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 crate::errors::{
   5     self, CannotStabilizeDeprecated, DeprecatedAttribute, DuplicateFeatureErr,
   6     FeatureOnlyOnNightly, ImpliedFeatureNotExist, InvalidDeprecationVersion, InvalidStability,
   7     MissingConstErr, MissingConstStabAttr, MissingStabilityAttr, TraitImplConstStable,
   8     UnknownFeature, UselessStability,
   9 };
  10 use rustc_attr::{
  11     self as attr, rust_version_symbol, ConstStability, Stability, StabilityLevel, Unstable,
  12     UnstableReason, VERSION_PLACEHOLDER,
  13 };
  14 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
  15 use rustc_errors::Applicability;
  16 use rustc_hir as hir;
  17 use rustc_hir::def::{DefKind, Res};
  18 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
  19 use rustc_hir::hir_id::CRATE_HIR_ID;
  20 use rustc_hir::intravisit::{self, Visitor};
  21 use rustc_hir::{FieldDef, Item, ItemKind, TraitRef, Ty, TyKind, Variant};
  22 use rustc_middle::hir::nested_filter;
  23 use rustc_middle::middle::privacy::EffectiveVisibilities;
  24 use rustc_middle::middle::stability::{AllowUnstable, DeprecationEntry, Index};
  25 use rustc_middle::ty::{query::Providers, TyCtxt};
  26 use rustc_session::lint;
  27 use rustc_session::lint::builtin::{INEFFECTIVE_UNSTABLE_TRAIT_IMPL, USELESS_DEPRECATED};
  28 use rustc_span::symbol::{sym, Symbol};
  29 use rustc_span::Span;
  30 use rustc_target::spec::abi::Abi;
  31
  32 use std::cmp::Ordering;
  33 use std::iter;
  34 use std::mem::replace;
  35 use std::num::NonZeroU32;
  36
  37 #[derive(PartialEq)]
  38 enum AnnotationKind {
  39     /// Annotation is required if not inherited from unstable parents.
  40     Required,
  41     /// Annotation is useless, reject it.
  42     Prohibited,
  43     /// Deprecation annotation is useless, reject it. (Stability attribute is still required.)
  44     DeprecationProhibited,
  45     /// Annotation itself is useless, but it can be propagated to children.
  46     Container,
  47 }
  48
  49 /// Whether to inherit deprecation flags for nested items. In most cases, we do want to inherit
  50 /// deprecation, because nested items rarely have individual deprecation attributes, and so
  51 /// should be treated as deprecated if their parent is. However, default generic parameters
  52 /// have separate deprecation attributes from their parents, so we do not wish to inherit
  53 /// deprecation in this case. For example, inheriting deprecation for `T` in `Foo<T>`
  54 /// would cause a duplicate warning arising from both `Foo` and `T` being deprecated.
  55 #[derive(Clone)]
  56 enum InheritDeprecation {
  57     Yes,
  58     No,
  59 }
  60
  61 impl InheritDeprecation {
  62     fn yes(&self) -> bool {
  63         matches!(self, InheritDeprecation::Yes)
  64     }
  65 }
  66
  67 /// Whether to inherit const stability flags for nested items. In most cases, we do not want to
  68 /// inherit const stability: just because an enclosing `fn` is const-stable does not mean
  69 /// all `extern` imports declared in it should be const-stable! However, trait methods
  70 /// inherit const stability attributes from their parent and do not have their own.
  71 enum InheritConstStability {
  72     Yes,
  73     No,
  74 }
  75
  76 impl InheritConstStability {
  77     fn yes(&self) -> bool {
  78         matches!(self, InheritConstStability::Yes)
  79     }
  80 }
  81
  82 enum InheritStability {
  83     Yes,
  84     No,
  85 }
  86
  87 impl InheritStability {
  88     fn yes(&self) -> bool {
  89         matches!(self, InheritStability::Yes)
  90     }
  91 }
  92
  93 /// A private tree-walker for producing an `Index`.
  94 struct Annotator<'a, 'tcx> {
  95     tcx: TyCtxt<'tcx>,
  96     index: &'a mut Index,
  97     parent_stab: Option<Stability>,
  98     parent_const_stab: Option<ConstStability>,
  99     parent_depr: Option<DeprecationEntry>,
 100     in_trait_impl: bool,
 101 }
 102
 103 impl<'a, 'tcx> Annotator<'a, 'tcx> {
 104     /// Determine the stability for a node based on its attributes and inherited stability. The
 105     /// stability is recorded in the index and used as the parent. If the node is a function,
 106     /// `fn_sig` is its signature.
 107     fn annotate<F>(
 108         &mut self,
 109         def_id: LocalDefId,
 110         item_sp: Span,
 111         fn_sig: Option<&'tcx hir::FnSig<'tcx>>,
 112         kind: AnnotationKind,
 113         inherit_deprecation: InheritDeprecation,
 114         inherit_const_stability: InheritConstStability,
 115         inherit_from_parent: InheritStability,
 116         visit_children: F,
 117     ) where
 118         F: FnOnce(&mut Self),
 119     {
 120         let attrs = self.tcx.hir().attrs(self.tcx.hir().local_def_id_to_hir_id(def_id));
 121         debug!("annotate(id = {:?}, attrs = {:?})", def_id, attrs);
 122
 123         let depr = attr::find_deprecation(&self.tcx.sess, attrs);
 124         let mut is_deprecated = false;
 125         if let Some((depr, span)) = &depr {
 126             is_deprecated = true;
 127
 128             if kind == AnnotationKind::Prohibited || kind == AnnotationKind::DeprecationProhibited {
 129                 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
 130                 self.tcx.emit_spanned_lint(
 131                     USELESS_DEPRECATED,
 132                     hir_id,
 133                     *span,
 134                     errors::DeprecatedAnnotationHasNoEffect { span: *span },
 135                 );
 136             }
 137
 138             // `Deprecation` is just two pointers, no need to intern it
 139             let depr_entry = DeprecationEntry::local(*depr, def_id);
 140             self.index.depr_map.insert(def_id, depr_entry);
 141         } else if let Some(parent_depr) = self.parent_depr {
 142             if inherit_deprecation.yes() {
 143                 is_deprecated = true;
 144                 info!("tagging child {:?} as deprecated from parent", def_id);
 145                 self.index.depr_map.insert(def_id, parent_depr);
 146             }
 147         }
 148
 149         if !self.tcx.features().staged_api {
 150             // Propagate unstability.  This can happen even for non-staged-api crates in case
 151             // -Zforce-unstable-if-unmarked is set.
 152             if let Some(stab) = self.parent_stab {
 153                 if inherit_deprecation.yes() && stab.is_unstable() {
 154                     self.index.stab_map.insert(def_id, stab);
 155                 }
 156             }
 157
 158             self.recurse_with_stability_attrs(
 159                 depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 160                 None,
 161                 None,
 162                 visit_children,
 163             );
 164             return;
 165         }
 166
 167         let (stab, const_stab, body_stab) = attr::find_stability(&self.tcx.sess, attrs, item_sp);
 168         let mut const_span = None;
 169
 170         let const_stab = const_stab.map(|(const_stab, const_span_node)| {
 171             self.index.const_stab_map.insert(def_id, const_stab);
 172             const_span = Some(const_span_node);
 173             const_stab
 174         });
 175
 176         // If the current node is a function, has const stability attributes and if it doesn not have an intrinsic ABI,
 177         // check if the function/method is const or the parent impl block is const
 178         if let (Some(const_span), Some(fn_sig)) = (const_span, fn_sig) {
 179             if fn_sig.header.abi != Abi::RustIntrinsic
 180                 && fn_sig.header.abi != Abi::PlatformIntrinsic
 181                 && !fn_sig.header.is_const()
 182             {
 183                 if !self.in_trait_impl
 184                     || (self.in_trait_impl && !self.tcx.is_const_fn_raw(def_id.to_def_id()))
 185                 {
 186                     self.tcx
 187                         .sess
 188                         .emit_err(MissingConstErr { fn_sig_span: fn_sig.span, const_span });
 189                 }
 190             }
 191         }
 192
 193         // `impl const Trait for Type` items forward their const stability to their
 194         // immediate children.
 195         if const_stab.is_none() {
 196             debug!("annotate: const_stab not found, parent = {:?}", self.parent_const_stab);
 197             if let Some(parent) = self.parent_const_stab {
 198                 if parent.is_const_unstable() {
 199                     self.index.const_stab_map.insert(def_id, parent);
 200                 }
 201             }
 202         }
 203
 204         if let Some((rustc_attr::Deprecation { is_since_rustc_version: true, .. }, span)) = &depr {
 205             if stab.is_none() {
 206                 self.tcx.sess.emit_err(DeprecatedAttribute { span: *span });
 207             }
 208         }
 209
 210         if let Some((body_stab, _span)) = body_stab {
 211             // FIXME: check that this item can have body stability
 212
 213             self.index.default_body_stab_map.insert(def_id, body_stab);
 214             debug!(?self.index.default_body_stab_map);
 215         }
 216
 217         let stab = stab.map(|(stab, span)| {
 218             // Error if prohibited, or can't inherit anything from a container.
 219             if kind == AnnotationKind::Prohibited
 220                 || (kind == AnnotationKind::Container && stab.level.is_stable() && is_deprecated)
 221             {
 222                 self.tcx.sess.emit_err(UselessStability { span, item_sp });
 223             }
 224
 225             debug!("annotate: found {:?}", stab);
 226
 227             // Check if deprecated_since < stable_since. If it is,
 228             // this is *almost surely* an accident.
 229             if let (&Some(dep_since), &attr::Stable { since: stab_since, .. }) =
 230                 (&depr.as_ref().and_then(|(d, _)| d.since), &stab.level)
 231             {
 232                 // Explicit version of iter::order::lt to handle parse errors properly
 233                 for (dep_v, stab_v) in
 234                     iter::zip(dep_since.as_str().split('.'), stab_since.as_str().split('.'))
 235                 {
 236                     match stab_v.parse::<u64>() {
 237                         Err(_) => {
 238                             self.tcx.sess.emit_err(InvalidStability { span, item_sp });
 239                             break;
 240                         }
 241                         Ok(stab_vp) => match dep_v.parse::<u64>() {
 242                             Ok(dep_vp) => match dep_vp.cmp(&stab_vp) {
 243                                 Ordering::Less => {
 244                                     self.tcx
 245                                         .sess
 246                                         .emit_err(CannotStabilizeDeprecated { span, item_sp });
 247                                     break;
 248                                 }
 249                                 Ordering::Equal => continue,
 250                                 Ordering::Greater => break,
 251                             },
 252                             Err(_) => {
 253                                 if dep_v != "TBD" {
 254                                     self.tcx
 255                                         .sess
 256                                         .emit_err(InvalidDeprecationVersion { span, item_sp });
 257                                 }
 258                                 break;
 259                             }
 260                         },
 261                     }
 262                 }
 263             }
 264
 265             if let Stability { level: Unstable { implied_by: Some(implied_by), .. }, feature } =
 266                 stab
 267             {
 268                 self.index.implications.insert(implied_by, feature);
 269             }
 270
 271             self.index.stab_map.insert(def_id, stab);
 272             stab
 273         });
 274
 275         if stab.is_none() {
 276             debug!("annotate: stab not found, parent = {:?}", self.parent_stab);
 277             if let Some(stab) = self.parent_stab {
 278                 if inherit_deprecation.yes() && stab.is_unstable() || inherit_from_parent.yes() {
 279                     self.index.stab_map.insert(def_id, stab);
 280                 }
 281             }
 282         }
 283
 284         self.recurse_with_stability_attrs(
 285             depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 286             stab,
 287             if inherit_const_stability.yes() { const_stab } else { None },
 288             visit_children,
 289         );
 290     }
 291
 292     fn recurse_with_stability_attrs(
 293         &mut self,
 294         depr: Option<DeprecationEntry>,
 295         stab: Option<Stability>,
 296         const_stab: Option<ConstStability>,
 297         f: impl FnOnce(&mut Self),
 298     ) {
 299         // These will be `Some` if this item changes the corresponding stability attribute.
 300         let mut replaced_parent_depr = None;
 301         let mut replaced_parent_stab = None;
 302         let mut replaced_parent_const_stab = None;
 303
 304         if let Some(depr) = depr {
 305             replaced_parent_depr = Some(replace(&mut self.parent_depr, Some(depr)));
 306         }
 307         if let Some(stab) = stab {
 308             replaced_parent_stab = Some(replace(&mut self.parent_stab, Some(stab)));
 309         }
 310         if let Some(const_stab) = const_stab {
 311             replaced_parent_const_stab =
 312                 Some(replace(&mut self.parent_const_stab, Some(const_stab)));
 313         }
 314
 315         f(self);
 316
 317         if let Some(orig_parent_depr) = replaced_parent_depr {
 318             self.parent_depr = orig_parent_depr;
 319         }
 320         if let Some(orig_parent_stab) = replaced_parent_stab {
 321             self.parent_stab = orig_parent_stab;
 322         }
 323         if let Some(orig_parent_const_stab) = replaced_parent_const_stab {
 324             self.parent_const_stab = orig_parent_const_stab;
 325         }
 326     }
 327 }
 328
 329 impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
 330     /// Because stability levels are scoped lexically, we want to walk
 331     /// nested items in the context of the outer item, so enable
 332     /// deep-walking.
 333     type NestedFilter = nested_filter::All;
 334
 335     fn nested_visit_map(&mut self) -> Self::Map {
 336         self.tcx.hir()
 337     }
 338
 339     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 340         let orig_in_trait_impl = self.in_trait_impl;
 341         let mut kind = AnnotationKind::Required;
 342         let mut const_stab_inherit = InheritConstStability::No;
 343         let mut fn_sig = None;
 344
 345         match i.kind {
 346             // Inherent impls and foreign modules serve only as containers for other items,
 347             // they don't have their own stability. They still can be annotated as unstable
 348             // and propagate this instability to children, but this annotation is completely
 349             // optional. They inherit stability from their parents when unannotated.
 350             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 351             | hir::ItemKind::ForeignMod { .. } => {
 352                 self.in_trait_impl = false;
 353                 kind = AnnotationKind::Container;
 354             }
 355             hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => {
 356                 self.in_trait_impl = true;
 357                 kind = AnnotationKind::DeprecationProhibited;
 358                 const_stab_inherit = InheritConstStability::Yes;
 359             }
 360             hir::ItemKind::Struct(ref sd, _) => {
 361                 if let Some(ctor_hir_id) = sd.ctor_hir_id() {
 362                     self.annotate(
 363                         self.tcx.hir().local_def_id(ctor_hir_id),
 364                         i.span,
 365                         None,
 366                         AnnotationKind::Required,
 367                         InheritDeprecation::Yes,
 368                         InheritConstStability::No,
 369                         InheritStability::Yes,
 370                         |_| {},
 371                     )
 372                 }
 373             }
 374             hir::ItemKind::Fn(ref item_fn_sig, _, _) => {
 375                 fn_sig = Some(item_fn_sig);
 376             }
 377             _ => {}
 378         }
 379
 380         self.annotate(
 381             i.owner_id.def_id,
 382             i.span,
 383             fn_sig,
 384             kind,
 385             InheritDeprecation::Yes,
 386             const_stab_inherit,
 387             InheritStability::No,
 388             |v| intravisit::walk_item(v, i),
 389         );
 390         self.in_trait_impl = orig_in_trait_impl;
 391     }
 392
 393     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 394         let fn_sig = match ti.kind {
 395             hir::TraitItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 396             _ => None,
 397         };
 398
 399         self.annotate(
 400             ti.owner_id.def_id,
 401             ti.span,
 402             fn_sig,
 403             AnnotationKind::Required,
 404             InheritDeprecation::Yes,
 405             InheritConstStability::No,
 406             InheritStability::No,
 407             |v| {
 408                 intravisit::walk_trait_item(v, ti);
 409             },
 410         );
 411     }
 412
 413     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 414         let kind =
 415             if self.in_trait_impl { AnnotationKind::Prohibited } else { AnnotationKind::Required };
 416
 417         let fn_sig = match ii.kind {
 418             hir::ImplItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 419             _ => None,
 420         };
 421
 422         self.annotate(
 423             ii.owner_id.def_id,
 424             ii.span,
 425             fn_sig,
 426             kind,
 427             InheritDeprecation::Yes,
 428             InheritConstStability::No,
 429             InheritStability::No,
 430             |v| {
 431                 intravisit::walk_impl_item(v, ii);
 432             },
 433         );
 434     }
 435
 436     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>) {
 437         self.annotate(
 438             self.tcx.hir().local_def_id(var.id),
 439             var.span,
 440             None,
 441             AnnotationKind::Required,
 442             InheritDeprecation::Yes,
 443             InheritConstStability::No,
 444             InheritStability::Yes,
 445             |v| {
 446                 if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
 447                     v.annotate(
 448                         v.tcx.hir().local_def_id(ctor_hir_id),
 449                         var.span,
 450                         None,
 451                         AnnotationKind::Required,
 452                         InheritDeprecation::Yes,
 453                         InheritConstStability::No,
 454                         InheritStability::Yes,
 455                         |_| {},
 456                     );
 457                 }
 458
 459                 intravisit::walk_variant(v, var)
 460             },
 461         )
 462     }
 463
 464     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 465         self.annotate(
 466             self.tcx.hir().local_def_id(s.hir_id),
 467             s.span,
 468             None,
 469             AnnotationKind::Required,
 470             InheritDeprecation::Yes,
 471             InheritConstStability::No,
 472             InheritStability::Yes,
 473             |v| {
 474                 intravisit::walk_field_def(v, s);
 475             },
 476         );
 477     }
 478
 479     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 480         self.annotate(
 481             i.owner_id.def_id,
 482             i.span,
 483             None,
 484             AnnotationKind::Required,
 485             InheritDeprecation::Yes,
 486             InheritConstStability::No,
 487             InheritStability::No,
 488             |v| {
 489                 intravisit::walk_foreign_item(v, i);
 490             },
 491         );
 492     }
 493
 494     fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
 495         let kind = match &p.kind {
 496             // Allow stability attributes on default generic arguments.
 497             hir::GenericParamKind::Type { default: Some(_), .. }
 498             | hir::GenericParamKind::Const { default: Some(_), .. } => AnnotationKind::Container,
 499             _ => AnnotationKind::Prohibited,
 500         };
 501
 502         self.annotate(
 503             self.tcx.hir().local_def_id(p.hir_id),
 504             p.span,
 505             None,
 506             kind,
 507             InheritDeprecation::No,
 508             InheritConstStability::No,
 509             InheritStability::No,
 510             |v| {
 511                 intravisit::walk_generic_param(v, p);
 512             },
 513         );
 514     }
 515 }
 516
 517 struct MissingStabilityAnnotations<'tcx> {
 518     tcx: TyCtxt<'tcx>,
 519     effective_visibilities: &'tcx EffectiveVisibilities,
 520 }
 521
 522 impl<'tcx> MissingStabilityAnnotations<'tcx> {
 523     fn check_missing_stability(&self, def_id: LocalDefId, span: Span) {
 524         let stab = self.tcx.stability().local_stability(def_id);
 525         if !self.tcx.sess.opts.test
 526             && stab.is_none()
 527             && self.effective_visibilities.is_reachable(def_id)
 528         {
 529             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 530             self.tcx.sess.emit_err(MissingStabilityAttr { span, descr });
 531         }
 532     }
 533
 534     fn check_missing_const_stability(&self, def_id: LocalDefId, span: Span) {
 535         if !self.tcx.features().staged_api {
 536             return;
 537         }
 538
 539         let is_const = self.tcx.is_const_fn(def_id.to_def_id())
 540             || self.tcx.is_const_trait_impl_raw(def_id.to_def_id());
 541         let is_stable = self
 542             .tcx
 543             .lookup_stability(def_id)
 544             .map_or(false, |stability| stability.level.is_stable());
 545         let missing_const_stability_attribute = self.tcx.lookup_const_stability(def_id).is_none();
 546         let is_reachable = self.effective_visibilities.is_reachable(def_id);
 547
 548         if is_const && is_stable && missing_const_stability_attribute && is_reachable {
 549             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 550             self.tcx.sess.emit_err(MissingConstStabAttr { span, descr });
 551         }
 552     }
 553 }
 554
 555 impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
 556     type NestedFilter = nested_filter::OnlyBodies;
 557
 558     fn nested_visit_map(&mut self) -> Self::Map {
 559         self.tcx.hir()
 560     }
 561
 562     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 563         // Inherent impls and foreign modules serve only as containers for other items,
 564         // they don't have their own stability. They still can be annotated as unstable
 565         // and propagate this instability to children, but this annotation is completely
 566         // optional. They inherit stability from their parents when unannotated.
 567         if !matches!(
 568             i.kind,
 569             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 570                 | hir::ItemKind::ForeignMod { .. }
 571         ) {
 572             self.check_missing_stability(i.owner_id.def_id, i.span);
 573         }
 574
 575         // Ensure stable `const fn` have a const stability attribute.
 576         self.check_missing_const_stability(i.owner_id.def_id, i.span);
 577
 578         intravisit::walk_item(self, i)
 579     }
 580
 581     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 582         self.check_missing_stability(ti.owner_id.def_id, ti.span);
 583         intravisit::walk_trait_item(self, ti);
 584     }
 585
 586     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 587         let impl_def_id = self.tcx.hir().get_parent_item(ii.hir_id());
 588         if self.tcx.impl_trait_ref(impl_def_id).is_none() {
 589             self.check_missing_stability(ii.owner_id.def_id, ii.span);
 590             self.check_missing_const_stability(ii.owner_id.def_id, ii.span);
 591         }
 592         intravisit::walk_impl_item(self, ii);
 593     }
 594
 595     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>) {
 596         self.check_missing_stability(self.tcx.hir().local_def_id(var.id), var.span);
 597         if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
 598             self.check_missing_stability(self.tcx.hir().local_def_id(ctor_hir_id), var.span);
 599         }
 600         intravisit::walk_variant(self, var);
 601     }
 602
 603     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 604         self.check_missing_stability(self.tcx.hir().local_def_id(s.hir_id), s.span);
 605         intravisit::walk_field_def(self, s);
 606     }
 607
 608     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 609         self.check_missing_stability(i.owner_id.def_id, i.span);
 610         intravisit::walk_foreign_item(self, i);
 611     }
 612     // Note that we don't need to `check_missing_stability` for default generic parameters,
 613     // as we assume that any default generic parameters without attributes are automatically
 614     // stable (assuming they have not inherited instability from their parent).
 615 }
 616
 617 fn stability_index(tcx: TyCtxt<'_>, (): ()) -> Index {
 618     let mut index = Index {
 619         stab_map: Default::default(),
 620         const_stab_map: Default::default(),
 621         default_body_stab_map: Default::default(),
 622         depr_map: Default::default(),
 623         implications: Default::default(),
 624     };
 625
 626     {
 627         let mut annotator = Annotator {
 628             tcx,
 629             index: &mut index,
 630             parent_stab: None,
 631             parent_const_stab: None,
 632             parent_depr: None,
 633             in_trait_impl: false,
 634         };
 635
 636         // If the `-Z force-unstable-if-unmarked` flag is passed then we provide
 637         // a parent stability annotation which indicates that this is private
 638         // with the `rustc_private` feature. This is intended for use when
 639         // compiling `librustc_*` crates themselves so we can leverage crates.io
 640         // while maintaining the invariant that all sysroot crates are unstable
 641         // by default and are unable to be used.
 642         if tcx.sess.opts.unstable_opts.force_unstable_if_unmarked {
 643             let stability = Stability {
 644                 level: attr::StabilityLevel::Unstable {
 645                     reason: UnstableReason::Default,
 646                     issue: NonZeroU32::new(27812),
 647                     is_soft: false,
 648                     implied_by: None,
 649                 },
 650                 feature: sym::rustc_private,
 651             };
 652             annotator.parent_stab = Some(stability);
 653         }
 654
 655         annotator.annotate(
 656             CRATE_DEF_ID,
 657             tcx.hir().span(CRATE_HIR_ID),
 658             None,
 659             AnnotationKind::Required,
 660             InheritDeprecation::Yes,
 661             InheritConstStability::No,
 662             InheritStability::No,
 663             |v| tcx.hir().walk_toplevel_module(v),
 664         );
 665     }
 666     index
 667 }
 668
 669 /// Cross-references the feature names of unstable APIs with enabled
 670 /// features and possibly prints errors.
 671 fn check_mod_unstable_api_usage(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 672     tcx.hir().visit_item_likes_in_module(module_def_id, &mut Checker { tcx });
 673 }
 674
 675 pub(crate) fn provide(providers: &mut Providers) {
 676     *providers = Providers {
 677         check_mod_unstable_api_usage,
 678         stability_index,
 679         stability_implications: |tcx, _| tcx.stability().implications.clone(),
 680         lookup_stability: |tcx, id| tcx.stability().local_stability(id.expect_local()),
 681         lookup_const_stability: |tcx, id| tcx.stability().local_const_stability(id.expect_local()),
 682         lookup_default_body_stability: |tcx, id| {
 683             tcx.stability().local_default_body_stability(id.expect_local())
 684         },
 685         lookup_deprecation_entry: |tcx, id| {
 686             tcx.stability().local_deprecation_entry(id.expect_local())
 687         },
 688         ..*providers
 689     };
 690 }
 691
 692 struct Checker<'tcx> {
 693     tcx: TyCtxt<'tcx>,
 694 }
 695
 696 impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
 697     type NestedFilter = nested_filter::OnlyBodies;
 698
 699     /// Because stability levels are scoped lexically, we want to walk
 700     /// nested items in the context of the outer item, so enable
 701     /// deep-walking.
 702     fn nested_visit_map(&mut self) -> Self::Map {
 703         self.tcx.hir()
 704     }
 705
 706     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 707         match item.kind {
 708             hir::ItemKind::ExternCrate(_) => {
 709                 // compiler-generated `extern crate` items have a dummy span.
 710                 // `std` is still checked for the `restricted-std` feature.
 711                 if item.span.is_dummy() && item.ident.name != sym::std {
 712                     return;
 713                 }
 714
 715                 let Some(cnum) = self.tcx.extern_mod_stmt_cnum(item.owner_id.def_id) else {
 716                     return;
 717                 };
 718                 let def_id = cnum.as_def_id();
 719                 self.tcx.check_stability(def_id, Some(item.hir_id()), item.span, None);
 720             }
 721
 722             // For implementations of traits, check the stability of each item
 723             // individually as it's possible to have a stable trait with unstable
 724             // items.
 725             hir::ItemKind::Impl(hir::Impl {
 726                 of_trait: Some(ref t),
 727                 self_ty,
 728                 items,
 729                 constness,
 730                 ..
 731             }) => {
 732                 let features = self.tcx.features();
 733                 if features.staged_api {
 734                     let attrs = self.tcx.hir().attrs(item.hir_id());
 735                     let (stab, const_stab, _) =
 736                         attr::find_stability(&self.tcx.sess, attrs, item.span);
 737
 738                     // If this impl block has an #[unstable] attribute, give an
 739                     // error if all involved types and traits are stable, because
 740                     // it will have no effect.
 741                     // See: https://github.com/rust-lang/rust/issues/55436
 742                     if let Some((Stability { level: attr::Unstable { .. }, .. }, span)) = stab {
 743                         let mut c = CheckTraitImplStable { tcx: self.tcx, fully_stable: true };
 744                         c.visit_ty(self_ty);
 745                         c.visit_trait_ref(t);
 746                         if c.fully_stable {
 747                             self.tcx.struct_span_lint_hir(
 748                                 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
 749                                 item.hir_id(),
 750                                 span,
 751                                 "an `#[unstable]` annotation here has no effect",
 752                                 |lint| lint.note("see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information")
 753                             );
 754                         }
 755                     }
 756
 757                     // `#![feature(const_trait_impl)]` is unstable, so any impl declared stable
 758                     // needs to have an error emitted.
 759                     if features.const_trait_impl
 760                         && *constness == hir::Constness::Const
 761                         && const_stab.map_or(false, |(stab, _)| stab.is_const_stable())
 762                     {
 763                         self.tcx.sess.emit_err(TraitImplConstStable { span: item.span });
 764                     }
 765                 }
 766
 767                 for impl_item_ref in *items {
 768                     let impl_item = self.tcx.associated_item(impl_item_ref.id.owner_id);
 769
 770                     if let Some(def_id) = impl_item.trait_item_def_id {
 771                         // Pass `None` to skip deprecation warnings.
 772                         self.tcx.check_stability(def_id, None, impl_item_ref.span, None);
 773                     }
 774                 }
 775             }
 776
 777             _ => (/* pass */),
 778         }
 779         intravisit::walk_item(self, item);
 780     }
 781
 782     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, id: hir::HirId) {
 783         if let Some(def_id) = path.res.opt_def_id() {
 784             let method_span = path.segments.last().map(|s| s.ident.span);
 785             let item_is_allowed = self.tcx.check_stability_allow_unstable(
 786                 def_id,
 787                 Some(id),
 788                 path.span,
 789                 method_span,
 790                 if is_unstable_reexport(self.tcx, id) {
 791                     AllowUnstable::Yes
 792                 } else {
 793                     AllowUnstable::No
 794                 },
 795             );
 796
 797             let is_allowed_through_unstable_modules = |def_id| {
 798                 self.tcx
 799                     .lookup_stability(def_id)
 800                     .map(|stab| match stab.level {
 801                         StabilityLevel::Stable { allowed_through_unstable_modules, .. } => {
 802                             allowed_through_unstable_modules
 803                         }
 804                         _ => false,
 805                     })
 806                     .unwrap_or(false)
 807             };
 808
 809             if item_is_allowed && !is_allowed_through_unstable_modules(def_id) {
 810                 // Check parent modules stability as well if the item the path refers to is itself
 811                 // stable. We only emit warnings for unstable path segments if the item is stable
 812                 // or allowed because stability is often inherited, so the most common case is that
 813                 // both the segments and the item are unstable behind the same feature flag.
 814                 //
 815                 // We check here rather than in `visit_path_segment` to prevent visiting the last
 816                 // path segment twice
 817                 //
 818                 // We include special cases via #[rustc_allowed_through_unstable_modules] for items
 819                 // that were accidentally stabilized through unstable paths before this check was
 820                 // added, such as `core::intrinsics::transmute`
 821                 let parents = path.segments.iter().rev().skip(1);
 822                 for path_segment in parents {
 823                     if let Some(def_id) = path_segment.res.opt_def_id() {
 824                         // use `None` for id to prevent deprecation check
 825                         self.tcx.check_stability_allow_unstable(
 826                             def_id,
 827                             None,
 828                             path.span,
 829                             None,
 830                             if is_unstable_reexport(self.tcx, id) {
 831                                 AllowUnstable::Yes
 832                             } else {
 833                                 AllowUnstable::No
 834                             },
 835                         );
 836                     }
 837                 }
 838             }
 839         }
 840
 841         intravisit::walk_path(self, path)
 842     }
 843 }
 844
 845 /// Check whether a path is a `use` item that has been marked as unstable.
 846 ///
 847 /// See issue #94972 for details on why this is a special case
 848 fn is_unstable_reexport<'tcx>(tcx: TyCtxt<'tcx>, id: hir::HirId) -> bool {
 849     // Get the LocalDefId so we can lookup the item to check the kind.
 850     let Some(def_id) = tcx.hir().opt_local_def_id(id) else { return false; };
 851
 852     let Some(stab) = tcx.stability().local_stability(def_id) else {
 853         return false;
 854     };
 855
 856     if stab.level.is_stable() {
 857         // The re-export is not marked as unstable, don't override
 858         return false;
 859     }
 860
 861     // If this is a path that isn't a use, we don't need to do anything special
 862     if !matches!(tcx.hir().expect_item(def_id).kind, ItemKind::Use(..)) {
 863         return false;
 864     }
 865
 866     true
 867 }
 868
 869 struct CheckTraitImplStable<'tcx> {
 870     tcx: TyCtxt<'tcx>,
 871     fully_stable: bool,
 872 }
 873
 874 impl<'tcx> Visitor<'tcx> for CheckTraitImplStable<'tcx> {
 875     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _id: hir::HirId) {
 876         if let Some(def_id) = path.res.opt_def_id() {
 877             if let Some(stab) = self.tcx.lookup_stability(def_id) {
 878                 self.fully_stable &= stab.level.is_stable();
 879             }
 880         }
 881         intravisit::walk_path(self, path)
 882     }
 883
 884     fn visit_trait_ref(&mut self, t: &'tcx TraitRef<'tcx>) {
 885         if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
 886             if let Some(stab) = self.tcx.lookup_stability(trait_did) {
 887                 self.fully_stable &= stab.level.is_stable();
 888             }
 889         }
 890         intravisit::walk_trait_ref(self, t)
 891     }
 892
 893     fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
 894         if let TyKind::Never = t.kind {
 895             self.fully_stable = false;
 896         }
 897         if let TyKind::BareFn(f) = t.kind {
 898             if rustc_target::spec::abi::is_stable(f.abi.name()).is_err() {
 899                 self.fully_stable = false;
 900             }
 901         }
 902         intravisit::walk_ty(self, t)
 903     }
 904
 905     fn visit_fn_decl(&mut self, fd: &'tcx hir::FnDecl<'tcx>) {
 906         for ty in fd.inputs {
 907             self.visit_ty(ty)
 908         }
 909         if let hir::FnRetTy::Return(output_ty) = fd.output {
 910             match output_ty.kind {
 911                 TyKind::Never => {} // `-> !` is stable
 912                 _ => self.visit_ty(output_ty),
 913             }
 914         }
 915     }
 916 }
 917
 918 /// Given the list of enabled features that were not language features (i.e., that
 919 /// were expected to be library features), and the list of features used from
 920 /// libraries, identify activated features that don't exist and error about them.
 921 pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
 922     let is_staged_api =
 923         tcx.sess.opts.unstable_opts.force_unstable_if_unmarked || tcx.features().staged_api;
 924     if is_staged_api {
 925         let effective_visibilities = &tcx.effective_visibilities(());
 926         let mut missing = MissingStabilityAnnotations { tcx, effective_visibilities };
 927         missing.check_missing_stability(CRATE_DEF_ID, tcx.hir().span(CRATE_HIR_ID));
 928         tcx.hir().walk_toplevel_module(&mut missing);
 929         tcx.hir().visit_all_item_likes_in_crate(&mut missing);
 930     }
 931
 932     let declared_lang_features = &tcx.features().declared_lang_features;
 933     let mut lang_features = FxHashSet::default();
 934     for &(feature, span, since) in declared_lang_features {
 935         if let Some(since) = since {
 936             // Warn if the user has enabled an already-stable lang feature.
 937             unnecessary_stable_feature_lint(tcx, span, feature, since);
 938         }
 939         if !lang_features.insert(feature) {
 940             // Warn if the user enables a lang feature multiple times.
 941             tcx.sess.emit_err(DuplicateFeatureErr { span, feature });
 942         }
 943     }
 944
 945     let declared_lib_features = &tcx.features().declared_lib_features;
 946     let mut remaining_lib_features = FxIndexMap::default();
 947     for (feature, span) in declared_lib_features {
 948         if !tcx.sess.opts.unstable_features.is_nightly_build() {
 949             tcx.sess.emit_err(FeatureOnlyOnNightly {
 950                 span: *span,
 951                 release_channel: env!("CFG_RELEASE_CHANNEL"),
 952             });
 953         }
 954         if remaining_lib_features.contains_key(&feature) {
 955             // Warn if the user enables a lib feature multiple times.
 956             tcx.sess.emit_err(DuplicateFeatureErr { span: *span, feature: *feature });
 957         }
 958         remaining_lib_features.insert(feature, *span);
 959     }
 960     // `stdbuild` has special handling for `libc`, so we need to
 961     // recognise the feature when building std.
 962     // Likewise, libtest is handled specially, so `test` isn't
 963     // available as we'd like it to be.
 964     // FIXME: only remove `libc` when `stdbuild` is active.
 965     // FIXME: remove special casing for `test`.
 966     remaining_lib_features.remove(&sym::libc);
 967     remaining_lib_features.remove(&sym::test);
 968
 969     /// For each feature in `defined_features`..
 970     ///
 971     /// - If it is in `remaining_lib_features` (those features with `#![feature(..)]` attributes in
 972     ///   the current crate), check if it is stable (or partially stable) and thus an unnecessary
 973     ///   attribute.
 974     /// - If it is in `remaining_implications` (a feature that is referenced by an `implied_by`
 975     ///   from the current crate), then remove it from the remaining implications.
 976     ///
 977     /// Once this function has been invoked for every feature (local crate and all extern crates),
 978     /// then..
 979     ///
 980     /// - If features remain in `remaining_lib_features`, then the user has enabled a feature that
 981     ///   does not exist.
 982     /// - If features remain in `remaining_implications`, the `implied_by` refers to a feature that
 983     ///   does not exist.
 984     ///
 985     /// By structuring the code in this way: checking the features defined from each crate one at a
 986     /// time, less loading from metadata is performed and thus compiler performance is improved.
 987     fn check_features<'tcx>(
 988         tcx: TyCtxt<'tcx>,
 989         remaining_lib_features: &mut FxIndexMap<&Symbol, Span>,
 990         remaining_implications: &mut FxHashMap<Symbol, Symbol>,
 991         defined_features: &[(Symbol, Option<Symbol>)],
 992         all_implications: &FxHashMap<Symbol, Symbol>,
 993     ) {
 994         for (feature, since) in defined_features {
 995             if let Some(since) = since && let Some(span) = remaining_lib_features.get(&feature) {
 996                 // Warn if the user has enabled an already-stable lib feature.
 997                 if let Some(implies) = all_implications.get(&feature) {
 998                     unnecessary_partially_stable_feature_lint(tcx, *span, *feature, *implies, *since);
 999                 } else {
1000                     unnecessary_stable_feature_lint(tcx, *span, *feature, *since);
1001                 }
1002
1003             }
1004             remaining_lib_features.remove(feature);
1005
1006             // `feature` is the feature doing the implying, but `implied_by` is the feature with
1007             // the attribute that establishes this relationship. `implied_by` is guaranteed to be a
1008             // feature defined in the local crate because `remaining_implications` is only the
1009             // implications from this crate.
1010             remaining_implications.remove(feature);
1011
1012             if remaining_lib_features.is_empty() && remaining_implications.is_empty() {
1013                 break;
1014             }
1015         }
1016     }
1017
1018     // All local crate implications need to have the feature that implies it confirmed to exist.
1019     let mut remaining_implications =
1020         tcx.stability_implications(rustc_hir::def_id::LOCAL_CRATE).clone();
1021
1022     // We always collect the lib features declared in the current crate, even if there are
1023     // no unknown features, because the collection also does feature attribute validation.
1024     let local_defined_features = tcx.lib_features(()).to_vec();
1025     if !remaining_lib_features.is_empty() || !remaining_implications.is_empty() {
1026         // Loading the implications of all crates is unavoidable to be able to emit the partial
1027         // stabilization diagnostic, but it can be avoided when there are no
1028         // `remaining_lib_features`.
1029         let mut all_implications = remaining_implications.clone();
1030         for &cnum in tcx.crates(()) {
1031             all_implications.extend(tcx.stability_implications(cnum));
1032         }
1033
1034         check_features(
1035             tcx,
1036             &mut remaining_lib_features,
1037             &mut remaining_implications,
1038             local_defined_features.as_slice(),
1039             &all_implications,
1040         );
1041
1042         for &cnum in tcx.crates(()) {
1043             if remaining_lib_features.is_empty() && remaining_implications.is_empty() {
1044                 break;
1045             }
1046             check_features(
1047                 tcx,
1048                 &mut remaining_lib_features,
1049                 &mut remaining_implications,
1050                 tcx.defined_lib_features(cnum).to_vec().as_slice(),
1051                 &all_implications,
1052             );
1053         }
1054     }
1055
1056     for (feature, span) in remaining_lib_features {
1057         tcx.sess.emit_err(UnknownFeature { span, feature: *feature });
1058     }
1059
1060     for (implied_by, feature) in remaining_implications {
1061         let local_defined_features = tcx.lib_features(());
1062         let span = *local_defined_features
1063             .stable
1064             .get(&feature)
1065             .map(|(_, span)| span)
1066             .or_else(|| local_defined_features.unstable.get(&feature))
1067             .expect("feature that implied another does not exist");
1068         tcx.sess.emit_err(ImpliedFeatureNotExist { span, feature, implied_by });
1069     }
1070
1071     // FIXME(#44232): the `used_features` table no longer exists, so we
1072     // don't lint about unused features. We should re-enable this one day!
1073 }
1074
1075 fn unnecessary_partially_stable_feature_lint(
1076     tcx: TyCtxt<'_>,
1077     span: Span,
1078     feature: Symbol,
1079     implies: Symbol,
1080     since: Symbol,
1081 ) {
1082     tcx.struct_span_lint_hir(
1083         lint::builtin::STABLE_FEATURES,
1084         hir::CRATE_HIR_ID,
1085         span,
1086         format!(
1087             "the feature `{feature}` has been partially stabilized since {since} and is succeeded \
1088              by the feature `{implies}`"
1089         ),
1090         |lint| {
1091             lint.span_suggestion(
1092                 span,
1093                 &format!(
1094                 "if you are using features which are still unstable, change to using `{implies}`"
1095             ),
1096                 implies,
1097                 Applicability::MaybeIncorrect,
1098             )
1099             .span_suggestion(
1100                 tcx.sess.source_map().span_extend_to_line(span),
1101                 "if you are using features which are now stable, remove this line",
1102                 "",
1103                 Applicability::MaybeIncorrect,
1104             )
1105         },
1106     );
1107 }
1108
1109 fn unnecessary_stable_feature_lint(
1110     tcx: TyCtxt<'_>,
1111     span: Span,
1112     feature: Symbol,
1113     mut since: Symbol,
1114 ) {
1115     if since.as_str() == VERSION_PLACEHOLDER {
1116         since = rust_version_symbol();
1117     }
1118     tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, format!("the feature `{feature}` has been stable since {since} and no longer requires an attribute to enable"), |lint| {
1119         lint
1120     });
1121 }