compiler/rustc_hir_analysis/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::check::intrinsic::intrinsic_operation_unsafety;
  19 use crate::errors;
  20 use hir::def::DefKind;
  21 use rustc_data_structures::captures::Captures;
  22 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  23 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed, StashKey};
  24 use rustc_hir as hir;
  25 use rustc_hir::def_id::{DefId, LocalDefId};
  26 use rustc_hir::intravisit::{self, Visitor};
  27 use rustc_hir::{GenericParamKind, Node};
  28 use rustc_infer::infer::TyCtxtInferExt;
  29 use rustc_infer::traits::ObligationCause;
  30 use rustc_middle::hir::nested_filter;
  31 use rustc_middle::ty::query::Providers;
  32 use rustc_middle::ty::util::{Discr, IntTypeExt};
  33 use rustc_middle::ty::{self, AdtKind, Const, IsSuggestable, ToPredicate, Ty, TyCtxt};
  34 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  35 use rustc_span::Span;
  36 use rustc_target::spec::abi;
  37 use rustc_trait_selection::infer::InferCtxtExt;
  38 use rustc_trait_selection::traits::error_reporting::suggestions::NextTypeParamName;
  39 use rustc_trait_selection::traits::ObligationCtxt;
  40 use std::iter;
  41
  42 mod generics_of;
  43 mod item_bounds;
  44 mod lifetimes;
  45 mod predicates_of;
  46 mod type_of;
  47
  48 ///////////////////////////////////////////////////////////////////////////
  49 // Main entry point
  50
  51 fn collect_mod_item_types(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
  52     tcx.hir().visit_item_likes_in_module(module_def_id, &mut CollectItemTypesVisitor { tcx });
  53 }
  54
  55 pub fn provide(providers: &mut Providers) {
  56     lifetimes::provide(providers);
  57     *providers = Providers {
  58         opt_const_param_of: type_of::opt_const_param_of,
  59         type_of: type_of::type_of,
  60         item_bounds: item_bounds::item_bounds,
  61         explicit_item_bounds: item_bounds::explicit_item_bounds,
  62         generics_of: generics_of::generics_of,
  63         predicates_of: predicates_of::predicates_of,
  64         predicates_defined_on,
  65         explicit_predicates_of: predicates_of::explicit_predicates_of,
  66         super_predicates_of: predicates_of::super_predicates_of,
  67         super_predicates_that_define_assoc_type:
  68             predicates_of::super_predicates_that_define_assoc_type,
  69         trait_explicit_predicates_and_bounds: predicates_of::trait_explicit_predicates_and_bounds,
  70         type_param_predicates: predicates_of::type_param_predicates,
  71         trait_def,
  72         adt_def,
  73         fn_sig,
  74         impl_trait_ref,
  75         impl_polarity,
  76         is_foreign_item,
  77         generator_kind,
  78         collect_mod_item_types,
  79         ..*providers
  80     };
  81 }
  82
  83 ///////////////////////////////////////////////////////////////////////////
  84
  85 /// Context specific to some particular item. This is what implements
  86 /// [`AstConv`].
  87 ///
  88 /// # `ItemCtxt` vs `FnCtxt`
  89 ///
  90 /// `ItemCtxt` is primarily used to type-check item signatures and lower them
  91 /// from HIR to their [`ty::Ty`] representation, which is exposed using [`AstConv`].
  92 /// It's also used for the bodies of items like structs where the body (the fields)
  93 /// are just signatures.
  94 ///
  95 /// This is in contrast to `FnCtxt`, which is used to type-check bodies of
  96 /// functions, closures, and `const`s -- anywhere that expressions and statements show up.
  97 ///
  98 /// An important thing to note is that `ItemCtxt` does no inference -- it has no [`InferCtxt`] --
  99 /// while `FnCtxt` does do inference.
 100 ///
 101 /// [`InferCtxt`]: rustc_infer::infer::InferCtxt
 102 ///
 103 /// # Trait predicates
 104 ///
 105 /// `ItemCtxt` has information about the predicates that are defined
 106 /// on the trait. Unfortunately, this predicate information is
 107 /// available in various different forms at various points in the
 108 /// process. So we can't just store a pointer to e.g., the AST or the
 109 /// parsed ty form, we have to be more flexible. To this end, the
 110 /// `ItemCtxt` is parameterized by a `DefId` that it uses to satisfy
 111 /// `get_type_parameter_bounds` requests, drawing the information from
 112 /// the AST (`hir::Generics`), recursively.
 113 pub struct ItemCtxt<'tcx> {
 114     tcx: TyCtxt<'tcx>,
 115     item_def_id: DefId,
 116 }
 117
 118 ///////////////////////////////////////////////////////////////////////////
 119
 120 #[derive(Default)]
 121 pub(crate) struct HirPlaceholderCollector(pub(crate) Vec<Span>);
 122
 123 impl<'v> Visitor<'v> for HirPlaceholderCollector {
 124     fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
 125         if let hir::TyKind::Infer = t.kind {
 126             self.0.push(t.span);
 127         }
 128         intravisit::walk_ty(self, t)
 129     }
 130     fn visit_generic_arg(&mut self, generic_arg: &'v hir::GenericArg<'v>) {
 131         match generic_arg {
 132             hir::GenericArg::Infer(inf) => {
 133                 self.0.push(inf.span);
 134                 intravisit::walk_inf(self, inf);
 135             }
 136             hir::GenericArg::Type(t) => self.visit_ty(t),
 137             _ => {}
 138         }
 139     }
 140     fn visit_array_length(&mut self, length: &'v hir::ArrayLen) {
 141         if let &hir::ArrayLen::Infer(_, span) = length {
 142             self.0.push(span);
 143         }
 144         intravisit::walk_array_len(self, length)
 145     }
 146 }
 147
 148 struct CollectItemTypesVisitor<'tcx> {
 149     tcx: TyCtxt<'tcx>,
 150 }
 151
 152 /// If there are any placeholder types (`_`), emit an error explaining that this is not allowed
 153 /// and suggest adding type parameters in the appropriate place, taking into consideration any and
 154 /// all already existing generic type parameters to avoid suggesting a name that is already in use.
 155 pub(crate) fn placeholder_type_error<'tcx>(
 156     tcx: TyCtxt<'tcx>,
 157     generics: Option<&hir::Generics<'_>>,
 158     placeholder_types: Vec<Span>,
 159     suggest: bool,
 160     hir_ty: Option<&hir::Ty<'_>>,
 161     kind: &'static str,
 162 ) {
 163     if placeholder_types.is_empty() {
 164         return;
 165     }
 166
 167     placeholder_type_error_diag(tcx, generics, placeholder_types, vec![], suggest, hir_ty, kind)
 168         .emit();
 169 }
 170
 171 pub(crate) fn placeholder_type_error_diag<'tcx>(
 172     tcx: TyCtxt<'tcx>,
 173     generics: Option<&hir::Generics<'_>>,
 174     placeholder_types: Vec<Span>,
 175     additional_spans: Vec<Span>,
 176     suggest: bool,
 177     hir_ty: Option<&hir::Ty<'_>>,
 178     kind: &'static str,
 179 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
 180     if placeholder_types.is_empty() {
 181         return bad_placeholder(tcx, additional_spans, kind);
 182     }
 183
 184     let params = generics.map(|g| g.params).unwrap_or_default();
 185     let type_name = params.next_type_param_name(None);
 186     let mut sugg: Vec<_> =
 187         placeholder_types.iter().map(|sp| (*sp, (*type_name).to_string())).collect();
 188
 189     if let Some(generics) = generics {
 190         if let Some(arg) = params.iter().find(|arg| {
 191             matches!(arg.name, hir::ParamName::Plain(Ident { name: kw::Underscore, .. }))
 192         }) {
 193             // Account for `_` already present in cases like `struct S<_>(_);` and suggest
 194             // `struct S<T>(T);` instead of `struct S<_, T>(T);`.
 195             sugg.push((arg.span, (*type_name).to_string()));
 196         } else if let Some(span) = generics.span_for_param_suggestion() {
 197             // Account for bounds, we want `fn foo<T: E, K>(_: K)` not `fn foo<T, K: E>(_: K)`.
 198             sugg.push((span, format!(", {}", type_name)));
 199         } else {
 200             sugg.push((generics.span, format!("<{}>", type_name)));
 201         }
 202     }
 203
 204     let mut err =
 205         bad_placeholder(tcx, placeholder_types.into_iter().chain(additional_spans).collect(), kind);
 206
 207     // Suggest, but only if it is not a function in const or static
 208     if suggest {
 209         let mut is_fn = false;
 210         let mut is_const_or_static = false;
 211
 212         if let Some(hir_ty) = hir_ty && let hir::TyKind::BareFn(_) = hir_ty.kind {
 213             is_fn = true;
 214
 215             // Check if parent is const or static
 216             let parent_id = tcx.hir().parent_id(hir_ty.hir_id);
 217             let parent_node = tcx.hir().get(parent_id);
 218
 219             is_const_or_static = matches!(
 220                 parent_node,
 221                 Node::Item(&hir::Item {
 222                     kind: hir::ItemKind::Const(..) | hir::ItemKind::Static(..),
 223                     ..
 224                 }) | Node::TraitItem(&hir::TraitItem {
 225                     kind: hir::TraitItemKind::Const(..),
 226                     ..
 227                 }) | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Const(..), .. })
 228             );
 229         }
 230
 231         // if function is wrapped around a const or static,
 232         // then don't show the suggestion
 233         if !(is_fn && is_const_or_static) {
 234             err.multipart_suggestion(
 235                 "use type parameters instead",
 236                 sugg,
 237                 Applicability::HasPlaceholders,
 238             );
 239         }
 240     }
 241
 242     err
 243 }
 244
 245 fn reject_placeholder_type_signatures_in_item<'tcx>(
 246     tcx: TyCtxt<'tcx>,
 247     item: &'tcx hir::Item<'tcx>,
 248 ) {
 249     let (generics, suggest) = match &item.kind {
 250         hir::ItemKind::Union(_, generics)
 251         | hir::ItemKind::Enum(_, generics)
 252         | hir::ItemKind::TraitAlias(generics, _)
 253         | hir::ItemKind::Trait(_, _, generics, ..)
 254         | hir::ItemKind::Impl(hir::Impl { generics, .. })
 255         | hir::ItemKind::Struct(_, generics) => (generics, true),
 256         hir::ItemKind::OpaqueTy(hir::OpaqueTy { generics, .. })
 257         | hir::ItemKind::TyAlias(_, generics) => (generics, false),
 258         // `static`, `fn` and `const` are handled elsewhere to suggest appropriate type.
 259         _ => return,
 260     };
 261
 262     let mut visitor = HirPlaceholderCollector::default();
 263     visitor.visit_item(item);
 264
 265     placeholder_type_error(tcx, Some(generics), visitor.0, suggest, None, item.kind.descr());
 266 }
 267
 268 impl<'tcx> Visitor<'tcx> for CollectItemTypesVisitor<'tcx> {
 269     type NestedFilter = nested_filter::OnlyBodies;
 270
 271     fn nested_visit_map(&mut self) -> Self::Map {
 272         self.tcx.hir()
 273     }
 274
 275     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 276         convert_item(self.tcx, item.item_id());
 277         reject_placeholder_type_signatures_in_item(self.tcx, item);
 278         intravisit::walk_item(self, item);
 279     }
 280
 281     fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
 282         for param in generics.params {
 283             match param.kind {
 284                 hir::GenericParamKind::Lifetime { .. } => {}
 285                 hir::GenericParamKind::Type { default: Some(_), .. } => {
 286                     self.tcx.ensure().type_of(param.def_id);
 287                 }
 288                 hir::GenericParamKind::Type { .. } => {}
 289                 hir::GenericParamKind::Const { default, .. } => {
 290                     self.tcx.ensure().type_of(param.def_id);
 291                     if let Some(default) = default {
 292                         // need to store default and type of default
 293                         self.tcx.ensure().type_of(default.def_id);
 294                         self.tcx.ensure().const_param_default(param.def_id);
 295                     }
 296                 }
 297             }
 298         }
 299         intravisit::walk_generics(self, generics);
 300     }
 301
 302     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 303         if let hir::ExprKind::Closure(closure) = expr.kind {
 304             self.tcx.ensure().generics_of(closure.def_id);
 305             self.tcx.ensure().codegen_fn_attrs(closure.def_id);
 306             // We do not call `type_of` for closures here as that
 307             // depends on typecheck and would therefore hide
 308             // any further errors in case one typeck fails.
 309         }
 310         intravisit::walk_expr(self, expr);
 311     }
 312
 313     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
 314         convert_trait_item(self.tcx, trait_item.trait_item_id());
 315         intravisit::walk_trait_item(self, trait_item);
 316     }
 317
 318     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 319         convert_impl_item(self.tcx, impl_item.impl_item_id());
 320         intravisit::walk_impl_item(self, impl_item);
 321     }
 322 }
 323
 324 ///////////////////////////////////////////////////////////////////////////
 325 // Utility types and common code for the above passes.
 326
 327 fn bad_placeholder<'tcx>(
 328     tcx: TyCtxt<'tcx>,
 329     mut spans: Vec<Span>,
 330     kind: &'static str,
 331 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
 332     let kind = if kind.ends_with('s') { format!("{}es", kind) } else { format!("{}s", kind) };
 333
 334     spans.sort();
 335     let mut err = struct_span_err!(
 336         tcx.sess,
 337         spans.clone(),
 338         E0121,
 339         "the placeholder `_` is not allowed within types on item signatures for {}",
 340         kind
 341     );
 342     for span in spans {
 343         err.span_label(span, "not allowed in type signatures");
 344     }
 345     err
 346 }
 347
 348 impl<'tcx> ItemCtxt<'tcx> {
 349     pub fn new(tcx: TyCtxt<'tcx>, item_def_id: DefId) -> ItemCtxt<'tcx> {
 350         ItemCtxt { tcx, item_def_id }
 351     }
 352
 353     pub fn to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
 354         <dyn AstConv<'_>>::ast_ty_to_ty(self, ast_ty)
 355     }
 356
 357     pub fn hir_id(&self) -> hir::HirId {
 358         self.tcx.hir().local_def_id_to_hir_id(self.item_def_id.expect_local())
 359     }
 360
 361     pub fn node(&self) -> hir::Node<'tcx> {
 362         self.tcx.hir().get(self.hir_id())
 363     }
 364 }
 365
 366 impl<'tcx> AstConv<'tcx> for ItemCtxt<'tcx> {
 367     fn tcx(&self) -> TyCtxt<'tcx> {
 368         self.tcx
 369     }
 370
 371     fn item_def_id(&self) -> DefId {
 372         self.item_def_id
 373     }
 374
 375     fn get_type_parameter_bounds(
 376         &self,
 377         span: Span,
 378         def_id: DefId,
 379         assoc_name: Ident,
 380     ) -> ty::GenericPredicates<'tcx> {
 381         self.tcx.at(span).type_param_predicates((
 382             self.item_def_id,
 383             def_id.expect_local(),
 384             assoc_name,
 385         ))
 386     }
 387
 388     fn re_infer(&self, _: Option<&ty::GenericParamDef>, _: Span) -> Option<ty::Region<'tcx>> {
 389         None
 390     }
 391
 392     fn allow_ty_infer(&self) -> bool {
 393         false
 394     }
 395
 396     fn ty_infer(&self, _: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
 397         self.tcx().ty_error_with_message(span, "bad placeholder type")
 398     }
 399
 400     fn ct_infer(&self, ty: Ty<'tcx>, _: Option<&ty::GenericParamDef>, span: Span) -> Const<'tcx> {
 401         let ty = self.tcx.fold_regions(ty, |r, _| match *r {
 402             ty::ReErased => self.tcx.lifetimes.re_static,
 403             _ => r,
 404         });
 405         self.tcx().const_error_with_message(ty, span, "bad placeholder constant")
 406     }
 407
 408     fn projected_ty_from_poly_trait_ref(
 409         &self,
 410         span: Span,
 411         item_def_id: DefId,
 412         item_segment: &hir::PathSegment<'_>,
 413         poly_trait_ref: ty::PolyTraitRef<'tcx>,
 414     ) -> Ty<'tcx> {
 415         if let Some(trait_ref) = poly_trait_ref.no_bound_vars() {
 416             let item_substs = <dyn AstConv<'tcx>>::create_substs_for_associated_item(
 417                 self,
 418                 span,
 419                 item_def_id,
 420                 item_segment,
 421                 trait_ref.substs,
 422             );
 423             self.tcx().mk_projection(item_def_id, item_substs)
 424         } else {
 425             // There are no late-bound regions; we can just ignore the binder.
 426             let mut err = struct_span_err!(
 427                 self.tcx().sess,
 428                 span,
 429                 E0212,
 430                 "cannot use the associated type of a trait \
 431                  with uninferred generic parameters"
 432             );
 433
 434             match self.node() {
 435                 hir::Node::Field(_) | hir::Node::Ctor(_) | hir::Node::Variant(_) => {
 436                     let item = self
 437                         .tcx
 438                         .hir()
 439                         .expect_item(self.tcx.hir().get_parent_item(self.hir_id()).def_id);
 440                     match &item.kind {
 441                         hir::ItemKind::Enum(_, generics)
 442                         | hir::ItemKind::Struct(_, generics)
 443                         | hir::ItemKind::Union(_, generics) => {
 444                             let lt_name = get_new_lifetime_name(self.tcx, poly_trait_ref, generics);
 445                             let (lt_sp, sugg) = match generics.params {
 446                                 [] => (generics.span, format!("<{}>", lt_name)),
 447                                 [bound, ..] => {
 448                                     (bound.span.shrink_to_lo(), format!("{}, ", lt_name))
 449                                 }
 450                             };
 451                             let suggestions = vec![
 452                                 (lt_sp, sugg),
 453                                 (
 454                                     span.with_hi(item_segment.ident.span.lo()),
 455                                     format!(
 456                                         "{}::",
 457                                         // Replace the existing lifetimes with a new named lifetime.
 458                                         self.tcx.replace_late_bound_regions_uncached(
 459                                             poly_trait_ref,
 460                                             |_| {
 461                                                 self.tcx.mk_region(ty::ReEarlyBound(
 462                                                     ty::EarlyBoundRegion {
 463                                                         def_id: item_def_id,
 464                                                         index: 0,
 465                                                         name: Symbol::intern(&lt_name),
 466                                                     },
 467                                                 ))
 468                                             }
 469                                         ),
 470                                     ),
 471                                 ),
 472                             ];
 473                             err.multipart_suggestion(
 474                                 "use a fully qualified path with explicit lifetimes",
 475                                 suggestions,
 476                                 Applicability::MaybeIncorrect,
 477                             );
 478                         }
 479                         _ => {}
 480                     }
 481                 }
 482                 hir::Node::Item(hir::Item {
 483                     kind:
 484                         hir::ItemKind::Struct(..) | hir::ItemKind::Enum(..) | hir::ItemKind::Union(..),
 485                     ..
 486                 }) => {}
 487                 hir::Node::Item(_)
 488                 | hir::Node::ForeignItem(_)
 489                 | hir::Node::TraitItem(_)
 490                 | hir::Node::ImplItem(_) => {
 491                     err.span_suggestion_verbose(
 492                         span.with_hi(item_segment.ident.span.lo()),
 493                         "use a fully qualified path with inferred lifetimes",
 494                         format!(
 495                             "{}::",
 496                             // Erase named lt, we want `<A as B<'_>::C`, not `<A as B<'a>::C`.
 497                             self.tcx.anonymize_bound_vars(poly_trait_ref).skip_binder(),
 498                         ),
 499                         Applicability::MaybeIncorrect,
 500                     );
 501                 }
 502                 _ => {}
 503             }
 504             self.tcx().ty_error_with_guaranteed(err.emit())
 505         }
 506     }
 507
 508     fn probe_adt(&self, _span: Span, ty: Ty<'tcx>) -> Option<ty::AdtDef<'tcx>> {
 509         // FIXME(#103640): Should we handle the case where `ty` is a projection?
 510         ty.ty_adt_def()
 511     }
 512
 513     fn set_tainted_by_errors(&self, _: ErrorGuaranteed) {
 514         // There's no obvious place to track this, so just let it go.
 515     }
 516
 517     fn record_ty(&self, _hir_id: hir::HirId, _ty: Ty<'tcx>, _span: Span) {
 518         // There's no place to record types from signatures?
 519     }
 520 }
 521
 522 /// Synthesize a new lifetime name that doesn't clash with any of the lifetimes already present.
 523 fn get_new_lifetime_name<'tcx>(
 524     tcx: TyCtxt<'tcx>,
 525     poly_trait_ref: ty::PolyTraitRef<'tcx>,
 526     generics: &hir::Generics<'tcx>,
 527 ) -> String {
 528     let existing_lifetimes = tcx
 529         .collect_referenced_late_bound_regions(&poly_trait_ref)
 530         .into_iter()
 531         .filter_map(|lt| {
 532             if let ty::BoundRegionKind::BrNamed(_, name) = lt {
 533                 Some(name.as_str().to_string())
 534             } else {
 535                 None
 536             }
 537         })
 538         .chain(generics.params.iter().filter_map(|param| {
 539             if let hir::GenericParamKind::Lifetime { .. } = &param.kind {
 540                 Some(param.name.ident().as_str().to_string())
 541             } else {
 542                 None
 543             }
 544         }))
 545         .collect::<FxHashSet<String>>();
 546
 547     let a_to_z_repeat_n = |n| {
 548         (b'a'..=b'z').map(move |c| {
 549             let mut s = '\''.to_string();
 550             s.extend(std::iter::repeat(char::from(c)).take(n));
 551             s
 552         })
 553     };
 554
 555     // If all single char lifetime names are present, we wrap around and double the chars.
 556     (1..).flat_map(a_to_z_repeat_n).find(|lt| !existing_lifetimes.contains(lt.as_str())).unwrap()
 557 }
 558
 559 fn convert_item(tcx: TyCtxt<'_>, item_id: hir::ItemId) {
 560     let it = tcx.hir().item(item_id);
 561     debug!("convert: item {} with id {}", it.ident, it.hir_id());
 562     let def_id = item_id.owner_id.def_id;
 563
 564     match it.kind {
 565         // These don't define types.
 566         hir::ItemKind::ExternCrate(_)
 567         | hir::ItemKind::Use(..)
 568         | hir::ItemKind::Macro(..)
 569         | hir::ItemKind::Mod(_)
 570         | hir::ItemKind::GlobalAsm(_) => {}
 571         hir::ItemKind::ForeignMod { items, .. } => {
 572             for item in items {
 573                 let item = tcx.hir().foreign_item(item.id);
 574                 tcx.ensure().generics_of(item.owner_id);
 575                 tcx.ensure().type_of(item.owner_id);
 576                 tcx.ensure().predicates_of(item.owner_id);
 577                 match item.kind {
 578                     hir::ForeignItemKind::Fn(..) => {
 579                         tcx.ensure().codegen_fn_attrs(item.owner_id);
 580                         tcx.ensure().fn_sig(item.owner_id)
 581                     }
 582                     hir::ForeignItemKind::Static(..) => {
 583                         tcx.ensure().codegen_fn_attrs(item.owner_id);
 584                         let mut visitor = HirPlaceholderCollector::default();
 585                         visitor.visit_foreign_item(item);
 586                         placeholder_type_error(
 587                             tcx,
 588                             None,
 589                             visitor.0,
 590                             false,
 591                             None,
 592                             "static variable",
 593                         );
 594                     }
 595                     _ => (),
 596                 }
 597             }
 598         }
 599         hir::ItemKind::Enum(..) => {
 600             tcx.ensure().generics_of(def_id);
 601             tcx.ensure().type_of(def_id);
 602             tcx.ensure().predicates_of(def_id);
 603             convert_enum_variant_types(tcx, def_id.to_def_id());
 604         }
 605         hir::ItemKind::Impl { .. } => {
 606             tcx.ensure().generics_of(def_id);
 607             tcx.ensure().type_of(def_id);
 608             tcx.ensure().impl_trait_ref(def_id);
 609             tcx.ensure().predicates_of(def_id);
 610         }
 611         hir::ItemKind::Trait(..) => {
 612             tcx.ensure().generics_of(def_id);
 613             tcx.ensure().trait_def(def_id);
 614             tcx.at(it.span).super_predicates_of(def_id);
 615             tcx.ensure().predicates_of(def_id);
 616         }
 617         hir::ItemKind::TraitAlias(..) => {
 618             tcx.ensure().generics_of(def_id);
 619             tcx.at(it.span).super_predicates_of(def_id);
 620             tcx.ensure().predicates_of(def_id);
 621         }
 622         hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
 623             tcx.ensure().generics_of(def_id);
 624             tcx.ensure().type_of(def_id);
 625             tcx.ensure().predicates_of(def_id);
 626
 627             for f in struct_def.fields() {
 628                 tcx.ensure().generics_of(f.def_id);
 629                 tcx.ensure().type_of(f.def_id);
 630                 tcx.ensure().predicates_of(f.def_id);
 631             }
 632
 633             if let Some(ctor_def_id) = struct_def.ctor_def_id() {
 634                 convert_variant_ctor(tcx, ctor_def_id);
 635             }
 636         }
 637
 638         // Don't call `type_of` on opaque types, since that depends on type
 639         // checking function bodies. `check_item_type` ensures that it's called
 640         // instead.
 641         hir::ItemKind::OpaqueTy(..) => {
 642             tcx.ensure().generics_of(def_id);
 643             tcx.ensure().predicates_of(def_id);
 644             tcx.ensure().explicit_item_bounds(def_id);
 645             tcx.ensure().item_bounds(def_id);
 646         }
 647
 648         hir::ItemKind::TyAlias(..) => {
 649             tcx.ensure().generics_of(def_id);
 650             tcx.ensure().type_of(def_id);
 651             tcx.ensure().predicates_of(def_id);
 652         }
 653
 654         hir::ItemKind::Static(ty, ..) | hir::ItemKind::Const(ty, ..) => {
 655             tcx.ensure().generics_of(def_id);
 656             tcx.ensure().type_of(def_id);
 657             tcx.ensure().predicates_of(def_id);
 658             if !is_suggestable_infer_ty(ty) {
 659                 let mut visitor = HirPlaceholderCollector::default();
 660                 visitor.visit_item(it);
 661                 placeholder_type_error(tcx, None, visitor.0, false, None, it.kind.descr());
 662             }
 663         }
 664
 665         hir::ItemKind::Fn(..) => {
 666             tcx.ensure().generics_of(def_id);
 667             tcx.ensure().type_of(def_id);
 668             tcx.ensure().predicates_of(def_id);
 669             tcx.ensure().fn_sig(def_id);
 670             tcx.ensure().codegen_fn_attrs(def_id);
 671         }
 672     }
 673 }
 674
 675 fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::TraitItemId) {
 676     let trait_item = tcx.hir().trait_item(trait_item_id);
 677     let def_id = trait_item_id.owner_id;
 678     tcx.ensure().generics_of(def_id);
 679
 680     match trait_item.kind {
 681         hir::TraitItemKind::Fn(..) => {
 682             tcx.ensure().codegen_fn_attrs(def_id);
 683             tcx.ensure().type_of(def_id);
 684             tcx.ensure().fn_sig(def_id);
 685         }
 686
 687         hir::TraitItemKind::Const(.., Some(_)) => {
 688             tcx.ensure().type_of(def_id);
 689         }
 690
 691         hir::TraitItemKind::Const(hir_ty, _) => {
 692             tcx.ensure().type_of(def_id);
 693             // Account for `const C: _;`.
 694             let mut visitor = HirPlaceholderCollector::default();
 695             visitor.visit_trait_item(trait_item);
 696             if !tcx.sess.diagnostic().has_stashed_diagnostic(hir_ty.span, StashKey::ItemNoType) {
 697                 placeholder_type_error(tcx, None, visitor.0, false, None, "constant");
 698             }
 699         }
 700
 701         hir::TraitItemKind::Type(_, Some(_)) => {
 702             tcx.ensure().item_bounds(def_id);
 703             tcx.ensure().type_of(def_id);
 704             // Account for `type T = _;`.
 705             let mut visitor = HirPlaceholderCollector::default();
 706             visitor.visit_trait_item(trait_item);
 707             placeholder_type_error(tcx, None, visitor.0, false, None, "associated type");
 708         }
 709
 710         hir::TraitItemKind::Type(_, None) => {
 711             tcx.ensure().item_bounds(def_id);
 712             // #74612: Visit and try to find bad placeholders
 713             // even if there is no concrete type.
 714             let mut visitor = HirPlaceholderCollector::default();
 715             visitor.visit_trait_item(trait_item);
 716
 717             placeholder_type_error(tcx, None, visitor.0, false, None, "associated type");
 718         }
 719     };
 720
 721     tcx.ensure().predicates_of(def_id);
 722 }
 723
 724 fn convert_impl_item(tcx: TyCtxt<'_>, impl_item_id: hir::ImplItemId) {
 725     let def_id = impl_item_id.owner_id;
 726     tcx.ensure().generics_of(def_id);
 727     tcx.ensure().type_of(def_id);
 728     tcx.ensure().predicates_of(def_id);
 729     let impl_item = tcx.hir().impl_item(impl_item_id);
 730     match impl_item.kind {
 731         hir::ImplItemKind::Fn(..) => {
 732             tcx.ensure().codegen_fn_attrs(def_id);
 733             tcx.ensure().fn_sig(def_id);
 734         }
 735         hir::ImplItemKind::Type(_) => {
 736             // Account for `type T = _;`
 737             let mut visitor = HirPlaceholderCollector::default();
 738             visitor.visit_impl_item(impl_item);
 739
 740             placeholder_type_error(tcx, None, visitor.0, false, None, "associated type");
 741         }
 742         hir::ImplItemKind::Const(..) => {}
 743     }
 744 }
 745
 746 fn convert_variant_ctor(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 747     tcx.ensure().generics_of(def_id);
 748     tcx.ensure().type_of(def_id);
 749     tcx.ensure().predicates_of(def_id);
 750 }
 751
 752 fn convert_enum_variant_types(tcx: TyCtxt<'_>, def_id: DefId) {
 753     let def = tcx.adt_def(def_id);
 754     let repr_type = def.repr().discr_type();
 755     let initial = repr_type.initial_discriminant(tcx);
 756     let mut prev_discr = None::<Discr<'_>>;
 757
 758     // fill the discriminant values and field types
 759     for variant in def.variants() {
 760         let wrapped_discr = prev_discr.map_or(initial, |d| d.wrap_incr(tcx));
 761         prev_discr = Some(
 762             if let ty::VariantDiscr::Explicit(const_def_id) = variant.discr {
 763                 def.eval_explicit_discr(tcx, const_def_id)
 764             } else if let Some(discr) = repr_type.disr_incr(tcx, prev_discr) {
 765                 Some(discr)
 766             } else {
 767                 let span = tcx.def_span(variant.def_id);
 768                 struct_span_err!(tcx.sess, span, E0370, "enum discriminant overflowed")
 769                     .span_label(span, format!("overflowed on value after {}", prev_discr.unwrap()))
 770                     .note(&format!(
 771                         "explicitly set `{} = {}` if that is desired outcome",
 772                         tcx.item_name(variant.def_id),
 773                         wrapped_discr
 774                     ))
 775                     .emit();
 776                 None
 777             }
 778             .unwrap_or(wrapped_discr),
 779         );
 780
 781         for f in &variant.fields {
 782             tcx.ensure().generics_of(f.did);
 783             tcx.ensure().type_of(f.did);
 784             tcx.ensure().predicates_of(f.did);
 785         }
 786
 787         // Convert the ctor, if any. This also registers the variant as
 788         // an item.
 789         if let Some(ctor_def_id) = variant.ctor_def_id() {
 790             convert_variant_ctor(tcx, ctor_def_id.expect_local());
 791         }
 792     }
 793 }
 794
 795 fn convert_variant(
 796     tcx: TyCtxt<'_>,
 797     variant_did: Option<LocalDefId>,
 798     ident: Ident,
 799     discr: ty::VariantDiscr,
 800     def: &hir::VariantData<'_>,
 801     adt_kind: ty::AdtKind,
 802     parent_did: LocalDefId,
 803 ) -> ty::VariantDef {
 804     let mut seen_fields: FxHashMap<Ident, Span> = Default::default();
 805     let fields = def
 806         .fields()
 807         .iter()
 808         .map(|f| {
 809             let dup_span = seen_fields.get(&f.ident.normalize_to_macros_2_0()).cloned();
 810             if let Some(prev_span) = dup_span {
 811                 tcx.sess.emit_err(errors::FieldAlreadyDeclared {
 812                     field_name: f.ident,
 813                     span: f.span,
 814                     prev_span,
 815                 });
 816             } else {
 817                 seen_fields.insert(f.ident.normalize_to_macros_2_0(), f.span);
 818             }
 819
 820             ty::FieldDef {
 821                 did: f.def_id.to_def_id(),
 822                 name: f.ident.name,
 823                 vis: tcx.visibility(f.def_id),
 824             }
 825         })
 826         .collect();
 827     let recovered = match def {
 828         hir::VariantData::Struct(_, r) => *r,
 829         _ => false,
 830     };
 831     ty::VariantDef::new(
 832         ident.name,
 833         variant_did.map(LocalDefId::to_def_id),
 834         def.ctor().map(|(kind, _, def_id)| (kind, def_id.to_def_id())),
 835         discr,
 836         fields,
 837         adt_kind,
 838         parent_did.to_def_id(),
 839         recovered,
 840         adt_kind == AdtKind::Struct && tcx.has_attr(parent_did.to_def_id(), sym::non_exhaustive)
 841             || variant_did.map_or(false, |variant_did| {
 842                 tcx.has_attr(variant_did.to_def_id(), sym::non_exhaustive)
 843             }),
 844     )
 845 }
 846
 847 fn adt_def(tcx: TyCtxt<'_>, def_id: DefId) -> ty::AdtDef<'_> {
 848     use rustc_hir::*;
 849
 850     let def_id = def_id.expect_local();
 851     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 852     let Node::Item(item) = tcx.hir().get(hir_id) else {
 853         bug!();
 854     };
 855
 856     let repr = tcx.repr_options_of_def(def_id.to_def_id());
 857     let (kind, variants) = match item.kind {
 858         ItemKind::Enum(ref def, _) => {
 859             let mut distance_from_explicit = 0;
 860             let variants = def
 861                 .variants
 862                 .iter()
 863                 .map(|v| {
 864                     let discr = if let Some(ref e) = v.disr_expr {
 865                         distance_from_explicit = 0;
 866                         ty::VariantDiscr::Explicit(e.def_id.to_def_id())
 867                     } else {
 868                         ty::VariantDiscr::Relative(distance_from_explicit)
 869                     };
 870                     distance_from_explicit += 1;
 871
 872                     convert_variant(
 873                         tcx,
 874                         Some(v.def_id),
 875                         v.ident,
 876                         discr,
 877                         &v.data,
 878                         AdtKind::Enum,
 879                         def_id,
 880                     )
 881                 })
 882                 .collect();
 883
 884             (AdtKind::Enum, variants)
 885         }
 886         ItemKind::Struct(ref def, _) | ItemKind::Union(ref def, _) => {
 887             let adt_kind = match item.kind {
 888                 ItemKind::Struct(..) => AdtKind::Struct,
 889                 _ => AdtKind::Union,
 890             };
 891             let variants = std::iter::once(convert_variant(
 892                 tcx,
 893                 None,
 894                 item.ident,
 895                 ty::VariantDiscr::Relative(0),
 896                 def,
 897                 adt_kind,
 898                 def_id,
 899             ))
 900             .collect();
 901
 902             (adt_kind, variants)
 903         }
 904         _ => bug!(),
 905     };
 906     tcx.alloc_adt_def(def_id.to_def_id(), kind, variants, repr)
 907 }
 908
 909 fn trait_def(tcx: TyCtxt<'_>, def_id: DefId) -> ty::TraitDef {
 910     let item = tcx.hir().expect_item(def_id.expect_local());
 911
 912     let (is_auto, unsafety, items) = match item.kind {
 913         hir::ItemKind::Trait(is_auto, unsafety, .., items) => {
 914             (is_auto == hir::IsAuto::Yes, unsafety, items)
 915         }
 916         hir::ItemKind::TraitAlias(..) => (false, hir::Unsafety::Normal, &[][..]),
 917         _ => span_bug!(item.span, "trait_def_of_item invoked on non-trait"),
 918     };
 919
 920     let paren_sugar = tcx.has_attr(def_id, sym::rustc_paren_sugar);
 921     if paren_sugar && !tcx.features().unboxed_closures {
 922         tcx.sess
 923             .struct_span_err(
 924                 item.span,
 925                 "the `#[rustc_paren_sugar]` attribute is a temporary means of controlling \
 926                  which traits can use parenthetical notation",
 927             )
 928             .help("add `#![feature(unboxed_closures)]` to the crate attributes to use it")
 929             .emit();
 930     }
 931
 932     let is_marker = tcx.has_attr(def_id, sym::marker);
 933     let skip_array_during_method_dispatch =
 934         tcx.has_attr(def_id, sym::rustc_skip_array_during_method_dispatch);
 935     let spec_kind = if tcx.has_attr(def_id, sym::rustc_unsafe_specialization_marker) {
 936         ty::trait_def::TraitSpecializationKind::Marker
 937     } else if tcx.has_attr(def_id, sym::rustc_specialization_trait) {
 938         ty::trait_def::TraitSpecializationKind::AlwaysApplicable
 939     } else {
 940         ty::trait_def::TraitSpecializationKind::None
 941     };
 942     let must_implement_one_of = tcx
 943         .get_attr(def_id, sym::rustc_must_implement_one_of)
 944         // Check that there are at least 2 arguments of `#[rustc_must_implement_one_of]`
 945         // and that they are all identifiers
 946         .and_then(|attr| match attr.meta_item_list() {
 947             Some(items) if items.len() < 2 => {
 948                 tcx.sess
 949                     .struct_span_err(
 950                         attr.span,
 951                         "the `#[rustc_must_implement_one_of]` attribute must be \
 952                          used with at least 2 args",
 953                     )
 954                     .emit();
 955
 956                 None
 957             }
 958             Some(items) => items
 959                 .into_iter()
 960                 .map(|item| item.ident().ok_or(item.span()))
 961                 .collect::<Result<Box<[_]>, _>>()
 962                 .map_err(|span| {
 963                     tcx.sess
 964                         .struct_span_err(span, "must be a name of an associated function")
 965                         .emit();
 966                 })
 967                 .ok()
 968                 .zip(Some(attr.span)),
 969             // Error is reported by `rustc_attr!`
 970             None => None,
 971         })
 972         // Check that all arguments of `#[rustc_must_implement_one_of]` reference
 973         // functions in the trait with default implementations
 974         .and_then(|(list, attr_span)| {
 975             let errors = list.iter().filter_map(|ident| {
 976                 let item = items.iter().find(|item| item.ident == *ident);
 977
 978                 match item {
 979                     Some(item) if matches!(item.kind, hir::AssocItemKind::Fn { .. }) => {
 980                         if !tcx.impl_defaultness(item.id.owner_id).has_value() {
 981                             tcx.sess
 982                                 .struct_span_err(
 983                                     item.span,
 984                                     "function doesn't have a default implementation",
 985                                 )
 986                                 .span_note(attr_span, "required by this annotation")
 987                                 .emit();
 988
 989                             return Some(());
 990                         }
 991
 992                         return None;
 993                     }
 994                     Some(item) => {
 995                         tcx.sess
 996                             .struct_span_err(item.span, "not a function")
 997                             .span_note(attr_span, "required by this annotation")
 998                             .note(
 999                                 "all `#[rustc_must_implement_one_of]` arguments must be associated \
1000                                  function names",
1001                             )
1002                             .emit();
1003                     }
1004                     None => {
1005                         tcx.sess
1006                             .struct_span_err(ident.span, "function not found in this trait")
1007                             .emit();
1008                     }
1009                 }
1010
1011                 Some(())
1012             });
1013
1014             (errors.count() == 0).then_some(list)
1015         })
1016         // Check for duplicates
1017         .and_then(|list| {
1018             let mut set: FxHashMap<Symbol, Span> = FxHashMap::default();
1019             let mut no_dups = true;
1020
1021             for ident in &*list {
1022                 if let Some(dup) = set.insert(ident.name, ident.span) {
1023                     tcx.sess
1024                         .struct_span_err(vec![dup, ident.span], "functions names are duplicated")
1025                         .note("all `#[rustc_must_implement_one_of]` arguments must be unique")
1026                         .emit();
1027
1028                     no_dups = false;
1029                 }
1030             }
1031
1032             no_dups.then_some(list)
1033         });
1034
1035     ty::TraitDef::new(
1036         def_id,
1037         unsafety,
1038         paren_sugar,
1039         is_auto,
1040         is_marker,
1041         skip_array_during_method_dispatch,
1042         spec_kind,
1043         must_implement_one_of,
1044     )
1045 }
1046
1047 fn are_suggestable_generic_args(generic_args: &[hir::GenericArg<'_>]) -> bool {
1048     generic_args.iter().any(|arg| match arg {
1049         hir::GenericArg::Type(ty) => is_suggestable_infer_ty(ty),
1050         hir::GenericArg::Infer(_) => true,
1051         _ => false,
1052     })
1053 }
1054
1055 /// Whether `ty` is a type with `_` placeholders that can be inferred. Used in diagnostics only to
1056 /// use inference to provide suggestions for the appropriate type if possible.
1057 fn is_suggestable_infer_ty(ty: &hir::Ty<'_>) -> bool {
1058     debug!(?ty);
1059     use hir::TyKind::*;
1060     match &ty.kind {
1061         Infer => true,
1062         Slice(ty) => is_suggestable_infer_ty(ty),
1063         Array(ty, length) => {
1064             is_suggestable_infer_ty(ty) || matches!(length, hir::ArrayLen::Infer(_, _))
1065         }
1066         Tup(tys) => tys.iter().any(is_suggestable_infer_ty),
1067         Ptr(mut_ty) | Ref(_, mut_ty) => is_suggestable_infer_ty(mut_ty.ty),
1068         OpaqueDef(_, generic_args, _) => are_suggestable_generic_args(generic_args),
1069         Path(hir::QPath::TypeRelative(ty, segment)) => {
1070             is_suggestable_infer_ty(ty) || are_suggestable_generic_args(segment.args().args)
1071         }
1072         Path(hir::QPath::Resolved(ty_opt, hir::Path { segments, .. })) => {
1073             ty_opt.map_or(false, is_suggestable_infer_ty)
1074                 || segments.iter().any(|segment| are_suggestable_generic_args(segment.args().args))
1075         }
1076         _ => false,
1077     }
1078 }
1079
1080 pub fn get_infer_ret_ty<'hir>(output: &'hir hir::FnRetTy<'hir>) -> Option<&'hir hir::Ty<'hir>> {
1081     if let hir::FnRetTy::Return(ty) = output {
1082         if is_suggestable_infer_ty(ty) {
1083             return Some(&*ty);
1084         }
1085     }
1086     None
1087 }
1088
1089 #[instrument(level = "debug", skip(tcx))]
1090 fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
1091     use rustc_hir::Node::*;
1092     use rustc_hir::*;
1093
1094     let def_id = def_id.expect_local();
1095     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
1096
1097     let icx = ItemCtxt::new(tcx, def_id.to_def_id());
1098
1099     match tcx.hir().get(hir_id) {
1100         TraitItem(hir::TraitItem {
1101             kind: TraitItemKind::Fn(sig, TraitFn::Provided(_)),
1102             generics,
1103             ..
1104         })
1105         | Item(hir::Item { kind: ItemKind::Fn(sig, generics, _), .. }) => {
1106             infer_return_ty_for_fn_sig(tcx, sig, generics, def_id, &icx)
1107         }
1108
1109         ImplItem(hir::ImplItem { kind: ImplItemKind::Fn(sig, _), generics, .. }) => {
1110             // Do not try to infer the return type for a impl method coming from a trait
1111             if let Item(hir::Item { kind: ItemKind::Impl(i), .. }) =
1112                 tcx.hir().get_parent(hir_id)
1113                 && i.of_trait.is_some()
1114             {
1115                 <dyn AstConv<'_>>::ty_of_fn(
1116                     &icx,
1117                     hir_id,
1118                     sig.header.unsafety,
1119                     sig.header.abi,
1120                     sig.decl,
1121                     Some(generics),
1122                     None,
1123                 )
1124             } else {
1125                 infer_return_ty_for_fn_sig(tcx, sig, generics, def_id, &icx)
1126             }
1127         }
1128
1129         TraitItem(hir::TraitItem {
1130             kind: TraitItemKind::Fn(FnSig { header, decl, span: _ }, _),
1131             generics,
1132             ..
1133         }) => <dyn AstConv<'_>>::ty_of_fn(
1134             &icx,
1135             hir_id,
1136             header.unsafety,
1137             header.abi,
1138             decl,
1139             Some(generics),
1140             None,
1141         ),
1142
1143         ForeignItem(&hir::ForeignItem { kind: ForeignItemKind::Fn(fn_decl, _, _), .. }) => {
1144             let abi = tcx.hir().get_foreign_abi(hir_id);
1145             compute_sig_of_foreign_fn_decl(tcx, def_id.to_def_id(), fn_decl, abi)
1146         }
1147
1148         Ctor(data) | Variant(hir::Variant { data, .. }) if data.ctor().is_some() => {
1149             let ty = tcx.type_of(tcx.hir().get_parent_item(hir_id));
1150             let inputs = data.fields().iter().map(|f| tcx.type_of(f.def_id));
1151             ty::Binder::dummy(tcx.mk_fn_sig(
1152                 inputs,
1153                 ty,
1154                 false,
1155                 hir::Unsafety::Normal,
1156                 abi::Abi::Rust,
1157             ))
1158         }
1159
1160         Expr(&hir::Expr { kind: hir::ExprKind::Closure { .. }, .. }) => {
1161             // Closure signatures are not like other function
1162             // signatures and cannot be accessed through `fn_sig`. For
1163             // example, a closure signature excludes the `self`
1164             // argument. In any case they are embedded within the
1165             // closure type as part of the `ClosureSubsts`.
1166             //
1167             // To get the signature of a closure, you should use the
1168             // `sig` method on the `ClosureSubsts`:
1169             //
1170             //    substs.as_closure().sig(def_id, tcx)
1171             bug!(
1172                 "to get the signature of a closure, use `substs.as_closure().sig()` not `fn_sig()`",
1173             );
1174         }
1175
1176         x => {
1177             bug!("unexpected sort of node in fn_sig(): {:?}", x);
1178         }
1179     }
1180 }
1181
1182 fn infer_return_ty_for_fn_sig<'tcx>(
1183     tcx: TyCtxt<'tcx>,
1184     sig: &hir::FnSig<'_>,
1185     generics: &hir::Generics<'_>,
1186     def_id: LocalDefId,
1187     icx: &ItemCtxt<'tcx>,
1188 ) -> ty::PolyFnSig<'tcx> {
1189     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
1190
1191     match get_infer_ret_ty(&sig.decl.output) {
1192         Some(ty) => {
1193             let fn_sig = tcx.typeck(def_id).liberated_fn_sigs()[hir_id];
1194             // Typeck doesn't expect erased regions to be returned from `type_of`.
1195             let fn_sig = tcx.fold_regions(fn_sig, |r, _| match *r {
1196                 ty::ReErased => tcx.lifetimes.re_static,
1197                 _ => r,
1198             });
1199
1200             let mut visitor = HirPlaceholderCollector::default();
1201             visitor.visit_ty(ty);
1202             let mut diag = bad_placeholder(tcx, visitor.0, "return type");
1203             let ret_ty = fn_sig.output();
1204             if ret_ty.is_suggestable(tcx, false) {
1205                 diag.span_suggestion(
1206                     ty.span,
1207                     "replace with the correct return type",
1208                     ret_ty,
1209                     Applicability::MachineApplicable,
1210                 );
1211             } else if matches!(ret_ty.kind(), ty::FnDef(..)) {
1212                 let fn_sig = ret_ty.fn_sig(tcx);
1213                 if fn_sig
1214                     .skip_binder()
1215                     .inputs_and_output
1216                     .iter()
1217                     .all(|t| t.is_suggestable(tcx, false))
1218                 {
1219                     diag.span_suggestion(
1220                         ty.span,
1221                         "replace with the correct return type",
1222                         fn_sig,
1223                         Applicability::MachineApplicable,
1224                     );
1225                 }
1226             } else if let Some(sugg) = suggest_impl_trait(tcx, ret_ty, ty.span, hir_id, def_id) {
1227                 diag.span_suggestion(
1228                     ty.span,
1229                     "replace with an appropriate return type",
1230                     sugg,
1231                     Applicability::MachineApplicable,
1232                 );
1233             } else if ret_ty.is_closure() {
1234                 diag.help("consider using an `Fn`, `FnMut`, or `FnOnce` trait bound");
1235             }
1236             // Also note how `Fn` traits work just in case!
1237             if ret_ty.is_closure() {
1238                 diag.note(
1239                     "for more information on `Fn` traits and closure types, see \
1240                      https://doc.rust-lang.org/book/ch13-01-closures.html",
1241                 );
1242             }
1243             diag.emit();
1244
1245             ty::Binder::dummy(fn_sig)
1246         }
1247         None => <dyn AstConv<'_>>::ty_of_fn(
1248             icx,
1249             hir_id,
1250             sig.header.unsafety,
1251             sig.header.abi,
1252             sig.decl,
1253             Some(generics),
1254             None,
1255         ),
1256     }
1257 }
1258
1259 fn suggest_impl_trait<'tcx>(
1260     tcx: TyCtxt<'tcx>,
1261     ret_ty: Ty<'tcx>,
1262     span: Span,
1263     hir_id: hir::HirId,
1264     def_id: LocalDefId,
1265 ) -> Option<String> {
1266     let format_as_assoc: fn(_, _, _, _, _) -> _ =
1267         |tcx: TyCtxt<'tcx>,
1268          _: ty::SubstsRef<'tcx>,
1269          trait_def_id: DefId,
1270          assoc_item_def_id: DefId,
1271          item_ty: Ty<'tcx>| {
1272             let trait_name = tcx.item_name(trait_def_id);
1273             let assoc_name = tcx.item_name(assoc_item_def_id);
1274             Some(format!("impl {trait_name}<{assoc_name} = {item_ty}>"))
1275         };
1276     let format_as_parenthesized: fn(_, _, _, _, _) -> _ =
1277         |tcx: TyCtxt<'tcx>,
1278          substs: ty::SubstsRef<'tcx>,
1279          trait_def_id: DefId,
1280          _: DefId,
1281          item_ty: Ty<'tcx>| {
1282             let trait_name = tcx.item_name(trait_def_id);
1283             let args_tuple = substs.type_at(1);
1284             let ty::Tuple(types) = *args_tuple.kind() else { return None; };
1285             if !types.is_suggestable(tcx, false) {
1286                 return None;
1287             }
1288             let maybe_ret =
1289                 if item_ty.is_unit() { String::new() } else { format!(" -> {item_ty}") };
1290             Some(format!(
1291                 "impl {trait_name}({}){maybe_ret}",
1292                 types.iter().map(|ty| ty.to_string()).collect::<Vec<_>>().join(", ")
1293             ))
1294         };
1295
1296     for (trait_def_id, assoc_item_def_id, formatter) in [
1297         (
1298             tcx.get_diagnostic_item(sym::Iterator),
1299             tcx.get_diagnostic_item(sym::IteratorItem),
1300             format_as_assoc,
1301         ),
1302         (
1303             tcx.lang_items().future_trait(),
1304             tcx.get_diagnostic_item(sym::FutureOutput),
1305             format_as_assoc,
1306         ),
1307         (tcx.lang_items().fn_trait(), tcx.lang_items().fn_once_output(), format_as_parenthesized),
1308         (
1309             tcx.lang_items().fn_mut_trait(),
1310             tcx.lang_items().fn_once_output(),
1311             format_as_parenthesized,
1312         ),
1313         (
1314             tcx.lang_items().fn_once_trait(),
1315             tcx.lang_items().fn_once_output(),
1316             format_as_parenthesized,
1317         ),
1318     ] {
1319         let Some(trait_def_id) = trait_def_id else { continue; };
1320         let Some(assoc_item_def_id) = assoc_item_def_id else { continue; };
1321         if tcx.def_kind(assoc_item_def_id) != DefKind::AssocTy {
1322             continue;
1323         }
1324         let param_env = tcx.param_env(def_id);
1325         let infcx = tcx.infer_ctxt().build();
1326         let substs = ty::InternalSubsts::for_item(tcx, trait_def_id, |param, _| {
1327             if param.index == 0 { ret_ty.into() } else { infcx.var_for_def(span, param) }
1328         });
1329         if !infcx.type_implements_trait(trait_def_id, substs, param_env).must_apply_modulo_regions()
1330         {
1331             continue;
1332         }
1333         let ocx = ObligationCtxt::new_in_snapshot(&infcx);
1334         let item_ty = ocx.normalize(
1335             &ObligationCause::misc(span, hir_id),
1336             param_env,
1337             tcx.mk_projection(assoc_item_def_id, substs),
1338         );
1339         // FIXME(compiler-errors): We may benefit from resolving regions here.
1340         if ocx.select_where_possible().is_empty()
1341             && let item_ty = infcx.resolve_vars_if_possible(item_ty)
1342             && item_ty.is_suggestable(tcx, false)
1343             && let Some(sugg) = formatter(tcx, infcx.resolve_vars_if_possible(substs), trait_def_id, assoc_item_def_id, item_ty)
1344         {
1345             return Some(sugg);
1346         }
1347     }
1348     None
1349 }
1350
1351 fn impl_trait_ref(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ty::TraitRef<'_>> {
1352     let icx = ItemCtxt::new(tcx, def_id);
1353     let item = tcx.hir().expect_item(def_id.expect_local());
1354     match item.kind {
1355         hir::ItemKind::Impl(ref impl_) => impl_.of_trait.as_ref().map(|ast_trait_ref| {
1356             let selfty = tcx.type_of(def_id);
1357             <dyn AstConv<'_>>::instantiate_mono_trait_ref(
1358                 &icx,
1359                 ast_trait_ref,
1360                 selfty,
1361                 check_impl_constness(tcx, impl_.constness, ast_trait_ref),
1362             )
1363         }),
1364         _ => bug!(),
1365     }
1366 }
1367
1368 fn check_impl_constness(
1369     tcx: TyCtxt<'_>,
1370     constness: hir::Constness,
1371     ast_trait_ref: &hir::TraitRef<'_>,
1372 ) -> ty::BoundConstness {
1373     match constness {
1374         hir::Constness::Const => {
1375             if let Some(trait_def_id) = ast_trait_ref.trait_def_id() && !tcx.has_attr(trait_def_id, sym::const_trait) {
1376                 let trait_name = tcx.item_name(trait_def_id).to_string();
1377                 tcx.sess.emit_err(errors::ConstImplForNonConstTrait {
1378                     trait_ref_span: ast_trait_ref.path.span,
1379                     trait_name,
1380                     local_trait_span: trait_def_id.as_local().map(|_| tcx.def_span(trait_def_id).shrink_to_lo()),
1381                     marking: (),
1382                     adding: (),
1383                 });
1384                 ty::BoundConstness::NotConst
1385             } else {
1386                 ty::BoundConstness::ConstIfConst
1387             }
1388         },
1389         hir::Constness::NotConst => ty::BoundConstness::NotConst,
1390     }
1391 }
1392
1393 fn impl_polarity(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ImplPolarity {
1394     let is_rustc_reservation = tcx.has_attr(def_id, sym::rustc_reservation_impl);
1395     let item = tcx.hir().expect_item(def_id.expect_local());
1396     match &item.kind {
1397         hir::ItemKind::Impl(hir::Impl {
1398             polarity: hir::ImplPolarity::Negative(span),
1399             of_trait,
1400             ..
1401         }) => {
1402             if is_rustc_reservation {
1403                 let span = span.to(of_trait.as_ref().map_or(*span, |t| t.path.span));
1404                 tcx.sess.span_err(span, "reservation impls can't be negative");
1405             }
1406             ty::ImplPolarity::Negative
1407         }
1408         hir::ItemKind::Impl(hir::Impl {
1409             polarity: hir::ImplPolarity::Positive,
1410             of_trait: None,
1411             ..
1412         }) => {
1413             if is_rustc_reservation {
1414                 tcx.sess.span_err(item.span, "reservation impls can't be inherent");
1415             }
1416             ty::ImplPolarity::Positive
1417         }
1418         hir::ItemKind::Impl(hir::Impl {
1419             polarity: hir::ImplPolarity::Positive,
1420             of_trait: Some(_),
1421             ..
1422         }) => {
1423             if is_rustc_reservation {
1424                 ty::ImplPolarity::Reservation
1425             } else {
1426                 ty::ImplPolarity::Positive
1427             }
1428         }
1429         item => bug!("impl_polarity: {:?} not an impl", item),
1430     }
1431 }
1432
1433 /// Returns the early-bound lifetimes declared in this generics
1434 /// listing. For anything other than fns/methods, this is just all
1435 /// the lifetimes that are declared. For fns or methods, we have to
1436 /// screen out those that do not appear in any where-clauses etc using
1437 /// `resolve_lifetime::early_bound_lifetimes`.
1438 fn early_bound_lifetimes_from_generics<'a, 'tcx: 'a>(
1439     tcx: TyCtxt<'tcx>,
1440     generics: &'a hir::Generics<'a>,
1441 ) -> impl Iterator<Item = &'a hir::GenericParam<'a>> + Captures<'tcx> {
1442     generics.params.iter().filter(move |param| match param.kind {
1443         GenericParamKind::Lifetime { .. } => !tcx.is_late_bound(param.hir_id),
1444         _ => false,
1445     })
1446 }
1447
1448 /// Returns a list of type predicates for the definition with ID `def_id`, including inferred
1449 /// lifetime constraints. This includes all predicates returned by `explicit_predicates_of`, plus
1450 /// inferred constraints concerning which regions outlive other regions.
1451 #[instrument(level = "debug", skip(tcx))]
1452 fn predicates_defined_on(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
1453     let mut result = tcx.explicit_predicates_of(def_id);
1454     debug!("predicates_defined_on: explicit_predicates_of({:?}) = {:?}", def_id, result,);
1455     let inferred_outlives = tcx.inferred_outlives_of(def_id);
1456     if !inferred_outlives.is_empty() {
1457         debug!(
1458             "predicates_defined_on: inferred_outlives_of({:?}) = {:?}",
1459             def_id, inferred_outlives,
1460         );
1461         let inferred_outlives_iter =
1462             inferred_outlives.iter().map(|(clause, span)| ((*clause).to_predicate(tcx), *span));
1463         if result.predicates.is_empty() {
1464             result.predicates = tcx.arena.alloc_from_iter(inferred_outlives_iter);
1465         } else {
1466             result.predicates = tcx.arena.alloc_from_iter(
1467                 result.predicates.into_iter().copied().chain(inferred_outlives_iter),
1468             );
1469         }
1470     }
1471
1472     debug!("predicates_defined_on({:?}) = {:?}", def_id, result);
1473     result
1474 }
1475
1476 fn compute_sig_of_foreign_fn_decl<'tcx>(
1477     tcx: TyCtxt<'tcx>,
1478     def_id: DefId,
1479     decl: &'tcx hir::FnDecl<'tcx>,
1480     abi: abi::Abi,
1481 ) -> ty::PolyFnSig<'tcx> {
1482     let unsafety = if abi == abi::Abi::RustIntrinsic {
1483         intrinsic_operation_unsafety(tcx, def_id)
1484     } else {
1485         hir::Unsafety::Unsafe
1486     };
1487     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
1488     let fty = <dyn AstConv<'_>>::ty_of_fn(
1489         &ItemCtxt::new(tcx, def_id),
1490         hir_id,
1491         unsafety,
1492         abi,
1493         decl,
1494         None,
1495         None,
1496     );
1497
1498     // Feature gate SIMD types in FFI, since I am not sure that the
1499     // ABIs are handled at all correctly. -huonw
1500     if abi != abi::Abi::RustIntrinsic
1501         && abi != abi::Abi::PlatformIntrinsic
1502         && !tcx.features().simd_ffi
1503     {
1504         let check = |ast_ty: &hir::Ty<'_>, ty: Ty<'_>| {
1505             if ty.is_simd() {
1506                 let snip = tcx
1507                     .sess
1508                     .source_map()
1509                     .span_to_snippet(ast_ty.span)
1510                     .map_or_else(|_| String::new(), |s| format!(" `{}`", s));
1511                 tcx.sess
1512                     .struct_span_err(
1513                         ast_ty.span,
1514                         &format!(
1515                             "use of SIMD type{} in FFI is highly experimental and \
1516                              may result in invalid code",
1517                             snip
1518                         ),
1519                     )
1520                     .help("add `#![feature(simd_ffi)]` to the crate attributes to enable")
1521                     .emit();
1522             }
1523         };
1524         for (input, ty) in iter::zip(decl.inputs, fty.inputs().skip_binder()) {
1525             check(input, *ty)
1526         }
1527         if let hir::FnRetTy::Return(ref ty) = decl.output {
1528             check(ty, fty.output().skip_binder())
1529         }
1530     }
1531
1532     fty
1533 }
1534
1535 fn is_foreign_item(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
1536     match tcx.hir().get_if_local(def_id) {
1537         Some(Node::ForeignItem(..)) => true,
1538         Some(_) => false,
1539         _ => bug!("is_foreign_item applied to non-local def-id {:?}", def_id),
1540     }
1541 }
1542
1543 fn generator_kind(tcx: TyCtxt<'_>, def_id: DefId) -> Option<hir::GeneratorKind> {
1544     match tcx.hir().get_if_local(def_id) {
1545         Some(Node::Expr(&rustc_hir::Expr {
1546             kind: rustc_hir::ExprKind::Closure(&rustc_hir::Closure { body, .. }),
1547             ..
1548         })) => tcx.hir().body(body).generator_kind(),
1549         Some(_) => None,
1550         _ => bug!("generator_kind applied to non-local def-id {:?}", def_id),
1551     }
1552 }