compiler/rustc_passes/src/stability.rs

   1 //! A pass that annotates every item and method with its stability level,
   2 //! propagating default levels lexically from parent to children ast nodes.
   3
   4 use rustc_attr::{self as attr, ConstStability, Stability};
   5 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
   6 use rustc_errors::struct_span_err;
   7 use rustc_hir as hir;
   8 use rustc_hir::def::{DefKind, Res};
   9 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
  10 use rustc_hir::hir_id::CRATE_HIR_ID;
  11 use rustc_hir::intravisit::{self, Visitor};
  12 use rustc_hir::{FieldDef, Generics, HirId, Item, ItemKind, TraitRef, Ty, TyKind, Variant};
  13 use rustc_middle::hir::nested_filter;
  14 use rustc_middle::middle::privacy::AccessLevels;
  15 use rustc_middle::middle::stability::{AllowUnstable, DeprecationEntry, Index};
  16 use rustc_middle::ty::{self, query::Providers, TyCtxt};
  17 use rustc_session::lint;
  18 use rustc_session::lint::builtin::{INEFFECTIVE_UNSTABLE_TRAIT_IMPL, USELESS_DEPRECATED};
  19 use rustc_session::parse::feature_err;
  20 use rustc_session::Session;
  21 use rustc_span::symbol::{sym, Symbol};
  22 use rustc_span::{Span, DUMMY_SP};
  23 use rustc_target::spec::abi::Abi;
  24
  25 use std::cmp::Ordering;
  26 use std::iter;
  27 use std::mem::replace;
  28 use std::num::NonZeroU32;
  29
  30 #[derive(PartialEq)]
  31 enum AnnotationKind {
  32     // Annotation is required if not inherited from unstable parents
  33     Required,
  34     // Annotation is useless, reject it
  35     Prohibited,
  36     // Deprecation annotation is useless, reject it. (Stability attribute is still required.)
  37     DeprecationProhibited,
  38     // Annotation itself is useless, but it can be propagated to children
  39     Container,
  40 }
  41
  42 /// Whether to inherit deprecation flags for nested items. In most cases, we do want to inherit
  43 /// deprecation, because nested items rarely have individual deprecation attributes, and so
  44 /// should be treated as deprecated if their parent is. However, default generic parameters
  45 /// have separate deprecation attributes from their parents, so we do not wish to inherit
  46 /// deprecation in this case. For example, inheriting deprecation for `T` in `Foo<T>`
  47 /// would cause a duplicate warning arising from both `Foo` and `T` being deprecated.
  48 #[derive(Clone)]
  49 enum InheritDeprecation {
  50     Yes,
  51     No,
  52 }
  53
  54 impl InheritDeprecation {
  55     fn yes(&self) -> bool {
  56         matches!(self, InheritDeprecation::Yes)
  57     }
  58 }
  59
  60 /// Whether to inherit const stability flags for nested items. In most cases, we do not want to
  61 /// inherit const stability: just because an enclosing `fn` is const-stable does not mean
  62 /// all `extern` imports declared in it should be const-stable! However, trait methods
  63 /// inherit const stability attributes from their parent and do not have their own.
  64 enum InheritConstStability {
  65     Yes,
  66     No,
  67 }
  68
  69 impl InheritConstStability {
  70     fn yes(&self) -> bool {
  71         matches!(self, InheritConstStability::Yes)
  72     }
  73 }
  74
  75 enum InheritStability {
  76     Yes,
  77     No,
  78 }
  79
  80 impl InheritStability {
  81     fn yes(&self) -> bool {
  82         matches!(self, InheritStability::Yes)
  83     }
  84 }
  85
  86 // A private tree-walker for producing an Index.
  87 struct Annotator<'a, 'tcx> {
  88     tcx: TyCtxt<'tcx>,
  89     index: &'a mut Index,
  90     parent_stab: Option<Stability>,
  91     parent_const_stab: Option<ConstStability>,
  92     parent_depr: Option<DeprecationEntry>,
  93     in_trait_impl: bool,
  94 }
  95
  96 impl<'a, 'tcx> Annotator<'a, 'tcx> {
  97     // Determine the stability for a node based on its attributes and inherited
  98     // stability. The stability is recorded in the index and used as the parent.
  99     // If the node is a function, `fn_sig` is its signature
 100     fn annotate<F>(
 101         &mut self,
 102         def_id: LocalDefId,
 103         item_sp: Span,
 104         fn_sig: Option<&'tcx hir::FnSig<'tcx>>,
 105         kind: AnnotationKind,
 106         inherit_deprecation: InheritDeprecation,
 107         inherit_const_stability: InheritConstStability,
 108         inherit_from_parent: InheritStability,
 109         visit_children: F,
 110     ) where
 111         F: FnOnce(&mut Self),
 112     {
 113         let attrs = self.tcx.hir().attrs(self.tcx.hir().local_def_id_to_hir_id(def_id));
 114         debug!("annotate(id = {:?}, attrs = {:?})", def_id, attrs);
 115
 116         let depr = attr::find_deprecation(&self.tcx.sess, attrs);
 117         let mut is_deprecated = false;
 118         if let Some((depr, span)) = &depr {
 119             is_deprecated = true;
 120
 121             if kind == AnnotationKind::Prohibited || kind == AnnotationKind::DeprecationProhibited {
 122                 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
 123                 self.tcx.struct_span_lint_hir(USELESS_DEPRECATED, hir_id, *span, |lint| {
 124                     lint.build("this `#[deprecated]` annotation has no effect")
 125                         .span_suggestion_short(
 126                             *span,
 127                             "remove the unnecessary deprecation attribute",
 128                             "",
 129                             rustc_errors::Applicability::MachineApplicable,
 130                         )
 131                         .emit();
 132                 });
 133             }
 134
 135             // `Deprecation` is just two pointers, no need to intern it
 136             let depr_entry = DeprecationEntry::local(*depr, def_id);
 137             self.index.depr_map.insert(def_id, depr_entry);
 138         } else if let Some(parent_depr) = self.parent_depr {
 139             if inherit_deprecation.yes() {
 140                 is_deprecated = true;
 141                 info!("tagging child {:?} as deprecated from parent", def_id);
 142                 self.index.depr_map.insert(def_id, parent_depr);
 143             }
 144         }
 145
 146         if !self.tcx.features().staged_api {
 147             // Propagate unstability.  This can happen even for non-staged-api crates in case
 148             // -Zforce-unstable-if-unmarked is set.
 149             if let Some(stab) = self.parent_stab {
 150                 if inherit_deprecation.yes() && stab.is_unstable() {
 151                     self.index.stab_map.insert(def_id, stab);
 152                 }
 153             }
 154
 155             self.recurse_with_stability_attrs(
 156                 depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 157                 None,
 158                 None,
 159                 visit_children,
 160             );
 161             return;
 162         }
 163
 164         let (stab, const_stab) = attr::find_stability(&self.tcx.sess, attrs, item_sp);
 165         let mut const_span = None;
 166
 167         let const_stab = const_stab.map(|(const_stab, const_span_node)| {
 168             self.index.const_stab_map.insert(def_id, const_stab);
 169             const_span = Some(const_span_node);
 170             const_stab
 171         });
 172
 173         // If the current node is a function, has const stability attributes and if it doesn not have an intrinsic ABI,
 174         // check if the function/method is const or the parent impl block is const
 175         if let (Some(const_span), Some(fn_sig)) = (const_span, fn_sig) {
 176             if fn_sig.header.abi != Abi::RustIntrinsic
 177                 && fn_sig.header.abi != Abi::PlatformIntrinsic
 178                 && !fn_sig.header.is_const()
 179             {
 180                 if !self.in_trait_impl
 181                     || (self.in_trait_impl && !self.tcx.is_const_fn_raw(def_id.to_def_id()))
 182                 {
 183                     missing_const_err(&self.tcx.sess, fn_sig.span, const_span);
 184                 }
 185             }
 186         }
 187
 188         // `impl const Trait for Type` items forward their const stability to their
 189         // immediate children.
 190         if const_stab.is_none() {
 191             debug!("annotate: const_stab not found, parent = {:?}", self.parent_const_stab);
 192             if let Some(parent) = self.parent_const_stab {
 193                 if parent.is_const_unstable() {
 194                     self.index.const_stab_map.insert(def_id, parent);
 195                 }
 196             }
 197         }
 198
 199         if let Some((rustc_attr::Deprecation { is_since_rustc_version: true, .. }, span)) = &depr {
 200             if stab.is_none() {
 201                 struct_span_err!(
 202                     self.tcx.sess,
 203                     *span,
 204                     E0549,
 205                     "deprecated attribute must be paired with \
 206                     either stable or unstable attribute"
 207                 )
 208                 .emit();
 209             }
 210         }
 211
 212         let stab = stab.map(|(stab, span)| {
 213             // Error if prohibited, or can't inherit anything from a container.
 214             if kind == AnnotationKind::Prohibited
 215                 || (kind == AnnotationKind::Container && stab.level.is_stable() && is_deprecated)
 216             {
 217                 self.tcx.sess.struct_span_err(span,"this stability annotation is useless")
 218                     .span_label(span, "useless stability annotation")
 219                     .span_label(item_sp, "the stability attribute annotates this item")
 220                     .emit();
 221             }
 222
 223             debug!("annotate: found {:?}", stab);
 224
 225             // Check if deprecated_since < stable_since. If it is,
 226             // this is *almost surely* an accident.
 227             if let (&Some(dep_since), &attr::Stable { since: stab_since }) =
 228                 (&depr.as_ref().and_then(|(d, _)| d.since), &stab.level)
 229             {
 230                 // Explicit version of iter::order::lt to handle parse errors properly
 231                 for (dep_v, stab_v) in
 232                     iter::zip(dep_since.as_str().split('.'), stab_since.as_str().split('.'))
 233                 {
 234                     match stab_v.parse::<u64>() {
 235                         Err(_) => {
 236                             self.tcx.sess.struct_span_err(span, "invalid stability version found")
 237                                 .span_label(span, "invalid stability version")
 238                                 .span_label(item_sp, "the stability attribute annotates this item")
 239                                 .emit();
 240                             break;
 241                         }
 242                         Ok(stab_vp) => match dep_v.parse::<u64>() {
 243                             Ok(dep_vp) => match dep_vp.cmp(&stab_vp) {
 244                                 Ordering::Less => {
 245                                     self.tcx.sess.struct_span_err(span, "an API can't be stabilized after it is deprecated")
 246                                         .span_label(span, "invalid version")
 247                                         .span_label(item_sp, "the stability attribute annotates this item")
 248                                         .emit();
 249                                     break;
 250                                 }
 251                                 Ordering::Equal => continue,
 252                                 Ordering::Greater => break,
 253                             },
 254                             Err(_) => {
 255                                 if dep_v != "TBD" {
 256                                     self.tcx.sess.struct_span_err(span, "invalid deprecation version found")
 257                                         .span_label(span, "invalid deprecation version")
 258                                         .span_label(item_sp, "the stability attribute annotates this item")
 259                                         .emit();
 260                                 }
 261                                 break;
 262                             }
 263                         },
 264                     }
 265                 }
 266             }
 267
 268             self.index.stab_map.insert(def_id, stab);
 269             stab
 270         });
 271
 272         if stab.is_none() {
 273             debug!("annotate: stab not found, parent = {:?}", self.parent_stab);
 274             if let Some(stab) = self.parent_stab {
 275                 if inherit_deprecation.yes() && stab.is_unstable() || inherit_from_parent.yes() {
 276                     self.index.stab_map.insert(def_id, stab);
 277                 }
 278             }
 279         }
 280
 281         self.recurse_with_stability_attrs(
 282             depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 283             stab,
 284             if inherit_const_stability.yes() { const_stab } else { None },
 285             visit_children,
 286         );
 287     }
 288
 289     fn recurse_with_stability_attrs(
 290         &mut self,
 291         depr: Option<DeprecationEntry>,
 292         stab: Option<Stability>,
 293         const_stab: Option<ConstStability>,
 294         f: impl FnOnce(&mut Self),
 295     ) {
 296         // These will be `Some` if this item changes the corresponding stability attribute.
 297         let mut replaced_parent_depr = None;
 298         let mut replaced_parent_stab = None;
 299         let mut replaced_parent_const_stab = None;
 300
 301         if let Some(depr) = depr {
 302             replaced_parent_depr = Some(replace(&mut self.parent_depr, Some(depr)));
 303         }
 304         if let Some(stab) = stab {
 305             replaced_parent_stab = Some(replace(&mut self.parent_stab, Some(stab)));
 306         }
 307         if let Some(const_stab) = const_stab {
 308             replaced_parent_const_stab =
 309                 Some(replace(&mut self.parent_const_stab, Some(const_stab)));
 310         }
 311
 312         f(self);
 313
 314         if let Some(orig_parent_depr) = replaced_parent_depr {
 315             self.parent_depr = orig_parent_depr;
 316         }
 317         if let Some(orig_parent_stab) = replaced_parent_stab {
 318             self.parent_stab = orig_parent_stab;
 319         }
 320         if let Some(orig_parent_const_stab) = replaced_parent_const_stab {
 321             self.parent_const_stab = orig_parent_const_stab;
 322         }
 323     }
 324 }
 325
 326 impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
 327     /// Because stability levels are scoped lexically, we want to walk
 328     /// nested items in the context of the outer item, so enable
 329     /// deep-walking.
 330     type NestedFilter = nested_filter::All;
 331
 332     fn nested_visit_map(&mut self) -> Self::Map {
 333         self.tcx.hir()
 334     }
 335
 336     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 337         let orig_in_trait_impl = self.in_trait_impl;
 338         let mut kind = AnnotationKind::Required;
 339         let mut const_stab_inherit = InheritConstStability::No;
 340         let mut fn_sig = None;
 341
 342         match i.kind {
 343             // Inherent impls and foreign modules serve only as containers for other items,
 344             // they don't have their own stability. They still can be annotated as unstable
 345             // and propagate this instability to children, but this annotation is completely
 346             // optional. They inherit stability from their parents when unannotated.
 347             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 348             | hir::ItemKind::ForeignMod { .. } => {
 349                 self.in_trait_impl = false;
 350                 kind = AnnotationKind::Container;
 351             }
 352             hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => {
 353                 self.in_trait_impl = true;
 354                 kind = AnnotationKind::DeprecationProhibited;
 355                 const_stab_inherit = InheritConstStability::Yes;
 356             }
 357             hir::ItemKind::Struct(ref sd, _) => {
 358                 if let Some(ctor_hir_id) = sd.ctor_hir_id() {
 359                     self.annotate(
 360                         self.tcx.hir().local_def_id(ctor_hir_id),
 361                         i.span,
 362                         None,
 363                         AnnotationKind::Required,
 364                         InheritDeprecation::Yes,
 365                         InheritConstStability::No,
 366                         InheritStability::Yes,
 367                         |_| {},
 368                     )
 369                 }
 370             }
 371             hir::ItemKind::Fn(ref item_fn_sig, _, _) => {
 372                 fn_sig = Some(item_fn_sig);
 373             }
 374             _ => {}
 375         }
 376
 377         self.annotate(
 378             i.def_id,
 379             i.span,
 380             fn_sig,
 381             kind,
 382             InheritDeprecation::Yes,
 383             const_stab_inherit,
 384             InheritStability::No,
 385             |v| intravisit::walk_item(v, i),
 386         );
 387         self.in_trait_impl = orig_in_trait_impl;
 388     }
 389
 390     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 391         let fn_sig = match ti.kind {
 392             hir::TraitItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 393             _ => None,
 394         };
 395
 396         self.annotate(
 397             ti.def_id,
 398             ti.span,
 399             fn_sig,
 400             AnnotationKind::Required,
 401             InheritDeprecation::Yes,
 402             InheritConstStability::No,
 403             InheritStability::No,
 404             |v| {
 405                 intravisit::walk_trait_item(v, ti);
 406             },
 407         );
 408     }
 409
 410     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 411         let kind =
 412             if self.in_trait_impl { AnnotationKind::Prohibited } else { AnnotationKind::Required };
 413
 414         let fn_sig = match ii.kind {
 415             hir::ImplItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 416             _ => None,
 417         };
 418
 419         self.annotate(
 420             ii.def_id,
 421             ii.span,
 422             fn_sig,
 423             kind,
 424             InheritDeprecation::Yes,
 425             InheritConstStability::No,
 426             InheritStability::No,
 427             |v| {
 428                 intravisit::walk_impl_item(v, ii);
 429             },
 430         );
 431     }
 432
 433     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 434         self.annotate(
 435             self.tcx.hir().local_def_id(var.id),
 436             var.span,
 437             None,
 438             AnnotationKind::Required,
 439             InheritDeprecation::Yes,
 440             InheritConstStability::No,
 441             InheritStability::Yes,
 442             |v| {
 443                 if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
 444                     v.annotate(
 445                         v.tcx.hir().local_def_id(ctor_hir_id),
 446                         var.span,
 447                         None,
 448                         AnnotationKind::Required,
 449                         InheritDeprecation::Yes,
 450                         InheritConstStability::No,
 451                         InheritStability::No,
 452                         |_| {},
 453                     );
 454                 }
 455
 456                 intravisit::walk_variant(v, var, g, item_id)
 457             },
 458         )
 459     }
 460
 461     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 462         self.annotate(
 463             self.tcx.hir().local_def_id(s.hir_id),
 464             s.span,
 465             None,
 466             AnnotationKind::Required,
 467             InheritDeprecation::Yes,
 468             InheritConstStability::No,
 469             InheritStability::Yes,
 470             |v| {
 471                 intravisit::walk_field_def(v, s);
 472             },
 473         );
 474     }
 475
 476     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 477         self.annotate(
 478             i.def_id,
 479             i.span,
 480             None,
 481             AnnotationKind::Required,
 482             InheritDeprecation::Yes,
 483             InheritConstStability::No,
 484             InheritStability::No,
 485             |v| {
 486                 intravisit::walk_foreign_item(v, i);
 487             },
 488         );
 489     }
 490
 491     fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
 492         let kind = match &p.kind {
 493             // Allow stability attributes on default generic arguments.
 494             hir::GenericParamKind::Type { default: Some(_), .. }
 495             | hir::GenericParamKind::Const { default: Some(_), .. } => AnnotationKind::Container,
 496             _ => AnnotationKind::Prohibited,
 497         };
 498
 499         self.annotate(
 500             self.tcx.hir().local_def_id(p.hir_id),
 501             p.span,
 502             None,
 503             kind,
 504             InheritDeprecation::No,
 505             InheritConstStability::No,
 506             InheritStability::No,
 507             |v| {
 508                 intravisit::walk_generic_param(v, p);
 509             },
 510         );
 511     }
 512 }
 513
 514 struct MissingStabilityAnnotations<'tcx> {
 515     tcx: TyCtxt<'tcx>,
 516     access_levels: &'tcx AccessLevels,
 517 }
 518
 519 impl<'tcx> MissingStabilityAnnotations<'tcx> {
 520     fn check_missing_stability(&self, def_id: LocalDefId, span: Span) {
 521         let stab = self.tcx.stability().local_stability(def_id);
 522         if !self.tcx.sess.opts.test && stab.is_none() && self.access_levels.is_reachable(def_id) {
 523             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 524             self.tcx.sess.span_err(span, &format!("{} has missing stability attribute", descr));
 525         }
 526     }
 527
 528     fn check_missing_const_stability(&self, def_id: LocalDefId, span: Span) {
 529         if !self.tcx.features().staged_api {
 530             return;
 531         }
 532
 533         let is_const = self.tcx.is_const_fn(def_id.to_def_id())
 534             || self.tcx.is_const_trait_impl_raw(def_id.to_def_id());
 535         let is_stable = self
 536             .tcx
 537             .lookup_stability(def_id)
 538             .map_or(false, |stability| stability.level.is_stable());
 539         let missing_const_stability_attribute = self.tcx.lookup_const_stability(def_id).is_none();
 540         let is_reachable = self.access_levels.is_reachable(def_id);
 541
 542         if is_const && is_stable && missing_const_stability_attribute && is_reachable {
 543             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 544             self.tcx.sess.span_err(span, &format!("{descr} has missing const stability attribute"));
 545         }
 546     }
 547 }
 548
 549 impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
 550     type NestedFilter = nested_filter::OnlyBodies;
 551
 552     fn nested_visit_map(&mut self) -> Self::Map {
 553         self.tcx.hir()
 554     }
 555
 556     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 557         // Inherent impls and foreign modules serve only as containers for other items,
 558         // they don't have their own stability. They still can be annotated as unstable
 559         // and propagate this instability to children, but this annotation is completely
 560         // optional. They inherit stability from their parents when unannotated.
 561         if !matches!(
 562             i.kind,
 563             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 564                 | hir::ItemKind::ForeignMod { .. }
 565         ) {
 566             self.check_missing_stability(i.def_id, i.span);
 567         }
 568
 569         // Ensure stable `const fn` have a const stability attribute.
 570         self.check_missing_const_stability(i.def_id, i.span);
 571
 572         intravisit::walk_item(self, i)
 573     }
 574
 575     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 576         self.check_missing_stability(ti.def_id, ti.span);
 577         intravisit::walk_trait_item(self, ti);
 578     }
 579
 580     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 581         let impl_def_id = self.tcx.hir().get_parent_item(ii.hir_id());
 582         if self.tcx.impl_trait_ref(impl_def_id).is_none() {
 583             self.check_missing_stability(ii.def_id, ii.span);
 584             self.check_missing_const_stability(ii.def_id, ii.span);
 585         }
 586         intravisit::walk_impl_item(self, ii);
 587     }
 588
 589     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 590         self.check_missing_stability(self.tcx.hir().local_def_id(var.id), var.span);
 591         intravisit::walk_variant(self, var, g, item_id);
 592     }
 593
 594     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 595         self.check_missing_stability(self.tcx.hir().local_def_id(s.hir_id), s.span);
 596         intravisit::walk_field_def(self, s);
 597     }
 598
 599     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 600         self.check_missing_stability(i.def_id, i.span);
 601         intravisit::walk_foreign_item(self, i);
 602     }
 603     // Note that we don't need to `check_missing_stability` for default generic parameters,
 604     // as we assume that any default generic parameters without attributes are automatically
 605     // stable (assuming they have not inherited instability from their parent).
 606 }
 607
 608 fn stability_index(tcx: TyCtxt<'_>, (): ()) -> Index {
 609     let mut index = Index {
 610         stab_map: Default::default(),
 611         const_stab_map: Default::default(),
 612         depr_map: Default::default(),
 613     };
 614
 615     {
 616         let mut annotator = Annotator {
 617             tcx,
 618             index: &mut index,
 619             parent_stab: None,
 620             parent_const_stab: None,
 621             parent_depr: None,
 622             in_trait_impl: false,
 623         };
 624
 625         // If the `-Z force-unstable-if-unmarked` flag is passed then we provide
 626         // a parent stability annotation which indicates that this is private
 627         // with the `rustc_private` feature. This is intended for use when
 628         // compiling `librustc_*` crates themselves so we can leverage crates.io
 629         // while maintaining the invariant that all sysroot crates are unstable
 630         // by default and are unable to be used.
 631         if tcx.sess.opts.debugging_opts.force_unstable_if_unmarked {
 632             let reason = "this crate is being loaded from the sysroot, an \
 633                           unstable location; did you mean to load this crate \
 634                           from crates.io via `Cargo.toml` instead?";
 635             let stability = Stability {
 636                 level: attr::StabilityLevel::Unstable {
 637                     reason: Some(Symbol::intern(reason)),
 638                     issue: NonZeroU32::new(27812),
 639                     is_soft: false,
 640                 },
 641                 feature: sym::rustc_private,
 642             };
 643             annotator.parent_stab = Some(stability);
 644         }
 645
 646         annotator.annotate(
 647             CRATE_DEF_ID,
 648             tcx.hir().span(CRATE_HIR_ID),
 649             None,
 650             AnnotationKind::Required,
 651             InheritDeprecation::Yes,
 652             InheritConstStability::No,
 653             InheritStability::No,
 654             |v| tcx.hir().walk_toplevel_module(v),
 655         );
 656     }
 657     index
 658 }
 659
 660 /// Cross-references the feature names of unstable APIs with enabled
 661 /// features and possibly prints errors.
 662 fn check_mod_unstable_api_usage(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 663     tcx.hir().deep_visit_item_likes_in_module(module_def_id, &mut Checker { tcx });
 664 }
 665
 666 pub(crate) fn provide(providers: &mut Providers) {
 667     *providers = Providers {
 668         check_mod_unstable_api_usage,
 669         stability_index,
 670         lookup_stability: |tcx, id| tcx.stability().local_stability(id.expect_local()),
 671         lookup_const_stability: |tcx, id| tcx.stability().local_const_stability(id.expect_local()),
 672         lookup_deprecation_entry: |tcx, id| {
 673             tcx.stability().local_deprecation_entry(id.expect_local())
 674         },
 675         ..*providers
 676     };
 677 }
 678
 679 struct Checker<'tcx> {
 680     tcx: TyCtxt<'tcx>,
 681 }
 682
 683 impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
 684     type NestedFilter = nested_filter::OnlyBodies;
 685
 686     /// Because stability levels are scoped lexically, we want to walk
 687     /// nested items in the context of the outer item, so enable
 688     /// deep-walking.
 689     fn nested_visit_map(&mut self) -> Self::Map {
 690         self.tcx.hir()
 691     }
 692
 693     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 694         match item.kind {
 695             hir::ItemKind::ExternCrate(_) => {
 696                 // compiler-generated `extern crate` items have a dummy span.
 697                 // `std` is still checked for the `restricted-std` feature.
 698                 if item.span.is_dummy() && item.ident.name != sym::std {
 699                     return;
 700                 }
 701
 702                 let Some(cnum) = self.tcx.extern_mod_stmt_cnum(item.def_id) else {
 703                     return;
 704                 };
 705                 let def_id = cnum.as_def_id();
 706                 self.tcx.check_stability(def_id, Some(item.hir_id()), item.span, None);
 707             }
 708
 709             // For implementations of traits, check the stability of each item
 710             // individually as it's possible to have a stable trait with unstable
 711             // items.
 712             hir::ItemKind::Impl(hir::Impl {
 713                 of_trait: Some(ref t),
 714                 self_ty,
 715                 items,
 716                 constness,
 717                 ..
 718             }) => {
 719                 let features = self.tcx.features();
 720                 if features.staged_api {
 721                     let attrs = self.tcx.hir().attrs(item.hir_id());
 722                     let (stab, const_stab) = attr::find_stability(&self.tcx.sess, attrs, item.span);
 723
 724                     // If this impl block has an #[unstable] attribute, give an
 725                     // error if all involved types and traits are stable, because
 726                     // it will have no effect.
 727                     // See: https://github.com/rust-lang/rust/issues/55436
 728                     if let Some((Stability { level: attr::Unstable { .. }, .. }, span)) = stab {
 729                         let mut c = CheckTraitImplStable { tcx: self.tcx, fully_stable: true };
 730                         c.visit_ty(self_ty);
 731                         c.visit_trait_ref(t);
 732                         if c.fully_stable {
 733                             self.tcx.struct_span_lint_hir(
 734                                 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
 735                                 item.hir_id(),
 736                                 span,
 737                                 |lint| {lint
 738                                     .build("an `#[unstable]` annotation here has no effect")
 739                                     .note("see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information")
 740                                     .emit();}
 741                             );
 742                         }
 743                     }
 744
 745                     // `#![feature(const_trait_impl)]` is unstable, so any impl declared stable
 746                     // needs to have an error emitted.
 747                     if features.const_trait_impl
 748                         && *constness == hir::Constness::Const
 749                         && const_stab.map_or(false, |(stab, _)| stab.is_const_stable())
 750                     {
 751                         self.tcx
 752                             .sess
 753                             .struct_span_err(item.span, "trait implementations cannot be const stable yet")
 754                             .note("see issue #67792 <https://github.com/rust-lang/rust/issues/67792> for more information")
 755                             .emit();
 756                     }
 757                 }
 758
 759                 for impl_item_ref in *items {
 760                     let impl_item = self.tcx.associated_item(impl_item_ref.id.def_id);
 761
 762                     if let Some(def_id) = impl_item.trait_item_def_id {
 763                         // Pass `None` to skip deprecation warnings.
 764                         self.tcx.check_stability(def_id, None, impl_item_ref.span, None);
 765                     }
 766                 }
 767             }
 768
 769             // There's no good place to insert stability check for non-Copy unions,
 770             // so semi-randomly perform it here in stability.rs
 771             hir::ItemKind::Union(..) if !self.tcx.features().untagged_unions => {
 772                 let ty = self.tcx.type_of(item.def_id);
 773                 let ty::Adt(adt_def, substs) = ty.kind() else { bug!() };
 774
 775                 // Non-`Copy` fields are unstable, except for `ManuallyDrop`.
 776                 let param_env = self.tcx.param_env(item.def_id);
 777                 for field in &adt_def.non_enum_variant().fields {
 778                     let field_ty = field.ty(self.tcx, substs);
 779                     if !field_ty.ty_adt_def().map_or(false, |adt_def| adt_def.is_manually_drop())
 780                         && !field_ty.is_copy_modulo_regions(self.tcx.at(DUMMY_SP), param_env)
 781                     {
 782                         if field_ty.needs_drop(self.tcx, param_env) {
 783                             // Avoid duplicate error: This will error later anyway because fields
 784                             // that need drop are not allowed.
 785                             self.tcx.sess.delay_span_bug(
 786                                 item.span,
 787                                 "union should have been rejected due to potentially dropping field",
 788                             );
 789                         } else {
 790                             feature_err(
 791                                 &self.tcx.sess.parse_sess,
 792                                 sym::untagged_unions,
 793                                 self.tcx.def_span(field.did),
 794                                 "unions with non-`Copy` fields other than `ManuallyDrop<T>` are unstable",
 795                             )
 796                             .emit();
 797                         }
 798                     }
 799                 }
 800             }
 801
 802             _ => (/* pass */),
 803         }
 804         intravisit::walk_item(self, item);
 805     }
 806
 807     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, id: hir::HirId) {
 808         if let Some(def_id) = path.res.opt_def_id() {
 809             let method_span = path.segments.last().map(|s| s.ident.span);
 810             self.tcx.check_stability_allow_unstable(
 811                 def_id,
 812                 Some(id),
 813                 path.span,
 814                 method_span,
 815                 if is_unstable_reexport(self.tcx, id) {
 816                     AllowUnstable::Yes
 817                 } else {
 818                     AllowUnstable::No
 819                 },
 820             )
 821         }
 822         intravisit::walk_path(self, path)
 823     }
 824 }
 825
 826 /// Check whether a path is a `use` item that has been marked as unstable.
 827 ///
 828 /// See issue #94972 for details on why this is a special case
 829 fn is_unstable_reexport<'tcx>(tcx: TyCtxt<'tcx>, id: hir::HirId) -> bool {
 830     // Get the LocalDefId so we can lookup the item to check the kind.
 831     let Some(def_id) = tcx.hir().opt_local_def_id(id) else { return false; };
 832
 833     let Some(stab) = tcx.stability().local_stability(def_id) else {
 834         return false;
 835     };
 836
 837     if stab.level.is_stable() {
 838         // The re-export is not marked as unstable, don't override
 839         return false;
 840     }
 841
 842     // If this is a path that isn't a use, we don't need to do anything special
 843     if !matches!(tcx.hir().item(hir::ItemId { def_id }).kind, ItemKind::Use(..)) {
 844         return false;
 845     }
 846
 847     true
 848 }
 849
 850 struct CheckTraitImplStable<'tcx> {
 851     tcx: TyCtxt<'tcx>,
 852     fully_stable: bool,
 853 }
 854
 855 impl<'tcx> Visitor<'tcx> for CheckTraitImplStable<'tcx> {
 856     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _id: hir::HirId) {
 857         if let Some(def_id) = path.res.opt_def_id() {
 858             if let Some(stab) = self.tcx.lookup_stability(def_id) {
 859                 self.fully_stable &= stab.level.is_stable();
 860             }
 861         }
 862         intravisit::walk_path(self, path)
 863     }
 864
 865     fn visit_trait_ref(&mut self, t: &'tcx TraitRef<'tcx>) {
 866         if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
 867             if let Some(stab) = self.tcx.lookup_stability(trait_did) {
 868                 self.fully_stable &= stab.level.is_stable();
 869             }
 870         }
 871         intravisit::walk_trait_ref(self, t)
 872     }
 873
 874     fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
 875         if let TyKind::Never = t.kind {
 876             self.fully_stable = false;
 877         }
 878         intravisit::walk_ty(self, t)
 879     }
 880 }
 881
 882 /// Given the list of enabled features that were not language features (i.e., that
 883 /// were expected to be library features), and the list of features used from
 884 /// libraries, identify activated features that don't exist and error about them.
 885 pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
 886     let is_staged_api =
 887         tcx.sess.opts.debugging_opts.force_unstable_if_unmarked || tcx.features().staged_api;
 888     if is_staged_api {
 889         let access_levels = &tcx.privacy_access_levels(());
 890         let mut missing = MissingStabilityAnnotations { tcx, access_levels };
 891         missing.check_missing_stability(CRATE_DEF_ID, tcx.hir().span(CRATE_HIR_ID));
 892         tcx.hir().walk_toplevel_module(&mut missing);
 893         tcx.hir().deep_visit_all_item_likes(&mut missing);
 894     }
 895
 896     let declared_lang_features = &tcx.features().declared_lang_features;
 897     let mut lang_features = FxHashSet::default();
 898     for &(feature, span, since) in declared_lang_features {
 899         if let Some(since) = since {
 900             // Warn if the user has enabled an already-stable lang feature.
 901             unnecessary_stable_feature_lint(tcx, span, feature, since);
 902         }
 903         if !lang_features.insert(feature) {
 904             // Warn if the user enables a lang feature multiple times.
 905             duplicate_feature_err(tcx.sess, span, feature);
 906         }
 907     }
 908
 909     let declared_lib_features = &tcx.features().declared_lib_features;
 910     let mut remaining_lib_features = FxIndexMap::default();
 911     for (feature, span) in declared_lib_features {
 912         if !tcx.sess.opts.unstable_features.is_nightly_build() {
 913             struct_span_err!(
 914                 tcx.sess,
 915                 *span,
 916                 E0554,
 917                 "`#![feature]` may not be used on the {} release channel",
 918                 env!("CFG_RELEASE_CHANNEL")
 919             )
 920             .emit();
 921         }
 922         if remaining_lib_features.contains_key(&feature) {
 923             // Warn if the user enables a lib feature multiple times.
 924             duplicate_feature_err(tcx.sess, *span, *feature);
 925         }
 926         remaining_lib_features.insert(feature, *span);
 927     }
 928     // `stdbuild` has special handling for `libc`, so we need to
 929     // recognise the feature when building std.
 930     // Likewise, libtest is handled specially, so `test` isn't
 931     // available as we'd like it to be.
 932     // FIXME: only remove `libc` when `stdbuild` is active.
 933     // FIXME: remove special casing for `test`.
 934     remaining_lib_features.remove(&sym::libc);
 935     remaining_lib_features.remove(&sym::test);
 936
 937     let check_features = |remaining_lib_features: &mut FxIndexMap<_, _>, defined_features: &[_]| {
 938         for &(feature, since) in defined_features {
 939             if let Some(since) = since {
 940                 if let Some(span) = remaining_lib_features.get(&feature) {
 941                     // Warn if the user has enabled an already-stable lib feature.
 942                     unnecessary_stable_feature_lint(tcx, *span, feature, since);
 943                 }
 944             }
 945             remaining_lib_features.remove(&feature);
 946             if remaining_lib_features.is_empty() {
 947                 break;
 948             }
 949         }
 950     };
 951
 952     // We always collect the lib features declared in the current crate, even if there are
 953     // no unknown features, because the collection also does feature attribute validation.
 954     let local_defined_features = tcx.lib_features(()).to_vec();
 955     if !remaining_lib_features.is_empty() {
 956         check_features(&mut remaining_lib_features, &local_defined_features);
 957
 958         for &cnum in tcx.crates(()) {
 959             if remaining_lib_features.is_empty() {
 960                 break;
 961             }
 962             check_features(&mut remaining_lib_features, tcx.defined_lib_features(cnum));
 963         }
 964     }
 965
 966     for (feature, span) in remaining_lib_features {
 967         struct_span_err!(tcx.sess, span, E0635, "unknown feature `{}`", feature).emit();
 968     }
 969
 970     // FIXME(#44232): the `used_features` table no longer exists, so we
 971     // don't lint about unused features. We should re-enable this one day!
 972 }
 973
 974 fn unnecessary_stable_feature_lint(tcx: TyCtxt<'_>, span: Span, feature: Symbol, since: Symbol) {
 975     tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
 976         lint.build(&format!(
 977             "the feature `{}` has been stable since {} and no longer requires \
 978                       an attribute to enable",
 979             feature, since
 980         ))
 981         .emit();
 982     });
 983 }
 984
 985 fn duplicate_feature_err(sess: &Session, span: Span, feature: Symbol) {
 986     struct_span_err!(sess, span, E0636, "the feature `{}` has already been declared", feature)
 987         .emit();
 988 }
 989
 990 fn missing_const_err(session: &Session, fn_sig_span: Span, const_span: Span) {
 991     const ERROR_MSG: &'static str = "attributes `#[rustc_const_unstable]` \
 992          and `#[rustc_const_stable]` require \
 993          the function or method to be `const`";
 994
 995     session
 996         .struct_span_err(fn_sig_span, ERROR_MSG)
 997         .span_help(fn_sig_span, "make the function or method const")
 998         .span_label(const_span, "attribute specified here")
 999         .emit();
1000 }