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                     match stab_v.parse::<u64>() {
 186                         Err(_) => {
 187                             self.tcx.sess.span_err(item_sp, "Invalid stability version found");
 188                             break;
 189                         }
 190                         Ok(stab_vp) => match dep_v.parse::<u64>() {
 191                             Ok(dep_vp) => match dep_vp.cmp(&stab_vp) {
 192                                 Ordering::Less => {
 193                                     self.tcx.sess.span_err(
 194                                         item_sp,
 195                                         "An API can't be stabilized after it is deprecated",
 196                                     );
 197                                     break;
 198                                 }
 199                                 Ordering::Equal => continue,
 200                                 Ordering::Greater => break,
 201                             },
 202                             Err(_) => {
 203                                 if dep_v != "TBD" {
 204                                     self.tcx
 205                                         .sess
 206                                         .span_err(item_sp, "Invalid deprecation version found");
 207                                 }
 208                                 break;
 209                             }
 210                         },
 211                     }
 212                 }
 213             }
 214
 215             self.index.stab_map.insert(hir_id, stab);
 216             stab
 217         });
 218
 219         if stab.is_none() {
 220             debug!("annotate: stab not found, parent = {:?}", self.parent_stab);
 221             if let Some(stab) = self.parent_stab {
 222                 if inherit_deprecation.yes() && stab.level.is_unstable() {
 223                     self.index.stab_map.insert(hir_id, stab);
 224                 }
 225             }
 226         }
 227
 228         self.recurse_with_stability_attrs(
 229             depr.map(|(d, _)| DeprecationEntry::local(d, hir_id)),
 230             stab,
 231             const_stab,
 232             visit_children,
 233         );
 234     }
 235
 236     fn recurse_with_stability_attrs(
 237         &mut self,
 238         depr: Option<DeprecationEntry>,
 239         stab: Option<&'tcx Stability>,
 240         const_stab: Option<&'tcx ConstStability>,
 241         f: impl FnOnce(&mut Self),
 242     ) {
 243         // These will be `Some` if this item changes the corresponding stability attribute.
 244         let mut replaced_parent_depr = None;
 245         let mut replaced_parent_stab = None;
 246         let mut replaced_parent_const_stab = None;
 247
 248         if let Some(depr) = depr {
 249             replaced_parent_depr = Some(replace(&mut self.parent_depr, Some(depr)));
 250         }
 251         if let Some(stab) = stab {
 252             replaced_parent_stab = Some(replace(&mut self.parent_stab, Some(stab)));
 253         }
 254         if let Some(const_stab) = const_stab {
 255             replaced_parent_const_stab =
 256                 Some(replace(&mut self.parent_const_stab, Some(const_stab)));
 257         }
 258
 259         f(self);
 260
 261         if let Some(orig_parent_depr) = replaced_parent_depr {
 262             self.parent_depr = orig_parent_depr;
 263         }
 264         if let Some(orig_parent_stab) = replaced_parent_stab {
 265             self.parent_stab = orig_parent_stab;
 266         }
 267         if let Some(orig_parent_const_stab) = replaced_parent_const_stab {
 268             self.parent_const_stab = orig_parent_const_stab;
 269         }
 270     }
 271
 272     // returns true if an error occurred, used to suppress some spurious errors
 273     fn forbid_staged_api_attrs(
 274         &mut self,
 275         hir_id: HirId,
 276         attrs: &[Attribute],
 277         inherit_deprecation: InheritDeprecation,
 278     ) -> bool {
 279         // Emit errors for non-staged-api crates.
 280         let unstable_attrs = [
 281             sym::unstable,
 282             sym::stable,
 283             sym::rustc_deprecated,
 284             sym::rustc_const_unstable,
 285             sym::rustc_const_stable,
 286         ];
 287         let mut has_error = false;
 288         for attr in attrs {
 289             let name = attr.name_or_empty();
 290             if unstable_attrs.contains(&name) {
 291                 self.tcx.sess.mark_attr_used(attr);
 292                 struct_span_err!(
 293                     self.tcx.sess,
 294                     attr.span,
 295                     E0734,
 296                     "stability attributes may not be used outside of the standard library",
 297                 )
 298                 .emit();
 299                 has_error = true;
 300             }
 301         }
 302
 303         // Propagate unstability.  This can happen even for non-staged-api crates in case
 304         // -Zforce-unstable-if-unmarked is set.
 305         if let Some(stab) = self.parent_stab {
 306             if inherit_deprecation.yes() && stab.level.is_unstable() {
 307                 self.index.stab_map.insert(hir_id, stab);
 308             }
 309         }
 310
 311         has_error
 312     }
 313 }
 314
 315 impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
 316     /// Because stability levels are scoped lexically, we want to walk
 317     /// nested items in the context of the outer item, so enable
 318     /// deep-walking.
 319     type Map = Map<'tcx>;
 320
 321     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 322         NestedVisitorMap::All(self.tcx.hir())
 323     }
 324
 325     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 326         let orig_in_trait_impl = self.in_trait_impl;
 327         let mut kind = AnnotationKind::Required;
 328         match i.kind {
 329             // Inherent impls and foreign modules serve only as containers for other items,
 330             // they don't have their own stability. They still can be annotated as unstable
 331             // and propagate this unstability to children, but this annotation is completely
 332             // optional. They inherit stability from their parents when unannotated.
 333             hir::ItemKind::Impl { of_trait: None, .. } | hir::ItemKind::ForeignMod { .. } => {
 334                 self.in_trait_impl = false;
 335                 kind = AnnotationKind::Container;
 336             }
 337             hir::ItemKind::Impl { of_trait: Some(_), .. } => {
 338                 self.in_trait_impl = true;
 339                 kind = AnnotationKind::DeprecationProhibited;
 340             }
 341             hir::ItemKind::Struct(ref sd, _) => {
 342                 if let Some(ctor_hir_id) = sd.ctor_hir_id() {
 343                     self.annotate(
 344                         ctor_hir_id,
 345                         &i.attrs,
 346                         i.span,
 347                         AnnotationKind::Required,
 348                         InheritDeprecation::Yes,
 349                         |_| {},
 350                     )
 351                 }
 352             }
 353             _ => {}
 354         }
 355
 356         self.annotate(i.hir_id, &i.attrs, i.span, kind, InheritDeprecation::Yes, |v| {
 357             intravisit::walk_item(v, i)
 358         });
 359         self.in_trait_impl = orig_in_trait_impl;
 360     }
 361
 362     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 363         self.annotate(
 364             ti.hir_id,
 365             &ti.attrs,
 366             ti.span,
 367             AnnotationKind::Required,
 368             InheritDeprecation::Yes,
 369             |v| {
 370                 intravisit::walk_trait_item(v, ti);
 371             },
 372         );
 373     }
 374
 375     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 376         let kind =
 377             if self.in_trait_impl { AnnotationKind::Prohibited } else { AnnotationKind::Required };
 378         self.annotate(ii.hir_id, &ii.attrs, ii.span, kind, InheritDeprecation::Yes, |v| {
 379             intravisit::walk_impl_item(v, ii);
 380         });
 381     }
 382
 383     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 384         self.annotate(
 385             var.id,
 386             &var.attrs,
 387             var.span,
 388             AnnotationKind::Required,
 389             InheritDeprecation::Yes,
 390             |v| {
 391                 if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
 392                     v.annotate(
 393                         ctor_hir_id,
 394                         &var.attrs,
 395                         var.span,
 396                         AnnotationKind::Required,
 397                         InheritDeprecation::Yes,
 398                         |_| {},
 399                     );
 400                 }
 401
 402                 intravisit::walk_variant(v, var, g, item_id)
 403             },
 404         )
 405     }
 406
 407     fn visit_struct_field(&mut self, s: &'tcx StructField<'tcx>) {
 408         self.annotate(
 409             s.hir_id,
 410             &s.attrs,
 411             s.span,
 412             AnnotationKind::Required,
 413             InheritDeprecation::Yes,
 414             |v| {
 415                 intravisit::walk_struct_field(v, s);
 416             },
 417         );
 418     }
 419
 420     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 421         self.annotate(
 422             i.hir_id,
 423             &i.attrs,
 424             i.span,
 425             AnnotationKind::Required,
 426             InheritDeprecation::Yes,
 427             |v| {
 428                 intravisit::walk_foreign_item(v, i);
 429             },
 430         );
 431     }
 432
 433     fn visit_macro_def(&mut self, md: &'tcx hir::MacroDef<'tcx>) {
 434         self.annotate(
 435             md.hir_id,
 436             &md.attrs,
 437             md.span,
 438             AnnotationKind::Required,
 439             InheritDeprecation::Yes,
 440             |_| {},
 441         );
 442     }
 443
 444     fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
 445         let kind = match &p.kind {
 446             // FIXME(const_generics:defaults)
 447             hir::GenericParamKind::Type { default, .. } if default.is_some() => {
 448                 AnnotationKind::Container
 449             }
 450             _ => AnnotationKind::Prohibited,
 451         };
 452
 453         self.annotate(p.hir_id, &p.attrs, p.span, kind, InheritDeprecation::No, |v| {
 454             intravisit::walk_generic_param(v, p);
 455         });
 456     }
 457 }
 458
 459 struct MissingStabilityAnnotations<'tcx> {
 460     tcx: TyCtxt<'tcx>,
 461     access_levels: &'tcx AccessLevels,
 462 }
 463
 464 impl<'tcx> MissingStabilityAnnotations<'tcx> {
 465     fn check_missing_stability(&self, hir_id: HirId, span: Span) {
 466         let stab = self.tcx.stability().local_stability(hir_id);
 467         let is_error =
 468             !self.tcx.sess.opts.test && stab.is_none() && self.access_levels.is_reachable(hir_id);
 469         if is_error {
 470             let def_id = self.tcx.hir().local_def_id(hir_id);
 471             let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
 472             self.tcx.sess.span_err(span, &format!("{} has missing stability attribute", descr));
 473         }
 474     }
 475
 476     fn check_missing_const_stability(&self, hir_id: HirId, span: Span) {
 477         let stab_map = self.tcx.stability();
 478         let stab = stab_map.local_stability(hir_id);
 479         if stab.map_or(false, |stab| stab.level.is_stable()) {
 480             let const_stab = stab_map.local_const_stability(hir_id);
 481             if const_stab.is_none() {
 482                 self.tcx.sess.span_err(
 483                     span,
 484                     "`#[stable]` const functions must also be either \
 485                     `#[rustc_const_stable]` or `#[rustc_const_unstable]`",
 486                 );
 487             }
 488         }
 489     }
 490 }
 491
 492 impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
 493     type Map = Map<'tcx>;
 494
 495     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 496         NestedVisitorMap::OnlyBodies(self.tcx.hir())
 497     }
 498
 499     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
 500         // Inherent impls and foreign modules serve only as containers for other items,
 501         // they don't have their own stability. They still can be annotated as unstable
 502         // and propagate this unstability to children, but this annotation is completely
 503         // optional. They inherit stability from their parents when unannotated.
 504         if !matches!(
 505             i.kind,
 506             hir::ItemKind::Impl { of_trait: None, .. } | hir::ItemKind::ForeignMod { .. }
 507         ) {
 508             self.check_missing_stability(i.hir_id, i.span);
 509         }
 510
 511         // Ensure `const fn` that are `stable` have one of `rustc_const_unstable` or
 512         // `rustc_const_stable`.
 513         if self.tcx.features().staged_api
 514             && matches!(&i.kind, hir::ItemKind::Fn(sig, ..) if sig.header.is_const())
 515         {
 516             self.check_missing_const_stability(i.hir_id, i.span);
 517         }
 518
 519         intravisit::walk_item(self, i)
 520     }
 521
 522     fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
 523         self.check_missing_stability(ti.hir_id, ti.span);
 524         intravisit::walk_trait_item(self, ti);
 525     }
 526
 527     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
 528         let impl_def_id = self.tcx.hir().local_def_id(self.tcx.hir().get_parent_item(ii.hir_id));
 529         if self.tcx.impl_trait_ref(impl_def_id).is_none() {
 530             self.check_missing_stability(ii.hir_id, ii.span);
 531         }
 532         intravisit::walk_impl_item(self, ii);
 533     }
 534
 535     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
 536         self.check_missing_stability(var.id, var.span);
 537         intravisit::walk_variant(self, var, g, item_id);
 538     }
 539
 540     fn visit_struct_field(&mut self, s: &'tcx StructField<'tcx>) {
 541         self.check_missing_stability(s.hir_id, s.span);
 542         intravisit::walk_struct_field(self, s);
 543     }
 544
 545     fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
 546         self.check_missing_stability(i.hir_id, i.span);
 547         intravisit::walk_foreign_item(self, i);
 548     }
 549
 550     fn visit_macro_def(&mut self, md: &'tcx hir::MacroDef<'tcx>) {
 551         self.check_missing_stability(md.hir_id, md.span);
 552     }
 553
 554     // Note that we don't need to `check_missing_stability` for default generic parameters,
 555     // as we assume that any default generic parameters without attributes are automatically
 556     // stable (assuming they have not inherited instability from their parent).
 557 }
 558
 559 fn new_index(tcx: TyCtxt<'tcx>) -> Index<'tcx> {
 560     let is_staged_api =
 561         tcx.sess.opts.debugging_opts.force_unstable_if_unmarked || tcx.features().staged_api;
 562     let mut staged_api = FxHashMap::default();
 563     staged_api.insert(LOCAL_CRATE, is_staged_api);
 564     let mut index = Index {
 565         staged_api,
 566         stab_map: Default::default(),
 567         const_stab_map: Default::default(),
 568         depr_map: Default::default(),
 569         active_features: Default::default(),
 570     };
 571
 572     let active_lib_features = &tcx.features().declared_lib_features;
 573     let active_lang_features = &tcx.features().declared_lang_features;
 574
 575     // Put the active features into a map for quick lookup.
 576     index.active_features = active_lib_features
 577         .iter()
 578         .map(|&(s, ..)| s)
 579         .chain(active_lang_features.iter().map(|&(s, ..)| s))
 580         .collect();
 581
 582     {
 583         let krate = tcx.hir().krate();
 584         let mut annotator = Annotator {
 585             tcx,
 586             index: &mut index,
 587             parent_stab: None,
 588             parent_const_stab: None,
 589             parent_depr: None,
 590             in_trait_impl: false,
 591         };
 592
 593         // If the `-Z force-unstable-if-unmarked` flag is passed then we provide
 594         // a parent stability annotation which indicates that this is private
 595         // with the `rustc_private` feature. This is intended for use when
 596         // compiling `librustc_*` crates themselves so we can leverage crates.io
 597         // while maintaining the invariant that all sysroot crates are unstable
 598         // by default and are unable to be used.
 599         if tcx.sess.opts.debugging_opts.force_unstable_if_unmarked {
 600             let reason = "this crate is being loaded from the sysroot, an \
 601                           unstable location; did you mean to load this crate \
 602                           from crates.io via `Cargo.toml` instead?";
 603             let stability = tcx.intern_stability(Stability {
 604                 level: attr::StabilityLevel::Unstable {
 605                     reason: Some(Symbol::intern(reason)),
 606                     issue: NonZeroU32::new(27812),
 607                     is_soft: false,
 608                 },
 609                 feature: sym::rustc_private,
 610             });
 611             annotator.parent_stab = Some(stability);
 612         }
 613
 614         annotator.annotate(
 615             hir::CRATE_HIR_ID,
 616             &krate.item.attrs,
 617             krate.item.span,
 618             AnnotationKind::Required,
 619             InheritDeprecation::Yes,
 620             |v| intravisit::walk_crate(v, krate),
 621         );
 622     }
 623     index
 624 }
 625
 626 /// Cross-references the feature names of unstable APIs with enabled
 627 /// features and possibly prints errors.
 628 fn check_mod_unstable_api_usage(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
 629     tcx.hir().visit_item_likes_in_module(module_def_id, &mut Checker { tcx }.as_deep_visitor());
 630 }
 631
 632 pub(crate) fn provide(providers: &mut Providers) {
 633     *providers = Providers { check_mod_unstable_api_usage, ..*providers };
 634     providers.stability_index = |tcx, cnum| {
 635         assert_eq!(cnum, LOCAL_CRATE);
 636         new_index(tcx)
 637     };
 638 }
 639
 640 struct Checker<'tcx> {
 641     tcx: TyCtxt<'tcx>,
 642 }
 643
 644 impl Visitor<'tcx> for Checker<'tcx> {
 645     type Map = Map<'tcx>;
 646
 647     /// Because stability levels are scoped lexically, we want to walk
 648     /// nested items in the context of the outer item, so enable
 649     /// deep-walking.
 650     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 651         NestedVisitorMap::OnlyBodies(self.tcx.hir())
 652     }
 653
 654     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
 655         match item.kind {
 656             hir::ItemKind::ExternCrate(_) => {
 657                 // compiler-generated `extern crate` items have a dummy span.
 658                 // `std` is still checked for the `restricted-std` feature.
 659                 if item.span.is_dummy() && item.ident.as_str() != "std" {
 660                     return;
 661                 }
 662
 663                 let def_id = self.tcx.hir().local_def_id(item.hir_id);
 664                 let cnum = match self.tcx.extern_mod_stmt_cnum(def_id) {
 665                     Some(cnum) => cnum,
 666                     None => return,
 667                 };
 668                 let def_id = DefId { krate: cnum, index: CRATE_DEF_INDEX };
 669                 self.tcx.check_stability(def_id, Some(item.hir_id), item.span);
 670             }
 671
 672             // For implementations of traits, check the stability of each item
 673             // individually as it's possible to have a stable trait with unstable
 674             // items.
 675             hir::ItemKind::Impl { of_trait: Some(ref t), self_ty, items, .. } => {
 676                 if self.tcx.features().staged_api {
 677                     // If this impl block has an #[unstable] attribute, give an
 678                     // error if all involved types and traits are stable, because
 679                     // it will have no effect.
 680                     // See: https://github.com/rust-lang/rust/issues/55436
 681                     if let (Some(Stability { level: attr::Unstable { .. }, .. }), _) =
 682                         attr::find_stability(&self.tcx.sess, &item.attrs, item.span)
 683                     {
 684                         let mut c = CheckTraitImplStable { tcx: self.tcx, fully_stable: true };
 685                         c.visit_ty(self_ty);
 686                         c.visit_trait_ref(t);
 687                         if c.fully_stable {
 688                             let span = item
 689                                 .attrs
 690                                 .iter()
 691                                 .find(|a| a.has_name(sym::unstable))
 692                                 .map_or(item.span, |a| a.span);
 693                             self.tcx.struct_span_lint_hir(
 694                                 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
 695                                 item.hir_id,
 696                                 span,
 697                                 |lint| lint
 698                                     .build("an `#[unstable]` annotation here has no effect")
 699                                     .note("see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information")
 700                                     .emit()
 701                             );
 702                         }
 703                     }
 704                 }
 705
 706                 if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
 707                     for impl_item_ref in items {
 708                         let impl_item = self.tcx.hir().impl_item(impl_item_ref.id);
 709                         let trait_item_def_id = self
 710                             .tcx
 711                             .associated_items(trait_did)
 712                             .filter_by_name_unhygienic(impl_item.ident.name)
 713                             .next()
 714                             .map(|item| item.def_id);
 715                         if let Some(def_id) = trait_item_def_id {
 716                             // Pass `None` to skip deprecation warnings.
 717                             self.tcx.check_stability(def_id, None, impl_item.span);
 718                         }
 719                     }
 720                 }
 721             }
 722
 723             // There's no good place to insert stability check for non-Copy unions,
 724             // so semi-randomly perform it here in stability.rs
 725             hir::ItemKind::Union(..) if !self.tcx.features().untagged_unions => {
 726                 let def_id = self.tcx.hir().local_def_id(item.hir_id);
 727                 let ty = self.tcx.type_of(def_id);
 728                 let (adt_def, substs) = match ty.kind() {
 729                     ty::Adt(adt_def, substs) => (adt_def, substs),
 730                     _ => bug!(),
 731                 };
 732
 733                 // Non-`Copy` fields are unstable, except for `ManuallyDrop`.
 734                 let param_env = self.tcx.param_env(def_id);
 735                 for field in &adt_def.non_enum_variant().fields {
 736                     let field_ty = field.ty(self.tcx, substs);
 737                     if !field_ty.ty_adt_def().map_or(false, |adt_def| adt_def.is_manually_drop())
 738                         && !field_ty.is_copy_modulo_regions(self.tcx.at(DUMMY_SP), param_env)
 739                     {
 740                         if field_ty.needs_drop(self.tcx, param_env) {
 741                             // Avoid duplicate error: This will error later anyway because fields
 742                             // that need drop are not allowed.
 743                             self.tcx.sess.delay_span_bug(
 744                                 item.span,
 745                                 "union should have been rejected due to potentially dropping field",
 746                             );
 747                         } else {
 748                             feature_err(
 749                                 &self.tcx.sess.parse_sess,
 750                                 sym::untagged_unions,
 751                                 self.tcx.def_span(field.did),
 752                                 "unions with non-`Copy` fields other than `ManuallyDrop<T>` are unstable",
 753                             )
 754                             .emit();
 755                         }
 756                     }
 757                 }
 758             }
 759
 760             _ => (/* pass */),
 761         }
 762         intravisit::walk_item(self, item);
 763     }
 764
 765     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, id: hir::HirId) {
 766         if let Some(def_id) = path.res.opt_def_id() {
 767             self.tcx.check_stability(def_id, Some(id), path.span)
 768         }
 769         intravisit::walk_path(self, path)
 770     }
 771 }
 772
 773 struct CheckTraitImplStable<'tcx> {
 774     tcx: TyCtxt<'tcx>,
 775     fully_stable: bool,
 776 }
 777
 778 impl Visitor<'tcx> for CheckTraitImplStable<'tcx> {
 779     type Map = Map<'tcx>;
 780
 781     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 782         NestedVisitorMap::None
 783     }
 784
 785     fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _id: hir::HirId) {
 786         if let Some(def_id) = path.res.opt_def_id() {
 787             if let Some(stab) = self.tcx.lookup_stability(def_id) {
 788                 self.fully_stable &= stab.level.is_stable();
 789             }
 790         }
 791         intravisit::walk_path(self, path)
 792     }
 793
 794     fn visit_trait_ref(&mut self, t: &'tcx TraitRef<'tcx>) {
 795         if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
 796             if let Some(stab) = self.tcx.lookup_stability(trait_did) {
 797                 self.fully_stable &= stab.level.is_stable();
 798             }
 799         }
 800         intravisit::walk_trait_ref(self, t)
 801     }
 802
 803     fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
 804         if let TyKind::Never = t.kind {
 805             self.fully_stable = false;
 806         }
 807         intravisit::walk_ty(self, t)
 808     }
 809 }
 810
 811 /// Given the list of enabled features that were not language features (i.e., that
 812 /// were expected to be library features), and the list of features used from
 813 /// libraries, identify activated features that don't exist and error about them.
 814 pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
 815     let access_levels = &tcx.privacy_access_levels(LOCAL_CRATE);
 816
 817     if tcx.stability().staged_api[&LOCAL_CRATE] {
 818         let krate = tcx.hir().krate();
 819         let mut missing = MissingStabilityAnnotations { tcx, access_levels };
 820         missing.check_missing_stability(hir::CRATE_HIR_ID, krate.item.span);
 821         intravisit::walk_crate(&mut missing, krate);
 822         krate.visit_all_item_likes(&mut missing.as_deep_visitor());
 823     }
 824
 825     let declared_lang_features = &tcx.features().declared_lang_features;
 826     let mut lang_features = FxHashSet::default();
 827     for &(feature, span, since) in declared_lang_features {
 828         if let Some(since) = since {
 829             // Warn if the user has enabled an already-stable lang feature.
 830             unnecessary_stable_feature_lint(tcx, span, feature, since);
 831         }
 832         if !lang_features.insert(feature) {
 833             // Warn if the user enables a lang feature multiple times.
 834             duplicate_feature_err(tcx.sess, span, feature);
 835         }
 836     }
 837
 838     let declared_lib_features = &tcx.features().declared_lib_features;
 839     let mut remaining_lib_features = FxHashMap::default();
 840     for (feature, span) in declared_lib_features {
 841         if remaining_lib_features.contains_key(&feature) {
 842             // Warn if the user enables a lib feature multiple times.
 843             duplicate_feature_err(tcx.sess, *span, *feature);
 844         }
 845         remaining_lib_features.insert(feature, *span);
 846     }
 847     // `stdbuild` has special handling for `libc`, so we need to
 848     // recognise the feature when building std.
 849     // Likewise, libtest is handled specially, so `test` isn't
 850     // available as we'd like it to be.
 851     // FIXME: only remove `libc` when `stdbuild` is active.
 852     // FIXME: remove special casing for `test`.
 853     remaining_lib_features.remove(&sym::libc);
 854     remaining_lib_features.remove(&sym::test);
 855
 856     let check_features = |remaining_lib_features: &mut FxHashMap<_, _>, defined_features: &[_]| {
 857         for &(feature, since) in defined_features {
 858             if let Some(since) = since {
 859                 if let Some(span) = remaining_lib_features.get(&feature) {
 860                     // Warn if the user has enabled an already-stable lib feature.
 861                     unnecessary_stable_feature_lint(tcx, *span, feature, since);
 862                 }
 863             }
 864             remaining_lib_features.remove(&feature);
 865             if remaining_lib_features.is_empty() {
 866                 break;
 867             }
 868         }
 869     };
 870
 871     // We always collect the lib features declared in the current crate, even if there are
 872     // no unknown features, because the collection also does feature attribute validation.
 873     let local_defined_features = tcx.lib_features().to_vec();
 874     if !remaining_lib_features.is_empty() {
 875         check_features(&mut remaining_lib_features, &local_defined_features);
 876
 877         for &cnum in &*tcx.crates() {
 878             if remaining_lib_features.is_empty() {
 879                 break;
 880             }
 881             check_features(&mut remaining_lib_features, tcx.defined_lib_features(cnum));
 882         }
 883     }
 884
 885     for (feature, span) in remaining_lib_features {
 886         struct_span_err!(tcx.sess, span, E0635, "unknown feature `{}`", feature).emit();
 887     }
 888
 889     // FIXME(#44232): the `used_features` table no longer exists, so we
 890     // don't lint about unused features. We should re-enable this one day!
 891 }
 892
 893 fn unnecessary_stable_feature_lint(tcx: TyCtxt<'_>, span: Span, feature: Symbol, since: Symbol) {
 894     tcx.struct_span_lint_hir(lint::builtin::STABLE_FEATURES, hir::CRATE_HIR_ID, span, |lint| {
 895         lint.build(&format!(
 896             "the feature `{}` has been stable since {} and no longer requires \
 897                       an attribute to enable",
 898             feature, since
 899         ))
 900         .emit();
 901     });
 902 }
 903
 904 fn duplicate_feature_err(sess: &Session, span: Span, feature: Symbol) {
 905     struct_span_err!(sess, span, E0636, "the feature `{}` has already been declared", feature)
 906         .emit();
 907 }