compiler/rustc_passes/src/stability.rs

   1 //! A pass that annotates every item and method with its stability level,
   2 //! propagating default levels lexically from parent to children ast nodes.
   3
   4 use rustc_attr::{self as attr, ConstStability, Stability};
   5 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
   6 use rustc_errors::struct_span_err;
   7 use rustc_hir as hir;
   8 use rustc_hir::def::{DefKind, Res};
   9 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
  10 use rustc_hir::hir_id::CRATE_HIR_ID;
  11 use rustc_hir::intravisit::{self, Visitor};
  12 use rustc_hir::{FieldDef, Generics, HirId, Item, TraitRef, Ty, TyKind, Variant};
  13 use rustc_middle::hir::nested_filter;
  14 use rustc_middle::middle::privacy::AccessLevels;
  15 use rustc_middle::middle::stability::{DeprecationEntry, Index};
  16 use rustc_middle::ty::{self, query::Providers, TyCtxt};
  17 use rustc_session::lint;
  18 use rustc_session::lint::builtin::{INEFFECTIVE_UNSTABLE_TRAIT_IMPL, USELESS_DEPRECATED};
  19 use rustc_session::parse::feature_err;
  20 use rustc_session::Session;
  21 use rustc_span::symbol::{sym, Symbol};
  22 use rustc_span::{Span, DUMMY_SP};
  23 use rustc_target::spec::abi::Abi;
  24
  25 use std::cmp::Ordering;
  26 use std::iter;
  27 use std::mem::replace;
  28 use std::num::NonZeroU32;
  29
  30 #[derive(PartialEq)]
  31 enum AnnotationKind {
  32     // Annotation is required if not inherited from unstable parents
  33     Required,
  34     // Annotation is useless, reject it
  35     Prohibited,
  36     // Deprecation annotation is useless, reject it. (Stability attribute is still required.)
  37     DeprecationProhibited,
  38     // Annotation itself is useless, but it can be propagated to children
  39     Container,
  40 }
  41
  42 /// Whether to inherit deprecation flags for nested items. In most cases, we do want to inherit
  43 /// deprecation, because nested items rarely have individual deprecation attributes, and so
  44 /// should be treated as deprecated if their parent is. However, default generic parameters
  45 /// have separate deprecation attributes from their parents, so we do not wish to inherit
  46 /// deprecation in this case. For example, inheriting deprecation for `T` in `Foo<T>`
  47 /// would cause a duplicate warning arising from both `Foo` and `T` being deprecated.
  48 #[derive(Clone)]
  49 enum InheritDeprecation {
  50     Yes,
  51     No,
  52 }
  53
  54 impl InheritDeprecation {
  55     fn yes(&self) -> bool {
  56         matches!(self, InheritDeprecation::Yes)
  57     }
  58 }
  59
  60 /// Whether to inherit const stability flags for nested items. In most cases, we do not want to
  61 /// inherit const stability: just because an enclosing `fn` is const-stable does not mean
  62 /// all `extern` imports declared in it should be const-stable! However, trait methods
  63 /// inherit const stability attributes from their parent and do not have their own.
  64 enum InheritConstStability {
  65     Yes,
  66     No,
  67 }
  68
  69 impl InheritConstStability {
  70     fn yes(&self) -> bool {
  71         matches!(self, InheritConstStability::Yes)
  72     }
  73 }
  74
  75 enum InheritStability {
  76     Yes,
  77     No,
  78 }
  79
  80 impl InheritStability {
  81     fn yes(&self) -> bool {
  82         matches!(self, InheritStability::Yes)
  83     }
  84 }
  85
  86 // A private tree-walker for producing an Index.
  87 struct Annotator<'a, 'tcx> {
  88     tcx: TyCtxt<'tcx>,
  89     index: &'a mut Index,
  90     parent_stab: Option<Stability>,
  91     parent_const_stab: Option<ConstStability>,
  92     parent_depr: Option<DeprecationEntry>,
  93     in_trait_impl: bool,
  94 }
  95
  96 impl<'a, 'tcx> Annotator<'a, 'tcx> {
  97     // Determine the stability for a node based on its attributes and inherited
  98     // stability. The stability is recorded in the index and used as the parent.
  99     // If the node is a function, `fn_sig` is its signature
 100     fn annotate<F>(
 101         &mut self,
 102         def_id: LocalDefId,
 103         item_sp: Span,
 104         fn_sig: Option<&'tcx hir::FnSig<'tcx>>,
 105         kind: AnnotationKind,
 106         inherit_deprecation: InheritDeprecation,
 107         inherit_const_stability: InheritConstStability,
 108         inherit_from_parent: InheritStability,
 109         visit_children: F,
 110     ) where
 111         F: FnOnce(&mut Self),
 112     {
 113         let attrs = self.tcx.hir().attrs(self.tcx.hir().local_def_id_to_hir_id(def_id));
 114         debug!("annotate(id = {:?}, attrs = {:?})", def_id, attrs);
 115
 116         let depr = attr::find_deprecation(&self.tcx.sess, attrs);
 117         let mut is_deprecated = false;
 118         if let Some((depr, span)) = &depr {
 119             is_deprecated = true;
 120
 121             if kind == AnnotationKind::Prohibited || kind == AnnotationKind::DeprecationProhibited {
 122                 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
 123                 self.tcx.struct_span_lint_hir(USELESS_DEPRECATED, hir_id, *span, |lint| {
 124                     lint.build("this `#[deprecated]` annotation has no effect")
 125                         .span_suggestion_short(
 126                             *span,
 127                             "remove the unnecessary deprecation attribute",
 128                             String::new(),
 129                             rustc_errors::Applicability::MachineApplicable,
 130                         )
 131                         .emit();
 132                 });
 133             }
 134
 135             // `Deprecation` is just two pointers, no need to intern it
 136             let depr_entry = DeprecationEntry::local(*depr, def_id);
 137             self.index.depr_map.insert(def_id, depr_entry);
 138         } else if let Some(parent_depr) = self.parent_depr {
 139             if inherit_deprecation.yes() {
 140                 is_deprecated = true;
 141                 info!("tagging child {:?} as deprecated from parent", def_id);
 142                 self.index.depr_map.insert(def_id, parent_depr);
 143             }
 144         }
 145
 146         if !self.tcx.features().staged_api {
 147             // Propagate unstability.  This can happen even for non-staged-api crates in case
 148             // -Zforce-unstable-if-unmarked is set.
 149             if let Some(stab) = self.parent_stab {
 150                 if inherit_deprecation.yes() && stab.level.is_unstable() {
 151                     self.index.stab_map.insert(def_id, stab);
 152                 }
 153             }
 154
 155             self.recurse_with_stability_attrs(
 156                 depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 157                 None,
 158                 None,
 159                 visit_children,
 160             );
 161             return;
 162         }
 163
 164         let (stab, const_stab) = attr::find_stability(&self.tcx.sess, attrs, item_sp);
 165         let mut const_span = None;
 166
 167         let const_stab = const_stab.map(|(const_stab, const_span_node)| {
 168             self.index.const_stab_map.insert(def_id, const_stab);
 169             const_span = Some(const_span_node);
 170             const_stab
 171         });
 172
 173         // If the current node is a function, has const stability attributes and if it doesn not have an intrinsic ABI,
 174         // check if the function/method is const or the parent impl block is const
 175         if let (Some(const_span), Some(fn_sig)) = (const_span, fn_sig) {
 176             if fn_sig.header.abi != Abi::RustIntrinsic
 177                 && fn_sig.header.abi != Abi::PlatformIntrinsic
 178                 && !fn_sig.header.is_const()
 179             {
 180                 if !self.in_trait_impl
 181                     || (self.in_trait_impl && !self.tcx.is_const_fn_raw(def_id.to_def_id()))
 182                 {
 183                     missing_const_err(&self.tcx.sess, fn_sig.span, const_span);
 184                 }
 185             }
 186         }
 187
 188         // `impl const Trait for Type` items forward their const stability to their
 189         // immediate children.
 190         if const_stab.is_none() {
 191             debug!("annotate: const_stab not found, parent = {:?}", self.parent_const_stab);
 192             if let Some(parent) = self.parent_const_stab {
 193                 if parent.level.is_unstable() {
 194                     self.index.const_stab_map.insert(def_id, parent);
 195                 }
 196             }
 197         }
 198
 199         if let Some((rustc_attr::Deprecation { is_since_rustc_version: true, .. }, span)) = &depr {
 200             if stab.is_none() {
 201                 struct_span_err!(
 202                     self.tcx.sess,
 203                     *span,
 204                     E0549,
 205                     "deprecated attribute must be paired with \
 206                     either stable or unstable attribute"
 207                 )
 208                 .emit();
 209             }
 210         }
 211
 212         let stab = stab.map(|(stab, span)| {
 213             // Error if prohibited, or can't inherit anything from a container.
 214             if kind == AnnotationKind::Prohibited
 215                 || (kind == AnnotationKind::Container && stab.level.is_stable() && is_deprecated)
 216             {
 217                 self.tcx.sess.struct_span_err(span,"this stability annotation is useless")
 218                     .span_label(span, "useless stability annotation")
 219                     .span_label(item_sp, "the stability attribute annotates this item")
 220                     .emit();
 221             }
 222
 223             debug!("annotate: found {:?}", stab);
 224
 225             // Check if deprecated_since < stable_since. If it is,
 226             // this is *almost surely* an accident.
 227             if let (&Some(dep_since), &attr::Stable { since: stab_since }) =
 228                 (&depr.as_ref().and_then(|(d, _)| d.since), &stab.level)
 229             {
 230                 // Explicit version of iter::order::lt to handle parse errors properly
 231                 for (dep_v, stab_v) in
 232                     iter::zip(dep_since.as_str().split('.'), stab_since.as_str().split('.'))
 233                 {
 234                     match stab_v.parse::<u64>() {
 235                         Err(_) => {
 236                             self.tcx.sess.struct_span_err(span, "invalid stability version found")
 237                                 .span_label(span, "invalid stability version")
 238                                 .span_label(item_sp, "the stability attribute annotates this item")
 239                                 .emit();
 240                             break;
 241                         }
 242                         Ok(stab_vp) => match dep_v.parse::<u64>() {
 243                             Ok(dep_vp) => match dep_vp.cmp(&stab_vp) {
 244                                 Ordering::Less => {
 245                                     self.tcx.sess.struct_span_err(span, "an API can't be stabilized after it is deprecated")
 246                                         .span_label(span, "invalid version")
 247                                         .span_label(item_sp, "the stability attribute annotates this item")
 248                                         .emit();
 249                                     break;
 250                                 }
 251                                 Ordering::Equal => continue,
 252                                 Ordering::Greater => break,
 253                             },
 254                             Err(_) => {
 255                                 if dep_v != "TBD" {
 256                                     self.tcx.sess.struct_span_err(span, "invalid deprecation version found")
 257                                         .span_label(span, "invalid deprecation version")
 258                                         .span_label(item_sp, "the stability attribute annotates this item")
 259                                         .emit();
 260                                 }
 261                                 break;
 262                             }
 263                         },
 264                     }
 265                 }
 266             }
 267
 268             self.index.stab_map.insert(def_id, stab);
 269             stab
 270         });
 271
 272         if stab.is_none() {
 273             debug!("annotate: stab not found, parent = {:?}", self.parent_stab);
 274             if let Some(stab) = self.parent_stab {
 275                 if inherit_deprecation.yes() && stab.level.is_unstable()
 276                     || inherit_from_parent.yes()
 277                 {
 278                     self.index.stab_map.insert(def_id, stab);
 279                 }
 280             }
 281         }
 282
 283         self.recurse_with_stability_attrs(
 284             depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 285             stab,
 286             if inherit_const_stability.yes() { const_stab } else { None },
 287             visit_children,
 288         );
 289     }
 290
 291     fn recurse_with_stability_attrs(
 292         &mut self,
 293         depr: Option<DeprecationEntry>,
 294         stab: Option<Stability>,
 295         const_stab: Option<ConstStability>,
 296         f: impl FnOnce(&mut Self),
 297     ) {
 298         // These will be `Some` if this item changes the corresponding stability attribute.
 299         let mut replaced_parent_depr = None;
 300         let mut replaced_parent_stab = None;
 301         let mut replaced_parent_const_stab = None;
 302
 303         if let Some(depr) = depr {
 304             replaced_parent_depr = Some(replace(&mut self.parent_depr, Some(depr)));
 305         }
 306         if let Some(stab) = stab {
 307             replaced_parent_stab = Some(replace(&mut self.parent_stab, Some(stab)));
 308         }
 309         if let Some(const_stab) = const_stab {
 310             replaced_parent_const_stab =
 311                 Some(replace(&mut self.parent_const_stab, Some(const_stab)));
 312         }
 313
 314         f(self);
 315
 316         if let Some(orig_parent_depr) = replaced_parent_depr {
 317             self.parent_depr = orig_parent_depr;
 318         }
 319         if let Some(orig_parent_stab) = replaced_parent_stab {
 320             self.parent_stab = orig_parent_stab;
 321         }
 322         if let Some(orig_parent_const_stab) = replaced_parent_const_stab {
 323             self.parent_const_stab = orig_parent_const_stab;
 324         }
 325     }
 326 }
 327
 328 impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
 329     /// Because stability levels are scoped lexically, we want to walk
 330     /// nested items in the context of the outer item, so enable
 331     /// deep-walking.
 332     type NestedFilter = nested_filter::All;
 333
 334     fn nested_visit_map(&mut self) -> Self::Map {
 335         self.tcx.hir()
 336     }
 337
 338     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 339         let orig_in_trait_impl = self.in_trait_impl;
 340         let mut kind = AnnotationKind::Required;
 341         let mut const_stab_inherit = InheritConstStability::No;
 342         let mut fn_sig = None;
 343
 344         match i.kind {
 345             // Inherent impls and foreign modules serve only as containers for other items,
 346             // they don't have their own stability. They still can be annotated as unstable
 347             // and propagate this instability to children, but this annotation is completely
 348             // optional. They inherit stability from their parents when unannotated.
 349             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 350             | hir::ItemKind::ForeignMod { .. } => {
 351                 self.in_trait_impl = false;
 352                 kind = AnnotationKind::Container;
 353             }
 354             hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => {
 355                 self.in_trait_impl = true;
 356                 kind = AnnotationKind::DeprecationProhibited;
 357                 const_stab_inherit = InheritConstStability::Yes;
 358             }
 359             hir::ItemKind::Struct(ref sd, _) => {
 360                 if let Some(ctor_hir_id) = sd.ctor_hir_id() {
 361                     self.annotate(
 362                         self.tcx.hir().local_def_id(ctor_hir_id),
 363                         i.span,
 364                         None,
 365                         AnnotationKind::Required,
 366                         InheritDeprecation::Yes,
 367                         InheritConstStability::No,
 368                         InheritStability::Yes,
 369                         |_| {},
 370                     )
 371                 }
 372             }
 373             hir::ItemKind::Fn(ref item_fn_sig, _, _) => {
 374                 fn_sig = Some(item_fn_sig);
 375             }
 376             _ => {}
 377         }
 378
 379         self.annotate(
 380             i.def_id,
 381             i.span,
 382             fn_sig,
 383             kind,
 384             InheritDeprecation::Yes,
 385             const_stab_inherit,
 386             InheritStability::No,
 387             |v| intravisit::walk_item(v, i),
 388         );
 389         self.in_trait_impl = orig_in_trait_impl;
 390     }
 391
 392     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 393         let fn_sig = match ti.kind {
 394             hir::TraitItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 395             _ => None,
 396         };
 397
 398         self.annotate(
 399             ti.def_id,
 400             ti.span,
 401             fn_sig,
 402             AnnotationKind::Required,
 403             InheritDeprecation::Yes,
 404             InheritConstStability::No,
 405             InheritStability::No,
 406             |v| {
 407                 intravisit::walk_trait_item(v, ti);
 408             },
 409         );
 410     }
 411
 412     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 413         let kind =
 414             if self.in_trait_impl { AnnotationKind::Prohibited } else { AnnotationKind::Required };
 415
 416         let fn_sig = match ii.kind {
 417             hir::ImplItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 418             _ => None,
 419         };
 420
 421         self.annotate(
 422             ii.def_id,
 423             ii.span,
 424             fn_sig,
 425             kind,
 426             InheritDeprecation::Yes,
 427             InheritConstStability::No,
 428             InheritStability::No,
 429             |v| {
 430                 intravisit::walk_impl_item(v, ii);
 431             },
 432         );
 433     }
 434
 435     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 436         self.annotate(
 437             self.tcx.hir().local_def_id(var.id),
 438             var.span,
 439             None,
 440             AnnotationKind::Required,
 441             InheritDeprecation::Yes,
 442             InheritConstStability::No,
 443             InheritStability::Yes,
 444             |v| {
 445                 if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
 446                     v.annotate(
 447                         v.tcx.hir().local_def_id(ctor_hir_id),
 448                         var.span,
 449                         None,
 450                         AnnotationKind::Required,
 451                         InheritDeprecation::Yes,
 452                         InheritConstStability::No,
 453                         InheritStability::No,
 454                         |_| {},
 455                     );
 456                 }
 457
 458                 intravisit::walk_variant(v, var, g, item_id)
 459             },
 460         )
 461     }
 462
 463     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 464         self.annotate(
 465             self.tcx.hir().local_def_id(s.hir_id),
 466             s.span,
 467             None,
 468             AnnotationKind::Required,
 469             InheritDeprecation::Yes,
 470             InheritConstStability::No,
 471             InheritStability::Yes,
 472             |v| {
 473                 intravisit::walk_field_def(v, s);
 474             },
 475         );
 476     }
 477
 478     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 479         self.annotate(
 480             i.def_id,
 481             i.span,
 482             None,
 483             AnnotationKind::Required,
 484             InheritDeprecation::Yes,
 485             InheritConstStability::No,
 486             InheritStability::No,
 487             |v| {
 488                 intravisit::walk_foreign_item(v, i);
 489             },
 490         );
 491     }
 492
 493     fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
 494         let kind = match &p.kind {
 495             // Allow stability attributes on default generic arguments.
 496             hir::GenericParamKind::Type { default: Some(_), .. }
 497             | hir::GenericParamKind::Const { default: Some(_), .. } => AnnotationKind::Container,
 498             _ => AnnotationKind::Prohibited,
 499         };
 500
 501         self.annotate(
 502             self.tcx.hir().local_def_id(p.hir_id),
 503             p.span,
 504             None,
 505             kind,
 506             InheritDeprecation::No,
 507             InheritConstStability::No,
 508             InheritStability::No,
 509             |v| {
 510                 intravisit::walk_generic_param(v, p);
 511             },
 512         );
 513     }
 514 }
 515
 516 struct MissingStabilityAnnotations<'tcx> {
 517     tcx: TyCtxt<'tcx>,
 518     access_levels: &'tcx AccessLevels,
 519 }
 520
 521 impl<'tcx> MissingStabilityAnnotations<'tcx> {
 522     fn check_missing_stability(&self, def_id: LocalDefId, span: Span) {
 523         let stab = self.tcx.stability().local_stability(def_id);
 524         if !self.tcx.sess.opts.test && stab.is_none() && self.access_levels.is_reachable(def_id) {
 525             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 526             self.tcx.sess.span_err(span, &format!("{} has missing stability attribute", descr));
 527         }
 528     }
 529
 530     fn check_missing_const_stability(&self, def_id: LocalDefId, span: Span) {
 531         if !self.tcx.features().staged_api {
 532             return;
 533         }
 534
 535         let is_const = self.tcx.is_const_fn(def_id.to_def_id());
 536         let is_stable = self
 537             .tcx
 538             .lookup_stability(def_id)
 539             .map_or(false, |stability| stability.level.is_stable());
 540         let missing_const_stability_attribute = self.tcx.lookup_const_stability(def_id).is_none();
 541         let is_reachable = self.access_levels.is_reachable(def_id);
 542
 543         if is_const && is_stable && missing_const_stability_attribute && is_reachable {
 544             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 545             self.tcx.sess.span_err(span, &format!("{descr} has missing const stability attribute"));
 546         }
 547     }
 548 }
 549
 550 impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
 551     type NestedFilter = nested_filter::OnlyBodies;
 552
 553     fn nested_visit_map(&mut self) -> Self::Map {
 554         self.tcx.hir()
 555     }
 556
 557     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 558         // Inherent impls and foreign modules serve only as containers for other items,
 559         // they don't have their own stability. They still can be annotated as unstable
 560         // and propagate this instability to children, but this annotation is completely
 561         // optional. They inherit stability from their parents when unannotated.
 562         if !matches!(
 563             i.kind,
 564             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 565                 | hir::ItemKind::ForeignMod { .. }
 566         ) {
 567             self.check_missing_stability(i.def_id, i.span);
 568         }
 569
 570         // Ensure stable `const fn` have a const stability attribute.
 571         self.check_missing_const_stability(i.def_id, i.span);
 572
 573         intravisit::walk_item(self, i)
 574     }
 575
 576     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 577         self.check_missing_stability(ti.def_id, ti.span);
 578         intravisit::walk_trait_item(self, ti);
 579     }
 580
 581     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 582         let impl_def_id = self.tcx.hir().get_parent_item(ii.hir_id());
 583         if self.tcx.impl_trait_ref(impl_def_id).is_none() {
 584             self.check_missing_stability(ii.def_id, ii.span);
 585             self.check_missing_const_stability(ii.def_id, ii.span);
 586         }
 587         intravisit::walk_impl_item(self, ii);
 588     }
 589
 590     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 591         self.check_missing_stability(self.tcx.hir().local_def_id(var.id), var.span);
 592         intravisit::walk_variant(self, var, g, item_id);
 593     }
 594
 595     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 596         self.check_missing_stability(self.tcx.hir().local_def_id(s.hir_id), s.span);
 597         intravisit::walk_field_def(self, s);
 598     }
 599
 600     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 601         self.check_missing_stability(i.def_id, i.span);
 602         intravisit::walk_foreign_item(self, i);
 603     }
 604     // Note that we don't need to `check_missing_stability` for default generic parameters,
 605     // as we assume that any default generic parameters without attributes are automatically
 606     // stable (assuming they have not inherited instability from their parent).
 607 }
 608
 609 fn stability_index(tcx: TyCtxt<'_>, (): ()) -> Index {
 610     let mut index = Index {
 611         stab_map: Default::default(),
 612         const_stab_map: Default::default(),
 613         depr_map: Default::default(),
 614     };
 615
 616     {
 617         let mut annotator = Annotator {
 618             tcx,
 619             index: &mut index,
 620             parent_stab: None,
 621             parent_const_stab: None,
 622             parent_depr: None,
 623             in_trait_impl: false,
 624         };
 625
 626         // If the `-Z force-unstable-if-unmarked` flag is passed then we provide
 627         // a parent stability annotation which indicates that this is private
 628         // with the `rustc_private` feature. This is intended for use when
 629         // compiling `librustc_*` crates themselves so we can leverage crates.io
 630         // while maintaining the invariant that all sysroot crates are unstable
 631         // by default and are unable to be used.
 632         if tcx.sess.opts.debugging_opts.force_unstable_if_unmarked {
 633             let reason = "this crate is being loaded from the sysroot, an \
 634                           unstable location; did you mean to load this crate \
 635                           from crates.io via `Cargo.toml` instead?";
 636             let stability = Stability {
 637                 level: attr::StabilityLevel::Unstable {
 638                     reason: Some(Symbol::intern(reason)),
 639                     issue: NonZeroU32::new(27812),
 640                     is_soft: false,
 641                 },
 642                 feature: sym::rustc_private,
 643             };
 644             annotator.parent_stab = Some(stability);
 645         }
 646
 647         annotator.annotate(
 648             CRATE_DEF_ID,
 649             tcx.hir().span(CRATE_HIR_ID),
 650             None,
 651             AnnotationKind::Required,
 652             InheritDeprecation::Yes,
 653             InheritConstStability::No,
 654             InheritStability::No,
 655             |v| tcx.hir().walk_toplevel_module(v),
 656         );
 657     }
 658     index
 659 }
 660
 661 /// Cross-references the feature names of unstable APIs with enabled
 662 /// features and possibly prints errors.
 663 fn check_mod_unstable_api_usage(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 664     tcx.hir().visit_item_likes_in_module(module_def_id, &mut Checker { tcx }.as_deep_visitor());
 665 }
 666
 667 pub(crate) fn provide(providers: &mut Providers) {
 668     *providers = Providers {
 669         check_mod_unstable_api_usage,
 670         stability_index,
 671         lookup_stability: |tcx, id| tcx.stability().local_stability(id.expect_local()),
 672         lookup_const_stability: |tcx, id| tcx.stability().local_const_stability(id.expect_local()),
 673         lookup_deprecation_entry: |tcx, id| {
 674             tcx.stability().local_deprecation_entry(id.expect_local())
 675         },
 676         ..*providers
 677     };
 678 }
 679
 680 struct Checker<'tcx> {
 681     tcx: TyCtxt<'tcx>,
 682 }
 683
 684 impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
 685     type NestedFilter = nested_filter::OnlyBodies;
 686
 687     /// Because stability levels are scoped lexically, we want to walk
 688     /// nested items in the context of the outer item, so enable
 689     /// deep-walking.
 690     fn nested_visit_map(&mut self) -> Self::Map {
 691         self.tcx.hir()
 692     }
 693
 694     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 695         match item.kind {
 696             hir::ItemKind::ExternCrate(_) => {
 697                 // compiler-generated `extern crate` items have a dummy span.
 698                 // `std` is still checked for the `restricted-std` feature.
 699                 if item.span.is_dummy() && item.ident.name != sym::std {
 700                     return;
 701                 }
 702
 703                 let Some(cnum) = self.tcx.extern_mod_stmt_cnum(item.def_id) else {
 704                     return;
 705                 };
 706                 let def_id = cnum.as_def_id();
 707                 self.tcx.check_stability(def_id, Some(item.hir_id()), item.span, None);
 708             }
 709
 710             // For implementations of traits, check the stability of each item
 711             // individually as it's possible to have a stable trait with unstable
 712             // items.
 713             hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref t), self_ty, items, .. }) => {
 714                 if self.tcx.features().staged_api {
 715                     // If this impl block has an #[unstable] attribute, give an
 716                     // error if all involved types and traits are stable, because
 717                     // it will have no effect.
 718                     // See: https://github.com/rust-lang/rust/issues/55436
 719                     let attrs = self.tcx.hir().attrs(item.hir_id());
 720                     if let (Some((Stability { level: attr::Unstable { .. }, .. }, span)), _) =
 721                         attr::find_stability(&self.tcx.sess, attrs, item.span)
 722                     {
 723                         let mut c = CheckTraitImplStable { tcx: self.tcx, fully_stable: true };
 724                         c.visit_ty(self_ty);
 725                         c.visit_trait_ref(t);
 726                         if c.fully_stable {
 727                             self.tcx.struct_span_lint_hir(
 728                                 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
 729                                 item.hir_id(),
 730                                 span,
 731                                 |lint| {lint
 732                                     .build("an `#[unstable]` annotation here has no effect")
 733                                     .note("see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information")
 734                                     .emit();}
 735                             );
 736                         }
 737                     }
 738                 }
 739
 740                 for impl_item_ref in *items {
 741                     let impl_item = self.tcx.associated_item(impl_item_ref.id.def_id);
 742
 743                     if let Some(def_id) = impl_item.trait_item_def_id {
 744                         // Pass `None` to skip deprecation warnings.
 745                         self.tcx.check_stability(def_id, None, impl_item_ref.span, None);
 746                     }
 747                 }
 748             }
 749
 750             // There's no good place to insert stability check for non-Copy unions,
 751             // so semi-randomly perform it here in stability.rs
 752             hir::ItemKind::Union(..) if !self.tcx.features().untagged_unions => {
 753                 let ty = self.tcx.type_of(item.def_id);
 754                 let ty::Adt(adt_def, substs) = ty.kind() else { bug!() };
 755
 756                 // Non-`Copy` fields are unstable, except for `ManuallyDrop`.
 757                 let param_env = self.tcx.param_env(item.def_id);
 758                 for field in &adt_def.non_enum_variant().fields {
 759                     let field_ty = field.ty(self.tcx, substs);
 760                     if !field_ty.ty_adt_def().map_or(false, |adt_def| adt_def.is_manually_drop())
 761                         && !field_ty.is_copy_modulo_regions(self.tcx.at(DUMMY_SP), param_env)
 762                     {
 763                         if field_ty.needs_drop(self.tcx, param_env) {
 764                             // Avoid duplicate error: This will error later anyway because fields
 765                             // that need drop are not allowed.
 766                             self.tcx.sess.delay_span_bug(
 767                                 item.span,
 768                                 "union should have been rejected due to potentially dropping field",
 769                             );
 770                         } else {
 771                             feature_err(
 772                                 &self.tcx.sess.parse_sess,
 773                                 sym::untagged_unions,
 774                                 self.tcx.def_span(field.did),
 775                                 "unions with non-`Copy` fields other than `ManuallyDrop<T>` are unstable",
 776                             )
 777                             .emit();
 778                         }
 779                     }
 780                 }
 781             }
 782
 783             _ => (/* pass */),
 784         }
 785         intravisit::walk_item(self, item);
 786     }
 787
 788     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, id: hir::HirId) {
 789         if let Some(def_id) = path.res.opt_def_id() {
 790             let method_span = path.segments.last().map(|s| s.ident.span);
 791             self.tcx.check_stability(def_id, Some(id), path.span, method_span)
 792         }
 793         intravisit::walk_path(self, path)
 794     }
 795 }
 796
 797 struct CheckTraitImplStable<'tcx> {
 798     tcx: TyCtxt<'tcx>,
 799     fully_stable: bool,
 800 }
 801
 802 impl<'tcx> Visitor<'tcx> for CheckTraitImplStable<'tcx> {
 803     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _id: hir::HirId) {
 804         if let Some(def_id) = path.res.opt_def_id() {
 805             if let Some(stab) = self.tcx.lookup_stability(def_id) {
 806                 self.fully_stable &= stab.level.is_stable();
 807             }
 808         }
 809         intravisit::walk_path(self, path)
 810     }
 811
 812     fn visit_trait_ref(&mut self, t: &'tcx TraitRef<'tcx>) {
 813         if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
 814             if let Some(stab) = self.tcx.lookup_stability(trait_did) {
 815                 self.fully_stable &= stab.level.is_stable();
 816             }
 817         }
 818         intravisit::walk_trait_ref(self, t)
 819     }
 820
 821     fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
 822         if let TyKind::Never = t.kind {
 823             self.fully_stable = false;
 824         }
 825         intravisit::walk_ty(self, t)
 826     }
 827 }
 828
 829 /// Given the list of enabled features that were not language features (i.e., that
 830 /// were expected to be library features), and the list of features used from
 831 /// libraries, identify activated features that don't exist and error about them.
 832 pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
 833     let is_staged_api =
 834         tcx.sess.opts.debugging_opts.force_unstable_if_unmarked || tcx.features().staged_api;
 835     if is_staged_api {
 836         let access_levels = &tcx.privacy_access_levels(());
 837         let mut missing = MissingStabilityAnnotations { tcx, access_levels };
 838         missing.check_missing_stability(CRATE_DEF_ID, tcx.hir().span(CRATE_HIR_ID));
 839         tcx.hir().walk_toplevel_module(&mut missing);
 840         tcx.hir().visit_all_item_likes(&mut missing.as_deep_visitor());
 841     }
 842
 843     let declared_lang_features = &tcx.features().declared_lang_features;
 844     let mut lang_features = FxHashSet::default();
 845     for &(feature, span, since) in declared_lang_features {
 846         if let Some(since) = since {
 847             // Warn if the user has enabled an already-stable lang feature.
 848             unnecessary_stable_feature_lint(tcx, span, feature, since);
 849         }
 850         if !lang_features.insert(feature) {
 851             // Warn if the user enables a lang feature multiple times.
 852             duplicate_feature_err(tcx.sess, span, feature);
 853         }
 854     }
 855
 856     let declared_lib_features = &tcx.features().declared_lib_features;
 857     let mut remaining_lib_features = FxIndexMap::default();
 858     for (feature, span) in declared_lib_features {
 859         if !tcx.sess.opts.unstable_features.is_nightly_build() {
 860             struct_span_err!(
 861                 tcx.sess,
 862                 *span,
 863                 E0554,
 864                 "`#![feature]` may not be used on the {} release channel",
 865                 env!("CFG_RELEASE_CHANNEL")
 866             )
 867             .emit();
 868         }
 869         if remaining_lib_features.contains_key(&feature) {
 870             // Warn if the user enables a lib feature multiple times.
 871             duplicate_feature_err(tcx.sess, *span, *feature);
 872         }
 873         remaining_lib_features.insert(feature, *span);
 874     }
 875     // `stdbuild` has special handling for `libc`, so we need to
 876     // recognise the feature when building std.
 877     // Likewise, libtest is handled specially, so `test` isn't
 878     // available as we'd like it to be.
 879     // FIXME: only remove `libc` when `stdbuild` is active.
 880     // FIXME: remove special casing for `test`.
 881     remaining_lib_features.remove(&sym::libc);
 882     remaining_lib_features.remove(&sym::test);
 883
 884     let check_features = |remaining_lib_features: &mut FxIndexMap<_, _>, defined_features: &[_]| {
 885         for &(feature, since) in defined_features {
 886             if let Some(since) = since {
 887                 if let Some(span) = remaining_lib_features.get(&feature) {
 888                     // Warn if the user has enabled an already-stable lib feature.
 889                     unnecessary_stable_feature_lint(tcx, *span, feature, since);
 890                 }
 891             }
 892             remaining_lib_features.remove(&feature);
 893             if remaining_lib_features.is_empty() {
 894                 break;
 895             }
 896         }
 897     };
 898
 899     // We always collect the lib features declared in the current crate, even if there are
 900     // no unknown features, because the collection also does feature attribute validation.
 901     let local_defined_features = tcx.lib_features(()).to_vec();
 902     if !remaining_lib_features.is_empty() {
 903         check_features(&mut remaining_lib_features, &local_defined_features);
 904
 905         for &cnum in tcx.crates(()) {
 906             if remaining_lib_features.is_empty() {
 907                 break;
 908             }
 909             check_features(&mut remaining_lib_features, tcx.defined_lib_features(cnum));
 910         }
 911     }
 912
 913     for (feature, span) in remaining_lib_features {
 914         struct_span_err!(tcx.sess, span, E0635, "unknown feature `{}`", feature).emit();
 915     }
 916
 917     // FIXME(#44232): the `used_features` table no longer exists, so we
 918     // don't lint about unused features. We should re-enable this one day!
 919 }
 920
 921 fn unnecessary_stable_feature_lint(tcx: TyCtxt<'_>, span: Span, feature: Symbol, since: Symbol) {
 922     tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
 923         lint.build(&format!(
 924             "the feature `{}` has been stable since {} and no longer requires \
 925                       an attribute to enable",
 926             feature, since
 927         ))
 928         .emit();
 929     });
 930 }
 931
 932 fn duplicate_feature_err(sess: &Session, span: Span, feature: Symbol) {
 933     struct_span_err!(sess, span, E0636, "the feature `{}` has already been declared", feature)
 934         .emit();
 935 }
 936
 937 fn missing_const_err(session: &Session, fn_sig_span: Span, const_span: Span) {
 938     const ERROR_MSG: &'static str = "attributes `#[rustc_const_unstable]` \
 939          and `#[rustc_const_stable]` require \
 940          the function or method to be `const`";
 941
 942     session
 943         .struct_span_err(fn_sig_span, ERROR_MSG)
 944         .span_help(fn_sig_span, "make the function or method const")
 945         .span_label(const_span, "attribute specified here")
 946         .emit();
 947 }