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