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 attr::StabilityLevel;
   5 use rustc_attr::{self as attr, ConstStability, Stability, Unstable, UnstableReason};
   6 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
   7 use rustc_errors::{struct_span_err, Applicability};
   8 use rustc_hir as hir;
   9 use rustc_hir::def::{DefKind, Res};
  10 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
  11 use rustc_hir::hir_id::CRATE_HIR_ID;
  12 use rustc_hir::intravisit::{self, Visitor};
  13 use rustc_hir::{FieldDef, Generics, HirId, Item, ItemKind, TraitRef, Ty, TyKind, Variant};
  14 use rustc_middle::hir::nested_filter;
  15 use rustc_middle::middle::privacy::AccessLevels;
  16 use rustc_middle::middle::stability::{AllowUnstable, DeprecationEntry, Index};
  17 use rustc_middle::ty::{query::Providers, TyCtxt};
  18 use rustc_session::lint;
  19 use rustc_session::lint::builtin::{INEFFECTIVE_UNSTABLE_TRAIT_IMPL, USELESS_DEPRECATED};
  20 use rustc_session::Session;
  21 use rustc_span::symbol::{sym, Symbol};
  22 use rustc_span::Span;
  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 stability. The
  98     /// stability is recorded in the index and used as the parent. If the node is a function,
  99     /// `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                             "",
 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.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.is_const_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             if let Stability { level: Unstable { implied_by: Some(implied_by), .. }, feature } = stab {
 269                 self.index.implications.insert(implied_by, feature);
 270             }
 271
 272             self.index.stab_map.insert(def_id, stab);
 273             stab
 274         });
 275
 276         if stab.is_none() {
 277             debug!("annotate: stab not found, parent = {:?}", self.parent_stab);
 278             if let Some(stab) = self.parent_stab {
 279                 if inherit_deprecation.yes() && stab.is_unstable() || inherit_from_parent.yes() {
 280                     self.index.stab_map.insert(def_id, stab);
 281                 }
 282             }
 283         }
 284
 285         self.recurse_with_stability_attrs(
 286             depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 287             stab,
 288             if inherit_const_stability.yes() { const_stab } else { None },
 289             visit_children,
 290         );
 291     }
 292
 293     fn recurse_with_stability_attrs(
 294         &mut self,
 295         depr: Option<DeprecationEntry>,
 296         stab: Option<Stability>,
 297         const_stab: Option<ConstStability>,
 298         f: impl FnOnce(&mut Self),
 299     ) {
 300         // These will be `Some` if this item changes the corresponding stability attribute.
 301         let mut replaced_parent_depr = None;
 302         let mut replaced_parent_stab = None;
 303         let mut replaced_parent_const_stab = None;
 304
 305         if let Some(depr) = depr {
 306             replaced_parent_depr = Some(replace(&mut self.parent_depr, Some(depr)));
 307         }
 308         if let Some(stab) = stab {
 309             replaced_parent_stab = Some(replace(&mut self.parent_stab, Some(stab)));
 310         }
 311         if let Some(const_stab) = const_stab {
 312             replaced_parent_const_stab =
 313                 Some(replace(&mut self.parent_const_stab, Some(const_stab)));
 314         }
 315
 316         f(self);
 317
 318         if let Some(orig_parent_depr) = replaced_parent_depr {
 319             self.parent_depr = orig_parent_depr;
 320         }
 321         if let Some(orig_parent_stab) = replaced_parent_stab {
 322             self.parent_stab = orig_parent_stab;
 323         }
 324         if let Some(orig_parent_const_stab) = replaced_parent_const_stab {
 325             self.parent_const_stab = orig_parent_const_stab;
 326         }
 327     }
 328 }
 329
 330 impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
 331     /// Because stability levels are scoped lexically, we want to walk
 332     /// nested items in the context of the outer item, so enable
 333     /// deep-walking.
 334     type NestedFilter = nested_filter::All;
 335
 336     fn nested_visit_map(&mut self) -> Self::Map {
 337         self.tcx.hir()
 338     }
 339
 340     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 341         let orig_in_trait_impl = self.in_trait_impl;
 342         let mut kind = AnnotationKind::Required;
 343         let mut const_stab_inherit = InheritConstStability::No;
 344         let mut fn_sig = None;
 345
 346         match i.kind {
 347             // Inherent impls and foreign modules serve only as containers for other items,
 348             // they don't have their own stability. They still can be annotated as unstable
 349             // and propagate this instability to children, but this annotation is completely
 350             // optional. They inherit stability from their parents when unannotated.
 351             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 352             | hir::ItemKind::ForeignMod { .. } => {
 353                 self.in_trait_impl = false;
 354                 kind = AnnotationKind::Container;
 355             }
 356             hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => {
 357                 self.in_trait_impl = true;
 358                 kind = AnnotationKind::DeprecationProhibited;
 359                 const_stab_inherit = InheritConstStability::Yes;
 360             }
 361             hir::ItemKind::Struct(ref sd, _) => {
 362                 if let Some(ctor_hir_id) = sd.ctor_hir_id() {
 363                     self.annotate(
 364                         self.tcx.hir().local_def_id(ctor_hir_id),
 365                         i.span,
 366                         None,
 367                         AnnotationKind::Required,
 368                         InheritDeprecation::Yes,
 369                         InheritConstStability::No,
 370                         InheritStability::Yes,
 371                         |_| {},
 372                     )
 373                 }
 374             }
 375             hir::ItemKind::Fn(ref item_fn_sig, _, _) => {
 376                 fn_sig = Some(item_fn_sig);
 377             }
 378             _ => {}
 379         }
 380
 381         self.annotate(
 382             i.def_id,
 383             i.span,
 384             fn_sig,
 385             kind,
 386             InheritDeprecation::Yes,
 387             const_stab_inherit,
 388             InheritStability::No,
 389             |v| intravisit::walk_item(v, i),
 390         );
 391         self.in_trait_impl = orig_in_trait_impl;
 392     }
 393
 394     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 395         let fn_sig = match ti.kind {
 396             hir::TraitItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 397             _ => None,
 398         };
 399
 400         self.annotate(
 401             ti.def_id,
 402             ti.span,
 403             fn_sig,
 404             AnnotationKind::Required,
 405             InheritDeprecation::Yes,
 406             InheritConstStability::No,
 407             InheritStability::No,
 408             |v| {
 409                 intravisit::walk_trait_item(v, ti);
 410             },
 411         );
 412     }
 413
 414     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 415         let kind =
 416             if self.in_trait_impl { AnnotationKind::Prohibited } else { AnnotationKind::Required };
 417
 418         let fn_sig = match ii.kind {
 419             hir::ImplItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 420             _ => None,
 421         };
 422
 423         self.annotate(
 424             ii.def_id,
 425             ii.span,
 426             fn_sig,
 427             kind,
 428             InheritDeprecation::Yes,
 429             InheritConstStability::No,
 430             InheritStability::No,
 431             |v| {
 432                 intravisit::walk_impl_item(v, ii);
 433             },
 434         );
 435     }
 436
 437     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 438         self.annotate(
 439             self.tcx.hir().local_def_id(var.id),
 440             var.span,
 441             None,
 442             AnnotationKind::Required,
 443             InheritDeprecation::Yes,
 444             InheritConstStability::No,
 445             InheritStability::Yes,
 446             |v| {
 447                 if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
 448                     v.annotate(
 449                         v.tcx.hir().local_def_id(ctor_hir_id),
 450                         var.span,
 451                         None,
 452                         AnnotationKind::Required,
 453                         InheritDeprecation::Yes,
 454                         InheritConstStability::No,
 455                         InheritStability::No,
 456                         |_| {},
 457                     );
 458                 }
 459
 460                 intravisit::walk_variant(v, var, g, item_id)
 461             },
 462         )
 463     }
 464
 465     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 466         self.annotate(
 467             self.tcx.hir().local_def_id(s.hir_id),
 468             s.span,
 469             None,
 470             AnnotationKind::Required,
 471             InheritDeprecation::Yes,
 472             InheritConstStability::No,
 473             InheritStability::Yes,
 474             |v| {
 475                 intravisit::walk_field_def(v, s);
 476             },
 477         );
 478     }
 479
 480     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 481         self.annotate(
 482             i.def_id,
 483             i.span,
 484             None,
 485             AnnotationKind::Required,
 486             InheritDeprecation::Yes,
 487             InheritConstStability::No,
 488             InheritStability::No,
 489             |v| {
 490                 intravisit::walk_foreign_item(v, i);
 491             },
 492         );
 493     }
 494
 495     fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
 496         let kind = match &p.kind {
 497             // Allow stability attributes on default generic arguments.
 498             hir::GenericParamKind::Type { default: Some(_), .. }
 499             | hir::GenericParamKind::Const { default: Some(_), .. } => AnnotationKind::Container,
 500             _ => AnnotationKind::Prohibited,
 501         };
 502
 503         self.annotate(
 504             self.tcx.hir().local_def_id(p.hir_id),
 505             p.span,
 506             None,
 507             kind,
 508             InheritDeprecation::No,
 509             InheritConstStability::No,
 510             InheritStability::No,
 511             |v| {
 512                 intravisit::walk_generic_param(v, p);
 513             },
 514         );
 515     }
 516 }
 517
 518 struct MissingStabilityAnnotations<'tcx> {
 519     tcx: TyCtxt<'tcx>,
 520     access_levels: &'tcx AccessLevels,
 521 }
 522
 523 impl<'tcx> MissingStabilityAnnotations<'tcx> {
 524     fn check_missing_stability(&self, def_id: LocalDefId, span: Span) {
 525         let stab = self.tcx.stability().local_stability(def_id);
 526         if !self.tcx.sess.opts.test && stab.is_none() && self.access_levels.is_reachable(def_id) {
 527             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 528             self.tcx.sess.span_err(span, &format!("{} has missing stability attribute", descr));
 529         }
 530     }
 531
 532     fn check_missing_const_stability(&self, def_id: LocalDefId, span: Span) {
 533         if !self.tcx.features().staged_api {
 534             return;
 535         }
 536
 537         let is_const = self.tcx.is_const_fn(def_id.to_def_id())
 538             || self.tcx.is_const_trait_impl_raw(def_id.to_def_id());
 539         let is_stable = self
 540             .tcx
 541             .lookup_stability(def_id)
 542             .map_or(false, |stability| stability.level.is_stable());
 543         let missing_const_stability_attribute = self.tcx.lookup_const_stability(def_id).is_none();
 544         let is_reachable = self.access_levels.is_reachable(def_id);
 545
 546         if is_const && is_stable && missing_const_stability_attribute && is_reachable {
 547             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 548             self.tcx.sess.span_err(span, &format!("{descr} has missing const stability attribute"));
 549         }
 550     }
 551 }
 552
 553 impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
 554     type NestedFilter = nested_filter::OnlyBodies;
 555
 556     fn nested_visit_map(&mut self) -> Self::Map {
 557         self.tcx.hir()
 558     }
 559
 560     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 561         // Inherent impls and foreign modules serve only as containers for other items,
 562         // they don't have their own stability. They still can be annotated as unstable
 563         // and propagate this instability to children, but this annotation is completely
 564         // optional. They inherit stability from their parents when unannotated.
 565         if !matches!(
 566             i.kind,
 567             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 568                 | hir::ItemKind::ForeignMod { .. }
 569         ) {
 570             self.check_missing_stability(i.def_id, i.span);
 571         }
 572
 573         // Ensure stable `const fn` have a const stability attribute.
 574         self.check_missing_const_stability(i.def_id, i.span);
 575
 576         intravisit::walk_item(self, i)
 577     }
 578
 579     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 580         self.check_missing_stability(ti.def_id, ti.span);
 581         intravisit::walk_trait_item(self, ti);
 582     }
 583
 584     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 585         let impl_def_id = self.tcx.hir().get_parent_item(ii.hir_id());
 586         if self.tcx.impl_trait_ref(impl_def_id).is_none() {
 587             self.check_missing_stability(ii.def_id, ii.span);
 588             self.check_missing_const_stability(ii.def_id, ii.span);
 589         }
 590         intravisit::walk_impl_item(self, ii);
 591     }
 592
 593     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 594         self.check_missing_stability(self.tcx.hir().local_def_id(var.id), var.span);
 595         intravisit::walk_variant(self, var, g, item_id);
 596     }
 597
 598     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 599         self.check_missing_stability(self.tcx.hir().local_def_id(s.hir_id), s.span);
 600         intravisit::walk_field_def(self, s);
 601     }
 602
 603     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 604         self.check_missing_stability(i.def_id, i.span);
 605         intravisit::walk_foreign_item(self, i);
 606     }
 607     // Note that we don't need to `check_missing_stability` for default generic parameters,
 608     // as we assume that any default generic parameters without attributes are automatically
 609     // stable (assuming they have not inherited instability from their parent).
 610 }
 611
 612 fn stability_index(tcx: TyCtxt<'_>, (): ()) -> Index {
 613     let mut index = Index {
 614         stab_map: Default::default(),
 615         const_stab_map: Default::default(),
 616         depr_map: Default::default(),
 617         implications: Default::default(),
 618     };
 619
 620     {
 621         let mut annotator = Annotator {
 622             tcx,
 623             index: &mut index,
 624             parent_stab: None,
 625             parent_const_stab: None,
 626             parent_depr: None,
 627             in_trait_impl: false,
 628         };
 629
 630         // If the `-Z force-unstable-if-unmarked` flag is passed then we provide
 631         // a parent stability annotation which indicates that this is private
 632         // with the `rustc_private` feature. This is intended for use when
 633         // compiling `librustc_*` crates themselves so we can leverage crates.io
 634         // while maintaining the invariant that all sysroot crates are unstable
 635         // by default and are unable to be used.
 636         if tcx.sess.opts.unstable_opts.force_unstable_if_unmarked {
 637             let stability = Stability {
 638                 level: attr::StabilityLevel::Unstable {
 639                     reason: UnstableReason::Default,
 640                     issue: NonZeroU32::new(27812),
 641                     is_soft: false,
 642                     implied_by: None,
 643                 },
 644                 feature: sym::rustc_private,
 645             };
 646             annotator.parent_stab = Some(stability);
 647         }
 648
 649         annotator.annotate(
 650             CRATE_DEF_ID,
 651             tcx.hir().span(CRATE_HIR_ID),
 652             None,
 653             AnnotationKind::Required,
 654             InheritDeprecation::Yes,
 655             InheritConstStability::No,
 656             InheritStability::No,
 657             |v| tcx.hir().walk_toplevel_module(v),
 658         );
 659     }
 660     index
 661 }
 662
 663 /// Cross-references the feature names of unstable APIs with enabled
 664 /// features and possibly prints errors.
 665 fn check_mod_unstable_api_usage(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 666     tcx.hir().visit_item_likes_in_module(module_def_id, &mut Checker { tcx });
 667 }
 668
 669 pub(crate) fn provide(providers: &mut Providers) {
 670     *providers = Providers {
 671         check_mod_unstable_api_usage,
 672         stability_index,
 673         stability_implications: |tcx, _| tcx.stability().implications.clone(),
 674         lookup_stability: |tcx, id| tcx.stability().local_stability(id.expect_local()),
 675         lookup_const_stability: |tcx, id| tcx.stability().local_const_stability(id.expect_local()),
 676         lookup_deprecation_entry: |tcx, id| {
 677             tcx.stability().local_deprecation_entry(id.expect_local())
 678         },
 679         ..*providers
 680     };
 681 }
 682
 683 struct Checker<'tcx> {
 684     tcx: TyCtxt<'tcx>,
 685 }
 686
 687 impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
 688     type NestedFilter = nested_filter::OnlyBodies;
 689
 690     /// Because stability levels are scoped lexically, we want to walk
 691     /// nested items in the context of the outer item, so enable
 692     /// deep-walking.
 693     fn nested_visit_map(&mut self) -> Self::Map {
 694         self.tcx.hir()
 695     }
 696
 697     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 698         match item.kind {
 699             hir::ItemKind::ExternCrate(_) => {
 700                 // compiler-generated `extern crate` items have a dummy span.
 701                 // `std` is still checked for the `restricted-std` feature.
 702                 if item.span.is_dummy() && item.ident.name != sym::std {
 703                     return;
 704                 }
 705
 706                 let Some(cnum) = self.tcx.extern_mod_stmt_cnum(item.def_id) else {
 707                     return;
 708                 };
 709                 let def_id = cnum.as_def_id();
 710                 self.tcx.check_stability(def_id, Some(item.hir_id()), item.span, None);
 711             }
 712
 713             // For implementations of traits, check the stability of each item
 714             // individually as it's possible to have a stable trait with unstable
 715             // items.
 716             hir::ItemKind::Impl(hir::Impl {
 717                 of_trait: Some(ref t),
 718                 self_ty,
 719                 items,
 720                 constness,
 721                 ..
 722             }) => {
 723                 let features = self.tcx.features();
 724                 if features.staged_api {
 725                     let attrs = self.tcx.hir().attrs(item.hir_id());
 726                     let (stab, const_stab) = attr::find_stability(&self.tcx.sess, attrs, item.span);
 727
 728                     // If this impl block has an #[unstable] attribute, give an
 729                     // error if all involved types and traits are stable, because
 730                     // it will have no effect.
 731                     // See: https://github.com/rust-lang/rust/issues/55436
 732                     if let Some((Stability { level: attr::Unstable { .. }, .. }, span)) = stab {
 733                         let mut c = CheckTraitImplStable { tcx: self.tcx, fully_stable: true };
 734                         c.visit_ty(self_ty);
 735                         c.visit_trait_ref(t);
 736                         if c.fully_stable {
 737                             self.tcx.struct_span_lint_hir(
 738                                 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
 739                                 item.hir_id(),
 740                                 span,
 741                                 |lint| {lint
 742                                     .build("an `#[unstable]` annotation here has no effect")
 743                                     .note("see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information")
 744                                     .emit();}
 745                             );
 746                         }
 747                     }
 748
 749                     // `#![feature(const_trait_impl)]` is unstable, so any impl declared stable
 750                     // needs to have an error emitted.
 751                     if features.const_trait_impl
 752                         && *constness == hir::Constness::Const
 753                         && const_stab.map_or(false, |(stab, _)| stab.is_const_stable())
 754                     {
 755                         self.tcx
 756                             .sess
 757                             .struct_span_err(item.span, "trait implementations cannot be const stable yet")
 758                             .note("see issue #67792 <https://github.com/rust-lang/rust/issues/67792> for more information")
 759                             .emit();
 760                     }
 761                 }
 762
 763                 for impl_item_ref in *items {
 764                     let impl_item = self.tcx.associated_item(impl_item_ref.id.def_id);
 765
 766                     if let Some(def_id) = impl_item.trait_item_def_id {
 767                         // Pass `None` to skip deprecation warnings.
 768                         self.tcx.check_stability(def_id, None, impl_item_ref.span, None);
 769                     }
 770                 }
 771             }
 772
 773             _ => (/* pass */),
 774         }
 775         intravisit::walk_item(self, item);
 776     }
 777
 778     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, id: hir::HirId) {
 779         if let Some(def_id) = path.res.opt_def_id() {
 780             let method_span = path.segments.last().map(|s| s.ident.span);
 781             let item_is_allowed = self.tcx.check_stability_allow_unstable(
 782                 def_id,
 783                 Some(id),
 784                 path.span,
 785                 method_span,
 786                 if is_unstable_reexport(self.tcx, id) {
 787                     AllowUnstable::Yes
 788                 } else {
 789                     AllowUnstable::No
 790                 },
 791             );
 792
 793             let is_allowed_through_unstable_modules = |def_id| {
 794                 self.tcx
 795                     .lookup_stability(def_id)
 796                     .map(|stab| match stab.level {
 797                         StabilityLevel::Stable { allowed_through_unstable_modules, .. } => {
 798                             allowed_through_unstable_modules
 799                         }
 800                         _ => false,
 801                     })
 802                     .unwrap_or(false)
 803             };
 804
 805             if item_is_allowed && !is_allowed_through_unstable_modules(def_id) {
 806                 // Check parent modules stability as well if the item the path refers to is itself
 807                 // stable. We only emit warnings for unstable path segments if the item is stable
 808                 // or allowed because stability is often inherited, so the most common case is that
 809                 // both the segments and the item are unstable behind the same feature flag.
 810                 //
 811                 // We check here rather than in `visit_path_segment` to prevent visiting the last
 812                 // path segment twice
 813                 //
 814                 // We include special cases via #[rustc_allowed_through_unstable_modules] for items
 815                 // that were accidentally stabilized through unstable paths before this check was
 816                 // added, such as `core::intrinsics::transmute`
 817                 let parents = path.segments.iter().rev().skip(1);
 818                 for path_segment in parents {
 819                     if let Some(def_id) = path_segment.res.as_ref().and_then(Res::opt_def_id) {
 820                         // use `None` for id to prevent deprecation check
 821                         self.tcx.check_stability_allow_unstable(
 822                             def_id,
 823                             None,
 824                             path.span,
 825                             None,
 826                             if is_unstable_reexport(self.tcx, id) {
 827                                 AllowUnstable::Yes
 828                             } else {
 829                                 AllowUnstable::No
 830                             },
 831                         );
 832                     }
 833                 }
 834             }
 835         }
 836
 837         intravisit::walk_path(self, path)
 838     }
 839 }
 840
 841 /// Check whether a path is a `use` item that has been marked as unstable.
 842 ///
 843 /// See issue #94972 for details on why this is a special case
 844 fn is_unstable_reexport<'tcx>(tcx: TyCtxt<'tcx>, id: hir::HirId) -> bool {
 845     // Get the LocalDefId so we can lookup the item to check the kind.
 846     let Some(def_id) = tcx.hir().opt_local_def_id(id) else { return false; };
 847
 848     let Some(stab) = tcx.stability().local_stability(def_id) else {
 849         return false;
 850     };
 851
 852     if stab.level.is_stable() {
 853         // The re-export is not marked as unstable, don't override
 854         return false;
 855     }
 856
 857     // If this is a path that isn't a use, we don't need to do anything special
 858     if !matches!(tcx.hir().item(hir::ItemId { def_id }).kind, ItemKind::Use(..)) {
 859         return false;
 860     }
 861
 862     true
 863 }
 864
 865 struct CheckTraitImplStable<'tcx> {
 866     tcx: TyCtxt<'tcx>,
 867     fully_stable: bool,
 868 }
 869
 870 impl<'tcx> Visitor<'tcx> for CheckTraitImplStable<'tcx> {
 871     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _id: hir::HirId) {
 872         if let Some(def_id) = path.res.opt_def_id() {
 873             if let Some(stab) = self.tcx.lookup_stability(def_id) {
 874                 self.fully_stable &= stab.level.is_stable();
 875             }
 876         }
 877         intravisit::walk_path(self, path)
 878     }
 879
 880     fn visit_trait_ref(&mut self, t: &'tcx TraitRef<'tcx>) {
 881         if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
 882             if let Some(stab) = self.tcx.lookup_stability(trait_did) {
 883                 self.fully_stable &= stab.level.is_stable();
 884             }
 885         }
 886         intravisit::walk_trait_ref(self, t)
 887     }
 888
 889     fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
 890         if let TyKind::Never = t.kind {
 891             self.fully_stable = false;
 892         }
 893         intravisit::walk_ty(self, t)
 894     }
 895 }
 896
 897 /// Given the list of enabled features that were not language features (i.e., that
 898 /// were expected to be library features), and the list of features used from
 899 /// libraries, identify activated features that don't exist and error about them.
 900 pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
 901     let is_staged_api =
 902         tcx.sess.opts.unstable_opts.force_unstable_if_unmarked || tcx.features().staged_api;
 903     if is_staged_api {
 904         let access_levels = &tcx.privacy_access_levels(());
 905         let mut missing = MissingStabilityAnnotations { tcx, access_levels };
 906         missing.check_missing_stability(CRATE_DEF_ID, tcx.hir().span(CRATE_HIR_ID));
 907         tcx.hir().walk_toplevel_module(&mut missing);
 908         tcx.hir().visit_all_item_likes_in_crate(&mut missing);
 909     }
 910
 911     let declared_lang_features = &tcx.features().declared_lang_features;
 912     let mut lang_features = FxHashSet::default();
 913     for &(feature, span, since) in declared_lang_features {
 914         if let Some(since) = since {
 915             // Warn if the user has enabled an already-stable lang feature.
 916             unnecessary_stable_feature_lint(tcx, span, feature, since);
 917         }
 918         if !lang_features.insert(feature) {
 919             // Warn if the user enables a lang feature multiple times.
 920             duplicate_feature_err(tcx.sess, span, feature);
 921         }
 922     }
 923
 924     let declared_lib_features = &tcx.features().declared_lib_features;
 925     let mut remaining_lib_features = FxIndexMap::default();
 926     for (feature, span) in declared_lib_features {
 927         if !tcx.sess.opts.unstable_features.is_nightly_build() {
 928             struct_span_err!(
 929                 tcx.sess,
 930                 *span,
 931                 E0554,
 932                 "`#![feature]` may not be used on the {} release channel",
 933                 env!("CFG_RELEASE_CHANNEL")
 934             )
 935             .emit();
 936         }
 937         if remaining_lib_features.contains_key(&feature) {
 938             // Warn if the user enables a lib feature multiple times.
 939             duplicate_feature_err(tcx.sess, *span, *feature);
 940         }
 941         remaining_lib_features.insert(feature, *span);
 942     }
 943     // `stdbuild` has special handling for `libc`, so we need to
 944     // recognise the feature when building std.
 945     // Likewise, libtest is handled specially, so `test` isn't
 946     // available as we'd like it to be.
 947     // FIXME: only remove `libc` when `stdbuild` is active.
 948     // FIXME: remove special casing for `test`.
 949     remaining_lib_features.remove(&sym::libc);
 950     remaining_lib_features.remove(&sym::test);
 951
 952     // We always collect the lib features declared in the current crate, even if there are
 953     // no unknown features, because the collection also does feature attribute validation.
 954     let local_defined_features = tcx.lib_features(());
 955     let mut all_lib_features: FxHashMap<_, _> =
 956         local_defined_features.to_vec().iter().map(|el| *el).collect();
 957     let mut implications = tcx.stability_implications(rustc_hir::def_id::LOCAL_CRATE).clone();
 958     for &cnum in tcx.crates(()) {
 959         implications.extend(tcx.stability_implications(cnum));
 960         all_lib_features.extend(tcx.defined_lib_features(cnum).iter().map(|el| *el));
 961     }
 962
 963     // Check that every feature referenced by an `implied_by` exists (for features defined in the
 964     // local crate).
 965     for (implied_by, feature) in tcx.stability_implications(rustc_hir::def_id::LOCAL_CRATE) {
 966         // Only `implied_by` needs to be checked, `feature` is guaranteed to exist.
 967         if !all_lib_features.contains_key(implied_by) {
 968             let span = local_defined_features
 969                 .stable
 970                 .get(feature)
 971                 .map(|(_, span)| span)
 972                 .or_else(|| local_defined_features.unstable.get(feature))
 973                 .expect("feature that implied another does not exist");
 974             tcx.sess
 975                 .struct_span_err(
 976                     *span,
 977                     format!("feature `{implied_by}` implying `{feature}` does not exist"),
 978                 )
 979                 .emit();
 980         }
 981     }
 982
 983     if !remaining_lib_features.is_empty() {
 984         for (feature, since) in all_lib_features.iter() {
 985             if let Some(since) = since && let Some(span) = remaining_lib_features.get(&feature) {
 986                 // Warn if the user has enabled an already-stable lib feature.
 987                 if let Some(implies) = implications.get(&feature) {
 988                     unnecessary_partially_stable_feature_lint(tcx, *span, *feature, *implies, *since);
 989                 } else {
 990                     unnecessary_stable_feature_lint(tcx, *span, *feature, *since);
 991                 }
 992             }
 993             remaining_lib_features.remove(&feature);
 994             if remaining_lib_features.is_empty() {
 995                 break;
 996             }
 997         }
 998     }
 999
1000     for (feature, span) in remaining_lib_features {
1001         struct_span_err!(tcx.sess, span, E0635, "unknown feature `{}`", feature).emit();
1002     }
1003
1004     // FIXME(#44232): the `used_features` table no longer exists, so we
1005     // don't lint about unused features. We should re-enable this one day!
1006 }
1007
1008 fn unnecessary_partially_stable_feature_lint(
1009     tcx: TyCtxt<'_>,
1010     span: Span,
1011     feature: Symbol,
1012     implies: Symbol,
1013     since: Symbol,
1014 ) {
1015     tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
1016         lint.build(&format!(
1017             "the feature `{feature}` has been partially stabilized since {since} and is succeeded \
1018              by the feature `{implies}`"
1019         ))
1020         .span_suggestion(
1021             span,
1022             &format!(
1023                 "if you are using features which are still unstable, change to using `{implies}`"
1024             ),
1025             implies,
1026             Applicability::MaybeIncorrect,
1027         )
1028         .span_suggestion(
1029             tcx.sess.source_map().span_extend_to_line(span),
1030             "if you are using features which are now stable, remove this line",
1031             "",
1032             Applicability::MaybeIncorrect,
1033         )
1034         .emit();
1035     });
1036 }
1037
1038 fn unnecessary_stable_feature_lint(tcx: TyCtxt<'_>, span: Span, feature: Symbol, since: Symbol) {
1039     tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
1040         lint.build(&format!(
1041             "the feature `{feature}` has been stable since {since} and no longer requires an \
1042              attribute to enable",
1043         ))
1044         .emit();
1045     });
1046 }
1047
1048 fn duplicate_feature_err(sess: &Session, span: Span, feature: Symbol) {
1049     struct_span_err!(sess, span, E0636, "the feature `{}` has already been declared", feature)
1050         .emit();
1051 }
1052
1053 fn missing_const_err(session: &Session, fn_sig_span: Span, const_span: Span) {
1054     const ERROR_MSG: &'static str = "attributes `#[rustc_const_unstable]` \
1055          and `#[rustc_const_stable]` require \
1056          the function or method to be `const`";
1057
1058     session
1059         .struct_span_err(fn_sig_span, ERROR_MSG)
1060         .span_help(fn_sig_span, "make the function or method const")
1061         .span_label(const_span, "attribute specified here")
1062         .emit();
1063 }