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_ast::Attribute;
   5 use rustc_attr::{self as attr, ConstStability, Stability};
   6 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
   7 use rustc_errors::struct_span_err;
   8 use rustc_hir as hir;
   9 use rustc_hir::def::{DefKind, Res};
  10 use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID, CRATE_DEF_INDEX, LOCAL_CRATE};
  11 use rustc_hir::hir_id::CRATE_HIR_ID;
  12 use rustc_hir::intravisit::{self, Visitor};
  13 use rustc_hir::{FieldDef, Generics, HirId, Item, TraitRef, Ty, TyKind, Variant};
  14 use rustc_middle::hir::nested_filter;
  15 use rustc_middle::middle::privacy::AccessLevels;
  16 use rustc_middle::middle::stability::{DeprecationEntry, Index};
  17 use rustc_middle::ty::{self, query::Providers, TyCtxt};
  18 use rustc_session::lint;
  19 use rustc_session::lint::builtin::{INEFFECTIVE_UNSTABLE_TRAIT_IMPL, USELESS_DEPRECATED};
  20 use rustc_session::parse::feature_err;
  21 use rustc_session::Session;
  22 use rustc_span::symbol::{sym, Symbol};
  23 use rustc_span::{Span, DUMMY_SP};
  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
  99     // stability. The stability is recorded in the index and used as the parent.
 100     // If the node is a function, `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.get_attrs(def_id.to_def_id());
 115         debug!("annotate(id = {:?}, attrs = {:?})", def_id, attrs);
 116         let mut did_error = false;
 117         if !self.tcx.features().staged_api {
 118             did_error = self.forbid_staged_api_attrs(def_id, attrs, inherit_deprecation.clone());
 119         }
 120
 121         let depr = if did_error { None } else { attr::find_deprecation(&self.tcx.sess, attrs) };
 122         let mut is_deprecated = false;
 123         if let Some((depr, span)) = &depr {
 124             is_deprecated = true;
 125
 126             if kind == AnnotationKind::Prohibited || kind == AnnotationKind::DeprecationProhibited {
 127                 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
 128                 self.tcx.struct_span_lint_hir(USELESS_DEPRECATED, hir_id, *span, |lint| {
 129                     lint.build("this `#[deprecated]` annotation has no effect")
 130                         .span_suggestion_short(
 131                             *span,
 132                             "remove the unnecessary deprecation attribute",
 133                             String::new(),
 134                             rustc_errors::Applicability::MachineApplicable,
 135                         )
 136                         .emit()
 137                 });
 138             }
 139
 140             // `Deprecation` is just two pointers, no need to intern it
 141             let depr_entry = DeprecationEntry::local(depr.clone(), def_id);
 142             self.index.depr_map.insert(def_id, depr_entry);
 143         } else if let Some(parent_depr) = self.parent_depr.clone() {
 144             if inherit_deprecation.yes() {
 145                 is_deprecated = true;
 146                 info!("tagging child {:?} as deprecated from parent", def_id);
 147                 self.index.depr_map.insert(def_id, parent_depr);
 148             }
 149         }
 150
 151         if self.tcx.features().staged_api {
 152             if let Some(a) = attrs.iter().find(|a| a.has_name(sym::deprecated)) {
 153                 self.tcx
 154                     .sess
 155                     .struct_span_err(a.span, "`#[deprecated]` cannot be used in staged API")
 156                     .span_label(a.span, "use `#[rustc_deprecated]` instead")
 157                     .span_label(item_sp, "")
 158                     .emit();
 159             }
 160         } else {
 161             self.recurse_with_stability_attrs(
 162                 depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 163                 None,
 164                 None,
 165                 visit_children,
 166             );
 167             return;
 168         }
 169
 170         let (stab, const_stab) = attr::find_stability(&self.tcx.sess, attrs, item_sp);
 171         let mut const_span = None;
 172
 173         let const_stab = const_stab.map(|(const_stab, const_span_node)| {
 174             self.index.const_stab_map.insert(def_id, const_stab);
 175             const_span = Some(const_span_node);
 176             const_stab
 177         });
 178
 179         // If the current node is a function, has const stability attributes and if it doesn not have an intrinsic ABI,
 180         // check if the function/method is const or the parent impl block is const
 181         if let (Some(const_span), Some(fn_sig)) = (const_span, fn_sig) {
 182             if fn_sig.header.abi != Abi::RustIntrinsic
 183                 && fn_sig.header.abi != Abi::PlatformIntrinsic
 184                 && !fn_sig.header.is_const()
 185             {
 186                 if !self.in_trait_impl
 187                     || (self.in_trait_impl && !self.tcx.is_const_fn_raw(def_id.to_def_id()))
 188                 {
 189                     missing_const_err(&self.tcx.sess, fn_sig.span, const_span);
 190                 }
 191             }
 192         }
 193
 194         // `impl const Trait for Type` items forward their const stability to their
 195         // immediate children.
 196         if const_stab.is_none() {
 197             debug!("annotate: const_stab not found, parent = {:?}", self.parent_const_stab);
 198             if let Some(parent) = self.parent_const_stab {
 199                 if parent.level.is_unstable() {
 200                     self.index.const_stab_map.insert(def_id, parent);
 201                 }
 202             }
 203         }
 204
 205         if let Some((rustc_attr::Deprecation { is_since_rustc_version: true, .. }, span)) = &depr {
 206             if stab.is_none() {
 207                 struct_span_err!(
 208                     self.tcx.sess,
 209                     *span,
 210                     E0549,
 211                     "rustc_deprecated attribute must be paired with \
 212                     either stable or unstable attribute"
 213                 )
 214                 .emit();
 215             }
 216         }
 217
 218         let stab = stab.map(|(stab, span)| {
 219             // Error if prohibited, or can't inherit anything from a container.
 220             if kind == AnnotationKind::Prohibited
 221                 || (kind == AnnotationKind::Container && stab.level.is_stable() && is_deprecated)
 222             {
 223                 self.tcx.sess.struct_span_err(span,"this stability annotation is useless")
 224                     .span_label(span, "useless stability annotation")
 225                     .span_label(item_sp, "the stability attribute annotates this item")
 226                     .emit();
 227             }
 228
 229             debug!("annotate: found {:?}", stab);
 230
 231             // Check if deprecated_since < stable_since. If it is,
 232             // this is *almost surely* an accident.
 233             if let (&Some(dep_since), &attr::Stable { since: stab_since }) =
 234                 (&depr.as_ref().and_then(|(d, _)| d.since), &stab.level)
 235             {
 236                 // Explicit version of iter::order::lt to handle parse errors properly
 237                 for (dep_v, stab_v) in
 238                     iter::zip(dep_since.as_str().split('.'), stab_since.as_str().split('.'))
 239                 {
 240                     match stab_v.parse::<u64>() {
 241                         Err(_) => {
 242                             self.tcx.sess.struct_span_err(span, "invalid stability version found")
 243                                 .span_label(span, "invalid stability version")
 244                                 .span_label(item_sp, "the stability attribute annotates this item")
 245                                 .emit();
 246                             break;
 247                         }
 248                         Ok(stab_vp) => match dep_v.parse::<u64>() {
 249                             Ok(dep_vp) => match dep_vp.cmp(&stab_vp) {
 250                                 Ordering::Less => {
 251                                     self.tcx.sess.struct_span_err(span, "an API can't be stabilized after it is deprecated")
 252                                         .span_label(span, "invalid version")
 253                                         .span_label(item_sp, "the stability attribute annotates this item")
 254                                         .emit();
 255                                     break;
 256                                 }
 257                                 Ordering::Equal => continue,
 258                                 Ordering::Greater => break,
 259                             },
 260                             Err(_) => {
 261                                 if dep_v != "TBD" {
 262                                     self.tcx.sess.struct_span_err(span, "invalid deprecation version found")
 263                                         .span_label(span, "invalid deprecation version")
 264                                         .span_label(item_sp, "the stability attribute annotates this item")
 265                                         .emit();
 266                                 }
 267                                 break;
 268                             }
 269                         },
 270                     }
 271                 }
 272             }
 273
 274             self.index.stab_map.insert(def_id, stab);
 275             stab
 276         });
 277
 278         if stab.is_none() {
 279             debug!("annotate: stab not found, parent = {:?}", self.parent_stab);
 280             if let Some(stab) = self.parent_stab {
 281                 if inherit_deprecation.yes() && stab.level.is_unstable()
 282                     || inherit_from_parent.yes()
 283                 {
 284                     self.index.stab_map.insert(def_id, stab);
 285                 }
 286             }
 287         }
 288
 289         self.recurse_with_stability_attrs(
 290             depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 291             stab,
 292             if inherit_const_stability.yes() { const_stab } else { None },
 293             visit_children,
 294         );
 295     }
 296
 297     fn recurse_with_stability_attrs(
 298         &mut self,
 299         depr: Option<DeprecationEntry>,
 300         stab: Option<Stability>,
 301         const_stab: Option<ConstStability>,
 302         f: impl FnOnce(&mut Self),
 303     ) {
 304         // These will be `Some` if this item changes the corresponding stability attribute.
 305         let mut replaced_parent_depr = None;
 306         let mut replaced_parent_stab = None;
 307         let mut replaced_parent_const_stab = None;
 308
 309         if let Some(depr) = depr {
 310             replaced_parent_depr = Some(replace(&mut self.parent_depr, Some(depr)));
 311         }
 312         if let Some(stab) = stab {
 313             replaced_parent_stab = Some(replace(&mut self.parent_stab, Some(stab)));
 314         }
 315         if let Some(const_stab) = const_stab {
 316             replaced_parent_const_stab =
 317                 Some(replace(&mut self.parent_const_stab, Some(const_stab)));
 318         }
 319
 320         f(self);
 321
 322         if let Some(orig_parent_depr) = replaced_parent_depr {
 323             self.parent_depr = orig_parent_depr;
 324         }
 325         if let Some(orig_parent_stab) = replaced_parent_stab {
 326             self.parent_stab = orig_parent_stab;
 327         }
 328         if let Some(orig_parent_const_stab) = replaced_parent_const_stab {
 329             self.parent_const_stab = orig_parent_const_stab;
 330         }
 331     }
 332
 333     // returns true if an error occurred, used to suppress some spurious errors
 334     fn forbid_staged_api_attrs(
 335         &mut self,
 336         def_id: LocalDefId,
 337         attrs: &[Attribute],
 338         inherit_deprecation: InheritDeprecation,
 339     ) -> bool {
 340         // Emit errors for non-staged-api crates.
 341         let unstable_attrs = [
 342             sym::unstable,
 343             sym::stable,
 344             sym::rustc_deprecated,
 345             sym::rustc_const_unstable,
 346             sym::rustc_const_stable,
 347         ];
 348         let mut has_error = false;
 349         for attr in attrs {
 350             let name = attr.name_or_empty();
 351             if unstable_attrs.contains(&name) {
 352                 struct_span_err!(
 353                     self.tcx.sess,
 354                     attr.span,
 355                     E0734,
 356                     "stability attributes may not be used outside of the standard library",
 357                 )
 358                 .emit();
 359                 has_error = true;
 360             }
 361         }
 362
 363         // Propagate unstability.  This can happen even for non-staged-api crates in case
 364         // -Zforce-unstable-if-unmarked is set.
 365         if let Some(stab) = self.parent_stab {
 366             if inherit_deprecation.yes() && stab.level.is_unstable() {
 367                 self.index.stab_map.insert(def_id, stab);
 368             }
 369         }
 370
 371         has_error
 372     }
 373 }
 374
 375 impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
 376     /// Because stability levels are scoped lexically, we want to walk
 377     /// nested items in the context of the outer item, so enable
 378     /// deep-walking.
 379     type NestedFilter = nested_filter::All;
 380
 381     fn nested_visit_map(&mut self) -> Self::Map {
 382         self.tcx.hir()
 383     }
 384
 385     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 386         let orig_in_trait_impl = self.in_trait_impl;
 387         let mut kind = AnnotationKind::Required;
 388         let mut const_stab_inherit = InheritConstStability::No;
 389         let mut fn_sig = None;
 390
 391         match i.kind {
 392             // Inherent impls and foreign modules serve only as containers for other items,
 393             // they don't have their own stability. They still can be annotated as unstable
 394             // and propagate this unstability to children, but this annotation is completely
 395             // optional. They inherit stability from their parents when unannotated.
 396             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 397             | hir::ItemKind::ForeignMod { .. } => {
 398                 self.in_trait_impl = false;
 399                 kind = AnnotationKind::Container;
 400             }
 401             hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => {
 402                 self.in_trait_impl = true;
 403                 kind = AnnotationKind::DeprecationProhibited;
 404                 const_stab_inherit = InheritConstStability::Yes;
 405             }
 406             hir::ItemKind::Struct(ref sd, _) => {
 407                 if let Some(ctor_hir_id) = sd.ctor_hir_id() {
 408                     self.annotate(
 409                         self.tcx.hir().local_def_id(ctor_hir_id),
 410                         i.span,
 411                         None,
 412                         AnnotationKind::Required,
 413                         InheritDeprecation::Yes,
 414                         InheritConstStability::No,
 415                         InheritStability::Yes,
 416                         |_| {},
 417                     )
 418                 }
 419             }
 420             hir::ItemKind::Fn(ref item_fn_sig, _, _) => {
 421                 fn_sig = Some(item_fn_sig);
 422             }
 423             _ => {}
 424         }
 425
 426         self.annotate(
 427             i.def_id,
 428             i.span,
 429             fn_sig,
 430             kind,
 431             InheritDeprecation::Yes,
 432             const_stab_inherit,
 433             InheritStability::No,
 434             |v| intravisit::walk_item(v, i),
 435         );
 436         self.in_trait_impl = orig_in_trait_impl;
 437     }
 438
 439     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 440         let fn_sig = match ti.kind {
 441             hir::TraitItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 442             _ => None,
 443         };
 444
 445         self.annotate(
 446             ti.def_id,
 447             ti.span,
 448             fn_sig,
 449             AnnotationKind::Required,
 450             InheritDeprecation::Yes,
 451             InheritConstStability::No,
 452             InheritStability::No,
 453             |v| {
 454                 intravisit::walk_trait_item(v, ti);
 455             },
 456         );
 457     }
 458
 459     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 460         let kind =
 461             if self.in_trait_impl { AnnotationKind::Prohibited } else { AnnotationKind::Required };
 462
 463         let fn_sig = match ii.kind {
 464             hir::ImplItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 465             _ => None,
 466         };
 467
 468         self.annotate(
 469             ii.def_id,
 470             ii.span,
 471             fn_sig,
 472             kind,
 473             InheritDeprecation::Yes,
 474             InheritConstStability::No,
 475             InheritStability::No,
 476             |v| {
 477                 intravisit::walk_impl_item(v, ii);
 478             },
 479         );
 480     }
 481
 482     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 483         self.annotate(
 484             self.tcx.hir().local_def_id(var.id),
 485             var.span,
 486             None,
 487             AnnotationKind::Required,
 488             InheritDeprecation::Yes,
 489             InheritConstStability::No,
 490             InheritStability::Yes,
 491             |v| {
 492                 if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
 493                     v.annotate(
 494                         v.tcx.hir().local_def_id(ctor_hir_id),
 495                         var.span,
 496                         None,
 497                         AnnotationKind::Required,
 498                         InheritDeprecation::Yes,
 499                         InheritConstStability::No,
 500                         InheritStability::No,
 501                         |_| {},
 502                     );
 503                 }
 504
 505                 intravisit::walk_variant(v, var, g, item_id)
 506             },
 507         )
 508     }
 509
 510     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 511         self.annotate(
 512             self.tcx.hir().local_def_id(s.hir_id),
 513             s.span,
 514             None,
 515             AnnotationKind::Required,
 516             InheritDeprecation::Yes,
 517             InheritConstStability::No,
 518             InheritStability::Yes,
 519             |v| {
 520                 intravisit::walk_field_def(v, s);
 521             },
 522         );
 523     }
 524
 525     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 526         self.annotate(
 527             i.def_id,
 528             i.span,
 529             None,
 530             AnnotationKind::Required,
 531             InheritDeprecation::Yes,
 532             InheritConstStability::No,
 533             InheritStability::No,
 534             |v| {
 535                 intravisit::walk_foreign_item(v, i);
 536             },
 537         );
 538     }
 539
 540     fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
 541         let kind = match &p.kind {
 542             // Allow stability attributes on default generic arguments.
 543             hir::GenericParamKind::Type { default: Some(_), .. }
 544             | hir::GenericParamKind::Const { default: Some(_), .. } => AnnotationKind::Container,
 545             _ => AnnotationKind::Prohibited,
 546         };
 547
 548         self.annotate(
 549             self.tcx.hir().local_def_id(p.hir_id),
 550             p.span,
 551             None,
 552             kind,
 553             InheritDeprecation::No,
 554             InheritConstStability::No,
 555             InheritStability::No,
 556             |v| {
 557                 intravisit::walk_generic_param(v, p);
 558             },
 559         );
 560     }
 561 }
 562
 563 struct MissingStabilityAnnotations<'tcx> {
 564     tcx: TyCtxt<'tcx>,
 565     access_levels: &'tcx AccessLevels,
 566 }
 567
 568 impl<'tcx> MissingStabilityAnnotations<'tcx> {
 569     fn check_missing_stability(&self, def_id: LocalDefId, span: Span) {
 570         let stab = self.tcx.stability().local_stability(def_id);
 571         if !self.tcx.sess.opts.test && stab.is_none() && self.access_levels.is_reachable(def_id) {
 572             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 573             self.tcx.sess.span_err(span, &format!("{} has missing stability attribute", descr));
 574         }
 575     }
 576
 577     fn check_missing_const_stability(&self, def_id: LocalDefId, span: Span) {
 578         if !self.tcx.features().staged_api {
 579             return;
 580         }
 581
 582         let is_const = self.tcx.is_const_fn(def_id.to_def_id());
 583         let is_stable = self
 584             .tcx
 585             .lookup_stability(def_id)
 586             .map_or(false, |stability| stability.level.is_stable());
 587         let missing_const_stability_attribute = self.tcx.lookup_const_stability(def_id).is_none();
 588         let is_reachable = self.access_levels.is_reachable(def_id);
 589
 590         if is_const && is_stable && missing_const_stability_attribute && is_reachable {
 591             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 592             self.tcx.sess.span_err(span, &format!("{descr} has missing const stability attribute"));
 593         }
 594     }
 595 }
 596
 597 impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
 598     type NestedFilter = nested_filter::OnlyBodies;
 599
 600     fn nested_visit_map(&mut self) -> Self::Map {
 601         self.tcx.hir()
 602     }
 603
 604     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 605         // Inherent impls and foreign modules serve only as containers for other items,
 606         // they don't have their own stability. They still can be annotated as unstable
 607         // and propagate this unstability to children, but this annotation is completely
 608         // optional. They inherit stability from their parents when unannotated.
 609         if !matches!(
 610             i.kind,
 611             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 612                 | hir::ItemKind::ForeignMod { .. }
 613         ) {
 614             self.check_missing_stability(i.def_id, i.span);
 615         }
 616
 617         // Ensure stable `const fn` have a const stability attribute.
 618         self.check_missing_const_stability(i.def_id, i.span);
 619
 620         intravisit::walk_item(self, i)
 621     }
 622
 623     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 624         self.check_missing_stability(ti.def_id, ti.span);
 625         intravisit::walk_trait_item(self, ti);
 626     }
 627
 628     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 629         let impl_def_id = self.tcx.hir().get_parent_item(ii.hir_id());
 630         if self.tcx.impl_trait_ref(impl_def_id).is_none() {
 631             self.check_missing_stability(ii.def_id, ii.span);
 632             self.check_missing_const_stability(ii.def_id, ii.span);
 633         }
 634         intravisit::walk_impl_item(self, ii);
 635     }
 636
 637     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 638         self.check_missing_stability(self.tcx.hir().local_def_id(var.id), var.span);
 639         intravisit::walk_variant(self, var, g, item_id);
 640     }
 641
 642     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 643         self.check_missing_stability(self.tcx.hir().local_def_id(s.hir_id), s.span);
 644         intravisit::walk_field_def(self, s);
 645     }
 646
 647     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 648         self.check_missing_stability(i.def_id, i.span);
 649         intravisit::walk_foreign_item(self, i);
 650     }
 651     // Note that we don't need to `check_missing_stability` for default generic parameters,
 652     // as we assume that any default generic parameters without attributes are automatically
 653     // stable (assuming they have not inherited instability from their parent).
 654 }
 655
 656 fn stability_index(tcx: TyCtxt<'_>, (): ()) -> Index {
 657     let is_staged_api =
 658         tcx.sess.opts.debugging_opts.force_unstable_if_unmarked || tcx.features().staged_api;
 659     let mut staged_api = FxHashMap::default();
 660     staged_api.insert(LOCAL_CRATE, is_staged_api);
 661     let mut index = Index {
 662         staged_api,
 663         stab_map: Default::default(),
 664         const_stab_map: Default::default(),
 665         depr_map: Default::default(),
 666         active_features: Default::default(),
 667     };
 668
 669     let active_lib_features = &tcx.features().declared_lib_features;
 670     let active_lang_features = &tcx.features().declared_lang_features;
 671
 672     // Put the active features into a map for quick lookup.
 673     index.active_features = active_lib_features
 674         .iter()
 675         .map(|&(s, ..)| s)
 676         .chain(active_lang_features.iter().map(|&(s, ..)| s))
 677         .collect();
 678
 679     {
 680         let mut annotator = Annotator {
 681             tcx,
 682             index: &mut index,
 683             parent_stab: None,
 684             parent_const_stab: None,
 685             parent_depr: None,
 686             in_trait_impl: false,
 687         };
 688
 689         // If the `-Z force-unstable-if-unmarked` flag is passed then we provide
 690         // a parent stability annotation which indicates that this is private
 691         // with the `rustc_private` feature. This is intended for use when
 692         // compiling `librustc_*` crates themselves so we can leverage crates.io
 693         // while maintaining the invariant that all sysroot crates are unstable
 694         // by default and are unable to be used.
 695         if tcx.sess.opts.debugging_opts.force_unstable_if_unmarked {
 696             let reason = "this crate is being loaded from the sysroot, an \
 697                           unstable location; did you mean to load this crate \
 698                           from crates.io via `Cargo.toml` instead?";
 699             let stability = Stability {
 700                 level: attr::StabilityLevel::Unstable {
 701                     reason: Some(Symbol::intern(reason)),
 702                     issue: NonZeroU32::new(27812),
 703                     is_soft: false,
 704                 },
 705                 feature: sym::rustc_private,
 706             };
 707             annotator.parent_stab = Some(stability);
 708         }
 709
 710         annotator.annotate(
 711             CRATE_DEF_ID,
 712             tcx.hir().span(CRATE_HIR_ID),
 713             None,
 714             AnnotationKind::Required,
 715             InheritDeprecation::Yes,
 716             InheritConstStability::No,
 717             InheritStability::No,
 718             |v| tcx.hir().walk_toplevel_module(v),
 719         );
 720     }
 721     index
 722 }
 723
 724 /// Cross-references the feature names of unstable APIs with enabled
 725 /// features and possibly prints errors.
 726 fn check_mod_unstable_api_usage(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 727     tcx.hir().visit_item_likes_in_module(module_def_id, &mut Checker { tcx }.as_deep_visitor());
 728 }
 729
 730 pub(crate) fn provide(providers: &mut Providers) {
 731     *providers = Providers { check_mod_unstable_api_usage, stability_index, ..*providers };
 732 }
 733
 734 struct Checker<'tcx> {
 735     tcx: TyCtxt<'tcx>,
 736 }
 737
 738 impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
 739     type NestedFilter = nested_filter::OnlyBodies;
 740
 741     /// Because stability levels are scoped lexically, we want to walk
 742     /// nested items in the context of the outer item, so enable
 743     /// deep-walking.
 744     fn nested_visit_map(&mut self) -> Self::Map {
 745         self.tcx.hir()
 746     }
 747
 748     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 749         match item.kind {
 750             hir::ItemKind::ExternCrate(_) => {
 751                 // compiler-generated `extern crate` items have a dummy span.
 752                 // `std` is still checked for the `restricted-std` feature.
 753                 if item.span.is_dummy() && item.ident.as_str() != "std" {
 754                     return;
 755                 }
 756
 757                 let Some(cnum) = self.tcx.extern_mod_stmt_cnum(item.def_id) else {
 758                     return;
 759                 };
 760                 let def_id = DefId { krate: cnum, index: CRATE_DEF_INDEX };
 761                 self.tcx.check_stability(def_id, Some(item.hir_id()), item.span, None);
 762             }
 763
 764             // For implementations of traits, check the stability of each item
 765             // individually as it's possible to have a stable trait with unstable
 766             // items.
 767             hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref t), self_ty, items, .. }) => {
 768                 if self.tcx.features().staged_api {
 769                     // If this impl block has an #[unstable] attribute, give an
 770                     // error if all involved types and traits are stable, because
 771                     // it will have no effect.
 772                     // See: https://github.com/rust-lang/rust/issues/55436
 773                     let attrs = self.tcx.hir().attrs(item.hir_id());
 774                     if let (Some((Stability { level: attr::Unstable { .. }, .. }, span)), _) =
 775                         attr::find_stability(&self.tcx.sess, attrs, item.span)
 776                     {
 777                         let mut c = CheckTraitImplStable { tcx: self.tcx, fully_stable: true };
 778                         c.visit_ty(self_ty);
 779                         c.visit_trait_ref(t);
 780                         if c.fully_stable {
 781                             self.tcx.struct_span_lint_hir(
 782                                 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
 783                                 item.hir_id(),
 784                                 span,
 785                                 |lint| lint
 786                                     .build("an `#[unstable]` annotation here has no effect")
 787                                     .note("see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information")
 788                                     .emit()
 789                             );
 790                         }
 791                     }
 792                 }
 793
 794                 for impl_item_ref in items {
 795                     let impl_item = self.tcx.associated_item(impl_item_ref.id.def_id);
 796
 797                     if let Some(def_id) = impl_item.trait_item_def_id {
 798                         // Pass `None` to skip deprecation warnings.
 799                         self.tcx.check_stability(def_id, None, impl_item_ref.span, None);
 800                     }
 801                 }
 802             }
 803
 804             // There's no good place to insert stability check for non-Copy unions,
 805             // so semi-randomly perform it here in stability.rs
 806             hir::ItemKind::Union(..) if !self.tcx.features().untagged_unions => {
 807                 let ty = self.tcx.type_of(item.def_id);
 808                 let ty::Adt(adt_def, substs) = ty.kind() else { bug!() };
 809
 810                 // Non-`Copy` fields are unstable, except for `ManuallyDrop`.
 811                 let param_env = self.tcx.param_env(item.def_id);
 812                 for field in &adt_def.non_enum_variant().fields {
 813                     let field_ty = field.ty(self.tcx, substs);
 814                     if !field_ty.ty_adt_def().map_or(false, |adt_def| adt_def.is_manually_drop())
 815                         && !field_ty.is_copy_modulo_regions(self.tcx.at(DUMMY_SP), param_env)
 816                     {
 817                         if field_ty.needs_drop(self.tcx, param_env) {
 818                             // Avoid duplicate error: This will error later anyway because fields
 819                             // that need drop are not allowed.
 820                             self.tcx.sess.delay_span_bug(
 821                                 item.span,
 822                                 "union should have been rejected due to potentially dropping field",
 823                             );
 824                         } else {
 825                             feature_err(
 826                                 &self.tcx.sess.parse_sess,
 827                                 sym::untagged_unions,
 828                                 self.tcx.def_span(field.did),
 829                                 "unions with non-`Copy` fields other than `ManuallyDrop<T>` are unstable",
 830                             )
 831                             .emit();
 832                         }
 833                     }
 834                 }
 835             }
 836
 837             _ => (/* pass */),
 838         }
 839         intravisit::walk_item(self, item);
 840     }
 841
 842     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, id: hir::HirId) {
 843         if let Some(def_id) = path.res.opt_def_id() {
 844             let method_span = path.segments.last().map(|s| s.ident.span);
 845             self.tcx.check_stability(def_id, Some(id), path.span, method_span)
 846         }
 847         intravisit::walk_path(self, path)
 848     }
 849 }
 850
 851 struct CheckTraitImplStable<'tcx> {
 852     tcx: TyCtxt<'tcx>,
 853     fully_stable: bool,
 854 }
 855
 856 impl<'tcx> Visitor<'tcx> for CheckTraitImplStable<'tcx> {
 857     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _id: hir::HirId) {
 858         if let Some(def_id) = path.res.opt_def_id() {
 859             if let Some(stab) = self.tcx.lookup_stability(def_id) {
 860                 self.fully_stable &= stab.level.is_stable();
 861             }
 862         }
 863         intravisit::walk_path(self, path)
 864     }
 865
 866     fn visit_trait_ref(&mut self, t: &'tcx TraitRef<'tcx>) {
 867         if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
 868             if let Some(stab) = self.tcx.lookup_stability(trait_did) {
 869                 self.fully_stable &= stab.level.is_stable();
 870             }
 871         }
 872         intravisit::walk_trait_ref(self, t)
 873     }
 874
 875     fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
 876         if let TyKind::Never = t.kind {
 877             self.fully_stable = false;
 878         }
 879         intravisit::walk_ty(self, t)
 880     }
 881 }
 882
 883 /// Given the list of enabled features that were not language features (i.e., that
 884 /// were expected to be library features), and the list of features used from
 885 /// libraries, identify activated features that don't exist and error about them.
 886 pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
 887     let access_levels = &tcx.privacy_access_levels(());
 888
 889     if tcx.stability().staged_api[&LOCAL_CRATE] {
 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().visit_all_item_likes(&mut missing.as_deep_visitor());
 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 = FxHashMap::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 FxHashMap<_, _>, 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 }