'_>,
1114     (trait_def_id, assoc_name): (DefId, Option<Ident>),
1115 ) -> ty::GenericPredicates<'_> {
1116     debug!(
1117         "super_predicates_that_define_assoc_type(trait_def_id={:?}, assoc_name={:?})",
1118         trait_def_id, assoc_name
1119     );
1120     if trait_def_id.is_local() {
1121         debug!("super_predicates_that_define_assoc_type: local trait_def_id={:?}", trait_def_id);
1122         let trait_hir_id = tcx.hir().local_def_id_to_hir_id(trait_def_id.expect_local());
1123
1124         let Node::Item(item) = tcx.hir().get(trait_hir_id) else {
1125             bug!("trait_node_id {} is not an item", trait_hir_id);
1126         };
1127
1128         let (generics, bounds) = match item.kind {
1129             hir::ItemKind::Trait(.., ref generics, ref supertraits, _) => (generics, supertraits),
1130             hir::ItemKind::TraitAlias(ref generics, ref supertraits) => (generics, supertraits),
1131             _ => span_bug!(item.span, "super_predicates invoked on non-trait"),
1132         };
1133
1134         let icx = ItemCtxt::new(tcx, trait_def_id);
1135
1136         // Convert the bounds that follow the colon, e.g., `Bar + Zed` in `trait Foo: Bar + Zed`.
1137         let self_param_ty = tcx.types.self_param;
1138         let superbounds1 = if let Some(assoc_name) = assoc_name {
1139             <dyn AstConv<'_>>::compute_bounds_that_match_assoc_type(
1140                 &icx,
1141                 self_param_ty,
1142                 bounds,
1143                 assoc_name,
1144             )
1145         } else {
1146             <dyn AstConv<'_>>::compute_bounds(&icx, self_param_ty, bounds)
1147         };
1148
1149         let superbounds1 = superbounds1.predicates(tcx, self_param_ty);
1150
1151         // Convert any explicit superbounds in the where-clause,
1152         // e.g., `trait Foo where Self: Bar`.
1153         // In the case of trait aliases, however, we include all bounds in the where-clause,
1154         // so e.g., `trait Foo = where u32: PartialEq<Self>` would include `u32: PartialEq<Self>`
1155         // as one of its "superpredicates".
1156         let is_trait_alias = tcx.is_trait_alias(trait_def_id);
1157         let superbounds2 = icx.type_parameter_bounds_in_generics(
1158             generics,
1159             item.hir_id(),
1160             self_param_ty,
1161             OnlySelfBounds(!is_trait_alias),
1162             assoc_name,
1163         );
1164
1165         // Combine the two lists to form the complete set of superbounds:
1166         let superbounds = &*tcx.arena.alloc_from_iter(superbounds1.into_iter().chain(superbounds2));
1167         debug!(?superbounds);
1168
1169         // Now require that immediate supertraits are converted,
1170         // which will, in turn, reach indirect supertraits.
1171         if assoc_name.is_none() {
1172             // Now require that immediate supertraits are converted,
1173             // which will, in turn, reach indirect supertraits.
1174             for &(pred, span) in superbounds {
1175                 debug!("superbound: {:?}", pred);
1176                 if let ty::PredicateKind::Trait(bound) = pred.kind().skip_binder() {
1177                     tcx.at(span).super_predicates_of(bound.def_id());
1178                 }
1179             }
1180         }
1181
1182         ty::GenericPredicates { parent: None, predicates: superbounds }
1183     } else {
1184         // if `assoc_name` is None, then the query should've been redirected to an
1185         // external provider
1186         assert!(assoc_name.is_some());
1187         tcx.super_predicates_of(trait_def_id)
1188     }
1189 }
1190
1191 fn trait_def(tcx: TyCtxt<'_>, def_id: DefId) -> ty::TraitDef {
1192     let item = tcx.hir().expect_item(def_id.expect_local());
1193
1194     let (is_auto, unsafety, items) = match item.kind {
1195         hir::ItemKind::Trait(is_auto, unsafety, .., items) => {
1196             (is_auto == hir::IsAuto::Yes, unsafety, items)
1197         }
1198         hir::ItemKind::TraitAlias(..) => (false, hir::Unsafety::Normal, &[][..]),
1199         _ => span_bug!(item.span, "trait_def_of_item invoked on non-trait"),
1200     };
1201
1202     let paren_sugar = tcx.has_attr(def_id, sym::rustc_paren_sugar);
1203     if paren_sugar && !tcx.features().unboxed_closures {
1204         tcx.sess
1205             .struct_span_err(
1206                 item.span,
1207                 "the `#[rustc_paren_sugar]` attribute is a temporary means of controlling \
1208                  which traits can use parenthetical notation",
1209             )
1210             .help("add `#![feature(unboxed_closures)]` to the crate attributes to use it")
1211             .emit();
1212     }
1213
1214     let is_marker = tcx.has_attr(def_id, sym::marker);
1215     let skip_array_during_method_dispatch =
1216         tcx.has_attr(def_id, sym::rustc_skip_array_during_method_dispatch);
1217     let spec_kind = if tcx.has_attr(def_id, sym::rustc_unsafe_specialization_marker) {
1218         ty::trait_def::TraitSpecializationKind::Marker
1219     } else if tcx.has_attr(def_id, sym::rustc_specialization_trait) {
1220         ty::trait_def::TraitSpecializationKind::AlwaysApplicable
1221     } else {
1222         ty::trait_def::TraitSpecializationKind::None
1223     };
1224     let must_implement_one_of = tcx
1225         .get_attr(def_id, sym::rustc_must_implement_one_of)
1226         // Check that there are at least 2 arguments of `#[rustc_must_implement_one_of]`
1227         // and that they are all identifiers
1228         .and_then(|attr| match attr.meta_item_list() {
1229             Some(items) if items.len() < 2 => {
1230                 tcx.sess
1231                     .struct_span_err(
1232                         attr.span,
1233                         "the `#[rustc_must_implement_one_of]` attribute must be \
1234                         used with at least 2 args",
1235                     )
1236                     .emit();
1237
1238                 None
1239             }
1240             Some(items) => items
1241                 .into_iter()
1242                 .map(|item| item.ident().ok_or(item.span()))
1243                 .collect::<Result<Box<[_]>, _>>()
1244                 .map_err(|span| {
1245                     tcx.sess
1246                         .struct_span_err(span, "must be a name of an associated function")
1247                         .emit();
1248                 })
1249                 .ok()
1250                 .zip(Some(attr.span)),
1251             // Error is reported by `rustc_attr!`
1252             None => None,
1253         })
1254         // Check that all arguments of `#[rustc_must_implement_one_of]` reference
1255         // functions in the trait with default implementations
1256         .and_then(|(list, attr_span)| {
1257             let errors = list.iter().filter_map(|ident| {
1258                 let item = items.iter().find(|item| item.ident == *ident);
1259
1260                 match item {
1261                     Some(item) if matches!(item.kind, hir::AssocItemKind::Fn { .. }) => {
1262                         if !tcx.impl_defaultness(item.id.def_id).has_value() {
1263                             tcx.sess
1264                                 .struct_span_err(
1265                                     item.span,
1266                                     "This function doesn't have a default implementation",
1267                                 )
1268                                 .span_note(attr_span, "required by this annotation")
1269                                 .emit();
1270
1271                             return Some(());
1272                         }
1273
1274                         return None;
1275                     }
1276                     Some(item) => {
1277                         tcx.sess
1278                             .struct_span_err(item.span, "Not a function")
1279                             .span_note(attr_span, "required by this annotation")
1280                             .note(
1281                                 "All `#[rustc_must_implement_one_of]` arguments \
1282                             must be associated function names",
1283                             )
1284                             .emit();
1285                     }
1286                     None => {
1287                         tcx.sess
1288                             .struct_span_err(ident.span, "Function not found in this trait")
1289                             .emit();
1290                     }
1291                 }
1292
1293                 Some(())
1294             });
1295
1296             (errors.count() == 0).then_some(list)
1297         })
1298         // Check for duplicates
1299         .and_then(|list| {
1300             let mut set: FxHashMap<Symbol, Span> = FxHashMap::default();
1301             let mut no_dups = true;
1302
1303             for ident in &*list {
1304                 if let Some(dup) = set.insert(ident.name, ident.span) {
1305                     tcx.sess
1306                         .struct_span_err(vec![dup, ident.span], "Functions names are duplicated")
1307                         .note(
1308                             "All `#[rustc_must_implement_one_of]` arguments \
1309                             must be unique",
1310                         )
1311                         .emit();
1312
1313                     no_dups = false;
1314                 }
1315             }
1316
1317             no_dups.then_some(list)
1318         });
1319
1320     ty::TraitDef::new(
1321         def_id,
1322         unsafety,
1323         paren_sugar,
1324         is_auto,
1325         is_marker,
1326         skip_array_during_method_dispatch,
1327         spec_kind,
1328         must_implement_one_of,
1329     )
1330 }
1331
1332 fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<Span> {
1333     struct LateBoundRegionsDetector<'tcx> {
1334         tcx: TyCtxt<'tcx>,
1335         outer_index: ty::DebruijnIndex,
1336         has_late_bound_regions: Option<Span>,
1337     }
1338
1339     impl<'tcx> Visitor<'tcx> for LateBoundRegionsDetector<'tcx> {
1340         fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
1341             if self.has_late_bound_regions.is_some() {
1342                 return;
1343             }
1344             match ty.kind {
1345                 hir::TyKind::BareFn(..) => {
1346                     self.outer_index.shift_in(1);
1347                     intravisit::walk_ty(self, ty);
1348                     self.outer_index.shift_out(1);
1349                 }
1350                 _ => intravisit::walk_ty(self, ty),
1351             }
1352         }
1353
1354         fn visit_poly_trait_ref(&mut self, tr: &'tcx hir::PolyTraitRef<'tcx>) {
1355             if self.has_late_bound_regions.is_some() {
1356                 return;
1357             }
1358             self.outer_index.shift_in(1);
1359             intravisit::walk_poly_trait_ref(self, tr);
1360             self.outer_index.shift_out(1);
1361         }
1362
1363         fn visit_lifetime(&mut self, lt: &'tcx hir::Lifetime) {
1364             if self.has_late_bound_regions.is_some() {
1365                 return;
1366             }
1367
1368             match self.tcx.named_region(lt.hir_id) {
1369                 Some(rl::Region::Static | rl::Region::EarlyBound(..)) => {}
1370                 Some(rl::Region::LateBound(debruijn, _, _)) if debruijn < self.outer_index => {}
1371                 Some(rl::Region::LateBound(..) | rl::Region::Free(..)) | None => {
1372                     self.has_late_bound_regions = Some(lt.span);
1373                 }
1374             }
1375         }
1376     }
1377
1378     fn has_late_bound_regions<'tcx>(
1379         tcx: TyCtxt<'tcx>,
1380         generics: &'tcx hir::Generics<'tcx>,
1381         decl: &'tcx hir::FnDecl<'tcx>,
1382     ) -> Option<Span> {
1383         let mut visitor = LateBoundRegionsDetector {
1384             tcx,
1385             outer_index: ty::INNERMOST,
1386             has_late_bound_regions: None,
1387         };
1388         for param in generics.params {
1389             if let GenericParamKind::Lifetime { .. } = param.kind {
1390                 if tcx.is_late_bound(param.hir_id) {
1391                     return Some(param.span);
1392                 }
1393             }
1394         }
1395         visitor.visit_fn_decl(decl);
1396         visitor.has_late_bound_regions
1397     }
1398
1399     match node {
1400         Node::TraitItem(item) => match item.kind {
1401             hir::TraitItemKind::Fn(ref sig, _) => {
1402                 has_late_bound_regions(tcx, &item.generics, sig.decl)
1403             }
1404             _ => None,
1405         },
1406         Node::ImplItem(item) => match item.kind {
1407             hir::ImplItemKind::Fn(ref sig, _) => {
1408                 has_late_bound_regions(tcx, &item.generics, sig.decl)
1409             }
1410             _ => None,
1411         },
1412         Node::ForeignItem(item) => match item.kind {
1413             hir::ForeignItemKind::Fn(fn_decl, _, ref generics) => {
1414                 has_late_bound_regions(tcx, generics, fn_decl)
1415             }
1416             _ => None,
1417         },
1418         Node::Item(item) => match item.kind {
1419             hir::ItemKind::Fn(ref sig, .., ref generics, _) => {
1420                 has_late_bound_regions(tcx, generics, sig.decl)
1421             }
1422             _ => None,
1423         },
1424         _ => None,
1425     }
1426 }
1427
1428 struct AnonConstInParamTyDetector {
1429     in_param_ty: bool,
1430     found_anon_const_in_param_ty: bool,
1431     ct: HirId,
1432 }
1433
1434 impl<'v> Visitor<'v> for AnonConstInParamTyDetector {
1435     fn visit_generic_param(&mut self, p: &'v hir::GenericParam<'v>) {
1436         if let GenericParamKind::Const { ty, default: _ } = p.kind {
1437             let prev = self.in_param_ty;
1438             self.in_param_ty = true;
1439             self.visit_ty(ty);
1440             self.in_param_ty = prev;
1441         }
1442     }
1443
1444     fn visit_anon_const(&mut self, c: &'v hir::AnonConst) {
1445         if self.in_param_ty && self.ct == c.hir_id {
1446             self.found_anon_const_in_param_ty = true;
1447         } else {
1448             intravisit::walk_anon_const(self, c)
1449         }
1450     }
1451 }
1452
1453 fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
1454     use rustc_hir::*;
1455
1456     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
1457
1458     let node = tcx.hir().get(hir_id);
1459     let parent_def_id = match node {
1460         Node::ImplItem(_)
1461         | Node::TraitItem(_)
1462         | Node::Variant(_)
1463         | Node::Ctor(..)
1464         | Node::Field(_) => {
1465             let parent_id = tcx.hir().get_parent_item(hir_id);
1466             Some(parent_id.to_def_id())
1467         }
1468         // FIXME(#43408) always enable this once `lazy_normalization` is
1469         // stable enough and does not need a feature gate anymore.
1470         Node::AnonConst(_) => {
1471             let parent_def_id = tcx.hir().get_parent_item(hir_id);
1472
1473             let mut in_param_ty = false;
1474             for (_parent, node) in tcx.hir().parent_iter(hir_id) {
1475                 if let Some(generics) = node.generics() {
1476                     let mut visitor = AnonConstInParamTyDetector {
1477                         in_param_ty: false,
1478                         found_anon_const_in_param_ty: false,
1479                         ct: hir_id,
1480                     };
1481
1482                     visitor.visit_generics(generics);
1483                     in_param_ty = visitor.found_anon_const_in_param_ty;
1484                     break;
1485                 }
1486             }
1487
1488             if in_param_ty {
1489                 // We do not allow generic parameters in anon consts if we are inside
1490                 // of a const parameter type, e.g. `struct Foo<const N: usize, const M: [u8; N]>` is not allowed.
1491                 None
1492             } else if tcx.lazy_normalization() {
1493                 if let Some(param_id) = tcx.hir().opt_const_param_default_param_hir_id(hir_id) {
1494                     // If the def_id we are calling generics_of on is an anon ct default i.e:
1495                     //
1496                     // struct Foo<const N: usize = { .. }>;
1497                     //        ^^^       ^          ^^^^^^ def id of this anon const
1498                     //        ^         ^ param_id
1499                     //        ^ parent_def_id
1500                     //
1501                     // then we only want to return generics for params to the left of `N`. If we don't do that we
1502                     // end up with that const looking like: `ty::ConstKind::Unevaluated(def_id, substs: [N#0])`.
1503                     //
1504                     // This causes ICEs (#86580) when building the substs for Foo in `fn foo() -> Foo { .. }` as
1505                     // we substitute the defaults with the partially built substs when we build the substs. Subst'ing
1506                     // the `N#0` on the unevaluated const indexes into the empty substs we're in the process of building.
1507                     //
1508                     // We fix this by having this function return the parent's generics ourselves and truncating the
1509                     // generics to only include non-forward declared params (with the exception of the `Self` ty)
1510                     //
1511                     // For the above code example that means we want `substs: []`
1512                     // For the following struct def we want `substs: [N#0]` when generics_of is called on
1513                     // the def id of the `{ N + 1 }` anon const
1514                     // struct Foo<const N: usize, const M: usize = { N + 1 }>;
1515                     //
1516                     // This has some implications for how we get the predicates available to the anon const
1517                     // see `explicit_predicates_of` for more information on this
1518                     let generics = tcx.generics_of(parent_def_id.to_def_id());
1519                     let param_def = tcx.hir().local_def_id(param_id).to_def_id();
1520                     let param_def_idx = generics.param_def_id_to_index[&param_def];
1521                     // In the above example this would be .params[..N#0]
1522                     let params = generics.params[..param_def_idx as usize].to_owned();
1523                     let param_def_id_to_index =
1524                         params.iter().map(|param| (param.def_id, param.index)).collect();
1525
1526                     return ty::Generics {
1527                         // we set the parent of these generics to be our parent's parent so that we
1528                         // dont end up with substs: [N, M, N] for the const default on a struct like this:
1529                         // struct Foo<const N: usize, const M: usize = { ... }>;
1530                         parent: generics.parent,
1531                         parent_count: generics.parent_count,
1532                         params,
1533                         param_def_id_to_index,
1534                         has_self: generics.has_self,
1535                         has_late_bound_regions: generics.has_late_bound_regions,
1536                     };
1537                 }
1538
1539                 // HACK(eddyb) this provides the correct generics when
1540                 // `feature(generic_const_expressions)` is enabled, so that const expressions
1541                 // used with const generics, e.g. `Foo<{N+1}>`, can work at all.
1542                 //
1543                 // Note that we do not supply the parent generics when using
1544                 // `min_const_generics`.
1545                 Some(parent_def_id.to_def_id())
1546             } else {
1547                 let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
1548                 match parent_node {
1549                     // HACK(eddyb) this provides the correct generics for repeat
1550                     // expressions' count (i.e. `N` in `[x; N]`), and explicit
1551                     // `enum` discriminants (i.e. `D` in `enum Foo { Bar = D }`),
1552                     // as they shouldn't be able to cause query cycle errors.
1553                     Node::Expr(&Expr { kind: ExprKind::Repeat(_, ref constant), .. })
1554                         if constant.hir_id() == hir_id =>
1555                     {
1556                         Some(parent_def_id.to_def_id())
1557                     }
1558                     Node::Variant(Variant { disr_expr: Some(ref constant), .. })
1559                         if constant.hir_id == hir_id =>
1560                     {
1561                         Some(parent_def_id.to_def_id())
1562                     }
1563                     Node::Expr(&Expr { kind: ExprKind::ConstBlock(_), .. }) => {
1564                         Some(tcx.typeck_root_def_id(def_id))
1565                     }
1566                     // Exclude `GlobalAsm` here which cannot have generics.
1567                     Node::Expr(&Expr { kind: ExprKind::InlineAsm(asm), .. })
1568                         if asm.operands.iter().any(|(op, _op_sp)| match op {
1569                             hir::InlineAsmOperand::Const { anon_const }
1570                             | hir::InlineAsmOperand::SymFn { anon_const } => {
1571                                 anon_const.hir_id == hir_id
1572                             }
1573                             _ => false,
1574                         }) =>
1575                     {
1576                         Some(parent_def_id.to_def_id())
1577                     }
1578                     _ => None,
1579                 }
1580             }
1581         }
1582         Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure { .. }, .. }) => {
1583             Some(tcx.typeck_root_def_id(def_id))
1584         }
1585         Node::Item(item) => match item.kind {
1586             ItemKind::OpaqueTy(hir::OpaqueTy {
1587                 origin:
1588                     hir::OpaqueTyOrigin::FnReturn(fn_def_id) | hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
1589                 in_trait,
1590                 ..
1591             }) => {
1592                 if in_trait {
1593                     assert!(matches!(tcx.def_kind(fn_def_id), DefKind::AssocFn))
1594                 } else {
1595                     assert!(matches!(tcx.def_kind(fn_def_id), DefKind::AssocFn | DefKind::Fn))
1596                 }
1597                 Some(fn_def_id.to_def_id())
1598             }
1599             ItemKind::OpaqueTy(hir::OpaqueTy { origin: hir::OpaqueTyOrigin::TyAlias, .. }) => {
1600                 let parent_id = tcx.hir().get_parent_item(hir_id);
1601                 assert_ne!(parent_id, hir::CRATE_OWNER_ID);
1602                 debug!("generics_of: parent of opaque ty {:?} is {:?}", def_id, parent_id);
1603                 // Opaque types are always nested within another item, and
1604                 // inherit the generics of the item.
1605                 Some(parent_id.to_def_id())
1606             }
1607             _ => None,
1608         },
1609         _ => None,
1610     };
1611
1612     enum Defaults {
1613         Allowed,
1614         // See #36887
1615         FutureCompatDisallowed,
1616         Deny,
1617     }
1618
1619     let no_generics = hir::Generics::empty();
1620     let ast_generics = node.generics().unwrap_or(&no_generics);
1621     let (opt_self, allow_defaults) = match node {
1622         Node::Item(item) => {
1623             match item.kind {
1624                 ItemKind::Trait(..) | ItemKind::TraitAlias(..) => {
1625                     // Add in the self type parameter.
1626                     //
1627                     // Something of a hack: use the node id for the trait, also as
1628                     // the node id for the Self type parameter.
1629                     let opt_self = Some(ty::GenericParamDef {
1630                         index: 0,
1631                         name: kw::SelfUpper,
1632                         def_id,
1633                         pure_wrt_drop: false,
1634                         kind: ty::GenericParamDefKind::Type {
1635                             has_default: false,
1636                             synthetic: false,
1637                         },
1638                     });
1639
1640                     (opt_self, Defaults::Allowed)
1641                 }
1642                 ItemKind::TyAlias(..)
1643                 | ItemKind::Enum(..)
1644                 | ItemKind::Struct(..)
1645                 | ItemKind::OpaqueTy(..)
1646                 | ItemKind::Union(..) => (None, Defaults::Allowed),
1647                 _ => (None, Defaults::FutureCompatDisallowed),
1648             }
1649         }
1650
1651         // GATs
1652         Node::TraitItem(item) if matches!(item.kind, TraitItemKind::Type(..)) => {
1653             (None, Defaults::Deny)
1654         }
1655         Node::ImplItem(item) if matches!(item.kind, ImplItemKind::TyAlias(..)) => {
1656             (None, Defaults::Deny)
1657         }
1658
1659         _ => (None, Defaults::FutureCompatDisallowed),
1660     };
1661
1662     let has_self = opt_self.is_some();
1663     let mut parent_has_self = false;
1664     let mut own_start = has_self as u32;
1665     let parent_count = parent_def_id.map_or(0, |def_id| {
1666         let generics = tcx.generics_of(def_id);
1667         assert!(!has_self);
1668         parent_has_self = generics.has_self;
1669         own_start = generics.count() as u32;
1670         generics.parent_count + generics.params.len()
1671     });
1672
1673     let mut params: Vec<_> = Vec::with_capacity(ast_generics.params.len() + has_self as usize);
1674
1675     if let Some(opt_self) = opt_self {
1676         params.push(opt_self);
1677     }
1678
1679     let early_lifetimes = early_bound_lifetimes_from_generics(tcx, ast_generics);
1680     params.extend(early_lifetimes.enumerate().map(|(i, param)| ty::GenericParamDef {
1681         name: param.name.ident().name,
1682         index: own_start + i as u32,
1683         def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
1684         pure_wrt_drop: param.pure_wrt_drop,
1685         kind: ty::GenericParamDefKind::Lifetime,
1686     }));
1687
1688     // Now create the real type and const parameters.
1689     let type_start = own_start - has_self as u32 + params.len() as u32;
1690     let mut i = 0;
1691
1692     const TYPE_DEFAULT_NOT_ALLOWED: &'static str = "defaults for type parameters are only allowed in \
1693     `struct`, `enum`, `type`, or `trait` definitions";
1694
1695     params.extend(ast_generics.params.iter().filter_map(|param| match param.kind {
1696         GenericParamKind::Lifetime { .. } => None,
1697         GenericParamKind::Type { ref default, synthetic, .. } => {
1698             if default.is_some() {
1699                 match allow_defaults {
1700                     Defaults::Allowed => {}
1701                     Defaults::FutureCompatDisallowed
1702                         if tcx.features().default_type_parameter_fallback => {}
1703                     Defaults::FutureCompatDisallowed => {
1704                         tcx.struct_span_lint_hir(
1705                             lint::builtin::INVALID_TYPE_PARAM_DEFAULT,
1706                             param.hir_id,
1707                             param.span,
1708                             |lint| {
1709                                 lint.build(TYPE_DEFAULT_NOT_ALLOWED).emit();
1710                             },
1711                         );
1712                     }
1713                     Defaults::Deny => {
1714                         tcx.sess.span_err(param.span, TYPE_DEFAULT_NOT_ALLOWED);
1715                     }
1716                 }
1717             }
1718
1719             let kind = ty::GenericParamDefKind::Type { has_default: default.is_some(), synthetic };
1720
1721             let param_def = ty::GenericParamDef {
1722                 index: type_start + i as u32,
1723                 name: param.name.ident().name,
1724                 def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
1725                 pure_wrt_drop: param.pure_wrt_drop,
1726                 kind,
1727             };
1728             i += 1;
1729             Some(param_def)
1730         }
1731         GenericParamKind::Const { default, .. } => {
1732             if !matches!(allow_defaults, Defaults::Allowed) && default.is_some() {
1733                 tcx.sess.span_err(
1734                     param.span,
1735                     "defaults for const parameters are only allowed in \
1736                     `struct`, `enum`, `type`, or `trait` definitions",
1737                 );
1738             }
1739
1740             let param_def = ty::GenericParamDef {
1741                 index: type_start + i as u32,
1742                 name: param.name.ident().name,
1743                 def_id: tcx.hir().local_def_id(param.hir_id).to_def_id(),
1744                 pure_wrt_drop: param.pure_wrt_drop,
1745                 kind: ty::GenericParamDefKind::Const { has_default: default.is_some() },
1746             };
1747             i += 1;
1748             Some(param_def)
1749         }
1750     }));
1751
1752     // provide junk type parameter defs - the only place that
1753     // cares about anything but the length is instantiation,
1754     // and we don't do that for closures.
1755     if let Node::Expr(&hir::Expr {
1756         kind: hir::ExprKind::Closure(hir::Closure { movability: gen, .. }),
1757         ..
1758     }) = node
1759     {
1760         let dummy_args = if gen.is_some() {
1761             &["<resume_ty>", "<yield_ty>", "<return_ty>", "<witness>", "<upvars>"][..]
1762         } else {
1763             &["<closure_kind>", "<closure_signature>", "<upvars>"][..]
1764         };
1765
1766         params.extend(dummy_args.iter().enumerate().map(|(i, &arg)| ty::GenericParamDef {
1767             index: type_start + i as u32,
1768             name: Symbol::intern(arg),
1769             def_id,
1770             pure_wrt_drop: false,
1771             kind: ty::GenericParamDefKind::Type { has_default: false, synthetic: false },
1772         }));
1773     }
1774
1775     // provide junk type parameter defs for const blocks.
1776     if let Node::AnonConst(_) = node {
1777         let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
1778         if let Node::Expr(&Expr { kind: ExprKind::ConstBlock(_), .. }) = parent_node {
1779             params.push(ty::GenericParamDef {
1780                 index: type_start,
1781                 name: Symbol::intern("<const_ty>"),
1782                 def_id,
1783                 pure_wrt_drop: false,
1784                 kind: ty::GenericParamDefKind::Type { has_default: false, synthetic: false },
1785             });
1786         }
1787     }
1788
1789     let param_def_id_to_index = params.iter().map(|param| (param.def_id, param.index)).collect();
1790
1791     ty::Generics {
1792         parent: parent_def_id,
1793         parent_count,
1794         params,
1795         param_def_id_to_index,
1796         has_self: has_self || parent_has_self,
1797         has_late_bound_regions: has_late_bound_regions(tcx, node),
1798     }
1799 }
1800
1801 fn are_suggestable_generic_args(generic_args: &[hir::GenericArg<'_>]) -> bool {
1802     generic_args.iter().any(|arg| match arg {
1803         hir::GenericArg::Type(ty) => is_suggestable_infer_ty(ty),
1804         hir::GenericArg::Infer(_) => true,
1805         _ => false,
1806     })
1807 }
1808
1809 /// Whether `ty` is a type with `_` placeholders that can be inferred. Used in diagnostics only to
1810 /// use inference to provide suggestions for the appropriate type if possible.
1811 fn is_suggestable_infer_ty(ty: &hir::Ty<'_>) -> bool {
1812     debug!(?ty);
1813     use hir::TyKind::*;
1814     match &ty.kind {
1815         Infer => true,
1816         Slice(ty) => is_suggestable_infer_ty(ty),
1817         Array(ty, length) => {
1818             is_suggestable_infer_ty(ty) || matches!(length, hir::ArrayLen::Infer(_, _))
1819         }
1820         Tup(tys) => tys.iter().any(is_suggestable_infer_ty),
1821         Ptr(mut_ty) | Rptr(_, mut_ty) => is_suggestable_infer_ty(mut_ty.ty),
1822         OpaqueDef(_, generic_args, _) => are_suggestable_generic_args(generic_args),
1823         Path(hir::QPath::TypeRelative(ty, segment)) => {
1824             is_suggestable_infer_ty(ty) || are_suggestable_generic_args(segment.args().args)
1825         }
1826         Path(hir::QPath::Resolved(ty_opt, hir::Path { segments, .. })) => {
1827             ty_opt.map_or(false, is_suggestable_infer_ty)
1828                 || segments.iter().any(|segment| are_suggestable_generic_args(segment.args().args))
1829         }
1830         _ => false,
1831     }
1832 }
1833
1834 pub fn get_infer_ret_ty<'hir>(output: &'hir hir::FnRetTy<'hir>) -> Option<&'hir hir::Ty<'hir>> {
1835     if let hir::FnRetTy::Return(ty) = output {
1836         if is_suggestable_infer_ty(ty) {
1837             return Some(&*ty);
1838         }
1839     }
1840     None
1841 }
1842
1843 #[instrument(level = "debug", skip(tcx))]
1844 fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
1845     use rustc_hir::Node::*;
1846     use rustc_hir::*;
1847
1848     let def_id = def_id.expect_local();
1849     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
1850
1851     let icx = ItemCtxt::new(tcx, def_id.to_def_id());
1852
1853     match tcx.hir().get(hir_id) {
1854         TraitItem(hir::TraitItem {
1855             kind: TraitItemKind::Fn(sig, TraitFn::Provided(_)),
1856             generics,
1857             ..
1858         })
1859         | Item(hir::Item { kind: ItemKind::Fn(sig, generics, _), .. }) => {
1860             infer_return_ty_for_fn_sig(tcx, sig, generics, def_id, &icx)
1861         }
1862
1863         ImplItem(hir::ImplItem { kind: ImplItemKind::Fn(sig, _), generics, .. }) => {
1864             // Do not try to inference the return type for a impl method coming from a trait
1865             if let Item(hir::Item { kind: ItemKind::Impl(i), .. }) =
1866                 tcx.hir().get(tcx.hir().get_parent_node(hir_id))
1867                 && i.of_trait.is_some()
1868             {
1869                 <dyn AstConv<'_>>::ty_of_fn(
1870                     &icx,
1871                     hir_id,
1872                     sig.header.unsafety,
1873                     sig.header.abi,
1874                     sig.decl,
1875                     Some(generics),
1876                     None,
1877                 )
1878             } else {
1879                 infer_return_ty_for_fn_sig(tcx, sig, generics, def_id, &icx)
1880             }
1881         }
1882
1883         TraitItem(hir::TraitItem {
1884             kind: TraitItemKind::Fn(FnSig { header, decl, span: _ }, _),
1885             generics,
1886             ..
1887         }) => <dyn AstConv<'_>>::ty_of_fn(
1888             &icx,
1889             hir_id,
1890             header.unsafety,
1891             header.abi,
1892             decl,
1893             Some(generics),
1894             None,
1895         ),
1896
1897         ForeignItem(&hir::ForeignItem { kind: ForeignItemKind::Fn(fn_decl, _, _), .. }) => {
1898             let abi = tcx.hir().get_foreign_abi(hir_id);
1899             compute_sig_of_foreign_fn_decl(tcx, def_id.to_def_id(), fn_decl, abi)
1900         }
1901
1902         Ctor(data) | Variant(hir::Variant { data, .. }) if data.ctor_hir_id().is_some() => {
1903             let ty = tcx.type_of(tcx.hir().get_parent_item(hir_id));
1904             let inputs =
1905                 data.fields().iter().map(|f| tcx.type_of(tcx.hir().local_def_id(f.hir_id)));
1906             ty::Binder::dummy(tcx.mk_fn_sig(
1907                 inputs,
1908                 ty,
1909                 false,
1910                 hir::Unsafety::Normal,
1911                 abi::Abi::Rust,
1912             ))
1913         }
1914
1915         Expr(&hir::Expr { kind: hir::ExprKind::Closure { .. }, .. }) => {
1916             // Closure signatures are not like other function
1917             // signatures and cannot be accessed through `fn_sig`. For
1918             // example, a closure signature excludes the `self`
1919             // argument. In any case they are embedded within the
1920             // closure type as part of the `ClosureSubsts`.
1921             //
1922             // To get the signature of a closure, you should use the
1923             // `sig` method on the `ClosureSubsts`:
1924             //
1925             //    substs.as_closure().sig(def_id, tcx)
1926             bug!(
1927                 "to get the signature of a closure, use `substs.as_closure().sig()` not `fn_sig()`",
1928             );
1929         }
1930
1931         x => {
1932             bug!("unexpected sort of node in fn_sig(): {:?}", x);
1933         }
1934     }
1935 }
1936
1937 fn infer_return_ty_for_fn_sig<'tcx>(
1938     tcx: TyCtxt<'tcx>,
1939     sig: &hir::FnSig<'_>,
1940     generics: &hir::Generics<'_>,
1941     def_id: LocalDefId,
1942     icx: &ItemCtxt<'tcx>,
1943 ) -> ty::PolyFnSig<'tcx> {
1944     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
1945
1946     match get_infer_ret_ty(&sig.decl.output) {
1947         Some(ty) => {
1948             let fn_sig = tcx.typeck(def_id).liberated_fn_sigs()[hir_id];
1949             // Typeck doesn't expect erased regions to be returned from `type_of`.
1950             let fn_sig = tcx.fold_regions(fn_sig, |r, _| match *r {
1951                 ty::ReErased => tcx.lifetimes.re_static,
1952                 _ => r,
1953             });
1954             let fn_sig = ty::Binder::dummy(fn_sig);
1955
1956             let mut visitor = HirPlaceholderCollector::default();
1957             visitor.visit_ty(ty);
1958             let mut diag = bad_placeholder(tcx, visitor.0, "return type");
1959             let ret_ty = fn_sig.skip_binder().output();
1960             if ret_ty.is_suggestable(tcx, false) {
1961                 diag.span_suggestion(
1962                     ty.span,
1963                     "replace with the correct return type",
1964                     ret_ty,
1965                     Applicability::MachineApplicable,
1966                 );
1967             } else if matches!(ret_ty.kind(), ty::FnDef(..)) {
1968                 let fn_sig = ret_ty.fn_sig(tcx);
1969                 if fn_sig
1970                     .skip_binder()
1971                     .inputs_and_output
1972                     .iter()
1973                     .all(|t| t.is_suggestable(tcx, false))
1974                 {
1975                     diag.span_suggestion(
1976                         ty.span,
1977                         "replace with the correct return type",
1978                         fn_sig,
1979                         Applicability::MachineApplicable,
1980                     );
1981                 }
1982             } else if ret_ty.is_closure() {
1983                 // We're dealing with a closure, so we should suggest using `impl Fn` or trait bounds
1984                 // to prevent the user from getting a papercut while trying to use the unique closure
1985                 // syntax (e.g. `[closure@src/lib.rs:2:5: 2:9]`).
1986                 diag.help("consider using an `Fn`, `FnMut`, or `FnOnce` trait bound");
1987                 diag.note("for more information on `Fn` traits and closure types, see https://doc.rust-lang.org/book/ch13-01-closures.html");
1988             }
1989             diag.emit();
1990
1991             fn_sig
1992         }
1993         None => <dyn AstConv<'_>>::ty_of_fn(
1994             icx,
1995             hir_id,
1996             sig.header.unsafety,
1997             sig.header.abi,
1998             sig.decl,
1999             Some(generics),
2000             None,
2001         ),
2002     }
2003 }
2004
2005 fn impl_trait_ref(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ty::TraitRef<'_>> {
2006     let icx = ItemCtxt::new(tcx, def_id);
2007     match tcx.hir().expect_item(def_id.expect_local()).kind {
2008         hir::ItemKind::Impl(ref impl_) => impl_.of_trait.as_ref().map(|ast_trait_ref| {
2009             let selfty = tcx.type_of(def_id);
2010             <dyn AstConv<'_>>::instantiate_mono_trait_ref(&icx, ast_trait_ref, selfty)
2011         }),
2012         _ => bug!(),
2013     }
2014 }
2015
2016 fn impl_polarity(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ImplPolarity {
2017     let is_rustc_reservation = tcx.has_attr(def_id, sym::rustc_reservation_impl);
2018     let item = tcx.hir().expect_item(def_id.expect_local());
2019     match &item.kind {
2020         hir::ItemKind::Impl(hir::Impl {
2021             polarity: hir::ImplPolarity::Negative(span),
2022             of_trait,
2023             ..
2024         }) => {
2025             if is_rustc_reservation {
2026                 let span = span.to(of_trait.as_ref().map_or(*span, |t| t.path.span));
2027                 tcx.sess.span_err(span, "reservation impls can't be negative");
2028             }
2029             ty::ImplPolarity::Negative
2030         }
2031         hir::ItemKind::Impl(hir::Impl {
2032             polarity: hir::ImplPolarity::Positive,
2033             of_trait: None,
2034             ..
2035         }) => {
2036             if is_rustc_reservation {
2037                 tcx.sess.span_err(item.span, "reservation impls can't be inherent");
2038             }
2039             ty::ImplPolarity::Positive
2040         }
2041         hir::ItemKind::Impl(hir::Impl {
2042             polarity: hir::ImplPolarity::Positive,
2043             of_trait: Some(_),
2044             ..
2045         }) => {
2046             if is_rustc_reservation {
2047                 ty::ImplPolarity::Reservation
2048             } else {
2049                 ty::ImplPolarity::Positive
2050             }
2051         }
2052         item => bug!("impl_polarity: {:?} not an impl", item),
2053     }
2054 }
2055
2056 /// Returns the early-bound lifetimes declared in this generics
2057 /// listing. For anything other than fns/methods, this is just all
2058 /// the lifetimes that are declared. For fns or methods, we have to
2059 /// screen out those that do not appear in any where-clauses etc using
2060 /// `resolve_lifetime::early_bound_lifetimes`.
2061 fn early_bound_lifetimes_from_generics<'a, 'tcx: 'a>(
2062     tcx: TyCtxt<'tcx>,
2063     generics: &'a hir::Generics<'a>,
2064 ) -> impl Iterator<Item = &'a hir::GenericParam<'a>> + Captures<'tcx> {
2065     generics.params.iter().filter(move |param| match param.kind {
2066         GenericParamKind::Lifetime { .. } => !tcx.is_late_bound(param.hir_id),
2067         _ => false,
2068     })
2069 }
2070
2071 /// Returns a list of type predicates for the definition with ID `def_id`, including inferred
2072 /// lifetime constraints. This includes all predicates returned by `explicit_predicates_of`, plus
2073 /// inferred constraints concerning which regions outlive other regions.
2074 #[instrument(level = "debug", skip(tcx))]
2075 fn predicates_defined_on(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2076     let mut result = tcx.explicit_predicates_of(def_id);
2077     debug!("predicates_defined_on: explicit_predicates_of({:?}) = {:?}", def_id, result,);
2078     let inferred_outlives = tcx.inferred_outlives_of(def_id);
2079     if !inferred_outlives.is_empty() {
2080         debug!(
2081             "predicates_defined_on: inferred_outlives_of({:?}) = {:?}",
2082             def_id, inferred_outlives,
2083         );
2084         if result.predicates.is_empty() {
2085             result.predicates = inferred_outlives;
2086         } else {
2087             result.predicates = tcx
2088                 .arena
2089                 .alloc_from_iter(result.predicates.iter().chain(inferred_outlives).copied());
2090         }
2091     }
2092
2093     debug!("predicates_defined_on({:?}) = {:?}", def_id, result);
2094     result
2095 }
2096
2097 /// Returns a list of all type predicates (explicit and implicit) for the definition with
2098 /// ID `def_id`. This includes all predicates returned by `predicates_defined_on`, plus
2099 /// `Self: Trait` predicates for traits.
2100 fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2101     let mut result = tcx.predicates_defined_on(def_id);
2102
2103     if tcx.is_trait(def_id) {
2104         // For traits, add `Self: Trait` predicate. This is
2105         // not part of the predicates that a user writes, but it
2106         // is something that one must prove in order to invoke a
2107         // method or project an associated type.
2108         //
2109         // In the chalk setup, this predicate is not part of the
2110         // "predicates" for a trait item. But it is useful in
2111         // rustc because if you directly (e.g.) invoke a trait
2112         // method like `Trait::method(...)`, you must naturally
2113         // prove that the trait applies to the types that were
2114         // used, and adding the predicate into this list ensures
2115         // that this is done.
2116         //
2117         // We use a DUMMY_SP here as a way to signal trait bounds that come
2118         // from the trait itself that *shouldn't* be shown as the source of
2119         // an obligation and instead be skipped. Otherwise we'd use
2120         // `tcx.def_span(def_id);`
2121
2122         let constness = if tcx.has_attr(def_id, sym::const_trait) {
2123             ty::BoundConstness::ConstIfConst
2124         } else {
2125             ty::BoundConstness::NotConst
2126         };
2127
2128         let span = rustc_span::DUMMY_SP;
2129         result.predicates =
2130             tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(std::iter::once((
2131                 ty::TraitRef::identity(tcx, def_id).with_constness(constness).to_predicate(tcx),
2132                 span,
2133             ))));
2134     }
2135     debug!("predicates_of(def_id={:?}) = {:?}", def_id, result);
2136     result
2137 }
2138
2139 /// Returns a list of user-specified type predicates for the definition with ID `def_id`.
2140 /// N.B., this does not include any implied/inferred constraints.
2141 #[instrument(level = "trace", skip(tcx), ret)]
2142 fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
2143     use rustc_hir::*;
2144
2145     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2146     let node = tcx.hir().get(hir_id);
2147
2148     let mut is_trait = None;
2149     let mut is_default_impl_trait = None;
2150
2151     let icx = ItemCtxt::new(tcx, def_id);
2152
2153     const NO_GENERICS: &hir::Generics<'_> = hir::Generics::empty();
2154
2155     // We use an `IndexSet` to preserves order of insertion.
2156     // Preserving the order of insertion is important here so as not to break UI tests.
2157     let mut predicates: FxIndexSet<(ty::Predicate<'_>, Span)> = FxIndexSet::default();
2158
2159     let ast_generics = match node {
2160         Node::TraitItem(item) => item.generics,
2161
2162         Node::ImplItem(item) => item.generics,
2163
2164         Node::Item(item) => {
2165             match item.kind {
2166                 ItemKind::Impl(ref impl_) => {
2167                     if impl_.defaultness.is_default() {
2168                         is_default_impl_trait = tcx.impl_trait_ref(def_id).map(ty::Binder::dummy);
2169                     }
2170                     &impl_.generics
2171                 }
2172                 ItemKind::Fn(.., ref generics, _)
2173                 | ItemKind::TyAlias(_, ref generics)
2174                 | ItemKind::Enum(_, ref generics)
2175                 | ItemKind::Struct(_, ref generics)
2176                 | ItemKind::Union(_, ref generics) => *generics,
2177
2178                 ItemKind::Trait(_, _, ref generics, ..) => {
2179                     is_trait = Some(ty::TraitRef::identity(tcx, def_id));
2180                     *generics
2181                 }
2182                 ItemKind::TraitAlias(ref generics, _) => {
2183                     is_trait = Some(ty::TraitRef::identity(tcx, def_id));
2184                     *generics
2185                 }
2186                 ItemKind::OpaqueTy(OpaqueTy {
2187                     origin: hir::OpaqueTyOrigin::AsyncFn(..) | hir::OpaqueTyOrigin::FnReturn(..),
2188                     ..
2189                 }) => {
2190                     // return-position impl trait
2191                     //
2192                     // We don't inherit predicates from the parent here:
2193                     // If we have, say `fn f<'a, T: 'a>() -> impl Sized {}`
2194                     // then the return type is `f::<'static, T>::{{opaque}}`.
2195                     //
2196                     // If we inherited the predicates of `f` then we would
2197                     // require that `T: 'static` to show that the return
2198                     // type is well-formed.
2199                     //
2200                     // The only way to have something with this opaque type
2201                     // is from the return type of the containing function,
2202                     // which will ensure that the function's predicates
2203                     // hold.
2204                     return ty::GenericPredicates { parent: None, predicates: &[] };
2205                 }
2206                 ItemKind::OpaqueTy(OpaqueTy {
2207                     ref generics,
2208                     origin: hir::OpaqueTyOrigin::TyAlias,
2209                     ..
2210                 }) => {
2211                     // type-alias impl trait
2212                     generics
2213                 }
2214
2215                 _ => NO_GENERICS,
2216             }
2217         }
2218
2219         Node::ForeignItem(item) => match item.kind {
2220             ForeignItemKind::Static(..) => NO_GENERICS,
2221             ForeignItemKind::Fn(_, _, ref generics) => *generics,
2222             ForeignItemKind::Type => NO_GENERICS,
2223         },
2224
2225         _ => NO_GENERICS,
2226     };
2227
2228     let generics = tcx.generics_of(def_id);
2229     let parent_count = generics.parent_count as u32;
2230     let has_own_self = generics.has_self && parent_count == 0;
2231
2232     // Below we'll consider the bounds on the type parameters (including `Self`)
2233     // and the explicit where-clauses, but to get the full set of predicates
2234     // on a trait we need to add in the supertrait bounds and bounds found on
2235     // associated types.
2236     if let Some(_trait_ref) = is_trait {
2237         predicates.extend(tcx.super_predicates_of(def_id).predicates.iter().cloned());
2238     }
2239
2240     // In default impls, we can assume that the self type implements
2241     // the trait. So in:
2242     //
2243     //     default impl Foo for Bar { .. }
2244     //
2245     // we add a default where clause `Foo: Bar`. We do a similar thing for traits
2246     // (see below). Recall that a default impl is not itself an impl, but rather a
2247     // set of defaults that can be incorporated into another impl.
2248     if let Some(trait_ref) = is_default_impl_trait {
2249         predicates.insert((trait_ref.without_const().to_predicate(tcx), tcx.def_span(def_id)));
2250     }
2251
2252     // Collect the region predicates that were declared inline as
2253     // well. In the case of parameters declared on a fn or method, we
2254     // have to be careful to only iterate over early-bound regions.
2255     let mut index = parent_count
2256         + has_own_self as u32
2257         + early_bound_lifetimes_from_generics(tcx, ast_generics).count() as u32;
2258
2259     trace!(?predicates);
2260     trace!(?ast_generics);
2261
2262     // Collect the predicates that were written inline by the user on each
2263     // type parameter (e.g., `<T: Foo>`).
2264     for param in ast_generics.params {
2265         match param.kind {
2266             // We already dealt with early bound lifetimes above.
2267             GenericParamKind::Lifetime { .. } => (),
2268             GenericParamKind::Type { .. } => {
2269                 let name = param.name.ident().name;
2270                 let param_ty = ty::ParamTy::new(index, name).to_ty(tcx);
2271                 index += 1;
2272
2273                 let mut bounds = Bounds::default();
2274                 // Params are implicitly sized unless a `?Sized` bound is found
2275                 <dyn AstConv<'_>>::add_implicitly_sized(
2276                     &icx,
2277                     &mut bounds,
2278                     &[],
2279                     Some((param.hir_id, ast_generics.predicates)),
2280                     param.span,
2281                 );
2282                 trace!(?bounds);
2283                 predicates.extend(bounds.predicates(tcx, param_ty));
2284                 trace!(?predicates);
2285             }
2286             GenericParamKind::Const { .. } => {
2287                 // Bounds on const parameters are currently not possible.
2288                 index += 1;
2289             }
2290         }
2291     }
2292
2293     trace!(?predicates);
2294     // Add in the bounds that appear in the where-clause.
2295     for predicate in ast_generics.predicates {
2296         match predicate {
2297             hir::WherePredicate::BoundPredicate(bound_pred) => {
2298                 let ty = icx.to_ty(bound_pred.bounded_ty);
2299                 let bound_vars = icx.tcx.late_bound_vars(bound_pred.bounded_ty.hir_id);
2300
2301                 // Keep the type around in a dummy predicate, in case of no bounds.
2302                 // That way, `where Ty:` is not a complete noop (see #53696) and `Ty`
2303                 // is still checked for WF.
2304                 if bound_pred.bounds.is_empty() {
2305                     if let ty::Param(_) = ty.kind() {
2306                         // This is a `where T:`, which can be in the HIR from the
2307                         // transformation that moves `?Sized` to `T`'s declaration.
2308                         // We can skip the predicate because type parameters are
2309                         // trivially WF, but also we *should*, to avoid exposing
2310                         // users who never wrote `where Type:,` themselves, to
2311                         // compiler/tooling bugs from not handling WF predicates.
2312                     } else {
2313                         let span = bound_pred.bounded_ty.span;
2314                         let predicate = ty::Binder::bind_with_vars(
2315                             ty::PredicateKind::WellFormed(ty.into()),
2316                             bound_vars,
2317                         );
2318                         predicates.insert((predicate.to_predicate(tcx), span));
2319                     }
2320                 }
2321
2322                 let mut bounds = Bounds::default();
2323                 <dyn AstConv<'_>>::add_bounds(
2324                     &icx,
2325                     ty,
2326                     bound_pred.bounds.iter(),
2327                     &mut bounds,
2328                     bound_vars,
2329                 );
2330                 predicates.extend(bounds.predicates(tcx, ty));
2331             }
2332
2333             hir::WherePredicate::RegionPredicate(region_pred) => {
2334                 let r1 = <dyn AstConv<'_>>::ast_region_to_region(&icx, &region_pred.lifetime, None);
2335                 predicates.extend(region_pred.bounds.iter().map(|bound| {
2336                     let (r2, span) = match bound {
2337                         hir::GenericBound::Outlives(lt) => {
2338                             (<dyn AstConv<'_>>::ast_region_to_region(&icx, lt, None), lt.span)
2339                         }
2340                         _ => bug!(),
2341                     };
2342                     let pred = ty::Binder::dummy(ty::PredicateKind::RegionOutlives(
2343                         ty::OutlivesPredicate(r1, r2),
2344                     ))
2345                     .to_predicate(icx.tcx);
2346
2347                     (pred, span)
2348                 }))
2349             }
2350
2351             hir::WherePredicate::EqPredicate(..) => {
2352                 // FIXME(#20041)
2353             }
2354         }
2355     }
2356
2357     if tcx.features().generic_const_exprs {
2358         predicates.extend(const_evaluatable_predicates_of(tcx, def_id.expect_local()));
2359     }
2360
2361     let mut predicates: Vec<_> = predicates.into_iter().collect();
2362
2363     // Subtle: before we store the predicates into the tcx, we
2364     // sort them so that predicates like `T: Foo<Item=U>` come
2365     // before uses of `U`.  This avoids false ambiguity errors
2366     // in trait checking. See `setup_constraining_predicates`
2367     // for details.
2368     if let Node::Item(&Item { kind: ItemKind::Impl { .. }, .. }) = node {
2369         let self_ty = tcx.type_of(def_id);
2370         let trait_ref = tcx.impl_trait_ref(def_id);
2371         cgp::setup_constraining_predicates(
2372             tcx,
2373             &mut predicates,
2374             trait_ref,
2375             &mut cgp::parameters_for_impl(self_ty, trait_ref),
2376         );
2377     }
2378
2379     ty::GenericPredicates {
2380         parent: generics.parent,
2381         predicates: tcx.arena.alloc_from_iter(predicates),
2382     }
2383 }
2384
2385 fn const_evaluatable_predicates_of<'tcx>(
2386     tcx: TyCtxt<'tcx>,
2387     def_id: LocalDefId,
2388 ) -> FxIndexSet<(ty::Predicate<'tcx>, Span)> {
2389     struct ConstCollector<'tcx> {
2390         tcx: TyCtxt<'tcx>,
2391         preds: FxIndexSet<(ty::Predicate<'tcx>, Span)>,
2392     }
2393
2394     impl<'tcx> intravisit::Visitor<'tcx> for ConstCollector<'tcx> {
2395         fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) {
2396             let def_id = self.tcx.hir().local_def_id(c.hir_id);
2397             let ct = ty::Const::from_anon_const(self.tcx, def_id);
2398             if let ty::ConstKind::Unevaluated(uv) = ct.kind() {
2399                 let span = self.tcx.hir().span(c.hir_id);
2400                 self.preds.insert((
2401                     ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(uv))
2402                         .to_predicate(self.tcx),
2403                     span,
2404                 ));
2405             }
2406         }
2407
2408         fn visit_const_param_default(&mut self, _param: HirId, _ct: &'tcx hir::AnonConst) {
2409             // Do not look into const param defaults,
2410             // these get checked when they are actually instantiated.
2411             //
2412             // We do not want the following to error:
2413             //
2414             //     struct Foo<const N: usize, const M: usize = { N + 1 }>;
2415             //     struct Bar<const N: usize>(Foo<N, 3>);
2416         }
2417     }
2418
2419     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
2420     let node = tcx.hir().get(hir_id);
2421
2422     let mut collector = ConstCollector { tcx, preds: FxIndexSet::default() };
2423     if let hir::Node::Item(item) = node && let hir::ItemKind::Impl(ref impl_) = item.kind {
2424         if let Some(of_trait) = &impl_.of_trait {
2425             debug!("const_evaluatable_predicates_of({:?}): visit impl trait_ref", def_id);
2426             collector.visit_trait_ref(of_trait);
2427         }
2428
2429         debug!("const_evaluatable_predicates_of({:?}): visit_self_ty", def_id);
2430         collector.visit_ty(impl_.self_ty);
2431     }
2432
2433     if let Some(generics) = node.generics() {
2434         debug!("const_evaluatable_predicates_of({:?}): visit_generics", def_id);
2435         collector.visit_generics(generics);
2436     }
2437
2438     if let Some(fn_sig) = tcx.hir().fn_sig_by_hir_id(hir_id) {
2439         debug!("const_evaluatable_predicates_of({:?}): visit_fn_decl", def_id);
2440         collector.visit_fn_decl(fn_sig.decl);
2441     }
2442     debug!("const_evaluatable_predicates_of({:?}) = {:?}", def_id, collector.preds);
2443
2444     collector.preds
2445 }
2446
2447 fn trait_explicit_predicates_and_bounds(
2448     tcx: TyCtxt<'_>,
2449     def_id: LocalDefId,
2450 ) -> ty::GenericPredicates<'_> {
2451     assert_eq!(tcx.def_kind(def_id), DefKind::Trait);
2452     gather_explicit_predicates_of(tcx, def_id.to_def_id())
2453 }
2454
2455 fn explicit_predicates_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> ty::GenericPredicates<'tcx> {
2456     let def_kind = tcx.def_kind(def_id);
2457     if let DefKind::Trait = def_kind {
2458         // Remove bounds on associated types from the predicates, they will be
2459         // returned by `explicit_item_bounds`.
2460         let predicates_and_bounds = tcx.trait_explicit_predicates_and_bounds(def_id.expect_local());
2461         let trait_identity_substs = InternalSubsts::identity_for_item(tcx, def_id);
2462
2463         let is_assoc_item_ty = |ty: Ty<'tcx>| {
2464             // For a predicate from a where clause to become a bound on an
2465             // associated type:
2466             // * It must use the identity substs of the item.
2467             //     * Since any generic parameters on the item are not in scope,
2468             //       this means that the item is not a GAT, and its identity
2469             //       substs are the same as the trait's.
2470             // * It must be an associated type for this trait (*not* a
2471             //   supertrait).
2472             if let ty::Projection(projection) = ty.kind() {
2473                 projection.substs == trait_identity_substs
2474                     && tcx.associated_item(projection.item_def_id).container_id(tcx) == def_id
2475             } else {
2476                 false
2477             }
2478         };
2479
2480         let predicates: Vec<_> = predicates_and_bounds
2481             .predicates
2482             .iter()
2483             .copied()
2484             .filter(|(pred, _)| match pred.kind().skip_binder() {
2485                 ty::PredicateKind::Trait(tr) => !is_assoc_item_ty(tr.self_ty()),
2486                 ty::PredicateKind::Projection(proj) => {
2487                     !is_assoc_item_ty(proj.projection_ty.self_ty())
2488                 }
2489                 ty::PredicateKind::TypeOutlives(outlives) => !is_assoc_item_ty(outlives.0),
2490                 _ => true,
2491             })
2492             .collect();
2493         if predicates.len() == predicates_and_bounds.predicates.len() {
2494             predicates_and_bounds
2495         } else {
2496             ty::GenericPredicates {
2497                 parent: predicates_and_bounds.parent,
2498                 predicates: tcx.arena.alloc_slice(&predicates),
2499             }
2500         }
2501     } else {
2502         if matches!(def_kind, DefKind::AnonConst) && tcx.lazy_normalization() {
2503             let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2504             if tcx.hir().opt_const_param_default_param_hir_id(hir_id).is_some() {
2505                 // In `generics_of` we set the generics' parent to be our parent's parent which means that
2506                 // we lose out on the predicates of our actual parent if we dont return those predicates here.
2507                 // (See comment in `generics_of` for more information on why the parent shenanigans is necessary)
2508                 //
2509                 // struct Foo<T, const N: usize = { <T as Trait>::ASSOC }>(T) where T: Trait;
2510                 //        ^^^                     ^^^^^^^^^^^^^^^^^^^^^^^ the def id we are calling
2511                 //        ^^^                                             explicit_predicates_of on
2512                 //        parent item we dont have set as the
2513                 //        parent of generics returned by `generics_of`
2514                 //
2515                 // In the above code we want the anon const to have predicates in its param env for `T: Trait`
2516                 let item_def_id = tcx.hir().get_parent_item(hir_id);
2517                 // In the above code example we would be calling `explicit_predicates_of(Foo)` here
2518                 return tcx.explicit_predicates_of(item_def_id);
2519             }
2520         }
2521         gather_explicit_predicates_of(tcx, def_id)
2522     }
2523 }
2524
2525 /// Converts a specific `GenericBound` from the AST into a set of
2526 /// predicates that apply to the self type. A vector is returned
2527 /// because this can be anywhere from zero predicates (`T: ?Sized` adds no
2528 /// predicates) to one (`T: Foo`) to many (`T: Bar<X = i32>` adds `T: Bar`
2529 /// and `<T as Bar>::X == i32`).
2530 fn predicates_from_bound<'tcx>(
2531     astconv: &dyn AstConv<'tcx>,
2532     param_ty: Ty<'tcx>,
2533     bound: &'tcx hir::GenericBound<'tcx>,
2534     bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
2535 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2536     let mut bounds = Bounds::default();
2537     astconv.add_bounds(param_ty, [bound].into_iter(), &mut bounds, bound_vars);
2538     bounds.predicates(astconv.tcx(), param_ty).collect()
2539 }
2540
2541 fn compute_sig_of_foreign_fn_decl<'tcx>(
2542     tcx: TyCtxt<'tcx>,
2543     def_id: DefId,
2544     decl: &'tcx hir::FnDecl<'tcx>,
2545     abi: abi::Abi,
2546 ) -> ty::PolyFnSig<'tcx> {
2547     let unsafety = if abi == abi::Abi::RustIntrinsic {
2548         intrinsic_operation_unsafety(tcx.item_name(def_id))
2549     } else {
2550         hir::Unsafety::Unsafe
2551     };
2552     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2553     let fty = <dyn AstConv<'_>>::ty_of_fn(
2554         &ItemCtxt::new(tcx, def_id),
2555         hir_id,
2556         unsafety,
2557         abi,
2558         decl,
2559         None,
2560         None,
2561     );
2562
2563     // Feature gate SIMD types in FFI, since I am not sure that the
2564     // ABIs are handled at all correctly. -huonw
2565     if abi != abi::Abi::RustIntrinsic
2566         && abi != abi::Abi::PlatformIntrinsic
2567         && !tcx.features().simd_ffi
2568     {
2569         let check = |ast_ty: &hir::Ty<'_>, ty: Ty<'_>| {
2570             if ty.is_simd() {
2571                 let snip = tcx
2572                     .sess
2573                     .source_map()
2574                     .span_to_snippet(ast_ty.span)
2575                     .map_or_else(|_| String::new(), |s| format!(" `{}`", s));
2576                 tcx.sess
2577                     .struct_span_err(
2578                         ast_ty.span,
2579                         &format!(
2580                             "use of SIMD type{} in FFI is highly experimental and \
2581                              may result in invalid code",
2582                             snip
2583                         ),
2584                     )
2585                     .help("add `#![feature(simd_ffi)]` to the crate attributes to enable")
2586                     .emit();
2587             }
2588         };
2589         for (input, ty) in iter::zip(decl.inputs, fty.inputs().skip_binder()) {
2590             check(input, *ty)
2591         }
2592         if let hir::FnRetTy::Return(ref ty) = decl.output {
2593             check(ty, fty.output().skip_binder())
2594         }
2595     }
2596
2597     fty
2598 }
2599
2600 fn is_foreign_item(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
2601     match tcx.hir().get_if_local(def_id) {
2602         Some(Node::ForeignItem(..)) => true,
2603         Some(_) => false,
2604         _ => bug!("is_foreign_item applied to non-local def-id {:?}", def_id),
2605     }
2606 }
2607
2608 fn generator_kind(tcx: TyCtxt<'_>, def_id: DefId) -> Option<hir::GeneratorKind> {
2609     match tcx.hir().get_if_local(def_id) {
2610         Some(Node::Expr(&rustc_hir::Expr {
2611             kind: rustc_hir::ExprKind::Closure(&rustc_hir::Closure { body, .. }),
2612             ..
2613         })) => tcx.hir().body(body).generator_kind(),
2614         Some(_) => None,
2615         _ => bug!("generator_kind applied to non-local def-id {:?}", def_id),
2616     }
2617 }
2618
2619 fn from_target_feature(
2620     tcx: TyCtxt<'_>,
2621     attr: &ast::Attribute,
2622     supported_target_features: &FxHashMap<String, Option<Symbol>>,
2623     target_features: &mut Vec<Symbol>,
2624 ) {
2625     let Some(list) = attr.meta_item_list() else { return };
2626     let bad_item = |span| {
2627         let msg = "malformed `target_feature` attribute input";
2628         let code = "enable = \"..\"";
2629         tcx.sess
2630             .struct_span_err(span, msg)
2631             .span_suggestion(span, "must be of the form", code, Applicability::HasPlaceholders)
2632             .emit();
2633     };
2634     let rust_features = tcx.features();
2635     for item in list {
2636         // Only `enable = ...` is accepted in the meta-item list.
2637         if !item.has_name(sym::enable) {
2638             bad_item(item.span());
2639             continue;
2640         }
2641
2642         // Must be of the form `enable = "..."` (a string).
2643         let Some(value) = item.value_str() else {
2644             bad_item(item.span());
2645             continue;
2646         };
2647
2648         // We allow comma separation to enable multiple features.
2649         target_features.extend(value.as_str().split(',').filter_map(|feature| {
2650             let Some(feature_gate) = supported_target_features.get(feature) else {
2651                 let msg =
2652                     format!("the feature named `{}` is not valid for this target", feature);
2653                 let mut err = tcx.sess.struct_span_err(item.span(), &msg);
2654                 err.span_label(
2655                     item.span(),
2656                     format!("`{}` is not valid for this target", feature),
2657                 );
2658                 if let Some(stripped) = feature.strip_prefix('+') {
2659                     let valid = supported_target_features.contains_key(stripped);
2660                     if valid {
2661                         err.help("consider removing the leading `+` in the feature name");
2662                     }
2663                 }
2664                 err.emit();
2665                 return None;
2666             };
2667
2668             // Only allow features whose feature gates have been enabled.
2669             let allowed = match feature_gate.as_ref().copied() {
2670                 Some(sym::arm_target_feature) => rust_features.arm_target_feature,
2671                 Some(sym::hexagon_target_feature) => rust_features.hexagon_target_feature,
2672                 Some(sym::powerpc_target_feature) => rust_features.powerpc_target_feature,
2673                 Some(sym::mips_target_feature) => rust_features.mips_target_feature,
2674                 Some(sym::riscv_target_feature) => rust_features.riscv_target_feature,
2675                 Some(sym::avx512_target_feature) => rust_features.avx512_target_feature,
2676                 Some(sym::sse4a_target_feature) => rust_features.sse4a_target_feature,
2677                 Some(sym::tbm_target_feature) => rust_features.tbm_target_feature,
2678                 Some(sym::wasm_target_feature) => rust_features.wasm_target_feature,
2679                 Some(sym::cmpxchg16b_target_feature) => rust_features.cmpxchg16b_target_feature,
2680                 Some(sym::movbe_target_feature) => rust_features.movbe_target_feature,
2681                 Some(sym::rtm_target_feature) => rust_features.rtm_target_feature,
2682                 Some(sym::f16c_target_feature) => rust_features.f16c_target_feature,
2683                 Some(sym::ermsb_target_feature) => rust_features.ermsb_target_feature,
2684                 Some(sym::bpf_target_feature) => rust_features.bpf_target_feature,
2685                 Some(sym::aarch64_ver_target_feature) => rust_features.aarch64_ver_target_feature,
2686                 Some(name) => bug!("unknown target feature gate {}", name),
2687                 None => true,
2688             };
2689             if !allowed {
2690                 feature_err(
2691                     &tcx.sess.parse_sess,
2692                     feature_gate.unwrap(),
2693                     item.span(),
2694                     &format!("the target feature `{}` is currently unstable", feature),
2695                 )
2696                 .emit();
2697             }
2698             Some(Symbol::intern(feature))
2699         }));
2700     }
2701 }
2702
2703 fn linkage_by_name(tcx: TyCtxt<'_>, def_id: LocalDefId, name: &str) -> Linkage {
2704     use rustc_middle::mir::mono::Linkage::*;
2705
2706     // Use the names from src/llvm/docs/LangRef.rst here. Most types are only
2707     // applicable to variable declarations and may not really make sense for
2708     // Rust code in the first place but allow them anyway and trust that the
2709     // user knows what they're doing. Who knows, unanticipated use cases may pop
2710     // up in the future.
2711     //
2712     // ghost, dllimport, dllexport and linkonce_odr_autohide are not supported
2713     // and don't have to be, LLVM treats them as no-ops.
2714     match name {
2715         "appending" => Appending,
2716         "available_externally" => AvailableExternally,
2717         "common" => Common,
2718         "extern_weak" => ExternalWeak,
2719         "external" => External,
2720         "internal" => Internal,
2721         "linkonce" => LinkOnceAny,
2722         "linkonce_odr" => LinkOnceODR,
2723         "private" => Private,
2724         "weak" => WeakAny,
2725         "weak_odr" => WeakODR,
2726         _ => tcx.sess.span_fatal(tcx.def_span(def_id), "invalid linkage specified"),
2727     }
2728 }
2729
2730 fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: DefId) -> CodegenFnAttrs {
2731     if cfg!(debug_assertions) {
2732         let def_kind = tcx.def_kind(did);
2733         assert!(
2734             def_kind.has_codegen_attrs(),
2735             "unexpected `def_kind` in `codegen_fn_attrs`: {def_kind:?}",
2736         );
2737     }
2738
2739     let did = did.expect_local();
2740     let attrs = tcx.hir().attrs(tcx.hir().local_def_id_to_hir_id(did));
2741     let mut codegen_fn_attrs = CodegenFnAttrs::new();
2742     if tcx.should_inherit_track_caller(did) {
2743         codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
2744     }
2745
2746     // The panic_no_unwind function called by TerminatorKind::Abort will never
2747     // unwind. If the panic handler that it invokes unwind then it will simply
2748     // call the panic handler again.
2749     if Some(did.to_def_id()) == tcx.lang_items().panic_no_unwind() {
2750         codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
2751     }
2752
2753     let supported_target_features = tcx.supported_target_features(LOCAL_CRATE);
2754
2755     let mut inline_span = None;
2756     let mut link_ordinal_span = None;
2757     let mut no_sanitize_span = None;
2758     for attr in attrs.iter() {
2759         if attr.has_name(sym::cold) {
2760             codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
2761         } else if attr.has_name(sym::rustc_allocator) {
2762             codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR;
2763         } else if attr.has_name(sym::ffi_returns_twice) {
2764             if tcx.is_foreign_item(did) {
2765                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_RETURNS_TWICE;
2766             } else {
2767                 // `#[ffi_returns_twice]` is only allowed `extern fn`s.
2768                 struct_span_err!(
2769                     tcx.sess,
2770                     attr.span,
2771                     E0724,
2772                     "`#[ffi_returns_twice]` may only be used on foreign functions"
2773                 )
2774                 .emit();
2775             }
2776         } else if attr.has_name(sym::ffi_pure) {
2777             if tcx.is_foreign_item(did) {
2778                 if attrs.iter().any(|a| a.has_name(sym::ffi_const)) {
2779                     // `#[ffi_const]` functions cannot be `#[ffi_pure]`
2780                     struct_span_err!(
2781                         tcx.sess,
2782                         attr.span,
2783                         E0757,
2784                         "`#[ffi_const]` function cannot be `#[ffi_pure]`"
2785                     )
2786                     .emit();
2787                 } else {
2788                     codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_PURE;
2789                 }
2790             } else {
2791                 // `#[ffi_pure]` is only allowed on foreign functions
2792                 struct_span_err!(
2793                     tcx.sess,
2794                     attr.span,
2795                     E0755,
2796                     "`#[ffi_pure]` may only be used on foreign functions"
2797                 )
2798                 .emit();
2799             }
2800         } else if attr.has_name(sym::ffi_const) {
2801             if tcx.is_foreign_item(did) {
2802                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_CONST;
2803             } else {
2804                 // `#[ffi_const]` is only allowed on foreign functions
2805                 struct_span_err!(
2806                     tcx.sess,
2807                     attr.span,
2808                     E0756,
2809                     "`#[ffi_const]` may only be used on foreign functions"
2810                 )
2811                 .emit();
2812             }
2813         } else if attr.has_name(sym::rustc_allocator_nounwind) {
2814             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
2815         } else if attr.has_name(sym::rustc_reallocator) {
2816             codegen_fn_attrs.flags |= CodegenFnAttrFlags::REALLOCATOR;
2817         } else if attr.has_name(sym::rustc_deallocator) {
2818             codegen_fn_attrs.flags |= CodegenFnAttrFlags::DEALLOCATOR;
2819         } else if attr.has_name(sym::rustc_allocator_zeroed) {
2820             codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR_ZEROED;
2821         } else if attr.has_name(sym::naked) {
2822             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED;
2823         } else if attr.has_name(sym::no_mangle) {
2824             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
2825         } else if attr.has_name(sym::no_coverage) {
2826             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_COVERAGE;
2827         } else if attr.has_name(sym::rustc_std_internal_symbol) {
2828             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
2829         } else if attr.has_name(sym::used) {
2830             let inner = attr.meta_item_list();
2831             match inner.as_deref() {
2832                 Some([item]) if item.has_name(sym::linker) => {
2833                     if !tcx.features().used_with_arg {
2834                         feature_err(
2835                             &tcx.sess.parse_sess,
2836                             sym::used_with_arg,
2837                             attr.span,
2838                             "`#[used(linker)]` is currently unstable",
2839                         )
2840                         .emit();
2841                     }
2842                     codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED_LINKER;
2843                 }
2844                 Some([item]) if item.has_name(sym::compiler) => {
2845                     if !tcx.features().used_with_arg {
2846                         feature_err(
2847                             &tcx.sess.parse_sess,
2848                             sym::used_with_arg,
2849                             attr.span,
2850                             "`#[used(compiler)]` is currently unstable",
2851                         )
2852                         .emit();
2853                     }
2854                     codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED;
2855                 }
2856                 Some(_) => {
2857                     tcx.sess.emit_err(errors::ExpectedUsedSymbol { span: attr.span });
2858                 }
2859                 None => {
2860                     // Unfortunately, unconditionally using `llvm.used` causes
2861                     // issues in handling `.init_array` with the gold linker,
2862                     // but using `llvm.compiler.used` caused a nontrival amount
2863                     // of unintentional ecosystem breakage -- particularly on
2864                     // Mach-O targets.
2865                     //
2866                     // As a result, we emit `llvm.compiler.used` only on ELF
2867                     // targets. This is somewhat ad-hoc, but actually follows
2868                     // our pre-LLVM 13 behavior (prior to the ecosystem
2869                     // breakage), and seems to match `clang`'s behavior as well
2870                     // (both before and after LLVM 13), possibly because they
2871                     // have similar compatibility concerns to us. See
2872                     // https://github.com/rust-lang/rust/issues/47384#issuecomment-1019080146
2873                     // and following comments for some discussion of this, as
2874                     // well as the comments in `rustc_codegen_llvm` where these
2875                     // flags are handled.
2876                     //
2877                     // Anyway, to be clear: this is still up in the air
2878                     // somewhat, and is subject to change in the future (which
2879                     // is a good thing, because this would ideally be a bit
2880                     // more firmed up).
2881                     let is_like_elf = !(tcx.sess.target.is_like_osx
2882                         || tcx.sess.target.is_like_windows
2883                         || tcx.sess.target.is_like_wasm);
2884                     codegen_fn_attrs.flags |= if is_like_elf {
2885                         CodegenFnAttrFlags::USED
2886                     } else {
2887                         CodegenFnAttrFlags::USED_LINKER
2888                     };
2889                 }
2890             }
2891         } else if attr.has_name(sym::cmse_nonsecure_entry) {
2892             if !matches!(tcx.fn_sig(did).abi(), abi::Abi::C { .. }) {
2893                 struct_span_err!(
2894                     tcx.sess,
2895                     attr.span,
2896                     E0776,
2897                     "`#[cmse_nonsecure_entry]` requires C ABI"
2898                 )
2899                 .emit();
2900             }
2901             if !tcx.sess.target.llvm_target.contains("thumbv8m") {
2902                 struct_span_err!(tcx.sess, attr.span, E0775, "`#[cmse_nonsecure_entry]` is only valid for targets with the TrustZone-M extension")
2903                     .emit();
2904             }
2905             codegen_fn_attrs.flags |= CodegenFnAttrFlags::CMSE_NONSECURE_ENTRY;
2906         } else if attr.has_name(sym::thread_local) {
2907             codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL;
2908         } else if attr.has_name(sym::track_caller) {
2909             if !tcx.is_closure(did.to_def_id()) && tcx.fn_sig(did).abi() != abi::Abi::Rust {
2910                 struct_span_err!(tcx.sess, attr.span, E0737, "`#[track_caller]` requires Rust ABI")
2911                     .emit();
2912             }
2913             if tcx.is_closure(did.to_def_id()) && !tcx.features().closure_track_caller {
2914                 feature_err(
2915                     &tcx.sess.parse_sess,
2916                     sym::closure_track_caller,
2917                     attr.span,
2918                     "`#[track_caller]` on closures is currently unstable",
2919                 )
2920                 .emit();
2921             }
2922             codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
2923         } else if attr.has_name(sym::export_name) {
2924             if let Some(s) = attr.value_str() {
2925                 if s.as_str().contains('\0') {
2926                     // `#[export_name = ...]` will be converted to a null-terminated string,
2927                     // so it may not contain any null characters.
2928                     struct_span_err!(
2929                         tcx.sess,
2930                         attr.span,
2931                         E0648,
2932                         "`export_name` may not contain null characters"
2933                     )
2934                     .emit();
2935                 }
2936                 codegen_fn_attrs.export_name = Some(s);
2937             }
2938         } else if attr.has_name(sym::target_feature) {
2939             if !tcx.is_closure(did.to_def_id())
2940                 && tcx.fn_sig(did).unsafety() == hir::Unsafety::Normal
2941             {
2942                 if tcx.sess.target.is_like_wasm || tcx.sess.opts.actually_rustdoc {
2943                     // The `#[target_feature]` attribute is allowed on
2944                     // WebAssembly targets on all functions, including safe
2945                     // ones. Other targets require that `#[target_feature]` is
2946                     // only applied to unsafe functions (pending the
2947                     // `target_feature_11` feature) because on most targets
2948                     // execution of instructions that are not supported is
2949                     // considered undefined behavior. For WebAssembly which is a
2950                     // 100% safe target at execution time it's not possible to
2951                     // execute undefined instructions, and even if a future
2952                     // feature was added in some form for this it would be a
2953                     // deterministic trap. There is no undefined behavior when
2954                     // executing WebAssembly so `#[target_feature]` is allowed
2955                     // on safe functions (but again, only for WebAssembly)
2956                     //
2957                     // Note that this is also allowed if `actually_rustdoc` so
2958                     // if a target is documenting some wasm-specific code then
2959                     // it's not spuriously denied.
2960                 } else if !tcx.features().target_feature_11 {
2961                     let mut err = feature_err(
2962                         &tcx.sess.parse_sess,
2963                         sym::target_feature_11,
2964                         attr.span,
2965                         "`#[target_feature(..)]` can only be applied to `unsafe` functions",
2966                     );
2967                     err.span_label(tcx.def_span(did), "not an `unsafe` function");
2968                     err.emit();
2969                 } else {
2970                     check_target_feature_trait_unsafe(tcx, did, attr.span);
2971                 }
2972             }
2973             from_target_feature(
2974                 tcx,
2975                 attr,
2976                 supported_target_features,
2977                 &mut codegen_fn_attrs.target_features,
2978             );
2979         } else if attr.has_name(sym::linkage) {
2980             if let Some(val) = attr.value_str() {
2981                 codegen_fn_attrs.linkage = Some(linkage_by_name(tcx, did, val.as_str()));
2982             }
2983         } else if attr.has_name(sym::link_section) {
2984             if let Some(val) = attr.value_str() {
2985                 if val.as_str().bytes().any(|b| b == 0) {
2986                     let msg = format!(
2987                         "illegal null byte in link_section \
2988                          value: `{}`",
2989                         &val
2990                     );
2991                     tcx.sess.span_err(attr.span, &msg);
2992                 } else {
2993                     codegen_fn_attrs.link_section = Some(val);
2994                 }
2995             }
2996         } else if attr.has_name(sym::link_name) {
2997             codegen_fn_attrs.link_name = attr.value_str();
2998         } else if attr.has_name(sym::link_ordinal) {
2999             link_ordinal_span = Some(attr.span);
3000             if let ordinal @ Some(_) = check_link_ordinal(tcx, attr) {
3001                 codegen_fn_attrs.link_ordinal = ordinal;
3002             }
3003         } else if attr.has_name(sym::no_sanitize) {
3004             no_sanitize_span = Some(attr.span);
3005             if let Some(list) = attr.meta_item_list() {
3006                 for item in list.iter() {
3007                     if item.has_name(sym::address) {
3008                         codegen_fn_attrs.no_sanitize |= SanitizerSet::ADDRESS;
3009                     } else if item.has_name(sym::cfi) {
3010                         codegen_fn_attrs.no_sanitize |= SanitizerSet::CFI;
3011                     } else if item.has_name(sym::memory) {
3012                         codegen_fn_attrs.no_sanitize |= SanitizerSet::MEMORY;
3013                     } else if item.has_name(sym::memtag) {
3014                         codegen_fn_attrs.no_sanitize |= SanitizerSet::MEMTAG;
3015                     } else if item.has_name(sym::shadow_call_stack) {
3016                         codegen_fn_attrs.no_sanitize |= SanitizerSet::SHADOWCALLSTACK;
3017                     } else if item.has_name(sym::thread) {
3018                         codegen_fn_attrs.no_sanitize |= SanitizerSet::THREAD;
3019                     } else if item.has_name(sym::hwaddress) {
3020                         codegen_fn_attrs.no_sanitize |= SanitizerSet::HWADDRESS;
3021                     } else {
3022                         tcx.sess
3023                             .struct_span_err(item.span(), "invalid argument for `no_sanitize`")
3024                             .note("expected one of: `address`, `cfi`, `hwaddress`, `memory`, `memtag`, `shadow-call-stack`, or `thread`")
3025                             .emit();
3026                     }
3027                 }
3028             }
3029         } else if attr.has_name(sym::instruction_set) {
3030             codegen_fn_attrs.instruction_set = match attr.meta_kind() {
3031                 Some(MetaItemKind::List(ref items)) => match items.as_slice() {
3032                     [NestedMetaItem::MetaItem(set)] => {
3033                         let segments =
3034                             set.path.segments.iter().map(|x| x.ident.name).collect::<Vec<_>>();
3035                         match segments.as_slice() {
3036                             [sym::arm, sym::a32] | [sym::arm, sym::t32] => {
3037                                 if !tcx.sess.target.has_thumb_interworking {
3038                                     struct_span_err!(
3039                                         tcx.sess.diagnostic(),
3040                                         attr.span,
3041                                         E0779,
3042                                         "target does not support `#[instruction_set]`"
3043                                     )
3044                                     .emit();
3045                                     None
3046                                 } else if segments[1] == sym::a32 {
3047                                     Some(InstructionSetAttr::ArmA32)
3048                                 } else if segments[1] == sym::t32 {
3049                                     Some(InstructionSetAttr::ArmT32)
3050                                 } else {
3051                                     unreachable!()
3052                                 }
3053                             }
3054                             _ => {
3055                                 struct_span_err!(
3056                                     tcx.sess.diagnostic(),
3057                                     attr.span,
3058                                     E0779,
3059                                     "invalid instruction set specified",
3060                                 )
3061                                 .emit();
3062                                 None
3063                             }
3064                         }
3065                     }
3066                     [] => {
3067                         struct_span_err!(
3068                             tcx.sess.diagnostic(),
3069                             attr.span,
3070                             E0778,
3071                             "`#[instruction_set]` requires an argument"
3072                         )
3073                         .emit();
3074                         None
3075                     }
3076                     _ => {
3077                         struct_span_err!(
3078                             tcx.sess.diagnostic(),
3079                             attr.span,
3080                             E0779,
3081                             "cannot specify more than one instruction set"
3082                         )
3083                         .emit();
3084                         None
3085                     }
3086                 },
3087                 _ => {
3088                     struct_span_err!(
3089                         tcx.sess.diagnostic(),
3090                         attr.span,
3091                         E0778,
3092                         "must specify an instruction set"
3093                     )
3094                     .emit();
3095                     None
3096                 }
3097             };
3098         } else if attr.has_name(sym::repr) {
3099             codegen_fn_attrs.alignment = match attr.meta_item_list() {
3100                 Some(items) => match items.as_slice() {
3101                     [item] => match item.name_value_literal() {
3102                         Some((sym::align, literal)) => {
3103                             let alignment = rustc_attr::parse_alignment(&literal.kind);
3104
3105                             match alignment {
3106                                 Ok(align) => Some(align),
3107                                 Err(msg) => {
3108                                     struct_span_err!(
3109                                         tcx.sess.diagnostic(),
3110                                         attr.span,
3111                                         E0589,
3112                                         "invalid `repr(align)` attribute: {}",
3113                                         msg
3114                                     )
3115                                     .emit();
3116
3117                                     None
3118                                 }
3119                             }
3120                         }
3121                         _ => None,
3122                     },
3123                     [] => None,
3124                     _ => None,
3125                 },
3126                 None => None,
3127             };
3128         }
3129     }
3130
3131     codegen_fn_attrs.inline = attrs.iter().fold(InlineAttr::None, |ia, attr| {
3132         if !attr.has_name(sym::inline) {
3133             return ia;
3134         }
3135         match attr.meta_kind() {
3136             Some(MetaItemKind::Word) => InlineAttr::Hint,
3137             Some(MetaItemKind::List(ref items)) => {
3138                 inline_span = Some(attr.span);
3139                 if items.len() != 1 {
3140                     struct_span_err!(
3141                         tcx.sess.diagnostic(),
3142                         attr.span,
3143                         E0534,
3144                         "expected one argument"
3145                     )
3146                     .emit();
3147                     InlineAttr::None
3148                 } else if list_contains_name(&items, sym::always) {
3149                     InlineAttr::Always
3150                 } else if list_contains_name(&items, sym::never) {
3151                     InlineAttr::Never
3152                 } else {
3153                     struct_span_err!(
3154                         tcx.sess.diagnostic(),
3155                         items[0].span(),
3156                         E0535,
3157                         "invalid argument"
3158                     )
3159                     .help("valid inline arguments are `always` and `never`")
3160                     .emit();
3161
3162                     InlineAttr::None
3163                 }
3164             }
3165             Some(MetaItemKind::NameValue(_)) => ia,
3166             None => ia,
3167         }
3168     });
3169
3170     codegen_fn_attrs.optimize = attrs.iter().fold(OptimizeAttr::None, |ia, attr| {
3171         if !attr.has_name(sym::optimize) {
3172             return ia;
3173         }
3174         let err = |sp, s| struct_span_err!(tcx.sess.diagnostic(), sp, E0722, "{}", s).emit();
3175         match attr.meta_kind() {
3176             Some(MetaItemKind::Word) => {
3177                 err(attr.span, "expected one argument");
3178                 ia
3179             }
3180             Some(MetaItemKind::List(ref items)) => {
3181                 inline_span = Some(attr.span);
3182                 if items.len() != 1 {
3183                     err(attr.span, "expected one argument");
3184                     OptimizeAttr::None
3185                 } else if list_contains_name(&items, sym::size) {
3186                     OptimizeAttr::Size
3187                 } else if list_contains_name(&items, sym::speed) {
3188                     OptimizeAttr::Speed
3189                 } else {
3190                     err(items[0].span(), "invalid argument");
3191                     OptimizeAttr::None
3192                 }
3193             }
3194             Some(MetaItemKind::NameValue(_)) => ia,
3195             None => ia,
3196         }
3197     });
3198
3199     // #73631: closures inherit `#[target_feature]` annotations
3200     if tcx.features().target_feature_11 && tcx.is_closure(did.to_def_id()) {
3201         let owner_id = tcx.parent(did.to_def_id());
3202         if tcx.def_kind(owner_id).has_codegen_attrs() {
3203             codegen_fn_attrs
3204                 .target_features
3205                 .extend(tcx.codegen_fn_attrs(owner_id).target_features.iter().copied());
3206         }
3207     }
3208
3209     // If a function uses #[target_feature] it can't be inlined into general
3210     // purpose functions as they wouldn't have the right target features
3211     // enabled. For that reason we also forbid #[inline(always)] as it can't be
3212     // respected.
3213     if !codegen_fn_attrs.target_features.is_empty() {
3214         if codegen_fn_attrs.inline == InlineAttr::Always {
3215             if let Some(span) = inline_span {
3216                 tcx.sess.span_err(
3217                     span,
3218                     "cannot use `#[inline(always)]` with \
3219                      `#[target_feature]`",
3220                 );
3221             }
3222         }
3223     }
3224
3225     if !codegen_fn_attrs.no_sanitize.is_empty() {
3226         if codegen_fn_attrs.inline == InlineAttr::Always {
3227             if let (Some(no_sanitize_span), Some(inline_span)) = (no_sanitize_span, inline_span) {
3228                 let hir_id = tcx.hir().local_def_id_to_hir_id(did);
3229                 tcx.struct_span_lint_hir(
3230                     lint::builtin::INLINE_NO_SANITIZE,
3231                     hir_id,
3232                     no_sanitize_span,
3233                     |lint| {
3234                         lint.build("`no_sanitize` will have no effect after inlining")
3235                             .span_note(inline_span, "inlining requested here")
3236                             .emit();
3237                     },
3238                 )
3239             }
3240         }
3241     }
3242
3243     // Weak lang items have the same semantics as "std internal" symbols in the
3244     // sense that they're preserved through all our LTO passes and only
3245     // strippable by the linker.
3246     //
3247     // Additionally weak lang items have predetermined symbol names.
3248     if tcx.is_weak_lang_item(did.to_def_id()) {
3249         codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
3250     }
3251     if let Some(name) = weak_lang_items::link_name(attrs) {
3252         codegen_fn_attrs.export_name = Some(name);
3253         codegen_fn_attrs.link_name = Some(name);
3254     }
3255     check_link_name_xor_ordinal(tcx, &codegen_fn_attrs, link_ordinal_span);
3256
3257     // Internal symbols to the standard library all have no_mangle semantics in
3258     // that they have defined symbol names present in the function name. This
3259     // also applies to weak symbols where they all have known symbol names.
3260     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
3261         codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
3262     }
3263
3264     // Any linkage to LLVM intrinsics for now forcibly marks them all as never
3265     // unwinds since LLVM sometimes can't handle codegen which `invoke`s
3266     // intrinsic functions.
3267     if let Some(name) = &codegen_fn_attrs.link_name {
3268         if name.as_str().starts_with("llvm.") {
3269             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
3270         }
3271     }
3272
3273     codegen_fn_attrs
3274 }
3275
3276 /// Computes the set of target features used in a function for the purposes of
3277 /// inline assembly.
3278 fn asm_target_features<'tcx>(tcx: TyCtxt<'tcx>, did: DefId) -> &'tcx FxHashSet<Symbol> {
3279     let mut target_features = tcx.sess.unstable_target_features.clone();
3280     if tcx.def_kind(did).has_codegen_attrs() {
3281         let attrs = tcx.codegen_fn_attrs(did);
3282         target_features.extend(&attrs.target_features);
3283         match attrs.instruction_set {
3284             None => {}
3285             Some(InstructionSetAttr::ArmA32) => {
3286                 target_features.remove(&sym::thumb_mode);
3287             }
3288             Some(InstructionSetAttr::ArmT32) => {
3289                 target_features.insert(sym::thumb_mode);
3290             }
3291         }
3292     }
3293
3294     tcx.arena.alloc(target_features)
3295 }
3296
3297 /// Checks if the provided DefId is a method in a trait impl for a trait which has track_caller
3298 /// applied to the method prototype.
3299 fn should_inherit_track_caller(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
3300     if let Some(impl_item) = tcx.opt_associated_item(def_id)
3301         && let ty::AssocItemContainer::ImplContainer = impl_item.container
3302         && let Some(trait_item) = impl_item.trait_item_def_id
3303     {
3304         return tcx
3305             .codegen_fn_attrs(trait_item)
3306             .flags
3307             .intersects(CodegenFnAttrFlags::TRACK_CALLER);
3308     }
3309
3310     false
3311 }
3312
3313 fn check_link_ordinal(tcx: TyCtxt<'_>, attr: &ast::Attribute) -> Option<u16> {
3314     use rustc_ast::{Lit, LitIntType, LitKind};
3315     if !tcx.features().raw_dylib && tcx.sess.target.arch == "x86" {
3316         feature_err(
3317             &tcx.sess.parse_sess,
3318             sym::raw_dylib,
3319             attr.span,
3320             "`#[link_ordinal]` is unstable on x86",
3321         )
3322         .emit();
3323     }
3324     let meta_item_list = attr.meta_item_list();
3325     let meta_item_list: Option<&[ast::NestedMetaItem]> = meta_item_list.as_ref().map(Vec::as_ref);
3326     let sole_meta_list = match meta_item_list {
3327         Some([item]) => item.literal(),
3328         Some(_) => {
3329             tcx.sess
3330                 .struct_span_err(attr.span, "incorrect number of arguments to `#[link_ordinal]`")
3331                 .note("the attribute requires exactly one argument")
3332                 .emit();
3333             return None;
3334         }
3335         _ => None,
3336     };
3337     if let Some(Lit { kind: LitKind::Int(ordinal, LitIntType::Unsuffixed), .. }) = sole_meta_list {
3338         // According to the table at https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#import-header,
3339         // the ordinal must fit into 16 bits.  Similarly, the Ordinal field in COFFShortExport (defined
3340         // in llvm/include/llvm/Object/COFFImportFile.h), which we use to communicate import information
3341         // to LLVM for `#[link(kind = "raw-dylib"_])`, is also defined to be uint16_t.
3342         //
3343         // FIXME: should we allow an ordinal of 0?  The MSVC toolchain has inconsistent support for this:
3344         // both LINK.EXE and LIB.EXE signal errors and abort when given a .DEF file that specifies
3345         // a zero ordinal.  However, llvm-dlltool is perfectly happy to generate an import library
3346         // for such a .DEF file, and MSVC's LINK.EXE is also perfectly happy to consume an import
3347         // library produced by LLVM with an ordinal of 0, and it generates an .EXE.  (I don't know yet
3348         // if the resulting EXE runs, as I haven't yet built the necessary DLL -- see earlier comment
3349         // about LINK.EXE failing.)
3350         if *ordinal <= u16::MAX as u128 {
3351             Some(*ordinal as u16)
3352         } else {
3353             let msg = format!("ordinal value in `link_ordinal` is too large: `{}`", &ordinal);
3354             tcx.sess
3355                 .struct_span_err(attr.span, &msg)
3356                 .note("the value may not exceed `u16::MAX`")
3357                 .emit();
3358             None
3359         }
3360     } else {
3361         tcx.sess
3362             .struct_span_err(attr.span, "illegal ordinal format in `link_ordinal`")
3363             .note("an unsuffixed integer value, e.g., `1`, is expected")
3364             .emit();
3365         None
3366     }
3367 }
3368
3369 fn check_link_name_xor_ordinal(
3370     tcx: TyCtxt<'_>,
3371     codegen_fn_attrs: &CodegenFnAttrs,
3372     inline_span: Option<Span>,
3373 ) {
3374     if codegen_fn_attrs.link_name.is_none() || codegen_fn_attrs.link_ordinal.is_none() {
3375         return;
3376     }
3377     let msg = "cannot use `#[link_name]` with `#[link_ordinal]`";
3378     if let Some(span) = inline_span {
3379         tcx.sess.span_err(span, msg);
3380     } else {
3381         tcx.sess.err(msg);
3382     }
3383 }
3384
3385 /// Checks the function annotated with `#[target_feature]` is not a safe
3386 /// trait method implementation, reporting an error if it is.
3387 fn check_target_feature_trait_unsafe(tcx: TyCtxt<'_>, id: LocalDefId, attr_span: Span) {
3388     let hir_id = tcx.hir().local_def_id_to_hir_id(id);
3389     let node = tcx.hir().get(hir_id);
3390     if let Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }) = node {
3391         let parent_id = tcx.hir().get_parent_item(hir_id);
3392         let parent_item = tcx.hir().expect_item(parent_id.def_id);
3393         if let hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) = parent_item.kind {
3394             tcx.sess
3395                 .struct_span_err(
3396                     attr_span,
3397                     "`#[target_feature(..)]` cannot be applied to safe trait method",
3398                 )
3399                 .span_label(attr_span, "cannot be applied to safe trait method")
3400                 .span_label(tcx.def_span(id), "not an `unsafe` function")
3401                 .emit();
3402         }
3403     }
3404 }