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_INDEX, LOCAL_CRATE};
  11 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  12 use rustc_hir::{FieldDef, Generics, HirId, Item, TraitRef, Ty, TyKind, Variant};
  13 use rustc_middle::hir::map::Map;
  14 use rustc_middle::middle::privacy::AccessLevels;
  15 use rustc_middle::middle::stability::{DeprecationEntry, Index};
  16 use rustc_middle::ty::{self, query::Providers, TyCtxt};
  17 use rustc_session::lint;
  18 use rustc_session::lint::builtin::{INEFFECTIVE_UNSTABLE_TRAIT_IMPL, USELESS_DEPRECATED};
  19 use rustc_session::parse::feature_err;
  20 use rustc_session::Session;
  21 use rustc_span::symbol::{sym, Symbol};
  22 use rustc_span::{Span, DUMMY_SP};
  23
  24 use std::cmp::Ordering;
  25 use std::mem::replace;
  26 use std::num::NonZeroU32;
  27
  28 #[derive(PartialEq)]
  29 enum AnnotationKind {
  30     // Annotation is required if not inherited from unstable parents
  31     Required,
  32     // Annotation is useless, reject it
  33     Prohibited,
  34     // Deprecation annotation is useless, reject it. (Stability attribute is still required.)
  35     DeprecationProhibited,
  36     // Annotation itself is useless, but it can be propagated to children
  37     Container,
  38 }
  39
  40 /// Whether to inherit deprecation flags for nested items. In most cases, we do want to inherit
  41 /// deprecation, because nested items rarely have individual deprecation attributes, and so
  42 /// should be treated as deprecated if their parent is. However, default generic parameters
  43 /// have separate deprecation attributes from their parents, so we do not wish to inherit
  44 /// deprecation in this case. For example, inheriting deprecation for `T` in `Foo<T>`
  45 /// would cause a duplicate warning arising from both `Foo` and `T` being deprecated.
  46 #[derive(Clone)]
  47 enum InheritDeprecation {
  48     Yes,
  49     No,
  50 }
  51
  52 impl InheritDeprecation {
  53     fn yes(&self) -> bool {
  54         matches!(self, InheritDeprecation::Yes)
  55     }
  56 }
  57
  58 /// Whether to inherit const stability flags for nested items. In most cases, we do not want to
  59 /// inherit const stability: just because an enclosing `fn` is const-stable does not mean
  60 /// all `extern` imports declared in it should be const-stable! However, trait methods
  61 /// inherit const stability attributes from their parent and do not have their own.
  62 enum InheritConstStability {
  63     Yes,
  64     No,
  65 }
  66
  67 impl InheritConstStability {
  68     fn yes(&self) -> bool {
  69         matches!(self, InheritConstStability::Yes)
  70     }
  71 }
  72
  73 enum InheritStability {
  74     Yes,
  75     No,
  76 }
  77
  78 impl InheritStability {
  79     fn yes(&self) -> bool {
  80         matches!(self, InheritStability::Yes)
  81     }
  82 }
  83
  84 // A private tree-walker for producing an Index.
  85 struct Annotator<'a, 'tcx> {
  86     tcx: TyCtxt<'tcx>,
  87     index: &'a mut Index<'tcx>,
  88     parent_stab: Option<&'tcx Stability>,
  89     parent_const_stab: Option<&'tcx ConstStability>,
  90     parent_depr: Option<DeprecationEntry>,
  91     in_trait_impl: bool,
  92 }
  93
  94 impl<'a, 'tcx> Annotator<'a, 'tcx> {
  95     // Determine the stability for a node based on its attributes and inherited
  96     // stability. The stability is recorded in the index and used as the parent.
  97     fn annotate<F>(
  98         &mut self,
  99         hir_id: HirId,
 100         item_sp: Span,
 101         kind: AnnotationKind,
 102         inherit_deprecation: InheritDeprecation,
 103         inherit_const_stability: InheritConstStability,
 104         inherit_from_parent: InheritStability,
 105         visit_children: F,
 106     ) where
 107         F: FnOnce(&mut Self),
 108     {
 109         let attrs = self.tcx.hir().attrs(hir_id);
 110         debug!("annotate(id = {:?}, attrs = {:?})", hir_id, attrs);
 111         let mut did_error = false;
 112         if !self.tcx.features().staged_api {
 113             did_error = self.forbid_staged_api_attrs(hir_id, attrs, inherit_deprecation.clone());
 114         }
 115
 116         let depr = if did_error { None } else { attr::find_deprecation(&self.tcx.sess, attrs) };
 117         let mut is_deprecated = false;
 118         if let Some((depr, span)) = &depr {
 119             is_deprecated = true;
 120
 121             if kind == AnnotationKind::Prohibited || kind == AnnotationKind::DeprecationProhibited {
 122                 self.tcx.struct_span_lint_hir(USELESS_DEPRECATED, hir_id, *span, |lint| {
 123                     lint.build("this `#[deprecated]` annotation has no effect")
 124                         .span_suggestion_short(
 125                             *span,
 126                             "remove the unnecessary deprecation attribute",
 127                             String::new(),
 128                             rustc_errors::Applicability::MachineApplicable,
 129                         )
 130                         .emit()
 131                 });
 132             }
 133
 134             // `Deprecation` is just two pointers, no need to intern it
 135             let depr_entry = DeprecationEntry::local(depr.clone(), hir_id);
 136             self.index.depr_map.insert(hir_id, depr_entry);
 137         } else if let Some(parent_depr) = self.parent_depr.clone() {
 138             if inherit_deprecation.yes() {
 139                 is_deprecated = true;
 140                 info!("tagging child {:?} as deprecated from parent", hir_id);
 141                 self.index.depr_map.insert(hir_id, parent_depr);
 142             }
 143         }
 144
 145         if self.tcx.features().staged_api {
 146             if let Some(a) = attrs.iter().find(|a| self.tcx.sess.check_name(a, sym::deprecated)) {
 147                 self.tcx
 148                     .sess
 149                     .struct_span_err(a.span, "`#[deprecated]` cannot be used in staged API")
 150                     .span_label(a.span, "use `#[rustc_deprecated]` instead")
 151                     .span_label(item_sp, "")
 152                     .emit();
 153             }
 154         } else {
 155             self.recurse_with_stability_attrs(
 156                 depr.map(|(d, _)| DeprecationEntry::local(d, hir_id)),
 157                 None,
 158                 None,
 159                 visit_children,
 160             );
 161             return;
 162         }
 163
 164         let (stab, const_stab) = attr::find_stability(&self.tcx.sess, attrs, item_sp);
 165
 166         let const_stab = const_stab.map(|(const_stab, _)| {
 167             let const_stab = self.tcx.intern_const_stability(const_stab);
 168             self.index.const_stab_map.insert(hir_id, const_stab);
 169             const_stab
 170         });
 171
 172         // `impl const Trait for Type` items forward their const stability to their
 173         // immediate children.
 174         if const_stab.is_none() {
 175             debug!("annotate: const_stab not found, parent = {:?}", self.parent_const_stab);
 176             if let Some(parent) = self.parent_const_stab {
 177                 if parent.level.is_unstable() {
 178                     self.index.const_stab_map.insert(hir_id, parent);
 179                 }
 180             }
 181         }
 182
 183         if let Some((rustc_attr::Deprecation { is_since_rustc_version: true, .. }, span)) = &depr {
 184             if stab.is_none() {
 185                 struct_span_err!(
 186                     self.tcx.sess,
 187                     *span,
 188                     E0549,
 189                     "rustc_deprecated attribute must be paired with \
 190                     either stable or unstable attribute"
 191                 )
 192                 .emit();
 193             }
 194         }
 195
 196         let stab = stab.map(|(stab, span)| {
 197             // Error if prohibited, or can't inherit anything from a container.
 198             if kind == AnnotationKind::Prohibited
 199                 || (kind == AnnotationKind::Container && stab.level.is_stable() && is_deprecated)
 200             {
 201                 self.tcx.sess.struct_span_err(span,"this stability annotation is useless")
 202                     .span_label(span, "useless stability annotation")
 203                     .span_label(item_sp, "the stability attribute annotates this item")
 204                     .emit();
 205             }
 206
 207             debug!("annotate: found {:?}", stab);
 208             let stab = self.tcx.intern_stability(stab);
 209
 210             // Check if deprecated_since < stable_since. If it is,
 211             // this is *almost surely* an accident.
 212             if let (&Some(dep_since), &attr::Stable { since: stab_since }) =
 213                 (&depr.as_ref().and_then(|(d, _)| d.since), &stab.level)
 214             {
 215                 // Explicit version of iter::order::lt to handle parse errors properly
 216                 for (dep_v, stab_v) in
 217                     dep_since.as_str().split('.').zip(stab_since.as_str().split('.'))
 218                 {
 219                     match stab_v.parse::<u64>() {
 220                         Err(_) => {
 221                             self.tcx.sess.struct_span_err(span, "invalid stability version found")
 222                                 .span_label(span, "invalid stability version")
 223                                 .span_label(item_sp, "the stability attribute annotates this item")
 224                                 .emit();
 225                             break;
 226                         }
 227                         Ok(stab_vp) => match dep_v.parse::<u64>() {
 228                             Ok(dep_vp) => match dep_vp.cmp(&stab_vp) {
 229                                 Ordering::Less => {
 230                                     self.tcx.sess.struct_span_err(span, "an API can't be stabilized after it is deprecated")
 231                                         .span_label(span, "invalid version")
 232                                         .span_label(item_sp, "the stability attribute annotates this item")
 233                                         .emit();
 234                                     break;
 235                                 }
 236                                 Ordering::Equal => continue,
 237                                 Ordering::Greater => break,
 238                             },
 239                             Err(_) => {
 240                                 if dep_v != "TBD" {
 241                                     self.tcx.sess.struct_span_err(span, "invalid deprecation version found")
 242                                         .span_label(span, "invalid deprecation version")
 243                                         .span_label(item_sp, "the stability attribute annotates this item")
 244                                         .emit();
 245                                 }
 246                                 break;
 247                             }
 248                         },
 249                     }
 250                 }
 251             }
 252
 253             self.index.stab_map.insert(hir_id, stab);
 254             stab
 255         });
 256
 257         if stab.is_none() {
 258             debug!("annotate: stab not found, parent = {:?}", self.parent_stab);
 259             if let Some(stab) = self.parent_stab {
 260                 if inherit_deprecation.yes() && stab.level.is_unstable()
 261                     || inherit_from_parent.yes()
 262                 {
 263                     self.index.stab_map.insert(hir_id, stab);
 264                 }
 265             }
 266         }
 267
 268         self.recurse_with_stability_attrs(
 269             depr.map(|(d, _)| DeprecationEntry::local(d, hir_id)),
 270             stab,
 271             if inherit_const_stability.yes() { const_stab } else { None },
 272             visit_children,
 273         );
 274     }
 275
 276     fn recurse_with_stability_attrs(
 277         &mut self,
 278         depr: Option<DeprecationEntry>,
 279         stab: Option<&'tcx Stability>,
 280         const_stab: Option<&'tcx ConstStability>,
 281         f: impl FnOnce(&mut Self),
 282     ) {
 283         // These will be `Some` if this item changes the corresponding stability attribute.
 284         let mut replaced_parent_depr = None;
 285         let mut replaced_parent_stab = None;
 286         let mut replaced_parent_const_stab = None;
 287
 288         if let Some(depr) = depr {
 289             replaced_parent_depr = Some(replace(&mut self.parent_depr, Some(depr)));
 290         }
 291         if let Some(stab) = stab {
 292             replaced_parent_stab = Some(replace(&mut self.parent_stab, Some(stab)));
 293         }
 294         if let Some(const_stab) = const_stab {
 295             replaced_parent_const_stab =
 296                 Some(replace(&mut self.parent_const_stab, Some(const_stab)));
 297         }
 298
 299         f(self);
 300
 301         if let Some(orig_parent_depr) = replaced_parent_depr {
 302             self.parent_depr = orig_parent_depr;
 303         }
 304         if let Some(orig_parent_stab) = replaced_parent_stab {
 305             self.parent_stab = orig_parent_stab;
 306         }
 307         if let Some(orig_parent_const_stab) = replaced_parent_const_stab {
 308             self.parent_const_stab = orig_parent_const_stab;
 309         }
 310     }
 311
 312     // returns true if an error occurred, used to suppress some spurious errors
 313     fn forbid_staged_api_attrs(
 314         &mut self,
 315         hir_id: HirId,
 316         attrs: &[Attribute],
 317         inherit_deprecation: InheritDeprecation,
 318     ) -> bool {
 319         // Emit errors for non-staged-api crates.
 320         let unstable_attrs = [
 321             sym::unstable,
 322             sym::stable,
 323             sym::rustc_deprecated,
 324             sym::rustc_const_unstable,
 325             sym::rustc_const_stable,
 326         ];
 327         let mut has_error = false;
 328         for attr in attrs {
 329             let name = attr.name_or_empty();
 330             if unstable_attrs.contains(&name) {
 331                 self.tcx.sess.mark_attr_used(attr);
 332                 struct_span_err!(
 333                     self.tcx.sess,
 334                     attr.span,
 335                     E0734,
 336                     "stability attributes may not be used outside of the standard library",
 337                 )
 338                 .emit();
 339                 has_error = true;
 340             }
 341         }
 342
 343         // Propagate unstability.  This can happen even for non-staged-api crates in case
 344         // -Zforce-unstable-if-unmarked is set.
 345         if let Some(stab) = self.parent_stab {
 346             if inherit_deprecation.yes() && stab.level.is_unstable() {
 347                 self.index.stab_map.insert(hir_id, stab);
 348             }
 349         }
 350
 351         has_error
 352     }
 353 }
 354
 355 impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
 356     /// Because stability levels are scoped lexically, we want to walk
 357     /// nested items in the context of the outer item, so enable
 358     /// deep-walking.
 359     type Map = Map<'tcx>;
 360
 361     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 362         NestedVisitorMap::All(self.tcx.hir())
 363     }
 364
 365     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 366         let orig_in_trait_impl = self.in_trait_impl;
 367         let mut kind = AnnotationKind::Required;
 368         let mut const_stab_inherit = InheritConstStability::No;
 369         match i.kind {
 370             // Inherent impls and foreign modules serve only as containers for other items,
 371             // they don't have their own stability. They still can be annotated as unstable
 372             // and propagate this unstability to children, but this annotation is completely
 373             // optional. They inherit stability from their parents when unannotated.
 374             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 375             | hir::ItemKind::ForeignMod { .. } => {
 376                 self.in_trait_impl = false;
 377                 kind = AnnotationKind::Container;
 378             }
 379             hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => {
 380                 self.in_trait_impl = true;
 381                 kind = AnnotationKind::DeprecationProhibited;
 382                 const_stab_inherit = InheritConstStability::Yes;
 383             }
 384             hir::ItemKind::Struct(ref sd, _) => {
 385                 if let Some(ctor_hir_id) = sd.ctor_hir_id() {
 386                     self.annotate(
 387                         ctor_hir_id,
 388                         i.span,
 389                         AnnotationKind::Required,
 390                         InheritDeprecation::Yes,
 391                         InheritConstStability::No,
 392                         InheritStability::Yes,
 393                         |_| {},
 394                     )
 395                 }
 396             }
 397             _ => {}
 398         }
 399
 400         self.annotate(
 401             i.hir_id(),
 402             i.span,
 403             kind,
 404             InheritDeprecation::Yes,
 405             const_stab_inherit,
 406             InheritStability::No,
 407             |v| intravisit::walk_item(v, i),
 408         );
 409         self.in_trait_impl = orig_in_trait_impl;
 410     }
 411
 412     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 413         self.annotate(
 414             ti.hir_id(),
 415             ti.span,
 416             AnnotationKind::Required,
 417             InheritDeprecation::Yes,
 418             InheritConstStability::No,
 419             InheritStability::No,
 420             |v| {
 421                 intravisit::walk_trait_item(v, ti);
 422             },
 423         );
 424     }
 425
 426     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 427         let kind =
 428             if self.in_trait_impl { AnnotationKind::Prohibited } else { AnnotationKind::Required };
 429         self.annotate(
 430             ii.hir_id(),
 431             ii.span,
 432             kind,
 433             InheritDeprecation::Yes,
 434             InheritConstStability::No,
 435             InheritStability::No,
 436             |v| {
 437                 intravisit::walk_impl_item(v, ii);
 438             },
 439         );
 440     }
 441
 442     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 443         self.annotate(
 444             var.id,
 445             var.span,
 446             AnnotationKind::Required,
 447             InheritDeprecation::Yes,
 448             InheritConstStability::No,
 449             InheritStability::Yes,
 450             |v| {
 451                 if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
 452                     v.annotate(
 453                         ctor_hir_id,
 454                         var.span,
 455                         AnnotationKind::Required,
 456                         InheritDeprecation::Yes,
 457                         InheritConstStability::No,
 458                         InheritStability::No,
 459                         |_| {},
 460                     );
 461                 }
 462
 463                 intravisit::walk_variant(v, var, g, item_id)
 464             },
 465         )
 466     }
 467
 468     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 469         self.annotate(
 470             s.hir_id,
 471             s.span,
 472             AnnotationKind::Required,
 473             InheritDeprecation::Yes,
 474             InheritConstStability::No,
 475             InheritStability::Yes,
 476             |v| {
 477                 intravisit::walk_field_def(v, s);
 478             },
 479         );
 480     }
 481
 482     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 483         self.annotate(
 484             i.hir_id(),
 485             i.span,
 486             AnnotationKind::Required,
 487             InheritDeprecation::Yes,
 488             InheritConstStability::No,
 489             InheritStability::No,
 490             |v| {
 491                 intravisit::walk_foreign_item(v, i);
 492             },
 493         );
 494     }
 495
 496     fn visit_macro_def(&mut self, md: &'tcx hir::MacroDef<'tcx>) {
 497         self.annotate(
 498             md.hir_id(),
 499             md.span,
 500             AnnotationKind::Required,
 501             InheritDeprecation::Yes,
 502             InheritConstStability::No,
 503             InheritStability::No,
 504             |_| {},
 505         );
 506     }
 507
 508     fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
 509         let kind = match &p.kind {
 510             // FIXME(const_generics_defaults)
 511             hir::GenericParamKind::Type { default, .. } if default.is_some() => {
 512                 AnnotationKind::Container
 513             }
 514             _ => AnnotationKind::Prohibited,
 515         };
 516
 517         self.annotate(
 518             p.hir_id,
 519             p.span,
 520             kind,
 521             InheritDeprecation::No,
 522             InheritConstStability::No,
 523             InheritStability::No,
 524             |v| {
 525                 intravisit::walk_generic_param(v, p);
 526             },
 527         );
 528     }
 529 }
 530
 531 struct MissingStabilityAnnotations<'tcx> {
 532     tcx: TyCtxt<'tcx>,
 533     access_levels: &'tcx AccessLevels,
 534 }
 535
 536 impl<'tcx> MissingStabilityAnnotations<'tcx> {
 537     fn check_missing_stability(&self, hir_id: HirId, span: Span) {
 538         let stab = self.tcx.stability().local_stability(hir_id);
 539         let is_error =
 540             !self.tcx.sess.opts.test && stab.is_none() && self.access_levels.is_reachable(hir_id);
 541         if is_error {
 542             let def_id = self.tcx.hir().local_def_id(hir_id);
 543             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 544             self.tcx.sess.span_err(span, &format!("{} has missing stability attribute", descr));
 545         }
 546     }
 547
 548     fn check_missing_const_stability(&self, hir_id: HirId, span: Span) {
 549         let stab_map = self.tcx.stability();
 550         let stab = stab_map.local_stability(hir_id);
 551         if stab.map_or(false, |stab| stab.level.is_stable()) {
 552             let const_stab = stab_map.local_const_stability(hir_id);
 553             if const_stab.is_none() {
 554                 self.tcx.sess.span_err(
 555                     span,
 556                     "`#[stable]` const functions must also be either \
 557                     `#[rustc_const_stable]` or `#[rustc_const_unstable]`",
 558                 );
 559             }
 560         }
 561     }
 562 }
 563
 564 impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
 565     type Map = Map<'tcx>;
 566
 567     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 568         NestedVisitorMap::OnlyBodies(self.tcx.hir())
 569     }
 570
 571     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 572         // Inherent impls and foreign modules serve only as containers for other items,
 573         // they don't have their own stability. They still can be annotated as unstable
 574         // and propagate this unstability to children, but this annotation is completely
 575         // optional. They inherit stability from their parents when unannotated.
 576         if !matches!(
 577             i.kind,
 578             hir::ItemKind::Impl(hir::Impl { of_trait: None, .. })
 579                 | hir::ItemKind::ForeignMod { .. }
 580         ) {
 581             self.check_missing_stability(i.hir_id(), i.span);
 582         }
 583
 584         // Ensure `const fn` that are `stable` have one of `rustc_const_unstable` or
 585         // `rustc_const_stable`.
 586         if self.tcx.features().staged_api
 587             && matches!(&i.kind, hir::ItemKind::Fn(sig, ..) if sig.header.is_const())
 588         {
 589             self.check_missing_const_stability(i.hir_id(), i.span);
 590         }
 591
 592         intravisit::walk_item(self, i)
 593     }
 594
 595     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 596         self.check_missing_stability(ti.hir_id(), ti.span);
 597         intravisit::walk_trait_item(self, ti);
 598     }
 599
 600     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 601         let impl_def_id = self.tcx.hir().local_def_id(self.tcx.hir().get_parent_item(ii.hir_id()));
 602         if self.tcx.impl_trait_ref(impl_def_id).is_none() {
 603             self.check_missing_stability(ii.hir_id(), ii.span);
 604         }
 605         intravisit::walk_impl_item(self, ii);
 606     }
 607
 608     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 609         self.check_missing_stability(var.id, var.span);
 610         intravisit::walk_variant(self, var, g, item_id);
 611     }
 612
 613     fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
 614         self.check_missing_stability(s.hir_id, s.span);
 615         intravisit::walk_field_def(self, s);
 616     }
 617
 618     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 619         self.check_missing_stability(i.hir_id(), i.span);
 620         intravisit::walk_foreign_item(self, i);
 621     }
 622
 623     fn visit_macro_def(&mut self, md: &'tcx hir::MacroDef<'tcx>) {
 624         self.check_missing_stability(md.hir_id(), md.span);
 625     }
 626
 627     // Note that we don't need to `check_missing_stability` for default generic parameters,
 628     // as we assume that any default generic parameters without attributes are automatically
 629     // stable (assuming they have not inherited instability from their parent).
 630 }
 631
 632 fn new_index(tcx: TyCtxt<'tcx>) -> Index<'tcx> {
 633     let is_staged_api =
 634         tcx.sess.opts.debugging_opts.force_unstable_if_unmarked || tcx.features().staged_api;
 635     let mut staged_api = FxHashMap::default();
 636     staged_api.insert(LOCAL_CRATE, is_staged_api);
 637     let mut index = Index {
 638         staged_api,
 639         stab_map: Default::default(),
 640         const_stab_map: Default::default(),
 641         depr_map: Default::default(),
 642         active_features: Default::default(),
 643     };
 644
 645     let active_lib_features = &tcx.features().declared_lib_features;
 646     let active_lang_features = &tcx.features().declared_lang_features;
 647
 648     // Put the active features into a map for quick lookup.
 649     index.active_features = active_lib_features
 650         .iter()
 651         .map(|&(s, ..)| s)
 652         .chain(active_lang_features.iter().map(|&(s, ..)| s))
 653         .collect();
 654
 655     {
 656         let krate = tcx.hir().krate();
 657         let mut annotator = Annotator {
 658             tcx,
 659             index: &mut index,
 660             parent_stab: None,
 661             parent_const_stab: None,
 662             parent_depr: None,
 663             in_trait_impl: false,
 664         };
 665
 666         // If the `-Z force-unstable-if-unmarked` flag is passed then we provide
 667         // a parent stability annotation which indicates that this is private
 668         // with the `rustc_private` feature. This is intended for use when
 669         // compiling `librustc_*` crates themselves so we can leverage crates.io
 670         // while maintaining the invariant that all sysroot crates are unstable
 671         // by default and are unable to be used.
 672         if tcx.sess.opts.debugging_opts.force_unstable_if_unmarked {
 673             let reason = "this crate is being loaded from the sysroot, an \
 674                           unstable location; did you mean to load this crate \
 675                           from crates.io via `Cargo.toml` instead?";
 676             let stability = tcx.intern_stability(Stability {
 677                 level: attr::StabilityLevel::Unstable {
 678                     reason: Some(Symbol::intern(reason)),
 679                     issue: NonZeroU32::new(27812),
 680                     is_soft: false,
 681                 },
 682                 feature: sym::rustc_private,
 683             });
 684             annotator.parent_stab = Some(stability);
 685         }
 686
 687         annotator.annotate(
 688             hir::CRATE_HIR_ID,
 689             krate.item.span,
 690             AnnotationKind::Required,
 691             InheritDeprecation::Yes,
 692             InheritConstStability::No,
 693             InheritStability::No,
 694             |v| intravisit::walk_crate(v, krate),
 695         );
 696     }
 697     index
 698 }
 699
 700 /// Cross-references the feature names of unstable APIs with enabled
 701 /// features and possibly prints errors.
 702 fn check_mod_unstable_api_usage(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 703     tcx.hir().visit_item_likes_in_module(module_def_id, &mut Checker { tcx }.as_deep_visitor());
 704 }
 705
 706 pub(crate) fn provide(providers: &mut Providers) {
 707     *providers = Providers { check_mod_unstable_api_usage, ..*providers };
 708     providers.stability_index = |tcx, cnum| {
 709         assert_eq!(cnum, LOCAL_CRATE);
 710         new_index(tcx)
 711     };
 712 }
 713
 714 struct Checker<'tcx> {
 715     tcx: TyCtxt<'tcx>,
 716 }
 717
 718 impl Visitor<'tcx> for Checker<'tcx> {
 719     type Map = Map<'tcx>;
 720
 721     /// Because stability levels are scoped lexically, we want to walk
 722     /// nested items in the context of the outer item, so enable
 723     /// deep-walking.
 724     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 725         NestedVisitorMap::OnlyBodies(self.tcx.hir())
 726     }
 727
 728     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 729         match item.kind {
 730             hir::ItemKind::ExternCrate(_) => {
 731                 // compiler-generated `extern crate` items have a dummy span.
 732                 // `std` is still checked for the `restricted-std` feature.
 733                 if item.span.is_dummy() && item.ident.as_str() != "std" {
 734                     return;
 735                 }
 736
 737                 let cnum = match self.tcx.extern_mod_stmt_cnum(item.def_id) {
 738                     Some(cnum) => cnum,
 739                     None => return,
 740                 };
 741                 let def_id = DefId { krate: cnum, index: CRATE_DEF_INDEX };
 742                 self.tcx.check_stability(def_id, Some(item.hir_id()), item.span);
 743             }
 744
 745             // For implementations of traits, check the stability of each item
 746             // individually as it's possible to have a stable trait with unstable
 747             // items.
 748             hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref t), self_ty, items, .. }) => {
 749                 if self.tcx.features().staged_api {
 750                     // If this impl block has an #[unstable] attribute, give an
 751                     // error if all involved types and traits are stable, because
 752                     // it will have no effect.
 753                     // See: https://github.com/rust-lang/rust/issues/55436
 754                     let attrs = self.tcx.hir().attrs(item.hir_id());
 755                     if let (Some((Stability { level: attr::Unstable { .. }, .. }, span)), _) =
 756                         attr::find_stability(&self.tcx.sess, attrs, item.span)
 757                     {
 758                         let mut c = CheckTraitImplStable { tcx: self.tcx, fully_stable: true };
 759                         c.visit_ty(self_ty);
 760                         c.visit_trait_ref(t);
 761                         if c.fully_stable {
 762                             self.tcx.struct_span_lint_hir(
 763                                 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
 764                                 item.hir_id(),
 765                                 span,
 766                                 |lint| lint
 767                                     .build("an `#[unstable]` annotation here has no effect")
 768                                     .note("see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information")
 769                                     .emit()
 770                             );
 771                         }
 772                     }
 773                 }
 774
 775                 if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
 776                     for impl_item_ref in items {
 777                         let impl_item = self.tcx.hir().impl_item(impl_item_ref.id);
 778                         let trait_item_def_id = self
 779                             .tcx
 780                             .associated_items(trait_did)
 781                             .filter_by_name_unhygienic(impl_item.ident.name)
 782                             .next()
 783                             .map(|item| item.def_id);
 784                         if let Some(def_id) = trait_item_def_id {
 785                             // Pass `None` to skip deprecation warnings.
 786                             self.tcx.check_stability(def_id, None, impl_item.span);
 787                         }
 788                     }
 789                 }
 790             }
 791
 792             // There's no good place to insert stability check for non-Copy unions,
 793             // so semi-randomly perform it here in stability.rs
 794             hir::ItemKind::Union(..) if !self.tcx.features().untagged_unions => {
 795                 let ty = self.tcx.type_of(item.def_id);
 796                 let (adt_def, substs) = match ty.kind() {
 797                     ty::Adt(adt_def, substs) => (adt_def, substs),
 798                     _ => bug!(),
 799                 };
 800
 801                 // Non-`Copy` fields are unstable, except for `ManuallyDrop`.
 802                 let param_env = self.tcx.param_env(item.def_id);
 803                 for field in &adt_def.non_enum_variant().fields {
 804                     let field_ty = field.ty(self.tcx, substs);
 805                     if !field_ty.ty_adt_def().map_or(false, |adt_def| adt_def.is_manually_drop())
 806                         && !field_ty.is_copy_modulo_regions(self.tcx.at(DUMMY_SP), param_env)
 807                     {
 808                         if field_ty.needs_drop(self.tcx, param_env) {
 809                             // Avoid duplicate error: This will error later anyway because fields
 810                             // that need drop are not allowed.
 811                             self.tcx.sess.delay_span_bug(
 812                                 item.span,
 813                                 "union should have been rejected due to potentially dropping field",
 814                             );
 815                         } else {
 816                             feature_err(
 817                                 &self.tcx.sess.parse_sess,
 818                                 sym::untagged_unions,
 819                                 self.tcx.def_span(field.did),
 820                                 "unions with non-`Copy` fields other than `ManuallyDrop<T>` are unstable",
 821                             )
 822                             .emit();
 823                         }
 824                     }
 825                 }
 826             }
 827
 828             _ => (/* pass */),
 829         }
 830         intravisit::walk_item(self, item);
 831     }
 832
 833     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, id: hir::HirId) {
 834         if let Some(def_id) = path.res.opt_def_id() {
 835             self.tcx.check_stability(def_id, Some(id), path.span)
 836         }
 837         intravisit::walk_path(self, path)
 838     }
 839 }
 840
 841 struct CheckTraitImplStable<'tcx> {
 842     tcx: TyCtxt<'tcx>,
 843     fully_stable: bool,
 844 }
 845
 846 impl Visitor<'tcx> for CheckTraitImplStable<'tcx> {
 847     type Map = Map<'tcx>;
 848
 849     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 850         NestedVisitorMap::None
 851     }
 852
 853     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _id: hir::HirId) {
 854         if let Some(def_id) = path.res.opt_def_id() {
 855             if let Some(stab) = self.tcx.lookup_stability(def_id) {
 856                 self.fully_stable &= stab.level.is_stable();
 857             }
 858         }
 859         intravisit::walk_path(self, path)
 860     }
 861
 862     fn visit_trait_ref(&mut self, t: &'tcx TraitRef<'tcx>) {
 863         if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
 864             if let Some(stab) = self.tcx.lookup_stability(trait_did) {
 865                 self.fully_stable &= stab.level.is_stable();
 866             }
 867         }
 868         intravisit::walk_trait_ref(self, t)
 869     }
 870
 871     fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
 872         if let TyKind::Never = t.kind {
 873             self.fully_stable = false;
 874         }
 875         intravisit::walk_ty(self, t)
 876     }
 877 }
 878
 879 /// Given the list of enabled features that were not language features (i.e., that
 880 /// were expected to be library features), and the list of features used from
 881 /// libraries, identify activated features that don't exist and error about them.
 882 pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
 883     let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
 884
 885     if tcx.stability().staged_api[&LOCAL_CRATE] {
 886         let krate = tcx.hir().krate();
 887         let mut missing = MissingStabilityAnnotations { tcx, access_levels };
 888         missing.check_missing_stability(hir::CRATE_HIR_ID, krate.item.span);
 889         intravisit::walk_crate(&mut missing, krate);
 890         krate.visit_all_item_likes(&mut missing.as_deep_visitor());
 891     }
 892
 893     let declared_lang_features = &tcx.features().declared_lang_features;
 894     let mut lang_features = FxHashSet::default();
 895     for &(feature, span, since) in declared_lang_features {
 896         if let Some(since) = since {
 897             // Warn if the user has enabled an already-stable lang feature.
 898             unnecessary_stable_feature_lint(tcx, span, feature, since);
 899         }
 900         if !lang_features.insert(feature) {
 901             // Warn if the user enables a lang feature multiple times.
 902             duplicate_feature_err(tcx.sess, span, feature);
 903         }
 904     }
 905
 906     let declared_lib_features = &tcx.features().declared_lib_features;
 907     let mut remaining_lib_features = FxHashMap::default();
 908     for (feature, span) in declared_lib_features {
 909         if remaining_lib_features.contains_key(&feature) {
 910             // Warn if the user enables a lib feature multiple times.
 911             duplicate_feature_err(tcx.sess, *span, *feature);
 912         }
 913         remaining_lib_features.insert(feature, *span);
 914     }
 915     // `stdbuild` has special handling for `libc`, so we need to
 916     // recognise the feature when building std.
 917     // Likewise, libtest is handled specially, so `test` isn't
 918     // available as we'd like it to be.
 919     // FIXME: only remove `libc` when `stdbuild` is active.
 920     // FIXME: remove special casing for `test`.
 921     remaining_lib_features.remove(&sym::libc);
 922     remaining_lib_features.remove(&sym::test);
 923
 924     let check_features = |remaining_lib_features: &mut FxHashMap<_, _>, defined_features: &[_]| {
 925         for &(feature, since) in defined_features {
 926             if let Some(since) = since {
 927                 if let Some(span) = remaining_lib_features.get(&feature) {
 928                     // Warn if the user has enabled an already-stable lib feature.
 929                     unnecessary_stable_feature_lint(tcx, *span, feature, since);
 930                 }
 931             }
 932             remaining_lib_features.remove(&feature);
 933             if remaining_lib_features.is_empty() {
 934                 break;
 935             }
 936         }
 937     };
 938
 939     // We always collect the lib features declared in the current crate, even if there are
 940     // no unknown features, because the collection also does feature attribute validation.
 941     let local_defined_features = tcx.lib_features().to_vec();
 942     if !remaining_lib_features.is_empty() {
 943         check_features(&mut remaining_lib_features, &local_defined_features);
 944
 945         for &cnum in &*tcx.crates() {
 946             if remaining_lib_features.is_empty() {
 947                 break;
 948             }
 949             check_features(&mut remaining_lib_features, tcx.defined_lib_features(cnum));
 950         }
 951     }
 952
 953     for (feature, span) in remaining_lib_features {
 954         struct_span_err!(tcx.sess, span, E0635, "unknown feature `{}`", feature).emit();
 955     }
 956
 957     // FIXME(#44232): the `used_features` table no longer exists, so we
 958     // don't lint about unused features. We should re-enable this one day!
 959 }
 960
 961 fn unnecessary_stable_feature_lint(tcx: TyCtxt<'_>, span: Span, feature: Symbol, since: Symbol) {
 962     tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
 963         lint.build(&format!(
 964             "the feature `{}` has been stable since {} and no longer requires \
 965                       an attribute to enable",
 966             feature, since
 967         ))
 968         .emit();
 969     });
 970 }
 971
 972 fn duplicate_feature_err(sess: &Session, span: Span, feature: Symbol) {
 973     struct_span_err!(sess, span, E0636, "the feature `{}` has already been declared", feature)
 974         .emit();
 975 }