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