compiler/rustc_passes/src/stability.rs

   1 //! A pass that annotates every item and method with its stability level,
   2 //! propagating default levels lexically from parent to children ast nodes.
   3
   4 use crate::errors;
   5 use rustc_attr::{
   6     self as attr, rust_version_symbol, ConstStability, Stability, StabilityLevel, Unstable,
   7     UnstableReason, VERSION_PLACEHOLDER,
   8 };
   9 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
  10 use rustc_errors::{struct_span_err, Applicability};
  11 use rustc_hir as hir;
  12 use rustc_hir::def::{DefKind, Res};
  13 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
  14 use rustc_hir::hir_id::CRATE_HIR_ID;
  15 use rustc_hir::intravisit::{self, Visitor};
  16 use rustc_hir::{FieldDef, Item, ItemKind, TraitRef, Ty, TyKind, Variant};
  17 use rustc_middle::hir::nested_filter;
  18 use rustc_middle::middle::privacy::AccessLevels;
  19 use rustc_middle::middle::stability::{AllowUnstable, DeprecationEntry, Index};
  20 use rustc_middle::ty::{query::Providers, TyCtxt};
  21 use rustc_session::lint;
  22 use rustc_session::lint::builtin::{INEFFECTIVE_UNSTABLE_TRAIT_IMPL, USELESS_DEPRECATED};
  23 use rustc_session::Session;
  24 use rustc_span::symbol::{sym, Symbol};
  25 use rustc_span::Span;
  26 use rustc_target::spec::abi::Abi;
  27
  28 use std::cmp::Ordering;
  29 use std::iter;
  30 use std::mem::replace;
  31 use std::num::NonZeroU32;
  32
  33 #[derive(PartialEq)]
  34 enum AnnotationKind {
  35     /// Annotation is required if not inherited from unstable parents.
  36     Required,
  37     /// Annotation is useless, reject it.
  38     Prohibited,
  39     /// Deprecation annotation is useless, reject it. (Stability attribute is still required.)
  40     DeprecationProhibited,
  41     /// Annotation itself is useless, but it can be propagated to children.
  42     Container,
  43 }
  44
  45 /// Whether to inherit deprecation flags for nested items. In most cases, we do want to inherit
  46 /// deprecation, because nested items rarely have individual deprecation attributes, and so
  47 /// should be treated as deprecated if their parent is. However, default generic parameters
  48 /// have separate deprecation attributes from their parents, so we do not wish to inherit
  49 /// deprecation in this case. For example, inheriting deprecation for `T` in `Foo<T>`
  50 /// would cause a duplicate warning arising from both `Foo` and `T` being deprecated.
  51 #[derive(Clone)]
  52 enum InheritDeprecation {
  53     Yes,
  54     No,
  55 }
  56
  57 impl InheritDeprecation {
  58     fn yes(&self) -> bool {
  59         matches!(self, InheritDeprecation::Yes)
  60     }
  61 }
  62
  63 /// Whether to inherit const stability flags for nested items. In most cases, we do not want to
  64 /// inherit const stability: just because an enclosing `fn` is const-stable does not mean
  65 /// all `extern` imports declared in it should be const-stable! However, trait methods
  66 /// inherit const stability attributes from their parent and do not have their own.
  67 enum InheritConstStability {
  68     Yes,
  69     No,
  70 }
  71
  72 impl InheritConstStability {
  73     fn yes(&self) -> bool {
  74         matches!(self, InheritConstStability::Yes)
  75     }
  76 }
  77
  78 enum InheritStability {
  79     Yes,
  80     No,
  81 }
  82
  83 impl InheritStability {
  84     fn yes(&self) -> bool {
  85         matches!(self, InheritStability::Yes)
  86     }
  87 }
  88
  89 /// A private tree-walker for producing an `Index`.
  90 struct Annotator<'a, 'tcx> {
  91     tcx: TyCtxt<'tcx>,
  92     index: &'a mut Index,
  93     parent_stab: Option<Stability>,
  94     parent_const_stab: Option<ConstStability>,
  95     parent_depr: Option<DeprecationEntry>,
  96     in_trait_impl: bool,
  97 }
  98
  99 impl<'a, 'tcx> Annotator<'a, 'tcx> {
 100     /// Determine the stability for a node based on its attributes and inherited stability. The
 101     /// stability is recorded in the index and used as the parent. If the node is a function,
 102     /// `fn_sig` is its signature.
 103     fn annotate<F>(
 104         &mut self,
 105         def_id: LocalDefId,
 106         item_sp: Span,
 107         fn_sig: Option<&'tcx hir::FnSig<'tcx>>,
 108         kind: AnnotationKind,
 109         inherit_deprecation: InheritDeprecation,
 110         inherit_const_stability: InheritConstStability,
 111         inherit_from_parent: InheritStability,
 112         visit_children: F,
 113     ) where
 114         F: FnOnce(&mut Self),
 115     {
 116         let attrs = self.tcx.hir().attrs(self.tcx.hir().local_def_id_to_hir_id(def_id));
 117         debug!("annotate(id = {:?}, attrs = {:?})", def_id, attrs);
 118
 119         let depr = attr::find_deprecation(&self.tcx.sess, attrs);
 120         let mut is_deprecated = false;
 121         if let Some((depr, span)) = &depr {
 122             is_deprecated = true;
 123
 124             if kind == AnnotationKind::Prohibited || kind == AnnotationKind::DeprecationProhibited {
 125                 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
 126                 self.tcx.emit_spanned_lint(
 127                     USELESS_DEPRECATED,
 128                     hir_id,
 129                     *span,
 130                     errors::DeprecatedAnnotationHasNoEffect { span: *span },
 131                 );
 132             }
 133
 134             // `Deprecation` is just two pointers, no need to intern it
 135             let depr_entry = DeprecationEntry::local(*depr, def_id);
 136             self.index.depr_map.insert(def_id, depr_entry);
 137         } else if let Some(parent_depr) = self.parent_depr {
 138             if inherit_deprecation.yes() {
 139                 is_deprecated = true;
 140                 info!("tagging child {:?} as deprecated from parent", def_id);
 141                 self.index.depr_map.insert(def_id, parent_depr);
 142             }
 143         }
 144
 145         if !self.tcx.features().staged_api {
 146             // Propagate unstability.  This can happen even for non-staged-api crates in case
 147             // -Zforce-unstable-if-unmarked is set.
 148             if let Some(stab) = self.parent_stab {
 149                 if inherit_deprecation.yes() && stab.is_unstable() {
 150                     self.index.stab_map.insert(def_id, stab);
 151                 }
 152             }
 153
 154             self.recurse_with_stability_attrs(
 155                 depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 156                 None,
 157                 None,
 158                 visit_children,
 159             );
 160             return;
 161         }
 162
 163         let (stab, const_stab, body_stab) = attr::find_stability(&self.tcx.sess, attrs, item_sp);
 164         let mut const_span = None;
 165
 166         let const_stab = const_stab.map(|(const_stab, const_span_node)| {
 167             self.index.const_stab_map.insert(def_id, const_stab);
 168             const_span = Some(const_span_node);
 169             const_stab
 170         });
 171
 172         // If the current node is a function, has const stability attributes and if it doesn not have an intrinsic ABI,
 173         // check if the function/method is const or the parent impl block is const
 174         if let (Some(const_span), Some(fn_sig)) = (const_span, fn_sig) {
 175             if fn_sig.header.abi != Abi::RustIntrinsic
 176                 && fn_sig.header.abi != Abi::PlatformIntrinsic
 177                 && !fn_sig.header.is_const()
 178             {
 179                 if !self.in_trait_impl
 180                     || (self.in_trait_impl && !self.tcx.is_const_fn_raw(def_id.to_def_id()))
 181                 {
 182                     missing_const_err(&self.tcx.sess, fn_sig.span, const_span);
 183                 }
 184             }
 185         }
 186
 187         // `impl const Trait for Type` items forward their const stability to their
 188         // immediate children.
 189         if const_stab.is_none() {
 190             debug!("annotate: const_stab not found, parent = {:?}", self.parent_const_stab);
 191             if let Some(parent) = self.parent_const_stab {
 192                 if parent.is_const_unstable() {
 193                     self.index.const_stab_map.insert(def_id, parent);
 194                 }
 195             }
 196         }
 197
 198         if let Some((rustc_attr::Deprecation { is_since_rustc_version: true, .. }, span)) = &depr {
 199             if stab.is_none() {
 200                 struct_span_err!(
 201                     self.tcx.sess,
 202                     *span,
 203                     E0549,
 204                     "deprecated attribute must be paired with \
 205                     either stable or unstable attribute"
 206                 )
 207                 .emit();
 208             }
 209         }
 210
 211         if let Some((body_stab, _span)) = body_stab {
 212             // FIXME: check that this item can have body stability
 213
 214             self.index.default_body_stab_map.insert(def_id, body_stab);
 215             debug!(?self.index.default_body_stab_map);
 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             if let Stability { level: Unstable { implied_by: Some(implied_by), .. }, feature } = stab {
 275                 self.index.implications.insert(implied_by, feature);
 276             }
 277
 278             self.index.stab_map.insert(def_id, stab);
 279             stab
 280         });
 281
 282         if stab.is_none() {
 283             debug!("annotate: stab not found, parent = {:?}", self.parent_stab);
 284             if let Some(stab) = self.parent_stab {
 285                 if inherit_deprecation.yes() && stab.is_unstable() || inherit_from_parent.yes() {
 286                     self.index.stab_map.insert(def_id, stab);
 287                 }
 288             }
 289         }
 290
 291         self.recurse_with_stability_attrs(
 292             depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
 293             stab,
 294             if inherit_const_stability.yes() { const_stab } else { None },
 295             visit_children,
 296         );
 297     }
 298
 299     fn recurse_with_stability_attrs(
 300         &mut self,
 301         depr: Option<DeprecationEntry>,
 302         stab: Option<Stability>,
 303         const_stab: Option<ConstStability>,
 304         f: impl FnOnce(&mut Self),
 305     ) {
 306         // These will be `Some` if this item changes the corresponding stability attribute.
 307         let mut replaced_parent_depr = None;
 308         let mut replaced_parent_stab = None;
 309         let mut replaced_parent_const_stab = None;
 310
 311         if let Some(depr) = depr {
 312             replaced_parent_depr = Some(replace(&mut self.parent_depr, Some(depr)));
 313         }
 314         if let Some(stab) = stab {
 315             replaced_parent_stab = Some(replace(&mut self.parent_stab, Some(stab)));
 316         }
 317         if let Some(const_stab) = const_stab {
 318             replaced_parent_const_stab =
 319                 Some(replace(&mut self.parent_const_stab, Some(const_stab)));
 320         }
 321
 322         f(self);
 323
 324         if let Some(orig_parent_depr) = replaced_parent_depr {
 325             self.parent_depr = orig_parent_depr;
 326         }
 327         if let Some(orig_parent_stab) = replaced_parent_stab {
 328             self.parent_stab = orig_parent_stab;
 329         }
 330         if let Some(orig_parent_const_stab) = replaced_parent_const_stab {
 331             self.parent_const_stab = orig_parent_const_stab;
 332         }
 333     }
 334 }
 335
 336 impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
 337     /// Because stability levels are scoped lexically, we want to walk
 338     /// nested items in the context of the outer item, so enable
 339     /// deep-walking.
 340     type NestedFilter = nested_filter::All;
 341
 342     fn nested_visit_map(&mut self) -> Self::Map {
 343         self.tcx.hir()
 344     }
 345
 346     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 347         let orig_in_trait_impl = self.in_trait_impl;
 348         let mut kind = AnnotationKind::Required;
 349         let mut const_stab_inherit = InheritConstStability::No;
 350         let mut fn_sig = None;
 351
 352         match i.kind {
 353             // Inherent impls and foreign modules serve only as containers for other items,
 354             // they don't have their own stability. They still can be annotated as unstable
 355             // and propagate this instability to children, but this annotation is completely
 356             // optional. They inherit stability from their parents when unannotated.
 357             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 358             | hir::ItemKind::ForeignMod { .. } => {
 359                 self.in_trait_impl = false;
 360                 kind = AnnotationKind::Container;
 361             }
 362             hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => {
 363                 self.in_trait_impl = true;
 364                 kind = AnnotationKind::DeprecationProhibited;
 365                 const_stab_inherit = InheritConstStability::Yes;
 366             }
 367             hir::ItemKind::Struct(ref sd, _) => {
 368                 if let Some(ctor_hir_id) = sd.ctor_hir_id() {
 369                     self.annotate(
 370                         self.tcx.hir().local_def_id(ctor_hir_id),
 371                         i.span,
 372                         None,
 373                         AnnotationKind::Required,
 374                         InheritDeprecation::Yes,
 375                         InheritConstStability::No,
 376                         InheritStability::Yes,
 377                         |_| {},
 378                     )
 379                 }
 380             }
 381             hir::ItemKind::Fn(ref item_fn_sig, _, _) => {
 382                 fn_sig = Some(item_fn_sig);
 383             }
 384             _ => {}
 385         }
 386
 387         self.annotate(
 388             i.def_id.def_id,
 389             i.span,
 390             fn_sig,
 391             kind,
 392             InheritDeprecation::Yes,
 393             const_stab_inherit,
 394             InheritStability::No,
 395             |v| intravisit::walk_item(v, i),
 396         );
 397         self.in_trait_impl = orig_in_trait_impl;
 398     }
 399
 400     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 401         let fn_sig = match ti.kind {
 402             hir::TraitItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 403             _ => None,
 404         };
 405
 406         self.annotate(
 407             ti.def_id.def_id,
 408             ti.span,
 409             fn_sig,
 410             AnnotationKind::Required,
 411             InheritDeprecation::Yes,
 412             InheritConstStability::No,
 413             InheritStability::No,
 414             |v| {
 415                 intravisit::walk_trait_item(v, ti);
 416             },
 417         );
 418     }
 419
 420     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 421         let kind =
 422             if self.in_trait_impl { AnnotationKind::Prohibited } else { AnnotationKind::Required };
 423
 424         let fn_sig = match ii.kind {
 425             hir::ImplItemKind::Fn(ref fn_sig, _) => Some(fn_sig),
 426             _ => None,
 427         };
 428
 429         self.annotate(
 430             ii.def_id.def_id,
 431             ii.span,
 432             fn_sig,
 433             kind,
 434             InheritDeprecation::Yes,
 435             InheritConstStability::No,
 436             InheritStability::No,
 437             |v| {
 438                 intravisit::walk_impl_item(v, ii);
 439             },
 440         );
 441     }
 442
 443     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>) {
 444         self.annotate(
 445             self.tcx.hir().local_def_id(var.id),
 446             var.span,
 447             None,
 448             AnnotationKind::Required,
 449             InheritDeprecation::Yes,
 450             InheritConstStability::No,
 451             InheritStability::Yes,
 452             |v| {
 453                 if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
 454                     v.annotate(
 455                         v.tcx.hir().local_def_id(ctor_hir_id),
 456                         var.span,
 457                         None,
 458                         AnnotationKind::Required,
 459                         InheritDeprecation::Yes,
 460                         InheritConstStability::No,
 461                         InheritStability::Yes,
 462                         |_| {},
 463                     );
 464                 }
 465
 466                 intravisit::walk_variant(v, var)
 467             },
 468         )
 469     }
 470
 471     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 472         self.annotate(
 473             self.tcx.hir().local_def_id(s.hir_id),
 474             s.span,
 475             None,
 476             AnnotationKind::Required,
 477             InheritDeprecation::Yes,
 478             InheritConstStability::No,
 479             InheritStability::Yes,
 480             |v| {
 481                 intravisit::walk_field_def(v, s);
 482             },
 483         );
 484     }
 485
 486     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 487         self.annotate(
 488             i.def_id.def_id,
 489             i.span,
 490             None,
 491             AnnotationKind::Required,
 492             InheritDeprecation::Yes,
 493             InheritConstStability::No,
 494             InheritStability::No,
 495             |v| {
 496                 intravisit::walk_foreign_item(v, i);
 497             },
 498         );
 499     }
 500
 501     fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
 502         let kind = match &p.kind {
 503             // Allow stability attributes on default generic arguments.
 504             hir::GenericParamKind::Type { default: Some(_), .. }
 505             | hir::GenericParamKind::Const { default: Some(_), .. } => AnnotationKind::Container,
 506             _ => AnnotationKind::Prohibited,
 507         };
 508
 509         self.annotate(
 510             self.tcx.hir().local_def_id(p.hir_id),
 511             p.span,
 512             None,
 513             kind,
 514             InheritDeprecation::No,
 515             InheritConstStability::No,
 516             InheritStability::No,
 517             |v| {
 518                 intravisit::walk_generic_param(v, p);
 519             },
 520         );
 521     }
 522 }
 523
 524 struct MissingStabilityAnnotations<'tcx> {
 525     tcx: TyCtxt<'tcx>,
 526     access_levels: &'tcx AccessLevels,
 527 }
 528
 529 impl<'tcx> MissingStabilityAnnotations<'tcx> {
 530     fn check_missing_stability(&self, def_id: LocalDefId, span: Span) {
 531         let stab = self.tcx.stability().local_stability(def_id);
 532         if !self.tcx.sess.opts.test && stab.is_none() && self.access_levels.is_reachable(def_id) {
 533             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 534             self.tcx.sess.span_err(span, &format!("{} has missing stability attribute", descr));
 535         }
 536     }
 537
 538     fn check_missing_const_stability(&self, def_id: LocalDefId, span: Span) {
 539         if !self.tcx.features().staged_api {
 540             return;
 541         }
 542
 543         let is_const = self.tcx.is_const_fn(def_id.to_def_id())
 544             || self.tcx.is_const_trait_impl_raw(def_id.to_def_id());
 545         let is_stable = self
 546             .tcx
 547             .lookup_stability(def_id)
 548             .map_or(false, |stability| stability.level.is_stable());
 549         let missing_const_stability_attribute = self.tcx.lookup_const_stability(def_id).is_none();
 550         let is_reachable = self.access_levels.is_reachable(def_id);
 551
 552         if is_const && is_stable && missing_const_stability_attribute && is_reachable {
 553             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 554             self.tcx.sess.span_err(span, &format!("{descr} has missing const stability attribute"));
 555         }
 556     }
 557 }
 558
 559 impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
 560     type NestedFilter = nested_filter::OnlyBodies;
 561
 562     fn nested_visit_map(&mut self) -> Self::Map {
 563         self.tcx.hir()
 564     }
 565
 566     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 567         // Inherent impls and foreign modules serve only as containers for other items,
 568         // they don't have their own stability. They still can be annotated as unstable
 569         // and propagate this instability to children, but this annotation is completely
 570         // optional. They inherit stability from their parents when unannotated.
 571         if !matches!(
 572             i.kind,
 573             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 574                 | hir::ItemKind::ForeignMod { .. }
 575         ) {
 576             self.check_missing_stability(i.def_id.def_id, i.span);
 577         }
 578
 579         // Ensure stable `const fn` have a const stability attribute.
 580         self.check_missing_const_stability(i.def_id.def_id, i.span);
 581
 582         intravisit::walk_item(self, i)
 583     }
 584
 585     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 586         self.check_missing_stability(ti.def_id.def_id, ti.span);
 587         intravisit::walk_trait_item(self, ti);
 588     }
 589
 590     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 591         let impl_def_id = self.tcx.hir().get_parent_item(ii.hir_id());
 592         if self.tcx.impl_trait_ref(impl_def_id).is_none() {
 593             self.check_missing_stability(ii.def_id.def_id, ii.span);
 594             self.check_missing_const_stability(ii.def_id.def_id, ii.span);
 595         }
 596         intravisit::walk_impl_item(self, ii);
 597     }
 598
 599     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>) {
 600         self.check_missing_stability(self.tcx.hir().local_def_id(var.id), var.span);
 601         if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
 602             self.check_missing_stability(self.tcx.hir().local_def_id(ctor_hir_id), var.span);
 603         }
 604         intravisit::walk_variant(self, var);
 605     }
 606
 607     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 608         self.check_missing_stability(self.tcx.hir().local_def_id(s.hir_id), s.span);
 609         intravisit::walk_field_def(self, s);
 610     }
 611
 612     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 613         self.check_missing_stability(i.def_id.def_id, i.span);
 614         intravisit::walk_foreign_item(self, i);
 615     }
 616     // Note that we don't need to `check_missing_stability` for default generic parameters,
 617     // as we assume that any default generic parameters without attributes are automatically
 618     // stable (assuming they have not inherited instability from their parent).
 619 }
 620
 621 fn stability_index(tcx: TyCtxt<'_>, (): ()) -> Index {
 622     let mut index = Index {
 623         stab_map: Default::default(),
 624         const_stab_map: Default::default(),
 625         default_body_stab_map: Default::default(),
 626         depr_map: Default::default(),
 627         implications: Default::default(),
 628     };
 629
 630     {
 631         let mut annotator = Annotator {
 632             tcx,
 633             index: &mut index,
 634             parent_stab: None,
 635             parent_const_stab: None,
 636             parent_depr: None,
 637             in_trait_impl: false,
 638         };
 639
 640         // If the `-Z force-unstable-if-unmarked` flag is passed then we provide
 641         // a parent stability annotation which indicates that this is private
 642         // with the `rustc_private` feature. This is intended for use when
 643         // compiling `librustc_*` crates themselves so we can leverage crates.io
 644         // while maintaining the invariant that all sysroot crates are unstable
 645         // by default and are unable to be used.
 646         if tcx.sess.opts.unstable_opts.force_unstable_if_unmarked {
 647             let stability = Stability {
 648                 level: attr::StabilityLevel::Unstable {
 649                     reason: UnstableReason::Default,
 650                     issue: NonZeroU32::new(27812),
 651                     is_soft: false,
 652                     implied_by: None,
 653                 },
 654                 feature: sym::rustc_private,
 655             };
 656             annotator.parent_stab = Some(stability);
 657         }
 658
 659         annotator.annotate(
 660             CRATE_DEF_ID,
 661             tcx.hir().span(CRATE_HIR_ID),
 662             None,
 663             AnnotationKind::Required,
 664             InheritDeprecation::Yes,
 665             InheritConstStability::No,
 666             InheritStability::No,
 667             |v| tcx.hir().walk_toplevel_module(v),
 668         );
 669     }
 670     index
 671 }
 672
 673 /// Cross-references the feature names of unstable APIs with enabled
 674 /// features and possibly prints errors.
 675 fn check_mod_unstable_api_usage(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 676     tcx.hir().visit_item_likes_in_module(module_def_id, &mut Checker { tcx });
 677 }
 678
 679 pub(crate) fn provide(providers: &mut Providers) {
 680     *providers = Providers {
 681         check_mod_unstable_api_usage,
 682         stability_index,
 683         stability_implications: |tcx, _| tcx.stability().implications.clone(),
 684         lookup_stability: |tcx, id| tcx.stability().local_stability(id.expect_local()),
 685         lookup_const_stability: |tcx, id| tcx.stability().local_const_stability(id.expect_local()),
 686         lookup_default_body_stability: |tcx, id| {
 687             tcx.stability().local_default_body_stability(id.expect_local())
 688         },
 689         lookup_deprecation_entry: |tcx, id| {
 690             tcx.stability().local_deprecation_entry(id.expect_local())
 691         },
 692         ..*providers
 693     };
 694 }
 695
 696 struct Checker<'tcx> {
 697     tcx: TyCtxt<'tcx>,
 698 }
 699
 700 impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
 701     type NestedFilter = nested_filter::OnlyBodies;
 702
 703     /// Because stability levels are scoped lexically, we want to walk
 704     /// nested items in the context of the outer item, so enable
 705     /// deep-walking.
 706     fn nested_visit_map(&mut self) -> Self::Map {
 707         self.tcx.hir()
 708     }
 709
 710     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 711         match item.kind {
 712             hir::ItemKind::ExternCrate(_) => {
 713                 // compiler-generated `extern crate` items have a dummy span.
 714                 // `std` is still checked for the `restricted-std` feature.
 715                 if item.span.is_dummy() && item.ident.name != sym::std {
 716                     return;
 717                 }
 718
 719                 let Some(cnum) = self.tcx.extern_mod_stmt_cnum(item.def_id.def_id) else {
 720                     return;
 721                 };
 722                 let def_id = cnum.as_def_id();
 723                 self.tcx.check_stability(def_id, Some(item.hir_id()), item.span, None);
 724             }
 725
 726             // For implementations of traits, check the stability of each item
 727             // individually as it's possible to have a stable trait with unstable
 728             // items.
 729             hir::ItemKind::Impl(hir::Impl {
 730                 of_trait: Some(ref t),
 731                 self_ty,
 732                 items,
 733                 constness,
 734                 ..
 735             }) => {
 736                 let features = self.tcx.features();
 737                 if features.staged_api {
 738                     let attrs = self.tcx.hir().attrs(item.hir_id());
 739                     let (stab, const_stab, _) =
 740                         attr::find_stability(&self.tcx.sess, attrs, item.span);
 741
 742                     // If this impl block has an #[unstable] attribute, give an
 743                     // error if all involved types and traits are stable, because
 744                     // it will have no effect.
 745                     // See: https://github.com/rust-lang/rust/issues/55436
 746                     if let Some((Stability { level: attr::Unstable { .. }, .. }, span)) = stab {
 747                         let mut c = CheckTraitImplStable { tcx: self.tcx, fully_stable: true };
 748                         c.visit_ty(self_ty);
 749                         c.visit_trait_ref(t);
 750                         if c.fully_stable {
 751                             self.tcx.struct_span_lint_hir(
 752                                 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
 753                                 item.hir_id(),
 754                                 span,
 755                                 |lint| {lint
 756                                     .build("an `#[unstable]` annotation here has no effect")
 757                                     .note("see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information")
 758                                     .emit();}
 759                             );
 760                         }
 761                     }
 762
 763                     // `#![feature(const_trait_impl)]` is unstable, so any impl declared stable
 764                     // needs to have an error emitted.
 765                     if features.const_trait_impl
 766                         && *constness == hir::Constness::Const
 767                         && const_stab.map_or(false, |(stab, _)| stab.is_const_stable())
 768                     {
 769                         self.tcx
 770                             .sess
 771                             .struct_span_err(item.span, "trait implementations cannot be const stable yet")
 772                             .note("see issue #67792 <https://github.com/rust-lang/rust/issues/67792> for more information")
 773                             .emit();
 774                     }
 775                 }
 776
 777                 for impl_item_ref in *items {
 778                     let impl_item = self.tcx.associated_item(impl_item_ref.id.def_id);
 779
 780                     if let Some(def_id) = impl_item.trait_item_def_id {
 781                         // Pass `None` to skip deprecation warnings.
 782                         self.tcx.check_stability(def_id, None, impl_item_ref.span, None);
 783                     }
 784                 }
 785             }
 786
 787             _ => (/* pass */),
 788         }
 789         intravisit::walk_item(self, item);
 790     }
 791
 792     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, id: hir::HirId) {
 793         if let Some(def_id) = path.res.opt_def_id() {
 794             let method_span = path.segments.last().map(|s| s.ident.span);
 795             let item_is_allowed = self.tcx.check_stability_allow_unstable(
 796                 def_id,
 797                 Some(id),
 798                 path.span,
 799                 method_span,
 800                 if is_unstable_reexport(self.tcx, id) {
 801                     AllowUnstable::Yes
 802                 } else {
 803                     AllowUnstable::No
 804                 },
 805             );
 806
 807             let is_allowed_through_unstable_modules = |def_id| {
 808                 self.tcx
 809                     .lookup_stability(def_id)
 810                     .map(|stab| match stab.level {
 811                         StabilityLevel::Stable { allowed_through_unstable_modules, .. } => {
 812                             allowed_through_unstable_modules
 813                         }
 814                         _ => false,
 815                     })
 816                     .unwrap_or(false)
 817             };
 818
 819             if item_is_allowed && !is_allowed_through_unstable_modules(def_id) {
 820                 // Check parent modules stability as well if the item the path refers to is itself
 821                 // stable. We only emit warnings for unstable path segments if the item is stable
 822                 // or allowed because stability is often inherited, so the most common case is that
 823                 // both the segments and the item are unstable behind the same feature flag.
 824                 //
 825                 // We check here rather than in `visit_path_segment` to prevent visiting the last
 826                 // path segment twice
 827                 //
 828                 // We include special cases via #[rustc_allowed_through_unstable_modules] for items
 829                 // that were accidentally stabilized through unstable paths before this check was
 830                 // added, such as `core::intrinsics::transmute`
 831                 let parents = path.segments.iter().rev().skip(1);
 832                 for path_segment in parents {
 833                     if let Some(def_id) = path_segment.res.opt_def_id() {
 834                         // use `None` for id to prevent deprecation check
 835                         self.tcx.check_stability_allow_unstable(
 836                             def_id,
 837                             None,
 838                             path.span,
 839                             None,
 840                             if is_unstable_reexport(self.tcx, id) {
 841                                 AllowUnstable::Yes
 842                             } else {
 843                                 AllowUnstable::No
 844                             },
 845                         );
 846                     }
 847                 }
 848             }
 849         }
 850
 851         intravisit::walk_path(self, path)
 852     }
 853 }
 854
 855 /// Check whether a path is a `use` item that has been marked as unstable.
 856 ///
 857 /// See issue #94972 for details on why this is a special case
 858 fn is_unstable_reexport<'tcx>(tcx: TyCtxt<'tcx>, id: hir::HirId) -> bool {
 859     // Get the LocalDefId so we can lookup the item to check the kind.
 860     let Some(def_id) = tcx.hir().opt_local_def_id(id) else { return false; };
 861
 862     let Some(stab) = tcx.stability().local_stability(def_id) else {
 863         return false;
 864     };
 865
 866     if stab.level.is_stable() {
 867         // The re-export is not marked as unstable, don't override
 868         return false;
 869     }
 870
 871     // If this is a path that isn't a use, we don't need to do anything special
 872     if !matches!(tcx.hir().expect_item(def_id).kind, ItemKind::Use(..)) {
 873         return false;
 874     }
 875
 876     true
 877 }
 878
 879 struct CheckTraitImplStable<'tcx> {
 880     tcx: TyCtxt<'tcx>,
 881     fully_stable: bool,
 882 }
 883
 884 impl<'tcx> Visitor<'tcx> for CheckTraitImplStable<'tcx> {
 885     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _id: hir::HirId) {
 886         if let Some(def_id) = path.res.opt_def_id() {
 887             if let Some(stab) = self.tcx.lookup_stability(def_id) {
 888                 self.fully_stable &= stab.level.is_stable();
 889             }
 890         }
 891         intravisit::walk_path(self, path)
 892     }
 893
 894     fn visit_trait_ref(&mut self, t: &'tcx TraitRef<'tcx>) {
 895         if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
 896             if let Some(stab) = self.tcx.lookup_stability(trait_did) {
 897                 self.fully_stable &= stab.level.is_stable();
 898             }
 899         }
 900         intravisit::walk_trait_ref(self, t)
 901     }
 902
 903     fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
 904         if let TyKind::Never = t.kind {
 905             self.fully_stable = false;
 906         }
 907         intravisit::walk_ty(self, t)
 908     }
 909 }
 910
 911 /// Given the list of enabled features that were not language features (i.e., that
 912 /// were expected to be library features), and the list of features used from
 913 /// libraries, identify activated features that don't exist and error about them.
 914 pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
 915     let is_staged_api =
 916         tcx.sess.opts.unstable_opts.force_unstable_if_unmarked || tcx.features().staged_api;
 917     if is_staged_api {
 918         let access_levels = &tcx.privacy_access_levels(());
 919         let mut missing = MissingStabilityAnnotations { tcx, access_levels };
 920         missing.check_missing_stability(CRATE_DEF_ID, tcx.hir().span(CRATE_HIR_ID));
 921         tcx.hir().walk_toplevel_module(&mut missing);
 922         tcx.hir().visit_all_item_likes_in_crate(&mut missing);
 923     }
 924
 925     let declared_lang_features = &tcx.features().declared_lang_features;
 926     let mut lang_features = FxHashSet::default();
 927     for &(feature, span, since) in declared_lang_features {
 928         if let Some(since) = since {
 929             // Warn if the user has enabled an already-stable lang feature.
 930             unnecessary_stable_feature_lint(tcx, span, feature, since);
 931         }
 932         if !lang_features.insert(feature) {
 933             // Warn if the user enables a lang feature multiple times.
 934             duplicate_feature_err(tcx.sess, span, feature);
 935         }
 936     }
 937
 938     let declared_lib_features = &tcx.features().declared_lib_features;
 939     let mut remaining_lib_features = FxIndexMap::default();
 940     for (feature, span) in declared_lib_features {
 941         if !tcx.sess.opts.unstable_features.is_nightly_build() {
 942             struct_span_err!(
 943                 tcx.sess,
 944                 *span,
 945                 E0554,
 946                 "`#![feature]` may not be used on the {} release channel",
 947                 env!("CFG_RELEASE_CHANNEL")
 948             )
 949             .emit();
 950         }
 951         if remaining_lib_features.contains_key(&feature) {
 952             // Warn if the user enables a lib feature multiple times.
 953             duplicate_feature_err(tcx.sess, *span, *feature);
 954         }
 955         remaining_lib_features.insert(feature, *span);
 956     }
 957     // `stdbuild` has special handling for `libc`, so we need to
 958     // recognise the feature when building std.
 959     // Likewise, libtest is handled specially, so `test` isn't
 960     // available as we'd like it to be.
 961     // FIXME: only remove `libc` when `stdbuild` is active.
 962     // FIXME: remove special casing for `test`.
 963     remaining_lib_features.remove(&sym::libc);
 964     remaining_lib_features.remove(&sym::test);
 965
 966     /// For each feature in `defined_features`..
 967     ///
 968     /// - If it is in `remaining_lib_features` (those features with `#![feature(..)]` attributes in
 969     ///   the current crate), check if it is stable (or partially stable) and thus an unnecessary
 970     ///   attribute.
 971     /// - If it is in `remaining_implications` (a feature that is referenced by an `implied_by`
 972     ///   from the current crate), then remove it from the remaining implications.
 973     ///
 974     /// Once this function has been invoked for every feature (local crate and all extern crates),
 975     /// then..
 976     ///
 977     /// - If features remain in `remaining_lib_features`, then the user has enabled a feature that
 978     ///   does not exist.
 979     /// - If features remain in `remaining_implications`, the `implied_by` refers to a feature that
 980     ///   does not exist.
 981     ///
 982     /// By structuring the code in this way: checking the features defined from each crate one at a
 983     /// time, less loading from metadata is performed and thus compiler performance is improved.
 984     fn check_features<'tcx>(
 985         tcx: TyCtxt<'tcx>,
 986         remaining_lib_features: &mut FxIndexMap<&Symbol, Span>,
 987         remaining_implications: &mut FxHashMap<Symbol, Symbol>,
 988         defined_features: &[(Symbol, Option<Symbol>)],
 989         all_implications: &FxHashMap<Symbol, Symbol>,
 990     ) {
 991         for (feature, since) in defined_features {
 992             if let Some(since) = since && let Some(span) = remaining_lib_features.get(&feature) {
 993                 // Warn if the user has enabled an already-stable lib feature.
 994                 if let Some(implies) = all_implications.get(&feature) {
 995                     unnecessary_partially_stable_feature_lint(tcx, *span, *feature, *implies, *since);
 996                 } else {
 997                     unnecessary_stable_feature_lint(tcx, *span, *feature, *since);
 998                 }
 999
1000             }
1001             remaining_lib_features.remove(feature);
1002
1003             // `feature` is the feature doing the implying, but `implied_by` is the feature with
1004             // the attribute that establishes this relationship. `implied_by` is guaranteed to be a
1005             // feature defined in the local crate because `remaining_implications` is only the
1006             // implications from this crate.
1007             remaining_implications.remove(feature);
1008
1009             if remaining_lib_features.is_empty() && remaining_implications.is_empty() {
1010                 break;
1011             }
1012         }
1013     }
1014
1015     // All local crate implications need to have the feature that implies it confirmed to exist.
1016     let mut remaining_implications =
1017         tcx.stability_implications(rustc_hir::def_id::LOCAL_CRATE).clone();
1018
1019     // We always collect the lib features declared in the current crate, even if there are
1020     // no unknown features, because the collection also does feature attribute validation.
1021     let local_defined_features = tcx.lib_features(()).to_vec();
1022     if !remaining_lib_features.is_empty() || !remaining_implications.is_empty() {
1023         // Loading the implications of all crates is unavoidable to be able to emit the partial
1024         // stabilization diagnostic, but it can be avoided when there are no
1025         // `remaining_lib_features`.
1026         let mut all_implications = remaining_implications.clone();
1027         for &cnum in tcx.crates(()) {
1028             all_implications.extend(tcx.stability_implications(cnum));
1029         }
1030
1031         check_features(
1032             tcx,
1033             &mut remaining_lib_features,
1034             &mut remaining_implications,
1035             local_defined_features.as_slice(),
1036             &all_implications,
1037         );
1038
1039         for &cnum in tcx.crates(()) {
1040             if remaining_lib_features.is_empty() && remaining_implications.is_empty() {
1041                 break;
1042             }
1043             check_features(
1044                 tcx,
1045                 &mut remaining_lib_features,
1046                 &mut remaining_implications,
1047                 tcx.defined_lib_features(cnum).to_vec().as_slice(),
1048                 &all_implications,
1049             );
1050         }
1051     }
1052
1053     for (feature, span) in remaining_lib_features {
1054         struct_span_err!(tcx.sess, span, E0635, "unknown feature `{}`", feature).emit();
1055     }
1056
1057     for (implied_by, feature) in remaining_implications {
1058         let local_defined_features = tcx.lib_features(());
1059         let span = local_defined_features
1060             .stable
1061             .get(&feature)
1062             .map(|(_, span)| span)
1063             .or_else(|| local_defined_features.unstable.get(&feature))
1064             .expect("feature that implied another does not exist");
1065         tcx.sess
1066             .struct_span_err(
1067                 *span,
1068                 format!("feature `{implied_by}` implying `{feature}` does not exist"),
1069             )
1070             .emit();
1071     }
1072
1073     // FIXME(#44232): the `used_features` table no longer exists, so we
1074     // don't lint about unused features. We should re-enable this one day!
1075 }
1076
1077 fn unnecessary_partially_stable_feature_lint(
1078     tcx: TyCtxt<'_>,
1079     span: Span,
1080     feature: Symbol,
1081     implies: Symbol,
1082     since: Symbol,
1083 ) {
1084     tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
1085         lint.build(&format!(
1086             "the feature `{feature}` has been partially stabilized since {since} and is succeeded \
1087              by the feature `{implies}`"
1088         ))
1089         .span_suggestion(
1090             span,
1091             &format!(
1092                 "if you are using features which are still unstable, change to using `{implies}`"
1093             ),
1094             implies,
1095             Applicability::MaybeIncorrect,
1096         )
1097         .span_suggestion(
1098             tcx.sess.source_map().span_extend_to_line(span),
1099             "if you are using features which are now stable, remove this line",
1100             "",
1101             Applicability::MaybeIncorrect,
1102         )
1103         .emit();
1104     });
1105 }
1106
1107 fn unnecessary_stable_feature_lint(
1108     tcx: TyCtxt<'_>,
1109     span: Span,
1110     feature: Symbol,
1111     mut since: Symbol,
1112 ) {
1113     if since.as_str() == VERSION_PLACEHOLDER {
1114         since = rust_version_symbol();
1115     }
1116     tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
1117         lint.build(&format!(
1118             "the feature `{feature}` has been stable since {since} and no longer requires an \
1119              attribute to enable",
1120         ))
1121         .emit();
1122     });
1123 }
1124
1125 fn duplicate_feature_err(sess: &Session, span: Span, feature: Symbol) {
1126     struct_span_err!(sess, span, E0636, "the feature `{}` has already been declared", feature)
1127         .emit();
1128 }
1129
1130 fn missing_const_err(session: &Session, fn_sig_span: Span, const_span: Span) {
1131     const ERROR_MSG: &'static str = "attributes `#[rustc_const_unstable]` \
1132          and `#[rustc_const_stable]` require \
1133          the function or method to be `const`";
1134
1135     session
1136         .struct_span_err(fn_sig_span, ERROR_MSG)
1137         .span_help(fn_sig_span, "make the function or method const")
1138         .span_label(const_span, "attribute specified here")
1139         .emit();
1140 }