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, ConstStability, Stability, StabilityLevel, Unstable, UnstableReason,
   6 };
   7 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
   8 use rustc_errors::{struct_span_err, Applicability};
   9 use rustc_hir as hir;
  10 use rustc_hir::def::{DefKind, Res};
  11 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
  12 use rustc_hir::hir_id::CRATE_HIR_ID;
  13 use rustc_hir::intravisit::{self, Visitor};
  14 use rustc_hir::{FieldDef, Generics, HirId, Item, ItemKind, TraitRef, Ty, TyKind, Variant};
  15 use rustc_middle::hir::nested_filter;
  16 use rustc_middle::middle::privacy::AccessLevels;
  17 use rustc_middle::middle::stability::{AllowUnstable, DeprecationEntry, Index};
  18 use rustc_middle::ty::{query::Providers, TyCtxt};
  19 use rustc_session::lint;
  20 use rustc_session::lint::builtin::{INEFFECTIVE_UNSTABLE_TRAIT_IMPL, USELESS_DEPRECATED};
  21 use rustc_session::Session;
  22 use rustc_span::symbol::{sym, Symbol};
  23 use rustc_span::Span;
  24 use rustc_target::spec::abi::Abi;
  25
  26 use std::cmp::Ordering;
  27 use std::iter;
  28 use std::mem::replace;
  29 use std::num::NonZeroU32;
  30
  31 #[derive(PartialEq)]
  32 enum AnnotationKind {
  33     /// Annotation is required if not inherited from unstable parents.
  34     Required,
  35     /// Annotation is useless, reject it.
  36     Prohibited,
  37     /// Deprecation annotation is useless, reject it. (Stability attribute is still required.)
  38     DeprecationProhibited,
  39     /// Annotation itself is useless, but it can be propagated to children.
  40     Container,
  41 }
  42
  43 /// Whether to inherit deprecation flags for nested items. In most cases, we do want to inherit
  44 /// deprecation, because nested items rarely have individual deprecation attributes, and so
  45 /// should be treated as deprecated if their parent is. However, default generic parameters
  46 /// have separate deprecation attributes from their parents, so we do not wish to inherit
  47 /// deprecation in this case. For example, inheriting deprecation for `T` in `Foo<T>`
  48 /// would cause a duplicate warning arising from both `Foo` and `T` being deprecated.
  49 #[derive(Clone)]
  50 enum InheritDeprecation {
  51     Yes,
  52     No,
  53 }
  54
  55 impl InheritDeprecation {
  56     fn yes(&self) -> bool {
  57         matches!(self, InheritDeprecation::Yes)
  58     }
  59 }
  60
  61 /// Whether to inherit const stability flags for nested items. In most cases, we do not want to
  62 /// inherit const stability: just because an enclosing `fn` is const-stable does not mean
  63 /// all `extern` imports declared in it should be const-stable! However, trait methods
  64 /// inherit const stability attributes from their parent and do not have their own.
  65 enum InheritConstStability {
  66     Yes,
  67     No,
  68 }
  69
  70 impl InheritConstStability {
  71     fn yes(&self) -> bool {
  72         matches!(self, InheritConstStability::Yes)
  73     }
  74 }
  75
  76 enum InheritStability {
  77     Yes,
  78     No,
  79 }
  80
  81 impl InheritStability {
  82     fn yes(&self) -> bool {
  83         matches!(self, InheritStability::Yes)
  84     }
  85 }
  86
  87 /// A private tree-walker for producing an `Index`.
  88 struct Annotator<'a, 'tcx> {
  89     tcx: TyCtxt<'tcx>,
  90     index: &'a mut Index,
  91     parent_stab: Option<Stability>,
  92     parent_const_stab: Option<ConstStability>,
  93     parent_depr: Option<DeprecationEntry>,
  94     in_trait_impl: bool,
  95 }
  96
  97 impl<'a, 'tcx> Annotator<'a, 'tcx> {
  98     /// Determine the stability for a node based on its attributes and inherited stability. The
  99     /// stability is recorded in the index and used as the parent. If the node is a function,
 100     /// `fn_sig` is its signature.
 101     fn annotate<F>(
 102         &mut self,
 103         def_id: LocalDefId,
 104         item_sp: Span,
 105         fn_sig: Option<&'tcx hir::FnSig<'tcx>>,
 106         kind: AnnotationKind,
 107         inherit_deprecation: InheritDeprecation,
 108         inherit_const_stability: InheritConstStability,
 109         inherit_from_parent: InheritStability,
 110         visit_children: F,
 111     ) where
 112         F: FnOnce(&mut Self),
 113     {
 114         let attrs = self.tcx.hir().attrs(self.tcx.hir().local_def_id_to_hir_id(def_id));
 115         debug!("annotate(id = {:?}, attrs = {:?})", def_id, attrs);
 116
 117         let depr = attr::find_deprecation(&self.tcx.sess, attrs);
 118         let mut is_deprecated = false;
 119         if let Some((depr, span)) = &depr {
 120             is_deprecated = true;
 121
 122             if kind == AnnotationKind::Prohibited || kind == AnnotationKind::DeprecationProhibited {
 123                 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
 124                 self.tcx.struct_span_lint_hir(USELESS_DEPRECATED, hir_id, *span, |lint| {
 125                     lint.build("this `#[deprecated]` annotation has no effect")
 126                         .span_suggestion_short(
 127                             *span,
 128                             "remove the unnecessary deprecation attribute",
 129                             "",
 130                             rustc_errors::Applicability::MachineApplicable,
 131                         )
 132                         .emit();
 133                 });
 134             }
 135
 136             // `Deprecation` is just two pointers, no need to intern it
 137             let depr_entry = DeprecationEntry::local(*depr, def_id);
 138             self.index.depr_map.insert(def_id, depr_entry);
 139         } else if let Some(parent_depr) = self.parent_depr {
 140             if inherit_deprecation.yes() {
 141                 is_deprecated = true;
 142                 info!("tagging child {:?} as deprecated from parent", def_id);
 143                 self.index.depr_map.insert(def_id, parent_depr);
 144             }
 145         }
 146
 147         if !self.tcx.features().staged_api {
 148             // Propagate unstability.  This can happen even for non-staged-api crates in case
 149             // -Zforce-unstable-if-unmarked is set.
 150             if let Some(stab) = self.parent_stab {
 151                 if inherit_deprecation.yes() && stab.is_unstable() {
 152                     self.index.stab_map.insert(def_id, stab);
 153                 }
 154             }
 155
 156             self.recurse_with_stability_attrs(
 157                 depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 158                 None,
 159                 None,
 160                 visit_children,
 161             );
 162             return;
 163         }
 164
 165         let (stab, const_stab, body_stab) = attr::find_stability(&self.tcx.sess, attrs, item_sp);
 166         let mut const_span = None;
 167
 168         let const_stab = const_stab.map(|(const_stab, const_span_node)| {
 169             self.index.const_stab_map.insert(def_id, const_stab);
 170             const_span = Some(const_span_node);
 171             const_stab
 172         });
 173
 174         // If the current node is a function, has const stability attributes and if it doesn not have an intrinsic ABI,
 175         // check if the function/method is const or the parent impl block is const
 176         if let (Some(const_span), Some(fn_sig)) = (const_span, fn_sig) {
 177             if fn_sig.header.abi != Abi::RustIntrinsic
 178                 && fn_sig.header.abi != Abi::PlatformIntrinsic
 179                 && !fn_sig.header.is_const()
 180             {
 181                 if !self.in_trait_impl
 182                     || (self.in_trait_impl && !self.tcx.is_const_fn_raw(def_id.to_def_id()))
 183                 {
 184                     missing_const_err(&self.tcx.sess, fn_sig.span, const_span);
 185                 }
 186             }
 187         }
 188
 189         // `impl const Trait for Type` items forward their const stability to their
 190         // immediate children.
 191         if const_stab.is_none() {
 192             debug!("annotate: const_stab not found, parent = {:?}", self.parent_const_stab);
 193             if let Some(parent) = self.parent_const_stab {
 194                 if parent.is_const_unstable() {
 195                     self.index.const_stab_map.insert(def_id, parent);
 196                 }
 197             }
 198         }
 199
 200         if let Some((rustc_attr::Deprecation { is_since_rustc_version: true, .. }, span)) = &depr {
 201             if stab.is_none() {
 202                 struct_span_err!(
 203                     self.tcx.sess,
 204                     *span,
 205                     E0549,
 206                     "deprecated attribute must be paired with \
 207                     either stable or unstable attribute"
 208                 )
 209                 .emit();
 210             }
 211         }
 212
 213         if let Some((body_stab, _span)) = body_stab {
 214             // FIXME: check that this item can have body stability
 215
 216             self.index.default_body_stab_map.insert(def_id, body_stab);
 217             debug!(?self.index.default_body_stab_map);
 218         }
 219
 220         let stab = stab.map(|(stab, span)| {
 221             // Error if prohibited, or can't inherit anything from a container.
 222             if kind == AnnotationKind::Prohibited
 223                 || (kind == AnnotationKind::Container && stab.level.is_stable() && is_deprecated)
 224             {
 225                 self.tcx.sess.struct_span_err(span,"this stability annotation is useless")
 226                     .span_label(span, "useless stability annotation")
 227                     .span_label(item_sp, "the stability attribute annotates this item")
 228                     .emit();
 229             }
 230
 231             debug!("annotate: found {:?}", stab);
 232
 233             // Check if deprecated_since < stable_since. If it is,
 234             // this is *almost surely* an accident.
 235             if let (&Some(dep_since), &attr::Stable { since: stab_since, .. }) =
 236                 (&depr.as_ref().and_then(|(d, _)| d.since), &stab.level)
 237             {
 238                 // Explicit version of iter::order::lt to handle parse errors properly
 239                 for (dep_v, stab_v) in
 240                     iter::zip(dep_since.as_str().split('.'), stab_since.as_str().split('.'))
 241                 {
 242                     match stab_v.parse::<u64>() {
 243                         Err(_) => {
 244                             self.tcx.sess.struct_span_err(span, "invalid stability version found")
 245                                 .span_label(span, "invalid stability version")
 246                                 .span_label(item_sp, "the stability attribute annotates this item")
 247                                 .emit();
 248                             break;
 249                         }
 250                         Ok(stab_vp) => match dep_v.parse::<u64>() {
 251                             Ok(dep_vp) => match dep_vp.cmp(&stab_vp) {
 252                                 Ordering::Less => {
 253                                     self.tcx.sess.struct_span_err(span, "an API can't be stabilized after it is deprecated")
 254                                         .span_label(span, "invalid version")
 255                                         .span_label(item_sp, "the stability attribute annotates this item")
 256                                         .emit();
 257                                     break;
 258                                 }
 259                                 Ordering::Equal => continue,
 260                                 Ordering::Greater => break,
 261                             },
 262                             Err(_) => {
 263                                 if dep_v != "TBD" {
 264                                     self.tcx.sess.struct_span_err(span, "invalid deprecation version found")
 265                                         .span_label(span, "invalid deprecation version")
 266                                         .span_label(item_sp, "the stability attribute annotates this item")
 267                                         .emit();
 268                                 }
 269                                 break;
 270                             }
 271                         },
 272                     }
 273                 }
 274             }
 275
 276             if let Stability { level: Unstable { implied_by: Some(implied_by), .. }, feature } = stab {
 277                 self.index.implications.insert(implied_by, feature);
 278             }
 279
 280             self.index.stab_map.insert(def_id, stab);
 281             stab
 282         });
 283
 284         if stab.is_none() {
 285             debug!("annotate: stab not found, parent = {:?}", self.parent_stab);
 286             if let Some(stab) = self.parent_stab {
 287                 if inherit_deprecation.yes() && stab.is_unstable() || inherit_from_parent.yes() {
 288                     self.index.stab_map.insert(def_id, stab);
 289                 }
 290             }
 291         }
 292
 293         self.recurse_with_stability_attrs(
 294             depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 295             stab,
 296             if inherit_const_stability.yes() { const_stab } else { None },
 297             visit_children,
 298         );
 299     }
 300
 301     fn recurse_with_stability_attrs(
 302         &mut self,
 303         depr: Option<DeprecationEntry>,
 304         stab: Option<Stability>,
 305         const_stab: Option<ConstStability>,
 306         f: impl FnOnce(&mut Self),
 307     ) {
 308         // These will be `Some` if this item changes the corresponding stability attribute.
 309         let mut replaced_parent_depr = None;
 310         let mut replaced_parent_stab = None;
 311         let mut replaced_parent_const_stab = None;
 312
 313         if let Some(depr) = depr {
 314             replaced_parent_depr = Some(replace(&mut self.parent_depr, Some(depr)));
 315         }
 316         if let Some(stab) = stab {
 317             replaced_parent_stab = Some(replace(&mut self.parent_stab, Some(stab)));
 318         }
 319         if let Some(const_stab) = const_stab {
 320             replaced_parent_const_stab =
 321                 Some(replace(&mut self.parent_const_stab, Some(const_stab)));
 322         }
 323
 324         f(self);
 325
 326         if let Some(orig_parent_depr) = replaced_parent_depr {
 327             self.parent_depr = orig_parent_depr;
 328         }
 329         if let Some(orig_parent_stab) = replaced_parent_stab {
 330             self.parent_stab = orig_parent_stab;
 331         }
 332         if let Some(orig_parent_const_stab) = replaced_parent_const_stab {
 333             self.parent_const_stab = orig_parent_const_stab;
 334         }
 335     }
 336 }
 337
 338 impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
 339     /// Because stability levels are scoped lexically, we want to walk
 340     /// nested items in the context of the outer item, so enable
 341     /// deep-walking.
 342     type NestedFilter = nested_filter::All;
 343
 344     fn nested_visit_map(&mut self) -> Self::Map {
 345         self.tcx.hir()
 346     }
 347
 348     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 349         let orig_in_trait_impl = self.in_trait_impl;
 350         let mut kind = AnnotationKind::Required;
 351         let mut const_stab_inherit = InheritConstStability::No;
 352         let mut fn_sig = None;
 353
 354         match i.kind {
 355             // Inherent impls and foreign modules serve only as containers for other items,
 356             // they don't have their own stability. They still can be annotated as unstable
 357             // and propagate this instability to children, but this annotation is completely
 358             // optional. They inherit stability from their parents when unannotated.
 359             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 360             | hir::ItemKind::ForeignMod { .. } => {
 361                 self.in_trait_impl = false;
 362                 kind = AnnotationKind::Container;
 363             }
 364             hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => {
 365                 self.in_trait_impl = true;
 366                 kind = AnnotationKind::DeprecationProhibited;
 367                 const_stab_inherit = InheritConstStability::Yes;
 368             }
 369             hir::ItemKind::Struct(ref sd, _) => {
 370                 if let Some(ctor_hir_id) = sd.ctor_hir_id() {
 371                     self.annotate(
 372                         self.tcx.hir().local_def_id(ctor_hir_id),
 373                         i.span,
 374                         None,
 375                         AnnotationKind::Required,
 376                         InheritDeprecation::Yes,
 377                         InheritConstStability::No,
 378                         InheritStability::Yes,
 379                         |_| {},
 380                     )
 381                 }
 382             }
 383             hir::ItemKind::Fn(ref item_fn_sig, _, _) => {
 384                 fn_sig = Some(item_fn_sig);
 385             }
 386             _ => {}
 387         }
 388
 389         self.annotate(
 390             i.def_id,
 391             i.span,
 392             fn_sig,
 393             kind,
 394             InheritDeprecation::Yes,
 395             const_stab_inherit,
 396             InheritStability::No,
 397             |v| intravisit::walk_item(v, i),
 398         );
 399         self.in_trait_impl = orig_in_trait_impl;
 400     }
 401
 402     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 403         let fn_sig = match ti.kind {
 404             hir::TraitItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 405             _ => None,
 406         };
 407
 408         self.annotate(
 409             ti.def_id,
 410             ti.span,
 411             fn_sig,
 412             AnnotationKind::Required,
 413             InheritDeprecation::Yes,
 414             InheritConstStability::No,
 415             InheritStability::No,
 416             |v| {
 417                 intravisit::walk_trait_item(v, ti);
 418             },
 419         );
 420     }
 421
 422     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 423         let kind =
 424             if self.in_trait_impl { AnnotationKind::Prohibited } else { AnnotationKind::Required };
 425
 426         let fn_sig = match ii.kind {
 427             hir::ImplItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 428             _ => None,
 429         };
 430
 431         self.annotate(
 432             ii.def_id,
 433             ii.span,
 434             fn_sig,
 435             kind,
 436             InheritDeprecation::Yes,
 437             InheritConstStability::No,
 438             InheritStability::No,
 439             |v| {
 440                 intravisit::walk_impl_item(v, ii);
 441             },
 442         );
 443     }
 444
 445     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 446         self.annotate(
 447             self.tcx.hir().local_def_id(var.id),
 448             var.span,
 449             None,
 450             AnnotationKind::Required,
 451             InheritDeprecation::Yes,
 452             InheritConstStability::No,
 453             InheritStability::Yes,
 454             |v| {
 455                 if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
 456                     v.annotate(
 457                         v.tcx.hir().local_def_id(ctor_hir_id),
 458                         var.span,
 459                         None,
 460                         AnnotationKind::Required,
 461                         InheritDeprecation::Yes,
 462                         InheritConstStability::No,
 463                         InheritStability::No,
 464                         |_| {},
 465                     );
 466                 }
 467
 468                 intravisit::walk_variant(v, var, g, item_id)
 469             },
 470         )
 471     }
 472
 473     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 474         self.annotate(
 475             self.tcx.hir().local_def_id(s.hir_id),
 476             s.span,
 477             None,
 478             AnnotationKind::Required,
 479             InheritDeprecation::Yes,
 480             InheritConstStability::No,
 481             InheritStability::Yes,
 482             |v| {
 483                 intravisit::walk_field_def(v, s);
 484             },
 485         );
 486     }
 487
 488     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 489         self.annotate(
 490             i.def_id,
 491             i.span,
 492             None,
 493             AnnotationKind::Required,
 494             InheritDeprecation::Yes,
 495             InheritConstStability::No,
 496             InheritStability::No,
 497             |v| {
 498                 intravisit::walk_foreign_item(v, i);
 499             },
 500         );
 501     }
 502
 503     fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
 504         let kind = match &p.kind {
 505             // Allow stability attributes on default generic arguments.
 506             hir::GenericParamKind::Type { default: Some(_), .. }
 507             | hir::GenericParamKind::Const { default: Some(_), .. } => AnnotationKind::Container,
 508             _ => AnnotationKind::Prohibited,
 509         };
 510
 511         self.annotate(
 512             self.tcx.hir().local_def_id(p.hir_id),
 513             p.span,
 514             None,
 515             kind,
 516             InheritDeprecation::No,
 517             InheritConstStability::No,
 518             InheritStability::No,
 519             |v| {
 520                 intravisit::walk_generic_param(v, p);
 521             },
 522         );
 523     }
 524 }
 525
 526 struct MissingStabilityAnnotations<'tcx> {
 527     tcx: TyCtxt<'tcx>,
 528     access_levels: &'tcx AccessLevels,
 529 }
 530
 531 impl<'tcx> MissingStabilityAnnotations<'tcx> {
 532     fn check_missing_stability(&self, def_id: LocalDefId, span: Span) {
 533         let stab = self.tcx.stability().local_stability(def_id);
 534         if !self.tcx.sess.opts.test && stab.is_none() && self.access_levels.is_reachable(def_id) {
 535             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 536             self.tcx.sess.span_err(span, &format!("{} has missing stability attribute", descr));
 537         }
 538     }
 539
 540     fn check_missing_const_stability(&self, def_id: LocalDefId, span: Span) {
 541         if !self.tcx.features().staged_api {
 542             return;
 543         }
 544
 545         let is_const = self.tcx.is_const_fn(def_id.to_def_id())
 546             || self.tcx.is_const_trait_impl_raw(def_id.to_def_id());
 547         let is_stable = self
 548             .tcx
 549             .lookup_stability(def_id)
 550             .map_or(false, |stability| stability.level.is_stable());
 551         let missing_const_stability_attribute = self.tcx.lookup_const_stability(def_id).is_none();
 552         let is_reachable = self.access_levels.is_reachable(def_id);
 553
 554         if is_const && is_stable && missing_const_stability_attribute && is_reachable {
 555             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 556             self.tcx.sess.span_err(span, &format!("{descr} has missing const stability attribute"));
 557         }
 558     }
 559 }
 560
 561 impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
 562     type NestedFilter = nested_filter::OnlyBodies;
 563
 564     fn nested_visit_map(&mut self) -> Self::Map {
 565         self.tcx.hir()
 566     }
 567
 568     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 569         // Inherent impls and foreign modules serve only as containers for other items,
 570         // they don't have their own stability. They still can be annotated as unstable
 571         // and propagate this instability to children, but this annotation is completely
 572         // optional. They inherit stability from their parents when unannotated.
 573         if !matches!(
 574             i.kind,
 575             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 576                 | hir::ItemKind::ForeignMod { .. }
 577         ) {
 578             self.check_missing_stability(i.def_id, i.span);
 579         }
 580
 581         // Ensure stable `const fn` have a const stability attribute.
 582         self.check_missing_const_stability(i.def_id, i.span);
 583
 584         intravisit::walk_item(self, i)
 585     }
 586
 587     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 588         self.check_missing_stability(ti.def_id, ti.span);
 589         intravisit::walk_trait_item(self, ti);
 590     }
 591
 592     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 593         let impl_def_id = self.tcx.hir().get_parent_item(ii.hir_id());
 594         if self.tcx.impl_trait_ref(impl_def_id).is_none() {
 595             self.check_missing_stability(ii.def_id, ii.span);
 596             self.check_missing_const_stability(ii.def_id, ii.span);
 597         }
 598         intravisit::walk_impl_item(self, ii);
 599     }
 600
 601     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 602         self.check_missing_stability(self.tcx.hir().local_def_id(var.id), var.span);
 603         intravisit::walk_variant(self, var, g, item_id);
 604     }
 605
 606     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 607         self.check_missing_stability(self.tcx.hir().local_def_id(s.hir_id), s.span);
 608         intravisit::walk_field_def(self, s);
 609     }
 610
 611     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 612         self.check_missing_stability(i.def_id, i.span);
 613         intravisit::walk_foreign_item(self, i);
 614     }
 615     // Note that we don't need to `check_missing_stability` for default generic parameters,
 616     // as we assume that any default generic parameters without attributes are automatically
 617     // stable (assuming they have not inherited instability from their parent).
 618 }
 619
 620 fn stability_index(tcx: TyCtxt<'_>, (): ()) -> Index {
 621     let mut index = Index {
 622         stab_map: Default::default(),
 623         const_stab_map: Default::default(),
 624         default_body_stab_map: Default::default(),
 625         depr_map: Default::default(),
 626         implications: Default::default(),
 627     };
 628
 629     {
 630         let mut annotator = Annotator {
 631             tcx,
 632             index: &mut index,
 633             parent_stab: None,
 634             parent_const_stab: None,
 635             parent_depr: None,
 636             in_trait_impl: false,
 637         };
 638
 639         // If the `-Z force-unstable-if-unmarked` flag is passed then we provide
 640         // a parent stability annotation which indicates that this is private
 641         // with the `rustc_private` feature. This is intended for use when
 642         // compiling `librustc_*` crates themselves so we can leverage crates.io
 643         // while maintaining the invariant that all sysroot crates are unstable
 644         // by default and are unable to be used.
 645         if tcx.sess.opts.unstable_opts.force_unstable_if_unmarked {
 646             let stability = Stability {
 647                 level: attr::StabilityLevel::Unstable {
 648                     reason: UnstableReason::Default,
 649                     issue: NonZeroU32::new(27812),
 650                     is_soft: false,
 651                     implied_by: None,
 652                 },
 653                 feature: sym::rustc_private,
 654             };
 655             annotator.parent_stab = Some(stability);
 656         }
 657
 658         annotator.annotate(
 659             CRATE_DEF_ID,
 660             tcx.hir().span(CRATE_HIR_ID),
 661             None,
 662             AnnotationKind::Required,
 663             InheritDeprecation::Yes,
 664             InheritConstStability::No,
 665             InheritStability::No,
 666             |v| tcx.hir().walk_toplevel_module(v),
 667         );
 668     }
 669     index
 670 }
 671
 672 /// Cross-references the feature names of unstable APIs with enabled
 673 /// features and possibly prints errors.
 674 fn check_mod_unstable_api_usage(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 675     tcx.hir().visit_item_likes_in_module(module_def_id, &mut Checker { tcx });
 676 }
 677
 678 pub(crate) fn provide(providers: &mut Providers) {
 679     *providers = Providers {
 680         check_mod_unstable_api_usage,
 681         stability_index,
 682         stability_implications: |tcx, _| tcx.stability().implications.clone(),
 683         lookup_stability: |tcx, id| tcx.stability().local_stability(id.expect_local()),
 684         lookup_const_stability: |tcx, id| tcx.stability().local_const_stability(id.expect_local()),
 685         lookup_default_body_stability: |tcx, id| {
 686             tcx.stability().local_default_body_stability(id.expect_local())
 687         },
 688         lookup_deprecation_entry: |tcx, id| {
 689             tcx.stability().local_deprecation_entry(id.expect_local())
 690         },
 691         ..*providers
 692     };
 693 }
 694
 695 struct Checker<'tcx> {
 696     tcx: TyCtxt<'tcx>,
 697 }
 698
 699 impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
 700     type NestedFilter = nested_filter::OnlyBodies;
 701
 702     /// Because stability levels are scoped lexically, we want to walk
 703     /// nested items in the context of the outer item, so enable
 704     /// deep-walking.
 705     fn nested_visit_map(&mut self) -> Self::Map {
 706         self.tcx.hir()
 707     }
 708
 709     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 710         match item.kind {
 711             hir::ItemKind::ExternCrate(_) => {
 712                 // compiler-generated `extern crate` items have a dummy span.
 713                 // `std` is still checked for the `restricted-std` feature.
 714                 if item.span.is_dummy() && item.ident.name != sym::std {
 715                     return;
 716                 }
 717
 718                 let Some(cnum) = self.tcx.extern_mod_stmt_cnum(item.def_id) else {
 719                     return;
 720                 };
 721                 let def_id = cnum.as_def_id();
 722                 self.tcx.check_stability(def_id, Some(item.hir_id()), item.span, None);
 723             }
 724
 725             // For implementations of traits, check the stability of each item
 726             // individually as it's possible to have a stable trait with unstable
 727             // items.
 728             hir::ItemKind::Impl(hir::Impl {
 729                 of_trait: Some(ref t),
 730                 self_ty,
 731                 items,
 732                 constness,
 733                 ..
 734             }) => {
 735                 let features = self.tcx.features();
 736                 if features.staged_api {
 737                     let attrs = self.tcx.hir().attrs(item.hir_id());
 738                     let (stab, const_stab, _) =
 739                         attr::find_stability(&self.tcx.sess, attrs, item.span);
 740
 741                     // If this impl block has an #[unstable] attribute, give an
 742                     // error if all involved types and traits are stable, because
 743                     // it will have no effect.
 744                     // See: https://github.com/rust-lang/rust/issues/55436
 745                     if let Some((Stability { level: attr::Unstable { .. }, .. }, span)) = stab {
 746                         let mut c = CheckTraitImplStable { tcx: self.tcx, fully_stable: true };
 747                         c.visit_ty(self_ty);
 748                         c.visit_trait_ref(t);
 749                         if c.fully_stable {
 750                             self.tcx.struct_span_lint_hir(
 751                                 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
 752                                 item.hir_id(),
 753                                 span,
 754                                 |lint| {lint
 755                                     .build("an `#[unstable]` annotation here has no effect")
 756                                     .note("see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information")
 757                                     .emit();}
 758                             );
 759                         }
 760                     }
 761
 762                     // `#![feature(const_trait_impl)]` is unstable, so any impl declared stable
 763                     // needs to have an error emitted.
 764                     if features.const_trait_impl
 765                         && *constness == hir::Constness::Const
 766                         && const_stab.map_or(false, |(stab, _)| stab.is_const_stable())
 767                     {
 768                         self.tcx
 769                             .sess
 770                             .struct_span_err(item.span, "trait implementations cannot be const stable yet")
 771                             .note("see issue #67792 <https://github.com/rust-lang/rust/issues/67792> for more information")
 772                             .emit();
 773                     }
 774                 }
 775
 776                 for impl_item_ref in *items {
 777                     let impl_item = self.tcx.associated_item(impl_item_ref.id.def_id);
 778
 779                     if let Some(def_id) = impl_item.trait_item_def_id {
 780                         // Pass `None` to skip deprecation warnings.
 781                         self.tcx.check_stability(def_id, None, impl_item_ref.span, None);
 782                     }
 783                 }
 784             }
 785
 786             _ => (/* pass */),
 787         }
 788         intravisit::walk_item(self, item);
 789     }
 790
 791     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, id: hir::HirId) {
 792         if let Some(def_id) = path.res.opt_def_id() {
 793             let method_span = path.segments.last().map(|s| s.ident.span);
 794             let item_is_allowed = self.tcx.check_stability_allow_unstable(
 795                 def_id,
 796                 Some(id),
 797                 path.span,
 798                 method_span,
 799                 if is_unstable_reexport(self.tcx, id) {
 800                     AllowUnstable::Yes
 801                 } else {
 802                     AllowUnstable::No
 803                 },
 804             );
 805
 806             let is_allowed_through_unstable_modules = |def_id| {
 807                 self.tcx
 808                     .lookup_stability(def_id)
 809                     .map(|stab| match stab.level {
 810                         StabilityLevel::Stable { allowed_through_unstable_modules, .. } => {
 811                             allowed_through_unstable_modules
 812                         }
 813                         _ => false,
 814                     })
 815                     .unwrap_or(false)
 816             };
 817
 818             if item_is_allowed && !is_allowed_through_unstable_modules(def_id) {
 819                 // Check parent modules stability as well if the item the path refers to is itself
 820                 // stable. We only emit warnings for unstable path segments if the item is stable
 821                 // or allowed because stability is often inherited, so the most common case is that
 822                 // both the segments and the item are unstable behind the same feature flag.
 823                 //
 824                 // We check here rather than in `visit_path_segment` to prevent visiting the last
 825                 // path segment twice
 826                 //
 827                 // We include special cases via #[rustc_allowed_through_unstable_modules] for items
 828                 // that were accidentally stabilized through unstable paths before this check was
 829                 // added, such as `core::intrinsics::transmute`
 830                 let parents = path.segments.iter().rev().skip(1);
 831                 for path_segment in parents {
 832                     if let Some(def_id) = path_segment.res.as_ref().and_then(Res::opt_def_id) {
 833                         // use `None` for id to prevent deprecation check
 834                         self.tcx.check_stability_allow_unstable(
 835                             def_id,
 836                             None,
 837                             path.span,
 838                             None,
 839                             if is_unstable_reexport(self.tcx, id) {
 840                                 AllowUnstable::Yes
 841                             } else {
 842                                 AllowUnstable::No
 843                             },
 844                         );
 845                     }
 846                 }
 847             }
 848         }
 849
 850         intravisit::walk_path(self, path)
 851     }
 852 }
 853
 854 /// Check whether a path is a `use` item that has been marked as unstable.
 855 ///
 856 /// See issue #94972 for details on why this is a special case
 857 fn is_unstable_reexport<'tcx>(tcx: TyCtxt<'tcx>, id: hir::HirId) -> bool {
 858     // Get the LocalDefId so we can lookup the item to check the kind.
 859     let Some(def_id) = tcx.hir().opt_local_def_id(id) else { return false; };
 860
 861     let Some(stab) = tcx.stability().local_stability(def_id) else {
 862         return false;
 863     };
 864
 865     if stab.level.is_stable() {
 866         // The re-export is not marked as unstable, don't override
 867         return false;
 868     }
 869
 870     // If this is a path that isn't a use, we don't need to do anything special
 871     if !matches!(tcx.hir().item(hir::ItemId { def_id }).kind, ItemKind::Use(..)) {
 872         return false;
 873     }
 874
 875     true
 876 }
 877
 878 struct CheckTraitImplStable<'tcx> {
 879     tcx: TyCtxt<'tcx>,
 880     fully_stable: bool,
 881 }
 882
 883 impl<'tcx> Visitor<'tcx> for CheckTraitImplStable<'tcx> {
 884     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _id: hir::HirId) {
 885         if let Some(def_id) = path.res.opt_def_id() {
 886             if let Some(stab) = self.tcx.lookup_stability(def_id) {
 887                 self.fully_stable &= stab.level.is_stable();
 888             }
 889         }
 890         intravisit::walk_path(self, path)
 891     }
 892
 893     fn visit_trait_ref(&mut self, t: &'tcx TraitRef<'tcx>) {
 894         if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
 895             if let Some(stab) = self.tcx.lookup_stability(trait_did) {
 896                 self.fully_stable &= stab.level.is_stable();
 897             }
 898         }
 899         intravisit::walk_trait_ref(self, t)
 900     }
 901
 902     fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
 903         if let TyKind::Never = t.kind {
 904             self.fully_stable = false;
 905         }
 906         intravisit::walk_ty(self, t)
 907     }
 908 }
 909
 910 /// Given the list of enabled features that were not language features (i.e., that
 911 /// were expected to be library features), and the list of features used from
 912 /// libraries, identify activated features that don't exist and error about them.
 913 pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
 914     let is_staged_api =
 915         tcx.sess.opts.unstable_opts.force_unstable_if_unmarked || tcx.features().staged_api;
 916     if is_staged_api {
 917         let access_levels = &tcx.privacy_access_levels(());
 918         let mut missing = MissingStabilityAnnotations { tcx, access_levels };
 919         missing.check_missing_stability(CRATE_DEF_ID, tcx.hir().span(CRATE_HIR_ID));
 920         tcx.hir().walk_toplevel_module(&mut missing);
 921         tcx.hir().visit_all_item_likes_in_crate(&mut missing);
 922     }
 923
 924     let declared_lang_features = &tcx.features().declared_lang_features;
 925     let mut lang_features = FxHashSet::default();
 926     for &(feature, span, since) in declared_lang_features {
 927         if let Some(since) = since {
 928             // Warn if the user has enabled an already-stable lang feature.
 929             unnecessary_stable_feature_lint(tcx, span, feature, since);
 930         }
 931         if !lang_features.insert(feature) {
 932             // Warn if the user enables a lang feature multiple times.
 933             duplicate_feature_err(tcx.sess, span, feature);
 934         }
 935     }
 936
 937     let declared_lib_features = &tcx.features().declared_lib_features;
 938     let mut remaining_lib_features = FxIndexMap::default();
 939     for (feature, span) in declared_lib_features {
 940         if !tcx.sess.opts.unstable_features.is_nightly_build() {
 941             struct_span_err!(
 942                 tcx.sess,
 943                 *span,
 944                 E0554,
 945                 "`#![feature]` may not be used on the {} release channel",
 946                 env!("CFG_RELEASE_CHANNEL")
 947             )
 948             .emit();
 949         }
 950         if remaining_lib_features.contains_key(&feature) {
 951             // Warn if the user enables a lib feature multiple times.
 952             duplicate_feature_err(tcx.sess, *span, *feature);
 953         }
 954         remaining_lib_features.insert(feature, *span);
 955     }
 956     // `stdbuild` has special handling for `libc`, so we need to
 957     // recognise the feature when building std.
 958     // Likewise, libtest is handled specially, so `test` isn't
 959     // available as we'd like it to be.
 960     // FIXME: only remove `libc` when `stdbuild` is active.
 961     // FIXME: remove special casing for `test`.
 962     remaining_lib_features.remove(&sym::libc);
 963     remaining_lib_features.remove(&sym::test);
 964
 965     // We always collect the lib features declared in the current crate, even if there are
 966     // no unknown features, because the collection also does feature attribute validation.
 967     let local_defined_features = tcx.lib_features(());
 968     let mut all_lib_features: FxHashMap<_, _> =
 969         local_defined_features.to_vec().iter().map(|el| *el).collect();
 970     let mut implications = tcx.stability_implications(rustc_hir::def_id::LOCAL_CRATE).clone();
 971     for &cnum in tcx.crates(()) {
 972         implications.extend(tcx.stability_implications(cnum));
 973         all_lib_features.extend(tcx.defined_lib_features(cnum).iter().map(|el| *el));
 974     }
 975
 976     // Check that every feature referenced by an `implied_by` exists (for features defined in the
 977     // local crate).
 978     for (implied_by, feature) in tcx.stability_implications(rustc_hir::def_id::LOCAL_CRATE) {
 979         // Only `implied_by` needs to be checked, `feature` is guaranteed to exist.
 980         if !all_lib_features.contains_key(implied_by) {
 981             let span = local_defined_features
 982                 .stable
 983                 .get(feature)
 984                 .map(|(_, span)| span)
 985                 .or_else(|| local_defined_features.unstable.get(feature))
 986                 .expect("feature that implied another does not exist");
 987             tcx.sess
 988                 .struct_span_err(
 989                     *span,
 990                     format!("feature `{implied_by}` implying `{feature}` does not exist"),
 991                 )
 992                 .emit();
 993         }
 994     }
 995
 996     if !remaining_lib_features.is_empty() {
 997         for (feature, since) in all_lib_features.iter() {
 998             if let Some(since) = since && let Some(span) = remaining_lib_features.get(&feature) {
 999                 // Warn if the user has enabled an already-stable lib feature.
1000                 if let Some(implies) = implications.get(&feature) {
1001                     unnecessary_partially_stable_feature_lint(tcx, *span, *feature, *implies, *since);
1002                 } else {
1003                     unnecessary_stable_feature_lint(tcx, *span, *feature, *since);
1004                 }
1005             }
1006             remaining_lib_features.remove(&feature);
1007             if remaining_lib_features.is_empty() {
1008                 break;
1009             }
1010         }
1011     }
1012
1013     for (feature, span) in remaining_lib_features {
1014         struct_span_err!(tcx.sess, span, E0635, "unknown feature `{}`", feature).emit();
1015     }
1016
1017     // FIXME(#44232): the `used_features` table no longer exists, so we
1018     // don't lint about unused features. We should re-enable this one day!
1019 }
1020
1021 fn unnecessary_partially_stable_feature_lint(
1022     tcx: TyCtxt<'_>,
1023     span: Span,
1024     feature: Symbol,
1025     implies: Symbol,
1026     since: Symbol,
1027 ) {
1028     tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
1029         lint.build(&format!(
1030             "the feature `{feature}` has been partially stabilized since {since} and is succeeded \
1031              by the feature `{implies}`"
1032         ))
1033         .span_suggestion(
1034             span,
1035             &format!(
1036                 "if you are using features which are still unstable, change to using `{implies}`"
1037             ),
1038             implies,
1039             Applicability::MaybeIncorrect,
1040         )
1041         .span_suggestion(
1042             tcx.sess.source_map().span_extend_to_line(span),
1043             "if you are using features which are now stable, remove this line",
1044             "",
1045             Applicability::MaybeIncorrect,
1046         )
1047         .emit();
1048     });
1049 }
1050
1051 fn unnecessary_stable_feature_lint(tcx: TyCtxt<'_>, span: Span, feature: Symbol, since: Symbol) {
1052     tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
1053         lint.build(&format!(
1054             "the feature `{feature}` has been stable since {since} and no longer requires an \
1055              attribute to enable",
1056         ))
1057         .emit();
1058     });
1059 }
1060
1061 fn duplicate_feature_err(sess: &Session, span: Span, feature: Symbol) {
1062     struct_span_err!(sess, span, E0636, "the feature `{}` has already been declared", feature)
1063         .emit();
1064 }
1065
1066 fn missing_const_err(session: &Session, fn_sig_span: Span, const_span: Span) {
1067     const ERROR_MSG: &'static str = "attributes `#[rustc_const_unstable]` \
1068          and `#[rustc_const_stable]` require \
1069          the function or method to be `const`";
1070
1071     session
1072         .struct_span_err(fn_sig_span, ERROR_MSG)
1073         .span_help(fn_sig_span, "make the function or method const")
1074         .span_label(const_span, "attribute specified here")
1075         .emit();
1076 }