compiler/rustc_passes/src/stability.rs

   1 //! A pass that annotates every item and method with its stability level,
   2 //! propagating default levels lexically from parent to children ast nodes.
   3
   4 use rustc_attr::{
   5     self as attr, rust_version_symbol, ConstStability, Stability, StabilityLevel, Unstable,
   6     UnstableReason, VERSION_PLACEHOLDER,
   7 };
   8 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
   9 use rustc_errors::{struct_span_err, Applicability};
  10 use rustc_hir as hir;
  11 use rustc_hir::def::{DefKind, Res};
  12 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
  13 use rustc_hir::hir_id::CRATE_HIR_ID;
  14 use rustc_hir::intravisit::{self, Visitor};
  15 use rustc_hir::{FieldDef, Item, ItemKind, TraitRef, Ty, TyKind, Variant};
  16 use rustc_middle::hir::nested_filter;
  17 use rustc_middle::middle::privacy::AccessLevels;
  18 use rustc_middle::middle::stability::{AllowUnstable, DeprecationEntry, Index};
  19 use rustc_middle::ty::{query::Providers, TyCtxt};
  20 use rustc_session::lint;
  21 use rustc_session::lint::builtin::{INEFFECTIVE_UNSTABLE_TRAIT_IMPL, USELESS_DEPRECATED};
  22 use rustc_session::Session;
  23 use rustc_span::symbol::{sym, Symbol};
  24 use rustc_span::Span;
  25 use rustc_target::spec::abi::Abi;
  26
  27 use std::cmp::Ordering;
  28 use std::iter;
  29 use std::mem::replace;
  30 use std::num::NonZeroU32;
  31
  32 #[derive(PartialEq)]
  33 enum AnnotationKind {
  34     /// Annotation is required if not inherited from unstable parents.
  35     Required,
  36     /// Annotation is useless, reject it.
  37     Prohibited,
  38     /// Deprecation annotation is useless, reject it. (Stability attribute is still required.)
  39     DeprecationProhibited,
  40     /// Annotation itself is useless, but it can be propagated to children.
  41     Container,
  42 }
  43
  44 /// Whether to inherit deprecation flags for nested items. In most cases, we do want to inherit
  45 /// deprecation, because nested items rarely have individual deprecation attributes, and so
  46 /// should be treated as deprecated if their parent is. However, default generic parameters
  47 /// have separate deprecation attributes from their parents, so we do not wish to inherit
  48 /// deprecation in this case. For example, inheriting deprecation for `T` in `Foo<T>`
  49 /// would cause a duplicate warning arising from both `Foo` and `T` being deprecated.
  50 #[derive(Clone)]
  51 enum InheritDeprecation {
  52     Yes,
  53     No,
  54 }
  55
  56 impl InheritDeprecation {
  57     fn yes(&self) -> bool {
  58         matches!(self, InheritDeprecation::Yes)
  59     }
  60 }
  61
  62 /// Whether to inherit const stability flags for nested items. In most cases, we do not want to
  63 /// inherit const stability: just because an enclosing `fn` is const-stable does not mean
  64 /// all `extern` imports declared in it should be const-stable! However, trait methods
  65 /// inherit const stability attributes from their parent and do not have their own.
  66 enum InheritConstStability {
  67     Yes,
  68     No,
  69 }
  70
  71 impl InheritConstStability {
  72     fn yes(&self) -> bool {
  73         matches!(self, InheritConstStability::Yes)
  74     }
  75 }
  76
  77 enum InheritStability {
  78     Yes,
  79     No,
  80 }
  81
  82 impl InheritStability {
  83     fn yes(&self) -> bool {
  84         matches!(self, InheritStability::Yes)
  85     }
  86 }
  87
  88 /// A private tree-walker for producing an `Index`.
  89 struct Annotator<'a, 'tcx> {
  90     tcx: TyCtxt<'tcx>,
  91     index: &'a mut Index,
  92     parent_stab: Option<Stability>,
  93     parent_const_stab: Option<ConstStability>,
  94     parent_depr: Option<DeprecationEntry>,
  95     in_trait_impl: bool,
  96 }
  97
  98 impl<'a, 'tcx> Annotator<'a, 'tcx> {
  99     /// Determine the stability for a node based on its attributes and inherited stability. The
 100     /// stability is recorded in the index and used as the parent. If the node is a function,
 101     /// `fn_sig` is its signature.
 102     fn annotate<F>(
 103         &mut self,
 104         def_id: LocalDefId,
 105         item_sp: Span,
 106         fn_sig: Option<&'tcx hir::FnSig<'tcx>>,
 107         kind: AnnotationKind,
 108         inherit_deprecation: InheritDeprecation,
 109         inherit_const_stability: InheritConstStability,
 110         inherit_from_parent: InheritStability,
 111         visit_children: F,
 112     ) where
 113         F: FnOnce(&mut Self),
 114     {
 115         let attrs = self.tcx.hir().attrs(self.tcx.hir().local_def_id_to_hir_id(def_id));
 116         debug!("annotate(id = {:?}, attrs = {:?})", def_id, attrs);
 117
 118         let depr = attr::find_deprecation(&self.tcx.sess, attrs);
 119         let mut is_deprecated = false;
 120         if let Some((depr, span)) = &depr {
 121             is_deprecated = true;
 122
 123             if kind == AnnotationKind::Prohibited || kind == AnnotationKind::DeprecationProhibited {
 124                 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
 125                 self.tcx.struct_span_lint_hir(USELESS_DEPRECATED, hir_id, *span, |lint| {
 126                     lint.build("this `#[deprecated]` annotation has no effect")
 127                         .span_suggestion_short(
 128                             *span,
 129                             "remove the unnecessary deprecation attribute",
 130                             "",
 131                             rustc_errors::Applicability::MachineApplicable,
 132                         )
 133                         .emit();
 134                 });
 135             }
 136
 137             // `Deprecation` is just two pointers, no need to intern it
 138             let depr_entry = DeprecationEntry::local(*depr, def_id);
 139             self.index.depr_map.insert(def_id, depr_entry);
 140         } else if let Some(parent_depr) = self.parent_depr {
 141             if inherit_deprecation.yes() {
 142                 is_deprecated = true;
 143                 info!("tagging child {:?} as deprecated from parent", def_id);
 144                 self.index.depr_map.insert(def_id, parent_depr);
 145             }
 146         }
 147
 148         if !self.tcx.features().staged_api {
 149             // Propagate unstability.  This can happen even for non-staged-api crates in case
 150             // -Zforce-unstable-if-unmarked is set.
 151             if let Some(stab) = self.parent_stab {
 152                 if inherit_deprecation.yes() && stab.is_unstable() {
 153                     self.index.stab_map.insert(def_id, stab);
 154                 }
 155             }
 156
 157             self.recurse_with_stability_attrs(
 158                 depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 159                 None,
 160                 None,
 161                 visit_children,
 162             );
 163             return;
 164         }
 165
 166         let (stab, const_stab, body_stab) = attr::find_stability(&self.tcx.sess, attrs, item_sp);
 167         let mut const_span = None;
 168
 169         let const_stab = const_stab.map(|(const_stab, const_span_node)| {
 170             self.index.const_stab_map.insert(def_id, const_stab);
 171             const_span = Some(const_span_node);
 172             const_stab
 173         });
 174
 175         // If the current node is a function, has const stability attributes and if it doesn not have an intrinsic ABI,
 176         // check if the function/method is const or the parent impl block is const
 177         if let (Some(const_span), Some(fn_sig)) = (const_span, fn_sig) {
 178             if fn_sig.header.abi != Abi::RustIntrinsic
 179                 && fn_sig.header.abi != Abi::PlatformIntrinsic
 180                 && !fn_sig.header.is_const()
 181             {
 182                 if !self.in_trait_impl
 183                     || (self.in_trait_impl && !self.tcx.is_const_fn_raw(def_id.to_def_id()))
 184                 {
 185                     missing_const_err(&self.tcx.sess, fn_sig.span, const_span);
 186                 }
 187             }
 188         }
 189
 190         // `impl const Trait for Type` items forward their const stability to their
 191         // immediate children.
 192         if const_stab.is_none() {
 193             debug!("annotate: const_stab not found, parent = {:?}", self.parent_const_stab);
 194             if let Some(parent) = self.parent_const_stab {
 195                 if parent.is_const_unstable() {
 196                     self.index.const_stab_map.insert(def_id, parent);
 197                 }
 198             }
 199         }
 200
 201         if let Some((rustc_attr::Deprecation { is_since_rustc_version: true, .. }, span)) = &depr {
 202             if stab.is_none() {
 203                 struct_span_err!(
 204                     self.tcx.sess,
 205                     *span,
 206                     E0549,
 207                     "deprecated attribute must be paired with \
 208                     either stable or unstable attribute"
 209                 )
 210                 .emit();
 211             }
 212         }
 213
 214         if let Some((body_stab, _span)) = body_stab {
 215             // FIXME: check that this item can have body stability
 216
 217             self.index.default_body_stab_map.insert(def_id, body_stab);
 218             debug!(?self.index.default_body_stab_map);
 219         }
 220
 221         let stab = stab.map(|(stab, span)| {
 222             // Error if prohibited, or can't inherit anything from a container.
 223             if kind == AnnotationKind::Prohibited
 224                 || (kind == AnnotationKind::Container && stab.level.is_stable() && is_deprecated)
 225             {
 226                 self.tcx.sess.struct_span_err(span,"this stability annotation is useless")
 227                     .span_label(span, "useless stability annotation")
 228                     .span_label(item_sp, "the stability attribute annotates this item")
 229                     .emit();
 230             }
 231
 232             debug!("annotate: found {:?}", stab);
 233
 234             // Check if deprecated_since < stable_since. If it is,
 235             // this is *almost surely* an accident.
 236             if let (&Some(dep_since), &attr::Stable { since: stab_since, .. }) =
 237                 (&depr.as_ref().and_then(|(d, _)| d.since), &stab.level)
 238             {
 239                 // Explicit version of iter::order::lt to handle parse errors properly
 240                 for (dep_v, stab_v) in
 241                     iter::zip(dep_since.as_str().split('.'), stab_since.as_str().split('.'))
 242                 {
 243                     match stab_v.parse::<u64>() {
 244                         Err(_) => {
 245                             self.tcx.sess.struct_span_err(span, "invalid stability version found")
 246                                 .span_label(span, "invalid stability version")
 247                                 .span_label(item_sp, "the stability attribute annotates this item")
 248                                 .emit();
 249                             break;
 250                         }
 251                         Ok(stab_vp) => match dep_v.parse::<u64>() {
 252                             Ok(dep_vp) => match dep_vp.cmp(&stab_vp) {
 253                                 Ordering::Less => {
 254                                     self.tcx.sess.struct_span_err(span, "an API can't be stabilized after it is deprecated")
 255                                         .span_label(span, "invalid version")
 256                                         .span_label(item_sp, "the stability attribute annotates this item")
 257                                         .emit();
 258                                     break;
 259                                 }
 260                                 Ordering::Equal => continue,
 261                                 Ordering::Greater => break,
 262                             },
 263                             Err(_) => {
 264                                 if dep_v != "TBD" {
 265                                     self.tcx.sess.struct_span_err(span, "invalid deprecation version found")
 266                                         .span_label(span, "invalid deprecation version")
 267                                         .span_label(item_sp, "the stability attribute annotates this item")
 268                                         .emit();
 269                                 }
 270                                 break;
 271                             }
 272                         },
 273                     }
 274                 }
 275             }
 276
 277             if let Stability { level: Unstable { implied_by: Some(implied_by), .. }, feature } = stab {
 278                 self.index.implications.insert(implied_by, feature);
 279             }
 280
 281             self.index.stab_map.insert(def_id, stab);
 282             stab
 283         });
 284
 285         if stab.is_none() {
 286             debug!("annotate: stab not found, parent = {:?}", self.parent_stab);
 287             if let Some(stab) = self.parent_stab {
 288                 if inherit_deprecation.yes() && stab.is_unstable() || inherit_from_parent.yes() {
 289                     self.index.stab_map.insert(def_id, stab);
 290                 }
 291             }
 292         }
 293
 294         self.recurse_with_stability_attrs(
 295             depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 296             stab,
 297             if inherit_const_stability.yes() { const_stab } else { None },
 298             visit_children,
 299         );
 300     }
 301
 302     fn recurse_with_stability_attrs(
 303         &mut self,
 304         depr: Option<DeprecationEntry>,
 305         stab: Option<Stability>,
 306         const_stab: Option<ConstStability>,
 307         f: impl FnOnce(&mut Self),
 308     ) {
 309         // These will be `Some` if this item changes the corresponding stability attribute.
 310         let mut replaced_parent_depr = None;
 311         let mut replaced_parent_stab = None;
 312         let mut replaced_parent_const_stab = None;
 313
 314         if let Some(depr) = depr {
 315             replaced_parent_depr = Some(replace(&mut self.parent_depr, Some(depr)));
 316         }
 317         if let Some(stab) = stab {
 318             replaced_parent_stab = Some(replace(&mut self.parent_stab, Some(stab)));
 319         }
 320         if let Some(const_stab) = const_stab {
 321             replaced_parent_const_stab =
 322                 Some(replace(&mut self.parent_const_stab, Some(const_stab)));
 323         }
 324
 325         f(self);
 326
 327         if let Some(orig_parent_depr) = replaced_parent_depr {
 328             self.parent_depr = orig_parent_depr;
 329         }
 330         if let Some(orig_parent_stab) = replaced_parent_stab {
 331             self.parent_stab = orig_parent_stab;
 332         }
 333         if let Some(orig_parent_const_stab) = replaced_parent_const_stab {
 334             self.parent_const_stab = orig_parent_const_stab;
 335         }
 336     }
 337 }
 338
 339 impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
 340     /// Because stability levels are scoped lexically, we want to walk
 341     /// nested items in the context of the outer item, so enable
 342     /// deep-walking.
 343     type NestedFilter = nested_filter::All;
 344
 345     fn nested_visit_map(&mut self) -> Self::Map {
 346         self.tcx.hir()
 347     }
 348
 349     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 350         let orig_in_trait_impl = self.in_trait_impl;
 351         let mut kind = AnnotationKind::Required;
 352         let mut const_stab_inherit = InheritConstStability::No;
 353         let mut fn_sig = None;
 354
 355         match i.kind {
 356             // Inherent impls and foreign modules serve only as containers for other items,
 357             // they don't have their own stability. They still can be annotated as unstable
 358             // and propagate this instability to children, but this annotation is completely
 359             // optional. They inherit stability from their parents when unannotated.
 360             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 361             | hir::ItemKind::ForeignMod { .. } => {
 362                 self.in_trait_impl = false;
 363                 kind = AnnotationKind::Container;
 364             }
 365             hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => {
 366                 self.in_trait_impl = true;
 367                 kind = AnnotationKind::DeprecationProhibited;
 368                 const_stab_inherit = InheritConstStability::Yes;
 369             }
 370             hir::ItemKind::Struct(ref sd, _) => {
 371                 if let Some(ctor_hir_id) = sd.ctor_hir_id() {
 372                     self.annotate(
 373                         self.tcx.hir().local_def_id(ctor_hir_id),
 374                         i.span,
 375                         None,
 376                         AnnotationKind::Required,
 377                         InheritDeprecation::Yes,
 378                         InheritConstStability::No,
 379                         InheritStability::Yes,
 380                         |_| {},
 381                     )
 382                 }
 383             }
 384             hir::ItemKind::Fn(ref item_fn_sig, _, _) => {
 385                 fn_sig = Some(item_fn_sig);
 386             }
 387             _ => {}
 388         }
 389
 390         self.annotate(
 391             i.def_id,
 392             i.span,
 393             fn_sig,
 394             kind,
 395             InheritDeprecation::Yes,
 396             const_stab_inherit,
 397             InheritStability::No,
 398             |v| intravisit::walk_item(v, i),
 399         );
 400         self.in_trait_impl = orig_in_trait_impl;
 401     }
 402
 403     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 404         let fn_sig = match ti.kind {
 405             hir::TraitItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 406             _ => None,
 407         };
 408
 409         self.annotate(
 410             ti.def_id,
 411             ti.span,
 412             fn_sig,
 413             AnnotationKind::Required,
 414             InheritDeprecation::Yes,
 415             InheritConstStability::No,
 416             InheritStability::No,
 417             |v| {
 418                 intravisit::walk_trait_item(v, ti);
 419             },
 420         );
 421     }
 422
 423     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 424         let kind =
 425             if self.in_trait_impl { AnnotationKind::Prohibited } else { AnnotationKind::Required };
 426
 427         let fn_sig = match ii.kind {
 428             hir::ImplItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 429             _ => None,
 430         };
 431
 432         self.annotate(
 433             ii.def_id,
 434             ii.span,
 435             fn_sig,
 436             kind,
 437             InheritDeprecation::Yes,
 438             InheritConstStability::No,
 439             InheritStability::No,
 440             |v| {
 441                 intravisit::walk_impl_item(v, ii);
 442             },
 443         );
 444     }
 445
 446     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>) {
 447         self.annotate(
 448             self.tcx.hir().local_def_id(var.id),
 449             var.span,
 450             None,
 451             AnnotationKind::Required,
 452             InheritDeprecation::Yes,
 453             InheritConstStability::No,
 454             InheritStability::Yes,
 455             |v| {
 456                 if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
 457                     v.annotate(
 458                         v.tcx.hir().local_def_id(ctor_hir_id),
 459                         var.span,
 460                         None,
 461                         AnnotationKind::Required,
 462                         InheritDeprecation::Yes,
 463                         InheritConstStability::No,
 464                         InheritStability::Yes,
 465                         |_| {},
 466                     );
 467                 }
 468
 469                 intravisit::walk_variant(v, var)
 470             },
 471         )
 472     }
 473
 474     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 475         self.annotate(
 476             self.tcx.hir().local_def_id(s.hir_id),
 477             s.span,
 478             None,
 479             AnnotationKind::Required,
 480             InheritDeprecation::Yes,
 481             InheritConstStability::No,
 482             InheritStability::Yes,
 483             |v| {
 484                 intravisit::walk_field_def(v, s);
 485             },
 486         );
 487     }
 488
 489     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 490         self.annotate(
 491             i.def_id,
 492             i.span,
 493             None,
 494             AnnotationKind::Required,
 495             InheritDeprecation::Yes,
 496             InheritConstStability::No,
 497             InheritStability::No,
 498             |v| {
 499                 intravisit::walk_foreign_item(v, i);
 500             },
 501         );
 502     }
 503
 504     fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
 505         let kind = match &p.kind {
 506             // Allow stability attributes on default generic arguments.
 507             hir::GenericParamKind::Type { default: Some(_), .. }
 508             | hir::GenericParamKind::Const { default: Some(_), .. } => AnnotationKind::Container,
 509             _ => AnnotationKind::Prohibited,
 510         };
 511
 512         self.annotate(
 513             self.tcx.hir().local_def_id(p.hir_id),
 514             p.span,
 515             None,
 516             kind,
 517             InheritDeprecation::No,
 518             InheritConstStability::No,
 519             InheritStability::No,
 520             |v| {
 521                 intravisit::walk_generic_param(v, p);
 522             },
 523         );
 524     }
 525 }
 526
 527 struct MissingStabilityAnnotations<'tcx> {
 528     tcx: TyCtxt<'tcx>,
 529     access_levels: &'tcx AccessLevels,
 530 }
 531
 532 impl<'tcx> MissingStabilityAnnotations<'tcx> {
 533     fn check_missing_stability(&self, def_id: LocalDefId, span: Span) {
 534         let stab = self.tcx.stability().local_stability(def_id);
 535         if !self.tcx.sess.opts.test && stab.is_none() && self.access_levels.is_reachable(def_id) {
 536             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 537             self.tcx.sess.span_err(span, &format!("{} has missing stability attribute", descr));
 538         }
 539     }
 540
 541     fn check_missing_const_stability(&self, def_id: LocalDefId, span: Span) {
 542         if !self.tcx.features().staged_api {
 543             return;
 544         }
 545
 546         let is_const = self.tcx.is_const_fn(def_id.to_def_id())
 547             || self.tcx.is_const_trait_impl_raw(def_id.to_def_id());
 548         let is_stable = self
 549             .tcx
 550             .lookup_stability(def_id)
 551             .map_or(false, |stability| stability.level.is_stable());
 552         let missing_const_stability_attribute = self.tcx.lookup_const_stability(def_id).is_none();
 553         let is_reachable = self.access_levels.is_reachable(def_id);
 554
 555         if is_const && is_stable && missing_const_stability_attribute && is_reachable {
 556             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 557             self.tcx.sess.span_err(span, &format!("{descr} has missing const stability attribute"));
 558         }
 559     }
 560 }
 561
 562 impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
 563     type NestedFilter = nested_filter::OnlyBodies;
 564
 565     fn nested_visit_map(&mut self) -> Self::Map {
 566         self.tcx.hir()
 567     }
 568
 569     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 570         // Inherent impls and foreign modules serve only as containers for other items,
 571         // they don't have their own stability. They still can be annotated as unstable
 572         // and propagate this instability to children, but this annotation is completely
 573         // optional. They inherit stability from their parents when unannotated.
 574         if !matches!(
 575             i.kind,
 576             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 577                 | hir::ItemKind::ForeignMod { .. }
 578         ) {
 579             self.check_missing_stability(i.def_id, i.span);
 580         }
 581
 582         // Ensure stable `const fn` have a const stability attribute.
 583         self.check_missing_const_stability(i.def_id, i.span);
 584
 585         intravisit::walk_item(self, i)
 586     }
 587
 588     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 589         self.check_missing_stability(ti.def_id, ti.span);
 590         intravisit::walk_trait_item(self, ti);
 591     }
 592
 593     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 594         let impl_def_id = self.tcx.hir().get_parent_item(ii.hir_id());
 595         if self.tcx.impl_trait_ref(impl_def_id).is_none() {
 596             self.check_missing_stability(ii.def_id, ii.span);
 597             self.check_missing_const_stability(ii.def_id, ii.span);
 598         }
 599         intravisit::walk_impl_item(self, ii);
 600     }
 601
 602     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>) {
 603         self.check_missing_stability(self.tcx.hir().local_def_id(var.id), var.span);
 604         if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
 605             self.check_missing_stability(self.tcx.hir().local_def_id(ctor_hir_id), var.span);
 606         }
 607         intravisit::walk_variant(self, var);
 608     }
 609
 610     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 611         self.check_missing_stability(self.tcx.hir().local_def_id(s.hir_id), s.span);
 612         intravisit::walk_field_def(self, s);
 613     }
 614
 615     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 616         self.check_missing_stability(i.def_id, i.span);
 617         intravisit::walk_foreign_item(self, i);
 618     }
 619     // Note that we don't need to `check_missing_stability` for default generic parameters,
 620     // as we assume that any default generic parameters without attributes are automatically
 621     // stable (assuming they have not inherited instability from their parent).
 622 }
 623
 624 fn stability_index(tcx: TyCtxt<'_>, (): ()) -> Index {
 625     let mut index = Index {
 626         stab_map: Default::default(),
 627         const_stab_map: Default::default(),
 628         default_body_stab_map: Default::default(),
 629         depr_map: Default::default(),
 630         implications: Default::default(),
 631     };
 632
 633     {
 634         let mut annotator = Annotator {
 635             tcx,
 636             index: &mut index,
 637             parent_stab: None,
 638             parent_const_stab: None,
 639             parent_depr: None,
 640             in_trait_impl: false,
 641         };
 642
 643         // If the `-Z force-unstable-if-unmarked` flag is passed then we provide
 644         // a parent stability annotation which indicates that this is private
 645         // with the `rustc_private` feature. This is intended for use when
 646         // compiling `librustc_*` crates themselves so we can leverage crates.io
 647         // while maintaining the invariant that all sysroot crates are unstable
 648         // by default and are unable to be used.
 649         if tcx.sess.opts.unstable_opts.force_unstable_if_unmarked {
 650             let stability = Stability {
 651                 level: attr::StabilityLevel::Unstable {
 652                     reason: UnstableReason::Default,
 653                     issue: NonZeroU32::new(27812),
 654                     is_soft: false,
 655                     implied_by: None,
 656                 },
 657                 feature: sym::rustc_private,
 658             };
 659             annotator.parent_stab = Some(stability);
 660         }
 661
 662         annotator.annotate(
 663             CRATE_DEF_ID,
 664             tcx.hir().span(CRATE_HIR_ID),
 665             None,
 666             AnnotationKind::Required,
 667             InheritDeprecation::Yes,
 668             InheritConstStability::No,
 669             InheritStability::No,
 670             |v| tcx.hir().walk_toplevel_module(v),
 671         );
 672     }
 673     index
 674 }
 675
 676 /// Cross-references the feature names of unstable APIs with enabled
 677 /// features and possibly prints errors.
 678 fn check_mod_unstable_api_usage(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 679     tcx.hir().visit_item_likes_in_module(module_def_id, &mut Checker { tcx });
 680 }
 681
 682 pub(crate) fn provide(providers: &mut Providers) {
 683     *providers = Providers {
 684         check_mod_unstable_api_usage,
 685         stability_index,
 686         stability_implications: |tcx, _| tcx.stability().implications.clone(),
 687         lookup_stability: |tcx, id| tcx.stability().local_stability(id.expect_local()),
 688         lookup_const_stability: |tcx, id| tcx.stability().local_const_stability(id.expect_local()),
 689         lookup_default_body_stability: |tcx, id| {
 690             tcx.stability().local_default_body_stability(id.expect_local())
 691         },
 692         lookup_deprecation_entry: |tcx, id| {
 693             tcx.stability().local_deprecation_entry(id.expect_local())
 694         },
 695         ..*providers
 696     };
 697 }
 698
 699 struct Checker<'tcx> {
 700     tcx: TyCtxt<'tcx>,
 701 }
 702
 703 impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
 704     type NestedFilter = nested_filter::OnlyBodies;
 705
 706     /// Because stability levels are scoped lexically, we want to walk
 707     /// nested items in the context of the outer item, so enable
 708     /// deep-walking.
 709     fn nested_visit_map(&mut self) -> Self::Map {
 710         self.tcx.hir()
 711     }
 712
 713     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 714         match item.kind {
 715             hir::ItemKind::ExternCrate(_) => {
 716                 // compiler-generated `extern crate` items have a dummy span.
 717                 // `std` is still checked for the `restricted-std` feature.
 718                 if item.span.is_dummy() && item.ident.name != sym::std {
 719                     return;
 720                 }
 721
 722                 let Some(cnum) = self.tcx.extern_mod_stmt_cnum(item.def_id) else {
 723                     return;
 724                 };
 725                 let def_id = cnum.as_def_id();
 726                 self.tcx.check_stability(def_id, Some(item.hir_id()), item.span, None);
 727             }
 728
 729             // For implementations of traits, check the stability of each item
 730             // individually as it's possible to have a stable trait with unstable
 731             // items.
 732             hir::ItemKind::Impl(hir::Impl {
 733                 of_trait: Some(ref t),
 734                 self_ty,
 735                 items,
 736                 constness,
 737                 ..
 738             }) => {
 739                 let features = self.tcx.features();
 740                 if features.staged_api {
 741                     let attrs = self.tcx.hir().attrs(item.hir_id());
 742                     let (stab, const_stab, _) =
 743                         attr::find_stability(&self.tcx.sess, attrs, item.span);
 744
 745                     // If this impl block has an #[unstable] attribute, give an
 746                     // error if all involved types and traits are stable, because
 747                     // it will have no effect.
 748                     // See: https://github.com/rust-lang/rust/issues/55436
 749                     if let Some((Stability { level: attr::Unstable { .. }, .. }, span)) = stab {
 750                         let mut c = CheckTraitImplStable { tcx: self.tcx, fully_stable: true };
 751                         c.visit_ty(self_ty);
 752                         c.visit_trait_ref(t);
 753                         if c.fully_stable {
 754                             self.tcx.struct_span_lint_hir(
 755                                 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
 756                                 item.hir_id(),
 757                                 span,
 758                                 |lint| {lint
 759                                     .build("an `#[unstable]` annotation here has no effect")
 760                                     .note("see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information")
 761                                     .emit();}
 762                             );
 763                         }
 764                     }
 765
 766                     // `#![feature(const_trait_impl)]` is unstable, so any impl declared stable
 767                     // needs to have an error emitted.
 768                     if features.const_trait_impl
 769                         && *constness == hir::Constness::Const
 770                         && const_stab.map_or(false, |(stab, _)| stab.is_const_stable())
 771                     {
 772                         self.tcx
 773                             .sess
 774                             .struct_span_err(item.span, "trait implementations cannot be const stable yet")
 775                             .note("see issue #67792 <https://github.com/rust-lang/rust/issues/67792> for more information")
 776                             .emit();
 777                     }
 778                 }
 779
 780                 for impl_item_ref in *items {
 781                     let impl_item = self.tcx.associated_item(impl_item_ref.id.def_id);
 782
 783                     if let Some(def_id) = impl_item.trait_item_def_id {
 784                         // Pass `None` to skip deprecation warnings.
 785                         self.tcx.check_stability(def_id, None, impl_item_ref.span, None);
 786                     }
 787                 }
 788             }
 789
 790             _ => (/* pass */),
 791         }
 792         intravisit::walk_item(self, item);
 793     }
 794
 795     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, id: hir::HirId) {
 796         if let Some(def_id) = path.res.opt_def_id() {
 797             let method_span = path.segments.last().map(|s| s.ident.span);
 798             let item_is_allowed = self.tcx.check_stability_allow_unstable(
 799                 def_id,
 800                 Some(id),
 801                 path.span,
 802                 method_span,
 803                 if is_unstable_reexport(self.tcx, id) {
 804                     AllowUnstable::Yes
 805                 } else {
 806                     AllowUnstable::No
 807                 },
 808             );
 809
 810             let is_allowed_through_unstable_modules = |def_id| {
 811                 self.tcx
 812                     .lookup_stability(def_id)
 813                     .map(|stab| match stab.level {
 814                         StabilityLevel::Stable { allowed_through_unstable_modules, .. } => {
 815                             allowed_through_unstable_modules
 816                         }
 817                         _ => false,
 818                     })
 819                     .unwrap_or(false)
 820             };
 821
 822             if item_is_allowed && !is_allowed_through_unstable_modules(def_id) {
 823                 // Check parent modules stability as well if the item the path refers to is itself
 824                 // stable. We only emit warnings for unstable path segments if the item is stable
 825                 // or allowed because stability is often inherited, so the most common case is that
 826                 // both the segments and the item are unstable behind the same feature flag.
 827                 //
 828                 // We check here rather than in `visit_path_segment` to prevent visiting the last
 829                 // path segment twice
 830                 //
 831                 // We include special cases via #[rustc_allowed_through_unstable_modules] for items
 832                 // that were accidentally stabilized through unstable paths before this check was
 833                 // added, such as `core::intrinsics::transmute`
 834                 let parents = path.segments.iter().rev().skip(1);
 835                 for path_segment in parents {
 836                     if let Some(def_id) = path_segment.res.opt_def_id() {
 837                         // use `None` for id to prevent deprecation check
 838                         self.tcx.check_stability_allow_unstable(
 839                             def_id,
 840                             None,
 841                             path.span,
 842                             None,
 843                             if is_unstable_reexport(self.tcx, id) {
 844                                 AllowUnstable::Yes
 845                             } else {
 846                                 AllowUnstable::No
 847                             },
 848                         );
 849                     }
 850                 }
 851             }
 852         }
 853
 854         intravisit::walk_path(self, path)
 855     }
 856 }
 857
 858 /// Check whether a path is a `use` item that has been marked as unstable.
 859 ///
 860 /// See issue #94972 for details on why this is a special case
 861 fn is_unstable_reexport<'tcx>(tcx: TyCtxt<'tcx>, id: hir::HirId) -> bool {
 862     // Get the LocalDefId so we can lookup the item to check the kind.
 863     let Some(def_id) = tcx.hir().opt_local_def_id(id) else { return false; };
 864
 865     let Some(stab) = tcx.stability().local_stability(def_id) else {
 866         return false;
 867     };
 868
 869     if stab.level.is_stable() {
 870         // The re-export is not marked as unstable, don't override
 871         return false;
 872     }
 873
 874     // If this is a path that isn't a use, we don't need to do anything special
 875     if !matches!(tcx.hir().item(hir::ItemId { def_id }).kind, ItemKind::Use(..)) {
 876         return false;
 877     }
 878
 879     true
 880 }
 881
 882 struct CheckTraitImplStable<'tcx> {
 883     tcx: TyCtxt<'tcx>,
 884     fully_stable: bool,
 885 }
 886
 887 impl<'tcx> Visitor<'tcx> for CheckTraitImplStable<'tcx> {
 888     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _id: hir::HirId) {
 889         if let Some(def_id) = path.res.opt_def_id() {
 890             if let Some(stab) = self.tcx.lookup_stability(def_id) {
 891                 self.fully_stable &= stab.level.is_stable();
 892             }
 893         }
 894         intravisit::walk_path(self, path)
 895     }
 896
 897     fn visit_trait_ref(&mut self, t: &'tcx TraitRef<'tcx>) {
 898         if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
 899             if let Some(stab) = self.tcx.lookup_stability(trait_did) {
 900                 self.fully_stable &= stab.level.is_stable();
 901             }
 902         }
 903         intravisit::walk_trait_ref(self, t)
 904     }
 905
 906     fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
 907         if let TyKind::Never = t.kind {
 908             self.fully_stable = false;
 909         }
 910         intravisit::walk_ty(self, t)
 911     }
 912 }
 913
 914 /// Given the list of enabled features that were not language features (i.e., that
 915 /// were expected to be library features), and the list of features used from
 916 /// libraries, identify activated features that don't exist and error about them.
 917 pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
 918     let is_staged_api =
 919         tcx.sess.opts.unstable_opts.force_unstable_if_unmarked || tcx.features().staged_api;
 920     if is_staged_api {
 921         let access_levels = &tcx.privacy_access_levels(());
 922         let mut missing = MissingStabilityAnnotations { tcx, access_levels };
 923         missing.check_missing_stability(CRATE_DEF_ID, tcx.hir().span(CRATE_HIR_ID));
 924         tcx.hir().walk_toplevel_module(&mut missing);
 925         tcx.hir().visit_all_item_likes_in_crate(&mut missing);
 926     }
 927
 928     let declared_lang_features = &tcx.features().declared_lang_features;
 929     let mut lang_features = FxHashSet::default();
 930     for &(feature, span, since) in declared_lang_features {
 931         if let Some(since) = since {
 932             // Warn if the user has enabled an already-stable lang feature.
 933             unnecessary_stable_feature_lint(tcx, span, feature, since);
 934         }
 935         if !lang_features.insert(feature) {
 936             // Warn if the user enables a lang feature multiple times.
 937             duplicate_feature_err(tcx.sess, span, feature);
 938         }
 939     }
 940
 941     let declared_lib_features = &tcx.features().declared_lib_features;
 942     let mut remaining_lib_features = FxIndexMap::default();
 943     for (feature, span) in declared_lib_features {
 944         if !tcx.sess.opts.unstable_features.is_nightly_build() {
 945             struct_span_err!(
 946                 tcx.sess,
 947                 *span,
 948                 E0554,
 949                 "`#![feature]` may not be used on the {} release channel",
 950                 env!("CFG_RELEASE_CHANNEL")
 951             )
 952             .emit();
 953         }
 954         if remaining_lib_features.contains_key(&feature) {
 955             // Warn if the user enables a lib feature multiple times.
 956             duplicate_feature_err(tcx.sess, *span, *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         struct_span_err!(tcx.sess, span, E0635, "unknown feature `{}`", feature).emit();
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
1069             .struct_span_err(
1070                 *span,
1071                 format!("feature `{implied_by}` implying `{feature}` does not exist"),
1072             )
1073             .emit();
1074     }
1075
1076     // FIXME(#44232): the `used_features` table no longer exists, so we
1077     // don't lint about unused features. We should re-enable this one day!
1078 }
1079
1080 fn unnecessary_partially_stable_feature_lint(
1081     tcx: TyCtxt<'_>,
1082     span: Span,
1083     feature: Symbol,
1084     implies: Symbol,
1085     since: Symbol,
1086 ) {
1087     tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
1088         lint.build(&format!(
1089             "the feature `{feature}` has been partially stabilized since {since} and is succeeded \
1090              by the feature `{implies}`"
1091         ))
1092         .span_suggestion(
1093             span,
1094             &format!(
1095                 "if you are using features which are still unstable, change to using `{implies}`"
1096             ),
1097             implies,
1098             Applicability::MaybeIncorrect,
1099         )
1100         .span_suggestion(
1101             tcx.sess.source_map().span_extend_to_line(span),
1102             "if you are using features which are now stable, remove this line",
1103             "",
1104             Applicability::MaybeIncorrect,
1105         )
1106         .emit();
1107     });
1108 }
1109
1110 fn unnecessary_stable_feature_lint(
1111     tcx: TyCtxt<'_>,
1112     span: Span,
1113     feature: Symbol,
1114     mut since: Symbol,
1115 ) {
1116     if since.as_str() == VERSION_PLACEHOLDER {
1117         since = rust_version_symbol();
1118     }
1119     tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
1120         lint.build(&format!(
1121             "the feature `{feature}` has been stable since {since} and no longer requires an \
1122              attribute to enable",
1123         ))
1124         .emit();
1125     });
1126 }
1127
1128 fn duplicate_feature_err(sess: &Session, span: Span, feature: Symbol) {
1129     struct_span_err!(sess, span, E0636, "the feature `{}` has already been declared", feature)
1130         .emit();
1131 }
1132
1133 fn missing_const_err(session: &Session, fn_sig_span: Span, const_span: Span) {
1134     const ERROR_MSG: &'static str = "attributes `#[rustc_const_unstable]` \
1135          and `#[rustc_const_stable]` require \
1136          the function or method to be `const`";
1137
1138     session
1139         .struct_span_err(fn_sig_span, ERROR_MSG)
1140         .span_help(fn_sig_span, "make the function or method const")
1141         .span_label(const_span, "attribute specified here")
1142         .emit();
1143 }